1,720,980 research outputs found
Detecting seismic waves induced by blast operations at a limestone quarry by means of different transducer mounting
No full textThe use of explosives to fragment the rock is very widespread in quarrying activities. This technology produces significant environmental impacts due to ground vibrations generated by blasting operations. In order to characterize this phenomenon, accurate measurements of seismic waves are required and one of the most critical aspects in field tests is represented by the coupling method between the transducers and the soil. This phenomenon may generate the distortion of the recorded waveform thus affecting the affordability of the sample itself. Moreover, the decoupling assumes a growing importance in those sites where the rock is not outcropping and the transducer is buried. For this purpose, different methods are tested in an opencast limestone quarry in the centre of Italy. Firstly, ground vibrations in terms of peak particle velocity (PPV) were recorded according with the method suggested in UNI 9, 916 and consisting in burying the detectors into the soil at a suitable depth. Secondly, the same parameters were recorded by means of transducers fixed to the ground with some sand bags thus maintaining the proper adherence. Finally, the data obtained through these two different methods are compared and discussed
Analysis of ground-transducer coupling in monitoring vibration from railways: A case study
No full textMonitoring railway-induced ground vibrations represents a fundamental step in assessing the environmental impact of train passage on buildings and surrounding receptors. For this purpose, accurate measurements of seismic waves are often required. Nevertheless, depending on soil structure, its characteristics or surface, the placement of transducer may affect the shape and phase of the seismic wave determining signal distortion and finally affecting the measurement itself. In particular, the most critical aspect of the sampling phase is represented by the coupling between the seismic transducer and the soil. Slipping or friction of the transducer may generate unacceptable results. For this purpose, different methods of coupling were tested in different conditions with regard to high speed train passages near a location in Rome. To start the test, some steel spikes of different shapes and lengths were tested in order to investigate their response to ground characteristics, surface and resonance frequency. The sampling campaign was carried out by fastening the transducers on the spikes fixed vertically in the soil at a certain distance from the railway track. Sampled data consisting of each passage in Peak Particle Velocity and acceleration were compared with those obtained by coupling transducers as defined in UNI 9916 norms. According to this norm, sensors are buried into the soil at a fixed depth depending on their dimensions. The final part of the sampling is aimed at comparing the sets of obtained values. This analysis is focused on the identification of those parameters to be taken into account in order to select the best coupling method for different conditions
Effectiveness of Antivibration Gloves When Used with a Light Electric Hammer. Differences Among Different Methods of Measurements
No full textSequential Gaussian Simulation as a tool to improve PM10 sampling scheme in industrial sites
No full textThis paper is focused on the role of spatial and variographic analysis in the phase of sampling design. In particular, when dealing with environmental variables such as airborne dust concentration all over a selected domain, the best approach to catch the spatial structure of the variable itself, implies the full and more detailed coverage of the domain. In this study this goal is achieved by means of about fifty airborne dust concentration field surveys all over a square area 350 mt wide in a quarry plant in the center of Italy. These data, sampled according with a regular pattern, did not allow to catch the spatial structure of the variable itself thus avoiding a satisfactory variographic modelling. To improve the sampling scheme an infilling procedure was performed by adding an increased number of samples. The selection of these further samples, less than 10% of the total amount, was carried out using sequential Gaussian simulations in those zones of the domain in which the highest variability was recorded. The final outcome shown a good result determining a good upgrade in terms of variographic modelling and final estimation at the cost of few further samples
Carlo Crivelli. La perfezione dell'arte
No full textIl saggio fornisce un riesame completo dell'attività di Carlo Crivelli (Venezia, 1430/35-Ascoli? 1494/95), personalità fra le più affascinanti del Rinascimento italiano, apportando diverse novità: fra esse spicca la ricostruzione del polittico di Force del 1482, di cui si conservano una Madonna con il Bambino ai Musei Vaticani e alcuni elementi della predella, oltre alla Pietà oggi a Boston e la nuova lettura della produzione più matura del pittore, legata alla raffinata corte di Camerino e ai centri delle Marche appenniniche.The essay provides a comprehensive re-examination of the activity of Carlo Crivelli (Venice, 1430/35-Ascoli? 1494/95), one of the most fascinating personalities of the Italian Renaissance, bringing several new features: among them the reconstruction of the 1482 Force polyptych, of which a Madonna and Child is preserved in the Vatican Museums and some elements of the predella, as well as the Pietà now in Boston, and the new reading of the painter's more mature production, linked to the refined court of Camerino and the centers of the Apennine Marche
Hand-arm vibrations induced by the use of radial arm polisher machines
No full textBackground: the exposure to high levels of vibrations could induce health problems resulting in the damage of joints, muscles, other than pathologies connected to the circulation and the sensory nerves. These phenomena are often related to the use of machines that require high efforts, repetitive movements, or not ergonomic postures. Methods: 13 Radial Arm Polisher Machines (RAPM) of different manufacturers and different ages were investigated in order to analyze the vibrations produced during a whole process of marble polishing. For each machine, 4 sets of different types of abrasives were used to complete the process. A total of 52 hand-arm vibrations measures were made according to the ISO 5349-2001 using a triaxial accelerometer fixed on the handle. Other measurements regarding the effort applied, the number of technical actions and the time required to complete each process of polishing were also made. Results: In 6 of the 13 RAPM examined, the overall vibration ahv was found to exceed the action limit (EAV) of 2.5 m/s2, among those, 3 were over the exposure limit (ELV) of 5 m/s2, independently by the age of the machines (ranging from the sixties to the mid-2000s). For the machines producing the highest vibrations, the EAV value is reached in a range of 26 - 190 minutes of usage per day. No correlation between the different roughness of the abrasives and the increment/decrement of the vibrations was found. Most of the cases resulting in the higher levels of vibrations were related both to the lack of maintenance of the machines and to the not uniform consumption of the tools used for polishing. A difference of vibrations ranging from a minimum of 0.32 to a maximum of 5.60 m/s2 was found in the use of different abrasives for the same RAPM. In one case the vertical transmission shaft of the RAPM, not perfectly straight, was the main cause of the high level of vibration produced. Some ergonomic and productivity considerations were also made: an average of 24 (SD=6.7) movements of pushing/pulling per minute, an initial and sustained force of 85 N (SD=18.6) and 38 N (SD=14.8) respectively, and an averaging time of 1193 s (SD=693) for polishing 1 m2 of marble. Conclusions: The results show that good maintenance of both the machines and the tools used for polishing the marble can highly contribute to the reduction of vibrations. Due to the high variability of the movements among different workers, depending also on the dimensions of the slabs, further investigations are required in order to asses possible ergonomics problems
The assessment of whole body vibration: A case study for bus drivers in the urban context of Rome
No full textIt is generally recognized that bus drivers are potentially being exposed to daily vibration levels higher than recommended by the international guidelines, especially on certain road types in the urban context. The literature shows up that the whole body vibrations exposure may contribute to low back pain and produce negative effects on the human health. The principal issue about the relationship between exposure and biodynamic response has not been clarified yet. The purpose of this paper is to determine the levels of vibration for bus drivers using A(8) and VDV(8) methods defined by ISO 2631-1 (1997) standard and highlight such as road condition influence on the WBV exposure. The measurements have been realized on different buses for fourteen drivers during their service route driving along urban routes in Rome with different driver's seat type. In addition, a test was realized on a new test route in order to highlight as the road type had a significant effect on all the whole body vibration exposure parameters. The vibration measurements were realized at the driver’s seat according to the recommendations of ISO 2631-1 (97). This guideline suggests measuring the vibration signal along the three translational axes on the seat pan but only the axis with the most severe vibration has been used in order to assess the driver's daily exposure. The data obtained show that the z-axis is the more stressed direction in all measurements with each surface road type. Furthermore, the results show that the type of seat employed reduces the vibration levels in a frequency range starting from 4 Hz up to 32.5 Hz. Finally this study points out as the severity of the whole-body vibration exposures in many work environments can be lessened by improvements of seating driving dynamics and road surface conditions
Towards a procedure to manage safety on construction sites of rockfall protective measures
No full textConstruction sites represent ones of the most dangerous workplaces, due to the huge number of hazards related to the performed activities that can cause discomfort, health diseases, and even death to workers. These issues might be even more amplified in construction sites of structures aiming at preventing or protecting against natural hazards. Among these lasts, rockfall represents one of the most unpredictable and dangerous. In these sites, the inherent added hazard is represented by the occurrence of the event against which the protection is required to be installed, i.e. the detachment of a rock block. As in the other situations, workers might be aware of the danger to which they are subjected and all the possible measures to mitigate the risk should be implemented. To address these issues and increase safety of workers, this paper proposes a quantitative risk assessment method to compute the probability of death of workers due to the occurrence of a rockfall event in the considered work duration. In addition, preliminary suggestions to improve safety of workers are delineated
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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