20,275 research outputs found
Study of crack-initiation phenomena associated with stress corrosion of aluminum alloys Annual report, 6 Jun. 1967 - 6 Jun. 1968
Electron microscopic, fractographic, and microprobe observations of crack initiation and propagation phenomena associated with stress corrosion of aluminum alloy
The Outer Edges of Dwarf Irregular Galaxies: Stars and Gas
We have in recent years come to view dwarf galaxy evolution in the broader
context of the cosmic evolution of large-scale structure. Dwarf galaxies, as
the putative building blocks of hierarchical galaxy formation, and also as the
most numerous galaxies in the Universe, play a central role in cosmic
evolution. In particular, the interplay of galactic and intergalactic material
around dwarf irregulars must be more extensive than in more massive disk
galaxies because of their lower gravitational potential and lower interstellar
pressures. The outer regions of dwarf irregular galaxies therefore yield vital
clues to the dominant processes in this interaction zone.
The Workshop addressed a number of questions related to the role of the outer
regions in the evolution of dwarf galaxies and broader consequences. On-line
Workshop Proceedings are at http://www.lowell.edu/Workshops/Lowell02/Comment: Summary of the 2002 Lowell Observatory Workshop, to appear in PASP
Conference Highlights; 6 pp, uses aaspp4.sty. On-line Proceedings at
http://www.lowell.edu/Workshops/Lowell02
Unconstrained video monitoring of breathing behavior and application to diagnosis of sleep apnea
This paper presents a new real-time automated infrared video monitoring technique for detection of breathing anomalies, and its application in the diagnosis of obstructive sleep apnea. We introduce a novel motion model to detect subtle, cyclical breathing signals from video, a new 3-D unsupervised self-adaptive breathing template to learn individuals' normal breathing patterns online, and a robust action classification method to recognize abnormal breathing activities and limb movements. This technique avoids imposing positional constraints on the patient, allowing patients to sleep on their back or side, with or without facing the camera, fully or partially occluded by the bed clothes. Moreover, shallow and abdominal breathing patterns do not adversely affect the performance of the method, and it is insensitive to environmental settings such as infrared lighting levels and camera view angles. The experimental results show that the technique achieves high accuracy (94% for the clinical data) in recognizing apnea episodes and body movements and is robust to various occlusion levels, body poses, body movements (i.e., minor head movement, limb movement, body rotation, and slight torso movement), and breathing behavior (e.g., shallow versus heavy breathing, mouth breathing, chest breathing, and abdominal breathing). Ă© 2013 IEEE
Length control of microtubules by depolymerizing motor proteins
In many intracellular processes, the length distribution of microtubules is
controlled by depolymerizing motor proteins. Experiments have shown that,
following non-specific binding to the surface of a microtubule, depolymerizers
are transported to the microtubule tip(s) by diffusion or directed walk and,
then, depolymerize the microtubule from the tip(s) after accumulating there. We
develop a quantitative model to study the depolymerizing action of such a
generic motor protein, and its possible effects on the length distribution of
microtubules. We show that, when the motor protein concentration in solution
exceeds a critical value, a steady state is reached where the length
distribution is, in general, non-monotonic with a single peak. However, for
highly processive motors and large motor densities, this distribution
effectively becomes an exponential decay. Our findings suggest that such motor
proteins may be selectively used by the cell to ensure precise control of MT
lengths. The model is also used to analyze experimental observations of
motor-induced depolymerization.Comment: Added section with figures and significantly expanded text, current
version to appear in Europhys. Let
Stabilization of colloidal suspensions by means of highly-charged nanoparticles
We employ a novel Monte Carlo simulation scheme to elucidate the
stabilization of neutral colloidal microspheres by means of highly-charged
nanoparticles [V. Tohver et al., Proc. Natl. Acad. Sci. U.S.A. 98, 8950
(2001)]. In accordance with the experimental observations, we find that small
nanoparticle concentrations induce an effective repulsion that prevents
gelation caused by the intrinsic van der Waals attraction between colloids.
Higher nanoparticle concentrations induce an attractive potential which is,
however, qualitatively different from the regular depletion attraction. We also
show how colloid-nanoparticle size asymmetry and nanoparticle charge can be
used to manipulate the effective interactions.Comment: Accepted for publication in Physical Review Letters. See also S.
Karanikas and A.A. Louis, cond-mat/0411279. Updated to synchronize with
published versio
The Gravitational Hamiltonian in the Presence of Non-Orthogonal Boundaries
This paper generalizes earlier work on Hamiltonian boundary terms by omitting
the requirement that the spacelike hypersurfaces intersect the
timelike boundary orthogonally. The expressions for the action and
Hamiltonian are calculated and the required subtraction of a background
contribution is discussed. The new features of a Hamiltonian formulation with
non-orthogonal boundaries are then illustrated in two examples.Comment: 23 pages, 1 figure, LaTeX. The action is altered to include a corner
term which results in a different value for the non-orthogonal term. An
additional appendix with Euclidean results is included. To appear in Class.
Quant. Gra
Iridovirus infection of cell cultures from the Diaprepes root weevil, Diaprepes abbreviatus
We here report the development and viral infection of a Diaprepes root weevil cell culture. Embryonic tissues of the root weevil were used to establish cell cultures for use in screening viral pathogens as potential biological control agents. Tissues were seeded into a prepared solution of insect medium and kept at a temperature of 24°C. The cell culture had primarily fibroblast-like morphology with some epithelial monolayers. Root weevil cells were successfully infected in vitro Abbreviation: / IIV-6: Invertebrate Iridescent Virus
Effects of Elevated H\u3csup\u3e+\u3c/sup\u3e And P\u3csub\u3ei\u3c/sub\u3e on The Contractile Mechanics of Skeletal Muscle Fibres From Young and Old Men: Implications for Muscle Fatigue in Humans
The present study aimed to identify the mechanisms responsible for the loss in muscle power and increased fatigability with ageing by integrating measures of wholeâmuscle function with single fibre contractile mechanics. After adjusting for the 22% smaller muscle mass in old (73â89 years, n = 6) compared to young men (20â29 years, n = 6), isometric torque and power output of the knee extensors were, respectively, 38% and 53% lower with age. Fatigability was âŒ2.7âfold greater with age and strongly associated with reductions in the electricallyâevoked contractile properties. To test whether crossâbridge mechanisms could explain ageârelated decrements in knee extensor function, we exposed myofibres (n = 254) from the vastus lateralis to conditions mimicking quiescent muscle and fatiguing levels of acidosis (H+) (pH 6.2) and inorganic phosphate (Pi) (30 mm). The fatigueâmimicking condition caused marked reductions in force, shortening velocity and power and inhibited the lowâ to highâforce state of the crossâbridge cycle, confirming findings from nonâhuman studies that these ions act synergistically to impair crossâbridge function. Other than severe ageârelated atrophy of fast fibres (â55%), contractile function and the depressive effects of the fatigueâmimicking condition did not differ in fibres from young and old men. The selective loss of fast myosin heavy chain II muscle was strongly associated with the ageârelated decrease in isometric torque (r = 0.785) and power (r = 0.861). These data suggest that the ageârelated loss in muscle strength and power are primarily determined by the atrophy of fast fibres, but the ageârelated increased fatigability cannot be explained by an increased sensitivity of the crossâbridge to H+ and Pi
The Action of Instantons with Nut Charge
We examine the effect of a non-trivial nut charge on the action of
non-compact four-dimensional instantons with a U(1) isometry. If the instanton
action is calculated by dimensionally reducing along the isometry, then the nut
charge is found to make an explicit non-zero contribution. For metrics
satisfying AF, ALF or ALE boundary conditions, the action can be expressed
entirely in terms of quantities (including the nut charge) defined on the fixed
point set of the isometry. A source (or sink) of nut charge also implies the
presence of a Misner string coordinate singularity, which will have an
important effect on the Hamiltonian of the instanton.Comment: 25 page
- âŠ