Doping dependence of charge-transfer excitations in La_{2-x}Sr_xCuO_4

We report a resonant inelastic x-ray scattering (RIXS) study of the doping dependence of charge-transfer excitations in $\rm La_{2-x}Sr_xCuO_4$. The mome ntum dependence of these charge excitations are studied over the whole Brillouin zone in underdoped (x=0.05) and optimally doped (x=0.17) samples, and compared with that of the undoped (x=0) sample. We observe a large change in the RIXS spectra between the x=0 and x=0.17 sample, while the RIXS spectra of the x=0.05 sample are similar to that of the x=0 sample. The most prominent effect of doped-holes on the charge excitation spectra is the appearance of a continuum of intensity, which exhibits a strong momentum-dependence below 2 eV. For the x=0.17 sample, some of the spectral weight from the lowest-lying charge-transfer excitation of the undoped compound is transferred to the continuum intensity below the gap, in agreement with earlier optical studies. However, the higher energy charge-transfer excitation carries significant spectral weight even for the x=0.17 sample. The doping dependence of the dispersion of this charge-transfer excitation is also discussed and compared with recent theoretical calculations.Comment: 7 pages, 6 figures, to appear in Phys. Rev.

Magnetic field dependence of charge stripe order in La2-xBaxCuO4 (x~1/8)

We have carried out a detailed investigation of the magnetic field dependence of charge ordering in La2-xBaxCuO4 (x~1/8) utilizing high-resolution x-ray scattering. We find that the charge order correlation length increases as the magnetic field greater than ~5T is applied in the superconducting phase (T=2K). The observed unusual field dependence of the charge order correlation length suggests that the static charge stripe order competes with the superconducting ground state in this sample.Comment: 4 pages, 4 figure

Electrical Conductivity of o-, m-, and p-Terphenyls

Many investigations have been carried out on the electrical properties of p-terphenyl1-9, and, as far as we know, only one on m-terphenyl10. In the present work, the d. c. electrical conductivities of the three isomeric terphenyls are compared to establish the influence of the molecular structure on the electrical properties and to explain the mechanism of the energy transport in organic molecules

Primary gas thermometry by means of laser-absorption spectroscopy: Determination of the Boltzmann constant

We report on a new optical implementation of primary gas thermometry based on laser absorption spectrometry in the near infrared. The method consists in retrieving the Doppler broadening from highly accurate observations of the line shape of the R(12) $\nu_{1} + 2 \nu_{2}^{\phantom{1}0} + \nu_{3}$ transition in CO$_{2}$ gas at thermodynamic equilibrium. Doppler width measurements as a function of gas temperature, ranging between the triple point of water and the gallium melting point, allowed for a spectroscopic determination of the Boltzmann constant with a relative accuracy of $\sim1.6\times10^{-4}$.Comment: Submitted to Physical Review Letter

Resonant inelastic x-ray scattering study of charge excitations in La2CuO4

We report a resonant inelastic x-ray scattering study of the dispersion relations of charge transfer excitations in insulating La$_2$CuO$_4$. These data reveal two peaks, both of which show two-dimensional characteristics. The lowest energy excitation has a gap energy of $\sim 2.2$ eV at the zone center, and a dispersion of $\sim 1$ eV. The spectral weight of this mode becomes dramatically smaller around ($\pi$, $\pi$). The second peak shows a smaller dispersion ($\sim 0.5$ eV) with a zone-center energy of $\sim 3.9$ eV. We argue that these are both highly dispersive exciton modes damped by the presence of the electron-hole continuum.Comment: 5 pages, 3 figure

Effect of stress and attention on startle response and prepulse inhibition

The startle reflex magnitude can be modulated when a weak stimulus is presented before the onset of the startle stimulus, a phenomenon termed prepulse inhibition (PPI). Previous research has demonstrated that emotional processes can modulate PPI and startle intensity, but the available evidence is inconclusive. In order to obtain additional evidence in this domain, we conducted two experiments intended to analyze the effect of induced stress and attentional load on PPI and startle magnitude. Specifically, in Experiment 1 we used a between subject strategy to evaluate the effect on startle response and PPI magnitude of performing a difficult task intended to induce stress in the participants, as compared to a group exposed to a control task. In Experiment 2 we evaluated the effect of diverting attention from the acoustic stimulus on startle and PPI intensity. The results seem to indicate that induced stress can reduce PPI, and that startle reflex intensity is reduced when attention is directed away from the auditory stimulus that induces the reflex.Ministerio de Economía y Competitividad PSI2012-32077Ministerio de Economía y Competitividad PSI2015-64965-P/MINECO-FEDE

Role of von Willebrand factor in shear induced platelet accumulation in a microfluidic device

Thrombus formation under high fluid shear rates at the site of atherosclerotic plaque rupture leads to myocardial infarction and stroke. At high shear rates, thrombus is formed by platelets adhering via the glycoprotein von Willebrand factor (vWF). To investigate the relative contributions of vWF and platelets in high shear thrombosis, the present work developed a microfluidic thrombosis assay to meet low blood volume requirements and fluid shear conditions (3500-6000 s-1). Microfluidic conditions were selected to mimic the high shear environment of a diseased coronary artery, with the long-term objective of developing a clinically relevant assay for the assessment of thrombosis risk and treatment efficacy. The microfluidic design also addressed the requirement for volumetric thrombus formation rather than only surface platelet adhesion. As part of the design of the microfluidic assay, the effect of flow pulsatility on high shear thrombosis was investigated. It was found that steady wall shear rate matched to the mean pulsatile wall shear rate reproduced bulk thrombus formation characteristics of occlusion time, lag time, and thrombus growth rate, allowing subsequent experiments and future device design to utilize steady flow. The microfluidic assay was implemented to study the roles of vWF and platelets to thrombus formation using blood analogs produced from whole human blood diluted with normal saline at 90% and 99%. Hematocrit was restored to normal in all cases with the addition of red blood cells, and vWF and platelets were selectively restored to normal levels. Results showed that 90% dilutions with only vWF restored to normal levels occluded in 6/7 subject tested. The addition of platelets accelerated thrombus formation, but blood analogs with only platelets restored to normal levels occluded in only 2/5 subjects, indicating that vWF is more contributory in high shear occlusive thrombosis. At 99% dilutions, large thrombus formed with the addition of both platelets and vWF but was unstable and did not fully occlude the channel, indicating the possible requirement of an additional stabilizing factor(s) in occlusive thrombosis. Results of this study may lead to the development of improved anti-thrombotic treatments and improve patient care by providing a potential assay to evaluate treatment effectiveness and predict thrombosis risk.Ph.D