3,641 research outputs found
Fractal templates in the escape dynamics of trapped ultracold atoms
We consider the dynamic escape of a small packet of ultracold atoms launched
from within an optical dipole trap. Based on a theoretical analysis of the
underlying nonlinear dynamics, we predict that fractal behavior can be seen in
the escape data. This data would be collected by measuring the time-dependent
escape rate for packets launched over a range of angles. This fractal pattern
is particularly well resolved below the Bose-Einstein transition temperature--a
direct result of the extreme phase space localization of the condensate. We
predict that several self-similar layers of this novel fractal should be
measurable and we explain how this fractal pattern can be predicted and
analyzed with recently developed techniques in symbolic dynamics.Comment: 11 pages with 5 figure
Effect of pseudouridylation on the structure and activity of the catalytically essential P6.1 hairpin in human telomerase RNA
Telomerase extends the 3′-ends of linear chromosomes by adding conserved telomeric DNA repeats and is essential for cell proliferation and genomic stability. Telomerases from all organisms contain a telomerase reverse transcriptase and a telomerase RNA (TER), which together provide the minimal functional elements for catalytic activity in vitro. The RNA component of many functional ribonucleoproteins contains modified nucleotides, including conserved pseudouridines (Ψs) that can have subtle effects on structure and activity. We have identified potential Ψ modification sites in human TER. Two of the predicted Ψs are located in the loop of the essential P6.1 hairpin from the CR4-CR5 domain that is critical for telomerase catalytic activity. We investigated the effect of P6.1 pseudouridylation on its solution NMR structure, thermodynamic stability of folding and telomerase activation in vitro. The pseudouridylated P6.1 has a significantly different loop structure and increase in stability compared to the unmodified P6.1. The extent of loop nucleotide interaction with adjacent residues more closely parallels the extent of loop nucleotide evolutionary sequence conservation in the Ψ-modified P6.1 structure. Pseudouridine-modification of P6.1 slightly attenuates telomerase activity but slightly increases processivity in vitro. Our results suggest that Ψs could have a subtle influence on human telomerase activity via impact on TER–TERT or TER–TER interactions
Community concepts of malaria-related illness with and without convulsions in southern Ghana
BACKGROUND: Malaria, both with or without convulsions, is a serious hardship for people living in endemic areas, especially in sub-Saharan Africa. Community references to malaria, however, may encompass other conditions, which was collectively designated malaria-related illness (MRI). Inasmuch as the presence or absence of convulsions reportedly affects timely help-seeking for malaria, a local comparison of these conditions is needed to inform malaria control. METHODS: Vignette-based EMIC interviews (insider-perspective interviews) for MRI with convulsions (convulsion positive, MRI-CP) and without convulsions (convulsion negative, MRI-CN) were developed to study relevant features of MRI-related experience, meaning and behaviour in two rural communities in Ghana. These semi-structured interviews elicited both qualitative narrative and categorical codes for quantitative analysis. Interviews with 201 respondents were conducted. RESULTS: The conditions depicted in the vignettes were well recognized by respondents and named with various local terms. Both presentations were considered serious, but MRI-CP was more frequently regarded potentially fatal than MRI-CN. More than 90.0% of respondents in both groups acknowledged the need to seek outside help. However, significantly more respondents advised appropriate help-seeking within 24 (p = 0.01) and 48 (p = 0.01) hours for MRI-CP. Over 50.0% of respondents responding to questions about MRI-CP identified MRI-CN as a cause of convulsions. CONCLUSION: Local comparison of MRI-CP and MRI-CN based on vignettes found a similar profile of reported categories of perceived causes, patterns of distress, help-seeking and preventive measures for both presentations. This differs from previous findings in sub-Saharan Africa, which assert communities regard the two conditions to be unrelated. The perceived relationships should be acknowledged in formulating strategies to control malaria through timely help-seeking and treatment to reduce childhood mortality
Calculation of a Deuterium Double Shock Hugoniot from Ab initio Simulations
We calculate the equation of state of dense deuterium with two ab initio
simulations techniques, path integral Monte Carlo and density functional theory
molecular dynamics, in the density range of 0.67 < rho < 1.60 g/cc. We derive
the double shock Hugoniot and compare with the recent laser-driven double shock
wave experiments by Mostovych et al. [1]. We find excellent agreement between
the two types of microscopic simulations but a significant discrepancy with the
laser-driven shock measurements.Comment: accept for publication in Phys. Rev. Lett., Nov. 2001, 4 pages, 4
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The effect of stress on paleomagnetic signals: A micromagnetic study of magnetite’s single-vortex response
In this study we use micromagnetic modeling to show that the magnetizations of magnetically single-vortex particles rotate toward the stress axis on the application of a differential compression stress. This is the exact opposite response to magnetically single-domain particles, which previously provided the theoretical underpinning of the effect of stress on the magnetic signals of rocks. We show that the magnetization directions of single-vortex and equant single-domain particles are altered by much lower stresses than previously predicted, c.f., 100 versus 1,000 MPa; where a change in magnetization is defined as a rotation of >3° after the removal of stress. The magnetization intensity of assemblages also drops by ∼20%–30% on the application and removal of stress of ∼100 MPa. Given that single-vortex particles are now thought to dominate the magnetization of most rocks, future studies should account for paleomagnetic directional uncertainties and potential underestimation of the ancient magnetic field intensity
Delayed Decision-making in Real-time Beatbox Percussion Classification
This is an electronic version of an article published in Journal of New Music Research, 39(3), 203-213, 2010. doi:10.1080/09298215.2010.512979. Journal of New Music Research is available online at: www.tandfonline.com/openurl?genre=article&issn=1744-5027&volume=39&issue=3&spage=20
Previous heat treatment inducing different plasma nitriding behaviors in martensitic stainless steel
In this work we report a study of the induced changes in structure and corrosion behavior of martensitic stainless steels nitrided by plasma immersion ion implantation (PI3) at different previous heat treatments. The samples were characterized by x-ray diffraction and glancing angle x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, and potentiodynamic measurements. Depending on the proportion of retained austenite in the unimplanted material, different phase transformations are obtained at lower and intermediate temperatures of nitrogen implantation. At higher temperatures, the great mobility of the chromium yields CrN segregations like spots in random distribution, and the alpha'-martensite is degraded to alpha-Fe (ferrite). The nitrided layer thickness follows a fairly linear relationship with the temperature and a parabolic law with the process time. The corrosion resistance depends strongly on chromium segregation from the martensitic matrix, as a result of the formation of CrN during the nitrogen implantation process and the formation of CrxC during the heat treatment process. Briefly speaking, the best results are obtained using low tempering temperature and low implantation temperature (below 375 degrees) due to the increment of the corrosion resistance and nitrogen dissolution in the structure with not too high diffusion depths (about 5-10 mu m). (c) 2006 American Vacuum Society
Topological Analysis of Metabolic Networks Integrating Co-Segregating Transcriptomes and Metabolomes in Type 2 Diabetic Rat Congenic Series
Background: The genetic regulation of metabolic phenotypes (i.e., metabotypes) in type 2 diabetes mellitus is caused by complex organ-specific cellular mechanisms contributing to impaired insulin secretion and insulin resistance. Methods: We used systematic metabotyping by 1H NMR spectroscopy and genome-wide gene expression in white adipose tissue to map molecular phenotypes to genomic blocks associated with obesity and insulin secretion in a series of rat congenic strains derived from spontaneously diabetic Goto-Kakizaki (GK) and normoglycemic Brown-Norway (BN) rats. We implemented a network biology strategy approach to visualise shortest paths between metabolites and genes significantly associated with each genomic block. Results: Despite strong genomic similarities (95-99%) among congenics, each strain exhibited specific patterns of gene expression and metabotypes, reflecting metabolic consequences of series of linked genetic polymorphisms in the congenic intervals. We subsequently used the congenic panel to map quantitative trait loci underlying specific metabotypes (mQTL) and genome-wide expression traits (eQTL). Variation in key metabolites like glucose, succinate, lactate or 3-hydroxybutyrate, and second messenger precursors like inositol was associated with several independent genomic intervals, indicating functional redundancy in these regions. To navigate through the complexity of these association networks we mapped candidate genes and metabolites onto metabolic pathways and implemented a shortest path strategy to highlight potential mechanistic links between metabolites and transcripts at colocalized mQTLs and eQTLs. Minimizing shortest path length drove prioritization of biological validations by gene silencing. Conclusions: These results underline the importance of network-based integration of multilevel systems genetics datasets to improve understanding of the genetic architecture of metabotype and transcriptomic regulations and to characterize novel functional roles for genes determining tissue-specific metabolism
Approximating a Behavioural Pseudometric without Discount for<br> Probabilistic Systems
Desharnais, Gupta, Jagadeesan and Panangaden introduced a family of
behavioural pseudometrics for probabilistic transition systems. These
pseudometrics are a quantitative analogue of probabilistic bisimilarity.
Distance zero captures probabilistic bisimilarity. Each pseudometric has a
discount factor, a real number in the interval (0, 1]. The smaller the discount
factor, the more the future is discounted. If the discount factor is one, then
the future is not discounted at all. Desharnais et al. showed that the
behavioural distances can be calculated up to any desired degree of accuracy if
the discount factor is smaller than one. In this paper, we show that the
distances can also be approximated if the future is not discounted. A key
ingredient of our algorithm is Tarski's decision procedure for the first order
theory over real closed fields. By exploiting the Kantorovich-Rubinstein
duality theorem we can restrict to the existential fragment for which more
efficient decision procedures exist
Designing Chatbots for Crises: A Case Study Contrasting Potential and Reality
Chatbots are becoming ubiquitous technologies, and their popularity and adoption are rapidly spreading. The potential of chatbots in engaging people with digital services is fully recognised. However, the reputation of this technology with regards to usefulness and real impact remains rather questionable. Studies that evaluate how people perceive and utilise chatbots are generally lacking. During the last Kenyan elections, we deployed a chatbot on Facebook Messenger to help people submit reports of violence and misconduct experienced in the polling stations. Even though the chatbot was visited by more than 3,000 times, there was a clear mismatch between the users’ perception of the technology and its design. In this paper, we analyse the user interactions and content generated through this application and discuss the challenges and directions for designing more effective chatbots
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