Efficient Algebraic Two-Level Schwarz Preconditioner for Sparse Matrices

Domain decomposition methods are among the most efficient for solving sparse linear systems of equations. Their effectiveness relies on a judiciously chosen coarse space. Originally introduced and theoretically proved to be efficient for self-adjoint operators, spectral coarse spaces have been proposed in the past few years for indefinite and non-self-adjoint operators. This paper presents a new spectral coarse space that can be constructed in a fully-algebraic way unlike most existing spectral coarse spaces. We present theoretical convergence result for Hermitian positive definite diagonally dominant matrices. Numerical experiments and comparisons against state-of-the-art preconditioners in the multigrid community show that the resulting two-level Schwarz preconditioner is efficient especially for non-self-adjoint operators. Furthermore, in this case, our proposed preconditioner outperforms state-of-the-art preconditioners

The Relationship Between Sedentary Behavior, Back Pain, and Psychosocial Correlates Among University Employees

Objectives: This study aims to investigate the relationship between levels of sedentary behavior, physical activity, and back pain and their psychosocial correlates among university employees.Methods: A cross-sectional study was conducted on both academic and non-academic professional staff at Qatar University. The data collection instrument was a combination of the International Physical Activity Questionnaire (IPAQ), the Global Physical Activity Questionnaire (GPAQ) and the Acute Low Back Pain Screening Questionnaire (ALBPSQ).Results: A total of 479 individuals (57% females) participated in the cross-sectional study. Two hundred and ninety three (61.2%) reported to have experienced back pain. The covariates adjusted odds ratios (aORs) showed that vigorous physical activity was a protective variable for those who experienced lower back pain [aOR = 0.84, 95%CI (0.56–0.98)], both lower and upper back pain [aOR = 0.61, 95% CI (0.33–0.87)] and either lower or upper back pain [aOR = 0.76, 95%CI (0.51–0.85)], respectively. Back pain was significantly higher in females than males (aORs: 1.37–2.21). Similarly, sedentary behavior (too much sitting) was significantly associated with those who experienced either LBP or UBP [aOR = 1.74, 95% CI (1.19, 2.57)]. All back pain categories were found to be significantly associated with those who reported a depressed mood.Conclusions: These findings suggest that sedentary employees are exposed to increasing occupational hazards such as back pain and mental health issues. Strategies should aim to reduce sitting time with planned and feasible physical activity interventions to be incorporated into the workplace health promotion policy to help prevent back pain, back injuries, and mental health complications

Approaches in biotechnological applications of natural polymers

Natural polymers, such as gums and mucilage, are biocompatible, cheap, easily available and non-toxic materials of native origin. These polymers are increasingly preferred over synthetic materials for industrial applications due to their intrinsic properties, as well as they are considered alternative sources of raw materials since they present characteristics of sustainability, biodegradability and biosafety. As definition, gums and mucilages are polysaccharides or complex carbohydrates consisting of one or more monosaccharides or their derivatives linked in bewildering variety of linkages and structures. Natural gums are considered polysaccharides naturally occurring in varieties of plant seeds and exudates, tree or shrub exudates, seaweed extracts, fungi, bacteria, and animal sources. Water-soluble gums, also known as hydrocolloids, are considered exudates and are pathological products; therefore, they do not form a part of cell wall. On the other hand, mucilages are part of cell and physiological products. It is important to highlight that gums represent the largest amounts of polymer materials derived from plants. Gums have enormously large and broad applications in both food and non-food industries, being commonly used as thickening, binding, emulsifying, suspending, stabilizing agents and matrices for drug release in pharmaceutical and cosmetic industries. In the food industry, their gelling properties and the ability to mold edible films and coatings are extensively studied. The use of gums depends on the intrinsic properties that they provide, often at costs below those of synthetic polymers. For upgrading the value of gums, they are being processed into various forms, including the most recent nanomaterials, for various biotechnological applications. Thus, the main natural polymers including galactomannans, cellulose, chitin, agar, carrageenan, alginate, cashew gum, pectin and starch, in addition to the current researches about them are reviewed in this article.. }To the Conselho Nacional de Desenvolvimento Cientfíico e Tecnológico (CNPq) for fellowships (LCBBC and MGCC) and the Coordenação de Aperfeiçoamento de Pessoal de Nvíel Superior (CAPES) (PBSA). This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2013 unit, the Project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462) and COMPETE 2020 (POCI-01-0145-FEDER-006684) (JAT)