122 research outputs found
Measuring 10-1000 GeV Cosmic Ray Electrons with GLAST/LAT
We present here the capabilities of the GLAST Large Area Telescope to detect
cosmic ray high-energy (HE) electrons in the energy range from 10 GeV to 1 TeV.
We also discuss the science topics that can be investigated with HE electron
data and quantify the results with LAT instrument simulations. The science
topics include CR propagation, calibration of the IC gamma-ray model, testing
hypotheses regarding the origin of HE energy cosmic-ray electrons, searching
for any signature of Kaluza Klein Dark Matter annihilation, and measuring the
HE electron anisotropy. We expect to detect ~ 107 electrons above 20 GeV per
year of LAT operation.Comment: 5 pages, 5 figures, 1 tabl
Pseudo steady-state period in non-stationary infinite-server queue with state dependent arrival intensity
An infinite-server queueing model with state-dependent arrival process and exponential distribution of service time is analyzed. It is assumed that the difference between the value of the arrival rate and total service rate becomes positive starting from a certain value of the number of customers in the system. In this paper, time until reaching this value by the number of customers in the system is called the pseudo steady-state period (PSSP). Distribution of duration of PSSP, its raw moments and its simple approximation under a certain scaling of the number of customers in the system are analyzed. Novelty of the considered problem consists of an arbitrary dependence of the rate of customer arrival on the current number of customers in the system and analysis of time until reaching from below a certain level by the number of customers in the system. The relevant existing papers focus on the analysis of time interval since exceeding a certain level until the number of customers goes down to this level (congestion period). Our main contribution consists of the derivation of a simple approximation of the considered time distribution by the exponential distribution. Numerical examples are presented, which confirm good quality of the proposed approximation
Fast and robust two- and three-qubit swapping gates on multi-atomic ensembles in quantum electrodynamic cavity
Creation of quantum computer is outstanding fundamental and practical
problem. The quantum computer could be used for execution of very complicated
tasks which are not solvable with the classical computers. The first prototype
of solid state quantum computer was created in 2009 with superconducting
qubits. However, it suffers from the decoherent processes and it is desirable
to find more practical encoding of qubits with long-lived coherence. It could
be single impurity or vacancy centers in solids, but their interaction with
electromagnetic radiation is rather weak. So, here, ensembles of atoms were
proposed for the qubit encoding by using the dipole blockade mechanism in order
to turn multilevel systems in two level ones. But dipole-dipole based blockade
introduces an additional decoherence that limits its practical significance.
Recently, the collective blockade mechanism has been proposed for the system of
three-level atoms by using the different frequency shifts for the Raman
transitions between the collective atomic states characterized by a different
number of the excited atoms. Here, we propose two qubit gate by using another
collective blockade mechanism in the system of two level atoms based on
exchange interaction via the virtual photons between the multi-atomic ensembles
in the resonator. Also we demonstrate the possibility of three qubit gate
(Controlled SWAP gate) using a suppression of the swap-process between two
multi-atomic ensembles due to dynamical shift of the atomic levels controlled
by the states of photon encoded qubit
Gamma-Ray Large Area Space Telescope- GLAST Mission Overview
This viewgraph presentation reviews the Gamma-ray Large Area Space Telescope (GLAST), and the instrumentation that will be on the spacecraft: Large Area Telescope (LAT) and GLAST Burst Monitor (GBM). The presentation revierws in detail the LAT instrument
Illuminating dark matter and primordial black holes with interstellar antiprotons
Interstellar antiproton fluxes can arise from dark matter annihilating or
decaying into quarks or gluons that subsequently fragment into antiprotons.
Evaporation of primordial black holes also can produce a significant antiproton
cosmic-ray flux. Since the background of secondary antiprotons from spallation
has an interstellar energy spectrum that peaks at \sim 2\gev and falls
rapidly for energies below this, low-energy measurements of cosmic antiprotons
are useful in the search for exotic antiproton sources. However, measurement of
the flux near the earth is challenged by significant uncertainties from the
effects of the solar wind. We suggest evading this problem and more effectively
probing dark-matter signals by placing an antiproton spectrometer aboard an
interstellar probe currently under discussion. We address the experimental
challenges of a light, low-power-consuming detector, and present an initial
design of such an instrument. This experimental effort could significantly
increase our ability to detect, and have confidence in, a signal of exotic,
nonstandard antiproton sources. Furthermore, solar modulation effects in the
heliosphere would be better quantified and understood by comparing results to
inverse modulated data derived from existing balloon and space-based detectors
near the earth.Comment: 18 pages, 3 figure
Neuromagnetic activation and oscillatory dynamics of stimulus-locked processing during naturalistic viewing
Naturalistic stimuli such as watching a movie while in the scanner provide an ecologically valid paradigm that has the potential of extracting valuable information on how the brain processes complex stimuli in realistic visual and auditory contexts. Naturalistic viewing is also easier to conduct with challenging participant groups including patients and children. Given the high temporal resolution of MEG, in the present study, we demonstrate how a short movie clip can be used to map distinguishable activation and connectivity dynamics underlying the processing of specific classes of visual stimuli such as face and hand manipulations, as well as contrasting activation dynamics for auditory words and non-words. MEG data were collected from 22 healthy volunteers (6 females, 3 left handed, mean age – 27.7 ± 5.28 years) during the presentation of naturalistic audiovisual stimuli. The MEG data were split into trials with the onset of the stimuli belonging to classes of interest (words, non-words, faces, hand manipulations). Based on the components of the averaged sensor ERFs time-locked to the visual and auditory stimulus onset, four and three time-windows, respectively, were defined to explore brain activation dynamics. Pseudo-Z, defined as the ratio of the source-projected time-locked power to the projected noise power for each vertex, was computed and used as a proxy of time-locked brain activation. Statistical testing using the mean-centered Partial Least Squares analysis indicated periods where a given visual or auditory stimuli had higher activation. Based on peak pseudo-Z differences between the visual conditions, time-frequency resolved analyses were performed to assess beta band desynchronization in motor-related areas, and inter-trial phase synchronization between face processing areas. Our results provide the first evidence that activation and connectivity dynamics in canonical brain regions associated with the processing of particular classes of visual and auditory stimuli can be reliably mapped using MEG during presentation of naturalistic stimuli. Given the strength of MEG for brain mapping in temporal and frequency domains, the use of naturalistic stimuli may open new techniques in analyzing brain dynamics during ecologically valid sensation and perception
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