Design and Performance Evaluation of Low‐Volume PM2.5 Inlet for Analyzing Chemical Composition

A new PM_2.5 inlet, based on the particle cup impactor configuration, was designed for sampling fine particles smaller than 2.5 μm in aerodynamic diameter and for operating at a flow rate of 5 l/min, as the devices, which are used to analyze the chemical composition of the particles, have good efficiency only at low‐volume flow rates. The performance of the inlet was evaluated in a test chamber, and the optimum dimensions of the particle cup impactor were determined by varying the nozzle‐to‐cup distance. Additional experiments covering flow rates between 3 and 10 l/min with particle sizes between 0.8 and 5.0 μm were carried out in the test chamber. The performance indicated that a nozzle‐to‐cup distance of 1.1 mm would yield a sharp size cutoff. The results from the tests showed that the inlet had a cutoff size of 2.55 μm in aerodynamic diameter at a flow rate of 5 l/min.     

Experimental study of surface and bulk plasmon losses induced in Al(001) by low energy electrons

We have measured the relative intensity of the elastic peak, and of the surface and bulk plasmon loss peaks, for electrons backscattered from an Al(001) single crystal surface. The exciting beam has an energy between 100 and 2000 eV, and impiges on the surface in an high symmetry plane of incidence with a colatitude angle of incidence varying between 0° and 80°. In a first series of experiments called “angle integrated experiment”, all the backscattered electrons are collected in a 2π solid angle retarding field analyser as a function of the primary beam energy and colatitude angle of incidence. In a second series called “angle resolved experiment”, the acceptance angle of the detector is set at 10° or $\text{1}\text{2}\text{°}$ and the variable parameters are colatitude angles of incidence and emission. We observe mainly that very clean aluminum exhibits large plasmon loss peaks with a negligible background. The results cannot be accounted for without sophisticated models, but “angular resolved experiments” are more suitable for a simple discussion than the “angle integrated experiment” and show mainly the phonon-plasmon coupling plus a θ dependent creation probability.     

Evaporative cooling of air in an adiabatic channel with partially wetted zones

The paper deals with the numerical study of heat and mass transfer in the process of direct evaporation air cooling in the laminar flow of forced convection in a channel between two parallel insulated plates with alternating wet and dry zones along the length. The system of Navier–Stokes equations and equations of energy and steam diffusion are being solved in two-dimensional approximation. At the channel inlet, all thermal gas-dynamic parameters are constant over the cross section, and the channel walls are adiabatic. The studies were carried out with varying number of dry zones (n = 0–16), their relative length (s/l = 0–1) and Reynolds number Re = 50–1000 in the flow of dry air (φ₀ = 0) with a constant temperature at the inlet (_{T 0} = 30 °C). The main attention is paid to optimization analysis of evaporation cell characteristics. It is shown that an increase in the number of alternating steps leads to an increase in the parameters of thermal and humid efficiency. With an increase in Re number and a decrease in the extent of wet areas, the efficiency parameter reduces.     

Constrained large-eddy simulation of supersonic turbulent boundary layer over a compression ramp

A supersonic turbulent boundary layer over a compression ramp is numerically investigated using the constrained large-eddy simulation (CLES) method. The compression corner is characterised by a deflection angle of 24°. The free-stream Mach number is Ma_∞ = 2.9, and the Reynolds number based on the momentum thickness of inlet boundary layer is Re_θ = 2300. The mean and statistical quantities, such as mean velocity, wall pressure and Reynolds stresses, are thoroughly analysed and compared with those from traditional large-eddy simulation (LES), experimental measurement and direct numerical simulation (DNS). It turns out that CLES can predict the friction coefficient, wall-pressure distribution, size of separation bubble, Reynolds stresses, etc. more accurately than traditional LES, and the results are in reasonable agreement with the experimental and/or DNS data. Also discussed are the effects of specific parameterisations of the Reynolds constraint and interfacial positions separating the constrained and unconstrained regions on the performance of the CLES method.     

Design and optimization of a cavitating device for Congo red decolorization: Experimental investigation and CFD simulation

The aim of this work is to perform design and optimization of a cavitating device based on CFD simulation. A set of operational and geometrical parameters such as convergence angle, divergence angle, length of throat, and inlet pressure that can affect the hydrodynamic cavitation phenomenon generating in a Venturi are evaluated through CFD simulation and experimental approaches. Response surface methodology (RSM) was employed to achieve the optimum geometrical configuration. The CFD results show that the maximum cavitation zone in the Venturi can be obtained when half angle of the convergence section, throat length and half angle of the divergence section are 22.7°, 4 mm, and 6.5°, respectively. A maximum decolorization of 38.8% has been obtained using the designed Venturi at cavitation number (Cv) of 0.12. Additionally, the results were compared to that of various orifice plates. A decolorization of 26.2% using 33 holes orifice plate and 11.55% in one hole orifice plate approved the superiority of the designed Venturi.     

Changes in Vocal Fold Morphology During Singing Over Two Octaves

ObjectiveVocal folds are widely assumed to only elongate to raise vocal pitch. However, the mechanisms seem to be more complex and involve both elongation and tensioning of the vocal folds in series. The aim of the present study was to show that changes in vocal fold morphology depend on vocal fold elongation and tensioning during singing.Study designThis was a prospective study.MethodsForty-nine professional female singers (25 sopranos, 24 altos) were recruited and three-dimensional laryngeal images analyzed in a coronal view derived from high-resolution computed tomography scans obtained at the mean speaking fundamental frequency (ƒ₀) and one (2ƒ₀) and two octaves (4ƒ₀) above ƒ₀.ResultsThe vocal fold angle, defined by a tangent above and below the vocal folds, was 58° at ƒ₀, 47° at 2ƒ₀, and 59° at 4ƒ₀.ConclusionThe decreased caudomedial angle of the vocal fold from ƒ₀ to 2ƒ₀ (change in muscle belly from “;fat” to “thin”) and increased angle from 2ƒ₀ to 4ƒ₀ (from “thin” to “fat”) strongly supports the hypothesis that the vocal folds elongate and then tension when singing from ƒ₀ to 4ƒ₀. This is the first study to show this relationship in vivo.     

Optical chirality of the double “L” structure

The optical chirality of the double “L” structures is investigated by the finite element method in this paper. The simulated results show that the double “L” structure has distinct chiral effect for the distance less than 300 nm. For the double “L” structure with the angle of 90°, the peak wavelength of the extinction coefficient for the left circular polarized light is larger than it for the right circular polarized light. The CD spectra are almost at the same wavelength for the distance 175–300 nm, while its wavelength increases with the decrease of the distance from 175 to 100 nm. Although the chiral effect of the double “L” structure for the angle 75° is similar with the structure for the angle 90°, the chiral effect of the structure with the angle 105° is opposite with the structure for the angle 75° and 90°.     

叶片弦向倾斜对损失发展的影响及叶片反弯降低损失机理的研究

早在六十年代初期,Ｓｍｉｔｈ提出了弦向倾斜叶片￣［１］。叶片的这种倾斜集叶片的后掠（叶片展向与气流不垂直）和上反（叶片表面与端壁斜交）于一身。根据理论分析可知,弦向倾斜叶片与周向倾斜叶片比较,在相同倾斜角下,它更能有效地抑制通道涡的形成和发展￣［２］。但是,到现在为止还没有实验数据证实这一计算结果。本文继文献￣［３］详细测量了弦向倾斜叶片叶栅由栅前至栅后诸截面上的气动参数。实验结果表明,弦向倾斜对损失的发展起到了与周向倾斜相类似的作用,但是前者比后者减小了叶栅进口段的流向逆压梯度,从而降低了二次旋涡损失。本文还测量了大转角常规直叶栅与反弯叶片叶栅端壁与叶片表面上的静压分布,探讨了反弯叶片降低损失的原因,认为：减小叶栅进口段流向逆压梯度,在叶片吸力面前部形成垂直于端壁的平行静压等值线、在中部形成反“Ｃ”型静压等值线,以及在流道内建立沿叶高的反“Ｃ”型静压分布,是反弯叶片降低损失的三要素。     

On the possibility of a radical decrease in the strength of many-body interactions in the organic metal α-(BETS)<Subscript>2</Subscript> KHg(SCN)<Subscript>4</Subscript>

Behavior of the de Haas-van Alphen (dHvA) oscillations depending on the angle between the magnetic field direction and the perpendicular to conducting layers in the quasi-two-dimensional organic metal α-(BETS)₂ KHg(SCN)₄ was studied in detail. The angular dependence of the dHvA oscillation amplitude exhibits a series of minima (at ±43.2°, ±64.6°, and ±72.0°) related to the “zero spin” effect, through which it is possible to estimate the splitting factor. An analysis of this value suggests that many-body interactions in the compound studied are either absent or at least radically weakened.     

Anisotropy of the mixed-state resistance of Tl2Ba2CaCu2O8 single crystals

The electrical resistance of single crystals of the high-temperature superconductor Tl₂Ba₂CaCu₂O₈ has been measured as a function of the angle θ between the direction of the magnetic field and the current-carrying CuO₂-planes. The resistance is maximal for θ = 90° ( B ?CuO₂-planes) and decreases to a minimum at θ = 0°. For small angles an anomalous enhancement of the resistance is found. While the general shape of the resistance is generated by the motion of “pancake vortices” in the CuO₂-planes, the anomaly is due to “Josephson vortices” moving perpendicular to the planes.     

Laminar-turbulent transition in Hagen–Poiseuille flow of a real gas

The effect of gas non-ideality on the laminar-turbulent transition is studied experimentally as the flow in a long circular tube at room temperature. The gases SF₆ and Ar, differing significantly in the value of the second virial coefficient, were chosen for this study. Experiments were carried out by varying the pressure at the tube inlet (the maximum pressure of 10⁵ Pa) and at the tube outlet up to the chock flow (formation of a supersonic flow at the outlet). The difference between the critical Reynolds numbers in the flow of SF₆ and Ar was found. The largest difference was observed for the maximum pressures; with a decrease in pressure, the critical Reynolds numbers become closer. The conclusion is an effect of the non-ideal character of gas exists on the laminar-turbulent transition in Hagen–Poiseuille flow. Some experiments were suggested to confirm this conclusion.     

Deflecting Atoms through a Submicron-Sized Slit with Near-Field Light

We report experiments on deflecting cold ⁸⁷Rb atoms by repulsive near-field light induced in a 200-nm-wide slit. The spatial profile is measured with a two-step photoionization scan. The number of outputted atoms from the slit increases by the amount of 40 ± 7.2% at a 5.1 ± 2.0° angle for the blue detuning of +1 GHz. We discuss the spatial profile involving an image of the atomic cloud by means of the scattering cross section.     

Neutron-neutron quasifree scattering in the 2H(n,nn)p reaction at En = 14.1 MeV

Neutron-neutron quasifree scattering has been studied in the deuteron break-up reaction ²H(n, nn)p at E_n = 14.1 MeV. Two coplanar and symmetric configurations have been investigated in a kinematically complete experiment where the detection of the spectator particle was not possible. The experimental cross sections are compared with “exact” calculations derived from Faddeev-type equations solved with S- and P-wave nucleon-nucleon separable interactions. These calculations agree both in shape and magnitude with the differential cross section for the θ₁ = ? θ₂ = 40° configuration (E_p^min = 0). At θ₁ = ? θ₂ = 30° (E_p^min = 180 keV). however, the absolute value of the measured cross section is too high and an observed structure in the shape of the differential cross section is in sharp conflict with the now available “exact” calculations.     

Anomalous pulse angle dependence of the single and double quantum echoes in a photoinduced spin-correlated coupled radical pair

In this work the response of a spin-correlated coupled radical pair to the sequence flash-t-P _ζ-τ-P _2ζ-T is investigated. For the theoretical analysis, the density operator formalism is used. Analytical expressions are derived for the electron spin single (SQ ESE) and double-quantum echoes (DQ ESE) as a function of pulse flip angle and singlet-triplet mixing angle. To illustrate the theoretical results, computer simulations are presented. In the limit of weak coupling, the “out-of-phase” SQ ESE is shown to be of a pure two-spin order having the maximal amplitude for the flip angle of 65.9°. The echo following the Hahn sequence vanishes in the same limit. This confirms the theoretical result already presented in the literature. However, the more general analysis shows that outside the weak coupling approximation the Hahn echo is of purely one-spin order, whereas the echo following the flash-t-P _ζ-τ-P _2ζ-t sequence has its maximal amplitude for the flip angle of 75° and the singlet-triplet mixing angle of 27°. The “in-phase” single- and double-quantum echoes are shown to vanish due to averaging out, within the electron spin resonance spectrometer deadtime, of contributions modulated with the sum and difference of the zero-quantum beat frequency and the frequency due to the spin-spin interaction within the pair. The calculated out-of-phase DQ ESE signal is inverted with respect to the out-of-phase SQ ESE and has only the half of its amplitude. The DQ ESE vanishes for the Hahn sequence. The echo has maximal amplitude in the weak-coupling limit for the flip angle of 65.9°. In contradiction to the analytical result previously published, the out-of-phase DQ ESE does not vanish for long τ and large zero-quantum-beat frequency.     

高速列车地面效应数值模拟研究

采用定常RANS方法对高速列车的地面效应进行分析,研究地面效应影响下高速列车气动力的变化规律.研究地面效应对不同侧偏角下高速列车气动力的影响,发现地面效应对073176;侧偏角下的气动力影响最大,并随着侧偏角的增大地面效应的影响逐渐变小;研究当列车与地面相对高度发生变化时高速列车气动力的变化规律,数值模拟结果揭示了高速列车气动升力存在的升力翻转效应,并对不同高度下列车底面的压力脉冲变化规律进行分析.     

Investigation of the noise emitting zones of a cold jet via causality correlations

Within the framework of lighthill's acoustic analogy the causality method proposed by Ribner and Siddon is used to identify equivalent noise sources inside a cold jet. An exploration of a few cross-sections shows that a two-dimensional investigation suffices in a first approach for integrating the source function provided the upper frequency limit does not exceed a Strouhal number approximately equal to 0·5. Furthermore the transverse distribution of the source term shows the jet region located on the microphone side to be dominant; the effective diameter of the source region is comparable with that of the nozzle. It is shown that in a direction with an angle of 30° to the jet axis, the “shear noise” is dominant (about 70% of the noise measured in the same frequency range). The noise emanates essentially from the transition region and from layers located between $\text{r}\text{D}\text{= ±0·25}$ and $\text{r}\text{D}\text{= ±0·375}$. This analysis is suitable for frequency range bounded above by St = 0·54. For the direction with an angle of 45° to the jet axis comparable results are obtained in a frequency range also limited at St = 0·54. However, this range contains only 40% of the total acoustic energy. The source region of the “shear noise” (near 70% of the total energy) and that of the “self-noise” remain always in the transition region located at 4–11 D. Radially the main part of the noise originates from the layers located on the microphone side between $\text{r}\text{D}\text{= 0·25}$ and 0·375. For the direction with an angle of 60° to the jet axis the “shear noise” is no longer measurable and the calculated “self-noise” represents only a few percent of the noise measured. For an acoustically excited jet (white noise filtered between St = 0·39 and St = 0·52, 320 Pa at the nozzle) another type of correlation appears which is believed to be related to a coherent structure travelling inside the jet at 0·75 v_j. The study of the source term shows that this structure must be related to noise originating from the nozzle outlet.     

Anomalous acid proton self-diffusion in N(CH3)4HSO4 — A candidate for proton superionic conductivity

The appearance of a “liquid-like” proton T₂ component above 100°C and the relatively high value of the proton self-diffusion coefficient D = (5–8) × 10^-7cm²sec^-1 between 175°C and 200°C demonstrate the onset of a super-ionic state in N(CH₃)₄HSO₄. The ratio between the “liquid” and “solid” like components shows that acid protons are responsible for the high ionic conductivity.     

MHD effects on the channel flow of a fractional viscous fluid through a porous medium: An application of the Caputo-Fabrizio time-fractional derivative

This research article considers the exact solutions and theoretical aspects of the channel flow of a fractional viscous fluid which is electrically conducting and flowing through a porous medium. Joint Laplace and Fourier transform techniques are used to solve the momentum equation. The Caputo-Fabrizio time fractional derivative is used in the constitutive equations. Exact solutions for an arbitrary velocity are obtained, and then in the limiting cases over a bottom plate three types of flow are considered: that is, the impulsive, accelerating and oscillating motion of the fluid. The case where the flow of the fractional fluid is unaffected by the side walls, is correspondingly taken into account. For oscillating flow the solutions are separated into steady and transient parts for both sine and cosine oscillations. Moreover these solutions are captured graphically, and the effect of the Reynolds number “Re”, fractional parameter “α”, effective permeability “K_eff” and the time “t”, on the fluid's motion are observed.     

Computer calculations of refractive indices in orthoconic SmC<Subscript>A</Subscript><Superscript>*</Superscript>. Is it possible to obtain “isotropic” antiferroelectric liquid crystal (IAFLC)?

Orthoconic antiferroelectric liquid crystals (OAFLC) are promising materials for applications. The saturated value of the tilt angle for such materials is 45°, while for “classical” antiferroelectric liquid crystals (AFLC) it reaches typically 30°. Homogeneously oriented slab of OAFLC, unwound by surface action of cell walls is apparently optically isotropic for the light beam at normal incidence. Such unwound structure of OAFLC one can call isotropic OAFLC (IOAFLC). Optical indicatrix of OAFLC is represented by an oblate sphere (ellipsoid of revolution) with its short axis perpendicular to cell walls. Here the question arises: “Is it possible to create isotropic AFLC (IAFLC)? An effective refractive index of IAFLC should have the same value for the light beam propagating at each direction, hence the optical indicatrix should be a sphere. In the way of theoretical considerations we found that IAFLC can exist for twisted structure of AFLC characterized by the tilt angle as high as 54.3°. Unfortunately, such a big tilt angle is still not achievable in practice. Calculations show that AFLC can be optically isotropic when the helix is not suppressed by cell walls action.     

透平叶栅气膜冷却效果的数值研究

本文基于二维粘性数值模拟分析了某透平叶片气膜冷却的效果。在系统分析了冷却气流的喷射速度、喷射角度和温度的影响之后，得到了一些对叶片设计非常有用的结果和结论，同时探讨了本研究发展的数值方法和程序用于工程设计的可能性。