224 research outputs found
Analysis of the quark sector in the 2HDM-III with a four-zero Yukawa texture using the most recent data on the CKM matrix
In this letter we analyse, in the context of the general 2-Higgs Doublet
Model, the structure of the Yukawa matrices, , by assuming a four-zero texture ansatz for their definition. In this
framework, we obtain compact expressions for , which are reduced to the Cheng and Sher ansatz with the difference that
they are obtained naturally as a direct consequence of the invariants of the
fermion mass matrices. Furthermore, in order to avoid large flavour violating
effects coming from charged Higgs exchange, we consider the main flavour
constraints on the off-diagonal terms of Yukawa texture {{}} (). We perform a -fit
based on current experimental data on the quark masses and the
Cabibbo-Kobayashi-Maskawa mixing matrix . Hence, we obtain
the allowed ranges for the parameters at
1 for several values of . The results are in complete
agreement with the bounds obtained taking into account constraints on Flavour
Changing Neutral Currents reported in the literature.Comment: 12 pages, 1 figure. Version accepted in Phys. Lett.
Mitochondrial inhibitors activate influx of external Ca2+ in sea urchin sperm
AbstractSea urchin sperm have a single mitochondrion which, aside from its main ATP generating function, may regulate motility, intracellular Ca2+ concentration ([Ca2+]i) and possibly the acrosome reaction (AR). We have found that acute application of agents that inhibit mitochondrial function via differing mechanisms (CCCP, a proton gradient uncoupler, antimycin, a respiratory chain inhibitor, oligomycin, a mitochondrial ATPase inhibitor and CGP37157, a Na+/Ca2+ exchange inhibitor) increases [Ca2+]i with at least two differing profiles. These increases depend on the presence of extracellular Ca2+, which indicates they involve Ca2+ uptake and not only mitochondrial Ca2+ release. The plasma membrane permeation pathways activated by the mitochondrial inhibitors are permeable to Mn2+. Store-operated Ca2+ channel (SOC) blockers (Ni2+, SKF96365 and Gd2+) and internal-store ATPase inhibitors (thapsigargin and bisphenol) antagonize Ca2+ influx induced by the mitochondrial inhibitors. The results indicate that the functional status of the sea urchin sperm mitochondrion regulates Ca2+ entry through SOCs. As neither CCCP nor dicycloexyl carbodiimide (DCCD), another mitochondrial ATPase inhibitor, eliminate the oligomycin induced increase in [Ca2+]i, apparently oligomycin also has an extra mitochondrial target
AGRONOMIC EVALUATION AND CHEMICAL COMPOSITION OF AFRICAN STAR GRASS (Cynodon plectostachyus) IN THE SOUTHERN REGION OF THE STATE OF MEXICO
African Star Grass is one of the forage resources most commonly used by farmers in regions with warm-humid climates. This study was carried out to determine the nutritional and agronomic characteristics of African Star Grass (Cynodon plectostachyus) through the following variables: crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), organic matter digestibility (OMD), net forage accumulation (NFA), stem:leaf ratio, and live:dead matter ratio in the three pastures evaluated. The work took place from April 2007 to March 2008, with evaluations carried out on a monthly basis. The data were analyzed in a randomized block design in which the blocks were the pastures, and the treatments were the months of evaluation. There were no differences between the pastures evaluated for the NDF, ADF or OMD (P>0.05). Differences were found, however, in CP, while in the monthly evaluation, differences were found between the periods evaluated (P<0.05) for these variables. Differences were also found in the agronomic evaluation of pastures (P<0.05) among height of pasture, net forage accumulation (NFA), live matter, dead matter, leaf and stem, both among pastures and in the monthly evaluations. African Star Grass can therefore be considered a good choice for milk production systems in the southern region of the state of Mexico, due to its nutritional and agronomic characteristics
Heavy metals as an indicator of ecological impact of a fragmented land uses, San Luis Potosi, Mexico
La necesidad de estudiar la presencia
de metales pesados en el suelo radica en su
impacto como indicador de contaminación
ambiental. Se determinó la presencia de Cu,
Zn, Pb y Cd en suelos donde se distribuyen
especies vegetales en un corredor ecológico.
Entre los municipios de Soledad de Graciano
Sánchez y San Luis Potosí (México) fueron
establecidos 30 puntos distribuidos en cinco
prácticas dominantes de usos de suelo:
agropecuario, residencial rural, comercio y
servicios, residencial urbano y minero. Los
muestreos se realizaron en cuatro épocas
durante 2009 y 2010 (verano, otoño, invierno y
primavera). Se encontró un efecto significativo
del uso del suelo en cuanto a los niveles de
Cu (p = 0,000), Pb (p = 0,043) y Cd (p = 0,010).
En el caso del Zn, el uso del suelo (p = 0,000)
y la estación (p = 0,059) fueron significativos.
El uso del suelo minero mostró las mayores
concentraciones de metales y el agrícola las
menores. Los niveles de los cuatro metales se
encuentran en el rango marcado como alto por
la EPA y por otras fuentes técnicas. En el caso
de Pb y Cd no rebasan los estándares NOM-147-
SEMARNAT-SSA1. Estos resultados reflejan
el potencial indicativo del uso del suelo en la
evaluación de la calidad ambiental, sin embargo,
se requiere continuar con un monitoreo de
metales pesados en la zona.The need to study the presence of heavy
metals in the soil lies on their impact as a indicator
of environmental pollution. Therefore, it was
determined the presence of Cu, Zn, Pb and Cd
in soils where plant species were distributed in
an ecological corridor. Among the municipalities
of Soledad Graciano Sanchez and San Luis
Potosi (Mexico), 30 points were established,
distributed in five land uses: agricultural , rural
residential, trade and services, urban residential
and mining. Sampling was conducted from
2009 to 2010 (summer, fall, winter and spring).
A significant effect of land use was found in
terms of Cu (p = 0.000), Pb (p = 0.043) and
Cd (p = 0.010). In the case of Zn both the land
use (p = 0.000) and season (p = 0.059) had
significant effects. It is emphasized that mining
land use presented the highest concentrations
of the studied metals and agricultural land use
the lowest. The levels of four metals are in the
range marked like high by the EPA and other
technical sources. The levels of Pb and Cd do not
exceed the NOM-147-SEMARNAT-SSA1. These
results reflect the indicative potential of the soil
and its consideration for future to evaluate the
habitat of plant species. These results reflect the
potential indicative land use in the assessment
of environmental quality, however, requires
continued monitoring of heavy metals in the area.Fil: Alcalá Jáuregui, Jorge.
Universidad Autónoma de San Luis Potosí. Facultad de AgronomíaFil: Ávila Castorena, Cecilia.
Universidad Autónoma de San Luis Potosí. Facultad de AgronomíaFil: Rodríguez Ortíz, Juan C..
Universidad Autónoma de San Luis Potosí. Facultad de AgronomíaFil: Hernández Montoya, Alejandra.
Universidad Autónoma de San Luis Potosí. Facultad de AgronomíaFil: Beltrán Morales, F. Alfredo.
Universidad Autónoma de Baja California Sur (México)Fil: Rodríguez Fuentes, Humberto.
Universidad Autónoma de Nuevo León (México). Facultad de Agronomía.Fil: Loya Ramírez, J. Guadalupe.
Universidad Autónoma de Baja California Sur (México
Vegetative as bioindicators of heavy metals in a semiarid system
Evaluar la contaminación por metales
pesados en los ecosistemas permite conocer la
capacidad bioindicativa de especies vegetativas.
El objetivo fue determinar la concentración
de metales pesados en Prosopis laevigata,
Acacia spp. y Schinus molle bajo el efecto de
usos suelo y temporalidad. El área se sitúa en
la colindancia de los Municipios de Soledad
de Graciano Sánchez y San Luis Potosí
fragmentada por usos de suelo: agropecuario,
comercio y servicios, residencial urbano y
minero. Fueron tomadas muestras de hojas de
las tres especies en las estaciones de verano,
otoño, invierno y primavera y se evaluó la
concentración de metales pesados a través de
la técnica de ICP-MS. Los análisis estadísticos
indicaron niveles de Aluminio (Al) > Cinc (Zn) >
Plomo (Pb) > Cobre (Cu) > Titanio (Ti) >
Vanadio (V) > Arsénico (As) > Cromo (Cr) >
Cadmio (Cd) > Cobalto (Co). Los elementos
Al, As, Cd, Cr, Pb y Ti presentaron niveles por
encima del umbral normal en vegetación. El
uso de suelo tuvo efecto significativo con Al,
Ti, Cd, As y Pb; los árboles ubicados en los
usos de suelo minero, comercio y servicios
tuvieron la mayor concentración. La especie
tuvo efecto significativo con Al y Pb siendo
Acacia spp. el que presentó la mayor capacidad
de acumulación. La temporada del año impactó
significativamente en la acumulación de As, Cd,
Co, Cu, Cr y Ti en las tres especies. La dinámica
antropogénica de los diferentes usos de suelo
genera partículas y residuos con metales
pesados impactando en la disponibilidad
y acumulación en las especies evaluadas.
Se contribuye a evaluar el impacto ambiental
en el sistema fragmentado recomendando dar
continuidad a este tipo de estudios.The evaluation of pollution by heavy metals
on ecosystems can determine the bioindicative
capacity of plant species. The presence of
heavy metals was determined in Prosopis
laevigata, Acacia spp. and Schinus molle under
the effect of different of land uses and seasons.
The area is located near of the municipalities
of Soledad de Graciano Sánchez and San
Luis Potosi which has fragmented land use
such as: agriculture, commercial and services,
urban residential and mining. Samples were
taken from leaves of the three species during
summer, autumn, winter and spring to assess
the concentrations of heavy metals through
the technique of ICP-MS. Statistical analyzes
showed levels of Aluminum (Al) > Zinc (Zn)
> Lead (Pb) > Copper (Cu) > Titanium (Ti) >
Vanadium (V) > Arsenic (As) > Chromium (Cr)
> Cadmium (Cd) > Cobalt (Co). The elements
Al, As, Cd, Cr, Pb and Ti had levels above the
normal threshold in vegetation. Land use had a
significant effect with Al, Ti, Cd, As and Pb having
the trees being located in the land with mining
and commercial and services use the greater
concentrations. The species had a significant
effect on Al and Pb with Acacia spp., having
the largest storage capacity. The season of the
year significantly impacted the accumulation of
As, Cd, Co, Cu, Cr and Ti in the three species.
The anthropogenic dynamics of different land
uses generated waste particles and residues
of heavy metals, impacting the availability and
accumulation in the species evaluated. This
study contribute to evaluate the environmental
impact in the system with a fragmented land
use and the continuation of this type of studies
is recommended.Fil: Alcalá Jáuregui, Jorge.
Universidad Autónoma de San Luis Potosí. Facultad de AgronomíaFil: Rodríguez Ortíz, Juan C..
Universidad Autónoma de San Luis Potosí. Facultad de AgronomíaFil: Villaseñor Zuñiga, María Elena.
Universidad Autónoma de San Luis Potosí. Facultad de AgronomíaFil: Hernández Montoya, Alejandra.
Universidad Autónoma de San Luis Potosí. Facultad de AgronomíaFil: García Arreola, María Elena.
Universidad Autónoma de San Luis Potosí. Facultad de AgronomíaFil: Beltrán Morales, F. Alfredo.
Universidad Autónoma de Baja California Sur (México)Fil: Rodríguez Fuentes, Humberto.
Universidad Autónoma de Nuevo León (México). Facultad de Agronomía
Synthesis and Structure of Trinuclear W3S4 Clusters Bearing Aminophosphine Ligands and Their Reactivity toward Halides and Pseudohalides
The aminophosphine ligand (2-aminoethyl)- diphenylphosphine (edpp) has been coordinated to the W3(μ-
S)(μ-S)3 cluster unit to afford trimetallic complex [W3S4Br3(edpp)3]+ (1+) in a one-step synthesis process with high yields. Related [W3S4X3(edpp)3]+ clusters (X = F−, Cl−, NCS−; 2+−4+) have been isolated by treating 1+ with the
corresponding halide or pseudohalide salt. The structure of complexes 1+ to 4+ contains an incomplete W3S4 cubane-type cluster unit, and only one of the possible isomers is formed: the one with the phosphorus atoms trans to the capping sulfur and the amino groups trans to the bridging sulphurs. The remaining coordination position on each metal is occupied by X. Detailed studies using stopped-flow, 31P{1H} NMR, and ESI-MS have been carried out in order to understand the solution behavior and the kinetics of interconversion among species 1+, 2+, 3+, and 4+ in solution. Density functional theory (DFT) calculations have been also carried out on the reactions of cluster 1+ with the different anions. The whole set of experimental and theoretical data indicate that the actual mechanism of substitutions in these clusters is strongly dependent on the nature of the leaving and entering anions. The interaction between an entering F− and the amino group coordinated to the adjacent metal have also been found to be especially relevant to the kinetics of these reactions
Signatures of a two-dimensional ferromagnetic electron gas at the La_(0.7)Sr_(0.3)MnO_(3)/SrTiO_(3) interface arising from orbital reconstruction
The magnetoresistance of La0.7Sr0.3MnO3/SrTiO3La0.7Sr0.3MnO3/SrTiO3 superlattices with magnetic field rotating out-of-plane shows unexpected peaks for in-plane fields. Resistivity calculations with spin–orbit coupling reveal that orbital reconstruction at the manganite interface leads to a 2D ferromagnetic electron gas coupled antiparallel to the manganite “bulk”. These orbital and magnetic reconstructions are supported by X-ray linear dichroism and ab initio calculations
Evaluation of the impact of residual stresses in crack initiation with the application of the Crack Compliance Method Part II, Experimental analysis
Abstract. The present work is based on a previous numerical simulation used for the introduction of a residual stress field in a modified compact tensile specimen. The main objective in that paper was to evaluate the effect that previous history has in crack initiation and to establish the new loading conditions needed to propagate a fracture. The experimental analysis presented in this paper was performed to compare and validate the numerical procedure. Several modified compact tensile specimens from a biocompatible material (AISI 316L) were manufactured to estimate the beneficial effect of a residual stress field. The specimens were separated in four batches; an initial group of uncracked specimens was used to establish an evaluation of the induction of a residual stress field produced by an overload; the remaining specimens were separated into three groups where a crack was introduced in each specimen (1 mm, 5 mm and 10 mm respectively) and the residual stress field caused by the application of an overload was determined. The assessment of all the residual stress fields introduced into the specimens was done by the application of the crack compliance method (CCM). The results obtained have provided useful information on the correlation between the numerical and experimental procedures. Furthermore, data concerning the understanding of diverse factors related to crack initiation are discussed in this paper. Finally, the beneficial aspects of the residual stresses are discussed
Evaluation of the impact of residual stresses in crack initiation with the application of the Crack Compliance Method Part I, Numerical analysis
Abstract. The understanding of how materials fail is still today a fundamental research problem for scientist and engineers. The main concern is the assessment of the necessary conditions to propagate a crack that will eventually lead to failure. Nevertheless, this kind of analysis tends to be more complicated, when a prior history in the material is taken into consideration and it will be extremely important to recognize all the factors involved in this process. In this work, a numerical simulation of the introduction of residual stresses, which change the crack initiation conditions, in a modified compact tensile specimen to change the condition of crack initiation is presented. Four numerical analyses were carried out; an initial evaluation was performed in a specimen without a crack and it was used for the estimation of a residual stress field produced by an overload; three more cases were simulated and a crack was introduced in each specimen (1 mm, 5 mm and 10 mm, respectively). The overload was then applied to set up a residual stress field into the component; furthermore, in each case the crack compliance method (CCM) was applied to measure the induced residual stress field. By performing this numerical simulation, the accuracy of the crack compliance method can be evaluated. On the other hand, elastic-plastic finite element analysis was utilized for the residual stress estimation. The numerical analysis was based on the mechanical properties of a biocompatible material (AISI 316L). The obtained results provided significant data about diverse factors, like; the manner in which a residual stress field could modify the crack initiation conditions, the convenient set up for induction of a beneficial residual stresses field, as well as useful information that can be applied for the experimental implementation of this research
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