de Haas-van Alphen measurement of the antiferromagnet URhIn5_5

We report on the results of a de Haas-van Alphen (dHvA) measurement performed on the recently discovered antiferromagnet URhIn$_5$ ($T_N$ = 98 K), a 5\textit{f}-analogue of the well studied heavy fermion antiferromagnet CeRhIn$_5$. The Fermi surface is found to consist of four surfaces: a roughly spherical pocket $\beta$, with $F_\beta \simeq 0.3$ kT; a pillow-shaped closed surface, $\alpha$, with $F_\alpha \simeq 1.1$ kT; and two higher frequencies $\gamma_1$ with $F_{\gamma_1} \simeq 3.2$ kT and $\gamma_2$ with $F_{\gamma_2} \simeq 3.5$ kT that are seen only near the \textit{c}-axis, and that may arise on cylindrical Fermi surfaces. The measured cyclotron masses range from 1.9 $m_e$ to 4.3 $m_e$. A simple LDA+SO calculation performed for the paramagnetic ground state shows a very different Fermi surface topology, demonstrating a need for more advanced electronic structure calculations

Nutrient Biomarker Patterns, Cognitive Function, and Mri Measures of Brain Aging

International audienc

Egy inváziós faj, a Solidago gigantea Aiton által kolonizált mocsárrétek diverzitása és fajkompozíciós koordináltsága

Számos vizsgálat történt korábban a Solidago gigantea Aiton elterjedtségével, ökológiai és növényélettani tulajdonságaival kapcsolatban, azonban a faj inváziójának cönológiai következményei kevéssé ismertek. Mocsárréti társulások diverzitását és belső koordináltságát hasonlítottuk össze, magas aranyvesszővel különböző mértékben fertőzött területeken. Hat, eltérő mértékben kolonizált gyepterületet vizsgáltunk, melyek közül kettő referenciaterületként is szolgált. Állományonként 8‒8 db 5 m hosszú transzszektet mintavételeztünk. Ezek mentén 100 db egymást érő 5 cm × 5 cm-es mikrokvadrátban rögzítettük a fajok jelenlétét. Az állományok belső szervezettségét és koordináltságát a diverzitás és az egyenletesség állományon belüli szóródásával (CV%) és a mintavételi egységek állományon belüli átlagos cönológiai hasonlóságával jellemeztük. A S. gigantea gyakorisága jelentősen különbözött a mintaterületeken, és mennyiségének növekedésével összefüggésben változtak az állományok cönológiai jellemzői: csökkent a diverzitás és a koordináltság. Különböző cönológiai jellemzőket összehasonlítva megállapítható, hogy az átlagos viselkedést kifejező alfa diverzitás és egyenletesség kevésbé érzékenyen mutatják az inváziós faj okozta degradációt, mint e jellemzők béta diverzitást is jelentő relatív szórása (CV%). Eredményeink szerint a cönológiai koordináltság állományon belüli változása (jelen esetben csökkenése) egyszerűen mérhető és jó indikátora az inváziós faj okozta cönológiai változásoknak

Higher gait variability is associated with decreased parietal gray matter volume among healthy older adults

The objectives of this study were to examine the association of stride time variability (STV) with gray and white matter volumes in healthy older adults, and to determine the specific location of any parenchymal loss associated with higher STV. A total of 71 participants (mean age 69.0 +/- 0.8 years; 59.7 % female) were included in this study. All participants had a 1.0 Tesla 3D T1-weighted MRI of the brain to measure gray and white matter volumes. STV was measured at steady-state self-selected walking speed using an electronic footswitch system. We found an association between higher STV and lower gray matter volume in the right parietal lobe (e.g., angular gyrus, Brodmann area 39, cluster corrected pFWE = 0.035). There were no significant associations between STV and higher gray matter volume or change in white matter volume. To the best of our knowledge this study is the first to identify a significant association of higher STV with lower right parietal gray matter volume in healthy older adults

Modification of ultra low-k dielectric films by O₂ and CO₂ plasmas

Low-k materials developed for ULSI interconnects should have sufficient resistance to processing plasma. CO2 plasma is being considered as a promising candidate for low damage photoresist ash and as a surface activation chemistry for self-assembled monolayers and atomic layer deposition on low-k materials. This article explores the interaction of two organosilicate (OSG) based low-k materials with different k-values (OSG2.4 and OSG2.2) with CO2 plasma in both CCP and ICP-remote plasma chambers. Time dependent exposure of the materials to CO2 plasma revealed quick and effective sealing of OSG2.4 surface whereas it takes longer time for OSG2.2. The sealing reduces further plasma damage and leads to accumulation of CO2 in the pores of both materials. The same behavior occurs in ICP-remote plasma but without a complete sealing of the surface. This suggests the important role of ion bombardment. Damage to low-k by conventional O-2 plasma was studied alongside and it was found that for t 60 s. Furthermore, lesser time exposure to CO2 plasma was investigated with respect to source power at constant pressure and it was discovered that damage although small, increases with varying source power

Motor cortex and gait in mild cognitive impairment: a magnetic resonance spectroscopy and volumetric imaging study

Gait disorders are common in the course of dementia, even at the stage of mild cognitive impairment, owing to probable changes in higher levels of motor control. Since motor control message is ultimately supported in the brain by the primary motor cortex and since cortical lesions are frequent in the dementia process, we hypothesized that impairments of the primary motor cortex may explain the early gait disorders observed in mild cognitive impairment. Our purpose was to determine whether the neurochemistry of the primary motor cortex measured with proton magnetic resonance spectroscopy, and its volume, were associated with gait performance while single and dual-tasking in mild cognitive impairment. Twenty community dwellers with mild cognitive impairment, aged 76 years (11) [median (interquartile range)] (30% female) from the \u27Gait and Brain Study\u27 were included in this analysis. Gait velocity and stride time variability were measured while single (i.e. walking alone) and dual tasking (i.e. walking while counting backwards by seven) using an electronic walkway (GAITRite System). Ratios of N-acetyl aspartate to creatine and choline to creatine and cortical volume were calculated in the primary motor cortex. Participants were categorized according to median N-acetyl aspartate to creatine and choline to creatine ratios. Age, gender, body mass index, cognition, education level and subcortical vascular burden were used as potential confounders. Participants with low N-acetyl aspartate to creatine (n = 10) had higher (worse) stride time variability while dual tasking than those with high N-acetyl aspartate to creatine (P = 0.007). Those with high choline to creatine had slower (worse) gait velocity while single (P = 0.015) and dual tasking (P = 0.002). Low N-acetyl aspartate to creatine was associated with increased stride time variability while dual tasking (adjusted beta = 5.51, P = 0.031). High choline to creatine was associated with slower gait velocity while single (adjusted beta = -26.56, P = 0.009) and dual tasking (adjusted beta = -41.92, P = 0.022). Cortical volume correlated with faster gait velocity while single (P = 0.029) and dual tasking (P = 0.037), and with decreased stride time variability while single tasking (P = 0.034). Finally, the probability of exhibiting abnormal metabolite ratios in the primary motor cortex was 63% higher among participants with major gait disturbances in dual task. Those with compromised gait velocity in dual task had a 2.05-fold greater risk of having a smaller cortical volume. In conclusion, the neurochemistry and volume of the primary motor cortex were associated with gait performance while single and dual tasking. Stride time variability was mainly sensitive to neuronal function (N-acetyl aspartate to creatine), whereas gait velocity was more affected by inflammatory damage (choline to creatine) and volumetric changes. These findings may contribute to a better understanding of the higher risks of mobility decline and falls in subjects with mild cognitive impairment

Association Between Serum 25-Hydroxyvitamin D Concentration and Optic Chiasm Volume

International audienc

Vitamin D concentration and lateral cerebral ventricle volume in older adults

Scope Vitamin D deficiency is associated with an enlargement of the lateral cerebral ventricles in rodents. The effect of low serum 25-hydroxyvitamin D (25OHD) on lateral cerebral ventricle volume has not been studied yet in humans. The purpose of this cross-sectional study was to determine whether vitamin D deficiency was associated with greater lateral cerebral ventricle volume in older adults. Methods and results Ninety-two Caucasian community-dwellers with no clinical hydrocephalus (mean, 72.2 +/- 6.2 years; 46.7% female) were divided into two groups according to serum 25OHD concentration (deficiency <= 50 nmol/L; normal > 50 nmol/L). Cerebral ventricular volume was quantified using semi-automated software from three-dimensional T1-weighted MRI. Age, gender, body mass index, blood pressure, education level, Mini-Mental State Examination, white matter lesions, and serum calcium concentrations were used as covariates. There was an inverse linear association between 25OHD concentration and ventricular volume (p = 0.049). Compared to individuals with normal 25OHD, those with 25OHD deficiency (n = 33) had 28% larger lateral ventricles (46.9 +/- 26.8 mL versus 36.6 +/- 16.4 mL, p = 0.026). Vitamin D deficiency was associated with an increase in ventricular volume (adjusted beta = 16.55, p = 0.023). The ventricular enlargement involved ventricle bodies (p = 0.025) but not temporal horns (p = 0.112). Conclusion Serum 25OHD deficiency was associated with larger lateral cerebral ventricles. These findings provide a scientific base for vitamin D replacement trials

Stretched chemical bonds in Si6H6: A transition from ring currents to localized pi-electrons?

Motivated by solid-state studies on the cleavage force in Si, and the consequent stretching of chemical bonds, we here study bond stretching in the, as yet unsynthesized, free space molecule Si6H6. We address the question as to whether substantial bond stretching (but constrained to uniform scaling on all bonds) can result in a transition from ring current behaviour, characteristic say of benzene at its equilibrium geometry, to localized pi-electrons on Si atoms. Some calculations are also recorded on dissociation into 6 SiH radicals. While the main studies have been carried out by unrestricted Hartree-Fock (HF) theory, the influence of electron correlation has been examined using two forms of density functional theory. Planar Si6H6 treated by HF is bound to be unstable, not all vibrational frequencies being real. Some buckling is then allowed, which results in real frequencies and stability. Evidence is then provided that the non-planar structure, as the Si-Si distance is increased, exhibits pi-electron localization in the range 1.2-1.5 times the equilibrium distance