848 research outputs found
POSITRONIUM LASER EXCITATION IN THE AEGIS EXPERIMENT
The AEgIS experimental program on antimatter systems involves the formation of antihydrogen
atoms for gravitational and CPT studies. One of the key ingredients of the
AEgIS strategy for the synthesis of antihydrogen atoms is the creation and manipulation
of Positronium (Ps) atoms laser excited to Rydberg states (n > 15).
In AEgIS, Ps is produced in bunched mode and the Rydberg excitation is achieved with
a two laser pulse technique, by passing through a n = 3 intermediate level. Because
excitation on Ps n = 3 state has never been proposed before, in AEgIS a dedicated experimental
apparatus and several detection strategies have been studied in order to observe
the first measurement ever on this interesting process. In this work we present and discuss
the experimental findings about the successful Ps n = 3 excitation.
Moreover, in this thesis, a study of the impact of involved nonlinear processes on the
excitation efficiency of a Doppler broadened atomic cloud is carried out. Presented simulation
results show that, by exploiting properly nonlinear processes in the generation of
the desired wavelength, it is possible to improve the excitation efficiency of a laser pulse.
It is crucial, in AEgIS, the use of a periodically poled crystal in quasi phase matching
regime. This gives a broadband continuous output spectrum whose wings survive to the
spectral cutting of the last nonlinear crystal of the chain (which has insufficient spectral
acceptance). This means that, at high laser energies, these wings can be amplified and
the spectrum gaps can be filled in, leading to high reachable saturation efficiencies. On
the contrary, in a laser pulse with a comb-shaped spectrum with a Gaussian envelope,
both wings and gaps drop rapidly to zero, and amplification hardly occurs at usually
employed energy regimes.
The presented model is finally used to fit AEgIS Ps n = 3 excitation experimental data
Characterization of angularly resolved EUV emission from 2-μm-wavelength laser-driven Sn plasmas using preformed liquid disk targets
The emission properties of tin plasmas, produced by the irradiation of preformed liquid tin targets by several-ns-long 2 µm-wavelength laser pulses, are studied in the extreme ultraviolet (EUV) regime. In a two-pulse scheme, a pre-pulse laser is first used to deform tin microdroplets into thin, extended disks before the main (2 µm) pulse creates the EUV-emitting plasma. Irradiating 30- to 300 µm-diameter targets with 2 µm laser pulses, we find that the efficiency in creating EUV light around 13.5 nm follows the fraction of laser light that overlaps with the target. Next, the effects of a change in 2 µm drive laser intensity (0.6–1.8 × 1011 W cm−2) and pulse duration (3.7–7.4 ns) are studied. It is found that the angular dependence of the emission of light within a 2% bandwidth around 13.5 nm and within the backward 2π hemisphere around the incoming laser beam is almost independent of intensity and duration of the 2 µm drive laser. With increasing target diameter, the emission in this 2% bandwidth becomes increasingly anisotropic, with a greater fraction of light being emitted into the hemisphere of the incoming laser beam. For direct comparison, a similar set of experiments is performed with a 1 µm-wavelength drive laser. Emission spectra, recorded in a 5.5–25.5 nm wavelength range, show significant self-absorption of light around 13.5 nm in the 1 µm case, while in the 2 µm case only an opacity-related broadening of the spectral feature at 13.5 nm is observed. This work demonstrates the enhanced capabilities and performance of 2 µm-driven plasmas produced from disk targets when compared to 1 µm-driven plasmas, providing strong motivation for the use of 2 µm lasers as drive lasers in future high-power sources of EUV light
Exogenous WNT5A and WNT11 proteins rescue CITED2 dysfunction in mouse embryonic stem cells and zebrafish morphants
Mutations and inadequate methylation profiles of CITED2 are associated with human congenital heart disease (CHD). In mouse, Cited2 is necessary for embryogenesis, particularly for heart development, and its depletion in embryonic stem cells (ESC) impairs cardiac differentiation. We have now determined that Cited2 depletion in ESC affects the expression of transcription factors and cardiopoietic genes involved in early mesoderm and cardiac specification. Interestingly, the supplementation of the secretome prepared from ESC overexpressing CITED2, during the onset of differentiation, rescued the cardiogenic defects of Cited2-depleted ESC. In addition, we demonstrate that the proteins WNT5A and WNT11 held the potential for rescue. We also validated the zebrafish as a model to investigate cited2 function during development. Indeed, the microinjection of morpholinos targeting cited2 transcripts caused developmental defects recapitulating those of mice knockout models, including the increased propensity for cardiac defects and severe death rate. Importantly, the co-injection of anti-cited2 morpholinos with either CITED2 or WNT5A and WNT11 recombinant proteins corrected the developmental defects of Cited2-morphants. This study argues that defects caused by the dysfunction of Cited2 at early stages of development, including heart anomalies, may be remediable by supplementation of exogenous molecules, offering the opportunity to develop novel therapeutic strategies aiming to prevent CHD.Agência financiadora:
Fundação para a Ciência e a Tecnologia (FCT)
Comissão de Coordenação e Desenvolvimento Regional do Algarve (CCDR Algarve)
ALG-01-0145-FEDER-28044; DFG 568/17-2 Algarve Biomedical Center (ABC)
Municipio de Louléinfo:eu-repo/semantics/publishedVersio
Signatures of the slow solar wind streams from active regions in the inner corona
Some of local sources of the slow solar wind can be associated with
spectroscopically detected plasma outflows at edges of active regions
accompanied with specific signatures in the inner corona. The EUV telescopes
(e.g. SPIRIT/CORONAS-F, TESIS/CORONAS-Photon and SWAP/PROBA2) sometimes
observed extended ray-like structures seen at the limb above active regions in
1MK iron emission lines and described as "coronal rays". To verify the
relationship between coronal rays and plasma outflows, we analyze an isolated
active region (AR) adjacent to small coronal hole (CH) observed by different
EUV instruments in the end of July - beginning of August 2009. On August 1 EIS
revealed in the AR two compact outflows with the Doppler velocities V =10-30
km/s accompanied with fan loops diverging from their regions. At the limb the
ARCH interface region produced coronal rays observed by EUVI/STEREO-A on July
31 as well as by TESIS on August 7. The rays were co-aligned with open magnetic
field lines expanded to the streamer stalks. Using the DEM analysis, it was
found that the fan loops diverged from the outflow regions had the dominant
temperature of ~1 MK, which is similar to that of the outgoing plasma streams.
Parameters of the solar wind measured by STEREO-B, ACE, WIND, STEREO-A were
conformed with identification of the ARCH as a source region at the
Wang-Sheeley-Arge map of derived coronal holes for CR 2086. The results of the
study support the suggestion that coronal rays can represent signatures of
outflows from ARs propagating in the inner corona along open field lines into
the heliosphere.Comment: Accepted for publication in Solar Physics; 31 Pages; 13 Figure
Dielectronic recombination data for dynamic finite-density plasmas I. Goals and methodology
A programme is outlined for the assembly of a comprehensive dielectronic
recombination database within the generalized collisional--radiative (GCR)
framework. It is valid for modelling ions of elements in dynamic finite-density
plasmas such as occur in transient astrophysical plasmas such as solar flares
and in the divertors and high transport regions of magnetic fusion devices. The
resolution and precision of the data are tuned to spectral analysis and so are
sufficient for prediction of the dielectronic recombination contributions to
individual spectral line emissivities. The fundamental data are structured
according to the format prescriptions of the Atomic Data and Analysis Structure
(ADAS) and the production of relevant GCR derived data for application is
described and implemented following ADAS. The requirements on the dielectronic
recombination database are reviewed and the new data are placed in context and
evaluated with respect to older and more approximate treatments. Illustrative
results validate the new high-resolution zero-density dielectronic
recombination data in comparison with measurements made in heavy-ion storage
rings utilizing an electron cooler. We also exemplify the role of the
dielectronic data on GCR coefficient behaviour for some representative light
and medium weight elements.Comment: 14 Pages, 9 Figures. Submitted to Astronomy & Astrophysics April 12,
200
Pulse-driven nonlinear Alfv\'en waves and their role in the spectral line broadening
We study the impulsively generated non-linear Alfv\'en waves in the solar
atmosphere, and describe their most likely role in the observed non-thermal
broadening of some spectral lines in solar coronal holes. We solve numerically
the time-dependent magnetohydrodynamic equations to find temporal signatures of
large-amplitude Alfv\'en waves in the model atmosphere of open and expanding
magnetic field configuration, with a realistic temperature distribution. We
calculate the temporally and spatially averaged, instantaneous transversal
velocity of non-linear Alfv\'en waves at different heights of the model
atmosphere, and estimate its contribution to the unresolved non-thermal motions
caused by the waves. We find that the pulse-driven nonlinear Alfv\'en waves
with the amplitude =50 km s are the most likely candidates
for the non-thermal broadening of Si VIII 1445.75 \AA\ line profiles
in the polar coronal hole as reported by Banerjee et al. (1998). We also
demonstrate that the Alfv\'en waves driven by comparatively smaller velocity
pulse with its amplitude =25 km s may contribute to the
spectral line width of the same line at various heights in coronal hole without
any significant broadening. The main conclusion of this paper is that
non-linear Alfv\'en waves excited impulsively in the lower solar atmosphere are
responsible for the observed spectral line broadening in polar coronal holes.
This is an important result as it allows us to conclude that such large
amplitude and pulse-driven Alfv\'en waves do indeed exist in solar coronal
holes. The existence of these waves and their undamped growth may impart the
required momentum to accelerate the solar wind
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