Intercept Factor Research Articles

Influence of optical errors on the thermal and thermodynamic performance of a solar parabolic trough receiver

This paper presents results of an investigation covering the influence of optical errors on the thermal and thermodynamic performance of a solar parabolic trough system. The optical performance was evaluated by using Monte Carlo ray tracing for slope errors and specularity errors in the range 0–5mrad. A parabolic trough collector (PTC) with a rim angle of 80° and a concentration ratio of 86 was considered in this study. The heat flux profiles obtained from the optical analysis were coupled with a computational fluid dynamics tool (ANSYS FLUENT) to numerically investigate the thermal and thermodynamic performance of the receiver. In the numerical analysis, inlet temperatures and Reynolds numbers ranging from 350K–650K and 6800–1,140,000 were considered, respectively. Results show that, slope and specularity errors influence the heat flux distribution on the receiver’s absorber tube. Results further show that the optical performance and thermal performance reduce significantly as the slope errors increase. For the range of parameters considered, the intercept factor reduces by up to 21% while the overall thermal efficiency reduces by up to 17% as optical errors increase. Receiver thermodynamic performance is shown to deteriorate as slope errors increase.

The role of caregiver social support, depressed mood, and perceived stress in changes in pediatric secondhand smoke exposure and asthma functional morbidity following an asthma exacerbation.

Caregiver depressed mood and stress are associated with increased child asthma functional morbidity (AFM) and secondhand smoke exposure (SHSe), whereas social support (SS) reduces risk. This study extends previous literature by examining (1) longitudinal patterns of pediatric AFM and SHSe and (2) how caregiver stress, depressed mood, and SS are related to child SHSe and AFM changes. Participants were 334 caregivers who smoked, had a child with asthma, and were enrolled in a smoking cessation induction/asthma intervention. SHSe and AFM were measured at baseline and 4, 6, and 12 months. All measures were caregiver self-report. We used an autoregressive latent trajectory model to examine the intercept, linear, and quadratic growth factors and autoregressive and cross-lagged effects of SHSe and AFM. After an asthma exacerbation, decreases in child AFM and SHSe were followed by respective increases over time. Child SHSe at 4 months and 6 months predicted subsequent child AFM. Autoregressive paths were significant for only AFM. Higher baseline caregiver depressed mood and stress predicted higher baseline child AFM but not other growth factors. Higher baseline caregiver self-esteem SS was associated with only lower baseline child AFM and fewer increases in AFM across time. Exploratory analyses indicated higher baseline caregiver depressed mood and stress were associated with less-favorable changes in child SHSe and AFM. Caregiver depressed mood, stress, and SS should be considered when addressing pediatric SHSe and AFM. Caregiver support may be needed to maintain intervention gains. (PsycINFO Database Record

A model-based approach for optical performance assessment and optimization of a solar dish

The solar dish is a point-focusing concentrator with a very high concentration ratio ranging from hundreds to thousands. Practical assessment and optimization methods are necessary to assemble solar dishes with satisfying concentration ratios and flux density distributions, which is very important for the overall solar thermal systems to achieve high efficiency. A solar dish usually consists of many mirror facets installed on a supporting structure with a dual-axis tracking system. Small mirror facets are easy to manufacture, but the alignment of many mirror facets is very challenging. A model-based approach for optical performance assessment and optimization of a solar dish was proposed, and flux density measurements were carried out to validate the approach. The simulation and experimental results showed very good consistency and suggested that the concentration ratio and the intercept factor could be increased from ∼500 to ∼1500 and 0.66 to 0.9 respectively after assembly optimization.

The aetiological association between the dynamics of cortisol productivity and ADHD.

Attention-deficit/hyperactivity disorder (ADHD) has been linked to dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis, indexed by salivary cortisol. The phenotypic and aetiological association of cortisol productivity with ADHD was investigated. A selected twin design using 68 male twin-pairs aged 12–15, concordant or discordant for high ADHD symptom scores, or control twin-pairs with low ADHD symptoms, based on developmentally stable parental ADHD ratings. A genetic growth curve model was applied to cortisol samples obtained across three points during a cognitive-electroencephalography assessment, to examine the aetiological overlap of ADHD affection status (high versus low ADHD symptom scores) with latent intercept and slope factors. A significant phenotypic correlation emerged between ADHD and the slope factor, with cortisol levels dropping faster for the group with high ADHD symptom scores. The analyses further suggested this overlap was mostly driven by correlated genetic effects. We identified change in cortisol activity over time as significantly associated with ADHD affection status, primarily explained by shared genetic effects, suggesting that blunted cortisol productivity can be a marker of genetic risk in ADHD.

Optical Analysis of a Two Stage XX Concentrator for Parametric Trough Primary and Tubular Absorber With Application in Solar Thermal Energy Trough Power Plants

A new symmetric nonimaging parametric trough collector (PmTC) for an evacuated circular receiver is proposed having an absorber diameter of 70 mm similar to the LS3/Eurotrough absorber one, and a circular secondary. The optical design method is explained and a sensitivity analysis is conducted with respect to the diameter of the secondary and to the acceptance angle. In the design process, transmission, absorption, and reflection losses are neglected. A secondary mirror radius of 145 mm and an acceptance angle of ±14 mrad were chosen as realistic values. For these values a concentrator geometry having 8.7 m gross aperture and 100% intercept factor for rays impinging on the primary within the referred acceptance angle is obtained producing a net concentration ratio relative to the thermodynamic ideal limit of 0.52 compared to 0.31 for traditional parabolic trough collectors. The new concentrator is composed of a primary discontinuous reflector with two symmetrical portions with parametric geometry, and a central parabolic portion located between the other two. The ensemble secondary receiver can be dressed up with the secondary concentrator manufactured by partially mirroring a diameter adapted glass tube—either internally or externally—or alternatively by means of a commercial evacuated receiver and an independent 145 mm radius arc of circumference external secondary reflector. Monte Carlo ray-tracing results show that only 15% of the rays undergo secondary reflection before arriving to the absorber and a sharp angle transmission curve. The new concentrator is proposed for application in solar thermal energy (STE) trough power plants.

Design and analysis of a gravity-based passive tracking mechanism to a linear solar concentrating collector

A novel gravity-based power-free solar tracking mechanism has been developed to track a linear solar concentrating collector. Multireflector compound parabolic collectors having three parabolic segments and two flat surfaces is chosen due to its high intercept factor and suitability to the current tracking. The working of tracking mechanism is studied to find the tracking loads in the east and the west sides of collector. A generalized mathematical model is derived to simulate the tracking motion from the sunrise to sunset. The identified design variants are sprocket wheel diameter, spring stiffness, solar collector’s weight, counter balance, and tracking wheel radius. The spring length is derived from the constraints. To make a compact product, the tracking load has been minimized at large sprocket wheel, low stiff spring, lighter collector weight, and small radius of tracking. For a typical collector load of 50 kg, the designed tracking load is 50 kg with 620 mm spring length, 250 mm of sprocket wheel diameter and 60 mm tracking radius.

Differentiation of Pore Fluids Using Amplitude versus Offset Attributes in Clastic Reservoirs, Middle Indus Basin, Pakistan

Lower Goru sand intervals of the Cretaceous age in Kadanwari field of the middle Indus Basin, Pakistan, are interpreted as reservoir intervals. Based on seismic interpretation and geology, several wells were drilled in these sands. However, most of the wells drilled were dry and declared abundant because highly saturated brine was encountered with minute amount of hydrocarbon gas. The main reason for drilling dry wells was limitation of seismic reflection data to differentiate seismic response of hydrocarbon-saturated reservoir interval from non-hydrocarbon-saturated interval. Amplitude versus offset (AVO) analysis is widely used to differentiate hydrocarbon intervals from background lithology. In this work, AVO-derived attributes are used for fluid discrimination in the sand intervals. Amplitude differences are associated with density and compressibility of fluid under in situ temperature and pressure conditions of the reservoir interval. The results reveal that seismic amplitude anomalies associated with AVO analysis can differentiate hydrocarbon fluids from non-hydrocarbon fluids and thus can optimize the exploration of gas. The gas sand anomaly in the study area is of weak impedance as compared to brine sand. The intercept and fluid factor are very promising attribute pairs to discriminate gas sands from background sands. The results may be helpful to discriminate low gas saturation or fizz water from high gas saturation.

Comparison of line focusing solar concentrator fields considering shading and blocking

The performance of line focusing solar collectors [Parabolic Trough Concentrator (PTC), Linear Fresnel Reflector (LFR) and Compact Linear Fresnel Reflector (CLFR)] is affected by many factors. Due to end effect, inter-row shading and blocking (for LFR and CLFR), the complete aperture of the collector cannot be utilized. Besides, the cosine effect, reflectivity of reflectors, intercept factor, transmissivity of receiver cover, absorptivity of absorber tube and thermal losses are the other major contributors to the energy losses. In the current work, PTC, LFR and CLFR fields are compared in terms of energy losses, net energy collection by fluid, electricity generation and cost of electricity. The ratio of collector aperture area to land area is named as land coverage ratio. The appropriate values of land coverage ratio are found out corresponding to minimum cost of electricity for different technologies. The corresponding annual energy collection by fluid and the annual electricity generation have also been calculated. It is seen that there is no significant difference in the performance of LFR and CLFR fields. For low values of receiver height to collector width ratio, the LFR field results in the largest levelised cost of electricity and the PTC field results in the lowest.

A design method of an S-curved parabolic trough collector absorber with a three-dimensional heat flux density distribution

This paper presents the first study on the feasibility of an S-curved/sinusoidal absorber for a use in parabolic trough collectors (PTCs). The conventional straight absorber located along the focal line of the PTC is replaced by an S-curved/sinusoidal one for which the heat flux density distribution on the outer surface varies in both axial and azimuthal directions while it varies only in the azimuthal direction on the former. On the basis of the heat flux density distribution (q) for horizontal straight absorbers, a simplified method is proposed to generate the 3D character of q for the newly designed S-shaped absorber. The results show that for specular reflectors of perfect alignment, to collect the entire reflected solar beam, the amplitude of the sinusoidal centreline of the new absorber must not be larger than a maximum deviation, Δmax, established with reference to the focal line. The heat flux density distributions of two newly designed S-curved pipes are performed and shape effects on the flux distribution are shown. So far, the concentrated heat flux distribution analysed in details revealed the almost homogeneous heating of the new absorber pipe. The design should achieve other indirect benefits, as the reduction of the absorber pipe deflection in consequence of a better flux distribution around the pipe. It is also established that the intercept factor of a solar collector unit equipped with the S-curved absorber should be comparatively better than that of the former equipped with the conventional straight absorber.

Inferring Longitudinal Relationships Between Variables: Model Selection Between the Latent Change Score and Autoregressive Cross-Lagged Factor Models

This research focuses on the problem of model selection between the latent change score (LCS) model and the autoregressive cross-lagged (ARCL) model when the goal is to infer the longitudinal relationship between variables. We conducted a large-scale simulation study to (a) investigate the conditions under which these models return statistically (and substantively) different results concerning the presence of bivariate longitudinal relationships, and (b) ascertain the relative performance of an array of model selection procedures when such different results arise. The simulation results show that the primary sources of differences in parameter estimates across models are model parameters related to the slope factor scores in the LCS model (specifically, the correlation between the intercept factor and the slope factor scores) as well as the size of the data (specifically, the number of time points and sample size). Among several model selection procedures, correct selection rates were higher when using model fit indexes (i.e., comparative fit index, root mean square error of approximation) than when using a likelihood ratio test or any of several information criteria (i.e., Akaike’s information criterion, Bayesian information criterion, consistent AIC, and sample-size-adjusted BIC).

A powerful phenotype for gene-finding studies derived from trajectory analyses of symptoms of anxiety and depression between age seven and 18.

To investigate the utility of longitudinal data in genetic analyses of symptoms of anxiety and depression, we assessed individual differences between age 7 and 18 using growth mixture models, and investigated the genetic and non-genetic factors contributing to the trajectories. Mothers of 7,706 girl and 7,418 boy twins from the Netherlands Twin Register rated the anxious depression scale (SxAnxDep) of the Child Behavior Check List (CBCL) at age 7, 10, and 12 years. Two thousand seven hundred and six girl and 1,856 boy twins completed the Youth Self Report (YSR) at age 14, 16, and 18. While individual trajectories varied considerably, these differences were largely idiosyncratic and could not be grouped into separate latent classes with class-specific average growth curves. The intercept, which reflects the individuals' baseline level of SxAnxDep across time, explained 55-58% of the total phenotypic variance. The slope factor, which captures a common average trend over time, did not explain variance in the phenotype. This finding also underlines the high level of idiosyncrasy of trajectories that lack a common longitudinal structure. The analyses of twin data showed that the random intercept factor of SxAnxDep during childhood and during adolescence is considerably more heritable than the observations at any single age, namely between 60% and 84%. One explanation is that different factors contribute to the level of symptoms of anxiety and depression at any given time point, including temporary events and emotions. When considering baseline stability, these temporary influences average out, with the result of a more reliable and more heritable phenotype. © 2015 Wiley Periodicals, Inc.

Optical qualification of a solar parabolic concentrator using photogrammetry technique

The purpose of this work is to determine the optical performance of a solar parabolic concentrator which was designed and realized in the Research and Technology Center of Energy in Borj Cedria Tunisia in order to improve its thermal efficiency. In this order an experimental and optical study was carried out and Photogrammetry measurement technique has been used to determine geometric errors of the solar concentrating system. Intercept factor, slope error and displacement error has been identified and analyzed. Analytical calculation of the intercept factor for parabolic reflector with a spherical receiver under Gaussian distribution along with optical efficiency has been developed and determined according to the experimental results given by the Photogrammetry technique. Obtained results showed a relevant impact of the solar concentrator optical analyze on the overall system efficiency.

The Effects of Solar Irradiance, Reflecting Material and Intercept Factor to the Solar Power Intercepted by Receiver 1kW Parabolic Dish

Parabolic Dish (PD) system is one of the Concentrating Solar Power (CSP) technologies that converts the thermal energy from solar irradiance into mechanical energy and then to electrical energy. The concentrator in PD system works by focusing the solar radiation onto the receiver located at the focal point. The solar power that produced from the concentration process is intercepted by the receiver and then used for the energy conversion process in PD system. This study is carried out to understand the effect of the intercept factor, reflecting material and the DNI to the solar power intercepted by the receiver in PD 1kW system. Meanwhile, Matlab Simulink was used in this study as the simulation tool. The study shows that the solar power intercepted by the receiver in 1kW PD system are strongly depending on the intercept factor, DNI of the locations and reflecting material used for the concentrator. Whereas, the results from this study are useful for a better understanding especially on the effects of the intercept factor, reflecting material and the DNI to the solar power intercepted by the receiver for 1kW PD system in different locations with different DNI level.

The Impact of the Solar Irradiation, Collector and the Receiver to the Receiver Losses in Parabolic Dish System

Parabolic Dish (PD) is one of Concentrating Solar Power (CSP) technologies that convert sunlight to electricity. PD has shown the highest efficiency by converting nearly 31.25% of solar radiation into electricity and PD has emerged as one of reliable and efficient Renewable Energy (RE) technology. However, the evaluation for the PD system performance by using experimental approach is costly and time consuming. Therefore, a model has become necessary to predict the system performance under several of operating conditions. Nevertheless, current literature on PD modelling is scattered, focusing on individual components and rarely organised in one cohesive report. This paper is to study on the impact of the Direct Solar Irradiance (DNI), collector and receiver to the value of heat transfer to the receiver; solar power intercept by a receiver as well as the receiver loses in 25kW PD system. This study is using a simulation approach and Matlab Simulink was used as the simulation tool. The irradiation data were downloaded from the Meteonorm 7 Software and George Town, Penang in Malaysia has been selected as the location for simulation. Meanwhile, the aluminium and silver was used as the reflective material and the intercepted factor used for the simulation is in the range of 0.9 to 1.0. As a conclussion, the simulation result has shown that variations of the solar irradiation on the site, reflective material and the intercept factors influence the value of the value of the rate of heat transfer to the receiver; solar power intercept by a receiver as well as the receiver loses.

Prediction of the Ym factor for livestock from on-farm accessible data

Methane emission factor (Ym) is directly involved to calculate the worldwide livestock methane inventories, hence it is important to refine the estimation of this parameter for different livestock production systems. The purpose of this work was to generate refined mathematical models to predict CH4 emissions from an extensive compilated database at on-farm level and to compare them with different models already available in the literature. Methane emission predictive models (expressed as Ym, % gross energy intake; and methane production, CH4p, gan−1d−1) where fitted taken into account the production system, the livestock type and the feed characteristics available at on-farm level within a reasonable uncertainty range. In order to develop the models, only easy available parameters were selected to fit new mathematical models. Hence, the full model included: ruminant types (beef cattle, dairy cattle, and sheep), fibre sources (fresh forage, conserved forage, and straw) and concentrate levels (DM basis) in the diet (Low, <35%; Intermediate, 35–65%; High, >65%). Full models were assessed by the Bayesian Information Criterion (BIC) and terms that did not reach significance level (P≤0.05) were dropped from the model. Furthermore, predicted results were assessed through correlation and regression analyses considering the model significance. Models developed in this study were compared by the degree of adjustment of a simple regression. Additive and technique terms were initially dropped from the full model used to predict Ym because they did not have effect in the prediction (P>0.10). Therefore, the final equation for Model 1 was: Ym(a)=Intercept−0.243(±0.051)×DMI (kgd−1)+5.9×10−3(±1.17×10−3)×NDF (gkg−1DM−1)+5.7×10−3(±1.63×10−3)×DMD (gkg−1MS−1) (BIC=559). All terms of this model, intercept factor (type of cattle×source of fibre×level of concentrate), DMI, NDF, and DMD were significant (P<0.0001). DMI was the term with the greatest weight in the model. The predicted Ym value decreased about 0.243 percentage units (P<0.0001) per each additional kg in DMI. When the equation was compared with previous publicated models, our model showed a satisfactory degree of fitting.In conclusion, this new model improved the estimation of the Ym factor from beef and dairy production systems, using different forage quality characteristics from on-farm level to increase precision.

Inverse MCRT Method for Obtaining Solar Concentrators with Quasi-Planar Flux Distribution

Abstract A numerical algorithm has been developed in order to get reflectors geometry so that the desired flux distribution is approximately obtained. This new method opens up the opportunity to design ad-hoc line-focus solar reflectors for a specific purpose from the required concentrated flux distribution. A new design for PTC reflectors is proposed, getting a quasi-planar distribution around the absorber. This algorithm can also be applied not only to round absorbers in PTC applications but others like flat absorbers useful for concentrated solar photovoltaic/thermal systems. The proposed new reflector geometries will be compared to the classical Eurotrough-type parabolic-trough geometry by means of the intercept factor and the tolerance to absorber displacements respect to the design location.

Optimization of heliostat field layout in solar central receiver systems on annual basis using differential evolution algorithm

Optimization of a heliostat field is an essential task to make a solar central receiver system effective because major optical losses are associated with the heliostat fields. In this study, a mathematical model was developed to effectively optimize the heliostat field on annual basis using differential evolution, which is an evolutionary algorithm. The heliostat field layout optimization is based on the calculation of five optical performance parameters: the mirror or the heliostat reflectivity, the cosine factor, the atmospheric attenuation factor, the shadowing and blocking factor, and the intercept factor. This model calculates all the aforementioned performance parameters at every stage of the optimization, until the best heliostat field layout based on annual performance is obtained. Two different approaches were undertaken to optimize the heliostat field layout: one with optimizing insolation weighted annual efficiency and the other with optimizing the un-weighted annual efficiency. Moreover, an alternate approach was also proposed to efficiently optimize the heliostat field in which the number of computational time steps was considerably reduced. It was observed that the daily averaged annual optical efficiency was calculated to be 0.5023 as compared to the monthly averaged annual optical efficiency, 0.5025. Moreover, the insolation weighted daily averaged annual efficiency of the heliostat field was 0.5634 for Dhahran, Saudi Arabia. The code developed can be used for any other selected location.

Effects of shading and blocking in linear Fresnel reflector field

In a linear Fresnel reflector field, parallel rows of reflectors in a collector direct the incident sun rays towards a common linear receiver. Some portion of reflector aperture remains unused due to end effect, inter-row shading and blocking. In addition to these factors, cosine effect, cleanliness factor, reflectivity of reflectors, intercept factor, transmissivity of receiver cover, reflectivity of secondary reflector, absorptivity of absorber tube and thermal losses are other factors that contribute to energy losses and thus affect net energy collection by the heat transfer fluid in the absorber, electricity generation and cost of electricity. Conventionally, the collectors are oriented either along North–South or East–West directions in most cases. However the energy collection, electricity generation and cost of electricity need to be found out for all possible collector-orientations lying between North–South and East–West. This can be used in designing collectors for places where the available land strip does not align with any of these two directions. In this work, explicit analytical expressions for energy losses due to cosine effect, end effect, shading and blocking are derived for any desired time interval as functions of length (L) and width (w) of aperture of reflector-row, spacing between adjacent reflector-rows (p), number of reflector-rows in a collector (n), height of receiver (H), collector-orientation angle (Ω) and location. The expressions for the net energy collected by the working fluid, electricity generated by a collector and the cost of electricity are presented. The effects of L, w, p, n, H, Ω and location on energy losses, net energy collection by fluid, electricity generation and cost of electricity are studied. The minimum cost of electricity is found out for different collector-orientations at various locations and relative comparisons have been made. The corresponding collector parameters, annual energy collection by fluid and the annual electricity generation are also found out.

Mutual information–based LPI optimisation for radar network

Radar network can offer significant performance improvement for target detection and information extraction employing spatial diversity. For a fixed number of radars, the achievable mutual information (MI) for estimating the target parameters may extend beyond a predefined threshold with full power transmission. In this paper, an effective low probability of intercept (LPI) optimisation algorithm is presented to improve LPI performance for radar network. Based on radar network system model, we first provide Schleher intercept factor for radar network as an optimisation metric for LPI performance. Then, a novel LPI optimisation algorithm is presented, where for a predefined MI threshold, Schleher intercept factor for radar network is minimised by optimising the transmission power allocation among radars in the network such that the enhanced LPI performance for radar network can be achieved. The genetic algorithm based on nonlinear programming (GA-NP) is employed to solve the resulting nonconvex and nonlinear optimisation problem. Some simulations demonstrate that the proposed algorithm is valuable and effective to improve the LPI performance for radar network.

Estimating and interpreting latent variable interactions

Latent variables are common in psychological research. Research questions involving the interaction of two variables are likewise quite common. Methods for estimating and interpreting interactions between latent variables within a structural equation modeling framework have recently become available. The latent moderated structural equations (LMS) method is one that is built into Mplus software. The potential utility of this method is limited by the fact that the models do not produce traditional model fit indices, standardized coefficients, or effect sizes for the latent interaction, which renders model fitting and interpretation of the latent variable interaction difficult. This article compiles state-of-the-science techniques for assessing LMS model fit, obtaining standardized coefficients, and determining the size of the latent interaction effect in order to create a tutorial for new users of LMS models. The recommended sequence of model estimation and interpretation is demonstrated via a substantive example and a Monte Carlo simulation. Finally, extensions of this method are discussed, such as estimating quadratic effects of latent factors and interactions between latent slope and intercept factors, which hold significant potential for testing and advancing developmental theories.