1,821 research outputs found
The colour-magnitude relation of Globular Clusters in Centaurus and Hydra - Constraints on star cluster self-enrichment with a link to massive Milky Way GCs
We investigate the colour-magnitude relation of metal-poor globular clusters,
the 'blue tilt', in the Hydra and Centaurus galaxy clusters and constrain the
primordial conditions for star cluster self-enrichment. We analyse U,I
photometry for about 2500 globular clusters in the central regions of Hydra and
Centaurus, based on FORS1@VLT data. We convert the measured colour-magnitude
relations into mass-metallicity space and obtain a scaling of Z \propto M^{0.27
\pm 0.05} for Centaurus GCs and Z \propto M^{0.40 \pm 0.06} for Hydra GCs,
consistent with results in other environments. We find that the GC
mass-metallicity relation already sets in at present-day masses of a few 10^5
solar masses and is well established in the luminosity range of massive MW
clusters like omega Centauri. We compare the mass-metallicity relation with
predictions from the star cluster self-enrichment model by Bailin & Harris
(2009). For this we include effects of dynamical and stellar evolution and a
physically well motivated primordial mass-radius scaling. The self-enrichment
model reproduces the observed relations well for average primordial half-light
radii r_h ~ 1-1.5 pc, star formation efficiencies f_* ~ 0.3-0.4, and
pre-enrichment levels of [Fe/H] ~ -1.7 dex. Within the self-enrichment
scenario, the observed blue tilt implies a correlation between GC mass and
width of the stellar metallicity distribution. We find that this implied
correlation matches the trend of width with GC mass measured in Galactic GCs,
including extreme cases like omega Cen and M54. We conclude that 1. A
primordial star cluster mass-radius relation provides a significant improvement
to the self-enrichment model fits. 2. Broadenend metallicity distributions as
found in some massive MW globular clusters may have arisen naturally from
self-enrichment processes, without the need of a dwarf galaxy progenitor.Comment: 15 pages, 13 figures. Language edited version of paper accepted for
publication in Astronomy & Astrophysics. Colour-composite in Figure 1 reduced
in resolutio
Xenon lighting adjusted to plant requirements
Xenon lamps are available as low and high power lamps with relatively high efficiency and a relatively long lifetime up to several thousand hours. Different construction types of short-arc and long-arc lamps permit a good adaptation to various applications in projection and illumination techniques without substantial changes of the spectral quality. Hence, the xenon lamp was the best choice for professional technical purposes where high power at simultaneously good spectral quality of the light was required. However, technical development does not stand still. Between the luminous efficacy of xenon lamps of 25-50 lm/W and the theoretical limit for 'white light' of 250 lm/W is still much room for improvement. The present development mainly favors other lamp types, like metal halide lamps and fluorescent lamps for commercial lighting purposes. The enclosed sections deal with some of the properties of xenon lamps relevant to plant illumination; particularly the spectral aspects, the temporal characteristics of the emission, and finally the economy of xenon lamps will be addressed. Due to radiation exceeding the natural global radiation in both the ultraviolet (UV) and the infrared (IR) regions, filter techniques have to be included into the discussion referring to the requirements of plant illumination. Most of the presented results were obtained by investigations in the GSF phytotron or in the closed Phytocell chambers of the University of Erlangen. As our experiences are restricted to area plant illumination rather than spot lights our discussion will concentrate on low pressure long-arc xenon lamps which are commonly used for such plant illuminations. As the spectral properties of short-arc lamps do not differ much from those of long-arc lamps most of our conclusions will be valid for high pressure xenon lamps too. These lamps often serve as light sources for small sun simulators and for monochromators which are used for action spectroscopy of plant responses
Conservative and disruptive modes of adolescent change in human brain functional connectivity
Adolescent changes in human brain function are not entirely understood. Here, we used multiecho functional MRI (fMRI) to measure developmental change in functional connectivity (FC) of resting-state oscillations between pairs of 330 cortical regions and 16 subcortical regions in 298 healthy adolescents scanned 520 times. Participants were aged 14 to 26 y and were scanned on 1 to 3 occasions at least 6 mo apart. We found 2 distinct modes of age-related change in FC: âconservativeâ and âdisruptive.â Conservative development was characteristic of primary cortex, which was strongly connected at 14 y and became even more connected in the period from 14 to 26 y. Disruptive development was characteristic of association cortex and subcortical regions, where connectivity was remodeled: connections that were weak at 14 y became stronger during adolescence, and connections that were strong at 14 y became weaker. These modes of development were quantified using the maturational index (MI), estimated as Spearmanâs correlation between edgewise baseline FC (at 14 y, FC14) and adolescent change in FC (ÎFC14â26), at each region. Disruptive systems (with negative MI) were activated by social cognition and autobiographical memory tasks in prior fMRI data and significantly colocated with prior maps of aerobic glycolysis (AG), AG-related gene expression, postnatal cortical surface expansion, and adolescent shrinkage of cortical thickness. The presence of these 2 modes of development was robust to numerous sensitivity analyses. We conclude that human brain organization is disrupted during adolescence by remodeling of FC between association cortical and subcortical areas
UV filters for lighting of plants
The wavelength dependent interaction of biological systems with radiation is commonly described by appropriate action spectra. Particularly effective plant responses are obtained for ultraviolet (UV) radiation. Excess shortwave UV-B radiation will induce genetic defects and plant damage. Besides the ecological discussion of the deleterious effects of the excess UV radiation there is increasing interest in horticultural applications of this spectral region. Several metabolic pathways leading to valuable secondary plant products like colors, odors, taste, or resulting in mechanical strength and vitality are triggered by UV radiation. Thus, in ecologically as well as in economically oriented experiments the exact generation and knowledge of the spectral irradiance, particularly near the UV absorption edge, is essential. The ideal filter 'material' to control the UV absorption edge would be ozone itself. However, due to problems in controlling the toxic and chemically aggressive, instable gas, only rather 'small ozone filters' have been realized so far. In artificial plant lighting conventional solid filter materials such as glass sheets and plastic foils (celluloseacetate or cellulosetriacetate) which can be easily handled have been used to absorb the UV-C and the excess shortwave UV-B radiation of the lamp emissions. Different filter glasses are available which provide absorption properties suitable for gradual changes of the spectral UV-B illumination of artificial lighting. Using a distinct set of lamps and filter glasses an acceptable simulation of the UV-B part of natural global radiation can be achieved. The aging of these and other filter materials under the extreme UV radiation in the lamphouse of a solar simulator is presently unavoidable. This instability can be dealt with only by a precise spectral monitoring and by replacing the filters accordingly. For this reason attempts would be useful to develop real ozone filters which can replace glass filters. In any case chamber experiments require a careful selection of the filter material used and must be accompanied by a continuous UV-B monitoring
Study of bound states in 12Be through low-energy 11Be(d,p)-transfer reactions
The bound states of 12Be have been studied through a 11Be(d,p)12Be transfer
reaction experiment in inverse kinematics. A 2.8 MeV/u beam of 11Be was
produced using the REX-ISOLDE facility at CERN. The outgoing protons were
detected with the T-REX silicon detector array. The MINIBALL germanium array
was used to detect gamma rays from the excited states in 12Be. The gamma-ray
detection enabled a clear identification of the four known bound states in
12Be, and each of the states has been studied individually. Differential cross
sections over a large angular range have been extracted. Spectroscopic factors
for each of the states have been determined from DWBA calculations and have
been compared to previous experimental and theoretical results
Clinically feasible brain morphometric similarity network construction approaches with restricted magnetic resonance imaging acquisitions
Morphometric similarity networks (MSNs) estimate organization of the cortex as a biologically meaningful set of similarities between anatomical features at the macro-and microstructural level, derived from multiple structural MRI (sMRI) sequences. These networks are clinically relevant, predicting 40% variance in IQ. However, the sequences required (T1w, T2w, DWI) to produce these networks are longer acquisitions, less feasible in some populations. Thus, estimating MSNs using features from T1w sMRI is attractive to clinical and developmental neuroscience. We studied whether reduced-feature approaches approximate the original MSN model as a potential tool to investigate brain structure. In a large, homogenous dataset of healthy young adults (from the Human Connectome Project, HCP), we extended previous investigations of reduced-feature MSNs by comparing not only T1w-derived networks, but also additional MSNs generated with fewer MR sequences, to their full acquisition counterparts. We produce MSNs that are highly similar at the edge level to those generated with multimodal imaging; however, the nodal topology of the networks differed. These networks had limited predictive validity of generalized cognitive ability. Overall, when multimodal imaging is not available or appropriate, T1w-restricted MSN construction is feasible, provides an appropriate estimate of the MSN, and could be a useful approach to examine outcomes in future studies
Low-energy Coulomb excitation of Fe and Mn following in-beam decay of Mn
Sub-barrier Coulomb-excitation was performed on a mixed beam of Mn and
Fe, following in-trap decay of Mn at REX-ISOLDE,
CERN. The trapping and charge breeding times were varied in order to alter the
composition of the beam, which was measured by means of an ionisation chamber
at the zero-angle position of the Miniball array. A new transition was observed
at 418~keV, which has been tentatively associated to a
transition. This fixes the relative
positions of the -decaying and states in Mn for
the first time. Population of the state was observed in Fe
and the cross-section determined by normalisation to the Ag target
excitation, confirming the value measured in recoil-distance lifetime
experiments.Comment: 9 pages, 10 figure
Country-level gender inequality is associated with structural differences in the brains of women and men
Significance Gender inequality is associated with worse mental health and academic achievement in women. Using a dataset of 7,876 MRI scans from healthy adults living in 29 different countries, we here show that gender inequality is associated with differences between the brains of men and women: cortical thickness of the right hemisphere, especially in limbic regions such as the right caudal anterior cingulate and right medial orbitofrontal, as well as the left lateral occipital, present thinner cortices in women compared to men only in gender-unequal countries. These results suggest a potential neural mechanism underlying the worse outcome of women in gender-unequal settings, as well as highlight the role of the environment in the brain differences between women and men. Abstract Gender inequality across the world has been associated with a higher risk to mental health problems and lower academic achievement in women compared to men. We also know that the brain is shaped by nurturing and adverse socio-environmental experiences. Therefore, unequal exposure to harsher conditions for women compared to men in gender-unequal countries might be reflected in differences in their brain structure, and this could be the neural mechanism partly explaining womenâs worse outcomes in gender-unequal countries. We examined this through a random-effects meta-analysis on cortical thickness and surface area differences between adult healthy men and women, including a meta-regression in which country-level gender inequality acted as an explanatory variable for the observed differences. A total of 139 samples from 29 different countries, totaling 7,876 MRI scans, were included. Thickness of the right hemisphere, and particularly the right caudal anterior cingulate, right medial orbitofrontal, and left lateral occipital cortex, presented no differences or even thicker regional cortices in women compared to men in gender-equal countries, reversing to thinner cortices in countries with greater gender inequality. These results point to the potentially hazardous effect of gender inequality on womenâs brains and provide initial evidence for neuroscience-informed policies for gender equality
Brain charts for the human lifespan
Over the past few decades, neuroimaging has become a ubiquitous tool in basic
research and clinical studies of the human brain. However, no reference standards
currently exist to quantify individual diferences in neuroimaging metrics over time,
in contrast to growth charts for anthropometric traits such as height and weight1
.
Here we assemble an interactive open resource to benchmark brain morphology
derived from any current or future sample of MRI data (http://www.brainchart.io/).
With the goal of basing these reference charts on the largest and most inclusive
dataset available, acknowledging limitations due to known biases of MRI studies
relative to the diversity of the global population, we aggregated 123,984 MRI scans,
across more than 100 primary studies, from 101,457 human participants between 115
days post-conception to 100 years of age. MRI metrics were quantifed by centile
scores, relative to non-linear trajectories2
of brain structural changes, and rates of
change, over the lifespan. Brain charts identifed previously unreported neurodevelo pmental milestones3
, showed high stability of individuals across longitudinal
assessments, and demonstrated robustness to technical and methodological
diferences between primary studies. Centile scores showed increased heritability
compared with non-centiled MRI phenotypes, and provided a standardized measure
of atypical brain structure that revealed patterns of neuroanatomical variation across
neurological and psychiatric disorders. In summary, brain charts are an essential step
towards robust quantifcation of individual variation benchmarked to normative
trajectories in multiple, commonly used neuroimaging phenotypes
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