Practical Product Importance Sampling for Direct Illumination

We present a practical algorithm for sampling the product of environment map lighting and surface reflectance. Our method builds on wavelet‐based importance sampling, but has a number of important advantages over previous methods. Most importantly, we avoid using precomputed reflectance functions by sampling the BRDF on‐the‐fly. Hence, all types of materials can be handled, including anisotropic and spatially varying BRDFs, as well as procedural shaders. This also opens up for using very high resolution, uncompressed, environment maps. Our results show that this gives a significant reduction of variance compared to using lower resolution approximations. In addition, we study the wavelet product, and present a faster algorithm geared for sampling purposes. For our application, the computations are reduced to a simple quadtree‐based multiplication. We build the BRDF approximation and evaluate the product in a single tree traversal, which makes the algorithm both faster and more flexible than previous methods.     

Efficient product sampling using hierarchical thresholding

We present an efficient method for importance sampling the product of multiple functions. Our algorithm computes a quick approximation of the product on the fly, based on hierarchical representations of the local maxima and averages of the individual terms. Samples are generated by exploiting the hierarchical properties of many low-discrepancy sequences, and thresholded against the estimated product. We evaluate direct illumination by sampling the triple product of environment map lighting, surface reflectance, and a visibility function estimated per pixel. Our results show considerable noise reduction compared to existing state-of-the-art methods using only the product of lighting and BRDF.     

Oxygen saturation-dependent effects on blood transverse relaxation at low fields

Objective

Blood oxygenation can be measured using magnetic resonance using the paramagnetic effect of deoxy-haemoglobin, which decreases the \(\textit{T}_{2}\) relaxation time of blood. This \(\textit{T}_{2}\) contrast has been well characterised at the \(\textit{B}_{{0}}\) fields used in MRI (1.5 T and above). However, few studies have characterised this effect at lower magnetic fields. Here, the feasibility of blood oximetry at low field based on \(\textit{T}_{2}\) changes that are within a physiological relevant range is explored. This study could be used for specifying requirements for construction of a monitoring device based on low field permanent magnet systems.

Methods

A continuous flow circuit was used to control parameters such as oxygen saturation and temperature in a sample of blood. It flowed through a variable field magnet, where CPMG experiments were performed to measure its \(\textit{T}_{2}\). In addition, the oxygen saturation was monitored by an optical sensor for comparison with the \(\textit{T}_{2}\) changes.

Results

These results show that at low \(\textit{B}_{{0}}\) fields, the change in blood \(\textit{T}_{2}\) due to oxygenation is small, but still detectable. The data measured at low fields are also in agreement with theoretical models for the oxy-deoxy \(\textit{T}_{2}\) effect.

Conclusion

\(\textit{T}_{2}\) changes in blood due to oxygenation were observed at fields as low as 0.1 T. These results suggest that low field NMR relaxometry devices around 0.3 T could be designed to detect changes in blood oxygenation.

     

Reconditioning rotor components of gas turbine engines produced from titanium alloys by welding using modified submicrocrystalline filler materials

Experimental results show that the application of standard methods of reconditioning components of titanium alloys reduces the mechanical properties of welded joints by up to 30%. The main reasons for this are structural changes and weld defects. The modified (La, Y and B) filler materials were developed from titanium alloys with a submicrocrystalline structure. These materials produce the equiaxed and ductile structures in welded joints in titanium alloys so that the mechanical properties of the welded joints equal 0.9 of the properties of the parent metal. Consequently, the range of repairs of rotors of gas turbine engines can be greatly widened.     

Effect of welding methods on the structure and mechanical properties of welded joints in creep-resisting titanium alloys with different initial structural conditions

Problems of welding rotor components made of creep-resisting titanium alloys are investigated. Comparative tests of the effects of fusion welding and rotational friction welding (FW) on the structure and properties of welded joints in titanium alloys are carried out. The experimental results show that welded joints produced by rotational FW have a structure identical to the structure of the parent metal, and the heat-affected zone does not form at all. The optimum conditions of FW of creep-resisting titanium alloys are determined. Irrespective of the initial type of structure, these conditions result in the mechanical properties of the welded joint at a level of 0.9 of the properties of the parent metal.     

Learning parallel portfolios of algorithms

A wide range of combinatorial optimization algorithms have been developed for complex reasoning tasks. Frequently, no single algorithm outperforms all the others. This has raised interest in leveraging the performance of a collection of algorithms to improve performance. We show how to accomplish this using a Parallel Portfolio of Algorithms (PPA). A PPA is a collection of diverse algorithms for solving a single problem, all running concurrently on a single processor until a solution is produced. The performance of the portfolio may be controlled by assigning different shares of processor time to each algorithm. We present an effective method for finding a PPA in which the share of processor time allocated to each algorithm is fixed. Finding the optimal static schedule is shown to be an NP-complete problem for a general class of utility functions. We present bounds on the performance of the PPA over random instances and evaluate the performance empirically on a collection of 23 state-of-the-art SAT algorithms. The results show significant performance gains over the fastest individual algorithm in the collection.      

Combat experience and youth: Influences on reported violence against women.

A study of 101 VA psychiatric and chemically dependent inpatients (mean age 44.8 yrs) was conducted to investigate the hypothesis that combat veterans (n?=?54) would report a higher frequency of physical violence against female partners than noncombat veterans (n?=?47). Veterans were interviewed by staff psychologists seeking information about the frequency and severity of violence toward their female partners and about whether or not they had been in combat. Results show no significant differences in reported violence toward female partners between the combat and noncombat veterans even when age was controlled. Younger men were, however, more violent toward women than older men. Data cast doubt on the view that combat experience leads to violence within marital relationships. (11 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Current–Voltage Characteristics of Two-Electrode Elements with Carbon Nanotubes

Planar two-electrode nonlinear elements using carbon nanotubes doped with platinum metals are created and investigated. Among the nanotubes, branched ones are found. If doped, these nanotubes take a regular form. With appropriate doping, limiting currents above 1 A are achieved. However, the problem of contact between carbon nanotubes and electrodes has yet to be solved.