Heterogeneous Diffusion in Highly Supercooled Liquids

The diffusivity of tagged particles is demonstrated to be very heterogeneous on time scales comparable to or shorter than the $\alpha$ relaxation time $\tau_{\alpha}$ ($\cong$ the stress relaxation time) in a highly supercooled liquid via 3D molecular dynamics simulation. The particle motions in the relatively active regions dominantly contribute to the mean square displacement, giving rise to a diffusion constant systematically larger than the Einstein-Stokes value. The van Hove self-correlation function $G_s(r,t)$ is shown to have a long distance tail which can be scaled in terms of $r/t^{1/2}$ for t \ls 3\tau_{\alpha}. Its presence indicates heterogeneous diffusion in the active regions. However, the diffusion process eventually becomes homogeneous on time scales longer than the life time of the heterogeneity structure ($\sim 3 \tau_{\alpha}$).Comment: 4 pages, 5 figure

Diffusion and viscosity in a supercooled polydisperse system

We have carried out extensive molecular dynamics simulations of a supercooled polydisperse Lennard-Jones liquid with large variations in temperature at a fixed pressure. The particles in the system are considered to be polydisperse both in size and mass. The temperature dependence of the dynamical properties such as the viscosity ($\eta$) and the self-diffusion coefficients ($D_i$) of different size particles is studied. Both viscosity and diffusion coefficients show super-Arrhenius temperature dependence and fit well to the well-known Vogel-Fulcher-Tammann (VFT) equation. Within the temperature range investigated, the value of the Angell's fragility parameter (D $\approx 1.4$) classifies the present system into a strongly fragile liquid. The critical temperature for diffusion ($T_o^{D_i}$) increases with the size of the particles. The critical temperature for viscosity ($T_o^{\eta}$) is larger than that for the diffusion and a sizeable deviations appear for the smaller size particles implying a decoupling of translational diffusion from viscosity in deeply supercooled liquid. Indeed, the diffusion shows markedly non-Stokesian behavior at low temperatures where a highly nonlinear dependence on size is observed. An inspection of the trajectories of the particles shows that at low temperatures the motions of both the smallest and largest size particles are discontinuous (jump-type). However, the crossover from continuous Brownian to large length hopping motion takes place at shorter time scales for the smaller size particles.Comment: Revtex4, 7 pages, 8 figure

Global Substrate Profiling of Proteases in Human Neutrophil Extracellular Traps Reveals Consensus Motif Predominantly Contributed by Elastase

Neutrophil extracellular traps (NETs) consist of antimicrobial molecules embedded in a web of extracellular DNA. Formation of NETs is considered to be a defense mechanism utilized by neutrophils to ensnare and kill invading pathogens, and has been recently termed NETosis. Neutrophils can be stimulated to undergo NETosis ex vivo, and are predicted to contain high levels of serine proteases, such as neutrophil elastase (NE), cathepsin G (CG) and proteinase 3 (PR3). Serine proteases are important effectors of neutrophil-mediated immunity, which function directly by degrading pathogenic virulent factors and indirectly via proteolytic activation or deactivation of cytokines, chemokines and receptors. In this study, we utilized a diverse and unbiased peptide library to detect and profile protease activity associated with NETs induced by phorbol-12-myristate-13-acetate (PMA). We obtained a "proteolytic signature" from NETs derived from healthy donor neutrophils and used proteomics to assist in the identification of the source of this proteolytic activity. In addition, we profiled each neutrophil serine protease and included the newly identified enzyme, neutrophil serine protease 4 (NSP4). Each enzyme had overlapping yet distinct endopeptidase activities and often cleaved at unique sites within the same peptide substrate. The dominant proteolytic activity in NETs was attributed to NE; however, cleavage sites corresponding to CG and PR3 activity were evident. When NE was immunodepleted, the remaining activity was attributed to CG and to a lesser extent PR3 and NSP4. Our results suggest that blocking NE activity would abrogate the major protease activity associated with NETs. In addition, the newly identified substrate specificity signatures will guide the design of more specific probes and inhibitors that target NET-associated proteases

Investigation of Touch-Sensitive Responses by Hyphae of the Human Pathogenic Fungus Candida albicans

Candida albicans is a fungus that commonly infects the mucosal surface of humans. The hyphal growth form of this fungus may initiate the primary invasion of the host. Here we show that hyphae respond thigmotropically and morphologically to cues such as the presence of a surface, pores, grooves and ridges. Growth on some firm surfaces elicits a helical growth response. Hyphae follow grooves and ridges of inert substrates and penetrate pores of filtration membranes. Our in vitro experiments suggest that thigmotropism may enhance the ability of a hypha to invade epithelia of a host at sites of weakened integrity

Heterogeneous slow dynamics in a two dimensional doped classical antiferromagnet

We introduce a lattice model for a classical doped two dimensional antiferromagnet which has no quenched disorder, yet displays slow dynamics similar to those observed in supercooled liquids. We calculate two-time spatial and spin correlations via Monte Carlo simulations and find that for sufficiently low temperatures, there is anomalous diffusion and stretched-exponential relaxation of spin correlations. The relaxation times associated with spin correlations and diffusion both diverge at low temperatures in a sub-Arrhenius fashion if the fit is done over a large temperature-window or an Arrhenius fashion if only low temperatures are considered. We find evidence of spatially heterogeneous dynamics, in which vacancies created by changes in occupation facilitate spin flips on neighbouring sites. We find violations of the Stokes-Einstein relation and Debye-Stokes-Einstein relation and show that the probability distributions of local spatial correlations indicate fast and slow populations of sites, and local spin correlations indicate a wide distribution of relaxation times, similar to observ ations in other glassy systems with and without quenched disorder.Comment: 12 pages, 17 figures, corrected erroneous figure, and improved quality of manuscript, updated reference

Post-tsunami natural regeneration of coastal vegetation in the Hambantota district in south-eastern Sri Lanka

A qualitative rapid survey was conducted in 45 plots distributed in the gentle seashore vegetation andsand dunes (n = 13), coastal scrublands (n = 19), and mangroves (n = 13) along the coastline ofHambantota District, affected by the Indian Ocean tsunami. The objective of the survey was toinvestigate the natural regeneration of coastal vegetation 20 months after the tsunami disturbance21 plant species belonging to 19 families were recorded as the prominent plants regenerating inaffected mangroves, while 16 species in 15 families and 32 species in 23 families were observed asprom inent plants to regenerate in affected areas of the gentle sea-shore vegetation and coastalscrublands respectively.In tsunami affected mangrove stands Acanthus iltctfolius (in 50% of study plots), Achrosticumaureum (40%) and Lumnitzera racemosa (17%) were the dominant species establishing in openmuddy substrates, while Clerodendrum inerme (57%), Lumnitzera racemosa and Excoecariaaga//ocha (29% each) were regenerating in sand deposited in the mangrove patches.Ipomoea pes-caprae (85%), Scaevola taccada and Calotropis gigantea (23% each) were observedas the dominant species re-establishing in the gentle seashore vegetation, while Spinifex littoreusshows a slow rate of regeneration. Most of the destroyed Pandanus odoratissimus bushes facingthe beach are not regenerating. Instead a new row of Pandanus was observed regenerating immediatelybacking the original stands. Prominent species regenerating in coastal scrublands are Crotonbonplandianus and Gymnema sylvestre (37% each), Clerodendrum inerme (16%), Calotropisgigantea (10%) and Crateva adansonii (10%) and saplings of Azadirachta indica and Limoniaacidissitna .Invasive alien plants, mainly Opuntia dillennii have established well and spreading vigorously inaffected coastal scrublands (58%), some study plots of gentle seashore vegetation (31 %) as wellas on sand depositions in the affected mangroves (15%). This species was observed replacing thespaces occupied by destroyed Pandanus odoratissimus bushes and Spinifex littoreus beds.Invasive alien plants such as Prosopis juliflora and Lantana camara were also spreading intsunami disturbed coastal scrublands.

Random Packings of Frictionless Particles

We study random packings of frictionless particles at T=0. The packing fraction where the pressure becomes nonzero is the same as the jamming threshold, where the static shear modulus becomes nonzero. The distribution of threshold packing fractions narrows and its peak approaches random close-packing as the system size increases. For packing fractions within the peak, there is no self-averaging, leading to exponential decay of the interparticle force distribution.Comment: 4 pages, 3 figure

FitFlame – Health and Fitness Coaching Application to Mitigate the Issues in the Current Applications

Online fitness coaches help people achieve a healthy lifestyle by offering customized solutions. The demand for professional coaching is expected to grow in the coming years. Nevertheless, no applications in the market address the problems in the coaching process. Today, coaches and clients had to use many third-party apps. The reason for this is that no single fitness coaching app offers communication and exercise-tracking features. Even though some apps meet some of these requirements, they are out of reach for most people's budgets. This paper aims to suggest a robust and full-fledged app to mitigate those issues. FitFlame is the name of the proposed app. Both coaches and clients can benefit from this app. Also, FitFlame is a fitness coaching system available on mobile and the web. It helps clients locate and contact coaches, subscribe to coaching plans, and track their progress. It does away with third-party programs and gives users a better experience

Kinetic Heterogeneities in a Highly Supercooled Liquid

We study a highly supercooled two-dimensional fluid mixture via molecular dynamics simulation. We follow bond breakage events among particle pairs, which occur on the scale of the $\alpha$ relaxation time $\tau_{\alpha}$. Large scale heterogeneities analogous to the critical fluctuations in Ising systems are found in the spatial distribution of bonds which are broken in a time interval with a width of order $0.05\tau_{\alpha}$. The structure factor of the broken bond density is well approximated by the Ornstein-Zernike form. The correlation length is of order $100 \sigma_1$ at the lowest temperature studied, $\sigma_1$ being the particle size. The weakly bonded regions thus identified evolve in time with strong spatial correlations.Comment: 3 pages, 6 figure