An interactive graphics-based model of the lower extremity to studyorthopaedic surgical procedures

We have developed a model of the human lower extremity to study how surgical changes in musculoskeletal geometry and musculotendon parameters affect muscle force and its moment about the joints. The lines of action of 43 musculotendon actuators were defined based on their anatomical relationships to three-dimensional bone surface representations. A model for each actuator was formulated to compute its isometric force-length relation. The kinematics of the lower extremity were defined by modeling the hip, knee, ankle, subtalar, and metatarsophalangeal joints. Thus, the force and joint moment that each musculotendon actuator develops can be computed for any body position. The joint moments calculated with the model compare well with experimentally measured isometric joint moments. We developed a graphical interface to the model that allows the user to visualize the musculoskeletal geometry and to manipulate the model parameters to study the biomechanical consequences of orthopaedic surgical procedures. For example, tendon transfer and lengthening procedures can be simulated by adjusting the model parameters according to various surgical techniques. Results of the simulated surgeries can be analyzed quickly in terms of postsurgery muscle forces and other biomechanical variables. Just as interactive graphics have enhanced engineering design and analysis, we have found that graphics-based musculoskeletal models are effective tools for designing and analyzing surgical procedures.     

Modeling of failure mode of laser welds in lap-shear specimens of HSLA steel sheets

Failure mode of laser welds in lap-shear specimens of high strength low alloy (HSLA) steel sheets is investigated in this paper. The experiments for laser welds in lap-shear specimens under quasi-static loading conditions are briefly reviewed first. The experimental results showed that the laser welds failed in a ductile necking/shear failure mode and the ductile failure was initiated at a distance away from the crack tip near the boundary of the base metal and heat affected zone. In order to understand the failure mode of these welds, finite element analyses under plane strain conditions were conducted to identify the effects of the different plastic behaviors of the base metal, heat affected zone, and weld zone as well as the weld geometry on the ductile failure. The results of the reference finite element analysis based on the homogenous material model show that the failure mode is most likely to be a middle surface shear failure mode in the weld. The results of the finite element analysis based on the multi-zone non-homogeneous material models show that the higher effective stress–plastic strain curves of the weld and heat affected zones and the geometry of the weld protrusion result in the necking/shear failure mode in the load carrying sheet. The results of another finite element analysis based on the non-homogeneous material model and the Gurson yield function for porous materials indicate that the consideration of void nucleation and growth is necessary to identify the ductile failure initiation site that matches well with the experimental observations. Finally, the results of this investigation indicate that the failure mode of the welds should be examined carefully and the necking/shear failure mode needs to be considered for development of failure or separation criteria for welds under more complex loading conditions.     

Reproducible Enhancement of Fluorescence by Bimetal Mediated Surface Plasmon Coupled Emission for Highly Sensitive Quantitative Diagnosis of Double‐Stranded DNA

Plasmonic enhancement of fluorescence from SYBR Green I conjugated with a double‐stranded DNA (dsDNA) amplicon is demonstrated on polymerase chain reaction (PCR) products. Theoretical computation leads to use of the bimetallic (Au 2 nm–Ag 50 nm) surface plasmons due to larger local fields (higher quality factors) than monometallic (Ag or Au) ones at both dye excitation and emission wavelengths simultaneously, optimizing fluorescence enhancement with surface plasmon coupled emission (SPCE). Two kinds of reverse Kretschmann configurations are used, which favor, in signal‐to‐noise ratio, a fluorescence assay that uses optically dense buffer such as blood plasma. The fluorescence enhancement (12.9 fold at maximum) with remarkably high reproducibility (coefficient of variation (CV) < 1%) is experimentally demonstrated. This facilitates credible quantitation of enhanced fluorescence, however unlikely to obtain by localized surface plasmons. The plasmon‐induced optical gain of 46 dB due to SPCE‐active dye molecules is also estimated. The fluorescence enhancement technologies with PCR enables LOD of the dsDNA template concentration of ≈400 fg µL^?1 (CV < 1%), the lowest ever reported in DNA fluorescence assay to date. SPCE also reduces photobleaching significantly. These technologies can be extended for a highly reproducible and sufficiently sensitive fluorescence assay with small volumes of analytes in multiplexed diagnostics.     

Proposed improvements in sand-lime bricks and mortar bonding

The results of a study by Asim Yeginobali and Hikmat Hammdouni provides valuable information for improving the quality of local masonry mortars, the sand-lime bricks and the bonding between them. As a result of this study, improvements have been recommended for both mortar content and sand-lime brick manufacture.     

A Hessenberg-Schur method for the problem AX + XB= C

One of the most effective methods for solving the matrix equationAX+XB=Cis the Bartels-Stewart algorithm. Key to this technique is the orthogonal reduction ofAandBto triangular form using theQRalgorithm for eigenvalues. A new method is proposed which differs from the Bartels-Stewart algorithm in thatAis only reduced to Hessenberg form. The resulting algorithm is between 30 and 70 percent faster depending upon the dimensions of the matricesAandB. The stability of the new method is demonstrated through a roundoff error analysis and supported by numerical tests. Finally, it is shown how the techniques described can be applied and generalized to other matrix equation problems.     

Computing integrals involving the matrix exponential

A new algorithm for computing integrals involving the matrix exponential is given. The method employs diagonal Padé approximation with scaling and squaring. Rigorous truncation error bounds are given and incorporated in a Fortran subroutine. The computational aspects of this program are discussed and compared with existing techniques.     

A new mesoporous FeBO3 material having dominant surface magnetism

A new mesoporous iron(III) borate material has been synthesized hydrothermally by using supramolecular assembly of cationic (cetyltrimethylammonium bromide, CTAB) or anionic (sodiumdodecyl sulfate, SDS) surfactant as structure directing agent (SDA) during co-condensation of Fe(III) and H₃BO₃ under controlled pH condition. Powder X-ray diffraction, N₂ sorption, HRTEM, FE-SEM-EDS, AAS, FT-IR and UV–Vis spectroscopic tools, Mössbauer and magnetization measurements are used to characterize the nanostructure, porosity, morphology, chemical composition and magnetic properties. Template molecules can be removed from the as-synthesized material by two consecutive HCl–EtOH extraction and the template-free sample showed good surface area with a peak pore width of ca. 2.6 nm. Spectroscopic results suggested the octahedral coordination of Fe(III) in the FeBO₃ framework. Magnetic measurements suggested the coexistence of antiferromagnetic core and the glassy magnetic behavior. The glassy magnetic behavior is ascribed to the dominant surface magnetism for mesoporous FeBO₃. Acid catalytic properties of this material in liquid phase benzylation of mesityline and anisole have been studied.