7,818 research outputs found
Tuning of tetrahedrality in a silicon potential yields a series of monatomic (metal-like) glassformers of very high fragility
We obtain monatomic glass formers in simulations by modifying the tetrahedral
character in a silicon potential to explore a triple point zone between
potentials favoring diamond (dc) and bcc crystals. dc crystallization is always
preceded by a polyamorphic transformation of the liquid, and is frustrated when
the Kauzmann temperature of the high temperature liquid intersects the
liquid-liquid coexistence line. The glass forming liquids are extraordinarily
fragile. Our results suggest that Si and Ge liquids may be vitrified at a
pressure close to the diamond-beta-tin-liquid triple point.Comment: 12 pages, including 3 figures. This revised version covers the same
as the original submission plus a discussion of the effect of the
polyamorphic transformation on the glass formation ability of the tetrahedral
liquids studie
Constraints on coupled dark energy using CMB data from WMAP and SPT
We consider the case of a coupling in the dark cosmological sector, where a
dark energy scalar field modifies the gravitational attraction between dark
matter particles. We find that the strength of the coupling {\beta} is
constrained using current Cosmic Microwave Background (CMB) data, including
WMAP7 and SPT, to be less than 0.063 (0.11) at 68% (95%) confidence level.
Further, we consider the additional effect of the CMB-lensing amplitude,
curvature, effective number of relativistic species and massive neutrinos and
show that the bound from current data on {\beta} is already strong enough to be
rather stable with respect to any of these variables. The strongest effect is
obtained when we allow for massive neutrinos, in which case the bound becomes
slightly weaker, {\beta} < 0.084(0.14). A larger value of the effective number
of relativistic degrees of freedom favors larger couplings between dark matter
and dark energy as well as values of the spectral index closer to 1. Adding the
present constraints on the Hubble constant, as well as from baryon acoustic
oscillations and supernovae Ia, we find {\beta} < 0.050(0.074). In this case we
also find an interesting likelihood peak for {\beta} = 0.041 (still compatible
with 0 at 1{\sigma}). This peak comes mostly from a slight difference between
the Hubble parameter HST result and the WMAP7+SPT best fit. Finally, we show
that forecasts of Planck+SPT mock data can pin down the coupling to a precision
of better than 1% and detect whether the marginal peak we find at small non
zero coupling is a real effect.Comment: 22 pages, 17 figure
Role of magnetic resonance imaging in the detection and characterization of solid pancreatic nodules: an update
Pancreatic ductal adenocarcinoma is the most common malignant tumor of the pancreas. The remaining pancreatic tumors are a diverse group of pancreatic neoplasms that comprises cystic pancreatic neoplasms, endocrine tumors and other uncommon pancreatic tumors. Due to the excellent soft tissue contrast resolution, magnetic resonance imaging (MRI) is frequently able to readily separate cystic from noncystic tumors. Cystic tumors are often easy to diagnose with MRI; however, noncystic non-adenocarcinoma tumors may show a wide spectrum of imaging features, which can potentially mimic ductal adenocarcinoma. MRI is a reliable technique for the characterization of pancreatic lesions. The implementation of novel motion-resistant pulse sequences and respiratory gating techniques, as well as the recognized benefits of MR cholangiopancreatography, make MRI a very accurate examination for the evaluation of pancreatic masses. MRI has the distinctive ability of non-invasive assessment of the pancreatic ducts, pancreatic parenchyma, neighbouring soft tissues, and vascular network in one examination. MRI can identify different characteristics of various solid pancreatic lesions, potentially allowing the differentiation of adenocarcinoma from other benign and malignant entities. In this review we describe the MRI protocols and MRI characteristics of various solid pancreatic lesions. Recognition of these characteristics may establish the right diagnosis or at least narrow the differential diagnosis, thus avoiding unnecessary tests or procedures and permitting better management
Magneto-elastic effects and magnetization plateaus in two dimensional systems
We show the importance of both strong frustration and spin-lattice coupling
for the stabilization of magnetization plateaus in translationally invariant
two-dimensional systems. We consider a frustrated spin-1/2 Heisenberg model
coupled to adiabatic phonons under an external magnetic field. At zero
magnetization, simple structures with two or at most four spins per unit cell
are stabilized, forming dimers or plaquettes, respectively. A much
richer scenario is found in the case of magnetization , where larger
unit cells are formed with non-trivial spin textures and an analogy with the
corresponding classical Ising model is detectable. Specific predictions on
lattice distortions and local spin values can be directly measured by X-rays
and Nuclear Magnetic Resonance experiments.Comment: 4 pages and 4 figure
Clarifying spherical collapse in coupled dark energy cosmologies
The spherical collapse model is often used to follow the evolution of
overdensities into the nonlinear regime. We describe the correct approach to be
used in coupled dark energy cosmologies, where a fifth force, different from
gravity and mediated by the dark energy scalar field, influences the collapse.
We reformulate the spherical collapse description by deriving it directly from
the set of nonlinear hydrodynamical Navier Stokes equations. By comparing with
the corresponding relativistic equations, we show how the fifth force should be
taken into account within the spherical collapse picture and clarify the
problems arising when an inhomogeneous scalar field is considered within a
spherical collapse picture. We then apply our method to the case of coupled
quintessence, where the fifth force acts among cold dark matter particles, and
to growing neutrino quintessence, where the fifth force acts between neutrinos.
Furthermore, we review this method when applied to standard cosmologies and
apply our analysis to minimally coupled quintessence and check past results for
early dark energy parametrizations.Comment: 16 pages, 13 figures, published in Physical Review D, minor changes
and correction
Testing coupled dark energy with next-generation large-scale observations
Coupling dark energy to dark matter provides one of the simplest way to
effectively modify gravity at large scales without strong constraints from
local (i.e. solar system) observations. Models of coupled dark energy have been
studied several times in the past and are already significantly constrained by
cosmic microwave background experiments. In this paper we estimate the
constraints that future large-scale observations will be able to put on the
coupling and in general on all the parameters of the model. We combine cosmic
microwave background, tomographic weak lensing, redshift distortions and power
spectrum probes. We show that next-generation observations can improve the
current constraint on the coupling to dark matter by two orders of magnitude;
this constraint is complementary to the current solar-system bounds on a
coupling to baryons.Comment: 18 pages, 12 figs, 8 table
Detection of bovine papillomavirus type 2 in the peripheral blood of cattle with urinary bladder tumours: possible biological role
Bovine papillomavirus type 2 (BPV-2) infection has been associated with urinary bladder tumours in adult cattle grazing on bracken fern-infested land. In this study, we investigated the
simultaneous presence of BPV-2 in whole blood and urinary bladder tumours of adult cattle in an attempt to better understand the biological role of circulating BPV-2. Peripheral blood samples were collected from 78 cattle clinically suffering from a severe chronic enzootic haematuria. Circulating BPV-2 DNA was detected in 61 of them and in two blood samples from healthy cows. Fifty of the affected animals were slaughtered at public slaughterhouses and neoplastic proliferations in the urinary bladder were detected in all of them. BPV-2 DNA was amplified and sequenced in 78% of urinary bladder tumour samples and in 38.9% of normal samples as a control. Circulating episomal BPV-2 DNA was detected in 78.2% of the blood samples. Simultaneous presence of BPV-2 DNA in neoplastic bladder and blood samples was detected in 37 animals. Specific viral E5 mRNA and E5 oncoprotein were also detected in blood by RT-PCR
and Western blot/immunocytochemistry, respectively. It is likely that BPV-2 can persist and be maintained in an active status in the bloodstream, in particular in the lymphocytes, as a reservoir of viral infection that, in the presence of co-carcinogens, may cause the development of urinary bladder tumours
Dispersion for the Schr\"odinger Equation on Networks
In this paper we consider the Schr\"odinger equation on a network formed by a
tree with the last generation of edges formed by infinite strips. We give an
explicit description of the solution of the linear Schr\"odinger equation with
constant coefficients. This allows us to prove dispersive estimates, which in
turn are useful for solving the nonlinear Schr\"odinger equation. The proof
extends also to the laminar case of positive step-function coefficients having
a finite number of discontinuities.Comment: 16 pages, 2 figure
Isolation and characterisation of polychlorinated biphenyl (PCB) degrading fungi from a historically contaminated soil
<p>Abstract</p> <p>Background</p> <p>Polychlorinated biphenyls (PCBs) are widespread toxic pollutants. Bioremediation might be an effective, cost competitive and environment-friendly solution for remediating environmental matrices contaminated by PCBs but it is still unsatisfactory, mostly for the limited biodegradation potential of bacteria involved in the processes. Very little is known about mitosporic fungi potential in PCB bioremediation and their occurrence in actual site historically contaminated soils. In the present study, we characterised the native mycoflora of an aged dump site soil contaminated by about 0.9 g kg<sup>-1 </sup>of Aroclor 1260 PCBs and its changing after aerobic biotreatment with a commercial complex source of bacteria and fungi. Fungi isolated from the soil resulting from 120 days of treatment were screened for their ability to adsorb or metabolise 3 target PCBs.</p> <p>Results</p> <p>The original contaminated soil contained low loads of few fungal species mostly belonging to the Scedosporium, Penicillium and Aspergillus genera. The fungal load and biodiversity generally decreased throughout the aerobic treatment. None of the 21 strains isolated from the treated soil were able to grow on biphenyl (200 mg L<sup>-1</sup>) or a mixture of 2-chlorobiphenyl, 4,4'-dichlorobiphenyl and 2,2',5,5'-tetrachlorobiphenyl (20 mg L<sup>-1 </sup>each) as sole carbon sources. However, 16 of them grew in a mineral medium containing the same PCBs mixture and glucose (10 g L<sup>-1</sup>). Five of the 6 isolates, which displayed the faster and more extensive growth under the latter conditions, were found to degrade the 3 PCBs apparently without the involvement of ligninolytic enzymes; they were identified as Penicillium chrysogenum, Scedosporium apiospermum, Penicillium digitatum and Fusarium solani. They are the first PCB degrading strains of such species reported so far in the literature.</p> <p>Conclusion</p> <p>The native mycoflora of the actual site aged heavily contaminated soil was mainly constituted by genera often reported as able to biodegrade organopollutants. It was generally remarkably reduced after the biotreatment, which however resulted in the selection of few mitosporic fungal species able to biodegrade PCBs. This is the first study in which an extensive characterisation of the cultivable indigenous mycoflora of an actual site aged PCB contaminated soil, as well as its changes upon soil bioremediation treatment, was conducted. Moreover, this is the first paper in which 5 strains ascribable to 4 mitosporic species able to biodegrade PCB are reported in the literature.</p
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