We have investigated the initial stage nucleation and growth of epitaxial SrRuO sub(3) thin films grown on both polished (as received) and buffered HF (BHF) etched single crystal (0 0 1) SrTiO sub(3) ...substrates by 90 degree off-axis sputtering. Atomic force microscopy indicates a dramatic difference in the initial stage growth of SrRuO sub(3) films on the two substrates. The films on polished substrates nucleate as rectangular islands, which merge together to form a continuous film as the thickness increases. Complete coverage is obtained at film thickness of 20 nm. In contrast, the film on BHF etched substrate nucleates as finger-shaped islands at the step sites and continues to grow by adatom diffusion to the step sites. Complete coverage is obtained at a film thickness of 10 nm. This difference in the initial stage nucleation is attributed to the difference in surface morphology and termination layer of the two substrates. However, the thicker films on both as received and BHF etched substrates have identical surface morphologies. Such studies on the initial stage nucleation will also help us understanding the growth kinetics and development of surface morphology and interfaces in multilayered perovskite thin film heterostructures and devices.
Design of a new 6-dof parallel haptie device Lee, J H; Eom, K S; Yi, B-J ...
Proceedings - IEEE International Conference on Robotics and Automation,
01/2001, Letnik:
1
Journal Article
In this paper, a new 6-dof parallel haptic master device is proposed. Many existing haptic devices require large power due to having floating actuator and also have small workspaces. The proposed new ...mechanism is relatively light by employing non-floating actuators and has large workspace. Kinematic analysis and kinematic optimal design problem is performed for this mechanism. Dexterous workspace, global isotropic index, and global maximum force transmission ratio are considered as kinematic design indices. To deal with such multi-criteria optimization problem, composite design index is employed. Actuator sizing for this mechanism is also carried out.
The utilization of both polarimetric amplitude and relative phase terms of the polarization scattering matrix (S), given for each pixel, is pursued for polarimetric SAR imagery interpretation. The ...existing amplitude-only backscattering approaches hitherto used are extended and modified to accommodate the interpretation of information contained in the amplitude and/or phase terms. Both a vector radiative transfer model for surface versus volume scattering from rough terrain with and without vegetation canopy and a high-frequency electrical curvature model for perfectly conducting surfaces are examined to come up with theoretical models that out-perform other hitherto known approaches.
The discovery of superconductivity at 39 K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. ...This compound has twice the transition temperature of Nb3Sn and four times that of Nb-Ti alloy, and the vital prerequisite of strongly linked current flow has already been demonstrated. One possible drawback, however, is that the magnetic field at which superconductivity is destroyed is modest. Furthermore, the field which limits the range of practical applications-the irreversibility field H*(T)-is approximately 7 T at liquid helium temperature (4.2 K), significantly lower than about 10 T for Nb-Ti (ref. 6) and ∼20 T for Nb3Sn (ref. 7). Here we show that MgB2 thin films that are alloyed with oxygen can exhibit a much steeper temperature dependence of H*(T) than is observed in bulk materials, yielding an H* value at 4.2 K greater than 14 T. In addition, very high critical current densities at 4.2 K are achieved: 1 MA cm-2 at 1 T and 105 A cm-2 at 10 T. These results demonstrate that MgB2 has potential for high-field superconducting applications.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The detection of ultrashort laser-generated acoustic pulses at a metal surface and the reconstruction of the acoustic strain profile are investigated. A 2 ps-long acoustic pulse generated in an ...SrRuO\(_{3}\) layer propagates through an adjacent gold layer and is detected at its surface by a reflected probe pulse. We show that the intricate shape of the transient reflectivity waveform and the ability to resolve acoustic pulses shorter than the optical skin depth are controlled by a single parameter, which is determined by the ratio of the real and imaginary parts of the photoelastic constant of the material. We also demonstrate a Fourier transform-based algorithm that can be used to extract acoustic strain profiles from transient reflectivity measurements.
l(+)‐Lactate dehydrogenase (LDH) is a key enzyme in anaerobic metabolism which converts pyruvate to lactate. LDH from the hyperthermophilic archaebacterium Methanococcus jannaschii has been ...overexpressed in Escherichia coli and crystallized in two crystal forms at 297 K using 2‐methyl‐2,4‐pentanediol as precipitant. Type I crystals grew rapidly and diffracted to at least 2.8 Å Bragg spacing upon exposure to Cu Kα X‐rays. X‐ray diffraction data to 2.9 Å have been collected from a native crystal. The type I crystal is tetragonal, belonging to the space group P42212, with unit‐cell parameters a = b = 99.74, c = 170.00 Å. The asymmetric unit contains two LDH subunits, with a corresponding crystal volume per protein mass (Vm) of 3.05 Å3 Da−1 and a solvent content of 59.7%. Type II crystals, which grew more slowly, diffracted to at least 1.8 Å Bragg spacing upon exposure to Cu Kα X‐rays. X‐ray diffraction data to 1.9 Å have been collected from a native crystal. The type II crystal is orthorhombic, belonging to the space group P21212, with unit‐cell parameters a = 47.65, b = 125.10, c = 58.08 Å. The asymmetric unit contains a single LDH subunit, with a corresponding crystal volume per protein mass (Vm) of 2.50 Å3 Da−1 and a solvent content of 50.8%. Therefore, the type II crystal is more suitable for high‐resolution structure determination than the type I crystal.
The discovery of superconductivity at 39K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. ...This compound has twice the transition temperature of Nb sub(3)Sn and four times that of Nb-Ti alloy, and the vital prerequisite of strongly linked current flow has already been demonstrated. One possible drawback, however, is that the magnetic field at which superconductivity is destroyed is modest. Furthermore, the field which limits the range of practical applications--the irreversibility field H*(T)--is approximately 7T at liquid helium temperature (4.2K), significantly lower than about 10T for Nb-Ti (ref. 6) and similar to 20T for Nb sub(3)Sn (ref. 7). Here we show that MgB sub(2) thin films that are alloyed with oxygen can exhibit a much steeper temperature dependence of H*(T) than is observed in bulk materials, yielding an H* value at 4.2K greater than 14T. In addition, very high critical current densities at 4.2K are achieved: 1MAcm super(-2) at 1T and 10 super(5)Acm super(-2) at 10T. These results demonstrate that MgB sub(2) has potential for high-field superconducting applications.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Fe-based superconductors (FBS) are an important new class of superconducting materials. As with any new superconductor with a high transition temperature and upper critical field, there is a need ...to establish what their applications potential might be. Applications require high critical current densities, so the usefulness of any new superconductor is determined both by the capability to develop strong vortex pinning and by the absence or ability to overcome any strong current-limiting mechanisms of which grain boundaries in the cuprates are a cautionary example. In this review we first consider the positive role that grain boundary properties play in the metallic, low temperature superconductors and then review the theoretical background and current experimental data relating to the properties of grain boundaries in FBS polycrystals, bi-crystal thin films, and wires. Based on this evidence, we conclude that grain boundaries in FBS are weak linked in a qualitatively similar way to grain boundaries in the cuprate superconductors, but also that the effects are a little less marked. Initial experiments with the textured substrates used for cuprate coated conductors show similar benefit for the critical current density of FBS thin films too. We also note that the particular richness of the pairing symmetry and the multiband parent state in FBS may provide opportunities for grain boundary modification as a better understanding of their pairing state and grain boundary properties are developed.
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