5,202 research outputs found
Pilot Power Allocation Through User Grouping in Multi-Cell Massive MIMO Systems
In this paper, we propose a relative channel estimation error (RCEE) metric,
and derive closed-form expressions for its expectation and
the achievable uplink rate holding for any number of base station antennas ,
with the least squares (LS) and minimum mean squared error (MMSE) estimation
methods. It is found that RCEE and converge to the same
constant value when , resulting in the pilot power
allocation (PPA) is substantially simplified and a PPA algorithm is proposed to
minimize the average per user with a total pilot power
budget in multi-cell massive multiple-input multiple-output systems.
Numerical results show that the PPA algorithm brings considerable gains for the
LS estimation compared with equal PPA (EPPA), while the gains are only
significant with large frequency reuse factor (FRF) for the MMSE estimation.
Moreover, for large FRF and large , the performance of the LS approaches to
the performance of the MMSE, which means that simple LS estimation method is a
very viable when co-channel interference is small. For the achievable uplink
rate, the PPA scheme delivers almost the same average achievable uplink rate
and improves the minimum achievable uplink rate compared with the EPPA scheme.Comment: 30 pages, 5 figures, submitted to IEEE Transactions on Communication
A description of the transverse momentum distributions of charged particles produced in heavy ion collisions at RHIC and LHC energies
By assuming the existing of memory effects and long-range interactions in the
hot and dense matter produced in high energy heavy ion collisions, the
nonextensive statistics together with the relativistic hydrodynamics including
phase transition is used to discuss the transverse momentum distributions of
charged particles produced in heavy ion collisions. It is shown that the
combined contributions from nonextensive statistics and hydrodynamics can give
a good description to the experimental data in Au+Au collisions at sqrt(s_NN )=
200 GeV and in Pb+Pb collisions at sqrt(s_NN) )= 2.76 TeV for pi^(+ -) , K^(+
-) in the whole measured transverse momentum region, and for p(p-bar) in the
region of p_T<= 2.0 GeV/c. This is different from our previous work, where, by
using the conventional statistics plus hydrodynamics, the describable region is
only limited in p_T<= 1.1 GeV/c.Comment: 14 pages, 3 figures, 2 table
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Convenient and General Zinc-Catalyzed Borylation of Aryl Diazonium Salts and Aryltriazenes under Mild Conditions
A convenient and general zinc-catalyzed borylation of aryl diazonium salts and aryltriazenes has been developed. With bis- (pinacolato)diboron as the borylation reagent, aryldiazonium tetrafluoroborate salts and aryltriazenes were transformed into the corresponding arylboronates in moderate to excellent yields under mild conditions. As a convenient and practical methodology, no additional ligands, base, or any other additives are required here
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Sulfated tyrosines 27 and 29 in the N-terminus of human CXCR3 participate in binding native IP-10
Aim: Human CXCR3, a seven-transmembrane segment (7TMS), is predominantly expressed in Th1-mediated responses. Interferon-γ-inducible protein 10 (IP-10) is an important ligand for CXCR3. Their interaction is pivotal for leukocyte migration and activation. Tyrosine sulfation in 7TMS is a posttranslational modification that contributes substantially to ligand binding. We aimed to study the role of tyrosine sulfation of CXCR3 in the protein's binding to IP-10. Methods: Plasmids encoding CXCR3 and its mutants were prepared by PCR and site-directed mutagenesis. HEK 293T cells were transfected with plasmids encoding CXCR3 or its variants using calcium phosphate. Transfected cells were labeled with [35S]-cysteine and methionine or [35S]-Na2SO3 and then analyzed by immunoprecipitation to measure sulfation. Experiments with 125I-labeled IP-10 were carried out to evaluate the affinity of CXCR3 for its ligand. Calcium influx assays were used to measure intercellular signal transduction. Results: Our data show that sulfate moieties are added to tyrosines 27 and 29 of CXCR3. Mutation of these two tyrosines to phenylalanines substantially decreases binding of CXCR3 to IP-10 and appears to eliminate the associated signal transduction. Tyrosine sulfation of CXCR3 is enhanced by tyrosyl protein sulfotransferases (TPSTs), and it is weakened by shRNA constructs. The binding ability of CXCR3 to IP-10 is increased by TPSTs and decreased by shRNAs. Conclusions: This study identifies two sulfated tyrosines in the N-terminus of CXCR3 as part of the binding site for IP-10, and it underscores the fact that tyrosine sulfation in the N-termini of 7TMS receptors is functionally important for ligand interactions. Our study suggests a molecular target for inhibiting this ligand-receptor interaction
Testing the spatial geometry of the universe with TianQin: the prospect of using supermassive black hole binaries
The determination of the spatial geometry of the universe plays an important
role in modern cosmology. Any deviation from the cosmic curvature
would have a profound impact on the primordial inflation paradigm and
fundamental physics. In this paper, we carry out a systematic study of the
prospect of measuring cosmic curvature with the inspiral signal of supermassive
black hole binaries (SMBHBs) that could be detected with TianQin. The study is
based on a cosmological-model-independent method that extended the application
of gravitational wave (GW) standard sirens in cosmology. By comparing the
distances from future simulated GW events and simulated data, we
evaluate if TianQin would produce robust constraints on the cosmic curvature
parameter . More specifically, we consider 3-yr to 10-yr
observations of supermassive black hole binaries with total masses ranging from
to . Our results show that in the future, with
the synergy of 10-yr high-quality observations, we can tightly constrain the
curvature parameter at the level of .
Moreover, our findings indicate that the total mass of SMBHB does influence the
estimation of cosmic curvature, implied by the analysis performed on different
subsamples of gravitational wave data. Therefore, TianQin is expected to
provide a powerful and competitive probe of the spatial geometry of the
universe, compared to future spaced-based detectors such as DECIGO.Comment: This article has been accepted by Astronomy & Astrophysic
Study on the Lowest Energy Density of Welding Heat Source Required by Fusion Welding Metal
AbstractWelding is a common metal-processing method, which uses heating or press or both, at the same time, uses or disuses filled composites to achieve the atomic binding of workpieces. The basic welding methods are usually divided into three classes according to the conjunct property of weld metal, namely fusion welding, press welding and braze welding[1,2]. Powder composite welding rod is constituted with powder and termites, which belongs to fusion welding[3]. In order to make sure that the energy of this welding rod can achieve the requirement of fusion welding, so the lowest energy density required by fusing melt should be determined firstly
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