181 research outputs found
Robust Transceiver Design Based on Interference Alignment for Multi-User Multi-Cell MIMO Networks with Channel Uncertainty
In this paper, we firstly exploit the inter-user interference (IUI) and
inter-cell interference (ICI) as useful references to develop a robust
transceiver design based on interference alignment for a downlink multi-user
multi-cell multiple-input multiple-output (MIMO) interference network under
channel estimation error. At transmitters, we propose a two-tier transmit
beamforming strategy, we first achieve the inner beamforming direction and
allocated power by minimizing the interference leakage as well as maximizing
the system energy efficiency, respectively. Then, for the outer beamformer
design, we develop an efficient conjugate gradient Grassmann manifold subspace
tracking algorithm to minimize the distances between the subspace spanned by
interference and the interference subspace in the time varying channel. At
receivers, we propose a practical interference alignment based on fast and
robust fast data projection method (FDPM) subspace tracking algorithm, to
achieve the receive beamformer under channel uncertainty. Numerical results
show that our proposed robust transceiver design achieves better performance
compared with some existing methods in terms of the sum rate and the energy
efficiency.Comment: 12 pages, 8 figure
Deep CFHT Y-band imaging of VVDS-F22 field: I. data products and photometric redshifts
We present our deep -band imaging data of a two square degree field within
the F22 region of the VIMOS VLT Deep Survey. The observations were conducted
using the WIRCam instrument mounted at the Canada--France--Hawaii Telescope
(CFHT). The total on-sky time was 9 hours, distributed uniformly over 18 tiles.
The scientific goals of the project are to select faint quasar candidates at
redshift , and constrain the photometric redshifts for quasars and
galaxies. In this paper, we present the observation and the image reduction, as
well as the photometric redshifts that we derived by combining our -band
data with the CFHTLenS optical data and UKIDSS DXS
near-infrared data. With -band image as reference total 80,000
galaxies are detected in the final mosaic down to -band point
source limiting depth of 22.86 mag. Compared with the 3500 spectroscopic
redshifts, our photometric redshifts for galaxies with and
mag have a small systematic offset of
, 1 scatter ,
and less than 4.0% of catastrophic failures. We also compare to the CFHTLenS
photometric redshifts, and find that ours are more reliable at
because of the inclusion of the near-infrared bands. In particular, including
the -band data can improve the accuracy at because the
location of the 4000\AA-break is better constrained. The -band images, the
multi-band photometry catalog and the photometric redshifts are released at
\url{http://astro.pku.edu.cn/astro/data/DYI.html}.Comment: 16 pages, 12 figures, 4 tables. AJ accepted. Updated access to the
data: https://zenodo.org/record/140003
Advanced NOMA Assisted Semi-Grant-Free Transmission Schemes for Randomly Distributed Users
Non-orthogonal multiple access (NOMA) assisted semi-grant-free (SGF)
transmission has recently received significant research attention due to its
outstanding ability of serving grant-free (GF) users with grant-based (GB)
users' spectrum, {\color{blue}which can greatly improve the spectrum efficiency
and effectively relieve the massive access problem of 5G and beyond networks.
In this paper, we investigate the performance of SGF schemes under more
practical settings.} Firstly, we study the outage performance of the best user
scheduling SGF scheme (BU-SGF) by considering the impacts of Rayleigh fading,
path loss, and random user locations. Then, a fair SGF scheme is proposed by
applying cumulative distribution function (CDF)-based scheduling (CS-SGF),
which can also make full use of multi-user diversity. Moreover, by employing
the theories of order statistics and stochastic geometry, we analyze the outage
performances of both BU-SGF and CS-SGF schemes. Results show that full
diversity orders can be achieved only when the served users' data rate is
capped, which severely limit the rate performance of SGF schemes. To further
address this issue, we propose a distributed power control strategy to relax
such data rate constraint, and derive closed-form expressions of the two
schemes' outage performances under this strategy. Finally, simulation results
validate the fairness performance of the proposed CS-SGF scheme, the
effectiveness of the power control strategy, and the accuracy of the
theoretical analyses.Comment: 41 pages, 8 figure
The Pressure Relief and Permeability Increase Mechanism of Crossing-Layers Directional Hydraulic Fracturing and Its Application
AbstractIn order to reduce roof-floor blind area of hydrofracture in underground mines, expand influenced range of fracturing, improve the effect of hydrofracture, a pressure relief and permeability increase model of hydraulic fracturing was built on the basis of analysing the mechanism of crack initiation and the characteristics of fracture development. After discussing the mechanism of directional hydraulic fracturing and carrying out related numerical simulation, a directional hydraulic fracturing technique was proposed. The coal fracture development distribution rule in the process of directional hydraulic fracturing was analysed, and the directional hydraulic fracturing technique was applied in the F15-31010 mining workface of The Twelfth Coal of Pingdingshan Coal Mining Group. The results show that single-drill hole fracturing effective radius rise to 6m under the pressure of 27Mpa, which is 3-5 times more than before, and the average concentration of single-drill hole gas drainage promote to 87.5%, average flow up 55.6% than no-directional hydraulic fracturing. All these suggest that the technology obtains remarkable effect, and has a high application value
Cold-adaptive alkaline protease from the psychrophilic Planomicrobium sp. 547: enzyme characterization and gene cloning
A psychrophilic bacterium strain 547 producing cold-adaptive alkaline protease was isolated from the deep sea sediment of Prydz Bay, Antarctica. The organism was identified as a Planomicrobium species by 16S rRNA analysis. The optimal and highest growth temperatures for strain 547 were 15℃ and 30℃, respectively. The extracellular protease was purified by ammonium sulfate precipitation and DEAE cellulose-52 chromatography. The optimal temperature and pH for the activity of the purified enzyme were 35℃ and pH 9.0, respectively. The enzyme retained approximately 40% of its activity after 2 h of incubation at 50℃. The enzymatic activity was inhibited by 1 mmol/L phenylmethyl sulfonylfluoride (PMSF) and hydrochloride 4-(2-aminoethyl)-benzenesulfonyl fluoride (AEBSF), indicating that it was a serine protease. The presence of Ca2+ and Mn2+ increased the activity of the enzyme. The protease gene with a size of 1 269 bp was cloned from Planomicrobium sp. 547 using primers designed based on the conserved sequences of proteases in GenBank. The Planomicrobium sp. 547 protease contained a domain belonging to the peptidase S8 family, which has a length of 309 amino acid (AA) residues. The alignment and phylogenetic analysis of the AA sequence indicated that the protease belonged to the subtilisin family
Response of "Glacier-Runoff" system in a typical monsoonal temperate glacier region, Hailuogou Basin in Mt. Gongga of China, to global warming
International audienceThe method of correlation analysis and trend analysis were used in this research in order to confirm the response of "glacier-runoff" system to global warming. Hailuogou glacier had retreated by 1871.8 m over the past 76 years, Hailuogou No. 2 glacier had also retreated by 1100 m. Glaciers retreats are contrary to the climatic warming trend in China and the Northern Hemisphere. Glaciers in Hailuogou basin were in the loss with a fluctuating manner since 1950s, and accumulative value of mass balance is ?10 825.5 mm water equivalent with an annual mean value of ?240.6 mm. The inverse correlation is highly significant between mass balance variation and climatic fluctuation of China and the Northern Hemisphere after 1950s. Glacier ablation is intensive with a ratio of 7.86 m yr?1. A steady rise tendency toward glaciers runoff has been observed since 1980s, and the runoff rise is mainly responsible for melt water in Hailuogou basin. It is noticeable that climatic warming not only strengthened ablation extent and enlarged ablation area, but also prolonged ablation period. Global warming is the main cause of glacier retreat, mass loss and runoff rise in Hailuogou basin
First Spectroscopic Confirmations of z ~ 7.0 Lya Emitting Galaxies in the LAGER Survey
Narrowband imaging is a highly successful approach for finding large numbers
of high redshift Lya emitting galaxies (LAEs) up to z~6.6. However, at z>~7
there are as yet only 3 narrowband selected LAEs with spectroscopic
confirmations (two at z~6.9-7.0, one at z~7.3), which hinders extensive studies
on cosmic reionization and galaxy evolution at this key epoch. We have selected
23 candidate z~6.9 LAEs in COSMOS field with the large area narrowband survey
LAGER (Lyman-Alpha Galaxies at the End of Reionization). In this work we
present spectroscopic followup observations of 12 candidates using IMACS on
Magellan. For 9 of these, the observations are sufficiently deep to detect the
expected lines. Lya emission lines are identified in six sources (yielding a
success rate of 2/3), including 3 luminous LAEs with Lya luminosities of L(Lya)
~ 10^{43.5} erg/s, the highest among known spectroscopically confirmed galaxies
at >~7.0. This triples the sample size of spectroscopically confirmed
narrowband selected LAEs at z>~7, and confirms the bright end bump in the Lya
luminosity function we previously derived based on the photometric sample,
supporting a patchy reionization scenario. Two luminous LAEs appear physically
linked with projected distance of 1.1 pMpc and velocity difference of ~ 170
km/s. They likely sit in a common ionized bubble produced by themselves or with
close neighbors, which reduces the IGM attenuation of Lya. A tentative narrow
NV1240 line is seen in one source, hinting at activity of a central
massive black hole with metal rich line emitting gas.Comment: 6 pages, 3 figures, 2 tables, accepted by ApJ
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