Gli hedge fund: caratteristiche, impatto sui mercati e ruolo nelle crisi finanziarie

Gli hedge fund (HF) sono sempre pi`u diffusamente considerati responsabili delle crisi finanziarie che si sono susseguite nel corso degli ultimi decenni. La loro natura di segretezza e la fama di particolare propensione al rischio, unite ad un ampio ricorso alla leva finanziaria, fanno si che questi operatori siano spesso indicati come principale causa dellaumento della volatilit`a ed instabilit`a dei mercati o quantomeno in grado di accentuarne fortemente le turbolenze. Per comprenderne correttamente il ruolo nelle situazioni di stress dei mercati, il lavoro ne analizza dapprima la natura e le caratteristiche distintive: principali strategie di investimento adottate, modalit`a di misurazione delle performance, struttura organizzativa tipica. Si esaminano poi i vantaggi che tipicamente la dottrina e la prassi riconoscono alla loro operativit` a: efficienza dei prezzi, liquidit`a dei mercati, innovazione innanzitutto. Si analizzano inoltre gli aspetti critici connessi allattivit degli HF, soprattutto in relazione alle situazioni di turbolenza dei mercati finanziari. Questa analisi `e essenziale per comprenderne il ruolo nellattuale crisi globale. Lo studio si conclude con alcune riflessioni sul dibattito che divide la comunit finanziaria circa lopportunit`a di introdurre misure specifiche di regolamentazione anche per lindustria degli HF

Joint PDF modelling of turbulent flow and dispersion in an urban street canyon

The joint probability density function (PDF) of turbulent velocity and concentration of a passive scalar in an urban street canyon is computed using a newly developed particle-in-cell Monte Carlo method. Compared to moment closures, the PDF methodology provides the full one-point one-time PDF of the underlying fields containing all higher moments and correlations. The small-scale mixing of the scalar released from a concentrated source at the street level is modelled by the interaction by exchange with the conditional mean (IECM) model, with a micro-mixing time scale designed for geometrically complex settings. The boundary layer along no-slip walls (building sides and tops) is fully resolved using an elliptic relaxation technique, which captures the high anisotropy and inhomogeneity of the Reynolds stress tensor in these regions. A less computationally intensive technique based on wall functions to represent boundary layers and its effect on the solution are also explored. The calculated statistics are compared to experimental data and large-eddy simulation. The present work can be considered as the first example of computation of the full joint PDF of velocity and a transported passive scalar in an urban setting. The methodology proves successful in providing high level statistical information on the turbulence and pollutant concentration fields in complex urban scenarios.Comment: Accepted in Boundary-Layer Meteorology, Feb. 19, 200

Monitoring and modelling of soil–plant interactions: the joint use of ERT, sap flow and eddy covariance data to characterize the volume of an orange tree root zone

Abstract. Mass and energy exchanges between soil, plants and atmosphere control a number of key environmental processes involving hydrology, biota and climate. The understanding of these exchanges also play a critical role for practical purposes e.g. in precision agriculture. In this paper we present a methodology based on coupling innovative data collection and models in order to obtain quantitative estimates of the key parameters of such complex flow system. In particular we propose the use of hydro-geophysical monitoring via "time-lapse" electrical resistivity tomography (ERT) in conjunction with measurements of plant transpiration via sap flow and evapotranspiration (ET) from eddy covariance (EC). This abundance of data is fed to spatially distributed soil models in order to characterize the distribution of active roots. We conducted experiments in an orange orchard in eastern Sicily (Italy), characterized by the typical Mediterranean semi-arid climate. The subsoil dynamics, particularly influenced by irrigation and root uptake, were characterized mainly by the ERT set-up, consisting of 48 buried electrodes on 4 instrumented micro-boreholes (about 1.2 m deep) placed at the corners of a square (with about 1.3 m long sides) surrounding the orange tree, plus 24 mini-electrodes on the surface spaced 0.1 m on a square grid. During the monitoring, we collected repeated ERT and time domain reflectometry (TDR) soil moisture measurements, soil water sampling, sap flow measurements from the orange tree and EC data. We conducted a laboratory calibration of the soil electrical properties as a function of moisture content and porewater electrical conductivity. Irrigation, precipitation, sap flow and ET data are available allowing for knowledge of the system's long-term forcing conditions on the system. This information was used to calibrate a 1-D Richards' equation model representing the dynamics of the volume monitored via 3-D ERT. Information on the soil hydraulic properties was collected from laboratory and field experiments. The successful results of the calibrated modelling exercise allow for the quantification of the soil volume interested by root water uptake (RWU). This volume is much smaller (with a surface area less than 2 m2, and about 40 cm thick) than expected and assumed in the design of classical drip irrigation schemes that prove to be losing at least half of the irrigated water which is not taken up by the plants

2016 Central Italy Earthquakes: comparison between GPS signals and low-cost distributed MEMS arrays

Abstract. Modern seismic ground-motion sensors have reached an excellent performance quality in terms of dynamic range and bandwidth resolution. The weakest point in the recording of seismic events remains spatial sampling and spatial resolution, due to the limited number of installed sensors. A significant improvement in spatial resolution can be achieved by the use of non-conventional motion sensors, such as low-cost distributed sensors arrays or positioning systems, capable of increasing the density of classical seismic recording networks. In this perspective, we adopted micro-electro mechanical system (MEMS) sensors to integrate the use of standard accelerometers for moderate-to-strong seismic events. In addition, we analyse high-rate distributed positioning system data that also record soil motion. In this paper, we present data from the 2016 Central Italy earthquakes as recorded by a spatially dense prototype MEMS array installed in the proximity of the epicentral area, and we compare the results to the signal of local 1s GPS stations. We discuss advantages and limitations of this joint approach, reaching the conclusion that such low-cost sensors and the use of high rate GPS signal could be an effective choice for integrate the spatial density of stations providing strong-motion parameters

Combining Models of Root-Zone Hydrology and Geoelectrical Measurements: Recent Advances and Future Prospects

Recent advances in measuring and modeling root water uptake along with refined electrical petrophysical models may help fill the existing gap in hydrological root model parametrization. In this paper, we discuss the choices to be made to combine root-zone hydrology and geoelectrical data with the aim of characterizing the active root zone. For each model and observation type we discuss sources of uncertainty and how they are commonly addressed in a stochastic inversion framework. We point out different degrees of integration in the existing hydrogeophysical approaches to parametrize models of root-zone hydrology. This paper aims at giving emphasis to stochastic approaches, in particular to Data Assimilation (DA) schemes, that are generally identified as the best way to combine geoelectrical data with Root Water Uptake (RWU) models. In addition, the study points out a more suitable objective function taken from the optimal transport theory that better captures complex geometry of root systems. Another pathway for improvement of geoelectrical data integration into RWU models using DA relies on the use of stem based methods as a leverage to introduce more extensive root knowledge into RWU macroscopic hydrological models

Site adverse reactions after intramuscular injections in adults: review of literature

Trata-se de um “survey” descritivo, com o objetivo de verificar os estudos das áreas médica e de enfermagem, que tratam da temática: complicações pós-injeções intramusculares, publicados no período de janeiro de 1970 a agosto de 1997. Foi realizado levantamento bibliográfico, através dos bancos de dados MEDLINE E LILACS. Os artigos foram catalogados em fichas individuais e analisados de acordo com complicações relatadas, causas apontadas, número de casos e tipo de medicação utilizada. Foram encontrados dezoito artigos abordando a temática. A reação adversa mais relatada foi a dor, embora dos seiscentos e setenta (670) casos de pacientes investigados, 61 (sessenta e um) apresentaram os tipos mais diversos de complicações, tais como manchas avermelhadas no local, hipertemia, edema e outros. Na amostra investigada, não houve artigos descrevendo complicações na região ventroglútea, o que permite sugerir que isso deve ser a região prioritária de aplicação de injeções intramusculares. A técnica de aplicação das injeções é importante e exige atenção e cuidados de todos os profissionais, não devendo ser utilizada por pessoas sem orientação técnica e científica.This study was a descriptive survey. The objetive was to verify the medical and nursing literature published between January, 1970 and August, 1997 about adverse reactions afterintramuscular injections. The MEDLINE and LILACS databases were used. The articles were classified into individual bases and analyzed following the complications cited, causes, number of cases and the medication used. It was found eighteen articles. The adverse reaction more cited was pain, although others reactions were cited as dermatitis, fever and others. In the investigated sample there were not articles describing adverse reactions in the ventro-glútea site. This confirms that it isthe best site of intramuscular injections. The technique of the intramuscular injections is very important and it is necessary attention, responsibility, scientific and technical knowledge of the professionals

Intramuscular site complications after sodium diclofenac injections

O uso da injeção intramuscular na terapêutica medicamentosa envolve, na atualidade, uma série de aspectos como: desvantagens quanto ao local, reações adversas e complicações surgidas após as injeções. Este estudo tem o objetivo de relatar o caso de uma paciente com complicações pós-aplicação de dezoito injeções de Diclofenaco de Sódio. As complicações apresentadas foram dermatológicas e musculares. Ao final, são discutidos cuidados a serem tomados na aplicação de injeções intramusculares, em especial, no uso de Diclofenaco de Sódio, a fim de se evitarem mais casos de complicações, após administração de medicações por via intramuscular.The use of intramuscular injections involves some disadvantages in the site of the injectons as adverse reactions and complications after the injections. This study aims to report a case of a patient with complications after eighteen injections of Diclofenac Sodium. The complications presented were of dermatological level and in the muscles. Authors discussed technical procedures to the administration of injections, specially in the use of the Diclofenac Sodium in order, to minimize cases with complications after intramuscular injections

Small-scale characterization of vine plant root water uptake via 3-D electrical resistivity tomography and mise-à-la-masse method

The investigation of plant roots is inherently difficult and often neglected. Being out of sight, roots are often out of mind. Nevertheless, roots play a key role in the exchange of mass and energy between soil and the atmosphere, in addition to the many practical applications in agriculture. In this paper, we propose a method for roots imaging based on the joint use of two electrical noninvasive methods: electrical resistivity tomography (ERT) and mise-à-la-masse (MALM). The approach is based on the key assumption that the plant root system acts as an electrically conductive body, so that injecting electrical current into the plant stem will ultimately result in the injection of current into the subsoil through the root system, and particularly through the root terminations via hair roots. Evidence from field data, showing that voltage distribution is very different whether current is injected into the tree stem or in the ground, strongly supports this hypothesis. The proposed procedure involves a stepwise inversion of both ERT and MALM data that ultimately leads to the identification of electrical resistivity (ER) distribution and of the current injection root distribution in the three-dimensional soil space. This, in turn, is a proxy to the active (hair) root density in the ground. We tested the proposed procedure on synthetic data and, more importantly, on field data collected in a vineyard, where the estimated depth of the root zone proved to be in agreement with literature on similar crops. The proposed noninvasive approach is a step forward towards a better quantification of root structure and functioning.</p