Fractional anisotropy‐weighted front evolution algorithm for white matter tractography based on diffusion tensor imaging data

Tractography is one of the most important applications of diffusion tensor imaging (DTI) which noninvasively reconstructs 3D trajectories of the white matter tracts. Because of the intravoxel orientation heterogeneity of DTI data, some of tractography algorithms are unable to follow the correct pathways after the crossing and branching regions. Front propagation techniques are efficient methods in tracking the crossing fibers. A key parameter influencing the performance of these algorithms is the cost function which is mainly based on the colinearity of tensors' eigenvectors. The effect of the eigenvalues on the anisotropy strength of tensor has not been previously addressed in the definition of the speed function. In this article, a new speed function, based on the effect of diffusion anisotropy and the colinearity of eigenvectors is proposed. The performance of the suggested method on fiber tracking and crossing fiber detection has been evaluated using synthetic datasets, and the feasibility of the proposed method was shown by fiber tracking implemented on real DTI data. © 2011 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 21, 307–314, 2011     

Effect of formulation ingredients on the physical characteristics of salmeterol xinafoate microparticles tailored by spray freeze drying

Series of microparticles containing salmeterol xinafoate (SX) as active pharmaceutical ingredient (API) and lactose, mannitol or trehalose as a bulking agents were prepared using spray freeze drying (SFD) technique and the effects of sugar type and presence of hydroxy propyl beta cyclodextrin (HPβCD) on the physical properties of powders were evaluated. Precipitation of salmeterol in the presence of lactose and mannitol resulted in the formation of irregular shapes of microparticles with broad size distributions. However application of trehalose resulted in the formation of porous particles with spherical morphology. Addition of cyclodextrin in the formulations was generally helpful for formation of porous and spherical particles with narrow size distribution with a mean size of 10–30 μm. Dissolution of SX from processed particles was substantially higher (～90% drug release in 30 min) than that of unprocessed drug and physical mixture of drug and cyclodextrin (～22% drug release in 30 min). This study showed that, processing of SX by SFD technique could be a constructive approach to the production of various forms of drug and drastic changes in the physical characteristics of microparticles could be achieved by changing the composition of bulking agent and cyclodextrin.     

Ultrasonic-assisted ball burnishing of aluminum 6061 and AISI 1045 steel

In the present work, experimental study was carried out to enhance the surface properties of aluminum 6061 and AISI 1045 steel plates by ultrasonic-assisted ball burnishing process. Full factorial experimental design was utilized here to find the effect of ultrasonic vibration, feed rate, and pass number on surface roughness and hardness. The results were discussed according to interaction effect of process factors for different material. It is found from the results that for conventional burnishing process, the highest surface hardness is attained at 5000?mm/min feed rate and 5 pass number, while for ultrasonic-assisted burnishing, the highest hardness is attained at 1000?mm/min feed rate and 5 pass number. On the other hand, it is found from the results that exerting ultrasonic vibration significantly enhances the hardness value and hardened depth. Also, it is found that irrespective of type of operation and material, increase in feed rate causes higher roughness, whereas increase in pass number causes reduction in roughness. Furthermore, surface roughness of ultrasonic-assisted burnishing is lower than that of conventional burnishing process. This enhancement is due to the association of both static and dynamic loading in ultrasonic-assisted burnishing process that causes microstructure modification and limits the elastic recovery of the surface.     

3D Biomaterial Microarrays for Regenerative Medicine: Current State‐of‐the‐Art,Emerging Directions and Future Trends

Three dimensional (3D) biomaterial microarrays hold enormous promise for regenerative medicine because of their ability to accelerate the design and fabrication of biomimetic materials. Such tissue‐like biomaterials can provide an appropriate microenvironment for stimulating and controlling stem cell differentiation into tissue‐specific lineages. The use of 3D biomaterial microarrays can, if optimized correctly, result in a more than 1000‐fold reduction in biomaterials and cells consumption when engineering optimal materials combinations, which makes these miniaturized systems very attractive for tissue engineering and drug screening applications.     

Investigation of thermoelastic damping in rectangular microplate resonator using modified couple stress theory

Thermoelastic damping is a significant energy lost mechanism at room temperature in micro-scale resonators. Prediction of thermoelastic damping (TED) is crucial in the design of high quality MEMS resonators. In this study the governing equations of motion and the thermal couple equation of a microplate with an arbitrary rectangular shape are derived using the modified version of the couple stress theory. Analytical expressions are presented for calculating the quality factor (QF) of TED in a rectangular microplate considering the plane stress and plane strain conditions. As a case study, a rectangular microplate resonator is considered with material property of gold that has a considerably high value of length-scale parameter in comparison with silicon and the effect of the length-scale parameter on the QF of TED is discussed in detail. The relation between QF and temperature increment for microplates with clamped boundary conditions based on plane stress and plane strain models are studied and results obtained by considering classical and modified couple stress theory (MCST) are compared. The effect of thickness of the plate on the rigidity ratio is studied and the critical thickness which is an important design parameter is obtained using the MCST for three boundary conditions. Variations of TED versus the plate thickness for various boundary conditions according to the classical and the modified couple stress theories are investigated.     

Photonic crystal directional coupler for all-optical switching,tunable multi/demultiplexing and beam splitting applications

In this paper, we introduce a new configuration based on the combination of photonic crystal directional coupler and nonlinear electromagnetically induced transparency (EIT) phenomenon in solid-state materials. The proposed structure has the abilities of switching, tunable multi/demultiplexing and tunable power beam splitting. These applications are attainable in the same structure by modulating the refractive index of special regions via EIT effect. This effect causes a high reduction in the required optical control power for the desired refractive index change, compared to the other nonlinear methods. Band structure calculations and simulations of optical field propagation through the device are done by plane wave expansion and finite difference time domain methods, respectively. In the switching mechanism, extinction ratios of 11.38?dB in the linear regime (with the control signal being off) and 26.63?dB in the nonlinear regime (with the presence of control signal) are achievable. Also, the proposed structure operates as a two-channel multi/demultiplexer for wavelengths of 1550?nm and 1480?nm in the linear regime, for wavelengths of 1550?nm and 1600?nm in both linear and nonlinear regimes, and for wavelengths of 1480?nm and 1600?nm in the nonlinear regime (the nonlinear regime is the same as the nonlinear regime for the switching). Since different refractive indices are obtained by changing the power of the control signal, the wavelengths for multi/demultiplexer operation can be tunable. Finally, simulation results show that the suggested structure can operate as a tunable power beam splitter at the wavelength of 1550?nm.     

25th Anniversary Article: Double Emulsion Templated Solid Microcapsules: Mechanics And Controlled Release

How droplet microfluidics can be used to fabricate solid‐shelled microcapsules having precisely controlled release behavior is described. Glass capillary devices enable the production of monodisperse double emulsion drops, which can then be used as templates for microcapsule formation. The exquisite control afforded by microfluidics can be used to tune the compositions and geometrical characteristics of the microcapsules with exceptional precision. The use of this approach to fabricate microcapsules that only release their contents when exposed to a specific stimulus – such as a change in temperature, exposure to light, a change in the chemical environment, or an external stress – only after a prescribed time delay, and at a prescribed rate is reviewed.     

Magnetic field enhancement in electromagnetic forming systems using anisotropic materials

Electromagnetic Forming (EMF) is a type of high rate forming which exploits pulsed power techniques to create high intensive pulsed magnetic fields to rapidly reshape metal parts. This technique is sometimes called magnetic pulse forming. In this technique, a metal work-piece is pushed to a die and formed by a pressure created using an intensive, transient magnetic field. This magnetic field is produced by passing a pulse of electric current through a forming coil in a pulsed power circuit. Application of field shapers has been proposed to enhance the magnetic fields and consequently to increase the applied magnetic pressure at some desired regions. In this paper, 3D Finite element simulations have been applied to study the magnetic field distribution during an electromagnetic forming process with anisotropic material. Anisotropic magnetic material is described using a permeability tensor. Elements of this tensor are obtained from different magnetization curves dependent on the direction of the magnetic field. It has been shown that application of anisotropic materials with appropriate lamination directions can result in an enhancement of the magnetic field at desired points as well as in better overall efficiencies.     

Temperature control of the ultra-short laser pulse compression in a one-dimensional photonic band gap structure with nematic liquid crystal as a defect layer

We investigate numerically the controllable chirped pulse compression in a one-dimensional photonic structure containing a nematic liquid crystal defect layer using the temperature dependent refractive index of the liquid crystal. We consider the structure under irradiation by near-infrared ultra-short laser pulses polarized parallel to the liquid crystal director at a normal angle of incidence. It is found that the dispersion behaviour and consequently the compression ability of the system can be changed in a controlled manner due to the variation in the defect temperature. When the temperature increased from 290 to 305 K, the transmitted pulse duration decreased from 75 to 42 fs in the middle of the structure, correspondingly. As a result, a novel low-loss tunable pulse compressor with a really compact size and high compression factor is achieved. The so-called transfer matrix method is utilized for numerical simulations of the band structure and reflection/transmission spectra of the structure under investigation.     

Approximate design and performance of the robust control charts for monitoring dispersion in Phase I

This article designs and studies the approximate performance of robust dispersion charts, namely, MAD chart, S_n chart, and Q_n chart, in Phase I analysis (recently developed in the literature). The proposed limits are based on false alarm probability for monitoring the dispersion of a process in Phase I analysis. The charting constants are determined to achieve the required nominal FAP (FAP₀). The performance of these structures is evaluated in (i) the attained false alarm rate and (ii) the probability of signals for out‐of‐control situations. The analysis shows that the proposed design of Phase I robust dispersion charts correctly controls the FAP and shows a good performance in detecting the shifts in the process variation. An illustrative example is used to explain the practical implementation of these limits.