408 research outputs found
MAPAS DE PARÂMETROS TEXTURAIS DE SEDIMENTOS DE FUNDO DO COMPLEXO ESTUARINO DE PARANAGUÁ PR
This study aims to describe the bottom sediments distribution on the Paranaguá Bay Complex, a synthesizing of the available data. Between 1988 and 2001 1.187 samples were obtained, which were used in this analysis. The CEP is compose by two main axis denominated Laranjeiras bay (N-S) and Paranaguá bay (EW).
The main results shown differences between bottom sediments characteristics of both bays, where the mean grain size on Laranjeiras bay is bigger than on Paranaguá bay, and selection coefficient is near to the same in both bays, except on Guaraqueçaba bay. The quantities of carbonate vary between 5 and 20%, and organic matter varies between 0 and 35% on the CEP.Este estudo tem por objetivo verificar a distribuição das características dos sedimentos de fundo do Complexo Estuarino de Paranaguá, fazendo uma síntese integrada dos dados. As análises foram embasadas em 1.187 amostras coletadas entre os anos de 1988 e 2001. Este Complexo Estuarino é composto por dois eixos principais, denominados baía das Laranjeiras (N-S) e de Paranaguá (L-O). Os resultados obtidos destacam diferenças entre as características dos sedimentos das referidas baías. O diâmetro médio granulométrico da baía das Laranjeiras é maior que na baía de Paranaguá, com grau de seleção semelhante em ambas, exceto a baía de Guaraqueçaba. A distribuição das porcentagens de carbonato biodetrítico (CaCO3) varia entre 5 e 20%, enquanto que a quantidade de matéria orgânica varia entre 0 e 35% no CEP
Biologically active Phytophthora mating hormone prepared by catalytic asymmetric total synthesis
A Phytophthora mating hormone with an array of 1,5-stereogenic centers has been synthesized by using our recently developed methodology of catalytic enantioselective conjugate addition of Grignard reagents. We applied this methodology in a diastereo- and enantioselective iterative route and obtained two of the 16 possible stereoisomers of Phytophthora hormone α1. These synthetic stereoisomers induced the formation of sexual spores (oospores) in A2 mating type strains of three heterothallic Phytophthora species, P. infestans, P. capsici, and P. nicotianae but not in A1 mating type strains. The response was concentration-dependent, and the oospores were viable. These results demonstrate that the biological activity of the synthetic hormone resembles that of the natural hormone α1. Mating hormones are essential components in the sexual life cycle of a variety of organisms. For plant pathogens like Phytophthora, sexual reproduction is important as a source of genetic variation. Moreover, the thick-walled oospores are the most durable propagules that can survive harsh environmental conditions. Sexual reproduction can thus greatly affect disease epidemics. The availability of synthetic compounds mimicking the activity of Phytophthora mating hormone will be instrumental for further unravelling sexual reproduction in this important group of plant pathogens.
Measurement of the electric dipole moments for transitions to rubidium Rydberg states via Autler-Townes splitting
We present the direct measurements of electric-dipole moments for
transitions with for Rubidium atoms. The
measurements were performed in an ultracold sample via observation of the
Autler-Townes splitting in a three-level ladder scheme, commonly used for
2-photon excitation of Rydberg states. To the best of our knowledge, this is
the first systematic measurement of the electric dipole moments for transitions
from low excited states of rubidium to Rydberg states. Due to its simplicity
and versatility, this method can be easily extended to other transitions and
other atomic species with little constraints. Good agreement of the
experimental results with theory proves the reliability of the measurement
method.Comment: 12 pages, 6 figures; figure 6 replaced with correct versio
Electronic temperatures, densities and plasma X-ray emission of a 14.5 GHz Electron-Cyclotron Resonance Ion Source
We have performed a systematic study of the Bremsstrahlung emission from the
electrons in the plasma of a commercial 14.5 GHz Electron-Cyclotron Resonance
Ion Source. The electronic spectral temperature and the product of ionic and
electronic densities of the plasma are measured by analyzing the Bremsstrahlung
spectra recorded for several rare gases (Ar, Kr, Xe) as a function of the
injected power. Within our uncertainty, we find an average temperature of ? 48
keV above 100W, with a weak dependency on the injected power and gas
composition. Charge state distributions of extracted ion beams have been
determined as well, providing a way to disentangle the ionic density from the
electronic density. Moreover X-ray emission from highly charged argon ions in
the plasma has been observed with a high-resolution mosaic crystal
spectrometer, demonstrating the feasibility for high-precision measurements of
transition energies of highly charged ions, in particular of the magnetic
dipole (M1) transition of He-like of argon ions
A planar multipole ion trap
We report on the realisation of a chip-based multipole ion trap manufactured
using micro-electromechanical systems (MEMS) technology. It provides ion
confinement in an almost field-free volume between two planes of radiofrequency
electrodes, deposited on glass substrates, which allows for optical access to
the trap. An analytical model of the effective trapping potential is presented
and compared with numerical calculations. Stable trapping of argon ions is
achieved and a lifetime of 16s is measured. Electrostatic charging of the chip
surfaces is studied and found to agree with a numerical estimate
A linear radiofrequency quadrupole ion trap for the cooling and bunching of radioactive ion beams
A linear radiofrequency quadrupole ion guide and beam buncher has been installed at the ISOLTRAP mass spectrometry experiment at the ISOLDE facility at CERN. The apparatus is being used as a beam cooling, accumulation, and bunching system. It operates with a buffer gas that cools the injected ions and converts the quasicontinuous 60- keV beam from the ISOLDE facility to 2.5-keV beam pulses with improved normalized transverse emittance. Recent measurements suggest a capture efficiency of the ion guide of up to 40% and a cooling and bunching efficiency of at least 12% which is expected to still be increased. The improved ISOLTRAP setup has so far been used very successfully in three on-line experiments. (12 refs)
Observation of coherent many-body Rabi oscillations
A two-level quantum system coherently driven by a resonant electromagnetic
field oscillates sinusoidally between the two levels at frequency
which is proportional to the field amplitude [1]. This phenomenon, known as the
Rabi oscillation, has been at the heart of atomic, molecular and optical
physics since the seminal work of its namesake and coauthors [2]. Notably, Rabi
oscillations in isolated single atoms or dilute gases form the basis for
metrological applications such as atomic clocks and precision measurements of
physical constants [3]. Both inhomogeneous distribution of coupling strength to
the field and interactions between individual atoms reduce the visibility of
the oscillation and may even suppress it completely. A remarkable
transformation takes place in the limit where only a single excitation can be
present in the sample due to either initial conditions or atomic interactions:
there arises a collective, many-body Rabi oscillation at a frequency
involving all N >> 1 atoms in the sample [4]. This is true even
for inhomogeneous atom-field coupling distributions, where single-atom Rabi
oscillations may be invisible. When one of the two levels is a strongly
interacting Rydberg level, many-body Rabi oscillations emerge as a consequence
of the Rydberg excitation blockade. Lukin and coauthors outlined an approach to
quantum information processing based on this effect [5]. Here we report initial
observations of coherent many-body Rabi oscillations between the ground level
and a Rydberg level using several hundred cold rubidium atoms. The strongly
pronounced oscillations indicate a nearly complete excitation blockade of the
entire mesoscopic ensemble by a single excited atom. The results pave the way
towards quantum computation and simulation using ensembles of atoms
Prevalence of and risk factors for suicidal ideation in adolescents during the COVID-19 pandemic: a cross-sectional study.
Pandemic-related life changes may have had a deleterious impact on suicidal behaviours. Early detection of suicidal ideation and identification of subgroups at increased risk could help prevent suicide, one of the leading causes of death among adolescents worldwide. Here, we aimed to investigate the prevalence of and risk factors for suicidal ideation in adolescents using a population-based sample from Switzerland, two years into the pandemic.
Between December 2021 and June 2022, adolescents aged 14 to 17 years already enrolled in a population-based cohort study (State of Geneva, Switzerland) were asked about suicidal ideation over the previous year. In addition to a regression model, we conducted a network analysis of exposures which identified direct and indirect risk factors for suicidal ideation (i.e. those connected through intermediate risk factors) using mixed graphical models.
Among 492 adolescents, 14.4% (95% CI: 11.5-17.8) declared having experienced suicidal ideation over the previous year. Using network analysis, we found that high psychological distress, low self-esteem, identifying as lesbian, gay or bisexual, suffering from bullying, extensive screen time and a severe COVID-19 pandemic impact were major risk factors for suicidal ideation, with parent-adolescent relationship having the highest centrality strength in the network.
Our results show that a significant proportion of adolescents experience suicidal ideation, yet these rates are comparable with pre-pandemic results. Providing psychological support is fundamental, with a focus on improving parent-adolescent relationships
Observation of mesoscopic crystalline structures in a two-dimensional Rydberg gas
The ability to control and tune interactions in ultracold atomic gases has
paved the way towards the realization of new phases of matter. Whereas
experiments have so far achieved a high degree of control over short-ranged
interactions, the realization of long-range interactions would open up a whole
new realm of many-body physics and has become a central focus of research.
Rydberg atoms are very well-suited to achieve this goal, as the van der Waals
forces between them are many orders of magnitude larger than for ground state
atoms. Consequently, the mere laser excitation of ultracold gases can cause
strongly correlated many-body states to emerge directly when atoms are
transferred to Rydberg states. A key example are quantum crystals, composed of
coherent superpositions of different spatially ordered configurations of
collective excitations. Here we report on the direct measurement of strong
correlations in a laser excited two-dimensional atomic Mott insulator using
high-resolution, in-situ Rydberg atom imaging. The observations reveal the
emergence of spatially ordered excitation patterns in the high-density
components of the prepared many-body state. They have random orientation, but
well defined geometry, forming mesoscopic crystals of collective excitations
delocalised throughout the gas. Our experiment demonstrates the potential of
Rydberg gases to realise exotic phases of matter, thereby laying the basis for
quantum simulations of long-range interacting quantum magnets.Comment: 10 pages, 7 figure
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