1,871 research outputs found
Ultraviolet-laser induced desorption of NO from the Cr<sub>2</sub>O<sub>3</sub>(0001) surface: Involvement of a precursor state?
NO molecules interact with the Cr2O3(0001) surface to form a chemisorption bond of 1.0 eV. At higher coverages an additional more weakly bound species appears in thermal desorption spectra with a binding energy of 0.35 eV. By infrared spectroscopy the weakly adsorbed species is identified to be an unusually strong bound NO-dimer exhibiting a weak feature at 1857 cm−1 beside the chemisorbate absorption band at 1794 cm−1. Laser induced desorption experiments performed at 6.4 eV are presented with main emphasis on the high coverage regime. The desorbing molecules are detected quantum state selectively using resonance enhanced multiphoton ionization. The desorbing molecules are strongly rotationally and vibrationally excited conform with a nonthermal excitation process. The velocity distributions of single rovibronic states of desorbing NO are bimodal and exhibit a strong coupling of rotation and translation. With increasing coverages an additional channel is observed appearing in the time-of-flight spectra of ν“=0 as smoothly increasing intensity at long flight times. The numeric values of these unusually long flight times are indicative for long residence times on the surface rather than small kinetic energies. The desorption efficiencies weakly depend on the concentration and vibrational state ranging from (2.0±0.3)x10−17cm2 at low coverages to (1.0±0.4)x10−17cm2 at high coverages for ν“=0. The intensity of the desorption signal per laser pulse only increases proportional to the chemisorbate coverage. The data are interpreted assuming the dimers to act as extrinsic precursors within the desorption process
Accounting for Dilution of SARS-CoV-2 in Wastewater Samples Using Physico-Chemical Markers
Most sewer networks collect domestic wastewater and a variable proportion of extraneous water, such as rainwater, through surface runoff and industrial discharges. Accounting for wastewater dilution is essential to properly quantify wastewater particle loads, whether these are molecular fragments of SARS-CoV-2, or other substances of interest such as illicit drugs or microplastics. This paper presents a novel method for obtaining real-time estimates of wastewater dilution and total daily volume through wastewater treatment works, namely when flow data is not available or unreliable. The approach considers the levels of several physico-chemical markers (ammonia, electrical conductivity, and orthophosphate) in the wastewater against their dry-weather levels. Using high-resolution data from the national Wastewater Surveillance Programme of Wales, we illustrate how the method is robust to spikes in markers and can recover peaks in wastewater flow measurements that may have been capped by hydraulic relief valves. We show the method proves effective in normalising SARS-CoV-2 viral loads in wastewater samples and discuss other applications for this method, looking at wastewater surveillance as a vital tool to monitor both human and environmental health
Nature of 45 degree vortex lattice reorientation in tetragonal superconductors
The transformation of the vortex lattice in a tetragonal superconductor which
consists of its 45 degree reorientation relative to the crystal axes is studied
using the nonlocal London model. It is shown that the reorientation occurs as
two successive second order (continuous) phase transitions. The transition
magnetic fields are calculated for a range of parameters relevant for
borocarbide superconductors in which the reorientation has been observed
Graphene-based photovoltaic cells for near-field thermal energy conversion
Thermophotovoltaic devices are energy-conversion systems generating an
electric current from the thermal photons radiated by a hot body. In far field,
the efficiency of these systems is limited by the thermodynamic
Schockley-Queisser limit corresponding to the case where the source is a black
body. On the other hand, in near field, the heat flux which can be transferred
to a photovoltaic cell can be several orders of magnitude larger because of the
contribution of evanescent photons. This is particularly true when the source
supports surface polaritons. Unfortunately, in the infrared where these systems
operate, the mismatch between the surface-mode frequency and the semiconductor
gap reduces drastically the potential of this technology. Here we show that
graphene-based hybrid photovoltaic cells can significantly enhance the
generated power paving the way to a promising technology for an intensive
production of electricity from waste heat.Comment: 5 pages, 4 figure
'Reclaiming the criminal' : the role and training of prison officers in England, 1877-1914
This article examines the role and training of prison officers in England, between 1877 and 1914. It is concerned with the changing penal philosophies and practices of this period and how these were implemented in local prisons, and the duties of the prison officer. More broadly, this article argues that the role of the prison officer and their training (from 1896) reflect wider ambiguities in prison policy and practice during this period
Actors and networks or agents and structures: towards a realist view of information systems
Actor-network theory (ANT) has achieved a measure of popularity in the analysis of information systems. This paper looks at ANT from the perspective of the social realism of Margaret Archer. It argues that the main issue with ANT from a realist perspective is its adoption of a `flat' ontology, particularly with regard to human beings. It explores the value of incorporating concepts from ANT into a social realist approach, but argues that the latter offers a more productive way of approaching information systems
Sobolev spaces on non-Lipschitz subsets of Rn with application to boundary integral equations on fractal screens
We study properties of the classical fractional Sobolev spaces on non-Lipschitz subsets of Rn. We investigate the extent to which the properties of these spaces, and the relations between them, that hold in the well-studied case of a Lipschitz open set, generalise to non-Lipschitz cases. Our motivation is to develop the functional analytic framework in which to formulate and analyse integral equations on non-Lipschitz sets. In particular we consider an application to boundary integral equations for wave scattering by planar screens that are non-Lipschitz, including cases where the screen is fractal or has fractal boundary
Computing Fresnel integrals via modified trapezium rules
In this paper we propose methods for computing Fresnel integrals based on truncated trapezium rule approximations to integrals on the real line, these trapezium rules modified to take into account poles of the integrand near the real axis. Our starting point is a method for computation of the error function of complex argument due to Matta and Reichel (J Math Phys 34:298–307, 1956) and Hunter and Regan (Math Comp 26:539–541, 1972). We construct approximations which we prove are exponentially convergent as a function of N , the number of quadrature points, obtaining explicit error bounds which show that accuracies of 10−15 uniformly on the real line are achieved with N=12 , this confirmed by computations. The approximations we obtain are attractive, additionally, in that they maintain small relative errors for small and large argument, are analytic on the real axis (echoing the analyticity of the Fresnel integrals), and are straightforward to implement
Dissipative Electron Transport through Andreev Interferometers
We consider the conductance of an Andreev interferometer, i.e., a hybrid
structure where a dissipative current flows through a mesoscopic normal (N)
sample in contact with two superconducting (S) "mirrors". Giant conductance
oscillations are predicted if the superconducting phase difference is
varied. Conductance maxima appear when is on odd multiple of due
to a bunching at the Fermi energy of quasiparticle energy levels formed by
Andreev reflections at the N-S boundaries. For a ballistic normal sample the
oscillation amplitude is giant and proportional to the number of open
transverse modes. We estimate using both analytical and numerical methods how
scattering and mode mixing --- which tend to lift the level degeneracy at the
Fermi energy --- effect the giant oscillations. These are shown to survive in a
diffusive sample at temperatures much smaller than the Thouless temperature
provided there are potential barriers between the sample and the normal
electron reservoirs. Our results are in good agreement with previous work on
conductance oscillations of diffusive samples, which we propose can be
understood in terms of a Feynman path integral description of quasiparticle
trajectories.Comment: 24 pages, revtex, 12 figures in eps forma
Quasiparticle Inelastic Lifetime from Paramagnons in Disordered Superconductors
The paramagnon contribution to the quasiparticle inelastic scattering rate in
disordered superconductors is presented. Using Anderson's exact eigenstate
formalism, it is shown that the scattering rate is Stoner enhanced and is
further enhanced by the disorder relative to the clean case in a manner similar
to the disorder enhancement of the long-range Coulomb contribution. The results
are discussed in connection with the possibility of conventional or
unconventional superconductivity in the borocarbides. The results are compared
to recent tunneling experiments on LuNiBC.Comment: 5 pages, no figure
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