Counterfactuals, Irreversible Laws and The Direction of Time

The principle of Information Conservation or Determinism is a governing assumption of physical theory. Determinism has counterfactual consequences. It entails that if the present were different, then the future would be different. But determinism is temporally symmetric: it entails that if the present were different, the past would also have to be different. This runs contrary to our commonsense intuition that what has happened in the future depends on the past in a way the past does not depend on the future. To understand how this can be so we observe that while the truth of some counterfactuals is guaranteed by the laws of logic or the laws of nature, some are not. It is among the latter contingent, counterfactuals that we find temporal asymmetry. It is this asymmetry that gives causation a temporal direction. The temporal asymmetry of these counterfactuals is explained by the fact that the dynamical laws of nature are logically irreversible functions from partial states of the world onto other partial states. (Logical reversibility is not to be confused, though it too often is, with time-reversal invariance). Though these irreversible laws are locally indeterministic, they can sum to give a globally deterministic description of the world. This combination of global determinism and local indeterminism gives rise to contingent counterfactual dependence and gives that dependence a direction. That direction is independent of the direction of entropy. The direction of contingent counterfactual dependence is time's arrow

Numerical study of thin superconducting plates subjected to transverse magnetic fields

Electromagnetic properties of the superconductors predestine them to serve as materials for the efficient and light magnetic shields. Very high attenuation factors are possible to be obtained. Superconducting elements of different geometry can be used. However, shielding effect is limited by the critical current of a superconductor. This work describes the model of an arbitrarily shaped thin superconducting plates made of BSCCO, with the focus on circular and rectangular samples. The plates are subjected to transverse magnetic fields of different strength and shape. Changes of critical current density are considered. The distribution of the shielded magnetic field and shielding current is presented. Results show that the magnetic field attenuation occurs and depend on the shape and material of a plate. It was also observed that coarse meshes can be used to obtain reliable results concerning magnetic field distribution, thus saving computational time

Causation

Causation is defined as a relation between facts: C causes E if and only if C and E are nomologically independent facts and C is a necessary part of a nomologically sufficient condition for E. The analysis is applied to problems of overdetermination, preemption, trumping, intransitivity, switching, and double prevention. Preventing and allowing are defined and distinguished from causing. The analysis explains the direction of causation in terms of the logical form of dynamic laws. Even in a universe that is deterministic in both temporal directions, not every fact must have a cause and present facts may have no future causes

Calculation of a magnetic force acting on small superconducting celestial bodies

Funder: CERNAbstractRecent discoveries of superconducting phases in the samples of meteorites suggest the possibility of a natural occurrence of superconducting state in space. Superconductors are known to exhibit interesting behaviours when subjected to external magnetic fields, such as levitation. Similar force may act on a superconducting bit in space. The goal of this paper is to quantify this force and assess its effects. Several scenarios in which a superconducting bit can be produced and interact with a magnetic field in space are suggested. The force acting on a superconductor in different conditions is calculated with numerical simulations. The dependence on a magnetic flux density, its gradient, and the geometry and the properties of the superconductor are found. The empirical formulas are derived and used to calculate a magnetic force. The resultant force is extremely weak in all analysed scenarios. It is found that its strength decreases rapidly with the distance from the source of the magnetic flux. Its effect on trajectory of the superconductor is almost negligible. Some possibilities of increasing its strength and the effects are considered.</jats:p

Beyond the biomedical: an evaluation of the introduction of social gerontology into a postgraduate geriatric medicine education program.

Geriatric Medicine education tends to adopt a biomedical lens, despite the practice of Geriatric Medicine involving the comprehensive assessment of the functional, psychological, and social aspects of older people's lives. In this commentary, we describe the delivery of a Social Gerontology education program for Geriatric Medicine trainees in the Northwest of England. Education in Social Gerontology-a field that focuses on how social, cultural, economic, and environmental factors shape the lives of older adults-is thought to mitigate against ageism, a pervasive and multifaceted form of discrimination. We describe the rationale for, and context of, the program delivery, before presenting an overview of trainee's feedback. Thematic analysis of feedback centered around three main themes: knowledge acquisition, change in clinical practice, and enjoyment of the sessions. Trainees (n = 20) reported enjoying the sessions, with 100% likely to recommend to peers. The focus on underserved groups, the novel content of the sessions, which were not taught elsewhere, and the non-medical perspective of the speakers were described as particularly valuable. By sharing our approach and reflecting on the early success of the program, we argue for an increased focus on Social Gerontology in Geriatric Medicine education. [Abstract copyright: © 2023. The Author(s).

Testing of Surface Mounted Superconducting Stacks as Trapped-Flux Magnets in a Synchronous Machine

Stacks of high temperature superconducting tapes may offer a technically affordable solution for the application of superconducting materials as trapped-flux magnets in the rotor of synchronous electrical machines. Nevertheless, several concerns must be first addressed, among others, the optimal procedure to induce the current vortexes previously to operation (magnetization), the survivability of these vortexes in the electromagnetic environment present in an electrical machine and the accuracy of recently developed numerical models. With the aim of exploring such practicalities, this paper presents a modified synchronous machine to test under liquid nitrogen conditions thin stacks of superconducting tapes. The machine is run under realistic conditions: currents in the stacks are induced from the stator, then the shaft is rotated and finally the machine is connected to a load, working as a generator. The results confirm previous numerical and experimental studies and establish a procedure for assessing the behavior of stacks in their actual operational environment.Also EPSRC EP/P000738/

Frequency-dependent demagnetisation rate of a shielded HTS tape stack

Abstract This work presents results of investigation of crossed-field demagnetization in 2G high temperature superconducting stacks at temperatures in the range of 77 - 20 K and in a variable frequency, corresponding to the particular rotor application. We propose a method to reduce the demagnetization rate for a given stack configuration necessary for the superconducting rotor operating at a cryogenic temperature. This technique involves 3-D wrapping the stack of tapes with perpendicular layers of similar superconducting properties. Previous ‘proof of concept’ studies documented some improvements in flux demagnetisation reduction for basic configuration. In the present study a more advanced approach based on magnetic flux shielding is adopted. The presented results provide an important contribution to development for design solutions that aim to increase the operational time before remagnetisation of the stacks would be required.</jats:p