20,869 research outputs found
Combining exclusive semi-leptonic and hadronic B decays to measure |V_ub|
The Cabibbo-Kobayashi-Maskawa matrix element |V_ub| can be extracted from the
rate for the semi-leptonic decay B -> pi + l + antineutrino_l, with little
theoretical uncertainty, provided the hadronic form factor for the B -> pi
transition can be measured from some other B decay. In here, we suggest using
the decay B -> pi J\psi. This is a color suppressed decay, and it cannot be
properly described within the usual factorization approximation; we use instead
a simple and very general phenomenological model for the b d J\psi vertex. In
order to relate the hadronic form factors in the B -> pi J\psi and B -> pi + l
+ antineutrino_l decays, we use form factor relations that hold for
heavy-to-light transitions at large recoil.Comment: Latex, 7 pages, no figure
Strong evidences for a nonextensive behavior of the rotation period in Open Clusters
Time-dependent nonextensivity in a stellar astrophysical scenario combines
nonextensive entropic indices derived from the modified Kawaler's
parametrization, and , obtained from rotational velocity distribution. These
's are related through a heuristic single relation given by , where is the cluster age. In a nonextensive
scenario, these indices are quantities that measure the degree of
nonextensivity present in the system. Recent studies reveal that the index
is correlated to the formation rate of high-energy tails present in the
distribution of rotation velocity. On the other hand, the index is
determined by the stellar rotation-age relationship. This depends on the
magnetic field configuration through the expression , where
and denote the saturation level of the star magnetic field and its
topology, respectively. In the present study, we show that the connection
is also consistent with 548 rotation period data for single
main-sequence stars in 11 Open Clusters aged less than 1 Gyr. The value of
2.5 from our unsaturated model shows that the mean magnetic field
topology of these stars is slightly more complex than a purely radial field.
Our results also suggest that stellar rotational braking behavior affects the
degree of anti-correlation between and cluster age . Finally, we suggest
that stellar magnetic braking can be scaled by the entropic index .Comment: 6 pages and 2 figures, accepted to EPL on October 17, 201
The Mass-to-Light Ratio of Binary Galaxies
We report on the mass-to-light ratio determination based on a newly selected
binary galaxy sample, which includes a large number of pairs whose separations
exceed a few hundred kpc. The probability distributions of the projected
separation and the velocity difference have been calculated considering the
contamination of optical pairs, and the mass-to-light ratio has been determined
based on the maximum likelihood method. The best estimate of in the B
band for 57 pairs is found to be 28 36 depending on the orbital
parameters and the distribution of optical pairs (solar unit, km
s Mpc). The best estimate of for 30 pure spiral pairs is
found to be 12 16. These results are relatively smaller than those
obtained in previous studies, but consistent with each other within the errors.
Although the number of pairs with large separation is significantly increased
compared to previous samples, does not show any tendency of increase, but
found to be almost independent of the separation of pairs beyond 100 kpc. The
constancy of beyond 100 kpc may indicate that the typical halo size of
spiral galaxies is less than kpc.Comment: 18 pages + 8 figures, to appear in ApJ Vol. 516 (May 10
Detrended Fluctuation Analysis of Systolic Blood Pressure Control Loop
We use detrended fluctuation analysis (DFA) to study the dynamics of blood
pressure oscillations and its feedback control in rats by analyzing systolic
pressure time series before and after a surgical procedure that interrupts its
control loop. We found, for each situation, a crossover between two scaling
regions characterized by exponents that reflect the nature of the feedback
control and its range of operation. In addition, we found evidences of
adaptation in the dynamics of blood pressure regulation a few days after
surgical disruption of its main feedback circuit. Based on the paradigm of
antagonistic, bipartite (vagal and sympathetic) action of the central nerve
system, we propose a simple model for pressure homeostasis as the balance
between two nonlinear opposing forces, successfully reproducing the crossover
observed in the DFA of actual pressure signals
Current advances in the bacterial toolbox for the biotechnological production of monoterpene-based aroma compounds
Monoterpenes are plant secondary metabolites, widely used in industrial processes as precursors of important aroma compounds, such as vanillin and (−)-menthol. However, the physicochemical properties of monoterpenes make difficult their conventional conversion into value-added aromas. Biocatalysis, either by using whole cells or enzymes, may overcome such drawbacks in terms of purity of the final product, ecological and economic constraints of the current catalysis processes or extraction from plant material. In particular, the ability of oxidative enzymes (e.g., oxygenases) to modify the monoterpene backbone, with high regio- and stereo-selectivity, is attractive for the production of “natural” aromas for the flavor and fragrances industries. We review the research efforts carried out in the molecular analysis of bacterial monoterpene catabolic pathways and biochemical characterization of the respective key oxidative enzymes, with particular focus on the most relevant precursors, β-pinene, limonene and β-myrcene. The presented overview of the current state of art demonstrates that the specialized enzymatic repertoires of monoterpene-catabolizing bacteria are expanding the toolbox towards the tailored and sustainable biotechnological production of values-added aroma compounds (e.g., isonovalal, α-terpineol, and carvone isomers) whose implementation must be supported by the current advances in systems biology and metabolic engineering approaches.This work was supported by the project VALEU (PTDC/EAM-AMB/30488/2017); by the
strategic program UID/BIA/04050/2019 through the Fundação para a Ciência e a Tecnologia (FCT)
I.P.; and by the European Regional Development Fund (ERDF) through the COMPETE2020-Programa
Operacional Competitividade e Internacionalização (POCI). The work was also supported by a Ph.D
grant (grant number PD/BD/146184/2019) to F.S
Evidence for entanglement at high temperatures in an engineered molecular magnet
The molecular compound
[Fe(-oxo)(CHN)(CO)]
was designed and synthesized for the first time and its structure was
determined using single-crystal X-ray diffraction. The magnetic susceptibility
of this compound was measured from 2 to 300 K. The analysis of the
susceptibility data using protocols developed for other spin singlet
ground-state systems indicates that the quantum entanglement would remain at
temperatures up to 732 K, significantly above the highest entanglement
temperature reported to date. The large gap between the ground state and the
first-excited state (282 K) suggests that the spin system may be somewhat
immune to decohering mechanisms. Our measurements strongly suggest that
molecular magnets are promising candidate platforms for quantum information
processing
Towards the metabolic engineering of myrcene pathway of pseudomonas sp. M1 using an integrated omic approach
Pseudomonas sp. M1, isolated from the Rhine River, is able to utilize a large variety of toxic and/or recalcitrant compounds as sole carbon and energy sources, including phenols, benzene and monoterpenes like myrcene [1-3]. Therefore, M1 strain holds great potential as a source of novel biomolecules and cell factories for various biotechnological applications namely in biocatalysis, biosensors, bioremediation and biomedicine. However, the full exploitation of its enzymatic repertoire requires detailed and integrated information about the biomolecular catalog of M1 strain, including genes, proteins and metabolites.
In this context, the genome of Pseudomonas sp. M1 was sequenced by NGS technologies, using Illumina Genome Analyser IIx and Roche 454 FLX. The resulting raw data was assembled into 41 contigs and annotated using different pipelines. The current genome draft of Pseudomonas sp. M1 has an estimated GC content of 67%, a size of about 6.9 Mbps and includes 6214 CDS. Importantly, in silico genome analysis predicted a number of metabolic pathways involved in utilization/biotransformation of several unusual carbons sources (e.g. biphenyls, halophenols and different monoterpenes).
Proteomic and transcriptomic approaches have been setup envisaging the elucidation of the myrcene stimulon. In 2009, a set of myrcene-dependent proteins has been described using subproteome analysis of the cytoplasmic fraction [3]. More recently, a RNA-seq transcriptome analysis led to the identification of a 28kb genomic island of key importance in the catabolism of myrcene. This island includes genes involved in: i) myrcene oxidation and bioconversion of myrcene derivatives via a beta-oxidation like pathway; ii) regulation of myrcene pathway; iii) myrcene sensing. In addition several other gene clusters spread in the genome of Pseudomonas sp. M1 have been found to be myrcene-dependently expressed and are currently being characterized.
Integration of genomic, transcriptomic, proteomic and metabolic data (which is currently being setup) will deliver a very solid and detailed description of the myrcene catabolism (and other monoterpenes), and on the associated molecular mechanisms of adaptation, providing the adequate support for the application of M1 as a biocatalyst in whole-cell biotransformations of plant-derived volatiles.Fundação para a Ciência e a Tecnologia (FCT
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