A<Subscript>4</Subscript> model for the quark mass matrices

We propose a model for the quark masses and mixings based on an A₄ family symmetry. Three scalar SU(2) doublets form a triplet of A₄. The three left-handed-quark SU(2) doublets are also united in a triplet of A₄. The right-handed quarks are singlets of A₄. The A₄-symmetric scalar potential leads to a vacuum in which two of the three scalar SU(2) doublets have expectation values with equal moduli. Our model makes an excellent fit of the observed |V_ub/V_cb|. CP symmetry is respected in the charged gauge interactions of the quarks.     

Line Positions and Intensities in the 2nu(2)/nu(4) Vibrational System of (14)NH(3) near 5-7 µm

Line positions and intensities belonging to the vibrational system 2nu(2)/nu(4) of ammonia (14)NH(3) are measured and analyzed between 1200 and 2200 cm(-1) in order to improve the molecular database. For this, laboratory spectra are obtained at 0.006 and 0.011 cm(-1) unapodized resolution and with 4% precisions for the intensities using Fourier transform spectrometers located at the Kitt Peak National Observatory and the Jet Propulsion Laboratory. The observed data contain transitions of the nu(4) fundamental band near 1626.276(1) and 1627.375(2) cm(-1) (for s and a inversion upper states, respectively) and the 2nu(2) overtone band near 1597.470(3) and 1882.179(5) cm(-1) (for s and a inversion states, respectively). A total of 2345 lines with J' 相似文献   

Peierls-like transition induced by frustration in a two-dimensional antiferromagnet

We show that the introduction of frustration into the spin- 1/2 two-dimensional (2D) antiferromagnetic Heisenberg model on a square lattice via a next-nearest-neighbor exchange interaction can lead to a Peierls-like transition, from a tetragonal to an orthorhombic phase, when the spins are coupled to adiabatic phonons. The two different orthorhombic ground states define an Ising order parameter, which is expected to lead to a finite temperature transition. Implications for Li(2)VOSiO(4), the first realization of that model, will be discussed.     

The antiferromagnetic Potts model in two dimensions: Berker-Kadanoff phase, antiferromagnetic transition, and the role of Beraha numbers

Using methods of integrable systems and conformal field theory, we study the Q-state Potts model on the square lattice with e^K real. We discover a surprisingly rich phase diagram that involves, besides the usual ferromagnetic critical line, an antiferromagnetic critical line and a Berker-Kadanoff phase (i.e., a massless low-temperature phase with coupling-independent exponents) that has singularities at the Baraha numbers (including Q integer) Q = 4cos²π/n. Critical properties are derived; we show in particular that the Q = 4cos²π/δ antiferromagnetic critical Potts model is in the “Z_δ−2” universality class with c = 2−6/δ. Extensions to other lattices are considered. We discuss the consequences of our results on the coloring problem and the Beraha conjecture. Three appendices deal with the geometrical interpretation of the Temperley-Lieb algebra and U_qsl(2) symmetry in the Potts and associated loops model, and with the vertex-Potts model correspondence in systems with free boundary conditions.     

Exact solution of the spin-1/2 Ising model on the Shastry–Sutherland (orthogonal-dimer) lattice

A star-triangle mapping transformation is used to establish an exact correspondence between the spin-1/2 Ising model on the Shastry–Sutherland (orthogonal-dimer) lattice and respectively, the spin-1/2 Ising model on a bathroom tile (4–8) lattice. Exact results for the critical temperature and spontaneous magnetization are obtained and compared with corresponding results on the regular Ising lattices.     

Quantum many-body calculation of mixed-parity pairing in the Sr2RuO4 superconductor induced by spin-orbit coupling

The unusual superconducting state in Sr(2)RuO(4) has long been viewed as being analogous to a superfluid state in liquid (3)He. Nevertheless, calculations based on this odd-parity state are presently unable to completely reconcile the properties of Sr(2)RuO(4). Using a self-consistent quantum many-body scheme that employs realistic parameters, we are able to model several signature properties of the normal and superconducting states of Sr(2)RuO(4). We find that the dominant component of the model superconducting state is of even parity and closely related to superconducting state for the high-T(c) cuprates although a smaller odd-parity component is induced by spin-orbit coupling. This mixed pairing state gives a more complete representation of the complex phenomena measured in Sr(2)RuO(4).     

平均键能模型的物理基础及该模型的应用

平均键能模型是一种建立在数值基础上的用来确定半导体异质界面能带偏移的模型方法。本文首先对这一模型方法的物理基础进行了理论分析,并给予其完整的物理解释。通过与TB“pinned”模型、介电隙能级(DME)模型以及电中性点(CNP)模型的比较,揭示了各模型之间的相互关系,并分析了平均键能模型的优点及其局限性。在此基础上,本文应用这一模型方法对二十七种异质界面的价带偏移值进行了全面的计算,并对结果进行了广泛的分析和比较。结果表明:(1)阳离子浅d轨道是影响价带偏移理论值的一个重要因素;(2)界面偶极子势是决定异质界面价带偏移值的一个关键要素;(3)在与实验的比较上,平均键能模型的准确性优于几种其它的模型方法;(4)平均键能模型不适用于不具有sp³杂化特性的材料系统。     

Investigation of the Statistical and Formative Time Lags Associated with the Breakdown of a Gas in a Gap at High Overvoltage

The results of an investigation of the statistical behavior of the observational time lag to breakdown in an overvolted sparkchamber are presented as a function of pressure (up to 1350 torr of nitrogen), electrode separation (1 and 2 cm) and percent overvoltage (up to 2800 percent). Rogowski contoured, graphite, brass, and aluminum electrodes have been investigated. Automated diagnostic equipment has allowed the reduction of large amounts of data. The results indicate: 1) the shapes of the distributions are strong functions of pressure, 2) the electron emission rate associated with graphite is an order of magnitude greater than that associated with aluminum and brass, 3) the cathode emission rate is much higher than the "apparent" rate determined from a simple stochastic model, and 4) the formative time (taken as the minimum observed time lag) is an order of magnitude greater than that predicted by the streamer model of breakdown.     

Precise simulation of near-critical fluid coexistence

We present a novel method to derive liquid-gas coexisting densities, rho(+/-)(T), from grand canonical simulations (without knowledge of T(c) or criticality class). The minima of Q(L) identical with (2)(L)/(L) in an LxLxL box with m=rho-(L) are used to generate recursively an unbiased universal finite-size scaling function. Monte Carlo data for a hard-core square-well fluid and for the restricted primitive model electrolyte yield rho(+/-) to +/-1%-2% of rho(c) down to 1 part in 10(4)-10(3) of T(c) (and confirm well Ising character). Pressure mixing in the scaling fields is unequivocally revealed and indicates Yang-Yang ratios R(mu)=-0.04(4) and 0.2(6) for the two models, respectively.     

Single-crystal (57)Fe Q-band ENDOR study of the 4 iron-4 sulfur cluster in its reduced [4Fe-4S](1+) state.

(57)Fe Q-band ENDOR has been used to study the [4Fe-4S](1+) state created by gamma irradiation of single crystals of the synthetic model compound [N(C(2)H(5))(4)](2)[Fe(4)S(4)(SCH(2)C(6)H(5))(4)] enriched in (57)Fe. This compound is an excellent biomimetic model of the active sites of many 4 iron-4 sulfur proteins, enabling detailed and systematic studies of its oxidized [4Fe-4S](3+) and reduced [4Fe-4S](1+) paramagnetic states. Taking advantage of the fact that Q-band ENDOR, in contrast with X-Band ENDOR, allows for a very good separation of the (57)Fe transitions from those of the protons, the complete hyperfine tensors of the four iron atoms for the [4Fe-4S](1+) species has been measured with precision. For each iron atom, the electron orbital and electron spin isotropic contributions have been determined separately. Moreover, it is remarkable that two (57)Fe hyperfine tensors attributed to the ferrous pair of iron atoms are very different. In effect, one tensor presents a much larger anisotropic part and a much smaller isotropic part than those of the other. This difference has been interpreted in terms of a differential electron orbital hyperfine interaction among the two ferrous ions.     

NH_3多光子电离和裂解动力学过程分析

本文分析了在XeCl准分子激光作用下NH_3分子的多光子电离质谱形成机理。所建立的动力学模型包括主要由经过中间态(6)和(1)的(2+1)共振多光子电离,生成NH_3~+;离子-分子反应形成大量的NH_4~+;经(6)态的(2+2)共振多光子电离,可能产生低产额的NH_2~+。这个模型的速率方程解与实验测量符合得很好,并在离子流强度对激光脉冲宽度的依赖关系中预示直接电离或间接电离机制的信息。     

Observation of true c(8 × 2) symmetry in scanning tunnelling microscopy images of the clean InSb(001) surface

Filled and empty state scanning tunnelling microscopy images of the sputtered and annealed InSb(001) surface are presented. The sputter-anneal preparation generates a surface with two distinct phases. The dominant phase possesses a unit cell with true c(8 × 2) symmetry, whereas the other phase is attributed to an asymmetric 1 × 3 reconstruction. The presence of a c(8 × 2) unit cell in filled state images is in contrast to previous reports, which identified only a 4 × 1 unit cell. The true c(8 × 2) symmetry further indicates, the available structural model is used as a guide, that the current interpretation of features in filled state images is incorrect. This result may necessitate a reevaluation of the structural model for the InSb(001)-c(8 × 2) surface.     

Magnetization and spin gap in two-dimensional organic ferrimagnet BIPNNBNO

A magnetization process in the two-dimensional ferrimagnet BIPNNBNO is analyzed. The compound consists of ferrimagnetic (1,1/2) chains coupled by two sorts of antiferromagnetic interaction. Whereas the behavior of the magnetization curve in higher magnetic fields can be understood within a process for the separate ferrimagnetic chain, the appearance of the singlet plateau at lower fields is an example of non-Lieb-Mattis type ferrimagnetism. By using the exact diagonalization technique for finite clusters of size 4 × 6, 4 × 8 and 4 × 10 we show that the interchain frustration coupling plays an essential role in stabilization of the singlet phase. These results are complemented by an analysis of four cylindrically coupled ferrimagnetic (1,1/2) chains via an Abelian bosonization technique and an effective theory based on the XXZ spin-1/2 Heisenberg model when the interchain interactions are sufficiently weak/strong, respectively.     

Probabilistic model for fluences and peak fluxes of solar energetic particles.

The model is intended for calculating the probability for solar energetic particles (SEP), i.e., protons and Z=2-28 ions, to have an effect on hardware and on biological and other objects in the space. The model describes the probability for the > or = 10 MeV/nucleon SEP fluences and peak fluxes to occur in the near-Earth space beyond the Earth magnetosphere under varying solar activity. The physical prerequisites of the model are as follows. 1. The occurrence of SEP is a probabilistic process. 2. The mean SEP occurrence frequency is a power-law function of solar activity (sunspot number). 3. The SEP size (taken to be the > or = 30 MeV proton fluence size) distribution is a power-law function within a 10(5)-10(11) proton/cm2 range. 4. The SEP event particle energy spectra are described by a common function whose parameters are distributed log-normally. 5. The SEP mean composition is energy-dependent and suffers fluctuations described by log-normal functions in separate events.     

Twisted Hubbard model for Sr2IrO4: magnetism and possible high temperature superconductivity

Sr(2)IrO(4) has been suggested as a Mott insulator from a single J(eff)=1/2 band, similar to the cuprates. However, this picture is complicated by the measured large magnetic anisotropy and ferromagnetism. Based on a careful mapping to the J(eff)=1/2 (pseudospin-1/2) space, we propose that the low energy electronic structure of Sr(2)IrO(4) can indeed be described by a SU(2) invariant pseudospin-1/2 Hubbard model very similar to that of the cuprates, but with a twisted coupling to an external magnetic field (a g tensor with a staggered antisymmetric component). This perspective naturally explains the magnetic properties of Sr(2)IrO(4). We also derive several simple facts based on this mapping and the known results about the Hubbard model and the cuprates, which may be tested in future experiments on Sr(2)IrO(4). In particular, we propose that (electron-)doping Sr(2)IrO(4) can potentially realize high-temperature superconductivity.     

A Pati–Salam model from branes

We explore the possibility of embedding the Pati–Salam model in the context of Type I brane models. We study a generic model with U(4)_C×U(2)_L×U(2)_R gauge symmetry and matter fields compatible with a Type I brane configuration. Examining the anomaly cancellation conditions of the surplus abelian symmetries we find an alternative hypercharge embedding that is compatible with a low string/brane scale of the order of 5–7 TeV, when the U(4)_C and U(2)_R brane stack couplings are equal. Proton stability is assured as baryon number is associated to a global symmetry remnant of the broken abelian factors. It is also shown that this scenario can accommodate an extra low energy abelian symmetry that can be associated to lepton number. The issue of fermion and especially neutrino masses is also discussed.     

Proximity of the layered organic conductors alpha-(BEDT-TTF)2MHg(SCN)4 (M = K,NH4) to a charge-ordering transition

While the optical properties of the superconducting salt alpha-(BEDT-TTF)(2)-NH4Hg(SCN)(4) remain metallic down to 2 K, in the nonsuperconducting K analog a pseudogap develops at frequencies of about 200 cm(-1) for temperatures T<200 K. We show that the optical conductivity calculated with exact-diagonalization techniques on an extended Hubbard model at quarter filling is consistent with the observed low-frequency feature. We argue that the different optical responses observed are a consequence of the proximity of these compounds to a charge-ordering transition driven by the intermolecular Coulomb repulsion.     

A Modified Potential Method for Electrons Scattering Total Cross Section Calculations on Several Molecules at 30 ～ 5000 eV: CF4, CCl4, CFCl3, CF2Cl2, and CF3Cl

A complex optical model potential modified by the concept of bonded atom, which takes into consideration the overlapping effect of electron clouds between two atoms in a molecule, is employed to calculate the total cross sections (TCSs) for electrons scattering from several molecules (CF4, CCl4, CFCl3, CF2 Cl2, and CF3 Cl) over an incident energy range 30 ～ 5000 eV using the additivity rule model at Hartree-Fock level. The quantitative TCSs are compared with those obtained by experiments and other theories wherever available, and good agreement is obtained above 100 eV.It is shown that the modified potential can successfully calculate the TCSs of electron-molecule scattering over a wide energy range, especially at lower energies.     

Lattice gas model of the (7 × 7), (5 × 5) and (2 × 8) structures of Si(111) and Ge(111)

It is shown that the (2 × 8), (7 × 7) and (5 × 5) reconstructions of the (111) surface of Si and Ge can be interpreted as the structures minimizing pairwise interactions of extended range in the lattice gas model. They are concluded to be modulations of the (2 × 2) structure which are stabilized by a repulsive sixth neighbor interaction and/or an attractive seventh one if the (2 × 2) state is nearly degenerate with the (2 × 4) one for up to fourth neighbor interactions. The analysis is carried out rigorously by use of the method of inequalities.     

Search for anomalous production of multilepton events in pp collisions at sqrt s=1.96 TeV

We report a search for the anomalous production of events with multiple charged leptons in pp[over] collisions at sqrt[s]=1.96 TeV using a data sample corresponding to an integrated luminosity of 346 pb(-1) collected by the CDF II detector at the Fermilab Tevatron. The search is divided into three-lepton and four-or-more-lepton data samples. We observe six events in the three-lepton sample and zero events in the > or =4-lepton sample. Both numbers of events are consistent with standard model background expectations. Within the framework of an R-parity-violating supergravity model, the results are interpreted as mass limits on the lightest neutralino (chi[over](1)(0)) and chargino (chi[over](1+/-) particles. For one particular choice of model parameters, the limits are M(chi[over](1)(0)>110 GeV/c2 and M(chi[over](1+/-)>203 GeV/c2 at 95% confidence level; the variation of these mass limits with model parameters is presented.