Neutrino oscillation phase dynamically induced by f(R)-gravity

The gravitational phase shift of neutrino oscillation can be discussed in the framework of f(R)-gravity. We show that the shift of quantum mechanical phase can depend on the given f(R)-theory that we choose. This fact is general and could constitute a fundamental test to discriminate among the various alternative relativistic theories of gravity. Estimations of ratio between the gravitational phase shift and the standard phase are carried out for the electronic Solar neutrinos.Comment: 4 page

The Influence of Base Oil Properties on the Friction Behaviour of Lithium Greases in Rolling/Sliding Concentrated Contacts

This study investigates the influence of base oil type and viscosity on the frictional behaviour of lithium-thickened bearing greases. A series of model lithium greases were manufactured by systematically varying viscosity and type of base oil, so that the influence of a single base oil property could be studied in isolation. In addition, selected greases were blended with oleic acid, with the purpose of evaluating its effectiveness in further reducing grease friction. Friction coefficient and film thickness were measured in laboratory ball-on-disc tribometers over a range of speeds and temperatures. For a specific oil type, the influence of base oil viscosity on friction was found to be closely related to its effect on film thickness: greases formulated with PAO oils covering a wide range of viscosities gave very similar friction at the same nominal film thickness. For a given base oil viscosity, base oil type was found to have a strong influence on grease friction under all test conditions. PAO-based greases generally produced lower friction than mineral- and ester-based greases. Addition of oleic acid to the test greases did not significantly affect friction within the range of test conditions employed in this study. The results provide new insight into the frictional behaviour of greases, which may be used to help inform new low-friction grease formulations for rolling bearing applications

Invariant solutions and Noether symmetries in Hybrid Gravity

Symmetries play a crucial role in physics and, in particular, the Noether symmetries are a useful tool both to select models motivated at a fundamental level, and to find exact solutions for specific Lagrangians. In this work, we consider the application of point symmetries in the recently proposed metric-Palatini Hybrid Gravity in order to select the $f({\cal R})$ functional form and to find analytical solutions for the field equations and for the related Wheeler-DeWitt (WDW) equation. We show that, in order to find out integrable $f({\cal R})$ models, conformal transformations in the Lagrangians are extremely useful. In this context, we explore two conformal transformations of the forms $d\tau=N(a) dt$ and $d\tau=N(\phi) dt$. For the former conformal transformation, we found two cases of $f({\cal R})$ functions where the field equations admit Noether symmetries. In the second case, the Lagrangian reduces to a Brans-Dicke-like theory with a general coupling function. For each case, it is possible to transform the field equations by using normal coordinates to simplify the dynamical system and to obtain exact solutions. Furthermore, we perform quantization and derive the WDW equation for the minisuperspace model. The Lie point symmetries for the WDW equation are determined and used to find invariant solutions.Comment: 12 pages, 1 figur

f(T) teleparallel gravity and cosmology

Over the past decades, the role of torsion in gravity has been extensivelyinvestigated along the main direction of bringing gravity closer to its gaugeformulation and incorporating spin in a geometric description. Here we reviewvarious torsional constructions, from teleparallel, to Einstein-Cartan, andmetric-affine gauge theories, resulting in extending torsional gravity in theparadigm of f(T) gravity, where f(T) is an arbitrary function of the torsionscalar. Based on this theory, we further review the corresponding cosmologicaland astrophysical applications. In particular, we study cosmological solutionsarising from f(T) gravity, both at the background and perturbation levels, indifferent eras along the cosmic expansion. The f(T) gravity construction canprovide a theoretical interpretation of the late-time universe acceleration,and it can easily accommodate with the regular thermal expanding historyincluding the radiation and cold dark matter dominated phases. Furthermore, ifone traces back to very early times, a sufficiently long period of inflationcan be achieved and hence can be investigated by cosmic microwave backgroundobservations, or alternatively, the Big Bang singularity can be avoided due tothe appearance of non-singular bounces. Various observational constraints,especially the bounds coming from the large-scale structure data in the case off(T) cosmology, as well as the behavior of gravitational waves, are describedin detail. Moreover, the spherically symmetric and black hole solutions of thetheory are reviewed. Additionally, we discuss various extensions of the f(T)paradigm. Finally, we consider the relation with other modified gravitationaltheories, such as those based on curvature, like f(R) gravity, trying toenlighten the subject of which formulation might be more suitable forquantization ventures and cosmological applications

Studies of friction in grease lubricated rolling bearings using ball-on-disc and full bearing tests

This article evaluates the frictional performance of different bearing grease formulations in full rolling bearings and a ball-on-disc rig and subsequently assesses whether the ball-on-disc test results can be used to predict the grease performance in actual bearings. A selection of custom-made greases with systematically varied formulations as well as their base oils were tested. Bearing torque was measured in two different cylindrical roller thrust bearings and a thrust ball bearing. The same lubricants were tested with ball-on-disc tribometers, a mini traction machine (MTM) to measure friction and an optical elastohydrodynamic (EHD) rig to measure film thickness. Both lithium complex and diurea greases were observed to produce lower friction than their base oils within the low speed, low nominal lambda ratio region, whereas the greases and oils had the same friction at high nominal lambda ratio values. These relative trends were the same in full bearing and single-contact MTM tests. The reduction in friction was seen to be related to the level of film thickness enhancement provided by greases at lower speeds, which leads to an increase in the effective lambda ratio and hence reduced friction. By extracting the sliding torque component from the overall measured bearing torque, a plot of the friction coefficient against the effective lambda ratio was produced encompassing all bearing and single-contact tests and all lubricants and test conditions. This plot was seen to follow a general shape of a master Stribeck curve, indicating that the numerical values of the friction coefficient from ball-on-disc and full bearing tests overlap and can be related to each other using this approach over the range of conditions employed here. Thus, single-contact ball-on-disc tests can provide a fast and economical way of establishing the frictional performance of bearing greases in full bearings in terms of both relative performance rankings and quantitative values of bearing frictional power losses

The design, hysteresis modeling and control of a novel SMA-fishing-line actuator

Fishing line can be combined with shape memory alloy (SMA) to form novel artificial muscle actuators which have low cost, are lightweight and soft. They can be applied in bionic, wearable and rehabilitation robots, and can reduce system weight and cost, increase power-to-weight ratio and offer safer physical human-robot interaction. However, these actuators possess several disadvantages, for example fishing line based actuators possess low strength and are complex to drive, and SMA possesses a low percentage contraction and has high hysteresis. This paper presents a novel artificial actuator (known as an SMA-fishing-line) made of fishing line and SMA twisted then coiled together, which can be driven directly by an electrical voltage. Its output force can reach 2.65N at 7.4V drive voltage, and the percentage contraction at 4V driven voltage with a 3N load is 7.53%. An antagonistic bionic joint driven by the novel SMA-fishing-line actuators is presented, and based on an extended unparallel Prandtl-Ishlinskii (EUPI) model, its hysteresis behavior is established, and the error ratio of the EUPI model is determined to be 6.3%. A Joule heat model of the SMA-fishing-line is also presented, and the maximum error of the established model is 0.510mm. Based on this accurate hysteresis model, a composite PID controller consisting of PID and an integral inverse (I-I) compensator is proposed and its performance is compared with a traditional PID controller through simulations and experimentation. These results show that the composite PID controller possesses higher control precision than basic PID, and is feasible for implementation in an SMA-fishing-line driven antagonistic bionic joint

Short Gamma Ray Bursts as possible electromagnetic counterpart of coalescing binary systems

Coalescing binary systems, consisting of two collapsed objects, are among the most promising sources of high frequency gravitational waves signals detectable, in principle, by ground-based interferometers. Binary systems of Neutron Star or Black Hole/Neutron Star mergers should also give rise to short Gamma Ray Bursts, a subclass of Gamma Ray Bursts. Short-hard-Gamma Ray Bursts might thus provide a powerful way to infer the merger rate of two-collapsed object binaries. Under the hypothesis that most short Gamma Ray Bursts originate from binaries of Neutron Star or Black Hole/Neutron Star mergers, we outline here the possibility to associate short Gamma Ray Bursts as electromagnetic counterpart of coalescing binary systems.Comment: 4 pages, 1 figur

Archimedes: a feasibility study of an experiment to weigh the electromagnetic vacuum

Archimedes is a feasibility study of a future experiment to ascertain the interaction of vacuum fluctuations with gravity. The experiment should measure the force that the earth's gravitational field exerts on a Casimir cavity by using a small force detector. Here we analyse the main parameters of the experiment and we present its conceptual scheme, which overcomes in principle the most critical problems.Comment: 3 pages, MG14 Conferenc

Analytic approximations, perturbation methods, and their applications

The paper summarizes the parallel session B3 {\em Analytic approximations, perturbation methods, and their applications} of the GR18 conference. The talks in the session reported notably recent advances in black hole perturbations and post-Newtonian approximations as applied to sources of gravitational waves.Comment: Summary of the B3 parallel session of the GR18 conferenc