Studies of polymer-cellulose blends prepared from solution

The conditions under which cellulose-cellulose triacetate (CTA) and cellulose-poly(acrylonitrile) (PAN) blends can be prepared from solution, are described in this paper. These two systems form transparent films when the blend contains less than 50% PAN or 60% CTA. Young's modulus, tensile strength, and elongation at rupture were measured for these blends. These values usually are between those of the corresponding homopolymers, except for the blend containing 10% polymer (PAN or CTA) which has a tensile strength value larger than that of cellulose. This result seems to indicate a certain level of compatibility for this blend. However, x-ray measurements indicate the presence of two crystal structures for these systems, suggesting that compatibility does not exist at the molecular level, in the crystalline fraction of the samples.     

Linear stability analysis and experimental verification of stratified air–water flow in a horizontal bend

Stratified flow in gas–liquid systems is a basic flow configuration which occurs frequently in industries due to the large density differential between the phases that helps to sustain stable stratification for relatively wide ranges of flow rates. The study on stability of stratified flow and the development of transitional criteria to various flow patterns have been very actively pursued for straight pipes, resulting in a broad understanding of the underlying mechanisms. Beside straight pipes, pipelines contain other fittings, which pose abrupt changes to the flow direction, and hence their impact on the flow stability needs to be ascertained.This study attempts to extend the linear stability analysis of stratified flows in a straight pipe to a horizontal bend. A model for the effect of a horizontal elbow on the transition from stratified to non-stratified patterns using the two-fluid approach is presented. The Inviscid Kelvin–Helmholtz (IKH) and Viscous Kelvin–Helmholtz (VKH) stability criteria for stratified flow transition are derived.Experiments are carried out using air and water in a 0.05 m diameter horizontal pipe work containing an intermediate bend of 0.5 m radius of curvature and the flow pattern observed in the bend is compared with the stability theory. The results show that the IKH and VKH stability criteria for stratified flow in a bend have identical forms as their counterparts in an inclined straight pipe, except that the tilt of the liquid lump in the bend which depends on the liquid velocity replaces the inclination angle for a straight pipe. The stable region is over-predicted by the IKH criterion while the VKH criterion shows good agreement for transition from stratified to slug flow if the liquid surface gradient is taken into account in the solution of the flow parameters under fully developed conditions.The work presented in this paper is of tremendous help to oil production engineers who need to know and control the flow regime transitions in order to avoid problems associated during production. These problems are mainly due to the generation of slug flow which leads to severe unwanted jigging.     

Error Detection Enhancement in COTS Superscalar Processors with Performance Monitoring Features

Increasing use of commercial off-the-shelf (COTS) superscalar processors in industrial, embedded, and real-time systems necessitates the development of error detection mechanisms for such systems. This paper presents an error detection scheme called Committed Instructions Counting (CIC) to increase error detection in such systems. The scheme uses internal Performance Monitoring features and an external watchdog processor (WDP). The Performance Monitoring features enable counting the number of committed instructions in a program. The scheme is experimentally evaluated on a 32-bit Pentium® processor using software implemented fault injection (SWIFI). A total of 8181 errors were injected into the Pentium® processor. The results show that the error detection coverage varies between 90.92 and 98.41%, for different workloads. To verify the experimental results an analytical evaluation of the coverage is also performed.     

Repair of Cracked Steel Girders Connected to Concrete Slabs Using Carbon-Fiber-Reinforced Polymer Sheets

This paper presents the results of an experimental study on the repair of artificially damaged steel–concrete composite beams repaired using adhesively bonded carbon-fiber-reinforced polymer (CFRP) sheets. Eleven, 2 m long, beams composed of W150×22 steel sections with 465×75?mm concrete slabs were tested in four-point bending. Severe damage was first introduced in ten beams by saw cutting the tension flange completely at mid span, to simulate a fatigue crack or a localized severe corrosion. Standard modulus (SM) and high modulus (HM) CFRP sheets were then used to repair nine damaged beams. The length and number of CFRP layers applied to the cracked flange on the underside, or on both sides, were varied. Results showed that the damage had reduced flexural strength and stiffness by 60 and 54%, respectively. Nevertheless, CFRP-repaired beams achieved various levels of recovery, and in some cases, exceeded the original capacities. The strength of beams repaired with sheets, ranging in length from 8 to 97% of the span, varied from 46–116% of the original undamaged strength, whereas the stiffness range was 86–126% of original stiffness. SM-CFRP failed by debonding whereas HM-CFRP was ruptured. Bonding the sheets to both sides of the flange was not very advantageous over bonding to the underside only.     

Preloaded RC columns strengthened with high-strength concrete jackets under uniaxial compression

Although use of high-strength reinforced concrete (RC) jackets has become common practice worldwide, there are still two unresolved issues regarding the contribution of the original concrete and the effects of existing loads. Twelve RC-jacketed columns were tested with and without preloading under uniaxial compression. Tests showed the entire core to contribute to the capacity of the jacketed column, as long as adequate confinement is provided. Also, preloading does not adversely affect the capacity of the jacketed column, while it may increase its deformability, especially in square sections. Transverse reinforcement in the jacket directly improves ductility of the strengthened column, especially in circular sections.     

Improved Two-Dimensional Millimeter-Wave Imaging for Concealed Weapon Detection Through Partial Fourier Sampling

Active millimeter-wave imaging based on synthetic aperture focusing offers certain unique and practical advantages in nondestructive testing applications. Traditionally, the imaging for this purpose is performed through a long procedure of raster scanning with a single antenna across a two-dimensional grid, leading to a slow, bulky, and expensive scanning platform. In this paper, an improved bistatic structure based on radial compressive sensing is proposed, where one fixed transmitter antenna and a linear array of receiving antennas are used. The main contributions of this paper are (a) reducing the scanning time, (b) improving the output quality, and (c) designing an inexpensive setup. These improvements are the result of the underlying proposed simpler scanning structure and faster reconstruction process.     

The influence of longitudinal cracks on the corrosion protection afforded reinforcing steel in high performance concrete

It is almost impossible to produce crack-free concrete and, therefore, codes of concrete structural design (such as ACI 318 [ACI 318, Building Code Requirements for Structural Concrete, American Concrete Institute: Farmington Hills, MI, USA]) take cracking into account and relate permissible crack widths to exposure conditions. Chloride ingress is significantly enhanced by cracks because the ions can penetrate the concrete cover from the walls of the crack as well as from the outer surface of the concrete [P. P. Win, M. Watanabe, and A. Machida, Penetration profile of chloride ion in cracked reinforced concrete. Cement and Concrete Research, 2004. 34(7): p. 1073–1079]. Thus, while the chlorides reach the steel very rapidly directly through the crack, they also reach adjacent areas of steel more rapidly than in uncracked concrete.The objective of the project was to ascertain whether high performance concrete (HPC) could provide superior protection to Ordinary Portland Cement Concrete (OPCC) even when the structure was cracked parallel to the reinforcing bars (longitudinal cracks) while being exposed to a de-icing salt environment. Two HPCs, as specified by the Ministry of Transportation of Ontario (MTO) [MTO, SSP 904 S13 High Performance Concrete, Amendment to OPSS 904 Construction Specification for Concrete Structures. 1995, Ontario Provincial Standard Specification] were tested: both used blended silica fume cement (Canadian Type 10 E-SF) and had 25% replacement of the cement by either fly ash or ground granulated blast furnace slag. A Class C-2 ordinary Portland cement concrete was used as control.In the case of cracks parallel to the rebar, HPC does not appear to have any beneficial influence on the corrosion of bars, which is not surprising in view of the fact that the whole length of the bar is directly exposed to the environment via the crack. In contrast, HPC has been found to provide better protection for steel exposed to transverse cracks than does OPCC. However, the benefits of HPC are not as great as they are for sound (uncracked) concrete. The reasons for the better protection are (i) the greater resistance of HPC to chloride penetration from the walls of the crack, (ii) its greater tendency to crack healing and (ii) the different crack path in HPC.     

Radiative and nonradiative relaxation phenomena in hydrogen- and oxygen-terminated porous silicon

Abstract

Using time-resolved photoluminescence spectroscopy over a wide range of temperatures, we were able to probe both radiative and nonradiative relaxation processes in luminescent porous silicon. By comparing the photoluminescence decay times from freshly prepared and oxidized porous silicon, we show that radiative processes should be linked with quantum confinement in small Si nanocrystallites and are not affected by oxidation. In contrast, nonradiative relaxation processes are associated with the state of oxidation where slower relaxation times characterize hydrogen-terminated porous silicon. These results are in a good agreement with the extended vibron model for small Si nanocrystallites.

PACS

78.55.Mb; 78.67.Rb; 78.47.jd     

Magnetic molecularly imprinted polymer nanoparticles coupled with high performance liquid chromatography for solid‐phase extraction of carvedilol in serum samples

Herein, we report a magnetic molecularly imprinted polymers (m‐MIPs) using Fe₃O₄ as a magnetic component, carvedilol as a template molecule for the solid‐phase extraction (MISPE) as the sample clean‐up technique combined with high‐performance liquid chromatography (HPLC) and for the controlled release of carvedilol at different pH values of 1.0 (simulated gastric fluid), 6.8 (simulated intestinal fluid), and 7.4 (simulated biological fluid). The adsorption kinetics was modeled with the pseudo‐first‐order and pseudo‐second‐order kinetics, and the adsorption isotherms were fitted with Langmuir and Freundlich models. The performance of the m‐MIPs for the controlled release of carvedilol was assessed and results indicated that the magnetic MIPs also have potential applications in controlled drug release. Furthermore, the m‐MIPs were applied to the extraction of carvedilol from human blood plasma samples. Carvedilol can be quantified by this method in the 2–350 μg L^?1 concentration range. The limit of detection and limit of quantification in plasma samples are 0.13 and 0.45 μg L^?1. The results from HPLC showed good precision (3.5% for 50.0 μg L^?1) and recoveries (between 85 and 93) using m‐MIP from human plasma samples. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41209.     

Amphiphilic Bicyclic Peptides as Cellular Delivery Agents

Two bicyclic peptides composed of tryptophan and arginine residues were synthesized from monocyclic peptide building blocks and evaluated as cellular delivery agents. [W₅G]‐(triazole)‐[KR₅] and [W₅E]‐(β‐Ala)‐[KR₅] containing triazole and β‐alanine linkers improved the cellular delivery of fluorescein (F′)‐labeled phosphopeptide F′‐GpYEEI (F′‐PP) by 7.6‐ and 19.3‐fold, respectively, in human ovarian adenocarcinoma cells. However, parent monocyclic peptide [R₅] and monocyclic peptide [WR]₄ only enhanced the cellular uptake of the phosphopeptide by only 1.3‐ and 3.7‐fold, respectively. Confocal microscopy showed that the corresponding fluorescein‐labeled bicyclic peptide F′‐[KW₄E]‐(β‐Ala)‐[KR₅] was localized in the cytosol and nucleus. Studying the cellular uptake of F′‐[KW₄E]‐(β‐Ala)‐[KR₅] in the presence of endocytosis inhibitors indicated that the clathrin‐ and caveolin‐dependent endocytosis are the main pathways for cellular uptake. The bicyclic peptide was able to improve antiproliferative activity of doxorubicin by 20 %. These data suggest that this bicyclic peptide can be utilized as a new class of cell‐penetrating peptides and cellular delivery tools.