The effect of matrix microstructure on the tensile and fatigue behavior of SiC particle-reinforced 2080 Al matrix composites

The effect of matrix microstructure on the stress-controlled fatigue behavior of a 2080 Al alloy reinforced with 30 pct SiC particles was investigated. A thermomechanical heat treatment (T8) produced a fine and homogeneous distribution of S′ precipitates, while a thermal heat treatment (T6) resulted in coarser and inhomogeneously distributed S′ precipitates. The cyclic and monotonic strength, as well as the cyclic stress-strain response, were found to be significantly affected by the microstructure of the matrix. Because of the finer and more-closely spaced precipitates, the composite given the T8 treatment exhibited higher yield strengths than the T6 materials. Despite its lower yield strength, the T6 matrix composite exhibited higher fatigue resistance than the T8 matrix composite. The cyclic deformation behavior of the composites is compared to monotonic deformation behavior and is explained in terms of microstructural instabilities that cause cyclic hardening or softening. The effect of precipitate spacing and size has a significant effect on fatigue behavior and is discussed. The interactive role of matrix strength and SiC reinforcement on stress within “rogue” inclusions was quantified using a finite-element analysis (FEA) unit-cell model.     

A Unified Curvature Definition for Regular,Polygonal, and Digital Planar Curves

In this paper, we propose a new definition of curvature, called visual curvature. It is based on statistics of the extreme points of the height functions computed over all directions. By gradually ignoring relatively small heights, a multi-scale curvature is obtained. The theoretical properties and the experiments presented demonstrate that multi-scale visual curvature is stable, even in the presence of significant noise. To our best knowledge, the proposed definition of visual curvature is the first ever that applies to regular curves as defined in differential geometry as well as to turn angles of polygonal curves. Moreover, it yields stable curvature estimates of curves in digital images even under sever distortions. We also show a relation between multi-scale visual curvature and convexity of simple closed curves.     

Preoccupied with predictive validity: An alternative perspective.

Psychologists have expressed concern over the problems of empirically establishing the predictive validity of individual assessments, and in particular the lack of empirical evidence for this practice. A case study is used to illustrate the benefits and drawbacks of externally conducted individual assessments to illustrate why predictive validity is only part of the picture. The consulting psychologist and client relationship are compared with the doctor and patient relationship, and this analogy is used to analyze the role of the consulting psychologist, and of the individual assessments that they conduct. Finally, the implications of conducting individual assessments for practicing within a scientist-practitioner model are examined. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Design of variable-stiffness conical shells for maximum fundamental eigenfrequency

Fiber-reinforced composite conical shells with given geometry and material properties are optimized for maximum fundamental frequency. The shells are assumed to be built using an advanced tow-placement machine, which allows in-plane steering of the fibers, resulting in a variable-stiffness structure. In this paper, different path definitions for variable-stiffness shells are provided and used to optimize conical shells for maximum fundamental frequency, while manufacturing constraints that apply for tow placement are taken into account in the process. The influence of manufacturing constraints on the performance is shown; and improvements of variable-stiffness conical shells over conventional, constant-stiffness shells are demonstrated.     

Capillary array electrophoresis-MALDI mass spectrometry using a vacuum deposition interface.

We previously introduced a vacuum deposition interface for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI/TOF MS) on a moving surface (e.g., quartz wheel, Mylar tape, metal target). In our present work, the approach has been extended to demonstrate parallel analysis for multiple on-line infusion MALDI MS and capillary array electrophoresis (CAE)-MALDI MS. In the infusion mode, individual peptide samples were simultaneously deposited on a Mylar tape cartridge using an array of eight capillaries, yielding eight parallel traces. For CAE-MALDI/TOF MS, the same number of separation capillaries were coupled with an array of eight infusion capillaries using a common liquid junction, containing matrix solution. A fast-scanning mirror was employed to traverse the beam of the desorption laser across the Mylar tape to probe one trace at a time. The positions of the eight sample traces formed on the tape were automatically determined, and all samples were analyzed in rapid sequence using a kilohertz repetition rate laser and a high-throughput data acquisition system. The instrumentation was operated with CAE MS for high-throughput analysis without compromising data quality. The principles of parallel separation-vacuum deposition should be generally applicable to MALDI/TOF MS analysis for proteomics and other areas where separation and high throughput are required.     

Calculating for concrete creep

The authors present an approximate method for calculating creep effects in concrete members and structures without recourse to computers. This 'effective time' method has been verified for accuracy by comparing the values thus predicted with results obtained by the step-by-step computer solution. Examples are given to illustrate its application. The authors are respectively Chief Scientific Officer and a PhD researcher at Prague Technical University.     

Polyphenol content and antioxidative activity in apple purées with rhubarb juice supplement

The purpose of the present study was to evaluate the effect of rhubarb juice addition and peeling in apple purée production and storage on its phenolic composition, antioxidant activity and colour. The apple material used in this study was of two varieties: Sampion and Idared. The apple purées prepared in three variants (control purées, peeling purées and purées with 5% of rhubarb juice) were stored for 3 and 6 months at 30 °C. Apple purées were investigated for their antioxidant activity, change of colour and contents of phenolic compounds plus the polymer procyanidins and degree of polymerization (DP). The preparation of purées from apples without peeling and the addition of rhubarb juice during purée preparation had significant influence on polyphenol content. The purée prepared from peeled apples of Idared variety had phenolic content 2.2 times lower than the control sample (non‐peeled apples). The highest level of total polyphenols was found in Idared + rhubarb sample (129.82 mg 100 g^?1 purée). The content of this compound in Idared control sample was more than 2.8 times lower than in Idared purées with rhubarb. The use of non‐peeled Idared apples and 5% of rhubarb juice in purée preparation significantly increased polymeric procyanidins from 11.68 to 75.20 mg 100 g^?1 and other phenolics from 9.23 to 54.62 mg/100 g. This effect for Sampion apples was smaller. The procyanidins during purées storage were more stable in samples with rhubarb juice addition. The purée samples with the addition of rhubarb juice had higher antioxidant activity measured using ABTS (2,2′azinobis‐(3‐ethylbenzthiazoline‐6‐sulphonic acid)) than purée samples without the addition (two times higher for Idared variety) of rhubarb juice. After 3 and 6 months of storage at temperature 30 °C, the antioxidant capacity decreased in all purées. Rhubarb juice had only high and positive effect on L* value in the case of Idared variety. The results showed that all Sampion apple purées had higher L* values than Idared.     

Influence of technological conditions on electronic transitions in chemical vapor deposited poly(azomethine) thin films

Thin films of poly(1,4-phenylenemethilidynenitrilo-1,4-phenylenenitrilomethilidyne) (PPI) have been prepared by chemical vapor deposition in the horizontal geometry using gaseous argon as a transport agent. PPI thin films have been grown by polycondensation of para-phenylene diamine (PPDA) and terephtal aldehyde (TPA). Fourier Transform Infrared spectra confirm formation of PPI layers without end groups. The strongest absorption band with discernible vibronic progression has been found to be due to superposition of 2.64, 2.82 and 3.03 eV bands corresponding to interband transitions connecting electronic ground state and vibrational levels of electronic excited state. A feature seen at about 2.6 eV in the spectra of PPI films prepared at higher temperatures of PPDA and TPA sources are attributed to excitons connected with the π-π? gap. Shoulder at 3.31 eV is attributed to interband transitions between delocalized states, while a peak at 4.2 eV is attributed to excitons formed by localized holes and delocalized electrons and vice versa and interband transitions connecting delocalized and localized bands, with the binding energy of about 0.8 eV. Thin films prepared at low temperatures of monomers consist of randomly distributed PPI chains weakly bound together.     

Effect of gate length in InAs/AlSb HEMTs biased for low power or high gain

The effect of gate-length variation on DC and RF performance of InAs/AlSb HEMTs, biased for low DC power consumption or high gain, is reported. Simultaneously fabricated devices, with gate lengths between 225 nm and 335 nm, have been compared. DC measurements revealed higher output conductance g_ds and slightly increased impact ionization with reduced gate length. When reducing the gate length from 335 nm to 225 nm, the DC power consumption was reduced by approximately 80% at an f_T of 120 GHz. Furthermore, a 225 nm gate-length HEMT biased for high gain exhibited an extrinsic f_T of 165 GHz and an extrinsic f_max of 115 GHz, at a DC power consumption of 100 mW/mm. When biased for low DC power consumption of 20 mW/mm the same HEMT exhibited an extrinsic f_T and f_max of 120 GHz and 110 GHz, respectively.     

Computer attitude scales: How relevant today?

Since the increase in the use of computers as learning tools, there have been many scales developed that can measure various aspects of ‘computer attitude’. The aim of this study is to examine the relevance of a number of these scales and determine whether they are still appropriate for use today. Four computer attitude scales, which are used widely, are assessed. It was found that the scales are reliable. However, the degree of predictive validity for each scale varied and the various underlying constructs appear to reflect different aspects of attitude. In addition, these constructs had changed since the original creation of the scales. This suggests that the traditional style of computer attitude scale is no longer as relevant as when first developed, and judicious selection and care need to be exercised over their use and the interpretation of findings.