23,152 research outputs found
Effect of crack curvature on stress intensity factors for ASTM standard compact tension specimens
The stress intensity factors (SIF) are calculated using the method of lines for the compact tension specimen in tensile and shear loading for curved crack fronts. For the purely elastic case, it was found that as the crack front curvature increases, the SIF value at the center of the specimen decreases while increasing at the surface. For the higher values of crack front curvatures, the maximum value of the SIF occurs at an interior point located adjacent to the surface. A thickness average SIF was computed for parabolically applied shear loading. These results were used to assess the requirements of ASTM standards E399-71 and E399-81 on the shape of crack fronts. The SIF is assumed to reflect the average stress environment near the crack edge
Screening-Limited Response of NanoBiosensors
Despite tremendous potential of highly sensitive electronic detection of
bio-molecules by nanoscale biosensors for genomics and proteomic applications,
many aspects of experimentally observed sensor response (S) are unexplained
within consistent theoretical frameworks of kinetic response or electrical
screening. In this paper, we combine analytic solutions of Poisson-Boltzmann
and reaction-diffusion equations to show that the electrical response of
nanobiosensor varies logarithmically with the concentration of target
molecules, time, the salt concentration, and inversely with the fractal
dimension of sensor surface. Our analysis provides a coherent theoretical
interpretation of wide variety of puzzling experimental data that have so far
defied intuitive explanation.Comment: 7 pages, 2 figure
Fundamentals of PV Efficiency Interpreted by a Two-Level Model
Elementary physics of photovoltaic energy conversion in a two-level atomic PV
is considered. We explain the conditions for which the Carnot efficiency is
reached and how it can be exceeded! The loss mechanisms - thermalization, angle
entropy, and below-bandgap transmission - explain the gap between Carnot
efficiency and the Shockley-Queisser limit. Wide varieties of techniques
developed to reduce these losses (e.g., solar concentrators, solar-thermal,
tandem cells, etc.) are reinterpreted by using a two level model. Remarkably,
the simple model appears to capture the essence of PV operation and reproduce
the key results and important insights that are known to the experts through
complex derivations.Comment: 7 pages, 6 figure
SET based experiments for HTSC materials: II
The cuprates seem to exhibit statistics, dimensionality and phase transitions
in novel ways. The nature of excitations
[i.e. quasiparticle or collective], spin-charge separation, stripes [static
and dynamics], inhomogeneities, psuedogap, effect of impurity dopings [e.g. Zn,
Ni] and any other phenomenon in these materials must be consistently
understood. In this note we further discuss our original suggestion of using
Single Electron Tunneling Transistor
[SET] based experiments to understand the role of charge dynamics in these
systems. Assuming that SET operates as an efficient charge detection system we
can expect to understand the underlying physics of charge transport and charge
fluctuations in these materials for a range of doping. Experiments such as
these can be classed in a general sense as mesoscopic and nano characterization
of cuprates and related materials. In principle such experiments can show if
electron is fractionalized in cuprates as indicated by ARPES data. In contrast
to flux trapping experiments SET based experiments are more direct in providing
evidence about spin-charge separation. In addition a detailed picture of nano
charge dynamics in cuprates may be obtained.Comment: 10 pages revtex plus four figures; ICMAT 2001 Conference Symposium P:
P10-0
Inflation is the generic feature of phantom field-not the big-rip
A class of solutions for phantom field corresponding to a generalized
k-essence lagrangian has been presented, employing a simple method which
provides the scope to explore many such. All the solutions having dynamical
state parameter are found to touch the magic line w = -1, asymptotically. The
solutions with constant equation of state can represent phantom, quitessence or
an ordinary scalar field cosmologies depending on the choice of a couple of
parameters of the theory. For w approximately equal to -1, quintessence and
phantom models are indistinguishable through the Hubble parameter. Finally,
inflation rather than big-rip has been found to be the generic feature of
phantom cosmology.Comment: 8 pages, 3 figure
Seismic vulnerability assessment and evaluation of high rise buildings in Islamabad
Primarily the aim of this research is to carry out seismic evaluation study of buildings structures in Islamabad in order to propose basic guidelines and suggestions for Pakistan Code. Knowing the important nature of the subject, the earthquake based organizations are serious to compile a document for seismic threatened countries and areas. It is aimed that the document will work as a guideline source for the seismic evaluation, calculation and assessment of strength, behavior and expected performance and also the safety of already existing buildings. This study is based on review of already available documents on seismic vulnerability and evaluation of present buildings at different sites is carried out in order to know the key components of this very procedure so that it can be used in Pakistan and also in other developing countries as well. This would not only be robust, safe and reliable, but also can be convenient to use within the domain of available resources. ASCE 31-03 guidelines among the available documents are considered to be a suitable and the most reliable for to be in Pakistan
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