2,285 research outputs found
Time-gated transillumination and reflection by biological tissues and tissuelike phantoms: simulation versus experiment
A numerical method is presented to solve exactly the time-dependent diffusion equation that describes light transport in turbid media. The simulation takes into account spatial variations of the scattering and absorption factors of the medium and the objects as well as random fluctuations of these quantities. The technique is employed to explore the possibility of locating millimeter-sized objects immersed in turbid media from time-gated measurements of the transmitted or reflected (near-infrared) light. The simulation results for tissue-like phantoms are compared with experimental transillumination data, and excellent agreement is found. Simulations of time-gated reflection experiments indicate that it may be possible to detect objects of 1-mm radius.
Dynamical Interactions and the Black Hole Merger Rate of the Universe
Binary black holes can form efficiently in dense young stellar clusters, such
as the progenitors of globular clusters, via a combination of gravitational
segregation and cluster evaporation. We use simple analytic arguments supported
by detailed N-body simulations to determine how frequently black holes born in
a single stellar cluster should form binaries, be ejected from the cluster, and
merge through the emission of gravitational radiation. We then convolve this
``transfer function'' relating cluster formation to black hole mergers with (i)
the distribution of observed cluster masses and (ii) the star formation history
of the universe, assuming that a significant fraction gcl of star formation
occurs in clusters and that a significant fraction gcand of clusters undergo
this segregation and evaporation process. We predict future ground--based
gravitational wave (GW) detectors could observe ~500 (gcl/0.5) (gcand/0.1)
double black hole mergers per year, and the presently operating LIGO
interferometer would have a chance (50%) at detecting a merger during its first
full year of science data. More realistically, advanced LIGO and similar
next-generation gravitational wave observatories provide unique opportunities
to constrain otherwise inaccessible properties of clusters formed in the early
universe.Comment: 4 pages, 2 figures. To appear in PRD Rapid Communication
Attractor Metadynamics in Adapting Neural Networks
Slow adaption processes, like synaptic and intrinsic plasticity, abound in
the brain and shape the landscape for the neural dynamics occurring on
substantially faster timescales. At any given time the network is characterized
by a set of internal parameters, which are adapting continuously, albeit
slowly. This set of parameters defines the number and the location of the
respective adiabatic attractors. The slow evolution of network parameters hence
induces an evolving attractor landscape, a process which we term attractor
metadynamics. We study the nature of the metadynamics of the attractor
landscape for several continuous-time autonomous model networks. We find both
first- and second-order changes in the location of adiabatic attractors and
argue that the study of the continuously evolving attractor landscape
constitutes a powerful tool for understanding the overall development of the
neural dynamics
Self-organization of the in vitro attached human embryo
Implantation of the blastocyst is a developmental milestone in mammalian embryonic development. At this time, a coordinated program of lineage diversification, cell-fate specification, and morphogenetic movements establishes the generation of extra-embryonic tissues and the embryo proper, and determines the conditions for successful pregnancy and gastrulation. Despite its basic and clinical importance, this process remains mysterious in humans. Here we report the use of a novel in vitro system1,2 to study the post-implantation development of the human embryo. We unveil the self-organizing abilities and autonomy of in vitro attached human embryos. We find human-specific molecular signatures of early cell lineage, timing, and architecture. Embryos display key landmarks of normal development, including epiblast expansion, lineage segregation, bi-laminar disc formation, amniotic and yolk sac cavitation, and trophoblast diversification. Our findings highlight the species-specificity of these developmental events and provide a new understanding of early human embryonic development beyond the blastocyst stage. In addition, our study establishes a new model system relevant to early human pregnancy loss. Finally, our work will also assist in the rational design of differentiation protocols of human embryonic stem cells to specific cell types for disease modelling and cell replacement therapy
Formation of black-hole X-ray binaries in globular clusters
Inspired by the recent identification of the first candidate BH-WD X-ray
binaries, where the compact accretors may be stellar-mass black hole candidates
in extragalactic globular clusters, we explore how such binaries could be
formed in a dynamical environment. We provide analyses of the formation rates
via well known formation channels like binary exchange and physical collisions
and propose that the only possibility to form BH-WD binaries is via coupling
these usual formation channels with subsequent hardening and/or triple
formation. Indeed, we find that the most important mechanism to make a BH-WD
X-ray binary from an initially dynamically formed BH-WD binary is triple
induced mass transfer via the Kozai mechanism. Even using the most optimistic
estimates for the formation rates, we cannot match the observationally inferred
production rates if black holes undergo significant evaporation from the
cluster or form a completely detached subcluster of black holes. We estimate
that at least 1% of all formed black holes, or presumably 10% of the black
holes present in the core now, must be involved in interactions with the rest
of the core stellar population.Comment: 10 pages, 2 figures, submitted to Ap
Experimental evidence for 56Ni-core breaking from the low-spin structure of the N=Z nucleus 58Cu
Low-spin states in the odd-odd N=Z nucleus 58Cu were investigated with the
58Ni(p,n gamma)58Cu fusion evaporation reaction at the FN-tandem accelerator in
Cologne. Seventeen low spin states below 3.6 MeV and 17 new transitions were
observed. Ten multipole mixing ratios and 17 gamma-branching ratios were
determined for the first time. New detailed spectroscopic information on the
2+,2 state, the Isobaric Analogue State (IAS) of the 2+,1,T=1 state of 58Ni,
makes 58Cu the heaviest odd-odd N=Z nucleus with known B(E2;2+,T=1 --> 0+,T=1)
value. The 4^+ state at 2.751 MeV, observed here for the first time, is
identified as the IAS of the 4+,1,T=1 state in 58Ni. The new data are compared
to full pf-shell model calculations with the novel GXPF1 residual interaction
and to calculations within a pf5/2 configurational space with a residual
surface delta interaction. The role of the 56Ni core excitations for the
low-spin structure in 58Cu is discussed.Comment: 15 pages, 7 figures, submitted to Phys. Rev.
Drawing the Line: How African, Caribbean and White British Women Live Out Psychologically Abusive Experiences
The final, definitive version of this paper has been published in Violence Against Women, 19 (9):1104-32, Sept 2013 by SAGE Publications Ltd, All rights reserved. © The Author(s) 2013.
The online version of this article can be found at: http://vaw.sagepub.com/content/19/9/110
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