Time Span Of Hours Research Articles

Ultrasmall CsPbBr3 Blue Emissive Perovskite Quantum Dots Using K-Alloyed Cs4PbBr6 Nanocrystals as Precursors.

We report a colloidal synthesis of blue emissive, stable cube-shaped CsPbBr3 quantum dots (QDs) in the strong quantum confinement regime via dissolution-recrystallization starting from pre-syntesized (K x Cs1-x )4PbBr6 nanocrystals which are then reacted with PbBr2. This is markedly different from the known case of Cs4PbBr6 nanocrystals that react within seconds with PbBr2 and get transformed into much larger, green emitting CsPbBr3 nanocrystals. Here, instead, the conversion of (K x Cs1-x )4PbBr6 nanocrystals to CsPbBr3 QDs occurs in a time span of hours, and tuning of the QD size is achieved by adjusting the concentration of the precursors. The QDs exhibit excitonic features in optical absorption that are tunable in the 420-452 nm range, accompanied by blue photoluminescence with quantum yield around 60%. Detailed spectroscopic investigations in both the single and multiexciton regime reveal the exciton fine structure and the effect of Auger recombination of these CsPbBr3 QDs, confirming theoretical predictions for this system.

Characteristics and stability of sensorimotor activity driven by isolated-muscle group activation in a human with tetraplegia

Understanding the cortical representations of movements and their stability can shed light on improved brain-machine interface (BMI) approaches to decode these representations without frequent recalibration. Here, we characterize the spatial organization (somatotopy) and stability of the bilateral sensorimotor map of forearm muscles in an incomplete-high spinal-cord injury study participant implanted bilaterally in the primary motor and sensory cortices with Utah microelectrode arrays (MEAs). We built representation maps by recording bilateral multiunit activity (MUA) and surface electromyography (EMG) as the participant executed voluntary contractions of the extensor carpi radialis (ECR), and attempted motions in the flexor carpi radialis (FCR), which was paralytic. To assess stability, we repeatedly mapped and compared left- and right-wrist-extensor-related activity throughout several sessions, comparing somatotopy of active electrodes, as well as neural signals both at the within-electrode (multiunit) and cross-electrode (network) levels. Wrist motions showed significant activation in motor and sensory cortical electrodes. Within electrodes, firing strength stability diminished as the time increased between consecutive measurements (hours within a session, or days across sessions), with higher stability observed in sensory cortex than in motor, and in the contralateral hemisphere than in the ipsilateral. However, we observed no differences at network level, and no evidence of decoding instabilities for wrist EMG, either across timespans of hours or days, or across recording area. While map stability differs between brain area and hemisphere at multiunit/electrode level, these differences are nullified at ensemble level.

Quantifying the Precipitation Loss of Radiation Belt Electrons During a Rapid Dropout Event

AbstractRelativistic electron flux in the radiation belt can drop by orders of magnitude within the timespan of hours. In this study, we used the drift‐diffusion model that includes azimuthal drift and pitch angle diffusion of electrons to simulate low‐altitude electron distribution observed by POES/MetOp satellites for rapid radiation belt electron dropout event occurring on 1 May 2013. The event shows fast dropout of MeV energy electrons at L > 4 over a few hours, observed by the Van Allen Probes mission. By simulating the electron distributions observed by multiple POES satellites, we resolve the precipitation loss with both high spatial and temporal resolutions and a range of energies. We estimate the pitch angle diffusion coefficients as a function of energy, pitch angle, and L‐shell and calculate corresponding electron lifetimes during the event. The simulation results show fast electron precipitation loss at L > 4 during the electron dropout, with estimated electron lifetimes on the order of half an hour for MeV energies. The electron loss rate shows strong energy dependence with faster loss at higher energies, which suggest that this dropout event is dominated by quick and localized scattering process that prefers higher energy electrons. The improved temporal and spatial resolutions of electron precipitation rates provided by multiple low‐altitude observations can resolve fast‐varying electron loss during rapid electron dropouts (over a few hours), which occur too fast for a single low‐altitude satellite. The capability of estimating the fast‐varying electron lifetimes during rapid dropout events is an important step in improving radiation belt model accuracy.

Simvastatin Rapidly and Reversibly Inhibits Insulin Secretion in Intact Single-Islet Cultures.

IntroductionEpidemiological studies suggest that statins may promote the development or exacerbation of diabetes, but whether this occurs through inhibition of insulin secretion is unclear. This lack of understanding is partly due to the cellular models used to explore this phenomenon (cell lines or pooled islets), which are non-physiologic and have limited clinical transferability.MethodsHere, we study the effect of simvastatin on insulin secretion using single-islet cultures, an optimal compromise between biological observability and physiologic fidelity. We develop and validate a microfluidic device to study single-islet function ex vivo, which allows for switching between media of different compositions with a resolution of seconds. In parallel, fluorescence imaging provides real-time analysis of the membrane voltage potential, cytosolic Ca2+ dynamics, and insulin release during perfusion under 3 or 11 mM glucose.ResultsWe found that simvastatin reversibly inhibits insulin secretion, even in high-glucose. This phenomenon is very rapid (<60 s), occurs without affecting Ca2+ concentrations, and is likely unrelated to cholesterol biosynthesis and protein isoprenylation, which occur on a time span of hours.ConclusionsOur data provide the first real-time live demonstration that a statin inhibits insulin secretion in intact islets and that single islets respond differently from cell lines on a short time scale.FundingUniversity of Padova, EASD Foundation.Electronic supplementary materialThe online version of this article (doi:10.1007/s13300-016-0210-y) contains supplementary material, which is available to authorized users.

Boolean Modeling Reveals the Necessity of Transcriptional Regulation for Bistability in PC12 Cell Differentiation.

The nerve growth factor NGF has been shown to cause cell fate decisions toward either differentiation or proliferation depending on the relative activity of downstream pERK, pAKT, or pJNK signaling. However, how these protein signals are translated into and fed back from transcriptional activity to complete cellular differentiation over a time span of hours to days is still an open question. Comparing the time-resolved transcriptome response of NGF- or EGF-stimulated PC12 cells over 24 h in combination with protein and phenotype data we inferred a dynamic Boolean model capturing the temporal sequence of protein signaling, transcriptional response and subsequent autocrine feedback. Network topology was optimized by fitting the model to time-resolved transcriptome data under MEK, PI3K, or JNK inhibition. The integrated model confirmed the parallel use of MAPK/ERK, PI3K/AKT, and JNK/JUN for PC12 cell differentiation. Redundancy of cell signaling is demonstrated from the inhibition of the different MAPK pathways. As suggested in silico and confirmed in vitro, differentiation was substantially suppressed under JNK inhibition, yet delayed only under MEK/ERK inhibition. Most importantly, we found that positive transcriptional feedback induces bistability in the cell fate switch. De novo gene expression was necessary to activate autocrine feedback that caused Urokinase-Type Plasminogen Activator (uPA) Receptor signaling to perpetuate the MAPK activity, finally resulting in the expression of late, differentiation related genes. Thus, the cellular decision toward differentiation depends on the establishment of a transcriptome-induced positive feedback between protein signaling and gene expression thereby constituting a robust control between proliferation and differentiation.

CoRE: Cooperative End-to-End Traffic Redundancy Elimination for Reducing Cloud Bandwidth Cost

The pay-as-you-go service model impels cloud customers to reduce the usage cost of bandwidth. Traffic Redundancy Elimination (TRE) has been shown to be an effective solution for reducing bandwidth costs, and thus has recently captured significant attention in the cloud environment. By studying the TRE techniques in a trace driven approach, we found that both short-term (time span of seconds) and long-term (time span of hours or days) data redundancy can concurrently appear in the traffic, and solely using either sender-based TRE or receiver-based TRE cannot simultaneously capture both types of traffic redundancy. Also, the efficiency of existing receiver-based TRE solution is susceptible to the data changes compared to the historical data in the cache. In this paper, we propose a Cooperative end-to-end TRE solution (CoRE) that can detect and remove both short-term and long-term redundancy through a two-layer TRE design with cooperative operations between layers. An adaptive prediction algorithm is further proposed to improve TRE efficiency through dynamically adjusting the prediction window size based on the hit ratio of historical predictions. Besides, we enhance CoRE to adapt to different traffic redundancy characteristics of cloud applications to improve its operation cost. Extensive evaluation with several real traces show that CoRE is capable of effectively identifying both short-term and long-term redundancy with low additional cost while ensuring TRE efficiency from data changes.

Investigation of Electron Transfer Properties of the SEI on Metallic Lithium Electrodes by SECM at Open Circuit

The electron transfer at metallic lithium was characterized using the feedback mode of scanning electrochemical microscopy (SECM) and 2,5-di-tert-butyl-1,4-dimethoxybenzene (DBDMB) as redox mediator at open circuit. As a result the solid electrolyte interphase (SEI) at Li is not passivating towards DBDMB as redox mediator. In comparison to charged graphite composite electrodes, the electron transfer rate is smaller at Li and the ranges for the electron transfer rates at both electrodes overlap. Both, graphite composite and Li electrodes show a local variation of electron transfer rates and temporal changes within a time span of hours. In addition, significant short term changes of SEI passivity occur at both electrodes. However, the frequency of such events is smaller for metallic Li then on graphite.

Comparison of Electron Transfer Properties of the SEI on Graphite Composite and Metallic Lithium Electrodes by SECM at OCP

The passivating properties of solid electrolyte interphases (SEI) at metallic lithium were characterized using the feedback mode of scanning electrochemical microscopy (SECM) and 2,5-di-tert-butyl-1,4-dimethoxybenzene (DBDMB) as redox mediator at OCP. The SEI at Li allows electron transfer toward DBDMB with finite rate. In comparison to charged graphite composite electrodes, the electron transfer rate tends to be smaller at Li. Both, graphite composite and Li electrodes, show a local variation of electron transfer rates and temporal changes within a time span of hours. The long-term changes of SEI passivity at metallic Li are dependent on the solvents in the liquid electrolyte. In addition, significant short-term changes of SEI passivity occur at both electrodes. However, the frequency of such events is smaller for metallic Li compared to graphite. A strong decrease of SEI passivity and a strong increase of fluctuations in the passivating properties are observed when the microelectrode mechanically touches the metallic Li and damages the SEI. The changes of SEI passivity by a mechanical touch are orders of magnitude larger compared to spontaneous changes. A local SEI damage by the microelectrode decreases not only the SEI passivity locally, but also a few hundreds of μm apart.

Orbital mechanics about small bodies

Small solar system bodies such as asteroids and comets are of significant interest for both scientific and human exploration missions. However, their orbital environments are among the most highly perturbed and extreme environments found in the solar system. Uncontrolled trajectories are highly unstable in general and may either impact or escape in timespans of hours to days. Even with active control, the chaotic nature of motion about these bodies can effectively randomize a trajectory within a few orbits, creating fundamental difficulties for the navigation of spacecraft in these environments. In response to these challenges our research has identified robust and stable orbit solutions and mission designs across the whole range of small body sizes and spin states that are of interest for scientific and human exploration. This talk will describe the challenges of exploring small bodies and present the practical solutions that have been discovered which enable their exploration across the range of small body types and sizes.

Variable sediment oxygen uptake in response to dynamic forcing

Seiche‐induced turbulence and the vertical distribution of dissolved oxygen above and within the sediment were analyzed to evaluate the sediment oxygen uptake rate (JO2), diffusive boundary layer thickness (δDBL), and sediment oxic zone depth (zmax) in situ. High temporal‐resolution microprofiles across the sediment‐water interface and current velocity data within the bottom boundary layer in a medium‐sized mesotrophic lake were obtained during a 12‐h field study. We resolved the dynamic forcing of a full 8‐h seiche cycle and evaluated JO2 from both sides of the sediment‐water interface. Turbulence (characterized by the energy dissipation rate, ε), the vertical distribution of dissolved oxygen across the sediment‐water interface (characterized by δDBL and zmax), JO2, and the sediment oxygen consumption rate (RO2) are all strongly correlated in our freshwater system. Seiche‐induced turbulence shifted from relatively active (ε = 1.2 × 10−8 W kg−1) to inactive (ε = 7.8 × 10−12 W kg−1). In response to this dynamic forcing, δDBL increased from 1.0 mm to the point of becoming undefined, zmax decreased from 2.2 to 0.3 mm as oxygen was depleted from the sediment, and JO2 decreased from 7.0 to 1.1 mmol m−2 d−1 over a time span of hours. JO2 and oxygen consumption were found to be almost equivalent (within ~ 5% and thus close to steady state), with RO2 adjusting rapidly to changes in JO2. Our results reveal the transient nature of sediment oxygen uptake and the importance of accurately characterizing turbulence when estimating JO2.

Influence of combustion conditions on the PCDD/F-, PCB-, PCBz- and PAH-concentrations in the post-combustion chamber of a waste incineration pilot plant

Experiments at a pilot scale waste incinerator (0.5 MW thermal power) showed that the conditions in the post-combustion chamber (650–900°C) are strongly influencing the formation of chlorinated and non-chlorinated aromatics. Non-optimal combustion conditions resulted in increased concentrations of mono- to trichlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF) and polycyclic aromatic hydrocarbons (PAH), while chlorinated benzenes (PCBz), polychlorinated biphenyls (PCB) and the higher chlorinated PCDD/F are only weakly affected or even decrease. The changes in concentration of the compounds investigated over a time span of hours gave hints on `memory effects' in this combustion zone. For mono- and dichlorinated benzenes, a high correlation (r2=0.80) with the international toxicity equivalent (I-TEQ) value of PCDD/F was observed. As recently has been demonstrated, this correlation can be utilized for an indirect on-line measurement of the I-TEQ by a novel laser mass spectrometric technique (REMPI–TOFMS).

Application of Optical-Fibre Temperature Logging (DTS) in Monitoring Subsurface Transient Temperature Changes Resulting from Fluid Flow: ABSTRACT

The DTS technique is a temperature sensing method that recently was tested successfully in boreholes of the North American Midcontinent (Kansas). The method is based on the Raman effect of the backscattering of light along an optical fibre and allows the measurement of temperature instantaneously over the entire length of the cable by real-time surface data readout. Consequently, temperature changes resulting from transient effects can be monitored for a long time because the DTS cable can be left in place and temperatures are not affected by lowering of a probe. Here, we report the results from a fluid-flow experiment in a borehole that was logged previously under thermal equilibrium conditions, in which fluid flow was stimulated by inputting of 520 gallons (about 2000 liter) of water heated to a temperature of 120{degrees}F (48.9{degrees}C). Through temperature monitoring in minute intervals over a time span of hours, the elevated watertable was observed until recovered to static conditions, thus allowing a determination of the rate of stimulated fluid flow (5 liter/minute) into the carbonate aquifer at the bottom of the well. The monitoring shows the cooling of the hot water remaining in the uppermost part of the water column while temperatures below themore » cold/warm water interface decrease because of active down-hole water flow. The experiment clearly indicates the potential of the technique to monitor subsurface temperature changes, for example in connection with natural or artificially stimulated fluid-flow conditions in oil and gas reservoirs undergoing secondary or tertiary recovery.« less

A Skin-Stretching Device for the Harnessing of the Viscoelastic Properties of Skin

A skin-stretching device that is designed to harness the viscoelastic properties of the skin using incremental traction is presented as an addition to the surgeon's armamentarium. It has proved to be of value in helping to close problematic areas of skin shortage which would otherwise have required more complicated procedures for their solution. It is simple in application and can even be put to use at the bedside. It consists of two pins that are threaded through the dermis of the wound margins on either side of the defect and which are in turn engaged by the hooks of the stretching device. The stretching force on the skin margins is spread over a wide area, thus preventing damage to the skin itself that individual hooks applied to the skin might cause. The device is employed over a duration of 20 to 30 minutes to 1 to 3 days depending on the condition of the skin adjoining the defect. The device can be applied over three different periods of time: (1) preoperatively (presuturing), lasting 1 to 2 days, (2) intraoperatively, extending over a period of 20 to 30 minutes, and (3) postoperatively (or delayed), which takes place over a time span of hours to 1 to 3 days. Five illustrative cases are presented.

Earthquake precursors

Abstract An analysis of existing earthquake precursor data leads to a conclusion that the precursors reported so far can be classified into three types, i.e., A1, A2 and B types. Most of type B precursors, observed in terms of anomalous tilts and strains or foreshocks, have no magnitude-dependent precursor time. Meanwhile the A2-type precursors observed by means of geodetic work, changes in seismic-wave velocities and the like seem to have a precursor time which is closely correlated to the magnitude of coming earthquakes. A precursor of this type may possibly be interpreted by the current theory of dilatancy. The A1-type precursors, observed mostly several hours prior to the main shock, may be caused by a creep-like failure before the main rupture of the Earth's crust. Probabilities for an anomalous signal of various geophysical elements to be related to a forthcoming earthquake are estimated on the basis of the existing data of precursors. A feasible strategy for predicting a large earthquake as suggested by the present study will be as follows: First of all, we monitor accumulation of crustal strain by means of geodetic work. The next task is to detect an A2 signal which would arise from a highly strained crust sooner or later. If the spatial extent of the A2-type precursor is known, it is possible to estimate roughly the magnitude as well as the occurrence time of the coming earthquake. Finally, detection of an A1-type precursor, if it should occur, would provide a short-range forecast having a time span of hours.