18,158 research outputs found
Analysis of Power-aware Buffering Schemes in Wireless Sensor Networks
We study the power-aware buffering problem in battery-powered sensor
networks, focusing on the fixed-size and fixed-interval buffering schemes. The
main motivation is to address the yet poorly understood size variation-induced
effect on power-aware buffering schemes. Our theoretical analysis elucidates
the fundamental differences between the fixed-size and fixed-interval buffering
schemes in the presence of data size variation. It shows that data size
variation has detrimental effects on the power expenditure of the fixed-size
buffering in general, and reveals that the size variation induced effects can
be either mitigated by a positive skewness or promoted by a negative skewness
in size distribution. By contrast, the fixed-interval buffering scheme has an
obvious advantage of being eminently immune to the data-size variation. Hence
the fixed-interval buffering scheme is a risk-averse strategy for its
robustness in a variety of operational environments. In addition, based on the
fixed-interval buffering scheme, we establish the power consumption
relationship between child nodes and parent node in a static data collection
tree, and give an in-depth analysis of the impact of child bandwidth
distribution on parent's power consumption.
This study is of practical significance: it sheds new light on the
relationship among power consumption of buffering schemes, power parameters of
radio module and memory bank, data arrival rate and data size variation,
thereby providing well-informed guidance in determining an optimal buffer size
(interval) to maximize the operational lifespan of sensor networks
HEAO 3 upper limits to the expected 1634 KeV line from SS 483
A model based on 24 Mg(1369) was developed as the source of the lines in which refractory grains in the jets, containing Mg and 0, are bombarded, by ambient protons in the local ISM. The narrowness of the features results because the recoil Mg nucleus is stopped in the grain before the 1369 keV excited state decays. A consequence of the 24 Mg interpretation is the expected appearance of other emission lines, due to 20 Ne and 20 Na, which are produced by proton bombardment of 24 Mg at the 33 MeV/nucleon energy corresponding to the velocity of the jets. These lines appear at rest energies of 1634 keV and 1636 keV, respectively, and should have essentially the same total flux as that emited at 1369 keV. The HEAO 3 data are examined to search for the 1634 keV (rest) emission. The observation and analysis, the results, and the implications for the understanding of SS 433 are discussed
High-resolution spectrum of Cygnus X-1
A high resolution spectrum of Cygnus X-1 in the 45 to 600 keV range is presented. The measurement was made by the HEAO 3 gamma ray spectrometer during 82 days in the fall of 1979 and spring of 1980, when the source was in its normal low state. Results of a search for narrow emission lines from the source are reported. The spectrum shows no significant narrow features. The 3 delta upper limit to a narrow 511 keV annihilation line is 3 x 0.0001 photons/sq cm/s. There is also no evidence in HEAO 3 broadband data above 500 keV for the broad annihilation feature observed by HEAO 1
Fate of the Peak Effect in a Type-II Superconductor: Multicriticality in the Bragg-Glass Transition
We have used small-angle-neutron-scattering (SANS) and ac magnetic
susceptibility to investigate the global magnetic field H vs temperature T
phase diagram of a single crystal Nb in which a first-order transition of
Bragg-glass melting (disordering), a peak effect, and surface superconductivity
are all observable. It was found that the disappearance of the peak effect is
directly related to a multicritical behavior in the Bragg-glass transition.
Four characteristic phase boundary lines have been identified on the H-T plane:
a first-order line at high fields, a mean-field-like continuous transition line
at low fields, and two continuous transition line associated with the onset of
surface and bulk superconductivity. All four lines are found to meet at a
multicritical point.Comment: 4 figure
Gamma-ray burst variability above 4 MeV
The relationship between the hard X-ray and gamma ray emissions during four bursts using the anti-coincidence shields of the High Energy Astronomy Observatory 3 (HEAO 3) Gamma Ray Spectrometer is explored. Recent observations of gamma ray bursts by the Solar Maximum Mission Gamma Ray Spectrometer (GRS) have shown that high energy emission above 1 MeV is a common and energetically important feature (Matz et al. 1985). Time histories of four gamma ray bursts in 3 energy bands ( keV, around 511 keV, and 4 MeV) with 10.24 a resolution show that the 4 MeV flux is only weakly coupled to the spectrum below approximately 600 keV
Galactic distribution of interstellar Al-26
A narrow cosmic gamma ray line at 1809 keV was discovered which was interpreted as resulting from the decay of approximately 3 M sub theta of Al-26 residing in the galactic disk. While its intrinsic width was unresolved by the HEAO 3 spectrometer, a (1 sigma) limit of 3 keV FWHM was obtained; this corresponds to bulk motions of v 250 km/s, which is consistent with material at rest in the ISM. Sites which have been suggested include type II supernovae and massive stars which are members of the extreme population I, as well as novae and red giants which are associated with an older disk population. The HEAO 3 data was used to distinguish between these two stellar populations
Optimization of aircraft seat cushion fire blocking layers
This report describes work completed by the National Aeronautics and Space Administration - for the Federal Aviation Administration Technical Center. The purpose of this work was to examine the potential of fire blocking mechanisms for aircraft seat cushions in order to provide an optimized seat configuration with adequate fire protection and minimum weight. Aluminized thermally stable fabrics were found to provide adequate fire protection when used in conjunction with urethane foams, while maintaining minimum weight and cost penalty
Steering far-field spin-dependent splitting of light by inhomogeneous anisotropic media
An inhomogeneous anisotropic medium with specific structure geometry can
apply the tunable spin-dependent geometrical phase to the light passing through
the medium, and thus can be used to steer the spin-dependent splitting (SDS) of
light. In this paper, we exemplify this inference by the q plate, an
inhomogeneous anisotropic medium. It is demonstrated that when a linearly
polarized light beam normally passes through a q plate, k-space SDS first
occurs, and then the real-space SDS in the far-field focal plane of a
converging lens is distinguishable. Interestingly, the SDS, described by the
normalized Stokes parameter S3 shows a multilobe and rotatable splitting
pattern with rotational symmetry. Further, by tailoring the structure geometry
of the q plate and/or the incident polarization angle of light, the lobe number
and the rotation angle both are tunable. Our result suggests that the q plate
can serve as a potential device for manipulating the photon spin states and
enable applications such as in nano-optics and quantum information.Comment: 5 pages, 5 figure
Development of High Efficiency (14%) Solar Cell Array Module
High efficiency solar cells required for the low cost modules was developed. The production tooling for the manufacture of the cells and modules was designed. The tooling consisted of: (1) back contact soldering machine; (2) vacuum pickup; (3) antireflective coating tooling; and (4) test fixture
BATSE Soft Gamma-Ray Observations of GROJ0422+32
We report results of a comprehensive study of the soft gamma-ray (30 keV to
1.7 MeV) emission of GROJ0422+32 during its first known outburst in 1992. These
results were derived from the BATSE earth-occultation database with the JPL
data analysis package, EBOP (Enhanced BATSE Occultation Package). Results
presented here focus primarily on the long-term temporal and spectral
variability of the source emission associated with the outburst. The light
curves with 1-day resolution in six broad energy-bands show the high-energy
flux (>200 keV) led the low-energy flux (<200 keV) by ~5 days in reaching the
primary peak, but lagged the latter by ~7 days in starting the declining phase.
We confirm the "secondary maximum" of the low-energy (<200 keV) flux at TJD
8970-8981, ~120 days after the first maximum. Our data show that the "secondary
maximum" was also prominent in the 200-300 keV band, but became less pronounced
at higher energies. During this 200-day period, the spectrum evolved from a
power-law with photon index of 1.75 on TJD 8839, to a shape that can be
described by a Comptonized model or an exponential power law below 300 keV,
with a variable power-law tail above 300 keV. The spectrum remained roughly in
this two-component shape until ~9 November (TJD 8935) and then returned to the
initial power-law shape with an index of ~2 until the end of the period. The
correlation of the two spectral shapes with the high and low luminosities of
the soft gamma-ray emission is strongly reminiscent of that seen in Cygnus X-1.
We interpret these results in terms of the Advection Dominated Accretion Flow
(ADAF) model with possibly a "jet-like" region that persistently produced the
non-thermal power-law gamma rays observed throughout the event.Comment: 40 pages total, including 10 figures and 2 table
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