675 research outputs found
Observational Signatures of Massive Black Hole Progenitor Pathways: is Leo I a Smoking Gun?
Observational evidence is mounting regarding the population demographics of
Massive Black Holes (MBHs), from the most massive cluster galaxies down to the
dwarf galaxy regime. However, the progenitor pathways from which these central
MBHs formed remain unclear. Here we report a potentially powerful observational
signature of MBH formation in dwarf galaxies. We argue that a continuum in the
mass spectrum of MBHs in (fossil) dwarf galaxies would be a unique signature of
a heavy seed formation pathway. Under the robust assumption of initial
fragmentation of the parent gas cloud resulting in a burst of heavy seed
production, a significant fraction of these seeds will survive to the present
day as off-nuclear MBHs with masses less than that of the central object.
Motivated by the recent discovery of a MBH in the relatively low central
density Leo I galaxy, we show that such a continuum in MBH seed masses should
persist from the lightest black hole masses up to the mass of the central MBH
in contrast to the light seeding scenario where no such continuum should exist.
The detection of off-centered MBHs and a central MBH would represent strong
evidence of a heavy seeding pathway.Comment: Submitted to MNRAS Letters. 6 pages, 2 figures. Comments welcom
Bioingeniería e ingeniería biomédica en Colombia: trasegando en sus inicios y en la construcción de su futuro
Invitado a que transmita la experiencia personal en el área de la bioingeniería e ingeniería biomédica, de aquellos
inicios y desarrollos que fueron dando madurez a esta disciplina profesional en Colombia, sus desafíos y aportes, considero
importante en primer lugar contextualizar el punto de partida en esta área de la investigación y de la práctica profesional
Current Concepts and Trends in Human-Automation Interaction
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The purpose of this panel was to provide a general overview and discussion of some of the most current and controversial concepts and trends in human-automation interaction. The panel was composed of eight researchers and practitioners. The panelists are well-known experts in the area and offered differing views on a variety of different human-automation topics. The range of concepts and trends discussed in this panel include: general taxonomies regarding stages and levels of automation and function allocation, individualized adaptive automation, automation-induced complacency, economic rationality and the use of automation, the potential utility of false alarms, the influence of different types of false alarms on trust and reliance, and a system-wide theory of trust in multiple automated aids
Genetic recombination is targeted towards gene promoter regions in dogs
The identification of the H3K4 trimethylase, PRDM9, as the gene responsible
for recombination hotspot localization has provided considerable insight into
the mechanisms by which recombination is initiated in mammals. However,
uniquely amongst mammals, canids appear to lack a functional version of PRDM9
and may therefore provide a model for understanding recombination that occurs
in the absence of PRDM9, and thus how PRDM9 functions to shape the
recombination landscape. We have constructed a fine-scale genetic map from
patterns of linkage disequilibrium assessed using high-throughput sequence data
from 51 free-ranging dogs, Canis lupus familiaris. While broad-scale properties
of recombination appear similar to other mammalian species, our fine-scale
estimates indicate that canine highly elevated recombination rates are observed
in the vicinity of CpG rich regions including gene promoter regions, but show
little association with H3K4 trimethylation marks identified in spermatocytes.
By comparison to genomic data from the Andean fox, Lycalopex culpaeus, we show
that biased gene conversion is a plausible mechanism by which the high CpG
content of the dog genome could have occurred.Comment: Updated version, with significant revision
Segmentation and Additive Approach: A Reliable Technique to Study Noncovalent Interactions of Large Molecules at the Surface of Single‐Wall Carbon Nanotubes
This investigation explores a new protocol, named Segmentation and Additive approach (SAA), to study exohedral noncovalent functionalization of single-walled carbon nanotubes (SWNTs) with large molecules, such as polymers, bio-molecules etc, by segmenting the entire system into smaller units to reduce computational cost. A key criterion of the segmentation process is the preservation of the molecular structure responsible for stabilization of the entire system in smaller segments. Noncovalent interaction of linoleic acid (LA, C18H32O2), a fatty acid, at the surface of a (10,0) zigzag nanotubeis considered for test purposes. Three smaller segmented models have been created from the full (10,0)-LA system and interaction energies were calculated for these models and compared with the full system at different levels of theory, namely ωB97XD, LDA. The success of this SAA is confirmed as the sum of the interaction energies is in very good agreement with the total interaction energy. Besides reducing computational cost, another merit of SAA is an estimation of the contributions from different sections of the large system to the total interaction energy which can be studied in-depth using a higher level of theory to estimate several properties of each segment. On the negative side, bulk properties, such as HOMO-LUMO gap, of the entire system cannot be estimated by adding results from segment models
Unzipping Dynamics of Long DNAs
The two strands of the DNA double helix can be `unzipped' by application of
15 pN force. We analyze the dynamics of unzipping and rezipping, for the case
where the molecule ends are separated and re-approached at constant velocity.
For unzipping of 50 kilobase DNAs at less than about 1000 bases per second,
thermal equilibrium-based theory applies. However, for higher unzipping
velocities, rotational viscous drag creates a buildup of elastic torque to
levels above kBT in the dsDNA region, causing the unzipping force to be well
above or well below the equilibrium unzipping force during respectively
unzipping and rezipping, in accord with recent experimental results of Thomen
et al. [Phys. Rev. Lett. 88, 248102 (2002)]. Our analysis includes the effect
of sequence on unzipping and rezipping, and the transient delay in buildup of
the unzipping force due to the approach to the steady state.Comment: 15 pages Revtex file including 9 figure
Mesoscopic models for DNA stretching under force: new results and comparison to experiments
Single molecule experiments on B-DNA stretching have revealed one or two
structural transitions, when increasing the external force. They are
characterized by a sudden increase of DNA contour length and a decrease of the
bending rigidity. It has been proposed that the first transition, at forces of
60--80 pN, is a transition from B to S-DNA, viewed as a stretched duplex DNA,
while the second one, at stronger forces, is a strand peeling resulting in
single stranded DNAs (ssDNA), similar to thermal denaturation. But due to
experimental conditions these two transitions can overlap, for instance for
poly(dA-dT). We derive analytical formula using a coupled discrete worm like
chain-Ising model. Our model takes into account bending rigidity, discreteness
of the chain, linear and non-linear (for ssDNA) bond stretching. In the limit
of zero force, this model simplifies into a coupled model already developed by
us for studying thermal DNA melting, establishing a connexion with previous
fitting parameter values for denaturation profiles. We find that: (i) ssDNA is
fitted, using an analytical formula, over a nanoNewton range with only three
free parameters, the contour length, the bending modulus and the monomer size;
(ii) a surprisingly good fit on this force range is possible only by choosing a
monomer size of 0.2 nm, almost 4 times smaller than the ssDNA nucleobase
length; (iii) mesoscopic models are not able to fit B to ssDNA (or S to ss)
transitions; (iv) an analytical formula for fitting B to S transitions is
derived in the strong force approximation and for long DNAs, which is in
excellent agreement with exact transfer matrix calculations; (v) this formula
fits perfectly well poly(dG-dC) and -DNA force-extension curves with
consistent parameter values; (vi) a coherent picture, where S to ssDNA
transitions are much more sensitive to base-pair sequence than the B to S one,
emerges.Comment: 14 pages, 9 figure
Minimally invasive robotic surgery: force and torque analysis
La cirugía mínimamente invasiva y la incorporación de la robótica en este tipo de procedimientos representa
grandes ventajas para el paciente, el cirujano y los sistemas de salud. Sin embargo, los dispositivos comerciales disponibles
en la actualidad no cuentan con realimentación de fuerza y tacto, que faciliten al cirujano la identificación de los tejidos y
consecuentemente, la reducción de errores en los procedimientos quirúrgicos; por lo cual, el desarrollo de sistemas que cuenten
con este tipo de realimentación se convierte en un tema de interés a nivel mundial. El presente artículo contiene una revisión del
estado de la técnica con respecto a los sistemas comerciales y experimentales desarrollados en esta área. También, se presentan
algunos sensores y modelos matemáticos utilizados para calcular las fuerzas y torques en cirugía mínimamente invasiva.Minimally Invasive Surgery and the adaptation of robotics to these procedures represent many advantages for the
patient, the surgeon, and the health program. However, commercial devices used nowadays lack haptic feedback. This fact makes
the tissue identification more difficult and increments the injuries risk during the surgical procedure. The development of systems
with this kind of feedback has become a topic of interest throughout the world. The present article contains a revision of the state
of the art about commercial and experimental systems developed in this area. Models for the force and torque propagation, used in
Minimally Invasive Surgery, are also presented
Mate similarity in foraging Kerguelen shags: a combined bio-logging and stable isotope investigation
Similarity or dissimilarity between 2 individuals that have formed a pair to breed can occur in morphology, behaviour and diet. Such patterns influence partners’ cooperation when rearing their offspring, consequently influencing reproductive success. They may confer different benefits, depending on species and contexts. However, the extent to which breeding partners are more similar in morphology, behaviour, and diet is poorly documented. Furthermore, the relationship between behavioural consistency and mate choice is particularly poorly understood. To investigate these issues, Kerguelen shags Phalacrocorax verrucosus, which are monogamous with high mate fidelity across years, were studied. Partners were equipped with GPS and diving behaviour loggers. Feather and blood samples were analysed for stable isotopes (δ13C, a proxy of foraging habitat, and δ15N, a proxy of diet/trophic position). Generalized linear mixed effects models and permutation tests were used to investigate pair similarity in morphology, foraging behaviour, behavioural consistency, overlap in foraging areas, and diets/foraging habitats. Mates were found not to exhibit size-assortative mating, but were more similar in foraging behaviour. They did not show assortative or disassortative mating based on foraging behavioural consistency. Furthermore, they followed more similar bearings and overlapped more in foraging areas. In accordance with this, partners were more similar in δ15N. Given the lack of assortative mating by morphology, the similarity in behaviour could be due to individuals selecting mates with similar foraging abilities, linked with individual quality, and/or subsequently using information gained from their partners’ foraging strategies (e.g. local enhancement). This could help breeding pairs increase their foraging efficiency and reproductive success.<br /
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