Risk based bridge data collection and asset management and the role of structural health monitoring

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Impurity effect on low-temperature polarisation of the charge-density-waves in o-TaS3_3

The temperature dependence of the low-temperature dielectric response is studied in o-TaS$_3$ samples doped by Nb, Se, and Ni and for nominally pure ones. It is found, that the low-temperature dielectric constant depends anomalously on doping and is higher for doped crystals, whereas the temperature dependence of the characteristic time of all samples follows the activation law with nearly the same activation energy $\sim 400$ K (T>20 K). The observed behaviour is inconsistent with all available explanations of the low-temperature dielectric anomaly.Comment: RevTex, 12 pages, epsf, 2 postscript Figures. Accepted for publication in Physics Letters

Temporally ordered collective creep and dynamic transition in the charge-density-wave conductor NbSe3

We have observed an unusual form of creep at low temperatures in the charge-density-wave (CDW) conductor NbSe$_3$. This creep develops when CDW motion becomes limited by thermally-activated phase advance past individual impurities, demonstrating the importance of local pinning and related short-length-scale dynamics. Unlike in vortex lattices, elastic collective dynamics on longer length scales results in temporally ordered motion and a finite threshold field. A first-order dynamic phase transition from creep to high-velocity sliding produces "switching" in the velocity-field characteristic.Comment: 4 pages, 4 eps figures; minor clarifications To be published in Phys. Rev. Let

Contributions of spontaneous phase slippage to linear and non-linear conduction near the Peierls transition in thin samples of o-TaS_3

In the Peierls state very thin samples of TaS_3 (cross-section area \sim 10^{-3} mkm^2) are found to demonstrate smearing of the I-V curves near the threshold field. With approaching the Peierls transition temperature, T_P, the smearing evolves into smooth growth of conductance from zero voltage interpreted by us as the contribution of fluctuations to the non--linear conductance. We identify independently the fluctuation contribution to the linear conductance near T_P. Both linear and non-linear contributions depend on temperature with close activation energies \sim (2 - 4) x 10^3 K and apparently reveal the same process. We reject creep of the {\it continuous} charge-density waves (CDWs) as the origin of this effect and show that it is spontaneous phase slippage that results in creep of the CDW. A model is proposed accounting for both the linear and non-linear parts of the fluctuation conduction up to T_P.Comment: 6 pages, 5 Postscript figure, RevTeX, accepted for publication in PR

Thermal Rounding of the Charge Density Wave Depinning Transition

The rounding of the charge density wave depinning transition by thermal noise is examined. Hops by localized modes over small barriers trigger ``avalanches'', resulting in a creep velocity much larger than that expected from comparing thermal energies with typical barriers. For a field equal to the $T=0$ depinning field, the creep velocity is predicted to have a {\em power-law} dependence on the temperature $T$; numerical computations confirm this result. The predicted order of magnitude of the thermal rounding of the depinning transition is consistent with rounding seen in experiment.Comment: 12 pages + 3 Postscript figure

NbSe3: Effect of Uniaxial Stress on the Threshold Field and Fermiology

We have measured the effect of uniaxial stress on the threshold field ET for the motion of the upper CDW in NbSe3. ET exhibits a critical behavior, ET ~ (1 - e/ec)^g, wher e is the strain, and ec is about 2.6% and g ~ 1.2. This ecpression remains valid over more than two decades of ET, up to the highest fields of about 1.5keV/m. Neither g nor ec is very sensitive to the impurity concentraction. The CDW transition temperature Tp decreases linearly with e at a rate dTp/de = -10K/%, and it does not show any anomaly near ec. Shubnikov de-Haas measurements show that the extremal area of the Fermi surface decreases with increasing strain. The results suggest that there is an intimate relationship between pinning of the upper CDW and the Fermiology of NbSe3.Comment: 4 pages, 5 figure

Tunable Charge Density Wave Transport in a Current-Effect Transistor

The collective charge density wave (CDW) conduction is modulated by a transverse single-particle current in a transistor-like device. Nonequilibrium conditions in this geometry lead to an exponential reduction of the depinning threshold, allowing the CDWs to slide for much lower bias fields. The results are in excellent agreement with a recently proposed dynamical model in which ''wrinkles'' in the CDW wavefronts are ''ironed'' by the transverse current. The experiment might have important implications for other driven periodic media, such as moving vortex lattices or ''striped phases'' in high-Tc superconductors.Comment: 4 pages, 4 figure

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

Dynamic ordering and frustration of confined vortex rows studied by mode-locking experiments

The flow properties of confined vortex matter driven through disordered mesoscopic channels are investigated by mode locking (ML) experiments. The observed ML effects allow to trace the evolution of both the structure and the number of confined rows and their match to the channel width as function of magnetic field. From a detailed analysis of the ML behavior for the case of 3-rows we obtain ({\it i}) the pinning frequency $f_p$, ({\it ii}) the onset frequency $f_c$ for ML ($\propto$ ordering velocity) and ({\it iii}) the fraction $L_{ML}/L$ of coherently moving 3-row regions in the channel. The field dependence of these quantities shows that, at matching, where $L_{ML}$ is maximum, the pinning strength is small and the ordering velocity is low, while at mismatch, where $L_{ML}$ is small, both the pinning force and the ordering velocity are enhanced. Further, we find that $f_c \propto f_p^2$, consistent with the dynamic ordering theory of Koshelev and Vinokur. The microscopic nature of the flow and the ordering phenomena will also be discussed.Comment: 10 pages, 7 figure, submitted to PRB. Discussion has been improved and a figure has been adde