X-Ray Scattering Measurements of the Transient Structure of a Driven Charge-Density-Wave

We report time-resolved x-ray scattering measurements of the transient structural response of the sliding {\bf Q}$_{1}$ charge-density-wave (CDW) in NbSe$_{3}$ to a reversal of the driving electric field. The observed time scale characterizing this response at 70K varies from $\sim$ 15 msec for driving fields near threshold to $\sim$ 2 msec for fields well above threshold. The position and time-dependent strain of the CDW is analyzed in terms of a phenomenological equation of motion for the phase of the CDW order parameter. The value of the damping constant, $\gamma = (3.2 \pm 0.7) \times 10^{-19}$ eV $\cdot$ seconds $\cdot$ \AA$^{-3}$, is in excellent agreement with the value determined from transport measurements. As the driving field approaches threshold from above, the line shape becomes bimodal, suggesting that the CDW does not depin throughout the entire sample at one well-defined voltage.Comment: revtex 3.0, 7 figure

Evanescent wave transport and shot noise in graphene: ballistic regime and effect of disorder

We have investigated electrical transport and shot noise in graphene field effect devices. In large width over length ratio $W/L$ graphene strips, we have measured shot noise at low frequency ($f$ = 600--850 MHz) in the temperature range of 4.2--30 K. We observe a minimum conductivity of $\frac{4e^{2}}{\pi h}$ and a finite and gate dependent Fano factor reaching the universal value of 1/3 at the Dirac point, i.e. where the density of states vanishes. These findings are in good agreement with the theory describing that transport at the Dirac point should occur via evanescent waves in perfect graphene samples with large $W/L$. Moreover, we show and discuss how disorder and non-parallel leads affect both conductivity and shot noise.Comment: Extended version (19 pages, 10 figures) of Phys. Rev. Lett. 100, 196802 (2008). Additional data on the effect of disorder and non-parallel leads. Submitted for publication in Journal of Low Temperature Physics for the Proceedings of the International Symposium on Quantum Phenomena and Devices at Low Temperatures (ULTI 2008), Espoo, Finlan

Structure and kinetics of the sliding Q1 CDW in NbSe3

Using crystallographically perfect single crystal whiskers of NbSe3 and the synchrotron x-ray scattering facilities at CHESS, we have performed detailed high resolution measurements of the structure of a sliding CDW. We observe the longitudinal strain of the CDW associated with the phase slip necessary to convert between normal and collective current at the electrical contacts. Using a stroboscopic x-ray scattering technique, we have extended these measurements into the time domain and studied the evolution of the structure of the sliding CDW as it responds to a reversal of the direction of an applied d.c. electric field. The time constant characterizing this structural evolution is on the order of milliseconds for fields well above threshold. Near threshold the CDW splits into two components ; one component is pinned and the other is sliding. As the electric field strength is increased, the fraction of the CDW which remains pinned decreases monotonicaily

Capillary pressure overshoot for unstable wetting fronts is explained by Hoffman's velocity-dependent contact-angle relationship

Pore velocity-dependent dynamic contact angles provide a mechanism for explaining the formation of fingers/columns in porous media. To study those dynamic contact angles when gravity is present, rectangular capillary tubes were used to facilitate observation of the complete interface without geometric distortion. Results show that the Hoffman (1975) relationship between dynamic contact angle and water velocity applies to gravity-affected flow fields, and that it (when adjusted for nonzero static contact angles) can be used to model dynamic capillary pressures for unstable wettings fronts in porous media by assuming that (1) pressure at the wetting front is discontinuous, (2) the flow field behind the fingertip is highly heterogeneous, and (3) the front line advances one or a few pores at the time. We demonstrate the utility of the Hoffman relationship for porous media with a published infiltration experiment by calculating the capillary pressure successfully at the unstable wetting front as a function of the flux of water in the finger and the grain size diameter

SUSTAINED IMPROVEMENTS IN MAGNETIC RESONANCE IMAGING OUTCOMES WITH ABATACEPT FOLLOWING THE WITHDRAWAL OF ALL TREATMENT IN PATIENTS WITH EARLY RHEUMATOID ARTHRITIS

Pathophysiology and treatment of rheumatic disease

The ISMRM Open Science Initiative for Perfusion Imaging (OSIPI): Results from the OSIPI–Dynamic Contrast-Enhanced challenge

Purpose: K trans has often been proposed as a quantitative imaging biomarker for diagnosis,prognosis,andtreatmentresponseassessmentforvarioustumors.Noneofthe many software tools for K trans quantification are standardized. The ISMRM OpenScience Initiative for Perfusion Imaging–Dynamic Contrast-Enhanced (OSIPI-DCE)challenge was designed to benchmark methods to better help the efforts to standardize K trans measurement. Methods: A framework was created to evaluate K trans values produced by DCE-MRI analysis pipelines to enable benchmarking. The perfusion MRI community was invited to apply their pipelines for K trans quantification in glioblastoma from clinical and synthetic patients. Submissions were required to include the entrants’ K trans values, the applied software, and a standard operating procedure. These were evaluated using the proposed OSIPIgold score defined with accuracy, repeatability, and reproducibility components. Results: Across the 10 received submissions, the OSIPIgold score ranged from28% to 78% with a 59% median. The accuracy, repeatability, and reproducibility scores ranged from 0.54 to 0.92, 0.64 to 0.86, and 0.65 to 1.00, respectively(0–1=lowest–highest). Manual arterial input function selection markedly affected the reproducibility and showed greater variability in K trans analysis than automated methods. Furthermore, provision of a detailed standard operating procedure was critical for higher reproducibility. Conclusions: This study reports results from the OSIPI-DCE challenge and high-lights the high inter-software variability within K trans estimation, providing a framework for ongoing benchmarking against the scores presented. Through this challenge, the participating teams were ranked based on the performance of their software tools in the particular setting of this challenge. In a real-world clinical setting, many of these tools may perform differently with different benchmarking methodology