1,301 research outputs found
USSR Space Life Sciences Digest, issue 1
The first issue of the bimonthly digest of USSR Space Life Sciences is presented. Abstracts are included for 49 Soviet periodical articles in 19 areas of aerospace medicine and space biology, published in Russian during the first quarter of 1985. Translated introductions and table of contents for nine Russian books on topics related to NASA's life science concerns are presented. Areas covered include: botany, cardiovascular and respiratory systems, cybernetics and biomedical data processing, endocrinology, gastrointestinal system, genetics, group dynamics, habitability and environmental effects, health and medicine, hematology, immunology, life support systems, man machine systems, metabolism, musculoskeletal system, neurophysiology, perception, personnel selection, psychology, radiobiology, reproductive system, and space biology. This issue concentrates on aerospace medicine and space biology
USSR Space Life Sciences Digest, issue 6
This is the sixth issue of NASA's USSR Space Life Sciences Digest. It contains abstracts of 54 papers recently published in Russian language periodicals and bound collections and of 10 new Soviet monographs. Selected abstracts are illustrated with figures and tables from the original. Additional features include a table of Soviet EVAs and information about English translations of Soviet materials available to readers. The topics covered in this issue have been identified as relevant to 26 areas of aerospace medicine and space biology. These areas are adaptation, biospherics, body fluids, botany, cardiovascular and respiratory systems, developmental biology, endocrinology, enzymology, exobiology, genetics, habitability and environment effects, health and medical treatment, hematology, human performance, immunology, life support systems, mathematical modeling, metabolism., microbiology, morphology and cytology, musculoskeletal system, neurophysiology, nutrition, perception, personnel selection, psychology, radiobiology, reproductive biology, and space medicine
Optimization of -Layer Systems for Josephson Junctions from a Microstructure Point of View
-layer systems are frequently used for Josephson junction-based
superconducting devices. Although much work has been devoted to the
optimization of the superconducting properties of these devices, systematic
studies on influence of deposition conditions combined with structural analyses
on the nanoscale are rare up to now. We have focused on the optimization of the
structural properties of -layer systems deposited on Si(111)
substrates with a particular focus on the thickness homogeneity of the
-tunnel barrier. A standard high-vacuum electron-beam deposition system
was used and the effect of substrate pretreatment, different Al-deposition
temperatures and Al-deposition rates was studied. Transmission electron
microscopy was applied to analyze the structural properties of the
-layer systems to determine the thickness homogeneity of the
layer, grain size distribution in the Al layers, Al-grain boundary
types and the morphology of the interface. We show that the
structural properties of the lower Al layer are decisive for the structural
quality of the whole -layer system. Optimum conditions yield an
epitaxial Al(111) layer on a Si(111) substrate with an Al-layer thickness
variation of only 1.6 nm over more than 10 and large lateral grain
sizes up to 1 . Thickness fluctuations of the -tunnel barrier are
minimized on such an Al layer which is essential for the homogeneity of the
tunnel current. Systematic variation of the Al-deposition rate and deposition
temperature allows to develop an understanding of the growth mechanisms
USSR Space Life Sciences Digest, issue 3
This is the third issue of NASA's USSR Space Life Sciences Digest. Abstracts are included for 46 Soviet periodical articles in 20 areas of aerospace medicine and space biology and published in Russian during the second third of 1985. Selected articles are illustrated with figures and tables from the original. In addition, translated introductions and tables of contents for seven Russian books on six topics related to NASA's life science concerns are presented. Areas covered are adaptation, biospherics, body fluids, botany, cardiovascular and respiratory systems, endocrinology, exobiology, gravitational biology, habitability and environmental effects, health and medical treatment, immunology, life support systems, metabolism, microbiology, musculoskeletal system; neurophysiology, nutrition, perception, personnel selection, psychology, radiobiology, and space physiology. Two book reviews translated from the Russian are included and lists of additional relevant titles available in English with pertinent ordering information are given
Correlating the nanostructure of Al-oxide with deposition conditions and dielectric contributions of two-level systems in perspective of superconducting quantum circuits
This work is concerned with Al/Al-oxide(AlO)/Al-layer systems which are
important for Josephson-junction-based superconducting devices such as quantum
bits. The device performance is limited by noise, which has been to a large
degree assigned to the presence and properties of two-level tunneling systems
in the amorphous AlO tunnel barrier. The study is focused on the
correlation of the fabrication conditions, nanostructural and nanochemical
properties and the occurrence of two-level tunneling systems with particular
emphasis on the AlO-layer. Electron-beam evaporation with two different
processes and sputter deposition were used for structure fabrication, and the
effect of illumination by ultraviolet light during Al-oxide formation is
elucidated. Characterization was performed by analytical transmission electron
microscopy and low-temperature dielectric measurements. We show that the
fabrication conditions have a strong impact on the nanostructural and
nanochemical properties of the layer systems and the properties of two-level
tunneling systems. Based on the understanding of the observed structural
characteristics, routes are derived towards the fabrication of
Al/AlO/Al-layers systems with improved properties.Comment: 28 pages, 4 figure
Use of Otolith Strontium:Calcium Ratios for Hindcasting Larval Cod Gadus Morhua Distributions Relative to Water Masses on Georges Bank
The concentration ratios of strontium to calcium in laboratory-reared larval cod otoliths are shown to be related to the water temperature (T) at the time of otolith precipitation. This relationship is curvilinear, and is best described by a simple exponential equation of the form (Sr/Ca x 1000 = a exp(-T/b). We show that when Sr/Ca elemental analyses are related to the daily growth increments in the larval otoliths, relative temperature histories of individual field-caught larvae can be reconstructed from the egg stage to the time of capture. We present preliminary examples of how such reconstructed temperature histories of Atlantic cod Gadus morhua larvae, collected on Georges Bank during April and May 1993, may be interpreted in relation to the broad-scale larval distributions and the hydrography of the Bank
Theory of the c-Axis Penetration Depth in the Cuprates
Recent measurements of the London penetration depth tensor in the cuprates
find a weak temperature dependence along the c-direction which is seemingly
inconsistent with evidence for d-wave pairing deduced from in-plane
measurements. We demonstrate in this paper that these disparate results are not
in contradiction, but can be explained within a theory based on incoherent
quasiparticle hopping between the CuO2 layers. By relating the calculated
temperature dependence of the penetration depth \lambda_c(T) to the c-axis
resistivity, we show how the measured ratio \lambda_c^2(0) / \lambda_c^2(T) can
provide insight into the behavior of c-axis transport below Tc and the related
issue of ``confinement.''Comment: 4 pages, REVTEX with psfig, 3 PostScript figures included in
compressed for
Structural and nanochemical properties of AlOx layers in Al/AlOx/Al -layer systems for Josephson junctions
The structural and nanochemical properties of thin AlOx layers are decisive for the performance of advanced electronic devices. For example, they are frequently used as tunnel barriers in Josephson junction-based superconducting devices. However, systematic studies of the influence of oxidation parameters on structural and nanochemical properties are rare up to now, as most studies focus on the electrical properties of AlOx layers. This study aims to close this gap by applying transmission electron microscopy in combination with electron energy loss spectroscopy to analyze the structural and nanochemical properties of differently fabricated AlOx layers and correlate them with fabrication parameters. With respect to the application of AlOx as tunnel barrier in superconducting Josephson junctions, Al/AlOx/Al-layer systems were deposited on Si substrates. We will show that the oxygen content and structure of amorphous AlOx layers is strongly dependent on the fabrication process and oxidation parameters. Dynamic and static oxidation of Al yields oxygen-deficient amorphous AlOx layers, where the oxygen content ranges from x=0.5 to x=1.3 depending on oxygen pressure and substrate temperature. Thicker layers of stoichiometric crystalline γ−Al2O3 layers were grown by electron-beam evaporation of Al2O3 and reactive sputter deposition
The Effect of Surfaces on the Tunneling Density of States of an Anisotropically Paired Superconductor
We present calculations of the tunneling density of states in an
anisotropically paired superconductor for two different sample geometries: a
semi-infinite system with a single specular wall, and a slab of finite
thickness and infinite lateral extent. In both cases we are interested in the
effects of surface pair breaking on the tunneling spectrum. We take the stable
bulk phase to be of symmetry. Our calculations are performed
within two different band structure environments: an isotropic cylindrical
Fermi surface with a bulk order parameter of the form ,
and a nontrivial tight-binding Fermi surface with the order parameter structure
coming from an anti-ferromagnetic spin-fluctuation model. In each case we find
additional structures in the energy spectrum coming from the surface layer.
These structures are sensitive to the orientation of the surface with respect
to the crystal lattice, and have their origins in the detailed form of the
momentum and spatial dependence of the order parameter. By means of tunneling
spectroscopy, one can obtain information on both the anisotropy of the energy
gap, |\Delta(\p)|, as well as on the phase of the order parameter,
\Delta(\p) = |\Delta(\p)|e^{i\varphi(\p)}.Comment: 14 pages of revtex text with 11 compressed and encoded figures. To
appear in J. Low Temp. Phys., December, 199
Pseudogap in the microwave response of YBa_2Cu_3O_{7-x}
The in-plane and out-of-plane surface impedance and microwave conductivity
components of one and the same YBa_2Cu_3O_{7-x} (0.07\le x\le 0.47) single
crystal are determined in the wide ranges of temperature T and carrier
concentration p in CuO_2 planes. The following features of the superfluid
density n_s(T,p)\propto\lambda_{ab}^{-2}(T,p) are observed at T<Tc/2 and
0.078\le p\le 0.16: (i) n_s(0,p) depends linearly on p, (ii) the derivative
|dn_s(T,p)/dT|_{T\to 0} depends on p slightly in the optimally and moderately
doped regions (0.10<p\le 0.16); however, it rapidly increases with p further
lowering and (iii) the latter finding is accompanied by the linear
low-temperature dependence \Delta n_s(T)\propto(-T) changing to \Delta
n_s(T)\propto(-\sqrt{T}). For optimum oxygen content the temperature dependence
of the normalized imaginary part of the c-axis conductivity
\lambda_c^2(0)/\lambda_c^2(T) is found to be strikingly similar to that of
\lambda_{ab}^2(0)/\lambda_{ab}^2(T) and becomes more convex with p lowering.
\lambda_c^{-2}(0,p) values are roughly proportional to the normal state
conductivities \sigma_c(T_c,p) along the c-axis. All these properties can be
treated in the framework of d-density wave order of pseudogap.Comment: 7 pages, 9 figures, presented at EUCAS 2003 (September 14-18),
submitted to SUS
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