Diffraction spectra of order–order transition structural states in titanium monoxide

A new class of M_(n?i)X_(n?i) superstructures (n is an integer constant and i is a rational variable) that are formed after incomplete equilibrium second-order order–order phase transitions in solid solutions and in compounds with atom–vacancy ordering is proposed. New superstructures are superpositions of partially disordered M _n ?X _n superstructures of various symmetries in the matrix of the basic crystal structure. The model parameters affecting the positions and intensities of superstructure reflections on diffraction patterns have been studied by example of the high-temperature ordered phase β-TiO of titanium monoxide. It has been shown that the diffraction spectra of the low-symmetric M_(5-i)X_(5-i) superstructure (space group P1m1) and the high-symmetric M₅X₅ superstructure (space group Pm3?m) at certain parameters are identical in the positions of superstructure reflections.     

Special features of the long-range order – short-range order phase transition in FCC-based alloys

Results of x-ray analysis of the long-range order in FCC-based alloys with L1₂, L1₂(M), L1₂(MM), and D1_a superstructures are generalized. Regularities of the behavior of the long-range order parameter and average size of the thermal and periodic antiphase boundaries (APB) are traced, main mechanisms of temperature order-disorder phase transition are elucidated, and influence of the thermal and periodic APB on the special features of the order-disorder phase transition is revealed. The character of change of the periodic antiphase boundary density determines the special features of the order-disorder phase transition in alloys with longperiod superstructures.     

Magnetic-octupole order in neptunium dioxide?

The phase transition occurring at 25 K in NpO2, discovered almost 50 years ago, is the most long-lasting mystery in the physics of actinide compounds. Theories based on magnetic or electric-quadrupole order lead inevitably to fundamental, qualitative inconsistencies with observations. We show that the phenomenology of NpO2 can be understood if the order parameter is assumed to be a magnetic octupole of gamma(2) ( xyz) symmetry. NpO2 is the first compound for which indications of an octupolar phase transition have been found.     

Cavity quantum chromodynamics to order αs2

Based on perturbative QCD in a cavity, we have calculated, for the two-quark and quark-antiquark systems, all non-diverging graphs to order α_s² which do not involve additional quark-antiquark pairs in the intermediate states. Using the two-body interactions that include the two-gluon exchange and annihilation graphs, we obtain a fit to the low-energy spectrum of hadrons consisting of massless quarks and anti-quarks, in particular the splitting of the masses of the π- and η-mesons.     

Short-range order in metallic Co−Zr glasses

For melt-spun metallic Co_xZr_100–x glasses (22x53) the total pair correlation functionG(r) has been derived from X-ray diffraction measurements. In most samples, the first maximum ofG(r) can be resolved into two single maxima belonging to the Co–Zr and Zr–Zr nearest-neighbor distance, respectively. Partial correlation numbers are estimated in the whole concentration range. The density of the samples has been measured with a buoyancy method. It is compared to those of otherM–Zr glasses (M=Fe, Ni, Cu) and to predictions deduced from Miedema's model of alloy formation.     

Néel order in doped quasi-one-dimensional antiferromagnets

We study the Néel temperature of quasi-one-dimensional S = 1/2 antiferromagnets containing nonmagnetic impurities. We first consider the temperature dependence of the staggered susceptibility of finite chains with open boundary conditions, which shows an interesting difference for even and odd length chains. We then use a mean field theory treatment to incorporate the three-dimensional interchain couplings. The resulting Néel temperature shows a pronounced drop as a function of doping by up to a factor of 5.     

CP N−1 models beyond the leading order

We analyse the CP ^N?1 models in two and three dimensions. We discuss the effective potential, Greens functions and β functions to leading order. To non-leading order we formally evaluate and renormalise the effective potential. In three dimensions we also calculate the β function to \(0\left( {\frac{1}{N}} \right)\) . We show that it has a non-trivial fixed point which corresponds to a phase transition. This phenomenon persists beyond the leading order. The vacuum states are also unchanged by the nonleading order corrections.     

High order spectrum phase data for time delay estimation

I.IntroductionThetimedelayestimationisaveryimportantprobleminmanyapplicationfieldssuchassonar(activeandpassive),radar,biomedicine,geophysics,cdots.Manyapproacheshavebeenproposedandstudied.TheseexistingapproachescanbeclassifiedintothIeecategories'1)phasedata,2)generalizedcrosscorrelation,3)parameter..tim.ti..[1].Recently,withthedevelopmentofpolyspectrumestimationtheory,highorderspectrumhasbeenwidelyusedinunderwateracousticfield.Itcanpreservethehighorderinformationofnon-Gaussianstationaryrando…     

An upgraded analysis of ɛ′/ɛ at the next-to-leading order

An upgraded analysis of ,x _d and /, using the latest determinations of the relevant experimental and theoretical parameters, is presented. Using the recent determination of the top quark mass,m _t =(174±17) GeV, our best estimate is /=(3.1±2.5)×10^–, which lies in the range given by E731. We describe our detemination of / and make a comparison with other similar studies. A detailed discussion of the matching of the full theory to the effective Hamiltonian, written in terms of lattice operators, is also given.     

Finite size scaling at first order phase transitions?

It is demonstrated that finite size scaling at first order phase transitions is something basically very simple: As the number of particlesN in the system goes to infinity,s _N (), the entropy per particle, rapidly approaches its limiting behaviours (). Onces () has been determined, the thermal behaviour of the infinite system is completely known and in case of a first order phase transition the specific heat exhibitis a -function singularity. If, however, the specific heatc _N (T) per particle is calculated from the canonical partition functionZ _N ()=d exp {N[s _N ()-]}, then even ifs _N () is replaced by its limiting forms (),c _N (T) only exhibits a peak with a finite maximum value proportional toN which is due to the explicit factorN in front of the angular bracket in the exponent. This is theN-dependence which has recently been called finite size scaling at first order phase transitions. The entropys _N () can very efficiently be determined in the dynamical ensemble.     

On the large order behavior of Φ 4 4

We continue the rigorous study of the large order behavior of the perturbation series for the ⁴ model in 4 dimensions started in [1]. In this paper we prove a result announced in [1]. We show that the exact radius of convergence of the Borel transform of the renormalized perturbation series for ₄ ⁴ is greater than or equal to the expected value given by the position of the first renormalon [2]. This result holds for any vector (²)² model withN components, and makes use of the Lipatov bound of [1]. This result is based on a partial resummation of counterterms similar to the one of [3], but in a phase-space analysis of the renormalized series.     

Longitudinal jet cross sections in order α s 2

We calculate the cross section fore ⁺ e ^–3 jets for longitudinally polarized virtual photons up to order _s ² in the quark-gluon coupling.Dedicated to the memory of Kurt Symanzik     

Why is the DNA denaturation transition first order?

We study a model for the denaturation transition of DNA in which the molecules are considered as being composed of a sequence of alternating bound segments and denaturated loops. We take into account the excluded-volume interactions between denaturated loops and the rest of the chain by exploiting recent results on scaling properties of polymer networks of arbitrary topology. The phase transition is found to be first order in d = 2 dimensions and above, in agreement with experiments and at variance with previous theoretical results, in which only excluded-volume interactions within denaturated loops were taken into account. Our results agree with recent numerical simulations.     

Compact first and second order polarization mode dispersion emulator

Polarization mode dispersion (PMD) is becoming major system impairment in high speed and long distance opti- cal fiber transmission systems. Since the PMD-induced pulse spreading is a frequency-dependent statistic pa- rameter and varies randomly over time, it is difficult to be compensated[1-3]. Large length of single mode opti- cal fiber is needed to generate certain amount of PMD in laboratory, and the PMD effect in the fiber varies slightly and slowly over time. Therefore, PMD emula- …     

Scintillation advantages of lowest order Bessel–Gaussian beams

For a weak turbulence propagation environment, the scintillation index of the lowest order Bessel–Gaussian beams is formulated. Its triple and single integral versions are presented. Numerical evaluations show that at large source sizes and large width parameters, when compared at the same source size, Bessel–Gaussian beams tend to exhibit lower scintillations than the Gaussian beam scintillations. This advantage is lost however for excessively large width parameters and beyond certain propagation lengths. Large width parameters also cause rises and falls in the scintillation index of off-axis positions toward the edges of the received beam. Comparisons against the fundamental Gaussian beam are made on equal source size and equal power basis. PACS  42.25.Dd; 42.25.Bs; 42.68.Bz; 42.68.-w     

Investigation of multicomponent chemical short-range order in NiZr2

The local atomic configuration of multicomponent chemical short-range order (MCSRO) in NiZr2 has been investigated by means of molecular dynamics simulation (MD) in a wide temperature range. The potential functions for the system based on the embedded atom method are constructed and the parameters are obtained by fitting the structure and properties of NiZr2 crystal. The static structures such as pair distribution functions and the distribution of coordination number have been calculated. The local atomic configurations of the MCSI~Os in the melt were demonstrated as distorted coordination polyhedron of the compound structure and/or the structure similar to cubooctahedron analogues. It is indicated by the results of MD simulation that above the melting point the atomic packing of long-range order disappears, but the chemical interaction of coordinated atoms still exists, which leads to the formation of various MCSROs with atomic configurations similar to the stable or metastable unit cell of NiZr2 compound. When the system is just melted, many icosahedral polyhedron configurations appear, which decrease as the over-heating temperature increases.     

High order operation of distributed feedback dye-doped sol-gel silica laser

High order Bragg scattering (M = 2 and M = 3) operations of the distributed feedback dye doped sol-gel silica lasers are achieved using the second harmonic output of a Nd:YAG laser as the pump. Laser linewidth of less than 0.06 nm and conversion efficiency of 0.7% for M = 3 and 11% for M = 2 are measured. Wavelength tuning of about 15 nm around the emission center has been realized by varying the intersection angle.