52,183 research outputs found
Organs from animals for man
In the following review some of the problems of xenotransplantation shall be discussed, based on the few experimental data available so far and on reports in the literature describing investigations which may be of importance for xenotransplantation. The impact of gravity on the upright posture of man versus almost all other mammals, the dysfunction between enzymes and hormones in different species and the lack of interactions between interleukins, cytokines and vasoactive substances will be taken into consideration. The question must be asked whether different levels of carrier molecules or serum proteins play a role in the physiological network. Even though the development of transgenic animals or other imaginative manipulations may lead to the acceptance of any type of xenografted organ, it has to be established for how long the products of the xenografts are able to act in the multifactorial orchestra. We are far from understanding xenogeneic molecular mechanisms involved in toxicity, necrosis and apoptosis or even reperfusion injury and ischemia in addition to the immediate mechanisms of the hyperacute xenogeneic rejection. Here, cell adhesion, blood clotting and vasomotion collide and bring micro-and macrocirculation to a standstill. All types of xenogeneic immunological mechanisms studied so far were found to have a more serious impact than those seen in allogeneic transplantation. In addition we are now only beginning to understand that so-called immunological parameters in allogeneic mechanisms act also in a true physiological manner in the xenogeneic situation. These molecular mechanisms occur behind the curtain of hyperacute, accelerated, acute or chronic xenograft rejection of which only some folds have been lifted to allow glimpses of part of the total scene. Other obstacles are likely to arise when long-term survival is achieved. These obstacles include retroviral infections, transfer of prions and severe side effects of the massive immunosuppression which will be needed. Moral, ethical and religious concerns are under debate and the species-specific production of proteins of the foreign donor species developed for clinical use suddenly appears to be a greater problem than anticipated
How the Liquid-Liquid Transition Affects Hydrophobic Hydration in Deeply Supercooled Water
We determine the phase diagram of liquid supercooled water by extensive
computer simulations using the TIP5P-E model [J. Chem. Phys. {\bf 120}, 6085
(2004)]. We find that the transformation of water into a low density liquid in
the supercooled range strongly enhances the solubility of hydrophobic
particles. The transformation of water into a tetrahedrally structured liquid
is accompanied by a minimum in the hydration entropy and enthalpy. The
corresponding change in sign of the solvation heat capacity indicates a loss of
one characteristic signature of hydrophobic hydration. The observed behavior is
found to be qualitatively in accordance with the predictions of the information
theory model of Garde et al. [Phys. Rev. Lett. {\bf 77}, 4966 (1996)].Comment: 4 pages, 4 figures, twocolumn Revtex, modified text applied changes
to figure 1, 2d, 3,
Radiation from a charged particle-in-flight from a laminated medium to vacuum
The radiation from a charged particle-in-flight from a semi-infinite
laminated medium to vacuum and back,- from vacuum to the laminated medium, has
been investigated. Expressions for the spectral-angular distribution of
radiation energy in vacuum (at large distances from the boundary of laminated
medium) were obtained for both the cases with no limitations on the amplitude
and variation profile of the laminated medium permittivity. The results of
appropriate numerical calculations are presented and possible applications of
the obtained results are discussed.Comment: 8 pages, 6 figures, contribution to Proceedings of International
Symposium RREPS-2009, 07-11 September, 2009, Zvenigorod, Russi
Probing Pauli Blocking Factors in Quantum Pumps with Broken Time-Reversal Symmetry
A recently demonstrated quantum electron pump is discussed within the
framework of photon-assisted tunneling. Due to lack of time-reversal symmetry,
different results are obtained for the pump current depending on whether or not
final-state Pauli blocking factors are used when describing the tunneling
process. Whilst in both cases the current depends quadratically on the driving
amplitude for moderate pumping, a marked difference is predicted for the
temperature dependence. With blocking factors the pump current decreases
roughly linearly with temperature until k_B T ~ \hbar\omega is reached, whereas
without them it is unaffected by temperature, indicating that the entire Fermi
sea participates in the electronic transport.Comment: 4 pages in RevTex4 (beta4), 6 figures; status: to appear in PR
Reducing sample variance: halo biasing, non-linearity and stochasticity
Comparing clustering of differently biased tracers of the dark matter
distribution offers the opportunity to reduce the cosmic variance error in the
measurement of certain cosmological parameters. We develop a formalism that
includes bias non-linearities and stochasticity. Our formalism is general
enough that can be used to optimise survey design and tracers selection and
optimally split (or combine) tracers to minimise the error on the
cosmologically interesting quantities. Our approach generalises the one
presented by McDonald & Seljak (2009) of circumventing sample variance in the
measurement of . We analyse how the bias, the noise,
the non-linearity and stochasticity affect the measurements of and explore
in which signal-to-noise regime it is significantly advantageous to split a
galaxy sample in two differently-biased tracers. We use N-body simulations to
find realistic values for the parameters describing the bias properties of dark
matter haloes of different masses and their number density.
We find that, even if dark matter haloes could be used as tracers and
selected in an idealised way, for realistic haloes, the sample variance limit
can be reduced only by up to a factor .
This would still correspond to the gain from a three times larger survey volume
if the two tracers were not to be split. Before any practical application one
should bear in mind that these findings apply to dark matter haloes as tracers,
while realistic surveys would select galaxies: the galaxy-host halo relation is
likely to introduce extra stochasticity, which may reduce the gain further.Comment: 21 pages, 13 figures. Published version in MNRA
Integration of remote sensing and surface geophysics in the detection of faults
Remote sensing was included in a comprehensive investigation of the use of geophysical techniques to aid in underground mine placement. The primary objective was to detect faults and slumping, features which, due to structural weakness and excess water, cause construction difficulties and safety hazards in mine construction. Preliminary geologic reconnaissance was performed on a potential site for an underground oil shale mine in the Piceance Creek Basin of Colorado. LANDSAT data, black and white aerial photography and 3 cm radar imagery were obtained. LANDSAT data were primarily used in optical imagery and digital tape forms, both of which were analyzed and enhanced by computer techniques. The aerial photography and radar data offered supplemental information. Surface linears in the test area were located and mapped principally from LANDSAT data. A specific, relatively wide, linear pointed directly toward the test site, but did not extend into it. Density slicing, ratioing, and edge enhancement of the LANDSAT data all indicated the existence of this linear. Radar imagery marginally confirmed the linear, while aerial photography did not confirm it
Imaging Pauli repulsion in scanning tunneling microscopy
A scanning tunneling microscope (STM) has been equipped with a nanoscale
force sensor and signal transducer composed of a single D2 molecule that is
confined in the STM junction. The uncalibrated sensor is used to obtain
ultra-high geometric image resolution of a complex organic molecule adsorbed on
a noble metal surface. By means of conductance-distance spectroscopy and
corresponding density functional calculations the mechanism of the
sensor/transducer is identified. It probes the short-range Pauli repulsion and
converts this signal into variations of the junction conductance.Comment: 4 pages, 4 figures, accepted to Phys. Rev. Let
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