Sobrepresiones de vaciado

No. 78 of Informes de la Construcción published a paper by Mr. Reimbert, in which a study was made of the turbulences in the suction currents which are used in wheat storing silos. The present paper, which is a continuation of the previous one, gives practical methods for calculating the strength of silo structures. These methods are based on the idea of introducing a perforated tube into the mass of material stored in the silo. The tube makes it possible to reduce the emptying overpressures. It is possible to find a coefficient to determine the true emptying pressure. This also enables the calculation of the thickness and amount of reinforcement of the silo structure, which is usually cellular and cylindrical in shape. Another aspect discussed in this paper is that dealing with accidents and repairs of the cracks which arise due to overpressures during the process of emptying. The conclusions and recommendations developed in this study are applicable both to reinforced concrete and metal silos.En el número 78 de Informes de la Construcción se publicó un artículo, del autor que figura en primer lugar en este trabajo, en el cual se estudiaba el régimen turbulento que aparece en las corrientes de vaciado de los silos destinados al almacenamiento de cereales. En el presente artículo, continuación del anterior, se proponen los procedimientos prácticos para el cálculo estable y resistente de las estructuras de los silos. La base de estos cálculos, parte del principio de introducir un tubo perforado en el seno de la masa ensilada. Este tubo tiene por objeto reducir las sobrepresiones de vaciado y, por tanto, se puede hallar un coeficiente para determinar la verdadera presión de vaciado y, con ello, el espesor y armaduras del silo corrientemente celular y cilíndrico. Otro de los aspectos tratados son los accidentes y reparaciones de los agrietamientos que se producen en los silos por causa de las sobrepresiones que aparecen en el período de vaciado. Las recomendaciones y conclusiones a que se llega racionalmente pueden hacerse extensibles, tanto a los silos de hormigón armado como a los metálicos

The influence of anisotropic growth and geometry on the stress of solid tumors

Solid stresses can affect tumor patho-physiology in at least two ways: directly, by compressing cancer and stromal cells, and indirectly, by deforming blood and lymphatic vessels. In this work, we model the tumor mass as a growing hyperelastic material. We enforce a multiplicative decomposition of the deformation gradient to study the role of anisotropic tumor growth on the evolution and spatial distribution of stresses. Specifically, we exploit radial symmetry and analyze the response of circumferential and radial stresses to (a) degree of anisotropy, (b) geometry of the tumor mass (cylindrical versus spherical shape), and (c) different tumor types (in terms of mechanical properties). According to our results, both radial and circumferential stresses are compressive in the tumor inner regions, whereas circumferential stresses are tensile at the periphery. Furthermore, we show that the growth rate is inversely correlated with the stresses’ magnitudes. These qualitative trends are consistent with experimental results. Our findings therefore elucidate the role of anisotropic growth on the tumor stress state. The potential of stress-alleviation strategies working together with anticancer therapies can result in better treatments

The role of malignant tissue on the thermal distribution of cancerous breast

The present work focuses on the integration of analytical and numerical strategies to investigate the thermal distribution of cancerous breasts. Coupled stationary bioheat transfer equations are considered for the glandular and heterogeneous tumor regions, which are characterized by different thermophysical properties. The cross-section of the cancerous breast is identified by a homogeneous glandular tissue that surrounds the heterogeneous tumor tissue, which is assumed to be a two-phase periodic composite with non-overlapping circular inclusions and a square lattice distribution, wherein the constituents exhibit isotropic thermal conductivity behavior. Asymptotic periodic homogenization method is used to find the effective properties in the heterogeneous region. The tissue effective thermal conductivities are computed analytically and then used in the homogenized model, which is solved numerically. Results are compared with appropriate experimental data reported in the literature. In particular, the tissue scale temperature profile agrees with experimental observations. Moreover, as a novelty result we find that the tumor volume fraction in the heterogeneous zone influences the breast surface temperature

Incoherent interaction of nematicons in bias-free liquid-crystal cells

We study experimentally the propagation dynamics and interaction of a pair of mutually incoherent nematicons: spatial optical solitons in nematic liquid crystals. In contrast to earlier studies, we consider a bias-free liquid-crystal cell and compare the soliton interaction in copropagating and counterpropagating geometries. We analyze the dependence of nematicon interaction on input power and observe a direct manifestation of a long-range nonlocal nonlinearity. Attraction of counterpropagating solitons requires higher powers and longer relaxation times than that of copropagating nematicons due to losses-induced power asymmetry of counterpropagating nematicons.Comment: 5 pages, z figure

Mathematical modeling of the interplay between stress and anisotropic growth of avascular tumors

In this work, we propose a new mathematical framework for the study of the mutual interplay between anisotropic growth and stresses of an avascular tumor surrounded by an external medium. The mechanical response of the tumor is dictated by anisotropic growth, and reduces to that of an elastic, isotropic, and incompressible material when the latter is not taking place. Both proliferation and death of tumor cells are in turn assumed to depend on the stresses. We perform a parametric analysis in terms of key parameters representing growth anisotropy and the influence of stresses on tumor growth in order to determine how these effects affect tumor progression. We observe that tumor progression is enhanced when anisotropic growth is considered, and that mechanical stresses play a major role in limiting tumor growth

Shaking-table tests of flat-bottom circular silos containing grain-like material

According to Eurocode 8, the seismic design of flat-bottom circular silos containing grain-like material is based on a rough estimate of the inertial force imposed on the structure by the ensiled content during an earthquake: 80% of the mass of the content multiplied by the peak ground acceleration. A recent analytical consideration of the horizontal shear force mobilised within the ensiled material during an earthquake proposed by some of the authors has resulted in a radically reduced estimate of this load suggesting that, in practice, the effective mass of the content is significantly less than that specified. This paper describes a series of laboratory tests that featured shaking table and a silo model, which were conducted in order to obtain some experimental data to verify the proposed theoretical formulations and to compare with the established code provisions. Several tests have been performed with different heights of ensiled material – about 0.5 mm diameter Ballotini glass – and different magnitudes of grain–wall friction. The results indicate that in all cases, the effective mass is indeed lower than the Eurocode specification, suggesting that the specification is overly conservative, and that the wall–grain friction coefficient strongly affects the overturning moment at the silo base. At peak ground accelerations up to around 0.35 g, the proposed analytical formulation provides an improved estimate of the inertial force imposed on such structures by their contents.The authors acknowledge the financial support received from the European Community's Seventh Framework Program [FP7/2007-2013] under grant agreement n° 227887 for the SERIES Project (ASESGRAM project: “Assessment of the seismic behaviour of flat-bottom silos containing grain-like materials”)

Self-confined light waves in nematic liquid crystals

The study of light beams propagating in the nonlinear, dispersive, birefringent and nonlocal medium of nematic liquid crystals has attracted widespread interest in the last twenty years or so. We review hereby the underlying physics, theoretical modelling and numerical approximations for nonlinear beam propagation in planar cells filled with nematic liquid crystals, including bright and dark solitary waves, as well as optical vortices. The pertinent governing equations consist of a nonlinear Schrödinger-type equation for the light beam and an elliptic equation for the medium response. Since the nonlinear and coupled nature of this system presents difficulties in terms of finding exact solutions, we outline the various approaches used to resolve them, pinpointing the good agreement obtained with numerical solutions and experimental results. Measurement and material details complement the theoretical narration to underline the power of the modelling