This combination of material properties and the range of their values has expanded in recent times and continues to expand with the development of composite materials. However, the use of composite ...materials also brings with it a number of disadvantages, which are generally offset by the great advantages that these materials provide. In this article, we intend to carry out a small study of a metal matrix composite material reinforced with ceramic particles, so one of the main objectives is to check the influence that the geometry and the size of the reinforcement particles have on the final properties of the composite material. The material used consists of a nickel alloy-based metal matrix reinforced with silicon nitride particles, and the methodology combines finite element analysis and scanning electron microscope analysis. For this purpose, different forms of reinforcement are going to be considered, with the existence of different types of particles and different sizes. It has been concluded that the process of decohesion of the reinforcement particles is ratified as a possible failure mechanism, which, together with the fracture of the reinforcements already considered for the calculation of the material properties, makes up the two main damage mechanisms that cause the fracture of metal matrix composite materials reinforced with particles.
Progress in composite materials is leading to new research lines in this field, creating analytical models to study their mechanical behaviour, improving manufacturing procedures or trying to improve ...the problems that appear at the matrix-particle interface. The material to be studied consists of a nickel alloy-based metal matrix reinforced with Silicon Nitride particles (Si3N4). According to the manufacturer's data, the particle fraction is 12% of the total volume of the material. The data used are the results of a microscopic analysis carried out on a series of specimens to establish the following concepts: mean size, size distribution and generic dimensions of the particles; distribution, orientation and orientation trends of the particles in the matrix; existence or not of clusters and probability of breakage, among others. The main objective of the research, to determine the influence of the geometry of the reinforcement particles on the mechanical behaviour of a composite material. It is concluded that the slenderness of the reinforcement particles influences the material properties by making these particles break more easily. In addition, the stress–strain graphs also show that their slenderness influences the stress and strain field, the elongated shape means that the reinforcement is located closer to the point of load application and, consequently, is subject to higher stresses due to the smaller amount of matrix it possesses.
In this work, the performance of a point-to-point fiber communication system that use a directly modulated (DML) VCSEL have been studied at 2.5, 10, and 40 Gb/s. We have demonstrated that a low-cost ...error-free transmission is possible by the appropriate choice of the shape of the driving electric pulse, the extinction ratio (ER) and the On-Off Keying (OOK) signal code (Non Return to Zero-NRZ and Return to Zero-RZ). Additionally, a theoretical model is developed to research and simulate the behavior of chirped signal transmission in dispersive media such as an optical fiber. Thus, the VCSEL-DML generated frequency chirp can be handled in order to avoid the effects of the interaction of laser chirp with fiber dispersion. The transmission performance of a 40 Gb/s optical link over Standard Single-Mode Fiber (SSMF) and over Negative Non-Zero Dispersion Shifted Fiber (NZDSF(−)) is researched by simulation.
This article discusses the influence of the thickness of the damping rings used for interrupting a dynamic tension experiments on the results of a modified split Hopkinson tension bar (SHTB). In this ...paper a device enclosed in an external fixture used for interrupting a dynamic tension experiment in a SHTB is studied. The novelty of this manuscript with respect to previous studies lies in the fact that the dynamic tension experiment in a SHTB is interrupted in order to study the mechanical behavior of the material at high strain rates. The role played by such device is to interrupt the experiment at different levels of plastic deformation, particularly when the specimen is about to reach its failure strength. Finite-element (FE) simulations of high-strain-rate tension experiments are accomplished on a particle-reinforced metal matrix composite specimen (namely SiC-reinforced ZC71 magnesium alloy) when varying the thickness of the damping rings. Interrupting the test before the specimen breaks offers the possibility of being able to study in a more detailed way the deformation process of such material at high strain rates. Therefore, this work focuses on the study of the behaviour of materials undergoing high strain rates, developing a tool which allows materials to withstand different levels of strain rates in a controlled manner and providing guidance for future studies. In view of this research, it can be concluded that the thickness of the damping rings is a factor that can resolutely influence the interrupted dynamic tension experiment results avoiding the specimen's failure by optimally buffering the experiment using 0.8 mm thick lead damping rings.
Clinical audits have reported considerable variability in COPD medical care and frequent inconsistencies with recommendations. The objectives of this study were to identify factors associated with a ...better adherence to clinical practice guidelines and to explore determinants of this variability at the the hospital level.
EPOCONSUL is a Spanish nationwide clinical audit that evaluates the outpatient management of COPD. Multilevel logistic regression with two levels was performed to assess the relationships between individual and disease-related factors, as well as hospital characteristics.
A total of 4508 clinical records of COPD patients from 59 Spanish hospitals were evaluated. High variability was observed among hospitals in terms of medical care. Some of the patient's characteristics (airflow obstruction, degree of dyspnea, exacerbation risk, presence of comorbidities), the hospital factors (size and respiratory nurses available) and treatment at a specialized COPD outpatient clinic were identified as factors associated with a better adherence to recommendations, although this only explains a small proportion of the total variance.
To be treated at a specialized COPD outpatient clinic and some intrinsic patient characteristics were factors associated with a better adherence to guideline recommendations, although these variables were only explaining part of the high variability observed among hospitals in terms of COPD medical care.
Highlights • We analyzed long-term adherence to CPAP in non-sleepy OSA. • 64.4% of the patients had good CPAP adherence after four years of follow-up. • Greater OSA severity was an independent ...predictor of good CPAP adherence. • Hypertension associated with high AHI predicted better CPAP adherence.
Background
Biologicals, in combination with chemotherapy, are recommended as first-line treatment of metastatic colorectal cancer (mCRC); however, evidence guiding the appropriate management of older ...patients with mCRC is limited.
Objective
This study was undertaken to compare the efficacy and safety outcomes in older versus younger patients with mCRC who received first-line biological therapy.
Methods
This retrospective analysis used pooled data from five trials undertaken by the Spanish Cooperative Group for the Treatment of Digestive Tumours. All were studies of adults with advanced CRC who received first-line treatment with chemotherapy plus bevacizumab, cetuximab or panitumumab, stratified by age (≥ 65 vs. < 65 years). Endpoints included progression-free survival (PFS), overall survival (OS), overall response rate (ORR) and safety.
Results
In total, 999 patients from five studies were included in the analysis: 480 (48%) were aged ≥ 65 years, and 519 (52%) were aged < 65 years. Median PFS did not differ significantly between patients aged ≥ 65 and < 65 years (9.9 vs. 9.4 months; hazard ratio HR 1.01; 95% confidence interval CI 0.88–1.17). Median OS was significantly shorter in older than in younger patients (21.3 vs. 25.0 months; HR 1.21; 95% CI 1.04–1.41). There was no significant difference between older and younger patients in ORR (59 vs. 62%). Patients aged ≥ 65 years experienced significantly more treatment-related grade 3 or higher adverse events (61.67%) than did patients aged < 65 years (45.86%).
Conclusions
Biologicals plus chemotherapy is an effective first-line treatment option for selected patients aged ≥ 65 years with mCRC and has a manageable safety profile and efficacy comparable to that observed in younger patients.
PDF
