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We build and test a single-photon detector based on a Si avalanche photodiode Excelitas 30902SH thermoelectrically cooled to -100 deg. C. Our detector has dark count rate below 1 Hz, 500 um diameter photosensitive area, photon detection efficiency around 50%, afterpulsing less than 0.35%, and timing jitter under 1 ns. These characteristics make it suitable for long-distance free-space quantum communication links, which we briefly discuss. We also report an improved method that we call long-time afterpulsing analysis, used to determine and visualise long trap lifetimes at different temperatures., Comment: 10 pages, 9 figures, 1 table

A generalization of Stokesian dynamics is formulated to describe hydrodynamic interactions between two spheres in a viscous fluid. The analysis quantifies transient mutual interactions in terms of frequency-dependent friction coefficients of both spheres as well as their temporally varying mobility response to an impulsive force. The analysis also contributes to work on many-body unsteady Brownian motions.

Optical Wireless Communications (OWCs) can play vital role in providing communication in healthcare infrastructure’s, where contagious patients are admitted or treated as well as other patients are coming without any side effects as of radio frequency communication. In this paper, we propose high-speed cost-efficient free space optical (FSO) system for transmission of information (20 Gbps) inside healthcare premises comprising of number of buildings by integrating mode division multiplexing (MDM) scheme. The MDM scheme uses Laguerre Gaussian (LG) 00 and 01 modes whereas a simple On off Key (OOK) encoding scheme is employed for the proposed MDM-FSO system. The reported results show the efficient transmission of 20 Gbps data over 27 km of FSO link under clear atmospheric condition. Moreover, the proposed MDM-FSO link is evaluated under the impact of different fog conditions—low, medium and heavy.

E.G. Bessonov suggested the time integrated strength of electric field $\int_{-\infty}^{\infty}E(r,t)dt=S_E(r)$ as a parameter to classify electromagnetic (EM) waves. Since then, this parameter has been studied and used in many works on microwave and laser physics, especially when it comes to unipolar, bipolar and few cycle EM pulses. In this paper, it is shown that $S_E(r)=0$ is an identity for a wide class of free space pulses of finite total energy. This property can be useful in various applications of few cycle radiation and as a benchmark in EM and QED computations.

Medium-range terrestrial free-space quantum key distribution systems enable widespread secure networked communications in dense urban environments, where it would be infeasible to install a large number of short optical fibre links. Such networks need to perform over a wide range of conditions and their design has to balance key rate maximisation versus robust key generation over the greatest range of circumstances. Practicalities, such as manufacturability and deployment, further constrain the design space. Here, we examine challenges in translating experiment into engineering reality and identify efficient BB84 weak coherent pulse-decoy state protocol parameter regimes suitable for medium-range QKD systems considering likely system performance and environmental conditions.

We demonstrate a free-space transmission with a direct electrical modulation in a quantum cascade laser emitting in one of the transparency windows of the atmosphere, near $8.1\ \mu \mathrm{m}$ . The advantages of the presented work are a room-temperature setup, real-time high-speed operation and low-power consumption.

In this work, a free-space optical (FSO) communication system with the integration of mode division multiplexing and circular polarization shift keying (CpolSK) is proposed at 2 × 40 Gbps using LG00 and LG01 modes. Effects of diverse weather conditions such as clear weather, light rain, moderate rain, heavy rain, thin fog, thick fog, and heavy fog are studied on system performance. Further, a detailed comparison of CpolSK and polarization shift keying (PolSK) is performed at different FSO lengths in terms of log bit error rate. For implementation, analysis, and comparison, Optiwave Optisystem software is used and results show that CpolSK covers 100 km link distance and PolSK limits to 90 km only. Also, LG00 mode performs better than LG01 mode under all weather instabilities in the proposed system.

Hybrid wavelength-division-multiplexing (WDM) and free space optical (FSO) access networks are getting great attention due to numerous advantages. In this work, hybrid WDM-FSO system is demonstrated for 55 km at capacity of 5 × 10 Gbit/s using compressed spectrum return to zero (CSRZ) WDM-FSO in downstream and nonreturn to zero (NRZ) in upstream for demonstrating transmitter diversity which inturn decrease the interchannel interference. For the suppression of Rayleigh backscattering (RB) interferometric beat noise, bidirectional cyclic multiplexer is employed. Cyclic multiplexer provide λ 1 to λ 5 wavelengths for optical line terminal (OLT) to ONU transmission and λ 2 to λ 6 for ONU to OLT transmission. Insertion losses of each component are considered and in the end, power budget is also calculated. Results revealed that FSO length of 780–1050 m are obtained using various WDM-FSO downstream signals and their power budget, redundant budget, maximum distance, and insertion losses also calculated.

The ultra-high accuracy indoor and outdoor positioning is fundamental for a variety of applications such as industrial automation, Internet of Things and structure monitoring. Approaches based on optical methods, ultrasound and computer vision areoften suffer from limited coverage areas, obstruction by objects and high computing load. While the GNSS and conventionalradar-like radio frequency (RF) methods can suffer from insufficient accuracy and are not feasible for many scenarios. Now weachieve an inverse GPS microwave positioning system based on ultra-stable frequency synchronization in free space andcarrier phase difference principle to surpass the limitation of current methods. The stability of frequency synchronization link isbetter than 10−13/s . The distance resolution retrieved from phase information is 25 micrometres and the Mean Squred Error(MSE) of three-dimensional positioning is 16 micrometres. An ultra-high accuracy positioning system with large coverage area,compatibility and versatility can potentially be achieved gearing to extensive needs.

Autonomous driving demands the most reliable perception and navigation technologies. These systems should consider both the other agents in the road and the limitations of the on-board sensors. Knowing sensor limitations in real time allows not only to predict the movement of the other agents but also to robustly identify the free space in the road. This paper presents a novel approach that adapts the control of an autonomous vehicle to the real road circumstances in specifically challenging scenarios, i.e., roundabouts. The proposal provides a visibility map that helps the system to calculate collision-free trajectories and to adapt the control techniques to the traffic demands, selecting among comfortable or more ambitious configurations. Tests performed in real traffic have successfully assessed the suitability of the proposed solution.

[ES] Las comunicaciones ópticas inalámbricas (OWC) constituyen una tecnología muy prometedora para el desarrollo de futuras comunicaciones inalámbricas. De hecho, ha despertado un interés creciente entre los investigadores y varias empresas de todo el mundo trabajan actualmente en el desarrollo de redes inalámbricas de muy alta velocidad. Las comunidades científica e industrial consideran la OWC como una tecnología complementaria en sus diversas formas: comunicaciones ópticas en el espacio libre (FSO), comunicaciones de luz visible (VLC) o fidelidad de la luz (Li-Fi). El espectro óptico ha sido considerado durante muchos años como una gran oportunidad para las comunicaciones inalámbricas, especialmente debido a la saturación del espectro de radiofrecuencia (RF). Esta disertación trata del uso de fuentes de banda ancha en sistemas de transmisión de luz visible (VLC), así como en sistemas de transmisión en el espectro infrarrojo por fibra óptica. En el trabajo de investigación realizado se pueden distinguir tres partes: En la primera parte, se considera el estudio y la simulación de componentes de Diodos Emisores de Luz (LED) con el software WIEN2k centrándose en las propiedades ópticas y eléctricas de los elementos II-VI. La segunda parte trata del diseño, la implementación y las pruebas de diferentes prototipos de comunicación VLC para la transmisión analógica y digital en modo simplex y semidúplex. Hemos demostrado un sistema OWC empleando una fuente de banda ancha (LED) para la transmisión no sólo de datos, sino también para la transmisión inalámbrica de energía. Además, se aborda el problema de la sincronización y la detección del nivel "1" o "0" de un bit en los sistemas de comunicación inalámbrica óptica implementados que surge como consecuencia de la atenuación de la luz a lo largo de la distancia y al problema de la pérdida de línea de visión (NLOS) entre el emisor y el receptor. Para hacer frente a este problema, se ha proporcionado un protocolo de comunicación que garantiza la transmisión fiable de datos digitales con un algoritmo de detección de nivel de bits adaptativo y se ha demostrado su eficacia mediante la transmisión de textos e imágenes. Además, esta tesis aporta una solución para la implementación de transmisores multiplexados en redes con división de longitud de onda (WDM) para formatos de modulación con multiplexación por división de frecuencia ortogonal (OFDM) basados en el uso de fuentes de banda ancha en el espectro infrarrojo para redes de fibra bidireccionales centralizadas. A pesar de las limitaciones impuestas por la dispersión cromática en el uso de este tipo de fuentes ópticas, la inclusión de ciertas estructuras antes de la detección permite la transmisión de señales OFDM en enlaces ópticos. En este trabajo se ha demostrado experimentalmente la reutilización de portadoras, la asignación dinámica de ancho de banda y la transmisión de señales OFDM multibanda mediante el uso de fuentes ópticas de banda ancha en redes WDM. Los principales resultados obtenidos en cada parte de esta tesis doctoral muestran los procedimientos de estudio, la eficacia de las soluciones propuestas y las limitaciones encontradas., [CA] Les comunicacions òptiques sense fils (OWC) constitueixen una tecnologia molt prometedora per al desenvolupament de futures comunicacions sense fils. De fet, ha despertat un interés creixent entre els investigadors i diverses empreses de tot el món treballen actualment en el desenvolupament de xarxes sense fils de molt alta velocitat. Les comunitats científica i industrial consideren la OWC com una tecnologia complementària en les seues diverses formes: comunicacions òptiques en l'espai lliure (FSO), comunicacions de llum visible (VLC) o fidelitat de la llum (Li-Fi). L'espectre òptic ha sigut considerat durant molts anys com una gran oportunitat per a les comunicacions sense fils, especialment a causa de la saturació de l'espectre de radiofreqüència (RF). Aquesta dissertació tracta de l'ús de fonts de banda ampla en sistemes de transmissió de llum visible (VLC), així com en sistemes de transmissió en l'espectre infraroig per fibra òptica. En el treball de recerca realitzat es poden distingir tres parts: ¿ En la primera part, es considera l'estudi i la simulació de components de Díodes Emissors de Llum (LED) amb el software WIEN2k centrant-se en les propietats òptiques i elèctriques dels elements II-VI. ¿ La segona part tracta del disseny, la implementació i les proves de diferents prototips de comunicació VLC per a la transmissió analògica i digital de manera simplex i semidúplex. Hem demostrat un sistema OWC emprant una font de banda ampla (LED) per a la transmissió no sols de dades, sinó també per a la transmissió sense fil d'energia. A més, s'aborda el problema de la sincronització i la detecció del nivell "1" o "0" d'un bit en els sistemes de comunicació sense fil òptica implementats, que sorgeix a conseqüència de l'atenuació de la llum al llarg de la distància i al problema de la pèrdua de línia de visió (NLOS) entre l'emissor i el receptor. Per a fer front a aquest problema, s'ha proporcionat un protocol de comunicació que garanteix la transmissió fiable de dades digitals amb un algorisme de detecció de nivell de bits adaptatiu i s'ha demostrat la seua eficàcia mitjançant la transmissió de textos i imatges. ¿ A més, aquesta tesi aporta una solució per a la implementació de transmissors multiplexats en xarxes amb divisió de longitud d'ona (WDM) per a formats de modulació amb multiplexació per divisió de freqüència ortogonal (OFDM) basats en l'ús de fonts de banda ampla en l'espectre infraroig per a xarxes de fibra bidireccionals centralitzades. Malgrat les limitacions imposades per la dispersió cromàtica en l'ús d'aquest tipus de fonts òptiques, la inclusió d'unes certes estructures abans de la detecció permet la transmissió de senyals OFDM en enllaços òptics. En aquest treball s'ha demostrat experimentalment la reutilització de portadores, l'assignació dinàmica d'amplada de banda i la transmissió de senyals OFDM multibanda mitjançant l'ús de fonts òptiques de banda ampla en xarxes WDM. Els principals resultats obtinguts en cada part d'aquesta tesi doctoral mostren els procediments d'estudi, l'eficàcia de les solucions proposades i les limitacions trobades., [EN] Optical wireless communication (OWC) is a very promising technology for future wireless communications developments. It has attracted increasing interest from researchers and several companies around the world are currently working on the development of very high-speed wireless networks. The scientific and industrial communities believe that OWC will be a complementary technology in its various forms: Free Space Optical communications (FSO), Visible Light Communications (VLC), Light Fidelity (Li-Fi). In fact, the optical spectrum has been considered for many years as a great opportunity for wireless communications especially due to the saturation of the radio frequency (RF) spectrum. This dissertation deals with the use of broadband sources in visible light transmission systems (VLC) as well as fiber optic systems. To carry out the research, three parts can be distinguished: In the first part, we consider the study and simulation of Light Emitting Diode (LED) components with the WIEN2k software by focusing on the optical and electrical properties of elements II-VI. The second part deals with the design, implementation and testing of different VLC communication prototypes for analog and digital transmission in simplex and half-duplex mode. We have demonstrated that an OWC system using a broadband source (i.e. an LED) can be used not only for data transmission, but also for wireless power transmission. Moreover, the synchronization problem and the detection of level "1" or "0" of a bit often arise in the optical wireless communication systems. This is a result of the attenuation nature of the light over the distance and the problem of Non Line-Of-Sight (NLOS) between the emitter and the receiver. To deal with this problem, a communication protocol ensuring reliable digital data transmission with an adaptive bit level detection algorithm has been provided and its effectiveness has been demonstrated by the transmission of texts and images. In addition, this thesis provides a solution for the implementation of wavelength division multiplexed - orthogonal frequency division multiplexed (WDM-OFDM) transmitters based on the use of broadband sources in the infrared spectrum for centralized bidirectional fiber networks. Despite the chromatic dispersion that avoids the use of this type of optical sources, the inclusion of certain structures before detection allows the transmission of OFDM signals in optical links. Carrier reuse, dynamic bandwidth allocation and multiband OFDM signals transmission will be experimentally demonstrated by using optical broadband sources in WDM networks. The main results obtained during this thesis work demonstrate the study procedures, for each part, the effectiveness of the proposed solutions as well as the constraints encountered.

Despite the prevalence of gender-based theories of feminism and women language after 19 th century, several female scholars emerged from the Sangam era and sowed the seeds of this idea. The lists of the female poets are Avvaiyar, Perunkopendu, Andal, Karaikalammaiyar and present women language poets. With the changing times and the voices of various feminist rebellions, the social texture that is limited to women has not only changed, but the plight of women has increased on a daily basis. In particular, the definitions of women in the two different contexts of home and work are still unchanged. Although women are projected to have created a free space for education and economic quality, there are still women who accept subjugation as on unwritten rule. This paper is a study of women language verse, which has recorded this constant dehumanization as a weapon of language and provoking social conscience as feminism.

The three articles in this special section review modern developments in interconnects and packaging for frequencies above 100 GHz. In the last several years, useful systems operating at such frequencies have become feasible because of the cost reductions brought about by semiconductor device development, especially in silicon. But, for useable systems, there must also be advances in the packaging of such devices and in the means of coupling signals from the package to the transport medium. The medium of interest is free space for imaging or dielectric waveguides for interconnect.

This paper studies the design and performance analysis of relay-assisted satellite free-space optics (FSO) quantum key distribution (QKD) systems for secure vehicular networks. High-altitude platforms (HAPs) equipped with optical amplify-and-forward nodes are used as relay stations. Secrecy performances in terms of quantum bit error rate and ergodic secret-key rate are analytically investigated under the effects of transceiver misalignment, receiver's velocity variation, receiver noises, and atmospheric turbulence conditions. Based on the analyzed results, the design criteria for the legitimate user are determined so that the security of the considered system could be guaranteed.

The trade-off between more user bandwidth and quality of service requirements introduces unprecedented challenges to the next generation smart optical networks. In this regard, the use of optical performance monitoring (OPM) and modulation format identification (MFI) techniques becomes a common need to enable the development of next-generation autonomous optical networks, with ultra-low latency and self-adaptability. Recently, machine learning (ML)-based techniques have emerged as a vital solution to many challenging aspects of OPM and MFI in terms of reliability, quality, and implementation efficiency. This article surveys ML-based OPM and MFI techniques proposed in the literature. First, we address the key advantages of employing ML algorithms in optical networks. Then, we review the main optical impairments and modulation formats being monitored and classified, respectively, using ML algorithms. Additionally, we discuss the current status of optical networks in terms of MFI and OPM. This includes standards, monitoring parameters, and the available commercial products with their limitations. Second, we provide a comprehensive review of the available ML-based techniques for MFI, OPM, and joint MFI/OPM, describing their performance, advantages, and limitations. Third, we give an overview of the exiting ML-based OPM and MFI techniques for the emerging optical networks such as the new fiber-based networks that use future space division multiplexing techniques (e.g., few-mode fiber), the hybrid radio-over-fiber networks, and the free space optical networks. Finally, we discuss the open issues, potential future research directions, and recommendations for the potential implementation of ML-based OPM and MFI techniques. Some lessons learned are presented after each section throughout the paper to help the reader identifying the gaps, weaknesses, and strengths in this field.

Küresel köy olarak nitelenen günümüzde farklı tecrübe tarzlarının veya söylemlerin çok sık şekilde yüzleşildiği bir dünya insanları kuşatmaktadır. Bu durum insan bilincinin ahlaki olanı nasıl anlamlandıracağı sorununu ortaya çıkarmaktadır. Zira hızla dönüşen küresel dünyada insanlar arası ilişkinin ahlaki boyutunu tartışabileceğimiz “en iyi”ye dair ortak eleştirel alan giderek kaybolmaktadır. Bu makalede ahlaki bilince dair evrensel ve tarihsel perspektif, kartezyen ve hermenötik gibi zıt bağlamlar içinde analiz edilmekte, “tarihi” boyutun ahlaki bilince dair eleştirel alanın oluşumuna nasıl katkı sunduğu irdelenmektedir. Bu analizin amacı küresel dünyada birbirinden gittikçe soyutlanan fakat birbirine daha sık maruz kalan insani iliş-kilere dair eleştirel ve özgür alanın nasıl anlamlandırıldığını soruşturmaktır. Bu incelemede evrensellik düşüncesinin aksine hermenötik düşüncenin mevcut pratik dünyanın “tarihi” vasfını dikkate alarak ahlaki bilince dair eleştirel ve özgür alanı mümkün gördüğüne dikkat çekilmektedir. Dolayısıyla insanların mevcut tecrübelerini ve bu tecrübeye şekil veren dini, gelenek-sel, kültürel söylemlerini dikkate alarak yorum geliştiren hermenötik perspektifin, “en iyi” ekseninde sürekli şekilde sorgulanıp zenginleştirilen ahla-ki bir bilincin geliştirilmesine katkıda bulunabileceği dile getirilmektedir., In today's world, which is described as a global village, in which different styles of experience or discourses are often confronted surrounds people. This fact confronts human consciousness with the question of how to make sense of the moral. Because in the rapidly transforming global world, the common critical area for “the best” to discuss the moral dimension of the interpersonal relationship is gradually disappearing. In this article, the universal and historical perspective of moral consciousness is analyzed in opposite contexts such as cartesian and hermeneutics and how the “histo-rical” dimension contributes to the development of the critical field of mo-ral consciousness is examined. The aim of this analysis is to investigate how the meaning of the critical and free space of human relationships, which are increasingly isolated from each other in the global world, but more often exposed to each other, is understood. In this study, it is pointed out that, contrary to the notion of universality, hermeneutic thought sees the critical and free space of moral consciousness by considering the historical character of the present practical world. Therefore, it is stated that hermeneutic perspective, which develop comments by considering the exis-ting experiences of people and the religious, traditional and cultural disco-urses that shape this experience, can contribute to the development of a moral consciousness which is constantly questioned and enriched on the “best” axis.

IoT networks have some important characteristics. Some key requirements of the IoT are low device cost, low deployment cost, high energy efficiency, high security and privacy, and support for a large number of devices. The LED-based OWC systems have all the great features required to support the IoT. The key technologies currently used for IoT connectivity are Zigbee, Bluetooth Low Energy (BLE), and WiFi. ZigBee is a low-cost, low-power, wireless mesh network standard that has been widely used for IoT applications. The Internet of Things (IoT) based on the tactile internet will also be an essential part of the 5G communication systems. Accordingly, 5G wireless networks will face numerous challenges in supporting the extensive verities of heterogeneous networks and in satisfying the mentioned service-quality-related parameters. Optical wireless communication (OWC), along with many other wireless technologies, is a promising candidate for serving the demands of 5G communication systems.

In this work, we developed an adaptive optical correction module and polarization control module to compensate for the effects of atmospheric turbulence on long-distance free-space coherent optical...

This article intended to reveal the description of pre-Islamic women as far as the Qur’an is taken. This was done to provide a foundation of insight that how true Islam greatly elevates the dignity and status of women. Because the discussion in this paper links a theme that is in the Koran, the method used refers to the framework of the interpretation method maudhu’i (thematic). Operationally, in this article verses about pre-Islamic women was inventoried and then organized into several subthemes which all refer to the main theme, namely pre-Islamic women. The results of the discussion by thematizing the verse shows that: first, Islam highly upholds women and gives equal status to men. Second, Islam also gives women adequate and free space to play a role in the public sphere. Third, related to the situation of women in the pre-Islamic era to the extent recorded by the Koran shows that they were oppressed at that time. A number of their rights are not granted or reduced by the ignorance system which is in favor of only men. The culmination of the cruel behavior of the ignorance system towards women is their habit of being surly when their wives give birth to baby girls, even at the extreme level they are buried alive because they are considered disgrace.

In this high-speed transit era, the prediction of sound radiation from a moving and vibrating object is an important research topic. A typical example is a high-speed train wheel that not only moves fast in the railway direction but, due to wheel/rail interaction, also vibrates at high frequency, generating a complex sound field. By making use of sound spectra generated by moving harmonic compact sources, three-dimensional (3D) boundary integral equations are established in this paper for sound radiation from a harmonically vibrating body moving uniformly in a free space. The 3D boundary integral equations are reduced to 2D ones for a special case in which the body is axisymmetric and moves in its axial direction. The 2D boundary element method is applied to solve the 2D boundary integral equations and to produce results for a pulsating and moving sphere. Results show that the moving speed of the pulsating sphere has a significant effect on the generated sound field. This means that, for sounds radiated from a high-speed train wheel vibro-acoustically, the motion of the wheel has to be taken into account.

In this work, poly(sodium styrene sulfonate) brushes have been employed as a precursor to prepare thermosensitive strong polyelectrolyte brushes (SPBs) through a counterion exchange strategy. The substitution of hydrophilic Na+ counterions by hydrophobic tetraalkylphosphonium counterions leads to a thermoresponsivity of the SPBs. The thermosensitive properties including hydration, stiffness, and surface water wettability of the SPBs can be modulated by the type of the tetraalkylphosphonium counterions. Nevertheless, the wet thickness of the SPBs with tetraalkylphosphonium counterions does not exhibit an obvious temperature dependency due to the high steric barrier in the crowded environment of SPBs generated by the large tetraalkylphosphonium counterions. The mixtures of small Na+ counterions and large tetraalkylphosphonium counterions are employed to realize the thermosensitive wet thickness without sacrificing other thermoresponsive properties of the SPBs because the mixed counterions can bring both a certain hydrophobicity and some free space to the brushes. This work opens up the opportunities available for the use of counterions to tune the thermosensitivity of SPBs.

Free Space Optics (FSO) is a wireless optical communication technology which depends on propagation of optical beam through air. FSO communication system provides secure communication link, cost-effective solution and license-free operation. In this paper, the FSO communication link has been analysed in turbulent atmosphere using homotopy perturbation method (HPM). We have designed a FSO system operating at an optical wavelength of 850 nm with a signal power of 4 dBm having a link range of 2 km between transmitter and receiver unit. It has been observed that in atmospheric turbulence high performance FSO link is achieved by increasing the aperture diameter of receiver telescope.

Free space optical (FSO) communication systems are gaining high popularity from the last decade due to its various advantages such as no license spectrum, low-cost implementation etc. In this work, 160 Gbps data is transmitted over 8 km FSO link by adopting alternate mark inversion (AMI), wavelength division multiplexing (WDM) and polarization division multiplexing (PDM) schemes. The results are reported in terms of Q factor, bit error rate, signal to noise ratio, total received power and eye diagrams.

Based on the analytical expression of the spatiotemporal collinear self-decelerating Airy Elegant–Laguerre–Gaussian (AiELG) wave packets by solving the (3+1)D free-space Schrodinger equatio...

The fundamental problem of propagation invariant Bessel beams is that they are not square-integrable in the transverse direction, and are therefore associated with an infinite power flux. H...

Much scholarly energy has been invested in understanding how rhetors covertly invoke racial bias and how “color-blind” rhetoric produces unintended racist effects. Less scholarly attention ...

Background: Subcutaneous echogenicity grade (SEG) and subcutaneous echo-free space (SEFS) grade allow semiquantitation of nonspecific subcutaneous tissue inflammation and fluid accumulatio...

This article presents the design, manufacturing, and testing of a transmitting active discrete lens antenna demonstrator in the Ka band. These antennas permit generating multibeam coverage using only a single main aperture and exhibit excellent scanning capabilities and a large-frequency bandwidth. Because the beamforming is mainly achieved in the free space, the complexity and cost of the antenna grows marginally with the number of beams and radiating elements. For these characteristics, active discrete lens antennas are a promising alternative to more conventional antenna solutions that are based on phased arrays and reflectors antennas, especially for Ka-band and higher frequencies where the dimensions become smaller.

A novel high-speed coherent modulating retro-reflector (MRR) is presented and experimentally demonstrated for free-space optical (FSO) communications by using an in-phase quadrature (IQ) modulator with quadrature phase-shift keying (QPSK) signals to break the conventional speed limitation. The transmission performance is tested in a turbulence-tunable atmospheric cell. The received sensitivity is measured to be 14.7 dB PPB, and the power penalty is 2.0 dB for 20 Gbit/s single-channel QPSK signal at the BER of 0.01 when the temperature difference is 250 °C. Moreover, this MRR scheme is compatible to wavelength-division multiplexing (WDM) technology, and a 60 Gbit/s WDM MRR is demonstrated using three channels with only about 0.6 dB degradation.

Olive is one of the important products in many parts of the world. A series of olive fruits is harvested for oral consumption, and the other harvested for extraction of oil. The quality of the olive is somewhat important for the consumer in terms of stiffness. In this study, the effect of cold plasma technology on the stiffness of olive fruit was investigated in different preservation conditions. The olives were treated under atmospheric and low-pressure plasma at 1, 3, and 5 min. To determine the stiffness of olive fruit, a rapture energy factor was used. Olive samples were evaluated after the third day and sixth day. The results showed that the packed olive showed very little rigidity change compared to the fresh fruit. Plasma also had a significant impact on the amount of olive fruit stiffness (kept in free space) and the results showed that olive which was exposed to plasma in vacuum condition for 5 min had the least rigidity among other samples.

Jiménez and Maroto [Phys. Rev. D 83, 023514 (2011)] predicted free-space, longitudinal electrodynamic waves in curved space-time, if the Lorenz condition is relaxed. A general-relativistic extension of Woodside’s electrodynamics [Am. J. Phys. 77, 438 (2009)] includes a dynamical, scalar field in both the potential- and electric/magnetic-field formulations without mixing the two. We formulate a longitudinal-wave theory, eliminating curvature polarization, magnetization density, and scalar field in favor of the electric/magnetic fields and the metric tensor. We obtain a wave equation for the longitudinal electric field for a spatially flat, expanding universe with a scale factor. This work is important, because: (i) the scalar- and longitudinal-fields do not cancel, as in classical quantum electrodynamics; and (ii) this new approach provides a first-principles path to an extended quantum theory that includes acceleration and gravity.

Using a simple three-dimensional printed element, i.e., ridge prism, we generate a new diffraction-free structured terahertz (THz) beam: THz sheet in free space. Numerical and experimental results show that the output beam from such an element has an one-dimensional invariant transverse profile. Note that the THz sheet generated by a ridge prism is always close to the element, which limits its application. Thus, we design a lens group system to deliver the THz sheet to a distance, as well as increase the diffraction-free length of the THz sheet six times. Finally, we experimentally demonstrate that this structured beam can be used to extend the depth of fields of a THz transmission imaging system.

An implementation of a computational geometry algorithm is robust if the combinatorial output is correct for every input. Robustness is achieved by ensuring that the predicates in the algorithm are evaluated correctly. A predicate is the sign of an algebraic expression whose variables are input parameters. The hardest case is detecting degenerate predicates where the value of the expression equals zero. We encounter this case in constructing the free space of a polyhedron that rotates around a fixed axis and translates freely relative to a stationary polyhedron. Each predicate involved in the construction is expressible as the sign of a univariate polynomial [Formula: see text] evaluated at a zero [Formula: see text] of a univariate polynomial [Formula: see text], where the coefficients of [Formula: see text] and [Formula: see text] are polynomials in the coordinates of the polyhedron vertices. A predicate is degenerate when [Formula: see text] is a zero of a common factor of [Formula: see text] and [Formula: see text]. We present an efficient degeneracy detection algorithm based on a one-time factoring of all the univariate polynomials over the ring of multivariate polynomials in the vertex coordinates. Our algorithm is 3500 times faster than the standard algorithm based on greatest common divisor computation. It reduces the share of degeneracy detection in our free space computations from 90% to 0.5% of the running time.

It is still a great challenge to prepare novel CuO-based crystal materials with low-dimensional magnetic structures. A new copper oxyborate, namely, PbCu6B6O16 was synthesized and structurally characterized for the first time. Its structure features a novel 3D framework which can be considered as building from the layers of [Cu6B6O16]2−∞ interconnected by corner or edge sharing of CuO4、BO3、B2O5、and B3O7 groups, where Pb2+ cations are located in the free space within the layer. It is unexpected that the compound contains fundamental building block (FBB) formed by three different borate anionic groups, including BO3 triangle, and condensed branched BO3 triangles (B2O5 and B3O7). In particular, according to our survey, the branched B3O7 group is unprecedented. Our work provides useful information on the design and search for novel low dimensional copper borates, and also helps to strengthen the understanding of the investigation of borate structures.

Aerial vehicles (AVs) have challenges in terms of realizing low complexity and wide coverage area wireless communications architectures, especially for crowded or high density groups of AVs with state-of-the-art free space optical (FSO) and radio frequency (RF) based system designs. FSO architectures generally target point-to-point high gain directional links while requiring strict acquisition and tracking due to the narrow beam width of laser transmitters with challenges of vibration, turbulence, misalignment, atmospheric absorption, scattering, and fading. In this article, a novel multiuser free space optical system design of modulation and coding denoted by space-track modulation and coding (STMC) is proposed for crowded downlink communications. STMC does not require high accuracy tracking and costly system components by utilizing large beam divergence angles, more transmitter units with smaller aperture sizes and weights, and large spatial regions to receive modulated data at AV tracks. In addition, the spatio-optical wireless caching problem is introduced for AV networks while defining STMC problem information theoretically. STMC combines track based multiuser modulation and coding, with geographical and positional data for low data rate broadcasting applications with wide area coverage. Numerical simulations provide tens of bit/s data rates for thousands of kilometers of coverage area while simultaneously serving a significantly larger number of AVs. Finally, future works and open issues are discussed. The novel modulation and coding mechanisms are promising future applications for both high altitude AVs and low altitude drone networks with low complexity hardware for multiuser low data rate communications.

Electrides are ionic crystals in which the electrons prefer to occupy free space, serving as anions. Because the electrons prefer to be in the pockets, channels, or layers to the atomic orbitals around the nuclei, it has been challenging to find electrides with partially filled d-shell transition metals, since an unoccupied d-shell provides an energetically favorable location for the electrons to occupy. We recently predicted the existence of electrides with partially filled d-shells using high-throughput computational screening. Here, we provide experimental support using X-ray absorption spectroscopy and X-ray and neutron diffraction to show that Sr3CrN3 is indeed an electride despite its partial d-shell configuration. Our findings indicate that Sr3CrN3 is the first known electride with a partially filled d-shell transition metal, in agreement with theory, which significantly broadens the criteria for the search for new electride materials.