1,310 research outputs found
Shot noise in a diffusive F-N-F spin valve
Fluctuations of electric current in a spin valve consisting of a diffusive
conductor connected to ferromagnetic leads and operated in the giant
magnetoresistance regime are studied. It is shown that a new source of
fluctuations due to spin-flip scattering enhances strongly shot noise up to a
point where the Fano factor approaches the full Poissonian value.Comment: 5 pages, 3 figure
Involvement of Plasmodium falciparum protein kinase CK2 in the chromatin assembly pathway
<p>Abstract</p> <p>Background</p> <p>Protein kinase CK2 is a pleiotropic serine/threonine protein kinase with hundreds of reported substrates, and plays an important role in a number of cellular processes. The cellular functions of <it>Plasmodium falciparum </it>CK2 (PfCK2) are unknown. The parasite's genome encodes one catalytic subunit, PfCK2α, which we have previously shown to be essential for completion of the asexual erythrocytic cycle, and two putative regulatory subunits, PfCK2β1 and PfCK2β2.</p> <p>Results</p> <p>We now show that the genes encoding both regulatory PfCK2 subunits (PfCK2β1 and PfCK2β2) cannot be disrupted. Using immunofluorescence and electron microscopy, we examined the intra-erythrocytic stages of transgenic parasite lines expressing hemagglutinin (HA)-tagged catalytic and regulatory subunits (HA-CK2α, HA-PfCK2β1 or HA-PfCK2β2), and localized all three subunits to both cytoplasmic and nuclear compartments of the parasite. The same transgenic parasite lines were used to purify PfCK2β1- and PfCK2β2-containing complexes, which were analyzed by mass spectrometry. The recovered proteins were unevenly distributed between various pathways, with a large proportion of components of the chromatin assembly pathway being present in both PfCK2β1 and PfCK2β2 precipitates, implicating PfCK2 in chromatin dynamics. We also found that chromatin-related substrates such as nucleosome assembly proteins (Naps), histones, and two members of the Alba family are phosphorylated by PfCK2α <it>in vitro</it>.</p> <p>Conclusions</p> <p>Our reverse-genetics data show that each of the two regulatory PfCK2 subunits is required for completion of the asexual erythrocytic cycle. Our interactome study points to an implication of PfCK2 in many cellular pathways, with chromatin dynamics being identified as a major process regulated by PfCK2. This study paves the way for a kinome-wide interactomics-based approach to elucidate protein kinase function in malaria parasites.</p
Hidden vector dark matter
We show that dark matter could be made of massive gauge bosons whose
stability doesn't require to impose by hand any discrete or global symmetry.
Stability of gauge bosons can be guaranteed by the custodial symmetry
associated to the gauge symmetry and particle content of the model. The
particle content we consider to this end is based on a hidden sector made of a
vector multiplet associated to a non-abelian gauge group and of a scalar
multiplet charged under this gauge group. The hidden sector interacts with the
Standard Model particles through the Higgs portal quartic scalar interaction in
such a way that the gauge bosons behave as thermal WIMPS. This can lead easily
to the observed dark matter relic density in agreement with the other various
constraints, and can be tested experimentally in a large fraction of the
parameter space. In this model the dark matter direct detection rate and the
annihilation cross section can decouple if the Higgs portal interaction is
weak.Comment: 13 pages, 7 figures, JHEP published version (2009) + update of
section 7 (reference to arXiv:0912.4496
Confusing the extragalactic neutrino flux limit with a neutrino propagation limit
We study the possible suppression of the extragalactic neutrino flux due to a
nonstandard interaction during its propagation. In particular, we study
neutrino interaction with an ultra-light scalar field dark matter. It is shown
that the extragalactic neutrino flux may be suppressed by such an interaction,
leading to a new mechanism to reduce the ultra-high energy neutrino flux. We
study both the cases of non-self-conjugate as well as self-conjugate dark
matter. In the first case, the suppression is independent of the neutrino and
dark matter masses. We conclude that care must be taken when explaining limits
on the neutrino flux through source acceleration mechanisms only, since there
could be other mechanisms for the reduction of the neutrino flux.Comment: 15 pages, 4 figures. Important changes implemented. Abstract
modified. Conclusions remain. To be published in JCA
Density functional method for nonequilibrium electron transport
We describe an ab initio method for calculating the electronic structure,
electronic transport, and forces acting on the atoms, for atomic scale systems
connected to semi-infinite electrodes and with an applied voltage bias. Our
method is based on the density functional theory (DFT) as implemented in the
well tested Siesta approach (which uses non-local norm-conserving
pseudopotentials to describe the effect of the core electrons, and linear
combination of finite-range numerical atomic orbitals to describe the valence
states). We fully deal with the atomistic structure of the whole system,
treating both the contact and the electrodes on the same footing. The effect of
the finite bias (including selfconsistency and the solution of the
electrostatic problem) is taken into account using nonequilibrium Green's
functions. We relate the nonequilibrium Green's function expressions to the
more transparent scheme involving the scattering states. As an illustration,
the method is applied to three systems where we are able to compare our results
to earlier ab initio DFT calculations or experiments, and we point out
differences between this method and existing schemes. The systems considered
are: (1) single atom carbon wires connected to aluminum electrodes with
extended or finite cross section, (2) single atom gold wires, and finally (3)
large carbon nanotube systems with point defects.Comment: 18 pages, 23 figure
Trophic niche overlap between native freshwater mussels (Order: Unionida) and the invasive Corbicula fluminea
Freshwater mussels (Order Unionida) are highly threatened. Interspecific competition for food sources with invasive alien species is considered to be one of the factors responsible for their decline because successful invaders are expected to have wider trophic niches and more flexible feeding strategies than their native counterparts. In this study, carbon (δ13C: 13C/12C) and nitrogen (δ15N: 15N/14N) stable isotopes were used to investigate the trophic niche overlap between the native freshwater mussel species, Anodonta anatina, Potomida littoralis, and Unio delphinus, and the invasive bivalve Corbicula fluminea living in sympatry in the Tua basin (south-west Europe). The species presenting the widest trophic niches were C. fluminea and A. anatina, which indicate that they have broader diets than U. delphinus and P. littoralis. Nonetheless, all the species assimilated microphytobenthos, sediment organic matter, and detritus derived from vascular plants, although with interspecific variability in the assimilated proportions of each source. The trophic niche of the invasive species overlapped with the trophic niche of all the native species, with the extent varying between sites and according to the species. From the three native species analysed, Potomida littoralis may be at a higher risk for competition for food with C. fluminea in the Tua basin, if food sources become limited, because this native mussel presented the narrowest trophic niche across sites and the highest probability of overlapping with the trophic niche of C. fluminea. Given the global widespread distribution of C. fluminea, the implementation of management measures devoted to the control or even eradication of this invasive alien species should be a conservation priority given its potential for competition with highly threatened native freshwater mussels.V.M. and P.C. were supported by doctoral grants SFRH/BD/108298/2015 and SFRH/BD/131814/2017, respectively, from
the Portuguese Foundation for Science and Technology—FCT through
POPH/FSE funds. FCT also supported M.L.L. under contract
(2020.03608.CEECIND). This study was conducted within the project
FRESHCO – Multiple implications of invasive species on Freshwater
Mussel coextinction processes, supported by FCT and COMPETE
funds (contract: PTDC/AGRFOR/1627/2014). This study was also
supported by national funds through FCT – Foundation for Science
and Technology within the scope of UIDB/04423/2020 and
UIDP/04423/2020. We thank Jacinto Cunha for providing Figure 1.info:eu-repo/semantics/publishedVersio
Background model systematics for the Fermi GeV excess
The possible gamma-ray excess in the inner Galaxy and the Galactic center
(GC) suggested by Fermi-LAT observations has triggered a large number of
studies. It has been interpreted as a variety of different phenomena such as a
signal from WIMP dark matter annihilation, gamma-ray emission from a population
of millisecond pulsars, or emission from cosmic rays injected in a sequence of
burst-like events or continuously at the GC. We present the first comprehensive
study of model systematics coming from the Galactic diffuse emission in the
inner part of our Galaxy and their impact on the inferred properties of the
excess emission at Galactic latitudes and 300 MeV to 500
GeV. We study both theoretical and empirical model systematics, which we deduce
from a large range of Galactic diffuse emission models and a principal
component analysis of residuals in numerous test regions along the Galactic
plane. We show that the hypothesis of an extended spherical excess emission
with a uniform energy spectrum is compatible with the Fermi-LAT data in our
region of interest at CL. Assuming that this excess is the extended
counterpart of the one seen in the inner few degrees of the Galaxy, we derive a
lower limit of ( CL) on its extension away from the GC. We
show that, in light of the large correlated uncertainties that affect the
subtraction of the Galactic diffuse emission in the relevant regions, the
energy spectrum of the excess is equally compatible with both a simple broken
power-law of break energy GeV, and with spectra predicted by the
self-annihilation of dark matter, implying in the case of final
states a dark matter mass of GeV.Comment: 65 pages, 28 figures, 7 table
An investigation of the potential application of chitosan/aloe-based membranes for regenerative medicine
A significant number of therapeutics derived from natural polymers and plants have been developed to
replace or to be used in conjunction with existing dressing products. The use of the therapeutic properties
of aloe vera could be very useful in the creation of active wound dressing materials. The present work was
undertaken to examine issues concerning structural features, topography, enzymatic degradation behavior,
antibacterial activity and cellular response of chitosan/aloe vera-based membranes. The chitosan/aloe
vera-based membranes that were developed displayed satisfactory degradation, roughness, wettability
and mechanical properties. A higher antibacterial potency was displayed by the blended membranes.
Moreover, in vitro assays demonstrated that these blended membranes have good cell compatibility with
primary human dermal fibroblasts. The chitosan/aloe vera-based membranes might be promising wound
dressing materials.The authors acknowledge financial support from the Portuguese Foundation for Science and Technology (grants SFRH/BPD/45307/2008 and SFRH/BD/64601/2009), the "Fundo Social Europeu", and the "Programa Diferencial de Potencial Humano". This work was partially supported by the FEDER through POCTEP 0330_IBEROMARE_1_P
Adsorption of mono- and multivalent cat- and anions on DNA molecules
Adsorption of monovalent and multivalent cat- and anions on a deoxyribose
nucleic acid (DNA) molecule from a salt solution is investigated by computer
simulation. The ions are modelled as charged hard spheres, the DNA molecule as
a point charge pattern following the double-helical phosphate strands. The
geometrical shape of the DNA molecules is modelled on different levels ranging
from a simple cylindrical shape to structured models which include the major
and minor grooves between the phosphate strands. The densities of the ions
adsorbed on the phosphate strands, in the major and in the minor grooves are
calculated. First, we find that the adsorption pattern on the DNA surface
depends strongly on its geometrical shape: counterions adsorb preferentially
along the phosphate strands for a cylindrical model shape, but in the minor
groove for a geometrically structured model. Second, we find that an addition
of monovalent salt ions results in an increase of the charge density in the
minor groove while the total charge density of ions adsorbed in the major
groove stays unchanged. The adsorbed ion densities are highly structured along
the minor groove while they are almost smeared along the major groove.
Furthermore, for a fixed amount of added salt, the major groove cationic charge
is independent on the counterion valency. For increasing salt concentration the
major groove is neutralized while the total charge adsorbed in the minor groove
is constant. DNA overcharging is detected for multivalent salt. Simulations for
a larger ion radii, which mimic the effect of the ion hydration, indicate an
increased adsorbtion of cations in the major groove.Comment: 34 pages with 14 figure
- …