1,152 research outputs found
Apex Exponents for Polymer--Probe Interactions
We consider self-avoiding polymers attached to the tip of an impenetrable
probe. The scaling exponents and , characterizing the
number of configurations for the attachment of the polymer by one end, or at
its midpoint, vary continuously with the tip's angle. These apex exponents are
calculated analytically by -expansion, and numerically by simulations
in three dimensions. We find that when the polymer can move through the
attachment point, it typically slides to one end; the apex exponents quantify
the entropic barrier to threading the eye of the probe
Fully data-driven time-delay interferometry with time-varying delays
We recently introduced the basic concepts of an approach to filtering
strongly laser-noise dominated space-based gravitational-wave data, like LISA's
phase comparison data streams, which does not rely on independent knowledge of
a temporal delays pattern in the dominant noise that generates the data.
Instead, our automated Principal Component Interferometry (aPCI) approach only
assumes that one can produce some linear combinations of the temporally nearby
regularly spaced phase measurements, which cancel the laser noise. Then we let
the data reveal those combinations, thus providing us with a set of
laser-noise-free data channels. Our basic approach relied on the simplifying
additional assumption that laser-noise-cancelling data combinations or the
filters which lead to the laser-noise-free data streams are time-independent.
In LISA, however, these filters will vary as the constellation armlengths
evolve. Here, we discuss a generalization of the basic aPCI concept compatible
with data dominated by a still unmodeled but slowly varying dominant noise
covariance. We find that despite its independence on any model, the aPCI
processing successfully mitigates laser frequency noise below the other noise
sources level, and that its sensitivity to gravitational waves is the same as
the state-of-the-art second-generation time-delay interferometry, up to a 2%
error.Comment: 11 pages, 7 figure
Micrometeoroid events in LISA Pathfinder
The zodiacal dust complex, a population of dust and small particles that pervades the solar system, provides important insight into the formation and dynamics of planets, comets, asteroids, and other bodies. We present a new set of data obtained from direct measurements of momentum transfer to a spacecraft from individual particle impacts. This technique is made possible by the extreme precision of the instruments flown on the LISA Pathfinder spacecraft, a technology demonstrator for a future space-based gravitational wave observatory. Pathfinder employed a technique known as drag-free control that achieved rejection of external disturbances, including particle impacts, using a micropropulsion system. Using a simple model of the impacts and knowledge of the control system, we show that it is possible to detect impacts and measure properties such as the transferred momentum, direction of travel, and location of impact on the spacecraft. In this paper, we present the results of a systematic search for impacts during 4348 hr of Pathfinder data. We report a total of 54 candidates with transferred momenta ranging from 0.2 to 230 µNs. We furthermore make a comparison of these candidates with models of micrometeoroid populations in the inner solar system, including those resulting from Jupiter-family comets (JFCs), Oort Cloud comets, Halley-type comets, and asteroids. We find that our measured population is consistent with a population dominated by JFCs, with some evidence for a smaller contribution from Halley-type comets, in agreement with consensus models of the zodiacal dust complex in the momentum range sampled by LISA Pathfinder.Peer ReviewedPostprint (published version
High-Definition Optical Coherence Tomography for the in vivo Detection of Demodex Mites
Background: Demodex mites are involved in different skin diseases and are commonly detected by skin scrape tests or superficial biopsies. A new high-definition optical coherence tomography (HD-OCT) with high lateral and axial resolution in a horizontal (en-face) and vertical (slice) imaging mode might offer the possibility of noninvasive and fast in vivo examination of demodex mites. Methods: Twenty patients with demodex-related skin diseases and 20 age- and gender-matched healthy controls were examined by HD-OCT. Mites per follicle and follicles per field of view were counted and compared to skin scrape tests. Results: HD-OCT images depicted mites in the en-face mode as bright round dots in groups of 3-5 mites per hair follicle. In the patients with demodex-related disease, a mean number of 3.4 mites per follicle were detected with a mean number of 2.9 infested follicles per area of view compared to a mean of 0.6 mites in 0.4 infested follicles in the controls. The skin scrape tests were negative in 21% of the patients. Conclusion: The innovative HD-OCT enables fast and noninvasive in vivo recognition of demodex mites and might become a useful tool in the diagnosis and treatment monitoring of demodex-related skin diseases. Copyright (C) 2012 S. Karger AG, Base
The Critical Coupling Likelihood Method: A new approach for seamless integration of environmental and operating conditions of gravitational wave detectors into gravitational wave searches
Any search effort for gravitational waves (GW) using interferometric
detectors like LIGO needs to be able to identify if and when noise is coupling
into the detector's output signal. The Critical Coupling Likelihood (CCL)
method has been developed to characterize potential noise coupling and in the
future aid GW search efforts. By testing two hypotheses about pairs of
channels, CCL is able to identify undesirable coupled instrumental noise from
potential GW candidates. Our preliminary results show that CCL can associate up
to of observed artifacts with , to local noise sources,
while reducing the duty cycle of the instrument by . An approach
like CCL will become increasingly important as GW research moves into the
Advanced LIGO era, going from the first GW detection to GW astronomy.Comment: submitted CQ
APPLICATION OF MODIFYING ALLOYING ALLOY CONTAINING NANOSIZED POWDERS OF ACTIVE ELEMENTS IN PRODUCTION OF HIGH-STRENGTH CAST IRON WITH GLOBULAR GRAPHITE
Scientific and practical interest is the application of alloying alloy-modifiers for secondary treatment of high-strength cast iron to stabilize the process of spheroidization graphite and achieving higher physical-mechanical properties of castings. The peculiarity of the high-strength cast irons manufacturing technology is their tendency to supercooling during solidification in the mold. This leads to the formation of shrinkage defects and structurally free cementite, especially in thin-walled sections of the finished castings. To minimize these effects in foundry practice during production of ductile iron the secondary inoculation is widely used. In this regard, the question of the choice of the additives with effective impact not only on the graphitization process but also on the formation of the metallic base of ductile iron is relevant. The aim of the present work is to study the peculiarities of structure formation in cast iron with nodular graphite when alloying alloy-modifier based on tin with additions of nanoparticles of titanium carbide, yttrium oxide and graphite nano-pipes is used for secondary treatment. Melting of iron in laboratory conditions was performed in crucible induction furnace IST-006 with an acid lining held. Spheroidizing treatment of melt was realized with magnesium containing alloying alloy FeSiMg7 by means of ladle method. Secondary treatment of high strength cast iron was carried out by addition of alloying alloy-modifier in an amount of 0.1% to the bottom of the pouring ladle. Cast samples for chemical composition analysis, study of microstructure, technological and mechanical properties of the resultant alloy were made. Studies have shown that the secondary treatment of high strength cast iron with developed modifier-alloying alloy results in formation of the perlite metallic base due to the tin impact and nodular graphite with regular shape under the influence of titanium carbide, yttrium oxide and graphite nano-pipes. The tendency of high strength cast iron to «white cast iron» formation has been minimized, and the mechanical properties of the alloy produced correspond to HSCI80
Security of quantum cryptography using balanced homodyne detection
In this paper we investigate the security of a quantum cryptographic scheme
which utilizes balanced homodyne detection and weak coherent pulse (WCP). The
performance of the system is mainly characterized by the intensity of the WCP
and postselected threshold. Two of the simplest intercept/resend eavesdropping
attacks are analyzed. The secure key gain for a given loss is also discussed in
terms of the pulse intensity and threshold.Comment: RevTeX4, 8pages, 7 figure
Methods for Reducing False Alarms in Searches for Compact Binary Coalescences in LIGO Data
The LIGO detectors are sensitive to a variety of noise transients of
non-astrophysical origin. Instrumental glitches and environmental disturbances
increase the false alarm rate in the searches for gravitational waves. Using
times already identified when the interferometers produced data of questionable
quality, or when the channels that monitor the interferometer indicated
non-stationarity, we have developed techniques to safely and effectively veto
false triggers from the compact binary coalescences (CBCs) search pipeline
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