217 research outputs found
Climate variability and international migration: an empirical analysis
No full textIs international migration an adaptation strategy to sudden or gradual climatic shocks? In this paper we investigate the direct and the indirect role of climatic shocks in developing countries as a determinant of out-migration flows toward rich OECD countries in the period 1990–2001. Contrarily to the bulk of existing studies, we use a macro approach and explicitly consider the heterogeneity of climatic shocks (type, size, sign of shocks and seasonal effects). Our results show that the occurrence of adverse climatic events in origin countries has significative direct and indirect effects on out-migration from poor to rich countries
Climate Variability, Extreme Weather Events and International Migration
No full textConiglio ND, Pesce G. Climate Variability, Extreme Weather Events and International Migration. COMCAD Arbeitspapiere - Working Papers, 92. Bielefeld: COMCAD - Center on Migration, Citizenship and Development; 2011
Network optimization problems subject to max-min fair flow allocation
No full textWe propose a novel way to consider the max-min fairness (MMF) paradigm in traffic engineering. Since MMF appears as a reference model for a fair capacity allocation when the traffic flows are elastic and rates are adapted based on resource availability, we consider it as a requirement due to the way resources are shared by the distributed rate control scheme (like that of the transport protocol), rather than the
routing objective. In particular, we define the traffic engineering problem where, given a network topology with link capacities and a set of elastic traffic demands to route, we must select a single path for each demand
so as to maximize a network utility function, assuming an MMF bandwidth allocation. We propose a compact
mixed-integer linear programming formulation as well
as a restricted path formulation. We show with com-
putational experiments that the exact formulation can
be solved in a reasonable amount of computing time
for medium-size networks and that the restricted path
model provides solutions of comparable quality much
faster
Noninvasive positive pressure ventilation in patients with acute exarcerbations of COPD and varying levels of consciousness
No full textA severely altered level of consciousness (ALC) has been considered a contraindication to noninvasive positive pressure ventilation (NPPV). We compared the clinical outcome of patients with acute respiratory failure (ARF) due to COPD exacerbations and different degrees of ALC.
DESIGN:
A 5-year case-control study with a prospective data collection.
SETTING:
Respiratory Monitoring Unit.
PATIENTS:
Eighty of 153 consecutive COPD patients requiring NPPV for ARF were divided into four groups, which were carefully matched for the main physiologic variables, according to the level of consciousness assessed with the Kelly-Matthay Score, in which 1 is normal (control subjects) and 6 is severely impaired.
MEASUREMENT AND RESULTS:
Changes from baseline in arterial blood gas (ABG) levels and Kelly score, the rate and causes of NPPV failure, the rate of nosocomial pneumonia, and the 90-day mortality rate were compared. NPPV significantly improved ABG levels and Kelly score in all groups after 1 to 2 h. NPPV failure (Kelly score 1 = 15%; Kelly score 2 = 25%; Kelly score 3 = 30%; Kelly score > 3 = 45%) and 90-day mortality rate (Kelly score 1 = 20%; Kelly score 2 = 35%; Kelly score 3 = 35%; Kelly score > 3 = 50%) significantly increased with the worsening of the level of consciousness. Using a multivariate analysis, the acute nonrespiratory component of the acute physiology and chronic health evaluation (APACHE) III score, and baseline pH independently predicted baseline Kelly score. After 1 to 2 h of NPPV, changes in the Kelly score were associated with those in pH. No correlation was found with Pa(CO2).
CONCLUSIONS:
This study confirms that NPPV may be successfully applied to patients experiencing COPD exacerbations with milder ALCs, whereas the rate of failure in patients with severely ALCs (ie, Kelly score > 3) is higher, even though better than expected, so that an initial and cautious attempt with NPPV may be performed even in this latter group. Changes in the level of consciousness induced by NPPV are not correlated with those in Pa(CO2)
Human capital accumulation and migration in a peripheral EU region: the case of Basilicata
No full textWe investigate the challenges that migration flows pose on policymaking aimed at fostering human capital accumulation in peripheral regions. We employ a unique data set generated through a postal survey designed and conducted by the authors. The focus of our analysis is on the micro-level location decisions of a sample of highly educated and skilled individuals residing in Basilicata, an Italian Mezzogiorno region, who have benefited from a locally funded human capital investment policy. Copyright (c) 2007 the author(s).
Reconstruction of high resolution rain patterns in space and time: a multisensor approach
No full textElastic traffic engineering subject to a fair bandwidth allocation via bilevel programming
No full textThe ability of TCP's congestion control scheme to adapt the rate of traffic flows and fairly use all the available resources is one of the Internet's pillars. So far, however, the elasticity of traffic has been disregarded in traffic engineering (TE) methodologies mainly because, only recently, the increase in access capacity has moved the bottlenecks from the access network to the operator network and hungry cloud-based applications have begun to use all the available bandwidth. We propose a new approach to TE with elastic demands which models the interaction between the network operator and the end-to-end congestion control scheme as a Stackelberg game. Given a set of elastic traffic demands only specified by their origin-destination pairs, the network operator chooses a set of routing paths (leader's problem) which, when coupled with the fair bandwidth allocation that the congestion control scheme would determine for the chosen routing (follower's problem), maximizes a network utility function. We present bilevel programming formulations for the above TE problem with two widely-adopted bandwidth allocation models, namely, max-min fairness and proportional fairness, and derive corresponding exact and approximate single-level mathematical programming reformulations. After discussing some key properties, we report on computational results obtained for different network topologies and instance sizes. Interestingly, even feasible solutions to our bilevel TE problems with large optimality gaps yield substantially higher network utility values than those obtained by solving a standard single-level TE problem and then fairly reallocating the bandwidth a posteriori
Elastic Traffic Engineering Subject to a Fair Bandwidth Allocation via Bilevel Programming
No full textThe ability of TCP’s congestion control scheme to adapt the rate of traffic flows and fairly use all the available resources is one of the Internet’s pillars. So far, however, the elasticity of traffic has been disregarded in traffic
engineering (TE) methodologies mainly because, only recently, the increase in access capacity has moved the bottlenecks from the access network to the operator network and hungry cloud-based applications have begun to use all the available bandwidth. We propose a new approach to TE with elastic demands which
models the interaction between the network operator and the end-to-end congestion control scheme as a Stackelberg game. Given a set of elastic traffic demands only specified by their origin-destination pairs, the network operator chooses a set of routing paths (leader’s problem) which, when coupled with the fair bandwidth allocation that the congestion control scheme would determine for the chosen routing (follower’s problem), maximizes a network utility function. We present bilevel programming formulations for the above TE problem with two widely-adopted bandwidth allocation models, namely, max-min fairness and proportional fairness, and derive corresponding exact and approximate single-level mathematical programming reformulations. After discussing some key properties, we report on computational results obtained for different network topologies and instance sizes. Interestingly, even feasible solutions to our bilevel TE problems with large optimality gaps yield substantially higher network utility values than those obtained by solving a standard single-level TE problem and then fairly reallocating the bandwidth a posteriori
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