The Shape of the Edge of a Leaf

Leaves and flowers frequently have a characteristic rippling pattern at their edges. Recent experiments found similar patterns in torn plastic. These patterns can be reproduced by imposing metrics upon thin sheets. The goal of this paper is to discuss a collection of analytical and numerical results for the shape of a sheet with a non-flat metric. First, a simple condition is found to determine when a stretched sheet folded into a cylinder loses axial symmetry, and buckles like a flower. General expressions are next found for the energy of stretched sheets, both in forms suitable for numerical investigation, and for analytical studies in the continuum. The bulk of the paper focuses upon long thin strips of material with a linear gradient in metric. In some special cases, the energy-minimizing shapes of such strips can be determined analytically. Euler–Lagrange equations are found which determine the shapes in general. The paper closes with numerical investigations of these equations.     

Regularity analysis of wrinkles under the action of capillary force in an annular thin film

The wrinkling law of annular sheet which is induced by capillary force with inner liquid film is analyzed in this paper. The results show that the inner liquid film can wrinkle the annular sheet when the surface tension of the liquid film reaches a critical value, and the critical value can be dramatically altered by changing the geometry and properties of the annular sheet. The results obtained in this article may hold potential applications in generating three-dimensional structures through capillary effects.     

Vibration analysis of defected and pristine triangular single-layer graphene nanosheets

This paper investigates the vibration behavior of pristine and defected triangular graphene sheets; which has recently attracted the attention of researchers and compare these two types in natural frequencies and sensitivity. Here, the molecular dynamics method has been employed to establish a virtual laboratory for this purpose. After measuring the different parameters obtained by the molecular dynamics approach, these data have been analyzed by using the frequency domain decomposition (FDD) method, and the dominant frequencies and mode shapes of the system have been extracted. By analyzing the vibration behaviors of pristine triangular graphene sheets in four cases (right angle of 45-90-45 configuration, right angle of 60-90-30 configuration, equilateral triangle and isosceles triangle), it has been demonstrated that the natural frequencies of these sheets are higher than the natural frequency of a square sheet, with the same number of atoms, by a minimum of 7.6% and maximum of 26.6%. Therefore, for increasing the resonance range of sensors based on 2D materials, non-rectangular structures, and especially the triangular structure, can be considered as viable candidates. Although the pristine and defective equilateral triangular sheets have the highest values of resonance, the sensitivity of defective (45,90,45) triangular sheet is more than other configurations and then, defective (45,90,45) sheet is the worst choice for sensor applications.     

On-line measurement of texture,thickness and plastic strain ratio using laser-ultrasound resonance spectroscopy

Laser-ultrasound resonance spectroscopy, a non-contact ultrasonic technique, was used to determine reliably and rapidly the crystallographic texture, the average plastic strain ratio, and the thickness of sheet metal on the production line. As with laser-ultrasonics, a short laser pulse is used to generate a wide-band pulse of ultrasound and a laser interferometer is used for its detection. In this paper, a large number of echoes are collected and analyzed together using Fourier techniques to measure the natural resonance frequencies in the thickness of the sheet. One longitudinal and two shear resonance frequencies were measured together with their harmonics. From these frequencies, two crystallographic orientation distribution coefficients, W(400) and W(420), are obtained, as well as a highly accurate measurement of the sheet thickness that is corrected for changes in ultrasonic velocity caused by texture variations. Using these coefficients, the average and in-plane twofold and fourfold variations of the plastic strain ratio, respectively r delta(2)r, and delta(4)r, can be evaluated. These parameters are indications of the formability of metals sheets, which is of industrial interest. Measurements on 1 mm thick, low carbon steel sheets have shown the following measurement accuracies: r to within +/-0.08, delta(2)r, and delta(4)r to within +/-0.1, and thickness to better than +/-1 microm. On-line tests at LTV Steel Company showed that the sensitivity of the apparatus is sufficient to detect systematic variations in texture along the length of similar production coils and that the on-line repeatability for r was of order +/-0.02.     

Experimental studies of influence of the turbulent flow structure on temperature distribution in a compact heat exchanger

Results of experimental investigation of temperature distribution over the surface of a complex heat exchanger (the Frenkel packing type) are presented. Measurements were carried out in the air flow between two sheets with triangular corrugations directed at 90° to each other. Measurements were carried out by the microthermocouples glued on the heated outer surface. The effect of Reynolds numbers, a gap between corrugated sheets, and substitution of one corrugated sheet by the smooth one on temperature distribution over the heat exchanger surface in the turbulent air flow is analysed. According to the performed experiments, there is a significant effect of a gap and applied perturbations on the type of temperature distribution over the perimeter of a heated cell.     

Defects in hexagonal-AlN sheets by first-principles calculations

Theoretical calculations focused on the stability of an infinite hexagonal AlN (h-AlN)sheet and its structural and electronic properties were carried out within the frameworkof DFT at the GGA-PBE level of theory. For the simulations, an h-AlN sheet model systemconsisting in 96 atoms per super-cell has been adopted. For h-AlN, we predict an Al-N bondlength of 1.82 Å and an indirect gap of 2.81 eV as well as a cohesive energy which is by6% lower than that of the bulk (wurtzite) AlN which can be seen as a qualitativeindication for synthesizability of individual h-AlN sheets. Besides the study of a perfecth-AlN sheet, also the most typical defects, namely, vacancies, anti-site defects andimpurities were also explored. The formation energies for these defects were calculatedtogether with the total density of states and the corresponding projected states were alsoevaluated. The charge density in the region of the defects was also addressed.Energetically, the anti-site defects are the most costly, while the impurity defects arethe most favorable, especially so for the defects arising from Si impurities. Defects suchas nitrogen vacancies and Si impurities lead to a breaking of the planar shape of theh-AlN sheet and in some cases to the formation of new bonds. The defects significantlychange the band structure in the vicinity of the Fermi level in comparison to the bandstructure of the perfect h-AlN which can be used for deliberately tailoring the electronicproperties of individual h-AlN sheets.     

Verringerung der schallentstehung und — Abstrahlung von platten bei stoßförmiger anregung

In this paper the sound power level for shocks applied to plates is calculated approximately and noise reducing parameters are derived from theoretical relations. During the grinding of a 1 mm steel sheet, for instance, a sound level reduction of up to 15 dB(A) is achieved by magnetically fixed plastic covers. These covers have been tested on various thicknesses of curved steel sheets which were being hammered and ground.     

Vertical displacements of the current sheet and Hall currents

Vertical displacements of the peripheral regions of the current sheet with respect to its mean plane have been detected in the case of the sheet formation in the three-dimensional configuration with the X line and longitudinal component of the magnetic field. It has been shown that this effect is due to the generation of Hall currents and the appearance of vertically directed forces. Change in the sign of vertical displacements at the late stage of the sheet evolution has been detected, indicating the generation of opposite Hall currents when the direction of the main current near the side edges of the sheet changes. It has been shown that Hall currents significantly affect the structure of current sheets, and vertical oscillations of the peripheral regions of the current sheet, which appear owing to oppositely directed Hall currents, are involved in the dynamic processes in current sheets.     

First-principles studies of BN sheets with absorbed transition metal single atoms or dimers: stabilities, electronic structures, and magnetic properties

BN sheets with absorbed transition metal (TM) single atoms, including Fe, Co, and Ni, and their dimers have been investigated by using a first-principles method within the generalized gradient approximation. All of the TM atoms studied are found to be chemically adsorbed on BN sheets. Upon adsorption, the binding energies of the Fe and Co single atoms are modest and almost independent of the adsorption sites, indicating the high mobility of the adatoms and isolated particles to be easily formed on the surface. However, Ni atoms are found to bind tightly to BN sheets and may adopt a layer-by-layer growth mode. The Fe, Co, and Ni dimers tend to lie (nearly) perpendicular to the BN plane. Due to the wide band gap of the pure BN sheet, the electronic structures of the BN sheets with TM adatoms are determined primarily by the distribution of TM electronic states around the Fermi level. Very interesting spin gapless semiconductors or half-metals can be obtained in the studied systems. The magnetism of the TM atoms is preserved well on the BN sheet, very close to that of the corresponding free atoms and often weakly dependent on the adsorption sites. The present results indicate that BN sheets with adsorbed TM atoms have potential applications in fields such as spintronics and magnetic data storage due to the special spin-polarized electronic structures and magnetic properties they possess.     

载能氢原子与石墨(001)面碰撞过程中的能量传递行为的分子动力学研究

本文采用分子动力学方法研究了单一载能氢原子与石墨碰撞时氢原子被石墨反射、 吸附和石墨被氢原子穿透的发生系数以及碰撞中的能量传递机理. 研究发现: 与单层石墨相比, 多层石墨之间的长程相互作用增加了氢原子发生反射的能量范围, 尤其当入射能量大于20.0 eV时, 对反射过程的影响很明显; 当氢原子的入射能量大于25.0 eV时, 有一定的概率穿透四层石墨; 当氢原子入射能量高于28.0 eV时, 载能氢原子的能量传递给第二层石墨烯的比传递给第一层石墨烯的多. 这些结果对理解聚变反应中, 碳基材料的化学腐蚀及氚滞留有重要意义.     

The influence of compressive stress applied by hard coatings on the power loss of grain oriented electrical steel sheet

To reduce the core loss of electrical steel the vacuum arc ion plating technique has been used to deposit titanium nitride (TiN) layers on highly grain oriented electrical steel sheets. The layer thickness, the stresses of layers and coated sheets and the achieved reduction in core losses have been measured as functions of coating duration and applied bias voltage. Well adhered layers with high compressive stress up to 6.8 GPa have been produced. With increasing bias voltage the layer thickness decreases and the intrinsic stress of the layers increase. A further increase of bias voltage leads to a drop in stress due to thermal relaxation. In general, the tensile stress of the coated sheets rises with increasing layer thickness while the core loss of the coated material decreases with increasing tensile stress of the steel sheet and increasing bias voltage. The highest reduction of core loss has been found to be 28% (from P_1.7=0.86 W/kg for commercially coated HGO electrical steel sheet with glass film to 0.62 W/kg for TiN coated material) and is due to the reduction of excess loss only.     

Development of an advanced multimode automatic ultrasonic texture measurement system for laboratory and production line application

We present work on the development of an ultrasonic texture measurement system for sheet metals using non-contact transducers, suitable for use both in the laboratory and on the production line. Variation of the velocity of the zero-order symmetric (S0) Lamb wave is used to determine the crystallographic texture of polycrystalline metal sheets ranging in thickness from 0.1 to 3 mm. This system features improvements on previous state-of-the-art ultrasonic technology in that it probes velocity over a continuous range of angles using only two electromagnetic acoustic transducers (EMATs). This is demonstrated to offer a significant improvement in accuracy and allows the detection and investigation of asymmetric anisotropies in the sheets. Another advantage of the system is its potential for combining several different measurements using a single pair of transducers. The capability is demonstrated for through-thickness shear wave measurements as well as the zero-order symmetric Lamb wave measurements which are the primary means of determining the texture. The change between generating Lamb and through-thickness bulk waves can be made entirely by changing the electrical circuit connected to the EMATs without modifying the transducer assembly in any way. Measurement of all of the above waves can provide information on the sheet thickness and other physical properties of the sheet in addition to texture. Certain texture parameters can be calculated from both Lamb and shear wave velocities, allowing self-calibration of the system.     

Taguchi based fuzzy logic optimization of multiple quality characteristics in laser cutting of Duralumin sheet

Capability of laser cutting mainly depends on optical and thermal properties of work material. Highly reflective and thermally conductive Duralumin sheets are difficult-to-laser-cut. Application of Duralumin sheets in aeronautic and automotive industries due to its high strength to weight ratio demand narrow and complex cuts with high geometrical accuracy. The present paper experimentally investigates the laser cutting of Duralumin sheet with the aim to improve geometrical accuracy by simultaneously minimizing the kerf width and kerf deviations at top and bottom sides. A hybrid approach, obtained by combining robust parameter design methodology and Fuzzy logic theory has been applied to compute the fuzzy multi-response performance index. This performance index is further used for multi-objective optimization. The predicted optimum results have been verified by performing the confirmation tests. The confirmation tests show considerable reduction in kerf deviations at top and bottom sides.     

环状出口气泡雾化喷嘴研究

本文对环状出口气泡雾化喷嘴出口下游液膜的破碎过程进行了研究,发现气体的介入是促使液膜破碎的主要原因。利用DUALPDA对其下游流场的速度分布、颗粒直径分布以及通量分布进行了实验测量。发现喷嘴出口附近主流区域存在大量具有负向速度的颗粒,并且此处的颗粒平均直径显著减小,为气泡雾化机理提供了佐证;在喷嘴出口下游轴心处液雾呈现逆向流动趋势,证明此处存在负压回流;沿轴向的速度分布曲线与颗粒直径分布曲线的变化趋势说明气泡"爆炸"发生在出口下游5-15 mm距离内。     

Existence of extraordinary zero-curvature slowness curve in anisotropic elastic media

Acoustic wave propagation in elastic media is characterized by the slowness surface. The slowness surface consists of three sheets associated with three modes of wave propagation and the two outer sheets can have zero-curvature locally. It is shown that the outmost sheet can admit extraordinary zero-curvature and the slowness curve can appear as a straight line locally. Using the perturbation method, the conditions for the extraordinary zero-curvature are derived analytically without violating the thermodynamic condition for elastic media. The results can be applied to crystals with higher symmetry and to the study of phonon focusing and surface waves.     

Interaction of Annular Air Jet with a Non-Evaporating Liquid Spray

The effects of a concentric annular air jet on the structure of a liquid spray have been examined under isothermal conditions using Phase Doppler interferometry, and flow visualization techniques. Local measurements of drop size, velocity, volume flux, and number density have been made simultaneously and non-intrusively. The results show that the initial spray cone widens substantially with increasing air flow while the overall spray envelope remains essentially the same. The air jet creates a narrow high mass flux region of small droplets in the core of the spray, surrounded by a nearly uniform flux region extending almost to the boundary of the spray. Line averaged mean diameters are found to be slightly smaller, indicating that the annular air jet plays a role improving the atomization process as well.     

Electrostatic properties and characterization of two-layer paper sheets

The aim of the research is to determine the electrostatic properties of two-layer paper sheets composed of laboratory filter paper and polyethylene. The volume resistivity and conductivity in a filter paper sheet, polyethylene film and a two-layer sheet consisting of them were studied. The experiment was done using two techniques. The investigated samples were exposed to static electric field and the surface and volume conductivity were measured in accordance with ASTM D257 standard. The same samples were also exposed to positive and negative air ion flux that allows a periodical deposition of a dosed amount of charge in order to measure electrostatic properties of the samples, i.e. to measure maximum surface voltage, sheet capacitance, surface voltage decay half time, volume resistivity, et cetera. A study of a two-layer sample consisting of laboratory filter paper and polyethylene film superimposed on the conductive surface in one position when the polyethylene film is on top and in other when the sample is in turned over position shows that the electrostatic properties of the top layer become dominant. The obtained results appear to be useful for more precise understanding of the phenomena occurring in multilayer sheets and to find a way to improve the multilayer sheets features.     

Fermi surface of LaAg

Electronic structure, especially the Fermi surface, is calculated for the intermetallic rare-earth compound LaAg, known to show the structural phase transition when In is substituted for Ag, by a self-consistent fully-relativistic APW method with the exchange-correlation potential in a local-density approximation. The Fermi surface is found to consist of large hole and electron sheets as well as small hole and electron sheets. This result confirms well the theoretical prediction by Niksch et al. (1987). These Fermi surface sheets are found to explain the experimental results for the de Haas-van Alphen effect by Niksch et al. (1987) and Motoki et al. (1995) reasonably well. But, the frequency branches originating from the large hole sheet have been observed only partially. Local curvature of the large hole sheet is investigated as a possible origin of the disappearance of these frequency branches.     

High accuracy non-contact ultrasonic thickness gauging of aluminium sheet using electromagnetic acoustic transducers.

Aluminium sheet thickness has been calculated from ultrasonic data obtained using a send-receive, radially polarised electromagnetic acoustic transducer (EMAT). Sheets in the thickness range between 0.1 and 0.5 mm have been measured using this non-contact approach at a stand-off of up to 1.5 mm. Normal incidence shear waves generated and detected in the sheet and the resultant waveforms have been processed using transit time measurements and Fourier analysis. Two broad band EMAT systems have been used to perform the measurements with centre frequencies of approximately 5 MHz and frequency content up to 10 and 20 MHz respectively. The most accurate measurements of thickness on thin sheets have been made using Fourier analysis and have yielded measurements accurate to within 0.2% (or 0.4 microm) for 280 microm thick aluminium sheets. Discrete shear wave echoes can be observed for sheets down to a thickness of 250 microm using the higher frequency EMAT system. However temporal measurements of these signals yield lower accuracy results when compared to the Fourier analysis method which is capable of sub-micron accuracy.     

实验探索原子核中手征与空间反射对称性的联立自发破缺

原子核的手征对称性和空间反射对称性研究是近来原子核结构研究的前沿热点问题,吸引了大量的实验和理论研究。通过在束伽玛谱学的实验方法,在原子核78Br中发现了两对宇称相反的手征双重带,以及它们之间表征八极关联的电偶极跃迁。这是首次在原子核中发现了八极关联的多重手征带,给出了原子核存在手征对称性和空间反射对称性联立自发破缺的实验证据。Spontaneous symmetry breaking is a fundamental concept in nature. Chiral Symmetry Breaking and reflection-asymmetry in nuclei has been a subject of intensive experimental and theoretical investigation. Two pairs of positive-and negative-parity doublet bands together with eight strong electric dipole transitions linking their yrast positive-and negative-parity bands have been identified in 78Br by means of in-beam gamma-ray spectroscopy techniques. These four rotational bands are suggested as multiple chiral doublet bands with octupole correlations. This observation indicates that nuclear chirality can be robust against the octupole correlations. It is of highly scientific interest to search for the chirality-parity quartet bands in nucleus with both stable triaxial and octupole deformations.