1,085 research outputs found
Surface Specific Kinetics of Lipid Vesicle Adsorption Measured with a Quartz Crystal Microbalance
AbstractWe have measured the kinetics of adsorption of small (12.5-nm radius) unilamellar vesicles onto SiO2, oxidized gold, and a self-assembled monolayer of methyl-terminated thiols, using a quartz crystal microbalance (QCM). Simultaneous measurements of the shift in resonant frequency and the change in energy dissipation as a function of time provide a simple way of characterizing the adsorption process. The measured parameters correspond, respectively, to adsorbed mass and to the mechanical properties of the adsorbed layer as it is formed. The adsorption kinetics are surface specific; different surfaces cause monolayer, bilayer, and intact vesicle adsorption. The formation of a lipid bilayer on SiO2 is a two-phase process in which adsorption of a layer of intact vesicles precedes the formation of the bilayer. This is, to our knowledge, the first direct evidence of intact vesicles as a precursor to bilayer formation on a planar substrate. On an oxidized gold surface, the vesicles adsorb intact. The intact adsorption of such small vesicles has not previously been demonstrated. Based on these results, we discuss the capacity of QCM measurements to provide information about the kinetics of formation and the properties of adsorbed layers
Generalised Moore spectra in a triangulated category
In this paper we consider a construction in an arbitrary triangulated
category T which resembles the notion of a Moore spectrum in algebraic
topology. Namely, given a compact object C of T satisfying some finite tilting
assumptions, we obtain a functor which "approximates" objects of the module
category of the endomorphism algebra of C in T. This generalises and extends a
construction of Jorgensen in connection with lifts of certain homological
functors of derived categories. We show that this new functor is well-behaved
with respect to short exact sequences and distinguished triangles, and as a
consequence we obtain a new way of embedding the module category in a
triangulated category. As an example of the theory, we recover Keller's
canonical embedding of the module category of a path algebra of a quiver with
no oriented cycles into its u-cluster category for u>1.Comment: 26 pages, improvement to exposition of the proof of Theorem 3.
Is the Sgr dSph a dark matter dominated system?
We study the evolution of possible progenitors of Sgr dSph}using several
numerical N-body simulations of different dwarf spheroidal galaxies both with
and without dark matter, as they orbit the Milky Way. The barionic and dark
components of the dwarfs were made obeying a Plummer and NFW potentials of one
million particles respectively. The Milky Way was modeled like a tree-component
rigid potential and the simulations were performed using a modified Gadget-2
code. We found that none of the simulated galaxies without dark matter
reproduced the physical properties observed in Sgr dSph, suggesting that, at
the beginning of its evolution, Sgr dSph might have been immersed in a dark
matter halo.
The simulations of progenitors immersed in dark matter halos suggest that Sgr
dSph at its beginning might have been an extended system, i.e. its Plummer
radius could have had a value approximated to 1.2 kpc or higher; furthermore,
this galaxy could have been immersed in a dark halo with a mass higher than
10^8 solar masses. These results are important for the construction of a model
of the formation of Sgr dSph.Comment: 13 pages, 6 figures, New Astronomy - accepte
Triangle-generation in topological D-brane categories
Tachyon condensation in topological Landau-Ginzburg models can generally be
studied using methods of commutative algebra and properties of triangulated
categories. The efficiency of this approach is demonstrated by explicitly
proving that every D-brane system in all minimal models of type ADE can be
generated from only one or two fundamental branes.Comment: 34 page
First mineralogical maps of 4 Vesta
Before Dawn arrived at 4 Vesta only very low spatial resolution (~50 km) albedo and color maps were available from HST data. Also ground-based color and spectroscopic data were utilized as a first attempt to map Vesta’s mineralogical diversity [1-4]. The VIR spectrometer [5] onboard Dawn has ac-quired hyperspectral data while the FC camera [6] ob-tained multi-color data of the Vestan surface at very high spatial resolutions, allowing us to map complex geologic, morphologic units and features. We here re-port about the results obtained from a preliminary global mineralogical map of Vesta, based on data from the Survey orbit. This map is part of an iterative map-ping effort; the map is refined with each improvement in resolution
Thermodynamic formalism for contracting Lorenz flows
We study the expansion properties of the contracting Lorenz flow introduced
by Rovella via thermodynamic formalism. Specifically, we prove the existence of
an equilibrium state for the natural potential for the contracting Lorenz flow and for in an interval
containing . We also analyse the Lyapunov spectrum of the flow in terms
of the pressure
Residual cognitive deficits 50 years after lead poisoning during childhood
The long term neurobehavioural consequences of childhood lead poisoning are not known. In this study adult subjects with a documented history of lead poisoning before age 4 and matched controls were examined with an abbreviated battery of neuropsychological tests including measures of attention, reasoning, memory, motor speed, and current mood. The subjects exposed to lead were inferior to controls on almost all of the cognitive tasks. This pattern of widespread deficits resembles that found in children evaluated at the time of acute exposure to lead rather than the more circumscribed pattern typically seen in adults exposed to lead. Despite having completed as many years of schooling as controls, the subjects exposed to lead were lower in lifetime occupational status. Within the exposed group, performance on the neuropsychological battery and occupational status were related, consistent with the presumed impact of limitations in neuropsychological functioning on everyday life. The results suggest that many subjects exposed to lead suffered acute encephalopathy in childhood which resolved into a chronic subclinical encephalopathy with associated cognitive dysfunction still evident in adulthood. These findings lend support to efforts to limit exposure to lead in childhood
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