Unary enhancements of inherently nonfinitely based semigroups

We exhibit a simple condition under which a finite involutary semigroup whose semigroup reduct is inherently nonfinitely based is also inherently nonfinitely based as a unary semigroup. As applications, we get already known as well as new examples of inherently nonfinitely based involutory semigroups. We also show that for finite regular semigroups, our condition is not only sufficient but also necessary for the property of being inherently nonfinitely based to persist. This leads to an algorithmic description of regular inherently nonfinitely based involutory semigroups.Comment: 11 pages, 1 figure. Section 4 has been improved and expanded according to suggestions of an anonymous referee of the journal version. A few minor improvements have been done in Section

Genetic Analysis of Invasive Populations of Ventenata Dubia (Poaceae): An Assessment of Propagule Pressure and Pattern of Range Expansion in the Western United States

Molecular markers prove to be an invaluable tool in assessing the introduction dynamics, pattern of range expansion, and population genetics of an invasive species. Ventenata dubia (Leers) Coss. (Aveneae; ventenata) is a diploid, primarily self-pollinating, annual grass native to Eurasia and Northern Africa. The grass has a detailed herbarium collection history in the western United States since its discovery in eastern Washington in 1952. Genetic analysis of 51 invasive populations (1636 individuals) of V. dubia, coupled with historical records, suggests moderate propagule pressure from multiple introductions, followed by local or regional range expansion. Enzyme electrophoresis detected nine multilocus genotypes (MLGs) across eight western US states. A single MLG, referred to as the most common genotype (MCG), was detected in 37 of 51 (72.5%) invasive populations across all states. The other eight MLGs were generally found in fewer populations, with limited geographic distributions. Despite multiple introductions, invasive populations exhibit low levels of genetic admixture, low levels of genetic diversity within populations (A = 1.03, %P = 2.94, Hexp = 0.007) and high genetic differentiation among populations (GST = 0.864). The apparent reduced evolutionary potential of most V. dubia populations did not preclude the initial establishment and rapid spread of this species across its new range in the western US

An analytic model for the stress-induced anisotropy of dry rocks

One of the main causes of azimuthal anisotropy in sedimentary rocks is anisotropy of tectonic stresses in the earth's crust. We have developed an analytic model for seismic anisotropy caused by the application of a small anisotropic stress. We first considered an isotropic linearly elastic medium (porous or nonporous) permeated by a distribution of discontinuities with random (isotropic) orientation (such as randomly oriented compliant grain contacts or cracks). The geometry of individual discontinuities is not specified. Instead, their behavior is defined by a ratio B of the normal to tangential excess compliances. When this isotropic rock is subjected to a small compressive stress (isotropic or anisotropic), the number of cracks along a particular plane is reduced in proportion to the normal stress traction acting on that plane. This effect is modeled using the Sayers-Kachanov noninteractive approximation. The model predicts that such anisotropic crack closure yields elliptical anisotropy, regardless of the value of the compliance ratio B. It also predicts the ratio of Thomsen's anisotropy parameters epsilon/gamma as a function of the compliance ratio B and Poisson's ratio of the unstressed rock. A comparison of the model predictions with the results of laboratory measurements indicates a reasonable agreement for moderate magnitudes of uniaxial stress (as high as 30 MPa).These results can be used for differentiating stress-induced anisotropy from that caused by aligned fractures. Conversely, if the cause of anisotropy is known, then the anisotropy pattern allows one to estimate P-wave anisotropy from S-wave anisotropy

Modelling anisotropy pattern of dry rocks as a function of applied stress

We propose an analytical model for seismic anisotropy caused by application of an anisotropic stress to an isotropic dry rock. We first consider an isotropic linearly elastic medium (porous or non-porous) permeated by a distribution of discontinuities with random (isotropic) orientation (such as randomly oriented compliant grain contacts or cracks). Geometry of individual discontinuities is not specified. Instead, their behaviour is defined by a ratio of the normal to tangential excess compliances. When this isotropic rock is subjected to a small compressive stress (isotropic or anisotropic), the specific surface area of cracks aligned parallel to a particular plane is reduced in proportion to the normal stress traction acting on that plane. This effect is modelled using the Sayers-Kachanov non-interactive approximation. The integral over the orientation distribution is evaluated using Taylor expansion of the stress dependency of the specific surface area of cracks. Comparison of the model predictions with the results of laboratory measurements shows a reasonable agreement for moderate magnitudes of uniaxial stress (up to 30 MPa). The results suggest that the relations between anisotropy parameters do not change with increasing stress

The Action Result of the Concentrated Load on the Briquettes which Obtained from the Technogenous Material

In this study, the calculation results of the briquette stress state by the Finite element method are presented. The fields of compressive and tensile stresses in briquette are determined. The conditions affecting the process of the briquette destruction are considered. Keywords: metallurgical briquette, finite element method, stress stat

Testing Gassmann fluid substitution in carbonates: sonic log versus ultrasonic core measurements

The technique of fluid substitution is widely used to model elastic properties of rocks saturated with different fluids The applicability of this technique to in-situ seismic and sonic measurements is a matter of frequent debate. Most of the analysis is based on laboratory measurements, with little or no constraints from field environments. In addition, until recently, most of the data were from sand reservoirs. Applicability of Gassmann fluid substitution to carbonates is even more uncertain. To analyze this problem, we compare elastic moduli obtained using fluid substitution against the moduli obtained from sonic and density logs The dry moduli for fluid substitution are obtained from ultrasonic measurements on 50 core samples from a cretaceous reservoir buried at 5000 meters depth in Santos Basin, offshore Brazil. The good agreement between the saturated moduli obtained from cores and logs is obtained. This shows that the Gassmann equations can be applied not only in siliciclastic reservoirs, but also deep and complex carbonates reservoirs