1,838 research outputs found
Accurate Evaluation of Charge Asymmetry in Aqueous Solvation
Charge hydration asymmetry (CHA)--a characteristic dependence of hydration
free energy on the sign of the solute charge--quantifies the asymmetric
response of water to electric field at microscopic level. Accurate estimates of
CHA are critical for understanding hydration effects ubiquitous in chemistry
and biology. However, measuring hydration energies of charged species is
fraught with significant difficulties, which lead to unacceptably large (up to
300%) variation in the available estimates of the CHA effect. We circumvent
these difficulties by developing a framework which allows us to extract and
accurately estimate the intrinsic propensity of water to exhibit CHA from
accurate experimental hydration free energies of neutral polar molecules.
Specifically, from a set of 504 small molecules we identify two pairs that are
analogous, with respect to CHA, to the K+/F- pair--a classical probe for the
effect. We use these "CHA-conjugate" molecule pairs to quantify the intrinsic
charge-asymmetric response of water to the microscopic charge perturbations:
the asymmetry of the response is strong, ~50% of the average hydration free
energy of these molecules. The ability of widely used classical water models to
predict hydration energies of small molecules correlates with their ability to
predict CHA
Ground Versus Soil: A New Paradigm in Geotechnical Engineering Education
me of the practitioners of geotechnical
engineering tend to confuse Ground with
Soil. It is not just semantics but the terms have d
eeper technical and philosophical implications. Soi
l
is a material which can be handled, felt, seen, sme
lt, tasted, and tested in small to medium size
samples while ‘Ground’ is an entity that exists in-
situ. Just as the adage, ‘The total is more than th
e
sum of the individual parts’, predicting the behavi
or of ground from the so-called properties
measured on samples collected from the field is muc
h more complex and involves judgment.
Ground is an intricate natural entity very similar
to ‘Humans’ and exhibits behavioral responses
rather than merely possess properties like other en
gineering materials. Humans have organs and
traits such as being jovial, sad, friendly, angry,
misanthropic, etc. but do not have properties. Thei
r
behavioral responses depend on genetics, environmen
t in which they grow, personality they
develop and to impetus they experience. Similarly,
the genetics of ground is defined by its
formation (alluvial, marine, residual, colluvial, a
eolin, etc.) depending upon how physiogamy forms
the deposit. Ground, one tends to believe, is a sol
id mass on which structures are built, becomes
suddenly a fluid under specific aggravating circums
tances such as consisting loose saturated sand
with small amount of fines but subjected to seismic
activity of medium to high intensity. On the
other hand, a river in flood can erode the ground b
y removing particles by its high velocity leading
to scour. Slopes on which civilizations thrive, bec
ome unstable and sometimes even catastrophic
under heavy rainfall, coupled with human activities
of deforestation, cutting/steepening of slopes,
saturating it by ignorance or callousness, etc. The
paper presents a new paradigm that emphasizes
the need to visualize Ground, not just as a materia
l but rather an entity, and view Geotechnical
Engineering comprehensively, beyond a mechanistic s
tandpoint
Large Miscibility Gap in the Ba(Mn_xFe_{1-x})2As2 System
The compounds BaMn2As2 and BaFe2As2 both crystallize in the
body-centered-tetragonal ThCr2Si2-type (122-type) structure at room temperature
but exhibit quite different unit cell volumes and very different magnetic and
electronic transport properties. Evidently reflecting these disparities, we
have discovered a large miscibility gap in the system Ba(Mn_xFe_{1-x})2As2.
Rietveld refinements of powder x-ray diffraction (XRD) measurements on samples
slow-cooled from 1000 C to room temperature (RT) reveal a two-phase mixture of
BaMn2As2 and Ba(Mn_{0.12}Fe_{0.88})2As2 phases together with impurity phases
for x = 0.2, 0.4, 0.5, 0.6 and 0.8. We infer that there exists a miscibility
gap in this system at 300 K with composition limits 0.12 < x < 1. For samples
quenched from 1000 C to 77 K, the refinements of RT XRD data indicate that the
miscibility gap at RT narrows at 1000 C to 0.2 < x < 0.8. Samples with x=0.4,
0.5 and 0.6 quenched from 1100-1400 C to 77 K contain a single 122-type phase
together with significant amounts of Fe_{1-x}Mn_xAs and FeAs2 impurity phases.
These results indicate that the system is not a pseudo-binary system over the
whole composition range and that the 122-type phase has a significant
homogeneity range at these temperatures. Magnetic susceptibility, electrical
resistivity and heat capacity measurements versus temperature of the
single-phase quenched polycrystalline samples with x = 0.2 and 0.8 and for
lightly doped BaMn2As2 crystals are reported.Comment: 14 pages, 16 figures, 3 tables; published versio
Modelling Ground-Foundation Interactions
Geotechnical practice deals with designing foundations and earth structures. Structure
–
Foundation
–\ud
Grou
nd
interaction is a unique field or topic that concerns both structural and geotechnical engineers. Most
geotechnical problems are very sensitive to foundation geometry (length, diameter, spacing), flexural
stiffness etc. Even basic parameters such as bearing capacity of shallow foundations, ultimate axial and
lateral load capacities of deep/pile foundations, are influenced by the foundation characteristics. More
importantly, the serviceability criterion can be satisfied only by proper and rational estimates of structure
–
found
ation
–
ground interactions. The paper summarizes modelling approaches for foundation
–
ground
interactions, a leaning instability approach for tall structures, and analysis of geosynthetic-reinforced
foundation beds
Steady state, relaxation and first-passage properties of a run-and-tumble particle in one-dimension
We investigate the motion of a run-and-tumble particle (RTP) in one
dimension. We find the exact probability distribution of the particle with and
without diffusion on the infinite line, as well as in a finite interval. In the
infinite domain, this probability distribution approaches a Gaussian form in
the long-time limit, as in the case of a regular Brownian particle. At
intermediate times, this distribution exhibits unexpected multi-modal forms. In
a finite domain, the probability distribution reaches a steady state form with
peaks at the boundaries, in contrast to a Brownian particle. We also study the
relaxation to the steady state analytically. Finally we compute the survival
probability of the RTP in a semi-infinite domain. In the finite interval, we
compute the exit probability and the associated exit times. We provide
numerical verifications of our analytical results
An overview of drugs approved in India from 1999 through 2015
Background: The drug approval regulations in India have changed since 2005 with new regulations for the conduct of clinical trials from 2013 onward. The present study was planned to see the number of drugs approved by Drugs Controller General of India (DCGI) and their trend over the last 16 years in view of new regulatory guidelines.Methods: Data obtained from website of the regulatory authority, i.e., Central Drugs Standard Control Organizationregarding DGCI approval of drugs in India from 1999 until May 2015 was noted for analysis.Results: We identified 1716 drug approvals by the DCGI from 1999 to 2015, with a mean of 100.94±83.80 (standard deviation) approvals per year (median approvals per year: 57; range: 3-270). There is a rising trend for approval of drugs as a single agent, as well as in combination from 2004 showing a peak in 2008 with a decline from 2010 onward. Thus, very few drugs have been approved in last 3 years.Conclusions: Thus, the present study highlights the changing scenario of drug approval, with few drugs being approved for clinical practice in the last 3 years
Isospectrality in Chaotic Billiards
We consider a modification of isospectral cavities whereby the classical
dynamics changes from pseudointegrable to chaotic. We construct an example
where we can prove that isospectrality is retained. We then demonstrate this
explicitly in microwave resonators.Comment: 5 pages, 7 figure
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