157 research outputs found
Quantum Information Metric on
We present a formula for the information metric on for a scalar primary operator of integral dimension . This formula is checked for various space-time dimensions
and in the field theory side. We check the formula in the gravity
side using the holographic setup. We clarify the regularization and
renormalization involved in these computations. We also show that the quantum
information metric of an exactly marginal operator agrees with the leading
order of the interface free energy of the conformal Janus on Euclidean ,
which is checked for .Comment: 21 pages, 2 figure
Mechanism and Machine Science Educational Workshop Based on Schröder-Reuleaux Ancient Models of Politecnico di Torino
Around the world, there are many collections of models of mechanisms and machine components of historical value. Among these, there is an important collection kept at the Politecnico di Torino, Department of Mechanical and Aerospace Engineering-DIMEAS. It consists of about 85 Reuleaux models manufactured by the Schröder company of Darmstadt in the second half of the 19th century. It includes linkages, gears, cam-follower systems, belt drives, couplings and clutches whose history is reconstructed. Some models are still used effectively today in teaching the science of mechanisms and machine. The paper presents both the important historical collection and the didactic methodology adopted in the course âMechanics of Automatic Machinesâ in which students practice the developing of virtual models of some selected mechanisms
Non-conventional lip seal mountings for pneumatic cylinders
Sliding lip seals are used in pneumatic cylinders to prevent leakage past the piston and rod. Though they
guarantee excellent sealing, the friction forces at contact between lip and counterpart can be relatively high.
This results in energy losses and problems with wear on components in relative motion, as well as
difficulties in controlling actuator positioning. Standards for compressed air cleanliness restrict the use of
greases and lubricants, especially in applications such as the food processing and pharmaceutical industries.
A number of studies are thus under way in order to find effective alternatives to the use of common
lubricants. These studies address both seal configuration [1-4], and the use of innovative materials [5-7].
Other approaches employ systems permitting small amounts of air leakage that operate as lubricated
supports, variable-profile pistons [8], or rings with special micromachined surfaces [9-10]. Such solutions
are not always economical, both because they require precision tolerances and geometries, and because they
use special seals, often produced ad hoc.
This paper discusses the possibility of using commercial lip seals with a non-conventional mounting on the
piston in order to obtain a simple controlled-leakage system that reduces friction forces in pneumatic
cylinders economically and effectively. The non-conventional mounting consists of positioning the lip seal in
the direction opposite to that used in a conventional installation, so that the contact pressure reduces as air
pressure in the chamber rises. In this way, an air gap is created at the sliding interface which allows air in the
pressurized chamber to escape past the seal lip, thus reducing the contact force on the barrel. The piston is
provided with a hole which exhausts the leakage flow to the atmosphere.
To evaluate the validity of this approach, a number of preliminary tests were carried out in [11] to measure
flow rate on a type of spring-loaded lip seal consisting of graphite-filled PTFE for barrel diameters of 50
mm. In particular, the tests determined air leakage behavior for different mounting tolerances.
This paper presents further tests conducted on the same samples examined in [11] and on another PTFE and
graphite-filled PTFE configuration, measuring leakage flow rates and friction forces. Leakage flow rate
measurements were carried out with single and double seal installations. The results obtained are discussed
together with the advantages of the proposed solution compared to the conventional mountings in ordinary
use
Experimental analysis and preliminary model of non-conventional lip seals
The paper describes the tests carried out to determine the applicability of a simple means for reducing friction force in linear pneumatic actuators. The idea is based on the use of commercial lip seals mounted in the direction opposite to that used in conventional systems. Two different non-conventional installations were tested using commercial spring-energized seals consisting of two different materials: virgin PTFE and graphite-filled PTFE. Tests assessed the effect of bore manufacturing tolerances with nominal bore diameters of 50.0 mm and 50.2 mm. Performance was evaluated in terms of leakage flow rate and friction force, comparing the proposed installation with conventionally mounted seals. Friction coefficient and stiffness of the two seal materials were measured on a seal segment mounted on a pin-on-disk tribometer featuring a special pin design. Tests were carried out by loading the seal segment against a portion of the cylinder barrel in reciprocating motion. Stiffness and friction coefficient measurements served as the basis for developing a preliminary lumped parameter model of the lip seal which was used to analyze lip deflections, exchanged forces and leakage flow rate between seal and barrel
Non-Invasive Experimental Identification of a Single Particle Model for LiFePO4 Cells
The rapid spread of Lithium-ions batteries (LiBs) for electric vehicles calls
for the development of accurate physical models for Battery Management Systems
(BMSs). In this work, the electrochemical Single Particle Model (SPM) for a
high-power LiFePO4 cell is experimentally identified through a set of
non-invasive tests (based on voltage-current measurements only). The SPM is
identified through a two-step procedure in which the equilibrium potentials and
the kinetics parameters are characterized sequentially. The proposed
identification procedure is specifically tuned for LiFePO4 chemistry, which is
particularly challenging to model due to the non-linearity of its open circuit
voltage (OCV) characteristic. The identified SPM is compared with a
second-order Equivalent Circuit Model (ECM) with State of Charge dependency.
Models performance is compared on dynamic current profiles. They exhibit
similar performance when discharge currents peak up to 1C (RMSE between
simulation and measures smaller than 20 mV) while, increasing the discharge
peaks up to 3C, ECM's performance significantly deteriorates while SPM
maintains acceptable RMSE (< 50 mV).Comment: Accepted for publication at the IFAC World Congress 202
Design and Analysis of an Aerostatic Pad Controlled by a Diaphragm Valve
Because of their distinctive characteristics, aerostatic bearings are particularly suitable for high-precision applications. However, because of the compressibility of the lubricant, this kind of bearing is characterized by low relative stiffness and poor damping. Compensation methods represent a valuable solution to these limitations. This paper presents a design procedure for passively compensated bearings controlled by diaphragm valves. Given a desired air gap height at which the system should work, the procedure makes it possible to maximize the stiffness of the bearing around this value. The designed bearings exhibit a quasi-static infinite stiffness for load variation ranging from 20% to almost 50% of the maximum load capacity of the bearing. Moreover, the influence of different parameters on the performance of the compensated pad is evaluated through a sensitivity analysi
An Identification Method for Orifice-Type Restrictors Based on the Closed-Form Solution of Reynolds Equation
Even though the behavior of aerostatic bearings has for long been the topic of extensive research, there are still many aspects that require further investigation. Among these, the identification of the discharge coefficients is one the most crucial. This paper presents a hybrid method to identify the discharge coefficients of aerostatic bearing orifices. The method is termed as hybrid since it exploits experimental data and the equations of the analytical model of a circular and centrally fed aerostatic pad. The obtained results demonstrate the accuracy of the method. The proposed method further offers practical advantages compared to the conventional methods
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