Response of plates with unconstrained layer damping treatment to random acoustic excitation,part II: Response evaluation

Theoretical and experimental investigations on the response of a plate with unconstrained layer damping treatment to random acoustic excitation have been carried out. The theoretical response evaluation consisted of determining the power spectral density of the acceleration response of the layered plate by the use of generalized harmonic analysis under a specific random acoustic excitation, with use being made of modal frequencies and associated loss factors estimated as described in Part I. A study was made on the contribution of cross coupling terms of the acceleration response for the two boundary conditions investigated: namely, all edges simply supported and all edges clamped. In the experimental investigation, plates with different damping layer thicknesses were subjected to high intensity random acoustic excitation generated by an exponential horn driven by an electropneumatic transducer. The acceleration responses were recorded and later analyzed to yield the power spectral densities. Experimental and theoretical results are compared.     

Numerical simulation of ultrafast expansion as the driving mechanism for confined laser ablation with ultra-short laser pulses

Recently, a so-called “directly induced” laser ablation effect has been reported, where an ultra-short laser pulse (660 fs and 1053 nm) irradiates a thin Mo film through a glass substrate, resulting in a “lift-off” of the irradiated layer in form of a thin, solid, cylindrical fragment. This effect provides a new and very energy-efficient selective structuring process for the Mo back electrode in thin-film solar cell production. To understand the underlying physical mechanisms, a 3D axisymmetric finite element model was created and numerically solved. The model is verified by a direct comparison of experimental and numerical results. It includes volume absorption of the laser pulse, heat diffusion in the electron gas and the lattice, thermal expansion of the solid phase and further volume expansion from phase transition to fluid and gas, and finally the mechanical motion of the layer caused by the resulting stress wave and the interaction with the substrate. The simulation revealed that irradiation of the molybdenum layer with an ultra-short pulse causes a rapid acceleration in the direction of the surface normal within a time frame of a hundred picoseconds to a peak velocity of about 100 m/s. The molybdenum layer continues to move as an oscillating membrane, and finally forms a dome after about 100 ns. The calculated strain at the edges of the dome exceeds the tensile stress limit at fluences that initiate the “lift-off” in experimental investigations. In addition, the simulation reveals that the driving mechanism of the “lift-off” is the ultrafast expansion of the interface layer and not the generated gas pressure.     

EPR imaging study of paramagnetic centre distribution in thiokol-epoxy hermetics

The distribution of paramagnetic centres in carbon black filler in the interphase layer of the thiokol-epoxy hermetics on the border of brass or glass substrate was studied using EPR-imaging method. It was shown that the relative content of radicals decreases near the hermetic-“rigid” surface contact border. The thickness of the layer with a low concentration of radicals is estimated as 0.5±0.3 mm. The inhomogeneous distribution of radicals is more obvious in the case of hermetic hardening on a brass surface. These results are explained by a catalytic acceleration of the thiokol-epoxy polymerization reaction in the region of hermetic-metal surface contact.     

A crack layer approach to creep crack propagation in high-density polyethylene

Creep crack propagation in high-density polyethylene (HDPE) is observed to occur with an accompanying layer of damage ahead of the crack tip. The crack layer theory, which accounts for the presence of both the damage and the main crack, is applied to the problem. It is observed that the kinetic behavior of HDPE under creep consists of three regions: initial acceleration, constant crack speed, and reac-celeration to failure. Within the first two regions crack propagation appears “brittle,” while in the third region “ductile” behavior is manifested. Ultimate failure occurs via massive yielding of the unbroken ligament. The notion of critical crack length, well defined in many polymers, is shown     

Non-linear free vibrations of buckled plates with deformable loaded edges

In the great majority of papers dealing with non-linear dynamic buckling of plates it is assumed that the edge at which the in-plane load is applied is not deformable (rigid). In those few references in which buckling with deformable edges is examined normally a variational approach is used, based on “trial” functions for the in-plane displacements, which approach often leads to incorrect results. In this paper an exact form of the solution is found for the in-plane displacements, it being assumed that the membrane force is, at all times, exactly equal to the load applied at the corresponding loaded edge. As is well known, when the plate is buckled through a rigid beam these two forces are only on average equal to each other. It is shown here that the deformability of the loaded edges for plates undergoing large deformations should be taken into account for square-shaped plates, especially for those close to the so-called “golden-cut” shape (the aspect ratio between the edges equal to √2), while for long rectangular plates this effect may be disregarded.     

Modeling of Drug Release from a Novel Temperature-Responsive Phase-Transient Drug Delivery System in Cylindrical Coordinates

In this study, a novel phase-transient multilayer drug delivery system responsive to a unique stimulus, i.e., temperature, was introduced in cylindrical coordinates. The system is composed of three individual sections, including the drug core, phase-transient intermediate layer, and protecting polymeric coverage. The phase-transient layer gives smartness to the system and creates an “On-Off” release profile with increasing or decreasing the environmental temperature around the melting point of the layer. The “On-Off” response of the system was mathematically modeled by analyzing the heat and mass transfer equations in the pseudo-steady state and the effects of various parameters on the performance of the system were investigated. The modeling results showed the intensity of the effects of different kinds of factors, including the geometrical characteristics of the system (e.g., the radius of the drug core and the thicknesses of the intermediate and polymeric layers), the physical properties of the matrix materials (e.g., the thermal conductivities and diffusion coefficients of the intermediate and polymeric layers), and the operation conditions, on the response time lag and release kinetics of the presented system. The obtained results in this study predict methods to prepare multilayer temperature-responsive drug delivery systems with desired and optimized responses (e.g., with a short lag time) for practical biomedical applications.     

Calculated electrode-edge effects in flash-excited charge-transits and comparison with measurements on Sulphur

Current-time (transit, profiles for charge flash-excited near edges of “sandwich” electrodes have been obtained theoretically and experimentally (the latter for electrons in sulphur). Agreement is good for all three electrode configurations considered, namely small-large, large-small, small-small. Characteristic features are high-current spikes at short time, rising currents during the transit and current tails extending to twice the normal transit time. The effects are relevant when “overall” flash excitation is used, and non-appreciation of them could lead to substantial misinterpretation of results on a variety of materials. Present results for sulphur give an electron mobility of about 4.5 × 10^?8 m² V^?1 s^?1.     

The linear acceleration time integration method revisited

An unconditionally stable “two-node” finite element in time is proposed that can be used to integrate numerically the semidiscretized equations of motion of a continuous body. In analogy to the popular “linear acceleration” scheme [1,2], the proposed procedure may be termed a “linear displacement” algorithm for it is based on linear approximations of the displacement vector, x, within each time interval. On the basis of a rigorous mathematical analysis, it is shown that the algorithmic characteristics (i.e., accuracy, computational effort, etc.) are identical with those of the linear acceleration procedure. The advantages of the proposed technique over the assumed acceleration method [3] become evident in the case of higher order one-step time integration algorithms.     

On “Fermi accelerated” ions from an expanding plasma sheath

Ions with a velocity equal to twice the expansion velocity of a sheath are observed. The acceleration mechanism is interpreted in terms of “Fermi acceleration”.     

Plasma cluster acceleration by means of external magnetic field

The possibility to employ external magnetic field for acceleration of plasma clusters is discussed in this paper both theoretically and experimentally. The optimum value of the magnetic field has been found for the “snow plough” model, in which case there is the maximum cluster acceleration. The obtained results show a real possibility of further increasing the plasma cluster velocity in the electromagnetic shock tube.     

Interpretation of a layer mechanical impedance measured using a hard round die

Theoretical expressions for the impedance characteristics of a layer bound to a rigid base are obtained for various profiles of the normal pressure under a die that vibrates on the layer surface without producing any shear stresses. The frequency dependences of the impedance characteristics of a homogeneous gelatin layer and their variation with changes in the die diameter are measured by means of a specialized software-hardware system. The impedance characteristics are calculated for the models with “uniform,” “parabolic,” and “hyperbolic” pressure profiles under the die, and the results are compared with the experimental data. The model with a uniformly distributed pressure under the die is found to be the most adequate one.     

振动颗粒混合物中的三明治式分离

在竖直振动两种颗粒的混合物的实验中，观察到了一种新的分离现象——“三明治”式分离，即大而重的颗粒被夹在两层小的轻颗粒之间.这不同于“巴西果”效应导致的大而重的颗粒在上的两层有序结构.实验表明当振动加速度大于某个临界值时这种三层有序将取代两层结构，而且是稳定的.实验中观察到导致“三明治”式分离的两种不同的分离过程.对这两种过程的物理机理及其与振动加速度、振动频率及颗粒尺寸等因素的关系做了研究，并给出了相图. 关键词： 颗粒物质 振动 有序结构 三明治式分离 巴西果效应     

On synchrotron radiation in non-uniform magnetic fields

We study the conditions in which a charged particle in an inhomogeneous magnetic field (particularly at the edges of a “long” uniform magnet or in a “short” magnet) can emit synchrotron radiation with a spectrum extending beyond the “critical frequency”. We suggest that this effect should be clearly visible (and also useful) in the case of very high energy proton storage rings.     

Bulk dissolved Si as a cause of the “oxide” formation on Pt(111) surfaces

The influence of silicon atoms dissolved in the bulk of a Pt(111) crystal on the high temperature “oxidation” of Pt was studied by Auger spectrometry (AES) and low energy ion scattering (IS). The “oxidation” procedure was applied on clean and Si-prepared crystals. The preparation was performed by depositing a Si layer on the Pt(111) surface and thermally diffusing it into the bulk beyond the AES detectability. The results show that even deeply diffused silicon plays a decisive part in the “oxidation” process. This seems to explain the observations of other authors concerning the unexpected high stability of the “oxide” and the poor reproducibility of its rate of formation as well as of its saturation density. There is evidence that the “oxide” is primarily a silicon-oxygen bond.     

Solvable and/or Integrable and/or Linearizable N-Body Problems in Ordinary (Three-Dimensional) Space. I

Abstract

Several N -body problems in ordinary (3-dimensional) space are introduced which are characterized by Newtonian equations of motion (“acceleration equal force;” in most cases, the forces are velocity-dependent) and are amenable to exact treatment (“solvable” and/or “integrable” and/or “linearizable”). These equations of motion are always rotation-invariant, and sometimes translation-invariant as well. In many cases they are Hamiltonian, but the discussion of this aspect is postponed to a subsequent paper. We consider “few-body problems” (with, say, N =1,2,3,4,6,8,12,16,...) as well as “many-body problems” (N an arbitrary positive integer). The main focus of this paper is on various techniques to uncover such N -body problems. We do not discuss the detailed behavior of the solutions of all these problems, but we do identify several models whose motions are completely periodic or multiply periodic, and we exhibit in rather explicit form the solutions in some cases.     

Response of plates with unconstrained layer damping treatment to random acoustic excitation,part I: Damping and frequency evaluations

For theoretical evaluation of the response of a structure under random acoustic excitation a complete understanding is required of the various modes of vibration and the modal damping associated with each mode. In order to evaluate these parameters for plates with unconstrained layer damping treatment, some of the theoretical approaches applicable are used. Experimentally observed modal frequencies and associated loss factors are compared with those estimated by different theories for all edges simply supported and all edges clamped boundaries, after accounting for the damping at supports. The modes of vibration used in the theoretical analysis for these boundaries are compared with those observed in the experiments. These results are made use of in Part II for the evaluation of response under random acoustic excitation.     

Infrared image enhancement with learned features

Due to the variation of imaging environment and limitations of infrared imaging sensors, infrared images usually have some drawbacks: low contrast, few details and indistinct edges. Hence, to promote the applications of infrared imaging technology, it is essential to improve the qualities of infrared images. To enhance image details and edges adaptively, we propose an infrared image enhancement method under the proposed image enhancement scheme. On the one hand, on the assumption of high-quality image taking more evident structure singularities than low-quality images, we propose an image enhancement scheme that depends on the extractions of structure features. On the other hand, different from the current image enhancement algorithms based on deep learning networks that try to train and build the end-to-end mappings on improving image quality, we analyze the significance of first layer in Stacked Sparse Denoising Auto-encoder and propose a novel feature extraction for the proposed image enhancement scheme. Experiment results prove that the novel feature extraction is free from some artifacts on the edges such as blocking artifacts, “gradient reversal”, and pseudo contours. Compared with other enhancement methods, the proposed method achieves the best performance in infrared image enhancement.     

Diagonal Metrics of Static, Spherically Symmetric Fields: The Geodesic Equations and the Mass-Energy Relation from the Coordinate Perspective

The geodesic equations for the general case of diagonal metrics of static, spherically symmetric fields are calculated. The elimination of the proper time variable gives the motion equations for test particles with respect to coordinate time and an account of “gravitational acceleration from the coordinate perspective”. The results are applied to the Schwarzschild metric and to the so-called exponential metric. In an attempt to add an account of “gravitational force from the coordinate perspective”, the special relativistic mass-energy relation is generalized to diagonal metrics involving location dependent and possibly anisotropic light speeds. This move requires a distinction between two aspects of the mass of a test particle (parallel and perpendicular to the field). The obtained force expressions do not reveal “gravitational repulsion” for the Schwarzschild metric and for the exponential metric.     

后掠叶片锯齿尾缘宽频噪声实验研究

本文采用线性传声器阵列分别对具有常规尾缘及锯齿形尾缘的后掠叶片的尾缘噪声进行了实验测量;运用CLEAN-SC数据处理方法精确地识别出叶片尾缘噪声的声学参数.并且基于多组实验结果的对比,深入研究了不同的尾缘锯齿长度、周期、几何比例对后掠叶片尾缘噪声降噪效果的影响.实验结果表明:在低湍流度、自由来流情况下,在总声压级降噪方...     

Development of Hybrid Transport Systems for Delivering Cryogenic Fusion Targets Into Focus of High-Power Laser System or ICF Reactor

We present our results on utilization of the quantum levitation effect for HTSC samples (superconducting ceramics based on YBa₂Cu₃O_7?x and SuperOx J-PI-12-20Ag-20Cu superconducting tapes) in magnetic fields of different configurations with respect to developing special carriers for hybrid systems of noncontact transport of cryogenic targets in ICF experiments. We implement the obtained results for developing and engineering of “HTSC-MAGLEV” delivery system to minimize the risk for damage of the fuel layer at the target acceleration and during target injection into the center of the ICF reaction chamber.