1,613 research outputs found

    Fluid flow and heat transfer in a dual-wet micro heat pipe

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    Micro heat pipes have been used to cool micro electronic devices, but their heat transfer coefficients are low compared with those of conventional heat pipes. In this work, a dual-wet pipe is proposed as a model to study heat transfer in micro heat pipes. The dual-wet pipe has a long and narrow cavity of rectangular cross-section. The bottom-half of the horizontal pipe is made of a wetting material, and the top-half of a non-wetting material. A wetting liquid fills the bottom half of the cavity, while its vapour fills the rest. This configuration ensures that the liquid–vapour interface is pinned at the contact line. As one end of the pipe is heated, the liquid evaporates and increases the vapour pressure. The higher pressure drives the vapour to the cold end where the vapour condenses and releases the latent heat. The condensate moves along the bottom half of the pipe back to the hot end to complete the cycle. We solve the steady-flow problem assuming a small imposed temperature difference between the two ends of the pipe. This leads to skew-symmetric fluid flow and temperature distribution along the pipe so that we only need to focus on the evaporative half of the pipe. Since the pipe is slender, the axial flow gradients are much smaller than the cross-stream gradients. Thus, we can treat the evaporative flow in a cross-sectional plane as two-dimensional. This evaporative motion is governed by two dimensionless parameters: an evaporation number E defined as the ratio of the evaporative heat flux at the interface to the conductive heat flux in the liquid, and a Marangoni number M. The motion is solved in the limit E→∞ and M→∞. It is found that evaporation occurs mainly near the contact line in a small region of size E−1W, where W is the half-width of the pipe. The non-dimensional evaporation rate Q* ~ E−1 ln E as determined by matched asymptotic expansions. We use this result to derive analytical solutions for the temperature distribution Tp and vapour and liquid flows along the pipe. The solutions depend on three dimensionless parameters: the heat-pipe number H, which is the ratio of heat transfer by vapour flow to that by conduction in the pipe wall and liquid, the ratio R of viscous resistance of vapour flow to interfacial evaporation resistance, and the aspect ratio S. If HRxs226B1, a thermal boundary layer appears near the pipe end, the width of which scales as (HR)−1/2L, where L is the half-length of the pipe. A similar boundary layer exists at the cold end. Outside the boundary layers, Tp varies linearly with a gradual slope. Thus, these regions correspond to the evaporative, adiabatic and condensing regions commonly observed in conventional heat pipes. This is the first time that the distinct regions have been captured by a single solution, without prior assumptions of their existence. If HR ~ 1 or less, then Tp is linear almost everywhere. This is the case found in most micro-heat-pipe experiments. Our analysis of the dual-wet pipe provides an explanation for the comparatively low effective thermal conductivity in micro heat pipes, and points to ways of improving their heat transfer capabilities

    Long-Term Climate Trends and Northern Bobwhite Populations in South Texas

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    Because climate change and its associated weather changes may influence population trends of birds, we analyzed northern bobwhite (Colinus virginianus; bobwhite hereafter) age ratios and abundance in relation to climate trends during 1908-1997 in south Texas. Weather variables included regional mean temperature maxima for June, July, and August, and precipitation totals for autumn (Sep-Nov), winter (Dec-Feb), spring (Mar-May), and summer (Jun-Aug). Long-term temporal trends for these weather variables were estimated with a linear regression. Yearly weather data were used to predict bobwhite age ratios (juv/ad in autumn and winter) and abundance between 1908 and 1997 using neural network models. We compared these predictions with data available from various bobwhite surveys in south Texas over the period 1940-1999. Means for daily maximum temperature during summer declined at rates between 1.6 and 2.3°C/century. No temporal trends were detected for seasonal precipitation (1908-1997), age ratios (1940-1999), or abundance (1977-1998). Neural models developed independently to predict bobwhite age ratios and bobwhite abundance from weather data produced predictions that were consistent with each other. Years with high age ratios tended to coincide with or precede years of high abundance

    Radio Properties of Low Redshift Broad Line Active Galactic Nuclei

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    The question as to whether the distribution of radio-loudness in active galactic nuclei (AGN) is actually bimodal has been discussed extensively in the literature. Futhermore, there have been claims that radio-loudness depends on black hole mass and Eddington ratio. We investigate these claims using the low redshift broad line AGN sample of Greene & Ho (2007), which consists of 8434 objects at z < 0.35 from the Sloan Digital Sky Survey Fourth Data Release (SDSS DR4). We obtained radio fluxes from the Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey for the SDSS AGN. Out of the 8434 SDSS AGN, 821 have corresponding observed radio fluxes in the FIRST survey. We calculated the radio-loudness parameter (R) for all objects above the FIRST detection limit (1 mJy), and an upper limit to R for the undetected objects. Using these data, the question of radio bimodality is investigated for different subsets of the total sample. We find no clear demarcation between the radio-loud (RL, R > 10) and radio-quiet (RQ, R < 10) objects, but instead fill in a more radio-intermediate population in a continuous fashion for all subsamples. We find that 4.7% of the AGN in the flux-limited subsample are RL based on core radio emission alone. We calculate the radio-loud fraction (RLF) as both a function of black hole mass and Eddington ratio. The RLF decreases (from 13% to 2%) as Eddington ratio increases over 2.5 order of magnitude. The RLF is nearly constant (~5%) over 4 decades in black hole mass, except for an increase at masses greater than 10^8 solar masses. We find for the FIRST detected subsample that 367 of the RL AGN have black hole masses less than 10^8 solar masses, a large enough number to indicate that RL AGN are not a product of only the most massive black holes in the local universe.Comment: 28 pages, 14 figures, accepted to A

    A Comparison of Two Quail Abundance Indices and Their Relationship to Quail Harvest in Texas

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    Surveys are used to monitor status and trends of animal populations. However, different surveys may give conflicting results for the same species and population being surveyed. Therefore, we compared results of the North American Breeding Bird Survey (BBS) and Texas Parks and Wildlife (TPW) roadside counts for scaled quail (Callipepla squamata) and northern bobwhite (Colinus virginianus) in Texas. Surveys were compared on both an ecoregion and statewide basis. The BBS and TPW surveys gave similar trends for bobwhites and scaled quail for 5 of 8, and 3 of 5 ecoregions, respectively. Survey trends differed at the statewide scale for both species. We compared estimated statewide harvest as an independent index of quail population status in Texas with results from both surveys. The TPW roadside survey was more closely related to estimated statewide harvest for northern bobwhites (R2 = 0.86, P \u3c= 0.001) and scaled quail (R2 = 0.75, P = 0.0001) than the BBS survey (R2 = 0.60, P = 0.001; and R2 = 0.35, P = \u3c0.0001, respectively). Survey methods, sampling frameworks, and issues of scale are important variables to consider when interpreting survey results. The BBS provides useful data on quail populations at a multi-state or national scale. However, most state wildlife agencies require surveys that provide information at finer spatial scales

    Heme Oxygenase Induction Suppresses Hepatic Hepcidin and Rescues Ferroportin and Ferritin Expression in Obese Mice

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    Hepcidin, a phase II reactant secreted by hepatocytes, regulates cellular iron levels by increasing internalization of ferroportin-a transmembrane protein facilitating egress of cellular iron. Chronic low-grade inflammatory states, such as obesity, have been shown to increase oxidative stress and enhance hepcidin secretion from hepatocytes and macrophages. Heme-heme oxygenase (HO) is a stress response system which reduces oxidative stress. We investigated the effects of HO-1 induction on hepatic hepcidin levels and on iron homeostasis in hepatic tissues from lean and obese mice. Obese mice exhibited hyperglycemia (p < 0.05); increased levels of proinflammatory cytokines (MCP-1, IL-6, p < 0.05); oxidative stress (p < 0.05); and increased hepatic hepcidin levels (p < 0.05). Enhancement of hepcidin was reflected in the reduced expression of ferroportin in obese mice (p < 0.05). However, this effect is accompanied by a significant decline in ferritin expression. Additionally, there are reduced insulin receptor phosphorylation and attenuation of metabolic regulators pAMPK, pAKT, and pLKB1. Cobalt protoporphyrin- (CoPP-) induced HO-1 upregulation in obese mice reversed these alterations (p < 0.05), while attenuating hepatic hepcidin levels. These effects of CoPP were prevented in obese mice concurrently exposed to an inhibitor of HO (SnMP) (p < 0.05). Our results highlight a modulatory effect of HO on iron homeostasis mediated through the suppression of hepatic hepcidin

    Role of the Cyclooxygenase Pathway in Chemotherapy-Induced Oral Mucositis: A Pilot Study

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    Goals Oral mucositis can be a significant and dose-limiting complication of high-dose cancer therapy. Mucositis is a particularly severe problem in patients receiving myeloablative chemotherapy prior to bone marrow or hematopoetic stem cell transplant (HSCT). The cyclooxygenase (COX) pathway mediates tissue injury and pain through upregulation of pro-inflammatory prostaglandins, including prostaglandin E2 (PGE2) and prostacyclin (PGI2). The objective of this small (n=3) pilot study was to examine the role of the COX pathway in causing mucosal injury and pain in chemotherapy-induced oral mucositis. Materials and methods We collected blood, saliva, and oral mucosal biopsy specimens from three autologous HSCT patients at the following time-points before and after administration of conditioning chemotherapy: Day −10, +10, +28, and +100, where day 0 is day of transplant. RNA extracted from full-thickness tissue samples was measured by RT-PCR for the following: COX-1, COX-2, microsomal prostaglandin E synthase (mPGES), IL-1β, and TNF-α. Blood and saliva samples were measured by ELISA for PGE2 and PGI2, which are markers of COX activity. Severity of oral mucositis was determined using the Oral Mucositis Index. Severity of pain due to oral mucositis was measured using a Visual Analog Scale. Relationships between the different variables were examined using Spearman rank correlation coefficients. Main results Mean mucositis and pain scores increased significantly after administration of chemotherapy and then gradually declined. The correlation between changes in mucositis and pain scores was strong and statistically significant. The following additional correlations were statistically significant: between tissue COX-1 and pain; between tissue mPGES and pain; between salivary PGE1 and pain; between salivary PGI2 and pain. Other relationships were not statistically significant. Conclusions Our finding of significant associations of pain scores with tissue COX-1 and mPGES, as well as salivary prostaglandins, is suggestive of a role for the cyclooxygenase pathway in mucositis, possibly via upregulation of pro-inflammatory prostaglandins. However, our small sample size may have contributed to the lack of significant associations between COX-2 and other inflammatory mediators with mucosal injury and pain. Thus, additional studies with larger numbers of subjects are warranted to confirm the involvement of the cyclooxygenase pathway in chemotherapy-induced mucositis
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