The influence of temperature on viscoelastic friction properties

Viscoelastic friction strongly depends on temperature, which determines the material stiffness and, therefore, given a constant load, the volume that is deformed and dissipates energy. We compare the results obtained by a numerical approach introduced by Carbone and Putignano (2013) [1] with measurements that separate viscoelastic losses from Coulomb contribution. This is done for a range of temperatures. We show that viscoelastic friction curves for different temperatures can be arranged into a single master curve using a frequency shift coefficient, which can be found from the characterization of the viscoelastic material response. This shows that it is possible to accurately (a) use dynamic material analysis data to extrapolate viscoelastic friction measurements to values outside the tested range, and (b) use a tribometer to obtain fundamental viscoelastic material properties

A parametrically time-dependent methodology for reciprocating contact mechanics between viscoelastic solids

We implement an original Boundary Element methodology to study the reciprocating contact mechanics between linear viscoelastic materials. Results are shown for the case of a rigid sphere sinusoidally driven in sliding contact with a viscoelastic half-space. We observe the presence of multi-peaked pressure and displacement distributions; the hysteric friction curve is finally shown for different values of the frequency

A parametrically time-dependent methodology for reciprocating contact mechanics between viscoelastic solids

We implement an original Boundary Element methodology to study the reciprocating contact mechanics between linear viscoelastic materials. Results are shown for the case of a rigid sphere sinusoidally driven in sliding contact with a viscoelastic half-space. We observe the presence of multi-peaked pressure and displacement distributions; the hysteric friction curve is finally shown for different values of the frequency

Laser microtextured surfaces for friction reduction: Does the pattern matter?

Frictional performances of different textures, including axisymmetric and directional patterns, have been tested in the mixed and the hydrodynamic lubrication regimes. Experimental results, corroborated by numerical simulations, show that the leading parameter is the geometrical pattern void ratio since a large number of dimples offers, at low speed, a trap for debris whereas, at high speed, due to the flow expansion in each micro-hole, fosters a fluid pressure drop, the consequent insurgence of micro-cavitation and, ultimately, the reductions of the shear stresses. Furthermore, in this paper, it is shown that, by means of directional textures, equivalent hydrodynamic wedges can be built up, thus establishing different friction performances depending on the flow direction

A theoretical-experimental framework for the analysis of the dynamic response of a QEPAS tuning fork device immersed in a fluid medium

Quartz-enhanced photoacoustic spectroscopy (QEPAS) is a trace gas sensing technique that employs a designed high-quality factor quartz tuning fork (QTF) as acousto-electric transducer. The first in-plane skew-symmetric flexural mode of the QTF is excited when weak resonant sound waves are generated between the QTF prongs. Thus, the performance of a QEPAS sensor strongly depends on the resonance properties of the QTF, namely the determination of flexural eigenfrequencies and air damping loss. In this work, we present a mixed theoretical-experimental framework to study the dynamic response of a QTF while vibrating in a fluid environment. Due to the system linearity, the dynamic response of the resonator immersed in a fluid medium is obtained by employing a Boundary Element formulation based on an ad hoc calculated Green's function. In particular, the QTF is modelled as constituted by a pair of two Euler-Bernoulli cantilevers partially coupled by a distributed linear spring. As for the forces exerted by the fluid on QTF structure, the fluid inertia and viscosity as well as an additional diffusivity term, whose influence is crucial for the correct evaluation of the system response, have been taken into account. By corroborating the theoretical analysis with the experimental outcomes obtained by means of a vibro-acoustic setup, the fluid response coefficients and the dynamics of the QTF immersed in a fluid environment are fully determined

Development of an organ failure score in acute liver failure for transplant selection and identification of patients at high risk of futility.

INTRODUCTION: King's College Hospital criteria are currently used to select liver transplant candidates in acetaminophen-related acute liver failure (ALF). Although widely accepted, they show a poor sensitivity in predicting pre-transplant mortality and cannot predict the outcome after surgery. In this study we aimed to develop a new prognostic score that can allow patient selection for liver transplantation more appropriately and identify patients at high risk of futile transplantation. METHODS: We analysed consecutive patients admitted to the Royal Free and Beaujon Hospitals between 1990 and 2015. Clinical and laboratory data at admission were collected. Predictors of 3-month mortality in the non-transplanted patients admitted to the Royal Free Hospital were used to develop the new score, which was then validated against the Beaujon cohort. The Beaujon-transplanted group was also used to assess the ability of the new score in identifying patients at high risk of transplant futility. RESULTS: 152 patients were included of who 44 were transplanted. SOFA, CLIF-C OF and CLIF-ACLF scores were the best predictors of 3-month mortality among non-transplanted patients. CLIF-C OF score and high dosages of norepinephrine requirement were the only significant predictors of 3-month mortality in the non-transplanted patients, and therefore were included in the ALF-OFs score. In non-transplanted patients, ALF-OFs showed good performance in both exploratory (AUC = 0.89; sensitivity = 82.6%; specificity = 89.5%) and the validation cohort (AUC = 0.988; sensitivity = 100%; specificity = 92.3%). ALF-OFs score was also able to identify patients at high risk of transplant futility (AUC = 0.917; sensitivity = 100%; specificity = 79.2%). CONCLUSION: ALF-OFs is a new prognostic score in acetaminophen-related ALF that can predict both the need for liver transplant and high risk of transplant futility, improving candidate selection for liver transplantation

Investigation of the Luco dei Marsi DSGSD revealing the first evidence of a basal shear zone in the central Apennine belt (Italy)

Deep-seated gravitational slope deformations (DSGSDs) show a wide range of geomorphological characteristics and kinematic behaviours. In many cases, deforming rock masses move on a continuous surface or a thick basal shear zone (BSZ) overlying the stable bedrock. The nature of this boundary is a significant issue in scientific debates since examples of BSZs have been observed or inferred in some DSGSDs worldwide. In the central Apennines, although several cases of DSGSDs have been described in recent decades, no evidence of BSZs has been documented thus far. This work presents the first case of a BSZ found in the region at the bottom of a large-scale gravitational deformation that affects the Mesozoic-Cenozoic carbonate ridge overhanging the Luco dei Marsi village (Abruzzi region). The BSZ consists of several metres-thick, cataclastic breccia developed within middle-Upper Cretaceous biodetritic limestone. The breccia level is exposed for approximately 200 m with a subhorizontal geometry and shows severe rock damage and weathering. The DSGSD hosting the BSZ affects an NNW-SSE-oriented and wide Miocene anticline whose eastern limb is dismembered by Pliocene-Quaternary normal faults delimiting the edge of a large Quaternary intermontane basin (the Fucino Basin). Field survey, aerial photointerpretation, and remote sensing (DInSAR technique) analyses outline an active gravity-driven process. This is characterized by several kinds of geomorphological features, including downhill- and uphill-facing scarps, ridge-top depressions, gravitational grabens and trenches in the upper and middle parts of the ridge, and bulging at the toe of the slope. These features, which can be distinguished from tectonic elements due to their shape and extension, are an indication of a high degree of internal deformation and a compound sagging geometry for the Luco dei Marsi DSGSD. The short-term activity of the process was revealed by DInSAR time series covering almost thirty years of satellite datasets, including ERS1/2, ENVISAT, COSMO-SkyMed, and SENTINEL 1 constellations. Strain rates on the order of a few mm/yr were inferred, with a marked difference between different sectors of the DSGSD area. The long-term (y > 102) lifespan of the DSGSD was framed into a multiple-step conceptual model summarizing the Early Pleistocene-Holocene geological evolution of the area. The model results outline the control exercised by extensional tectonics on DSGSD development, as progressive displacements along normal faults in the latest Pleistocene were the cause of lateral unconfinement at the toe of the slope. This work further contributes to the increasing knowledge on DSGSDs in the central Apennines and the understanding of the relationship between deformation features induced by slope morphogenesis, such as the BSZ, and Quaternary tectonics within the mountain belt

Midwives autonomy in discharge women after physiological childbirth

BACKGROUND: International literature identifies the midwife as the professional figure deals with women and newborns in the context of childbirth; it is however found to be still difficult to ensure this continuity of care. In Italy both the national laws and the indications of Emilia Romagna region promote this practice, ensuring the midwives management of the low risk women immediately after childbirth. The aim of the study is to investigate and describe the midwives autonomy as regards the post-partum discharge. METHODS: The computerised medical records were consulted to identify the mothers after childbirth who can be discharged independently by the obstetrician following the guidelines of the Emilia-Romagna region. RESULT S: A retrospective analysis of 1371 medical records related to the period January-June 2017 showed that 41% of discharges were managed handled by the midwives, while the remaining 59% by obstetricians. Fifty-seven percent of the women followed by the family counselling service were discharged by the obstetricians and 43% independently by the midwives. Considering the women followed by a private physician 62% were discharged by the obstetricians and 38% by the midwives. CONCLUSIONS: The study shows that, in a short time from the beginning of the project, the results as regards midwives autonomy were excellent. Indeed the midwives discharges does not differed significantly from the medical ones, and care continuity between the hospital and territory is strengthened. Further studies must include questionnaires concerning satisfaction of the mother not administered in this sample of women