8,186 research outputs found
Predictive haemodynamics in a one-dimensional human carotid artery bifurcation. Part II: application to graft design
A Bayesian surrogate modelling technique is proposed that may be able to predict an optimal bypass graft configuration for patients suffering with stenosis in the internal carotid artery (ICA). At the outset, this statistical technique is considered as a means for identifying key geometric parameters influencing haemodynamics in the human carotid bifurcation. This methodology uses a design of experiments (DoE) technique to generate candidate geometries for flow analysis. A pulsatile one dimensional Navier-Stokes solver incorporating fluid-wall interactions for a Newtonian fluid which predicts pressure and flow in the carotid bifurcation (comprising a stenosed segment in the internal carotid artery) is used for the numerical simulations. Two metrics, pressure variation factor (PVF) and maximum pressure (pm) are employed to directly compare the global and local effects, respectively, of variations in the geometry. The values of PVF and pm are then used to construct two Bayesian surrogate models. These models are statistically analysed to visualise how each geometric parameter influences PVF and pm. Percentage of stenosis is found to influence these pressure based metrics more than any other geometric parameter. Later, we identify bypass grafts with optimal geometric and material properties which have low values of PVF on five test cases with 70%, 75%, 80%, 85% and 90% stenosis in the ICA, respectively
Supersymmetry and Mass Gap in 2+1 Dimensions: A Gauge Invariant Hamiltonian Analysis
A Hamiltonian formulation of Yang-Mills-Chern-Simons theories with supersymmetry in terms of gauge-invariant variables is presented,
generalizing earlier work on nonsupersymmetric gauge theories. Special
attention is paid to the volume measure of integration (over the gauge orbit
space of the fields) which occurs in the inner product for the wave functions
and arguments relating it to the renormalization of the Chern-Simons level
number and to mass-gaps in the spectrum of the Hamiltonians are presented. The
expression for the integration measure is consistent with the absence of mass
gap for theories with extended supersymmetry (in the absence of additional
matter hypermultiplets and/or Chern-Simons couplings), while for the minimally
supersymmetric case, there is a mass-gap, the scale of which is set by a
renormalized level number, in agreement with indications from existing
literature. The realization of the supersymmetry algebra and the Hamiltonian in
terms of the gauge invariant variables is also presented.Comment: 31 pages, References added, typos correcte
Massive Spin-2 fields of Geometric Origin in Curved Spacetimes
We study the consistency of a model which includes torsion as well as the
metric as dynamical fields and has massive spin-2 particle in its spectrum. The
massive spin-2 mode resides in the torsion, rather than in the metric. It is
known that this model is tachyon- and ghost-free in Minkowski background. We
show that this property remains valid and no other pathologies emerge in de
Sitter and anti-de Sitter backgrounds, with some of our results extending to
arbirary Einstein space backgrounds. This suggests that the model is
consistent, at least at the classical level, unlike, e.g., the Fierz--Pauli
theory.Comment: 17 pages, Clarifying remarks added in section 5, minor changes,
version to be published in the Phys. Rev.
Unimpeded permeation of water through helium-leak-tight graphene-based membranes
Permeation through nanometer pores is important in the design of materials
for filtration and separation techniques and because of unusual fundamental
behavior arising at the molecular scale. We found that submicron-thick
membranes made from graphene oxide can be completely impermeable to liquids,
vapors and gases, including helium, but allow unimpeded permeation of water
(H2O permeates through the membranes at least 10^10 times faster than He). We
attribute these seemingly incompatible observations to a low-friction flow of a
monolayer of water through two dimensional capillaries formed by closely spaced
graphene sheets. Diffusion of other molecules is blocked by reversible
narrowing of the capillaries in low humidity and/or by their clogging with
water
Effect of Environment on Underwater Acoustic Communication Data Rates
Underwater acoustic communication has several applications for civilians and defence. It is a challenging engineering problem, where large variability of ambient noise and highly variable channel characteristics limits the performance of communication system. In addition horizontal transmissions in shallow water is considered very challenging due to time varying delay spread and significant Doppler spread. An experiment was conducted to study the diurnal variability of underwater acoustic communication channel properties of the south west coast of India. Time spread and bit error rate for different ranges and depths are compared in this paper. Influence of prevailing sound speed profile on acoustic communication link is also discussed
Low Frequency Broad Band Acoustic Propagation in Andaman Sea
During November 2017, an active source seismic survey was performed in Andaman sea to study the acoustic propagation characteristics. High power low frequency acoustic signals generated by 20-air gun array onboard ORV Samudra Ratnagar were recorded from INS Sagardhwani at four different depths within 8 km ranges in shallow and deep waters. Low frequency sound levels were estimated using root mean square and power spectral values. Amplitude levels were analysed with respect to arrival time variation with frequency and is presented
Numerical Model Studies on Coastal Processes in a Critically Eroding Sector of South West Coast of India
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
Non-scalpel Vasectomy Camps: Our Experience and Recent Trends in 2021
Background: Camp approach has been advocated as an effective means of motivating the target population to adopt vasectomy as a method of permanent sterilization. There is a high degree of acceptance of Non-scalpel Vasectomy (NSV) among physicians and laypersons. With this knowledge, we organized camps and found good results which we share in this article.Methods: Four NSV camps were organized in four different villages across India on a vehicle-mounted mobile operation theater. The meticulous and detailed planning, dissemination of information, careful execution, and post-procedure follow-up is enumerated.Results: A total of 76 individuals underwent the operation in these camps. The mean age of the participants was 35 ± 5.2 years (range, 27–44 years). The complication rate was negligible and there was no failure of vasectomy. There was a high level of satisfaction among those who underwent this procedure as seen by the increased number wanting to undergo the procedure from places where camps were located. Conclusion: NSV as a procedure is perceived as being simple and pain-free. Re-enforcing this fact and removing doubts, and conducting operations at the camp in an environment the client is familiar with achieved rewarding results.
Keywords: non-scalpel vasectomy, camp, mobile operation theater, male sterilization, va
Color Skyrmions in the Quark-Gluon Plasma
We consider the general formulation of nonabelian fluid dynamics based on
symmetry considerations. We point out that, quite generally, this admits
solitonic excitations which are the color analog of skyrmions. Some general
properties of the solitons are discussed.Comment: LaTeX, 13 pages, references adde
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