1,595 research outputs found
Drawing Muscles with Diagrams: How a Novel Dissection Cut Inspired Nicolaus Steno's Mathematical Myology (1667)
In 1667, twenty years before Isaac Newton published his mathematization of physics, and more than ten years before the publication of Giovanni Borelli's De motu animalium, the Danish anatomist Nicolaus Steno published an entirely new geometrical theory of muscle motion in the book Elementorum myologiæ specimen. Historians of science have studied this book in recent decades, but the recent rediscovery of a seventeenth-century muscle atlas at the Bibliothèque interuniversitaire de Santé in Paris sheds new light on the largely overlooked origin of Steno's mathematical theory of muscles. In this article, we show that Steno's muscle diagrams result from a tension that Steno faced when combining his interest in illustrations with presenting his mathematical insights about the inner structure of muscle fibres. Furthermore, we argue that Steno's diagrams are deeply connected to observations through a new method of dissecting the muscles. The observational origins of Steno's mathematical insight are further confirmed by the strong correlation between Steno's depictions of the structure and function of skeletal muscles and the results of current biomechanical investigations
High Precision CTE-Measurement of SiC-100 for Cryogenic Space-Telescopes
We present the results of high precision measurements of the thermal
expansion of the sintered SiC, SiC-100, intended for use in cryogenic
space-telescopes, in which minimization of thermal deformation of the mirror is
critical and precise information of the thermal expansion is needed for the
telescope design. The temperature range of the measurements extends from room
temperature down to 10 K. Three samples, #1, #2, and #3 were
manufactured from blocks of SiC produced in different lots. The thermal
expansion of the samples was measured with a cryogenic dilatometer, consisting
of a laser interferometer, a cryostat, and a mechanical cooler. The typical
thermal expansion curve is presented using the 8th order polynomial of the
temperature. For the three samples, the coefficients of thermal expansion
(CTE), \bar{\alpha}_{#1}, \bar{\alpha}_{#2}, and \bar{\alpha}_{#3} were
derived for temperatures between 293 K and 10 K. The average and the dispersion
(1 rms) of these three CTEs are 0.816 and 0.002 (/K),
respectively. No significant difference was detected in the CTE of the three
samples from the different lots. Neither inhomogeneity nor anisotropy of the
CTE was observed. Based on the obtained CTE dispersion, we performed an
finite-element-method (FEM) analysis of the thermal deformation of a 3.5 m
diameter cryogenic mirror made of six SiC-100 segments. It was shown that the
present CTE measurement has a sufficient accuracy well enough for the design of
the 3.5 m cryogenic infrared telescope mission, the Space Infrared telescope
for Cosmology and Astrophysics (SPICA).Comment: in press, PASP. 21 pages, 4 figure
Chiral three-nucleon interaction and the carbon-14 dating beta decay
We present a shell model calculation for the beta decay of 14-C to the 14-N
ground-state, treating the relevant nuclear states as two 0p-holes in an 16-O
core. Employing the universal low-momentum nucleon-nucleon potential V(low-k)
only, one finds that the Gamow-Teller matrix element is too large to describe
the known (very long) lifetime of 14-C. As a novel approach to the problem, we
invoke the chiral three-nucleon force (3NF) at leading order and derive from it
a density-dependent in-medium NN interaction. Including this effective
in-medium NN interaction, the Gamow-Teller matrix element vanishes for a
nuclear density close to that of saturated nuclear matter. The genuine
short-range part of the three-nucleon interaction plays a particularly
important role in this context, since the medium modifications to the pion
propagator and pion-nucleon vertex (due to the long-range 3NF) tend to cancel
out in the relevant observable. We discuss also uncertainties related to the
off-shell extrapolation of the in-medium NN interaction. Using the off-shell
behavior of V(low-k) as a guide, we find that these uncertainties are rather
small.Comment: 22 pages, 11 figure
Dominant g(9/2)^2 neutron configuration in the 4+1 state of 68Zn based on new g factor measurements
The factor of the state in Zn has been remeasured with
improved energy resolution of the detectors used. The value obtained is
consistent with the previous result of a negative factor thus confirming
the dominant neutron nature of the state. In addition, the
accuracy of the factors of the , and states has been
improved an d their lifetimes were well reproduced. New large-scale shell model
calculations based on a Ni core and an model space
yield a theoretical value, . Although the calculated value
is small, it cannot fully explain the experimental value, . The magnitude of the deduced B(E2) of the and
transition is, however, rather well described. These results demonstrate again
the importance of factor measurements for nuclear structure determination s
due to their specific sensitivity to detailed proton and neutron components in
the nuclear wave functions.Comment: 7 pages, 3 figs, submitted to PL
Shell-Model Effective Operators for Muon Capture in ^{20}Ne
It has been proposed that the discrepancy between the partially-conserved
axial-current prediction and the nuclear shell-model calculations of the ratio
in the muon-capture reactions can be solved in the case of ^{28}Si by
introducing effective transition operators. Recently there has been
experimental interest in measuring the needed angular correlations also in
^{20}Ne. Inspired by this, we have performed a shell-model analysis employing
effective transition operators in the shell-model formalism for the transition
. Comparison of
the calculated capture rates with existing data supports the use of effective
transition operators. Based on our calculations, as soon as the experimental
anisotropy data becomes available, the limits for the ratio can be
extracted.Comment: 9 pages, 3 figures include
TREX-DM: a low background Micromegas-based TPC for low-mass WIMP detection
Dark Matter experiments are recently focusing their detection techniques in
low-mass WIMPs, which requires the use of light elements and low energy
threshold. In this context, we describe the TREX-DM experiment, a low
background Micromegas-based TPC for low-mass WIMP detection. Its main goal is
the operation of an active detection mass 0.3 kg, with an energy
threshold below 0.4 keVee and fully built with previously selected radiopure
materials. This work describes the commissioning of the actual setup situated
in a laboratory on surface and the updates needed for a possible physics run at
the Canfranc Underground Laboratory (LSC) in 2016. A preliminary background
model of TREX-DM is also presented, based on a Geant4 simulation, the
simulation of the detector's response and two discrimination methods: a
conservative muon/electron and one based on a neutron source. Based on this
background model, TREX-DM could be competitive in the search for low-mass
WIMPs. In particular it could be sensitive, e.g., to the low-mass WIMP
interpretation of the DAMA/LIBRA and other hints in a conservative scenario.Comment: Proceedings of the XIV International Conference on Topics in
Astroparticle and Underground Physics (TAUP 2015), 7-11 September 2015,
Torino, Ital
Parasitémies à Plasmodium falciparum ou P. malariae chez les porteurs du trait drépanocytaire dans différents biotopes du Bénin
La prévalence du paludisme en fonction du phénotype de l'hémoglobine et la fréquence du gène S ont été recherchées dans deux différents biotopes du Bénin. Dans aucun d'eux, la prévalence du paludisme n'est significativement différente entre les porteurs du trait drépanocytaire et les autres. De même, la prévalence du trait drépanocytaire n'est pas modifiée par l'âge. En revanche, en région holoendémique, la densité parasitaire moyenne à #P. falciparum$ est significativement plus faible chez les sujets AS que chez les sujets AA. La présence du trait drépanocytaire ne réduit pas le risque d'infection palustre mais semble diminuer l'importance de la parasitémie. (Résumé d'auteur
Lowering the background level and the energy threshold of Micromegas x-ray detectors for axion searches
Axion helioscopes search for solar axions by their conversion in x-rays in
the presence of high magnetic fields. The use of low background x-ray detectors
is an essential component contributing to the sensitivity of these searches. In
this work, we review the recent advances on Micromegas detectors used in the
CERN Axion Solar Telescope (CAST) and proposed for the future International
Axion Observatory (IAXO). The actual setup in CAST has achieved background
levels below 10 keV cm s, a factor 100 lower than
the first generation of Micromegas detectors. This reduction is based on active
and passive shielding techniques, the selection of radiopure materials, offline
discrimination techniques and the high granularity of the readout. We describe
in detail the background model of the detector, based on its operation at CAST
site and at the Canfranc Underground Laboratory (LSC), as well as on Geant4
simulations. The best levels currently achieved at LSC are low than 10
keV cm s and show good prospects for the application of
this technology in IAXO. Finally, we present some ideas and results for
reducing the energy threshold of these detectors below 1 keV, using
high-transparent windows, autotrigger electronics and studying the cluster
shape at different energies. As a high flux of axion-like-particles is expected
in this energy range, a sub-keV threshold detector could enlarge the physics
case of axion helioscopes.Comment: Proceedings of 3rd International Conference on Technology and
Instrumentation in Particle Physics (TIPP 2014
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