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227 results on '"Lotfi, Vahid"'

10. Effect of the COVID-19 pandemic on depression, perceived stress and hypochondria of frontline dental staff (FDS): A cohort study

Author

Karim Jafari, Somayeh Hekmatfar, Dara Lotfi Vahid, Esmaeil Sadri Damirchi, and Hamed Zandian

Subjects
Rehabilitation, Public Health, Environmental and Occupational Health
Abstract

BACKGROUND: The coronavirus 2019 (COVID-19) pandemic had several mental effects on medical staff. OBJECTIVE: This study intended to evaluate deviations in Frontline Dental Staff (FDS) depression, perceived stress and hypochondria during the COVID-19 outbreak, and to assess whether the existence of potential risk-factors influenced these symptoms over time. METHODS: This prospective cohort study surveyed FDS three periods from February 1, 2021 to April 8, 2022. FDSs’ mental health was assessed through Beck Depression Inventory, Cohen Perceived Stress and the Evans Self-Illness Questionnaires; multivariate linear regression were used to identify potential factors associated with changes on each outcome (depression, perceived stress and hypochondria) over time. All analyses were performed in STATA ver.14. RESULTS: In a total of 635 FDS, about 69%, 83%, and 71% reported relative depression, 77%, 87%, and 64% reported moderate to high stress level, and 60%, 76% and 74% reported moderate hypochondriac from first, second, and third survives, respectively. The mean and standard deviation of the variables increased dramatically at second survive (July 17 to October 21, 2021) and decreased again at third survive significantly. Being female, working in public sector, and low socioeconomic level were main predictors of higher levels of depression (p

Published
2023
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30. Modal analysis of concrete arch dam–reservoir–massed foundation system in frequency domain.

Author

Farzad, Reza and Lotfi, Vahid

Subjects
*ARCH dams, *MODAL analysis, *CONCRETE analysis, *THEORY of wave motion, *MODE shapes, *ABSORPTION coefficients
Abstract

Modal analysis of concrete arch dam–reservoir–foundation rock systems is a challenging task. The complexities arise mainly due to computing mode shapes encountered when solving an eigenvalue problem with asymmetric generalized mass and stiffness matrices. Moreover, the problem becomes complicated when wave propagation is occurring due to the inclusion of water compressibility and foundation rock mass. In the present study, a computational tool is especially developed for this purpose. The theoretical background is explained initially. Subsequently, dynamic analysis of the Morrow Point arch dam–reservoir–foundation rock system is carried out with different values of reservoir bottom absorption coefficient. In addition, some of the modal characteristics of such systems, including resonant frequencies and natural periods, are discussed. The main objective is to perform these analyses by modal analysis. However, the direct method of analysis is also carried out in each case as a basis for comparison from the perspectives of accuracy and efficiency. [ABSTRACT FROM AUTHOR]

Published
2023
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47. Flexible automation investments: a problem formulation and solution procedure

Author

Lotfi, Vahid and Suresh, Nallan C.

Subjects
Capital investments -- Research, Dynamic programming -- Usage, Flexible manufacturing systems -- Research, Business, Business, general, Business, international
Abstract

The introduction of computer numerical control-based manufacturing systems has highlighted the need to develop new models for determining optimal equipment replacement schedules and levels of investment. A multi-period replacement model based on a mixed integer nonlinear programming formulation has been developed. However, validation of the new model has been inconclusive because several other factors such as system setups and lot sizes need to be considered.

Published
1994

50. An Introduction to Redundancy

Author

Karwan, Mark H., Lotfi, Vahid, Zionts, Stanley, Telgen, Jan, Beckmann, M., editor, Krelle, W., editor, Karwan, Mark H., Lotfi, Vahid, Zionts, Stanley, and Telgen, Jan

Published
1983
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