Mixed Variational Principles in Nondissipative Coupled Thermoelasticity

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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

Generalized Hooke's law for isotropic second gradient materials

In the spirit of Germain the most general objective stored elastic energy for a second gradient material is deduced using a literature result of Fortun\'e & Vall\'ee. Linear isotropic constitutive relations for stress and hyperstress in terms of strain and strain-gradient are then obtained proving that these materials are characterized by seven elastic moduli and generalizing previous studies by Toupin, Mindlin and Sokolowski. Using a suitable decomposition of the strain-gradient, it is found a necessary and sufficient condition, to be verified by the elastic moduli, assuring positive definiteness of the stored elastic energy. The problem of warping in linear torsion of a prismatic second gradient cylinder is formulated, thus obtaining a possible measurement procedure for one of the second gradient elastic moduli.Comment: 20 page

The application of soil gas technique to geothermal exploration:study of “hidden” potential geothermal systems

Geochemical studies were conducted using soil-gas and flux surveyings for locating both permeable zones in buried reservoirs and the presence of possible gaseous haloes linked to active geothermal systems. In this work we focused our interest on the distribution of soil-gas concentrations (Rn, Th, He, H2, O2, N2, CO2, CH4 and H2S) in the soil air of the Tetitlan area (Nayarit, Mexico) considered a potential thermal field and characterized by scarcity of surface manifestations. A total of 154 soil-gas samples and 346 CO2 and CH4 flux measurements were collected in an area of about 80 square kilometres. The performed soil-gas and flux geochemical surveys highlighted a general rising patterns linked to local fault system, with the important implication that the highest CO2 and CH4 fluxes, as well as Rn concentrations, could be used in undeveloped geothermal systems to identify main upflow regions and areas of increased and deep permeability

The application of soil gas technique to geothermal exploration:

Geochemical studies were conducted throughout soil gas and flux surveying for locating both permeable zones in buried reservoirs and the presence of possible gaseous haloes linked to active geothermal systems. In this work we focused our interest on the distribution of soil gas concentrations (Rn, Th, He, H2, O2, N2, CO2, CH4 and H2S) in the soil air of the Tetitlan area considered a potential thermal field and characterized by scarcity of surface manifestations. Radon is used as a tracer gas to provide a qualitative idea of gas transfer (velocity and flux), carbon dioxide and methane are believed to act as carriers for other gases (i.e., Rn and He), helium and hydrogen are used as shallow signals of crustal leaks along faults (Ciotoli et al., 2005). Methane is also considered both a characteristic biogenic indicator of organic matter deposits and a tracer of major crustal discontinuity. A total of 154 soil gas samples were collected in an area of about 80 square kilometres. The same area was investigated throughout a total of 346 of CO2 and CH4 flux measurements

The geometric paradigm in computational elasto-plasticity

Computational methods, for large displacements of continua in the elastoplastic range, rely on the mathematical modeling of the nonlinear constitutive behavior. In last decades an increasing favor has been deserved to nonlinear models based on a chain decomposition of the deformation gradient. The troubles involved in a structural analysis based on this model are well-known and have not been overcome although many efforts devoted to this end. Our investigation towards a more satisfactory model starts from the new analysis of the rate elastic behavior performed in [1, 2] since the difficulties faced by previous formulations were the very motivation for the discard of rate constitutive models in elasto-plasticity [3]. The new definition of hypo-elasticity, the detection of simple integrability conditions and a new formulation of conservativeness, lead to a definition of rate elasticity suitable for an effective modeling of rate elasto-plastic constitutive behaviors [4]. The treatment is based on a geometric definition of spatial and material fields and on the statement of a geometric paradigm assessing the rules for comparison of material fields naturally provided by push-pull according to the relevant transformation. The rates involved in constitutive relations are Lie-derivatives of stress field and constitutive parameters. Geometric compatibility requires that elastic and plastic stretchings additively give the Lie-derivative of metric field. No privileged reference configuration is involved and no consequent multiplicative decomposition of deformation gradient is assumed. Computational methods are shown to be based on the pull-back of constitutive relations to a straightened out trajectory segment which plays the role of computation chamber wherein linear operations of differentiation and integration may be performed. Accordingly, finite elastic and plastic stretches are considered as purely computational tools with no physical interpretation in constitutive relations. Both 3-D and lower dimensional structural models, such as wires and membranes, may be analysed by a direct application of the theory. The outcome is a significant improvement of physical insight and computational effectiveness with respect to previous treatments of finite elasto-plasticity

Analytical Solutions of Viscoelastic Nonlocal Timoshenko Beams

A consistent nonlocal viscoelastic beam model is proposed in this paper. Specifically, a Timoshenko bending problem, where size-and time-dependent effects cannot be neglected, is investigated. In order to inspect scale phenomena, a stress-driven nonlocal formulation is used, whereas to simulate time-dependent effects, fractional linear viscoelasticity is considered. These two approaches are adopted to develop a new Timoshenko bending model. Analytical solutions and application samples of the proposed formulation are presented. Moreover, in order to show influences of viscoelastic and size effects on mechanical response, parametric analyses are provided. The contributed results can be useful for the design and optimization of small-scale devices exhibiting flexural behaviour

Can the intraprostatic concentration of epidermal growth factor influence the variance of serum prostate specific antigen levels in patients with benign prostatic hyperplasia?

Purpose: Except for prostate volume, little is known about the factors influencing serum prostate specific antigen (PSA) levels. Considering that dihydrotestosterone and epidermal growth factor are regulators of the proliferation and differentiation in the epithelial component of human prostate tissue and that PSA is produced only by the epithelial cells of the gland, studies were performed on patients with a histological diagnosis of benign prostatic hyperplasia (BPH) to establish whether a significant association exists between the intraprostatic concentration of dihydrotestosterone or epidermal growth factor and serum PSA levels. Materials and Methods: A total of 20 patients with BPH who had not been previously treated were part of a larger study on the correlation among PSA, prostate volume and age, and were evaluated according to the algorithm in the guidelines of the international consultation on BPH. All men underwent open suprapubic prostatectomy to enucleate the entire adenoma and in each case sections were made in the periurethral, subcapsular and intermediate zones of the BPH tissue. Dihydrotestosterone and epidermal growth factor concentrations were evaluated by radioimmunoassay in the periurethral zone and in total BPH tissue. Results: In these 20 patients with BPH serum PSA levels were significantly associated with epidermal growth factor but not with dihydrotestosterone concentrations in total BPH tissue (r = 0.7762, p = 0.00002836 and r = 0.3923, p = 0.0956307, respectively). A stronger association was found between PSA levels and the periurethral concentration of epidermal growth factor and dihydrotestosterone (r = 0.8117, p = 0.000005 and r = 0.5656, p = 0.0098326, respectively). On the contrary, epidermal growth factor and dihydrotestosterone were not significantly associated with prostate volume (p = 0.957415 and p = 0.531439, respectively). Conclusions: To our knowledge this study is the first report in the literature to demonstrate an association between serum PSA, and dihydrotestosterone and epidermal growth factor levels, particularly in the periurethral zone of human BPH tissue. These data suggest the importance of epidermal growth factor and dihydrotestosterone in influencing serum PSA levels

Fingering and strain localization in porous media during imbibition processes

Fingered infiltration of a wetting fluid through a porous network is a widely studied subject in the field of fluid mechanics. However, the effect of this heterogeneous percolation on the response of granular materials, in particular fine-grained soils, is a poorly investigated and badly understood topic which deserves deep analysis, considering, among others, possible applications in soil remediation and underground energy storage. This paper presents a first application of a new formulation of unsaturated poromechanics based on a phase field approach that allows to characterize on the one hand the occurrence of fingering hydraulic instabilities and on the other one to capture their effects on the irreversible, and possible unstable, deformation of the solid skeleton. The envisaged application concerns the behavior of fine-grained soils whose dilatant/contractant behavior is more and more attracting the interest of the scientific community both in the fields of experimental research and numerical modeling

Chemical and isotopic characterisation of gas and water in a scientific

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