Large scale PV systems under non-uniform and fault conditions

Current codes of practice for PV systems lack detailed guidance regarding circuit mismatch, over or reverse current protection and unbalanced operational conditions in large PV systems. Experimental work in this field is expensive and limited by hardware and environmental resources. The available commercial simulation tools do not rigorously model the complex behaviour of PV systems operating under non-uniform conditions. In this paper a detailed cell-by-cell model of large scale PV systems is developed. The parameter set used for simulations is based on real PV modules power tolerance data and the variance in its principal parameters, thus representing a realistic power frequency distribution. The model is used to estimate and analyse losses due to circuit mismatch, analyse the causes of reverse current in the system's strings and its consequences in the system performance and to estimate energy losses due to string's fuses failures

Weak localization and conductance fluctuations of a chaotic quantum dot with tunable spin-orbit coupling

In a two-dimensional quantum dot in a GaAs heterostructure, the spin-orbit scattering rate is substantially reduced below the rate in a bulk two-dimensional electron gas [B.I. Halperin et al, Phys. Rev. Lett. 86, 2106 (2001)]. Such a reduction can be undone if the spin-orbit coupling parameters acquire a spatial dependence, which can be achieved, e.g., by a metal gate covering only a part of the quantum dot. We calculate the effect of such spatially non-uniform spin-orbit scattering on the weak localization correction and the universal conductance fluctuations of a chaotic quantum dot coupled to electron reservoirs by ballistic point contacts, in the presence of a magnetic field parallel to the plane of the quantum dot.Comment: 4 pages, RevTeX; 2 figures. Substantial revision

Creation of maximally entangled photon-number states using optical fiber multiports

We theoretically demonstrate a method for producing the maximally path-entangled state (1/Sqrt[2]) (|N,0> + exp[iN phi] |0,N>) using intensity-symmetric multiport beamsplitters, single photon inputs, and either photon-counting postselection or conditional measurement. The use of postselection enables successful implementation with non-unit efficiency detectors. We also demonstrate how to make the same state more conveniently by replacing one of the single photon inputs by a coherent state.Comment: 4 pages, 1 figure. REVTeX4. Replaced with published versio

Growth forms and life-history strategies predict the occurrence of aquatic macrophytes in relation to environmental factors in a shallow peat lake complex

Aquatic ecosystems provide vital services, and macrophytes play a critical role in their functioning. Conceptual models indicate that in shallow lakes, plants with different growth strategies are expected to inhabit contrasting habitats. For shallow peat lakes, characterized by incohesive sediments, roles of growth forms, life-history strategies and environmental factors in determining the occurrence of aquatic vegetation remain unknown. In a field survey, we sampled 64 points in a peat lake complex and related macrophyte occurrence to growth forms (floating-leaved rooted and submerged), life-history strategies for overwintering (turions, seeds, rhizomes) and environmental factors (water depth, fetch, and porewater nutrients). Our survey showed that macrophyte occurrence relates to water depth, wind-fetch, and nutrients, and depends on growth form and life-history strategies. Specifically, rooted floating-leaved macrophytes occur at lower wind-fetch/shallower waters. Submerged macrophytes occur from low to greater wind-fetch/water depth, depending on life-history strategies; macrophytes with rhizomes occur at greater wind-fetch/depth relative to species that overwinter with seeds or turions. We conclude that growth form and life-history strategies for overwintering predict macrophytes occurrence regarding environmental factors in peat lakes. Therefore, we propose an adapted model for macrophyte occurrence for such lakes. Altogether, these results may aid in species-selection to revegetate peat lakes depending on its environment

One in a Billion: MSSM-like D-Brane Statistics

Continuing our recent work hep-th/0411173, we study the statistics of four-dimensional, supersymmetric intersecting D-brane models in a toroidal orientifold background. We have performed a vast computer survey of solutions to the stringy consistency conditions and present their statistical implications with special emphasis on the frequency of Standard Model features. Among the topics we discuss are the implications of the K-theory constraints, statistical correlations among physical quantities and an investigation of the various statistical suppression factors arising once certain Standard Model features are required. We estimate the frequency of an MSSM like gauge group with three generations to be one in a billion.Comment: 36 pages, 12 figures; v2: typos corrected, one ref. added; v3: minor changes, version to appear in JHE

The microscopic spin-phonon coupling constants in CuGeO_3

Using RPA results, mean field theory, and refined data for the polarization vectors we determine the coupling constants of the four Peierls-active phonon modes to the spin chains of CuGeO_3. We then derive the values of the coupling of the spin system to the linear ionic displacements, the bond lengths and the angles between bonds. Our values are consistent with microscopic theories and various experimental results. We discuss the applicability of static approaches to the spin-phonon coupling. The c-axis anomaly of the thermal expansion is explained. We give the values of the coupling constants in an effective one-dimensional Hamiltonian.Comment: 11 pages, two figures, 13 tables, PRB 59 (in press

Moduli Stabilisation versus Chirality for MSSM like Type IIB Orientifolds

We investigate the general question of implementing a chiral MSSM like D-brane sector in Type IIB orientifold models with complete moduli stabilisation via F-terms induced by fluxes and space-time instantons, respectively gaugino condensates. The prototype examples are the KKLT and the so-called large volume compactifications. We show that the ansatz of first stabilising all moduli via F-terms and then introducing the Standard Model module is misleading, as a chiral sector notoriously influences the structure of non-perturbative effects and induces a D-term potential. Focusing for concreteness on the large volume scenario, we work out the geometry of the swiss-cheese type Calabi-Yau manifold P_[1,3,3,3,5][15]_(3,75) and analyse whether controllable and phenomenologically acceptable Kaehler moduli stabilisation can occur by the combination of F- and D-terms.Comment: 43 pages, 4 figures, v2: refs. adde

Gauge Unification in Supersymmetric Intersecting Brane Worlds

We show that contrary to first expectations realistic three generation supersymmetric intersecting brane world models give rise to phenomenologically interesting predictions about gauge coupling unification. Assuming the most economical way of realizing the matter content of the MSSM via intersecting branes we obtain a model independent relation among the three gauge coupling constants at the string scale. In order to correctly reproduce the experimentally known values of sin^2[theta_W(M_z)] and alpha_s(M_z) this relation leads to natural gauge coupling unification at a string scale close to the standard GUT scale 2 x 10^16 GeV. Additional vector-like matter can push the unification scale up to the Planck scale.Comment: 18 pages, harvmac & 3 figures; v2: one ref. adde