73 research outputs found
A survey ofacute histopathological effects of silver nanoparticles on liver, kidney with blood cells during oral administration in male mice (Mus musculus
Get PDFزمینه و هدف : امروزه با افزایش استفاده از نانوذرات نقره در محصولات مختلف از جمله محصولات مصرفی و پزشکی، بررسی سمیت نانوذرات نقره، برای امنیت استفاده کنندگان از این محصولات، لازم و ضروری می باشد. بعضی از مطالعات نشان می دهد که کبد و کلیه اندام اصلی برای تجمع و ذخیره این مواد می باشند. این مطالعه با هدف بررسی اثر خوراکی نانوذرات نقره بر بافت کبد ، کلیه و بررسی تغییرات در سلول های خونی در موش سفید آزمایشگاهی طراحی و اجرا شد. روش بررسی : در این مطالعه تجربی، 45 سر موش نر Balb/c) با وزن 3±2/24 گرم) به طور تصادفی در 3 گروه 15 تایی (تیمار1وتیمار2 و کنترل) مورد بررسی قرار گرفتند. درمان خوراکی با نانونقره روزانه در گروه تیمار1 با محلول ppm 20 و برای گروه تیمار2 با ppm 50 وگروه کنترل با همان مقدار آب مقطر تیمار شد. در روز های 2و7و14 نمونه گیری بافت از کبد و کلیه انجام شد. جهت بررسی های بافت شناسی از روش رنگ آمیزی هماتوکسیلین و ائوزین استفاده شد. یافته ها : آسیب های وارد شده به کبد ، منجر به واکوئله شدن سیتوپلاسم سلول های کبدی همراه با دژنراسیون و نکروز برخی سلول ها و تجمع کانونی سلول های آماسی در کبد همراه با پرخونی می شود. آسیب های وارد شده به کلیه در موش های دریافت کننده ی نانوذرات نقره شامل پرخونی ، حضور سلولهای آماسی، نکروز سلولهای توبولی وگلومرونفریت کلیه می باشد. این یافته هانشان می دهد که استفاده از نانوذرات نقره در دوز بالاتر( ppm 50) باعث افزایش شدت ضایعات در بافت کبد وکلیه می شود. در بررسی شمارش گلبول های قرمز و اندازه گیری هموگلوبین و هماتوکریت تفاوت معنی داری میان گروه تیمار و کنترل مشاهده نشد اما تعداد گلبول های سفید در گروه تیمار (غلظت ppm50 ) نسبت به گروه کنترل افزایش معنی داری نشان داد(p<0.05). نتیجه گیری: این آزمایشات نشان داد که کبد و کلیه بافت هدف برای نانوذرات نقره می باشند و استفاده از نانوذرات نقره به صورت خوراکی باعث آسیب بافت کبد و کلیه موش ها می شود. این مطالعه نشان ‌داد که درمان خوراکی نانوذرات نقره باعث تغییرات قابل توجهی بر تعداد گلبول های سفید خون می شوند
Analytical Solution for the Free Over-Fall Weir Flow Using Conformal Mapping and Potential Flow Theory
Get PDFAbstract In this study an analytical approach is presented based on the potential flow theory and conformal mapping technique to solve the problem of an ideal and steady flow over a free over-fall weir. The results are arranged for rectangular sharp-crested over-fall weirs with different vertical aspect ratios (h/P, h is the water head above the weir and P is the weir height). To validate the results of this approach, the free over-fall weir d ischarge equation and the water free-surface profiles obtained with the potential flow theory have been calibrated with the experimental data. In conclusion, the information made available and the close correlation among the results of present analytical ap proach and the experimental data are adequate to warrant the reco mmendation of this method as a valuable supplement to existing methods employed in engineering design
High porosity and light weight graphene foam heat sink and phase change material container for thermal management
Get PDFDuring the last decade, graphene foam emerged as a promising high porosity 3-dimensional (3D) structure for various applications. More specifically, it has attracted significant interest as a solution for thermal management in electronics. In this study, we investigate the possibility to use such porous materials as a heat sink and a container for a phase change material (PCM). Graphene foam (GF) was produced using chemical vapor deposition (CVD) process and attached to a thermal test chip using sintered silver nanoparticles (Ag NPs). The thermal conductivity of the graphene foam reached 1.3 W m(-1)K(-1), while the addition of Ag as a graphene foam silver composite (GF/Ag) enhanced further its effective thermal conductivity by 54%. Comparatively to nickel foam, GF and GF/Ag showed lower junction temperatures thanks to higher effective thermal conductivity and a better contact. A finite element model was developed to simulate the fluid flow through the foam structure model and showed a positive and a non-negligible contributions of the secondary microchannel within the graphene foam. A ratio of 15 times was found between the convective heat flux within the primary and secondary microchannel. Our paper successfully demonstrates the possibility of using such 3D porous material as a PCM container and heat sink and highlight the advantage of using the carbon-based high porosity material to take advantage of its additional secondary porosity
Reliability investigation of a carbon nanotube array thermal interface material
Get PDFAs feature density increases within microelectronics, so does the dissipated power density, which puts an increased demand on thermal management. Thermal interface materials (TIMs) are used at the interface between contacting surfaces to reduce the thermal resistance, and is a critical component within many electronics systems. Arrays of carbon nanotubes (CNTs) have gained significant interest for application as TIMs, due to the high thermal conductivity, no internal thermal contact resistances and an excellent conformability. While studies show excellent thermal performance, there has to date been no investigation into the reliability of CNT array TIMs. In this study, CNT array TIMs bonded with polymer to close a Si-Cu interface were subjected to thermal cycling. Thermal interface resistance measurements showed a large degradation of the thermal performance of the interface within the first 100 cycles. More detailed thermal investigation of the interface components showed that the connection between CNTs and catalyst substrate degrades during thermal cycling even in the absence of thermal expansion mismatch, and the nature of this degradation was further analyzed using X-ray photoelectron spectroscopy. This study indicates that the reliability will be an important consideration for further development and commercialization of CNT array TIMs
Fluctuating Characteristics of Two-Phase Air-Water Slug Flow in Pressurized Pipelines
No full textTwo-phase gas-liquid flows occur in a wide variety of situations, e.g., in chemical processing, power generation, water supply systems, and petroleum industry. The study of two-phase fluid flows is of great importance in hydraulic engineering. This type of flow typically occurs in pressurized flow tunnels, culverts, siphons, and bends in which the gas trapped in water pipelines releases from the water as the pressure reduces. The relative discharge rate of fluids and the pipe slope produce a wide variety of flow patterns including stratified, wavy, and slug flows. In this paper, the unstable two-phase air-water flow is experimentally investigated. The image processing technique is applied for estimating the fluctuations of such parameters as void fraction and length, period and celerity of slug waves. It is shown that the pipe inclination and air flow rate have significant effects on flow characteristics. Also, the relative wave length (L/D, D is the pipe diameter) in a slug flow varies from 10 to 85, while air bubble length varies from 1/3 to 1/2 of wave length
Thermal characterization and thermal tuning in nanostructured materials
No full textIn this dissertation, the experimental investigation of the heat transport in crystalline nanostructured materials is studied. Different methods to reduce their thermal conductivity to create user-specific materials are presented as well. It is shown that by using different methods such as the incorporation of additional elements in the crystalline structure, controlling the deposition and embedding metallic nanoinclusions in the semiconductor matrix, it is possible to reduce the thermal conductivity. Thermal conductivity measurements have been conducted by using pulsed photothermal reflectance (PPR) and 3ω techniques at room temperature. The materials studied in this work include Ti-based hard coatings, multilayer TiN/TiAlN coatings and n-type Bi2Te2.7Se0.3 thermoelectric films.
Firstly, the effect of the incorporation of Al on the thermal conductivity of TiAlN coatings prepared by a lateral rotating cathode arc (LARC) technique has been investigated. To study this, a series of TiAlN coatings were deposited on stainless steel substrates and the thermal conductivity of the coatings was measured by the PPR technique. The Microstructure of the coatings was analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). These techniques reveal that TiN coating shows a clear columnar structure with a predominant (111) preferential orientation. With the incorporation of Al, the columnar structure of the coatings is disrupted, the grain size of the coatings is decreased and the dislocation density is increased. A significant decrease in thermal conductivity was found with increasing Al content and a minimum thermal conductivity of about 4.63 W/mK was obtained at the Al/Ti atomic ratio of around 0.72. The decrease in thermal conductivity of the TiAlN coatings is explained in terms of increased phonon scattering due to the decrease in the grain size and increasing dislocation density.
The effect of the incorporation of Al and Si on the thermal conductivity of the TiAlSiN nanocomposite coatings prepared by the LARC technique has been studied. A series of TiAlSiN nanocomposite coatings were deposited on stainless steel substrates and the room temperature thermal conductivity of the coatings was measured by the PPR technique. A significant decrease in thermal conductivity was found with increasing Al and Si contents and it was shown that the thermal conductivity of the TiAlSiN nanocomposite coatings is about 1.8 W/mK at a (Al+Si)/Ti atomic ratio of around 1.76. The decrease in thermal conductivity of the TiAlSiN nanocomposite coatings can be attributed to the reduced grain size and the formation of a nanocomposite structure which consists of crystalline nanograins embedded in a disordered, lower thermal conductivity than TiAlN, amorphous SiNx matrix.
In order to study the effect of a multilayer structure on the thermal conductivity, a series of multilayer [TiN/TiAlN]n coatings with different bilayer numbers n were deposited on stainless steel substrates by the LARC technique. The PPR technique was employed to measure thermal conductivity of the coatings at room temperature. TEM observation and microstructure analysis of multilayer coatings show a lattice mismatch and misfit dislocations at the interfaces between TiN and TiAlN layers, and a decrease of the grain size with increasing number of layers. Results show that the thermal conductivity of the multilayer coatings reduces with increasing bilayer number n. Phonon scattering is increased at the interfaces and grain boundaries due to the existence of misfit dislocations and to the decreasing grain size, respectively.
For the study of the effect of metallic nanoinclusions in thermoelectric (TE) film on the thermal conductivity, textured n-type Bi2Te2.7Se0.3 thin films with Pt nanoinclusions were successfully prepared via pulsed laser deposition. The thermal conductivity of the TE films was measured by the 3ω technique. The TEM observation shows that the Pt nanoinclusions are embedded at the grain boundaries of the semiconductor matrix. By introducing Pt nanoinclusions, the thermal conductivity is reduced due to scattering phonon at the grain boundaries.ELECTRICAL and ELECTRONIC ENGINEERIN
CIRCULAR HYDRAULIC JUMP OVER THE BEDS WITH ADVERSE SLOPE
No full textOne of the most common energy dissipator structures is the hydraulic jump-type
stilling basins, in which the flow excess kinetic energy is dissipated by the generation of a hydraulic jump, changing the flow regime from super- to sub-critical flow. Due to the extensive use of stilling basins in hydraulic systems and irrigation and drainage networks, their study was the focus of several investigations. For the hydraulic design of stilling basins, three parameters including the length, sequent depth, and head loss of the jump are the major parameters having great effects on designing economical stilling basins.
In the present study, analytical and experimental investigations were performed
to study the profile of circular hydraulic jumps on slopped beds with adverse
slope. The study mainly focused on the conjugate depth ratio, relative head
loss, and relative length. In the analytical model, we applied a series of
reasonable assumptions and used integral equations governing the fluid dynamics to derive relationships for the conjugate depth ratio and the relative head loss, which are applicable to both classical and circular hydraulic jumps.
Experimental study was carried out in a cubic reservoir, in which a circular
bed of 2 m in diameter was applied as the circular bed in its center. In the
experimental study, flow discharge, initial and secondary depth, and length of
the jump were measured. According to the results, by increasing the ratio of
the conjugate radius and the bed slope, the ratio of the conjugate depth and
jump length decrease and the relative head loss increases. The accuracy of the
analytical relationships compared to the experimental was checked, applying
four error functions including; coefficient of determination, normalized root
mean square, weighted quadratic deviation, and efficiency function, showing a
relatively good correlation between the experimental and the analytical results. Furthermore, by using the experimental data, the length of the circular hydraulic jump was investigated. Results show that, in this type of jump, the length of the hydraulic jump is approximately half that of the classical hydraulic jump
Depth-averaged Velocity Distribution in Smooth Trapezoidal and Rectangular Open Channels with the Best Hydraulic Section
No full textGeneral equations for predicting depth-averaged velocity in open channels are not well suited for trapezoidal open channels. In this study, an innovative method is developed for predicting the depth-averaged velocity distributions in smooth trapezoidal open channels with the best hydraulic section. Depth-averaged velocity was obtained using the boundary shear stress obtained in the present study. To calibrate the present analytical results, an experimental investigation was also performed. Analytical results compared well with the experimental data
Prevalence of Virulence Genes and Antibiotic Resistance Pattern in Enterococcus Faecalis Isolated from Urinary Tract Infection in Shahrekord, Iran
No full textBackground: This study aims to specify the antimicrobial resistance pattern and virulence genes of Enterococcus faecalis isolated from urinary tract infections in Shahrekord, Iran.Methods: Urine samples of 1000 people suspected of having urinary tract infections referred to Shahrekord medical diagnostic laboratories were examined. Biofilm assays were performed by microtiter plate test through reading the OD490. Polymerase Chain Reaction (PCR) was applied to study the virulence factors.Results:Enterococcus faecalis was detected in 60 samples. After performing microbiological tests, all samples were positive in the molecular analysis. Strong, moderate and weak biofilm reactions reported 66.67, 25, and 8.33 respectively. The most resistance reported to cotrimoxazole, vancomycin and amikacin and the lowest resistance to nitrofurantoin (8.33) was reported. Statistical analysis with Fisher's exact test showed a statistically significant relationship between biofilm production and resistance to cotrimoxazole, vancomycin and cefotaxime. Prevalence of efe A, ace, gel E, esp, cyl M, agg, cyl A and cyl B in strong biofilm formation isolates was reported 100, 87.5, 82, 62.5, 55, 37.5 25 and 22.5 respectively. There was a significant relationship between the frequency of efa A and strong biofilm reaction.Conclusions: The presence ofE. faecalis strains resistant to co-trimoxazole and vancomycin and present of some virulence factors is alarming the researchers. Since antibiotic resistance genes are probably transmitted among enterococci, and Staphylococci, controlling infections made by enterococci as well as the appropriate administration of antibiotics could treat the nosocomial infections effectivel
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