1,721,009 research outputs found
Disclose river morphodynamics processes through experiments
No full textRivers' behavior is increasingly of interest to wide engineering and scientific communities. In fact, fluvial dynamics have an impact on infrastructure and anthropic environments as well as on natural habitats. In addition, the economic values of river as routes of commerce is great, as is the importance of precious minerals deriving from fluvial sedimentary structures. One of the more fascinating river's peculiarity is the wide range of space and time scales that impact on the overall fluvial dynamics: from the small scales typical of turbulence that are responsible for the motion of single bed's grains to wider scales typical of fluvial catchment and climate changes. Such a variety of impacting scales firstly accounting for the difficulties of fluvial investigations. Moreover, a second source of difficulty comes from the wide interactions between the fluvial scales: typical hydrodynamics scales influences and being influenced by the scales of sediment transport and bed deformation. It follows that non-linear and non-trivial behavior characterizes the river dynamic. Notwithstanding, great improvements in the fluvial knowledges have been done up to now. Nowadays, fluvial engineer and researchers can take advantage of field studies, laboratory experiments and hydrodynamic models to improve and deepen the study of the various fluvial phenomena. A rough chronology of fluvial advances dates back to 50s the development of field studies and laboratory experiments, and to 80s the growth of mathematical theories and numerical models. All these investigation methods are nowadays being improved and each result to be fundamental to the others. Field study represents the only way to study the real fluvial system, but imply two disadvantages: firstly, they are difficult to be performed (mainly during flood periods) and expensive, and secondly are site-sensitive (i.e., it is difficult to drawn general laws and lessons from a specific fluvial environment). Laboratory experiments are useful to operate in a reductionist manner, since they allow to isolate and separate physical issues that in nature are merged and somehow hidden. Being a strong simplification of complex natural phenomena, experiments must be carefully designed and run in order to be a realistic reproduction of what happens in nature. Mathematical theories and physically-based numerical models are a strongly quantitative way to face to fluvial behavior. Nowadays, we can see an increasingly number of theoretical models and this is due to the increase of computing power of computers and to advances in mathematical modeling. At the same time, the 4 a) b) d) e) f) g) c) Figure 1.1: Examples of various river channel patterns. From a) to g): Brahmaputra River, India (10 km wide braid plain), Rakaia River, New Zealand (1.7 km widebraid plain), Allier River, France (0.8 km wide meander belt), Koyukuk River, Alaska (10 km wide meander belt), Columbia river, Canada (2.1 km wide fluvial valley), Escalante River, Utah (60 m wide channel) and Nanedi Valles, Mars (2 km wide channel) (after Kleinhans (2010)). Introduction 5 theoretical advances risk to provide models that, even though mathematically refined, are not useful to resolve practical fluvial problems. It follows that a correct mix of field observation, experiments, and theories can be the only way to face the fascinating and still not completely discovered fluvial world. The consequence of all the physical processes that characterize rivers is the wide and fascinating range of planimetric patterns that a river can exhibit. On the basis of the channel form on the horizontal plane, rivers are traditionally classified as straight, braiding or meandering (e.g., Leopold and Wolman, 1957). Each of these planforms present different mobility on the floodplain and different degree of pattern stability. Moreover, every river planform has its peculiar natural habitat, in terms of different riparian vegetation, geochemical characteristics, and fauna. Figure 1.1 shows a good example of the different channel patterns that are present in nature. The planimetric patterns shown from panels 1.1a to 1.1g are qualitatively characterized by a decreasingly stream power versus bank strength ratio. Another peculiar feature of rivers, common to all the planimetric patterns, is the intrinsic bed instability. Once the motion threshold is exceeded the water flow over a granular bed leads the bed to presents transversely oriented wave-like features, for example ripples and dunes. This bedforms travel beneath the current, take part to sediment transport, and increase the hydraulic resistances. Dunes are of the order of magnitude of water depth, presenting in nature typical wavelength of 100-102m. Figure 1.2 shows an example of a train of dunes obtained in laboratory. Figure 1.2: Dunes in an our laboratory run. Flow was from right to left. For scaling, channel width was 50 cm. Major sizes are typical of another ubiquitous bedforms, called bars. River bars are 6 longitudinal sedimentary accumulation, submerged and moved only during high flows. Bars can assume a classical alternate configuration with respect to channel axis (alternate bar) or be present on the inner side of bends (forced bars). Bars play different morphodynamics role on different river planform: e.g., they can trigger and enhance bend evolution in meandering river and separate the single channels of braiding network. Figure 1.3 reports two alternate bar in our experiments on the pseudo-meandering pattern. Figure 1.3: Alternate bars in an experimental channel. Flow was from left to right. For scaling, the distance between the triangular markers was about 3 m. In our work we study both issues about fluvial planforms and bedforms, investigating some connections between planimetric and bed deformation. In particular we face with a planimetric configuration called "pseudo-meandering". The pseudomeandering pattern exhibits several features of both meandering rivers (alternate bars, migrating bends and asymmetrical cross-sections) and braiding rivers (flow diversion and tendency to create secondary channels due to the development of a chute channel between the inner side of the bar and the bank) which coexist in the same reach. Thanks to an experimental approach and some field observation we demonstrate how such pattern is strictly influenced and determined by the water discharge variability. Fluvial planforms were also focused in experiments reproducing some pattern changes (from braiding to single-thread) that are induced by strong sediment supply decline, that mainly happens caused by anthropic activities and infrastructures. Bedforms issue are instead presented by coupling experiments and a mathematical models, with the aim to investigate and clarify the initial stages of alternate bar formation. In particular we present results showing how our model is able to predict the wavelength selection typical of alternate bar. A great part of the experimental runs presented in this work has taken advantage Geomorphological background 7 of a new instrument that is able to profile the flume bed during the run and in a non- invasive way. We underwent this newly-developed device to several trials to test its accuracy. The maximum errors in the bed's elevation measurement resulted to be less than 1 mm in hydraulic conditions that are typical of morphodynamics runs. The present thesis is organized as follows. Chapter 2 presents a general introduction about fluvial geomorphology, introducing the various river planforms that are present in nature and the bedforms typical of river's beds. In chapter 3, the novel instrument used to scan in a non-invasive way the flume bed is described. The following chapters represent the core of the experimental researches: experiments regarding the influence of a varying discharge on a pseudomeadering channel are reported in chapter 4, chapter 5 is devoted to elucidate the transition from multi to single-thread fluvial patterns, and in chapter 6 a new theory and its experimental verification is developed to explain the wavelength selection typical of alternate bar
Replication Data for: The Legislative Representation of Public Opinion Policy Priorities in Italy
No full textNormative democratic theory requires political actors in parliament and government to represent not only the citizens’ policy preferences, but also their issue priorities. This article investigates Italian dynamic agenda representation – the transmission of public priorities into the policy priorities of the Italian political system. To assess the public’s policy priorities, data on the Most Important Problem from the Eurobarometer polls are used, while the legislative agendas of the members of parliament (MPs) and government are built following the rules of the Comparative Agendas Project. The results of longitudinal analyses across 10 policy areas and 20 semesters (2003–2013) suggest a persistent link between the public’s agenda and the prioritisation of legislation by the Italian parliament, majority MPs and government. Contrary to expectations, the opposition does not seem to be responsive to public opinion policy problems when introducing bills
Replication Data for: The Legislative Representation of Public Opinion Policy Priorities in Italy
No full textNormative democratic theory requires political actors in parliament and government to represent not only the citizens’ policy preferences, but also their issue priorities. This article investigates Italian dynamic agenda representation – the transmission of public priorities into the policy priorities of the Italian political system. To assess the public’s policy priorities, data on the Most Important Problem from the Eurobarometer polls are used, while the legislative agendas of the members of parliament (MPs) and government are built following the rules of the Comparative Agendas Project. The results of longitudinal analyses across 10 policy areas and 20 semesters (2003–2013) suggest a persistent link between the public’s agenda and the prioritisation of legislation by the Italian parliament, majority MPs and government. Contrary to expectations, the opposition does not seem to be responsive to public opinion policy problems when introducing bills
The legislative representation of public opinion priorities. A study of Italian parties, governments, and public opinion policy agendas.
Full text linkThe objective of this dissertation is to offer a study of dynamic agenda representation for the Italian case that looks at how parties and governments structure their policy agendas. In doing so, it attempts to address the academic gap affecting studies of Italian policy representation that put in relation public opinion priorities with the policy agenda of decision-makers. The theoretical framework argues that political actors have an incentive to represent not only the policy preferences of citizens but also their priorities. One of the available ways to do so consists in prioritising legislation covering policy areas deemed important by citizens. The research also investigates parallel issues: first, it provides an analysis of the dynamics of policy agendas of parties and governments from the 10th to the 16th legislature; secondly, it evaluates political equality in policy representation, addressing whether different Italian publics do exist and if some sub-groups attracts more attention from policy-makers. The analyses reveal that ideology and public opinion are associated with changes in the structure of legislative agendas of parties and governments. In the years investigated a persistent link between the agenda of the public and the prioritisation of legislation by Italian MPs, parties, and government emerged
Voting across borders? The electoral consequences of individual transnationalism
No full textThis article investigates the association between individual-level
transnationalism, interactions and cultural skills cutting across European
Union (EU) member states, and voting behaviour in the 2019 European
elections. The process of EU integration has expanded significantly virtual
and physical forms of cross-border mobility in the last decades. Previous
works have shown that transnational social exchange furthers Europhile
attitudes and dilutes fears for immigrants. Against this backdrop, it is argued
that people with high levels of transnationalism have the incentive to vote
for parties with pro-EU integration and pro-immigration platforms. Empirical
analyses conducted on original public opinion data show that transnational
traits significantly affected vote choices in the 2019 European elections.
Individual transnationalism is relevant per se in increasing the probability of
voting for green and radical-left parties, instead, its negative association with
voting for radical right parties runs through EU and immigration attitudes
Mapping citizens, voters, and parties’ preferences on European solidarity across EU member states
No full textSince 2008, the European Union (EU) witnessed a growing tension
between the social and economic dimensions of integration as
a consequence of the ‘polycrisis’. The increasing politicisation of EU issues
in national political arenas that led to the rise of Eurosceptic parties mostly
revolved around the issue of European solidarity. Against this background,
this study investigates the congruence between voters and incumbent
members of national parliaments on the highly contentious aspects of EU
solidarity. First, the article maps the extent to which national political
elites share similar views on EU solidarity with their voters. Secondly, we
assess members of parliaments (MPs)-voters’ congruence at the party
level. Employing original data from an elite and a mass survey conducted
in six EU countries between 2017 and 2018, we find that both voters and
MPs expressed a high level of support for policies strengthening European
solidarity in the Eurozone periphery. Instead, voters in Northern and
Eastern EU member states shared more positive preferences than their
national representatives. Furthermore, the party-voter distance was
higher for radical-right Eurosceptic MPs, especially in Northern Europe,
than for other parties
European Solidarity Takes the Field: The Dimensional Structure of Political Competition in the European Union After the Polycrisis
No full textMost studies investigating the dimensionality of political space in Europe demonstrate that European Union (EU)-related issues are orthogonal to the economic left–right dimension. This literature usually employs survey items tapping into general support for the EU. However, the multiple crises that hit Europe after 2008 have polarized even Europhile voters on the more specific issue of European solidarity. This article aims to investigate how voters' attitudes towards European solidarity interplay with their position on the left–right and European integration dimensions, as well as specific economic and cultural issues. Empirical analyses employ original survey data collected in 2019 in 10 EU countries. Results partially support the expectations of regional differences in the dimensionality of the political space, with European solidarity more strongly associated with left–right, EU integration and immigration in Northern EU member states than in Eastern and Southern countries, in which voters are more likely to support solidarity notwithstanding their general political orientations
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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