Determination of Silicon Electrical Properties Using First Principles Approach

Silicon nanowires have attracted attention as basis for reconfigurable electronics. However, as the size decreases, the electronic properties of the nanowires vary as a result of confinement, strain and crystal topology effects. Thus, at the thin diameter regime the band gap of Silicon nanowires can no longer be derived from a simple extrapolation of the isotropic bulk behaviour. This study compares band gap parameters in sub 10nm nanowires obtained from first-principles density-functional band structure calculations with extrapolations using continuum theory in order to rationalize the changes of the overall conductance, resistance and band gap. The device consists of silicon nanowire of size between 1 nm to 6nm. The results indicate an increase of, both the energy gap and the resistance along with reduced conductivity for the thinnest wires and a dependence on the crystal orientation with gaps reaching up to 4.3 eV along <111>, 4.0 eV along <110>, and 3.7 along <100>.

Cadmium and zinc uptake by dried activated sludge: Equilibrium and experimental design study

Removal of Cd2+ and Zn2+ ions from single and binary solutions by dried activated sludge was studied in batch experiments. It was shown that the metal removal is a rapid process significantly influenced by solution pH. Maximum uptake of both Cd and Zn was reached at pH 6.0 and negligible uptake was observed at pH 2.0. The Langmuir isotherm was found to well represent the measured equilibrium sorption data in single metal systems and the maximum sorption capacities Qmax of the activated sludge (d.w.), calculated from Langmuir model were 540 ± 16 μmol/g for Zn2+ and 510 ± 17 μmol/g for Cd2+ ions. The Response surface methodology (RSM) was used for investigation of interaction and competitive effects in binary metal system. It was found that dried activated sludge in binary system Cd-Zn has slightly higher affinity for Cd2+ comparing with Zn2+ ions. Competitive effect of Cd on Zn uptake increased with increasing solution pH and Cd initial concentration. Maximum sorption capacities of the activated sludge were 321 μmol Cd2+/g and 312 μmol Zn2+/g. RSM appears to be a better tool for the evaluation of interaction and competitive effects in binary systems than both the simple extrapolation from single-component systems and experimentally difficult study of multi-component systems.

Dark extinction: the problem of unknown historical extinctions

The extinction of species before they are discovered and named (dark extinction, DE) is widely inferred as a significant part of species loss in the ‘pre-taxonomic’ period (approx. 1500–1800 CE) and, to some extent, in the ‘taxonomic period’ (approx. 1800–present) as well. The discovery of oceanic islands and other pristine habitats by European navigators and the consequent introduction of destructive mammals, such as rats and goats, started a process of anthropogenic extinction. Much ecosystem change happened before systematic scientific recording, so has led to DE. Statistical methods are available to robustly estimate DE in the ‘taxonomic period’. For the ‘pre-taxonomic period’, simple extrapolation can be used. The application of these techniques to world birds, for example, suggests that approximately 56 DEs occurred in the ‘taxonomic period’ (1800–present) and approximately 180 in the ‘pre-taxonomic period’ (1500–1800). Targeting collection activities in extinction hotspots, to make sure organisms are represented in collections before their extinction, is one way of reducing the number of extinct species without a physical record (providing that collection efforts do not themselves contribute to species extinction).

A minimal space interferometer configuration for imaging at low radio frequencies

The radio sky at lower frequencies, particularly below 20 MHz, is expected to be a combination of increasingly bright non-thermal emission and significant absorption from intervening thermal plasma. The sky maps at these frequencies cannot therefore be obtained by simple extrapolation of those at higher frequencies. However, due to severe constraints in ground-based observations, this spectral window still remains greatly unexplored. In this paper, we propose and study, through simulations, a novel minimal configuration for a space interferometer system which would enable imaging of the radio sky at frequencies well below 20 MHz with angular resolutions comparable to those achieved at higher radio frequencies in ground-based observations by using the aperture synthesis technique. The minimal configuration consists of three apertures aboard Low Earth Orbit (LEO) satellites orbiting the Earth in mutually orthogonal orbits. Orbital periods for the satellites are deliberately chosen to differ from each other so as to obtain maximum (u,v) coverage in short time spans with baselines greater than 15 000 km, thus, giving us angular resolutions finer than 10 arcsec even at these low frequencies. The sensitivity of the (u,v) coverage is assessed by varying the orbit and the initial phase of the satellites. We discuss the results obtained from these simulations and highlight the advantages of such a system.

Characterization of water-based liquid scintillator for Cherenkov and scintillation separation

This paper presents measurements of the scintillation light yield and time profile for a number of concentrations of water-based liquid scintillator, formulated from linear alkylbenzene (LAB) and 2,5-diphenyloxazole (PPO). We find that the scintillation light yield is linear with the concentration of liquid scintillator in water between 1 and 10% with a slope of $$127.9\pm 17.0$$ 127.9 ± 17.0 ph/MeV/concentration and an intercept value of $$108.3\pm 51.0$$ 108.3 ± 51.0 ph/MeV, the latter being illustrative of non-linearities with concentration at values less than 1%. This is larger than expected from a simple extrapolation of the pure liquid scintillator light yield. The measured time profiles are consistently faster than that of pure liquid scintillator, with rise times less than 250 ps and prompt decay constants in the range of 2.1–2.85 ns. Additionally, the separation between Cherenkov and scintillation light is quantified using cosmic muons in the CHESS experiment for each formulation, demonstrating an improvement in separation at the centimeter scale. Finally, we briefly discuss the prospects for large-scale detectors.

On the eccentricity evolution of massive black hole binaries in stellar backgrounds

ABSTRACT We study the dynamical evolution of eccentric massive black hole binaries (MBHBs) interacting with unbound stars by means of an extensive set of three-body scattering experiments. Compared to previous studies, we extend the investigation down to a MBHB mass ratio of q = m2/m1 = 10−4, where m1 and m2 are the masses of the primary and secondary hole, respectively. Contrary to a simple extrapolation from higher mass ratios, we find that for q ≲ 10−3 the eccentricity growth rate becomes negative, i.e. the binary circularizes as it shrinks. This behaviour is due to the subset of interacting stars captured in metastable counter-rotating orbits; those stars tend to extract angular momentum from the binary, promoting eccentricity growth for q &gt; 10−3, but tend to inject angular momentum into the binary driving it towards circularization for q &lt; 10−3. The physical origin of this behaviour requires a detailed study of the orbits of this subset of stars and is currently under investigation. Our findings might have important consequences for intermediate massive black holes (IMBHs) inspiralling on to MBHs (e.g. a putative $10^3\,\rm M_{\odot }$ black hole inspiralling on to Sgr A*).

A search for Centaurus A-like features in the spectra of Fermi-LAT detected radio galaxies

ABSTRACT Motivated by the detection of a hardening in the γ-ray spectrum of the radio galaxy Centaurus A, we have analysed $\mathord {\sim }10$ yr of Fermi-Large Area Telescope (LAT) observations of 26 radio galaxies to search for similar spectral features. We find that the majority of the radio galaxies’ γ-ray spectral energy distributions are best fitted with a simple power-law model, and no spectral hardening similar to that found in Centaurus A was detected. We show that, had there been any such spectral features present in our sample of radio galaxies, they would have been seen, but note that seven of the radio galaxies (3C 111, 3C 120, 3C 264, IC 4516, NGC 1218, NGC 2892, and PKS 0625−35) show evidence for flux variability on 6-month time-scales, which makes the detection of any steady spectral features difficult. We find a strong positive correlation (r = 0.9) between the core radio power at 5 GHz and the γ-ray luminosity and, using a simple extrapolation to TeV energies, we expect around half of the radio galaxies studied will be detectable with the forthcoming Cherenkov Telescope Array.