935 research outputs found
Laser-induced Fluorescence Studies of Hematoporphyrin Derivative (hpd) In Normal and Tumor-tissue of Rat
Mixing of ultracold atomic clouds by merging of two magnetic traps
We demonstrate a method to make mixtures of ultracold atoms that does not
make use of a two-species magneto-optical trap. We prepare two clouds of 87Rb
atoms in distinct magnetic quadrupole traps and mix the two clouds by merging
the traps. For correctly chosen parameters the mixing can be done essentially
without loss of atoms and with only minor heating. The basic features of the
process can be accounted for by a classical simulation of particle
trajectories. Such calculations indicate that mixing of different mass species
is also feasible, opening the way for using the method as a starting point for
making quantum gas mixtures.Comment: 12 pages, 13 figures. Fig. 10 corrected. Fig. 13 updated with more
points and better statistics. A couple of paragraphs rephrased and typos
corrected. References update
Discovery of a very extended X-ray halo around a quiescent spiral galaxy - the "missing link" of galaxy formation
Hot gaseous haloes surrounding galaxies and extending well beyond the
distribution of stars are a ubiquitous prediction of galaxy formation
scenarios. The haloes are believed to consist of gravitationally trapped gas
with a temperature of millions of Kelvin. The existence of such hot haloes
around massive elliptical galaxies has been established through their X-ray
emission. While gas out-flowing from starburst spiral galaxies has been
detected, searches for hot haloes around normal, quiescent spiral galaxies have
so far failed, casting doubts on the fundamental physics in galaxy formation
models. Here we present the first detection of a hot, large-scale gaseous halo
surrounding a normal, quiescent spiral galaxy, NGC 5746, alleviating a
long-standing problem for galaxy formation models. In contrast to starburst
galaxies, where the X-ray halo can be powered by the supernova energy, there is
no such power source in NGC 5746. The only compelling explanation is that we
are here witnessing a galaxy forming from gradually in-flowing hot and dilute
halo gas.Comment: New Astronomy, in pres
Hyperfine-structure and Radiative-lifetime Determination For the 4d106p2p States of Neutral Silver Using Pulsed Laser Spectroscopy
Multi-channel conduction in redox-based resistive switch modelled using quantum point contact theory
A simple analytic model for the electron transport through filamentary-type structures in Si-rich silica (SiOx)-based resistive switches is proposed. The model is based on a mesoscopic description and is able to account for the linear and nonlinear components of conductance that arise from both fully and partially formed conductive channels spanning the dielectric film. Channels are represented by arrays of identical scatterers whose number and quantum transmission properties determine the current magnitude in the low and high resistance states. We show that the proposed model not only reproduces the experimental current-voltage (I-V) characteristics but also the normalized differential conductance (dln(I)/dln(V)-V) curves of devices under test
Real-time gas-correlation imaging employing thermal background radiation
Real-time imaging of gas leaks was demonstrated using an IR camera employing outdoor thermal background radiation. Ammonia, ethylene and methane detection was demonstrated in the spectral region 7-13 mu m. Imaging was accomplished using an optical filter and a gas-correlation cell matching the absorption band of the gas. When two gases, such as ammonia and ethylene, are absorbing in the same wavelength region it is possible to isolate one for display by using gas-correlation multispectral imaging. Results from a field test on a leaking gas tanker are presented as QuickTime movies. A detection limit of 200 ppm x meter for ammonia was accomplished in this setup when the temperature difference between the background and the gas was 18 K and the frame rate was 15 Hz. (C) 2000 Optical Society of America
Frequency-modulation spectroscopy with blue diode lasers
Frequency-modulation spectroscopy provides ultrasensitive absorption measurements. The technique is especially adaptable to diode lasers, which can be modulated easily, and has been used extensively in the near-infrared and infrared spectral regions. The availability of blue diode lasers now means that the accessible wavelength region can be increased. We successfully demonstrate wavelength-modulation spectroscopy and two-tone frequency-modulation spectroscopy for the weak second resonance line of potassium at 404.8 nm and for the transition at 405.8 nm in lead, starting from the thermally populated 6p(2) P-3(2) metastable level, information on the modulation parameters is obtained with a fitting procedure. Experimental signal-to-noise ratios: at different absorption levels are compared with theoretical signal-to-noise ratios and show good agreement. Detection sensitivities of 2 x 10(-6) and 5 x 10(-6) for wavelength and two-tone frequency-modulation spectroscopy, respectively, for a 120-Hz bandwidth are demonstrated. (C) 2000 Optical Society of America
Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters, 430 (2015): 511-522, doi:10.1016/j.epsl.2015.07.027.The marine biogeochemical cycle of Ba is thought to be controlled by particulate BaSO4 (barite) precipitation associated
with the microbial oxidation of organic carbon and its subsequent dissolution in the BaSO4-undersaturated
water column. Despite many of these processes being largely unique to Ba cycling, concentrations of Ba and Si in
seawater exhibit a strong linear correlation. The reasons for this correlation are ambiguous, as are the depth ranges
corresponding to the most active BaSO4 cycling and the intermediate sources of Ba to particulate BaSO4. Stable
isotopic analyses of dissolved Ba in seawater should help address these issues, as Ba-isotopic compositions are
predicted to be sensitive to the physical and biogeochemical process that cycle Ba. We report a new methodology
for the determination of dissolved Ba-isotopic compositions in seawater and results from a 4, 500 m depth profile
in the South Atlantic at 39.99 S, 0.92 E that exhibit oceanographically-consistent variation with depth. These data
reveal that water masses obtain their [Ba] and Ba-isotopic signatures when at or near the surface, which relates to
the cycling of marine BaSO4. The shallow origin of these signatures requires that the substantial Ba-isotopic variations
in the bathypelagic zone were inherited from when those deep waters were last ventilated. Indeed, the water
column below 600 m is well explained by conservative mixing of water masses with distinct [Ba] and Ba-isotopic
compositions. This leads us to conclude that large scale oceanic circulation is important for sustaining the similar
oceanographic distributions of Ba and Si in the South Atlantic, and possibly elsewhere. These data demonstrate
that the processes of organic carbon oxidation, BaSO4 cycling, and Ba-isotopic fractionation in seawater are closely
coupled, such that Ba-isotopic analyses harbor great potential as a tracer of the carbon cycle in the modern and
paleo-oceans.T.J.H. acknowledges support from Makoto
A. Saito (Gordon and Betty Moore Foundation; Project # 3782) and the Postdoctoral Scholar Program at the Woods
Hole Oceanographic Institution, with funding provided by the Doherty Foundation. Development of Ba-isotopic
protocols at NIRVANA was made possible with funding from The Andrew W. Mellon Foundation Endowed Fund
for Innovative Research (T.J.H. and S.G.N.)
Analysis of high-precision vanadium isotope ratios by medium resolution MC-ICP-MS
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Royal Society of Chemistry for personal use, not for redistribution. The definitive version was published in Journal of Analytical Atomic Spectrometry 31 (2016): 531-536 , doi:10.1039/C5JA00397K.We present and verify a new method to measure vanadium isotope ratios using a
Thermo Scientific Neptune multi-collector inductively-coupled plasma mass spectrometer (MCICP-
MS) operated in medium mass resolution mode. We collect masses 48 through 53
simultaneously using the L2, L1, Center, H1, H2 and H3 collectors. The Center cup is equipped
with a 1012 ; resistor, H1 is equipped with a 1010 ; resistor, while the rest of the collectors have
standard 1011 ; resistors. Unlike previous low-resolution methods, the use of medium mass
resolution (=M/M ~ 4,000) permits separation of V, Ti and Cr isotopes from all interfering
molecular species representing combinations of C, N, O, S, Cl, and Ar. We show that the
external reproducibility follows a power law function with respect to the number of V+ ions
collected and achieve an external reproducibility of ± 0.15 ‰ with total V+ ion beam intensities
of ~ 1 nA. The separation of interfering molecular species from the V mass spectrum reduces the
V requirement for precise isotope data to as little as 200-300 ng V per analysis — a reduction of
~90% compared with previous methods — making several low-V matrices amenable to V
isotope analysis.This study was funded by a WHOI IR&D grant to SGN and NSF OCE grant 1434785 to
JDO and SGN and Agouron Geobiology Fellowships to JDO and TJH.2016-11-1
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