273 research outputs found
Improved Energy Model for Membrane Electroporation in Biological Cells Subjected to Electrical Pulses
A self-consistent model analysis of electroporation in biological cells has been carried out based on an improved energy model. The simple energy model used in the literature is somewhat incorrect and unphysical for a variety of reasons. Our model for the pore formation energy E(r) includes a dependence on pore population and density. It also allows for variable surface tension, incorporates the effects of finite conductivity on the electrostatic correction term, and is dynamic in nature. Self-consistent calculations, based on a coupled scheme involving the Smoluchowski equation and the improved energy model, are presented. It is shown that E(r) becomes self-adjusting with variations in its magnitude and profile, in response to pore population, and inhibits uncontrolled pore growth and expansion. This theory can be augmented to include pore-pore interactions to move beyond the independent pore picture
Theoretical Predictions of Electromechanical Deformation of Cells Subjected to High Voltages for Membrane Electroporation
An electromechanical analysis based on thin-shell theory is presented to analyze cell shape changes in response to external electric fields. This approach can be extended to include osmotic-pressure changes. Our calculations demonstrate that at large fields, the spherical cell geometry can be significantly modified, and even ellipsoidal forms would be inappropriate to account for the deformation. Values of the surface forces obtained from our calculations are in very good agreement with the 1–10 mN/m range for membrane rupture reported in the literature. The results, in keeping with reports in the literature, demonstrate that the final shape depends on membrane thickness. This has direct implications for tissues in which significant molecular restructuring can occur. It is also shown that, at least for the smaller electric fields, both the cellular surface area and volume change roughly in a quadratic manner with the electric field. Finally, it is shown that the bending moments are generally quite small and can be neglected for a simpler analysis
Organic molecules in the spectral line survey of Orion KL with the Odin Satellite from 486492 GHz and 541577 GHz
Proceedings of the International Astronomical Union, 2008, v. 4 n. S251, p. 29-30A spectral line survey of Orion KL has been performed over the frequency range of 486492 GHz and 541577 GHz using the Odin satellite. Over 1000 lines have been identified from 40 different molecular species, including several organic compounds such as methyl cyanide (CH3CN), methanol (CH3OH, 13CH3OH), and dimethyl ether (CH3OCH3). © 2008 International Astronomical Union.published_or_final_versio
Self-Consistent Simulations of Electroporation Dynamics in Biological Cells Subjected to Ultrashort Electrical Pulses
The temporal dynamics of electroporation of cells subjected to ultrashort voltage pulses are studied based on a coupled scheme involving the Laplace, Nernst-Plank, and Smoluchowski equations. A pore radius dependent energy barrier for ionic transport, accounts for cellular variations. It is shown that a finite time delay exists in pore formation, and leads to a transient overshoot of the transmembrane potential Vmem beyond 1.0 V. Pore resealing is shown to consist of an initial fast process, a 10−4s delay, followed by a much slower closing at a time constant of about 10 −1s. This establishes a time-window during which the pores are mostly open, and hence, the system is most vulnerable to destruction by a second electric pulse. The existence of such a time window for effective killing by a second pulse is amply supported by our experimental data for E. coli cells. The time constant for the longer process also matches experiments. The study suggests that controlled manipulation of the pore “open times” can be achieved through multiple, ultrashort pulses
TiO2 Breakdown Under Pulsed Conditions
Model studies of current conduction and breakdown in TiO2 were carried out. Our simulation results indicate that electrical breakdown of TiO2 under multiple-pulsed conditions can occur at lower voltages as compared to quasi-dc biasing. This is in agreement with recent experimental data and is indicative of a cumulative phenomena. We demonstrate that the lower breakdown voltages observed in TiO2 under pulsed conditions is a direct rise-time effect, coupled with successive detrapping at the grain boundaries. 2007 American Institute of Physics
On the accretion process in a high-mass star forming region - A multitransitional THz Herschel-HIFI study of ammonia toward G34.26+0.15
[Abridged] Our aim is to explore the gas dynamics and the accretion process
in the early phase of high-mass star formation. The inward motion of molecular
gas in the massive star forming region G34.26+0.15 is investigated by using
high-resolution profiles of seven transitions of ammonia at THz frequencies
observed with Herschel-HIFI. The shapes and intensities of these lines are
interpreted in terms of radiative transfer models of a spherical, collapsing
molecular envelope. An accelerated Lambda Iteration (ALI) method is used to
compute the models. The seven ammonia lines show mixed absorption and emission
with inverse P-Cygni-type profiles that suggest infall onto the central source.
A trend toward absorption at increasingly higher velocities for higher
excitation transitions is clearly seen in the line profiles. The lines show only very weak emission, so these absorption profiles
can be used directly to analyze the inward motion of the gas. This is the first
time a multitransitional study of spectrally resolved rotational ammonia lines
has been used for this purpose. Broad emission is, in addition, mixed with the
absorption in the ortho-NH line, possibly tracing a molecular
outflow from the star forming region. The best-fitting ALI model reproduces the
continuum fluxes and line profiles, but slightly underpredicts the emission and
absorption depth in the ground-state ortho line . The derived
ortho-to-para ratio is approximately 0.5 throughout the infalling cloud core
similar to recent findings for translucent clouds in sight lines toward W31C
and W49N. We find evidence of two gas components moving inwards toward the
central region with constant velocities: 2.7 and 5.3 kms, relative
to the source systemic velocity. The inferred mass accretion rates derived are
sufficient to overcome the expected radiation pressure from G34.26+0.15.Comment: 20 pages, 18 figures, accepted by A&A 3 October 201
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An impact ionization model for optically-triggered current filaments in GaAs
A new impact ionization theory is proposed for current filaments in optically triggered semi-insulating (SI) GaAs switches. The theory explains the rapid switching and lock-on voltage observed in these switches in terms of hot carriers which become more effective at impact ionization at higher carrier densities. The theory is implemented by hydrodynamic transport equations which include kinetic terms for hot carriers and hot phonons. The solutions of these equations are in good agreement with current versus voltage data for optically triggered GaAs switches
Submillimeter Emission from Water in the W3 Region
We have mapped the submillimeter emission from the 1(10)-1(01) transition of
ortho-water in the W3 star-forming region. A 5'x5' map of the W3 IRS4 and W3
IRS5 region reveals strong water lines at half the positions in the map. The
relative strength of the Odin lines compared to previous observations by SWAS
suggests that we are seeing water emission from an extended region. Across much
of the map the lines are double-peaked, with an absorption feature at -39 km/s;
however, some positions in the map show a single strong line at -43 km/s. We
interpret the double-peaked lines as arising from optically thick,
self-absorbed water emission near the W3 IRS5, while the narrower blue-shifted
lines originate in emission near W3 IRS4. In this model, the unusual appearance
of the spectral lines across the map results from a coincidental agreement in
velocity between the emission near W3 IRS4 and the blue peak of the more
complex lines near W3 IRS5. The strength of the water lines near W3 IRS4
suggests we may be seeing water emission enhanced in a photon-dominated region.Comment: Accepted to A&A Letters as part of the special Odin issue; 4 page
First detection of NH3 (1,0 - 0,0) from a low mass cloud core: On the low ammonia abundance of the rho Oph A core
Odin has successfully observed the molecular core rho Oph A in the 572.5 GHz
rotational ground state line of ammonia, NH3 (J,K = 1,0 - 0,0). The
interpretation of this result makes use of complementary molecular line data
obtained from the ground (C17O and CH3OH) as part of the Odin preparatory work.
Comparison of these observations with theoretical model calculations of line
excitation and transfer yields a quite ordinary abundance of methanol, X(CH3OH)
= 3e-9. Unless NH3 is not entirely segregated from C17O and CH3OH, ammonia is
found to be significantly underabundant with respect to typical dense core
values, viz. X(NH3) = 8e-10.Comment: 4 pages, 2 figures, 2 tables, to appear in Astron. Astrophys. Letter
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