On the Strain Rate Sensitivity of Abs and Abs Plus Fused Deposition Modeling Parts

In this work the effect of strain rate on the tensile strength of fused deposition modeling parts built with Acrylonitrile-butadiene-styrene (ABS) and ABS plus material is presented. ASTM D638-02a specimens were built with ABS and ABS plus and they were tested on a Schenck Trebel Co. tensile test machine at three different test speeds, equal, lower, and higher to the test speed required by the ASTM D638-02a standard. The experimental tensile strength results were compared and evaluated. The fracture surfaces of selected specimens were examined with a scanning electron microscope, to determine failure mode of the filament strands. It was found that, as the test speed increases, specimens develop higher tensile strength and have higher elastic modulus. Specimens tested in the highest speed of the experiment had on average about 10% higher elastic modulus and developed on average about 11% higher tensile strength.     

Fast quantum key distribution with decoy number states

We investigate the use of photon number states to identify eavesdropping attacks on quantum key distribution (QKD) schemes. The technique is based on the fact that different photon numbers traverse a channel with different transmittivity. We then describe two QKD schemes that utilize this method, one of which overcomes the upper limit on the key generation rate imposed by the dead time of detectors when using a heralded source of photons.     

Impact of surface state in probeless friction stir spot welding of an Al–Li alloy

ABSTRACT

Sheets of AA2198 alloy with various surface conditions were welded with probeless friction stir spot welding (P-FSSW). Results show that the oxide layer on the original lap-weld surface produces continuously distributed oxide impurities at the interface of the P-FSSWed joint with a large amount of voids. The visual flow at the interface provides a persuasive explanation of local preferential abrasion. Following surface grinding, local abrasion increases with surface roughness and results in the dispersion of voids and oxides, which contributes to the improvement of metallurgical connection. The corresponding mechanical strength of the P-FSSWed joints shows a relatively significant increase, while the fracture mode remains affected by the hook defect regardless of the surface state.     

Continuous electromagnetic radiation monitoring in the environment: analysis of the results in Greece

Non-ionising radiation-monitoring networks were initiated as a result of the public concerns about the potential health effects from telecommunication emissions. In the present study, the data acquired from such networks in Greece are used to assess the changes in the outdoor electromagnetic environment with respect to location and time. The study shows that there is a statistically significant difference between the urban (median electric field: 1.1 V m(-1)) and the rural (median electric field: 0.3 V m(-1)) installations of monitoring units and also shows that there is a median diurnal variation (daily maximum to minimum) of 20.2 and 33.8 % for the broadcasting and mobile telecommunication emissions, respectively. Moreover, there is a difference in the electric field between daytime and night, but not between morning and afternoon. The results are in line with previously published data from spot measurements, monitoring networks and personal exposimeter studies performed in several European countries.     

Becoming team players: Team members' mastery of teamwork knowledge as a predictor of team task proficiency and observed teamwork effectiveness.

The authors explored the idea that teams consisting of members who, on average, demonstrate greater mastery of relevant teamwork knowledge will demonstrate greater task proficiency and observed teamwork effectiveness. In particular, the authors posited that team members' mastery of designated teamwork knowledge predicts better team task proficiency and higher observer ratings of effective teamwork, even while controlling for team task proficiency. The authors investigated these hypotheses by developing a structural model and testing it with field data from 92 teams (1,158 team members) in a United States Air Force officer development program focusing on a transportable set of teamwork competencies. The authors obtained proficiency scores on 3 different types of team tasks as well as ratings of effective teamwork from observers. The empirical model supported the authors' hypotheses. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Displaying employee testimonials on recruitment web sites: Effects of communication media, employee race, and job seeker race on organizational attraction and information credibility.

This study investigated participants’ reactions to employee testimonials presented on recruitment Web sites. The authors manipulated the presence of employee testimonials, richness of media communicating testimonials (video with audio vs. picture with text), and representation of racial minorities in employee testimonials. Participants were more attracted to organizations and perceived information as more credible when testimonials were included on recruitment Web sites. Testimonials delivered via video with audio had higher attractiveness and information credibility ratings than those given via picture with text. Results also showed that Blacks responded more favorably, whereas Whites responded more negatively, to the recruiting organization as the proportion of minorities shown giving testimonials on the recruitment Web site increased. However, post hoc analyses revealed that use of a richer medium (video with audio vs. picture with text) to communicate employee testimonials tended to attenuate these racial effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of microstructural asymmetries across friction stir welded AA2024 joints on mechanical properties

The effect of offset of the centre of a tensile specimen to the weldline on global tensile properties of friction stir welded AA2024 joints was investigated using experiments and numerical analysis. The size and geometry of these discrete zones, such as the central low hardness zone, the low hardness zone-I near the thermo-mechanically affected zone, the low hardness zone-II near the base metal and the base metal, were determined from a cross-sectional hardness map. Results show that tensile specimens with different area of the joint placed in the centre of the specimen do not affect the tensile strength and fracture path of a joint, strain is affected. Predictions based on local tensile properties follow well the measured global tensile behaviour.     

The effects of forging pressure and temperature field on residual stresses in linear friction welded Ti6Al4V joints

Linear friction welding (LFW), as a solid state joining process, has been developed to manufacture and repair blisks in aeroengines. The residual stresses after welding may greatly influence the performance of the welded components. In this paper, the distribution of residual stresses in Ti6Al4V joints after LFW was investigated with numerical simulations. The effects of applied forging pressure and temperature field at the end of the oscillating stages on the residual stresses within the joints were investigated. The results show that, the residual tensile stresses at the welded interface in the y-direction are the largest, while the largest compressive stresses being present at the flash root in the z-direction. Furthermore, the forging pressure and temperature field at the end of the oscillating stages strongly affect the magnitude of the residual stresses. The larger forging pressure produced lower residual stresses in the weld plane in all three directions (x-, y-, and z-directions). Larger variance, σ, which decides the Gaussian distribution of the temperature field, also yields lower residual stresses. There is good agreement between simulation results and experimental data.     

America''s ‘Achilles Heel’?: Security of US energy infrastructure

America's security may ultimately be more vulnerable to terrorist attacks (as well as technical mishaps or natural disasters) involving its domestic energy supply and particularly its distribution system than as a result of actions of any foreign army. And yet, key energy observers believe that the US energy supply does not need to be insecure, and that it could be made infinitely more secure with a blending of renewable energy, aggressive emphasis on energy efficiency, and the development of a distributed system of energy delivery. Amory B. Lovins, Chief Executive Officer (Research) of the Rocky Mountain Institute (RMI), in Colorado, USA, has been making this case for nearly two decades. He spoke to Don Smith, Refocus magazine recently in Denver, Colorado, about the national importance of viewing energy security in the context of the new world realities.