Black hole shadow with a cosmological constant for cosmological observers

We investigate the effect of the cosmological constant on the angular size of a black hole shadow. It is known that the accelerated expansion which is created by the cosmological constant changes the angular size of the black hole shadow for static observers. However, the shadow size must be calculated for the appropriate cosmological observes. We calculate the angular size of the shadow measured by cosmological comoving observers by projecting the shadow angle to this observer rest frame. We show that the shadow size tends to zero as the observer approaches the cosmological horizon. We estimate the angular size of the shadow for a typical supermassive black hole, e.g M87. It is found that the angular size of the shadow for cosmological observers and static observers is approximately the same at these scales of mass and distance. We present a catalog of supermassive black holes and calculate the effect of the cosmological constant on their shadow size and find that the effect could be $3\; precent$ for distant known sources like the Phoenix Cluster supermassive black hole.Comment: 8 pages, 2 figures, a few typos in table numbers and text correcte

Shoulder girdle muscle activity and fatigue in traditional and improved design carpet weaving workstations

Objectives: Work-related musculoskeletal disorders in the neck and shoulder regions are common among carpet weavers. Working for prolonged hours in a static and awkward posture could result in an increased muscle activity and may lead to musculoskeletal disorders. Ergonomic workstation improvements can reduce muscle fatigue and the risk of musculoskeletal disorders. Material and Methods: The aim of this study is to assess and to compare upper trapezius and middle deltoid muscle activity in 2 traditional and improved design carpet weaving workstations. These 2 workstations were simulated in a laboratory and 12 women carpet weavers worked for 3 h. Electromyography (EMG) signals were recorded during work in bilateral upper trapezius and bilateral middle deltoid. The root mean square (RMS) and median frequency (MF) values were calculated and used to assess muscle load and fatigue. Repeated measure ANOVA was performed to assess the effect of independent variables on muscular activity and fatigue. The participants were asked to report shoulder region fatigue on the Borg�s Category-Ratio scale (Borg CR-10). Results: Root mean square values in workstation A are significantly higher than in workstation B. Furthermore, EMG amplitude was higher in bilateral trapezius than in bilateral deltoid. However, muscle fatigue was not observed in any of the workstations. Conclusions: The results of the study revealed that muscle load in a traditional workstation was high, but fatigue was not observed. Further studies investigating other muscles involved in carpet weaving tasks are recommended. © 2016, Nofer Institute of Occupational Medicine. All rights reserved

Experimental Research on the Shear Connectors in Foam Concrete

In order to improve the longitudinal shear resistance between foam concrete and C-Channels, an investigation is carried out on the shear connectors in foam concrete with cold-formed steel double C-Channels embedment. Twenty-four tests have been carried out in two groups. Two types of connectors: flange connectors and web connectors are installed using self-drilling screws for a rapid construction. The experimental results show that they can effectively improve the longitudinal shear-resist capacity of the concrete. After the experiment, the specimens are dismantled for an interior observation. Based on the observation, the form of damage, the failure mechanism was discovered, and the equation of longitudinal shear capacity was developed. It is concluded that the failure involves independent slippage between two C-Channels and the shear connection fractures. Since the composite structure requires sufficient slip between the two materials, these types of shear connectors will have good enhancement for this type of composite structures subjected to dynamic loads

Developing a new adjustable ergonomic armrests for computer keyboard operators

Background and aims   The study is aimed at designing and testing a new ergonomic armrest that can address musculoskeletal problems among computer keyboard operators in Iran.   Methods   Twenty seven operators from an educational institute were selected as subjects. Direct observations and subjective assessment using Karlqvist et al.'s (1996) questionnaires were  used to discover the weaknesses of their existing armrest. The existing armrest was replaced with  the new armrest which allows height adjustment, and length, width and direction/rotation  movements to suite various arm positions for keying and mousing tasks. Data on the hand and arm postures were collected and compared to common armrest.   Results   With the new armrest, results showed significant improvements in the postures of forearm, elbow, hand and wrist which facilitate easy access of the entire surface of keyboard and mouse. In addition, majority of the subjects were satisfied, in different aspects, with the use of the ergonomic armrest .   Conclusion   Because of its positive and dynamic features, the new armrest could well be  replaced with the traditional and even forign ergonomic armrests attachable to the table. The new   armrest do not disrupt the user’s job