Modeling of Thermal Joint Resistance for Sphere-Flat Contacts in a Vacuum

As a result of manufacturing processes, real surfaces have roughness and surface curvature. The real contact occurs only over microscopic contacts, which are typically only a few percent of the apparent contact area. Because of the surface curvature of contacting bodies, the macrocontact area is formed, the area where microcontacts are distributed randomly. The heat flow must pass through the macrocontact and then microcontacts to transfer from one body to another. This phenomenon leads to a relatively high temperature drop across the interface. Thermal contact resistance (TCR) is a complex interdisciplinary problem, which includes geometrical, mechanical, and thermal analyses. Each part includes a micro and a macro scale sub-problem. Analytical, experimental, and numerical models have been developed to predict TCR since the 1930's. Through comparison with more than 400 experimental data points, it is shown that the existing models are applicable only to the limiting cases and none of them covers the general non-conforming rough contact. The objective of this study is to develop a compact analytical model for predicting TCR for the entire range of non-conforming contacts, i. e. , from conforming rough to smooth sphere-flat in a vacuum. The contact mechanics of the joint must be known prior to solving the thermal problem. A new mechanical model is developed for spherical rough contacts. The deformation modes of the surface asperities and the bulk material of contacting bodies are assumed to be plastic and elastic, respectively. A closed set of governing relationships is derived. An algorithm and a computer code are developed to solve the relationships numerically. Applying Buckingham Pi theorem, the independent non-dimensional parameters that describe the contact problem are specified. A general pressure distribution is proposed that covers the entire spherical rough contacts, including the Hertzian smooth contact. Simple correlations are proposed for the general pressure distribution and the radius of the macrocontact area, as functions of the non-dimensional parameters. These correlations are compared with experimental data collected by others and good agreement is observed. Also a criterion is proposed to identify the flat surface, where the influence of surface curvature on the contact pressure is negligible. Thermal contact resistance is considered as the superposition of macro and micro thermal components. The flux tube geometry is chosen as the basic element in the thermal analysis of microcontacts. Simple expressions for determining TCR of non-conforming rough joints are derived which cover the entire range of TCR by using the general pressure distribution and the flux tube solution. A complete parametric study is performed; it is seen that there is a value of surface roughness that minimizes TCR. The thermal model is verified with more than 600 data points, collected by many researchers during the last 40 years, and good agreement is observed. A new approach is taken to study the thermal joint resistance. A novel model is developed for predicting the TCR of conforming rough contacts employing scale analysis methods. It is shown that the microcontacts can be modeled as heat sources on a half-space for engineering applications. The scale analysis model is extended to predict TCR over the entire range of non-conforming rough contacts by using the general pressure distribution developed in the mechanical model. It is shown that the surface curvature and contact pressure distribution have no effect on the effective micro thermal resistance. A new non-dimensional parameter is introduced as a criterion to identify the three regions of TCR, i. e. , the conforming rough, the smooth spherical, and the transition regions. An experimental program is designed and data points are collected for spherical rough contacts in a vacuum. The radius of curvature of the tested specimens are relatively large (in the order of m) and can not be seen by the naked eye. However, even at relatively large applied loads the measured joint resistance (the macro thermal component) is still large which shows the importance of surface out-of-flatness/curvature. Collected data are compared with the scale analysis model and excellent agreement is observed. The maximum relative difference between the model and the collected data is 6. 8 percent and the relative RMS difference is approximately 4 percent. Additionally, the proposed scale analysis model is compared/verified with more than 880 TCR data points collected by many researchers. These data cover a wide range of materials, surface characteristics, thermal and mechanical properties, mean joint temperature, directional heat transfer effect, and contact between dissimilar metals. The RMS difference between the model and all data is less than 13. 8 percent

Passive smoking is associated with cognitive and emotional impairment in adolescent girls

It is well established that smoking is associated with impaired mental health and sleep problems. However, the possible effects of passive smoking on cognitive and emotional characteristics have not previously been evaluated in adolescents. We investigated the association between passive smoking and cognitive and emotional function, and sleep patterns in 940 adolescent girls. The girls were divided into 2 groups [305 exposed subjects and 635 non-exposed subjects (the controls)]. The passive smokers had a significantly lower cognitive function and higher depression, aggression, and insomnia scores compared to the control group (P <0.05). No significant difference was detected with respect to day-time sleepiness and sleep apnea. Logistic regression analyses showed that the passive smokers were more likely than the controls to have cognitive impairments, depressive mood, aggressive behavior and insomnia. Adolescent passive smokers had significant differences in their cognitive abilities and emotional function

Natural Graphite Sheet Heat Sinks with Embedded Heat Pipes

Natural graphite sheet (NGS) is a candidate material for lightweight, high-performance heat sinks. We show that the low through–plane thermal conductivity can be mitigated by using heat pipes. In the measured configuration, the thermal resistance of an NGS heat sink with embedded heat pipes is comparable to that of a geometrically-identical aluminum one. The achieved weight reduction is 37 %. When electrical insulation of a heat sink is not required, soft and conforming NGS does not require thermal grease at the interface between the heat source and the heat sink. The low electrical conductivity of NGS does not lead to a decrease in common mode conducted emissions, but the potential to reduce the radiated emissions was quantified to be 12 to 97 % based on an analogy with antennas. In practical applications, replacing an existing heat sink with a geometrically identical NGS one is not recommended because it limits the achievable improvements in thermal performance, weight, and cost. Instead, we suggest using an optimization algorithm to determine the optimal heat sink geometry

In vitro antifungal activity of plant extracts on Saprolegnia parasitica from cutaneous lesions of rainbow trout (Oncorhynchus mykiss) eggs

Saprolegnia parasitica Coker is the main agent of saprolegniosis, one of the most important causes of economic losses in the rainbow trout farming industry in Iran. In this work, seven essential oils (2 species) and ethanol extracts (5 species) were tested against a strain of S. parasitica from cutaneous lesions of Oncorhynchus mykiss eggs, using a continuously agitated broth technique that allows both the minimum inhibitory concentration (MIC > 50 %) and the minimum lethal concentration (MLC> 99.9 %) to be evaluated. The essential oils of Thymus daenensis and Thymus khuzestanicum (MIC > 50 % = 0.63 µl ml-1 and MLC> 99.9 % = 22 µl ml-1) and ethanol extracts of Tanacetum parthenium and Mentha longifolia (MIC > 50 % = 31.25 and 62.5 µg ml-1 and MLC> 99.9 % = 600 and 550 µg ml-1, respectively) showed higher inhibition against S. parasitica than the other extracts. In general, our study suggests that natural products derived from some medicinal plants have the potential to be used as health rainbow trout eggs

Comparative Investigation of Health Quality of Air in Tehran, Isfahan and Shiraz Metropolises in 2011-2012

Background and Aims: Air pollution causes wide spectrum acute and chronic effects of health from slight physiological disorders to death from cardiovascular and respiratory diseases. In order to set the control programs, air pollution monitoring and determination of air quality are necessary. The objective of this study was to compare health quality of air in Tehran, Isfahan and Shiraz cities in 2011- 2012.Materials and Methods: This Study was a descriptive–analytic study. The moment concentrations of Tehran,Isfahan and Shiraz air pollutants were gathered through referring to the environmental protection agency.Then, Air Quality Index (AQI) was calculated based on the criteria pollutants’ levels (CO, NO2, SO2, PM10,PM2.5 and O3) for three cities through linear interpolation and was classified into describing classes accordingto tables of National Ambient Air Quality Standards. Data analysis was performed with Excel and SPSS software using One-Way ANOVA test.Results: The results showed that the AQI in Tehran, Isfahan and Shiraz was higher than Iran’s environmental protection agency standards (AQI&gt;100) in 341, 323 and 85 days, respectively. Furthermore, particulate matter (PM10) has been the critical pollutant in three cities for most days of the year. One-Way ANOVA test between AQI mean of the three cities showed a significant difference.Conclusion: The air quality of the three cities was unhealthy in 2011-2012 and the situation of Tehran andIsfahan air, however, was in the “bad situation”.Key words: Air pollutants, Air quality index, Pollution standard index, Responsible pollutan

Evaluation of Nerium oleander aqueous extract effect on Staphylococcus aureus and Staphylococcus epidermis

زمینه و هدف: مقاومت‌ آنتی‌بیوتیکی زمینه را برای جایگزین نمودن روش های درمانی گیاهی دارای عوارض جانبی کمتر نسبت به داروهای رایج فراهم نموده است. این مطالعه با هدف تعیین اثر ضد میکروبی گیاه خرزهره (Nerium oleander) بر باکتری های استافیلوکوکوس اورئوس و اپیدرمیس انجام شده است. روش بررسی: در این مطالعه تجربی اثر عصاره آبی برگ و گل گیاه خرزهره به صورت مجزا با روش جوشاندن در سه غلظت 5/12، 25 و50 میلی گرم بر میلی لیتر با مقادیر 20،40 و 80 میکرولیتر بر دو گونه استافیلوکوکوس اورئوس و استافیلوکوکوس اپیدرمیس، با ایجاد چاهک و تلقیح عصاره بررسی شد. همچنین تست آنتی بیوگرام با سه آنتی‌بیوتیک اکسی‌تتراسایکلین، اریترومایسین و پنی‌سیلین بر روی این دو گونه انجام گرفت. قطر هاله‌ های عدم رشد اندازه گیری شد و اثر عصاره مورد ارزیابی قرار گرفت. یافته‌ها: در تست آنتی‌بیوگرام استافیلوکوکوس اورئوس به اریترومایسین حساس و به پنی‌سیلین و اکسیتتراسایکلین مقاوم بود. استافیلوکوکوس اپیدرمیس به اریترومایسین نسبتاً مقاوم و به اکسی تتراسایکلین و اریترومایسین مقاوم بود. استافیلوکوکوس اورئوس به مقادیر 40 و 80 میکرولیتر از غلظت mg/ml 25، کلیه مقادیر از غلظت mg/ml50 عصاره برگ و کلیه مقادیر از غلظت mg/ml 50 عصاره گل حساس بود ولی استافیلوکوکوس اپیدرمیس به هیچ کدام از غلظت های عصاره حساسیت نشان نداد. در تمامی غلظت ها با افزایش میزان عصاره از 20 تا 80 میکرولیتر، میانگین قطر هاله افزایش نشان داد. عصاره برگ از عصاره گل گیاه اثر مهاری بیشتری داشت. نتیجه گیری: با توجه به افزایش روز افزون مقاومت‌های آنتی‌بیوتیکی، عصاره گیاه خرزهره می تواند به عنوان یک ترکیب ضد میکروبی جدید جهت استعمال خارجی عفونت‌های زخمی و رفع آلودگی‌های سطحی پیشنهاد گردد

Catalytic ozonation of azo dye Reactive Red 120 in the presence of MgO nanoparticles

Background and Aims: Dyes are widely used in different industries and consequently are disposed through different industrial effluents into the environment. Chronic and/or acute effects of the chemicals on microorganisms have been documented. Dyes may absorb and reflect the entering sun lights into the water and thereby decrease the algal photosynthesis. The later in turn can affect the food chain seriously. The aim of this study was, therefore, to use MgO nanoparticles as catalyst in heterogenic catalytic ozonation process (COP) for reactive red 120 dye removal (decolorization) from synthetic wastewater.Materials and Methods: MgO nanoparticles were produced by sol-gel method. The influences of several operational parameters including solution pH, reaction time, MgO dosage and initial dye concentration on removal (decolorization) efficiency were evaluated.Results: The optimum pH and MgO dosage for COP were determined as 10 and 3 g/L, respectively. Decolorization of 500 mg/L of dye was almost complete after 12 min under achieved optimum conditions. MgO nanocrystals markedly affected the COP and enhanced the dye removal efficiency by approximately 49% compared with the sole ozonation process.Conclusion: Higher O3 decomposition in presence a small amounts of catalyst and alkaline pH increases the radical production which in turn improves the decolorization efficiency. Increasing the initial concentration of dye deteriorated the removal efficiency; however, this can be compensated by increasing the ozonation rate.Key words: Catalytic Ozonation, MgO Nanoparticles, Reactive Red 120 dye (RR120)

POVIJESNI PREGLED NEUROLOŠKIH POREMEĆAJA POVEZANIH S GASTROINTESTINALNIM BOLESTIMA S AVICENNINA STAJALIŠTA

Reviewing historical medical manuscripts shows that neurological disorders have been previously described in the Islamic Golden Age. Ibn Sina, also known as Avicenna (980-1037 AD), was one of the most renowned scientists during this period. He widely practiced medicine, especially those disorders related to neurology, neurosurgery, and psychiatry in conventionalmedicine. In his extant book al-Qānūn fī al-Tibb (the Canon of Medicine), he claimed that some types of brain diseases can be related to the “marāqq” and called them marāqq-related disorders. From Avicenna’s viewpoint, “marāqq” is considered a membranous structure in the abdomen. Ibn Sina has illustrated the association between the “marāqq” and the brain through some direct and indirect pathways. As a result, some disturbances in the “marāqq” can influence the brain, which can contribute to the pathogenesis of a number of brain diseases. Accordingly, those patients who regularly had gastrointestinal discomfortsexperienced a higher prevalence of headache, melancholia, and epilepsy. This study aimed to explore the relationship between abdominal and brain diseases from Avicenna’s viewpoint. Furthermore, the definition, clinical manifestation, and therapeutic strategies of marāqq-related disorders were described.Pregled povijesnih medicinskih rukopisa pokazuje da su neurološki poremećaji već bili opisani u islamskome zlatnom dobu. Ibn Sina, poznat i kao Avicenna (980. – 1 037.), bio je jedan od najpoznatijih znanstvenika toga vremena. Djelovao je u mnogim područjima medicine. Posebno je proučavao poremećaje vezane uz neurologiju, neurokirurgiju i psihijatriju u konvencionalnoj medicini. U svojoj knjizi „al-Qānūn fī al-Tibb“ (Kanon medicine) tvrdio je da se neke bolesti mozga mogu povezati s „marāqqom“ i nazvao ih poremećajima povezanim s marāqqom. S Avicennina stajališta, „marāqq“ je membranska struktura u abdomenu. Ibn Sina ilustrirao je vezu između „marāqqa“ i mozga pomoću nekih izravnih i neizravnih veza. Kao rezultat toga, neki poremećaji u „marāqqu“ mogu utjecati na mozak, što može pridonijeti patogenezi brojnih bolesti mozga. Sukladno tome, pacijenti s redovitim gastrointestinalnim tegobama imali su učestalije glavobolje, melankolije i epilepsije. Cilj je ovog istraživanja bio istražiti odnos između bolesti abdomena i mozga s Avicennina stajališta. Opisana je i definicija, klinička manifestacija i terapijske strategije poremećaja povezanih s „marāqqom“

Evaluation of cardiovascular and respiratory mortality attributed to atmospheric SO2 and CO using AirQ model

Background: Air pollutants have multiple adverse effects on human health. In this study, the health effects of exposure to carbon monoxide (CO) and SO2 in the air of 6 Iranian metropolises in 2011-2012 were examined. Methods: Raw data was collected from the Iranian Department of Environment and the Iran Meteorological Organization. After validation, the required statistical indices were calculated through programming and modifying temperature and pressure in Excel software. The output of Excel was given to the AirQ model, and the results were presented as the cases of death. Results: The annual mean concentrations of SO2 were 2.45, 1.55, 0.6, 0.55, 1.05, and 3.8 times higher than the guidelines of the World Health Organization (WHO) (20 μg/m3) in Tehran, Mashhad, Isfahan, Shiraz, Tabriz, and Urmia, respectively. The concentrations of CO did not exceed the standard limit in any of the studied cities. The cumulative numbers of total deaths attributed to SO2 were 744, 122, 132, 44, 37, and 107 in Tehran, Mashhad, Isfahan, Shiraz, Tabriz, and Urmia, respectively. The highest mortality rate was found in Urmia at 2.9% followed by Tehran at 1.52%; the lowest rate of 0.46% was found in Tabriz. Conclusion: The results show that of the 6 metropolises, the highest CO mortality rate of about 2.15% belonged to Isfahan followed by Arak with about 1.38%, and the lowest rate of 0.68% belonged to Mashhad. Because of the growing trend of air pollution and its mortality rate and adverse effects, practical solutions for the control and reduction of air pollution in Iranian metropolises are necessary