1,109 research outputs found
Categorification of persistent homology
We redevelop persistent homology (topological persistence) from a categorical
point of view. The main objects of study are diagrams, indexed by the poset of
real numbers, in some target category. The set of such diagrams has an
interleaving distance, which we show generalizes the previously-studied
bottleneck distance. To illustrate the utility of this approach, we greatly
generalize previous stability results for persistence, extended persistence,
and kernel, image and cokernel persistence. We give a natural construction of a
category of interleavings of these diagrams, and show that if the target
category is abelian, so is this category of interleavings.Comment: 27 pages, v3: minor changes, to appear in Discrete & Computational
Geometr
The effect of 12C + 12C rate uncertainties on s-process yields
The slow neutron capture process in massive stars (the weak s-process)
produces most of the s-only isotopes in the mass region 60 < A < 90. The
nuclear reaction rates used in simulations of this process have a profound
effect on the final s-process yields. We generated 1D stellar models of a 25
solar mass star varying the 12C + 12C rate by a factor of 10 and calculated
full nucleosynthesis using the post-processing code PPN. Increasing or
decreasing the rate by a factor of 10 affects the convective history and
nucleosynthesis, and consequently the final yields.Comment: Conference proceedings for the Nuclear Physics in Astrophysics IV
conference, 8-12 June 2009. 4 pages, 3 figures. Accepted for publication to
the Journal of Physics: Conference Serie
Solar neutrino detection in a large volume double-phase liquid argon experiment
Precision measurements of solar neutrinos emitted by specific nuclear
reaction chains in the Sun are of great interest for developing an improved
understanding of star formation and evolution. Given the expected neutrino
fluxes and known detection reactions, such measurements require detectors
capable of collecting neutrino-electron scattering data in exposures on the
order of 1 ktonne yr, with good energy resolution and extremely low background.
Two-phase liquid argon time projection chambers (LAr TPCs) are under
development for direct Dark Matter WIMP searches, which possess very large
sensitive mass, high scintillation light yield, good energy resolution, and
good spatial resolution in all three cartesian directions. While enabling Dark
Matter searches with sensitivity extending to the "neutrino floor" (given by
the rate of nuclear recoil events from solar neutrino coherent scattering),
such detectors could also enable precision measurements of solar neutrino
fluxes using the neutrino-electron elastic scattering events. Modeling results
are presented for the cosmogenic and radiogenic backgrounds affecting solar
neutrino detection in a 300 tonne (100 tonne fiducial) LAr TPC operating at
LNGS depth (3,800 meters of water equivalent). The results show that such a
detector could measure the CNO neutrino rate with ~15% precision, and
significantly improve the precision of the 7Be and pep neutrino rates compared
to the currently available results from the Borexino organic liquid
scintillator detector.Comment: 21 pages, 7 figures, 6 table
A proximal femoral implant preserves physiological bone deformation: a biomechanical investigation in cadaveric bones
The aim of this study was to compare the perturbances in bone deformation patterns of the proximal femur due to a conventional cemented femoral stem and a novel uncemented implant designed on the principles of osseointegration. Five matched pairs of fresh frozen human femora were mechanically tested. Bone deformation patterns, measured with a video digitizing system under 1.5 kN joint force, showed that the cemented Spectron femoral implant caused significant alterations to the proximal femoral deformation pattern, whereas the Gothenburg osseointegrated titanium femoral implant did not significantly alter the bone behaviour (p < 0.05). Vertical micromotions measured under 1 kN after 1000 cycles were within the threshold of movement tolerable for bone ingrowth (21 microm for the Gothenburg system and 26 microm for the cemented implant).Published versio
The Neutrino Bubble Instability: A Mechanism for Generating Pulsar Kicks
An explanation for the large random velocities of pulsars is presented. Like
many other models, we propose that the momentum imparted to the star is given
at birth. The ultimate source of energy is provided by the intense optically
thick neutrino flux that is responsible for radiating the proto-neutron star's
gravitational binding energy during the Kelvin-Helmholtz phase. The central
feature of the kick mechanism is a radiative-driven magnetoacoustic
instability, which we refer to as ``neutrino bubbles.'' Identical in nature to
the photon bubble instability, the neutrino bubble instability requires the
presence of an equilibrium radiative flux as well as a coherent steady
background magnetic field. Over regions of large magnetic flux densities, the
neutrino bubble instability is allowed to grow on dynamical timescales ~ 1ms,
potentially leading to large luminosity enhancements and density fluctuations.
Local luminosity enhancements, which preferentially occur over regions of
strong magnetic field, lead to a net global asymmetry in the neutrino emission
and the young neutron star is propelled in the direction opposite to these
regions. For favorable values of magnetic field structure, size, and strength
as well as neutrino bubble saturation amplitude, momentum kicks in excess of
1000 km/s can be achieved. Since the neutrino-powered kick is delivered over
the duration of the Kelvin-Helmholtz time ~ a few seconds, one expects
spin-kick alignment from this neutrino bubble powered model.Comment: submitted to Ap
Aniline incorporated silica nanobubbles
We report the synthesis of stearate functionalized nanobubbles of SiO2 with a few aniline
molecules inside, represented as C6H5NH2@SiO2@stearate, exhibiting fluorescence with red-shifted
emission. Stearic acid functionalization allows the materials to be handled just as free molecules, for dissolution,
precipitation, storage etc. The methodology adopted involves adsorption of aniline on the surface of
gold nanoparticles with subsequent growth of a silica shell through monolayers, followed by the selective
removal of the metal core either using sodium cyanide or by a new reaction involving halocarbons. The
material is stable and can be stored for extended periods without loss of fluorescence. Spectroscopic and
voltammetric properties of the system were studied in order to understand the interaction of aniline with
the shell as well as the monolayer, whilst transmission electron microscopy has been used to study the
silica shell
On Haagerup's list of potential principal graphs of subfactors
We show that any graph, in the sequence given by Haagerup in 1991 as that of
candidates of principal graphs of subfactors, is not realized as a principal
graph except for the smallest two. This settles the remaining case of a
previous work of the first author.Comment: 19 page
Constraints on Type Ib/c and GRB Progenitors
Although there is strong support for the collapsar engine as the power source
of long-duration gamma-ray bursts (GRBs), we still do not definitively know the
progenitor of these explosions. Here we review the current set of progenitor
scenarios for long-duration GRBs and the observational constraints on these
scenarios. Examining these, we find that single-star models cannot be the only
progenitor for long-duration GRBs. Several binary progenitors can match the
solid observational constraints and also have the potential to match the trends
we are currently seeing in the observations. Type Ib/c supernovae are also
likely to be produced primarily in binaries; we discuss the relationship
between the progenitors of these explosions and those of the long-duration
GRBs.Comment: 36 pages, 6 figure
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