Unique gap structure and symmetry of the charge density wave in single-layer VSe2_2

Single layers of transition metal dichalcogenides (TMDCs) are excellent candidates for electronic applications beyond the graphene platform; many of them exhibit novel properties including charge density waves (CDWs) and magnetic ordering. CDWs in these single layers are generally a planar projection of the corresponding bulk CDWs because of the quasi-two-dimensional nature of TMDCs; a different CDW symmetry is unexpected. We report herein the successful creation of pristine single-layer VSe$_2$, which shows a ($\sqrt7 \times \sqrt3$) CDW in contrast to the (4 $\times$ 4) CDW for the layers in bulk VSe$_2$. Angle-resolved photoemission spectroscopy (ARPES) from the single layer shows a sizable ($\sqrt7 \times \sqrt3$) CDW gap of $\sim$100 meV at the zone boundary, a 220 K CDW transition temperature twice the bulk value, and no ferromagnetic exchange splitting as predicted by theory. This robust CDW with an exotic broken symmetry as the ground state is explained via a first-principles analysis. The results illustrate a unique CDW phenomenon in the two-dimensional limit

Sodium vacancy ordering and the co-existence of localized spins and itinerant charges in NaxCoO2

The sodium cobaltate family (NaxCoO2) is unique among transition metal oxides because the Co sits on a triangular lattice and its valence can be tuned over a wide range by varying the Na concentration x. Up to now detailed modeling of the rich phenomenology (which ranges from unconventional superconductivity to enhanced thermopower) has been hampered by the difficulty of controlling pure phases. We discovered that certain Na concentrations are specially stable and are associated with superlattice ordering of the Na clusters. This leads naturally to a picture of co-existence of localized spins and itinerant charge carriers. For x = 0.84 we found a remarkably small Fermi energy of 87 K. Our picture brings coherence to a variety of measurements ranging from NMR to optical to thermal transport. Our results also allow us to take the first step towards modeling the mysterious ``Curie-Weiss'' metal state at x = 0.71. We suggest the local moments may form a quantum spin liquid state and we propose experimental test of our hypothesis.Comment: 16 pages, 5 figure

Development and Evaluation of an Autonomous Sensor for the Observation of Sediment Motion

Abstract Measurements within the mobile bed layer have been limited by previous Eulerian-based technologies. A microelectromechanical system device, called a smart sediment grain (SSG), that can measure and record Lagrangian observations of coastal sediments at incipient motion has been developed. These sensors have the potential to resolve fundamental hypotheses regarding the incipient motion of coastal sediments. Angle of repose experiments verified that the sensor enclosure has mobility characteristics similar to coarse gravel. Experiments conducted in a small oscillating flow tunnel verified that the sensors detect incipient motion under various hydrodynamic conditions. Evidence suggests the influence of pressure-gradient-induced sediment motion, contrary to the more commonly assumed bed shear stress criterion. Lagrangian measurements of rotation measured with the newly developed SSG agreed to within 5% of the rotation estimates made simultaneously with high-speed video cameras

In Vivo Breast Cancer Measurement with a Handheld Laser Breast Scanner

Abstract — HBS is a handheld system for noninvasive breast cancer detection based on frequency domain photon migration. It performs broadband modulation on near-infrared laser intensity and derives the scattering and absorption coefficients from phase and amplitude measurements. Recovered optical properties of phantom and tissue by HBS clearly show the difference between normal and cancer tissue. Measurements show HBS can replace the current prototype while costing a small fraction. I

Smart wireless sensor system for lifeline health monitoring under a disaster event

ABSTRACT This paper discusses issues of using wireless sensor systems to monitor structures and pipelines in the case of disastrous events. The platforms are deployed and monitored remotely on lifetime systems, such as underground water pipelines. Although similar systems have been proposed for monitoring seismic events and the structure health of bridges and buildings, several fundamental differences necessitate adaptation or redesign of the module. Specifically, rupture detection in water delivery networks must respond to higher frequency and wider bandwidth than those used in the monitoring of seismic events, structures, or bridges. The monitoring and detection algorithms can also impose a wide range of requirements on the fidelity of the acquired data and the flexibility of wireless communication technologies. We employ a non-invasive methodology based on MEMS accelerometers to identify the damage location and to estimate the extent of the damage. The key issues are low-noise power supply, noise floor of sensors, higher sampling rate, and the relationship among displacement, frequency, and acceleration. Based on the mentioned methodology, PipeTECT, a smart wireless sensor platform was developed. The platform was validated on a bench-scale uniaxial shake table, a small-scale water pipe network, and portions of several regional water supply networks. The laboratory evaluation and the results obtained from a preliminary field deployment show that such key factors in the implementation are crucial to ensure high fidelity of the acquired data. This is expected to be helpful in the understanding of lifeline infrastructure behavior under disastrous events