High-frequency oscillations in low-dimensional conductors and semiconductor superlattices induced by current in stack direction

A narrow energy band of the electronic spectrum in some direction in low-dimensional crystals may lead to a negative differential conductance and N-shaped I-V curve that results in an instability of the uniform stationary state. A well-known stable solution for such a system is a state with electric field domain. We have found a uniform stable solution in the region of negative differential conductance. This solution describes uniform high-frequency voltage oscillations. Frequency of the oscillation is determined by antenna properties of the system. The results are applicable also to semiconductor superlattices.Comment: 8 pages, 3 figure

Providence Independent, V. 8, Thursday, December 14, 1882, [Whole Number: 392]

[4] p. “Persistent in the Right – Fearless in Opposing Wrong.” Newspaper published in Trappe, Pa. Weekly. Contains local, national and international news, fiction and advertisements.https://digitalcommons.ursinus.edu/providence/1172/thumbnail.jp

Оцінка параметра Грюнайзена гексаборидів металів

The basis for the estimation of the Gruneisen parameter γ is laid  (θД – Debye’s characteristic temperature, V– molar volume) from which the mathematical expression follows . In previous publications in order to determine θД the Lindemann formula was used. However, due to the ambiguity of the dimensional coefficient C in the Lindemann formula, the authors used the method of high-temperature roentgenography within the limits of 293–973 K. On the basis of analisys of the intensity of one maximum interference (hkl) at different temperatures, was determined by Chipman’s method X-ray characteristic temperature  θр(Т) groups of hexaboard type CaB6, namely CaB6, YB6, LaB6, CeB6, PrB6 , NdB6, ErB6, ThB6, YbB6. Considering, that neither the structure nor the interatomic connections within the temperature search of hexaborides does not change, the value of the parameter γ is determined. Its value was obtained within 2.5–4.7 for CeB6, NdB6, ErB6, YbB6, ThB6 and order 5.5–6.6 for CaB6, YB6, LaB6, PrB6. The parameters of Gruneisen proved to be practically independent of temperature. The presence of the meanings of γ made it possible to divide the implicit and explicit parts of the anagrammonism into a calming measure. The generalizing measure of anharmonism is mainly exhausted by the product γβ (β – the coefficient of the volumetric expansion of the crystalline lattice.В основу оцінки параметра Грюнайзена γ покладено співвідношення  ( θД — характеристична температура Дебая, V – молярний об’єм), з якого випливає математичний вираз . В попередніх публікаціях для визначення θД використовувалась формула Ліндемана. Однак через неоднозначність розмірного коефіцієнта С у формулі Ліндемана автори застосували метод високотемпературного рентгенографування у межах 293–973 К. На основі аналізу зміни інтенсивності одного інтерференційного максимуму (hkl) при різних температурах визначалася за методом Чіпмана рентгенівська характеристична температура θр(Т) групи гексаборидів типу CaB6, а саме: CaB6, YB6, LaB6, CeB6, PrB6, NdB6, ErB6, ThB6, YbB6. Враховуючи, що ні структура, ні міжатомні зв’язки в межах температурного дослідження гексаборидів не змінюються, визначено значення параметра γ. Були отримані його значення в межах 2,5–4,7 для CeB6, NdB6, ErB6, YbB6, ThB6 і порядку 5,5–6,6 для CaB6, YB6, LaB6, PrB6. Параметри Грюнайзена виявилися практично незалежними від температури. Наявність значень γ дало змогу розділити неявну і явну частини узагальнюючої міри ангармонізму. Узагальнююча міра ангармонізму в основному вичерпується добутком γβ (β – коефіцієнт об’ємного розширення кристалічної гратки)

Оцінка параметра Грюнайзена та явної міри ангармонізму додекаборидів

In previous works on the ratio   (θД – the characteristic temperature of Debye, was calculated according to the Lindemann formula; V – molar volume of hypothetical lattice atoms; γ is the Gruneisen parameter) for the group of dodecaborides (TbB12, DyB12, HoB12, ErB12, TuB12, LaB12, UB12) the average value of γ = 1.3 was determined. However, due to the ambiguity of the coefficient of proportionality in the Lindemann formula by definition θD, the authors selected an independent high-temperature X-ray method for determining the dependence θr (T). Taking into account the immutability of the structure and type of interatomic connection in the temperature interval of the search (293–973 K), the authors evaluated the value and temperature dependence of γ (T) of each dodecaboride separately. The results of the search showed that the value of γ for each given dodecaboride is different, but practically independent from temperature. For some dodecaborides, the parameter γ is about 2–3 units, and for others it is overestimated. The values of γ made it possible to estimate the magnitude of the implicit γβ and the explicit  parts of the universal measure of anharmonicity of dodecaborides , where β – real coefficient of volumetric expansion of the crystalline lattice. Because    (n – dimensionless coefficient of proportionality), then the temperature change n(T) is also determined.В попередніх роботах за співвідношенням  (θД – характеристична температура Дебая, розрахована за формулою Ліндемана; V – молярний об’єм гіпотетичних атомів гратки; γ – параметр Грюнайзена) для групи додекаборидів (TbB12, DyB12, HoB12, ErB12, TuB12, LaB12, UB12) було визначене середнє значення γ = 1,3. Однак у зв’язку із неоднозначністю коефіцієнта пропорційності у формулі Ліндемана з визначення θД авторами вибрано незалежний високотемпературний рентгенографічний метод визначення залежності θр(Т). Враховуючи незмінність структури і типу міжатомного зв’язку в температурному інтервалі дослідження (293–973 К), автори здійснили оцінку  значення і температурну залежність γ(Т) кожного додекаборида окремо. Результати дослідження показали, що значення γ для кожного зазначеного додекаборида різне, але практично незалежне від температури. Для одних додекаборидів параметр γ порядку 2–3 одиниць, а для інших він завищений. Значення γ дали можливість оцінити величину неявної γβ і явної  частин універсальної міри ангармонізму додекаборидів , де β – дійсний коефіцієнт об’ємного розширення кристалічної гратки. Оскільки  (n – безрозмірний коефіцієнт пропорційності), то також визначено температурну зміну n(T)

Transformation of Optical Vortices by Polarization Dynamic Holograms

Results of theoretical and experimental studies of regularities in the transformation of the topological and polarization structures of optical vortices by polarization dynamic holograms formed by pulse Gaussian and singular light beams in dye solutions are presented

Linear waves in sheared flows. Lower bound of the vorticity growth and propagation discontinuities in the parameters space

This study provides sufficient conditions for the temporal monotonic decay of enstrophy for two-dimensional perturbations traveling in the incompressible, viscous, plane Poiseuille and Couette flows. Extension of J. L. Synge's procedure (1938) to the initial-value problem allowed us to find the region of the wavenumber-Reynolds number map where the enstrophy of any initial disturbance cannot grow. This region is wider than the kinetic energy's one. We also show that the parameters space is split in two regions with clearly distinct propagation and dispersion properties

Towards human-robot collaboration in meat processing: Challenges and possibilities

Background: Meat is one of the main sources of protein in human nutrition. During recent years meat production volume has been showing significant growth worldwide. The total growth of red meat production is expected to show an 80% increase by 2029, according to the Organisation for Economic Co-operation Development (OECD). Such growth indicates the necessity for existing production line modernisation to satisfy future increased demand for meat products. Scope and approach: This article critically reviews automation challenges for robotic applications in the meat industry, among those are heterogeneity of meat pieces and inconsistency of cutting trajectories that must be overcome to achieve the final quality product. It specifically focuses on human-robot collaboration (HRC) that could be applied in the meat industry to address these challenges. The paper elaborates on possible adaptation of HRC in meat industry, based on its achievements in other industries. Key finding and conclusions: With increased customisation for both hardware and software robots can offer a flexible, scalable, compact and cost-effective production line alternative to older machinery that require large floor space, are difficult to adapt and include higher maintenance costs. However, in the case of red meat industry there are no off-the-shelf robotic solutions that can cover all the production steps in the secondary meat processing. Introducing collaborative robots into meat processing could help to promote higher standards in food safety and human-working conditions in the industry and make automation more affordable for smaller production plants

Quantum analogue of the spin-flop transition for a spin pair

Quantum (step-like) magnetization curves are studies for a spin pair with antiferromagnetic coupling in the presence of a magnetic field parallel to the easy axis of the magnetic anisotropy. The consideration is done both analytically and numerically for a wide range of the anisotropy constants and spins up to $S \gtrsim 100$. Depending on the origin of the anisotropy (exchange or single-ion), the magnetization curve can demonstrate the jumps more than unity and the concentration of the unit jumps in a narrow range of the field. We also point the region of the problem parameters, where the behavior is quasiclassical for $S = 5$, and where system is substantially quantum in the limit $S \to \infty$.Comment: 5 pages, 5 figure

Преобразование сингулярных световых пучков при невырожденном четырехволновом взаимодействии в растворах красителей

An analysis of a frequency transformation of singular light beams by the dynamic hologram at a frequency nondegenerated four-wave mixing in dye solutions has been carried out. The transformation of optical vortices of the first and second order from the infrared spectrum to the visible one has been demonstrated experimentally with simultaneous inversion of the topological charge

Weak ferromagnetism and field-induced spin reorientation in K2V3O8

Magnetization and neutron diffraction measurements indicate long-range antiferromagnetic ordering below TN=4 K in the 2D, S=1/2 Heisenberg antiferromagnet K2V3O8. The ordered state exhibits ``weak ferromagnetism'' and novel, field-induced spin reorientations. These experimental observations are well described by a classical, two-spin Heisenberg model incorporating Dzyaloshinskii-Moriya interactions and an additional c-axis anisotropy. This additional anisotropy can be accounted for by inclusion of the symmetric anisotropy term recently described by Kaplan, Shekhtman, Entin-Wohlman, and Aharony. This suggests that K2V3O8 may be a very unique system where the qualitative behavior relies on the presence of this symmetric anisotropy.Comment: 5 pages, 4 ps figures, REVTEX, submitted to PR