473 research outputs found
Identifying a site for maximum delivery of oxygen to transplanted cells
For in vivo cell implantation techniques to be successful, the energy and metabolic substrate requirement of the cells being grown must be met. Certain cells with high-energy requirements (e.g., hepatocytes, pancreatic island cells) experience a high degree of cell death after implantation due to a limited supply of oxygen. We proposed that the pleural cavity might be an oxygen-rich environment and hence an excellent site for cell implantation. To test the hypothesis that the delivery of oxygen to the pleural cavity is directly proportional to the inspired oxygen concentration we measured the pO(2) of saline instilled in the pleural cavity as compared to that of the peritoneal cavity. We postulated that the physiologic basis for any difference was the result of direct diffusion of oxygen into the pleural space across the alveoli. The study was conducted on sheep (n = 6), after induction of general anesthesia, in two phases, control and experimental. Saline was instilled into the peritoneal and pleural cavities via catheters, after equilibration at given FiO(2), the pO(2) of the paline aspirated from the two cavities was compared. In the experimental group, animals were sacrificed (no circulation) and ventilated. The same sequence of steps as in the control phase were repeated. In the control group, the pO(2) of saline aspirated from the pleural cavity approached the arterial pO(2) at all FiO(2) levels. The pO(2) of the peritoneal saline aspirate fell over time. In the experimental phase (no circulation), the pO(2) of the pleural cavity saline rose to \u3e400 mm Hg. We conclude that this is a result of direct diffusion and is a potential source of unlimited oxygen supply not dependent on vascular supply
Protecting subspaces by acting on the outside
Many quantum control tasks aim at manipulating the state of a quantum
mechanical system within a finite subspace of states. However, couplings to the
outside are often inevitable. Here we discuss strategies which keep the system
in the controlled subspace by applying strong interactions onto the outside.
This is done by drawing analogies to simple toy models and to the quantum Zeno
effect. Special attention is paid to the constructive use of dissipation in the
protection of subspaces.Comment: 16 pages, 10 figure
Dynamical control of quantum state transfer within hybrid open systems
We analyze quantum state-transfer optimization within hybrid open systems,
from a "noisy" (write-in) qubit to its "quiet" counterpart (storage qubit).
Intriguing interplay is revealed between our ability to avoid bath-induced
errors that profoundly depend on the bath-memory time and the limitations
imposed by leakage out of the operational subspace. Counterintuitively, under
no circumstances is the fastest transfer optimal (for a given transfer energy)
Selective laser sintering of hydroxyapatite reinforced polyethylene composites for bioactive implants and tissue scaffold development
Selective laser sintering (SLS) has been investigated for the production of bioactive implants and tissue scaffolds using composites of high-density polyethylene (HDPE) reinforced with hydroxyapatite (HA) with the aim of achieving the rapid manufacturing of customized implants. Single-layer and multilayer block specimens made of HA-HDPE composites with 30 and 40 vol % HA were sintered successfully using a CO2 laser sintering system. Laser power and scanning speed had a significant effect on the sintering behaviour. The degree of particle fusion and porosity were influenced by the laser processing parameters, hence control can be attained by varying these parameters. Moreover, the SLS processing allowed exposure of HA particles on the surface of the composites and thereby should provide bioactive products. Pores existed in the SLS-fabricated composite parts and at certain processing parameters a significant fraction of the pores were within the optimal sizes for tissue regeneration. The results indicate that the SLS technique has the potential not only to fabricate HA-HDPE composite products but also to produce appropriate features for their application as bioactive implants and tissue scaffolds
On the Absorption of High Energy Gamma-Rays by Intergalactic Infrared Radiation
We present a new calculation of the intergalactic -ray
pair-production absorption coefficient as a function of both energy and
redshift up to the redshift of 3C279, z = 0.54. In reexamining this problem, we
make use of new observational data on the intergalactic infrared radiation
field (IIRF), together with recent theoretical models of the galactic spectral
energy distributions of the IIRF from stars and dust reradiation and estimates
of the IIRF from galaxy counts and {\it COBE} results. We present our results
for two fairly well defined IIRF spectral energy distributions, one of which is
within of our previous estimate of the IIRF at m.
We then apply our results to the -ray spectrum of Mrk 421, and obtain
good agreement with the observational data, including the recent results of the
{\it HEGRA} group.Comment: Plain TeX file with text in abs96.tex, 3 postscript figures (Fig. 1 -
ircobe.eps, Fig. 2 - taupl.eps, Fig. 3 - mki.eps), stylefile epsf.sty
included, accepted for publication in the Astrophysical Journa
Gamma rays and neutrinos from the Crab Nebula produced by pulsar accelerated nuclei
We investigate the consequences of the acceleration of heavy nuclei (e.g.
iron nuclei) by the Crab pulsar. Accelerated nuclei can photodisintegrate in
collisions with soft photons produced in the pulsar's outer gap, injecting
energetic neutrons which decay either inside or outside the Crab Nebula. The
protons from neutron decay inside the nebula are trapped by the Crab Nebula
magnetic field, and accumulate inside the nebula producing gamma-rays and
neutrinos in collisions with the matter in the nebula. Neutrons decaying
outside the Crab Nebula contribute to the Galactic cosmic rays. We compute the
expected fluxes of gamma-rays and neutrinos, and find that our model could
account for the observed emission at high energies and may be tested by
searching for high energy neutrinos with future neutrino telescopes currently
in the design stage.Comment: 8 pages, 4 figures, LaTeX uses revtex.sty, submitted to Phys. Rev.
Let
- …