The electron beam with virtual cathode in a two-section drift tube

An analysis based on the law of conservation of the z component of field and particle momentum in a thin annular magnetized monoenergetic electron beam in a two-section drift tube composed of tube segments with different radii (R ₁<R ₂) allowed the critical injected beam current to be determined for which a virtual cathode, formed in the wider tube at the joint section, starts traveling through the narrower tube toward the beam injection region. A region behind the traveling virtual cathode features a “squeezed” single-flux state of the beam (corresponding to the “slow” left branch of the current characteristic, high charge density, but low relativistic factor). When the injected current decreases below a critical transition level (I _in<I _Tr), the virtual cathode returns to the initial position and restores the double-flux electron beam. This current is smaller than (I _lim1+I _lim2)/2, and, depending on R ₂, varies from the limiting transport current for the narrower section (I _lim1) up to I _F/2, where I _F is the Fedosov current for this tube section.     

Dew- and bubble-point measurements for the mixtures of dichlorodifluoromethane and bromotrifluoromethane

The dew and bubble points for the mixtures of dichlorodifluoromethane (CCl₂F₂; R 12) and bromotrifluoromethane (CBrF₃; R13B1) were measured with the use of a constant-volume method coupled with an expansion procedure and visual observation of the meniscus at the vapor-liquid interface. In order to check the reliability of the apparatus used, vapor pressure measurements were conducted for carbon dioxide at 273.15 K and for two pure components, CCl₂F₂ and CBrF₃. Thirty-eight dew and bubble points of the CCl₂F₂+CBrF₃ system were determined for four different compositions of 0, 21, 45, and 70 mol % CBrF₃ in the range of temperatures from 299 to 384 K, pressures up to 4.2 MPa, and densities from 89 to 1228 kg · m^–1.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Graphicoanalytical method for calculation of heat transfer through the piston of an internal combustion engine

Using a quantitative estimate of deposit formation on the pistons of a diesel engine and results of engine thermometry, a graphicoanalytical method is developed for calculation of heat transfer through an oil-cooled piston.Notation T_m mean resultant gas temperature in engine cylinder - t_h temperature of heated side of piston - t_c temperature of cooled piston surface - t_o temperature of cooling oil - q specific thermal flux through piston - P_e mean effective engine pressure - C_m mean piston speed - T_i injected air temperature, °K - P_i injected air pressure - g_e effective fuel flow rate - mean thickness of piston bottom - thermal-conductivity coefficient of piston bottom - Z number of strokes in engine cycle - _w gas-to-wall heat-transfer coefficient - _o wall-to-oil heat-transfer coefficient - R total thermal resistance Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 918–925, November, 1979.     

The current of an annular electron beam with virtual cathode in a drift tube

An analysis based on the laws of conservation of energy and the z components of the field and particle momentum shows that a thin magnetized annular electron beam in a homogeneous drift tube behind a virtual cathode under stationary conditions occurs in a “squeezed” state corresponding to a slow left-hand branch of the current characteristic with a relativistic factor in the interval 1≤γ≤Γ^1/3. The beam current I ₁ behind the virtual cathode in a homogeneous drift tube can vary from zero up to a limiting value I _lim, while the injection currents (I ₂) and the current of electrons reflected from the virtual cathode (I ₃) for every stationary state are single-valued functions of I ₁ and fall within the intervals I _F/2≤I ₂≤I _lim and 0≤I ₃≤I _F/2, respectively, where I _F is the Fedosov current.     

Highly‐Anisotropic Dion–Jacobson Hybrid Perovskite by Tailoring Diamine into CsPbBr3 for Polarization‐Sensitive Photodetection

2D materials with inherent attributes of structural anisotropy have been well applied in the field of polarization‐sensitive photodetection. However, to explore new 2D members with strong polarized‐light responses still remains a challenge. Herein, by alloying diamine molecule into the 3D prototype of CsPbBr₃, a new Dion–Jacobson (DJ) type 2D perovskite of (HDA)CsPb₂Br₇ ( 1 , where HDA²⁺ is 1,6‐hexamethylenediammonium), containing both inorganic Cs metal and organic cations is designed. The natural anisotropy characteristics of 1 are solidly elucidated by analyzing crystal structure, electric conductivity, and optical properties. Strikingly, distinct polarization‐sensitive responses are observed in 1 , owing to its strong anisotropy of optical absorption (the ratio of α_c/α_b ≈ 2.2). Consequently, crystal‐based detectors of 1 exhibit fascinating photo‐activities to polarized‐light, including high detectivity (1.5 × 10⁹ Jones), large dichroism ratio (I_ph^c/I_ph^b ≈ 1.6) and fast responding rate (200 µs). All these polarization‐sensitive performances along with intriguing phase stability make 1 a potential candidate for polarized‐light detection. This work paves a pathway toward new functionalities of DJ‐type 2D hybrid perovskites for their future optoelectronic device applications.     

Similarity analysis of axisymmetric free convection on a horizontal infinite plate subjected to a mixed thermal boundary condition

Summary Similarity analysis of the problem of axisymmetric free convection on a horizontal infinite plate is considered assuming that the plate is subjected to a mixed thermal boundary condition. It is shown that the thermal boundary condition is characterized by a nonnegative parameterm and the two cases ofm=0 andm=1 correspond to prescribed plate temperature and prescribed surface heat flux respectively. If one has to compute the heat transfer coefficient for various values ofm, there is no need to solve the boundary value problem everytime; it is enough to solve a certain polynomial equation provided the solution is known for any particular value ofm.Notation a ₀(r),a ₁(r),a ₂(r) coefficients in Eq. (1) - A transition parameter used in Eq. (22) - C function ofr defined in Eq. (8.1) - f dimensionless stream function - F dimensionless pressure - g acceleration due to gravity - G function ofr defined in Eq. (8.2) - m mixed thermal boundary condition parameter - N normalized heat transfer coefficient in Eq. (26) - Nu _r Nusselt number - p fluid pressure - p _e ambient pressure - P normalized pressure drop at the plate - Pr Prandtl number - r radial coordinate - S normalized stress at the plate - T temperature - T _e ambient temperature - u velocity in the radial direction - w velocity in the axial direction - z axial coordinate - coefficient of thermal expansion - dimensionless similarity variable - dimensionless temperature - exponent inC - kinematic viscosity - ambient fluid density - stream function     

Radial current in tokamak during neutral beam injection

Generation of radial current I _r during the ionization of fast deuterons in their neutral beam injected into a tokamak is considered. The current I _r and force F determined by the [I _r × B] product vary in a complicated manner along the tokamak radius. For this reason, the torque that arises together with force F also nonuniformly varies along the radius, which can lead to a shear in the rotation velocity. A sufficiently large magnitude of this shear can result in reduction of both micro- and macroinstabilities in tokamak plasma [1, 2]. The influence of injected beam characteristics and other experimental parameters on the spatial distribution of I _r in the TUMAN-3M tokamak is considered.     

A response-modeling alternative to surrogate models for support in computational analyses

Often, the objectives in a computational analysis involve characterization of system performance based on some function of the computed response. In general, this characterization includes (at least) an estimate or prediction for some performance measure and an estimate of the associated uncertainty. Surrogate models can be used to approximate the response in regions where simulations were not performed. For most surrogate modeling approaches, however, (1) estimates are based on smoothing of available data and (2) uncertainty in the response is specified in a point-wise (in the input space) fashion. These aspects of the surrogate model construction might limit their capabilities.One alternative is to construct a probability measure, G(r), for the computer response, r, based on available data. This “response-modeling” approach will permit probability estimation for an arbitrary event, E(r), based on the computer response. In this general setting, event probabilities can be computed: prob(E)=∫_rI(E(r))dG(r) where I is the indicator function. Furthermore, one can use G(r) to calculate an induced distribution on a performance measure, pm. For prediction problems where the performance measure is a scalar, its distribution F_pm is determined by: F_pm(z)=∫_rI(pm(r)z)dG(r). We introduce response models for scalar computer output and then generalize the approach to more complicated responses that utilize multiple response models.     

Selecting the particle size distribution for drugs with low water solubility – mathematical model

Purpose: To introduce guidelines in selecting the particle size distribution (n₀, cm^?1) that will guarantee optimal oral absorption for drugs with low solubility.

Methods: Unlike other multi-compartmental models the gastrointestinal tract is modeled as a continuous tube with spatially varying properties. The transport through the intestinal lumen is described using the dispersion model. The model accounts for the dissolution of poly-dispersed powders.

Results: The model was used to examine the sensitivity of the absorption on permeability (P) and water solubility (C_s) following administration in different log-normal powders. The absorption exhibits inverse sigmoidal dependence on the mean particle size (r_m, µm) regardless of the administrated dose or drug properties. Thus, there is an optimal r_m that maximizes the benefit-cost ratio of the formulation; finer particles do not improve the absorption while coarser particles decrease it. Using the model we find that the optimal r_m depends mainly on the drug C_s and on the geometrical standard deviation (gSTD).

Conclusions: The results of this work provide the formulator with guidelines to select both r_m and gSTD that guarantee optimal absorption.     

A study of mechanical configuration optimisation in micro-systems

This paper shows that there are three main categories of factors that make the optimum mechanical design of micro-systems different from macro-systems: scale effects, a limited range of materials, and a limited range of production processes. The combined effect of these factors can make the optimum configuration of a micro-system potentially very different from that of the same system on a macro-scale. In particular, the use of flexible elements for hinges is much more feasible and desirable on a micro-scale.Notation a acceleration (m/s²) - A cross-sectional area (m²) - B magnetic flux [wb/m²] - b width [m] - C constant - d depth [m] - D drag [N] - E Young's modulus [N/m²] - E*= - f resonant frequency [Hz] - F _D drive force [N] - F _E electrostatic pulling force [N] - F emmisivity function - F _G geometric view factor - g gravitational constant [m/s²] - h _c convention heat transfer coefficient [W/m²K] - h height [m] - i current [A] - I _A second moment of area [m⁴] - I _I moment of inertia [kg m²] - J polar second moment of area [m⁴] - k stiffness [N/m] - K thermal conductivity [W/m K] - l length [m] - m mass [kg] - M moment [N m] - P load [N] - P _H Hertz contact pressure [N/m²] - P _C cylinder pressure [N/m²] - q heat transfer rate [W] - R, r radius [m] - Re Reynolds number - T, t temperature [K] - T _A atomic friction torque [N m] - T _D drive torque [N m] - T _F Coulomb friction torque [N m] - T _I inertial resistive torque [N m] - u velocity [m/s] - mean velocity [m/s] - V volume [m³] - V _e voltage [V] - x distance between electrodes [m] - y maximum distance to neutral axis [m] - angular acceleration [rad/s²] - _d thermal diffusivity [1/K] - rolling friction factor - P pressure difference [N/m²] - ₀ dialectric constant [F/m] - strain - dynamic viscosity [Pa s] - scale factor - _S coefficient of sliding friction - _R coefficient of rolling friction - _{1, 2} Poisson's ratio - density (kg/m³) - temperature rise [°C] - _B bending stress [N/m²] - _y yield strength [N/m²] - shear stress [N/m²] - reliability constant     

Aligning Solution‐Derived Carbon Nanotube Film with Full Surface Coverage for High‐Performance Electronics Applications

The main challenge for application of solution‐derived carbon nanotubes (CNTs) in high performance field‐effect transistor (FET) is how to align CNTs into an array with high density and full surface coverage. A directional shrinking transfer method is developed to realize high density aligned array based on randomly orientated CNT network film. Through transferring a solution‐derived CNT network film onto a stretched retractable film followed by a shrinking process, alignment degree and density of CNT film increase with the shrinking multiple. The quadruply shrunk CNT films present well alignment, which is identified by the polarized Raman spectroscopy and electrical transport measurements. Based on the high quality and high density aligned CNT array, the fabricated FETs with channel length of 300 nm present ultrahigh performance including on‐state current I_on of 290 µA µm^?1 (V_ds = ?1.5 V and V_gs = ?2 V) and peak transconductance g_m of 150 µS µm^?1, which are, respectively, among the highest corresponding values in the reported CNT array FETs. High quality and high semiconducting purity CNT arrays with high density and full coverage obtained through this method promote the development of high performance CNT‐based electronics.     

Hydrodynamic reaction to accelerated onedimensional motion of gas bubbles of variable volume in an unbounded liquid

A solution is given for the problem of the hydrodynamic reaction of an ellipsoidal gas bubble of variable volume to accelerated motion and the relation between the value of the apparent mass and the eccentricity of the bubble.Notation (,) velocity potential - V velocity of motion of the bubble with respect to the liquid - (, ) velocity potential of the near field - T₂ kinetic energy of the liquid due to the variation in bubble volume - F_r reaction force of the liquid - B₁ momentum of the liquid - _e apparent mass of the ellipsoid - density of the liquid - V_e volume of the ellipsoidal bubble Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 1, pp. 47–50, July, 1980.     

Progress on the boundary element method to study the disturbance fields of bodies moving in an unbounded medium

For studying flow problems involved with complex physics it is now common to use numerical field methods for solving Navier-Stokes or Euler equations. However, for a large class of fluid mechanics problems, which can be dealt with linearized potential equations, the boundary element method proves to be quite useful, especially for its easy application and relatively less computational effort compared to the field methods. The boundary element method has undergone some significant advancements in the last decade with respect to the study of steady and unsteady flow problems concerning wing aerodynamics in compressible medium, flow fields of propellers and rotors and acoustical disturbance propagation from moving bodies. In this paper a few recent contributions which evolved in the DLR as research projects and as doctoral and diploma thesis of the Technical University Braunschweig are concisely described.List of symbols a Sound velocity - b Span of a wing - c _p Coefficient of static pressure - c _dp Coefficient of profile drag - c ₁, c _d, c_m Coefficient of lift, drag and moment per unit span width - c _L, c_D, c_M Total lift, drag and moment-coefficients - c _T, c_P Thrust and power-coefficient of a propeller - d Distance - D Doublet strength - e Specific heat energy - E Total energy in a moving medium element - f Frequency - F Field point - g Gravitational acceleration - h Radial distance in cylinder coordinates - I ₁, I ₂ Inducing functions - i, j, k Unit vectors in cartesian coordinates - k Wave number [/a ] - l Local wing-chord - l ₀, l _v Length of singularity element at t _oand t _v - m Notation for Fourier-component - M, M ^* Mach number based on local and critical sound speed - n Number of rotation per second - n Unit normal vector to a surface     

The effect of particles on the gas velocity in a free turbulent flow

The article describes experimental studies carrid out to investigate the interaction between gas and particles in a free turbulent two-phase flow at the outlet from a rather long vertical tube.Notation A cross-sectional area of the flow - A ₀ initial cross-sectional area of the flow - d diameter of the flow - d _p average diameter of particles - I _i initial momentum of the two-phase flow - k mass ratio of particles and gas (k=m _p/m _g) - k ₀ mass ratio of particles and gas in the initial cross-section of the two-phase flow (x=0) - m _g mass flow rate of gas - m _p mass flow rate of particles - r instantaneous radius of the flow - r ₀ radius of the initial cross-section of the flow - r _1/2 normal distance from the flow axis to the point at which the velocity of gas is equal to the half of the axial velocity - R cross-sectional radius of the flow - u velocity - u _a air velocity - u _fa gas velocity on the flow axis - u _g gas velocity - u _av average gas velocity in the initial cross-section for two-phase and single-phase flows - u ₀ gas velocity on the axis of the initial cross-section of the flow - u _p particle velocity - x distance along the axis from the original of coordinates - _g gas density Institute of Nuclear Research Vina, Laboratory of Thermal and Power Engineering, Belgrade, Yugoslavia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 3, pp. 361–365, May–June, 1995.     

Experimental study of polymers femtosecond laser ablation opto-mechanical characteristics at ambient and vacuum conditions

Values of the momentum coupling coefficient, spectral energy thresholds for laser ablation, and efficiency of the laser radiation energy conversion into kinetic energy of a gas-plasma flow during femtosecond pulsed laser ablation of condensed (polymeric) targets under vacuum and atmospheric conditions have been determined. Methods are developed for measuring the recoil momentum in a sub-nanonewton range to within ΔI _M < 10⁻¹¹ N s and for high-precision combined pulsed laser microinterferometry of the surface of targets and radiative-erosive gas-plasma flows.     

On cyclic self-dual codes

We investigate cyclic self-dual codes over \mathbbF_2^r{\mathbb{F}_{2^{r}}} . We give a decomposition of a repeated-root cyclic codes over \mathbbF_p^r{\mathbb{F}_{p^{r}}} . The decomposition is used to analyze cyclic self-dual codes over \mathbbF_2^r{\mathbb{F}_{2^{r}}} . We obtain a necessary and sufficient condition for the existence of nontrivial cyclic self-dual codes over \mathbbF_2^r{\mathbb{F}_{2^{r}}} , and prove that all cyclic self-dual codes over \mathbbF_2^r{\mathbb{F}_{2^{r}}} are Type I. Finally we classify cyclic self-dual codes of some lengths over \mathbbF₄{\mathbb{F}_{4}} , \mathbbF₈{\mathbb{F}_{8}} , and \mathbbF₁₆{\mathbb{F}_{16}} .     

Core electron level structure in C<Subscript>60</Subscript>F<Subscript>18</Subscript> and C<Subscript>60</Subscript>F<Subscript>36</Subscript> fluorinated fullerenes

The structure of C1s and F1s core electron levels in C₆₀F₁₈ and C₆₀F₃₆ fluorinated fullerenes has been studied by X-ray photoelectron spectroscopy using synchrotron radiation. It is established that C1s levels of carbon atoms not bound to fluorine in these compounds are shifted down by 1.0 and 1.6 eV relative to the C1s level in the usual C₆₀ fullerene, so that the binding energies of the core electron levels in C₆₀F₁₈ and C₆₀F₃₆ amount to E _b (C1s, C-C) = 285.7 and 286.3 eV, respectively. These values are characteristic and can be used for the identification of both homogeneous fluorinated fullerenes and combined materials comprising a mixture of various fluorinated fullerenes with each other and with different carbon-containing based materials.     

Mass Spectrometric Observations of Enhanced Rates of Association Reactions: nLiF = Li n F n (n = 2, 3) at LiF Single Crystal Surfaces

A mass spectrometric method was used to study the kinetics of lithium fluoride single-crystal sublimation. In electron impact ionization mass spectra, Li⁺, LiF⁺, Li₂F⁺, and Li₃ F ₂ ⁺ ions originating from monomer (LiF), dimer (Li₂F₂), and trimer (Li₃F₃) molecular precursors were detected in the temperature range 970–1070 K. The dimer-to-monomer and trimer-to-monomer flux ratios were found to increase progressively with increasing temperature and also in comparison with those measured under equilibrium of crystalline LiF with its saturated vapor. The temperature dependence of the ion current ratio I(Li₂F⁺)/I(Li⁺) measured over the interval 916–1087 K was shown to pass reproducibly through a minimum at about 975 K. The enhancement of the rate of association reactions at LiF crystal surfaces is discussed in light of the terrace-ledge-kink model of vaporization and surface charge concept.     

A Note on Estimation from a Type I Extreme-Value Distribution

If the random variable T has the ta-o-parameter Weibull distribution with cumulative distribution function F(t; θ, K) = 1 – exp[–(t/θ) ^k ], where θ is the scale parameter and K is the shape parameter, then the random vatiable X = In T has the Type I extreme-value distribution of smallest values with cumulative distribution function F(x; u, b) = 1 – exp {–exp [(x – u)/b}, where u = In θ is the location parameter (mode) and b = 1/K is the scale parameter. It is therefore possible to obtain the maximum-likelihood estimator û _mn | b of u, based on the first m order statistics of a sample of size n, when b is known, by a simple transformation of the corresponding estimator of θ when K is known. Use is made of the fact that û _mn | b = In _mn | K, where 2m( _mn | K) ^k /θ ^k has the chi-square distribution with 2m degrees of freedom, to set confidence bounds on u. The probability density function of û _mn | b which for given m is the same for any n ≥ m, is obtained by a simple transformation of that of _mn | K. Integration yields expressions, involving digamma and trigamma functions, for the bias E = E[(û _mn |b) – u] and the variance V = V(û _mn | b). By subtracting the bias E](û _mn |b) – u] from û _mn |b, one obtains an unbiased estimator û|b which has the same variance as the maximum-likelihood estimator. Values of E/b(6DP) and of V/b ²(6DP) are tabulated for m = 1(1)100. The use of the table is discussed and illustrated by a numerical example.     

Studies on heat processing and storage of seer fish curry in retort pouches

Seer fish in curry medium packed in locally manufactured retort pouches, having a three‐layer configuration of thickness 12.5 µm polyester/12.5 µm aluminium foil/80 µm cast polypropylene was processed in a steam/air mixture over a pressure retort. About 210 g fish curry, having 110 g fish slices, was packed in a retort pouch of size 17 cm × 15.5 cm, each fitted with a thermocouple. Time–temperature data were collected during heat processing using an Ellab data recorder F_O and cook value integrator. The heat penetration characteristics were determined using a mathematical method. The f_h value was 25 min with a F_O value of 11.5 and cook value of 95 min. These samples remained in good condition for up to 24 months at room temperature. Copyright © 2002 John Wiley & Sons, Ltd.