843 research outputs found
Spin-Crossing in the (Z)-Selective Alkyne Semihydrogenation Mechanism Catalyzed by Mo3S4 Clusters: A Density Functional Theory Exploration
Semihydrogenation of internal alkynes catalyzed by the air-stable imidazolyl amino [Mo3S4Cl3(ImNH2)3]+ cluster selectively affords the (Z)-alkene under soft conditions in excellent yields. Experimental results suggest a sulfur-based mechanism with the formation of a dithiolene adduct through interaction of the alkyne with the bridging sulfur atoms. However, computational studies indicate that this mechanism is unable to explain the experimental outcome: mild reaction conditions, excellent selectivity toward the (Z)-isomer, and complete deuteration of the vinylic positions in the presence of CD3OD and CH3OD. An alternative mechanism that explains the experimental results is proposed. The reaction begins with the hydrogenation of two of the Mo3(μ3-S)(μ-S)3 bridging sulfurs to yield a bis(hydrosulfide) intermediate that performs two sequential hydrogen atom transfers (HAT) from the S–H groups to the alkyne. The first HAT occurs with a spin change from singlet to triplet. After the second HAT, the singlet state is recovered. Although the dithiolene adduct is more stable than the hydrosulfide species, the large energy required for the subsequent H2 addition makes the system evolve via the second alternative pathway to selectively render the (Z)-alkene with a lower overall activation barrier.CRUE-Universitat Jaume
Quantified HI Morphology I: Multi-Wavelengths Analysis of the THINGS Galaxies
Galaxy evolution is driven to a large extent by interactions and mergers with
other galaxies and the gas in galaxies is extremely sensitive to the
interactions. One method to measure such interactions uses the quantified
morphology of galaxy images. Well-established parameters are Concentration,
Asymmetry, Smoothness, Gini, and M20 of a galaxy image. Thus far, the
application of this technique has mostly been restricted to restframe
ultra-violet and optical images. However, with the new radio observatories
being commissioned (MeerKAT, ASKAP, EVLA, WSRT/APERTIF, and ultimately SKA), a
new window on the neutral atomic hydrogen gas (HI) morphology of a large
numbers of galaxies will open up. The quantified morphology of gas disks of
spirals can be an alternative indicator of the level and frequency of
interaction. The HI in galaxies is typically spatially more extended and more
sensitive to low-mass or weak interactions. In this paper, we explore six
morphological parameters calculated over the extent of the stellar (optical)
disk and the extent of the gas disk for a range of wavelengths spanning UV,
Optical, Near- and Far-Infrared and 21 cm (HI) of 28 galaxies from The HI
Nearby Galaxy Survey (THINGS). Though the THINGS sample is small and contains
only a single ongoing interaction, it spans both non-interacting and
post-interacting galaxies with a wealth of multi-wavelength data. We find that
the choice of area for the computation of the morphological parameters is less
of an issue than the wavelength at which they are measured. The signal of
interaction is as good in the HI as in any of the other wavelengths in which
morphology has been used to trace the interaction rate to date, mostly
star-formation dominated ones (near- and far-ultraviolet). The Asymmetry and
M20 parameters are the ones which show the most promise as tracers of
interaction in 21 cm line observations.Comment: 16 pages, 11 figure, table 1, accepted by MNRAS, appendix not
include
Efficient (Z)-selective semihydrogenation of alkynes catalyzed by air-stable imidazolyl amino molybdenum cluster sulfides
Imidazolyl amino cuboidal Mo3(μ3-S)(μ-S)3 clusters have been investigated as catalysts for the semihydrogenation of alkynes. For that purpose, three new air-stable cluster salts [Mo3S4Cl3(ImNH2)3]BF4 ([1]BF4), [Mo3S4Cl3(ImNH(CH3))3]BF4 ([2]BF4) and [Mo3S4Cl3(ImN(CH3)2)3]BF4 ([3]BF4) have been isolated in moderate to high yields and fully characterized. Crystal structures of complexes [1]PF6 and [2]Cl confirm the formation of a single isomer in which the nitrogen atoms of the three imidazolyl groups of the ligands are located trans to the capping sulfur atom which leaves the three bridging sulfur centers on one side of the trimetallic plane while the amino groups lie on the opposite side. Kinetic studies show that the cluster bridging sulfurs react with diphenylacetylene (dpa) in a reversible equilibrium to form the corresponding dithiolene adduct. Formation of this adduct is postulated as the first step in the catalytic semihydrogenation of alkynes mediated by molybdenum sulfides. These complexes catalyze the (Z)-selective semihydrogenation of diphenylacetylene (dpa) under hydrogen in the absence of any additives. The catalytic activity lowers sequentially upon replacement of the hydrogen atoms of the N–H2 moiety in 1+ without reaching inhibition. Mechanistic experiments support a sulfur centered mechanism without participation of the amino groups. Different diphenylacetylene derivatives are selectively hydrogenated using complex 1+ to their corresponding Z-alkenes in excellent yields. Extension of this protocol to 3,7,11,15-tetramethylhexadec-1-yn-3-ol, an essential intermediate for the production of vitamin E, affords the semihydrogenation product in very good yield
Retrospectivas en el aula. Una experiencia práctica
En la docencia tradicional, se imparte clase durante un periodo concreto y, después, se evalúa a los alumnos. Sin embargo, una vez que se realiza esta evaluación no suele quedar tiempo para arreglar cualquier problema que esta evaluación pueda detectar. Las retrospectivas son reuniones y dinámicas de trabajo en grupo que han alcanzado una enorme popularidad en el ámbito del desarrollo de productos tecnológicos innovadores. El objetivo de estas reuniones y técnicas es reunir a todos los participantes en un proyecto, reflexionar sobre cómo se está trabajando y proponer mejoras en el trabajo del día a día. Con el fin de detectar con la mayor antelación posible cualquier elemento disonante dentro del aula y en el proceso de formación, además de favorecer que los alumnos expresen sus opiniones, hemos aplicado en los tres últimos años técnicas de retrospectivas El objetivo de este trabajo es exponer nuestras experiencias aplicando retrospectivas en el aula con el alumnado incluyendo las técnicas que hemos usado, cómo las hemos aplicado y ejemplos de los resultados que hemos obtenido.In traditional teaching, classes are taught during a specific period and, afterwards, students are evaluated. However, once this evaluation is done, there is usually no time to fix any problem that this evaluation can detect. The retrospectives are meetings and dynamics of group work that have achieved enormous popularity in the field of the development of innovative technological products. The purpose of these meetings and techniques is to bring all the participants together in a project, reflect on how they are working and propose improvements in day-to-day work. In order to detect as early as possible any dissonant element within the classroom and in the training process, in addition to encouraging students to express their opinions, we have applied retrospective techniques in the last three years. The objective of this work is to provide our experiences by applying retrospectives in the classroom with the students, including the techniques we have used, how we have applied them and examples of the results we have obtained
Quantitative Morphology of the Intermediate-Redshift Galaxy Cluster Abell 2443 from Ground-Based Imaging -- Evidence for a galaxy concentration index correlation with cluster density
We present broad-band photometry and provide a quantitative analysis of the
structure of galaxies in the inner region of the Abell Cluster 2443 (z~0.1).
The galaxy parameters have been derived by fitting a two-component model
(Sersic r^{1/n} bulge and exponential disk) to a magnitude-limited sample.
Using a new method of analysis which takes into account the effects of seeing
on the structural parameters and considers the ellipticity as an active
parameter, we avoid systematic errors arising from assumptions of circular
symmetry. 76% of the sample galaxies were classified with these models, the
rest were morphologically peculiar. For the spiral galaxies, the relation
between n and B/D is consistent with the trend observed in nearby field galaxy
samples. The Sersic index n (which can be considered as a concentration index)
of the elliptical galaxies is correlated with the local surface density of the
cluster. Monte Carlo simulations were used to check the reliability of the
method and determine the magnitude selection criteria.Comment: Accepted for publication in the Astronomical Journal, LaTeX document,
15 pages, 9 figures, 3 tables. Fig 6 is not included due to its siz
Adipose tissue as a therapeutic target for vascular damage in Alzheimer's disease
Adipose tissue has recently been recognized as an important endocrine organ that plays a crucial role in energy metabolism and in the immune response in many metabolic tissues. With this regard, emerging evidence indicates that an important crosstalk exists between the adipose tissue and the brain. However, the contribution of adipose tissue to the development of age-related diseases, including Alzheimer's disease, remains poorly defined. New studies suggest that the adipose tissue modulates brain function through a range of endogenous biologically active factors known as adipokines, which can cross the blood–brain barrier to reach the target areas in the brain or to regulate the function of the blood–brain barrier. In this review, we discuss the effects of several adipokines on the physiology of the blood–brain barrier, their contribution to the development of Alzheimer's disease and their therapeutic potential.Funding for open access charge; Universidad de Málaga / CBU
Efficacy of a dilemma-focused intervention for unipolar depression : study protocol for a multicenter randomized controlled trial
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedDepression is one of the more severe and serious health problems because of its morbidity, disabling effects and for its societal and economic burden. Despite the variety of existing pharmacological and psychological treatments, most of the cases evolve with only partial remission, relapse and recurrence. Cognitive models have contributed significantly to the understanding of unipolar depression and its psychological treatment. However, success is only partial and many authors affirm the need to improve those models and also the treatment programs derived from them. One of the issues that requires further elaboration is the difficulty these patients experience in responding to treatment and in maintaining therapeutic gains across time without relapse or recurrence. Our research group has been working on the notion of cognitive conflict viewed as personal dilemmas according to personal construct theory. We use a novel method for identifying those conflicts using the repertory grid technique (RGT). Preliminary results with depressive patients show that about 90% of them have one or more of those conflicts. This fact might explain the blockage and the difficult progress of these patients, especially the more severe and/or chronic. These results justify the need for specific interventions focused on the resolution of these internal conflicts. This study aims to empirically test the hypothesis that an intervention focused on the dilemma(s) specifically detected for each patient will enhance the efficacy of cognitive behavioral therapy (CBT) for depressionPeer reviewe
TNOs are cool: a survey of the transneptunian region
Over one thousand objects have so far been discovered orbiting beyond Neptune. These trans-Neptunian objects (TNOs) represent the primitive remnants of the planetesimal disk from which the planets formed and are perhaps analogous to the unseen dust parent-bodies in debris disks observed around other main-sequence stars. The dynamical and physical properties of these bodies provide unique and important constraints on formation and evolution models of the Solar System. While the dynamical architecture in this region (also known as the Kuiper Belt) is becoming relatively clear, the physical properties of the objects are still largely unexplored. In particular, fundamental parameters such as size, albedo, density and thermal properties are difficult to measure. Measurements of thermal emission, which peaks at far-IR wavelengths, offer the best means available to determine the physical properties. While Spitzer has provided some results, notably revealing a large albedo diversity in this population, the increased sensitivity of Herschel and its superior wavelength coverage should permit profound advances in the field. Within our accepted project we propose to perform radiometric measurements of 139 objects, including 25 known multiple systems. When combined with measurements of the dust population beyond Neptune (e.g. from the New Horizons mission to Pluto), our results will provide a benchmark for understanding the Solar debris disk, and extra-solar ones as well
Dwarf Galaxies in the Coma Cluster: II. Spectroscopic and Photometric Fundamental Planes
We present a study of the fundamental plane, FP, for a sample of 71 dwarf
galaxies in the core of Coma cluster in magnitude range .
Taking advantage of high resolution DEIMOS spectrograph on Keck II for
measuring the internal velocity dispersion of galaxies and high resolution
imaging of HST/ACS, which allows an accurate surface brightness modeling, we
extend the fundamental plane (FP) of galaxies to 1 magnitude fainter
luminosities than all the previous studies of the FP in Coma cluster. We find
that, the scatter about the FP depends on the faint-end luminosity cutoff, such
that the scatter increases for fainter galaxies. The residual from the FP
correlates with the galaxy colour, with bluer galaxies showing larger residuals
from FP.
We find in F814W-band indicating that in faint
dwarf ellipticals, the ratio is insensitive to the mass. We find that
less massive dwarf ellipticals are bluer than their brighter counterparts,
possibly indicating ongoing star formation activity. Although tidal encounters
and harassment can play a part in removing stars and dark matter from the
galaxy, we believe that the dominant effect will be the stellar wind associated
with the star formation, which will remove material from the galaxy resulting
in larger ratios. We attribute the deviation of a number of faint blue
dwarfs from the FP of brighter ellipticals to this effect.
We also study other scaling relations involving galaxy photometric properties
including the photometric plane. We show that, compared to the FP, the scatter
about the photometric plane is smaller at the faint end.Comment: 19 pages, 12 figures and 4 tables. Accepted for publication in
Monthly Notices of the Royal Astronomical Society Main Journal. (ref.
MN-11-0266-MJ.R1) Accepted 2011 October 10. Received 2011 September 13; in
original form 2011 February
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