2,327 research outputs found
Ionic partition and transport in multi-ionic channels: A Molecular Dynamics Simulation study of the OmpF bacterial porin
We performed all-atom molecular dynamics simulations studying the partition
of ions and the ionic current through the bacterial porin OmpF and two selected
mutants. The study is motivated by new interesting experimental findings
concerning their selectivity and conductance behaviour at neutral pH. The
mutations considered here are designed to study the effect of removal of
negative charges present in the constriction zone of the wild type OmpF channel
(which contains on one side a cluster with three positive residues and on the
other side two negatively charged residues). Our results show that these
mutations induce an exclusion of cations from the constriction zone of the
channel, substantially reducing the flow of cations. In fact, the partition of
ions inside the mutant channels is strongly inhomogeneous, with regions
containing excess of cations and regions containing excess of anions.
Interestingly, the overall number of cations inside the channel is larger than
the number of anions in the two mutants, as in the OmpF wild type channel. We
found that the differences in ionic charge inside these channels are justified
by the differences in electric charge between the wild type OmpF and the
mutants, following an electroneutral balance
Effective connectivity reveals strategy differences in an expert calculator
Mathematical reasoning is a core component of cognition and the study of experts defines the upper limits of human cognitive abilities, which is why we are fascinated by peak performers, such as chess masters and mental calculators. Here, we investigated the neural bases of calendrical skills, i.e. the ability to rapidly identify the weekday of a particular date, in a gifted mental calculator who does not fall in the autistic spectrum, using functional MRI. Graph-based mapping of effective connectivity, but not univariate analysis, revealed distinct anatomical location of “cortical hubs” supporting the processing of well-practiced close dates and less-practiced remote dates: the former engaged predominantly occipital and medial temporal areas, whereas the latter were associated mainly with prefrontal, orbitofrontal and anterior cingulate connectivity. These results point to the effect of extensive practice on the development of expertise and long term working memory, and demonstrate the role of frontal networks in supporting performance on less practiced calculations, which incur additional processing demands. Through the example of calendrical skills, our results demonstrate that the ability to perform complex calculations is initially supported by extensive attentional and strategic resources, which, as expertise develops, are gradually replaced by access to long term working memory for familiar material
A novel method for the isolation of subpopulations of rat adipose stem cells with different proliferation and osteogenic differentiation potentials
Bone marrow has been the elected cell source of studies published so far concerning bone and cartilage tissue-engineering approaches. Recent studies indicate that adipose tissue presents significant advantages over bone marrow as a cell source for tissue engineering. Most of these
studies report the use of adipose stem cells (ASCs) isolated by a method based on the enzymatic digestion of the adipose tissue and on the ability of stem cells to adhere to a cell culture plastic surface. Using this method, a heterogeneous population was obtained containing different cell types that have been shown to compromise the proliferation and differentiation potential of the
stem cells. This paper reports the development and optimization of a new isolation method that
enables purified cell populations to be obtained that exhibit higher osteogenic differentiation
and/or proliferation potential. This method is based on the use of immunomagnetic beads coated
with specific antibodies and it is compared with other methods described in the literature for
the selection of stem cell populations, e.g. methods based on a gradient solution and enzymatic
digestion. The results showed that the isolation method based on immunomagnetic beads allows
distinct subpopulations of rat ASCs to be isolated, showing different stem cells marker expressions
and different osteogenic differentiation potentials. Therefore, this method can be used to study
niches in ASC populations and/or also allow adipose tissue to be used as a stem cell source in a more efficient manner, increasing the potential of this cell source in future clinical applications.T. Rada thanks the EU Marie Curie Actions Alea Jacta Est for a PhD fellowship. This work was partially supported by the European Union-funded STREP Project HIPPOCRATES (Grant
No. NMP3-CT-2003-505758) and was carried out under the scope of the European NoE EXPERTISSUES (Grant No. NMP3-CT-2004-500283)
Evidence for an excess of B -> D(*) Tau Nu decays
Based on the full BaBar data sample, we report improved measurements of the
ratios R(D(*)) = B(B -> D(*) Tau Nu)/B(B -> D(*) l Nu), where l is either e or
mu. These ratios are sensitive to new physics contributions in the form of a
charged Higgs boson. We measure R(D) = 0.440 +- 0.058 +- 0.042 and R(D*) =
0.332 +- 0.024 +- 0.018, which exceed the Standard Model expectations by 2.0
sigma and 2.7 sigma, respectively. Taken together, our results disagree with
these expectations at the 3.4 sigma level. This excess cannot be explained by a
charged Higgs boson in the type II two-Higgs-doublet model. We also report the
observation of the decay B -> D Tau Nu, with a significance of 6.8 sigma.Comment: Expanded section on systematics, text corrections, improved the
format of Figure 2 and included the effect of the change of the Tau
polarization due to the charged Higg
Investigating reaction pathways in rare events simulations of antibiotics diffusion through protein channels
A search for the decay modes B+/- to h+/- tau l
We present a search for the lepton flavor violating decay modes B+/- to h+/-
tau l (h= K,pi; l= e,mu) using the BaBar data sample, which corresponds to 472
million BBbar pairs. The search uses events where one B meson is fully
reconstructed in one of several hadronic final states. Using the momenta of the
reconstructed B, h, and l candidates, we are able to fully determine the tau
four-momentum. The resulting tau candidate mass is our main discriminant
against combinatorial background. We see no evidence for B+/- to h+/- tau l
decays and set a 90% confidence level upper limit on each branching fraction at
the level of a few times 10^-5.Comment: 15 pages, 7 figures, submitted to Phys. Rev.
Search for the decay modes D^0 → e^+e^-, D^0 → μ^+μ^-, and D^0 → e^±μ∓
We present searches for the rare decay modes D^0→e^+e^-, D^0→μ^+μ^-, and D^0→e^±μ^∓ in continuum e^+e^-→cc events recorded by the BABAR detector in a data sample that corresponds to an integrated luminosity of 468 fb^(-1). These decays are highly Glashow–Iliopoulos–Maiani suppressed but may be enhanced in several extensions of the standard model. Our observed event yields are consistent with the expected backgrounds. An excess is seen in the D^0→μ^+μ^- channel, although the observed yield is consistent with an upward background fluctuation at the 5% level. Using the Feldman–Cousins method, we set the following 90% confidence level intervals on the branching fractions: B(D^0→e^+e^-)<1.7×10^(-7), B(D^0→μ^+μ^-) within [0.6,8.1]×10^(-7), and B(D^0→e^±μ^∓)<3.3×10^(-7)
Recommended from our members
The development of perceptual averaging: learning what to do, not just how to do it
The mature visual system condenses complex scenes into simple summary statistics (e.g., average size, location, orientation, etc.). However, children, often perform poorly on perceptual averaging tasks. Children's difficulties are typically thought to represent the suboptimal implementation of an adult-like strategy. This paper examines another possibility: that children actually make decisions in a qualitatively different way to adults (optimal implementation of a non-ideal strategy).
Ninety children (6-7, 8-9, 10-11 years) and 30 adults were asked to locate the middle of randomly generated dot-clouds. Nine plausible decision strategies were formulated, and each was fitted to observers' trial-by-trial response data (Reverse Correlation). When the number of visual elements was low (N < 6), children used a qualitatively different decision strategy from adults: appearing to "join up the dots" and locate the gravitational center of the enclosing shape. Given denser displays, both children and adults used an ideal strategy of arithmetically averaging individual points. Accounting for this difference in decision strategy explained 29% of children's lower precision. These findings suggest that children are not simply suboptimal at performing adult-like computations, but may at times use sensible, but qualitatively different strategies to make perceptual judgments. Learning which strategy is best in which circumstance might be an important driving factor of perceptual development
- …