378 research outputs found
More on the Narrowing of Impact Broadened Radio Recombination Lines at High Principal Quantum Number
Recently Alexander and Gulyaev have suggested that the apparent decrease in
impact broadening of radio recombination lines seen at high principal quantum
number n may be a product of the data reduction process, possibly resulting
from the presence of noise on the telescope spectra that is not present on the
calculated comparison spectra. This is an interesting proposal. However, there
are serious problems with their analysis that need to be pointed out. Perhaps
the most important of these is the fact that for principal quantum numbers
below n = 200, where the widths are not in question, their processed generated
profile widths do not fit the widths of the processed lines obtained at the
telescope. After processing, the halfwidths of the generated and telescope
profiles must agree below n = 200 if we are to believe that the processed
generated linewidths above n = 200 are meaningful. Theirs do not. Furthermore,
we find that after applying the linewidth reduction factors found by Alexander
and Gulyaev for their noise added profiles to our generated profiles to
simulate their noise adding effect, the processed widths we obtain still do not
come close to explaining the narrowing seen in the telescope lines for n values
in the range 200 < n < 250. It is concluded that what is needed to solve this
mystery is a completely new approach using a different observing technique
instead of simply a further manipulation of the frequency-switched data.Comment: Six pages with 4 figures. Accepted for publication in Astrophysics
and Space Scienc
Optical immersion of mid-infrared LEDs and photodiodes for gas-sensing applications
The high gains in performance predicted for optical immersion are difficult to achieve in practice due to total internal reflection at the lens/detector interface. By reducing the air gap at this interface optical tunneling becomes possible and the predicted gains can be realized in practical devices. Using this technique we have demonstrated large performance gains by optically immersing mid-infrared heterostructure InA1Sb LEDs and photodiodes using hypershperical germanium lenses. The development of an effective method of optical immersion that gives excellent optical coupling has produced a photodiode with a peak room temperature detectivity (D*) of 5.3 x 109 cmHz½W-1 at λpeak=5.4μm and a 40° field of view. A hyperspherically immersed LED showed a f-fold improvement in the external efficiency, and a 3-fold improvement in the directionality compared with a conventional planar LED for f/2 optical systems. The incorporation of these uncooled devices in a White cell produced a NO2 gas sensing system with 2 part-per-million sensitivity, with an LED drive current of <5mA. These results represent a significant advance in the use of solid state devices for portable gas sensing systems
The Caledonian face test: A new test of face discrimination
yesThis study aimed to develop a clinical test of face perception which is applicable to a wide range of patients and can capture normal variability. The Caledonian face test utilises synthetic faces which combine simplicity with sufficient realism to permit individual identification. Face discrimination thresholds (i.e. minimum difference between faces required for accurate discrimination) were determined in an "odd-one-out" task. The difference between faces was controlled by an adaptive QUEST procedure. A broad range of face discrimination sensitivity was determined from a group (N=52) of young adults (mean 5.75%; SD 1.18; range 3.33-8.84%). The test is fast (3-4min), repeatable (test-re-test r2=0.795) and demonstrates a significant inversion effect. The potential to identify impairments of face discrimination was evaluated by testing LM who reported a lifelong difficulty with face perception. While LM's impairment for two established face tests was close to the criterion for significance (Z-scores of -2.20 and -2.27) for the Caledonian face test, her Z-score was -7.26, implying a more than threefold higher sensitivity. The new face test provides a quantifiable and repeatable assessment of face discrimination ability. The enhanced sensitivity suggests that the Caledonian face test may be capable of detecting more subtle impairments of face perception than available tests.Non
Sensitive Observations of Radio Recombination Lines in Orion and W51: The Data and Detection of Systematic Recombination Line Blueshifts Proportional to Impact Broadening
Sensitive spectral observations made in two frequency bands near 6.0 and 17.6
GHz are described for Orion and W51. Using frequency switching we were able to
achieve a dynamic range in excess of 10,000 without fitting sinusoidal or
polynomial baselines. This enabled us to detect lines as weak as T\Delta n$ as
high as 25 have been detected in Orion. In the Orion data, where the lines are
stronger, we have also detected a systematic shift in the line center
frequencies proportional to linewidth that cannot be explained by normal
optical depth effects.Comment: 22 pages, 13 figures. Accepted for publication in Astrophysics and
Space Scienc
Kondo Effect of Quantum Dots in the Quantum Hall Regime
Quantum dots in the quantum Hall regime can have pairs of single Slater
determinant states that are degenerate in energy. We argue that these pairs of
many body states may give rise to a Kondo effect which can be mapped into an
ordinary Kondo effect in a fictitious magnetic field. We report on several
properties of this Kondo effect using scaling and numerical renormalization
group analysis. We suggest an experiment to investigate this Kondo effect.Comment: To appear in Phys. Rev. B (5 pages, 4 figures); references added;
several changes in tex
Resistance training enhances delayed memory in healthy middle-aged and older adults: A randomised controlled trial
Objectives
High-intensity exercise is a potential therapeutic tool to postpone or prevent the onset of cognitive decline. However, there is a lack of sufficient evidence regarding the longitudinal effects of structured resistance training on cognitive function in healthy adults. The purpose of this study was to investigate the effect of two ecologically valid, intense 12-week resistance training programs on cognitive function in late middle-aged adults.
Design
Single-site parallel randomised controlled trial at the Department of Exercise Science strength and conditioning laboratory. Groups allocated by minimisation randomisation.
Methods
Forty-five healthy adults (age range = 41-69 years) were enrolled and randomised into A.) high-load, long rest resistance training (n = 14), or B.) moderate-load, short rest resistance training (n = 15) twice per week for 12 weeks, or a non-exercising control (n = 16). Follow-up within 7 days. Data were collected September 2016-December 2017. Cognitive function assessed using the CogState computerised battery. Assessors were blinded to participant group allocation. Secondary outcomes were maximal muscle strength and body composition.
Results
Forty-four participants were analysed in 2018. Delayed verbal memory performance was improved (p = 0.02) in resistance training groups (g = 0.67-0.79) when compared to the control group, with no differences between training groups. Likewise, increases in maximal muscle strength were observed (p < 0.01) in resistance training groups when compared to the control group, with no differences between training groups. No differences in body composition were observed. There were no adverse events or side-effects of the intervention.
Conclusions
12 weeks of intense resistance training improves delayed verbal memory irrespective of training design (i.e., high-load vs. moderate-load)
Magnetotransport through a strongly interacting quantum dot
We study the effect of a magnetic field on the conductance through a strongly
interacting quantum dot by using the finite temperature extension of Wilson's
numerical renormalization group method to dynamical quantities. The quantum dot
has one active level for transport and is modelled by an Anderson impurity
attached to left and right electron reservoirs. Detailed predictions are made
for the linear conductance and the spin-resolved conductance as a function of
gate voltage, temperature and magnetic field strength. A strongly coupled
quantum dot in a magnetic field acts as a spin filter which can be tuned by
varying the gate voltage. The largest spin-filtering effect is found in the
range of gate voltages corresponding to the mixed valence regime of the
Anderson impurity model.Comment: Revised version, to appear in PRB, 4 pages, 4 figure
A randomized controlled trial of high-intensity exercise and executive functioning in cognitively normal older adults
Background
There is a paucity of interventional research that systematically assesses the role of exercise intensity and cardiorespiratory fitness, and their relationship with executive function in older adults. To address this limitation, we have examined the effect of a systematically manipulated exercise intervention on executive function.
Methods
Ninety-nine cognitively normal participants (age = 69.10 ± 5.2 years; n = 54 female) were randomized into either a high-intensity cycle-based exercise, moderate-intensity cycle-based exercise, or no-intervention control group. All participants underwent neuropsychological testing and fitness assessment at baseline (preintervention), 6-month follow-up (postintervention), and 12-month postintervention. Executive function was measured comprehensively, including measures of each subdomain: Shifting, Updating/ Working Memory, Inhibition, Verbal Generativity, and Nonverbal Reasoning. Cardiorespiratory fitness was measured by analysis of peak aerobic capacity; VO2peak.
Results
First, the exercise intervention was found to increase cardiorespiratory fitness (VO2peak) in the intervention groups, in comparison to the control group (F =10.40, p≤0.01). However, the authors failed to find mean differences in executive function scores between the high-intensity, moderate intensity, or inactive control group. On the basis of change scores, cardiorespiratory fitness was found to associate positively with the executive function (EF) subdomains of Updating/Working Memory (β = 0.37, p = 0.01, r = 0.34) and Verbal Generativity (β = 0.30, p = 0.03, r = 0.28) for intervention, but not control participants.
Conclusion
At the aggregate level, the authors failed to find evidence that 6-months of high-intensity aerobic exercise improves EF in older adults. However, it remains possible that individual differences in experimentally induced changes in cardiorespiratory fitness may be associated with changes in Updating/ Working Memory and Verbal Generativity
Haplotyping the human leukocyte antigen system from single chromosomes
We describe a method for determining the parental HLA haplotypes of a single individual without recourse to conventional segregation genetics. Blood samples were cultured to identify and sort chromosome 6 by bivariate flow cytometry. Single chromosome 6 amplification products were confirmed with a single nucleotide polymorphism (SNP) array and verified by deep sequencing to enable assignment of both alleles at the HLA loci, defining the two haplotypes. This study exemplifies a rapid and efficient method of haplotyping that can be applied to any chromosome pair, or indeed all chromosome pairs, using a single sorting operation. The method represents a cost-effective approach to complete phasing of SNPs, which will facilitate a deeper understanding of the links between SNPs, gene regulation and protein function
Quantum trajectory approach to stochastically-induced quantum interference effects in coherently-driven two-level atoms
Stochastic perturbation of two-level atoms strongly driven by a coherent
light field is analyzed by the quantum trajectory method. A new method is
developed for calculating the resonance fluorescence spectra from numerical
simulations. It is shown that in the case of dominant incoherent perturbation,
the stochastic noise can unexpectedly create phase correlation between the
neighboring atomic dressed states. This phase correlation is responsible for
quantum interference between the related transitions resulting in anomalous
modifications of the resonance fluorescence spectra.Comment: paper accepted for publicatio
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