Calculation of combined conduction-radiation heat transfer reduction using thick concentric spheres with temperature-dependent emissivity as radiation shields

In this study, the rate of conduction-radiation heat transfer between two thick concentric spheres is analytically investigated because of the ever-increasing importance of radiation shield applications. The heat transfer rate, the percentage of reduction in heat transfer, temperature and emissivity of surfaces are calculated when one and two thick radiation shields are placed between two thick spheres. The calculations show that the use of a radiation shield with a lower emissivity is better than two radiation shields with a higher emissivity to reduce the heat transfer rate. In addition, optimal combinations of radiation shields with different materials are proposed.     

Near-field heat transfer: A radiative interpretation of thermal conduction

It is shown in this article that the near-field radiative heat transfer can be interpreted as a conduction heat transfer due to the propagation of polaritons. We consider two situations. In the first one, two heated bodies at different temperatures are separated by a gap and in the second one a temperature gradient is imposed to a bulk material. In both situations, the radiative heat transfer is calculated by means of fluctuational electrodynamics. Asymptotic expressions of a thermal conductivity are obtained from the radiative heat transfer calculation. We interpret this conductivity as a consequence of the heat transfer by propagation and collisions of polaritons.     

两原子相干共振能量传递的单次与N次能量提取

两原子间隔一定距离且两原子跃迁频率接近时,两原子之间可发生能量传递.理论研究了供能原子和受能原子两共振原子的能量传递.求解薛定谔方程得出两原子共振能量传递效率.结果表明,供能原子在真空场中的激发态寿命在能量传递效率中起到十分重要的作用.能量传递效率与两原子间距离的负三次幂的正弦值的平方成正比,在一阶近似条件下,与两原子间距离的6次方成反比.以供能原子处于激发态时为初始时刻,能量从初始时刻随时间由供能原子向受能原子传递,对受能原子的单次能量提取的最大值大约在供能原子寿命的2/3时刻;对受能原子的连续N次能量提取的最大值,每次提取时间大约在供能原子寿命的1/2时刻.     

Controlled quantum state transfer via parity measurement

In this work, a scheme for controlled quantum state transfer is proposed using parity measurement in a cavity-waveguide system. As two special cases, two schemes of controlled quantum state transfer for one qubit and two qubits are investigated in detail. An important advantage is that controlled quantum state transfer can be completed by single-qubit rotations and the measurement of parity. Therefore, the present scheme might be realized in the scope of current experimental technology.     

R134a在水平三维内微肋管内的沸腾换热

本文以 Ｒ１３４ａ为工质,在外径为 １６ ｍｍ的两种不同几何结构的水平三维微肋管内进行了沸腾换热实验,研究了质量流率、热流密度、蒸汽干度等因素对沸腾换热系数的影响。与相同工况下的水平光管比较, １＃微肋管的换热强化因子在１．５～２．１之间,２＃微肋管的换热强化因子在１．９～２．８之间。两种三维微肋管的比较结果显示,单位内表面积上具有更多的微肋数目的 ２＃管的平均沸腾换热系数比 １＃管增加了 ２８～４３％。     

The effect of magnetic fields on the stability of a cylindrical flow with mass and heat transfer

The effect of axial and radial magnetic fields on the Kelvin-Helmholtz stability of a cylindrical interface between the vapor and liquid phases of a fluid is studied when the vapor is hotter than the liquid and the two phases are enclosed between two cylindrical surfaces coaxial with the interface, and when there is mass and heat transfer across the interface. Both axisymmetric and asymmetric disturbances are considered. The linear dispersion relations are obtained and discussed. It is found that a uniform axial magnetic field has a stabilizing effect on the interface, while the effect of a radial magnetic field depends strongly on the choice of some physical parameters of the system. It is also found that the instability criterion is independent of heat and mass transfer coefficient, but it is different fromthat in the same problem without heat and mass transfer. Finally, the heat and mass transfer has a destabilizing influence on the system.     

Analysis of two neutron (proton) transfer reaction data in the Zr-region

The spectroscopic amplitudes, form factors, angular distributions and total cross-sections for two nucleon transfer reactions in Zr-region in the zero range distorted wave Born approximation are calculated using consistent set of shell model wave functions. A single normalisation factor gives a good fit to all the two neutron transfer reaction data whereas the corresponding fit for the two-proton transfer reaction data is less satisfactory.     

耦合双Tavis-Cummings模型中的纠缠演化和转移特性

研究了由光纤模连接的两个Tavis-Cummings模型中纠缠演化和纠缠转移的特性。结果表明,初始两原子间的纠缠可转移为另两原子间的纠缠,在纠缠转移过程中,光纤模起到中间传递的作用。纠缠的转移与初始两原子间的纠缠、原子与腔场的耦合强度以及光纤模与腔场的耦合强度、原子与腔场的失谐量和腔场耗散有关。初始纠缠决定了另两原子间纠缠产生的大小;在原子与腔场的耦合强度一定的条件下,随着光纤模与腔场耦合强度的增强,纠缠转移的时间缩短,且产生的纠缠值增加;腔场耗散对纠缠演化的衰减影响是显著的,而失谐量的增加可以有效地抑制这一现象。在整个纠缠转移过程中,系统中其他任两子体系间的纠缠起到了桥梁的作用,实现了两量子纠缠态的远程传递和制备。     

Phase Transitions in Transfer Learning for High-Dimensional Perceptrons

Transfer learning seeks to improve the generalization performance of a target task by exploiting the knowledge learned from a related source task. Central questions include deciding what information one should transfer and when transfer can be beneficial. The latter question is related to the so-called negative transfer phenomenon, where the transferred source information actually reduces the generalization performance of the target task. This happens when the two tasks are sufficiently dissimilar. In this paper, we present a theoretical analysis of transfer learning by studying a pair of related perceptron learning tasks. Despite the simplicity of our model, it reproduces several key phenomena observed in practice. Specifically, our asymptotic analysis reveals a phase transition from negative transfer to positive transfer as the similarity of the two tasks moves past a well-defined threshold.     

Differentiating information transfer and causal effect

The concepts of information transfer and causal effect have received much recent attention, yet often the two are not appropriately distinguished and certain measures have been suggested to be suitable for both. We discuss two existing measures, transfer entropy and information flow, which can be used separately to quantify information transfer and causal information flow respectively. We apply these measures to cellular automata on a local scale in space and time, in order to explicitly contrast them and emphasize the differences between information transfer and causality. We also describe the manner in which the measures are complementary, including the conditions under which they in fact converge. We show that causal information flow is a primary tool to describe the causal structure of a system, while information transfer can then be used to describe the emergent computation on that causal structure.     

Virtual-Excitation Induced High-Dimensional State Transfer in a Quantum Network

We propose a scheme for quantum state transfer within the high-dimensional state subspaces between any two nodes in a quantum network. The states are encoded in the collective ground states of multiple atoms. The transfer processes are controlled by only applying external laser pulses. The prominent feature of the scheme is that the state transfer of any dimension can be achieved through virtually coupling all the excitations of the total system.     

Quantum State Transfer with Tunable Couplings for Superconducting Qubits

Currently, scalability and decoherence are still the two crucial problems for realizing large-scale quantum computation. To transfer information efficiently in the field of quantum computer and quantum communication, we must solve the two problems reasonably. Here, we propose an efficient scheme for the implementation of quantum states transfer in different couplings of superconducting devices, which are coupled weakly over a long distance. It is found that the isotropic Heisenberg coupling can offer the perfect operation for arbitrary states transfer with the shortest time. The scheme is feasible because the couplings have been demonstrated in actual experiments recently.     

Effects of dipole-dipole interaction on entanglement transfer

A system consisting of two different atoms interacting with a two-mode vacuum, where each atom is resonant only with one cavity mode, is considered. The effects of dipole-dipole （dd） interaction between two atoms on the atom-atom entanglement and mode--mode entanglement are investigated. For a weak dd interaction, when the atoms are initially separable, the entanglement between them can be induced by the dd interaction, and the entanglement transfer between the atoms and the modes occurs efficiently; when the atoms are initially entangled, the entanglement transfer is almost not influenced by the dd interaction. However, for a strong dd interaction, it is difficult to transfer the entanglement from the atoms to the modes, but the atom-atom entanglement can be maintained when the atoms are initially entangled.     

折转光管在光电瞄准系统中的应用

介绍了折转光管在瞄准系统中的使用位置、结构、工作原理和装调方法,分析了折转光管安装误差和两块平面反射镜之间的装调误差对方位传递精度的影响。使用MATLAB软件编程、计算、绘制出方位传递误差和高低传递误差的统计直方图,其分析结果为折转光管的装调提供了指导数据。计算分析表明,影响折转光管方位传递误差的主要因素是折转光管中两平面反射镜的装调误差,只要两平面反射镜的装调满足技术要求：方位误差≤4”、高低误差≤0．5’,即使折转光管在3个方向的安装误差极限值达到15°,也可满足折转光管方位传递误差≤10”的设计要求。     

Pairing effects in quasi-elastic neutron transfer between Tin isotopes

The transfer of neutrons between low-lying states of Tin isotopes has been measured in the reaction¹²⁰Sn→¹¹²Sn at energies below the Coulomb barrier. The transfer probabilities are deduced as function of the classical minimum distance from transfer and scattering cross sections at different angles and two energies. At the smallest distances very large transfer probabilities,p _t =0.5, are observed for one- and two-neutron transfer. The two-neutron transfer is significantly enhanced as compared to a successive independent single-nucleon transfer. The definition of enhancement is discussed.     

Driven state transfer and state storage in a tight-binding chain using two local barriers

A theoretical scheme to realize quantum state transfer and state storage in a uniformly coupled tight-binding chain is introduced in this paper. Two controllable gate voltages acting as local barriers are applied onto specific sites of the system, which separate the chain into three regions. By setting two gate voltages being equal, we show that an initially localized quantum wave packet undergoes perfect periodic revivals, allowing for perfect quantum state transfer between two nonadjacent spatial regions of the system. We also show that the wave packet can be trapped in its initial region by setting two gate voltages being unequal, which relates to the problem of storing quantum information. Moreover an efficient time-dependent quantum state transfer protocol is presented by smoothly varying the two gate voltages. Significantly, in our setup, the transferred state can be trapped, with a high fidelity of storage, at the end of the transfer protocol.     

Natural and forced convective heat transfer on slender cylinders

This paper presents an experimental study of free and forced convective heat transfer along vertical slender cylinders. The local heat transfer coefficient is determined from the measurement of the surface temperature distribution performed by quantitative infrared thermography. It is found that the convective heat transfer is strongly dependent on the cylinder curvature and misalignment with the flow. The effect of proximity of two cylinders is emphasized in the case of forced convection. Correlations are proposed for the two types of convection. It is worth noting that circumstances exist where the turbulent heat transfer in free convection can be of the same order of magnitude as for laminar forced convection. The outcome of the study demonstrates the suitability of quantitative infrared thermography to solve complex problems and to provide a deeper understanding of the heat transfer on slender cylinders.     

Effect of reflecting modes on combined heat transfer within an anisotropic scattering slab

Under various interface reflecting modes, different transient thermal responses will occur in the media. Combined radiative-conductive heat transfer is investigated within a participating, anisotropic scattering gray planar slab. The two interfaces of the slab are considered to be diffuse and semitransparent. Using the ray tracing method, an anisotropic scattering radiative transfer model for diffuse reflection at boundaries is set up, and with the help of direct radiative transfer coefficients, corresponding radiative transfer coefficients (RTCs) are deduced. RTCs are used to calculate the radiative source term in energy equation. Transient energy equation is solved by the full implicit control-volume method under the external radiative-convective boundary conditions. The influences of two reflecting modes including both specular reflection and diffuse reflection on transient temperature fields and steady heat flux are examined. According to numerical results obtained in this paper, it is found that there exits great difference in thermal behavior between slabs with diffuse interfaces and that with specular interfaces for slabs with big refractive index.     

内螺旋肋管流动与传热特性的实验研究

对六种内螺旋肋管进行了流动与传热的实验研究,实验管内径为16．25-16．69 mm,内螺旋肋高为0．28-0．44 mm,螺旋肋牙数为40-45,螺旋角为43°-45°．研究表明,内螺旋肋管可以有效地强化传热,本文所研究的管型的传热强化倍率为1．67-2．99．比较了两种评价内螺旋肋管性能的方法．用Webb模型及Ravigururajan模型对内螺旋肋管进行了性能预测并与实验值进行了比较．两个模型的预测值与本试验结果有较大偏差,相对而言,传热模型稍优．     

固定换热面积的回热器优化设计研究

为探究印刷电路板换热器（PCHE）Z型通道中超临界CO₂的换热特性,在换热面积固定的前提下指导回热器优化设计,采用数值模拟方法对CO₂-CO₂耦合换热的局部和整体特性进行了分析,通过CFD计算得到典型PCHE结构和典型工况下回热器的换热特性,与实验结果进行对比,验证计算模型。并利用此模型计算具有相同换热面积、不同通道结构的回热器的局部和整体换热性能,厘清结构参数对换热性能的影响规律。研究表明,计算结果与实验结果吻合,当通道夹角从110°增加至115°时换热系数出现最大幅度的下降,根据不同的设计需求,最佳的夹角范围为110°～120°。