arXiv subjects

Wei Du

Publications and source records attributed to Wei Du.

At least 145 records · Page 8Linked to original sources

arXiv2019

Identifying Parameter Space for Robust Stability in Nonlinear Networks: A Microgrid Application

As modern engineering systems grow in complexity, attitudes toward a modular design approach become increasingly more favorable. A key challenge to a modular design approach is the certification of robust stability under uncertainties in the rest of the network. In this paper, we consider the problem of identifying the parametric region, which guarantees stability of the connected module in the robust sense under uncertainties. We derive the conditions under which the robust stability of the connected module is guaranteed for some values of the design parameters, and present a sum-of-squares (SOS) optimization-based algorithm to identify such a parametric region for polynomial systems. Using the example of an inverter-based microgrid, we show how this parametric region changes with variations in the level of uncertainties in the network.

math.OC↗

arXiv2019

Service Capacity Enhanced Task Offloading and Resource Allocation in Multi-Server Edge Computing Environment

An edge computing environment features multiple edge servers and multiple service clients. In this environment, mobile service providers can offload client-side computation tasks from service clients' devices onto edge servers to reduce service latency and power consumption experienced by the clients. A critical issue that has yet to be properly addressed is how to allocate edge computing resources to achieve two optimization objectives: 1) minimize the service cost measured by the service latency and the power consumption experienced by service clients; and 2) maximize the service capacity measured by the number of service clients that can offload their computation tasks in the long term. This paper formulates this long-term problem as a stochastic optimization problem and solves it with an online algorithm based on Lyapunov optimization. This NP-hard problem is decomposed into three sub-problems, which are then solved with a suite of techniques. The experimental results show that our approach significantly outperforms two baseline approaches.

cs.DC↗

arXiv2018

Low Surface Brightness Galaxy catalogue selected from the alpha.40-SDSS DR7 Survey and Tully-Fisher relation

We present a catalogue of an HI-selected sample of 1129 low surface brightness galaxies (LSBGs) searched from the alpha.40-SDSS DR7 survey. This sample, consisting of various types of galaxies in terms of luminosity and morphology, has extended the parameter space covered by the existing LSBG samples. Based on a subsample of 173 LSBGs which are selected from our entire LSBG sample to have the 2-horn shapes of the HI line profiles, minor-to-major axial ratios (b/a) less than 0.6 and signal-to-noise ratio (S/N) of HI detection greater than 6.5, we investigated the Tully-Fisher relation (TFr) of LSBGs in the optical B, g and r bands and near-infrared J, H and K bands as well. In optical bands, the LSBG subsample follows the fundamental TFr which was previously defined for normal spiral galaxies. In NIR bands, the TFrs for our LSBG subsample are slightly different from the TFrs for the normal bright galaxies. This might be due to the internal extinction issue. Furthermore, the mass-to-light ratio (M/L),disk scale length (h) and mass surface density (sigma) for our LSBG subsample were deduced from the optical TFr results. Compared with High Surface Brightness Galaxies(HSBGs), our LSBGs have higher M/L, larger h and lower sigma than HSBGs.

astro-ph.GA↗

arXiv2018

High-speed and high-responsivity hybrid silicon/black-phosphorus waveguide photodetectors at 2 μm

Silicon photonics is being extended from the near-infrared (near-IR) window of 1.3-1.5 μm for optical fiber communications to the mid-infrared (mid-IR) wavelength-band of 2 μm or longer for satisfying the increasing demands in many applications. Mid-IR waveguide photodetectors on silicon have attracted intensive attention as one of the indispensable elements for various photonic systems. Previously high-performance waveguide photodetectors on silicon were realized for the near-IR window of 1.3-1.5 μm by introducing another semiconductor material (e.g., Ge, and III-V compounds) in the active region. Unfortunately, these traditional semiconductor materials do not work well for the wavelength of ~2 μm or longer because the light absorption becomes very weak. As an alternative, two-dimensional materials provide a new and promising option for enabling active photonic devices on silicon. Here black-phosphorus (BP) thin films with optimized medium thicknesses (~40 nm) are introduced as the active material for light absorption and silicon/BP hybrid ridge waveguide photodetectors are demonstrated with a high responsivity at a low bias voltage. And up to 4.0Gbps data transmission is achieved at 2μm.

physics.app-ph↗

arXiv2018

Privacy-Preserving Multiparty Learning For Logistic Regression

In recent years, machine learning techniques are widely used in numerous applications, such as weather forecast, financial data analysis, spam filtering, and medical prediction. In the meantime, massive data generated from multiple sources further improve the performance of machine learning tools. However, data sharing from multiple sources brings privacy issues for those sources since sensitive information may be leaked in this process. In this paper, we propose a framework enabling multiple parties to collaboratively and accurately train a learning model over distributed datasets while guaranteeing the privacy of data sources. Specifically, we consider logistic regression model for data training and propose two approaches for perturbing the objective function to preserve ε-differential privacy. The proposed solutions are tested on real datasets, including Bank Marketing and Credit Card Default prediction. Experimental results demonstrate that the proposed multiparty learning framework is highly efficient and accurate.

cs.CR↗

arXiv2018

Observing of the super-Planckian near-field thermal radiation between graphene sheets

Thermal radiation can be substantially enhanced in the near-field scenario due to the tunneling of evanescent waves. The monolayer graphene could play a vital role in this process owning to its strong infrared plasmonic response, however, which still lacks an experimental verification due to the technical challenges. Here, we manage to make a direct measurement about plasmon-mediated thermal radiation between two macroscopic graphene sheets using a custom-made setup. Super-Planckian radiation with efficiency 4.5 times larger than the blackbody limit is observed at a 430-nm vacuum gap on insulating silicon hosting substrates. The positive role of graphene plasmons is further confirmed on conductive silicon substrates which have strong infrared loss and thermal emittance. Based on these, a thermophotovoltaic cell made of the graphene-silicon heterostructure is lastly discussed. The current work validates the classic thermodynamical theory in treating graphene and also paves a way to pursue the application of near-field thermal management.

physics.optics↗

arXiv2018

Privacy-Preserving Outsourcing of Large-Scale Nonlinear Programming to the Cloud

The increasing massive data generated by various sources has given birth to big data analytics. Solving large-scale nonlinear programming problems (NLPs) is one important big data analytics task that has applications in many domains such as transport and logistics. However, NLPs are usually too computationally expensive for resource-constrained users. Fortunately, cloud computing provides an alternative and economical service for resource-constrained users to outsource their computation tasks to the cloud. However, one major concern with outsourcing NLPs is the leakage of user's private information contained in NLP formulations and results. Although much work has been done on privacy-preserving outsourcing of computation tasks, little attention has been paid to NLPs. In this paper, we for the first time investigate secure outsourcing of general large-scale NLPs with nonlinear constraints. A secure and efficient transformation scheme at the user side is proposed to protect user's private information; at the cloud side, generalized reduced gradient method is applied to effectively solve the transformed large-scale NLPs. The proposed protocol is implemented on a cloud computing testbed. Experimental evaluations demonstrate that significant time can be saved for users and the proposed mechanism has the potential for practical use.

cs.CR↗

arXiv2018

An H$α$ Imaging Survey of the Low-surface-brightness Galaxies Selected from the Fall Sky Region of the 40$\%$ ALFALFA \ion{H}{1} Survey

We present the observed H$α$ flux and derived star formation rates (SFRs) for a fall sample of low$-$surface$-$brightness galaxies (LSBGs). The sample is selected from the fall sky region of the 40$\%$ ALFALFA {\ion{H}{1}} survey $-$ SDSS DR7 photometric data, and all the $Hα$ images were obtained using the 2.16 m telescope, operated by the National Astronomy Observatories, Chinese Academy of Sciences. A total of 111 LSBGs were observed and $Hα$ flux was measured in 92 of them. Though almost all the LSBGs in our sample are {\ion{H}{1}}$-$rich, their SFRs derived from the extinction and filter$-$transmission$-$corrected $Hα$ flux, are less than 1$M_{\sun}$$yr^{-1}$. LSBGs and star forming galaxies have similar {\ion{H}{1}} surface densities, but LSBGs have much lower SFRs and SFR surface densities than star$-$forming galaxies. Our results show that LSBGs deviate from the Kennicutt-Schmidt law significantly, which indicate that they have low star formation efficiency. The SFRs of LSBGs are close to average SFRs in Hubble time and support the previous arguments that most of the LSBGs are stable systems and they tend to seldom contain strong interactions or major mergers during their star formation histories.

astro-ph.GA↗

arXiv2018

Daytime passive radiative cooler using porous alumina

We report a daytime passive radiative cooler using chemically fabricated porous anodic aluminum oxide (AAO) membranes. Effective medium theory (EMT) has been applied to analyzing the optical properties of the air-doped porous medium. The composite structure is specifically optimized so that it has a high absorbance (emittance) in the far-infrared atmospheric window and nearly no loss in the solar spectrum. The calculated emittance is well reproduced in the experiment by our AAO sample. The fabricated porous membrane shows a potential cooling power density of 64 W/m2 at ambient (humidity = 75%) under direct sunlight irradiance (AM1.5). Experimentally, the sample is cooled by a 2.6C temperature reduction below the ambient air temperature in the sunlight. This performance shows little variance at night. The AAO approach proposed here may provide a promising way to produce low-cost and efficient radiative cooler in large scales for feasible energy conservation.

physics.app-ph↗

arXiv2017

The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic Survey DR14 quasar sample: First measurement of Baryon Acoustic Oscillations between redshift 0.8 and 2.2

We present measurements of the Baryon Acoustic Oscillation (BAO) scale in redshift-space using the clustering of quasars. We consider a sample of 147,000 quasars from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) distributed over 2044 square degrees with redshifts $0.8 < z < 2.2$ and measure their spherically-averaged clustering in both configuration and Fourier space. Our observational dataset and the 1400 simulated realizations of the dataset allow us to detect a preference for BAO that is greater than 2.8$σ$. We determine the spherically averaged BAO distance to $z = 1.52$ to 3.8 per cent precision: $D_V(z=1.52)=3843\pm147 \left(r_{\rm d}/r_{\rm d, fid}\right)\ $Mpc. This is the first time the location of the BAO feature has been measured between redshifts 1 and 2. Our result is fully consistent with the prediction obtained by extrapolating the Planck flat $Λ$CDM best-fit cosmology. All of our results are consistent with basic large-scale structure (LSS) theory, confirming quasars to be a reliable tracer of LSS, and provide a starting point for numerous cosmological tests to be performed with eBOSS quasar samples. We combine our result with previous, independent, BAO distance measurements to construct an updated BAO distance-ladder. Using these BAO data alone and marginalizing over the length of the standard ruler, we find $Ω_Λ > 0$ at 6.6$σ$ significance when testing a $Λ$CDM model with free curvature.

astro-ph.CO↗

arXiv2017

Absolute sensitivity of phase measurement in an SU(1,1) type interferometer

Absolute sensitivity is measured for the phase measurement in an SU(1,1) type interferometer and the results are compared to that of a Mach-Zehnder interferometer operated under the condition of the same intra-interferometer intensity. The interferometer is phase locked to a point with the largest quantum noise cancellation, and a simulated phase modulation is added in one arm of SU(1,1) interferometer. Both the signal and noise level are estimated at the same frequency range, and we obtain 3dB improvement in sensitivity for the SU(1,1) interferometer over the Mach-Zehnder interferometer. Our results demonstrate a direct phase estimation, and may pave the way for practical applications of nonlinear interferometer.

quant-ph↗

arXiv2017

The LAMOST Complete Spectroscopic Survey of Pointing Area (LaCoSSPAr) in the Southern Galactic Cap I. The Spectroscopic Redshift Catalog

We present a spectroscopic redshift catalog from the LAMOST Complete Spectroscopic Survey of Pointing Area (LaCoSSPAr) in the Southern Galactic Cap (SGC), which is designed to observe all sources (Galactic and extra-galactic) by using repeating observations with a limiting magnitude of $r=18.1~mag$ in two $20~deg^2$ fields. The project is mainly focusing on the completeness of LAMOST ExtraGAlactic Surveys (LEGAS) in the SGC, the deficiencies of source selection methods and the basic performance parameters of LAMOST telescope. In both fields, more than 95% of galaxies have been observed. A post-processing has been applied to LAMOST 1D spectrum to remove the majority of remaining sky background residuals. More than 10,000 spectra have been visually inspected to measure the redshift by using combinations of different emission/absorption features with uncertainty of $σ_{z}/(1+z)<0.001$. In total, there are 1528 redshifts (623 absorption and 905 emission line galaxies) in Field A and 1570 redshifts (569 absorption and 1001 emission line galaxies) in Field B have been measured. The results show that it is possible to derive redshift from low SNR galaxies with our post-processing and visual inspection. Our analysis also indicates that up to 1/4 of the input targets for a typical extra-galactic spectroscopic survey might be unreliable. The multi-wavelength data analysis shows that the majority of mid-infrared-detected absorption (91.3%) and emission line galaxies (93.3%) can be well separated by an empirical criterion of $W2-W3=2.4$. Meanwhile, a fainter sequence paralleled to the main population of galaxies has been witnessed both in $M_r$/$W2-W3$ and $M_*$/$W2-W3$ diagrams, which could be the population of luminous dwarf galaxies but contaminated by the edge-on/highly inclined galaxies ($\sim30\%$).

astro-ph.GA↗

arXiv2017

Si-based GeSn lasers with wavelength coverage of 2 to 3 μm and operating temperatures up to 180 K

A Si-based monolithic laser is highly desirable for full integration of Si-photonics. Lasing from direct bandgap group-IV GeSn alloy has opened a completely new venue from the traditional III-V integration approach. We demonstrated optically pumped GeSn lasers on Si with broad wavelength coverage from 2 to 3 μm. The GeSn alloys were grown using newly developed approaches with an industry standard chemical vapor deposition reactor and low-cost commercially available precursors. The achieved maximum Sn composition of 17.5% exceeded the generally acknowledged Sn incorporation limits for using similar deposition chemistries. The highest lasing temperature was measured as 180 K with the active layer thickness as thin as 260 nm. The unprecedented lasing performance is mainly due to the unique growth approaches, which offer high-quality epitaxial materials. The results reported in this work show a major advance towards Si-based mid-infrared laser sources for integrated photonics.

physics.app-ph↗

arXiv2017

Molecular Gas and Star-Formation In Low Surface Brightness Galaxies

We have obtained CO(J=2-1) spectra of nine face-on low surface brightness galaxies(LSBGs) using the JCMT 15-meter telescope and observed Ha images using the 2.16-meter telescope of NAOC. As no CO has been detected, only upper limits on the H2 masses are given. The upper limits of total molecular hydrogen masses are about (1.2-82.4) x 10^7 Msun. Their star formation rates are mainly lower than 0.4 Msun/yr and star formation efficiencies are lower than 1.364 x 10^10 /yr. Our results show that the absence of molecular gas content is the direct reason for the low star formation rate. The low star formation efficiency probably resulted from the low efficiency of HI gas transforming to H2 gas.

astro-ph.GA↗

arXiv2017

Prepaid or Postpaid? That is the question. Novel Methods of Subscription Type Prediction in Mobile Phone Services

In this paper we investigate the behavioural differences between mobile phone customers with prepaid and postpaid subscriptions. Our study reveals that (a) postpaid customers are more active in terms of service usage and (b) there are strong structural correlations in the mobile phone call network as connections between customers of the same subscription type are much more frequent than those between customers of different subscription types. Based on these observations we provide methods to detect the subscription type of customers by using information about their personal call statistics, and also their egocentric networks simultaneously. The key of our first approach is to cast this classification problem as a problem of graph labelling, which can be solved by max-flow min-cut algorithms. Our experiments show that, by using both user attributes and relationships, the proposed graph labelling approach is able to achieve a classification accuracy of $\sim 87\%$, which outperforms by $\sim 7\%$ supervised learning methods using only user attributes. In our second problem we aim to infer the subscription type of customers of external operators. We propose via approximate methods to solve this problem by using node attributes, and a two-ways indirect inference method based on observed homophilic structural correlations. Our results have straightforward applications in behavioural prediction and personal marketing.

cs.SI↗

arXiv2017

Long-slit Spectroscopy of Edge-on Low Surface Brightness Galaxies

We present long-slit optical spectra of 12 edge-on low surface brightness galaxies (LSBGs) positioned along their major axes. After performing reddening corrections for the emission-line fluxes measured from the extracted integrated spectra, we measured the gas-phase metallicities of our LSBG sample using both the [NII]/Ha and the R_23 diagnostics. Both sets of oxygen abundances show good agreement with each other, giving a median value of 12 + log(O/H) = 8.26 dex. In the luminosity-metallicity plot, our LSBG sample is consistent with the behavior of normal galaxies. In the mass-metallicity diagram, our LSBG sample has lower metallicities for lower stellar mass, similar to normal galaxies. The stellar masses estimated from z-band luminosities are comparable to those of prominent spirals. In a plot of the gas mass fraction versus metallicity, our LSBG sample generally agrees with other samples in the high gas mass fraction space. Additionally, we have studied stellar populations of 3 LSBGs which have relatively reliable spectral continua and high signal-to-noise ratios, and qualitatively conclude that they have a potential dearth of stars with ages <1 Gyr instead of being dominated by stellar populations with ages >1Gyr. Regarding the chemical evolution of our sample, the LSBG data appear to allow for up to 30 % metal loss, but we cannot completely rule out the closed-box model. Additionally, we find evidence that our galaxies retain up to about 3 times as much of their metals compared with dwarfs, consistent with metal retention being related to galaxy mass. In conclusion, our data support the view that LSBGs are probably just normal disk galaxies continuously extending to the low end of surface brightness.

astro-ph.GA↗

arXiv2017

Robust Order Scheduling in the Fashion Industry: A Multi-Objective Optimization Approach

In the fashion industry, order scheduling focuses on the assignment of production orders to appropriate production lines. In reality, before a new order can be put into production, a series of activities known as pre-production events need to be completed. In addition, in real production process, owing to various uncertainties, the daily production quantity of each order is not always as expected. In this research, by considering the pre-production events and the uncertainties in the daily production quantity, robust order scheduling problems in the fashion industry are investigated with the aid of a multi-objective evolutionary algorithm (MOEA) called nondominated sorting adaptive differential evolution (NSJADE). The experimental results illustrate that it is of paramount importance to consider pre-production events in order scheduling problems in the fashion industry. We also unveil that the existence of the uncertainties in the daily production quantity heavily affects the order scheduling.

cs.AI↗

arXiv2016

Compressive Data Aggregation on Mobile Wireless Sensor Networks for Sensing in Bike Races

-This paper presents an efficient approach to data collection in mobile wireless sensor networks, with the specific application of sensing in bike races. Recent sensor technology permits to track GPS position of each bike. Because of the inherent correlation between bike positions in a bike race, a simple GPS log is inefficient. The idea presented in this work is to aggregate GPS data at sensors using compressive sensing techniques. We enforce, in addition to signal sparsity, a spatial prior on biker motion because of the group behaviour (peloton) in bike races. The spatial prior is modeled by a graphical model and the data aggregation problem is solved, with both the sparsity and the spatial prior, by belief propagation. We validate our approach on a bike race simulator using trajectories of motorbikes in a real bike race, the "crit{é}rium du dauphin{é} 20XX" .

cs.NI↗