A Census of White Dwarfs Within 40 Parsecs of the Sun

Our aim is to compile a catalog of white dwarfs within 40 parsecs of the Sun, in which newly discovered objects would significantly increase the completeness of the current census. White dwarf candidates are identified from the SUPERBLINK proper motion database (Lepine & Shara 2005), which allows us to investigate stars down to a proper motion limit as low as 40 mas yr-1. The selection criteria and distance estimates are based on a combination of color-magnitude and reduced proper motion diagrams. Candidates with distances less than 50 parsecs are selected for spectroscopic follow-up. We present our preliminary sample of spectroscopically confirmed white dwarfs, as well as their atmospheric parameters. These parameters are obtained using the spectroscopic technique developed in Bergeron et al.(1992) for DA stars. DB, DQ, and DZ stars are also analyzed spectroscopically. For featureless spectra as well as those showing only Halpha, we perform a detailed photometric analysis of their energy distribution.Comment: 4 pages, 3 figures, to appear in AIP Conference Proceedings for the 17th European White Dwarf Worksho

Novel topological beam-splitting in photonic crystals

We create a passive wave splitter, created purely by geometry, to engineer three-way beam splitting in electromagnetism in transverse electric polarisation. We do so by considering arrangements of Indium Phosphide dielectric pillars in air, in particular we place several inclusions within a cell that is then extended periodically upon a square lattice. Hexagonal lattice structures more commonly used in topological valleytronics but, as we discuss, three-way splitting is only possible using a square, or rectangular, lattice. To achieve splitting and transport around a sharp bend we use accidental, and not symmetry-induced, Dirac cones. Within each cell pillars are either arranged around a triangle or square; we demonstrate the mechanism of splitting and why it does not occur for one of the cases. The theory is developed and full scattering simulations demonstrate the effectiveness of the proposed designs

Transmission channels for light in absorbing random media: from diffusive to ballistic-like transport

While the absorption of light is ubiquitous in nature and in applications, the question remains how absorption modifies the transmission channels in random media. We present a numerical study on the effects of optical absorption on the maximal transmission and minimal reflection channels in a two-dimensional disordered waveguide. In the weak absorption regime, where the system length is less than the diffusive absorption length, the maximal transmission channel is dominated by diffusive transport and it is equivalent to the minimal reflection channel. Its frequency bandwidth is determined by the underlying quasimode width. However, when the absorption is strong, light transport in the maximal transmission channel undergoes a sharp transition and becomes ballistic-like transport. Its frequency bandwidth increases with absorption, and the exact scaling varies with the sample's realization. The minimal reflection channel becomes different from the maximal transmission channel and becomes dominated by absorption. Counterintuitively, we observe in some samples that the minimum reflection eigenvalue increases with absorption. Our results show that strong absorption turns open channels in random media from diffusive to ballistic-like.Comment: 11 pages, 7 figure

Weak non-linearities and cluster states

We propose a scalable approach to building cluster states of matter qubits using coherent states of light. Recent work on the subject relies on the use of single photonic qubits in the measurement process. These schemes have a low initial success probability and low detector efficiencies cause a serious blowup in resources. In contrast, our approach uses continuous variables and highly efficient measurements. We present a two-qubit scheme, with a simple homodyne measurement system yielding an entangling operation with success probability 1/2. Then we extend this to a three-qubit interaction, increasing this probability to 3/4. We discuss the important issues of the overhead cost and the time scaling, showing how these can be vastly improved with access to this new probability range.Comment: 5 pages, to appear in Phys. Rev.

Estimation of the symbol period: the frequency offset case

Publication in the conference proceedings of EUSIPCO, Toulouse, France, 200

The annual cycle of air-sea fluxes in the northwest tropical Atlantic

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bigorre, S. P., & Plueddemann, A. J. The annual cycle of air-sea fluxes in the northwest tropical Atlantic. Frontiers in Marine Science, 7, (2021): 612842, https://doi.org/10.3389/fmars.2020.612842.In this article we analyze 11 years of near-surface meteorology using observations from an open-ocean surface mooring located in the Northwestern Tropical Atlantic (51°W, 15°N). Air-sea fluxes of heat, freshwater, and momentum are derived from these observations using the Coupled Ocean–Atmosphere Response Experiment (COARE) bulk parameterization. Using this dataset, we compute a climatology of the annual cycle of near-surface meteorological conditions and air-sea fluxes. These in situ data are then compared with three reanalyses: the National Centers for Environmental Prediction-Department of Energy [NCEP-DOE (hereafter referred to as NCEP-2)], the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim and the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) reanalyses. Products from the Clouds and the Earth’s Radiant Energy System (CERES) and the Tropical Rainfall Measuring Mission (TRMM) are also used for comparison. We identify the agreements and characterize the discrepancies in the annual cycles of meteorological variables and the different components of air-sea heat fluxes (latent, sensible, shortwave, and longwave radiation). Recomputing the reanalyses fluxes by applying the COARE algorithm to the reanalyses meteorological variables results in better agreement with the in situ fluxes than using the reanalyses fluxes directly. However, the radiative fluxes (longwave and shortwave) from some of the reanalyses show significant discrepancies when compared with the in situ measurements. Longwave radiation from MERRA-2 is biased high (too much oceanic heat loss), and NCEP-2 longwave does not correlate to in situ observations and other reanalyses. Shortwave radiation from NCEP-2 is biased low in winter and does not track the observed variability in summer. The discrepancies in radiative fluxes versus in situ fluxes are explored, and the potential regional implications are discussed using maps of satellite and reanalyses products, including radiation and cloud cover.The NTAS project was funded by the Global Ocean Monitoring and Observing Program of the National Oceanic and Atmospheric Administration (CPO FundRef number 100007298), through the Cooperative Institute for the North Atlantic Region (CINAR) under Cooperative Agreement NA14OAR4320158

NTAS 16 sixteenth setting of the NTAS Ocean Reference Station cruise on board RV Endeavor January 21 - February 8, 2017 Narragansett, Rhode Island - San Juan, Puerto Rico

The Northwest Tropical Atlantic Station (NTAS) was established to address the need for accurate air-sea flux estimates and upper ocean measurements in a region with strong sea surface temperature anomalies and the likelihood of significant local air–sea interaction on inter-annual to decadal timescales. The approach is to maintain a surface mooring outfitted for meteorological and oceanographic measurements at a site near 15N, 51W by successive mooring turnarounds. These observations are used to investigate air–sea interaction processes related to climate variability. The NTAS Ocean Reference Station (ORS NTAS) is supported by the National Oceanic and Atmospheric Administration’s (NOAA) Ocean Observing and Monitoring Division. This report documents recovery of the NTAS-15 mooring and deployment of the NTAS-16 mooring. Both moorings used Surlyn foam buoys as the surface element. These buoys were outfitted with two Air–Sea Interaction Meteorology (ASIMET) systems. Each system measures, records, and transmits via Argos satellite the surface meteorological variables necessary to compute air–sea fluxes of heat, moisture and momentum. The upper 160 m of the mooring line were outfitted with oceanographic sensors for the measurement of temperature, salinity and velocity. The mooring turnaround was done by the Upper Ocean Processes Group of the Woods Hole Oceanographic Institution (WHOI), onboard R/V Endeavor (cruise EN590). The cruise took place between January 21 and February 8 2017. The NTAS-16 mooring was deployed on January 30, and the NTAS-15 mooring was recovered on January 31. A 24-hour intercomparison period was conducted on January 29 in front of the NTAS 15 buoy, and again on February 1 in front of the NTAS 16 buoy. During the inter-comparisons, data from instrumentation on the buoys, telemetered through Argos satellite system, and the ship’s meteorological and oceanographic measurements were monitored while the ship was stationed 0.2 nm downwind of the buoys. This report describes these operations, as well as other work done on the cruise and some of the pre-cruise buoy preparations. Other operations during EN590 consisted in the recovery and deployment of the Meridional Overturning Variability Experiment (MOVE) Pressure Inverted Echo Sounders (PIES) at two MOVE arrays (MOVE 1 in the east, and MOVE 3 in the west near Guadeloupe). Acoustic downloads of data from (PIES) and subsurface mooring (MOVE1, 3 and 4) were also conducted. MOVE is designed to monitor the integrated deep meridional flow in the tropical North Atlantic.Funding was provided by the National Oceanic and Atmospheric Administration under Grant No. NA14OAR4320158