Between photocatalysis and photosynthesis: Synchrotron spectroscopy methods on molecules and materials for solar hydrogen generation

Energy research is to a large extent materials research, encompassing the physics and chemistry of materials, including their synthesis, processing toward components and design toward architectures, allowing for their functionality as energy devices, extending toward their operation parameters and environment, including also their degradation, limited life, ultimate failure and potential recycling. In all these stages, X-ray and electron spectroscopy are helpful methods for analysis, characterization and diagnostics for the engineer and for the researcher working in basic science.This paper gives a short overview of experiments with X-ray and electron spectroscopy for solar energy and water splitting materials and addresses also the issue of solar fuel, a relatively new topic in energy research. The featured systems are iron oxide and tungsten oxide as photoanodes, and hydrogenases as molecular systems. We present surface and subsurface studies with ambient pressure XPS and hard X-ray XPS, resonant photoemission, light induced effects in resonant photoemission experiments and a photo-electrochemical in situ/operando NEXAFS experiment in a liquid cell, and nuclear resonant vibrational spectroscopy (NRVS). (C) 2012 Elsevier B.V. All rights reserved.

Next-generation optical microscopy

A new breed of microscopy techniques is coming to the forefront of optical imaging. They enhance the attainable 3D resolution of imaging in live and ``fixed'' cells' (with minimal structural perturbation) by greater than tenfold, bringing subcellular structures in sharp focus Along with long-term imaging, deep tissue and high throughput capablities, new insights in various fields of biology are being generated. The main set of these next-generation optical microscopy techniques along with select applications is described in this article.

EFFICIENT QUANTUM RANDOM NUMBER GENERATION USING QUANTUM INDISTINGUISHABILITY

In this paper, we propose a quantum method for generation of random numbers based on bosonic stimulation. Randomness arises through the path-dependent indeterministic amplification of two competing bosonic modes. We show that the process provides an efficient method for macroscopic extraction of microscopic randomness.

In Vivo Genotoxicity Assessment of Titanium Dioxide Nanoparticles by Allium cepa Root Tip Assay at High Exposure Concentrations

The industrial production and commercial applications of titanium dioxide nanoparticles have increased considerably in recent times, which has increased the probability of environmental contamination with these agents and their adverse effects on living systems. This study was designed to assess the genotoxicity potential of TiO2 NPs at high exposure concentrations, its bio-uptake, and the oxidative stress it generated, a recognised cause of genotoxicity. Allium cepa root tips were treated with TiO2 NP dispersions at four different concentrations (12.5, 25, 50, 100 mu g/mL). A dose dependant decrease in the mitotic index (69 to 21) and an increase in the number of distinctive chromosomal aberrations were observed. Optical, fluorescence and confocal laser scanning microscopy revealed chromosomal aberrations, including chromosomal breaks and sticky, multipolar, and laggard chromosomes, and micronucleus formation. The chromosomal aberrations and DNA damage were also validated by the comet assay. The bio-uptake of TiO2 in particulate form was the key cause of reactive oxygen species generation, which in turn was probably the cause of the DNA aberrations and genotoxicity observed in this study.

Nonlinear optical second harmonic generation in ZnS quantum dots and observation on optical properties of ZnS/PMMA nanocomposites

ZnS quantum dots (QDs) of different sizes are synthesized by a simple chemical co-precipitation method at room temperature, by varying pH value of the reaction mixture. Samples are characterized by an X-ray diffractometer, transmission electron microscope, energy-dispersive X-ray analysis, etc. Linear optical properties, including UV-visible absorption and photoluminescence emission characteristics, of as-prepared QDs are measured. Size dependent nonlinear optical property, such as second harmonic generation (SHG) of 1064 nm Nd:YAG laser fundamental radiation in the synthesized ZnS QDs, is reported for the first time, to the best of our knowledge, by using the standard Kurtz-Perry powder method. In not to study the possibility of the synthesized ZnS QDs in different device applications ZnS/PMMA (polymethylmethacrylate) nanocomposites are also synthesized. The presence of weak chemical interaction between the polymer matrix and ZnS QDs is confirmed by Fourier transform infrared spectroscopy. Thermal properties of the nanocomposites are studied by differential scanning calorimetry and thermo-gravimetric analysis techniques, which show that the composites are stable up to similar to 300 degrees C temperature. (C) 2013 Elsevier B.V. All rights reserved.

High Speed Imaging of Generation and Collapse of Multielectron Bubbles in Liquid Helium

We present experimental results on the generation and collapse of multielectron bubbles in liquid helium. By applying voltage pulses to a tungsten tip above the surface of the liquid, millimetre sized deformations were formed. Using high speed photography, we have imaged the disintegration of these deformations into bubbles of sizes ranging from ten to few hundred microns. At temperatures less than 2 K, the bubbles split into smaller bubbles and then disappeared in a time scale of few milliseconds. Smaller bubbles were formed at temperatures around 3 K, but were visible for more than hundreds of milliseconds. Although we have not been able to measure their charge directly, some of these bubbles responded to electric fields, implying these were indeed multielectron bubbles. With the existing theoretical picture, it is not possible to understand the strong dependence of the lifetime of multielectron bubbles on temperature.

A rapid, efficient, and economical inverse polymerase chain reaction-based method for generating a site saturation mutant library

With the development of deep sequencing methodologies, it has become important to construct site saturation mutant (SSM) libraries in which every nucleotide/codon in a gene is individually randomized. We describe methodologies for the rapid, efficient, and economical construction of such libraries using inverse polymerase chain reaction (PCR). We show that if the degenerate codon is in the middle of the mutagenic primer, there is an inherent PCR bias due to the thermodynamic mismatch penalty, which decreases the proportion of unique mutants. Introducing a nucleotide bias in the primer can alleviate the problem. Alternatively, if the degenerate codon is placed at the 5' end, there is no PCR bias, which results in a higher proportion of unique mutants. This also facilitates detection of deletion mutants resulting from errors during primer synthesis. This method can be used to rapidly generate SSM libraries for any gene or nucleotide sequence, which can subsequently be screened and analyzed by deep sequencing. (C) 2013 Elsevier Inc. All rights reserved.

Effects of temperature on complexes I and II mediated respiration, ROS generation and oxidative stress status in isolated gill mitochondria of the mud crab Scylla serrata

Effects of fluctuations in habitat temperature (18-30 degrees) on mitochondrial respiratory behavior and oxidative metabolic responses in the euryhaline ectotherm Scylla serrate are not fully understood. In the present study, effects of different temperatures ranging from 12 to 40 degrees C on glutamate and succinate mediated mitochondrial respiration, respiratory control ratio (RCR), ATP generation rate, ratio for the utilization of phosphate molecules per atomic oxygen consumption (P/O), levels of lipid peroxidation and H2O2 in isolated gill mitochondria of S. serrata are reported. The pattern of variation in the studied parameters was similar for the two substrates at different temperatures. The values recorded for RCR ( >= 3) and P/O ratio (1.4-2.7) at the temperature range of 15-25 degrees C were within the normal range reported for other animals (3-10 for RCR and 1.5-3 for P/O). Values for P/O ratio, ATP generation rate and RCR were highest at 18 degrees C when compared to the other assay temperatures. However, at low and high extreme temperatures, i.e. at 12 and 40 degrees C, states III and IV respiration rates were not clearly distinguishable from each other indicating that mitochondria were completely uncoupled. Positive correlations were noticed between temperature and the levels of both lipid peroxidation and H2O2. It is inferred that fluctuations on either side of ambient habitat temperature may adversely influence mitochondria respiration and oxidative metabolism in S. serrata. The results provide baseline data to understand the impacts of acute changes in temperature on ectotherms inhabiting estuarine or marine environments. (C) 2014 Elsevier Ltd. All rights reserved.

MazF-induced Growth Inhibition and Persister Generation in Escherichia coli

Background: MazEF is a chromosomally encoded bacterial toxin-antitoxin system whose cellular role is controversial. Results: Expression of chromosomal MazF inhibits cell killing by multiple antibiotics in a Lon and ClpP dependent manner. Conclusion: MazF is involved in reversible growth inhibition and bacterial drug tolerance. Significance: Inactive, active-site toxin mutants yield functional insights by selectively activating the corresponding WT toxin in vivo. Toxin-antitoxin systems are ubiquitous in nature and present on the chromosomes of both bacteria and archaea. MazEF is a type II toxin-antitoxin system present on the chromosome of Escherichia coli and other bacteria. Whether MazEF is involved in programmed cell death or reversible growth inhibition and bacterial persistence is a matter of debate. In the present work the role of MazF in bacterial physiology was studied by using an inactive, active-site mutant of MazF, E24A, to activate WT MazF expression from its own promoter. The ectopic expression of E24A MazF in a strain containing WT mazEF resulted in reversible growth arrest. Normal growth resumed on inhibiting the expression of E24A MazF. MazF-mediated growth arrest resulted in an increase in survival of bacterial cells during antibiotic stress. This was studied by activation of mazEF either by overexpression of an inactive, active-site mutant or pre-exposure to a sublethal dose of antibiotic. The MazF-mediated persistence phenotype was found to be independent of RecA and dependent on the presence of the ClpP and Lon proteases. This study confirms the role of MazEF in reversible growth inhibition and persistence.

Trans-spliced Heat Shock Protein 90 Modulates Encystation in Giardia lamblia

Background: Hsp90 from Giardia lamblia is expressed by splicing of two independently transcribed RNA molecules, coded by genes named HspN and HspC located 777 kb apart. The reasons underlying such unique trans-splicing based generation of GlHsp90 remain unclear. Principle Finding: In this study using mass-spectrometry we identify the sequence of the unique, junctional peptide contributed by the 5' UTR of HspC ORF. This peptide is critical for the catalytic function of Hsp90 as it harbours an essential ``Arg'' in its sequence. We also show that full length GlHsp90 possesses all the functional hall marks of a canonical Hsp90 including its ability to bind and hydrolyze ATP. Using qRT-PCR as well as western blotting approach we find the reconstructed Hsp90 to be induced in response to heat shock. On the contrary we find GlHsp90 to be down regulated during transition from proliferative trophozoites to environmentally resistant cysts. This down regulation of GlHsp90 appears to be mechanistically linked to the encystation process as we find pharmacological inhibition of GlHsp90 function to specifically induce encystation. Significance: Our results implicate the trans-spliced GlHsp90 from Giardia lamblia to regulate an essential stage transition in the life cycle of this important human parasite.

Consequences of Converting Graded to Action Potentials upon Neural Information Coding and Energy Efficiency

Information is encoded in neural circuits using both graded and action potentials, converting between them within single neurons and successive processing layers. This conversion is accompanied by information loss and a drop in energy efficiency. We investigate the biophysical causes of this loss of information and efficiency by comparing spiking neuron models, containing stochastic voltage-gated Na+ and K+ channels, with generator potential and graded potential models lacking voltage-gated Na+ channels. We identify three causes of information loss in the generator potential that are the by-product of action potential generation: (1) the voltage-gated Na+ channels necessary for action potential generation increase intrinsic noise and (2) introduce non-linearities, and (3) the finite duration of the action potential creates a `footprint' in the generator potential that obscures incoming signals. These three processes reduce information rates by similar to 50% in generator potentials, to similar to 3 times that of spike trains. Both generator potentials and graded potentials consume almost an order of magnitude less energy per second than spike trains. Because of the lower information rates of generator potentials they are substantially less energy efficient than graded potentials. However, both are an order of magnitude more efficient than spike trains due to the higher energy costs and low information content of spikes, emphasizing that there is a two-fold cost of converting analogue to digital; information loss and cost inflation.

Optimal Trajectory Generation for Convergence to a Rectilinear Path

This paper presents a strategy to determine the shortest path of a fixed-wing Miniature Air Vehicle (MAV), constrained by a bounded turning rate, to eventually fly along a given straight line, starting from an arbitrary but known initial position and orientation. Unlike the work available in the literature that solves the problem using the Pontryagin's Minimum Principle (PMP) the trajectory generation algorithm presented here considers a geometrical approach which is intuitive and easy to understand. This also computes the explicit solution for the length of the optimal path as a function of the initial configuration. Further, using a 6-DOF model of a MAV the generated optimal path is tracked by an autopilot consisting of proportional-integral-derivative (PID) controllers. The simulation results show the path generation and tracking for different cases.

The Glycosylated Rv1860 Protein of Mycobacterium tuberculosis Inhibits Dendritic Cell Mediated TH1 and TH17 Polarization of T Cells and Abrogates Protective Immunity Conferred by BCG

We previously reported interferon gamma secretion by human CD4(+) and CD8(+) T cells in response to recombinant E. coli-expressed Rv1860 protein of Mycobacterium tuberculosis (MTB) as well as protection of guinea pigs against a challenge with virulent MTB following prime-boost immunization with DNA vaccine and poxvirus expressing Rv1860. In contrast, a Statens Serum Institute Mycobacterium bovis BCG (BCG-SSI) recombinant expressing MTB Rv1860 (BCG-TB1860) showed loss of protective ability compared to the parent BCG strain expressing the control GFP protein (BCG-GFP). Since Rv1860 is a secreted mannosylated protein of MTB and BCG, we investigated the effect of BCG-TB1860 on innate immunity. Relative to BCG-GFP, BCG-TB1860 effected a significant near total reduction both in secretion of cytokines IL-2, IL-12p40, IL-12p70, TNF-alpha, IL-6 and IL-10, and up regulation of co-stimulatory molecules MHC-II, CD40, CD54, CD80 and CD86 by infected bone marrow derived dendritic cells (BMDC), while leaving secreted levels of TGF-beta unchanged. These effects were mimicked by BCG-TB1860His which carried a 6-Histidine tag at the C-terminus of Rv1860, killed sonicated preparations of BCG-TB1860 and purified H37Rv-derived Rv1860 glycoprotein added to BCG-GFP, but not by E. coli-expressed recombinant Rv1860. Most importantly, BMDC exposed to BCG-TB1860 failed to polarize allogeneic as well as syngeneic T cells to secrete IFN-gamma and IL-17 relative to BCG-GFP. Splenocytes from mice infected with BCG-SSI showed significantly less proliferation and secretion of IL-2, IFN-gamma and IL-17, but secreted higher levels of IL-10 in response to in vitro restimulation with BCG-TB1860 compared to BCG-GFP. Spleens from mice infected with BCG-TB1860 also harboured significantly fewer DC expressing MHC-II, IL-12, IL-2 and TNF-alpha compared to mice infected with BCG-GFP. Glycoproteins of MTB, through their deleterious effects on DC may thus contribute to suppress the generation of a TH1- and TH17-dominated adaptive immune response that is vital for protection against tuberculosis.

Evaluating FuncSION: A software for automated synthesis of design solutions for stimulating ideation during mechanical conceptual design

The goal of the work reported in this paper is to use automated, combinatorial synthesis to generate alternative solutions to be used as stimuli by designers for ideation. FuncSION, a computational synthesis tool that can automatically synthesize solution concepts for mechanical devices by combining building blocks from a library, is used for this purpose. The objectives of FuncSION are to help generate a variety of functional requirements for a given problem and a variety of concepts to fulfill these functions. A distinctive feature of FuncSION is its focus on automated generation of spatial configurations, an aspect rarely addressed by other computational synthesis programs. This paper provides an overview of FuncSION in terms of representation of design problems, representation of building blocks, and rules with which building blocks are combined to generate concepts at three levels of abstraction: topological, spatial, and physical. The paper then provides a detailed account of evaluating FuncSION for its effectiveness in providing stimuli for enhanced ideation.

Generation of multiple sheets of light using spatial-filtering technique

We develop an optical system for generating multiple light sheets. This is enabled by employing a special class of spatial filters in a cylindrical lens geometry. The proposed binary filter placed at the back aperture of the cylindrical lens results in the generation of a periodic transverse pattern extending along the z axis (i.e., multiple light sheets). Experimental results confirm the generation of multiple light sheets of thickness 6.6 mu m with an intersheet spacing of 13.4 mu m. The proposed imaging technique may facilitate three-dimensional imaging in nano-optics, fluorescence microscopy, and nanobiology. (C) 2014 Optical Society of America