Ultrathin Metals on a Transparent Seed and Application to Infrared Reflectors.

Ultrathin metal films (UTMFs) are widely used in optoelectronic applications, from transparent conductors to photovoltaic cells, low emissivity windows, and plasmonic metasurfaces. During the initial deposition phase, many metals tend to form islands on the receiving substrate rather than a physically connected (percolated) network, which eventually evolves into continuous films as the thickness increases. For example, in the case of Ag and Au on dielectric surfaces, percolation begins when the thickness of the metal film is at least about 5 nm. It is known that the type of growth can be changed when a proper seed layer is used. Here, we show that a CuO layer directly deposited on a substrate can dramatically influence surface wetting and promote early percolation of polycrystalline Ag and Au UTMFs. We demonstrate that the proposed seed is effective even when its thickness is sub-nanometric, in this way maintaining the full transparency of the receiving substrate. The Ag and Au films seeded with CuO showed a percolation thickness close to 1 nm and were morphologically and optically characterized from an ultraviolet (λ = 300 nm) to a midinfrared (λ = 15 µm) wavelength. Infrared reflectors, a mirror and a resonant plasmonic structure, were also demonstrated and uniquely tuned by electrical gating, this being possible owing to the small thickness of the constituting Au UTMF.

Structure-based functional fitness analyses of carbapenemase variants identified among pathogenic carbapenem-resistant Gram-negative bacteria.

Carbapenemase-mediated carbapenem resistance is a major public health concerns worldwide. In the present study, prevalence of circulating carbapenemases was estimated among carbapenem-resistant clinical isolates using PCR and sequencing. Diameters of zone of inhibition (ZDs) were compared for imipenem, meropenem and ertapenem among single carbapenemase producing isolates. Structure-based functional fitness of those carbapenemases was predicted through several in silico analyses. Approximately, 63.76% isolates demonstrated carbapenem resistance, of which 39.13% harboured carbapenemases like blaNDM-1 (33.23%), blaNDM-1-like (0.31%), blaVIM-2 (4.35%), blaKPC-2 (4.04%), blaOXA-181 (6.85%), blaOXA-23 (16.50%), blaOXA-69 (3.88%), blaOXA-66 (2.91%) and blaOXA-104 (1.94%). Omega values indicated selection pressure over blaOXA-69, blaOXA-66 and blaOXA-104. Protein structural dynamics predicted NDM-1 and KPC-2 to have the highest and least flexibility, indicating differences in ß-lactam binding and catalytic efficiency. Increased requirement of free folding energy, improved solvent accessibility and decreased melting temperatures among NDM-1-like, OXA-181, OXA-66, OXA-69 and OXA-104 predicted functional improvement over their ancestral variants. NDM-1-like carbapenemases demonstrated improvement in binding stability, affinity and catalysis of meropenem than that of NDM-1. Catalytic activity of imipenem was predicted to improve among OXA-181, which could be correlated with more than 1.5 folds smaller ZDs around imipenem disc, than that of meropenem/ertapenem, among OXA-181 producing isolates. However, OXA-66 indicated greater binding stability and affinity for imipenem and meropenem. This study indicated structural/functional convergence as well as divergence among several carbapenemase variants and provided useful insights into carbapenemase-mediated carbapenem resistance that might help in identifying appropriate treatment regimen for bacterial infections.

Reactions of liquid and solid aluminum clusters with N2: the role of structure and phase in Al114 (+), Al115 (+), and Al117 (+).

Kinetic energy thresholds have been measured for the chemisorption of N2 onto Al114 (+), Al115 (+), and Al117 (+) as a function of the cluster's initial temperature, from around 200 K up to around 900 K. For all three clusters there is a sharp drop in the kinetic energy threshold of 0.5-0.6 eV at around 450 K, that is correlated with the structural transition identified in heat capacity measurements. The decrease in the thresholds corresponds to an increase in the reaction rate constant, k(T) at 450 K, of around 10(6)-fold. No significant change in the thresholds occurs when the clusters melt at around 600 K. This contrasts with behavior previously reported for smaller clusters where a substantial drop in the kinetic energy thresholds is correlated with the melting transition.

Understanding the patterns of antibiotic susceptibility of bacteria causing urinary tract infection in West Bengal, India.

Urinary tract infection (UTI) is one of the most common infectious diseases at the community level. In order to assess the adequacy of empirical therapy, the susceptibility of antibiotics and resistance pattern of bacteria responsible for UTI in West Bengal, India, were evaluated throughout the period of 2008-2013. The infection reports belonging to all age groups and both sexes were considered. Escherichia coli was the most abundant uropathogen with a prevalence rate of 67.1%, followed by Klebsiella spp. (22%) and Pseudomonas spp. (6%). Penicillin was least effective against UTI-causing E. coli and maximum susceptibility was recorded for the drugs belonging to fourth generation cephalosporins. Other abundant uropathogens, Klebsiella spp., were maximally resistant to broad-spectrum penicillin, followed by aminoglycosides and third generation cephalosporin. The antibiotic resistance pattern of two principal UTI pathogens, E. coli and Klebsiella spp. in West Bengal, appears in general to be similar to that found in other parts of the Globe. Higher than 50% resistance were observed for broad-spectrum penicillin. Fourth generation cephalosporin and macrolides seems to be the choice of drug in treating UTIs in Eastern India. Furthermore, improved maintenance of infection incident logs is needed in Eastern Indian hospitals in order to facilitate regular surveillance of the occurrence of antibiotic resistance patterns, since such levels continue to change.

Incidence of Japanese encephalitis among acute encephalitis syndrome cases in West Bengal, India.

BACKGROUND AND OBJECTIVES: Japanese encephalitis (JE) is the most important cause of acute and epidemic viral encephalitis. Every year sporadic JE cases are reported from the various districts of West Bengal, indicating its endemicity in this state. JE vaccination programme has been undertaken by the State Health Department of West Bengal. This study was aimed at seeing the present scenario of JE among acute encephalitis syndrome (AES) cases in West Bengal. MATERIALS AND METHODS: Blood and/or CSF samples were referred from suspected AES cases to the referral virology laboratory of the Calcutta School of Tropical Medicine from different hospitals of Kolkata. IgM antibody capture ELISA was performed on the CSF and serum samples by JE virus MAC ELISA kit supplied by the National Institute of Virology, Pune. RESULTS: The present study reveals that 22.76% and 5% of the AES cases were positive for JE IgM in 2011 and 2012, respectively. JE is mainly prevalent in children and adolescents below 20 years of age with no gender predilection. Although the percentages of JE positive cases were high in 2011, it sharply decreased thereafter possibly due to better awareness programs, due to mass vaccination, or simply due to natural epidemiological niche periodicity due to herd immunity.

Charge separation from the bursting of bubbles on water.

Film droplets formed from the bursting of 2.4 mm diameter bubbles on the surface of pure water are predominantly negatively charged. The charge generated per bubble varies chaotically; a few bubbles generate more than -3 × 10(6) elementary charges (e) but the vast majority generate much less. The average is -5 × 10(4)e/bubble, and it is not significantly affected by bubbling rate or temperature. The charge diminishes with increasing salt concentration and vanishes for concentrations above 10(-3) M. We propose a mechanism consistent with the observed charge separation. The model relies on the assumption that the surface of pure water has a slight excess of hydroxide ions. The charge separation results when water with entrained counterions (H(3)O(+)) flows out of the thinning film of the bubble cap, leaving behind the excess OH(-) on the surface. Addition of salt reduces the Debye length, and the charge separation mechanism becomes less effective as the Debye length becomes small compared with the film thickness. The excess charge near the surface of pure water is very small, around -4 nC/m(2).

Activation of dinitrogen by solid and liquid aluminum nanoclusters: a combined experimental and theoretical study.

Cross sections for chemisorption of N2 onto Al44(+/-) cluster ions have been measured as a function of relative kinetic energy and the temperature of the metal cluster. There is a kinetic energy threshold for chemisorption, indicating that it is an activated process. The threshold energies are around 3.5 eV when the clusters are in their solid phase and drop to around 2.5 eV when the clusters melt, indicating that the liquid clusters are much more reactive than the solid. Below the melting temperature the threshold for Al44(-) is smaller than for Al44(+), but for the liquid clusters the anion and cation have similar thresholds. At high cluster temperatures and high collision energies the Al44N2(+/-) chemisorption product dissociates through several channels, including loss of Al, N2, and Al3N. Density functional calculations are employed to understand the thermodynamics and the dynamics of the reaction. The theoretical results suggest that the lowest energy pathway for activation of dinitrogen is not dynamically accessible under the experimental conditions, so that an explicit account of dynamical effects, via molecular dynamics simulations, is necessary in order to interpret the experimental measurements. The calculations reproduce all of the main features of the experimental results, including the kinetic energy thresholds of the anion and cation and the dissociation energies of the liquid Al44N2(+/-) product. The strong increase in reactivity on melting appears to be due to the volume change of melting and to atomic disorder.

Melting of size-selected aluminum nanoclusters with 84-128 atoms.

Heat capacities have been measured as a function of temperature for isolated aluminum nanoclusters with 84-128 atoms. Most clusters show a single sharp peak in the heat capacity which is attributed to a melting transition. However, there are several size regimes where additional features are observed; for clusters with 84-89 atoms the peak in the heat capacity is either broad or bimodal. For Al(115) (+), Al(116) (+), and Al(117) (+) there are two well-defined peaks, and for Al(126) (+), Al(127) (+), and Al(128) (+) there is a dip in the heat capacity at lower temperature than the peak. The broad or bimodal peaks for clusters with 84-89 atoms are not significantly changed by annealing to 823 K (above the melting temperature), but the dips for Al(126) (+), Al(127) (+), and Al(128) (+) disappear when these clusters are annealed to 523 K (above the temperature of the dip but below the melting temperature). Both the melting temperatures and the latent heats change fairly smoothly with the cluster size in the size regime examined here. There are steps in the melting temperatures for clusters with around 100 and 117 atoms. The step at Al(100) (+) is correlated with a substantial peak in the latent heats but the step at Al(117) (+) correlates with a minimum. Since the latent heats are correlated with the cluster cohesive energies, the substantial peak in the latent heats at Al(100) (+) indicates this cluster is particularly strongly bound.

Metal clusters with hidden ground states: Melting and structural transitions in Al115(+), Al116(+), and Al117(+).

Heat capacities measured as a function of temperature for Al(115)(+), Al(116)(+), and Al(117)(+) show two well-resolved peaks, at around 450 and 600 K. After being annealed to 523 K (a temperature between the two peaks) or to 773 K (well above both peaks), the high temperature peak remains unchanged but the low temperature peak disappears. After considering the possible explanations, the low temperature peak is attributed to a structural transition and the high temperature peak to the melting of the higher enthalpy structure generated by the structural transition. The annealing results show that the liquid clusters freeze exclusively into the higher enthalpy structure and that the lower enthalpy structure is not accessible from the higher enthalpy one on the timescale of the experiments. We suggest that the low enthalpy structure observed before annealing results from epitaxy, where the smaller clusters act as a nucleus and follow a growth pattern that provides access to the low enthalpy structure. The solid-to-solid transition that leads to the low temperature peak in the heat capacity does not occur under equilibrium but requires a superheated solid.