5,520 research outputs found
Measuring thickness in thin NbN films for superconducting devices
We present the use of a commercially available fixed-angle multi-wavelength
ellipsometer for quickly measuring the thickness of NbN thin films for the
fabrication and performance improvement of superconducting nanowire single
photon detectors. The process can determine the optical constants of absorbing
thin films, removing the need for inaccurate approximations. The tool can be
used to observe oxidation growth and allows thickness measurements to be
integrated into the characterization of various fabrication processes
Wireless Medical Sensor Networks: Design Requirements and Enabling Technologies
This article analyzes wireless communication protocols that could be used in healthcare environments (e.g., hospitals and small clinics) to transfer real-time medical information obtained from noninvasive sensors. For this purpose the features of the three currently most widely used protocols—namely, Bluetooth® (IEEE 802.15.1), ZigBee (IEEE 802.15.4), and Wi-Fi (IEEE 802.11)—are evaluated and compared. The important features under consideration include data bandwidth, frequency band, maximum transmission distance, encryption and authentication methods, power consumption, and current applications. In addition, an overview of network requirements with respect to medical sensor features, patient safety and patient data privacy, quality of service, and interoperability between other sensors is briefly presented. Sensor power consumption is also discussed because it is considered one of the main obstacles for wider adoption of wireless networks in medical applications. The outcome of this assessment will be a useful tool in the hands of biomedical engineering researchers. It will provide parameters to select the most effective combination of protocols to implement a specific wireless network of noninvasive medical sensors to monitor patients remotely in the hospital or at home
The Frequency of Rapid Rotation Among K Giant Stars
We present the results of a search for unusually rapidly rotating giant stars
in a large sample of K giants (~1300 stars) that had been spectroscopically
monitored as potential targets for the Space Interferometry Mission's
Astrometric Grid. The stars in this catalog are much fainter and typically more
metal-poor than those of other catalogs of red giant star rotational
velocities, but the spectra generally only have signal-to-noise (S/N) of
~20-60, making the measurement of the widths of individual lines difficult. To
compensate for this, we have developed a cross-correlation method to derive
rotational velocities in moderate S/N echelle spectra to efficiently probe this
sample for rapid rotator candidates. We have discovered 28 new red giant rapid
rotators as well as one extreme rapid rotator with a vsini of 86.4 km/s. Rapid
rotators comprise 2.2% of our sample, which is consistent with other surveys of
brighter, more metal-rich K giant stars. Although we find that the temperature
distribution of rapid rotators is similar to that of the slow rotators, this
may not be the case with the distributions of surface gravity and metallicity.
The rapid rotators show a slight overabundance of low gravity stars and as a
group are significantly more metal-poor than the slow rotators, which may
indicate that the rotators are tidally-locked binaries.Comment: Accepted for publication in ApJ. 25 pages, 9 figures, 3 tables.
Tables 1 and 2 are provided in their full form as plain text ancillary file
Effects of calcium carbonate particulate releasing surgical anchors on bone and tendon healing
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Cataloged from PDF version of thesis.Includes bibliographical references (p. 31-32).The Calaxo ® screw, developed by Smith and Nephew, is a novel biomedical composite composed of poly-DL-lactide-co-glycolide (PLLA:PGA) 85:15 and calcium carbonate particulates. Comparisons to an identical surgical anchor composed of PLLA, largely considered an industry standard, shows increased mean failure strength in surgical reconstructions of the patellar-tibia complex in sheep. SEM imaging confirms the osteoconductivity of the Calaxo ® screw proposed in previous studies and also suggest a positive effect on the differentiation of tissues along the tendon-bone interface. These findings support the intended use of the Calaxo ® screw as a fixation device for rotator cuff repair procedures.by Jordan-Ryan J.I.K. Medeiros.S.B
Abundant cyanopolyynes as a probe of infall in the Serpens South cluster-forming region
We have detected bright HC7N J = 21-20 emission toward multiple locations in
the Serpens South cluster-forming region using the K-Band Focal Plane Array at
the Robert C. Byrd Green Bank Telescope. HC7N is seen primarily toward cold
filamentary structures that have yet to form stars, largely avoiding the dense
gas associated with small protostellar groups and the main central cluster of
Serpens South. Where detected, the HC7N abundances are similar to those found
in other nearby star forming regions. Toward some HC7N `clumps', we find
consistent variations in the line centroids relative to NH3 (1,1) emission, as
well as systematic increases in the HC7N non-thermal line widths, which we
argue reveal infall motions onto dense filaments within Serpens South with
minimum mass accretion rates of M ~ 2-5 M_sun Myr^-1. The relative abundance of
NH3 to HC7N suggests that the HC7N is tracing gas that has been at densities n
~ 10^4 cm^-3, for timescales t < 1-2 x 10^5 yr. Since HC7N emission peaks are
rarely co-located with those of either NH3 or continuum, it is likely that
Serpens South is not particularly remarkable in its abundance of HC7N, but
instead the serendipitous mapping of HC7N simultaneously with NH3 has allowed
us to detect HC7N at low abundances in regions where it otherwise may not have
been looked for. This result extends the known star-forming regions containing
significant HC7N emission from typically quiescent regions, like the Taurus
molecular cloud, to more complex, active environments.Comment: 19 pages, 13 figures, accepted to MNRAS. Version with full resolution
figures available at http://www.dunlap.utoronto.ca/~friesen/Friesen_HC7N.pd
Does rotation of B stars depend on metallicity? preliminary results from GIRAFFE spectra
We show the vsini distribution of main sequence B stars in sites of various
metallicities, in the absolute magnitude range -3.34 < Mv < -2.17. These
include Galactic stars in the field measured by Abt et al. (2002), members of
the h & chi Per open clusters measured by North et al. (2004), and five fields
in the SMC and LMC measured at ESO Paranal with the FLAMES-GIRAFFE
spectrograph, within the Geneva-Lausanne guaranteed time. Following the
suggestion by Maeder et al. (1999), we do find a higher rate of rapid rotators
in the Magellanic Clouds than in the Galaxy, but the vsini distribution is the
same in the LMC and in the SMC in spite of their very different metallicities.Comment: 2 pages, 1 figure, poster presented at the ESO/Arcetri Workshop on
"Chemical abundances and mixing in stars in the Milky Way and its
satellites", 13-17 Sept. 200
Linear Parsing Expression Grammars
PEGs were formalized by Ford in 2004, and have several pragmatic operators
(such as ordered choice and unlimited lookahead) for better expressing modern
programming language syntax. Since these operators are not explicitly defined
in the classic formal language theory, it is significant and still challenging
to argue PEGs' expressiveness in the context of formal language theory.Since
PEGs are relatively new, there are several unsolved problems.One of the
problems is revealing a subclass of PEGs that is equivalent to DFAs. This
allows application of some techniques from the theory of regular grammar to
PEGs. In this paper, we define Linear PEGs (LPEGs), a subclass of PEGs that is
equivalent to DFAs. Surprisingly, LPEGs are formalized by only excluding some
patterns of recursive nonterminal in PEGs, and include the full set of ordered
choice, unlimited lookahead, and greedy repetition, which are characteristic of
PEGs. Although the conversion judgement of parsing expressions into DFAs is
undecidable in general, the formalism of LPEGs allows for a syntactical
judgement of parsing expressions.Comment: Parsing expression grammars, Boolean finite automata, Packrat parsin
Constant Curvature Algebras and Higher Spin Action Generating Functions
The algebra of differential geometry operations on symmetric tensors over
constant curvature manifolds forms a novel deformation of the sl(2,R)
[semidirect product] R^2 Lie algebra. We present a simple calculus for
calculations in its universal enveloping algebra. As an application, we derive
generating functions for the actions and gauge invariances of massive,
partially massless and massless (for both bose and fermi statistics) higher
spins on constant curvature backgrounds. These are formulated in terms of a
minimal set of covariant, unconstrained, fields rather than towers of auxiliary
fields. Partially massless gauge transformations are shown to arise as
degeneracies of the flat, massless gauge transformation in one dimension
higher. Moreover, our results and calculus offer a considerable simplification
over existing techniques for handling higher spins. In particular, we show how
theories of arbitrary spin in dimension d can be rewritten in terms of a single
scalar field in dimension 2d where the d additional dimensions correspond to
coordinate differentials. We also develop an analogous framework for
spinor-tensor fields in terms of the corresponding superalgebra.Comment: 44 pages, LaTeX, 2 .eps figure
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