Is there an observable limit to Lorentz invariance at the Compton wavelength scale?

The possibility of a frame-induced violation of Lorentz invariance due to non-inertial spin-1/2 particle motion is explored in detail for muon decay while in orbit near the event horizon of a microscopic Kerr black hole. It is explicitly shown that kinematic and curvature contributions to the muon’s decay spectrum—in the absence of any unforeseen processes due to quantum gravity—lead to its stabilization at the muon’s Compton wavelength scale. This example is emblematic of the search for unambiguous indicators to critically assess current and future approaches to quantum gravity research.     

A device for X‐Ray elemental mapping using annular radioisotope source

An energy‐dispersive system is described for elemental mapping by X‐ray fluorescence spectrometry. The present study describes the design of an X‐ray fluorescence spectrometer and presents its performance in elemental mapping applications. The spectrometer is based on a new ring‐shaped collimator with a pinhole in the center of it and a ring‐shaped Am‐241 isotope mounted in the collimator as a source for excitation of X‐ray fluorescence. The photons were detected by high‐resolution Si (Li) detector coupled to a multi‐channel analyser and cooled by liquid nitrogen. In this study, we used two samples; one of them was made from pure elemental powders, and the second one was a piece of a stone and three types of maps were plotted. In the maps type one, the areas of the elements were shown with a single color. These maps only show the location of the elements in the sample. In the maps type two, the area of each element was shown with different colors because of the count (intensity) related to the area. In the third type of the maps for each element, depending on the elements' position on the sample, the counts were plotted in three dimensions. The areas with higher intensity have greater height, and areas with lower intensity have lower altitude. These two last types of maps provide information about the homogeneity or heterogeneity of the elemental distribution in the samples. The spectrometer can perform non‐destructive analyses of samples and objects in the air. Copyright © 2017 John Wiley & Sons, Ltd.     

Optimizing immersion media refractive index improves optical trapping by compensating spherical aberrations

The efficiency of an optical trap is limited by its axial strength. Light focused by oil-immersion objectives provides stronger traps but suffers from spherical aberrations, thus restricting the axial stability and working distance. By changing the refractive index of the immersion media we compensate spherical aberrations and measure axial trapping strengths at least twice as large as previously reported. Moreover, the spherical aberrations can be compensated at any desired depth. The improved trapping efficiency implies significantly less heating of the particles, thus diminishing previously published concerns about using gold nanoparticles as handles for optical manipulation.     

Molecular dynamics simulation of manipulation of metallic nanoclusters on stepped surfaces

Molecular dynamics simulations are carried out to investigate the manipulation of metallic clusters on stepped surfaces. Five surface forms are considered in the simulations. The system parts are made of pure transition metals and Sutton-Chen many-body potential is used as interatomic potential. The conditions which are subjected to change in the tests include: materials used for particles and substrate, and surface step conditions. In addition to qualitative observations, two criteria which represent the particle deformation and substrate abrasion are utilized as evaluation tools and are computed for each case. Simulation results show the effect of the aforementioned working conditions on the particle behavior as well as changes in the pushing forces. Obtaining this sort of knowledge is highly beneficial for further experiments in order to be able to plan the conditions and routines which guarantee better success in the manipulation process.     

On an open problem concerning total domination critical graphs

A graph G   with no isolated vertex is total domination vertex critical if for any vertex v$v$ of G   that is not adjacent to a vertex of degree one, the total domination number of G-v$G-v$ is less than the total domination number of G  . We call these graphs _γt${\gamma }_t$-critical. If such a graph G has total domination number k, we call it k  -_γt${\gamma }_t$-critical. We verify an open problem of k  -_γt${\gamma }_t$-critical graphs and obtain some results on the characterization of total domination critical graphs of order n=Δ(G)(_γt(G)-1)+1$n=\Delta (G)({\gamma }_t(G)-1)+1$.     

Some Progress on Total Bondage in Graphs

The total bondage number b _t (G) of a graph G with no isolated vertex is the cardinality of a smallest set of edges ${E^{\prime}\subseteq E(G)}$ for which (1) G?E′ has no isolated vertex, and (2) ${\gamma_{t}(G-E^{\prime})>\gamma_{t}(G)}$ . We improve some results on the total bondage number of a graph and give a constructive characterization of a certain class of trees achieving the upper bound on the total bondage number.     

Exploiting code division multiplexing with decentralized multiuser detection in the satellite multibeam forward link

In recent years, the need for increased satellite throughput has been tackled by extending the number of satellite beams thus allowing a higher spectrum reuse and peak throughput. However, the satellite antenna size and the number of simultaneous beams that can be generated onboard over a given coverage region cannot grow beyond certain limits because of payload accommodation constraints. The next step being pursued to increase the system throughput resides in extending the frequency reuse among the loaded beams and to mitigate the effects of the increased co‐channel interference through more advanced digital signal processing. This can be achieved in 2 different ways. The first one, which received a large attention in recent years, is to centrally mitigate the multibeam channel cross talk by exploiting precoding techniques at the gateway. The second approach, less investigated in the past, is to put in place decentralized multiuser detection (MUD) at the user terminal side. The precoding approach has the advantage of concentrating the extra processing complexity at the gateway, but it requires nonstandard payloads or accurate payload calibration techniques and periodic channel estimation reporting from the user terminal. Instead, the decentralized approach can operate in combination with existing payloads and does not require any terminal's periodic channel estimate reporting to the gateway. Only the signal‐to‐noise plus interference variations due to possible fading as for conventional adaptive coding and modulation shall be reported. One of the main barriers to the decentralized MUD approach so far was the demodulator complexity. Some simplified approach for conventional frequency/time division multiplexing schemes has been recently published, and its applicability to the forward link investigated. In this paper, we investigate the possible advantages deriving from the adoption of direct‐sequence code division multiplexing associated with affordable complexity of the MUD at the user terminal side. It is shown that the proposed MUD scheme can be practically implemented and provides sizeable advantages compared to current state‐of‐the‐art when the traffic is not evenly distributed among the beams, ie, when a subset of beams has a higher load than the others.     

$${\varvec{}}$$-Jorda homomorphisms ad pseudo $${\varvec{}}$$-Jorda homomorphisms o Baach algebras

Let \(n\in \mathbb {N}\), A and B be Banach algebras and let B be a right A-module. We say that a linear mapping \(\varphi :A\longrightarrow B\) is a pseudo n-Jordan homomorphism if there exists an element \(w\in A\) such that \(\varphi (a^nw)=\varphi (a)^n\cdot w\), for every \(a\in A\) and \(n\ge \) 2. In this paper, among other things, we show that under some conditions if a linear mapping \(\varphi \) is a (pseudo) n-Jordan homomorphism, then it is a (pseudo) \((n + 1)\)-Jordan homomorphism. Additionally, we investigate automatic continuity of surjective pseudo n-Jordan homomorphisms under some conditions.     

Modelling dependence structure with Archimedean copulas and applications to the iTraxx CDS index

In this paper we model the dependence structure between credit default swap (CDS) and jump risk using Archimedean copulas. The paper models and estimates the different relationships that can exist in different ranges of behaviour. It studies the bivariate distributions of CDS index spreads and the kurtosis of equity return distribution. To take into account nonlinear relationships and different structures of dependency, we employ three Archimedean copula functions: Gumbel, Clayton, and Frank. We adopt nonparametric estimation of copula parameters and we find an extreme co-movement of CDS and stock market conditions. In addition, tail dependence indicates the extreme co-movements and the potential for a simultaneous large loss in stock markets and a significant default risk. Ignoring the tail dependence would lead to underestimation of the default risk premium.