Roles of Free Electrons and H2O2 in the Optical Breakdown-Induced Photochemical Reduction of Aqueous [AuCl4]-

Free electrons and H2O2 formed in an optical breakdown plasma are found to directly control the kinetics of [AuCl4]− reduction to form Au nanoparticles (AuNPs) during femtosecond laser-assisted synthesis of AuNPs. The formation rates of both free electrons and H2O2 strongly depend on the energy and duration of the 800 nm laser pulses over the ranges of 10−2400 μJ and 30−1500 fs. By monitoring the conversion of [AuCl4]− to AuNPs using in situ UV−vis spectroscopy during laser irradiation, the first- and second-order rate constants in the autocatalytic rate law, k1 and k2, were extracted and compared to the computed free electron densities and experimentally measured H2O2 formation rates. For laser pulse energies of 600 μJ and lower at all pulse durations, the first-order rate constant, k1, was found to be directly proportional to the theoretically calculated plasma volume, in which the electron density exceeds the threshold value of 1.8 × 1020 cm−3. The second-order rate constant, k2, was found to correlate with the measured H2O2 formation rate at all pulse energies and durations, resulting in the empirical relationship k2 ≈ H2O20.5. We have demonstrated that the relative composition of free electrons and H2O2 in the optical breakdown plasma may be controlled by changing the pulse energy and duration, which may make it possible to tune the size and dispersity of AuNPs and other metal nanoparticle products synthesized with femtosecond laser-based methods

Radical Chemistry in a Femtosecond Laser Plasma: Photochemical Reduction of Ag+ in Liquid Ammonia Solution

Plasmas with dense concentrations of reactive species such as hydrated electrons and hydroxyl radicals are generated from focusing intense femtosecond laser pulses into aqueous media. These radical species can reduce metal ions such as Au3+ to form metal nanoparticles (NPs). However, the formation of H2O2 by the recombination of hydroxyl radicals inhibits the reduction of Ag+ through back-oxidation. This work has explored the control of hydroxyl radical chemistry in a femtosecond laser-generated plasma through the addition of liquid ammonia. The irradiation of liquid ammonia solutions resulted in a reaction between NH3 and OH·, forming peroxynitrite and ONOO−, and significantly reducing the amount of H2O2 generated. Varying the liquid ammonia concentration controlled the Ag+ reduction rate, forming 12.7 ± 4.9 nm silver nanoparticles at the optimal ammonia concentration. The photochemical mechanisms underlying peroxynitrite formation and Ag+ reduction are discussed

Dynamic Overlap Concentration Scale of Active Colloids

By introducing the notion of a dynamic overlap concentration scale, we identify universal and previously unreported features of the mechanical properties of active colloids. These features are codified by recognizing that the characteristic length scale of an active particle's trajectory, the run-length, introduces a new concentration scale ϕ∗. Large-scale simulations of repulsive active Brownian particles (ABPs) confirm that this new run-length dependent concentration, which is the trajectory-space analogue of the overlap concentration in polymer solutions, delineates distinct concentration regimes in which interparticle collisions alter particle trajectories. Using ϕ∗ and concentration scales associated with colloidal jamming, the mechanical equation-of-state for ABPs can be collapsed onto a set of principal curves that contain a number of previously overlooked features. The inclusion of these features qualitatively alters previous predictions of the behavior for active colloids as we demonstrate by computing the spinodal for a suspension of purely-repulsive ABPs. Our findings suggest that dynamic overlap concentration scales should be of great utility in unraveling the behavior of active and driven systems

Mechanical Theory of Nonequilibrium Coexistence and Motility-Induced Phase Separation

Nonequilibrium phase transitions are routinely observed in both natural and synthetic systems. The ubiquity of these transitions highlights the conspicuous absence of a general theory of phase coexistence that is broadly applicable to both nonequilibrium and equilibrium systems. Here, we present a general mechanical theory for phase separation rooted in ideas explored nearly a half-century ago in the study of inhomogeneous fluids. The core idea is that the mechanical forces within the interface separating two coexisting phases uniquely determine coexistence criteria, regardless of whether a system is in equilibrium or not. We demonstrate the power and utility of this theory by applying it to active Brownian particles, predicting a quantitative phase diagram for motility-induced phase separation in both two and three dimensions. This formulation additionally allows for the prediction of novel interfacial phenomena, such as an increasing interface width while moving deeper into the two-phase region, a uniquely nonequilibrium effect confirmed by computer simulations. The self-consistent determination of bulk phase behavior and interfacial phenomena offered by this mechanical perspective provide a concrete path forward towards a general theory for nonequilibrium phase transitions.Comment: 9 page main text + 7 page SI. Comments welcome

Effects of Prior Fasting on Fat Oxidation during Resistance Exercise

International Journal of Exercise Science 11(2): 827-833, 2018. Prior research has demonstrated that the percentage of fuel utilization contributed by CHO compared to fat rises with an increase in exercise intensity. The role of food intake prior to exercise has been well studied and fasting prior to exercise generally increases reliance on fat as fuel. However, data on the role of fasting prior to resistance exercise is limited. Therefore, the purpose of this study was to assess the effects of one bout of resistance training in a fasted state compared to ingestion of standardized meal on fat and carbohydrate utilization. Twelve female (n = 12, age = 20.1 ± 0.79 yrs, height = 67.0 ± 2.63 in, weight = 143 ± 21.8 lbs) NCAA Division 1 athletes participated in the study. Each participant completed one 10 hour fasted resistance training session and one postprandial resistance training session. The respiratory exchange ratio (RER) and METs were measured using a Cosmed K4b2portable metabolic cart (Cosmed, Rome, Italy) and heart rate was measured by a Polar H1 heart rate monitor. Participants consumed the prescribed food, waited 15 minutes, and then completed three sets of five repetitions of bench press, back squat, and military press at 60% of their 1-repetition maximum. The mean fasted RER was significantly lower than postprandial for back squat (p=0.01) and military press (p=0.02), but not bench press (p=0.19). There was no difference in METs, RPE, or HR between fasted and postprandial trials for any exercise. Results suggest that fasted resistance exercise relies more heavily on fat metabolism than carbohydrate

Pervasive and dynamic protein binding sites of the mRNA transcriptome in Saccharomyces cerevisiae

Abstract Background Protein-RNA interactions are integral components of nearly every aspect of biology, including regulation of gene expression, assembly of cellular architectures, and pathogenesis of human diseases. However, studies in the past few decades have only uncovered a small fraction of the vast landscape of the protein-RNA interactome in any organism, and even less is known about the dynamics of protein-RNA interactions under changing developmental and environmental conditions. Results Here, we describe the gPAR-CLIP (global photoactivatable-ribonucleoside-enhanced crosslinking and immunopurification) approach for capturing regions of the untranslated, polyadenylated transcriptome bound by RNA-binding proteins (RBPs) in budding yeast. We report over 13,000 RBP crosslinking sites in untranslated regions (UTRs) covering 72% of protein-coding transcripts encoded in the genome, confirming 3' UTRs as major sites for RBP interaction. Comparative genomic analyses reveal that RBP crosslinking sites are highly conserved, and RNA folding predictions indicate that secondary structural elements are constrained by protein binding and may serve as generalizable modes of RNA recognition. Finally, 38% of 3' UTR crosslinking sites show changes in RBP occupancy upon glucose or nitrogen deprivation, with major impacts on metabolic pathways as well as mitochondrial and ribosomal gene expression. Conclusions Our study offers an unprecedented view of the pervasiveness and dynamics of protein-RNA interactions in vivo.http://deepblue.lib.umich.edu/bitstream/2027.42/112318/1/13059_2012_Article_3050.pd

Genetic analysis of seed traits in \u3ci\u3eSorghum bicolor\u3c/i\u3e that affect the human gut microbiome

Prebiotic fibers, polyphenols and other molecular components of food crops significantly affect the composition and function of the human gut microbiome and human health. The abundance of these, frequently uncharacterized, microbiome-active components vary within individual crop species. Here, we employ high throughput in vitro fermentations of pre-digested grain using a human microbiome to identify segregating genetic loci in a food crop, sorghum, that alter the composition and function of human gut microbes. Evaluating grain produced by 294 sorghum recombinant inbreds identifies 10 loci in the sorghum genome associated with variation in the abundance of microbial taxa and/or microbial metabolites. Two loci co-localize with sorghum genes regulating the biosynthesis of condensed tannins. We validate that condensed tannins stimulate the growth of microbes associated with these two loci. Our work illustrates the potential for genetic analysis to systematically discover and characterize molecular components of food crops that influence the human gut microbiome

Association of High-Sensitivity Troponin with Cardiac CT Angiography Evidence of Myocardial and Coronary Disease in a Primary Prevention Cohort of Men: Results from MACS.

BackgroundHigh-sensitivity cardiac troponin (hs-cTn) elevations are associated with incident cardiovascular disease events in primary prevention samples. However, the mechanisms underlying this association remain unclear.MethodsWe studied 458 men without known cardiovascular disease who participated in the cardiovascular disease substudy of the Multicenter AIDS Cohort Study and had cardiac CT angiography. We used multivariable linear and logistic regression models to examine the cross-sectional associations between coronary artery stenosis, coronary artery plaque, indexed left ventricular mass (LVMi), and the outcome of hs-cTnI. We also evaluated the associations between HIV serostatus or use of highly active antiretroviral therapy (HAART) and hs-cTnI.ResultsThe mean age was 54 years, 54% were white, and 61% were HIV infected. In multivariable-adjusted logistic models, comparing the highest quartile of LVMi with the lowest quartile, the odds ratio (OR) of hs-cTnI ≥75th percentile was 2.59 (95% CI, 1.20-5.75). There was no significant association between coronary stenosis severity or plaque type and hs-cTnI in linear models; however, in logistic regression models, coronary artery stenosis ≥70% (8% of sample) was marginally associated with a higher likelihood (OR, 2.75 [95% CI, 1.03, 7.27]) of having hs-cTnI ≥75th percentile. There were no associations between HIV serostatus or HAART use and hs-cTnI in either linear or logistic models.ConclusionAmong primary prevention men with or at risk for HIV, hs-cTnI concentrations were strongly associated with LVMi but were not associated with HIV infection or treatment status or with coronary plaque type or stenosis until the extremes of severity (≥70% stenosis)

Electroless Nickel Deposition:An Alternative for Graphene Contacting

We report the first investigation into the potential of electroless nickel deposition to form ohmic contacts on single layer graphene. To minimize the contact resistance on graphene, a statistical model was used to improve metal purity, surface roughness, and coverage of the deposited film by controlling the nickel bath parameters (pH and temperature). The metalized graphene layers were patterned using photolithography and contacts deposited at temperatures as low as 60 °C. The contact resistance was 215 ± 23 ω over a contact area of 200 μm × 200 μm, which improved upon rapid annealing to 107 ± 9 ω. This method shows promise toward low-cost and large-scale graphene integration into functional devices such as flexible sensors and printed electronics