What is negative refraction?

We review various published definitions associated with the phenomenon of negative phase velocity propagation of electromagnetic waves in meta-media, as observed through negative refraction. For the principal definition, based on the Poynting vector and the wave vector having negative scalar product, we summarise the various material constraints that have been derived. The distinction between criteria based on the Poynting vector and the group velocity are considered, both in respect of causality, and in the context of moving media. Instances where a fully covariant definition is necessary are also identified, and compared with other results from the extant literature. Satisfaction of the NPV propagation criterion is also considered for surface plasmons.     

Response to ‘On negative refraction in classical vacuum’

An analysis [McCall, M.W. J. Mod. Opt. 2007, 54, 119–128] based on the electromagnetic energy-momentum tensor, to explore the prospects for negative-phase-velocity (NPV) propagation in gravitationally affected vacuum, did not consider (i) the total energy-momentum tensor and (ii) the global perspective of curved spacetime. Also, the appearance of NPV was wrongly attributed to a change in signature of the spacetime metric.     

Comment on ‘Economic analysis of inventory systems’

This paper deals with the problem of designing a hierarchical production planning system, where higher level decisions impose constraints on lower level decisions. This paper supports the choice of a production planning system for a two-stage process. First, analytical models clarify the relationship between production planning rules and the role of buffer inventory level in terms of manufacturing performance. Second, from the results of the analysis, a numerical example is presented on a production planning system designed under various management policies.     

Author's reply to ‘Response to “On negative refraction in classical vacuum” ’

The ‘subregional frames’ considered by Mackay and Lakhtakia (ML) in their comment [Mackay, T.G.; Lakhtakia, A. J. Mod. Opt. 2007, 55, 323–328] to be noninertial within the ‘global perspective of curved spacetime’, are actually isomorphic to flat, inertial, Minkowski spacetime. Their claims of gravitationally induced vacuum negative refraction originate from the non-covariance of the criterion they used. When a covariant criterion is applied (as in [McCall, M.W. J. Mod. Opt., 2007, 54, 119–128; Phys. Rev. Lett. 2007, 98, 091102]) vacuum NPV does not occur. This argument is unaffected by noting that the sign changes of the metric eigenvalues were incorrectly stated in [McCall, M.W. J. Mod. Opt., 2007, 54, 119–128].     

What is going on in magnesium alloys?

China has been developed into one of the most active regions in terms of both fundamental and applied research on magnesium (Mg) and its alloys in the world from a solid base laid by its prominent metallurgist and materials scientists over the past decades. Nowadays, a large number of young-generation researchers have been inspired by their predecessors and become the key participants in the fields of Mg alloys, which consequently led to the establishment of China Youth Scholar Society for Magnesium Alloys Research in 2015. Since then, the first two China Youth Scholars Symposiums on Mg Alloys Research had been held at Harbin (2015) and Chongqing (2016) China, respectively. A number of crucial research interests related to fundamental and applied Mg research were discussed at the conferences and summarized in this short perspective, aiming to boost far-reaching initiatives for development of new Mg-based materials to satisfy the requirements for a broad range of industrial employments. Herein, four main aspects are included as follows: i) Plastic deformation mechanism and strengthening strategy, ii) Design and development of new Mg-based materials, iii) Key service properties, and iv) New processing technologies.     

Comment on ‘Wigner equation of motion for time-dependent potentials’

Abstract

A correction is pointed out to a statement made by Galleani and Cohen (2002, J. mod. Optics, 49, 561) regarding the impossibility of deriving an equation of evolution for the Wigner function corresponding to the Schrödinger equation with a time-dependent potential.     

Comment on ‘Operator formalism for the Wigner phase distribution’

Abstract

The operator associated with the radially integrated Wigner function is found to lack justification as a phase operator.     

What affects publications’ popularity on Twitter?

Scientometrics - Social media is one of the major channels for knowledge diffusion, including scientific discovery. As a consequence, it has been under discussion whether altmetrics can be used as...     

Comment on ‘The Fractional Fourier Transform in Optical Propagation Problems’

Although their mathematical forms apparently resemble each other, the diffraction integral and fractional Fourier transformation (FRT) have completely different physical meanings. We point out that an interpretation of the FRT given recently in a paper by Alieva et al. is not physically appropriate. We then show how those integral transformations can be treated in a unified way within the framework of the special affine Fourier transformation. Finally the multidimensional FRT presented in the above paper is further generalized to allow n independent fractional degrees.     

Why is ‘smart’ still a frontier technology?

That’s what the market research fraternity seem to think. Talking to the analysts, those financial heavyweights with the power to urge ‘buy’ or ‘sell’, Frost & Sullivan’s Joseph Constance discussed the newest first part of a Frost & Sullivan two part report on Smart Materials, but never let a figure slip.As disappointing as the 3i survey on nanotechnology, this report considers that smart materials are, still, after decades, only a ‘frontier’ technology. Expect plenty of interesting applications, lots of research, but no hard figures.In other reports on Smart Materials from BCC, market figures give way to a technology assessment, (a patent review, and a look at market potential) and finally a report that focus on niche smart areas – sol gel. But, frontier or emerging, everyone is still shy of smart market numbers, year on year.     

What is a proof?

To those brought up in a logic-based tradition there seems to be a simple and clear definition of proof. But this is largely a twentieth century invention; many earlier proofs had a different nature. We will look particularly at the faulty proof of Euler's Theorem and Lakatos' rational reconstruction of the history of this proof. We will ask: how is it possible for the errors in a faulty proof to remain undetected for several years-even when counter-examples to it are known? How is it possible to have a proof about concepts that are only partially defined? And can we give a logic-based account of such phenomena? We introduce the concept of schematic proofs and argue that they offer a possible cognitive model for the human construction of proofs in mathematics. In particular, we show how they can account for persistent errors in proofs.     

What is Simulated Annealing?

Beginning in 1983, simulated annealing was marketed as a global optimization methodology that mimics the physical annealing process by which molten substances cool to crystalline lattices of minimal energy. This marketing strategy had a polarizing effect, attracting those who delighted in metaphor and alienating others who found metaphor insufficient at best and facile at worst. In fact, the emotional outbursts that accompany many discussions of simulated annealing are an unfortunate distraction. Whatever its pros and cons, simulated annealing can be grounded in rigorous mathematics. Here we provide an elementary, self-contained introduction to simulated annealing in terms of Markov chains.     

Comment on ‘Two-state Description of Total Polarization by Means of Singular Eigenvalue Problems’

We derive a formulation that can be used to determine the electromagnetic field distribution in the focal region of a wide-angle spherical mirror illuminated by an obliquely incident and linearly polarized plane monochromatic wave. The integrals representing the diffracted fields derived in part 1 [1] for the two cases of polarization of the incident field are first suitably expanded in series form. The integrals with respect to the azimuth 0 are then evaluated analytically with the help of some new integration formulae developed in this paper. The diffracted field components for the two cases of incident polarization are finally expressed in forms suitable for numerical computation. Our formulae can be used to determine the three-dimensional field distribution in the caustic region of the mirror for any obliquity of the incident beam. Simpler expressions for the field components for a few special cases of interest are also derived. In particular, it is shown that the series solution obtained for the case of oblique incidence reduces to the simpler results found by previous authors for the case of normal incidence.     

‘A Pretence of What is Not’? A Study of Simulation(s) from the ENIAC Perspective

What is the significance of high-speed computation for the sciences? How far does it result in a practice of simulation which affects the sciences on a very basic level? To offer more historical context to these recurring questions, this paper revisits the roots of computer simulation in the development of the ENIAC computer and the Monte Carlo method.

With the aim of identifying more clearly what really changed (or not) in the history of science in the 1940s and 1950s due to the computer, I will emphasize the continuities with older practices and develop a two-fold argument. Firstly, one can find a diversity of practices around ENIAC which tends to be ignored if one focuses only on the ENIAC itself as the originator of Monte Carlo simulation. Following from this, I claim, secondly, that there was no simulation around ENIAC. Not only is the term ‘simulation’ not used within that context, but the analysis also shows how ‘simulation’ is an effect of three interrelated sets of different practices around the machine: (1) the mathematics which the ENIAC users employed and developed, (2) the programs, (3) the physicality of the machine. I conclude that, in the context discussed, the most important shifts in practice are about rethinking existing computational methods. This was done in view of adapting them to the high-speed and programmability of the new machine. Simulation then is but one facet of this process of adaptation, singled out by posterity to be viewed as its principal aspect.

     

What’s in a name?

SomerecentsubmissiontoCARBONhaveindicatedatrendtogetcertain“buzz”wordsintothetitle .Themostcommonbeing“nano” ,andmore recently“fullerene like” .Inthelasteightmonthsover 35 %ofallpaperssubmittedtomehavenanointhetitle .WithrespecttotheformerIhavebeenp     

What is a surrogate marker for optimal dialysis?

To find a surrogate marker to obtain optimal dialysis delivery from the viewpoint of nutrition, 180 maintenance hemodialysis patients (109 males/71 females) were enrolled between October 1999 and June 2006 at our kidney center. In the 449 hemodialysis treatments, ultrapure dialysis solutions and high-flux synthetic membranes were utilized. Parameters were measured by Kt/V(urea) and postdialysis urea rebound, Kc (the cellular membrane clearance for urea), urea clear space (CS), %creatinine generation rate, %lean body mass, total body water, and so on. We examined the correlation between dialysis delivery and nutritional parameters: Kt/V(urea) and postdialysis urea rebound were found to be strongly and negatively correlated with nutritional parameters. However, Kc and CS have shown positive and strong correlations with nutritional parameters such as %creatinine generation rate, %lean body mass, and total body water as well. In addition, the age factor was correlated with Kt/V(urea) positively, and it influenced Kc and CS negatively. As a conventional dialysis parameter, Kt/V(urea) did not reflect nutrition, but Kc was found to improve nutrition due to the increase of the dialysis delivery. Therefore, Kc might be a reliable surrogate marker for optimal dialysis.