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