339 research outputs found
Gain properties of dye-doped polymer thin films
Hybrid pumping appears as a promising compromise in order to reach the much
coveted goal of an electrically pumped organic laser. In such configuration the
organic material is optically pumped by an electrically pumped inorganic device
on chip. This engineering solution requires therefore an optimization of the
organic gain medium under optical pumping. Here, we report a detailed study of
the gain features of dye-doped polymer thin films. In particular we introduce
the gain efficiency , in order to facilitate comparison between different
materials and experimental conditions. The gain efficiency was measured with
various setups (pump-probe amplification, variable stripe length method, laser
thresholds) in order to study several factors which modify the actual gain of a
layer, namely the confinement factor, the pump polarization, the molecular
anisotropy, and the re-absorption. For instance, for a 600 nm thick 5 wt\% DCM
doped PMMA layer, the different experimental approaches give a consistent value
80 cm.MW. On the contrary, the usual model predicting the gain
from the characteristics of the material leads to an overestimation by two
orders of magnitude, which raises a serious problem in the design of actual
devices. In this context, we demonstrate the feasibility to infer the gain
efficiency from the laser threshold of well-calibrated devices. Besides,
temporal measurements at the picosecond scale were carried out to support the
analysis.Comment: 15 pages, 17 figure
An insight into polarization states of solid-state organic lasers
The polarization states of lasers are crucial issues both for practical
applications and fundamental research. In general, they depend in a combined
manner on the properties of the gain material and on the structure of the
electromagnetic modes. In this paper, we address this issue in the case of
solid-state organic lasers, a technology which enables to vary independently
gain and mode properties. Different kinds of resonators are investigated:
in-plane micro-resonators with Fabry-Perot, square, pentagon, stadium, disk,
and kite shapes, and external vertical resonators. The degree of polarization P
is measured in each case. It is shown that although TE modes prevail generally
(P>0), kite-shaped micro-laser generates negative values for P, i.e. a flip of
the dominant polarization which becomes mostly TM polarized. We at last
investigated two degrees of freedom that are available to tailor the
polarization of organic lasers, in addition to the pump polarization and the
resonator geometry: upon using resonant energy transfer (RET) or upon pumping
the laser dye to an higher excited state. We then demonstrate that
significantly lower P factors can be obtained.Comment: 12 pages, 12 figure
Multi-phase characterization of AGN winds in 5 local type-2 quasars
We present MEGARA (Multi-Espectr\'ografo en GTC de Alta Resoluci\'on para
Astronom\'ia) Integral Field Unit (IFU) observations of 5 local type-2 quasars
(QSO2s, z ) from the Quasar Feedback (QSOFEED) sample. These active
galactic nuclei (AGN) have bolometric luminosities of 10 erg/s and
stellar masses of 10 M. We explore the kinematics of the
ionized gas through the [O~III]5007 emission line. The nuclear
spectra of the 5 QSO2s, extracted in a circular aperture of 1.2" (
2.2 kpc) in diameter, show signatures of high velocity winds in the form of
broad (full width at half maximum; 1300FWHM2240 km/s and
blueshifted components. We find that 4 out of the 5 QSO2s present outflows that
we can resolve with our seeing-limited data, and they have radii ranging from
3.1 to 12.6 kpc. In the case of the two QSO2s with extended radio emission, we
find that it is well-aligned with the outflows, suggesting that low-power jets
might be compressing and accelerating the ionized gas in these radio-quiet
QSO2s. In the four QSO2s with spatially resolved outflows, we measure ionized
mass outflow rates of 3.3-6.5 Msun/yr when we use [S~II]-based densities, and
of 0.7-1.6 Msun/yr when trans-auroral line-based densities are considered
instead. We compare them with the corresponding molecular mass outflow rates (8
- 16 Msun/yr), derived from CO(2-1) ALMA observations at 0.2" resolution. Both
phases show lower outflow mass rates than those expected from observational
scaling relations where uniform assumptions on the outflow properties were
adopted. This might be indicating that the AGN luminosity is not the only
driver of massive outflows and/or that these relations need to be re-scaled
using accurate outflow properties. We do not find a significant impact of the
outflows on the global star formation rates.Comment: 24 pages, 13 figures and 4 tables. Accepted for publication in A&A;
A&A 665, A55 (2023); doi: 10.1051/0004-6361/20234771
An expression signature of the angiogenic response in gastrointestinal neuroendocrine tumours: correlation with tumour phenotype and survival outcomes.
BACKGROUND: Gastroenteropancreatic neuroendocrine tumours (GEP-NETs) are heterogeneous with respect to biological behaviour and prognosis. As angiogenesis is a renowned pathogenic hallmark as well as a therapeutic target, we aimed to investigate the prognostic and clinico-pathological role of tissue markers of hypoxia and angiogenesis in GEP-NETs. METHODS: Tissue microarray (TMA) blocks were constructed with 86 tumours diagnosed from 1988 to 2010. Tissue microarray sections were immunostained for hypoxia inducible factor 1α (Hif-1α), vascular endothelial growth factor-A (VEGF-A), carbonic anhydrase IX (Ca-IX) and somatostatin receptors (SSTR) 1–5, Ki-67 and CD31. Biomarker expression was correlated with clinico-pathological variables and tested for survival prediction using Kaplan–Meier and Cox regression methods. RESULTS: Eighty-six consecutive cases were included: 51% male, median age 51 (range 16–82), 68% presenting with a pancreatic primary, 95% well differentiated, 51% metastatic. Higher grading (P=0.03), advanced stage (P<0.001), high Hif-1α and low SSTR-2 expression (P=0.03) predicted for shorter overall survival (OS) on univariate analyses. Stage, SSTR-2 and Hif-1α expression were confirmed as multivariate predictors of OS. Median OS for patients with SSTR-2+/Hif-1α-tumours was not reached after median follow up of 8.8 years, whereas SSTR-2-/Hif-1α+ GEP-NETs had a median survival of only 4.2 years (P=0.006). CONCLUSION: We have identified a coherent expression signature by immunohistochemistry that can be used for patient stratification and to optimise treatment decisions in GEP-NETs independently from stage and grading. Tumours with preserved SSTR-2 and low Hif-1α expression have an indolent phenotype and may be offered less aggressive management and less stringent follow up
Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes
We review the different excitation processes in the interstellar mediumComment: Accepted in Chem. Re
Maintaining quality of health services after abolition of user fees: A Uganda case study
<p>Abstract</p> <p>Background</p> <p>It has been argued that quality improvements that result from user charges reduce their negative impact on utilization especially of the poor. In Uganda, because there was no concrete evidence for improvements in quality of care following the introduction of user charges, the government abolished user fees in all public health units on 1<sup>st </sup>March 2001. This gave us the opportunity to prospectively study how different aspects of quality of care change, as a country changes its health financing options from user charges to free services, in a developing country setting. The outcome of the study may then provide insights into policy actions to maintain quality of care following removal of user fees.</p> <p>Methods</p> <p>A population cohort and representative health facilities were studied longitudinally over 3 years after the abolition of user fees. Quantitative and qualitative methods were used to obtain data. Parameters evaluated in relation to quality of care included availability of drugs and supplies and; health worker variables.</p> <p>Results</p> <p>Different quality variables assessed showed that interventions that were put in place were able to maintain, or improve the technical quality of services. There were significant increases in utilization of services, average drug quantities and stock out days improved, and communities reported health workers to be hardworking, good and dedicated to their work to mention but a few. Communities were more appreciative of the services, though expectations were lower. However, health workers felt they were not adequately motivated given the increased workload.</p> <p>Conclusion</p> <p>The levels of technical quality of care attained in a system with user fees can be maintained, or even improved without the fees through adoption of basic, sustainable system modifications that are within the reach of developing countries. However, a trade-off between residual perceptions of reduced service quality, and the welfare gains from removal of user fees should guide such a policy change.</p
From grape to wine: Fate of ochratoxin A during red, rose, and white winemaking process and the presence of ochratoxin derivatives in the final products.
The presence of ochratoxin A (OTA) in wine is mainly due to the contamination of grapes by Aspergillus carbonarius and A. niger, still in the vineyard or at stages prior to winemaking. Throughout winemaking process, although there is a reduction in OTA levels, modified mycotoxins may also be formed. In fact, modified mycotoxins are compounds that normally remain undetectable during the conventional analysis used for the parent toxin. In this context, the current study aimed to evaluate the effect of grape variety and winemaking steps on OTA fate as well as the formation of modified ochratoxins. White, rose and red wines were prepared from Muscat Italia, Syrah and Touriga Nacional varieties, respectively. OTA was determined during different steps of winemaking by UHPLC-ESI-MS/MS. Identification of ochratoxin derivatives was performed using tandem MS experiments. A reduction of 90.72, 92.44 and 88.15% in OTA levels was observed for white, rose and red wines, respectively. Among the sought targets, the following ochratoxin-derived candidates were identified: ochratoxin β, ochratoxin α methyl ester, ochratoxin B methyl ester, ochratoxin A methyl ester, ethylamide ochratoxin A, ochratoxin C and ochratoxin A glucose ester. These results indicate that the formation of ochratoxin derivatives leads to an underestimation of total mycotoxin levels in wine and, therefore, the inclusion of techniques for multi-mycotoxins detection should be considered
Aggregation by exponential weighting, sharp PAC-Bayesian bounds and sparsity
We study the problem of aggregation under the squared loss in the model of
regression with deterministic design. We obtain sharp PAC-Bayesian risk bounds
for aggregates defined via exponential weights, under general assumptions on
the distribution of errors and on the functions to aggregate. We then apply
these results to derive sparsity oracle inequalities
S-Phase Favours Notch Cell Responsiveness in the Drosophila Bristle Lineage
We have studied cell sensitivity to Notch pathway signalling throughout the cell cycle. As model system, we used the Drosophila bristle lineage where at each division N plays a crucial role in fate determination. Using in vivo imaging, we followed this lineage and activated the N-pathway at different moments of the secondary precursor cell cycle. We show that cells are more susceptible to respond to N-signalling during the S-phase. Thus, the period of heightened sensitivity coincided with the period of the S-phase. More importantly, modifications of S-phase temporality induced corresponding changes in the period of the cell's reactivity to N-activation. Moreover, S-phase abolition was correlated with a decrease in the expression of tramtrack, a downstream N-target gene. Finally, N cell responsiveness was modified after changes in chromatin packaging. We suggest that high-order chromatin structures associated with the S-phase create favourable conditions that increase the efficiency of the transcriptional machinery with respect to N-target genes
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