This paper describes a 50 mhz system being developed for gmrt to provide imaging capability in the...

the giant metrewave radio telescope ( gmrt ) is an interferometric array consisting of thirty 45-m diameter antennas spread over 25 km , operating in frequency bands centred around 151 , 325 , 610/235 , and 1400 mhz . receivers and feeds for operation at frequencies below 100 mhz are currently not available . a 50 mhz system for gmrt is being built by the raman research institute , bangalore , to carry out a low frequency survey of the sky visible to gmrt with arcmin resolution and better surface brightness sensitivity . the survey results and the observing system will be made available to the astronomy community . with a primary beam area of 0.03 steradians , a mosaic of about 300 pointings is required to cover the northern sky . expected survey parameters , at 50 mhz , assuming a 10 mhz bandwidth , are given below and a comparison with other major surveys is given in table [ t : surveycomparison ] . nominal system temperature : k ( sky dominated ) . synthesized beam : . rms sensitivity ( 4 hr synthesis with dual polarization ) : mjy beam ( thermal noise limited ) . this is about two orders of magnitude better than the 74 mhz vla survey . we expect the proposed 50 mhz survey to be at least an order of magnitude better even if we do not achieve the thermal noise limited sensitivity but get limited by the dynamic range . r | c c c c c c + * survey * & * sky * & * telescope * & * surveying * & * rms * & * equivalent rms * + * name * & * coverage * & * time * & * speed * & * noise * & * noise at 50 mhz * + ( frequency ) & steradians & hours & hours / steradian & - in mjy & - in mjy + + + * rri - gmrt ( 50 mhz ) * & 3 & 1200 & 128 & 2(10 ) * & 2(10 ) * + * nvss ( 1.4 ghz ) * & 10.3 & 2700 & 262 & 0.45 & 6.5 + * wenss ( 325 mhz ) * & & 960 & 305 & 3.6 & 16 + * vlss ( 74 mhz ) * & & 900 & 95 & 100 & 137 + + + * terms in brackets denote dynamic range limited performance . [ t : surveycomparison ] the main goals of the feed system design were to obtain a reasonable aperture

We present a survey of the northern sky at 50 mhz with a spectral resolution of. The system is being built by the raman research institute in bangalore to carry out a low frequency survey of gmrt with arcmin resolution and better surface brightness sensitivity. We expect the survey to be at least an order of magnitude better than the 74 m.

this paper describes a 50 mhz system being developed for gmrt to provide imaging capability in the frequency range 30 - 90 mhz . due to its larger collecting area and higher antenna efficiency , the low frequency gmrt system will be several times more sensitive than the present 74 mhz vla system and is likely to remain a competitive instrument in this frequency band . in the first phase of this project , receiver systems consisting of v - dipole feeds and front - ends have been installed on four


We consider cosmological consequences of a heavy axino , decaying to the neutralino in r - parity...

neutralino , if it is the lightest supersymmetric particle ( lsp ) in r - parity conserving models , is a natural candidate for dark matter . because of the tev scale sparticle interactions , the thermal history of neutralinos allows the neutralino dark matter possibility . but , imposing a solution of the strong cp problem , the thermal history involves contributions from the additional sector . the strong cp problem is naturally solved by introducing a very light axion . most probably , it appears when the peccei - quinn ( pq ) symmetry is broken at a scale of . below the pq scale , the effective axion interaction with gluons is where is the strong coupling constant . the pq scale is constrained by the astrophysical and cosmological considerations in the narrow window . tev scale supersymmetry ( susy ) suggests axino , the superpartner of axion , around the electroweak scale in the gravity mediation scenario . here , we consider the effects of _ heavy _ axinos in cosmology . the axino cosmology depends crucially on the axino decoupling temperature , where . the axion supermultiplet includes axion , saxion ( the scalar partner ) and axino . both saxion and axino masses are split from the almost vanishing axion mass if susy is broken . the precise value of the axino mass depends on the model , specified by the susy breaking sector and the mediation sector to the axion supermultiplet . in principle , the axion supermultiplet is independent from the observable sector in which case we may take the axino mass as a free parameter of order from kev to a value much larger than the gravitino mass . light axinos can be a dark matter ( dm ) candidate , which has been studied extensively . heavy axinos , however , can not be the lsp and can decay to the lsp plus light particles . this heavy axino decay to neutralino was considered in the literature where the neutralino relic density was not considered seriously . some considered the axino as the next lsp decaying to the gravit

We study the effects of heavy axinos on the cosmology of neutralino. We consider the effect of heavy ( ) axino decays to the axion supermultiplet, which is independent of the observable sector. The _ heavy _ axinian mass is calculated by using the tev scale supersymmetry ( susy ) and the astrophysical and cosmological considerations in the narrow window.

we consider cosmological consequences of a heavy axino , decaying to the neutralino in r - parity conserving models . the importance and influence of the axino decay on the resultant abundance of neutralino dark matter depends on the lifetime and the energy density of axino . for a high reheating temperature after inflation , copiously produced axinos dominate the energy density of the universe and its decay produces a large amount of entropy . as a bonus , we obtain that the upper bound on the


Extending the concepts of light - front field theory to quantum statistics provides a novel...

at first sight , it seems difficult to define proper temperature for a system `` on the light - front '' , because there is no lorentz transformation to the rest frame of an observer , who is holding the thermometer . despite the fact that this is formally clarified by now ( see sect . 2 ) , i would like to motivate , how temperature could survive `` on the light - front '' . consider the fermi distribution for the canonical ensemble of a noninteracting gas in the instant form ^{-1}, \ ] ] where is the on - shell energy of a one - particle state with respect to the medium frame . let the velocity of the medium be given by the time - like vector , where . if the medium is at rest with respect to the observer , . for convenience we introduce the momentum of the medium can be achieved by summing all the single - particle energies . ] with . following susskind we now assume an observer moving with a large velocity along the axis in the negative direction . the one - particle momentum components seen from this moving frame are denoted . the momentum of the medium measured with respect to this system is with . as long as the relation between the medium system and the observer s system are given by lorentz transformations . for we introduce the momentum fraction via and expand and , hence , up to and finally arrive at ( in the limit ) this form suggests to introduce light - cone components and to identify the longitudinal fraction with the ( kinematically invariant ) light - cone momentum fraction . after doing so ( [ eqn : imf ] ) becomes the well known transformation of momentum variables , hence the fermi distribution `` on the light - front '' is given by ^{-1 } , \ ] ] where the on - shell condition in ( [ eqn : fermi ] ) is evaluated for the light - front coordinates , viz . . despite the fact that we have introduced light - front coordinates and done a limiting process the components of the four vector that appear in ( [ eqn : fermilc ] ) are given with respect to t

We consider the fermi distribution of a noninteracting gas in the instant form,, where is the on - shell energy of a one - particle state with respect to the medium frame. For convenience we introduce the momentum of the medium by summing all the single - particles energies with. After doing so ( [ eqn: imf ] ) becomes the well known transformation of momentum variables, hence the fermions are evaluated for the light - front coordinates.

extending the concepts of light - front field theory to quantum statistics provides a novel approach towards nuclear matter under extreme conditions . such conditions exist , e.g. , in neutron stars or in the early stage of our universe . they are experimentally expected to occur in heavy ion collisions , e.g. , at rhic and accelerators to be build at gsi and cern . light - front field theory is particularly suited , since it is based on a relativistic hamiltonian approach . it allows us to trea


From a search of a deg region covered by both the sloan digital sky survey and ukirt infrared deep...

massive galaxies found at comprising only relatively old ( gyr ) stars appear to be essentially pristine examples of galaxies that apparently formed at redshifts of 510 or more . virtually all of these , as well as a significant fraction of the population of passive galaxies at , are extremely compact when compared with galaxies of similar mass in the present - day universe ( e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? * ; * ? ? ? importantly , these massive compact galaxies must each have formed in a strongly dissipational event over a very short time period ; they are remnants of the very first major episodes of star formation in the universe . the morphologies of these galaxies are important because they can preserve information relevant to formation mechanisms of early - epoch massive galaxies in general . found that % of the massive -band - selected galaxies at have old stellar populations , and estimated that % of the stellar mass in red - sequence galaxies with masses above today was already in place in similar - mass galaxies on the red sequence at . in any case , a significant fraction of the _ very oldest _ stars incorporated into the most massive present - day galaxies may have had their origin in these passive compact galaxies at high redshifts . , using high resolution hubble space telescope ( _ hst _ ) images of the kriek et al . sample , estimated that %100% of these massive galaxies with old stellar populations are extremely compact , with mean effective radii of kpc . in figure 1 , we show the most extreme example of such a galaxy that we have found in a survey of radio - source fields ( a. stockton et al . , in preparation ) . this galaxy , at a redshift of 2.472 , has an apparent stellar mass ( based on a model fit ) of , a stellar population age of 1.9 gyr for an exponentially declining star - formation model with an -folding time of 0.3 gyr , a srsic index , and a circularized ef

We present a survey of the radio - source fields of the kriek et al. Sample of massive galaxies at redshifts of 510 or more. We find that %100% of these massive compact galaxii are extremely compact, with mean effective radii of kpc. This is consistent with the observational results obtained by _ hst _ in the _ red - sequence _ survey.

from a search of a deg region covered by both the sloan digital sky survey and ukirt infrared deep sky survey databases , we have attempted to identify galaxies at that are consistent with their being essentially unmodified examples of the luminous passive compact galaxies found at . after isolating good candidates via deeper imaging , we further refine the sample with keck moderate - resolution spectroscopy and laser guide star adaptive - optics imaging . for four of the five galaxies that so f


A simple regge - eikonal model with the eikonal represented as a single - reggeon - exchange term...

the fraction of the elastic diffractive scattering events in the total number of the collision events at the collision energy 7 - 8 tev is about 25% . at higher energies it is expected to be even higher . hence , understanding of the physical pattern of the small - angle elastic scattering of hadrons is indispensable for general understanding of the strong interaction at ultra - high energies . however , the special status of diffractive studies at high - energy colliders is determined by the fact that diffraction of hadrons takes place due to interaction at large distances . indeed , the transverse size of the hadron interaction region can be estimated through straight application of the corresponding heisenberg uncertainty relation to the experimental elastic angular distributions . for example , at the sps , tevatron , and lhc energies it is of order 1 fm . therefore , exploitation of perturbative qcd for treatment of hadronic diffraction is disabled . the absence of exact theory leads to the emergence of numerous phenomenological models with very different underlying physics ( the references to various models of the nucleon - nucleon elastic diffraction can be found in mini - review ) . the co - existence of a large number of rather complicated ( and , often , incompatible ) models points to the relevance of the question if construction of a much simpler ( but adequate ) approximation is possible . the word `` adequate '' in the last sentence implies as the theoretical correctness , so the satisfactory description of the high - energy evolution of the diffractive pattern . the aim of this work is to demonstrate that a very simple and physically transparent description can be provided in the framework of the well - known regge - eikonal approach which originates from the synthesis of regge theory and quasi - potential approximation . the regge - eikonal approach to description of the elastic scattering of hadrons exploits the eikonal representation of the nonflip

We present a new approach to the description of the elastic scattering of hadrons at high - energy colliders. The regge - eikonal approach is based on the eisenberg uncertainty relation to the experimental elastic angular distributions, which can be used for the treatment of hadronic diffraction. We show that the regges - and eeional approach can be applied to the diffractive scattering at high energies; however, it is not suitable for the application of perturbative q.

a simple regge - eikonal model with the eikonal represented as a single - reggeon - exchange term is applied to description of the nucleon - nucleon elastic diffractive scattering at ultra - high energies . the range of validity of the proposed approximation is discussed . the model predictions for the proton - proton cross - sections at the collision energy 14 tev are given .


A simple agent - based model ( abm ) of the evolution of faith - based systems ( fbs ) in human...

human societies tend to hold sets of shared and interrelated beliefs that are not directly or easily accessible to proof or disproof . such sets of beliefs , which will be called faith - based systems ( fbss ) , may include , for example , cultural preferences , personal worldview , and belief or disbelief in one or more supreme beings . fbss are often highly detailed and tend to be shared within local communities , but are highly diverse among global communities . dawkins suggested that the evolution and spread of fbss and other cultural information ( memes ) may be subject to natural selection , noting that both parasites and memes are transmissible between hosts and show heritable variation , creating the potential for competition for survival and reproduction . while the meme hypothesis has received considerable theoretical attention , there have been few attempts to explicitly model it . previous models of social transmission have examined mainly two - state systems ; in such models , agent opinions are considered to be transmissible boolean states . such boolean state models do not allow for the evolutionary potential of memetic transmission , which may influence final state distribution , or for the potential for a large number of fbss to exist simultaneously in a single social system . in contrast , fbss can be modelled as continuous states on a binary vector , allowing for memetic evolution among populations of varying fbss . in this paper an agent - based model of the evolution and spread of fbss in a two - dimensional lattice is presented . agent - based models are useful for examining how local properties of individual units interact to produce macroscopic properties of systems , and have been applied in the analysis of social opinion formation , cultural interactions , epidemiology and population dynamics . the current model explores the development of fbss with evolutionarily relevant properties ( faith , proselytism and mutability ) , in simple , indi

We present an agent - based model of the evolution and spread of faith -based systems ( fbss ) in a two -dimensional lattice. The model is based on a simple, indian vector, which allows for the evolution of fcss with evolutionary properties ( faith, proselytism and mutability ). We show that the current model can be applied to the analysis of social opinion formation, cultural interactions, epidemiology and population dynamics.

a simple agent - based model ( abm ) of the evolution of faith - based systems ( fbs ) in human social networks is presented . in the model , each agent subscribes to a single fbs , and may be converted to share a different agent s fbs during social interactions . fbss and agents each possess heritable quantitative traits that affect the probability of transmission of fbss . the influence of social network conditions on the intermediate and final macroscopic states is examined .


We introduce a one - dimensional two - component system with the self - focusing cubic nonlinearity...

a fundamental effect caused by the interplay of nonlinearity with symmetric potentials is spontaneous symmetry breaking ( ssb ) . the simplest setting where this effect occurs is represented by double - well potentials . a commonly known property of one - dimensional quantum mechanics is that the ground state shares the symmetry of the underlying double - well potential . if the self - attractive cubic nonlinearity is added to the consideration , the corresponding schrdinger equation is transformed into the gross - pitaevskii equation for a bose - einstein condensate ( bec)loaded into the double - well potential , or the nonlinear schrdinger equation for photonic counterparts of the system . the nonlinear term may break the symmetry of the ground state , replacing it by an asymmetric one which minimizes the energy of the system , provided that the strength of the nonlinearity exceeds a certain critical value ( see ref . for the general analysis , and ref . for the consideration of the ssb of self - trapped states in bec ) . the experimental realization of the ssb in double - well potentials was reported in bec markus ( this was done in the condensate with the self - repulsive nonlinearity , which implies the spontaneous breaking of the _ antisymmetry _ of the lowest - energy antisymmetric mode ) and in nonlinear optics . the _ symmetry - breaking bifurcation _ , which destabilizes the original symmetric ground state and gives rise to the ssb in the nonlinear systems , was originally predicted in a discrete model of self - trapping . in nonlinear optics , a similar bifurcation was analyzed in ref . for continuous - wave ( spatially uniform ) light signals in dual - core fibers . the allied bifurcation for solitons in nonlinear dual - core fibers was studied in detail in ref . later , the ssb was studied for gap solitons in the model of the dual - core fiber bragg gratings with the same cubic nonlinearity as in the ordinary fibers . the ssbeffects were also predicted

We study the spontaneous symmetry breaking ( ssb ) of two - core fibers in the model of the dual - Core fiber bragg grat. The s - tev - de - lattice is a nonlinear system with a single - well potential. It is characterized by a bifurcation for solitons and gap sOLITONs, which destabilizes the ground state and gives rise to the _ symmetry - breaking _ of the lowest - energy antisymmetric.

we introduce a one - dimensional two - component system with the self - focusing cubic nonlinearity concentrated at a symmetric set of two spots . effects of the spontaneous symmetry breaking ( ssb ) of localized modes were previously studied in the single - component version of this system . in this work , we study the evolution ( in the configuration space of the system ) and ssb scenarios for two - component modes of three generic types , as concerns the spatial symmetry of each component : s


Time reversal of quantum dynamics can be achieved by a global change of the hamiltonian sign ( a...

while the 1d dynamics in the model considered can be obtained analytically by the continued fraction method , we also evaluate it numerically by developing an algorithm , the pair partitioning , inspired in the trotter strategy used in quantum dynamics . we split the kinetic terms to rewrite the hamiltonian asnow , each term represents an effective hamiltonian for two coupled oscillators , with twice the mass and half of the natural frequency each . pair dynamics is solved analytically and impose a periodic evolution sequence that alternates each coupled pair according to their parity . the total energy is not exactly conserved but fluctuates with an amplitude around the ideal conserved value . since is proportional to , the square of the temporal step , it becomes negligible for typical cases where . the fact that each piecelike dynamics is perfectly reversible is very important for the test of different time reversal procedures . 99 m. fink , sci . am . 281 , may issue ( 1999 ) 67 . r. jalabert and h.m . pastawski , phys . 86 ( 2001 ) 2490 . m. fink , g. montaldo , m. tanter , annual rev . eng . 5 ( 2003 ) 465 . edelman , t. akal , w.s . hodkiss , s. kim , w.a . kuperman , h.c . song , ieee j. ocean eng . 27 ( 2002 ) 602 . pastawski , e.p . danieli , h.l . calvo , l.e.f . foa torres , europhys . 77 ( 2007 ) 40001 . rubin , phys . 131 3 ( 1963 ) 964 . calvo , h.m . pastawski , braz . j. phys . 36 3b ( 2006 ) 963 . e. rufeil fiori and h.m . pastawski , chem . 420 ( 2006 ) 35 . pastawski and e. medina , rev . fsica 47s1 ( 2001 ) 1 , cond - mat/0103219 . h. de raedt , ann . rev . of comp . physics iv ( 1996 )

We study the hamiltonian asnow for two coupled oscillators in the model of a quantum waveguide. The trotter strategy is used to solve the kinetic terms and the rewrite the HAMILTONIA asnow. We find that the corresponding hamILtonian is not exactly conserved but fluctuates with an amplitude around the ideal conserved value.

time reversal of quantum dynamics can be achieved by a global change of the hamiltonian sign ( a hasty loschmidt daemon ) , as in the loschmidt echo experiments in nmr , or by a local but persistent procedure ( a stubborn daemon ) as in the time reversal mirror ( trm ) used in ultrasound acoustics . while the first is limited by chaos and disorder , the last procedure seems to benefit from it . as a first step to quantify such stability we develop a procedure , the perfect inverse filter ( pif )


The field containing the candidate high mass x - ray binary igr j01363 + 6610 was observed by _ xmm...

the hard x - ray imaging of the galactic plane by the _ international gamma - ray astrophysics laboratory ( integral ) _ satellite has uncovered a large number of new or previously poorly studied `` igr '' sources . while _ integral _ excels at detecting sources in the 2050 kev band , it only localizes the sources to , requiring follow - up observations with other x - ray satellites to obtain secure optical or ir counterparts , allowing for a determination of the nature of the sources . as more and more of these sources have been identified , possibly the biggest surprise is the large number of high mass x - ray binaries ( hmxbs ) as well as the properties of these systems . many of the dozens of _ integral _ hmxbs have large levels of intrinsic absorption with ( e.g. , * ? ? ? * ) , and these are commonly called obscured hmxbs . in many cases , it appears that this is due to the compact object being embedded in a strong stellar wind . some members of the group of _ integral _ hmxbs exhibit other extreme properties , including the high amplitude x - ray flaring of the supergiant fast x - ray transients ( sfxts , * ? ? ? * ; * ? ? ? * ) or long - period pulsations from very slowly rotating neutron stars . _ integral _ observations have also led to the addition of more hmxbs in the be x - ray binary class . the optical flux from these systems is dominated by an early - type star with emission lines from a circumstellar disk . in most cases , transient x - ray emission demonstrates the binary nature of the system as eccentric orbits lead to periodic x - ray outbursts when the compact object approaches periastron . of the 64 known be x - ray binary systems , x - ray pulsations indicate the presence of a neutron star in 42 cases , and the compact object type is unknown for the remaining systems . one of the interesting properties of this class is the observed correlation between the orbital period and the spin period of the neutron star . igr j01363 + 6610 has been tenta

We present a new study of the optical flux from high mass x - ray binaries ( hmxbs ) in the 2050 kev band. The _ integral _ satellite has been used to detect a large number of new or previously poorly studied igr sources, and is currently undergoing follow - up observations with other x.

the field containing the candidate high mass x - ray binary igr j01363 + 6610 was observed by _ xmm - newton _ on 2009 july 31 for 28 ks . a be star was previously suggested as the possible counterpart of the _ integral _ source , and although _ chandra _ , during a 2007 observation , did not detect an x - ray source at the position of the be star , we find a variable source ( xmmu j013549.5 + 661243 ) with an average x - ray flux of ergs s ( 0.212 kev , unabsorbed ) at this position with _ xmm


We present the results of a search for submillimetre - luminous host galaxies of optically dark...

it is generally now accepted that the afterglow emission resulting from ( long - duration , soft - spectrum ) gamma - ray bursts ( grbs ) can be explained by an ultra - relativistic shock - wave expanding into a surrounding medium . the precise nature of the progenitor systems is not a settled issue . the two most popular theories both involve stellar remnants : the collapsar / hypernova model , in which a single massive progenitor star undergoes core collapse ; and the binary merger theory , in which two massive stellar remnants , such as neutron stars , merge . both of these scenarios may be able to explain the energetics of the explosion that produces the grbs , particularly if they are beamed , since the energies of grbs are comparable to those involved in the formation of typical stellar - progenitor black holes . recently , the collapsar / hypernova model has gained support from three sets of observations : firstly , it was confirmed that the positions of some grbs accurately localized by the observation of optical and/or radio afterglows , were found to be within star - forming regions of their host galaxies , which themselves are frequently starburst galaxies . this is supported by x - ray determinations of the hi column density along the line of sight to grbs , which is consistent with their residing in grbs . during their creation , it is likely that the massive stellar remnants required in the binary merger scenario would receive a substantial ` kick ' velocity , so that the merger event causing the grb would take place outside of the star - forming region of the host galaxy . also , the delay required between formation of the remnants and their merger may well be long enough for star formation to have ceased in the host , suggesting that the host galaxy would no longer be luminous . hence the position measurements of support the single massive progenitor theory . note though , that one should be wary of a potential selection effect : the detection of a g

We present a new method for the detection of long - duration soft - spectrum gamma - ray bursts ( grbs ) in the host galaxy. This technique is used to detect the afterglow emission from the gam - radio burstic explosion, which is a result of a shock wave expanding into a surrounding medium. The results are consistent with the theory that the grb is based on a single massive progenitor star.

we present the results of a search for submillimetre - luminous host galaxies of optically dark gamma - ray bursts ( grbs ) using the submillimetre common - user bolometer array ( scuba ) on the james clerk maxwell telescope ( jcmt ) . we made photometry measurements of the 850- flux at the location of four ` dark bursts ' , which are those with no detected optical afterglow despite rapid deep searches , and which may therefore be within galaxies containing substantial amounts of dust . we were


The theoretical treatment of homogeneous static magnetic fields in periodic systems is challenging...

the ability to compute the response of periodic systems to homogeneous electric fields , strain and atomic displacements is a key ingredient in our current understanding of dielectric materials ( also ferroelectrics , piezoelectrics ) : from first principles, one obtains easily the polarization , dielectric constants , piezoelectric coefficients , phonon band structure , etc . compared to the treatment of such responses for molecules , the handling of periodic boundary conditions has raised numerous challenges : for instance , the linear potential associated with a static homogeneous electric field breaks the translational symmetry . while such problems have been successfully addressed for the above - mentioned perturbations , the treatment of _ homogeneous magnetic fields _ is not as mature . with the current interest in multiferroc materials, and the long - term interest in magnetic field - based spectroscopies , a unified framework for all these responses is highly desirable . the first strategy followed to treat a periodicity breaking was to consider perturbations with specific commensurate wavevectors and corresponding supercells . for atomic displacements , this approach is known as the `` frozen - phonon '' method. homogeneous magnetic fields can be treated in this spirit , with an artificial modulation, although ( 1 ) working with supercells is cpu time - consuming , ( 2 ) the study of couplings is tedious in this approach . more powerful formalisms , based on perturbation theory , that do not rely on supercells or long - wavelength limits , have been developed for atomic displacements and electric fields. for phonons , the long - wavelength phases can be factorized , such that a purely periodic treatment is recovered . for the electric field , the position operator can be replaced by the differentiation with respect to the wavevector . the berry phase approach to the electrical polarization is probably the most striking consequence of the latter link. owing

We present a new approach to the treatment of periodic systems with homogeneous electric fields, strains and atomic displacements. This approach is based on the berry phase approach, which can be used to treat phonons, atomic déplacements and asymmetric magnetic field. The Berry phase approach is an effective method for treating periodic systems, but it requires a large number of parameters: the length of the wavevector, the position operator, and the long - wavelength phases. In particular, we show that the berries.

the theoretical treatment of homogeneous static magnetic fields in periodic systems is challenging , as the corresponding vector potential breaks the translational invariance of the hamiltonian . based on density operators and perturbation theory , we propose , for insulators , a periodic framework for the treatment of magnetic fields up to arbitrary order of perturbation , similar to widely used schemes for electric fields . the second - order term delivers a new , remarkably simple , formulati


The purpose of this paper is to present a comparison between the modified nonlinear schrdinger (...

this paper is concerned with the semiclassically scaled modified nonlinear schrdinger ( mnls ) equation : which can be thought of as a perturbation ( with perturbation parameter ) of the nonlinear schrdinger ( nls ) equation : taken in the so - called focusing case of . ( for one has the so - called defocusing case . ) our goal is to describe connections between the mnls equation on the one hand and the nls equation ( perhaps surprisingly , both focusing and defocusing types are related to mnls ) on the other , connections that become especially clear in the semiclassical limit . erwin madelung was probably the first person to propose thinking of schrdinger - type equations for a complex field as describing the motion of a kind of fluid . he introduced the real - valued fluid dynamical variables ( density ) and ( velocity ) given in terms of by here is defined by continuation to be a smooth function of . a key observation is that if the complex - valued field initially has the form of an oscillatory wavepacket : where and are real - valued functions independent of , then the corresponding initial values of the madelung variables are independent of as well : without approximation , the nls equation can be written in terms of the madelung variables as : }{ x } \ ] ] where $ ] denotes the expression :={2}{ x^2}-({2}{ x})^2 . \ ] ] with -independent initial data of the form taken in , it seems reasonable to neglect the dispersive term $ ] to obtain limiting -independent equations that one might expect to govern the leading terms of the -dependent fields when . the truncated system of equations which we call the _ dispersionless nls system _ , is really a classical euler system of compressible fluid ( gas ) dynamics . the term in the flux for represents the pressure as a function of density . if ( the defocusing case of the nls equation ) then the pressure is an increasing function of the gas density and the physical dynamics is that of the gas `` trying to get out of it

We study the semiclassically scaled modified nonlinear schrdinger ( mnls ) equation: which can be thought of as a perturbation of the nonlineal schredinger equation. The m - type equation is taken in the so - called focusing case of. We show that the _ dispersionless _ nlS equation is a classical euler system of compressible fluid dynamics.

the purpose of this paper is to present a comparison between the modified nonlinear schrdinger ( mnls ) equation and the focusing and defocusing variants of the ( unmodified ) nonlinear schrdinger ( nls ) equation in the semiclassical limit . we describe aspects of the limiting dynamics and discuss how the nature of the dynamics is evident theoretically through inverse - scattering and noncommutative steepest descent methods . the main message is that , depending on initial data , the mnls equat


Different mechanisms for the creation of strange nonchaotic attractors ( snas ) are studied in a...

interest in the dynamics of quasiperiodically driven systems has grown in recent years largely due to the existence of novel behavior such as strange nonchaotic dynamics . the initial work of grebogi showed that with quasiperiodic forcing , nonlinear systems could have strange nonchaotic attractors ( snas ) , namely attractors with a fractal geometry , but with non - positive lyapunov exponent . subsequent studies have dealt with a number of important issues pertaining to theoretical as well as experimental aspects of snas . while the existence of snas is firmly established , a question that remains interesting is the mechanism or bifurcations through which these are created from regular or chaotic attractors . to date a number of different scenarios have been identified : these include torus doubling to chaos via snas , fractalization of torus , the re - emergence of torus doubling sequence and the birth of snas , the occurrence of snas via blow out bifurcation , the appearance of snas through type - i intermittent phenomenon , or type - iii intermittency , and so on . scenarios for the formation of snas often have parallels in scenarios for the formation of chaotic attractors . the most common route to snas is the gradual `` fractalization '' of a torus where an amplitude or phase instability causes the collapse of the torus which progressively gets more and more wrinkled as a parameter in the system changes , eventually becoming a fractal attractor . this is also the least well understood mechanism for the formation of snas since there is no apparent bifurcation , unlike the crisis like torus collision mechanisms identified by heagy and hammel and feudel , kurths and pikovsky . in the former instance , a period doubled torus collides with its unstable parent , while in the latter , a stable and unstable torus collide at a dense set of points , leading to snas . the quasiperiodic analogue of a saddle node bifurcation gives rise to snas through the intermittent rou

We study the fractalization of a torus in quasiperiodic driven systems with quasiperionically driven forcing. We show that the snas are created by the re - emergence of torus doubling to chaos via s, and the occurrence of s in the resulting chaotic attractors.

different mechanisms for the creation of strange nonchaotic attractors ( snas ) are studied in a two frequency parametrically driven duffing oscillator . we focus on intermittency transitions in particular , and show that snas in this system are created through quasiperiodic saddle - node bifurcations ( type - i intermittency ) as well as through a quasiperiodic subharmonic bifurcation ( type - iii intermittency ) . the intermittent attractors are characterized via a number of lyapunov measures


The main focus of space - time coding design and analysis for mimo systems has been so far focused...

multiple - input multiple - output or mimo wireless systems have received a significant amount of interest due to their capability of dramatically increasing the capacity of a communication link . also , there has been considerable work on a variety of schemes which exploit multiple antennas at both the transmitter and receiver in order to obtain spatial diversity , i.e. to improve the reliability of the system such as orthogonal space - time block codes ( ostbc ) and space - time trellis codes ( sttc ) . an simple example for a sttc is the delay diversity code , first proposed in and also discussed in , where the data stream on the first transmit antenna is transmitted with delays on the other antennas . the delay diversity code achieves full diversity but has a disadvantage of a slight rate loss due to some leading and tailing zeros . in order to avoid this drawback , cyclic delay diversity ( cdd ) has been proposed in . the main advantage of cdd over ostbc is that a code rate of one is achieved independent of the number of transmit antennas , whereas ostbc suffer a rate loss by increasing the number of transmit antennas . the performance of cdd in terms of error probability was analyzed in for frequency flat and frequency selective channels . the diversity - multiplexing tradeoff for delay diversity was characterized in . based on the assumption that statistical information about the channel is available at the transmitter , transmit filters employed at the transmitter are optimized in in order to minimize the chernoff bound on the error probability of cdd . the average rate for cdd by assuming gaussian as well as psk / qam input signals for a point - to - point transmission with or transmit antennas and receive antennas was investigated in terms of monte - carlo simulations in . as noticed in , most of the work on space - time coding so far is focused on single - user systems . for such single - user systems , it was shown that the loss in terms of spectral effi

We study the performance of cyclic delay diversity ( cdd ) in terms of error probability for point - to - point transmissions with and transmit antennas and receivers. The average rate for ccd is obtained by assuming gaussian as well as psk / qam input signals for a point, to, point transmission with or transmit antenna and receive antennas, respectively. We find that the loss in terms.

the main focus of space - time coding design and analysis for mimo systems has been so far focused on single - user systems . for single - user systems , transmit diversity schemes suffer a loss in spectral efficiency if the receiver is equipped with more than one antenna , making them unsuitable for high rate transmission . one such transmit diversity scheme is the cyclic delay diversity code ( cdd ) . the advantage of cdd over other diversity schemes such as orthogonal space - time block codes


It is extremely uncommon to be able to predict analytically , from first principles , the velocity...

this section is devoted to the computation of the reynold s stress using the stochastic equation for the fluctuations which is equation ( 5 ) in the article . the noise is white in time and has spatial correlation function . using the ito convention for stochastic calculus , it is straightforward to obtain the enstrophy balance for the fluctuations and thus in statistical stationary state we get the very useful relation .\ ] ] thanks to the incompressibility condition , is related to the reynolds stress through . first we can take advantage of the invariance along the direction by taking the fourier transform of ( [ eq : fluctuations ] ) in . the fourier transform in does not provide an obvious simplification as the profile depends on . however , we can use the linearity to express the solution as the sum of particular solutions for independent stochastic forcings . each of these forcings has a correlation function , this means that we have the relation * _ =e^{il(y - y')}(t - t')$]_*. we take the fourier transform in defined by with taking the values , is an integer . is then defined as the function that is solution of ( [ eq : fluctuations ] ) with a stochastic forcing with only one fourier component . we then obtain ,\ ] ] where the positive constants are the fourier coefficients of the spatial correlation function of the noise , =c(x - x',y - y')(t - t').$ ] be careful that * * in this formula the bracket denotes a stochastic averaging , because the zonal average is already taken into account by the sum over all vector . the vorticity is the solution of the stochastic partial differential equation is the stream function defined through . as the reader would have notice , we try to reduce the problem by expressing the solution as the sum of particular problems that we hope to be much simpler . now we have to find an expression for instead of the full solution . we will go one step further and show that the stochastic problem described by the two equations ( [ eq

We calculate the reynolds stress using the stochastic equation for the fluctuations which is equation ( 5 ) in the article. The noise is white in time and has spatial correlation function. We take the fourier transform of ( [ eq: fluctuations ] ) into account. It is then defined as the function that is solution of ( ( [.

it is extremely uncommon to be able to predict analytically , from first principles , the velocity profile of a turbulent flow . in two - dimensional flows , atmosphere dynamics , and plasma physics , large scale coherent jets are created through inverse energy transfers from small scales to the largest scales of the flow . we prove that in the limits of vanishing energy injection , vanishing friction , and small scale forcing , the velocity profile of a jet obeys a universal equation independen


Lattice fermions have well - known difficulties with chiral symmetry

a long - standing problem in quantum field theory is a nonperturbative formulation of chiral fermions . our only general nonperturbative formulation of quantum field theory is the renormalization - group limit of functional integrals defined on a lattice . but when chiral symmetry is an issue , there are notorious problems . briefly , one must either sacrifice locality or positivity , tolerate additional states ( doubling or mirror states ) , or break chiral symmetry explicitly . when the coupling of fermions to gauge fields is vector - like , the standard formulations are adequate , if imperfect . on the other hand , when fermions couple to chiral gauge fields , it has been difficult to prove a conceptually clean theory ; see ref . for a review . an encouraging proposal replaces the functional integral over fermions with an auxiliary quantum - mechanical system , inspired by domain - wall and lattice pauli - villars methods . this paper offers constructions of vector - like and chiral gauge theories , coupling continuum fermions to lattice gauge fields by introducing an interpolation of the latter . ideas of this type were first discussed by flume and wyler for the schwinger model , and recently t hooft advocated a similar approach for four - dimensional gauge theories . the appeal stems from the nontrivial ( instanton ) topology of continuum gauge fields , because the atiyah - singer index theorem implies an intimate relation between chiral properties of fermions and the topology of the gauge field . in 19871988 there was some discussion about topology and fermions in lattice gauge theory . except for a conference reports , however , none of the applications to chiral gauge theories have been published . spurred by ref . , i would like to present my variation on the theme . regulates the gauge field with the lattice and the fermions with a standard pauli - villars scheme . the number of fermionic degrees of freedom ( per unit volume ) remains infinite in the words

We present a new formulation of the vector - like gauge theory for lattice gauge fields by introducing an interpolation of the latter. The proposed scheme is based on the atiyah - singer index theorem, which is a nonperturbative formulation of chiral fermions. It is shown that the chirality of the gauge field is not perturbed by the interpolated function over fermions and that the coupling to the gauge fields is purely a linear process.

lattice fermions have well - known difficulties with chiral symmetry . to evade them it is possible to couple _ continuum _ fermions to _ lattice _ gauge fields , by introducing an interpolation of the latter . following this line of thinking , this paper presents two euclidean formulations of the effective action that appears after functional integration over fermion fields , one for vector - like and the other for chiral couplings . with suitable finite - mode regulators both effective actions


Motivated by the diversity and complexity of two - dimensional crystals formed by triangular...

two - dimensional ( 2d ) materials present some fascinating challenges to condensed - matter theory , with even the most simple 2d systems harboring surprises . one of the most famous problems involves the precise description of melting in 2d solids made up of hard , disk - like particles with short - range repulsive interactions. specifically , does the fluid undergo a weak first - order transition to the solid , or is there an intermediate hexatic phase linked by two continuous phase transitions ? related avenues of research concern the existence of exotic phases in systems made up of more complex particles , such as ( non)periodic solids of hard - disk dimers, pentamers and hexamers, tetratic phases of hard squares and hard rectangles, and orientationally ordered solids of hard pentagons and heptagons. the effects of additional interactions on the phase behavior and dynamics of 2d systems are also of interest , as evidenced by recent studies on dipolar potentials in the context of magnetic colloids. such models provide an ideal testing ground for condensed - matter theories , and in some cases challenge our most fundamental understanding of the properties of matter . despite their simplicity , 2d models can provide reliable descriptions of some real , and rather complex , experimental situations . for example , in a number of recent studies , 2d models have been employed to help interpret and understand the clustering and crystallization of proteins at interfaces . the conformations and interactions of proteins are central to biological activity , and ideally one would like to investigate these properties _ in vivo_. unfortunately , structural information is most commonly obtained from x - ray diffraction studies on crystals . there is a class of proteins , however , that can be studied under conditions resembling those _ in vivo_. membrane proteins constitute a large class of molecules found within the lipid bilayers that constitute cell walls . they fulfill a v

We present a new study of the structure and dynamics of membrane proteins in two - dimensional ( 2d ) systems. We show that the structural properties of these molecules are similar to those of their counterparts in vivo, and that they can be studied under conditions resembling those of x -ray diffraction studies on crystals.

motivated by the diversity and complexity of two - dimensional crystals formed by triangular proteins and protein trimers , we have investigated the structures and phase behavior of hard - disk trimers . in order to mimic specific binding interactions , each trimer possesses on ` attractive ' disk which can interact with similar disks on other trimers _ via _ an attractive square - well potential . at low density and low temperature , the fluid phase mainly consists of tetramers , pentamers , or


Ic 348 is a young ( tmyr ) and nearby ( dpc ) star forming region in the perseus molecular cloud

in the framework of the eu marie curie network `` constellation : the origin of stellar masses '' , we conducted a deep imaging survey of the star forming region ic 348 with the aim to find isolated planetary mass objects , with a mass of a few m , and constrain the low mass end of the initial mass function . deep , wide - field broad - band zjhk and narrow - band ch4 on / off images were obtained at cfht . image analysis focused on faint source detection , and a number of photometric tests were conducted to ensure good photometric reliability and completeness down to k.5 mag . [ cols= " < , < " , ] we report the detection of 4 methane dwarf candidates in the young star forming region ic 348 . we tentatively estimate a spectral type in the range t3-t5 or even later , which would make these candidates amongst the least massive isolated objects ever detected in a star forming region . although follow up observations are clearly needed , spectroscopic confirmation will be difficult owing to the faintness of the candidates . this research is supported by the marie curie research training network `` constellation '' under grant no . mrtn - ct-2006 - 035890 . this research has made use of the nasa/ ipac infrared science archive , which is operated by the jet propulsion laboratory , california institute of technology , under contract with the national aeronautics and space administration . this research has also made use of the simbad database , operated at cds , strasbourg , france . many thanks also goes to p. delorme for computing the empirical sequence of l1-t8 field dwarfs used in the figures of this paper .

We report the detection of 4 methane dwarf candidates in the young star forming region ic 348. We tentatively estimate a spectral type in the range t3-t5 or even later, which would make these candidates amongst the least massive isolated objects ever detected in a star formation region. This is a first study of the spectroscopic properties of the candidate stars.

ic 348 is a young ( tmyr ) and nearby ( dpc ) star forming region in the perseus molecular cloud . we performed a deep imaging survey using the megacam ( z - band ) and wircam ( jhk and narrowband ch on / off ) wide - field cameras on the canada - france - hawaii telescope . from the analysis of the narrowband ch on / off deep images , we report 4 t - dwarf candidates , of which 3 clearly lie within the limits of the ic 348 cluster . an upper limit on the extinction was estimated for each candid


Structural disambiguation in sentence analysis is still a central problem in natural language...

i would like to express my sincere appreciation to my supervisor , prof . junichi tsujii of the university of tokyo , for his continuous encouragement and guidance . it was prof . tsujii who guided me in the fundamentals of natural language processing when i was an undergraduate student at kyoto university . his many helpful suggestions and comments have also been crucial to the completion of this thesis . i would also like to express my gratitude to the members of my dissertation committee : prof . toshihisa takagi and prof . hiroshi imai of the university of tokyo , prof . yuji matsumoto of nara institute of science and technology ( naist ) , and prof . kenji kita of tokushima university , who have been good enough to give this work a very serious review . very special thanks are also due to prof . makoto nagao of kyoto university for his encouragement and guidance , particularly in his supervision of my master thesis when i was a graduate student at kyoto university i learned a lot from him , especially in the skills of conducting research . he is one of the persons who continue to influence me strongly in my research carrer , even though the approach i am taking right now is quite different from his own . i also would like to express my sincere gratitude to prof . yuji matsumoto . he has given me much helpful advice with regard to the conduct of research , both when i was at kyoto university and after i left there . the use of dependency graphs for representation of case frame patterns was inspired by one of his statements in a personal conversation . i would like to thank prof . junichi nakamura of kyoto university , prof . satoshi sato of the japan advance institute of science and technology , and other members of the nagao lab . for their advice and contributions to our discussions . the research reported in this dissertation was conducted at c&c media research laboratories , nec corporation and the theory nec laboratory , real world computing partnership ( r

We present a new approach to the study of dependency graphs for representation of case frame patterns in natural language processing. The method is based on the use of dependency - graphs, which are used to represent case frame pattern patterns. We show that the technique can be applied to many different cases, including those with a large number of frames.

structural disambiguation in sentence analysis is still a central problem in natural language processing . past researches have verified that using lexical semantic knowledge can , to a quite large extent , cope with this problem . although there have been many studies conducted in the past to address the lexical knowledge acquisition problem , further investigation , especially that based on a _ principled methodology _ is still needed , and this is , in fact , the problem i address in this the


We present 1

the cygnus ob7 association is part of the extensive cygnus molecular cloud complex which contain the more commonly studied cygnus x , north american , and pelican nebulae regions . the recent comprehensive review of reipurth & schneider ( 2008 ) gives extensive background information on the whole area . cygnus ob7 is one of the nine ob associations in cygnus and is generally considered the nearest at a distance of around 800 pc ( hiltner 1956 ; schmidt 1958 ; de zeeuw et al . cygnus ob7 contains numerous dark cloud complexes , identified with lynds catalog numbers ( lynds 1962 ) , and forms part of the large - scale dark cloud designated kh 141 ( khavtassi 1960 ) . one lynds cloud , l 1003 , was first investigated in detail by cohen ( 1980 ) who found a red nebulous object ( designated rno 127 ) which was later identified as a bright herbig - haro ( hh ) object ( hh448 , melikian & karapetian 2001 , 2003 ) . the region was the focus of optical / near - ir ( nir ) studies by devine , reipurth , & bally ( 1997 ) and movsessian et al . both groups found a number of additional hh objects in the region and , together with the presence of numerous iras sources , confirmed that l 1003 was the site of significant star formation activity . in addition , movsessian et al . ( 2006 ) confirmed the presence of a new fu orionis eruptive variable ( fuor , herbig 1989 ) in the cloud . this object is not optically visible and the outburst was observed in the nir by the appearance of a bright point - source and extensive reflection nebulosity between the 2mass survey ( taken in 1999 ) and the acquisition of the movsessian et al . ( 2003 ) images ( taken in 2001 ) . they interpreted the morphology of the nir nebula as being a double - spiral or `` braid '' , created in the walls of both high- and low - velocity outflow cavities , and the object has henceforth been referred to as the braid nebula . the illuminating star of the braid nebula will henceforth be referred to as the braid st

We present a detailed study of the cygnus ob7 association in the region of l 1003. We find that the outburst is a bright herbig - haro object ( hh448, melikian & karapetian 2001, 2003 ) and a new fu orionis eruptive variable ( fuor, herbig 1989 ). The hr - 448 object is not optically visible and is not observed by the optical / near - Ir.

we present 1.4 to 2.5 m integral field spectroscopy of 16 stars in the braid nebula star formation region in cygnus ob7 . these data forms one aspect of a large - scale multi - wavelength survey aimed at determining an unbiased estimate of the number , mass distribution , and evolutionary state of the young stars within this one square degree area of the previously poorly studied lynds 1003 molecular cloud . our new spectroscopic data , when combined with 2mass near - ir photometry , provide evi


The seyfert 2 galaxy ngc 2110 has been observed with bepposax between 0

active galactic nuclei ( agn ) classified as narrow emission line galaxies ( nelg ) were first discovered in x - rays because of their intense 210 kev emission . like seyfert 2 galaxies , their optical spectra are dominated by narrow emission lines . this fact , together with the presence of a broad h feature in the spectrum of a few of them ( shuder 1980 ) , has led to the suggestion that nelg can form a transition class between seyfert 1 and seyfert 2 galaxies ( e.g. lawrence and elvis 1982 ) . the nelg ngc 2110 ( =0.0076 ) was first observed in x - rays with sas-3 ( bradt et al . 1978 ) , and then by heao 1 ( mushotzky 1982 ) , and by exosat ( turner & pounds 1989 ) . the 210 kev asca data revealed a moderately flat ( ) absorbed power law plus fek line spectrum attenuated by partial covering material , while ginga did not measure a significant reflection component ( hayashi et al . the scenario described by the data available prior to the present work indicates ( smith & done 1996 ) the possibility that the 210 kev spectrum of ngc 2110 is intrinsically flatter than the slope observed for seyfert 1 galaxies by ginga ( nandra & pounds 1994 ) . this situation , if confirmed , would clearly pose questions to the unified models ( antonucci 1993 ) . in the following , we present bepposax observation of ngc 2110 which highlights the key role played by the measurement of the spectrum above 20 kev in disentangling the intrinsic nuclear emission . the bepposax x - ray observatory ( boella et al . 1997a ) is a major programme of the italian space agency with participation of the netherlands agency for aereospace programs . this work concerns results obtained with three of the narrow field instruments ( nfi ) onboard : the low energy concentrator spectrometer ( lecs ; parmar et al . 1997 ) , the medium energy concentrator spectrometers ( mecs ; boella et al . 1997b ) , and the phoswich detector system ( pds ; frontera et al . 1997 ) . lecs and mecs operate in the 0.14.5 kev

We present a bepposax observation of the active galactic nuclei ( agn ) ngc 2110 ( =0.0076 ) in x - rays with sas-3 and exosat. The data obtained by ginga and exon 1 reveal a flat absorbed power law plus fek line spectrum attenuated by partial covering material, while ginga did not measure a significant reflection component. This result suggests that the 210 kev spectrum of ng ng.

the seyfert 2 galaxy ngc 2110 has been observed with bepposax between 0.5 and 150 kev . the high energy instrument onboard , pds , has succeeded in measuring for the first time the spectrum of this source in the 13 - 150 kev range . the pds spectrum , having a photon index is fully compatible with that expected from a seyfert 1 nucleus . in the framework of unified models , the harder ( ) 210 kev spectrum is well explained assuming the presence of a complex partial + total absorber ( % + % ) . t


We observed the sh 2 - 233ir ( s233ir ) region with better sensitivity in near - infrared than...

within 2 kpc , % of stars have been found to form in the clusters . these newly formed stars , however , are embedded deeply in dense molecular cloud and there exists various difficulties in identifying sources and deriving physical parameters . several statistical tools , such as the k - band luminosity function ( klf ) , the color - color or color - magnitude diagrams , etc . , have been successfully used to constrain the characteristics of deeply embedded stellar clusters ( e.g. , * ? ? ? development of new sensitive equipments , such as , large mosaic ir array , enables us to observe embedded stellar cluster in greater detail than previous effort . the sh 2 - 233ir region is a well studied star - forming region in our galaxy ( e.g. , * ? ? ? * ) and it provides an ideal laboratory for understanding properties of embedded clusters . therefore , we revisit this region with higher sensitivity near - infrared data taken toward a wider region to better constrain the properties of the embedded stellar cluster than previous studies . toward the direction of the galactic anticenter , sh 2 - 233ir ( hereafter s233ir ) , as a part of the sh 2 - 235 gmc complex , is located at a distance of about 1.8 kpc , in association with four extended hii regions , sh 2 - 231 , 232 , 233 , and 235 . its position coincides with an iras source , iras 05358 + 3543 ( ) . s233ir is classified as a massive star formation region , showing co outflows and various maser emissions associated with this region . the band image of this region shows many bright stellar sources and also extended nebulous features associated with dust emission . the two embedded young clusters , sh 2 - 233ir sw ( hereafter sw , located in the south - west direction from the center ) and sh 2 - 233ir ne ( hereafter ne , in the north - east direction ) , are notable in this region , with remarkable h bow shocks associated with the ne cluster . in addition , numerous studies have been reported , especially for the ne cl

We present a new ir array to study the properties of the embedded cluster sh 2 - 233ir ( sw ) and sh 2.

we observed the sh 2 - 233ir ( s233ir ) region with better sensitivity in near - infrared than previous studies for this region . by applying statistical subtraction of the background stars , we identified member sources and derived the age and mass of three distinguishable sub - groups in this region : sh 2 - 233ir ne , sh 2 - 233ir sw , and the `` distributed stars '' over the whole cloud . star formation may be occurring sequentially with a relatively small age difference ( myrs ) between sub


We study the maximum - confidence ( mc ) measurement strategy for discriminating among...

the understanding that a quantum system carries information encoded in its quantum state and , thereby , could be used to accomplish information processing tasks gave rise to the fields of quantum information and computation . in order to accomplish such tasks , in the final step one has to read out the previously processed information , which corresponds to determine the final state of the system by measuring it . however , as the quantum state is not itself an observable , it is not possible to determine it through a single shot measurement , unless it belongs to a _ known _ set of states which are mutually orthogonal . when this is not the case , i.e. , the possible final states are not orthogonal , they can not be , deterministically , discriminated with certainty and without error even if they belong to a known set . this has led to the development of the area known as quantum - state discrimination ( qsd ) , where a measurement strategy is devised in order to discriminate _ optimally _ , according to some figure of merit , among nonorthogonal states . despite that , originally , the qsd problem has been introduced in the context of quantum detection ( or decision ) theory long before the birth of quantum information and computation , it quickly became a fundamental tool for these fields . for instance , there is an intimate connection among qsd and probabilistic protocols , like entanglement concentration , cloning , and some quantum algorithms . also , there is a connection among qsd and probabilistic realizations of quantum communication protocols like teleportation , entanglement swapping , and superdense coding . finally , the use of nonorthogonal states , and , consequently , the impossibility of perfectly discriminating among them , underlies the security in some quantum key distribution protocols . the problem addressed in qsd can be briefly posed as follows . a quantum system is prepared in one of possible states in the set , with associated _ a priori

We present a quantum - state discrimination ( qsd ) method for the determination of the final state of a system in one of possible states in the set, with associated priori. The method is based on the _ a priori_- asymmetry - preserving _ method, which is a generalization of the q - key distribution protocol. It is shown that the asymmetric arithmetic - and a - priori ( ap ) - previous - order - time.

we study the maximum - confidence ( mc ) measurement strategy for discriminating among nonorthogonal symmetric qudit states . restricting to linearly dependent and equally likely pure states , we find the optimal positive operator valued measure ( povm ) that maximizes our confidence in identifying each state in the set and minimizes the probability of obtaining inconclusive results . the physical realization of this povm is completely determined and it is shown that after an inconclusive outcom


We report on the preparation and characterization of single crystal phase nacoo with using a non -...

the lamellar cobaltates nacoo have attracted much attention since the discovery of superconductivity in the hydrated composition nacoo.4ho. the complete phase diagram of nacoo shows a variety of rich phenomena , such as a - type antiferromagnetic ( af ) ordering for 0.75 , large thermopower enhancement for , and af ordering with a metal - to - insulator transition for . nacoo is composed of alternating layers of na and coo , where the na ions are surrounded by six oxygens which form a prismatic cage in the phase. sodium de - intercalation in powder samples has been effectively performed via chemical extraction , such as a topochemical process using a br/acetonitrile solution. we have demonstrated previously an electrochemical method as an alternative route to produce homogeneous compounds using a controlled overpotential ( above the open circuit potential). using an aqueous naoh / ho solution as the electrolyte , high quality single crystals were obtained , and measurements of their conducting , superconducting and magnetic properties have been reported. however , detailed studies of the voltage versus na concentration diagram for have been hindered due to difficulties related to an oxygen evolution side - reaction in the aqueous solution. na ordering - in particular its impact on the geometry of the fermi surface - is a key issue that requires further study in order to better understand the transport and magnetic properties. local density approximation ( lda ) calculations indicate that a band with a character should create a large hexagonal fermi surface centered around the point. the existence of such a large fermi surface has been verified from angle - resolved photo - emission(arpes). however , subtle effects due to possible superstructure formation and/or strong electron correlation remain elusive , such as the missing small hole pockets predicted by lda calculation . proposed a nesting scenario based on an orthorhombic reduced brillouin zone caused by na orde

We present a new method for the study of the structure and magnetization of lamellar cobaltates nacoo using an aqueous solution of naoh / ho. The method is based on a - type antiferromagnetic ordering with a metal - to - insulator transition, which is characterized by a large hexagonal fermi surface centered around the point. We show that the ne orde can be induced by ni - orde in the acoustic phase.

we report on the preparation and characterization of single crystal phase nacoo with using a non - aqueous electrochemical chronoamperemetry technique . by carefully mapping the overpotential versus ( for ) , we find six distinct stable phases with na levels corresponding to 0.75 , 0.71 , 0.50 , 0.43 , 0.33 and 0.25 . the composition with appears to have a critical na concentration which separates samples with different magnetic behavior as well as different na ion diffusion mechanisms . chemica


Competition among cooperators , defectors , and loners is studied in an evolutionary prisoner s...

evolutionary prisoner s dilemma games ( pdg ) were introduced to study the emergence and maintenance of cooperation among selfish individuals in societies where strategies are either inherited or adopted through basic imitation rules . in the original pdg two players simultaneously decide whether to cooperate or defect . mutual cooperation ( defection ) yields the highest ( lowest ) _ collective _ payoff which is shared equally . however , still higher _ individual _ payoffs are achieved by defectors facing cooperators leaving the latter with the lowest possible payoff . thus , defection is dominant because they fare better ( or at least equal ) regardless of the co - players decision . consequentially , rational players always end up with the lowest collective payoff instead of the higher reward for mutual cooperation . obviously , this result is at odds with observations in human and animal societies . indeed , cooperation may emerge under certain circumstances ( see e.g. ) . in well - mixed populations , i.e. with random matchings , cooperative strategies succeed provided that interactions between the same individuals are repeated with sufficiently high probability . computer tournaments emphasized the importance of particularly simple strategies such as ( always defect ) , ( always cooperate ) , and ( tit for tat , cooperate on the first move and then repeat the co - player s move ) . in spatially extended systems with limited local interaction , cooperators may thrive by forming clusters and thereby reducing exploitation by defectors . for example , on square lattices with , strategies and suitable parameter values , clusters of cooperators typically expand along straight boundaries while being invaded by defectors along corners and irregular boundaries . the competition between these two invasion processes maintains persistent co - existence of both strategies . when tuning the model parameters , universal phase transitions between states of homogenous defecti

The evolutionary prisoner s dilemma games ( pdg ) are an evolutionary game where two players simultaneously decide whether to cooperate or defect. In the original pcdg two players randomly choose whether to cooperate or defect and each player is given a collective payoff which is shared equally. However, still higher individual payoffs are achieved by defectors facing cooperators leaving the latter with the lowest possible payoff. Consequently, defection is dominant because they fare better ( or at least equal ) regardless of the co - player s decision.

competition among cooperators , defectors , and loners is studied in an evolutionary prisoner s dilemma game with optional participation . loners are risk averse i.e. unwilling to participate and rather rely on small but fixed earnings . this results in a rock - scissors - paper type cyclic dominance of the three strategies . the players are located either on square lattices or random regular graphs with the same connectivity . occasionally , every player reassesses its strategy by sampling the


We present a theory for the photon energy and polarization dependence of arpes intensities from the...

their quasi-2d nature makes cuprate superconductors ideal materials for angle resolved photoemission spectroscopy ( arpes ) studies , and by now a wealth of experimental data is available . on the other hand , it does not seem as if these data are really well - understood , the major reason being that we still lack even a rudimentary understanding of the matrix element effects present in these materials . it has recently turned out that matrix element effects are ( or rather : should be ) the central issue in the discussion of arpes data . + arpes is generally believed to measure the single particle spectral function , which near the chemical potential ( and neglecting the finite lifetime ) can be written as here denotes the dispersion of the ` quasiparticle band ' , and denote the ground state and quasiparticle state , respectively . in other words , the experiment gives a ` peak ' whose dispersion follows the quasiparticle band , with the total intensity of the peak being given by the so - called quasiparticle weight . for free particles we have , whence the only reason for a sudden vanishing of the peak with changing can be the fermi factor , i.e. the crossing of the quasiparticle band through the fermi energy . under these circumstances , it would be very easy to infer the fermi surface geometry from the measured photoelectron spectra , and indeed this very assumption , namely that a sudden drop of the photoemission intensity automatically indicates a fermi level crossing , has long been made in the interpretation of all experimental spectra on metallic cuprates . + several experimental findings have shown , however , that this assumption is not tenable in the cuprates . the first indication comes from the study of the insulating compounds srcuclo and cacuocl . although these insulators can not have any fermi surface in the usual sense , which means that the factor is always equal to unity , the experiments show that also in these compounds the quasiparticle pea

We present a new method for the analysis of photoemission spectroscopy ( arpes ) data on cuprate superconductors. In this paper, we show that the fermi surface geometry is not always equal to unity, and that the quasiparticle pea is also found in the insulating compounds srcuclo and cacuocl.

we present a theory for the photon energy and polarization dependence of arpes intensities from the cuo plane in the framework of strong correlation models . we show that for electric field vector in the cuo plane the ` radiation characteristics ' of the and orbitals are strongly peaked along the cuo plane , i.e. most photoelectrons are emitted at grazing angles . this suggests that surface states play an important role in the observed arpes spectra , consistent with recent data from srcuclo . w


We report the discovery of 105-ms x - ray pulsations from the compact central object ( cco ) in the...

the discovery in recent years of many isolated neutron stars ( nss ) at the centers of supernova remnants ( snrs ) confirms the long - held notion that these ultra - dense stellar remnants are born in supernova explosions . most of these nss are identified as pulsars , whose emission derives either from rotational energy loss , as for the rapidly spinning pulsars in the crab ( ms ) and vela ( ms ) remnants , or from magnetic field decay , as posited for the slower ( s ) anomalous x - ray pulsars ( axps ) and related objects ( see mereghetti 2000 for a review ) . however , the nature of a small but growing collection of young ( yrs ) nss in snrs remains a mystery . these so - called compact central objects ( ccos ) are seemingly isolated nss , distinguished by their steady flux , predominantly thermal emission , lack of optical or radio counterparts , and absence of a surrounding pulsar wind nebula ( see for a review ) . the six firm examples of ccos are the central x - ray sources discovered in cas a , pup a , g347.3.5 , pks 120951/52 , g266.21.2 , and kes 79 . their luminosities range over erg s , typical of the younger pulsars ; however their spectra are best characterized as hot blackbody emission of kev , rather than by power - law models . this is significantly hotter than radio pulsars or other radio - quiet nss ( rqnss ; e.g. , * ? ? ? * ) , but similar to the thermal component of the more luminous axps / sgrs . distinct from the rest , psr j12105226 in pks 120951/52 is a ms pulsar that displays large deviations in its spin - down rate , a softer spectrum of kev , and cyclotron resonance lines . these properties suggest that psr j12105226 is variously a wide - binary system , a strongly glitching ns , or an accretor from fall - back material . is the recently discovered cco in supernova remnant kes 79 ( g33.6.1 ; ) . the distance to this unresolved _ chandra _ source is estimated as kpc , derived from and oh absorption studies and updated using the galactic r

We present a new study of the x - ray emission from neutron stars in supernova remnants ( snrs ). We find that the spectra of these sources are consistent with the observed x- -ray fluxes, which are generally consistent with a pulsar wind nebula. The spectral structure of the source is similar to that of the radio pul.

we report the discovery of 105-ms x - ray pulsations from the compact central object ( cco ) in the supernova remnant using data acquired with the _ newton x - ray multi - mirror mission_. two observations of the pulsar taken 6 days apart yield an upper limit on its spin - down rate of s s and no evidence for binary orbital motion . the implied energy loss rate is ergs s , surface magnetic field strength is g , and spin - down age is kyr . the latter exceeds the remnant s estimated age , suggest


We have performed high precision measurements of the zero - energy neutron scattering amplitudes of...

the last decade has seen a revolution in the accuracy with which low energy phenomena in nuclear few body systems can be calculated . insight into certain features of few - nucleon systems has come both from greatly - improved calculations using potential models based on the measured nucleon - nucleon ( nn ) interaction and also from the development of effective field theory ( eft ) approaches based on the chiral symmetry of qcd . such theories have been used to develop a physical understanding rooted ultimately in qcd for the relative sizes of many quantities in nuclear physics , such as nuclear n - body forces and in particular the nuclear 3-body force ( 3n ) , which is now investigated intensively . although it is well understood that 3n forces must exist with a weaker strength and shorter range than the nn force , little else is known . eft has been used to solve the two and three nucleon problems with short - range interactions . for the two - body system , eft is equivalent to effective range theory and reproduces its well - known results for nn forces . the chiral eft expansion does not require the introduction of an operator corresponding to a 3n force until next - to - next - to leading order in the expansion , and at this order it requires only two low energy constants , which are taken to be the triton binding energy and the zero energy doublet n - d scattering amplitude . there have also been significant advances in other approaches to the computation of the properties of few - body nuclei with modern potentials such as the av18 potential , which includes electromagnetic effects and terms to account for charge - independence breaking and charge symmetry breaking of the strong interaction . these calculations accurately reproduce the well - measured energy levels of few body bound states only with the phonomological inclusion of a nuclear 3-body force , so it is clear that more information on this force is needed for further progress . precision measureme

We present a new approach to the calculation of low energy phenomena in nuclear few body systems with a nuclear 3-body force. This approach is based on the chiral eft expansion and is equivalent to effective range theory for the two - body system, which requires only two low energy constants, taken to be the triton binding energy and the zero energy doublet n - d scattering amplitude. The results are consistent with the well - known results for the three nucleon problems with short - range interactions.

we have performed high precision measurements of the zero - energy neutron scattering amplitudes of gas phase molecular hydrogen , deuterium , and he using neutron interferometry . we find fm , fm , and fm . when combined with the previous world data , properly corrected for small multiple scattering , radiative corrections , and local field effects from the theory of neutron optics and combined by the prescriptions of the particle data group , the zero - energy scattering amplitudes are : fm ,


Near - threshold production of boson pairs is considered within the framework of the model of...

near - threshold production of the unstable particles ( ups ) is the most suitable process to observe the finite - width effects ( fwes ) . these effects are closely connected with the instability which depends on the width and energy of the products with being the threshold energy . it equals to the sum of masses of the final state particles . the measurements of boson - pair production at the threshold ( e.g. lep ii experiments ) have provided us with an important information about the masses of bosons and non - abelian triple gauge - boson couplings . to extract the exact information from the boson - pair production we have to calculate the radiative corrections ( rcs ) , which give a noticeable contribution to the corresponding cross - section . ideally , one would like to have the full rcs to the processes . in practice , this problem is very complicated and can not be considered analytically . for discussion of the lep ii situation and strategy it is useful to distinguish three levels of sophistication in description of the boson - pair production : 1 . on - shell boson - pair production , , with subsequent on - shell boson decays . all rcs to these processes are well - known . off - shell production of boson pairs which then decay into four fermions . full set of the rcs is very bulky for the analytical observation and analysis . 3 . total process with an account of the complete set of the corrections . this problem leads to the additional diagrams with the same final states , and complete electroweak ( ew ) corrections are described by many thousands diagrams . on - shell -pair production was considered in refs . , where the cross - section of the process was given . at the tree level , this process is described by two -channel diagrams with -exchange and one -channel diagram with -exchange . the complete radiative corrections , comprising the virtual one - loop corrections and real - photon bremsstrahlung , were calculated and represented in refs . . the de

We present a complete radiative corrections to the lep ii process. The total process is described by two -channel diagrams with -exchange and one - channel diagram with -Exchange. In this paper, we consider the complete radiatives corrections, including the virtual one / loop corrections and real - photon bremsstrahlung.

near - threshold production of boson pairs is considered within the framework of the model of unstable particles with smeared mass . we describe the principal aspects of the model and consider the strategy of calculations including the radiative corrections . the results of calculations are in good agreement with lep ii data and monte - carlo simulations . suggested approach significantly simplifies calculations with respect to the standard perturbative one .


We have identified an optical / x - ray binary with orbital period h as the likely counterpart of...

as identification of the 1873 0.1100gev sources in the second _ fermi _ large area telescope ( lat ) catalog progresses , blazars and spin - powered pulsars increasingly dominate the associations . for the brightest remaining unidentified sources gamma - ray spectral curvature and variability provide an excellent discrimination between these two possibilities . 2fgl j2039.6 = 3fgl 2039.6 ( hereafter j2039 ) is a relatively bright ( 25.4 , * ? ? ? * ) source with a good localization at galactic latitude -37 , a 3fgl `` variability index '' value of 34 , and a `` curvature significance '' of 5.1 . thus it is one of the least variable bright unidentified sources and displays significant spectral curvature , placing it well within the pulsar zone of the curvature - variability plane . accordingly it has been repeatedly searched for radio and gamma - ray pulsations . the lack of any detection is best understood if the source is a millisecond pulsar rapidly accelerated and/or wind - shrouded in a close , interacting binary . we have examined new and archival optical and x - ray data , discovering a short period ( 5.47h ) binary . the system shows evidence of heating , and the x - ray light curve is reminiscent of other shrouded ( black widow bw and redback rb ) millisecond pulsar binaries . the optical light curve is oddly double - peaked and asymmetric . nevertheless we conclude that this is another short period gamma - ray pulsar binary . with our well measured period and position , this is a fruitful target for renewed pulse searches . j2039 has a good 3fgl localization ( radius ) and we initially observed this field as part of our lat unidentified source campaign , using the goodman high throughput spectrograph ( ghts ) at the 4.2 m soar telescope on 2013 august 10 ( mjd 56514 , ut dates are used throughout ) . a sequence of 180s images plus a 600s h frame were obtained , spaced over 2 hours and largely covering the error ellipse . despite relatively poor conditions ,

We present a new optical and x - ray data analysis of the 2fgl 2039.6 source j2039.6, which is a relatively bright ( 25.4, *?? * ) source with a good localization at galactic latitude -37. The light curve is oddly double - peaked and asymmetric, and it is reminiscent of other shrouded millisecond pulsars.

we have identified an optical / x - ray binary with orbital period h as the likely counterpart of the _ fermi _ source 2fgl j2039.6 . grond , soar and des observations provide an accurate orbital period and allow us to compare with the light curve of an archival _ xmm _ exposure . like many short - period optical x - ray binaries associated with lat sources this may be a interacting ( black widow / redback ) millisecond pulsar binary . the x - ray light curve is consistent with the emission asso


We observe signatures of disorder - induced order in 1d spin chains with an external , site -...

we consider a ferromagnetic spin chain with spins in a random external magnetic field , described by the following hamiltonian : where are the -pauli spin matrices at site , and is the random field at site . the field points along an arbitrary direction inside the plane and . also within the plane , we will distinguish observables ( and measurements ) aligned about the axis with a subscript , and observables perpendicular to with a subscript . as mentioned before , the second term of eq . ( [ eq : hamiltonian ] ) does not have the same symmetry as the first term ( which is invariant with respect to rotations along the axis ) . the relevant order parameters are the mean expectation values of the magnetization along the parallel and orthogonal directions : and . typically , we also consider the local magnetization and , indicating which regions of the chain are being discussed . both and vanish as the amplitude of the external fields approaches zero . for large field intensity , follows the local direction of the field . in this case , the average is essentially zero . entanglement is known to be a good predictor of quantum phase transitions . although there is a variety of possibilities , the observation of a singularity in an entanglement measure most certainly implies a second order quantum phase transition . in order to measure entanglement we will use the block entropy , defined as the von neumann entropy of the reduced density matrix obtained by tracing out the degrees of freedom of spins of the chain . by means of a schmidt decomposition , any pure state of the system can be expressed as } \}$ ] and }  \}$ ] are orthonormal states in the hilbert space of the first and last spins respectively . because of the orthonormality property , in this basis it is easy to write down the reduced density matrix for the first spins , }   _i^{[1  p]}|$ ] . the positive numbers are the so called schmidt coefficients , and give the block entropy the value of depends on both cla

We consider a ferromagnetic spin chain with spins in a random external magnetic field. The -pauli spin matrices are at site and is the random field at site. We also consider the local magnetization and, indicating which regions of the chain are being discussed.

we observe signatures of disorder - induced order in 1d spin chains with an external , site - dependent uni - axial random field within the plane . we numerically investigate signatures of a quantum phase transition at , in particular an upsurge of the magnetization in the direction orthogonal to the external magnetic field , and the scaling of the block - entropy with the amplitude of this field . also , we discuss possible realizations of this effect in ultra - cold atom experiments . disorder


The polarimetric measurement on the prompt phase of grb 100826a shows that the polarization angle...

gamma - ray bursts ( grbs ) are the most energetic explosions in the universe since the big bang ( for recent reviews , see , e.g. , ) . they are divided into two categories ( short and long ) according to the duration the time interval in which 90% of the photons are counted , seconds for long grbs , and seconds for short grbs seconds is not strict , because in some cases a long lasting grb seems to be a short one , and vice versa ( see , e.g. , , and the references therein ) . besides , a third group with intermediate duration can also exist ( see , e.g. , and the references therein ) . ] . the isotropic equivalent energy radiated during the prompt phase of a grb , which typically lasts a few seconds , is as large as the energy radiated from the sun during its whole life . after decades of extensive research since its discovery in the 1960s , it is still not clear how does the energy release in such a short time . the most accepted assumptions are the core collapse of a massive star , or the merger of two compact objects , such as neutron star neutron star or neutron star black hole binaries . the light curves of grbs have various types , ranging from smooth , fast - rise and quasi - exponential decay , through curves with several peaks , to highly variable curves with many peaks . the spectra can often be fitted well by the band function , and the spectra generally peak at mev . photons with energy higher than 1 gev have also been detected in some brightest grbs . in order to avoid the compactness problem " , it is believed that gamma - rays are emitted from a highly relativistic outflow ejected by the central engine . however , there are still controversies on some basic questions , e.g. , is the outflow isotropic or collimated , magnetic - dominated or baryon - dominated ? the information extracted from spectrum and light curve observation is not complete enough to distinguish one model from another . the polarimetric measurement provides a deep insight into th

We present a new method for the analysis of the light curves of gamma - ray bursts ( grbs ). We use the spectral data from the gamboss - lee telescope to study the spectra of the ghz - 1 and gghs, respectively, in the presence of a large number of photons. The results are presented in terms of the time interval between the initial phase of the grb and the subsequent prompt phase.

the polarimetric measurement on the prompt phase of grb 100826a shows that the polarization angle changes between two adjacent time intervals . we will show that this phenomenon can be naturally interpreted in the framework of the magnetic - dominated jet ( mdj ) model . the mdj model suggests that the bulk lorentz factor of the outflow increases as , until reaching a saturated value . electrons move in the globally ordered magnetic field advected by the jet from the central engine and produce s


We study numerically the localization properties of two - dimensional electrons in a weak...

scaling theory of localization predicts that evolution with size , , of the conductivity , , ( in the units of ) of a 2d sample is governed only by the value of , regardless of the type of disorder in the sample , i.e. , together with initial condition , , where is the fermi momentum , and is the transport mean free path , eq . ( [ scaling ] ) suggests that , in zero magnetic field , where , localization radius of electron states is given by with increasing magnetic field , when crosses from the orthogonal to the unitary form , , the localization radius crosses over from to , given by crossover takes place when weak localization is suppressed , i.e. , when the magnetic flux through the vector area spanned by the electron travelling diffusively over the area , is of the order of the flux quantum . with vector area being , we get the following estimate for crossover magnetic field where is the cyclotron frequency , and is the scattering time . and , as a function of magnetic field , , as predicted in ref . . at a given , delocalization transition occurs at low field ( point ) and at high field ( point ) . right : same dependencies , replotted in the axis inverse filling factor vs. zero - field resistivity , constitute a part of the global phase diagram ref . . depending on , the system undergoes a sequence of transitions , or .,width=321 ] the origin of the crossover eq . ( [ estimate ] ) is that the paths , which interfere in a zero field , acquire field - induced random aharonov - bohm phases . justification for considering exclusively the _ phase _ action of magnetic field is that in high - mobility samples with the crossover field is so weak that its orbital action can be neglected . it is a very delicate fact that , after the crossover , this orbital action causes a drastic change of the eigenstates even for classically weak magnetic fields , . this conclusion was drawn by khmelinitskii from the analysis of the renormalization group flows . originally , these equ

We study the localization of electron states in a zero magnetic field with a crossover, and show that the delocalization transition occurs at low field ( point ) and at high field ( points ). The delokalization phase is characterized by a series of transitions, or. Width=321 ], which are caused by the orbital action of magnetic field.

we study numerically the localization properties of two - dimensional electrons in a weak perpendicular magnetic field . for this purpose we construct _ weakly chiral _ network models on the square and triangular lattices . the prime idea is to separate in space the regions with _ phase _ action of magnetic field , where it affects interference in course of multiple disorder scattering , and the regions with _ orbital _ action of magnetic field , where it bends electron trajectories . in our mod