14,399 research outputs found
Gluon gravitational form factors of the proton from the charmonium photoproduction
Inspired by the recent near-threshold photoproduction measurements,
we discuss gluon gravitational form factors (GFFs) and internal properties of
the proton. This work presents a complete set analysis of the proton gluon GFFs
connecting the gluon part of the energy-momentum tensor and the heavy
quarkonium photoproduction. In particular, the gluon GFFs as functions of the
squared momentum transfer are determined by a global fitting of the
differential and total cross section experimental data. Combined with
the quark contributions to the -term form factor extracted from the deeply
virtual Compton scattering experiment, the total -term are obtained to
investigate their applications for the description of the proton mechanical
properties. Specifically, the distributions of pressure and shear forces inside
the proton have been presented. The proton mechanical radius and the pressure
density in the nucleon center are reported. These researches provide a unique
perspective for studying the proton gluon GFFs and important information for
improving QCD constraints on the gluon GFFs.Comment: 7 pages, 4 figure
Cram\'er-Rao Bounds for Near-Field Sensing with Extremely Large-Scale MIMO
Mobile communication networks were designed to mainly support ubiquitous
wireless communications, yet they are also expected to achieve radio sensing
capabilities in the near future. However, most prior studies on radio sensing
usually rely on far-field assumption with uniform plane wave (UPW) models. With
the ever-increasing antenna size, together with the growing demands to sense
nearby targets, the conventional far-field UPW assumption may become invalid.
Therefore, this paper studies near-field radio sensing with extremely
large-scale (XL) antenna arrays, where the more general uniform spheric wave
(USW) sensing model is considered. Closed-form expressions of the Cram\'er-Rao
Bounds (CRBs) for both angle and range estimations are derived for near-field
XL-MIMO radar mode and XL-phased array radar mode, respectively. Our results
reveal that different from the conventional UPW model where the CRB for angle
decreases unboundedly as the number of antennas increases, for XL-MIMO
radar-based near-field sensing, the CRB decreases with diminishing return and
approaches to a certain limit as the number of antennas increases. Besides,
different from the far-field model where the CRB for range is infinity since it
has no range estimation capability, that for the near-field case is finite.
Furthermore, it is revealed that the commonly used spherical wave model based
on second-order Taylor approximation is insufficient for near-field CRB
analysis. Extensive simulation results are provided to validate our derived
CRBs
Miniaturization of Branch-Line Coupler Using Composite Right/Left-Handed Transmission Lines with Novel Meander-shaped-slots CSSRR
A novel compact-size branch-line coupler using composite right/left-handed transmission lines is proposed in this paper. In order to obtain miniaturization, composite right/left-handed transmission lines with novel complementary split single ring resonators which are realized by loading a pair of meander-shaped-slots in the split of the ring are designed. This novel coupler occupies only 22.8% of the area of the conventional approach at 0.7 GHz. The proposed coupler can be implemented by using the standard printed-circuit-board etching processes without any implementation of lumped elements and via-holes, making it very useful for wireless communication systems. The agreement between measured and stimulated results validates the feasible configuration of the proposed coupler
Linear Precoding for Relay Networks with Finite-Alphabet Constraints
In this paper, we investigate the optimal precoding scheme for relay networks
with finite-alphabet constraints. We show that the previous work utilizing
various design criteria to maximize either the diversity order or the
transmission rate with the Gaussian-input assumption may lead to significant
loss for a practical system with finite constellation set constraint. A linear
precoding scheme is proposed to maximize the mutual information for relay
networks. We exploit the structure of the optimal precoding matrix and develop
a unified two-step iterative algorithm utilizing the theory of convex
optimization and optimization on the complex Stiefel manifold. Numerical
examples show that this novel iterative algorithm achieves significant gains
compared to its conventional counterpart.Comment: Accepted by IEEE Int. Conf. Commun. (ICC), Kyoto, Japan, 201
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