arXiv subjects

Dong Han

Publications and source records attributed to Dong Han.

54 records · Page 3Linked to original sources

arXiv2019

Optimal Sequential Tests for Monitoring Changes in the Distribution of Finite Observation Sequences

This article develops a method to construct the optimal sequential test for monitoring the changes in the distribution of finite observation sequences with a general dependence structure. This method allows us to prove that different optimal sequential tests can be constructed for different performance measures of detection delay times. We also provide a formula to calculate the value of the generalized out-of-control average run length for every optimal sequential test. Moreover, we show that there is an equivalent optimal control limit which does not depend on the test statistic directly when the post-change conditional densities (probabilities) of the observation sequences do not depend on the change time.

math.ST↗

arXiv2019

Coverage Probability Analysis Under Clustered Ambient Backscatter Nodes

In this paper, we consider a new large-scale communication scheme where randomly distributed AmBC nodes are involved as secondary users to primary transmitter (PT) and primary receiver (PR) pairs. The secondary communication between a backscatter transmitter (BT) and a backscatter receiver (BR) is conducted by the BT's reflecting its corresponding PT's signal with different antenna impedances, which introduces additional double fading channels and potential inter-symbol-interference to the primary communications. Thus, at a typical PR, the backscatter signals are regarded as either decodable signals or interference. Assuming the locations of PTs form a Poisson point process and the locations of BTs form a Poisson cluster process, we derive the SINR and SIR based coverage probabilities for two network configuration scenarios. Numerical results on the coverage probabilities indicate the possibility to involve a large amount of AmBC nodes in existing wireless networks.

cs.IT↗

arXiv2019

Stacking-Dependent Spatial Charge Separation in Graphitic Carbonic Nitride layers

We reveal the existence of stacking-dependent spatial(SDS) charge separation in graphitic carbonic nitride (g-C3N4) layers, with the density functional theory (DFT) calculations. In g-C3N4 bilayers, such SDS charge separation is found in particular effective for top valence bands that can drive electrons 100% away from one layer to the other. However, for bottom conduction ones, it results in little charge redistribution between layers. As spatial charge separation naturally suppresses the electron-hole recombination, that makes g-C3N4 layers with proper stacking much more efficient for harvesting solar energy in photovoltaic or photocatalytic applications. The SDS charge separation has been understood as a result of the inter-layer quantum entanglement from those g-C3N4 band electrons, whose unique chirality and phases in corner-atom-shared C6N10 units are relatively isolated and in tune only through the corner N atoms. The SDS charge separation in g-C3N4 may lead to an intrinsic way, i.e. without alien dopings, interfaces or electrical fields, to manipulate charge carriers in semiconducting materials. That may lead to new physics in the future optoelectronics or electronics of two-dimensional (2D) materials, such as realizing the layer-selected charge transport through the bilayer or multi-layer 2D materials.

cond-mat.mtrl-sci↗

arXiv2018

Multi-distance Support Matrix Machines

Real-world data such as digital images, MRI scans and electroencephalography signals are naturally represented as matrices with structural information. Most existing classifiers aim to capture these structures by regularizing the regression matrix to be low-rank or sparse. Some other methodologies introduce factorization technique to explore nonlinear relationships of matrix data in kernel space. In this paper, we propose a multi-distance support matrix machine (MDSMM), which provides a principled way of solving matrix classification problems. The multi-distance is introduced to capture the correlation within matrix data, by means of intrinsic information in rows and columns of input data. A complex hyperplane is established upon these values to separate distinct classes. We further study the generalization bounds for i.i.d. processes and non i.i.d. process based on both SVM and SMM classifiers. For typical hypothesis classes where matrix norms are constrained, MDSMM achieves a faster learning rate than traditional classifiers. We also provide a more general approach for samples without prior knowledge. We demonstrate the merits of the proposed method by conducting exhaustive experiments on both simulation study and a number of real-word datasets.

stat.ML↗

arXiv2018

The study of a new time reconstruction method for MRPC read out by waveform digitizer

The measurement of the $K^{\pm}$ production in the Semi-Inclusive Deep Inelastic Scattering (SIDIS) can provide further knowledge about the structure of nucleon, and thus it is purposed in the Solenoidal Large Intensity Device(SoLID) at Jefferson Lab(JLab). In this experiment, the identification of the kaons is planed to be accomplished with the Multi-gap Resistive Plate Chambers(MRPC), and the requirement for the time resolution is around 20 $\rm ps$. This is very challenging for the present MRPC systems (typical resolution 60 $\rm ps$), while in this paper, it is proved that the performance can be improved largely if the signal waveform is obtained and analyzed with a neural network method. In a cosmic ray experiment, the time resolution of a 6-gap 0.25$\rm mm$-thick MRPC reaches 36 $\rm ps$ with this method, and a even better performance is expected with a thinner MRPC.

physics.ins-det↗

arXiv2018

A standalone simulation framework of the MRPC detector read out in waveforms

Dedicated detector simulations are very important for the success of high energy physics experiments. They not only bring benefits to the optimization of the detectors, but can also improve the precision of the physics results. To design a Multi-gap Resistive Plate Chamber (MRPC) with a very good time resolution, a detailed monte-carlo simulation of the detector is needed and described in this paper. The simulation can produce detector signal waveforms which contain a complete information about the events. The detector performance filled with different gas mixtures is studied, and comparison between simulation and experimental results show a good agreement.

physics.ins-det↗

arXiv2018

Sample size determination in superiority or non-inferiority clinical trials with time-to-event data under exponential, Weibull and Gompertz distributions

To examine the effect of exponential, Weibull and Gompertz distributions on sample size determination for superiority trials (STs) or non-inferiority trials (NTs) with time-to-event data, we present two sample size formulas for STs or NTs based on Weibull and Gompertz distributions, respectively. The formulas are compared with the current exponential formula to examine their performance. The simulation results show that the sample size formula based on the Weibull distribution is the most robust among the three formulas in STs or NTs. We suggest that recognizing the appropriate distribution in advance is beneficial for proper project planning and that assuming a Weibull distributed survival time is most advantageous in STs or NTs.

stat.AP↗

arXiv2018

Status of technology of MRPC time of flight system

Time of flight system (TOF) based on MRPC technology is widely used in modern physics experiments, and it also plays an important role in particle identification. With the increase of accelerator energy and luminosity, TOF system is required to indentify definite particles precisely under high rate environment. The MRPC technology TOF system can be defined as three generations. The first generation TOF is based on float glass MRPC and its time resolution is around 80ps, but the rate is relatively low (typically lower than 100Hz/cm2). The typical systems are TOF of RHIC-STAR, LHC-ALICE and BES III endcap. For the second generation TOF, its time resolution is in the same order with the first generation, but the rate capability is much higher. Its rate capability can reach 30kHz/cm2. The typical experiment with this high rate TOF is FAIR-CBM. The biggest challenge is on the third generation TOF. For example, the momentum upper limit of K/PI separation is around 7GeV/c for JLab-SoLID TOF system under high particle rate as high as 20kHz/cm2, the time requirement is around 20ps. The readout electronics of first two generations is based on time over threshold method and pulse shape sampling technology will be used in the third generation TOF. In the same time, the machine learning technology is also designed to analysis the time performance. In this paper, we will describe the evolution of MRPC TOF technology and key technology of each generation TOF.

physics.ins-det↗

arXiv2018

A neural network based algorithm for MRPC time reconstruction

Multi-gap Resistive Plate Chamber(MRPC) is a widely used timing detector with a typical time resolution of about 60 ps. This makes MRPC an optimal choice for the time of flight(ToF) system in many large physics experiments. The prior work on improving the time resolution is mainly focused on altering the detector geometry, and therefore the improvement of the data analysis algorithm has not been fully explored. This paper proposes a new time reconstruction algorithm based on the deep neural networks(NN) and improves the MRPC time resolution by about 10 ps. Since the development of the high energy physics experiments has pushed the timing requirements for the MRPC to a higher level, this algorithm could become a potential substitution of the time over threshold(ToT) method to achieve a time resolution below 30 ps.

physics.ins-det↗

arXiv2018

Sample size for a non-inferiority clinical trial with time-to-event data in the presence of competing risks

The analysis and planning methods for competing risks model have been described in the literatures in recent decades, and non-inferiority clinical trials are helpful in current pharmaceutical practice. Analytical methods for non-inferiority clinical trials in the presence of competing risks were investigated by Parpia et al., who indicated that the proportional sub-distribution hazard model is appropriate in the context of biological studies. However, the analytical methods of competing risks model differ from those appropriate for analyzing non-inferiority clinical trials with a single outcome; thus, a corresponding method for planning such trials is necessary. A sample size formula for non-inferiority clinical trials in the presence of competing risks based on the proportional sub-distribution hazard model is presented in this paper. The primary endpoint relies on the sub-distribution hazard ratio. A total of 120 simulations and an example based on a randomized controlled trial verified the empirical performance of the presented formula. The results demonstrate that the empirical power of sample size formulas based on the Weibull distribution for non-inferiority clinical trials with competing risks can reach the targeted power.

stat.AP↗

arXiv2018

Normal elements of completed group algebras over ${\rm SL}_3(\mathbb{Z}_p) $

Let $p$ be a prime integer and $\mathbb{Z}_p$ be the ring of $p$-adic integers. By a purely computational approach we prove that each nonzero normal element of a completed group algebra over the special linear group ${\rm SL}_3(\mathbb{Z}_p)$ is a unit. This give a positive answer to an open question in \cite{WeiBian2} and make up for an earlier mistake in \cite{WeiBian1} simultaneously.

math.NT↗

arXiv2016

Characterizations of Lie Higher Derivations on J-Subspace Lattice Algebras

Let $\mathcal{L}$ be a $\mathcal{J}$-subspace lattice on a Banach space $X$ over the real or complex field $\mathbb{F}$ and $ \mathrm{Alg}\mathcal{L}$ be the associated $\mathcal{J}$-subspace lattice algebras. In this paper, we characterize the structure of a family $\{L_n\}_{n=0}^{\infty}: \mathrm{Alg}\mathcal{L}\rightarrow \mathrm{Alg}\mathcal{L}$ of linear mappings satisfying the condition $$L_n([A, B])=\sum_{i+j=n}[L_i(A), L_j(B)]$$ for any $A, B\in\mathrm{Alg}\mathcal{L}$ with $AB = 0$. Moreover, the family $\{L_n\}_{n=0}^{\infty}: \mathrm{Alg}\mathcal{L}\rightarrow \mathrm{Alg}\mathcal{L}$ of linear mappings satisfying $L_n([A, B]_ξ)=\sum_{i+j=n}[L_i(A), L_j(B)]_ξ$ for any $A, B\in\mathrm{Alg}\mathcal{L}$ with $AB = 0$ and $1\neq ξ\in \mathbb{F}$ is also considered in the current work.

math.RA↗

arXiv2016

Sum Secrecy Rate Maximization for Full-Duplex Two-Way Relay Networks Using Alamouti-based Rank-Two Beamforming

Consider a two-way communication scenario where two single-antenna nodes, operating under full-duplex mode, exchange information to one another through the aid of a (full-duplex) multi-antenna relay, and there is another single-antenna node who intends to eavesdrop. The relay employs artificial noise (AN) to interfere the eavesdropper's channel, and amplify-forward (AF) Alamouti-based rank-two beamforming to establish the two-way communication links of the legitimate nodes. Our problem is to optimize the rank-two beamformer and AN covariance for sum secrecy rate maximization (SSRM). This SSRM problem is nonconvex, and we develop an efficient solution approach using semidefinite relaxation (SDR) and minorization-maximization (MM). We prove that SDR is tight for the SSRM problem and thus introduces no loss. Also, we consider an inexact MM method where an approximately but computationally cheap MM solution update is used in place of the exact update in conventional MM. We show that this inexact MM method guarantees convergence to a stationary solution to the SSRM problem. The effectiveness of our proposed approach is further demonstrated by an energy-harvesting scenario extension, and by extensive simulation results.

cs.IT↗

arXiv2016

Development and test of a real-size MRPC for CBM-TOF

In the CBM (Compressed Baryonic Matter) experiment constructed at the Facility for Anti-proton and Ion Research (Fair) at GSI, Darmstadt, Germany, MRPC(Multi-gap Resistive Plate Chamber) is adopted to construct the large TOF (Time-of-Flight) system to achieve an unprecedented precision of hadron identification, benefiting from its good time resolution, relatively high efficiency and low building price. We have developed a kind of double-ended readout strip MRPC. It uses low resistive glass to keep good performance of time resolution under high-rate condition. The differential double stack structure of 2x4 gas gaps help to reduce the required high voltage to half. There are 24 strips on one counter, and each is 270mm long, 7mm wide and the interval is 3mm. Ground is placed onto the MRPC electrode and feed through is carefully designed to match the 100 Ohm impedance of PADI electronics. The prototype of this strip MRPC has been tested with cosmic ray, a 98% efficiency and 60ps time resolution is gotten. In order to further examine the performance of the detector working under higher particle flux rate, the prototype has been tested in the 2014 October GSI beam time and 2015 February CERN beam time. In both beam times a relatively high rate of 1 kHz/cm2 was obtained. The calibration is done with CBM ROOT. A couple of corrections has been considered in the calibration and analysis process (including time-walk correction, gain correction, strip alignment correction and velocity correction) to access actual counter performances such as efficiency and time resolution. An efficiency of 97% and time resolution of 48ps are obtained. All these results show that the real-size prototype is fully capable of the requirement of the CBM-TOF, and new designs such as self-sealing are modified into the strip counter prototype to obtain even better performance.

physics.ins-det↗

arXiv2015

A Transmissive X-ray Polarimeter Design For Hard X-ray Focusing Telescopes

The X-ray Timing and Polarization (XTP) is a mission concept for a future space borne X-ray observatory and is currently selected for early phase study. We present a new design of X-ray polarimeter based on the time projection gas chamber. The polarimeter, placed above the focal plane, has an additional rear window that allows hard X-rays to penetrate (a transmission of nearly 80% at 6 keV) through it and reach the detector on the focal plane. Such a design is to compensate the low detection efficiency of gas detectors, at a low cost of sensitivity, and can maximize the science return of multilayer hard X-ray telescopes without the risk of moving focal plane instruments. The sensitivity in terms of minimum detectable polarization, based on current instrument configuration, is expected to be 3% for a 1mCrab source given an observing time of 10^5 s. We present preliminary test results, including photoelectron tracks and modulation curves, using a test chamber and polarized X-ray sources in the lab.

astro-ph.IM↗

arXiv2015

Online aging study of high rate MRPC

With the constant increase of accelerator luminosity, the rate requirements of the MRPC detectors become important. In the same time, aging problem of the detector has to be studied meticulously. An online aging test system is set up in our Lab. The setup of the system is described and the purpose is to study the performance stability during the long time running under high luminosity environment. The high rate MRPC has been irradiated by X-ray for 36 days and accumulated charge density reached 0.1C/cm2. No obvious performance degradation is observed for the detector.

physics.ins-det↗

arXiv2014

Noise Equivalent Counts Based Emission Image Reconstruction Algorithm of Tomographic Gamma Scanning

Tomographic Gamma Scanning (TGS) is a technique used to assay the nuclide distribution and radioactivity in nuclear waste drums. Both transmission and emission scans are performed in TGS and the transmission image is used for the attenuation correction in emission reconstructions. The error of the transmission image, which is not considered by the existing reconstruction algorithms, negatively affects the final results. An emission reconstruction method based on Noise Equivalent Counts (NEC) is presented. Noises from the attenuation image are concentrated to the projection data to apply the NEC Maximum-Likelihood Expectation-Maximization algorithm. Experiments are performed to verify the effectiveness of the proposed method.

nucl-ex↗

arXiv2011

A Large Area LaBr3/NaI Phoswich for Hard X-ray Astronomy

In terms of energy resolution, temporal response to burst events, and thermal stability, lanthanum bromide doped with Ce is a much better choice than the traditional NaI(Tl) scintillator for hard X-ray astronomy. We present the test results of a phoswich detector with a diameter of 101.6 mm consisting of 6 mm thick LaBr3:Ce and 40 mm thick NaI(Tl), which is the largest one of this type reported so far. The measured energy resolution is 10.6% at 60 keV, varying inversely proportional to the square root of the energy, and the energy nonlinearity is found to be less than 1%, as good as those of smaller phoswiches. The coupled scintillators and phototube also show excellent uniformity across the detecting surface, with a deviation of 0.7% on the pulse amplitude produced by 60 keV gamma-rays. Thanks to the large ratio of light decay times of NaI(Tl) and LaBr3:Ce, 250 ns vs. 16 ns, pulse shape discrimination is much easier for this combination than for NaI(Tl)/CsI(Na). As the light decay time of LaBr3:Ce is about 15 times faster than that of NaI(Tl), this phoswich is more suitable for detection of bright, transient sources such as gamma-ray bursts and soft gamma-ray repeaters. The internal activity of lanthanum produces a count rate of about 6 counts/s at 37.5 keV in the detector. This peak could be used for in-flight spectral calibration and gain correction.

astro-ph.IM↗