A complex analysis approach to the motion of uniform vortices     

Giorgio Riccardi 《Ocean Dynamics》2018,68(2):273-293

A new mathematical approach to kinematics and dynamics of planar uniform vortices in an incompressible inviscid fluid is presented. It is based on an integral relation between Schwarz function of the vortex boundary and induced velocity. This relation is firstly used for investigating the kinematics of a vortex having its Schwarz function with two simple poles in a transformed plane. The vortex boundary is the image of the unit circle through the conformal map obtained by conjugating its Schwarz function. The resulting analysis is based on geometric and algebraic properties of that map. Moreover, it is shown that the steady configurations of a uniform vortex, possibly in presence of point vortices, can be also investigated by means of the integral relation. The vortex equilibria are divided in two classes, depending on the behavior of the velocity on the boundary, measured in a reference system rotating with this curve. If it vanishes, the analysis is rather simple. However, vortices having nonvanishing relative velocity are also investigated, in presence of a polygonal symmetry. In order to study the vortex dynamics, the definition of Schwarz function is then extended to a Lagrangian framework. This Lagrangian Schwarz function solves a nonlinear integrodifferential Cauchy problem, that is transformed in a singular integral equation. Its analytical solution is here approached in terms of successive approximations. The self-induced dynamics, as well as the interactions with a point vortex, or between two uniform vortices are analyzed.  相似文献   

Glacial Isostatic Adjustment and Contemporary Sea Level Rise: An Overview     

Giorgio Spada 《Surveys in Geophysics》2017,38(1):153-185

Glacial isostatic adjustment (GIA) encompasses a suite of geophysical phenomena accompanying the waxing and waning of continental-scale ice sheets. These involve the solid Earth, the oceans and the cryosphere both on short (decade to century) and on long (millennia) timescales. In the framework of contemporary sea-level change, the role of GIA is particular. In fact, among the processes significantly contributing to contemporary sea-level change, GIA is the only one for which deformational, gravitational and rotational effects are simultaneously operating, and for which the rheology of the solid Earth is essential. Here, I review the basic elements of the GIA theory, emphasizing the connections with current sea-level changes observed by tide gauges and altimetry. This purpose is met discussing the nature of the “sea-level equation” (SLE), which represents the basis for modeling the sea-level variations of glacial isostatic origin, also giving access to a full set of geodetic variations associated with GIA. Here, the SLE is employed to characterize the remarkable geographical variability of the GIA-induced sea-level variations, which are often expressed in terms of “fingerprints”. Using harmonic analysis, the spatial variability of the GIA fingerprints is compared to that of other components of contemporary sea-level change. In closing, some attention is devoted to the importance of the “GIA corrections” in the context of modern sea-level observations, based on tide gauges or satellite altimeters.  相似文献   

The ARIEL Instrument Control Unit design     

M. Focardi  E. Pace  M. Farina  A. M. Di Giorgio  J. Colomé Ferrer  I. Ribas  C. Sierra Roig  L. Gesa Bote  J. C. Morales  J. Amiaux  C. Cara  J. L. Augurés  E. Pascale  G. Morgante  V. Da Deppo  M. Pancrazzi  V. Noce  S. Pezzuto  M. Frericks  F. Zwart  G. Bishop  K. Middleton  P. Eccleston  G. Micela  G. Tinetti 《Experimental Astronomy》2018,45(1):1-20

In this paper we present the electromagnetic modeling and beam pattern measurements of a 16-elements ultra wideband sparse random test array for the low frequency instrument of the Square Kilometer Array telescope. We discuss the importance of a small array test platform for the development of technologies and techniques towards the final telescope, highlighting the most relevant aspects of its design. We also describe the electromagnetic simulations and modeling work as well as the embedded-element and array pattern measurements using an Unmanned Aerial Vehicle system. The latter are helpful both for the validation of the models and the design as well as for the future instrumental calibration of the telescope thanks to the stable, accurate and strong radio frequency signal transmitted by the UAV. At this stage of the design, these measurements have shown a general agreement between experimental results and numerical data and have revealed the localized effect of un-calibrated cable lengths in the inner side-lobes of the array pattern.  相似文献   

Nekhoroshev estimate for isochronous non resonant symplectic maps     

Armando Bazzani  Stefano Marmi  Giorgio Turchetti 《Celestial Mechanics and Dynamical Astronomy》1989,47(4):333-359

We prove that non resonant isochronous symplectic maps in a neighborhood of an elliptic fixed point are stable for exponentially long times with the inverse of the distance from the fixed point. In the proof we make use of the majorant series method together with an idea for optimizing remainder estimates first applied to Hamiltonian problems by Nekhoroshev.  相似文献   

Effects of clogging on stream macroinvertebrates: An experimental approach     

Tiziano Bo  Giorgio Malacarne  Massimo Pessino  Francesca Sgariboldi 《Limnologica》2007,37(2):186-192

The influence of streambed sediment clogging on macroinvertebrate communities was investigated in the Lemme creek (NW Italy). To assess how fine sediment accumulation can influence the colonisation process and community composition of macroinvertebrates, we placed 48 traps in the riverbed. The traps consisted of boxes built with metal net (mesh 1 cm, height 15 cm, sides 5 cm) covered with nylon net except for the apex, allowing access exclusively from the top. We created four trap types filled with 100% gravel, 30% sand and 70% gravel, 70% sand and 30% gravel and 100% sand. After 20 and 40 days, we removed 6 traps/type. Macroinvertebrates rapidly colonised the traps, as we found no significant community differences between the two removal dates. Among the four trap types, we found significant differences in taxa number and abundance, which both decreased with increasing clogging. Thus, our study supports the hypothesis that clogging and the accumulation of fine substratum elements strongly affects benthic stream communities.  相似文献   

An incentive mechanism for reducing emissions from conversion of intact and non-intact forests   总被引：1，自引：0，他引：1  

Danilo Mollicone  Frédéric Achard  Sandro Federici  Hugh D. Eva  Giacomo Grassi  Alan Belward  Frank Raes  Günther Seufert  Hans-Jürgen Stibig  Giorgio Matteucci  Ernst-Detlef Schulze 《Climatic change》2007,83(4):477-493

This paper presents a new accounting mechanism in the context of the UNFCCC issue on reducing emissions from deforestation in developing countries, including technical options for determining baselines of forest conversions. This proposal builds on the recent scientific achievements related to the estimation of tropical deforestation rates and to the assessment of ‘intact’ forest areas. The distinction between ‘intact’ and ‘non intact’ forests used here arises from experience with satellite-based deforestation measurements and allows accounting for carbon losses from forest degradation. The proposed accounting system would use forest area conversion rates as input data. An optimal technical solution to set baselines would be to use historical average figures during the time period from 1990 to 2005. The system introduces two different schemes to account for preserved carbon: one for countries with high forest conversion rates where the desired outcome would be a reduction in their rates, and another for countries with low rates. A ‘global’ baseline rate would be used to discriminate between these two country categories (high and low rates). For the hypothetical accounting period 2013–2017 and considering 72% of the total tropical forest domain for which data are available, the scenario of a 10% reduction of the high rates and of the preservation of low rates would result in approximately 1.6 billion tCO₂ of avoided emissions. The resulting benefits of this reduction would be shared between those high-rate countries which reduced deforestation and those low-rate countries which did not increase their deforestation over an agreed threshold (e.g., half of “global” baseline rate).  相似文献   

A note on the equilibrium points of the restricted problem of three bodies     

Giorgio E. O. Giacaglia 《Celestial Mechanics and Dynamical Astronomy》1975,12(4):519-520

Using Sylvester's theorem on matrices, an elegant expression is obtained for the solutions of the restricted problem of three bodies in the neighborhood of the equilibrium points.  相似文献   

Spatial variability of phytoplankton, nutrients and new production estimates in the waters around Svalbard   总被引：3，自引：0，他引：3  

Georgina Owrid  Giorgio Socal  Giuseppe Civitarese  Anna Luchetta  Jozef Wiktor  Eva-Maria Nöthig  Inger Andreassen  Ursula Schauer  Volker Strass 《Polar research》2000,19(2):155-171

Phytoplankton dynamics and carbon input into Arctic and sub-Arctic ecosystems were investigated around Svalbard, in summer 1991. Phytoplankton biomass, species composition and dissolved nutrient concentrations were analysed from water samples collected along seven transects. Phytoplankton biomass was low especially to the north (Chlorophyll-a mean 0.3 pg 1- '), where flagellates dominated the communities and only ice-diatoms were present. To the west, the phytoplankton composition was representative of a summer Atlantic community, in a post-bloom state. Zooplankton grazing, mainly by copepods, appeared to be the main control on biomass to the west and north of Svalbard.
In the Barents Sea (east of Svalbard), an ice edge bloom was observed (Chlorophyll-a max. 6.8 pgl-') and the ice edge receded at a rate of approximately 1 1 km day-'. The phytoplankton community was represented by marginal ice species, especially Phaeocystis poucherii and Chaeroceros socialis. South of the ice edge, Deep Chlorophyll Maxima (DCM) were observed, as surface waters became progressively nutrient-depleted. In these surface waters, the phytoplankton were predominantly auto- and heterotrophic flagellates.
Carbon production measurements revealed high net production (new and regenerated) to the north of the Barents Sea Polar Front (BSPF); it was especially high at the receding ice edge (reaching 1.44gC m-'day-'). To the south, a low level of production was maintained, mainly through regenerative processes.  相似文献   

Potential evidence for slab detachment from the flexural backstripping of a foredeep: Insight on the evolution of the Pescara basin (Italy)          下载免费PDF全文

Paolo Mancinelli  Cristina Pauselli  Giorgio Minelli  Massimiliano R. Barchi  Guy Simpson 《地学学报》2018,30(3):222-232

The discrepancy between the size of the Apenninic chain and the depth of the Adriatic foredeep is investigated using 2D flexural backstripping on well‐constrained depth‐converted cross‐sections in the Pescara basin (Central Italy). The procedure consisted of removal, uplift, unfolding and unfaulting of the Pliocene–Pleistocene foreland deposits to produce a palaeogeographic map of the basin at the end of the Messinian and to constrain sedimentary rates since the Miocene. Results are found to support the contribution of an external load to the foreland evolution together with the Apenninic chain load. The interplay of the two types of loads resulted in spatial and temporal variations of the foredeep evolution that are quantified by palaeogeographic maps and sedimentation rates obtained through backstripping. Results are interpreted as representing the effects of a southward‐migrating wave linked to slab detachment beneath the Adriatic foredeep. This procedure can be useful to investigate similar problems on other chains worldwide.  相似文献   

Mantle-derived carbon in Hercynian granites. Stable isotopes signatures and C/He associations in the thermomineral waters,N-Portugal     

Paula M. Carreira  José M. Marques  M. Rosário Carvalho  Giorgio Capasso  Fausto Grassa 《Journal of Volcanology and Geothermal Research》2010,189(1-2):49-56

Na–HCO₃–CO₂-rich thermomineral waters issue in the N of Portugal, within the Galicia-Trás-os-Montes region, linked to a major NNE-trending fault, the so-called Penacova-Régua-Verin megalineament. Along this tectonic structure different occurrences of CO₂-rich thermomineral waters are found: Chaves hot waters (67 °C) and also several cold (16.1 °C) CO₂-rich waters. The δ²H and δ¹⁸O values of the thermomineral waters are similar to those of the local meteoric waters. The chemical composition of both hot and cold mineral waters suggests that water–rock reactions are mainly controlled by the amount of dissolved CO₂ (g) rather than by the water temperature. Stable carbon isotope data indicate an external CO₂ inorganic origin for the gas. δ¹³C_CO2 values ranging between ? 7.2‰ and ? 5.1‰ are consistent with a two-component mixture between crustal and mantle-derived CO₂. Such an assumption is supported by the ³He/⁴He ratios measured in the gas phase, are between 0.89 and 2.68 times the atmospheric ratio (Ra). These ratios which are higher than that those expected for a pure crustal origin (≈ 0.02 Ra), indicating that 10 to 30% of the He has originated from the upper mantle. Release of deep-seated fluids having a mantle-derived component in a region without recent volcanic activity indicates that extensive neo-tectonic structures originating during the Alpine Orogeny are still active (i.e., the Chaves Depression).  相似文献