Silver Nanoparticle Aggregates as Highly Efficient Plasmonic Antennas for Fluorescence Enhancement

The enhanced local fields around plasmonic structures can lead to enhancement of the excitation and modification of the emission quantum yield of fluorophores. So far, high enhancement of fluorescence intensity from dye molecules was demonstrated using bow-tie gap antenna made by e-beam lithography. However, the high manufacturing cost and the fact that currently there are no effective ways to place fluorophores only at the gap prevent the use of these structures for enhancing fluorescence-based biochemical assays. We report on the simultaneous modification of fluorescence intensity and lifetime of dye-labeled DNA in the presence of aggregated silver nanoparticles. The nanoparticle aggregates act as efficient plasmonic antennas, leading to more than 2 orders of magnitude enhancement of the average fluorescence. This is comparable to the best-reported fluorescence enhancement for a single molecule but here applies to the average signal detected from all fluorophores in the system. This highlights the remarkable efficiency of this system for surface-enhanced fluorescence. Moreover, we show that the fluorescence intensity enhancement varies with the plasmon resonance position and measure a significant reduction (300×) of the fluorescence lifetime. Both observations are shown to be in agreement with the electromagnetic model of surface-enhanced fluorescence

Multifractality and Conformal Invariance at 2D Metal-Insulator Transition in the Spin-Orbit Symmetry Class

We study the multifractality (MF) of critical wave functions at boundaries and corners at the metal-insulator transition (MIT) for noninteracting electrons in the two-dimensional (2D) spin-orbit (symplectic) universality class. We find that the MF exponents near a boundary are different from those in the bulk. The exponents at a corner are found to be directly related to those at a straight boundary through a relation arising from conformal invariance. This provides direct numerical evidence for conformal invariance at the 2D spin-orbit MIT. The presence of boundaries modifies the MF of the whole sample even in the thermodynamic limit.Comment: 5 pages, 4 figure

Conceptual design study of a coal gasification combined-cycle powerplant for industrial cogeneration

A conceptual design study was conducted to assess technical feasibility, environmental characteristics, and economics of coal gasification. The feasibility of a coal gasification combined cycle cogeneration powerplant was examined in response to energy needs and to national policy aimed at decreasing dependence on oil and natural gas. The powerplant provides the steam heating and baseload electrical requirements while serving as a prototype for industrial cogeneration and a modular building block for utility applications. The following topics are discussed: (1) screening of candidate gasification, sulfur removal and power conversion components; (2) definition of a reference system; (3) quantification of plant emissions and waste streams; (4) estimates of capital and operating costs; and (5) a procurement and construction schedule. It is concluded that the proposed powerplant is technically feasible and environmentally superior

Role of Tunable Acid Catalysis in Decomposition of α-Hydroxyalkyl Hydroperoxides and Mechanistic Implications for Tropospheric Chemistry

This is the published version. Copyright 2014 Royal Society of ChemistryElectronic structure calculations have been used to investigate possible gas-phase decomposition pathways of α-hydroxyalkyl hydroperoxides (HHPs), an important source of tropospheric hydrogen peroxide and carbonyl compounds. The uncatalyzed as well as water- and acid-catalyzed decomposition of multiple HHPs have been examined at the M06-2X/aug-cc-pVTZ level of theory. The calculations indicate that, compared to an uncatalyzed or water-catalyzed reaction, the free-energy barrier of an acid-catalyzed decomposition leading to an aldehyde or ketone and hydrogen peroxide is dramatically lowered. The calculations also find a direct correlation between the catalytic effect of an acid and the distance separating its hydrogen acceptor and donor sites. Interestingly, the catalytic effect of an acid on the HHP decomposition resulting in the formation of carboxylic acid and water is relatively much smaller. Moreover, since the free-energy barrier of the acid-catalyzed aldehyde- or ketone-forming decomposition is ∼25% lower than that required to break the O–OH linkage of the HHP leading to the formation of hydroxyl radical, these results suggest that HHP decomposition is likely not an important source of tropospheric hydroxyl radical. Finally, transition state theory estimates indicate that the effective rate constants for the acid-catalyzed aldehyde- or ketone-forming HHP decomposition pathways are 2–3 orders of magnitude faster than those for the water-catalyzed reaction, indicating that an acid-catalyzed HHP decomposition is kinetically favored as well

Boundary criticality and multifractality at the 2D spin quantum Hall transition

Multifractal scaling of critical wave functions at a disorder-driven (Anderson) localization transition is modified near boundaries of a sample. Here this effect is studied for the example of the spin quantum Hall plateau transition using the supersymmetry technique for disorder averaging. Upon mapping of the spin quantum Hall transition to the classical percolation problem with reflecting boundaries, a number of multifractal exponents governing wave function scaling near a boundary are obtained exactly. Moreover, additional exact boundary scaling exponents of the localization problem are extracted, and the problem is analyzed in other geometries.Comment: v2, 17 pages, 10 figures, published versio

Genome sequence of an alphaherpesvirus from a beluga whale (Delphinapterus leucas)

Beluga whale alphaherpesvirus 1 was isolated from a blowhole swab taken from a juvenile beluga whale. The genome is 144,144 bp in size and contains 86 putative genes. The virus groups phylogenetically with members of the genus Varicellovirus in subfamily Alphaherpesvirinae and is the first alphaherpesvirus sequenced from a marine mammal

Autoxidation of 2,6-di-tert-butylphenol with cobalt Schiff base catalysts by oxygen in CO2-expanded liquids

This is the published version. Copyright 2004 Royal Society of Chemistry.CO2-expanded acetonitrile and methylene chloride have been used in this first detailed study of catalytic O2 oxidations in these remarkably effective reaction media. The autoxidation of 2,6-di-tert-butylphenol (DTBP) with the cobalt Schiff-base (Co(salen*) in these so-called CO2-expanded liquids (CXLs) has been extensively studied using precisely controlled and monitored batch reactions. The dependence of conversion, selectivity and turn-over-frequency on various reaction parameters, including temperature, [O2], [catalyst], and solvent composition has been evaluated. The rates of O2-oxidation in CXLs are typically 1–2 orders of magnitude greater than those obtained with either the neat organic solvent or supercritical CO2 as reaction media. In keeping with the proposed mechanism, the dependence of both the selectivity and conversion on O2 concentration and catalyst concentration indicates that the O2 adduct, and not free O2, serves as oxidant in two critical steps in these systems. The increase in conversion with increasing temperature supports formation of the phenoxy radical as the rate determining step. In contrast, the temperature independence of selectivity is as expected for two competing radical coupling reactions. The balance between O2 solubility and mixed-solvent dielectric constant determines some of the benefits of the CXLs. Because of the greatly increased solubility of O2 in CXLs, the conversion in those media is substantially greater than that in either scCO2 or the neat organic solvent. However, conversion eventually decreases with increasing CO2 content of the solvent because of the decreasing dielectric constant of the medium. The solubilities of O2 and Co(salen*) have been determined in CXLs based on methylene chloride

EVALUATION OF ANTIBACTERIAL, ANTIMICROBIAL, AND HYPOGLYCEMIC EFFECTS OF THE LEAVES OF EMBELIA RIBES

Objective: The purpose of this work is to evaluate the antimicrobial, antibacterial, and hypoglycemic effects of methanolic and ethanolic extracts of Embelia ribes leaves using in vitro studies.Methods: Antibacterial activities of the methanolic and ethanolic extract of E. ribes leaves against Escherichia coli, Staphylococcus aureus, Enterococci, and Klebsiella pneumoniae at different concentrations ranging from 10, 25, 50, and 75 μg/mL and their antibacterial activities were compared to those of the reference controls such as ciprofloxacin and clindamycin. Furthermore, the effect of leaf extracts on α-amylase and α-glucosidase enzymes was assayed.Results: The methanolic and ethanolic extract of E. ribes leaves effectively inhibited the activity of α-amylase and α-glucosidase in a dose-dependent manner. The effect of the methanolic extract was more prominent than that of ethanolic extract. At the same time, both the extracts showed markable inhibition of bacterial growth at a concentration of 75 μg/mL compared to the other three doses (10, 25, and 50 μg/ml) and also commercially available antibiotic drugs ciprofloxacin and clindamycin that were used as positive control drugs. The antibacterial activity of methanolic extract is significantly higher than that of ethanolic extract.Conclusion: The preliminary results of this study have put forward E. ribes into promising herb with respect to its therapeutic potential although further studies are needed to evaluate its mechanism of action

A discrete event modeling and simulation of wave division multiplexing unidirectional slotted ring metropolitan area network

Problem statement: The lack of uniformity in the choice of simulation platforms for optical WDM networks stands behind the difficulty of developing a common simulation environment. Correlating WDM unidirectional slotted ring network to Discrete Event Simulation (DES) encompassing event definition, time advancing mechanism and scheduler has yet to be developed. Approach: The study focused on the proposed and the development of an event based discrete simulator for the WDM unidirectional slotted ring network to facilitate the reuse of the protocol modules under a common simulation environment. The proposed network architecture implemented for the developed simulator employs a separate wavelength as the control information channel. This control information enabled the nodes to monitor their access to the transmission media. Each node was equipped with a tunable transmitter and fixed receiver for data communication. Access nodes were equipped with a fixed transmitter and fixed receiver for the control information exchange. The developed simulator had derived the use of dividing the wavelength into slots. Nodes used these slots to transmit fixed size packets. Slots can be reused by the access node after receiving packets by the deployment of the spatial reuse scheme, thus enhancing the bandwidth utilization. The developed simulator had derived the set of the parameters, events, performance metrics and other unique WDM simulator elements according to a detailed analysis of the base model. Results: The network delay and packet loss were investigated and compared to a benchmark of the modeled domain. Successful deployment of the developed simulator was proven by the generated results. Conclusion: Extensive performance analysis of WDM unidirectional slotted ring network can be deployed using the developed simulator with low computational overheads. Further enhancements were to extend the developed simulator for bidirectional slotted ring supporting fairness control and considering both uniform and non-uniform traffic

Studying food reward and motivation in humans

A key challenge in studying reward processing in humans is to go beyond subjective self-report measures and quantify different aspects of reward such as hedonics, motivation, and goal value in more objective ways. This is particularly relevant for the understanding of overeating and obesity as well as their potential treatments. In this paper are described a set of measures of food-related motivation using handgrip force as a motivational measure. These methods can be used to examine changes in food related motivation with metabolic (satiety) and pharmacological manipulations and can be used to evaluate interventions targeted at overeating and obesity. However to understand food-related decision making in the complex food environment it is essential to be able to ascertain the reward goal values that guide the decisions and behavioral choices that people make. These values are hidden but it is possible to ascertain them more objectively using metrics such as the willingness to pay and a method for this is described. Both these sets of methods provide quantitative measures of motivation and goal value that can be compared within and between individuals