Pipelined digital SAR azimuth correlator using hybrid FFT-transversal filter

A synthetic aperture radar system (SAR) having a range correlator is provided with a hybrid azimuth correlator which utilizes a block-pipe-lined fast Fourier transform (FFT). The correlator has a predetermined FFT transform size with delay elements for delaying SAR range correlated data so as to embed in the Fourier transform operation a corner-turning function as the range correlated SAR data is converted from the time domain to a frequency domain. The azimuth correlator is comprised of a transversal filter to receive the SAR data in the frequency domain, a generator for range migration compensation and azimuth reference functions, and an azimuth reference multiplier for correlation of the SAR data. Following the transversal filter is a block-pipelined inverse FFT used to restore azimuth correlated data in the frequency domain to the time domain for imaging

Kelu-1 is a Binary L Dwarf: First Brown Dwarf Science from Laser Guide Star Adaptive Optics

(Abridged) We present near-IR imaging of the nearby L dwarf Kelu-1 obtained with the Keck sodium laser guide star adaptive optics (LGS AO) system as part of a high angular resolution survey for substellar binaries. Kelu-1 was one of the first free-floating L dwarfs identified, and the origin of its overluminosity compared to other similar objects has been a long-standing question. Our images clearly resolve Kelu-1 into a 0.29'' (5.4 AU) binary, and a previous non-detection by HST demonstrates that the system is a true physical pair. Binarity explains the properties of Kelu-1 that were previously noted to be anomalous compared to other early-L dwarfs. We estimate spectral types of L1.5-L3 and L3-L4.5 for the two components, giving model-derived masses of 0.05-0.07 Msun and 0.045-0.065 Msun for an estimated age of 0.3-0.8 Gyr. More distant companions are not detected to a limit of 5-9 Mjup. The presence of lithium absorption indicates that both components are substellar, but the weakness of this feature relative to other L dwarfs can be explained if only Kelu-1B is Li-bearing. Determining whether both or only one of the components possesses lithium could constrain the age of Kelu-1 (and other Li-bearing L binaries) with higher precision than is possible for most ultracool field objects. These results are the first LGS AO observations of brown dwarfs and demonstrate the potential of this new instrumental capability for substellar astronomy.Comment: 24 pages, Astrophysical Journal, in press (Nov 20, 2005 issue). Note that Figure 1 of the PDF version is degraded by arxiv.org, but the Postscript version is fine. Version 2 includes very minor changes to match the published versio

A Near-Infrared Spectroscopic Study of Young Field Ultracool Dwarfs

We present a near-infrared (0.9-2.4 microns) spectroscopic study of 73 field ultracool dwarfs having spectroscopic and/or kinematic evidence of youth (~10-300 Myr). Our sample is composed of 48 low-resolution (R~100) spectra and 41 moderate-resolution spectra (R>~750-2000). First, we establish a method for spectral typing M5-L7 dwarfs at near-IR wavelengths that is independent of gravity. We find that both visual and index-based classification in the near-IR provide consistent spectral types with optical spectral types, though with a small systematic offset in the case of visual classification at J and K band. Second, we examine features in the spectra of ~10 Myr ultracool dwarfs to define a set of gravity-sensitive indices based on FeH, VO, K, Na and H-band continuum shape. We then create an index-based method for classifying the gravities of M6-L5 dwarfs that provides consistent results with gravity classifications from optical spectroscopy. Our index-based classification can distinguish between young and dusty objects. Guided by the resulting classifications, we propose a set of low-gravity spectral standards for the near-IR. Finally, we estimate the ages corresponding to our gravity classifications.Comment: Published in ApJ. IDL program for calculating indices (allers13_index.pro) included in the source gzipped ta

The Micro-Bubble Distribution in the Wake of a Cavitating Circular Cylinder

Bubble nuclei populations in the wake of a circular cylinder under cavitating and noncavitating conditions were measured using a Phase Doppler Anemometry (PDA) system. In addition, the mean velocity defect and the turbulent fluctuations were monitored in order to try to understand the nuclei population dynamics within the flow. At the Reynolds numbers of these experiments (20000->33000) the laminar near-wake is fairly steady and under very limited cavitation conditions nuclei accumulate in this wake so that the population there is several orders of magnitude larger than in the upstream flow. Further downstream the population declines again as nuclei are entrained into the wake. However at fifteen diameters downstream the population is still much larger than in the upstream flow

Crystallized merons and inverted merons in the condensation of spin-1 Bose gases with spin-orbit coupling

The non-equilibrium dynamics of a rapidly quenched spin-1 Bose gas with spin-orbit coupling is studied. By solving the stochastic projected Gross-Pitaevskii equation, we show that crystallization of merons can occur in a spinor condensate of ^{87}Rb. Analytic form and stability of the crystal structure are given. Likewise, inverted merons can be created in a spin-polarized spinor condensate of ^{23}Na. Our studies provide a chance to explore the fundamental properties of meron-like matter.Comment: 5 pages, 6 figure

Superior removal of arsenic from water with zirconium metal-organic framework UiO-66

10.1038/srep16613Scientific Reports51661

A search for a superconducting effect on alpha particle differential energy loss in type 1 superconductors

Superconducting effects on alpha particle differential energy loss in tin, vanadium, and lead superconductor

Energy dependence of Normal Branch Oscillation in Scorpius X-1

We report the energy dependence of normal branch oscillations (NBOs) in Scorpius X-1, a low-mass X-ray binary Z-source. Three characteristic quantities (centroid frequency, quality factor, and fractional root-mean-squared (rms) amplitude) of a quasi-periodic oscillation signal as functions of photon energy are investigated. We found that, although it is not yet statistically well established, there is a signature indicating that the NBO centroid frequency decreases with increasing photon energy when it is below 6-8 keV, which turns out to be positively correlated with the photon energy at the higher energy side. In addition, the rms amplitude increases significantly with the photon energy below 13 keV and then decreases in the energy band of 13-20 keV. There is no clear dependence on photon energy for the quality factor. Based on these results, we suggest that the NBO originates mainly in the transition layer.Comment: 6 pages, 4 figure

Discovery of a Highly Unequal-Mass Binary T Dwarf with Keck Laser Guide Star Adaptive Optics: A Coevality Test of Substellar Theoretical Models and Effective Temperatures

(Abridged) Highly unequal-mass ratio binaries are rare among field brown dwarfs, with the known census described by q^(4.9+/-0.7). However, such systems can test the joint accuracy of evolutionary and atmospheric models, under the constraint of coevality (the "isochrone test''). We carry out this test using two of the most extreme field substellar binaries currently known, the T1+T6 \eps Ind Bab binary and a newly discovered 0.14" T2.0+T7.5 binary, 2MASS 1209-10AB. Based on the locations of the components on the H-R diagram, models successfully indicate that the systems are coeval, with internal age differences of log(age) = 0.5{+0.4}{-0.3} and -0.8+/-1.3 dex, respectively. However, the total mass of \eps Ind Bab derived from the H-R diagram (~80 Mjup) is discrepant with the reported dynamical mass. This problem, which is independent of the assumed age of the system, can be explained by a ~50-100 K systematic error in the model atmosphere fitting; bringing the two mass determinations into consistency leads to an inferred age of ~6 Gyr for the \eps Ind system, older than previously assumed. Overall, the two T dwarf binaries studied here, along with recent results from T dwarfs in age and mass benchmark systems, yield evidence for small (~100 K) errors in the evolutionary models and/or model atmospheres, but not significantly larger. Finally, the binary nature of 2MASS 1209-10AB reduces its utility as the primary T3 near-IR spectral typing standard; we suggest SDSS 1206+28 as a replacement.Comment: ApJ, in press. Version 2 has tiny changes to match the published versio