On the double and triple-humped fission barriers and half-lives of actinide elements

The deformation barriers standing in the quasi-molecular shape path have been determined in the actinide region within a macroscopic-microscopic energy derived from a generalized liquid drop model, the algebraic droplet model shell corrections and analytic expressions for the pairing energies. Double and triple-humped fission barriers appear. The second barrier corresponds to the transition from one-body shapes to two touching ellipsoids. The third minimum and third peak, when they exist, come from shell rearrangements in the deformed fragment. The shape of the other almost magic one is close to the sphere. The barrier heights agreewith the experimental results, the energy of the second minimum being a little too high. The predicted half-lives follow the experimental data trend

A study of the links in between the ASPPs and the Wnt/beta-catenin signalling pathway

The identification of the ASPP family of proteins has helped towards a better understanding of how the function of the tumour suppressor p53 could be specifically regulated. Hence, ASPP1 and ASPP2 bind to- and specifically enhance the transactivation function of p53 on the promoters of proapoptotic genes, whereas iASPP acts as an inhibitor. However, yeast-two-hybrid experiments have shown that the ASPPs, and in particular ASPP2, also interacts with a large number of proteins involved in other major signalling pathways, suggesting that they could be a multi-function family of proteins. One of ASPP2-interacting partners is Adenomatous Polyposis Coli 2/L (APC2/APCL). APCL is a central nervous system-specific homologue of APC, a key factor in the Wnt signalling pathway. As the biological significance of this interaction remains unknown, we explored the interplay between the ASPPs and the APC family. We show that APC and APCL can affect the subcellular localization of ASPP1 and ASPP2 as well as positively regulate their function on p53. As APCL, like APC. is believed to be able to target p-catenin for degradation, we investigated whether ASPP2 could play a role in the regulation of P-catenin. Herein, we show that ASPP2 is a negative regulator of p-catenin transcriptional activity and that they can form a complex at the level of the adherens junctions. In vivo, ASPP2-null mice exhibit severe anomalies in the central nervous system (CNS) formation during embryonic development. Hence, the eyes and the brain were characterized by increased number of cells, poor cellular differentiation and tissue disorganization. Cells expressing nuclear p-catenin were found in a very limited and organized apical region of the developing cortex in the wild-type, whereas in the ASPP2-deficient embryos, they were disseminated throughout the overgrown regions of the brain, suggesting that ASPP2 may regulate p-catenin function during CNS development. Finally, the involvement of ASPP2 in the regulation of p-catenin transcriptional activity could contribute to its function as a tumour suppressor and, importantly, its role in epithelial integrity suggests that it could be determinant in preventing cellular invasion and metastasis

Coefficients and terms of the liquid drop model and mass formula

The coefficients of different combinations of terms of the liquid drop model have been determined by a least square fitting procedure to the experimental atomic masses. The nuclear masses can also be reproduced using a Coulomb radius taking into account the increase of the ratio $R\_0/A^{1/3}$ with increasing mass, the fitted surface energy coefficient remaining around 18 MeV

Identification of pathogenicity factors in the xylem-invading pathogen Xanthomonas albilineans by Transposon Mutagenesis

Xanthomonas albilineans is a systemic, xylem-invading pathogen that causes sugarcane leaf scald. Leaf symptoms vary from a single, white, narrow, sharply defined stripe to complete wilting and necrosis of infected leaves, leading to plant death. X albilineans produces the toxin albicidin that blocks chloroplast differentiation, resulting in disease symptoms. Albicidin is the only previously known pathogenicity factor in X albilineans, yet albicidin-deficient mutant strains are still able to efficiently colon\ze sugarcane. We used TnS (transposome) mutagenesis in an attempt to identifY additional X albilineans pathogenicity factors. Sugarcane cultivar CP80-1743, moderately susceptible to leaf scald, was inoculated by the decapitation method with 1,216 independently derived TnS insertions in Florida strain XaFL07-1. Leaf scald symptoms were recorded on emerging leaves one month after inoculation, and stalk colonization by the pathogen was determined two months after inoculation. In addition to the previously identified albicidin biosynthesis gene ciuster mutations, 33 new loci were identified in which insertions were correlated with reduced pathogenicity. These insertions affected genes predicted to encode proteins involved in a variety of functions, inciuding exopolysaccharide and lipopolysaccharide biosynthesis, fatty acid biosynthesis, regulatory and cell signaling, and secretion systems. Several of these have been associated with virulence in other bacterial plant pathogens that invade the xylem. However, sorne loci were identified that are predicted to encode previously unrecognized and apparently essential pathogenicity factors, at least for sugarcane leaf scald, inciuding an OmpA family outer membrane protein. Five independent TnS insertions in OmpA locus XALc_0557 of X albilineans strain XaFL07-1 produced no or very few leaf symptoms. These mutants produced albicidin in vitro and were able to multiply in sugarcane leaf tissue to levels similar to the wild-type strain, but did not efficiently colonize the sugarcane stalk. These ompA mutants were also affected in growth rate, motility and biofilm formation in vitro. (Résumé d'auteur

Quorum sensing genes rpfF and xanB2 are not essential for albicidin production nor sugarcane colonization by Xanthomonas albilineans

Xanthomonas albilineans (Xa) produces albicidin, a unique and specific toxin that causes foliar symptoms of sugarcane leaf scald disease. In X. campestris pv. campestris, a cluster of rpf (for regulation of pathogenicity factors) genes and xanB2 are involved in control of various cellular processes. rpfF and xanB2 encode DSF (diffusible signal factor) and DF (diffusible factor), respectively, which are two quorum sensing signalling molecules. Both quorum sensing systems appear to be used by Xa, since mutation of rpfF in Florida strain XaFL07-1 resulted in reduced protease production, and mutation of xanB2 resulted in loss of xanthomonadin (yellow pigment) production. Mutations of rpfF and xanB2 were verified by PCR analyses. Mutations of rpfF and complementation in trans were also verified by use of an X. campestris DSF reporter strain. Sugarcane cultivar CP80-1743, moderately susceptible to leaf scald, exhibited pencil line symptoms indicative of albicidin production on emerging leaves and colonization of leaf vessels after inoculation of stalks by the decapitation method with all mutants, including separate deletion mutations of rpfG and rpfC (encoding two sensor components of the DSF system). Preliminary experiments indicated that several rpfF and xanB2 mutants colonized sugarcane stalks as efficiently, both spatially and in intensity, as wild type Xa. Additional inoculation experiments are in progress to assess disease severity caused by rpf mutants, including deletion of the entire rpfGCF region. However, our preliminary data showed that neither DSF nor DF is essential for albicidin production or sugarcane colonization by Xa. Therefore, albicidin production and sugarcane colonization by Xa may not be controlled by quorum sensing or may involve another system. (Texte intégral

The use of a prefabricated radial forearm free flap for closure of a large tracheocutaneous fistula: a case report and review of the literature

The closure of complex tracheocutaneous fistulae is a surgical challenge. We describe a staged approach for management of a patient with a large tracheocutaneous fistula in the setting of prior surgery and local radiation therapy

Herschel imaging and spectroscopy of the nebula around the luminous blue variable star WRAY 15-751

We have obtained far-infrared Herschel PACS imaging and spectroscopic observations of the nebular environment of the luminous blue variable WRAY 15-751. These images clearly show that the main, dusty nebula is a shell of radius 0.5 pc and width 0.35 pc extending outside the H-alpha nebula. They also reveal a second, bigger and fainter dust nebula, observed for the first time. Both nebulae lie in an empty cavity, likely the remnant of the O-star wind bubble formed when the star was on the main sequence. The kinematic ages of the nebulae are about 20000 and 80000 years and each nebula contains about 0.05 Msun of dust. Modeling of the inner nebula indicates a Fe-rich dust. The far-infrared spectrum of the main nebula revealed forbidden emission lines coming from ionized and neutral gas. Our study shows that the main nebula consists of a shell of ionized gas surrounded by a thin photodissociation region illuminated by an "average" early-B star. The derived abundance ratios N/O=1.0+/-0.4 and C/O=0.4+/-0.2 indicate a mild N/O enrichment. We estimate that the inner shell contains 1.7+/-0.6 Msun of gas. Assuming a similar dust-to-gas ratio for the outer nebula, the total mass ejected by WRAY 15-751 amounts to 4+/-2 Msun. The measured abundances, masses and kinematic ages of the nebulae were used to constrain the evolution of the star and the epoch at which the nebulae were ejected. Our results point to an ejection of the nebulae during the RSG evolutionary phase of an ~ 40 Msun star. The presence of multiple shells around the star suggests that the mass-loss was not a continuous ejection but rather a series of episodes of extreme mass-loss. Our measurements are compatible with the recent evolutionary tracks computed for an 40 Msun star with little rotation. They support the O-BSG-RSG-YSG-LBV filiation and the idea that high-luminosity and low-luminosity LBVs follow different evolutionary paths.Comment: 19 pages, 13 figures, accepted for publication in A&

The Herschel view of the nebula around the luminous blue variable star AG Carinae

Far-infrared Herschel PACS imaging and spectroscopic observations of the nebula around the luminous blue variable (LBV) star AG Car have been obtained along with optical imaging in the Halpha+[NII] filter. In the infrared light, the nebula appears as a clumpy ring shell that extends up to 1.2 pc with an inner radius of 0.4 pc. It coincides with the Halpha nebula, but extends further out. Dust modeling of the nebula was performed and indicates the presence of large grains. The dust mass is estimated to be ~ 0.2 Msun. The infrared spectrum of the nebula consists of forbidden emission lines over a dust continuum. Apart from ionized gas, these lines also indicate the existence of neutral gas in a photodissociation region that surrounds the ionized region. The abundance ratios point towards enrichment by processed material. The total mass of the nebula ejected from the central star amounts to ~ 15 Msun, assuming a dust-to-gas ratio typical of LBVs. The abundances and the mass-loss rate were used to constrain the evolutionary path of the central star and the epoch at which the nebula was ejected, with the help of available evolutionary models. This suggests an ejection during a cool LBV phase for a star of ~ 55 Msun with little rotation.Comment: accepted for publication in A&

Multiple-humped fission and fusion barriers of actinide and superheavy elements

The energy of a deformed nucleus has been determined within a Generalized Liquid Drop Model taking into account the proximity energy, the microscopic corrections and quasi-molecular shapes. In the potential barrier a third peak exists for actinides when one fragment is close to a magic spherical nucleus while the other one varies from oblate to prolate shapes. The barrier heights and half-lives agree with the experimental data. The different entrance channels leading possibly to superheavy elements are studied as well as their $\alpha$-decay