231 research outputs found
Genetic variation in early fitness traits across European populations of silver birch (Betula pendula)
Given that the ecological niche of tree species is typically narrower for earlier life stages, intraspecific genetic variation at early fitness traits may greatly influence the adaptive response of tree populations to changing environmental conditions. In this study, we evaluated genetic variation in early fitness traits among 12 populations of Betula pendula from a wide latitudinal range in Europe (41-55 degrees N). We first conducted a chamber experiment to test for population differences in germination and the effect of pre-chilling treatment on seed dormancy release. We then established three common gardens spread across the species latitudinal range in order to evaluate levels of quantitative genetic variation and genotype-by-environment interaction at different early life traits. Our results showed significant variation in chamber germination rates among populations (0-60 %), with southern populations exhibiting lower germination. Pre-chilling treatments did not generally improve germination success. Population seedling emergence rates in the field were correlated with chamber germination rates, though being an order of magnitude lower, with an average ranging from 0 to 1.3 % across gardens. Highly significant variation was found in field emergence rates among populations, and between seed-crop years within populations, but not among families within populations. Populations differed in seedling height, diameter, slenderness and budburst date, with significant among-family variation. Population latitude was positively associated with chamber germination rate and with seedling emergence rate in one of the central field sites. Overall, genetic, environmental and demographic factors seem to influence the observed high levels of variation in early fitness traits among B. pendula populations. Our results suggest limited regeneration capacity for the study species under drier conditions, but further field trials with sufficient replication over environments and seed crops will improve our understanding of its vulnerability to climate change
Controlling spin relaxation with a cavity
Spontaneous emission of radiation is one of the fundamental mechanisms by
which an excited quantum system returns to equilibrium. For spins, however,
spontaneous emission is generally negligible compared to other non-radiative
relaxation processes because of the weak coupling between the magnetic dipole
and the electromagnetic field. In 1946, Purcell realized that the spontaneous
emission rate can be strongly enhanced by placing the quantum system in a
resonant cavity -an effect which has since been used extensively to control the
lifetime of atoms and semiconducting heterostructures coupled to microwave or
optical cavities, underpinning single-photon sources. Here we report the first
application of these ideas to spins in solids. By coupling donor spins in
silicon to a superconducting microwave cavity of high quality factor and small
mode volume, we reach for the first time the regime where spontaneous emission
constitutes the dominant spin relaxation mechanism. The relaxation rate is
increased by three orders of magnitude when the spins are tuned to the cavity
resonance, showing that energy relaxation can be engineered and controlled
on-demand. Our results provide a novel and general way to initialise spin
systems into their ground state, with applications in magnetic resonance and
quantum information processing. They also demonstrate that, contrary to popular
belief, the coupling between the magnetic dipole of a spin and the
electromagnetic field can be enhanced up to the point where quantum
fluctuations have a dramatic effect on the spin dynamics; as such our work
represents an important step towards the coherent magnetic coupling of
individual spins to microwave photons.Comment: 8 pages, 6 figures, 1 tabl
Health care utilization in the elderly Mexican population: Expenditures and determinants
<p>Abstract</p> <p>Background</p> <p>Worldwide population aging has been considered one of the most important demographic phenomena, and is frequently referred as a determinant of health costs and expenditures. These costs are an effect either of the aging process itself (social) or because of the increase that comes with older age (individual).</p> <p>Objective</p> <p>To analyze health expenditures and its determinants in a sample of Mexican population, for three dimensions acute morbidity, ambulatory care and hospitalization focusing on different age groups, particularly the elderly.</p> <p>Methods</p> <p>A secondary analysis of the Mexican National Health and Nutrition Survey (ENSANUT), 2006 was conducted. A descriptive analysis was performed to establish a health profile by socio-demographic characteristics. Logistic regression models were estimated to determine the relation between acute morbidity, ambulatory care, hospitalization and age group; to establish the determinants of hospitalization among the population 60 years and older; and to determine hospitalization expenditures by age.</p> <p>Results</p> <p>Higher proportion of elderly reporting health problems was found. Average expenditures of hospitalization in households were 308.9 am dlls, the highest among the considered age groups. The multivariate analysis showed higher probability of being hospitalized among the elderly, but not for risks for acute morbidity and ambulatory care. Among the elderly, older age, being male or living in a city or in a metro area implied a higher probability of hospitalization during the last year, with chronic diseases playing a key role in hospitalization.</p> <p>Conclusions</p> <p>The conditions associated with age, such as chronic diseases, have higher weight than age itself; therefore, they are responsible for the higher expenditures reported. Conclusions point towards a differentiated use and intensity of health services depending on age. The projected increase in hospitalization and health care needs for this group requires immediate attention.</p
Ecological implications of a flower size/number trade-off in tropical forest trees
Peer reviewedPublisher PD
Cognitive impairment induced by delta9-tetrahydrocannabinol occurs through heteromers between cannabinoid CB1 and serotonin 5-HT2A receptors
Delta-9-tetrahydrocannabinol (THC), the main psychoactive compound of marijuana, induces numerous undesirable effects, including memory impairments, anxiety, and dependence. Conversely, THC also has potentially therapeutic effects, including analgesia, muscle relaxation, and neuroprotection. However, the mechanisms that dissociate these responses are still not known. Using mice lacking the serotonin receptor 5-HT2A, we revealed that the analgesic and amnesic effects of THC are independent of each other: while amnesia induced by THC disappears in the mutant mice, THC can still promote analgesia in these animals. In subsequent molecular studies, we showed that in specific brain regions involved in memory formation, the receptors for THC and the 5-HT2A receptors work together by physically interacting with each other. Experimentally interfering with this interaction prevented the memory deficits induced by THC, but not its analgesic properties. Our results highlight a novel mechanism by which the beneficial analgesic properties of THC can be dissociated from its cognitive side effects
Expression of Distal-less, dachshund, and optomotor blind in Neanthes arenaceodentata (Annelida, Nereididae) does not support homology of appendage-forming mechanisms across the Bilateria
The similarity in the genetic regulation of
arthropod and vertebrate appendage formation has been
interpreted as the product of a plesiomorphic gene
network that was primitively involved in bilaterian
appendage development and co-opted to build appendages
(in modern phyla) that are not historically related
as structures. Data from lophotrochozoans are needed to
clarify the pervasiveness of plesiomorphic appendage forming
mechanisms. We assayed the expression of three
arthropod and vertebrate limb gene orthologs, Distal-less
(Dll), dachshund (dac), and optomotor blind (omb), in
direct-developing juveniles of the polychaete Neanthes
arenaceodentata. Parapodial Dll expression marks premorphogenetic
notopodia and neuropodia, becoming restricted
to the bases of notopodial cirri and to ventral
portions of neuropodia. In outgrowing cephalic appendages,
Dll activity is primarily restricted to proximal
domains. Dll expression is also prominent in the brain. dac
expression occurs in the brain, nerve cord ganglia, a pair
of pharyngeal ganglia, presumed interneurons linking a
pair of segmental nerves, and in newly differentiating
mesoderm. Domains of omb expression include the brain,
nerve cord ganglia, one pair of anterior cirri, presumed
precursors of dorsal musculature, and the same pharyngeal
ganglia and presumed interneurons that express dac.
Contrary to their roles in outgrowing arthropod and
vertebrate appendages, Dll, dac, and omb lack comparable
expression in Neanthes appendages, implying independent
evolution of annelid appendage development. We infer
that parapodia and arthropodia are not structurally or
mechanistically homologous (but their primordia might
be), that Dll’s ancestral bilaterian function was in sensory
and central nervous system differentiation, and that
locomotory appendages possibly evolved from sensory
outgrowths
Biometric variability of goat populations revealed by means of principal component analysis
The signatures of Anthropocene defaunation: cascading effects of the seed dispersal collapse
Anthropogenic activity is driving population declines and extinctions of large-bodied, fruit-eating animals worldwide. Loss of these frugivores is expected to trigger negative cascading effects on plant populations if remnant species fail to replace the seed dispersal services provided by the extinct frugivores. A collapse of seed dispersal may not only affect plant demography (i.e., lack of recruitment), but should also supress gene flow via seed dispersal. Yet little empirical data still exist demonstrating the genetic consequences of defaunation for animal-dispersed plant species. Here, we first document a significant reduction of seed dispersal distances along a gradient of human-driven defaunation, with increasing loss of large- and medium-bodied frugivores. We then show that local plant neighbourhoods have higher genetic similarity and smaller effective population sizes when large seed dispersers become extinct (i.e., only small frugivores remain) or are even partially downgraded (i.e., medium-sized frugivores providing less efficient seed dispersal). Our results demonstrate that preservation of large frugivores is crucial to maintain functional seed dispersal services and their associated genetic imprints, a central conservation target. Early signals of reduced dispersal distances that accompany the Anthropogenic defaunation forecast multiple, cascading effects on plant populations
Решение оптимизационных задач для систем массового обслуживання с отказами в условиях неопределенности
Построены математические модели расчета показателей качества функционирования вычислительных
сетей, которые можно представить в виде сетей массового обслуживания с отказами. Сформулированы
задачи оптимизации показателей качества функционирования таких сетей при заданных ограничениях
на максимальную пропускную способность каналов связи и на выделяемые для модернизации сети ресурсы. Построены алгоритмы, которые позволяют решать поставленные оптимизационные задачи в
рамках оговоренных ограничений
Congenital and childhood atrioventricular blocks: pathophysiology and contemporary management
Atrioventricular block is classified as congeni-
tal if diagnosed in utero, at birth, or within the first
month of life. The pathophysiological process is believed
to be due to immune-mediated injury of the conduction
system, which occurs as a result of transplacental pas-
sage of maternal anti-SSA/Ro-SSB/La antibodies.
Childhood atrioventricular block is therefore diagnosed
between the first month and the 18th year of life.
Genetic variants in multiple genes have been described
to date in the pathogenesis of inherited progressive car-
diac conduction disorders. Indications and techniques of
cardiac pacing have also evolved to allow safe perma-
nent cardiac pacing in almost all patients, including
those with structural heart abnormalities
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