Fluctuating charge density waves in a cuprate superconductor

Cuprate materials hosting high-temperature superconductivity (HTS) also exhibit various forms of charge and/or spin ordering whose significance is not fully understood. To date, static charge-density waves (CDWs) have been detected by diffraction probes only at special doping or in an applied external field. However, dynamic CDWs may also be present more broadly and their detection, characterization and relationship with HTS remain open problems. Here, we present a new method, based on ultrafast spectroscopy, to detect the presence and measure the lifetimes of CDW fluctuations in cuprates. In an underdoped La1.9Sr0.1CuO4 film (Tc = 26 K), we observe collective excitations of CDW that persist up to 100 K. This dynamic CDW fluctuates with a characteristic lifetime of 2 ps at T = 5 K which decreases to 0.5 ps at T = 100 K. In contrast, in an optimally doped La1.84Sr0.16CuO4 film (Tc = 38.5 K), we detect no signatures of fluctuating CDWs at any temperature, favoring the competition scenario. This work forges a path for studying fluctuating order parameters in various superconductors and other materials.Comment: 16 pages, 4 figures, accepted to Nature Material

Requirements for regional short-haul air service and the definition of a flight program to determine neighborhood reactions to small transport aircraft

An evaluation of the current status and future requirements of an intraregional short haul air service is given. A brief definition of the different types of short haul air service is given. This is followed by a historical review of previous attempts to develop short haul air service in high density urban areas and an assessment of the current status. The requirements for intraregional air service, the need for economic and environmental viability and the need for a flight research program are defined. A detailed outline of a research program that would determine urban community reaction to frequent operations of small transport aircraft is also given. Both the operation of such an experiment in a specific region (San Francisco Bay area) and the necessary design modifications of an existing fixed wing aircraft which could be used in the experiment are established. An estimate is made of overall program costs

Phase-coherent detection of an optical dipole force by Doppler velocimetry

We report phase-coherent Doppler detection of optical dipole forces using large ion crystals in a Penning trap. The technique is based on laser Doppler velocimetry using a cycling transition in $^{9}$Be$^{+}$ near 313 nm and the center-of-mass (COM) ion motional mode. The optical dipole force is tuned to excite the COM mode, and measurements of photon arrival times synchronized with the excitation potential show oscillations with a period commensurate with the COM motional frequency. Experimental results compare well with a quantitative model for a driven harmonic oscillator. This technique permits characterization of motional modes in ion crystals; the measurement of both frequency and phase information relative to the driving force is a key enabling capability -- comparable to lockin detection -- providing access to a parameter that is typically not available in time-averaged measurements. This additional information facilitates discrimination of nearly degenerate motional modes.Comment: Related manuscripts at http://www.physics.usyd.edu.au/~mbiercuk

Dynamics of quartz tuning fork force sensors used in scanning probe microscopy

We have performed an experimental characterization of the dynamics of oscillating quartz tuning forks which are being increasingly used in scanning probe microscopy as force sensors. We show that tuning forks can be described as a system of coupled oscillators. Nevertheless, this description requires the knowledge of the elastic coupling constant between the prongs of the tuning fork, which has not yet been measured. Therefore tuning forks have been usually described within the single oscillator or the weakly coupled oscillators approximation that neglects the coupling between the prongs. We propose three different procedures to measure the elastic coupling constant: an opto-mechanical method, a variation of the Cleveland method and a thermal noise based method. We find that the coupling between the quartz tuning fork prongs has a strong influence on the dynamics and the measured motion is in remarkable agreement with a simple model of coupled harmonic oscillators. The precise determination of the elastic coupling between the prongs of a tuning fork allows to obtain a quantitative relation between the resonance frequency shift and the force gradient acting at the free end of a tuning fork prong.Comment: 16 pages, 6 figures, 2 Table

Estimation with Response Error and Non-Response: Food Stamp Participation in the SIPP

Estimation with Response Error and Non-response: Food Stamp Participation in the SIPP

Observation of a parity oscillation in the conductance of atomic wires

Using a scanning tunnel microscope or mechanically controlled break junctions, atomic contacts of Au, Pt and Ir are pulled to form chains of atoms. We have recorded traces of conductance during the pulling process and averaged these for a large amount of contacts. An oscillatory evolution of conductance is observed during the formation of the monoatomic chain suggesting a dependence on even or odd numbers of atoms forming the chain. This behaviour is not only present in the monovalent metal Au, as it has been previously predicted, but is also found in the other metals which form chains suggesting it to be a universal feature of atomic wires

Changes in phasic femoral artery flow induced by various stimuli: a study with percutaneous pulsed Doppler ultrasound

Transcutaneous blood flow measurements were performed by means of a pulsed Doppler ultrasound flowmeter in the femoral artery of healthy subjects. The pulsatile flow pattern was changed characteristically from resting state by postocclusive reactive hyperaemia, by the application of amyl nitrite, xanthinol nicotinate, and angiotensin amide. During reactive hyperaemia systolic flow was increased, diastolic reverse flow was abolished, and the forward flow continued throughout diastole. Amyl nitrite augmented the negative flow phase and reduced mean flow, while xanthinol nicotinate decreased the negative component and augmented mean flow. Angiotensin amide produced enhancement of the average flow by elevating systolic and diastolic flow equally over the base line. In each of these interventions the changes in flow were determined mainly by variations during the diastolic flow phas