Testing General Relativity with Current Cosmological Data

Deviations from general relativity, such as could be responsible for the cosmic acceleration, would influence the growth of large scale structure and the deflection of light by that structure. We clarify the relations between several different model independent approaches to deviations from general relativity appearing in the literature, devising a translation table. We examine current constraints on such deviations, using weak gravitational lensing data of the CFHTLS and COSMOS surveys, cosmic microwave background radiation data of WMAP5, and supernova distance data of Union2. Markov Chain Monte Carlo likelihood analysis of the parameters over various redshift ranges yields consistency with general relativity at the 95% confidence level.Comment: 11 pages; 7 figures; typographical errors corrected; this is the published versio

Depth of penetration effects in eddy current testing

The simple depth of penetration equation used for most eddy current calculations does not take into account the effect of the size of the coil or the effect of flaw morphology. The work described in this paper describes use of the CIVA eddy current model to investigate this effect and some experimental investigations. Knowledge of this effect is important in examination of thin sections with eddy currents. Two examples of this are the small sections required to be inspected in laser metal deposition, and welds in thin sections joining dissimilar metals such as copper and aluminium for electrical connections

Testing current synthesis models of the X-ray background

We present synthesis models of the X-ray background where the available X-ray observational constraints are used to derive information on the AGN population properties. We show the need for luminous X-ray absorbed AGNs, the QSO2s, in reproducing the 2-10 keV source counts at relatively bright fluxes. We compare a model where the evolution of absorbed AGNs is faster than that of unabsorbed ones, with a standard model where absorbed and unabsorbed AGNs evolve at the same rate. It is found that an increase by a factor of ~2 from z=0 to z~1.3 in the ratio between absorbed and unabsorbed AGNs would provide a significant improvement in the data description. Finally, we make predictions on the AGNs to be observed in deep X-ray surveys which contain information on the AGN space density at high redshift.Comment: 11 pages with 8 figures, A&A accepte

Testing LCDM with the Growth Function \delta(a): Current Constraints

We have compiled a dataset consisting of 22 datapoints at a redshift range (0.15,3.8) which can be used to constrain the linear perturbation growth rate f=\frac{d\ln\delta}{d\ln a}. Five of these data-points constrain directly the growth rate f through either redshift distortions or change of the power spectrum with redshift. The rest of the datapoints constrain f indirectly through the rms mass fluctuation \sigma_8(z) inferred from Ly-\alpha at various redshifts. Our analysis tests the consistency of the LCDM model and leads to a constraint of the Wang-Steinhardt growth index \gamma (defined from f=\Omega_m^\gamma) as \gamma=0.67^{+0.20}_{-0.17}. This result is clearly consistent at $1\sigma$ with the value \gamma={6/11}=0.55 predicted by LCDM. A first order expansion of the index \gamma in redshift space leads to similar results.We also apply our analysis on a new null test of LCDM which is similar to the one recently proposed by Chiba and Nakamura (arXiv:0708.3877) but does not involve derivatives of the expansion rate $H(z)$. This also leads to the fact that LCDM provides an excellent fit to the current linear growth data.Comment: 7 pages, 4 figures. Added comments on the data of Table I (after eq. (2.16)). Corrected a typo on eq. (2.15). The mathematica files with the numerical analysis of this study may be found at http://nesseris.physics.uoi.gr/growth/growth.ht

Design and testing of a contra-rotating tidal current turbine

A contra-rotating marine current turbine has a number of attractive features: nearzero reactive torque on the support structure, near-zero swirl in the wake, and high relative inter-rotor rotational speeds. Modified blade element modelling theory has been used to design and predict the characteristics of such a turbine, and a model turbine and test rig have been constructed. Tests in a towing tank demonstrated the feasibility of the concept. Power coefficients were high for such a small model and in excellent agreement with predictions, confirming the accuracy of the computational modelling procedures. High-frequency blade loading data were obtained in the course of the experiments. These show the anticipated dynamic components for a contra-rotating machine. Flow visualization of the wake verified the lack of swirl behind the turbine. A larger machine is presently under construction for sea trials

High current pulse testing for ground rod integrity

A test technique was developed to assess various grounding system concepts used for mobile facilities. The test technique involves applying a high current pulse to the grounding system with the proper waveshape and magnitude to simulate a lightning return stroke. Of concern were the step voltages present along the ground near the point of lightning strike. Step voltage is equated to how fast the current pulse is dissipated by the grounding system. The applied current pulse was produced by a high current capacitor bank with a total energy content of 80 kilojoules. A series of pulse tests were performed on two types of mobile facility grounding systems. One system consisted of an array of four 10 foot copper clad steel ground rods connected by 1/0 gauge wire. The other system was an array of 10 inch long tapered ground rods, strung on stainless steel cable. The focus here is on the pulse test technique used and its relevance to actual lightning strike conditions

Amorphous-silicon module hot-spot testing

Hot spot heating occurs when cell short-circuit current is lower than string operating current. Amorphous cell hot spot are tested to develop the techniques required for performing reverse bias testing of amorphous cells. Also, to quantify the response of amorphous cells to reverse biasing. Guidelines are developed from testing for reducing hot spot susceptibility of amorphous modules and to develop a qualification test for hot spot testing of amorphous modules. It is concluded that amorphous cells undergo hot spot heating similarly to crystalline cells. Comparison of results obtained with submodules versus actual modules indicate heating levels lower in actual modules. Module design must address hot spot testing and hot spot qualification test conducted on modules showed no instabilities and minor cell erosion

Current Practices for Product Usability Testing in Web and Mobile Applications

Software usability testing is a key methodology that ensures applications are intuitive and easy to use for the target audience. Usability testing has direct benefits for companies as usability improvements often are fundamental to the success of a product. A standard usability test study includes the following five steps: obtain suitable participants, design test scripts, conduct usability sessions, interpret test outcomes, and produce recommendations. Due to the increasing importance for more usable applications, effective techniques to develop usable products, as well as technologies to improve usability testing, have been widely utilized. However, as companies are developing more cross-platform web and mobile apps, traditional single-platform usability testing has shortcomings with respect to ensuring a uniform user experience. In this report, a new strategy is proposed to promote a consistent user experience across all application versions and platforms. This method integrates the testing of different application versions, e.g., the website, mobile app, mobile website. Participants are recruited with a better-defined criterion according to their preferred devices. The usability session is conducted iteratively on several different devices, and the test results of individual application versions are compared on a per-device basis to improve the test outcomes. This strategy is expected to extend on current practices for usability testing by incorporating cross-platform consistency of software versions on most devices