362 research outputs found
Radio Emission from Cosmic Ray Air Showers: Coherent Geosynchrotron Radiation
Cosmic ray air showers have been known for over 30 years to emit pulsed radio
emission in the frequency range from a few to a few hundred MHz, an effect that
offers great opportunities for the study of extensive air showers with upcoming
fully digital "software radio telescopes" such as LOFAR and the enhancement of
particle detector arrays such as KASCADE Grande or the Pierre Auger
Observatory. However, there are still a lot of open questions regarding the
strength of the emission as well as the underlying emission mechanism.
Accompanying the development of a LOFAR prototype station dedicated to the
observation of radio emission from extensive air showers, LOPES, we therefore
take a new approach to modeling the emission process, interpreting it as
"coherent geosynchrotron emission" from electron-positron pairs gyrating in the
earth's magnetic field. We develop our model in a step-by-step procedure
incorporating increasingly realistic shower geometries in order to disentangle
the coherence effects arising from the different scales present in the air
shower structure and assess their influence on the spectrum and radial
dependence of the emitted radiation. We infer that the air shower "pancake"
thickness directly limits the frequency range of the emitted radiation, while
the radial dependence of the emission is mainly governed by the intrinsic
beaming cone of the synchrotron radiation and the superposition of the emission
over the air shower evolution as a whole. Our model succeeds in reproducing the
qualitative trends in the emission spectrum and radial dependence that were
observed in the past, and is consistent with the absolute level of the emission
within the relatively large systematic errors in the experimental data.Comment: 17 pages, 18 figures, accepted for publication by Astronomy &
Astrophysic
Recommended from our members
Cognitive tests used in chronic adult human randomised controlled trial micronutrient and phytochemical intervention studies
In recent years there has been a rapid growth of interest in exploring the relationship between nutritional therapies and the maintenance of cognitive function in adulthood. Emerging evidence reveals an increasingly complex picture with respect to the benefits of various food constituents on learning, memory and psychomotor function in adults. However, to date, there has been little consensus in human studies on the range of cognitive domains to be tested or the particular tests to be employed. To illustrate the potential difficulties that this poses, we conducted a systematic review of existing human adult randomised controlled trial (RCT) studies that have investigated the effects of 24 d to 36 months of supplementation with flavonoids and micronutrients on cognitive performance. There were thirty-nine studies employing a total of 121 different cognitive tasks that met the criteria for inclusion. Results showed that less than half of these studies reported positive effects of treatment, with some important cognitive domains either under-represented or not explored at all. Although there was some evidence of sensitivity to nutritional supplementation in a number of domains (for example, executive function, spatial working memory), interpretation is currently difficult given the prevailing 'scattergun approach' for selecting cognitive tests. Specifically, the practice means that it is often difficult to distinguish between a boundary condition for a particular nutrient and a lack of task sensitivity. We argue that for significant future progress to be made, researchers need to pay much closer attention to existing human RCT and animal data, as well as to more basic issues surrounding task sensitivity, statistical power and type I error
Synthesis of kinase inhibitors containing a pentafluorosulfanyl moiety
A series of 3-methylidene-1H-indol-2(3H)-ones substituted with a 5- or 6- pentafluorosulfanyl group has been synthesized by a Knoevenagel condensation reaction of SF5-substituted oxindoles with a range of aldehydes. The resulting products were characterized by x-ray crystallography studies and were tested for biological activity versus a panel of cell lines and protein kinases. Some exhibited single digit nM activity
Predictors of care home and hospital admissions and their costs for older people with Alzheimer’s disease: findings from a large London case register
Objectives. To examine links between clinical and other characteristics of people with Alzheimer’s disease living in the community, likelihood of care home or hospital admission, and associated costs. Design. Observational data extracted from clinical records using natural language processing and Hospital Episode Statistics. Statistical analyses examined effects of cognition, physical health, mental health, sociodemographic factors and living circumstances on risk of admission to care home or hospital over 6 months and associated costs, adjusting for repeated observations. Setting. Catchment area for South London and Maudsley National Health Service Foundation Trust, provider for 1.2 million people in Southeast London. Participants. Every individual with diagnosis of Alzheimer’s disease seen and treated by mental health services in the catchment area, with at least one rating of cognition, not resident in care home at time of assessment (n=3075). Interventions. Usual treatment. Main outcome measures. Risk of admission to, and days spent in three settings during 6-month period following routine clinical assessment: care home, mental health inpatient care, and general hospital inpatient care. Results. Predictors of probability of care home or hospital admission and/or associated costs over 6 months include cognition, functional problems, agitation, depression, physical illness, previous hospitalisations, age, gender, ethnicity, living alone, and having a partner. Patterns of association differed considerably by destination. Conclusions. Most people with dementia prefer to remain in their own homes, and funding bodies see this as cheaper than institutionalisation. Better treatment in the community that reduces health and social care needs of Alzheimer’s patients would reduce admission rates. Living alone, poor living circumstances and functional problems all raise admission rates, and so major cuts in social care budgets increase the risk of high-cost admissions which older people do not want. Routinely collected data can be used to reveal local patterns of admission and costs
Centerscope
Centerscope, formerly Scope, was published by the Boston University Medical Center "to communicate the concern of the Medical Center for the development and maintenance of improved health care in contemporary society.
N-Methylimidazole Promotes The Reaction Of Homophthalic Anhydride With Imines
The addition of N-methylimidazole (NMI) to the reaction of homophthalic anhydride with imines such as pyridine-3-carboxaldehyde-N-trifluoroethylimine (9) reduces the amount of elimination byproduct and improves the yield of the formal cycloadduct, tetrahydroisoquinolonic carboxylate 10. Carboxanilides of such compounds are of interest as potential antimalarial agents. A mechanism that rationalizes the role of NMI is proposed, and a gram-scale procedure for the synthesis and resolution of 10 is also described
W Hya : molecular inventory by ISO-SWS
Infrared spectroscopy is a powerful tool to probe the inventory of solid
state and molecular species in circumstellar ejecta. Here we analyse the
infrared spectrum of the Asymptotic Giant Branch star W Hya, obtained by the
Short and Long Wavelength Spectrometers on board of the Infrared Satellite
Observatory. These spectra show evidence for the presence of amorphous
silicates, aluminum oxide, and magnesium-iron oxide grains. We have modelled
the spectral energy distribution using laboratory measured optical properties
of these compounds and derive a total dust mass loss rate of 3E-10 Msol/yr. We
find no satisfactory fit to the 13 micron dust emission feature and the
identification of its carrier is still an open issue. We have also modelled the
molecular absorption bands due to H2O, OH, CO, CO2, SiO, and SO2 and estimated
the excitation temperatures for different bands which range from 300 to 3000K.
It is clear that different molecules giving rise to these absorption bands
originate from different gas layers. We present and analyse high resolution
Fabry-Perot spectra of the three CO2 bands in the 15 micron region. In these
data, the bands are resolved into individual Q-lines in emission, which allows
the direct determination of the excitation temperature and column density of
the emitting gas. This reveals the presence of a warm (about 450K) extended
layer of CO2, somewhere between the photosphere and the dust formation zone.
The gas in this layer is cooler than the 1000K CO2 gas responsible for the
low-resolution absorption bands at 4.25 and 15 micron. The rotational and
vibrational excitation temperatures derived from the individual Q-branch lines
of CO2 are different (450K and 150K, respectively) so that the CO2 level
population is not in LTE.Comment: To appear in Astronomy and Astrophysics A reference is adde
Land Settlement Alternatives for the Chugach Region: Effects on Public Values of Transferring Public Lands to Private Ownership. Volume I
Prepared for U.S. Forest Service Department of Agricultur
Narrow genetic base in forest restoration with holm oak (Quercus ilex L.) in Sicily
In order to empirically assess the effect of actual seed sampling strategy on
genetic diversity of holm oak (Quercus ilex) forestations in Sicily, we have
analysed the genetic composition of two seedling lots (nursery stock and
plantation) and their known natural seed origin stand by means of six nuclear
microsatellite loci. Significant reduction in genetic diversity and significant
difference in genetic composition of the seedling lots compared to the seed
origin stand were detected. The female and the total effective number of
parents were quantified by means of maternity assignment of seedlings and
temporal changes in allele frequencies. Extremely low effective maternity
numbers were estimated (Nfe 2-4) and estimates accounting for both
seed and pollen donors gave also low values (Ne 35-50). These values
can be explained by an inappropriate forestry seed harvest strategy limited to
a small number of spatially close trees
- …