Pattern forming instability induced by light in pure and dye-doped nematic liquid crystals

We study theoretically the instabilities induced by a linearly polarized ordinary light wave incident at a small oblique angle on a thin layer of homeotropically oriented nematic liquid crystal with special emphasis on the dye-doped case. The spatially periodic Hopf bifurcation that occurs as the secondary instability after the stationary Freedericksz transition is analyzed.Comment: 8 pages, 7 figures, LaTeX, accepted to Phys. Rev.

Strain induced pressure effect in pulsed laser deposited thin films of the strongly correlated oxide V2O3

V2O3 thin films about 10 nm thick were grown on Al2O3 (0001) by pulsed laser deposition. The XRD analysis is in agreement with R-3c space group. Some of them exhibit the metal / insulator transition characteristic of V2O3 bulk material and others samples exhibit a metallic behavior. For the latter, the XPS analysis indicates an oxidation state of +III for vanadium. There is no metal / insulator transition around 150 K in this sample and a strongly correlated Fermi liquid rho = AT2 behavior of the resistivity at low temperature is observed, with a value of A of 1.2 10-4 ohm cm, 3 times larger than the bulk value at 25 kbar

Solution-processable thienoisoindigo-based molecular donors for organic solar cells with high open-circuit voltage

Two acetylene-bridged Donor–Acceptor–Donor (D-A-D) type small pi-conjugated molecules involving triphenylamine or N-phenylcarbazole as donor blocks (D) and thienoisoindigo as the acceptor unit (A) were synthesized and characterized by UV–Vis absorption and cyclic voltammetry. These donor materials were mixed with [6,6]-phenyl-C61-butyric acid methyl ester to prepare bulk heterojunction solar cells by simple solution processing. Due to their low-lying highest occupied molecular orbital energy levels, high open-circuit voltages up to 0.99 V were measured. The triphenylamine end-capped derivative led to the best power conversion efficiency of ca 2.20%, which ranks among the highest reported value for thienoisoindigo-based materials

Existing opportunities to adapt the Rio Grande/Bravo Basin Water Resources Allocation Framework

The study of the Rio Grande/Bravo (RGB) Basin water allocation demonstrates how the United States (U.S.) and Mexico have consolidated a transboundary framework based on water sharing. However, the water supply no longer meets the ever-increasing demand for water or the expectations of different stakeholders. This paper explores opportunities for an enhanced management regime that will address past problems and better examine how to balance demands for a precious resource and environmental needs. Based on an overview of the RGB Basin context and the water allocation framework, as well as a discussion on stakeholders’ ability to achieve solutions, this paper explores three key questions: (1) Does the current binational water allocation framework meet current and future human and environmental needs? (2) How can the U.S.-Mexico water allocation framework be adapted to balance social and environmental water demands so it can support and preserve the RGB Basin ecosystem? (3) What are the main opportunities to be explored for expanding the U.S.-Mexico water resources allocation framework? The U.S.-Mexico water resources framework is subject to broad interpretation and may be adapted to the circumstances taking the fullest advantage of its flexibility. Policy recommendations highlight the existing flexibility of the binational framework, the potential to move forward with an ad hoc institutional arrangement, and the creation of political will to achieve change through stakeholders recommendations

HIV-1 Reverse Transcriptase Connection Domain Mutations: Dynamics of Emergence and Implications for Success of Combination Antiretroviral Therapy

Background. Factors promoting the emergence of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) connection domain mutations and their effect on antiretroviral therapy (ART) are still largely undetermined.We investigated this matter by analyzing genotypic resistance tests covering 400 amino acid positions in the RT of HIV-1 subtype B viruses and corresponding treatment histories and laboratory measurements. Methods. The emergence of connection domain mutations was studied in 334 patients receiving monotherapy or dual therapy with thymidine analogues at the time of the genotypic resistance test. Response to subsequent combination ART (cART) was analyzed using Cox regression for 291 patients receiving unboosted protease inhibitors. Response was defined by ever reaching an HIV RNA level <50 copies/mL during the first cART. Results. The connection domain mutations N348I, R356K, R358K, A360V, and A371V were more frequently observed in ART-exposed than ART-naive patients, of which only N348I and A360V were nonpolymorphic (with a prevalence of <1.5% in untreated patients). N348I correlated with M184V and predominantly occurred in patients receiving lamivudine and zidovudine concomitantly. A360V was not associated with specific drug combinations and was found to emerge later than M184V or thymidine analogue mutations. Nonpolymorphic connection domain mutations were rarely detected in the absence of established drug resistance mutations in ART-exposed individuals (prevalence, <1%). None of the 5 connection domain mutations associated with treatment showed a statistically significant effect on response to cART. Conclusions. Despite their frequent emergence, connection domain mutations did not show large detrimental effects on response to cART. Currently, routine implementation of connection domain sequencing seems unnecessary for developed health care setting

Epidemiological and Biological Evidence for a Compensatory Effect of Connection Domain Mutation N348I on M184V in HIV-1 Reverse Transcriptase

Background. The connection domain mutation N348I confers resistance to zidovudine (AZT) and is associated with the lamivudine (3TC) mutation M184V. We explored the biochemical and virological influence of N348I in the context of M184V. Methods. Genotypic resistance data for patients receiving monotherapy or dual therapy with AZT, lamivudine (3TC), or AZT/3TC were analyzed. Rates of N348I emergence were compared between treatment groups. Mutant reverse transcriptases (RTs) containing M184V and/or N348I were generated to study enzymatic and virological properties. Results. We included 50 AZT-treated, 11 3TC-treated, and 10 AZT/3TC-treated patients. N348I was observed in 3 (6%), 0, and 4 (40%) of these patients, respectively. The rate of N348I emergence was increased by 5-fold in the AZT/3TC group (11.7 instances [95% confidence interval {CI}, 3.2-30.1 instances] per 100 person-years of receipt of AZT), compared with the rate noted for the AZT group (2.3 instances [95% CI, 0.4-6.8 instances] per 100 person-years of receipt of AZT; P = .04). Biochemical data show that N348I can partially compensate for the diminution in processive DNA synthesis and the reduction in AZT excision associated with M184V. Furthermore, virological analyses demonstrate that N348I confers low-level resistance to AZT and partly restores the reduced RT activity of the M184V variant. Conclusion. In vivo selection of N348I is driven by AZT and is further facilitated when 3TC is coadministered. Compensatory interactions between N348I and M184V help to explain these finding

Electronic structure of MgB2_2: X-ray emission and absorption studies

Measurements of x-ray emission and absorption spectra of the constituents of MgB$_2$ are presented. The results obtained are in good agreement with calculated x-ray spectra, with dipole matrix elements taken into account. The comparison of x-ray emission spectra of graphite, AlB$_2$, and MgB$_2$ in the binding energy scale supports the idea of charge transfer from $\sigma$ to $\pi$ bands, which creates holes at the top of the bonding $\sigma$ bands and drives the high-T$_c$Comment: final version as published in PR