Nonlinear diffusion and particle production in relativistic systems

The short parton production phase in high-energy heavy-ion collisions is treated analytically as a nonlinear diffusion process. The initial buildup of the rapidity density distributions of produced charged hadrons within τ_p0.25 fm/c occurs in three sources during the colored partonic phase. In a two-step approach, the subsequent diffusion in pseudorapidity space during the interaction time of τ_int7–10 fm/c (mean duration of the collision) is essentially linear as expressed in the Relativistic Diffusion Model (RDM) which yields excellent agreement with the data at RHIC energies, and allows for predictions at LHC energies. Results for d+Au are discussed in detail.     

Time Evolution of the two-jet eventse +−e −→Hadrons in the Dynamical String Model

The time dependent pion emission rate and the mean life time of the pion source in the center of mass frame of the two-jet events have been determined fore ⁺?e ^?→hadrons at √s=20 – 50 GeV by the Dynamical String Model. It was established that the time needed for the creation of the pion source is 5 fm/c, whereas its life time is τ₀=7 – 13 fm/c for energies √s=20 – 50 GeV, respectively.     

The reconstructed final state of Au+AU collisions from PHENIX and STAR data at √s=130 AgeV— Indication for quark deconfinement at RHIC

The final state of Au+Au collisions at √s=130 AGeV at RHIC has been reconstructed within the framework of the Buda-Lund hydrodynamical model, by performing a simultaneous fit to final data on twoparticle Bose-Einstein correlations of the STAR and PHENIX Collaboration, and final identified single-particle spectra as measured by the PHENIX Collaboration. The results indicate a strongly three dimensional expansion, with a four-velocity field that is almost a spherically symmetric Hubble flow. We find large transverse geometrical source sizes, R _G=9.8±1.2 fm, relatively short mean freeze-out time, τ₀=6.1±0.3 fm/c and a short duration of particle emission, Δτ=0.02±1.5 fm/c. Most strikingsly, we find an indication for a hot central part of the hydrodynamically evolving core, characterized by a central temperature T ₀=202±13 MeV that is close to (or even above) the deconfinement temperature of the quark-hadron phase transition. The best fit indicates a cold surface temperature T _s=110±16 MeV. When the possibility of the hot center is excluded, the confidence level of the fit decreases from 28.9% to 1.0%. Predictions are made for the rapidity dependence of the slope parameters and for the transverse mass depedence of the rapidity width of the single-particle spectra, and the transverse mass dependence of the non-identical particle correlations.     

25MeV/u40Ar+197Au反应中高激发热核的时空演化

报道了25MeV/u⁴⁰Ar+¹⁹⁷Au反应中从两粒子相对动量关联函数提取的发射时间随空间大小演化的规律.结果表明，即使发射源质量数减小50%，对计算的关联函数及提取的发射时间影响仍然很小.在短发射时间(τ≤100fm/c)情况下，较小的核物质密度，导致提取的发射时间变小.因此，在正常核物质密度参数下提取的τ值可作为发射时间的上限值.在长发射时间(τ≥300fm/c)情况下发射时间不随空间大小变化，提取的τ即为实际的发射时间. 关键词：     

The Shear‐Dependent Phase Separation Behavior of the Ternary Blend Polystyrene/Polyvinyl Methyl Ether/Styrene–Acrylonitrile Copolymer

The phase behavior and phase separation dynamics of a PS/PVME/SAN ternary blend using light scattering under a shear rate range of 0.1～40 s^?1 were investigated. The cloud point temperature first increases and then decreases with the increase of shear rates. At higher shear rates, the cloud point temperature again increases. The phase separation behavior in the early and later stages under shear field can be explained by the Cahn–Hilliard theory and the exponential growth law, respectively. The delay time τ _d ?, the apparent diffusion coefficient D _app, the growth rate R(q), and the exponent term show strong dependence on the difference between the experimental temperature and the cloud point temperature (ΔT), and on the shear rates. Compared with PS/PVME binary blends at lower shear rates, τ _d for a PS/PVME/SAN ternary blend is smaller, while at higher shear rates τ _d is larger. At higher shear rates, the introduction of the third component SAN to a PS/PVME binary blends slows the phase separation process.     

Generating Metallic Amorphous Core–Shell Nanoparticles by a Solid‐State Amorphization Process

Metallic crystalline/amorphous core–shell nanoparticles consisting of a crystalline Pd core (c‐Pd) surrounded by an amorphous Fe₂₅Sc₇₅ shell (a‐FeSc) are prepared by inert‐gas condensation. A phase transformation of the c‐Pd by a solid‐state diffusion process resulting in an amorphous core (a‐PdSc) surrounded by an amorphous FeSc shell is observed if the core–shell structure is irradiated at ambient temperature with 300 keV electrons. The amorphization process seems to involve the diffusion of irradiation‐induced defects and is presumably driven by the large negative heat of mixing of Pd and Sc, as well as by the excess enthalpy of the interfaces between the c‐Pd regions and the surrounding a‐FeSc. The structural transformation reported here opens a new way to producing metallic amorphous core–shell nanoparticles of different chemical compositions and probably novel properties.     

Molecular motion in liquid benzene by nuclear magnetic resonance

The proton spin-lattice relaxation time, T ₁, has been measured for a series of mixtures of benzene in perdeuterobenzene for the liquid in equilibrium with its vapour over the temperature range from below the normal freezing point up to the critical temperature. The two contributions to T ₁ due to interactions within the molecule (T _{1 intra}) and between molecules (T _{1 inter}) have been separated and are found to be very different in magnitude and in variation with temperature. The variation and magnitude of T _{1 inter} correlates well with other translational motion dependent properties such as self diffusion and viscosity. The correlation of T _{1 intra} with other re-orientation dependent properties such as deuteron T ₁ and Rayleigh scattering is poor.

The observed variation in T _{1 intra} and in particular the broad maximum at higher temperatures is then interpreted as due to a combination of dipolar and spin-rotation effects. This interpretation results in good agreement between the activation energies for re-orientational molecular motion deduced from proton T ₁ and deuteron T ₁. It supports the Hubbard theory for the relation between the dipolar and spin-rotation correlation times τ_d and τ_sr. It gives a rough value, 3·8 kc/s, for the spin-rotation interaction constant for protons in benzene. Reasonable values for τ_d and τ_sr are predicted and for all temperatures τ_sr < τ_d as expected.

There is clearly a considerable difference between the re-orientational and translational motion of the molecules in liquid benzene but the exact nature of the difference cannot be elucidated.     

Elastic scattering of 40Ar on 40Ca at Elab = 191, 236 and 272 MeV

Cross sections for elastic scattering of ⁴⁰Ar on ⁴⁰Ca have been measured at energies E_lab = 191, 236 and 272 MeV employing position-sensitive detectors and the method of kinematical coincidences. The experimental data are first compared with the ordinary and the generalized Fresnel models. Only the generalized Fresnel model describes the experimental data well. An optical model analysis with a Woods-Saxon potential yields an energy independent set of parameters (V_R = ?21.76 MeV, r_OR = 1.37 fm, a_R = 0.45 fm; W₁ = ?13.69 MeV, r₀₁ = 1.40 fm, a₁ = 0.36 fm) very similar to the one found in ⁴⁰Ca-⁴⁰Ca scattering at corresponding energies. Values deduced for the total reaction cross sections for the three energies are in good agreement with those predicted by the generalized Fresnel model. The data are also compared with optical model calculations with the real part of the potential replaced by various microscopically determined potentials. The proximity, Fleckner-Mosel and the Krappe-Nix-Sierk potentials like the phenomenological optical model potential reproduce the measured data fairly well over several orders of magnitude.     

Proton spin-lattice relaxation in liquid water and liquid ammonia

The proton spin-lattice relaxation time has been measured at 20·8 Mc/s for a series of solutions of water in heavy water and solutions of ammonia in heavy ammonia for the temperature range from the melting point to the liquid-vapour critical temperature. Measurements have also been made for water over limited temperature ranges at several fixed densities.

The contributions to the spin-lattice relaxation time from direct dipolar and spin-rotation interactions have been separated. The spin-rotation interaction contribution appears to be the same for H₂O as for HDO and also as between NH₃, NH₂D and NHD₂ and this result is justified. The correlation times for molecular re-orientation, τ_d, and for molecular angular velocity, τ_sr, are derived from the results and in so doing some support for the Hubbard [12] relation betweent τ_sr and τ_d is adduced. It is found that at the critical temperature τ_sr?τ_d which contrasts with other liquids for which it is usually found that τ_sr??τ_d. The spin-rotation interaction constants in the water and ammonia molecules are found to be approximately 120 kc/s and 80 kc/s, respectively.

An attempt to separate the inter- and intra-molecular contributions to the dipolar spin-lattice relaxation time is possible in principle, in spite of the rapid proton exchange, but is frustrated by the fact that the equilibrium constants are little different from their statistical values. Nevertheless there is evidence that the two interactions vary in much the same way with temperature.

The correlation times deduced from the dipolar relaxation time show close relationship with dielectric, self diffusion and deuteron relaxation time data.

It is suggested that the re-orientation of both water and ammonia molecules may be by a small angle Brownian diffusion even near the critical temperature.     

EBSD study of crystallographic identification of Fe-Al-Si intermetallic phases in Al-Si coating on Cr-Mo steel

5Cr-0.5Mo steel was coated by hot-dipping in a molten Al-10 wt.% Si bath at 700 °C for 10, 60, 120 or 180 s. The identification of the phases in the Fe-Al-Si intermetallic phases formed in the aluminide layers during hot-dipping was carried out by using a combination of scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The EDS results show a τ_5(H)-Al₇Fe₂Si phase, which exhibited 2 distinct morphologies, small particles widely dispersed and a continuous layer. Also revealed by EDS were τ₆-Al₄FeSi and τ₄-Al₃FeSi₂ phases, which showed plate-shaped morphology, in an Al-Si topcoat. However, the XRD results show the intermetallic phases in the aluminide layer were composed of outer cubic τ_5(C)-Al₇(Fe,Cr)₂Si and inner hexagonal τ_5(H)-Al₇Fe₂Si. EBSPs and mapping functions in EBSD helped to clarify the confused phase identifications yielded by EDS and XRD. In this way, the small intermetallic particles and the continuous intermetallic layer were identified as cubic τ_5(C)-Al₇(Fe,Cr)₂Si and hexagonal τ_5(H)-Al₇Fe₂Si, respectively, and the plate-shaped intermetallic phase was identified as monoclinic τ₆-Al₄FeSi and tetragonal τ₄-Al₃FeSi₂ with the same metallographic morphology. EBSD proved to be a very effective technique for local phase identification of aluminide layers with complicated multiphase morphologies.     

In situ synchrotron diffraction studies on the formation kinetics of jarosites

This paper reports the results of time‐resolved synchrotron powder diffraction experiments where jarosites with different K/H₃O, K/Na and Na/H₃O ratios were synthesized in situ at temperatures of 353, 368 and 393 K in order to observe the effect on kinetics and species produced. The Na/H₃O sample formed monoclinic jarosite at all three temperatures, whereas the K/H₃O and K/Na samples formed as rhombohedral jarosites at 353 K, and as mixtures of rhombohedral and monoclinic jarosites at the higher temperatures. The relative amount of the monoclinic phase increased with increase in temperature. Unit‐cell parameter changes with reaction time could be explained by changes in iron stoichiometry (samples become more stoichiometric with time) together with changes in K/H₃O and Na/H₃O ratios. The reaction kinetics have been fitted using a two‐stage Avrami model, with two different Avrami exponents corresponding to initial two‐dimensional growth followed by one‐dimensional diffusion‐controlled growth. Activation energies for the initial growth stage were calculated to be in the range 90–126 kJ mol^?1.     

Nuclear charge radii of Al and Si from elastic electron scattering between 25 and 60 MeV

Elastic electron scattering cross sections of²⁷Al and Si (natural isotopic mixture) have been measured relative to carbon. The rms charge radiiR _m , deduced with partial wave calculations, are (3.01±0.05) fm for²⁷Al and (3.06±0.05) fm for Si, in good agreement with results from muonic X-ray energies. The values given are those for a Fermi charge distribution with skin thickness 2.5 fm; harmonic oscillator shell model distributions yield radii smaller by 0.03 fm. The ratioR _m (²⁷Al)/R_m(Si) is 0.984±0.016.     

New determination of the neutron-proton scattering amplitude and precise measurements of the scattering amplitudes on carbon,chlorine, fluorine and bromine

After an improvement on the theory of the neutron-gravity-refractometer and after refinements of the experimental procedure we have performed new measurements of the absolute value of the neutron-proton scattering amplitude at low neutron energies. In order to obtain and to confirm a very high accuracy we carried out neutron-reflection experiments on 18 various liquids of 11 different organic substances containing the elements carbon, hydrogen and/or chlorine. Compounds with fluorine and bromine were used to measure the scattering amplitudes of these elements. We found the coherent scattering amplitudes of the bound atoms to be:a _H=?3.7409(1l)fm,a _c=6.6484(13)fm,a _c1=9.5792(8)fm,a _F=5.66(2)fm anda _Br=6.79(2)fm. The low energy (n, p)-parametersa _t anda _s were calculated with the presenta _H and a new value of the (n, p) scattering cross-sectionσ ₀. By comparing the measureda _C with values obtained from precise transmission experiments we could determine the gravitational accelerationg _f of the free neutron in terms of the local value g. We found the two values to be equal:g _f =0.9996(7)g.     

The proton relaxation of methyl cyanide in the presence of Ni(II) ions,as studied by spin-echo techniques

The proton relaxation times (T ₁ and T ₂) of methyl cyanide, in the presence of Ni(II) ions, have been measured as a function of temperature and frequency by spin-echo techniques. The observed decay times (T ₂?) have also been measured as a function of the separation, t _ep, between the pulses in a Carr-Purcell train of echos. The results obtained in the limit of long pulse separation have been fitted to existing theories. The rotational correlation time of the Ni/MeCN complex, τ _R , the electron spin relaxation time, τ _S , and the distance of closest approach of the protons to the nickel have been estimated from the results. In addition the scalar coupling constant, the exchange rate τ _B and the activation energies for τ _B , τ _S and τ _R have been evaluated. The chemical exchange parameters obtained differ significantly from those obtained by previous workers. There is evidence from the pulse dependence experiments that the complex is a distorted octahedron.     

New methods for interferometric neutron scattering lengths measurements

A skew symmetric neutron interferometer has been used for tests of a nondispersive and phase contrast variation measuring technique of scattering lengths and for the measurement of anomalous scattering lengths of strongly absorbing substances. The following bound coherent scattering lengths have been obtained: b_c(Pt)=9.60 ± 0.01 fm, b_c(Te) =5.6 ± 0.1 fm and as real parts of anomalous scattering lengths at λ=l.86Å: b_c(Sm) =0.7 ± 0.2 fm, b_c(Eu)=5.3 ± 0.3fm, b_c(Gd)=5.1 ±0.4 fm, b_c(Dy)=16.9 ± 0.3 fm.     

Do chemically saturated antihyperon abundancies signal the quark gluon plasma?

We first review the production and the possible chemical equilibration of strange particles at CERN-SPS energies within a microscopic hadronic transport calculation. It is shown in particular that the strange quarks are produced initially via string excitations in the primary, secondary and ternary interactions. We then further elaborate on a recent idea of antihyperon production by multi-mesonic reactions like $n_1 \pi + n_2 K \to \bar Y + p$ corresponding to the inverse of the strong binary baryon-antibaryon annihilation process. It is argued that by these reactions the (rare) antihyperons are driven towards local chemical equilibrium with pions, nucleons and kaons on a timescale of 1–3 fm/c in the still moderately baryon-dense initial hadronic environment after the termination of the prehadronic string phase. Accordingly this mechanism can provide a convenient explanation for the antihyperon yields at CERN-SPS energies without any need of a deconfined quark gluon plasma phase.     

Influence of coalescence parameters on the production of protons and Helium-3 fragments

The time evolution of protons and ³He fragments from Au+Au/Pb+Pb reactions at 0.25, 2, and 20 GeV/nucleon is investigated with the potential version of the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model combined with the traditional coalescence afterburner. In the coalescence process, the relative distance R₀ and relative momentum P₀ are surveyed in the range of 3-4 fm and 0.25-0.35 GeV/c, respectively. For both clusters, a strong reversed correlation between R₀ and P₀ is seen and it is time-dependent as well. For protons, the accepted (R₀, P₀) bands lie in the time interval 30-60 fm/c, while for 3He, a longer time evolution (at about 60-90 fm/c) is needed. Otherwise, much smaller R₀ and P₀ values should be chosen. If we further look at the rapidity distributions from both central and semi-central collisions, it is found that the accepted [t_cut, (R₀, P₀)] assemble can provide consistent results for proton yield and collective flows especially at mid-rapdities, while for ³He, the consistency is destroyed at both middle and projectile-target rapidities.     

Drying of heterogels swollen in organic vapor

Fast transient fluorescence technique (FTRF), which uses a Strobe Master System (SMS), is used to study swelling and drying of disc shape heterogels. Disc shape heterogels are prepared by free radical copolymerization (FCC) of methyl (methacrylate) (MMA) and styrene (S) with ethylene glycol dimethacrylate (EGDM). Pyrene (P_y) is introduced as a fluorescence probe during polymerization and lifetimes, τ, of P_y are measured during the in-situ swelling process. Chloroform was used as an organic vapor agent to induce gel swelling. It is observed that τ values decrease as swelling proceeds. The Li-Tanaka equation is used to determine the time constant, τ_c, and cooperative diffusion coefficients, D _c, for the swelling processes. Lifetimes of pyrene increase during drying. An empirical equation is introduced to determine the desorption coefficient, D, for drying. Heterogels with high S content swell and dry much more slowly than heterogels with low S content.     

Momentum and energy relaxation of warm carriers in semiconductors

Non-linear microwave optics of semiconductors is influenced by two relaxation times τ _m and τ_? which determine energy and momentum relaxation. In the range of warm carriers τ_? is assumed to be not dependent and τ _m linearly dependent on energy. The simple model of band structure of semiconductors and a monoenergetic energy distribution of carriers are assumed. The calculation yields the frequency dependence of the nonlinearity coefficient β as observed by Seeger with Morgan's experimental arrangement (parallel d.c. and a.c. electric fields) also at high frequencies and low temperatures. Furthermore, the h.f. behaviour of frequency multiplication and harmonic mixing are given.     

Relativistic effects in heavy-ion collisions at SIS energies

The covariant and non-covariant Quantum Molecular Dynamics models are applied to investigate possible relativistic effects in heavy ion collisions at SIS energies. These relativistic effects which arise due to the full covariant treatment of the dynamics are studied at bombarding energiesE _lab=50, 250, 500, 750, 1000, 1250, 1500, 1750 and 2000 MeV/nucl. A wide range of the impact parameter fromb=0 fm tob=10 fm is also considsered. In the present study, five systems¹²C-¹²C,¹⁶O-¹⁶O,²⁰Ne-²⁰Ne,²⁸Si-²⁸Si and⁴⁰Ca-⁴⁰Ca are investigated. The full covariant treatment at low energies shows quite good agreement with the corresponding non-covariant whereas at higher energies it shows less stopping and hence less thermal equilibrium as compared to the non-covariant approach. The collisions dynamics is less affected. The density using RQMD rises and drops faster than with QMD. The relativistic effects show some influence on the resonance matter production. Overall, the relativistic effects at SIS energies (≦2000 MeV/nucl.) are less significant.