General decay of the solution for a viscoelastic wave equation with a time-varying delay term in the internal feedback

In this paper we consider a viscoelastic wave equation with a time-varying delay term, the coefficient of which is not necessarily positive. By introducing suitable energy and Lyapunov functionals, under suitable assumptions, we establish a general energy decay result from which the exponential and polynomial types of decay are only special cases.Comment: 11 page

Experiment Pointing Subsystems (EPS) requirements for Spacelab missions

The goal of the experiment pointing subsystems (EPS) is to accommodate a broad spectrum of instrument types by providing a number of stability and control functions that greatly exceed the capability of the shuttle. These functions include target acquisition, target tracking through wide gimbal ranges, stabilization, simultaneous pointing to one or more targets, instrument rastering, and on-orbit calibration. The experiments will vary widely in size, weight, geometry, and instrument types, and many have not been completely defined. This great diversity of requirements reflects the long term plans of the user community and establishes challenging performance requirements for the EPS

An assessment of the Instrument Pointing Subsystems (IPS) requirements for spacelab missions

Instrument Pointing Subsystem requirements for Spacelab missions in solar physics, stellar astronomy, and earth observation are analyzed and design guidelines for fine pointing instrument platforms are presented. The requirements for the platforms are time-phased based on NASA projections of flight mission models and payload scheduling. The experiments used for these projections are to be viewed as representative payloads. Other experiments or experiment groupings within any one discipline may be accommodated by an Instrument Pointing Subsystem that meets these requirements

EFFECTS OF AGRICULTURAL LOANS IN DEVELOPING COUNTRIES – BENIN CASE STUDY

Limited access to financial services is known as a major constraint to agricultural development (FAO, 2002). Farmers need liquidity to face agricultural expenses throughout the production cycle but mainly at the beginning. Mainstream financial institutions are reluctant to serve the agricultural sector for several reasons. First, they consider the sector to be highly risky with low performance. Also, agricultural activities depend on the weather, they take place in remote rural areas, and commodities prices are volatile. All these aspects make it hard for standard banks to reach their profit goals when lending to farmers. Since microfinance was conceived, it has generated a lot of hope for alleviating poverty in low-income countries. Microfinance provides the poor with access to affordable capital by granting low-income individuals with loans they would not otherwise have access to, because of economic and geographic constraints. The goal of the dissertation is to examine the role and the importance of microfinance in the agricultural sector of developing countries. A survey took place in October 2017, in both rural and urban areas of Benin and involved 750 agricultural households. Three different agricultural zones were selected: the North-East (cotton zone); the Center (tubers and cashew nut zone) and the South (a region with special crops such as vegetables, pineapple, palm tree, exotic plants). The study focuses on agricultural loans. It includes clients of the major microfinance institution in Benin: FECECAM - Faîtière des Caisses d’Epargne et de Crédit Agricole Mutuel. This research contributes to the literature in several ways. The study allows shedding light on the effects of agricultural loans, specifically, on households’ efficiency and labor employment, which are mostly overlooked in the microfinance literature. To overcome selection bias in microcredit evaluation, the research employs a pipeline design. Control and treatment groups consist of individuals who have chosen to participate in the microfinance program. The loan treatment considered is the experience with loans which includes program entry timing, loan take-up frequency, and the average amount of loan obtained over the 2012-2017 period. The study employs a cluster analysis technique to create reliable comparable groups. Multiple variables and indicators are analyzed. A descriptive analysis of loan impact on farmers’ labor input choices shows that past loans have residual effects on both hired and family labor use. Farm loans, especially those obtained for farm machinery significantly reduce expenditure on hired labor but more family labor is employed using machine loans while other loan categories reduced the use of family labor. The evaluation of the whole-farm efficiency of borrowers in the presence of agricultural loans reveals significant technical and allocative errors leading to profit loss in all studied regions. However, experience with loans significantly increases farmers’ whole-farm efficiency, particularly in the North. Finally, the assessment of well-being indicators suggests that those farm loans have a significant positive impact on sampled recipients’ net farm income, food security and food quality statuses. Agricultural loans also have a positive impact on women’s empowerment. The monitoring and implementation mechanism of FECECAM played a crucial role in the success of its loan programs

Some multilevel methods on graded meshes

AbstractWe consider Yserentant's hierarchical basis method and multilevel diagonal scaling method on a class of refined meshes used in the numerical approximation of boundary value problems on polygonal domains in the presence of singularities. We show, as in the uniform case, that the stiffness matrix of the first method has a condition number bounded by (ln(1/h))2, where h is the meshsize of the triangulation. For the second method, we show that the condition number of the iteration operator is bounded by ln(1/h), which is worse than in the uniform case but better than the hierarchical basis method. As usual, we deduce that the condition number of the BPX iteration operator is bounded by ln(1/h). Finally, graded meshes fulfilling the general conditions are presented and numerical tests are given which confirm the theoretical bounds

Dirichlet problems in polyhedral domains II: Approximation by FEM and BEM

AbstractThe convergence of the classical finite element method (FEM) and boundary element method (BEM) is poor due to the edge and vertex singularities of the solution of the involved Dirichlet problem relative to an elliptic operator in a polyhedron. Using the global regularity results of Lubuma and Nicaise (1994), we analyse refined FEM and BEM with optimal rates of convergence

Localization effects in a periodic quantum graph with magnetic field and spin-orbit interaction

A general technique for the study of embedded quantum graphs with magnetic fields and spin-orbit interaction is presented. The analysis is used to understand the contribution of Rashba constant to the extreme localization induced by magnetic field in the T3 shaped quantum graph. We show that this effect is destroyed at generic values of the Rashba constant. On the other hand, for certain combinations of the Rashba constant and the magnetic parameters another series of infinitely degenerate eigenvalues appears.Comment: 25 pages, typos corrected, references extende

Exponential stability of the wave equation with memory and time delay

We study the asymptotic behaviour of the wave equation with viscoelastic damping in presence of a time-delayed damping. We prove exponential stability if the amplitude of the time delay term is small enough

The neural stem cell secretome and its role in brain repair.

Compelling evidence from experimental animal disease models and early-phase clinical trials identifies the transplantation of neural progenitor/stem cells (NSCs) as a viable path towards the development of clinically applicable exogenous stem cell therapies. Building from current advances in the field of NSC biology and following the positive outcomes of NSC transplantation studies, the contemporary view is that transplanted NSCs act as local 'factories' capable of producing and secreting a wide array of immune and neurotrophic factors. This has launched a 'stem cell race' to identify the mechanisms behind stem-cell mediated repair in what has been labeled the paracrine hypothesis. This hypothesis proposes that NSC grafts act as a natural source of potent biologics capable of modulating and promoting the restoration of several key functions in the central nervous system (CNS) tissue following acute or chronic tissue damage. Investigators have been inspired to examine novel ways to harness and utilize the pro-regenerative properties of NSC therapies as an alternative approach to a more classical (small molecule based) treatment of CNS diseases. In this review, we will discuss the most recent findings of human NSC (hNSCs) transplants in experimental animal models of CNS diseases that identify of hNSC-secreted factors, including those trafficked within extracellular membrane vesicles (EVs), and the outcomes of recent clinical trials utilizing hNSC therapeutics in CNS diseases

Stem Cells of the Aging Brain.

The adult central nervous system (CNS) contains resident stem cells within specific niches that maintain a self-renewal and proliferative capacity to generate new neurons, astrocytes, and oligodendrocytes throughout adulthood. Physiological aging is associated with a progressive loss of function and a decline in the self-renewal and regenerative capacities of CNS stem cells. Also, the biggest risk factor for neurodegenerative diseases is age, and current in vivo and in vitro models of neurodegenerative diseases rarely consider this. Therefore, combining both aging research and appropriate interrogation of animal disease models towards the understanding of the disease and age-related stem cell failure is imperative to the discovery of new therapies. This review article will highlight the main intrinsic and extrinsic regulators of neural stem cell (NSC) aging and discuss how these factors impact normal homeostatic functions within the adult brain. We will consider established in vivo animal and in vitro human disease model systems, and then discuss the current and future trajectories of novel senotherapeutics that target aging NSCs to ameliorate brain disease