A map-matching algorithm dealing with sparse cellular fingerprint observations     

Andrea Dalla Torre  Paolo Gallo  Chris Marshall  Angelo Montanari  Federico Pittino 《地球空间信息科学学报》2019,22(2):89-106

ABSTRACT

The widespread availability of mobile communication makes mobile devices a resource for the collection of data about mobile infrastructures and user mobility. In these contexts, the problem of reconstructing the most likely trajectory of a device on the road network on the basis of the sequence of observed locations (map-matching problem) turns out to be particularly relevant. Different contributions have demonstrated that the reconstruction of the trajectory of a device with good accuracy is technically feasible even when only a sparse set of GNSS positions is available. In this paper, we face the problem of coping with sparse sequences of cellular fingerprints. Compared to GNSS positions, cellular fingerprints provide coarser spatial information, but they work even when a device is missing GNSS positions or is operating in an energy saving mode. We devise a new map-matching algorithm, that exploits the well-known Hidden Markov Model and Random Forests to successfully deal with noisy and sparse cellular observations. The performance of the proposed solution has been tested over a medium-sized Italian city urban environment by varying both the sampling of the observations and the density of the fingerprint map as well as by including some GPS positions into the sequence of fingerprint observations.  相似文献   

Response of faults to climate‐induced changes of ice sheets,glaciers and lakes          下载免费PDF全文

Andrea Hampel 《Geology Today》2017,33(1):12-18

Glacial–interglacial cycles are characterized by strong variations in climatic conditions, which affect the size of continental ice sheets, glaciers and lakes. Such climate‐triggered fluctuations in ice and water masses lead to transient stresses in the Earth's crust, which can be large enough to affect the slip behaviour of faults. In particular, postglacial unloading may increase the slip rate of active faults or re‐activate dormant faults. In the past, numerical modelling has helped to better understand the response of faults to mass fluctuations on Earth's surface. This article provides an overview of the mechanisms and controlling parameters of climate‐induced variations in fault slip as derived from the numerical models. Geological records of postglacial faulting from Scandinavia, the European Alps and the Basin‐and‐Range Province (western USA) are presented. Taken together, modelling and case studies provide a basis for evaluating the future seismic potential in regions that are currently experiencing ice loss or lake regression.  相似文献   

Multiproxy reconstructions of climate for three sites in the Canadian High Arctic using Cassiope tetragona     

Shelly A. Rayback  Gregory H. R. Henry  Andrea Lini 《Climatic change》2012,114(3-4):593-619

We developed calibration models and reconstructed climate for sites in the central and eastern Canadian High Arctic using dendroclimatological and stable isotope analysis techniques on the dwarf-shrub, Cassiope tetragona. Our results may suggest complex temporal and spatial patterns of climate change in the region over the past century. For sites on Bathurst and Devon Islands, we reconstructed fall mean and June–July mean temperature using multiple linear regression analysis that explained 54?% and 40?% of the variance, respectively. The predictor variables included annual growth, annual production of leaves, flower buds and annual δ13C values for the Bathurst Island model, and annual growth and δ13C values for the Devon Island model. Both models revealed warmer than average temperatures throughout the mid-20th century, followed by a cooling trend from the early 1960s and mid-1970s at the Devon and Bathurst Island sites, respectively. Temperatures remained cool until the early 1980s and then increased until 1998/1999 at both sites. Our models are supported by other paleoclimate proxies and the instrumental record from the Canadian Arctic. For sites on Axel Heiberg and Bathurst Islands, we developed models using multivariate regresssion for February and March total precipitation that explained 44?% and 42?% of the variance, respectively. The Axel Heiberg Island model included annual production of flowers and flower buds, as well as annual δ13C values as predictor variables, while the Bathurst Island model only included the annual production of flower buds as a predictor. Both models showed lower than average precipitation from the early to mid-1900s, followed by increasing precipitation from the late 1980s to 1998/1999. Our precipitation models, supported by instrumental and proxy data, suggest a trend of increasing late-winter/early spring precipitation in the late 20th century. The lack of a single detectable climate signal across the study sites suggests local climate, topography, genetic variation and/or ecological conditions may dictate, in part, site responses and result in a heterogeneous climatescape over space and time. Yet, like other arctic paleoclimate proxies, chronology error and temporal discrepancies may complicate our interpretations. However, comparisons with other arctic proxies and the meteorological record suggest our models have also registered a regional climate signal.  相似文献   

Climate affects severity and altitudinal distribution of outbreaks in an eruptive bark beetle     

Lorenzo Marini  Matthew P. Ayres  Andrea Battisti  Massimo Faccoli 《Climatic change》2012,115(2):327-341

Temperature warming and the increased frequency of climatic anomalies are expected to trigger bark beetle outbreaks with potential severe consequences on forest ecosystems. We characterized the combined effects of climatic factors and density-dependent feedbacks on forest damage caused by Ips typographus (L.), one of the most destructive pests of European spruce forests, and tested whether climate modified the interannual variation in the altitudinal outbreak range of the species. We analyzed a 16-year time-series from the European Alps of timber loss in Picea abies Karsten forests due to I. typographus attacks and used a discrete population model and an information theoretic approach to compare multiple competing hypotheses. The occurrence of dry summers combined with warm temperatures appeared as the main abiotic triggers of severity of outbreaks. We also found an endogenous negative feedback with a 2-year lag suggesting a potential important role of natural enemies. Forest damage per hectare averaged 7-fold higher where spruce was planted in sites warmer than those within its historical climatic range. Dry summers, but not temperature, was related to upward shifts in the altitudinal outbreak range. Considering the potential increased susceptibility of spruce forests to insect outbreaks due to climate change, there is growing value in mitigating these effects through sustainable forest management, which includes avoiding the promotion of spruce outside its historical climatic range.  相似文献   

Sensitivity of the Atlantic meridional overturning circulation to South Atlantic freshwater anomalies     

Andrea A. Cimatoribus  Sybren S. Drijfhout  Matthijs den Toom  Henk A. Dijkstra 《Climate Dynamics》2012,39(9-10):2291-2306

The sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to changes in basin integrated net evaporation is highly dependent on the zonal salinity contrast at the southern border of the Atlantic. Biases in the freshwater budget strongly affect the stability of the AMOC in numerical models. The impact of these biases is investigated, by adding local anomaly patterns in the South Atlantic to the freshwater fluxes at the surface. These anomalies impact the freshwater and salt transport by the different components of the ocean circulation, in particular the basin-scale salt-advection feedback, completely changing the response of the AMOC to arbitrary perturbations. It is found that an appropriate dipole anomaly pattern at the southern border of the Atlantic Ocean can collapse the AMOC entirely even without a further hosing. The results suggest a new view on the stability of the AMOC, controlled by processes in the South Atlantic.  相似文献   

The formation and evolution of massive stellar clusters in IC4662     

Andrea M. Gilbert  William D. Vacca 《Astrophysics and Space Science》2009,324(2-4):147-154

We present a multiwavelength study of the formation of massive stellar clusters, their emergence from cocoons of gas and dust, and their feedback on surrounding matter. Using data that span from radio to optical wavelengths, including Spitzer and Hubble Space Telescope ACS observations, we examine the population of young star clusters in the central starburst region of the irregular Wolf–Rayet galaxy IC4662. We model the radio-to-infrared (IR) spectral energy distributions of embedded clusters to determine the properties of their Hii regions and dust cocoons (sizes, masses, densities, temperatures), and use near-IR and optical data with mid-IR spectroscopy to constrain the properties of the embedded clusters themselves (mass, age, extinction, excitation, abundance). The two massive star-formation regions in IC4662 are excited by stellar populations with ages of ～4 Myr and masses of ～3×10⁵ M_⊙ (assuming a Kroupa initial mass function). They have high excitation and subsolar abundances, and they may actually be comprised of several massive clusters rather than the single monolithic massive compact objects known as ‘super star clusters’ (SSCs). Mid-IR spectra reveal that these clusters have very high extinction values, A _V ～20–25 mag, and that the dust in IC4662 is well mixed with the emitting gas, not in a foreground screen.  相似文献   

The Argentinean Patagonia and the Martian landscape     

Andrea Pacifici 《Planetary and Space Science》2009,57(5-6):571-578

Throughout the Cenozoic Era, the geological history of the Argentinean Patagonia was dominated by basaltic volcanism and glacial and periglacial environments. Several geological and geomorphological processes that concurred to the sculpting of the landscape of this area could have been similar to those responsible of the shaping of the Martian surface. In this work a survey of some high-resolution satellite images of the Argentinean Patagonia is performed in order to identify possible geomorphological analogs of the Martian surface. Several morphologies that resemble Martian features are presented and discussed. They consist of proglacial and periglacial features, relatively small circular depressions, gullies, fan-deltas, eolian streaks, and diluvial dunes. Results suggest that the Argentinean Patagonia appears to consist of an interesting terrestrial analog for the Martian landscape. Furthermore, the study area shows to be interesting in order to test robotic instruments and human missions equipment, to train astronauts of future human expeditions to Mars, and to perform astrobiological experiments.  相似文献   

Influence of glass polymerisation and oxidation on micro-Raman water analysis in alumino-silicate glasses   总被引：1，自引：0，他引：1  

Maxime Mercier  Andrea Di Muro  Daniele Giordano  Priscille Lesne  Bruno Scaillet  Gilles Montagnac 《Geochimica et cosmochimica acta》2009,73(1):197-217

The development of an accurate analytical procedure for determination of dissolved water in complex alumino-silicate glasses via micro-Raman analysis requires the assessment of the spectra topology dependence on glass composition. We report here a detailed study of the respective influence of bulk composition, iron oxidation state and total water content on the absolute and relative intensities of the main Raman bands related to glass network vibrations (LF: ∼490 cm⁻¹; HF: ∼960 cm⁻¹) and total water stretching (H₂O_T: ∼3550 cm⁻¹) in natural glasses. The evolution of spectra topology was examined in (i) 33 anhydrous glasses produced by the re-melting of natural rock samples, which span a very large range of polymerisation degree (NBO/T from 0.00 to 1.16), (ii) 2 sets of synthetic anhydrous basaltic glasses with variable iron oxidation state (Fe³⁺/Fe_T from 0.05 to 0.87), and (iii) 6 sets of natural hydrous glasses (C_H2OT from 0.4 to 7.0 wt%) with NBO/T varying from 0.01 to 0.76.In the explored domain of water concentration, external calibration procedure based on the H₂O_T band height is matrix-independent but its accuracy relies on precise control of the focusing depth and beam energy on the sample. Matrix-dependence strongly affects the internal calibrations based on H₂O_T height scaled to that of LF or HF bands but its effect decreases from acid (low NBO/T, SM) to basic (high NBO/T, SM) glasses. Structural parameters such as NBO/T (non-bridging oxygen per tetrahedron) and SM (sum of structural modifiers) describe the matrix-dependence better than simple compositional parameters (e.g. SiO₂, Na₂O + K₂O). Iron oxidation state has only a minor influence on band topology in basalts and is thus not expected to significantly affect the Raman determinations of water in mafic (e.g. low SiO₂, iron-rich) glasses. Modelling the evolution of the relative band height with polymerisation degree allows us to propose a general equation to predict the dissolved water content in natural glasses: