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1.
We report accurate measurements of the current-phase relationship in the flow of superfluid 3He through a single orifice. While ideal sinusoidal 2π-periodic Josephson behavior prevails close to Tc, increasingly strong π-periodic admixture is usually observed at lower temperatures. 相似文献
2.
We discuss recent observations of the heat capacity and magnetization of a fluid 3He monolayer adsorbed on graphite plated with a bilayer of HD. Approaching the density at which the monolayer solidifies into a
commensurate solid, we observe an apparent divergence of the effective mass. However, the inferred values of F0a tend to a constant. We interpret this in terms of a Mott–Hubbard transition between a 2D Fermi liquid and a magnetically disordered solid occurring via the Brinkman–Rice–Anderson–Vollhardt scenario. 相似文献
3.
We observe spectacular features on the force–velocity characteristic of a vibrating wire resonator in superfluid 3He–B at ultralow temperatures. There are both plateaux and discontinuities in the characteristic. The plateaux seem to have two separate critical velocities where firstly some ‘event’ occurs, which causes the wire to lose energy and slow down, followed by a second critical velocity where the ‘event’ decouples. The shape of the pulses so created depends on the precise position on the particular plateau. At the low-velocity end of the plateau, the pulses show a sudden decrease in velocity followed by a gradual growth, whereas at the high-velocity end the pulses consist of a sudden increase in velocity followed by a gradual decrease. Eventually, the pulsing ceases indicating a saturation effect. We speculate that these events are due to vortex creation and annihilation/separation. 相似文献
4.
The magma activity of the North Luzon Arc is considered to have ceased, due to collision with the Asian continental margin, since late Miocene. New fission track dates of zircons taken from dike swarms in the central Coastal Range of East Taiwan show very young ages of 0.5 Ma. Furthermore, the high 3He/4He ratios (2.5 RA; RA is the air ratio) of hot spring gases near the same area indicate that more than 30% of a mantle-derived source component is necessary to account for the helium composition. These results suggest the existence of later remnant magmatic activity (more than 4 Ma) in the central Coastal Range. Therefore, arc magmatism may survive longer than the previously expected after collision. 相似文献
5.
We investigate a superconducting Kosterlitz–Thouless transition in the two-dimensional (2D) Hubbard model using auxiliary quantum Monte Carlo method for the ground state. The pair susceptibility is computed for both the attractive and repulsive Hubbard model. The numerical results show that the s-wave pair susceptibility scales as χ L2 for the attractive case, in agreement with previous quantum Monte Carlo studies. The scaling χ L2 also holds for the d-wave pair susceptibility for the repulsive Hubbard model if we adjust the band parameter t′. 相似文献
6.
Metal–Insulator transition using an exact two-dimensional (2D) dielectric function is investigated for a shallow donor in an isolated well of a GaAs/Ga1−xAlsAs superlattice system within the effective mass approximation. Vanishing of the donor ionization energy as a function of well width and the donor concentration suggests that a phase transition is not possible even below a well width of 10 Å, supporting the scaling theory of localization. The effects of Anderson localization, exchange and correlation in the Hubbard model are included in a simple way. The relationship between the present model and the Mott criterion in terms of Hubbard model is also brought out. The critical concentration appears to be enhanced when a random distribution of impurities is considered. The limiting behaviour of the well width for a quantum 2D well is brought out. A simple expression is derived for a Mott constant in 2D, a*Nc1/2 exp (9.86 exp (−L/a*))=0.123, where Nc is the critical concentration per area. Results are compared with the existing data available and discussed in the light of existing literature. 相似文献
7.
R. D. Jggi M. von Waldkirch T. Heinzel E. Ribeiro K. Ensslin G. Medeiros-Ribeiro P. M. Petroff 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
A metal–insulator transition at zero magnetic field is observed in Ga[Al]As-heterostructures where a high density of self-assembled InAs-quantum dots is located in the region of the two-dimensional electron gas (2DEG). This transition occurs only in samples with high dot densities. In contrast to other two-dimensional systems showing a metallic phase the Coulomb energy is comparable to the kinetic energy in our systems. Measurements in perpendicular fields reveal that the resistivity at B=0 is composed of several contributions. In the metallic regime a weak localization peak is superposed on top of a broad negative magnetoresistivity. In the insulating regime, the weak localization peak at B=0 develops into a very pronounced negative magnetoresistivity with decreasing electron density. Pronounced, almost B-periodic oscillations in the magnetoresistivity are observed in addition to universal conductance fluctuations. 相似文献
8.
Ionization energies of a shallow donor in a quantum well of the Cd1-xinMnxinTe/Cd1-xoutMnxoutTe superlattice system are obtained. A variational procedure within the effective mass approximation is employed in the presence of magnetic field. Within the one-electron approximation the occurrence of Mott transition is seen when the binding energy of a donor vanishes is observed. The effects of Anderson localization and exchange and correlation in the Hubbard model are included in our model. It is found that the ionization energy (i) decreases as well width increases for a given magnetic field, (ii) decreases when well width increases, (iii) the critical concentration at which the metal–insulator transition occurs is enhanced in the external magnetic field and (iv) spin polaronic shifts not only with the increase in a magnetic field but also with the well width increases. All the calculations have been carried out with finite barriers and the results are compared with available data in the literature. 相似文献
9.
《等离子体物理论文集》2017,57(4):151-166
The structure of stationary electron–positive ion plasmas in spatially limited vessels is analysed with special emphasis on the plasma–wall transition using different physical models. Basic investigations are carried out in a two‐fluid model, which is supplemented by ionization and oblique magnetic fields. Collisions between the two particle species were taken into account, as well as the dependence of the collision frequency on the particle density. For the case of non‐vanishing magnetic fields, electrons are not assumed to be in Boltzmann equilibrium. The investigated one‐dimensional domain is limited by totally absorbing walls on each side. Stationary states are considered, in which ionization sources balance the wall losses. To also take into account kinetic effects, simulations in a quasi‐neutral hybrid model are performed. The hybrid model assumes the electrons as a fluid and treats the ions using a particle‐in‐cell (PIC) method. A new way of ensuring the Bohm criterion is used by removing those superparticles impeding the wall. When comparing the results, both models reveal differences, especially when ionization from a resting neutral gas or weakly magnetized plasmas is considered, causing a broadening of the ion distribution or anisotropy effects, respectively. 相似文献
10.
Javier Catalán 《Journal of Physical Organic Chemistry》2013,26(11):948-952
The solvatochromism of β‐carotene confirms its high sensitivity not only to the polarizability of the medium, but is also contaminated by additional solute/solvent interactions due to its dipolarity and acidity, as well as to changes in its molecular structure in some solvents. A thermochromic analysis of β‐carotene dissolved in 2‐methylbutane and 1‐chlorobutane (ClB) revealed the influence of the solvent dipolarity on its UV/Vis‐spectroscopy behavior in these solvents. Applying Abe's method to the solvent‐induced shift of the first Vis absorption band of β‐carotene in ClB revealed that the electronic excitation substantially increases its polarizability and its dipole moment. Other experimental evidence also confirms that β‐carotene is not a suitable polarizability probe of the medium. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
11.
Jun Wang Yaxun Zhou Shixun Dai Tiefeng Xu Qiuhua Nie 《Physica B: Condensed Matter》2007,400(1-2):224-228
The spectroscopic properties of Er3+/Yb3+ co-doped Bi2O3–B2O3–WO3 (BBW) glasses were analyzed and discussed. The effect of WO3 content on the absorption spectra, the Judd–Ofelt parameters Ωt (t=2, 4, 6), emission spectra and the lifetime of the 4I13/2 level and the quantum efficiency of Er3+:4I13/2→4I15/2 transition were also investigated. With the substitution of WO3 for B2O3, the measured lifetime of the 4I13/2 level and the quantum efficiency of Er3+:4I13/2→4I15/2 transition increase from 0.98 to 1.31 ms and from 38.2% to 49.2%, respectively. The effective width of emission band and the emission cross-section both decrease slightly. And the emission spectra is analyzed via the different curve (σe−σa) of BBW glasses, the influence of OH−is also discussed. 相似文献
12.
All relevant low-energy transition amplitudes for the D(d,n)3He and D(d,p)3H reactions were determined from a fit to Legendre expansion coefficients of the available experimental data. A simple barrier penetrability model was used. Quintet S-wave transitions are found to contribute strongly thus obliterating the idea of neutron-lean “polarized” fusion energy production. The D+D interaction radius was determined with good accuracy for both reactions individually. The astrophysical S functions show a small S-wave enhancement and P-wave suppression of the D(d,p)3H branch. 相似文献
13.
The phase transition in the perovskite (Pv) SrRuO3 under pressure has been studied by using first-principles calculations based on density functional theory. The post-perovskite (Ppv) phase transition of SrRuO3 will take place under hydrostatic pressure of about 40 GPa. The stability of Ppv- SrRuO3 is justified by the enthalpy calculations, and this phase transition accompanies volume disconnection and magnetic moment collapses. The crystallographic data and the electronic structure of Ppv- SrRuO3 are also predicted. The crystal structure of Ppv- SrRuO3 is similar to that of Ppv- CaRuO3. A non-magnetic ground state is found in Ppv- SrRuO3. The strong hybridization of Ru and O is evident in the electronic structures of both phases. We expect that these results will help further understanding of SrRuO3 under high pressure. 相似文献
14.
We reanalyze the non-linear population dynamics of a Bose–Einstein condensate (BEC) in a double well trap considering a semiclassical approach based on a time dependent variational principle applied to coherent states associated to SU(2) group. Employing a two-mode local approximation and hard sphere type interaction, we show in the Schwinger’s pseudo-spin language the occurrence of a fixed point bifurcation that originates a separatrix of motion on a sphere. This separatrix corresponds to the borderline between two dynamical regimes of Josephson oscillations and mesoscopic self-trapping. We also consider the effects of interaction between particles in different wells, known as cross-collisions. Such terms are usually neglected for traps sufficiently far apart, but recently it has been shown that they contribute to the effective tunneling constant with a factor growing linearly with the particle number. This effect changes considerably the effective tunneling of the system for sufficiently large number of trapped atoms, in perfect accord with experimental data. Finally, we identify analytically the transition parameter associated to the bifurcation in the generalized phase space of the model with cross-collision terms, and show how the dynamical regime depends on the initial conditions of the system and the collisional parameters values. 相似文献
15.
Libing Chen Ruihong LiangHengchang Nie Zhiyong ZhouFei Cao Xianlin Dong 《Current Applied Physics》2014,14(11):1411-1415
Pure and Nb-doped Pb(Zr1−xTix)O3 (x = 0.47, 0.48, 0.50) ceramics were prepared by conventional solid-state reaction technique. Dielectric anomalies are observed in both kinds of samples near room temperature. The anomalies could be depressed by donor doping and prefer to be significant in ceramics with tetragonal crystallographic phase. Phase transition mechanism and domain wall pinning effect are proposed to explain this anomaly, and the former is considered as the dominated reason. Further results of the pyroelectric measurements confirm the existence of the ferroelectric–ferroelectric phase transition. 相似文献
16.
The variations with temperature of the line-shape, spin-lattice relaxation time, T1, and spin-spin relaxation time, T2, of the 1H nuclei in NH4HSeO4 single crystals were investigated, and with these 1H NMR results we were able to distinguish the crystals’ “ammonium” and “hydrogen-bond” protons. The line width of the signal due to the ammonium protons abruptly narrows near the temperature of the superionic phase transition, TSI, which indicates that they play an important role in this phase transition. The 1H T1 for NH4+ and HSeO4− in NH4HSeO4 do not change significantly near the ferroelectric phase transition of TC1 (=250 K) and the incommensurate phase transition of Ti (=261 K), whereas they change near the temperature of the superionic phase transition TSI (=400 K). Our results indicate that the main contribution to the low-temperature phase transition below TSI is that of the molecular motion of ammonium and hydrogen-bond protons, and the main contribution to the conductivity at high temperatures above TSI is the breaking of the O-H?O bonds and the formation of new H- bonds in HSeO4−. In addition, we compare these results with those for the NH4HSO4 and (NH4)3H(SO4)2 single crystals, which have similar hydrogen-bonded structure. 相似文献
17.
Erix A. Miln‐Garcs Sayan Mondal Jayant B. Udgaonkar Mrinalini Puranik 《Journal of Raman spectroscopy : JRS》2014,45(9):814-821
Identification of specific packing interactions within in the hydrophobic core of proteins is important for understanding the integrity of protein structure. Finding such interactions is challenging because few tools allow monitoring of a specific interaction in the presence of several non‐specific forces that hold proteins together. It is important to understand how and when such interactions develop during protein folding. In this study, we have used the intrinsic tryptophan residue, Trp53, as an ultraviolet resonance Raman probe to elucidate the packing interactions in the hydrophobic core of the protein barstar. Barstar is extensively studied for its folding, unfolding and aggregation properties. The Trp53 residue is known to be completely buried in the hydrophobic core of the protein and is used extensively as an intrinsic probe to monitor the folding and unfolding reactions of barstar. A comparison of the resonance Raman cross sections of some bands of Trp53 with those observed for N‐acetyl‐tryptophanoamide in water suggests that Trp53 in barstar is indeed isolated from water. Intensity ratio of the Fermi doublet suggests that Trp53 is surrounded by several aliphatic amino acid residues in corroboration with the crystal structure of barstar. Importantly, we show that the side chain of Trp53 is involved in a unique CH–π interaction with CH groups of Phe56 as well as a steric interaction with the methyl group of Ile5. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
18.
LiBo Wang Wenfei Zhang Shaosong Shen Huigang Wang Xuming Zheng Anmin Zheng Yueying Chu 《Journal of Raman spectroscopy : JRS》2012,43(10):1465-1471
Excitation wavelengths of 282.4, 273.9 (A band), 252.7, 239.5 and 228.7 nm (B band) resonance Raman spectra were acquired for di‐2‐pyridylketone, and density functional calculations were carried out to help in the elucidation of the photo relaxation dynamics of A‐band and B‐band electronic transitions. The resonance Raman spectra show that the intensity pattern of the A band presents great difference from that of the B band, which indicate that the short‐time A‐band (S0→S4) photo relaxation dynamics have substantial difference from that of B band (S0→S10) . The overall picture of short‐time dynamics and the vibronic coupling mechanisms are interpreted using Albrecht's theory. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
19.
The astrophysical S-factor for the reaction 7Be(p, γ)8B up to an energy of 2 MeV (c.m.) and the capture cross section of 7Li(n,γ)8Li up to 1 MeV (c.m.) are calculated using the Direct Capture model (DC). Both calculations are in good agreement with experimental data. 相似文献
20.
Magnetically tuned singlet–triplet perturbations in the 41Ã1A2–2131ã3A2 system of thioformaldehyde, found in ortho-rotational states (I = 1, the two hydrogen spins parallel) have been identified as being caused by vibronic spin–orbit coupling. This perturbation mechanism has been confirmed in several avoided crossings observed in this work for para states (I = 0, hydrogen spins antiparallel) which are much stronger. Parametrization of the theory has led to a quantitative understanding of the experimental frequency-field relations, and to an accurate prediction of the rovibrational energies of the triplet state. This in turn permitted the detection of about 100 Doppler-limited 2131ã3A2–00
1A1 rovibronic transitions which led into fine structure states. The combined data was then used to determine a set of rotational, fine, and hyperfine triplet-state parameters, the term value T0(2131ã3A2) = (16 685.385 ± 0.002) cm−1, and the spin–orbit vibronic singlet–triplet coupling constant, WST = (0.0691 ± 0.0016) cm−1. A large number of frequency perturbations observed in the crossings, ranging from 2 to 300 MHz, can be explained with this single parameter. 相似文献