343 research outputs found
Low-frequency climate modes and Antarctic sea ice variations, 1982-2013
No full textThe NCEP-NCAR composite dataset (comprising sea level pressure, 500-hPa geopotential height, 500-hPa temperature, and meridional wind stress at 10 m above the surface) is used for compiling a set of climate indices describing the most important physical modes of variability in the Southern Hemisphere (SH): the southern annular mode (SAM), semiannual oscillation (SAO), Pacific-South American (PSA), and quasi-stationary zonal wavenumber 3 (ZW3) patterns. Compelling evidence indicates that the large increase in the SH sea ice, recorded over recent years, arises from the impact of climate modes and their long-term trends. The examination of variability ranging from seasonal to interdecadal scales, and of trends within the climate patterns and total Antarctic sea ice concentration (SIC) for the 32-yr period (1982-2013), is the key focus of this paper. The results herein indicate that a progressive cooling has affected the year-to-year climate of the sub-Antarctic since the 1990s. This feature is found in association with increased positive SAM and SAO phases detected in terms of upward annual and seasonal trends (in autumn and summer) and upward decadal trends. In addition, the SIC shows upward annual, spring, and summer trends, indicating the insulation of Antarctica from the warmer flows in the midlatitudes. This picture of variations is also found to be consistent with the upward trends detected for the PSA and ZW3 patterns on the annual scale and during the last two decades. Evidence of a more frequent occurrence of the PSA-ZW3 combination could explain, in part, the significant increase of the regional and total Antarctic sea ice coverages
L'intervento del Presidente del consiglio e del Presidente della giunta regionale, in V. Angiolini (a cura di) Il contraddittorio nel giudizio sulle leggi, Quaderni del Gruppo di Pisa, Atti del seminario di Milano del 16-17 maggio 1997, Torino, Giappichelli
No full textStudio sulle caratteristiche dell'intervento del pres. del cons. dei ministri e del pres. della g. reg. nel contraddittorio del giudizio incide. di leg. costituzional
Appunti intorno ad interpretazione e principi (con particolare riferimento alle fonti del diritto) nel pensiero di Alessandro Giuliani
No full textThe antarctic circumpolar wave: Its presence and interdecadal changes during the last 142 years
No full textThe Southern Ocean (SO) is the region of the World Ocean bordering on Antarctica over which significant exchanges between the atmosphere, the ocean, and the sea ice take place. Here, the strong and nearly unhindered eastward flow of the Antarctic Circumpolar Current plays an important role in mean global climate as it transmits climate anomalies around the hemisphere. Features of interannual variability have been observed to propagate eastward around the SO with the circumpolar flow in the form of a system of coupled anomalies, known as the Antarctic circumpolar wave (ACW). In the present study, the 142-yr series of the Twentieth Century Reanalysis, version 2, dataset (850-hPa geopotential height, sea level pressure, sea surface temperature, surface meridional wind, and surface air temperature) spanning from 1871 to 2012 is used to investigate the presence and variability of ACWs. This examination shows, for the first time, the presence of the ACW before the mid-1950s and interdecadal changes in its characteristics. Modifications in the strength and speed of the circumpolar wave are shown to be linked with large-scale climate changes. Complex empirical orthogonal function analyses confirm that the ACW becomes apparent when the tropical El Niño- Southern Oscillation (ENSO) signal gives rise to the Pacific-South American (PSA) pattern and is a consequence of the constructive combination of the PSA and the subantarctic zonal wavenumber 3. Correlation analyses are also performed to quantify the role played by ENSO teleconnections for the appearance of the ACW, and the impact on the presence of ACWs of three super-El Niño events is investigated
Surface Heat Budgets in the Ross and Weddell Seas and Global Climate Variability
No full textThe monthly mean surface heat budgets, over last fifty years, in the Ross and Weddell Seas have been estimated using meteorological parameters provided by the ECMWF and sea ice information from SSM/I data and SIT (sea ice thickness) algorithm. The areas show opposite variations before 1998 and synchronous behaviour after 1999. This may be explained by the global climate variability expressed by ENSO, SAM and wavenumber-3 pattern or by combination among them. Also ACW could be involved. The interaction among these signals can imply a different behaviour of surface heat budgets in the two areas. Our results show that circumpolar SLP and SST signals exhibit coherent components on interannual whereas covarying significant energy between SAM and ENSO variability is observed. This implies that SAM and ENSO modes play a superimposed role interfering constructively or destructively on interannual scale. Furthermore, the hovmoller diagrams for interannual SLP anomalies exhibits two stronger ACW cycles around 1982-1991. Before 1982 and after 1991 the absence of ACW seems to be related to the dominant signature of SAM in modulating circumpolar variability. Also CEOF analysis show that the SAM has assumed a leading role between 1972-81 and 1991-2000 determining no ACW events. Starting from 2003 until present a wavenumber-3 pattern could have played a role in continuing the phase relationship between heat fluxes in the two Antarctic sectors
Dominant covarying climate signals in the southern ocean and antarctic sea ice influence during the last three decades
No full textA composite dataset (comprising geopotential height, sea surface temperature, zonal and meridional surface winds, precipitation, cloud cover, surface air temperature, latent plus sensible heat fluxes, and sea ice concentration) has been investigated with the aim of revealing the dominant time scales of variability from 1982 to 2013. Three covarying climate signals associated with variations in the sea ice distribution around Antarctica have been detected through the application of the multiple-taper method with singular value decomposition (MTM-SVD). Features of the established patterns of variation over the Southern Hemisphere extratropics have been identified in each of these three climate signals in the form of coupled or individual oscillations. The climate patterns considered here are the southern annular mode (SAM), the Pacific-South American (PSA) teleconnection, the semiannual oscillation (SAO), and the zonal wavenumber-3 (ZW3) mode. It is shown that most of the sea ice temporal variance is concentrated at the quasi-triennial scale resulting from the constructive superposition of the PSA and ZW3 patterns. In addition, the combination of the SAM and SAO patterns is found to promote the interannual sea ice variations underlying a general change in the Southern Ocean atmospheric and oceanic circulations. These two modes of variability are also found to be consistent with the occurrence of the positive SAM/negative PSA (SAM+/PSA-) or negative SAM/positive PSA (SAM-/PSA+) combinations, which could have favored the cooling of the sub-Antarctic region and important changes in the Antarctic sea ice distribution since 2000
The rainbow spanning forest problem
No full textGiven an undirected and edge-colored graph G, a rainbow component of G is a subgraph of G having all the edges with different colors. The Rainbow Spanning Forest Problem consists of finding a spanning forest of G with the minimum number of rainbow components. The problem is known to be NP-hard on general graphs and on trees. In this paper, we present an integer linear mathematical formulation and a greedy algorithm to solve it. To further improve the results, we applied a multi-start scheme to the greedy algorithm. Computational results are reported on randomly generated instances
Genetics of sudden death: focus on inherited channelopathies
No full textAbstract
Since the discovery of the genetic bases of the long QT syndrome, several new genetically mediated arrhythmias have been described, defining a new group of syndromes, called inherited arrhythmogenic diseases. This allowed clarifying the substrate of several cases of juvenile sudden death, previously defined as 'idiopathic ventricular fibrillation'. Studies derived from this field also contributed to advance the field of electrophysiology, elucidating some of the mechanisms that regulate the cardiac electrical properties of the heart. Recently, new genes and new proteins have been called into play, expanding the knowledge on the complexity of the regulatory processes modulating the cardiac action potential. Moreover, the collaboration between clinicians and basic scientists opened new approaches in the management of patients affected by genetic arrhythmias. This body of knowledge has then moved into the realization that genetic variations may also influence the predisposition to acquired cardiac diseases. The new exciting challenges that investigators are now facing are connected to the possibility of expanding the field towards the use of these information to shape a newer vision in the management and cure of patients
A Memetic Algorithm for the Weighted Feedback Vertex Set Problem
No full textGiven an undirected and vertex weighted graph G = (V,E,w), the Weighted Feedback Vertex Set Problem consists of finding the subset F ⊆ V of vertices, with minimum weight, whose removal results in an acyclic graph. Finding the minimum feedback vertex set in a graph is an important combinato- rial problem that has a variety of real applications. In this paper we introduce a memetic algorithm for this problem. We propose an efficient greedy procedure that quickly generates chromosomes with specific characteristics and a wise application of a recent local search procedures based on k-diamonds. Computa- tional results show that the proposed algorithm outperforms the effectiveness of two other metaheuristics recently proposed in the literature for this problem
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