The genetics and biochemistry of a propane-utilizing "Rhodococcus rhodochrous"

The pathways of terminal and subterminal propane oxidation have been investigated in a propane-utilizing R. rhodochrous PNKbl. NTG-generated pleiotrophic mutants, characterized by their inability to utilize propane have been isolated. Several classes of mutants have been obtained which are unable to metabolize potential propane oxidation intermediates, e. g. propanol (alcA- or alcB-), propanal (ald-), acetone (ket-), propanoate (oate-) and acetate (ace-). Only ket- mutants retained the ability to metabolize propane. Mutants defective in the first step of propane metabolism (aik-), were also unable to metabolize acetol (a potential subterminal intermediate). Mutant analysis suggests that propane is oxidized via terminal and subterminal pathways in R. rhodochrous PNKbl. However, acetone (a potential subterminal intermediate) does not appear to have a role in propane metabolism. A propane-specific 86 kDa NAD+-dependent secondary alcohol dehydrogenase has been purified to homogeneity. This enzyme oxidizes a range of primary and secondary aliphatic alochols (C2 to C8). It is also responsible for both propan-l-ol and propan-2-ol dehydrogenase activities measured in cell-free extracts of propane-grown cells. Western-blot analysis has shown that it is induced during growth on propane, propan-2-ol, acetol and acetate (subterminal intermediates); but not propan-l-ol, propanal propanoate (terminal intermediates) or acetone. This technique has also demonstrated that a conserved NAD+-dependent alcohol dehydrogenase was induced in Rhodococcus - Nocardia bacteria after growth on propane. SDS-PAGE revealed proteins specific to cells grown on propane and acetol, which may be components of a novel propane/acetol oxygenase system. Oxygenase activity, as demonstrated by the epoxidation of propene, was induced after growth on propane and acetol. NADPHdependent acetol oxygenase activity was also detected. These results suggest a relationship between the metabolism of propane and acetol. Mutants unable to utilize propan-l-ol or propan-2-ol (aicA- and aicB- respectively) were examined by assaying for NAD+-dependent propan-l-ol and propan-2-ol dehydrogenase activities, by using SDS-PAGE analysis of cell-free extracts and comparing the pattern and distribution of pol peptides with the wild-type, and by Western-blot analysis of the NAD -dependent secondary alcohol dehydrogenase synthesized by aicmutants. Results demonstrated the aic- mutants had generally lower NAD+-dependent alcohol dehydrogenase activities altered polypeptide patterns and that alcB mutants synthesized NAD-dependent secondary alcohol dehydrogenase which had altered electrophoretic mobility after non-denaturing PAGE. The latter result may explain the inability of these mutants to utilize propan-2-ol as a growth substrate. The development of a plasmid transformation and gene transfer system for R. rhodochrous PNKbl based on previously published methods has also been assessed. Finally, a model for the pathway of propane oxidation in R. rhodochrous PNKbl is also presented showing oxidation via terminal and subterminal carbon atoms

Out-of-plane motion of a planar dielectric elastomer actuator with distributed stiffeners

A new design for a multi-layer dielectric elastomer actuator, reinforced with periodic stiffeners is presented. The resulting actuator enables complex out-of- plane motion without the need of the elastomer membrane prestretch. An in situ optical imaging system is used to capture the complex deformation pattern and track the non-planar displacement and curvature under the applied voltage. The role of the stiffeners periodicity, φ, on the macroscopic actuator response is analyzed numerically utilizing ABAQUS finite element software. A user-material subroutine is developed to represent the elastomer deformation under the applied electric field. It is found that the actuator force-stroke characteristics can be greatly changed by varying φ, while maintaining the same overall actuator stiffness. The numerical results showed a band of localized deformation around the stiffeners. The refinement of the stiffener, φ, increases the total actuated volume within the span of the actuator, and thereby the macroscopic actuator stroke. The stored elastic strain energy within the actuator is also increased. φ might be further refined down to the actuator sheet thickness, wherein the localized deformation bands overlaps. This is the practical limit of the stiffeners spacing to achieve the largest macroscopic actuator stroke. The developed experimental and modeling framework would enable the exploitation and optimization of different actuator designs to achieve a preset load-stroke characteristic

Classification with the matrix-variate-t distribution

Matrix-variate distributions can intuitively model the dependence structure of matrix-valued observations that arise in applications with multivariate time series, spatio-temporal or repeated measures. This paper develops an Expectation-Maximization algorithm for discriminant analysis and classification with matrix-variate t-distributions. The methodology shows promise on simulated datasets or when applied to the forensic matching of fractured surfaces or the classification of functional Magnetic Resonance, satellite or hand gestures images

Improving the Efficiency of Electrical Stimulation Activities After Spinal Cord Injury

In order to enhance spinal cord injury (SCI) rehabilitation programs using neuromuscular electrical stimulation (NMES) and functional electrical stimulation (FES) it is important to examine the manner in which muscle fibers are recruited and the dose–response relationship. A review of the literature suggests that premature force decline and early fatigue with NMES and FES activities may be alleviated with decreased current frequency and increased current intensity. Dose–response relationships with NMES and FES are dependent on the goals of interest as reversing muscle atrophy can be achieved with activities 2–3 times per week for 6 or more weeks while increasing bone mass is more limited and requires more intense activity with greater exercise frequency and duration, e.g., 3–5 days per week for at least 6–12 months. The best known protocol to elicit neurological improvement is massed practice activities-based restorative therapies (ABRT) (3–5 h per day for several weeks)

Dielectric elastomer actuator with dual mechanical stiffness response

Inspired by bat wings which exhibit compliant response at lower stretch level to expand and a drastic stiffness change at higher stretch level to enable flapping. The bat-wing skin is highly anisotropic. The skin is more stretchable on spanwise direction and its stiffness becomes more than two orders of magnitude higher after stretched on chordwise direction. On the other hand, the skin on chordwise direction itself is less stretchable and with one order of magnitude of stiffness increase. A new composite dielectric elastomer actuator is developed to mimic such complex mechanical response of the bat through sets of variable stiffness reinforcement ligaments. The composite actuator is capable of initial large predetermined stretch, then exhibiting an order of magnitude increase in the actuator structural stiffness. The stiffners dimensions and geometric layout controls both the initial stretch and the final actuator stiffness. Details of the design, fabrication, and structural performance will be given in this study. Design domain limitations will also be explored

Fracture Mechanics-Based Quantitative Matching of Forensic Evidence Fragments

Fractured metal fragments with rough and irregular surfaces are often found at crime scenes. Current forensic practice visually inspects the complex jagged trajectory of fractured surfaces to recognize a ``match'' using comparative microscopy and physical pattern analysis. We developed a novel computational framework, utilizing the basic concepts of fracture mechanics and statistical analysis to provide quantitative match analysis for match probability and error rates. The framework employs the statistics of fracture surfaces to become non-self-affine with unique roughness characteristics at relevant microscopic length scale, dictated by the intrinsic material resistance to fracture and its microstructure. At such a scale, which was found to be greater than two grain-size or micro-feature-size, we establish that the material intrinsic properties, microstructure, and exposure history to external forces on an evidence fragment have the premise of uniqueness, which quantitatively describes the microscopic features on the fracture surface for forensic comparisons. The methodology utilizes 3D spectral analysis of overlapping topological images of the fracture surface and classifies specimens with very high accuracy using statistical learning. Cross correlations of image-pairs in two frequency ranges are used to develop matrix variate statistical models for the distributions among matching and non-matching pairs of images, and provides a decision rule for identifying matches and determining error rates. A set of thirty eight different fracture surfaces of steel articles were correctly classified. The framework lays the foundations for forensic applications with quantitative statistical comparison across a broad range of fractured materials with diverse textures and mechanical properties.Comment: 18 pages, 14 figures, 3 table