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Li Zhou

Publications and source records attributed to Li Zhou.

198 records · Page 11Linked to original sources
arXiv2014

Aging research of the LAB-based liquid scintillator in stainless steel container

Stainless steel is the material used for the storage vessels and piping systems of LAB-based liquid scintillator in JUNO experiment. Aging is recognized as one of the main degradation mechanisms affecting the properties of liquid scintillator. LAB-based liquid scintillator aging experiments were carried out in different material of containers (type 316 and 304 stainless steel and glass) at two different temperature (40 and 25 degrees Celsius). For the continuous liquid scintillator properties tests, the light yield and the absorption spectrum are nearly the same as that of the unaged one. The attenuation length of the aged samples is 6%~12% shorter than that of the unaged one. But the concentration of element Fe in the LAB-based liquid scintillator does not show a clear change. So the self aging has small effect on liquid scintillator, as well as the stainless steel impurity quenching. Type 316 and 304 stainless steel can be used as LAB-based liquid scintillator vessel, transportation pipeline material.

physics.ins-det↗
arXiv2014

Relations of stellar mass between electron temperature-based metallicity of star-forming galaxies in a wide mass range

We select 947 star-forming galaxies from SDSS-DR7 with [O~{\sc iii}]$λ$4363 emission lines detected at a signal-to-noise {ratio }larger than 5$σ$. Their electron temperatures and direct oxygen abundances are {then }determined. {W}e compare the results from different methods. $t_2${, the} electron temperature in {the }low ionization region{,} estimated from $t_3${, that} in {the }high ionization region{,} {is} compared {using} three analysis relations between $t_2-t_3${. These} show obvious differences, which result in some different ionic oxygen abundances. The results of $t_3$, $t_2$, {$\rm O^{++}$/$\rm H^+$} and {$\rm O^{+}$/$\rm H^+$} derived by using methods from IRAF and literature are also compared. The ionic abundances $\rm O^{++}$/$\rm H^+$ {are} higher than $\rm O^{+}$/$\rm H^+$ for most cases. The{ different} oxygen abundances derived from $T_{\rm e}$ and the strong-line ratios show {a }clear discrepancy, which is more obvious following increasing stellar mass and strong-line ratio $R_{23}$. The sample{ of} galaxies from SDSS {with} detected [O~{\sc iii}]$λ$4363 have lower metallicites and higher {star formation rates}, {so} they may not be typical representatives of the whole{ population of} galaxies. Adopting data objects from {Andrews \& Martini}, {Liang et al.} and {Lee et al.} data, we derive new relations of stellar mass and metallicity for star-forming galaxies in a much wider stellar mass range: from $10^6\,M_\odot$ to $10^{11}\,M_\odot$.

astro-ph.GA↗
arXiv2014

Measurement of the liquid scintillator nonlinear energy response to electron

Nonlinearity of the liquid scintillator energy response is a key to measuring the neutrino energy spectrum in reactor neutrino experiments such as Daya Bay and JUNO. We measured in laboratory the nonlinearity of the Linear Alkyl Benzene based liquid scintillator, which is used in Daya Bay and will be used in JUNO, via Compton scattering process. By tagging the scattered gamma from the liquid scintillator sample simultaneously at seven angles, the instability of the system was largely cancelled. The accurately measured nonlinearity will improve the precision of the $θ_{13}$, $Δm^2$, and reactor neutrino spectrum measurements at Daya Bay.

physics.ins-det↗
arXiv2014

Production of Gadolinium-loaded Liquid Scintillator for the Daya Bay Reactor Neutrino Experiment

We report on the production and characterization of liquid scintillators for the detection of electron antineutrinos by the Daya Bay Reactor Neutrino Experiment. One hundred eighty-five tons of gadolinium-loaded (0.1% by mass) liquid scintillator (Gd-LS) and two hundred tons of unloaded liquid scintillator (LS) were successfully produced from a linear-alkylbenzene (LAB) solvent in six months. The scintillator properties, the production and purification systems, and the quality assurance and control (QA/QC) procedures are described.

physics.ins-det↗
arXiv2014

Turbulence Mitigation Scheme for Optical Communications using Orbital Angular Momentum Multiplexing Based on Channel Coding and Wavefront Correction

The free-space optical (FSO) communication links with orbital angular momentum (OAM) multiplexing have been demonstrated that they can largely enhance the systems' capacity without a corresponding increase in spectral bandwidth, but the performance of the system is unavoidably disturbed by atmospheric turbulence (AT). Different from the existed AT disturbance, the OAM-multiplexed systems will cause both the burst and random errors for a single OAM state carrier and the `crosstalk' interference between the different OAM states carriers. In this paper, we propose a turbulence mitigation method to improve AT tolerance of OAM-multiplexed FSO communication links. In the proposed scheme, we use channel codes to correct the burst and random errors caused by AT for a single OAM state carrier; And we use wavefront correction method to correct the `crosstalk' interference between the different OAM states carriers. The improvements of AT tolerance are discussed by comparing the performance of OAM-multiplexed FSO communication links with or without channel coding or Shark-Hartmann wavefront correction method. The numerical simulation results show that the OAM-multiplexed FSO communication links have enhanced their AT tolerance. The usage of channel codes and wavefront correction methods together has improved greatly the performance of OAM-multiplexed FSO communication links over atmospheric turbulence.

physics.optics↗
arXiv2013

On Approximation of the Backward Stochastic Differential Equation

We consider the problem of approximation of the solution of the backward stochastic differential equation in the Markovian case. We suppose that the trend coefficient of the diffusion process depends on some unknown parameter and the diffusion coefficient of this equation is small. We propose an approximation of this solution based on the one-step MLE of the unknown parameter and we show that this approximation is asymptotically efficient in the asymptotics of "small noise".

math.ST↗
arXiv2012

On Goodness-of-fit Testing for Ergodic Diffusion Process with Shift Parameter

A problem of goodness-of-fit test for ergodic diffusion processes is presented. In the null hypothesis the drift of the diffusion is supposed to be in a parametric form with unknown shift parameter. Two Cramer-Von Mises type test statistics are studied. The first one is based on local time estimator of the invariant density, the second one is based on the empirical distribution function. The unknown parameter is estimated via the maximum likelihood estimator. It is shown that both the limit distributions of the two test statistics do not depend on the unknown parameter, so the distributions of the tests are asymptotically parameter free. Some considerations on the consistency of the proposed tests and some simulation studies are also given.

math.ST↗
arXiv2011

Experimental study of THGEM detector with mini-rim

The gas gain and energy resolution of single and double THGEM detectors (5{\times}5cm2 effective area) with mini-rims (rim is less than 10μm) were studied. The maximum gain can reach 5{\times}103 and 2{\times}105 for single and double THGEM respectively, while the energy resolution of 5.9 keV X-ray varied from 18% to 28% for both single and double THGEM detectors of different hole sizes and thicknesses.All the experiments were investigated in mixture of noble gases(argon,neon) and small content of other gases(iso-butane,methane) at atmospheric pressure.

physics.ins-det↗
arXiv2011

The fast light of CsI(Na) crystals

The responds of different common alkali halide crystals to alpha-rays and gamma-rays are tested in our research. It is found that only CsI(Na) crystals have significantly different waveforms between alpha and gamma scintillations, while others have not this phenomena. It is suggested that the fast light of CsI(Na) crystals arises from the recombination of free electrons with self-trapped holes of the host crystal CsI. Self-absorption limits the emission of fast light of CsI(Tl) and NaI(Tl) crystals.

physics.ins-det↗
arXiv2011

Neutron-gamma discrimination of CsI(Na) crystals for dark matter searches

The luminescent properties of CsI(Na) crystals are studied in this report. By using a TDS3054C oscilloscope with a sampling frequency of 5 GS/s, we find out that nuclear recoil signals are dominated by very fast light pulse with a decay time of ~20 ns, while γ-ray signals have a decay time of ~600 ns. The wavelength of nuclear recoil and γ-ray signals are also different. The study of n/γ separation shows that the rejection factor can reach an order of 10-7 with signal efficiency more than 80% at an equivalent electron recoil energy of 20 keV or more. Such a property makes CsI(Na) an ideal candidate for dark matter searches.

physics.ins-det↗
arXiv2010

Viviani Polytopes and Fermat Points

Given a set of oriented hyperplanes $\mathcal{P}=\{p_1, ..., p_k\}$ in $\mathbb{R}^n$, define $v(P)$ for any point $P\in\mathbb{R}^n$ as the sum of the signed distances from $P$ to $p_1$,..., $p_k$. We give a simple geometric characterization of $\mathcal{P}$ so that $v$ is a constant. The characterization leads to a connection with the Fermat point of $k$ points in $\mathbb{R}^n$. Finally, we discuss historically the full content of Viviani's theorem.

math.MG↗
arXiv2010

Irrationality proofs à la Hermite

As rewards of reading two great papers of Hermite from 1873, we trace the historical origin of the integral Niven used in his well-known proof of the irrationality of $π$, uncover a rarely acknowledged simple proof by Hermite of the irrationality of $π^2$, give a new proof of the irrationality of $r\tan r$ for nonzero rational $r^2$, and generalize it to a proof of the irrationality of certain ratios of Bessel functions.

math.NT↗
arXiv2006

Little Higgs models and single top production at the LHC

We investigate the corrections of the littlest Higgs(LH) model and the SU(3) simple group model to single top production at the CERN Large Hardon Collider(LHC). We find that the new gauge bosons $W_{H}^{\pm}$ predicted by the LH model can generate significant contributions to single top production via the s-channel process. The correction terms for the tree-level $Wqq'$ couplings coming from the SU(3) simple group model can give large contributions to the cross sections of the t-channel single top production process. We expect that the effects of the LH model and the SU(3) simple group model on single top production can be detected at the LHC experiments.

hep-ph↗
arXiv2005

Single production of the gauge boson $W$ via polarized $e^{-}γ$ collisions in the littlest Higgs model

In the framework of the littlest Higgs($LH$) model, we study single production of the standard model($SM$) gauge boson $W_{s}^{-}$ and the heavy gauge boson $W_{H}^{-}$ via polarized $e^{-}γ$ collisions. We find that the corrections of the $LH$ model to the cross section $σ(W_{s}^{-})$ might be observed only for the scale parameter $f\leq 1.5TeV$ and the mixing parameter $c'\geq 0.4$ in future high energy linear $e^{+}e^{-}$ collider($LC$) experiment with the center-of-mass($CM$) energy $\sqrt{S}=500GeV$ and a yearly integrated luminosity $£=100fb^{-1}$. However, with a suitably chosen polarization of the initial electron and position beams, the possible signals of the heavy gauge boson $W_{H}^{-}$ can be easily detected via $e^{-}γ$ collisions in future $LC$ experiment with $\sqrt{S}=3TeV$ and $£=500fb^{-1}$.

hep-ph↗
arXiv2005

Lepton flavor violating signals of the neutral top-pion in future lepton colliders

The presence of the top-pions $π_{t}^{0,\pm}$ in the low-energy spectrum is an inevitable feature of the topcolor scenario. Taking into account the constraints of the present experimental limit of the lepton flavor violating($LFV$) process $μ\to eγ$ on the free parameters of topcolor-assisted techicolor(TC2) models, we study the contributions of the neutral top-pion $π^{0}_{t}$ to the $LFV$ processes $μ^{+}μ^{-}\toτμ$ (or $τe$), $ γγ\toτμ$ (or $τe$), $e^{+} e^{-}\toτμ$, and $e γ\to e π_{t}^{0}\to e τμ(e)$ via the flavor changing ($FC$) couplings $π_{t}^{0}l_{i}l_{j}$ and discuss the possibility of searching for the $LFV$ signals via these processes in future lepton colliders.

hep-ph↗
arXiv2000

Realization of an ultra-high magnetic field on a nano-scale

In tunnel junctions of which at least one side is a ferromagnet, very large magnetic polarization change ($\approx 0.1 μ_B$) and splitting of the spin up and spin down Fermi energy ($\approx 0.1 eV$) can be created under steady state finite current conditions (bias voltage $\approx$ 1 volt). This is {\bf much higher} than can be created by the highest magnetic field on earth. We illustrate this with a specific calculation of a recently observed very large Hall effect in the Al side of a Co-I-Al tunnel junction. Other recent experiments that support this idea are discussed.

cond-mat.mtrl-sci↗