Orbital character of O 2p unoccupied states near the Fermi level in CrO2

The orbital character, orientation, and magnetic polarization of the O 2$p$ unoccupied states near the Fermi level ($E_F$) in CrO$_2$ was determined using polarization-dependent X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) from high-quality, single-crystal films. A sharp peak observed just above $E_F$ is excited only by the electric field vector ($\bf E$) normal to the tetragonal $c$-axis, characteristic of a narrow band ($\approx$ 0.7 eV bandwidth) constituted from O 2$p$ orbitals perpendicular to $c$ (O 2$p_y$) hybridized with Cr 3$d_{xz-yz}$ $t_{2g}$ states. By comparison with band-structure and configuration-interaction (CI) cluster calculations our results support a model of CrO$_2$ as a half-metallic ferromagnet with large exchange-splitting energy ($\Delta_{exch-split}$ $\approx$ 3.0 eV) and substantial correlation effects.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. B Rapid Com

Ultrahigh vacuum sample mount for x-ray photoelectron spectroscopy up to very high temperature (150-1400 K)

Spectroscopic studies are rarely performed at very high temperature, especially when combined with light from a synchrotron source. Demanding conditions of maintaining ultrahigh vacuum (UHV) during heating, together with the typically brief access to beam time at multiuser synchrotron end stations, may contribute to some of the reasons for the difficulty of such experiments. Consequently, a large number of materials with interesting properties and industrial applications at high temperature remain unexplored. The authors describe here a simple portable sample mount assembly that can be easily utilized at a beamline, with potential utility for a variety of spectroscopic measurements requiring elevated temperatures and an UHV environment. In the specific application described here, the authors use a resistive cartridge heater interfaced with a standard manipulator previously designed for cooling by liquid nitrogen with an UHV chamber and a cylindrical mirror analyzer for x-ray photoemission spectroscopy (XPS) [also known as electron spectroscopy for chemical analysis (ESCA)] at the Synchrotron Radiation Center in Stoughton, WI. The heater cartridge required only modest power to reach target temperatures using an open-loop temperature control. Finally, the authors describe the measurements of XPS (ESCA) and total-electron yield x-ray absorption spectroscopy on nanopowders and on single crystals grown by them. They emphasize the simplicity of the setup, which they believe would be of interest to groups performing measurements at large facilities, where access and time are both limited. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3571528

EphrinB2 regulates VEGFR2 during dendritogenesis and hippocampal circuitry development

Vascular endothelial growth factor (VEGF) is an angiogenic factor that play important roles in the nervous system, although it is still unclear which receptors transduce those signals in neurons. Here, we show that in the developing hippocampus VEGFR2 (also known as KDR or FLK1) is expressed specifically in the CA3 region and it is required for dendritic arborization and spine morphogenesis in hippocampal neurons. Mice lacking VEGFR2 in neurons (Nes-cre Kdr(lox/-)) show decreased dendritic arbors and spines as well as a reduction in long-term potentiation (LTP) at the associational-commissural - CA3 synapses. Mechanistically, VEGFR2 internalization is required for VEGF-induced spine maturation. In analogy to endothelial cells, ephrinB2 controls VEGFR2 internalization in neurons. VEGFR2-ephrinB2 compound mice (Nes-cre Kdr(lox/+) Efnb2(lox/+)) show reduced dendritic branching, reduced spine head size and impaired LTP. Our results demonstrate the functional crosstalk of VEGFR2 and ephrinB2 in vivo to control dendritic arborization, spine morphogenesis and hippocampal circuitry development

AGE-RELATED CARDIOVASCULAR HEALTH AMONG ELITE ULTRA-ENDURANCE ATHLETES

BACKGROUND: Aging is associated with increased cardiovascular (CV) disease risk which is partly attributable to increased blood pressure (BP) and central arterial stiffness. Regular exercise is recommended to slow CV aging, but it is unclear whether “extreme exercise”, such as ultra-endurance running (\u3e42.2 km), elicits the same CV benefits as lower-volume training. Therefore, the purpose of this investigation was to test the hypothesis that ultra-endurance running preserves CV health across the lifespan. METHODS: We measured supine BP with an automated brachial cuff and arterial stiffness (carotid-to-femoral pulse wave velocity [cfPWV]) with applanation tonometry (SphygmoCor XCEL, AtCor Medical) among 72 athletes (16F/56M; BMI: 22.6 ± 1.8 kg/m2) 1-3 days before they competed in the 161-km Western States Endurance Race (WSER) (Olympic Valley, CA; elevation: 1890 m). We present data as mean ± SD and confirmed normality using Shapiro-Wilk tests (α ≥ 0.05). We used simple linear regression to assess the relationship between age and systolic BP (SBP), diastolic BP (DBP), and cfPWV. We compared individual cfPWV outcomes to available normative data. RESULTS: Among 72 WSER athletes, age (46 ± 10 years; range: 26-69 yrs), SBP (129 ± 9 mmHg), DBP (78 ± 7 mmHg), and cfPWV (n = 70; 6.5 ± 1.0 m/s) were normally distributed (Ws ≥ 0.97, Ps ≥ 0.06). Approximately 60% (43/72) of the athletes presented with hypertension (≥130mmHg SBP and/or \u3e80 mmHg DBP) but age was not associated with SBP (R2 = 0.02, P = 0.23) or DBP (R2 = 0.05, P = 0.06). Age was positively associated with cfPWV (R2 = 0.25, P \u3c 0.001) but 84% (59/70) of participants had cfPWV values below their age-predicted value (mean difference: -0.9 m/s). CONCLUSIONS: Among these WSER athletes, a majority were hypertensive, but there was not a meaningful relationship between age and BP. Moreover, in this sample, the increase in SBP per decade (1.3 mmHg/decade) was much lower compared to previously reported increases among the general population (6.5 mmHg/decade). Despite an age-related increase in cfPWV, 84% of athletes had cfPWV values below their age-predicted value. These findings suggest that ultra-endurance training is associated with preserved CV health across the lifespan via attenuated age-related increases in BP and cfPWV values below age-predicted norms