Feed aggregator

Electrical Engineer for Building Design | Bessolo Design Group

SPS Jobs - 1 July 2016
US - FL - St Petersburg, Electrical Engineer - Qualifications, Knowledge and Experience in: Licensed Professional Engineer - Required  Bachelor’s degree in Electrical Engineering 10 years minimum experience i

Forensic Mechanical Engineer | PT&C|LWG Forensic Consulting Services

SPS Jobs - 1 July 2016
US - MN - Minneapolis, Qualifications: Baccalaureate degree in Mechanical Engineering or a related field is required. Significant experience (typically 6+ years) as a professional engineer is required.   Exp

Propulsion Engineer | Astrobotic

SPS Jobs - 1 July 2016
US - PA - Pittsburgh,   Knowledge and Skill Competencies: Experience specifying, and analyzing spacecraft propulsion system components Knowledge/experience of MMH and MON-25 propulsion systems or similar Knowled

Ice-age temperature swings may have been caused by fluctuating Atlantic Ocean currents

Science: During the last ice age, temperatures on Earth’s surface seesawed several times between the Northern and Southern Hemispheres: As the north got colder, the south grew warmer, and vice versa. Now researchers have found that the abrupt temperature changes in the two hemispheres may have been caused by a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), an ocean current that drives shallower, warmer waters north and deeper, colder waters south. Studying a sediment core drilled from the Bermuda Rise in the Atlantic Ocean, Jerry McManus of Columbia University and colleagues say they saw at least four instances when the ratio of two radioactive daughter isotopes changed sharply, which indicated a weakening of the AMOC. Such slowdowns could have caused the north to receive less warm water and temperatures there to drop while the south heated up due to the backlog of warm water. What caused the slowdowns is still unknown, but one explanation is the breaking off of Canadian icebergs, whose melting would have increased the amount of freshwater in the North Atlantic and possibly disrupted ocean flow. Over some 1500 years, the freshwater would have dissipated, allowing the AMOC to increase once again in strength.

Research/ Staff Scientist | Lawrence Berkeley National Laboratory

Latest Jobs - 1 July 2016
US - CA - Berkeley, Research/Staff Scientist - 82576Organization: AF-Accelerator Tech-Applied PhysBerkeley Lab is Bringing Science Solutions to the World, and YOU can be a part of it!In the world of science, Lawrence Be

More than 100 Nobel laureates call for end to opposition of GMOs

Washington Post: On 30 June more than 100 Nobel laureates, including 25 physics awardees, released a letter that called for the environmental activism group Greenpeace to end its opposition to the use of genetically modified organisms (GMOs) in agriculture. The letter primarily focused on Golden Rice, a form of rice that produces high levels of beta-carotene, a precursor of vitamin A. Golden Rice was developed as a potential crop for areas where the populations suffer from vitamin A deficiency. The letter says that Greenpeace has driven the resistance to the commercialization of Golden Rice and to GMOs in general, despite the lack of evidence that engineered crops are harmful. The signature campaign was organized by Richard Roberts of New England Biolabs, who shared with Phillip Sharp the 1993 Nobel Prize in Physiology or Medicine for the discovery of genetic sequences called introns.

Antarctic ozone hole appears to be shrinking

Nature: Three decades after the introduction of the Montreal Protocol, the ozone hole over the Antarctic is beginning to disappear. The hole was first observed in the late 1970s, when scientists realized that the use of chlorofluorocarbons and similar substances in aerosol spray cans and cooling systems was having an adverse effect on Earth's ozone layer, which shields the planet from the Sun's UV radiation. Now Susan Solomon of MIT and colleagues, who have been monitoring polar ozone with weather balloons, say that since 2000 the Antarctic ozone hole has been shrinking in the month of September—a key time of year because it marks the beginning of the Antarctic spring and the return of more sunlight to the region. Although no measurable improvement has been seen in the hole over the Arctic, the researchers say the improvement in the Antarctic is a sign that the Montreal Protocol is having a positive effect. “We as a planet have avoided what would have been an environmental catastrophe,” says Solomon.

Tesla's Autopilot feature involved in fatal crash for first time

Wired: On 7 May, a Tesla Model S driver, who was using the vehicle's semiautonomous Autopilot feature, died after the car crashed into a tractor trailer. In a statement Tesla indicated that the accident occurred when the tractor trailer made a left turn across a divided highway. The Model S went underneath the side of the trailer, which made contact only at the height of the windshield. Neither the vehicle's driver nor the Autopilot feature engaged the Tesla's brake. Tesla claims that the Autopilot (and the driver) failed to detect the white trailer, which would have been hard to see against the bright sky. The company says that its vehicles have accumulated more than 130 million miles using the feature without any other fatal accident. Autopilot, which must be activated by the driver, uses a combination of radar, cameras, GPS, and ultrasonic sensors to control the vehicle. When activated, it reminds drivers that they are supposed to keep their hands on the steering wheel and should be ready to assume complete control of the vehicle at any time.

Mars' Atmosphere Blew Away Billions Of Years Ago

Inside Science - 1 July 2016

New observations point to processes driving away the atmosphere, rendering the planet's surface inhospitable to life.

Joint Position between EPFL and PSI | EPFL / PSI

Latest Jobs - 1 July 2016
CHE - Nationwide, Professor of Physical Chemistry at Ecole polytechnique fédérale de Lausanne (EPFL) and Head of the Laboratory for Femtochemistry at the Paul Scherrer Institute (PSI)  

NIF quest hobbled from the start

Extra Dimensions: Any progress in the pursuit of laser-initiated fusion is overshadowed by the project’s failure to meet an absurdly ambitious deadline.

Mode localization in the cooperative dynamics of protein recognition

The biological function of proteins is encoded in their structure and expressed through the mediation of their dynamics. This paper presents a study on the correlation between local fluctuations, binding, and biological function for two sample proteins, starting from the Langevin Equation for Protein Dynamics (LE4PD). The LE4PD is a microscopic and residue-specific coarse-grained approach to protein dynamics, which starts from the static structural ensemble of a protein and predicts the dynamics analytically. It has been shown to be accurate in its prediction of NMR relaxation experiments and Debye-Waller factors. The LE4PD is solved in a set of diffusive modes which span a vast range of time scales of the protein dynamics, and provides a detailed picture of the mode-dependent localization of the fluctuation as a function of the primary structure of the protein. To investigate the dynamics of protein complexes, the theory is implemented here to treat the coarse-grained dynamics of interacting macromolecules. As an example, calculations of the dynamics of monomeric and dimerized HIV protease and the free Insulin Growth Factor II Receptor (IGF2R) domain 11 and its IGF2R:IGF2 complex are presented. Either simulation-derived or experimentally measured NMR conformers are used as input structural ensembles to the theory. The picture that emerges suggests a dynamical heterogeneous protein where biologically active regions provide energetically comparable conformational states that are trapped by a reacting partner in agreement with the conformation-selection mechanism of binding.

Adlayer structure dependent ultrafast desorption dynamics in carbon monoxide adsorbed on Pd (111)

We report our ultrafast photoinduced desorption investigation of the coverage dependence of substrate–adsorbate energy transfer in carbon monoxide adlayers on the (111) surface of palladium. As the CO coverage is increased, the adsorption site population shifts from all threefold hollows (up to 0.33 ML), to bridge and near bridge (>0.5 to 0.6 ML) and finally to mixed threefold hollow plus top site (at saturation at 0.75 ML). We show that between 0.24 and 0.75 ML this progression of binding site motifs is accompanied by two remarkable features in the ultrafast photoinduced desorption of the adsorbates: (i) the desorption probability increases roughly two orders magnitude, and (ii) the adsorbate–substrate energy transfer rate observed in two-pulse correlation experiments varies nonmonotonically, having a minimum at intermediate coverages. Simulations using a phenomenological model to describe the adsorbate–substrate energy transfer in terms of frictional coupling indicate that these features are consistent with an adsorption-site dependent electron-mediated energy coupling strength, η el, that decreases with binding site in the order: three-fold hollow > bridge and near bridge > top site. This weakening of η el largely counterbalances the decrease in the desorption activation energy that accompanies this progression of adsorption site motifs, moderating what would otherwise be a rise of several orders of magnitude in the desorption probability. Within this framework, the observed energy transfer rate enhancement at saturation coverage is due to interadsorbate energy transfer from the copopulation of molecules bound in three-fold hollows to their top-site neighbors.

Ab initio study of vacancy formation in cubic LaMnO3 and SmCoO3 as cathode materials in solid oxide fuel cells

Doped LaMnO3 and SmCoO3 are important solid oxide fuel cell cathode materials. The main difference between these two perovskites is that SmCoO3 has proven to be a more efficient cathode material than LaMnO3 at lower temperatures. In order to explain the difference in efficiency, we need to gain insight into the materials’ properties at the atomic level. However, while LaMnO3 has been widely studied, ab initio studies on SmCoO3 are rare. Hence, in this paper, we perform a comparative DFT + U study of the structural, electronic, and magnetic properties of these two perovskites. To that end, we first determined a suitable Hubbard parameter for the Co d–electrons to obtain a proper description of SmCoO3 that fully agrees with the available experimental data. We next evaluated the impact of oxygen and cation vacancies on the geometry, electronic, and magnetic properties. Oxygen vacancies strongly alter the electronic and magnetic structures of SmCoO3, but barely affect LaMnO3. However, due to their high formation energy, their concentrations in the material are very low and need to be induced by doping. Studying the cation vacancy concentration showed that the formation of cation vacancies is less energetically favorable than oxygen vacancies and would thus not markedly influence the performance of the cathode.

Note: Application of a novel 2(3HUS+S) parallel manipulator for simulation of hip joint motion

In the paper, a novel 2(3HUS+S) parallel manipulator, which has two moving platforms, is proposed. The parallel manipulator is adopted to simulate hip joint motion and can conduct an experiment for two hip joints simultaneously. Motion experiments are conducted in the paper, and the recommended hip joint motion curves from ISO14242 and actual hip joint motions during jogging and walking are selected as the simulated motions. The experimental results indicate that the 2(3HUS+S) parallel manipulator can realize the simulation of many kinds of hip joint motions without changing the structure size.

Accurate measurements of cross-plane thermal conductivity of thin films by dual-frequency time-domain thermoreflectance (TDTR)

Accurate measurements of the cross-plane thermal conductivity Λcross of a high-thermal-conductivity thin film on a low-thermal-conductivity (Λs) substrate (e.g., Λcross/Λs > 20) are challenging, due to the low thermal resistance of the thin film compared with that of the substrate. In principle, Λcross could be measured by time-domain thermoreflectance (TDTR), using a high modulation frequency f h and a large laser spot size. However, with one TDTR measurement at f h, the uncertainty of the TDTR measurement is usually high due to low sensitivity of TDTR signals to Λcross and high sensitivity to the thickness h Al of Al transducer deposited on the sample for TDTR measurements. We observe that in most TDTR measurements, the sensitivity to h Al only depends weakly on the modulation frequency f. Thus, we performed an additional TDTR measurement at a low modulation frequency f 0, such that the sensitivity to h Al is comparable but the sensitivity to Λcross is near zero. We then analyze the ratio of the TDTR signals at f h to that at f 0, and thus significantly improve the accuracy of our Λcross measurements. As a demonstration of the dual-frequency approach, we measured the cross-plane thermal conductivity of a 400-nm-thick nickel-iron alloy film and a 3-μm-thick Cu film, both with an accuracy of ∼10%. The dual-frequency TDTR approach is useful for future studies of thin films.

Load-cell based characterization system for a “Violin-Mode” shadow-sensor in advanced LIGO suspensions

The background to this work was a prototype shadow sensor, which was designed for retro-fitting to an advanced LIGO (Laser Interferometer Gravitational wave Observatory) test-mass/mirror suspension, in which 40 kg test-mass/mirrors are each suspended by four approximately 600 mm long by 0.4 mm diameter fused-silica suspension fibres. The shadow sensor comprised a LED source of Near InfraRed (NIR) radiation and a rectangular silicon photodiode detector, which, together, were to bracket the fibre under test. The aim was to detect transverse Violin-Mode resonances in the suspension fibres. Part of the testing procedure involved tensioning a silica fibre sample and translating it transversely through the illuminating NIR beam, so as to measure the DC responsivity of the detection system to fibre displacement. However, an equally important part of the procedure, reported here, was to keep the fibre under test stationary within the beam, whilst trying to detect low-level AC Violin-Mode resonances excited on the fibre, in order to confirm the primary function of the sensor. Therefore, a tensioning system, incorporating a load-cell readout, was built into the test fibre’s holder. The fibre then was excited by a signal generator, audio power amplifier, and distant loudspeaker, and clear resonances were detected. A theory for the expected fundamental resonant frequency as a function of fibre tension was developed and is reported here, and this theory was found to match closely with the detected resonant frequencies as they varied with tension. Consequently, the resonances seen were identified as being proper Violin-Mode fundamental resonances of the fibre, and the operation of the Violin-Mode detection system was validated.

Thermal conductivity versus depth profiling of inhomogeneous materials using the hot disc technique

Transient measurements of thermal conductivity are performed with hot disc sensors on samples having a thermal conductivity variation adjacent to the sample surface. A modified computational approach is introduced, which provides a method of connecting the time-variable to a corresponding depth-position. This allows highly approximate—yet reproducible—estimations of the thermal conductivity vs. depth. Tests are made on samples incorporating different degrees of sharp structural defects at a certain depth position inside a sample. The proposed methodology opens up new possibilities to perform non-destructive testing; for instance, verifying thermal conductivity homogeneity in a sample, or estimating the thickness of a deviating zone near the sample surface (such as a skin tumor), or testing for presence of other defects.

3D analysis of eddy current loss in the permanent magnet coupling

This paper first presents a 3D analytical model for analyzing the radial air-gap magnetic field between the inner and outer magnetic rotors of the permanent magnet couplings by using the Amperian current model. Based on the air-gap field analysis, the eddy current loss in the isolation cover is predicted according to the Maxwell’s equations. A 3D finite element analysis model is constructed to analyze the magnetic field spatial distributions and vector eddy currents, and then the simulation results obtained are analyzed and compared with the analytical method. Finally, the current losses of two types of practical magnet couplings are measured in the experiment to compare with the theoretical results. It is concluded that the 3D analytical method of eddy current loss in the magnet coupling is viable and could be used for the eddy current loss prediction of magnet couplings.

Pages

Subscribe to American Institute of Physics aggregator