194 research outputs found
Confinement of knotted polymers in a slit
We investigate the effect of knot type on the properties of a ring polymer
confined to a slit. For relatively wide slits, the more complex the knot, the
more the force exerted by the polymer on the walls is decreased compared to an
unknotted polymer of the same length. For more narrow slits the opposite is
true. The crossover between these two regimes is, to first order, at smaller
slit width for more complex knots. However, knot topology can affect these
trends in subtle ways. Besides the force exerted by the polymers, we also study
other quantities such as the monomer-density distribution across the slit and
the anisotropic radius of gyration.Comment: 9 pages, 6 figures, submitted for publicatio
Caracterização de produtores de leite orgùnico e em transição agroecológica do Distrito Federal e RegiÔes Integradas do entorno - Brasil.
Foi elaborada uma pesquisa de campo utilizando o instrumento de diagnĂłstico rĂĄpido participativo-DRP, desenvolvido para colher informaçÔes relacionadas a produção de leite orgĂąnico e em transição agroecolĂłgica a fim de caracterizar unidades familiares na regiĂŁo do Distrito Federal e integrada do entorno (DF-RIDE), Brasil. Com estas açÔes foi possĂvel mapear os produtores na atividade, como tambĂ©m identificar gargalos da produção a partir dos Ăndices estimados, e relacionĂĄ-los com a importĂąncia da conservação das pastagens por meio de parĂąmetros econĂŽmicos e tĂ©cnicos das unidades produtivas da regiĂŁo enfatizando e relacionando-as com o manejo de pastagens agroecolĂłgicas nesses sistemas de produção. O instrumento utilizado auxiliou o produtor de leite a melhor observar suas atividades tĂ©cnicas e econĂŽmicas, promovendo melhorias na gestĂŁo da propriedade. Foi possĂvel ainda construir de forma participativa, mĂ©todos alternativos para melhorar o manejo de pastagens. Abstract: Was elaborate field research using the instrument of participatory rapid diagnosis-DRP, developed to gather information related to organic milk production and agroecological transition and characterize family units in the Federal District and surroundings integrated region (DF-RIDE), Brazil. With these actions was possible to map producers in activity, as well as identify bottlenecks of production from the estimated indices, and relates them with the importance of the pastures conservation, through economic and technical parameters of the productive units in the region emphasizing and relating it to the management of pastures in agroecological production systems. The instrument used assisted the milk producer to better observe their technical and economic activities, promoting improvements in the management of the property. It was still possible to build in a participative manner, alternative methods to improve pasture management
How to reach a few percent level in determining the Lense-Thirring effect?
In this paper we discuss and compare a node-only LAGEOS-LAGEOS II combination
and a node-only LAGEOS-LAGEOS II-Ajisai-Jason1 combination for the
determination of the Lense-Thirring effect. The new combined EIGEN-CG01C Earth
gravity model has been adopted. The second combination cancels the first three
even zonal harmonics along with their secular variations but introduces the
non-gravitational perturbations of Jason1. The first combination is less
sensitive to the non-conservative forces but is sensitive to the secular
variations of the uncancelled even zonal harmonics of low degree J4 and J6
whose impact grows linearly in time.Comment: Latex2e, 22 pag. 1 table, 2 figures, 45 references. Changes in the
Abstract, Introduction and Conclusions. Discussion on the non-gravitational
perturbations on Ajisai and on the impact of the secular rates of the even
zonal harmonics added. EIGEN-CG01C CHAMP+GRACE+terrestrial
gravimetry/altimetry Earth gravity model used. Reference adde
Model Convolution: A Computational Approach to Digital Image Interpretation
Digital fluorescence microscopy is commonly used to track individual proteins and their dynamics in living cells. However, extracting molecule-specific information from fluorescence images is often limited by the noise and blur intrinsic to the cell and the imaging system. Here we discuss a method called âmodel-convolution,â which uses experimentally measured noise and blur to simulate the process of imaging fluorescent proteins whose spatial distribution cannot be resolved. We then compare model-convolution to the more standard approach of experimental deconvolution. In some circumstances, standard experimental deconvolution approaches fail to yield the correct underlying fluorophore distribution. In these situations, model-convolution removes the uncertainty associated with deconvolution and therefore allows direct statistical comparison of experimental and theoretical data. Thus, if there are structural constraints on molecular organization, the model-convolution method better utilizes information gathered via fluorescence microscopy, and naturally integrates experiment and theory
A Feedback Quenched Oscillator Produces Turing Patterning with One Diffuser
Efforts to engineer synthetic gene networks that spontaneously produce patterning in multicellular ensembles have focused on Turing's original model and the âactivator-inhibitorâ models of Meinhardt and Gierer. Systems based on this model are notoriously difficult to engineer. We present the first demonstration that Turing pattern formation can arise in a new family of oscillator-driven gene network topologies, specifically when a second feedback loop is introduced which quenches oscillations and incorporates a diffusible molecule. We provide an analysis of the system that predicts the range of kinetic parameters over which patterning should emerge and demonstrate the system's viability using stochastic simulations of a field of cells using realistic parameters. The primary goal of this paper is to provide a circuit architecture which can be implemented with relative ease by practitioners and which could serve as a model system for pattern generation in synthetic multicellular systems. Given the wide range of oscillatory circuits in natural systems, our system supports the tantalizing possibility that Turing pattern formation in natural multicellular systems can arise from oscillator-driven mechanisms
Transcriptional and Proteomic Analysis of the Aspergillus fumigatus ÎprtT Protease-Deficient Mutant
Aspergillus fumigatus is the most common opportunistic mold pathogen of humans, infecting immunocompromised patients. The fungus invades the lungs and other organs, causing severe damage. Penetration of the pulmonary epithelium is a key step in the infectious process. A. fumigatus produces extracellular proteases to degrade the host structural barriers. The A. fumigatus transcription factor PrtT controls the expression of multiple secreted proteases. PrtT shows similarity to the fungal Gal4-type Zn(2)-Cys(6) DNA-binding domain of several transcription factors. In this work, we further investigate the function of this transcription factor by performing a transcriptional and a proteomic analysis of the ÎprtT mutant. Unexpectedly, microarray analysis revealed that in addition to the expected decrease in protease expression, expression of genes involved in iron uptake and ergosterol synthesis was dramatically decreased in the ÎprtT mutant. A second finding of interest is that deletion of prtT resulted in the upregulation of four secondary metabolite clusters, including genes for the biosynthesis of toxic pseurotin A. Proteomic analysis identified reduced levels of three secreted proteases (ALP1 protease, TppA, AFUA_2G01250) and increased levels of three secreted polysaccharide-degrading enzymes in the ÎprtT mutant possibly in response to its inability to derive sufficient nourishment from protein breakdown. This report highlights the complexity of gene regulation by PrtT, and suggests a potential novel link between the regulation of protease secretion and the control of iron uptake, ergosterol biosynthesis and secondary metabolite production in A. fumigatus
Visualization of lipid-receptor interactions on single cells by time-resolved imaging fluorescence microscopy
Evidence for widespread hydrated minerals on asteroid (101955) Bennu
Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the form of a near-infrared absorption near 2.7â”m and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the visible and near-infrared (0.4 to 2.4â”m) Bennuâs spectrum appears featureless and with a blue (negative) slope, confirming previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic chemistry to Earth
The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx measurements
The top-shaped morphology characteristic of asteroid (101955) Bennu, often found among fast-spinning asteroids and binary asteroid primaries, may have contributed substantially to binary asteroid formation. Yet a detailed geophysical analysis of this morphology for a fast-spinning asteroid has not been possible prior to the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission. Combining the measured Bennu mass and shape obtained during the Preliminary Survey phase of the OSIRIS-REx mission, we find a notable transition in Bennuâs surface slopes within its rotational Roche lobe, defined as the region where material is energetically trapped to the surface. As the intersection of the rotational Roche lobe with Bennuâs surface has been most recently migrating towards its equator (given Bennuâs increasing spin rate), we infer that Bennuâs surface slopes have been changing across its surface within the last million years. We also find evidence for substantial density heterogeneity within this body, suggesting that its interior is a mixture of voids and boulders. The presence of such heterogeneity and Bennuâs top shape are consistent with spin-induced failure at some point in its past, although the manner of its failure cannot yet be determined. Future measurements by the OSIRIS-REx spacecraft will provide insight into and may resolve questions regarding the formation and evolution of Bennuâs top-shape morphology and its link to the formation of binary asteroids
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