In grinding, the convective heat transfer coefficient (CHTC) determines the heat transfer ratio and the grinding temperature, and it indirectly identifies the surface integrity. No effective method ...for calculating CHTC is available for aerosol cooling, and it still lacks the measuring equipment that accords with the actual condition of aerosol cooling. On this basis, the atomization mechanism of nanofluid aerosol cooling (NAC) was studied, the influence of jet parameters on the spray boundary was revealed, and the probability density of droplet size in the grinding zone was statistically analyzed. A theoretical model for the CHTC of NAC was developed on the basis of the analysis of the heat transfer coefficient of a single nanofluid droplet. Furthermore, a new method for measuring the CHTC of aerosol cooling was proposed, and the measuring equipment was designed and built. The measurement error of the measurement system was calculated, and results showed that the measurement error of the new measuring equipment is 0.044 (10−2 W/mm2·K). Nanofluids were prepared by using medical nanoparticles and normal saline, and the CHTC was calculated and measured. The results showed that the theoretical model error is 7.26%, which verifies the correctness of the theoretical model.
This article identifies problems arising from implementing the procedure for determining the breaking forces of hexagonal gabion meshed nets according to standard number EN 10223–3:2013. The primary ...focus was directed towards the construction and conditions of use of an originally developed instrument that allows gabion meshed net samples to be mounted in the grips of a conventional strength testing machine. This paper presents a device prototype adapted to the conditions of mounting samples (for strength testing) in the jaws of a Zwick Z100 strength testing machine. An instrument designed for the purpose of scientific research, expert opinions and direct determination of the mechanical properties of hexagonal gabion meshed nets compliant with all the requirements of the aforementioned standard.
●Measurement problems of load bearing capacity of hexagonal gabion meshed nets.●Reference to the procedure for testing nets according to the standard EN 10223-3:2013.●A prototype of installed fixture in a conventional strength testing machine.●Method of installation of gabion meshed net samples.●A universal instrument that facilitates measure strength of hexagonal meshed nets.
Recently, two different L-band digital aeronautical communication systems (L-DACS), i.e., L-DACS1 and L-DACS2, have been proposed as two future communication infrastructure candidates for ...air-to-ground (AG) communication systems, with L-DACS1 selected as the best candidate. In this paper, we describe a filter bank multicarrier (FBMC)-based communication system and show its advantages over the L-DACS systems. We provide simulation results for all three communication systems to fairly compare their power spectral density, peak-to-average power ratio (PAPR), and bit error ratio (BER) performance. We show that in a measurement-based AG communication channel model, FBMC has better performance (and spectral containment) than the L-DACS schemes, and this is particularly true in the presence of actual interfering signals from distance measuring equipment (DME). Simulation results show that FBMC can substantially reduce the out-of-band power and can suppress DME interference by at least 19.5 dB, due to its well-localized subcarrier prototype filters. FBMC can also increase throughput and spectral efficiency by reducing the number of guard-band subcarriers and removal of the cyclic prefix, postfix, as well as windowing techniques used in L-DACS1. These results show that an FBMC-based communication system can be an appealing candidate for future AG communication systems.
•Availability area analysis of distance measuring equipment global network.•Service volume is estimated based on path loss model.•Distance measuring equipment.•DME service can be provided only in ...27.76% of global airspace.
Safety of air transportation strongly depends on the performance of on-board positioning sensors. Positioning by data from navigational aids is considered by international aviation community as one of the main stand-by positioning approaches onboard of civil airplanes. However, only positioning by pair of distance measuring equipment (DME) meets requirements of Performance-Based Navigation. A DME service volume model based on path loss between a pair of transmitting and receiving antennas has been proposed in the paper. The model takes into account the influence of relief on radio waves propagation and diffraction from high-altitude elements of relief. The proposed model has been used in the analysis of DME global network performance. In particular, performance of a global network is analyzed based on availability area of DME service, area of positioning by pairs of DME/DME support, availability of particular positioning accuracy, and areas of meeting various RNAV requirements. Obtained results indicate that only in 27.76% of global airspace a DME service can be provided. However, only within 15.9% of airspace, a DME/DME positioning can be used. Results of the analysis indicate about the necessity of actions for further development of global navigational aids network in order to guarantee safe airlines connections around the globe.
The Stretched-FrOnt-Leg (SFOL) pulse is a high-accuracy distance measuring equipment (DME) pulse developed to support alternative positioning and navigation for aircraft during global navigation ...satellite system outages. To facilitate the use of the SFOL pulse, it is best to use legacy DMEs that are already deployed to transmit the SFOL pulse, rather than the current Gaussian pulse, through software changes only. When attempting to transmit the SFOL pulse in legacy DMEs, the greatest challenge is the pulse shape distortion caused by the pulse-shaping circuits and power amplifiers (PAs) in the transmission unit such that the original SFOL pulse shape is no longer preserved. This letter proposes an inverse-learning-based DME digital predistortion method and presents successfully transmitted SFOL pulses from a testbed based on a commercial legacy DME that was designed to transmit Gaussian pulses.
•We critically examine current practice in conducting Exploratory Factor Analysis (EFA) in transportation studies.•A comprehensive overview of the main topics and choices involved in the EFA ...methodology is presented.•A significant gap between current practice and experts' recommendations was observed.•Guidelines for authors and reviewers are provided.
Exploratory factor analysis (EFA) is a widely used statistical method in traffic and transportation research, particularly for the development and validation of measurement instruments. This article critically examines current practices in conducting and reporting EFA in published transportation studies. One hundred and eighty papers published between 2016 and 2018 were examined, of which eighty-two were included in the present study after applying eligibility criteria. The review suggests that the quality of EFA reported in the field is routinely poor: (a) researchers fail to provide sufficient information to be able to adequately assess the appropriateness and quality of both the input data and the reported output; and (b) the decisions underlying the choices of EFA methods are not justified and rely mostly on procedures advised against, particularly the Little-Jiffy approach. In summary, a significant gap between current practice and experts' recommendations exists. We provide some guidelines that may help in conducting, reporting and reviewing EFA in transportation research.
Background: In places associated with the entertainment industry in which music is performed or played, sounds with high sound pressure levels may occur. Such exposure is a threat to both people ...spending their free time at concerts, in discos or pubs, as well as employees in these places. The aim of the research conducted in 2017 was to assess on-the-job noise exposure in the case of bartenders at various premises of the entertainment industry. Material and Methods: The measurements included 15 entertainment venues in Lodz, out of which 3 were selected: a music club, disco and pub. The exposure measurements were taken together for 4 work stations for bartenders using individual dosimetry in accordance with the PN-EN ISO 9612: 2011 standard. Results: A total of 64 measurements were carried out, which showed that the equivalent sound levels A at the bartenders' workplaces vary considerably depending on the type of premises and the day of the week and the range of 67.6-108.7 dB. The highest sound levels occurred during the weekend (Fridays and Saturdays). The determined daily noise exposure levels exceeded the threshold of preventive action (80 dB) in 95% of the analyzed cases. Exceeding the maximum permissible noise level (NDN = 85 dB) was found in 66% of cases. Conclusions: It has been found that on-the-job noise levels in the case of bartenders significantly exceed the acceptable values of exposure levels and pose a risk of hearing damage. Med Pr 2018;69(6):633-641Key words: noise measurements, bartenders, discotheque, music club, noise exposure level, entertainment venuesWstep: W miejscach zwiazanych z branza rozrywkowa, w ktorych wykonuje sie lub odtwarza muzyke, moga wystepowac dzwieki o wysokich poziomach cisnienia akustycznego. Taka ekspozycja stanowi zagrozenie zarowno dla osob spedzajacych wolny czas na koncertach, w dyskotekach czy pubach, jak i dla pracownikow tych lokali. Celem przeprowadzonych w 2017 r. badan byla ocena narazenia na halas na stanowisku pracy barmana w roznych miejscach zwiazanych z branza rozrywkowa. Material i metody: Pomiarami objeto 15 lokali rozrywkowych w Lodzi, sposrod ktorych wytypowano 3: klub muzyczny, dyskoteke i pub. Badania ekspozycji na halas (nadmierne dzwieki) wykonano lacznie na 4 stanowiskach pracy barmanow z zastosowaniem dozymetrii indywidualnej (trzeciej strategii pomiarowej) wedlug PN-EN ISO 9612:2011. Wyniki: Przeprowadzono lacznie 64 pomiarow, ktore wykazaly, ze rownowazne poziomy dzwieku A na stanowisku pracy barmana w zaleznosci od rodzaju lokalu i dnia tygodnia znacznie sie roznia, przyjmujac wartosci 67,6-108,7 dB. Najwyzsze poziomy dzwieku wystepowaly podczas weekendu (piatki 1 soboty). Wyznaczone dzienne poziomy ekspozycji na halas przekraczaly wartosci progu dzialania prewencyjnego (80 dB) w 95% analizowanych przypadkow. Przekroczenie wartosci najwyzszego dopuszczalnego natezenia halasu (NDN = 85 dB) stwierdzono w 66% przypadkow. Wnioski: Stwierdzono, ze wystepujace na stanowiskach pracy barmanow poziomy halasu znacznie przekraczaja dopuszczalne wartosci poziomow ekspozycji oraz stwarzaja ryzyko uszkodzenia sluchu. Med. Pr. 2018;69(6):633-641Slowa kluczowe: pomiary halasu, barmani, dyskoteka, klub muzyczny, ekspozycja na halas, lokale rozrywkowe
Water wave attenuation by grease ice is a key mechanism for the polar regions, as waves in ice influence many phenomena such as ice drift, ice breaking and ice formation. However, the models ...presented so far in the literature are limited in a number of regards, and more insights are required from either laboratory experiments or fieldwork for these models to be validated and improved. Unfortunately, performing detailed measurements of wave propagation in grease ice, either in the field or in the laboratory, is challenging. As a consequence, laboratory data are relatively scarce, and often consist of only a couple of wave elevation measurements along the length of the wave tank. We present combined measurements of wave elevation using an array of ultrasonic probes, and water kinematics using particle image velocimetry (PIV), in a small-scale wave tank experiment. Experiments are performed over a wider frequency range than has been previously investigated. The wave elevation measurements are used to compute the wavenumber and exponential damping coefficient. In contrast to a previous study in grease ice, we find that the wavenumber is consistent with the mass loading model, i.e. it increases compared with the open water case. Wave attenuation is compared with a series of one-layer models, and we show that they satisfactorily describe the viscous damping occurring. PIV data are also consistent with exponential wave amplitude attenuation, and a proper orthogonal decomposition analysis reveals the existence of mean flows under the ice that are a consequence of the displacement and packing of the ice induced by the gradient in the wave-induced stress. Finally, we show that the dynamics of grease ice can generate eddy structures that inject eddy viscosity into the water under the grease ice, which would lead to enhanced mixing and participating in energy dissipation.
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