2,366 research outputs found
Constrained optimization in seismic reflection tomography: a Gauss-Newton augmented Lagrangian approach
International audienceS U M M A R Y Seismic reflection tomography is a method for determining a subsurface velocity model from the traveltimes of seismic waves reflecting on geological interfaces. From an optimization viewpoint , the problem consists in minimizing a non-linear least-squares function measuring the mismatch between observed traveltimes and those calculated by ray tracing in this model. The introduction of a priori information on the model is crucial to reduce the under-determination. The contribution of this paper is to introduce a technique able to take into account geological a priori information in the reflection tomography problem expressed as inequality constraints in the optimization problem. This technique is based on a Gauss-Newton (GN) sequential quadratic programming approach. At each GN step, a solution to a convex quadratic optimization problem subject to linear constraints is computed thanks to an augmented Lagrangian algorithm. Our choice for this optimization method is motivated and its original aspects are described. First applications on real data sets are presented to illustrate the potential of the approach in practical use of reflection tomography
The factor structure of the Forms of Self-Criticising/Attacking & Self-Reassuring Scale in thirteen distinct populations
There is considerable evidence that self-criticism plays a major role in the vulnerability to and recovery from psychopathology. Methods to measure this process, and its change over time, are therefore important for research in psychopathology and well-being. This study examined the factor structure of a widely used measure, the Forms of Self-Criticising/Attacking & Self-Reassuring Scale in thirteen nonclinical samples (N = 7510) from twelve different countries: Australia (N = 319), Canada (N = 383), Switzerland (N = 230), Israel (N = 476), Italy (N = 389), Japan (N = 264), the Netherlands (N = 360), Portugal (N = 764), Slovakia (N = 1326), Taiwan (N = 417), the United Kingdom 1 (N = 1570), the United Kingdom 2 (N = 883), and USA (N = 331). This study used more advanced analyses than prior reports: a bifactor item-response theory model, a two-tier item-response theory model, and a non-parametric item-response theory (Mokken) scale analysis. Although the original three-factor solution for the FSCRS (distinguishing between Inadequate-Self, Hated-Self, and Reassured-Self) had an acceptable fit, two-tier models, with two general factors (Self-criticism and Self-reassurance) demonstrated the best fit across all samples. This study provides preliminary evidence suggesting that this two-factor structure can be used in a range of nonclinical contexts across countries and cultures. Inadequate-Self and Hated-Self might not by distinct factors in nonclinical samples. Future work may benefit from distinguishing between self-correction versus shame-based self-criticism.Peer reviewe
A multibaker map for shear flow and viscous heating
A consistent description of shear flow and the accompanied viscous heating as
well the associated entropy balance is given in the framework of a
deterministic dynamical system. A laminar shear flow is modeled by a
Hamiltonian multibaker map which drives velocity and temperature fields. In an
appropriate macroscopic limit one recovers the Navier-Stokes and heat
conduction equations along with the associated entropy balance. This indicates
that results of nonequilibrium thermodynamics can be described by means of an
abstract, sufficiently chaotic and mixing dynamics. A thermostating algorithm
can also be incorporated into this framework.Comment: 11 pages; RevTex with multicol+graphicx packages; eps-figure
Cost-Effectiveness of Pediatric Central Venous Catheters in the UK: A Secondary Publication from the CATCH Clinical Trial
Background: Antibiotic-impregnated central venous catheters (CVCs) reduce the risk of
bloodstream infections (BSIs) in patients treated in pediatric intensive care units (PICUs).
However, it is unclear if they are cost-effective from the perspective of the National Health
Service (NHS) in the UK.
Methods: Economic evaluation alongside the CATCH trial (ISRCTN34884569) to
estimate the incremental cost effectiveness ratio (ICER) of antibiotic-impregnated
(rifampicin and minocycline), heparin-bonded and standard polyurethane CVCs. The
6-month costs of CVCs and hospital admissions and visits were determined from
administrative hospital data and case report forms.
Results: BSIs were detected in 3.59% (18/502) of patients randomized to standard,
1.44% (7/486) to antibiotic and 3.42% (17/497) to heparin CVCs. Lengths of hospital stay
did not differ between intervention groups. Total mean costs (95% confidence interval)
were: £45,663 (£41,647–£50,009) for antibiotic, £42,065 (£38,322–£46,110) for heparin,
and £44,503 (£40,619–£48,666) for standard CVCs. As heparin CVCs were not clinically
effective at reducing BSI rate compared to standard CVCs, they were considered not to
be cost-effective. The ICER for antibiotic vs. standard CVCs, of £54,057 per BSI avoided,
was sensitive to the analytical time horizon.
Conclusions: Substituting standard CVCs for antibiotic CVCs in PICUs will result in
reduced occurrence of BSI but there is uncertainty as to whether this would be a
cost-effective strategy for the NH
Systems developmental biology: the use of ontologies in annotating models and in identifying gene function within and across species
Systems developmental biology is an approach to the study of embryogenesis that attempts to analyze complex developmental processes through integrating the roles of their molecular, cellular, and tissue participants within a computational framework. This article discusses ways of annotating these participants using standard terms and IDs now available in public ontologies (these are areas of hierarchical knowledge formalized to be computationally accessible) for tissues, cells, and processes. Such annotations bring two types of benefit. The first comes from using standard terms: This allows linkage to other resources that use them (e.g., GXD, the gene-expression [G-E] database for mouse development). The second comes from the annotation procedure itself: This can lead to the identification of common processes that are used in very different and apparently unrelated events, even in other organisms. One implication of this is the potential for identifying the genes underpinning common developmental processes in different tissues through Boolean analysis of their G-E profiles. While it is easiest to do this for single organisms, the approach is extendable to analyzing similar processes in different organisms. Although the full computational infrastructure for such an analysis has yet to be put in place, two examples are briefly considered as illustration. First, the early development of the mouse urogenital system shows how a line of development can be graphically formalized using ontologies. Second, Boolean analysis of the G-E profiles of the mesenchyme-to-epithelium transitions that take place during mouse development suggest Lhx1, Foxc1, and Meox1 as candidate transcription factors for mediating this process
Constraints on a second planet in the WASP-3 system
There have been previous hints that the transiting planet WASP-3 b is
accompanied by a second planet in a nearby orbit, based on small deviations
from strict periodicity of the observed transits. Here we present 17 precise
radial velocity measurements and 32 transit light curves that were acquired
between 2009 and 2011. These data were used to refine the parameters of the
host star and transiting planet. This has resulted in reduced uncertainties for
the radii and masses of the star and planet. The radial-velocity data and the
transit times show no evidence for an additional planet in the system.
Therefore, we have determined the upper limit on the mass of any hypothetical
second planet, as a function of its orbital period.Comment: Accepted for publication in The Astronomical Journa
Fully compressive tides in galaxy mergers
The disruptive effect of galactic tides is a textbook example of
gravitational dynamics. However, depending on the shape of the potential, tides
can also become fully compressive. When that is the case, they might trigger or
strengthen the formation of galactic substructures (star clusters, tidal dwarf
galaxies), instead of destroying them. We perform N-body simulations of
interacting galaxies to quantify this effect. We demonstrate that tidal
compression occurs repeatedly during a galaxy merger, independently of the
specific choice of parameterization. With a model tailored to the Antennae
galaxies, we show that the distribution of compressive tides matches the
locations and timescales of observed substructures. After extending our study
to a broad range of parameters, we conclude that neither the importance of the
compressive tides (~15% of the stellar mass) nor their duration (~ 10 Myr) are
strongly affected by changes in the progenitors' configurations and orbits.
Moreover, we show that individual clumps of matter can enter compressive
regions several times in the course of a simulation. We speculate that this may
spawn multiple star formation episodes in some star clusters, through e.g.,
enhanced gas retention.Comment: 17 pages, 16 figures, accepted for publication in Ap
Lactadherin blocks thrombosis and hemostasis in vivo : correlation with platelet phosphatidylserine exposure
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73556/1/j.1538-7836.2008.03010.x.pd
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