Collisional excitation among the seven lowest states of TiXII

Collision strengths have been calculated for electron impact excitation of sodium-like TiXII for all 21 transitions amongst its lowest seven states. Configuration interaction wave functions have been used to represent the target states. The standard and no-exchangeR-matrix codes have been used to calculate the contribution of partial waves withL⩽8 andL>8 respectively. Collision strengths are tabulated at selected energies in the range 26 to 50 Ryd. Effective collision strengths are tabulated for electron temperatures in the range logT _e=4.0 to logT _e=6.0, withT _e in K. This is the first detailed calculation on this ion in which the effects of exchange, channel couplings and short-range correlation are taken into account.     

Hyperfine coupling of12B in noble metals and Al; enhancement of the conduction-electron spin susceptibility by e-e exchange

We have remeasured the Korringa contributionT _1e to the nuclear spin lattice relaxation time of the interstitial¹²B in nobel metals and in Al. TheT _1e T times the squared Knight shiftK of¹²B taken from the literature, that is the Korringa product of¹²B, shows that the conduction-electron spin susceptibility is exchange enhanced similarly to that sensed by the matrix nucleus. The enhancement factors are equal within the experimental errors for both interstitial and matrix positions in Cu and Ag. The enhancement factors at the boron and at the matrix position are different in Au and Al.     

Electron heating in a submicron-size n GaAs wire

We have studied electron heating in a submicron-size GaAs wire from 4.2 K to 50 K. We find that the energy relaxation rate for the electrons is of the form τ_E⁻¹ = α + βT_eⁿ where α, β are constants and T_e is the electron temperature. We associate the temperature-independent term with a quasi-elastic surface scattering process in which an electron losses 1% of its energy at each collision. The temperature dependent term may be due to electron-phonon scattering. It is possible to fit the data to 2 < n < 3.     

Initiation and Sustainment of Unipolar Arc Discharges by a Microsecond Pulse Plasma

Unipolar arcs have been produced by contacting metal surfaces with microsecond pulse plasmas. Plasma temperature T_e, density n_e and potential (with respect to ground) were controlled in the limits 7–12 eV, 10¹⁸–10¹⁹ m^?3, 20–40 V, respectively, and the influence of these parameters on arc current amplitude (50–500 A) and ignition probability has been investigated. It was found that the ignition is the most limiting process requiring surface contaminations as well as the transport of net currents to the surface. The amplitude of the current was proportional to n_eT_e^1/2.     

Electron cooling in three‐dimensional Dirac fermion systems at low temperature: Effect of screening

Hot electron cooling rate P, due to acoustic phonons, is investigated in three‐dimensional Dirac fermion systems at low temperature taking account of the screening of electron–acoustic phonon interaction. P is studied as a function of electron temperature T_e and electron concentration n_e. Screening is found to suppress P very significantly for about T_e < 0.5 K and its effect reduces considerably for about T_e > 1 K in Cd₃As₂. In Bloch–Grüneisen (BG) regime, for screened (unscreened) case the T_e dependence is P ～ T_e⁹(T_e⁵) and the n_e dependence gives P ～ n_e^–5/3 (n_e^–1/3). The T_e dependence is characteristic of 3D phonons and n_e dependence is characteristics of 3D Dirac fermions. The plot of P /T_e⁴ vs. T_e shows a maximum at temperature T_em which shifts to higher values for larger n_e. Interestingly, the maximum is nearly same for different n_e and T_em/n_e^1/3 being nearly constant. More importantly, we propose, the n_e dependent measurements of P would provide a clearer signature to identify 3D Dirac semimetal phase. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Temperature dependence of muonium spin exchange with O2 in the range 88 K to 478 K

Our group at TRIUMF reported earlier a study of the spin exchange reactions of Mu with O₂ and NO in the range 295 K to 478 K. We have extended the measurement with O₂ to a low temperature region down to 88 K. From 135 K to 296 K, the spin depolarization rate constantk _d(T) was found to vary according to the relative velocity of the colliding species,T ^1/2, which indicates that the spin exchange cross section of Mu-O₂ is temperature independent in this temperature range. The value ofk _d(T) at 296 K is in good agreement with our earlier study. However, it was found that below 105 K and above 400 K,k _d(T) tends to have stronger temperature dependences (T ⁿ , withn>1/2). This deviation fromT ^1/2-behavior can be attributed to the velocity (energy) dependence of the spin exchange cross section.     

Ultra-low temperature study of the even-denominator FQHE state

We present experimental data showing unambiguously an even-denominator fractional quantum Hall effect (FQHE) state at . At a bath temperature T_b=8 mK, we observe a Hall plateau quantized to a value of 2h/5e² with an uncertainty smaller than 2 parts in 10⁶ and a vanishing R_xx (R_xx=1.7±1.7 Ω). The thermal activation energy gaps Δ at Landau level filling factors , and are 0.11, 0.10, and 0.055 K, respectively. Adding a disorder broadening (typically 2 K) to these values, we deduce that all three FQHE states have probably very similar energy gaps. The electron heating experiment shows that the 2D electrons are efficiently cooled to the bath temperature for T_b8 mK. We also explore the density dependence of the activation gap at . Preliminary results at T_b25 mK show that the state is very sensitive to disorder.     

Directed polymers in a random environment: Some results on fluctuations

We consider a polymer model on ℤ ₊ ^d where to each edgee is associated a random variable v(e). A polymer configuration is represented by a directed pathr and has a weight exp[-β ∑ _e ∈r ν(e)], withβ=1/T the inverse temperature. We extend some rigorous results that have been obtained for the ground state of this model to finite temperatures. In particular we obtain some upper and lower bounds on sample-to-sample free energy fluctuations, and also rigorous scaling inequalities between the exponents describing free energy fluctuations and transversal displacements of polymer configurations     

Metal-insulator transition in electron-doped Ba1−x La x MnO3 compounds

Electron-doped (Ba_1−x La _x )MnO₃ compounds were prepared for x=0−0.5. Measurements of X-ray diffraction (XRD) at room temperature and temperature variation of dc electrical resistivity down to 20 K were carried out. Samples with x=0.2–0.5 exhibit metal-insulator (M-I) transition. The maximum M-I transition temperature (T _c) of 289 K was observed for 30% of La doping (x=0.3). XRD patterns of these samples (x=0.2−0.5) were analyzed using Rietveld refinement. These samples are found to be mostly in single-phase form with orthorhombic symmetry (space group Pbnm). We have found strong correlation between Mn-O-Mn bond angles and T _c of M-I transition. The resistivity data below T _c could be fitted to the expression ρ=ρ ₁+ρ ₂ T ² and this shows that double exchange interaction plays a major role even in Mn⁴⁺-rich compound. Above T _c the resistivity data were fitted to variable range hopping and small polaron models.     

Effects of impurity on the entanglement of the three-qubit Heisenberg XXX spin chain

We investigate the entanglement of the three-qubit Heisenberg XXX chain in the presence of impurity and obtain the analytical expressions of the concurrence C. It is found that for impurity entanglement, C appears only when J ₁ > J for J > 0, and J ₁ > 0 for J < 0, and in these two regions C increases with the increase of J ₁, so is the critical temperature T _c. When J ₁ ≫ | J |, C reaches its maximum value 0.5 and T _c reaches the asymptotic value T _c = 3.41448J ₁. For entanglement between the normal lattices, C appears only when J > 0 and −2J < J ₁ < J, and initially increases with the increase of J ₁ and arrives at the maximum value C _max = (e^4J/T −3)/(e^4J/T + 3) before it decays to zero gradually, so is the critical temperature T _c with, however, the maximum value T _cmax = 4J/In3. Supported by the Natural Science Research Project of Shaanxi Province (Grant No. 2004A15)     

VUV emission model of REB-heated plasma

VUV emission model of a hygrogen plasma with oxygen impurity (T _e=tens of eV,n _e 10¹⁴–10¹⁶ cm^–3,ⁿimp=1–3 % n_e) is constructed in order to judge different possibilities of plasma diagnostics (especiallyT _e measurements) in the REBEX experiments. Two sets of calculations based on the nonstationary corona model are performed: time dependent continuous and line spectra in the range 5 eV—5 keV in the constantT _e approximation (discussion ofT _e measurements by the filter-method) and time dependent intensities of selected spectral lines (2s-2p type) of ionsO ²⁺–O⁵⁺ at variableT _e (including plasma heating by REB and radiative cooling). A possibility of plasma energy content determination from radiation losses is shown.We would like to acknowledge many helpful discussions with dr. P. unka; we thank also dr. J. Ullschmied for comparing our results with diamagnetic measurements.     

Searches for physics beyond the standard model inf-f production at LEP II

Preliminary combinations of measurements of the 4 LEP Collaborations of the processe ⁺ e ⁻→f-f at LEP II are presented. The combined results are interpreted in terms of contact interactions and the exchange ofZ′ bosons and within models of low-scale gravity in large extra dimensions.     

Atomic Model Calculations of Gain Saturation in the 46.9 nm Line of Ne‐like Ar

The gain saturation in the 46.9 nm line of the Ar⁺⁸ laser is analyzed using an atomic kinetics code. The dependence of the gain (G) on the electron kinetic temperature (T_e) in the region (50 ‐150 eV) is calculated in the quasi steady‐state approximation for the different values of the electron density (N_e) and the plasma radius (r_pl). The influence of radiat on trapping, ion random and mean velocities, Stark line broadening and refraction losses on the gain saturation is taken into consideration. For r_pl = 150‐600 μm, the amplplication (G > 0 cm^‐1) exists in the large temperature/density domain (T_e = 60‐150 eV, N_e = 0.5‐10 × 10¹⁸ cm^‐3). However, the value G_s ∼ 1.4 cm^‐1 required for the gain saturation at the typical plasma length L_pl ∼ 15 cm is reached in the extremely narrow density regions at the high temperatures. The saturation is reached for r_pl = 600 μm at T^s_e = 150 eV in the region N^s_e = 1.8‐2 × 10¹⁸ cm ^‐3, for r_pl = 300 μm at T^s_e = 125 eV and N^s_e = 2.5‐3 × 10¹⁸ cm^‐3, and for r_pl = 150 μm at T^s_e = 110 eV and N^s_e = 3‐4 × 10¹⁸ cm^‐3. The broadest density region (N^s_e = 2 ‐8 × 10¹⁸ cm^‐3) is predicted for the narrowest column (r_pl = 150 μm) at the highest temperature (T^s_e = 150 eV). The operation in the broadest density region N^s_e, should make easier achievement of the gain saturation in the experiments.     

Estimating the entropy of liquids from atom–atom radial distribution functions: silica,beryllium fluoride and water

Molecular dynamics simulations of water, liquid beryllium fluoride and silica melt are used to study the accuracy with which the entropy of ionic and molecular liquids can be estimated from atom–atom radial distribution function data. The pair correlation entropy is demonstrated to be sufficiently accurate that the density–temperature regime of anomalous behaviour as well as the strength of the entropy anomaly can be predicted reliably for both ionic melts as well as different rigid-body pair potentials for water. Errors in the total thermodynamic entropy for ionic melts due to the pair correlation approximation are of the order of 10% or less for most state points, but can be significantly larger in the anomalous regime at very low temperatures. In the case of water, the rigid-body constraints result in larger errors in the pair correlation approximation, between 20 and 30%, for most state points. Comparison of the excess entropy, S _e, of ionic melts with the pair correlation entropy, S ₂, shows that the temperature dependence of S _e is well described by T ^?2/5 scaling across both the normal and anomalous regimes, unlike in the case of S ₂. The residual multiparticle entropy, ΔS = S _e ? S ₂, shows a strong negative correlation with tetrahedral order in the anomalous regime.     

Electronic properties of metals at low temperatures

A many body theory of an electron gas is developed to find the internal and correlation energies at low but finite temperatures. The contribution from the first order exchange, second order (regular and anomalous) exchange, and ring diagrams are treated. The Fermi momentum and the correlation energy are determined as functions of the density by two different methods, one being based on iteration and the other a direct solution of the number density relation. It was found that the iterative solutions which are correct to ordere ² ore ⁴ become negative forr _s of order 5 while the direct solutions do not, indicating the invalidity of the former. Hence, the correlation energy evaluated to the same orders by iteration will not be satisfactory in the same range. The highest order iterative solution which includes terms of ordere ⁶ does not show such a breakdown. These terms which give the contribution of orderr _s to the correlation energy are therefore important and tend to reduce the magnitude of the correlation energy. The corresponding curve is indeed close to that determined by the direct method for smallr _s but a significant deviation takes place at largerr _s . The Coulomb interaction seems less effective at higher temperatures. The internal energy is also determined as a function of density and temperature.     

Electron‐Ion Relaxation,Phase Transitions,and Surface Nano‐Structuring Produced by Ultrashort Laser Pulses in Metals

Fundamental physical phenomena in metals irradiated by ultrashort laser pulses with absorbed fluences higher than few tens of mJ/cm² are investigated. For those fluences, laser‐produced electron distribution function relaxes to equilibrium Fermi distribution with electron temperature T_e within a short time of 10‐100 fs. Because the electron subsystem has T_e highly exceeding much the ion subsystem temperature T_i the well‐known twotemperature hydrodynamic model (2T‐HD) is used to evaluate heat propagation associated with hot conductive electron diffusion and electron‐ion energy exchange. The model coefficients of electron heat conductivity κ (?, T_e, T_i) and electron‐ion coupling parameter α (?, T_e) together with 2T equation of state E (?, T_e, T_i) and P (?, T_e, T_i) are calculated. Modeling with 2T‐HD code shows transition of electron heat wave from supersonic to subsonic regime of prop‐agation. At the moment of transition the heat wave emits a compression wave moving into the bulk of met al. Nonlinear evolution of the compression wave after its separation from the subsonic heat wave till spallation of rear‐side layer of a film is traced in both 2T‐HD modeling and molecular dynamics (MD) simulation. For fluences above some threshold the nucleation of voids in frontal surface layer is initiated by strong tensile wave following the compression wave. If the absorbed fluence is ～30 % above the ablation threshold than void nucleation develops quickly to heavily foam the molten met al. Long‐term evolution of the metal foam including foam breaking and freezing is simulated. It is shown that surface nano‐structures observed in experiments are produced by very fast cooling of surface molten layer followed by recrystallization of supercooled liquid in disintegrating foam having complex geometry. Characteristic lengths of such surface nanostructures, including frozen pikes and bubbles, are of the order of thickness of molten layer formed right after laser irradiation. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of Plasma Resistance and Fluctuation on Probe Characteristics in Detached Recombining Plasmas

In order to find the causes of the strong anomaly of current‐voltage characteristics of Langmuir probe observed in detached recombining plasmas in a linear divertor plasma simulator, NAGDIS‐II, we have investigated plasma resistance along a magnetic field and potential fluctuations in the detached recombining plasmas. Simple calculation on the ratio between the plasma length, at which plasma resistance and resistance of ion sheath formed around a probe tip become equal, and an electron collection length indicates that the evaluation of electron temperature T_e becomes inaccurate at T_e of less than 0.6 eV when plasma density and neutral pressure are 1.0 × 10¹⁸ m^—3 and 10 mtorr, respectively. The potential fluctuation in detached recombining plasmas was found to be so large compared to T_e/e, which can also modify the probe characteristics.     

Limits on electron compositeness from Bhabha scattering

We have studied the reactione ⁺ e ^–e ⁺ e ^– using data taken by the CELLO detector at 35 GeV centre of mass energy with an integrated luminosity of 86 pb^–1. The differential cross section is found to agree with the Standard Model and is used to set limits on possible deviations from the pointlike structure of the electron. The lower limits obtained for the compositeness scale range from 0.8 to 6.0 TeV (95% C.L.), depending on the structure of the current.     

New fermions at e+e− colliders II. Signals and backgrounds

We discuss the production, at high-energye ⁺ e ^– linear colliders, of new heavy fermions predicted by extensions of the Standard Model. We analyze in great details the various signals and the corresponding backgrounds for both pair production and single production in association with ordinary fermions. Concentrating on new leptons, we use a model detector fore ⁺ e ^– collisions at a center of mass energy of 500 GeV, to illustrate the discovery potential of the next linear colliders.