Charged particle energy analyzer based on a modified cylindrical mirror in the ring-axis focusing mode

The electron-optical properties of systems with a modified structure of the energy analyzer in the form of a cylindrical mirror proposed earlier are investigated. The analyzer operating mode in which the source of charged particles is in the inner cylinder and the detector is on the cylinder axis (ring-axis focusing) is considered. It is shown using numerical simulation that the modified structure ensures higher focusing quality as compared to the traditional cylindrical mirror. The optimal structure and voltage supply are determined for which spherical aberration is five times smaller than with a conventional cylindrical mirror.     

The mechanism of the attracting acoustic radiation force on a polymer-coated gold sphere in plane progressive waves

Acoustic plane progressive waves incident on a sphere immersed in a nonviscous fluid exert a steady force acting along the direction of wave motion. It is shown here that when an elastic gold sphere is coated with a polymer-type (polyethylene) viscoelastic layer, this force becomes a force of attraction in the long wavelength limit. Kinetic, potential and Reynolds stress energy densities are defined and evaluated with and in the absence of absorption in the layer. Without absorption, the mechanical energy density counteracts the Reynolds stress energy density, which causes a repulsive force. However, in the case of absorption, the attractive force is predicted to be a physical consequence of a mutual contribution of both the mechanical and the Reynolds stress energy densities. This condition provides an impetus for further designing acoustic tweezers operating with plane progressive waves as well as fabricating polymer-coated gold particles for specific biophysical and biomedical applications.     

Correlation between dynamical heterogeneities, structure and potential-energy distribution in a 2D amorphous solid

We investigate the collective properties of particles in a 2D experimental system which consists of a bi-disperse mixture of colloidal particles confined at an air/water interface. We find a direct correlation between structure and dynamical heterogeneities in this system: particles belonging to locally ordered structures have lower potential energy and are slower than other particles. In a more general way we show that particles with high potential energy are dominating the dynamics especially in the α-relaxation regime.     

Structure and phase transitions in a network-forming associating Lennard-Jones fluid in a slit-like pore: a density functional approach

A study is reported of adsorption of an associating Lennard-Jones fluid with four associative sites per molecule in a slit-like pore. The density distribution of particles in the pore and thermodynamics properties are evaluated by using a density functional method. It is found that at low temperatures the fluid exhibits a set of layering transitions, followed by capillary condensation. Transitions are localized by analysing the grand canonical potential. The density profiles of particles and the distribution of unbound and differently bonded particles demonstrate changes in the structure of the fluid in the pore along the phase coexistence. The critical temperature is lower for a confined fluid, compared with the bulk counterpart. However, an increase in the energy of association increases the critical temperature. The envelope of the capillary condensation is narrower than the bulk liquid-vapour phase diagram. The dependence of the solvation force on the energy of association and on the bulk density is discussed.     

Nonequilibrium accumulation of surface species and triboelectric charging in single component particulate systems

Triboelectric charging occurs in granular systems composed of chemically identical particles even though there is no apparent driving force for charge transfer. We show that such charging can result from nonequilibrium dynamics in which collision-induced electron transfer generates electron accumulation on a particle-size-dependent subset of the system. This idea rationalizes experimental results that suggest that smaller particles charge negatively while the large ones charge positively. This effect occurs generally when there are high energy electrons on a surface that cannot equilibrate to lower energy states on the same surface, but can transfer to lower energy states on other particles during collisions.     

A method of investigation of the evolution of a nonlinear system driven by pulsed noise

A numerical method is proposed for determining the evolution of nonlinear systems subjected to noise. The method is based on a recurrence equation for the probability density which has been obtained analytically due to the choice of noise in the form of discrete series of random pulses. The method is applied to a dynamical system which describes the motion of a particle in a plane-wave field. The evolution of the probability density in phase and energy space is obtained. It is shown that because of noise effects, the region in phase space where particles can be found rapidly reaches the separatrix and then spreads over the phase space, mainly along the separatrix. In the energy spectrum a new peak appears at the separatrix's energy. This peak grows in time, while the main peak corresponding to the initial energy drops in time and shifts to lower energy. The moments of motion were analyzed. The character of their evolution indicates a high rate of chaotization. The growth of the fraction of energetic particles is very rapid (exponential at the beginning), whereas the mean energy grows linearly.     

Calculation of the parameters of a high-current reflective discharge with a hot cathode

A physical model of a self-sustaining reflective discharge is formulated based on the continuity equation for the electron flux and the equation of energy balance on the hot cathode. The model allows one to calculate the current-voltage characteristic of a high current reflective discharge with a hot cathode in a wide range of magnetic fields, discharge cell dimensions, and cathode material work functions. An advantage of the model is that it is capable of describing the ordinary operating mode of a reflective discharge with cold cathodes as a limiting case. The model predicts the existence of two discharge operating modes with thermionic electron emission on the cathode: a low-voltage mode with a high current density and a high-voltage mode with a significantly lower current density. It is shown that the low-voltage operating mode can occur in a wide range of the discharge currents, while the discharge voltage can be substantially reduced by using a cathode material with a low work function.     

Exploring the SUSY Higgs sector ate +e− linear colliders: a synopsis

We discuss the Higgs scenario in the minimal supersymmetric extension of the Standard Model ate ⁺e^? linear colliders operating in the c.m. energy range between 300 and 500 GeV. Besides decays of the Higgs particles into ordinary fermions and cascade decays, we analyze also decays into gaugino/Higgsinos and in particular, neutral Higgs decays into the lightest supersymmetric particles which are invisible ifR-parity is conserved. The cross sections for the various production channels of SUSY Higgs particles ine ⁺e^? collisions are discussed in detail. The lightest Higgs boson cannot escape detection, and in major parts of the MSSM parameter space all five Higgs particles can be observed.     

Adiabatic similarity and dependence of the energy of molecular systems on the masses of particles

The dependence of the energy of three-particle molecules on their masses is examined. It is shown that such molecules with the same values of the ratio of the reduced masses for motion in a “fast” and “slow” Jacobi coordinates have the property of adiabatic similarity: In the adiabatic approximation, their energies are proportional to the reduced masses. This allows information on the energy of molecules symmetric in the masses of particles to be extended to asymmetric molecules adiabatically similar to the symmetric molecules. For molecules with arbitrary masses of the particles, an analytic expression for the adiabatic energy and a formula approximating the exact energy are constructed using the principle of adiabatic similarity. Along with the adiabatic energy, which is the lower bound of the exact energy, a simple procedure is considered for determining the upper bound of the energy of asymmetric molecules from the energy of their symmetric counterparts. Based on these results, values of the lower and upper energy bounds are calculated and an approximation of the exact energy is obtained for 43 three-particle molecular systems.     

Segregation in the Falicov--Kimball Model

The Falicov–Kimball model is a simple quantum lattice model that describes light and heavy electrons interacting with an on-site repulsion; alternatively, it is a model of itinerant electrons and fixed nuclei. It can be seen as a simplification of the Hubbard model; by neglecting the kinetic (hopping) energy of the spin up particles, one gets the Falicov–Kimball model. We show that away from half-filling, i.e. if the sum of the densities of both kinds of particles differs from 1, the particles segregate at zero temperature and for large enough repulsion. In the language of the Hubbard model, this means creating two regions with a positive and a negative magnetization. Our key mathematical results are lower and upper bounds for the sum of the lowest eigenvalues of the discrete Laplace operator in an arbitrary domain, with Dirichlet boundary conditions. The lower bound consists of a bulk term, independent of the shape of the domain, and of a term proportional to the boundary. Therefore, one lowers the kinetic energy of the itinerant particles by choosing a domain with a small boundary. For the Falicov- Kimball model, this corresponds to having a single “compact” domain that has no heavy particles. Received: 21 June 2001 / Accepted: 4 January 2002     

Anomalous kinetic energy of a system of dust particles in a gas discharge plasma

The system of equations of motion of dust particles in a near-electrode layer of a gas discharge has been formulated taking into account fluctuations of the charge of a dust particle and the features of the nearelectrode layer of the discharge. The molecular dynamics simulation of the system of dust particles has been carried out. Performing a theoretical analysis of the simulation results, a mechanism of increasing the average kinetic energy of dust particles in the gas discharge plasma has been proposed. According to this mechanism, the heating of the vertical oscillations of dust particles is initiated by induced oscillations generated by fluctuations of the charge of dust particles, and the energy transfer from vertical to horizontal oscillations can be based on the parametric resonance phenomenon. The combination of the parametric and induced resonances makes it possible to explain an anomalously high kinetic energy of dust particles. The estimate of the frequency, amplitude, and kinetic energy of dust particles are close to the respective experimental values.     

Optimization of an ion-to-photon detector for large molecules in mass spectrometry

Ion packets can be detected in time-of-flight mass spectrometry by collecting the photons that are produced during the impact of the packets with a scintillator. The photon yield is a function of the ion energy. It was found that post-acceleration of the particles in front of the scintillator was an efficient way of increasing signal intensities. For the same total ion energy, the intensities were larger with post-acceleration than when only increasing the initial ion kinetic energy. A venetian blind dynode, converting the primary ion beam into electrons/secondary ions, was also introduced. Positive or negative secondary particles produced on the dynode surface could be accelerated to the scintillator. Electrons were found to give the highest signals. Intensities similar to those measured with microchannel plates were found. The linearity and onset of saturation of the microchannel plates and the ion-to-photon detector were compared. At optimum operating conditions, the ion-to-photon detector gave around 10 times higher signals than the microchannel plates for heavy ions (150 kDa), with similar mass resolution. Copyright 1999 John Wiley & Sons, Ltd.     

Measurements of the spread in the initial electron energy in a gyrotron

An analyzer intended for measuring electron energy in gyrotrons is described. Electron energy spectra are measured in various operating modes of an experimental gyrotron. It is shown that, even when no microwave field is generated, the spread in electron energy due to the space-charge effect can be as high as several percent.     

Optimizing a refinery using the pinch technology and the mind method

The Pinch Technology and the MIND method are combined in the analysis of a Swedish refinery. The heat exchanger network of the crude distillation system is analysed using the Pinch Technology. The results show that the steam demand from the boiler units in the energy supply part of the system can be reduced by 20% in the optimized heat exchanger network and by 21% when a heat pump is added to the system. A multi-period cost optimization of the operating strategy is performed using the MIND method. The results from the Pinch analysis are then input to the MIND optimization. The system cost of the total energy system of the refinery is optimized with regard to flexibility in the process system as well as changes of energy costs and the operating conditions of the cogeneration unit. The combination of methods shows that significant capital savings can be achieved when the energy saving potential of the process system is integrated in the overall operating strategy of the energy system. It is, in this case, possible to compare investments in energy saving measures to investments in increased steam production capacity.     

聚变堆燃烧等离子体温度剖面数值分析

采用聚变等离子体中α粒子慢化、扩散的多能群计算方法,结合本底等离子体的能量平衡方程,对α粒子自加热及扩散情形下对聚变堆而言甚为重要的等离子体温度剖面进行了自洽性的数值分析。对动态及稳态等离子体运行方式的模拟结果表明燃烧等离子体温度剖面比起目前实验得出的剖面更峰状化。这一特性不依α粒子在其慢化过程有无显著的扩散损失而改变,在今后对聚变堆α粒子行为及效应的严格分析中应加以考虑。     

Self-similar Solution of a Cylindrical Shock Wave under the Action of Monochromatic Radiation in a Rotational Axisymmetric Dusty Gas

A self-similar flow behind a cylindrical shock wave is studied under the action of monochromatic radiation in a rotational axisymmetric dusty gas. The dusty gas is taken to be a mixture of small solid particles and perfect gas,and solid particles are continuously distributed in the mixture. The similarity solutions are obtained and the effects of the variation of the radiation parameter, the ratio of the density of solid particles to the initial density of the gas, the mass concentration of solid particles in the mixture and the index for the time dependent energy law are investigated.It is observed that an increase in the radiation parameter has decaying effect on the shock waves; whereas the shock strength increases with an increase in the ratio of the density of solid particles to the initial density of the gas or the index for the time dependent energy law. Also, it is found that an increase in the radiation parameter has effect to decrease the flow variables except the density and the azimuthal component of fluid velocity. A comparison is also made between rotating and non-rotating cases.     

Effect of a dust component on the rates of elementary processes in low-temperature plasmas

Elementary processes in dusty, beam-driven plasma discharges are studied experimentally and theoretically for the first time. A theoretical model is constructed for a beam-driven plasma containing macroscopic particles. The effect of macroscopic particles on the electron energy distribution function is estimated assuming a Coulomb field for the particles. The resulting rate of electron-ion recombination on the macroscopic particles is compared with the electron loss constant calculated from the electron energy distribution function with an electron absorption constant in the orbital-motion approximation. This approximation, which is valid in the collisionless case, is found to work satisfactorily beyond its range of applicability. The distributions of the charged particles and electric fields created by macroscopic particles in a helium plasma are determined. The experimental data demonstrate the importance of secondary emission by high-energy electrons. Zh. éksp. Teor. Fiz. 115, 2020–2036 (June 1999)     

All-optical switching and pulse routing in a distributed-feedback waveguide device

Results of all-optical switching and pulse-routing experiments with a distributed-feedback multiple-quantum-well (MQW) nonlinear waveguide, operating at 1.55microm , are reported. The MQW material has been engineered, through the controlled introduction of defects, to lower the carrier lifetime from 2.5 ns to 280 ps. The energy required for switching is of the order of 1 pJ or less, the switching time is ~600 ps , and the on-off contrast exceeds 17 dB.     

Chaotic diffusion for particles moving in a time dependent potential well

The chaotic diffusion for particles moving in a time dependent potential well is described by using two different procedures: (i) via direct evolution of the mapping describing the dynamics and; (ii) by the solution of the diffusion equation. The dynamic of the diffusing particles is made by the use of a two dimensional, nonlinear area preserving map for the variables energy and time. The phase space of the system is mixed containing both chaos, periodic regions and invariant spanning curves limiting the diffusion of the chaotic particles. The chaotic evolution for an ensemble of particles is treated as random particles motion and hence described by the diffusion equation. The boundary conditions impose that the particles can not cross the invariant spanning curves, serving as upper boundary for the diffusion, nor the lowest energy domain that is the energy the particles escape from the time moving potential well. The diffusion coefficient is determined via the equation of the mapping while the analytical solution of the diffusion equation gives the probability to find a given particle with a certain energy at a specific time. The momenta of the probability describe qualitatively the behavior of the average energy obtained by numerical simulation, which is investigated either as a function of the time as well as some of the control parameters of the problem.     

Search for supersymmetric particles in scenarios with a gravitino LSP and stau NLSP

Sleptons, neutralinos and charginos were searched for in the context of scenarios where the lightest supersymmetric particle is the gravitino. It was assumed that the stau is the next-to-lightest supersymmetric particle. Data collected with the DELPHI detector at a centre-of-mass energy near 189 GeV were analysed combining the methods developed in previous searches at lower energies. No evidence for the production of these supersymmetric particles was found. Hence, limits were derived at 95% confidence level. Received: 3 February 2000 / Revised version: 3 March 2000 / Published online: 8 May 2000