235 research outputs found
Relativistic magnetic reconnection at X-type neutral points
Relativistic effects in the oscillatory damping of magnetic disturbances near
two-dimensional X-points are investigated. By taking into account displacement
current, we study new features of extremely magnetized systems, in which the
Alfv\'en velocity is almost the speed of light. The frequencies of the
least-damped mode are calculated using linearized relativistic MHD equations
for wide ranges of the Lundquist number S and the magnetization parameter
. These timescales approach constant values in the large resistive
limit: the oscillation time becomes a few times the light crossing time,
irrespective of , and the decay time is proportional to and
therefore is longer for a highly magnetized system.Comment: 6 pages, 4 figure
Direct dark matter search by annual modulation in XMASS-I
A search for dark matter was conducted by looking for an annual modulation
signal due to the Earth's rotation around the Sun using XMASS, a single phase
liquid xenon detector. The data used for this analysis was 359.2 live days
times 832 kg of exposure accumulated between November 2013 and March 2015. When
we assume Weakly Interacting Massive Particle (WIMP) dark matter elastically
scattering on the target nuclei, the exclusion upper limit of the WIMP-nucleon
cross section 4.310cm at 8 GeV/c was obtained and we
exclude almost all the DAMA/LIBRA allowed region in the 6 to 16 GeV/c range
at 10cm. The result of a simple modulation analysis, without
assuming any specific dark matter model but including electron/ events,
showed a slight negative amplitude. The -values obtained with two
independent analyses are 0.014 and 0.068 for null hypothesis, respectively. we
obtained 90\% C.L. upper bounds that can be used to test various models. This
is the first extensive annual modulation search probing this region with an
exposure comparable to DAMA/LIBRA.Comment: 5 pages, 4 figure
InterPack2003-35028 CRACK AREA ANALYSIS OF SnPb AND SnAg SOLDER JOINTS IN PLASTIC BALL GRID ARRAY PACKAGES FROM DYE PENETRATION STUDIES
ABSTRACT Crack growth in solder joints caused by thermal cycling is a critical issue for reliability in electronic packages. This study presents experimental data on crack growth in SnPb and SnAg solder joints of 357-joint PBGA packages attached to PWBs and subjected to 30-minute, 0°C to 100°C temperature cycles. The board assemblies were exposed to three process conditions upon exiting the solder reflow furnace-air cooled to room temperature, quenched at 0°C, and aged at 150°C (SnPb) or 160°C (SnAg) for 1008 hours-prior to the accelerated thermal cycle testing. At scheduled intervals, the packages were dye-penetrated, removed from the board, and the joint crack areas in several regions measured. The experimental data and statistical analysis of 9000 joints show that SnAg solder joints have half the crack areas of their SnPb counterparts for all regions, cycles and aging conditions. For both solders, the joints located under the die edge have the largest cracks of any region, and the three adjacent joints at each of the four corners under the die edge are the joints most likely to have the largest crack areas. Comparing aging conditions, the differences in the means of % crack area for SnPb packages were not statistically different, but for SnAg packages, the aged joints had 50% smaller crack areas than non-aged joints (air and quench)
A variable absorption feature in the X-ray spectrum of a magnetar
Soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are slowly
rotating, isolated neutron stars that sporadically undergo episodes of
long-term flux enhancement (outbursts) generally accompanied by the emission of
short bursts of hard X-rays. This behaviour can be understood in the magnetar
model, according to which these sources are mainly powered by their own
magnetic energy. This is supported by the fact that the magnetic fields
inferred from several observed properties of AXPs and SGRs are greater than -
or at the high end of the range of - those of radio pulsars. In the peculiar
case of SGR 0418+5729, a weak dipole magnetic moment is derived from its timing
parameters, whereas a strong field has been proposed to reside in the stellar
interior and in multipole components on the surface. Here we show that the
X-ray spectrum of SGR 0418+5729 has an absorption line, the properties of which
depend strongly on the star's rotational phase. This line is interpreted as a
proton cyclotron feature and its energy implies a magnetic field ranging from
2E14 gauss to more than 1E15 gauss.Comment: Nature, 500, 312 (including Supplementary Information
How to avoid complications of distraction osteogenesis for first brachymetatarsia
Background and purpose Distraction osteogenesis may be used for the treatment of brachymetatarsia. However, few reports have been published on first metatarsal lengthening by this method. We evaluated the complications of distraction osteogenesis for first brachymetatarsia and here we provide a solution
Magnetic Reconnection in Extreme Astrophysical Environments
Magnetic reconnection is a basic plasma process of dramatic rearrangement of
magnetic topology, often leading to a violent release of magnetic energy. It is
important in magnetic fusion and in space and solar physics --- areas that have
so far provided the context for most of reconnection research. Importantly,
these environments consist just of electrons and ions and the dissipated energy
always stays with the plasma. In contrast, in this paper I introduce a new
direction of research, motivated by several important problems in high-energy
astrophysics --- reconnection in high energy density (HED) radiative plasmas,
where radiation pressure and radiative cooling become dominant factors in the
pressure and energy balance. I identify the key processes distinguishing HED
reconnection: special-relativistic effects; radiative effects (radiative
cooling, radiation pressure, and Compton resistivity); and, at the most extreme
end, QED effects, including pair creation. I then discuss the main
astrophysical applications --- situations with magnetar-strength fields
(exceeding the quantum critical field of about 4 x 10^13 G): giant SGR flares
and magnetically-powered central engines and jets of GRBs. Here, magnetic
energy density is so high that its dissipation heats the plasma to MeV
temperatures. Electron-positron pairs are then copiously produced, making the
reconnection layer highly collisional and dressing it in a thick pair coat that
traps radiation. The pressure is dominated by radiation and pairs. Yet,
radiation diffusion across the layer may be faster than the global Alfv\'en
transit time; then, radiative cooling governs the thermodynamics and
reconnection becomes a radiative transfer problem, greatly affected by the
ultra-strong magnetic field. This overall picture is very different from our
traditional picture of reconnection and thus represents a new frontier in
reconnection research.Comment: Accepted to Space Science Reviews (special issue on magnetic
reconnection). Article is based on an invited review talk at the
Yosemite-2010 Workshop on Magnetic Reconnection (Yosemite NP, CA, USA;
February 8-12, 2010). 30 pages, no figure
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