15,772 research outputs found
Bounds of Efficiency at Maximum Power for Normal-, Sub- and Super-Dissipative Carnot-Like Heat Engines
The Carnot-like heat engines are classified into three types (normal-, sub-
and super-dissipative) according to relations between the minimum irreversible
entropy production in the "isothermal" processes and the time for completing
those processes. The efficiencies at maximum power of normal-, sub- and
super-dissipative Carnot-like heat engines are proved to be bounded between
and , and , 0 and
, respectively. These bounds are also shared by linear, sub-
and super-linear irreversible Carnot-like engines [Tu and Wang, Europhys. Lett.
98, 40001 (2012)] although the dissipative engines and the irreversible ones
are inequivalent to each other.Comment: 1 figur
Numerical Simulations of Flows over a Forced Oscillating Cylinder
A numerical study of incompressible laminar flow past a circular cylinder forced to oscillate longitudinally, transversely and at an angle to the uniform freestream is performed using the dynamic mesh method. The simulations are conducted at a fixed Reynolds number of 80 with amplitude ratios varying between 0.14 to 0.50 and excitation frequency ratios of 0.05 to 3.0. Good agreement to previous experimental and numerical investigations is achieved in the prediction of the lock-on range, force amplifications and vortex shedding modes for longitudinal and transverse oscillations. For excitations at an angle of 60 degrees relative to the oncoming flow, previously identified modes of AI and, AII were successfully predicted. In addition, at higher amplitude ratios the entire synchronised von Karman wake street displayed a deviating effect from the centreline. Analysis of the wake response via phase plane diagrams and the transverse force coefficients revealed two lock-on regions. The extents of these lock-on regions, and the variation of the forces and near wake vortex shedding modes are presented and discussed herein
Comprehensive HIV care and Anti-Retroviral Therapy in a conflict setting-outcomes, experiences, and lessons learned from Bukavu, Democratic Republic of Congo
2006 AIDS Conference in Toront
Molecular Motor of Double-Walled Carbon Nanotube Driven by Temperature Variation
An elegant formula for coordinates of carbon atoms in a unit cell of a
single-walled nanotube (SWNT) is presented and a new molecular motor of
double-walled carbon nanotube whose inner tube is a long (8,4) SWNT and outer
tube a short (14,8) SWNT is constructed. The interaction between inner an outer
tubes is analytically derived by summing the Lennard-Jones potentials between
atoms in inner and outer tubes. It is proved that the molecular motor in a
thermal bath exhibits a directional motion with the temperature variation of
the bath.Comment: 9 pages, 4 figures, revtex
Semantic Context Forests for Learning-Based Knee Cartilage Segmentation in 3D MR Images
The automatic segmentation of human knee cartilage from 3D MR images is a
useful yet challenging task due to the thin sheet structure of the cartilage
with diffuse boundaries and inhomogeneous intensities. In this paper, we
present an iterative multi-class learning method to segment the femoral, tibial
and patellar cartilage simultaneously, which effectively exploits the spatial
contextual constraints between bone and cartilage, and also between different
cartilages. First, based on the fact that the cartilage grows in only certain
area of the corresponding bone surface, we extract the distance features of not
only to the surface of the bone, but more informatively, to the densely
registered anatomical landmarks on the bone surface. Second, we introduce a set
of iterative discriminative classifiers that at each iteration, probability
comparison features are constructed from the class confidence maps derived by
previously learned classifiers. These features automatically embed the semantic
context information between different cartilages of interest. Validated on a
total of 176 volumes from the Osteoarthritis Initiative (OAI) dataset, the
proposed approach demonstrates high robustness and accuracy of segmentation in
comparison with existing state-of-the-art MR cartilage segmentation methods.Comment: MICCAI 2013: Workshop on Medical Computer Visio
Dysflective cones: Visual function and cone reflectivity in long-term follow-up of acute bilateral foveolitis.
PURPOSE:Confocal adaptive optics scanning laser ophthalmoscope (AOSLO) images provide a sensitive measure of cone structure. However, the relationship between structural findings of diminished cone reflectivity and visual function is unclear. We used fundus-referenced testing to evaluate visual function in regions of apparent cone loss identified using confocal AOSLO images. METHODS:A patient diagnosed with acute bilateral foveolitis had spectral-domain optical coherence tomography (SD-OCT) (Spectralis HRA + OCT system [Heidelberg Engineering, Vista, CA, USA]) images indicating focal loss of the inner segment-outer segment junction band with an intact, but hyper-reflective, external limiting membrane. Five years after symptom onset, visual acuity had improved from 20/80 to 20/25, but the retinal appearance remained unchanged compared to 3 months after symptoms began. We performed structural assessments using SD-OCT, directional OCT (non-standard use of a prototype on loan from Carl Zeiss Meditec) and AOSLO (custom-built system). We also administered fundus-referenced functional tests in the region of apparent cone loss, including analysis of preferred retinal locus (PRL), AOSLO acuity, and microperimetry with tracking SLO (TSLO) (prototype system). To determine AOSLO-corrected visual acuity, the scanning laser was modulated with a tumbling E consistent with 20/30 visual acuity. Visual sensitivity was assessed in and around the lesion using TSLO microperimetry. Complete eye examination, including standard measures of best-corrected visual acuity, visual field tests, color fundus photos, and fundus auto-fluorescence were also performed. RESULTS:Despite a lack of visible cone profiles in the foveal lesion, fundus-referenced vision testing demonstrated visual function within the lesion consistent with cone function. The PRL was within the lesion of apparent cone loss at the fovea. AOSLO visual acuity tests were abnormal, but measurable: for trials in which the stimulus remained completely within the lesion, the subject got 48% correct, compared to 78% correct when the stimulus was outside the lesion. TSLO microperimetry revealed reduced, but detectible, sensitivity thresholds within the lesion. CONCLUSIONS AND IMPORTANCE:Fundus-referenced visual testing proved useful to identify functional cones despite apparent photoreceptor loss identified using AOSLO and SD-OCT. While AOSLO and SD-OCT appear to be sensitive for the detection of abnormal or absent photoreceptors, changes in photoreceptors that are identified with these imaging tools do not correlate completely with visual function in every patient. Fundus-referenced vision testing is a useful tool to indicate the presence of cones that may be amenable to recovery or response to experimental therapies despite not being visible on confocal AOSLO or SD-OCT images
Structure and energetics of the Si-SiO_2 interface
Silicon has long been synonymous with semiconductor technology. This unique
role is due largely to the remarkable properties of the Si-SiO_2 interface,
especially the (001)-oriented interface used in most devices. Although Si is
crystalline and the oxide is amorphous, the interface is essentially perfect,
with an extremely low density of dangling bonds or other electrically active
defects. With the continual decrease of device size, the nanoscale structure of
the silicon/oxide interface becomes more and more important. Yet despite its
essential role, the atomic structure of this interface is still unclear. Using
a novel Monte Carlo approach, we identify low-energy structures for the
interface. The optimal structure found consists of Si-O-Si "bridges" ordered in
a stripe pattern, with very low energy. This structure explains several
puzzling experimental observations.Comment: LaTex file with 4 figures in GIF forma
A Completely Covariant Approach to Transformation Optics
We show that the Plebanski based approach to transformation optics overlooks
some subtleties in the electrodynamics of moving dielectrics that restricts its
applicability to a certain class of transformations. An alternative, completely
covariant, approach is developed that is more generally applicable and provides
a clearer picture of transformation optics.Comment: 10 pages. This version: Additional references added, corrected a
small error in Eq. (28) (Eq. (29) in present version), some revision of the
text, appendix content moved to the main body of the text, figure removed.
Corresponds more closely to published version. Prepared for a special issue
on transformation optics published by Journal of Optic
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