Geometric Loss Research Articles

Analysis of optical resonant cavity composed of nonparallel reflectors

We propose and numerically investigate a novel optical resonant cavity composed of nonparallel reflectors. The top reflector employs a ridge-shaped structure and consists of two flat mirrors, which are positioned symmetrically with the same inclined angle, it extends the interaction length between the reflectors and optical field. The total-energy density and optical field distribution are analyzed by means of the finite element method. One of the most important features of the cavity is that light beams can be confined in a smaller region drastically and the geometric loss of the cavity is reduced. Results indicate that, compared with the parallel F–P cavity with the same height, width, and material, this optical resonant cavity is characteristic of smaller linewidth, higher quality factor, and smaller mode volume, which can be useful for lasers, photodetectors, and displacement sensing.

Performance enhancement of hybrid diversity for M-ary modified pulse-position modulation and spatial modulation of MIMO-FSO systems under the atmospheric turbulence effects with geometric spreading

In this paper, we propose a novel model for hybrid spatial diversity of M-ary pulse position modulation (M-ary PPM) and spatial modulation (SM) with a multiple-input multiple-output (MIMO) links (i.e., optical receiver diversity) in a free-space optical (FSO) communication system under the atmospheric turbulence (AT) effects with geometric spreading (GS). In the proposed design, the spatial index modulator (SIM) and modified pulse position modulation (MPPM) schemes are combined to improve the system efficiency of the spatial diversity for the M-ary PPM modulated MIMO–FSO communication. In this work, we investigate and enhance the performance of the MIMO-FSO link using a digital pulse position modulation (DPPM) and on–off keying non-return-to-zero (OOK–NRZ). We propose a MIMO-based FSO link using spatial diversity and M-ary PPM modulation technique to compensate for the performance degradation due to geometric losses and atmospheric attenuation. Here, we have combined the N-SM with L-MPPM (N-SM/L-MPPM) and (M × N MIMO) to improve the system performance and provide high bandwidth and a higher throughput under the impact of the AT and GS. We analyze the GS impact on the performance of MIMO–FSO systems using SM over the Gamma–Gamma (GG) model. The performance is achieved by using the PPM technique, so the AT influences and fading are mitigated hence the ability to combat AT and the FSO link systems are enhanced sufficiently. Also, we improve the performance of the proposed link using a novel hybrid of SM/PPM and DPPM over GG to maximize the range and enhance the receiver sensitivity. Simulation results obtained for the bit-error-rate (BER) and average transmitted optical power for the DPPM and OOK modulation against various AT conditions are compared with the spatial diversity techniques and proved that both of the FSO systems based MIMO–SM/MPPM offers better performance in the receiver sensitivity and channel capacity. The obtained results show that the conjunction of the receiver diversity and SM/M-ary MPPM is a magnificent solution for mitigating the strong turbulence (ST) and GS effects. The proposed design provides an excellent optical signal-to-noise ratio (SNR) and high-sensitivity for the SIM/PPM-MIMO in the ST regime and GS. The numerical results report that the DPPM sensitivity improves about 10–11 dB at a distance of 2.5 km and the BER of 10−12 more than an equivalent OOK–NRZ modulation. The SIM/PPM-MIMO offers about 4 dB, 2 dB optical SNR improvements over without SIM/PPM-MIMO for the no turbulence and ST with GS for the FSO link, respectively. This work could be beneficial to the practical implementation of the hybrid spatial diversity for the SM/M-ary MPPM based MIMO-FSO links under the AT effects with GS.

Leveraging the Potential of BIM towards Sustainable Construction

The need to recognize the importance of sustainable construction is becoming a major concern. The innovative technologies around the construction industry can be of major help to achieve the aim of sustainable construction. There are various diverse sustainability rating frameworks around the world, everyone with the same aim of improving the performance of whole building to achieve the goals of creating a healthy built environment. Integration of data is key to sustainable construction which needs a shift from traditional methods of sharing information among various stakeholders. Nowadays, BIM is emerging as more dominant technology by progressively integrating more and more people of the AEC industry. However, the uninterrupted use of digital data information along the complete process sequence falls notably behind other industry sectors. For a successful construction project, an uninterrupted understanding and widespread exchange of information among these stakeholders is essential. Main role of BIM is to improve the collaboration and communication between various people and phases of construction by integration of exchange of information. BIM process, implemented successfully is able to improve the delivery of information in a project and reduce extra cost incurred due to design changes during subsequent construction phases. In this paper to achieve a sustainable BIM model, the capability to share the information using most popular open source, vendor neutral platform IFC, between two of the most accepted BIM software was investigated. Round trip tests were performed for the IFC models produced in two software and an evaluation is made in terms of geometric distortion, information loss and misrepresentation. Several issues were found in exchanging both object geometry information and other semantically significant data. Complete exchange of geometry was not observed in any of the exchanges. The reason for these imperfections is due to the fact that different software prefer to use methods to generate the information in their internal data schemas.

Impact of angular pointing error on BER performance of underwater optical wireless links.

Even in clear ocean water, underwater optical wireless communication (UOWC) is impaired not only by absorption and scattering, but also by oceanic turbulence and dynamic pointing errors which result in a fading channel, degrading the bit error rate (BER) performance. In this paper, for the first time, we quantify analytically the trade-off between geometric loss and misalignment in underwater scattering channels. A novel geometric loss model is developed which is used to compute the average BER in the presence of absorption and scattering over salinity-induced oceanic turbulence channels. Our findings suggest that UOWC systems are less sensitive to angular pointing errors due to jitter since scattering is able to alleviate such a fading effect at the expense of a higher attenuation due to geometric spread. Monte Carlo simulation results are further included to verify the developed BER expression which is valid over a wide range of signal-to-noise-ratio (SNR). Finally, the impact of inter-symbol interference (ISI) is also quantified by measuring the optical power penalty.

Sectorised base stations for FSO ground‐to‐train communications

Evolution and accessibility of smart-phones have led to a huge demand in network bandwidth. The ubiquitous use of smart-phones in high-speed trains poses a unique challenge in delivering high-speed internet service on board. This challenge can be overcome by employing free-space optics, an alternative to radio-frequency technology. Previous coverage models for ground–train communications employed single laser systems with a larger divergence angle to cover a larger distance. Larger divergence angles lead to larger geometric losses, which may result in a non-reliable communication link. This study proposes a sectorised multi-beam coverage model with a smaller divergence angle to reduce the impact of geometric losses in the system. This study also proposes two receiver (Rx) architectures for Rxs deployed on the train. Along with geometric losses, the atmospheric attenuation is taken into consideration for the FSO link. The performance of the ground–train communications system in terms of bit-error-rate is evaluated under weak turbulence conditions via numerical simulation.

Mixed geometric loss for bounding box regression in object detection

Predicting bounding box with higher intersection over union (IoU) is one of the most important issues in many computer vision tasks. The ln-norm loss and IoU-based loss are two conventional approaches to guide a training process in recent methods. However, the optimization direction of ln-norm loss is not exactly the same as maximizing the metric. In addition, IoU-based loss suffers from some inevitable disadvantages due to the direct addition of IoU. According to the shape, size, and position properties, we design a mixed geometric (MG) regression loss to increase the similarity and the overlapping area of two bounding boxes. The shape is described by the cosine similarity of diagonal vectors, the size is measured by the length or width of the boxes, and the location is calculated by the center positions of the boxes. Simulation experiments verify that the proposed MG loss can achieve competitive convergence speed and regression accuracy. By introducing the state-of-the-art models in object detection, experiments are carried out on a well-known benchmark dataset, and the results demonstrate the effectiveness of our method in object detection.

INCREASING OF RESOURCE OF SUPERCHARGERS' AND FANS' VEINS WITH WELDING METHODS

Influence of gas and dust stream's parameters on wear durability of protection elements (of veins and bearing disk) of fans and supercharges is analyzed. Data about wear pattern of the most charged details of labor devices, which are operated in conditions of thermal power and mining plants is given. The results of direct measurements of geometric dimensions' loss, the shape of blades and the bearing (central) disk were accounted until the moment of their replacement (renovation). Traditional measuring instruments and ultrasonic thickness gauge UT-31 were used. Beginning of wear with the smallest defects in the surface layer (irregularities, depressions, surface cracks, local bumps, etc.) is found. First of all, the inlet edge of the scapula on the side of the suction pipe is worn. The measurements of blade showed wear of the inlet edge to its complete destruction, blade decreased by 30 mm in length. In case of a two-layer structure, there is a «stripping» of base metal of the blade and further wear of the part is accelerated. The wear of the deposited layer up to 3 mm (25% of blade thickness) is critical for further operation. Considering the different mode of operation of the devices and the uneven nature of the wear, a differentiated approach is proposed when choosing the composition of the metal for hardening and facing of the most worn surfaces. As reserves for increasing of inter-repair periods, arc surfacing with adding of different carbide-forming agents (in unequal amounts by zones) and using of surfaced bimetallic sheets are named. Spherical granules of tungsten carbides instead of crushed particles and the working bimetal layer molded in composition as durable high-chromium cast iron are recommended for reinforcement.

AUTOMATIC ONTOLOGY GENERATION OF BIM AND GIS DATA

Abstract. Data represented in the form of geospatial context and detailed building information are prominently nurturing infrastructure development and smart city applications. Bringing open-formats from data acquisition level to information engineering accelerates geospatial technologies towards urban sustainability and knowledge-based systems. BIM and GIS technologies are known to excel in this domain. However, fundamental level differences lie among their data-formats, which developed integration methods to bridge the gap between these distinct domains. Several studies have conducted data, process, and application-level integration, considering the significance of collaboration among these information systems. Although integration methods have narrowed the gap of geometric dissimilarity, semantic inconsistency, and information loss yet add constraints towards achieving interoperability. Integration using semantic web technology is more flexible and enables process-level integration without changing data format and structure. However, due to its developing nature and complex BIM-GIS data-formats, most approaches adapted requires human intervention. This paper presents a method, named OGGD (Ontology Generation for Geospatial Data), that implements a formal method for automatic ontology generation from XSD documents using transformation patterns following three extensive processes; first, formalization of XSD elements and transformation patterns; the second process identifies corresponding patterns explicitly, and the last process generates ontology for XSD schema. XSD elements from open-standard data models of BIM and GIS, ifcXML and CityGML, are manipulated and transformed into a semantically rich OWL model. The ontology models created can be applicable for information-based integration systems that will nurture knowledge-discovery and urban applications.

Semantic Context Encoding for Accurate 3D Point Cloud Segmentation

Semantic context plays a significant role in image segmentation. However, few prior works have explored semantic contexts for 3D point cloud segmentation. In this paper, we propose a simple yet effective Point Context Encoding (PointCE) module to capture semantic contexts of a point cloud and adaptively highlight intermediate feature maps. We also introduce a Semantic Context Encoding loss (SCE-loss) to supervise the network to learn rich semantic context features. To avoid hyperparameter tuning and achieve better convergence performance, we further propose a geometric mean loss to integrate both SCE-loss and segmentation loss. Our PointCE module is general and lightweight, and can be integrated into any point cloud segmentation architecture to improve its segmentation performance with only marginal extra overheads. Experimental results on the ScanNet, S3DIS and Semantic3D datasets show that consistent and significant improvement can be achieved for several different networks by integrating our PointCE module.

Channel Modelling and Performance Limits of Vehicular Visible Light Communication Systems

Visible light communication (VLC) has been proposed as an alternative or complementary technology to radio frequency vehicular communications. Front and back vehicle lights can serve as wireless transmitters making VLC a natural vehicular connectivity solution. In this paper, we evaluate the performance limits of vehicular VLC systems. First, we use non-sequential ray tracing to obtain the channel impulse responses (CIRs) for vehicle-to-vehicle (V2V) link in various weather conditions. Based on these CIRs, we present a closed-form path loss expression which builds upon the summation of geometrical loss and attenuation loss and takes into account asymmetrical patterns of vehicle light sources and geometry of V2V transmission. The proposed expression is an explicit function of link distance, lateral shift between two vehicles, weather type (quantified by the extinction coefficient), transmitter beam divergence angle and receiver aperture diameter. Then, we utilize this expression to determine the maximum achievable link distance of V2V systems for clear, rainy and foggy weather conditions while ensuring a targeted bit error rate.

Sensitivity analysis of the artificial neural networks in a system for durability prediction of forging tools to forgings made of C45 steel

The article presents the results of a sensitivity analysis of artificial neural networks developed for a system which predicts the durability of forging tools used in the selected hot die forging process. The developed system makes it possible to calculate the geometric loss of the examined tool for the given values of its operating parameters (number of forgings, tool temperature at selected points, type of the applied protective layer, pressure and path of friction) and estimates the intensity of the occurrence of typical mechanisms of tool destruction, i.e. thermo-mechanical fatigue, mechanical wear, abrasive wear and plastic deformation. Nine neural networks operate in the developed system. Five of them determine the geometric loss of the material used for tools operating with protective layers, including a nitrided layer, a pad welded layer and three hybrid layers, i.e. AlCrTiSiN, Cr/CrN and Cr/AlCrTiN. Four networks make calculations determining the intensity of the occurrence of typical destructive mechanisms. The developed sensitivity analysis allows for each neural network to show which input parameters are most important and have the greatest impact on the explained variables. This is determined based on the network error analysis in the case of elimination of individual variables from the input data. The greater the network error calculated after rejecting an input variable relative to the error obtained for the network with all the input variables, the more sensitive the network to the lack of this variable. The best compliance was obtained for the first developed set of networks regarding the geometric loss of material, while the lowest compliance was obtained for the second developed set of networks regarding the applied protective layers, and in particular for plastic deformation and mechanical fatigue, probably due to the smallest size of these sets in the knowledge base. The obtained results of this analysis are important for the system operation, i.e. supporting the technologist’s decision in the selection of such process parameter values that will increase the die’s lifetime.

Performance Analysis of Free Space Optical Networks Using the Beta-Average Recursive Estimator

The present paper aims to investigate and analyze the performance of a point-to-point optical network under a free-space optical (FSO) communication system. Free-space optical communication is a sophisticated technique that has been employed as a channel model of optical wireless communication to transfer large amounts of data at high speeds. However, two important issues, that could affect the source of the FSO link, have been added. The first one is related to chromatic dispersion which is attributed to the chirping phenomenon of the optical signal; the second issue concerns the secondary jamming power that can be generated by some Radio Frequencies from base stations. It is important to note that the effects of atmospheric turbulence, misalignment fading, and atmospheric attenuation as well as geometric losses were also taken into account. The purpose of this research work is to overcome these effects, in order to increase the data transmission rate from 1.25 to 50 Gbps in the proposed system. Consequently, a very efficient solution is suggested to correct these problems and to make the FSO link more reliable using the Beta-Average Recursive Estimator. In addition, the numerical results obtained are presented for the purpose of validating our proposal through the evaluation of the performance of a transmission link in terms of the bit error rate and Q-factor. In the end, the resulting conclusions are listed, explained and discussed.

Optical losses and durability of flawed Fresnel lenses for concentrated photovoltaic application

Recycling optical devices and materials for solar concentrator devices is a relatively unstudied area but one which is likely to grow in importance as we progress towards an increasingly sustainable and minimum waste environment. As such, considerations into major optical flaws are required. Here, we have investigated the durability of a cracked Silicon on Glass (SOG) Fresnel lens incorporated as the primary optical component in a concentrated photovoltaic (CPV) application. Optical and electrical characterisations of the flawed glass have been conducted to show the effect on the performance. The optical characterisation has shown a drop of 3.2% in optical efficiency. As well, I-V and power curves of cracked and non-cracked Fresnel lens were compared to shows a drop of 3.2% in short circuit current (Isc) and power. The results have confirmed that the power loss is directly related to only the area of the primary optic flawed, which has been calculated through as a percentage of geometrical loss (a form of shadowing) which was estimated to be 2.7% of the concentrator area. From the results, we can confirm that although the performance has slightly declined for the significantly flawed Fresnel lens, there are no other detrimental optical effects. The durability of such optics still needs to be tested, but from these results, we recommend that similarly critically flawed optics can be utilised, likely in non-demanding singular CPV units where <5% loss is acceptable.

Analytical Channel Model and Link Design Optimization for Ground-to-HAP Free-Space Optical Communications

Integrating high altitude platforms (HAPs) and free space optical (FSO) communications is a promising solution to establish high data rate aerial links for the next generation wireless networks. However, practical limitations such as pointing errors and angle-of-arrival (AOA) fluctuations of the optical beam due to the orientation deviations of hovering HAPs make it challenging to implement HAP-based FSO links. For a ground-to-HAP FSO link, tractable, closed-form statistical channel models are derived in this article to simplify optimal design of such systems. The proposed models include the combined effects of atmospheric turbulence regimes (i.e., log-normal and gamma-gamma), pointing error induced geometrical loss, pointing jitter variance caused by beam wander, detector aperture size, beam-width, and AOA fluctuations of the received optical beam. The analytical expressions are corroborated by performing Monte--Carlo simulations. Furthermore, closed-form expressions for the outage probability of the considered link under different turbulence regimes are derived. Detailed analysis is carried out to optimize the transmitted laser beam and the field-of-view of the receiver for minimizing outage probability under different channel conditions. The obtained analytical results can be applied to finding the optimal parameter values and designing ground-to-HAP FSO links without resorting to time-consuming simulations.

Support Possibilities for 3D Scanning of Forging Tools with Deep and Slim Impressions for an Evaluation of Wear by Means of Replication Methods.

This article discusses the problems related to the use of non-contact 3D scanning techniques and their support by means of replication methods for the analysis of the geometrical changes in deep tool impressions used for the forward extrusion of valve-type elements assigned for motor truck engines. The 3D scanning method, despite its unquestionable advantages, also has certain limitations, such as scanning the inner surfaces of deep cavities. This is caused by the fact that the larger the angle between the reflected laser light and the normal direction to the measured surface, the larger the area covered for the analysis, yet at the same time, the higher the measurement error. The authors performed an analysis of the geometrical loss of the tools as well as the corresponding replication masses, together with a discussion of the results related to minimization of the measuring errors. For the analyzed tool, the maximum angle during direct scanning was 40 degrees, which unfortunately does not enable an analysis of the entire pattern, while for larger angles, it is necessary to make the measurement by indirect scanning, i.e., by replicating the cavity imprint of the tool. Therefore, for a given geometry, the reflection angle should be determined individually.

Statistical Modeling of the FSO Fronthaul Channel for UAV-Based Communications

In this paper, we investigate the statistics of the free space optics (FSO) communication channel between a hovering unmanned aerial vehicle (UAV) and a central unit. Two unique characteristics make UAV-based FSO systems significantly different from conventional FSO systems with static transceivers. First, for UAV-based FSO systems, the incident laser beam is not always orthogonal to the receiver lens plane. Second, both position and orientation of the UAV fluctuate over time due to dynamic wind load, inherent random air fluctuations in the atmosphere around the UAV, and internal vibrations of the UAV. On the contrary, for conventional FSO systems, the laser beam is always perpendicular to the receiver lens plane and the relative movement of the transceivers is limited. In this paper, we develop a novel channel model for UAV-based FSO systems by quantifying the corresponding geometric and misalignment losses (GML), while taking into account the non-orthogonality of the laser beam and the random fluctuations of the position and orientation of the UAV. In particular, for diverse weather conditions, we propose different fluctuation models for the position and orientation of the UAV and derive corresponding statistical models for the GML. We further analyze the performance of a UAV-based FSO link in terms of outage probability and ergodic rate and simplify the resulting analytical expressions for the high signal-to-noise ratio (SNR) regime. Finally, simulations validate the accuracy of the presented analysis and provide important insights for system design. For instance, we show that for a given variance of the fluctuations, the beam width should be properly adjusted to minimize the outage probability.

Learning the distribution of latent variables in paired comparison models with round-robin scheduling

Paired comparison data considered in this paper originate from the comparison of a large number $N$ of individuals in couples. The dataset is a collection of results of contests between two individuals when each of them has faced $n$ opponents, where $n\ll N$. Individuals are represented by independent and identically distributed random parameters characterizing their abilities. The paper studies the maximum likelihood estimator of the parameters distribution. The analysis relies on the construction of a graphical model encoding conditional dependencies of the observations which are the outcomes of the first $n$ contests each individual is involved in. This graphical model allows to prove geometric loss of memory properties and deduce the asymptotic behavior of the likelihood function. This paper sets the focus on graphical models obtained from round-robin scheduling of these contests. Following a classical construction in learning theory, the asymptotic likelihood is used to measure performance of the maximum likelihood estimator. Risk bounds for this estimator are finally obtained by sub-Gaussian deviation results for Markov chains applied to the graphical model.

Investigation of 3 dB Optical Intensity Spot Radius of Laser Beam under Scattering Underwater Channel.

An important step in the design of receiver aperture and optimal spacing of the diversity scheme for an underwater laser communication system is to accurately characterize the two-dimensional (2D) spatial distribution of laser beam intensity. In this paper, the 2D optical intensity distribution and 3 dB optical intensity spot radius (OISR) are investigated due to the dominating optical intensity of laser beam being within the 3 dB OISR. By utilizing the Henyey–Greenstein function to compute the scattering angles of photons, the effects of the scattering underwater optical channel and optical system parameters on 3 dB OISR are examined based on the Monte Carlo simulation method. We have shown for the first time that in the channel with a high density of scattering particles, the divergence angle of the laser source plays a negligible role in 3 dB OISR. This is an interesting phenomenon and important for optical communication as this clearly shows that the geometric loss is no longer important for the design of receiver aperture and optimal spacing of the diversity scheme for the underwater laser communication system in the highly scattering channel.

Analysis of stability catastrophe of confocal cavity

Optical cavity is a fundamental device of modern optics and has a wide range of applications in the fields of laser generation, nonlinear optical conversion, and optical sensors. A major aspect of the properties of optical cavity is the stability analysis. According to different geometric losses, these optical cavities can be divided into three types: stable cavity, critical cavity, and unstable cavity. The determination of the stability of the optical cavity is the basic problem of a classic system, but the research and analysis of this point have been much insufficient in the past. In this paper, by extending the definition domain of the inverse trigonometric function, the propagation matrices of the symmetric confocal cavity and the asymmetric confocal cavity are solved. The sudden change of stability with the change of geometric parameters is explained by algebraic analysis and optical ray topology.The mathematical analysis shows that the stability catastrophe of confocal cavity is due to the sudden change in the value of inverse cosine function at the critical point of the traditional domain of definition. From the perspective of geometric topology, we define the topological charge of the cavities according to the geometric propagation path of light in the cavity. Only the cavities with zero topological charge are found to be stable, and the change of topological charge is quantized, which explains the sudden change of confocal cavity stability. Finally, we build a coupled stable cavity consisting of two unstable cavities with the same parameters. The quality factors of the coupled stable cavity and the unstable cavity are analyzed by the finite difference time domain method, which further verifies the origin of the sudden change in the stability of the confocal cavity. We propose that the coupled unstable dual cavities with opposite topological charges are able to be stable, and we also find that there are new modes in the coupled cavities which are not found in the corresponding single cavity. These findings suggest a new method for controlling microcavity loss, which has a certain value for studying the new micro-nano lasers, on-chip nonlinear devices, and non-Hermitian optical sensors.

Un-VDNet: unsupervised network for visual odometry and depth estimation

Monocular visual odometry and depth estimation play an important role in augmented reality and robot applications. Recently, deep learning technologies have been widely used in these areas. However, most existing works utilize supervised learning, which requires large amounts of labeled data and assumes that the scene is static. We propose a framework, called Un-VDNet, based on unsupervised convolutional neural networks to predict camera ego-motion and depth maps from image sequences. The framework includes three subnetworks (PoseNet, DepthNet, and FlowNet) and learns temporal motion and spatial association information in an end-to-end network. We propose a pose-consistency loss to penalize errors about the translation and rotation drifts of the pose estimated from the PoseNet. Furthermore, a geometric consistency loss, between the structure flow and scene flow learned from the FlowNet, is proposed to deal with dynamic objects in the real-world scene, which is combined with spatial and temporal photometric consistency constraints. Extensive experiments on the KITTI and TUM datasets demonstrate that our proposed Un-VDNet outperforms the state-of-the-art methods for visual odometry and depth estimation in dealing with dynamic objects of outdoor and indoor scenes.