73 research outputs found
Resonantly enhanced filamentation in gases
In this Letter, a low-loss Kerr-driven optical filament in Krypton gas is
experimentally reported in the ultraviolet. The experimental findings are
supported by ab initio quantum calculations describing the atomic optical
response. Higher-order Kerr effect induced by three-photon resonant transitions
is identified as the underlying physical mechanism responsible for the
intensity stabilization during the filamentation process, while ionization
plays only a minor role. This result goes beyond the commonly-admitted paradigm
of filamentation, in which ionization is a necessary condition of the filament
intensity clamping. At resonance, it is also experimentally demonstrated that
the filament length is greatly extended because of a strong decrease of the
optical losses
Probing photo-ionization: simulations of positive streamers in varying N2:O2 mixtures
Photo-ionization is the accepted mechanism for the propagation of positive
streamers in air though the parameters are not very well known; the efficiency
of this mechanism largely depends on the presence of both nitrogen and oxygen.
But experiments show that streamer propagation is amazingly robust against
changes of the gas composition; even for pure nitrogen with impurity levels
below 1 ppm streamers propagate essentially with the same velocity as in air,
but their minimal diameter is smaller, and they branch more frequently.
Additionally, they move more in a zigzag fashion and sometimes exhibit a
feathery structure. In our simulations, we test the relative importance of
photo-ionization and of the background ionization from pulsed repetitive
discharges, in air as well as in nitrogen with 1 ppm O2 . We also test
reasonable parameter changes of the photo-ionization model. We find that photo-
ionization dominates streamer propagation in air for repetition frequencies of
at least 1 kHz, while in nitrogen with 1 ppm O2 the effect of the repetition
frequency has to be included above 1 Hz. Finally, we explain the feather-like
structures around streamer channels that are observed in experiments in
nitrogen with high purity, but not in air.Comment: 12 figure
Investigation of Linum flavum (L.) Hairy Root Cultures for the Production of Anticancer Aryltetralin Lignans.
Collaboration with:
Université d’Orléans, 28000 Chartres, France,
Université de Picardie Jules Verne, F-80037 Amiens, France
De Montfort University
Open access articleLinum flavum hairy root lines were established from hypocotyl pieces using Agrobacterium rhizogenes strains LBA 9402 and ATCC 15834. Both strains were effective for transformation but induction of hairy root phenotype was more stable with strain ATCC 15834. Whereas similar accumulation patterns were observed in podophyllotoxin-related compounds (6-methoxy-podophyllotoxin, podophyllotoxin and deoxypodophyllotoxin), significant quantitative variations were noted between root lines. The influence of culture medium and various treatments (hormone, elicitation and precursor feeding) were evaluated. The highest accumulation was obtained in Gamborg B5 medium. Treatment with methyl jasmonate, and feeding using ferulic acid increased the accumulation of aryltetralin lignans. These results point to the use of hairy root culture lines of Linum flavum as potential sources for these valuable metabolites as an alternative, or as a complement to Podophyllum collected from wild stands
Phenolic and furanic compounds of Portuguese chestnut and French, American and Portuguese oak wood chips
Botanical species used on aging process must
be wisely and judiciously chosen, and for this selection, a
basic knowledge of the chemical composition of woods is
warranted. Aiming to contribute to extend the knowledge
of the chemical composition of several wood species useful
for enological purposes, we have focused our studies on
Portuguese chestnut and French, American and Portuguese
oak chips. The profile of low molecular weight phenolic
composition of these chips was achieved, using an optimized
extraction method based on pressurized liquid
extraction, followed by the quantification of phenolic acids,
phenolic aldehydes and furanic derivatives by high-performance
liquid chromatography (HPLC-DAD). The
identification of those compounds was also confirmed by
LC-DAD/ESI-MS. This study allowed the determination of
the low molecular phenolic composition of Portuguese
chestnut and French, American and Portuguese oak wood.
According to our results, the influence of the botanical
species seems to be more relevant than the geographic
origin of the wood species
A measurement of the CMB temperature power spectrum and constraints on cosmology from the SPT-3G 2018 TT/TE/EE Data Set
We present a sample-variance-limited measurement of the temperature power spectrum () of the cosmic microwave background (CMB) using observations of a field made by SPT-3G in 2018. We report multifrequency power spectrum measurements at 95, 150, and 220GHz covering the angular multipole range . We combine this measurement with the published polarization power spectrum measurements from the 2018 observing season and update their associated covariance matrix to complete the SPT-3G 2018 data set. This is the first analysis to present cosmological constraints from SPT , , and power spectrum measurements jointly. We blind the cosmological results and subject the data set to a series of consistency tests at the power spectrum and parameter level. We find excellent agreement between frequencies and spectrum types and our results are robust to the modeling of astrophysical foregrounds. We report results for CDM and a series of extensions, drawing on the following parameters: the amplitude of the gravitational lensing effect on primary power spectra , the effective number of neutrino species , the primordial helium abundance , and the baryon clumping factor due to primordial magnetic fields . We find that the SPT-3G 2018 data are well fit by CDM with a probability-to-exceed of . For CDM, we constrain the expansion rate today to and the combined structure growth parameter to . The SPT-based results are effectively independent of Planck, and the cosmological parameter constraints from either data set are within of each other. (abridged)..
Flaring Stars in a Non-targeted mm-wave Survey with SPT-3G
We present a flare star catalog from four years of non-targeted
millimeter-wave survey data from the South Pole Telescope (SPT). The data were
taken with the SPT-3G camera and cover a 1500-square-degree region of the sky
from to in right ascension and
to in declination. This region was observed on a
nearly daily cadence from 2019-2022 and chosen to avoid the plane of the
galaxy. A short-duration transient search of this survey yields 111 flaring
events from 66 stars, increasing the number of both flaring events and detected
flare stars by an order of magnitude from the previous SPT-3G data release. We
provide cross-matching to Gaia DR3, as well as matches to X-ray point sources
found in the second ROSAT all-sky survey. We have detected flaring stars across
the main sequence, from early-type A stars to M dwarfs, as well as a large
population of evolved stars. These stars are mostly nearby, spanning 10 to 1000
parsecs in distance. Most of the flare spectral indices are constant or gently
rising as a function of frequency at 95/150/220 GHz. The timescale of these
events can range from minutes to hours, and the peak luminosities
range from to erg s in the SPT-3G frequency bands
A Measurement of Gravitational Lensing of the Cosmic Microwave Background Using SPT-3G 2018 Data
We present a measurement of gravitational lensing over 1500 deg of the
Southern sky using SPT-3G temperature data at 95 and 150 GHz taken in 2018. The
lensing amplitude relative to a fiducial Planck 2018 CDM cosmology is
found to be , excluding instrumental and astrophysical
systematic uncertainties. We conduct extensive systematic and null tests to
check the robustness of the lensing measurements, and report a minimum-variance
combined lensing power spectrum over angular multipoles of , which
we use to constrain cosmological models. When analyzed alone and jointly with
primary cosmic microwave background (CMB) spectra within the CDM
model, our lensing amplitude measurements are consistent with measurements from
SPT-SZ, SPTpol, ACT, and Planck. Incorporating loose priors on the baryon
density and other parameters including uncertainties on a foreground bias
template, we obtain a constraint on using the SPT-3G 2018 lensing data alone, where
is a common measure of the amplitude of structure today and
is the matter density parameter. Combining SPT-3G 2018 lensing
measurements with baryon acoustic oscillation (BAO) data, we derive parameter
constraints of , , and Hubble constant
km s Mpc. Using CMB anisotropy and lensing measurements from
SPT-3G only, we provide independent constraints on the spatial curvature of
(95% C.L.) and the dark energy density
of (68% C.L.). When combining SPT-3G
lensing data with SPT-3G CMB anisotropy and BAO data, we find an upper limit on
the sum of the neutrino masses of eV (95% C.L.)
A Measurement of the CMB Temperature Power Spectrum and Constraints on Cosmology from the SPT-3G 2018 TT/TE/EE Data Set
We present a sample-variance-limited measurement of the temperature power
spectrum () of the cosmic microwave background (CMB) using observations of
a field made by SPT-3G in 2018. We report
multifrequency power spectrum measurements at 95, 150, and 220GHz covering the
angular multipole range . We combine this
measurement with the published polarization power spectrum measurements from
the 2018 observing season and update their associated covariance matrix to
complete the SPT-3G 2018 data set. This is the first analysis to
present cosmological constraints from SPT , , and power spectrum
measurements jointly. We blind the cosmological results and subject the data
set to a series of consistency tests at the power spectrum and parameter level.
We find excellent agreement between frequencies and spectrum types and our
results are robust to the modeling of astrophysical foregrounds. We report
results for CDM and a series of extensions, drawing on the following
parameters: the amplitude of the gravitational lensing effect on primary power
spectra , the effective number of neutrino species
, the primordial helium abundance , and the
baryon clumping factor due to primordial magnetic fields . We find that the
SPT-3G 2018 data are well fit by CDM with a
probability-to-exceed of . For CDM, we constrain the expansion
rate today to and the
combined structure growth parameter to . The SPT-based
results are effectively independent of Planck, and the cosmological parameter
constraints from either data set are within of each other.
(abridged)Comment: 35 Pages, 17 Figures, 11 Table
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