Shape detection with vision: implementing shape grammars in conceptual design

Despite more than 30 years of research, shape grammar implementations have limited functionality. This is largely due to the difficult problem of subshape detection. Previous research has addressed this problem analytically and has proposed solutions that directly compare geometric representations of shapes. Typically, such work has concentrated on shapes composed of limited geometry, for example straight lines or parametric curves, and as a result, their application has been restricted. The problem of general subshape detection has not been resolved. In this paper, an alternative approach is proposed, in which subshape detection is viewed as a problem of object recognition, a sub-domain of computer vision. In particular, a general method of subshape detection is introduced based on the Hausdorff distance. The approach is not limited in terms of geometry, and any shapes that can be represented in an image can be compared according to the subshape relation. Based on this approach, a prototype shape grammar system has been built in which the geometry of two-dimensional shapes is not restricted. The system automates the discovery of subshapes in a shape, enabling the implementation of shape rules in a shape grammar. Application of the system is illustrated via consideration of shape exploration in conceptual design. The manipulations of sketched design concepts are formalised by shape rules that reflect the types of shape transformations employed by designers when sketching.     

Highly reflective nc-Si:H/a-CNx:H multilayer films prepared by r.f. PECVD technique

Multilayer thin films consisting of a-CN_x:H/nc-Si:H layers prepared by radio-frequency plasma enhanced chemical vapour (r.f. PECVD) deposition technique were studied. High optical reflectivity at a specific wavelength is one of major concern for its application. By using this technique, a-CN_x:H/nc-Si:H multilayered thin films (3-11 periods) were deposited on substrates of p-type (111) crystal silicon and quartz. These films were characterized using ultra-violet-visible-near infrared (UV-Vis-NIR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, field effect scanning electron microscopy (FESEM) and AUGER electron spectroscopy (AES). The multilayered films show high reflectivity and wide stop band width at a wavelength of approximately 650 ± 60 nm. The FTIR spectrum of this multilayered structure showed the formation of Si-H and Si-H₂ bonds in the nc-Si:H layer and CC and N-H bonds in a-CN_x:H layer. SEM image and AES reveal distinct formation of a-CN_x:H and nc-Si:H layers in the cross section image with a decrease in interlayer cross contamination with increasing number of periods.     

Fresh-cut lettuce in modified atmosphere packages stored at improper temperatures supports enterohemorrhagic E. coli isolates to survive gastric acid challenge

ABSTRACT:  Incidences of foodborne outbreaks involving enterohemorrhagic Escherichia coli strains with mutations in a key regulatory gene, rpoS , have been reported. Incentives, if any, for losing this regulatory function are not clear since the RpoS regulator is required for the expression of several environmental stress tolerance genes. RpoS also positively regulates 2 of the 3 acid-resistance systems of E. coli under aerobic growth conditions and enables the pathogen to survive gastric acid challenge. We selected 7 enterohemorrhagic E. coli isolates, 6 of which are known to carry defective rpoS gene, and then analyzed resistance to synthetic gastric juice after the strains were inoculated on fresh-cut lettuce and stored under modified atmosphere packaging (MAP) conditions. Subatmospheric oxygen partial pressures in MAP enabled all 6 rpoS- defective isolates to induce acid resistance over the 8-d storage period if the temperature was ≥ 15 °C. No acid resistance was induced for MAP-stored lettuce left at temperatures ≤ 10 °C or for lettuce packed and stored under aerobic conditions. The data underscore the impending danger of abusive storage temperatures especially with regard to the application of MAP to extend the shelf life of fresh produce. The results also highlight the biological significance of having multiple acid-resistance pathways and the complex regulatory network of enterohemorrhagic E. coli strains.     

Thermo-mechanical properties of poly(vinylidene fluoride) modified graphite/poly(methyl methacrylate) nano composites

Poly(methyl methacrylate) (PMMA) nano composites were synthesized by melt compounding technique. Different graphite loadings were investigated, including some treated with poly(vinylidene fluoride) (PVDF). A homogeneous dispersion of graphite throughout the PMMA matrix was observed under microscopic analysis. Thermo-gravimetric analysis showed the incorporation of graphite resulted in improvement of thermal stability of neat PMMA. Dynamic mechanical thermal analysis also showed a significant improvement in the storage modulus over the temperature range of 25–150 °C. Coating the graphite with a small amount of PVDF was found to further extend the improvement in the modulus of the PMMA nano composite at 1 wt.% graphite loading.     

Coordinating Multiple Agents via Reinforcement Learning

In this paper, we attempt to use reinforcement learning techniques to solve agent coordination problems in task-oriented environments. The Fuzzy Subjective Task Structure model (FSTS) is presented to model the general agent coordination. We show that an agent coordination problem modeled in FSTS is a Decision-Theoretic Planning (DTP) problem, to which reinforcement learning can be applied. Two learning algorithms, coarse-grained and fine-grained, are proposed to address agents coordination behavior at two different levels. The coarse-grained algorithm operates at one level and tackle hard system constraints, and the fine-grained at another level and for soft constraints. We argue that it is important to explicitly model and explore coordination-specific (particularly system constraints) information, which underpins the two algorithms and attributes to the effectiveness of the algorithms. The algorithms are formally proved to converge and experimentally shown to be effective.     

Structural integrity of polypropylene prosthetic sockets manufactured using the polymer deposition technique

Rapid prototyping (RP) technology has been used recently as a means for automated socket fabrication. Although the technology has proven to be promising and has truly automated the socket fabrication process, the structural integrity of RP sockets remains questionable. For the long term, unsupervised use of these 'unconventional' sockets, their material properties and structural integrity must be determined. This study investigated the structural integrity of polypropylene sockets manufactured using a polymer deposition technique, in which a socket is formed by a continuous strand of partially melted polypropylene that is spirally deposited according to the socket's cross-sectional contour. To investigate the problem of delamination of the socket, the tensile properties of the socket material were determined according to ASTM D638-99. The ultimate tensile strength was found to be approximately 13-23 per cent lower than that of polypropylene sheets that are at present normally used for socket fabrication. In order to improve the load-bearing capacity of the socket, it was reinforced using a double-wall arrangement at the distal region, where failure normally occurs. The structural integrity of the complete prosthesis was then investigated according to ISO 10328 (loading condition II). The prosthesis passed the static loading test registering only 12 mm permanent deformation, and it successfully completed a preliminary cyclic test of 250,000 cycles with no observable failure.     

Glass transition of polyethylene as studied by Brillouin spectroscopy

Summary The Brillouin spectrum of polyethylene has been measured as a function of temperature. Slope discontinuities of opposite directions have been observed in the Brillouin shift and width near the glass transition temperature. The former is attributed to a corresponding discontinuity in the temperature coefficient of specific volume, while the latter to the onset of long-range coordinated molecular motion near the transition region.     

Synthesis of fullerene-containing poly(alkyl methacrylate)s with narrow polydispersities

Copolymers of allyl methacrylate with methyl methacrylate or n-butyl methacrylate were synthesized by group transfer polymerization. The pendant allyl groups of the copolymers were then hydrobrominated, followed by reaction with sodium azide. Fullerene was incorporated via an addition reaction of fullerene with azide group. The resulting fullerene-containing poly(alkyl methacrylate)s have fairly narrow polydispersities. Received: 17 September 1997/Revised version: 4 November 1997/Accepted: 7 November 1997     

Studies on the incorporation of trans-polyoctenylene in polystyrene and PVC blends

trans-Polyoctenylene rubber, TOR, has been melt blended with PVC and with polystyrene, PS, in various proportions. PVC/TOR and PS/TOR blends were rigid, lending support to the claim that TOR improves dimensional stability of polymer and rubber blends. A processability study of PVC/TOR blends using a Brabender Plasti-corder showed that TOR is a suitable processing aid for PVC.     

Homolytic cleavage and aggregation processes in cyclopentadienylchromium chemistry

The reactivity of the cyclopentadienylchromium tricarbonyl dimer [CpCr(CO)3]2 (Cp = C5H5, 1) toward several classes of organo-P-, -S- and -N-compounds will be described. The organic substrates include the following: (i) bis(diphenylthiophosphinyl)disulfane, R2P(S)SSP(S)R2; (ii) bis(thiophosphoryl)disulfane, (RO)2P(S)SSP(S)(OR)2; (iii) tetraalkylthiuram disulfides, R2NC(S)SSC(S)NR2; (iv) tetraalkyldiphosphine disulfides, R2P(S)P(S)R2; (v) dibenzothiazolyl disulfide, (C6H4NSC)2; and (vi) Lawesson's reagent, (CH3OC6H4)2P2S4. The primary products, namely, the complexes CpCr(CO)2(SPR2), CpCr(CO)2)(S2CNR2), CpCr(CO)2(SCSN(C6H4)), and CpCr(CO)2(SPC6H4OCH3), containing the thiophosphinito, dithiocarbamate, 2-mercaptobenzothiazole, and dithiophosphorane ligands, respectively, arise from facile cleavage of the S-S, P-P, and P-S bonds in the organic substrates. Further treatment of these complexes with 1 under thermal activation results in cleavage of C-X (X = N, S), P-S, and Cr-E (E = C, N, P, S) bonds, accompanied by C-C and P-P bond formation in some cases, generating a variety of organometallic compounds belonging to the phosphido, phosphinidene, thiocarbenoid, dithiooxamide, aminocarbyne, aminoalkenylacyl, and cuboidal types.