Gaussian elimination as an iterative algorithm

Gaussian elimination (GE) for solving an $n \times n$ linear system of equations $Ax=b$ is the archetypical direct method of numerical linear algebra, as opposed to iterative. In this note we want to point out that GE has an iterative side too

An extension of Chebfun to two dimensions

An object-oriented MATLAB system is described that extends the capabilities of Chebfun to smooth functions of two variables defined on rectangles. Functions are approximated to essentially machine precision by using iterative Gaussian elimination with complete pivoting to form “chebfun2” objects representing low rank approximations. Operations such as integration, differentiation, function evaluation, and transforms are particularly efficient. Global optimization, the singular value decomposition, and rootfinding are also extended to chebfun2 objects. Numerical applications are presented

The unidirectional relationship of nightmares on self-harmful thoughts and behaviors

Understanding the direction of the predictive relationship between nightmares and suicidal behaviors is important to model its underlying mechanisms. We examine the direction of this relationship and the mediating role of negative affect. A fixed interval diary study obtained pre-sleep and post-sleep measures of affect, nightmares, and self-harmful thoughts and behaviors (SHTBs) from 72 university students (88.9% female). The results show predictive utility of nightmares on SHTBs - indicating a fourfold increased risk of SHTBs. Additionally, results support the suggestion of a unidirectional predictive influence (of nightmares on likelihood of SHTBs but not vice versa). Moreover, postsleep negative affect partially mediated the relationship between nightmares and postsleep SHTBs. This empirically validates assumptions of directionality for future models

Correlates of Compulsive Buying

Compulsive buying is a chronic issue for shoppers exacerbated by a nation obsessed with consumption. To predict compulsive buying behavior, a survey was administered to 283 college students in southern Nevada. The results suggested that the compulsive buyer exhibits am ex­ternal consumer locus of control and purchases goods with the intent to increase social status or quell anxiety. Given that responsible financial behavior changes as a function of age, college students are particularly vulnerable to compulsive purchasing behavior, as it is exacerbated by irresponsible credit spending behaviors

Accelerating Cosmologies from S-Branes

We point out that the recently proposed model of a flat 4-dimensional universe with accelerated expansion in string/M-theory is a special case of time-dependent solutions that the author found under the name of ``S-branes.'' We also show that similar accelerating models can be obtained from S-branes if the internal space is chosen to be hyperbolic or flat spaces.Comment: 8 pages, 4 figures, comments added, a typo corrected, final version to appear in Phys. Rev. Let

Surface fatigue life of M50NiL and AISI 9310 spur gears and R C bars

Spur gear endurance tests and rolling element surface fatigue tests were conducted to study vacuum induction melted, vacuum arc remelted (VIM-VAR) M50NiL steel for use as a gear steel in advanced aircraft applications, to determine its endurance characteristics, and to compare the results with those for standard VAR and VIM-VAR AISI 9310 gear material. Tests were conducted with spur gears and rolling contact bars manufactured from VIM-VAR M50NiL and VAR and VIM-VAR AISI 9310. The gear pitch diameter was 8.9 cm. Gear test conditions were an inlet oil temperature of 320 K, and outlet oil temperature of 350 K, a maximum Hertz stress of 1.71 GPa, and a speed of 10000 rpm. Bench rolling element fatigue tests were conducted at ambient temperatures with a bar speed of 12,500 rpm and a maximum Hertz stress of 4.83 GPa. The VIM-VAR M50NiL gears had a surface fatigue life that was 4.5 and 11.5 times that for VIM-VAR and VAR AISI 9310 gears, respectively. The surface fatigue life of the VIM-VAR M50NiL rolling contact bars was 13.2 and 21.6 times that for the VIM-VAR and VAR AISI 9310, respectively. The VIM-VAR M50NiL material was shown to have good resistance to fracture through a fatigue spall and superior fatigue life to both other gears

Surface fatigue life of carburized and hardened M50NiL and AISI 9310 spur gears and rolling-contact test bars

Spur gear endurance tests and rolling-element surface tests were conducted to investigate vacuum-induction-melted, vacuum-arc-melted (VIM-VAR) M50NiL steel for use as a gear steel in advanced aircraft applications, to determine its endurance characteristics, and to compare the results with those for standard VAR and VIM-VAR AISI 9310 gear material. Tests were conducted with spur gears and rolling-contact bars manufactured from VIM-VAR M50NiL and VAR and VIM-VAR AISI 9310. The gear pitch diameter was 8.9 cm (3.5 in.). Gear test conditions were an inlet oil temperature of 320 K (116 F), and outlet oil temperature of 350 K (170 F), a maximum Hertz stress of 1.71 GPa (248 ksi), and a speed of 10,000 rpm. Bench rolling-element fatigue tests were conducted at ambient temperatures with a bar speed of 12,500 rpm and a maximum Hertz stress of 4.83 GPA (700 ksi). The VIM-VAR M50NiL gears had a surface fatigue life that was 4.5 and 11.5 times that for VIM-VAR and VAR AISI 9310 gears, respectively. The surface fatigue life of the VIM-VAR M50NiL rolling-contact bars was 13.2 and 21.6 times that for the VIM-VAR and VAR AISI 9310, respectively. The VIM-VAR M50NiL material was shown to have good resistance to fracture through a fatigue spall and to have fatigue life far superior to that of both VIM-VAR and VAR AISI 9310 gears and rolling-contact bars

Conductance impedance effects in atomically thin semiconductors

The rapidly unfolding innovation based on two-dimensional (2D) electronic materials is paving the way to numerous exciting applications in electronics, photovoltaics and sensing. Atomically thin transition metal dichalcogenides are an exciting family of 2D materials that can complement state-of-the-art devices through added functionality (e.g. mechanical flexibility). For optimal device performance, the complete picture of the charge transport mechanisms through the device, i.e. charge injection, transport and retention, needs to be fully understood. This work presents experimental evidence for the formation of Schottky barriers as low as 10 meV between MoTe₂ and metal electrodes at cryogenic temperatures. By varying the electrode work functions, it is demonstrated that Fermi level pinning due to metal induced gap states at the interfaces occurs at 0.14 eV above the valence band maximum. This is the first experimental observation of thermionic emission at temperatures as low as 40 K, which is unexpected since tunnelling usually is the dominant effect at these temperatures. However, as the formed barrier is uniquely broad and shallow, and as the thermal width of the Fermi-Dirac distribution is comparable with these measured barrier heights, thermionic emission is found to be the dominant mechanism. A further investigation reveals a novel transport effect, dubbed threshold voltage transient effect, which is manifested in a hysteresis in the transfer curves. By probing the transient currents measured during cycles of pulses through the gate electrode, it is possible to distinguish between charge trapping that occurs at the semiconductor/dielectric interface, and that which happens at the semiconductor/metal interface, showing that the time-dependent change in threshold voltage is the dominant effect on observed hysteretic behaviour. This new method is then extended into a spectroscopic technique, which allows the density of trap states to be mapped within the band gap of these atomically thin semiconductors. Finally, the threshold voltage transient method is adapted to investigate the changes in charge dynamics with variations in temperature.Defence Science and Technology Laboratory (DSTL

Two-point velocity average of turbulence: statistics and their implications

For turbulence, although the two-point velocity difference u(x+r)-u(x) at each scale r has been studied in detail, the velocity average [u(x+r)+u(x)]/2 has not thus far. Theoretically or experimentally, we find interesting features of the velocity average. It satisfies an exact scale-by-scale energy budget equation. The flatness factor varies with the scale r in a universal manner. These features are not consistent with the existing assumption that the velocity average is independent of r and represents energy-containing large-scale motions alone. We accordingly propose that it represents motions over scales >= r as long as the velocity difference represents motions at the scale r.Comment: 8 pages, accepted by Physics of Fluids (see http://pof.aip.org/

MUM00705 Gary Hawkins Multimedia Collection

Physical and digital files including moving image files, audio, photographs, small manuscripts, and ephemera related to the films Joe and The Rough South of Larry Brown created by filmmaker Gary Hawkins