1,203 research outputs found
The Relationship between Trial-by-Trial Variability and Oscillations of Cortical Population Activity
Liberalismo
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Realidad: Revista de Ciencias Sociales y Humanidades No. 162, 2023: 72-75.
Influence of Climate Change and Postdelisting Management on Longâterm Population Viability of the Conservationâreliant Kirtland\u27s Warbler
Rapid global climate change is resulting in novel abiotic and biotic conditions and inâ teractions. Identifying management strategies that maximize probability of longâterm persistence requires an understanding of the vulnerability of species to environmenâ tal changes. We sought to quantify the vulnerability of Kirtland\u27s Warbler (Setophaga kirtlandii), a rare Neotropical migratory songbird that breeds almost exclusively in the Lower Peninsula of Michigan and winters in the Bahamian Archipelago, to proâ jected environmental changes on the breeding and wintering grounds. We develâ oped a populationâlevel simulation model that incorporates the influence of annual environmental conditions on the breeding and wintering grounds, and parameterâ ized the model using empirical relationships. We simulated independent and addiâ tive effects of reduced breeding grounds habitat quantity and quality, and wintering grounds habitat quality, on population viability. Our results indicated the Kirtland\u27s Warbler population is stable under current environmental and management condiâ tions. Reduced breeding grounds habitat quantity resulted in reductions of the stable population size, but did not cause extinction under the scenarios we examined. In contrast, projected large reductions in wintering grounds precipitation caused the population to decline, with risk of extinction magnified when breeding habitat quanâ tity or quality also decreased. Our study indicates that probability of longâterm perâ sistence for Kirtland\u27s Warbler will depend on climate change impacts to wintering grounds habitat quality and contributes to the growing literature documenting the importance of considering the full annual cycle for understanding population dynamâ ics of migratory species
On the Origin of Nuclear Star Clusters in Late Type Spiral Galaxies
A large fraction of bulgeless disk galaxies contain young compact stellar
systems at their centers, in spite of the local gravitational stability of
these disks. We evaluate two contrasting hypotheses for the origin of the
nuclear star clusters in late-type disk galaxies. The clusters could not have
migrated from distant eccentric locations in the disk. Instead they must have
formed in situ, requiring radial transport of gas toward the center of the
disk. This transport could be a consequence of the development of the
magnetorotational instability in the differentially rotating warm neutral
medium. We evaluate the rate of gas transport into the disk center and find
that it is sufficient to support continuous star formation in that location.
Enhanced stellar surface brightness in the inner few hundred parsecs and the
formation of a compact stellar system in the central few parsecs are
unavoidable in dark matter halos with divergent density profiles. We illustrate
our conclusions on a model of the nearest late-type disk galaxy M33.Comment: 4 pages, ApJ Letters, in pres
Atomic Hydrogen and Star Formation in the Bridge/Ring Interacting Galaxy Pair NGC 7714/7715 (Arp 284)
We present high spatial resolution 21 cm HI maps of the interacting galaxy
pair NGC 7714/7715. We detect a massive (2 x 10**9 M(sun)) HI bridge connecting
the galaxies that is parallel to but offset from the stellar bridge. A chain of
HII regions traces the gaseous bridge, with H-alpha peaks near but not on the
HI maxima. An HI tidal tail is also detected to the east of the smaller galaxy
NGC 7715, similarly offset from a stellar tail. The strong partial stellar ring
on the eastern side of NGC 7714 has no HI counterpart, but on the opposite side
of NGC 7714 there is a 10**9 M(sun) HI loop 11 kpc in radius. Within the NGC
7714 disk, clumpy HI gas is observed associated with star formation regions.
Redshifted HI absorption is detected towards the starburst nucleus. We compare
the observed morphology and gas kinematics with gas dynamical models in which a
low-mass companion has an off-center prograde collision with the outer disk of
a larger galaxy. These simulations suggest that the bridge in NGC 7714/7715 is
a hybrid between bridges seen in systems like M51 and the purely gaseous
`splash' bridges found in ring galaxies like the Cartwheel. The offset between
the stars and gas in the bridge may be due to dissipative cloud-cloud
collisions occuring during the impact of the two gaseous disks.Comment: 31 pages, Latex, 11 figures, to be published in the July 10, 1997
issue of the Astrophysical Journa
Time interval distributions of atoms in atomic beams
We report on the experimental investigation of two-particle correlations
between neutral atoms in a Hanbury Brown and Twiss experiment. Both an atom
laser beam and a pseudo-thermal atomic beam are extracted from a Bose-Einstein
condensate and the atom flux is measured with a single atom counter. We
determine the conditional and the unconditional detection probabilities for the
atoms in the beam and find good agreement with the theoretical predictions.Comment: 4 pages, 3 figure
Predicting the risk of falling â efficacy of a risk assessment tool compared to nurses' judgement: a cluster-randomised controlled trial [ISRCTN37794278]
BACKGROUND: Older people living in nursing homes are at high risk of falling because of their general frailty and multiple pathologies. Prediction of falls might lead to an efficient allocation of preventive measures. Although several tools to assess the risk of falling have been developed, their impact on clinically relevant endpoints has never been investigated. The present study will evaluate the clinical efficacy and consequences of different fall risk assessment strategies. STUDY DESIGN: Cluster-randomised controlled trial with nursing home clusters randomised either to the use of a standard fall risk assessment tool alongside nurses' clinical judgement or to nurses' clinical judgement alone. Standard care of all clusters will be optimised by structured education on best evidence strategies to prevent falls and fall related injuries. 54 nursing home clusters including 1,080 residents will be recruited. Residents must be â„ 70 years, not bedridden, and living in the nursing home for more than three months. The primary endpoint is the number of participants with at least one fall at 12 months. Secondary outcome measures are the number of falls, clinical consequences including side effects of the two risk assessment strategies. Other measures are fall related injuries, hospital admissions and consultations with a physician, and costs
Bathypelagic particle flux signatures from a suboxic eddy in the oligotrophic tropical North Atlantic: production, sedimentation and preservation
Particle fluxes at the Cape Verde Ocean Observatory (CVOO) in the eastern tropical North Atlantic for the period December 2009 until May 2011 are discussed based on bathypelagic sediment trap time-series data collected at 1290 and 3439âŻm water depth. The typically oligotrophic particle flux pattern with weak seasonality is modified by the appearance of a highly productive and low oxygen (minimum concentration below 2âŻÂ”molâŻkgâ1 at 40âŻm depth) anticyclonic modewater eddy (ACME) in winter 2010. The eddy passage was accompanied by unusually high mass fluxes of up to 151âŻmgâŻmâ2âŻdâ1, lasting from December 2009 to May 2010. Distinct biogenic silica (BSi) and organic carbon flux peaks of âŒâŻ15 and 13.3âŻmgâŻmâ2âŻdâ1, respectively, were observed in FebruaryâMarch 2010 when the eddy approached the CVOO. The flux of the lithogenic component, mostly mineral dust, was well correlated with that of organic carbon, in particular in the deep trap samples, suggesting a tight coupling. The lithogenic ballasting obviously resulted in high particle settling rates and, thus, a fast transfer of epi-/meso-pelagic signatures to the bathypelagic traps. We suspect that the two- to three-fold increase in particle fluxes with depth as well as the tight coupling of mineral dust and organic carbon in the deep trap samples might be explained by particle focusing processes within the deeper part of the eddy. Molar CâŻ:âŻN ratios of organic matter during the ACME passage were around 18 and 25 for the upper and lower trap samples, respectively. This suggests that some productivity under nutrient (nitrate) limitation occurred in the euphotic zone of the eddy in the beginning of 2010 or that a local nitrogen recycling took place. The ÎŽ15N record showed a decrease from 5.21 to 3.11âŻâ° from January to March 2010, while the organic carbon and nitrogen fluxes increased. The causes of enhanced sedimentation from the eddy in February/March 2010 remain elusive, but nutrient depletion and/or an increased availability of dust as a ballast mineral for organic-rich aggregates might have contributed. Rapid remineralisation of sinking organic-rich particles could have contributed to oxygen depletion at shallow depth. Although the eddy formed in the West African coastal area in summer 2009, no indications of coastal flux signatures (e.g. from diatoms) were found in the sediment trap samples, confirming the assumption that the suboxia developed within the eddy en route. However, we could not detect biomarkers indicative of the presence of anammox (anaerobic ammonia oxidation) bacteria or green sulfur bacteria thriving in photic zone suboxia/hypoxia, i.e. ladderane fatty acids and isorenieratene derivatives, respectively. This could indicate that suboxic conditions in the eddy had recently developed and/or the respective bacterial stocks had not yet reached detection thresholds. Another explanation is that the fast-sinking organic-rich particles produced in the surface layer did not interact with bacteria from the suboxic zone below. Carbonate fluxes dropped from âŒâ52 to 21.4âŻmgâŻmâ2âŻdâ1 from January to February 2010, respectively, mainly due to reduced contribution of shallow-dwelling planktonic foraminifera and pteropods. The deep-dwelling foraminifera Globorotalia menardii, however, showed a major flux peak in February 2010, most probably due to the suboxia/hypoxia. The low oxygen conditions forced at least some zooplankton to reduce diel vertical migration. Reduced âflux feedingâ by zooplankton in the epipelagic could have contributed to the enhanced fluxes of organic materials to the bathypelagic traps during the eddy passage. Further studies are required on eddy-induced particle production and preservation processes and particle focusin
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