Collapse of ρxx\rho_{xx} ringlike structures in 2DEGs under tilted magnetic fields

In the quantum Hall regime, the longitudinal resistivity $\rho_{xx}$ plotted as a density--magnetic-field ($n_{2D}-B$) diagram displays ringlike structures due to the crossings of two sets of spin split Landau levels from different subbands [e.g., Zhang \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 216801 (2005)]. For tilted magnetic fields, some of these ringlike structures "shrink" as the tilt angle is increased and fully collapse at $\theta_c \approx 6^\circ$. Here we theoretically investigate the topology of these structures via a non-interacting model for the 2DEG. We account for the inter Landau-level coupling induced by the tilted magnetic field via perturbation theory. This coupling results in anti-crossings of Landau levels with parallel spins. With the new energy spectrum, we calculate the corresponding $n_{2D}-B$ diagram of the density of states (DOS) near the Fermi level. We argue that the DOS displays the same topology as $\rho_{xx}$ in the $n_{2D}-B$ diagram. For the ring with filling factor $\nu=4$, we find that the anti-crossings make it shrink for increasing tilt angles and collapse at a large enough angle. Using effective parameters to fit the $\theta = 0^\circ$ data, we find a collapsing angle $\theta_c \approx 3.6^\circ$. Despite this factor-of-two discrepancy with the experimental data, our model captures the essential mechanism underlying the ring collapse.Comment: 3 pages, 2 figures; Proceedings of the PASPS V Conference Held in August 2008 in Foz do Igua\c{c}u, Brazi

Longitudinal variation in O6-alkylguanine DNA-alkyltransferase activity in the human colon and rectum

In a systematic study of O6-alkylguanine DNA-alkyltransferase activity in the human colon and rectum, tumours were found to occur in regions of low activity. These results are consistent with the hypothesis that O6-alkylguanine DNA-alkyltransferase levels and alkylating agent exposure may be important determinants of large bowel tumorigenesis

Nonlinear Dynamics of the Perceived Pitch of Complex Sounds

We apply results from nonlinear dynamics to an old problem in acoustical physics: the mechanism of the perception of the pitch of sounds, especially the sounds known as complex tones that are important for music and speech intelligibility

Crack-cocaine users have less family cohesion than alcohol users

Objective: Many studies correlate characteristics of family functioning and the development of drug addiction. This study sought to evaluate and compare the family environment styles of two groups of psychoactive substance users: 1) alcohol-only users and 2) crack-cocaine users. Methods: Three hundred and sixty-four users of alcohol, crack-cocaine, and other drugs, recruited from research centers in four Brazilian capitals participated in this study. Subjects were evaluated through the Family Environment Scale and the Addiction Severity Index, 6th version (ASI-6). ASI-6 t-scores were compared by analysis of variance (ANOVA) and post-hoc tests. A final model was obtained using a logistic regression analysis. All analyses were adjusted for partner, age, and psychiatric t-score. Results: We found a significant difference between groups in the cohesion subscale (p = 0.044). The post-hoc test revealed a difference of 1.06 points (95% CI 0.11-2.01) between groups 1 (6.45 +/- 0.28) and 2 (5.38 +/- 0.20). No significant between-group differences were observed in the other subscales. However, categorical analyses of variables regarding family dynamic showed that crack users more often reported that sometimes people in their family hit each other (30.4% vs. 13.2%, p = 0.007) and that people in their family frequently compared each other regarding work and/or school achievement (57.2% vs. 42.6%, p = 0.041). Conclusion: These results suggest that families of crack-cocaine users are less cohesive than families of alcohol users. This type of family environment may affect treatment outcome, and should thus be adequately approached.SENADNational Institutes of Health/National Institute on Drug AbuseUniv Fed Rio do Grande UFRGS, HCPA, CPAD, Porto Alegre, RS, BrazilHCPA, Unidade Bioestat, Porto Alegre, RS, BrazilUniv Fed Rio Grande do Sul, Lab Biossinais Fenomenol & Cognicao, Inst Psicol, Porto Alegre, RS, BrazilUniv Fed Sao Paulo UNIFESP, Dept Psicobiol, Sao Paulo, SP, BrazilUniv Fed Rio de Janeiro UFRJ, Inst Psiquiatria, Rio De Janeiro, RJ, BrazilUniv Fed Sao Paulo UNIFESP, Dept Psicobiol, Sao Paulo, SP, BrazilSENAD: TC 005/2005Web of Scienc

The September 2004 stench off the southern Malabar coast - A consequence of holococcolithophore bloom

During the third week of September 2004, particularly on 16th and 17th, an unusual and strong stench was reported from the coast at Kollam and Vizhinjam in Kerala (India). Local dailies reported that over 200 children, mostly below 15 years, complained of nausea, chest pain and short periods of breathlessness because of the stench. Many were hospitalized, but were discharged within a couple of hours. A press report stated that the stench was due to dead fish scattered on the beaches and in the water. The report linked the fish death to oxygen depletion and choking of fish gills. Both were reported to be possibly due to proliferation and eventual putrefaction of a fish-toxic alga Cochlodinium polykreikoides. Information was put up on the web that the bloom was caused by Karenia brevis, a toxic dinoflagellate. It was reported that the stench could be felt up to 5 km inland from the coast. On 20 September 2004, the Government of Kerala requested the National Institute of Oceanography (NIO), Goa to determine the cause of the phenomenon. In response, a team from NIO collected near-shore samples of water on 23 and 26 September off Vizhinjam, Shanghumugham and Kollam. During 3-7 October 2004, RV Sagar Sukti, a coastal research vessel of NIO, was used to collect samples in the waters offshore of Vizhinjam, Veli, Kollam in the depth zones of 20-50 m. The water samples collected on 23 and 26 September from the near-shore spots were analysed for various chemical (dissolved oxygen, hydrogen sulphide, nutrients, and salinity) and biological (microbiological, phytoplankton counting and identification) variables. Data from sea-level records at Cochin Port were also examined to learn about the possible evolution of physical conditions before and after the episode described above. In this preliminary report inferences based on analysis of the data is presented

Avaliação da dinâmica litorânea da região de Baixio/Barra do Itariri, litoral norte do Estado da Bahia, utilizando o Sistema de Modelagem Costeira (SMC-Brasil)

The software Sistema de Modelagem Costeira (SMC-Brasil) performs various numerical models that allow for conducting short-, middle- and long-term analyses on beaches, thus contributing to coastal studies and management plans. The objective of the present study was to characterize wave and coastal current dynamics of the coastal area of the settlings of Baixio and Barra do Itariri, northern coast of the State of Bahia, producing wave propagation, sediment transport and flux, and inundation level. The wave statistical analysis for the study area, in terms of mean and extreme conditions, performed for intermediate waters, in Point 1 (Dow Point), indicated a predominance of waves from ESE and SE, with heights ranging between 1.61 and 3.25 m and periods, between 7.87 and 13.81 s. Shallow-water wave climate modelling was performed based on Point 1, analyzing others seven profiles along the coast. This analysis indicated a predominance of waves from SE, reaching approximately 1.4 m of height in the surf zone, and the occurrence of three rip currents. The calculation of mean annual longshore transport rates indicated the existence of a divergence zone in the direction of the net transport near Baixio and a northward increase in the percentage of incidence of waves from SE. The combination of storm events with positive meteorological tides, astronomical spring tides and extreme run-up values, can result in high-risk situations for ecosystems and properties, with great impacts on the studied coast, which currently presents high vulnerability to coastal erosion.O Sistema de Modelagem Costeira (SMC-Brasil) integra diferentes modelos numéricos que permitem realizar análises em curto, médio e longo prazo de uma praia, contribuindo para estudos e planos de gestão litorâneos. O objetivo deste trabalho é caracterizar a dinâmica de ondas e correntes costeiras do trecho litorâneo entre os povoados de Baixio e Barra do Itariri, litoral norte do Estado da Bahia, a fim de gerar modelos de propagação de ondas, transporte, fluxo sedimentar e cota de inundação. A análise estatística de ondas para a área de estudo, em termos de condições médias e extremas, realizada para águas intermediárias, no Ponto 1 (Ponto Dow), indicou um predomínio das ondas vindas de ESE e SE, com alturas variando de 1,61 a 3,25 m e períodos variando de 7,87 a 13,81 s. A partir deste ponto foi realizada a modelagem do clima de ondas em águas rasas, analisada em outros sete pontos do litoral. Esta análise indicou uma predominância das ondas de SE, alcançando alturas em torno de 1,4 m na zona de arrebentação, e a ocorrência de três zonas de correntes de retorno. O cálculo das taxas médias anuais de transporte longitudinal mostrou a existência de uma zona de divergência no sentido do transporte líquido nas proximidades de Baixio e um aumento no percentual de incidência das ondas de SE seguindo para norte da área. A combinação de eventos de tempestades com marés meteorológicas positivas, marés astronômicas de sizígia e valores extremos de espraiamento de onda, pode resultar em situações de alto risco para ecossistemas e propriedades, com grandes impactos para o litoral estudado, que atualmente já apresenta uma alta vulnerabilidade à erosão costeira