535 research outputs found
Dynacore Final Report , Plasma Physics prototype
The generation and behaviour of plasma in a fusion device and its interaction with sur-rounding materials is studied by observing several phenomena that will accompany a plasma discharge. These phenomena are recorded by means of so called Diagnostics. These are instruments that comprise complex electronic equipment, coupled to various sensors. The generation of the plasma is also governed by electronic systems that control different parameters of the fusion device, the Tokamak, and of auxiliary equipment
On the Cause of the Mid‐Pleistocene Transition
The Mid-Pleistocene Transition (MPT), where the Pleistocene glacial cycles changed from 41 to ∼100 kyr periodicity, is one of the most intriguing unsolved issues in the field of paleoclimatology. Over the course of over four decades of research, several different physical mechanisms have been proposed to explain the MPT, involving non-linear feedbacks between ice sheets and the global climate, the solid Earth, ocean circulation, and the carbon cycle. Here, we review these different mechanisms, comparing how each of them relates to the others, and to the currently available observational evidence. Based on this discussion, we identify the most important gaps in our current understanding of the MPT. We discuss how new model experiments, which focus on the quantitative differences between the different physical mechanisms, could help fill these gaps. The results of those experiments could help interpret available proxy evidence, as well as new evidence that is expected to become available
On the Cause of the Mid-Pleistocene Transition
The Mid-Pleistocene Transition (MPT), where the Pleistocene glacial cycles changed from 41 to ∼100 kyr periodicity, is one of the most intriguing unsolved issues in the field of paleoclimatology. Over the course of over four decades of research, several different physical mechanisms have been proposed to explain the MPT, involving non-linear feedbacks between ice sheets and the global climate, the solid Earth, ocean circulation, and the carbon cycle. Here, we review these different mechanisms, comparing how each of them relates to the others, and to the currently available observational evidence. Based on this discussion, we identify the most important gaps in our current understanding of the MPT. We discuss how new model experiments, which focus on the quantitative differences between the different physical mechanisms, could help fill these gaps. The results of those experiments could help interpret available proxy evidence, as well as new evidence that is expected to become available
Genetic diversity of Kenyan Prosopis populations based on random amplified polymorphic DNA markers
Several Prosopis species and provenances were introduced in Kenya, either as a single event or repeatedly. To date, naturally established Prosopis populations are described as pure species depending on site, despite the aforementioned introduction of several species within some sites. To determine whether naturally established stands consist of a single or mixture of species, six populations from Bamburi, Bura, Isiolo, Marigat, Taveta and Turkwel were compared for relatedness with reference to Prosopis chilensis, Prosopis juliflora and Prosopis pallida using random amplified polymorphic DNA markers. Cluster analysis based on Nei’s genetic distance clustered Kenyan populations as follows: Marigat, Bura and Isiolo with P. juliflora, Bamburi with P. pallida and Taveta with P. chilensis, whereas the Turkwel population is likely to be a hybrid between P. chileneis and P. juliflora. Four populations had private markers, revealing germplasm uniqueness. Expected heterozygosity tended to be larger for Kenyan populations (ranging from 0.091 to 0.191) than in the three reference (ranging from 0.065 to 0.144). For the six Kenyan populations and two P. juliflora provenances from the Middle East, molecular variation was larger within populations than between population. Higher molecular variance among populations is attributed to their geographical separation and the low variation within populations is due to gene flow between individuals within a population. Overall, this study shows that (1) the Kenyan Prosopis populations are genetically isolated, (2) multiple introductions enhanced genetic diversity within sites and (3) P. juliflora and its hybrid are the most aggressive invaders.Key words: Prosopis chilensis, Prosopis juliflora, Prosopis pallida, multiple introductions, genetic diversity
Direct comparisons of astronomical and Ar-40/Ar-39 ages of ash beds - potential implications for the age of mineral dating standards
Extending the geographical distribution of Side-striped Jackal, Lupulella adusta (Sundevall, 1847) (Carnivora, Canidae), in South Africa
Side-striped Jackal, Lupulella adusta (Sundevall, 1847), occurs in a vast area within sub-Saharan Africa. In South Africa, the current geographical distribution is limited to eastern coastal regions. Recent sightings from north-central areas of the country suggest a wider geographical distribution. Here we report on 5,130 confirmed, repeated detections of Side-striped Jackal. Of these, 3,625 captures were from 471 new locations not previously recorded in the scientific literature, thereby expanding their current geographical distribution. These new records were captured in 33 vegetation types, including the forest and grassland biomes where they are not commonly detected
Comet C/2011 W3 (Lovejoy): Orbit Determination, Outbursts, Disintegration of Nucleus, Dust-Tail Morphology, and Relationship to New Cluster of Bright Sungrazers
We describe the physical and orbital properties of C/2011 W3. After surviving
perihelion, the comet underwent major changes (permanent loss of nuclear
condensation, formation of spine tail). The process of disintegration
culminated with an outburst on December 17.6 (T+1.6 d) and this delayed
response is inconsistent with the rubble pile model. Probable cause was thermal
stress from the heat pulse into the nucleus after perihelion, which could also
produce fragmentation of sungrazers far from the Sun. The spine tail was a
synchronic feature, made up of dust released at <30 m/s. Since the nucleus
would have been located on the synchrone, we computed the astrometric positions
of the missing nucleus as the coordinates of the points of intersection of the
spine tail's axis with lines of forced orbital-period variation, derived from
orbital solutions based on preperihelion astrometry from the ground. The
resulting osculating orbital period was 698+/-2 years, which proves that C/2011
W3 is the first major member of the predicted new, 21st-century cluster of
bright Kreutz-system sungrazers. The spine tail's tip contained dust 1-2 mm in
diameter. The bizarre appearance of the dust tail in images taken hours after
perihelion with coronagraphs on SOHO and STEREO is readily understood. The
disconnection of the comet's head from the preperihelion tail and the apparent
activity attenuation near perihelion are both caused by sublimation of all dust
at heliocentric distances smaller than ~1.8 solar radii. The tail's brightness
is strongly affected by forward scattering of sunlight by dust. The
longest-imaged grains had a radiation-pressure parameter beta ~ 0.6, probably
submicron-sized silicate grains. The place of C/2011 W3 within the hierarchy of
the Kreutz system and its genealogy via a 14th century parent suggest that it
is indirectly related to the celebrated sungrazer X/1106 C1.Comment: Submitted to Astrophysical Journal; 35 pages, 18 figures, 8 table
Equine encephalosis in Thoroughbred foals on a South African stud farm
Thoroughbred foal body temperature data were collected from shortly after birth until shortly
after weaning during the 2007/2008 season on a stud farm in the Western Cape Province of
South Africa. Equine encephalosis (EE) caused by EE virus (EEV) serotype 4 (EEV-4) occurred
in the foal group during the first autumn after their birth (March and April 2008). A descriptive
study was undertaken to provide data on the EEV maternal antibody status, the association
between pyrexia and EEV infection, and the incidence of infection amongst the foals prior to
and during the episode. This included the frequent capturing of foal body temperature data
and regular collection of serum and whole blood during pyretic episodes. Infection by EEV
was determined using both virological and serological methods. A high EE incidence of at least
94% occurred amongst the foal cohort, despite the fact that 37% of foals had previously shown
maternal antibody to EEV-4. Pyrexia in foals was not directly associated with EE infection
and 41% of infected foals showed no detectable pyretic episode. Information obtained from
this EE episode showed the high incidence of EEV infection in foals during the first autumn
after their birth. Monitoring foal body temperature can alert farmers to outbreaks of infectious
disease, such as EE. These results are relevant to the epidemiology of EE and facilitate greater
understanding of it as a differential diagnosis of African horse sickness (AHS), given that EE
and AHS have similar epidemiologic profiles.The Equine Research Centre, Faculty of Veterinary Science,
University of Pretoria, South Africa.http://www.ojvr.orgam201
Challenges in Patient Enrollment and Retention in Clinical Studies for Alcoholic Hepatitis: Experience of the TREAT Consortium
The TREAT Consortium has carried out clinical studies on alcoholic hepatitis (AH) for over 4 years. We encountered problems with participant recruitment, retention, and eligibility for specific protocols. To improve our ability to carry out such trials, we reviewed recruitment screening logs, end of study logs, and surveyed study coordinators to learn the reasons for missing patients, why patients declined enrollment, and the number of patients eligible for treatment trials. Associations of the recruited subjects’ demographics with their adherence to follow-up appointments were examined. Three hundred eight-seven patients (AH and heavy drinking controls) were enrolled in the observational study, and 55 AH patients were recruited into treatment trials. About half of patients identified with AH could not be recruited; no specific reason could be determined for about two-thirds of these. Among the patients who gave a reason for not participating, the most common reasons were feeling too sick to participate, desire to concentrate on abstinence, and lack of interest in research. Approximately a quarter of the AH patients met eligibility criteria for treatment trials for moderate or severe AH and we were able to recruit half to two-thirds of those eligible. Approximately 35% of participants in the observational study returned for both 6- and 12-month follow-up visits. We did not identify biopsychosocial or demographic correlates of retention in the study. This analysis revealed that attempts at recruitment into trials for AH miss some subjects because of structural issues surrounding their hospital admission, and encounter a high rate of patient refusal to participate. Nonetheless, more than half of the patients who met the eligibility criteria for moderate or severe AH were entered into clinical trials. Retention rates for the observational study are relatively low. These findings need to be accounted for in clinical trial design and power analysis
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