2,061 research outputs found
Sub-MHz Linewidth at 240 GHz from an Injection-Locked Free-Electron Laser
Radiation from an ultra-stable 240 GHz solid-state source has been injected,
through an isolator, into the cavity of the University of California Santa
Barbara (UCSB) MM-wave free-electron laser (FEL). High-power FEL emission,
normally distributed among many of the cavity's longitudinal modes, is
concentrated into the single mode to which the solid state source has been
tuned. The linewidth of the FEL emission is 0.5 MHz, consistent with the
Fourier transform limit for the 2 microsecond pulses. This demonstration of
frequency-stable, ultra-narrow-band FEL emission is a critical milestone on the
road to FEL-based pulsed electron paramagnetic resonance spectroscopy.Comment: 3 pages including 3 figure
Modelling the relative contribution of seed nitrogen reserves and external nitrogen uptake during heterotrophic growth in Medicago truncatula
Background and aims Heterotrophic growth relies on remobilisation of seed reserves and mineral absorption. We used a compartmental model to investigate the fluxes of N absorption and remobilisation of N reserves in a legume seed with high protein content. Methods Seedling growth was studied during the heterotrophic stage in two genotypes of Medicago truncatula as a function of N supply. N absorption and seed remobilisation fluxes were distinguished in a 15 N labelling experiment. Results Remobilisation of seed N reserves was high during germination, but N uptake started as soon as the radicle protruded. Both sources contributed to high elongation rates of the radicle and hypocotyl. When organ lengths stabilised, there was an efflux of N from the cotyledons and roots indicating that seedling growth was limited by carbohydrate production. No significant differences between genotypes were observed except for early N uptake, which was lower in the genotype with the highest initial seed N content. Conclusions N fluxes were similar to those of other non-legume dicotyledonous species but differed from monocotyledonous species. These results improve our understanding of the effects of mineral fertilisation on crop establishment. The compartmental model is a useful tool to analyse N fluxes patterns within and between diverse species, in relation to seed characteristics and soil N availability
Physiological serum 25-hydroxyvitamin D concentrations are associated with improved thyroid function—observations from a community-based program
Purpose: Vitamin D deficiency has been associated with an increased risk of hypothyroidism and autoimmune thyroid disease. Our aim was to investigate the influence of vitamin D supplementation on thyroid function and anti-thyroid antibody levels. Methods: We constructed a database that included 11,017 participants in a health and wellness program that provided vitamin D supplementation to target physiological serum 25-hydroxyvitmain D [25(OH)D] concentrations (>100 nmol/L). Participant measures were compared between entry to the program (baseline) and follow-up (12 ± 3 months later) using an intent-to-treat analysis. Further, a nested case-control design was utilized to examine differences in thyroid function over 1 year in hypothyroid individuals and euthyroid controls. Results: More than 72% of participants achieved serum 25(OH)D concentrations >100 nmol/L at follow-up, with 20% above 125 nmol/L. Hypothyroidism was detected in 2% (23% including subclinical hypothyroidism) of participants at baseline and 0.4% (or 6% with subclinical) at follow-up. Serum 25(OH)D concentrations ≥125 nmol/L were associated with a 30% reduced risk of hypothyroidism and a 32% reduced risk of elevated anti-thyroid antibodies. Hypothyroid cases were found to have higher mean serum 25(OH)D concentrations at follow-up, which was a significant positive predictor of improved thyroid function. Conclusion: The results of the current study suggest that optimal thyroid function might require serum 25(OH)D concentrations above 125 nmol/L. Vitamin D supplementation may offer a safe and economical approach to improve thyroid function and may provide protection from developing thyroid disease
ESR Study of (C_5H_{12}N)_2CuBr_4
ESR studies at 9.27, 95.4, and 289.7 GHz have been performed on
(CHN)CuBr down to 3.7 K. The 9.27 GHz data were acquired
with a single crystal and do not indicate the presence of any structural
transitions. The high frequency data were collected with a polycrystalline
sample and resolved two absorbances, consistent with two crystallographic
orientations of the magnetic sites and with earlier ESR studies performed at
300 K. Below T, our data confirm the presence of a spin singlet
ground state.Comment: 2 pages, 4 figs., submitted 23rd International Conference on Low
Temperature Physics (LT-23), Aug. 200
Finite-size and correlation-induced effects in Mean-field Dynamics
The brain's activity is characterized by the interaction of a very large
number of neurons that are strongly affected by noise. However, signals often
arise at macroscopic scales integrating the effect of many neurons into a
reliable pattern of activity. In order to study such large neuronal assemblies,
one is often led to derive mean-field limits summarizing the effect of the
interaction of a large number of neurons into an effective signal. Classical
mean-field approaches consider the evolution of a deterministic variable, the
mean activity, thus neglecting the stochastic nature of neural behavior. In
this article, we build upon two recent approaches that include correlations and
higher order moments in mean-field equations, and study how these stochastic
effects influence the solutions of the mean-field equations, both in the limit
of an infinite number of neurons and for large yet finite networks. We
introduce a new model, the infinite model, which arises from both equations by
a rescaling of the variables and, which is invertible for finite-size networks,
and hence, provides equivalent equations to those previously derived models.
The study of this model allows us to understand qualitative behavior of such
large-scale networks. We show that, though the solutions of the deterministic
mean-field equation constitute uncorrelated solutions of the new mean-field
equations, the stability properties of limit cycles are modified by the
presence of correlations, and additional non-trivial behaviors including
periodic orbits appear when there were none in the mean field. The origin of
all these behaviors is then explored in finite-size networks where interesting
mesoscopic scale effects appear. This study leads us to show that the
infinite-size system appears as a singular limit of the network equations, and
for any finite network, the system will differ from the infinite system
Comparison between audio and tactile systems for delivering simple navigational information to visually impaired pedestrians
Many of the current GPS (Global Positioning Systems) navigation aids use an audio method to deliver navigation information to the user. For the visually impaired person this method can be problematic. The visually impaired pedestrian relies heavily on information contained within the ambient sound environment; for location and orientation information, navigation information, and importantly, safety information. In this paper we present the design of an innovative tactile interface and verification of results obtained through experimental trials. This pilot study compared the efficiency of the tactile interface, to an audio method of delivering simple navigational information. The findings indicate that the tactile interface could be used successfully by blind and sighted pedestrians and may offer advantages over auditory interfaces
Preparing multi-partite entanglement of photons and matter qubits
We show how to make event-ready multi-partite entanglement between qubits
which may be encoded on photons or matter systems. Entangled states of matter
systems, which can also act as single photon sources, can be generated using
the entangling operation presented in quant-ph/0408040. We show how to entangle
such sources with photon qubits, which may be encoded in the dual rail,
polarization or time-bin degrees of freedom. We subsequently demonstrate how
projective measurements of the matter qubits can be used to create entangled
states of the photons alone. The state of the matter qubits is inherited by the
generated photons. Since the entangling operation can be used to generate
cluster states of matter qubits for quantum computing, our procedure enables us
to create any (entangled) photonic quantum state that can be written as the
outcome of a quantum computer.Comment: 10 pages, 4 figures; to appear in Journal of Optics
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