Search

In this research, 8-mm-thick plates of 25%SiC/2124Al composite have been joined successfully by using an un-threaded WC¿Co tool which showed minimal tool wear. Decreasing the rotational and advancing speeds is a key factor to obtain successful joints. Defect-free welds, and a joint efficiency (100UTSjoint/UTSBaseMaterial) of up to 97%, can be achieved if a high forge force, Fz, (above some 15¿kN) is reached. Proportionality between the torque, M, and Fz is observed. High Fz values, and corresponding M, lead to high values of the total energy per unit length of weld, Htot, supplied by the tool to the workpiece. It is proposed that most of this energy is spent in plastic deformation of the high strength composite., Support from Projects MAT-05-0527, MAT-09-09545, and MAT13-48483-C2-2-P from MICINN, Spain, is gratefully acknowledged. The support of PhD grant BES-2010-030247 for one of the authors (F.C.) from MINECO is acknowledged.

Using standard Earned Value Management (EVM) protocols, the current approach to Earned Schedule (ES) is extended and formalized to establish its rigorous, theoretical foundation. A precise definition is provided for what we term the project's earned duration, whose creation completes the triad of planned, actual, and earned durations. The published ES formula emerges as a linear approximation, but is found to work with some nonlinear cost profiles, and the conditions under which it gives both correct and incorrect duration estimates are noted. In the several planned and earned value functional profiles examined, no approximations are required to derive an exact analytical expression for the final duration; most duration formulas are straightforward and useful. The reliability and accuracy of the duration formulas are demonstrated with several examples of real, nonlinear project data that represent large classes of projects. We conclude with practical guidance for project managers.

© 2014 Elsevier Ltd. Welding a high quality aluminum matrix discontinuously reinforced composite is a difficult task and can be expensive. Joining the composite to a commercial aluminum alloy can reduce costs by only using the expensive material where it is needed. The solid state process Friction Stir Welding, FSW, is a promising alternative to fusion welding techniques since it can avoid the problems related to the molten metal and its solidification. We study the effect of the lateral off-set on the strength and fracture location in welds of 8. mm thick 2024Al alloy and 17%SiC/2124Al composite. We used a novelty diagonal set up to adjust the rotational and welding speed, and to select the three lateral off-sets for straight welds. The lateral off-set determines the amount of plastic deformation that the plates' contact surface undergoes. Therefore, it affects the shape and bonding quality of the alloy-composite boundary, which determines the strength of these welds. The highest joint efficiency (90% of 2024Al-T351) was obtained for the centered off-set, which had the most resistant boundary. However, the results suggest that a joint with an off-set of around 1.5. mm into the retreating side could exceed the efficiency obtained.

The microstructure and mechanical properties of joints conducted by friction stir welding, FSW, at different rotational speeds in thick plates of a composite material with a high volume fraction of reinforcement, namely 2124Al/25vol%SiCp, are studied. Original particle-free regions vanish during the stirring process, leading to a homogeneous particle distribution. Occasional breakage of some large particles occurs. Tunnel defects appear at low rpm, and disappear at high rotational speeds. The size of the thermo mechanically affected zone, TMAZ, increases with increasing rpm. Ductility of the welds in the range of 10-15% is achieved in compression tests whereas a rather brittle behavior is obtained in tension. A strength difference, SD, effect between compression and tensile test is obtained. This accounts for the little detrimental effect of the FSW process on the matrix-reinforcement interface. The SD effect is attributed to the presence of a microscopic residual stress. © 2013 Elsevier Ltd. All rights reserved.

A model for project budgeting and scheduling with uncertainty is developed. The traditional critical-path method (CPM) misleads because there are few, if any, real-life deterministic situations for which CPM is a great match; program evaluation and review technique (PERT) has been seen to have its problems, too (e.g., merge bias, unavailability of data, difficulty of implementation by practitioners). A dual focus on the distributions of the possible errors in the time and cost estimates and on the reliability of the estimates used as planned values suggests an approach for developing reliable schedules and budgets with buffers for time and cost. This method for budgeting and scheduling is executed through either simulation or a simple analytical approximation. The dynamic buffers provide much-needed flexibility, accounting for the errors in cost and duration estimates associated with planning any real project, thus providing a realistic, practical, and dynamic approach to planning and scheduling.

In this paper, three simultaneous objectives – material requirements planning (MRP) completion time minimization, total cost minimization, and maximization of the quality of raw materials in an MRP system – are balanced by using a fuzzy multi-objective programming (F-MOP) model. Crashing the total MRP completion time; that is, reducing the time by increasing the resources, can improve on-time delivery to the customer. The goal is to determine the optimum crashing in an MRP context such that maximum total satisfaction is achieved. The approach proposed in this paper is given in both symmetric and asymmetric cases, and relevant results are presented and discussed. The model can help manufacturers deliver products on time, at low cost, with high quality.

Given a collection of accepted risks with corresponding impacts and probabilities over the life of a project (or a relevant portion), a method to estimate the total potential impact at a given certainty is presented. Project sponsors and managers can decide their risk tolerance and set aside corresponding contingency funds. This analytic method uses a binomial distribution with a probability equal to the risks’ average probability. At a desired statistical confidence level, the number of risks to consider is determined, and risks are ranked in descending order of either impact or expected value of impact. The ranked risks’ impacts are then summed over the specified number of risks, leading to an appropriate contingency budget. The budget found with this method compares extremely well with the one ascertained from numerical simulations of the risk occurrences.

A pragmatic procedure is suggested to determine the size of a projectpsilas, a programpsilas, or a system's risk contingency budget at any specified level of certainty, e.g., 99% confidence. The size of the budget is a function of the number of risks expected at the specified confidence level. The number of risks used for developing the contingency budget depends on the total number of risks to be considered and the estimated probabilities of occurrence of the risks. The exact number, derived from the binomial distribution, is given in a table or, when the number of risks to be considered is greater than about 20, by a simple formula. The findings suggest that a specific contingency budget amount can be set aside for the small fraction of risks that typically materialize. The specific numbers would depend on the risk tolerance of the organization.

Fly ashes from municipal waste incineration represent today an environmental problem because of their extremely fine size and the relevant quantities of heavy metals (Pb, Zn, Cd, etc.) mainly condensed on their surface. The inertisation by a vitrification process of municipal waste incineration fly ashes together with other inorganic waste such as coal combustion, fly ashes, steel dust, foundry sand, etc. can produce an inert and chemically stable glass. With this process, developed within the Waste Based Reinforced Materials project, cofinanced by the Life Environment Programme, a good quality glass has been produced. With this glass continuous fibres have been produced in a pilot bushing plant. The plastic and bituminous materials reinforced with these fibres have physical and mechanical properties comparable with those of commercial glass fibres.

This paper presents an evolutionary based method to obtain the un-stressed lattice spacing, d0, required to calculate the residual stress profile across a weld of an age-hardenable aluminum alloy, AA2024. Due to the agehardening nature of this alloy, the d0 value depends on the heat treatment. In the case of welds, the heat treatment imposed by the welding operation differs significantly depending on the distance to the center of the joint. This implies that a variation of d0 across the weld is expected, a circumstances which limits the possibilities of conventional analytical methods to determine the required d0 profile. The interest of the paper is, therefore, two-fold: First, to demonstrate that the application of an evolutionary algorithm solves a problem not addressed in the literature such is the determination of the required data to calculate the residual stress state across a weld. Second, to show the robustness of the approximation used, which allows obtaining solutions for different constraints of the problem. Our results confirm the capacity of evolutionary computation to reach realistic solutions under three different scenarios of the initial conditions and the available experimental data., Support from Projects MAT-09-09545 from MICINN and MAT2014-55415-C3-1-R from MINECO, Spain is gratefully acknowledged. Financial help from the ILL to conduct the neutron diffraction measurements on SALSA, experiments 1-02-6 and 1-02-10 is recognized. Support from Spanish Government Grant TIN 2008-00508 and TIN2014-54806-R, Spain is also acknowledged by J.I.H. and J.M.C.

A new formalism and a corresponding new notation for earned value analysis are presented. With compact, consistent, mnemonic notation, earned value calculations become more transparent and flexible, leading to insights about standard quantities and advances through new measures. As an example of the notation’s utility, it is used to generate a modified earned value approach that weights quantities according to their position in a project’s timeline.

The solution to a differential equation used frequently in ecology is found to reproduce the well-known S-curve seen in various aspects of project management. The solution is modified in a minor way to fit project management boundary conditions. An excellent fit of this theoretical curve to two samples of project cost data shows the utility of the formula. Numerical approximations valid under typical project conditions are utilized to produce an analytic expression that can easily generate classic project management evolution curves under a variety of conditions. The curves are normalized to two basic parameters: the total of the relevant quantity (e.g., project costs) and the duration of the project. The user can choose the steepness of the climb and the point in time at which half the total has been accumulated.

Delayed neurological sequelae of radiotherapy have several manifestations; leukoencephalopathy is one of the most common. Pathogenetic relationships between radiation leukoencephalopathy and other findings of diffuse radiation injury (brain atrophy and progressive ventriculomegaly) are not well defined. Moreover, no guidelines have been established for the treatment of hydrocephalus when associated with radiation leukoencephalopathy. Our study reports intracranial pressure (ICP) monitoring in two patients with radiation leukoencephalopathy with moderate hydrocephalus. High intraventricular mean pressure and high peaks were found, and marked improvement of clinical status after shunting was achieved. This study, although restricted to only two patients, shows that ventriculoperitoneal shunting insertion is useful in radiation-induced hydrocephalus, when ICP monitoring detects high mean pressure. A hypothesis is advanced concerning radiation-induced hydrocephalus with high ICP, emphasizing periventricular astrocytosis and its connections with cerebral compliance.

Procedures based on equilibrium conditions (stress and bending moment) have been used to obtain an unstressed lattice spacing, d0, as a crucial requirement for calculating the residual stress (RS) profile across a joint conducted on a 10 mm thick plate of age-hardenable AA2024 alloy by friction stir welding (FSW). Two procedures have been used that take advantage of neutron diffraction measurements. First, equilibrium conditions were imposed on sections parallel to the weld so that a constant d0 value corresponding to the base material region could be calculated analytically. Second, balance conditions were imposed on a section transverse to the weld. Then, using the data and a genetic algorithm, suitable d0 values for the different regions of the weld have been found. For several reasons, the comb method has proved to be inappropriate for RS determination in the case of age-hardenable alloys. However, the equilibrium conditions, together with the genetic algorithm, has been shown to be very suitable for determining RS profiles in FSW joints of these alloys, where inherent microstructural variations of d 0 across the weld are expected. © Published by Elsevier Ltd. All rights reserved., Support from Projects MAT-05-0527 and MAT-09-09545 from MICINN, and PIE 200960I076 from C.S.I.C., Spain, is gratefully acknowledged. Financial help from the ILL to conduct the neutron diffraction measurements on SALSA, experiments 1-02-6 and 1-02-10, is recognized. Support from Spanish Government Grants TIN 2008-00508 and MEC CONSOLIDER CSD00C-07-20811 and from Spanish MINECO (projects MAT2011-23455 and MAT2011-25991) is also acknowledged by J.I.H. and I.P.O., respectively.

Le cisti aracnoidee spinali costituiscono una causa rara di compressione midollare. Viene discussa la classificazione di questa entità patologica e presentate quattro osservazioni: una cisti intradurale dorsale, una in corrispondenza del tratto lombare, sempre intradurale, una extradurale con doppia localizzazione a livello del tratto dorsale ed una quarta intradurale in corrispondenza del foro di co-niugazione di C6. Dopo aver discusso l'eziopatogenesi delle cisti aracnoidee secondo i diversi autori, viene analizzato il meccanismo di crescita di queste cisti e le lesioni vertebrali associate. La presenza di concomitanti dismorfie vertebrali, il riscontro di una piccola massa lipomatosa in prossimità del polo inferiore della cisti, e l'osservazione della stessa lesione in consanguinei, fanno ritenere estremamente probabile l'eziopatogenesi disembriogenetica. Dopo aver descritto gli aspetti clinici e le diverse indagini neuroradiologiche utili per lo studio delle cisti aracnoidee, vengono riportati i principi di tecnica chirurgica ed i risultati ottenuti.

Carstensen and Rhodes1 have suggested that when, in stability programs, assays cannot be performed immediately after the protocol-designated storage time, then freezing them until such a time when assays can be performed would be a reasonable manner to retain the protocol schedule. They caution, however, that such a procedure may not be valid for dissolution data. The article to follow deals with real-time data showing that such a process is feasible for Nalidixic Acid tablets (and presumably for other tablets as well), and that, furthermore, the dissolution pattern would seem to be “frozen” as well.

Forty-nine patients with cerebral arteriovenous malformations (AVMs) were treated with preoperative embolization followed by resection using a microsurgical approach. In 27 patients, the AVM was located in an eloquent area; in 32 patients, the volume of the AVM was over 20 cm3. Preoperatively, flow-directed embolization was performed in 10 patients (28 procedures), selective embolization with threads was performed in 35 patients (46 procedures), and a combination of flow-directed and selective embolization was performed in 4 patients (12 procedures). The percentage of reduction of the AVM volume averaged 36% after embolization. Five minor complications (transient neurological deficits, in 2 cases associated with ischemic areas on the CT scan) were observed after embolization. The interval between the last embolization and surgery was as follows: within 10 days in 7 patients; between 11 and 20 days in 3 patients; between 21 and 30 days in 10 patients; between 31 and 60 days in 11 patients; and 2 months later in 18 patients. The efficacy of this combined treatment (embolization plus surgery) was evaluated by the incidence of hyperemic complications and the clinical outcome. Hyperemic complications occurred more frequently in patients with an AVM volume greater than 20 cm3. When compared with flow-directed embolization, selective embolization was linked with decreased bleeding during surgery; postoperatively, the incidence of cerebral edema was also lower. Clinical outcome was better after selective embolization, with no occurrence of major deficits and no mortality. When the percentage of reduction of the AVM volume after embolization was 40% or more, the incidence of intraoperative hyperemic complications was lower; moreover, new permanent deficits were never observed in patients with this volume reduction. A retrospective clinical comparison of two groups of patients with similar AVM volumes (>20 cm3)—those given combined treatment (n = 32) versus those treated by direct surgery alone (n = 27)—showed that intraoperative bleeding appeared to decrease in patients treated by embolization; the incidence of postoperative hyperemic complications was not different in the two groups. New major deficits and deaths were less frequent in patients treated by embolization (P= 0.05 for the incidence of major deficits); postoperative epilepsy was also less common in these patients. In conclusion, combined treatment with selective preoperative embolization and direct surgery may help the neurosurgeon in the treatment of large, high-flow AVMs, reducing the risks connected with their surgical removal. (Neurosurgery 29:358-368, 1991)

Potential prognostic anatomic and hemodynamic factors were evaluated in 248 patients with cerebral arteriovenous malformations (AVMs), all treated by direct microsurgical removal. The size of each AVM was calculated by its volume, obtained by the multiplication of the three AVM diameters by 0.52. A surgical classification of AVM location (in 11 groups) is proposed. Types of feeders and of drainage were classified as superficial or deep; the extent of the drainage system was classified according to a four-degree scale. The mean flow velocity in the main AVM feeder, detected using transcranial Doppler ultrasonography, was used as an indirect measure of AVM shunt flow in a small number of patients (n = 29). AVM volume was a very important prognostic factor: the incidence of hyperemic complications and the morbidity and mortality rate were significantly higher when the volume of the lesion was >20 cm3 (P< 0.0001 for hyperemic complications; P < 0.001 for permanent morbidity and mortality). The incidence of hyperemic complications and the morbidity rate were higher in AVMs in rolandic, inferior limbic, and insular locations than in AVMs in other locations. As for other anatomic factors: a) the presence of deep feeders significantly increased the incidence of hyperemic complications, as well as the morbidity and mortality rate; b) the presence of deep drainage significantly increased permanent morbidity only; c) the extension of the venous system was significantly related to the development of hyperemic complications, and to morbidity and mortality. Transcranial Doppler examination showed that mean flow velocities >120 cm/s in the main feeder were associated with a significantly higher rate of postoperative hematomas and transient deficits. A classification of cerebral AVMs that takes into account AVM volume and location, the type of feeders, the extent of the drainage system, and the main feeder flow velocity is suggested.

By estimating the X-ray intensities of old supernova remnants in the disk-halo interface, deductions can be made about the ability of isolated supernovae to have created a coronal halo.

A simple physical model of the dynamics of a young supernova remnant is used to derive a straightforward kinematical description of the reverse shock. With suitable approximations, formulae can then be developed to give the X-ray emission of the reverse-shocked ejecta. The results are found to agree favorably with observations of SN1006.

We introduce a million-second observation of the supernova remnant Cassiopeia A with the Chandra X-ray Observatory. The bipolar structure of the Si-rich ejecta (NE jet and SW counterpart) is clearly evident in the new images, and their chemical similarity is confirmed by their spectra. These are most likely due to jets of ejecta as opposed to cavities in the circumstellar medium, since we can reject simple models for the latter. The properties of these jets and the Fe-rich ejecta will provide clues to the explosion of Cas A., Comment: 4 pages LaTeX with 2 figures; ApJL,in press

Although meningiomas of the spinal district are frequently found, first presentation of these growths during pregnancy is extremely rare. Few cases have been reported in the literature up to now. In a series of 122 spinal meningiomas operated-on at our institution over the period 1962-1994, first neurological symptoms and signs became evident during pregnancy in two cases. Considering this noteworthy, the hydrodynamic and hormone-mediated mechanisms regarding meningioma growth during pregnancy and a review of the pertinent literature are discussed.

Success in the health care marketplace depends largely on satisfaction of the needs of patients and their physicians. To assess the success of specific physician bonding techniques and compare them to results obtained in an institution-specific study, the author surveyed hospital-based members of the College in late 1990. The outcome of the latter survey is summarized in this article.