196 research outputs found
Electroformation in a flow chamber with solution exchange as a means of preparation of flaccid giant vesicles
A recently described technique (Estes and Mayer, Biochim. Biophys. Acta 1712
(2005) 152--160) for the preparation of giant unilamellar vesicles (GUVs) in
solutions with high ionic strength is examined. By observing a series of
osmotic swellings followed by vesicle bursts upon a micropipette transfer of a
single POPC GUV from a sucrose solution into an isoosmolar glycerol solution, a
value for the permeability of POPC membrane for glycerol, P = (2.09+/-0.82) x
10^{-8} m/s, has been obtained. Based on this result, an alternative mechanism
is proposed for the observed exchange of vesicle interior. With modifications,
the method of Estes and Mayer is then applied to preparation of flaccid GUVs.Comment: 13 pages, 10 figures, accepted for publication in Colloids and
Surfaces B: Biointerface
Permeability of phospholipid membrane for small polar molecules determined from osmotic swelling of giant phospholipid vesicles
A method for determining permeability of phospholipid bilayer based on the
osmotic swelling of micrometer-sized giant unilamellar vesicles (GUVs) is
presented as an alternative to the two established techniques, dynamic light
scattering on liposome suspension, and electrical measurements on planar lipid
bilayers. In the described technique, an individual GUV is transferred using a
micropipette from a sucrose/glucose solution into an isomolar solution
containing the solute under investigation. Throughout the experiment, vesicle
cross-section is monitored and recorded using a digital camera mounted on a
phase-contrast microscope. Using a least-squares procedure for circle fitting,
vesicle radius R is computed from the recorded images of vesicle cross-section.
Two methods for determining membrane permeability from the obtained R(t)
dependence are described: the first one uses the slope of R(t) for a spherical
GUV, and the second one the R(t) dependence around the transition point at
which a flaccid vesicle transforms into a spherical one. We demonstrate that
both methods give consistent estimates for membrane permeability.Comment: 40 pages, 8 figures, to appear in Advances in Planar Lipid Membranes
and Liposomes vol. 1
First-Fit is Linear on Posets Excluding Two Long Incomparable Chains
A poset is (r + s)-free if it does not contain two incomparable chains of
size r and s, respectively. We prove that when r and s are at least 2, the
First-Fit algorithm partitions every (r + s)-free poset P into at most
8(r-1)(s-1)w chains, where w is the width of P. This solves an open problem of
Bosek, Krawczyk, and Szczypka (SIAM J. Discrete Math., 23(4):1992--1999, 2010).Comment: v3: fixed some typo
Law of corresponding states for osmotic swelling of vesicles
As solute molecules permeate into a vesicle due to a concentration difference
across its membrane, the vesicle swells through osmosis. The swelling can be
divided into two stages: (a) an "ironing" stage, where the volume-to-area ratio
of the vesicle increases without a significant change in its area; (b) a
stretching stage, where the vesicle grows while remaining essentially
spherical, until it ruptures. We show that the crossover between these two
stages can be represented as a broadened continuous phase transition.
Consequently, the swelling curves for different vesicles and different
permeating solutes can be rescaled into a single, theoretically predicted,
universal curve. Such a data collapse is demonstrated for giant unilamellar
POPC vesicles, osmotically swollen due to the permeation of urea, glycerol, or
ethylene glycol. We thereby gain a sensitive measurement of the solutes'
membrane permeability coefficients, finding a concentration-independent
coefficient for urea, while those of glycerol and ethylene glycol are found to
increase with solute concentration. In addition, we use the width of the
transition, as extracted from the data collapse, to infer the number of
independent bending modes that affect the thermodynamics of the vesicle in the
transition region.Comment: 10 page
Controlled trial on the effect of 10 days low-frequency repetitive transcranial magnetic stimulation (rTMS) on motor signs in Parkinson´s disease
[Abstract] We evaluated the effect of low-frequency rTMS
on motor signs in Parkinson’s disease (PD), under a doubleblind
placebo-controlled trial design. PD patients were randomly
assigned to received either real (n 5 9) or sham (n 5
9) rTMS for 10 days. Each session comprises two trains of
50 stimuli each delivered at 1 Hz and at 90% of daily rest
motor threshold using a large circular coil over the vertex.
The effect of the stimulation, delivered during the ON-period,
was evaluated during both ON and OFF periods. Tests were
carried out before and after the stimulation period, and again
1 week after. The effect of the stimulation was evaluated
through several gait variables (cadence, step amplitude, velocity,
the CVstride-time, and the turn time), hand dexterity,
and also the total and motor sections of the UPDRS. Only
the total and motor section of the UPDRS and the turn time
during gait were affected by the stimulation, the effect
appearing during either ON or OFF evaluation, and most
importantly, equally displayed in both real and sham group.
The rest of the variables were not influenced. We conclude
the protocol of stimulation used, different from most protocols
that apply larger amount of stimuli, but very similar to
some previously reported to have excellent results, has no
therapeutic value and should be abandoned. This contrasts
with the positive reported effects using higher frequency and
focal coils. Our work also reinforces the need for sham stimulation
when evaluating the therapeutic effect of
rTMS.Galicia. Consellería de Educación; 2007/000140-0Galicia. Consellería de Innovación, Industria e Comercio; PGIDIT06PXIC137004PNGalicia. Consellería de Economía e Industria; INCITE09137 379 PRMinisterio de Ciencia e Innovación; BFU2009-0816
On the Optimization of Broad-Band Photometry for Galaxy Evolution Studies
We have derived the uncertainties to be expected in the derivation of galaxy
physical properties (star formation history, age, metallicity, reddening) when
comparing broad-band photometry to the predictions of evolutionary synthesis
models. We have obtained synthetic colors for a large sample (9000) of
artificial galaxies assuming different star formation histories, ages,
metallicities, reddening values, and redshifts. The colors derived have been
perturbed by adopting different observing errors, and compared back to the
evolutionary synthesis models grouped in different sets. The comparison has
been performed using a combination of Monte Carlo simulations, a Maximum
Likelihood Estimator and Principal Component Analysis. After comparing the
input and derived output values we have been able to compute the uncertainties
and covariant degeneracies between the galaxy physical properties as function
of (1) the set of observables available, (2) the observing errors, and (3) the
galaxy properties themselves. In this work we have considered different sets of
observables, some of them including the standard Johnson/Cousins (UBVRI) and
Sloan Digital Sky Survey (SDSS) bands in the optical, the 2 Micron All Sky
Survey (2MASS) bands in the near-infrared, and the Galaxy Evolution Explorer
(GALEX) bands in the UV, at three different redshifts, z=0.0, 0.7, and 1.4.
This study is intended to represent a basic tool for the design of future
projects on galaxy evolution, allowing an estimate of the optimal band-pass
combinations and signal-to-noise ratios required for a given scientific
objective.Comment: 20 pages, 9 postscript figures, 3 tables, accepted for publication in
A
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