Linear semigroups with coarsely dense orbits

Let $S$ be a finitely generated abelian semigroup of invertible linear operators on a finite dimensional real or complex vector space $V$. We show that every coarsely dense orbit of $S$ is actually dense in $V$. More generally, if the orbit contains a coarsely dense subset of some open cone $C$ in $V$ then the closure of the orbit contains the closure of $C$. In the complex case the orbit is then actually dense in $V$. For the real case we give precise information about the possible cases for the closure of the orbit.Comment: We added comments and remarks at various places. 14 page

Sedimentary geology of the Middle Carboniferous of the Donbas region (Dniepr-Donets basin, Ukraine)

Peer reviewedPublisher PD

Coercivity and stability results for an extended Navier-Stokes system

In this article we study a system of equations that is known to {\em extend} Navier-Stokes dynamics in a well-posed manner to velocity fields that are not necessarily divergence-free. Our aim is to contribute to an understanding of the role of divergence and pressure in developing energy estimates capable of controlling the nonlinear terms. We address questions of global existence and stability in bounded domains with no-slip boundary conditions. Even in two space dimensions, global existence is open in general, and remains so, primarily due to the lack of a self-contained $L^2$ energy estimate. However, through use of new $H^1$ coercivity estimates for the linear equations, we establish a number of global existence and stability results, including results for small divergence and a time-discrete scheme. We also prove global existence in 2D for any initial data, provided sufficient divergence damping is included.Comment: 29 pages, no figure

Grain-size characterization of reworked fine-grained aeolian deposits

After a previous review of the grain-size characteristics of in situ (primary) fine-grained aeolian deposits, reworked (secondary) aeolian deposits, as modified in lacustrine environments and by alluvial and pedogenic processes, are discussed in this paper. As a reference, the grain-size characteristics of primary loess deposits are shortly described. Commonly, pedogenesis and weathering of primary loess may lead to clay neoformation and thus to an enrichment in grain diameters of 4-8 mu m, a size which is comparable to the fine background loess. Remarkably, the modal grain-size values of primary loess are preserved after re -deposition in lakes and flood plains. But, secondary lacustrine settings show a very characteristic admixture with a clayey population of 1-2,5 mu m diameter due to the process of settling in standing water. Similarly, alluvial settings show often an addition with coarse-grained sediment supplied by previously eroded sediment. However, floodplain settings show also often the presence of pools and other depressions which behave similarly to lacustrine environments. As a result, alluvial secondary loess sediments are characterized by the poorest grain-size sorting when compared with the other secondary loess and primary loess. Despite the characteristic texture of each of these deposits, grain-size characteristics of the described individual sediment categories are not always fully diagnostic and thus grain-size analysis should be complemented by other information, as sedimentary structures and fauna or flora, to reliably reconstruct the sedimentary processes and environments

Expansion in perfect groups

Let Ga be a subgroup of GL_d(Q) generated by a finite symmetric set S. For an integer q, denote by Ga_q the subgroup of Ga consisting of the elements that project to the unit element mod q. We prove that the Cayley graphs of Ga/Ga_q with respect to the generating set S form a family of expanders when q ranges over square-free integers with large prime divisors if and only if the connected component of the Zariski-closure of Ga is perfect.Comment: 62 pages, no figures, revision based on referee's comments: new ideas are explained in more details in the introduction, typos corrected, results and proofs unchange

The discontinuous Galerkin method for fractional degenerate convection-diffusion equations

We propose and study discontinuous Galerkin methods for strongly degenerate convection-diffusion equations perturbed by a fractional diffusion (L\'evy) operator. We prove various stability estimates along with convergence results toward properly defined (entropy) solutions of linear and nonlinear equations. Finally, the qualitative behavior of solutions of such equations are illustrated through numerical experiments

Ethics Shock: Technology, Life Styles and Future Practice

During the past ten years a new movement has developed in the United States which has taken as its major emphasis the study of the future. The futureologists led by Kahn, Weiner, and Theobald, have projected a number of alternatives for the United States. The value of this movement has been: 1) to alert the country to the fact that change is occurring at an extremely rapid pace; 2) to provide a transdisciplinary view, not only utilizing projections from various disciplines, but illustrating the multiplier effect that the combination of developments from many disciplines may have on our society; and 3) to illustrate that we can, if we wish, and if we act soon enough, influence the change. The purpose of this paper is to examine selected changes from the vast visions of possible change, most likely to have impacts on society which will have to be taken into account by social work. How will these changes influence our profession? And, what techniques and approaches will our profession have to construct in order to deal with the changes taking place? If we do not prepare, we too will find ourselves in shock - reacting on the spur of the moment, reeling without plan, purpose, professional means or goals to guide us. Weightless, we will drift, seeking a role in a society which needs help, but in which we make no impact. Clearly this would constitute failure to meet our professional responsibilities. We shall conclude by examining the potential of the ethical code of the profession as a source of guidance in dealing with these dilemmas and questions. In evaluating the code we shall consider the extent to which it meets the standards set in other areas for achieving a cognitive base for action. We shall propose that steps be taken to make it more scientific

Ethics Shock: Technology, Life Styles and Future Practice

During the past ten years a new movement has developed in the United States which has taken as its major emphasis the study of the future. The futureologists led by Kahn, Weiner, and Theobald, have projected a number of alternatives for the United States. The value of this movement has been: 1) to alert the country to the fact that change is occurring at an extremely rapid pace; 2) to provide a transdisciplinary view, not only utilizing projections from various disciplines, but illustrating the multiplier effect that the combination of developments from many disciplines may have on our society; and 3) to illustrate that we can, if we wish, and if we act soon enough, influence the change. The purpose of this paper is to examine selected changes from the vast visions of possible change, most likely to have impacts on society which will have to be taken into account by social work. How will these changes influence our profession? And, what techniques and approaches will our profession have to construct in order to deal with the changes taking place? If we do not prepare, we too will find ourselves in shock - reacting on the spur of the moment, reeling without plan, purpose, professional means or goals to guide us. Weightless, we will drift, seeking a role in a society which needs help, but in which we make no impact. Clearly this would constitute failure to meet our professional responsibilities. We shall conclude by examining the potential of the ethical code of the profession as a source of guidance in dealing with these dilemmas and questions. In evaluating the code we shall consider the extent to which it meets the standards set in other areas for achieving a cognitive base for action. We shall propose that steps be taken to make it more scientific

Jewish and non-Jewish club leaders in Jewish community centers

Thesis (M.S.)--Boston Universit