The auxiliary space preconditioner for the de Rham complex

We generalize the construction and analysis of auxiliary space preconditioners to the n-dimensional finite element subcomplex of the de Rham complex. These preconditioners are based on a generalization of a decomposition of Sobolev space functions into a regular part and a potential. A discrete version is easily established using the tools of finite element exterior calculus. We then discuss the four-dimensional de Rham complex in detail. By identifying forms in four dimensions (4D) with simple proxies, form operations are written out in terms of familiar algebraic operations on matrices, vectors, and scalars. This provides the basis for our implementation of the preconditioners in 4D. Extensive numerical experiments illustrate their performance, practical scalability, and parameter robustness, all in accordance with the theory

Assessment of symptoms and prevention of musculoskeletal disorders among IT specialists in Varna, Bulgaria

INTRODUCTIONThe modern digitalization of the economy increases significantly the amount of work with video display terminals (VDTs) on a daily basis. Work-related musculoskeletal disorders (WMSDs) are cumulative disorders of the muscles, joints, nerves, and local blood circulation. Common symptoms are pain, numbness, formication of the upper, lower limbs, back, and shoulders.AIM:The aim of this article is to evaluate the prevalence of symptoms of WMSDs among IT workers in Varna and the use of breaks and stretch exercises during their daily shift.MATERIALS AND METHODS:An ergonomic evaluation of the office work spaces of 173 employees was performed in the period October–December 2021. They were also asked to report any discomfort related to pain during work in individual interviews. The data gathered included reports on pain in different body areas and musculoskeletal disorder (MSD) symptoms. Information regarding daily breaks and use of stretch exercises was gathered from employees using a structured questionnaire.RESULTS:The average age of the employees who received ergonomic evaluation was 32.5 (SD 0.59, range: 21–54 years) years. Males were prevalent in the gender distribution of the workers—117, or 67.6% of all participants with women being 56, or 32.4%.The mean work experience with VDTs of the studied group was 10.3 (SD 0.49, range 1-30 years). A total of 34.7% of the employees reported discomfort or pain during work. Almost two thirds, or 65.3%, of the respondents did not report any discomfort during their work day. The number of employees who used regular breaks and stretches during the shift was 91 (52.6%).CONCLUSION:Stretch exercises and microbreaks during the workday are common prevention methods, whose impact on the symptoms of WMSDs needs further studies. Adequate prevention strategies in regard to the safety and health at the office are needed to reduce the risk of WMSDs

Ergonomic workplace evaluation among office IT workers in Varna, Bulgaria

INTRODUCTION:The frequency of office-based work has increased significantly in the last decades. Employees are exposed to multiple occupational hazards, some of which are related to the static pressure on the muscles of the back, neck, and shoulders due to improper posture, irregularities in the office furniture, and improper breaks during the shift. The ocular complaints of office workers are also common and can be related to non-ergonomically designed work furniture and insufficient, irregular breaks during the shift.AIM:The aim of this article is to create and apply an instrument for ergonomic assessment of office facilities. In addition, it includes evaluation of the ergonomic factors in the office environment during the work shift and prescribe preventive measures.MATERIALS AND METHODS:For the needs of ergonomic evaluation of the working environment in the IT industry, an assessment instrument was developed.RESULTS:Office IT workers (173) received ergonomic evaluation of their workplace in the period October–December 2021. The mean age of the employees was 32.49 +/- 0.59 (21 to 54 years). Gender distribution of the workers was with dominance of the men—117 individuals, or 67.6% of all participants. The assessment of the office furniture showed: 85 (49.1%) of the cases had ergonomic irregularities regarding the chair, 51 (29.5%) had irregularities of the desk. Correction of the work posture was recommended to 113 (65.3%) workers.CONCLUSION:Further studies are needed in Bulgarian companies to assess the proportion of employees affected by ergonomic occupational hazards and their impact

A Combined Preconditioning Strategy for Nonsymmetric Systems

We present and analyze a class of nonsymmetric preconditioners within a normal (weighted least-squares) matrix form for use in GMRES to solve nonsymmetric matrix problems that typically arise in finite element discretizations. An example of the additive Schwarz method applied to nonsymmetric but definite matrices is presented for which the abstract assumptions are verified. A variable preconditioner, combining the original nonsymmetric one and a weighted least-squares version of it, is shown to be convergent and provides a viable strategy for using nonsymmetric preconditioners in practice. Numerical results are included to assess the theory and the performance of the proposed preconditioners.Comment: 26 pages, 3 figure

Infrasound exposure and health effects among seafarers

Seas and oceans are some of the most powerful natural sources of infrasound oscillations and the study literature suggests that transport is also a powerful anthropogenic source of infrasound. Noise in ships has a very wide frequency range - from infrasonic to ultrasonic. A literature review has been made using theavailable data on infrasound sources when working at sea and the risk factors for the health and safety of the crew. Historical and documentary methods were used to process the collected information, analyze and summarize data. Regarding the pathogenesis of infrasound effects, many researchers adhere to the so-calledresonance theory. A number of studies have shown a link between low-frequency noise and various physiological and psychological reactions such as irritation,change in hearing perception, concentration problems, sleep depression, mood effects, and the so-called vibroacoustic disease (VAD). Adverse health effects fromoccupational exposure are observed in memory, anxiety and effectiveness. Evidence of vascular and respiratory effects exists but is inconclusive. VAD has a whole body pathology that develops in people who are exposed to infrasound. The mutagenic potential of infrasound exposures is also discussed in humans and animal experiments. The frequency-specific effects are not yet known, valid dose-response relationships are difficult to identify and there are still no large-scale epidemiologicalstudies.Infrasound and very low frequency sounds are a widespread pollutant in the work and communal environment. Their combined biological exposure action and generic vibration on board of vessels is a specific risk factor for the health and safety of seafarers. Maritime occupational medicine doctors need to know the specific pathology and carefully look for the early manifestations of the preclinical stages of cardiovascular, central-nervous, respiratory and auditory-vestibular function abnormalities

Organisation of shipboard working hours

Ships function twenty-four hours a day, seven days per week and generally work is being done by as few people from the staff as possible. The role of working hours organisation as a health risk factor for workers on a ship is being studied. The participants in the study are 155 sailors - 153 men (98.7%) and 2 women (1.3%), at a mean age of 45.35±0.8 years. The duration of the period on board according tothe last contract of the interviewed people varies from 1 to 7 months. The average working period for workers in offshore companies is 1.15±1.4 months, which is much shorter in comparison to the merchant fleet with a duration of 3.2±2.5 months (Ñ€0.05).A lack of time for daily routine tasks is more common among sailors from the merchant fleet - 26 people or 44.8% as well as among those working on a drillship- 23 people or 25%, (χ² square test of Pearson =6.358, where Ñ€<0.05). Extra labour and psycho-emotional tension are established without any credible differences in both groups.Assessment and management of the health risk among sailors needs an optimisation of the labour organisation, which aims at increasing the hours of sleep,reduction of extra labour and long work shifts. There is a legislative requirement for the ships to be exploited by an optimal number of staff but in the modern shipping industry sailors are being hired at the minimum allowed number without any possibility for change during shifts and any physiological regimens ofwork and rest. Reducing the staff leads to fatigue and stress among seaworkers

Nonlinear multigrid based on local spectral coarsening for heterogeneous diffusion problems

This work develops a nonlinear multigrid method for diffusion problems discretized by cell-centered finite volume methods on general unstructured grids. The multigrid hierarchy is constructed algebraically using aggregation of degrees of freedom and spectral decomposition of reference linear operators associated with the aggregates. For rapid convergence, it is important that the resulting coarse spaces have good approximation properties. In our approach, the approximation quality can be directly improved by including more spectral degrees of freedom in the coarsening process. Further, by exploiting local coarsening and a piecewise-constant approximation when evaluating the nonlinear component, the coarse level problems are assembled and solved without ever re-visiting the fine level, an essential element for multigrid algorithms to achieve optimal scalability. Numerical examples comparing relative performance of the proposed nonlinear multigrid solvers with standard single-level approaches -- Picard's and Newton's methods -- are presented. Results show that the proposed solver consistently outperforms the single-level methods, both in efficiency and robustness