189 research outputs found
Evolutionary dynamics of insertion sequences in relation to the evolutionary histories of the chromosome and symbiotic plasmid genes of Rhizobium etli populations
Insertion sequences (IS) are mobile genetic elements that are distributed in many prokaryotes. In particular, in the genomes of the symbiotic nitrogen-fixing bacteria collectively known as rhizobia, IS are fairly abundant in plasmids or chromosomal islands that carry the genes needed for symbiosis. Here, we report an analysis of the distribution and genetic conservation of the IS found in the genome of Rhizobium etli CFN42 in a collection of 87 Rhizobium strains belonging to populations with different geographical origins. We used PCR to generate presence/absence profiles of the 39 IS found in R. etli CFN42 and evaluated whether the IS were located in consistent genomic contexts. We found that the IS from the symbiotic plasmid were frequently present in the analyzed strains, whereas the chromosomal IS were observed less frequently. We then examined the evolutionary dynamics of these strains based on a population genetic analysis of two chromosomal housekeeping genes (glyA and dnaB) and three symbiotic sequences (nodC and the two IS elements). Our results indicate that the IS contained within the symbiotic plasmid have a higher degree of genomic context conservation, lower nucleotide diversity and genetic differentiation, and fewer recombination events than the chromosomal housekeeping genes. These results suggest that the R. etli populations diverged recently in Mexico, that the symbiotic plasmid also had a recent origin, and that the IS elements have undergone a process of cyclic infection and expansion
Structural, electrical, and optical properties of CuGaSe2 rf sputtered thin films
Thin films of CuGaSe2 have been produced by rf sputtering. Compositional, structural, electrical, and optical properties are strongly influenced by growthtemperature. At substrate temperatures lower than 300â°C amorphous or poorly crystalline Seâexcess films are obtained, showing high resistivity (â103 Ωâcm) and optical transitions at 1.62, 1.80, and 2.4 eV (values lower than the singleâcrystal counterparts). At the higher growthtemperatures,polycrystalline films are obtained (average grain size 0.7 ÎŒm) with lower values of resistivity (1 Ωâcm), and optical transitions at 1.68, 1.90, and 2.55 eV (very close to the singleâcrystal values). A hopping conduction mechanism has been detected at the lower measuringtemperature (T150 K). Structural and compositional characteristics are used to explain the behavior observed in the electrical and optical properties
Role of deep levels and interface states in the capacitance characteristics of allâsputtered CuInSe2/CdS solar cell heterojunctions
Allâsputtered CuInSe2/CdS solar cellheterojunctions have been analyzed by means of capacitanceâfrequency (CâF) and capacitanceâbias voltage (CâV) measurements. Depending on the CuInSe2 layer composition, two kinds of heterojunctions were analyzed: type 1 heterojunctions (based on stoichiometric or slightly Inârich CuInSe2 layers) and type 2 heterojunctions (based on Cuârich CuInSe2 layers). In type 1 heterojunctions, a 80âmeV donor level has been found. Densities of interface states in the range 101 0â101 1 cm2âeVâ 1 (type 1) and in the range 101 2â101 3 cmâ 2âeVâ 1 (type 2) have been deduced. On the other hand, doping concentrations of 1.6Ă101 6 cmâ 3 for stoichiometric CuInSe2 (type 1 heterojunction) and 8Ă101 7 cmâ 3 for the CdS (type 2 heterojunction) have been deduced from CâVmeasurements
Sfrp3 modulates stromal-epithelial crosstalk during mammary gland development by regulating Wnt levels
Mammary stroma is essential for epithelial morphogenesis and development. Indeed, postnatal mammary gland (MG) development is controlled locally by the repetitive and bi-directional cross-talk between the epithelial and the stromal compartment. However, the signalling pathways involved in stromalâepithelial communication are not entirely understood. Here, we identify Sfrp3 as a mediator of the stromalâepithelial communication that is required for normal mouse MG development. Using Drosophila wing imaginal disc, we demonstrate that Sfrp3 functions as an extracellular transporter of Wnts that facilitates their diffusion, and thus, their levels in the boundaries of different compartments. Indeed, loss of Sfrp3 in mice leads to an increase of ductal invasion and branching mirroring an early pregnancy state. Finally, we observe that loss of Sfrp3 predisposes for invasive breast cancer. Altogether, our study shows that Sfrp3 controls MG morphogenesis by modulating the stromal-epithelial cross-talk during pubertal development
CuInSe2 thin films produced by rf sputtering in Ar/H2 atmospheres
Structural, compositional, optical, and electrical properties of CuInSe2thin filmsgrown by rf reactive sputtering from a Se excess target in Ar/H2 atmospheres are presented. The addition of H2 to the sputtering atmospheres allows the control of stoichiometry of films giving rise to remarkable changes in the film properties. Variation of substrate temperature causes changes in film composition because of the variation of hydrogen reactivity at the substrate. Measurements of resistivity at variable temperatures indicate a hopping conduction mechanism through gap states for films grown at low temperature (100â250â°C), the existence of three acceptor levels at about 0.046, 0.098, and 0.144 eV above valence band for films grown at intermediate temperature (250â350â°C), and a pseudometallic behavior for film grown at high temperatures (350â450â°C). Chalcopyrite polycrystalline thin films of CuInSe2 with an average grain size of 1 ÎŒm, an optical gap of 1.01 eV, and resistivities from 10â 1 to 103 Ωâcm can be obtained by adding 1.5% of H2 to the sputtering atmosphere and by varying the substrate temperature from 300 to 400â°C
Broken R-parity, stop decays, and neutrino physics
We discuss the phenomenology of the lightest stop in models where R-parity is
broken by bilinear superpotential terms. In this class of models we consider
scenarios where the R-parity breaking two-body decay ~t_1->\tau^+b competes
with the leading three-body decays such as ~t_1->W^+b~\chi^0_1. We demonstrate
that the R-parity violating decay can be sizable and in some parts of the
parameter space even the dominant one. Moreover we discuss the expectations for
\~t_1->\mu^+b and ~t_1->e^+b. The recent results from solar and atmospheric
neutrinos suggest that these are as important as the tau bottom mode. The
\~t_1->l^+b decays are of particular interest for hadron colliders, as they may
allow a full mass reconstruction of the lighter stop. Moreover these decay
modes allow cross checks on the neutrino mixing angle involved in the solar
neutrino puzzle complementary to those possible using neutralino decays. For
the so--called small mixing angle or SMA solution ~t_1->e^+b should be
negligible, while for the large mixing angle type solutions all ~t_1->l^+b
decays should have comparable magnitude.Comment: 51 pages, 6 figures, LaTeX2e and RevTeX4, published versio
On the nature of the fourth generation neutrino and its implications
We consider the neutrino sector of a Standard Model with four generations.
While the three light neutrinos can obtain their masses from a variety of
mechanisms with or without new neutral fermions, fourth-generation neutrinos
need at least one new relatively light right-handed neutrino. If lepton number
is not conserved this neutrino must have a Majorana mass term whose size
depends on the underlying mechanism for lepton number violation. Majorana
masses for the fourth generation neutrinos induce relative large two-loop
contributions to the light neutrino masses which could be even larger than the
cosmological bounds. This sets strong limits on the mass parameters and mixings
of the fourth generation neutrinos.Comment: To be published. Few typos corrected, references update
Omics approaches in pancreatic adenocarcinoma
Pancreatic ductal adenocarcinoma, which represents 80% of pancreatic cancers, is mainly diagnosed when treatment with curative intent is not possible. Consequently, the overall five-year survival rate is extremely dismalâaround 5% to 7%. In addition, pancreatic cancer is expected to become the second leading cause of cancer-related death by 2030. Therefore, advances in screening, prevention and treatment are urgently needed. Fortunately, a wide range of approaches could help shed light in this area. Beyond the use of cytological or histological samples focusing in diagnosis, a plethora of new approaches are currently being used for a deeper characterization of pancreatic ductal adenocarcinoma, including genetic, epigenetic, and/or proteo-transcriptomic techniques. Accordingly, the development of new analytical technologies using body fluids (blood, bile, urine, etc.) to analyze tumor derived molecules has become a priority in pancreatic ductal adenocarcinoma due to the hard accessibility to tumor samples. These types of technologies will lead us to improve the outcome of pancreatic ductal adenocarcinoma patients
Reconstructing Seesaws
We explore some aspects of "reconstructing" the heavy singlet sector of
supersymmetric type I seesaw models, for two, three or four singlets. We work
in the limit where one light neutrino is massless. In an ideal world, where
selected coefficients of the TeV-scale effective Lagrangian could be measured
with arbitrary accuracy, the two-singlet case can be reconstructed, two three
or more singlets can be differentiated, and an inverse seesaw with four
singlets can be reconstructed. In a more realistic world, we estimate \ell_\a
\to \ell_\b \gamma expectations with a "Minimal-Flavour-Violation-like"
ansatz, which gives a relation between ratios of the three branching ratios.
The two singlet model predicts a discrete set of ratios.Comment: 14 page
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