Segmented object manufacturing

Rapid Prototyping (RP) is a technology based on a “divide-and-conquer” strategy that enables automatic physical realization of a design without any special tooling. However, existing RP processes suffer from staircase defects since they are all based on 2.5-axis kinematics. To minimize the error due to staircase defects parts are normally built from very thin layers typically with thickness values of 0.010 to 0.300 mm. Therefore, hundreds of layers are required to produce a typical object making RP a slow and costly process. To overcome these limitations, a new RP process called Segmented Object Manufacturing (SOM) is proposed in this paper. SOM makes use of three-axis kinematics in conjunction with a novel slicing method. Slicing in SOM is based on certain visibility-based considerations and is independent of the part accuracy. Since only a few thick layers are used in the SOM technique, a part can be produced faster and cheaper with an accuracy comparable to that of CNC machining.     

The interaction between molten gallium and the hydrocarbon medium induced by ultrasonic energy—can gallium carbide be formed?

Ultrasonic irradiation of molten gallium in organic liquids (decane, dodecane, etc.) results in dispersion of the gallium into nanometric spheres. These were examined by several analytical methods XRD, DSC, Raman and IR spectroscopy) as well as electron microscopy (SEM, TEM) and found to be composed of Ga and C. The DSC analysis indicates that the Ga has possibly reacted with carbon, while the Raman spectrum of the product demonstrates a strong additional peak that could not be identified. This work explores the possibility that the product is gallium carbide or another gallium‐carbon complex. To investigate the nature of the product, we performed detailed extended X‐ray absorption fine structure (EXAFS) and X‐ray absorption near‐edge structure (XANES) analyses. On the basis of DSC, IR, and Raman it appear to be formation of GaC, whereas the analysis by EXAFS and XANES demonstrated that the gallium is found to be in a higher reduced state (almost metallic), supported by carbon. The question that remains open in addition to the one related to the formation of galium carbide is whether a complex structure, including oxygen contamination is involved in the layers surrounding the Ga as indicated by the EXAFS results.     

Aroma volatile compositions of high- and low-aromatic guava varieties

BACKGROUND: The traditional guava variety cultivated in Israel, ‘Ben Dov’, emits a very strong odour, whereas some newly bred varieties have a mild odour. In this study the aroma profile composition of the high‐aromatic ‘Ben Dov’ variety was compared with those of four new low‐aromatic varieties. RESULTS: Overall, using gas chromatography/mass spectrometry, a total of 30 aroma volatiles were detected in fresh ripe guava fruit: 15 of them were specifically detected only in the high‐aromatic ‘Ben Dov’ variety, 13 were detected in both the high‐ and low‐aromatic varieties and two were detected only in the new low‐aromatic varieties. Interestingly, 11 out of the 15 volatiles specifically detected in ‘Ben Dov’ were esters that contribute sweet, tropical and fruity notes. In contrast, ten out of 13 detected terpenes and two detected aldehydes, contributing green, spicy, herbal and woody notes, were common to both the high‐ and low‐aromatic varieties. CONCLUSION: Based on these findings, it is concluded that accumulation of esters is the main reason why the traditional ‘Ben Dov’ guava variety emits such a strong tropical fruity odour. In contrast, the newly bred low‐aromatic guava varieties did not synthesise esters at all and thus lacked fruity aromatic notes. Overall, the results of this study point out the important role of esters in forming tropical fruity guava odours. Copyright © 2011 Society of Chemical Industry     

Silver nanoparticles deposited on porous silicon as a surface-enhanced Raman scattering (SERS) active substrate

Silver nanoparticles were deposited spontaneously from their aqueous solution on a porous silicon (PS) layer. The PS acts both as a reducing agent and as the substrate on which the nanoparticles nucleate. At higher silver ion concentrations, layers of nanoparticle aggregates were formed on the PS surface. The morphology of the metallic layers and their SERS activity were influenced by the concentrations of the silver ion solutions used for deposition. Raman measurements of rhodamine 6G (R6G) and crystal violet (CV) adsorbed on these surfaces showed remarkable enhancement of up to about 10 orders of magnitude.     

Development of Through-Thickness Reinforcement in Advanced Composites Incorporating Rigid Cellular Foams

This paper presents a method of joining carbon-fibre plies and rigid cellular foam core with stitching for producing light-weight composite structures. After resin infusion and consolidation, the stitched sandwich panel exhibits superior damage tolerance as well as improved transverse properties due to the presence of through-thickness fibre reinforcement. First part of the paper deals with the conceptual development of a multi-needle stitching machine for rigid foams. A needle penetration model for computing the penetration forces has been reported—there is a good agreement between the experimental and theoretical penetration force-displacement curves. A number of sandwich panels with orthogonal and bias stitch orientations have been developed and examined for stitch quality with the aid of X-ray tomography. The paper also presents results from quasi-static indentation, three-point bending and transverse compression tests, on both the stitched and unstitched sandwich panels.     

Identification of aroma-active compounds in ‘wonderful’ pomegranate fruit using solvent-assisted flavour evaporation and headspace solid-phase micro-extraction methods

During the last few years, there has been a tremendous increase in consumption of pomegranate fruit and juice. Nevertheless, very little is yet known regarding the volatile constituents that determine the unique aroma of pomegranate fruit. We extracted aroma volatiles from fresh ‘Wonderful’ pomegranate juice using solvent-assisted flavour evaporation (SAFE) and headspace solid-phase micro-extraction (HS-SPME) methods, and applied gas chromatography–olfactometry (GC–O) (‘sniffing’) combined with gas chromatography–mass spectrometry (GC–MS) analysis, in order to identify volatile aroma-active compounds. In addition, we performed stir bar sorptive extraction (SBSE) of pomegranate aroma volatiles, coupled with GC–MS analysis, in order to assist in identifying aroma-active compounds. Overall, we tentatively identified 23 volatiles in the SAFE and HS-SPME extracts; they belonged to various chemical classes, including aldehydes, terpenes, alcohols, esters, furans and acids. Using the GC–O nasal impact frequency method, we tentatively detected 12 aroma-active peaks and identified the corresponding odourants by GC–MS. The aroma-active compounds of ‘Wonderful’ pomegranates were ethyl-2-methylbutanoate (fruity, apple), hexanal (green), β-pinene (pine, herbal), β-myrecene (woody, musty), cis-3-hexenal (green), limonene (fruity, musty), cis-2-heptenal (soapy, mushroom), cis-3-hexenol (earthy, grassy), 2-ethylhexanol (floral), β-caryophyllene (fruity, musty), 2(5H)-furanone (sweet, fruity) and β-sesquiphellandrene (terpene, almond). Overall, the flavour of ‘Wonderful’ pomegranate fruit derives from a mixture of various ‘green’, ‘woody’, ‘earthy’, ‘fruity’, ‘floral’, ‘sweet’ and ‘musty’ notes.     

Weldability of thin sheet metals by small-scale resistance spot welding using high-frequency inverter and capacitor-discharge power supplies

An investigation has been conducted of the weldability of 0.2-mm-thick sheet aluminum, brass, and copper in small-scale resistance spot welding using a high-frequency inverter and a capacitor-discharge power supply. The results have been compared to those of previous investigations using a line-frequency alternating current power supply. The effects of electrode materials and process parameters on joint strength, nugget diameter, weld-metal expulsion and electrode-sheet sticking were studied. This work has also provided practical guidelines for selection of power supplies, process parameters (welding current/pulse energy, welding time/pulse width, electrode forces, etc.) and electrode materials for small-scale resistance spot welding of thin sheet aluminum, brass and copper.     

A novel simultaneous unipolar multispectral integrated technology approach for HgCdTe IR detectors and focal plane arrays

In the last few years Rockwell has developed a novel simultaneous unipolar multispectral integrated HgCdTe detector and focal plane array technology that is a natural and relatively straightforward derivative of our baseline double layer planar heterostructure (DLPH) molecular beam epitaxial (MBE) technology. Recently this technology was awarded a U.S. patent. This simultaneous unipolar multispectral integrated technology (SUMIT) shares the high performance characteristics of its DLPH antecedent. Two color focal plane arrays with low-10¹³ cm⁻²s⁻¹ background limited detectivity performance (BLIP D^*) have been obtained for mid-wave infrared (MWIR, 3–5 m) devices at T>130 K and for long-wave infrared (LWIR, 8–10 m) devices at T∼80 K.