1,336 research outputs found
Inorganic Photovoltaics Materials and Devices: Past, Present, and Future
This report describes recent aspects of advanced inorganic materials for photovoltaics or solar cell applications. Specific materials examined will be high-efficiency silicon, gallium arsenide and related materials, and thin-film materials, particularly amorphous silicon and (polycrystalline) copper indium selenide. Some of the advanced concepts discussed include multi-junction III-V (and thin-film) devices, utilization of nanotechnology, specifically quantum dots, low-temperature chemical processing, polymer substrates for lightweight and low-cost solar arrays, concentrator cells, and integrated power devices. While many of these technologies will eventually be used for utility and consumer applications, their genesis can be traced back to challenging problems related to power generation for aerospace and defense. Because this overview of inorganic materials is included in a monogram focused on organic photovoltaics, fundamental issues and metrics common to all solar cell devices (and arrays) will be addressed
An analyst's take on the BPHZ theorem
We provide a self-contained formulation of the BPHZ theorem in the Euclidean
context, which yields a systematic procedure to "renormalise" otherwise
divergent integrals appearing in generalised convolutions of functions with a
singularity of prescribed order at their origin. We hope that the formulation
given in this article will appeal to an analytically minded audience and that
it will help to clarify to what extent such renormalisations are arbitrary (or
not). In particular, we do not assume any background whatsoever in quantum
field theory and we stay away from any discussion of the physical context in
which such problems typically arise.Comment: Accepted versio
Quantum control without access to the controlling interaction
In our model a fixed Hamiltonian acts on the joint Hilbert space of a quantum
system and its controller. We show under which conditions measurements, state
preparations, and unitary implementations on the system can be performed by
quantum operations on the controller only.
It turns out that a measurement of the observable A and an implementation of
the one-parameter group exp(iAr) can be performed by almost the same sequence
of control operations. Furthermore measurement procedures for A+B, for (AB+BA),
and for i[A,B] can be constructed from measurements of A and B. This shows that
the algebraic structure of the set of observables can be explained by the Lie
group structure of the unitary evolutions on the joint Hilbert space of the
measuring device and the measured system.
A spin chain model with nearest neighborhood coupling shows that the border
line between controller and system can be shifted consistently.Comment: 10 pages, Revte
Heated-Atmosphere Airship for the Titan Environment: Thermal Analysis
Future exploration of Saturn's moon Titan can be carried out by airships. Several lighter-than-atmosphere gas airships and passive drifting heated-atmosphere balloon designs have been studied, but a heated-atmosphere airship could combine the best characteristics of both. This work analyses the thermal design of such a heated-atmosphere vehicle, and compares the result with a lighter-than-atmosphere (hydrogen) airship design. A design tool was created to enable iteration through different design parameters of a heated-atmosphere airship (diameter, number of layers, and insulating gas pocket thicknesses) and evaluate the feasibility of the resulting airship. A baseline heated-atmosphere airship was designed to have a diameter of 6 m (outer diameter of 6.2 m), three-layers of material, and an insulating gas pocket thickness of 0.05 m between each layer. The heated-atmosphere airship has a mass of 161.9 kg. A similar mission making use of a hydrogen-filled airship would require a diameter of 4.3 m and a mass of about 200 kg. For a long-duration mission, the heated-atmosphere airship appears better suited. However, for a mission lifetime under 180 days, the less complex hydrogen airship would likely be a better option
Public engagement in local government: the voice and influence of citizens in online communicative spaces
The communications and engagement strategies of local councils play an important role in contributing to the public's understanding of local democracies, and their engagement with local issues. Based on a study of the local authority in the third largest city in the UK, Leeds, this article presents an empirically based analysis of the impact of new opportunities for public engagement afforded by digital media on the Council's communication with citizens. Drawing on over 20 face-to-face semi-structured interviews with elected politicians, Council strategists, Council communications specialists, mainstream journalists, and citizen journalists, the article explores perceptions of the Council's engagement and communication with citizens from the perspective of a range of actors involved in the engagement process. The research asks what the differing motivations behind the Council's communications and engagement strategies mean for the way that digital media are and might be used in the future to enhance the role of citizens in local governance. The research suggests that while there are no grounds for expecting digital media to displace existing channels of public engagement, digital media are beginning to play an important role in defining and reconfiguring the role of citizens within local governance
A model of quantum reduction with decoherence
The problem of reduction (wave packet reduction) is reexamined under two
simple conditions: Reduction is a last step completing decoherence. It acts in
commonplace circumstances and should be therefore compatible with the
mathematical frame of quantum field theory and the standard model.
These conditions lead to an essentially unique model for reduction.
Consistency with renormalization and time-reversal violation suggest however a
primary action in the vicinity of Planck's length. The inclusion of quantum
gravity and the uniqueness of space-time point moreover to generalized quantum
theory, first proposed by Gell-Mann and Hartle, as a convenient framework for
developing this model into a more complete theory.Comment: 20 pages. To be published in Physical Review
Electrodeposited CuInSe2 Thin Film Junctions
We have investigated thin films and junctions based on copper indium diselenide (CIS) which have been grown by electrochemical deposition. CIS is a leading candidate for use in polycrystalline thin film photovoltaic solar cells. Electrodeposition is a cost-effective method for producing thin-film CIS. We have produced both p and n type CIS thin films from the same aqueous solution by simply varying the deposition potential. A CIS pn junction was deposited using a step-function potential. Stoichiometry of the single layer films was determined by energy dispersive spectroscopy. Carrier densities of these films increased with deviation from stoichiometry, as determined by the capacitance versus voltage dependence of Schottky contacts. Optical bandgaps for the single layer films as determined by transmission spectroscopy were also found to increase with deviation from stoichiometry. Rectifying current versus voltage characteristics were demonstrated for the Schottky barriers and for the pn junction
Quantum measurement problem and cluster separability
A modified Beltrametti-Cassinelli-Lahti model of measurement apparatus that
satisfies both the probability reproducibility condition and the
objectification requirement is constructed. Only measurements on microsystems
are considered. The cluster separability forms a basis for the first working
hypothesis: the current version of quantum mechanics leaves open what happens
to systems when they change their separation status. New rules that close this
gap can therefore be added without disturbing the logic of quantum mechanics.
The second working hypothesis is that registration apparatuses for microsystems
must contain detectors and that their readings are signals from detectors. This
implies that separation status of a microsystem changes during both preparation
and registration. A new rule that specifies what happens at these changes and
that guarantees the objectification is formulated and discussed. A part of our
result has certain similarity with 'collapse of the wave function'.Comment: 31 pages, no figure. Published versio
Quantum theory of successive projective measurements
We show that a quantum state may be represented as the sum of a joint
probability and a complex quantum modification term. The joint probability and
the modification term can both be observed in successive projective
measurements. The complex modification term is a measure of measurement
disturbance. A selective phase rotation is needed to obtain the imaginary part.
This leads to a complex quasiprobability, the Kirkwood distribution. We show
that the Kirkwood distribution contains full information about the state if the
two observables are maximal and complementary. The Kirkwood distribution gives
a new picture of state reduction. In a nonselective measurement, the
modification term vanishes. A selective measurement leads to a quantum state as
a nonnegative conditional probability. We demonstrate the special significance
of the Schwinger basis.Comment: 6 page
Renormalizing the Schwinger-Dyson equations in the auxiliary field formulation of field theory
In this paper we study the renormalization of the Schwinger-Dyson equations
that arise in the auxiliary field formulation of the O(N) field
theory. The auxiliary field formulation allows a simple interpretation of the
large-N expansion as a loop expansion of the generating functional in the
auxiliary field , once the effective action is obtained by integrating
over the fields. Our all orders result is then used to obtain finite
renormalized Schwinger-Dyson equations based on truncation expansions which
utilize the two-particle irreducible (2-PI) generating function formalism. We
first do an all orders renormalization of the two- and three-point function
equations in the vacuum sector. This result is then used to obtain explicitly
finite and renormalization constant independent self-consistent S-D equations
valid to order~1/N, in both 2+1 and 3+1 dimensions. We compare the results for
the real and imaginary parts of the renormalized Green's functions with the
related \emph{sunset} approximation to the 2-PI equations discussed by Van Hees
and Knoll, and comment on the importance of the Landau pole effect.Comment: 20 pages, 10 figure
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