Evaluation available encapsulation materials for low-cost long-life silicon photovoltaic arrays

Experimental evaluation of selected encapsulation designs and materials based on an earlier study which have potential for use in low cost, long-life photovoltaic arrays are reported. The performance of candidate materials and encapsulated cells were evaluated principally for three types of encapsulation designs based on their potentially low materials and processing costs: (1) polymeric coatings, transparent conformal coatings over the cell with a structural-support substrate; (2) polymeric film lamination, cells laminated between two films or sheets of polymeric materials; and (3) glass-covered systems, cells adhesively bonded to a glass cover (superstrate) with a polymeric pottant and a glass or other substrate material. Several other design types, including those utilizing polymer sheet and pottant materials, were also included in the investigation

The genomic basis of rapid adaptation to antibiotic combination therapy in Pseudomonas aeruginosa

Combination therapy is a common antibiotic treatment strategy that aims at minimizing the risk of resistance evolution in several infectious diseases. Nonetheless, evidence supporting its efficacy against the nosocomial opportunistic pathogen Pseudomonas aeruginosa remains elusive. Identification of the possible evolutionary paths to resistance in multidrug environments can help to explain treatment outcome. For this purpose, we here performed whole-genome sequencing of 127 previously evolved populations of P. aeruginosa adapted to sublethal doses of distinct antibiotic combinations and corresponding single-drug treatments, and experimentally characterized several of the identified variants. We found that alterations in the regulation of efflux pumps are the most favored mechanism of resistance, regardless of the environment. Unexpectedly, we repeatedly identified intergenic variants in the adapted populations, often with no additional mutations and usually associated with genes involved in efflux pump expression, possibly indicating a regulatory function of the intergenic regions. The experimental analysis of these variants demonstrated that the intergenic changes caused similar increases in resistance against single and multidrug treatments as those seen for efflux regulatory gene mutants. Surprisingly, we could find no substantial fitness costs for a majority of these variants, most likely enhancing their competitiveness toward sensitive cells, even in antibiotic-free environments. We conclude that the regulation of efflux is a central target of antibiotic-mediated selection in P. aeruginosa and that, importantly, changes in intergenic regions may represent a usually neglected alternative process underlying bacterial resistance evolution, which clearly deserves further attention in the future

Sphaleron Effects Near the Critical Temperature

We discuss one-loop radiative corrections to the sphaleron-induced baryon number-violating transition rate near the electroweak phase transition in the standard model. We emphasize that in the case of a first-order transition a rearrangement of the loop expansion is required close to the transition temperature. The corresponding expansion parameter, the effective 3-dimensional gauge coupling approaches a finite $\lambda$ dependent value at the critical temperature. The $\lambda$ (Higgs mass) dependence of the 1-loop radiative corrections is discussed in the framework of the heat kernel method. Radiative corrections are small compared to the leading sphaleron contribution as long as the Higgs mass is small compared to the W mass. To 1-loop accuracy, there is no Higgs mass range compatible with experimental limits where washing-out of a B+L asymmetry could be avoided for the minimal standard model with one Higgs doublet.Comment: 17 pages, RevTeX, (4 figures in a separate uuencoded file), HD-THEP-93-23re

Maximal variance reduction for stochastic propagators with applications to the static quark spectrum

We study a new method -- maximal variance reduction -- for reducing the variance of stochastic estimators for quark propagators. We find that while this method is comparable to usual iterative inversion for light-light mesons, a considerable improvement is achieved for systems containing at least one infinitely heavy quark. Such systems are needed for heavy quark effective theory. As an illustration of the effectiveness of the method we present results for the masses of the ground state and excited states of $\bar{Q}q$ mesons and $\bar{Q}qq$ baryons. We compare these results with the experimental spectra involving $b$ quarks.Comment: 31 pages with 7 postscript file

Phase transitions in two dimensions - the case of Sn adsorbed on Ge(111) surfaces

Accurate atomic coordinates of the room-temperature (root3xroot3)R30degree and low-temperature (3x3) phases of 1/3 ML Sn on Ge(111) have been established by grazing-incidence x-ray diffraction with synchrotron radiation. The Sn atoms are located solely at T4-sites in the (root3xroot3)R30degree structure. In the low temperature phase one of the three Sn atoms per (3x3) unit cell is displaced outwards by 0.26 +/- 0.04 A relative to the other two. This displacement is accompanied by an increase in the first to second double-layer spacing in the Ge substrate.Comment: RevTeX, 5 pages including 2 figure

Subcritical Fluctuations at the Electroweak Phase Transition

We study the importance of thermal fluctuations during the electroweak phase transition. We evaluate in detail the equilibrium number density of large amplitude subcritical fluctuations and discuss the importance of phase mixing to the dynamics of the phase transition. Our results show that, for realistic Higgs masses, the phase transition can be completed by the percolation of the true vacuum, induced by the presence of subcritical fluctuations.Comment: RevTeX, 4 eps figs (uses epsf.sty), 26 pages, to be published in Phys. Rev.

Electroweak Bubble Nucleation, Nonperturbatively

We present a lattice method to compute bubble nucleation rates at radiatively induced first order phase transitions, in high temperature, weakly coupled field theories, nonperturbatively. A generalization of Langer's approach, it makes no recourse to saddle point expansions and includes completely the dynamical prefactor. We test the technique by applying it to the electroweak phase transition in the minimal standard model, at an unphysically small Higgs mass which gives a reasonably strong phase transition (lambda/g^2 =0.036, which corresponds to m(Higgs)/m(W) = 0.54 at tree level but does not correspond to a positive physical Higgs mass when radiative effects of the top quark are included), and compare the results to older perturbative and other estimates. While two loop perturbation theory slightly under-estimates the strength of the transition measured by the latent heat, it over-estimates the amount of supercooling by a factor of 2.Comment: 48 pages, including 16 figures. Minor revisions and typo fixes, nothing substantial, conclusions essentially unchange

Determination of the (3x3)-Sn/Ge(111) structure by photoelectron diffraction

At a coverage of about 1/3 monolayer, Sn deposited on Ge(111) below 550 forms a metastable (sqrt3 x sqrt3)R30 phase. This phase continuously and reversibly transforms into a (3x3) one, upon cooling below 200 K. The photoemission spectra of the Sn 4d electrons from the (3x3)-Sn/Ge(111) surface present two components which are attributed to inequivalent Sn atoms in T4 bonding sites. This structure has been explored by photoelectron diffraction experiments performed at the ALOISA beamline of the Elettra storage ring in Trieste (Italy). The modulation of the intensities of the two Sn components, caused by the backscattering of the underneath Ge atoms, has been measured as a function of the emission angle at fixed kinetic energies and viceversa. The bond angle between Sn and its nearest neighbour atoms in the first Ge layer (Sn-Ge1) has been measured by taking polar scans along the main symmetry directions and it was found almost equivalent for the two components. The corresponding bond lengths are also quite similar, as obtained by studying the dependence on the photoelectron kinetic energy, while keeping the photon polarization and the collection direction parallel to the Sn-Ge1 bond orientation (bond emission). A clear difference between the two bonding sites is observed when studying the energy dependence at normal emission, where the sensitivity to the Sn height above the Ge atom in the second layer is enhanced. This vertical distance is found to be 0.3 Angstroms larger for one Sn atom out of the three contained in the lattice unit cell. The (3x3)-Sn/Ge(111) is thus characterized by a structure where the Sn atom and its three nearest neighbour Ge atoms form a rather rigid unit that presents a strong vertical distortion with respect to the underneath atom of the second Ge layer.Comment: 10 pages with 9 figures, added reference

Do associations support authoritarian rule? Evidence from Algeria, Mozambique, and Vietnam

Whether associations help to democratize authoritarian rule or support those in power is a contested issue that so far lacks a cross-regional, comparative perspective. In this article we focus on five types of associations in three post-socialist countries, situated in different world regions, that are governed by authoritarian regimes. We first explore how infrastructural and discursive state power impact such associations and vice versa. We then discuss whether these associations support the development of citizens' collective and individual self-determination and autonomy and/or whether they negate such self-determination and autonomy - a state of affairs that is at the core of authoritarianism. Our analysis addresses decision-making in associations and three specific policy areas. We find that most of the covered associations accept or do not openly reject state/ruling party interference in their internal decision-making processes. Moreover, in most of these associations the self-determination and autonomy of members are restricted, if not negated. With respect to HIV/AIDS policy, associations in Algeria and Vietnam toe the official line, and thus contribute, unlike their counterparts in Mozambique, to negating the self-determination and autonomy of affected people and other social minorities. Looking at enterprise promotion policy, we find that the co-optation of business and professionals’ associations in all three countries effectively limits democratizing impulses. Finally, in all three countries many, but not all, of the interviewed associations support state-propagated norms concerning gender and gender relationships, thus contributing to limiting the self-determination and autonomy of women in the private sphere

The Growth of Bubbles in Cosmological Phase Transitions

We study how bubbles grow after the initial nucleation event in generic first-order cosmological phase transitions characterised by the values of latent heat, interface tension and correlation length, and driven by a scalar order parameter $\phi$. Equations coupling $\phi$ and the fluid variables $v$ and $T$ and depending on a dissipative constant $\Gamma$ are derived and solved numerically in the 1+1 dimensional case starting from a slightly deformed critical bubble configuration. Parameters corresponding to QCD and electroweak phase transitions are chosen and the whole history of the bubble with formation of combustion and shock fronts is computed as a function of $\Gamma$. Both deflagrations and detonations can appear depending on the values of the parameters. Reheating due to collisions of bubbles is also computed.Comment: 24 LaTeX-pages with 20 figures not included. The complete PostScript file, including figures, is available by anonymous ftp from fltxc.helsinki.fi, as /pub/bubble.ps, or as a hardcopy by airmail (a dublicate lies at nic.funet.fi:/pub/sci/physics/papers/bubble.ps). Helsinki Preprint HU-TFT-93-4