Evaluation of Fracture Surfaces in Carbon Fiber/Epoxy Composites

We have investigated carbon fiber/resin debonding mechanisms using wetting force scanning to examine the fracture surfaces. The wettability of the site of a resin microdroplet (50-150 μm long) on a fiber after debonding is compared with that of the original fiber surface by scanning along the fiber with an appropriate probe liquid. For an HMS/Epon828 system, debonding seems to involve removal of a layer of carbon fiber, while for an AS4/Epon828 system, there is evidence for adhesive failure as well as cohesive failures in both fiber and resin. These contrasting failure mechanisms are consistent with the morphological structures of the carbon fibers studied.     

Semi-parametric estimation in the compositional modeling of multicomponent systems from Raman spectroscopic data

Identification and quantification of molecular species are central applications of molecular spectroscopy. In complex multicomponent systems like tissue samples, linear parametric models are often used to estimate the relative concentrations of the biochemical components of the sample. In situations where not all of the components of the sample are known or modeled, such parametric models can suffer from omitted variable bias and result in skewed estimates of component concentrations. We propose a semi-parametric approach that tries to avoid this omitted variable bias by effectively including unknown covariates as a non-parametric term in the regression equation. Constituent concentrations estimated with such partial linear models should outperform strict parametric linear models when the user has limited information on the composition of a multi-constituent system.     

Transport behavior and negative magnetoresistance in chemically reduced graphene oxide nanofilms

The electron transport behavior in chemically reduced graphene oxide (rGO) sheets with different thicknesses of 2, 3, and 5?nm was investigated. The four-probe method for the sheet resistance (R(S)) measurement on the intensively reduced graphene oxide samples indicates an Arrhenius characteristic of the electron transport at zero magnetic field B = 0, consistent with previous experimental results on well-reduced GO samples. The anticipated variable range hopping (VRH) transport of electrons in a two-dimensional electron system at low temperatures was not observed. The measured R(S) of the rGO samples are below 52?kΩ/square at room temperature. With the application of a magnetic field up to 4?T, negative magnetoresistance in the Mott VRH regime was observed. The magnetotransport features support a model based on the spin-coupling effect from the vacancy-induced midgap states that facilitate the Mott VRH conduction in the presence of an external magnetic field.     

A Design of a PET Detector Using Micro-Channel Plate Photomultipliers with Transmission-Line Readout

A computer simulation study has been conducted to investigate the feasibility of a positron emission tomography (PET) detector design by using micro-channel plate (MCP) photomultiplier tubes (PMT) with transmission-line (TL) read-out and waveform sampling. The detector unit consisted of a 24×24 array of pixelated LSO crystals, each of which was 4×4×25 mm(3) in size, and two 102×102 mm(2) MCP-PMTs coupled to both sides of the scintillator array. The crystal (and TL) pitch was 4.25 mm and reflective medium was inserted between the crystals. The transport of the optical photons inside the scintillator were simulated by using the Geant4 package. The output pulses of the MCP-PMT/TL unit were formed by applying the measured single photo-electron response of the MCP-PMT/TL unit to each individual photon that interacts with the photo-cathode of the MCP-PMT. The waveforms of the pulses at both ends of the TL strips were measured and analyzed to produce energy and timing information for the detected event. An experimental setup was developed by employing a Photonis Planacon MCP-PMT (XP85022) and a prototype TL board for measuring the single photo-electron response of the MCP-PMT/TL. The simulation was validated by comparing the predicted output pulses to measurements obtained with a single MCP-PMT/TL coupled to an LSO crystal exposed to 511 keV gamma rays. The validated simulation was then used to investigate the performance of the proposed new detector design. Our simulation result indicates an energy resolution of ~11% at 511 keV. When using a 400-600 keV energy window, we obtain a coincidence timing resolution of ~323 ps FWHM and a coincidence detection efficiency of ~40% for normally-incident 511keV photons. For the positioning accuracy, it is determined by the pitch of the TLs (and crystals) in the direction normal to the TLs and measured to be ~2.5 mm in the direction parallel to the TLs. The energy and timing obtained at the front- and back-end of the scintillator array also show differences that are correlated with the depth of interaction of the event.     

Myofibrillar protein extracts from spent hen meat to improve whole muscle processed meats

Myofibrillar protein (MP) from spent hen meat was used as an ingredient for chicken breasts and pork hams. Cooking loss (CL) and texture of both products were evaluated. Salt-soluble MP was extracted following centrifugation. A brine with 6% MP or a brine without MP were injected into meat to 20% of the original meat weight. CL was reduced in pork hams treated with 6% MP (P<0.05). Chicken breasts with 6% MP had greater hardness and gumminess than those without MP (P<0.05). Pork hams with 6% MP had greater hardness, gumminess and chewiness than those without MP (P<0.05). It was concluded MP from spent hen meat may be used to improve the functional properties of whole-muscle meat products.     

Lidar observations of the diurnal variations in the depth of urban mixing layer: a case study on the air quality deterioration in Taipei, Taiwan

An aerosol light detection and ranging (LIDAR) system was used to measure the depth of the atmospheric mixing layer over Taipei, Taiwan in the spring of 2005. This paper presents the variations of the mixing height and the mixing ratios of air pollutants during an episode of air quality deterioration (March 7-10, 2005), when Taipei was under an anti-cyclonic outflow of a traveling high-pressure system. It was found that, during those days, the urban mixing height reached its daily maximum of 1.0-1.5 km around noon and declined to 0.3-0.5 km around 18:00 (LST). In terms of hourly averages, the mixing height increased with the ambient temperature linearly by a slope of 166 m/degrees C in daytime. The consistency between the changes in the mixing height and in the ambient temperature implied that the mixing layer dynamics were dominated by solar thermal forcing. As the cap of the mixing layer descended substantially in the afternoon, reduced dispersion in the shallow mixing layer caused the concentrations of primary air pollutants to increase sharply. Consequently, the pollutant concentration exhibited an anti-correlation with the mixing height. While attentions are usually focused on the pollution problems occurring in a morning inversion layer, the results of this study indicate that the air pollution and its health impacts could be even more severe as the mixing layer is getting shallow in the afternoon.     

Protection of copper corrosion by carbazole and N-vinylcarbazole self-assembled films in NaCl solution

Self-assembled films of carbazole (CZ) and N-vinylcarbazole (NVC) were prepared on copper surfaces. The corrosion protection abilities of the films were evaluated in an air-saturated 0.5 mol dm^–3 NaCl solution using electrochemical impedance spectroscopy (EIS), polarization and cyclic voltammetry. The results indicate that CZ and NVC form dense protective films on copper. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the film. It was found that the NVC molecules are tilted at an angle to the copper surface. The theoretical ab initio calculations support the experimental results.     

Room temperature ionic liquids as replacements for conventional solvents – A review

Room temperature ionic liquids are salts that are liquids at ambient temperature. They are excellent solvents for a broad range of polar organic compounds and they show partial miscibility with aromatic hydrocarbons. Typical room temperature ionic liquids have a stable liquid range of over 300 K and have a very low vapor pressure at room temperature. Ionic liquids that are not hydrolyzed show a wide range of solubility in water. These unique properties have suggested that they might be useful as environmentally benign solvents that could replace volatile organic compounds (VOC). By varying the length and branching of the alkane chains of the cationic core and the anionic precursor, the solvent properties of ionic liquids should be able to be tailored to meet the requirements of specific applications to create an almost infinitely set of “designer solvents”. A review of recent applications of ionic liquids is presented along with some results of measurements of liquid-liquid equilibria and partition coefficients with alcohols. The results are compared with predictions based on quantum mechanic calculations.     

A visualisation approach to learning the concept of recursion

This study investigated how a schematic-based visualisation approach implemented in an electronic learning environment facilitated the learning of the complex programming concept. The semantic-based visualisation approach applied Visualcode Rules and utilised various pictorial notations modeling the execution of recursive procedures. In this study, 38 college students studied the Scheme language and its recursive procedures in three different conditions. The three conditions were (a) the VisualScheme environment in which schematic-based pictorial notations (e.g. coloured icons and environment trees) were employed to help learners trace intermediate steps of executing procedures; (b) an Internet learning environment in which an ordered sequence of static pictorial notations provide a snap shot and illuminate execution of recursive procedures; (c) an Internet learning environment in which on-line source codes were annotated with detailed textual information. Results of the study indicated schematic-based pictorial notations helped students to form a better conceptual framework for learning the concept of recursion. It is suggested that the design of an electronic learning environment may appropriately apply meaningful pictorial information to help students learn complex programming concepts.