HART EFFECT AND EQUILIBRIUM IN INCOMPLETE MARKETS I

In this paper I reconsider the problem of the existence for GEI models. It is well known that existence for this kind of models can fail since there are bad spot prices. Using tools from Algebraic Geometry I show that the set of bad spot prices is tipically empty if the information tree, the number of secruities and the number of tradable goods at each node satisfy a well defined inequality. Even if such inequality is not staisfied I show that the set of bad spot price can be fully characterized and described using an algorithm and I give an universal bound for the cardinality of this set. Moreover, using these results, I prove that the equilibrium always exists for all endowment profiles.

Incomplete markets with no Hart points

We provide a geometric test of whether a general equilibrium incomplete markets (GEI) economy has Hart points---points at which the rank of the securities payoff matrix drops. Condition (H) says that, at each nonterminal node, there is an affine set (of appropriate dimension) that intersects all of a well-specified set of convex polyhedra. If the economy has Hart points, then Condition (H) is satisfied; consequently, if condition (H) fails, the economy has no Hart points. The shapes of the convex polyhedra are determined by the number of physical goods and the dividends of the securities, but are independent of the endowments and preferences of the agents. Condition (H) fails, and thus there are no Hart points, in interesting classes of economies with only short-lived securities, including economies obtained by discretizing an economy with a continuum of states and sufficiently diverse payoffs.Incomplete Markets, GEI model, Hart points

Evolution of floral morphology in Brunsvigia and Crossyne (Amaryllidaceae)

Floral morphology and its relationship to pollination syndromes is examined, for the genera Brunsvigia and Crossyne (Amaryllidaceae). These two genera have similar vegetative morphologies and share the same mode of seed dispersal (anemogeochory). They differ in their floral and inflorescence structures. The species Brunsvigia bosmaniae and Crossyne flava are chosen as representative species of the two genera Brunsvigia and Crossyne. Floral morphology is studied in relationship to an outgroup species Nerine humilis. Pollination syndrome, ability to self-pollinate, levels of natural seed set and patterns of seed dispersal are studied so that reproductive strategies pf the two species can be compared. Crossyne flava is pollinated by a suite of small diurnal insects and can be considered to have a generalist pollination syndrome. The first observation of pollination by moths in Brunsvigia bosmaniae is reported. I show that neither species is able to self, hence pollination events are important. Experimental manipulation reveals that Brunsvigia bosmaniae is pollinator limited. Although this experimental manipulation was not possible for Crossyne flava, high seed set levels in Crossyne flava suggests that levels of pollination are high in Crossyne and low for Brunsvigia. The amount of pollination that takes place is shown to be closely related to floral morphology. Floral divergence of the two genera is thus proposed to be the result of adaptation to a pollinator driven selective regime

Fatigue analysis of a post-buckled composite single-stringer specimen taking into account the local stress ratio

The fatigue life prediction of post-buckled composite structures represents still an unresolved issue due to the complexity of the phenomenon and the high costs of experimental testing. In this paper, a novel numerical approach, called “Min-Max Load Approach”, is used to analyze the behavior of a composite single-stringer specimen with an initial skin-stringer delamination subjected to post-buckling fatigue compressive load. The proposed approach, based on cohesive zone model technique, is able to evaluate the local stress ratio during the delamination growth, performing, in a single Finite Element analysis, the simulation of the structure at the maximum and minimum load of the fatigue cycle. The knowledge of the actual value of the local stress ratio is crucial to correctly calculate the crack growth rate. At first, the specimen is analyzed under quasi-static loading conditions, then the fatigue simulation is performed. The results of the numerical analysis are compared with the data of an experimental campaign previously conducted, showing the capabilities of the proposed approach

Monitoring the performance of residents during training in off-pump coronary surgery.

OBJECTIVE: Control charts (eg, cumulative sum charts) plot changes in performance with time and can alert a surgeon to suboptimal performance. They were used to compare performance of off-pump coronary artery bypass surgery between a consultant and four resident surgeons and to compare performance of off-pump coronary artery bypass surgery and conventional coronary artery bypass grafting within surgeons. METHODS: Data were analyzed for consecutive patients undergoing coronary artery bypass grafting who were operated on by one consultant or one of four residents. Conversions were analyzed by intention to treat. Perioperative death or one or more of 10 adverse events constituted failure. Predicted risks of failure for individual patients were derived from the study population. Variable life-adjusted displays and risk-adjusted sequential probability ratio test charts were plotted. RESULTS: Data for 1372 patients were analyzed; 769 of the procedures were off-pump coronary artery bypass operations (56.0%). The consultant operated on 382 patients (293 off-pump, 76.7%), and the residents operated on 990 (474 off-pump, 47.9%). Patients operated on by residents tended to be older, more obese, more likely to require an urgent operation, and more likely to need a circumflex artery graft but less likely to have triple-vessel disease. There were 7 conversions (consultant 5, residents 2). The overall failure rate was 8.5% (9.2% for consultant's operations and 8.2% for residents' operations), including 10 deaths (0.7%). Predicted and observed risks of failure were similar for all five surgeons. After 100 off-pump coronary artery bypass operations, performance was the same or better for the residents as for the consultant. For all surgeons, performance was the same or better for off-pump as for conventional coronary artery bypass grafting. CONCLUSIONS: Off-pump coronary artery bypass surgery can be safely taught to cardiothoracic residents. Implementation of continuous performance monitoring for residents is practicable

Cohesive analysis of a 3D benchmark for delamination growth under quasi-static and fatigue loading conditions

This paper evaluates the capabilities of the recently developed CF20 cohesive fatigue model, which can predict crack initiation as well as the rates of crack propagation by relying on intrinsic relationships between a stress-life diagram and its corresponding Paris law. The model is validated here using a partially reinforced double cantilever beam (R-DCB) benchmark proposed in literature. The two parameters needed for the CF20 cohesive fatigue model were obtained by performing preliminary analyses of a conventional DCB. The analysis results indicate that the CF20 cohesive fatigue model can accurately reproduce the complex evolution of the delamination observed in the R-DCB

Thermal, mechanical and electrical performance of structural epoxy resins filled with carbon nanofibers

Carbon nanofibers (CNFs) were heat-treated at 1100 & DEG;C (CNF1100) and 2500 & DEG;C (CNF2500), respectively, and embedded as fillers at different mass percentages into an epoxy mixture. The paper aims at evaluating, through a comparison between the two different types of resulting nanocomposites, the influence of the CNF heat treatment on the thermal, mechanical, and electrical performance of the formulated samples. Thermogravimetric analysis (TGA) showed oxidative stability in the air of CNF2500 approximately 200 & DEG;C higher than the CNF1100 ones. The first oxidation stage of the resins embedding the two typologies of CNFs falls between 380 and 480 & DEG;C. This means that the temperature of the heat treatment of the nanofiller does not influence the temperature at which the thermodegradation of the nanocomposites starts. Differential Scanning Calorimetry (DSC) data show that the highest degree of cure (DC) was recorded for the epoxy samples filled with CNF2500. CNF thermal treatment increases the direct current (dc) conductivity of the nanocomposite by 3 orders of magnitude around the electrical percolation threshold (EPT) and increases the storage modulus of the CNF2500-based resins up to 60 & DEG;C compared with the unfilled resin. The peculiar wall structure of CNF1100 determines a further slight enhancement. Tunneling Atomic Force Microscopy (TUNA) reveals that the CNFs are evenly distributed on the nanodomains showing higher electric current values for samples loaded with CNF2500

New records of Malus crescimannoi (Rosaceae) in Sicily

New findings for Malus crescimmanoi, originally known from the mountain area near Floresta (Nebrodi Mts.). The new sites fall in Madonie Mts., where the species is found at the edge of Quercus petraea (Matt.) Liebl. and Fagus sylvatica woods, growing on quartzarenitic substratum at 1200-1800 m of elevation. These new localities are placed at the south-western limit of Fagus sylvatica distribution area, on both north-facing [Contrada Sempria (Castelbuono) and slopes of Madonna dell\u2019Alto (Castellana Sicula)], and south-facing slopes [Locality Prato (Polizzi Generosa)]

Influence of interface ply orientation on delamination growth in composite laminates

The standard experimental procedures for determining the interlaminar fracture toughness are designed for delamination propagation in unidirectional specimens. However, in aerospace structural components, delamination usually occurs between plies at different orientations resulting in different damage mechanisms which can increase the value of the fracture toughness as the delamination propagates. Generally, numerical analyses employ the value measured at the delamination onset, leading to conservative results since the increase resistance of the delamination is neglected. In this paper, the fracture toughness and the R-curves of carbon/epoxy IM7/8552 are experimentally evaluated in coupons with delamination positioned at 0°/0° and 45°/−45° interfaces using Double Cantilever Beam (DCB) and Mixed-Mode Bending (MMB) tests. A simplified numerical approach based on the Virtual Crack Closure Technique (VCCT) is developed to simulate variable fracture toughness with the delamination length within a Finite Element code using a predefined field variable. The results of the numerical analyses compared with the experimental data in terms of load-displacement curves demonstrate the effectiveness of the proposed technique in simulating the increase resistance in delamination positioned between plies at 45°/−45° interface