Universal linear relations between susceptibility and Tc in cuprates

We developed an experimental method for measuring the intrinsic susceptibility \chi of powder of cuprate superconductors in the zero field limit using a DC-magnetometer. The method is tested with lead spheres. Using this method we determine \chi for a number of cuprate families as a function of doping. A universal linear (and not proportionality) relation between Tc and \chi is found. We suggest possible explanations for this phenomenon.Comment: Accepted for publication in PR

Public Opinions of Unmanned Aerial Technologies in 2014 to 2019: A Technical and Descriptive Report

The primary purpose of this report is to provide a descriptive and technical summary of the results from similar surveys administered in fall 2014 (n = 576), 2015 (n = 301), 2016 (ns = 1946 and 2089), and 2018 (n = 1050) and summer 2019 (n = 1300). In order to explore a variety of factors that may impact public perceptions of unmanned aerial technologies (UATs), we conducted survey experiments over time. These experiments randomly varied the terminology (drone, aerial robot, unmanned aerial vehicle (UAV), unmanned aerial system (UAS)) used to describe the technology, the purposes of the technology (for economic, environmental, or security goals), the actors (public or private) using the technology, the technology’s autonomy (fully autonomous, partially autonomous, no autonomy), and the framing (promotion or prevention) used to describe the technology’s purpose. Initially, samples were recruited through Amazon’s Mechanical Turk, required to be Americans, and paid a small amount for participation. In 2016 we also examined a nationally representative samples recruited from Qualtrics panels. After 2016 we only used nationally representative samples from Qualtrics. Major findings are reported along with details regarding the research methods and analyses

Energy Distribution for SH-Waves in Slightly Anisotropic Materials

Many polycrystalline metal aggregates display a slight amount of anisotropy due to texture that develops during fabrication procedures such as rolling. This macroscopic anisotropy produces a birefringence of SH-waves propagating normal to the plate, i.e., the velocity of SH-waves polarized parallel to the rolling direction is usually faster than that of SH-waves polarized perpendicular to the rolling direction. For polarization angles not in or perpendicular to the rolling direction the wave is assumed to split into two waves, one polarized parallel and one polarized perpendicular to the rolling (similar to what is observed for particular propagation directions in single crystals). However slightly anisotropic materials have only a small percentage of preferential grain alignment, the bulk of the grains being of random orientation. In consideration of these materials being nearly isotropic, having slight anisotropy superimposed, and the possibility of multiple textures, we address the energy distribution of SH-waves as a function of polarization angle with respect to the material symmetry axes and the transducer orientation. The importance of considering attenuation in this work is also addressed

Quasiparticle spectroscopy and high-field phase diagrams of cuprate superconductors -- An investigation of competing orders and quantum criticality

We present scanning tunneling spectroscopic and high-field thermodynamic studies of hole- and electron-doped (p- and n-type) cuprate superconductors. Our experimental results are consistent with the notion that the ground state of cuprates is in proximity to a quantum critical point (QCP) that separates a pure superconducting (SC) phase from a phase comprised of coexisting SC and a competing order, and the competing order is likely a spin-density wave (SDW). The effect of applied magnetic field, tunneling current, and disorder on the revelation of competing orders and on the low-energy excitations of the cuprates is discussed.Comment: 10 pages, 5 figures. Accepted for publication in the International Journal of Modern Physics B. (Correspondence author: Nai-Chang Yeh, e-mail: [email protected]

Suppression of matching field effects by splay and pinning energy dispersion in YBa_2Cu_3O_7 with columnar defects

We report measurements of the irreversible magnetization M_i of a large number of YBa_2Cu_3O_7 single crystals with columnar defects (CD). Some of them exhibit a maximum in M_i when the density of vortices equals the density of tracks, at temperatures above 40K. We show that the observation of these matching field effects is constrained to those crystals where the orientational and pinning energy dispersion of the CD system lies below a certain threshold. The amount of such dispersion is determined by the mass and energy of the irradiation ions, and by the crystal thickness. Time relaxation measurements show that the matching effects are associated with a reduction of the creep rate, and occur deep into the collective pinning regime.Comment: 7 pages, 5 figures, submitted to Phys. Rev.

The Effect of Splayed Pins on Vortex Creep and Critical Currents

We study the effects of splayed columnar pins on the vortex motion using realistic London Langevin simulations. At low currents vortex creep is strongly suppressed, whereas the critical current j_c is enhanced only moderately. Splaying the pins generates an increasing energy barrier against vortex hopping, and leads to the forced entanglement of vortices, both of which suppress creep efficiently. On the other hand splaying enhances kink nucleation and introduces intersecting pins, which cut off the energy barriers. Thus the j_c enhancement is strongly parameter sensitive. We also characterize the angle dependence of j_c, and the effect of different splaying geometries.Comment: 4 figure

Public Opinions of Unmanned Aerial Technologies in 2014 to 2019: A Technical and Descriptive Report

The primary purpose of this report is to provide a descriptive and technical summary of the results from similar surveys administered in fall 2014 (n = 576), 2015 (n = 301), 2016 (ns = 1946 and 2089), and 2018 (n = 1050) and summer 2019 (n = 1300). In order to explore a variety of factors that may impact public perceptions of unmanned aerial technologies (UATs), we conducted survey experiments over time. These experiments randomly varied the terminology (drone, aerial robot, unmanned aerial vehicle (UAV), unmanned aerial system (UAS)) used to describe the technology, the purposes of the technology (for economic, environmental, or security goals), the actors (public or private) using the technology, the technology’s autonomy (fully autonomous, partially autonomous, no autonomy), and the framing (promotion or prevention) used to describe the technology’s purpose. Initially, samples were recruited through Amazon’s Mechanical Turk, required to be Americans, and paid a small amount for participation. In 2016 we also examined a nationally representative samples recruited from Qualtrics panels. After 2016 we only used nationally representative samples from Qualtrics. Major findings are reported along with details regarding the research methods and analyses

Magnetocaloric Studies of the Peak Effect in Nb

We report a magnetocaloric study of the peak effect and Bragg glass transition in a Nb single crystal. The thermomagnetic effects due to vortex flow into and out of the sample are measured. The magnetocaloric signature of the peak effect anomaly is identified. It is found that the peak effect disappears in magnetocaloric measurements at fields significantly higher than those reported in previous ac-susceptometry measurements. Investigation of the superconducting to normal transition reveals that the disappearance of the bulk peak effect is related to inhomogeneity broadening of the superconducting transition. The emerging picture also explains the concurrent disappearance of the peak effect and surface superconductivity, which was reported previously in the sample under investigation. Based on our findings we discuss the possibilities of multicriticality associated with the disappearance of the peak effect.Comment: 30 pages, 10 figure

Sensing Through the Continent: Towards Monitoring Migratory Birds Using Cellular Sensor Networks

This paper presents CraneTracker, a novel sensor platform for monitoring migratory birds. The platform is designed to monitor Whooping Cranes, an endangered species that conducts an annual migration of 4, 000 km between southern Texas and north-central Canada. CraneTracker includes a rich set of sensors, a multi-modal radio, and power control circuitry for sustainable, continental-scale information delivery during migration. The need for large-scale connectivity motivates the use of cellular technology in low-cost sensor platforms augmented by a low-power transceiver for ad-hoc connectivity. This platform leads to a new class of cellular sensor networks (CSNs) for time-critical and mobile sensing applications. The CraneTracker is evaluated via field tests on Wild Turkeys, Siberian Cranes, and an on-going alpha deployment with wild Sandhill Cranes. Experimental evaluations demonstrate the potential of energy-harvesting CSNs for wildlife monitoring in large geographical areas, and reveal important insights into the movements and behaviors of migratory animals. In addition to benefiting ecological research, the developed platform is expected to extend the application domain of sensor networks and enable future research applications