Condensed Matter Physics Commons^™

True-Time Delay Steering Of Phased Array Radars Using Slow Light, Mark Bashkansky, Zachary Dutton, Armen Gulian, David Walker, Fredrik Fatemi, Michael Steiner

Mathematics, Physics, and Computer Science Faculty Articles and Research

Application of slow light linear delay to squint-free (true-time delay) steering of phased array radar antennae is discussed. Theoretical analysis is provided on true-time delay radar requirements, including delay precision, amplitude precision, and bandwidth. We also discuss an improvement to the slow light technique based on stimulated Brillouin scattering by using a Faraday rotator mirror that provides temporally stable, linear (with pump power) delay, applicable to practical implementations. Future directions are considered.

Dielectric Relaxation Behaviour Of Glycine In Acqueous Solution Medium In The Microwave Frequency Region, Ajaya Kumar Kavala

Mr Ajaya Kumar Kavala

No abstract provided.

Laser-Powered Thermoelectric Generators Operating At Cryogenic Temperatures, S. R. Harutyunyan, V. H. Vardanyan, A. S. Kuzanyan, V. R. Nikoghosyan, S. Kunii, K. Winzer, K. S. Wood, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

A thermoelectric generator, operating in a cryostat at liquid helium temperatures, is described. Energy to the generator is supplied via an external laser beam. For this prototype device the associated heat load at permanent operation is comparable with the heat load associated with power delivery via metallic wires. Estimates indicate that still better performance can be enabled with existing thermoelectric materials, thereby far exceeding efficiency of traditional cryostat wiring. We used a prototype generator to produce electric power for measuring critical currents in Nb₃Sn-films at 4K.

Specification Of Jecp/Holz, An Interactive Computer Program For Simulation Of Holz Pattern, Xingzhong Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

1. Purpose of the program 2. Graphic user interface and program design 3. Formulas for calculating the positions of the HOLZ lines 4. System requirement 5. Installation and user instruction 6. How to contact the author 7. References

1. Purpose of the program JECP/HOLZ (Li, 2005a) is one computer program in the Java Electron Crystallography Package (JECP), which is designed and written by Dr. XingZhong Li. The package is developed for quantitative electron diffraction and image processing purpose, JECP/HOLZ is an interactive program for simulation of the higher-order Laue zone (HOLZ) lines using kinematical approximation and a first-order dynamic correction. …

Qvd Sensors As Focal Plane Instruments For X-Ray Timing Applications, Kent S. Wood, Armen Gulian, Paul S. Ray

Mathematics, Physics, and Computer Science Faculty Articles and Research

“QVD” detectors are based on thermoelectric heat‐to‐voltage (Q→V) conversion and digital (V→D) readout. For spectroscopic applications, the theoretical performance limits are competitive with superconducting tunnel junction (STJ) detectors and transition edge sensor (TES) devices. We discuss theoretical and demonstrated timing performance of QVD detectors with different design architectures. Detectors with lanthanum‐cerium hexaboride sensors can be very fast, up to 100 MHz/pixel counting rates. They can serve as focal plane detectors for X‐ray timing, in situations where very large apertures are used to gather X‐ray photons at high event rates. Practical implementation of thermoelectric (QVD) detectors requires cryogenic thermoelectric sensors with …

Tem Study Of Crystalline Structures Of Cr–N Thin Films, Xingzhong Li, J. Zhang, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Cr–N films were grown on Si (001) substrates by reactive magnetron sputtering under an N2/Ar atmosphere at room temperature. The composition of the films, expressed as Cr_1–xN_x, can be varied by changing the N₂/Ar pressure ratio during the synthesis process. Crystalline states of Cr–N films have been studied using electron diffraction. It is well known that two intermediate phases, Cr₂N (hexagonal) and CrN (cubic), exist in the Cr–N system, and small variations around the ideal stoichiometry are tolerated. The present study shows that cubic CrN with vacancies rather than hexagonal Cr_{2 …}

Refrigerator With Phonon Filters: An Application Of The Phonon Deficit Effect In Superconducting Tunnel Junctions, G. G. Melkonyan, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

Nonequilibrium phenomena in thin solid films can result in cooling effects. These types of effects were predicted theoretically a while ago, and only recently were demonstrated experimentally in superconductor-insulator-normal metal (SIN) tunnel junctions. Since then, there is a growing interest in tunneling effects for the purpose to develop on-chip refrigerators. Thin film devices have the advantage of being extremely compact, operate in a continuous mode, dissipate little power, and can easily be integrated in cryogenic detectors. Currently these refrigerators can generate cooling in the order of 100 mK in an environment of 0.3–0.5 K. There are reasons to expect that …

Triplet Superconductors From The Viewpoint Of Basic Elements For Quantum Computers, Armen M. Gulian, Kent S. Wood

Mathematics, Physics, and Computer Science Faculty Articles and Research

We discuss possibilities of utilizing superconductors with Cooper condensates in triplet pairing states (where the spin of condensate pairs is S=1) for practical realization of quantum computers. Superconductors with triplet pairing condensates have features that are unique and cannot be found in the usual (singlet pairing, S=0) superconductors. The symmetry of the order parameter in some triplet superconductors (e.g., ruthenates) corresponds to doubly-degenerate chiral states. These states can serve as qubit base states for quantum computing.

Thermoelectric Cooling At Cryogenic Temperatures, S. R. Harutyunyan, V. H. Vardanyan, A. S. Kuzanyan, V. R. Nikoghosyan, S. Kunii, K. S. Wood, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

Experimental results demonstrating Peltier cooling below 10 K are reported, using crystals of the thermoelectric cerium hexaboride (CeB₆). Direct measurements of the Peltier cooling showed δT up to ∼0.2 K in magnitude at T∼4–5 K. All three kinetic parameters: resistivity (ρ), heat conductivity (k), and Seebeck coefficient (S), characterizing the thermoelectric figure of merit ZT=S²T/ρk, were measured, giving high-confidence results.

Sensor Development For Single-Photon Thermoelectric Detectors, Armen Gulian, K. S. Wood, G. G. Fritz, D. Van Vechten, H.-D. Wu, J. S. Horwitz, G. R. Badalyantz, S. R. Harutyunyan, V. H. Vartanyan, S. A. Petrosyan, A. S. Kuzanyan

Mathematics, Physics, and Computer Science Faculty Articles and Research

As we reported earlier [1], thermoelectric detectors can be competitive as nondispersive energy resolving focal-plane instruments in X-ray/UV spectrum. The first generations of prototype devices demonstrated the viability of detector design and provided good agreement between theoretical expectations and experimental data. These devices exploited sensors made of gold with a small fraction of iron impurity. To get the projected high resolution one needs another type of material, namely, lanthanum-cerium hexaborides. We report on the first experimental tests of the feasibility of lanthanum-cerium films as sensor materials. Progress with thin films of these materials argues for the success of these thermoelectric …

Specification Of Jecp/Sp: Stereographic Projection With An Application For Specimen Orientation Adjustment Using Tem Holders, Xingzhong Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

1. Purpose of the program 2. Graphic user interface and program design 3. Crystallographic principle and implementation 4. System requirement 5. Installation and user instruction 6. How to contact the author 7. References

1. Purpose of the program JECP/SP is a computer program in Java Electron Crystallography Package. JECP is developed for quantitative electron diffraction and image processing, the package is designed and written by Dr. XingZhong Li. JECP/SP provides the all necessary functions of stereographic projection for regular application and furthermore it can be used to minimized the difficulties encountered when tilting highly beam-sensitive, or small-grain-size specimens with known …

Jecp/Ed Manual, Xingzhong Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

JECP/ED is a Java program with graphic interface for simulating electron diffraction pattern. It is designed and written by Dr. Xingzhong in University of Nebraska- Lincoln. This is verision 12-2002. It can be used for simulating electron diffraction zone pattern(ZOLZ with/without FOLZ), it allows to select zone axis, high voltage, sample thickness in the simulation, optional to show index, intensity and Laue center, featureed with manuniplating the pattern with slightly tilting, 360 degree rotation, zoom. The diffraction intensity is calculated on the basis of the kinematical theory. The program is extended to simulate electron diffraction with a precession of incident …

Vortex-Defect Interactions In High-Temperature Superconductors, Valentina Tobos

Dissertations

The topics covered in this thesis are related to two objectives: one refers to the search for methods of improving die critical current density of high-temperature superconductors, a subject which remains of continuing interest for its importance in technological applications. The other direction is aimed at clarifying the phase diagram of high-Tc materials.

The interaction between the structural defects and the vortex system plays a significant role in the capability of these materials to carry large electrical transport currents. Through proton irradiation induced defects we follow the evolution of the critical current density, and its enhancement with increasing point-like defects …

Thermoelectric Single-Photon Detectors For X-Ray/Uv Radiation, G. G. Fritz, K. S. Wood, D. Van Vechten, A. L. Gyulamiryan, A. S. Kuzanyan, N. J. Giordano, T. M. Jacobs, H.-D. Wu, J. S. Horwitz, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

A feasibility study of megapixel microcalorimeter arrays, based on thermoelectric energy to voltage conversion and digital superconducting readout, is presented. The design concept originated from the philosophy of employing the simplest principles at the single-pixel level to enable large arrays without sacrificing energy resolution, fast operation speed, and quantum efficiency. Initial experimental tests confirm the basic predictions of theory, and show no major obstacle in achieving the desired characteristics.

Voltage Responses To Optical Pulses Of Unbiased Normal And Superconducting Samples, D. Van Vechten, K. S. Wood, G. G. Fritz, J. S. Horitz, G. M. Daly, J. B. Thrasher, D. M. Photiadis, J. Ding, J. F. Pinto, M. G. Blamire, G. Burnell, A. L. Gyulamiryan, V. H. Vartanyan, R. B. Akopyan, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

The direct transformation of the energy of an incident high-energy photon into a measurable potential difference within an absorbing metal is investigated. Experimental evidence is presented that the effect arises from the inherent energy dependence of the electronic density of states, rather than from a simple temperature excursion. The similarities between the results on Al and YBa₂Cu₃O₇ samples indicate that the effect is universal in nature. We assert it may be used as the basis of a fast, energy resolving, individual photon detector for the ultraviolet radiation and x-rays.

Nonequilibrium Dynamic Conductivity Of Superconductors: An Exploitable Basis For High Energy Resolution X-Ray Detectors, Armen Gulian, D. Van Vechten

Mathematics, Physics, and Computer Science Faculty Articles and Research

A new design for high‐energy radiation/particle detectors is presented. The nonequilibrium response of a superconductor to the absorption of the incident quanta is sensed by electromagnetic measurements of the altered dynamic conductivity. Microwave absorption may be used to amplify the signal. Such a detector will provide better energy resolution than semiconducting charge‐collection devices once the statistical resolution limit is reached.

Hysteresis And Anchoring Energy In Ferroelectric Liquid Crystals, Yuri Panarin

Articles

The frequency dispersion of the coercive force of Ferroelectric Liquid Crystals (FLC) cells has been detected and examined in the range of infralow (lower than 0.1 Hz) frequencies. To clarify the low-frequency dispersion, the model has been suggested, based on the arrangement of free charges and well describing the experimental curves. The method for determination of the energy of FLC anchoring at the surface, developed on the basis of the static hysteresis loop, has been proposed. The dependence of bistability and the anchoring energy upon the orientant layer thickness has experimentally been investigated.