On the different manifestations of particle accumulation structures (PAS) in thermocapillary flows

Particle de-mixing in flows in liquid-bridges driven by the Marangoni effect is investigated using primarily analytical models of the flow. The mechanism of particle–free-surface collisions is shown to explain the formation of experimentally observed particle depletion zones. This mechanism causes a mapping (or transfer) of particles moving on certain streamlines to other streamlines resulting in creation of a distinct depletion zone. Moreover, we demonstrate line-like particle accumulation along a chaotic streamline corresponding to SL2-PAS which is closed by a trajectory segment which is created by particle–free-surface interaction. The resulting limit cycle is stable due to the combined properties of the bulk transport and gathering at the free surface.     

Jet–jet and hadron–jet correlations in hadro- and electroproduction

We discuss, in the framework of perturbative QCD at next to leading order, two related observables which are usually considered to provide tests of the BFKL dynamics: jet–jet correlations at Tevatron energies and forward particle–jet correlations at HERA. In the first case we study the rapidity gap dependence of the azimuthal correlations and find slightly too strong correlations at large gap. In the second case we discuss the cross section as well as the azimuthal correlations over a rapidity gap range of 5 units. We find that the requirement of a forward particle imposes strong kinematical constraints which distort the distributions, notably at small rapidity gaps. We also show that the decorrelation is stronger in electroproduction than in hadron–hadron collisions. Unfortunately data are not yet available for comparison.     

Attraction of dust particles in current-carrying recombination plasma: influence of the space charge and recombination processes

We consider the problem about interaction of two conducting particles located in a weakly ionized collisional plasma with an external electric field. It is shown that the regions of the space charge, which are formed as a result of electrodynamical and recombination processes can lead to the attraction of “large particle–space charge” systems for similarly charged large particles. Thedependencies of the energy of interaction of the system on their mutual position are found and the conditions under which the interaction energy corresponds to the attraction of the systems are determined.     

The Boundary Condition in the Classical Derivation of the BBR

The classical derivation of the black body radiation (BBR) spectrum by Boyer was based on an equilibrium mechanism such that in the absence of thermal radiation particles in a container can gain kinetic energy from the random electromagnetic zero point field (ZPF) radiation. Their loss of that energy was to be by means of their collisions with the walls of the container. Theoretically, energy dissipation through collisions with the walls might lead to a divergent kinetic energy value for the particles. This is because the box can be taken large enough to minimize the collisions probability, and that can lead to a particle’s indefinite growth in energy. Furthermore, a derivation of a general phenomenon such as the BBR should be possible without relying on the walls boundary of a box. Therefore, a new boundary condition is proposed here which is related to relativistic effects. It is shown that with the new boundary condition one may still recover the BBR spectrum. A discussion is presented that shows how the new boundary condition is indeed responsible for energy dissipations.     

An analytic perturbation approach for classical spinning particle dynamics

A perturbation method to analytically describe the dynamics of a classical spinning particle, based on the Mathisson–Papapetrou–Dixon (MPD) equations of motion, is presented. By a power series expansion with respect to the particle’s spin magnitude, it is shown how to obtain in general form an analytic representation of the particle’s kinematic and dynamical degrees of freedom that is formally applicable to infinite order in the expansion. Within this formalism, it is possible to identify a classical analogue of radiative corrections to the particle’s mass and spin due to spin–gravity interaction. The robustness of this approach is demonstrated by showing how to explicitly compute the first-order momentum and spin tensor components for arbitrary particle motion in a general space–time background. Potentially interesting applications based on this perturbation approach are outlined.     

Morphology of supported silver nanoparticles characterized by?optical and thermal desorption spectroscopy

Silver nanoparticles grown on a quartz substrate are investigated with optical and thermal desorption spectroscopy (TDS). Detailed information on the nanoparticle morphology is gained with new methods of data analysis. First, fitting the extinction spectra, using a comprehensive model, allows an estimation of the effective particle–particle distance. Second, the total surface area of the particles is determined with TDS of xenon. Third, the dependence of the plasmon resonance position on the amount of adsorbed xenon or benzene is used as a measure of the average particle size. The results for these three parameters, which are critical for potential applications of nanoparticle arrays, are shown to be mutually consistent. The methods demonstrated here are complementary to scanning probe techniques which characterize the particle morphology on a microscopic length scale.     

Characterizing the dynamic behavior of nano-TiO<Subscript>2</Subscript> agglomerates in suspensions by photocorrelation spectroscopy

Metal oxide nanoparticles are small but easily form agglomerates in suspension, depending on the strength of particle–particle and particle–media interactions. To understand the agglomeration behavior of nanoparticles in media and relate to it to product performance testing, measurement methods are desired to characterize highly scattering metal oxide nanoparticle suspensions without dilution. In this article, we describe the advantages of using photocorrelation spectroscopy (PCS) in a backscattering detection configuration to carry out a realistic agglomerate size measurement in multiple scattering media found in most metal oxide nanoparticle suspensions. The dynamic behavior of nano-titanium dioxide (TiO₂) particles in buffer solutions of different chemical composition and pH values was investigated as a sample system using PCS. The resulting autocorrelation functions (AFs) at different time intervals, particle concentrations, and pH values were measured at several detection angles. The AF exhibits a multi-mode relaxation time feature and the calculated hydrodynamic diameters strongly depended on media composition and detection angle. This result indicates that the size and dispersion of nano-TiO₂ agglomerates are significantly affected by solution media. A measurement protocol for determining size and dispersion of metal oxide particles in media is proposed and related to a performance test found in industry.     

Tunneling of massive particles from noncommutative inspired Schwarzschild black hole

We apply the generalization of the Parikh–Wilczek method to the tunneling of massive particles from noncommutative inspired Schwarzschild black holes. By deriving the equation of radial motion of the tunneling particle directly, we calculate the emission rate which is shown to be dependent on the noncommutative parameter besides the energy and mass of the tunneling particle. After equating the emission rate to the Boltzmann factor, we obtain the modified Hawking temperature which relates to the noncommutativity and recovers the standard Hawking temperature in the commutative limit. We also discuss the entropy of the noncommutative inspired Schwarzschild black hole and its difference after and before a massive particle’s emission.     

The Vlasov–Maxwell–Boltzmann System in the Whole Space

The Vlasov–Maxwell–Boltzmann system is one of the most fundamental models to describe the dynamics of dilute charged particles, where particles interact via collisions and through their self-consistent electromagnetic field. We prove existence of global in time classical solutions to the Cauchy problem near Maxwellians.     

Strangeness enhancement at midrapidity in Pb–Pb collisions at 158 A GeV/c: A comparison with VENUS and RQMD models

Recently the WA97 Collaboration has measured , , , and negative particle yields and transverse mass spectra at central rapidity in Pb–Pb and p–Pb collisions at 158 A GeV/c. These results are compared with the predictions of two of the most widely used event generators for heavy-ion collisions: VENUS 4.12 and RQMD 2.3. Both models predict that enhancements increase with the strangeness content of the particle. They fail, however, to reproduce completely the measured values of yields at central rapidity. In particular, for multistrange particles, VENUS fails to reproduce both the p–Pb and the Pb–Pb data, while RQMD works for p–Pb collisions but seems to be unable to reproduce the data in Pb–Pb collisions. Moreover, the predicted behavior for strangeness production as a function of the centrality of the collision appears to be different from the observed behavior. Received: 29 April 1999 / Published online: 14 October 1999     

Dirac particles in a gravitational field

The semiclassical approximation for the Hamiltonian of Dirac particles interacting with an arbitrary gravitational field is investigated. The time dependence of the metric leads to new contributions to the in-band energy operator in comparison to previous works in the static case. In particular we find a new coupling term between the linear momentum and the spin, as well as couplings that contribute to the breaking of the particle–antiparticle symmetry.     

Phenomenological analysis connecting proton–proton and antiproton–proton elastic scattering

Based on the behavior of the elastic scattering data, we introduce an almost model-independent parameterization for the imaginary part of the scattering amplitude, with the energy and momentum transfer dependences inferred on an empirical basis and selected by rigorous theorems and bounds from axiomatic quantum field theory. The corresponding real part is analytically evaluated by means of dispersion relations, allowing connections between particle–particle and particle–antiparticle scattering. Simultaneous fits to proton–proton and antiproton–proton experimental data in the forward direction and also including data beyond the forward direction lead to a predictive formalism in both energy and momentum transfer. We compare our extrapolations with predictions from some popular models and discuss the applicability of the results in the normalization of elastic rates that can be extracted from present and future accelerator experiments (Tevatron, RHIC and LHC). PACS 13.85.Dz, 13.85.-t     

The Vlasov–Poisson–Boltzmann System Near Vacuum

Global classical solutions with small amplitude are constructed for the Cauchy problem to the Vlasov–Poisson–Boltzmann system, which describes the dynamics of charged particles interacting with their self-consistent electrostatic potential as well as with themselves through collisions. Received: 29 September 2000 / Accepted: 27 November 2000     

Large-angle production of charged pions by 3-12.9?GeV/c protons on beryllium, aluminium and lead targets

Measurements of the double-differential π^± production cross-section in the range of momentum 100 MeV/c≤p< 800 MeV/c and angle 0.35 rad ≤θ<  2.15 rad in proton–beryllium, proton–aluminium and proton–lead collisions are presented. The data were taken with the HARP detector in the T9 beam line of the CERN PS. The pions were produced by proton beams in a momentum range from 3 GeV/c to 12.9 GeV/c hitting a target with a thickness of 5% of a nuclear interaction length. The tracking and identification of the produced particles was performed using a small-radius cylindrical time projection chamber (TPC) placed inside a solenoidal magnet. Incident particles were identified by an elaborate system of beam detectors. Results are obtained for the double-differential cross-sections d²σ/dpdθ at six incident proton beam momenta (3 GeV/c, 5 GeV/c, 8 GeV/c, 8.9 GeV/c (Be only), 12 GeV/c and 12.9 GeV/c (Al only)) and compared to previously available data.     

Large-angle production of charged pions by 3?GeV/c–12?GeV/c protons on carbon, copper and tin targets

A measurement of the double-differential π^± production cross-section in proton–carbon, proton–copper and proton–tin collisions in the range of pion momentum 100 MeV/c≤p<800 MeV/c and angle 0.35 rad≤θ<2.15 rad is presented. The data were taken with the HARP detector in the T9 beam line of the CERN PS. The pions were produced by proton beams in a momentum range from 3 GeV/c to 12 GeV/c hitting a target with a thickness of 5% of a nuclear interaction length. The tracking and identification of the produced particles was done using a small-radius cylindrical time projection chamber (TPC) placed in a solenoidal magnet. An elaborate system of detectors in the beam line ensured the identification of the incident particles. Results are shown for the double-differential cross-sections d²σ/dpdθ at four incident proton beam momenta (3 GeV/c, 5 GeV/c, 8 GeV/c and 12 GeV/c). PACS 13.75.Cs; 13.85.Ni     

Transverse mass spectra of strange and multi–strange particles in Pb–Pb collisions at 158 A GeV/c

The WA97 experiment has measured the transverse mass spectra for negative hadrons () and strange particles produced at mid–rapidity in Pb–Pb collisions. The increased statistics of analysed data samples allowed us to perform a study of the spectra of , , , and as a function of the collision centrality. The data, which correspond to the most central 40% of the total inelastic cross section, have been divided into four centrality classes according to the estimated number of nucleons taking part in the collision. The spectra, analysed separately for each centrality bin, exhibit only weak ( 15%) centrality dependence. The deviation of the inverse slope from the linear dependence on the particle mass is confirmed even for the most central Pb–Pb collisions. Received: 5 January 2000 / Revised version: 28 February 2000 / Published online: 14 April 2000     

Research on Hawking Radiation as Tunneling from Schwarzshild-anti-de Sitter Black Hole

After taking into account energy conservation and the particle’s self-gravitation interaction, Hawking radiation of the massive particle as tunneling from Schwarzshild-anti-de Sitter black hole is studied by using Parikh-Wilczek’s semi-classical quantum tunneling approach. Meanwhile, Hawking radiation as tunneling from the black hole is reexamined by developing Angheben–Nadalini–Vanzo–Zerbini (ANVZ) covariant method to cover energy conservation and the particle’s self-gravitation interaction. Both the results perfectly generalize those obtained by Parikh and Wilczek, and show that the tunneling rate is related to the change of Bekenstein-Hawking entropy, and the factual emission spectrum is not exactly thermal, but satisfies the underlying unitary theory. PACS: 04.70-s, 9760. Lf.     

Fermion tunneling from a non-static black hole with the internal global monopole

Kerner and Mann’s recent research shows that the Hawking temperature and tunneling rate can be obtained by the fermion tunneling method from the Rindler space-time and a general non-rotating black hole. In this paper, considering the tunneling particles with spin 1/2 and taking into account the particle’s self-gravitation in the dynamical background space-time, we further improve Kerner and Man’s fermion tunneling method to investigate Hawking radiation via tunneling from a non-static black hole with the internal global monopole. The result shows that the tunneling rate of the non-static black hole is related to the integral of the changing horizon besides the change of Bekenstein–Hawking entropy, which is different from the stationary cases. It also essentially implies that the unitary is violated for the reason that the black hole is non-stationary and cannot be treated as an isolated system.     

Collisional effects on the collective laser cooling . of trapped bosonic gases

We analyse the effects of atom–atom collisions on a collective laser cooling scheme. We derive a quantum master equation which describes the laser cooling in presence of atom–atom collisions in the weak-condensation regime. Using such equation, we perform Monte Carlo simulations of the population dynamics in one and three dimensions. We observe that the ground-state laser-induced condensation is maintained in the presence of collisions. Laser cooling causes a transition from a Bose–Einstein distribution describing collisionally induced equilibrium, to a distribution with an effective zero temperature. We analyse also the effects of atom–atom collisions on the cooling into an excited state of the trap. Received: 18 June 1999 / Revised version: 24 September 1999 / Published online: 10 November 1999     

A general derivation of differential cross section in quark–quark and quark–gluon scatterings at fixed impact parameter

We propose a general derivation of differential cross section in quark–quark and quark–gluon scatterings at fixed impact parameters. The derivation is well defined and free of ambiguity in the conventional one. The approach can be applied to a variety of partonic and hadronic scatterings in low- or high-energy particle collisions.