Single Camera Spectral Domain Polarization-sensitive Optical Coherence Tomography Using Offset B-scan Modulation

doi:10.1364/OE.18.007281We report a simple implementation to acquire spectral domain polarization-sensitive optical coherence tomography (PSOCT) using a single camera. By combining a dual-delay assembly in the reference arm and offset B-scan in the sample arm, the orthogonal vertical- and horizontalpolarized images were acquired in parallel and spatially separated by a fixed distance in the full range image space. The two orthogonal polarization images were recombined to calculate the intensity, retardance and fast-axis images. This system was easy to implement and capable of acquiring highspeed in vivo 3D polarization-sensitive OCT images

Correcting Optical-Axis Calculation in Polarization-Sensitive Optical Coherence Tomography

Digital Object Identifier 10.1109/TBME.2010.2053927Polarization-sensitive optical coherence tomography (PSOCT) has found many applications in imaging birefringence tissue samples. Polarization-sensitive detection is often implemented by utilizing a circularly polarized incident light and detecting the two orthogonal horizontal- and vertical-polarized interference components. However, the obtained optical axes images were inappropriately represented as depth-dependent periodic maps in all reported studies. A detailed analysis confirmed that this misrepresentation was caused by the accumulation of optical retardation with depth. A simple method was proposed to numerically correct this optical-axis calculation. Experimental studies in tendon tissue demonstrated that this method can be applied to map the 2-D optical-axis distributions in enface PSOCT images.IEEE Engineering in Medicine and Biology Societ

Automatic input rectification

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 51-55).We present a novel technique, automatic input rectification, and a prototype implementation, SOAP. SOAP learns a set of constraints characterizing typical inputs that an application is highly likely to process correctly. When given an atypical input that does not satisfy these constraints, SOAP automatically rectifies the input (i.e., changes the input so that it satisfies the learned constraints). The goal is to automatically convert potentially dangerous inputs into typical inputs that the program is highly likely to process correctly. Our experimental results show that, for a set of benchmark applications (Google Picasa, ImageMagick, VLC, Swfdec, and Dillo), this approach effectively converts malicious inputs (which successfully exploit vulnerabilities in the application) into benign inputs that the application processes correctly. Moreover, a manual code analysis shows that, if an input does satisfy the learned constraints, it is incapable of exploiting these vulnerabilities. We also present the results of a user study designed to evaluate the subjective perceptual quality of outputs from benign but atypical inputs that have been automatically rectified by SOAP to conform to the learned constraints. Specifically, we obtained benign inputs that violate learned constraints, used our input rectifier to obtain rectified inputs, then paid Amazon Mechanical Turk users to provide their subjective qualitative perception of the difference between the outputs from the original and rectified inputs. The results indicate that rectification can often preserve much, and in many cases all, of the desirable data in the original input.by Fan Long.S.M

Grain refinement in a AlZnMgCuTi alloy by intensive melt shearing: A multi-step nucleation mechanism

This is a post-print version of the article. Copyright @ 2010 Elsevier B.V.Direct chill (DC) cast ingots of wrought Al alloys conventionally require the deliberate addition of a grain refiner to provide a uniform as-cast microstructure for the optimisation of both mechanical properties and processability. Grain refiner additions have been in widespread industrial use for more than half a century. Intensive melt shearing can provide grain refinement without the need for a specific grain refiner addition for both magnesium and aluminium based alloys. In this paper we present experimental evidence of the grain refinement in an experimental wrought aluminium alloy achieved by intensive melt shearing in the liquid state prior to solidification. The mechanisms for high shear induced grain refinement are correlated with the evolution of oxides in alloys. The oxides present in liquid aluminium alloys, normally as oxide films and clusters, can be effectively dispersed by intensive shearing and then provide effective sites for the heterogeneous nucleation of Al3Ti phase. As a result, Al3Ti particles with a narrow size distribution and hence improved efficiency as active nucleation sites of alpha-aluminium grains are responsible for the achieved significant grain refinement. This is termed a multi-step nucleation mechanism.Funding was obtained from the EPRSC

Increase in Weight in Low Birth Weight and Very Low Birth Weight Infants Fed Fortified Breast Milk versus Formula Milk: A Retrospective Cohort Study

There has been a dramatic rise in preterm births in developed countries owing to changes in clinical practices and greater use of assisted reproductive techniques. However, few studies have examined the growth and outcomes of preterm infants according to the type of feeding (with fortified breast milk or formula). The purpose of this study was to examine the effect of breast milk feedings and formula on the growth and short-term outcomes of preterm infants in Hong Kong. In a single-center retrospective cohort study, we included 642 preterm infants at gestational age <37 weeks with birth weights <2200 g. According to World Health Organization criteria, 466 were classified as low birth weight (LBW) infants (≥1500 g and <2200 g) and 176 were classified as very low birth weight (VLBW) infants (<1500 g). The mothers of approximately 80% of VLBW infants and 60% LBW infants initiated breast milk feeding. When compared with no breast milk intake, LBW infants that received breast milk were significantly more likely to have growth z-scores closer to the median of the reference population on admission and experienced slower weight gain from birth to discharge. When breast milk was categorized by percent of total enteral intake, significant differences were seen among LBW infants, with lower percentages of small-for-gestational-age (SGA) status at discharge with increased proportions of breast milk intake. Our results suggest that LBW infants fed breast milk had better growth z-scores and lower SGA status at discharge compared with those predominately fed preterm formula.published_or_final_versio

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We thank the U.S. Environmental Protection Agency (Office of Water; Nationa

Paediatric Epilepsy Surgery Programme in Hong Kong: experience in Queen Mary Hospital / Duchess of Kent Children's Hospital

Poster: no. P6BACKGROUND: Surgery is a well-established treatment for adults with intractable seizures. Increasingly, infants and children are being considered for epilepsy surgery. In a growing child, epilepsy surgery has the additional benefit of aborting cognitive decline and improving development and behaviour ...published_or_final_versio

Paediatric Epilepsy Surgery Programme in Hong Kong: experience in Queen Mary Hospital/Duchess of Kent Children's Hospital

Poster: no. P6BACKGROUND: Surgery is a well-established treatment for adults with intractable seizures. Increasingly, infants and children are being considered for epilepsy surgery. In a growing child, epilepsy surgery has the additional benefit of aborting cognitive decline and improving development and behaviour. METHODS: The paediatric epilepsy surgery programme ...published_or_final_versio

Atomistic simulation of defect structure evolution and mechanical properties at long time scales

Thesis (Ph. D.)--Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 127-146).This thesis is a computational and theoretical investigation of the response of materials' mechanical properties to a wide range of environmental conditions, with a particular focus on the coupled effects of strain rate and temperature. The thesis provides original contributions to the fundamental understanding of how the materials mechanical properties change, as manifested by defect structure evolution, with temperature and strain rate conditions, as well as to the development of methodology used for enabling the investigation of dislocation-defect interactions over a much wider range of time scales than of reach to traditional techniques. This thesis advanced the capabilities of a recently developed activation-relaxation based atomistic method to enhance the accuracy of kinetic predictions, and to enable the investigation of dislocation-defect interactions dynamically at long time scales. We took the Autonomous Basin Climbing (ABC) method as a starting point, and incorporated the ability to sample multiple transition pathways associated with a given state. This new feature addresses the problem of overestimating the system evolution time due to the one-dimensional nature of the original ABC algorithm. The ABC method was further implemented in a dynamic framework, which makes it possible for the first time to directly simulate the dislocation-obstacle interactions at very low strain rates. This approach allows for a new way to connect the atomistic results to models at the meso-scale for simulating the plasticity of metals. We analytically derived how the applied strain rate couples with the thermal activation process, based on the framework of transition state theory informed by the atomistic approach described above. We demonstrated the coupling effect is a common mechanism behind many important phenomena, and provide three examples from the atomic level on the dislocation mobility and dislocation interactions with radiation induced defects. (i) A well-known universal flow stress upturn behavior in metals has been examined. We provide a simple physically based model to predict the flow stress at various strain rates, without invoking any assumed mechanisms or fitting parameters as in the traditional constitutional models. (ii) We implemented this new model in (i) to investigate the dislocation-obstacle interactions. The approach enabled us to map the interaction between an edge dislocation and a self interstitial atom (SIA) cluster in Zr in a two-parameter space consisting of temperature and strain rate. This approach allows the direct atomistic simulation of dislocation-obstacle interactions at experimental time scale, namely at low strain rates, which cannot be reached by traditional atomistic techniques. The dislocation is found to absorb the SIA cluster and climb at low strain rates and high temperatures, while it passes through the SIA cluster at high strain rates and low temperatures. The predicted mechanism map is able to reconcile the seeming controversy between previous experimental and computational findings. (iii) A dislocation-void interaction in bcc Fe at prescribed strain rate is also investigated. We demonstrated that different applied strain rates can affect the interaction mechanism and the defect microstructure, and eventually lead to a negative strain rate sensitivity (nSRS) of yield strength below a critical strain rate. This finding at the unit process level supplements the previous explanations of the nSRS with higher level constitutive relations. Beyond the specific cases analyzed in metals in this thesis, the insights gained on the coupling between strain rate and thermal activation can be used to explain the dependence on strain rate and temperature in other important classes of materials (e.g. colloids, cement) and phenomena (e.g. corrosion, creep).by Yue Fan.Ph.D