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Jia Xu

Publications and source records attributed to Jia Xu.

At least 109 records · Page 6Linked to original sources
arXiv2016

Massively parallel dual-comb molecular detection with subharmonic optical parametric oscillators

Mid-infrared (mid-IR) spectroscopy offers unparalleled sensitivity for the detection of trace gases, solids and liquids, which is based on the existence of strong telltale vibrational bands in this part of the spectrum. It was shown more than a decade ago that a dual-comb Fourier spectroscopy could provide superior spectral coverage combined with high resolution and extremely fast data acquisition. Capabilities of this method were limited because of difficulty of producing twins of mutually coherent frequency combs in the mid- IR. Here we report a phase-coherent and broadband dual-comb system that is based on a pair of subharmonic (frequency-divide-by-two) optical parametric oscillators, pumped in turn by two phase-locked thulium fiber lasers at 2-micron wavelength. We demonstrate simultaneous detection of multiple molecular species in the whole band of 3.2-5.3 microns (frequency span 1200 cm^{-1}) augmented by the pump laser band of 1.85-2 microns (span 400 cm^{-1}), with spectral resolution 0.01-0.07 cm^{-1} and acquisition speed of up to 160,000 resolution elements in few seconds.

physics.optics↗
arXiv2015

Converting Instance Checking to Subsumption: A Rethink for Object Queries over Practical Ontologies

Efficiently querying Description Logic (DL) ontologies is becoming a vital task in various data-intensive DL applications. Considered as a basic service for answering object queries over DL ontologies, instance checking can be realized by using the most specific concept (MSC) method, which converts instance checking into subsumption problems. This method, however, loses its simplicity and efficiency when applied to large and complex ontologies, as it tends to generate very large MSC's that could lead to intractable reasoning. In this paper, we propose a revision to this MSC method for DL SHI, allowing it to generate much simpler and smaller concepts that are specific-enough to answer a given query. With independence between computed MSC's, scalability for query answering can also be achieved by distributing and parallelizing the computations. An empirical evaluation shows the efficacy of our revised MSC method and the significant efficiency achieved when using it for answering object queries.

cs.AI↗
arXiv2015

Phrase Based Language Model For Statistical Machine Translation

We consider phrase based Language Models (LM), which generalize the commonly used word level models. Similar concept on phrase based LMs appears in speech recognition, which is rather specialized and thus less suitable for machine translation (MT). In contrast to the dependency LM, we first introduce the exhaustive phrase-based LMs tailored for MT use. Preliminary experimental results show that our approach outperform word based LMs with the respect to perplexity and translation quality.

cs.CL↗
arXiv2014

A Successive Resultant Projection for Cylindrical Algebraic Decomposition

This note shows the equivalence of two projection operators which both can be used in cylindrical algebraic decomposition (CAD) . One is known as Brown's Projection (C. W. Brown (2001)); the other was proposed by Lu Yang in his earlier work (L.Yang and S.~H. Xia (2000)) that is sketched as follows: given a polynomial $f$ in $x_1,\,x_2,\,\cdots$, by $f_1$ denote the resultant of $f$ and its partial derivative with respect to $x_1$ (removing the multiple factors), by $f_2$ denote the resultant of $f_1$ and its partial derivative with respect to $x_2$, (removing the multiple factors), $\cdots$, repeat this procedure successively until the last resultant becomes a univariate polynomial. Making use of an identity, the equivalence of these two projection operators is evident.

cs.SC↗
arXiv2014

On the finite convergence of a projected cutter method

The subgradient projection iteration is a classical method for solving a convex inequality. Motivated by works of Polyak and of Crombez, we present and analyze a more general method for finding a fixed point of a cutter, provided that the fixed point set has nonempty interior. Our assumptions on the parameters are more general than existing ones. Various limiting examples and comparisons are provided.

math.OC↗
arXiv2014

The Data Acquisition System for the KOTO Experiment

We developed and built a new system of readout and trigger electronics, based on the waveform digitization and pipeline readout, for the KOTO experiment at J-PARC, Japan. KOTO aims at observing the rare kaon decay $K_{L}\rightarrowπ^{0}ν\barν$. A total of 4000 readout channels from various detector subsystems are digitized by 14-bit 125-MHz ADC modules equipped with a 10-pole Bessel filter in order to reduce the pile-up effects. The trigger decision is made every 8-ns using the digitized waveform information. To avoid dead time, the ADC and trigger modules have pipelines in their FPGA chips to store data while waiting for the trigger decision. The KOTO experiment performed the first physics run in May 2013. The data acquisition system worked stably during the run.

physics.ins-det↗
arXiv2014

Extract ABox Modules for Efficient Ontology Querying

The extraction of logically-independent fragments out of an ontology ABox can be useful for solving the tractability problem of querying ontologies with large ABoxes. In this paper, we propose a formal definition of an ABox module, such that it guarantees complete preservation of facts about a given set of individuals, and thus can be reasoned independently w.r.t. the ontology TBox. With ABox modules of this type, isolated or distributed (parallel) ABox reasoning becomes feasible, and more efficient data retrieval from ontology ABoxes can be attained. To compute such an ABox module, we present a theoretical approach and also an approximation for $\mathcal{SHIQ}$ ontologies. Evaluation of the module approximation on different types of ontologies shows that, on average, extracted ABox modules are significantly smaller than the entire ABox, and the time for ontology reasoning based on ABox modules can be improved significantly.

cs.AI↗
arXiv2014

On subgradient projectors

The subgradient projector is of considerable importance in convex optimization because it plays the key role in Polyak's seminal work - and the many papers it spawned - on subgradient projection algorithms for solving convex feasibility problems. In this paper, we offer a systematic study of the subgradient projector. Fundamental properties such as continuity, nonexpansiveness, and monotonicity are investigated. We also discuss the Yamagishi-Yamada operator. Numerous examples illustrate our results.

math.OC↗
arXiv2013

Simulation studies of the behavior of positrons in a microtrap with long aspect ratio

The charged particles storage capacity of microtraps (micro-Penning-Malmberg traps) with large length to radius aspect ratios and radii of the order of tens of microns was explored. Simulation studies of the motions of charged particles were conducted with particle-in-cell WARP code and the Charged Particle Optics (CPO) program. The new design of the trap consisted of an array of microtraps with substantially lower end electrodes potential than conventional Penning-Malmberg traps, which makes this trap quite portable. It was computationally shown that each microtrap with 50 micron radius stored positrons with a density (1.6x10^11 cm^-3) even higher than that in conventional Penning-Malmberg traps (about 10^11 cm^-3) while the confinement voltage was only 10 V. It was presented in this work how to evaluate and lower the numerical noise by controlling the modeling parameters so the simulated plasma can evolve toward computational equilibrium. The local equilibrium distribution, where longitudinal force balance is satisfied along each magnetic field line, was attained in time scales of the simulation for plasmas initialized with a uniform density and Boltzmann energy distribution. The charge clouds developed the expected radial soft edge density distribution and rigid rotation evolved to some extent. To reach global equilibrium (i.e. rigid rotation) longer runs are required. The plasma confinement time and its thermalization were independent of the length. The length-dependency, reported in experiments, is due to fabrication and field errors. Computationally, more than one hundred million positrons were trapped in one microtrap with 50 micron radius and 10 cm length immersed in a 7 T uniform, axial magnetic field, and the density scaled as r^-2 down to 3 micron. Larger densities were trapped with higher barrier potentials.

physics.plasm-ph↗
arXiv2012

Exclusive decay of $Υ$ into $J/ψ+χ_{c0,1,2}$

We study the $Υ$ exclusive decay into double charmonium, specifically, the $S$-wave charmonium $ J/ψ$ plus the $P$-wave charmonium $χ_{c0,1,2}$ in the NRQCD factorization framework. Three distinct decay mechanisms, i.e., the strong, electromagnetic and radiative decay channels are included and their interference effects are investigated. The decay processes $Υ(1S,2S,3S)\to J/ψ+χ_{c1,0}$ are predicted to have the branching fractions of order $10^{-6}$, which should be observed in the prospective Super $B$ factory.

hep-ph↗
arXiv2012

Low-voltage Driving Phototransistor Based on Dye-sensitized Nanocrystalline Titanium Dioxide Thin Films

Photo-gated transistors based on dye-sensitized nanocrystalline titanium dioxide thin film are established. A transistor-like transport behavior characterized by the linear increase, saturated plateau, and breakdown-like increase in the voltage-current curve is achievable with a low driven bias for the present device. The response current exhibits a linear dependence on the intensity of gated light, and the measured maximum photosensitivity is approximately 0.1 A/W. The dynamic responses for various light frequencies and their dependences on the load resistances are investigated as well. The cut-off frequency of ~50 Hz is abstracted, indicating the potential application for economical and efficient light switch or optical communication unit. The dc photo-gated response is explained by the energy level diagram, and is numerically simulated by an equivalent circuit model, suggesting a clear correlation between photovoltaic and photoconductive behaviors as well as their optical responses.

physics.chem-ph↗
arXiv2012

Inclusive $h_c$ production at $B$ factories

Within the nonrelativistic QCD (NRQCD) factorization framework, we investigate the inclusive production of the $h_c$ meson associated with either light hadrons or charmed hadrons at $B$ factory energy $\sqrt{s}=10.58$ GeV. Both the leading color-singlet and color-octet channels are included. For the $h_c$ production associated with light hadrons, the total production rate is dominated by the color-octet channel, thus the future measurement of this process may impose useful constraint on the value of the color-octet matrix element $<{\cal O}^{h_c}_8({}^1S_0)>$; for the $h_c$ production associated with charmed hadrons, the total production rate is about one order of magnitude smaller, and dominated by the color-singlet channel.

hep-ph↗
arXiv2012

The expansion of real forms on the simplex and applications

If n points B_1,---,B_n$ in the standard simplex Δ_n are affinely independent, then they can span an (n-1)-simplex denoted by Λ=Con(B_1,---,B_n). Here Λcorresponds to an n*n matrix [Λ] whose columns are B_1,---,B_n. In this paper, we firstly proved that if Λof diameter sufficiently small contains a point $P$, and f(P)>0 (<0) for a form f in R[X], then the coefficients of f([Λ] X) are all positive (negative). Next, as an application of this result, a necessary and sufficient condition for determining the real zeros on Δ_n of a system of homogeneous algebraic equations with integral coefficients is established.

math.AG↗
arXiv2012

Four Jets as a Probe of O(100 GeV) Physics beyond Standard Model at Hadron Colliders

O(100 GeV) physics beyond the standard model (BSM) could be overlooked provided that it is hidden in the untouched Higgs sector or jets. The top quark forward-backward asymmetry measurements and di-jet bump, which is observed in the associated production with charged lepton plus missing energy (supposed arising from W decay), may indicate the existence of a new color-octet axial-vector Z_C with a mass about 145 GeV. Here Z_C only decays into two jets. In this paper we investigated the possibility to discover Z_C pair via analyzing the four jets as the final states, which are heavily polluted by huge QCD background. Our simulation showed that, however, both Tevatron and LHC have the excellent chance to discover Z_C through analyzing the four jets events in the current accumulated data.

hep-ph↗
arXiv2011

An algorithm for determining copositive matrices

In this paper, we present an algorithm of simple exponential growth called COPOMATRIX for determining the copositivity of a real symmetric matrix. The core of this algorithm is a decomposition theorem, which is used to deal with simplicial subdivision of $\hat{T}^{-}=\{y\in Δ_{m}| β^Ty\leq 0\}$ on the standard simplex $Δ_m$, where each component of the vector $β$ is -1, 0 or 1.

math.RA↗
arXiv2011

$O(α_s v^2)$ correction to pseudoscalar quarkonium decay to two photons

We investigate the $O(α_s v^2)$ correction to the process of pseudoscalar quarkonium decay to two photons in nonrelativistic QCD (NRQCD) factorization framework. The short-distance coefficient associated with the relative-order $v^2$ NRQCD matrix element is determined to next-to-leading order in $α_s$ through the perturbative matching procedure. Some technical subtleties encountered in calculating the ${O(α_s)$ QCD amplitude are thoroughly addressed.

hep-ph↗
arXiv2011

Sparse Support Recovery with Phase-Only Measurements

Sparse support recovery (SSR) is an important part of the compressive sensing (CS). Most of the current SSR methods are with the full information measurements. But in practice the amplitude part of the measurements may be seriously destroyed. The corrupted measurements mismatch the current SSR algorithms, which leads to serious performance degeneration. This paper considers the problem of SSR with only phase information. In the proposed method, the minimization of the l1 norm of the estimated sparse signal enforces sparse distribution, while a nonzero constraint of the uncorrupted random measurements' amplitudes with respect to the reconstructed sparse signal is introduced. Because it only requires the phase components of the measurements in the constraint, it can avoid the performance deterioration by corrupted amplitude components. Simulations demonstrate that the proposed phase-only SSR is superior in the support reconstruction accuracy when the amplitude components of the measurements are contaminated.

cs.IT↗