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Efficient treatment of rubber friction problems in industrial applications
Hofstetter, K.,Eberhardsteiner, J.,Mang, H.A. Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.22 No.5
Friction problems involving rubber components are frequently encountered in industrial applications. Their treatment within the framework of numerical simulations by means of the Finite Element Method (FEM) is the main issue of this paper. Special emphasis is placed on the choice of a suitable material model and the formulation of a contact model specially designed for the particular characteristics of rubber friction. A coupled thermomechanical approach allows for consideration of the influence of temperature on the frictional behavior. The developed tools are implemented in the commercial FE code ABAQUS. They are validated taking the sliding motion of a rubber tread block as example. Such simulations are frequently encountered in tire design and development. The simulations are carried out with different formulations for the material and the frictional behavior. Comparison of the obtained results with experimental observations enables to judge the suitability of the applied formulations on a structural scale.
A finite element algorithm for contact problems with friction
Liu, C.H.,Hofstetter, G.,Mang, H.A. Techno-Press 1995 Structural Engineering and Mechanics, An Int'l Jou Vol.3 No.3
A finite element algorithm for consideration of contact constraints is presented. It is characterized by introducing the geometric constraints, resulting from contact conditions, directly into the algebraic system of equations for the incremental displacements of an incremental iterative solution procedure. The usefulness of the proposed algorithm for efficient solutions of contact problems involving large displacements and large strains is demonstrated in the numerical investigation.
C. Feist,G. Hofstetter 한국계산역학회 2007 Computers and Concrete, An International Journal Vol.4 No.1
The objective of this paper is to provide experimental data on the propagation of curved crack-surfaces and the respective load-displacement diagrams for the validation of numerical models for cracking of concrete, subjected to three-dimensional stress states. To this end beam-shaped specimens are subjected to combined bending and torsional loading, leading to the formation of a spatially curved crack-surface. The experimental data contain the evolution of the load and of the strains at selected points in terms of the crack mouth opening displacement and the propagation of the crack surface.
Irvin, Veronica L.,Hofstetter, C. Richard,Nichols, Jeanne F.,Chambers, Christina D.,Usita, Paula M.,Norman, Gregory J.,Kang, Sunny,Hovell, Melbourne F. Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.3
Background: Compliance with California's smoke-free restaurant and bar policies may be more a function of social contingencies and less a function of legal contingencies. The aims of this study were: 1) to report indications of compliance with smoke-free legislation in Korean bars and restaurants in California; 2) to examine the demographic, smoking status, and acculturation factors of who smoked indoors; and 3) to report social cues in opposition to smoking among a sample of Koreans in California. Materials and Methods: Data were collected by telephone surveys administered by bilingual interviewers between 2007-2009, and included California adults of Korean descent who visited a Korean bar or restaurant in a typical month (N=2,173, 55% female). Results: 1% of restaurant-going participants smoked inside while 7% observed someone else smoke inside a Korean restaurant. Some 23% of bar-going participants smoked inside and 65% observed someone else smoke inside a Korean bar. Presence of ashtrays was related to indoor smoking in bars and restaurants. Among participants who observed smoking, a higher percentage observed someone ask a smoker to stop (17.6%) or gesture to a smoker (27.0%) inside Korean restaurants (N=169) than inside Korean bars (n=141, 17.0% observed verbal cue and 22.7% observed gesture). Participants who smoked inside were significantly younger and more acculturated than participants who did not. Less acculturated participants were significantly more to likely to be told to stop smoking. Conclusions: Ten years after implementation of ordinances, smoking appears to be common in Korean bars in California.
Leyendecker Jannik,Prasse Tobias,Rahhal Ahmad Al,Hofstetter Christoph Paul,Wetsch Wolfgang,Eysel Peer,Bredow Jan 대한척추외과학회 2023 Asian Spine Journal Vol.17 No.6
Study Design: This was a retrospective multivariate analysis of preoperative risk factors leading to intensive care unit (ICU) admissions in patients undergoing elective or acute dorsal spine surgery.Purpose: Numerous studies have predicted a substantial increase in spine surgeries within the next decades, potentially overwhelming hospitals’ resources, including ICU occupancy. Accurate estimates of whether patients need postsurgical ICU treatment are pivotal for both resource allocation and patient safety.Overview of Literature: Risk factors leading to ICU admissions after dorsal spine surgery have been extensively examined for lumbar elective surgery. Studies including other anatomical segments of the spine and nonelective surgery regarding postsurgical ICU treatment probability are lacking.Methods: This study was designed to be a single-center multivariate analysis of data retrospectively collected from a tertiary care university hospital. Patients undergoing dorsal spine surgery from 2009 to 2019 were included in this study. The patients’ demographic data were analyzed to determine potential preoperative risk factors for ICU admission after surgery using multiple logistic regression.Results: In our cohort, 962 patients with a mean age of 71.1±0.55 years were included. Surgeries involved 3.24±0.08 spinal levels on average. The incidence of ICU treatment after surgery was 30.4% (n=292). Multivariate logistic regression showed a markedly increased odds ratio (OR) for patients undergoing surgery of the cervicothoracic junction (OR, 8.86) and those undergoing surgery for spinal deformity treatment (OR, 7.7). Additionally, cervical procedures (OR, 3.29), American Society of Anesthesiologists (ASA) class 3–4 (OR, 2.74), spondylodiscitis (OR, 2.47), fusion of ≥3 levels (OR, 1.94), and age >75 years (OR, 1.33) were associated with an increased risk of postsurgical ICU admission.Conclusions: The findings highlight the relevance of anatomical location, preoperative diagnosis, ASA class, and length of surgery regarding the predictability of postoperative ICU admission. Our data allowed for more sophisticated estimates regarding the need for ICU treatment after dorsal spine surgery, guiding the surgeon through patient selection, communication, and ICU admission predictability.
Choi, Hyun Joo,Nam, Seung Jin,Hofstetter, Jasmin,Buonassisi, Tonio,Bae, Dong Hyun SAGE Publications 2015 Journal of composite materials Vol.49 No.22
<P>The present study investigates the effect of multi-walled carbon nanotubes (MWCNTs) on atomic diffusion processes in the metal matrix, by comparing growth kinetics of interfacial phases in Al–Cu and Al/MWCNT–Cu diffusion couples. Multiple intermetallic layers such as Al<SUB>2</SUB>Cu, AlCu, Al<SUB>3</SUB>Cu<SUB>4</SUB>, Al<SUB>2</SUB>Cu<SUB>3</SUB>, and Al<SUB>4</SUB>Cu<SUB>9</SUB> are formed at the interface between Al and Cu during heat treatment of an Al/Cu diffusion couple at 530. For the diffusion couple of ultrafine-grained Al and cast Cu, the growth rate of intermetallic layers is comparable with theoretical expectations based on Fick’s second law. On the other hand, MWCNTs significantly restrict the diffusion of Al atoms in the composite because the atoms tend to detour around the long tube for diffusion, particularly when MWCNTs are oriented perpendicular to the atomic diffusion path. This accelerates the growth of voids at the contact interface of the diffusion couple during heat treatment.</P>
Agne, Birgit,Infanger, Sibylle,Wang, Fei,Hofstetter, Valè,re,Rahim, Gwendoline,Martin, Meryll,Lee, Dong Wook,Hwang, Inhwan,Schnell, Danny,Kessler, Felix American Society for Biochemistry and Molecular Bi 2009 The Journal of biological chemistry Vol.284 No.13
<P>The heterotrimeric Toc core complex of the chloroplast protein import apparatus contains two GTPases, Toc159 and Toc34, together with the protein-conducting channel Toc75. Toc159 and Toc34 are exposed at the chloroplast surface and function in preprotein recognition. Together, they have been shown to facilitate the import of photosynthetic proteins into chloroplasts in Arabidopsis. Consequently, the ppi2 mutant lacking atToc159 has a non-photosynthetic albino phenotype. Previous mutations in the conserved G1 and G3 GTPase motifs abolished the function of Toc159 in vivo by disrupting targeting of the receptor to chloroplasts. Here, we demonstrate that a mutant in a conserved G1 lysine (atToc159 K868R) defective in GTP binding and hydrolysis can target and assemble into Toc complexes. We show that atToc159 K868R can support protein import into isolated chloroplasts, albeit at lower preprotein binding and import efficiencies compared with the wild-type receptor. Considering the absence of measurable GTPase activity in the K868R mutant, we conclude that GTP hydrolysis at atToc159 is not strictly required for preprotein translocation. The data also indicate that preprotein import requires at least one additional GTPase other than Toc159.</P>