10,641 research outputs found
Fano Lineshapes Revisited: Symmetric Photoionization Peaks from Pure Continuum Excitation
In a photoionization spectrum in which there is no excitation of the discrete
states, but only the underlying continuum, we have observed resonances which
appear as symmetric peaks, not the commonly expected window resonances.
Furthermore, since the excitation to the unperturbed continuum vanishes, the
cross section expected from Fano's configuration interaction theory is
identically zero. This shortcoming is removed by the explicit introduction of
the phase shifted continuum, which demonstrates that the shape of a resonance,
by itself, provides no information about the relative excitation amplitudes to
the discrete state and the continuum.Comment: 4 pages, 3 figure
Measurements and comparison of primary biological aerosol above and below a tropical forest canopy using a dual channel fluorescence spectrometer
Original article can be found at: http://www.atmos-chem-phys.net/10/issue10.html Copyright - the authors. Authors grant any third party the right to use the article freely as long as its original authors and citation details are identified. The article and any associated published material is distributed under the Creative Commons Attribution 3.0 License.Aerosol particle size distributions were measured below and above a tropical rainforest canopy in Borneo, Malaysia, in June/July 2008 using the WIBS-3: a single particle dual channel fluorescence spectrometer. Material in the size range 0.8–20 μm was characterized according to optical equivalent diameter (DP), morphology and fluorescence at 310–400 nm and 400–600 nm following excitation at 280 nm and 370 nm respectively. Particles fluorescent after both excitations are likely to be fluorescent primary biological aerosol particles (FBAP). Measured FBAP number concentration (NFBAP) at both sites exhibited clear diurnal cycles. The largest variability was observed in the understorey, where NFBAP reached a minimum of 50–100 L−1 in late morning. In mid afternoon it exhibited strong transient fluctuations as large as 4000 L−1 that were followed by sustained concentrations of 1000–2500 L−1 that reduced steadily between midnight and sunrise. Above the canopy FBAP number ranged from 50–100 L−1 during the daytime to 200–400 L−1 at night but did not exhibit the transient enhancements seen in the understorey. The strong FBAP fluctuations were attributed to the release of fungal spores below the canopy and appeared to be linked to elevated relative humidity. The mean FBAP number fraction in the size range 0.8 μm<DP<20 μm was 55% in the understorey and 28% above canopy. A size mode at 2 μm<DP<4 μm appears at both sites and is primarily FBAP, which dominated the coarse (DP≥2.5 μm) number concentration at both sites, accounting for 75% in the understorey and 57% above the canopy. In contrast, the concentration of non-fluorescent particles (NNON) at both sites was typically 200–500 L−1, the majority of which occupied a size mode at 0.8<DP<1.5 μm. Enhanced understorey NNON was observed daily in mid-afternoon and also at midday on three occasions: the former coincided with the FBAP enhancements and measured approximately 10% of their magnitude; the latter occurred independently of the NFBAP diurnal cycle and comprised particles smaller than 2 μm. Particle diameter of 3–5 μm is consistent with smaller fungal spores, though absolute identification of biological species is not possible with the UV-LIF technique. Based on the measured FBAP and non-fluorescent particle abundances and their observed recovery times following rain showers, FBAP originated beneath the canopy while the non-fluorescent material was transported from further away. It is concluded that these separate sources contributed the majority of the aerosol measured by the WIBS-3 at both sites.Peer reviewe
Constraining FeLoBAL outflows from absorption line variability
FeLoBALs are a rare class of quasar outflows with low-ionization broad
absorption lines (BALs), large column densities, and potentially large kinetic
energies that might be important for `feedback' to galaxy evolution. In order
to probe the physical properties of these outflows, we conducted a
multiple-epoch, absorption line variability study of 12 FeLoBAL quasars
spanning a redshift range between 0.7 and 1.9 over rest frame time-scales of
approximately 10 d to 7.6 yr. We detect absorption line variability with
greater than 8 sigma confidence in 3 out of the 12 sources in our sample over
time-scales of 0.6 to 7.6 yr. Variable wavelength intervals are associated with
ground and excited state Fe II multiplets, the Mg II 2796, 2803 doublet, Mg I
2852, and excited state Ni II multiplets. The observed variability along with
evidence of saturation in the absorption lines favors transverse motions of gas
across the line of sight (LOS) as the preferred scenario, and allows us to
constrain the outflow distance from the supermassive black hole (SMBH) to be
less than 69, 7, and 60 pc for our three variable sources. In combination with
other studies, these results suggest that the outflowing gas in FeLoBAL quasars
resides on a range of scales and includes matter within tens of parsecs of the
central source.Comment: 21 pages, 6 figures, 2 supplementary figures (attached at the end of
the manuscript), accepted to Monthly Notices of the Royal Astronomical
Societ
A study of the effects of environmental and ablator performance uncertainties on heat shielding requirements for hyperbolic entry vehicles. Volume 2 - Summary of calculations
Calculated ablative quantities for nylon phenolic heat shielding materials of hyperbolic reentry vehicle
A prospective comparison of the AUSDRISK and HbA1c for persons with spinal cord injury
© 2016, Australian Nursing Federation. All rights reserved. Objective The primary object of this study was to determine the validity of the Australian Type 2 Diabetes Risk Assessment Tool (AUSDRISK) for predicting the development of type 2 diabetes in persons with spinal cord injury (SCI). Design and setting The prospective comparative study (December 2013-March 2014) collected data on AUSDRISK and haemoglobin A1c (HbA1c) in participants’ homes. Participants Participation rate was 67% (n=79). Study criteria: over 18 years of age, a SCI for more than 12 months, living at home, wheelchair dependant and no diabetes diagnosis. Main outcome measures AUSDRISK sensitivity and specificity in predicting incident type 2 diabetes in persons with SCI. Results Of the 79 participants, 81% were male, mean age was 53 years (SD 14.14) with 23.2years (median 23; SD +/- 13.2yrs) since injury. There was a positive correlation between length of time since SCI and risk score (AUSDRISK) (r =. 242, p =. 032). Participants with high AUSDRISK scores had higher HbA1c% (5.38 versus 5.2, p =. 026) level. The high risk classification explained a moderate amount of HbA1c % (area under curve =. 651; 95% CI. 53 -. 77). The level of HbA1c which had the highest sensitivity (.59) and specificity (.73) for risk classification was 5.25%. Waist circumference and physical activity items require further powered studies to determine if appropriately weighted. Conclusion Comparing the AUSDRISK with HbA1c assays, the AUSDRISK can predict type 2 diabetes risk in a person with SCI, although further powered studies are needed to be undertaken, to refine the predictive capacity of the tool
Low-field diffusion magneto-thermopower of a high mobility two-dimensional electron gas
The low magnetic field diffusion thermopower of a high mobility
GaAs-heterostructure has been measured directly on an electrostatically defined
micron-scale Hall-bar structure at low temperature (T = 1.6 K) in the low
magnetic field regime (B < 1.2 T) where delocalized quantum Hall states do not
influence the measurements. The sample design allowed the determination of the
field dependence of the thermopower both parallel and perpendicular to the
temperature gradient, denoted respectively by Sxx (longitudinal thermopower)
and Syx (Nernst-Ettinghausen coefficient). The experimental data show clear
oscillations in Sxx and Syx due to the formation of Landau levels for 0.3 T < B
< 1.2 T and reveal that Syx is approximately 120 times larger than Sxx at a
magnetic field of 1 T, which agrees well with the theoretical prediction.Comment: 4 pages, 4 figure
Reexamining Black-Body Shifts for Hydrogenlike Ions
We investigate black-body induced energy shifts for low-lying levels of
atomic systems, with a special emphasis on transitions used in current and
planned high-precision experiments on atomic hydrogen and ionized helium.
Fine-structure and Lamb-shift induced black-body shifts are found to increase
with the square of the nuclear charge number, whereas black-body shifts due to
virtual transitions decrease with increasing nuclear charge as the fourth power
of the nuclear charge. We also investigate the decay width acquired by the
ground state of atomic hydrogen, due to interaction with black-body photons.
The corresponding width is due to an instability against excitation to higher
excited atomic levels, and due to black-body induced ionization. These effects
limit the lifetime of even the most fundamental, a priori absolutely stable,
"asymptotic" state of atomic theory, namely the ground state of atomic
hydrogen.Comment: 11 pages; LaTe
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