754 research outputs found
Interference enhanced thermoelectricity in quinoid type structures
Quantum interference (QI) effects in molecular junctions may be used to
obtain large thermoelectric responses. We study the electrical conductance G
and the thermoelec- tric response of a series of molecules featuring a quinoid
core using density functional theory (DFT), as well as a semi-empirical
interacting model Hamiltonian describing the {\pi}-system of the molecule which
we treat in the GW approximation. Molecules with a quinoid type structure are
shown to have two distinct destructive QI features close to the frontier
orbital energies. These manifest themselves as two dips in the transmission,
that remain separated, even when either electron donating or withdraw- ing side
groups are added. We find that the position of the dips in the transmission and
the frontier molecular levels can be chemically controlled by varying the
electron donating or withdrawing character of the side groups as well as the
conjugation length inside the molecule. This feature results in a very high
thermoelectric power factor S^2G and figure of merit ZT, where S is the Seebeck
coefficient, making quinoid type molecules potential candidates for efficient
thermoelectric devices.Comment: 22 pages, 11 figure
Dynamics of hard-sphere suspension using Dynamic Light Scattering and X-Ray Photon Correlation Spectroscopy: dynamics and scaling of the Intermediate Scattering Function
Intermediate Scattering Functions (ISF's) are measured for colloidal hard
sphere systems using both Dynamic Light Scattering (DLS) and X-ray Photon
Correlation Spectroscopy (XPCS). We compare the techniques, and discuss the
advantages and disadvantages of each. Both techniques agree in the overlapping
range of scattering vectors. We investigate the scaling behaviour found by
Segre and Pusey [1] but challenged by Lurio et al. [2]. We observe a scaling
behaviour over several decades in time but not in the long time regime.
Moreover, we do not observe long time diffusive regimes at scattering vectors
away from the peak of the structure factor and so question the existence of a
long time diffusion coefficients at these scattering vectors.Comment: 21 pages, 11 figure
Time-dependent embedding: surface electron emission
An embedding method for solving the time-dependent Schr\"odinger equation is
developed using the Dirac-Frenkel variational principle. Embedding allows the
time-evolution of the wavefunction to be calculated explicitly in a limited
region of space, the region of physical interest, the embedding potential
ensuring that the wavefunction satisfies the correct boundary conditions for
matching on to the rest of the system. This is applied to a study of the
excitation of electrons at a metal surface, represented by a one-dimensional
model potential for Cu(111). Time-dependent embedding potentials are derived
for replacing the bulk substrate, and the image potential and vacuum region
outside the surface, so that the calculation of electron excitation by a
surface perturbation can be restricted to the surface itself. The excitation of
the Shockley surface state and a continuum bulk state is studied, and the
time-structure of the resulting currents analysed. Non-linear effects and the
time taken for the current to arrive outside the surface are discussed. The
method shows a clear distinction between emission from the localized surface
state, where the charge is steadily depleted, and the extended continuum state
where the current emitted into the vacuum is compensated by current approaching
the surface from the bulk.Comment: 15 figure
Emulsification in binary liquids containing colloidal particles: a structure-factor analysis
We present a quantitative confocal-microscopy study of the transient and
final microstructure of particle-stabilised emulsions formed via demixing in a
binary liquid. To this end, we have developed an image-analysis method that
relies on structure factors obtained from discrete Fourier transforms of
individual frames in confocal image sequences. Radially averaging the squared
modulus of these Fourier transforms before peak fitting allows extraction of
dominant length scales over the entire temperature range of the quench. Our
procedure even yields information just after droplet nucleation, when the
(fluorescence) contrast between the two separating phases is scarcely
discernable in the images. We find that our emulsions are stabilised on
experimental time scales by interfacial particles and that they are likely to
have bimodal droplet-size distributions. We attribute the latter to coalescence
together with creaming being the main coarsening mechanism during the late
stages of emulsification and we support this claim with (direct)
confocal-microscopy observations. In addition, our results imply that the
observed droplets emerge from particle-promoted nucleation, possibly followed
by a free-growth regime. Finally, we argue that creaming strongly affects
droplet growth during the early stages of emulsification. Future investigations
could clarify the link between quench conditions and resulting microstructure,
paving the way for tailor-made particle-stabilised emulsions from binary
liquids.Comment: http://iopscience.iop.org/0953-8984/22/45/455102
Two phase transitions in the fully frustrated model
The fully frustrated model on a square lattice is studied by means of
Monte Carlo simulations. A Kosterlitz-Thouless transition is found at , followed by an ordinary Ising transition at a slightly
higher temperature, . The non-Ising exponents reported by
others, are explained as a failure of finite size scaling due to the screening
length associated with the nearby Kosterlitz-Thouless transition.Comment: REVTEX file, 8 pages, 5 figures in uuencoded postscrip
Radicalization processes and transitional phases in female and male detainees residing in Dutch terrorism wings.
Background: Radicalization, violent extremism, and terrorism are risks to societal security. Although research on terrorism-related behaviors is increasing, thorough empirical studies are rare. Methods: This study investigates radicalization processes and transitions in a matched sample of female and male terrorist suspects and convicts (N = 26) residing in Dutch penitentiary terrorism wings. Results:Results show that both men and women often experienced discrimination. A subgroup of women grew up in a stressful family environment and lacked emotional support from their family, whereas the other women did not experience such circumstances. The majority of the study sample was susceptible to connecting with radicalized friends or family members. Interestingly, factors that initially led to radicalization (e.g., a utopian image of the Islamic State) could later turn out to be factors associated with abandoning extremism. Conclusions: In this study, differences in radicalization processes and transitional phases between women and men emerged. Men more often had police contact prior to a terrorism-related offense. Making an effort to right old mistakes seemed important in the radicalization processes of men, whereas women had a stronger desire for emotional support and were more driven by experienced trauma and feelings of loneliness. This study provides input for gender-specific prevention and disengagement interventions
Transfer of arbitrary quantum emitter states to near-field photon superpositions in nanocavities
We present a method to analyze the suitability of particular photonic cavity
designs for information exchange between arbitrary superposition states of a
quantum emitter and the near-field photonic cavity mode. As an illustrative
example, we consider whether quantum dot emitters embedded in "L3" and "H1"
photonic crystal cavities are able to transfer a spin superposition state to a
confined photonic superposition state for use in quantum information transfer.
Using an established dyadic Green's function (DGF) analysis, we describe
methods to calculate coupling to arbitrary quantum emitter positions and
orientations using the modified local density of states (LDOS) calculated using
numerical finite-difference time-domain (FDTD) simulations. We find that while
superposition states are not supported in L3 cavities, the double degeneracy of
the H1 cavities supports superposition states of the two orthogonal modes that
may be described as states on a Poincar\'{e}-like sphere. Methods are developed
to comprehensively analyze the confined superposition state generated from an
arbitrary emitter position and emitter dipole orientation.Comment: 22 pages, 9 figure
Biodesulphurized subbituminous coal by different fungi and bacteria studied by reductive pyrolysis. Part 1: Initial coal
One of the perspective methods for clean solid fuels production is biodesulphurization. In order to increase the effect of this approach
it is necessary to apply the advantages of more informative analytical techniques. Atmospheric pressure temperature programming
reduction (AP-TPR) coupled with different detection systems gave us ground to attain more satisfactory explanation of the effects of
biodesulphurization on the treated solid products.
Subbituminous high sulphur coal from ‘‘Pirin” basin (Bulgaria) was selected as a high sulphur containing sample. Different types of
microorganisms were chosen and maximal desulphurization of 26% was registered. Biodesulphurization treatments were performed with
three types of fungi: ‘‘Trametes Versicolor” – ATCC No. 200801, ‘‘Phanerochaeta Chrysosporium” – ME446, Pleurotus Sajor-Caju and
one Mixed Culture of bacteria – ATCC No. 39327. A high degree of inorganic sulphur removal (79%) with Mixed Culture of bacteria
and consecutive reduction by 13% for organic sulphur (Sorg) decrease with ‘‘Phanerochaeta Chrysosporium” and ‘‘Trametes Versicolor”
were achieved.
To follow the Sorg changes a set of different detection systems i.e. AP-TPR coupled ‘‘on-line” with mass spectrometry (AP-TPR/MS),
on-line with potentiometry (AP-TPR/pot) and by the ‘‘off-line” AP-TPR/GC/MS analysis was used. The need of applying different
atmospheres in pyrolysis experiments was proved and their effects were discussed. In order to reach more precise total sulphur balance,
oxygen bomb combustion followed by ion chromatography was used
Single-Particle Density of States of a Superconductor with a Spatially Varying Gap and Phase Fluctuations
Recent experiments have shown that the superconducting energy gap in some
cuprates is spatially inhomogeneous. Motivated by these experiments, and using
exact diagonalization of a model d-wave Hamiltonian, combined with Monte Carlo
simulations of a Ginzburg-Landau free energy functional, we have calculated the
single-particle density of states LDOS of a model high-T
superconductor as a function of temperature. Our calculations include both
quenched disorder in the pairing potential and thermal fluctuations in both
phase and amplitude of the superconducting gap. Most of our calculations assume
two types of superconducting regions: , with a small gap and large
superfluid density, and , with the opposite. If the regions are
randomly embedded in an host, the LDOS on the sites still has
a sharp coherence peak at , but the component does not, in
agreement with experiment. An ordered arrangement of regions leads to
oscillations in the LDOS as a function of energy. The model leads to a
superconducting transition temperature well below the pseudogap
temperature , and has a spatially varying gap at very low , both
consistent with experiments in underdoped Bi2212. Our calculated
LDOS shows coherence peaks for , in agreement with previous work considering phase but not amplitude
fluctuations in a homogeneous superconductor. Well above , the gap in the
LDOS disappears.Comment: 37 pages, 12 figures. Accepted by Phys. Rev. B. Scheduled Issue: 01
Nov 200
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