Tunneling Spectroscopy of Disordered Two-Dimensional Electron Gas in the Quantum Hall Regime

Recently, Dial et al. presented measurements of the tunneling density of states into the bulk of a two dimensional electron gas under strong magnetic fields. Several high energy features appear in the measured spectrum showing a distinct dependence on filling factor and a unique response to temperature. We present a quantitative account of the observed structure, and argue it results from the repulsive Coulomb interactions between the tunneling electron and states localized at disorder potential wells. The quenching of the kinetic energy by the applied magnetic field leads to an electron addition spectrum that is primarily determined by the external magnetic field and is nearly independent of the disorder potential. Using a Hartree-Fock model we reproduce the salient features of the observed structure

Tunneling Spectroscopy of Disordered Two-Dimensional Electron Gas in the Quantum Hall Regime

The tunneling density of states (TDOS) into a disordered two-dimensional electron gas is calculated in the quantum Hall regime, including electron-electron interactions. Combining general arguments and a detailed Hartree-Fock calculation, it is demonstrated that the quenching of the kinetic energy by the applied magnetic field leads to several universal features, nearly independent of the disorder potential, corresponding to the addition and removal spectrum in the valleys and tips of the disorder potential. These features are manifested as “sashes” in the TDOS spectra, and are in quantitative agreement with recent measurements. It is predicted that more such features will become observable with decreasing potential fluctuations.Physic

Microvalve-Based Tunability of Electrically Driven Ion Transport Through a Microfluidic System with Ion-Exchange Membrane

Microfluidic channels with embedded ion permselective medium under the application of electric current are commonly used for electrokinetic processes as on-chip ion concentration polarization (ICP) and bioparticle preconcentration to enhance biosensing. Herein, we demonstrate the ability to dynamically control the electrically driven ion transport by integrating individually addressable microvalves. The microvalves are located along a main microchannel that is uniformly coated with a thin layer of an ion-exchange membrane (IEM). The interplay of ionic transport between the solution within the microchannel and the thin IEM, under an applied electric current, can be locally tuned by the deformation of the microvalve. This tunability provides a robust and simple means of implementing new functionalities into lab-on-a-chip devices, e.g., dynamic control over multiple ICP layers and their associated preconcentrated molecule plugs, multiplex sensing, suppression of biofouling as well as plug dispersion, while maintaining the well-known application of microvalves as steric filtration

Designing with Iontronic Logic Gates -- From a Single Polyelectrolyte Diode to Small Scale Integration

This article presents the implementation of on-chip iontronic circuits via small-scale integration of multiple ionic logic gates made of bi-polar polyelectrolyte diodes. These ionic circuits are analogous to solid-state electronic circuits, with ions as the charge carriers instead of electrons/holes. We experimentally characterize the responses of a single fluidic diode made of a junction of oppositely charged polyelectrolytes (i.e., anion and cation exchange membranes), with a similar underlying mechanism as a solid-state p- and n-type junction. This served to carry out pre-designed logical computations in various architectures by integrating multiple diode-based logic gates, where the electrical signal between the integrated gates was transmitted entirely through ions. The findings shed light on the limitations affecting the number of logic gates that can be integrated, the degradation of the electrical signal, their transient response, and the design rules that can improve the performance of iontronic circuits

Slow oscillations in neural networks with facilitating synapses

The synchronous oscillatory activity characterizing many neurons in a network is often considered to be a mechanism for representing, binding, conveying, and organizing information. A number of models have been proposed to explain high-frequency oscillations, but the mechanisms that underlie slow oscillations are still unclear. Here, we show by means of analytical solutions and simulations that facilitating excitatory (E f) synapses onto interneurons in a neural network play a fundamental role, not only in shaping the frequency of slow oscillations, but also in determining the form of the up and down states observed in electrophysiological measurements. Short time constants and strong E f synapse-connectivity were found to induce rapid alternations between up and down states, whereas long time constants and weak E f synapse connectivity prolonged the time between up states and increased the up state duration. These results suggest a novel role for facilitating excitatory synapses onto interneurons in controlling the form and frequency of slow oscillations in neuronal circuit

Coupled sulfur and oxygen isotope insight into bacterial sulfate reduction in the natural environment

We present new sulfur and oxygen isotope data in sulfate (δ34SSO4 and δ18OSO4 respectively), from globally distributed marine and estuary pore fluids. We use this data with a model of the biochemical steps involved in bacterial sulfate reduction (BSR) to explore how the slope on a δ18OSO4 vs. δ34SSO4 plot relates to the net sulfate reduction rate (nSRR) across a diverse range of natural environments. Our data demonstrate a correlation between the nSRR and the slope of the relative evolution of oxygen and sulfur isotopes (δ18OSO4 vs. δ34SSO4) in the residual sulfate pool, such that higher nSRR results in a lower slope (sulfur isotopes increase faster relative to oxygen isotopes). We combine these results with previously published literature data to show that this correlation scales over many orders of magnitude of nSRR. Our model of the mechanism of BSR indicates that the critical parameter for the relative evolution of oxygen and sulfur isotopes in sulfate during BSR in natural environments is the rate of intracellular sulfite oxidation. In environments where sulfate reduction is fast, such as estuaries and marginal marine environments, this sulfite reoxidation is minimal, and the δ18OSO4 increases more slowly relative to the δ34SSO4. In contrast, in environments where sulfate reduction is very slow, such as deep sea sediments, our model suggests sulfite reoxidation is far more extensive, with as much as 99% of the sulfate being thus recycled; in these environments the δ18OSO4 increases much more rapidly relative to the δ34SSO4. We speculate that the recycling of sulfite plays a physiological role during BSR, helping maintain microbial activity where the availability of the electron donor (e.g. available organic matter) is low

White Blood Cell Count and the Risk for Coronary Artery Disease in Young Adults

Background: The association between white blood cell (WBC) count and coronary artery disease (CAD) is unknown in young adults. Our objective was to assess the association between WBC count and its changes over time with CAD incidence in the Metabolic, Life-style and Nutrition Assessment in Young adults (MELANY) study, a cohort of Israeli army personnel. Methods and Findings 29,120 apparently healthy young men (mean age; 31.2±5.5 years) with a normal baseline WBC count (3,000–12,000 cells/mm3) were followed during a mean follow up of 7.5±3.8 years for incidence of CAD. Participants were screened every 3–5 years using a stress test, and CAD was confirmed by coronary angiography. In a multivariate model adjusted for age, body mass index (BMI), LDL- and HDL-cholesterol, blood pressure, family history of CAD, physical activity, diabetes, triglycerides and smoking status, WBC levels (divided to quintiles) above 6,900 cells/mm3 (quintile 4) were associated with a 2.17-fold increase (95%CI = 1.18–3.97) in the risk for CAD as compared with men in quintile 1 (WBC≤5,400 cells/mm3). When modeled as a continuous variable, a WBC increment of 1000 cells/mm3 was associated with a 17.4% increase in CAD risk (HR 1.174; 95%CI = 1.067–1.290, p = 0.001). A decrease in the WBC level (within the normal range) during the follow-up period was associated with increased physical activity and decreased triglyceride levels as well as with reduced incidence of CAD. Conclusions: WBC count is an independent risk factor for CAD in young adults at values well within the normal range. WBC count may assist in detecting subgroups of young men at either low or high risk for progression to CAD

White Blood Cells Count and Incidence of Type 2 Diabetes in Young Men

OBJECTIVE Association between white blood cell (WBC) count and diabetes risk has been recently suggested. We assessed whether WBC count is an independent risk factor for diabetes incidence among young healthy adults. RESEARCH DESIGN AND METHODS WBC count was measured in 24,897 young (mean age 30.8 ± 5.36 years), normoglycemic men with WBC range of 3,000 to 12,000 cells/mm3. Participants were periodically screened for diabetes during a mean follow-up of 7.5 years. RESULTS During 185,354 person-years of follow-up, diabetes was diagnosed in 447 subjects. A multivariate model adjusted for age, BMI, family history of diabetes, physical activity, and fasting glucose and triglyceride levels revealed a 7.6% increase in incident diabetes for every increment of 1,000 cells/mm3 (P = 0.046). When grouped in quintiles, a baseline WBC count above 6,900 cells/mm3 had an independent 52% increase in diabetes risk (hazard ratio 1.52 [95% CI 1.06–2.18]) compared with the lowest quintile (WBC <5,400 cells/mm3). Men at the lowest WBC quintile were protected from diabetes incidence even in the presence of overweight, family history of diabetes, or elevated triglyceride levels. After simultaneous control for risk factors, BMI was the primary contributor of the variation in multivariate models (P < 0.001), followed by age and WBC count (P < 0.001), and family history of diabetes and triglyceride levels (P = 0.12). CONCLUSIONS WBC count, a commonly used and widely available test, is an independent risk factor for diabetes in young men at values well within the normal range