Quasi-equilibrium states in thermotropic liquid crystals studied by multiple quantum NMR

We study the nature of the quasiinvariants in nematic 5CB and measure their relaxation times by encoding the multiple quantum coherences of the states following the JB pulse pair on two orthogonal bases, Z and X. The experiments were also performed in powder adamantane at 301 K which is used as a reference compound having only one dipolar quasiinvariant. We show that the evolution of the quantum states during the build up of the quasi-equilibrium state in 5CB prepared under the S condition is similar to the case of adamantane and that their quasi-equilibrium density operators have the same tensor structure. In contrast, the second constant of motion, whose explicit operator form is not known, involves a richer composition of multiple quantum coherences on the X basis of even order, in consistency with the truncation inherent in its definition. We exploited the exclusive presence coherences 4, 6, 8, besides 0 and 2 under the W condition to measure the spin-lattice relaxation time T_{W} accurately, so avoiding experimental difficulties that usually impair dipolar order relaxation measurement such as Zeeman contamination at high fields, and also superposition of the different quasiinvariants. This procedure opens the possibility of measuring the spin-lattice relaxation of a quasiinvariant independent of the Zeeman and S reservoirs, so incorporating a new relaxation parameter useful for studying the complex molecular dynamics in mesophases. In fact, we report the first measurement of T_{W} in a liquid crystal at high magnetic fields. The comparison of the obtained value with the one corresponding to a lower field (16 MHz) points out that the relaxation of the W-order strongly depends on the intensity of the external magnetic field, similarly to the case of the S reservoir, indicating that the relaxation of the W-quasiinvariant is also governed by the cooperative molecular motions.Comment: 7 figures. http://www.famaf.unc.edu.ar/series/AFis2005.ht

Generalized Stueckelberg-Higgs gauge theories

The aim of this work is to discuss and explorer some generalized aspects of generation of photon mass respecting gauge symmetry. So with this intention we introduce the generalized Stueckelberg and Higgs gauge theories and present the classical and quantum conceptual aspects. We construct the quantum theory by writing the transition amplitude in the Fadeev-Senjanovic formalism and put it in a covariant form by the Fadeev-Popov method. Posteriorly we analyze the independence of physics by gauge choices via BRST symmetry. As we will see, the Stueckelberg structure has influence in the quantization process of the Higgs theory in the Gerardus 't Hooft shape, in which we see an intimate relationship between the Stueckelberg compensating field and the Goldstone boson. The degrees of freedom are explored not only in the quantization process, due to the constraints in gauge theories, but also in the Goldstone theorem, wherein we understand how the generalized gauge field eat the Goldstone boson and acquire mass

The role of HPV in keratinocyte skin cancer development: A systematic review

Keratinocyte skin cancers are the most frequent malignancy, accounting for approximately 30% of all cancers. Although beta genus HPV are the main etiologic agents for squamous cell carcinoma development in patients with epidermodysplasia verruciformis and organ transplant recipients, their role in non-melanoma skin cancer (NMSC) progression in the general population remains controversial. The aim of our review is to summarize current scientific data and to systematically analyze evidence regarding the role of HPV in keratinocyte skin cancers. A total of 2284 patients were included, of which 724 with actinic keratoses, 290 with Bowen’s disease, 949 with cutaneous squamous cell carcinomas and 321 with keratoacanthomas. In the case of actinic keratoses, the majority were positive for beta (n=372, 58.49%) and gamma HPV (n=256, 40.25%) and only a few (n=6, 0.94%) were positive for alpha subtypes. Similarly, most of the cutaneous squamous cell carcinomas were positive for beta (n=248, 55.98%) and gamma HPV (n=172, 33.82%) and 23 cases (2.42%) were positive for alpha subtypes. Bowen’s disease lesions were mostly positive for beta (n=43, 55.84%) and alpha HPV (n=30, 38.96%), in contrast to the gamma genus (n=4, 5.19%). Keratoacanthomas showed a high distribution among beta genus (n=79, 50.31%) and an equal proportion between alpha (n=39, 24.84%) and gamma (n=39, 24.84%) genera. Studies published so far identifying HPV in keratinocyte skin cancers reflect the difference in detection methods rather than a type-specific tendency towards either actinic keratoses, Bowen’s disease, squamous cell carcinoma, or keratoacanthoma. On the other hand, recent evidence regarding the role of HPV vaccination in patients with no-melanoma skin cancer brings into perspective the idea of a beta HPV vaccine or a combined alpha and beta HPV vaccine that could be used as an adjuvant treatment measure in patients with recalcitrant non-melanoma skin cancer

Podolsky Electromagnetism at Finite Temperature: Implications on Stefan-Boltzmann Law

In this work we study Podolsky electromagnetism in thermodynamic equilibrium. We show that a Podolsky mass-dependent modification to the Stefan-Boltzmann law is induced and we use experimental data to limit the possible values for this free parameter.Comment: 13 pages, submitted to Physical Review

Information sharing and credit : firm-level evidence from transition countries

We investigate whether information sharing among banks has affected credit market performance in the transition countries of Eastern Europe and the former Soviet Union, using a large sample of firm-level data. Our estimates show that information sharing is associated with improved availability and lower cost of credit to firms. This correlation is stronger for opaque firms than transparent ones and stronger in countries with weak legal environments than in those with strong legal environments. In cross-sectional estimates, we control for variation in country-level aggregate variables that may affect credit, by examining the differential impact of information sharing across firm types. In panel estimates, we also control for the presence of unobserved heterogeneity at the firm level, as well as for changes in macroeconomic variables and the legal environment