708 research outputs found
Non-thermal ablation of expanded polytetrafluoroethylene with an intense femtosecond-pulse laser
Ablation of expanded polytetrafluoroethylene without disruption of the fine porous structure is demonstrated using an intense femtosecond-pulse laser. As a result of laser-matter interactions near ablation threshold fluence, high-energy ions are emitted, which cannot be produced by thermal dissociation of the molecules. The ion energy is produced by Coulomb explosion of the elements of (-CF_{2}-CF_{2-})n and the energy spectra of the ions show contributions from the Coulomb explosions of the ions rather than those of thermal expansion to generate high-energy ions. The dependence of ion energy on the laser fluence of a 180-fs pulse, compared with that of a 400-ps pulse, also suggests that the high-energy ions are accelerated by Coulomb explosio
Kinetics of water flow through polymer gel
The water flow through the poly(acrylamide) gel under a constant water
pressure is measured by newly designed apparatus. The time evolution of the
water flow in the gel, is calculated based on the collective diffusion model of
the polymer network coupled with the friction between the polymer network and
the water. The friction coefficient are determined from the equilibrium
velocity of water flow. The Young modulus and the Poisson's ratio of the rod
shape gels are measured by the uni-axial elongation experiments, which
determine the longitudinal modulus independently from the water flow
experiments. With the values of the longitudinal modulus and of the friction
determined by the experiments, the calculated results are compared with the
time evolution of the flow experiments. We find that the time evolution of the
water flow is well described by a single characteristic relaxation time
predicted by the collective diffusion model coupled with the water friction.Comment: 7 pages, 5 figures, 27 references, Eqs adde
Anatomic characterisation of the parietal branches arising from the internal iliac artery in the foetal pig (Sus scrofa domestica)
Background: It is critical for surgeons to have a full understanding of the complex courses and ramifications of the human internal iliac artery and its parietal branches. Although numerous anatomical studies have been performed, not all variations at this site are currently understood. Therefore, we characterised these blood vessels in foetal pigs to provide additional insight from a comparative anatomical perspective. Materials and methods: Eighteen half-pelvis specimens from foetal pigs were dissected and examined on macroscopic scale. Results: Among our findings, we identified the internal iliac artery as a descending branch of the abdominal aorta. A very thick umbilical artery arose from the internal iliac artery. The superior gluteal, inferior gluteal, and internal pudendal arteries formed the common arterial trunk. Although the superior gluteal artery emerged from the common trunk from inside the pelvis, the inferior gluteal and internal pudendal arteries bifurcated at deep layer within the gluteus muscles after leaving pelvic cavity. We were unable to detect an typical obturator artery emerging from the internal iliac artery. A branch supplying the hip adductors was identified as arising from the inferior epigastric artery which itself was derived from the distal end of the external iliac artery. Conclusions: We identified the anatomic characteristics of the internal iliac artery and its parietal branches in the foetal pig. Our findings provide new insight into the comparative anatomy of the internal iliac artery and will promote understanding of related morphogenetic processes
Mechanism of femtosecond laser nano-ablation for metals
Metals have three ablation threshold fluences (high,middle and low-threshold fluence, here called) forfemtosecond laser pulses. In order to investigatethe physics of metal ablation under an intenseoptical field, the ions emitted from a laserirradiatedcopper surface were studied by time-offlightenergy spectroscopy. The low laser fluenceat which ions are emitted, Fth,L is 0.028 J/cm2, andtwo higher emission thresholds were identified atfluences of Fth,M =0.195 J/cm2 and Fth,H =0.470J/cm2. The relation between the number of emittedions per pulse Ni and laser fluence F was in goodagreement with Ni ∝F4 for Fth,L - Fth,M, Ni ∝F3 forFth,M - Fth,H, and Ni ∝F2 for ≥ Fth,H. Thedependence of ion production on laser energyfluence is explained well by multiphotonabsorption and optical field ionization.For fluence levels near the middle to high ablationthreshold, the formation of grating structures onmetal surfaces has been observed. The interspacesof grating structures were shorter than the laserwavelength, and the interspaces depend on fluencefor Mo and W with a 160 fs laser pulse. Thisphenomenon is well explained by the parametricdecay model proposed by Sakabe et al
Species Abundance Patterns in Complex Evolutionary Dynamics
An analytic theory of species abundance patterns (SAPs) in biological
networks is presented. The theory is based on multispecies replicator dynamics
equivalent to the Lotka-Volterra equation, with diverse interspecies
interactions. Various SAPs observed in nature are derived from a single
parameter. The abundance distribution is formed like a widely observed
left-skewed lognormal distribution. As the model has a general form, the result
can be applied to similar patterns in other complex biological networks, e.g.
gene expression.Comment: 4 pages, 3 figures. Physical Review Letters, in pres
Discovery of a Gravitationally Lensed Quasar from the Sloan Digital Sky Survey: SDSS J133222.62+034739.9
We report the discovery of the two-image gravitationally lensed quasar SDSS
J133222.62+034739.9 (SDSS J1332+0347) with an image separation of
Delta_theta=1.14". This system consists of a source quasar at z_s=1.445 and a
lens galaxy at z_l=0.191. The agreement of the luminosity, ellipticity and
position angle of the lens galaxy with those expected from lens model confirms
the lensing hypothesis.Comment: 16 pages, 4 figures, the Astronomical Journal accepte
A Universal Lifetime Distribution for Multi-Species Systems
Lifetime distributions of social entities, such as enterprises, products, and
media contents, are one of the fundamental statistics characterizing the social
dynamics. To investigate the lifetime distribution of mutually interacting
systems, simple models having a rule for additions and deletions of entities
are investigated. We found a quite universal lifetime distribution for various
kinds of inter-entity interactions, and it is well fitted by a
stretched-exponential function with an exponent close to 1/2. We propose a
"modified Red-Queen" hypothesis to explain this distribution. We also review
empirical studies on the lifetime distribution of social entities, and
discussed the applicability of the model.Comment: 10 pages, 6 figures, Proceedings of Social Modeling and Simulations +
Econophysics Colloquium 201
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