1,007 research outputs found
Writhing Geometry of Open DNA
Motivated by recent experiments on DNA torsion-force-extension
characteristics we consider the writhing geometry of open stiff molecules. We
exhibit a cyclic motion which allows arbitrarily large twisting of the end of a
molecule via an activated process. This process is suppressed for forces larger
than femto-Newtons which allows us to show that experiments are sensitive to a
generalization of the Calugareanu-White formula for the writhe. Using numerical
methods we compare this formulation of the writhe with recent analytic
calculations.Comment: 12 pages 10 figures. Revtex
Geometric depolarization in patterns formed by backscattered light
We formulate a framework for the depolarization of linearly polarized
backscattered light based on the concept of geometric phase, {\it i.e} Berry's
phase. The predictions of this theory are applied to the patterns formed by
backscattered light between crossed or parallel polarizers. This theory should
be particularly adapted to the situation in which polarized light is scattered
many times but predominantly in the forward direction. We apply these ideas to
the patterns which we obtained experimentally with backscattered polarized
light from a colloidal suspension.Comment: 3 pages and 3 figure
The lexical nature of alpha-beta oscillations in context-driven word production
In context-driven word production, picture naming is faster following constrained than neutral sentential contexts (e.g., âThe farmer milked the⊠[picture]â vs. âThe child drew a⊠[picture]â, followed by the picture of a cow), suggesting conceptual-lexical pre-activation of the target response. Power decreases in the alpha-beta oscillatory band (8â25 Hz) are consistently found for constrained relative to neutral contexts prior to picture onset, when conceptual and lexical retrieval is ongoing. However, it remains a matter of debate whether the alpha-beta power decreases reflect (low-level) expectations of the visual input, conceptual and lexical retrieval, or motor preparation. The present study aimed at investigating the lexical-semantic nature of alpha-beta oscillations. Participants performed context-driven picture naming with constrained and neutral contexts. In addition, an auditory distractor word was presented before picture onset. Distractors were either semantically related (e.g., âgoatâ) or unrelated (e.g., âbeanâ) to the picture to be named. Picture naming was faster with constrained than neutral contexts. Distractor type did not affect naming latencies nor the behavioural context effect. In the oscillatory brain responses, the context-related alpha-beta power decreases were observed throughout the pre-picture interval when distractors were semantically unrelated to the picture, in line with previous findings. However, with semantically related distractors, the context effect was delayed until a period after distractor processing. Thus, alpha-beta power seems to be sensitive to the semantic relationship between the distractor word and the picture to be named. We interpret these results as suggesting that alpha-beta power decreases in context-driven word production reflect lexical-semantic retrieval mechanisms
Comment on "Elasticity Model of a Supercoiled DNA Molecule"
We perform simulations to numerically study the writhe distribution of a
stiff polymer. We compare with analytic results of Bouchiat and Mezard (PRL 80
1556- (1998); cond-mat/9706050).Comment: 1 page, 1 figure revtex
DNA loop statistics and torsional modulus
The modelling of DNA mechanics under external constraints is discussed. Two
analytical models are widely known, but disagree for instance on the value of
the torsional modulus. The origin of this embarassing situation is located in
the concept of writhe. This letter presents a unified model for DNA
establishing a relation between the different approaches. I show that the
writhe created by the loops of DNA is at the origin of the discrepancy. To take
this into account, I propose a new treatment of loop statistics based on
numerical simulations using the most general formula for the writhe, and on
analytic calculations with only one fit parameter. One can then compute the
value of the torsional modulus of DNA without the need of any cut-off.Comment: 8 pages, 1 figure. Accepted by Europhysics Letter
Extending displacement-based earthquake loss assessment (DBELA) for the computation of fragility curves
This paper presents a new procedure to derive fragility functions for populations of buildings that relies on the
displacement-based earthquake loss assessment (DBELA) methodology. In the method proposed herein,
thousands of synthetic buildings have been produced considering the probabilistic distribution describing the
variability in geometrical and material properties. Then, their nonlinear capacity has been estimated using the
DBELA method and their response against a large set of ground motion records has been estimated. Global limit
states are used to estimate the distribution of buildings in each damage state for different levels of ground
motion, and a regression algorithm is applied to derive fragility functions for each limit state. The proposed
methodology is demonstrated for the case of ductile and non-ductile Turkish reinforced concrete frames with
masonry infills
Tuberculosis/HIV/AIDS coinfection in Porto Alegre, RS/Brazil - invisibility and silencing of the most affected groups
OBJECTIVE: To analyze how belonging to certain social groups contributes to constituting the vulnerabilities associated with illnesses due to tuberculosis/HIV/AIDS coinfection. METHODOLOGYThis is a qualitative study carried out in the city of Porto Alegre, state of Rio Grande do Sul, in regions of high social vulnerability. Twenty coinfected people were interviewed in specialized health services between August and December 2016. The analysis was based on the frameworks The Sound of Silence and Vulnerability and Human Rights. RESULTS: Socioeconomic conditions were decisive for the constitution of the vulnerability conditions. Processes of people invisibilization, and the silencing of their voices, in a scenario marked by economic, racial and gender inequalities, contributed for their health needs not to be understood and effectively taken into account in the services actions. FINAL CONSIDERATIONS: The more effective strategies are to legitimize voices and to understand the needs of those affected by coinfection, the greater the chances that programmatic responses to the problem will be successful
Gate stability of GaN-Based HEMTs with P-Type Gate
status: publishe
- âŠ