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1

Altered Fractional Anisotropy in Early Huntington's Disease  

PubMed Central

Huntington's disease (HD) is a dominantly inherited neurodegenerative disease best known for chorea. The disorder includes numerous other clinical features including mood disorder, eye movement abnormalities, cognitive disturbance, pendular knee reflexes, motor impersistence, and postural instability. We describe a mild case of HD early in the disease course with depression and subtle neurological manifestations. In addition, we review MRI and diffusion tensor imaging features in this patient. The bicaudate ratio, a measure of caudate atrophy, was increased. Fractional anisotropy values of the bilateral caudate and putamen were increased, signifying neurodegeneration of these structures in HD.

Singh, Silky; Mehta, Hasit; Fekete, Robert

2013-01-01

2

White Matter Integrity Measured by Fractional Anisotropy Correlates Poorly with Actual Individual Fiber Anisotropy  

Microsoft Academic Search

Fractional anisotropy (FA), a very widely used measure of fiber integrity based on diffusion tensor imaging (DTI), is a problematic concept as it is influenced by several quantities including the number of dominant fiber directions within each voxel, each fiber's anisotropy, and partial volume effects from neighboring gray matter. High-angular resolution diffusion imaging (HARDI) can resolve more complex diffusion geometries

Alex D. Leow; Liang Zhan; Siwei Zhu; Nathan S. Hageman; Ming-Chang Chiang; Marina Barysheva; Arthur W. Toga; Katie McMahon; Greig I. de Zubicaray; Margaret J. Wright; Paul M. Thompson

2009-01-01

3

Multimodal white matter imaging to investigate reduced fractional anisotropy and its age-related decline in schizophrenia.  

PubMed

We hypothesized that reduced fractional anisotropy (FA) of water diffusion and its elevated aging-related decline in schizophrenia patients may be caused by elevated hyperintensive white matter (HWM) lesions, by reduced permeability-diffusivity index (PDI), or both. We tested this hypothesis in 40/30 control/patient participants. FA values for the corpus callosum were calculated from high angular resolution diffusion tensor imaging (DTI). Whole-brain volume of HWM lesions was quantified by 3D-T2w-fluid-attenuated inversion recovery (FLAIR) imaging. PDI for corpus callosum was ascertained using multi b-value diffusion imaging (15 b-shells with 30 directions per shell). Patients had significantly lower corpus callosum FA values, and there was a significant age-by-diagnosis interaction. Patients also had significantly reduced PDI but no difference in HWM volume. PDI and HWM volume were significant predictors of FA and captured the diagnosis-related variance. Separately, PDI robustly explained FA variance in schizophrenia patients, but not in controls. Conversely, HWM volume made equally significant contributions to variability in FA in both groups. The diagnosis-by-age effect of FA was explained by a PDI-by-diagnosis interaction. Post hoc testing showed a similar trend for PDI of gray mater. Our study demonstrated that reduced FA and its accelerated decline with age in schizophrenia were explained by pathophysiology indexed by PDI, rather than HWM volume. PMID:24909602

Kochunov, Peter; Chiappelli, Joshua; Wright, Susan N; Rowland, Laura M; Patel, Beenish; Wijtenburg, S Andrea; Nugent, Katie; McMahon, Robert P; Carpenter, William T; Muellerklein, Florian; Sampath, Hemalatha; Elliot Hong, L

2014-08-30

4

Acute nicotine administration effects on fractional anisotropy of cerebral white matter and associated attention performance  

PubMed Central

Introduction: Nicotinic acetylcholine receptors are present in the cerebral white matter (WM). We hypothesized that WM response to nicotine can be detected by diffusion tensor imaging (DTI); and that such responses may be associated with nicotine-led cognitive enhancement in sustained attention. Methods: A randomized, nicotine-placebo patch, crossover, double-blind clinical trial in two non-overlapping cohorts of smokers was used to test the hypothesis. The discovery cohort consisted of 39 subjects (N = 20/19 controls/schizophrenic patients, age = 36.8 ± 10.1 years) and the replication cohorts consisted of 38 healthy smokers (31.7 ± 10.5 years). WM integrity was measured by fractional anisotropy (FA) values for the whole brain and nine preselected WM tracts using tract-based-spatial-statistics. Results: Nicotine significantly enhanced FA values for the genu of corpus callosum compared with placebo (?FAgenu) (p = 0.01) in smokers with low recent smoking exposure as measured by low average cotinine level. This finding was replicated in the second cohort (p = 0.02). ?FAgenu values explained 22% of variance in performance of a sustained attention task during the nicotine session (p = 0.006). However, this effect was limited to schizophrenia patients (r = 0.62 and 0.09; p = 0.003 and 0.7 for patients and controls, respectively). Conclusion: Acute pharmacological influence of nicotine patch on WM integrity appeared present, but was dependent on nicotine intake from recent smoking. Change in the WM integrity in the genu of corpus callosum was associated with a significant proportion of variability of nicotine-led changes in sustained attention/working memory of the smokers. Further studies will be necessary to understand biophysical underpinning of the nicotine-related changes in FA.

Kochunov, Peter; Du, Xiaoming; Moran, Lauren V.; Sampath, Hemalatha; Wijtenburg, S. Andrea; Yang, Yihong; Rowland, Laura M.; Stein, Elliot A.; Hong, L. Elliot

2013-01-01

5

Fractional anisotropy helps predicts memory rehabilitation outcome after traumatic brain injury.  

PubMed

Traumatic brain injury (TBI) commonly results in residual memory difficulties. Such deficits are amenable to cognitive rehabilitation, but optimal selection of rehabilitation interventions remains a challenge. We hypothesized that diffusion tensor imaging (DTI) could be used to predict which individuals were likely to benefit from a specific memory rehabilitation intervention. Thirty-seven individuals with TBI, of all severities, first underwent DTI scanning, along with 18 matched controls. Participants with TBI then attended a 12-session memory intervention emphasizing internal memory strategies (I-MEMS). Primary outcome measures (HVLT, RBMT) were collected at the time of DTI scanning, and both immediately and one month post-therapy. In contrast to typical neuroimaging analysis, fractional anisotropy (FA) was used to predict long-term outcome scores, adjusting for typical predictors (injury severity, age, education, time since injury, pretest score). FA of the parahippocampal white matter was a significant negative predictor of HVLT, while the anterior corpus callosum, left anterior internal capsule, and right anterior corona radiata were negative predictors of RBMT outcome. The importance of these predictors rivaled those of pretest scores. Thus, FA measures may provide substantial predictive value for other cognitive interventions as well. The reason why higher FA was associated with less successful response to cognitive intervention remains unclear and will require further study. PMID:23093456

Strangman, Gary E; O'Neil-Pirozzi, Therese M; Supelana, Christina; Goldstein, Richard; Katz, Douglas I; Glenn, Mel B

2012-01-01

6

White Matter Fractional Anisotropy Correlates With Speed of Processing and Motor Speed in Young Childhood Cancer Survivors  

SciTech Connect

Purpose: To determine whether childhood medulloblastoma and acute lymphoblastic leukemia (ALL) survivors have decreased white matter fractional anisotropy (WMFA) and whether WMFA is related to the speed of processing and motor speed. Methods and Materials: For this study, 17 patients (6 medulloblastoma, 5 ALL treated with high-dose methotrexate (MTX) (4 x 5 g/m{sup 2}) and 6 with low-dose MTX (3 x 2 g/m{sup 2})) and 17 age-matched controls participated. On a 3.0-T magnetic resonance imaging (MRI) scanner, diffusion tensor imaging (DTI) was performed, and WMFA values were calculated, including specific regions of interest (ROIs), and correlated with the speed of processing and motor speed. Results: Mean WMFA in the patient group, mean age 14 years (range 8.9 - 16.9), was decreased compared with the control group (p = 0.01), as well as WMFA in the right inferior fronto-occipital fasciliculus (IFO) (p = 0.03) and in the genu of the corpus callosum (gCC) (p = 0.01). Based on neurocognitive results, significant positive correlations were present between processing speed and WMFA in the splenium (sCC) (r = 0.53, p = 0.03) and the body of the corpus callosum (bCC) (r = 0.52, p = 0.03), whereas the right IFO WMFA was related to motor speed (r = 0.49, p < 0.05). Conclusions: White matter tracts, using a 3.0-T MRI scanner, show impairment in childhood cancer survivors, medulloblastoma survivors, and also those treated with high doses of MTX. In particular, white matter tracts in the sCC, bCC and right IFO are positively correlated with speed of processing and motor speed.

Aukema, Eline J. [Pediatric Psychosocial Department, Emma Children's Hospital/Academic Medical Center, Amsterdam (Netherlands)], E-mail: e.j.aukema@amc.uva.nl; Caan, Matthan W.A. [Department of Radiology, Academic Medical Center, University of Amsterdam, Amsterdam (Netherlands); Delft University of Technology, Delft (Netherlands); Oudhuis, Nienke [Pediatric Psychosocial Department, Emma Children's Hospital/Academic Medical Center, Amsterdam (Netherlands); Majoie, Charles [Department of Radiology, Academic Medical Center, University of Amsterdam, Amsterdam (Netherlands); Vos, Frans M. [Department of Radiology, Academic Medical Center, University of Amsterdam, Amsterdam (Netherlands); Delft University of Technology, Delft (Netherlands); Reneman, Liesbeth [Department of Radiology, Academic Medical Center, University of Amsterdam, Amsterdam (Netherlands); Last, Bob F. [Pediatric Psychosocial Department, Emma Children's Hospital/Academic Medical Center, Amsterdam (Netherlands); Department of Developmental Psychology, Free University of Amsterdam, Amsterdam (Netherlands); Grootenhuis, Martha A. [Pediatric Psychosocial Department, Emma Children's Hospital/Academic Medical Center, Amsterdam (Netherlands); Schouten-van Meeteren, Antoinette Y.N. [Department of Pediatric Oncology, Emma Children's Hospital/Academic Medical Center, Amsterdam (Netherlands)

2009-07-01

7

Abnormal White Matter Integrity in the Corpus Callosum among Smokers: Tract-Based Spatial Statistics  

PubMed Central

In the present study, we aimed to investigate the difference in white matter between smokers and nonsmokers. In addition, we examined relationships between white matter integrity and nicotine dependence parameters in smoking subjects. Nineteen male smokers were enrolled in this study. Eighteen age-matched non-smokers with no current or past psychiatric history were included as controls. Diffusion tensor imaging scans were performed, and the analysis was conducted using a tract-based special statistics approach. Compared with nonsmokers, smokers exhibited a significant decrease in fractional anisotropy (FA) throughout the whole corpus callosum. There were no significant differences in radial diffusivity or axial diffusivity between the two groups. There was a significant negative correlation between FA in the whole corpus callosum and the amount of tobacco use (cigarettes/day; R?=?? 0.580, p?=?0.023). These results suggest that the corpus callosum may be one of the key areas influenced by chronic smoking.

Umene-Nakano, Wakako; Yoshimura, Reiji; Kakeda, Shingo; Watanabe, Keita; Hayashi, Kenji; Nishimura, Joji; Takahashi, Hidehiko; Moriya, Junji; Ide, Satoru; Ueda, Issei; Hori, Hikaru; Ikenouchi-Sugita, Atsuko; Katsuki, Asuka; Atake, Kiyokazu; Abe, Osamu; Korogi, Yukunori; Nakamura, Jun

2014-01-01

8

Evolution of Water Diffusion and Anisotropy in Hyperacute Stroke: Significant Correlation between Fractional Anisotropy and T2  

Microsoft Academic Search

BACKGROUND AND PURPOSE: We hypothesized that, in acute cerebral ischemic stroke, anisotropic diffusion increases if T2 signal intensity is not substantially elevated and decreases once T2 hyperintensity becomes apparent. Our purpose was to correlate fractional anisotropy (FA) measurements with the clinical time of stroke onset, apparent diffusion coefficients (ADC), and T2 signal intensity. METHODS: Tensor diffusion-weighted images (DWIs) of 25

Yelda Ozsunar; P. Ellen Grant; Thierry A. G. M. Huisman; Pamela W. Schaefer; A. Gregory Sorensen; Walter J. Koroshetz; R. Gilberto Gonzalez

2004-01-01

9

Segmented corpus callosum diffusivity correlates with the Expanded Disability Status Scale score in the early stages of relapsing-remitting multiple sclerosis  

PubMed Central

OBJECTIVE: The aim of this study was to characterize the microscopic damage to the corpus callosum in relapsing-remitting multiple sclerosis (RRMS) with diffusion tensor imaging and to investigate the correlation of this damage with disability. The diffusion tensor imaging parameters of fractional anisotropy and mean diffusivity provide information about the integrity of cell membranes, offering two more specific indices, namely the axial and radial diffusivities, which are useful for discriminating axon loss from demyelination. METHOD: Brain magnetic resonance imaging exams of 30 relapsing-remitting multiple sclerosis patients and 30 age- and sex-matched healthy controls were acquired in a 3T scanner. The axial diffusivities, radial diffusivities, fractional anisotropy, and mean diffusivity of five segments of the corpus callosum, correlated to the Expanded Disability Status Scale score, were obtained. RESULTS: All corpus callosum segments showed increased radial diffusivities and mean diffusivity, as well as decreased fractional anisotropy, in the relapsing-remitting multiple sclerosis group. The axial diffusivity was increased in the posterior midbody and splenium. The Expanded Disability Status Scale scores correlated more strongly with axial diffusivities and mean diffusivity, with an isolated correlation with radial diffusivities in the posterior midbody of the corpus callosum. There was no significant correlation with lesion loads. CONCLUSION: Neurological dysfunction in relapsing-remitting multiple sclerosis can be influenced by commissural disconnection, and the diffusion indices of diffusion tensor imaging are potential biomarkers of disability that can be assessed during follow-up.

de Medeiros Rimkus, Carolina; de Faria Junqueira, Thiago; Callegaro, Dagoberto; Otaduy, Maria Concepcion Garcia; da Costa Leite, Claudia

2013-01-01

10

Longitudinal changes of fractional anisotropy in Alzheimer's disease patients treated with galantamine: a 12-month randomized, placebo-controlled, double-blinded study.  

PubMed

Diffusion tensor imaging (DTI) demonstrates decline of fractional anisotropy (FA) as a marker of fiber tract integrity in Alzheimer's disease (AD). We aimed to assess the longitudinal course of white matter microstructural changes in AD and healthy elderly control (HC) subjects and to evaluate the effects of treatment with the cholinesterase inhibitor galantamine on white matter microstructure in AD patients. We enrolled 28 AD patients and 11 healthy elderly control subjects (HC). AD patients were randomly assigned to 6-month double-blind galantamine treatment or placebo, with a 6-month open-label extension phase. DTI was performed at baseline, as well as at 6 and 12-month follow-up in AD patients. The HC subjects underwent DTI at baseline and 12-month follow-up without treatment. We measured FA in regions of interest covering the posterior cingulate and corpus callosum. At 6-month follow-up, the AD group showed significant FA decline in the left posterior cingulate. FA decline was significantly preserved in the posterior body of the corpus callosum in AD group with treatment compared to placebo. At 12-month follow-up, the AD patients showed no differences in FA decline between initial treatment and placebo groups after the 6-month open-label extension phase. A significant FA decline occurred in the left posterior cingulate across the AD and HC groups without between-group differences. DTI demonstrated FA decline in intracortically projecting fiber tracts in aging and AD over 1 year. Galantamine had limited impact on regional FA decline, which was not preserved after additional 6-month open-label treatment. PMID:21818628

Likitjaroen, Y; Meindl, T; Friese, U; Wagner, M; Buerger, K; Hampel, H; Teipel, S J

2012-06-01

11

Bilingual Corpus Callosum Variability  

ERIC Educational Resources Information Center

Magnetic resonance imaging was used to produce midsagittal images of the corpus callosum of 19 right-handed adult male and female subjects. The preliminary findings of this study indicate that significant adaptation in the anterior midbody of the corpus callosum has occurred to accommodate multiple language capacity in bilingual individuals…

Coggins, Porter E., III.; Kennedy, Teresa J.; Armstrong, Terry A.

2004-01-01

12

Connecting fractional anisotropy from medical images with mechanical anisotropy of a hyperviscoelastic fibre-reinforced constitutive model for brain tissue.  

PubMed

Brain tissue modelling has been an active area of research for years. Brain matter does not follow the constitutive relations for common materials and loads applied to the brain turn into stresses and strains depending on tissue local morphology. In this work, a hyperviscoelastic fibre-reinforced anisotropic law is used for computational brain injury prediction. Thanks to a fibre-reinforcement dispersion parameter, this formulation accounts for anisotropic features and heterogeneities of the tissue owing to different axon alignment. The novelty of the work is the correlation of the material mechanical anisotropy with fractional anisotropy (FA) from diffusion tensor images. Finite-element (FE) models are used to investigate the influence of the fibre distribution for different loading conditions. In the case of tensile-compressive loads, the comparison between experiments and simulations highlights the validity of the proposed FA-k correlation. Axon alignment affects the deformation predicted by FE models and, when the strain in the axonal direction is large with respect to the maximum principal strain, decreased maximum deformations are detected. It is concluded that the introduction of fibre dispersion information into the constitutive law of brain tissue affects the biofidelity of the simulations. PMID:24258158

Giordano, Chiara; Kleiven, Svein

2014-02-01

13

Band mass anisotropy and the intrinsic metric of fractional quantum Hall systems  

NASA Astrophysics Data System (ADS)

It was recently pointed out that topological liquid phases arising in the fractional quantum Hall effect (FQHE) are not required to be rotationally invariant, as most variational wave functions proposed to date have been. Instead, they possess a geometric degree of freedom corresponding to a shear deformation that acts like an intrinsic metric. We apply this idea to a system with an anisotropic band mass, as is intrinsically the case in many-valley semiconductors such as AlAs and Si or in isotropic systems like GaAs in the presence of a tilted magnetic field, which breaks the rotational invariance. We perform exact diagonalization calculations with periodic boundary conditions (torus geometry) for various filling fractions in the lowest, first, and second Landau levels. In the lowest Landau level, we demonstrate that FQHE states generally survive the breakdown of rotational invariance by moderate values of the band mass anisotropy. At 1/3 filling, we generate a variational family of Laughlin wave functions parametrized by the metric degree of freedom. We show that the intrinsic metric of the Laughlin state adjusts as the band mass anisotropy or the dielectric tensor is varied, while the phase remains robust. In the n=1 Landau level, mass anisotropy drives transitions between incompressible liquids and compressible states with charge density wave ordering. In n?2 Landau levels, mass anisotropy selects and enhances stripe ordering with compatible wave vectors at partial 1/3 and 1/2 fillings.

Yang, Bo; Papi?, Z.; Rezayi, E. H.; Bhatt, R. N.; Haldane, F. D. M.

2012-04-01

14

Vestibular Loss and Balance Training Cause Similar Changes in Human Cerebral White Matter Fractional Anisotropy  

PubMed Central

Patients with bilateral vestibular loss suffer from severe balance deficits during normal everyday movements. Ballet dancers, figure skaters, or slackliners, in contrast, are extraordinarily well trained in maintaining balance for the extreme balance situations that they are exposed to. Both training and disease can lead to changes in the diffusion properties of white matter that are related to skill level or disease progression respectively. In this study, we used diffusion tensor imaging (DTI) to compare white matter diffusivity between these two study groups and their age- and sex-matched controls. We found that vestibular patients and balance-trained subjects show a reduction of fractional anisotropy in similar white matter tracts, due to a relative increase in radial diffusivity (perpendicular to the main diffusion direction). Reduced fractional anisotropy was not only found in sensory and motor areas, but in a widespread network including long-range connections, limbic and association pathways. The reduced fractional anisotropy did not correlate with any cognitive, disease-related or skill-related factors. The similarity in FA between the two study groups, together with the absence of a relationship between skill or disease factors and white matter changes, suggests a common mechanism for these white matter differences. We propose that both study groups must exert increased effort to meet their respective usual balance requirements. Since balance training has been shown to effectively reduce the symptoms of vestibular failure, the changes in white matter shown here may represent a neuronal mechanism for rehabilitation.

Hummel, Nadine; Hufner, Katharina; Stephan, Thomas; Linn, Jennifer; Kremmyda, Olympia; Brandt, Thomas; Flanagin, Virginia L.

2014-01-01

15

Vestibular loss and balance training cause similar changes in human cerebral white matter fractional anisotropy.  

PubMed

Patients with bilateral vestibular loss suffer from severe balance deficits during normal everyday movements. Ballet dancers, figure skaters, or slackliners, in contrast, are extraordinarily well trained in maintaining balance for the extreme balance situations that they are exposed to. Both training and disease can lead to changes in the diffusion properties of white matter that are related to skill level or disease progression respectively. In this study, we used diffusion tensor imaging (DTI) to compare white matter diffusivity between these two study groups and their age- and sex-matched controls. We found that vestibular patients and balance-trained subjects show a reduction of fractional anisotropy in similar white matter tracts, due to a relative increase in radial diffusivity (perpendicular to the main diffusion direction). Reduced fractional anisotropy was not only found in sensory and motor areas, but in a widespread network including long-range connections, limbic and association pathways. The reduced fractional anisotropy did not correlate with any cognitive, disease-related or skill-related factors. The similarity in FA between the two study groups, together with the absence of a relationship between skill or disease factors and white matter changes, suggests a common mechanism for these white matter differences. We propose that both study groups must exert increased effort to meet their respective usual balance requirements. Since balance training has been shown to effectively reduce the symptoms of vestibular failure, the changes in white matter shown here may represent a neuronal mechanism for rehabilitation. PMID:24776524

Hummel, Nadine; Hüfner, Katharina; Stephan, Thomas; Linn, Jennifer; Kremmyda, Olympia; Brandt, Thomas; Flanagin, Virginia L

2014-01-01

16

Spatially fractional-order viscoelasticity, non-locality, and a new kind of anisotropy  

NASA Astrophysics Data System (ADS)

A class of non-local viscoelastic equations of motion including equations of fractional order with respect to the spatial variables is studied. It is shown that space-fractional equations of motion of an order strictly less than 2 allow for a new kind of anisotropy, associated with azimuthal dependence of non-local interactions between stress and strain at different material points. Constitutive equations of such viscoelastic media are determined. Relaxation effects are additionally accounted for by replacing second-order time derivatives by lower-order fractional derivatives. Explicit fundamental solutions of the Cauchy problem for scalar equations with isotropic and anisotropic non-locality are constructed. For some particular choices of the parameters, numerical solutions are constructed.

Hanyga, A.; Seredy?ska, M.

2012-05-01

17

Relationship between fractional anisotropy of cerebral white matter and metabolite concentrations measured using 1H magnetic resonance spectroscopy in healthy adults  

PubMed Central

Fractional anisotropy (FA) of water diffusion in cerebral white matter (WM), derived from diffusion tensor imaging (DTI), is a sensitive index of microscopic WM integrity. Physiological and metabolic factors that explain intersubject variability in FA values were evaluated in two cohorts of healthy adults of different age spans (N=65, range: 28–50 years; and N=25, age=66.6±6.2, range:57–80 years). Single voxel magnetic resonance spectroscopy (MRS) was used to measure N-acetylaspartate (NAA), total choline-containing compounds, and total creatine, bilaterally in an associative WM tract: anterior corona radiata (ACR). FA values were calculated for the underlying, proximal and two distal WM regions. Two-stage regression analysis was used to calculate the proportion of variability in FA values explained by spectroscopy measurements, at the first stage, and subject’s age, at the second stage. WM NAA concentration explained 23% and 66% of intersubject variability (p<0.001) in the FA of the underlying WM in the younger and older cohorts, respectively. WM NAA concentration also explained a significant proportion of variability in FA of the genu of corpus callosum (CC), a proximal WM tract where some of the fibers contained within the spectroscopic voxel decussate spectroscopic voxel decussate. NAA concentrations also explained a significant proportion of variability in the FA values in the splenium of CC, a distal WM tract that also carries associative fibers, in both cohorts. These results suggest that MRS measurements explained a significant proportion of variability in FA values in both proximal and distal WM tracts that carry similar fiber-types.

Wijtenburg, S.A.; McGuire, S.A.; Rowland, L.M.; Sherman, P.M.; Lancaster, J.L.; Tate, D.F.; Hardies, L.J.; Patel, B.; Glahn, D.C.; Hong, L.E.; Fox, P.T.; Kochunov, P.

2012-01-01

18

Fractional anisotropy distributions in 2- to 6-year-old children with autism  

PubMed Central

Background Increasing evidence suggests that autism is a disorder of distributed neural networks that may exhibit abnormal developmental trajectories. Characterisation of white matter early in the developmental course of the disorder is critical to understanding these aberrant trajectories. Methods A cross-sectional study of 2- to 6-year-old children with autism was conducted using diffusion tensor imaging combined with a novel statistical approach employing fractional anisotropy distributions. Fifty-eight children aged 18–79 months were imaged: 33 were diagnosed with autism, 8 with general developmental delay, and 17 were typically developing. Fractional anisotropy values within global white matter, cortical lobes and the cerebellum were measured and transformed to random F distributions for each subject. Each distribution of values for a region was summarised by estimating ?, the estimated mean and standard deviation of the approximating F for each distribution. Results The estimated ? parameter, ??, was significantly decreased in individuals with autism compared to the combined control group. This was true in all cortical lobes, as well as in the cerebellum, but differences were most robust in the temporal lobe. Predicted developmental trajectories of ?? across the age range in the sample showed patterns that partially distinguished the groups. Exploratory analyses suggested that the variability, rather than the central tendency, component of ?? was the driving force behind these results. Conclusions While preliminary, our results suggest white matter in young children with autism may be abnormally homogeneous, which may reflect poorly organised or differentiated pathways, particularly in the temporal lobe, which is important for social and emotional cognition.

Cascio, C.; Gribbin, M.; Gouttard, S.; Smith, R. G.; Jomier, M.; Field, S.; Graves, M.; Hazlett, H. C.; Muller, K.; Gerig, G.; Piven, J.

2012-01-01

19

Case series: fractional anisotropy along the trajectory of selected white matter tracts in adolescents born preterm with ventricular dilation.  

PubMed

This case series assesses white matter microstructure in 3 adolescents born preterm with nonshunted ventricular dilation secondary to intraventricular hemorrhage. Subjects (ages 12-17 years, gestational age 26-29 weeks, birth weight 825-1624 g) were compared to 3 full-term controls (13-17 years, 39-40 weeks, 3147-3345 g) and 3 adolescents born preterm without ventricular dilation (10-13 years, 26-29 weeks, 630-1673 g). Tractography using a 2 region of interest method reconstructed the following white matter tracts: superior longitudinal/arcuate fasciculus, inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, uncinate fasciculus, and corticospinal tract. Subjects showed increased fractional anisotropy and changes in the pattern of fractional anisotropy along the trajectory of tracts adjacent to the lateral ventricles. Tensor shape at areas of increased fractional anisotropy demonstrated increased linear anisotropy at the expense of planar and spherical anisotropy. These findings suggest increased axonal packing density and straightening of fibers secondary to ventricular enlargement. PMID:22859695

Myall, Nathaniel J; Yeom, Kristen W; Yeatman, Jason D; Gaman-Bean, Shayna; Feldman, Heidi M

2013-06-01

20

Agenesis of the Corpus Callosum  

MedlinePLUS

... of the Corpus Callosum Information Page Publications Organizations News Research literature Other related groups Organizations Professional Societies Government Resources NINDS Clinical Trials En Español Order ...

21

Agenesis of the corpus callosum  

PubMed Central

Attention is drawn to the neonata ultrasound appearances in agenesis of the corpus callosum. Although rare, such appearances are highly characteristic, and, if seen, the diagnosis should be easy. ImagesFig. 1Fig. 2

Skeffington, F Sheehy

1982-01-01

22

MRI of the Corpus Callosum in Multiple Sclerosis: Association with Disability  

PubMed Central

Background Inflammatory demyelination and axon damage in the corpus callosum are prominent features of multiple sclerosis (MS) and may partially account for impaired performance on complex tasks. Objective To characterize quantitative callosal MRI abnormalities and their association with disability. Methods In 69 participants with MS and 29 healthy volunteers, lesional and extralesional callosal MRI indices were estimated via diffusion tensor tractography. Expanded disability status scale (EDSS) and MS functional composite (MSFC) scores were recorded in 53 of the participants with MS. Results All tested callosal MRI indices were diffusely abnormal in MS. EDSS score was correlated only with age (r=0.51). Scores on the overall MSFC and its paced serial auditory addition test (PASAT) and 9-hole peg test components were correlated with callosal fractional anisotropy (r=0.27, 0.35, 0.31, respectively) and perpendicular diffusivity (r=?0.29, ?0.30, and ?0.31) but not with overall callosal volume or callosal lesion volume; the PASAT score was more weakly correlated with callosal magnetization-transfer ratio (r=0.21). Anterior callosal abnormalities were associated with impaired PASAT performance and posterior abnormalities with slow performance on the 9-hole peg test. Conclusion Abnormalities in the corpus callosum can be assessed with quantitative MRI and are associated with cognitive and complex upper-extremity dysfunction in MS.

Ozturk, A.; Smith, S. A.; Gordon-Lipkin, E. M.; Harrison, D. M.; Shiee, N.; Pham, D. L.; Caffo, B. S.; Calabresi, P. A.; Reich, D. S.

2009-01-01

23

Genetic Analysis of Cortical Thickness and Fractional Anisotropy of Water Diffusion in the Brain  

PubMed Central

Objectives: The thickness of the brain’s cortical gray matter (GM) and the fractional anisotropy (FA) of the cerebral white matter (WM) each follow an inverted U-shape trajectory with age. The two measures are positively correlated and may be modulated by common biological mechanisms. We employed four types of genetic analyses to localize individual genes acting pleiotropically upon these phenotypes. Methods: Whole-brain and regional GM thickness and FA values were measured from high-resolution anatomical and diffusion tensor MR images collected from 712, Mexican American participants (438 females, age?=?47.9?±?13.2?years) recruited from 73 (9.7?±?9.3 individuals/family) large families. The significance of the correlation between two traits was estimated using a bivariate genetic correlation analysis. Localization of chromosomal regions that jointly influenced both traits was performed using whole-genome quantitative trait loci (QTL) analysis. Gene localization was performed using SNP genotyping on Illumina 1M chip and correlation with leukocyte-based gene-expression analyses. The gene-expressions were measured using the Illumina BeadChip. These data were available for 371 subjects. Results: Significant genetic correlation was observed among GM thickness and FA values. Significant logarithm of odds (LOD???3.0) QTLs were localized within chromosome 15q22–23. More detailed localization reported no significant association (p?

Kochunov, Peter; Glahn, David C.; Nichols, Thomas E.; Winkler, Anderson M.; Hong, Elliot L.; Holcomb, Henry H.; Stein, Jason L.; Thompson, Paul M.; Curran, Joanne E.; Carless, Melanie A.; Olvera, Rene L.; Johnson, Matthew P.; Cole, Shelley A.; Kochunov, Valeria; Kent, Jack; Blangero, John

2011-01-01

24

Intercentre reproducibility of cardiac apparent diffusion coefficient and fractional anisotropy in healthy volunteers  

PubMed Central

Background Diffusion tensor cardiac magnetic resonance (DT-CMR) enables probing of the microarchitecture of the myocardium, but the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) reported in healthy volunteers have been inconsistent. The aim of this study was to validate a stimulated-echo diffusion sequence using phantoms, and to assess the intercentre reproducibility of in-vivo diffusion measures using the sequence. Methods and results A stimulated-echo, cardiac-gated DT-CMR sequence with a reduced-field-of-view, single-shot EPI readout was used at two centres with 3 T MRI scanners. Four alkane phantoms with known diffusivities were scanned at a single centre using a stimulated echo sequence and a spin-echo Stejskal-Tanner diffusion sequence. The median (maximum, minimum) difference between the DT-CMR sequence and Stejskal-Tanner sequence was 0.01 (0.04, 0.0006) × 10-3 mm2/s (2%), and between the DT-CMR sequence and literature diffusivities was 0.02 (0.05, 0.006) × 10-3 mm2/s (4%). The same ten healthy volunteers were scanned using the DT-CMR sequence at the two centres less than seven days apart. Average ADC and FA were calculated in a single mid-ventricular, short axis slice. Intercentre differences were tested for statistical significance at the p??0.05), and only the diastolic ADC showed a statistically significant, but numerically small, difference of 0.07 × 10-3 mm2/s (p?=?0.047). The intercentre, intrasubject coefficients of variance were: systolic ADC 7%, FA 6%; diastolic ADC 7%, FA 3%. Conclusions This is the first study to demonstrate the accuracy of a stimulated-echo DT-CMR sequence in phantoms, and demonstrates the feasibility of obtaining reproducible ADC and FA in healthy volunteers at separate centres with well-matched sequences and processing.

2014-01-01

25

Influence of the packing fraction and host matrix on the magnetoelastic anisotropy in Ni nanowire composite arrays  

NASA Astrophysics Data System (ADS)

The influence of the packing fraction on thermally induced magnetoelastic effects has been studied in Ni nanowires embedded in polycarbonate, poly(vinylidene difluoride), and alumina nanoporous membranes of different porosities for temperatures between 77 K and 345 K. For nanowires embedded in polymer membranes, the contrasting shift in the ferromagnetic resonance frequency when the temperature is either above or below ambient temperature is consistent with the occurrence of uniaxial magnetoelastic anisotropy effects due to the large thermal expansion coefficient mismatch between the metal nanowires and the membrane. A model which considers the influence of the nanowires packing fraction and the membrane material on the magnetoelastic effects, arising from the matrix-assisted deformation process, is proposed. The model is able to successfully explain the experimentally observed effects for the Ni nanowire arrays embedded in the different porous membranes and their variation with the packing fraction. The possibility to modulate the magnetic anisotropy of such nanocomposites by an appropriate choice of membrane material, packing fraction, and sample temperature is of considerable importance to achieve magnetically tunable devices.

Piraux, Luc; Hamoir, Gaël; Encinas, Armando; De La Torre Medina, Joaquin; Abreu Araujo, Flavio

2013-09-01

26

Instrument specific use-dependent plasticity shapes the anatomical properties of the corpus callosum: a comparison between musicians and non-musicians  

PubMed Central

Long-term musical expertise has been shown to be associated with a number of functional and structural brain changes, making it an attractive model for investigating use-dependent plasticity in humans. Physiological interhemispheric inhibition (IHI) as examined by transcranial magnetic stimulation has been shown to be correlated with anatomical properties of the corpus callosum as indexed by fractional anisotropy (FA). However, whether or not IHI or the relationship between IHI and FA in the corpus callosum can be modified by different musical training regimes remains largely unknown. We investigated this question in musicians with different requirements for bimanual finger movements (piano and string players) and non-expert controls. IHI values were generally higher in musicians, but differed significantly from non-musicians only in string players. IHI was correlated with FA in the posterior midbody of the corpus callosum across all participants. Interestingly, subsequent analyses revealed that this relationship may indeed be modulated by different musical training regimes. Crucially, while string players had greater IHI than non-musicians and showed a positive structure-function relationship, the amount of IHI in pianists was comparable to that of non-musicians and there was no significant structure-function relationship. Our findings indicate instrument specific use-dependent plasticity in both functional (IHI) and structural (FA) connectivity of motor related brain regions in musicians.

Vollmann, Henning; Ragert, Patrick; Conde, Virginia; Villringer, Arno; Classen, Joseph; Witte, Otto W.; Steele, Christopher J.

2014-01-01

27

Early musical training and white-matter plasticity in the corpus callosum: evidence for a sensitive period.  

PubMed

Training during a sensitive period in development may have greater effects on brain structure and behavior than training later in life. Musicians are an excellent model for investigating sensitive periods because training starts early and can be quantified. Previous studies suggested that early training might be related to greater amounts of white matter in the corpus callosum, but did not control for length of training or identify behavioral correlates of structural change. The current study compared white-matter organization using diffusion tensor imaging in early- and late-trained musicians matched for years of training and experience. We found that early-trained musicians had greater connectivity in the posterior midbody/isthmus of the corpus callosum and that fractional anisotropy in this region was related to age of onset of training and sensorimotor synchronization performance. We propose that training before the age of 7 years results in changes in white-matter connectivity that may serve as a scaffold upon which ongoing experience can build. PMID:23325263

Steele, Christopher J; Bailey, Jennifer A; Zatorre, Robert J; Penhune, Virginia B

2013-01-16

28

Microstructural White Matter Changes in the Corpus Callosum of Young People with Bipolar Disorder: A Diffusion Tensor Imaging Study  

PubMed Central

To date, most studies of white matter changes in Bipolar Disorder (BD) have been conducted in older subjects and with well-established disorders. Studies of young people who are closer to their illness onset may help to identify core neurobiological characteristics and separate these from consequences of repeated illness episodes or prolonged treatment. Diffusion tensor imaging (DTI) was used to examine white matter microstructural changes in 58 young patients with BD (mean age 23 years; range 16–30 years) and 40 controls. Whole brain voxelwise measures of fractional anisotropy (FA), parallel diffusivity (?//) and radial diffusivity (??) were calculated for all subjects. White matter microstructure differences (decreased FA corrected p<.05) were found between the patients with BD and controls in the genu, body and splenium of the corpus callosum as well as the superior and anterior corona radiata. In addition, significantly increased radial diffusivity (p<.01) was found in the BD group. Neuroimaging studies of young patients with BD may help to clarify neurodevelopmental aspects of the illness and for identifying biomarkers of disease onset and progression. Our findings provide evidence of microstructural white matter changes early in the course of illness within the corpus callosum and the nature of these changes suggest they are associated with abnormalities in the myelination of axons.

Lagopoulos, Jim; Hermens, Daniel F.; Hatton, Sean N.; Tobias-Webb, Juliette; Griffiths, Kristi; Naismith, Sharon L.; Scott, Elizabeth M.; Hickie, Ian B.

2013-01-01

29

Reduced Fractional Anisotropy and Axial Diffusivity in White Matter in 22q11.2 Deletion Syndrome: A Pilot Study  

PubMed Central

Individuals with 22q11.2 deletion syndrome (22q11.2DS) evince a 30% incidence of schizophrenia. We compared the white matter (WM) of 22q11.2DS patients without schizophrenia to a group matched healthy controls using Tract-Based-Spatial-Statistics (TBSS). We found localized reduction of Fractional Anisotropy (FA) and Axial Diffusivity (AD; measure of axonal integrity) in WM underlying the left parietal lobe. No changes in Radial Diffusivity (RD; measure of myelin integrity) were observed. Of note, studies in chronic schizophrenia patients report reduced FA, no changes in AD, and increases in RD in WM. Our findings suggest different WM microstructure in 22q11.2DS than in patients with schizophrenia.

Kikinis, Z.; Asami, T.; Bouix, S.; Finn, C. T.; Ballinger, T.; Tworog-Dube, E.; Kucherlapati, R.; Kikinis, R.; Shenton, M. E.; Kubicki, M.

2012-01-01

30

Differences in the architecture of low-grade and high-grade gliomas evaluated using fiber density index and fractional anisotropy  

Microsoft Academic Search

Accurate pre-operative assessment of tumor grade is important for the selection of appropriate treatment strategies. The aim of this study was to retrospectively evaluate whether the fiber density index (FDi) and fractional anisotropy (FA) via diffusion tensor MRI (DTI) could assist with pre-operative diagnosis of glioma grade. A total of 31 patients who had histologically confirmed gliomas underwent DTI performed

Yiyong Chen; Yonghong Shi; Zhijian Song

2010-01-01

31

Biaxial normal strength behavior in the axial-transverse plane for human trabecular bone--effects of bone volume fraction, microarchitecture, and anisotropy.  

PubMed

The biaxial failure behavior of the human trabecular bone, which has potential relevance both for fall and gait loading conditions, is not well understood, particularly for low-density bone, which can display considerable mechanical anisotropy. Addressing this issue, we investigated the biaxial normal strength behavior and the underlying failure mechanisms for human trabecular bone displaying a wide range of bone volume fraction (0.06-0.34) and elastic anisotropy. Micro-computed tomography (CT)-based nonlinear finite element analysis was used to simulate biaxial failure in 15 specimens (5 mm cubes), spanning the complete biaxial normal stress failure space in the axial-transverse plane. The specimens, treated as approximately transversely isotropic, were loaded in the principal material orientation. We found that the biaxial stress yield surface was well characterized by the superposition of two ellipses--one each for yield failure in the longitudinal and transverse loading directions--and the size, shape, and orientation of which depended on bone volume fraction and elastic anisotropy. However, when normalized by the uniaxial tensile and compressive strengths in the longitudinal and transverse directions, all of which depended on bone volume fraction, microarchitecture, and mechanical anisotropy, the resulting normalized biaxial strength behavior was well described by a single pair of (longitudinal and transverse) ellipses, with little interspecimen variation. Taken together, these results indicate that the role of bone volume fraction, microarchitecture, and mechanical anisotropy is mostly accounted for in determining the uniaxial strength behavior and the effect of these parameters on the axial-transverse biaxial normal strength behavior per se is minor. PMID:24121715

Sanyal, Arnav; Keaveny, Tony M

2013-12-01

32

Automated assessment of the quality of diffusion tensor imaging data using color cast of color-encoded fractional anisotropy images.  

PubMed

Diffusion tensor imaging (DTI) data often suffer from artifacts caused by motion. These artifacts are especially severe in DTI data from infants, and implementing tight quality controls is therefore imperative for DTI studies of infants. Currently, routine procedures for quality assurance of DTI data involve the slice-wise visual inspection of color-encoded, fractional anisotropy (CFA) images. Such procedures often yield inconsistent results across different data sets, across different operators who are examining those data sets, and sometimes even across time when the same operator inspects the same data set on two different occasions. We propose a more consistent, reliable, and effective method to evaluate the quality of CFA images automatically using their color cast, which is calculated on the distribution statistics of the 2D histogram in the color space as defined by the International Commission on Illumination (CIE) on lightness and a and b (LAB) for the color-opponent dimensions (also known as the CIELAB color space) of the images. Experimental results using DTI data acquired from neonates verified that this proposed method is rapid and accurate. The method thus provides a new tool for real-time quality assurance for DTI data. PMID:24637081

He, Xiaofu; Liu, Wei; Li, Xuzhou; Li, Qingli; Liu, Feng; Rauh, Virginia A; Yin, Dazhi; Bansal, Ravi; Duan, Yunsuo; Kangarlu, Alayar; Peterson, Bradley S; Xu, Dongrong

2014-06-01

33

Relationship between diffusion tensor fractional anisotropy and motor outcome in patients with hemiparesis after corona radiata infarct.  

PubMed

This study examined the relationship between fractional anisotropy (FA) values of magnetic resonance-diffusion tensor imaging (DTI) and motor outcome (1 month after onset) in 15 patients with hemiparesis after ischemic stroke of corona radiata lesions. DTI data were obtained on days 14-18. FA values within the cerebral peduncle were analyzed using a computer-automated method. Motor outcome of hemiparesis was evaluated according to Brunnstrom stage (BRS; 6-point scale: severe to normal) for separate shoulder/elbow/forearm, wrist/hand, and lower extremity functions. The ratio of FA values in the affected hemisphere to those in the unaffected hemisphere (rFA) was assessed in relation to the BRS data (Spearman rank correlation test, P<.05). rFA values ranged from .715 to 1.002 (median=.924). BRS ranged from 1 to 6 (median=4) for shoulder/elbow/forearm, from 1 to 6 (median=5) for wrist/hand, and from 2 to 6 (median=4) for the lower extremities. Analysis revealed statistically significant relationships between rFA and upper extremity functions (correlation coefficient=.679 for shoulder/elbow/forearm and .706 for wrist/hand). Although slightly less evident, the relationship between rFA and lower extremity function was also statistically significant (correlation coefficient=.641). FA values within the cerebral peduncle are moderately associated with the outcome of both upper and lower extremity functions, suggesting that DTI may be applicable for outcome prediction in stroke patients with corona radiata infarct. PMID:23510690

Koyama, Tetsuo; Marumoto, Kohei; Miyake, Hiroji; Domen, Kazuhisa

2013-11-01

34

Relationship between diffusion-tensor fractional anisotropy and long-term outcome in patients with hemiparesis after intracerebral hemorrhage.  

PubMed

We assessed the relationship between fractional anisotropy (FA) values of magnetic resonance-diffusion tensor imaging (DTI) and long-term outcome (3-7 months after onset) in patients with hemiparesis after intracerebral hemorrhage (N = 12). DTI data were obtained on days 14-18. FA values within the cerebral peduncle were analyzed using a computer-automated method. Motor outcome of hemiparesis was evaluated using Brunnstrom stage (six-point scale: severe to normal) for separate shoulder/elbow/forearm, wrist/hand, and lower extremity functions when patients were discharged from a long-term rehabilitation facility 3-7 months after onset. In addition, the motor component of the functional independence measure (FIM-motor) was scored. The ratio of FA values in the affected hemisphere to those in the unaffected hemisphere (rFA) was assessed in relation to the clinical data (Spearman's rank correlation test, P < 0.05). Analysis revealed a statistically significant relationship between rFA and upper extremity function (R = 0.863 for shoulder/elbow/forearm; 0.834 for wrist/hand). Although statistically significant, the relationship between rFA and lower extremity function was less evident (R = 0.609). In contrast, analysis of rFA and FIM-motor scores did not reveal statistical significance. FA values within the cerebral peduncle are tightly associated with long-term outcomes of upper extremity function. PMID:23422461

Koyama, Tetsuo; Marumoto, Kohei; Miyake, Hiroji; Ohmura, Takehisa; Domen, Kazuhisa

2013-01-01

35

Fiber density index, fractional anisotropy, adc and clinical motor findings in the white matter of patients with glioblastoma.  

PubMed

Whether fractional anisotropy (FA), apparent diffusion coefficient (ADC), and fiber density index (FDi) values differ in the white matter close to glioblastomas of both symptomatic and asymptomatic patients was investigated. Twenty patients with glioblastomas underwent magnetic resonance imaging study. The FDi, FA and ADC values were calculated in areas of white matter in close proximity to the tumor (perWM) and encompassing fibers of cortico-spinal tract and in the contralateral normal-appearing white matter (nWM). The clinical compromise of the cortico-spinal tract was graded using Brunnstrom's criteria. FA and FDi were significantly decreased and ADC increased in perWM compared with the contralateral. Mean FDi, FA, and ADC values comparing perWM and nWM in symptomatic patients showed similar differences. Comparing the perWM of symptomatic and asymptomatic patients, mean FDi and ADC values were lower in symptomatic patients than in asymptomatic ones. A positive correlation was found between the clinical score (CS) and, separately, FDi, FA and ADC per WM values. In a multiple stepwise regression among the same factors, only the ADC of perWM values showed a positive correlation with the CS. An increased ADC plays a major role in reducing the number of fibers (reduced FDi) in symptomatic patients. PMID:17899109

Romano, Andrea; Fasoli, Fabrizio; Ferrante, Michele; Ferrante, Luigi; Fantozzi, Luigi Maria; Bozzao, Alessandro

2008-02-01

36

Alterations in frontal lobe tracts and corpus callosum in young children with autism spectrum disorder.  

PubMed

Major frontal lobe tracts and corpus callosum (CC) were investigated in 32 children with autism spectrum disorder (ASD, mean age: 5 years), 12 nonautistic developmentally impaired children (DI, mean age: 4.6 years), and 16 typically developing children (TD, mean age: 5.5 years) using diffusion tensor imaging tractography and tract-based spatial statistics. Various diffusion and geometric properties were calculated for uncinate fasciculus (UF), inferior fronto-occipital fasciculus (IFO), arcuate fasciculus (AF), cingulum (Cg), CC, and corticospinal tract. Fractional anisotropy was lower in the right UF, right Cg and CC in ASD and DI children; in right AF in ASD children; and in bilateral IFO in DI children, compared with TD children. Apparent diffusion coefficient was increased in right AF in both ASD and DI children. The ASD group showed shorter length of left UF and increased length, volume, and density of right UF; increased length and density of CC; and higher density of left Cg, compared with the TD group. Compared with DI group, ASD group had increased length, volume, and density of right UF; higher volume of left UF; and increased length of right AF and CC. Volume of bilateral UF and right AF and fiber density of left UF were positively associated with autistic features. PMID:20019145

Kumar, Ajay; Sundaram, Senthil K; Sivaswamy, Lalitha; Behen, Michael E; Makki, Malek I; Ager, Joel; Janisse, James; Chugani, Harry T; Chugani, Diane C

2010-09-01

37

Fractions!  

NSDL National Science Digital Library

Practice all of the activities to help you learn fractions! Go through all five levels of Fractions Review Activities Practice Naming Fractions Do you remember how to do Fraction Sets? Play these games when you have finished the top three activities: Cross the River Pizza Party Fractions Rescue Island Adding Subtracting Fractions SPLAT Mrs. Anderson's Fraction Games Action Fraction Soccer Shootout Fraction Multiplication Soccer Shootout Fraction Division Dirt Bike Fractions Comparisons ...

Lerdahl, Miss

2011-02-01

38

Response inhibition deficits in children with Fetal Alcohol Spectrum Disorder: Relationship between diffusion tensor imaging of the corpus callosum and eye movement control  

PubMed Central

Response inhibition is the ability to suppress irrelevant impulses to enable goal-directed behavior. The underlying neural mechanisms of inhibition deficits are not clearly understood, but may be related to white matter connectivity, which can be assessed using diffusion tensor imaging (DTI). The goal of this study was to investigate the relationship between response inhibition during the performance of saccadic eye movement tasks and DTI measures of the corpus callosum in children with or without Fetal Alcohol Spectrum Disorder (FASD). Participants included 43 children with an FASD diagnosis (12.3 ± 3.1 years old) and 35 typically developing children (12.5 ± 3.0 years old) both aged 7–18, assessed at three sites across Canada. Response inhibition was measured by direction errors in an antisaccade task and timing errors in a delayed memory-guided saccade task. Manual deterministic tractography was used to delineate six regions of the corpus callosum and calculate fractional anisotropy (FA), mean diffusivity (MD), parallel diffusivity, and perpendicular diffusivity. Group differences in saccade measures were assessed using t-tests, followed by partial correlations between eye movement inhibition scores and corpus callosum FA and MD, controlling for age. Children with FASD made more saccade direction errors and more timing errors, which indicates a deficit in response inhibition. The only group difference in DTI metrics was significantly higher MD of the splenium in FASD compared to controls. Notably, direction errors in the antisaccade task were correlated negatively to FA and positively to MD of the splenium in the control, but not the FASD group, which suggests that alterations in connectivity between the two hemispheres of the brain may contribute to inhibition deficits in children with FASD.

Paolozza, Angelina; Treit, Sarah; Beaulieu, Christian; Reynolds, James N.

2014-01-01

39

Fractions!  

NSDL National Science Digital Library

On this page you will practice adding, subtracting, multiplying, and dividing fractions. 1. Practice identifying equivalent fractions. Finding equivalent fractions 2. Add and subtract fractions. The first levels have like denominators, but then the levels get harder with unlike denominators. Make sure you use some scratch paper. Get to the highest level you can! Fraction Race (adding and subtracting, like and unlike denominators) 3. Practice adding fractions with mixed numbers. Math splat -adding fractions using mixed numbers 4. Finally, get with a partner ...

Hbinggeli

2010-08-24

40

Obsessive Patient with Agenesis of the Corpus Callosum  

Microsoft Academic Search

Agenesis of the corpus callosum is an uncommon congenital anomaly. The following is a report of a patient with agenesis of the corpus callosum with cavum septum pellucidum and colpocephaly. This patient has also been diagnosed with anankastic personality disorder.

DWH Tam

2002-01-01

41

Corpus Callosum Area in Children and Adults with Autism  

ERIC Educational Resources Information Center

Despite repeated findings of abnormal corpus callosum structure in autism, the developmental trajectories of corpus callosum growth in the disorder have not yet been reported. In this study, we examined corpus callosum size from a developmental perspective across a 30-year age range in a large cross-sectional sample of individuals with autism…

Prigge, Molly B. D.; Lange, Nicholas; Bigler, Erin D.; Merkley, Tricia L.; Neeley, E. Shannon; Abildskov, Tracy J.; Froehlich, Alyson L.; Nielsen, Jared A.; Cooperrider, Jason R.; Cariello, Annahir N.; Ravichandran, Caitlin; Alexander, Andrew L.; Lainhart, Janet E.

2013-01-01

42

Diffusion Tensor Tractography Analysis of the Corpus Callosum Fibers in Amyotrophic Lateral Sclerosis  

PubMed Central

Background and Purpose Involvement of the corpus callosum (CC) is reported to be a consistent feature of amyotrophic lateral sclerosis (ALS). We examined the CC pathology using diffusion tensor tractography analysis to identify precisely which fiber bundles are involved in ALS. Methods Diffusion tensor imaging was performed in 14 sporadic ALS patients and 16 age-matched healthy controls. Whole brain tractography was performed using the multiple-region of interest (ROI) approach, and CC fiber bundles were extracted in two ways based on functional and structural relevance: (i) cortical ROI selection based on Brodmann areas (BAs), and (ii) the sulcal-gyral pattern of cortical gray matter using FreeSurfer software, respectively. Results The mean fractional anisotropy (FA) values of the CC fibers interconnecting the primary motor (BA4), supplementary motor (BA6), and dorsolateral prefrontal cortex (BA9/46) were significantly lower in ALS patients than in controls, whereas those of the primary sensory cortex (BA1, BA2, BA3), Broca's area (BA44/45), and the orbitofrontal cortex (BA11/47) did not differ significantly between the two groups. The FreeSurfer ROI approach revealed a very similar pattern of abnormalities. In addition, a significant correlation was found between the mean FA value of the CC fibers interconnecting the primary motor area and disease severity, as assessed using the revised Amyotrophic Lateral Sclerosis Functional Rating Scale, and the clinical extent of upper motor neuron signs. Conclusions Our findings suggest that there is some degree of selectivity or a gradient in the CC pathology in ALS. The CC fibers interconnecting the primary motor and dorsolateral prefrontal cortices may be preferentially involved in ALS.

Kim, Jee-Eun; Oh, Jungsu S.; Sung, Jung-Joon; Lee, Kwang-Woo

2014-01-01

43

Diffusion Tensor Imaging in Cocaine Dependence: Regional Effects of Cocaine on Corpus Callosum and Effect of Cocaine Administration Route  

PubMed Central

Recent studies demonstrated that diffusion tensor imaging (DTI) can provide information regarding white matter integrity of the corpus callosum (CC). In this study, DTI parameters were compared between cocaine dependent subjects (CDs) and non-drug-using controls (NCs) in midsagittal CC. DTI images were acquired from 19 CDs and 18 age-matched NCs. The midsagittal CC was segmented into: genu, rostral body, anterior midbody, posterior midbody, isthmus, and splenium. Linear Mixed Models analyses showed that, relative to NCs, CDs had lower fractional anisotropy (FA), higher radial diffusivity (??), and higher mean diffusivity (Dav) in the isthmus; higher ?? and Dav in the rostral body; and lower FA in the splenium. After including mass of lifetime alcohol use in the mixed model ANCOVA as a covariate, significant between-group differences in ?? in the rostral body and isthmus remained. These results suggest that alterations in ?? in the rostral body and isthmus were mainly due to cocaine use, consistent with previous studies showing that cocaine may alter myelin integrity. Between-group differences in FA in the isthmus and splenium, and Dav in the rostral body and isthmus became non-significant after inclusion of alcohol use as a covariate. This is suggestive of alcohol influencing these values, or may be related to the decreased degrees of freedom for these effects. Consistent with clinical data of greater severity of drug use in smoked versus intranasal cocaine, subjects who smoked cocaine showed lower FA and higher ?? compared to intranasal CDs.

Ma, Liangsuo; Hasan, Khader M.; Steinberg, Joel L.; Narayana, Ponnada A.; Lane, Scott D.; Zuniga, Edward A.; Kramer, Larry A.; Moeller, F. Gerard

2009-01-01

44

Ictal EEG changes with corpus callosum section.  

PubMed

Corpus callosum section diminishes but does not completely abolish secondary bilaterally synchronous interictal EEG discharges, yet often causes cessation of generalized seizures. The effects of corpus callosum section on ictal EEG patterns have not been described. We contrasted ictal EEG patterns before and after anterior callosotomy in 18 patients and before and after total callosotomy in 10 patients. Bilaterally synchronous seizure onset was disrupted in 5 of 11 anterior section patients and 5 of 5 total section patients. Seven of 18 anterior section patients and 5 of 10 total section patients had more localized seizure onset after the procedure; localization to the frontal lobe was observed after anterior or total section, but only total section patients had newly demonstrated posterior locations of seizure onset. These data suggest that the mechanisms by which bilaterally synchronous interictal and ictal discharges are generated differ. Although brainstem or diencephalic structures may contribute to formation of interictal bilateral synchrony, the corpus callosum may be the only pathway used in producing apparent bilateral synchronous seizure onset in patients with secondarily generalized seizures. PMID:8504788

Spencer, S S; Katz, A; Ebersole, J; Novotny, E; Mattson, R

1993-01-01

45

Diffusion Tensor Anisotropy in Adolescents and Adults  

Microsoft Academic Search

We acquired diffusion tensor images on 33 normal adults aged 22–64 and 15 adolescents aged 14–21. We assessed relative anisotropy in stereotaxically located regions of interest in the internal capsule, corpus callosum, anterior thalamic radiations, frontal anterior fasciculus, fronto-occipital fasciculus, temporal lobe white matter, cingulum bundle, frontal inferior longitudinal fasciculus, frontal superior longitudinal fasciculus, and optic radiations. All of these

Jason S. Schneiderman; Monte S. Buchsbaum; M. Mehmet. Haznedar; Erin A. Hazlett; Adam M. Brickman; Lina Shihabuddin; Jesse G. Brand; Yuliya Torosjan; Randall E. Newmark; Cheuk Tang; Jonathan Aronowitz; Reshmi Paul-Odouard; William Byne; Patrick R. Hof

2007-01-01

46

Fractional Anisotropy Changes in Alzheimer's Disease Depend on the Underlying Fiber Tract Architecture: A Multiparametric DTI Study using Joint Independent Component Analysis.  

PubMed

Diffusion tensor imaging (DTI) allows the simultaneous measurement of several diffusion indices that provide complementary information on the substrate of white matter alterations in neurodegenerative diseases. These indices include fractional anisotropy (FA) as measure of fiber tract integrity, and the mode of anisotropy (Mode) reflecting differences in the shape of the diffusion tensor. We used a multivariate approach based on joint independent component analysis of FA and Mode in a large sample of 138 subjects with Alzheimer's disease (AD) dementia, 37 subjects with cerebrospinal fluid biomarker positive mild cognitive impairment (MCI-AD), and 153 healthy elderly controls from the European DTI Study on Dementia to comprehensively study alterations of microstructural white matter integrity in AD dementia and predementia AD. We found a parallel decrease of FA and Mode in intracortically projecting fiber tracts, and a parallel increase of FA and Mode in the corticospinal tract in AD patients compared to controls. Subjects with MCI-AD showed a similar, but spatially more restricted pattern of diffusion changes. Our findings suggest an early axonal degeneration in intracortical projecting fiber tracts in dementia and predementia stages of AD. An increase of Mode, parallel to an increase of FA, in the corticospinal tract suggests a more linear shape of diffusion due to loss of crossing fibers along relatively preserved cortico-petal and cortico-fugal fiber tracts in AD. Supporting this interpretation, we found three populations of fiber tracts, namely cortico-petal and cortico-fugal, commissural, and intrahemispherically projecting fiber tracts, in the peak area of parallel FA and Mode increase. PMID:24577476

Teipel, Stefan J; Grothe, Michel J; Filippi, Massimo; Fellgiebel, Andreas; Dyrba, Martin; Frisoni, Giovanni B; Meindl, Thomas; Bokde, Arun L W; Hampel, Harald; Klöppel, Stefan; Hauenstein, Karlheinz

2014-01-01

47

Corpus Callosum Morphometrics in Young Children with Autism Spectrum Disorder  

ERIC Educational Resources Information Center

This study assessed digital corpus callosum cross sectional areas in 3-4 year olds with autism spectrum disorder (ASD) compared to typically developing (TD) and developmentally delayed (DD) children. Though not different in absolute size compared to TD, ASD callosums were disproportionately small adjusted for increased ASD cerebral volume. ASD…

Boger-Megiddo, Inbal; Shaw, Dennis W. W.; Friedman, Seth D.; Sparks, Bobbi F.; Artru, Alan A.; Giedd, Jay N.; Dawson, Geraldine; Dager, Stephen R.

2006-01-01

48

Agenesis and lipoma of corpus callosum. Case report.  

PubMed

The agenesis and lipoma of the corpus callosum is a very rare association. We report the case of a 18-years old woman with rare epileptic seizures since the age of 6 years, normal neurological examination, as well as normal electroencephalogram. The brain computed tomography scanning and the magnetic resonance showed the lipoma and the agenesis of the corpus callosum. PMID:8585829

Silva, D F; Lima, M M; Oliveira, C O; Oliveira, W N; Anghinah, R; Lima, J G

1995-09-01

49

The corpus callosum: white matter or terra incognita  

PubMed Central

The corpus callosum is the largest white matter structure in the brain, consisting of 200–250 million contralateral axonal projections and the major commissural pathway connecting the hemispheres of the human brain. The pathology of the corpus callosum includes a wide variety of entities that arise from different causes such as congenital, inflammatory, tumoural, degenerative, infectious, metabolic, traumatic, vascular and toxic agents. The corpus callosum, or a specific part of it, can be affected selectively. Numerous pathologies of the corpus callosum are encountered during CT and MRI. The aim of this study is to facilitate a better understanding and thus treatment of the pathological entities of the corpus callosum by categorising them according to their causes and their manifestations in MR and CT imaging. Familiarity with its anatomy and pathology is important to the radiologist in order to recognise its disease at an early stage and help the clinician establish the optimal therapeutic approach.

Fitsiori, A; Nguyen, D; Karentzos, A; Delavelle, J; Vargas, M I

2011-01-01

50

Use of fractional anisotropy for determination of the cut-off value in 11C-methionine positron emission tomography for glioma.  

PubMed

Multimodal imaging is one of the necessary steps in the treatment of malignant brain tumors, and use of magnetic resonance imaging (MRI) and positron emission tomography (PET) are the current gold standard technique for the morphological and biological assessment of malignant brain tumors. In addition, fractional anisotropy (FA) obtained from diffusion tensor imaging (DTI) and 11C-methionine PET are useful to determine the tumor border at the tumor and white matter interface. Although there is no question of their value, a universally accepted cut-off value to discriminate normal and abnormal tissue has not been established. In this study we attempted to calculate and determine the cut-off values in FA and 11C-methionine PET that will allow delineation of the tumor border at the tumor and white matter interface by combining these two modalities. We were able to determine individual cut-off values for 11 patients, and then found an average cut-off value in the T/N ratio of 11C-methionine PET of 1.27 and in FA of 0.26, values similar to those previously confirmed by histological study. Moreover, reconstructing images delineating the tumor border was possible combining these two imaging modalities. We propose that the combined analysis of DTI and 11C-methionine PET has the potential to improve tumor border imaging in glioma patients, providing important information for establishing neurosurgical strategies. PMID:19111621

Kinoshita, Manabu; Hashimoto, Naoya; Goto, Tetsu; Yanagisawa, Takufumi; Okita, Yoshiko; Kagawa, Naoki; Kishima, Haruhiko; Tanaka, Hisashi; Fujita, Norihiko; Shimosegawa, Eku; Hatazawa, Jun; Yoshimine, Toshiki

2009-04-01

51

Fractional anisotropy (FA) changes after several weeks of daily left high frequency rTMS of the prefrontal cortex to treat major depression  

PubMed Central

Objectives As part of a sham controlled treatment trial using daily left rTMS, brain changes associated with four to six weeks of treatment were examined using diffusion tensor imaging (DTI) in order to non-invasively evaluate prefrontal white matter microstructure. A decrease in fractional anisotropy (FA) values of the left prefrontal white matter could indicate damage to the region. Methods DTI was performed prior to and after 4–6 weeks of daily rTMS treatments. Mean FA levels associated with active rTMS and sham rTMS for the right and left prefrontal white matter (LPF-WM) were assessed. Results Adequate images were acquired for eight participants (active n=4, sham n=4) before and after rTMS. A mean increase was found for the LPF-WM. The mixed model revealed a trend toward a significant Treatment Group × Region interaction effect (p=0.11). Further, simple Region effects (left prefrontal WM vs. right prefrontal WM) were at a trend toward significance for difference after treatment within the active rTMS group (p=.07), but not within the sham rTMS group (p=.88). Conclusions RTMS resulted in no evidence of damage to WM on the side of stimulation. DTI may offer a unique modality to increase our understanding of mechanisms of action for rTMS.

Kozel, F. Andrew; Johnson, Kevin A.; Nahas, Ziad; Nakonezny, Paul A.; Morgan, Paul S.; Anderson, Berry; Kose, Samet; Li, Xingbao; Lim, Kelvin O.; Trivedi, Madhukar; George, Mark S.

2010-01-01

52

Alteration of Fractional Anisotropy and Mean Diffusivity in Glaucoma: Novel Results of a Meta-Analysis of Diffusion Tensor Imaging Studies  

PubMed Central

Objectives We hypothesized that a meta-analysis of existing studies may help to reveal significant changes on diffusion tensor imaging (DTI) in patients with glaucoma. Therefore, a meta-analysis was utilized to investigate the possibility that DTI can detect white matter damage in patients with glaucoma. Methods The study design and report adhered to the PRISMA Statement guidelines. DTI studies that compared glaucoma patients and controls were surveyed using PubMed, Web of Science and EMBASE (January 2008 to September 2013). Stata was used to analyze the decrease in fractional anisotropy (FA) and increase in mean diffusivity (MD) in the optic nerve and optic radiation in patients with glaucoma. Results Eleven DTI studies were identified through a comprehensive literature search, and 10 independent DTI studies of glaucoma patients were eligible for the meta-analysis. A random effects model revealed a significant FA reduction in the optic nerve and optic radiation, as well as a significant MD increase in the tracts. A heterogeneity analysis suggested that FA may be related to glaucoma severity. Conclusions Our findings revealed that the optic nerve and optic radiation were vulnerable regions in patients with glaucoma and that FA may be correlated with glaucoma severity and age. Furthermore, this study suggests that magnetic resonance imaging in patients with glaucoma may help to provide objective evidence to aid in the diagnosis and management of glaucoma.

Li, Ke; Lu, Cuixin; Huang, Yufei; Yuan, Li; Zeng, Dong; Wu, Kan

2014-01-01

53

Tract-specific fractional anisotropy predicts cognitive outcome in a community sample of middle-aged participants with white matter lesions.  

PubMed

Cerebral white matter lesions (WMLs) have been consistently related to cognitive dysfunction but the role of white matter (WM) damage in cognitive impairment is not fully determined. Diffusion tensor imaging is a promising tool to explain impaired cognition related to WMLs. We investigated the separate association of high-grade periventricular hyperintensities (PVHs) and deep white matter hyperintensities (DWMHs) with fractional anisotropy (FA) in middle-aged individuals. We also assessed the predictive value to cognition of FA within specific WM tracts associated with high-grade WMLs. One hundred participants from the Barcelona-AsIA Neuropsychology Study were divided into groups based on low- and high-grade WMLs. Voxel-by-voxel FA were compared between groups, with separate analyses for high-grade PVHs and DWMHs. The mean FA within areas showing differences between groups was extracted in each tract for linear regression analyses. Participants with high-grade PVHs and participants with high-grade DWMHs showed lower FA in different areas of specific tracts. Areas showing decreased FA in high-grade DWMHs predicted lower cognition, whereas areas with decreased FA in high-grade PVHs did not. The predictive value to cognition of specific WM tracts supports the involvement of cortico-subcortical circuits in cognitive deficits only in DWMHs. PMID:24549185

Soriano-Raya, Juan José; Miralbell, Júlia; López-Cancio, Elena; Bargalló, Núria; Arenillas, Juan Francisco; Barrios, Maite; Cáceres, Cynthia; Toran, Pere; Alzamora, Maite; Dávalos, Antoni; Mataró, Maria

2014-05-01

54

Fractions  

NSDL National Science Digital Library

This is an accessible, easy-to-read book introducing fractions. It can be downloaded in PowerPoint, Impress, and Flash formats. For struggling or non-readers the book can be read aloud in a variety of voices. All of the books on the Tar Heel Reader site can be used with the Intellikeys keyboard with a custom overlay, a touch screen, and/or 1-3 switches. The text and background colors can be modified for students with visual impairments.

Cowley, K.

2011-05-09

55

Shape anisotropy: tensor distance to anisotropy measure  

NASA Astrophysics Data System (ADS)

Fractional anisotropy, defined as the distance of a diffusion tensor from its closest isotropic tensor, has been extensively studied as quantitative anisotropy measure for diffusion tensor magnetic resonance images (DT-MRI). It has been used to reveal the white matter profile of brain images, as guiding feature for seeding and stopping in fiber tractography and for the diagnosis and assessment of degenerative brain diseases. Despite its extensive use in DT-MRI community, however, not much attention has been given to the mathematical correctness of its derivation from diffusion tensors which is achieved using Euclidean dot product in 9D space. But, recent progress in DT-MRI has shown that the space of diffusion tensors does not form a Euclidean vector space and thus Euclidean dot product is not appropriate for tensors. In this paper, we propose a novel and robust rotationally invariant diffusion anisotropy measure derived using the recently proposed Log-Euclidean and J-divergence tensor distance measures. An interesting finding of our work is that given a diffusion tensor, its closest isotropic tensor is different for different tensor distance metrics used. We demonstrate qualitatively that our new anisotropy measure reveals superior white matter profile of DT-MR brain images and analytically show that it has a higher signal to noise ratio than fractional anisotropy.

Weldeselassie, Yonas T.; El-Hilo, Saba; Atkins, M. S.

2011-03-01

56

Diffusion Tensor Anisotropy in Adolescents and Adults  

PubMed Central

We acquired diffusion tensor images on 33 normal adults aged 22–64 and 15 adolescents aged 14–21. We assessed relative anisotropy in stereotaxically located regions of interest in the internal capsule, corpus callosum, anterior thalamic radiations, frontal anterior fasciculus, fronto-occipital fasciculus, temporal lobe white matter, cingulum bundle, frontal inferior longitudinal fasciculus, frontal superior longitudinal fasciculus, and optic radiations. All of these structures except the optic radiations, corpus callosum, and frontal inferior longitudinal fasciculus exhibited differences in anisotropy between adolescents and adults. Areas with anisotropy increasing with age included the anterior limb of the internal capsule, superior levels of the frontal superior longitudinal fasciculus and the inferior portion of the temporal white matter. Areas with anisotropy decreasing with age included the posterior limb of the internal capsule, anterior thalamic radiations, fronto-occipital fasciculus, anterior portion of the frontal anterior fasciculus, inferior portion of the frontal superior longitudinal fasciculus, cingulum bundle and superior portion of the temporal axis. Sex differences were found in the majority of areas but were most marked in the cingulum bundle and internal capsule. These results suggest continuing white matter development between adolescence and adulthood.

Schneiderman, Jason S.; Buchsbaum, Monte S.; Haznedar, M. Mehmet; Hazlett, Erin A.; Brickman, Adam M.; Shihabuddin, Lina; Brand, Jesse G.; Torosjan, Yuliya; Newmark, Randall E.; Tang, Cheuk; Aronowitz, Jonathan; Paul-Odouard, Reshmi; Byne, William; Hof, Patrick R.

2009-01-01

57

Corpus callosum agenesis and rehabilitative treatment  

PubMed Central

Corpus callosum agenesis is a relatively common brain malformation. It can be isolated or included in a complex alteration of brain (or sometimes even whole body) morphology. It has been associated with a number of neuropsychiatric disorders, from subtle neuropsychological deficits to Pervasive Developmental Disorders. Etiology and pathogenetic mechanisms have been better understood in recent years, due to the availability of more adequate animal models and the relevant progresses in developmental neurosciences. These recent findings are reviewed (through a MedLine search including papers published in the last 5 years and most relevant previously published papers) in view of the potential impact on children's global functioning and on the possible rehabilitative treatment, with an emphasis on the possibility to exploit brain plasticity and on the use of the ICF-CY framework.

2010-01-01

58

Corpus callosum agenesis and rehabilitative treatment.  

PubMed

Corpus callosum agenesis is a relatively common brain malformation. It can be isolated or included in a complex alteration of brain (or sometimes even whole body) morphology. It has been associated with a number of neuropsychiatric disorders, from subtle neuropsychological deficits to Pervasive Developmental Disorders.Etiology and pathogenetic mechanisms have been better understood in recent years, due to the availability of more adequate animal models and the relevant progresses in developmental neurosciences. These recent findings are reviewed (through a MedLine search including papers published in the last 5 years and most relevant previously published papers) in view of the potential impact on children's global functioning and on the possible rehabilitative treatment, with an emphasis on the possibility to exploit brain plasticity and on the use of the ICF-CY framework. PMID:20849621

Chiappedi, Matteo; Bejor, Maurizio

2010-01-01

59

[Epidermoid cyst of the corpus callosum].  

PubMed

Epidermoid cysts are most commonly located in the cerebellopontine angle and the parasellar regions. The authors report a case of an epidermoid cyst of unusual location: it arises in the midline and involves the body of the corpus callosum with interhemispheric exophytic growth. Reviewing the literature they did not find any similar report. C.T. scan and M.R.I. are the methods of choice for establishing the diagnosis and differentiating between epidermoid cyst, dermoid cyst, lipoma and arachnoid cyst. M.R.I. is highly sensitive and is especially useful in determining tumour extension, particularly in the sagittal and coronal planes, essential for surgical treatment planning. Treatment should be complete surgical resection in order to avoid recurrence and chemical meningitis. PMID:1299776

Urculo, E; Arrazola, M

1992-01-01

60

Maximum principal strain and strain rate associated with concussion diagnosis correlates with changes in corpus callosum white matter indices.  

PubMed

On-field monitoring of head impacts, combined with finite element (FE) biomechanical simulation, allow for predictions of regional strain associated with a diagnosed concussion. However, attempts to correlate these predictions with in vivo measures of brain injury have not been published. This article reports an approach to and preliminary results from the correlation of subject-specific FE model-predicted regions of high strain associated with diagnosed concussion and diffusion tensor imaging to assess changes in white matter integrity in the corpus callosum (CC). Ten football and ice hockey players who wore instrumented helmets to record head impacts sustained during play completed high field magnetic resonance imaging preseason and within 10 days of a diagnosed concussion. The Dartmouth Subject-Specific FE Head model was used to generate regional predictions of strain and strain rate following each impact associated with concussion. Maps of change in fractional anisotropy (FA) and median diffusivity (MD) were generated for the CC of each athlete to correlate strain with change in FA and MD. Mean and maximum strain rate correlated with change in FA (Spearman ? = 0.77, p = 0.01; 0.70, p = 0.031), and there was a similar trend for mean and maximum strain (0.56, p = 0.10; 0.6, p = 0.07), as well as for maximum strain with change in MD (-0.63, p = 0.07). Change in MD correlated with injury-to-imaging interval (? = -0.80, p = 0.006) but change in FA did not (? = 0.18, p = 0.62). These results provide preliminary confirmation that model-predicted strain and strain rate in the CC correlate with changes in indices of white matter integrity. PMID:21994062

McAllister, Thomas W; Ford, James C; Ji, Songbai; Beckwith, Jonathan G; Flashman, Laura A; Paulsen, Keith; Greenwald, Richard M

2012-01-01

61

Cavernous Angioma of the Corpus Callosum Presenting with Acute Psychosis  

PubMed Central

Psychiatric symptoms may occasionally be related to anatomic alterations of brain structures. Particularly, corpus callosum lesions seem to play a role in the change of patients' behavior. We present a case of a sudden psychotic attack presumably due to a hemorrhagic cavernous angioma of the corpus callosum, which was surgically removed with complete resolution of symptoms. Although a developmental defect like agenesis or lipoma is present in the majority of these cases, a growing lesion of the corpus callosum can rarely be the primary cause. Since it is potentially possible to cure these patients, clinicians should be aware of this association.

Pavesi, Giacomo; Causin, Francesco; Feletti, Alberto

2014-01-01

62

Corpus Callosum Microstructural Changes Correlate with Cognitive Dysfunction in Early Stages of Relapsing-Remitting Multiple Sclerosis: Axial and Radial Diffusivities Approach  

PubMed Central

The corpus callosum is the largest fiber bundle in the central nervous system and it takes part in several cognitive pathways. It can be affected by multiple sclerosis (MS) early in the disease. DTI is capable of infering the microstructural organization of the white matter. The vectorial analysis of the DTI offers the more specific indices of axial diffusivity (AD) and radial diffusivity (RD), which have shown to be useful to discriminate myelin damage from axon loss, respectively. This study presents DTI results (mean diffusivity (MD), fractional anisotropy (FA), RD, and AD) of 23 relapsing-remitting MS patients and its correlation with cognitive performance. There were 47.8% of cognitive impaired patients (MS CI). We found signs of demyelination, reflected by increased RD, and incipient axon loss, reflected by AD increase, which was slightly higher in the MS CI. The cognitive changes correlated with the DTI parameters, suggesting that loss of complexity in CC connections can impair neural conduction. Thus, cognitive impairment can be related to callosal disconnection, and DTI can be a promising tool to evaluate those changes.

Rimkus, Carolina de Medeiros; Junqueira, Thiago de Faria; Lyra, Katarina Paz; Jackowski, Marcel P.; Machado, Melissa A. R.; Miotto, Eliane C.; Callegaro, Dagoberto; Otaduy, Maria Concepcion Garcia; Leite, Claudia da Costa

2011-01-01

63

Left hemisphere fractional anisotropy increase in noise-induced tinnitus: a diffusion tensor imaging (DTI) study of white matter tracts in the brain.  

PubMed

Diffusion tensor imaging (DTI) is a contemporary neuroimaging modality used to study connectivity patterns and microstructure of white matter tracts in the brain. The use of DTI in the study of tinnitus is a relatively unexplored methodology with no studies focusing specifically on tinnitus induced by noise exposure. In this investigation, participants were two groups of adults matched for etiology, age, and degree of peripheral hearing loss, but differed by the presence or absence (+/-) of tinnitus. It is assumed that matching individuals on the basis of peripheral hearing loss, allows for differentiating changes in white matter microstructure due to hearing loss from changes due to the effects of chronic tinnitus. Alterations in white matter tracts, using the fractional anisotropy (FA) metric, which measures directional diffusion of water, were quantified using tract-based spatial statistics (TBSS) with additional details provided by in vivo probabilistic tractography. Our results indicate that 10 voxel clusters differentiated the two groups, including 9 with higher FA in the group with tinnitus. A decrease in FA was found for a single cluster in the group with tinnitus. However, seven of the 9 clusters with higher FA were in left hemisphere thalamic, frontal, and parietal white matter. These foci were localized to the anterior thalamic radiations and the inferior and superior longitudinal fasciculi. The two right-sided clusters with increased FA were located in the inferior fronto-occipital fasciculus and superior longitudinal fasciculus. The only decrease in FA for the tinnitus-positive group was found in the superior longitudinal fasciculus of the left parietal lobe. PMID:24212050

Benson, Randall R; Gattu, Ramtilak; Cacace, Anthony T

2014-03-01

64

Multi-site study of additive genetic effects on fractional anisotropy of cerebral white matter: Comparing meta and megaanalytical approaches for data pooling.  

PubMed

Combining datasets across independent studies can boost statistical power by increasing the numbers of observations and can achieve more accurate estimates of effect sizes. This is especially important for genetic studies where a large number of observations are required to obtain sufficient power to detect and replicate genetic effects. There is a need to develop and evaluate methods for joint-analytical analyses of rich datasets collected in imaging genetics studies. The ENIGMA-DTI consortium is developing and evaluating approaches for obtaining pooled estimates of heritability through meta-and mega-genetic analytical approaches, to estimate the general additive genetic contributions to the intersubject variance in fractional anisotropy (FA) measured from diffusion tensor imaging (DTI). We used the ENIGMA-DTI data harmonization protocol for uniform processing of DTI data from multiple sites. We evaluated this protocol in five family-based cohorts providing data from a total of 2248 children and adults (ages: 9-85) collected with various imaging protocols. We used the imaging genetics analysis tool, SOLAR-Eclipse, to combine twin and family data from Dutch, Australian and Mexican-American cohorts into one large "mega-family". We showed that heritability estimates may vary from one cohort to another. We used two meta-analytical (the sample-size and standard-error weighted) approaches and a mega-genetic analysis to calculate heritability estimates across-population. We performed leave-one-out analysis of the joint estimates of heritability, removing a different cohort each time to understand the estimate variability. Overall, meta- and mega-genetic analyses of heritability produced robust estimates of heritability. PMID:24657781

Kochunov, Peter; Jahanshad, Neda; Sprooten, Emma; Nichols, Thomas E; Mandl, René C; Almasy, Laura; Booth, Tom; Brouwer, Rachel M; Curran, Joanne E; de Zubicaray, Greig I; Dimitrova, Rali; Duggirala, Ravi; Fox, Peter T; Elliot Hong, L; Landman, Bennett A; Lemaitre, Hervé; Lopez, Lorna M; Martin, Nicholas G; McMahon, Katie L; Mitchell, Braxton D; Olvera, Rene L; Peterson, Charles P; Starr, John M; Sussmann, Jessika E; Toga, Arthur W; Wardlaw, Joanna M; Wright, Margaret J; Wright, Susan N; Bastin, Mark E; McIntosh, Andrew M; Boomsma, Dorret I; Kahn, René S; den Braber, Anouk; de Geus, Eco J C; Deary, Ian J; Hulshoff Pol, Hilleke E; Williamson, Douglas E; Blangero, John; van 't Ent, Dennis; Thompson, Paul M; Glahn, David C

2014-07-15

65

Reduced fractional anisotropy in the uncinate fasciculus in patients with major depression carrying the met-allele of the Val66Met brain-derived neurotrophic factor genotype.  

PubMed

Experimental studies support a neurotrophic hypothesis of major depressive disorder (MDD). The aim of this study was to determine the effect of Val66Met brain-derived neurotrophic factor (BDNF) polymorphism on the white matter fiber tracts connecting hippocampus and amygdala with the prefrontal lobe in a sample of patients with MDD and healthy controls. Thirty-seven patients with MDD and 42 healthy volunteers were recruited. Diffusion tensor imaging (DTI) data with 61 diffusion directions were obtained with MRI 3 Tesla scanner. Deterministic tractography was applied with ExploreDTI and Val66Met BDNF SNP (rs6265) was genotyped. Fiber tracts connecting the hippocampus and amygdala with the prefrontal lobe, namely uncinate fasciculus (UF), fornix, and cingulum were analyzed. A significant interaction was found in the UF between BDNF alleles and diagnosis. Patients carrying the BDNF met-allele had smaller fractional anisotropy (FA) in the UF compared to those patients homozygous for val-allele and compared to healthy subjects carrying the met-allele. A significant three-way interaction was detected between region of the cingulum (dorsal, rostral, and parahippocampal regions), brain hemisphere and BDNF genotype. Larger FA was detectable in the left rostral cingulum for met-allele carriers when compared to val/val alelle carriers. We provide evidence for the importance of the neurotrophic involvement in limbic and prefrontal connections. The met-allele of the BDNF polymorphism seems to render subjects more vulnerable for dysfunctions associated with the UF, a tract known to be related to negative emotional-cognitive processing bias, declarative memory problems, and autonoetic self awareness. PMID:22585743

Carballedo, A; Amico, F; Ugwu, I; Fagan, A J; Fahey, C; Morris, D; Meaney, J F; Leemans, A; Frodl, T

2012-07-01

66

Agenesis of the Corpus Callosum Is Associated With Feeding Difficulties  

Microsoft Academic Search

Our objective was to characterize the common occurrence of feeding and swallowing disorders noticed by our speech therapy department among patients with agenesis of the corpus callosum. All patients with suspected or presumed agenesis of the corpus callosum undergoing therapy for feeding and\\/or swallowing disorders, including oral and\\/or pharyngeal dysphagia and oral-sensory disorder, were identified. Their brain magnetic resonance imaging

Yu-tze Ng; Colleen M. McCarthy; Theodore J. Tarby; John B. Bodensteiner

2004-01-01

67

Evaluation of normal appearing spinal cord by diffusion tensor imaging, fiber tracking, fractional anisotropy, and apparent diffusion coefficient measurement in 13 dogs  

PubMed Central

Background Functional magnetic resonance (fMR) imaging offers plenty of new opportunities in the diagnosis of central nervous system diseases. Diffusion tensor imaging (DTI) is a technique sensitive to the random motion of water providing information about tissue architecture. We applied DTI to normal appearing spinal cords of 13 dogs of different breeds and body weights in a 3.0 T magnetic resonance (MR) scanner. The aim was to study fiber tracking (FT) patterns by tractography and the variations of the fractional anisotropy (FA) and the apparent diffusion coefficient (ADC) observed in the spinal cords of dogs with different sizes and at different locations (cervical and thoracolumbar). For that reason we added a DTI sequence to the standard clinical MR protocol. The values of FA and ADC were calculated by means of three regions of interest defined on the cervical or the thoracolumbar spinal cord (ROI 1, 2, and 3). Results The shape of the spinal cord fiber tracts was well illustrated following tractography and the exiting nerve roots could be differentiated from the spinal cord fiber tracts. Routine MR scanning times were extended for 8 to 12 min, depending on the size of the field of view (FOV), the slice thickness, and the size of the interslice gaps. In small breed dogs (?25 kg body weight) the traceable fiber length was about 5 vertebral bodies which took 10 to 12 min scanning time. FA and ADC values showed mean values of 0.447 (FA), and 0.560?×?10-3 mm2/s (ADC), respectively without any differences detected with regard to different dog sizes and spinal cord 45 segments examined. Conclusion FT is suitable for the graphical depiction of the canine spinal cord and the exiting nerve roots. The FA and ADC values offer an objective measure for evaluation of the spinal cord fiber integrity in dogs.

2013-01-01

68

Corpus callosum: musician and gender effects.  

PubMed

Previously we found that musicians have significantly larger anterior corpus callosum (CC). In the current study, we intended to replicate and extend our previous results using a new and larger sample of gender-matched subjects (56 right-handed professional musicians and 56 age- and handedness-matched controls). We found a significant gender x musicianship interaction for anterior and posterior CC size; male musicians had a larger anterior CC than non-musicians, while females did not show a significant effect of musicianship. The lack of a significant effect in females may be due to a tendency for a more symmetric brain organization and a disproportionately high representation of absolute pitch (AP) musicians among females. Although a direct causal effect between musicianship and alterations in the midsagittal CC size cannot be established, it is likely that the early commencement and continuous practice of bimanual motor training serves as an external trigger that can influence midsagittal CC size through changes in the actual callosal fiber composition and in the degree of myelinization, which will have implications for interhemispheric connectivity. PMID:12598730

Lee, Dennis J; Chen, Yi; Schlaug, Gottfried

2003-02-10

69

Lesions of the corpus callosum in children with neurofibromatosis 1.  

PubMed

Our aim was to determine the rate of focal lesions of the corpus callosum in children with neurofibromatosis type 1, and to characterize their natural history. Magnetic resonance imaging scans of the brain in 79 children with neurofibromatosis type 1 who were followed at the Neurology Clinic of Schneider Children's Medical Center (Petah Tiqwa, Israel) from 1990-2005 were reviewed. Focal lesions of the corpus callosum were identified in 11 (14%). These included unidentified bright objects in 7 patients (9%), and a neoplastic process in 4 (5%). Follow-up ranged from 1-16 years. Two of 4 tumors had enlarged during follow-up, and one was excised. Neurofibromatosis type 1 may be associated with a 14% prevalence of corpus callosum lesions. Owing to the apparently high frequency of callosal neoplasms in this population (5% in our series), and their tendency to enlarge, careful evaluation and prolonged follow-up are warranted. PMID:18486822

Mimouni-Bloch, Aviva; Kornreich, Liora; Kaadan, Walid; Steinberg, Tamar; Shuper, Avinoam

2008-06-01

70

Corpus Callosum Morphology and Its Relationship to Cognitive Function in Neurofibromatosis Type 1  

Microsoft Academic Search

Neurofibromatosis type 1 (NF1) is associated with cognitive dysfunction and structural brain abnormalities such as an enlarged corpus callosum. This study aimed to determine the relationship between corpus callosum morphology and cognitive function in children with neurofibromatosis type 1 using quantitative neuroanatomic imaging techniques. Children with neurofibromatosis type 1 (n = 46) demonstrated a significantly larger total corpus callosum and

Natalie Pride; Jonathan M. Payne; Richard Webster; E. Arthur Shores; Caroline Rae; Kathryn N. North

2010-01-01

71

Parenting, corpus callosum, and executive function in preschool children.  

PubMed

In this longitudinal population-based study (N?=?544), we investigated whether early parenting and corpus callosum length predict child executive function abilities at 4 years of age. The length of the corpus callosum in infancy was measured using postnatal cranial ultrasounds at 6 weeks of age. At 3 years, two aspects of parenting were observed: maternal sensitivity during a teaching task and maternal discipline style during a discipline task. Parents rated executive function problems at 4 years of age in five domains of inhibition, shifting, emotional control, working memory, and planning/organizing, using the Behavior Rating Inventory of Executive Function-Preschool Version. Maternal sensitivity predicted less executive function problems at preschool age. A significant interaction was found between corpus callosum length in infancy and maternal use of positive discipline to determine child inhibition problems: The association between a relatively shorter corpus callosum in infancy and child inhibition problems was reduced in children who experienced more positive discipline. Our results point to the buffering potential of positive parenting for children with biological vulnerability. PMID:24028215

Kok, Rianne; Lucassen, Nicole; Bakermans-Kranenburg, Marian J; van IJzendoorn, Marinus H; Ghassabian, Akhgar; Roza, Sabine J; Govaert, Paul; Jaddoe, Vincent W; Hofman, Albert; Verhulst, Frank C; Tiemeier, Henning

2014-09-01

72

Corpus Callosum Differences Associated with Persistent Stuttering in Adults  

ERIC Educational Resources Information Center

Recent studies have implicated anatomical differences in speech-relevant brain regions of adults who stutter (AWS) compared to normally fluent adults (NFA). The present study focused on the region of the corpus callosum (CC) which is involved in interhemispheric processing between the left and right cerebral hemispheres. Two-dimensional…

Choo, Ai Leen; Kraft, Shelly Jo; Olivero, William; Ambrose, Nicoline G.; Sharma, Harish; Chang, Soo-Eun; Loucks, Torrey M.

2011-01-01

73

Autism Traits in Individuals with Agenesis of the Corpus Callosum  

ERIC Educational Resources Information Center

Autism spectrum disorders (ASD) have numerous etiologies, including structural brain malformations such as agenesis of the corpus callosum (AgCC). We sought to directly measure the occurrence of autism traits in a cohort of individuals with AgCC and to investigate the neural underpinnings of this association. We screened a large AgCC cohort (n =…

Lau, Yolanda C.; Hinkley, Leighton B. N.; Bukshpun, Polina; Strominger, Zoe A.; Wakahiro, Mari L. J.; Baron-Cohen, Simon; Allison, Carrie; Auyeung, Bonnie; Jeremy, Rita J.; Nagarajan, Srikantan S.; Sherr, Elliott H.; Marco, Elysa J.

2013-01-01

74

Outcome in Prenatally Diagnosed Fetal Agenesis of the Corpus callosum  

Microsoft Academic Search

This study of the outcome and prognostic factors in prenatally diagnosed agenesis of the corpus callosum (ACC) was undertaken to see if there are any differences between subgroups, what relationship they have to neurodevelopmental outcome and whether this information aids the counselling of parents of fetuses with the condition. The outcome of 14 prenatally diagnosed fetuses with ACC and 61

P. W. A. Goodyear; C. M. Bannister; S. Russell; S. Rimmer

2001-01-01

75

Agenesis of the corpus callosum and autism: a comprehensive comparison.  

PubMed

The corpus callosum, with its ?200 million axons, remains enigmatic in its contribution to cognition and behaviour. Agenesis of the corpus callosum is a congenital condition in which the corpus callosum fails to develop; such individuals exhibit localized deficits in non-literal language comprehension, humour, theory of mind and social reasoning. These findings together with parent reports suggest that behavioural and cognitive impairments in subjects with callosal agenesis may overlap with the profile of autism spectrum disorders, particularly with respect to impairments in social interaction and communication. To provide a comprehensive test of this hypothesis, we directly compared a group of 26 adults with callosal agenesis to a group of 28 adults with a diagnosis of autism spectrum disorder but no neurological abnormality. All participants had full-scale intelligence quotient scores >78 and groups were matched on age, handedness, and gender ratio. Using the Autism Diagnostic Observation Schedule together with current clinical presentation to assess autistic symptomatology, we found that 8/26 (about a third) of agenesis subjects presented with autism. However, more formal diagnosis additionally involving recollective parent-report measures regarding childhood behaviour showed that only 3/22 met complete formal criteria for an autism spectrum disorder (parent reports were unavailable for four subjects). We found no relationship between intelligence quotient and autism symptomatology in callosal agenesis, nor evidence that the presence of any residual corpus callosum differentiated those who exhibited current autism spectrum symptoms from those who did not. Relative to the autism spectrum comparison group, parent ratings of childhood behaviour indicated children with agenesis were less likely to meet diagnostic criteria for autism, even for those who met autism spectrum criteria as adults, and even though there was no group difference in parent report of current behaviours. The findings suggest two broad conclusions. First, they support the hypothesis that congenital disruption of the corpus callosum constitutes a major risk factor for developing autism. Second, they quantify specific features that distinguish autistic behaviour associated with callosal agenesis from autism more generally. Taken together, these two findings also leverage specific questions for future investigation: what are the distal causes (genetic and environmental) determining both callosal agenesis and its autistic features, and what are the proximal mechanisms by which absence of the callosum might generate autistic symptomatology? PMID:24771497

Paul, Lynn K; Corsello, Christina; Kennedy, Daniel P; Adolphs, Ralph

2014-06-01

76

Autism traits in individuals with agenesis of the corpus callosum  

PubMed Central

Autism spectrum disorders (ASD) have numerous etiologies, including structural brain malformations such as agenesis of the corpus callosum (AgCC). We sought to directly measure the occurrence of autism traits in a cohort of individuals with AgCC and to investigate the neural underpinnings of this association. We screened a large AgCC cohort (n = 106) with the Autism Spectrum Quotient (AQ) and found that 45% of children, 35% of adolescents, and 18% of adults exceeded the predetermined autism-screening cut-off. Interestingly, performance on the AQ’s imagination domain was inversely correlated with magnetoencephalography measures of resting-state functional connectivity in the right superior temporal gyrus. Individuals with AgCC should be screened for ASD and disorders of the corpus callosum should be considered in autism diagnostic evaluations as well.

Lau, Yolanda C.; Hinkley, Leighton B. N.; Bukshpun, Polina; Strominger, Zoe A.; Wakahiro, Mari L. J.; Baron-Cohen, Simon; Allison, Carrie; Auyeung, Bonnie; Jeremy, Rita J.; Nagarajan, Srikantan S.; Sherr, Elliott H.; Marco, Elysa J.

2013-01-01

77

Selectively diminished corpus callosum fibers in congenital central hypoventilation syndrome  

Microsoft Academic Search

Congenital central hypoventilation syndrome (CCHS), a condition associated with mutations in the PHOX2B gene, is characterized by loss of breathing drive during sleep, insensitivity to CO2 and O2, and multiple somatomotor, autonomic, neuropsychological, and ophthalmologic deficits, including impaired intrinsic and extrinsic eye muscle control. Brain structural studies show injury in peri-callosal regions and the corpus callosum (CC), which has the

R. Kumar; P. M. Macey; M. A. Woo; R. M. Harper

2011-01-01

78

Statistical shape analysis of the corpus callosum in Schizophrenia  

PubMed Central

We present a statistical shape-analysis framework for characterizing and comparing morphological variation of the corpus callosum. The midsagittal boundary of the corpus callosum is represented by a closed curve and analyzed using an invariant shape representation. The shape space of callosal curves is endowed with a Riemannian metric. Shape distances are given by the length of shortest paths (geodesics) that are invariant to shape-confounding transformations. The statistical framework enables computation of shape averages and covariances on the shape space in an intrinsic manner (unique to the shape space). The statistical framework makes use of the tangent principal component approach to achieve dimension reduction on the space of corpus callosum shapes. The advantages of this approach are – it is fully automatic, invariant, and avoids the use of landmarks to define shapes. We applied our method to determine the effects of sex, age, schizophrenia and schizophrenia-related genetic liability on callosal shape in a large sample of patients and controls and their first-degree relatives (N=218). Results showed significant age, sex, and schizophrenia effects on both global and local callosal shape structure.

Joshi, Shantanu H.; Narr, Katherine L.; Philips, Owen R.; Nuechterlein, Keith H.; Asarnow, Robert F.; Toga, Arthur W.; Woods, Roger P.

2013-01-01

79

[Agenesis of the corpus callosum. Neuropathologic study and physiopathologic hypotheses].  

PubMed

The neuropathological study of corpus callosum agenesis requires a two-phase approach: first it should analyze the putative causal factors, i.e. absence of callosal neurons, commissuration inability or synapse remodelling defect; secondly it has to detect any morphogenetic effects stemming from the absence of commissure such as nonregression of archicortical structures, ventricular enlargement or possible invasion of the remaining telencephaplic commissure by callosal neurons. Absence of callosal neurons due to abnormal corticogenesis gives rise to corpus callosum agenesis without callosal axon, that is without Probst's bundles. Conversely, corpus callosum agenesis occurring secondary to a commissuration default is associated with the presence of callosal axons which travel along the midline instead of crossing, that leads to the formation of Probst's bundles. This inability to cross the midline could be secondary to an obstacle, such as lipoma or as interhemispheric cysts, or primitive due to axonal guidance disturbance. In the latter situation, the commissural defect could affect the other cerebral commissures i.e. anterior or hippocampal commissures, or could become integrated into a more diffuse midline pathology involving both cerebral and extracerebral structures. Finally, it could be assumed that a synapse remodelling defect could lead to atrophy or hypertrophy of the commissure, that occurs in the absence of white matter pathology. PMID:9757326

Gelot, A; Lewin, F; Moraine, C; Pompidou, A

1998-05-01

80

Diffusion Tensor Imaging in the Corpus Callosum in Children after Moderate to Severe Traumatic Brain Injury  

Microsoft Academic Search

Diffusion tensor imaging (DTI) is a recent imaging technique that assesses the microstructure of the cerebral white matter (WM) based on anisotropic diffusion (i.e., water molecules move faster in par- allel to nerve fibers than perpendicular to them). Fractional anisotropy (FA), which ranges from 0 to 1.0, increases with myelination of WM tracts and is sensitive to diffuse axonal injury

Elisabeth A. Wilde; Zili Chu; Erin D. Bigler; Jill V. Hunter; Michael A. Fearing; Gerri Hanten; Mary R. Newsome; Randall S. Scheibel; Xiaoqi Li; Harvey S. Levin

2006-01-01

81

Microstructural Integrity of the Corpus Callosum Linked with Neuropsychological Performance in Adolescents  

ERIC Educational Resources Information Center

Background: Diffusion tensor imaging (DTI) has revealed microstructural aspects of adolescent brain development, the cognitive correlates of which remain relatively uncharacterized. Methods: DTI was used to assess white matter microstructure in 18 typically developing adolescents (ages 16-18). Fractional anisotropy (FA) and mean diffusion (MD)…

Fryer, Susanna L.; Frank, Lawrence R.; Spadoni, Andrea D.; Theilmann, Rebecca J.; Nagel, Bonnie J.; Schweinsburg, Alecia D.; Tapert, Susan F.

2008-01-01

82

Difference between smokers and non-smokers in the corpus callosum volume.  

PubMed

The purpose of this study was to analyze the effects of smoking on corpus callosum volume. In addition, the relationships between smoking duration, smoking frequency, and corpus callosum volume were analyzed. Magnetic resonance brain images were acquired for 58 normal Korean men (30 smokers (age 32.82±14.12 years) and 28 non-smokers (age 35.49±13.11 years)). The corpus callosum volume was measured using Brain Voyager 2000S/W and was normalized by intracranical volume, which was calculated using cerebral sizes. The corpus callosum volume for smokers was significantly smaller than that for non-smokers. Also, there was a negative correlation between corpus callosum volume and smoking duration. The change of white matter volume (e.g., corpus callosum) might be a primary factor for characterizing the effects of smoking. PMID:20804817

Choi, Mi-Hyun; Lee, Su-Jeong; Yang, Jae-Woong; Kim, Ji-Hye; Choi, Jin-Seung; Park, Jang-Yeon; Jun, Jae-Hoon; Tack, Gye-Rae; Lee, Beob-Yi; Kim, Hyun-Jun; Chung, Soon-Cheol

2010-11-12

83

A note on the relative positions of the corpus callosum and the hippocampal formation  

Microsoft Academic Search

ABBIE (1939) has recently questioned the classical hypothesis of Elliot Smith on the relation of the corpus callosum to the hippocampus and the lamina terminalis in the callosal mammals. The fibres of the corpus callosum, according to Elliot Smith, reach the opposite hemisphere by invading the lamina terminalis in the region of the dorsal (hippocampal) commissure which is itself ventral

Y. Appajee

1940-01-01

84

Spatial attention in agenesis of the corpus callosum: shifting attention between visual fields  

Microsoft Academic Search

The role of the corpus callosum in spatially selective visual attention is uncertain. Research using commissurotomy and callosotomy patients has attempted to determine if the corpus callosum plays a role in reorienting attention between visual fields, as if spatial attention is unitary or divisible between the cerebral hemispheres. Reorienting of selective visuospatial attention within versus between visual fields was tested

Robert J Hines; Lynn K Paul; Warren S Brown

2002-01-01

85

Three sibs with microcephaly, clubfeet and agenesis of corpus callosum: a new genetic syndrome?  

PubMed

Clubfoot is a common birth deformity, and agenesis of the corpus callosum is one of the most prevalent brain malformations. We describe three sibs of Arab origin, who were born with clubfeet, agenesis of corpus callosum, and minor anomalies. Two of them were born with microcephaly. This phenotype may represent a novel autosomal recessive genetic condition. PMID:21465661

Shkalim, Vered; Ben-Sira, Liat; Inbar, Dov; Kaadan, Walid; Basel-Vanagaite, Lina; Straussberg, Rachel

2011-05-01

86

Corpus callosum size in children with spastic cerebral palsy: relationship to clinical outcome.  

PubMed

This study examines corpus callosum pathology in children with spastic cerebral palsy aged 7 to 15 years and to investigates the relation between corpus callosum areas and clinical picture. Magnetic resonance images of 46 patients were reviewed prospectively. Twenty-two patients with cerebral palsy were age and gender matched with the control patients. The cerebral palsy group had a significantly smaller mean corpus callosum surface area than did the control group. The cerebral palsy group also had a significantly smaller mean internal skull surface area measurement than did the control group. The corpus callosum/internal skull surface area ratio was also smaller for those with cerebral palsy. Wechsler Intelligence Scale Verbal IQ scores were associated with the surface area of the corpus callosum in cerebral palsy patients. A significant relationship between corpus callosum surface area and IQ scores in children with cerebral palsy was found. A positive correlation between internal skull surface area and IQ scores in children with cerebral palsy was noted. A significant correlation between Apgar score and corpus callosum surface area in the cerebral palsy group was found. A negative correlation between corpus callosum surface area and the Gross Motor Function Classification System in patients with cerebral palsy was noted. PMID:17621513

Ku?ak, Wojciech; Sobaniec, Wojciech; Kubas, Bozena; Walecki, Jerzy

2007-04-01

87

The Lamina Rostralis: Modification of Concepts Concerning the Anatomy, Embryology, and MR Appearance of the Rostrum of the Corpus Callosum  

Microsoft Academic Search

PURPOSE: To study the anatomy and embryology of the lamina rostralis, and to determine whether the rostrum is, as frequently stated, the last section of the corpus callosum to develop. METHODS: The rostrum was analyzed in dissected adult brains and on MR studies in 300 patients with a normal corpus callosum and in 84 patients with a hypogenetic corpus callosum.

E. Leon Kier; Charles L. Truwit

88

Reduced area of the corpus callosum in posttraumatic stress disorder.  

PubMed

Magnetic resonance imaging (MRI) studies have revealed decreases in the mid-sagittal area of the corpus callosum (CC) in pediatric posttraumatic stress disorder (PTSD), but at present no data are available in adult PTSD patients. We have previously reported decreased whole-brain white matter (WM) volume in adults with PTSD and now report corpus callosum area from the same sample. MRI was used to obtain whole-brain images in 12 adult patients with PTSD and 10 matched controls. Total parenchyma (white matter plus gray matter [GM]) volume, mid-sagittal area of the CC and seven sub-regions of this structure were calculated. In PTSD patients, the total CC area, absolute and normalized to total brain parenchyma, was smaller compared with control values. Several absolute and normalized CC sub-regions were also smaller in PTSD patients: genu (region 2), mid-body (region 5) and isthmus (region 6). There was also a trend for the anterior mid-body (area 4) to be smaller in PTSD patients. No differences were found in the rostrum (region 1), rostral body (region 3) or splenium (region 7). Adult patients with PTSD had decreased CC area after correcting for total brain tissue, indicating that these differences are not attributable to generalized white matter atrophy. These findings are similar to previous results in children with PTSD and suggest specific changes in the CC. PMID:15465292

Villarreal, Gerardo; Hamilton, Derek A; Graham, David P; Driscoll, Ira; Qualls, Clifford; Petropoulos, Helen; Brooks, William M

2004-09-15

89

Corpus callosum size and shape alterations in adolescent inhalant users.  

PubMed

Inhalants, frequently abused during adolescence, are neurotoxic to white matter. We investigated the impact of inhalant misuse on the morphology of the corpus callosum (CC), the largest white matter bundle in the brain, in an adolescent sample of inhalant users [n = 14; mean age = 17.3; standard deviation (SD) = 1.7], cannabis users (n = 11; mean age = 19.7; SD = 1.7) and community controls (n = 9; mean age = 19.5; SD = 2.6). We identified significant morphological differences in the CC among inhalant users compared with community controls. There were no morphological differences between inhalant and cannabis users. Our findings may represent the early stages of neurobiological damage associated with chronic inhalant misuse. PMID:21955104

Takagi, Michael; Lubman, Dan I; Walterfang, Mark; Barton, Sarah; Reutens, David; Wood, Amanda; Yücel, Murat

2013-09-01

90

Axon position within the corpus callosum determines contralateral cortical projection.  

PubMed

How developing axons in the corpus callosum (CC) achieve their homotopic projection to the contralateral cortex remains unclear. We found that axonal position within the CC plays a critical role in this projection. Labeling of nearby callosal axons in mice showed that callosal axons were segregated in an orderly fashion, with those from more medial cerebral cortex located more dorsally and subsequently projecting to more medial contralateral cortical regions. The normal axonal order within the CC was grossly disturbed when semaphorin3A/neuropilin-1 signaling was disrupted. However, the order in which axons were positioned within the CC still determined their contralateral projection, causing a severe disruption of the homotopic contralateral projection that persisted at postnatal day 30, when the normal developmental refinement of contralateral projections is completed in wild-type (WT) mice. Thus, the orderly positioning of axons within the CC is a primary determinant of how homotopic interhemispheric projections form in the contralateral cortex. PMID:23812756

Zhou, Jing; Wen, Yunqing; She, Liang; Sui, Ya-Nan; Liu, Lu; Richards, Linda J; Poo, Mu-Ming

2013-07-16

91

Axon position within the corpus callosum determines contralateral cortical projection  

PubMed Central

How developing axons in the corpus callosum (CC) achieve their homotopic projection to the contralateral cortex remains unclear. We found that axonal position within the CC plays a critical role in this projection. Labeling of nearby callosal axons in mice showed that callosal axons were segregated in an orderly fashion, with those from more medial cerebral cortex located more dorsally and subsequently projecting to more medial contralateral cortical regions. The normal axonal order within the CC was grossly disturbed when semaphorin3A/neuropilin-1 signaling was disrupted. However, the order in which axons were positioned within the CC still determined their contralateral projection, causing a severe disruption of the homotopic contralateral projection that persisted at postnatal day 30, when the normal developmental refinement of contralateral projections is completed in wild-type (WT) mice. Thus, the orderly positioning of axons within the CC is a primary determinant of how homotopic interhemispheric projections form in the contralateral cortex.

Zhou, Jing; Wen, Yunqing; She, Liang; Sui, Ya-nan; Liu, Lu; Richards, Linda J.; Poo, Mu-ming

2013-01-01

92

Diffusion Tensor Magnetic Resonance Imaging Finding of Discrepant Fractional Anisotropy Between the Frontal and Parietal Lobes After Whole-Brain Irradiation in Childhood Medulloblastoma Survivors: Reflection of Regional White Matter Radiosensitivity?  

SciTech Connect

Purpose: To test the hypothesis that fractional anisotropy (FA) is more severely reduced in white matter of the frontal lobe compared with the parietal lobe after receiving the same whole-brain irradiation dose in a cohort of childhood medulloblastoma survivors. Methods and Materials: Twenty-two medulloblastoma survivors (15 male, mean [{+-} SD] age = 12.1 {+-} 4.6 years) and the same number of control subjects (15 male, aged 12.0 {+-} 4.2 years) were recruited for diffusion tensor magnetic resonance imaging scans. Using an automated tissue classification method and the Talairach Daemon atlas, FA values of frontal and parietal lobes receiving the same radiation dose, and the ratio between them were quantified and denoted as FFA, PFA, and FA{sub f/p}, respectively. The Mann-Whitney U test was used to test for significant differences of FFA, PFA, and FA{sub f/p} between medulloblastoma survivors and control subjects. Results: Frontal lobe and parietal lobe white matter FA were found to be significantly less in medulloblastoma survivors compared with control subjects (frontal p = 0.001, parietal p = 0.026). Moreover, these differences were found to be discrepant, with the frontal lobe having a significantly larger difference in FA compared with the parietal lobe. The FA{sub f/p} of control and medulloblastoma survivors was 1.110 and 1.082, respectively (p = 0.029). Conclusion: Discrepant FA changes after the same irradiation dose suggest radiosensitivity of the frontal lobe white matter compared with the parietal lobe. Special efforts to address the potentially vulnerable frontal lobe after treatment with whole-brain radiation may be needed so as to balance disease control and treatment-related morbidity.

Qiu Deqiang [Department of Diagnostic Radiology, Queen Mary Hospital, University of Hong Kong, Hong Kong (China); Kwong, Dora [Department of Clinical Oncology, Queen Mary Hospital, University of Hong Kong, Hong Kong (China); Chan, Godfrey [Department of Pediatric and Adolescent Medicine, Queen Mary Hospital, University of Hong Kong, Hong Kong (China); Leung, Lucullus [Department of Oncology, Princess Margaret Hospital, Hong Kong (China); Khong, P.-L. [Department of Diagnostic Radiology, Queen Mary Hospital, University of Hong Kong, Hong Kong (China)], E-mail: plkhong@hkucc.hku.hk

2007-11-01

93

Biomarkers of increased diffusion anisotropy in semi-acute mild traumatic brain injury: a longitudinal perspective  

PubMed Central

Mild traumatic brain injury is the most prevalent neurological insult and frequently results in neurobehavioural sequelae. However, little is known about the pathophysiology underlying the injury and how these injuries change as a function of time. Although diffusion tensor imaging holds promise for in vivo characterization of white matter pathology, both the direction and magnitude of anisotropic water diffusion abnormalities in axonal tracts are actively debated. The current study therefore represents both an independent replication effort (n = 28) of our previous findings (n = 22) of increased fractional anisotropy during semi-acute injury, as well as a prospective study (n = 26) on the putative recovery of diffusion abnormalities. Moreover, new analytical strategies were applied to capture spatially heterogeneous white matter injuries, which minimize implicit assumptions of uniform injury across diverse clinical presentations. Results indicate that whereas a general pattern of high anisotropic diffusion/low radial diffusivity was present in various white matter tracts in both the replication and original cohorts, this pattern was only consistently observed in the genu of the corpus callosum across both samples. Evidence for a greater number of localized clusters with increased anisotropic diffusion was identified across both cohorts at trend levels, confirming heterogeneity in white matter injury. Pooled analyses (50 patients; 50 controls) suggested that measures of diffusion within the genu were predictive of patient classification, albeit at very modest levels (71% accuracy). Finally, we observed evidence of recovery in lesion load in returning patients across a 4-month interval, which was correlated with a reduction in self-reported post-concussive symptomatology. In summary, the corpus callosum may serve as a common point of injury in mild traumatic brain injury secondary to anatomical (high frequency of long unmyelinated fibres) and biomechanics factors. A spatially heterogeneous pattern of increased anisotropic diffusion exists in various other white matter tracts, and these white matter anomalies appear to diminish with recovery. This macroscopic pattern of diffusion abnormalities may be associated with cytotoxic oedema following mechanical forces, resulting in changes in ionic homeostasis, and alterations in the ratio of intracellular and extracellular water. Animal models more specific to the types of mild traumatic brain injury typically incurred by humans are needed to confirm the histological correlates of these macroscopic markers of white matter pathology.

Ling, Josef M.; Pena, Amanda; Yeo, Ronald A.; Merideth, Flannery L.; Klimaj, Stefan; Gasparovic, Charles

2012-01-01

94

Haploinsufficiency of ZNF238 is associated with corpus callosum abnormalities in 1q44 deletions.  

PubMed

A variety of candidate genes have been proposed to cause corpus callosum abnormalities (CCAs) in patients with terminal chromosome 1q deletions. Recent data excluded AKT3 and implicated ZNF238 and/or CEP170 as genes causative of corpus callosum anomalies in patients with 1q43-1q44 deletions. We report on a girl with dysmorphic features, seizures beginning in infancy, hypotonia, marked developmental delay, and dysgenesis of the corpus callosum. Chromosomal microarray analysis detected a de novo 1.47 Mb deletion at 1q44. The deleted interval encompasses the ZNF238 gene but not the CEP170 or AKT3 genes, thus providing additional evidence for the former and against the latter as being causative of corpus callosum anomalies in patients with such deletions. PMID:23494996

Perlman, Seth J; Kulkarni, Shashikant; Manwaring, Linda; Shinawi, Marwan

2013-04-01

95

Agenesis of the Corpus Callosum in a Newborn with Turner Mosaicism  

PubMed Central

The agenesis of the corpus callosum results from a failure in the development of the largest fiber bundle that connects cerebral hemispheres. Patient’s outcome is influenced by etiology and associated central nervous system malformations. We describe a child with Turner syndrome (TS) mosaicism, with particular phenotype features and a complete agenesis of the corpus callosum. To our knowledge, this is the second case report of TS mosaicism associated with complete agenesis of the corpus callosum. Anatomical brain magnetic resonance imaging and diffusion tensor imaging were useful to confirm the complete absence of the corpus callosum, evaluate associated central nervous system malformations, visualize abnormal white matter tracts (Probst bundles) and assess the remaining commissures.

Pereira, Ester; Polo, Monica Rebollo; Lopez, Jordi Muchart; Quijano, Thais Agut; Garcia-Alix, Alfredo; Fons, Carmen

2014-01-01

96

Whole-exome sequencing identifies mutated c12orf57 in recessive corpus callosum hypoplasia.  

PubMed

The corpus callosum is the principal cerebral commissure connecting the right and left hemispheres. The development of the corpus callosum is under tight genetic control, as demonstrated by abnormalities in its development in more than 1,000 genetic syndromes. We recruited more than 25 families in which members affected with corpus callosum hypoplasia (CCH) lacked syndromic features and had consanguineous parents, suggesting recessive causes. Exome sequence analysis identified C12orf57 mutations at the initiator methionine codon in four different families. C12orf57 is ubiquitously expressed and encodes a poorly annotated 126 amino acid protein of unknown function. This protein is without significant paralogs but has been tightly conserved across evolution. Our data suggest that this conserved gene is required for development of the human corpus callosum. PMID:23453666

Akizu, Naiara; Shembesh, Nuri M; Ben-Omran, Tawfeg; Bastaki, Laila; Al-Tawari, Asma; Zaki, Maha S; Koul, Roshan; Spencer, Emily; Rosti, Rasim Ozgur; Scott, Eric; Nickerson, Elizabeth; Gabriel, Stacey; da Gente, Gilberto; Li, Jiang; Deardorff, Matthew A; Conlin, Laura K; Horton, Margaret A; Zackai, Elaine H; Sherr, Elliott H; Gleeson, Joseph G

2013-03-01

97

Whole-Exome Sequencing Identifies Mutated C12orf57 in Recessive Corpus Callosum Hypoplasia  

PubMed Central

The corpus callosum is the principal cerebral commissure connecting the right and left hemispheres. The development of the corpus callosum is under tight genetic control, as demonstrated by abnormalities in its development in more than 1,000 genetic syndromes. We recruited more than 25 families in which members affected with corpus callosum hypoplasia (CCH) lacked syndromic features and had consanguineous parents, suggesting recessive causes. Exome sequence analysis identified C12orf57 mutations at the initiator methionine codon in four different families. C12orf57 is ubiquitously expressed and encodes a poorly annotated 126 amino acid protein of unknown function. This protein is without significant paralogs but has been tightly conserved across evolution. Our data suggest that this conserved gene is required for development of the human corpus callosum.

Akizu, Naiara; Shembesh, Nuri M.; Ben-Omran, Tawfeg; Bastaki, Laila; Al-Tawari, Asma; Zaki, Maha S.; Koul, Roshan; Spencer, Emily; Rosti, Rasim Ozgur; Scott, Eric; Nickerson, Elizabeth; Gabriel, Stacey; da Gente, Gilberto; Li, Jiang; Deardorff, Matthew A.; Conlin, Laura K.; Horton, Margaret A.; Zackai, Elaine H.; Sherr, Elliott H.; Gleeson, Joseph G.

2013-01-01

98

Agenesis of the corpus callosum in a newborn with turner mosaicism.  

PubMed

The agenesis of the corpus callosum results from a failure in the development of the largest fiber bundle that connects cerebral hemispheres. Patient's outcome is influenced by etiology and associated central nervous system malformations. We describe a child with Turner syndrome (TS) mosaicism, with particular phenotype features and a complete agenesis of the corpus callosum. To our knowledge, this is the second case report of TS mosaicism associated with complete agenesis of the corpus callosum. Anatomical brain magnetic resonance imaging and diffusion tensor imaging were useful to confirm the complete absence of the corpus callosum, evaluate associated central nervous system malformations, visualize abnormal white matter tracts (Probst bundles) and assess the remaining commissures. PMID:24987509

Pereira, Ester; Polo, Monica Rebollo; López, Jordi Muchart; Quijano, Thais Agut; García-Alix, Alfredo; Fons, Carmen

2014-05-01

99

MRI evaluation of pathologies affecting the corpus callosum: A pictorial essay  

PubMed Central

The corpus callosum is a midline cerebral structure and has a unique embryological development pattern. In this article, we describe the pathophysiology and present imaging findings of various typical/atypical conditions affecting the corpus callosum. Since many of these pathologies have characteristic appearances on magnetic resonance imaging (MRI) and their therapeutic approaches are poles apart, ranging from medical to surgical, the neuroradiologist should be well aware of them.

Kazi, Aamish Z; Joshi, Priscilla C; Kelkar, Abhimanyu B; Mahajan, Mangal S; Ghawate, Amit S

2013-01-01

100

The structure of the corpus callosum in obsessive compulsive disorder.  

PubMed

Abnormal brain connectivity has recently been reported in obsessive compulsive disorder (OCD). However, structural differences in the corpus callosum (CC), the primary structure connecting the two hemispheres, have not been extensively studied. In this case-control study, we recruited 30 patients with OCD and 30 healthy control subjects carefully matched for age, sex and handedness. Combining surface-based mesh-modeling and voxel-based morphometry (VBM), we compared callosal thickness and white matter (WM) density in patients and controls. We investigated associations between callosal structure and cortical gray matter (GM) density, and we related CC measures to neuropsychological performance in OCD. OCD patients showed small anterior and posterior callosal regions compared to healthy control subjects. In the OCD group, anterior callosal thickness was positively correlated with GM density of the right mid-dorso-lateral prefrontal (BA 9/46) area, while posterior callosal thickness was positively correlated with GM density in the left supramarginal gyrus (BA 40). Moreover, posterior callosal WM density was positively correlated with verbal memory, visuo-spatial memory, verbal fluency, and visuo-spatial reasoning performances. Callosal attributes were related to GM density in cortical areas innervated by the CC, and were also related to performance in cognitive domains impaired in the disorder. The CC may therefore be integrally involved in OCD. PMID:23078960

Di Paola, M; Luders, E; Rubino, I A; Siracusano, A; Manfredi, G; Girardi, P; Martinotti, G; Thompson, P M; Chou, Y-Y; Toga, A W; Caltagirone, C; Spalletta, G

2013-10-01

101

Automatic corpus callosum segmentation for standardized MR brain scanning  

NASA Astrophysics Data System (ADS)

Magnetic Resonance (MR) brain scanning is often planned manually with the goal of aligning the imaging plane with key anatomic landmarks. The planning is time-consuming and subject to inter- and intra- operator variability. An automatic and standardized planning of brain scans is highly useful for clinical applications, and for maximum utility should work on patients of all ages. In this study, we propose a method for fully automatic planning that utilizes the landmarks from two orthogonal images to define the geometry of the third scanning plane. The corpus callosum (CC) is segmented in sagittal images by an active shape model (ASM), and the result is further improved by weighting the boundary movement with confidence scores and incorporating region based refinement. Based on the extracted contour of the CC, several important landmarks are located and then combined with landmarks from the coronal or transverse plane to define the geometry of the third plane. Our automatic method is tested on 54 MR images from 24 patients and 3 healthy volunteers, with ages ranging from 4 months to 70 years old. The average accuracy with respect to two manually labeled points on the CC is 3.54 mm and 4.19 mm, and differed by an average of 2.48 degrees from the orientation of the line connecting them, demonstrating that our method is sufficiently accurate for clinical use.

Xu, Qing; Chen, Hong; Zhang, Li; Novak, Carol L.

2007-03-01

102

Detecting corpus callosum abnormalities in autism based on anatomical landmarks  

PubMed Central

Autism is a severe developmental disorder whose neurological basis is largely unknown. Autism is a subtype of autism that displays more homogeneous features within group. The aim of this study was to identify the shape differences of the corpus callosum between patients with autism and the controls. Anatomical landmarks were collected from mid-sagittal MRI of 25 patients and 18 controls. Euclidean distance matrix analysis and thin-plate spline were used to analyze the landmark forms. Point-by-point shape comparison was performed both globally and locally. A new local shape comparison scheme was proposed which compared each part of the shape in its local coordinate system. Point correspondence was established among individual shapes based on the inherent landmark correspondence. No significant difference was found in the landmark form between patients and controls, but the distance between interior genu and posterior most was found significantly shorter in patients. Thin-plate spline analysis showed significant group difference between the landmark configurations in terms of the deformation from the overall mean configuration. Significant global shape differences were found in the anterior lower body and posterior bottom, and local shape difference existed in the anterior bottom. This study can serve as both clinical reference and a detailed procedure guideline for similar studies in the future.

He, Qing; Duan, Ye; Karsch, Kevin; Miles, Judith

2010-01-01

103

Magnetic resonance findings of the corpus callosum in canine and feline lysosomal storage diseases.  

PubMed

Several reports have described magnetic resonance (MR) findings in canine and feline lysosomal storage diseases such as gangliosidoses and neuronal ceroid lipofuscinosis. Although most of those studies described the signal intensities of white matter in the cerebrum, findings of the corpus callosum were not described in detail. A retrospective study was conducted on MR findings of the corpus callosum as well as the rostral commissure and the fornix in 18 cases of canine and feline lysosomal storage diseases. This included 6 Shiba Inu dogs and 2 domestic shorthair cats with GM1 gangliosidosis; 2 domestic shorthair cats, 2 familial toy poodles, and a golden retriever with GM2 gangliosidosis; and 2 border collies and 3 chihuahuas with neuronal ceroid lipofuscinoses, to determine whether changes of the corpus callosum is an imaging indicator of those diseases. The corpus callosum and the rostral commissure were difficult to recognize in all cases of juvenile-onset gangliosidoses (GM1 gangliosidosis in Shiba Inu dogs and domestic shorthair cats and GM2 gangliosidosis in domestic shorthair cats) and GM2 gangliosidosis in toy poodles with late juvenile-onset. In contrast, the corpus callosum and the rostral commissure were confirmed in cases of GM2 gangliosidosis in a golden retriever and canine neuronal ceroid lipofuscinoses with late juvenile- to early adult-onset, but were extremely thin. Abnormal findings of the corpus callosum on midline sagittal images may be a useful imaging indicator for suspecting lysosomal storage diseases, especially hypoplasia (underdevelopment) of the corpus callosum in juvenile-onset gangliosidoses. PMID:24386203

Hasegawa, Daisuke; Tamura, Shinji; Nakamoto, Yuya; Matsuki, Naoaki; Takahashi, Kimimasa; Fujita, Michio; Uchida, Kazuyuki; Yamato, Osamu

2013-01-01

104

Structural changes of the corpus callosum in tinnitus  

PubMed Central

Objectives: In tinnitus, several brain regions seem to be structurally altered, including the medial partition of Heschl's gyrus (mHG), the site of the primary auditory cortex. The mHG is smaller in tinnitus patients than in healthy controls. The corpus callosum (CC) is the main interhemispheric commissure of the brain connecting the auditory areas of the left and the right hemisphere. Here, we investigate whether tinnitus status is associated with CC volume. Methods: The midsagittal cross-sectional area of the CC was examined in tinnitus patients and healthy controls in which an examination of the mHG had been carried out earlier. The CC was extracted and segmented into subregions which were defined according to the most common CC morphometry schemes introduced by Witelson (1989) and Hofer and Frahm (2006). Results: For both CC segmentation schemes, the CC posterior midbody was smaller in male patients than in male healthy controls and the isthmus, the anterior midbody, and the genou were larger in female patients than in female controls. With CC size normalized relative to mHG volume, the normalized CC splenium was larger in male patients than male controls and the normalized CC splenium, the isthmus and the genou were larger in female patients than female controls. Normalized CC segment size expresses callosal interconnectivity relative to auditory cortex volume. Conclusion: It may be argued that the predominant function of the CC is excitatory. The stronger callosal interconnectivity in tinnitus patients, compared to healthy controls, may facilitate the emergence and maintenance of a positive feedback loop between tinnitus generators located in the two hemispheres.

Diesch, Eugen; Schummer, Verena; Kramer, Martin; Rupp, Andre

2012-01-01

105

Shape analysis of the corpus callosum in Alzheimer's disease and frontotemporal lobar degeneration subtypes.  

PubMed

Morphology of the corpus callosum is a useful biomarker of neuronal loss, as different patterns of cortical atrophy help to distinguish between dementias such as Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD). We used a sophisticated morphometric analysis of the corpus callosum in FTLD subtypes including frontotemporal dementia (FTD), semantic dementia (SD), and progressive non-fluent aphasia (PNFA), and compared them to AD patients and 27 matched controls. FTLD patient subgroups diverged in their callosal morphology profiles, with FTD patients showing marked widespread differences, PNFA patients with differences largely in the anterior half of the callosum, and SD patients differences in a small segment of the genu. AD patients showed differences in predominantly posterior callosal regions. This study is consistent with our previous findings showing significant cortical and subcortical regional atrophy across FTLD subtypes, and suggests that callosal atrophy patterns differentiate AD from FTLD, and FTLD subtypes. PMID:24531157

Walterfang, Mark; Luders, Eileen; Looi, Jeffrey C L; Rajagopalan, Priya; Velakoulis, Dennis; Thompson, Paul M; Lindberg, Olof; Ostberg, Per; Nordin, Love E; Svensson, Leif; Wahlund, Lars-Olof

2014-01-01

106

Corpus callosum abnormalities in women with borderline personality disorder and comorbid attention-deficit hyperactivity disorder  

PubMed Central

Objective Decreased brain volumes in prefrontal, limbic and parietal areas have been found in women with borderline personality disorder (BPD). Recent models suggest impaired structural and functional connectivity in this condition. To investigate this, we studied the thickness of the corpus callosum, the largest connecting fibre bundle in the human brain. Methods We acquired magnetic resonance imaging scans from 20 healthy women and 20 women with BPD and comorbid attention-deficit hyperactivity disorder. A novel computational mesh-based method was applied to measure callosal thickness at high spatial resolution. Results Women with BPD had a thinner isthmus of the corpus callosum, compared with healthy women. In the patient group, a history of childhood sexual abuse was associated with a thinner posterior body of the corpus callosum. Conclusion Interhemispheric structural connectivity involving parietal and temporal areas may be impaired in women with BPD and comorbid attention-deficit hyperactivity disorder.

Rusch, Nicolas; Luders, Eileen; Lieb, Klaus; Zahn, Roland; Ebert, Dieter; Thompson, Paul M.; Toga, Arthur W.; van Elst, Ludger Tebartz

2007-01-01

107

An Analysis Method of the Fiber Tractography of Corpus Callosum in Autism Based on Diffusion Tensor Imaging Data  

Microsoft Academic Search

OBJECTIVE: A new method of segmentation and fiber tractography of corpus callosum in diffusion tensor imaging (DTI) is provided, and applied in the study of children with high functioning autism. METHOD: Diffusion tensor imaging data has been used to analyze the fiber tractography of corpus callosum, which has been manually extracted out and subdivided into five subregions in the scheme

Xiaoyan Ke; Shanshan Hong; Tianyu Tang; Haiqing Huang; Bing Zou; Huiguo Li; Yueyue Hang; Zuhong Lu

2008-01-01

108

Patterns of lesions of corpus callosum in inner cerebral trauma visualized by computed tomography.  

PubMed

Computed tomographic analysis of lesions of the corpus callosum in 13 patients with "inner cerebral trauma" showed significant congruence of linear translation of acceleration and the topographic distribution of such lesions. This congruence permits computed tomography to be used to reconstruct the course of linear translation and the site of the main blow, which can be important for forensic use. The findings of even a small lesion in the corpus callosum indicates the need for further investigation of other structures which are usually involved in inner cerebral trauma, such as the hippocampus and brain stem. PMID:1603310

Besenski, N; Jadro-Santel, D; Grcevi?, N

1992-01-01

109

Diffusion tensor imaging of normal white matter maturation from late childhood to young adulthood: Voxel-wise evaluation of mean diffusivity, fractional anisotropy, radial and axial diffusivities, and correlation with reading development  

Microsoft Academic Search

Using diffusion tensor MR imaging (DTI) and advanced voxel-wise analysis tools, we study diffusivity and anisotropy changes of white matter from late childhood to young adulthood, and correlate quantitative diffusion indices with Chinese and English reading performance scores. Seventy-five normal healthy school going ethnic Chinese students and young adults of three age groups were recruited (group 1, n=24, mean±SD=7.4±0.3 years; group

Deqiang Qiu; Li-Hai Tan; Ke Zhou; Pek-Lan Khong

2008-01-01

110

Dividing Fractions by Fractions  

NSDL National Science Digital Library

This site gives a description of how to divide fractions and gives a sample problem in which the denominator fraction is inverted, the numerators and denominators are multiplied, and the resulting fraction is simplified. It also includes the same problem solved by 'canceling' the fractions to simplify, and completing the process. There is also a game for students to practice their new skill of dividing and simplifying fractions.

Banfill, J. C.

2007-12-12

111

A Two-Year Longitudinal MRI Study of the Corpus Callosum in Autism  

ERIC Educational Resources Information Center

A growing body of literature has identified size reductions of the corpus callosum (CC) in autism. However, to our knowledge, no published studies have reported on the growth of CC volumes in youth with autism. Volumes of the total CC and its sub-divisions were obtained from 23 male children with autism and 23 age- and gender-matched controls at…

Frazier, Thomas W.; Keshavan, Matcheri S.; Minshew, Nancy J.; Hardan, Antonio Y.

2012-01-01

112

Diffusion tensor tractography quantification of the human corpus callosum fiber pathways across the lifespan  

Microsoft Academic Search

Several anatomical attributes of the human corpus callosum (CC) including the midsagittal cross-sectional area, thickness, and volume, have been used to assess CC integrity. We extended our previous lifespan quantitative diffusion tensor imaging (DTI) study of the regional CC midsagittal areas to include the CC volumes obtained from DTI fiber tracking. In addition to the entire CC tracked subvolumes we

Khader M. Hasan; Arash Kamali; Amal Iftikhar; Larry A. Kramer; Andrew C. Papanicolaou; Jack M. Fletcher; Linda Ewing-Cobbs

2009-01-01

113

Early-life stress, corpus callosum development, hippocampal volumetrics, and anxious behavior in male nonhuman primates  

Microsoft Academic Search

Male bonnet monkeys (Macaca radiata) were subjected to the variable foraging demand (VFD) early stress paradigm as infants, MRI scans were completed an average of 4years later, and behavioral assessments of anxiety and ex-vivo corpus callosum (CC) measurements were made when animals were fully matured. VFD rearing was associated with smaller CC size, CC measurements were found to correlate with

Andrea Jackowski; Tarique D. Perera; Chadi G. Abdallah; Griselda Garrido; Cheuk Y. Tang; Jose Martinez; Sanjay J. Mathew; Jack M. Gorman; Leonard A. Rosenblum; Eric L. P. Smith; Andrew J. Dwork; Dikoma C. Shungu; Arie Kaffman; Joel Gelernter; Jeremy D. Coplan; Joan Kaufman

2011-01-01

114

Quantitative Analysis of the Shape of the Corpus Callosum in Patients with Autism and Comparison Individuals  

ERIC Educational Resources Information Center

Multiple studies suggest that the corpus callosum in patients with autism is reduced in size. This study attempts to elucidate the nature of this morphometric abnormality by analyzing the shape of this structure in 17 high-functioning patients with autism and an equal number of comparison participants matched for age, sex, IQ, and handedness. The…

Casanova, Manuel F.; El-Baz, Ayman; Elnakib, Ahmed; Switala, Andrew E.; Williams, Emily L.; Williams, Diane L.; Minshew, Nancy J.; Conturo, Thomas E.

2011-01-01

115

Spatial attention in agenesis of the corpus callosum: shifting attention between visual fields.  

PubMed

The role of the corpus callosum in spatially selective visual attention is uncertain. Research using commissurotomy and callosotomy patients has attempted to determine if the corpus callosum plays a role in reorienting attention between visual fields, as if spatial attention is unitary or divisible between the cerebral hemispheres. Reorienting of selective visuospatial attention within versus between visual fields was tested in 10 individuals with agenesis of the corpus callosum (ACC) and nine matched controls. Spatially focused attention to the most likely location of target appearance was created using both peripheral sensory cues and central symbolic cues in separate tests. Results demonstrated that individuals with ACC have significantly greater difficulty reorienting attention to an invalidly cued target stimulus occurring in the opposite visual field. However, this effect did not interact with the type of cueing (sensory or symbolic). Individuals with ACC did not differ from controls either with respect to the laterality of within-field reorientation of attention, or with respect to the most efficient direction of between-field shifting of attention. Since congenital absence of the corpus callosum significantly reduces efficiency in the reorienting of attention between visual fields, spatial attention cannot be completely unified based on a subcortical mechanism and the mobilization of attentional resources within each hemisphere must depend on callosal processes. PMID:12062892

Hines, Robert J; Paul, Lynn K; Brown, Warren S

2002-01-01

116

[A case of autosomal dominant, pure form spastic paraplegia with thinning of the corpus callosum].  

PubMed

Autosomal dominant hereditary spastic paraplegia (HSP) is genetically classified into three types, all of which are characterized by insidiously progressive spasticity of the lower extremities. Patients with a complicated form of autosomal recessive HSP associated with hypoplasia of the corpus callosum have been reported by Iwabuchi et al. Here we report a 64-year-old patient with a pure form of autosomal dominant HSP with thinning of the corpus callosum. He had been well until 12 years of age, when spasticity and weakness of the lower extremities began to develop. His symptoms gradually worsened and he had difficulty in walking at the age of 44. When he was 56 years old, he visited our hospital. Eleven family members over five generations have been affected, and anticipation, i.e., an apparent decrease in age of onset, has been observed. On admission, he had mild cataracts, equinovarus and pes cavus, and neurological examination revealed spastic paraplegia. However, the intelligence test was normal, and nystagmus, ataxia of the extremities, involuntary movement, orthostatic hypotension or urinary disturbance was not observed. Trinucleotide repeat diseases, such as Huntington's disease, spinocerebellar ataxia type 1, spinocerebellar ataxia type 2, Machado-Joseph disease and dentatorubral-pallidoluysian atrophy, were excluded by DNA analysis. Brain MRI at the age of 64 revealed marked thinning of the corpus callosum. We considered this patient had a pure form of HSP. However, thinning of the corpus callosum has never been reported in autosomal dominant HSP. PMID:9805990

Tomiyasu, H; Hayashi, R; Watanabe, R; Honda, M; Yoshii, F

1998-05-01

117

MRI Findings of Coexistence of Ectopic Neurohypophysis, Corpus Callosum Dysgenesis, and Periventricular Neuronal Heterotopia  

PubMed Central

Ectopic neurohypophysis is a pituitary gland abnormality, which can accompany growth hormone deficiency associated with dwarfism. Here we present magnetic resonance imaging (MRI) findings of a rare case of ectopic neurohypophysis, corpus callosum dysgenesis, and periventricular neuronal heterotopia coexisting, with a review of the literature.

Arslan, Harun; Sayl?k, Metin; Akdeniz, Huseyin

2014-01-01

118

A magnetization transfer imaging study of corpus callosum myelination in young children with autism  

PubMed Central

Background Several lines of evidence suggest that autism may be associated with abnormalities in white matter development. However, inconsistencies remain in the literature regarding the nature and extent of these abnormalities, partly due to the limited types of measurements that have been used. Here, we used Magnetization Transfer Imaging (MTI) to provide insight into the myelination of the corpus callosum in children with autism. Methods MTI scans were obtained in 101 children with autism and 35 typically developing children who did not significantly differ with regard to gender or age. The midsagittal area of the corpus callosum was manually traced and the magnetization transfer ratio (MTR) was calculated for each voxel within the corpus callosum. Mean MTR and height and location of the MTR histogram peak were analyzed. Results Mean MTR and MTR histogram peak height and location were significantly higher in children with autism than typically developing children, suggesting abnormal myelination of the corpus callosum in autism. Conclusions The differences in callosal myelination suggested by these results may reflect an alteration in the normally well-regulated process of myelination of the brain, with broad implications for neuropathology, diagnosis, and treatment of autism.

Gozzi, Marta; Nielson, Dylan M.; Lenroot, Rhoshel K.; Ostuni, John L.; Luckenbaugh, David A.; Thurm, Audrey E.; Giedd, Jay N.; Swedo, Susan E.

2012-01-01

119

Moebius syndrome with Dandy-Walker variant and agenesis of corpus callosum.  

PubMed

Moebius syndrome is a rare congenital neurological disorder. The most frequent mode of presentation is facial diplegia with bilateral lateral rectus palsy, but there are variations. Here, we report a rare case of Moebius syndrome in a 15-month-old child with unilateral facial palsy, bilateral abducens nerve palsy with Dandy Walker variant, and complete agenesis of corpus callosum. PMID:24470815

John, Jomol Sara; Vanitha, R

2013-09-01

120

A 23-Year Review of Communication Development in an Individual with Agenesis of the Corpus Callosum.  

ERIC Educational Resources Information Center

Twenty-three years of observation and testing of the communication skills of a male with agenesis of the corpus callosum and normal IQ revealed initial weakness in language. Difficulties with fluent speech persisted into young adulthood. With intensive intervention, communication and academic skills developed and the participant completed high…

Stickles, Judith L.; Schilmoeller, Gary L.; Schilmoeller, Kathryn J.

2002-01-01

121

Effects of prenatal irradiation on the development of cerebral cortex and corpus callosum of the mouse  

Microsoft Academic Search

Defects of the cerebral cortex and corpus callosum of mice subjected prenatally to gamma irradiation were evaluated as a function of dose and of embryonic age at irradiation. Pregnant mice were exposed to a gamma source at 16, 17, and 19 days of gestation (E16, E17, and E19, respectively), with total doses of 2 Gy and 3 Gy, in order

Sergio L. Schmidt; Roberto Lent

1987-01-01

122

Contribution of alcoholism to brain dysmorphology in HIV infection: Effects on the ventricles and corpus callosum  

Microsoft Academic Search

Nonrigid registration and atlas-based parcellation methods were used to compare the volume of the ventricular system and the cross-sectional area of the midsagittal corpus callosum on brain MRIs from 272 subjects in four groups: patients with HIV infection, with and without alcoholism comorbidity, alcoholics, and controls. Prior to testing group differences in regional brain metrics, each measure was corrected by

Adolf Pfefferbaum; Margaret J. Rosenbloom; Torsten Rohlfing; Elfar Adalsteinsson; Carol A. Kemper; Edith V. Sullivan

2006-01-01

123

Distribution of traumatic lesions of corpus callosum in "inner cerebral trauma".  

PubMed

This study deals with the topographic distribution of traumatic lesions in the corpus callosum within the pattern of "inner cerebral trauma". Material for neuropathological investigations consisted of 49 brains of patients who suffered closed head injury of the acceleration type with linear translation of acceleration acting along the longer axis of the head. As a control, 5 brains were investigated in which the direction of linear translation was latero-lateral. The patients were divided into 4 groups according to reconstruction of the traumatic event and ascertaining of the direction of the linear translation of acceleration: (1) Medial blow (antero-posterior and postero-anterior), (2) Semioblique left blow (frontal left-occipital right and occipital right-frontal left), (3) Semioblique right blow (frontal right-occipital left and occipital left-frontal right), (4) Vertex-base direction. Fornix and septum pellucidum, as anatomically adjacent structures were also investigated. The results showed that the lesions in the corpus callosum were related to the pattern of "inner cerebral trauma" (ICT) (Grcevi? 1982), and the biomechanical conditions originally proposed by Lindenberg. These investigations, carried out on a representative material of 54 brains and by subserial histological analysis of the entire corpus callosum, produced a new evidence for our previous preliminary observations about the correlation of the shape and distribution of the periaxial lesions of the pattern of "inner cerebral trauma" and direction of the linear translation of accelerating forces. Our present investigations showed a striking congruence between the pattern of lesions within the corpus callosum in such type of cerebral trauma and the course of linear translation of acceleration. Furthermore, this study proved the importance of topographic interpretation of lesions in the corpus callosum in vivo i.e. by the CT and MRI examinations, because they may serve as a significant information for reconstruction of the biomechanical conditions of the injury which can be of importance for early therapeutical strategy and forensic interpretations of the accident. By using silver impregnation-techniques for histopathological study of the corpus callosum, we could confirm our previously expressed concept on "focalized" and not "diffuse" axonal injures in ICT (Grcevi? 1988). In this study corpus callosum served as a representative anatomical structure for axonal studies showing that axonal lesions strictly follow the pattern of tissue lesions with definite focal principle. PMID:1932439

Zarkovi?, K; Jadro-Santel, D; Grcevi?, N

1991-01-01

124

Magnetic multilayer interface anisotropy  

SciTech Connect

Ni/Mo and Ni/V multilayer magnetic anisotropy has been investigated as a function of Ni layer thickness, frequency and temperature. Variable frequency ferromagnetic resonance (FMR) measurements show, for the first time, significant frequency dependence associated with the multilayer magnetic anisotropy. The thickness dependence allows one to extract the interface contribution from the total anisotropy. Temperature dependent FMR (9 GHz) and room temperature magnetization indicate that strain between Ni and the non-magnetic layers is contributing significantly to the source of the interface anisotropy and the state of the interfacial magnetization. In order to examine the interface properties of other transition metal multilayer systems, investigations on Fe/Cu are underway and CoCr/Ag is being proposed. ESR measurements have been reported on Gd substituted YBaCuO superconductors and a novel quasi-equilibrium method has been developed to determine quickly and precisely the ransition temperature.

Pechan, M.J.

1992-01-01

125

Magnetic multilayer interface anisotropy  

SciTech Connect

Ni/Mo and Ni/V multilayer magnetic anisotropy has been investigated as a function of Ni layer thickness, frequency and temperature. Variable frequency ferromagnetic resonance (FMR) measurements show, for the first time, significant frequency dependence associated with the multilayer magnetic anisotropy. The thickness dependence allows one to extract the interface contribution from the total anisotropy. Temperature dependant FMR (9 GHz) and room temperature magnetization indicate that strain between Ni and the non-magnetic layers if contributing significantly to the source of the interface anisotropy and the state of the interfacial magnetization. In order to examine the interface properties of other transition metal multilayer systems, investigations on Fe/Cu are underway and CoCr/Ag is being proposed. ESR measurements have been reported on Gd substituted YBaCuO superconductors and a novel quasi-equilibrium method has been developed to determine quickly and precisely the transition temperature. During the next project the P.I. proposes to (1) extend the variable frequency FMR measurements to low temperature, where extremely large interface anisotropies are known to obtain in Ni/Mo and Ni/V and are proposed to exist in Ni/W; (2) obtain accurate dc anisotropies via a novel, variable temperature torque magnetometer currently under construction; (3) expand upon his initial findings in Fe/Cu multilayer investigations; (4) begin anisotropy investigations on Co/Ag and CoCr/Ag multilayers where the easy magnetization direction depends upon the Cr concentration; (4) make and characterize Bi based superconductors according to resistivity, thermal conductivity and thermoelectric power and construct YBaCuO based superconducting loop-gap'' resonators for use in his magnetic resonance work. 2 figs.

Pechan, M.J.

1991-01-01

126

Cerebral metabolic and structural alterations in hereditary spastic paraplegia with thin corpus callosum assessed by MRS and DTI  

Microsoft Academic Search

Introduction  Hereditary spastic paraplegia with thin corpus callosum (HSP-TCC) is a complicated form of autosomal-recessive hereditary spastic paraplegia. Characteristic clinical features comprise progressive spastic gait, cognitive impairment, and ataxia. Diagnostic MRI findings include thinning of the corpus callosum and non-progressive white matter (WM) alterations.Methods  To study the extent of axonal involvement, we performed localized proton magnetic resonance spectroscopy (MRS) of the cerebral

Steffi Dreha-Kulaczewski; Peter Dechent; Gunther Helms; Jens Frahm; Jutta Gärtner; Knut Brockmann

2006-01-01

127

Corpus Callosum Size Is Highly Heritable in Humans, and May Reflect Distinct Genetic Influences on Ventral and Rostral Regions  

PubMed Central

Anatomical differences in the corpus callosum have been found in various psychiatric disorders, but data on the genetic contributions to these differences have been limited. The current study used morphometric MRI data to assess the heritability of corpus callosum size and the genetic correlations among anatomical sub-regions of the corpus callosum among individuals with and without mood disorders. The corpus callosum (CC) was manually segmented at the mid-sagittal plane in 42 women (healthy, n?=?14; major depressive disorder, n?=?15; bipolar disorder, n?=?13) and their 86 child or adolescent offspring. Four anatomical sub-regions (CC-genu, CC2, CC3 and CC-splenium) and total CC were measured and analyzed. Heritability and genetic correlations were estimated using a variance components method, with adjustment for age, sex, diagnosis, and diagnosis x age, where appropriate. Significant heritability was found for several CC sub-regions (P<0.01), with estimated values ranging from 48% (splenium) to 67% (total CC). There were strong and significant genetic correlations among most sub regions. Correlations between the genu and mid-body, between the genu and total corpus callosum, and between anterior and mid body were all >90%, but no significant genetic correlations were detected between ventral and rostral regions in this sample. Genetic factors play an important role in corpus callosum size among individuals. Distinct genetic factors seem to be involved in caudal and rostral regions, consistent with the divergent functional specialization of these brain areas.

Woldehawariat, Girma; Martinez, Pedro E.; Hauser, Peter; Hoover, David M.; Drevets, Wayne W. C.; McMahon, Francis J.

2014-01-01

128

Fraction Basics  

NSDL National Science Digital Library

This iOS app contains 12 computer animated videos on understanding fractions, improper fractions & mixed fractions, equivalent fractions, adding fractions, adding fractions examples, subtracting fractions, multiplying fractions. Each video presents important vocabulary and concepts, there is a table of contents, and an option to skip to later lessons.

Chong, Ng W.

2012-11-24

129

Fun Fractions  

NSDL National Science Digital Library

Fractions mean that we are breaking up one thing into smaller things! See how you can do! Let's see How Fractions Work!! Let's make a flag using Flag Fractions. Let's try some more fractions with Fraction Blocks!! ...

Terch, Ms.

2010-03-11

130

CT appearances of haematomas in the corpus callosum in patients with subarachnoid haemorrhage  

Microsoft Academic Search

Corpus callosum heamatoma is a rare feature in subarachnoid haemorrhage (SAH), which may result from aneurysms of the anterior communicating artery (ACoA) or pericallosal artery (PCA). In 348 patients with aneurysmal SAH, bleeding from ACoA aneurysms in 88 cases produced no abnormality on CT in 7. Blood in the cistern of the lamina terminalis was the most frequent abnormality (76\\/88);

A. Jackson; J. B. Fitzgerald; R. W. J. Hartley; A. Leonard; J. Yates

1993-01-01

131

Corpus Callosum Subdivision Based on a Probabilistic Model of Inter-hemispheric Connectivity  

Microsoft Academic Search

\\u000a Statistical shape analysis has become of increasing interest to the neuroimaging community due to its potential to locate\\u000a morphological changes. In this paper, we present the a novel combination of shape analysis and Diffusion Tensor Image (DTI)\\u000a Tractography to the computation of a probabilistic, model based corpus callosum (CC) subdivision. The probabilistic subdivision\\u000a is based on the distances of arc-length

Martin Andreas Styner; Ipek Oguz; Rachel Gimpel Smith; Carissa Cascio; Matthieu Jomier

2005-01-01

132

Local–global interference is modulated by age, sex and anterior corpus callosum size  

Microsoft Academic Search

To identify attentional and neural mechanisms affecting global and local feature extraction, we devised a global–local hierarchical letter paradigm to test the hypothesis that aging reduces functional cerebral lateralization through corpus callosum (CC) degradation. Participants (37 men and women, 26–79 years) performed a task requiring global, local, or global+local attention and underwent structural MRI for CC measurement. Although reaction time

Eva M. Müller-Oehring; Tilman Schulte; Carla Raassi; Adolf Pfefferbaum; Edith V. Sullivan

2007-01-01

133

Relationship between intelligence and the size and composition of the corpus callosum  

Microsoft Academic Search

We investigated the relationship between the morphology of the corpus callosum (CC) and IQ in a healthy sample of individuals\\u000a in their late teens and early twenties. The relationship between the area of the CC, measured at the midline, and IQ showed\\u000a regional differences. We observed that a higher estimated performance IQ was associated with smaller area in the posterior

Amanda D. Hutchinson; J. L. Mathias; B. L. Jacobson; L. Ruzic; A. N. Bond; Marie T. Banich

2009-01-01

134

Genetic epidemiology of sensorimotor polyneuropathy with or without agenesis of the corpus callosum in northeastern Quebec  

Microsoft Academic Search

Sensorimotor polyneuropathy with or without agenesis of the corpus callosum (McKusick number 218000) is a disorder that has a high frequency in Saguenay-Lac-St-Jean (SLSJ), a geographically isolated region of northeastern Quebec. The incidence at birth and the carrier rate were estimated, respectively, at 1\\/2117 liveborns and 1\\/23 inhabitants. Remote consanguinity was found in several polyneuropathic families while the mean kinship

M. De Braekeleer; A. Dallaire; J. Mathieu

1993-01-01

135

Lipoma of corpus callosum associated with dysraphic lesions and trisomy 13  

SciTech Connect

We report on a further case of corpus callosal lipoma and frontal cranial defects. Most cases in the literature of corpus callosal lipoma in association with {open_quotes}dysraphic{close_quotes} lesions have been frontal in location. Malformation of the corpus callosum is said to be associated with 50% of these lipomas. Trisomy 13 was confirmed by the 13q14 cosmid probe on paraffin-embedded liver tissue. 19 refs., 5 figs.

Wainwright, H.; Bowen, R.; Radcliffe, M. [Univ. of Cape Town Medical School (South Africa)

1995-05-22

136

Agenesis of the corpus callosum: genetic, developmental and functional aspects of connectivity  

Microsoft Academic Search

Agenesis of the corpus callosum (AgCC), a failure to develop the large bundle of fibres that connect the cerebral hemispheres, occurs in 1:4000 individuals. Genetics, animal models and detailed structural neuroimaging are now providing insights into the developmental and molecular bases of AgCC. Studies using neuropsychological, electroencephalogram and functional MRI approaches are examining the resulting impairments in emotional and social

Warren S. Brown; Ralph Adolphs; J. Michael Tyszka; Linda J. Richards; Pratik Mukherjee; Lynn K. Paul; Elliott H. Sherr

2007-01-01

137

Regional heterogeneity of cuprizone-induced demyelination: topographical aspects of the midline of the corpus callosum.  

PubMed

The cuprizone model is a suitable animal model of de- and remyelination secondary to toxin-induced oligodendrogliopathy. From a pharmaceutical point of view, the cuprizone model is a valuable tool to study the potency of compounds which interfere with toxin-induced oligodendrocyte cell death or boost/inhibit remyelinating pathways and processes. The aim of this study was to analyze the vulnerability of neighboring white mater tracts (i.e., the fornix and cingulum) next to the midline of the corpus callosum which is the region of interest of most studies using this model. Male mice were fed cuprizone for various time periods. Different white matter areas were analyzed for myelin (anti-PLP), microglia (anti-IBA1), and astrocyte (anti-GFAP) responses by means of immunohistochemistry. Furthermore, Luxol fast blue-periodic acid Schiff stains were performed to validate loss of myelin-reactive fibers in the different regions. Cuprizone induced profound demyelination of the midline of the corpus callosum and medial parts of the cingulum that was paralleled by a significant astrocyte and microglia response. In contrast, lateral parts of the corpus callosum and the cingulum, as well as the fornix region which is just beneath the midline of the corpus callosum appeared to be resistant to cuprizone exposure. Furthermore, resistant areas displayed reduced astrogliosis and microgliosis. This study clearly demonstrates that neighboring white matter tracts display distinct vulnerability to toxin-induced demyelination. This important finding has direct relevance for evaluation strategies in this frequently used animal model for multiple sclerosis. PMID:23054589

Schmidt, T; Awad, H; Slowik, A; Beyer, C; Kipp, M; Clarner, T

2013-01-01

138

Probing dark energy anisotropy  

NASA Astrophysics Data System (ADS)

Wide area cosmological surveys enable investigation of whether dark energy properties are the same in different directions on the sky. Cosmic microwave background observations strongly restrict any dynamical effects from anisotropy, in an integrated sense. For more local constraints we compute limits from simulated distance measurements for various distributions of survey fields in a Bianchi I anisotropic universe. We then consider the effects of fitting for line of sight properties where isotropic dynamics is assumed (testing the accuracy through simulations) and compare sensitivities of observational probes for anisotropies, from astrophysical systematics as well as dark energy. We also point out some interesting features of anisotropic expansion in Bianchi I cosmology.

Appleby, Stephen A.; Linder, Eric V.

2013-01-01

139

Anisotropy in magnetoelectric composites  

NASA Astrophysics Data System (ADS)

Anisotropy of piezoelectric and magnetostrictive materials is considered in order to determine the ideal directions and orientation relationships for which the maximum magnetoelectric response may be observed in a composite or heterostructure of these constituent materials. A formalism for the magnetoelectric effect is introduced that takes into account the independent anisotropy of the piezoelectric and magnetostrictive phases and their relative orientation. A maximum magnetoelectric effect is achieved in orientations that have not yet been achieved experimentally, suggesting a need for the development of new routes to synthesize and fabricate designed composite materials with enhanced magnetoelectric response.

Jones, Jacob L.; Starr, Justin D.; Andrew, Jennifer S.

2014-06-01

140

Regionally specific atrophy of the corpus callosum in AD, MCI and cognitive complaints  

PubMed Central

The goal of the present study was to determine if there are global or regionally specific decreases in callosal area in early Alzheimer’s disease (AD) and mild cognitive impairment (MCI). In addition, this study examined the corpus callosum of healthy older adults who have subjective cognitive complaints (CC) but perform within normal limits on neuropsychological tests. We used a semi-automated procedure to examine the total and regional areas of the corpus callosum in 22 patients with early AD, 28 patients with amnestic MCI, 28 healthy older adults with cognitive complaints, and 50 demographically matched healthy controls (HC). The AD, MCI, and CC groups all showed a significant reduction of the posterior region (isthmus and splenium) relative to healthy controls. The AD group also had a significantly smaller overall callosum than the controls. The demonstration of callosal atrophy in older adults with cognitive complaints suggests that callosal changes occur very early in the dementing process, and that these earliest changes may be too subtle for detection by neuropsychological assessments, including memory tests.

Wang, Paul J.; Saykin, Andrew J.; Flashman, Laura A.; Wishart, Heather A.; Rabin, Laura A.; Santulli, Robert B.; McHugh, Tara L.; MacDonald, John W.; Mamourian, Alexander C.

2012-01-01

141

Growth of the Human Corpus Callosum: Modular and Laminar Morphogenetic Zones  

PubMed Central

The purpose of this focused review is to present and discuss recent data on the changing organization of cerebral midline structures that support the growth and development of the largest commissure in humans, the corpus callosum. We will put an emphasis on the callosal growth during the period between 20 and 45 postconceptual weeks (PCW) and focus on the advantages of a correlated histological/magnetic resonance imaging (MRI) approach. The midline structures that mediate development of the corpus callosum in rodents, also mediate its early growth in humans. However, later phases of callosal growth in humans show additional medial transient structures: grooves made up of callosal septa and the subcallosal zone. These modular (septa) and laminar (subcallosal zone) structures enable the growth of axons along the ventral callosal tier after 18?PCW, during the rapid increase in size of the callosal midsagittal cross-section area. Glial fibrillary acidic protein positive cells, neurons, guidance molecule semaphorin3A in cells and extracellular matrix (ECM), and chondroitin sulfate proteoglycan in the ECM have been identified along the ventral callosal tier in the protruding septa and subcallosal zone. Postmortem MRI at 3?T can demonstrate transient structures based on higher water content in ECM, and give us the possibility to follow the growth of the corpus callosum in vivo, due to the characteristic MR signal. Knowledge about structural properties of midline morphogenetic structures may facilitate analysis of the development of interhemispheric connections in the normal and abnormal fetal human brain.

Jovanov-Milosevic, Natasa; Culjat, Marko; Kostovic, Ivica

2009-01-01

142

Antenatal diagnosis and outcome of agenesis of corpus callosum: A retrospective review of 33 cases  

PubMed Central

Objective To present antenatal sonographic findings and postnatal outcome of a population of foetuses diagnosed with agenesis of corpus callosum. Material and Methods The database of our ultrasound laboratory was retrospectively searched for cases of agenesis of the corpus callosum suspected at antenatal sonography between 2002 and 2012. The following variables were assessed: maternal age, gestational age at diagnosis, gender, any additional cerebral and extra-cerebral malformations, results of karyotype analysis and pregnancy and foetal/neonatal outcomes. Results During the study period, 33 foetuses with agenesis of the corpus callosum were identified antenatally, with a male preponderance. The mean maternal age was 28.48 years. In all cases, pre/postnatal MRI and/or necropsy were performed in order to confirm the diagnosis. Among those, there were additional brain findings in 23 (69.7%) and additional extra-cerebral anomalies in 3 (9.1%) foetuses. Karyotype analysis was performed in 21 of 33 (63.6%) cases. As for pregnancy outcome, the pregnancy was terminated in 14 (42.4%) of the remaining 19 foetuses; eighteen (54.5%) were delivered near term and one (3.1%) who was delivered prematurely died during the neonatal period. Conclusion The diagnosis of congenital brain malformation is a challenging issue, since additional findings have a considerable effect on prognosis; detailed examination with genetic counselling should be performed.

Ozyuncu, Ozgur; Yaz?c?oglu, Asl?han; Turgal, Mert

2014-01-01

143

Processing Speed Delays Contribute to Executive Function Deficits in Individuals with Agenesis of the Corpus Callosum  

PubMed Central

Corpus callosum malformation and dysfunction are increasingly recognized causes of cognitive and behavioral disability. Individuals with agenesis of the corpus callosum (AgCC) offer unique insights regarding the cognitive skills that depend specifically upon callosal connectivity. We examined the impact of AgCC on cognitive inhibition, flexibility, and processing speed using the Color-Word Interference Test (CWIT) and Trail Making Test (TMT) from the Delis-Kaplan Executive Function System. We compared 36 individuals with AgCC and IQs within the normal range to 56 matched controls. The AgCC cohort was impaired on timed measures of inhibition and flexibility; however, group differences on CWIT Inhibition, CWIT Inhibition/Switching and TMT Number-Letter Switching appear to be largely explained by slow performance in basic operations such as color naming and letter sequencing. On CWIT Inhibition/Switching, the AgCC group was found to commit significantly more errors which suggests that slow performance is not secondary to a cautious strategy. Therefore, while individuals with agenesis of the corpus callosum show real deficits on tasks of executive function, this impairment appears to be primarily a consequence of slow cognitive processing. Additional studies are needed to investigate the impact of AgCC on other aspects of higher order cortical function.

Marco, Elysa J.; Harrell, Kathryn M.; Brown, Warren S.; Hill, Susanna S.; Jeremy, Rita J.; Kramer, Joel H.; Sherr, Elliott H.; Paul, Lynn K.

2013-01-01

144

Clinical, genetic and imaging findings identify new causes for corpus callosum development syndromes.  

PubMed

The corpus callosum is the largest fibre tract in the brain, connecting the two cerebral hemispheres, and thereby facilitating the integration of motor and sensory information from the two sides of the body as well as influencing higher cognition associated with executive function, social interaction and language. Agenesis of the corpus callosum is a common brain malformation that can occur either in isolation or in association with congenital syndromes. Understanding the causes of this condition will help improve our knowledge of the critical brain developmental mechanisms required for wiring the brain and provide potential avenues for therapies for callosal agenesis or related neurodevelopmental disorders. Improved genetic studies combined with mouse models and neuroimaging have rapidly expanded the diverse collection of copy number variations and single gene mutations associated with callosal agenesis. At the same time, advances in our understanding of the developmental mechanisms involved in corpus callosum formation have provided insights into the possible causes of these disorders. This review provides the first comprehensive classification of the clinical and genetic features of syndromes associated with callosal agenesis, and provides a genetic and developmental framework for the interpretation of future research that will guide the next advances in the field. PMID:24477430

Edwards, Timothy J; Sherr, Elliott H; Barkovich, A James; Richards, Linda J

2014-06-01

145

Anisotropy across Superplume Boundaries  

NASA Astrophysics Data System (ADS)

Sdiff data sets are presented for paths that run parallel to the African and the Pacific superplume boundaries. Objective clustering of waveforms illustrates sharp changes across these boundaries. The African plume shows a sharp offset in travel times in the SHdiff phase, while a more gradual offset towards slower arrivals is seen in the case of the Pacific superplume. Additionally, Pdiff phases display no offset around the African plume and a weak one around the Pacific plume. Here we focus mainly on another striking feature observed in both cases: outside of the superplume the Sdiff particle motion is strongly elliptical, but becomes linear within the superplume (first noticed by To et al. 2005 in the African superplume case). For the African plume we argue that these observations of delayed SV at large distances (~120 degrees) are indicative of the occurrence of azimuthal anisotropy. The SV arrivals have similar polarity as SH, opposite from what their radiation pattern predicts. Azimuthal anisotropy causes SH energy to be converted to SV (Maupin, 1994), explaining the travel time, polarity and amplitude. Forward modeling through different isotropic and anisotropic models supports this statement, although there are trade-offs between direction and magnitude of azimuthal anisotropy. The strong elliptical particle motions are also observed outside the Pacific plume, but at shorter distances (95-105 degrees). Elliptical motions can occur in the absence of anisotropy when strong velocity deviations or layering occurs close to the CMB, which, based on velocity profiles with depth in global tomographic models would be more likely within the superplume rather than on the fast side. The elliptical particle motions here can be modelled with a simple transverse isotropic model with VSH>VSV, but azimuthal anisotropy cannot be ruled out. The complexities within the Pacific superplume, including strong amplitude drop and existence of a post-cursor, are likely caused by an ultra low velocity zone (Cottaar and Romanowicz, this meeting) and make it difficult to constrain anisotropy within the Pacific superplume. Notably, however, in both cases, elliptical particle motions become more linear, and thus anisotropy decreases, from the fast side towards the slow side across superplume boundaries. Possibly this is caused by a rotation in the deformational regime, causing rotation of the pre-existing anisotropic fast directions. Forward modeling of deformation using tracers in mantle convection models, considering different mineral physics scenarios (Wenk et al., 2011) suggest that the boundaries in anisotropy from downwellings to upwellings can be sharp, and could possibly contribute to explaining the sharp boundary in VSH, in addition to effects of lateral variations in temperature and composition. Moreover the model for post-perovskite with (001)-slip predicts anti-correlation between S and P wave anisotropy. Variation in VPH due to anisotropy would then be anti-correlated with the variation caused by temperature, and this could explain the lack of correlation in the variations of VSH and VPH across the superplume boundary. Our modeling shows that care must be taken when computing R=dlnVs/dlnVp in the presence of anisotropy.

Cottaar, S.; Romanowicz, B. A.

2011-12-01

146

Elastic energy anisotropy effects on antiphase boundaries  

SciTech Connect

The effect of elastic energy on the anisotropy of antiphase boundary (APB) interfacial energy has been studied theoretically. The model used, a generalization of one developed by Kikuchi and Cahn, treats composition and atomic ordering as local variables defined one each of the atomic planes parallel to the APB. The equilibrium APB structure is found as the set of planar variables that minimizes the free energy. A strain energy term involving an orientation-dependent stiffness parameter and a phenomenological law giving lattice constant as a function of local composition and order parameter is included in the definition of the free energy. Elastic effects in APBs in B2 ordered Fe-Al alloys with 0.2--0.3 atomic fraction Al were investigated. It was found that, despite the high elastic anisotropy of Fe-Al alloys, elastic effects would not result in any substantial anisotropy in APB interfacial energy. This is because in Fe-Al alloys the variation in lattice constant due to order parameter variation at the APB is almost completely canceled out by the variation in lattice constant due to compositional variation. In a hypothetical model with physically reasonable parameter, APB energies were found to vary by up to 9% with orientation, purely as a result of elastic effects. It was concluded that elastically induced APB anisotropy would be observable in alloys such as Fe-Si in which lattice constant variations due to order parameter variation are cooperative with those due to compositional variation.

Van Der Heide, R.G.; Allen, S.M. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Materials Science and Engineering] [Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Materials Science and Engineering

1996-04-01

147

Magnetic Anisotropy and Paleomagnetism  

Microsoft Academic Search

The natural remanent magnetization of certain Welsh slates lies in the cleavage plane, which was found to be a plane of high susceptibility defined by the alignment of aniso- tropic crystals of pyrrhotite. A correlation between the magnitude of susceptibility anisotropy and the bulk susceptibility of the slates has been observed. This is interpreted as a partial masking of the

M. D. Fuller

1963-01-01

148

Shear wave anisotropy imaging  

Microsoft Academic Search

Shear wave anisotropy imaging (SWAI) is a novel method that images local variations in tissue shear wave velocity. A commercial ultrasound scanner is used to generate and track propagating shear waves. Radiation force from a brief high-energy pulse generates the shear waves. The pulse and resultant shear waves are steered in order to launch the waves at oblique angles. The

Stephen J. Hsu; Mark L. Palermi; Kathryn R. Nightingale; Stephen A. McAleavey; Jeremy D. Dahl; Gregg E. Trahey

2003-01-01

149

Shear wave anisotropy imaging  

Microsoft Academic Search

Shear wave anisotropy imaging is a novel method that images local variations in tissue shear wave velocity. A commercial ultrasound scanner is used to generate and track propagating shear waves. Radiation force from a brief high-energy pulse generates shear waves. The pulses are steered in order to launch the waves at oblique angles. The Helmholtz equation is used to extract

Stephen J. Hsu; Mark L. Palermi; Kathryn R. Nightingale; Stephen A. McAleavey; Jeremy D. Dahl; Gregg E. Trahey

2003-01-01

150

Atrophy of the corpus callosum associated with a decrease in cortical benzodiazepine receptor in large cerebral arterial occlusive diseases  

PubMed Central

OBJECTIVES—It remains controversial whether selective neuronal ischaemic change develops in patients with occlusion of the large cerebral arteries. Previous studies have shown atrophy of the corpus callosum with reduced cortical oxygen metabolism in large cerebral arterial occlusive diseases, which might be indirect evidence of loss of the neurons in cortical layer 3. Recent studies of patients with ischaemic cerebrovascular diseases have demonstrated reduced central benzodiazepine receptor (BZR) binding in the normal appearing cortical areas, which might be more direct evidence of changes of the neurons. Although pathophysiology of the decreased BZR is unclear, a decrease in the cortical BZR binding with neuronal loss would cause atrophy of the corpus callosum. The purpose of this study was to determine whether atrophy of the corpus callosum is associated with a decrease in cortical BZR binding in large cerebral arterial occlusive diseases.?METHODS—Seven patients with occlusive diseases of the middle cerebral or internal carotid artery and only minor subcortical infarctions were studied. Single photon emission tomographic images of 123I labelled iomazenil (IMZ) obtained 180 minutes after injection were analysed for BZR binding. The midsagittal corpus callosum area/skull area ratio (on T1 weighted magnetic resonance images) was compared with the cerebral IMZ uptake/cerebellar IMZ uptake ratio.?RESULTS—Compared with 23 age and sex matched control subjects, the patients had significantly decreased callosal area/skull area ratio. The degree of corpus callosum atrophy was significantly and strongly (?=0.99, p<0.02) correlated with that of the decreases in the mean cerebral cortical IMZ uptake ratio.?CONCLUSION—Corpus callosum atrophy may occur in association with a decrease in cortical BZR binding in large cerebral arterial occlusive diseases. Corpus callosum atrophy with decreased cortical BZR binding might reflect cortical neuronal damage in large cerebral arterial occlusive diseases.??

Yamauchi, H; Fukuyama, H; Dong, Y; Nabatame, H; Nagahama, Y; Nishizawa, S; Konishi, J; Shio, H

2000-01-01

151

Interface anisotropy: Simple fitting model  

NASA Astrophysics Data System (ADS)

In studying interface anisotropy, it is common to use a simple model in which the magnetization is assumed uniform (coherent). There are then only two parameters, the bulk anisotropy energy Kbulk and the surface anisotropy energy ?, which can be extracted from the thickness-dependence of the effective anisotropy. This procedure depends on assuming the magnetization is coherent—we show here that incoherence will bias the extracted anisotropy and suggest a method for decreasing this bias. We also suggest an alternative model (also with only two parameters) which includes incoherence effects and may be closer to real systems.

Visscher, P. B.

2014-05-01

152

Fraction Fun  

NSDL National Science Digital Library

In this lesson you will learn about equivalent fractions, how to add fractions, and factoring Learn how to create equivalent fractions Equivalent Fractions In this game you will practice using smaller pieces or fractions to fill the larger circle Equivalent Fractions Practice adding fractions with unlike denominators. Adding Fractions Identify the Least Common Multiple and Greatest Common Factor LCM and GCF Plug in a number and find the Least Common Multiple or Greatest Common ...

Evans, Miss

2007-10-03

153

Texture and anisotropy  

NASA Astrophysics Data System (ADS)

A large number of polycrystalline materials, both manmade and natural, display preferred orientation of crystallites. Such alignment has a profound effect on anisotropy of physical properties. Preferred orientation or texture forms during growth or deformation and is modified during recrystallization or phase transformations and theories exist to predict its origin. Different methods are applied to characterize orientation patterns and determine the orientation distribution, most of them relying on diffraction. Conventionally x-ray pole-figure goniometers are used. More recently single orientation measurements are performed with electron microscopes, both SEM and TEM. For special applications, particularly texture analysis at non-ambient conditions, neutron diffraction and synchrotron x-rays have distinct advantages. The review emphasizes such new possibilities. A second section surveys important texture types in a variety of materials with emphasis on technologically important systems and in rocks that contribute to anisotropy in the earth. In the former group are metals, structural ceramics and thin films. Seismic anisotropy is present in the crust (mainly due to phyllosilicate alignment), the upper mantle (olivine), the lower mantle (perovskite and magnesiowuestite) and the inner core (egr-iron) and due to alignment by plastic deformation. There is new interest in the texturing of biological materials such as bones and shells. Preferred orientation is not restricted to inorganic substances but is also present in polymers that are not discussed in this review.

Wenk, H.-R.; Van Houtte, P.

2004-08-01

154

Effects of prenatal irradiation on the development of cerebral cortex and corpus callosum of the mouse  

SciTech Connect

Defects of the cerebral cortex and corpus callosum of mice subjected prenatally to gamma irradiation were evaluated as a function of dose and of embryonic age at irradiation. Pregnant mice were exposed to a gamma source at 16, 17, and 19 days of gestation (E16, E17, and E19, respectively), with total doses of 2 Gy and 3 Gy, in order to produce brain defects on their progeny. At 60 postnatal days, the brains of the offspring were analyzed qualitatively and quantitatively and compared with those of nonirradiated animals. Mice irradiated at E16 were all acallosal. Those that were exposed to 2 Gy displayed an aberrant longitudinal bundle typical of other acallosals, but this was not the case in those irradiated with 3 Gy. The corpus callosum of animals irradiated at E17 with 3 Gy was pronouncedly hypotrophic, but milder effects were observed in the other groups. Quantitative analysis confirmed a dependence of callosal midsagittal area upon dose and age at irradiation, and, in addition, indicated an interaction between these variables. The neocortex of irradiated animals was hypotrophic: layers II-III were much more affected than layer V, and this was more affected than layer VI. Quantitative analysis indicated that this effect also depended on dose and age at irradiation and that it was due to a loss of cortical neurons. Furthermore, a positive correlation was found between the number of neurons within layers II-III, and V and the midsagittal area of the corpus callosum. Ectopic neurons were found in the white matter and in layer I of animals irradiated at E16 and E17, indicating that fetal exposure to ionizing radiation interfered with the migration of cortical neuroblasts.

Schmidt, S.L.; Lent, R.

1987-10-08

155

Microglia shape corpus callosum axon tract fasciculation: functional impact of prenatal inflammation.  

PubMed

Microglia colonise the brain parenchyma at early stages of development and accumulate in specific regions where they participate in cell death, angiogenesis, neurogenesis and synapse elimination. A recurring feature of embryonic microglial is their association with developing axon tracts, which, together with in vitro data, supports the idea of a physiological role for microglia in neurite development. Yet the demonstration of this role of microglia is lacking. Here, we have studied the consequences of microglial dysfunction on the formation of the corpus callosum, the largest commissure of the mammalian brain, which shows consistent microglial accumulation during development. We studied two models of microglial dysfunction: the loss-of-function of DAP12, a key microglial-specific signalling molecule, and a model of maternal inflammation by peritoneal injection of lipopolysaccharide at embryonic day (E)15.5. We also took advantage of the Pu.1(-/-) mouse line, which is devoid of microglia. We performed transcriptional profiling of maternally inflamed and Dap12-mutant microglia at E17.5. The two treatments principally down-regulated genes involved in nervous system development and function, particularly in neurite formation. We then analysed the developmental consequences of these microglial dysfunctions on the formation of the corpus callosum. We show that all three models of altered microglial activity resulted in the defasciculation of dorsal callosal axons. Our study demonstrates that microglia display a neurite-development-promoting function and are genuine actors of corpus callosum development. It further shows that microglial activation impinges on this function, thereby revealing that prenatal inflammation impairs neuronal development through a loss of trophic support. PMID:24593277

Pont-Lezica, Lorena; Beumer, Wouter; Colasse, Sabrina; Drexhage, Hemmo; Versnel, Marjan; Bessis, Alain

2014-05-01

156

Automatic corpus callosum segmentation using a deformable active Fourier contour model  

NASA Astrophysics Data System (ADS)

The corpus callosum (CC) is a structure of interest in many neuroimaging studies of neuro-developmental pathology such as autism. It plays an integral role in relaying sensory, motor and cognitive information from homologous regions in both hemispheres. We have developed a framework that allows automatic segmentation of the corpus callosum and its lobar subdivisions. Our approach employs constrained elastic deformation of flexible Fourier contour model, and is an extension of Szekely's 2D Fourier descriptor based Active Shape Model. The shape and appearance model, derived from a large mixed population of 150+ subjects, is described with complex Fourier descriptors in a principal component shape space. Using MNI space aligned T1w MRI data, the CC segmentation is initialized on the mid-sagittal plane using the tissue segmentation. A multi-step optimization strategy, with two constrained steps and a final unconstrained step, is then applied. If needed, interactive segmentation can be performed via contour repulsion points. Lobar connectivity based parcellation of the corpus callosum can finally be computed via the use of a probabilistic CC subdivision model. Our analysis framework has been integrated in an open-source, end-to-end application called CCSeg both with a command line and Qt-based graphical user interface (available on NITRC). A study has been performed to quantify the reliability of the semi-automatic segmentation on a small pediatric dataset. Using 5 subjects randomly segmented 3 times by two experts, the intra-class correlation coefficient showed a superb reliability (0.99). CCSeg is currently applied to a large longitudinal pediatric study of brain development in autism.

Vachet, Clement; Yvernault, Benjamin; Bhatt, Kshamta; Smith, Rachel G.; Gerig, Guido; Cody Hazlett, Heather; Styner, Martin

2012-02-01

157

S100B is downregulated in the nuclear proteome of schizophrenia corpus callosum.  

PubMed

Here we report the downregulation of S100B in the nuclear proteome of the corpus callosum from nine schizophrenia patients compared to seven mentally healthy controls. Our data have been obtained primarily by mass spectrometry and later confirmed by Western blot. This is an intriguing finding coming from a brain region which is essentially composed by white matter, considering the potential role of S100B in the control of oligodendrocyte maturation. This data reinforce the importance of oligodendrocytes in schizophrenia, shedding more light to its pathobiology. PMID:24504531

Steiner, Johann; Schmitt, Andrea; Schroeter, Matthias L; Bogerts, Bernhard; Falkai, Peter; Turck, Christoph W; Martins-de-Souza, Daniel

2014-06-01

158

Prenatal MR diffusion tractography in a fetus with complete corpus callosum agenesis.  

PubMed

Diffusion tensor imaging (DTI) in combination with 3D-tractography reconstructions allows studying the neuro-architecture of complex brain malformations in vivo. Prenatal, in utero DTI has been limited by long acquisition times, poor signal to noise ratio and multiple artifacts. Recent developments in hard- and software allow collection of high quality DTI data sets in utero. We report on the DTI and tractography data of a fetus with a corpus callosum agenesis. Our case shows that nowadays the neuro-architecture of the fetal brain can be studied in excellent detail. Prenatal DTI and tractography may help to improve our understanding of complex brain malformations. PMID:21739404

Meoded, A; Poretti, A; Tekes, A; Flammang, A; Pryde, S; Huisman, T A G M

2011-06-01

159

Distinct regional atrophy in the corpus callosum of patients with temporal lobe epilepsy  

PubMed Central

We analysed the influence of mesial temporal lobe epilepsy on the thickness of the corpus callosum (CC) in a large sample of well-characterized patients (n = 96) and healthy controls (n = 28). In particular, we investigated whether callosal structures are differentially affected depending on the affected hemisphere and age of epilepsy onset. Overall, we observed that epilepsy is associated with a decreased thickness in posterior callosal regions. Patients with an early onset, especially patients with left onset, additionally exhibited a smaller callosal thickness in more anterior and midbody regions. These findings may reflect non-specific as well as specific effects of temporal lobe epilepsy on CC development and interhemispheric connectivity.

Weber, Bernd; Luders, Eileen; Faber, Jennifer; Richter, Sabine; Quesada, Carlos M.; Urbach, Horst; Thompson, Paul M.; Toga, Arthur W.; Elger, Christian E.; Helmstaedter, Christoph

2009-01-01

160

Corpus callosum hematoma secondary to cerebral venous malformation presenting as alien hand syndrome.  

PubMed

A 26-year-old right-handed female presented with alien hand syndrome (AHS) secondary to corpus callosum (CC) hematoma. The patient had abnormal feelings in the left upper limb and exhibited intermanual conflict. Imaging studies demonstrated acute hemorrhage in the genu and body of the CC secondary to cerebral venous malformation. Callosal hemorrhage is usually caused by head trauma or a ruptured arteriovenous that extends beyond the CC. We report what may be the first case of AHS caused by callosal hemorrhage due to venous malformation. PMID:22784383

Huang, Ying; Jia, Jianping

2013-08-01

161

Megalencephaly, mega corpus callosum, and complete lack of motor development: delineation of a rare syndrome.  

PubMed

Unlike atrophy of the corpus callosum (CC), callosal hypertrophy is a rare neuroimaging finding with only few reported patients. The "megalencephaly, mega CC, and complete lack of motor development" syndrome is morphologically characterized by generalized megalencephaly, a thickened CC, and extensive polymicrogyria causing a pachygyric appearance. We report on the fifth patient showing this rare syndrome, a 3-year-old girl displaying the typical neuroimaging features. Clinically she showed a severely impaired motor, mental, and speech development with marked muscular hypotonia but no dysmorphic facial signs. She also retained the ability to move by rolling sidewards so that complete lack of motor development may not be a consistent feature. PMID:20803648

Hengst, Meike; Tücke, Jens; Zerres, Klaus; Blaum, Marcus; Häusler, Martin

2010-09-01

162

Fractions 1  

NSDL National Science Digital Library

This lesson is a review of fractions. dsd video 1. Start at the district web page 2. Go to My DSD 3. Click on OnDemand 4. In the custom search box, type "fractions" 5. Watch the "Fun with Fractions, Math all Around us" video. Visual Fractions Follow this link to explore fractions. Click on "Identify Fractions". Work on identifying fractions with lines until you have done at ...

Taylor, Mrs.

2010-09-28

163

Improper Fractions  

NSDL National Science Digital Library

Let's review improper fractions by playing some fun games! Ice Cream Fractions Shop! Improper Fractions Jeopardy! For this game, type in your name and select "one player game". Click on different number amounts to try many different improper fraction problems! Improper Fractions Jeopardy! Type in your name to begin the ice cream shop game. Convert the improper fractions given to proper fractions then deliver the proper amount of ice ...

Kellersberger, Ms.

2011-12-12

164

Fraction Track  

NSDL National Science Digital Library

This interactive applet provides a visual model to help students compare fractions and understand equivalent fractions. The applet displays eight fraction tracks (unit number lines) divided into fractional increments from halves to twelfths. The user turns over cards displaying fractions and moves sliders on the tracks a distance equal to or less than the target fractions. The goal is to move all the sliders to the end of each fraction track in the least number of moves.

2009-01-01

165

Anisotropy in structure and properties of extruded DRA composites  

Microsoft Academic Search

such as particle size and volume fraction of the reinforcements on the anisotropy in the structure and mechanical properties of the extruded 2124 Al\\/SiCp composites. Atomized 2124 Al powder was mixed with SiC powder having two different particle sizes (14 µm and 1.9 µm) in different volume fractions (15% and 30%). The resultant composites are named as 15C, 15F and

V. V. Bhanu Prasad; B. V. R. Bhat; Y. R. Mahajan; P. Ramakrishnan

2002-01-01

166

Equivalent Fractions  

NSDL National Science Digital Library

What is an equivalent fraction? Students, I want you to create song about fractions. Here is a fraction song video to help you get and idea. Remember your song should be at least five sentences long. Math Song- Equivalent Fractions Students, I want you to click on the website below and the play the fraction game. Let's see how many ...

Ogle, Miss

2012-04-05

167

Fraction Match  

NSDL National Science Digital Library

In this online game students must match the fraction to a model of the fraction (rectangular, triangular, or circular). For each fraction several representations match and each one must be chosen before a new fraction appears. Each round of the game is timed for 1-minute and score is tracked to see how many fraction matches can be made in that time frame.

Games, Mari

2013-01-01

168

Fantastic Fractions  

NSDL National Science Digital Library

Fractions are fabulous! Fractions are new for us, so let's start out slow and then pick up some speed! First, Create Your Own Flag by coloring in half the flag with the colors! Next, have some more Fun with Fractions by picking out which picture shows the fraction! Finally, let's have some Fraction Pie - count the pieces of pie to figure out how much ...

Stabler, Ms.

2011-03-29

169

Separating intrinsic and apparent anisotropy  

NASA Astrophysics Data System (ADS)

Seismic anisotropy plays a key role in studies of the Earth's rheology and deformation because of its relation to flow-induced lattice-preferred orientation (LPO) of intrinsically anisotropic minerals. In addition to LPO, small-scale heterogeneity produces apparent anisotropy that need not be related to deformation in the same way as intrinsic anisotropy. Quantitative interpretations of observed anisotropy therefore require the separation of its intrinsic and apparent components. We analyse the possibility to separate intrinsic and apparent anisotropy in media with hexagonal symmetry - typically used in surface wave tomography and SKS splitting studies. Our analysis is on the level of the wave equation, which makes it general and independent of specific data types or tomographic techniques. We find that observed anisotropy can be explained by isotropic heterogeneity when elastic parameters take specific combinations of values. In practice, the uncertainties of inferred anisotropy are large enough to ensure that such a combination is always within the error bars. It follows that commonly observed anisotropy can always be explained completely by a purely isotropic laminated medium unless all anisotropic parameters are known with unrealistic accuracy. Most importantly, minute changes in the poorly constrained P wave anisotropy and the parameter ? can switch between the possible or impossible existence of an isotropic equivalent. Important implications of our study include: (1) Intrinsic anisotropy over tomographically resolved length scales is never strictly required when reasonable error bars for anisotropic parameters are taken into account. (2) Currently available seismic observables provide weak constraints on the relative contributions of intrinsic and apparent anisotropy. (3) Therefore, seismic observables alone are not sufficient to constrain the magnitude of mantle flow. (4) Quantitative interpretations of anisotropy in terms of mantle flow require combined seismic/geodynamic inversions, as well as the incorporation of additional data such as topography, gravity and scattered waves.

Fichtner, Andreas; Kennett, Brian L. N.; Trampert, Jeannot

2013-06-01

170

Fraction Sorter  

NSDL National Science Digital Library

Visualize fractions by coloring in the appropriate portions of either a circle or a square, then order those fractions from least to greatest. Fraction Sorter is one of the Interactivate assessment explorers.

171

Fraction Pointer  

NSDL National Science Digital Library

Graphically determine the value of 2 given fractions represented as points on a number line then graphically find a fraction whose value is in between the value of the 2 given fractions and determine its value.

The Shodor Education Foundation, Inc.

2007-12-12

172

Fraction Track  

NSDL National Science Digital Library

"This applet allows students to individually practice working with relationships among fractions and ways of combining fractions. For a two person version of this applet see the Fraction Track E-Example." from NCTM Illuminations.

Mathematics, Illuminations N.

2009-05-12

173

Fraction Finder  

NSDL National Science Digital Library

In this activity, you will graphically determine the value of two given fractions represented as points on a number line. You will then graphically find a fraction whose value is between the two given fractions and determine its value.

2010-01-01

174

Shape analysis of corpus callosum in autism subtype using planar conformal mapping  

NASA Astrophysics Data System (ADS)

A number of studies have documented that autism has a neurobiological basis, but the anatomical extent of these neurobiological abnormalities is largely unknown. In this study, we aimed at analyzing highly localized shape abnormalities of the corpus callosum in a homogeneous group of autism children. Thirty patients with essential autism and twenty-four controls participated in this study. 2D contours of the corpus callosum were extracted from MR images by a semiautomatic segmentation method, and the 3D model was constructed by stacking the contours. The resulting 3D model had two openings at the ends, thus a new conformal parameterization for high genus surfaces was applied in our shape analysis work, which mapped each surface onto a planar domain. Surface matching among different individual meshes was achieved by re-triangulating each mesh according to a template surface. Statistical shape analysis was used to compare the 3D shapes point by point between patients with autism and their controls. The results revealed significant abnormalities in the anterior most and anterior body in essential autism group.

He, Qing; Duan, Ye; Yin, Xiaotian; Gu, Xianfeng; Karsch, Kevin; Miles, Judith

2009-02-01

175

Early-life stress, corpus callosum development, hippocampal volumetrics, and anxious behavior in male nonhuman primates  

PubMed Central

Male bonnet monkeys (Macaca radiata) were subjected to the Variable Foraging Demand (VFD) early stress paradigm as infants, MRI scans were completed an average of four years later, and behavioral assessments of anxiety and ex-vivo corpus callosum (CC) measurements were made when animals were fully matured. VFD rearing was associated with smaller CC size, CC measurements were found to correlate with fearful behavior in adulthood, and ex-vivo CC assessments showed high consistency with earlier MRI measures. Region of Interest (ROI) hippocampus and whole brain voxel- based morphometry assessments were also completed and VFD rearing was associated with reduced hippocampus and inferior and middle temporal gyri volumes. Animals were also characterized according to serotonin transporter genotype (5-HTTLPR), and the effect of genotype on imaging parameters was explored. The current findings highlight the importance of future research to better understand the effects of stress on brain development in multiple regions, including the corpus callosum, hippocampus, and other regions involved in emotion processing. Nonhuman primates provide a powerful model to unravel the mechanisms by which early stress and genetic makeup interact to produce long-term changes in brain development, stress reactivity, and risk for psychiatric disorders.

Jackowski, Andrea; Perera, Tarique D.; Abdallah, Chadi G.; Garrido, Griselda; Tang, Cheuk Y.; Martinez, Jose; Mathew, Sanjay J.; Gorman, Jack M.; Rosenblum, Leonard A.; Smith, Eric L.P.; Dwork, Andrew J.; Shungu, Dikoma C.; Kaffman, Arie; Gelernter, Joel; Coplan, Jeremy D.; Kaufman, Joan

2014-01-01

176

Genetic, Morphometric, and Behavioral Factors Linked to the Midsagittal Area of the Corpus Callosum  

PubMed Central

The corpus callosum is the main commissure connecting left and right cerebral hemispheres, and varies widely in size. Differences in the midsagittal area of the corpus callosum (MSACC) have been associated with a number of cognitive and behavioral phenotypes, including obsessive-compulsive disorders, psychopathy, suicidal tendencies, bipolar disorder, schizophrenia, autism, and attention deficit hyperactivity disorder. Although there is evidence to suggest that MSACC is heritable in normal human populations, there is surprisingly little evidence concerning the genetic modulation of this variation. Mice provide a potentially ideal tool to dissect the genetic modulation of MSACC. Here, we use a large genetic reference panel – the BXD recombinant inbred line – to dissect the natural variation of the MSACC. We estimated the MSACC in over 300 individuals from nearly 80 strains. We found a 4-fold difference in MSACC between individual mice, and a 2.5-fold difference among strains. MSACC is a highly heritable trait (h2?=?0.60), and we mapped a suggestive QTL to the distal portion of Chr 14. Using sequence data and neocortical expression databases, we were able to identify eight positional and plausible biological candidate genes within this interval. Finally, we found that MSACC correlated with behavioral traits associated with anxiety and attention.

Newbury, Alex J.; Rosen, Glenn D.

2012-01-01

177

When more is less: associations between corpus callosum size and handedness lateralization  

PubMed Central

Although not consistently replicated, a substantial number of studies suggest that left-handers have larger callosal regions than right-handers. We challenge this notion and propose that callosal size is not linked to left-handedness or right-handedness per se but to the degree of handedness lateralization. To test this hypothesis, we investigated the thickness of the corpus callosum in a large data set (n=361). We analyzed the correlations between callosal thickness and the degree of handedness lateralization in 324 right-handers and 37 left-handers at 100 equidistant points across the corpus callosum. We revealed significant negative correlations within the anterior and posterior midbody suggesting that larger callosal dimensions in these regions are associated with a weaker handedness lateralization. Significant positive correlations were completely absent. In addition, we compared callosal thickness between moderately lateralized left-handers (n=37) and three equally sized groups (n=37) of right-handers (strongly, moderately, and weakly lateralized). The outcomes of these group analyses confirmed the negative association between callosal size and handedness lateralization, although callosal differences between right- and left-handers did not reach statistical significance. This suggests that callosal differences are rather small, if examined as a dichotomy between two handedness groups. Future studies will expand this line of research by increasing the number of left-handers to boost statistical power, and by combining macro- and micro-structural, as well as functional and behavioral measurements to identify the biological mechanisms linking callosal morphology and handedness lateralization.

Luders, Eileen; Cherbuin, Nicolas; Thompson, Paul M.; Gutman, Boris; Anstey, Kaarin J.; Sachdev, Perminder; Toga, Arthur W.

2010-01-01

178

Electromagnetic electron temperature anisotropy instabilities  

NASA Technical Reports Server (NTRS)

This paper considers electromagnetic Vlasov instabilities driven by electron temperature anisotropies in a homogeneous, nonrelativistic magnetized plasma. Numerical solutions of the full linear dispersion equation for bi-Maxwellian distribution functions and instabilities propagating parallel to the magnetic field are presented. Parametric dependences of the maximum growth rates of the electron fire hose and whistler anisotropy instabilities are given.

Gary, S. P.; Madland, C. D.

1985-01-01

179

Thermal conductivity anisotropy of rocks  

NASA Astrophysics Data System (ADS)

The interior heat of the lithosphere of the Earth is mainly transferred by conduction that depends on thermal conductivity of rocks. Many sedimentary and metamorphic rocks have thermal conductivity anisotropy, i.e. heat is preferentially transferred in the direction parallel to the bedding and foliation of these rocks. Deming (JGR, 1994) proposed an empirical relationship between K(perp) and anisotropy (K(par)/K(perp)) using 89 measurements on rock samples from literatures. In Deming's model, thermal conductivity is almost isotropic for K(perp) > 4 W/mK, but anisotropy is exponentially increasing with decreasing K(perp), with final anisotropy of ~2.5 at K(perp) < 1.0 W/mK. However, Davis et al. (JGR, 2007) argued that there is little evidence for Deming's suggestion that thermal conductivity anisotropy of all rocks increases systematically to about 2.5 for rocks with low thermal conductivity. Davis et al. insisted that Deming's increase in anisotropy for 1 < K(perp) < 4 W/mK with decreasing K(perp) could be due to the fractures filled with air or water, which causes thermal conductivity anisotropy. To test Deming's suggestion and Davis et al.'s argument on thermal conductivity anisotropy, we measured thermal conductivity parallel (K(par)) and perpendicular (K(perp)) to bedding or foliation and performed analytical & numerical modeling. Our measurements on 53 rock samples show the anisotropy range from 0.79 to 1.36 for 1.84 < K(prep) < 4.06 W/mK. Analytical models show that anisotropy can increase or stay the same at the range of 1 < K(perp) < 4 W/mK. Numerical modeling for gneiss shows that anisotropy ranges 1.21 to 1.36 for 2.5 < K(perp) < 4.8 W/mK. Another numerical modeling with interbedded coal layers in high thermal conductivity rocks (3.5 W/mK) shows anisotropy of 1.87 when K(perp) is 1.7 W/mK. Finally, numerical modeling with fractures indicates that the fractures does not seem to affect thermal conductivity anisotropy significantly. In conclusion, our preliminary results imply that thermal conductivity anisotropy can increase or stay at low value in the range of 1.0 < K(perp) < 4.0 W/mK. Both cases are shown to be possible through lab measurements and analytical & numerical modeling.

Lee, Youngmin; Keehm, Youngseuk; Shin, Sang Ho

2013-04-01

180

Fractional Wall  

NSDL National Science Digital Library

This problem with multiple solutions is an opportunity for students to practice finding equivalent fractions using a visual fraction bar model. The goal is for the student to develop a deep understanding of equivalent fractions using the model in order to determine a rule for finding equivalent fractions without a model. A Teacher's Note page, hints, possible solutions, and a printable page are provided.

2005-10-01

181

Multiplying Fractions  

NSDL National Science Digital Library

This site gives a description of how to multiply fractions and gives a sample problem in which the numerators and denominators are multiplied and the resulting fraction is simplified. It also includes the same problem solved by 'canceling' the fractions to simplify, and completing the process. There is also a game for students to practice their new skill of multiplying and simplifying fractions.

Banfill, J. C.

2007-12-12

182

Agenesis of the Corpus Callosum and Skeletal Deformities in Two Unrelated Patients: Analysis via MRI and Radiography  

PubMed Central

Purpose. Mental retardation, mild to severe epilepsy and cerebral palsy often of hemiplegic type are common accompaniments in patients with agenesis/hypoplasia of the corpus callosum. Skeletal deformities of bilateral radiohumeral synostosis, brachydactyly, bilateral elbow dislocation, talipes equinovarus, and juxtacalcaneal accessory bones have been encountered in two unrelated children with agenesis of the corpus callosum. Methods. We report on two unrelated children who presented with the full clinical criteria of agenesis of the corpus callosum. Strikingly, both presented with variable upper and lower limb deformities. The clinical features, radiographic and MRI findings in our current patients, have been compared with previously reported cases identified through a PubMed literature review. Results. Bilateral radiohumeral synostosis associated with pyruvate dehydrogenase deficiency has been encountered in one patient. The other patient manifested bilateral elbow dislocation, coxa valga, talipes equinovarus, and bilateral juxtacalcaneal accessory bones. Conclusion. The constellation of malformation complexes in our current patients have the hitherto not been reported and expanding the spectrum of skeletal deformities in connection with agenesis of the corpus callosum.

Bock, Wolfgang; Partan, Gerald; Klaushofer, Klaus; Ganger, Rudolf; Grill, Franz

2014-01-01

183

Atrophy of the corpus callosum associated with a decrease in cortical benzodiazepine receptor in large cerebral arterial occlusive diseases  

Microsoft Academic Search

OBJECTIVESIt remains controversial whether selective neuronal ischaemic change develops in patients with occlusion of the large cerebral arteries. Previous studies have shown atrophy of the corpus callosum with reduced cortical oxygen metabolism in large cerebral arterial occlusive diseases, which might be indirect evidence of loss of the neurons in cortical layer 3. Recent studies of patients with ischaemic cerebrovascular diseases

H Yamauchi; H Fukuyama; Y Dong; H Nabatame; Y Nagahama; S Nishizawa; J Konishi; H Shio

2000-01-01

184

Agenesis of the Corpus Callosum and Skeletal Deformities in Two Unrelated Patients: Analysis via MRI and Radiography.  

PubMed

Purpose. Mental retardation, mild to severe epilepsy and cerebral palsy often of hemiplegic type are common accompaniments in patients with agenesis/hypoplasia of the corpus callosum. Skeletal deformities of bilateral radiohumeral synostosis, brachydactyly, bilateral elbow dislocation, talipes equinovarus, and juxtacalcaneal accessory bones have been encountered in two unrelated children with agenesis of the corpus callosum. Methods. We report on two unrelated children who presented with the full clinical criteria of agenesis of the corpus callosum. Strikingly, both presented with variable upper and lower limb deformities. The clinical features, radiographic and MRI findings in our current patients, have been compared with previously reported cases identified through a PubMed literature review. Results. Bilateral radiohumeral synostosis associated with pyruvate dehydrogenase deficiency has been encountered in one patient. The other patient manifested bilateral elbow dislocation, coxa valga, talipes equinovarus, and bilateral juxtacalcaneal accessory bones. Conclusion. The constellation of malformation complexes in our current patients have the hitherto not been reported and expanding the spectrum of skeletal deformities in connection with agenesis of the corpus callosum. PMID:24592343

Al Kaissi, Ali; Kurz, Herbert; Bock, Wolfgang; Pärtan, Gerald; Klaushofer, Klaus; Ganger, Rudolf; Grill, Franz

2014-01-01

185

Abnormal brain connectivity in first-episode psychosis: A diffusion MRI tractography study of the corpus callosum  

Microsoft Academic Search

A model of disconnectivity involving abnormalities in the cortex and connecting white matter pathways may explain the clinical manifestations of schizophrenia. Recently, diffusion imaging tractography has made it possible to study white matter pathways in detail and we present here a study of patients with first-episode psychosis using this technique. We selected the corpus callosum for this study because there

Gary Price; Mara Cercignani; Geoffrey J. M. Parker; Daniel R. Altmann; Thomas R. E. Barnes; Gareth J. Barker; Eileen M. Joyce; Maria A. Ron

2007-01-01

186

DTI tractography based parcellation of white matter: Application to the mid-sagittal morphology of corpus callosum  

Microsoft Academic Search

Morphology of the corpus callosum (CC) at the mid-sagittal level has been a target of extensive studies. However, the lack of internal structures and its polymorphism make it a challenging task to quantitatively analyze shape differences among subjects. In this paper, diffusion tensor Imaging (DTI) and tract tracing technique were applied to incorporate cortical connectivity information to the morphological study.

Hao Huang; Jiangyang Zhang; Hangyi Jiang; Setsu Wakana; Lidia Poetscher; Michael I. Miller; Peter C. M. van Zijl; Argye E. Hillis; Robert Wytik; Susumu Mori

2005-01-01

187

Topography of the human corpus callosum revisited—Comprehensive fiber tractography using diffusion tensor magnetic resonance imaging  

Microsoft Academic Search

Several tracing studies have established a topographical distribution of fiber connections to the cortex in midsagittal cross-sections of the corpus callosum (CC). The most prominent example is Witelson's scheme, which defines five vertical partitions mainly based on primate data. Conventional MRI of the human CC does not reveal morphologically discernable structures, although microscopy techniques identified myelinated axons with a relatively

Sabine Hofer; Jens Frahm

2006-01-01

188

Visual Fractions  

NSDL National Science Digital Library

Visual Fractions is "a tutorial that offers instruction and practice in identifying, renaming, and operating on fractions" and was created by Richard E. Rand. The website reviews examples of fractions, which are modeled with number lines or circles. Throughout the website are instructions to follow, encouraging students to try a few activities on their own. For a more light-hearted approach, Rand has a game that involves using fractions to help Grammy find Grampy and to make treats for Grampy. The software programs used to create the line and circle fractions, Fraction Modeler and Fraction Maker, are available for purchase and described on this website.

189

MRI study of corpus callosum in patients with borderline personality disorder: a pilot study.  

PubMed

This pilot study examined the integrity of the corpus callosum in a sample of patients with borderline personality disorder (BPD), as abnormalities in inter-hemispheric communication could possibly be involved in illness pathophysiology. We utilized magnetic resonance imaging (MRI) signal intensity (SI) and morphometric measures. Ten BPD and 20 healthy control subjects were assessed for current and past Axis I and Axis II comorbidities and histories of childhood abuse. Regional CC SI and areas were measured with semi-automated software from three-dimensional gradient echo imaging scans. Analysis of covariance was conducted to evaluate the results. No significant differences were observed between BPD and controls in the SI or area of any CC region. Abnormalities in interhemispheric connectivity do not appear necessary for the development of BPD. Further studies with larger samples are needed to confirm this preliminary finding. PMID:17703861

Zanetti, Marcus V; Soloff, Paul H; Nicoletti, Mark A; Hatch, John P; Brambilla, Paolo; Keshavan, Matcheri S; Soares, Jair C

2007-10-01

190

Neurophysiological investigation of congenital mirror movements in a patient with agenesis of the corpus callosum.  

PubMed

We describe a patient with complete agenesis of the corpus callosum and congenital mirror movements in which primary motor cortex (M1) excitability of both hemispheres was assessed with transcranial magnetic stimulation. Voluntary contraction of the index finger was associated with bilateral electromyographic activity in the first dorsal interosseus muscle. Motor-evoked potentials of identical latencies were produced bilaterally after unilateral M1 stimulation. Measures of intracortical inhibition and facilitation were within normal limits bilaterally although a shorter contralateral silent period was found for both hemispheres. Taken together, the current data suggest a pattern of M1 excitability very similar to that found in patients with congenital mirror movements and no other motor abnormality. PMID:22037131

Lepage, Jean-François; Beaulé, Vincent; Srour, Myriam; Rouleau, Guy; Pascual-Leone, Alvaro; Lassonde, Maryse; Théoret, Hugo

2012-04-01

191

Agenesis of the corpus callosum: a United Kingdom series of 56 cases  

PubMed Central

A survey of cases of agenesis of the corpus callosum was carried out to examine its associations, utilising the British Neurological Surveillance Unit (BNSU). Fifty six cases were reported (36 male), 37 were adults. Nearly two thirds had epilepsy; half of the adult cases had intellectual impairment as estimated clinically, and a third a psychiatric disorder. Nine cases (five adults) were apparently normal neurologically, and may have escaped detection but for a coincidental or minor disorder leading to neurological investigation. The BNSU is a valuable aid in the study of rare disorders but in less severe conditions, such methods of ascertainment inevitably underestimate prevalence and are prone to selection bias towards patients with associated morbidity.??

Taylor, M; David, A

1998-01-01

192

Sudden worsening after subdural haematoma surgery: will there be a corpus callosum injury?  

PubMed

We report a case of mild encephalopathy with a reversible splenial lesion (MERS) which occurred after chronic subdural haematoma (CSDH) surgery. The patient was admitted to our hospital for drowsiness and marked asthenia. The cerebral CT scan revealed a CSDH and surgery allowed to improve the symptoms, but after several days we observed a sudden worsening. The patient developed left-sided myoclonic seizures followed by left hemiplegia and worsening drowsiness. Electrolytes imbalance and inflammatory causes were excluded. The CT scan showed a right cerebral swelling and the subsequent MRI revealed a single lesion in the splenium of the corpus callosum, hyperintense on diffusion-weighted images. After osmotic therapy the patient improved and on day 10 of admission the MRI showed a complete resolution of the lesion. This is the first report that described an association between CSDH and MERS. Possible aetiopathogenetic mechanisms are discussed. PMID:24862419

Panciani, Pier Paolo; Roca, Elena; Lodoli, Giovanni; Fontanella, Marco Maria

2014-01-01

193

Transient lesion in the splenium of the corpus callosum in acute uncomplicated falciparum malaria.  

PubMed

Patients with acute uncomplicated Plasmodium falciparum malaria have no evident neurologic disorder, vital organ dysfunction, or other severe manifestations of infection. Nonetheless, parasitized erythrocytes cytoadhere to the endothelium throughout their microvasculature, especially within the brain. We aimed to determine if 3 Tesla magnetic resonance imaging studies could detect evidence of cerebral abnormalities in these patients. Within 24 hours of admission, initial magnetic resonance imaging examinations found a lesion with restricted water diffusion in the mid-portion of the splenium of the corpus callosum of 4 (40%) of 10 male patients. The four patients who had a splenial lesion initially had evidence of more severe hemolysis and thrombocytopenia than the six patients who had no apparent abnormality. Repeat studies four weeks later found no residua of the lesions and resolution of the hematologic differences. These observations provide evidence for acute cerebral injury in the absence of severe or cerebral malaria. PMID:24615139

Laothamatas, Jiraporn; Sammet, Christina L; Golay, Xavier; Van Cauteren, Marc; Lekprasert, Varinee; Tangpukdee, Noppadon; Krudsood, Srivicha; Leowattana, Wattana; Wilairatana, Polrat; Swaminathan, Srirama V; DeLaPaz, Robert L; Brown, Truman R; Looareesuwan, Sornchai; Brittenham, Gary M

2014-06-01

194

Callosal disconnection syndrome after corpus callosum infarct: a diffusion tensor tractography study.  

PubMed

We report a patient who presented with callosal disconnection syndrome (CDS) and fiber disconnection on diffusion tensor tractography (DTT) after an infarct of the corpus callosum (CC). A 72-year-old woman presented with manifestations of CDS, including frontal alien hand syndrome (AHS), left agraphia, right hemiparesis, right somatosensory deficit, left neglect, and impaired visual recognition. DTT was performed for the evaluation of CC fibers, followed by comparison with DTT findings of normal subjects. DTT of the normal subject revealed bilateral extension of CC fibers to the frontal, parietal, and occipitotemporal cortices. By contrast, CC fibers of the patient revealed extensive disruption, with the exception of CC fibers passing through the anterior genu and the posterior splenium. The extensive disruption of CC fibers appears to explain the patient's various CDS symptoms. In brief, DTT could be useful for detection of CC lesions in patients with CDS. PMID:23246180

Jang, Sung Ho; Lee, Jun; Yeo, Sang Seok; Chang, Min Cheol

2013-10-01

195

Quantitative morphology of the corpus callosum in obsessive-compulsive disorder  

PubMed Central

Neuroimaging studies have implicated the corpus callosum (CC) in the pathophysiology of obsessive-compulsive disorder (OCD). Putative dysfunctions in prefrontal cortical regions suggest anomalies in anterior segments of the CC. However, recent studies have also implicated the middle and posterior CC. The present study soughts to examine the CC using parcellation scheme informed by diffusion tensor imaging. Anatomic brain magnetic resonance scans were obtained from 21 OCD subjects (mean age = 26.9±9.93) and 42 healthy age- and sex-matched controls (mean age = 26.6±9.46) between the ages of 14 and 49. Area and volume measures of five subregions of the CC were obtained via manual tracings. A multivariate analysis of variance (after correcting for multiple comparisons) identified smaller area and volume in the mid-anterior region of the CC in OCD patients relative to controls. These findings implicate medio-frontal regions of the cortex in the pathophysiology of OCD.

Lopez, Katherine C.; Lalonde, Francois; Mattai, Anand; Wade, Benjamin; Clasen, Liv; Rapoport, Judith; Giedd, Jay N.

2014-01-01

196

Transient Lesion in the Splenium of the Corpus Callosum in Acute Uncomplicated Falciparum Malaria  

PubMed Central

Patients with acute uncomplicated Plasmodium falciparum malaria have no evident neurologic disorder, vital organ dysfunction, or other severe manifestations of infection. Nonetheless, parasitized erythrocytes cytoadhere to the endothelium throughout their microvasculature, especially within the brain. We aimed to determine if 3 Tesla magnetic resonance imaging studies could detect evidence of cerebral abnormalities in these patients. Within 24 hours of admission, initial magnetic resonance imaging examinations found a lesion with restricted water diffusion in the mid-portion of the splenium of the corpus callosum of 4 (40%) of 10 male patients. The four patients who had a splenial lesion initially had evidence of more severe hemolysis and thrombocytopenia than the six patients who had no apparent abnormality. Repeat studies four weeks later found no residua of the lesions and resolution of the hematologic differences. These observations provide evidence for acute cerebral injury in the absence of severe or cerebral malaria.

Laothamatas, Jiraporn; Sammet, Christina L.; Golay, Xavier; Van Cauteren, Marc; Lekprasert, Varinee; Tangpukdee, Noppadon; Krudsood, Srivicha; Leowattana, Wattana; Wilairatana, Polrat; Swaminathan, Srirama V.; DeLaPaz, Robert L.; Brown, Truman R.; Looareesuwan, Sornchai; Brittenham, Gary M.

2014-01-01

197

Fractional Clothesline  

NSDL National Science Digital Library

A string will be stretched across the classroom and various points will be marked for 0, 1, 2, 3, and 4. This classroom number line will be used to show that all proper fractions are grouped between 0 and 1, and that improper fractions or mixed numbers are all grouped above 1. Students clip index cards with various proper fractions, improper fractions, and mixed numbers on the clothesline to visually see groupings. Students then play an estimation game with groups using the same principle. Encouraging students to look at fractions in various ways will help foster their conceptual fraction sense (from NCTM's Illuminations).

Mathematics, Illuminations N.

2009-07-23

198

Fraction Game  

NSDL National Science Digital Library

This interactive game provides an opportunity for students to think about how fractions are related to a unit whole, compare fractional parts of a whole, and find equivalent fractions. Players move markers a total distance that is less than or equal to the random target fraction, along their choice of seven parallel number line tracks, which are divided into different fractional parts. The goal is to move each of the seven markers to the right side of the game board using as few fraction target cards as possible. Instructions and exploration questions are included.

2011-01-01

199

PEG-PDLLA Micelle Treatment Improves Axonal Function of the Corpus Callosum following Traumatic Brain Injury.  

PubMed

Abstract The initial pathological changes of diffuse axonal injury following traumatic brain injury (TBI) include membrane disruption and loss of ionic homeostasis, which further lead to dysfunction of axonal conduction and axon disconnection. Resealing the axolemma is therefore a potential therapeutic strategy for the early treatment of TBI. Monomethoxy poly (ethylene glycol)-poly (D, L-lactic acid) di-block copolymer micelles (mPEG-PDLLA) have been shown to restore depressed compound action potentials (CAPs) of spinal axons and promote functional recovery after spinal cord injury. Here, we evaluate the effect of the micelles on repairing the injured cortical axons following TBI. Adult mice subjected to controlled cortical impact (CCI) were treated with intravenous injection of the micelles at 0?h or 4?h after injury. Evoked CAPs were recorded from the corpus callosum of coronal cortical slices at 2 days after injury. The CCI caused significant decreases in the amplitudes of two CAP peaks that were respectively generated by the faster myelinated axons and slower unmyelinated axons. Micelle treatment at both 0?h and 4?h after CCI resulted in significant increases in both CAP peak amplitudes. Injection of fluorescent dye-labeled micelles revealed high fluorescent staining in cortical gray and white matters underneath the impact site. Labeling membrane-perforated neurons by injecting a membrane impermeable dye Texas Red-labeled dextran into lateral ventricles at 2?h post-CCI revealed that immediate micelle injection after CCI did not reduce the number of dye-stained cortical neurons and dentate granule cells of the hippocampus, indicating its ineffectiveness in repairing plasma membrane of neuronal somata. We conclude that intravenous administration of mPEG-PDLLA micelles immediately or at 4?h after TBI allows brain penetration via the compromised blood brain-barrier, and thereby improves the function of both myelinated and unmyelinated axons of the corpus callosum. PMID:24579802

Ping, Xingjie; Jiang, Kewen; Lee, Seung-Young; Cheng, Ji-Xing; Jin, Xiaoming

2014-07-01

200

Quantifying reflectance anisotropy of photosynthetically active radiation in grasslands  

SciTech Connect

This work is part of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE), an international land-surface-atmosphere experiment aimed at improving the way climate models represent energy, water, heat, and carbon exchanges, and improving the utilization of satellite based remote sensing to monitor such parameters. This paper reports on a study to quantify the reflectance anisotropy of the photosynthetically active radiation (PAR) for grasslands. PAR falls in the wavelength range 0.4 to 0.7[mu]m. The study looks at the variation of PAR with illumination and vegetative canopy conditions. It uses bidirectional reflectance distribution function data, and measures of anisotropy derived from reflectance factor and reflectance fraction data to aid in the analysis. The data used for this analysis came from an intense effort mounted to measure diurnal changes in the anisotropy of surface reflectance from prairie grassland as a function of the vegetative canopy.

Middleton, E.M. (NASA Goddard Space Flight Center, Greenbelt, MD (United States))

1992-11-30

201

Fractions Jigsaw  

NSDL National Science Digital Library

This problem provides students an opportunity to find equivalent fractions and carry out some simple additions and subtractions of fractions in a context that may challenge and motivate students. Users need to download, print, and cut-out the fraction jigsaw. Then, they must arrange the square pieces right-side up so that the edges that touch contain equivalent fractions. The Teachers' Notes page offers rationale, suggestions for implementation, discussion questions, and ideas for extension and support.

2007-05-01

202

Equivalent Fractions!  

NSDL National Science Digital Library

How good at determining equivalent fractions are you? Test your skills with these various fraction games to find out! You have recently been learning about fractions and their equivalency. Try this game to test your knowledge of Equivalent Fractions!! Be sure to notice the "hints" under some of the questions to help you get the correct answer. Good Luck! Continue to master your skills by playing the Dirt Bike Proportions! game. How quickly you ...

Pearce, Ms.

2011-11-06

203

Ordering Fractions  

NSDL National Science Digital Library

This interactive Flash applet develops a student's fractional understanding and provides practice with comparing and ordering fractions. The learner is given five fractions in "frames" and must place them on the wall hooks in order from least to greatest. If help is needed, a student can enter the Testing Room and manipulate a pair of pipes to see and/or compare the two fractions side by side.

Bunker, Dan

2011-01-01

204

Equivalent Fractions  

NSDL National Science Digital Library

In this interactive activity a user identifies two pairs of equivalent fractions for a given random fraction or one of the player's own and the user creates their representations by dividing and shading either a square or circular region. The fractions are shown as locations on the number line and their equivalency is demonstrated when they are at the same point. The user has the ability to construct a table of equivalent fractions. Instructions and exploration questions are given.

2011-01-01

205

Rod Fractions  

NSDL National Science Digital Library

This problem allows students an opportunity to think about fraction comparisons and equivalencies in a different way using interactive rods. Students are given two different fraction rods of unknown lengths and the goal is to find out what fraction the shorter rod is of the longer rod. A Teacher's Notes page, hints, solution, and printable pages are provided.

2005-10-01

206

Anisotropy in solid inflation  

NASA Astrophysics Data System (ADS)

In the model of solid / elastic inflation, inflation is driven by a source that has the field theoretical description of a solid. To allow for prolonged slow roll inflation, the solid needs to be extremely insensitive to the spatial expansion. We point out that, because of this property, the solid is also rather inefficient in erasing anisotropic deformations of the geometry. This allows for a prolonged inflationary anisotropic solution, providing the first example with standard gravity and scalar fields only which evades the conditions of the so called cosmic no-hair conjecture. We compute the curvature perturbations on the anisotropic solution, and the corresponding phenomenological bound on the anisotropy. Finally, we discuss the analogy between this model and the f(phi)F2 model, which also allows for anisotropic inflation thanks to a suitable coupling between the inflaton phi and a vector field. We remark that the bispectrum of the curvature perturbations in solid inflation is enhanced in the squeezed limit and presents a nontrivial angular dependence, as had previously been found for the f(phi)F2 model.

Bartolo, Nicola; Matarrese, Sabino; Peloso, Marco; Ricciardone, Angelo

2013-08-01

207

Fraction Addition  

NSDL National Science Digital Library

The following sites will provide some review and practice adding fractions. These links will help with finding common denominators. Equivalent Fractions Fraction Addition-Common Denominators Do some practice with visuals. Add Fractions with Like Denominators Add Fractions with Unlike Denominators See how fast you can get through these problems! Race the Clock-Add with Like Denominators Race the Clock-Add with Unlike Denominators Race the Clock-Add with Mixed Numbers Do you need a \\"How to...\\" refresher? Look here! How Do You Do That? Add with Like Demoninators How Do You Do That? Add with Unlike Demoninators How Do You Do That? Add with Mixed Numbers ...

Romney, Mrs.

2005-06-18

208

The Fractionator  

NSDL National Science Digital Library

Created by math teacher Jeff LeMieux, the Fractionator offers hands-on tools to help students develop an understanding of fractions. The online tools model two fractions to be added (or subtracted) based on unit squares and then creates equivalent fraction models, allowing students to solve the problem. Two of the online demonstrations show a unique problem each time a new problem is requested, while a third tool allows students themselves to enter the two fractions. Also provided are links to printable materials, such as overhead transparencies and student worksheets.

Lemieux, Jeff

2007-12-12

209

Fraction finder  

NSDL National Science Digital Library

Each problem generated by this applet states two fractional endpoints for a line segment. The student representations each fraction by subdividing and coloring areas displayed as either circles or squares. The applet indicates if a colored area correctly represents the fraction. Finally, the student must model and name in the lowest terms a fraction between the two given fractions. The applet allows students to either work with circles or squares and can keep the student's score for a series of problems. From the applet page, What, How, and Why buttons open sections that explain the activity's purpose, function, and where the mathematics fits into the curriculum, as well as lists the related NCTM standards. Also included are student handouts and discussion questions about approximating fractions and whether it is easier to reduce a fraction expressed as a square or circle. Copyright 2005 Eisenhower National Clearinghouse

Foundation, Shodor E.

2004-01-01

210

Laboratory seismic anisotropy in mylonites  

NASA Astrophysics Data System (ADS)

Tectonic strain is often accommodated along narrow zones in the Earth's crust and upper mantle, and these high-strain zones represent an important mechanical and rheological component in geodynamics. In outcrop we observe the intense deformation along and across these structures. But at depth, in the mid and lower crust, and in the mantle, we are dependent on geophysical methods for analysis of structures, such as seismic reflection and refraction surveys. A natural progression has therefore been to understand the remote geophysical signal in terms of laboratory ultrasonic pulse transmission measurements on rock cores, collected in the field or from borehole drill core. Here we first present a brief review that consider key studies in the area of laboratory seismic measurements in strongly anisotropic rocks, ranging from calcite mylonites to metapelites. In the second part we focus attention on ongoing research projects targetting laboratory seismic anisotropy in mylonitized rocks, and associated challenges. Measurements of compressional (P) and shear (S) waves were made at high confining pressure (up to 5 kbar). Mineral texture analysis was performed with electron backscatter diffraction (EBSD) and neutron texture diffraction to determine crystallographic preferred orientation (CPO). So-called "rock-recipe" models are used to calculate seismic anisotropy, which consider the elastic properties of minerals that constitutes the rock, and their respective CPO. However, the outcome of such models do not always simply correspond to the measured seismic anisotropy. Differences are attributed to several factors, such as grain boundaries, mineral microstructures including shape-preferred orientation (SPO), micro-cracks and pores, and grain-scale stress-strain conditions. We highlight the combination of these factors in case studies on calcite and peridotite mylonites. In calcite mylonites, sampled in the Morcles nappe shear zone, the measured seismic anisotropy generally match the calculated seismic anisotropy. However, anisotropy may be reinforced by the contribution of grain-boundary effects and calcite SPO, as is indicated by microCT imaging and SEM analysis. This is evident in one case where the measured P wave anisotropy exceeded the calculated anisotropy by more than 5%, and by ~4 % higher shear-wave splitting. An even greater discrepancy can be found when comparing measured and calculated seismic anisotropy in mylonitized peridotites from shear zones in the Lanzo (Italy) and Ronda (Spain) massifs. This is in part related to serpentinization of olivine, which remains a challenge for laboratory measurements of peridotites. Highest values of calculated anisotropy, for both the calcite and peridotite mylonites, are found in near monomineralic specimens (i.e., 8 - 10% P wave anisotropy). In comparison, polymineralic specimens have calculated P wave anisotropy ranging between <2 - 5%. In contrast, the laboratory measured seismic anisotropy do not display a simple relationship as a function of mono- versus polymineralic composition. Seismic properties and anisotropy are discussed in light of conditions and mechanisms of deformation, and the possible role and influence of second-phase minerals. Laboratory measurements offers a venue for exploring the relationship between deformation and seismic anisotropy. Such investigation may, in combination with high-resolution geophysical methods and increasingly sophisticated numerical models, yield further insight on remote active deformation in the mid and lower crust, and in the upper mantle.

Almqvist, B. S. G.; Herwegh, M.; Hirt, A. M.; Ebert, A.; Linckens, J.; Precigout, J.; Leiss, B.; Walter, J. M.; Burg, J.-P.

2012-04-01

211

Beginning Fractions  

NSDL National Science Digital Library

For the learner just being introduced to fractions, this site is an excellent resource. It contain a very basic explanation of what a fraction is and a game for students to practice naming the fraction presented. The game can also be manipulated to have a time limit, to award time for each correct answer, and to time how fast students can get 20 more answers right than wrong.

Banfill, J. C.

2007-12-12

212

First-Episode ‘Coenesthetic’ Schizophrenia Presenting with Alien Hand Syndrome and Partial Agenesis of the Corpus Callosum  

Microsoft Academic Search

We describe the case of a 23-year-old Caucasian woman who presented with alien hand syndrome and a first episode of the coenesthetic subtype of schizophrenia. ‘Alienness’ of her non-dominant hand was intimately phenomenologically associated with the onset of first-psychosis. Cerebral MRI revealed a partial agenesis of the corpus callosum with a complete absence of the rostrum, hypoplastic anterior and inferior

Andor Simon; Mark Walterfang; Carlo Petralli; Dennis Velakoulis

2008-01-01

213

Effects of severing the corpus callosum on electrical and BOLD functional connectivity and spontaneous dynamic activity in the rat brain.  

PubMed

Functional networks, defined by synchronous spontaneous blood oxygenation level-dependent (BOLD) oscillations between spatially distinct brain regions, appear to be essential to brain function and have been implicated in disease states, cognitive capacity, and sensing and motor processes. While the topographical extent and behavioral function of these networks has been extensively investigated, the neural functions that create and maintain these synchronizations remain mysterious. In this work callosotomized rodents are examined, providing a unique platform for evaluating the influence of structural connectivity via the corpus callosum on bilateral resting state functional connectivity. Two experimental groups were assessed, a full callosotomy group, in which the corpus callosum was completely sectioned, and a sham callosotomy group, in which the gray matter was sectioned but the corpus callosum remained intact. Results indicated a significant reduction in interhemispheric connectivity in the full callosotomy group as compared with the sham group in primary somatosensory cortex and caudate-putamen regions. Similarly, electrophysiology revealed significantly reduced bilateral correlation in band limited power. Bilateral gamma Band-limited power connectivity was most strongly affected by the full callosotomy procedure. This work represents a robust finding indicating the corpus callosum's influence on maintaining integrity in bilateral functional networks; further, functional magnetic resonance imaging (fMRI) and electrophysiological connectivity share a similar decrease in connectivity as a result of the callosotomy, suggesting that fMRI-measured functional connectivity reflects underlying changes in large-scale coordinated electrical activity. Finally, spatiotemporal dynamic patterns were evaluated in both groups; the full callosotomy rodents displayed a striking loss of bilaterally synchronous propagating waves of cortical activity. PMID:24117343

Magnuson, Matthew E; Thompson, Garth J; Pan, Wen-Ju; Keilholz, Shella D

2014-02-01

214

Equivalent Fractions  

NSDL National Science Digital Library

In this NCTM iOS app a user identifies equivalent fractions for a given random fraction or one of the player's own. The user creates their representations by dividing and shading either a square or circular region. The fractions are shown as locations on the number line and their equivalency is demonstrated when they are at the same point. The user has the ability to construct a table of equivalent fractions. This app is related to an Illuminations activity and an Android app that are cataloged separately.

2012-08-10

215

Equivalent Fractions  

NSDL National Science Digital Library

In this NCTM Android app a user identifies equivalent fractions for a given random fraction or one of the player's own. The user creates their representations by dividing and shading either a square or circular region. The fractions are shown as locations on the number line and their equivalency is demonstrated when they are at the same point. The user has the ability to construct a table of equivalent fractions. This app is related to an Illuminations activity and an iOS app that are cataloged separately.

2012-07-31

216

Cerebral specialization and interhemispheric communication: does the corpus callosum enable the human condition?  

PubMed

The surgical disconnection of the cerebral hemispheres creates an extraordinary opportunity to study basic neurological mechanisms: the organization of the sensory and motors systems, the cortical representation of the perceptual and cognitive processes, the lateralization of function, and, perhaps most importantly, how the divided brain yields clues to the nature of conscious experience. Studies of split-brain patients over the last 40 years have resulted in numerous insights into the processes of perception, attention, memory, language and reasoning abilities. When the constellation of findings is considered as a whole, one sees the cortical arena as a patchwork of specialized processes. When this is considered in the light of new studies on the lateralization of functions, it becomes reasonable to suppose that the corpus callosum has enabled the development of the many specialized systems by allowing the reworking of existing cortical areas while preserving existing functions. Thus, while language emerged in the left hemisphere at the cost of pre-existing perceptual systems, the critical features of the bilaterally present perceptual system were spared in the opposite half-brain. By having the callosum serve as the great communication link between redundant systems, a pre-existing system could be jettisoned as new functions developed in one hemisphere, while the other hemisphere could continue to perform the previous functions for both half-brains. Split-brain studies have also revealed the complex mosaic of mental processes that participate in human cognition. And yet, even though each cerebral hemisphere has its own set of capacities, with the left hemisphere specialized for language and speech and major problem-solving capacities and the right hemisphere specialized for tasks such as facial recognition and attentional monitoring, we all have the subjective experience of feeling totally integrated. Indeed, even though many of these functions have an automatic quality to them and are carried out by the brain prior to our conscious awareness of them, our subjective belief and feeling is that we are in charge of our actions. These phenomena appear to be related to our left hemisphere's interpreter, a device that allows us to construct theories about the relationship between perceived events, actions and feelings. PMID:10869045

Gazzaniga, M S

2000-07-01

217

Constraining crustal anisotropy: The anisotropic H-? stacking technique  

NASA Astrophysics Data System (ADS)

Measuring anisotropy in the crust and mantle is commonly performed to make inferences on crust/upper mantle deformation, tectonic history or the presence of fluids. However, separating the contribution of the crust and mantle to the anisotropic signature remains a challenge. This is because common seismic techniques to determine anisotropy (e.g., SKS splitting, surface waves) lack the resolution to distinguish between the two, particular in regions where deep crustal earthquakes are lacking. Receiver functions offer the chance to determine anisotropy in the crust alone, offering both the depth resolution that shear-wave splitting lacks and the lateral resolution that surface waves are unable to provide. Here I present a new anisotropic H-? stacking technique which constrains anisotropy in the crust. I show that in a medium with horizontally transverse isotropy a strong variation in ? (VP-to-VS ratio) with back azimuth is present which characterises the anisotropic medium. In a vertically transverse isotropic medium no variation in ? with back azimuth is observed, but ? is increased across all back azimuths. While, these results show that estimates of ? are more difficult to relate to composition than previously thought, they offer the opportunity to constrain anisotropy in the crust. Based on these observations I develop a new anisotropic H-? stacking technique which inverts H-? data for anisotropy. I apply these new techniques to data from the Afar Depression, Ethiopia and extend the technique to invert for melt induced anisotropy solving for melt fraction, aspect ratio and orientation of melt inclusions. I show that melt is stored in interconnected stacked sills in the lower crust, which likely supply the recent volcanic eruptions and dike intrusions. The crustal anisotropic signal can explain much of the SKS-splitting results, suggesting minimal influence from the mantle. This results show that it is essential to consider anisotropy when performing H-? stacking on receiver function data. The new technique presented here can be applied to any anisotropic medium where it can provide constraints on the average crustal anisotropy.

Hammond, James

2014-05-01

218

Fraction Beach  

NSDL National Science Digital Library

In this interactive Flash game, students are challenged to identify a fraction from a picture of a group of objects or from a geometric diagram, or they are asked to create a diagram or picture given a common fraction. Motivation is provided by earning buckets of sand to built a sand castle.

2007-01-01

219

Understanding Fractions  

NSDL National Science Digital Library

In this article Pennant and Woodham discuss the importance of rich tasks in the teaching of fractions. In order to prepare for new more rigorous standards, the authors have compiled a list of rich tasks and a description of others that aim to improve how children think about fractions.

Pennant, Jennie; Woodham, Liz

2013-01-01

220

Kakooma - Fractions  

NSDL National Science Digital Library

In this online game created by Greg Tang, students complete a puzzle by finding the number that is the sum of two others fractions within each grouping. The application allows for a variety of abilities by allowing a choice between easy or hard, depending on the number of equivalent fractions and five levels of challenge, depending on the number of shapes within the puzzle.

Tang, Greg

2013-01-01

221

Heliospheric Influence on the Anisotropy of TeV Cosmic Rays  

NASA Astrophysics Data System (ADS)

This paper provides a theory of using Liouville's theorem to map the anisotropy of TeV cosmic rays seen at Earth using the particle distribution function in the local interstellar medium (LISM). The ultimate source of cosmic ray anisotropy is the energy, pitch angle, and spatial dependence of the cosmic ray distribution function in the LISM. Because young nearby cosmic ray sources can make a special contribution to the cosmic ray anisotropy, the anisotropy depends on the source age, distance and magnetic connection, and particle diffusion of these cosmic rays, all of which make the anisotropy sensitive to the particle energy. When mapped through the magnetic and electric field of a magnetohydrodynamic model heliosphere, the large-scale dipolar and bidirectional interstellar anisotropy patterns become distorted if they are seen from Earth, resulting in many small structures in the observations. Best fits to cosmic ray anisotropy measurements have allowed us to estimate the particle density gradient and pitch angle anisotropies in the LISM. It is found that the heliotail, hydrogen deflection plane, and the plane perpendicular to the LISM magnetic field play a special role in distorting cosmic ray anisotropy. These features can lead to an accurate determination of the LISM magnetic field direction and polarity. The effects of solar cycle variation, the Sun's coronal magnetic field, and turbulence in the LISM and heliospheric magnetic fields are minor but clearly visible at a level roughly equal to a fraction of the overall anisotropy amplitude. The heliospheric influence becomes stronger at lower energies. Below 1 TeV, the anisotropy is dominated by small-scale patterns produced by disturbances in the heliosphere.

Zhang, Ming; Zuo, Pingbing; Pogorelov, Nikolai

2014-07-01

222

Crustal Anisotropy in Eastern Tibet  

NASA Astrophysics Data System (ADS)

A growing list and wide variety of evidence suggests that the Tibetan middle and lower crust is warm and presumably ductile. This list includes extensive Cenozoic volcanism, low electrical resistivity, satellite magnetic anomalies consistent with a raised Curie isotherm, and the lack of mid- to lower-crustal earthquakes. Seismological observations include strong P-to-S conversion bright-spots on active source wide-angle reflection data, strong crustal attenuation, pervasive crustal low velocity zones (LVZs) inferred from receiver functions or surface wave dispersion that are strongest near the periphery of the Plateau, and strong radial anisotropy, characteristic of significant shear strains, in the middle crust. Yet, surface strain rates and finite strains, as measured by GPS and SKS splitting fast axis orientations, respectively, appear to imply a vertical coherence of deformation from the uppermost crust into the upper mantle. Thus, questions about the mechanism of deformation of the Tibetan crust remain, including: (1) To what extent is deformation of the middle crust localized in a channel (channel flow) and hence different from that above and perhaps below it? (2) Or, conversely, to what extent is deformation of the entire lithosphere vertically coherent? Observations of crustal anisotropy can help to answer these questions, but although such observations are widespread, for the most part they remain either localized or so poorly resolved that exploiting such observations to answer these questions remains difficult. We summarize recently constructed models of radial and azimuthal anisotropy in the middle and lower crust beneath eastern Tibet. The models result from Bayesian Monte Carlo inversion of surface wave dispersion derived from ambient noise cross-correlations for Rayleigh and Love waves using Chinese Earthquake Array and PASSCAL data in and surrounding Tibet. (1) Significant middle-to-lower crustal radial anisotropy characterizes the crust beneath most of E. Tibet, but vanishes toward the S. China block in the east and north of the Kunlun fault in the north. Radial anisotropy is confined to the middle to perhaps lower crust with an upper boundary at about 20 km depth and a less well resolved lower boundary, but, on average, radial anisotropy is found between 40%-80% of the Moho depth. (2) In the upper crust, azimuthal anisotropy is strong (~4%) and fast axis orientations are roughly parallel to strikes of major strike-slip faults. Azimuthal anisotropy is weak in the middle crust (<2%) where radial anisotropy is strongest and increases in the lower crust. The azimuthal anisotropy in the lower crust and uppermost mantle is coherent with upper crustal anisotropy across some but not all of E. Tibet. On a preliminary basis, the seismological evidence is consistent with channel flow in the middle crust but with vertically coherent deformation across only part of E. Tibet. The marked radial anisotropy in the middle crust may result from layers of partial melt, which would not affect shear on vertical planes.

Ritzwoller, M. H.; Xie, J.; Shen, W.; Molnar, P. H.; Yang, Y.; Zhou, L.; Zheng, Y.

2012-12-01

223

Transcriptome analysis of amoeboid and ramified microglia isolated from the corpus callosum of rat brain  

PubMed Central

Background Microglia, the resident immune cells of the central nervous system (CNS), have two distinct phenotypes in the developing brain: amoeboid form, known to be amoeboid microglial cells (AMC) and ramified form, known to be ramified microglial cells (RMC). The AMC are characterized by being proliferative, phagocytic and migratory whereas the RMC are quiescent and exhibit a slow turnover rate. The AMC transform into RMC with advancing age, and this transformation is indicative of the gradual shift in the microglial functions. Both AMC and RMC respond to CNS inflammation, and they become hypertrophic when activated by trauma, infection or neurodegenerative stimuli. The molecular mechanisms and functional significance of morphological transformation of microglia during normal development and in disease conditions is not clear. It is hypothesized that AMC and RMC are functionally regulated by a specific set of genes encoding various signaling molecules and transcription factors. Results To address this, we carried out cDNA microarray analysis using lectin-labeled AMC and RMC isolated from frozen tissue sections of the corpus callosum of 5-day and 4-week old rat brain respectively, by laser capture microdissection. The global gene expression profiles of both microglial phenotypes were compared and the differentially expressed genes in AMC and RMC were clustered based on their functional annotations. This genome wide comparative analysis identified genes that are specific to AMC and RMC. Conclusions The novel and specific molecules identified from the trancriptome explains the quiescent state functioning of microglia in its two distinct morphological states.

2012-01-01

224

Clinical significance of corpus callosum atrophy in a mixed elderly population.  

PubMed

Corpus callosum (CC) is the main tract connecting the hemispheres, but the clinical significance of CC atrophy is poorly understood. The aim of this work was to investigate clinical and functional correlates of CC atrophy in subjects with age-related white matter changes (ARWMC). In 569 elderly subjects with ARWMC from the Leukoaraiosis And DISability (LADIS) study, the CC was segmented on the normalised mid-sagittal magnetic resonance imaging (MRI) slice and subdivided into five regions. Correlations between the CC areas and subjective memory complaints, mini mental state examination (MMSE) score, history of depression, geriatric depression scale (GDS) score, subjective gait difficulty, history of falls, walking speed, and total score on the short physical performance battery (SPPB) were analyzed. Significant correlations between CC atrophy and MMSE, SPPB, and walking speed were identified, and the CC areas were smaller in subjects with subjective gait difficulty. The correlations remained significant after correction for ARWMC grade. In conclusion, CC atrophy was independently associated with impaired global cognitive and motor function in subjects with ARWMC. PMID:16797787

Ryberg, C; Rostrup, E; Stegmann, M B; Barkhof, F; Scheltens, P; van Straaten, E C W; Fazekas, F; Schmidt, R; Ferro, J M; Baezner, H; Erkinjuntti, T; Jokinen, H; Wahlund, L-O; O'brien, J; Basile, A M; Pantoni, L; Inzitari, D; Waldemar, G

2007-06-01

225

Case study: A patient with agenesis of the corpus callosum with minimal associated neuropsychological impairment.  

PubMed

This is a case study of an 88-year-old man who presented with agenesis of the corpus callosum and colpocephaly. Symptomatically, he reported a sudden onset of mild, intermittent left hand apraxia, but denied any previous manifestations consistent with this type of brain malformation. The patient underwent neuroimaging, evaluation by neurology, and comprehensive neuropsychological testing to determine the nature of any other associated impairments. Test results indicated that he was, with a few exceptions, neuropsychologically normal. He performed well on tests that are highly sensitive to acquired brain dysfunction. His most notable deficit was failed performance in the simultaneous and coordinated use of both hands in using tactile and proprioceptive feedback on the Tactual Performance Test. This case is discussed in terms of plasticity of the developing brain, including compensatory mechanisms, highlighting the variability in clinical outcome in the context of congenital brain malformation. This case study illustrates the strong influence of cerebral plasticity as well as a possible circumscribed manifestation of interhemispheric disconnection. PMID:23962137

Brescian, Natalie E; Curiel, Rosie E; Gass, Carlton S

2014-12-01

226

Automatic segmentation of corpus callosum using Gaussian mixture modeling and Fuzzy C means methods.  

PubMed

This paper presents a comparative study of the success and performance of the Gaussian mixture modeling and Fuzzy C means methods to determine the volume and cross-sectionals areas of the corpus callosum (CC) using simulated and real MR brain images. The Gaussian mixture model (GMM) utilizes weighted sum of Gaussian distributions by applying statistical decision procedures to define image classes. In the Fuzzy C means (FCM), the image classes are represented by certain membership function according to fuzziness information expressing the distance from the cluster centers. In this study, automatic segmentation for midsagittal section of the CC was achieved from simulated and real brain images. The volume of CC was obtained using sagittal sections areas. To compare the success of the methods, segmentation accuracy, Jaccard similarity and time consuming for segmentation were calculated. The results show that the GMM method resulted by a small margin in more accurate segmentation (midsagittal section segmentation accuracy 98.3% and 97.01% for GMM and FCM); however the FCM method resulted in faster segmentation than GMM. With this study, an accurate and automatic segmentation system that allows opportunity for quantitative comparison to doctors in the planning of treatment and the diagnosis of diseases affecting the size of the CC was developed. This study can be adapted to perform segmentation on other regions of the brain, thus, it can be operated as practical use in the clinic. PMID:23871683

?çer, Semra

2013-10-01

227

Light microscopic identification of immature glial cells in semithin sections of the developing mouse corpus callosum.  

PubMed Central

Four distinct types of glial cell were recognized in the corpus callosum of young postnatal mice: the early glioblast; the small glioblast; the large glioblast; and the young astrocyte. As well as these, mature microglia could be recognized from birth. In semithin, toluidine blue stained sections early glioblasts had large, fair to moderately stained nuclei, and a thin rim of pale cytoplasm; small glioblasts had small, dark nuclei and a rim of darkly stained cytoplasm; large glioblasts had moderately unevenly stained nuclei and a thin rim of moderately stained cytoplasm; and young astrocytes had fairly small nuclei, moderately stained cytoplasm, and one or more processes, which could usually be seen extending for 5 mum or more from the perikaryon. Differential glial counts using the criteria described above, in conjunction with electron microscopic analysis, suggested that early glioblasts gave rise to small glioblasts and large glioblasts; that small glioblasts gave rise directly to astrocytes, large glioblasts, oligodendrocytes and possibly microglia; that large glioblasts formed oligodendrocytes only, and might be immature light oligodendrocytes; and that part of the microglial population might arise from vascular pericytes. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 10 Fig. 11 Fig. 12 Fig. 13 Fig. 14

Sturrock, R R

1976-01-01

228

A developmental study of sex and age interactions in the human corpus callosum.  

PubMed

Regional analysis of the corpus callosum (CC) has demonstrated that the development of this fiber tract is sexually dimorphic. Midsagittal CC tracings from magnetic resonance images (MRIs) of 73 pairs of age-matched (age 2-79 years) males and females were digitized using computer assisted software. Area, axis length, perimeter, and 99 widths were obtained. Widths were grouped into the following regions based upon prior factor analysis: widths 3-18 (W3-18), W22-39, W49-62, W65-74, W77-85, W89-94, and W95-99. Trend analyses were performed with Sex and Age (blocked into 10-year bins) as independent variables. Higher order Sex by Age interactions were significant in regions W3-18 and W22-39 and were marginal in W95-99. In all 3 regions, females did not attain maximum width until Age 41-50 whereas males had peaked at 20 years and declined thereafter. There were no significant interactions between Sex and Age in the remaining CC regions, nor were there any dramatic decreases once maximum width was reached in adulthood. These results suggest that sex differences may also exist in CC ultrastructure over the human lifespan. PMID:1606684

Cowell, P E; Allen, L S; Zalatimo, N S; Denenberg, V H

1992-04-24

229

Improved corpus callosum area measurements by analysis of adjoining parasagittal slices  

PubMed Central

The corpus callosum (CC) is a bundle of approximately 180 million axons connecting homologous areas of the left and right cerebral cortex. Because CC projections are topographically organized, regional CC morphological abnormalities may reflect regional cortical developmental abnormalities. We assess the variance characteristics of three CC area measurement techniques by comparing a single midsagittal slice versus three slices (midsagittal plus one parasagittal on each side) and five slices (midsagittal plus two parasagittal on each side). CC images were partitioned into five subregions using the Hofer–Frahm scheme under the three methods and variance was examined via two complementary data sets. In the first, to control for intersubject variability, 12 scans were acquired from a single subject over the course of 3 h. In the second, we used scans from 56 healthy male volunteers between the ages of 10 and 27 years (mean=17.47, S.D.=3.42). Increasing the number of slices from one to three to five diminished the coefficient of variation (CV) within subregions and increased the power to detect differences between groups. A power analysis was conducted for the sample under each method to determine the sample size necessary to discern a given percent change (delta) ranging from 1 to 20% iteratively.

Wade, Benjamin Seavey Cutler; Stockman, Michael; McLaughlin, Michael Joseph; Raznahan, Armin; Lalonde, Francois; Giedd, Jay Norman

2014-01-01

230

Corpus callosum anatomy in right-handed homosexual and heterosexual men.  

PubMed

The results of several studies have shown that homosexual men have an increased prevalence of non-right-handedness and atypical patterns of hemispheric functional asymmetry. Non-right-handedness in men has been associated with increased size of the corpus callosum (CC), particularly of the isthmus, which is the posterior region of the callosal body connecting parietotemporal cortical regions. We hypothesized that isthmal area would be greater in homosexual men, even among right handers. Twelve homosexual and ten heterosexual healthy young men, all consistently right-handed, underwent a research-designed magnetic resonance imaging scan. We found that the isthmal area was larger in the homosexual group, adding to the body of findings of structural brain differences between homosexual and heterosexual men. This result suggests that right-handed homosexual men have less marked functional asymmetry compared to right-handed heterosexual men. The results also indicate that callosal anatomy and laterality for motoric functions are dissociated in homosexual men. A logistic regression analysis to predict sexual orientation category correctly classified 21 of the 22 men (96% correct classification) based on area of the callosal isthmus, a left-hand performance measure, water level test score, and a measure of abstraction ability. Our findings indicate that neuroanatomical structure and cognition are associated with sexual orientation in men and support the hypothesis of a neurobiological basis in the origin of sexual orientation. PMID:17975723

Witelson, Sandra F; Kigar, Debra L; Scamvougeras, Anton; Kideckel, David M; Buck, Brian; Stanchev, Peter L; Bronskill, Michael; Black, Sandra

2008-12-01

231

Structural and functional brain rewiring clarifies preserved interhemispheric transfer in humans born without the corpus callosum.  

PubMed

Why do humans born without the corpus callosum, the major interhemispheric commissure, lack the disconnection syndrome classically described in callosotomized patients? This paradox was discovered by Nobel laureate Roger Sperry in 1968, and has remained unsolved since then. To tackle the hypothesis that alternative neural pathways could explain this puzzle, we investigated patients with callosal dysgenesis using structural and functional neuroimaging, as well as neuropsychological assessments. We identified two anomalous white-matter tracts by deterministic and probabilistic tractography, and provide supporting resting-state functional neuroimaging and neuropsychological evidence for their functional role in preserved interhemispheric transfer of complex tactile information, such as object recognition. These compensatory pathways connect the homotopic posterior parietal cortical areas (Brodmann areas 39 and surroundings) via the posterior and anterior commissures. We propose that anomalous brain circuitry of callosal dysgenesis is determined by long-distance plasticity, a set of hardware changes occurring in the developing brain after pathological interference. So far unknown, these pathological changes somehow divert growing axons away from the dorsal midline, creating alternative tracts through the ventral forebrain and the dorsal midbrain midline, with partial compensatory effects to the interhemispheric transfer of cortical function. PMID:24821757

Tovar-Moll, Fernanda; Monteiro, Myriam; Andrade, Juliana; Bramati, Ivanei E; Vianna-Barbosa, Rodrigo; Marins, Theo; Rodrigues, Erika; Dantas, Natalia; Behrens, Timothy E J; de Oliveira-Souza, Ricardo; Moll, Jorge; Lent, Roberto

2014-05-27

232

Differences in corpus callosum volume and diffusivity between temporal and frontal lobe epilepsy.  

PubMed

We analyzed volume and diffusivity measures of the corpus callosum (CC) in patients with temporal (TLE) and frontal (FLE) lobe epilepsy in comparison with healthy subjects. On high-resolution T1-weighted scans of 18 controls and 44 patients the volumes (cm(3)) of Witelson regions (WRs) and the entire CC were measured. The apparent diffusion coefficients (ADCs, 10(-5)mm(2)s(-1)) for the entire CC and three areas of interest were measured from co-registered ADC maps. The CC of patients with TLE and FLE, corrected for total brain volume, was smaller than that of controls. Patients' ADC values were higher than those of controls. Findings were significant for WR1, WR2, and WR6, the CC regions connecting the frontal and temporal lobes. Patients with FLE had smaller WR1 and higher ADC values; in patients with TLE, the findings were similar for WR6. Atrophy and increased diffusivity in subregions of the CC connecting homotopic contralateral cortical regions indicate anatomical abnormalities extending beyond the epileptogenic zone in FLE and TLE. PMID:20920892

O'Dwyer, R; Wehner, T; LaPresto, E; Ping, Liu; Tkach, J; Noachtar, S; Diehl, B

2010-11-01

233

Fraction Models  

NSDL National Science Digital Library

This interactive activity allows users the ability to explore different representations for fractions and how they are equivalent to mixed numbers, decimals, and percentages. Users adjust the numerator (up to 100) and the denominator (1 to 25) in order to see a visual representation of the fraction. The visual representation can be seen as a length, area, region, or set model. Users also have the ability to keep track of the equivalent forms of fractions in a table. Instructions and exploration questions are given.

2011-01-01

234

Fraction Fanatic  

NSDL National Science Digital Library

We are going to practice our fraction skills with addition, subtraction, and equivalents. Let\\'s save the bugs with Math Splat. Check your skill with Equivalents. Get it straight with Lines and Circles. ...

Jackson, Ms.

2007-10-25

235

Fraction Strip  

NSDL National Science Digital Library

This interactive Flash applet displays eight fraction strips (bars, ribbons) of unit length. Denominators range from halves to twelfths. Segments of each bar can be dragged and dropped for close comparisons.

2012-01-01

236

Adding Fractions  

NSDL National Science Digital Library

In this web-based tutorial, students learn procedures for adding fractions with like and unlike denominators. The tutorial includes visual representations of the problems using pizzas, animations of the algorithm, and links to related lessons, worksheets, and practice problems.

Website, Math I.

2011-09-23

237

Estimators for CMB statistical anisotropy  

NASA Astrophysics Data System (ADS)

We use quadratic maximum-likelihood (QML) estimators to constrain models with Gaussian but statistically anisotropic CMB fluctuations, using CMB maps with realistic sky-coverage and instrumental noise. This approach is optimal when the anisotropy is small, or when checking for consistency with isotropy. We demonstrate the power of the QML approach by applying it to the WMAP data to constrain several models which modulate the observed CMB fluctuations to produce a statistically anisotropic sky. We first constrain an empirically motivated spatial modulation of the observed CMB fluctuations, reproducing marginal evidence for a dipolar modulation pattern with amplitude 7% at l?60, but demonstrate that the effect decreases at higher multipoles and is ?1% at l˜500. We also look for evidence of a direction-dependent primordial power spectrum, finding a very statistically significant quadrupole signal nearly aligned with the ecliptic plane; however we argue this anisotropy is largely contaminated by observational systematics. Finally, we constrain the anisotropy due to a spatial modulation of adiabatic and isocurvature primordial perturbations, and discuss the close relationship between anisotropy and non-Gaussianity estimators.

Hanson, Duncan; Lewis, Antony

2009-09-01

238

Planar anisotropy in amorphous semiconductors  

Microsoft Academic Search

Theoretical work has been carried out towards the planar (non-axial) anisotropy in amorphous semiconductors. The spontaneous polarization (Ps) vector seems to move into the plane leaving the axial characters. The work has been done in zero and non-zero electric field modes. Existence of easy, hard axes and the existence of cones have been demonstrated. In the case of cones Ps

W. I. Khan; A. E. Rakhshani; A. Y. M. Al-Qenaie

1996-01-01

239

Planar anisotropy in amorphous semiconductors  

Microsoft Academic Search

Theoretical work has been carried out towards the planar (non-axial) anisotropy in amorphous semiconductors. The spontaneous polarization (Ps) vector seems to move into the plane leaving the axial characters. The work has been done in zero and non-zero electric field modes. Existence of easy, hard axes and the existence of cones have been demonstrated. In the case of cones, Ps

W. I. Khan; A. E. Rakhshani; A. Y. M. Al-Qenaie

1996-01-01

240

Anisotropy of machine building materials  

NASA Technical Reports Server (NTRS)

The results of experimental studies of the anisotropy of elastic and strength characteristics of various structural materials, including pressure worked metals and alloys, laminated fiberglass plastics, and laminated wood plastics, are correlated and classified. Strength criteria under simple and complex stresses are considered as applied to anisotropic materials. Practical application to determining the strength of machine parts and structural materials is discussed.

Ashkenazi, Y. K.

1981-01-01

241

Collapse anisotropy for massive stars  

Microsoft Academic Search

A series of numerical experiments to simulate the evolution of massive binary systems is described. The simulations yielded an estimate of 70-10 km\\/s for the kick velocity of a neutron star following the collapse of a normal star. It is demonstrated that kick velocity can be used as a measure of the mean anisotropy of the entire collapse process. Some

V. G. Kornilov; V. M. Lipunov

1984-01-01

242

Fantastic Fractions  

NSDL National Science Digital Library

In this math lesson, learners compare pattern blocks to visually understand halves, thirds, and sixths. First, learners look at all the different ways they can make a hexagon using other pattern block pieces. After the investigation, they represent their solutions using pictures and fractional notation. Then, learners play a game to increase their understanding of equivalence and fractions. The game can be played on its own--with or without the preceding lesson.

Lessonplans, Utah

2012-10-22

243

Fraction Pieces  

NSDL National Science Digital Library

Students use this Java applet to explore pieces representing fractional portions of a circle or square. This virtual manipulative can be used to explore patterns and symmetry with young children, or to develop fluency in fraction operations and equivalency in older students. Instructions for using the applet and teaching ideas for parents/teachers are available through the links at the top of the page.

2005-01-01

244

Magnetic anisotropy in obliquely deposited cobalt films  

Microsoft Academic Search

The anisotropy field in cobalt films deposited obliquely by sputtering was separated into the magnetocrystalline anisotropy field, Hk(cryst), and the anisotropy field due to the shape anisotropy, Hk(shape), based on the {0002} pole figure. The incidence angle was 45° and the substrate temperature was 332 K. The film thickness ranged from 0.4 to 3.8 ?m. The thickness dependence of Hk(shape)

K. Itoh; K. Hara; M. Kamiya; K. Okamoto; T. Hashimoto; H. Fujiwara

1995-01-01

245

The microwave background anisotropies: Observations  

PubMed Central

Most cosmologists now believe that we live in an evolving universe that has been expanding and cooling since its origin about 15 billion years ago. Strong evidence for this standard cosmological model comes from studies of the cosmic microwave background radiation (CMBR), the remnant heat from the initial fireball. The CMBR spectrum is blackbody, as predicted from the hot Big Bang model before the discovery of the remnant radiation in 1964. In 1992 the cosmic background explorer (COBE) satellite finally detected the anisotropy of the radiation—fingerprints left by tiny temperature fluctuations in the initial bang. Careful design of the COBE satellite, and a bit of luck, allowed the 30 ?K fluctuations in the CMBR temperature (2.73 K) to be pulled out of instrument noise and spurious foreground emissions. Further advances in detector technology and experiment design are allowing current CMBR experiments to search for predicted features in the anisotropy power spectrum at angular scales of 1° and smaller. If they exist, these features were formed at an important epoch in the evolution of the universe—the decoupling of matter and radiation at a temperature of about 4,000 K and a time about 300,000 years after the bang. CMBR anisotropy measurements probe directly some detailed physics of the early universe. Also, parameters of the cosmological model can be measured because the anisotropy power spectrum depends on constituent densities and the horizon scale at a known cosmological epoch. As sophisticated experiments on the ground and on balloons pursue these measurements, two CMBR anisotropy satellite missions are being prepared for launch early in the next century.

Wilkinson, David

1998-01-01

246

Anisotropy of the cosmic microwave background radiation  

Microsoft Academic Search

Theoretical predictions of the angular anisotropy in the cosmic microwave background radiation on both small and large angular scales are presented, and the effect of massive neutrinos on both the background radiation anisotropy and on the galaxy correlation function over very large scales is reviewed. Current observations show that the quadrupole anisotropy provides the greatest constraint on theory, and the

J. Silk

1981-01-01

247

Diffusion creep, grain rotation and mantle anisotropy  

Microsoft Academic Search

The mantle deforms by some combination of diffusion creep and dislocation creep. It is well established that dislocation creep gives rise to crystallographic preferred orientations (CPO) which in turn lead to seismic anisotropy. Consequently seismic anisotropy may be interpreted as indicating the action of dislocation creep, and an absence of anisotropy as indicating diffusion creep. One assumption involved is that

J. Wheeler

2007-01-01

248

Intrinsic versus extrinsic seismic anisotropy: The radial anisotropy in reference Earth models  

NASA Astrophysics Data System (ADS)

anisotropy usually arises from different mechanisms, which include lattice or crystallographic preferred orientation (LPO, CPO), alignment of cracks with or without fluid inclusions, fine layering, or partial melting. This makes the interpretation of anisotropy in terms of "intrinsic" (produced by LPO, CPO) versus "extrinsic" (produced by other mechanisms) properties difficult and nonunique. The radial anisotropy in the one-dimensional, global spherically symmetric reference Earth is usually claimed to be intrinsic. Here we explore whether the radial anisotropy in one-dimensional reference Earth models including preliminary reference Earth model (PREM) and the constrained reference Earth model ACY400 contains extrinsic anisotropy, especially in relation to fine layering. We conclude that as well as intrinsic anisotropy, extrinsic anisotropy introduced by finely layered models, can be considered to explain the lithospheric anisotropy in PREM, but cannot explain alone its asthenospheric anisotropy. We also find that radial anisotropy in model ACY400 is mainly intrinsic due to its petrological constraints.

Wang, Nian; Montagner, Jean-Paul; Fichtner, Andreas; Capdeville, Yann

2013-08-01

249

Social communication in young children with traumatic brain injury: relations with corpus callosum morphometry.  

PubMed

The purpose of the present investigation was to characterize the relations of specific social communication behaviors, including joint attention, gestures, and verbalization, with surface area of midsagittal corpus callosum (CC) subregions in children who sustained traumatic brain injury (TBI) before 7 years of age. Participants sustained mild (n=10) or moderate-severe (n=26) noninflicted TBI. The mean age at injury was 33.6 months; mean age at MRI was 44.4 months. The CC was divided into seven subregions. Relative to young children with mild TBI, those with moderate-severe TBI had smaller surface area of the isthmus. A semi-structured sequence of social interactions between the child and an examiner was videotaped and coded for specific social initiation and response behaviors. Social responses were similar across severity groups. Even though the complexity of their language was similar, children with moderate-severe TBI used more gestures than those with mild TBI to initiate social overtures; this may indicate a developmental lag or deficit as the use of gestural communication typically diminishes after age 2. After controlling for age at scan and for total brain volume, the correlation of social interaction response and initiation scores with the midsagittal surface area of the CC regions was examined. For the total group, responding to a social overture using joint attention was significantly and positively correlated with surface area of all regions, except the rostrum. Initiating joint attention was specifically and negatively correlated with surface area of the anterior midbody. Use of gestures to initiate a social interaction correlated significantly and positively with surface area of the anterior and posterior midbody. Social response and initiation behaviors were selectively related to regional callosal surface areas in young children with TBI. Specific brainbehavior relations indicate early regional specialization of anterior and posterior CC for social communication. PMID:21807088

Ewing-Cobbs, Linda; Prasad, Mary R; Swank, Paul; Kramer, Larry; Mendez, Donna; Treble, Amery; Payne, Christa; Bachevalier, Jocelyne

2012-05-01

250

Characterization of NO-producing neurons in the rat corpus callosum  

PubMed Central

Introduction The aim of this study was to determine the presence and distribution of nitric oxide (NO)-producing neurons in the rat corpus callosum (cc). Material and methods To investigate this aspect of cc organization we used nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and neuronal NO synthase (nNOS) immunocytochemistry. Results Intense NADPH-d-positive (NADPH-d+) neurons were found along the rostrocaudal extension of the cc (sagittal sections). They were more numerous in the lateral cc and gradually decreased in the more medial regions, where they were very few or absent. The Golgi-like appearance of NADPH-d+ intracallosal neurons allowed dividing them into five morphological types: (1) bipolar; (2) fusiform; (3) round; (4) polygonal; and (5) pyramidal. The number of NADPH-d+ neurons (both hemispheres) was counted in two brains using 50-?m thick sections. In the first brain, counts involved 145 sections and neurons were 2959; in the second, 2227 neurons were counted in 130 sections. The distribution and morphology of nNOS-immunopositive (nNOSIP) neurons was identical to that of NADPH-d+neurons. Some of these neurons were observed in the cc ependymal region, where they might be in contact with cerebrospinal fluid (CSF), monitoring its composition, pH, and osmolality changes, or playing a role in regulating the synthesis and release of several peptides. The somatic, dendritic, and axonal processes of many NADPH-d+/nNOSIP neurons were closely associated with intracallosal blood vessels. Conclusions Such close relationship raises the possibility that these neurons are a major source of NO during neural activity. As NO is a potent vasodilator, these findings strongly suggest that NO-positive neurons transduce neuronal signals into vascular responses in selected cc regions, thus giving rise to hemodynamic changes detectable by neuroimaging.

Barbaresi, Paolo; Fabri, Mara; Mensa, Emanuela

2014-01-01

251

Can we understand rocks without anisotropy?  

NASA Astrophysics Data System (ADS)

An effectively isotropic heterogeneous medium subject to deformation should develop compositional layering parallel to stretching direction. A layered anisotropic rock subject to layer-parallel extension may undergo mechanical instability leading to internal boudinage development. The question that arises is as to whether the formation of layering could be hampered by boudinage formation before the compositional layering is well developed. With regard to the issue, the three critical questions are: (1) How does the rock fabric evolution depend on the mechanical properties of rock constituents and the initial microstructure? (2) How does the mechanical (viscous) anisotropy relate to the shape anisotropy of a composite rock? (3) How does the internal boudinage development manifest in a rock consisting of elongated elements rather than well-developed layers? I will numerically investigate the development of shape preferred orientation and mechanical anisotropy in a composite two-phase rock undergoing stretching. A two-dimensional inclusion-host type of composite, in which an interconnected host embeds non-overlapping inclusions, is considered. Different inclusion fractions, shapes and size distributions are studied. The initial spatial distribution of the inclusions is intended to be random, statistically homogeneous (no clustering) and isotropic. In a series of complementary simulation runs, periodic inclusion arrays are analyzed. Both the inclusion and host materials are considered as viscous fluids and the intrinsic viscosities of the inclusion and the host phases are isotropic. A coherent inclusion-host interface is assumed and interfacial processes such as surface tension or diffusional mass transfer are neglected. The deformation is studied in the Stokes limit and under no gravity. A self-developed FEM code (www.milamin.org, Dabrowski et al., 2008) is used to find the velocity vectors at the inclusion interfaces. Unstructured triangular computational meshes fitting all the internal inclusion boundaries are used in the simulations. To achieve the necessary resolution of the complex geometry of evolving inclusion-host interfaces, a large number of computational points is required. References: Dabrowski, M., M. Krotkiewski, and D. W. Schmid MILAMIN: MATLAB-based finite element method solver for large problems, Geochem. Geophys. Geosyst., 9, Q04030, 2008

Dabrowski, Marcin

2014-05-01

252

Cup-Drawing Behavior of High-Strength Steel Sheets Containing Different Volume Fractions of Martensite  

Microsoft Academic Search

Planar anisotropy and cup-drawing behavior were investigated for high-strength steel sheets containing different volume fractions of martensite. Macrotexture analysis using XRD was conducted to capture the effect of crystallographic orientation on the planar anisotropy of high-strength steel sheets. A phenomenological yield function, Yld96, which accounts for the anisotropy of yield stress and r-values, was implemented into ABAQUS using the user

Shi-Hoon Choi; Dae-Wan Kim; Hoe-Seok Yang; Seong-Ho Han; Jeong Whan Yoon

2010-01-01

253

Matching Fractions  

NSDL National Science Digital Library

In this interactive game similar to Concentration(TM) students match fractions (1/2, 1/3, 3/4, and 5/9) to images that represent those fractions. This game can be played in pairs with the printed out cards or as a whole class on the interactive white board (IWB). This resource includes teacher notes with suggestions for introducing the game, discussion questions, support suggestions, a set of cards to be printed (PDF), a blank set of cards to make your own (PDF), and a full screen version of the game.

Team, Nrich

2012-01-01

254

LPO Induced Seismic Anisotropy in Naturally and Experimentally Deformed UHP Eclogites  

NASA Astrophysics Data System (ADS)

Eclogites with strong plastic deformation often show marked anisotropy of petrophysical properties. We report here seismic velocities and anisotropies of ultra-high-pressure eclogites calculated from the lattice preferred orientations (LPOs) of their constituent minerals (garnet, omphacite, quartz and rutile) and single crystal elastic properties using the Unicef Careware software package. The effects of garnet and omphacite layering in eclogite deformed to high strain were not included in calculation which could underestimate seismic anisotropy. We compared calculated results with measured results in similar eclogites. Our results suggest: 1) All minerals except garnet show strong seismic anisotropy (AVp = 23.0 - 40.9 %, Max. AVs = 18.51 - 47.07 %). The average seismic velocity is high in garnet and rutile, moderate in omphacite and coesite, and low in quartz. 2) The deformed eclogites have Vpmax (8.33 - 8.75 km/s) approximately parallel to foliation and lineation, Vpmin (8.25 - 8.62 km/s) approximately normal to foliation (S) and lineation (L) and Vp anisotropies of 1.0-1.7 %. Their Vs are 4.93-4.97 km/s, with maximum anisotropy (0.73-1.78 %) at ~45° to both S and L and minimum anisotropies normal to L in S. Their Vs1 polarization planes are approximately parallel to S. The Vp and Vs of eclogite under UHP peak metamorphic conditions (P = 3-5 GPa, T = 1173-1373 K) are estimated to be 3.4-7.2 % and 6.3-12.1 % higher than those at ambient pressure and temperature conditions, respectively. 3) Omphacite dominates the anisotropy of eclogite while garnet reduces the anisotropy and increases seismic velocity. The influence of rutile is negligible due to its trivial volume fraction. 4) The seismic velocity of eclogite decreases with volume fraction of omphacite and is minimum in omphacitite. In contrast, the anisotropy of eclogite increases with volume fraction of omphacite and is maximum in omphacitite. Omphacitite has seismic velocities reduced by 6-8 % and anisotropies increased to 3-4 % compared to garnetite. The calculated seismic properties of eclogite are comparable to those measured in the laboratory. Moreover, the calculations provide true 3D information on eclogite seismic properties and the corresponding mineral physical interpretations.

Zhang, J.; Green, H. W.

2006-12-01

255

Artificial anisotropy and polarizing filters  

NASA Astrophysics Data System (ADS)

The calculated spectral transmittance of a multilayer laser mirror is used to determine the effective index of the single layer equivalent to the multilayer stack. We measure the artificial anisotropy of photoresist thin films whose structure is a one-dimensional, subwavelength grating obtained from interference fringes. The limitation of the theory of the first-order effective index homogenization is discussed. We designed normal-incidence, polarizing coating and a polarization rotator by embedding anisotropic films in simple multilayer structures.

Flory, Francois; Escoubas, Ludovic; Lazarides, Basile

2002-06-01

256

Single-Molecule Anisotropy Imaging  

Microsoft Academic Search

A novel method, single-molecule anisotropy imaging, has been employed to simultaneously study lateral and rotational diffusion of fluorescence-labeled lipids on supported phospholipid membranes. In a fluid membrane composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, in which the rotational diffusion time is on the order of the excited-state lifetime of the fluorophore rhodamine, a rotational diffusion constant, Drot=7×107rad2\\/s, was determined. The lateral diffusion constant, measured

G. S. Harms; M. Sonnleitner; G. J. Schütz; H. J. Gruber; Th. Schmidt

1999-01-01

257

Azimuthal anisotropy of direct photons  

SciTech Connect

The electromagnetic bremsstrahlung produced by a quark interacting with nucleons or nuclei is azimuthally asymmetric. In the light-cone dipole approach this effect is related to the orientation dependent dipole cross section. Such a radiation anisotropy is expected to contribute to the azimuthal asymmetry of direct photons in pA and AA collisions, as well as in deep-inelastic scattering and in the production of dileptons.

Kopeliovich, B. Z. [Departamento de Fisica y Centro de Estudios Subatomicos, Universidad Tecnica Federico Santa Maria, Casilla 110-V, Valparaiso (Chile); Joint Institute for Nuclear Research, Dubna (Russian Federation); Pirner, H. J. [Institute for Theoretical Physics, University of Heidelberg, Philosophenweg 19, D-69120 Heidelberg (Germany); Rezaeian, A. H.; Schmidt, Ivan [Departamento de Fisica y Centro de Estudios Subatomicos, Universidad Tecnica Federico Santa Maria, Casilla 110-V, Valparaiso (Chile)

2008-02-01

258

Fraction Help  

NSDL National Science Digital Library

This FAQ page from the Teacher2Teacher service at The Math Forum @ Drexel contains many suggestions for learning about fractions. It includes ideas contributed by T2T Associates and teacher participants. There are links to Ask Dr. Math resources, children's literature connections, and outside websites with related resources.

The Math Forum @ Drexel

2000-01-01

259

Fraction War  

NSDL National Science Digital Library

This lesson is meant to be utilized as a means to enhance previous instruction of fractions that are greater than, or less than one. It is best utilized to build fluency, as this is meant to be a fast paced game to make learning interactive and engaging.

2013-01-24

260

Dividing Fractions  

NSDL National Science Digital Library

In this lesson students will explore the different methods available for dividing fractions through a student based investigation. The teacher will facilitate the discussion but the students will discover the different methods on their own or with a partner as they work through the different steps.

2012-10-17

261

Biaxial anisotropy in geoelectric prospecting  

NASA Astrophysics Data System (ADS)

In applied studies on electromagnetic well-logging and electric prospecting, a medium is supposed to be either isotropic or with conventional anisotropy of conductivity. However, in the meantime, there is a clear hint that a medium may exhibit even biaxial anisotropy; i.e., the resistances along all three directions X, and Y, Z are different. Based on the analytical solution by the method of separation of variables, the paper considers an algorithm for the calculation of the electromagnetic field in a layered medium with biaxial conductivity anisotropy involving an arbitrary direction of horizontal conductivities in each layer. In this case, the theoretical solution and the algorithm display substantial peculiarities, and the numerical implementation involves many complexities. These problems were examined and solved mainly due to the constant comparison with the calculations carried by the finite element method and their analysis. Programs for the calculation of electromagnetic fields in the frequency and time domains were developed, and results of geoelectric interest were obtained. For example, the excitement of a horizontally-layered section by a magnetic dipole produces a vertical electric component of the field.

Mogilatov, V. S.; Bespalov, A. N.

2009-09-01

262

Mechanical Anisotropy of Ankyrin Repeats  

PubMed Central

Red blood cells are frequently deformed and their cytoskeletal proteins such as spectrin and ankyrin-R are repeatedly subjected to mechanical forces. While the mechanics of spectrin was thoroughly investigated in vitro and in vivo, little is known about the mechanical behavior of ankyrin-R. In this study, we combine coarse-grained steered molecular dynamics simulations and atomic force spectroscopy to examine the mechanical response of ankyrin repeats (ARs) in a model synthetic AR protein NI6C, and in the D34 fragment of native ankyrin-R when these proteins are subjected to various stretching geometry conditions. Our steered molecular dynamics results, supported by AFM measurements, reveal an unusual mechanical anisotropy of ARs: their mechanical stability is greater when their unfolding is forced to propagate from the N-terminus toward the C-terminus (repeats unfold at ?60 pN), as compared to the unfolding in the opposite direction (unfolding force ? 30 pN). This anisotropy is also reflected in the complex refolding behavior of ARs. The origin of this unfolding and refolding anisotropy is in the various numbers of native contacts that are broken and formed at the interfaces between neighboring repeats depending on the unfolding/refolding propagation directions. Finally, we discuss how these complex mechanical properties of ARs in D34 may affect its behavior in vivo.

Lee, Whasil; Zeng, Xiancheng; Rotolo, Kristina; Yang, Ming; Schofield, Christopher J.; Bennett, Vann; Yang, Weitao; Marszalek, Piotr E.

2012-01-01

263

Metabolic alterations in corpus callosum may compromise brain functional connectivity in MTBI patients: an 1H-MRS study  

PubMed Central

After clinical resolution of signs and symptoms of mild traumatic brain injury (MTBI) it is still not clear if there are residual abnormalities of structural or functional brain networks. We have previously documented disrupted interhemispheric functional connectivity in “asymptomatic” concussed individuals during the sub-acute phase of injury. Testing of 15 normal volunteers (NV) and 15 subacute MTBI subjects was performed within 24 hours of clinical symptoms resolution and medical clearance for the first stage of aerobic activity. In this MRS study we report (a) both in the genu and splenium of the corpus callosum NAA/Cho and NAA/Cr ratios were significantly (p<0.05) lower in MTBI subjects shortly after the injury compared to NVs, and (b) the metabolic ratio NAA/Cho in the splenium significantly correlated with the magnitude of inter-hippocampal functional connectivity in normal volunteers, but not in MTBI. This novel finding supports our hypothesis that the functional disruption of interhemispheric brain networks in MTBI subjects results from compromised metabolic integrity of the corpus callosum and that this persists despite apparent clinical return to baseline.

Johnson, Brian; Zhang, Kai; Gay, Michael; Neuberger, Thomas; Horovitz, Silvina; Hallett, Mark; Sebastianelli, Wayne; Slobounov, Semyon

2011-01-01

264

Decision-making in individuals with agenesis of the corpus callosum: expectancy-valence in the Iowa Gambling Task.  

PubMed

Individuals with agenesis of the corpus callosum (ACC) can have intelligence within the normal range, but nevertheless have deficiencies in decision-making and complex novel problem-solving. The specific nature of these problems is not yet clearly understood. The Iowa Gambling Task was used to test decision-making ability and problem-solving in 40 individuals with complete or partial ACC (full-scale intelligence quotient >80) and 26 control participants. The expectancy-valence (EV) model was applied to the trial-by-trial responses of each participant to elucidate differences in decision processes utilized by each group. The ACC group had a lower overall net gain and fewer advantageous choices than controls, but these differences were not statistically significant. Within the EV model, individuals with ACC exhibited significantly higher attention to losses, less consistency in their choice strategy, and greater frequency of switching between decks. They also showed a tendency to be more influenced by recent trials. This outcome is similar to that seen in individuals with Asperger's disorder. Taken together, these results suggest that individuals with ACC have difficulty in inferring game contingencies and forming a coherent selection strategy, implicating the corpus callosum in these decision processes. PMID:22721927

Brown, Warren S; Anderson, Luke B; Symington, Melissa F; Paul, Lynn K

2012-08-01

265

Behavioural testing of standard inbred and 5HT(1B) knockout mice: implications of absent corpus callosum.  

PubMed

Rapid advances in biotechnology have created new demands for tests of mouse behaviour having both high reliability and high throughput for mass screening. This paper discusses several statistical and psychological factors pertinent to replication of results in different laboratories, and it considers the question of which inbred strains are best for test standardization. In this context, the problem of absent corpus callosum in the 129 strains is addressed with data from a recent study of six diverse tests of behaviour, and it is shown that effects of absent corpus callosum are usually nonsignificant and/or very small. Whether any 129 substrain is to be included in the list of standard strains depends on the goal of the standardization--collecting diverse phenotypic data on most available strains by a few expert investigators (the gold standard) or refining behavioural tests in order to establish a normal range of behaviour that can be used to judge a wider range of strains or even an individual mouse. PMID:11682089

Wahlsten, D; Crabbe, J C; Dudek, B C

2001-11-01

266

Fraction Tracks  

NSDL National Science Digital Library

This 17:29 minute video from the classic Annenberg Learner series illustrates the practice standard of communication about mathematics among a teacher and her students as they learn and play the "fraction tracks" game. The video also shows how activities like this allow students to use communication as a tool to deepen their understanding of mathematics. Three analysis questions are given at the end of the video to promote dialogue among teachers of mathematics.

Boston, Wgbh

1996-01-01

267

Fractional Triangles  

NSDL National Science Digital Library

This open-ended problem requires students to use the pattern of triangles on the given figure to divide the square into halves, thirds, sixths, and ninths. The problem asks students to find the part of the whole that is squares or triangles and then determine how these shapes represent each fraction of the whole. Included with this problem are teacher notes with suggestions for introducing the problem, discussion questions, support suggestions, and a printable version of the square.

Team, Nrich

2012-01-01

268

Isotope fractionation  

NASA Astrophysics Data System (ADS)

A rash of new controversy has emerged around the subject of mass-independent isotope fractionation effects, particularly in the case of the oxygen isotopes. To be sure, the controversy has been around for awhile, but it has been given new impetus by the results of a recent study by Mark H. Thiemens and John E. Heidenreich III of the University of California, San Diego (Science, March 4, 1983).Gustav Arrhenius has been trying to convince the planetary science community that chemical effects in isotope fractionation processes could explain observations in meteorites that appear to be outside of the traditionally understood mass-dependent fractionations (G. Arrhenius, J . L. McCrumb, and N. F. Friedman, Astrophys. Space Sci, 65, 297, 1974). Robert Clayton had made the basic observations of oxygen in carbonaceous chondrites that the slope of the ?17 versus ?18 line was 1 instead of the slope of ½ characteristic of terrestrial rocks and lunar samples (Ann. Rev. Nucl. Part. Sci., 28, 501, 1978). The mass-independent effects were ascribed to the apparent contribution of an ancient presolar system component of O16.

Bell, Peter M.

269

Interplay between local anisotropies in binuclear complexes.  

PubMed

A systematic study has been undertaken to determine how local distortions affect the overall (molecular) magnetic anisotropies in binuclear complexes. For this purpose we have applied a series of distortions to two binuclear Ni(II) model complexes and extracted the magnetic anisotropy parameters of multispin and giant-spin model Hamiltonians. Furthermore, local and molecular magnetic axes frames have been determined. It is shown that certain combinations of local distortions can lead to constructive interference of the local anisotropies and that the largest contribution to the anisotropic exchange does not arise from the second-rank tensor normally included in the multispin Hamiltonian, but rather from a fourth-rank tensor. From the comparison of the extracted parameters, simple rules are obtained to maximize the molecular anisotropy by controlling the local magnetic anisotropy, which opens the way to tune the anisotropy in binuclear or polynuclear complexes. PMID:24758235

Ruamps, Renaud; Maurice, Rémi; de Graaf, Coen; Guihéry, Nathalie

2014-05-01

270

Anisotropy of wall energy in orthoferrites  

Microsoft Academic Search

Wall anisotropy causes bubble domains to be elliptical. A formula relating the eccentricity of an elliptical bubble to the anisotropic wall energy is derived, and an experimental technique for measuring the wall anisotropy is described. In Sm0.55Tb0.45FeO3a measured anisotropy energy of 1.7 percent of the wall-energy density at room temperature is responsible for eccentricities as large as 0.4 at average

EDWARD DELLA TORRE; M. Dimyan

1970-01-01

271

Ion anisotropies in the outer Jovian magnetosphere  

Microsoft Academic Search

We present results from the Voyager 1 and 2 low-energy charged particle measurement of ion anisotropies in the outer Jovian magnetosphere (R> or approx. =20 R\\/sub J\\/). Theses anisotropies represent the first observed from an instrument rotating in the spin plane of Jupiter. For the several ion species ivestigated the first-order anisotropies are all strongly in the corotational sense throughout

J. F. Carbary; S. M. Krimigis; E. P. Keath; G. Gloeckler; W. I. Axford; T. P. Armstrong

1981-01-01

272

Statistical anisotropy from anisotropic inflation  

NASA Astrophysics Data System (ADS)

We review an inflationary scenario with the anisotropic expansion rate. An anisotropic inflationary universe can be realized by a vector field coupled with an inflaton, which can be regarded as a counter example to the cosmic no-hair conjecture. We show the generality of anisotropic inflation and derive a universal property. We formulate cosmological perturbation theory in anisotropic inflation. Using the formalism, we show that anisotropic inflation gives rise to the statistical anisotropy in primordial fluctuations. We also explain a method to test anisotropic inflation using the cosmic microwave background radiation.

Soda, Jiro

2012-04-01

273

Tensor anisotropy of cosmic rays  

NASA Astrophysics Data System (ADS)

Long-termobservations of the muon intensity of galactic cosmic rays at the Nagoya (35°10' N, 136°58' E) and Yakutsk (62°01' N, 129°43' E) stations have revealed amplitude-phase annual and semiannual oscillations of the semidiurnal variation. These oscillations are attributable to the properties of the cosmic-ray anisotropy tensor that result from shielding by the interplanetary magnetic field and solar-wind shear flow. The mentioned tensor is also shown to have a north-south asymmetry.

Krymsky, G. F.; Krivoshapkin, P. A.; Gerasimova, S. K.; Gololobov, P. Yu.

2014-04-01

274

Magnetic anisotropy and porosity of chondrites  

NASA Astrophysics Data System (ADS)

The measured magnetic anisotropy and porosity of various chondrites are found to be inversely correlated when they are considered by class of chondrites (E, H and L + LL). For chondrites with similar porosities, the anisotropies for H and E chondrites are smaller than for L and LL chondrites, which have lower metal contents. The anisotropy and porosity are not dependent on the metamorphic grade of chondrites. K-Ar ages of strongly anisotropic and/or less porous chondrites are younger than those of less anisotropic and/or more porous chondrites. These observations suggest that impacts which reset the K-Ar ages produced the anisotropy and reduced the porosity of chondrites.

Sugiura, N.; Strangway, D. W.

1983-01-01

275

Peripersonal spatial attention in children with spina bifida: Associations between horizontal and vertical line bisection and congenital malformations of the corpus callosum, midbrain, and posterior cortex  

Microsoft Academic Search

Horizontal and vertical line bisection was studied in 129 children and adolescents between 8 and 19 years of age, one group (n=32) of typically developing controls and one group (n=97) with spina bifida (SBM), a neurodevelopmental disorder associated with dysmorphology of the corpus callosum, posterior cortex, and midbrain. For each participant, structural brain MRIs were analyzed qualitatively to identify beaking

Maureen Dennis; Kim Edelstein; Jon Frederick; Kim Copeland; David Francis; Susan E. Blaser; Larry A. Kramer; James M. Drake; Michael Brandt; Ross Hetherington; Jack M. Fletcher

2005-01-01

276

Sex differences in the human corpus callosum microstructure: A combined T 2 myelin-water and diffusion tensor magnetic resonance imaging study  

Microsoft Academic Search

Sex differences in structure and organization of the corpus callosum (CC) have been identified in healthy adults and may be linked to distinct functional lateralization and processing in men and women. Magnetic resonance imaging (MRI) has facilitated noninvasive assessment of CC sex differences in morphology by volumetric imaging and microstructural organization by diffusion tensor imaging (DTI). Incorporation of recently developed

Fang Liu; Logi Vidarsson; Jeff D. Winter; Hien Tran; Andrea Kassner

2010-01-01

277

White matter anisotropy related to electrophysiology of first episode schizophrenia during NoGo inhibition.  

PubMed

Patients with schizophrenia have reduced execution functions and white matter alterations indicating cerebral disconnectivity. Here we investigated the relationship between white matter integrity and event related potentials (ERP) during a continuous performance test (CPT). Anisotropy values were correlated with the brain electrical P300 microstate duration and P300 latency associated to the NoGo- and the Go-stimuli of the CPT in 11 patients with first episode schizophrenia and 11 matched healthy controls. Both groups showed significant positive correlations of the NoGo-microstate duration with the white matter signal in the superior frontal region, the optic radiation, the posterior cingulate, and the inferolateral fascicle. In addition, patients with first episode schizophrenia had significant correlations with the right radiation and the left genu of the corpus callosum, bilateral geniculate, and the left middle and the superior temporal regions. We interpreted these findings as a sign of functional correlates of extended circuits for the active inhibition of a motor response in the visual CPT as compared to controls. PMID:18356066

Begré, Stefan; Kleinlogel, Horst; Kiefer, Claus; Strik, Werner; Dierks, Thomas; Federspiel, Andrea

2008-05-01

278

Azimuthal anisotropy measurements by STAR  

NASA Astrophysics Data System (ADS)

The recent study of centrality and transverse momentum (pT) dependence of inclusive charged hardron elliptic anisotropy (v2) at midrapidity (|?|<1.0) in Au+Au collision at ?{sNN}=7.7,11.5,19.6,27, and 39 GeV in STAR Beam Energy Scan program is presented. We show that the observed increase of inclusive v2 is mainly due to the average pT increase with energy. In Au+Au 200 GeV collisions, the triangular anisotropy (v3) measurements highly depend on measurement methods; v3 is strongly dependent on ??. The difference between two- and four-particle cumulants v2{2} and v2{4} for Au+Au and Cu+Cu collision at ?{sNN}=62.4 and 200 GeV is used to explore flow fluctuations. Furthermore, by exploiting the symmetry of average flow in pseudorapidity ? about midrapidity, the ??-dependent and independent components are separated using v2{2} and v2{4}.

Yi, Li

2014-06-01

279

Ferrites with Planar Anisotropy at Microwave Frequencies  

Microsoft Academic Search

Materials with an easy plane of magnetization (planar anisotropy) have recently been discovered. The large anisotropy field that tends to keep the magnetization in the easy plane reduces the field required to cause ferromagnetic resonance, which makes the material promising for microwave applications. Equations are derived for the susceptibility, taking into account losses and a finite medium. Propagation in a

I. Bady

1961-01-01

280

Uniaxial Anisotropy in Iron-Cobalt Ferrites  

Microsoft Academic Search

The uniaxial anisotropy induced by the magnetic annealing in both single and poly-crystals of iron-cobalt ferrites has been studied experimentally. It is shown that the magnitudes of the uniaxial anisotropy depend essentially on the degree of oxidation of the specimens and become almost zero after deoxidizing heat treatments. Contrary to the conclusion by Bozorth et al., the dependence of the

Shuichi Iida; Hisashi Sekizawa; Yoshimichi Aiyama

1958-01-01

281

Anisotropy factor of saturated and unsaturated soils  

Microsoft Academic Search

Variations in the degree of anisotropy in soil hydraulic conductivity with changes in water saturation (Se) may adversely impact predictability of flow and transport processes. The conceptual “layered cake” model was extended to consider effects of bulk density variations within a particular soil type. The anisotropy factor as function of matric potential A(?) exhibits different behavior for different soil textures.

S. Assouline; D. Or

2006-01-01

282

Measurements of crystalline anisotropy on longitudinal media  

Microsoft Academic Search

The crystalline anisotropy constant in both thin film and particulate recording media has been determined utilizing high field torque measurements and transmission electron microscopy (TEM). Extrapolation of torque measurements at 45° to the film plane yields a “infinite field torque” that depends solely on the anisotropy constant, the distribution of easy axes, and the saturation magnetization. The distribution of easy

J. J. K. Chang; Qingzhi Peng; H. N. Bertram; R. Sinclair

1996-01-01

283

[X-linked lissencephaly with absent corpus callosum and abnormal genitalia: a report of siblings followed from the prenatal period].  

PubMed

X-linked lissencephaly with absent corpus callosum and abnormal genitalia (XLAG) is caused by a mutation in the ARX gene. We herein report the clinical course of siblings with XLAG with a splicing mutation in ARX. Seizures were observed in utero. Cerebral atrophy was progressive postnatally, and fetal echoencephalography indicated that the atrophy might have started in the prenatal period. They had a typical phenotype, except that the genital abnormality of the younger brother was not remarkable. A portal-systemic shunt that has not been reported in cases with XLAG was seen in the older brother. The siblings had the different complications and severity of disease in spite of possessing the same mutation. PMID:17515135

Nanba, Yukiko; Oka, Akira; Ohno, Kousaku

2007-05-01

284

Hyperlexia and ambient echolalia in a case of cerebral infarction of the left anterior cingulate cortex and corpus callosum.  

PubMed

We report the case of a 69-year-old woman with cerebral infarction in the left anterior cingulate cortex and corpus callosum. She showed hyperlexia, which was a distinctive reading phenomenon, as well as ambient echolalia. Clinical features also included complex disorders such as visual groping, compulsive manipulation of tools, and callosal disconnection syndrome. She read words written on the cover of a book and repeated words emanating from unrelated conversations around her or from hospital announcements. The combination of these two features due to a focal lesion has never been reported previously. The supplementary motor area may control the execution of established subroutines according to external and internal inputs. Hyperlexia as well as the compulsive manipulation of tools could be interpreted as faulty inhibition of preexisting essentially intact motor subroutines by damage to the anterior cingulate cortex reciprocally interconnected with the supplementary motor area. PMID:19585352

Suzuki, Tadashi; Itoh, Shouichi; Hayashi, Mototaka; Kouno, Masako; Takeda, Katsuhiko

2009-10-01

285

High Anisotropy Magnetic Recording Media  

NASA Astrophysics Data System (ADS)

Areal densities in magnetic recording have exhibited Moore's Law like increases in the last ten years. This is partially due to improvements in the media microstructure where reduced grain sizes, tighter grain size distribution, and chemical isolation between grains to break exchange provided increased signal-to-noise from decreased transition noise. With the recent shift from longitudinal to perpendicular recording, areal densities have again continued to increase with demonstrations of over 250 Gbits/in^2. However, areal density is limited by thermal stability considerations where the ratio of stored magnetic energy KuV (anisotropy energy times the magnetic switching volume) to the thermal energy kT must be ˜ 50-70. The projected limit for traditional CoPtCr(X) granular media is on the order of 500 Gbits/in^2. Further increases in the areal density will require greater reduction in the grain size (switching volume), which necessitates finding media with higher anisotropy to maintain thermal stability. Possible candidate materials systems include FePt and SmCo5, which have bulk Ku values 50 to 100 times greater than CoPtCr(X) media materials. High Ku allows for thermally stable grains sizes down to ˜ 2.5 nm, which would permit areal densities in the Tbit/in^2 regime. Accompanying this increase in Ku is an increase in the media switching field (H0), which is proportional to the ratio Ku/Ms where Ms is the saturation magnetization. Therefore, while providing thermal stability, these high Ku materials would potentially require writing fields greater than 50 kOe which far exceed those of available recording head materials. One possible solution is heat-assisted magnetic recording (HAMR) where a laser locally heats the media in order to reduce the coercivity so that available head fields are sufficient. Numerous challenges exist for HAMR including high cooling rates so that the heating process does not render adjacent bits thermally unstable. This paper will review recent progress in this area and concentrate on the challenges for the production of high anisotropy media for Tbit/in^2 areal densities, such as maintaining grain sizes of 2 to 4 nm with the correct crystallographic texture and sufficient grain isolation to break exchange.

Wittig, James

2007-03-01

286

Global Tomography of Seismic Anisotropy and Interpretations  

NASA Astrophysics Data System (ADS)

Seismic anisotropy, in spite of its inherent complexity is becoming an important ingredient for explaining various kinds of seismic data. Global tomographic models have been improved over years not only by an increase in the number of data but more importantly by using more general parameterizations, now including general anisotropy (both radial and azimuthal anisotropies). Different physical processes (lattice preferred orientation of crystals, cracks or fluid inclusions, fine layering...) related to strain field and/or stress field, give rise to observable seismic anisotropy (S-wave splitting, surface wave radial and azimuthal anisotropies), which makes its interpretation sometimes difficult and non-unique. Surface waves are well suited for imaging large scale (>1000km) lateral heterogeneities of velocity and anisotropy in the mantle by using fundamental and higher modes, since they provide an almost uniform lateral and azimuthal coverages, particularly below oceanic areas. The interpretation of anisotropy makes it possible to relate surface geology and plate tectonics to underlying mantle convection processes, and to map at depth the origin of geological objects such as continents, mountain ranges, slabs, ridges and plumes. Since different processes creating anisotropy are in play in different layers, a complex stratification of mantle anisotropy is observed and can be unraveled by simultaneously taking account of effects of anisotropy on body waves and surface waves. We present results of simultaneous inversion of Rayleigh and Love wave overtone data obtained by Beucler et al. (2006) and Visser et al. (2008) down to 1500km depth. New determinations of seismic anisotropy in the upper mantle and the transition zones are obtained from these higher mode phase velocity measurements. We show that seismic anisotropy is small below most of the transition zones except below subduction zones, all around the Pacific Ocean and beneath eastern Eurasia, reflecting complex past slab interactions. Since the presence of anisotropy is due to intense deformation of minerals, it is related to the existence of boundary layers in convective systems. Therefore,the transition zone seems to be a secondary boundary layer within the mantle. In conclusion, The imaging of seismic anisotropy renews our vision of mantle convection processes covering a wide range of applications for structural geologists and geophysicists.

Montagner, Jean-Paul

2013-04-01

287

On radial anisotropy limits in stellar systems  

NASA Astrophysics Data System (ADS)

Following earlier authors we re-examine the upper limits on the radial velocity anisotropy of general stellar systems; these constraints coming generically from phase-space density positivity, stability, and separability. Galaxy models almost always satisfy an inequality ? < ?/2, i.e. the radial anisotropy is locally no greater than half of the logarithmic density slope. Some complex separable models are the only known cases which disobey this inequality and do so by having an exceptionally large anisotropy at the centre. Here we present new families of non-separable but simple models which have ? > ?/2. Such large, superthreshold anisotropy always occurs in a finite region in between an isotropic core and an isotropic outer boundary. Our models are always self-consistent and hence maintain the positivity of the phase-space density. Nevertheless, regions with superthreshold anisotropy are potentially subject to secular instability and may thus be observed in a short-lived phase of galaxies.

Barber, Jeremy A.; Zhao, Hongsheng

2014-08-01

288

Transient lesion in the splenium of the corpus callosum: three further cases in epileptic patients and a pathophysiological hypothesis  

PubMed Central

OBJECTIVE—Focal lesions limited to the splenium of the corpus callosum (SCC) are rare and little is known about their aetiology. Three patients were examined for presurgical evaluation in epilepsy with a transient lesion in the SCC and a pathophysiological hypothesis is presented.?METHODS—Three patients were identified with a circumscribed lesion in the centre of the corpus callosum. Follow up MRI was performed, the medical records examined retrospectively, and the literature reviewed.?RESULTS—The patients showed identical lesions in the SCC with reduced T1 and increased T2 signal intensity and an unaffected marginal hemline of a few mm. Patients were asymptomatic and control MRIs showed complete normalisation within 2 months. Patients had been treated with antiepileptic drugs (AEDs) without signs of toxicity. In all patients AEDs were rapidly reduced for diagnostic purposes, but only one had psychomotor seizures, 5 days before imaging.?CONCLUSIONS—A transient lesion in the SCC has so far only been described in 13 patients with epilepsy and has been interpreted either as reversible demyelination due to AED toxicity or transient oedema after secondary generalised seizures. The data confirm neither of these hypotheses. A transient lesion in the SCC seems to be a non-specific end point of different disease processes leading to a vasogenic oedema. This suggests, in these patients, a multifactorial pathology triggered by transient effects of AEDs on arginine vasopressine and its function in fluid balance systems in a condition of vitamin deficiency. The complete and rapid reversibility in all cases without specific intervention is emphasised and any invasive diagnostic or therapeutic approach is discouraged.??

Polster, T; Hoppe, M; Ebner, A

2001-01-01

289

Anisotropy in high-resolution diffusion-weighted MRI and anomalous diffusion.  

PubMed

It is shown below that complex diffusion anisotropy observed in diffusion-weighted MRI can be fully accounted for by allowing for non-locality of the spatial operator in the diffusion equation. The anisotropy is represented by a distribution over directions on a sphere. It allows recognition of fiber tracts crossing at arbitrary angles. A simple generalization of the Stejskal-Tanner equation for the determination of the ODF is presented. Furthermore, an explicit solution of the Bloch-Torrey equation for an anisotropic time-fractional diffusion equation is obtained in terms of a generalized Mittag-Leffler type function. PMID:22706028

Hanyga, A; Seredy?ska, M

2012-07-01

290

Thermal expansion and elastic anisotropies of SiC as related to polytype structure  

NASA Technical Reports Server (NTRS)

The concept of the fraction of hexagonal stacking is used to describe the anisotropic thermal expansion coefficients of polytypes of SiC. The single crystal elastic anisotropy for the SiC polytype structures and the temperature dependencies of the anisotropies are examined. The anisotropic thermoelastic stress index for the 3C and 6H SiC polytypes are illustrated graphically. It is shown that this index is useful for predicting the most desirable crystal growth orientations for SiC whisker incorporation into composite matrices.

Li, Z.; Bradt, R. C.

1989-01-01

291

A Model for Some Subcortical DTI Planar and Linear Anisotropy  

Microsoft Academic Search

Abstract: IntroductionLinear anisotropy, planar anisotropy and isotropy [1] are used as metrics for differentkinds of di#usions in di#usion imaging. While linear anisotropy is reportedto correlate to coherent neural fiber structures, the cause for planar anisotropy remainsambiguous. We hypothesize that overlapping linear structures and partialvolumeaveraging generate the planar anisotropy. We identify a subcortical regioncontaining both linear and planar anisotropy in a

Song Zhang; David H. Laidlaw

2004-01-01

292

The recoil shadow anisotropy method  

NASA Astrophysics Data System (ADS)

The Recoil Shadow Anisotropy Method (RSAM) is a new experimental method for identifying isomers in the nanosecond range and measuring their half-lives. This method can be applied to experiments performed with thin targets and ?-ray multidetector arrays including collimated composite detectors and does not require any additional device. It uses the shadow effect imposed by the collimators on the different elements of composite detectors for ?-rays emitted by recoiling nuclei. RSAM was developed for the clover detectors of the Eurogam-2 array and tested using several data sets obtained with this array. A number of known isomers with half-lives lying between 0.9 and 18 ns in 194Hg, 191Au, 148Gd, 149Gd, 193Pb and 194Pb have been successfully re-measured, proving the ability of RSAM for lifetime measurements.

Gueorguieva, E.; Kaci, M.; Schück, C.; Minkova, A.; Vieu, Ch.; Correia, J. J.; Dionisio, J. S.

2001-12-01

293

Continued fraction coherent anomaly approach for Blume-Capel model  

NASA Astrophysics Data System (ADS)

The continued fraction coherent anomaly method (CAM) is applied to study the criticality of the Blume-Capel model. For comparison, we present also the power series approach with a different way of calculating the critical coefficients. The variation of the Curie temperature Tc with respect to the single-ion anisotropy parameter D/J (where D is the single-ion anisotropy and J is the nearest-neighbour exchange constant) is studied using both methods. The method of continued fraction CAM approach consists in expressing the high-temperature static susceptibility series in the form of a continued fraction and subsequently in finding the roots of different order approximants, which are then used in analysing the critical data. The magnitude of confluent singularities has been estimated by the continued fraction CAM approach and the results are compared with those obtained from power series CAM approach.

Sardar, Shiladitya; Chakraborty, K. G.

1994-05-01

294

Primordial anisotropies in gauged hybrid inflation  

NASA Astrophysics Data System (ADS)

We study primordial anisotropies generated in the model of gauged hybrid inflation in which the complex waterfall field is charged under a U(1)gauge field. Primordial anisotropies are generated either actively during inflation or from inhomogeneities modulating the surface of end of inflation during waterfall transition. We present a consistent ?N mechanism to calculate the anisotropic power spectrum and bispectrum. We show that the primordial anisotropies generated at the surface of end of inflation do not depend on the number of e-folds and therefore do not produce dangerously large anisotropies associated with the IR modes. Furthermore, one can find the parameter space that the anisotropies generated from the surface of end of inflation cancel the anisotropies generated during inflation, therefore relaxing the constrains on model parameters imposed from IR anisotropies. We also show that the gauge field fluctuations induce a red-tilted power spectrum so the averaged power spectrum from the gauge field can change the total power spectrum from blue to red. Therefore, hybrid inflation, once gauged under a U(1) field, can be consistent with the cosmological observations.

Akbar Abolhasani, Ali; Emami, Razieh; Firouzjahi, Hassan

2014-05-01

295

Azimuthal anisotropy of the Pacific region  

NASA Astrophysics Data System (ADS)

Azimuthal anisotropy is the dependence of local seismic properties on the azimuth of propagation. We present the azimuthally anisotropic component of a 3D SV velocity model for the Pacific Ocean, derived from the waveform modeling of over 56,000 multi-mode Rayleigh waves followed by a simultaneous inversion for isotropic and azimuthally anisotropic vsv structure. The isotropic vsv model is discussed in a previous paper (A. Maggi, E. Debayle, K. Priestley, G. Barruol, Multi-mode surface waveform tomography of the Pacific Ocean: a close look at the lithospheric cooling signature, Geophys. J. Int. 166 (3) (2006). doi:10.1111/j.1365-246x.2006.03037.x). The azimuthal anisotropy we find is consistent with the lattice preferred orientation model (LPO): the hypothesis of anisotropy generation in the Earth's mantle by preferential alignment of anisotropic crystals in response to the shear strains induced by mantle flow. At lithospheric depths we find good agreement between fast azimuthal anisotropy orientations and ridge spreading directions recorded by sea-floor magnetic anomalies. At asthenospheric depths we find a strong correlation between fast azimuthal anisotropy orientations and the directions of current plate motions. We observe perturbations in the pattern of seismic anisotropy close to Pacific hot-spots that are consistent with the predictions of numerical models of LPO generation in plume-disturbed plate motion-driven mantle flow. These observations suggest that perturbations in the patterns of azimuthal anisotropy may provide indirect evidence for plume-like upwelling in the mantle.

Maggi, Alessia; Debayle, Eric; Priestley, Keith; Barruol, Guilhem

2006-10-01

296

Anisotropy-axis orientation effect on the magnetization of ?-Fe2O3 frozen ferrofluid  

NASA Astrophysics Data System (ADS)

The effect of magnetic anisotropy-axis alignment on the superparamagnetic (SPM) and superspin glass (SSG) states in a frozen ferrofluid has been investigated. The ferrofluid studied here consists of maghemite nanoparticles (?-Fe2O3, mean diameter = 8.6 nm) dispersed in glycerine at a volume fraction of ~15%. In the high temperature SPM state, the magnetization of aligned ferrofluid increased by a factor varying between 2 and 4 with respect to that in the randomly oriented state. The negative interaction energy obtained from the Curie-Weiss fit to the high temperature susceptibility in the SPM states as well as the SSG phase onset temperature determined from the linear magnetization curves were found to be rather insensitive to the anisotropy-axis alignment. The low temperature ageing behaviour, explored via 'zero-field cooled magnetization' relaxation measurements, however, shows a distinct difference in the ageing dynamics in the anisotropy-axis aligned and randomly oriented SSG states.

Nakamae, S.; Crauste-Thibierge, C.; Komatsu, K.; L'Hôte, D.; Vincent, E.; Dubois, E.; Dupuis, V.; Perzynski, R.

2010-12-01

297

Orthogonal Invariant Sets of the Diffusion Tensor and the Development of a Curvilinear Set Suitable for Low-Anisotropy Tissues  

PubMed Central

We develop a curvilinear invariant set of the diffusion tensor which may be applied to Diffusion Tensor Imaging measurements on tissues and porous media. This new set is an alternative to the more common invariants such as fractional anisotropy and the diffusion mode. The alternative invariant set possesses a different structure to the other known invariant sets; the second and third members of the curvilinear set measure the degree of orthotropy and oblateness/prolateness, respectively. The proposed advantage of these invariants is that they may work well in situations of low diffusion anisotropy and isotropy, as is often observed in tissues such as cartilage. We also explore the other orthogonal invariant sets in terms of their geometry in relation to eigenvalue space; a cylindrical set, a spherical set (including fractional anisotropy and the mode), and a log-Euclidean set. These three sets have a common structure. The first invariant measures the magnitude of the diffusion, the second and third invariants capture aspects of the anisotropy; the magnitude of the anisotropy and the shape of the diffusion ellipsoid (the manner in which the anisotropy is realised). We also show a simple method to prove the orthogonality of the invariants within a set.

Damion, Robin A.; Radjenovic, Aleksandra; Ingham, Eileen; Jin, Zhongmin; Ries, Michael E.

2013-01-01

298

Magnetic anisotropy of the visual pigment rhodopsin.  

PubMed Central

A new estimate of diamagnetic anisotropy of the frog rhodopsin is reported. The estimate is obtained by combining the data of magnetic field induced orientation of isolated frog rod outer segments as measured by Chagneux and Chalazonitis (1972) and the data of diamagnetic anisotropy of lecithin membranes as recently reported by Boroske and Helfrich (1978). The anisotropy of the volume susceptibilities of frog rhodopsin is calculated to be 4.4 X 10(-8) cgs unit/cm3, which corresponds to 1.5 X 10(-27) cgs unit/molecule, or 9.0 X 10(-4) cgs unit/mol.

Hong, F T

1980-01-01

299

Local control of single atom magnetocrystalline anisotropy.  

PubMed

Individual Fe atoms on a Cu(2)N/Cu(100) surface exhibit strong magnetic anisotropy due to the crystal field. We show that we can controllably enhance or reduce this anisotropy by adjusting the relative position of a second nearby Fe atom, with atomic precision, in a low-temperature scanning tunneling microscope. Local inelastic electron tunneling spectroscopy, combined with a qualitative first-principles model, reveal that the change in uniaxial anisotropy is driven by local strain due to the presence of the second Fe atom. PMID:24093296

Bryant, B; Spinelli, A; Wagenaar, J J T; Gerrits, M; Otte, A F

2013-09-20

300

Match My Fraction  

NSDL National Science Digital Library

The students will use pattern blocks to demonstrate fractions and equivalent fractions. They begin by finding and modeling equivalent fractions with pattern blocks, then they are asked to match cards to show the equivalent fractions.

Network, Utah E.

2012-04-30

301

Fractions Made Faster  

NSDL National Science Digital Library

In this problem students use a visual representation of fractions to compare fractions. Students are given two fractions and using the fraction wall they must compare them and find the difference between them. A Teacher's Notes page, hints, solutions, and printable pages are provided. The goal of this problem is for students to compare the two fractions given by using the visual fraction wall or their knowledge of equivalent fractions and subtracting fractions.

2005-10-01

302

On right fractional calculus  

Microsoft Academic Search

Here are presented fractional Taylor type formulae with fractional integral remainder and fractional differential formulae, regarding the right Caputo fractional derivative, the right generalized fractional derivative of Canavati type [Canavati JA. The Riemann–Liouville integral. Nieuw Archief Voor Wiskunde 1987;5(1):53–75] and their corresponding right fractional integrals.Then are given representation formulae of functions as fractional integrals of their above fractional derivatives, as

George A. Anastassiou

2009-01-01

303

Reflectance anisotropy for porphyrin ostaester  

NASA Astrophysics Data System (ADS)

We present a theoretical study for the reflectance anosotropy of prophyrin layers deposited onto gold substrates by Langmuir-Schaefer technique. We have used a polarizable dipole model, in which the effect of the electric local field is incorporated, to obtain the reflectance anisotropy spectra as function of the number of porphyrin layers. We show that the spectra changes from a peak-like to derivative-like line shape as the tilting and twisting of the molecules is varied. More specifically, at low coverage the molecules tend to be inclined relative to the substrate, due to stronger interaction with it, but as the number of layers is increased the substrate influence decreases as it is screened by the underlying layers, and the molecules tend to straighten up[1]. Our results coincide qualitatively with those of the experiments[2]. [1] C. Castillo, R. A. Vázquez-Nava and Bernardo S. Mendoza, Phys. stat. sol. (c) DOI 10.1002/pssc.200303859. [2] C. Goletti, R. Paolesse, E. Dalcanale, T. Berzina, C. Di Natale, G. Bussetti, P. Chiaradia, A. Froiio, L. Cristofolini, M. Costa and A. DÁmico, Lamgmuir 18, 6881 (2002).

Vázquez-Nava, Raúl; Castillo, César; Mendoza, Bernardo

2004-03-01

304

Photoionization affected by chemical anisotropy  

SciTech Connect

The kinetic constants of rhodamine 3B quenching by N,N-dimethyl aniline were extracted from the very beginning of the quenching kinetics, recently studied in a few solvents of different viscosities. They were well fitted with the conventional kinetic constant definition, provided the radial distribution function of simple liquids was ascribed to the reactant pair distribution and the contact electron transfer rate was different in all the cases. This difference was attributed to the chemical anisotropy averaging by the rotation of reactants, which is the faster in solvents of lower viscosity. With the proper choice of a space dependent encounter diffusion, the whole quenching kinetics was well fitted with an encounter theory, using the Marcus [J. Chem. Phys. 24, 966 (1956); 43, 679 (1965)] transfer rate instead of the contact Collins-Kimball [J. Colloid. Sci. 4, 425 (1949)] approximation. Not only the beginning and middle part of the quenching were equally well fitted, but the long time (Markovian) rate constant was also found to be the same as previously obtained. Moreover, the concentration dependencies of the fluorescence quantum yield and the Stern-Volmer constant were specified and await their experimental verification.

Gladkikh, V. S.; Burshtein, A. I. [Weizmann Institute of Science, Rehovot 76100 (Israel)

2007-01-07

305

Anisotropy in a non-singular bounce  

NASA Astrophysics Data System (ADS)

Following recent claims relative to the question of large anisotropy production in regular bouncing scenarios, we study the evolution of such anisotropies in a model where an ekpyrotic phase of contraction is followed by domination of a Galileon-type Lagrangian which generates a non-singular bounce. We show that the anisotropies decrease during the phase of ekpyrotic contraction (as expected) and that they can be constrained to remain small during the non-singular bounce phase (a non-trivial result). Specifically, we derive the e-folding number of the phase of ekpyrotic contraction which leads to a present-day anisotropy in agreement with current observational bounds. Communicated by P Singh

Cai, Yi-Fu; Brandenberger, Robert; Peter, Patrick

2013-04-01

306

SOLARMAX/Electron Pitch Angle Anisotropy Distributions  

NASA Technical Reports Server (NTRS)

This final research report summarizes the scientific work performed by The Aerospace Corporation on SOLARMAX/Electron Pitch Angle Anisotropy Distributions. The period of performance was from June 1, 2000 to December 31, 2001.

McKenzie, David L.; Anderson, Phillip C.

2002-01-01

307

Generalized complex anisotropy expression in excitable media  

NASA Astrophysics Data System (ADS)

In this letter, a complex expression is constructed to characterize the reaction diffusion phenomena in anisotropic excitable media. The theoretical model thus established has general significance and can effectively capture the basic properties of chemical-wave propagation in the real-world media. Particularly, an eikonal relation is derived to account for the effects of complex anisotropy. It indicates that a sufficiently strong complex anisotropy can lead to chemical-wave propagation instabilities such as the occurrences of shocks on the propagating wavefront. The correlation can also predict how the particular form of anisotropy induces complex pattern formation such as "polygon-shaped" patterns. Numerical simulations on a two-dimensional system with complex anisotropy sustain these analysis results.

Zhu He, Zhi; Liu, Jing

2009-01-01

308

Anisotropy and Strength of Ceramic Bodies.  

National Technical Information Service (NTIS)

The experimental and theoretical efforts in the report can be divided into 5 groups: computation of the theoretical tensile, compressive and shear strength as depending on the orientation of the applied stress (bulk strength anisotropy) based on higher or...

W. R. Buessem H. A. McKinstry

1969-01-01

309

Interrelationship Between Anisotropy and Crystallographic Structure.  

National Technical Information Service (NTIS)

The variations in normal and planar anisotropy in rolled metal products are shown to be functions of crystallographic structure. Each type (cubic and hexagonal) of crystallographic structure exhibits a characteristic strain ratio versus orientation curve....

R. M. Colton G. J. Enyedy

1965-01-01

310

Magnetic anisotropy due to the Casimir effect  

SciTech Connect

We consider the Casimir interaction between a ferromagnetic and a nonmagnetic mirror and show how the Casimir effect gives rise to a magnetic anisotropy in the ferromagnetic layer. The anisotropy is out of plane if the nonmagnetic plate is optically isotropic. If the nonmagnetic plate shows a uniaxial optical anisotropy (with optical axis in the plate plane), we find an in-plane magnetic anisotropy. In both cases, the energetically most favorable magnetization orientation is given by the competition between polar, longitudinal, and transverse contributions to the magneto-optical Kerr effect and will therefore depend on the interplate distance. Numerical results will be presented for a magnetic plate made out of Fe and nonmagnetic plates of Au (optically isotropic), quartz, calcite, and barium titanate (all uniaxially birefringent).

Metalidis, G.; Bruno, P. [Institut fuer Theoretische Festkoerperphysik, Karlsruhe Institut fuer Technologie (KIT), D-76131 Karlsruhe (Germany); European Synchrotron Radiation Facility, Boite Postale 220, F-38043 Grenoble Cedex (France)

2010-02-15

311

Strengthening Oxides by Reduction of Crystal Anisotropy.  

National Technical Information Service (NTIS)

In single phase polycrystalline ceramic bodies composed of anisotropic crystals the stresses resulting from applied loads, large scale residual stresses and localized stresses combine to cause fracture. The localized stresses caused by crystal anisotropy ...

H. P. Kirchner R. M. Grover

1971-01-01

312

Strengthening Oxides by Reduction of Crystal Anisotropy.  

National Technical Information Service (NTIS)

Literature information was used to demonstrate that the grain size dependence of strength increases with increasing crystal anisotropy in well-made pure oxide ceramics. Based upon this information a large grain size dependence of strength was predicted fo...

H. P. Kirchner R. M. Gruver R. A. Ewig

1970-01-01

313

Scattering anisotropy-weighted mesoscopic imaging  

PubMed Central

Abstract. We report that when tissue images are formed via a small solid angle in the backward direction (i.e., back-directional gating), the image intensity is dominantly determined by tissue scattering anisotropy. Thus, this configuration allows for scattering anisotropy-weighted imaging that can provide an intrinsic contrast by capturing tissue structures and organizations. To demonstrate the immediate feasibility, we apply scattering anisotropy-weighted imaging to tissue blocks including basal-cell carcinomas as a pilot study. The main feature of our imaging approach is the high sensitivity to tumor locations and the simplicity for large-area visualization. We further envision that scattering anisotropy-weighted imaging could potentially be used to visualize tissue microenvironments in a mesoscopic (between microscopic and macroscopic) imaging setting.

Xu, Zhengbin; Somani, Ally-Khan; Kim, Young L.

2012-01-01

314

Cortical depth dependence of the diffusion anisotropy in the human cortical gray matter in vivo.  

PubMed

Diffusion tensor imaging (DTI) is typically used to study white matter fiber pathways, but may also be valuable to assess the microstructure of cortical gray matter. Although cortical diffusion anisotropy has previously been observed in vivo, its cortical depth dependence has mostly been examined in high-resolution ex vivo studies. This study thus aims to investigate the cortical depth dependence of the diffusion anisotropy in the human cortex in vivo on a clinical 3 T scanner. Specifically, a novel multishot constant-density spiral DTI technique with inherent correction of motion-induced phase errors was used to achieve a high spatial resolution (0.625 × 0.625 × 3 mm) and high spatial fidelity with no scan time penalty. The results show: (i) a diffusion anisotropy in the cortical gray matter, with a primarily radial diffusion orientation, as observed in previous ex vivo and in vivo studies, and (ii) a cortical depth dependence of the fractional anisotropy, with consistently higher values in the middle cortical lamina than in the deep and superficial cortical laminae, as observed in previous ex vivo studies. These results, which are consistent across subjects, demonstrate the feasibility of this technique for investigating the cortical depth dependence of the diffusion anisotropy in the human cortex in vivo. PMID:24608869

Truong, Trong-Kha; Guidon, Arnaud; Song, Allen W

2014-01-01

315

Seismic anisotropy: Geological causes and its implications to reservoir geophysics  

Microsoft Academic Search

The primary focus of this dissertation is to improve the applicability of rock physics models for elastic anisotropy through useful approximations, empirical relations, and practical workflows considering the geological origins of rock anisotropy. Anisotropy arises from aligned heterogeneities at scales smaller than the scale of measurement. Ignoring elastic anisotropy may lead to poor seismic imaging, inaccurate well-ties, and incorrect interpretation

Kaushik Bandyopadhyay

2009-01-01

316

Anisotropy and Corotation of Galactic Cosmic Rays  

Microsoft Academic Search

The intensity of Galactic cosmic rays is nearly isotropic because of the influence of magnetic fields in the Milky Way. Here, we present two-dimensional high-precision anisotropy measurement for energies from a few to several hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of

M. Amenomori; S. Ayabe; X. J. Bi; D. Chen; S. W. Cui; Danzengluobu; L. K. Ding; X. H. Ding; C. F. Feng; Zhaoyang Feng; Z. Y. Feng; X. Y. Gao; Q. X. Geng; H. W. Guo; H. H. He; M. He; K. Hibino; N. Hotta; Haibing Hu; H. B. Hu; J. Huang; Q. Huang; H. Y. Jia; F. Kajino; K. Kasahara; Y. Katayose; C. Kato; K. Kawata; Labaciren; G. M. Le; A. F. Li; J. Y. Li; Y.-Q. Lou; H. Lu; S. L. Lu; X. R. Meng; K. Mizutani; J. Mu; K. Munakata; A. Nagai; H. Nanjo; M. Nishizawa; M. Ohnishi; I. Ohta; H. Onuma; T. Ouchi; S. Ozawa; J. R. Ren; T. Saito; M. Sakata; T. K. Sako; T. Sasaki; M. Shibata; A. Shiomi; T. Shirai; H. Sugimoto; M. Takita; Y. H. Tan; N. Tateyama; S. Torii; H. Tsuchiya; S. Udo; B. Wang; H. Wang; X. Wang; Y. G. Wang; H. R. Wu; L. Xue; Y. Yamamoto; C. T. Yan; X. C. Yang; S. Yasue; Z. H. Ye; G. C. Yu; A. F. Yuan; T. Yuda; H. M. Zhang; J. L. Zhang; N. J. Zhang; X. Y. Zhang; Y. Zhang; Yi Zhang; Zhaxisangzhu; X. X. Zhou

2006-01-01

317

Magnetic Anisotropy of a Single Cobalt Nanocluster  

Microsoft Academic Search

Using a new micro-SQUID setup, we investigate magnetic anisotropy in a single 1000-atom cobalt cluster. This system opens new fields in the characterization and understanding of the origin of magnetic anisotropy in such nanoparticles. For this purpose, we report three-dimensional switching field measurements performed on a 3 nm cobalt cluster embedded in a niobium matrix. We are able to separate

M. Jamet; W. Wernsdorfer; C. Thirion; D. Mailly; V. Dupuis; P. Mélinon; A. Pérez

2001-01-01

318

Anisotropy in thin Canning sheet metals  

Microsoft Academic Search

The in-plane anisotropy of ductile sheet metal may be characterised by r-values within a uniform tensile strain range. In iow ductiiity material, tensile failure occurs by the formation of an inciined groove within which the plasticity is localised. Under these conditions, where lateral and axial displacements cannot determine an r-value reliably, the inclination of the local groove is used. Anisotropy

D. W. A. Rees

2003-01-01

319

Dynamical models with a general anisotropy profile  

NASA Astrophysics Data System (ADS)

Aims:Both numerical simulations and observational evidence indicate that the outer regions of galaxies and dark matter haloes are typically mildly to significantly radially anisotropic. The inner regions can be significantly non-isotropic, depending on the dynamical formation and evolution processes. In an attempt to break the lack of simple dynamical models that can reproduce this behaviour, we explore a technique to construct dynamical models with an arbitrary density and an arbitrary anisotropy profile. Methods: We outline a general construction method and propose a more practical approach based on a parameterized anisotropy profile. This approach consists of fitting the density of the model with a set of dynamical components, each of which have the same anisotropy profile. Using this approach we avoid the delicate fine-tuning difficulties other fitting techniques typically encounter when constructing radially anisotropic models. Results: We present a model anisotropy profile that generalizes the Osipkov-Merritt profile, and that can represent any smooth monotonic anisotropy profile. Based on this model anisotropy profile, we construct a very general seven-parameter set of dynamical components for which the most important dynamical properties can be calculated analytically. We use the results to look for simple one-component dynamical models that generate simple potential-density pairs while still supporting a flexible anisotropy profile. We present families of Plummer and Hernquist models in which the anisotropy at small and large radii can be chosen as free parameters. We also generalize these two families to a three-parameter family that self-consistently generates the set of Veltmann potential-density pairs. These new analytical models are an important step forward compared to isotropic or Osipkov-Merritt models and can be used to generate the initial conditions for realistic simulations of galaxies or dark matter haloes. Appendices are only available in electronic form at http://www.aanda.org

Baes, M.; van Hese, E.

2007-08-01

320

Deterministic Diffusion Fiber Tracking Improved by Quantitative Anisotropy  

PubMed Central

Diffusion MRI tractography has emerged as a useful and popular tool for mapping connections between brain regions. In this study, we examined the performance of quantitative anisotropy (QA) in facilitating deterministic fiber tracking. Two phantom studies were conducted. The first phantom study examined the susceptibility of fractional anisotropy (FA), generalized factional anisotropy (GFA), and QA to various partial volume effects. The second phantom study examined the spatial resolution of the FA-aided, GFA-aided, and QA-aided tractographies. An in vivo study was conducted to track the arcuate fasciculus, and two neurosurgeons blind to the acquisition and analysis settings were invited to identify false tracks. The performance of QA in assisting fiber tracking was compared with FA, GFA, and anatomical information from T1-weighted images. Our first phantom study showed that QA is less sensitive to the partial volume effects of crossing fibers and free water, suggesting that it is a robust index. The second phantom study showed that the QA-aided tractography has better resolution than the FA-aided and GFA-aided tractography. Our in vivo study further showed that the QA-aided tractography outperforms the FA-aided, GFA-aided, and anatomy-aided tractographies. In the shell scheme (HARDI), the FA-aided, GFA-aided, and anatomy-aided tractographies have 30.7%, 32.6%, and 24.45% of the false tracks, respectively, while the QA-aided tractography has 16.2%. In the grid scheme (DSI), the FA-aided, GFA-aided, and anatomy-aided tractographies have 12.3%, 9.0%, and 10.93% of the false tracks, respectively, while the QA-aided tractography has 4.43%. The QA-aided deterministic fiber tracking may assist fiber tracking studies and facilitate the advancement of human connectomics.

Yeh, Fang-Cheng; Verstynen, Timothy D.; Wang, Yibao; Fernandez-Miranda, Juan C.; Tseng, Wen-Yih Isaac

2013-01-01

321

How to separate intrinsic and artificial anisotropy  

NASA Astrophysics Data System (ADS)

The effect of anisotropy on seismic waves and on the inversion for 3D tomographic models of velocity and anisotropy is not negligible and is used for different applications in geodynamics for both regional and global scale (Montagner, TOG, 2007). The exact determination and interpretation of anisotropy (amplitude and orientation) are quite difficult because the observed or inverted anisotropy is usually a mixture of intrinsic and artificial anisotropies, which may partly hide the true properties of the medium. The artificial anisotropy is due to two reasons: first of all, to the inversion technique and second of all, to the the fact that seismic waves do not see the real details of medium but a filtered (and imperfect) version of the earth model. Backus (1962) constructs the effective elastic coefficients for layered medium to present what is "seen" by the wave field at long periods which is called the "long-wavelength equivalent" effect. The homogenization method developed by Capdeville et al., (2007, 2010) uses a two-scale homogenization expansion to construct a new more continuous model based on filtering technique which can adapt the scales of the model to the seismic wavelengths. Such homogenized model is quite effective to compute full waveform seismograms in heterogeneous anisotropic medium. In this paper, we propose a strategy in order to separate artificial and intrinsic anisotropy. For the inversion technique, we use a quasi-Newton method (Tarantola, 2005) together with the GMRES method based on the first-order perturbation theory. We try to find and interpret the real and artificial anisotropy by introducing different prior information on both data and the reference model. We investigate a 1D isotropic smooth model and an isotropic discontinuous PREM model, together with their homogenized models which are anisotropic VTI models (Capdeville et al., 2007), try to estimate the amplitude of artificial radial anisotropy associated with the inversion technique and the homogenization as the effect of filtering. Actual seismic data for the 3D problem is left to the future for demonstrating the separation of intrinsic and artificial anisotropy.

Wang, N.; Montagner, J.-P.; Capdeville, Y.; Burgos, G.; Cupillard, P.

2012-04-01

322

Fractional derivatives, fractional integrals and electromagnetic theory  

Microsoft Academic Search

Summary form only given. Fractional derivatives\\/integrals are mathematical operators involving differentiation\\/integration to arbitrary noninteger orders-orders that may be fractional or even complex. These operators, which possess interesting mathematical properties, have been studied in the field of fractional calculus. In our study, we have applied the tools of fractional calculus in various problems in electromagnetic fields and waves, and have obtained

Nader Engheta

1999-01-01

323

Escape from Fraction Manor: Reasoning with Fractions  

NSDL National Science Digital Library

In this interactive game, students collect cards as they journey through the maze of a house (Fraction Manor), avoiding monsters. With each level they complete, they are presented with a math puzzle: given a series of digits, arrange them into fractions in a given order. Some fractions may already be given. Puzzles increase in difficulty with each level.

2010-01-01

324

Corpus callosum segment circumference is associated with response control in children with attention-deficit hyperactivity disorder (ADHD).  

PubMed

Response control is impaired in attention-deficit hyperactivity disorder (ADHD). Given the corpus callosum's role in response control, we compared callosal morphology in 64 children with ADHD and 64 typically developing children, aged 7 to 13 years, and investigated the relationships between callosal morphology and response control. Area and circumference of 5 callosal segments (genu, rostral body, midbody, isthmus, and splenium) were normalized for cerebral volume and examined for correlation with mean reaction time, intrasubject variability, and/or commission error rate from a go/no-go task. There were no between-group differences in segment areas or circumferences. Reaction time correlated with midbody circumference for boys with ADHD and isthmus circumference for girls with ADHD. For the entire cohort, rostral body circumference correlated with intrasubject variability. Impaired response control in ADHD is associated with anomalies in frontal interhemispheric connections. Future studies examining callosal shape will illuminate the anatomic basis of correlations between callosal segment circumference and response control. PMID:20139403

McNally, Melanie A; Crocetti, Deana; Mahone, E Mark; Denckla, Martha B; Suskauer, Stacy J; Mostofsky, Stewart H

2010-04-01

325

Agenesis of the corpus callosum and gray matter heterotopia in three patients with constitutional mismatch repair deficiency syndrome.  

PubMed

Constitutional mismatch repair deficiency (CMMR-D) syndrome is a rare inherited childhood cancer predisposition caused by biallelic germline mutations in one of the four mismatch repair (MMR)-genes, MLH1, MSH2, MSH6 or PMS2. Owing to a wide tumor spectrum, the lack of specific clinical features and the overlap with other cancer predisposing syndromes, diagnosis of CMMR-D is often delayed in pediatric cancer patients. Here, we report of three new CMMR-D patients all of whom developed more than one malignancy. The common finding in these three patients is agenesis of the corpus callosum (ACC). Gray matter heterotopia is present in two patients. One of the 57 previously reported CMMR-D patients with brain tumors (therefore all likely had cerebral imaging) also had ACC. With the present report the prevalence of cerebral malformations is at least 4/60 (6.6%). This number is well above the population birth prevalence of 0.09-0.36 live births with these cerebral malformations, suggesting that ACC and heterotopia are features of CMMR-D. Therefore, the presence of cerebral malformations in pediatric cancer patients should alert to the possible diagnosis of CMMR-D. ACC and gray matter heterotopia are the first congenital malformations described to occur at higher frequency in CMMR-D patients than in the general population. Further systematic evaluations of CMMR-D patients are needed to identify possible other malformations associated with this syndrome. PMID:22692065

Baas, Annette F; Gabbett, Michael; Rimac, Milan; Kansikas, Minttu; Raphael, Martine; Nievelstein, Rutger Aj; Nicholls, Wayne; Offerhaus, Johan; Bodmer, Danielle; Wernstedt, Annekatrin; Krabichler, Birgit; Strasser, Ulrich; Nyström, Minna; Zschocke, Johannes; Robertson, Stephen P; van Haelst, Mieke M; Wimmer, Katharina

2013-01-01

326

Corpus callosum agenesis, severe mental retardation, epilepsy, and dyskinetic quadriparesis due to a novel mutation in the homeodomain of ARX.  

PubMed

We report on a patient with agenesis of the corpus callosum (ACC), severe mental retardation, infantile spasms and subsequent intractable epilepsy, spastic/dyskinetic quadriparesis, severe limb contractures, and scoliosis. This complex, newly described phenotype, is due to a novel non-conservative missense mutation in the ARX homeodomain (c.1072A>T; p.R358W), inherited from the unaffected mother. Differently from previously reported non-conservative mutations falling within the same domain, p.R358W did not cause XLAG. It is therefore possible that differences in clinical manifestations between our patient and those with XLAG, are related to the different position of the amino acid substitution in the homeodomain, or to the different chemical properties introduced by the substitution itself. To test the hypothesis that the patient's mother was asymptomatic because of non-random X chromosome inactivation (XCI), we performed DNA methylation studies of the human androgen receptor gene, demonstrating skewing of the XCI ratio (85:15). The complex phenotype described here combines different traits that had previously been linked to various ARX mutations, including conservative missense mutations in the homeodomain and expansion in the first ARX polyalanine tract and contributes to the expanding pleiotropy associated with ARX mutations. PMID:21416597

Conti, Valerio; Marini, Carla; Gana, Simone; Sudi, Jyotsna; Dobyns, William B; Guerrini, Renzo

2011-04-01

327

Compare and Order Fractions  

NSDL National Science Digital Library

In this 7-minute video, users learn how to compare and order fractions. The video shows visual representations and guides the learner through steps for comparing and ordering like-denominator fractions, unit fractions, and fractions with unlike denominators (by using equivalent fractions).

2011-01-01

328

Fraction Number Line  

NSDL National Science Digital Library

Using this interactive fraction number line, students can identify and locate equivalent fractions as well as compare fractions. They can move the mouse to the left or right and "mark" fractions on the number line. A section called "Which is Larger?" provides examples of fraction pairs to compare.

2010-01-01

329

Tailoring the magnetic anisotropy of thin film permalloy microstrips by combined shape and induced anisotropies  

NASA Astrophysics Data System (ADS)

The sensitivity of magnetic sensors based on the Giant Magneto-Impedance effect can be enhanced using high permeability materials with a well-defined but small transverse anisotropy. We describe an experimental study performed on multilayered, permalloy-based thin films deposited by sputtering under a magnetic field that produces a homogeneous uniaxial anisotropy in the plane of the film. Patterning of the deposit by photolithographic methods into strip-shaped samples (with their long direction perpendicular to the induced anisotropy) establishes a longitudinal shape anisotropy that competes with the transversal one induced at deposition. The combination and competition of the two mutually perpendicular uniaxial anisotropies result in an effective one with a reduced magnitude (the difference between both of them) in the transversal direction. As the strength of the shape anisotropy is determined by the relation between width and length of the stripe, the magnitude of the effective anisotropy can be conveniently modulated by adequately selecting the aspect ratio of the patterned sample. The hysteresis loops measured by Kerr effect magnetometry confirm that the effective transversal anisotropy field can be reduced from 5 to 1 Oe which should concomitantly increase the sensitivity of thin film magneto-impedance sensors.

García-Arribas, Alfredo; Fernández, Eduardo; Svalov, Andrey V.; Kurlyandskaya, Galina V.; Barrainkua, Ane; Navas, David; Barandiaran, José Manuel

2013-04-01

330

Simultaneous measurements of fluorescence lifetimes, anisotropy, and FRAP recovery curves  

NASA Astrophysics Data System (ADS)

We present fluorescence lifetime imaging (FLIM) and fluorescence anisotropy imaging along with translational diffusion measurements of living cells labelled with green fluorescent protein (GFP) recorded in a single experiment. The experimental set-up allows for time and polarization-resolved fluorescence images to be measured in every frame of a fluorescence recovery after photobleaching (FRAP) series. We have validated the method using rhodamine 123 in homogeneous solution prior to measurements of living A431 cells labelled with cdc42-GFP, for which the FRAP recovery exhibits an immobile fraction and the rotational mobility of the protein is hindered while the fluorescence lifetime fairly homogeneous across the cell. By eliminating the need for sequential measurements to extract fluorescence lifetimes and molecular diffusion coefficients we remove artefacts arising from changes in sample morphology and excessive photobleaching during sequential experiments.

Levitt, James A.; Chung, Pei-Hua; Alibhai, Dominic R.; Suhling, Klaus

2011-02-01

331

Seismic Anisotropy in the Transition Zone  

NASA Astrophysics Data System (ADS)

The transition zone plays a key role in the understanding of mantle convection, particularly the 660km-discontinuity which might inhibit the passage of matter between the upper and the lower mantle. An efficient way for investigating mantle flow circulation is to map seismic anisotropy in this depth range. There are some good evidences of seismic anisotropy in the top 300km of the upper mantle and the bottom D"-layer. Montagner and Kennett (G.J.I., 1996) found that radial anisotropy (transverse isotropy with vertical symmetry axis) is also necessary in the mantle transition zone between 410 and 900km depth for explaining eigenfrequency data. There are also some other evidences of anisotropy by using different kinds of body wave data (P-to-S receiver functions, shear-wave splitting...), demonstrating lateral variations of anisotropy in the transition zone. On a global scale, Trampert and van Heijst} (2002) using overtone data show a long-wavelength azimuthal anisotropic structure in the transition zone. The rms amplitude of their lateral variations is small (about 1%), much smaller than in the uppermost and lowermost mantle. If we want to obtain a global mapping of seismic anisotropy in the upper (410-660km) and lower (660-900km) transition zones, only overtones of surface waves (higher modes) are able to achieve that. We will present some preliminary results of simultaneous inversion of Rayleigh and Love wave overtone data obtained by Beucler et al. (2006) and Visser et al. (2008). We obtain some new determinations of seismic anisotropy in the transition zone, from these higher mode phase velocity measurements. We show that seismic anisotropy is small below most of the transition zones except below subduction zones, all around the Pacific Ocean and beneath eastern Eurasia where the slab is stagnant. Since the presence of anisotropy is due to intense deformation of minerals, it is related to boundary layers and to flow circulation in convective systems. Therefore, the transition zone seems to be a secondary boundary layer within the mantle.

Montagner, J.; Burgos, G.; Beucler, E.; Drilleau, M.; Capdeville, Y.; Mocquet, A.; Trampert, J.

2011-12-01

332

Ion anisotropies in the outer Jovian magnetosphere  

SciTech Connect

We present results from the Voyager 1 and 2 low-energy charged particle measurement of ion anisotropies in the outer Jovian magnetosphere (R> or approx. =20 R/sub J/). Theses anisotropies represent the first observed from an instrument rotating in the spin plane of Jupiter. For the several ion species ivestigated the first-order anisotropies are all strongly in the corotational sense throughout most of the Jovian magnestophere and out to the magnetopause on the dayside. There is some evidence for a small component of outward flow in the corotating region. Beyond approx.130--150 R/sub J/ along the Voyager outbound trajectories the anisotropies indicate a magnetospheric wind flowing outward from Jupiter. The change corotational to tailward flow on the nightside occurs well inside the magnetopause. The anisotropy amplitudes increase linearly with radial distance and, in the disc regions, decrease with distance from the magnetodisc mid-plane. In one case examined in detail using separtely identified H, He, and O/S ions the convection speed at 58 R/sub J/ is found to agree with the corotation speed (..cap omega..R) to within approx.3%. A linear Compton-Getting analysis reveals that the convective speeds in the dayside magnetosphere are in agreement with rigid corotation whenever the plasma flow direction is approximately in the corotation sense, while at other times the convection speeds are substantially less than corotation.

Carbary, J.F.; Krimigis, S.M.; Keath, E.P.; Gloeckler, G.; Axford, W.I.; Armstrong, T.P.

1981-09-30

333

Bounded Fraction Finder  

NSDL National Science Digital Library

The same as "Bounded Fraction Pointer" but there is no arrow to help the user determine the value of a fraction between the two endpoints. Bounded Fraction Finder is one of the Interactivate assessment explorers.

334

Cup-Drawing Behavior of High-Strength Steel Sheets Containing Different Volume Fractions of Martensite  

SciTech Connect

Planar anisotropy and cup-drawing behavior were investigated for high-strength steel sheets containing different volume fractions of martensite. Macrotexture analysis using XRD was conducted to capture the effect of crystallographic orientation on the planar anisotropy of high-strength steel sheets. A phenomenological yield function, Yld96, which accounts for the anisotropy of yield stress and r-values, was implemented into ABAQUS using the user subroutine UMAT. Cup drawing of high-strength steel sheets was simulated using the FEM code. The profiles of earing and thickness strain were compared with the experimentally measured results.

Choi, Shi-Hoon; Kim, Dae-Wan; Yang, Hoe-Seok [Department of Materials Science and Metallurgical Engineering, Sunchon National University, Sunchon 540-742 (Korea, Republic of); Han, Seong-Ho [Automotive Steel Products Research Group, POSCO Technical Research Laboratories, Gwangyang 545-090 (Korea, Republic of); Yoon, Jeong Whan [Alcoa Technical Center, Materials Science Division, 100 Technical Drive, Alcoa Center, PA 15069-0001 (United States)

2010-06-15

335

Cup-Drawing Behavior of High-Strength Steel Sheets Containing Different Volume Fractions of Martensite  

NASA Astrophysics Data System (ADS)

Planar anisotropy and cup-drawing behavior were investigated for high-strength steel sheets containing different volume fractions of martensite. Macrotexture analysis using XRD was conducted to capture the effect of crystallographic orientation on the planar anisotropy of high-strength steel sheets. A phenomenological yield function, Yld96, which accounts for the anisotropy of yield stress and r-values, was implemented into ABAQUS using the user subroutine UMAT. Cup drawing of high-strength steel sheets was simulated using the FEM code. The profiles of earing and thickness strain were compared with the experimentally measured results.

Choi, Shi-Hoon; Kim, Dae-Wan; Yang, Hoe-Seok; Han, Seong-Ho; Yoon, Jeong Whan

2010-06-01

336

Modeling Multiplication with Fractions  

NSDL National Science Digital Library

Students will relate multiplication strategies with fractions through problem solving situations. This lesson connects prior understanding of multiplication and equal groups to multiplication of fractions.

Ratasky, Joseph

2012-08-18

337

Anisotropy of the cosmic microwave background radiation  

NASA Technical Reports Server (NTRS)

Theoretical predictions of the angular anisotropy in the cosmic microwave background radiation on both small and large angular scales are presented, and the effect of massive neutrinos on both the background radiation anisotropy and on the galaxy correlation function over very large scales is reviewed. Current observations show that the quadrupole anisotropy provides the greatest constraint on theory, and the values for the gravitational potential fluctuations indicate that small amplitude but sufficiently large-scale density fluctuations, both at the present epoch and on the surface of last scattering, can produce significant large angular scale variations in the radiation temperature. Most importantly, it is proposed that the quadrupole moment is most simply and elegantly interpreted in terms of the density fluctuations on very large scales whose presence is inferred from the requirement that an initial fluctuation spectrum is required in order for structure to develop.

Silk, J.

1981-01-01

338

Large Friction Anisotropy of a Polydiacetylene Monolayer  

SciTech Connect

Friction force microscopy measurements of a polydiacetylene monolayer film reveal a 300% friction anisotropy that is correlated with the film structure. The film consists of a monolayer of the red form of N-(2-ethanol)- 10,12 pentacosadiynamide, prepared on a Langmuir trough and deposited on a mica substrate. As confirmed by atomic force microscopy and fluorescence microscopy, the monolayer consists of domains of linearly oriented conjugated backbones with pendant hydrocarbon side chains above and below the backbones. Maximum friction occurs when the sliding direction is perpendicular to the backbone. We propose that the backbones impose anisotropic packing of the hydrocarbon side chains which leads to the observed friction anisotropy. Friction anisotropy is therefore a sensitive, optically-independent indicator of polymer backbone direction and monolayer structural properties.

Burns, A.R.; Carpick, R.W.; Sasaki, D.Y.

1999-05-11

339

Whistler instability: Electron anisotropy upper bound  

NASA Astrophysics Data System (ADS)

If the electron distribution function is approximately bi-Maxwellian with T?/T?>1, where the subscript symbols denote directions perpendicular and parallel to the background magnetic field, and if this temperature anisotropy is sufficiently large, the whistler anisotropy instability is excited. This mode is studied using two-dimensional particle-in-cell simulations in a spatially homogeneous plasma model. Theory predicts a threshold electron anisotropy for this instability which depends inversely on the electron parallel ?. The simulations show that wave-particle scattering by enhanced whistler fluctuations maintain the initially bi-Maxwellian character of the electron distribution, and that this scattering imposes an upper bound on the electron T?/T? commensurate with that predicted by linear theory.

Gary, S. Peter; Wang, Joseph

1996-05-01

340

COSMIC-RAY TRANSPORT AND ANISOTROPIES  

SciTech Connect

We show that the large-scale cosmic-ray anisotropy at {approx}10 TeV can be explained by a modified Compton-Getting effect in the magnetized flow field of old supernova remnants. Cosmic rays arrive isotropically to the flow field and are then carried along with the flow to produce a large-scale anisotropy in the arrival direction. This approach suggests an optimum energy scale for detecting the anisotropy. Two key assumptions are that propagation is based on turbulence following a Kolmogorov law and that cosmic-ray interactions are dominated by transport via cosmic-ray-excited magnetic irregularities through the stellar wind of an exploding star and its shock shell. A prediction is that the amplitude is smaller at lower energies due to incomplete sampling of the velocity field and also smaller at larger energies due to smearing.

Biermann, Peter L. [MPI for Radioastronomy, Auf dem Huegel 69, D-53121 Bonn (Germany); Becker Tjus, Julia; Mandelartz, Matthias [Ruhr-Universitaet Bochum, Fakultaet fuer Physik and Astronomie, Theoretische Physik I, D-44780 Bochum (Germany); Seo, Eun-Suk [Department of Physics, University of Maryland, College Park, MD 20742 (United States)

2013-05-10

341

Magnetic field anisotropy based MR tractography  

NASA Astrophysics Data System (ADS)

Non-invasive measurements of structural orientation provide unique information regarding the connectivity and functionality of fiber materials. In the present study, we use a capillary model to demonstrate that the direction of fiber structure can be obtained from susceptibility-induced magnetic field anisotropy. The interference pattern between internal and external magnetic field gradients carries the signature of the underlying anisotropic structure and can be measured by MRI-based water diffusion measurements. Through both numerical simulation and experiments, we found that this technique can determine the capillary orientation within 3°. Therefore, susceptibility-induced magnetic field anisotropy may be useful for an alternative tractography method when diffusion anisotropy is small at higher magnetic field strength without the need to rotate the subject inside the scanner.

Han, S. H.; Song, Y. K.; Cho, F. H.; Ryu, S.; Cho, G.; Song, Y.-Q.; Cho, H.

2011-10-01

342

Energetic ion anisotropies in the geomagnetic tail. I - A statistical survey. II - Magnetic field and substorm characteristics  

NASA Technical Reports Server (NTRS)

A comprehensive data set from the ISEE 2 spacecraft is used here to perform a statistical study of events in the earth's central magnetotail that are characterized by high anisotropies of energetic ions. In about 75 percent of the cases the anisotropy vector deviates no more than 45 deg from the tidal axis. High-anisotropy samples within 45 deg of the tidal axis are dominated by the earthward fraction. High ion anisotropies are observed continuously for longer than 1 min only in a few cases. The probability of observing high ion anisotropies is significantly enhanced beyond about 16 R(E) downtail distance within a few earth radii of the neutral sheet and on the duskside of the magnetotail. The analysis is extended with respect to the local magnetic field and to the relationship between energetic ion anisotropies and substorm phases. It is found that the events can be well organized in terms of substorm expansion phase and substorm recovery. These relations and the magnetic field characteristics during the events support the notion that the near-earth source of tailward streaming ions is identical with a substorm neutral line.

Kettmann, Georg; Fritz, Theodore A.; Hones, Edward W., Jr.; Daly, Patrick W.

1993-01-01

343

Upper Mantle Anisotropy and Normal Mode Coupling  

NASA Astrophysics Data System (ADS)

We show that upper mantle models that account for lateral variations in radial anisotropy offer a better explanation for the coupling of normal mode multiplets of the type {}0S_l-{}0}T_{l+1 than isotropic models. These modes are sensitive to the upper mantle only and, although their coupling is known to be mostly due to the Coriolis force, a large part of the degree 2 signal measured by Resovsky and Ritzwoller [1998] remains to be explained. Here, we compare the effect of isotropy and radial anisotropy on the coupling of these pairs of modes. We test several isotropic mantle models filtered at degree 2, and anisotropic models of the upper mantle previously obtained by Beghein and Trampert [2004] with surface wave phase velocity maps and a model space search approach. We find that most of the signal cannot be explained by Coriolis coupling and isotropic upper mantle structure. On the contrary, degree 2 models including shear-wave radial anisotropy in the upper mantle predict structure coefficients that are significantly closer to the data than any existing isotropic models. We also show that the correlation between predictions and data is much higher when anisotropy is included, especially for multiplets whose sensitivity to elastic parameter N=? VSH2 increases in the uppermost mantle and transition zone. Interestingly, coupled mode multiplets that are sensitive to the entire mantle (e.g. {}3S_1-{}1}S_{3 or {}3S_7-{}5}S_{5) can be relatively well explained by isotropic degree 2 structure. However, it should be noted that these modes are sensitive to both shear-wave and P-wave related elastic parameters, as opposed to modes such as {}0S_l-{}0}T_{l+1 which can only see shear-wave anomalies. {}nS_l-{}n'}S_{l' coupled mode structure coefficients could, therefore, bring some constraints on upper mantle P-wave anisotropy or on anisotropy at larger depths.

Beghein, C.; van der Hilst, R.; Trampert, J.

2004-12-01

344

Structural anisotropy of normal fault surfaces  

NASA Astrophysics Data System (ADS)

Precise description of natural fault surfaces is indispensable to understanding the geometry, mechanics and fluid transport properties of faults. Profiles of fault surfaces in the Wasatch fault zone and Oquirrh Mountains, Utah, are measured at 30° increments within the fault plane to determine the directional anisotropy of surface roughness at wavelengths between 10 -3 m and 30 m, and then compared with profiles of larger-scale fault surfaces. Surface anisotropy and an increasing ratio of surface amplitude to wavelength are consistent with self-affine fault topography at wavelengths between 1 mm and approximately 5 km. Fractal dimension of surface profiles generally decreases systematically as the angle to the slip direction increases. Directional anisotropy is described by an azimuthal scaling function ?? = K sin( ?) + ?0 or AF? = ( AFmax -1) sin( ?) + 1, where ?? and AF? are the amplitude to wavelength ratio and anisotropy factor respectively at azimuth ?, measured clockwise relative to slip direction within the fault surface, and ?0 is the amplitude to wavelength ratio parallel to slip direction. K = ( ?90 - ?0) is an anisotropy coefficient and increases systematically with spatial wavelength on the fault surface. Characterization of natural fault surfaces provides parameters such as fractal dimension ( D), intercept (log( C)) of power spectra, profile variance, and variation in anisotropy factor ( AF), which are needed to generate fractal models of natural fault surfaces using spectral synthesis. We generate sample models which illustrate the differences between fault surfaces characterized by constant versus azimuthally varying fractal dimension. The latter model surfaces contain low amplitude corrugations superimposed on elongate ridges which parallel slip direction. This surface texture resembles that of natural fault surfaces that refract across lithologic layering or are cut by secondary faults such as R and R' shears.

Lee, Joong-Jeek; Bruhn, Ronald L.

1996-08-01

345

Anisotropy in Gravity and Holography  

NASA Astrophysics Data System (ADS)

In this thesis, we examine the dynamical structure of Ho?ava-Lifshitz gravity, and investigate its relationship with holography for anisotropic systems. Ho?ava-Lifshitz gravity refers to a broad class of gravitational models that incorporate anisotropy at a fundamental level. The idea behind Ho?ava-Lifshitz gravity is to utilize ideas from the theory of dynamical critical phenomena into gravity to produce a theory of dynamical spacetime that is power-counting renormalizable, and is thus a candidate renormalizable quantum field theory of gravity. One of the most distinctive features of Ho?ava-Lifshitz gravity is that its group of symmetries consists not of the diffeomorphisms of spacetime, but instead of the group of diffeomorphisms that preserve a given foliation by spatial slices. As a result of having a smaller group of symmetries, HL gravity naturally has one more propagating degree of freedom than general relativity. The extra mode presents two possible difficulties with the theory, one relating to consistency, and the second to its viability as a phenomenological model. (1) It may destabilize the theory. (2) Phenomenologically, there are severe constraints on the existence of an extra propagating graviton polarization, as well as strong experimental constraints on the value of a parameter appearing in the dispersion relation of the extra mode. In the first part of this dissertation we show that the extra mode can be eliminated by introducing a new local symmetry which steps in and takes the place of general covariance in the anisotropic context. While the identification of the appropriate symmetry is quite subtle in the full non-linear theory, once the dust settles, the resulting theory has a spectrum which matches that of general relativity in the infrared. This goes a good way toward answering the question of how close Ho?ava-Lifshitz gravity can come to reproducing general relativity in the infrared regime. In the second part of the thesis we pursue the relationship between Ho?ava-Lifshitz gravity and holographic duals for anisotropic systems. A holographic correspondence is one that posits an equivalence between a theory of gravity on a given spacetime background and a field theory living on the "boundary" of that spacetime, which resides at infinite spatial separation from the interior. It is a non-trivial problem how to define this boundary, but in the case of relativistic boundary field theories, there is a well-known definition due to Penrose of the boundary which produces the geometric structure required to make sense of the correspondence. However, the proposed dual geometries to anisotropic quantum field theories have a Penrose boundary that is incompatible with the assumed correspondence. We generalize Penrose's approach, using concepts from Ho?ava-Lifshitz gravity, to spacetimes with anisotropic boundary conditions, thereby arriving at the concept of anisotropic conformal infinity that is compatible with the holographic correspondence in these spacetimes. We then apply this work to understanding the structure of holography for anisotropic systems in more detail. In particular, we examine the structure of divergences of a certain theory of gravity on Lifshitz space. We find, using our construction of anisotropic conformal infinity, that the appropriate geometric structure of the boundary is that of a foliated spacetime with an anisotropic metric complex. We then perform holographic renormalization in these spacetimes, yielding a computation of the divergent part of the effective action, and find that it exhibits precisely the structure of a Ho?ava-Lifshitz action. Moreover, we find that, for dynamical exponent z = 2, the logarithmic divergence gives rise to a conformal anomaly in 2+1 dimensions, whose general form is precisely that of conformal Ho?ava-Lifshitz gravity with detailed balance.

Melby-Thompson, Charles Milton

346

a Multiscale Autocorrelation Function for Anisotropy Studies  

NASA Astrophysics Data System (ADS)

In recent years many procedures have been proposed to check the anisotropy of a dataset. We present a new simple procedure, based on a scale dependent approach, to detect anisotropy signatures in a given distribution with particular attention to small dataset. The method provides a good discrimination power for both large and small datasets, even in presence of strong contaminating isotropic background. We present some applications to simulated datasets of events to investigate statistical features of the method and present and inspect its behavior under both the null or the alternative hypothesis.

Scuderi, M.; de Domenico, M.; Insolia, A.; Lyberis, H.

2012-12-01

347

Effects of anisotropy on dynamic tensile behavior  

SciTech Connect

A stability analysis for an anisotropic stretching rod is presented. We consider the particular case of a rapidly stretching titanium jet using a continuum code to examine anisotropic plastic response in the finite-neck regime. It was found that the classical analysis (yield strength is inversely proportional to stability) is insufficient; anisotropic jets can be more or less stable than their maximum or minimum yield strengths, depending on initial perturbations and the orientation of the anisotropy. One particular anisotropy -- with the weak direction along the jet axis -- appears to be generally stabilizing. 10 refs., 6 figs.

Schifert, S.K.; Davidson, R.F.; Maudlin, P.J.

1991-01-01

348

Global azimuthal anisotropy in the transition zone.  

PubMed

Surface wave dispersion measurements for Love wave overtones carry evidence of azimuthal anisotropy in the transition zone of Earth's mantle (400 to 660 kilometers deep). A Backus-Gilbert inversion of anisotropic phase velocity maps, with resolution kernels mainly sensitive to the transition zone, shows a robust long-wavelength azimuthally anisotropic velocity structure. This observation puts new constraints on the mineralogy and dynamics of the transition zone because this anisotropy may result from aligned minerals, tilted laminated structures, or even organized pockets of fluid inclusions. PMID:12016310

Trampert, Jeannot; van Heijst, Hendrik Jan

2002-05-17

349

Anisotropy of losses in amorphous ribbons  

NASA Astrophysics Data System (ADS)

The soft magnetic properties of amorphous ribbons are expected to be anistropic because of the shear deformation during the melt spinning procedure. In this paper the losses of an Fe 80B 14Si 6 amorphous ribbon were measured on stripes which were cut either parallel or perpendicular to the ribbon axis. The dependence of the losses as a function of peak induction and frequency suggests that there is an easy axis of magnetization parallel to the ribbon axis. After stress relief annealing this anisotropy is reduced. That is why this anisotropy is assumed to be due to internal stress introduced upon quenching.

Roth, S.; Habiger, D.-U.

1986-10-01

350

Anisotropy effects on 3D waveform inversion  

NASA Astrophysics Data System (ADS)

In the recent years 3D waveform inversion has become achievable procedure for seismic data processing. A number of datasets has been inverted and presented (Warner el al 2008, Ben Hadj at all, Sirgue et all 2010) using isotropic 3D waveform inversion. However the question arises will the results be affected by isotropic assumption. Full-wavefield inversion techniques seek to match field data, wiggle-for-wiggle, to synthetic data generated by a high-resolution model of the sub-surface. In this endeavour, correctly matching the travel times of the principal arrivals is a necessary minimal requirement. In many, perhaps most, long-offset and wide-azimuth datasets, it is necessary to introduce some form of p-wave velocity anisotropy to match the travel times successfully. If this anisotropy is not also incorporated into the wavefield inversion, then results from the inversion will necessarily be compromised. We have incorporated anisotropy into our 3D wavefield tomography codes, characterised as spatially varying transverse isotropy with a tilted axis of symmetry - TTI anisotropy. This enhancement approximately doubles both the run time and the memory requirements of the code. We show that neglect of anisotropy can lead to significant artefacts in the recovered velocity models. We will present inversion results of inverting anisotropic 3D dataset by assuming isotropic earth and compare them with anisotropic inversion result. As a test case Marmousi model extended to 3D with no velocity variation in third direction and with added spatially varying anisotropy is used. Acquisition geometry is assumed as OBC with sources and receivers everywhere at the surface. We attempted inversion using both 2D and full 3D acquisition for this dataset. Results show that if no anisotropy is taken into account although image looks plausible most features are miss positioned in depth and space, even for relatively low anisotropy, which leads to incorrect result. This may lead to misinterpretation of results. However if correct physics is used results agree with correct model. Our algorithm is relatively affordable and runs on standard pc clusters in acceptable time. Refferences: H. Ben Hadj Ali, S. Operto and J. Virieux. Velocity model building by 3D frequency-domain full-waveform inversion of wide-aperture seismic data, Geophysics (Special issue: Velocity Model Building), 73(6), P. VE101-VE117 (2008). L. Sirgue, O.I. Barkved, J. Dellinger, J. Etgen, U. Albertin, J.H. Kommedal, Full waveform inversion: the next leap forward in imaging at Valhall, First Brake April 2010 - Issue 4 - Volume 28 M. Warner, I. Stekl, A. Umpleby, Efficient and Effective 3D Wavefield Tomography, 70th EAGE Conference & Exhibition (2008)

Stekl, I.; Warner, M.; Umpleby, A.

2010-12-01

351

Fractional vector calculus and fractional Maxwell's equations  

SciTech Connect

The theory of derivatives and integrals of non-integer order goes back to Leibniz, Liouville, Grunwald, Letnikov and Riemann. The history of fractional vector calculus (FVC) has only 10 years. The main approaches to formulate a FVC, which are used in the physics during the past few years, will be briefly described in this paper. We solve some problems of consistent formulations of FVC by using a fractional generalization of the Fundamental Theorem of Calculus. We define the differential and integral vector operations. The fractional Green's, Stokes' and Gauss's theorems are formulated. The proofs of these theorems are realized for simplest regions. A fractional generalization of exterior differential calculus of differential forms is discussed. Fractional nonlocal Maxwell's equations and the corresponding fractional wave equations are considered.

Tarasov, Vasily E. [Skobeltsyn Institute of Nuclear Physics, Moscow State University, Leninskie gory, Moscow 119991 (Russian Federation)], E-mail: tarasov@theory.sinp.msu.ru

2008-11-15

352

Increased number of astrocytes and macrophages/microglial cells in the corpus callosum in amyotrophic lateral sclerosis.  

PubMed

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by degeneration of both upper and lower motor neurons. Neuropathologically, degeneration of the corticospinal tracts is evident and may be associated with loss of motor neurons in the motor cortex. The data from a recently developed imaging technology, the diffusion tensor imaging method of MRI have suggested that white matter in the corpus callosum (CC) is lost in patients with ALS. However, the specific neuropathologic changes of the commissural fibers remain unclear. To investigate the pathologic changes of the CC in ALS, we analyzed midsagittal sections of the CC from eight individuals with ALS and eight controls by using conventional staining and immunohistochemistry with antibodies against CD68, GFAP and phosphorylated neurofilament (SMI-31). The CC was divided into seven areas. The number of CD68-immunoreactive macrophages/microglia and GFAP-immunoreactive astrocytes was significantly higher in individuals with ALS than in controls in all areas of the CC except the rostrum. Among the patients with ALS, the number of macrophages/microglia and astrocytes was significantly higher in the posterior midbody and isthmus than in the rostrum. There was no significant difference in number of SMI-31 immunoreactive axons between ALS and control group as well as among each area of the CC. These findings suggest that pathologic changes in the CC in ALS are present in the posterior midbody and isthmus, where callosal motor fibers may traverse between the two hemispheres. CD68 and GFAP immunohistochemistry are sensitive methods to detect those pathologic changes in routine paraffin-embedded specimens. PMID:23530811

Sugiyama, Mikiko; Takao, Masaki; Hatsuta, Hiroyuki; Funabe, Sayaka; Ito, Shinji; Obi, Tomokazu; Tanaka, Fumiaki; Kuroiwa, Yoshiyuki; Murayama, Shigeo

2013-12-01

353

Oligodendrocytes in mouse corpus callosum are coupled via gap junction channels formed by connexin47 and connexin32.  

PubMed

According to previously published ultrastructural studies, oligodendrocytes in white matter exhibit gap junctions with astrocytes, but not among each other, while in vitro oligodendrocytes form functional gap junctions. We have studied functional coupling among oligodendrocytes in acute slices of postnatal mouse corpus callosum. By whole-cell patch clamp we dialyzed oligodendrocytes with biocytin, a gap junction-permeable tracer. On average 61 cells were positive for biocytin detected by labeling with streptavidin-Cy3. About 77% of the coupled cells stained positively for the oligodendrocyte marker protein CNPase, 9% for the astrocyte marker GFAP and 14% were negative for both CNPase and GFAP. In the latter population, the majority expressed Olig2 and some NG2, markers for oligodendrocyte precursors. Oligodendrocytes are known to express Cx47, Cx32 and Cx29, astrocytes Cx43 and Cx30. In Cx47-deficient mice, the number of coupled cells was reduced by 80%. Deletion of Cx32 or Cx29 alone did not significantly reduce the number of coupled cells, but coupling was absent in Cx32/Cx47-double-deficient mice. Cx47-ablation completely abolished coupling of oligodendrocytes to astrocytes. In Cx43-deficient animals, oligodendrocyte-astrocyte coupling was still present, but coupling to oligodendrocyte precursors was not observed. In Cx43/Cx30-double deficient mice, oligodendrocyte-to-astrocyte coupling was almost absent. Uncoupled oligodendrocytes showed a higher input resistance. We conclude that oligodendrocytes in white matter form a functional syncytium predominantly among each other dependent on Cx47 and Cx32 expression, while astrocytic connexins expression can promote the size of this network. PMID:20468052

Maglione, Marta; Tress, Oliver; Haas, Brigitte; Karram, Khalad; Trotter, Jacqueline; Willecke, Klaus; Kettenmann, Helmut

2010-07-01

354

Negative Associations between Corpus Callosum Midsagittal Area and IQ in a Representative Sample of Healthy Children and Adolescents  

PubMed Central

Documented associations between corpus callosum size and cognitive ability have heretofore been inconsistent potentially owing to differences in sample characteristics, differing methodologies in measuring CC size, or the use of absolute versus relative measures. We investigated the relationship between CC size and intelligence quotient (IQ) in the NIH MRI Study of Normal Brain Development sample, a large cohort of healthy children and adolescents (aged six to 18, n?=?198) recruited to be representative of the US population. CC midsagittal area was measured using an automated system that partitioned the CC into 25 subregions. IQ was measured using the Wechsler Abbreviated Scale of Intelligence (WASI). After correcting for total brain volume and age, a significant negative correlation was found between total CC midsagittal area and IQ (r?=??0.147; p?=?0.040). Post hoc analyses revealed a significant negative correlation in children (age<12) (r?=??0.279; p?=?0.004) but not in adolescents (age?12) (r?=??0.005; p?=?0.962). Partitioning the subjects by gender revealed a negative correlation in males (r?=??0.231; p?=?0.034) but not in females (r?=?0.083; p?=?0.389). Results suggest that the association between CC and intelligence is mostly driven by male children. In children, a significant gender difference was observed for FSIQ and PIQ, and in males, a significant age-group difference was observed for FSIQ and PIQ. These findings suggest that the correlation between CC midsagittal area and IQ may be related to age and gender.

Ganjavi, Hooman; Lewis, John D.; Bellec, Pierre; MacDonald, Penny A.; Waber, Deborah P.; Evans, Alan C.; Karama, Sherif

2011-01-01

355

Novel de novo SPOCK1 mutation in a proband with developmental delay, microcephaly and agenesis of corpus callosum.  

PubMed

Whole exome sequencing made it possible to identify novel de novo mutations in genes that might be linked to human syndromes (genotype first analysis). We describe a female patient with a novel de novo SPOCK1 variant, which has not been previously been associated with a human phenotype. Her features include intellectual disability with dyspraxia, dysarthria, partial agenesis of corpus callosum, prenatal-onset microcephaly and atrial septal defect with aberrant subclavian artery. Previous genetic, cytogenomic and metabolic studies were unrevealing. At age 13 years, exome sequencing on the patient and her parents revealed a de novo novel missense mutation in SPOCK1 (coding for Testican-1) on chromosome 5q31: c.239A>T (p.D80V). This mutation affects a highly evolutionarily conserved area of the gene, replacing a polar aspartic acid with hydrophobic nonpolar valine, and changing the chemical properties of the protein product, likely representing a pathogenic variant. Previous microdeletions of 5q31 including SPOCK1 have suggested genes on 5q31 as candidates for intellectual disability. No mutations or variants in other genes potentially linked to her phenotype were identified. Testicans are proteoglycans belonging to the BM-40/SPARC/osteonectin family of extracellular calcium-binding proteins. Testican-1 is encoded by the SPOCK1 gene, and mouse models have been shown it to be strongly expressed in the brain and to be involved in neurogenesis. We hypothesize that because this gene function is critical for neurogenesis, mutations could potentially lead to a phenotype with developmental delay and microcephaly. PMID:24583203

Dhamija, Radhika; Graham, John M; Smaoui, Nizar; Thorland, Erik; Kirmani, Salman

2014-03-01

356

Regional areas and widths of the midsagittal corpus callosum among HIV-infected patients on stable antiretroviral therapies.  

PubMed

Recent reports suggest that a growing number of human immunodeficiency virus (HIV)-infected persons show signs of persistent cognitive impairment even in the context of combination antiretroviral therapies (cART). The basis for this finding remains poorly understood as there are only a limited number of studies examining the relationship between CNS injury, measures of disease severity, and cognitive function in the setting of stable disease. This study examined the effects of HIV infection on cerebral white matter using quantitative morphometry of the midsagittal corpus callosum (CC) in 216 chronically infected participants from the multisite HIV Neuroimaging Consortium study currently receiving cART and 139 controls. All participants underwent MRI assessment, and HIV-infected subjects also underwent measures of cognitive function and disease severity. The midsagittal slice of the CC was quantified using two semi-automated procedures. Group comparisons were accomplished using ANOVA, and the relationship between CC morphometry and clinical covariates (current CD4, nadir CD4, plasma and CSF HIV RNA, duration of HIV infection, age, and ADC stage) was assessed using linear regression models. HIV-infected patients showed significant reductions in both the area and linear widths for several regions of the CC. Significant relationships were found with ADC stage and nadir CD4 cell count, but no other clinical variables. Despite effective treatment, significant and possibly irreversible structural loss of the white matter persists in the setting of chronic HIV disease. A history of advanced immune suppression is a strong predictor of this complication and suggests that antiretroviral intervention at earlier stages of infection may be warranted. PMID:21556960

Tate, David F; Sampat, Mehul; Harezlak, Jaroslaw; Fiecas, Mark; Hogan, Joseph; Dewey, Jeffrey; McCaffrey, Daniel; Branson, Daniel; Russell, Troy; Conley, Jared; Taylor, Michael; Schifitto, Giovanni; Schifitto, Giavoni; Zhong, J; Daar, Eric S; Alger, Jeffrey; Brown, Mark; Singer, Elyse; Campbell, T; McMahon, D; Tso, Y; Matesan, Janetta; Letendre, Scott; Paulose, S; Gaugh, Michelle; Tripoli, C; Yiannoutsos, Constantine; Bigler, Erin D; Cohen, Ronald A; Guttmann, Charles R G; Navia, Bradford

2011-08-01

357

Unfolding Fraction Multiplication  

ERIC Educational Resources Information Center

Students often have difficulty understanding fractions, in general, and understanding how to multiply fractions, in particular. To move past this potential problem area, students need to develop a deeper understanding of multiplication and connect the ideas to fractions. In this article, the authors share their insights into teaching fraction

Wyberg, Terry; Whitney, Stephanie R.; Cramer, Kathleen A.; Monson, Debra S.; Leavitt, Seth

2011-01-01

358

Fractions Are Fun!  

NSDL National Science Digital Library

This project will help you to become more familiar with fractions. Go to this website and go to the first three exercises.Complex Fraction -- from MathWorld Go to this website and go to the first three exercise.Reduced Fraction -- from MathWorld Go to this website and go to the first three exercise.Fractions ...

Holmgren, Mr.

2005-10-25

359

Fraction Matcher Game  

NSDL National Science Digital Library

This fraction game (Java) enables students to find matching fractions using numbers and pictures, to match fractions in different picture patterns, and to compare fractions using numbers and patterns. Included in this website are the interactive simulation, lesson plan in PDF or docx, student instruction sheet in PDF or docx, and a progress tracker in PDF or xlsx.

Loeblein, Trish; Simulations, Phet I.

2012-07-02

360

Multiply Fractions Jeopardy  

NSDL National Science Digital Library

This interactive game for one or two players is presented Jeopardy-style with five categories: Multiply a Whole Number by a Fraction, Multiply a Fraction by a Fraction, Problem Solving, Estimate Products, and More Multiplying Fractions. Participants gain or lose points as they get answers right or wrong, and correct answers are displayed with a solution is submitted.

2006-01-01

361

Introduction to Proper Fractions  

NSDL National Science Digital Library

In this lesson students learn the meaning of fractions as parts of a whole and parts of a set. They learn key vocabulary and how to compare and order fractions. The lesson links to an interactive game, Fraction Fun (catalogued separately), which gives practice in naming fractions, and to downloadable follow-up exercises (Word and pdf).

2011-01-01

362

Fractional statistical mechanics.  

PubMed

The Liouville and first Bogoliubov hierarchy equations with derivatives of noninteger order are derived. The fractional Liouville equation is obtained from the conservation of probability to find a system in a fractional volume element. This equation is used to obtain Bogoliubov hierarchy and fractional kinetic equations with fractional derivatives. Statistical mechanics of fractional generalization of the Hamiltonian systems is discussed. Liouville and Bogoliubov equations with fractional coordinate and momenta derivatives are considered as a basis to derive fractional kinetic equations. The Fokker-Planck-Zaslavsky equation that has fractional phase-space derivatives is obtained from the fractional Bogoliubov equation. The linear fractional kinetic equation for distribution of the charged particles is considered. PMID:17014213

Tarasov, Vasily E

2006-09-01

363

A Instrument and Technique for Measuring the Anisotropy in the Cosmic Microwave Background Radiation  

NASA Astrophysics Data System (ADS)

There is a wealth of information contained in the spatial temperature distribution of the Cosmic Microwave Background Radiation (CMB) >From the pioneering discovery of anisotropy by the COBE satellite to the latest balloon payloads and ground based observations, measurements of the CMB have become the cornerstone of our current understanding of the Universe. Currently, the second generation of CMB experiments are coming on-line. With improved detectors and novel observing strategies, these experiments are destined to make the transition from 'discovering' the anisotropy in the CMB to making precision measurements of the spatial correlation function. Herein I describe the most recent of these second generation experiments: the Medium Scale Anisotropy Measurement (MSAM II). MSAM II is a balloon-based telescope with a bolometric receiver cooled by an Adiabatic Demagnetization Refrigerator to 100 mK. MSAM II samples the sky with a 20 prime FWHM beam swept with a triangle wave at 2.5 Hz and will make a precision measurement of the spatial correlation function from 1 = 100 to 1 = 500. In addition to a comprehensive discussion of the fabrication and development of the cryogenic and optical systems of MSAM II, I present a novel method of estimating cosmological parameters from anisotropy measurements using a maximum Likelihood technique which employs the full covariance matrix of observations. This method has been used on the combined three years of MSAM I datasets to constrain the mass fraction of baryons in the universe, ?B, as well as a number of other cosmological parameters.

Wilson, Grant W.

1997-09-01

364

Can large magnetic anisotropy and high spin really coexist?  

PubMed

This theoretical study discusses the interplay of the magnetic anisotropy and magnetic exchange interaction of two Mn6 complexes and suggests that large magnetic anisotropy is not favoured by a high spin state of the ground state. PMID:18399403

Ruiz, Eliseo; Cirera, Jordi; Cano, Joan; Alvarez, Santiago; Loose, Claudia; Kortus, Jens

2008-01-01

365

On the Magnetic Susceptiability Anisotropy of Deep-Sea Sediment.  

National Technical Information Service (NTIS)

Susceptibility anisotropies in the form of vertically prolate ellipsoids have been reported in many deep-sea sediment cores. The results of the present investigation suggest that these anisotropies may not describe the original magnetic fabric of deep-sea...

D. V. Kent W. Lowrie

1975-01-01

366

Magnetic anisotropy data of C6HOCl5  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume C `Diamagnetic Susceptibility and Magnetic Anisotropy of Organic Compounds' of Volume 27 `Diamagnetic Susceptibility and Anisotropy' of Landolt-Börnstein - Group II Molecules and Radicals.

Kumar, M.; Gupta, R.

367

Tests for Strength Characteristics of a Shistose Gneiss. Mechanical Anisotropy.  

National Technical Information Service (NTIS)

The testing program was conducted to evaluate the mechanical anisotropy of a schistose gneiss and to develop and refine procedures for future studies of anisotropy. This second interim report concerns tests on a schistose gneiss from a surface excavation....

E. J. Deklotz J. Brown

1967-01-01

368

Magnetic anisotropy data of C76 (D2)  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume C `Diamagnetic Susceptibility and Magnetic Anisotropy of Organic Compounds' of Volume 27 `Diamagnetic Susceptibility and Anisotropy' of Landolt-Börnstein - Group II Molecules and Radicals.

Kumar, M.; Gupta, R.

369

Effects of Energy GAP Anisotropy in Pure Superconductors.  

National Technical Information Service (NTIS)

Various effects of anisotropy of the superconducting energy gap are theoretically considered. In order to estimate the effects of anisotropy upon the thermodynamic properties of pure, single-crystal superconductors, a factorable BCS-like model for the eff...

J. R. Clem

1966-01-01

370

Product of Simple Fractions  

NSDL National Science Digital Library

This Java applet displays the multiplication of two fractions as an overlaying of rectangular areas. The left rectangle illustrates the left fraction as a horizontal fraction bar; the right rectangle shows the right fraction as a vertical fraction bar; and the middle rectangle represents their overlay. To change the numerator or denominator of the multiplicands, click a digit slightly off-center (left to decrease, right to increase).

Interactive Math Miscellany And Puzzles, Alexander B.

2011-01-01

371

Interactive Fraction Number Lines  

NSDL National Science Digital Library

In this lesson students make models of fractions, including a human number line. Using a number line, students develop conceptual understanding of fractions. Students use the number line to represent and compare fractions less than one. The activities are engaging and include full participation/engagement of all students. The fractions are limited to positive fractions less than one with a denominator of 2 or 4 including 0 and 1 whole.

Green, Michael

2012-05-25

372

Single Fraction Pointer  

NSDL National Science Digital Library

This interactive Java applet helps users explore fractions through partitioning circles and squares. The applet provides a random fraction and the user creates a representation of that fraction by partitioning and coloring a circle or a square. The applet also plots the fraction on a number line and points from the shape to the number line displaying its equivalent value as the fraction is being built. An optional scoring feature allows users to keep track of the number correct.

2006-01-01

373

Anisotropy of Bottom Loss in Marine Sediments.  

National Technical Information Service (NTIS)

We observed anisotropy in the acoustic reflection amplitudes from the seafloor at Hydrate Ridge on the Oregon Margin. We analyzed acoustic data from several OBS receivers and several sound-source lines with one line being perpendicular to the others. We u...

D. A. Lindwall, W. T. Wood

2010-01-01

374

Response of bacterial colonies to imposed anisotropy  

Microsoft Academic Search

We present theoretical and experimental studies of bacterial growth patterns in the presence of imposed anisotropy. The role of chemotactic signaling in the cooperative response of the bacteria is demonstrated. In the presence of sixfold symmetry, patterns with a tantalizing similarity to those of snowflakes are formed. Transitions from concave to convex shaped envelope as a function of peptone level

Eshel Ben-Jacob; Ofer Shochet; Adam Tenenbaum; Inon Cohen; Andras Czirók; Tamas Vicsek

1996-01-01

375

Ion Temperature Anisotropies in Helicon Plasmas  

NASA Astrophysics Data System (ADS)

Laser induced fluorescence measurements of the ion temperature in an argon helicon plasma indicate a substantial ion temperature anisotropy (perpendicular over parallel). Anisotropies as large as 5 have been observed. We will present evidence that suggests the anisotropies are due to a difference in the parallel and perpendicular particle confinement times. The perpendicular ion temperature scales linearly with the applied magnetic field strength, indicative of Bohm-like particle confinement [Scime et al., Plasma Sources Sci. and Tech. 7, 186-191 (1998)]. The parallel ion temperature is independent of the magnetic field strength. Experimental tests of potential sources of error, such as Zeeman broadening, Stark broadening, power broadening, and frequency hole burning will be reviewed. The West Virginia University Hot hELicon eXperiment (HELIX) is part of a larger experiment designed to experimentally model the high pressure, highly anisotropic plasma of the Earth's magnetosheath. The implications of the observed ion temperature anisotropy control in HELIX will also be discussed with respect to the magnetosheath experiments.

Scime, Earl; Balkey, Matthew; Boivin, Robert; Keiter, Paul; Kline, John

1998-10-01

376

Numerical likelihood analysis of cosmic ray anisotropies  

SciTech Connect

A numerical likelihood approach to the determination of cosmic ray anisotropies is presented which offers many advantages over other approaches. It allows a wide range of statistically meaningful hypotheses to be compared even when full sky coverage is unavailable, can be readily extended in order to include measurement errors, and makes maximum unbiased use of all available information.

Carlos Hojvat et al.

2003-07-02

377

Correlation Functions of CMB Anisotropy and Polarization  

NASA Astrophysics Data System (ADS)

We work out the exact two-point correlation functions of the Stokes parameters of the cosmic microwave background in terms of the spin-weighted spherical harmonics. The window functions for the detector with Gaussian angular response in anisotropy as well as polarization measurements are derived.

Ng, K. W.

378

Correlation Functions of CMB Anisotropy and Polarization  

Microsoft Academic Search

We work out the exact two-point correlation functions of the Stokes parameters of the cosmic microwave background in terms of the spin-weighted spherical harmonics. The window functions for the detector with Gaussian angular response in anisotropy as well as polarization measurements are derived. Printing Options Send high resolution image to Level 2 Postscript Printer Send low resolution image to Level

K. W. Ng

1999-01-01

379

Anisotropy of Wood in the Microwave Region  

ERIC Educational Resources Information Center

Wood is transparent for microwaves and due to its anisotropic structure has anisotropic dielectric properties. A laboratory experiment that allows for the qualitative demonstration and quantitative measurements of linear dichroism and birefringence in the microwave region is presented. As the proposed experiments are based on the anisotropy (of…

Ziherl, Sasa; Bajc, Jurij; Urankar, Bernarda; Cepic, Mojca

2010-01-01

380

Anisotropy of p-wave Josephson junction  

NASA Astrophysics Data System (ADS)

The anisotropy of the dc Josephson current in the superconducting junctions of the p-wave equal spin pairing symmetry is theoretically investigated by the Furusaki-Tsukada-like formula. The current phase relations exhibit different oscillation periods and different phase shifts for the current along different directions, respectively.

Wang, Zhen-Yan; Shen, Rui

2010-08-01

381

Magnetic anisotropy of strained epitaxial manganite films  

SciTech Connect

The in-plane magnetic anisotropy of epitaxial La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO) films is studied at room temperature by the following three independent techniques: magnetooptical Kerr effect, ferromagnetic resonance at a frequency of 9.61 GHz, and recording of absorption spectra of electromagnetic radiation at a frequency of 290.6 MHz. The films are deposited onto NdGaO{sub 3} (NGO) substrates in which the (110)NGO plane is tilted at an angle of 0-25.7 Degree-Sign to the substrate plane. The uniaxial magnetic anisotropy induced by the strain of the film is found to increase with the tilt angle of the (110)NGO plane. A model is proposed to describe the change in the magnetic anisotropy energy with the tilt angle. A sharp increase in the radio-frequency absorption in a narrow angular range of a dc magnetic field near a hard magnetization axis is detected The anisotropy parameters of the LSMO films grown on (110)NGO, (001)SrTiO{sub 3}, and (001)[(LaAlO{sub 3}){sub 0.3} + (Sr{sub 2}AlTaO{sub 6}){sub 0.7}] substrates are compared.

Demidov, V. V., E-mail: demidov@cplire.ru; Borisenko, I. V.; Klimov, A. A.; Ovsyannikov, G. A.; Petrzhik, A. M.; Nikitov, S. A. [Russian Academy of Sciences, Institute of Radio-Engineering and Electronics (Russian Federation)

2011-05-15

382

The Kondo necklace model with planar anisotropy  

Microsoft Academic Search

We study the one-dimensional anisotropic Kondo necklace model at zero temperature through White's density matrix renormalization group technique. The ground state energy and the spin gap were calculated as a function of the exchange parameter for two anisotropy values. We found a finite critical point separating a Kondo singlet from an antiferromagnetic phase. The transition is highly congruent with a

J. J. Mendoza-Arenas; R. Franco; J. Silva-Valencia

2009-01-01

383

Measurement of Planar Substrate Uniaxial Anisotropy  

Microsoft Academic Search

A new technique to measure uniaxial anisotropy in planar substrates is described. The technique uses a single dual-mode resonator. Each mode of the resonator has a different distribution of horizontal (parallel to the substrate surface) and vertical (perpendicular to the substrate surface) directed fields. Using an electromagnetic analysis of the dual-mode resonator, the resonant frequencies of the modes are space

James C. Rautio; Serhend Arvas

2009-01-01

384

Relative sensitivity of formability to anisotropy  

SciTech Connect

This work compares the relative importance of material anisotropy in sheet forming as compared to other material and process variables. The comparison is made quantitative by the use of normalized dependencies of depth to failure (forming limit is reached) on various measures of anisotropy, as well as strain and rate sensitivity, friction, and tooling. Comparisons are made for a variety of forming processes examined previously in the literature as well as two examples of complex stampings in this work. 7 The examples rover a range from nearly pure draw to nearly pure stretch situations, and show that for materials following a quadratic yield criterion, anisotropy is among the most sensitive parameters influencing formability. For materials following higher-exponent yield criteria, the dependency is milder but is still of the order of most other process parameters. However, depending on the particular forming operation, it is shown that in some cases anisotropy may be ignored, whereas in others its consideration is crucial to a good quality analysis.

Logan, R.W.; Maker, B.N.

1997-01-01

385

Measurements of Magnetic Anisotropy in Sickle Cells.  

National Technical Information Service (NTIS)

Room temperature magnetic measurements in deoxigenated sickle cells showed the existence of magnetic anisotropy, delta chi=1,29 x 10 exp -3 . This effect was supposed paramagnetic and considered to be due to the iron atoms of the hemoglobin molecules whic...

L. H. Salvo Souza

1982-01-01

386

Optical anisotropy in photoactive yellow protein film  

NASA Astrophysics Data System (ADS)

Photoinduced anisotropy of photoactive yellow protein film in polyvinyl alcohol matrix was investigated. Studies were done for wavelengths longer than 446 nm, the location of the absorption maximum. Dicroism and birefringence of the sample were found to be wavelength dependent but intensity independent.

Vanhanen, J.; Leppanen, V. P.; Jaaskelainen, T.; Parkkinen, S.; Parkkinen, J. P. S.

2001-01-01

387

Effects of unidirectional exchange anisotropy in ferrites  

Microsoft Academic Search

A number of anomalous effects occurring at the compensation and Curie points of ferrites are explained on the basis of the concept of unidirectional exchange anisotropy. Among these are the violation of 'evennies' for the magnetostrictive, magnetoresistive, and magnetocaloric effects, the antiferromagnetic paraprocess, and some other phenomena. Based on the analysis of these effects, a piezomagnetic effect is predicted to

Konstantin P Belov

1999-01-01

388

Inner core anisotropy in three dimensions  

Microsoft Academic Search

The purpose of this paper is the investigation of cylindrical anisotropy in the inner core based on the travel time anomalies of the PKIKP phase. We use the arrival times reported in the International Seismological Centre Bulletins for years 1964-1990. We select only earthquakes which have a good azimuthal coverage and a sufficiently large number of reporting stations. The earthquakes

Wei-jia Su; Adam M. Dziewonski

1995-01-01

389

Theory of Optical Anisotropy of Chain Molecules.  

National Technical Information Service (NTIS)

The mean-square optical anisotropy (gamma squared)=3/2 trace (alpha alpha) where alpha is the anisotropic part of the optical polarizability tensor and ( ) denotes the average over all configurations of the chain molecule, is treated according to the revi...

P. J. Flory

1971-01-01

390

Analytical Spectra of CMB Anisotropies and Polarization  

NASA Astrophysics Data System (ADS)

We briefly present the results of our analytical studies on CMB anisotropies and polarizations generated by scalar metric perturbations in synchronous gauge, parallel to the previous work with RGW as a generating source. The analytical the spectra ClXX are explicitly given and the influences of various cosmological processes are examined.

Zhang, Yang; Cai, Zheng

391

Pizza Fractions: Beginning With Simple Fractions  

NSDL National Science Digital Library

In this iOS app students are introduced visually to the concept of fractions by having them identify the simple fraction (denominators 1-12, excluding sevenths and elevenths) represented by pizza picture example. Each round of the game includes ten visual models; at the end of the round students receive a score for accuracy and speed.

2013-01-15

392

Higher Fractions Theory of Fractional Hall Effect.  

National Technical Information Service (NTIS)

A theory of fractional quantum Hall effect is generalized to higher fractions. N-particle model interaction is used and the gap is expressed through n-particles wave function. The excitation spectrum in general and the mean field critical behaviour are de...

I. Z. Kostadinov V. N. Popov

1985-01-01

393

Anisotropy of magnetic susceptibility of some metamorphic minerals  

Microsoft Academic Search

The anisotropy of susceptibility of metamorphic rocks can be due to paramagnetic rock-forming silicates such as amphiboles, chlorites and micas. It is not always necessary to invoke fabrics of separate grains of iron oxide to explain the anisotropy. Minimum estimates of lattice anisotropies of typical samples of silicates have maximum-to-minimum ratios of 1.1-1.7. Since the magnetic anisotropies of most metamorphic

G. Borradaile; W. Keeler; C. Alford; P. Sarvas

1987-01-01

394

Angular anisotropy of fragments differing in their yields  

SciTech Connect

The angular anisotropy of individual fragments has been studied in fission of /sup 238/U by neutrons. In contrast to previous studies, as a result of the use of a radiochemical technique, were able to measure the anisotropy of fragments with greatly differing yields (up to 700 times, including symmetric fission) directly at the fission barrier and in the region of high anisotropy. The anisotropies coincide.

Gokhberg, B.M.; Lisin, S.K.; Morozov, L.N.; Morozov, N.A.; Pchelin, V.A.; Chistyakov, L.V.; Shigin, V.A.; Shubko, V.M.

1981-02-01

395

The role of geological structure in crustal seismic anisotropy: identification and quantification of "structural anisotropy"  

NASA Astrophysics Data System (ADS)

Seismic anisotropy is the cumulative interplay between propagating elastic waves and anisotropic earth material. Unraveling this effect in deformed crustal terranes is complex due to the roles of microscale fabric and macroscale structural geometry, the bending of seismic raypaths due to velocity gradients, and often the observation of anisotropy as second-order waveform/traveltime effects. While seismologists recognize that seismic anisotropy can originate from upper crustal fractures or by organized fine-scale layering of isotropic material, we focus on crustal anisotropy produced by the combined effects of microscale deformational fabrics and macroscale structural geometries formed during tectonic deformation and/or regional metamorphism. Material anisotropy involves at least four factors that contribute to seismic anisotropy: (1) microstructural characteristics including spatial arrangement, modal abundances, and crystallographic and shape orientations of constituent minerals, (2) inherent azimuthal variation of properties and approximation using symmetry classes, (3) bulk representation (effective media) of material properties at different scales, and (4) the types and internal geometries of macroscale structures. Based on the relative scales of fabric-filled geological structures and seismic wavelengths, a seismic wave may sample sub-portions of a structure or may pass through, responding to the bulk average of fine structure. While many seismologists focus on lattice preferred orientation (LPO), crystallographic preferred orientation (CPO), or shape preferred orientation (SPO) as the fine-scale cause of seismic anisotropy, we also recognize that a rock at the thin section to hand sample scale will define an amount of potential seismic anisotropy. However, the reorienting of sample-scale anisotropy by macroscale structures imparts its own effect. We define this response to larger-scale structure as "structural anisotropy". Furthermore, via the use of tensorial effective media concepts (bulk averaged elasticity tensors) we obtain an algebraic separation of the structural geometry from the rocks composing the structure. This allows for treatment of the structure as a geometry orientation operator that will map a small scale hand sample or representative rock into a large scale structure, from which elasticity tensors can be obtained that represent the earth structure. We demonstrate this with geological folds that can be represented by trigonometric sine waves. The fold hinge angle is a shape parameter that represents fold height to wavelength. If a foliated rock composes the folds, the net symmetry is not transverse isotropic (TI) rotating from horizontal to vertical sheets, but morphs from radial TI symmetry to weakly orthorhombic (at fold hinge angles of 60 degrees) to azimuthal TI symmetry. We describe the tensorial algebra that underlies structural anisotropy, show the net changes of rock symmetry due to sine wave folds, and the corresponding effects to seismic wave propagation as illustrated with synthetic anisotropic modeling.

Okaya, D. A.; Johnson, S. E.; Vel, S.

2010-12-01

396

Preferred Orientation and Anisotropy in Shales  

NASA Astrophysics Data System (ADS)

Anisotropy in clay-rich sedimentary rocks is receiving increasing attention. Seismic anisotropy is critical for prospecting of petroleum deposits. Anisotropy of diffusion is relevant for environmental contaminants, including nuclear waste. In both cases the orientation of component minerals is a primary ingredient and largely because of small grain size and poor crystallinity the orientation distribution of clay minerals has been difficult to quantify. A method is introduced that uses hard synchrotron X-rays to obtain diffraction images of shales and applies the crystallographic Rietveld method to deconvolute the images and obtain quantitative information about phase concentrations, particle size and preferred orientation that can then be used to model macroscopic physical properties. It is illustrated for European shales that are currently investigated for their suitability as potential nuclear waste repositories (Opalinus Clay, Switzerland; Callovo-Oxfordian Clay, France). Opalinus shales from Mont Terri show strong alignment of (001) poles perpendicular to the bedding plane, both for sheetsilicates illite (with a pole density maximum of 5.2 multiples of a random distribution), kaolinite (3.0 m.r.d.), chlorite (2.8 m.r.d.) as well as calcite (4.4 m.r.d.). In Opalinus shales from Benken preferred orientation increases with depth from 564 m to 641 m: Chlorite, illite/smetctite and calcite from 2.5 to 3.5 m.r.d. and illite and kaolinite from 4 to 7 m.r.d. Oxfordian shales from Bure show a much weaker alignment of clay minerals (2-3 m.r.d. for illite) and a random distribution for calcite and quartz. This intrinsic contribution to anisotropy of about 10% for Mt. Terri and Benken and <5% for Bure is consistent with macroscopic properties where overall anisotropy is caused both by the orientation distribution of crystallites and high-aspect ratio pores.

Wenk, H.; Lonardelli, I.; Mazurek, M.; van Loon, L.

2006-12-01

397

Strain, anisotropy of anhysteretic remanence, and anisotropy of magnetic susceptibility in a slaty tuff  

Microsoft Academic Search

Finite strain data for the Borrowdale slaty tuffs compare variably with the anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM). Finite strain, determined from lapilli-rims, shows that slaty cleavage was formed by coaxial flattening with X:Y:Z in the ratio 1.74:1.21 and 0.48. AARM was measured in different coercivity windows to isolate contributions from magnetite of different

Norihiro Nakamura; Graham J. Borradaile

2001-01-01

398

Anisotropy in MHD turbulence due to a mean magnetic field  

Microsoft Academic Search

The development of anisotropy in an initially isotropic spectrum is studied numerically for two-dimensional magnetohydrodynamic turbulence. The anisotropy develops due to the combined effects of an externally imposed dc magnetic field and viscous and resistive dissipation at high wave numbers. The effect is most pronounced at high mechanical and magnetic Reynolds numbers. The anisotropy is greater at the higher wave

John V. Shebalin; W. H. Matthaeus; David Montgomery

1983-01-01

399

Noncubic magnetic anisotropies in bulk and thin-film garnets  

Microsoft Academic Search

Magnetic bubbles have been reported in bulk grown, chemical vapor deposition (CVD), and liquid phase epitaxy (LPE) garnets, implying the existence of noncubic anisotropies in all of these materials. Anisotropy magnitudes, directions, nonuniformities, and annealing behaviors and effects of strain relief on the anisotropies of several potentially useful garnet materials are presented and compared. These observations indicate that the noncubic

ARJEH J. KURTZIG; FRED B. HAGEDORN

1971-01-01

400

Secondary fabrics revealed by remanence anisotropy: methodological study and examples from plutonic rocks  

NASA Astrophysics Data System (ADS)

The fabric of fine-grained magnetite is isolated by partial remanence anisotropy (pAAR) measurements that combine cycles of anhysteretic remanence acquisition and alternating frequency (AF) tumbling demagnetization of the low-coercivity fraction. Since remanence intensities of the most coercive, fine-grained magnetite are very weak (rarely exceeding 10 per cent of the measured remanence in the studied samples), a methodological study is presented that defines optimal measurement schemes and examines the role of gyroremanence and background remanences due to hard remanence carriers. This procedure is applied to some `reddened' granites from Tana (Corsica) and Wichita (Oklahoma) and to the Tellnes ilmenite-rich norite (Norway). The pAAR fabrics for fine-grained magnetites are compared to the fabrics of the coarse-grained, primary magnetite grains, as shown by both the anisotropy of magnetic susceptibility (AMS) and the remanence anisotropy of the low-coercivity fraction. In Tellnes, fine-grained magnetite is believed to be of secondary origin; this is strongly suggested by the correlation between the pAAR fabrics and the orientations of sets of microfractures decorated by oxides. In the `reddened' granites, although no direct correlation between pAAR fabrics and microstructures could be evidenced, the comparison between unaltered specimens and hydrothermally altered ones reveals changes in magnetic properties and fabrics that are ascribable to this secondary geological process.

Trindade, Ricardo I. F.; Bouchez, Jean-Luc; Bolle, Olivier; Nédélec, Anne; Peschler1, Anne; Poitrasson, Franck

2001-11-01

401

Polyethylenimine/Oligonucleotide Polyplexes Investigated by Fluorescence Resonance Energy Transfer and Fluorescence Anisotropy  

PubMed Central

To advance knowledge on polyplex structure and composition, fluorescence resonance energy transfer (FRET) and anisotropy measurements were applied to polyplexes of rhodamine-labeled polyethylenimine (PEI) and fluorescein-labeled double-stranded oligodeoxynucleotide (ODN). About 25?kDa PEI was compared with low-molecular-weight PEI of 2.7?kDa. FRET reached maxima at amine to phosphate (N/P) ratios of 2 and 3 for 2.7?kDa and 25?kDa PEI, respectively, with similar average distances between donor and acceptor dye molecules in polyplexes. Anisotropy measurements allowed estimating the bound fractions of PEI and ODN. At N/P?=?6, all ODN was bound, but only 58% of PEI 25?kDa and 45% of PEI 2.7?kDa. In conclusion, the higher molecular weight of PEI may conformationally restrict the availability of amino groups for charge interaction with phosphate groups in ODN. Moreover, significant fractions of both types of PEI remain free in solution at N/P ratios frequently used for transfection. FRET and anisotropy measurements provide effective tools for probing polyplex compositions and designing optimized delivery systems.

Bickel, Ulrich; Huang, Juyang

2011-01-01

402

Playing Fraction Tracks  

NSDL National Science Digital Library

This interactive game, similar to "Fraction Game" (catalogued separately) allows two students an opportunity to think about how fractions are related to a unit whole, compare fractional parts of a whole, and find equivalent fractions. Two players move markers a total distance (forwards and backwards directions) that equals the random target fraction box, along their choice of seven parallel number line tracks, which are divided into different fractional parts. The goal is to move each of the seven markers to the right side of the game board before your opponent does. Instructions and discussion questions are given.

2011-01-01

403

Equivalent Fraction Pointer  

NSDL National Science Digital Library

This interactive Java applet helps users explore equivalent fractions through partitioning circles and squares. The applet provides a random fraction and the user creates one or two equivalent representations of that fraction by partitioning and coloring a square (or circle). The applet also plots the fraction on a number line and points from the shape to the number line displaying its equivalent value while the fraction is being built. Options include choice of circles or squares, one or two equivalent fractions, and a scoring feature allows users to keep track of the number correct.

2006-01-01

404

Equivalent Fraction Finder  

NSDL National Science Digital Library

This interactive Java applet helps users explore equivalent fractions through partitioning circles and squares. The applet provides a random fraction and the user creates one or two equivalent representations of that fraction by partitioning and coloring a square (or circle). The applet also plots the fraction on a number line and points from the shape to the number line displaying its equivalent value after the fraction is built. Options include choice of circles or squares, one or two equivalent fractions, and a scoring feature allows users to keep track of the number correct.

2006-01-01

405

Identifying Equivalent Fractions  

NSDL National Science Digital Library

This site helps students understand how to identify equivalent fractions by explaining what equivalent fractions are and how to compare two fractions to see if they are equivalent. There is also a list of fractions equivalent to 1/2, 1/3, 1/4, 1/5, and 2/5 so students can begin to see the pattern that emerges. Finally, the site presents an interactive game in which students can practice by naming the equivalent fraction to a given fraction.

Banfill, J. C.

2007-12-12

406

A 6.9 Mb 1qter deletion/4.4 Mb 18pter duplication in a boy with extreme microcephaly with simplified gyral pattern, vermis hypoplasia and corpus callosum agenesis.  

PubMed

We here report a boy presenting with developmental delay, growth retardation, facial dysmorphisms, vermis hypoplasia, micropolygyria and corpus callosum agenesis. Conventional and high resolution cytogenetic analyses were normal but high resolution oligonucleotide array-CGH, performed at the age of 4 years, allowed the characterisation of a de novo 6.9 Mb 1qter deletion/4.4 Mb 18pter duplication. Numerous 1qter deletions have already been described associated with brain malformations. Among 1q44 deleted genes, AKT3 is the strongest candidate gene for vermis hypoplasia and corpus callosum agenesis. PMID:18053786

Andrieux, Joris; Cuvellier, Jean-Christophe; Duban-Bedu, Bénédicte; Joriot-Chekaf, Sylvie; Dieux-Coeslier, Anne; Manouvrier-Hanu, Sylvie; Delobel, Bruno; Vallee, Louis

2008-01-01

407

Complex-anisotropy-induced pattern formation in bistable media.  

PubMed

A construct of anisotropy in bistable media is adopted to characterize the effects of anisotropy on pattern formation by means of anisotropic line tension. A velocity curvature relation is further derived to account for the anisotropic wave propagations. Stability analysis of transverse perturbations indicates that a sufficiently strong complex anisotropy can induce dynamical instabilities and even lead to a breakup of the wave patterns. Numerical simulations show that complex anisotropy can induce rich spatiotemporal behaviors in bistable media. The results of analysis and simulations demonstrate that this method successfully incorporates complex anisotropy into the reaction diffusion model and has general significance. PMID:19391804

He, Zhi Zhu; Liu, Jing

2009-02-01

408

Self-referential and social cognition in a case of autism and agenesis of the corpus callosum  

PubMed Central

Background While models of autism spectrum conditions (ASC) are emerging at the genetic level of analysis, clear models at higher levels of analysis, such as neuroanatomy, are lacking. Here we examine agenesis of the corpus callosum (AgCC) as a model at the level of neuroanatomy that may be relevant for understanding self-referential and social-cognitive difficulties in ASC. Methods We examined performance on a wide array of tests in self-referential and social-cognitive domains in a patient with both AgCC and a diagnosis of ASC. Tests included a depth-of-processing memory paradigm with self-referential and social-cognitive manipulations, self-report measures of self-consciousness, alexithymia, and empathy, as well as performance measures of first-person pronoun usage and mentalizing ability. The performance of the AgCC patient was compared to a group of individuals with ASC but without AgCC and with neurotypical controls. These comparison groups come from a prior study where group differences were apparent across many measures. We used bootstrapping to assess whether the AgCC patient exhibited scores that were within or outside the 95% bias-corrected and accelerated bootstrap confidence intervals observed in both comparison groups. Results Within the depth-of-processing memory paradigm, the AgCC patient showed decreased memory sensitivity that was more extreme than both comparison groups across all conditions. The patient’s most pronounced difficulty on this task emerged in the social-cognitive domain related to information-processing about other people. The patient was similar to the ASC group in benefiting less from self-referential processing compared to the control group. Across a variety of other self-referential (i.e. alexithymia, private self-consciousness) and social-cognitive measures (i.e. self-reported imaginative and perspective-taking subscales of empathy, mentalizing), the AgCC patient also showed more extreme scores than those observed for both of the comparison groups. However, the AgCC patient scored within the range observed in the comparison groups on measures of first-person pronoun usage and self-reported affective empathy subscales. Conclusions We conclude that AgCC co-occurring with a diagnosis of ASC may be a relevant model at the level of neuroanatomy for understanding mechanisms involved in self-referential and high-level social-cognitive difficulties in ASC.

2012-01-01

409

In Vivo Imaging of the Actin Polymerization State with Two-Photon Fluorescence Anisotropy  

PubMed Central

Using two-photon fluorescence anisotropy imaging of actin-GFP, we have developed a method for imaging the actin polymerization state that is applicable to a broad range of experimental systems extending from fixed cells to live animals. The incorporation of expressed actin-GFP monomers into endogenous actin polymers enables energy migration FRET (emFRET, or homoFRET) between neighboring actin-GFPs. This energy migration reduces the normally high polarization of the GFP fluorescence. We derive a simple relationship between the actin-GFP fluorescence polarization anisotropy and the actin polymer fraction, thereby enabling a robust means of imaging the actin polymerization state with high spatiotemporal resolution and providing what to the best of our knowledge are the first direct images of the actin polymerization state in live, adult brain tissue and live, intact Drosophila larvae.

Vishwasrao, Harshad D.; Trifilieff, Pierre; Kandel, Eric R.

2012-01-01

410

Using nanoscale and mesoscale anisotropy to engineer the optical response of three-dimensional plasmonic metamaterials.  

PubMed

The a priori ability to design electromagnetic wave propagation is crucial for the development of novel metamaterials. Incorporating plasmonic building blocks is of particular interest due to their ability to confine visible light. Here we explore the use of anisotropy in nanoscale and mesoscale plasmonic array architectures to produce noble metal-based metamaterials with unusual optical properties. We find that the combination of nanoscale and mesoscale anisotropy leads to rich opportunities for metamaterials throughout the visible and near-infrared. The low volume fraction (<5%) plasmonic metamaterials explored herein exhibit birefringence, a skin depth approaching that of pure metals for selected wavelengths, and directionally confined waves similar to those found in optical fibres. These data provide design principles with which the electromagnetic behaviour of plasmonic metamaterials can be tailored using high aspect ratio nanostructures that are accessible via a variety of synthesis and assembly methods. PMID:24934374

Ross, Michael B; Blaber, Martin G; Schatz, George C

2014-01-01

411

Impact of in utero exposure to EtOH on corpus callosum development and paw preference in rats: protective effects of silymarin  

PubMed Central

Background Using a rat model we have found that the bioflavonoid silymarin (SY) ameliorates some of the negative consequences of in utero exposure to ethanol (EtOH). In the current study our aim was to determine if laterality preference and corpus callosum development were altered in rat offspring whose mothers were provided with a concomitant administration of SY with EtOH throughout gestation. Methods We provided pregnant Fisher/344 rats with liquid diets containing 35% ethanol derived calories (EDC) throughout the gestational period. A silymarin/phospholipid compound containing 29.8% silybin was co administered with EtOH to a separate experimental group. We tested the offspring for laterality preference at age 12 weeks. After testing the rats were sacrificed and their brains perfused for later corpus callosum extraction. Results We observed incomplete development of the splenium in the EtOH-only offspring. Callosal development was complete in all other treatment groups. Rats from the EtOH-only group displayed a left paw preference; whereas control rats were evenly divided between right and left paw preference. Inexplicably both SY groups were largely right paw preferring. Conclusions The addition of SY to the EtOH liquid diet did confer some ameliorative effects upon the developing fetal rat brain.

Moreland, Nicol; La Grange, Linda; Montoya, Rebecca

2002-01-01

412

Inflammatory response and chemokine expression in the white matter corpus callosum and gray matter cortex region during cuprizone-induced demyelination.  

PubMed

Brain inflammation plays a central role in multiple sclerosis (MS). Besides lymphocytes, the astroglia and microglia mainly contribute to the cellular composition of the inflammatory infiltrate in MS lesions. Several studies were able to demonstrate that cortical lesions are characterized by lower levels of inflammatory cells among activated microglia/macrophages. The underlying mechanisms for this difference, however, remain to be clarified. In the current study, we compared the kinetics and extent of microglia and astrocyte activation during early and late cuprizone-induced demyelination in the white matter tract corpus callosum and the telencephalic gray matter. Cellular parameters were related to the expression profiles of the chemokines Ccl2 and Ccl3. We are clearly able to demonstrate that both regions are characterized by early oligodendrocyte stress/apoptosis with concomitant microglia activation and delayed astrocytosis. The extent of microgliosis/astrocytosis appeared to be greater in the subcortical white matter tract corpus callosum compared to the gray matter cortex region. The same holds true for the expression of the key chemokines Ccl2 and Ccl3. The current study defines a model to study early microglia activation and to investigate differences in the neuroinflammatory response of white vs. gray matter. PMID:22528463

Buschmann, J P; Berger, K; Awad, H; Clarner, T; Beyer, C; Kipp, M

2012-09-01

413

Fractions--Naming  

NSDL National Science Digital Library

This applet lets students practice naming fractions, by presenting various shapes divided into equal parts with some parts shaded. Students write the fraction in the boxes provided, and check. Equivalent fractions are recognized, but students are encouraged to name the fraction using the denominator indicated by the shape. Instructions for using the applet and teaching ideas for parents/teachers are available through the links at the top of the page.

2005-01-01

414

Micro-Computed Tomography Derived Anisotropy Detects Tumor Provoked Deviations in Bone in an Orthotopic Osteosarcoma Murine Model  

PubMed Central

Radiographic imaging plays a crucial role in the diagnosis of osteosarcoma. Currently, computed-tomography (CT) is used to measure tumor-induced osteolysis as a marker for tumor growth by monitoring the bone fractional volume. As most tumors primarily induce osteolysis, lower bone fractional volume has been found to correlate with tumor aggressiveness. However, osteosarcoma is an exception as it induces osteolysis and produces mineralized osteoid simultaneously. Given that competent bone is highly anisotropic (systematic variance in its architectural order renders its physical properties dependent on direction of load) and that tumor induced osteolysis and osteogenesis are structurally disorganized relative to competent bone, we hypothesized that ?CT-derived measures of anisotropy could be used to qualitatively and quantitatively detect osteosarcoma provoked deviations in bone, both osteolysis and osteogenesis, in vivo. We tested this hypothesis in a murine model of osteosarcoma cells orthotopically injected into the tibia. We demonstrate that, in addition to bone fractional volume, ?CT-derived measure of anisotropy is a complete and accurate method to monitor osteosarcoma-induced osteolysis. Additionally, we found that unlike bone fractional volume, anisotropy could also detect tumor-induced osteogenesis. These findings suggest that monitoring tumor-induced changes in the structural property isotropy of the invaded bone may represent a novel means of diagnosing primary and metastatic bone tumors.

Ichikawa, Jiro; Nyman, Jeffry S.; Cates, Justin M. M.; Haro, Hirotaka; Schwartz, Herbert S.; Schoenecker, Jonathan G.

2014-01-01

415

Essentials of Fractional Calculus  

Microsoft Academic Search

The aim of these introductory lectures is to provide the reader with the essentialsof the fractional calculus according to dierent approaches that can be useful for ourapplications in the theory of probability and stochastic processes. We discuss thelinear operators of fractional integration and fractional dierentiation, which wereintroduced in pioneering works by Abel, Liouville, Riemann, Weyl, Marchaud, M.Riesz, Feller and Caputo.

Rudolf Goren; Francesco Mainardi

2000-01-01

416

Comparing and Ordering Fractions  

NSDL National Science Digital Library

Use area models to compare and order fractions. Also see a visual representation of the least common denominator of two fractions. With the visual representation of the LCD, this Gizmo can be an introduction to adding and subtracting fractions with unlike denominators.

2007-12-12

417

Fraction Model II  

NSDL National Science Digital Library

With this tool, students can explore different representations for fractions. They can create a fraction, selecting any numerator or denominator up to 20, and see a model of the fraction as well as its percent and decimal equivalents. For the model, they can choose either a circle, a rectangle, or a set model.

Illuminations, Nctm

2000-01-01

418

Fractions Decimals & Percentages  

NSDL National Science Digital Library

This web page contains three Flash applets that help students explore relationships among fractions, decimals and percents. Users adjust the values represented visually by bars to compare or find equivalents of fractions to percents, fractions to decimals, or percents to decimals. The applets lend themselves well to classroom discussions with interactive white boards.

Weddell, Mark

2003-01-01

419

Fractions Dolphin Racing Game  

NSDL National Science Digital Library

In this online interactive game, students are tasked with using a variety of strategies to quickly compare fractions. By choosing the largest fraction, the student's dolphin travels further faster. This game encourages students to interpret the meaning of fractions and rely on strategies that go beyond finding common denominators.

Adults, Skillwise: E.

2012-08-03

420

Single Fraction Finder  

NSDL National Science Digital Library

This interactive Java applet helps users explore fractions through partitioning circles and squares. The applet provides a random fraction displayed on the number line, and the user creates a representation of that fraction by partitioning and coloring a circle or a square. An optional scoring feature allows users to keep track of the number correct.

2006-01-01

421

Bounded Fraction Pointer  

NSDL National Science Digital Library

Learners use area models to display the value of each of two fractions they have chosen (which are represented as points on a number line). They also graphically find a fraction whose value is between the two fractions (using an arrow on the number line as a guide), then determine its value.

The Shodor Education Foundation, Inc.

2007-12-12

422

Building Fractions Game  

NSDL National Science Digital Library

In this math lesson, learners investigate fractions by playing a game. To play, learners roll two dice and create a fraction, using the larger number rolled as the denominator and the smaller number as the numerator. Learners then build that fractional amount on the game mat with pattern block pieces. The winner is the player who builds the greatest number of hexagons.

Lessonplans, Utah

2012-10-22

423

ISS radiation environment anisotropies measured by ALTEA  

NASA Astrophysics Data System (ADS)

The detailed knowledge of the radiation environment inside the International Space Station is mandatory for an accurate radiation risk assessment. The uneven shielding of the Station induces a modulation of this environment which must be taken into account. We present here the first measurements of the Station radiation environment, discriminating particle trajectory and charge, made possible utilizing the 3D, Z-discriminated detection capability of the ALTEA-space detector. We bring evidences for an anisotropy in the radiation flux of heavy ions between the main Station axis and normal directions. This anisotropy reduces integrating over all detected particles, showing that secondary particles produced in the most shielded direction approximately maintain flux isotropy.

di Fino, Luca; Casolino, Marco; de Santis, Cristian; Larosa, Marianna; La Tessa, Chiara; Narici, Livio; Picozza, Piergiorgio; Zaconte, Veronica

424

Shear acoustic energy anisotropy of subsurface formations  

SciTech Connect

A method is described for measuring shear acoustic energy anisotropy of a core sample taken from a subterranean formation, comprising the steps of: (a) shaping the core sample to provide a pair of planar outer surfaces along parallel spaced-apart planes, (b) transmitting shear acoustic energy into the core sample from a first of the planar outer surfaces. The acoustic energy travels through the core sample to the second of the planar outer surfaces in a transmission pattern having a first azimuthal direction within a plane parallel to the planar outer surfaces, (c) receiving the acoustic energy at the second planar outer surface, (d) repeating steps (b) and (c) for differing azimuthal directions of transmission patterns as a measure of the shear acoustic energy anisotropy characteristics of the subterranean formation from which the core sample was taken.

Sprunt, E.S.; Smallwood, L.D.

1986-12-30

425

Tailored magnetic anisotropy in an amorphous trilayer  

SciTech Connect

An amorphous Co{sub 68}Fe{sub 24}Zr{sub 8}(3 nm)/Al{sub 70}Zr{sub 30}(3 nm)/Co{sub 68}Fe{sub 24}Zr{sub 8}(3 nm) trilayer system has been investigated using in-plane and out-of-plane angular dependent ferromagnetic resonance at different frequencies. The in-plane magnetic anisotropy is uniaxial, retaining its value of (2.9 {+-} 0.1) x 10{sup 3} J/m{sup 3} for each magnetic layer, whereas its direction was tailored independently in an arbitrary manner by applying an external magnetic field during the film deposition. The perpendicular anisotropy constant, supposed to reflect the interface quality, is nearly identical for both layers. Furthermore, the magnetic layers act independently upon each other due to the absence of interlayer coupling.

Fu Yu [Department of Physics, Southeast University, 211189 Nanjing (China); Fakultaet fuer Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universitaet Duisburg-Essen, 47048 Duisburg (Germany); Barsukov, I.; Spasova, M.; Lindner, J.; Meckenstock, R.; Farle, M. [Fakultaet fuer Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universitaet Duisburg-Essen, 47048 Duisburg (Germany); Raanaei, H. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala (Sweden); Department of Physics, Persian Gulf University, Bushehr 75168 (Iran, Islamic Republic of); Hjoervarsson, B. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala (Sweden)

2011-06-01

426

Cosmic-ray streaming and anisotropies  

NASA Technical Reports Server (NTRS)

The paper is concerned with the differential current densities and anisotropies that exist in the interplanetary cosmic-ray gas, and in particular with a correct formulation and simple interpretation of the momentum equation that describes these on a local basis. Two examples of the use of this equation in the interpretation of previous data are given. It is demonstrated that in interplanetary space, the electric-field drifts and convective flow parallel to the magnetic field of cosmic-ray particles combine as a simple convective flow with the solar wind, and that there exist diffusive currents and transverse gradient drift currents. Thus direct reference to the interplanetary electric-field drifts is eliminated, and the study of steady-state and transient cosmic-ray anisotropies is both more systematic and simpler.

Forman, M. A.; Gleeson, L. J.

1975-01-01

427

Constraints on the anisotropy of dark energy  

SciTech Connect

If the equation of state of dark energy is anisotropic there will be additional quadrupole anisotropy in the cosmic microwave background induced by the time-dependent anisotropic stress quantified in terms of {Delta}w. Assuming that the entire amplitude of the observed quadrupole is due to this anisotropy, we conservatively impose a limit of |{Delta}w|<2.1x10{sup -4} for any value of w{>=}-1 assuming that {Omega}{sub m}<0.5. This is considerably tighter than that which comes from supernovae. Stronger limits, up to a factor of 10, are possible for specific values of {Omega}{sub m} and w. Since we assume this component is uncorrelated with the stochastic component from inflation, we find that both the expectation value and the sample variance are increased. There is no improvement in the likelihood of an anomalously low quadrupole as suggested by previous work on an elliptical universe.

Appleby, Stephen; Battye, Richard [Jodrell Bank Center for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL (United Kingdom); Moss, Adam [Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, V6T 1Z1 (Canada)

2010-04-15

428

Destabilization of TAE modes by particle anisotropy  

SciTech Connect

Plasmas heated by ICRF produce energetic particle distribution functions which are sharply peaked in pitch-angle, and the authors show that at moderate toroidal mode numbers, this anisotropy is a competitive and even dominant instability drive when compared with the universal instability drive due to spatial gradient. The universal drive, acting along, destabilizes only co-propagating waves (i.e., waves propagating in the same toroidal direction as the diamagnetic flow of the energetic particles), but stabilizes counter-propagating waves (i.e., waves propagating in the opposite toroidal direction as the diamagnetic flow of the energetic particles). Nonetheless, the authors show that in a tokamak, it is possible that particle anisotropy can produce a larger linear growth rate for counter-propagating waves, and provide a mechanism for preferred destabilization of the counter-propagating TAE modes that are sometimes experimentally observed.

Wong, H.V.; Berk, H.L.

1998-10-20

429

Quantum Spin Chains with Planar Anisotropy  

Microsoft Academic Search

A strong-coupling expansion is used to study the spectrum of elementary excitations of quantum spin-1 chains with strong planar anisotropy. In addition to the doubly degenerate excitonic mode, an exciton-antiexciton bound state is found and is shown to contribute significantly to the longitudinal dynamical two-point function. The low-temperature behavior of the specific heat of spin-1\\/2 and spin-1 chains with uniaxial

Paul Nicolaos Spathis

1990-01-01

430

Pn anisotropy in Mesozoic western Pacific lithosphere  

NASA Astrophysics Data System (ADS)

is the high-frequency, scattered P phase guided for great distances within the old oceanic lithosphere. Two arrays of ocean bottom seismometers were deployed on old (150-160 Ma) seafloor in the northwestern Pacific south of Shatsky Rise for the Pacific Lithosphere Anisotropy and Thickness Experiment. We use Pn phases from 403 earthquakes during the 1 year of deployment to measure apparent velocities across the arrays. Each array was deployed on a separate limb of a magnetic bight, formed near a fast-spreading, ridge-ridge-ridge triple junction. Using high-frequency waves (5-10 Hz), we look at variations of Pn velocities as a function of azimuth. In the western array, we find Pn anisotropy with velocities ranging from ~8.7 km/s in the back azimuth (?) direction of 310° to ~7.7 km/s at ~350°. In the eastern array, the velocity ranges from ~8.5 km/s in back azimuth direction of ~210° to ~7.7 km/s at 260° and ~310°. We observe rapid velocity changes with azimuth in the both arrays requiring sinusoidal variations of roughly equal amplitude as a function of both 2? and 4?, which is not expected for the orthorhombic symmetry of olivine or orthopyroxene. The fastest directions on the two limbs are roughly orthogonal to each other suggesting the dominance of fossil anisotropy, but the fast directions of the 2? components are skewed counterclockwise from the spreading directions. We speculate that the rapid azimuthal variations may be caused by vertical stratification with changing anisotropy with depth in the oceanic lithosphere.

Shintaku, Natsumi; Forsyth, Donald W.; Hajewski, Christina J.; Weeraratne, Dayanthie S.

2014-04-01

431

Deformation-Induced Anisotropy of Polymers  

NASA Technical Reports Server (NTRS)

New theory calculates anisotropies induced by large deformations in polymers. Theory was developed primarily for calculating anistropy of thermal expansivity, but is also applicable to thermal conductivity, elastic moduli and other properties. Theory assumes that in isotropic state, long polymer chains are randomly coiled and not oriented in particular direction. They acquire an orientation when material is deformed. As average molecular orientation increases with deformation, properties of bulk material exhibit averaging of the microscopic anistropies of the oriented molecular segments.

Peng, S. T. J.; Landel, R. F.

1982-01-01

432

Micromagnetics of shape anisotropy based permanent magnets  

NASA Astrophysics Data System (ADS)

In the search for rare-earth free permanent magnets, various ideas related to shape anisotropy are being pursued. In this work we assess the limits of shape contributions to the reversal stability using micromagnetic simulations. In a first series of tests we altered the aspect ratio of single phase prolate spheroids from 1 to 16. Starting with a sphere of radius 4.3 times the exchange length Lex we kept the total magnetic volume constant as the aspect ratio was modified. For a ferromagnet with zero magnetocrystalline anisotropy the maximum coercive field reached up to 0.5 times the magnetization Ms. Therefore, in materials with moderate uniaxial magnetocrystalline anisotropy, the addition of shape anisotropy could even double the coercive field. Interestingly due to non-uniform magnetization reversal there is no significant increase of the coercive field for an aspect ratio greater than 5. A similar limit of the maximum aspect ratio was observed in cylinders. The coercive field depends on the wire diameter. By decreasing the wire diameter from 8.7Lex to 2.2Lex the coercive field increased by 40%. In the cylinders nucleation of a reversed domain starts at the corners at the end. Smoothing the edges can improve the coercive field by about 10%. In further simulations we compacted soft magnetic cylinders into a bulk-like arrangement. Misalignment and magnetostatic interactions cause a spread of 0.1Ms in the switching fields of the rods. Comparing the volume averaged hysteresis loops computed for isolated rods and the hysteresis loop computed for interacting rods, we conclude that magnetostatic interactions reduce the coercive field by up to 20%.

Bance, Simon; Fischbacher, Johann; Schrefl, Thomas; Zins, Inga; Rieger, Gotthard; Cassignol, Caroline

2014-08-01

433

Influence of ferroelectric polarization on magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Thin film heterostructures of transition metal ferromagnets (FM) and polymer ferroelectrics (FE) are investigated to look for changes in the magnetic anisotropy of the FM layer that occur on switching the FE polarization (with an ensuing change in the electric field direction).[1] Samples of [Glass/ Pd (50 nm)/Co wedge (0.9-2.6nm)/ferroelectric P(VDF-TrFE) (53 nm)/Al (30nm)] are deposited via sputtering or evaporation for the metallic layers and via Langmuir-Schaefer deposition for the polymer ferroelectric. [2] Magnetic and FE properties have been characterized using the Magneto-Optical Kerr Effect (MOKE) and the pyroelectric effect. Polar and longitudinal MOKE loops are measured across the Co wedge for both positive and negative FE polarization and the difference in the two MOKE loops is ascribed to the changes in the magnetic anisotropy of the FM layer. [3] These changes are most apparent in the region where the Co undergoes a transition from in-plane to out-of-plane anisotropy. This research is supported by the NSF MRSEC through Grant No. DMR- 0820521 1. Chun-Gang Duan et al, Appl. Phys. Lett. 92, 122905 (2008) 2. A. V. Bune, et al, Nature (London) 391, 874 (1998) 3. P. F. Carcia, J.Appl. Phys. 63, 5066 (1988)

Mardana, A.; Ducharme, S.; Adenwalla, S.

2010-03-01

434

Magnetic anisotropy of the Trenton limestone revisited  

SciTech Connect

Previous studies have shown clear differences between the anisotropies of low-field magnetic susceptibility (LFS) and of anhysteretic remanent magnetization (ARM) in samples of the Ordovician Trenton limestone from Trenton Falls, NY. ARM was found to be significantly more anisotropic than LFS, and to exhibit a well-defined east-northeasterly lineation which was not apparent in anisotropy of magnetic susceptibility (AMS). Because of significant local variation in mean LFS (by approximately a factor of two) at this locality, it has been possible to reanalyze the AMS of these samples by the method of Henry (1983), which in some cases allows mathematical differentiation of the ferromagnetic and paramagnetic susceptibility tensors. The ferromagnetic susceptibility tensor obtained in this way shows the same tectonic shortening apparent in the ARM anisotropy, but surprisingly, it shows no evidence of horizontal foliation. The paramagnetic tensor is horizontally foliated, with no lineation. The difference between the ferromagnetic susceptibility and ARM tensors suggests different ferrromagnetic sources of ARM and LFS.