Search

In this article, we discuss the implementation of a quantum recommendation system that uses a quantum variant of the k-nearest neighbours algorithm and the Grover algorithm to search for a specific element in an unstructured database. In addition to the presentation of the recommendation system as an algorithm, the article also shows the main steps in construction of a suitable quantum circuit for realisation of a given recommendation system. The computational complexity of individual calculation steps in the recommendation system is also indicated. The verification of the correctness of the proposed system is analysed as well, indicating an algebraic equation describing the probability of success of the recommendation. The article also shows numerical examples presenting the behaviour of the recommendation system for two selected cases.

This paper deals with numerical option pricing methods based on a Schrödinger model rather than the Black-Scholes model. Nonlinear Schrödinger boundary value problems seem to be alternatives to linear models which better reflect the complexity and behavior of real markets. Therefore, based on the nonlinear Schrödinger option pricing model proposed in the literature, in this paper a model augmented by external atomic potentials is proposed and numerically tested. In terms of statistical physics the developed model describes the option in analogy to a pair of two identical quantum particles occupying the same state. The proposed model is used to price European call options on a stock index. the model is calibrated using the Levenberg-Marquardt algorithm based on market data. A Runge-Kutta method is used to solve the discretized boundary value problem numerically. Numerical results are provided and discussed. It seems that our proposal more accurately models phenomena observed in the real market than do linear models.

Low temperature scanning tunneling microscopy/ scanning tunneling spectroscopy, room temperature atomic force microscopy and X-ray photoelectron spectroscopy of the boron ions implanted into the magnesium substrate were performed in order to get information about the local superconducting behavior of thin MgBx film. Results confirm the island superconductivity far from the percolation threshold of the bulk superconducting MgB2 sample. [ABSTRACT FROM AUTHOR]

Abstract: Results of high-pressure directional growth of GaN on foreign substrates: SiC, sapphire and GaN/sapphire MOCVD templates are presented. The role of nitrogen pressure and supersaturation in the growth process is discussed. The conditions for stable growth of the nitride are determined. The results of the crystallization process are compared with those obtained for directional growth on pressure grown GaN crystals. [Copyright &y& Elsevier]

The great advantage of the growth of GaN from high temperature (∼1500°C) gallium solutions under high nitrogen pressure (∼10–15 kbar) is that the crystals grown by this method are almost free of dislocations (density of 10–100 cm−2). Typically, the crystals grown under pressure during 150–200 h are relatively thin (about 0.1 mm) hexagonal platelets of 10–14 mm in their lateral size, which indicates strong anisotropy of such growth. The evolution of the crystal morphological forms in time and as a function of temperature distribution allows the discovery of qualitative relations between supersaturation and the nucleation rates on particular growth surfaces. It is of special importance for growth in directions parallel to the c-axis, which is very sensitive to the changes at the crystallization front at the higher supersaturations needed to increase the thickness of the final crystal. This often leads to the growth instabilities which can be avoided by special control of the conditions at the particular growing surface that is achieved by the application of directional methods of crystallization. The possible mechanisms of hindering the lateral growth of the platelets after 150–200 h can be related to changes of the mass transport mechanisms in the solution due to the presence of the crystals. Modeling of the mass transport phenomena in liquid gallium, based on the experimental temperature distribution data, shows that the convectional flows are again quite sensitive to small changes in the temperature gradients in the system. Such changes can be induced by a set of GaN crystals appearing in the solution. Therefore, to increase the lateral size of the crystals, an additional modification of temperature distribution during the crystallization process is necessary. [Copyright &y& Elsevier]

This article analyses the organisation of the mass COVID-19 vaccination programme in Poland and its consequences for various aspects of the social identity of healthcare workers (HCWs). Based on 31 in-depth interviews with HCWs, our study reveals the following: (1) Certain elements of the programme (inclusion of other healthcare professionals like pharmacists and laboratory diagnosticians as vaccinators) and the provision of additional infrastructure (pharmacies and shopping malls) may prompt scepticism and criticism in physicians and nurses who feel challenged about their professional autonomy and hierarchies; (2) Given the high levels of professional uncertainty, the implementation of the COVID-19 vaccination is forcing HCWs to revise their attitude to medical standards, resulting in specific responses and adaptation strategies (ranging from the active involvement in the programme due to the sense of mission, to more or less evident scepticism); and (3) Confronting vaccine hesitancy, both among patients and other HCWs, contributes to the feeling of helplessness, leading to criticism of policymakers., (© 2024 The Authors. The International Journal of Health Planning and Management published by John Wiley & Sons Ltd.)