International Telecommunication Union Research Articles

Rain attenuation distribution for satellite microwave links application in Tanzania

<table width="741" border="1" cellspacing="0" cellpadding="0"><tbody><tr><td valign="top" width="484"><p>Rain rate and Rain Attenuation predictions are important in radio system operating at Ku and Ka bands as they affect telecommunication systems performance. To adequately estimate rain-induced attenuation and fading, the International Telecommunication Union (ITU) recommends use of rainfall data collected using 1-minute integration time. For Tanzania, no rainfall data with 1-minute integration time is available either through measurements or conversion from rainfall data with longer integration time. In this paper the rain attenuation is predicted for seven locations in the coastal area of Tanzania. The 1- minute rainfall rate is determined by Chebil’s model using long-term measurements from Tanzania Metrological Agency (TMA) collected for a period of forty years, results obtained are used to estimate rain attenuations. By using the International Telecommunication Union-Recommendation (ITU-R) model, rain attenuation is predicted at horizontal polarization at Ku and Ka band. The results show that Unguja has the highest average annual rainfall accumulation with rain attenuation as high as ~53.22dB for Ka band and ~15.14dB for Ku band making the difference of about 38.08 between the two frequency bands. On the other hand, Kibaha which has the lowest average annual rainfall accumulation along the coast has rain attenuation of ~47.27dB for Ka and ~13.41dB for Ku bands, making the difference of 33.86dB between the frequency bands. Results obtained from this study can be useful in designing earth-satellite microwave links in the coastal area of Tanzania.</p></td></tr></tbody></table>

Bibliography

Bibliography

A Novel Random Access Algorithm for Very High Frequency Data Exchange (VDE)

VHF Data Exchange System (VDES) is considered as an important component of the future maritime communication system by the International Maritime Organization (IMO). On the basis of the existing Automatic Identification System (AIS), VDES adds the other two higher capacity subsystems: Application Specific Message (ASM) and VHF Data Exchange (VDE). The Random Access Channel (RACH) of VDE was first introduced in the International Telecommunication Union (ITU) Recommendation M.2092-0. As the slot planning principle of RACH in VDE is by interval, which is significantly different from the continuous slot map for access algorithms in AIS, the existing slot access algorithms cannot meet the requirements of VDE. The simulation results show that the VDE slot map can reduce the normalized throughput of the existing algorithm by 39%. A novel random access algorithm called Adaptive Traffic Load Contention Resolution Diversity Slotted ALOHA (ATL-CRDSA) is proposed in this paper. The algorithm combines the load control strategy and contention resolution scheme to overcome the challenges of the new RACH of VDE. Simulation results show that ATL-CRDSA has remarkable improvement on RACH, making it very efficient and providing low latency of the packets. The insights gained from this study may be of assistance to the Media Access Control (MAC) layer design for upcoming versions of VDES standard.

Effects of dispersion on characterization of multi-wavelength Q-switched fiber laser

In this paper, a real-time switchable and reconfigurable multi-wavelength Q-switched fiber laser has been experimentally carried out, which is based on a real-time configurable filter (WaveShaper) and a section of unpumped erbium–ytterbium co-doped fiber (EYDF) as a saturable absorber (SA). The proposed multi-wavelength Q-switched laser has been demonstrated to generate different combination of wavelengths at 100 GHz and 200 GHz International Telecommunications Union (ITU) grids specifications. The WaveShaper not only acts as a multi-channel filter but also introduces wavelength-dependent loss (WDL) in the laser cavity. The WDL can effectively suppress the mode competition caused by homogeneous gain broadening of EDF. The attenuation at each wavelength is adjusted to equalize optical power of different channels. The effects of dispersion on the performance of multi-wavelength Q-switched fiber laser are investigated by introducing additional dispersion from WaveShaper. No significant wavelength drift was observed after monitoring of an hour, multi-wavelength Q-switched operation is clearly demonstrated with a good stability at room temperature.

Implementation of the Listen-Before-Talk Mode for SeaSonde High-Frequency Ocean Radars

The International Telecommunication Union (ITU) Resolution 612, in combination with Report ITU-R M2.234 (11/2011) and Recommendation ITU-R M.1874-1 (02/2013), regulates the use of the radiolocation services between 3 and 50 MHz to support high frequency oceanographic radar (HFR) operations. The operational frame for HFR systems include: band sharing capabilities, such as synchronization of the signal modulation; pulse shaping and multiple levels of filtering, to reduce out-of-band interferences; low radiated power; directional transmission antenna, to reduce emission over land. Resolution 612 also aims at reducing the use of spectral bands, either through the application of existing band-sharing capabilities, the reduction of the spectral leakage to neighboring frequency bands, or the development and implementation of listen-before-talk (LBT) capabilities. While the LBT mode is operational and commonly used at several phased-array HFR installations, the implementation to commercial direction-finding systems does not appear to be available yet. In this paper, a proof-of-concept is provided for the implementation of the LBT mode for commercial SeaSonde HFRs deployed in Australia, with potential for applications in other networks and installations elsewhere. Potential critical aspects for systems operated under this configuration are also pointed out. Both the receiver and the transmitter antennas may lose efficiency if the frequency offset from the resonant frequency or calibration pattern are too large. Radial resolution clearly degrades when a dynamical adaptation of the bandwidth is performed, which results in non-homogeneous spatial resolution and reduction of the quality of the data. A recommendation would be to perform the LBT-adapt scans after a full measurement cycle (1-h or 3-h, depending on the system configuration) is concluded. Mutual cross-interference from clock offsets between two HFR systems may bias the frequency scans when the site computers controlling data acquisitions are not properly time-synchronized.

5G is Real: Evaluating the Compliance of the 3GPP 5G New Radio System With the ITU IMT-2020 Requirements

The 3rd Generation Partnership Project (3GPP) submitted the 5G New Radio (NR) system specifications to International Telecommunication Union (ITU) as a candidate fifth generation (5G) mobile communication system (formally denoted as IMT-2020 systems). As part of the submission, 3GPP provided a self-evaluation for the compliance of 5G NR systems with the ITU defined IMT-2020 performance requirements. This paper considers the defined 5G use case families, Ultra Reliable Low-Latency Communication (URLLC), massive Machine Type Communication (mMTC) and enhanced Mobile Broadband (eMBB), and provides an independent evaluation of the compliance of the 3GPP 5G NR self-evaluation simulations with the IMT-2020 performance requirements for connection density, reliability, and spectral efficiency for future mobile broadband and emerging IoT applications. Independent evaluation indeed shows the compliance of the 3GPP 5G NR system with the ITU IMT-2020 performance requirements for all parameters evaluated by simulations.

Information and communication technology penetration level as an impetus for economic growth and development in Africa

Africa is an emerging, frontier economy that is gradually becoming a gold miner of the fourth industrial revolution (industry 4.0) to achieve speedy economic growth and development. Through the transmission channel of technological drive that relies on the penetration of modern communication means (information and communication technology [I.C.T.]). It is on this basis that this study examines the performance of I.C.T., economic growth and development in Africa. In capturing I.C.T. performance; penetration of I.C.T. indicators – mobile telephone, fixed-line telephone and Internet access subscriptions are used as measurements and reduced to a single index through principal components analysis (P.C.A.). Economic growth and development is measured with the real gross domestic product and the human development index (H.D.I.), respectively. The data for this study were sourced from the international telecommunication union (I.T.U.) and world development indicators from the World Bank databases. The results show that mobile telecommunication is growing faster than other telecommunication indicators and I.C.T. penetration has positive impacts on economic growth and development in Africa. The study, therefore, recommends that simultaneous investments are required in the fixed-line and Internet access telecommunications in Africa in order to fully tap into the optimal impetus of I.C.T. penetration for economic growth and development in Africa.

Inversion of vertical rainfall field based on earth-space links

The accurate measurement of rain intensity and its distribution in vertical direction can not only help to understand the process of rainfall development, but also play an important role in human life such as agriculture, weather forecasting, water resources management, and natural disaster warning. According to the analysis of the geometric structure of earth-space link and propagation model of electromagnetic wave in atmosphere, in this paper we propose a method to reconstruct two-dimensional(2D) vertical rainfall field by using earth-space links. Firstly, the measured data of micro rain radar (MRR) from Nanjing are used to generate three real vertical rainfall fields which are marked as I, II and III respectively. Secondly, based on the analysis of the earth-space link’s geometry and the effect of signal attenuation from other factors such as scintillation, atmosphere gas and cloud, the vertical rainfall field inversion model is established. According to the power-law relationship between rain intensity and rain attenuation, which is given by International Telecommunication Union (ITU), the simultaneous algebraic reconstruction technique (SART) is used to inverse the vertical rainfall field. Then, one earth station which can receive a 17 GHz signal from satellite is employed to detect the vertical rainfall field. However, the simulation results show that it is difficult for one earth station to achieve the inversion of rainfall field, and that the correlation coefficients between rainfall fields and inversed fields are 0.556, 0.504 and 0.364 respectively. Based on the result, two earth stations are jointly used. In this simulation, the result shows that after 500 iterations the correlation coefficients all increase above 0.98, and the average biases between rainfall field I, II, III and their inversed fields are 0.122, 0.159 and 0.537 mm/h, respectively. Meanwhile, the Euclidean distances decrease to 0.246, 0.235 and 0.812 mm/h, and the relative errors of entropy are both less than 2%. It can be seen from the inversion fields that the vertical distribution of rain rate is close to that of the real field, which suggests that the method proposed in this paper can basically achieve the inversion of vertical rainfall field by using earth-space links. In addition, with the combined detection of three earth stations the accuracy of the inversion results is significantly improved. The correlation coefficients are all close to 1 and the mean deviations are all on the order of 10<sup>–12</sup> mm/h, indicating that the 2D vertical rainfall fields are accurately reconstructed. In the near future, the satellite constellation system will be globally deployed, which can promote the applications of our method in areas, such as plateaus, mountains and islands, where there exist no traditional observation data, serving as a supplement to existing precipitation measurements.

Evaluation of Ka-Band Rain Attenuation for Satellite Communication in Tropical Regions Through a Measurement of Multiple Antenna Sizes

The Ka-band is modifying the mode of legacy communication towards versatile satellite-oriented systems with the beam-spot capability and a high-throughput architecture to provide twice the capability of classic Fixed Satellite Service (FSS) satellites, thus significantly reducing the cost per bit. Given this background, the contribution of precipitation rate and Ka-band downpour attenuation are expected to improve statistical models for effect prediction. The International Telecommunication Union (ITU) and local researchers are working tirelessly to determine the best prediction model for tropical climates. However, persistent and continuous efforts are required because currently available models do not perform well. The current prediction model for large datasets exhibits a certain deviation. Direct beacon measurement has been compared with an available prediction model that analyses rain effects in tropical regions. Theoretically, the size of the antenna and its gain influence the performance of the receiving signal. Size and availability are two factors which cause degradation and outage in the receiving signal. The majority of extant studies focus on a single antenna with a diameter lesser than 2.4m. Theoretically, antennas with a smaller diameter possess a smaller margin in comparison with antennas with larger diameters. This condition could affect the prediction model when the high attenuation causes a rapid outage in a small antenna and lead to the unavailability of measurement results. To study such effects and provide a good recommendation, the current work measures the beacon attenuation data at two locations, namely, Bukit Jalil (Kuala Lumpur) and Cyberjaya (Selangor). The locations are approximately 15 km apart and have antennas from 0.65m to 31.1m in sizes. Analyses using an available prediction model revealed that ITU-R P.618 provides the lowest RMS value of 14.37 with regards to rainfall rate on two selected samples in Malaysia. High-accuracy prediction can be achieved through the contribution of this study, and comparative data can be obtained for future research. This study is an encouraging step towards a highly comprehensive and accurate prediction of tropospheric impairments in Ka-band satellite communications in the tropical region.

An Analysis of the Challenges and Benefits of Digital Migration in Zambia

Digitization is the current trend in Television broadcasting, both in Zambia and the world over. The International Telecommunication Union (ITU), set 2015 as the year for the entire broadcasting stations in the world to go digital in order to have better signal quality and increase in the capacity of broadcast transmission networks by improving spectrum efficiency. Despite these and many other advantages that come with digital migration, Zambia is yet to realize the full benefits of digital migration implementation. It’s against this background that the study was conducted to assess the challenges of digital migration process and its benefits in Zambia. The emphasis was on assessing the television digital migration implementation process; examine the challenges of switching from analogue to digital technology and its benefits. To this effect, a quantitative research design was used on a sample of 300 stakeholders who had direct influence on the process to determine their views. The data collected was analysed using Statistical Package for Social Sciences (SPSS) to categorise the challenges of the migration process and its benefits. The results established that lack of awareness by the public was a major challenge was encountered. In addition, inadequate infrastructure for digital migration coupled with inadequate funding towards the hindered the process of migration. However, the study also established that the country has benefited from migrating from analog to digital broadcasting. Notable ones include; quality of transmission, improved content delivery, and ability of the viewers to view more than one TV channel at once thereby giving them a better viewing pleasure among other benefits. In view of the challenges and benefits of the digital migration to the country, the study recommends that deliberate policies should be put in place to ensure that the infrastructure needed for the digital migration are readily available and that Government should create public awareness with regards to the importance of the digital migration process to allow for more public participation.

Optimal Mode Decision Method for Interframe Prediction in H.264/AVC

Studies show that encoding technologies in H.264/AVC, including prediction and conversion, are essential technologies. However, these technologies are more complicated than the MPEG-4, which is a standard method and widely adopted worldwide. Therefore, the amount of calculation in H.264/AVC is significantly up-regulated compared to that of the MPEG-4. In the present study, it is intended to simplify the computational expenses in the international standard compression coding system H.264/AVC for moving images. Inter prediction refers to the most feasible compression technology, taking up to 60% of the entire encoding. In this regard, prediction error and motion vector information are proposed to simplify the computation of inter predictive coding technology. In the initial frame, motion compensation is performed in all target modes and then basic information is collected and analyzed. After the initial frame, motion compensation is performed only in the middle 8×8 modes, and the basic information amount shifts. In order to evaluate the effectiveness of the proposed method and assess the motion image compression coding, four types of motion images, defined by the international telecommunication union (ITU), are employed. Based on the obtained results, it is concluded that the developed method is capable of simplifying the calculation, while it is slightly affected by the inferior image quality and the amount of information.

LDPC-Coded Modulation Performance Analysis and System Design

In this work, the low-density parity-check (LDPC)-coded modulation scheme which has been selected for inclusion in the next generation of International Telecommunication Union (ITU) broadband standard is investigated. The multi-level mapping of this scheme offers excellent performance along with a straightforward modulation which is separable into simple one-dimensional schemes. A subset of modulated bit positions are protected by the LDPC code, while the remaining positions benefit from improved Euclidean distance through assignment to distinct constellation regions. To date, there has been a lack of analytical treatment of the scheme. This is problematic given the number of tunable scheme and code parameters, necessitating time-consuming Monte Carlo simulation. This motivates the novel analytical work of this article, which derives overall error-rate and threshold performances through considering separately the effects of the channel on the coded and uncoded bits. First, new closed-form expressions are derived for the hard-decision performance of the bit mapping of the multi-level modulation scheme, for both coded and uncoded bits. Extrinsic information transfer (EXIT) analysis is then applied to the coded bits in the scheme. The derived theoretical performance of the uncoded bit positions is used in combination with the derived EXIT threshold to provide for the first time for this modulation scheme a method to evaluate analytically whether a designed system will offer capacity-approaching performance. Following this, an approximation to the capacity curve for the coded modulation scheme is produced, again based on the derived analytical performance. Finally, through the relationship between mutual information and error rate performance for error control codes, the derived analytical expressions are used to produce a semi-analytical finite-length performance predictor, whereby error rate results for a given code on the binary input additive white Gaussian noise (AWGN) channel can be mapped to the coded modulation scheme under consideration for any coded system parameters.

Online LSTM-Based Channel Estimation for HF MIMO SC-FDE System

The long distance high frequency (HF) communication suffers from time varying multipath fading. Multiple-Input Multiple-Output (MIMO) and Single-Carrier Frequency Domain Equalization (SC-FDE) have been introduced to HF communication system to combat fading. Because accurate channel estimation is essential for system operation, an architecture of signal flow chart has been designed for the HF MIMO SC-FDE system. In the architecture, an online Long Short-Term Memory (LSTM) estimator is proposed. Different from the channel responses time series created by the LSTM training and prediction loop, a corrected channel responses that are obtained through the received data symbols and the restored transmitting data symbols make up the channel responses time series. In order to evaluate the performance of channel estimators, a simulation system has been built. The uncorrelated and correlated channels are simulated referring to International Telecommunication Union (ITU)-R F.1487 standard and Kronecker model. The simulation results demonstrate that the online LSTM estimator outperforms Least Square (LS) and Recursive Least Square (RLS) estimators in terms of Bits Error Rate (BER) and Mean Square Error (MSE). The online LSTM estimator is capable of tracking the time varying HF MIMO channels. It has potentiality in actual long distance HF communication.

Influence of impulsive noise from lifts on orthogonal frequency‐division multiplexing digital radio mondiale signals

Wireless communications are constantly growing with the aim of providing solutions in complex scenarios, such as industrial environments and indoor locations, where impulsive noise sources interfere with the desired signal. Orthogonal frequency-division multiplexing (OFDM) is the most widely used technology, robust against Gaussian noise but sensitive to impulsive noise. To ensure better system performance, it is necessary to the study the impulsive noise and its effects. This work responds to the International Telecommunication Union (ITU), which in ITU-R 214 6/3 question asks for new updated noise measurements to study the systems performance. On the one hand, the study provides novel results of the impulse noise parameters from lifts and, on the other hand, analyses the influence of the impulsive noise originated from lifts at 18 MHz on OFDM digital radio mondiale (DRM) signals. Some radio noise patterns have been measured when lifts are moving up and down. The Gaussian and the impulsive components of these measurements have been computed. The influence of noise patterns in the reception of DRM-OFDM audio signals has been tested with different configuration parameters. The results provided in this report prove that OFDM signals tested are significantly degraded in the vicinity of lifts.

ПРОГРАММНЫЙ КОМПЛЕКС МОДЕЛИРОВАНИЯ ПАКЕТНЫХ РАДИОСЕТЕЙ КВ-ДИАПАЗОНА

It is noted that the complexity and constant variability of the ionosphere structure, the presence of many factors affecting the propagation of radio waves in such an environment, as well as the complex topology of communication networks lead to the need the computer modeling of data transmission in HF-band networks. The existing models of representation of ionospheric processes and digital radio channels are described. It is shown that to solve the problems of designing a radio data transmission network, complex modeling is necessary, taking into account the network topology, signal propagation losses in the radio channel, noise level, type of digital modulation, and radio forecast of communication conditions. In this paper, we consider a modeling complex for packet radio networks of HF-band data transmission with changing communication conditions. The complex consists of a set of interacting models implemented in the Matlab software environment. The software model for predicting communication conditions complies with ITU-R recommendation P. 533–13 of the International Telecommunication Union (ITU). The description of the model for the "Point-to-point" and "Area" modes is given and the results of its application for calculating extended radio lines are shown. The initial data and system parameters of the model are described. A model of the HF-band digital radio channel is presented. The communications System Toolbox package, which is part of the Matlab software environment, is used for this modeling. The model's input and output data are described. A model of Ionospheric Wave Frequency Dispatcher service of the radio network has been developed. This model is intended for building a wave schedule for stable operation of HF radio lines in the network. The rules for building a two-frequency and multi-frequency wave schedule are described. A scheme for modeling the operation of a packet radio network under changing communication conditions is proposed. The complex allows you to evaluate the probabilistic and temporal characteristics of radio lines and zonal radio coverage depending on geographical coordinates, time, month, solar activity and selected system parameters for a period of up to one year. Examples of using the modeling complex are given. The purpose of this work is to formulate the problem of simulation of HF radio networks under changing communication conditions.

Morocco e-Readiness Assessment: University Contribution

The main purpose of this study is to explore the critical issues that impede an effective implementation of information communication technology (ICT) as related to higher education (HE) in Morocco. An e-readiness survey based on Harvard e-readiness assessment framework is administered in order to check the role of university in getting Morocco e-ready. First, a diagnosis is done at the level of preparedness of Moroccan institutions in networked areas of access, society, economy and policy. The data was collected from the annual reports of Moroccan Telecommunications regulations agency (ANRT), reports from the International Telecommunication Union (ITU), Global Information Technology Report (NRI), quantitative and qualitative surveys from previous research studies, and statistical websites. The findings reveal that Morocco has, apart from networked economy and local digital content, a fairly advanced e-readiness status in other indicators in the model of Harvard Centre of International Development. Ironically, such findings show that it is the Moroccan university that needs to catch up with society.

Design of a Broadband Coplanar Waveguide-Fed Antenna Incorporating Organic Solar Cells with 100% Insolation for Ku Band Satellite Communication.

A broadband coplanar waveguide (CPW)-fed monopole antenna based on conventional CPW-fed integration with an organic solar cell (OSC) of 100% insolation is suggested for Ku band satellite communication. The proposed configuration was designed to allow for 100% insolation of the OSC, thereby improving the performance of the antenna. The device structure was fabricated using a Leiterplatten-Kopierfrasen (LPKF) prototyping Printed circuit board (PCB) machine, while a vector network analyzer was utilized to measure the return loss. The simulated results demonstrated that the proposed antenna was able to cover an interesting operating frequency band from 11.7 to 12.22 GHz, which is in compliance with the International Telecommunication Union (ITU). Consequently, a 3 GHz broadband in the Ku band was achieved, along with an enhancement in the realized gain of about 6.30 dB. The simulation and experimental results showed good agreement, whereby the proposed structure could be specifically useful for fixed-satellite-services (FSS) operating over the frequency range from the 11.7 to 12.22 GHz (downlink) band.

ВЛИЯНИЕ СЕЗОННЫХ ВАРИАЦИЙ ПАРАМЕТРОВ ГРУНТА НА ЧУВСТВИТЕЛЬНОСТЬ ЭЛЕМЕНТА АКТИВНОЙ ФАЗИРОВАННОЙ АНТЕННОЙ РЕШЕТКИ РАДИОТЕЛЕСКОПА ГУРТ

ВЛИЯНИЕ СЕЗОННЫХ ВАРИАЦИЙ ПАРАМЕТРОВ ГРУНТА НА ЧУВСТВИТЕЛЬНОСТЬ ЭЛЕМЕНТА АКТИВНОЙ ФАЗИРОВАННОЙ АНТЕННОЙ РЕШЕТКИ РАДИОТЕЛЕСКОПА ГУРТ

Cybersecurity in the Making – Policy and Law: a Case Study of Georgia

Summary The given article is an evaluation of the implementation and development of Georgia’s cybersecurity policy, and its influence on Georgia’s global cybersecurity index. The study covers the period from 2008 to 2018. In 2008 Georgia became one of the first victims of hybrid warfare. During the August 2008 Russo-Georgian war, Georgian government websites were attacked by hackers affiliated with Russia. In the given period, cybersecurity was not the priority direction for Georgia, therefore government portals were easy targets for cybercriminals and the government couldn’t prevent the cyberattacks. After 2008, the government decided to develop a state cybersecurity policy. In 2012 the country ratified the Council of Europe’s cybersecurity convention. At the same time, the “Law of Georgia on Information Security” which had become a basic document of the cybersecurity state policy implementation, had been adopted. The document was followed by a cybersecurity strategy. During the following years, based on cybersecurity strategy document, Georgia implemented 2 action plans and defined the relevant state agencies responsible for “cyber safety” of the country. As a result of the reforms, in 2017, according to the International Telecommunication Union (ITU) Cybersecurity Global Index, Georgia has been ranked among the top ten countries. The given article is a chronological description of a Georgian cyberpolicy and cybercapabilities evolution. It includes cases of organized cybercrime carried out against the state and examples of the development of Georgian cybersecurity policy which was reflected on the global international cybersecurity index of the country.

Role of Nanotechnology in Lossless Video Compression Coding

High-Efficiency Video Coding (HEVC) is a standard that has been developed by a collaboration of the International Telecommunication Union (ITU) with Moving Picture Experts Group of International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). The standard, by and large, is achieving substantial spatial versatility and enhanced video compression. HEVC is a spatial coding method for video that reduces the size and number of images in it, allowing for great versatility. This allows for new benchmark for creating high-quality video encoders, as well as high-quality video streams while retaining lower bit rates. This article outlines the most recent video compression model identified as the H.26x family, including its most recent standard, H.265, also known as HEVC. In this work, we also propose the possibility of using nanotechnology to increase the efficiency of video compression process with very little loss. We also studied the possibility of using Spherical Piezo Acoustic Transducers instead of the traditional Context-based Adaptive Binary Arithmetic Coding. Finally, a nano-scale transducer was fabricated with a lossless infinite plate and a lossless waveguide, which has the ability to resist fracture due to a low von Mises stress along its surface.