Laser driven self-assembly of shape-controlled potassium nanoparticles in porous glass

We observe growth of shape-controlled potassium nanoparticles inside a random network of glass nanopores, exposed to low-power laser radiation. Visible laser light plays a dual role: it increases the desorption probability of potassium atoms from the inner glass walls and induces the self-assembly of metastable metallic nanoparticles along the nanopores. By probing the sample transparency and the atomic light-induced desorption flux into the vapour phase, the dynamics of both cluster formation/evaporation and atomic photo-desorption processes are characterized. Results indicate that laser light not only increases the number of nanoparticles embedded in the glass matrix but also influences their structural properties. By properly choosing the laser frequency and the illumination time, we demonstrate that it is possible to tailor the nanoparticles'shape distribution. Furthermore, a deep connection between the macroscopic behaviour of atomic desorption and light-assisted cluster formation is observed. Our results suggest new perspectives for the study of atom/surface interaction as well as an effective tool for the light-controlled reversible growth of nanostructures.Comment: 14 pages,6 figures, http://iopscience.iop.org/1612-202X/11/8/085902

Effects of polychaetes on silicate dynamics and fluxes in sediments: Importance of species, animal activity and polychaete effects on benthic diatoms

Laboratory experiments tested the effects of two polychaetes, a surface deposit feeder Eupolymnia heterobranchia, and a head-down deposit feeder Abarenicola pacifica, on silicate dynamics in sediment porewaters and overlying waters. Experimental chambers of sediment containing an individual deposit feeder, and controls with no macrofauna, were studied over a one month period during the summers of 1989 and 1990. Measurements included temporal changes in vertical depth profiles of pore water silicate concentrations, concurrent determinations of silicate accumulation in the water column, and the activities of experimental. organisms. A diffusion-nonlocal exchange-reaction model was devised to determine, from the pore water profiles, both the magnitude of, and variability associated with, organism effects on pore water silicate. Model results within chambers containing worms indicate that the changes in silicate concentrations due to worm activity varied by as much as an order of magnitude at a given point in the sediment column, over time periods of several days. Biologically-driven fluxes calculated from the sediment model indicate that fluxes attributable to macrofauna were positively correlated with the frequency of new burrow or tube construction, and were strongly related to the activity of the organism. Variability in the rate of silicate transport due to worms likely was related to the mechanism of habitat construction, as well as the relative distances involved in tube/burrow relocation. Silicate fluxes calculated from the model were compared with direct measures of silicate flux via the accumulation of silicate in the water column. These comparisons show that benthic diatoms at times exerted a significant effect on silicate removal from sediments and the water column. The relative importance of this effect was dictated by differences in the activity of diatoms and surrounding macrofauna between experiments, and the type of macrofaunal organisms involved. Strong interactions between the surface deposit feeder and benthic diatoms significantly affected the magnitude and direction of silicate flux across the sediment-water interface. Such interactions were lacking in experiments with the head-down deposit feeder. In combination, the sediment model and water column measurements showed that net silicate fluxes to the water column may be masked by diatom activity, even when bioirrigation serves to actively transport silicate directly from depth across the sediment-water interface

Experimental and numerical investigation on forced convection in circular tubes with nanofluids

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.In this paper an experimental and numerical study to investigate the convective heat transfer characteristics of fully developed turbulent flow of a water–Al2O3 nanofluid in a circular tube is presented. The numerical simulations are accomplished on the experimental test section configuration. In the analysis, the fluid flow and the thermal field are assumed axial-symmetric, two-dimensional and steady state. The single-phase model is employed to model the nanofluid mixture and k-ε model is used to describe the turbulent fluid flow. Experimental and numerical results are carried out for different volumetric flow rates and nanoparticles concentration values. Heat transfer convective coefficients as a function of flow rates and Reynolds numbers are presented. The results indicate that the heat transfer coefficients increase for all nanofluids concentrations compared to pure water at increasing volumetric flow rate. Heat transfer coefficient increases are observed at assigned volumetric flow rate for nanofluid mixture with higher concentrations whereas Nusselt numbers present lower values than the ones for pure water

The effect of experience and of dots\u2019 density and duration on the detection of coherent motion in dogs

Knowledge about the mechanisms underlying canine vision is far from being exhaustive, especially that concerning post- retinal elaboration. One aspect that has received little attention is motion perception, and in spite of the common belief that dogs are extremely apt at detecting moving stimuli, there is no scientific support for such an assumption. In fact, we recently showed that dogs have higher thresholds than humans for coherent motion detection (Kanizsar et al. in Sci Rep UK 7:11259, 2017). This term refers to the ability of the visual system to perceive several units moving in the same direction, as one coherently moving global unit. Coherent motion perception is commonly investigated using random dot displays, containing variable proportions of coherently moving dots. Here, we investigated the relative contribution of local and global integra- tion mechanisms for coherent motion perception, and changes in detection thresholds as a result of repeated exposure to the experimental stimuli. Dogs who had been involved in the previous study were given a conditioned discrimination task, in which we systematically manipulated dot density and duration and, eventually, re-assessed our subjects\u2019 threshold after extensive exposure to the stimuli. Decreasing dot duration impacted on dogs\u2019 accuracy in detecting coherent motion only at very low duration values, revealing the efficacy of local integration mechanisms. Density impacted on dogs\u2019 accuracy in a linear fashion, indicating less efficient global integration. There was limited evidence of improvement in the re-assessment but, with an average threshold at re-assessment of 29%, dogs\u2019 ability to detect coherent motion remains much poorer than that of humans

Absolute Continuity of Solutions to Reaction-Diffusion Equations with Multiplicative Noise

We prove absolute continuity of the law of the solution, evaluated at fixed points in time and space, to a parabolic dissipative stochastic PDE on L (G), where G is an open bounded domain in ℝ with smooth boundary. The equation is driven by a multiplicative Wiener noise and the nonlinear drift term is the superposition operator associated to a real function that is assumed to be monotone, locally Lipschitz continuous, and growing not faster than a polynomial. The proof, which uses arguments of the Malliavin calculus, crucially relies on the well-posedness theory in the mild sense for stochastic evolution equations in Banach spaces. 2

A modelling study of discontinuous biological irrigation

Irrigation of infaunal dwellings can lead to significant alteration of solute distributions in sediments. As a result, sediment-seawater fluxes of nutrients and dissolved carbon are greatly enhanced, and the biology of benthic communities is affected. The most realistic mathematical representation of irrigation and its effect on sediment geochemistry is Aller\u27s (1980) cylinder model. One critical assumption of this model is that burrows are irrigated continually, and that burrow water solute concentrations are identical to overlying water concentrations at all times. However, the vast majority of infaunal tube- and burrow-dwelling organisms irrigate periodically, i.e. in an on/off cycle. During periodic irrigation, the solute concentration at the tube wall may vary between the limits imposed by the flux from the porewater and the concentration in the overlying water. We introduce modifications to the cylinder model which allow for periodic irrigation. We assess how periodic irrigation affects solute profiles and fluxes of two chemical constituents, silica and ammonium, for different population densities (distance between burrows) and organism sizes (burrow radii). Silica and ammonium follow first and zeroth order reaction kinetics, respectively, and illustrate the behavior of two general reaction classes. Model results show that the effects of periodic irrigation vary with the class of reaction considered. For silica, radially-averaged profiles during discontinuous irrigation varied less than 15% from those with continuous irrigation for nearly all burrow sizes, burrow distances and reaction rate constants considered. However, we observed large temporal changes (as much as a factor of 6) in the areally-averaged silica flux over the irrigation cycle. Despite this time-dependence, the time-averaged silica flux was similar to that calculated for the continuous case. For ammonia, radially-averaged solute profiles were extremely sensitive to the duration of irrigation. In this case, the differences between discontinuous and continuous irrigation were greatest when the duration of irrigation was short (e.g. 5 min), and when the inter-burrow distance was small. As with silica, there was a strong time-dependence in areally-averaged ammonia flux when irrigation was periodic. However, the time-averaged ammonia flux is identical to the flux calculated for continuous irrigation. Our results suggest that irrigation behavior can affect the local burrow environment and this imposes a time dependence on solute fluxes

Evidence of infaunal effects on porewater advection and biogeochemistry in permeable sediments: A proposed infaunal functional group framework

Bioturbating infauna significantly modify reaction and transport processes in permeable sediments, though most studies to date are limited in the scope of species examined. We conducted a comparative field study measuring density-dependent effects of six common bioturbating species on porewater advection and biogeochemistry, across three intertidal permeable sediment habitats. The species in this study are; head-down like deposit feeders (Abarenicola pacifica and Balanoglossus aurantiacus), surface deposit feeders (Diopatra cuprea and Onuphis jenneri) and gallery diffusers (Upogebia pugettensis and Neotrypaea californiensis). Tracer loss from gel diffusers was used to assess relative differences in porewater advection among sites, and porewater peepers were used to measure solute concentrations of carbon, nitrogen, phosphate, and silicate in experimental plots. Characteristic surface features of different infauna were counted and used as a proxy for infaunal density. Density of surface features was then used in regression analyses as an explanatory variable affecting porewater transport and chemistry. Significant infaunal density effects on porewater transport or biogeochemistry were found in all but one species, D. cuprea. The species-specific attributes and mechanisms by which these infauna affect permeable sediment processes are explored. A process based functional group framework is presented for permeable sediments. Bulk granulometric properties also were assessed. There were little to no within-site effects of porosity, hydraulic conductivity, or organic matter on porewater transport and biogeochemistry. However, significant across-site differences in granulometry and site properties were found and these are addressed in relation to infaunal effects on porewater transport and chemistry

Temporal pattern of Klebsiella pneumoniae carbapenemase (KPC) on surface of an intensive care unit of a large hospital

Background: Carbapenem-resistant Enterobacteriaceae are an increasing cause of healthcare-associated infections worldwide. Patients with infections caused by Klebsiella pneumoniae resistant to carbapenems (KPC) have significant increases in both allcause mortality and 30-day mortality. The aims of this study was to investigate the prevalence of KPC on environmental samples collected during and after an outbreak caused by KPC in an intensive care unit (ICU) of a teaching hospital. Methods: Between 2010 and 2014 we conducted a total of 132 environmental monitoring campaigns from different critical surface of ICU ward in a Teaching Hospital Policlinico Umberto I. Samples were collected on surfaces in patient rooms and health care area. All samples were cultured and K. pneumoniae isolates were identified by standard microbiological techniques. The presumptive colonies were confirmed and tested for antibiotic resistance by an automated system. K. pneumoniae resitant to carbapenems were tested for carbapenemase production by modified Hodge test. Results: A total of 2526 environmental samples were collected from November 2010 to July 2014. Of those, 111 resulted positive for K. pneumoniae while KPC were 95 (85.6% of all K. pneumoniae, 3.8% of total samples). KPC was recovered in all patient rooms with similar proportion (5.1-5.6%) with the exception of patient 6 bed room where it was lower (2.4%). The pathogen was not recovered in rooms dedicated to healthcare personnel and doctors. Among surfaces, the highest proportion of KPC resulted on bedrail (6.8%), more than double than other surfaces. Washbasins had nearly half of samples KPC positive (1.2%). Conclusions: Despite previous studies suggested that environment plays a minor role in the transmission of carbapenem-resistant enterobacteriaceae, our data highlighted that surfaces represents a significant reservoir for KPC possibly supporting transiently contamination of hands of healthcare workers in our ICU. Our results confirm that KPC are more likely found on surfaces closer to the patient than on those situated further away

Recruitment responses of benthic infauna to manipulated sediment geochemical properties in natural flows

Recent studies have shown that local variation in surface sediment geochemistry can have significant effects on recruitment rates of benthic invertebrates. Experiments presented here tested (1) the utility of manipulating surface porewater concentrations using spiked polyacrylamide gels and (2) the recruitment responses of the polychaete Arenicola cristata and the bivalve Mercenaria mercenaria to manipulated ammonium concentrations in realistic flows provided by a straight flume and an annular flume. Data show that successful manipulation of sediment porewater ammonium concentration is feasible in flowing waters, i.e., overlying waters remained relatively free of ammonium while manipulated concentration levels were maintained within the upper sediment layers where new recruits explore. Thus, over short experimental periods, ammonium signals can be independently modified while variables such as grain size, organic content and flow are held constant. Responses of new recruits varied as a function of experimental condition. In straight flume trials, the manipulation of ammonium concentration was successful, and within the range of concentrations tested, retention of Mercenaria was significantly reduced at the highest ammonium level. However, retention of Arenicola was uniformly low among all treatments and no significant ammonium response was detected. In annular flume runs, overall ammonium concentrations were higher than in straight flume runs, but were consistent with the intended manipulation. Mercenaria retention was uniformly low, and no differences in retention, as a function of ammonium concentration, were found. However, for Arenicola, significant differences were observed, with highest retention in lower ammonium environments. These results suggest that ammonium, isolated from other cues, plays a significant role in determining recruitment patterns, with variation in recruit responses related to signal strength

An experimental and modeling study of pH and related solutes in an irrigated anoxic coastal sediment

Macrofaunal irrigation is an important process in nearshore sediments, facilitating greater exchange between sediments and seawater and imparting significant lateral heterogeneity to the porewater profiles of many constituents. Like many macrofaunal activities, irrigation is a transient behavior, i.e. tubes and burrows are flushed periodically, at frequencies that generally are species-specific. As a result, transient concentrations within the dwelling arise, potentially impacting gradients, fluxes and reaction rates in the vicinity of the dwelling. We investigated the impact of periodic burrow irrigation on the distribution of several diagenetically important porewater constituents. Laboratory experiments evaluated irrigation periodicity using artificially irrigated tubes embedded in nearshore organic-rich sediments, and microdistributions of oxygen and pH in laboratory experiments were measured with microelectrodes. To help interpret our results, we also constructed a simplified time and space-dependent transport-reaction model for oxygen, pH and sulfide in irrigated sediments. Laboratory results show substantial differences in the pH field of sediments surrounding an irrigated tube as a function of irrigation frequency. Higher pH values, indicative of an overlying water signature, were observed in the vicinity of the tube wall with increasing duration of irrigation. Conversely, oxygen concentrations did not vary significantly with the amount of irrigation, most likely a result of extremely high sediment oxygen demand. Model results are consistent with laboratory findings in predicting differences in the measured variables as a function of irrigation frequency. However, the nature and extent of the model-predicted differences are often at variance with the experimental data. Overall, experimental and modeling results both suggest irrigation periodicity can substantially influence porewater distributions and diagenetic processes in sediments. Future studies should examine the influence of irrigation periodicity on the types and rates of reactions, and the attendant biological features, in the environment encompassing the tube or burrow wall