364 research outputs found
Discovery of a 270 Hz X-Ray Burst Oscillation in the X-Ray Dipper 4U 1916-053
We report the discovery of a highly coherent oscillation in a type-I X-ray
burst observed from 4U 1916-053 by the Rossi X-ray Timing Explorer (RXTE). The
oscillation was most strongly detected approx. 1 s after the burst onset at a
frequency of 269.3 Hz, and it increased in frequency over the following 4
seconds of the burst decay to a maximum of around 272 Hz. The total measured
drift of 3.58 +/- 0.41 Hz (1 sigma) represents the largest fractional change in
frequency (1.32 +/- 0.15 %) yet observed in any burst oscillation. If the
asymptotic frequency of the oscillation is interpreted in terms of a decoupled
surface burning layer, the implied neutron star spin period is around 3.7 ms.
However, the expansion of the burning layer required to explain frequency drift
during the burst is around 80 m, substantially larger than expected
theoretically (assuming rigid rotation). The oscillation was not present in the
persistent emission before the burst, nor in the initial rise. When detected
its amplitude was 6-12% (RMS) with a roughly sinusoidal profile. The burst
containing the oscillation showed no evidence for photospheric radius
expansion, while at least 5 of the other 9 bursts observed from the source by
RXTE during 1996 and 1998 did. No comparable oscillations were detected in the
other bursts. A pair of kilohertz quasi-periodic oscillations (QPOs) has been
previously reported from this source with a mean separation of 348 +/- 12 Hz.
4U 1916-053 is the first example of a source where the burst oscillation
frequency is significantly smaller than the frequency separation of the kHz
QPOs.Comment: 8 pages, 2 figures, 2 tables; accepted for ApJ Letter
Joint source-channel coding for a quantum multiple access channel
Suppose that two senders each obtain one share of the output of a classical,
bivariate, correlated information source. They would like to transmit the
correlated source to a receiver using a quantum multiple access channel. In
prior work, Cover, El Gamal, and Salehi provided a combined source-channel
coding strategy for a classical multiple access channel which outperforms the
simpler "separation" strategy where separate codebooks are used for the source
coding and the channel coding tasks. In the present paper, we prove that a
coding strategy similar to the Cover-El Gamal-Salehi strategy and a
corresponding quantum simultaneous decoder allow for the reliable transmission
of a source over a quantum multiple access channel, as long as a set of
information inequalities involving the Holevo quantity hold.Comment: 21 pages, v2: minor changes, accepted into Journal of Physics
Ultra-Stretchable Interconnects for High-Density Stretchable Electronics
The exciting field of stretchable electronics (SE) promises numerous novel
applications, particularly in-body and medical diagnostics devices. However,
future advanced SE miniature devices will require high-density, extremely
stretchable interconnects with micron-scale footprints, which calls for proven
standardized (complementary metal-oxide semiconductor (CMOS)-type) process
recipes using bulk integrated circuit (IC) microfabrication tools and
fine-pitch photolithography patterning. Here, we address this combined
challenge of microfabrication with extreme stretchability for high-density SE
devices by introducing CMOS-enabled, free-standing, miniaturized interconnect
structures that fully exploit their 3D kinematic freedom through an interplay
of buckling, torsion, and bending to maximize stretchability. Integration with
standard CMOS-type batch processing is assured by utilizing the Flex-to-Rigid
(F2R) post-processing technology to make the back-end-of-line interconnect
structures free-standing, thus enabling the routine microfabrication of
highly-stretchable interconnects. The performance and reproducibility of these
free-standing structures is promising: an elastic stretch beyond 2000% and
ultimate (plastic) stretch beyond 3000%, with 10
million cycles at 1000% stretch with <1% resistance change. This generic
technology provides a new route to exciting highly-stretchable miniature
devices.Comment: 13 pages, 5 figure, journal publicatio
An abrupt extinction in the Middle Permian (Capitanian) of the Boreal Realm (Spitsbergen) and its link to anoxia and acidification
The controversial Capitanian (Middle Permian, 262 Ma) extinction event is only known from equatorial latitudes, and consequently its global extent is poorly resolved. We demonstrate that there were two, severe extinctions amongst brachiopods in northern Boreal latitudes (Spitsbergen) in the Middle to Late Permian, separated by a recovery phase. New age dating of the Spitsbergen strata (belonging to the Kapp Starostin Formation), using strontium isotopes and d13C trends and comparison with better-dated sections in Greenland, suggests that the first crisis occurred in the Capitanian. This age assignment indicates that this Middle Permian extinction is manifested at higher latitudes. Redox proxies (pyrite framboids and trace metals) show that the Boreal crisis coincided with an intensification of oxygen depletion, implicating anoxia in the extinction scenario. The widespread and near-total loss of carbonates across the Boreal Realm also suggests a role for acidification in the crisis. The recovery interval saw the appearance of new brachiopod and bivalve taxa alongside survivors, and an increased mollusk dominance, resulting in an assemblage reminiscent of younger Mesozoic assemblages. The subsequent end-Permian mass extinction terminated this Late Permian radiation
Insights into Li and Li isotope cycling and sub-arc metasomatism from veined mantle xenoliths, Kamchatka
Harzburgitic xenoliths cut by pyroxenite veins from Avachinsky volcano, Kamchatka, are derived from the sub-arc mantle and record element transfer from the slab to the arc. Olivine and orthopyroxene in the harzburgites have Li isotopic compositions (δ7Li = +2.8 to +5.6) comparable to estimates of the upper mantle (δ7Li ~ +4 ± 2). The pyroxenite veins, which represent modal metasomatism and may therefore provide information about the metasomatic agent, have mantle-normalized trace element characteristics that suggest overprinting of their mantle source by an aqueous, slab-derived fluid. These include relative enrichments of Pb over Ce, U over Th and Sr over Nd. Li is enriched relative to the HREE, and ortho- and clinopyroxene from the veins are in Li elemental and isotopic equilibrium with each other and the surrounding harzburgite. Vein samples (δ7Li = +3.0 to +5.0) do not record a significant slab-derived δ7Li signature. These observations can be reconciled if slab Li diffusively re-equilibrates in the mantle wedge. Modeling demonstrates that Li equilibration of small (1–2 cm width) veins or melt conduits is achieved at mantle wedge temperatures within 101–105 years. We conclude that strongly fractionated Li isotopic signatures cannot be sustained for long periods in the sub-arc mantle, at least at shallow (<70 km) depths
Petrogenesis of Eocene oceanic basalts from the West Philippine Basin and Oligocene arc volcanics from the Palau-Kyushu Ridge drilled at 20°N, 135°E (Western Pacific Ocean).
The West Philippine Basin (WPB) is a back-arc basin that opened within the Philippine Sea Plate (PSP) between the current position of the Palau-Kyushu
Ridge (PKR) and the margin of East Asia. Spreading occurred at the Central Basin Fault (CBF) mainly from 54 until 30 Ma. The PKR was active since ~ 48
to 35 Ma constituting a single volcanic arc with the Izu-Bonin-Mariana (IBM) Arc. At ~ 42 Ma ago spreading rate and direction changed from NE-SW to NS,
stopping at ~ 30 Ma. A late phase of spreading and volcanism took place between 30 and 26 Ma. ODP Leg 195 Site 1201 is located in the WPB, ~ 100 km
west of the PKR, on 49 Ma crust formed by NE-SW spreading at the CBF. From ~ 35 to 30 Ma, pelagic sedimentation at Site 1201 was followed by turbidite
sedimentation, fed mostly by arc-derived volcanic clasts. The geochemical and isotopic features of Site 1201 basement rocks, which represent Eocene WPB
oceanic crust, compared with those of Site 1201 volcanics from the turbidite sequence, representing products of the early Mariana Arc (PKR), provide some
insights into the early history of the IBM subduction factory. The WPB basement is made up of aphyric to porphyritic basalts with altered olivine, and preserved
plagioclase, clinopyroxene and opaques. The PKR volcanics are porphyritic basalts and andesites with plagioclase, clino- and orthopyroxene, hornblende,
alkali feldspar and opaques. Variable textures, and degree of alteration suggesting zeolite facies metamorphic grade, characterize both groups of rocks.
The mineralogical and geochemical characteristics of the investigated Site 1201 PKR volcanics highlight their calc-alkaline affinity. This feature is at variance
with both other PKR rocks, having mostly boninitic and arc tholeiitic affinity, and WPB basement basalt, having tholeiitic affinity, with some characters
transitional to arc-like, as expected for a back-arc basin. New Sr and Nd isotope data, coupled with published Sr, Nd, Pb and Hf isotope data (Savov et al.,
2006), highlight the Indian Ocean MORB-like character of Site 1201 basement basalts. This suggests that WPB volcanism tapped an upper mantle domain
distinct from that underlying the Pacific Plate. The isotopic features of Site 1201 PKR volcanics are more enriched relative to those of basement basalts reflecting
higher amounts of subduction-derived component(s) in the source of arc magmas. Th-Nb relationships and isotope geochemistry of the WPB basement
and overlaying arc volcanics suggest addition of subducted sediment mostly as siliceous melts, to the mantle source of the arc volcanics. In that respect,
Site 1201 PKR volcanics resemble calc-alkaline volcanics of the currently active Mariana Arc. In addition, the calc-alkaline affinity, unradiogenic neodymium,
and inferred Middle Oligocene age of PKR volcanics, suggest they might represent an evolved stage of arc volcanism at Palau-Kyushu Ridge, perhaps
shortly before the end of its activity
Coating thermal noise for arbitrary shaped beams
Advanced LIGO's sensitivity will be limited by coating noise. Though this
noise depends on beam shape, and though nongaussian beams are being seriously
considered for advanced LIGO, no published analysis exists to compare the
quantitative thermal noise improvement alternate beams offer. In this paper, we
derive and discuss a simple integral which completely characterizes the
dependence of coating thermal noise on shape. The derivation used applies
equally well, with minor modifications, to all other forms of thermal noise in
the low-frequency limit.Comment: 3 pages. Originally performed in August 2004. Submitted to CQG. (v2)
: Corrections from referee and other
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