Construction of Phase Cycles of Minimum Cycle Length: MakeCycle

An algorithm for the generation of a phase cycle of minimum length for a pulse sequence is developed from the basic requirement that only specified coherence transfer pathways will be accumulated. The efficacy of the algorithm is shown by determining the phase cycles of minimum length for DQFCOSY, GHMBC, and INEPT pulse sequences.     

Applicability of minimum entropy generation methodto optimizing thermodynamic cycles

Entropy generation is often used as a figure of merit in thermodynamic cycle optimizations. In this paper, it is shown that the applicability of the minimum entropy generation method to optimizing output power is conditional. The minimum entropy generation rate and the minimum entropy generation number do not correspond to the maximum output power when the total heat into the system of interest is not prescribed. For the cycles whose working medium is heated or cooled by streams with prescribed inlet temperatures and prescribed heat capacity flow rates, it is theoretically proved that both the minimum entropy generation rate and the minimum entropy generation number correspond to the maximum output power when the virtual entropy generation induced by dumping the used streams into the environment is considered. However, the minimum principle of entropy generation is not tenable in the case that the virtual entropy generation is not included, because the total heat into the system of interest is not fixed. An irreversible Carnot cycle and an irreversible Brayton cycle are analysed. The minimum entropy generation rate and the minimum entropy generation number do not correspond to the maximum output power if the heat into the system of interest is not prescribed.     

Features of cosmic ray variation at the phase of the minimum between the 23rd and 24th solar cycles

The minimum between the 23rd and 24th cycles of solar activity was unusually deep and extended. The modulation of cosmic rays was minimal for the more than 70-year-long period of direct measurements. The data from stratospheric measurements by the Lebedev Physical Institute suggest that the flux of cosmic rays with more than 100 MeV/nucleon of energy exceeded the highest ever observed level (May 1965) by almost 12%. However, the ground-based neutron monitors sensitive to relatively high energies indicated that the flux of cosmic rays increased by less than 3%. This work compares the variations in the cosmic rays over periods of five minima of solar activity (the 20th to the 24th cycle). It is shown that in late 2008, an extra flux of particles with energies less than several GeV/nucleon was detected in the Earth’s orbit. A similar (though far smaller in scale) phenomenon was also observed in 1987 at the same orientation of the Sun’s magnetic field A < 0, but was not observed in epochs where A > 0.     

Applicability of the minimum entropy generation method for optimizing thermodynamic cycles

Entropy generation is often used as a figure of merit in thermodynamic cycle optimizations. In this paper, it is shown that the applicability of the minimum entropy generation method to optimizing output power is conditional. The minimum entropy generation rate and the minimum entropy generation number do not correspond to the maximum output power when the total heat into the system of interest is not prescribed. For the cycles whose working medium is heated or cooled by streams with prescribed inlet temperatures and prescribed heat capacity flow rates, it is theoretically proved that both the minimum entropy generation rate and the minimum entropy generation number correspond to the maximum output power when the virtual entropy generation induced by dumping the used streams into the environment is considered. However, the minimum principle of entropy generation is not tenable in the case that the virtual entropy generation is not included, because the total heat into the system of interest is not fixed. An irreversible Carnot cycle and an irreversible Brayton cycle are analysed. The minimum entropy generation rate and the minimum entropy generation number do not correspond to the maximum output power if the heat into the system of interest is not prescribed.     

Diffusion of propylene adsorbed in Na-Y and Na-ZSM5 zeolites: Neutron scattering and FTIR studies

Here we report the quasielastic neutron scattering and FTIR studies on the dynamics of propylene adsorbed in Na-Y and Na-ZSM5 zeolites. QENS data show that although the mechanism of translational motion of propylene is jump diffusion in both the cases of Na-Y and Na-ZSM5 zeolites, the diffusivity is affected by the host size and is hindered in the case of Na-ZSM5. FTIR studies showed that guest-host interaction in Na-ZSM5 is stronger than that in Na-Y zeolite corroborating the QENS results.      

光学元件低频位相噪声的空间尺度

 建立求位相分布空间尺度的数学模型并计算了实际钕玻璃放大片所产生位相噪声的空间尺度。且就空间尺度对焦斑的影响及其在传输过程中的变化进行了数值模拟，结果表明：空间尺度对聚焦焦斑影响很小；在传输过程中，位相噪声的空间尺度会增大，而这种增长会增强变形镜等光束质量控制手段的效果。     

光学元件低频位相噪声的空间尺度

建立求位相分布空间尺度的数学模型并计算了实际钕玻璃放大片所产生位相噪声的空间尺度。且就空间尺度对焦斑的影响及其在传输过程中的变化进行了数值模拟,结果表明：空间尺度对聚焦焦斑影响很小;在传输过程中,位相噪声的空间尺度会增大,而这种增长会增强变形镜等光束质量控制手段的效果。     

PPLN晶体差频测量飞秒激光脉冲的载波包络相移

在飞秒激光频率梳系统中，通常采用自参考技术测量飞秒激光脉冲的载波包络相移，但该技术需要采用光子晶体光纤进行光谱扩展从而增加了系统的不稳定性，这种技术已经制约了高稳定度的飞秒激光频率梳的发展.采用PPLN晶体差频法测量了宽谱钛宝石振荡器输出的7fs激光脉冲的载波包络频移，得到了大于30dB的拍频信号，为研制无光纤的新一代高稳定度光学频率梳奠定了基础.     

Porous Semiconductors: Advanced Material for Gas Sensor Applications

The present review article is devoted to the analysis of the problems related to the design of gas sensors based on porous semiconductors (PS). The peculiarities of the semiconductor porosification by anodic etching and the principles of gas sensor design based on porous semiconductors, including gas sensor construction and main operating characteristics, are considered in the article. It is shown that the influence of the surrounding atmosphere on such parameters of porous semiconductors as refractive index, the intensity of photoluminescence, electroconductivity, dielectric constant, and surface potential might be used for gas sensor design. Based on the conducted analysis it is concluded that porous semiconductors have a great potential for the above-mentioned applications. However, the realization of those opportunities is restrained by such factors as bad reproducibility, increased temporal drift of characteristics, low selectivity, and an unsatisfactory level of understanding of the operating mechanism of sensors fabricated on the basis of porous semiconductors.     

Determination of NMR cogwheel phase cycle with XML

The selection of correct coherence transfer pathways is an essential component of an NMR pulse sequence. This article describes a new method based on the use of web tools (eXtensible Markup Language and eXtensible Stylesheet Language Transformation) to generate a cogwheel phase cycle for selecting coherence transfer pathways. We illustrate this method with the three-pulse phase-modulated shifted-echo or split-t₁ MQMAS sequences for triple-quantum spin-3/2 systems. After generalization to the different half-integer quadrupole spins, we use the SIMPSON program to confirm our results. Finally, we apply our method to the case of the z-filter 3QMAS sequence for I=3/2 systems.     

MR phase imaging: sensitive and contrast-enhancing visualization in cellular imaging

The successful translation of stem-cell therapies requires a detailed understanding of the fate of transplanted cells. Magnetic resonance imaging (MRI) has provided a noninvasive means of imaging cell dynamics in vivo by prelabeling cell with T(2) shortening iron oxide particles. However, this approach suffers from a gradual loss of sensitivity since active cell mitosis could decrease the cellular contrast agent (CA) concentration below detection level. In addition, the interpretation of images may be confounded by hypointensities induced by factors other than this CA susceptibility effect (CASE). We therefore examined the feasibility of exploiting the phase information in MRI to increase the sensitivity of cellular imaging and to differentiate the CASE from endogenous image hypointensity. Phase aliasing and the B(0) field inhomogeneity effect were removed by applying a reliable unwrapping algorithm and a high-pass filter, respectively, thus delineating phase variations originating from high spatial frequencies due to the CASE. We found that the filtered phase map detects labeled cells with high sensitivity and can readily differentiate the cell migration track from the white matter, both of which are hypointense in T(2)-weighted magnitude images. Furthermore, an approximate fivefold contrast-to-noise ratio enhancement can be achieved with an MRI phase map over conventional T(2)-weighted magnitude images.     

The effect of random dopant fluctuations on the minimum channel length of short-channel MOS transistors

Received: 20 August 1996/Accepted: 27 November 1996     

基于最小相位法的屏蔽电缆瞬态响应分析方法

为了分析屏蔽电缆在电磁脉冲作用下的时域响应,对基于最小相位法的频域等效方法进行了研究。首先,通过建立转移阻抗测试系统的电路模型,推导系统的频域传递函数,并验证其为最小相位系统与全通系统的级联;其次,采用最小相位法,对测得的幅频曲线进行相位重构,根据推导的传递函数的零、极点分布,对重构的最小相位传递函数进行相位补偿;最后,将补偿后的传递函数与瞬态干扰信号在频域相乘后变换到时域,得到了屏蔽电缆的时域响应。仿真及实验结果验证了该方法的有效性。     

Overview of phases and phase transitions

We provide an overview of some modern developments in the theory of phases and phase transitions in classical and quantum systems. We show the link between non-ergodicity and fidelity in quantum systems and discuss topological phase transitions. We show that the quantum phase transitions are associated with qualitative changes in some properties of the quantum wavefunctions across the phase transition. We discuss the topological phase transition associated with p-wave superconductor since it is a topic of wide interest because of the possible observation of Majorana fermions.     

Characterising the throat diameter of through-pores in network structures using a percolation criterion

We present a method for measuring the pore throat diameter of a simulated porous material. The pore throat diameter is the size of the narrowest pore that has both an entrance and an exit in a network structure. Knowledge of the pore throat diameter allows estimation of the size of the largest molecules that can travel through a network structure without interruption. In this method, a chain of virtual circles (in 2-dimensions) or spheres (in 3-dimensions) is constructed along a percolated path through the pores in a network. The diameter of the largest circle or sphere for which this is possible is the pore throat diameter. The method is applied to two 2-dimensional models (one where we know the pore throat diameter and one where we do not), and well predicts the pore throat diameters in each case. The pore throat diameter of a 3-dimensional DNA-mediated hydrogel model is also determined. This method is applicable to any porous structure for which molecular coordinate information is available. The ability to predict pore throat diameters in simulation could be useful for determining the size of molecules that can safely be administered by hydrogel drug delivery systems.     

First order phase transitions in unbounded spin systemsI: Construction of the phase diagram

The phase diagram and the corresponding infinite volume Gibbs states are constructed for a large class of continuous, unbounded spin models. Our construction relies on a partition of unity mapping our system onto an interacting contour system, a generalisation of Zahradnik's approach to Piragov Sinai theory to interacting contour systems, and a suitable mean field expansion around the minimas of the Hamiltonian.     

A simplified model for second-harmonic generation in uniaxial crystals: phase matching condition

The phase matching condition for second-harmonic generation can be satisfied by a simplified model making use of the conservation of energy and momentum. By using the crystal indicatrix together with our model, we are able to classify uniaxial crystals as Type I and II non-linear optical materials.     

Carrier envelope phase of few cycle pulsed Hermite-Gaussian beam

The complex q parameter method is used to analyze the propagation of the few cycle pulsed Hermite-Gaussian beam in the free space within the paraxial condition, and an approximate formula for the carrier envelope phase (CEP) is deduced by using the zero-order approximation in the amplitude and first-order approximation in the phase. The validity of the approximate formula is verified by the numerical simulation methods, which shows that they fit very well with each other on condition that the pulse duration is more than 5 fs or the propagation distance is longer than about 3 Rayleigh length. The order of the Hermite function, the beam waist and the position of the axis play important roles in the CEP of the few cycle pulsed Hermite-Gaussian beam; the conclusion is as follows: the CEP trends to −(m+n+1)π/2 in the far field and their variety are in inverse proportion to the beam waist on the axis. The beam waist is larger, the CEP is smaller and its variation changes slowly along the propagation distance. The variation of the CEP is in direct proportion to r² on any z-plane, and the maximal values all occur at the position .