831 research outputs found
Observation of Motion Dependent Nonlinear Dispersion with Narrow Linewidth Atoms in an Optical Cavity
As an alternative to state-of-the-art laser frequency stabilisation using
ultra-stable cavities, it has been proposed to exploit the non-linear effects
from coupling of atoms with a narrow transition to an optical cavity. Here we
have constructed such a system and observed non-linear phase shifts of a narrow
optical line by strong coupling of a sample of strontium-88 atoms to an optical
cavity. The sample temperature of a few mK provides a domain where the Doppler
energy scale is several orders of magnitude larger than the narrow linewidth of
the optical transition. This makes the system sensitive to velocity dependent
multi-photon scattering events (Dopplerons) that affect the cavity field
transmission and phase. By varying the number of atoms and the intra-cavity
power we systematically study this non-linear phase signature which displays
roughly the same features as for much lower temperature samples. This
demonstration in a relatively simple system opens new possibilities for
alternative routes to laser stabilization at the sub 100 mHz level and
superradiant laser sources involving narrow line atoms. The understanding of
relevant motional effects obtained here has direct implications for other
atomic clocks when used in relation with ultranarrow clock transitions.Comment: 9 pages (including 4 pages of Supplemental Information), 6 figures.
Updated to correspond to the published versio
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
Parity, age at first childbirth and the prognosis of primary breast cancer.
Reproductive factors are known to be aetiologically important in breast cancer, but less is known regarding their effect on breast cancer prognosis. We have investigated the prognostic effect of age at first birth and total parity using data from the Danish Breast Cancer Cooperative Group that, since 1977, has collected population-based information on tumour characteristics, treatment regimes and follow-up status on Danish women with breast cancer. Details of pregnancy history were added from the Danish Civil Registration System and the National Birth Registry. Included in the study were 10,703 women with primary breast cancer. After adjusting for age and stage of disease (tumour size, axillary nodal status and histological grading), the number of full-term pregnancies was found without prognostic value. However, women with primary childbirth between 20 and 29 years experienced a significantly reduced risk of death compared with women with primary childbirth below the age of 20 years [20-24 years: relative risk (RR) = 0.88, 95% confidence interval (CI) 0.78-0.99; 25-29 years: RR = 0.80, 95% CI 0.70-0.91]. Further adjustment for oestrogen receptor status did not influence these results. The effect was not modified by age at diagnosis, tumour size or nodal status. In conclusion, low age at first childbirth, but not parity, was associated with a poor prognosis of breast cancer. We speculate whether women who develop breast cancer despite an early first full-term pregnancy might represent a selected group with a more malignant disease
Towards Multi-Modality Therapy for Marfan Syndrome: Synergistic Effect of Angiotensin and TRPC4 Receptor Blockade on Ascending Aortic Aneurysms
Background:
Marfan syndrome (MFS) is a genetic disease that commonly presents with aortopathy. While promising therapies have been studied, complete attenuation of MFS-induced aortic aneurysms in the clinical arena has been elusive. The presence of significant, not-yet described MFS signaling pathways has been suggested as a reason for the less than ideal clinical response to single drug therapy. Transient receptor potential (TRP) channels have emerged as likely regulators of vascular smooth muscle cell (VSMC) activity. In this regard, they are abundantly found in VSMCs and are associated with increased matrix metalloproteinase 9 activity. The current study seeks to explore the role of TRP channels in MFS.
Methods:
A Fbn1C1039G/+ heterozygous mouse, with a mutation in fibrillin-1, was supplemented with angiotensin II (4.5 mg/kg/day) to accelerate aneurysmal formation. Mice analyzed were wild type (wt) (saline +/- angiotensin II) and heterozygous (saline +/- angiotensin II). Quantitative PCR and western blotting was used to examine differential expression of TRP channels across the various cohorts. The TRPC4 antagonist, ML204 (10mg/kg/day), was given daily during two weeks of angiotensin II infusion. Mice were echoed before and after to assess aortic diameter.
Results:
Quantitative PCR of the accelerated model revealed a near 10-fold increase in TRPC4 transcription with respect to wt mice. ML204 and losartan worked synergistically to ameliorate aortic dilation.
Conclusions:
These studies suggest a complementary role for TRPC4 in MFS-induced aortic pathology. Antagonism of this novel target shows promise toward multi-drug therapy for the treatment of aortic aneurysms in MFS
Calibration of the NuSTAR High Energy Focusing X-ray Telescope
We present the calibration of the \textit{Nuclear Spectroscopic Telescope
Array} (\nustar) X-ray satellite. We used the Crab as the primary effective
area calibrator and constructed a piece-wise linear spline function to modify
the vignetting response. The achieved residuals for all off-axis angles and
energies, compared to the assumed spectrum, are typically better than \%
up to 40\,keV and 5--10\,\% above due to limited counting statistics. An
empirical adjustment to the theoretical 2D point spread function (PSF) was
found using several strong point sources, and no increase of the PSF half power
diameter (HPD) has been observed since the beginning of the mission. We report
on the detector gain calibration, good to 60\,eV for all grades, and discuss
the timing capabilities of the observatory, which has an absolute timing of
3\,ms. Finally we present cross-calibration results from two campaigns
between all the major concurrent X-ray observatories (\textit{Chandra},
\textit{Swift}, \textit{Suzaku} and \textit{XMM-Newton}), conducted in 2012 and
2013 on the sources 3C\,273 and PKS\,2155-304, and show that the differences in
measured flux is within 10\% for all instruments with respect to \nustar
Anti-Nirvana: crime, culture and instrumentalism in the age of insecurity
‘Anti-Nirvana’ explores the relationship between consumer culture, media and criminal motivations. It has appeared consistently on the list of the top-ten most-read articles in this award-winning international journal, and it mounts a serious neo-Freudian challenge to the predominant naturalistic notion of ‘resistance’ at the heart of liberal criminology and media studies. It is also cited in the Oxford Handbook of Criminology and other criminology texts as a persuasive argument in support of the theory that criminality amongst young people is strongly linked to the acquisitive values of consumerism and the images of possessive individualism that dominate mass media
Making optical atomic clocks more stable with level laser stabilization
The superb precision of an atomic clock is derived from its stability. Atomic
clocks based on optical (rather than microwave) frequencies are attractive
because of their potential for high stability, which scales with operational
frequency. Nevertheless, optical clocks have not yet realized this vast
potential, due in large part to limitations of the laser used to excite the
atomic resonance. To address this problem, we demonstrate a cavity-stabilized
laser system with a reduced thermal noise floor, exhibiting a fractional
frequency instability of . We use this laser as a stable
optical source in a Yb optical lattice clock to resolve an ultranarrow 1 Hz
transition linewidth. With the stable laser source and the signal to noise
ratio (S/N) afforded by the Yb optical clock, we dramatically reduce key
stability limitations of the clock, and make measurements consistent with a
clock instability of
A NuSTAR observation of the center of the Coma Cluster
We present the results of a 55ks NuSTAR observation of the core of the Coma
Cluster. The global spectrum can be explained by thermal gas emission, with a
conservative 90% upper limit to non-thermal inverse Compton (IC) emission of
erg cm s in a 12 arcmin 12 arcmin
field of view . The brightness of the thermal component in this central region
does not allow more stringent upper limits on the IC component when compared
with non-imaging instruments with much larger fields of view where claims of
detections have been made. Future mosaic NuSTAR observations of Coma will
further address this issue. The temperature map shows a relatively uniform
temperature distribution with a gradient from the hot northwest side to the
cooler southeast, in agreement with previous measurements. The temperature
determination is robust given the flat effective area and low background in the
3-20 keV band, making NuSTAR an ideal instrument to measure high temperatures
in the intracluster medium.Comment: 8 pages, 7 figures, accepted for publication in ApJ. Minor changes to
match published versio
NuSTAR Hard X-ray Survey of the Galactic Center Region I: Hard X-ray Morphology and Spectroscopy of the Diffuse Emission
We present the first sub-arcminute images of the Galactic Center above 10
keV, obtained with NuSTAR. NuSTAR resolves the hard X-ray source IGR
J17456-2901 into non-thermal X-ray filaments, molecular clouds, point sources
and a previously unknown central component of hard X-ray emission (CHXE).
NuSTAR detects four non-thermal X-ray filaments, extending the detection of
their power-law spectra with - up to ~50 keV. A
morphological and spectral study of the filaments suggests that their origin
may be heterogeneous, where previous studies suggested a common origin in young
pulsar wind nebulae (PWNe). NuSTAR detects non-thermal X-ray continuum emission
spatially correlated with the 6.4 keV Fe K fluorescence line emission
associated with two Sgr A molecular clouds: MC1 and the Bridge. Broad-band
X-ray spectral analysis with a Monte-Carlo based X-ray reflection model
self-consistently determined their intrinsic column density (
cm), primary X-ray spectra (power-laws with ) and set a
lower limit of the X-ray luminosity of Sgr A* flare illuminating the Sgr A
clouds to erg s. Above ~20 keV, hard
X-ray emission in the central 10 pc region around Sgr A* consists of the
candidate PWN G359.95-0.04 and the CHXE, possibly resulting from an unresolved
population of massive CVs with white dwarf masses . Spectral energy distribution analysis suggests that G359.95-0.04 is
likely the hard X-ray counterpart of the ultra-high gamma-ray source HESS
J1745-290, strongly favoring a leptonic origin of the GC TeV emission.Comment: 27 pages. Accepted for publication in the Astrophysical Journa
Using Neural Networks for Relation Extraction from Biomedical Literature
Using different sources of information to support automated extracting of
relations between biomedical concepts contributes to the development of our
understanding of biological systems. The primary comprehensive source of these
relations is biomedical literature. Several relation extraction approaches have
been proposed to identify relations between concepts in biomedical literature,
namely, using neural networks algorithms. The use of multichannel architectures
composed of multiple data representations, as in deep neural networks, is
leading to state-of-the-art results. The right combination of data
representations can eventually lead us to even higher evaluation scores in
relation extraction tasks. Thus, biomedical ontologies play a fundamental role
by providing semantic and ancestry information about an entity. The
incorporation of biomedical ontologies has already been proved to enhance
previous state-of-the-art results.Comment: Artificial Neural Networks book (Springer) - Chapter 1
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