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Properties of dyons in N=4 theories at small charges
No full textWe study three properties of 1/4 BPS dyons at small charges in string compactifications which preserve N = 4 supersymmetry. We evaluate the non-trivial constant present in the one loop statistical entropy for N = 4 compactifications of type IIB theory on K3 x T-2 orbifolded by an order Z(N) freely acting orbifold g including all CHL compactifications. This constant is trivial for the un-orbifolded model but we show that it contributes crucially to the entropy of low charge dyons in all the orbifold models. We then show that the meromorphic Jacobi form which captures the degeneracy of 1/4 BPS states for the first two non-trivial magnetic charges can be decomposed into an Appell-Lerch sum and a mock Jacobi form transforming under (0)(N). This generalizes the earlier observation of Dabholkar-Murthy-Zagier to the orbifold models. Finally we study the sign of the Fourier coefficients of the inverse Siegel modular form which counts the index of 1/4 BPS dyons in N = 4 models obtained by freely acting Z(2) and Z(3) orbifolds of type II theory compactified on T-6. We show that sign of the index for sufficiently low charges and ensuring that it counts single centered black holes, violates the positivity conjecture of Sen which indicates that these states posses non-trivial hair
Effect of fusion and friction stir welding techniques on the microstructure, crystallographic texture and mechanical properties of mild steel
No full textThe present investigation aims at studying the effect of different welding techniques on the microstructure and mechanical properties of the welds. Weld zone (WZ) in the metal inert gas (MIG) welding, contains higher martensite fraction compared to arc and tungsten inert gas (TIG) welding. The micro-hardness of the WZ was found to be maximum after MIG welding (220 +/- 14 HV) in comparison to arc welding (190 +/- 12 HV), TIG welding (142 +/- 10 HV) and friction stir welding (FSW) (202 +/- 10 HV) as well as the base metal (BM) (108 +/- 14 HV). The joints fabricated via MIG welding exhibited higher tensile strength (371 +/- 10 MPa) as compared to other welding techniques (arc and FSW). The ductility of the parent metal was 42 +/- 2% whereas the ductility of the MIG and arc joints were lower (13 +/- 2% and 17 +/- 3% respectively) due to the presence of martensite during fusion welding. The FSW joint shows higher yield and tensile strengths (356 +/- 8 MPa) along with higher elongation (22 +/- 4%) compared to fusion-welded joints due to the presence of fine, equiaxed recrystallized grains in the WZ. Fracture occurs at the HAZ/base metal interface, where the hardness is lower compared to the WZ. Compressive and tensile residual stress is obtained in the WZ upon fusion and FSW, respectively. In this paper, analytical tools are used to calculate the orientation of prior austenite (gamma) in the MIG weld joint. The texture of high temperature gamma phase is simulated for the different welding techniques. The occurrence of the Kurdjumov-Sachs (K-S) orientation relationship (OR) is determined from the martensite grains in MIG weld. The texture investigation showed the occurrence of texture memory effect of ferrite in the HAZ after MIG welding
On the electronically nonadiabatic decomposition dynamics of furazan and triazole energetic molecules
No full textThe combined results of ab initio electronic-structure calculations, nonadiabatic molecular dynamics simulations using ab initio multiple spawning, and previous spectroscopic investigations of jet-cooled molecules provide strong evidence of a (pi, sigma*)-mediated decomposition mechanism for the furazan and triazole energetic molecules. The importance of dissociative excited states formed by electron promotion from a pi molecular orbital to a sigma* molecular orbital is explored for the furazan and triazole energetic molecules. Dissociative (pi, sigma*) states of furazan and triazole energetic molecules can be populated by nonadiabatic surface jump from the (pi, pi*) or the (n, pi*) state. Finally, conical intersections between (pi, sigma*) potential energy surfaces (PESs) and the ground PES influence the eventual fragmentation dynamics of the furazan and triazole energetic molecules. Due to structural similarity of the triazole molecule with the pyrrole molecule, a comparison of nonadiabatic dynamics of these two molecules is also presented. The N-N bond dissociation is found to be a barrierless pathway for the triazole molecule, whereas the N-H bond dissociation exhibits a barrierless pathway for the pyrrole molecule. The present work, thus, provides insights into the excited-state chemistry of furazan and triazole energetic functional groups. The same insight can also be relevant for other energetic molecules. Published under license by AIP Publishing
Termite mounds impact soil hydrostructural properties in southern Indian tropical forests
No full textMounds built by fungus-growing termites are often considered to be patches or fertile areas in tropical ecosystems because they contain more nutrients than the surrounding soil environments. However, the mechanism of how these habitats influence soil physical properties remains unknown. Therefore, this study aimed at comparing the soil hydrostructural properties of two common termite mounds in southern India, namely, cathedral and lenticular mounds. The shrinkage curves of the soil eroded from three cathedral mounds and of the soil sampled in the center or in the periphery of three lenticular mounds were measured and compared to those of their surrounding soil environment. This study revealed that the soil in the periphery of cathedral mounds was compact with a lower soil specific volume and macroporosity than the control soil. On the other hand, the accumulation of clay in lenticular mounds was associated with a lower soil specific volume at the end of the shrinkage period, higher microporosity, increased swelling capacity and higher water holding capacity than the control soil. These parameters reached intermediate values in the periphery of the lenticular mounds between those of the lenticular mound soil and the surrounding control soil. In conclusion, this study showed that cathedral and lenticular mounds impacted soil hydrostructural properties in two opposing directions. It also highlighted the link between the impact of termites on the clay and carbon contents of soil and their influence on soil porosity and water dynamics, and then the need for a better understanding of the influence of termites on the dynamic of carbon and clay in ecosystems
Getting older, getting smarter: ontogeny of foraging behaviour in the tropical social wasp Ropalidia marginata
No full textDesert ants and honey bees start foraging when they are a few days old, and subsequently increase their foraging effort and the amount of foraged food. This could be an optimal strategy for scavenger/gatherer animals inhabiting landscapes with fewer features. However, animals inhabiting cluttered landscapes, especially predatory animals, may require substantial familiarity with foraging landscapes to forage efficiently. They may acquire such spatial familiarity with increasing age/experience, and eventually reduce their foraging effort without compromising on foraging success/efficiency. To check whether this holds for the individually foraging predatory tropical paper-wasp Ropalidia marginata, we recorded the number and duration of all foraging trips, the identity of foraged materials, and the directions of outbound and inbound flights (with respect to the nest) of known-age wasps for three consecutive days from three naturally occurring colonies: thus, we measured behavioural profiles of wasps of various ages, and not from the same wasp throughout its lifespan. Wasps increased their foraging duration rapidly until about 4 weeks of age, during which they rarely brought food, although some wasps brought building material and water. Thereafter, their foraging duration started decreasing. Nevertheless, their foraging success/efficiency in bringing food kept on increasing. With age, wasps developed individual directional preferences for outbound and inbound flights, indicating the development of spatial memory for rewarding sites. Also, the angular difference between their outbound and subsequent inbound flights gradually increased, indicating older wasps may have followed tortuous foraging routes. High investment in early life to acquire familiarity with foraging landscapes and using that later to perform efficient foraging could be an optimal strategy for individually foraging animals inhabiting feature-rich landscapes
Recent spatial aggregation tendency of rainfall extremes over India
No full textSignificant increase in the frequency of occurrences of rainfall extremes has been reported over several parts of the world. These extreme events were defined at individual grids without considering their spatial extent. Here, using ground-based observations over India during boreal summer, we show that the average size of spatially collocated rainfall extremes has been significantly increasing since 1980. However, the frequency of occurrences of such collocated extreme events remains unchanged. Around 90% of the total number of large-sized events (area >= 70 x 10(3) km(2)) of our study period (1951 to 2015) have occurred after 1980. Some of the major floods in recent decades over India are attributed to these large events. These events have distinctive precursory planetary-scale conditions, unlike their smaller counterparts. As the underlying physical mechanisms of extremes rainfall events are size-dependent, their changing spatial extent needs to be considered to understand the observed trends correctly and obtain realistic future projections
Granulite-grade garnet pyroxenite from the Kolli-massif, southern India: Implications for Archean crustal evolution
No full textPyroxenite is a relatively rare but important rock type of mafic-ultramafic series, and provides a useful tool to understand deep crustal and crust mantle processes. Here we present petrology, phase equilibrium modelling and P-T estimates, zircon U-Pb geochronology and Hf isotopes on a recent find of garnet websterite from the Jambumalai hillock, Kolli-massif, southern India. The rock types in this location include metamorphosed orthopyroxenite, clinopyroxenite, garnet websterite and garnetite among which, garnet websterite is the most abundant variety. Petrological studies show that the peak metamorphic mineral assemblage of the garnet websterite is Grt + Cpx + Opx +/- Ilm. The garnet is Fe rich (X-Mg = 039-0.41) whereas the clinopyroxene composition varies from augite to sub-augite (X-Mg = 0.72-0.79). The orthopyroxene shows a compositional range between ferrosilite and hypersthene (X-Mg = 0.61-64). Clinopyroxene in some of the garnet websterite samples exhibits exsolution microstructure with blebs of orthopyroxene. The orthopyroxene is Ca poor and Fe rich and displays the features of `inverted pigeonite'. Phase-equilibria modelling in the NCFMASH system yielded a P-T estimate of c.22 Kbar and c.980 degrees C. Zircon U-Pb analysis using SIMS yielded a weighted mean age of 2526 +/- 38 Ma, which is regarded as the age of metamorphism. Zircon Lu-Hf isotope data shows initial epsilon Hf values between +2 and -7.7, indicating a dominantly reworked crustal source for the protolith. Our results suggest high pressure and high temperature metamorphism at the base of a thickened Archean continental crust
Understanding the Thermodynamics of the Binding of PAMAM Dendrimers to Graphene: A Combined Analytical and Simulation Study
No full textWe investigate the thermodynamics of the binding of a poly(amidoamine) dendrimer to an uncharged graphene sheet as a function of the pH level using umbrella sampling simulations and a mean-field theory for generations three and four. We find that the dendrimer strongly binds to the graphene sheet (0(100) kcal/mol) from our potential of mean force (PMF) calculations. In specific, we find that the dendrimer binds the most at neutral pH (similar to 7) and the least at low pH (similar to 4). We explain this nonmonotonic nature of the dendrimer's adsorption by studying the interactions contributing to the PMF, i.e., the dendrimer-graphene, dendrimer-water, and dendrimer-ion interactions. We also corroborate our PMF calculations with molecular mechanics generalized Born surface area analysis and free energies obtained from a mean-field theory of Flory-Huggins-Debye-Hiickel type Muthukumar, M., et al. J. Chem. Phys. 2010, 132, 084901], including electrostatic interactions. We find that the van der Waals interactions between the dendrimer and the graphene alone cannot capture the accurate trends in the binding free energies (BEs) as a function of pH. The solvent and the counterions present in the system are also found to have a major influence on these trends. We demonstrate that the dendrimer-graphene and dendrimer water interactions become favorable, whereas the dendrimer-ion interaction becomes unfavorable, as the dendrimer binds to graphene. These opposing effects lead to the observed nonmonotonicity in the BE trends. Our theoretical model also reproduces these trends in the subinteractions contributing to the PMF. To the best of our knowledge, this is a novel attempt where an equivalence between theory and simulations is made in the context of the dendrimer's adsorption
An Interplay Between Reaction-Diffusion and Cell-Matrix Adhesion Regulates Multiscale Invasion in Early Breast Carcinomatosis
No full textThe progression of cancer in the breast involves multiple reciprocal interactions between malignantly transformed epithelia, surrounding untransformed but affected stromal cells, and the extracellular matrix (ECM) that is remodeled during the process. A quantitative understanding of the relative contribution of such interactions to phenotypes associated with cancer cells can be arrived at through the construction of increasingly complex experimental and computational models. Herein, we introduce a multiscale three-dimensional (3D) organo- and pathotypic experimental assay that approximates, to an unprecedented extent, the histopathological complexity of a tumor disseminating into its surrounding stromal milieu via both bulk and solitary motility dynamics. End point and time-lapse microscopic observations of this assay allow us to study the earliest steps of cancer invasion as well as the dynamical interactions between the epithelial and stromal compartments. We then simulate our experimental observations using the modeling environment Compucell3D that is based on the Glazier-Graner-Hogeweg model. The computational model, which comprises adhesion between cancer cells and the matrices, cell proliferation and apoptosis, and matrix remodeling through reaction-diffusion-based morphogen dynamics, is first trained to phenocopy controls run with the experimental model, wherein one or the other matrices have been removed. The trained computational model successfully predicts phenotypes of the experimental counterparts that are subjected to pharmacological treatments (inhibition of N-linked glycosylation and matrix metalloproteinase activity) and scaffold modulation (alteration of collagen density). Further parametric exploration-based simulations suggest that specific permissive regimes of cell-cell and cell-matrix adhesions, operating in the context of a reaction-diffusion-regulated ECM dynamics, promote multiscale invasion of breast cancer cells and determine the extent to which the latter migrate through their surrounding stroma
Integrated Field's metal microelectrodes based microfluidic impedance cytometry for cell-in-droplet quantification
No full textMicrofluidic impedance cytometry (MIC) provides a non-optical and label-free method for single cell detection and classification in microfluidics. However, the cleanroom intensive infrastructure required for MIC electrode fabrication limits its wide implementation in microfluidic analysis. To bypass the conventional metal (platinum) electrode fabrication protocol, we fabricated coplanar `in-contact' Field's metal (icFM) microelectrodes in multilayer elastomer devices with a single photolithography step. Our icFM microelectrodes displayed excellent and comparable performance to the platinum electrodes for detection of single erythrocytes with a lock-in amplifier based MIC setup. We further characterized it for water-in-oil droplets generated in a T-junction microfluidic channel and found high sensitivity and long-term operational stability of these electrodes. Finally, to facilitate droplet based single cell analysis, we demonstrate detection and quantification of single cells entrapped in aqueous droplets