THERMAL ANALYSIS OF HIGH-CURRENT ELECTRIC CONTACT

This paper deals with mathematical modelling of the temperature distribution in the vicinity of a direct electrical high-current contact under the action of a nominal current of 3000 A. High-current electrical contacts belong among the elements by which a large number of electrical devices are connected. They play an important role especially in the transmission and distribution system, where they have to withstand adverse weather conditions that have a significant impact on their degradation.

An Examination of Social, Phonetic, and Lexical Variables on the Lenition of Intervocalic Voiced Stops by Spanish Heritage Speakers

The lenition of Spanish intervocalic voiced stops, commonly grouped as /bdg/, has increasingly been examined within Spanish as a Heritage Language research. This study seeks to identify social, phonetic, and lexical factors that predict the degree of lenition of /bdg/ among heritage speakers of Spanish. We analyzed 850 intervocalic productions of /bdg/ by 20 adult Spanish heritage speakers of various generations in an oral word list production task. Using spectrographic analyses, productions were categorized as full approximant, tense approximant, and occlusive. Results from linear mixed-effects models indicated that the phonetic context and the number of family generations residing in the US significantly predicted the degree of lenition of intervocalic voiced segments while age of acquisition of Spanish, current contact hours, and cognate status did not predict changes in the degree of lenition. Specifically, as the speaker’s number of family generations residing in the US increased, fewer segments were lenited. We conclude that variations in /bdg/ lenition among heritage speakers of Spanish reflect the changes in pronunciation of other segments of heritage speakers over generations.

NUMERICAL SIMULATION OF THERMAL CONDITION OF A LOW CURRENT ELECTRIC CONTACT

Electrical contacts may include various sub-systems or wiring harness connected via detachable connectors which depend on physical contacts for the electrical connectivity. Electrical contacts range from high, medium to low current depending on their usage. However, in the real-life condition, electrical contacts characteristics, especially at the interface, undergoes a gradual change which can be due to corrosion, temperature variation, aging, strained harnesses, discontinuities induced by vibration etc. These changes introduce additional parasitic circuits in the system. Moreover, in some cases where the contact resistance increases due to electrical loses, the local temperature may increase, thereby accelerating contact degradation. This paper presents a numerical analysis on the variation of temperature of a simple low current contact model having a thin oxide film layer at the interface which serves as the ageing factor using finite element method (FEM).

The Model of a Homopolar Electric Motor with High-Temperature Superconductors

The electromechanical model for analyzing a homopolar electric motor with a magnetic system made using second-generation high-temperature superconductors (HTSC 2G) is described. Homopolar electric motors made with a disk-shaped rotor have the simplest design of their magnetic system and heavy-current contact. Owing to the use of HTSC 2G conductors for producing constant magnetic field in the rotor area, it becomes possible to achieve a higher current density in the windings, thereby increasing the motor power capacity. Due to the HTSC ability to operate at the liquid nitrogen temperature (77 K), it becomes possible to have a simpler cryostat design in comparison with magnetic systems based on low-temperature superconductors. For large-capacity homopolar motors, the use of liquid metal contacts for supplying current to the rotating rotor seems to be the most promising design solution. The advantage of motors of this type is that their torque depends linearly on the rotor current. The homopolar motor operation governed by a proportional-integral-differentiating (PID) controller was simulated using the SciLab Xcos software. The application of the analysis model for selecting the optimal PID-controller coefficients is demonstrated. The electric motor dynamic operation modes are analyzed. The numerical simulation results are compared with the previously obtained experimental data.

A semi-analytical approach for rapid detection of roller-flange contacts in roller element bearings

For axially loaded cylindrical and tapered roller bearings, the dynamic behaviour of individual rollers, wear and friction losses are strongly influenced by roller-flange contact forces. For a realistic modelling of normal and friction forces of the roller-flange contact, it is essential to determine location and theoretical penetration of this contact. The rapid contact detection is particularly significant for rolling element bearing dynamic modelling in multibody systems. In this paper a semi-analytical algorithm for contact detection is introduced and compared to state of the art methods. The new approach adopts piecewise functions of spheres, cones and tori for modelling of roller end and flange geometry. The location of the contact and its theoretical penetration is calculated using analytical and combined analytical-numerical schemes. The semi-analytical approach proves to be significantly faster and numerically more stable than current contact detection algorithms without compromising precision.

Sleep Disturbances, Anxiety, and Burnout during the COVID-19 Pandemic: a nationwide cross-sectional study in Brazilian Healthcare Professionals.

Study objectives: To evaluate the impact of COVID-19 pandemic on sleep, anxiety, and Burnout in healthcare professionals. Methods: A survey was distributed using social media and organizational emails to Brazilian active healthcare professionals during the COVID-19 outbreak. We explored potential associated factors including age, gender, occupation, workplace, work hours, income, previous infection with COVID-19, recent/current contact with COVID-19 patients, regional number of incident deaths due to COVID-19, anxiety, and burnout. We evaluated new-onset or previous insomnia worsening (primary outcome), sleep quality, and duration (secondary outcomes). Results: A total of 4,384 health professionals from all regions of the country were included in the analysis (mean age: 44±12 years, 76% females, 53.8% physicians). Overall, 55.7% were assisting patients with COVID-19, and 9.2% had a previous COVID-19 infection. New-onset insomnia symptoms or previous insomnia worsening occurred in 41.4% of respondents in parallel to 13% (n=572) new pharmacological treatments for insomnia. Prevalent anxiety and burnout during the pandemic were observed in 44.2% and 21% of participants, respectively. Multivariate analyses showed that females (OR:1.756; 95% CI 1.487-2.075), weight change (decrease: OR:1.852; 95% CI 1.531-2.240; increase: OR:1.542; 95% CI 1.323-1.799), prevalent anxiety (OR:3.209; 95% CI 2.796-3.684), new-onset burnout (OR:1.986; 95% CI 1.677-2.352), family income reduction >30% (OR:1.366; 95% CI 1.140-1.636) and assisting patients with COVID-19 (OR:1.293; 95% CI 1.104-1.514) were independently associated with new-onset or worsening of previous insomnia. Conclusions: We observed a huge burden of insomnia in healthcare professionals during the COVID-19 pandemic. In this scenario, dedicated approaches for sleep health are highly desirable.