Retrospectively gated cardiac cine imaging with temporal and spatial acceleration

Parallel imaging methods are routinely used to accelerate the image acquisition process in cardiac cine imaging. The addition of a temporal acceleration method, whereby k-space is sampled differently for different time frames, has been shown in prior work to improve image quality as compared to parallel imaging by itself. However, such temporal acceleration strategies prove difficult to combine with retrospectively gated cine imaging. The only currently published method to feature such combination, by Hansen et al. [Magn Reson Med 55 (2006) 85-91] tends to be associated with prohibitively long reconstruction times. The goal of the present work was to develop a retrospectively gated cardiac cine method that features both parallel imaging and temporal acceleration, capable of achieving significant acceleration factors on commonly available hardware and associated with reconstruction times short enough for practical use in a clinical context.Seven cardiac patients and a healthy volunteer were recruited and imaged, with acceleration factors of 3.5 or 4.5, using an eight-channel product cardiac array on a 1.5-T system. The prescribed FOV value proved slightly too small in three patients, and one of the patients had a bigemini condition. Despite these additional challenges, good-quality results were obtained for all slices and all patients, with a reconstruction time of 0.98±0.07 s per frame, or about 20 s for a 20-frame slice, using a single processor on a single PC. As compared to using parallel imaging by itself, the addition of a temporal acceleration strategy provided much resistance to artifacts.     

Multisymplectic Lie group variational integrator for a geometrically exact beam in R3

In this paper we develop, study, and test a Lie group multisymplectic integrator for geometrically exact beams based on the covariant Lagrangian formulation. We exploit the multisymplectic character of the integrator to analyze the energy and momentum map conservations associated to the temporal and spatial discrete evolutions.     

An Interpenetrated Framework Material with Hysteretic CO2 Uptake

A new, twofold interpenetrated metal–organic framework (MOF) material has been synthesized that demonstrates dramatic steps in the adsorption and hysteresis in the desorption of CO₂. Measurement of the structure by powder X‐ray diffraction (PXRD) and pair distribution function (PDF) analysis indicates that structural changes upon CO₂ sorption most likely involve the interpenetrated frameworks moving with respect to each other.     

Voltage-Gated Metal-Enhanced Fluorescence

We demonstrate the influence of electrical current on the ability of surface plasmons to amplify fluorescence signatures. An applied direct current across Silver Island Films (SIFs) of low electrical resistance perturbs the fluorescence enhancement. For a given applied current, surface plasmons in just-continuous films are sparsely available for fluorophore dipole-coupling and hence the enhanced fluorescence is gated as a function of the applied current. For thicker, low resistance films, sufficient charge carriers are now present in the metal that metal-enhanced fluorescence (MEF) is perturbed to a lesser extent, induced surface plasmons readily formed on the surface by the close-proximity dipole.     

供应和需求不确定条件下物流服务供应链能力协调研究

为解决物流能力供应和需求不确定环境下,物流服务集成商和供应商能力采购和投资的协调问题,建立了Stackelberg主从博弈下物流服务集成商和供应商的决策模型,提出了基于收益共享的能力采购费用补偿协调机制,给出了实现供应链协同以及帕雷托改进的合约参数设计和取值区间.数值分析进一步验证了该协调机制的有效性,以及供应和需求波动对决策双方行为的影响.研究结果表明,物流服务集成商通过调节合约参数取值能有效协调供应和需求随机环境下物流服务供应链的采购和投资风险.     

Optical Imaging System with LaserGated Brightness Amplifier

l.IntroductionTheideaofusingahigh-gainactivemediumtoformbrightness-enhancedmicroscofr-.icimageswasproposedmorethan2oyearsago[1:.Introductionofbrightnessamplifierintousua1oPticalsystemwouldPermittoovercomethewellknownrestrictionaccordingtowhichthebrightnessattheoutputoftheopticalsystemcannotexceedthatatthein-put[zJ.SomepulsedmetalvaporlaserssuchasthecopPervaPOrlaser(CVL)havebeenusedasimage-brightnessamplifiersinvariousopticalprojectionsystem[3j-lnthiscase,wecanbenefitfromthattheactivemedium…     

An Efficient Geometric Integrator for Thermostatted Anti-/Ferromagnetic Models

(Anti)-/ferromagnetic Heisenberg spin models arise from discretization of Landau–Lifshitz models in micromagnetic modelling. In many applications it is essential to study the behavior of the system at a fixed temperature. A formulation for thermostatted spin dynamics was given by Bulgac and Kusnetsov, which incorporates a complicated nonlinear dissipation/driving term while preserving spin length. It is essential to properly model this term in simulation, and simplified schemes give poor numerical performance, e.g., requiring an excessively small timestep for stable integration. In this paper we present an efficient, structure-preserving method for thermostatted spin dynamics.     

Gated Polling Systems with Lévy Inflow and Inter-Dependent Switchover Times: A Dynamical-Systems Approach

We study asymmetric polling systems where: (i) the incoming workflow processes follow general Lévy-subordinator statistics; and, (ii) the server attends the channels according to the gated service regime, and incurs random inter-dependentswitchover times when moving from one channel to the other. The analysis follows a dynamical-systems approach: a stochastic Poincaré map, governing the one-cycle dynamics of the polling system is introduced, and its statistical characteristics are studied. Explicit formulae regarding the evolution of the mean, covariance, and Laplace transform of the Poincaré map are derived. The forward orbit of the maps transform – a nonlinear deterministic dynamical system in Laplace space – fully characterizes the stochastic dynamics of the polling system. This enables us to explore the long-term behavior of the system: we prove convergence to a (unique) steady-state equilibrium, prove the equilibrium is stationary, and compute its statistical characteristics.     

基于辛格式的深度哈密尔顿神经网络

HNN是一类基于物理先验学习哈密尔顿系统的神经网络.本文通过误差分析解释使用不同积分器作为超参数对HNN的影响.如果我们把网络目标定义为在任意训练集上损失为零的映射,那么传统的积分器无法保证HNN存在网络目标.我们引进反修正方程,并严格证明基于辛格式的HNN具有网络目标,且它与原哈密尔顿量之差依赖于数值格式的精度.数值实验表明,由辛HNN得到的哈密尔顿系统的相流不能精确保持原哈密尔顿量,但保持网络目标;网络目标在训练集、测试集上的损失远小于原哈密尔顿量的损失;在预测问题上辛HNN较非辛HNN具备更强大的泛化能力和更高的精度.因此,辛格式对于HNN是至关重要的.