Structure of exotic three-body systems

The classification of large halos formed by two identical particles and a core is systematically addressed according to interparticle distances. The root-mean-square distances between the constituents are described by universal scaling functions obtained from a renormalized zero-range model. Applications for halo nuclei, $^{11}$Li and $^{14}$Be, and for atomic $^4$He$_3$ are briefly discussed. The generalization to four-body systems is proposed.Comment: Contribution to the International workshop "Critical Stability of Few-Body Quantum Systems". To be published in "Few-Body Systems

A chemical genetic approach reveals distinct EphB signaling mechanisms during brain development.

EphB receptor tyrosine kinases control multiple steps in nervous system development. However, it remains unclear whether EphBs regulate these different developmental processes directly or indirectly. In addition, given that EphBs signal through multiple mechanisms, it has been challenging to define which signaling functions of EphBs regulate particular developmental events. To address these issues, we engineered triple knock-in mice in which the kinase activity of three neuronally expressed EphBs can be rapidly, reversibly and specifically blocked. We found that the tyrosine kinase activity of EphBs was required for axon guidance in vivo. In contrast, EphB-mediated synaptogenesis occurred normally when the kinase activity of EphBs was inhibited, suggesting that EphBs mediate synapse development by an EphB tyrosine kinase-independent mechanism. Taken together, our data indicate that EphBs control axon guidance and synaptogenesis by distinct mechanisms and provide a new mouse model for dissecting EphB function in development and disease

Tobacco retail policy landscape: a longitudinal survey of US states

There are ∼380 000 tobacco retailers in the USA, where the largest tobacco companies spend almost $9 billion a year to promote their products. No systematic survey has been conducted of state-level activities to regulate the retail environment, thus little is known about what policies are being planned, proposed or implemented

A new type of carbon resistance thermometer with excellent thermal contact at millikelvin temperatures

Using a new brand of commercially available carbon resistor we built a cryogenic thermometer with an extremely good thermal contact to its thermal environment. Because of its superior thermal contact the thermometer is insensitive to low levels of spurious radio frequency heating. We calibrated our thermometer down to 5mK using a quartz tuning fork He-3 viscometer and measured its thermal resistance and thermal response time.Comment: 5 pages, 4 figure

Abundance And Vertical Flux Of Pseudo-Nitzschia In The Northern Gulf Of Mexico

Many species of the ubiquitous pennate diatom genus Pseudo-nitzschia have recently been discovered to produce domoic acid, a potent neurotoxin which causes Amnesic Shellfish Poisoning (ASP). Pseudo-nitzschia spp. were extremely abundant (up to 10(8) cells l(-1); present in 67% of 2195 samples) from 1990 to 1994 on the Louisiana and Texas, USA, continental shelves and moderately abundant (up to 10(5) cells l(-1); present in 18% of 192 samples) over oyster beds in the Terrebonne Bay estuary in Louisiana in 1993 and 1994. On the shelf there was a strong seasonal cycle with maxima every spring for 5 yr and sometimes in the fall, which were probably related to river flow, water column stability, and nutrient availability. In contrast, in the estuary there was no apparent seasonal cycle in abundance, but the time series of data is relatively short and the environment highly variable. At one site on the shelf, where sediment traps were deployed from spring to fall and sampled at frequent intervals in both 1990 and 1991, approximately 50% of the Pseudo-nitzschia spp. cells present in the water sank into sediment traps. Pseudo-nitzschia spp. were also abundant in surficial sediments. The species of Pseudo-nitzschia present, during this study were not routinely identified with the methods employed. However, toxin-producing P. multiseries has been identified previously from Galveston Bay, Texas, and cells from a bloom on the shelf in June 1993 were identified by scanning electron microscopy as P. pseudodelicatissima, which is sometimes toxic. Although there have been no known outbreaks of ASP in this area, historical data suggests that Pseudo-nitzschia spp,abundance may have increased on the shelf since the 1950s. It is hypothesized that the increase is due to doubling of the nutrient loading from the Mississippi and Atchafalaya rivers and increased eutrophication on the shelf

Proteomic and network analysis characterize stage-specific metabolism in Trypanosoma cruzi

<p>Abstract</p> <p>Background</p> <p><it>Trypanosoma cruzi </it>is a Kinetoplastid parasite of humans and is the cause of Chagas disease, a potentially lethal condition affecting the cardiovascular, gastrointestinal, and nervous systems of the human host. Constraint-based modeling has emerged in the last decade as a useful approach to integrating genomic and other high-throughput data sets with more traditional, experimental data acquired through decades of research and published in the literature.</p> <p>Results</p> <p>We present a validated, constraint-based model of the core metabolism of <it>Trypanosoma cruzi </it>strain CL Brener. The model includes four compartments (extracellular space, cytosol, mitochondrion, glycosome), 51 transport reactions, and 93 metabolic reactions covering carbohydrate, amino acid, and energy metabolism. In addition, we make use of several replicate high-throughput proteomic data sets to specifically examine metabolism of the morphological form of <it>T. cruzi </it>in the insect gut (epimastigote stage).</p> <p>Conclusion</p> <p>This work demonstrates the utility of constraint-based models for integrating various sources of data (e.g., genomics, primary biochemical literature, proteomics) to generate testable hypotheses. This model represents an approach for the systematic study of <it>T. cruzi </it>metabolism under a wide range of conditions and perturbations, and should eventually aid in the identification of urgently needed novel chemotherapeutic targets.</p

Assembly of a high-resolution map of the Acadian Usher syndrome region and localization of the nuclear EF-hand acidic gene

Usher syndrome type 1C (USH1C) occurs in a small population of Acadian descendants from southwestern Louisiana. Linkage and linkage disequilibrium analyses localize USH1C to chromosome 11p between markers D11S1397 and D11S1888, an interval of less than 680 kb. Here, we refine the USH1C linkage to a region less than 400 kb, between genetic markers D11S1397 and D11S1890. Using 17 genetic markers from this interval, we have isolated a contiguous set of 60 bacterial artificial chromosomes (BACs) that span the USH1C critical region. Exon trapping of BAC clones from this region resulted in the recovery of an exon of the nuclear EF-hand acidic (NEFA) gene. However, DNA sequence analysis of the NEFA cDNA from lymphocytes of affected individuals provided no evidence of mutation, making structural mutations in the NEFA protein unlikely as the cellular cause of Acadian Usher syndrome. Copyright (C) 1998 Elsevier Science B.V

Scaling predictions for radii of weakly bound triatomic molecules

The mean-square radii of the molecules $^4$He$_3$, $^4$He$_2-^6$Li, $^4$He$_2-^7$Li and $^4$He$_2-^{23}$Na are calculated using a three-body model with contact interactions. They are obtained from a universal scaling function calculated within a renormalized scheme for three particles interacting through pairwise Dirac-delta interaction. The root-mean-square distance between two atoms of mass $m_A$ in a triatomic molecule are estimated to be of de order of ${\cal C}\sqrt{\hbar^2/[m_A(E_3-E_2)]}$, where $E_2$ is the dimer and $E_3$ the trimer binding energies, and ${\cal C}$ is a constant (varying from $\sim 0.6$ to $\sim 1$) that depends on the ratio between $E_2$ and $E_3$. Considering previous estimates for the trimer energies, we also predict the sizes of Rubidium and Sodium trimers in atomic traps.Comment: 7 pages, 2 figure

A Chemical Genetic Approach Reveals Distinct Mechanisms of EphB Signaling During Brain Development

EphB receptor tyrosine kinases control multiple steps in nervous system development. However, it remains unclear whether EphBs regulate these different developmental processes directly or indirectly. In addition, as EphBs signal through multiple mechanisms, it has been challenging to define which signaling functions of EphBs regulate particular developmental events. To address these issues, we engineered triple knockin mice in which the kinase activity of three neuronally expressed EphBs can be rapidly, reversibly, and specifically blocked. Using these mice we demonstrate that the tyrosine kinase activity of EphBs is required for axon guidance in vivo. By contrast, EphB-mediated synaptogenesis occurs normally when the kinase activity of EphBs is inhibited suggesting that EphBs mediate synapse development by an EphB tyrosine kinase-independent mechanism. Taken together, these experiments reveal that EphBs control axon guidance and synaptogenesis by distinct mechanisms, and provide a new mouse model for dissecting EphB function in development and disease