Modeling and experimental study of nucleate boiling on a vertical array of horizontal plain tubes

An investigation of nucleate boiling on a vertical array of horizontal plain tubes is presented in this paper. Experiments were performed with refrigerant RI 23 at reduced pressures varying from 0.022 to 0.64, tube pitch to diameter ratios of 1.32, 1.53 and 2.00, and heat fluxes from 0.5 to 40 kW/m(2). Brass tubes with external diameters of 19.05 mm and average roughness of 0.12 mu m were used in the experiments. The effect of the tube spacing on the local heat transfer coefficient along the tube array was negligible within the present range of experimental conditions. For partial nucleate boiling, characterized by low heat fluxes, and low reduced pressures, the tube positioning shows a remarkable effect on the heat transfer coefficient. Based on these data, a general correlation for the prediction of the nucleate boiling heat transfer coefficient on a vertical array of horizontal tubes under flooded conditions was proposed. According to this correlation, the ratio between the heat transfer coefficients of a given tube and the lowest tube in the array depends only on the tube row number, the reduced pressure and the heat flux. By using the proposed correlation, most of the experimental heat transfer coefficients obtained in the present study were predicted within +/- 15%. The new correlation compares reasonably well with independent data from the literature. (C) 2008 Elsevier Inc. All rights reserved.

Influência da função distribuição de quebra na modelagem e simulação do circuito de moagem de Carajás - Parte 1 - ajuste de modelos

The perfect mixing model (PMM) is based on parameters derived from the equipment characteristics as well as ore breakage characteristics. Ore characteristics are represented through the appearance function. This function may be determined using JKMRC laboratorial methods or by standard functions. This work describes the model fitting process of the Carajas grinding circuit, using the JKSimMet simulator Two scenarios were used in model fitting exercises: 1) standard appearance function; and 2) appearance fund ion based on testing carried out on samples taken at circuit feed. From this assessment, the appearance function`s influence in the PMM,fit and it`s relation with the breakage rate were determined. The influence of the appearance function on the respective breakage rate distribution was assessed.

Influência da função distribuição de quebra na modelagem e simulação do circuito de moagem de Carajás - parte 2 - simulação

Using the previously described method for appearance function determination, described in Part I of this article, the breakage characterization of the main Carajas ore types was carried out. Based on such characteristics, the ball mill circuit performance was evaluated through simulations. The model described in the first part was used. The results were assessed by comparing ball mill products and cyclone overflow size distribution, as well as simulated recirculating loads. The simulations indicated the potential for processing such ore types at the Carajas grinding circuit, which until now was unknown.

New Analytic Solution of Boltzmann Transform for Horizontal Water Infiltration into Sand

The use of the Boltzmann transform function, lambda(theta), to solve the Richards equation when the diffusivity, D, is a function of only soil water content,., is now commonplace in the literature. Nevertheless, a new analytic solution of the Boltzmann transform lambda(h) as a function of matric potential for horizontal water infiltration into a sand was derived without invoking the concept or use of D(theta). The derivation assumes that a similarity exists between the soil water retention function and the Boltzmann transform lambda(theta). The solution successfully described soil water content profiles experimentally measured for different infiltration times into a homogeneous sand and agrees with those presented by Philip in 1955 and 1957. The applicability of this solution for all soils remains open, but it is anticipated to hold for soils whose air-filled pore-size distribution before wetting is sufficiently narrow to yield a sharp increase of water content at the wetting front during infiltration. It also improves and provides a versatile alternative to the well-known analysis pioneered by Green and Ampt in 1911.

Interspecific and intraspecific horizontal transfer of Wolbachia in Drosophila

Cytoplasmic incompatibility (CI) in Drosophila simulans is related to infection of the germ line by a rickettsial endosymbiont (genus Wolbachia). Wolbachia were transferred by microinjection of egg cytoplasm into uninfected eggs of both D. simulans and D. melanogaster to generate infected populations. Transinfected strains of D. melanogaster with lower densities of Wolbachia than the naturally infected D. simulans strain did not express high levels of CI. However, transinfected D. melanogaster egg cytoplasm, transferred back into D. simulans, generated infected populations that expressed CI at levels near those of the naturally infected strain. A transinfected D. melanogaster line selected for increased levels of CI expression also displayed increased symbiont densities. These data suggest that a threshold level of infection is required for normal expression of CI and that host factors help determine the density of the symbiont in the host.

Comments on "Exact solution for horizontal redistribution by general similarity"

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Sudden drawdown and drainage of a horizontal aquifer

Drainage of a saturated horizontal aquifer following a sudden drawdown is reanalyzed using the Boussinesq equation. The effect of the finite length of the aquifer is considered in detail. An analytical approximation based on a superposition principle yields a very good estimate of the outflow when compared to accurate numerical solutions. An illustration of the new analytical approach to analyze basin-scale field data is used to demonstrate possible field applications of the new solution.

Horizontal alliances amongst small retailers in Brazil

Purpose - Application of the horizontal alliance paradigm has particularly relevance to small retailers. It is a powerful mechanism for independents and non-integrated chain retailers to develop competitive advantage, maintaining and improving their performance. The purpose of this article is to analyse the theory of alliance in the context of the retail sector. Design/methodology/approach - Both quantitative and qualitative research was carried out with horizontal retail alliances in Brazil. Findings - Focusing on the alliances among independents and non-integrated chain retailers, our discussion covers specifically the following issues: the reasons for forming a strategic alliance in retail; minimum criteria for the alliance activity amongst retailers; steps that managers must take to create a competitive retail alliance; critical core competencies to be developed on the retail alliance; types of retail alliances; and, finally, forms of strategic retail alliances and stages/steps to develop a retail alliance over time. Research limitations/implications - The study considers horizontal alliances in a Brazilian retail context, which is in some ways unique, however, key principles and findings are very much transferable. Practical implications/implications - The study is of value not only to researchers of retail horizontal alliances, but offers retail practitioners specific experience and guidance. Originality/value - It was identified from the literature that there have been relatively few theoretical and practical studies available that analyse the relationship between the outlined themes concerned with alliances and small retailers. The discussion in our paper provides useful information and new insights to both academics and practitioners.

Slant or occlusion: global factors resolve stereoscopic ambiguity in sets of horizontal lines

Perceived slant was measured for horizontal lines aligned on one side and of varying lengths whose length disparity was either a constant linear amount for all lines (consistent with uniocular occlusion) or proportional to line length (consistent with global slant). Although the disparity of any line was ambiguous with respect to these two possibilities, slant of individual lines did not occur in the former case, but a subjective contour in depth was reported along the alignment. For proportional disparity of the set, global slant was seen. Adding a constant length to each line on the invalid eye for occlusion resulted in multiple slants. Smooth uniocular variations in alignment shape elicited subjective contours slanting or curving in depth. Global context can disambiguate the depth status of individual disparate lines. (C) 2004 Elsevier Ltd. All rights reserved.

Molecular evidence of horizontal transmission of hepatitis C virus within couples

Hepatitis C virus (HCV) transmission has decreased with the adoption of universal blood donor screening and social policies to reduce the risk of infection in intravenous drug users, but remains a worldwide health problem. The objective of this study was to evaluate the phylogenetic relationships among sequences from different HCV genomic regions from sexual partners of infected patients. Nine couples with a stable relationship and without other risk factors for HCV infection and 42 control patients were selected, and the NS3 and NS5B regions were analysed. Phylogenetic analysis showed that viruses from five of the couples had a common origin, clustering in the same monophyletic group, with bootstrap values greater than 70. For the other couples, monophyletic groups were observed, but without bootstrap support. Thus, using two different viral genome regions, a common source of infection was observed in both members of five couples. These data strongly support HCV transmission within couples.

Detection of Horizontal Root Fracture with Small-volume Cone-Beam Computed Tomography in the Presence and Absence of Intracanal Metallic Post

Introduction: The aim of the present study was to test the accuracy of small-volume cone-beam computed tomography (CBCT) scanning in the detection of horizontal root fractures and to assess the influence of a metallic post. Methods: Forty teeth were divided into four groups based on the presence of metallic posts and horizontal root fracture. The teeth were examined by small-volume CBCT scanning at 0.2-mm voxel resolution. Three observers analyzed the samples for the presence of a horizontal root fracture. Sensitivity and specificity were calculated. Results: High values for accuracy (73%-88%) were obtained in the groups without a metallic post, and statistically significant differences were found when the group with a metallic post has been observed (55%-70%). Intraobserver agreement also showed statistically significant differences in the groups with a metallic post. Conclusions: Small-volume CBCT scanning showed high accuracy in detecting horizontal root fracture without a metallic post. However, the presence of a metallic post significantly reduced the specificity and sensitivity of this examination. (J Endod 2011;37:1456-1459)

Clinical management and subsequent healing of teeth with horizontal root fractures

Horizontal root fractures are uncommon, mainly occurring on the cervical and middle third of the root of permanent upper incisors. The diagnosis is essentially radiographic and requires different healing patterns, depending on some pre- and postinjury factors. The aim of this article was to report the clinical management and different healing types in three cases of horizontal root fractures on permanent dentition. In case 1, the pulp tissue was vital and no treatment was necessary. In case 2, a root canal treatment of the cervical fragment was necessary and in case 3, pulpal necrosis was verified and an apical surgery was performed.

Horizontal transmission of entomopathogenic fungi by the diamondback moth

The relative potential of the pathogenic fungi Beauveria bassiana and Zoophthora radicans for use as autodisseminated biological control agents of the diamondback moth (Plutella xylostella) was compared. The LC50 of B. bassiana conidia to third instar larvae was 499 conidia/mm(2) of leaf surface and individual cadavers of mycosed fourth instar larvae yielded a mean of 67.5 X 10(6) (+/- 7.5 x 10(6)) conidia. All concentrations of B. bassiana tested in inoculation chambers (0.24, 2.4, and 6.2 mug/mm(2)) induced 100% mortality in adult male moths within 7 days. The times to death and sporulation were concentration and exposure duration dependent. A standard procedure for inoculating male moths resulted in > 85% mortality from Z. radicans and > 93% mortality from B. bassiana. Pairing of inoculated males with clean moths of both sexes yielded higher rates of passive transmission of B. bassiana than Z. radicans, but there was no evidence for sexual transmission of either pathogen. Similarly, B. bassiana was more effectively transmitted from inoculated male moths to larvae foraging on whole plants. Single sporulating cadavers producing B. bassiana or Z. radicans conidia placed on plants infested with larvae resulted in a similar rate of transmission for both pathogens. However, an increase of the density of sporulating cadavers from one to three/plant increased Z. radicans transmission (greater than fourfold) but had no effect on B. bassiana transmission. Simultaneous inoculations of larvae with conidia of both fungi reduced the mortality induced by each pathogen, the reduction being most acute for B. bassiana-induced mortality. Inoculation of adults with both fungi showed that, at concentrations required for effective passive transmission to larvae, B. bassiana severely inhibited Z. radicans mycosis in adults. (C) 2001 Academic Press.

Confined-unconfined flow in a horizontal confined aquifer

Mixed confined and unconfined groundwater flow occurs in a bounded initially dry aquifer when the hydraulic head at the side boundary suddenly rises above the elevation of the aquifer's top boundary. The flow problem as modelled by the Boussinesq equation is non-trivial because of the involvement of two moving boundaries. The transformed equation (based on a similarity transformation) can, however, be dealt with more easily. Here, we present an approximate analytical solution for this flow problem. The approximate solution is compared with an 'exact' numerical solution and found to be a very accurate description for describing the mixed confined and unconfined flow in the confined aquifer. (C) 2002 Elsevier Science B.V. All rights reserved.