11,976 research outputs found
Simulations of a Scintillator Compton Gamma Imager for Safety and Security
We are designing an all-scintillator Compton gamma imager for use in security
investigations and remediation actions involving radioactive threat material.
To satisfy requirements for a rugged and portable instrument, we have chosen
solid scintillator for the active volumes of both the scatter and absorber
detectors. Using the BEAMnrc/EGSnrc Monte Carlo simulation package, we have
constructed models using four different materials for the scatter detector:
LaBr_3, NaI, CaF_2 and PVT. We have compared the detector performances using
angular resolution, efficiency, and image resolution. We find that while PVT
provides worse performance than that of the detectors based entirely on
inorganic scintillators, all of the materials investigated for the scatter
detector have the potential to provide performance adequate for our purposes.Comment: Revised text and figures, Presented at SORMA West 2008, Published in
IEEE Transactions on Nuclear Scienc
A novel probabilistic data association based MIMO detector using joint detection of consecutive symbol vectors
A new probabilistic data association (PDA) approach is proposed for symbol detection in spatial multiplexing multiple-input multiple-output (MIMO) systems. By designing a joint detection (JD) structure for consecutive symbol vectors in the same transmit burst, more a priori information is exploited when updating the estimated posterior marginal probabilities for each symbol per iteration. Therefore the proposed PDA detector (denoted as PDA-JD detector) outperforms the conventional PDA detectors in the context of correlated input bit streams. Moreover, the conventional PDA detectors are shown to be a special case of the PDA-JD detector. Simulations and analyses are given to demonstrate the effectiveness of the new method
Golden Coded Multiple Beamforming
The Golden Code is a full-rate full-diversity space-time code, which achieves
maximum coding gain for Multiple-Input Multiple-Output (MIMO) systems with two
transmit and two receive antennas. Since four information symbols taken from an
M-QAM constellation are selected to construct one Golden Code codeword, a
maximum likelihood decoder using sphere decoding has the worst-case complexity
of O(M^4), when the Channel State Information (CSI) is available at the
receiver. Previously, this worst-case complexity was reduced to O(M^(2.5))
without performance degradation. When the CSI is known by the transmitter as
well as the receiver, beamforming techniques that employ singular value
decomposition are commonly used in MIMO systems. In the absence of channel
coding, when a single symbol is transmitted, these systems achieve the full
diversity order provided by the channel. Whereas this property is lost when
multiple symbols are simultaneously transmitted. However, uncoded multiple
beamforming can achieve the full diversity order by adding a properly designed
constellation precoder. For 2 \times 2 Fully Precoded Multiple Beamforming
(FPMB), the general worst-case decoding complexity is O(M). In this paper,
Golden Coded Multiple Beamforming (GCMB) is proposed, which transmits the
Golden Code through 2 \times 2 multiple beamforming. GCMB achieves the full
diversity order and its performance is similar to general MIMO systems using
the Golden Code and FPMB, whereas the worst-case decoding complexity of
O(sqrt(M)) is much lower. The extension of GCMB to larger dimensions is also
discussed.Comment: accepted to conferenc
A probabilistic data association based MIMO detector using joint detection of consecutive symbol vectors
A new probabilistic data association (PDA) approach is proposed for symbol detection in spatial multiplexing multiple-input multiple-output (MIMO) systems. By designing a joint detection (JD) structure for consecutive symbol vectors in the same transmit burst, more a priori information is exploited when updating the estimated posterior marginal probabilities for each symbol per iteration. Therefore the proposed PDA detector (denoted as PDA-JD detector) outperforms the conventional PDA detectors in the context of correlated input bit streams. Moreover, the conventional PDA detectors are shown to be a special case of the PDA-JD detector. Simulations and analyses are given to demonstrate the effectiveness of the new method
Limiting the effects of earthquakes on gravitational-wave interferometers
Ground-based gravitational wave interferometers such as the Laser
Interferometer Gravitational-wave Observatory (LIGO) are susceptible to
high-magnitude teleseismic events, which can interrupt their operation in
science mode and significantly reduce the duty cycle. It can take several hours
for a detector to stabilize enough to return to its nominal state for
scientific observations. The down time can be reduced if advance warning of
impending shaking is received and the impact is suppressed in the isolation
system with the goal of maintaining stable operation even at the expense of
increased instrumental noise. Here we describe an early warning system for
modern gravitational-wave observatories. The system relies on near real-time
earthquake alerts provided by the U.S. Geological Survey (USGS) and the
National Oceanic and Atmospheric Administration (NOAA). Hypocenter and
magnitude information is generally available in 5 to 20 minutes of a
significant earthquake depending on its magnitude and location. The alerts are
used to estimate arrival times and ground velocities at the gravitational-wave
detectors. In general, 90\% of the predictions for ground-motion amplitude are
within a factor of 5 of measured values. The error in both arrival time and
ground-motion prediction introduced by using preliminary, rather than final,
hypocenter and magnitude information is minimal. By using a machine learning
algorithm, we develop a prediction model that calculates the probability that a
given earthquake will prevent a detector from taking data. Our initial results
indicate that by using detector control configuration changes, we could prevent
interruption of operation from 40-100 earthquake events in a 6-month
time-period
Interim Design Report
The International Design Study for the Neutrino Factory (the IDS-NF) was
established by the community at the ninth "International Workshop on Neutrino
Factories, super-beams, and beta- beams" which was held in Okayama in August
2007. The IDS-NF mandate is to deliver the Reference Design Report (RDR) for
the facility on the timescale of 2012/13. In addition, the mandate for the
study [3] requires an Interim Design Report to be delivered midway through the
project as a step on the way to the RDR. This document, the IDR, has two
functions: it marks the point in the IDS-NF at which the emphasis turns to the
engineering studies required to deliver the RDR and it documents baseline
concepts for the accelerator complex, the neutrino detectors, and the
instrumentation systems. The IDS-NF is, in essence, a site-independent study.
Example sites, CERN, FNAL, and RAL, have been identified to allow site-specific
issues to be addressed in the cost analysis that will be presented in the RDR.
The choice of example sites should not be interpreted as implying a preferred
choice of site for the facility
Receiver Multiuser Diversity Aided Multi-Stage MMSE Multiuser Detection for DS-CDMA and SDMA Systems Employing I-Q Modulation
The so-called receiver multiuser diversity aided multistage minimum mean-square error multiuser detector (RMD/MS-MMSE MUD), which was proposed previously by the author, is investigated in the context of the direct-sequence code-division multiple-access (DS- CDMA) and space-division multiple-access (SDMA) systems that employ in- and quadrature-phase (I-Q) modulation schemes. A detection scheme is studied, which is operated in real domain in the principles of successive interference cancellation (SIC). The concept of noise recognition factor (NRF) is proposed for explaining the efficiency of SIC-type detectors and also for motivating to design other high-efficiency detectors. The achievable bit error rate (BER) performance of the RMD/MS-MMSE MUD is investigated for DS-CDMA and SDMA systems of either full-load or overload, when communicating over Rayleigh fading channels for the SDMA and over either additive white Gaussian noise (AWGN) or Rayleigh fading channels for the DS-CDMA. The studies and performance results show that the RMD/MS-MMSE MUD is a highly promising MUD. It has low implementation complexity and good error performance. Furthermore, it is a high-flexibility detector suitable for various communication systems operated in different communication environments
An automated wrapper-based approach to the design of dependable software
The design of dependable software systems invariably comprises two main activities: (i) the design of dependability mechanisms, and (ii) the location of dependability mechanisms. It has been shown that these activities are intrinsically difficult. In this paper we propose an automated wrapper-based methodology to circumvent the problems associated with the design and location of dependability mechanisms. To achieve this we replicate important variables so that they can be used as part of standard, efficient dependability mechanisms. These well-understood mechanisms are then deployed in all relevant locations. To validate the proposed methodology we apply it to three complex software systems, evaluating the dependability enhancement and execution overhead in each case. The results generated demonstrate that the system failure rate of a wrapped software system can be several orders of magnitude lower than that of an unwrapped equivalent
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