323,757 research outputs found
On the nature of meander instability
No full textBend instability is the process whereby perturbations of the planform distribution of a channel relative to a straight configuration may grow, driven by erosion at concave banks and deposition at convex banks, leading to the development of a meandering pattern. Here we investigate the nature of this instability; that is, we ascertain under what conditions bend instability is convective or absolute. In the former case, an initial nonpersistent, small perturbation localized in space is convected away, eventually leaving the flow domain unperturbed. In the latter case, perturbations spread in both the upstream and downstream directions, eventually affecting the whole flow domain. In convective instabilities, the spatial-temporal development of perturbations is somewhat dependent on the characteristics of the initial perturbation which is required to be persistent in time. On the contrary, absolute instabilities are able to amplify perturbations, even if triggered at some initial time and then ceased. If bend instability is convective, planform information migrates only in one direction, while in the absolute regime, information is propagated in both directions. We show that bend instability is most often, though not invariably, convective at both a linear and nonlinear level. Moreover, the group velocity of perturbations changes sign as the width to depth ratio of the channel crosses some threshold value (the resonant value of Blondeaux and Seminara (1985)): Below (above) resonance, information is propagated downstream (upstream). We discuss the implications that these findings have on the morphological characteristics of meandering rivers (in particular, the sense of skewing of meander bends and the direction of meander migration). We also clarify how the choice of appropriate boundary conditions in numerical simulations of planform evolution is crucially dependent on the nature of bend instability and on its subresonant or superresonant regime
Una famiglia nobiliare di Terraferma: i Martinengo da Barco, a cura di P. Lanzoni – S. Onger, Roccafranca, La Compagnia della Stampa Massetti Rodella, 2009, 200 p
No full textin “Civiltà bresciana” 1-2 (2009), p. 224-227:
Una famiglia nobiliare di Terraferma: i Martinengo da Barco, a cura di P. Lanzoni – S. Onger, Roccafranca, La Compagnia della Stampa Massetti Rodella, 2009, 200
Coactive stresses in MEMS and NEMS based on periodically bent crystals
No full textA variety of MEMS and NEMS are base on chemical film deposition onto a ceramic substrate. Generally, the substrate consists of a Si (silicon) or Ge (germanium) plate. One of the most used chemical processes is low-pressure chemical vapor deposition (LPCVD). Through such a technology a wide class of MEMS/NEMS can be realized, with particular reference to crystalline undulators (CU)s [1]. CUs (Figure 1) are devices to generate intense coherent and collimated electromagnetic radiation across the UV and X-ray ranges. Electrical charges are forced to oscillate in the electromagnetic field of the crystalline lattice thus emitting electromagnetic radiation.The present study concerns the effects induced by coactive stresses on displacement and stress fields induced in the system by thermal loading due to the LPCVD process. The aim of the study is to find the optimum geometrical parameters (a, p, hf) suitable to obtain a CU. By imposing equilibrium conditions and perfect adhesion between the thin films and the substrate, a singular integral equation is derived. A closed-form solution is achieved by expanding the unknown interfacial shear stress fields in Chebyshev series. This leads to an algebraic system which solution allows assessing the stress, strain and displacement fields in the CU.
REFERENCES:
[1] Guidi V, Lanzoni L, Mazzolari A, et al. Design of a crystalline undulator based on patterning by tensile Si3N4 strips on a Si crystal. Appl Phys Lett 2007; 90(11): 11410
A simplified model for frictionally dominated tidal flows
No full textThe response of vegetated tidal wetlands to environmental changes is governed by vegetation-flow-landscape feedbacks occurring over large spatial and temporal scales, and thus typically studied using simplified models. Here, we present a new simplified approach to describe frictionally dominated tidal flows, characteristic of tidal wetlands. The derivation of the model follows from an expansion of the momentum and mass conservation equations in terms of small dimensionless parameters, which arise once the relevant variables are suitably scaled. A comparison with a full-fledged finite element model indicates that the proposed simplified approach ensures a reliable description of the flow field; suggesting that the model provides a key advancement to study the bio-morphodynamic feedbacks which shape intertidal landscapes. Citation: Van Oyen, T., S. Lanzoni, A. D'Alpaos, S. Temmerman, P. Troch, and L. Carniello (2012), A simplified model for frictionally dominated tidal flows, Geophys. Res. Lett., 39, L12403, doi:10.1029/2012GL051949
Primo Lanzoni e la Geografia Commerciale cafoscarina agli inizi del Novecento, nelle parole di Gabriele Zanetto. Introduzione a "Primo Lanzoni, ovvero l'economia come antitesi all'ambientalismo nel pensiero geografico ottocentesco", di Gabriele Zanetto (versione originale 1985)
No full textSi tratta di una breve introduzione al contributo scritto da Gabriele Zanetto sulla figura di Primo Lanzoni, pubblicato originariamente nella Rivista Ricerche Economiche, 1(1985), pp. 70-103, e ri-editato per il volume "Le discipline economiche e aziendali nei 150 anni di storia di Ca' Foscari".The evolution of Economic Geography in the past century has been very complex. The
older conception of Commercial Geography, as mere description of the distribution of economic
factors, was substituted by a scientific interpretation of the natural conditions of economic activities.
The later school, called environmental determinism, produced an estrangement of economics and
economic geography, which was removed only very recently. The paper examines the thought of
an Italian geographer, working in Venice around the turn of the century, whose work now appears
as a forerunning example of a modern conception of geography, anti-determinist and related to the
logic of economics
The characteristics of caregivers attending adult and paediatrics patients in a Milan hospital
No full textBackground
The role of the caregiver has received increasing attention in recent years. This is due in part to today’s longer life expectancy, which has resulted in a larger population affected by chronic pathologies. But it is also due to the lack of suitable solutions provided by the social and health structures. This research aims to investigate in greater depth the characteristics and the needs of caregivers involved with adult and paediatric patients who are receiving treatment for acute pathologies in hospitals.
Study Design
Questionnaire
Methods
A questionnaire was used that was validated in a previous study. It was administered in the period from March 2014 to January 2015 at the Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico di Milano in six wards. The questionnaire was done anonymously.
Results
We administered 364 questionnaires which enabled us to identify the characteristics of adult and paediatric patients’ caregivers. Those in hospitals are prevalently women. Adult patients’ caregivers tend to be from 40 to 79 years of age, those of paediatric patients from 20 to 59.
Adult patients’ caregivers may often be the husband/wife (35%), or a son/daughter (32%). Paediatric patients’ caregivers for paediatric patients are almost always parents (97%).
The states of mind and the sensations felt by caregivers are anxiety and tension.
Conclusions
The increasing number and severity of the conditions of people needing care, the changing family structures and the economic crisis have compelled caregivers to perform tasks requiring technical skills that should not be expected of them, but which the circumstances do not allow them to evade. It emerges from an analysis of the data provided by this research that fuller use could be made of caregivers’ potentials by involving them to a greater extent in the care process by the healthcare providers
The role of the non-playing hand during topspin forehand in table tennis
No full textTheoretical tutorials and the scientific literature do not provide information on the proper use of the non-playing hand in table tennis. This study aimed to evaluate the course of the movement in the joints of the non-playing limb during a table tennis topspin forehand stroke (played after a backspin ball) and to determine the inter-individual movement variability. The study involved 12 male table tennis players (178.7 ± 5.5 cm, 70.0 ± 6.6 kg, 23 ± 3 y) at a competitive level. The participants performed one topspin forehand as a response to a backspin ball. Kinematics were measured using an Inertial Motion Unit–MR3 myoMuscle Master Edition system. Changes in the angles of the upper limb joints (with particular emphasis on the non-playing hand) during the forehand topspin were analyzed. A novel method of normalized function of variance was used to characterize areas of high/low variability of movement. Most of the movements in the joints of the non-playing limb were performed symmetrically to the playing one, especially in the hitting phase. A rapid change of direction characterizes these movements, just before or during the hitting phase, which may indicate a supportive, ‘driving’ character for these movements. High inter-individual variability for the duration of the entire movement cycle in both limbs was observed; higher in the non-playing limb. This perhaps indicates a greater degree of individualization on the non-playing side
Coastal wetlands at risk: Learning from Venice and New Orleans
No full textCoastal regions have progressively become more vulnerable to intense hydrodynamic and atmospheric events, thus raising important questions about their fate in the century of global warming. A variety of natural and anthropogenic factors have contributed to this fragility: eustacy, isostasy, soil compaction, reduced sediment supply and reduced extension of natural defenses (barrier islands and coastal wetlands). With the aim to emphasize the crucial role played by the intense human manipulation of the environment, we provide a brief overview of the state of knowledge on this extremely complex problem, moving from two cases of special importance: Venice and New Orleans. We discuss similarities (causes of wetland degradation and related restoration problems) as well as differences (different economical scales involved in the restoration projects, different risk reduction ensured by wetland and natural defense restoration and, finally, cultural relevance of the environment to be preserved) between these two regions
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