Effect of Marangoni Convection Generated by Voids on Segregation During Low-G and 1-G Solidification

Solidification experiments, especially microgravity solidification experiments are often hampered by the evolution of unwanted voids or bubbles in the melt. Although these voids and/or bubbles are highly undesirable, there are currently no effective means of preventing their formation or eliminating their adverse effects, particularly, during low-g experiments. Marangoni Convection caused by these voids can drastically change the transport processes in the melt and, therefore, introduce enormous difficulties in interpreting the results of the space investigations. Recent microgravity experiments by Matthiesen, Andrews, and Fripp are all good examples of how the presence of voids and bubbles affect the outcome of costly space experiments and significantly increase the level of difficulty in interpreting their results. In this work we examine mixing caused by Marangoni convection generated by voids and bubbles in the melt during both 1-g and low-g solidification experiments. The objective of the research is to perform a detailed and comprehensive combined numerical-experimental study of Marangoni convection caused by voids during the solidification process and to show how it can affect segregation and growth conditions by modifying the flow, temperature, and species concentration fields in the melt. While Marangoni convection generated by bubbles and voids in the melt can lead to rapid mixing that would negate the benefits of microgravity processing, it could be exploited in some terrestrial processing to ensure effective communication between a melt/solid interface and a gas phase stoichiometry control zone. Thus we hope that this study will not only aid us in interpreting the results of microgravity solidification experiments hampered by voids and bubbles but to guide us in devising possible means of minimizing the adverse effects of Marangoni convection in future space experiments or of exploiting its beneficial mixing features in ground-based solidification

Microgravity science at Langley Research Center

Although space research is still in an embryonic state, a combination of Earth based and space flight experiments are being coupled to yield a better understanding of the complex interaction of heat and fluid flow on the dynamics of crystal growth. Continued efforts on the ground as well as additional flight opportunities are needed to continue the drive to fully understand the advantages, both scientifically and economically, of microgravity crystal growth

Automated 3D quantitative assessment and measurement of alpha angles from the femoral head-neck junction using MR imaging

To develop an automated approach for 3D quantitative assessment and measurement of alpha angles from the femoral head-neck (FHN) junction using bone models derived from magnetic resonance (MR) images of the hip joint

Book Reviews

Principles of Cardiac Arrhythmias. 3rd ed. By Edward K. Chung. Pp. xiii 809. Illustrated. Baltimore: Williams &Wilkins. 1983.Ethical Issues in Reproductive Medicine. Ed. by M. Reidy. Pp. 176. Illustrated. RI9,60. Dublin: Gill & Macmillan. 1982.From Parasitic Infection to Parasitic Disease (Contribution to Microbiology and Immunology, vol. 7). Ed. by P. L. Gigase and E. A. C. van Marck. Pp. ix + 269. Illustrated. DM 216,-. Basle: S. Karger. 1983.Prolonged Arrest of Cancer (New Horizons in Oncology, vol. I). Ed. by B. A. Stoll. Pp. xiv + 454. Illustrated. £25,75. London: John Wiley. 1982.Pediatric Angiography. Ed. by P. Stanley. Pp. xv + 425. Illustrated. Baltimore: Williams & Wilkins. 1982.Thin-needle Aspiration Biopsy (Major Problems in Pathology, vol. 14). By W. J. Frable. Pp. X\'iii + 358. Illustrated. £42,25. Philadelphia: \'(t B. Saunders. 1983.Essentials of Pulmonary Medicine. By M. H. Williams. Pp. xi + 190. Illustrated. Philadelphia: W. B. Saunders. 1982.Noninvasive Assessment of the Cardiovascular System: Diagnostic Principles and Techniques. Ed. by E. B. Diethrich. Pp. xxiii + 319. Illustrated. £25,75. London: Wright PSG. 1982.Periodic Abstinence for Family Planning. Ed. by R. L. Kleinman. Pp. 60. Illustrated. £1,75 (in K only). London: IPPF Medical Publications. 1983

Book Reviews

ImmunoparasitologyImmunoparasitology: Principles and Methods in Malaria and Schistosomiasis Research. Ed. by G. T. Strickland and K. W. Hunter. Pp. 294. Illustrated. £29,75. London: Praeger. 1982.Walsh and Hoyt's Clinical Neuro-Ophthalmology, vol. 1. By Neil R. Miller. Pp. xii +381. Illustrated. R66,-. Baltimore: Williams & Wilkins. 1982Urinary tract infectionUrinary Tract Infection (Currenr Topics in Infection, No. 3). By R. Maskell. Pp. viii + 144. Illustrated. R37,-. London: Edward Amold. 1982.Common Health Problems in Medical Practice. By E. Scott Medley. Pp. xvi +343. Illustrated. Baltimore: Williams & Wilkins. 1982.Endocrine pathologyEndocrine Pathology: General and Surgical. 2nd ed. Ed. by J. M. B. Bloodworth jun. Pp. xii + 895. Illustrated. Baltimore: Williams & Wilkins. 1982.Experimental Hematology Today, 1982. Ed. by S. J. Baum, D. D. Ledney and S. Thierfelder. Pp. xx +266. Illusuated. DM 237,-. Basle: S. Karger. 1982.Medical Disorders of Alcoholism: Pathogenesis and Treatment (Major Problems in International Medicine, vol. XXII). By C. S. Lieber. Pp. xvii + 589. Illusuated. ± RI08,-. Philadelphia: W. B. Saunders. 19.82.Breast Cancer (Clinics in Oncology, No. I, vol. 3). Guest ed. M. Baum. Pp. vii +647 + 955. Illustrated. Rll,75. Philadelphia: W. B. Saunders. 1982.Handbook of Medical Parasitology. By Viqar Zaman and Loh Ah Keong. Pp. viii + 218. Illustrated. £17,-. New York: ADIS Health Science Press. 1982

Comparative study of CuO supported on CeO2, Ce0.8Zr0.2O2 and Ce0.8Al0.2O2 based catalysts in the CO-PROX reaction

CuO supported on CeO2, Ce0.8Zr0.2O2 and Ce0.8Al0.2O2 based catalysts (6%wt Cu) were synthesized and tested in the preferential oxidation of CO in a H2-rich stream (CO-PROX). Nanocrystalline supports, CeO2 and solid solutions of modified CeO2 with zirconium and aluminum were prepared by a freeze-drying method. CuO was supported by incipient wetness impregnation and calcination at 400 C. All catalysts exhibit high activity in the CO-PROX reaction and selectivity to CO2 at low reaction temperature, being the catalyst supported on CeO2 the more active and stable. The influence of the presence of CO2 and H2O was also studied

Investigating brain connectivity heritability in a twin study using diffusion imaging data

Heritability of brain anatomical connectivity has been studied with diffusion-weighted imaging (DWI) mainly by modeling each voxel's diffusion pattern as a tensor (e.g., to compute fractional anisotropy), but this method cannot accurately represent the many crossing connections present in the brain. We hypothesized that different brain networks (i.e., their component fibers) might have different heritability and we investigated brain connectivity using High Angular Resolution Diffusion Imaging (HARDI) in a cohort of twins comprising 328 subjects that included 70 pairs of monozygotic and 91 pairs of dizygotic twins. Water diffusion was modeled in each voxel with a Fiber Orientation Distribution (FOD) function to study heritability for multiple fiber orientations in each voxel. Precision was estimated in a test-retest experiment on a sub-cohort of 39 subjects. This was taken into account when computing heritability of FOD peaks using an ACE model on the monozygotic and dizygotic twins. Our results confirmed the overall heritability of the major white matter tracts but also identified differences in heritability between connectivity networks. Inter-hemispheric connections tended to be more heritable than intra-hemispheric and cortico-spinal connections. The highly heritable tracts were found to connect particular cortical regions, such as medial frontal cortices, postcentral, paracentral gyri, and the right hippocampus

Statistical shape model reconstruction with sparse anomalous deformations: application to intervertebral disc herniation

Many medical image processing techniques rely on accurate shape modeling of anatomical features. The presence of shape abnormalities challenges traditional processing algorithms based on strong morphological priors. In this work, a sparse shape reconstruction from a statistical shape model is presented. It combines the advantages of traditional statistical shape models (defining a ‘normal’ shape space) and previously presented sparse shape composition (providing localized descriptors of anomalies). The algorithm was incorporated into our image segmentation and classification software. Evaluation was performed on simulated and clinical MRI data from 22 sciatica patients with intervertebral disc herniation, containing 35 herniated and 97 normal discs. Moderate to high correlation (R = 0.73) was achieved between simulated and detected herniations. The sparse reconstruction provided novel quantitative features describing the herniation morphology and MRI signal appearance in three dimensions (3D). The proposed descriptors of local disc morphology resulted to the 3D segmentation accuracy of 1.07 ± 1.00 mm (mean absolute vertex-to-vertex mesh distance over the posterior disc region), and improved the intervertebral disc classification from 0.888 to 0.931 (area under receiver operating curve). The results show that the sparse shape reconstruction may improve computer-aided diagnosis of pathological conditions presenting local morphological alterations, as seen in intervertebral disc herniation

Assessment of a polygenic hazard score for the onset of pre-clinical Alzheimer’s disease

Background: With a growing number of loci associated with late-onset (sporadic) Alzheimer’s disease (AD), the polygenic contribution to AD is now well established. The development of polygenic risk score approaches have shown promising results for identifying individuals at higher risk of developing AD, thereby facilitating the development of preventative and therapeutic strategies. A polygenic hazard score (PHS) has been proposed to quantify age-specific genetic risk for AD. In this study, we assessed the predictive power and transferability of this PHS in an independent cohort, to support its clinical utility. Results: Using genotype and imaging data from 780 individuals enrolled in the Australian Imaging, Biomarkers and Lifestyle (AIBL) study, we investigated associations between the PHS and several AD-related traits, including 1) cross-sectional Aβ-amyloid (Aβ) deposition, 2) longitudinal brain atrophy, 3) longitudinal cognitive decline, 4) age of onset. Except in the cognitive domain, we obtained results that were consistent with previously published findings. The PHS was associated with increased Aβ burden, faster regional brain atrophy and an earlier age of onset. Conclusion: Overall, the results support the predictive power of a PHS, however, with only marginal improvement compared to apolipoprotein E alone