2,683 research outputs found
Giant Anharmonic Phonon Scattering in PbTe
Understanding the microscopic processes affecting the bulk thermal
conductivity is crucial to develop more efficient thermoelectric materials.
PbTe is currently one of the leading thermoelectric materials, largely thanks
to its low thermal conductivity. However, the origin of this low thermal
conductivity in a simple rocksalt structure has so far been elusive. Using a
combination of inelastic neutron scattering measurements and first-principles
computations of the phonons, we identify a strong anharmonic coupling between
the ferroelectric transverse optic (TO) mode and the longitudinal acoustic (LA)
modes in PbTe. This interaction extends over a large portion of reciprocal
space, and directly affects the heat-carrying LA phonons. The LA-TO anharmonic
coupling is likely to play a central role in explaining the low thermal
conductivity of PbTe. The present results provide a microscopic picture of why
many good thermoelectric materials are found near a lattice instability of the
ferroelectric type
Hybrid time-domain and continuous-wave diffuse optical tomography instrument with concurrent, clinical magnetic resonance imaging for breast cancer imaging
Diffuse optical tomography has demonstrated significant potential for clinical utility in the diagnosis and prognosis of breast cancer, and its use in combination with other structural imaging modalities improves lesion localization and the quantification of functional tissue properties. Here, we introduce a hybrid diffuse optical imaging system that operates concurrently with magnetic resonance imaging (MRI) in the imaging suite, utilizing commercially available MR surface coils. The instrument acquires both continuous-wave and time-domain diffuse optical data in the parallel-plate geometry, permitting both absolute assignment of tissue optical properties and three-dimensional tomography; moreover, the instrument is designed to incorporate diffuse correlation spectroscopic measurements for probing tissue blood flow. The instrument is described in detail here. Image reconstructions of a tissue phantom are presented as an initial indicator of the system's ability to accurately reconstruct optical properties and the concrete benefits of the spatial constraints provided by concurrent MRI. Last, we briefly discuss how various data combinations that the instrument could facilitate, including tissue perfusion, can enable more comprehensive assessment of lesion physiology
Multi-modal diffuse optical techniques for breast cancer neoadjuvant chemotherapy monitoring (Conference Presentation)
We present high spatial density, multi-modal, parallel-plate Diffuse Optical Tomography (DOT) imaging systems for
the purpose of breast tumor detection. One hybrid instrument provides time domain (TD) and continuous wave
(CW) DOT at 64 source fiber positions. The TD diffuse optical spectroscopy with PMT- detection produces lowresolution
images of absolute tissue scattering and absorption while the spatially dense array of CCD-coupled
detector fibers (108 detectors) provides higher-resolution CW images of relative tissue optical properties.
Reconstruction of the tissue optical properties, along with total hemoglobin concentration and tissue oxygen
saturation, is performed using the TOAST software suite. Comparison of the spatially-dense DOT images and MR
images allows for a robust validation of DOT against an accepted clinical modality. Additionally, the structural
information from co-registered MR images is used as a spatial prior to improve the quality of the functional optical
images and provide more accurate quantification of the optical and hemodynamic properties of tumors. We also
present an optical-only imaging system that provides frequency domain (FD) DOT at 209 source positions with full
CCD detection and incorporates optical fringe projection profilometry to determine the breast boundary. This
profilometry serves as a spatial constraint, improving the quality of the DOT reconstructions while retaining the
benefits of an optical-only device. We present initial images from both human subjects and phantoms to display the
utility of high spatial density data and multi-modal information in DOT reconstruction with the two systems
CoRoT-22 b: a validated 4.9 RE exoplanet in 10-day orbit
The CoRoT satellite has provided high-precision photometric light curves for
more than 163,000 stars and found several hundreds of transiting systems
compatible with a planetary scenario. If ground-based velocimetric observations
are the best way to identify the actual planets among many possible
configurations of eclipsing binary systems, recent transit surveys have shown
that it is not always within reach of the radial-velocity detection limits. In
this paper, we present a transiting exoplanet candidate discovered by CoRoT
whose nature cannot be established from ground-based observations, and where
extensive analyses are used to validate the planet scenario. They are based on
observing constraints from radial-velocity spectroscopy, adaptive optics
imaging and the CoRoT transit shape, as well as from priors on stellar
populations, planet and multiple stellar systems frequency. We use the fully
Bayesian approach developed in the PASTIS analysis software, and conclude that
the planet scenario is at least 1400 times more probable than any other false
positive scenario. The primary star is a metallic solar-like dwarf, with Ms =
1.099+-0.049 Msun and Rs = 1.136 (+0.038,-0.090) Rsun . The validated planet
has a radius of Rp = 4.88 (+0.17,-0.39) RE and mass less than 49 ME. Its mean
density is smaller than 2.56 g/cm^3 and orbital period is 9.7566+-0.0012 days.
This object, called CoRoT-22 b, adds to a large number of validated Kepler
planets. These planets do not have a proper measurement of the mass but allow
statistical characterization of the exoplanet population
Four small puzzles that Rosetta doesn't solve
A complete macromolecule modeling package must be able to solve the simplest
structure prediction problems. Despite recent successes in high resolution
structure modeling and design, the Rosetta software suite fares poorly on
deceptively small protein and RNA puzzles, some as small as four residues. To
illustrate these problems, this manuscript presents extensive Rosetta results
for four well-defined test cases: the 20-residue mini-protein Trp cage, an even
smaller disulfide-stabilized conotoxin, the reactive loop of a serine protease
inhibitor, and a UUCG RNA tetraloop. In contrast to previous Rosetta studies,
several lines of evidence indicate that conformational sampling is not the
major bottleneck in modeling these small systems. Instead, approximations and
omissions in the Rosetta all-atom energy function currently preclude
discriminating experimentally observed conformations from de novo models at
atomic resolution. These molecular "puzzles" should serve as useful model
systems for developers wishing to make foundational improvements to this
powerful modeling suite.Comment: Published in PLoS One as a manuscript for the RosettaCon 2010 Special
Collectio
Transit Timing and Duration Variations for the Discovery and Characterization of Exoplanets
Transiting exoplanets in multi-planet systems have non-Keplerian orbits which
can cause the times and durations of transits to vary. The theory and
observations of transit timing variations (TTV) and transit duration variations
(TDV) are reviewed. Since the last review, the Kepler spacecraft has detected
several hundred perturbed planets. In a few cases, these data have been used to
discover additional planets, similar to the historical discovery of Neptune in
our own Solar System. However, the more impactful aspect of TTV and TDV studies
has been characterization of planetary systems in which multiple planets
transit. After addressing the equations of motion and parameter scalings, the
main dynamical mechanisms for TTV and TDV are described, with citations to the
observational literature for real examples. We describe parameter constraints,
particularly the origin of the mass/eccentricity degeneracy and how it is
overcome by the high-frequency component of the signal. On the observational
side, derivation of timing precision and introduction to the timing diagram are
given. Science results are reviewed, with an emphasis on mass measurements of
transiting sub-Neptunes and super-Earths, from which bulk compositions may be
inferred.Comment: Revised version. Invited review submitted to 'Handbook of
Exoplanets,' Exoplanet Discovery Methods section, Springer Reference Works,
Juan Antonio Belmonte and Hans Deeg, Eds. TeX and figures may be found at
https://github.com/ericagol/TTV_revie
Risk factors for delayed presentation and referral of symptomatic cancer: Evidence for common cancers
Background:It has been suggested that the known poorer survival from cancer in the United Kingdom, compared with other European countries, can be attributed to more advanced cancer stage at presentation. There is, therefore, a need to understand the diagnostic process, and to ascertain the risk factors for increased time to presentation.Methods:We report the results from two worldwide systematic reviews of the literature on patient-mediated and practitioner-mediated delays, identifying the factors that may influence these.Results:Across cancer sites, non-recognition of symptom seriousness is the main patient-mediated factor resulting in increased time to presentation. There is strong evidence of an association between older age and patient delay for breast cancer, between lower socio-economic status and delay for upper gastrointestinal and urological cancers and between lower education level and delay for breast and colorectal cancers. Fear of cancer is a contributor to delayed presentation, while sanctioning of help seeking by others can be a powerful mediator of reduced time to presentation. For practitioner delay, ‘misdiagnosis’ occurring either through treating patients symptomatically or relating symptoms to a health problem other than cancer, was an important theme across cancer sites. For some cancers, this could also be linked to inadequate patient examination, use of inappropriate tests or failing to follow-up negative or inconclusive test results.Conclusion:Having sought help for potential cancer symptoms, it is therefore important that practitioners recognise these symptoms, and examine, investigate and refer appropriately. © 2009 Cancer Research UK All rights reserved
The Calcitonin and Glucocorticoids Combination: Mechanistic Insights into Their Class-Effect Synergy in Experimental Arthritis
PMCID: PMC3564948This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Luminally expressed gastrointestinal biomarkers
Introduction: A biomarker is a measurable indicator of normal biologic processes, pathogenic processes or pharmacological responses. The identification of a useful biomarker is challenging, with several hurdles to overcome before clinical adoption. This review gives a general overview of a range of biomarkers associated with inflammatory bowel disease or colorectal cancer along the gastrointestinal tract.
Areas covered: These markers include those that are already clinically accepted, such as inflammatory markers such as faecal calprotectin, S100A12 (Calgranulin C), Fatty Acid Binding Proteins (FABP), malignancy markers such as Faecal Occult Blood, Mucins, Stool DNA, Faecal microRNA (miRNA), other markers such as Faecal Elastase, Faecal alpha-1-antitrypsin, Alpha2-macroglobulin and possible future markers such as microbiota, volatile organic compounds and pH.
Expert commentary: There are currently a few biomarkers that have been sufficiently validated for routine clinical use at present such as FC. However, many of these biomarkers continue to be limited in sensitivity and specificity for various GI diseases. Emerging biomarkers have the potential to improve diagnosis and monitoring but further study is required to determine efficacy and validate clinical utility
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