2,161 research outputs found
Reconstructing Holocene geomagnetic field variation: new methods, models and implications
Reconstructions of the Holocene geomagnetic field and how it varies on millennial timescales are important for understanding processes in the core but may also be used to study long-term solar-terrestrial relationships and as relative dating tools for geological and archaeological archives. Here, we present a new family of spherical harmonic geomagnetic field models spanning the past 9000 yr based on magnetic field directions and intensity stored in archaeological artefacts, igneous rocks and sediment records. A new modelling strategy introduces alternative data treatments with a focus on extracting more information from sedimentary data. To reduce the influence of a few individual records all sedimentary data are resampled in 50-yr bins, which also means that more weight is given to archaeomagnetic data during the inversion. The sedimentary declination data are treated as relative values and adjusted iteratively based on prior information. Finally, an alternative way of treating the sediment data chronologies has enabled us to both assess the likely range of age uncertainties, often up to and possibly exceeding 500 yr and adjust the timescale of each record based on comparisons with predictions from a preliminary model. As a result of the data adjustments, power has been shifted from quadrupole and octupole to higher degrees compared with previous Holocene geomagnetic field models. We find evidence for dominantly westward drift of northern high latitude high intensity flux patches at the core mantle boundary for the last 4000 yr. The new models also show intermittent occurrence of reversed flux at the edge of or inside the inner core tangent cylinder, possibly originating from the equator
The Dutch EPS Registry:increasing the knowledge of encapsulating peritoneal sclerosis
Encapsulating peritoneal sclerosis (EPS) is a rare condition characterised by fibrotic thickening of the visceral peritoneum, leading to encapsulating of the intestines with partial or total intestinal obstruction. EPS is a serious complication of peritoneal dialysis (PD) with high morbidity and a mortality exceeding 50%. At present, there is uncertainty concerning the incidence and the risk factors involved in the development of EPS. To address these questions a nationwide registry has been initiated. The primary goals of the registry are to record the incidence of EPS and investigate the association of different variables, such as PD duration, medication, dialysis solutions and kidney transplantation with EPS. The registry will improve the knowledge of EPS and will serve to develop guidelines and necessary management strategies. From the registry different research activities can be initiated. A major challenge lies in the establishment of criteria that allow a timely diagnosis of EPS. At present, there are no diagnostic tools that can accurately detect EPS at an early stage. For this reason, besides patients with proven EPS, the clinical suspicion of EPS will be a sufficient criterion for inclusion in the registry. This nationwide EPS registry is currently enrolling patients
Analysing the effects of travel information on public transport travellerâs decision making and learning
This thesis examines the effect of travel information on a public transport travellerâs decision making over time. It investigates whether the effect of information is sustained over time and is affected by its type and reliability. It is postulated that the traveller will attain better decision outcomes over time, and this process is reinforced when given information. It is postulated that dynamic information would produce the best outcomes, followed by static information and no information. A series of computer-based experiments, in which the participants made hypothetical trips by public bus under various travel information and operating conditions, were conducted. At the aggregate level, the hypothesised relationships are not observed at a statistically significant level. At the disaggregate level, day-to-day decisions are shown to relate significantly to the outcome of the previous day, with the participant more likely to seek a more rewarding but riskier choice if the previous day sees no adverse outcome, and vice-versa. When the information is static, decision changes are few and incremental. When it is dynamic, these changes are more frequent and pronounced, with choices âanchoredâ around values provided by the information. Nonetheless, a significant proportion of participants made no or few changes, regardless of information or operating conditions. The findings suggest a higher propensity for some travellers to use dynamic information over static information over time, regardless of reliability. On the other hand, those who acquire information do not necessarily maximise their utility, implying that they do so for other less quantifiable factors. The benefits of information provision could also be further circumscribed by the heterogeneity of responses. This set of findings suggests that assuming travellers respond to information in a utility-maximising and homogeneous manner may over-estimate the effect of information
RNA secondary structure design
We consider the inverse-folding problem for RNA secondary structures: for a
given (pseudo-knot-free) secondary structure find a sequence that has that
structure as its ground state. If such a sequence exists, the structure is
called designable. We implemented a branch-and-bound algorithm that is able to
do an exhaustive search within the sequence space, i.e., gives an exact answer
whether such a sequence exists. The bound required by the branch-and-bound
algorithm are calculated by a dynamic programming algorithm. We consider
different alphabet sizes and an ensemble of random structures, which we want to
design. We find that for two letters almost none of these structures are
designable. The designability improves for the three-letter case, but still a
significant fraction of structures is undesignable. This changes when we look
at the natural four-letter case with two pairs of complementary bases:
undesignable structures are the exception, although they still exist. Finally,
we also study the relation between designability and the algorithmic complexity
of the branch-and-bound algorithm. Within the ensemble of structures, a high
average degree of undesignability is correlated to a long time to prove that a
given structure is (un-)designable. In the four-letter case, where the
designability is high everywhere, the algorithmic complexity is highest in the
region of naturally occurring RNA.Comment: 11 pages, 10 figure
Rituximab for the treatment of glomerulonephritis in hepatitis C associated cryoglobulinaemia
The Low Quiescent X-Ray Luminosity of the Transient X-Ray Burster EXO 1747-214
We report on X-ray and optical observations of the X-ray burster EXO
1747-214. This source is an X-ray transient, and its only known outburst was
observed in 1984-1985 by the EXOSAT satellite. We re-analyzed the EXOSAT data
to derive the source position, column density, and a distance upper limit using
its peak X-ray burst flux. We observed the EXO 1747-214 field in 2003 July with
the Chandra X-ray Observatory to search for the quiescent counterpart. We found
one possible candidate just outside the EXOSAT error circle, but we cannot rule
out the possibility that the source is unrelated to EXO 1747-214. Our
conclusion is that the upper limit on the unabsorbed 0.3-8 keV luminosity is L
< 7E31 erg/s, making EXO 1747-214 one of the faintest neutron star transients
in quiescence. We compare this luminosity upper limit to the quiescent
luminosities of 19 neutron star and 14 black hole systems and discuss the
results in the context of the differences between neutron stars and black
holes. Based on the theory of deep crustal heating by Brown and coworkers, the
luminosity implies an outburst recurrence time of >1300 yr unless some form of
enhanced cooling occurs within the neutron star. The position of the possible
X-ray counterpart is consistent with three blended optical/IR sources with
R-magnitudes between 19.4 and 19.8 and J-magnitudes between 17.2 and 17.6. One
of these sources could be the quiescent optical/IR counterpart of EXO 1747-214.Comment: 7 pages, accepted by the Astrophysical Journa
Seeing motion and apparent motion
In apparent motion experiments, participants are presented with what is in fact a succession of two brief stationary stimuli at two different locations, but they report an impression of movement. Philosophers have recently debated whether apparent motion provides evidence in favour of a particular account of the nature of temporal experience. I argue that the existing discussion in this area is premised on a mistaken view of the phenomenology of apparent motion and, as a result, the space of possible philosophical positions has not yet been fully explored. In particular, I argue that the existence of apparent motion is compatible with an account of the nature of temporal experience that involves a version of direct realism. In doing so, I also argue against two other claims often made about apparent motion, viz. that apparent motion is the psychological phenomenon that underlies motion experience in the cinema, and that apparent motion is subjectively indistinguishable from real motion
Ground-State and Domain-Wall Energies in the Spin-Glass Region of the 2D Random-Bond Ising Model
The statistics of the ground-state and domain-wall energies for the
two-dimensional random-bond Ising model on square lattices with independent,
identically distributed bonds of probability of and of
are studied. We are able to consider large samples of up to
spins by using sophisticated matching algorithms. We study
systems, but we also consider samples, for different aspect ratios
. We find that the scaling behavior of the ground-state energy and
its sample-to-sample fluctuations inside the spin-glass region () are characterized by simple scaling functions. In particular, the
fluctuations exhibit a cusp-like singularity at . Inside the spin-glass
region the average domain-wall energy converges to a finite nonzero value as
the sample size becomes infinite, holding fixed. Here, large finite-size
effects are visible, which can be explained for all by a single exponent
, provided higher-order corrections to scaling are included.
Finally, we confirm the validity of aspect-ratio scaling for : the
distribution of the domain-wall energies converges to a Gaussian for ,
although the domain walls of neighboring subsystems of size are
not independent.Comment: 11 pages with 15 figures, extensively revise
Reduction of Two-Dimensional Dilute Ising Spin Glasses
The recently proposed reduction method is applied to the Edwards-Anderson
model on bond-diluted square lattices. This allows, in combination with a
graph-theoretical matching algorithm, to calculate numerically exact ground
states of large systems. Low-temperature domain-wall excitations are studied to
determine the stiffness exponent y_2. A value of y_2=-0.281(3) is found,
consistent with previous results obtained on undiluted lattices. This
comparison demonstrates the validity of the reduction method for bond-diluted
spin systems and provides strong support for similar studies proclaiming
accurate results for stiffness exponents in dimensions d=3,...,7.Comment: 7 pages, RevTex4, 6 ps-figures included, for related information, see
http://www.physics.emory.edu/faculty/boettcher
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