Bimodal Counting Statistics in Single Electron Tunneling through a Quantum Dot

We explore the full counting statistics of single electron tunneling through a quantum dot using a quantum point contact as non-invasive high bandwidth charge detector. The distribution of counted tunneling events is measured as a function of gate and source-drain-voltage for several consecutive electron numbers on the quantum dot. For certain configurations we observe super-Poissonian statistics for bias voltages at which excited states become accessible. The associated counting distributions interestingly show a bimodal characteristic. Analyzing the time dependence of the number of electron counts we relate this to a slow switching between different electron configurations on the quantum dot

Excitation of Na D-line radiation in collisions of sodium atoms with internally excited H2, D2, and N2

Excitation of D-line radiation in collisions of Na atoms with vibrationally excited N2, H2 and D2 was studied in two modulated crossed beam experiments. In both experiments, the vibrational excitation of the molecules was provided by heating the molecular beam source to temperatures in the range of 2000 to 3000 K, which was assumed to give populations according to the Boltzmann expression. In the first experiment, a total rate coefficient was measured as a function of molecular beam temperature, with absolute calibration of the photon detector being made using the black body radiation from the heated molecular beam source. Since heating affects both the internal energy and the collisional kinetic energy, the first experiment could not determine the relative contributions of internal energy transfer versus collisional excitation. The second experiment achieved partial separation of internal versus kinetic energy transfer effects by using a velocity-selected molecular beam. Using two simple models for the kinetic energy dependence of the transfer cross section for a given change in vibrational quantum number, the data from both experiments were used to determine parameters in the models

Percolation thresholds and fractal dimensions for square and cubic lattices with long-range correlated defects

We study long-range power-law correlated disorder on square and cubic lattices. In particular, we present high-precision results for the percolation thresholds and the fractal dimension of the largest clusters as function of the correlation strength. The correlations are generated using a discrete version of the Fourier filtering method. We consider two different metrics to set the length scales over which the correlations decay, showing that the percolation thresholds are highly sensitive to such system details. By contrast, we verify that the fractal dimension $d_{\rm f}$ is a universal quantity and unaffected by the choice of metric. We also show that for weak correlations, its value coincides with that for the uncorrelated system. In two dimensions we observe a clear increase of the fractal dimension with increasing correlation strength, approaching $d_{\rm f}\rightarrow 2$. The onset of this change does not seem to be determined by the extended Harris criterion.Comment: 12 pages, 8 figure

Scaling laws for random walks in long-range correlated disordered media

We study the scaling laws of diffusion in two-dimensional media with long-range correlated disorder through exact enumeration of random walks. The disordered medium is modelled by percolation clusters with correlations decaying with the distance as a power law, $r^{-a}$, generated with the improved Fourier filtering method. To characterize this type of disorder, we determine the percolation threshold $p_{\text c}$ by investigating cluster-wrapping probabilities. At $p_{\text c}$, we estimate the (sub-diffusive) walk dimension $d_{\text w}$ for different correlation exponents $a$. Above $p_{\text c}$, our results suggest a normal random walk behavior for weak correlations, whereas anomalous diffusion cannot be ruled out in the strongly correlated case, i.e., for small $a$.Comment: 11 pages, 6 figure

A Semiclassical Approach to Level Crossing in Supersymmetric Quantum Mechanics

Much use has been made of the techniques of supersymmetric quantum mechanics (SUSY QM) for studying bound-state problems characterized by a superpotential $\phi(x)$. Under the analytic continuation $\phi(x) \to i\phi(x)$, a pair of superpartner bound-state problems is transformed into a two-state level-crossing problem in the continuum. The description of matter-enhanced neutrino flavor oscillations involves a level-crossing problem. We treat this with the techniques of supersymmetric quantum mechanics. For the benefit of those not familiar with neutrino oscillations and their description, enough details are given to make the rest of the paper understandable. Many other level-crossing problems in physics are of exactly the same form. Particular attention is given to the fact that different semiclassical techniques yield different results. The best result is obtained with a uniform approximation that explicitly recognizes the supersymmetric nature of the system.Comment: 15 pages, Latex with lamuphys and psfig macros. Talk by first Author at the UIC "Supersymmetry and Integrable Models Workshop", Chicago, June 12-14, 1997; proceedings to be published in Springer Lecture Notes in Physics, H. Aratyn et al., eds. This paper also available at http://nucth.physics.wisc.edu/preprint

First record of the reticulated dragonet, Callionymus reticulatus Valenciennes, 1837 (Actinopterygii: Callionymiformes: Callionymidae), from the Balearic Islands, western Mediterranean

The reticulated dragonet, Callionymus reticulatus, was originally described based on a single specimen, the holotype from Malaga, Spain, south-western Mediterranean, probably collected before 1831. The holotype is now disintegrated; the specific characteristics are no longer discernible. The species was subsequently recorded from several north-eastern Atlantic localities (Western Sahara to central Norway), but missing in the Mediterranean. Specimens of C. reticulatus were observed and collected during two cruises in 2014 and 2016 in the Balearic Islands off Mallorca and Menorca. The collected specimens (8 females) have been deposited in the collection of the Hebrew University of Jerusalem (HUJ). All individuals of C. reticulatus were collected from beam trawl samples carried out during the DRAGONSAL0914 in September 2014, and during the MEDITS_ES05_16 bottom trawl survey in June 2016, on shelf and slope bottoms around the Balearic Islands. Both surveys used a ‘Jennings’ beam trawl to sample the epi-benthic communities, which was the main objective of the DRAGONSAL0914 and a complementary objective in the MEDITS_ES05_16. The ‘Jennings’ beam trawl has a 2 m horizontal opening, 0.5 m vertical opening and a 5 mm diamond mesh in the codend. Trawls had duration of 1 to 3 min of effective sampling (bottom time) at a speed of 2 knots. Catches were sorted out to species and standardized abundances of callionymid species (individuals per 500 m2) were obtained by calculating the sampled surface (distance covered × beam trawl horizontal opening). Callionymus reticulatus is recorded from the Balearic Islands for the first time; the specimens are described and illustrated. The new record confirms that the species is still extant in the Mediterranean. A key to Mediterranean callionymid fishes is provided to distinguish C. reticulatus from other species of the family in the area. The callionymid fish fauna of the Mediterranean now comprises 11 species, including three Lessepsian migrants originating from the Red SeaVersión del edito

First record of the Alboran dragonet, Protogrammus alboranensis (Actinopterygii: Callionymiformes: Callionymidae), from the Balearic Islands (western Mediterranean)

The Alboran dragonet, Protogrammus alboranensis Fricke, Ordines, Farias et García-Ruiz, 2016, was originally described based on four specimens from Alboran Island, Spain, south-western Mediterranean, collected in 2014 and 2015. This species was previously considered to be endemic to Alboran Island. A surprising new record of this rare species from the Balearic Islands is reported hereVersión del edito

Smart Medication Disposal: Subcritical Water Oxidation of Pharmaceutical Compounds

Disposal of unused or expired pharmaceuticals is neither safe nor environmentally-friendly. Current regulations for pharmaceutical disposal do not prevent environmental contamination. Industrial methods of disposing of waste medications can generate toxic compounds through incineration, or generate large volumes of waste through use of physical adsorbents. Medium sized providers (pharmacies, small clinics) typically hire expensive hazardous waste removal or dispose of these medications improperly. The project goal is to deliver a safe, sustainable process, suitable for retail pharmacies and the like, for rendering pharmaceuticals chemically inactive. This project encompasses the development of a degradation process via testing of 5 model pharmaceuticals and the design and prototyping of a device. Conceptualization proved challenging as the target market and regulatory landscape continually evolve. The process resulted in total degradation of 3 out of the 5 medicinal compounds at a reaction temperature of 150°C and pressure of 5 atm. Moreover, the team was able to develop a process that degraded these medications with subcritical water oxidation, utilizing microwave technology, allowing for greater safety by eliminating the need for a conduction heating unit, while simultaneously allowing for uniform heating throughout the solution. The process only requires tap-water as an input and coolant, which is inexpensive and ubiquitous. The lack of chemical transformation with 2 out of the 5 compounds indicates that further refinement and development are warranted. This machine will give the user the ability to dispose of medications without the worry of unintentional poisonings, illegal distribution, and environmental contamination.https://scholarscompass.vcu.edu/capstone/1087/thumbnail.jp