The Influence Of Wind On The Heat Losses From Solar Cavity Receivers

The principal objective of the present study is to assess the influence of wind on the heat loss from a generic cavity solar receiver under different geometrical configurations and operating conditions. This understanding is needed to provide insight into approaches with which to increase the thermal efficiency of a solar cavity receiver. The results from this work can be used to reduce the cost of concentrating solar energy and increase the rate of penetration of sustainable and renewable energy sources. A purpose built modular and cylindrical cavity receiver was mounted in a large-scale wind tunnel in order to quantify heat losses under the different conditions. The cylindrical cavity was lined up with 16 well controlled and separated heating strips to investigate the effect of the internal temperature and its distribution on heat losses. A systematic experimental study was performed to assess the influence of wind speed (= 0, 3, 6, 9 and 12 m/s), yaw angle (α = 0°, 22.5°, 45°, 77.5° and 90°), tilt angle (= 90°, 45°, 30°, 15° and -90°), cavity aperture ratio (0.33, 0.5, 0.75 and 1), internal walls temperature (=100, 200, 300 and 400 °) and 4 combination of temperature distribution inside the cavity. The data was analysed, then the total heat loss, normalised heat loss, and heat loss distribution through the internal walls of the heated cavities are presented. To further our understanding of the heat transfer and fluid flow inside and outside a cavity receiver, a numerical model of a solar cavity receiver was developed to assess the effect of aspect ratio (0.5 to 3) and head-on wind speed on the forced and natural (combined) convective heat loss and area-averaged convective heat flux from a cylindrical solar cavity receiver. The temperature distribution and velocity of air in the cavity are also presented. The present study found that increasing the cavity aspect ratio leads to a reduction in the influence of wind speed on the combined convective losses per unit of cavity internal area. Consequently, the overall efficiency of a solar cavity receiver increases with the cavity aspect ratio for the conditions assessed in this study (aspect ratio below 3). The influence of head-on wind speed on the heat losses was found to be ~ 4 times higher than the side-on wind for (1/ > 19). Decreasing the aperture ratio / from 1 to 0.33, acts to reduce the natural convective losses (at zero wind speed) by up of to a factor of 5, while the effect of this ratio diminishes as wind speed is increased. For high wind speed, the heat loss from the upward facing cases (=−90°) is approximately 3 times lower than the downward tilted cases (=15°) for a head-on wind condition. The heat losses from the upward facing cases are similar with the side-on wind conditions. For a downward tilted solar cavity receiver, an “upper or rear surface hotter” cavity has less overall heat losses compared with the other cases. There is also a slight advantage with respect to heat loss in keeping the tilt angle of a solar cavity between 15° and 30°.Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 201

reslife: Residual Lifetime Analysis Tool in R

Mean residual lifetime is an important measure utilized in various fields, including pharmaceutical companies, manufacturing companies, and insurance companies for survival analysis. However, the computation of mean residual lifetime can be laborious and challenging. To address this issue, the R package reslife has been developed, which enables efficient calculation of mean residual lifetime based on closed-form solution in a user-friendly manner. reslife offers the capability to utilize either the results of a flexsurv regression or user-provided parameters to compute mean residual lifetime. Furthermore, there are options to return median and percentile residual lifetime. If the user chooses to use the outputs of a flexsurv regression, there is an option to input a data frame with unobserved data. In this article, we present reslife, explain its underlying mathematical principles, illustrate its functioning, and provide examples on how to utilize the package. The aim is to facilitate the use of mean residual lifetime, making it more accessible and efficient for practitioners in various disciplines, particularly those involved in survival analysis within the pharmaceutical industry

Landmark-Matching Transformation with Large Deformation Via n-dimensional Quasi-conformal Maps

We propose a new method to obtain landmark-matching transformations between n-dimensional Euclidean spaces with large deformations. Given a set of feature correspondences, our algorithm searches for an optimal folding-free mapping that satisfies the prescribed landmark constraints. The standard conformality distortion defined for mappings between 2-dimensional spaces is first generalized to the n-dimensional conformality distortion K(f) for a mapping f between n-dimensional Euclidean spaces (n ≥ 3). We then propose a variational model involving K(f) to tackle the landmark-matching problem in higher dimensional spaces. The generalized conformality term K(f) enforces the bijectivity of the optimized mapping and minimizes its local geometric distortions even with large deformations. Another challenge is the high computational cost of the proposed model. To tackle this, we have also proposed a numerical method to solve the optimization problem more efficiently. Alternating direction method with multiplier is applied to split the optimization problem into two subproblems. Preconditioned conjugate gradient method with multi-grid preconditioner is applied to solve one of the sub-problems, while a fixed-point iteration is proposed to solve another subproblem. Experiments have been carried out on both synthetic examples and lung CT images to compute the diffeomorphic landmark-matching transformation with different landmark constraints. Results show the efficacy of our proposed model to obtain a folding-free landmark-matching transformation between n-dimensional spaces with large deformations

Counting Your Customers the Easy Way: An Alternative to the Pareto/NBD Model

Today’s managers are very interested in predicting the future purchasing patterns of their customers, which can then serve as an input into “lifetime value” calculations. Among the models that provide such capabilities, the Pareto/NBD “counting your customers” framework proposed by Schmittlein et al. (1987) is highly regarded. However, despite the respect it has earned, it has proven to be a difficult model to implement, particularly because of computational challenges associated with parameter estimation. We develop a new model, the beta-geometric/NBD (BG/NBD), which represents a slight variation in the behavioral “story” associated with the Pareto/NBD but is vastly easier to implement. We show, for instance, how its parameters can be obtained quite easily in Microsoft Excel. The two models yield very similar results in a wide variety of purchasing environments, leading us to suggest that the BG/NBD could be viewed as an attractive alternative to the Pareto/NBD in most applications

A Gentleman with Anemia and Cholestasis

Primary sclerosing cholangitis is a rare cause of cholestasis caused by progressive inflammation and fibrosis of both intrahepatic and extrahepatic bile ducts leading to multifocal ductal strictures. Herein, we report a case of primary sclerosing cholangitis and inflammatory bowel disease. The concomitant diagnosis of these two diseases is not typical. The management includes the treatment of inflammatory bowel disease and potential complications of primary sclerosing cholangitis, including dominant strictures of bile duct, portal hypertension, gallbladder diseases, cholangiocarcinoma, and colonoscopic surveillance

The photometric observation of the quasi-simultaneous mutual eclipse and occultation between Europa and Ganymede on 22 August 2021

Mutual events (MEs) are eclipses and occultations among planetary natural satellites. Most of the time, eclipses and occultations occur separately. However, the same satellite pair will exhibit an eclipse and an occultation quasi-simultaneously under particular orbital configurations. This kind of rare event is termed as a quasi-simultaneous mutual event (QSME). During the 2021 campaign of mutual events of jovian satellites, we observed a QSME between Europa and Ganymede. The present study aims to describe and study the event in detail. We observed the QSME with a CCD camera attached to a 300-mm telescope at the Hong Kong Space Museum Sai Kung iObservatory. We obtained the combined flux of Europa and Ganymede from aperture photometry. A geometric model was developed to explain the light curve observed. Our results are compared with theoretical predictions (O-C). We found that our simple geometric model can explain the QSME fairly accurately, and the QSME light curve is a superposition of the light curves of an eclipse and an occultation. Notably, the observed flux drops are within 2.6% of the theoretical predictions. The size of the event central time O-Cs ranges from -14.4 to 43.2 s. Both O-Cs of flux drop and timing are comparable to other studies adopting more complicated models. Given the event rarity, model simplicity and accuracy, we encourage more observations and analysis on QSMEs to improve Solar System ephemerides.Comment: 23 pages, 5 appendixes, 16 figures, 7 table