Search results for: EHD lubricated contacts

Authors: Vinod Kumar, Surjit Angra

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The objective of this theoretical study is to develop simple design formulas for the prediction of minimum film thickness and maximum mean film temperature rise in lightly loaded high-speed rolling/sliding lubricated elliptical contacts incorporating starvation effect. Herein, the reported numerical analysis focuses on thermoelastohydrodynamically lubricated rolling/sliding elliptical contacts, considering the Newtonian rheology of lubricant for wide range of operating parameters, namely load characterized by Hertzian pressure (PH = 0.01 GPa to 0.10 GPa), rolling speed (>10 m/s), slip parameter (S varies up to 1.0), and ellipticity ratio (k = 1 to 5). Starvation is simulated by systematically reducing the inlet supply. This analysis reveals that influences of load, rolling speed, and level of starvation are significant on the minimum film thickness. However, the maximum mean film temperature rise is strongly influenced by slip in addition to load, rolling speed, and level of starvation. In the presence of starvation, reduction in minimum film thickness and increase in maximum mean film temperature are observed. Based on the results of this study, empirical relations are developed for the prediction of dimensionless minimum film thickness and dimensionless maximum mean film temperature rise at the contacts in terms of various operating parameters.

Keywords: starvation, lubrication, elliptical contact, traction, minimum film thickness

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Authors: B. Chetti, W. A. Crosby

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This paper presents a numerical analysis for the dynamic performance of a finite journal bearing lubricated with couple stress fluid taking into account the effect of the deformation of the bearing liner. The modified Reynolds equation has been solved by using finite difference technique. The dynamic characteristics in terms of stiffness coefficients, damping coefficients, critical mass and whirl ratio are evaluated for different values of eccentricity ratio and elastic coefficient for a journal bearing lubricated with a couple stress fluids and a Newtonian fluid. The results show that the dynamic characteristics of journal bearings lubricated with couple stress fluids are improved compared to journal bearings lubricated with Newtonian fluids.

Keywords: journal bearing, elastohydrodynamic, stability, couple stress

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Authors: M. Amara, M. Tahar Abbes, A. Dokkiche, M. Benbrike

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Shear stresses generate frictional forces thus lead to the reduction of engine performance due to the power losses. This friction can also cause damage to the piston material. Thus, the choice of an optimal material for the piston is necessary to improve the elastohydrodynamical contacts of the piston. In this study, to achieve this objective, an elastohydrodynamical lubrication model that satisfies the best tribological behavior of the piston with the optimum choice of material is developed. Several aluminum alloys composed of different components are studied in this simulation. An application is made on the piston 60 x 120 mm Diesel engine type F8L413 currently mounted on Deutz trucks TB230 by using different aluminum alloys where alloys based on aluminum-silicon have better tribological performance.

Keywords: EHD lubricated contacts, friction, properties of materials, tribological performance

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Authors: Zhipeng Dong, Jing Guo

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Graphene-semiconductor contacts have been extensively studied recently, both as a stand-alone diode device for potential applications in photodetectors and solar cells, and as a building block to vertical transistors. Graphene is a two-dimensional nanomaterial with vanishing density-of-states at the Dirac point, which differs from conventional metal. In this work, image-charge-induced barrier lowering (BL) in graphene-semiconductor contacts is studied and compared to that in metal Schottky contacts. The results show that despite of being a semimetal with vanishing density-of-states at the Dirac point, the image-charge-induced BL is significant. The BL value can be over 50% of that of metal contacts even in an intrinsic graphene contacted to an organic semiconductor, and it increases as the graphene doping increases. The dependences of the BL on the electric field and semiconductor dielectric constant are examined, and an empirical expression for estimating the image-charge-induced BL in graphene-semiconductor contacts is provided.

Keywords: graphene, semiconductor materials, schottky barrier, image charge, contacts

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Authors: Nikolay Konukhov

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This paper to report on a new analytic model for predicting microcontact resistance and the design, fabrication, and testing of microelectromechanical systems (MEMS) metal contact switches with sputtered bimetallic (i.e., gold (Au)-on-Au-platinum (Pt), (Au-on-Au-(6.3at%)Pt)), binary alloy (i.e., Au-palladium (Pd), (Au-(3.7at%)Pd)), and ternary alloy (i.e., Au-Pt-copper (Cu), (Au-(5.0at%)Pt-(0.5at%)Cu)) electric contacts. The microswitches with bimetallic and binary alloy contacts resulted in contact resistance values between 1–2

Keywords: alloys, electric contacts, microelectromechanical systems (MEMS), microswitch

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Authors: Boualem Chetti, Samir Zahaf

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This paper presents the steady-state performance analysis of a four-lobe journal bearing lubricated with a couple stress fluids operating in the turbulent regime, following Constantinescu’s turbulent lubrication theory. The modified Reynolds equation is solved numerically using the finite difference method taking into consideration the effects of the turbulence and the couple stress. In this analysis, the steady-state parameters in terms of the attitude angle, load carrying capacity, side leakage and friction coefficient are determined at various values of eccentricities ratio. The computed results show that the turbulence increases the load carrying capacity, the attitude angle and the friction coefficient for a journal bearing lubricated with a Newtonian or a couple stress fluids. It is found that the turbulence has strongly influence on the steady-state performances of the four-lobe journal bearing lubricated with Newtonian fluids or a couple stress fluids.

Keywords: Four-lobe journal bearings, static characteristics, couple-stress fluids, turbulent flow

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Authors: Ravindra Mallya, B. Satish Shenoy, B. Raghuvir Pai

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The study deals with the challenges in developing a test rig to test the performance of water lubricated journal bearing. The test rig is designed to simulate the working conditions of the bearing in order to understand their performance before they are put in operation. The bearing that is studied is the commercially available water lubricated bearing which has a rubber liner bonded with a rigid metal shell. The lubricant enters the bearing axially through a pressurized inlet tank and exits to an outlet tank which is at sufficiently low pressure. The load on the bearing is applied through the dead weight system which acts both in upward and downward direction so that net load acts on the bearing. The issues in feeding the lubricant into the bearing from the inlet side and preventing the leakage of the lubricant is discussed. The application of the load on the test bearing while maintaining the bearing afloat is also discussed.

Keywords: axial groove, hydrodynamic pressure, journal bearing, test rig, water lubrication

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Authors: H. Singh, H. Bhowmick

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Now-a-days, particle based lubricants have been widely used to enhance the lubrication performance. Use of tailor made micro/nanofluids can reduce the friction losses and dissipate heat in a better way. Use of Carbon Nanotubes (CNTs) has gained interests because of its structure that can endure much better in a system mechanically or thermally in comparison to any other additive in oil. On the other hand, nanoclays have been characterized mechanically and tribologically for the use of clay/polymer composite, and they have been gaining huge interest. Hence it is interesting to be investigated the effect of nanoclays as additive in oil. Thermophysical characteristics of lubricant play a predominant role in defining the friction and wear characteristics of lubricated contacts. However, very limited studies have been carried out to correlate the thermophysical properties of nanolubricants with their lubricity characteristics. Besides, most of the lubricant formulations till dates are found to be optimized for steel/steel contacts. In the present study, Multiwall Carbon Nanotube (MWCNT) and nanoclay are used as particle additives in mineral oil to develop nanofluids of various concentrations. The prepared lubricants are tested for their rheological, thermal and lubricity characteristics under aluminium-steel contacts. From the thermophysical investigation, it is observed that nanoclay particles significantly improve the viscosity of lubricant with an insignificant improvement in thermal conductivity. On the other hand, MWCNT particles moderately increase the viscosity but significantly increase the thermal conductivity of the base oil. Frictional responses of the nanofluids are characterized using a Pin-on-Disc tribometer which reveal some interesting facts. The findings from this study will greatly aid in formulating the particle based lubricants for cutting fluid in metal forming industries as well as fully developed nanolubricants for aluminium and Aluminium Metal Matrix Composite (AMMC) tribocontact for the use in the automotive and their allied industries.

Keywords: MWCNT, Multiwall Carbon Nanotube, nanoclay, nanolubricant, rheology, thermal conductivity

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Authors: A. Sakavičius, A. Lukša, V. Nargelienė, V. Bukauskas, G. Astromskas, A. Šetkus

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We investigate the influence of annealing on the properties of a contact between graphene and metal (Au and Ni), using circular transmission line model (CTLM) contact geometry. Kelvin probe force microscopy (KPFM) and Raman spectroscopy are applied for characterization of the surface and interface properties. Annealing causes a decrease of the metal-graphene contact resistance for both Ni and Au.

Keywords: Au/Graphene contacts, graphene, Kelvin force probe microscopy, NiC/Graphene contacts, Ni/Graphene contacts, Raman spectroscopy

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Authors: Boualem Chetti

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The dynamic characteristics of a three-lobe journal bearing lubricated with micropolar fluids are determined by the linear stability theory. Lubricating oil containing additives and contaminants is modeled as micropolar fluid. The modified Reynolds equation is obtained using the micropolar lubrication theory and the finite difference technique has been used to solve it. The dynamic characteristics in terms of stiffness, damping coefficients, the critical mass and whirl ratio are determined for various values of size of material characteristic length and the coupling number. The computed results show compared with Newtonian fluids, that micropolar fluid exhibits better stability.

Keywords: three-lobe bearings, micropolar fluid, dynamic characteristics, stability analysis

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Authors: Mohammad M. Khan, Gajendra Dixit

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Partially lubricated sliding wear behaviour of a zinc-based alloy reinforced with 10wt% SiC particles has been studied as a function of applied load and solid lubricant particle size and has been compared with that of matrix alloy and conventionally used grey cast iron. The wear tests were conducted at the sliding velocities of 2.1m/sec in various partial lubricated conditions using pin on disc machine as per ASTM G-99-05. Base oil (SAE 20W-40) or mixture of the base oil with 5wt% graphite of particle sizes (7-10 µm) and (100 µm) were used for creating lubricated conditions. The matrix alloy revealed primary dendrites of a and eutectoid a + h and Î phases in the Inter dendritic regions. Similar microstructure has been depicted by the composite with an additional presence of the dispersoid SiC particles. In the case of cast iron, flakes of graphite were observed in the matrix; the latter comprised of (majority of) pearlite and (limited quantity of) ferrite. Results show a large improvement in wear resistance of the zinc-based alloy after reinforcement with SiC particles. The cast iron shows intermediate response between the matrix alloy and composite. The solid lubrication improved the wear resistance and friction behaviour of both the reinforced and base alloy. Moreover, minimum wear rate is obtained in oil+ 5wt % graphite (7-10 µm) lubricated environment for the matrix alloy and composite while for cast iron addition of solid lubricant increases the wear rate and minimum wear rate is obtained in case of oil lubricated environment. The cast iron experienced higher frictional heating than the matrix alloy and composite in all the cases especially at higher load condition. As far as friction coefficient is concerned, a mixed trend of behaviour was noted. The wear rate and frictional heating increased with load while friction coefficient was affected in an opposite manner. Test duration influenced the frictional heating and friction coefficient of the samples in a mixed manner.

Keywords: solid lubricant, sliding wear, grey cast iron, zinc based metal matrix composites

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Authors: C. Soffritti, A. Fortini, E. Baroni, M. Merlin, G. L. Garagnani

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Aluminum alloys are widely used in many engineering applications due to their advantages such ashigh electrical and thermal conductivities, low density, high strength to weight ratio, and good corrosion resistance. However, their low hardness and poor tribological properties still limit their use in industrial fields requiring sliding contacts. Hard anodizing is one of the most common solution for overcoming issues concerning the insufficient friction resistance of aluminum alloys. In this work, the tribological behavior ofhard-anodized AW-4006 aluminum alloys in dry and lubricated conditions was evaluated. Three different hard-anodizing treatments were selected: a conventional one (HA) and two innovative golden hard-anodizing treatments (named G and GP, respectively), which involve the sealing of the porosity of anodic aluminum oxides (AAO) with silver ions at different temperatures. Before wear tests, all AAO layers were characterized by scanning electron microscopy (VPSEM/EDS), X-ray diffractometry, roughness (Ra and Rz), microhardness (HV0.01), nanoindentation, and scratch tests. Wear tests were carried out according to the ASTM G99-17 standard using a ball-on-disc tribometer. The tests were performed in triplicate under a 2 Hz constant frequency oscillatory motion, a maximum linear speed of 0.1 m/s, normal loads of 5, 10, and 15 N, and a sliding distance of 200 m. A 100Cr6 steel ball10 mm in diameter was used as counterpart material. All tests were conducted at room temperature, in dry and lubricated conditions. Considering the more recent regulations about the environmental hazard, four bio-lubricants were considered after assessing their chemical composition (in terms of Unsaturation Number, UN) and viscosity: olive, peanut, sunflower, and soybean oils. The friction coefficient was provided by the equipment. The wear rate of anodized surfaces was evaluated by measuring the cross-section area of the wear track with a non-contact 3D profilometer. Each area value, obtained as an average of four measurements of cross-section areas along the track, was used to determine the wear volume. The worn surfaces were analyzed by VPSEM/EDS. Finally, in agreement with DoE methodology, a statistical analysis was carried out to identify the most influencing factors on the friction coefficients and wear rates. In all conditions, results show that the friction coefficient increased with raising the normal load. Considering the wear tests in dry sliding conditions, irrespective of the type of anodizing treatments, metal transfer between the mating materials was observed over the anodic aluminum oxides. During sliding at higher loads, the detachment of the metallic film also caused the delamination of some regions of the wear track. For the wear tests in lubricated conditions, the natural oils with high percentages of oleic acid (i.e., olive and peanut oils) maintained high friction coefficients and low wear rates. Irrespective of the type of oil, smallmicrocraks were visible over the AAO layers. Based on the statistical analysis, the type of anodizing treatment and magnitude of applied load were the main factors of influence on the friction coefficient and wear rate values. Nevertheless, an interaction between bio-lubricants and load magnitude could occur during the tests.

Keywords: hard anodizing treatment, silver ions, bio-lubricants, sliding wear, statistical analysis

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Authors: Trabelsi Mohamed, Kharrat Mohamed, Dammak Maher

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Guide rings play an important role in the performance and durability of hydraulic actuating cylinders. In service, guide rings surfaces are subjected to friction and wear against steel counterface. A good mastery of these phenomena is required for the improvement of the energy safeguard and the durability of the actuating cylinder. Polytetrafluoroethylene (PTFE) polymer is extensively used in guide rings thanks to its low coefficient of friction, its good resistance to solvents as well as its high temperature stability. In this study, friction and wear behavior of two PTFE composites filled with bronze and bronze plus MoS2 were evaluated under oil-lubricated condition, aiming as guide rings for hydraulic actuating cylinder. Wear tests of the PTFE composite specimen sliding against steel ball were conducted using reciprocating linear tribometer. The wear mechanisms of the composites under the same sliding condition were discussed, based on Scanning Electron Microscopy examination of the worn composite surface and the optical micrographs of the steel counter surface. As for the results, comparative friction behaviors of the PTFE composites and lower friction coefficients were recorded under oil lubricated condition. The wear behavior was considerably improved to compare with this in dry sliding, while the oil adsorbed layer limited the transfer of the PTFE to the steel counter face during the sliding test.

Keywords: PTFE, composite, bronze, MoS2, friction, wear, oil-lubrication

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Authors: Dih Ling Luh, Zhi Shih You, Szu Chieh Chen

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Social contact patterns among school-age children play an important role in the epidemiology of infectious disease. Since many of the greatest threats to human health are spread by direct person-to-person contact, understanding the spread of respiratory pathogens and patterns of human interactions are public health priorities. This study used social contact diaries to compare the number of contacts per day per participant across different flu/non-flu seasons and weekend/weekday. We also present contact properties such as sex, age, masking, setting, frequency, duration, and contact types among school-age children (grades 7–8). The sample size with pair-wise comparisons for the seasons (flu/non-flu) and stratification by location were 54 and 83, respectively. There was no difference in the number of contacts during the flu and non-flu seasons, with averages of 16.3 (S.D. = 12.9) and 14.6 (S.D. = 9.5) people, respectively. Weekdays were associated with 23% and 28% more contacts than weekend days during the non-flu and flu seasons, respectively (p < 0.001) (Wilcoxon signed-rank test).

Keywords: contact patterns, behavior, influenza, social mixing

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Authors: Rohit Kothari

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Background: Leprosyis a chronic granulomatous diseasecaused by Mycobacterium leprae (M. Lepra). Reactions may interrupt its usual chronic course.Type-1 (T1R)and type-2 lepra reaction(T2R) are acute events and signifytype-IV and type-III hypersensitivity responses, respectively. Various chemokines like CCL3, 5, 11, and CCL24 may be increased during the course of leprosy or during reactions and may serve as markers of early diagnosis, response to therapy, and prognosis. Objective: To find correlation of CCL3, 5, 11, and CCL24 in leprosy patients on multidrug therapy and their family contacts after ruling out active disease during leprosy treatment and during periods of lepra reactions. Methodology: This randomized control trial was conducted in 50 clinico-histopathologically diagnosed cases of leprosy in a tertiary care hospital in Bengaluru, India. 50 of their family contacts were adequately examined and investigated should the need be to rule out active disease. The two study-groups comprised of leprosy cases, and the age, sex, and area of residence matched healthy contactswho were given single-dose rifampicin prophylaxis, respectively. Blood samples were taken at baseline, six months, and after one yearin both the groups (on completion of MDT in leprosy cases)and also during periods of reaction if occurred in leprosy cases. Results: Our study found that at baseline, CCL5, 11, and 24 were higher in leprosy cases as compared to the healthy contacts, and the difference was statistically significant.CCL3 was also found to be higherat baseline in leprosy cases, however, the difference was not statistically significant. At six months and one year, the levels of CCL 5, 11, and 24 reduced, and the difference was statistically significant in leprosy cases, whereas it remained almost static in all the healthy contacts. Twenty patients of leprosy developed lepra reaction during the course of one year, and during reaction, the increase in CCL11 and 24 was statistically significant from baseline, whereas CCL3 and 5 did not rise significantly. One of the healthy contacts developed signs of leprosy in the form of hypopigmented numb patch and was clinico-histopathologically, and CCL11 and 24 were found to be higher with a statistically significant difference from the baseline values. Conclusion: CCL5, 11, and 24 are sensitive markers of diagnosing leprosy, response to MDT, and prognosis and are not increased in healthy contacts. CCL11 and 24 are sensitive markers of lepra reactions and may serve as one of the early diagnostic modalities for identifying lepra reaction and also leprosy in healthy contacts. To the best of our knowledge, this is the first study to evaluate these biomarkers in leprosy cases and their healthy contacts with a follow-up of upto one year with one of them developing the disease, and the same was confirmed based on these biomarkers as well.

Keywords: chemokine profile, healthy contacts, leprosy, lepra reactions

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Authors: Ioan Rusu

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In the operation of power transformers of 110 kV/MV from substations, these are traveled by fault current resulting from MV line damage. Defect electrical contacts are heated when they are travelled from fault currents. In the case of high temperatures when 135 °C is reached, the electrical insulating oil in the vicinity of the electrical faults comes into contact with these contacts releases gases, and activates the electrical protection. To avoid auto-flammability of electro-insulating oil, we designed a security system thermal of electrical contact defects by pouring fire-resistant polyurethane foam, mastic or mortar fire inside a cardboard electro-insulating cylinder. From practical experience, in the exploitation of power transformers of 110 kV/MT in oil electro-insulating were recorded some passing disconnecting commanded by the gas protection at internal defects. In normal operation and in the optimal load, nominal currents do not require thermal secure contacts inside electrical transformers, contacts are made at the fabrication according to the projects or to repair by solder. In the case of external short circuits close to the substation, the contacts inside electrical transformers, even if they are well made in sizes of Rcontact = 10^‑6 Ω, are subjected to short-circuit currents of the order of 10 kA-20 kA which lead to the dissipation of some significant second-order electric powers, 100 W-400 W, on contact. At some internal or external factors which action on electrical contacts, including electrodynamic efforts at short-circuits, these factors could be degraded over time to values in the range of 10^-4 Ω to 10^-5 Ω and if the action time of protection is great, on the order of seconds, power dissipation on electrical contacts achieve high values of 1,0 kW to 40,0 kW. This power leads to strong local heating, hundreds of degrees Celsius and can initiate self-ignition and burning oil in the vicinity of electro-insulating contacts with action the gas relay. Degradation of electrical contacts inside power transformers may not be limited for the duration of their operation. In order to avoid oil burn with gas release near electrical contacts, at short-circuit currents 10 kA-20 kA, we have outlined the following solutions: covering electrical contacts in fireproof materials that would avoid direct burn oil at short circuit and transmission of heat from electrical contact along the conductors with heat dissipation gradually over time, in a large volume of cooling. Flame retardant materials are: polyurethane foam, mastic, cement (concrete). In the normal condition of operation of transformer, insulating of conductors coils is with paper and insulating oil. Ignition points of its two components respectively are approximated: 135 °C heat for oil and 200 ⁰C for paper. In the case of a faulty electrical contact, about 10^-3 Ω, at short-circuit; the temperature can reach for a short time, a value of 300 °C-400 °C, which ignite the paper and also the oil. By burning oil, there are local gases that disconnect the power transformer. Securing thermal electrical contacts inside the transformer, in cardboard tube with polyurethane foams, mastik or cement, ensures avoiding gas release and also gas protection working.

Keywords: power transformer, oil insulatation, electric contacts, Bucholtz relay

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Authors: Carl-Magnus Everitt, Bo Alfredsson

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Contact mechanics and tribology have been combined with fundamental fatigue and fracture mechanics to form the asperity mechanism which supplies an explanation for the surface-initiated rolling contact fatigue damage, called pitting or spalling. The cracks causing the pits initiates at one surface point and thereafter they slowly grow into the material before chipping of a material piece to form the pit. In the current study, the lubrication aspects on fatigue initiation are simulated by passing a single asperity through a thermal elastohydrodynamic lubricated, TEHL, contact. The physics of the lubricant was described with Reynolds equation and the lubricants pressure-viscosity relation was modeled by Roelands equation, formulated to include temperature dependence. A pressure dependent shear limit was incorporated. To capture the full phenomena of the sliding contact the temperature field was resolved through the incorporation of the energy flow. The heat was mainly generated due to shearing of the lubricant and from dry friction where metal contact occurred. The heat was then transported, and conducted, away by the solids and the lubricant. The fatigue damage caused by the asperities was evaluated through Findley’s fatigue criterion. The results show that asperities, in the size of surface roughness found in applications, may cause surface initiated fatigue damage and crack initiation. The simulations also show that the asperities broke through the lubricant in the inlet, causing metal to metal contact with high friction. When the asperities thereafter moved through the contact, the sliding provided the asperities with lubricant releasing the metal contact. The release of metal contact was possible due to the high viscosity the lubricant obtained from the high pressure. The metal contact in the inlet caused higher friction which increased the risk of fatigue damage. Since the metal contact occurred in the inlet it increased the fatigue risk more for asperities subjected to negative slip than positive slip. Therefore the fatigue evaluations showed that the asperities subjected to negative slip yielded higher fatigue stresses than the asperities subjected to positive slip of equal magnitude. This is one explanation for why pitting is more common in the dedendum than the addendum on pinion gear teeth. The simulations produced further validation for the asperity mechanism by showing that asperities cause surface initiated fatigue and crack initiation.

Keywords: fatigue, rolling, sliding, thermal elastohydrodynamic

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Authors: Ying-Jung Hsieh, Angela S. Huang, Chu-Ming Chiu, Yu-Min Chou, Chin-Hui Yang

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Background and Objectives: Hepatitis A is primarily acquired by the fecal-oral route through person-to-person contact or ingestion of contaminated food or water. During 2010 to 2014, an average of 83 cases of locally-acquired disease was reported to Taiwan’s notifiable disease system. Taiwan Centers for Disease Control (TCDC) identified an outbreak of acute hepatitis A which began in June 2015. Of the 126 cases reported in 2015, 103 (82%) cases were reported during June–December and 95 cases (92%) of them were male. The average age of all male cases was 31 years (median, 29 years; range, 15–76 years). Among the 95 male cases, 49 (52%) were also infected with HIV, and all reported to have had sex with other men. To control this outbreak, TCDC launched a free hepatitis A vaccination program in January 2016 for close contacts of confirmed hepatitis A cases, including family members, sexual partners, and household contacts. Effect of the vaccination program was evaluated. Methods: All cases of hepatitis A reported to the National Notifiable Disease Surveillance System were included. A case of hepatitis A was defined as a locally-acquired disease in a person who had acute clinical symptoms include fever, malaise, loss of appetite, nausea or abdominal discomfort compatible with hepatitis, and tested positive for anti-HAV IgM during June 2015 to June 2016 in Taiwan. The rate of case accumulation was calculated using a simple regression model. Results: During January–June 2016, there were 466 cases of hepatitis A reported; of the 243 (52%) who were also infected with HIV, 232 (95%) had a history of having sex with men. Of the 346 cases that were followed up, 259 (75%) provided information on contacts but only 14 (5%) of them provided the name of their sexual partners. Among the 602 contacts reported, 349 (58%) were family members, 14 (2%) were sexual partners, and 239 (40%) were other household contacts. Among the 602 contacts eligible for free hepatitis A vaccination, 440 (73%) received the vaccine. There were 87 (25%) cases that refused to disclose their close contacts. The average case accumulation rate during January–June 2016 was 21.7 cases per month, which was 6.8 times compared to the average case accumulation rate during June–December 2015 of 3.2 cases per month. Conclusions: Despite vaccination program aimed to provide free hepatitis A vaccine to close contacts of hepatitis A patients, the outbreak continued and even gained momentum in transmission. Refusal by hepatitis A patients to provide names of their close contacts and rejection of contacts to take the hepatitis A vaccine may have contributed to the poor effect of the program. Targeted vaccination efforts of all MSM may be needed to control the outbreak among this population in the short term. In the long term, universal vaccination program is needed to prevent the infection of hepatitis A.

Keywords: hepatitis A, HIV, men who have sex with men, vaccination

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Authors: Marco Tulio C. Faria

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Fixed-geometry hydrodynamic journal bearings are one of the best supporting systems for several applications of rotating machinery. Cylindrical journal bearings present excellent load-carrying capacity and low manufacturing costs, but they are subjected to the oil-film instability at high speeds. An attempt of overcoming this instability problem has been the development of non-circular journal bearings. This work deals with an analysis of oil-lubricated elliptical journal bearings using the finite element method. Steady-state and dynamic performance characteristics of elliptical bearings are rendered by zeroth- and first-order lubrication equations obtained through a linearized perturbation method applied on the classical Reynolds equation. Four-node isoparametric rectangular finite elements are employed to model the bearing thin film flow. Curves of elliptical bearing load capacity and dynamic force coefficients are rendered at several operating conditions. The results presented in this work demonstrate the influence of the bearing ellipticity on its performance at different loading conditions.

Keywords: elliptical journal bearings, non-circular journal bearings, hydrodynamic bearings, finite element method

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Authors: Ammal M. Metwally, Lobna A. ElEtreby, Rehan M. Saleh, Ghada Abdrabou, Somia I. Salama, Amira Orabi, Mohamed Abdelrahman

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Hepatitis C virus infection is a public health threat in Egypt. To control infection, efforts should be spent to encourage healthy behavior. This study aimed to assess the level of behavioral development in order to create a positive environment for the adoption of the recommended behaviors. The study was conducted over one year from Jan. 2011 till Jan. 2012. Knowledge, attitude and behavior of 540 HCV patients and 102 of their contacts were assessed and the level of behavioral development was determined. The study revealed that the majority of patients and contacts knew that HCV infection is dangerous with perceived concern for early diagnosis and treatment. More than 75% knew the correct modes of transmission. The assessment showed positive attitudes towards the recommended practices with the intention to adopt those practices. Strategies to create opportunities to continue the recommended behaviors should be adopted together with the reinforcement of social support.

Keywords: hepatitis C virus, level of behavioral development, recommended behaviors

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Authors: Ambrish Tiwari, Sudhasini Panda, Archana Singh, Kalpana Luthra, S. K. Sharma

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Introduction: On the basis of available literature we know that various host factors play a role in outcome of Tuberculosis (TB) infection by modulating innate immunity. One such factor is Inducible Nitric Oxide Synthase enzyme (iNOS) which help in the production of Nitric Oxide (NO), an antimicrobial agent. Expression of iNOS is in control of various host factors in which Vitamin D along with its nuclear receptor Vitamin D receptor (VDR) is one of them. Vitamin D along with its receptor also produces cathelicidin (antimicrobicidal agent). With this background, we attempted to investigate the levels of Vitamin D and NO along with their associated molecules in tuberculosis patients and household contacts as compared to healthy controls and assess the implication of these findings in susceptibility to tuberculosis (TB). Study subjects and methods: 100 active TB patients, 75 household contacts, and 70 healthy controls were taken. VDR and iNOS mRNA levels were studied using real-time PCR. Serum VDR, cathelicidin, iNOS levels were measured using ELISA. Serum Vitamin D levels were measured in serum samples using chemiluminescence based immunoassay. NO was measured using colorimetry based kit. Results: VDR and iNOS mRNA levels were found to be lower in active TB group compared to household contacts and healthy controls (P=0.0001 and 0.005 respectively). The serum levels of Vitamin D were also found to be lower in active TB group as compared to healthy controls (P =0.001). Levels of cathelicidin and NO was higher in patient group as compared to other groups (p=0.01 and 0.5 respectively). However, the expression of VDR and iNOS and levels of vitamin D was significantly (P < 0.05) higher in household contacts compared to both active TB and healthy control groups. Inference: Higher levels of Vitamin D along with VDR and iNOS expression in household contacts as compared to patients suggest that vitamin D might have a protective role against TB which prevents activation of the disease. From our data, we can conclude that decreased vitamin D levels could be implicated in disease progression and we can use cathelicidin and NO as a biomarker for early diagnosis of pulmonary tuberculosis.

Keywords: vitamin D, VDR, iNOS, tuberculosis

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Authors: Ameni Mahmoudi, Manel Troudi, Paolo Bondavalli, Nabil Sghaier

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In this study, the charge storage on thin-film SWCNT transistors was investigated, and C-V hysteresis tests showed that interface charge trapping effects predominate the memory window. Two electrode materials were utilized to demonstrate that selecting the appropriate metal electrode clearly improves the conductivity and, consequently, the SWCNT thin-film’s memory effect. Because their work function is similar to that of thin-film carbon nanotubes, Ti contacts produce higher charge confinement and show greater charge storage than Pd contacts. For Pd-contact CNTFETs and CNTFETs with Ti electrodes, a sizable clockwise hysteresis window was seen in the dual sweep circle with a threshold voltage shift of V11.52V and V9.7V, respectively. The SWCNT thin-film based transistor is expected to have significant trapping and detrapping charges because of the large C-V hysteresis. We have found that the predicted stored charge density for CNTFETs with Ti contacts is approximately 4.01×10-2C.m-2, which is nearly twice as high as the charge density of the device with Pd contacts. We have shown that the amount of trapped charges can be changed by sweeping the range or Vgs rate. We also looked into the variation in the flat band voltage (V FB) vs. time in order to determine the carrier retention period in CNTFETs with Ti and Pd electrodes. The outcome shows that memorizing trapped charges is about 300 seconds, which is a crucial finding for memory function mimicking.

Keywords: charge storage, thin-film SWCNT based transistors, C-V hysteresis, memory effect, trapping and detrapping charges, stored charge density, the carrier retention time

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Authors: M. Mamor

Abstract:

GaN-based compounds have attracted much interest in the fabrication of high-power, high speed and high-frequency electronic devices. Other examples of GaN-based applications are blue and ultraviolet (UV) light-emitting diodes (LEDs). All these devices require high-quality ohmic and Schottky contacts. Gaining an understanding of the electrical characteristics of metal/GaN contacts is of fundamental and technological importance for developing GaN-based devices. In this work, the barrier characteristics of Pt and Pd Schottky contacts on n-type GaN were studied using temperature-dependent forward current-voltage (I-V) measurements over a wide temperature range 80–400 K. Our results show that the barrier height and ideality factor, extracted from the forward I-V characteristics based on thermionic emission (TE) model, exhibit an abnormal dependence with temperature; i.e., by increasing temperature, the barrier height increases whereas the ideality factor decreases. This abnormal behavior has been explained based on the TE model by considering the presence of double Gaussian distribution (GD) of nonhomogeneous barrier height at the metal/GaN interface. However, in the high-temperature range (160-400 K), the extracted value for the effective Richardson constant A* based on the barrier inhomogeneity (BHi) model is found in fair agreement with the theoretically predicted value of about 26.9 A.cm-2 K-2 for n-type GaN. This result indicates that in this temperature range, the conduction current transport is dominated by the thermionic emission mode. On the other hand, in the lower temperature range (80-160 K), the corresponding effective Richardson constant value according to the BHi model is lower than the theoretical value, suggesting the presence of other current transport, such as tunneling-assisted mode at lower temperatures.

Keywords: Schottky diodes, inhomogeneous barrier height, GaN semiconductors, Schottky barrier heights

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Authors: C. F. Ocoleanu, G. Cividjian, Gh. Manolea

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In this paper, we present two solutions for connections quality pre-control of Crimp Contacts and to identify in the first moments the connections improperly executed, before final assembly of a electrical machines. The first solution supposed experimental determination of specific losses by calculated the initial rate of temperature rise. This can be made drawing the tangent at the origin at heating curve. The method can be used to identify bad connections by passing a current through the winding at ambient temperature and simultaneously record connections temperatures in the first few minutes since the current is setting. The second proposed solution is to apply to each element crimping a thermal indicator one level, and making a test heating with a heating current corresponding to critical temperature indicator.

Keywords: temperature, crimp contact, thermal indicator, current distribution, specific losses

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Authors: Yongyi Chen, Li Qin, Peng Jia, Yongqiang Ning, Yun Liu, Lijun Wang

Abstract:

The distributed feedback (DFB) lasers are indispensable in optical phase array (OPA) used for light detection and ranging (LIDAR) techniques, laser communication systems and integrated optics, thanks to their stable single longitudinal mode and narrow linewidth properties. Traditional index-coupled (IC) DFB lasers with uniform gratings have an inherent problem of lasing two degenerated modes. Phase shifts are usually required to eliminate the mode degeneration, making the grating structure complex and expensive. High-quality antireflection (AR) coatings on both lasing facets are also essential owing to the random facet phases introduced by the chip cleavage process, which means half of the lasing energy is wasted. Gain-coupled DFB (GC-DFB) lasers based on the periodic gain (or loss) are announced to have single longitudinal mode as well as capable of the unsymmetrical coating to increase lasing power and efficiency thanks to facet immunity. However, expensive and time-consuming technologies such as epitaxial regrowth and nanoscale grating processing are still required just as IC-DFB lasers, preventing them from practical applications and commercial markets. In this research, we propose a low-cost, single-mode regrowth-free GC-DFB laser based on periodic surface p-contacts. The gain coupling effect is achieved simply by periodic current distribution in the quantum well caused by periodic surface p-contacts, introducing very little index-coupling effect that can be omitted. It is prepared by i-line lithography, without nanoscale grating fabrication or secondary epitaxy. Due to easy fabrication techniques, it provides a method to fabricate practical low cost GC-DFB lasers for widespread practical applications.

Keywords: DFB laser, gain-coupled, low cost, periodic p-contacts

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Authors: Mohamed Akbi, Aissa Bouchou

Abstract:

The present work aims to throw light on the effects of arcing in air on the surface state of contact pastilles made of silver-nickel Ag-Ni (60/40). Also, the photoelectric emission from these electrical contacts has been investigated in the spectral range of 196-256 nm. In order to study the effects of arcing on the EWF, the metallic samples were subjected to electrical arcs in air, at atmospheric pressure and room temperature, after that, they have been introduced into the vacuum chamber of an experimental UHV set-up for EWF measurements. Both Fowler method of isothermal curves and linearized Fowler plots were used for the measurement of the EWF by the photoelectric effect. It has been found that the EWF varies with the number of applied arcs. Thus, after 500 arcs in air, the observed EWF increasing is probably due to progressive inclusion of oxide on alloy surface. Microscopic examination is necessary to get better understandings on EWF of silver alloys, for both virgin and arced electrical contacts.

Keywords: Ag-Ni contact materials, arcing effects, electron work function, Fowler methods, photoemission

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Authors: Nabaweesi Josephine, Namwanje Regina Germina

Abstract:

Antenatal care is referred to as the totality of care given to pregnant women from conception to delivery from a certified health care setting. A number of 8 contacts is recommended throughout pregnancy, according to WHO, 2016. Antenatal services are free in Uganda courtesy of the government of Uganda, though attendance is still very low, which has continued to cause maternal and infant mortality and morbidity from preventable causes. Early booking has an advantage for proper pregnancy information sharing and pregnancy monitoring. The purpose of this study was to determine pregnant women's knowledge, attitudes, and practices towards attendance of antenatal care at Mukono General Hospital. A sample of 60 pregnant women was used, and a descriptive quantitative design was employed. Data was collected using a structured questionnaire consisting of questions about socio-demographic factors, knowledge, attitude, and practice, and this was affected using the structured interview method. Pregnant women had good practice at 90.2%, a positive attitude of 94.6%, and slightly less knowledge of 66.7%. Only 12% were knowledgeable about the number of antenatal care visits recommended, 45% had knowledge about when to initiate first antenatal care visit, and 79% had a positive attitude towards the early booking. We recommend that pregnant women are given all the necessary information regarding antenatal care with special emphasis on the recommended number of visits and when to initiate their first visit and encourage early booking in order to achieve the 8 contacts WHO policy for antenatal care since when we increase knowledge, we increase antenatal care utilization according to Anderson's behavioral model.

Keywords: ANC- antenatal care, contacts, mortality, morbidity

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Authors: Stanley Ibuchukwu Onwukwe

Abstract:

Most reservoir in mature oil fields are vulnerable to challenges of water and/or gas coning as the size of their oil column reduces due to long period of oil production. These often result to low oil production and excessive water and/or gas production. Since over 50 years of oil production in the Niger delta, it is apparent that most of the oil fields in the region have reached their mature stages, thereby susceptible to coning tendencies. As a result of these, a good number of wells have been shut-in and abandoned, with significant amount of oil left unproduced. Analysis of the movement of fluid contacts in the reservoir is a significant aspect of reservoir studies and can assist in the management of coning tendencies and production performance of reservoirs in a mature field. This study, therefore, seeks to evaluate the occurrence of coning through the movement of fluid contacts (GOC and OWC) and determine the critical rate for controlling coning tendencies in mature oil field. This study applies the principle of Nodal analysis to calibrate the thin oil column of a reservoir of a mature field, and was graphically evaluated using the Joshi’s equation of critical rate for gas-oil system and oil-water system respectively. A representative Proxy equation was developed and sensitivity analysis carried out to determine the trend of critical rate as the oil column is been depleted. The result shows the trend in the movement of the GOC and OWC, and the critical rate, beyond which will result in excessive water and gas production, resulting to decreasing oil production from the reservoir. This result of this study can be used as a first pass assessment in the development of mature oil field reservoirs anticipated to experience water and/or gas coning during production.

Keywords: coning, fluid contact movement, mature oil field, oil production

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Authors: Waqar Ahmad Butt, Gholamreza Vakili Nezhaad, Ali Soud Al Bemani, Yahya Al Wahaibi

Abstract:

Minimum miscibility pressure (MMP) plays a great role in determining the displacement efficiency of different gas injection processes. Experimental techniques for MMP determination include industrially recommended slim tube, vanishing interfacial tension (VIT) and rising bubble apparatus (RBA). In this paper, MMP measurement study using slim tube and VIT experimental techniques for two different crude oil samples (M and N) both in live and stock tank oil forms is being presented. VIT measured MMP values for both 'M' and 'N' live crude oils were close to slim tube determined MMP values with 6.4 and 5 % deviation respectively. Whereas for both oil samples in stock tank oil form, VIT measured MMP showed a higher unacceptable deviation from slim tube determined MMP. This higher difference appears to be related to high stabilized crude oil heavier fraction and lack of multiple contacts miscibility. None of the different nine deployed crude oil and CO2 MMP computing correlations could result in reliable MMP, close to slim tube determined MMP. Since VIT determined MMP values for both considered live crude oils are in close match with slim tube determined MMP values, it confirms reliable, reproducible, rapid and cheap alternative for live crude oil MMP determination. Whereas VIT MMP determination for stock tank oil case needed further investigation about stabilization / destabilization mechanism of oil heavier ends and multiple contacts miscibility development issues.

Keywords: minimum miscibility pressure, interfacial tension, multiple contacts miscibility, heavier ends

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Authors: Soran Aminiaghdam, Christian Rode, Reinhard Blickhan, Astrid Zech

Abstract:

Despite considerable studies on the impact of imposed trunk posture on human walking, less is known about such locomotion while negotiating changes in ground level. The aim of this study was to investigate the behavior of the VBCOM in response to a two-fold expected perturbation, namely alterations in body posture and in ground level. To this end, the kinematic data and ground reaction forces of twelve able participants were collected. We analyzed the vertical position of the body center of mass (VBCOM) from the ground determined by the body segmental analysis method relative to the laboratory coordinate system at touchdown and toe-off instants during walking across uneven ground — characterized by perturbation contact (a 10-cm visible drop) and pre- and post-perturbation contacts — in comparison to unperturbed level contact while maintaining three postures (regular erect, ~30° and ~50° of trunk flexion from the vertical). The VBCOM was normalized to the distance between the greater trochanter marker and the lateral malleoli marker at the instant of TD. Moreover, we calculated the backward rotation during step-down as the difference of the maximum of the trunk angle in the pre-perturbation contact and the minimal trunk angle in the perturbation contact. Two-way repeated measures ANOVAs revealed contact-specific effects of posture on the VBCOM at touchdown (F = 5.96, p = 0.00). As indicated by the analysis of simple main effects, during unperturbed level and pre-perturbation contacts, no between-posture differences for the VBCOM at touchdown were found. In the perturbation contact, trunk-flexed gaits showed a significant increase of VBCOM as compared to the pre-perturbation contact. In the post-perturbation contact, the VBCOM demonstrated a significant decrease in all gait postures relative to the preceding corresponding contacts with no between-posture differences. Main effects of posture revealed that the VBCOM at toe-off significantly decreased in trunk-flexed gaits relative to the regular erect gait. For the main effect of contact, the VBCOM at toe-off demonstrated changes across perturbation and post-perturbation contacts as compared to the unperturbed level contact. Furthermore, participants exhibited a backward trunk rotation during step-down possibly to control the angular momentum of their whole body. A more pronounced backward trunk rotation (2- to 3-fold compared with level contacts) in trunk-flexed walking contributed to the observed elevated VBCOM during the step-down which may have facilitated drop negotiation. These results may shed light on the interaction between posture and locomotion in able gait, and specifically on the behavior of the body center of mass during perturbed locomotion.

Keywords: center of mass, perturbation, posture, uneven ground, walking

Procedia PDF Downloads 146