Contact Reactions Research Articles

Investigation of Rotor Stator Rub Phenomenon Considering Pure Sticking Condition

Investigations on rotor stator rub have always been of great significance for researches on rotating machineries. The most common model for rub investigation is friction model until recently; where some studies are carried out using contact mechanics based interaction. This technique ensures correct enforcement of constraint on the contacting bodies and presents a more realistic modelling approach. Although, an exact physical situation for the contact interaction would be a combination of partial sticking and partial sliding, a preferably assumed situation is pure sliding of rotor over the stator during its interaction. The present work ensures the condition of stick is met while the rotor stator is in contact. Synchronous and sub synchronous motion of order 2 and 3 are observed. The amplitudes of contact reaction forces are on higher side with sticking considered. The whirl amplitudes are reduced with additional constraints in tangential direction.

Trophic behavior strategy of phytophagous insects (an example of leaf beetles Coleoptera, Chrysomelidae)

The feeding behavior and feed spectra of the active life phases (imago and larvae) of 25 background species of leaf beetles (Coleoptera, Chrysomelidae) were studied in Samara region during 1974-2014. The analysis of trophic relationships members of these insects associated with about 400 species of higher (angiosperms) plants from 50 families and 2 classes is interesting not only in terms of their agricultural value, but also when considering bioecology issues (clarification of possible contacts of the organism with the environment). The strategy of the feeding behavior of phytophagous is a complex, which includes 20 episodes of behavioral responses, focuses on the search and acquisition of food and requires choosing the right direction of the influences. Food specialization provides (in order to avoid competition between types of consumers) the existence a rich assortment of food resources and different ways of their use (herbivore and detritivore, optional - food pollen and predation, cannibalism - only 8 types). There are two groups of plants consumed by phytophagous. They are basic (normally developing larvae and imago) and additional (used by imago in unfavorable periods) plants. The search for insect food consists of three types of reactions. They are distant (coarse and fine setting) and contact reactions. Agricultural importance of leaf beetles is determined by not only damage to plants, but also the action stimulating the productivity of phytocoenosis.

Catalytic performance of H-ZSM-5 zeolites for conversion of ethanol or ethylene to propylene: Effect of reaction pressure and SiO2/Al2O3 ratio

In this work, the conversions of ethanol to propylene and ethylene to propylene were investigated over H-ZSM-5 zeolite catalysts with different SiO2/Al2O3 ratios (80 and 280). The effect of operating conditions (contact time and reaction pressure) has been studied. Special attention has been paid to the effect of reaction pressure on the propylene yield, space time yield and catalyst deactivation. Results show that the H-ZSM-5(280) catalyst was more stable for the ethanol or ethylene conversion reaction. High operating pressure favors the propylene production. However, the higher pressure leads to faster coking.

Reduction of carbon contamination during the melting process of Czochralski silicon crystal growth

Generation, incorporation, and accumulation of carbon (C) were investigated by transient global simulations of heat and mass transport during the melting process of Czochralski silicon (CZ-Si) crystal growth. Contact reaction between the quartz crucible and graphite susceptor was introduced as an extra origin of C contamination. The contribution of the contact reaction on C accumulation is affected by the back diffusion of C monoxide (CO) from the gap between the gas-guide and the crucible. The effect of the gas-guide coating on C reduction was elucidated by taking the reaction between the silicon carbide (SiC) coating and gaseous Si monoxide (SiO) into account. Application of the SiC coating on the gas-guide could effectively reduce the C contamination because of its higher thermochemical stability relative to that of graphite. Gas flow control on the back diffusion of the generated CO was examined by the parametric study of argon gas flow rate. Generation and back diffusion of CO were both effectively suppressed by the increase in the gas flow rate because of the high Péclet number of species transport. Strategies for C content reduction were discussed by analyzing the mechanisms of C accumulation process. According to the elucidated mechanisms of C accumulation, the final C content depends on the growth duration and contamination flux at the gas/melt interface.

Reversible Excited-State Proton Geminate Recombination: Revisited.

About three decades ago, Pines and Huppert found that the excited-state proton transfer to water from a photoacid (8-hydroxy-1,3,6-pyrene trisulfonate (HPTS)) is followed by an efficient diffusion-assisted reversible geminate-recombination of the proton. To model the reaction, Pines, Huppert, and Agmon used the Debye-Smoluchowski equation with boundary conditions appropriate for reversible contact reaction kinetics. This reaction model has been used successfully to quantitatively fit the experimental data of the time-resolved fluorescence of HPTS and several commonly used photoacids. A consequence of the reversibility of this reaction is an apparent long-time tail of the photoacid fluorescence signal, obeying (after lifetime correction) a t-3/2 power law asymptotics. Recently, Lawler and Fayer reported that in bulk water the observed power-law decay of the long-time fluorescence tail of HPTS is -1.1 rather than -1.5, as expected from the spherically symmetric diffusion model. In the current study, we reaffirm our previous reports of the power-law behavior of HPTS fluorescence. We also demonstrate that molecular-level complications such as the deviation from spherical symmetry, rotational dynamics, competitive proton binding to the sulfonate moieties of HPTS, distance-dependent diffusion coefficient, and the initial starting point of the proton can affect the observed kinetics only at intermediate times, but not at asymptotically long times. Theoretically, we analyze the rebinding kinetics in terms of the number of extrema of the logarithmic derivative, showing subtle effects on the direction of approach to the asymptotic line (whether from above or below), which also appears to be corroborated experimentally.

Skin Microstructure is a Key Contributor to Its Friction Behaviour

Due to its multifactorial nature, skin friction remains a multiphysics and multiscale phenomenon poorly understood despite its relevance for many biomedical and engineering applications (from superficial pressure ulcers, through shaving and cosmetics, to automotive safety and sports equipment). For example, it is unclear whether, and in which measure, the skin microscopic surface topography, internal microstructure and associated nonlinear mechanics can condition and modulate skin friction. This study addressed this question through the development of a parametric finite element contact homogenisation procedure which was used to study and quantify the effect of the skin microstructure on the macroscopic skin frictional response. An anatomically realistic two-dimensional image-based multilayer finite element model of human skin was used to simulate the sliding of rigid indenters of various sizes over the skin surface. A corresponding structurally idealised multilayer skin model was also built for comparison purposes. Microscopic friction specified at skin asperity or microrelief level was an input to the finite element computations. From the contact reaction force measured at the sliding indenter, a homogenised (or apparent) macroscopic friction was calculated. Results demonstrated that the naturally complex geometry of the skin microstructure and surface topography alone can play as significant role in modulating the deformation component of macroscopic friction and can significantly increase it. This effect is further amplified as the ground-state Young’s modulus of the stratum corneum is increased (for example, as a result of a dryer environment). In these conditions, the skin microstructure is a dominant factor in the deformation component of macroscopic friction, regardless of indenter size or specified local friction properties. When the skin is assumed to be an assembly of nominally flat layers, the resulting global coefficient of friction is reduced with respect to the local one. This seemingly counter-intuitive effect had already been demonstrated in a recent computational study found in the literature. Results also suggest that care should be taken when assigning a coefficient of friction in computer simulations, as it might not reflect the conditions of microscopic and macroscopic friction one intends to represent. The modelling methodology and simulation tools developed in this study go beyond what current analytical models of skin friction can offer: the ability to accommodate arbitrary kinematics (i.e. finite deformations), nonlinear constitutive properties and the complex geometry of the skin microstructural constituents. It was demonstrated how this approach offered a new level of mechanistic insight into plausible friction mechanisms associated with purely structural effects operating at the microscopic scale; the methodology should be viewed as complementary to physical experimental protocols characterising skin friction as it may facilitate the interpretation of observations and measurements and/or could also assist in the design of new experimental quantitative assays.

Graphene-enhanced Cu composite interlayer for contact reaction brazing aluminum alloy 6061

Contact Reaction Brazing of aluminum alloy 6061 using pure Cu nanoparticle interlayer usually encounters cracks and holes due to the intensive Al-Cu eutectic reaction. In order to solve these problems, here we report a new type of graphene-enhanced Cu composite (G-Cu) interlayer prepared by CVD to contact reaction braze aluminum alloy 6061. Results show that the G-Cu interlayer is conducive to retarding the intensive Al-Cu eutectic reaction. The average shear strength of the joint brazed with G-Cu interlayer reached 74 MPa.

Diclofenac-Induced Allergic Contact Dermatitis: A Series of Four Patients.

Allergic contact dermatitis is an immune-mediated antigen-specific skin reaction to an allergenic chemical that corresponds to a delayed-type hypersensitivity response (type IV reaction). Allergic contact dermatitis should be suspected when skin lesions are localized to the site of previous applications of the culprit drug. Lesions appear after re-exposure in susceptible persons, with delayed onset (more than 24 h after exposure). The gold standard for diagnosis is patch (epicutaneous) testing; identification and removal of any potential causal agents is crucial. Diclofenac sodium 1% topical gel contains active (diclofenac sodium) and inactive ingredients. It is a widely used non-steroidal anti-inflammatory drug, known to cause allergic contact dermatitis, and especially photoallergic contact reactions. We present four cases of diclofenac-sodium-induced allergic contact dermatitis, diagnosed based on clinical grounds: intensively itchy eczematous lesions on the sites of drug application after several days of treatment. No allergic history and no other drug intake were reported by the patients. The application of diclofenac sodium 1% topical gel was strictly forbidden in all cases; potent topical steroids proved to be effective in all cases within 2 weeks of therapy. Patch tests were performed in all cases with European standard battery, with patients’ own diclofenac sodium 1% topical gels and with diclofenac sodium 1% in petrolatum 3 weeks after completion of local steroid therapy. Readings were done after 48 h (Day 2) and 72 h (Day 3) and proved to be positive only to patients’ diclofenac sodium 1% topical gel and diclofenac sodium 1% in petrolatum. No sun exposure was allowed during the testing, and any other treatments were forbidden.

Effect of heat treatment on the interfacial microstructure and properties of Cu-Al joints

The purpose of this article is to study the effect of heat treatment on the interfacial microstructure and properties of the Cu-Al contact reaction brazed joint, and compare the results with a similar study performed on flash welding. The results show that the interfacial intermetallics in Cu-Al joint change from original two layers (Cu9Al4/CuAl2) to three layers (Cu9Al4/CuAl/CuAl2) both in contact reaction brazing and in flash welding. Some Kirkendall voids form during the growth of interfacial intermetallics. The voids in the contact reaction brazed joint form in the middle of interfacial intermetallic layer and lead a discontinuous crack after 500 h heat treatment. The voids in the flash welded joint form between copper and interfacial intermetallics and lead to a continuous crack after 500 h heat treatment. The growth rate of interfacial intermetallics conforms to the parabolic law for both joints. The relation between joint properties and the interfacial intermetallic thickness can be described by a linear function. The joint properties of contact reaction brazing are better than that of flash welding during the heat treatment. Therefore, contact reaction brazing is more preferred to maintain electrical stability and mechanical integrity of Cu-Al joint.

Spent nuclear fuel system dynamic stability under normal conditions of transportation

In a horizontal layout of a spent nuclear fuel (SNF) assembly under normal conditions of transportation (NCT), the fuel assembly’s skeleton formed by guide tubes and spacer grids is the primary load bearing structure for carrying and transferring the vibration loads within an SNF assembly. Therefore, the integrity of guide tubes and spacer grids will dictate the vibration amplitude/intensity of the fuel assembly during transport, and must be considered when designing multipurpose purpose canister (MPC) for safe SNF transport. This paper investigates the SNF assembly deformation dynamics during normal vibration mode, as well as the transient shock mode inside the cask during NCT. Dynamic analyses were performed in the frequency domain to study frequency characteristic of the fuel assembly system and in the time domain to simulate the transient dynamic response of the fuel assembly.To further evaluate the intensity of contact interaction induced by the local contacts’ impact loading at the spacer grid, detailed models of the actual spring and dimples of the spacer grids were created. The impacts between the fuel rod and springs and dimples were simulated with a 20g transient shock load. The associated contact interaction intensities, in terms of reaction forces, were estimated from the finite element analyses (FEA) results. The bending moment estimated from the resultant stress on the clad under 20g transient shock can be used to define the loading in cyclic integrated reversible-bending fatigue tester (CIRFT) vibration testing for the equivalent condition. To estimate the damage potential of the transient shock to the SNF vibration lifetime, drop tests were performed on the CIRFT specimens. FEA was used to investigate the contact reaction at CIRFT test samples during impact loading induced by drop tests, and the result was compared with that from a 20g acceleration transient shock load.

Nonlinear statics of extensible elastic belt on two pulleys

AbstractThe drive belt set on two pulleys is considered as a plane elastic rod. The nonlinear theory of rods with tension is used. The static frictionless contact problem for the rod is formulated. The derived boundary value problem for the nonlinear ordinary differential equations is solved by the finite difference method and by the shooting method by means of computer mathematics. The belt shape and the stresses are determined. The contact reaction and the contact area are obtained in the solution. A benchmark study of extensible and inextensible models is performed. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Main Causes of Occupational Allergic Contact Dermatitis: A Three Year Study in the Center of Portugal

Allergic contact dermatitis, along with irritant contact dermatitis and immediate contact reactions, contact urticarial, are the most frequent dermatological occupational disease, but seldom reported to the National authorities. We performed a 3-year retrospective study at the allergology section in the Dermatology Clinic of the University Hospital of Coimbra to evaluate the main occupations diagnosed as occupational allergic contact dermatitis, most common allergens and the effect of the modification of the work station in the evolution of the disease. During 2012 - 2014 among the 941 patch tested patients, 77 (8.2%) were diagnosed with occupational allergic contact dermatitis, with 169 positive patch tests related to occupational exposure, 55 detected within the baseline and 114 in complementary test series. In most cases allergic contact dermatitis involved the hands (88.3%), main professional activities were nail estheticians and hairdressers due to the manipulation of (meth)acrylates, the most common allergen in the study. After the diagnosis, 27.3% abandoned the work, 23.4% changed the work station, 49% avoided exposure to the responsible allergen. Contact dermatitis resolved in 39% of the patients, improved in 39% but had no change in the remaining 22%. This study, although including only patients from the center of Portugal, evaluates a large sample of patients with different occupations studied with a larger variety of allergens. Apart from classical allergens and professions responsible for occupational allergic contact dermatitis that we found in lower numbers (thiuram mix, paraphenylenodiamine, chromium and cobalt in health care workers, hairdressers and in the building industry), (meth)acrylates tested outside the European and Portuguese Baseline Series were the main cause of occupational allergic contact dermatitis, namely in nail estheticians. Methylisothiazolinone, the second more frequent occupational contact allergen in the present study was identified in different occupations as a result of the widespread use of this preservative that is causing a real 'epidemics' of allergic contact dermatitis all over Europe in the last years. Nail estheticians are not usually referred as an occupation with a high risk of developing allergic contact dermatitis. Nevertheless, the current fashion combined with professionals poorly informed about the risk of their activity and the high sensitizing potential of (meth)acrylates, leads to a higher frequency of allergic contact dermatitis in recent years.

자몽종자추출물, 구연산, 사과산 그리고 염화벤잘코늄을 주성분으로 하는 스프레이형 소독제의 조류인플루엔자바이러스에 대한 살바이러스 효과

Objectives: This study evaluated the virucidal efficacy against avian influenza virus (AIV) of a disinfectant spray containing 0.25% grapefruit seed extract, 0.2% citric acid, 0.0625% malic acid and 0.0125% benzalkonium chloride. Methods: The disinfectant spray was diluted several times with hard water (HW) and organic matter (OM). Two point five mL of each diluent was added into each test tube, and 2.5 mL of AIV suspension was inserted into each test tube. After 30 minutes of virus-disinfectant contact reaction at 4℃, 2.5 mL of 10% inactivated fetal bovine serum was added into each test tube to neutralize the sanitizer efficacy. The neutralized solutions were serial 10-fold dilutions with phosphate buffer solution, and 0.2 mL of the diluents was injected into the allantoic cavity of five ten-day-old-chickens per dilution time. After incubation of the embryos for five days, the viability of the AIV was examined by hemagglutination titer. The valid dilution of the disinfectant spray was estimated according to the dilution time that the virus titer was inactivated more than 104 50% egg-infective dose (EID50)/mL compared with pathogen control. Results: In HW and OM conditions, the valid dilutions of the disinfectant spray against AIV were seven- and three-fold dilutions, respectively. The AIV titer of the pathogen control was more than 6.1 log10EID50/mL, and there was no embryonic toxicity.

Painful Oral Ulceration Developed as Lichenoid Contact Reaction. A Case Report

Painful Oral Ulceration Developed as Lichenoid Contact Reaction. A Case Report

Long-term biocompatibility, imaging appearance and tissue effects associated with delivery of a novel radiopaque embolization bead for image-guided therapy.

The objective of this study was to undertake a comprehensive long-term biocompatibility and imaging assessment of a new intrinsically radiopaque bead (LC Bead LUMI™) for use in transarterial embolization. The sterilized device and its extracts were subjected to the raft of ISO10993 biocompatibility tests that demonstrated safety with respect to cytotoxicity, mutagenicity, blood contact, irritation, sensitization, systemic toxicity and tissue reaction. Intra-arterial administration was performed in a swine model of hepatic arterial embolization in which 0.22-1mL of sedimented bead volume was administered to the targeted lobe(s) of the liver. The beads could be visualized during the embolization procedure with fluoroscopy, DSA and single X-ray snapshot imaging modalities. CT imaging was performed before and 1h after embolization and then again at 7, 14, 30 and 90 days. LC Bead LUMI™ could be clearly visualized in the hepatic arteries with or without administration of IV contrast and appeared more dense than soluble contrast agent. The CT density of the beads did not deteriorate during the 90 day evaluation period. The beads embolized predictably and effectively, resulting in areas devoid of contrast enhancement on CT imaging suggesting ischaemia-induced necrosis nearby the sites of occlusion. Instances of off target embolization were easily detected on imaging and confirmed pathologically. Histopathology revealed a classic foreign body response at 14 days, which resolved over time leading to fibrosis and eventual integration of the beads into the tissue, demonstrating excellent long-term tissue compatibility.

Ergonomics and skin and respiratory tract reactions related to antibiotic reconstitution among nurses and ward pharmacists

Introduction Reconstituting antibiotics for clinical use requires static postures and repetitive motions which may contribute to the development of musculoskeletal symptoms. Exposure to drugs can cause allergic contact reactions, with antibiotics being the most common cause for occupational contact sensitization among health care workers.

Oral Lichenoid Contact Reaction to a Complete Denture

Oral Lichenoid Contact Reaction to a Complete Denture

The role of the antioxidant ascorbic acid in the elicitation of contact allergic reactions to p-phenylenediamine.

An allergic contact reaction is accompanied by high oxidative stress in the skin. Pretreatment of the skin with antioxidative substances could reduce the elicitation reaction. To investigate, in a proof-of-principle study, whether pretreatment of the skin with the antioxidant ascorbic acid reduces the elicitation reaction to a p-phenylenediamine (PPD)-containing hair dye in sensitized subjects. Twelve subjects with contact allergy to PPD, a documented skin reaction to a hair dye simulation exposure model and a history of hair dye-related skin complaints were included in this study. Skin areas on the forearms were, in a left versus right design, exposed to an emulsion with ascorbic acid and an emulsion without ascorbic acid, and then to a 2% PPD-containing hair dye testing formulation. In addition, control areas were exposed to the emulsions and to the PPD-containing hair dye formulation without pretreatment. Skin reactions were graded on day (D)2 and D3. Pretreatment with ascorbic acid emulsion resulted in a reduction in the elicitation reaction in 7 of 12 subjects at D3 (p = 0.046). No statistically significant difference was observed at D2. Pretreatment of the skin with the antioxidant ascorbic acid had an attenuating effect on the elicitation reaction to PPD in sensitized individuals.

Oral Lichenoid and Lichen Planus-like Lesions.

Many red and white lesions of the mouth are clinically indistinguishable from those of oral lichen planus (OLP). These lesions, often referred to as oral lichenoid lesions (OLL), can occur as a result of contact sensitivity (lichenoid contact reactions), drug reactions or as part of chronic graft versus host disease (GVHD). Oral lesions in discoid lupus erythematosus (DLE) and systemic lupus erythematosus (SLE) can also have a similar clinical appearance to OLP. Distinguishing oral lichen planus from oral lichenoid lesions, lupus lesions, or other red and white lesions of the mouth can be difficult (even impossible) but it is important, for optimal management of each condition. All patients with red and white pathological lesions should be referred to an oral medicine or a local oral or maxillofacial surgery department, where a biopsy and other investigations can help to establish a diagnosis, and appropriate treatment and monitoring can be commenced. Dentists and other members of the dental team, such as hygienists and dental therapists, should also equip themselves with the knowledge to be able to explain different pathologies of the mouth to their patients and discuss risk factors.

Hydrodeoxygenation of Guaiacol over Al-MCM-41 Supported Metal Catalysts: A Comparative Study of Co and Ni

The hydrodeoxygenation (HDO) of guaiacol, a model compound of pyrolysis oil, was catalyzed by Al-MCM-41 supported Co and Ni catalysts in a fixed-bed continuous reactor at ambient pressure. The effects of contact time (W/F) and reaction temperature on HDO of guaiacol over the Co and Ni catalyst were studied. Cobalt showed higher activity than nickel in HDO via C−O hydrogenolysis pathway. The conversion of guaiacol over Ni catalyst principally occurred via C−C hydrogenolysis pathway, resulting in methane formation. Besides, the acidic Al-MCM-41 support catalyzed the methyl transfer reaction to form the methylated products. Additionally, increasing reaction temperature improved the HDO and suppressed the hydrogenation but promoted the methanization activities.