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\ mathfrak { g } ( \ mathbf { c } ( r ) ) $ ) holds for $ r $ if and only if the $ n $ - th power of the ghost ideal in the derived category $ \ mathbf { d } ( r ) $ is zero if and only if the global dimension of $ r $ is less than $ n. $ if $ r $ is coherent, then the generating hypothesis holds for $ r $ if and only if $ r $ is von neumann regular. | arxiv:2411.05250 |
these notes are based on a series of three lectures given ( online ) by the first named author at the workshop " higher structures and operadic calculus " at crm barcelona in june 2021. the aim is to give a concise introduction to rational homotopy theory through the lens of higher structures. the rational homotopy type of a simply connected space of finite type is modeled by a $ c _ \ infty $ - algebra structure on the rational cohomology groups, or alternatively an $ l _ \ infty $ - algebra structure on the rational homotopy groups. the first lecture is devoted to explaining these models and their relation to the classical models of quillen and sullivan. the second lecture discusses the relation between koszul algebras, formality and coformality. the main result is that a space is formal if and only if the rational homotopy $ l _ \ infty $ - algebra is koszul and, dually, a space is coformal if and only if the cohomology $ c _ \ infty $ - algebra is koszul. for spaces that are both formal and coformal, this collapses to classical koszul duality between lie and commutative algebras. in the third lecture, we discuss certain higher structure in the rational homotopy theory of automorphisms of high dimensional manifolds, discovered by berglund and madsen. the higher structure in question is kontsevich ' s lie graph complex and variants of it. | arxiv:2310.11824 |
in this paper we provide the answer to the following question : given a noisy channel and epsilon > 0, how many bits can be transmitted with an error of at most epsilon by a single use of the channel? | arxiv:cs/0608018 |
we study the behavior of errors in the quantum simulation of spin systems with long - range multi - body interactions resulting from the trotter - suzuki decomposition of the time - evolution operator. we identify a regime where the floquet operator underlying the trotter decomposition undergoes sharp changes even for small variations in the simulation step size. this results in a time evolution operator that is very different from the dynamics generated by the targeted hamiltonian, which leads to a proliferation of errors in the quantum simulation. these regions of sharp change in the floquet operator, referred to as structural instability regions, appear typically at intermediate trotter step sizes and in the weakly - interacting regime, and are thus complementary to recently revealed quantum chaotic regimes of the trotterized evolution ( sieberer et al., npj quantum information 5, 1 ( 2019 ) ). we characterize these structural instability regimes in $ p $ - spin models, transverse - field ising models with all - to - all $ p $ - body interactions, and analytically predict their occurrence based on unitary perturbation theory. we further show that the effective hamiltonian associated with the trotter decomposition of the unitary time - evolution operator, when the trotter - step size is chosen to be in the structural instability region, is very different from the target hamiltonian, which explains the large errors that can occur in the simulation in the regions of instability. these results have implications for the reliability of near - term gate - based quantum simulators, and reveal an important interplay between errors and the physical properties of the system being simulated. | arxiv:2110.03568 |
in deep reinforcement learning ( rl ) models trained using gradient - based techniques, the choice of optimizer and its learning rate are crucial to achieving good performance : higher learning rates can prevent the model from learning effectively, while lower ones might slow convergence. additionally, due to the non - stationarity of the objective function, the best - performing learning rate can change over the training steps. to adapt the learning rate, a standard technique consists of using decay schedulers. however, these schedulers assume that the model is progressively approaching convergence, which may not always be true, leading to delayed or premature adjustments. in this work, we propose dynamic learning rate for deep reinforcement learning ( lrrl ), a meta - learning approach that selects the learning rate based on the agent ' s performance during training. lrrl is based on a multi - armed bandit algorithm, where each arm represents a different learning rate, and the bandit feedback is provided by the cumulative returns of the rl policy to update the arms ' probability distribution. our empirical results demonstrate that lrrl can substantially improve the performance of deep rl algorithms for some tasks. | arxiv:2410.12598 |
the sign uncertainty principle of bourgain, clozel & kahane asserts that if a function $ f : \ mathbb { r } ^ d \ to \ mathbb { r } $ and its fourier transform $ \ widehat { f } $ are nonpositive at the origin and not identically zero, then they cannot both be nonnegative outside an arbitrarily small neighborhood of the origin. in this article, we establish some equivalent formulations of the sign uncertainty principle, and in particular prove that minimizing sequences exist within the schwartz class when $ d = 1 $. we further address a complementary sign uncertainty principle, and show that corresponding near - minimizers concentrate a universal proportion of their positive mass near the origin in all dimensions. | arxiv:2003.10765 |
we study the mean - field theory of charge - density wave ( cdw ) order in a layered system, including the effect of the long - range coulomb interaction and of screening by uncondensed electrons. we particularly focus on the conditions necessary for an ` ` extraordinary ' ' transition, in which the surface orders at a higher temperature, and is more likely to be commensurate, than the bulk. we interpret recent experiments on naccoc as indicating the presence of commensurate cdw at the surface that is not present in the bulk. more generally, we show that poor screening of the coulomb interaction tends to stabilize incommensurate order, possibly explaining why the cdw order in lsco and nbse2 remains incommensurate to t - > 0, despite the small magnitude of the incommensurability. | arxiv:cond-mat/0501654 |
we investigate sarnak ' s conjecture on the m \ " obius function in the special case when the test function is the indicator of the set of integers for which a real additive function assumes a given value. | arxiv:1709.01194 |
the four major approximation schemes devised to study the modification of jets in dense matter are outlined. the comparisons are restricted to basic assumptions and approximations made in each case and the calculation methodology used. emergent underlying similarities between apparently disparate methods brought about by the approximation schemes are exposed. parameterizations of the medium in each scheme are discussed in terms of the transport coefficient $ \ hat { q } $. discrepancies between the estimates obtained from the four schemes are discussed. recent developments in the basic theory and phenomenology of energy loss are highlighted. | arxiv:nucl-th/0702066 |
training deep neural models in the presence of corrupted supervision is challenging as the corrupted data points may significantly impact the generalization performance. to alleviate this problem, we present an efficient robust algorithm that achieves strong guarantees without any assumption on the type of corruption and provides a unified framework for both classification and regression problems. unlike many existing approaches that quantify the quality of the data points ( e. g., based on their individual loss values ), and filter them accordingly, the proposed algorithm focuses on controlling the collective impact of data points on the average gradient. even when a corrupted data point failed to be excluded by our algorithm, the data point will have a very limited impact on the overall loss, as compared with state - of - the - art filtering methods based on loss values. extensive experiments on multiple benchmark datasets have demonstrated the robustness of our algorithm under different types of corruption. | arxiv:2102.06735 |
we develop a theoretical description of transport through quantum dots connected to reservoirs via spin - polarized ballistic contacts. rate equations account for spin accumulation inside the dot, electron - electron interactions, and stochastic fluctuations. it is shown that both the ac response ( admittance ) and the frequency - dependent shot noise are governed by spin - flip scattering, which can be used to detect spin polarization and spin - flip processes in the dot. | arxiv:cond-mat/0309634 |
quantum key distribution ( qkd ) is often, more correctly, called key growing. given a short key as a seed, qkd enables two parties, connected by an insecure quantum channel, to generate a secret key of arbitrary length. conversely, no key agreement is possible without access to an initial key. here, we consider another fundamental cryptographic task, commitments. while, similar to key agreement, commitments cannot be realized from scratch, we ask whether they may be grown. that is, given the ability to commit to a fixed number of bits, is there a way to augment this to commitments to strings of arbitrary length? using recently developed information - theoretic techniques, we answer this question to the negative. | arxiv:1105.1165 |
we prove the characteristic zero case of zilber ' s restricted trichotomy conjecture. that is, we show that if $ \ mathcal m $ is any non - locally modular strongly minimal structure interpreted in an algebraically closed field $ k $ of characteristic zero, then $ \ mathcal m $ itself interprets $ k $ ; in particular, any non - 1 - based structure interpreted in $ k $ is mutually interpretable with $ k $. notably, we treat both the ` one - dimensional ' and ` higher - dimensional ' cases of the conjecture, introducing new tools to resolve the higher - dimensional case and then using the same tools to recover the previously known one - dimensional case. | arxiv:2209.00730 |
does circumventing the curvature singularity of the kerr black hole affects the timescale of the scalar cloud formation around it? by definition, the scalar cloud, forms a gravitational atom with hydrogen - like bound states, lying on the threshold of a massive scalar field ' s superradiant instability regime ( time - growing quasi - bound states ) and beyond ( time - decaying quasi - bound states ). by taking a novel type of rotating hollow regular black hole proposed by simpson and visser which unlike its standard rivals has an asymptotically minkowski core, we address this question. the metric has a minimal extension relative to the standard kerr, originating from a single regularization parameter $ \ ell $, with length dimension. we show with the inclusion of the regularization length scale $ \ ell $ into the kerr spacetime, without affecting the standard superradiant instability regime, the timescale of scalar cloud formation gets shorter. since the scalar cloud after its formation, via energy dissipation, can play the role of a continuum source for gravitational waves, such a reduction in the instability growth time improves the phenomenological detection prospects of new physics because the shorter the time, the more astrophysically important. | arxiv:2210.06861 |
we investigate aspects of quantum cosmology in relation to string cosmology systems that are described in terms of the dirac - born - infeld action. using the silverstein - tong model, we analyze the wheeler - dewitt equation for the rolling scalar and gravity as well for $ r \ times { s ^ 3 } $ universe, by obtaining the wave functions for all dynamical degrees of freedom of the system. we show, that in some cases one can construct a time dependent version of the wheeler - dewitt ( wdw ) equation for the moduli field $ \ phi $. we also explore in detail the minisuperspace description of the rolling tachyon when non - minimal gravity tachyon couplings are inserted into the tachyon action. | arxiv:hep-th/0511270 |
gravitational theories with multiple scalar fields coupled to the metric and each other - - - a natural extension of the well studied single - scalar - tensor theories - - - are interesting phenomenological frameworks to describe deviations from general relativity in the strong - field regime. in these theories, the $ n $ - tuple of scalar fields takes values in a coordinate patch of an $ n $ - dimensional riemannian target - space manifold whose properties are poorly constrained by weak - field observations. here we introduce for simplicity a non - trivial model with two scalar fields and a maximally symmetric target - space manifold. within this model we present a preliminary investigation of spontaneous scalarization for relativistic, perfect fluid stellar models in spherical symmetry. we find that the scalarization threshold is determined by the eigenvalues of a symmetric scalar - matter coupling matrix, and that the properties of strongly scalarized stellar configurations additionally depend on the target - space curvature radius. in preparation for numerical relativity simulations, we also write down the $ 3 + 1 $ decomposition of the field equations for generic tensor - multi - scalar theories. | arxiv:1505.07462 |
this article provides extensions to existing path - velocity decomposition based time optimal trajectory planning algorithm \ cite { kant1986toward } to scenarios in which agents move in 2d obstacle environment under double integrator dynamics with drag term ( damped double integrator ). particularly, we extend the idea of a tangent graph \ cite { liu1992path } to $ \ calc ^ 1 $ - tangent graph to find continuously differentiable ( $ \ calc ^ 1 $ ) shortest path between any two points. $ \ calc ^ 1 $ - tangent graph has a continuously differentiable ( $ \ calc ^ 1 $ ) path between any two nodes. we also provide analytical expressions for a near time - optimal velocity profile for an agent moving on these shortest paths under the damped double integrator with bounded acceleration. | arxiv:2007.05155 |
tripartite interactions play a fundamental role in the quantum information processing and quantum technology. however, it is generally difficult to realize strong tripartite coupling. we investigate the estimation of a tripartite coupling strength in a hybrid setup composed of a single nitrogen - vacancy ( nv ) center and a micromagnet. a time - independent parametric drive can be utilized to increase the estimation precision of the tripartite coupling strength. by calculating the quantum fisher information ( qfi ), we can obtain the optimal estimation precision by measuring the eigenstate of the tripartite system. at the critical position, the qfi is divergent due to that the preparation time of the eigenstate is divergent. when the system is subjected to a dissipation, the qfi near the critical point of the driven - dissipation phase transition is analytically obtained. the direct intensity measurement is the optimal measurement near the dissipation phase transition point. in addition, we quantify the robustness of an imperfect measurement operator by the measurement noise susceptibility based on the error propagation formula. we find that the direct intensity measurement is enough robust against small measurement disturbance from a coherent drive. but it can be disturbed by the nonlinear anti - harmonic measurement noise, especially near the critical point. | arxiv:2305.12435 |
in two - dimensional tissues, such as developing germ layers, pair - wise forces ( or active stresses ) arise from the contractile activity of the cytoskeleton, with dissipation provided by the three - dimensional surroundings. we show analytically how these pair - wise stochastic forces, unlike the particle - wise independent fluctuating forces usually considered in active matter systems, produce conserved centre - of - mass dynamics and so are able to damp large - wavelength displacement fluctuations in elastic systems. a consequence of this is the stabilisation of long - range translational order in two dimensions, in clear violation of the celebrated mermin - wagner theorem, and the emergence of hyperuniformity with a structure factor $ s ( q ) \ sim q ^ 2 $ in the $ q \ to 0 $ limit. we then introduce two numerical cell tissue models which feature these pair - wise active forces. first a vertex model, in which the cell tissue is represented by a tiling of polygons where the edges represent cell junctions and with activity provided by stochastic junctional contractions. second an active disk model, derived from active brownian particles, but with pairs of equal and opposite stochastic forces between particles. we confirm our analytical prediction of long - range order in both numerical models and show that hyperuniformity survives in the disordered phase, thus constituting a hidden order in our model tissue. owing to the generality of this mechanism, we expect our results to be testable in living organisms, and to also apply to artificial systems with the same symmetry. | arxiv:2410.14840 |
code optimization is a challenging task requiring a substantial level of expertise from developers. nonetheless, this level of human capacity is not sufficient considering the rapid evolution of new hardware architectures and software environments. in light of this, recent research proposes adopting machine learning and artificial intelligence techniques to automate the code optimization process. in this paper, we introduce perfrl, an innovative framework designed to tackle the problem of code optimization. our framework leverages the capabilities of small language models ( slms ) and reinforcement learning ( rl ), facilitating a system where slms can assimilate feedback from their environment during the fine - tuning phase, notably through unit tests. when benchmarked against existing models, perfrl demonstrates superior efficiency in terms of speed and computational resource usage, attributed to its reduced need for training steps and its compatibility with slms. furthermore, it substantially diminishes the risk of logical and syntactical errors. to evaluate our framework, we conduct experiments on the pie dataset using a lightweight large language model ( i. e., codet5 ) and a new reinforcement learning algorithm, namely rrhf. for evaluation purposes, we use a list of evaluation metrics related to optimization quality and speedup. the evaluation results show that our approach achieves similar or better results compared to state - of - the - art models using shorter training times and smaller pre - trained models. | arxiv:2312.05657 |
we consider a mobile cloud computing system with multiple users, a remote cloud server, and a computing access point ( cap ). the cap serves both as the network access gateway and a computation service provider to the mobile users. it can either process the received tasks from mobile users or offload them to the cloud. we jointly optimize the offloading decisions of all users, together with the allocation of computation and communication resources, to minimize the overall cost of energy consumption, computation, and maximum delay among users. the joint optimization problem is formulated as a mixed - integer program. we show that the problem can be reformulated and transformed into a non - convex quadratically constrained quadratic program, which is np - hard in general. we then propose an efficient solution to this problem by semidefinite relaxation and a novel randomization mapping method. furthermore, when there is a strict delay constraint for processing each user ' s task, we further propose a three - step algorithm to guarantee the feasibility and local optimality of the obtained solution. our simulation results show that the proposed solutions give nearly optimal performance under a wide range of parameter settings, and the addition of a cap can significantly reduce the cost of multi - user task offloading compared with conventional mobile cloud computing where only the remote cloud server is available. | arxiv:1712.00030 |
a search is performed for higgs bosons decaying into invisible final states, produced in association with a zo boson in e + e - collisions at energies between 183 and 209 gev. the search is based on data samples collected by the opal detector at lep corresponding to an integrated luminosity of about 660 pb - 1. the analysis aims to select events containing the hadronic decay products of the zo boson and large missing momentum, as expected from higgs boson decay into a pair of stable weakly interacting neutral particles, such as the lightest neutralino in the minimal supersymmetric standard model. the same analysis is applied to a search for nearly invisible higgs boson cascade decays into stable weakly interacting neutral particles. no excess over the expected background from standard model processes is observed. limits on the production of invisibly decaying higgs bosons produced in association with a zo boson are derived. assuming a branching ratio br ( ho - > invisible ) = 1, a lower limit of 108. 2 gev is placed on the higgs boson mass at the 95 % confidence level. limits on the production of nearly invisibly decaying higgs bosons are also obtained. | arxiv:0707.0373 |
we propose a novel approach to obtain the growth rate of cosmic structures, $ f ( z ) $, from the evolution of the cosmic homogeneity scale, $ r _ { \ text { h } } ( z ) $. our methodology needs two ingredients in a specific functional form : $ r _ { \ text { h } } ( z ) $ data and the matter two - point correlation function today, i. e., $ \ xi ( r, z = 0 ) $. we use a gaussian process approach to reconstruct the function $ r _ { \ text { h } } $. in the absence of suitable observational information of the matter correlation function in the local universe, $ z \ simeq 0 $, we assume a fiducial cosmology to obtain $ \ xi ( r, z = 0 ) $. for this reason, our final result turns out to be a consistency test of the cosmological model assumed. our results show a good agreement between : ( i ) the growth rate $ f ^ { r _ { \ text { h } } } ( z ) $ obtained through our approach, ( ii ) the $ f ^ { \ lambda \ text { cdm } } ( z ) $ expected in the fiducial model, and ( iii ) the best - fit $ f ( z ) $ from data compiled in the literature. moreover, using this data compilation, we perform a gaussian process to reconstruct the growth rate function $ f ^ { \ text { data } } ( z ) $ and compare it with the function $ f ^ { r _ { \ text { h } } } ( z ) $ finding a concordance of $ < \! 2 \, \ sigma $, a good result considering the few data available for both reconstruction processes. with more accurate $ r _ { \ text { h } } ( z ) $ data, from forthcoming surveys, the homogeneity scale function might be better determined and would have the potential to discriminate between $ \ lambda $ cdm and alternative scenarios as a new cosmological observable. | arxiv:2111.08541 |
many collider observables suffer from non - global logarithms not captured by standard resummation techniques. classic examples are the light - jet mass event shape in the limit of small mass and the related hemisphere soft function. we derive factorization formulas for both of these and explicitly demonstrate that they capture all logarithms present at nnlo. these formulas achieve full scale separation and provide the basis for all - order resummations. a characteristic feature of non - global observables is that the soft radiation is driven by multi - wilson - line operators, and the ones arising here map onto those relevant for the case of narrow - cone jet cross sections. numerically, the contributions of non - global logarithms to resummed hemisphere - mass event shapes are sizeable. | arxiv:1610.01608 |
we review the spontaneous magnetization of the vacuum of non - abelian gauge fields at high temperature. the standard model of particles is investigated as a particular example. by using both analytic methods of quantum field theory and gauge field theory on a lattice, we determine the abelian ( chromo ) magnetic fields in the restored phase of the model at high temperatures $ t \ geq t _ { ew } $. the fields are stable and temperature dependent, $ b = b ( t ) $. we investigate the mechanisms of the field stabilization in detail. the screening parameters for electric and magnetic fields - the debye, $ m _ d ( b, t ), $ and magnetic, $ m _ { magn. } ( b, t ) $, masses - are calculated. it is shown that, in the field presence, the former one is smaller than at zero field. the magnetic mass of the ( chromo ) magnetic fields is determined to be zero, as for usual $ u ( 1 ) $ magnetic field. we also show that the vacuum magnetization stops at temperatures below the electroweak phase transition temperature, $ t \ leq t _ { ew } $, when a scalar condensate creates. these properties make reasonable a possibility that the intergalactic magnetic fields observed recently were spontaneously generated in the hot universe at the reheating epoch due to vacuum polarization of non - abelian gauge fields. we present a procedure for estimating the field strengths $ b ( t ) $ at different temperatures. in particular, the value of $ b ( t _ { ew } ) \ sim 10 ^ { 14 } g $, at $ t _ { ew } $ is estimated with taking into consideration the observed intergalactic magnetic field $ b _ 0 \ sim 10 ^ { - 15 } g $. the magnetic field scale is also estimated. some model dependent peculiarities of the phenomena studied are briefly discussed. | arxiv:1210.2924 |
mechanical oscillators which respond to radiation pressure are a promising means of transferring quantum information between light and matter. optical - - mechanical state swaps are a key operation in this setting. existing proposals for optomechanical state swap interfaces are only effective in the resolved sideband limit. here, we show that it is possible to fully and deterministically exchange mechanical and optical states outside of this limit, in the common case that the cavity linewidth is larger than the mechanical resonance frequency. this high - bandwidth interface opens up a significantly larger region of optomechanical parameter space, allowing generation of non - classical motional states of high - quality, low - frequency mechanical oscillators. | arxiv:1510.05368 |
we establish spatial a priori estimates for the solution u to a class of dilation invariant kolmogorov equation, where u is assumed to only have a certain amount of regularity in the diffusion ' s directions. the result is that u is also regular with respect to the remaining directions. the approach we propose is based on the commutators identities and allows us to obtain a sobolev exponent that does not depend on the integrability assumption of the right - hand side. lastly, we provide an alternative proof to that of theorem 1. 5 of [ 9 ] for the optimal spatial regularity. | arxiv:2110.06585 |
we report on a measurement of the differential and total cross sections of inclusive production of xi resonances in sigma - nucleus collisions at 345 gev / c. | arxiv:hep-ex/9907021 |
in the standard $ q $ - voter model, a given agent can change its opinion only if there is a full consensus of the opposite opinion within a group of influence of size $ q $. a more realistic extension is the threshold $ q $ - voter, where a minimal agreement ( at least $ 0 < q _ 0 \ le q $ opposite opinions ) is sufficient to flip the central agent ' s opinion, including also the possibility of independent ( non conformist ) choices. variants of this model including non - conformist behavior have been previously studied in fully connected networks ( mean - field limit ). here we investigate its dynamics in random networks. particularly, while in the mean - field case it is irrelevant whether repetitions in the influence group are allowed, we show that this is not the case in networks, and we study the impact of both cases, with or without repetition. furthermore, the results of computer simulations are compared with the predictions of the pair approximation derived for uncorrelated networks of arbitrary degree distributions. | arxiv:2002.04715 |
on the basis of comparing eigenvalues of an operator $ { \ hat { \ mathbf { \ cal c } } } { } ^ { ( { \ cal r } ) } $, that proved useful in distinguishing how off - shell 4d, $ \ cal n $ = 1 supermultiplets become off - shell 4d, $ \ cal n $ = 2 supermultiplets, the double tensor supermultiplet is shown to be radically different for other known multiplets. this suggests difficulties, if not impossibilities, to embed it into an off - shell structure. | arxiv:2012.14549 |
we derive general expressions for how the alcock - paczynski distortions affect the power spectrum and the bispectrum of cosmological fields. we compute explicit formulas for the mixing coefficients of bispectrum multipoles in the linear approximation. the leading - order effect for the bispectrum is the uniform dilation of all three wavevectors. the mixing coefficients depend on the shape of the bispectrum triplet. our results for the bispectrum multipoles are framed in terms of the " natural " basis of the lengths of three wavevectors but can be easily generalized for other bases and reduction schemes. our validation tests confirm that the linear approximation is extremely accurate for all power spectrum multipoles. the linear approximation is accurate for the bispectrum monopole but results in sub - percent level inaccuracies for the bispectrum quadrupole and fails for the bispectrum hexadecapole. our results can be used to simplify the analysis of the bispectrum from galaxy surveys, especially the measurement of the baryon acoustic oscillation peak position. they can be used to replace numeric schemes with exact analytic formulae. | arxiv:2307.16498 |
high - resolution optical spectra were obtained in 2017 - 2019 with the southern african large telescope of fifteen stars in the direction of the vela supernova remnant. interstellar ca ii h and k and na i d lines are discussed in this paper. in particular, the line profiles are compared with profiles at a comparable spectral resolution obtained in 1993 - 1996 by cha & sembach. ten of the lines of sight show changes to one or more of the components in that line of sight. changes include small changes ( 1 - 2 km / s ) in radial velocity and / or increases / decreases in equivalent width over the two decades between the periods of observation. changes are more obvious in the ca k line than in the na d lines. these changes are attributed to gas disturbed by interactions between the supernova ejecta and the surrounding interstellar medium. a representative timescale may be 20 - 50 years. small - scale variations in line profiles across the face of the remnant suggest, as previously remarked, that a linear scale for interactions is a small fraction of the 40 pc size of the present remnant. | arxiv:2001.05790 |
in this paper we consider the stability of some inflating brane - world models in quantum cosmology. it is shown that whereas the singular model based on the construction of inflating branes from euclidean five - dimensional anti - de sitter space is unstable to tensorial cosmological perturbations in the bulk, the nonsingular model which uses a five - dimensional asymptotically anti - de sitter wormhole to construct the inflating branes is stable to these perturbations. | arxiv:hep-th/0308148 |
autonomous robots have real - world applications in diverse fields, such as mobile manipulation and environmental exploration, and many such tasks benefit from a hands - off approach in terms of human user involvement over a long task horizon. however, the level of autonomy achievable by a deployment is limited in part by the problem definition or task specification required by the system. task specifications often require technical, low - level information that is unintuitive to describe and may result in generic solutions, burdening the user technically both before and after task completion. in this thesis, we aim to advance task specification abstraction toward the goal of increasing robot autonomy in real - world scenarios. we do so by tackling problems that address several different angles of this goal. first, we develop a way for the automatic discovery of optimal transition points between subtasks in the context of constrained mobile manipulation, removing the need for the human to hand - specify these in the task specification. we further propose a way to automatically describe constraints on robot motion by using demonstrated data as opposed to manually - defined constraints. then, within the context of environmental exploration, we propose a flexible task specification framework, requiring just a set of quantiles of interest from the user that allows the robot to directly suggest locations in the environment for the user to study. we next systematically study the effect of including a robot team in the task specification and show that multirobot teams have the ability to improve performance under certain specification conditions, including enabling inter - robot communication. finally, we propose methods for a communication protocol that autonomously selects useful but limited information to share with the other robots. | arxiv:2307.13163 |
antipredator behaviour is a self - preservation strategy present in many biological systems, where individuals join the effort in a collective reaction to avoid being caught by an approaching predator. we study a nonhierarchical tritrophic system, whose predator - prey interactions are described by the rock - paper - scissors game rules. we performed a set of spatial stochastic simulations where organisms of one out of the species can resist predation in a collective strategy. the drop in predation capacity is local, which means that each predator faces a particular opposition depending on the prey group size surrounding it. considering that the interference in a predator action depends on the prey ' s physical and cognitive ability, we explore the role of a conditioning factor that indicates the fraction of the species apt to perform the antipredator strategy. because of the local unbalancing of the cyclic predator - prey interactions, departed spatial domains mainly occupied by a single species emerge. unlike the rock - paper - scissors model with a weak species because a nonlocal reason, our findings show that if the predation probability of one species is reduced because individuals face local antipredator response, the species does not predominate. instead, the local unbalancing of the rock - paper - scissors model results in the prevalence of the weak species ' prey. finally, the outcomes show that local unevenness may jeopardise biodiversity, with the coexistence being more threatened for high mobility. | arxiv:2202.00149 |
we present new observations of 34 yso candidates in the smc. the anchor of the analysis is a set of spitzer - irs spectra, supplemented by groundbased 3 - 5 micron spectra, spitzer and nir photometry, optical spectroscopy and radio data. the sources ' seds and spectral indices are consistent with embedded ysos ; prominent silicate absorption is observed in the spectra of at least ten sources, silicate emission is observed towards four sources. pah emission is detected towards all but two sources. based on band ratios ( in particular the strength of the 11. 3 micron and the weakness of the 8. 6 micron bands ) pah emission towards smc ysos is dominated by predominantly small neutral grains. ice absorption is observed towards fourteen sources in the smc. the comparison of h2o and co2 ice column densities for smc, lmc and galactic samples suggests that there is a significant h2o column density threshold for the detection of co2 ice. this supports the scenario proposed by oliveira et al. ( 2011 ), where the reduced shielding in metal - poor environments depletes the h2o column density in the outer regions of the yso envelopes. no co ice is detected towards the smc sources. emission due to pure - rotational 0 - 0 transitions of h2 is detected towards the majority of smc sources, allowing us to estimate rotational temperatures and column densities. all but one source are spectroscopically confirmed as smc ysos. of the 33 ysos identified in the smc, 30 sources populate different stages of massive stellar evolution. the remaining three sources are classified as intermediate - mass ysos with a thick dusty disc and a tenuous envelope still present. we propose one of the sources is a d - type symbiotic system, based on the presence of raman, h and he emission lines in the optical spectrum, and silicate emission in the irs - spectrum. this would be the first dust - rich symbiotic system identified in the smc. ( abridged ) | arxiv:1210.5193 |
recently, a phase transition phenomenon has been established for parking on random trees. we extend the results of curien and h \ ' enard on general galton - - watson trees and allow different car arrival distributions depending on the vertex outdegrees. we then prove that this phase transition is sharp by establishing a large deviations result for the flux of exiting cars. this has consequences on the offcritical geometry of clusters of parked spots which displays similarities with the classical erd \ h { o } s - renyi random graph model. | arxiv:2012.00607 |
the alpha + 6he low - energy reactions and the structural changes of 10be in the microscopic alpha + alpha + n + n model are studied by the generalized two - center cluster model with the kohn - hulthen - kato variation method. it is found that, in the inelastic scattering to the alpha + 6he ( 2 + ) channel, characteristic enhancements are expected as the results of the parity - dependent non - adiabatic dynamics. in the positive parity state, the enhancement originates from the excited eigenstate generated by the radial excitation of the relative motion between two alpha - cores. on the other hand, the enhancement in the negative parity state is induced by the landau - zener level - crossing. these non - adiabatic processes are discussed in connection to the formation of the inversion doublet in the compound system of 10be. | arxiv:nucl-th/0508032 |
appearance of cosmic strings in the early universe is a common manifestation of new physics typically linked to some high energy scale. in this paper, we discuss a different situation, where a model underlying cosmic string formation is approximately scale free. string tension is naturally related to the square of the temperature of the hot primordial plasma in such a setting, and hence decreases with ( cosmic ) time. with gravitational backreaction neglected, the dynamics of these melting strings in an expanding universe is equivalent to the dynamics of constant tension strings in a minkowski spacetime. we provide an estimate for the emission of gravitational waves from string loops. contrary to the standard case, the resulting spectrum is markedly non - flat and has a characteristic falloff at frequencies below the peak one. the peak frequency is defined by the underlying model and lies in the range accessible by the future detectors for very weak couplings involved. | arxiv:2108.05377 |
schaefer ( 2024 ) has recently published observations of binary period derivatives $ \ dot p $ for 52 cataclysmic variables, and concluded that these strongly conflict with all proposed evolutionary pictures for these systems. we point out once again that using measurements of $ \ dot p $ is likely in practice to produce misleading evolutionary constraints in almost every case. the one identified exception to this is probably the recently - born x - ray binary sn 2022jli, because of its extremely high mass transfer rate. | arxiv:2406.03948 |
this paper presents a versatile hybrid framework for addressing 2d real - world reconstruction tasks formulated as jigsaw puzzle problems ( jpps ) with square, non - overlapping pieces. our approach integrates a deep learning ( dl ) - based compatibility measure ( cm ) model that evaluates pairs of puzzle pieces holistically, rather than focusing solely on their adjacent edges as traditionally done. this dl - based cm is paired with an optimized genetic algorithm ( ga ) - based solver, which iteratively searches for a global optimal arrangement using the pairwise cm scores of the puzzle pieces. extensive experimental results highlight the framework ' s adaptability and robustness across multiple real - world domains. notably, our unique hybrid methodology achieves state - of - the - art ( sota ) results in reconstructing portuguese tile panels and large degraded puzzles with eroded boundaries. | arxiv:2501.19325 |
we suggest an algorithm allowing to obtain some new integral - geometric formulae from the existing formulae of crofton type. these new formulae are applied to get smooth versions of bkk theorem. the algorithm is based on the calculations in the ring of normal densities on a manifold. | arxiv:1907.00633 |
in the present work, the masses of the decuplet baryons at finite temperature are investigated using thermal qcd sum rules. making use of the quark propagator at finite temperature, we calculate the spectral functions to $ t ^ { 8 } $ order, and find that there are no contributions to the spectral functions at $ t ^ { 8 } $ order and the temperature corrections mainly come from that containing $ t ^ 4 $ ones. the calculations show very little temperature dependence of the masses below $ t = 0. 11 { gev } $. while above that value, the masses decrease with increasing temperature. the results indicate that the hadron - quark phase transition temperature may be $ t _ c \ geq0. 11 { gev } $ for the decuplet bayons. | arxiv:1502.00429 |
we have used the iram 30 - m and fcrao 14 - m telescopes to observe the molecular clumps associated with 12 ultracompact ( uc ) hii regions in the j = 6 - 5, 8 - 7 and 13 - 12 rotational transitions of methyl - acetylene ( ch3c2h ). under the assumption of lte and optically thin emission, we have derived temperature estimates ranging from 30 to 56 k. we estimate that the clumps have diameters of 0. 2 - 1. 6 pc, h _ 2 densities of 10 ^ 5 - 10 ^ 6 { cm ^ { - 3 } }, and masses of 10 ^ 2 - 2 10 ^ 4 m _ \ odot. we compare these values with those obtained by other authors from different molecular tracers and find that the h _ 2 density and the temperature inside the clumps vary respectively like n _ { h _ 2 } ~ r ^ { - 2. 6 } and t ~ r ^ { - 0. 5 }, with r distance from the centre. we also find that the virial masses of the clumps are ~ 3 times less than those derived from the ch3c2h column densities : we show that a plausible explanation is that magnetic fields play an important role to stabilise the clumps, which are on the verge of gravitational collapse. finally, we show that the ch3c2h line width increases for decreasing distance from the clump centre : this effect is consistent with infall in the inner regions of the clumps. we conclude that the clumps around uc hii regions are likely to be transient ( ~ 10 ^ ( 5 ) yr ) entities, remnants of isothermal spheres currently undergoing gravitational collapse : the high mass accretion rates ( ~ 10 ^ { - 2 } m _ \ odot yr ^ { - 1 } ) lead to massive star formation at the centre of such clumps. | arxiv:astro-ph/0204313 |
data of the numerical solution of the time - dependent schr \ " odinger equation of a system containing one spin - 1 / 2 particle interacting with a bath of up to 32 spin - 1 / 2 particles is used to construct a markovian quantum master equation describing the dynamics of the system spin. the procedure of obtaining this quantum master equation, which takes the form of a bloch equation with time - independent coefficients, accounts for all non - markovian effects in as much the general structure of the quantum master equation allows. our simulation results show that, with a few rather exotic exceptions, the bloch - type equation with time - independent coefficients provides a simple and accurate description of the dynamics of a spin - 1 / 2 particle in contact with a thermal bath. a calculation of the coefficients that appear in the redfield master equation in the markovian limit shows that this perturbatively derived equation quantitatively differs from the numerically estimated markovian master equation, the results of which agree very well with the solution of the time - dependent schr \ " odinger equation. | arxiv:1605.06609 |
sulphur is one of the most abundant elements in the universe. surprisingly, sulphuretted molecules are not as abundant as expected in the interstellar medium, and the identity of the main sulphur reservoir is still an open question. our goal is to investigate the h $ _ { 2 } $ s chemistry in dark clouds, as this stable molecule is a potential sulphur reservoir. using millimeter observations of cs, so, h $ _ { 2 } $ s, and their isotopologues, we determine the physical conditions and h $ _ { 2 } $ s abundances along the cores tmc 1 - c, tmc 1 - cp, and barnard 1b. the gas - grain model nautilus is then used to model the sulphur chemistry and explore the impact of photo - desorption and chemical desorption on the h $ _ 2 $ s abundance. our model shows that chemical desorption is the main source of gas - phase h $ _ 2 $ s in dark cores. the measured h $ _ { 2 } $ s abundance can only be fitted if we assume that the chemical desorption rate decreases by more than a factor of 10 when $ n _ { \ rm h } > 2 \ times10 ^ { 4 } $. this change in the desorption rate is consistent with the formation of thick h $ _ 2 $ o and co ice mantles on grain surfaces. the observed so and h $ _ 2 $ s abundances are in good agreement with our predictions adopting an undepleted value of the sulphur abundance. however, the cs abundance is overestimated by a factor of $ 5 - 10 $. along the three cores, atomic s is predicted to be the main sulphur reservoir. we conclude that the gaseous h $ _ 2 $ s abundance is well reproduced, assuming undepleted sulphur abundance and chemical desorption as the main source of h $ _ 2 $ s. the behavior of the observed h $ _ { 2 } $ s abundance suggests a changing desorption efficiency, which would probe the snowline in these cores. our model, however, overestimates the observed gas - phase cs abundance. given the uncertainty in the sulphur chemistry, our data are consistent with a cosmic elemental s abundance with an uncertainty of a factor of 10. | arxiv:2004.03475 |
despite its common use in quantum theory, the mathematical requirement of dirac hermiticity of a hamiltonian is sufficient to guarantee the reality of energy eigenvalues but not necessary. by establishing three theorems, this paper gives physical conditions that are both necessary and sufficient. first, it is shown that if the secular equation is real, the hamiltonian is necessarily pt symmetric. second, if a linear operator c that obeys the two equations [ c, h ] = 0 and c ^ 2 = 1 is introduced, then the energy eigenvalues of a pt - symmetric hamiltonian that is diagonalizable are real only if this c operator commutes with pt. third, the energy eigenvalues of pt - symmetric hamiltonians having a nondiagonalizable, jordan - block form are real. these theorems hold for matrix hamiltonians of any dimensionality. | arxiv:0902.1365 |
##rgy and mineralogy ( e. g. face - centered cubic, body - centered cubic, etc. ). the fundamental difference in equilibrium structure is in the spatial scale of the unit cell ( or lattice parameter ) in each particular case. thus, self - assembly is emerging as a new strategy in chemical synthesis and nanotechnology. molecular self - assembly has been observed in various biological systems and underlies the formation of a wide variety of complex biological structures. molecular crystals, liquid crystals, colloids, micelles, emulsions, phase - separated polymers, thin films and self - assembled monolayers all represent examples of the types of highly ordered structures which are obtained using these techniques. the distinguishing feature of these methods is self - organization in the absence of any external forces. in addition, the principal mechanical characteristics and structures of biological ceramics, polymer composites, elastomers, and cellular materials are being re - evaluated, with an emphasis on bioinspired materials and structures. traditional approaches focus on design methods of biological materials using conventional synthetic materials. this includes an emerging class of mechanically superior biomaterials based on microstructural features and designs found in nature. the new horizons have been identified in the synthesis of bioinspired materials through processes that are characteristic of biological systems in nature. this includes the nanoscale self - assembly of the components and the development of hierarchical structures. = = ceramic composites = = substantial interest has arisen in recent years in fabricating ceramic composites. while there is considerable interest in composites with one or more non - ceramic constituents, the greatest attention is on composites in which all constituents are ceramic. these typically comprise two ceramic constituents : a continuous matrix, and a dispersed phase of ceramic particles, whiskers, or short ( chopped ) or continuous ceramic fibers. the challenge, as in wet chemical processing, is to obtain a uniform or homogeneous distribution of the dispersed particle or fiber phase. consider first the processing of particulate composites. the particulate phase of greatest interest is tetragonal zirconia because of the toughening that can be achieved from the phase transformation from the metastable tetragonal to the monoclinic crystalline phase, aka transformation toughening. there is also substantial interest in dispersion of hard, non - oxide phases such as sic, tib, tic, boron, carbon and especially oxide matrices like alumina and mullite. there is also interest too incorporating other ceramic particulates, especially those | https://en.wikipedia.org/wiki/Ceramic_engineering |
the de sitter invariant special relativity is a natural extension of the usual einstein special relativity. within this framework a generalization of special relativity ( sr ) for the de sitter space - time introduces a new length scale $ r $, serving an origin of geometrical cosmological constant $ \ lambda = 3 / r ^ 2 $. de sitter relativity predicts the departure from the lorentz invariance due to spacetime curvature, related to the geometrical cosmological constant. in this paper the possible impact of de sitter special relativity effects on threshold particle processes and equivalence principle violation is considered. the main conclusion is that constraints, coming from cosmological fine structure constant variations render this effects nowadays undetectable. a brief outlook is given thereafter. | arxiv:1604.00809 |
in this paper, we investigate the fidelity for the heisenberg chain with the next - nearest - neighbor interaction ( or the $ j _ 1 - j _ 2 $ model ) and analyze its connections with quantum phase transition. we compute the fidelity between the ground states and find that the phase transition point of the $ j _ 1 - j _ 2 $ model can not be well characterized by the ground state fidelity for finite - size systems. instead, we introduce and calculate the fidelity between the first excited states. our results show that the quantum transition can be well characterized by the fidelity of the first excited state even for a small - size system. | arxiv:0706.0072 |
we investigate symmetry and causality constraints on interacting fermi liquids. whereas galilean or lorentz boost symmetry leads to a well - known constraint on the first landau parameter $ f _ 1 $, we show that scale invariance similarly constrains $ f _ 0 $. in the case of conformal fermi liquids, we show that causality constraints on the particle - hole continuum and on zero sound strongly restrict the available parameter space for interacting fermi liquids. we also consider nonlinear response, which we show is sensitive to additional ` ` generalized landau parameters ' ' even at lowest orders in the long wavelength limit. we impose galilean, lorentz and scale symmetry on these generalized landau parameters, obtaining further nonlinear constraints. we test our constraints in several microscopic models that enter a fermi liquid phase. | arxiv:2501.02073 |
we report on a possible optical tuning of the spin hall conductivity in mono - layer transition metal dichalcogenides. light beams of frequencies much higher than the energy scale of the system ( the \ textit { off - resonant } condition ) does not excite electrons but rearranges the band structure. the rearrangement is quantitatively established using the floquet formalism. for such a system of mono - layer transition metal dichalcogenides, the spin hall conductivity ( calculated with the kubo expression in presence of disorder ) exhibits a drop at higher frequencies and lower intensities. finally, we compare the spin hall conductivity of the higher spin - orbit coupled wse $ _ { 2 } $ to mos $ _ { 2 } $ ; the spin hall conductivity of wse $ _ { 2 } $ was found to be larger. | arxiv:1606.02089 |
chest diseases rank among the most prevalent and dangerous global health issues. object detection and phrase grounding deep learning models interpret complex radiology data to assist healthcare professionals in diagnosis. object detection locates abnormalities for classes, while phrase grounding locates abnormalities for textual descriptions. this paper investigates how text enhances abnormality localization in chest x - rays by comparing the performance and explainability of these two tasks. to establish an explainability baseline, we proposed an automatic pipeline to generate image regions for report sentences using radiologists ' eye - tracking data. the better performance - miou = 0. 36 vs. 0. 20 - and explainability - containment ratio 0. 48 vs. 0. 26 - of the phrase grounding model infers the effectiveness of text in enhancing chest x - ray abnormality localization. | arxiv:2503.01037 |
we propose a simplified version of the kitaev ' s surface code in which error correction requires only three - qubit parity measurements for pauli operators xxx and zzz. the new code belongs to the class of subsystem stabilizer codes. it inherits many favorable properties of the standard surface code such as encoding of multiple logical qubits on a planar lattice with punctured holes, efficient decoding by either minimum - weight matching or renormalization group methods, and high error threshold. the new subsystem surface code ( ssc ) gives rise to an exactly solvable hamiltonian with 3 - qubit interactions, topologically ordered ground state, and a constant energy gap. we construct a local unitary transformation mapping the ssc hamiltonian to the one of the ordinary surface code thus showing that the two hamiltonians belong to the same topological class. we describe error correction protocols for the ssc and determine its error thresholds under several natural error models. in particular, we show that the ssc has error threshold approximately 0. 6 % for the standard circuit - based error model studied in the literature. we also consider a model in which three - qubit parity operators can be measured directly. we show that the ssc has error threshold approximately 0. 97 % in this setting. | arxiv:1207.1443 |
the curvature - dimension condition is a generalization of the bochner inequality to weighted riemannian manifolds and general metric measure spaces. it is now known to be equivalent to evolution variational inequalities for the heat semigroup, and quadratic wasserstein distance contraction properties at different times. on the other hand, in a compact riemannian manifold, it implies a same - time wasserstein contraction property for this semigroup. in this work we generalize the latter result to metric measure spaces and more importantly prove the converse : contraction inequalities are equivalent to curvature - dimension conditions. links with functional inequalities are also investigated. | arxiv:1510.07793 |
a link in the 3 - sphere is called ( smoothly ) slice if its components bound disjoint smoothly embedded disks in the 4 - ball. more generally, given a 4 - manifold m with a distinguished circle in its boundary, a link in the 3 - sphere is called m - slice if its components bound in the 4 - ball disjoint embedded copies of m. a 4 - manifold m is constructed such that the borromean rings are not m - slice but the hopf link is. this contrasts the classical link - slice setting where the hopf link may be thought of " the most non - slice " link. further examples and an obstruction for a family of decompositions of the 4 - ball are discussed in the context of the a - b slice problem. | arxiv:1305.7223 |
we consider the optimal control problem of transferring population between states of a quantum system where the coupling proceeds only via intermediate states that are subject to decay. we pose the question whether it is generally possible to carry out this transfer. for a single intermediate decaying state, we recover the stimulated raman adiabatic passage ( stirap ) process which we identify as the global optimum in the limit of infinite control time. we also present analytic solutions for the case of transfer that has to proceed via two consecutive intermediate decaying states. we show that in this case, for finite power the optimal control does not approach perfect state transfer even in the infinite time limit. we generalize our findings to characterize the topologies of paths that can be achieved by coherent control under the assumption of finite power. | arxiv:1004.4050 |
magnetic dipole emission ( mde ) from interstellar magnetic nanoparticles is an important galactic foreground in the microwave frequencies, and its polarization level may pose great challenges for achieving reliable measurements of cosmic microwave background ( cmb ) b - mode signal. to obtain theoretical constraints on the polarization of mde, we first compute the degree of alignment of big silicate grains incorporated with magnetic inclusions. we find that, in realistic conditions of the interstellar medium, thermally rotating big grains with magnetic inclusions are weakly aligned and achieve { \ it alignment saturation } when the magnetic alignment rate becomes much faster than the rotational damping rate. we then compute the degree of alignment for free - flying magnetic nanoparticles, taking into account various interaction processes of grains with the ambient gas and radiation field, including neutral collisions, ion collisions, and infrared emission. we find that the rotational damping by infrared emission can significantly decrease the degree of alignment of small particles from the saturation level, whereas the excitation by ion collisions can enhance the alignment of ultrasmall particles. using the computed degrees of alignment, we predict the polarization level of mde from free - flying magnetic nanoparticles to be rather low. such a polarization level is within the upper limits measured for anomalous microwave emission ( ame ), which indicates that mde from free - flying iron particles may not be ruled out as a source of ame. we also quantify spinning dust emission from free - flying iron nanoparticles with permanent magnetic moments and find that its emissivity is one order of magnitude lower than that from spinning polycyclic aromatic hydrocarbons ( pahs ). finally, we compute the polarization spectra of spinning dust emission from pahs for the different interstellar magnetic fields. | arxiv:1511.03691 |
when unmanned aerial vehicles ( uavs ) perform high - precision communication tasks, such as searching for users and providing emergency coverage, positioning errors between base stations and users make it challenging to deploy trajectory planning algorithms. to address these challenges caused by position errors, a framework was proposed to compensate it by channel knowledge map ( ckm ), which stores channel state information ( csi ). by taking the positions with errors as input, the generated ckm could give a prediction of signal attenuation which is close to true positions. based on that, the predictions are utilized to calculate the received power and a ppo - based algorithm is applied to optimize the compensation. after training, the framework is able to find a strategy that minimize the flight time under communication constraints and positioning error. besides, the confidence interval is calculated to assist the allocation of power and the update of ckm is studied to adapt to the dynamic environment. simulation results show the robustness of ckm to positioning error and environmental changes, and the superiority of ckm - assisted uav communication design. | arxiv:2409.15798 |
in numerous studies, deep learning algorithms have proven their potential for the analysis of histopathology images, for example, for revealing the subtypes of tumors or the primary origin of metastases. these models require large datasets for training, which must be anonymized to prevent possible patient identity leaks. this study demonstrates that even relatively simple deep learning algorithms can re - identify patients in large histopathology datasets with substantial accuracy. we evaluated our algorithms on two tcia datasets including lung squamous cell carcinoma ( lscc ) and lung adenocarcinoma ( luad ). we also demonstrate the algorithm ' s performance on an in - house dataset of meningioma tissue. we predicted the source patient of a slide with f1 scores of 50. 16 % and 52. 30 % on the lscc and luad datasets, respectively, and with 62. 31 % on our meningioma dataset. based on our findings, we formulated a risk assessment scheme to estimate the risk to the patient ' s privacy prior to publication. | arxiv:2403.12816 |
$ { \ rm caruo _ 3 } $ is a paramagnetic metal and since its low temperature resistivity is described by $ \ rho = \ rho _ 0 + at ^ \ gamma $ with $ \ gamma \ sim 1. 5 $, it is also considered a non - fermi liquid ( nfl ) metal. we have performed extensive magnetoresistance and hall effect measurements of untwinned epitaxial films of $ { \ rm caruo _ 3 } $. these measurements reveal that $ { \ rm caruo _ 3 } $ exhibits uniaxial magnetocrystalline anisotropy. in addition, the low - temperature nfl behavior is most effectively suppressed when a magnetic field is applied along the easy axis, suggesting that critical spin fluctuations, possibly due to proximity of a quantum critical phase transition, are related to the nfl behavior. | arxiv:nlin/0508038 |
this paper summarizes our studies on propaganda detection techniques for news articles in the semeval - 2020 task 11. this task is divided into the si and tc subtasks. we implemented the glove word representation, the bert pretraining model, and the lstm model architecture to accomplish this task. our approach achieved good results for both the si and tc subtasks. the macro - f1 - score for the si subtask is 0. 406, and the micro - f1 - score for the tc subtask is 0. 505. our method significantly outperforms the officially released baseline method, and the si and tc subtasks rank 17th and 22nd, respectively, for the test set. this paper also compares the performances of different deep learning model architectures, such as the bi - lstm, lstm, bert, and xgboost models, on the detection of news promotion techniques. the code of this paper is availabled at : https : / / github. com / daojiaxu / semeval _ 11. | arxiv:2008.10166 |
existing commercial search engines often struggle to represent different perspectives of a search query. argument retrieval systems address this limitation of search engines and provide both positive ( pro ) and negative ( con ) perspectives about a user ' s information need on a controversial topic ( e. g., climate change ). the effectiveness of such argument retrieval systems is typically evaluated based on topical relevance and argument quality, without taking into account the often differing number of documents shown for the argument stances ( pro or con ). therefore, systems may retrieve relevant passages, but with a biased exposure of arguments. in this work, we analyze a range of non - stochastic fairness - aware ranking and diversity metrics to evaluate the extent to which argument stances are fairly exposed in argument retrieval systems. using the official runs of the argument retrieval task touch \ ' e at clef 2020, as well as synthetic data to control the amount and order of argument stances in the rankings, we show that systems with the best effectiveness in terms of topical relevance are not necessarily the most fair or the most diverse in terms of argument stance. the relationships we found between ( un ) fairness and diversity metrics shed light on how to evaluate group fairness - - in addition to topical relevance - - in argument retrieval settings. | arxiv:2108.10442 |
in his papers [ 2 ], [ 3 ] brin introduced the higher dimensional thompson groups nv which are generalizations to the thompson ' s group v of self - homeomorphisms of the cantor set and found a finite set of generators and relations in the case n = 2. we show how to generalize his construction to obtain a finite presentation for every positive integer n. as a corollary, we obtain another proof that the groups nv are simple ( first proved by brin in [ 4 ] ). | arxiv:1105.3714 |
we report studies of thermal conductivity as functions of magnetic field and temperature in the helimagnetic insulator cu $ _ 2 $ oseo $ _ 3 $ that reveal novel features of the spin - phase transitions as probed by magnon heat conduction. the tilted conical spiral and low - temperature skyrmion phases, recently identified in small - angle neutron scattering studies, are clearly identified by sharp signatures in the magnon thermal conductivity. magnon scattering associated with the presence of domain boundaries in the tilted conical phase and regions of skyrmion and conical - phase coexistence are identified. | arxiv:1901.01242 |
using the relativistic impulse approximation with empirical nn scattering amplitude and the nuclear scalar and vector densities from the relativistic mean - field theory, we evaluate the dirac optical potential for neutrons and protons in asymmetric nuclear matter. from the resulting schr \ " { o } % dinger - equivalent potential, the high energy behavior of the nuclear symmetry potential is studied. we find that the symmetry potential at fixed baryon density is essentially constant once the nucleon kinetic energy is greater than about 500 mev. moreover, for such high energy nucleon, the symmetry potential is slightly negative below a baryon density of about $ % \ rho = 0. 22 $ fm $ ^ { - 3 } $ and then increases almost linearly to positive values at high densities. our results thus provide an important constraint on the energy and density dependence of nuclear symmetry potential in asymmetric nuclear matter. | arxiv:nucl-th/0508045 |
in order to sample from an unnormalized probability density function, we propose to combine continuous normalizing flows ( cnfs ) with rejection - resampling steps based on importance weights. we relate the iterative training of cnfs with regularized velocity fields to a jko scheme and prove convergence of the involved velocity fields to the velocity field of the wasserstein gradient flow ( wgf ). the alternation of local flow steps and non - local rejection - resampling steps allows to overcome local minima or slow convergence of the wgf for multimodal distributions. since the proposal of the rejection step is generated by the model itself, they do not suffer from common drawbacks of classical rejection schemes. the arising model can be trained iteratively, reduces the reverse kulback - leibler ( kl ) loss function in each step, allows to generate iid samples and moreover allows for evaluations of the generated underlying density. numerical examples show that our method yields accurate results on various test distributions including high - dimensional multimodal targets and outperforms the state of the art in almost all cases significantly. | arxiv:2407.20444 |
an explicit calculation is performed to check all the tangent bundle gravitational couplings of dirichlet branes and orientifold planes by scattering $ q $ gravitons with a $ p + 1 $ form ramond - ramond potential in the world - volume of a $ d ( p + 2q ) $ - brane. the structure of the d - brane wess - zumino term in the world - volume action is confirmed, while a different o - plane wess - zumino action is obtained. | arxiv:hep-th/9812088 |
the dibaryon states as six - quark clusters of exotic qcd states are investigated in this paper. with the inherent nodal surface structure analysis, the wave functions of the six - quark clusters ( in another word, the dibaryons ) are classified. the contribution of the hidden color channels are discussed. the quantum numbers of the low - lying dibaryon states are obtained. the states $ [ \ omega \ omega ] _ { ( 0, 0 ^ { + } ) } $, $ [ \ omega \ omega ] _ { ( 0, 2 ^ { - } ) } $, $ [ \ xi ^ { * } \ omega ] _ { ( 1 / 2, 0 ^ { + } ) } $, $ [ \ sigma ^ { * } \ sigma ^ { * } ] _ { ( 0, 4 ^ { - } ) } $ and the hidden color channel states with the same quantum numbers are proposed to be the candidates of dibaryons, which may be observed in experiments. | arxiv:nucl-th/0212069 |
to settle a large - scale integration of renewable distributed generations ( dgs ), it requires to assess the maximal dg hosting capacity of active distribution networks ( adns ). for fully exploiting the ability of adns to accommodate dg, this paper proposes a robust comprehensive dg capacity assessment method considering three - phase power flow modelling and active network management ( anm ) techniques. the two - stage adjustable robust optimization is employed to tackle the uncertainties of load demands and dg outputs. with our method, system planners can obtain the maximum penetration level of dgs with their optimal sizing and sitting decisions. meanwhile, the robust optimal anm schemes can be generated for each operation time period, including network reconfiguration, on - load - tap - changers regulation, and reactive power compensation. in addition, a three - step optimization algorithm is proposed to enhance the accuracy of dg capacity assessment results. the optimality and robustness of our method are validated via numerical tests on an unbalanced ieee 33 - bus distribution system. | arxiv:1709.03746 |
traditional models of rational action treat the agent as though it is cleanly separated from its environment, and can act on that environment from the outside. such agents have a known functional relationship with their environment, can model their environment in every detail, and do not need to reason about themselves or their internal parts. we provide an informal survey of obstacles to formalizing good reasoning for agents embedded in their environment. such agents must optimize an environment that is not of type " function " ; they must rely on models that fit within the modeled environment ; and they must reason about themselves as just another physical system, made of parts that can be modified and that can work at cross purposes. | arxiv:1902.09469 |
the stability conditions for the motion of classical test particles in an $ % n $ - dimensional induced matter kaluza - klein theory is studied. we show that stabilization requires a variance of the strong energy condition for the induced matter to hold and that it is related to the hierarchy problem. stabilization of test particles in a frw universe is also discussed. | arxiv:gr-qc/0608071 |
we observe large density modulations in time - of - flight images of elongated bose - einstein condensates, initially confined in a harmonic trap and in the presence of weak disorder. the development of these modulations during the time - of - flight and their dependence with the disorder are investigated. we render an account of this effect using numerical and analytical calculations. we conclude that the observed large density modulations originate from the weak initial density modulations induced by the disorder, and not from initial phase fluctuations ( thermal or quantum ). | arxiv:0710.1984 |
fourier transforms of lorentz invariant functions in minkowski space, with support on both the timelike and the spacelike domains are performed by means of direct integration. the cases of 1 + 1 and 1 + 2 dimensions are worked out in detail, and the results for 1 + n dimensions are given. | arxiv:math-ph/0212040 |
tensor networks are factorizations of high - dimensional tensors into networks of smaller tensors. they have applications in physics and mathematics, and recently have been proposed as promising machine learning architectures. to ease the integration of tensor networks in machine learning pipelines, we introduce tensorkrowch, an open source python library built on top of pytorch. providing a user - friendly interface, tensorkrowch allows users to construct any tensor network, train it, and integrate it as a layer in more intricate deep learning models. in this paper, we describe the main functionality and basic usage of tensorkrowch, and provide technical details on its building blocks and the optimizations performed to achieve efficient operation. | arxiv:2306.08595 |
twenty three years ago, cosmological n - body simulations revealed quasi - universal nfw dark matter halos, whose physical origin is still unclear. this work tries to solve this issue by landau - ginzburg ( lg ) theory in equilibrium statistical mechanics. we replace the order parameter in lg theory by density and consider the dark matter halos as fluctuations from the equilibrium state of the background, which can be the main halos for the subhalos, or the homogeneous and isotropic universe for the galaxy cluster halos. with the assumption that the fluctuations of helmholtz free energy depend mainly on the density and its gradient, which is shown to be consistent with the behavior of the power spectrum near the cluster scale, we can easily obtain the universal $ r ^ { - 1 } $ cusp of the equilibrium dark matte halo without other requirements. this work strongly suggests that more studies should be done for the self - gravitating systems by statistical mechanics. | arxiv:1912.09374 |
a ttf - triple $ ( \ mathcal { c }, \ mathcal { t }, \ mathcal { f } ) $ in an abelian category is called ' one - sided split ' in case either $ ( \ mathcal { c }, \ mathcal { t } ) $ or $ ( \ mathcal { t }, \ mathcal { f } ) $ is a split torsion theory. in this paper we classify one - sided split ttf - triples in module categories, thus completing jans ' classification of two - sided split ttf - triples and answering a question that has remained open for almost forty years. | arxiv:math/0511159 |
by quantitatively fitting simple emission line profile models that include both atomic opacity and porosity to the chandra x - ray spectrum of $ \ zeta $ pup, we are able to explore the trade - offs between reduced mass - loss rates and wind porosity. we find that reducing the mass - loss rate of $ \ zeta $ pup by roughly a factor of four, to 1. 5 \ times 10 ^ { - 6 } m _ sun / yr, enables simple non - porous wind models to provide good fits to the data. if, on the other hand, we take the literature mass - loss rate of 6 \ times 10 ^ { - 6 } m _ sun / yr, then to produce x - ray line profiles that fit the data, extreme porosity lengths - - of $ h _ { \ infty } \ approx 3 $ rstar - - are required. moreover, these porous models do not provide better fits to the data than the non - porous, low optical depth models. additionally, such huge porosity lengths do not seem realistic in light of 2 - d numerical simulations of the wind instability. | arxiv:0712.1050 |
the emission of particles after atomic muon capture was studied extensively during the early 70 ' s. in particular, proton and neutron spectra were measured in order to determine whether nuclear emission was due to a direct or a thermalized process. it was found that protons emitted after atomic muon capture decreased from a probability of 15 % in light nuclei ( c, n, o ) to essentially 0 % for heavy systems such as sn, and that only 10 % of this emission could be ascribed to statistical processes. on the other hand a significant thermal spectrum of neutrons in addition to a direct component was found. unfortunately these studies were not always self consistent so that information of relevance to the meco experiment is ambiguous. | arxiv:1803.08403 |
the o ( alpha ) virtual weak radiative corrections to many hadron collider processes are known to become large and negative at high energies, due to the appearance of sudakov - like logarithms. at the same order in perturbation theory, weak boson emission diagrams contribute. since the w and z bosons are massive, the o ( alpha ) virtual weak radiative corrections and the contributions from weak boson emission are separately finite. thus, unlike in qed or qcd calculations, there is no technical reason for including gauge boson emission diagrams in calculations of electroweak radiative corrections. in most calculations of the o ( alpha ) electroweak radiative corrections, weak boson emission diagrams are therefore not taken into account. another reason for not including these diagrams is that they lead to final states which differ from that of the original process. however, in experiment, one usually considers partially inclusive final states. weak boson emission diagrams thus should be included in calculations of electroweak radiative corrections. in this paper, i examine the role of weak boson emission in those processes at the fermilab tevatron and the cern lhc for which the one - loop electroweak radiative corrections are known to become large at high energies ( inclusive jet, isolated photon, z + 1 jet, drell - yan, di - boson, t - bar t, and single top production ). in general, i find that the cross section for weak boson emission is substantial at high energies and that weak boson emission and the o ( alpha ) virtual weak radiative corrections partially cancel. | arxiv:hep-ph/0611241 |
a system using a personal computer, speaker, and a microphone is used to detect objects, and make crude measurements using a carrier modulated by a pseudorandom noise ( pn ) code. this system can be constructed using a personal computer and audio equipment commonly found in the laboratory or at home, or more sophisticated equipment that can be purchased at reasonable cost. we demonstrate its value as an instructional tool for teaching concepts of remote sensing and digital signal processing. | arxiv:1106.2141 |
this document has been prepared as a snowmass contributed paper by the public policy & government engagement topical group ( cef06 ) within the community engagement frontier. the charge of cef06 is to review all aspects of how the high energy physics ( hep ) community engages with government at all levels and how public policy impacts members of the community and the community at large, and to assess and raise awareness within the community of direct community - driven engagement of the us federal government ( i. e. advocacy ). the focus of this paper is hep community engagement of government entities other than the u. s. federal legislature ( i. e. congress ). | arxiv:2207.00125 |
in this paper, we propose a first order energy stable linear semi - implicit method for solving the allen - cahn - ohta - kawasaki equation. by introducing a new nonlinear term in the ohta - kawasaki free energy functional, all the system forces in the dynamics are localized near the interfaces which results in the desire hyperbolic tangent profile. in our numerical method, the time discretization is done by some stabilization technique in which some extra nonlocal but linear term is introduced and treated explicitly together with other linear terms, while other nonlinear and nonlocal terms are treated implicitly. the spatial discretization is performed by the fourier collocation method with fft - based fast implementations. the energy stabilities are proved for this method in both semi - discretization and full discretization levels. numerical experiments indicate the force localization and desire hyperbolic tangent profile due to the new nonlinear term. we test the first order temporal convergence rate of the proposed scheme. we also present hexagonal bubble assembly as one type of equilibrium for the ohta - kawasaki model. additionally, the two - third law between the number of bubbles and the strength of long - range interaction is verified which agrees with the theoretical studies. | arxiv:1811.11306 |
critical current density of composite free layer ( cfl ) in magnetic tunneling junction is investigated. cfl consists of two exchange coupled ferromagnetic layers, where the coupling is parallel or anti - parallel. instability condition of the cfl under the spin transfer torque, which is related with critical current density, is obtained by analytic spin wave excitation model and confirmed by macro - spin landau - lifshitz - gilbert equation. the critical current densities for the coupled two identical layers are investigated with various coupling strengths, and spin transfer torque efficiencies. | arxiv:0909.2711 |
in this paper, we obtain complete characterization for nested canalyzing functions ( ncfs ) by obtaining its unique algebraic normal form ( polynomial form ). we introduce a new concept, layer number for ncf. based on this, we obtain explicit formulas for the the following important parameters : 1 ) number of all the nested canalyzing functions, 2 ) number of all the ncfs with given layer number, 3 ) hamming weight of any ncf, 4 ) the activity number of any variable of any ncf, 5 ) the average sensitivity of any ncf. based on these formulas, we show the activity number is greater for those variables in out layer and equal in the same layer. we show the average sensitivity attains minimal value when the ncf has only one layer. we also prove the average sensitivity for any ncf ( no matter how many variables it has ) is between 0 and 2. hence, theoretically, we show why ncf is stable since a random boolean function has average sensitivity $ \ frac { n } { 2 } $. finally we conjecture that the ncf attain the maximal average sensitivity if it has the maximal layer number $ n - 1 $. hence, we guess the uniform upper bound for the average sensitivity of any ncf can be reduced to 4 / 3 which is tight. | arxiv:1111.7217 |
we hope to see how much for a model m of some completion t of pa ( peano arithmetic ) does m restriction { < } determine m, say up to isomorphism. we advance in characterizing for non - standard models m of pa the " minimal " set { ( a, b ) : n < a < b for n in n and the linear orders { c : c < _ m a }, { c : c < _ m b } are isomorphic }, in particular include { ( a, b ) : for no c in m for every n in n we have m models ( forall n in n ) ( exists c ) [ 2 < c ^ n < a wedge b < a c ^ n ] } and for some model is equal to { ( a, b ) : a < b < a ^ n for some n in n }. | arxiv:1004.3342 |
self - supervised learning ( especially contrastive learning ) methods on heterogeneous graphs can effectively get rid of the dependence on supervisory data. meanwhile, most existing representation learning methods embed the heterogeneous graphs into a single geometric space, either euclidean or hyperbolic. this kind of single geometric view is usually not enough to observe the complete picture of heterogeneous graphs due to their rich semantics and complex structures. under these observations, this paper proposes a novel self - supervised learning method, termed as geometry contrastive learning ( gcl ), to better represent the heterogeneous graphs when supervisory data is unavailable. gcl views a heterogeneous graph from euclidean and hyperbolic perspective simultaneously, aiming to make a strong merger of the ability of modeling rich semantics and complex structures, which is expected to bring in more benefits for downstream tasks. gcl maximizes the mutual information between two geometric views by contrasting representations at both local - local and local - global semantic levels. extensive experiments on four benchmarks data sets show that the proposed approach outperforms the strong baselines, including both unsupervised methods and supervised methods, on three tasks, including node classification, node clustering and similarity search. | arxiv:2206.12547 |
unmanned aerial vehicles ( uavs ) are now beginning to be deployed for enhancing the network performance and coverage in wireless communication. however, due to the limitation of their on - board power and flight time, it is challenging to obtain an optimal resource allocation scheme for the uav - assisted internet of things ( iot ). in this paper, we design a new uav - assisted iot systems relying on the shortest flight path of the uavs while maximising the amount of data collected from iot devices. then, a deep reinforcement learning - based technique is conceived for finding the optimal trajectory and throughput in a specific coverage area. after training, the uav has the ability to autonomously collect all the data from user nodes at a significant total sum - rate improvement while minimising the associated resources used. numerical results are provided to highlight how our techniques strike a balance between the throughput attained, trajectory, and the time spent. more explicitly, we characterise the attainable performance in terms of the uav trajectory, the expected reward and the total sum - rate. | arxiv:2106.03129 |
we study the online influence maximization problem in social networks under the independent cascade model. specifically, we aim to learn the set of " best influencers " in a social network online while repeatedly interacting with it. we address the challenges of ( i ) combinatorial action space, since the number of feasible influencer sets grows exponentially with the maximum number of influencers, and ( ii ) limited feedback, since only the influenced portion of the network is observed. under a stochastic semi - bandit feedback, we propose and analyze imlinucb, a computationally efficient ucb - based algorithm. our bounds on the cumulative regret are polynomial in all quantities of interest, achieve near - optimal dependence on the number of interactions and reflect the topology of the network and the activation probabilities of its edges, thereby giving insights on the problem complexity. to the best of our knowledge, these are the first such results. our experiments show that in several representative graph topologies, the regret of imlinucb scales as suggested by our upper bounds. imlinucb permits linear generalization and thus is both statistically and computationally suitable for large - scale problems. our experiments also show that imlinucb with linear generalization can lead to low regret in real - world online influence maximization. | arxiv:1605.06593 |
we give a unified generalization of dugas ' construction on stable auto - equivalences of morita type from local symmetric algebras to arbitrary symmetric algebras. for group algebras $ kp $ of $ p $ - groups in characteristic $ p $, we recover all the stable auto - equivalences corresponding to endo - trivial modules over $ kp $ except that $ p $ is generalized quaternion of order $ 2 ^ m $. moreover, we give many examples of stable auto - equivalences of morita type for non - local symmetric algebras. | arxiv:2310.13934 |
in this paper, we study how to construct f ( r ) gravity models. cosmological observations and local gravity tests imply that a viable f ( r ) model should be very close to the lcdm model. we create procedures to construct viable lcdm - like f ( r ) models, and present multiple models of three types. the connections between some of these models are discussed. we also study the cosmological evolution of the lcdm - like f ( r ) gravity. exact numerical integration can generate accurate cosmological evolution, but the numerical simulation in the early - universe stage is slow due to the oscillations of the field phi ( = f ' ) near the minimum of the effective potential. to avoid this problem, we take the minimum of the effective potential as an approximate solution for phi, and obtain the cosmological evolution. this approximate method describes the cosmological evolution well except in the late universe. therefore, we use the approximate method in the early - universe evolution, and use the exact method in the late - universe one. | arxiv:1307.2660 |
the theory of general relativity has successfully passed a large number of observational tests. the theory has been extensively tested in the weak - field regime with experiments in the solar system and observations of binary pulsars. the past five years have seen significant advancements in the study of the strong - field regime, which can now be tested with gravitational waves, x - ray data, and mm very long baseline interferometry observations. here i summarize the state - of - the - art of the tests of general relativity with black hole x - ray data, discussing its recent progress and future developments. | arxiv:2103.11365 |
increasing the sensitivity of chiral spectroscopic techniques such as circular dichroism ( cd ) spectroscopy is a current aspiration in the research field of nanophotonics. enhancing cd spectroscopy depends upon of two complementary requirements : the enhancement of the electromagnetic fields perceived by the molecules under study and the conservation of the helicity of those fields, guaranteed by duality symmetry. in this work, we introduce a systematic method to design nanostructured dual periodic photonic systems capable of enhancing molecular cd spectroscopy resonantly. as an illustration, we engineer a dual 1d silicon nanoparticle array and show that its collective optical modes can be efficiently employed to resonantly enhance by two orders of magnitude the local density of optical chirality and, thus, the cd signal obtained from a given molecular sample on its vicinity. | arxiv:2003.07653 |
we prove central limit theorem under diffusive scaling for the displacement of a random walk on $ { \ mathbb z } ^ d $ in stationary divergence - free random drift field, under the $ { \ mathcal h } _ { - 1 } $ - condition imposed on the drift field. the condition is equivalent to assuming that the stream tensor be stationary and square integrable. this improves the best existing result of komorowski, landim and olla ( 2012 ), where it is assumed that the stream tensor be in $ { \ mathcal l } ^ { \ max \ { 2 + \ delta, d \ } } $, with $ \ delta > 0 $. our proof relies on the relaxed sector condition of horv \ ' ath, t \ ' oth and vet \ h { o } ( 2012 ), and is technically rather simpler than existing earlier proofs of similar results by oelschl \ " ager ( 1988 ) and komorowski, landim, olla ( 2012 ). | arxiv:1411.4171 |
variational bayesian monte carlo ( vbmc ) is a sample - efficient method for approximate bayesian inference with computationally expensive likelihoods. while vbmc ' s local surrogate approach provides stable approximations, its conservative exploration strategy and limited evaluation budget can cause it to miss regions of complex posteriors. in this work, we introduce stacking variational bayesian monte carlo ( s - vbmc ), a method that constructs global posterior approximations by merging independent vbmc runs through a principled and inexpensive post - processing step. our approach leverages vbmc ' s mixture posterior representation and per - component evidence estimates, requiring no additional likelihood evaluations while being naturally parallelizable. we demonstrate s - vbmc ' s effectiveness on two synthetic problems designed to challenge vbmc ' s exploration capabilities and two real - world applications from computational neuroscience, showing substantial improvements in posterior approximation quality across all cases. | arxiv:2504.05004 |
in this book, the authors define several new types of soft neutrosophic algebraic structures over neutrosophic algebraic structures and we study their generalizations. these soft neutrosophic algebraic structures are basically parameterized collections of neutrosophic sub - algebraic structures of the neutrosophic algebraic structure. an important feature of this book is that the authors introduce the soft neutrosophic group ring, soft neutrosophic semigroup ring with its generalization, and soft mixed neutrosophic n - algebraic structure over neutrosophic group ring, then the neutrosophic semigroup ring and mixed neutrosophic n - algebraic structure respectively. | arxiv:1409.3763 |
we present high signal to noise ratio spitzer infrared spectrograph observations of 17 virgo early - type galaxies. the galaxies were selected from those that define the colour - magnitude relation of the cluster, with the aim of detecting the silicate emission of their dusty, mass - losing evolved stars. to flux calibrate these extended sources we have devised a new procedure that allows us to obtain the intrinsic spectral energy distribution and to disentangle resolved and unresolved emission within the same object. we have found that thirteen objects of the sample ( 76 % ) are passively evolving galaxies with a pronounced broad silicate feature which is spatially extended and likely of stellar origin, in agreement with model predictions. the other 4 objects ( 24 % ) are characterized by different levels of activity. in ngc 4486 ( m 87 ) the line emission and the broad silicate emission are evidently unresolved and, given also the typical shape of the continuum, they likely originate in the nuclear torus. ngc 4636 shows emission lines superimposed on extended ( i. e. stellar ) silicate emission, thus pushing the percentage of galaxies with silicate emission to 82 %. finally, ngc 4550 and ngc 4435 are characterized by polycyclic aromatic hydrocarbon ( pah ) and line emission, arising from a central unresolved region. a more detailed analysis of our sample, with updated models, will be presented in a forthcoming paper. | arxiv:astro-ph/0602014 |
in this paper we present a new and simple language - independent method for word - alignment based on the use of external sources of bilingual information such as machine translation systems. we show that the few parameters of the aligner can be trained on a very small corpus, which leads to results comparable to those obtained by the state - of - the - art tool giza + + in terms of precision. regarding other metrics, such as alignment error rate or f - measure, the parametric aligner, when trained on a very small gold - standard ( 450 pairs of sentences ), provides results comparable to those produced by giza + + when trained on an in - domain corpus of around 10, 000 pairs of sentences. furthermore, the results obtained indicate that the training is domain - independent, which enables the use of the trained aligner ' on the fly ' on any new pair of sentences. | arxiv:1212.1192 |
recent x - ray variability studies suggest that the log of the square of the fractional rms variability amplitude, rms ^ 2, seems to correlate with the log of the agn black - hole mass, m _ bh, with larger black holes being less variable for a fixed time interval. this has motivated the theoretical modeling of the rms ^ 2 - m _ bh correlation with the aim of constraining agn masses based on x - ray variability. a viable approach to addressing this problem is to assume an underlying power spectral density with a suitable mass dependence, derive the functional form of the rms ^ 2 - m _ bh correlation for a given sampling pattern, and investigate whether the result is consistent with the observations. for simplicity, previous studies, inspired by the similarities shared by the timing properties of agn and x - ray binaries, have explored model power spectral densities characterized by broken power laws. and ignored, in general, the distorting effects that the particular sampling pattern imprints in the observed power spectral density. motivated by the latest timing results from x - ray binaries, obtained with rxte, we propose that agn broad - band noise spectra consist of a small number of lorentzian components. this assumption allows, for the first time, to fully account for sampling effects in theoretical models of x - ray variability in an analytic manner. we show that, neglecting sampling effects when deriving the fractional rms from the model power spectral density can lead to underestimating it by a factor of up to 80 % with respect to its true value for the typical sampling patterns used to monitor agn. we discuss the implications of our results for the derivation of agn masses using theoretical models of the rms ^ 2 - m _ bh correlation. ( abridged ) | arxiv:astro-ph/0509358 |
as the sizes of graphs grow rapidly, currently many real - world graphs can hardly be loaded in the main memory. it becomes a hot topic to compute depth - first search ( dfs ) results, i. e., depth - first order or dfs - tree, on semi - external memory model. semi - external algorithms assume the main memory could at least hold a spanning tree t of a graph g, and gradually restructure t into a dfs - tree, which is non - trivial. in this paper, we present a comprehensive study of semi - external dfs problem. based on our theoretical analysis of its main challenge, we introduce a new semi - external dfs algorithm, named ep - dfs, with a lightweight index n + - index. unlike traditional algorithms, we focus on addressing such complex problem efficiently not only with less i / os, but also with simpler cpu calculation ( implementation - friendly ) and less random i / o accesses ( key - to - efficiency ). extensive experimental evaluation is conducted on both synthetic and real graphs. the experimental results confirm that our ep - dfs algorithm significantly outperforms existing algorithms. | arxiv:2006.03198 |
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