TY - JOUR A1 - Wu, Y. S. A1 - Becker, Charles R. A1 - Waag, A. A1 - von Schierstedt, K. A1 - Bicknell-Tassius, R. N. A1 - Landwehr, G. T1 - Surface sublimation of zinc blende CdTe N2 - The surface sublimation of Cd and Te atoms from the zinc blende (111)A CdTe surface has been investigated in detail by reflection high energy electron diffraction and x-ray photoelectron spectroscopy. These experiments verify that Te is much easier to evaporate than Cd. The experimental value for the Te activation energy from a Te stabilized (111)A CdTe surface is 1.41 ±0.1O eV, which is apparently inconsistent with recent theoretical results. Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37829 ER - TY - JOUR A1 - Wu, Y. S. A1 - Becker, Charles R. A1 - Waag, A. A1 - Bicknell-Tassius, R. N. A1 - Landwehr, G. T1 - Thermal effects on (100) CdZnTe substrates as studied by x-ray photoelectron spectroscopy and reflection high energy electron diffraction N2 - The influence of different CdZnTe substrate treatments prior to II-VI molecular beam epitaxial growth on surface stoichiometry, oxygen, and carbon contamination has been studied using x-ray photoelectron spectroscopy and reflection high energy electron diffraction. Heating the substrate at 300 °C can eliminate oxygen contamination, but cannot completely remove carbon from the surface. Heating at higher temperatures decreases the carbon contamination only slightly, while increasing the Zn-Cd ratio on the surface considerably. The magnitude of the latter effect is surprising and is crucial when one is using lattice matched CdZnTe (Zn 4%) substrates. Y1 - 1992 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37801 SN - 0003-6951 ER - TY - JOUR A1 - Wu, Y.S. A1 - Becker, Charles R. A1 - Waag, A. A1 - Kraus, M. M. A1 - Bicknell-Tassius, R. N. A1 - Landwehr, G. T1 - Correlation of the Cd-to-Te ratio on CdTe surfaces with the surface structure N2 - We report here that reconstruction on (100), (1lIlA, and (1l1lB CdTe surfaces is either C(2X2), (2X2), and (l X I) or (2X I), (l X I), and (l X I) when they are Cd or Te stabilized, respectively. There is a mixed region between Cd and Te stabilization in which the reflected high-energy electron-diffraction (RHEED) patterns contain characteristics of both Cd- and Te-stabilized surfaces. We have also found that the Cd-to-Te ratio of the x-ray photoelectron intensities of their 3d\(_{3/ 2}\) core levels is about 20% larger for a Cd-stabilized (1lIlA, (1lIlB, or (100) CdTe surface than for a Te-stabilized one. According to a simple model calculation, which was normalized by means of the photoelectron intensity ratio of a Cd-stabilized (lll)A and aTe-stabilized (1l1lB CdTe surface, the experimental data for CdTe surfaces can be explained by a linear dependence of the photoelectron-intensity ratio on the fraction of Cd in the uppermost monatomic layer. This surface composition can be correlated with the surface structure, i.e., the corresponding RHEED patterns. This correlation can in turn be employed to determine Te and Cd evaporation rates. The Te reevaporation rate is increasingly slower for the Te-stabilized (Ill) A, (l1l)B, and (100) surfaces, while the opposite is true for Cd from Cd-stabilized (Ill) A and (Ill)B surfaces. In addition, Te is much more easily evaporated from all the investigated surfaces than is Cd, if the substrate is kept at normal molecular-beam-epitaxy growth temperatures ranging from 2oo·C to 300 ·C. KW - Festkörperphysik Y1 - 1991 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37789 SN - 0163-1829 ER - TY - JOUR A1 - Qiu, Yueming A1 - He, Li A1 - Li, Jie A1 - Yuan, Shixin A1 - Becker, Charles R. A1 - Landwehr, G. T1 - Infrared photoconductor fabricated with HgTe/CdTe superlattice grown by molecular beam epitaxy N2 - An infrared photoconductor fabricated with a HgTe/CdTe superlattice grown on a GaAs substrate by molecular beam epitaxy is described here for the first time. The growth procedure, device fabrication, and measurement results are described. The results show that the device has relatively high uniformity and 1000 K black-body detectivity 2.4 X 10\(^9\) cm Hz\(^{1/2}\) W\(^{-1}\) . The photoconductivity decay method was used for determining carrier lifetime of the HgTe/CdTe superlattice, the measured lifetime is 12\(\mu\)s at 77 K, which is the longest lifetime ever reported for HgTe/CdTe superlattices and we believe that the increase of lifetime is mainly due to the reduction of dimensions. Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37772 ER - TY - JOUR A1 - Tönnies, D. A1 - Bacher, G. A1 - Forchel, Alfred A1 - Waag, A. A1 - Litz, Th. A1 - Hommel, D. A1 - Becker, Charles R. A1 - Landwehr, G. A1 - Heuken, M. A1 - Scholl, M. T1 - Optical study of interdiffusion in CdTe and ZnSe based quantum wells N2 - No abstract available Y1 - 1994 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37750 ER - TY - JOUR A1 - Becker, Charles R. A1 - He, L. A1 - Regnet, M. M. A1 - Kraus, M.M. A1 - Wu, Y. S. A1 - Landwehr, G. A1 - Zhang, X. F. A1 - Zhang, H. T1 - The growth and structure of short period (001) Hg\(_{1-x}\)Cd\(_x\)Te-HgTe superlattices N2 - Molecular beam epitaxially grown short period (001) Hg\(_{1_x}\)Cd\(_x\)Te-HgTe superlattices have been systematically investigated. Several narrow well widths were chosen, e.g., 30, 35 and 40 Å, and the barrier widths were varied between 24 and 90 Å for a particular well width. Both the well width and the total period were determined directly by means of x-ray diffraction. The well width was determined by exploiting the high reflectivity from HgTe and the low reflectivity from CdTe for the (002) Bragg reflection. Knowing the well and barrier widths we have been able to set an upper limit on the average Cd concentration of the barriers, \(\overline x_b\), by annealing several superlattices and then measuring the composition of the resulting alloy. \(\overline x_b\) was shown to decrease exponentially with decreasing barrier width. The structure of a very short period superlattice, i.e., 31.4 Å, was also investigated by transmission electron microscopy, corroborating the x-ray diffraction results. Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37858 ER - TY - JOUR A1 - Wu, Y. S. A1 - Becker, Charles R. A1 - Waag, A. A1 - Schmiedl, R. A1 - Einfeldt, S. A1 - Landwehr, G. T1 - Oxygen on the (100) CdTe surface N2 - We have investigated oxygen on CdTe substrates by means of x-ray photoelectron spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED). A Te oxide layer that was at least 15 A thick was found on the surface of as-delivered CdTe substrates that were mechanically polished. This oxide is not easily evaporated at temperatures lower than 350°C. Furthermore, heating in air, which further oxidizes the CdTe layer, should be avoided. Etching with HCI acid (15% HCl) for at least 20 s and then rinsing with de-ionized water reduces the Te oxide layer on the surface down to 4% of a monoatomic layer. However, according to XPS measurements of the 0 Is peak, 20%-30% of a monoatomic layer of oxygen remains on the surface, which can be eliminated by heating at temperatures ranging between 300 and 340 cC. The RHEED patterns for a molecular beam epitaxially (MBE)-grown CdTe film on a (lOO) CdTe substrate with approximately one monoatomic layer of oxidized Te on the surface lose the characteristics of the normal RHEED pattems for a MBE-grown CdTe film on an oxygen-free CdTe substrate. Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37869 ER - TY - JOUR A1 - Kraus, M. M. A1 - Regnet, M. M. A1 - Becker, Charles R. A1 - Bicknell-Tassius, R. N. A1 - Landwehr, G. T1 - Comparison of band structure calculations and photoluminescence experiments on HgTe/CdTe superlattices grown by molecular beam epitaxy N2 - We have grown HgTe/CdTe superlattices by molecular beam epitaxy; barrier thicknesses were in the range from 15 to 91 Å and the well thickness was maintained at a constant value of 30 Å. The infrared photoluminescence was investigated by means of Fourier transform infrared spectroscopy in the temperature range from 4.2 to 300 K. All superlattices showed pronounced photoluminescence at temperatures up to 300 K. To gain more detailed insight into the band structure of the HgTe/CdTe superlattices, band structure calculations were performed. The concept of the envelope function approximation was followed. Employing the transfer matrix method, the calculations were completed taking into account an eight band k·p model. An important parameter in these calculations is the natural valence band offset (VBO) between the well and barrier materials. As a general trend, the value for the direct gap decreases with increasing VBO. The experimentally determined energies of the band gap are in reasonable agreement with the values obtained by the theoretical calculations. A comparison between theory and experiment shows that the observed transition energies are closer to calculations employing a large offset (350 meV) as opposed to a small VBO (40 meV). Y1 - 1992 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37878 ER - TY - JOUR A1 - Herrmann, K. H. A1 - Happ, M. A1 - Möllmann, K.-P. A1 - Tomm, J. W. A1 - Becker, Charles R. A1 - Kraus, M. M. A1 - Yuan, S. A1 - Landwehr, G. T1 - A new model for the absorption coefficient of narrow gap (Hg,Cd)Te that simultaneously considers band tails and band filling N2 - A semiempirical model is presented that correlates the broadening of the absorption edge with both transitions below the energy gap and with transitions by the Kane band model. This model correctly fits both the absorption and luminescence spectra of narrow-gap (Hg,Cd)Te samples that have been grown by the traveling heater method as well as by molecular-beam epitaxy. The accuracy of the band-gap determination is enhanced by this model. Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37894 ER - TY - JOUR A1 - Waag, A. A1 - Heinke, H. A1 - Scholl, S. A1 - Becker, Charles R. A1 - Landwehr, G. T1 - Growth of MgTe and Cd\(_{1-x}\)Mg\(_x\)Te thin films by molecular beam epitaxy N2 - We report on the growth of the compound semiconductor MgTe as weil as the ternary alloy Cd\(_{l-x}\)Mg, Te by molecular hcam cpitaxy. This is to our knowkdgc thc first time that this material has heen grown by any epitaxial technique. Bulk MgTe, which is hygroscopic, has a band gap of 3.0 eV and crystallizcs usually in thc wurtzite structure. Pseudomorphic films were grown on zincblende Cd Te suhstrates for a MgTe thickness helow a critical layer thickncss of approximately 500 nm. In addition, Cd\(_{l_x}\),Mg\(_x\)Te epilayers were grown with a Mg concentration between 0 and 68%, which corresponds to a band gap betwcen 1.5 and 2.5 eV at room temperature. The crystalline quality of thc layers is comparabk to CdTc thin films as long as they are fully strained. The lauice constant of zincblende MgTe is slightly smaller than that of CdTe, and the lattice mismatch is as low as O.7%. In addition highly n-type CdMgTe layers were fabricatcd by hromine doping. The tunability of the band gap as weil as the rather good laUice match with CdTc makes the matcrial interesting for optoelectronic device applications for the entire visible range. Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37917 ER - TY - JOUR A1 - Shanjia, Xu A1 - Xinzhang, Wu A1 - Greiner, P. A1 - Becker, Charles R. A1 - Geick, R. T1 - Microwave transmission and reflection of stratified lossy dielectric segments partially filled waveguide N2 - The microwave transmission and reßection is evaluated for stratified lossy dielectric segments partially filling the rectangular waveguide by the method which combines the multimode network theory with the rigorous mode matching procedure. As an example, we investigate in detail the microwave scattering properties of II-VI-epitaxial layer on a lossy dielectric substrate inserted in the rectangular waveguide. The experimental data verify the accuracy and the effectiveness of the present method. Extensive numerical results are presented to establish useful guidelines for the contactless microwave measurement of the conductivity of the epitaxiallayer. Y1 - 1992 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37958 ER - TY - JOUR A1 - Shanjia, Xu A1 - Xinzhang, Wu A1 - Boege, P. A1 - Schäfer, H. A1 - Becker, Charles R. A1 - Geick, R. T1 - Scattering characteristics of 3-D discontinuity consisting of semiconductor sample filled in waveguide with gaps N2 - No abstract available Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37964 ER - TY - JOUR A1 - He, L. A1 - Becker, Charles R. A1 - Bicknell-Tassius, R. N. A1 - Scholl, S. A1 - Landwehr, G. T1 - Molecular beam epitaxial growth and evaluation of intrinsic and extrinsically doped (100) Hg\(_{0.8}\)Cd\(_{0.2}\)Te on (100) Cd\(_{0.96}\)Zn\(_{0.04}\)Te N2 - No abstract available. Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37885 ER - TY - JOUR A1 - Schikora, D. A1 - Hausleitner, H. A1 - Einfeldt, S. A1 - Becker, Charles R. A1 - Widmer, T. A1 - Giftige, C. A1 - Lischka, K. A1 - von Ortenburg, M. A1 - Landwehr, G. T1 - Epitaxial overgrowth of II-VI compounds on patterned substrates N2 - The selected area epitaxial overgrowth of narrow gap HgTe as well as wide gap CdTe and ZnTe on CdTe/GaAs substrates, which had been structured by dry etching techniques, has been investigated. A plasma etching process using a barrel reactor with CH\(_4\)-CH\(_2\) gases has been employed to prepare stripes with a width of about 1 μm with anisotropic as well as isotropic etching profiles. It has been found, that the selected area HgTe overgrowth takes place with a high local selectivity to the low index planes of the patterned surface. In contrast, the selected area overgrowth of the wide gap CdTe and ZnTe is controlled by anisotropic growth kinetics provided that the substrate temperature is not lower than 220°C and the starting surface consists of well developed low index crystallographic planes. Y1 - 1994 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37985 ER - TY - JOUR A1 - Einfeldt, S. A1 - Heinke, H. A1 - Behringer, M. A1 - Becker, Charles R. A1 - Kurtz, E. A1 - Hommel, D. A1 - Landwehr, G. T1 - The growth of HgSe by molecular beam epitaxy for ohmic contacts to p-ZnSe N2 - The structural properties of HgSe grown by molecular beam epitaxy (MBE) are investigated for different lattice mismatches to the substrate and various growth conditions. The growth rate is shown to depend strongly on the growth temperature above lOO°C as well as on the Hg/Se flux ratio. It has been found that the crystalline perfection and the electrical properties are mainly determined by the layer thickness, especially for the growth on highly lattice mismatched substrates. Changes in the surface morphology are related to growth parameters. Differences between the electrical behavior of MBE-grown and bulk HgSe are discussed. The electrical properties of HgSe contacts on p-ZnSe are investigated as a function of different annealing procedures. Y1 - 1994 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-38001 ER - TY - JOUR A1 - Wu, Y. S. A1 - Becker, Charles R. A1 - Waag, A. A1 - Bicknell-Tassius, R. N. A1 - Landwehr, G. T1 - Removal of oxygen and reduction of carbon contamination on (100) Cd\(_{0.96}\)Zn\(_{0.04}\)Te N2 - No abstract available Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-38014 ER - TY - JOUR A1 - Zhang, X. F. A1 - Becker, Charles R. A1 - Zhang, H. A1 - He, L. A1 - Landwehr, G. T1 - Investigation of a short period (001) HgTe-Hg\(_{0.6}\)Cd\(_{0.4}\)Te superlattice by transmission electron microscopy N2 - No abstract available Y1 - 1994 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-38029 ER - TY - JOUR A1 - Becker, Charles R. A1 - Martin, T. P. T1 - Infrared absorption by Impurity-pair resonant modes in NaCl:F N2 - New resonant-mode infrared absorption lines have been observed in NaCl with high concentrations of fluorine impurities. The quadratic concentration dependence of the strength of these lines indicates that they are due to pairs of fluorine impurities. At the resonant frequencies, the motion of some host ions appears to be as important as the motion of the impurities themselves. KW - Festkörperphysik Y1 - 1972 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37840 SN - 1098-0121 ER - TY - JOUR A1 - Becker, Charles R. A1 - Nath, G. T1 - Optical properties of LiIO\(_3\) in the far infrared N2 - No abstract available Y1 - 1970 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37905 ER - TY - JOUR A1 - Röder, G. A1 - Steinlein, C. A1 - Schmid, M. A1 - Linsenmair, Karl Eduard T1 - Karyotype and chromosome banding in the Turkish desert woodlouse Desertellio elongatus (Crustacea, Isopoda, Oniscidea) N2 - The karyotype of D. elongatus was investigated by means of C-banding, silver staining, and mithramycinand quinacrine fluorescent staining. The diploid chromosome number is 2n = 50. C-banding shows pericentromerically localized constitutive heterochromatin in every chromosome. Two of the chromosome pairs carry two telomeric nucleolus organizer regions each. No heteromorphic sex chromosomes were found. KW - Karyotype; chromosome banding; Desertellio elongatus; Crustacea; Isopoda; Oniscidea Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30989 ER - TY - JOUR A1 - Linsenmair, Karl Eduard T1 - Comparative studies on the social behaviour of the desert isopod Hemilepistus reaumuri and of a Porcellio species N2 - Behavioural adaptations have made the desert isopod Hemilepistus reaumuri the most successful herbivore and detritivore of the macrofauna of many arid areas in North Africa and Asia Minor. For survival and reproduction Hemilepistus is dependent on burrows. New burrows can only be dug during spring. With the time-consuming digging of a burrow, Hemilepistus has only made the first step towards solving its ecological problems. The burrows are vital and have to be continuously defended against competitors. This requirement is met by co-operation of individuals within the framework of a highly developed social behaviour. In spring adults form monogamous pairs in which partners recognize each other individually and later form, with their progeny, strictly closed family communities. Hemilepistus is compared with a Porcellio' sp. which has developed, convergently, a social behaviour which resembles that of Hemilepistus in many respects, but differs essentially in some aspects, partly reflecting differences in ecological requirements. This and a few other Porcellio species demonstrate some possible steps in the evolution of the social behaviour of Hemilepistus. The female Hemilepistus is-in contrast to Porcellio sp. - semelparous and the selective advantages of monogamy in its environment are not difficult to recognize. This chapter discusses how this mating system could have evolved and especially why monogamous behaviour is also the best method for the Hemilepistus male to maximize its reproductive success. The cohesion of pairs and of family communities in Hemilepistus is based on a highly developed chemical communication system. Individual- and family-specific badges owe their specificity to genetically determined discriminating substances. The nature of the badges raises a series of questions: e.g. since alien badges release aggression, how do parents avoid cannibalizing their young? Similar problems arise from the fact that family badges are mixtures of chemical compounds of very low volatility with the consequence that they can only be transferred by direct contact and that during moulting all substances are lost which an individual does not produce itself. It is shown that in solving these problems inhibiting properties (presumably substances) and learning play a dominant role. Y1 - 1984 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30846 ER - TY - JOUR A1 - Linsenmair, Karl Eduard T1 - Individual and family recognition in subsocial arthropods, in particular in the desert isopod Hemilepistus reaumuri N2 - Individual recogmtlon in the non-eusocial arthropods is, according to our present knowledge, predominantly found in the frame of permanent or temporary monogamy. In some cases, e. g. in stomatopods and possibly other marine crustaceans too, individual recognition may serve to allow identification of (i) individuals within dominance hierarchies or (ii) neighbours in territorial species thus helping to avoid the repetition of unnecessary and costly fights. Kin recognition is experimentally proven only in some isopod species (genera Hemilepistus and Porcel/io) and in the primitive cockroach (termite?) Cryptocercus. The «signatures» or «discriminators» used in the arthropods are chemical. It is assumed that the identifying substances are mainly genetically determined and in this paper I shall discuss possible evolutionary origins. The main part of this account is devoted to the presentation of some aspects of the highly developed individual and kin identification and recognition system in the desert isopod Hemilepistus reaumuri - a pure monogamous species in which pairs together with their progeny form strictly exclusive family units. Amongst other things problems of (i) mate choice, (ii) learning to recognize a partner, (iii) avoiding the un adaptive familiarization with aliens are treated. Monogamy under present conditions is for both sexes the only suitable way of maximizing reproductive success; an extremely strong selection pressure must act against every attempt to abandon monogamy under the given ecological conditions. The family «badges» which are certainly always blends of different discriminator substances are extremely variable. This variability is mainly due to genetical differences and is not environmentally caused. It is to be expected that intra-family variabiliry exists in respect of the production of discriminator substances. Since the common badge of a family is the result of exchanging and mixing individual substances, and since the chemical nature of these discriminators requires direct body contacts in order to acquire those substances which an individual does not produce itself, problems must arise with molting. These difficulties do indeed exist and they are aggravated by the fact that individuals may produce substances which do not show up in the common family badge. An efficient learning capability on the one hand and the use of inhibiting properties of newly molted isopods help to solve these problems. In the final discussion three questions are posed and - partly at least - answered; (i) why are families so strictly exclusive, (ii) how many discriminator substances have to be produced to provide a variability allowing families to remain exclusive under extreme conditions of very high population densities, (iii) what is the structure of the family badge and what does an individual have to learn apart from the badge in order not to mistake a family member for an alien or vice versa. Y1 - 1985 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33957 ER - TY - JOUR A1 - Linsenmair, Karl Eduard A1 - Linsenmair, Christa T1 - Paarbildung und Paarzusammenhalt bei der monogamen Wüstenassel Hemilepistus reaumuri (Crustacea, Isopoda, Oniscoidea) N2 - No abstract available Y1 - 1971 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33937 ER - TY - JOUR A1 - Grafe, U. A1 - Linsenmair, Karl Eduard T1 - Protogynous sex change in the Reed Frog: Hyperolius viridiflavus N2 - Observations on captive reed frogs Hyperolius viridijlavus ommatostictus showed that seven out of 24 females changed into males. Sex change occurred without any hormone treatment and resulted in completely functional males. The adaptive value is discussed in terms of maximizing life-time reproductive success. Hyperolius r. ommatostictus is the first amphibian known to show functional sex reversal. Y1 - 1989 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30990 ER - TY - JOUR A1 - Schmuck, R. A1 - Geise, W. A1 - Linsenmair, Karl Eduard T1 - Life cycle strategies and physiological adjustments of Reedfrog Tadpoles (Amphibia, Anura, Hyperoliidae) in relation to environmental conditions. N2 - The relationship between different degrees of intraspecific crowding of reedfrog tadpoles and their physiological responses to a deterioration of the natal pond water quality was examined under laboratory conditions. Tadpoles that were reared at a lower density metamorphosed significantly earlier than those raised at a higher density. As density increases, the average body length at metamorphosis decreases. However, at low tadpole density, a significantly higher diversity of body size classes among freshly metamorphosed froglets was observed than under more crowded conditions. Mortality increased during metamorphic climax and was inversely correlated with the tadpole density. In ephemeral ponds, an accumulation of nitrogenous wastes from metabolic processes and/or a concentration by evaporation in prolonged rainless periods can pose a considerable chemical stress to reedfrog tadpoles. Hyperolius viridiflavus ommatostictus responded to an increasing ammonia concentration with an activity increase of the ornithine cycle (intensified urea synthesis). hi contrast, Hyperolius marmoratus taeniatus exhibited a strong tolerance against high ammonia levels. A deterioration of the natal pond water quality caused H. v. ommatostictus and H. v. nitidulus tadpoles to adjust to harsher climatic conditions at the time of metamorphosis. This physiological preadjustment enabled the froglets to start feeding and growing immediately after metamorphosis even at low air humidity and rare precipitation events. In contrast, froglets that were raised in daily refreshed water exhibited high mortality rates if subjected to identical conditions. As one possible indicator of the actual climatic conditions prevailing in the surrounding terrestrial habitat, fluctuations in the water ammonia level are discussed. Y1 - 1994 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31009 ER - TY - JOUR A1 - Tacke, M. A1 - Schuberth, W. A1 - Becker, Charles R. A1 - Haas, L. D. T1 - The dielectric constant of PbTe at 4.2 K and \(\tilde ν\)=84.15 cm\(^{-1}\), 96.97 cm\(^{-1}\), 103.60 cm\(^{-1}\) N2 - The dielectric constant of a PbTe epitaxial layer has been measured by surface wave spectroscopy using an optically pumped far-infrared laser and the technique of attenuated total reflection. Y1 - 1982 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30821 ER - TY - JOUR A1 - Geis, G. A1 - Geick, R. A1 - Becker, Charles R. A1 - Wagner, V. T1 - Antiferromagnetic resonance in CoO/NiO mixed crystals N2 - We have studied the lowest magnetic excitation of Ni\(_{1-x}\)Co\(_x\)O mixed crystals for 0.94 \(\leq\) x \(\leq\) 1. Together with previous results for 0.02 \(\leq\) x \(\leq\) 0.07 and neutron data for x = 0.14 and x = 0.30, the results are discussed by means of a model, especially the variation of AFMR frequency and preferred spin direction with Co concentration x. Y1 - 1977 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31239 ER - TY - JOUR A1 - Becker, Charles R. T1 - Impurity-induced absorption in or near the phonon gap of KI N2 - In or near the phonon gap of KI a single weak line due to OW (OD\(^-\)) at 69.7 (69.3) cm\(^{-1}\) has been observed. A second and much stronger line at 94.1 cm\(^{-1}\) was shown not to be related to OH\(^-\), but instead is thought to be due to CO\(_3\). Y1 - 1970 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30757 ER - TY - JOUR A1 - Köhler, H. A1 - Becker, Charles R. T1 - Optically active lattice vibrations in Bi\(_2\)Se\(_3\) N2 - The preparation of Bi2Sea single crystals with low free carrier densities allowed an investigation of the lattice vibrations to be carried out from the reflectivity of cleavage planes at nearly normal incidence of the radiation (E ~ c). The experimental results ean be explained with two classical oscillators, whose eigenfrequencies oceur at 92 and 69.5 cm-I. The static dielectric constant was determined to be 100 ± 10 for E ~ c. N2 - Die Praparation von Bi2Se3-Einkristallen mit niedriger Konzentration freier Ladungstrager erlaubte die Untersllchung der Gitterschwingungcn aus dem Reflexionsvermogen von Spaltflaclwn bci nahezu senkreehter Inzidenz der Stmhlung (E ~ c). Die .:\'IeBergebnisse konnen mit zwei klassischen Dispersionsoszillatoren erklart werden, deren Eigenfrequenzen bei 92 und 69,5 cm- I liegen. Dic st,atische Dielektrizitatskonstante wurde zu 100 ± 10 für E ~ c bestimmt. Y1 - 1974 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31296 ER - TY - JOUR A1 - Klitzing, K. von A1 - Becker, Charles R. T1 - Far infrared photoconductivity of residual acceptors in pure tellurium N2 - The photoconductivity of both undeformed and deformed Te samples has been investigated at liquid He temperature by means of a Fourier spectrometer. Three peaks were usually found in the spectra of undeformed samples at 11, 24 and 46 cm\(^{-1}\). These are shown to be due to three different chemical impurities. The deformed samples are characterized by additional structure at higher frequencies. Y1 - 1976 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-31278 ER - TY - JOUR A1 - Becker, Charles R. T1 - Evidence for a quasi-phonon gap in CsCl N2 - The observed impurity induced far-infrared absorption in CsCl : Rb\(^+\) and CsCl : K\(^+\) is compared with a calculated density of acoustic phonon states in CsCl. The absorption due to CsCl : Rb\(^+\) displays a minimum between the acoustic and optic phonon bands. A narrow line is observed in CsCl: K\(^+\) at 85.8 cm\(^{-1}\) which falls in this quasi-phonon gap. Y1 - 1971 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30767 ER - TY - JOUR A1 - Reimer, Georg A1 - Scheer, Ulrich A1 - Peters, Jan-Michael A1 - Tan, Eng M. T1 - Immunolocalization and partial characterization of a nucleolar autoantigen (PM-Scl) associated with polymyositis / scleroderma overlap syndromes. N2 - Precipitating anti-PM-Sel antibodies are present in sera from patients with polymyositis. scleroderma. and polymyositis/scleroderma overlap syndromes. By indirect immunofluorescence microscopy. anti-PM-Scl antibodies stained the nucleolus in cells of different tissues and species. suggesting that the antigen is highly conserved. By electron microscopy, anti-PM-Scl antibodies reacted primarily with the granular component of the nuc1eolus. Drugs that inhibit rRNA synthesis had a marked effect on the expression of PM-Scl antigen. In actinomycin D-treated cells, immunofluorescence staining by anti-PM-Scl was signüicantly reduced with residual staining restricted to the granular regions of nuc1eoli. Treatment with 5,6-dichloro-beta-D- ribofuranosylbenzimidazole (DRB) also selectively reduced nuc1eolar staining. On a molecular level, anti-PM-Sel antibodies precipitated 11 polypeptides with molecular weights (Mr) ranging from 110,000 to 20,000. The Mr 80,000 and 20.000 polypeptides were phosphorylated. Evidence suggests that the PM-Scl antigen complex may be related to a prerlbosomal particle. Y1 - 1986 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33191 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Sommerville, John A1 - Bustin, M. T1 - Injected histone antibodies interfere with transcription of lampbrush chromosome loops in oocytes of Pleurodeles N2 - Antibodies to calf thymus histone H2B were purified by chromatography on DEAE-cellulose and injected into oocyte nuclei of Pleurodeles waltlii. As shown by indirect immunofluorescence these antibodies cross-reacted strongly with corresponding histones associated with lampbrush chromosomes. Shortly after injection the lateral loops of the chromosomes retracted into the chromomeres and by 3 h postinjection the 'lampbrush' appearance was completely lost and the chromosomes appeared in light-microscopic preparations as rod-like structures consisting of 10ngitudina11y coalesced chromomeres. In control oocytes injected with non-immune immunoglobulins or antibodies against a ubiquitous transcript-associated protein no morphological alterations of the lampbrush chromosomes could be observed. Electron microscopic spreads of chromosomes prepared at various times after injection of anti-H2B revealed a progressive loss of transcriptional complexes from the loop axes. Finally, higher-order chromatin configurations, like supranuc1eosomal globules (' superbeads ') or cable-like chromatin strands 50- 60 nm thick predominated, indicating complete transcriptional inactivation of a11 chromosomal regions. The results indicate that H2B antibodies react specifically with his tones associated with the transcribed DNA of lateral loops in their native state. The resulting antigenantibody complexes seem to inhibit progression of the R A polymerases along the template, thus causing the premature release of transcripts, a process analogous to the stripping effect of actinomycin D. The demonstration of histones associated with heavily transcribed regions, which are not compacted into nucleosomes but largely extended, supports the current concept that unfolding of nucleosomes to a110w transcription of the DNA does not involve dissociation of histones. In contrast, amplified ribosomal RNA genes are unaffected by injected HzB antibodies. This does not necessarily indicate absence of his tones from nucleolar chromatin, since we do not know whether it is accessible in vivo to antibodies or whether the histone antigenie determinants are masked by the presence of other proteins. The technique of injecting specific antibodies should be widely applicable when analysing the in vivo distribution of chromosomal components at the electron-microscopic level and when studying complex metabolie processes, like the cleavage and modification of RNA, by selective inhibition of defined enzymic steps. Y1 - 1979 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33166 ER - TY - JOUR A1 - Reimer, Georg A1 - Rose, Kathleen M. A1 - Scheer, Ulrich A1 - Tan, Eng M. T1 - Autoantibody to RNA polymerase I in scleroderma sera N2 - Autoantibodies to components of the nucleolus are a unique serological feature of patients with scleroderma. There are autoantibodies of several specificities; one type produces a speckled pattern of nucleolar staining in immunofluorescence. In actinomycin D and 5,6-dichloro-{j-D-ribofuranosylbenzimidazoletreated Vero cells, staining was restricted to the fibrillar and not the granular regions. By double immunofluorescence, specific rabbit anti-RNA polymerase I antibodies stained the same fibrillar structures in drug-segregated nucleoli as scleroderma sera. Scleroderma sera immunoprecipitated 13 polypeptides from (35S)methionine-labeled HeLa cell extract with molecular weights ranging from 210,000 to 14,000. Similar polypeptides were precipitated by rabbit anti-RNA polymerase I antibodies, and their common identities were confirmed in immunoabsorption experiments. Microinjection of purified IgG from a patient with speckled nucleolar staining effectively inhibited ribosomal RNA transcription. Autoantibodies to RNA polymerase I were restricted to certain patients with scleroderma and were not found in other autoimmune diseases. Y1 - 1987 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34294 ER - TY - JOUR A1 - Reinhard, Matthias A1 - Halbrügge, Maria A1 - Scheer, Ulrich A1 - Wiegand, Christiane A1 - Jockusch, Brigitte M. A1 - Walter, Ulrich T1 - The 46/50 kDa phosphoprotein VASP purified from human platelets is a novel protein associated with actin filaments and focal contacts N2 - Vasoactive agents which elevate either cGMP or cAMP inhibit platelet activation by pathways sharing at least one component, the 46/50 kDa vasodilator-stimulated phosphoprotein (V ASP). V ASP is stoichiometrically phosphorylated by both cGMP-dependent and cAMPdependent protein kinases in intact human platelets, and its phosphorylation correlates very well with platelet inhibition caused by cGMP- and cAMP-elevating agents. Here we report that in human platelets spread on glass, V ASP is associated predominantly with the distal parts of radial micro filament bundles and with microfilaments outlining the periphery, whereas less V ASP is associated with a central microfilamentous ring. V ASP is also detectable in a variety of different cell types including fibroblasts and epithelial cells. In fibroblasts, V ASP is concentrated at focal contact areas, along microfilament bundles (stress fibres) in a punctate pattern, in the periphery of protruding lamellae, and is phosphorylated by cGMP- and cAMP-dependent protein kinases in response to appropriate stimuli. Evidence for the direct binding of V ASP to F -actin is also presented. The data demonstrate that V ASP is a novel phosphoprotein associated with actin filaments and focal contact areas, i.e. transmembrane junctions between microfilaments and the extracellular matrix. KW - cAMP / cGMP / cytoskeleton / phosphorylation / protein kinase Y1 - 1992 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34246 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Dabauvalle, Marie-Christine A1 - Merkert, Hilde A1 - Benavente, Ricardo T1 - The nuclear envelope and the organization of the pore complexes N2 - No abstract available Y1 - 1988 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34275 ER - TY - JOUR A1 - Schubert, D.W. A1 - Kraus, M.M A1 - Kenklies, R. A1 - Becker, Charles R. A1 - Bicknell-Tassius, R.N. T1 - Composition and wavelength dependence of the refractive index in Cd\(_{1-x}\)Mn\(_x\)Te epitaxial layers N2 - We have investigated Cd\(_{1-x}\)Mn\(_x\)Te thin films with Mn concentrations of x=0.12, 0.18, 0.30, 0.52, and 0.70. These single crystal layers were grown by molecular beam epitaxy on [001] CdTe substrates. The real part of the refractive index, n, was determined below the band-gap Eo in the range of 0.5-2.5 eV at T=300 K. The parallel reOectivity was measured near the Brewster angle at the YAG laser wavelength of 1.064 J.Lm (hv= 1.165 eV). Combining these results with the optical pathlength results (nd) of reOection measurements in a Fourier spectrometer we have determined n(x,v) over a wide spectral range by utilizing a three parameter fit. The accuracy of these results for n should improve waveguide designs based on this material. Y1 - 1992 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-37716 ER - TY - JOUR A1 - Bell, Peter A1 - Dabauvalle, Marie-Christine A1 - Scheer, Ulrich T1 - In vitro assembly of prenucleolar bodies in Xenopus egg extract N2 - Nuclei assembled in Xenopus egg extract from purified DNA or chromatin resemble their natural counterparts in a number of structural and functional features. However, the most obvious structural element of normal interphase nuclei, the nucleolus, is absent from the in vitro reconstituted nuclei. By EM, cytological silver staining, and immunofluorescence microscopy employing antibodies directed against various nucleolar components we show that nuclei assembled in vitro contain numerous distinct aggregates that resemble prenucleolar bodies (PNBs) by several criteria. Formation of these PNB-like structures requires pore complex-mediated nuclear transport of proteins but is independent of the genetic content of the in vitro nuclei as well as transcriptional and translational events. Our data indicate that nuclei assembled in vitro are capable of initiating early steps of nucleologenesis but that the resulting PNBs are unable to fuse with each other, probably due to the absence of a functional nucleolus organizer. With appropriate modifications, this experimental system should be useful to define and analyze conditions promoting the site-specific assembly of PNBs into a coherent nucleolar body. Y1 - 1992 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34233 ER - TY - JOUR A1 - Scheer, Ulrich T1 - Identification of a novel class of tandemly repeated genes transcribed on lampbrush chromosomes of Pleurodeles waltlii N2 - Electron microscope preparations of lampbrush chromosomes from oocytes of Pleurodeles waltl;; have revealed a new class of tandemly repeated genes. These genes are highly active, as judged by the close spacing of nascent transcripts. They occur in clusters of >100 copies and are transcribed in units containing roughly 940 base pairs of DNA that are separated by nontranscribed spacers of an estimated DNA content of 2,410 base pairs. The size and the pattern of arrangement of these transcription units can not be correlated with any of the repetitious genes so far described. Y1 - 1981 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33153 ER - TY - JOUR A1 - Franke, Werner W. A1 - Kleinschmidt, Jürgen A. A1 - Spring, Herbert A1 - Krohne, Georg A1 - Grund, Christine A1 - Trendelenburg, Michael F. A1 - Stöhr, Michael A1 - Scheer, Ulrich T1 - A nucleolar skeleton of protein filaments demonstrated in amplified nucleoli of Xenopus laevis N2 - The amplified, extrachromosomal nucleoli of Xenopus oocytes contain a meshwork of -4-nm-thick filaments, which are densely coiled into higher-order fibrils of diameter 30-40 nm and are resistant to treatment with high- and low-salt concentrations, nucleases (DNase I, pancreatic RNase, micrococcal nuclease), sulfhydryl agents, and various nonionic detergents. This filamentous "skeleton" has been prepared from manually isolated nuclear contents and nucleoli as weil as from nucleoli isolated by fluorescence-activated particle sorting. The nucleolar skeletons are observed in light and electron microscopy and are characterized by ravels of filaments that are especially densely packed in the nucleolar cortex. DNA as weil as RNA are not constituents of this structure, and precursors to ribosomal RNAs are completely removed from the extraction-resistant filaments by treatment with high-salt buffer or RN ase. Fractions of isolated nucleolar skeletons show specific enrichment of an acidic major protein of 145,000 mol wt and an apparent pi value of -6.15, accompanied in some preparations by various amounts of minor proteins. The demonstration of this skeletal structure in "free" extrachromosomal nucleoli excludes the problem of contaminations by nonnucleolar material such as perinucleolar heterochromatin normally encountered in studies of nucleoli from somatic cells. It is suggested that this insoluble protein filament complex forms a skeleton specific to the nucleolus proper that is different from other extraction-resistant components of the nucleus such as matrix and lamina and is involved in the spatial organization of the nucleolar chromatin and its transcriptional products. In studies of the organization of the interphase nucleus, considerable progress has been made in the elucidation of the arrangement of chromatin components and transcriptional products. However, relatively little is known about the composition and function of another category of nuclear structures, the nonnucleoproteinaceous architectural components that are insoluble in solutions of low and high ionic strength, despite numerous studies dedicated to this problem. Such structures include (a) the nuclear envelope and its pore complexes (I, 15, 18, 23, 37, 41), (b) a peripheral layer of insoluble protein ("lamina"; I, 15, 22, 23, 59), (e) certain skeletal proteins related to the chromosome "scaffold" described by Laemmli and coworkers (see references 2 and 3), and (d) ill-defined tangles of fibrillar structures of the nuclear interior that are collectively described as residual "matrix" (6, 21 ; for reviews, see references THE JOURNAL OF CEll BrOlOGY . VOlUME 90 AUGUST 1981 289-299 © The RockefeIler University Press · 0021 -9525/ 81 / 08/ 0289/ 11 $1 .00 4 and 12). The latter, preparatively Y1 - 1981 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33130 ER - TY - JOUR A1 - Franke, Werner W. A1 - Scheer, Ulrich A1 - Krohne, Georg A1 - Jarasch, Ernst-Dieter T1 - The nuclear envelope and the architecture of the nuclear periphery N2 - No abstract available Y1 - 1981 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33108 ER - TY - JOUR A1 - Bona, Marion A1 - Scheer, Ulrich A1 - Bautz, Ekkehard K. F. T1 - Antibodies to RNA polymerase II (B) inhibit transcription in lampbrush chromosomes after microinjection into living amphibian oocytes N2 - Antibodies directed against RNA polymerase II (B) from Drosophila melanogaster were obtained from rabbit sera and, as monoclonal immunoglobulins, from mouse hybridomas and shown to cross-react with the amphibian enzyme protein. Localization by indirect immunofluorescence microscopy revealed the association of this enzyme with chromatin of interphase nuclei of amphibian cells and its absence in nucleoli. Purified immunoglobulins were microinjected in to nuclei ofliving vitellogenic oocytes of Ple1lrodeles waltlii and X enopus laevis and their effects on transcriptional processes were monitored by biochemical and light and electron microscopic stud ies. RNA polymerase II antibodies from rabbit sera caused a rapid and almost complete release of nascent transcripts from the chromatin axis of the loops of lampbrush chromosomes, followed by collapse of the loops and their retraction on the main chromosome axis. Monoclonal murine antibodies to the Iarge RNA polymerase II subunits also inhibited transcription in chromosome Ioops but appeared to inhibit initiation rather than elongation events. Activities of class land III RNA polymerases were not significantly affected by injection of antibodies to polymerase II, indicating immunological differences between the three RNA polymerases. The potential value of the in vitro test system described , as a very sensitive assay for detecting proteins involved in transcription in living cells, is discussed. 1 Y1 - 1981 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33128 ER - TY - JOUR A1 - Trendelenburg, Michael F. A1 - Scheer, Ulrich A1 - Zentgraf, Hanswalter A1 - Franke, Werner W. T1 - Heterogeneity of spacer lengths in circles of amplified ribosomal DNA of two insect species, Dytiscus marginalis and Acheta domesticus N2 - No abstract available Y1 - 1976 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33055 ER - TY - JOUR A1 - Emmrich, F. A1 - Moll, Heidrun A1 - Simon, Markus M. T1 - Recombinant human interleukin 2 acts as a B cell growth and differentiation promoting factor N2 - Human B cells appropriately activated by a B cell mitogen are rendered susceptible to human Interleukin 2 (IL-2) as demonstrated with recombinant human IL-2 (rec. h IL-2). They show increased proliferation and drastically enhanced immunoglobulin secretion. Susceptibility to IL-2 is accompanied with the expression of the IL-2 receptor (Tac antigen) on B cells. The data suggest that IL-2 is one of the lymphokines directly involved in the activation of B lymphocytes. Y1 - 1985 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34132 ER - TY - JOUR A1 - Moll, Heidrun A1 - Emmrich, F. A1 - Simon, Markus M. T1 - Recombinant human interleukin 2 directly provides signals for the proliferation and functional maturation of murine B lymphocytes N2 - In this study the effect of recombinant human interleukin 2 (rec.hIL-2) on the proliferation and maturation of B lymphocytes was investigated. It was found that the presence of rec.hIL 2 results in proliferation of mitogen (LPS)-activated B cell blasts. In addition, it is shown that highly enriched murine B cells can be induced by rec.hIL-2 to proliferate and to develop into antibody-secreting cells (PFC) in the presence of antigen (SRBC). When tested for its effect on B cell preparations enriched for resting (small) or activated (blasted) B lymphocytes, it was found that rec.hIL 2 provides signals for both B cell populations to develop into PFC. In contrast, induction of proliferation by the same lymphokine source was only seen in blasted B cells. The data indicate that IL 2 is involved in the generation of B effector cells by directly acting on their precursors thereby providing differentiation as well as proliferation signals. Y1 - 1985 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34090 ER - TY - JOUR A1 - Simon, Markus M. A1 - Moll, Heidrun A1 - Prester, Marlot A1 - Nerz, Gaby A1 - Eichmann, Klaus T1 - Immunoregulation by mouse T-cell clones. I. Suppression and amplification of cytotoxic responses by cloned H-Y-specific cytolytic T lymphocytes. N2 - H-Y-specific and H-2Db-restricted, Lyt-1 "2+ T-cell clones (CTLL) with graded specific cytotoxic activities on male C57BL/6 (B6) target cells (1E3, +++; 2C5, ++; 2A5, +, 3E6, ±) were tested for their capacity to inhibit the generation of H-Y-specific cytotoxic T lymphocytes (CTL) in vitro. Addition of irradiated lymphocytes of CTLL 1E3 and CTLL 3E6 but not those of CTLL 2A5 or CTLL 2C5 abolished the generation of CTL from in vivo primed H-Y-specific precursor cells (CTLP) when added to fresh mixed-lymphocyte cultures (MLC). Exogenous sources of T-cell growth factors (TCGF) did not overcome suppression. Rather the presence of TCGF resulted in a further enhancement of suppressive activities in CTLL 1E3 and 3E6 and the induction of similar activities in cells from CTLL 2A5 and 2C5, which by themselves were not inhibitory. Moreover when added to similar MLC on Day 1 instead of Day 0, only irradiated cells of CTLL 3E6 but not those of the other three CTLL were suppressive. Induction of suppressive activities in H-Y-specific CTLL was independent of the appropriate male stimulator cells since it was also observed in MLC induced by irrelevant antigens (H-2, trinitrophenol). Furthermore at low cell numbers, irradiated lymphocytes from any of the CTLL consistently enhanced CTL activities generated from H-Y-specific CTLP. This augmenting activity, which was not TCGF, could be transferred by soluble mediators present in antigen-sensitized CTLL cultures. Thus, these data indicate (i) that cytotoxic effector cells can function as suppressor cells in the generation of CTL, (ii) that the cytotoxic activity of cloned CTL does not correlate with their capacity to suppress CTL responses, (iii) that the inhibition of CTL responses by CTLL is not due to simple consumption of T-cell growth factors produced in MLC, and (iv) that different CTL clones may interfere with the generation of CTL at different stages of their maturation. Moreover, the experiments suggest an antigen-independent enhancement of suppression by the interaction of CTL with lymphokines. Together with the augmenting activity evoked by cloned CTL the data provide strong evidence for the expression of multiple immunological functions by one particular subset of T cells and suggest that cytotoxic effector cells can differentially regulate the maturation and/or clonal expression of their precursor cells. Y1 - 1984 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30892 ER - TY - JOUR A1 - Moll, Heidrun A1 - Eichmann, K. A1 - Simon, M. M. T1 - Immunoregulation by mouse T-cell clones. II. The same H-Y-specific T helper clone can provide help for the generation of cytotoxic lymphocytes and of antibody-secreting cells. N2 - Mouse H-Y-specific and I-Ab restricted T-cell clones have been established and compared for their helper effects in the differentiation ofboth T and B Iymphocytes. The results demonstrate that three individual T -cell clones and one subclone could help in the antigen-driven induction of cytotoxic Iymphocytes (CTL) from their precursor cells (CTL-P), and were able to activate B cells to develop into antibody-secreting cells (PFC) in the presence of SRBC, provided the cloned T cells were restimulated by H-Y antigen on antigen-presenting cells. In addition, antigen or lectin could induce the same H -Y -specific T -cell clones to secrete factor(s) expressing helper activities similar to that ofthe cloned T cells. Furthermore, it is shown that the T cell-derived soluble mediator(s) was distinct from T-cell growth factor (TCGF) and from immune interferon (lFN-y). The data reveal a new type ofT cell with helper potential for the activation ofCTL-P and B Iymphocytes, and suggest the existence of distinct T helper cells which can provide help for both cytotoxic and antibody responses by virtue of different Iymphokine activities. Y1 - 1985 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30903 ER - TY - JOUR A1 - Frischholz., S. A1 - Röllinghoff, M. A1 - Moll, Heidrun T1 - Cutaneous leishmaniasis: Co-ordinate expression of granzyme A and lymphokines by CD4\(^+\) T cells from susceptible mice. JF - Immunology N2 - We have recently demonstrated that the frequency ofT cells expressing granzyme A is significantly higher in skin lesions and spleens of susceptible BALB/c mice compared with resistant C57BL/6 mice infected with Leishmania major, a cause of human cutaneous leishmaniasis. In the present study, we have performed in vitro studies to characterize the subpopulation, the antigen responsiveness and the lymphokine production pattern of granzyme A-expressing T cells in L. major-infected mice. Using a limiting dilution system for functional analysis of selected T cells at the clonallevel, we could show that granzyme A activity in infected BALB/c mice can be assigned to L. major-reactive CD4\(^+\) T cells secreting interleukin-2 (IL-2) and IL-4. Granzyme A production was most pronounced in the early phase of infection. On the other hand, granzyme A expression could not be detected in C57BL/6-derived T cells responding to L. major. The da ta support the suggestion that granzyme A is produced by L. major-responsive CD4\(^+\) T cells facilitating lesion formation and the dissemination of infection. Y1 - 1994 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-30954 VL - 82 SP - 255 EP - 260 ER - TY - JOUR A1 - Fiala, Brigitte A1 - Grunsky, Harald A1 - Maschwitz, Ulrich A1 - Linsenmair, Karl Eduard T1 - Diversity of ant-plant interactions: Protective efficacy in Macaranga species with different degrees of ant-association. N2 - The pioneer tree Macaranga in SE Asia has developed manyfold associations with ants. The genus comprises all stages of interaction with ants, from facultative relationships to obligate myrmecophytes. Only myrmecophytic Macaranga offer nesting space for ants and are associated with a specific ant partner. The nonmyrmecophytic species are visited by a variety of different ant species which are attracted by extrafloral nectaries (EFN) and food bodies. Transitional Macaranga species like M. hosei are colonized later in their development due to their stem structure. Before the colonization by their specific Crematogaster partner the young plants are visited by different ant species attracted by EFN. These nectaries are reduced and food body production starts as soon as colonization becomes possible. We demonstrated earlier that obligate ant partners can protect their Macaranga plants against herbivore damage and vine cover. In this study we focused on nonspecific interactions and studied M. tanarius and M. hosei, representing a non-myrmecophyte and a transitional species respectively. In ant exclusion experiments both M. tanarius and M. hosei suffered significantly higher mean leaf damage than controls, 37% versus 6% in M. hosei, 16% versus 7% in M. tanarius. M. tanarius offers both EFN and food bodies so that tests for different effects of these two food rewards could be conducted. Plants with food bodies removed but with EFN remaining had the lowest mean increase of herbivore damage of all experimental groups. Main herbivores on M. hosei were mites and caterpillars. Many M. tanarius plants were infested by a shootborer. Both Macaranga species were visited by various ant species. Crematogaster spp. being the most abundant. We found no evidence for any specific relationships. The results of this study strongly support the hypothesis that non-specific, facultative associations with ants can be advantageous for Macaranga plants. Food bodies appear to have lower attractive value for opportunistic ants than EFN and may require a specific dietary adaptation. This is also indicated by the fact that food body production in the transitional M. hosei does not start before stem structure allows a colonization by the obligate Crematogaster species. M. hosei thus benefits from facultative association with a variety of ants until it produces its first domatia and can be colonized by its obligate mutualist. KW - Ant-plant interactions ; Herbivory Macaranga ; Mutualism ; Myrmecophytes Y1 - 1994 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-32905 ER - TY - JOUR A1 - Fiala, Brigitte A1 - Maschwitz, Ulrich T1 - Studies on the south east asian ant-plant association Crematogaster borneensis / Macaranga: adaptations of the ant partner. N2 - C. borneensis (Myrmicinae) lives in dose association with several myrmecophytic species of the South East Asian pioneer tree genus Macaranga (Euphorbiaceae). The ants are adapted to the plants so dosely that they do not survive away from it. The only food they utilize is provided as food bodies by the plant and honeydew from specific scale insects kept inside the hollow internodes. The anatomy of the digestive tract is also adapted to life on the host plant: the crop is very sm all and can store only minute food quantities. C. borneensis exdusively colonizes certain Macaranga species. Queens as weIl as workers are able to recognize their host plant species, probably by chemical cues. Colony founding queens swarm throughout the year, mostly during darkness. There is strong competition among queens for host plants. Queens do not carry scale insects on their nuptial flight. Worker ants are active day and night. Most of them patrol and collect food bodies on the younger parts of the host plant. An important characteristic is their deaning behaviour, which results in removal of aIl foreign objects. Even though they are rather smalI, workers respond very aggressively to certain kinds of disturbance of the host plant. The ants attack most phytophagous insects and are especially effective in killing and removing smalI, softbodied herbivores (e.g. caterpillars). They do not possess a functional sting, but apply defensive secretion and-once biting an intruder-will not let go. Their effective alarm system results in a mass attack, which provides adequate defence for the colony and the host plant. A comparison with another Crematogaster species further illustrated the special adaptations of C. borneensis to its host plant. N2 - Untersuchungen über die südostasiatische Ameisen·Pflanzen-Vergesellschaftung Cremattogaster borneensis Maoaranga : Anpassungen des Ameisenpartners 213 C. borneensis (Myrmicinae) lebt in enger Gemeinschaft mit myrmekophytischen Arten der südostasiatischen Pionierbaumgattung Macaranga (Euphorbiaceae) . Die Ameise ist so eng an die Pflanze adaptiert, daß sie getrennt von ihr nicht lebensfähig ist. Die Nahrung bezieht C. borneensis in Form von Nährkörperchen ausschließlich von der Pflanze. Im Sproßachseninnern gehaltene spezifische Schildläuse bieten eine weitere Nahrungsquelle. Die Adaptationen erstrecken sich bis auf die Anatomie des Verdauungstraktes : Der Kropf ist sehr klein und kann nur geringe Nahrungsmengen speichern. C. borneensis besiedelt spezifisch nur Macaranga-Pflanzen. Sowohl Königinnen als auch Arbeiterinnen sind in der Lage, die Wirtspflanze zu erkennen, wobei offenbar chemische Reize eine Rolle spielen. Die koloniegründenden Königinnen schwärmen das gesamte Jahr über, das Schwärmen erfolgt überwiegend während der Dunkelheit. Um die besiedlungsfähigen Macaranga-Pflanzen herrscht ein starker Konkurrenzdruck. Die beteiligten Schildlausarten sind spezifisch für die Assoziation. Sie werden nicht von der Königin beim Hochzeitsflug mitgenommen. Die Arbeiterinnen sind tag- und nachtaktiv. Die meisten Tiere halten sich im jüngsten Drittel der Pflanze auf, wo sie patrouillieren und Nährkörperchen sammeln. Mittels eines spezifischen Säuberungsverhaltens entfernen die Arbeiterinnen alle Fremdobjekte von der Pflanze. Trotz ihrer geringen Größe attackieren die Ameisen eine Vielzahl phytophager Insekten und sind dabei besonders effektiv in der Abwehr kleiner, wenig sklerotisierter Tiere wie z.B. Raupen. Sie verfügen zwar nicht ' über einen funktionsfähigen Stachel, setzen aber Wehrsekrete ein und beißen sich hartnäckig fest . Mit Hilfe eines effektiven Alarmierungssystems, das einen Massenangriff ermöglicht, gewährleisten sie eine Verteidigung ihrer Kolonien und damit gleichzeitig ihrer Wirtspflanze. Eine Vergleich mit einer anderen Crematogaster-Art demonstriert die besonderen Adaptationen von C. borneensis an ihre Wirtspflanze. Y1 - 1990 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-32689 ER -