We report on the observation of terahertz radiation induced photogalvanic currents in semiconductor...

nonequilibrium spatially - periodic noncentrosymmetric systems are able to transport particles in the absence of an average macroscopic force . the directed transport in such systems , generally known as the ratchet effect , has a long history and is relevant for different fields of physics . if this effect is induced by electro - magnetic radiation it is usually referred to as photogalvanic ( or photovoltaic ) effect , particularly if breaking of the spatial inversion symmetry is related to the microscopic structure of the system . blanter and bttiker have shown that one of the possible realizations of the seebeck ratchet can be a superlattice irradiated by light through a mask of the same period but phase shifted with respect to the superlattice . in the present work we have experimentally realized this idea with some modifications . the photocurrent has been observed in semiconductor heterostructures with a one - dimensional lateral periodic potential induced by etching a noncentrosymmetric grating into the sample cap layer . the in - plane modulation of the pump radiation appears hence not via a mask with periodic structures but due to the near - field effects of radiation propagating through the grating . this photothermal ratchet effect was predicted by bttiker and is polarization independent under normal light incidence . in addition we have observed photocurrents sensitive to the plane of polarization of the linearly polarized terahertz ( thz ) radiation and to the helicity in case of circularly polarized photoexcitation . the theoretical analysis enables us to propose new mechanisms of the observed circular and linear photogalvanic effects which are related to the combined action of out - of - phase periodic potential and in - plane modulated pumping of the two - dimensional electron system . here we study photocurrents in ( 001)-grown gaas / algaas heterostructures with superimposed lateral grating having a period of 2.5 m . the electronic micrograph are s

We study photocurrents in gaas / algaas heterostructures with superimposed lateral grating having a period of 2.5 m. The photocurrent is sensitive to the plane of polarization of the linearly polarized terahertz ( thz ) radiation and to the helicity in case of circularly Polarized photoexcitation. We show that the photothermal ratchet effect can be observed in noncentrosymmetric systems with a one - dimensional lateral periodic potential induced by etching.

we report on the observation of terahertz radiation induced photogalvanic currents in semiconductor heterostructures with one - dimensional lateral periodic potential . the potential is produced by etching a grating into the sample surface . the electric current response is well described by phenomenological theory including both the circular and linear photogalvanic effects . experimental data demonstrate that the inversion asymmetry of the periodic lateral pattern can be varied by means of ele


New gmrt observations of the five - component pulsar b185726 provide detailed insight into its...

pulsar b185726 , though discovered early ( vaughn & large 1970 ) , has heretofore been studied almost entirely by average methods . one of the small group of pulsars with five - component ( * m * ) profiles , its aggregate polarization has been investigated over a broad frequency band ( hamilton 1977 ; mcculloch 1978 ; manchester 1980 ; morris 1980 ; van ommen 1997 ; & gould & lyne 1998 ) , and no effort to interpret the form of pulsar beams fails to mention it ( backer 1976 ; lyne & manchester 1988 ; rankin 1983a , 1986 , 1990 , 1993a , b ; mitra & deshpande 1999 ) . little has been learned , however , regarding its pulse - sequence ( hereafter ps ) behaviour . apart from one historical effort to determine its null fraction ( ritchings 1976 ) , only recently did the fluctuation - spectral analyses of weltevrede ( 2006 , 2007 ; hereafter wes , wse ) identify its 7-rotation - period ( hereafter ) modulation . psr b185726 is often compared with other prominent * m * pulsars , but it is not yet known whether it exhibits profile moding like b1237 + 25 ( , srostlik & rankin 2005 ) or core - component phenomena such as those seen in b0329 + 54 ( mitra 2007 ) . we have carried out a sensitive new 325-mhz polarimetric observation of b185726 using the giant metre - wave radio telescope ( hereafter gmrt ) in maharashtra , and a typical 200-pulse segment is given in figure [ fig1 ] . already we see evidence of interesting subpulse modulation . in the remainder of this paper , we describe the results of a series of ps analyses designed to address a number of these questions remaining about this star s individual pulse behaviour . to our surprise we found that we were able to identify and measure a long period cycle which almost certainly can be interpreted as the rotation interval of an emission - beam carousel in the manner of that found earlier for b0943 + 10 ( deshpande & rankin 1999 , 2001 ; hereafter dr99 , dr01 ) . such cycles are thought to be driven by forces within a p

We present a new polarimetric observation of the pulsar b185726 using the giant metre - wave radio telescope ( hereafter gmrt ) in maharashtra. The psr is a small group of pulses with five - component profiles, and its aggregate polarization has been studied over a broad frequency band. It is not yet known whether it exhibits profile modulation like b1237 + 25 or core - components such as those seen in b0329 + 54 ( mitra 2007.

new gmrt observations of the five - component pulsar b185726 provide detailed insight into its pulse - sequence modulation phenomena for the first time . the outer conal components exhibit a 7.4-rotation - period , longitude - stationary modulation . several lines of evidence indicate a carousel circulation time of about 147 stellar rotations , characteristic of a pattern with 20 beamlets . the pulsar nulls some 20% of the time , usually for only a single pulse , and these nulls show no discerni


We describe explicit open books on arbitrary plumbings of oriented circle bundles over closed...

in this article using 3dimensional simple surgery techniques we first construct explicit open books on oriented circle bundles over closed oriented surfaces . then we construct open books on plumbings of circle bundles according to a graph by appropriately gluing the open books we constructed for the circle bundles involved in the plumbing . ( we will use the word graph for a connected graph with at least two vertices . ) an open book on a circle bundle or more generally on a plumbing of circle bundles is called _ horizontal _ if its binding is a collection of some fibers and its pages are transverse to the fibers . here we require that the orientation induced on the binding by the pages coincides with the orientation of the fibers induced by the fibration . we will call a plumbing graph _ non - positive _ if the sum of the degree of the vertex and the euler number of the bundle corresponding to that vertex is non - positive for every vertex of the graph . we prove that the open book we construct on a circle bundle with negative euler number or on a non - positive plumbing of circle bundles is horizontal . it turns out that the contact structure compatible with this open book is also _ horizontal _ , i.e. the contact planes ( possibly after an isotopy of the contact structure ) are transverse to the fibers . furthermore we show that the monodromy of this horizontal open book is given by a product of right - handed dehn twists along disjoint curves . consequently , by a theorem of giroux , our horizontal open book is compatible with a stein fillable contact structure . recall that eliashberg and gromov proved that every fillable contact structure is tight . as a first application of our construction we describe explicit horizontal open books on some seifert fibered 3manifolds . a contact 3manifold is said to be _ milnor fillable _ if it is contactomorphic to the contact boundary of an isolated complex surface singularity . the germ is called a _ milnor filling _ of .

We construct explicit open books on oriented circle bundles over closed surfaces using 3dimensional simple surgery techniques. We construct open books in the form of a graph by appropriately gluing the open books we constructed for the circle bundle corresponding to that vertex. The orientation induced on the binding by the pages coincides with the orientation of the fibers induced by the fibration. Furthermore, we prove that the contact structure compatible with this open book is also horizontal, i. E. The contact planes ( possibly after an isotopy of the contact structures ) are trans.

we describe explicit open books on arbitrary plumbings of oriented circle bundles over closed oriented surfaces . we show that , for a non - positive plumbing , the open book we construct is horizontal and the corresponding compatible contact structure is also horizontal and stein fillable . in particular , we describe horizontal open books on some seifert fibered 3manifolds . as another application we describe horizontal open books isomorphic to milnor open books for some complex surface singul


Foreground subtraction is the biggest challenge for future redshifted observations to probe...

observations of redshifted radiation from the large scale distribution of neutral hydrogen ( hi ) are perceived as one of the most promising future probes of the universe at high redshifts ( see for a recent review ) . observational evidence from quasar absorption spectra and the cmbr together imply that the hi was reionized over an extended period spanning the redshift range ( for reviews see ) . determining how and when the universe was reionized is one of the most important issues that will be addressed by future observations . the giant meter wave radio telescope ( gmrt ; ) , currently functioning at several frequency bands in the range to is very well suited for carrying out initial investigations towards detecting the reionization hi signal . there are several upcoming low - frequency instruments such as lofar , mwa , 21cmapast/ ] and ska which are being built specifically with these observations in view . it is currently perceived that a statistical analysis of the fluctuations in the redshifted signal holds the greatest potential for observing hi at high redshifts . correlations among the visibilities measured in radio - interferometric observations directly probe the hi power spectrum at the epoch where the radiation originated . the reionization visibility signal at the gmrt is expected to be and smaller ( ) . this hi signal is present as a minute component of the background in all low frequency observations , and it is buried in foreground radiation from other astrophysical sources whose contribution is to orders of magnitude larger . extracting the hi signal from the foregrounds is a major challenge . individual sources can be identified and removed from the image at a flux level which depends on the sensitivity . the contribution from the remaining discrete sources could be large enough to overwhelm the hi signal . the diffuse synchrotron emission from our galaxy is another important component . foreground sources include free - free emission from ioniz

We present a new method for extracting the hi signal from the giant meter wave radio telescope ( gmrt ) at high redshifts. We use a combination of acoustic and radio - interferometric observations to investigate the hi power spectrum in the foregrounds of the galaxy. The sensitivity of our approach is based on the spectral resolution of the g - band data, which allows us to obtain an accurate estimate of the hi emission.

foreground subtraction is the biggest challenge for future redshifted observations to probe reionization . we use a short gmrt observation at to characterize the statistical properties of the background radiation across to sub - arcminutes angular scales , and across a frequency band of with resolution . the statistic we use is the visibility correlation function , or equivalently the angular power spectrum . we present the results obtained from using relatively unsophisticated , conventional da


Eternal inflation is studied in the context of warm inflation

one of the most peculiar consequences of inflation is the possibility of leading to a self - reproduction regime ( srr ) of inflating hubble regions ( h regions ) , a phenomenon that became known as eternal inflation ( for reviews , see , e.g. , refs . ) . in eternal inflation the dynamics of the universe during the inflationary phase is considered in a global perspective and refers to a semi - infinity ( past finite , future infinity ) mechanism of self - reproduction of causally disconnected h regions . looking at the spacetime structure as a whole , the distribution of h regions resembles much like that of a bubble foam . this scenario seems to be a generic feature present in several models of inflation . in recent years , eternal inflation attracted renewed attention due to several factors . one of them is the seemingly intrinsic connection between eternal inflation and extra dimensions theories , like string theory , and its multitude of possible solutions describing different false vacua , each one yielding its own low - energy constants , leading to what has been known by the `` multiverse '' , when combined with eternal inflation . collisions between pocket universes could upset in some level the homogeneity and isotropy of the bubble we live in and , therefore , lead to some detectable signature in the cosmic microwave background radiation ( cmbr ) . this has then led to different proposals to test eternal inflation . eternal inflation has also been recently studied in experiments involving analogue systems in condensed matter . for example , in ref . , an analogue model using magnetic particles in a cobalt - based ferrofluid system has been used to show that thermal fluctuations are capable of generating -dimensional minkowski - like regions inside a larger metamaterial that plays the role of the background of the multiverse . from the model building point of view , a relatively recent trend is to look for new models , or specific regimes in known models ,

We present a new model of eternal inflation in the context of a multiverse - like universe. This model is based on analogue systems in condensed matter and has been used to study the dynamics of the universe during the inflationary phase. We show that the dynamical structure of the Universe during the srr phase is asymmetric, with asymmetry due to the existence of -dimensional regions inside the metamaterial.

eternal inflation is studied in the context of warm inflation . we focus on different tools to analyze the effects of dissipation and the presence of a thermal radiation bath on the fluctuation - dominated regime , for which the self - reproduction of hubble regions can take place . the tools we explore are the _ threshold inflaton field _ and _ threshold number of _ e_-folds _ necessary to establish a self - reproduction regime and the _ counting of hubble regions _ , using generalized conditio


We study disorder - induced spectral correlations and their effect on the magnetic susceptibility...

we begin by presenting some more details concerning our semiclassical evaluation of the disorder correlation function , , and corresponding susceptibility . we consider non - interacting electrons in a weak , perpendicular magnetic field . in terms of retarded and advanced single particle green functions , , may be written as , where implies the inclusion of connected diagrams only . using a diagrammatic approach introduced by altland and gefen the field sensitive part of can be expressed as a sum including cooperon type diagrams defined by ^n =  _{j=1}^{n } d^dr_j_{m=1}^{n } ^{(c ) } ( {  r}_m,{ r}_{m+1}; ; h )  ;  {  r}_{n+1 }  {  r}_1 \ ; . \ ] ] here , is the disorder averaged single particle green function , , and . semiclassically , can be expressed as a sum over classical trajectories between and , } \ ; .\ ] ] the prefactor includes the classical phase space density , stands for the classical action along an orbit ( in the absence of disorder ) including the maslov index , and is the orbit length . is then given in terms of pairs of classical paths which explicitly include the effect of boundary scattering . however most pairs ( of different paths ) produce oscillating contributions which we assume to vanish after energy or size averaging . the main contribution to the field sensitive part of arises from diagonal terms ( otherwise known as the cooperon channel ) obtained by pairing paths with their time reverse . assuming that the magnetic field affects the phase of the particles but not their trajectories we can write where \ ; . \ ] ] here , is the period of the trajectory , is the vector potential , , and the level broadening was introduced via . ( [ zsc ] ) depends , besides , only on the system without disorder and holds for both integrable and chaotic geometries . the disorder induced contribution to the average susceptibility is given by ( ) : where the bulk landau susceptibility is for spinless electrons . in eq . ( [ stos ] ) the are now assumed to

We consider non - interacting electrons in a weak magnetic field and investigate the disorder correlation function, and susceptibility of the disorder averaged single particle green function. We find that the disorder induced contribution to the averaged green function is a sum over classical trajectories between and,, with respect to the orbit length. The prefactor includes the classical phase space density, stands for the classical action along an orbit ( in the absence of disorder ) including the maslov index,and is the orbitlength. However most pairs ( of different paths.

we study disorder - induced spectral correlations and their effect on the magnetic susceptibility of mesoscopic quantum systems in the non - diffusive regime . by combining a diagrammatic perturbative approach with semiclassical techniques we perform impurity averaging for non - translational invariant systems . this allows us to study the crossover from clean to diffusive systems . as an application we consider the susceptibility of non - interacting electrons in a ballistic microstructure in t


In this paper we consider the growth , large fluctuations and memory properties of an affine...

in this paper , we consider the asymptotic behaviour of an affine scalar stochastic functional differential equation where the average of the process over its entire history appears on the right hand side . accordingly , we study where is given by the continuous function , defined on $ ] , is a standard one dimensional brownian motion and . here and are real parameters . there is a unique strong solution of which is a gaussian process . the goal of the paper is to describe for all pairs of the parameters and the asymptotic behaviour of the paths , as well as information about the autocovariance function of in the case that the solution is recurrent on . this model was studied in , where the authors considered the case . under this condition the solution was shown to grow at a well defined exponential rate , with a polynomial correction . specifically , the rate of growth is given by where is an almost surely finite and gaussian distributed random variable . the results in rely on the theory of admissibility of linear deterministic volterra operators . while the present article establishes some new results concerning the case when , for the most part it is concerned with the case when , where the solution need not have a well - defined growth rate but rather may fluctuate . this behaviour is not wholly unexpected ; in the case when and , for example , the solution of is an asymptotically stationary ornstein uhlenbeck process , while when and , it is a scaled standard brownian motion . a complete asymptotic dynamical picture of the solution is determined for all real values of and in the paper . our analysis shows that there are only three principal regions in the ` ' parameter space , within which the process undergoes different pathwise asymptotic behaviour . for clarity we provide a bifurcation diagram of the parameter space : * in theorem [ thm.averagegaussian ] , corresponding to and , the solution is asymptotically equal to an ornstein uhlenbeck process and has

We study the asymptotic behaviour of a affine scalar stochastic functional differential equation where the average of the process over its entire history appears on the right hand side. In this paper, we study where is given by the continuous function, defined on $ ], is a standard one dimensional brownian motion and. Here and are real parameters. There is a unique strong solution of which is gaussian process. The goal of the paper is to describe for all pairs of the parameters and the as.

in this paper we consider the growth , large fluctuations and memory properties of an affine stochastic functional differential equation with an average functional where the contributions of the average and instantaneous terms are parameterised . an asymptotic analysis of the solution of this equation is conducted for all values of the parameters of the equation . when solutions are recurrent , we show that the autocovariance function of the solution decays at a polynomial rate , even though the


The path integral monte carlo method is used to simulate dilute trapped bose gases and to...

the experimental observation of bose - einstein condensation ( bec ) in dilute trapped and supercooled atomic vapors has stimulated enormous experimental and theoretical interest in the physics of the weakly interacting bose gas ( see for a review ) . especially intriguing is the role of dimensionality and two - body interactions . lower dimensional atomic gases have been realized with strong quantum confinement in one or more directions . these systems exhibit very peculiar properties , such as the exact mapping between interacting bosons and noninteracting fermions ( tonks - girardeau gas ) , because the role of quantum fluctuations and strong correlations is enhanced . although these gases are very dilute , bec of trapped atomic gases is strongly influenced by two - body interactions . within a mean - field approximation , the strength of the interatomic interactions can be typically characterized by a single parameter , the -wave scattering length , at very low temperatures . this van der waals type interaction is isotropic and short - range in comparison to the average interparticle separation . accordingly , bose - einstein condensates created thus far have been very accurately described by the gross - pitaevskii theory ( see for a review ) , a mean - field approach . furthermore , it has been possible to tune the s - wave scattering length to essentially any value , positive or negative , by utilizing a magnetic atom - atom feshbach resonance . studies of the influence of the interparticle interactions on the properties of bec have focused mainly on the short - range interactions . however , understanding new kinds of systems will require the investigation of the effects of additional interactions , since bose - einstein condensation of molecules has now been observed using new techniques for creating ultracold molecules . in addition , ling _ et al . _ proposed an efficient method to convert atomic condensates into stable molecules using a generalized raman

We present a new method for the conversion of bose - einstein condensation into stable molecules using a generalized raman. This method is based on the -wave scattering length and the s - wave scattering width, which are both used to describe the properties of boson - interacting condensates in supercooled atomic vapors. The method is applied to the formation of a single - particle - bound, asymmetric, non - fermionic, and asymmetry - free, quasi.

the path integral monte carlo method is used to simulate dilute trapped bose gases and to investigate the equilibrium properties at finite temperatures . the quantum particles have a long - range dipole - dipole interaction and a short - range -wave interaction . using an anisotropic pseudopotential for the long - range dipolar interaction and a hard - sphere potential for the short - range -wave interaction , we calculate the energetics and structural properties as a function of temperature and


Zrte and hfte have attracted increasingly attention recently since the theoretical prediction of...

topological insulator ( ti ) is a new class of material which is an insulator in its bulk , while having time reversal symmetry protected conducting states on the edge or surface . a large number of realistic materials have been theoretically proposed and experimentally confirmed , such as bise and bite . however , the layered transition - metal pentatelluride zrte ( and hfte ) is a particular example . zrte and hfte have been studied more than 30 years ago due to the large thermoelectric power and mysterious resistivity anomaly . recently , weng _ et al . _ predicted that mono - layer zrte and hfte are good quantum spin hall insulators with relatively large bulk band gap ( about 0.1 ev ) by first principles calculations . and the three - dimensional bulk phase of zrte and hfte are also predicted to be tis , which are located at the vicinity of a transition between strong and weak ti , but without detailed description . nevertheless , subsequent experiments show many contradictions about the topological nature of zrte or hfte . several experimental works suggested that zrte is a dirac semi - metal without a finite band gap by different characterization methods , such as shubnikov - de haas oscillations , angle - resolved photoemission spectroscopy ( arpes ) , and infrared reflectivity measurements . of course there are also other experimental works holding opposite point of view . for example , in two recent scanning tunneling microscopy ( stm ) experiments , they unambiguously observed a large bulk band gap about 80 or 100 mev in zrte , implying that there is no surface state on the top surface and therefore it should be a weak ti . another apres work also favored a weak ti for zrte . however , there are two other arpes works which believed that zrte is a strong ti . for instance , by using the comprehensive arpes , stm , and first principles calculations , manzoni _ et al . _ found a metallic dos at fermi energy , which arises from the two - dimensional surface st

We present a new study of the topological properties of layered transition - metal pentatelluride zrte ( and hfte ). We find that the bulk phase is a dirac semi - metallic with a large band gap, but it has no surface state on the edge or surface. The bulk band gap is about 0.1 ev, which implies that there is no surface states on the top surface, and therefore it should be a weak ti.

zrte and hfte have attracted increasingly attention recently since the theoretical prediction of being topological insulators ( tis ) . however , subsequent works show many contradictions about their topological nature . three possible phases , i.e. strong ti , weak ti , and dirac semi - metal , have been observed in different experiments until now . essentially whether zrte or hfte has a band gap or not is still a question . here , we present detailed first - principles calculations on the elec


Detection and quantification of entanglement in quantum resources are two key steps in the...

entanglement has long played a pivotal role in many quantum information processing tasks , such as secure communication using quantum - key distribution , teleportation of quantum states , quantum computation , reduction in communication complexity , and more recently , expansion and certification of randomness . as a result , the verification and quantification of this resource present in quantum systems is often an indispensable part of quantum - information processing ( qip ) protocols . traditionally , for low - dimensional composite systems that are made up of only a few subsystems , the process of entanglement certification and/or quantification is carried out using complete quantum state tomography followed by the application of certain separability criteria . this approach , however , suffers from the drawbacks that it is unnecessarily resource intensive and that the procedure of tomography may already be intractable for a physical system that is made up of only a handful of qubits ( see , for example , ref . and references therein ) . more recently , there has been considerable interest in verifying the presence of entanglement by measuring directly the expectation value of so - called _ entanglement witnesses _ . while this latter approach is much more economical in terms of both the number of measurement settings and the resource required for classical post - processing , it still requires detailed knowledge of the actual measurements performed on the physical system in question . this last feature is , of course , undesirable as there are examples of entanglement witnesses that are extremely fragile to the perturbations of the constituent measurement operators . also , in some qip tasks such as quantum key distribution , it is highly desirable to make minimal assumptions on the devices used in the protocol . in contrast , violation of bell - type inequalities is only a statement about the measurement statistics derived from an experiment . since entangle

We present a method for verifying the presence of entanglement in quantum systems by measuring the expectation value of such en Tang - type observers. This technique is based on the use of a simple, yet powerful, method to measure the expected value of _ en - tang - types _ ( _ quantum state tomography _). We show that the method can be used to verify the existence of entanglement in a number of different quantum systems.

detection and quantification of entanglement in quantum resources are two key steps in the implementation of various quantum - information processing tasks . here , we show that bell - type inequalities are not only useful in verifying the presence of entanglement but can also be used to bound the entanglement of the underlying physical system . our main tool consists of a family of clauser - horne - like bell inequalities that can not be violated maximally by any finite - dimensional maximally


We propose a tight binding model for the quantum spin hall system on triangular optical lattice and...

topological insulators ( tis ) are insulating in the bulk but have metallic states on their boundaries . robustness of these states against disorder and perturbations makes them promising for applications such as spintronics and topological quantum computation . topological invariants of the bulk material are essential for the robust boundary modes . this urged consideration of topological insulators on different lattice geometries . it is widely acknowledged that the cold atomic systems are ideal systems to simulate solid - state phenomena in a controlled way . the two and three dimensional topological insulators with band gaps in the order of the recoil energy have recently been proposed in ultracold fermionic atomic gases . the proposal utilizes interactions which preserves time reversal symmetry ( trs ) , analogous to synthesized spin - orbit coupling , so that the insulators are classified by the so called topological invariant . even if the band gap in tight binding models are not as large as in nearly free electron limit , tis in ultra cold atomic systems have been studied vastly in tight binding regime . the optical lattices are described by continuous potentials formed by the combinations of standing waves . it is convenient to treat them as deep potentials . our aim in this article is to propose a tight binding model for the quantum spin hall effect which can be realized in the ultracold atomic systems . the corresponding model in the nearly free electron limit is proposed by bri and cooper with this advantage that the band gap is large . we also determine the band structure of the edge state which exhibits the hallmark of tis due to its robustness against all perturbations that preserve the trs . in the sec . [ sec : tight ] of this paper we propose the tight binding model for quantum spin hall ( qsh ) system in the triangular optical lattice . in sec . [ sec : model ] we briefly review the proposal of topological insulator in ultracold atomic gases . we

We propose a tight binding model for the quantum spin hall effect in the triangular optical lattice. The band gap is large and the edge state is characterized by a strong band structure. We also study the band structure of the edge states which exhibits the hallmark of tis due to its robustness against all perturbations that preserve the trs.

we propose a tight binding model for the quantum spin hall system on triangular optical lattice and we determined the edge state spectrum which contains gap traversing states as the hallmark of topological insulator . the advantage of this system is the possibility of implementing it in the fermionic ultracold atomic system whose nearly free electron limit is proposed by b. bri and n. r. cooper , phys . rev . lett . * 107 * , 145301 ( 2011 ) .


Using a similarity hamiltonian renormalization procedure , we determine an effective spin-1/2...

the study of magnetic systems is one of the most active fields of research in condensed matter physics : the variety of emerging ground - states , as well as the rich phase diagram of magnetic lattices , makes these systems an optimal testbed to probe the competition between various orders and frustration effects . from this perspective , it would be very useful to be able to engineer synthetic physical systems effectively describing magnetic model hamiltonians , with tunable geometry and parameters . a promising route is provided by cold atomic setups : for instance , itinerant magnetism in bulk ultracold fermi systems with repulsive interactions has been experimentally studied , while small spin networks have been simulated with ion chains . effective nearest - neighbour spin - spin interactions for atoms in neighbour wells of an optical lattice may result from super - exchange couplings : the corresponding second - order tunneling has been observed in array of double wells . furthermore , using fast oscillations of the optical lattice , it is possible to control the sign of the nearest - neighbour tunneling , which has been recently used to simulate classical frustrated magnetism in triangular lattices . one may also use two - component gases where the two internal degrees of freedom correspond to the simulated ( pseudo)spins . spin interactions can be tuned by adjusting the external potential . the recent realization of controllable bose - bose mixtures paves the way towards the experimental simulation of spin hamiltonians , in which the atomic counterpart of magnetic phases , like antiferromagnetic nel and xy ferromagnetic phases ( respectively corresponding to the checkerboard and the supercounterfluid phases ) may be detected and studied . a key tool in the manipulation of ultracold atomic systems is the possibility to superimpose and control optical lattices . the low - energy properties of ultracold bosons in deep optical lattices are well captured by the b

We present a new method for the simulation of spin hamiltonians in deep optical lattices. The system is characterized by a large number of atoms and a small number of electrons, which are simulated with two - component gases. We show that the b - bose mixture can be used to superimpose and control the optical latice.

using a similarity hamiltonian renormalization procedure , we determine an effective spin-1/2 representation of the bose - hubbard model at half - integer filling and at a finite on - site interaction energy . by means of bosonization , we are able to recast the effective hamiltonian as that of a spin-1/2 xxz magnetic chain with pertinently renormalized coupling and anisotropy parameters . we use this mapping to provide analytical estimates of the correlation functions of the bose - hubbard mode


Peripheral nucleon - nucleon scattering is analysed in the framework of an effective field theory

following the suggestion of weinberg and the pioneering work of ordoez , ray and van kolck , there has been much interest in using chiral perturbation theory ( chpt ) to calculate long - range contributions to the nucleon - nucleon ( ) force . scattering , see ref . ] these have concentrated on two - pion exchange ( tpe ) , although work has also started on three - pion exchange . in an effective field theory like this , the residual short - distance interactions are represented by energy- or momentum - dependent contact interactions . these can be expanded in powers of the ratios between momenta or the pion mass and the scale of the physics which is responsible for these short - range interactions , for example the mass of the meson . provided these ratios are small enough , this expansion should converge rapidly . nucleon - nucleon scattering in peripheral waves provides the best place to look for clear signals of the long - range tpe force . various groups have done so but they often find quite large deviations from the experimental " phase shifts deduced from partial - wave analyses . this has led some to resort to introducing phenomenological cut - offs or additional degrees of freedom . recently the nijmegen group has started carrying out pwa s which include chiral tpe and they find that this makes significant improvements to their fits . the large differences between their results and available chpt predictions have led to a claim that the fits can not yield reliable values for parameters in the tpe potential . however it is hard to make a direct comparison between the nijmegen analyses and chpt because they are done with a coordinate - space cut - off of 1.4 fm or larger . this means that short - distance parameters in the fits have to play two roles . as well as parametrising true short - range physics they also have to correct for artefacts introduced by the cut - off . hence one can not immediately tell from the nijmegen parametrisation whether the residu

We present a new method for calculating the long - range contribution to the nucleon - nucleonal force in two - pion exchange ( tpe ). This technique is used to calculate the residual short - distance interactions in the te potential. We find that the nijmegen analysis can not yield reliable values for parameters in the long range tp force.

peripheral nucleon - nucleon scattering is analysed in the framework of an effective field theory . distorted - wave methods are used to remove the effects of one - pion exchange . two - pion exchange and recoil corrections to one - pion exchange are then subtracted pertubatively . this removes all contributions up to order in the chiral expansion . we have applied this to the , and waves , using phase shifts from various partial - wave analyses by the nijmegen group . in regions where these ana


We review the proof of a conjecture concerning the reality of the spectra of certain -symmetric...

the unexpected reality of the spectra of a class of non - hermitian quantum mechanical systems has provoked a fair amount of work since the first example was noted by bessis and zinn - justin . generalising the result at , a numerical study of the schrdinger equations led bender and boettcher to conjecture that under suitable boundary conditions the spectrum of ( [ bbeq ] ) was entirely real and positive provided . bender and boettcher also noticed the relevance of -symmetry to these problems . for all , the potentials are invariant under the combined action of parity and time reversal , and this implies the eigenvalues are either real or occur in complex - conjugate pairs . if all energy eigenstates are also eigenstates of the operator , then the spectrum is guaranteed to be entirely real , but this is not true in general : the -symmetry can be spontaneously broken , in which case the corresponding energies occur in complex - conjugate pairs . in fact , a proof of the reality conjecture has only recently been obtained , via a correspondence between ordinary differential equations and integrable models ( the so - called ` ode / im correspondence ' ) . here we review the proof and touch on a few of the byproducts of the correspondence relevant to the ode community . generalising the bessis zinn - justin and bender boettcher hamiltonians , we consider the class of -symmetric problems (x ) =  (x ) , (x )  l^2({{ c}})~. \ ] ] for , the contour may be taken to be the real axis with a small dip below the origin if . for larger , the contour should be distorted into the complex plane to ensure the correct analytical continuation of the original problem , as explained in . the result of is that the spectrum of ( [ ptg ] ) is _ real _ for and and _ positive _ for and . referring to figure [ regions ] , reality was proven for , and positivity for . rather than considering the -symmetric problem ( [ ptg ] ) alone , we introduce a related problem obtained from ( [ ptg ] ) by se

We consider the class of -symmetric problems ( x ) = (x, l ) l and ( ptg ) is a real axis with a small dip below the origin. For larger, the contour should be distorted into the complex plane to ensure the correct analytical continuation of the original problem.

we review the proof of a conjecture concerning the reality of the spectra of certain -symmetric quantum mechanical systems , obtained via a connection between the theories of ordinary differential equations and integrable models . spectral equivalences inspired by the correspondence are also discussed .


Laplace pressure driven snap - off is a technique that is used to produce droplets for emulsions...

with the development of numerous techniques to produce micron - scale droplets , there has been a growing interest in exploring the physical mechanisms behind these methods . a greater understanding of which parameters are most important to droplet production can permit fine - tuning of existing techniques or modification of systems where droplet production is undesirable . laplace pressure driven snap - off relies upon an instability that forms when a confined dispersed phase is allowed to penetrate into a larger space filled with an immiscible continuous phase ( see fig . [ fig : schematic]a ) . the instability requires no viscous interaction , but is due entirely to changes in the curvature of the interface between the two phases , affecting the laplace pressure . we have previously found that the resulting droplets are highly monodisperse , as the system becomes unstable immediately after the protrusion of the dispersed phase reaches a critical size . the snap - off phenomenon has been studied and used to produce droplets in many different geometries . however , the case of ejecting the dispersed phase from a cylindrically symmetric tube is the simplest from a theoretical standpoint . , minimum radius of the flowing dispersed phase column within the nozzle , and radius of the growing droplet define the important length scales . the relevant pressures are the pressure of the bulk continuous phase , pressure of the dispersed phase in the growing droplet , pressure of the dispersed phase in the nozzle , and the pressure of the continuous phase in the collar around the dispersed phase . b ) schematic of these pressures along the length of the pipette . snapoff occurs if , which happens as grows , decreasing and the other pressures relative to the fixed pressure .,width=264 ] by neglecting pressure gradients within the dispersed phase , several groups have been able to provide a theoretical framework for droplet sizes in a quasi - static regime . the approximation of

We present a theoretical framework for the snap - off phenomenon in a quasi - static regime. The model is based on the theory of the dispersed phase and its dependence on the laplace pressure. We show that the system becomes unstable when the disperse phase penetrates into a larger space filled with an immiscible continuous phase. This instability is due to changes in the curvature of the interface between the two phases, affecting the la place pressure, which is due entirely to changes within the disPERED phase, and the pressure of the continuous.

laplace pressure driven snap - off is a technique that is used to produce droplets for emulsions and microfluidics purposes . previous predictions of droplet size have assumed a quasi - equilibrium low flow limit . we present a simple model to predict droplet sizes over a wide range of flow rates , demonstrating a rich landscape of droplet stability depending on droplet size and growth rate . the model accounts for the easily adjusted experimental parameters of geometry , interfacial tension , a


We present the thermopower and the resistivity of luybrhsi in the temperature range 3 k k

ybrhsi is a stoichiometric heavy - fermion ( hf ) metal with an extremely low antiferromagnetic ordering temperature of 70 mk. it crystallizes in the tetragonal thcrsi structure and has been investigated extensively due to its pronounced non - fermi liquid ( nfl ) properties at low . this behavior was attributed to a quantum critical point , which can be attained by application of a small magnetic field of 60 mt within the plane. at intermediate temperatures ( 10 - 300 k ) the properties of ybrhsi are determined by a competition of crystal electric field ( cef ) excitations and the kondo interaction . a knowledge of the corresponding characteristic energy scales and is essential for an understanding of the low - temperature properties of the compound . the nfl behavior dominates the thermodynamic and transport properties up to 10 k. notably , the electronic specific heat divided by exhibits a logarithmic increase upon cooling with a spin fluctuation temperature k. the corresponding entropy revealed a doublet ground state of the yb ions with a kondo temperature of approximately 17 k. the cef level scheme of ybrhsi was determined from inelastic neutron scattering : the multiplet of the yb is split into 4 doublets at energies corresponding to 0 - 200 - 290 - 500 k , respectively. the strong interplay between kondo effect and cef splitting manifests itself in the transport properties of the system . the temperature dependencies of both resistivity and thermopower exhibit a single large extremum around 100 k , which was attributed to scattering on the full yb multiplet . no signature corresponding to kondo scattering on the ground - state doublet at has been found in and . such behavior was observed and theoretically predicted for compounds , where the energy scales and are of the same order of magnitude , i.e. for systems near the crossover from the hf to the intermediate - valent ( iv ) regime. upon applying pressure , the kondo temperature of yb - based hf systems is

We present a new study of the non - fermi liquid ( nfl ) properties of ybrhsi at intermediate temperatures. The nebula is split into four doublets with a kondo temperature of approximately 17 k. This result is consistent with the observed behavior for the yrh ions in the tetragonal thcrsi structure.

we present the thermopower and the resistivity of luybrhsi in the temperature range 3 k k. is found to change from two minima for dilute systems ( ) to a single large minimum in pure ybrhsi . a similar behavior has also been found for the magnetic contribution to the resistivity . the appearance of the low- extrema in and is attributed to the lowering of the kondo scale with decreasing . the evolution of the characteristic energy scales for both the kondo effect and the crystal electric field sp


1-d eulerian vlasov - maxwell simulations are presented which show kinetic enhancement of...

the role of kinetic effects in stimulated raman backscatter ( srbs ) is of much current interest . srbs is the three - wave parametric coupling of a pump light wave ( the laser , labeled mode 0 ) to a counter - propagating daughter light wave ( mode 1 ) and co - propagating electron plasma wave ( epw , mode 2 ) , and satisfies the resonance conditions and . it may remove a substantial amount of energy from a high - intensity laser propagating through a plasma and create energetic electrons . srbs and other laser - plasma interactions must be sufficiently controlled for laser - driven inertial fusion to succeed . in the high - temperature plasmas expected on ignition experiments such as the national ignition facility ( nif ) and laser mgajoule ( lmj ) , linear theory of parametric instabilities predicts srbs to have a weak spatial gain rate due to the large ( ^{1/2}$ ] is the electron debye length ) and resulting heavy landau damping . however , recent experiments and kinetic simulations have shown srbs reflectivities well above coupled - mode convective gain levels . this kinetic inflation or enhancement of srbs is widely attributed to electron trapping in the epw potential well , which flattens the electron distribution function near the epw phase velocity . as has long been known , trapping reduces the epw damping rate and induces an amplitude - dependent frequency downshift . srbs saturation results from the competition of nonlinear effects including the damping reduction , frequency shift , pump depletion , and trapped particle instability , and possibly spatio - temporal chaos after ion modes build up near the laser entrance , among others . a theory for the onset of kinetic inflation and the resulting time - averaged reflectivity is not yet in hand , but would be of great value for designing laser fusion implosions . this current work is aimed at better understanding kinetic effects such as electron trapping in srbs for time scales and frequencies such that io

We present a theoretical study of the kinetic effects of stimulated raman backscatter ( srbs ) in the presence of electron trapping in the epw potential well. We show that the onset of kinetic inflation and the resulting time - averaged reflectivity are dependent on the amplitude - dependent frequency downshift, which is attributed to the interaction of nonlinear effects such as the damping reduction, frequency shift, and trapped particle instability.

1-d eulerian vlasov - maxwell simulations are presented which show kinetic enhancement of stimulated raman backscatter ( srbs ) due to electron trapping in regimes of heavy linear landau damping . the conventional raman langmuir wave is transformed into a set of beam acoustic modes [ l. yin _ et al . _ , phys . rev . e * 73 * , 025401 ( 2006 ) ] . for the first time , a low phase velocity electron acoustic wave ( eaw ) is seen developing from the self - consistent raman physics . backscatter of


We show that all generalized pollicott - ruelle resonant states of a topologically transitiv anosov...

let be a smooth , compact riemannian manifold without boundary . let be a smooth anosov vector field and let us denote by the flow on generated by and let be a smooth potential function . then we can define the following differential operator it is a well established approach to study the dynamical properties of anosov flows by the discrete spectrum of the operator , the so called pollicott - ruelle resonances . the fact that for volume preserving flows and real valued potentials , the operator is an unbounded , essentially self adjoint operator on might suggest , that has good spectral properties on . however , due to the lack of ellipticity has mainly continuous spectrum which carries little information on the dynamics of the flow . a very important progress was thus to construct banach spaces or hilbert spaces for anosov flows in which the operator has discrete spectrum in a sufficiently large region ( see also for analogous results for anosov diffeomorphism ) . more precisely , it has been shown that there is a family of hilbert spaces parametrized by such that for any and for sufficiantly large the operator acting on has discrete spectrum in the region . this discrete spectrum is known to be intrinsic to the anosov flow together with the potential function and does not depend on the sufficiantly large parameter ( see section [ sec : micro_ruelle ] for a more precise statement ) . accordingly we call a _ pollicott - ruelle resonance _ if it is an eigenvalue of on for sufficiently large and we call the space of _ pollicott - ruelle resonant states_. as is not anymore a normal operator on , there might exist also exist finite dimensional jordan blocks and given a ruelle resonance we denote by the maximal size of a corresponding jordan block and we call the space of _ generalized pollicott - ruelle resonant states_. the interest in these pollicott - ruelle resonances and their resonant states arises from the fact that they govern the decay of correlations . in orde

We study the dynamical properties of anosov flows by the discrete spectrum of the operator, the so called pollicott - ruelle resonances. In this paper we show that for any and for sufficiantly large the operator acting on has discrete Spectrum in a sufficiently large region. We also discuss the possibility of constructing hilbert spaces for anosian flows.

we show that all generalized pollicott - ruelle resonant states of a topologically transitiv anosov flow with an arbitrary potential , have full support .


The plasmon excitations in coulomb - coupled spherical two - dimensional electron gases ( s2degs )...

the year 1995 was the culmination of several years of the search for fullerene materials. it also marks the beginning of a whole new area of investigation into the optical and thermal properties of fullerene aggregates . from both an experimental and theoretical perspective , this branch of condensed matter physics is receiving international attention . consequently , the theory for the properties of interacting fullerenes is a subject of considerable interest. following the recent advances in production techniques such as solvent - assisted self - assembly, fullerenes can now be produced in specific quantities even to form thin films of fullerene - like mos nanoparticles and those achievements have stimulated renewed interest in these materials . additionally , the ability to control optical fields has now made it feasible to ascertain the plasmon excitations in pre - arranged arrays of fullerenes. the present paper has been stimulated by these exciting new developments , even though it employs a relatively simple model which is reasonable when the separation between the energy bands is large. additionally , our results may serve as a guide for explaining experimental studies. specifically , we are interested in calculating the plasma excitations of coulomb coupled spherical two - dimensional electron gases ( s2degs). here , we model three coupled spherical shells as shown in fig.[fig:1 ] . in our discussion below , we refer to the s2deg at the origin as " , and the one centered on the and -axis as `` '' and `` '' , respectively . this notation then allows us to label the coulomb matrix elements between spherical shells `` '' and `` '' with subscript `` '' , where . electron energy loss spectroscopy ( eels ) has been used to probe the plasmon excitations for concentric - shell fullerenes embedded in a film. furthermore , perfectly spherical shells were used in the theoretical modeling of the eels data and the agreement was good . the model of lucas , et al. was sho

We present a model for the plasma excitations of coulomb coupled spherical two - dimensional electron gases ( s2degs ) in a thin film of fullerenes embedded in mos nanoparticles. The model is based on the cous - and -axis, which allows us to calculate the plasmon excitation of s 2deg at the origin. We also use the s3deg as an example of a simple model for s2/d.

the plasmon excitations in coulomb - coupled spherical two - dimensional electron gases ( s2degs ) reveal an interesting dependence on the displacement vector between the centers of the spheres with respect to the axis of quantization for the angular momentum quantum number . specifically , plasmon modes for a bundle of three s2degs have been obtained within the random - phase approximation ( rpa ) . the inter - sphere coulomb interaction matrix elements and their symmetry properties were also i


We obtain the leading orders of the maximum and the minimum of local times for the simple random...

the theory of local times of random walks is very profound . it is well - known that local times of random walks have close relationships with the gaussian free field(gff ) . the connection goes back to . eisenbaum , kaspi , marcus , rosen , and shi gave a powerful equivalence in law called generalized second ray - knight theorem " ( see remark [ local - time - gff ] ) . using the theorem , ding , lee , and peres established a useful connection between the expected maximum of the gff and the cover time , and quite recently zhai strengthened the result by constructing a coupling of the occupation time filed and the gff ( see theorem [ zhai s thm ] ) . much efforts have been made to study local times of the simple random walk on . erds and taylor obtained an estimate on the maximum of local times of the simple random walk on by time . dembo , peres , rosen and zeitouni improved the result ; they gave the leading order of the maximum and estimated the number of favorite points " ( see also ) . okada obtained a corresponding estimate on frequently visited sites in the inner boundary of the random walk range . sznitman studied convergences of occupation time fields and related the fields to the gff . as mentioned above , works are closely linked to the study of extremes of the two - dimensional gff . bolthausen , deuschel , and giacomin obtained the leading order of its maximum ( see remark [ remark ] ) . daviaud estimated the number of points with large values of the gff ( see remark [ remark ] ) . in this paper , we study the maximum and the minimum of local times of the simple random walk on the two - dimensional torus at time proportional to the cover time . while similar work has been done in for the gff , one can not apply their results to deduce corresponding local time estimates , and indeed considerable amounts of efforts are needed to obtain such estimates . we also note that the exponents for the local times are different from those of the gff ( see theorem [

We study the maximum and minimum of local times of the simple random walk on the two - dimensional torus at time proportional to the cover time. We find that the maximum is the lowest value of the gaussian free field ( gff ), while the minimum is the highest value of its minimum.

we obtain the leading orders of the maximum and the minimum of local times for the simple random walk on the two - dimensional torus at time proportional to the cover time . we also estimate the number of points with large ( or small ) values of the local times . these are analogues of estimates on the two - dimensional gaussian free fields by bolthausen , deuschel , and giacomin [ ann . probab . , * 29 * ( 2001 ) ] and daviaud [ ann . probab . , * 34 * ( 2006 ) ] , but we have different exponen


We review the interaction in intermediate and high mass stars between their evolution and magnetic...

observations reveal that around 5 - 10% of intermediate - mass main - sequence ( ms ) stars ( 1.6 - 8 ) have magnetic fields of strength 300 g - 30 kg ( see donati & landstreet 2009 for a recent review of the so - called ` chemically peculiar ' ( cp ) , or ap and bp stars ) . the fields are large - scale and apparently static , i.e. they do not evolve at all over periods of decades , and their host stars rotate much more slowly than normal a stars . it is worthwhile to look at magnetic middle ms stars in the broader context of stellar evolution . stars form by gravitational collapse on a timescale of a few 0.1 myr , set by the free - fall time . at a size of a few 100 au , angular momentum leads to slower growth through quasi - static disk accretion . the proto - star shrinks towards the ms as a t tau star , and later , if massive enough , as a herbig aebe star . during early stages of collapse much magnetic flux may be retained , or lost via ambipolar diffusion , but it is not clear how to retain flux whilst the star is almost fully convective , or how the field of some herbig aebe stars might be related to the earlier t tau dynamo activity phase . on the ms , surface chemistry changes occur as a result of gravitational and radiatively driven atomic diffusion , which must compete with convection , meridional circulation and turbulent diffusion , mass loss from the surface , the magnetic field ( especially in the upper atmosphere and beyond ) , and possibly even accretion . the complications of this multi - dimensional competition probably explain why some stars with fossil fields are marked by very distinctive chemical peculiarities ( hence ` cp ' stars ) while other , hotter magnetic stars are not , but the details of the effects are still far from clear . however , the way in which different effects predominate with changes in stellar parameters such as mass , age and rotation rate make these stars excellent laboratories for the study of the various important int

We present a new study of magnetic middle - mass main - sequence ( ms ) stars with chemically peculiar fields. The field is large - scale and appears static, i. E. They do not evolve at all over periods of decades. In particular, the field does not change during early stages of collapse, and its host stars rotate much slower than normal a stars. We find that the field of some herbig aebe stars has a strong magnetic field of 300 g - 30 kg, which is consistent with the observed evolution of.

we review the interaction in intermediate and high mass stars between their evolution and magnetic and chemical properties . we describe the theory of ap - star ` fossil ' fields , before touching on the expected secular diffusive processes which give rise to evolution of the field . we then present recent results from a spectropolarimetric survey of herbig ae / be stars , showing that magnetic fields of the kind seen on the main - sequence already exist during the pre - main sequence phase , in


We investigate the properties of the host galaxies of x ray selected ( high frequency peaked ) bl...

bl lacertae objects are the most extreme class of active galactic nuclei ( agn ) , exhibiting strong , rapidly variable polarization and continuum emission , and core - dominated radio emission with apparent superluminal motion ( see e.g. kollgaard et al . 1992 for references ) . these properties have led to the commonly accepted view that bl lacs are dominated by doppler - boosted synchrotron emission from a relativistic jet nearly along our line - of - sight ( blandford & rees 1978 ) . the line emission of bl lacs is absent or weak , making their redshift determination rather difficult . in the current unified models of radio - loud agn ( e.g. urry & padovani 1995 ) , bl lacs are identified as low luminosity , core - dominated f - r i ( fanaroff & riley 1974 ) radio galaxies ( rg ) viewed nearly along the axis of the relativistically boosted jet . this model appears supported by the comparison of their extended radio luminosity and morphology ( e.g. perlman & stocke 1993 ) , host galaxy luminosity and morphology ( e.g. wurtz et al . 1996 ; hereafter wsy96 ) and space density and beamed luminosity functions ( e.g. padovani & urry 1990 ; morris et al . 1991 ; celotti et al . 1993 ) . knowledge of the properties of the host galaxies and environments where agn live is fundamental for the understanding of the formation of agn in galaxies . comparison of orientation - independent properties of bl lacs , such as the host galaxies and environment , with those of rgs , allow one to test the unified model based on orientation ( antonucci 1993 ; urry & padovani 1995 ) . the frequency of close companions will determine whether interactions are important for triggering of the bl lac activity , as seems to be the case for quasars ( e.g. heckman 1990 ; hutchings & neff 1992 ) . possible cosmological evolution in the properties of the hosts and environments can be studied by comparing agn properties at different redshifts . finally , the alternative gravitational lensing hypothes

We present a new model for the formation of active galactic nuclei ( agn ) in bl lacertae objects. This model is based on the unified model of a b - lacerrae object with a high redshift and a low luminosity, core - dominated radio emission. The model is consistent with the observed bbl - galaxies, which are found to be dominated by doppler - enhanced synchrotron emission from a relativistic jet near our.

we investigate the properties of the host galaxies of x ray selected ( high frequency peaked ) bl lac objects using a large and homogeneous data set of high spatial resolution band observations of 52 bl lacs in the emss and slew samples . the redshift distribution of the bl lacs ranges from z = 0.04 to z.7 , with average and median redshifts z = 0.26 and z = 0.24 , respectively . eight objects are at unknown redshift . we are able to resolve 45 objects out of the 52 bl lacs . for all the well re


We carry out an analysis of the cosmological perturbations in general relativity for three...

cosmology has made a long way on the last years with the impressive amount of observations and theoretical advancements . yet , cosmology faces many challenging questions like the fundamental cause of the recent acceleration of the universe as predicted by sneia observations almost twenty years ago , and afterwards confirmed by several type of cosmological and astrophysical observations ( see for example for a recent account on this issue ) . the simplest approach is to assume a cosmological constant that started recently dominating the late - time energy density budget of the universe which is in agreement with the current observations . but then the issues _ of why is it so tiny ? _ and _ why this cosmological constant has begun to be important only right now ? _ have to be addressed as well ( see for example : ) . another , equally important , issue is what happens if the cosmological constant is not quite constant ? this has lead to a great interest in exploring other possible scenarios to explain the late - time acceleration of the cosmos by invoking either an additional matter component in the universe , which we name dark energy ( de ) , or by modifying appropriately the laws of gravity ( for a recent account on this issue see , for example , and the extensive list of references provided therein ) . we will focus on the third question : _ what happens if the cosmological constant is not quite constant ? _ more precisely , we will address this question on the framework of the cosmological perturbations and for some de models whose equations of state ; i.e. , the ratio between its pressure and its energy density , deviate slightly from the one corresponding to a cosmological constant . before proceeding let us remind the following well known fact : if the equation of state ( eos ) of de deviates from -1 , the universe fate might be quite different from the one corresponding to an empty de sitter universe . in particular , if the equation of state of dark energy

We consider the cosmological constant of dark energy ( de ) and its equations of state. We find that the eos of dark energies are not quite constant, but they are still very small. In particular, we show that the equation of state of darkenergies is much smaller than the one corresponding to an empty de sitter universe.

we carry out an analysis of the cosmological perturbations in general relativity for three different models which are good candidates to describe the current acceleration of the universe . these three set - ups are described classically by perfect fluids with a phantom nature and represent deviations from the most widely accepted cdm model . in addition , each of the models under study induce different future singularities or abrupt events known as ( i ) big rip , ( ii ) little rip and ( iii ) l


If the is a loosely - bound molecule of the charm mesons and , it can decay through the decay of a...

the is a narrow resonance near mev discovered by the belle collaboration in electron - positron collisions through the -meson decay followed by the decay . its existence has been confirmed by the cdf and d collaborations through its inclusive production in proton - antiproton collisions and by the babar collaboration through the discovery mode . the combined measurement of the mass of the is which is within 1 mev of the threshold for the charm mesons and . the presence of the among the decay products of the motivates its interpretation as a charmonium state with constituents . two possibilities motivated by the proximity of the mass in eq . ( [ xmass ] ) to the threshold are a hadronic molecule with constituents and a `` cusp '' at the threshold associated with strong coupling to or . other proposed interpretations include a tetraquark with constituents , a `` hybrid charmonium '' state with constituents , a glueball with constituents , and a diquark - antidiquark bound state with constituents . the interpretation as a molecule is particularly predictive because the small binding energy implies that the molecule has universal properties that are completely determined by the binding energy . the small binding energy can be further exploited through factorization formulas for production and decay rates of the . measurements of the decays of the can be used to determine its quantum numbers and narrow down the possibilities . the upper bound on the decay width of the is which is much narrower than other charmonium states above the threshold . the product of the branching fractions associated with the discovery channel is \ , {  br}[x j/^+^- ] = ( 1.3  0.3 )  10^{-5}. \ ] ] the invariant mass distribution of the two pions from the decay seems to peak near the upper endpoint , which suggests that the pions come from a virtual resonance . recently the belle collaboration has observed the in the decay mode with the branching ratio  {  br}[x j/ \ , ^+^- ] } & = & 1.0  0.4_{

We present a new analysis of the decays of the is in the decay mode with the branching ratio. The mass distribution of the two pions from the decay seems to peak near the upper endpoint, which suggests that the pion is from a virtual resonance.

if the is a loosely - bound molecule of the charm mesons and , it can decay through the decay of a constituent in a hadronic channel with a nearby threshold , such as or . the differential decay rates of the into , , , and are calculated in terms of and coupling constants using an effective lagrangian that reproduces the decay rates of the and the . the dependence of the coupling constants on the binding energy and the total width of the is determined by a factorization formula . results from a


A survey of problems , conjectures , and theorems about quasi - isometric classification and...

our story begins with a theorem of gromov , proved in 1980 . [ theorem : polynomial : growth ] let be any finitely generated group . if has polynomial growth then is virtually nilpotent , i.e. has a finite index nilpotent subgroup . gromov s theorem inspired the more general problem ( see , e.g. ) of understanding to what extent the asymptotic geometry of a finitely generated solvable group determines its algebraic structure . one way in which to pose this question precisely is via the notion of quasi - isometry . a ( coarse ) _ quasi - isometry _ between metric spaces is a map such that , for some constants : 1 . for all . the -neighborhood of is all of . and are _ quasi - isometric _ if there exists a quasi - isometry . note that the quasi - isometry type of a metric space is unchanged upon removal of any bounded subset of ; hence the term `` asymptotic '' . quasi - isometries are the natural maps to study when one is interested in the geometry of a group . in particular : the word metric on any f.g . group is unique up to quasi - isometry . any injective homomorphism with finite index image is a quasi - isometry , as is any surjective homomorphism with finite kernel . the equivalence relation generated by these two types of maps can be described more compactly : two groups are equivalent in this manner if and only if they are _ weakly commensurable _ , which means that there exists a group and homomorphisms , each having finite kernel and finite index image ( proof : show that `` weakly commensurable '' is in fact an equivalence relation ) . this weakens the usual notion of _ commensurability _ , i.e. when and have isomorphic finite index subgroups . weakly commensurable groups are clearly quasi - isometric . any two cocompact , discrete subgroups of a lie group are quasi - isometric . there are cocompact discrete subgroups of the same lie group which are not weakly commensurable , for example arithmetic lattices are not weakly commensurable to non - arithmetic o

We study the equivalence relation between two groups of a finitely generated group and a surjective homomorphism with finite index image. We show that the -neighborhood of is all of. And are _ quasi - isometric _ if there exists a quasi.

a survey of problems , conjectures , and theorems about quasi - isometric classification and rigidity for finitely generated solvable groups .


Logic - qubit entanglement has attracted much attention in both quantum communication and quantum...

entanglement is of very importance in most quantum communication protocols . the typical quantum communication protocols such as quantum teleportation , quantum key distribution ( qkd ) , quantum secure direct communication ( qsdc ) and other important quantum communication protocols all require entanglement to set up quantum channel . in a standard quantum communication protocol , one of the communication parties should create the entanglement locally and distribute it to another to share entanglement . unfortunately , during the entanglement distribution , the entanglement will suffer from the noise . the noise will make the photon loss and decoherence . if the photon is lost , the task of communication is a failure . on the other hand , if the entanglement is decoherence , it will induce error , which will decrease the communication efficiency . more seriously , it will make the communication insecure . quantum repeaters and quantum state amplification are two powerful approaches to overcome the obstacle of photon loss . quantum repeaters can connect the short distance entanglement to long distance entanglement . there are some important works of quantum repeaters in various physical systems , such as nitrogen vacancy ( nv ) centers in diamond , atomic ensembles , and optical microcavities . quantum state amplification is used to increase the probability of the single photon after transmission . there are also some important theory and experiment works in quantum state amplification , such as the single qubit amplification , the single qubit amplification encoded in polarization and time - bin degrees of freedom , single - photon entanglement amplification , and so on . on the other hand , entanglement concentration and entanglement purification are two important approaches to recover the degraded entangled states to maximally entangled states and high quality entangled states , respectively . compared with entanglement concentration , entanglement purification w

We study the entanglement distribution in quantum communication protocols. We find that the entangled states are degraded by the noise and the photon loss. The resulting en Tang - symmetries are compared with the corresponding en - state amplification.

logic - qubit entanglement has attracted much attention in both quantum communication and quantum computation . here , we present an efficient protocol to distill the logic - qubit entanglement with the help of cross - kerr nonlinearity . this protocol not only can purify the logic bit - flip error and logic phase - flip error , but also can correct the physical bit - flip error completely . we use cross - kerr nonlinearity to construct quantum nondemolition detectors . our distillation protocol


We study the possible relationship between the saturation properties of nuclear matter and the...

the effective nucleon - nucleon ( nn ) interaction is expected , on physical grounds , to be intrinsically non - local . the quark structure of nucleons implies that the potential between two interacting nucleons can not be expressed only in terms of the center of mass degree of freedom , at least for distances smaller than twice the nucleon radius . even a description of the nn interaction in terms of one - boson exchange processes introduces some degree of non - locality . for practical purposes , however , it is convenient to have a local ( energy independent ) nn interaction , to be used in numerical applications . the modeling of the nn interaction by a local potential , with possible guidance from meson exchange processes , has been extremely successful in reproducing the nn experimental phase shifts and deuteron properties . this approach has developed for many years and has reached a high degree of sophistication . it has been established by now that these local nn potentials , which are essentially phase equivalent , give slightly different results for the three- and four - nucleon systems . furthermore , in general they underestimate the binding energy and do not give the correct values for some polarization observables . this drawback has been usually overcome by introducing three - body forces , which can be again justified by the non - elementary nature of the nucleon . actually three - body forces can be generated also by meson - exchange processes of higher order , where the nucleon is excited in the intermediate states of the interaction processes or meson - meson couplings are introduced . both non - locality and three - body forces can be considered to have a common origin , the inner structure of the nucleon . however , one can not fully reduce one to another , since non - locality has definite effects already at the two - body level , e.g. a non - local potential can not be equivalent , in general , to an energy independent local potential . furt

We present a new approach to the modeling of the nucleon - nucleonal interaction by a local potential, with possible guidance from meson exchange processes. This approach is based on the theory of the three - body force and the non - locality of the two - boson exchange process. It is shown that the nonlocality of these two _ nn _ potentials can be reduced to a level of energy independent, which is consistent with the experimental phase shifts and deuteron properties.

we study the possible relationship between the saturation properties of nuclear matter and the inclusion of non - locality in the nucleon - nucleon interaction . to this purpose we compute the saturation curve of nuclear matter within the bethe - brueckner - goldstone theory using a recently proposed realistic non - local potential , and compare it with the corresponding curves obtained with a purely local realistic interaction ( argonne v ) and the most recent version of the one - boson exchang


We study popular local search and greedy algorithms for standard machine scheduling problems

the performance guarantee of local search and greedy algorithms for scheduling problems is well studied and understood . for most algorithms , matching upper and lower bounds on their approximation ratio are known . the lower bounds are often somewhat contrived , however , and it is questionable whether they resemble typical instances in practical applications . for that reason , we study these algorithms in the framework of smoothed analysis , in which instances are subject to some degree of random noise . by doing so , we find out for which heuristics and scheduling variants the lower bounds are robust and for which they are fragile and not very likely to occur in practical applications . since pure nash equilibria can be seen as local optima , our results also imply a new bound on the smoothed price of anarchy , showing that known worst - case results are too pessimistic in the presence of noise . let us first describe the scheduling problems that we study . we assume that there is a set of jobs each of which needs to be processed on one of the machines from the set . all jobs and machines are available for processing at time . the goal is to schedule the jobs on the machines such that the _ makespan _ , i.e. , the time at which the last job is completed , is minimized . each machine has a speed and each job has a processing requirement . the time it takes to fully process job on machine depends on the machine environment . we consider two machine environments . the first one is the one of _ uniform parallel machines _ , also known as _ related machines _ : . the second machine environment that we consider is the one of _ restricted related machines _ : a job is only allowed to be processed on a subset of the machines . the processing time is therefore if and if . an instance of a scheduling problem consists of the machine speeds , the processing requirements , and in the restricted case the allowed machine set for every job . a special case for both machine envi

We study the performance guarantees of local search and greedy algorithms for scheduling problems. We consider two machine environments: the one of uniform parallel machines, also known as _ related machines _, and the one with restricted related machines ( ). The processing time is therefore if and if. An instance of a scheduling problem consists of the machine speeds, the processing requirements,,and in the restricted case the allowed machine set for every job.

we study popular local search and greedy algorithms for standard machine scheduling problems . the performance guarantee of these algorithms is well understood , but the worst - case lower bounds seem somewhat contrived and it is questionable whether they arise in practical applications . to find out how robust these bounds are , we study the algorithms in the framework of smoothed analysis , in which instances are subject to some degree of random noise . while the lower bounds for all schedulin


We introduce the idea of discontinuous electric and magnetic fields at a boundary to design and...

one of the most basic boundary conditions in electromagnetic theory concerns the interface between two different materials . as propagating waves traverse the boundary they are reflected and refracted with different amplitudes . this occurs specifically because the tangential electric and magnetic fields across the boundary are conserved . one way to interpret this physical behaviour is that by maintaining the continuity of the tangential fields across a material boundary one can subsequently alter and control the propagation of electromagnetic fields in a region . this fact forms the basis for engineering and designing many electromagnetic and optical devices , including waveguides , lenses and scatterers . + + because this idea is so fundamental to electromagnetic theory , the continuity of the fields across interfaces is often taken for granted . however it is worth asking a simple question . what if instead of using material interfaces , and thus continuous fields , to engineer desired wave propagation effects we could somehow impose discontinuities in the field , and thereby alter the propagation and amplitude of the wave . in this scenario , a desired discontinuity in the electromagnetic field is introduced across a boundary by purposely engineering the boundary itself . here , we are building on work done in where we introduced a discontinuous field at a boundary to cloak an object . we now seek to generalize this idea by exploring in more detail how such boundaries are realized , and how can they be used to alter and control the electromagnetic field in a variety of scenarios . + + specifically , we approach this problem by proposing a general way to impose a discontinuity using currents at an interface . these currents will act like a huygens source which radiates the desired wavefront to create the discontinuity in the electromagnetic field . we first propose two ways to implement our discontinuity , one active and one passive . using the active method we

We propose a general way to impose a discontinuity in the electromagnetic field by using currents at an interface. These currents will act like a huygens source which radiates the desired wavefront to create the discontinuity. We first propose two ways to implement our discontinuity and one passive method.

we introduce the idea of discontinuous electric and magnetic fields at a boundary to design and shape wavefronts in an arbitrary manner . to create this discontinuity in the field we use electric and magnetic currents which act like a huygens source to radiate the desired wavefront . these currents can be synthesized either by an array of electric and magnetic dipoles or by a combined impedance and admittance surface . a dipole array is an active implementation to impose discontinuous fields whi


We consider the activated random walk model on general vertex - transitive graphs

in this paper we consider the activated random walk ( arw ) model on a vertex - transitive graph . this is a continuous - time interacting particle system with conserved number of particles , where each particle can be in one of two states : a ( active ) or s ( inactive , sleeping ) . initially , the number of particles at each vertex of is an independent bernoulli random variable of parameter $ ] , usually called the _ particle density _ , and all particles are of type a. each a - particle performs an independent , continuous time random walk on with jump rate , and with each jump being to a uniformly random neighbor . moreover , every a - particle has a poisson clock of rate ( called the _ sleeping rate _ ) . when the clock of a particle rings , if the particle does not share the site with other particles , the transition occurs ( that is , the particle becomes of type s ) ; otherwise nothing happens . each s - particle does not move and remains sleeping until another particle jumps into its location . at such an instant , the s - particle turns into type a , giving the transition a+s 2a . for any given , it is expected that arw undergoes a phase transition as varies . for example , if is very small , there is a lot of empty space between particles , which allows each particle to eventually fall asleep ( that is , turn into type ) and never become active again . when this happens , we say that _ arw fixates_. when this does not happen , we say that _ arw is active_. this case is expected to occur when is large , since active particles will repetitively jump on top of other particles , `` waking up '' the ones that had turned into type . in a seminal paper , rolla and sidoravicius showed that this process satisfies a 0 - 1 law ( i.e. , the process is either active or fixated with probability 1 ) and is monotone with respect to . this gives the existence of a critical value such that arw is active almost surely for all , and fixates almost surely for all . though ,

We consider the activated random walk ( arw ) model on a vertex - transitive graph. This is a continuous - time interacting particle system with conserved number of particles, where each particle can be in one of two states: a ( active ) or s ( inactive ). Initially, the number of particle at each vertex of is an independent bernoulli random variable of parameter $ ], and all particles are of type a. Each a- particle performs an independent random walk on with jump rate.

we consider the activated random walk model on general vertex - transitive graphs . a central question in this model is whether the critical density for sustained activity is strictly between 0 and 1 . it was known that on , , and that on for small enough sleeping rate . we show that as in all transient graphs , implying that for small enough sleeping rate . we also show that for any sleeping rate in any graph in which simple random walk has positive speed . furthermore , we prove that in any am


We have theoretically designed three families of the half - metallic ( hm ) antiferromagnets ( afm...

half - metallic ( hm ) ferromagnets ( fm ) was first discovered by de groot , _ et al . _ , based on their band structure calculations for magnetic semi - heusler compounds nimnsb and ptmnsb . shortly afterwards , other magnetic materials such as feo and cro were also found to be half - metals . half - metallic materials are characterized by the coexistence of metallic behaviour for one electron spin and insulating behaviour for the other . their electronic density of states is completely spin polarized at the fermi level , and the conductivity is dominated by these metallic single - spin charge carriers . therefore , half - metallic materials offer potential technological applications such as a single - spin electron source , and high - efficiency magnetic sensors . in this work , we search for another kind of hm materials with first - principles calculations . in a hm material , the spin magnetic moment per unit cell is quantized , i.e. , an integer number times bohr magneton ( ) . it may occur that this integer for some hm materials is zero this situation has been called half - matellic antiferromagnetism . most properties such as full spin - polarized conduction electrons , zero spin susceptibility , and no stoner continuum , of these hm antiferromagnts ( afm ) are the same as those of the hm - fms discussed above . however , there is one important difference : a hm - afm produces no macroscopic magnetic field . therefore , a hm - af could support 100% spin polarized charge transport without any net magnetization . furthermore , since there is no symmetry operation ( translation plus spin flip ) that connects its spin - up and spin - down bands , a hm - afm is qualitatively different from a conventional afm such as bcc cr . because of their unique properties mentioned above , hm - afms have recently attracted considerable attention . furthermore , they could be used as , e.g. , a probe of the spin - polarized scanning tunneling microscope without perturbing the

We study the properties of half - metallic ( hm ) antiferromagnets ( afms ) with first - principles calculations. In this work, we find that a hM - aF can support 100% spin polarized charge transport without any net magnetization.

we have theoretically designed three families of the half - metallic ( hm ) antiferromagnets ( afm ) , namely , lavoso , lamotco and lamoreo ( = ca , sr , ba ) , based on a systematic _ ab initio _ study of the ordered double perovskites lao with the possible and pairs from all the 3 , 4 and 5 transtion metal elements being considered . electronic structure calculations based on first - principles density - functional theory with generalized gradient approximation ( gga ) for more than sixty dou


A complete description of the multitudinous ways in which quantum particles can be entangled...

the simplest form of finite - dimensional system capable of exhibiting the fundamental , holistic property of entanglement``that feature of quantum formalism which makes it impossible to simulate quantum correlations within any classical formalism '' is that composed of a pair of two - level systems ( quantum bits or `` qubits '' ) . the joint state of two qubits is describable ( ) by a density matrix , that is a hermitian matrix ( its transpose equalling its complex conjugate ) having its four nonnegative diagonal entries ( probabilities)as well as its four nonnegative eigenvalues summing to one . the entirety of such density matrices with their entries restricted to real values which will be our principal subject of analysis here forms a nine - dimensional convex set . we note that density matrices with real entries have been termed `` rebits '' . endowing the nine - dimensional set of pairs of rebits with hilbert - schmidt ( hs ) ( euclidean / flat ) measure , we arrive at the following trio of computational results . the three are : ( 1 ) the average value or mean ( first moment ) of the ( necessarily nonnegative ) determinant of , denoted ( ) , is ; ( 2 ) the mean of the determinant of the partial transpose ( pt ) of negative values of which , by the celebrated results of peres and the horodecki family , are fully equivalent ( for qubit - qubit systems as well as qubit-_qutrit _ systems , representable by density matrices ) to the entanglement / nonseparability of is ; and ( 3 ) the mean of the product of these two determinants , that is ( by the cauchy - binet [ gram s ] theorem ) , is zero . ( the partial transpose identifiable with the antiunitary operation of time - reversal ( cf . )of a matrix can be obtained simply by transposing in place its four blocks . ) so , by assigning to each generic real density matrix , a value equal to this product of determinants , we find that the total ( but yet undetermined , necessarily negative ) value allotted to the ent

We study the entanglement properties of two qubits in a convex set of density matrices with real entries. We find that the mean of the determinant of the partial transpose of negative values is zero, and the mean is equal to the euclidean / flat measure of the average value of the nonnegative determinants of is.

a complete description of the multitudinous ways in which quantum particles can be entangled requires the use of high - dimensional abstract mathematical spaces . we report here a particularly interesting feature of the nine - dimensional convex set endowed with hilbert - schmidt ( euclidean / flat ) measure composed of two - rebit ( ) density matrices ( ) . to each is assigned the product of its ( nonnegative ) determinant and the determinant of its partial transpose negative values of which ,


Motivated by charge balancing constraints for rank modulation schemes , we introduce the notion of...

we consider a new constraint on permutations that requires moving averages of symbols to be closely concentrated around the mean running average . this constraint and the resulting coding schemes aim to balance charges across cells in rank modulation systems for flash memories . balanced codes may also potentially aid in detecting and correcting errors . this can be accomplished by monitoring whether the balancing constraint is satisfied during the decoding process . hence , the constraint complements existing constraints imposed so as to contain cross - leakage between neighboring cells . the permutation balancing constraint may also be seen as a block - by - block extension of classical bounded running digital sum codes , and some of the construction ideas pursued were inspired by the well known knuth s balancing algorithm . the constraint may be succinctly described as follows . let be a fixed positive integer , and let =\{{1,2, , n\}}$ ] . for any two non - negative integers , we use $ ] to denote the set and we use to denote the set of permutations of length . we are concerned with studying codes , where $ ] , defined as follows : if and only if for every and , one has here , takes values in the interval $ ] and is allowed to be a function of and . we refer to the constraint in as a _ balancing constraint _ , as it requires any -consecutive sum of elements in a permutation to stay close to the mean -consecutive sum , which equals . a constraint related to the balancing constraint was studied under the name of _ low - discrepancy permutation constraint _ in a handful of papers . the authors of studied the problem of finding _ a smallest discrepancy permutation_. in particular , they defined the discrepancy of a permutation according to and focused their attention on computing they showed that for any choice of the parameters and . in contrast to the work pertaining to permutation discrepancy , our work is not concerned with finding the smallest discrepancy permu

We consider a new constraint on permutations that requires moving averages of symbols to be closely concentrated around the mean running average. This constraint and the resulting coding schemes aim to balance charges across cells in rank modulation systems for flash memories. Hence, the constraint complements existing constraints imposed so as to contain cross - leakage between neighboring cells. Thus, we consider the problem of finding _ a smallest discrepancy permu _ in a handful of papers.

motivated by charge balancing constraints for rank modulation schemes , we introduce the notion of balanced permutations and derive the capacity of balanced permutation codes . we also describe simple interleaving methods for permutation code constructions and show that they approach capacity .