185 research outputs found
Weighing the Light Gravitino Mass with Weak Lensing Surveys
We explore the discovery potential of light gravitino mass m_{3/2} by
combining future cosmology surveys and collider experiments. The former probe
the imprint of light gravitinos in the cosmic matter density field, whereas the
latter search signatures of a supersymmetry breaking mechanism. Free-streaming
of light gravitinos suppresses the density fluctuations at galactic and
sub-galactic length scales, where weak gravitational lensing can be used as a
powerful probe. We perform numerical simulations of structure formation to
quantify the effect. We then run realistic ray-tracing simulations of
gravitational lensing to measure the cosmic shear in models with light
gravitino. We forecast the possible reach of future wide-field surveys by
Fisher analysis; the light gravitino mass can be determined with an accuracy of
m_{3/2}=4\pm 1 eV by a combination of the Hyper Suprime Cam survey and cosmic
microwave background anisotropy data obtained by Planck satellite. The
corresponding accuracy to be obtained by the future Large Synoptic Survey
Telescope is \delta m_{3/2}=0.6 eV. Data from experiments at Large Hadron
Collider at 14 TeV will provide constraint at m_{3/2} \simeq 5 eV in the
minimal framework of gauge-mediated supersymmetry breaking (GMSB) model. We
conclude that a large class of the GMSB model can be tested by combining the
cosmological observations and the collider experiments.Comment: 22 pages, 9 figure
V2X Sidelink Positioning in FR1: Scenarios, Algorithms, and Performance Evaluation
In this paper, we investigate sub-6 GHz V2X sidelink positioning scenarios in
5G vehicular networks through a comprehensive end-to-end methodology
encompassing ray-tracing-based channel modeling, novel theoretical performance
bounds, high-resolution channel parameter estimation, and geometric positioning
using a round-trip-time (RTT) protocol. We first derive a novel, approximate
Cram\'er-Rao bound (CRB) on the connected road user (CRU) position, explicitly
taking into account multipath interference, path merging, and the RTT protocol.
Capitalizing on tensor decomposition and ESPRIT methods, we propose
high-resolution channel parameter estimation algorithms specifically tailored
to dense multipath V2X sidelink environments, designed to detect multipath
components (MPCs) and extract line-of-sight (LoS) parameters. Finally, using
realistic ray-tracing data and antenna patterns, comprehensive simulations are
conducted to evaluate channel estimation and positioning performance,
indicating that sub-meter accuracy can be achieved in sub-6 GHz V2X with the
proposed algorithms
Einstein Probe - a small mission to monitor and explore the dynamic X-ray Universe
Einstein Probe is a small mission dedicated to time-domain high-energy
astrophysics. Its primary goals are to discover high-energy transients and to
monitor variable objects in the keV X-rays, at higher sensitivity by
one order of magnitude than those of the ones currently in orbit. Its
wide-field imaging capability, featuring a large instantaneous field-of-view
(, sr), is achieved by using established
technology of micro-pore (MPO) lobster-eye optics, thereby offering
unprecedentedly high sensitivity and large Grasp. To complement this powerful
monitoring ability, it also carries a narrow-field, sensitive follow-up X-ray
telescope based on the same MPO technology to perform follow-up observations of
newly-discovered transients. Public transient alerts will be downlinked
rapidly, so as to trigger multi-wavelength follow-up observations from the
world-wide community. Over three of its 97-minute orbits almost the entire
night sky will be sampled, with cadences ranging from 5 to 25 times per day.
The scientific objectives of the mission are: to discover otherwise quiescent
black holes over all astrophysical mass scales by detecting their rare X-ray
transient flares, particularly tidal disruption of stars by massive black holes
at galactic centers; to detect and precisely locate the electromagnetic sources
of gravitational-wave transients; to carry out systematic surveys of X-ray
transients and characterize the variability of X-ray sources. Einstein Probe
has been selected as a candidate mission of priority (no further selection
needed) in the Space Science Programme of the Chinese Academy of Sciences,
aiming for launch around 2020.Comment: accepted to publish in PoS, Proceedings of "Swift: 10 Years of
Discovery" (Proceedings of Science; ed. by P. Caraveo, P. D'Avanzo, N.
Gehrels and G. Tagliaferri). Minor changes in text, references update
Enabling Feedback-Free MIMO Transmission for FD-RAN: A Data-driven Approach
To enhance flexibility and facilitate resource cooperation, a novel
fully-decoupled radio access network (FD-RAN) architecture is proposed for 6G.
However, the decoupling of uplink (UL) and downlink (DL) in FD-RAN makes the
existing feedback mechanism ineffective. To this end, we propose an end-to-end
data-driven MIMO solution without the conventional channel feedback procedure.
Data-driven MIMO can alleviate the drawbacks of feedback including overheads
and delay, and can provide customized precoding design for different BSs based
on their historical channel data. It essentially learns a mapping from
geolocation to MIMO transmission parameters. We first present a codebook-based
approach, which selects transmission parameters from the statistics of discrete
channel state information (CSI) values and utilizes integer interpolation for
spatial inference. We further present a non-codebook-based approach, which 1)
derives the optimal precoder from the singular value decomposition (SVD) of the
channel; 2) utilizes variational autoencoder (VAE) to select the representative
precoder from the latent Gaussian representations; and 3) exploits Gaussian
process regression (GPR) to predict unknown precoders in the space domain.
Extensive simulations are performed on a link-level 5G simulator using
realistic ray-tracing channel data. The results demonstrate the effectiveness
of data-driven MIMO, showcasing its potential for application in FD-RAN and 6G
mmWave Mapping using PHD with Smoothed Track Confirmation and Multi-Bounce Suppression
The development of integrated sensing and communication systems together with increased carrier frequencies, larger bandwidth and massive antenna arrays are the key driving forces of future high resolution sensing services. This trend will turn the user device into a mobile radar, thereby opening interesting application scenarios in remote sensing. In this paper, we present a labeled probability hypothesis density filter for feature-based mapping in a mobile radar scenario. Smoothed track confirmation and multi-bounce signal suppression are proposed to enhance mapping quality and mitigate adverse effects of false landmarks. The mapping algorithm is evaluated using realistic ray-tracing data and the results imply that the mapping accuracy improves 31 % compared to a benchmark mapping algorithm.acceptedVersionPeer reviewe
Multicolor pyrometer for materials processing in space
The program goals are to design, construct, and program a prototype imaging pyrometer capable of measuring the temperature distribution across the surface of a moving object suspended in space. The approach is to utilize an optical system which operates at short wavelengths compared to the peak of the blackbody spectrum for the temperature range of interest, thus minimizing errors associated with a lack of knowledge about heated sample emissivity. An analysis of the system's temperature measurement capability based on the camera's responsivity was performed and bound to be satisfactory. Details for the evolving optical design and the progress towards construction of a working model are discussed. Details of the algorithm developed for selecting the optimum colors to be used by the pyrometer are reported. Though final selection of the colors will have to await a final design of the optical system, results using a preliminary optical design are presented
Ray Casting for Iso-surface in Volumetric Data
Volume data visualization is an active field of research and development. It can be
applied in many areas such as medical, oil and gas exploration, etc... Although volume
visualization is highly computational cost, there is a vision of real time volumetric
visualization systems based on interactive ray tracing. Over the years, many rendering
algorithms have been created and enhanced. The focus of this project is to develop a
simple ray casting program for volumetric data. The program will be able to render
specific volume data using a single processor in a reasonable amount of time. It is opento
improve for implementation on multiprocessors. The thesis will compare some existing
algorithms for ray casting in terms of image quality, computing time, complexity and so
forth. The thesis includes a proposal of new multisampling algorithm, which significantly
reduces rendering time while producing similar quality of image with existing algorithms
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