323 research outputs found
Lasing on a narrow transition in a cold thermal strontium ensemble
Highly stable laser sources based on narrow atomic transitions provide a
promising platform for direct generation of stable and accurate optical
frequencies. Here we investigate a simple system operating in the
high-temperature regime of cold atoms. The interaction between a thermal
ensemble of Sr at mK temperatures and a medium-finesse cavity produces
strong collective coupling and facilitates high atomic coherence which causes
lasing on the dipole forbidden SP transition. We
experimentally and theoretically characterize the lasing threshold and
evolution of such a system, and investigate decoherence effects in an
unconfined ensemble. We model the system using a Tavis-Cummings model, and
characterize velocity-dependent dynamics of the atoms as well as the dependency
on the cavity-detuning.Comment: 9 pages, 7 figure
Non-linear Spectroscopy of Sr Atoms in an Optical Cavity for Laser Stabilization
We study the non-linear interaction of a cold sample of strontium-88 atoms
coupled to a single mode of a low finesse optical cavity in the so-called bad
cavity limit and investigate the implications for applications to laser
stabilization. The atoms are probed on the weak inter-combination line \lvert
5s^{2} \, ^1 \textrm{S}_0 \rangle \,-\, \lvert 5s5p \, ^3 \textrm{P}_1 \rangle
at 689 nm in a strongly saturated regime. Our measured observables include the
atomic induced phase shift and absorption of the light field transmitted
through the cavity represented by the complex cavity transmission coefficient.
We demonstrate high signal-to-noise-ratio measurements of both quadratures -
the cavity transmitted phase and absorption - by employing FM spectroscopy
(NICE-OHMS). We also show that when FM spectroscopy is employed in connection
with a cavity locked to the probe light, observables are substantially modified
compared to the free space situation where no cavity is present. Furthermore,
the non-linear dynamics of the phase dispersion slope is experimentally
investigated and the optimal conditions for laser stabilization are
established. Our experimental results are compared to state-of-the-art cavity
QED theoretical calculations.Comment: 7 pages, 4 figure
Comparison of RNAi efficiency mediated by tetracycline-responsive H1 and U6 promoter variants in mammalian cell lines
Conditional expression of short hairpin RNAs (shRNAs) to knock down target genes is a powerful tool to study gene function. The most common inducible expression systems are based on tetracycline-regulated RNA polymerase III promoters. During the last years, several tetracycline-inducible U6 and H1 promoter variants have been reported in different experimental settings showing variable efficiencies. In this study, we compare the most common variants of these promoters in several mammalian cell lines. For all cell lines tested, we find that several inducible U6 and H1 promoters containing single tetracycline operator (tetO) sequences show high-transcriptional background in the non-induced state. Promoter variants containing two tetO sequences show tight suppression of transcription in the non-induced state, and high tet responsiveness and high gene knockdown efficiency upon induction in all cell lines tested. We report a variant of the H1 promoter containing two O2-type tetO sequences flanking the TATA box that shows little transcriptional background in the non-induced state and up to 90% target knockdown when the inducer molecule (dox–doxycycline) is added. This inducible system for RNAi-based gene silencing is a good candidate for use both in basic research on gene function and for potential therapeutic applications
Spatially self-similar spherically symmetric perfect-fluid models
Einstein's field equations for spatially self-similar spherically symmetric
perfect-fluid models are investigated. The field equations are rewritten as a
first-order system of autonomous differential equations. Dimensionless
variables are chosen in such a way that the number of equations in the coupled
system is reduced as far as possible and so that the reduced phase space
becomes compact and regular. The system is subsequently analysed qualitatively
with the theory of dynamical systems.Comment: 21 pages, 6 eps-figure
Collective physician perspectives on non-oral medication approaches for the management of clinically relevant unresolved issues in Parkinson's disease: Consensus from an international survey and discussion program
Navigate PD was an educational program established to supplement existing guidelines and provide recommendations on the management of Parkinson's disease (PD) refractory to oral/transdermal therapies. It involved 103 experts from 13 countries overseen by an International Steering Committee (ISC) of 13 movement disorder specialists. The ISC identified 71 clinical questions important for device-aided management of PD. Fifty-six experts responded to a web-based survey, rating 15 questions as ‘critically important;’ these were refined to 10 questions by the ISC to be addressed through available evidence and expert opinion. Draft guidance was presented at international/national meetings and revised based on feedback. Key take-home points are:
• Patients requiring levodopa >5 times daily who have severe, troublesome ‘off’ periods (>1–2 h/day) despite optimal oral/transdermal levodopa or non-levodopa-based therapies should be referred for specialist assessment even if disease duration is <4 years.
• Cognitive decline related to non-motor fluctuations is an indication for device-aided therapies. If cognitive impairment is mild, use deep brain stimulation (DBS) with caution. For patients who have cognitive impairment or dementia, intrajejunal levodopa infusion is considered as both therapeutic and palliative in some countries. Falls are linked to cognitive decline and are likely to become more frequent with device-aided therapies.
• Insufficient control of motor complications (or drug-resistant tremor in the case of DBS) are indications for device-aided therapies. Levodopa-carbidopa intestinal gel infusions or subcutaneous apomorphine pump may be considered for patients aged >70 years who have mild or moderate cognitive impairment, severe depression or other contraindications to DBS
230 days of ultra long‐term subcutaneous EEG : seizure cycle analysis and comparison to patient diary
© 2020 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.We describe the longest period of subcutaneous EEG (sqEEG) monitoring to date, in a 35-year-old female with refractory epilepsy. Over 230 days, 4791/5520 h of sqEEG were recorded (86%, mean 20.8 [IQR 3.9] hours/day). Using an electronic diary, the patient reported 22 seizures, while automatically-assisted visual sqEEG review detected 32 seizures. There was substantial agreement between days of reported and recorded seizures (Cohen's kappa 0.664), although multiple clustered seizures remained undocumented. Circular statistics identified significant sqEEG seizure cycles at circadian (24-hour) and multidien (5-day) timescales. Electrographic seizure monitoring and analysis of long-term seizure cycles are possible with this neurophysiological tool.This work was supported by the Epilepsy Foundation’s Epilepsy Innovation Institute My Seizure Gauge Project. MPR is supported by the NIHR Biomedical Research Centre; the MRC Centre for Neurodevelopmental Disorders (MR/N026063/1); the EPSRC Centre for Predictive Modelling in Healthcare (EP/N014391/1); the RADAR‐CNS project (www.radar‐cns.org, grant agreement 115902).info:eu-repo/semantics/publishedVersio
Transport Spectroscopy of Symmetry-Broken Insulating States in Bilayer Graphene
The flat bands in bilayer graphene(BLG) are sensitive to electric fields
E\bot directed between the layers, and magnify the electron-electron
interaction effects, thus making BLG an attractive platform for new
two-dimensional (2D) electron physics[1-5]. Theories[6-16] have suggested the
possibility of a variety of interesting broken symmetry states, some
characterized by spontaneous mass gaps, when the electron-density is at the
carrier neutrality point (CNP). The theoretically proposed gaps[6,7,10] in
bilayer graphene are analogous[17,18] to the masses generated by broken
symmetries in particle physics and give rise to large momentum-space Berry
curvatures[8,19] accompanied by spontaneous quantum Hall effects[7-9]. Though
recent experiments[20-23] have provided convincing evidence of strong
electronic correlations near the CNP in BLG, the presence of gaps is difficult
to establish because of the lack of direct spectroscopic measurements. Here we
present transport measurements in ultra-clean double-gated BLG, using
source-drain bias as a spectroscopic tool to resolve a gap of ~2 meV at the
CNP. The gap can be closed by an electric field E\bot \sim13 mV/nm but
increases monotonically with a magnetic field B, with an apparent particle-hole
asymmetry above the gap, thus providing the first mapping of the ground states
in BLG.Comment: 4 figure
On the Evolutionary Status of Class I Stars and Herbig-Haro Energy Sources in Taurus-Auriga
[abridged] We present high resolution optical spectra of stars in
Taurus-Auriga whose circumstellar environment suggests that they are less
evolved than optically revealed T Tauri stars. Many of the stars are seen only
via scattered light. These spectra are used to search for differences between
stars which power Herbig-Haro flows and stars which do not, and to reassess the
evolutionary state of so-called protostars (Class I stars) relative to
optically revealed T Tauri stars (Class II stars). The stellar mass
distribution of Class I stars is similar to that of Class II stars and includes
3 Class I brown dwarfs. Class I stars in Taurus are slowly rotating; the
angular momentum of a young star appears to dissipate prior to the optically
revealed T Tauri phase. The mass accretion rates of Class I stars are
surprisingly indistinguishable from those of Class II stars; they do not have
accretion dominated luminosities. We confirm previous results that find larger
forbidden-line emission associated with Class I stars than Class II stars. We
suggest that this is caused by an orientation bias that allows a more direct
view of the somewhat extended forbidden emission line regions than the obscured
stellar photospheres, rather than because of larger mass outflow rates.
Overall, the similar masses, luminosities, rotation rates, mass accretion
rates, mass outflow rates, and millimeter flux densities of Class I and Class
II stars are best explained by a scenario in which most Class I stars are no
longer in the main accretion phase and are older than traditionally assumed.
Similarly, although stars which power Herbig-Haro flows appear to have larger
mass outflow rates, their stellar and circumstellar properties are generally
indistinguishable from those of stars that do not power these flows.Comment: 84 pages, including 21 figures; accepted for publication in Ap
Continuum Halos in Nearby Galaxies -- an EVLA Survey (CHANG-ES) -- I: Introduction to the Survey
We introduce a new survey to map the radio continuum halos of a sample of 35
edge-on spiral galaxies at 1.5 GHz and 6 GHz in all polarization products. The
survey is exploiting the new wide bandwidth capabilities of the Karl G. Jansky
Very Large Array (i.e. the Expanded Very Large Array, or EVLA) in a variety of
array configurations (B, C, and D) in order to compile the most comprehensive
data set yet obtained for the study of radio halo properties. This is the first
survey of radio halos to include all polarization products.
In this first paper, we outline the scientific motivation of the survey, the
specific science goals, and the expected improvements in noise levels and
spatial coverage from the survey. Our goals include investigating the physical
conditions and origin of halos, characterizing cosmic ray transport and wind
speed, measuring Faraday rotation and mapping the magnetic field, probing the
in-disk and extraplanar far-infrared - radio continuum relation, and
reconciling non-thermal radio emission with high-energy gamma-ray models. The
sample size allows us to search for correlations between radio halos and other
properties, including environment, star formation rate, and the presence of
AGNs. In a companion paper (Paper II) we outline the data reduction steps and
present the first results of the survey for the galaxy, NGC 4631.Comment: 17 pages, 1 figure, accepted to the Astronomical Journal, Version 2
changes: added acknowledgement to NRA
High-quality factor, high-confinement microring resonators in 4H-silicon carbide-on-insulator
- …