9,530 research outputs found
Uncertainty quantification for the {BGK} model of the {B}oltzmann equation using multilevel variance reduced {M}onte {C}arlo methods
No full textWe propose a control variate multilevel Monte Carlo method for the kinetic BGK model of the Boltzmann equation subject to random inputs. The method combines a multilevel Monte Carlo technique with the computation of the optimal control variate multipliers derived from local or global variance minimization problems. Consistency and convergence analysis for the method equipped with a second-order positivity-preserving and asymptotic-preserving scheme in space and time is also performed. Various numerical examples confirm that the optimized multilevel Monte Carlo method outperforms the classical multilevel Monte Carlo method especially for problems with discontinuities
Asymptotic-Preserving Exponential Methods for the Quantum Boltzmann Equation with High-Order Accuracy
No full textIn this paper we develop high order asymptotic preserving methods for the spatially inhomogeneous quantum Boltzmann equation. We follow the work in Li and Pareschi (J Comput Phys 259:402–420, 2014) where asymptotic preserving exponential Runge–Kutta methods for the classical inhomogeneous Boltzmann equation were constructed. A major difficulty here is related to the non Gaussian steady states characterizing the quantum kinetic behavior. We show that the proposed schemes achieve high-order accuracy uniformly in time for all Planck constants ranging from classical regime to quantum regime, and all Knudsen number ranging from kinetic regime to fluid regime. Computational results are presented for both Bose gas and Fermi gas
Performance Evaluation of Distributed-Antenna Communications Systems Using Beam-Hopping
No full textDigital beamforming (DBF) techniques are capable of improving the performance of communications systems significantly. However, if the transmitted signals are conflicted with strong interference, especially, in the direction of the transmitted beams , these directional jamming signals will severely degrade the system performance. In order to efficiently mitigate the interference of the directional jammers, in this contribution a beam-hopping (BH) communications scheme is proposed. In the proposed BH communications scheme, only one pair of the beams is used for transmission and it hops from one to the next according to an assigned BH pattern. In this contribution a range of expressions in terms of the average SINR performance have been derived, when both the uplink and downlink are considered. The average SINR performance of the proposed BH scheme and that of the conventional single-beam (SB) as well as multiple-beam (MB) assisted beam-processing schemes have been investigated. Our analysis and results show that the proposed BH scheme is capable of efficiently combating the directional jamming, with the aid of utilizing the directional gain of the beams generated by both the transmitter and the receiver. Furthermore, the BH scheme is capable of reducing the intercept probability of the communications. Therefore, the proposed BH scheme is suitable for communications, when several distributed antenna arrays are available around a mobile
Tun hu: (du mu ju ji).
No full text復工之前 -- 母女們 -- 囤戶.吳天著.Drama.Wu Tian zhu.Fu gong zhi qian -- Mu nü men -- Tun hu
Conservative discontinuous Galerkin methods for the kinetic Fokker-Planck equation
No full textThesis (Master's)--University of Washington, 2023We consider the kinetic Fokker-Planck equation, a simplified model of the Vlasov-Landau equation, that describes collisions in plasma. This diffusion-type equation exhibits numerous noteworthy properties. One such property is the conservation of mass, momentum and energy. The numerical methods in this thesis, namely the local and recovery discontinuous Galerkin methods for diffusion-type equations, maintain this over large and truncated domains. Employing these methods results in stability results that fall in line with theoretical expectations. However, the findings also include unexpected convergence and asymptotic behaviors, which prompt further investigation
Flow dynamics on a U shaped channel flow: a numerical study
No full textThe paper deals with the numerical simulation of river channel flows at laboratory scale. The adopted geometry
consists of a U shaped trapezoidal smooth open channel with fixed slope. The branches, 3m of length each, are linked with a joint, 0.40m long, realizing two 90 degrees bends. The system is fed upstream with a water discharge under critical conditions while a Cipolletti weir is set downstream to control flow profiles.
Steady flow movements are obtained by means of two different softwares: a pure Lagrangian developed by the author, based on the Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) technique and Flow3D®, a commercial CFD software based on a Finite Volume formulation of the Navier Stokes equations in the Eulerian framework. Depending on the assumed boundary conditions, velocity profiles and water interfaces at certain cross sections are deducted by using the codes. Results are discussed and compared, showing a satisfactory agreement
HU Protein Induces Incoherent DNA Persistence Length
No full textHU is a highly conserved protein that is believed to play an important role in the architecture and dynamic compaction of bacterial DNA. Its ability to control DNA bending is crucial for functions such as transcription and replication. The effects of HU on the DNA structure have been studied so far mainly by single molecule methods that require us to apply stretching forces on the DNA and therefore may perturb the DNA-protein interaction. To overcome this hurdle, we study the effect of HU on the DNA structure without applying external forces by using an improved tethered particle motion method. By combining the results with DNA curvature analysis from atomic force microscopy measurements we find that the DNA consists of two different curvature distributions and the measured persistence length is determined by their interplay. As a result, the effective persistence length adopts a bimodal property that depends primarily on the HU concentration. The results can be explained according to a recently suggested model that distinguishes single protein binding from cooperative protein binding.Imaging Science and TechnologyApplied Science
Asymptotic and non-asymptotic model reduction for kinetic descriptions of plasma
No full textThesis (Ph.D.)--University of Washington, 2024Plasma dynamics are coupled across microscopic and macroscopic scales by a variety of nonlinear mechanisms. These include repartition of energy due to kinetic microinstabilities, suppression of fluid instabilities by kinetic stabilization effects, and other mechanisms. At the macroscopic scale plasmas are well-described by fluid equations, whose formal validity depends on the long-time regularization of the phase space distribution function by collisions and magnetic gyrotropization. However, accurately capturing multiscale coupling requires multiscale reduced models which are both efficient and accurate in transition regimes. These regimes, where either collisional or magnetic gyrotropic regularization are marginal, are characterized by the ratio of the (collisional or magnetic) mean free path to a characteristic gradient scale length. This work studies two families of reduced plasma models for transition regimes in depth. The first is an asymptotic expansion for Braginskii-type transport coefficients in the so-called drift ordering for low-beta plasmas. The expansion captures leading-order finite Larmor radius effects for arbitrary collisionality. We present a new derivation of this expansion, evaluate its performance numerically, and provide a numerically feasible approximation. The second family of methods is dynamical low-rank (DLR) methods, which are not based on an asymptotic expansion and have the potential to overcome the curse of dimensionality for kinetic equations. We present two novel DLR schemes for plasma kinetic equations with a focus on fluid-kinetic coupling. One is a DLR method that retains low rank in the highly collisional asymptotic limit. The other is a fully locally conservative DLR method for the Vlasov-Dougherty-Fokker-Planck equation which achieves second-order accuracy in time. All discretizations are described in detail and accompanied by numerical results demonstrating the merit of the proposed approach
Lightweight Key Encapsulation Using LDPC Codes on FPGAs
No full textIn this paper, we present a lightweight hardware design for a recently proposed quantum-safe key encapsulation mechanism based on QC-LDPC codes called LEDAkem, which has been admitted as a round-2 candidate to the NIST post-quantum standardization project. Existing implementations focus on high speed while few of them take into account area or power efficiency, which are particularly decisive for low-cost or power constrained IoT applications. The solution we propose aims at maximizing the metric of area efficiency by rotating the QC-LDPC code representations amongst the block RAMs in digit level. Moreover, optimized parallelized computing techniques, lazy accumulation and block partition are exploited to improve key decapsulation in terms of area and timing efficiency. We show for instance that our area-optimized implementation for 128-bit security requires 6.82× 1056.82×105 cycles and 2.26× 1062.26×106 cycles to encapsulate and decapsulate a shared secret, respectively. The area-optimized design uses only 39 slices (3 percent of the available logic) and 809 slices (39 percent of the available logic) for key encapsulation and key decapsulation respectively, on a small-size low-end Xilinx Spartan-6 FPGA
Elite collaboration in Japanese-occupied China: The cultural power and political influence of Hu Lancheng, 1938-1945
No full textResearch Enhancement Program Final ReportResults of the Project: I conducted research at the general library of the University of Hong Kong from 21-27 May and 11-18 June; at the Second Historical Archives in Nanjing, China from 28 May-10 June; and at the East Asian Collection of Stanford University and the Chinese Collection of the University of California-Berkeley from 14-24 August 2004. I perused and photocopied significant material about the project. For example, at the Second Archives I found an official document, signed by Chairman Wang Jingwei in 1941, which appointed Hu Lancheng as Deputy Propaganda Minister of Wang's puppet Chinese government headquartered in Nanjing (1940-1945). I also discovered an official message (dated November 1944), composed by a Japanese consul in Shanghai, in support of Hu's new journal titled Bitter Bamboo for publication in Occupied China. At the East Asian Collection I located the first edition (1940) of Hu's It Is Difficult to Go To War, But It Is Also Not Easy to Achieve Peace. This volume of essays was his primary work arguing for China's painful but necessary collaboration with the Japanese.Sponsored Program
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