Contribution of roughness parameters in the scuffing performance of metallic surfaces

2017 ◽  
Vol 69 (4) ◽  
pp. 507-515 ◽  
Author(s):  
Lukasz Wojciechowski ◽  
Radomir Majchrowski ◽  
Thomas G. Mathia
Keyword(s):  
Boundary Lubrication ◽  
Three Dimensional ◽  
Evaluation Study ◽  
Statistical Correlation ◽  
Morphological Parameters ◽  
Metallic Surfaces ◽  
Double Blind ◽  
Content Type ◽  
Lubrication Conditions

Purpose Boundary lubrication cannot provide long-term protection against scuffing. Therefore, it is fundamental to recognise the breaking point of the boundary layer that activates scuffing. Based on this assumption, three-dimensional (3D) morphologies of surfaces were characterised, and the fundamental conditions of the scuffing process were investigated to identify the transition from boundary lubrication conditions to catastrophic wear. Design/methodology/approach A series of systematic tribological double-blind experiments were carried out using a poorly lubricated cylinder/plane interface to model the tribological inverse problem in a boundary lubrication situation. Areal morphological analysis was performed, with the help of an optical interferometer, on a millimetric area corresponding to the contact surface during experimental tribological investigations. The statistical correlation between scuffing and the selected morphological parameters was evaluated. This evaluation study consisted of determining the linear, logarithmic, exponential, polynomial (of degree 2) or power dependency between time to scuffing and morphological parameters. Findings A clear, statistically confirmed relationship was observed between selected morphological parameters of the surface (Spd, Sha, Str, Sz) and its scuffing performance. Originality/value 3D morphological parameters that best specified the technological scuffing performance of metallic surfaces were selected and proposed.

Long-term effects of nimodipine on cerebral infarcts and outcome after aneurysmal subarachnoid hemorrhage and surgery

1991 ◽  
Vol 74 (1) ◽  
pp. 8-13 ◽  
Author(s):  
Juha Öhman ◽  
Antti Servo ◽  
Olli Heiskanen
Keyword(s):  
Subarachnoid Hemorrhage ◽  
Aneurysmal Subarachnoid Hemorrhage ◽  
Controlled Trial ◽  
Delayed Cerebral Ischemia ◽  
Ct Scanning ◽  
Long Term Effects ◽  
Cerebral Infarcts ◽  
Double Blind ◽  
Content Type

✓ A total of 213 patients with verified aneurysmal subarachnoid hemorrhage (SAH) of Grades I to III (Hunt and Hess classification) were enrolled in a double-blind placebo-controlled trial to determine the effect of intravenous nimodipine on delayed ischemic deterioration and computerized tomography (CT)-visualized infarcts after SAH and surgery. The administration of the drug or matching placebo was started immediately after the radiological diagnosis of a ruptured aneurysm had been made. Of the 213 patients enrolled in the study, 58 were operated on early (within 72 hours after the bleed: Days 0 to 3), 69 were operated on subacutely (between Days 4 and 7), and 74 had late surgery (on Day 8 or later). Eleven patients died before surgery was undertaken and one was not operated on. A follow-up examination with CT scanning, performed 1 to 3 years after the SAH (mean 1.4 years), revealed no significant differences in the overall outcome between the groups. However, nimodipine treatment was associated with a significantly lower incidence of deaths caused by delayed cerebral ischemia (p = 0.01) and significantly lower occurrence of cerebral infarcts visualized by CT scanning in the whole population (p = 0.05), especially in patients without an associated intracerebral hemorrhage on admission CT scan (p = 0.03).

Investigation of wear mechanism of forged steel piston skirt under boundary lubricated conditions

2018 ◽  
Vol 70 (7) ◽  
pp. 1303-1309
Author(s):  
Zhang Jian ◽  
Deng Lijun ◽  
Hao Guannan ◽  
Liu Shiying
Keyword(s):  
Surface Roughness ◽  
Wear Mechanism ◽  
Boundary Lubrication ◽  
Normal Load ◽  
Testing Machine ◽  
Wear Model ◽  
Content Type ◽  
Piston Skirt ◽  
Steel Piston ◽  
Lubrication Conditions

Purpose With the implementation of new emission standards, the thermal–mechanical coupling load of engine pistons becomes more important. In this case, forged steel material with higher fatigue limit and impact resistance has been applied gradually in piston manufacturing. However, new failure problems emerge, and the wear of skirt under boundary lubrication conditions is an essential problem which needs to be solved urgently. Design/methodology/approach In this research, the abrasion testing machine was used to simulate the wear behavior under different conditions of normal pressure, relative velocity and surface roughness. Besides, the wear morphology was observed by scanning electron microscope. Then, the wear model was established by using test results fitting method, offering a way to conduct qualitative analysis for the wear problem under the same conditions. Findings The results show that mainly the wear mechanism of the piston skirt under boundary lubricated conditions is adhesive wear and abrasive wear. In addition, the coefficient and wear rate will increase with the increase in the normal load and surface roughness and decrease with the increase in the relative speed. In the wear model, the wear loss is mainly influenced by the normal load, the relative sliding speed and the wear time. Originality/value The wear degree of piston skirt was qualitatively obtained in this investigation by factors such as pressure, velocity and so on, and the wear mechanism of forged steel piston skirt under boundary lubrication conditions was also determined. These could provide theoretical support for further optimization of cylinder motion and oil supply system, reduction of friction loss and power loss.

Chronic cerebellar stimulation for cerebral palsy

1980 ◽  
Vol 53 (2) ◽  
pp. 160-165 ◽  
Author(s):  
Richard D. Penn ◽  
Barbara M. Myklebust ◽  
Gerald L. Gottlieb ◽  
Gyan C. Agarwal ◽  
Mary E. Etzel
Keyword(s):  
Cerebral Palsy ◽  
Motor Skills ◽  
Standardized Assessments ◽  
Double Blind ◽  
Blind Test ◽  
Content Type ◽  
Chronic Electrical Stimulation ◽  
Objective Tests ◽  
Cerebellar Stimulation

✓ The effects of chronic electrical stimulation of the cerebellum in patients with cerebral palsy have been studied using objective tests of joint compliance, and standardized assessments of developmental reflexes and motor skills. Of 14 patients studied prospectively for 1 to 44 months, 11 showed improvement in motor function. A double-blind test of 10 patients off and on stimulation for an average 8-week period showed no significant changes. Thus, we have no proof that the functional improvements seen with long-term stimulation are the result of cerebellar stimulation.

Development and characterization of three-dimensional woven fabric for ultra violet protection

2018 ◽  
Vol 30 (4) ◽  
pp. 536-547
Author(s):  
Adeela Nasreen ◽  
Muhammad Umair ◽  
Khubab Shaker ◽  
Syed Talha Ali Hamdani ◽  
Yasir Nawab
Keyword(s):  
3D Structure ◽  
Three Dimensional ◽  
Air Permeability ◽  
Woven Fabrics ◽  
Woven Fabric ◽  
Protection Factor ◽  
Content Type ◽  
Ultraviolet Protection Factor ◽  
Ultraviolet Protection

Purpose The purpose of this paper is to investigate the effect of materials, three dimensional (3D) structure and number of fabric layers on ultraviolet protection factor (UPF), air permeability and thickness of fabrics. Design/methodology/approach Total 24 fabrics samples were developed using two 3D structures and two weft materials. In warp direction cotton (CT) yarn and in weft direction polypropylene (PP) and polyester (PET) were used. Air permeability, thickness and UPF testings were performed and relationship among fabric layers, air permeability, thickness and UPF was developed. Findings UPF and thickness of fabrics increases with number of fabric layers, whereas air permeability decreases with the increase in number of fabric layers. Furthermore, change of multilayer structure from angle interlock to orthogonal interlock having same base weave does not give significant effect on UPF. However, change of material from polyester (PET) to polypropylene (PP) has a dominant effect on UPF. Minimum of three layers of cotton/polyester fabric, without any aid of ultraviolet radiation (UV) resistant coating, are required to achieve good. Cotton/polyester fabrics are more appropriate for outdoor application due to their long-term resistance with sunlight exposure. Originality/value Long-term exposure to UV is detrimental. So, there is need of proper selection of material and fabric to achieve ultraviolet protection. 3D fabrics have yarns in X, Y as well as in Z directions which provide better ultraviolet protection as compared to two dimensional (2D) fabrics. In literature, mostly work was done on ultraviolet protection of 2D fabrics and surface coating of fabrics. There is limited work found on UPF of 3D woven fabrics.

Unilateral stimulation of the subthalamic nucleus in Parkinson disease: a double-blind 12-month evaluation study

2004 ◽  
Vol 101 (1) ◽  
pp. 36-42 ◽  
Author(s):  
Isabelle M. Germano ◽  
Jean-Michel Gracies ◽  
Donald J. Weisz ◽  
Winona Tse ◽  
William C. Koller ◽  
...  
Keyword(s):  
Parkinson Disease ◽  
Subthalamic Nucleus ◽  
Rating Scale ◽  
Evaluation Study ◽  
Double Blind ◽  
Levodopa Dose ◽  
Content Type ◽  
Additional Surgery ◽  
Second Procedure ◽  
Fine Print

Object. Bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been established as an effective treatment for Parkinson disease (PD). Nevertheless, bilateral surgical procedures can be associated with frequent and severe complications. The aim in the present study was to assess the safety and efficacy of unilateral STN stimulation, and the need for a second procedure. Methods. Twelve patients with PD underwent unilateral DBS of the STN and were followed up for 12 months. Patients were assessed at baseline and at each visit in a double-blind fashion by analyzing the Unified PD Rating Scale (UPDRS), ambulation speed, and home diaries. Levodopa-off/stimulation-on UPDRS motor scores were improved by 26 ± 8% (p < 0.05, mean ± standard deviation [SD]) compared with the baseline levodopa-off score; there was a 50% improvement in contralateral features, a 17% improvement ipsilaterally, and a 36% improvement in axial features. The mean ambulation speed increased by 83 ± 44% (p < 0.01, mean ± SD). The medication-on time with dyskinesias was significantly reduced (p < 0.01) and the daily levodopa dose was reduced by 19 ± 6% (p < 0.05, mean ± SD). There were no clinically significant side effects. Conclusions. Unilateral DBS of the STN is safe and well tolerated, and may provide sufficient benefit so that additional surgery is not required.

scholarly journals Novel Bioengineered Three-Dimensional Human Intestinal Model for Long-Term Infection of Cryptosporidium parvum

2017 ◽  
Vol 85 (3) ◽  
Author(s):  
Maria A DeCicco RePass ◽  
Ying Chen ◽  
Yinan Lin ◽  
Wenda Zhou ◽  
David L. Kaplan ◽  
...  
Keyword(s):  
Cryptosporidium Parvum ◽  
Drug Targets ◽  
Diarrheal Disease ◽  
Three Dimensional ◽  
Content Type ◽  
Tissue Model ◽  
Culture Models

ABSTRACT Cryptosporidium spp. are apicomplexan parasites of global importance that cause human diarrheal disease. In vitro culture models that may be used to study this parasite and that have physiological relevance to in vivo infection remain suboptimal. Thus, the pathogenesis of cryptosporidiosis remains poorly characterized, and interventions for the disease are limited. In this study, we evaluated the potential of a novel bioengineered three-dimensional (3D) human intestinal tissue model (which we developed previously) to support long-term infection by Cryptosporidium parvum. Infection was assessed by immunofluorescence assays and confocal and scanning electron microscopy and quantified by quantitative reverse transcription-PCR. We found that C. parvum infected and developed in this tissue model for at least 17 days, the extent of the study time used in the present study. Contents from infected scaffolds could be transferred to fresh scaffolds to establish new infections for at least three rounds. Asexual and sexual stages and the formation of new oocysts were observed during the course of infection. Additionally, we observed ablation, blunting, or distortion of microvilli in infected epithelial cells. Ultimately, a 3D model system capable of supporting continuous Cryptosporidium infection will be a useful tool for the study of host-parasite interactions, identification of putative drug targets, screening of potential interventions, and propagation of genetically modified parasites.

Finite element implementation of viscoelastic and viscoplastic models

2020 ◽  
Vol 37 (8) ◽  
pp. 2561-2585
Author(s):  
Hossein Sepiani ◽  
Maria Anna Polak ◽  
Alexander Penlidis
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Three Dimensional ◽  
Small Strain ◽  
Test Time ◽  
Nonlinear Behaviour ◽  
Content Type ◽  
Material Parameters ◽  
Viscoplastic Models

Purpose The purpose of this study is to present a finite element (FE) implementation of phenomenological three-dimensional viscoelastic and viscoplastic constitutive models for long term behaviour prediction of polymers. Design/methodology/approach The method is based on the small strain assumption but is extended to large deformation for materials in which the stress-strain relation is nonlinear and the concept of incompressibility is governing. An empirical approach is used for determining material parameters in the constitutive equations, based on measured material properties. The modelling process uses a spring and dash-pot and a power-law approximation function method for viscoelastic and viscoplastic nonlinear behaviour, respectively. The model improvement for long term behaviour prediction is done by modifying the material parameters in such a way that they account for the current test time. The determination of material properties is based on the non-separable type of relations for nonlinear materials in which the material properties change with stress coupled with time. Findings The proposed viscoelastic and viscoplastic models are implemented in a user material algorithm of the FE general-purpose program ABAQUS and the validity of the models is assessed by comparisons with experimental observations from tests on high-density polyethylene samples in one-dimensional tensile loading. Comparisons show that the proposed constitutive model can satisfactorily represent the time-dependent mechanical behaviour of polymers even for long term predictions. Originality/value The study provides a new approach in long term investigation of material behaviour using FE analysis.

Effect of perioperative platelet inhibition on postcarotid endarterectomy mural thrombus formation

1985 ◽  
Vol 63 (5) ◽  
pp. 693-698 ◽  
Author(s):  
J. Max Findlay ◽  
William M. Lougheed ◽  
Fred Gentili ◽  
Paul M. Walker ◽  
Michael F. X. Glynn ◽  
...  
Keyword(s):  
Carotid Endarterectomy ◽  
Thrombus Formation ◽  
Treated Group ◽  
Platelet Inhibition ◽  
Mural Thrombus ◽  
Double Blind ◽  
Content Type ◽  
Indium 111 ◽  
Platelet Accumulation

✓ A prospective randomized double-blind trial was conducted to study the effect of platelet-inhibiting drugs on mural thrombus formation after carotid endarterectomy. Twenty-two patients undergoing carotid endarterectomy were randomly assigned to perioperative administration of an aspirin/dipyridamole combination or a placebo, and the postoperative results were compared. Autologous indium-111-labeled platelets were injected postoperatively, and platelet deposition was measured at the endarterectomy site. It was found that the treated group had a significant reduction in platelet accumulation compared with the placebo group. The results suggest that the perioperative use of aspirin/dipyridamole may reduce the risk of operative stroke and the long-term risk of repeat carotid stenosis.

scholarly journals The Glycoside Hydrolase Family 8 Reducing-End Xylose-Releasing Exo-oligoxylanase Rex8A from Paenibacillus barcinonensis BP-23 Is Active on Branched Xylooligosaccharides

2016 ◽  
Vol 82 (17) ◽  
pp. 5116-5124 ◽  
Author(s):  
Susana V. Valenzuela ◽  
Sergi Lopez ◽  
Peter Biely ◽  
Julia Sanz-Aparicio ◽  
F. I. Javier Pastor
Keyword(s):  
3D Structure ◽  
Three Dimensional ◽  
Glycoside Hydrolase Family ◽  
Biomass Valorization ◽  
Content Type ◽  
Paenibacillus Barcinonensis ◽  
Catalytic Cleft ◽  
Hydrolase Family ◽  
Minor Activity

ABSTRACTA GH8 family enzyme involved in xylan depolymerization has been characterized. The enzyme, Rex8A, is a reducing-end xylose-releasing exo-oligoxylanase (Rex) that efficiently hydrolyzes xylooligosaccharides and shows minor activity on polymeric xylan. Rex8A hydrolyzes xylooligomers of 3 to 6 xylose units to xylose and xylobiose in long-term incubations. Kinetic constants of Rex8A were determined on xylotriose, showing aKmof 1.64 ± 0.03 mM and akcatvalue of 118.8 s−1. Besides linear xylooligosaccharides, the enzyme hydrolyzed decorated xylooligomers. The catalytic activity on branched xylooligosaccharides, i.e., the release of xylose from the reducing end, is a newly described trait of xylose-releasing exo-oligoxylanases, as the exo-activity on these substrates has not been reported for the few of these enzymes characterized to date. Modeling of the three-dimensional (3D) structure of Rex8A shows an (α/α)6barrel fold where the loops connecting the α-helices contour the active site. These loops, which show high sequence diversity among GH8 enzymes, shape a catalytic cleft with a −2 subsite that can accommodate methyl-glucuronic acid decorations. The hydrolytic ability of Rex8A on branched oligomers can be crucial for the complete depolymerization of highly substituted xylans, which is indispensable to accomplish biomass deconstruction and to generate efficient catalysts.IMPORTANCEA GH8 family enzyme involved in xylan depolymerization has been characterized. The Rex8A enzyme fromPaenibacillus barcinonensisis involved in depolymerization of glucuronoxylan, a major component of the lignocellulosic substrates. The study shows that Rex8A is a reducing-end xylose-releasing exo-oligoxylanase that efficiently hydrolyzes xylose from neutral and acidic xylooligosaccharides generated by the action of other xylanases also secreted by the strain. The activity of a Rex enzyme on branched xylooligosaccharides has not been described to date. This report provides original and useful information on the properties of a new example of the rarely studied Rex enzymes. Depolymerization of highly substituted xylans is crucial for biomass valorization as a platform for generation of biofuels, chemicals, and solvents.

Investigating facemask problems associated with wearing comfort and fit

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Mika Morishima ◽  
Koya Kishida ◽  
Miho Fukagawa
Keyword(s):  
High Performance ◽  
Three Dimensional ◽  
Female Students ◽  
Male Students ◽  
Content Type ◽  
Japanese Male ◽  
Japanese Female ◽  
Survey Results ◽  
Local Students

PurposeA facemask is used to cover the nose and mouth to protect a wearer's health in daily life. The authors’ long-term goal aimed to ensure more people with different physical characteristics and different attitudes can wear a high performance and comfortable facemask. In the present paper, wearers were surveyed by a questionnaire. Additionally, a prototype improvement pattern with a fit performance was investigated.Design/methodology/approachThe survey of facemask wearers was conducted with local students and international students in Japan. A basic pattern with high fit performance was analyzed using a combination of triangles based on the measured three-dimensional coordinates of the head shape of a Japanese mannequin.FindingsThe aggregated survey data indicated that 85.0% of the Japanese female students, 77.2% of international female students, 70.8% of Japanese male students and 54.3% of international male students were facemask wearers. Wearers had problems related to their masks' thermal, hygroscopic and airflow properties. Japanese nonusers did not wear them due to dislike related to the problems above. International nonusers had no experience of wearing them. It was concerned that these discomfort factors influence fit performance and reduction of wearing effects. Therefore, the authors analyzed a sheet pattern with a high fit performance for a Japanese head mannequin.Originality/valueThese results will contribute in improving hygienic facemasks for people at the global level. The survey results and pattern analysis provide of necessary conditions of development of the mask with comfortable and high fit performance.

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