The physics of angular momentum radio

Wireless communications, radio astronomy and other radio science applications are predominantly implemented with techniques built on top of the electromagnetic linear momentum (Poynting vector) physical layer. As a supplement and/or alternative to this conventional approach, techniques rooted in the electromagnetic angular momentum physical layer have been advocated, and promising results from proof-of-concept radio communication experiments using angular momentum were recently published. This sparingly exploited physical observable describes the rotational (spinning and orbiting) physical properties of the electromagnetic fields and the rotational dynamics of the pertinent charge and current densities. In order to facilitate the exploitation of angular momentum techniques in real-world implementations, we present a systematic, comprehensive theoretical review of the fundamental physical properties of electromagnetic angular momentum observable. Starting from an overview that puts it into its physical context among the other Poincar\'e invariants of the electromagnetic field, we describe the multi-mode quantized character and other physical properties that sets electromagnetic angular momentum apart from the electromagnetic linear momentum. These properties allow, among other things, a more flexible and efficient utilization of the radio frequency spectrum. Implementation aspects are discussed and illustrated by examples based on analytic and numerical solutions.Comment: Fixed LaTeX rendering errors due to inconsistencies between arXiv's LaTeX machine and texlive in OpenSuSE 13.

Using bijective maps to improve free energy estimates

We derive a fluctuation theorem for generalized work distributions, related to bijective mappings of the phase spaces of two physical systems, and use it to derive a two-sided constraint maximum likelihood estimator of their free energy difference which uses samples from the equilibrium configurations of both systems. As an application, we evaluate the chemical potential of a dense Lennard-Jones fluid and study the construction and performance of suitable maps.Comment: 17 pages, 11 figure

Investigation of ConViT on COVID-19 Lung Image Classification and the Effects of Image Resolution and Number of Attention Heads

COVID-19 has been one of the popular foci in the research community since its first outbreak in China, 2019. Radiological patterns such as ground glass opacity (GGO) and consolidations are often found in CT scan images of moderate to severe COVID-19 patients. Therefore, a deep learning model can be trained to distinguish COVID-19 patients using their CT scan images. Convolutional Neural Networks (CNNs) has been a popular choice for this type of classification task. Another potential method is the use of vision transformer with convolution, resulting in Convolutional Vision Transformer (ConViT), to possibly produce on par performance using less computational resources. In this study, ConViT is applied to diagnose COVID-19 cases from lung CT scan images. Particularly, we investigated the relationship of the input image pixel resolutions and the number of attention heads used in ConViT and their effects on the model’s performance. Specifically, we used 512x512, 224x224 and 128x128 pixels resolution to train the model with 4 (tiny), 9 (small) and 16 (base) number of attention heads used. An open access dataset consisting  of 2282 COVID-19 CT images and 9776 Normal CT images from Iran is used in this study. By using 128x128 image pixels resolution, training using 16 attention heads, the ConViT model has achieved an accuracy of 98.01%, sensitivity of 90.83%, specificity of 99.69%, positive predictive value (PPV) of 95.58%, negative predictive value (NPV) of 97.89% and F1-score of 94.55%. The model has also achieved improved performance over other recent studies that used the same dataset. In conclusion, this study has shown that the ConViT model can play a meaningful role to complement RT-PCR test on COVID-19 close contacts and patients

Investigation of ConViT on COVID-19 Lung Image Classification and the Effects of Image Resolution and Number of Attention Heads

COVID-19 has been one of the popular foci in the research community since its first outbreak in China, 2019. Radiological patterns such as ground glass opacity (GGO) and consolidations are often found in CT scan images of moderate to severe COVID-19 patients. Therefore, a deep learning model can be trained to distinguish COVID-19 patients using their CT scan images. Convolutional Neural Networks (CNNs) has been a popular choice for this type of classification task. Another potential method is the use of vision transformer with convolution, resulting in Convolutional Vision Transformer (ConViT), to possibly produce on par performance using less computational resources. In this study, ConViT is applied to diagnose COVID-19 cases from lung CT scan images. Particularly, we investigated the relationship of the input image pixel resolutions and the number of attention heads used in ConViT and their effects on the model’s performance. Specifically, we used 512x512, 224x224 and 128x128 pixels resolution to train the model with 4 (tiny), 9 (small) and 16 (base) number of attention heads used. An open access dataset consisting  of 2282 COVID-19 CT images and 9776 Normal CT images from Iran is used in this study. By using 128x128 image pixels resolution, training using 16 attention heads, the ConViT model has achieved an accuracy of 98.01%, sensitivity of 90.83%, specificity of 99.69%, positive predictive value (PPV) of 95.58%, negative predictive value (NPV) of 97.89% and F1-score of 94.55%. The model has also achieved improved performance over other recent studies that used the same dataset. In conclusion, this study has shown that the ConViT model can play a meaningful role to complement RT-PCR test on COVID-19 close contacts and patients

Enhanced xanthan production process in shake flasks and pilot scale bioreactors using industrial semidefined medium

Xanthan gum, a heteropolysaccharide produced by Xanthomonas campasteris, is a widely used biopolymer in food industries. The production process is highly influenced by the type and concentration of the different carbon and nitrogen source as well as other medium components. Theaim of this work was to develop an economic industrial medium for industrial production. In shake flask level, the maximal production of xanthan of 19.9 gL-1 was achieved by excluding ammonium nitrate fromthe industrial medium and making new medium formulation composed of (sucrose, soybean meal, ammonium phosphate and magnesium sulphate). Further optimization in the production process was achieved by transferring the process to 16-L bioreactor and cultivation under controlled pH condition. The maximal volumetric and specific xanthan production [YP/X] obtained were 28 gL-1 and 11.06 g g-1, respectively. Thus, the semi-defined medium formulation developed in this work could be better and alternatively used for large scale production process for xanthan production when compared to other published media in respect to yield and cost.Key words: Xanthan gum, Xanthomonas campestris, batch culture, semi-defined medium, biopolymer

Occurrence of periodic Lam\'e functions at bifurcations in chaotic Hamiltonian systems

We investigate cascades of isochronous pitchfork bifurcations of straight-line librating orbits in some two-dimensional Hamiltonian systems with mixed phase space. We show that the new bifurcated orbits, which are responsible for the onset of chaos, are given analytically by the periodic solutions of the Lam\'e equation as classified in 1940 by Ince. In Hamiltonians with C_${2v}$ symmetry, they occur alternatingly as Lam\'e functions of period 2K and 4K, respectively, where 4K is the period of the Jacobi elliptic function appearing in the Lam\'e equation. We also show that the two pairs of orbits created at period-doubling bifurcations of touch-and-go type are given by two different linear combinations of algebraic Lam\'e functions with period 8K.Comment: LaTeX2e, 22 pages, 14 figures. Version 3: final form of paper, accepted by J. Phys. A. Changes in Table 2; new reference [25]; name of bifurcations "touch-and-go" replaced by "island-chain

Enhanced five-port ring circuit reflectometer for synthetic breast tissue dielectric determination

In this study,a Six-port Reflectometer (SPR) with dielectric probe sensor is used to predict relative dielectric,εr of normal and tumorous breast tissue in frequency range from 2.34GHz to 3.0GHz. Other than that,a superstrate with an exterior copper layer is overlaid on the surface of a primitive Five-port Ring Circuit (FPRC),which is also a denominated,enhanced superstrate FPRC. It is the main component of the SPR and is presented in this paper as well. The enhanced superstrate FPRC is capable of improving its operating bandwidth by 26% and shifting the operating centre frequency to a lower value without increasing circuit physical size. The detailed design and characteristics of the FPRC are described here. In addition,the enhanced superstrate FPRC is integrated into the SPR for one-port reflection coefficient measurement. The measurement using the SPR is benchmarked with Agilent’s E5071C Vector Network Analyzer (VNA) for one-port reflection coefficient. Maximum absolute mean error of the linear magnitude and phase measurements are recorded to be 0.03 and 5.50°,respectively. In addition,maximum absolute error of the predicted dielectric and loss factor are 1.77 and 0.61,respectively

Using nexus thinking to identify opportunities for mangrove management in the Klang Islands, Malaysia

Despite wide recognition of the multiple ecosystem services provided by mangroves, they continue to experience decline and degradation especially in the face of urbanization. Given the interplay between multiple resources and stakeholders in the fate of mangroves, mangrove management can be framed as a nexus challenge and nexus thinking used to identify potential solutions. Using the Klang Islands, Malaysia, as a case study site, this paper characterizes the mangrove nexus and stakeholders visions for the future to identify potential options for future management. Through a series of stakeholder workshops and focus group discussions conducted over two years results show that local communities can identify benefits from mangroves beyond the provisioning of goods and significant impacts to their lives from mangrove loss. While better protected and managed mangroves remained a central part of participants' visions for the islands, participants foresaw a limited future for fishing around the islands, preferring instead alternative livelihood opportunities such as eco-tourism. The network of influencers of the Klang Islands’ mangroves extends far beyond the local communities and many of these actors were part of the visions put forward. Stakeholders with a high interest in the mangroves typically have a low influence over their management and many high influence stakeholders (e.g. private sector actors) were missing from the engagement. Future nexus action should focus on integrating stakeholders and include deliberate and concerted engagement with high influence stakeholders while at the same time ensuring a platform for high interest/low influence groups. Fortifying existing plans to include mangroves more explicitly will also be essential. Lessons learnt from this study are highly relevant for coastal mangrove systems elsewhere in the Southeast Asian region

Utilization of photon orbital angular momentum in the low-frequency radio domain

We show numerically that vector antenna arrays can generate radio beams which exhibit spin and orbital angular momentum characteristics similar to those of helical Laguerre-Gauss laser beams in paraxial optics. For low frequencies (< 1 GHz), digital techniques can be used to coherently measure the instantaneous, local field vectors and to manipulate them in software. This opens up for new types of experiments that go beyond those currently possible to perform in optics, for information-rich radio physics applications such as radio astronomy, and for novel wireless communication concepts.Comment: 4 pages, 5 figures. Changed title, identical to the paper published in PR

Crystal structure and Hirshfeld surface analysis of (2E,20E)-3,30-(1,4-phenylene)bis[1-(2,4-difluorophenyl) prop-2-en-1-one]

The asymmetric unit of the title compound, C24H14F4O2, comprises of one and a half molecules; the half-molecule is completed by crystallographic inversion symmetry. In the crystal, molecules are linked into a three-dimensional network by C—H� � �F and C—H� � �O hydrogen bonds. Some of the C—H� � �F links are unusually short (< 2.20 A ° ). Hirshfeld surface analyses (dnorm surfaces and twodimensional fingerprint plots) for the title compound are presented and discussed