529 research outputs found
Holonomic constraints : an analytical result
Systems subjected to holonomic constraints follow quite complicated dynamics
that could not be described easily with Hamiltonian or Lagrangian dynamics. The
influence of holonomic constraints in equations of motions is taken into
account by using Lagrange multipliers. Finding the value of the Lagrange
multipliers allows to compute the forces induced by the constraints and
therefore, to integrate the equations of motions of the system. Computing
analytically the Lagrange multipliers for a constrained system may be a
difficult task that is depending on the complexity of systems. For complex
systems, it is most of the time impossible to achieve. In computer simulations,
some algorithms using iterative procedures estimate numerically Lagrange
multipliers or constraint forces by correcting the unconstrained trajectory. In
this work, we provide an analytical computation of the Lagrange multipliers for
a set of linear holonomic constraints with an arbitrary number of bonds of
constant length. In the appendix of the paper, one would find explicit formulas
for Lagrange multipliers for systems having 1, 2, 3, 4 and 5 bonds of constant
length, linearly connected.Comment: 13 pages, no figures. To appear in J. Phys. A : Math. The
Atrial natriuretic factor during atrial fibrillation and supraventricular tachycardia
Plasma immunoreactive atrial natriuretic factor was measured in 10 patients with chronic atrial fibrillation before and after cardioversion to sinus rhythm, and in 14 patients during electrophysiologic evaluation of paroxysmal supraventricular tachycardia. The mean plasma concentration of atrial natriuretic factor in atrial fibrillation was 138 ± 48 pg/ml and decreased to 116 ± 45 pg/ml 1 hour after cardioversion to sinus rhythm (p < 0.005). The mean plasma concentration of atrial natriuretic factor increased from 117 ± 53 pg/ml in sinus rhythm to 251 ± 137 pg/ml during laboratory-induced supraventricular tachycardia (p < 0.005). Right atrial pressures were recorded in 12 patients; the baseline atrial pressure was 4.3 ± 1.9 mm Hg and increased to 7.4 ± 3.6 mm Hg during supraventricular tachycardia (p < 0.005). A modest but significant linear relation was noted between the changes in plasma atrial natriuretic factor and right atrial pressure measurements during induced supraventricular tachycardia (r = 0.60, p < 0.05).In conclusion, changes in atrial rhythm and pressure may be an important factor modulating the release of atrial natriuretic factor in the circulation and raised levels of this hormone may be a contributing factor for the polyuria and the hypotension associated with paroxysmal supraventricular tachyarrhythmias
Uniqueness of the compactly supported weak solutions of the relativistic Vlasov-Darwin system
We use optimal transportation techniques to show uniqueness of the compactly
supported weak solutions of the relativistic Vlasov-Darwin system. Our proof
extends the method used by Loeper in J. Math. Pures Appl. 86, 68-79 (2006) to
obtain uniqueness results for the Vlasov-Poisson system.Comment: AMS-LaTeX, 21 page
Helical Stacking in DNA 3-Way Junctions Containing 2 Unpaired Pyrimidines - Proton NMR-Studies
The proton NMR spectra of DNA three-way junction complexes (TWJ) having unpaired pyrimidines, 5\u27-TT- and 5\u27-TC- on one strand at the junction site were assigned from 2D NOESY spectra acquired in H2O and D2O solvents and homonuclear 3D NOESY-TOCSY and 3D NOESY-NOESY in D2O solvent. TWJ are the simplest branched structures found in biologically active nucleic acids. Unpaired nucleotides are common features of such structures and have been shown to stabilize junction formation. The NMR data confirm that the component oligonucleotides assemble to form conformationally homogeneous TWJ complexes having three double-helical, B-form arms. Two of the helical arms stack upon each other. The unpaired pyrimidine bases lie in the minor groove of one of the helices and are partly exposed to solvent. The coaxial stacking arrangement deduced is different from that determined by Rosen and Patel (Rosen, M. A., and D. J. Patel. 1993. Biochemistry. 32:6576-6587) for a DNA three-way junction having two unpaired cytosines, but identical to that suggested by Welch et al. (Welch, J. B., D. R. Duckett, D. M. J. Lilley. 1993. Nucleic Acids Res. 21:4548-4555) on the basis of gel electrophoretic studies of DNA three-way junctions containing unpaired adenosines and thymidines
Structure and thermodynamics of a ferrofluid bilayer
We present extensive Monte Carlo simulations for the thermodynamic and
structural properties of a planar bilayer of dipolar hard spheres for a wide
range of densities, dipole moments and layer separations. Expressions for the
stress and pressure tensors of the bilayer system are derived. For all
thermodynamic states considered the interlayer energy is shown to be attractive
and much smaller than the intralayer contribution to the energy. It vanishes at
layer separations of the order of two hard sphere diameters. The normal
pressure is negative and decays as a function of layer separation as
. Intralayer and interlayer pair distribution functions and angular
correlation functions are presented. Despite the weak interlayer energy strong
positional and orientational correlations exist between particles in the two
layers.Comment: 45 pages, 4 Tables, 9 Figure
Climate and Soil Characteristics Determine Where No-Till Management Can Store Carbon in Soils and Mitigate Greenhouse Gas Emissions
Article number: 11665 (2019)201
Resting Heart Rate and Metabolic Syndrome in Patients With Diabetes and Coronary Artery Disease in Bypass Angioplasty Revascularization Investigation 2 Diabetes (BARI 2D) Trial
The relation between the metabolic syndrome (MetS) and resting heart rate (rHR) in patients with diabetes and coronary artery disease is unknown. The authors examined the cross-sectional association at baseline between components of the MetS and rHR and between rHR and left ventricular ejection fraction in the population from the Bypass Angioplasty Revascularization Investigation 2 Diabetes (BARI 2D) randomized clinical trial. The mean rHR in the MetS group was significantly higher than in those without (68.4±12.3 vs 65.6±11.8 beats per min, P=.0017). The rHR was higher (P<.001 for trend) with increasing number of components for MetS. Linear regression analyses demonstrated that as compared to individuals without MetS, rHR was significantly higher in participants with MetS (regression coefficient, 2.9; P=.0015). In patients with type 2 diabetes and coronary artery disease, the presence of higher rHR is associated with increasing number of criteria of MetS and the presence of ventricular dysfunction.Prev Cardiol. 2010;13:112–116. © 2009 Wiley Periodicals, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79383/1/j.1751-7141.2010.00067.x.pd
Power laws in microrheology experiments on living cells: comparative analysis and modelling
We compare and synthesize the results of two microrheological experiments on
the cytoskeleton of single cells. In the first one, the creep function J(t) of
a cell stretched between two glass plates is measured after applying a constant
force step. In the second one, a micrometric bead specifically bound to
transmembrane receptors is driven by an oscillating optical trap, and the
viscoelastic coefficient is retrieved. Both and
exhibit power law behavior: and , with the same exponent
. This power law behavior is very robust ; is
distributed over a narrow range, and shows almost no dependance on the cell
type, on the nature of the protein complex which transmits the mechanical
stress, nor on the typical length scale of the experiment. On the contrary, the
prefactors and appear very sensitive to these parameters. Whereas
the exponents are normally distributed over the cell population, the
prefactors and follow a log-normal repartition. These results are
compared with other data published in the litterature. We propose a global
interpretation, based on a semi-phenomenological model, which involves a broad
distribution of relaxation times in the system. The model predicts the power
law behavior and the statistical repartition of the mechanical parameters, as
experimentally observed for the cells. Moreover, it leads to an estimate of the
largest response time in the cytoskeletal network: s.Comment: 47 pages, 14 figures // v2: PDF file is now Acrobat Reader 4 (and up)
compatible // v3: Minor typos corrected - The presentation of the model have
been substantially rewritten (p. 17-18), in order to give more details -
Enhanced description of protocols // v4: Minor corrections in the text : the
immersion angles are estimated and not measured // v5: Minor typos corrected.
Two references were clarifie
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