1,002 research outputs found
Measuring working memory load effects on electrophysiological markers of attention orienting during a simulated drive
Intersection accidents result in a significant proportion of road fatalities, and attention allocation likely plays a role. Attention allocation may depend on (limited) working memory (WM) capacity. Driving is often combined with tasks increasing WM load, consequently impairing attention orienting. This study (n = 22) investigated WM load effects on event-related potentials (ERPs) related to attention orienting. A simulated driving environment allowed continuous lane-keeping measurement. Participants were asked to orient attention covertly towards the side indicated by an arrow, and to respond only to moving cars appearing on the attended side by pressing a button. WM load was manipulated using a concurrent memory task. ERPs showed typical attentional modulation (cue: contralateral negativity, LDAP; car: N1, P1, SN and P3) under low and high load conditions. With increased WM load, lane-keeping performance improved, while dual task performance degraded (memory task: increased error rate; orienting task: increased false alarms, smaller P3).
Practitioner Summary: Intersection driver-support systems aim to improve traffic safety and flow. However, in-vehicle systems induce WM load, increasing the tendency to yield. Traffic flow reduces if drivers stop at inappropriate times, reducing the effectiveness of systems. Consequently, driver-support systems could include WM load measurement during driving in the development phase
Organochlorines in common dolphins caught in shark nets during the Natal ‘sardine run’
The concentrations of organochlorines were determined in blubber and liver samples from common dolphins inhabiting the coastal waters of the south-east coast of southern Africa. Liver levels of PCBs and DDTs are far lower and do not appear directly associated with those in blubber. In males, blubber residue concentrations increased with age but in females a marked rapid decline in concentrations of PCBs and t-DDT was evident between the eighth and eleventh growth layer groups, approximately the age of sexual maturity and subsequent to their first or second ovulation. Lower levels in females are explained through transfer to the new-born calf during lactation and the consequences of this for the newborn calf are discussed
X-ray Reflection By Photoionized Accretion Discs
We present the results of reflection calculations that treat the relevant
physics with a minimum of assumptions. The temperature and ionization structure
of the top five Thomson depths of an illuminated disc are calculated while also
demanding that the atmosphere is in hydrostatic equilibrium. In agreement with
Nayakshin, Kazanas & Kallman, we find that there is a rapid transition from hot
to cold material in the illuminated layer. However, the transition is usually
not sharp so that often we find a small but finite region in Thomson depth
where there is a stable temperature zone at T \sim 2 x 10^{6} K due to
photoelectric heating from recombining ions. As a result, the reflection
spectra often exhibit strong features from partially-ionized material,
including helium-like Fe K lines and edges. We find that due to the highly
ionized features in the spectra these models have difficulty correctly
parameterizing the new reflection spectra. There is evidence for a spurious
correlation in the ASCA energy range, where is the reflection
fraction for a power-law continuum of index , confirming the suggestion
of Done & Nayakshin that at least part of the R-Gamma correlation reported by
Zdziarski, Lubinski & Smith for Seyfert galaxies and X-ray binaries might be
due to ionization effects. Although many of the reflection spectra show strong
ionized features, these are not typically observed in most Seyfert and quasar
X-ray spectra.Comment: 16 pages, accepted by MNRAS, Fig. 8 is in colour Figures and tables
changed by a code update. Conclusions unchange
Atomic X-ray Spectroscopy of Accreting Black Holes
Current astrophysical research suggests that the most persistently luminous
objects in the Universe are powered by the flow of matter through accretion
disks onto black holes. Accretion disk systems are observed to emit copious
radiation across the electromagnetic spectrum, each energy band providing
access to rather distinct regimes of physical conditions and geometric scale.
X-ray emission probes the innermost regions of the accretion disk, where
relativistic effects prevail. While this has been known for decades, it also
has been acknowledged that inferring physical conditions in the relativistic
regime from the behavior of the X-ray continuum is problematic and not
satisfactorily constraining. With the discovery in the 1990s of iron X-ray
lines bearing signatures of relativistic distortion came the hope that such
emission would more firmly constrain models of disk accretion near black holes,
as well as provide observational criteria by which to test general relativity
in the strong field limit. Here we provide an introduction to this phenomenon.
While the presentation is intended to be primarily tutorial in nature, we aim
also to acquaint the reader with trends in current research. To achieve these
ends, we present the basic applications of general relativity that pertain to
X-ray spectroscopic observations of black hole accretion disk systems, focusing
on the Schwarzschild and Kerr solutions to the Einstein field equations. To
this we add treatments of the fundamental concepts associated with the
theoretical and modeling aspects of accretion disks, as well as relevant topics
from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian
Journal of Physics, in pres
Trends in sexually transmitted infections in general practice 1990-2000: population based study using data from the UK general practice research database
Objective: To describe the contribution of primary care to the
diagnosis and management of sexually transmitted infections in
the United Kingdom, 1990-2000, in the context of increasing
incidence of infections in genitourinary medicine clinics.
Design: Population based study.
Setting: UK primary care.
Participants: Patients registered in the UK general practice
research database.
Main outcome measures: Incidence of diagnosed sexually
transmitted infections in primary care and estimation of the
proportion of major such infections diagnosed in primary care.
Results: An estimated 23.0% of chlamydia cases in women but
only 5.3% in men were diagnosed and treated in primary care
during 1998-2000, along with 49.2% cases of non-specific
urethritis and urethral discharge in men and 5.7% cases of
gonorrhoea in women and 2.9% in men. Rates of diagnosis in
primary care rose substantially in the late 1990s.
Conclusions: A substantial and increasing number of sexually
transmitted infections are diagnosed and treated in primary
care in the United Kingdom, with sex ratios differing from
those in genitourinary medicine clinics. Large numbers of men
are treated in primary care for presumptive sexually
transmitted infections
Two-year impact of praziquantel treatment for Schistosoma japonicum infection in China: re-infection, subclinical disease and fibrosis marker measurements
We studied a community cohort of 193 individuals exposed to endemic Schistosoma japonicum infection in the Dongting Lake region of China to assess subclinical morbidity and the 2-year benefit of curative therapy (praziquantel) administered in 1996. Prevalence and intensity of S. japonicum infection before treatment were 28% and 192 eggs per gram faeces (epg), respectively. Two years after cure, 22% of the cohort were reinfected, but with a lighter intensity (67 epg). Sixty-four subjects (37%) showed significant improvement in ultrasound parenchyma images after treatment and 51 subjects (54%) showed significant improvement of periportal fibrosis. Left-lobe enlargement also reversed (P 0·05). The serum levels of laminin and collagen IV associated with reinfection and intensity and hyaluronic acid levels correlated with ultrasound findings (P < 0·01). Overall, treatment induced a marked decrease in subclinical hepatosplenic morbidity attributable to S. japonicum although low-intensity re-infection after treatment remained relatively frequent. Stratified analysis and logistic models evaluated potential confounding factors for assessment of treatment effects on hepatic fibrosis. S. japonicum infection and moderate-heavy alcohol intake interacted: improvement in parenchymal morbidity was impeded among drinkers (P < 0·05). Chemotherapy focused on at-risk residents controls prevalent subclinical hepatic fibrosis but re-infection indicates the need for complementary control strategie
Tracking rates of ecotone migration due to salt-water encroachment using fossil mollusks in coastal South Florida
We determined the rate of migration of coastal vegetation zones in response to salt-water encroachment through paleoecological analysis of mollusks in 36 sediment cores taken along transects perpendicular to the coast in a 5.5 km2 band of coastal wetlands in southeast Florida. Five vegetation zones, separated by distinct ecotones, included freshwater swamp forest, freshwater marsh, and dwarf, transitional and fringing mangrove forest. Vegetation composition, soil depth and organic matter content, porewater salinity and the contemporary mollusk community were determined at 226 sites to establish the salinity preferences of the mollusk fauna. Calibration models allowed accurate inference of salinity and vegetation type from fossil mollusk assemblages in chronologically calibrated sediments. Most sediments were shallow (20–130 cm) permitting coarse-scale temporal inferences for three zones: an upper peat layer (zone 1) representing the last 30–70 years, a mixed peat-marl layer (zone 2) representing the previous ca. 150–250 years and a basal section (zone 3) of ranging from 310 to 2990 YBP. Modern peat accretion rates averaged 3.1 mm yr)1 while subsurface marl accreted more slowly at 0.8 mm yr)1. Salinity and vegetation type for zone 1 show a steep gradient with freshwater communities being confined west of a north–south drainage canal constructed in 1960. Inferences for zone 2 (pre-drainage) suggest that freshwater marshes and associated forest units covered 90% of the area, with mangrove forests only present along the peripheral coastline. During the entire pre-drainage history, salinity in the entire area was maintained below a mean of 2 ppt and only small pockets of mangroves were present; currently, salinity averages 13.2 ppt and mangroves occupy 95% of the wetland. Over 3 km2 of freshwater wetland vegetation type have been lost from this basin due to salt-water encroachment, estimated from the mollusk-inferred migration rate of freshwater vegetation of 3.1 m yr)1 for the last 70 years (compared to 0.14 m yr)1 for the pre-drainage period). This rapid rate of encroachment is driven by sea-level rise and freshwater diversion. Plans for rehydrating these basins with freshwater will require high-magnitude re-diversion to counteract locally high rates of sea-level rise
A ray of sunshine in the COVID-19 environment, with a virtual sunburst elective
Traditionally there has always been a one-month elective opportunity for
third-year medical students at the Univesity of Pretoria, South Africa. In
pre-pandemic years, students have used this elective to explore a future
area of specialisation and/or gain practical experience at a self-selected
suitable health facility or placement. The completion mark for the elective
was based on the submission of a student-generated reflective report about
their experience. This practice was, however, severely challenged in the
prevailing COVID‑19 pandemic with movement restrictions and concerns
about transmission. Therefore, a decision was made and supported by the
Deanery to explore the possibility of a virtual self-paced online elective
for 300 medical students. Of note here is that not only were these students
adjusting to lecture-led online-synchronised classes, but they also had never
before been exposed to online learning in the form of massive open online
courses (MOOCs) as part of their formal qualification.http://www.ajhpe.org.zaSchool of Health Systems and Public Health (SHSPH
Measuring Black Hole Spin using X-ray Reflection Spectroscopy
I review the current status of X-ray reflection (a.k.a. broad iron line)
based black hole spin measurements. This is a powerful technique that allows us
to measure robust black hole spins across the mass range, from the stellar-mass
black holes in X-ray binaries to the supermassive black holes in active
galactic nuclei. After describing the basic assumptions of this approach, I lay
out the detailed methodology focusing on "best practices" that have been found
necessary to obtain robust results. Reflecting my own biases, this review is
slanted towards a discussion of supermassive black hole (SMBH) spin in active
galactic nuclei (AGN). Pulling together all of the available XMM-Newton and
Suzaku results from the literature that satisfy objective quality control
criteria, it is clear that a large fraction of SMBHs are rapidly-spinning,
although there are tentative hints of a more slowly spinning population at high
(M>5*10^7Msun) and low (M<2*10^6Msun) mass. I also engage in a brief review of
the spins of stellar-mass black holes in X-ray binaries. In general,
reflection-based and continuum-fitting based spin measures are in agreement,
although there remain two objects (GROJ1655-40 and 4U1543-475) for which that
is not true. I end this review by discussing the exciting frontier of
relativistic reverberation, particularly the discovery of broad iron line
reverberation in XMM-Newton data for the Seyfert galaxies NGC4151, NGC7314 and
MCG-5-23-16. As well as confirming the basic paradigm of relativistic disk
reflection, this detection of reverberation demonstrates that future large-area
X-ray observatories such as LOFT will make tremendous progress in studies of
strong gravity using relativistic reverberation in AGN.Comment: 19 pages. To appear in proceedings of the ISSI-Bern workshop on "The
Physics of Accretion onto Black Holes" (8-12 Oct 2012). Revised version adds
a missing source to Table 1 and Fig.6 (IRAS13224-3809) and corrects the
referencing of the discovery of soft lags in 1H0707-495 (which were in fact
first reported in Fabian et al. 2009
Isoperimetric problems of the calculus of variations with fractional derivatives
In this paper we study isoperimetric problems of the calculus of variations
with left and right Riemann-Liouville fractional derivatives. Both situations
when the lower bound of the variational integrals coincide and do not coincide
with the lower bound of the fractional derivatives are considered.Comment: Submitted 02-Oct-2009; revised 30-Jun-2010; accepted 10-May-2011; for
publication in the journal Acta Mathematica Scienti
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