Growing Length Scales and Their Relation to Timescales in Glass-Forming Liquids

The question of whether the dramatic slowing down of the dynamics of glass-forming liquids near the structural glass transition is caused by the growth of one or more correlation lengths has received much attention in recent years. Several proposals have been made for both static and dynamic length scales that may be responsible for the growth of timescales as the glass transition is approached. These proposals are critically examined with emphasis on the dynamic length scale associated with spatial heterogeneity of local dynamics and the static point-to-set or mosaic length scale of the random first order transition theory of equilibrium glass transition. Available results for these length scales, obtained mostly from simulations, are summarized, and the relation of the growth of timescales near the glass transition with the growth of these length scales is examined. Some of the outstanding questions about length scales in glass-forming liquids are discussed, and studies in which these questions may be addressed are suggested.

Haloarchaeal gas vesicle nanoparticles displaying Salmonella SopB antigen reduce bacterial burden when administered with live attenuated bacteria

Innovative vaccines against typhoid and other Salmonella diseases that are safe, effective, and inexpensive are urgently needed. In order to address this need, buoyant, self-adjuvating gas vesicle nanoparticles (GVNPs) from the halophilic archaeon Halobacterium sp. NRC-1 were bioengineered to display the highly conserved Salmonella enterica antigen SopB, a secreted inosine phosphate effector protein injected by pathogenic bacteria during infection into the host cell. Two highly conserved sopB gene segments near the 3'-coding region, named sopB4 and B5, were each fused to the gvpC gene, and resulting GVNPs were purified by centrifugally accelerated flotation. Display of SopB4 and B5 antigenic epitopes on GVNPs was established by Western blotting analysis using antisera raised against short synthetic peptides of SopB. Immunostimulatory activities of the SopB4 and B5 nanoparticles were tested by intraperitoneal administration of recombinant GVNPs to BALB/c mice which had been immunized with S. enterica serovar Typhimurium 14028 Delta pmrG-HM-D (DV-STM-07), a live attenuated vaccine strain. Proinflammatory cytokines IFN-gamma, IL-2, and IL-9 were significantly induced in mice boosted with SopB5-GVNPs, consistent with a robust Th1 response. After challenge with virulent S. enterica serovar Typhimurium 14028, bacterial burden was found to be diminished in spleen of mice boosted with SopB4-GVNPs and absent or significantly diminished in liver, mesenteric lymph node, and spleen of mice boosted with SopB5-GVNPs, indicating that the C-terminal portions of SopB displayed on GVNPs elicit a protective response to Salmonella infection in mice. SopB antigen-GVNPs were found to be stable at elevated temperatures for extended periods without refrigeration in Halobacterium cells. The results all together show that bioengineered GVNPs are likely to represent a valuable platform for the development of improved vaccines against Salmonella diseases. (C) 2014 Elsevier Ltd. All rights reserved.

Fragility correlates thermodynamic and kinetic properties of glass forming liquids

In our earlier communication we proposed a simple fragility determining function, (NBO]/(VmTg)-T-3), which we have now used to analyze several glass systems using available thermal data. A comparison with similar fragility determining function, Delta C-p/C-p(1), introduced by Chryssikos et al. in their investigation of lithium borate glasses has also been performed and found to be more convenient quantity for discussing fragilities. We now propose a new function which uses both Delta C-p and Delta T and which gives a numerical fragility parameter, F whose value lies between 0 and 1 for glass forming liquids. F can be calculated through the use of measured thermal parameters Delta C-p, C-p(1), T-g and T-m. Use of the new fragility values in reduced viscosity equation reproduces the whole range of viscosity curves of the Angell plot. The reduced viscosity equation can be directly compared with the Adam-Gibbs viscosity equation and a heat capacity function can be formulated which reproduces satisfactorily the Delta C-p versus In(T-r) curves and hence the configurational entropy. (C) 2014 Elsevier Ltd. All rights reserved.

Fragility correlates thermodynamic and kinetic properties of glass forming liquids

In our earlier communication we proposed a simple fragility determining function, (NBO]/(VmTg)-T-3), which we have now used to analyze several glass systems using available thermal data. A comparison with similar fragility determining function, Delta C-p/C-p(1), introduced by Chryssikos et al. in their investigation of lithium borate glasses has also been performed and found to be more convenient quantity for discussing fragilities. We now propose a new function which uses both Delta C-p and Delta T and which gives a numerical fragility parameter, F whose value lies between 0 and 1 for glass forming liquids. F can be calculated through the use of measured thermal parameters Delta C-p, C-p(1), T-g and T-m. Use of the new fragility values in reduced viscosity equation reproduces the whole range of viscosity curves of the Angell plot. The reduced viscosity equation can be directly compared with the Adam-Gibbs viscosity equation and a heat capacity function can be formulated which reproduces satisfactorily the Delta C-p versus In(T-r) curves and hence the configurational entropy. (C) 2014 Elsevier Ltd. All rights reserved.

Stability of Filaments in Star-Forming Clouds and the Formation of Prestellar Cores in Them

The exact process(es) that generate(s) dense filaments which then form prestellar cores within them is unclear. Here we study the formation of a dense filament using a relatively simple set-up of a pressure-confined, uniform-density cylinder. We examine if its propensity to form a dense filament and further, to the formation of prestellar cores along this filament, bears on the gravitational state of the initial volume of gas. We report a radial collapse leading to the formation of a dense filamentary cloud is likely when the initial volume of gas is at least critically stable (characterised by the approximate equality between the mass line-density for this volume and its maximum value). Though self-gravitating, this volume of gas, however, is not seen to be in free-fall. This post-collapse filament then fragments along its length due to the growth of a Jeans-like instability to form prestellar cores. We suggest dense filaments in typical star-forming clouds classified as gravitationally super-critical under the assumption of: (i) isothermality when in fact, they are not, and (ii) extended radial profiles as against pressure-truncated, that significantly over-estimates their mass line-density, are unlikely to experience gravitational free-fall. The radial density and temperature profile derived for this post-collapse filament is consistent with that deduced for typical filamentary clouds mapped in recent surveys of nearby star-forming regions.

Unusual Fragility and Cooperativity in Glass-Forming and Crystalline PVDF/PMMA Blends in the Presence of Multiwall Carbon Nanotubes

Poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) are completely miscible below 50 wt % PVDF in the blends. In this work, an attempt was made to understand the fragility/cooperativity relation in glass-forming and crystalline blends of PVDF/PMMA and in the presence of a heteronucleating agent, multiwall carbon nanotubes (CNTs). Hence, three representative blends were chosen: a completely amorphous (10/90 by wt, PVDF/PMMA), on the verge of amorphous miscibility (50/50 by wt, PVDF/PMMA), and crystalline (60/40 by wt, PVDF/PMMA) blends. The intermolecular cooperativity/coupling, fragility, and configurational entropy near the glass transition temperature (T-g) were studied using differential scanning calorimetry (DSC) and broadband dielectric relaxation spectroscopy (DRS). It was observed that the blends with higher concentration of PMMA were more fragile (fragility index m = 141) and those with higher concentration of PVDF were more strong (m = 78). Interestingly, the coupling was less in the glass-forming blends (10/90 by wt, PVDF/PMMA) than the crystalline blends as manifested from DRS. This observation was also supported by DSC measurements which reflected that the cooperative rearranging region (CRR) existed over a smaller length scales in fragile blends as compared to strong blends, possibly due to restricted amorphous mobility. This effect was more prominent in the presence of CNTs, in particular for 50/50 (by wt) and 60/40 (by wt) PVDF/PMMA blends. Further, the configurational entropy, as manifested from DRS, decreased significantly in the strong blends in striking contrast to the fragile blends, supported by DSC, which manifested in an increase in the volume of cooperativity in the strong blends. The higher coupling in the crystalline blends can be attributed to good packing of the amorphous regions. While this is understood for crystalline blends (60/40 by wt, PVDF/PMMA), it is envisaged that enhanced dynamic heterogeneity is accountable for increased coupling in the case of blends which are on the verge of amorphous miscibility (50/50 by wt, PVDF/PMMA). The latter is also supported by broad relaxations near the T-g in DRS. Interestingly, the intermolecular coupling in the blends in the presence of CNTs has reduced, though the potential energy barrier hindering the rearrangement of CRR is lower than the blends without CNTs. In addition, the amorphous packing is not as effective as the blends without CNTs. This is manifested from reduced volume of cooperativity in particular, for 50/50 (by wt) and 60/40 (by wt) blends.

N-Terminal Disordered Domain of Saccharomyces cerevisiae Hop1 Protein Is Dispensable for DNA Binding, Bridging, and Synapsis of Double-Stranded DNA Molecules But Is Necessary for Spore Formation

The cytological architecture of the synaptonemal complex (SC), a meiosis-specific proteinaceous structure, is evolutionarily conserved among eukaryotes. However, little is known about the biochemical properties of SC components or the mechanisms underlying their roles in meiotic chromosome synapsis and recombination. Functional analysis of Saccharomyces cerevisiae Hop1, a key structural component of SC, has begun to reveal important insights into its function in interhomolog recombination. Previously, we showed that Hop1 is a structure-specific DNA-binding protein, exhibits higher binding affinity for the Holliday junction, and induces structural distortion at the core of the junction. Furthermore, Hop1 promotes DNA condensation and intra- and intermolecular synapsis between duplex DNA molecules. Here, we show that Hop1 possesses a modular domain organization, consisting of an intrinsically disordered N-terminal domain and a protease-resistant C-terminal domain (Hop1CTD). Furthermore, we found that Hop1CTD exhibits strong homotypic as well as heterotypic protein protein interactions, and its biochemical activities were similar to those of the full-length Hop1 protein. However, Hop1CTD failed to complement the meiotic recombination defects of the Delta hop1 strain, indicating that both N- and C-terminal domains of Hop1 are essential for meiosis and spore formation. Altogether, our findings reveal novel insights into the structure-function relationships of Hop1 and help to further our understanding of its role in meiotic chromosome synapsis and recombination.

Dynamics of Glass Forming Liquids with Randomly Pinned Particles

It is frequently assumed that in the limit of vanishing cooling rate, the glass transition phenomenon becomes a thermodynamic transition at a temperature T-K. However, with any finite cooling rate, the system falls out of equilibrium at temperatures near T-g(> T-K), implying that the very existence of the putative thermodynamic phase transition at T-K can be questioned. Recent studies of systems with randomly pinned particles have hinted that the thermodynamic glass transition may be observed for liquids with randomly pinned particles. This expectation is based on the results of approximate calculations that suggest that the thermodynamic glass transition temperature increases with increasing concentration of pinned particles and it may be possible to equilibrate the system at temperatures near the increased transition temperature. We test the validity of this prediction through extensive molecular dynamics simulations of two model glass-forming liquids in the presence of random pinning. We find that extrapolated thermodynamic transition temperature T-K does not show any sign of increasing with increasing pinning concentration. The main effect of pinning is found to be a rapid decrease in the kinetic fragility of the system with increasing pin concentration. Implications of these observations for current theories of the glass transition are discussed.

Novel AgBr/Ag3PO4 Decorated Ceria Nanoflake Composites for Enhanced Photocatalytic Activity toward Dyes and Bacteria under Visible Light

The aim of this study was to develop heterogeneous visible light active photocatalysts using AgBr and Ag3PO4 using CeO2 nanoflakes as an efficient substrate. Ascorbic acid was employed as a fuel to synthesize fine ceria nanoflakes by a facile solution combustion process. AgBr and Ag3PO4 were decorated on ceria to prepare AgBr/Ag3PO4/ceria nanocomposites. The structure of the composite was determined by X-ray diffraction analysis. Novel flakelike morphology was revealed using electron microscopy techniques. The nanocomposites exhibit excellent photocatalytic activity under visible light compared to pristine ceria nanoparticles. The nanocomposite catalyst particles degraded both anionic and cationic dyes. It also exhibited efficient antimicrobial activity under visible light. The AgBr/Ag3PO4/ceria nanocomposite was characterized using X-ray diffraction analysis, diffuse reflectance spectroscopy, electron microscopy, BET surface area analysis, and X-ray photoelectron spectroscopy, and the reasons for enhanced photocatalytic activity were elucidated. The presence of silver based semiconductors on ceria has shown to decrease charge recombination through photoluminescence analysis that attributed for enhanced photocatalytic activity. The AgBr/Ag3PO4/ceria nanocomposite has shown a stable performance after many repeated cycles.

Differential viability response of prokaryotes and eukaryotes to high strength pulsed magnetic stimuli

The present study examines the efficacy of a high strength pulsed magnetic field (PMF) towards bacterial inactivation in vitro, without compromising eukaryotic cell viability. The differential response of prokaryotes Staphylococcus aureus (MESA), Staphylococcus epidermidis, and Escherichia coli], and eukaryotes C2C12 mouse myoblasts and human mesenchymal stem cells, hMSCs] upon exposure to varying PMF stimuli (1-4 T, 30 pulses, 40 ms pulse duration) is investigated. Among the prokaryotes, similar to 60% and similar to 70% reduction was recorded in the survival of staphylococcal species and E. coli, respectively at 4 T PMF as evaluated by colony forming unit (CPU) analysis and flow cytometry. A 2-5 fold increase in intracellular ROS (reactive oxygen species) levels suggests oxidative stress as the key mediator in PMF induced bacterial death/injury. The 4 T PMF treated staphylococci also exhibited longer doubling times. Both TEM and fluorescence microscopy revealed compromised membranes of PMF exposed bacteria. Under similar PMF exposure conditions, no immediate cytotoxicity was recorded in C2C12 mouse myoblasts and hMSCs, which can be attributed to the robust resistance towards oxidative stress. The ion interference of iron containing bacterial proteins is invoked to analytically explain the PMF induced ROS accumulation in prokaryotes. Overall, this study establishes the potential of PMF as a bactericidal method without affecting eukaryotic viability. This non-invasive stimulation protocol coupled with antimicrobial agents can be integrated as a potential methodology for the localized treatment of prosthetic infections. (C) 2015 Elsevier B.V. All rights reserved.

Epigenetics and miRNA during bacteria-induced host immune responses

Various cellular processes including the pathogen-specific immune responses, host-pathogen interactions and the related evasion mechanisms rely on the ability of the immune cells to be reprogrammed accurately and in many cases instantaneously. In this context, the exact functions of epigenetic and miRNA-mediated regulation of genes, coupled with recent advent in techniques that aid such studies, make it an attractive field for research. Here, we review examples that involve the epigenetic and miRNA control of the host immune system during infection with bacteria. Interestingly, many pathogens utilize the epigenetic and miRNA machinery to modify and evade the host immune responses. Thus, we believe that global epigenetic and miRNA mapping of such host-pathogen interactions would provide key insights into their cellular functions and help to identify various determinants for therapeutic value.

Length scales in glass-forming liquids and related systems: a review

The central problem in the study of glass-forming liquids and other glassy systems is the understanding of the complex structural relaxation and rapid growth of relaxation times seen on approaching the glass transition. A central conceptual question is whether one can identify one or more growing length scale(s) associated with this behavior. Given the diversity of molecular glass-formers and a vast body of experimental, computational and theoretical work addressing glassy behavior, a number of ideas and observations pertaining to growing length scales have been presented over the past few decades, but there is as yet no consensus view on this question. In this review, we will summarize the salient results and the state of our understanding of length scales associated with dynamical slow down. After a review of slow dynamics and the glass transition, pertinent theories of the glass transition will be summarized and a survey of ideas relating to length scales in glassy systems will be presented. A number of studies have focused on the emergence of preferred packing arrangements and discussed their role in glassy dynamics. More recently, a central object of attention has been the study of spatially correlated, heterogeneous dynamics and the associated length scale, studied in computer simulations and theoretical analysis such as inhomogeneous mode coupling theory. A number of static length scales have been proposed and studied recently, such as the mosaic length scale discussed in the random first-order transition theory and the related point-to-set correlation length. We will discuss these, elaborating on key results, along with a critical appraisal of the state of the art. Finally we will discuss length scales in driven soft matter, granular fluids and amorphous solids, and give a brief description of length scales in aging systems. Possible relations of these length scales with those in glass-forming liquids will be discussed.

DIFFUSE X-RAY EMISSION FROM STAR-FORMING GALAXIES

We study the diffuse X-ray luminosity (L-X) of star-forming galaxies using two-dimensional axisymmetric hydrodynamical simulations and analytical considerations of supernovae-(SNe-) driven galactic outflows. We find that the mass loading of the outflows, a crucial parameter for determining the X-ray luminosity, is constrained by the availability of gas in the central star-forming region, and a competition between cooling and expansion. We show that the allowed range of the mass loading factor can explain the observed scaling of L-X with star formation rate (SFR) as L-X alpha SFR2 for SFR greater than or similar to 1 M-circle dot yr(-1), and a flatter relation at low SFRs. We also show that the emission from the hot circumgalactic medium (CGM) in the halo of massive galaxies can explain the large scatter in the L-X-SFR relation for low SFRs (less than or similar to few M-circle dot yr(-1)). Our results suggest that galaxies with small SFRs and large diffuse X-ray luminosities are excellent candidates for the detection of the elusive CGM.

Localized Excitations and the Morphology of Cooperatively Rearranging Regions in a Colloidal Glass-Forming Liquid

We develop a scheme based on a real space microscopic analysis of particle dynamics to ascertain the relevance of dynamical facilitation as a mechanism of structural relaxation in glass-forming liquids. By analyzing the spatial organization of localized excitations within clusters of mobile particles in a colloidal glass former and examining their partitioning into shell-like and corelike regions, we establish the existence of a crossover from a facilitation-dominated regime at low area fractions to a collective activated hopping-dominated one close to the glass transition. This crossover occurs in the vicinity of the area fraction at which the peak of the mobility transfer function exhibits a maximum and the morphology of cooperatively rearranging regions changes from stringlike to a compact form. Collectively, our findings suggest that dynamical facilitation is dominated by collective hopping close to the glass transition, thereby constituting a crucial step towards identifying the correct theoretical scenario for glass formation.

Short-Time Beta Relaxation in Glass-Forming Liquids Is Cooperative in Nature

Temporal relaxation of density fluctuations in supercooled liquids near the glass transition occurs in multiple steps. Using molecular dynamics simulations for three model glass-forming liquids, we show that the short-time beta relaxation is cooperative in nature. Using finite-size scaling analysis, we extract a growing length scale associated with beta relaxation from the observed dependence of the beta relaxation time on the system size. We find, in qualitative agreement with the prediction of the inhomogeneous mode coupling theory, that the temperature dependence of this length scale is the same as that of the length scale that describes the spatial heterogeneity of local dynamics in the long-time alpha-relaxation regime.