超宽带穿墙雷达偏离网格目标稀疏成像方法

在超宽带穿墙雷达成像应用中,由于目标成像空间的稀疏性表示可以采用压缩感知在较少数据采集下获得高分辨、低旁瓣的成像结果。然而,这些稀疏成像方法要求真实目标必须位于预设的网格点上才能保证较好的成像质量,否则会出现严重的虚假目标像。本文提出一种基于修正贝叶斯压缩感知的偏离网格目标稀疏成像方法。该方法对偏离网格目标的感知矩阵在预设网格点进行一阶泰勒级数展开,把真实目标与网格点之间的偏移量视为稀疏贝叶斯模型的参数,然后通过构造的联合概率密度函数利用最大期望方法联合估计目标散射系数和偏移量,保证了目标真实像的准确恢复。仿真和实验结果表明,该方法通过校正目标偏离网格引起的模型误差有效改善了传统稀疏重建方法的成像质量。     

Tandem mass spectrometry in the study of fatty acids,bile acids,and steroids

Over the last 50 years, the mass spectrometry of lipids has evolved to become one of the most mature techniques in biomolecule analysis. Many volatile and non-polar lipids are directly amenable to analysis by gas-chromatography-mass spectrometry (GC-MS), a technique that combines the unsurpassed separation properties of gas-chromatography with the sensitivity and selectivity of electron ionization mass spectrometry. Less volatile and/or thermally labile lipids can be analyzed by GC-MS, following appropriate sample derivatization. However, many complex lipids are not readily analyzed by GC-MS, and it is these molecules that are the subject of the current review. Since the early 1970s, there have been three outstanding developments in mass spectrometry that are particularly appropriate in lipid analysis; i.e., the introduction of (i) fast atom bombardment (FAB); (ii) electrospray (ES); and (iii) tandem mass spectrometry (MS/MS). The FAB and ES ionization techniques will be discussed in relation to MS/MS, and examples of their application in biochemical studies will be presented. The review will concentrate on the analysis of fatty acids, bile acids, steroid conjugates, and neutral steroids.     

探究生牛乳中游离氨基酸的测定方法一分光光度法

本试验是在加热条件下,氨基酸与茚三酮反应生成紫色物质,该物质颜色深浅与氨基酸含量成正比,用分光光度法可计算出样品中氨基酸含量。     

Non-classical stiffness strengthening size effects for free vibration of a nonlocal nanostructure

New analytical solutions for free vibration of thick nanostructures are presented based on the nonlocal elastic stress field theory and the Timoshenko shear deformable nanobeam model. By applying the variational principle, new governing equations of motion and higher-order boundary conditions for these thick nanobeams are derived and their physical characteristics interpreted. The nonlinear history of straining involving higher-order strain gradients is considered in the derivation of strain energy and the contribution of higher-order strain gradients results in non-classical equations of motion thereby indicating that direct replacement of stress and moment quantities into the classical equations of motion is invalid. The Timoshenko nanobeam models are well suited for modeling and investigating the nonlocal behaviors of size-dependent carbon nanotubes. The effects of nanobeam size and various boundary conditions including simple supports, free and clamp constraints, such as a cantilevered nanotube, on the natural vibration frequency of nanotubes are discussed. The effects of nonlocal nanoscale are confirmed by comparing with molecular dynamic simulation solutions for (5,5) and (10,10) carbon nanotubes with four types of boundary conditions. The influence by nanoscale effect on the frequency ratio of nanotubes with different diameters is investigated. Further analysis based on the analytical nonlocal Timoshenko nanobeam model and the Euler–Bernoulli nanobeam model shows that the frequency ratio is more sensitive to nonlocal effect for free vibration of a nonlocal nanostructure if shear deformation is considered.     

Boundary lubrication of low‐sulphur diesel fuel in the presence of fatty acids

This paper presents an overview of the effect of aliphatic acids on the tribological properties of selected hydrocarbons and petroleum fractions. The major experimental part of the work focuses on improvements to the lubricity of low‐sulphur diesel fuel. Experiments were carried out using a pin‐on‐disc friction machine and HFRR test rig. The wear results obtained clearly show a specific effect of the test acids dissolved in hydrocarbons in the concentration range 0.005–0.1% (50–1000 ppm). Although the overall picture presented by these results is very complex, it can be concluded that a very small amount of the selected acids dramatically improves low‐sulphur diesel fuel lubricity.     

On the effects of friction on free volume holes in PTFE

Since the macroscopic properties of materials are relevant to their micro structure, the detection of microscopic defects or their changes in size and concentration is an interesting topic in materials science. The positron annihilation lifetime (PAL) method used here is established as a unique technique that can provide information about the size and concentration of free volume holes directly without significantly intervening in the bulk properties of the specimens. To our knowledge, this is the first time that PAL techniques have been used to study the wear mechanism of macromolecular tribomaterials. Here we present the results of a study in which the correlation between the fretting wear behaviour of polytetrafluorethylene (PTFE) and the changes in its free volume size and concentration in amorphous-crystal interface regions was found to be δω =A.δτ₃, where δω is the wear loss of PTFE under fretting wear conditions, A is a constant, and δτ₃ represents the relative change in the third lifetime components after the friction test. The results indicate that fretting mainly influences the characteristics of atomic-scale free volume holes in the amorphous-crystal region in PTFE, and under high-load fretting wear conditions the ductile polymer PTFE possesses a self-curing function for its defect-free micro volume holes.     

Choroid plexus: target for polypeptides and site of their synthesis

Choroid plexus (CP) is an important target organ for polypeptides. The fenestrated phenotype of choroidal endothelium facilitates the penetration of blood-borne polypeptides across the capillary walls. Thus, both circulating and cerebrospinal fluid (CSF)-borne polypeptides can reach their receptors on choroidal epithelium. Several polypeptides have been demonstrated to regulate CSF formation by controlling blood flow to choroid plexus and/or the activity of ion transport in choroidal epithelium. However, many ligand-receptor interactions occurring in the CP are not involved in the regulation of fluid secretion. Increasing evidence suggests that the choroidal epithelium plays an important role in hormonal signaling via a receptor-mediated transport into the brain (e.g., leptin) and helps to clear certain CSF-borne polypeptides (e.g., soluble amyloid beta-protein). Thus, impaired choroidal transport or insufficient clearance of polypeptides may contribute to pathogenesis of systemic or central nervous system (CNS) disorders, such as obesity or Alzheimer's disease. CP epithelium is not only a target but is also a source of neuropeptides, growth factors, and cytokines in the CNS. These polypeptides following their release into the CSF may exert distal, endocrine-like effects on target cells in the brain due to bulk flow of this fluid. Distinct temporal patterns of choroidal expression of several polypeptides are observed during brain development and in various CNS disorders, including traumatic brain injury and ischemia. Therefore, it is proposed that the CP plays an integral role not only in normal brain functioning, but also in the recovery from the injury. This review attempts to critically analyze the available data to support the above hypothesis.     

Actin machinery of phagocytic cells: universal target for bacterial attack

Uptake of microorganisms by eukaryotic cells depends on proper functioning of the actin machinery. It creates a driving force for the cell membrane deformations necessary for ingestion and killing of microbes by phagocytes. Therefore, specific alterations in the activity of the actin apparatus could be favorable for pathogenic bacteria, representing an efficient mechanism in their virulence. Such alterations are supposed to be achieved in two principle ways. One is accomplished via binding of bacterial ligands to certain surface receptors, which initiate subsequent actin cytoskeleton rearrangements. Another is to introduce cytoskeleton-targeted products directly into eukaryotic cells and in this way modulate the activity of the actin apparatus. Indeed, Legionella and some other intracellular parasites possess ligands able to stimulate certain receptors on the surface of phagocytes and possess devices suitable for translocation of effector molecules into eukaryotic cytoplasm. The results of such events could be increased uptake of these microbes and their subsequent transportation to permit multiplication in their intracellular niche. On the contrary, representatives of Clostridium and a number of other extracellular pathogens create products which penetrate eukaryotic cells and disorganize the actin cytoskeleton network, thus making uptake of these pathogens by phagocytes impossible.     

Cram be abyssinica oil and its derivatives as renewable lubricants: Synthesis and characterisation of different esters based on crambe fatty acids

The authors have studied the possibility of using Crambe abyssinica oil as a starting material for synthetic lubricants, and in this paper the procedures for the preparation of monoesters from methyl, ethyl, isopropyl, and 2-ethylhexyl alcohol, as well as diesters from neopentylglycol, triesters from trimethylolpropane and tetraesters from pentaerythritol, are described. The different reactions were set up using free fatty acids, methyl esters, and Crambe oil as starting materials. All reactions were carried out in a solvent-free medium, using normally available catalysts and under experimental conditions which could easily be scaled up to industrial level. All the products obtained, along with the refined Crambe abyssinica oil used as a reference, were analysed for viscosity, viscosity index, low-temperature behaviour and oxidative and hydrolytic stability. Results of tests, such as four-ball machine and Noack, are reported. The results show that several products covering a wide range of different applications can be obtained from the basic Crambe abyssinica oil, and, furthermore, the chemical modification of the Crambe abyssinica oil can, in some cases, improve thermal and hydrolytic sensitivity and even the tribological properties.     

产品目标成本管理控制信息系统

阐述重型机械行业单件小批生产企业的产品目标成本管理方式和控制方法，计算机辅助产品目标成本管理和控制信息系统的开发要点及功能。     

Effects of wall material hardness on choice of wall materials for design of hoppers and silos for the discharge of hard bulk solids

This paper presents the results of a programme of experimental work designed to assess the industrial significance of plate hardness in hopper and silo construction upon the obtaining of reliable flow of hard bulk solids from the vessel. Previously, it has generally been thought that plate finish is the dominant effect in determining frictional characteristics, and no attention has been given to the effect of plate hardness. However this programme has shown that the effect of plate hardness can in practice be quite significant, to the extent that choosing increased plate hardness can reduce the steepness of the hopper wall needed for reliable discharge and hence the headroom requirement for the vessel.     

Experimental study on the effects of bearing wall thickness and bearing length on the frictional characteristics of sintered bearings

Experiments were conducted on bronze sintered bearings to determine the effect of bearing wall thickness and bearing length on the coefficient of friction. Parameters such as the radial clearance, the surface roughness of the shaft and the lubricating oil were kept constant in all the test bearings during the experiments. It was found that the coefficient of friction increases with the wall thickness and decreases with an increase in bearing length. It is felt that the above result will be useful for the users of sintered bearings in making a judicious selection of the wall thickness and the length of the bearing such that the selection results in a larger bearing metal volume to store more lubricating oil giving a longer life and a reduced coefficient of friction.     

水冷壁清扫、检测爬壁机器人防尘密封系统的研制

气幕密封技术是水冷壁清扫、检测爬壁机器人的关键技术之一。在此介绍了机器人气幕密封系统的设计和理论分析,为推广爬壁机器人技术在电力领域的应用奠定了基础。     

Relationships between the electrocardiogram and phonocardiogram: potential for improved heart monitoring

Improvements in current heart monitoring techniques could reduce the number of heart attacks and resulting deaths. The potential for using time intervals measured between waveforms of the electrocardiogram (ECG), phonocardiogram (PCG), and peripheral blood flow pulse (PP) for heart monitoring was studied. The waveform locations identified in the simultaneously recorded signals included the R- and T-wave peaks of the ECG, the first (S1) and second (S2) sounds of the PCG, and the systolic peak of the PP. The signals were found to be highly consistent from one cardiac cycle to the next. Further, the time intervals measured between the different signals were stable with time. Strong relationships were found between the intervals R to T and R to S2 and the R to R interval. In contrast, R to PP and R to S1 correlated poorly with the R to R but strongly with each other. Additional differences between the measured intervals were revealed by studying changes due to exercise and different body positions. The relationships between the measured intervals were found to be independent of PCG recording location. This study demonstrates the feasibility and potential of using the electrical-contractile indices of heart function for monitoring heart patients. Design of a computer-based monitor using the techniques specified in this study is discussed along with relative strengths and weaknesses of such a system.     

Tribocorrosion behaviour of overlay welded Ni-Cr 625 alloy in sulphuric and nitric acids: Electrochemical and chemical effects

The tribocorrosion behaviour of overlay welded Ni-Cr 625 alloy sliding against alumina in 0.5 M H₂SO₄ and 0.5 M HNO₃ solutions under potentiostatic conditions was investigated. The passivation of the samples in the two electrolytes at different potentials (−1.5, −0.3 and +0.3 V_MSE) was studied by means of potentiodynamic polarization curves and XPS. The tribocorrosion behaviour of the alloy in sulphuric acid was similar to the behaviour of stainless steels found in other studies, with much lower wear at cathodic potential compared to passive conditions. However, the behaviour in nitric acid was highly influenced by the reduction of nitric acid at the electrode-electrolyte interface. This reaction leads to the oxidation of the alloy even at cathodic potential. This feature influenced the tribocorrosion properties of the alloy in nitric acid, the wear rate at cathodic potential being in the same range as at passive potentials.     

Exact solutions for the free in-plane vibrations of rectangular plates

All classical boundary conditions including two distinct types of simple support boundary conditions are formulated by using the Rayleigh quotient variational principle for rectangular plates undergoing in-plane free vibrations. The direct separation of variables is employed to obtain the exact solutions for all possible cases. It is shown that the exact solutions of natural frequencies and mode shapes can be obtained when at least two opposite plate edges have either type of the simply-supported conditions, and some of the exact solutions were not available before. The present results agree well with FEM results, which show that the present solutions are correct and the direct separation of variables is practical. The exact solutions can be taken as the benchmarks for the validation of approximate methods.     

Exact solution for the free vibration of axially-loaded pretwisted rods

For a pretwisted rod, in which torsional and flexural effects are decoupled, both vibration and buckling behaviour may be described by a pair of fourth-order linear ordinary differential equations. By considering the free vibration of axially-loaded pretwisted rods, a superset of the buckling and vibration equations may be obtained, and these equations may be solved analytically. Such solutions indicate that the relationship between the natural frequency and the applied load is effectively independent of the pretwist angle, for compressive loads and moderate tensile loads.     

Experimental investigation of the effects of short roughness strip and wall suction on the anisotropy in a turbulent boundary layer

Hot wire measurements have been made in a turbulent boundary layer subjected to a short roughness strip and concentrated suction. The suction is applied through a porous wall strip for a range of suction rate. The aim of the study is to examine the effects of short roughness strip and suction on the anisotropy of Reynolds stress tensor. The result indicates that the anisotropy of Reynolds stress tensor is increased marginally downstream of the combination of suction and roughness strip. Although, roughness strip control the magnitude of the variations of the effect of suction on the anisotropy of Reynolds stress tensor, they act independently on the mechanism of the wall turbulence of the layer. While suction acts to increase the anisotropy, roughness strip act to reduce the anisotropy.     

The study on the drop detachment for automatic pipeline GMAW system: free flight mode

In the automatic pipeline welding systems, the mechanical properties and weld bead geometry are changed following to angle variation around the pipe. It occurred since during a weld pass, there are all of possible positions. In this work, first an augmented state-space model of process is presented that includes the travel motion and angle of robot. Also, gravitational force and arc voltage equations are modified. This model covers the free flight transfer modes (spray and globular). Then, accuracy of model is shown by model validation and comparing to real experiments. Finally, the angle effect on detachment is studied for all positions using simulation results. Detachment frequency variations, disturbance effects, and irregularity in detachments are analyzed using time–frequency representation.