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A 3D dislocation dynamics code linked to the finite element procedures is used to simulate the case of a matrix containing a cubical precipitate. Since the matrix and the precipitate do not have the same elastic moduli and thermal expansion coefficients, a heterogeneous stress field is generated in the whole volume when the sample is submitted to a temperature change. In many cases this may nucleate dislocations in the matrix as experimentally observed. Here, the phenomenon of dislocations nucleation in the matrix is simulated using dislocation dynamics and the first results are presented. In a first time, a glissile loop has been put surrounding a precipitate. The equilibrium position of the glissile loop is investigated in terms of the image stress field and the line tension of the loop. In a second time, the dislocations are introduced as a prismatic loop admitting a Burgers vector perpendicular to the plane containing the loop. The prismatic loops are moving in the sample according to the heterogeneous stress field resulting from the summation of the internal stress field generated by the dislocations and the stress field enforcing the boundary conditions, which is computed by the finite element method. The latter takes into account the presence of the precipitate as well as the interactions between the precipitate and the dislocations. The equilibrium configuration of the rows of prismatic loops is analysed and the spacing of loops is compared to the analytic solution.

The structure and strength of three-dimensional Lomer-Cottrell junctions are studied using four different models. These models represent increasing levels of sophistication, with each case including some new physical effect. The line tension approximation makes use only of the elastic self energy of the dislocation lines. The edge-screw dislocation dynamics model increases the sophistication by including the elastic interactions between all of the dislocation segments. At the next level of sophistication, the nodal dislocation dynamics method accounts for the dissociation of the core into partial dislocations. Finally, the quasicontinuum method takes into account the core effects at the atomic level. The results show that although the line tension model represents a huge simplification of the physics of dislocations, it is able to reproduce the equilibrium structure of any type of Lomer-Cottrell interaction, both in the absence and presence of an externally applied stress. The pseudo-analytical description can thus be used as a bench mark for the development of dislocation dynamics simulations.

NiTi endodontic rotary instruments subjected to alternating tension and compression stress in root canals may fracture without prior warning. Once broken, extracting the fractured part from the canal is a difficult job and is annoying to both the patient and the dentist. Warning of an imminent fracture during clinical use will be a great help to avoid medical and legal complications. A monitoring system employing Fiber Bragg Grating (FBG) sensors has been attempted. The reason of using FBG is its small size which is very promising in integrating with the handpiece of the endodontic equipment. When cracking developed in an rotary instrument, we expect the natural vibration frequency of the instrument changes. If we can pick up the stress wave transmitted through the structural components of the rotary instruments, we may be able to detect the occurrence of a crack. In the current work, we found that we can successfully locate the operation period in the time domain by picking up and analyzing the sound wave using FBG. Furthermore, by employing Fast Fourier Transform (FFT) on the signal, we can reveal the energy variation and the frequency shifting phenomenon in specific section of frequency domain. For some characteristic frequencies, it was found that the energy and frequency varied in a well-defined pattern during the period of crack growth. It is hoped that with these information, the fatigue failure of rotary instruments can be closely monitored to avoid/alleviate the occurrence of unexpected fracture during clinical use.

Some structures are vulnerable to localized internal damages incurred by impact of small objects. Previous work showed that the whereabouts of an impact event on a 0.8m×0.8m square aluminum plate can be located by analyzing the differential time-of-flight among signals picked up by a four-FBG (fiber Bragg grating) array. However, good location accuracy was obtained only when the impact position was well within the envelop of the sensor arrays. In the current work, it will be demonstrated when an impact occurs within ±60o on either sides of the FBG axis, the signal is strong and the time-of-flight can be measured accurately so that an impact can be located accurately to better than 1 cm. Beyond that range, the signal became heavily attenuated and masked by noises and the location errors could be larger than 20 cm. To investigate the possible directions for improvement on the system accuracy, FBG rosettes with two mutually perpendicular FBGs are used to replace single FBGs to alleviate the angular sensitivity problem. It was shown that with the rosette array, good location accuracy can virtually be extended to all over the plate.

ABSTRACTA distributed Brillouin fiber sensor was used to monitor the health of steel structures. We used this method on two steel beam specimens and longitudinal strain and cracks were detected well under different loads. The difference between the longitudinal strain measured by the distributed fiber sensor and that measured by strain gages is less than 4%. Traditional sensors or transducers that measure the average strain over a small region always miss cracks. The method proposed in this study gives very good results for the detection of cracks and the surrounding strain on a square pipe.

An impact monitoring system using an array of fibre Bragg grating (FBG) sensors has been established on a wind turbine blade. The effect of the locations and detection capability of the FBG have been investigated. The possibility to identify the location of an impact is also discussed. This preliminary work may shed some light on how to establish an optimal monitoring system with a minimum number of sensors while achieving the acceptable sensitivity and coverage. With such a system, the corresponding strain history and occurrence of local damage can be monitored, thus helping to narrow down the scope of more detailed examination during an overhaul and enabling the integrity of a wind turbine blade to be more reliably assessed and monitored.

Impact event monitoring and source location in some critical structures. The current work evaluated the feasibility and limitation of using fiber Bragg gratings (FBGs) for this purpose. Impact testing carried out on a cold rolled aluminum plate showed that impact event monitoring with the FBGs is feasible with the current intensity modulation interrogation method. Source location is successful at part of the impact location but not at the others. This phenomenon is caused by the complex wave propagation pattern on the plate so that differently oriented FBGs receive the signal from the same impact at different time.

This work aims at assessing the use of embedded fiber Bragg grating to monitor the internal damage evolution in polymeric composite during fatigue loading . The results suggested that the embedded FBGs have good potentials to detect the appearance of damage and to differentiate the damage types. The evolution in light spectrum during fatigue may be divided into four stages when compared against X-ray, C-scan and optical microscope (OM) results. These stages are associated with (1) matrix cracking in 90o lamina; (2) fiber splitting in the ±45o laminae; (3) fiber splitting in the 0o lamina ; and (4) delamination.

Acarbose fermentation was conducted by cultivation of Actinoplanes sp. CKD485-16. Approximately 2,300 mg/L of acarbose was produced at the end of cultivation along with 600 mg/L of the acarbose byproduct component C. Maltose, a known moiety of acarbose, should be maintained at high concentration levels in culture broths for efficient acarbose production. The acarbose yield increased with an increasing osmolality of the culture medium, with a maximum value of 3,200 mg/L obtained at 500 mOsm/kg. Component C was also produced in proportion to the osmolality. Conversion of acarbose to component C was accomplished with resting whole cells. Inhibitors of the conversion of acarbose to component C were sought since component C is probably derived from acarbose. Valienamine was found to be a potent inhibitor, resulting in a more than 90% reduction in component C formation at a 10 μM concentration. Effects were similar in a 1,500-L pilot fermentor with acarbose and component C yields of 3,490 and 43 mg/L at 500 mOsm/kg, respectively.

Imprinted polymers were synthesized using a mixture of pigments, N-glutamyl-rubropuctamine, and N-glutamyl-monascorubramine (I) as the template, and 2-methacrylamido-6-picoline or 4-aminostyrene as functional monomers, to obtain recognition materials capable of forming hydrogen bonds and charge interactions, respectively, with carboxyl groups of target I in the binding sites. The polymers were prepared thermally at a template loading of 5 mol% using ethylene-glycol dimethacrylate or trimethylolpropane trimethacrylate as crosslinkers and acetonitrile or tetrahydrofuran as porogens. The selective binding of I to both types of polymer was demonstrated, although aminostyrene-based materials showed higher overall adsorption and were studied in more detail. It was shown that the kinetics of binding of I from ethyl-acetate extracts of fermented Monascus sp. was very rapid and virtually all the pigment adsorbed can be released by washing the polymer with ethanol–water mixtures. The feasibility of reusing imprinted polymer in consecutive adsorption/desorption cycles was also demonstrated. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 232–239, 1999.

In order to predict the fatigue crack growth curve under random loading, an analytical model is proposed in this paper. In addition to the mean crack growth curve, the model also considers the statistical variation of the crack growth curves under the same nature of random loading, as well as the material reliability after certain loading cycles are applied. To check the applicability of the prediction model, several fatigue experiments are performed. After comparing the analytical result with the experimental result, the following conclusions are drawn. (i) Under the same mean value and standard deviation for the stress amplitudes, the fatigue crack growth curves are influenced by the probability density function of the stresses. (ii) An “equivalent constant loading” and a crack closure model lead to better prediction than any other model. (iii) The variation of the crack growth curves can be predicted accurately for shorter crack lengths and conservatively for longer crack lengths. (iv) The prediction of the statistical variation can be improved by modifying the definition of the equivalent constant loading. (v) Fatigue reliability can be reasonably estimated. The foregoing conclusions can be taken into consideration in the design of pressure vessels which are frequently subjected to transients of random nature.

In order to predict the fatigue crack growth curve under random loading, an analytical model is proposed in this paper. In addition to the mean crack growth curve, the model also considers the statistical variation of the crack growth curves under the same nature of random loading, as well as the material reliability after certain loading cycles are applied. To check the applicability of the prediction model, several fatigue experiments are performed. After comparing the analytical result with the experimental result, the following conclusions are drawn. (i) Under the same mean value and standard deviation for the stress amplitudes, the fatigue crack growth curves are influenced by the probability density function of the stresses. (ii) An “equivalent constant loading” and a crack closure model lead to better prediction than any other model. (iii) The variation of the crack growth curves can be predicted accurately for shorter crack lengths and conservatively for longer crack lengths. (iv) The prediction of the statistical variation can be improved by modifying the definition of the equivalent constant loading. (v) Fatigue reliability can be reasonably estimated. The foregoing conclusions can be taken into consideration in the design of pressure vessels which are frequently subjected to transients of random nature.

Abstract: Synthesis of two recombinant proteins (human glucagon and human growth hormone) was investigated in fed-batch cultures at high cell concentrations of recombinant Escherichia coli. The glucose-limited growth was achieved without accumulation of metabolic by-products and hence the cellular environment is presumed invariable during growth and recombinant protein synthesis. Via exponential feeding in the two-phase fed-batch operation, the specific cell growth rate was successfully controlled at the desired rates and the fed-batch mode employed is considered appropriate for examining the correlation between the specific growth rate and the efficiency of recombinant product formation in the recombinant E. coli strains. The two recombinant proteins were expressed as fusion proteins and the concentration in the culture broth was increased to 15 g fusion growth hormone l−1 and 7 g fusion glucagon l−1. The fusion growth hormone was initially expressed as soluble protein but seemed to be gradually aggregated into inclusion bodies as the expression level increased, whereas the synthesized fusion glucagon existed as a cytoplasmic soluble protein during the whole induction period. The stressful conditions of cultivation employed (i.e. high-cell-density cultivation at low growth rate) may induce the increased production of various host-derived chaperones and thereby enhance the folding efficiency of synthesized heterologous proteins. The synthesis of the recombinant fusion proteins was strongly growth-dependent and more efficient at a higher specific growth rate. The mechanism linking specific growth rate with recombinant protein productivity is likely to be related to the change in cellular ribosomal content.

Synthesis of recombinant protein (human mini-proinsulin) is investigated in fed-batch cultures at high cell concentration of recombinant Escherichia coli BL21(DE3)[pET-3aT2M2]. Transcription of the recombinant gene is controlled by a T7 promoter system. The human mini-proinsulin is characterized by a C-chain peptide consisting of only nine amino acids, whereas the C-chain peptide of natural human proinsulin is made up of 35 amino acids. It is expressed in a fusion protein with a small fusion partner (a peptide with 18 amino acids) and finally aggregated into insoluble inclusion bodies in cytoplasm of recombinant E. coli. The fermentative production of this small fusion mini-proinsulin may be of great advantage in enhancing the yield of human insulin. To find an optimum induction strategy, effects of various key cultivation variables on the mini-proinsulin production are examined in high cell density fed-batch cultures. No general correlation is found between preinduction specific growth rate and recombinant protein synthesis, which confers a flexibility in choosing the feeding strategy of preinduction media for achieving the high cell density cultures. A culture temperature below 37 °C is unfavorable for recombinant gene expression, and the T7-based expression system is almost completely repressed at 30 °C. The nutrient glucose and yeast extract concentration in postinduction feed media is optimized by applying a statistical method for medium optimization, i.e. response surface methodology, and an effective amount of inducer molecule (IPTG) is determined to maximize the specific recombinant protein formation. The mini-proinsulin production in E. coli culture is significantly influenced by the volumetric feed rate of postinduction media, which is shown to be closely related to the plasmid copy number in the recombinant cell. Consequently, in a single-stage fed-batch process, the mini-proinsulin concentration is increased up to 7 g/L, approximately 62 wt % of which corresponds to mature human insulin. A two-stage fed-batch fermentation process, with recombinant cell growth occurring at a constant growth rate and constant cell concentration in a growth fermenter and mini-proinsulin production in an induction fermenter, is designed, and its efficacy in increasing volumetric productivity of mini-proinsulin is demonstrated.