988 research outputs found
Compacton formation under Allen--Cahn dynamics
We study the solutions of a generalized Allen-Cahn equation deduced from a
Landau energy functional, endowed with a non-constant higher order stiffness.
We analytically solve the stationary problem and deduce the existence of
so-called compactons, namely, connections on a finite interval between the two
phases. The dynamics problem is numerically solved and compacton formation is
described
Temperature-driven volume transition in hydrogels: phase--coexistence and interface localization
We study volume transition phenomenon in hydrogels within the framework of
Flory-Rehner thermodynamic modelling; we show that starting from different
models for the Flory parameter different conclusions can be achieved, in terms
of admissible coexisting equilibria of the system. In particular, with explicit
reference to a one-dimensional problem we establish the ranges of both
temperature and traction which allow for the coexistence of a swollen and a
shrunk phase. Through consideration of an augmented Flory-Rehner free-energy,
which also accounts for the gradient of volume changes, we determine the
position of the interface between the coexisting phases, and capture the
connection profile between them
A simple and sensitive gas chromatography–electron capture detection method for analyzing perfluorocarbon tracers in soil gas samples for storage of carbon dioxide
Co-injection of a conservative tracer during the geological sequestration of CO2 can imprint a marker to the injected gas that can be easily recognized during soil gas surveys in case of CO2 leakage from the reservoir toward the surface.
In this work, an ultra-trace detection method, based on gas chromatography with electron capture detection for analyzing perfluorocarbon tracers (PFTs) in soil gas samples was optimized.
Three totally fluorinated cycloalcane compounds consisting of five and six atom carbon rings were selected for this purpose. We evaluated the feasibility of collecting PFTs on adsorbent tube packed with a commercial graphitized carbon black (Carbotrap™ 100) sampling 2 L of soil gas. The sorbent tubes were then analyzed by using a two-stage thermal desorption process.
The developed method allows to quickly determine these compounds at very low fL/L level, method identification limits ranged from 1.3 to 5.8 fL/L. Moreover, it shows good precision, evaluated by within-day and between-day studies.
A preliminary survey of the PFT soil gas background concentrations, conducted by analyzing some soil gas samples collected in two different areas in Central Italy and in the Po Plain, ascertained the PFT background concentration lower than MIL
Kink Localization under Asymmetric Double-Well Potential
We study diffuse phase interfaces under asymmetric double-well potential
energies with degenerate minima and demonstrate that the limiting sharp
profile, for small interface energy cost, on a finite space interval is in
general not symmetric and its position depends exclusively on the second
derivatives of the potential energy at the two minima (phases). We discuss an
application of the general result to porous media in the regime of solid-fluid
segregation under an applied pressure and describe the interface between a
fluid-rich and a fluid-poor phase. Asymmetric double-well potential energies
are also relevant in a very different field of physics as that of Brownian
motors. An intriguing analogy between our result and the direction of the dc
soliton current in asymmetric substrate driven Brownian motors is pointed out
Aortic regurgitation in athletes. Pieces of the puzzle we have so far omitted
The prevalence of valvular heart disease (VHD) rises with age, reaching 11.7% in individuals older than 75 years.1 In young individuals, VHD is usually related to the presence of a congenital valve abnormality, as bicuspid aortic valve (BAV) or mitral valve prolapse. This is also the case for athletes, where in the presence of these abnormalities few restrictions exist in eligibility
for competitive sports participation, even if a strict follow-up would be desirable. BAV is the most common congenital valve abnormality (1%) found in the general population and in athletes. BAV is more prevalent in males and it can lead to aortic regurgitation (AR), aortic stenosis and/or aortic root dilation. At present, no definitive studies have proved that intensive
sports participation could worsen the progression of BAV and limited data are available on athletes
Stability of the stationary solutions of the Allen-Cahn equation with non-constant stiffness
We study the solutions of a generalized Allen-Cahn equation deduced from a
Landau energy functional, endowed with a non-constant higher order stiffness.
We assume the stiffness to be a positive function of the field and we discuss
the stability of the stationary solutions proving both linear and local
non-linear stability
Elevated serum levels of macrophage migration inhibitory factor and stem cell growth factor β in patients with idiopathic and systemic sclerosis associated pulmonary arterial hypertension.
Pulmonary arterial hypertension (PAH) can be idiopathic or secondary to autoimmune diseases, and it represents one of the most threatening complications of systemic sclerosis (SSc). Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine with proinflammatory functions that appears to be involved in the pathogenesis of hypoxia-induced PH. In SSc patients, high serum levels of MIF have been associated with the development of ulcers and PAH. Stem cell growth factor β (SCGF β) is a human growth factor that, together with MIF, is involved in the pathogenesis of chronic spinal cord injury. The aim of our study was to measure serum levels of MIF in patients with idiopathic and SSc-associated PAH. We enrolled 13 patients with idiopathic PAH and 15 with SSc-associated PAH. We also selected 14 SSc patients without PAH and 12 normal healthy controls, matched for sex and age. PAH was confirmed by right hearth catheterism (mPAP>25 mmHg). MIF and SCGF β levels were measured by ELISA. We found significantly higher circulating levels of MIF and of SCGF β in patients with idiopathic PAH (P=0.03 and P=0.004) and with PAH secondary to SSc (P=0.018 and P=0.023) compared to SSc patients without PAH. Higher levels of MIF were found in those patients with an higher New York Heart Association (NYHA) class (P=0.03). We can hypothesize that MIF and SCGF β are able to play a role in PAH, both idiopathic or secondary, and in the future they may be evaluated as useful biomarkers and prognostic factors for this serious vascular disease
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