Search results for " mechanics."

On modelling and stability of axially moving viscoelastic materials

2013

Modelling of rotations by using matrix solutions of nonlinear wave equations

2007

A family of matrix solutions of nonlinear wave equations is extended and its application to modelling is given. It is shown that a similarity transformation, induced by the matrix solution, is equivalent to the rotation. Matrix solutions are used for modelling helical motions and vortex rings, simultaneous rotations and particles collision, mapping contraction and pulsating spheres. Geometrical interpretation of the doubling of rotation angle in each step of sequential mapping contraction is given. First Published Online: 14 Oct 2010

Effect of Stacking Sequence and Sodium Bicarbonate Treatment on Quasi-Static and Dynamic Mechanical Properties of Flax/Jute Epoxy-Based Composites

2019

The present paper deals with the investigation of quasi-static and dynamic mechanical response of epoxy-based composites reinforced with flax and/or jute plain weave fabrics. In order to evaluate the influence of the stacking sequence, two monolithic laminates reinforced with flax or jute fibers and two hybrid flax/jute laminates were manufactured through the vacuum infusion technique. Furthermore, an eco-friendly and cost-effective surface treatment based on fiber soaking in a sodium bicarbonate solution was employed to improve the fiber-matrix adhesion. The mechanical characterization (by means of quasi-static flexural, dynamic mechanical thermal analysis and Charpy impact tests) allowed …

Rhombi-chain Bose-Hubbard model: Geometric frustration and interactions

2018

We explore the effects of geometric frustration within a one-dimensional Bose-Hubbard model using a chain of rhombi subject to a magnetic flux. The competition of tunnelling, self-interaction and magnetic flux gives rise to the emergence of a pair-superfluid (pair-Luttinger liquid) phase besides the more conventional Mott-insulator and superfluid (Luttinger liquid) phases. We compute the complete phase diagram of the model by identifying characteristic properties of the pair-Luttinger liquid phase such as pair correlation functions and structure factors and find that the pair-Luttinger liquid phase is very sensitive to changes away from perfect frustration (half-flux). We provide some propo…

Robustness of asymmetry and coherence of quantum states

2016

Quantum states may exhibit asymmetry with respect to the action of a given group. Such an asymmetry of states can be considered as a resource in applications such as quantum metrology, and it is a concept that encompasses quantum coherence as a special case. We introduce explicitly and study the robustness of asymmetry, a quantifier of asymmetry of states that we prove to have many attractive properties, including efficient numerical computability via semidefinite programming, and an operational interpretation in a channel discrimination context. We also introduce the notion of asymmetry witnesses, whose measurement in a laboratory detects the presence of asymmetry. We prove that properly c…

Quantum memories with zero-energy Majorana modes and experimental constraints

2016

In this work we address the problem of realizing a reliable quantum memory based on zero-energy Majorana modes in the presence of experimental constraints on the operations aimed at recovering the information. In particular, we characterize the best recovery operation acting only on the zero-energy Majorana modes and the memory fidelity that can be therewith achieved. In order to understand the effect of such restriction, we discuss two examples of noise models acting on the topological system and compare the amount of information that can be recovered by accessing either the whole system, or the zero-modes only, with particular attention to the scaling with the size of the system and the e…

The Principles of Quantum Theory

2013

This chapter develops the formal framework of quantum mechanics: the mathematical tools, generalization and abstraction of the notion of state, representation theory, and a first version of the postulates on which quantum theory rests.

Refractory Death Rattle: Deep Aspiration Facilitates the Effects of Antisecretory Agents

2011

Anticholinergic drugs, including atropine, hyoscine butylbromide, and scopolamine, have been shown to be equally effective in the treatment of death rattle. However, anticholinergic drugs may only be effective in reducing the production of further secretions, rather than eliminating the existing ones. A case is described in which a preventive procedure was undertaken to carefully eliminate secretions before starting anticholinergic drugs. Airway aspiration under light anesthesia removed secretions before starting anticholinergic drugs. Low doses of propofol were given intravenously to make a laryngoscopy feasible, allowing the complete aspiration of large amounts of tracheal secretions. No …

Biophysics of venous return from the brain from the perspective of the pathophysiology of chronic cerebrospinal venous insufficiency

2011

This article discusses the biophysical aspects of venous outflow from the brain in healthy individuals and in patients with chronic cerebrospinal venous insufficiency. Blood flows out of the brain differently, depending on body position. In the supine position it flows out mainly through internal jugular veins, while in the upright position it uses the vertebral veins. This phenomenon is probably not due to the active regulation of the flow but instead results from the collapse of jugular veins when the head is elevated. Such a collapse is associated with a significant increase in flow resistance, which leads to redirection of the flow towards the vertebral pathway. Theoretical calculations…

Energy spectral density as valid parameter to compare postural control between subjects with nonspecific chronic low back pain vs healthy subjects : …

2021

Abstract Background Nonspecific chronic low back pain (NSCLBP) is one of the most common and frequent health problems. Objetive to compare postural control (i.e. center of pressure (CoP) displacement and energy spectral density (ESD)) using technological devices (accelerometers and pressure platform) between subjects with NSCLBP and healthy subjects. Methods A cross-sectional case-control study was conducted. Observational study (STROBE). The final sample consisted of 60 subjects (30 NSCLBP subjects and 30 healthy subjects). Triaxial accelerometer and pressure platform were used in order to obtain ESD and CoP displacement measurements during four balance tasks (i.e. with and without vision …