494 research outputs found
Assessment of viral and non-viral gene transfer into adult rat brains using HSV-1, calcium phosphate and PEI-based methods
CNS gene transfer could provide new approaches to the modelling of neurodegenerative
diseases and devising potential therapies. One such disorder is Parkinson’s
disease (PD), in which dysfunction of several different metabolic processes
has been implicated. Here we review the literature on gene transfer systems
based on herpes simplex virus type 1 (HSV-1) and non-viral
polyethyleneimine (PEI) and calcium phosphate nanoparticle methods. We also
assess the usefulness of various CNS gene delivery methods and present some
of our own data to exemplify such usefulness. Our data result from vectors
stereotaxically introduced to the substantia nigra (SN) of adult rats and evaluated
1 week and/or 1 month post injection using histochemical methods to assess
recombinant Ăź-galactosidase enzyme activity. Gene transfer using PEI or calcium
phosphate-mediated transfections was observed for both methods and PEI was
comparable to that of HSV-1 amplicon. Our data show that the amplicon delivery
was markedly increased when packaged with a helper virus and was similar
to the expression profile achieved with a full-size replication-defective HSV-1
recombinant (8117/43). We also examine whether PEI or HSV-1 amplicon-mediated
gene transfer could facilitate assessment of the biological effects induced
by a dominant negative FGF receptor-1 mutant to model the reduced FGF signalling
thought to occur in Parkinson’s disease
Can dark matter be a Bose-Einstein condensate?
We consider the possibility that the dark matter, which is required to
explain the dynamics of the neutral hydrogen clouds at large distances from the
galactic center, could be in the form of a Bose-Einstein condensate. To study
the condensate we use the non-relativistic Gross-Pitaevskii equation. By
introducing the Madelung representation of the wave function, we formulate the
dynamics of the system in terms of the continuity equation and of the
hydrodynamic Euler equations. Hence dark matter can be described as a
non-relativistic, Newtonian Bose-Einstein gravitational condensate gas, whose
density and pressure are related by a barotropic equation of state. In the case
of a condensate with quartic non-linearity, the equation of state is polytropic
with index . To test the validity of the model we fit the Newtonian
tangential velocity equation of the model with a sample of rotation curves of
low surface brightness and dwarf galaxies, respectively. We find a very good
agreement between the theoretical rotation curves and the observational data
for the low surface brightness galaxies. The deflection of photons passing
through the dark matter halos is also analyzed, and the bending angle of light
is computed. The bending angle obtained for the Bose-Einstein condensate is
larger than that predicted by standard general relativistic and dark matter
models. Therefore the study of the light deflection by galaxies and the
gravitational lensing could discriminate between the Bose-Einstein condensate
dark matter model and other dark matter models.Comment: 20 pages, 7 figures, accepted for publication in JCAP, references
adde
HMG1A and PPARG are differently expressed in the liver of fat and lean broilers
The expression of nine functional candidates for QT abdominal fat weight and relative abdominal fat content was investigated by real-time polymerase chain reaction (PCR) in the liver, adipose tissue, colon, muscle, pituitary gland and brain of broilers. The high mobility group AT-hook 1 (HMG1A) gene was up-regulated in liver with a ratio of means of 2.90 (P ≤ 0.01) in the «fatty» group (relative abdominal fat content 3.5 ± 0.18%, abdominal fat weight 35.4 ± 6.09 g) relative to the «lean» group (relative abdominal fat content 1.9 ± 0.56%, abdominal fat weight 19.2 ± 5.06 g). Expression of this gene was highly correlated with the relative abdominal fat content (0.70, P ≤ 0.01) and abdominal fat weight (0.70, P ≤ 0.01). The peroxisome proliferator-activated receptor gamma (PPARG) gene was also up-regulated in the liver with a ratio of means of 3.34 (P ≤ 0.01) in the «fatty» group relative to the «lean» group. Correlation of its expression was significant with both the relative abdominal fat content (0.55, P ≤ 0.05) and the abdominal fat weight (0.57, P ≤ 0.01). These data suggest that the HMG1A and PPARG genes were candidate genes for abdominal fat deposition in chickens. Searching of rSNPs in regulatory regions of the HMG1A and PPARG genes could provide a tool for gene-assisted selection
Classical big-bounce cosmology: dynamical analysis of a homogeneous and irrotational Weyssenhoff fluid
A dynamical analysis of an effective homogeneous and irrotational Weyssenhoff
fluid in general relativity is performed using the 1+3 covariant approach that
enables the dynamics of the fluid to be determined without assuming any
particular form for the space-time metric. The spin contributions to the field
equations produce a bounce that averts an initial singularity, provided that
the spin density exceeds the rate of shear. At later times, when the spin
contribution can be neglected, a Weyssenhoff fluid reduces to a standard
cosmological fluid in general relativity. Numerical solutions for the time
evolution of the generalised scale factor in spatially-curved models are
presented, some of which exhibit eternal oscillatory behaviour without any
singularities. In spatially-flat models, analytical solutions for particular
values of the equation-of-state parameter are derived. Although the scale
factor of a Weyssenhoff fluid generically has a positive temporal curvature
near a bounce, it requires unreasonable fine tuning of the equation-of-state
parameter to produce a sufficiently extended period of inflation to fit the
current observational data.Comment: 34 pages, 18 figure
Depletion-Driven Morphological Control of Bundled Actin Networks
The actin cytoskeleton is a semiflexible biopolymer network whose morphology
is controlled by a wide range of biochemical and physical factors. Actin is
known to undergo a phase transition from a single-filament state to a bundled
state by the addition of polyethylene glycol (PEG) molecules in sufficient
concentration. While the depletion interaction experienced by these biopolymers
is well-known, the effect of changing the molecular weight of the depletant is
less well understood. Here, we experimentally identify a phase transition in
solutions of actin from networks of filaments to networks of bundles by varying
the molecular weight of PEG polymers, while holding the concentration of these
PEG polymers constant. We examine the states straddling the phase transition in
terms of micro and macroscale properties. We find that the mesh size, bundle
diameter, persistence length, and intra-bundle spacing between filaments across
the line of criticality do not show significant differences, while the
relaxation time, storage modulus, and degree of bundling change between the two
states do show significant differences. Our results demonstrate the ability to
tune actin network morphology and mechanics by controlling depletant size, a
property which could be exploited to develop actin-based materials with
switchable rigidity.Comment: 22 pages, 10 figures. Authors James Clarke and Francis Cavanna
contributed equally; Changes: Added modeling work, extended dynamic light
scattering analysi
Friction and wear properties of nano-Si<inf>3</inf>N<inf>4</inf>/nano-SiC composite under nanolubricated conditions
Friction and wear properties of nano-Si3N4/nano-SiC composite were studied under nanolubricated conditions. Mineral oil mixed with nanoparticles of diamond was used as lubricant. A friction coefficient of 0.043 and a wear coefficient of 4.2Ă—10-7 were obtained for nano-Si3N4/nano-SiC composite under normal load of 600 N with mineral oil + 0.5 wt% nanodiamond, whereas a friction coefficient of 0.077 and a wear coefficient of 10.3Ă—10-7 were obtained for nano-Si3N4/nano-SiC composite under normal load of 600 N with mineral oil. 3D surface profilometer was used to study the surface morphology of wear scars. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies were conducted to illustrate reduction in friction and wear
Friction and wear phenomena of vegetable oil based lubricants with additives at severe sliding wear conditions
The tribological responses of palm oil and soybean oil, combined with two commercial antiwear
additives (zinc dialkyl dithiophosphate and boron compound), were investigated at a lubricant
temperature of 100 °C and under severe contact conditions in a reciprocating sliding contact. The
friction coefficient of palm oil with zinc dialkyl dithiophosphate was closest to the commercial
mineral engine oil, with a 2% difference. The soybean oil with zinc dialkyl dithiophosphate
produced a 57% improvement in wear resistance compared to its pure oil state. The existence of
boron nitride in vegetable oils was only responsive in reduction of wear rather than friction. The
response of commercial antiwear additives with vegetable oils showed a potential for the future
improvement in the performance of vegetable oils
Two-dimensional finite element simulation of fracture and fatigue behaviours of alumina microstructures for hip prosthesis
This paper describes a two-dimensional (2D) finite element simulation for
fracture and fatigue behaviours of pure alumina microstructures such as those
found at hip prostheses. Finite element models are developed using actual Al2O3
microstructures and a bilinear cohesive zone law. Simulation conditions are
similar to those found at a slip zone in a dry contact between a femoral head
and an acetabular cup of hip prosthesis. Contact stresses are imposed to
generate cracks in the models. Magnitudes of imposed stresses are higher than
those found at the microscopic scale. Effects of microstructures and contact
stresses are investigated in terms of crack formation. In addition, fatigue
behaviour of the microstructure is determined by performing simulations under
cyclic loading conditions. It is shown that crack density observed in a
microstructure increases with increasing magnitude of applied contact stress.
Moreover, crack density increases linearly with respect to the number of
fatigue cycles within a given contact stress range. Meanwhile, as applied
contact stress increases, number of cycles to failure decreases gradually.
Finally, this proposed finite element simulation offers an effective method for
identifying fracture and fatigue behaviours of a microstructure provided that
microstructure images are available
Coupled dark energy: Towards a general description of the dynamics
In dark energy models of scalar-field coupled to a barotropic perfect fluid,
the existence of cosmological scaling solutions restricts the Lagrangian of the
field \vp to p=X g(Xe^{\lambda \vp}), where X=-g^{\mu\nu} \partial_\mu \vp
\partial_\nu \vp /2, is a constant and is an arbitrary function.
We derive general evolution equations in an autonomous form for this Lagrangian
and investigate the stability of fixed points for several different dark energy
models--(i) ordinary (phantom) field, (ii) dilatonic ghost condensate, and
(iii) (phantom) tachyon. We find the existence of scalar-field dominant fixed
points (\Omega_\vp=1) with an accelerated expansion in all models
irrespective of the presence of the coupling between dark energy and dark
matter. These fixed points are always classically stable for a phantom field,
implying that the universe is eventually dominated by the energy density of a
scalar field if phantom is responsible for dark energy. When the equation of
state w_\vp for the field \vp is larger than -1, we find that scaling
solutions are stable if the scalar-field dominant solution is unstable, and
vice versa. Therefore in this case the final attractor is either a scaling
solution with constant \Omega_\vp satisfying 0<\Omega_\vp<1 or a
scalar-field dominant solution with \Omega_\vp=1.Comment: 21 pages, 5 figures; minor clarifications added, typos corrected and
references updated; final version to appear in JCA
Dark energy problem: from phantom theory to modified Gauss-Bonnet gravity
The solution of dark energy problem in the models without scalars is
presented. It is shown that late-time accelerating cosmology may be generated
by the ideal fluid with some implicit equation of state. The universe evolution
within modified Gauss-Bonnet gravity is considered. It is demonstrated that
such gravitational approach may predict the (quintessential, cosmological
constant or transient phantom) acceleration of the late-time universe with
natural transiton from deceleration to acceleration (or from non-phantom to
phantom era in the last case).Comment: LaTeX 8 pages, prepared for the Proceedings of QFEXT'05, minor
correctons, references adde
- …