179 research outputs found
Capacitance Measurements for Subcell Characterization in Multijunction Solar Cells.
On this paper we present an alternative way to analyze de electronic properties of each subcell from the complete device. By illuminating the cell with light sources which energy is near one of the subcell bandgaps, it is possible to “erase” the presence of such subcell on the CV curve. The main advantages of this technique are that it is not destructive, it can be measured on the complete cell so can be easily implemented as a diagnostic technique for controlling electronic deviations
String-String Duality in Ten Dimensions
The heterotic string occurs as a soliton of the type I superstring in ten
dimensions, supporting the conjecture that these two theories are equivalent.
The conjecture that the type IIB string is self-dual, with the strong
coupling dynamics described by a dual type IIB theory, is supported by the
occurrence of the dual string as a Ramond-Ramond soliton of the weakly-coupled
theory.Comment: 14 pages, phyzz
Interacting Open Wilson Lines in Noncommutative Field Theories
In noncommutative field theories, it was known that one-loop effective action
describes propagation of non-interacting open Wilson lines, obeying the flying
dipole's relation. We show that two-loop effective action describes cubic
interaction among `closed string' states created by open Wilson lines. Taking
d-dimensional noncommutative [\Phi^3] theory as the simplest setup, we compute
nonplanar contribution at low-energy and large noncommutativity limit. We find
that the contribution is expressible in a remarkably simple cubic interaction
involving scalar open Wilson lines only and nothing else. We show that the
interaction is purely geometrical and noncommutative in nature, depending only
on sizes of each open Wilson line.Comment: v1: 27 pages, Latex, 7 .eps figures v2: minor wording change +
reference adde
Pseudo-Duality
Proper symmetries act on fields while pseudo-symmetries act on both fields
and coupling constants. We identify the pseudo-duality groups that act as
symmetries of the equations of motion of general systems of scalar and vector
fields and apply our results to and supergravity theories. We
present evidence that the pseudo-duality group for both the heterotic and type
II strings toroidally compactified to four dimensions is ,
where is a certain subgroup of the diffeomorphism group of the scalar field
target space. This contains the conjectured heterotic or type II
proper duality group as a subgroup.Comment: 13 pages, phyzzx macr
Properties of hyperkahler manifolds and their twistor spaces
We describe the relation between supersymmetric sigma-models on hyperkahler
manifolds, projective superspace, and twistor space. We review the essential
aspects and present a coherent picture with a number of new results.Comment: 26 pages. v2: Sign mistakes corrected; Kahler potential explicitly
calculated in example; references added. v3: Published version--several small
clarifications per referee's reques
Unity of Superstring Dualities
The effective action for type II string theory compactified on a six torus is
supergravity, which is known to have an duality symmetry. We show
that this is broken by quantum effects to a discrete subgroup, , which
contains both the T-duality group and the S-duality group
. We present evidence for the conjecture that is an exact
\lq U-duality' symmetry of type II string theory. This conjecture requires
certain extreme black hole states to be identified with massive modes of the
fundamental string. The gauge bosons from the Ramond-Ramond sector couple not
to string excitations but to solitons. We discuss similar issues in the context
of toroidal string compactifications to other dimensions, compactifications of
the type II string on and compactifications of
eleven-dimensional supermembrane theory.Comment: 45 pages. Some minor corrections made and some references adde
Singularities In Scalar-Tensor Cosmologies
In this article, we examine the possibility that there exist special
scalar-tensor theories of gravity with completely nonsingular FRW solutions.
Our investigation in fact shows that while most probes living in such a
Universe never see the singularity, gravity waves always do. This is because
they couple to both the metric and the scalar field, in a way which effectively
forces them to move along null geodesics of the Einstein conformal frame. Since
the metric of the Einstein conformal frame is always singular for
configurations where matter satisfies the energy conditions, the gravity wave
world lines are past inextendable beyond the Einstein frame singularity, and
hence the geometry is still incomplete, and thus singular. We conclude that the
singularity cannot be entirely removed, but only be made invisible to most, but
not all, probes in the theory.Comment: 23 pages, latex, no figure
Time Evolution via S-branes
Using S(pacelike)-branes defined through rolling tachyon solutions, we show
how the dynamical formation of D(irichlet)-branes and strings in tachyon
condensation can be understood. Specifically we present solutions of S-brane
actions illustrating the classical confinement of electric and magnetic flux
into fundamental strings and D-branes. The role of S-branes in string theory is
further clarified and their RR charges are discussed. In addition, by examining
``boosted'' S-branes, we find what appears to be a surprising dual S-brane
description of strings and D-branes, which also indicates that the critical
electric field can be considered as a self-dual point in string theory. We also
introduce new tachyonic S-branes as Euclidean counterparts to non-BPS branes.Comment: 62 pages, 10 figures. v2 references adde
Drinking water temperature around the globe : understanding, policies, challenges and opportunities
Water temperature is often monitored at water sources and treatment works; however, there is limited monitoring of the water temperature in the drinking water distribution system (DWDS), despite a known impact on physical, chemical and microbial reactions which impact water quality. A key parameter influencing drinking water temperature is soil temperature, which is influenced by the urban heat island effects. This paper provides critique and comprehensive summary of the current knowledge, policies and challenges regarding drinking water temperature research and presents the findings from a survey of international stakeholders. Knowledge gaps as well as challenges and opportunities for monitoring and research are identified. The conclusion of the study is that temperature in the DWDS is an emerging concern in various countries regardless of the water source and treatment, climate conditions, or network characteristics such as topology, pipe material or diameter. More research is needed, especially to determine (i) the effect of higher temperatures, (ii) a legislative limit on temperature and (iii) measures to comply with this limit
Cosmological Spacetimes from Negative Tension Brane Backgrounds
We identify a time-dependent class of metrics with potential applications to
cosmology, which emerge from negative-tension branes. The cosmology is based on
a general class of solutions to Einstein-dilaton-Maxwell theory, presented in
{hep-th/0106120}. We argue that solutions with hyperbolic or planar symmetry
describe the gravitational interactions of a pair of negative-tension
-branes. These spacetimes are static near each brane, but become
time-dependent and expanding at late epoch -- in some cases asymptotically
approaching flat space. We interpret this expansion as being the spacetime's
response to the branes' presence. The time-dependent regions provide explicit
examples of cosmological spacetimes with past horizons and no past naked
singularities. The past horizons can be interpreted as S-branes. We prove that
the singularities in the static regions are repulsive to time-like geodesics,
extract a cosmological `bounce' interpretation, compute the explicit charge and
tension of the branes, analyse the classical stability of the solution (in
particular of the horizons) and study particle production, deriving a general
expression for Hawking's temperature as well as the associated entropy.Comment: 43 pages, 8 figures. Published versio
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