1,440 research outputs found
Crack barriers improve the mechanical and thermal properties of non-metallic sinter materials
Means of improving the tensile strength of ceramic composites by introducing ductile intermediate layers capable of absorbing the elastic energy at the rupture front are studied. Tests with an Al203 laminate with niobium inclusions showed that crack propagation could be successfully precluded by dissipation of the energy by deformation and/or delamination at the inclusion/matrix interface
A Transiting Planet of a Sun-like Star
A planet transits an 11th magnitude, G1V star in the constellation Corona
Borealis. We designate the planet XO-1b, and the star, XO-1, also known as GSC
02041-01657. XO-1 lacks a trigonometric distance; we estimate it to be 200+-20
pc. Of the ten stars currently known to host extrasolar transiting planets, the
star XO-1 is the most similar to the Sun in its physical characteristics: its
radius is 1.0+-0.08 R_Sun, its mass is 1.0+-0.03 M_Sun, V sini < 3 km/s, and
its metallicity [Fe/H] is 0.015+-0.04. The orbital period of the planet XO-1b
is 3.941534+-0.000027 days, one of the longer ones known. The planetary mass is
0.90+-0.07 M_Jupiter, which is marginally larger than that of other transiting
planets with periods between 3 and 4 days. Both the planetary radius and the
inclination are functions of the spectroscopically determined stellar radius.
If the stellar radius is 1.0+-0.08 R_Sun, then the planetary radius is
1.30+-0.11 R_Jupiter and the inclination of the orbit is 87.7+-1.2 degrees. We
have demonstrated a productive international collaboration between professional
and amateur astronomers that was important to distinguishing this planet from
many other similar candidates.Comment: 31 pages, 9 figures, accepted for part 1 of Ap
Stable and reproducible electronic conduction through DNA molecular junctions
This letter presents the observation of stable and reproducible electronic conduction through double stranded (ds) DNA molecules in a nominally dry state. Stable conduction was realized by immobilizing 15 base-pair guanine:cytosine rich dsDNA within gold nanogap junctions, stabilizing the dsDNA with a polycation, and characterizing in nitrogen. In air, the current levels decrease with successive voltage scans likely due to oxidation of the guanine bases under bias. In nitrogen, reproducible current-voltage traces are observed and the current levels at specific bias points are stable with time. The stability allows comprehensive electrical studies and could enable conductance-based DNA sensors
XO-5b: A Transiting Jupiter-sized Planet With A Four Day Period
The star XO-5 (GSC 02959-00729, V=12.1, G8V) hosts a Jupiter-sized,
Rp=1.15+/-0.12 Rjup, transiting extrasolar planet, XO-5b, with an orbital
period of P=4.187732+/-0.00002 days. The planet mass (Mp=1.15+/-0.08 Mjup) and
surface gravity (gp=22+/-5 m/s^2) are significantly larger than expected by
empirical Mp-P and Mp-P-[Fe/H] relationships. However, the deviation from the
Mp-P relationship for XO-5b is not large enough to suggest a distinct type of
planet as is suggested for GJ 436b, HAT-P-2b, and XO-3b. By coincidence XO-5
overlies the extreme H I plume that emanates from the interacting galaxy pair
NGC 2444/NGC 2445 (Arp 143).Comment: 10 pages, 9 Figures, Submitted to Ap
XO-2b: Transiting Hot Jupiter in a Metal-rich Common Proper Motion Binary
We report on a V=11.2 early K dwarf, XO-2 (GSC 03413-00005), that hosts a
Rp=0.98+0.03/-0.01 Rjup, Mp=0.57+/-0.06 Mjup transiting extrasolar planet,
XO-2b, with an orbital period of 2.615857+/-0.000005 days. XO-2 has high
metallicity, [Fe/H]=0.45+/-0.02, high proper motion, mu_tot=157 mas/yr, and has
a common proper motion stellar companion with 31" separation. The two stars are
nearly identical twins, with very similar spectra and apparent magnitudes. Due
to the high metallicity, these early K dwarf stars have a mass and radius close
to solar, Ms=0.98+/-0.02 Msolar and Rs=0.97+0.02/-0.01 Rsolar. The high proper
motion of XO-2 results from an eccentric orbit (Galactic pericenter, Rper<4
kpc) well confined to the Galactic disk (Zmax~100 pc). In addition, the phase
space position of XO-2 is near the Hercules dynamical stream, which points to
an origin of XO-2 in the metal-rich, inner Thin Disk and subsequent dynamical
scattering into the solar neighborhood. We describe an efficient Markov Chain
Monte Carlo algorithm for calculating the Bayesian posterior probability of the
system parameters from a transit light curve.Comment: 14 pages, 10 Figures, Accepted in ApJ. Negligible changes to XO-2
system properties. Removed Chi^2 light curve analysis section, and simplified
MCMC light curve analysis discussio
The XO Project: Searching for Transiting Extra-solar Planet Candidates
The XO project's first objective is to find hot Jupiters transiting bright
stars, i.e. V < 12, by precision differential photometry. Two XO cameras have
been operating since September 2003 on the 10,000-foot Haleakala summit on
Maui. Each XO camera consists of a 200-mm f/1.8 lens coupled to a 1024x1024
pixel, thinned CCD operated by drift scanning. In its first year of routine
operation, XO has observed 6.6% of the sky, within six 7 deg-wide strips
scanned from 0 deg to +63 deg of declination and centered at RA=0, 4, 8, 12,
16, and 20 hours. Autonomously operating, XO records 1 billion pixels per clear
night, calibrates them photometrically and astrometrically, performs aperture
photometry, archives the pixel data and transmits the photometric data to STScI
for further analysis. From the first year of operation, the resulting database
consists of photometry of 100,000 stars at more than 1000 epochs per star with
differential photometric precision better than 1% per epoch. Analysis of the
light curves of those stars produces transiting-planet candidates requiring
detailed follow up, described elsewhere, culminating in spectroscopy to measure
radial-velocity variation in order to differentiate genuine planets from the
more numerous impostors, primarily eclipsing binary and multiple stars.Comment: 29 pages, 12 figures, accepted by PASP for Aug 2005 issu
âEngage the Worldâ: examining conflicts of engagement in public museums
Public engagement has become a central theme in the mission statements of many cultural institutions, and in scholarly research into museums and heritage. Engagement has emerged as the go-to-it-word for generating, improving or repairing relations between museums and society at large. But engagement is frequently an unexamined term that might embed assumptions and ignore power relationships. This article describes and examines the implications of conflicting and misleading uses of âengagementâ in relation to institutional dealings with contested questions about culture and heritage. It considers the development of an exhibition on the Dead Sea Scrolls by the Royal Ontario Museum, Toronto in 2009 within the new institutional goal to âEngage the Worldâ. The chapter analyses the motivations, processes and decisions deployed by management and staff to âEngage the Worldâ, and the degree to which the museum was able to re-think its strategies of public engagement, especially in relation to subjects,issues and publics that were more controversial in nature
Design, fabrication, and characterization of a compact hierarchical manifold microchannel heat sink array for two-phase cooling
High-heat-flux removal is critical for the nextgeneration electronic devices to reliably operate within their temperature limits. A large portion of the thermal resistance in a traditional chip package is caused by thermal resistances at interfaces between the device, heat spreaders, and the heat sink; embedding the heat sink directly into the heat-generating device can eliminate these interface resistances and drastically reduce the overall thermal resistance. Microfluidic cooling within the embedded heat sink improves the heat dissipation, with two-phase operation offering the potential for dissipation of very high heat fluxes while maintaining moderate chip temperatures. To enable multichip stacking and other heterogeneous packaging approaches, it is important to densely integrate all fluid flow paths into the device; volumetric heat dissipation emerges as a performance metric in this new heat sinking paradigm. In this paper, a compact hierarchical manifold microchannel design is presented that utilizes an integrated multilevel manifold distributor to feed coolant to an array of microchannel heat sinks. The flow features in the manifold layers and microchannels are fabricated in silicon wafers using deep reactive-ion etching. The heat source is simulated via Joule heating using thin-film platinum heaters. The on-chip spatial temperature measurements are made using four-wire resistance temperature detectors. The individual manifold layers and the microchannel-bearing wafers are diced and bonded into a sealed stack via thermocompression bonding using gold layers at the mating surfaces. Thermal and hydrodynamic testing is performed by pumping the dielectric fluid HFE-7100 through the device at a known flow rate
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