192 research outputs found
A sub-determinant approach for pseudo-orbit expansions of spectral determinants in quantum maps and quantum graphs
We study implications of unitarity for pseudo-orbit expansions of the
spectral determinants of quantum maps and quantum graphs. In particular, we
advocate to group pseudo-orbits into sub-determinants. We show explicitly that
the cancellation of long orbits is elegantly described on this level and that
unitarity can be built in using a simple sub-determinant identity which has a
non-trivial interpretation in terms of pseudo-orbits. This identity yields much
more detailed relations between pseudo orbits of different length than known
previously. We reformulate Newton identities and the spectral density in terms
of sub-determinant expansions and point out the implications of the
sub-determinant identity for these expressions. We analyse furthermore the
effect of the identity on spectral correlation functions such as the
auto-correlation and parametric cross correlation functions of the spectral
determinant and the spectral form factor.Comment: 25 pages, one figur
Relationship between the entomologic inoculation rate and the force of infection for Plasmodium falciparum malaria.
We propose a stochastic model for the relationship between the entomologic inoculation rate (EIR) for Plasmodium falciparum malaria and the force of infection in endemic areas. The model incorporates effects of increased exposure to mosquito bites as a result of the growth in body surface area with the age of the host, naturally acquired pre-erythrocytic immunity, and the reduction in the proportion of entomologically assessed inoculations leading to infection, as the EIR increases. It is fitted to multiple datasets from field studies of the relationship between malaria infection and the EIR. We propose that this model can account for non-monotonic relationships between the age of the host and the parasite prevalence and incidence of disease. It provides a parsimonious explanation for the faster acquisition of natural immunity in adults than in children exposed to high EIRs. This forms one component of a new stochastic model for the entire transmission cycle of P. falciparum that we have derived to estimate the potential epidemiologic impact of malaria vaccines and other malaria control interventions
Application of Photogrammetry in Geology: 3D Investigation of Rock Fracture Distributions
Geology as a science has an important
visual component and the knowledge of
any geologist is deeply linked to visual
experience of rock outcrops, thin sections
and analytical images. One of the
shortcomings of most geological images
such as maps, cross sections and outcrop
photographs is that they are 2D, while processes geologists are interested
in are typically occurring in 3D space.
The 3D geometry of faults, fractures
and joints is crucial to quantify geological
processes related to fracture mechanics,
such as hydrothermal mineralization
and ground water flow, but also geotechnical
problems such as rock mass stability.
A number of studies have shown
that some geological structures can be
described with a scale invariant, fractal
distribution. So far these observations
on which these findings are based were
restricted to one and two dimensions
and has been difficult to obtain a full
spatial geometric picture of fracture sets
from rock outcrops, because much of the
rock is not directly accessible. However,
without taking into account the spatial
distribution of geological structures the
true geometry of joint patterns cannot
be fully described and scaling laws, fractal
or not, cannot be derived.
We present images of joint patterns
based on datasets acquired by digital
photographs which are processed
to three dimensional images using the
photogrammetry software Siro3D. This
technique allows to obtain a highly accurate
3D picture of the visible outcrop.
The spatial pattern of joints in
nature is investigated using the software
SiroJoint. For the analysis of joint
systems a large data set was collected
from the Heavitree Quarzite at Ormiston
Gorge, near Alice Springs. The
Heavitree Quartzite is fragmented by a
spectacularly regular three-dimensional
joint pattern, which is repeated at different
scales and therefore represents a
perfect laboratory for our investigations
(Hobbs 1993). Siro3D generates a spatially
fully referenced 3D image from
overlapping digital images, such that
each pixel of the image is assigned spatial
coordinates. The software SiroJoint
routinely constructs planes from the intersection
of the rock-face with the linear
trace of planar features (Poropat
2001). It provides stereographic plots
of structural elements and additionally
measures joint persistence, area, and
joint spacing. Our measurements allow
to analyse geometrical scaling relationships
of joint sets with high accuracy
and will help explore the character of
their 3D complexity.
Several hundred joint planes were defined
with SiroJoint in an Ormiston
Gorge outcrop. Three different joint
sets can be distinguished. Joint set one
and two are characterized by steeply inclined
planes with joint spacings ranging
between 2 cm to 40 cm and 2 cm to
10m respectively. Both joints sets depict
a power law distribution in joint
spacing/frequency plots. The third set
is defined by a subhorizontal orientation.
It shows a very regular spacing in
the meter scale and lacks an exponential
distribution. We intend to use the
results as a basis to compare observed
fracture pattern with those generated
by computational methods like Iterated
Function Systems. This might help to
understand how physical rock properties
influence the spatial complexity of
fracture systems and develop constitutive
scaling relationships for certain rock
types.conferenc
So rare we need to hunt for them: reframing the ethical debate on incidental findings
Incidental findings are the subject of intense ethical debate in medical genomic research. Every human genome contains a number of potentially disease-causing alterations that may be detected during comprehensive genetic analyses to investigate a specific condition. Yet available evidence shows that the frequency of incidental findings in research is much lower than expected. In this Opinion, we argue that the reason for the low level of incidental findings is that the filtering techniques and methods that are applied during the routine handling of genomic data remove these alterations. As incidental findings are systematically filtered out, it is now time to evaluate whether the ethical debate is focused on the right issues. We conclude that the key question is whether to deliberately target and search for disease-causing variations outside the indication that has originally led to the genetic analysis, for instance by using positive lists and algorithms
Leading off-diagonal contribution to the spectral form factor of chaotic quantum systems
We semiclassically derive the leading off-diagonal correction to the spectral
form factor of quantum systems with a chaotic classical counterpart. To this
end we present a phase space generalization of a recent approach for uniformly
hyperbolic systems (M. Sieber and K. Richter, Phys. Scr. T90, 128 (2001); M.
Sieber, J. Phys. A: Math. Gen. 35, L613 (2002)). Our results coincide with
corresponding random matrix predictions. Furthermore, we study the transition
from the Gaussian orthogonal to the Gaussian unitary ensemble.Comment: 8 pages, 2 figures; J. Phys. A: Math. Gen. (accepted for publication
PI3K/p110α inhibition selectively interferes with arterial thrombosis and neointima formation, but not re-endothelialization: potential implications for drug-eluting stent design
Background Impaired re-endothelialization and stent thrombosis are a safety concern associated with drug-eluting stents (DES). PI3K/p110α controls cellular wound healing pathways, thereby representing an emerging drug target to modulate vascular homoeostasis after injury. Methods and results PI3K/p110α was inhibited by treatment with the small molecule inhibitor PIK75 or a specific siRNA. Arterial thrombosis, neointima formation, and re-endothelialization were studied in a murine carotid artery injury model. Proliferation and migration of human vascular smooth muscle cell (VSMC) and endothelial cell (EC) were assessed by cell number and Boyden chamber, respectively. Endothelial senescence was evaluated by the ÎČ-galactosidase assay, endothelial dysfunction by organ chambers for isometric tension. Arterial thrombus formation was delayed in mice treated with PIK75 when compared with controls. PIK75 impaired arterial expression and activity of tissue factor (TF) and plasminogen activator inhibitor-1 (PAI-1); in contrast, plasma clotting and platelet aggregation did not differ. In VSMC and EC, PIK75 inhibited expression and activity of TF and PAI-1. These effects occurred at the transcriptional level via the RhoA signalling cascade and the transcription factor NFkB. Furthermore, inhibition of PI3K/p110α with PIK75 or a specific siRNA selectively impaired proliferation and migration of VSMC while sparing EC completely. Treatment with PIK75 did not induce endothelial senescence nor inhibit endothelium-dependent relaxations. In line with this observation, treatment with PIK75 selectively inhibited neointima formation without affecting re-endothelialization following vascular injury. Conclusion Following vascular injury, PI3K/p110α inhibition selectively interferes with arterial thrombosis and neointima formation, but not re-endothelialization. Hence, PI3K/p110α represents an attractive new target in DES desig
Diagnostic Methods for and Clinical Pictures of Polyomavirus Primary Infections in Children, Finland
Peer reviewe
Association of Human Bocavirus 1 Infection with Respiratory Disease in Childhood Follow-up Study, Finland
Since its discovery in 2005, human bocavirus type 1 has often been found in the upper airways of young children with respiratory disease. But is this virus the cause of the respiratory disease or just an innocent bystander? A unique study in Finland, which examined follow-up blood samples of 109 healthy children with no underlying illness starting at birth and until they were 13 years of age, found that acute bocavirus infection resulted in respiratory disease. All children had been infected by age 6. Most retained their antibodies to this virus; some lost them. Children who were later re-exposed to bocavirus did not get sick from this virus. Thus, human bocavirus type 1 is a major cause of respiratory disease in childhood
Publishing SNP Genotypes of Human Embryonic Stem Cell Lines: Policy Statement of the International Stem Cell Forum Ethics Working Party
Novel methods and associated tools permitting individual identification in publicly accessible SNP databases have become a debatable issue. There is growing concern that current technical and ethical safeguards to protect the identities of donors could be insufficient. In the context of human embryonic stem cell research, there are no studies focusing on the probability that an hESC line donor could be identified by analyzing published SNP profiles and associated genotypic and phenotypic information. We present the International Stem Cell Forum (ISCF) Ethics Working Partyâs Policy Statement on âPublishing SNP Genotypes of Human Embryonic Stem Cell Lines (hESC)â. The Statement prospectively addresses issues surrounding the publication of genotypic data and associated annotations of hESC lines in open access databases. It proposes a balanced approach between the goals of open science and data sharing with the respect for fundamental bioethical principles (autonomy, privacy, beneficence, justice and research merit and integrity)
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