6,827 research outputs found

    Characterization of the precipitation in southwestern part of Greece with X-band Doppler radar, 2-D video disdrometer and rain gauges

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    International audienceWe document precipitation in the southwestern part of Greece with the National Observatory of Athens (NOA) X-band radar, NOA 2D video disdrometer and a network of rain gauges. The observations were collected between February and April 2004. Time evolution of the drop size distribution (DSD) is presented for the 9 March 2004 case where rain rate (computed on 1-min period) was measured up to 80 mm/h and reflectivity at the location of the disdrometer exceeded 40 dBZ. We then present the differences of DSD as function of the rain rate for the studied case as well as for the entire observations of the field experiment. It shows that higher the rain rate is, larger the range of the DSD and higher the concentration of the raindrops are

    The Effect of Consolidation on TBM Shield Loading in Water-Bearing Squeezing Ground

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    Jamming or overstressing of the shield due to ground pressure are potential problems for tunnel boring machine (TBM) tunnelling in squeezing ground. The risk of shield jamming depends essentially on the deformation rate of the ground in the vicinity of the working face. The time-dependency of the ground response to the excavation is associated with its rheological properties as well as with the transient consolidation process that takes place around the opening in the case of a low-permeability saturated ground. The present paper focuses on the second mechanism and investigates the interaction between the advancing shield, tunnel lining and consolidating ground by means of transient numerical analyses. For a given set of geotechnical conditions and a given TBM configuration, the load exerted by the ground upon the shield during TBM operation decreases with increasing gross advance rate. During a long break in operations, the ground pressure may increase significantly, thereby necessitating a higher thrust force to overcome shield skin friction and restart the TBM. It is interesting to note that a high advance rate reduces the risk of shield jamming not only during TBM advance, but is also favourable with respect to any subsequent long standstill

    The Interaction Between Shield, Ground and Tunnel Support in TBM Tunnelling Through Squeezing Ground

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    When planning a TBM drive in squeezing ground, the tunnelling engineer faces a complex problem involving a number of conflicting factors. In this respect, numerical analyses represent a helpful decision aid as they provide a quantitative assessment of the effects of key parameters. The present paper investigates the interaction between the shield, ground and tunnel support by means of computational analysis. Emphasis is placed on the boundary condition, which is applied to model the interface between the ground and the shield or tunnel support. The paper also discusses two cases, which illustrate different methodical approaches applied to the assessment of a TBM drive in squeezing ground. The first case history—the Uluabat Tunnel (Turkey)—mainly involves the investigation of TBM design measures aimed at reducing the risk of shield jamming. The second case history—the Faido Section of the Gotthard Base Tunnel (Switzerland)—deals with different types of tunnel support installed behind a gripper TB

    Coral skeleton P/Ca proxy for seawater phosphate: Multi-colony calibration with a contemporaneous seawater phosphate record

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    A geochemical proxy for surface ocean nutrient concentrations recorded in coral skeleton could provide new insight into the connections between sub-seasonal to centennial scale nutrient dynamics, ocean physics, and primary production in the past. Previous work showed that coralline P/Ca, a novel seawater phosphate proxy, varies synchronously with annual upwelling-driven cycles in surface water phosphate concentration. However, paired contemporaneous seawater phosphate time-series data, needed for rigorous calibration of the new proxy, were lacking. Here we present further development of the P/Ca proxy in Porites lutea and Montastrea sp. corals, showing that skeletal P/Ca in colonies from geographically distinct oceanic nutrient regimes is a linear function of seawater phosphate (PO4 SW) concentration. Further, high-resolution P/Ca records in multiple colonies of Pavona gigantea and Porites lobata corals grown at the same upwelling location in the Gulf of Panama were strongly correlated to a contemporaneous time-series record of surface water PO4 SW at this site (r2 = 0.7–0.9). This study supports application of the following multi-colony calibration equations to down-core records from comparable upwelling sites, resulting in ±0.2 and ±0.1 lmol/kg uncertainties in PO4 SW reconstructions from P. lobata and P. gigantea, respectively.P/Ca Porites lobata (lmol/mol) = (21.1 ? 2.4)PO4 SW (lmol/kg) + (14.3 ? 3.8)P/Ca Pavona gigantea (lmol/mol) = (29.2 ? 1.4)PO4 SW (lmol/kg) + (33.4 ? 2.7)Inter-colony agreement in P/Ca response to PO4 SW was good (±5–12% about mean calibration slope), suggesting that species-specific calibration slopes can be applied to new coral P/Ca records to reconstruct past changes in surface ocean phosphate. However, offsets in the y-intercepts of calibration regressions among co-located individuals and taxa suggest that biologically-regulated “vital effects” and/or skeletal extension rate may also affect skeletal P incorporation. Quantification of the effect of skeletal extension rate on P/Ca could lead to corrected calibration equations and improved inter-colony P/Ca agreement. Nevertheless, the efficacy of the P/Ca proxy is thus supported by both broad scale correlation to mean surface water phosphate and regional calibration against documented local seawater phosphate variations

    The Random Bit Complexity of Mobile Robots Scattering

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    We consider the problem of scattering nn robots in a two dimensional continuous space. As this problem is impossible to solve in a deterministic manner, all solutions must be probabilistic. We investigate the amount of randomness (that is, the number of random bits used by the robots) that is required to achieve scattering. We first prove that nlognn \log n random bits are necessary to scatter nn robots in any setting. Also, we give a sufficient condition for a scattering algorithm to be random bit optimal. As it turns out that previous solutions for scattering satisfy our condition, they are hence proved random bit optimal for the scattering problem. Then, we investigate the time complexity of scattering when strong multiplicity detection is not available. We prove that such algorithms cannot converge in constant time in the general case and in o(loglogn)o(\log \log n) rounds for random bits optimal scattering algorithms. However, we present a family of scattering algorithms that converge as fast as needed without using multiplicity detection. Also, we put forward a specific protocol of this family that is random bit optimal (nlognn \log n random bits are used) and time optimal (loglogn\log \log n rounds are used). This improves the time complexity of previous results in the same setting by a logn\log n factor. Aside from characterizing the random bit complexity of mobile robot scattering, our study also closes its time complexity gap with and without strong multiplicity detection (that is, O(1)O(1) time complexity is only achievable when strong multiplicity detection is available, and it is possible to approach it as needed otherwise)

    PRELIMINARY STUDIES ON SEDIMENT CORE FROM THE TYRO BASIN

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    Η παρούσα εργασία παρουσιάζει τα προκαταρκτικά αποτελέσματα της ορυκτολογικής και μικροπαλαιοντολογικής ανάλυσης που πραγματοποιήθηκε σε δείγματα ιζημάτων από τον πυρήνα TYR05 που συλλέχθηκε από την ανοξική και υπεράλμυρη λεκάνη Τύρου στην ανατολική Μεσόγειο. Ο πυρήνας αποτελεί μία σύνθετη λιθοστρωματογραφική ακολουθία που αποδίδεται στο ισχυρό γεωδυναμικό καθεστώς της περιοχής. Οι συγκεντρώσεις πλαγκτονικών τρηματοφόρων παρουσιάζουν διακυμάνσεις οι οποίες συμπίπτουν με αλλαγές στη λιθολογία του πυρήνα. Η ορυκτολογική σύσταση των ιζημάτων δείχνει επίδραση από τους εβαπορίτες που δημιουργούνται στον πυθμένα της λεκάνης. Τα ορυκτά συστατικά σε σχέση με τις συγκεντρώσεις της μικροπανίδας δείχνουν ότι τα ιζήματα περιλαμβάνουν σαπροπηλικά στρώματα. Χρειάζονται επιπλέον αναλύσεις για τον ασφαλή προσδιορισμό των σαπροπηλικών αποθέσεων.The present paper summarizes the preliminary results of the mineralogical and micropaleontological analysis conducted on sediment samples from core TYR05 retrieved from the anoxic and hypersaline Tyro basin in the eastern Mediterranean Sea. The core comprises a complex lithostratigraphic sequence attributed to the strong geodynamic regime of the area. The planktonic foraminifera associations present fluctuations which coincide with changes in the lithology of the core. The mineralogical composition of the sediments shows influence from the evaporites developed on the bottom of the basin. The mineral constituents in association to the microfauna assemblages suggest that the sediments include sapropelic layers. Further analyses are needed in order to determine safely the sapropelic deposits

    An innovative radiation hardened CAM architecture

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    An innovative Content Addressable Memory (CAM) cell with radiation hardened (RH) architecture is presented. The RH-CAM is designed using a commercial 28 nm CMOS technology. The circuit has been simulated in worst-case conditions, and the effects due to single particles have been analyzed by injecting a current pulse into a circuit node. The proposed architecture is suitable for real-time pattern recognition tasks in harsh environments, such as front-end electronics in the ATLAS experiment at the Large Hadron Collider (LHC) and in space applications

    Evaluation of predictive models for post-fire debris flow occurrence in the western United States

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    Abstract. Rainfall-induced debris flows in recently burned mountainous areas cause significant economic losses and human casualties. Currently, prediction of post-fire debris flows is widely based on the use of power-law thresholds and logistic regression models. While these procedures have served with certain success in existing operational warning systems, in this study we investigate the potential to improve the efficiency of current predictive models with machine-learning approaches. Specifically, the performance of a predictive model based on the random forest algorithm is compared with current techniques for the prediction of post-fire debris flow occurrence in the western United States. The analysis is based on a database of post-fire debris flows recently published by the United States Geological Survey. Results show that predictive models based on random forest exhibit systematic and considerably improved performance with respect to the other models examined. In addition, the random-forest-based models demonstrated improvement in performance with increasing training sample size, indicating a clear advantage regarding their ability to successfully assimilate new information. Complexity, in terms of variables required for developing the predictive models, is deemed important but the choice of model used is shown to have a greater impact on the overall performance

    From Pharmacognosia to DNA-Based Medicinal Plant Authentication – Pharmacognosy through the Centuries

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    For centuries, pharmacognosy was essential for the identification, quality, purity, and, until the end of the 18th century, even for the efficacy of medicinal plants. Since the 19th century, it concentrated on authenticity, purity, quality and the analysis of active substances, and was established as an academic branch discipline within pharmacy and continuously developed into a modern, highly sophisticated science. Even though the paradigm in pharmacy changed in the 19th century with the discovery of morphine and concentrated on single substances that could be synthesized fast by the upcoming industry, medicinal plants always remained an important element of the Materia medica, and during the last decades, medicinal plants continue to be a source of remedies, and natural products are an inspiration for new medicine. In this research, pharmacognostic skills remain an essential element, both with regards to identity, quality assurance of botanicals (both herbal medicines and supplements), and the discovery and development of new medicines. Over the years, the specific pharmacognostical tools have changed dramatically, and most recently, DNA-based techniques have become another element of our spectrum of scientific methods

    Dissolved organic matter cycling in eastern Mediterranean rivers experiencing multiple pressures. The case of the trans-boundary Evros River

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    The objective of our study was to provide a comprehensive evaluation on C, N, P cycling in medium sized Mediterranean rivers, such as the Evros, experiencing multiple pressures (intensive agriculture, industrial activities, population density). Our work aims also to contribute to the development of integrated management policies. Dissolved organic matter (DOM) cycling were investigated, during a one-year study. It was shown that the organic component of N and P was comparable to those of large Mediterranean rivers (Rhone, Po). In the lower parts of the river where all point and non-point inputs converge, the high inorganic N input favour elevated assimilation rates by phytoplankton and result in increased chl-a concentrations and autochthonous dissolved organic matter (DOM) production during the dry season with limited water flow. Moreover, carbohydrate distribution revealed that there is a constant background of soil derived mono-saccharides on top of which are superimposed impulses of poly-saccharides during blooms. During the dry season, inorganic nutrients and DOM are trapped in the lower parts of the river, whereas during high flow conditions DOM is flushed towards the sea and organic nitrogen forms can become an important TDN constituent (at least 40%) transported to shelf waters. The co-existence of terrigenous material with autochthonous and some anthropogenic is supported by the relatively low DOC:DON and DOC:DOP ratios, the positive correlation of DOC vs chl-a and the decoupling between DOC and DON. Overall, this study showed that in medium size Mediterranean rivers, such as the Evros, intensive agriculture and pollution sources in combination with water management practices and climatic variability are important factors determining C, N, P dynamics and export to coastal seas. Also, it highlights the importance of the organic fraction of N and P when considering management practices
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