Analysis of a dry friction problem under small displacements: application to a bolted joint

This study presents an analysis of the problem of macroscopic contact of steel upon steel with dry friction, in the specific case of a bolted joint. The configurations of these types of joints result in very small displacements and interface sliding velocities. To understand how the system formed by the two surfaces in contact works, an experiment was carried out. The analysis of the results obtained made it possible to define the behavior of the system and to model the variations of the main parameters by original and continuous laws. These laws accurately correlate to all the results of the tests effectuated

Solution of the Roth-Marques-Durian Rotational Abrasion Model

We solve the rotational abrasion model of Roth, Marques and Durian (arXiv:1009.3492), a one-dimensional quasilinear partial differential equation resembling the inviscid Burgers equation with the unusual feature of a step function factor as a coefficient. The complexity of the solution is primarily in keeping track of the cases in the piecewise function that results from certain amputation and interpolation processes, so we also extract from it a model of an evolving planar tree graph that tracks the evolution of the coarse features of the contour.Comment: 5 pages, 4 figure

The distance upon contact: Determination from roughness profile

The point at which two random rough surfaces make contact takes place at the contact of the highest asperities. The distance upon contact d_0 in the limit of zero load has crucial importance for determination of dispersive forces. Using gold films as an example we demonstrate that for two parallel plates d_0 is a function of the nominal size of the contact area L and give a simple expression for d_0(L) via the surface roughness characteristics. In the case of a sphere of fixed radius R and a plate the scale dependence manifests itself as an additional uncertainty \delta d(L) in the separation, where the scale L is related with the separation d via the effective area of interaction L^2\sim\pi Rd. This uncertainty depends on the roughness of interacting bodies and disappears in the limit L\to \infty.Comment: 5 pages, 4 figures, to be published in PR

Targeting the centriolar replication factor STIL synergizes with DNA damaging agents for treatment of ovarian cancer

Advanced ovarian cancer is an incurable disease. Thus, novel therapies are required. We wished to identify new therapeutic targets for ovarian cancer. ShRNA screen performed in 42 ovarian cancer cell lines identified the centriolar replication factor STIL as an essential gene for ovarian cancer cells. This was verified in-vivo in orthotopic human ovarian cancer mouse models. STIL depletion by administration of siRNA in neutral liposomes resulted in robust anti-tumor effect that was further enhanced in combination with cisplatin. Consistent with this finding, STIL depletion enhanced the extent of DNA double strand breaks caused by DNA damaging agents. This was associated with centrosomal depletion, ongoing genomic instability and enhanced formation of micronuclei. Interestingly, the ongoing DNA damage was not associated with reduced DNA repair. Indeed, we observed that depletion of STIL enhanced canonical homologous recombination repair and increased BRCA1 and RAD51 foci in response to DNA double strand breaks. Thus, inhibition of STIL significantly enhances the efficacy of DNA damaging chemotherapeutic drugs in treatment of ovarian cancer.Junta de andalucía P12-BIO-515, P. HuertasEspaña Ministerio de Economía y Competitividad SAF2013-43255-

Body-assisted van der Waals interaction between two atoms

Using fourth-order perturbation theory, a general formula for the van der Waals potential of two neutral, unpolarized, ground-state atoms in the presence of an arbitrary arrangement of dispersing and absorbing magnetodielectric bodies is derived. The theory is applied to two atoms in bulk material and in front of a planar multilayer system, with special emphasis on the cases of a perfectly reflecting plate and a semi-infinite half space. It is demonstrated that the enhancement and reduction of the two-atom interaction due to the presence of a perfectly reflecting plate can be understood, at least in the nonretarded limit, by using the method of image charges. For the semi-infinite half space, both analytical and numerical results are presented.Comment: 17 pages, 9 figure

Impact of the COVID-19 pandemic on emergency adult surgical patients and surgical services: an international multi-center cohort study and department survey.

OBJECTIVES: The PREDICT study aimed to determine how the COVID-19 pandemic affected surgical services and surgical patients and to identify predictors of outcomes in this cohort. BACKGROUND: High mortality rates were reported for surgical patients with COVID-19 in the early stages of the pandemic. However, the indirect impact of the pandemic on this cohort is not understood, and risk predictors are yet to be identified. METHODS: PREDICT is an international longitudinal cohort study comprising surgical patients presenting to hospital between March and August 2020, conducted alongside a survey of staff redeployment and departmental restructuring. A subgroup analysis of 3176 adult emergency patients, recruited by 55 teams across 18 countries is presented. RESULTS: Among adult emergency surgical patients, all-cause in-hospital mortality (IHM) was 3 6%, compared to 15 5% for those with COVID-19. However, only 14 1% received a COVID-19 test on admission in March, increasing to 76 5% by July.Higher Clinical Frailty Scale scores (CFS >7 aOR 18 87), ASA grade above 2 (aOR 4 29), and COVID-19 infection (aOR 5 12) were independently associated with significantly increased IHM.The peak months of the first wave were independently associated with significantly higher IHM (March aOR 4 34; April aOR 4 25; May aOR 3 97), compared to non-peak months.During the study, UK operating theatre capacity decreased by a mean of 63 6% with a concomitant 27 3% reduction in surgical staffing. CONCLUSION: The first wave of the COVID-19 pandemic significantly impacted surgical patients, both directly through co-morbid infection and indirectly as shown by increasing mortality in peak months, irrespective of COVID-19 status.Higher CFS scores and ASA grades strongly predict outcomes in surgical patients and are an important risk assessment tool during the pandemic

Rolling friction of a viscous sphere on a hard plane

A first-principle continuum-mechanics expression for the rolling friction coefficient is obtained for the rolling motion of a viscoelastic sphere on a hard plane. It relates the friction coefficient to the viscous and elastic constants of the sphere material. The relation obtained refers to the case when the deformation of the sphere $\xi$ is small, the velocity of the sphere $V$ is much less than the speed of sound in the material and when the characteristic time $\xi/V$ is much larger than the dissipative relaxation times of the viscoelastic material. To our knowledge this is the first ``first-principle'' expression of the rolling friction coefficient which does not contain empirical parameters.Comment: 6 pages, 2 figure

Stability analysis and \mu-synthesis control of brake systems

The concept of friction-induced brake vibrations, commonly known as judder, is investigated. Judder vibration is based on the class of geometrically induced or kinematic constraint instability. After presenting the modal coupling mechanism and the associated dynamic model, a stability analysis as well as a sensitivity analysis have been conducted in order to identify physical parameters for a brake design avoiding friction-induced judder instability. Next, in order to reduce the size of the instability regions in relation to possible system parameter combinations, robust stability via \mu-synthesis is applied. By comparing the unstable regions between the initial and controlled brake system, some general indications emerge and it appears that robust stability via \mu-synthesis has some effect on the instability of the brake system