Hasil untuk "Periodicals"

P. Yeh, A. Yariv, C. Hong

P. Vaidyanathan

M. Sigalas, E. Economou

V. Dulić, E. Lees, S. Reed

I. Chalmers

A. Herzberg, Stanislaw Jarecki, H. Krawczyk et al.

C. Sanchez, C. Boissière, D. Grosso et al.

S. Maier, S. R. Andrews, L. Martín-Moreno et al.

In this Letter, we show how the dispersion relation of surface plasmon polaritons (SPPs) propagating along a perfectly conducting wire can be tailored by corrugating its surface with a periodic array of radial grooves. In this way, highly localized SPPs can be sustained in the terahertz region of the electromagnetic spectrum. Importantly, the propagation characteristics of these spoof SPPs can be controlled by the surface geometry, opening the way to important applications such as energy concentration on cylindrical wires and superfocusing using conical structures.

V. Sharma, U. Mukherji, V. Joseph et al.

We study a sensor node with an energy harvesting source. The generated energy can be stored in a buffer. The sensor node periodically senses a random field and generates a packet. These packets are stored in a queue and transmitted using the energy available at that time. We obtain energy management policies that are throughput optimal, i.e., the data queue stays stable for the largest possible data rate. Next we obtain energy management policies which minimize the mean delay in the queue. We also compare performance of several easily implementable sub-optimal energy management policies. A greedy policy is identified which, in low SNR regime, is throughput optimal and also minimizes mean delay.

Marc Fares

Cristofaro-Gardiner and Kleinman showed the complete period collapse of the Ehrhart quasipolynomial of Fibonacci triangles and their irrational limits, by studying the Fourier-Dedekind sums involved in the Ehrhart function of right-angled rational triangles. We generalize this result using integral affine geometrical methods to all Markov triangles, as defined by Vianna. In particular, we show new occurrences of strong period collapse, namely by constructing for each Markov number $p$ a two-sided sequence of rational triangles and two irrational limits with quasipolynomial Ehrhart function of period $p$.

M. Jankowski, C. Langrock, B. Desiatov et al.

Quasi-phasematched interactions in waveguides with quadratic nonlinearities enable highly efficient nonlinear frequency conversion. In this article, we demonstrate the first generation of devices that combine the dispersion-engineering available in nanophotonic waveguides with quasi-phasematched nonlinear interactions available in periodically poled lithium niobate (PPLN). This combination enables quasi-static interactions of femtosecond pulses, reducing the pulse energy requirements by several orders of magnitude, from picojoules to femtojoules. We experimentally demonstrate two effects associated with second harmonic generation. First, we observe efficient quasi-phasematched second harmonic generation with <100 fJ of pulse energy. Second, in the limit of strong phase-mismatch, we observe spectral broadening of both harmonics with as little as 2-pJ of pulse energy. These results lay a foundation for a new class of nonlinear devices, in which co-engineering of dispersion with quasi-phasematching enables efficient nonlinear optics at the femtojoule level.

H. Pälike, R. Norris, J. Herrle et al.

D. Abanin, Wojciech De Roeck, W. Ho et al.

Prethermalization refers to the transient phenomenon where a system thermalizes according to a Hamiltonian that is not the generator of its evolution. We provide here a rigorous framework for quantum spin systems where prethermalization is exhibited for very long times. First, we consider quantum spin systems under periodic driving at high frequency $${\nu}$$ν. We prove that up to a quasi-exponential time $${\tau_* \sim {\rm e}^{c \frac{\nu}{\log^3 \nu}}}$$τ∗∼ecνlog3ν, the system barely absorbs energy. Instead, there is an effective local Hamiltonian $${\widehat D}$$D^ that governs the time evolution up to $${\tau_*}$$τ∗, and hence this effective Hamiltonian is a conserved quantity up to $${\tau_*}$$τ∗. Next, we consider systems without driving, but with a separation of energy scales in the Hamiltonian. A prime example is the Fermi–Hubbard model where the interaction U is much larger than the hopping J. Also here we prove the emergence of an effective conserved quantity, different from the Hamiltonian, up to a time $${\tau_*}$$τ∗ that is (almost) exponential in $${U/J}$$U/J.

Dongan Li, Mou Lin, Shunxiang Cao et al.

Spectral methods are renowned for their high accuracy and efficiency in solving partial differential equations. The Fourier pseudo-spectral method is limited to periodic domains and suffers from Gibbs oscillations in non-periodic problems. The Chebyshev method mitigates this issue but requires edge-clustered grids, which does not match the characteristics of many physical problems. To overcome these restrictions, we propose a B-spline-periodized Fourier (BSPF) method that extends to non-periodic problems while retaining spectral-like accuracy and efficiency. The method combines a B-spline approximation with a Fourier-based residual correction. The B-spline component enforces the smooth matching of boundary values and derivatives, while the periodic residual is efficiently treated by Fourier differentiation/integration. This construction preserves spectral convergence within the domain and algebraic convergence at the boundaries. Numerical tests on differentiation and integration confirm the accuracy of the BSPF method superior to Chebyshev and finite-difference schemes for interior-oscillatory data. Analytical mapping further extends BSPF to non-uniform meshes, which enables selective grid refinement in regions of sharp variation. Applications of the BSPF method to the one-dimensional Burgers' equation and two-dimensional shallow water equations demonstrate accurate resolution of sharp gradients and nonlinear wave propagation, proving it as a flexible and efficient framework for solving non-periodic PDEs with high-order accuracy.

Islam V. Pashtov, Petr A. Kuz’minov

The article is devoted to the analysis of the role of horse breeding in the socio-economic life of Kabarda in the second half of the 19th century and the identification of signs of its crisis in the pages of the Russian periodicals of that time. The article examines the features of the development of horse breeding, its importance in the economic system of the region, as well as the direct and indirect influence of political and economic factors on this sector. Special attention is paid to the assessments of contemporaries reflected in the periodicals that covered the state of horse breeding, the analysis of the causes of its decline, and proposals for overcoming the crisis. The article identifies the factors of the decline of this industry, which the authors attribute to the reluctance of most horse breeders to use new methods of horse breeding and raising. Using the example of horse breeding, the article explores the process of transformation and modernization of traditional farming in the region during the land reform of the 1860s.

N. Selwyn, Thomas Hillman, R. Eynon et al.

In many ways, the passing of another decade is nothing remarkable. The world does not transform periodically every ten years. Nevertheless, the fact that the 2020s are now upon us provides good rea...

Weiqiu Chen, Wen-wu Wang, Bingqing Peng et al.

Time series forecasting is a critical and challenging problem in many real applications. Recently, Transformer-based models prevail in time series forecasting due to their advancement in long-range dependencies learning. Besides, some models introduce series decomposition to further unveil reliable yet plain temporal dependencies. Unfortunately, few models could handle complicated periodical patterns, such as multiple periods, variable periods, and phase shifts in real-world datasets. Meanwhile, the notorious quadratic complexity of dot-product attentions hampers long sequence modeling. To address these challenges, we design an innovative framework Quaternion Transformer (Quatformer), along with three major components: 1). learning-to-rotate attention (LRA) based on quaternions which introduces learnable period and phase information to depict intricate periodical patterns. 2). trend normalization to normalize the series representations in hidden layers of the model considering the slowly varying characteristic of trend. 3). decoupling LRA using global memory to achieve linear complexity without losing prediction accuracy. We evaluate our framework on multiple real-world time series datasets and observe an average 8.1% and up to 18.5% MSE improvement over the best state-of-the-art baseline.

Yan Liu, Jun Liu, Wenxue Li

This article considers the stabilization of highly nonlinear stochastic coupled systems (HNSCSs) with time delay via periodically intermittent control. This article is motivated by that known differential inequalities to deal with periodically intermittent control do not work for HNSCSs, since the coefficients of the system do not satisfy the linear growth condition. In order to cope with this problem, a novel Halanay-type inequality is established to handle periodically intermittent control, which generalizes previous results. Then, based on this differential inequality, the graph theory, and the Lyapunov method, two main theorems are shown, whose conditions indicate how the control duration, the control gain, and the coupling strength affect the realization of the stability. Then, the theoretical results are applied to the modified van der Pol–Duffing oscillators. Finally, corresponding simulation results are presented to illustrate the effectiveness of the theoretical results.

Anatoli Ivanov, Sergiy Shelyag

We construct stable periodic solutions for a simple form nonlinear delay differential equation (DDE) with a periodic coefficient. The equation involves one underlying nonlinearity with the multiplicative periodic coefficient. The well-known idea of reduction to interval maps is used in the case under consideration, when both the defining nonlinearity and the periodic coefficient are piece-wise constant functions. The stable periodic dynamics persist under a smoothing procedure in a small neighborhood of the discontinuity set. This work continues the research in recent paper [7] on stable periodic solutions of differential delay equations with periodic coefficients.

S. T. Khapchaev

The relevance of the research topic. Wherever slavery existed, people attempted to escape, and American history is no exception. Sometimes such efforts took on organized and institutionalized forms, a notable example of which is the so-called Underground Railroad, a secret and organized system of resistance to enslavement by facilitating the escape of African Americans to northern states and other territories. In the chosen context of the research, the Underground Railroad can rightfully be considered one of the first mass movements for human rights not only in the United States, but also in the world.The purpose of the research is to reveal the main aspects of the functioning of the Underground Railroad, since this problem is extremely poorly covered by domestic science.The research is based on a scientific analysis of biographical data, literary sources, legal documents, materials from periodicals and has been carried out by applying the principle of historicism, comparative historical, problem-chronological, biographical and descriptive methods.The research results demonstrate that, in order to prevent human trafficking, individuals, families, and communities with anti-slavery attitude created preconditions for the formation of a large-scale institutionalized system that stretched from the Canadian provinces of Quebec and Ontario east to the Atlantic coast, south to Florida and the Caribbean, and west to the border enclaves of Kansas, Texas, and Mexico.On the basis of the research results, it has been concluded that the term «Underground Railroad», although it does not reflect the specifics of its activities, denotes a very real historical phenomenon. The organization and activities of the Underground Railroad became an important component in the difficult task of eradicating slavery in the United States.