Average Attenuation Factor Research Articles

Influence of metal foam thickness on the conduction and convective heat transfer for a flat plate with metal foam impinged by a rectangular slot jet

The local heat transfer distribution is measured for the case of a flat plate with a porous metal foam impinged by a rectangular slot air jet. The main objective is to separate the convection and conduction heat transfer effects in a flat plate with metal foam. For this purpose, flat plate with attached and detached metal foam are studied. The effect of the thickness of the metal foam on the convection and conduction heat transfer is also investigated. An open-cell aluminium metal foam having a porosity of 92% and pore density of 20 PPI (pores per inch) is studied. The thickness of the metal foam studied is 4 mm, 8 mm and 12 mm. Reynolds number ranges from 5200 to 12,000 and impinging distance varies from 2 to 10 times the width of the rectangular slot. The local Nusselt number of a flat plate with attached and detached metal foam is independent of the impinging distance irrespective of the metal foam thickness. The impinging jet on the flat plate with metal foam experiences extra hydraulic resistance depending on the thickness of the metal foam. The 12 mm thick metal foam offers the highest extra hydraulic resistance. However, the 4 mm thick metal foam offers negligible extra hydraulic resistance. The flat plate with detached metal foam experiences attenuation in the convective heat transfer due to extra hydraulic resistance. However, the flat plate with attached metal foam experiences conduction heat transfer due to metallic foam along with attenuation in the convective heat transfer due to extra hydraulic resistance. The attenuation in the convection heat transfer and conduction heat transfer due to the presence of the metal foam is quantified by the attenuation factor and enhancement factor respectively. The average attenuation factor is 1.12, 0.96 and 0.84 for 4 mm, 8 mm and 12 mm respectively. The enhancement factor for the metal foam having 4 mm, 8 mm and 12 mm are 1.91, 2.20 and 2.90 respectively. Hence, the effect of the enhancement due to conduction heat transfer dominates over the effect of the attenuation in the convective heat transfer due to extra hydraulic resistance. Under slot jet impingement, a flat plate with 4 mm, 8 mm and 12 mm thick metal foam shows 2.02, 2.12 and 2.41 times overall enhancement in comparison with the smooth flat plate respectively. Region-wise correlations for Nusselt number are developed using multiple regression analysis.

Measurement Error Affecting Web- and Paper-Based Dietary Assessment Instruments: Insights From the Multi-Cohort Eating and Activity Study for Understanding Reporting Error.

Few biomarker-based validation studies have examined error in online self-report dietary assessment instruments, and food records (FRs) have been considered less than food frequency questionnaires (FFQs) and 24-hour recalls (24HRs). We investigated measurement error in online and paper-based FFQs, online 24HRs, and paper-based FRs in 3 samples drawn primarily from 3 cohorts, comprising 1,393 women and 1,455 men aged 45-86 years. Data collection occurred from January 2011 to October 2013. Attenuation factors and correlation coefficients between reported and true usual intake for energy, protein, sodium, potassium, and respective densities were estimated using recovery biomarkers. Across studies, average attenuation factors for energy were 0.07, 0.07, and 0.19 for a single FFQ, 24HR, and FR, respectively. Correlation coefficients for energy were 0.24, 0.23, and 0.40, respectively. Excluding energy, the average attenuation factors across nutrients and studies were 0.22 for a single FFQ, 0.22 for a single 24HR, and 0.51 for a single FR. Corresponding correlation coefficients were 0.31, 0.34, and 0.53, respectively. For densities (nutrient expressed relative to energy), the average attenuation factors across studies were 0.37, 0.17, and 0.50, respectively. The findings support prior research suggesting different instruments have unique strengths that should be leveraged in epidemiologic research.

The matter of size: On the moment magnitude of microseismic events

We investigated the method of estimating seismic moment and moment magnitude for microseismic events. We determined that the [Formula: see text] defined by Bowers and Hudson is the proper scalar moment to be used in microseismic studies for characterizing the size of an event and calculating its moment magnitude. For non-double-couple sources, the proportional relationship between body-wave amplitude and seismic moment in the Brune model breaks down. So under such situations, the Brune model is not an appropriate way to estimate the seismic moment and magnitude. Moreover, the S-wave alone is not sufficient for determining the total seismic moment. Instead, the P-wave must be analyzed. An example Barnett Shale data set was studied, and the results concluded that the magnitudes estimated with the Brune model could be off by as much as 1.92, with an absolute average of 0.35. The moment magnitudes based on the scalar moment [Formula: see text] also gave a significantly different event size distribution and b-value estimation. Finally, attenuation also played a role in estimating the moment magnitude. With a typical average attenuation factor of [Formula: see text], the average magnitude correction for our field data set was on the order of 0.15. However, it could reach 0.3 for events far away from the monitoring well.

经络与周边非经络组织的光传输特性探究

According to the principle of light propagation,an automatic measurement system for scattering light survey of meridian and surrounding non-meridian at 808 nm central wavelength was designed and the effect of laser power on light decay rate of tissue were discussed.The diffusion theory of light transporting in biological tissues was used to analyze the experimental results.The results showed that there were statistical differences between meridian and surrounding non-meridian(P0.05).We also found the differences in optical parameters that the average attenuation factor value of pericardium meridian was lower than spleen meridian.In this article,our study showed laser power had no influence on attenuation of light in biological tissues that proved the attenuation is determined by tissue optical characteristics.

The Dust in Lyman Break Galaxies

We present our analysis of UV attenuation by internal dust of a large sample (N=906 galaxies) of Lyman Break Galaxies (LBGs). Using spectral energy distributions (SEDs) from the P\'EGASE galaxy spectral evolution model we apply dust attenuation corrections to the G-R colors using the Witt & Gordon (2000) models for radiative transfer in dusty galactic environments to arrive at the UV attenuation factors. We show that the dust in the LBGs exhibit SMC-like characteristics rather than MW-like, and that the dust geometry in these systems is most likely to be represented by a clumpy shell configuration. We show that the attenuation factor exhibits a pronounced dependence on the luminosity of the LBG, $a_{1600}\propto (L/L_\sun)^\alpha$, where $0.5\leq\alpha\leq1.5$. The exponent $\alpha$ depends on the initial parameters of the stellar population chosen to model the galaxies and the dust properties. We find that the luminosity weighted average attenuation factor is likely to be in the range from $5.7-18.5$, which is consistent with the upper limits to the star formation rate at $2<z<4$ set by the FIR background. This implies that the current UV/optical surveys do detect the bulk of the star formation during the epoch $2<z<4$, but require substantial correction for internal dust attenuation.

METHODS FOR DETERMINING THE FERMENTABILITY AND PREDICTED SPIRIT YIELD OF DISTILLING MALTS

Fermentability and predicted spirit yield (PSY) are two fundamental quality parameters of distilling malt, both of which rely on empirical factors for their calculation. Experiments were carried out using modern barley varieties to assess whether these factors were still valid for use in today's distilling industry. Using the 450 g IOB mash, an average attenuation factor of 81.46 from fifty-two determinations was found which was not significantly different from the existing factor of 81.4. A novel method to calculate the attenuation factor at different alcohol strengths was demonstrated which confirmed the factor to be 81.46. The PSY factor was shown to be 6.11 for a 450 g IOB mash, calculated using methods based on predicted and actual alcohol produced. However, a high gravity mashing procedure which more closely simulated distillery conditions confirmed that the current standard factor of 6.06 was still acceptable. Results indicated that it was not necessary to change either the attenuation or PSY factors when changing from the 515 ml mash to the 450 g mash in the standard IOB Recommended Methods.

Correction for photon attenuation in SPECT: analytical framework, average attenuation factors, and a new hybrid approach

The authors provide a unified framework for the investigation of convergence properties of the iterative algorithms for photon attenuation correction in SPECT, including the iterative Chang method - a commonly used approach in which an average attenuation factor calculated over all projection angles is employed in a pointwise correction scheme. A new average attenuation factor calculated along the projection line is introduced, which can compensate exactly for the attenuation effect in the case of a uniform activity distribution. The authors propose a new hybrid approach in which they use this new average attenuation factor initially and when shift to the iterative Chang method in later iterations. This hybrid approach was evaluated in a simulation study by use of a computer-generated phantom with both nonuniform activity and nonuniform attenuation distributions. The results demonstrate that this hybrid approach improves the convergence speed of the iterative Chang method and produces reconstructed images of high quality.

Left ventricular stroke volume determinations from radionuclide ventriculograms: the effects of photon attenuation.

To improve the accuracy of scintigraphic ventricular volume determination, which is limited by photon attenuation between the heart and the gamma camera, a method was developed for directly measuring the photon attenuation of radioactivity delivered as a bolus through a Swan-Ganz catheter into the right atrium. Comparison of the count rate recovered from this bolus with the total ex vivo measured activity determined by imaging an aliquot of the administered activity allowed calculation of the attenuation factor. Left ventricular stroke volumes determined scintigraphically by the count method in gated blood pool studies and then corrected with this attenuation factor correlated well with stroke volumes determined from thermodilution cardiac output and heart rate (r = 0.92; SEE, 6.1 ml). The agreement between the two measurements was markedly less when an average attenuation factor was employed for correction of scintigraphic volumes (r = 0.52; SEE, 14.8 ml). The results indicate that correction for photon attenuation is needed for accurate measurement of left ventricular volumes. Correction of left ventricular counts based on body weight or body surface area improves the accuracy of volume estimates.