555 research outputs found
The spin temperature of high-redshift damped Lyman- systems
We report results from a programme aimed at investigating the temperature of
neutral gas in high-redshift damped Lyman- absorbers (DLAs). This
involved (1) HI 21cm absorption studies of a large DLA sample, (2) VLBI studies
to measure the low-frequency quasar core fractions, and (3) optical/ultraviolet
spectroscopy to determine DLA metallicities and velocity widths.
Including literature data, our sample consists of 37 DLAs with estimates of
the spin temperature and the covering factor. We find a strong )
difference between the distributions in high-z (z>2.4) and low-z (z<2.4)
DLA samples. The high-z sample contains more systems with high values,
K. The distributions in DLAs and the Galaxy are also
clearly (~) different, with more high- sightlines in DLAs than in
the Milky Way. The high values in the high-z DLAs of our sample arise due
to low fractions of the cold neutral medium.
For 29 DLAs with metallicity [Z/H] estimates, we confirm the presence of an
anti-correlation between and [Z/H], at significance via a
non-parametric Kendall-tau test. This result was obtained with the assumption
that the DLA covering factor is equal to the core fraction. Monte Carlo
simulations show that the significance of the result is only marginally
decreased if the covering factor and the core fraction are uncorrelated, or if
there is a random error in the inferred covering factor.
We also find evidence for redshift evolution in DLA values even for the
z>1 sub-sample. Since z>1 DLAs have angular diameter distances comparable to or
larger than those of the background quasars, they have similar efficiency in
covering the quasars. Low covering factors in high-z DLAs thus cannot account
for the observed redshift evolution in spin temperatures. (Abstract abridged.)Comment: 37 pages, 22 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Karlstadter Positionspapier zum Schutz der Ackerwildkräuter. Erarbeitet von den Teilnehmerinnen und Teilnehmern der "Tagung zum Schutz der Ackerwildflora" am 25./26.6.2004 in Karlstadt am Main
Der Erhalt von Ackerwildkräutern, die historisch erst mit der Landbewirtschaftung in Mitteleuropa heimisch geworden sind, ist eine Kulturaufgabe, damit auch künftige Generationen die Arten- und Farbenvielfalt in der Kulturlandschaft erleben können
Magnetic states at the surface of alpha Fe2O3 thin films doped with Ti, Zn, or Sn
The spin states at the surface of epitaxial thin films of hematite, both
undoped and doped with 1% Ti, Sn or Zn, respectively, were probed with x-ray
magnetic linear dichroism (XMLD) spectroscopy. Morin transitions were observed
for the undoped (T_M~200 K) and Sn-doped (T_M~300 K) cases, while Zn and
Ti-doped samples were always in the high and low temperature phases,
respectively. In contrast to what has been reported for bulk hematite doped
with the tetravalent ions Sn4+ and Ti4+, for which T_M dramatically decreases,
these dopants substantially increase T_M in thin films, far exceeding the bulk
values. The normalized Fe LII-edge dichroism for T<T_M does not strongly depend
on doping or temperature, except for an apparent increase of the peak
amplitudes for T<100 K. We observed magnetic field-induced inversions of the
dichroism peaks. By applying a magnetic field of 6.5 T on the Ti-doped sample,
a transition into the T>T_M state was achieved. The temperature dependence of
the critical field for the Sn-doped sample was characterized in detail. It was
demonstrated the sample-to-sample variations of the Fe LIII-edge spectra were,
for the most part, determined solely by the spin orientation state.
Calculations of the polarization-depedent spectra based on a spin-multiplet
model were in reasonable agreement with the experiment and showed a mixed
excitation character of the peak structures.Comment: 8 pages, 8 figure
G Electronics and Data Acquisition (Forward-Angle Measurements)
The G parity-violation experiment at Jefferson Lab (Newport News, VA) is
designed to determine the contribution of strange/anti-strange quark pairs to
the intrinsic properties of the proton. In the forward-angle part of the
experiment, the asymmetry in the cross section was measured for
elastic scattering by counting the recoil protons corresponding to the two
beam-helicity states. Due to the high accuracy required on the asymmetry, the
G experiment was based on a custom experimental setup with its own
associated electronics and data acquisition (DAQ) system. Highly specialized
time-encoding electronics provided time-of-flight spectra for each detector for
each helicity state. More conventional electronics was used for monitoring
(mainly FastBus). The time-encoding electronics and the DAQ system have been
designed to handle events at a mean rate of 2 MHz per detector with low
deadtime and to minimize helicity-correlated systematic errors. In this paper,
we outline the general architecture and the main features of the electronics
and the DAQ system dedicated to G forward-angle measurements.Comment: 35 pages. 17 figures. This article is to be submitted to NIM section
A. It has been written with Latex using \documentclass{elsart}. Nuclear
Instruments and Methods in Physics Research Section A: Accelerators,
Spectrometers, Detectors and Associated Equipment In Press (2007
Intensity and safety of community-based physical activities for people with COPD
Background: long-term maintenance of the benefits obtained with pulmonary rehabilitation (PR) in people with COPD is of upmost importance, yet highly challenging. Integrating these people in community-based physical activities (PAs), after PR, can be a promising strategy to maintain achieved benefits. Nevertheless, to confidently advise people with COPD to enrol these community-based PAs, clinicians must ensure those are safe and ideally are of at least moderate intensity (following PAs guidelines). This study aimed to explore safety and intensity level of community-based PAs (cardiofitness room, senior gymnastics, and aquatic gymnastics) in people with COPD, after PR.
Methods: an observational cross-sectional study, part of a larger trial (NCT04223362) was conducted. People with COPD that had finished a community-based PR programme, conducted in the Respiratory Research and Rehabilitation Laboratory (Lab3R) or in four primary health care centres (Aveiro, Estarreja, Oliveira do Bairro and Montemor-o-Velho), and that had a positive risk-benefit analysis regarding their inclusion on community-based PAs were included. Participants were given the opportunity to choose among the available community-based PAs (previously identified as adequate), the one(s), they wanted to try, and were then accompanied by a physiotherapist. During the community-based PAs, dyspnoea and fatigue perception were assessed every 20 minutes using the modified Borg 0-10 scale; and heart rate (HR) and percentage of peripheral oxygen saturation (SpO2) were constantly monitored. Participants wore the SenseWear Armband on the left triceps to estimate the Metabolic Equivalent Task (METs) of each community-based PA. The final community-based PAs intensity level was obtained by summing the intensity levels yielded by: dyspnoea and fatigue Borg scores, maximal HR percentage predicted (HRmax%predicted) (where HRmaxpredicted=220-age), and METs; with 3-6 Borg scores, 64-76% of HRmax%predicted, and 3-6 METs identifying moderate intensities. For security standards, SpO2 below 88% and HRmax%predicted above 85% were considered. The occurrence of any adverse event during the PAs was registered.
Results: three community-based PAs were included, cardiofitness room (9 people with COPD, 68±9 years, 100% men, 58±21 FEV1 %predicted), senior gymnastics (8 people with COPD, 70±9 years, 75% men, 53±11 FEV1 %predicted), and aquatic gymnastics (6 people with COPD, 68±10 years, 100% men, 49±16 FEV1 %predicted). Overall, the explored community-based PAs were classified as of moderate intensity (Figure 1 – a, b, c). Only one participant presented a SpO2 below 88% on the cardiofitness room (lowest SpO2 registered was 86%) and the HRmax%predicted was below 85% in all participants. Mean values of SpO2 and HRmax%predicted are presented in Figure 1 (d, e, f). No adverse event was registered.
Conclusion: Cardiofitness room, senior gymnastics, and aquatic gymnastics seem safe and of moderate intensity for people with COPD. Enrolment of people with COPD on these community-based PAs, following PR, should be advised, as these may facilitate the long-term maintenance of PR benefits, while promoting a more physically active lifestyle in this population. Nevertheless, caution is needed when interpreting these results, since intensity of PA is highly influenced by individual factors and patients’ enrolment must be preceded by a careful patient selection to ensure their safety.publishe
Carbon Nanotubes by a CVD Method. Part I: Synthesis and Characterization of the (Mg, Fe)O Catalysts
The controlled synthesis of carbon nanotubes by chemical vapor deposition requires tailored and wellcharacterized catalyst materials. We attempted to synthesize Mg1-xFexO oxide solid solutions by the combustion route, with the aim of performing a detailed investigation of the influence of the synthesis conditions (nitrate/urea ratio and the iron content) on the valency and distribution of the iron ions and phases. Notably, characterization of the catalyst materials is performed using 57Fe Mo¨ssbauer spectroscopy, X-ray diffraction, and electron microscopy. Several iron species are detected including Fe2+ ions substituting for Mg2+ in the MgO lattice, Fe3+ ions dispersed in the octahedral sites of MgO, different clusters of Fe3+ ions, and MgFe2O4-like nanoparticles. The dispersion of these species and the microstructure of the oxides are discussed. Powders markedly different from one another that may serve as model systems for further study are identified. The formation of carbon nanotubes upon reduction in a H2/CH4 gas atmosphere of the selected powders is reported in a companion paper
Evidence for Quantum Interference in SAMs of Arylethynylene Thiolates in Tunneling Junctions with Eutectic Ga-In (EGaIn) Top-Contacts
This paper compares the current density (J) versus applied bias (V) of self-assembled monolayers (SAMs) of three different ethynylthiophenol-functionalized anthracene derivatives of approximately the same thickness with linear-conjugation (AC), cross-conjugation (AQ), and broken-conjugation (AH) using liquid eutectic Ga-In (EGaIn) supporting a native skin (~1 nm thick) of Ga2O3 as a nondamaging, conformal top-contact. This skin imparts non-Newtonian rheological properties that distinguish EGaIn from other top-contacts; however, it may also have limited the maximum values of J observed for AC. The measured values of J for AH and AQ are not significantly different (J ≈ 10-1 A/cm2 at V = 0.4 V). For AC, however, J is 1 (using log averages) or 2 (using Gaussian fits) orders of magnitude higher than for AH and AQ. These values are in good qualitative agreement with gDFTB calculations on single AC, AQ, and AH molecules chemisorbed between Au contacts that predict currents, I, that are 2 orders of magnitude higher for AC than for AH at 0 < |V| < 0.4 V. The calculations predict a higher value of I for AQ than for AH; however, the magnitude is highly dependent on the position of the Fermi energy, which cannot be calculated precisely. In this sense, the theoretical predictions and experimental conclusions agree that linearly conjugated AC is significantly more conductive than either cross-conjugated AQ or broken conjugate AH and that AQ and AH cannot necessarily be easily differentiated from each other. These observations are ascribed to quantum interference effects. The agreement between the theoretical predictions on single molecules and the measurements on SAMs suggest that molecule-molecule interactions do not play a significant role in the transport properties of AC, AQ, and AH.
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Rapid eye movements to a virtual target are biased by illusory context in the Poggendorff figure.
In order to determine the influence of perceptual input upon oculomotor responses, we examined rapid saccadic eye movements made by healthy human observers to a virtual target defined by the extrapolated intersection of a pointer with a distant landing line. While corresponding perceptual judgments showed no evidence of systematic bias, eye movements showed a strong bias, in the direction of assimilation of the saccade trajectory to the shortest path between the end of the pointer and the landing line. Adding an abutting vertical inducing line to make an angle of 45 deg with the pointer led to a larger bias in the same direction as the classical Poggendorff illusion. This additional Poggendorff effect was similar in direction and magnitude for the eye movements and the perceptual responses. Latency and dynamics of the eye movements were closely similar to those recorded for a control task in which observers made a saccade from the start fixation to an explicit target on the landing line. Further experiments with inducing lines presented briefly at various times during the saccade latency period showed that the magnitude of the saccade bias was affected by inducer presentation during the saccade planning process, but not during the saccade itself. We conclude that the neural mechanisms for extrapolation can feed into the control of eye movements without obvious penalties in timing and accuracy and that this information can instantaneously modify motor response throughout the planning phase, suggesting close association between perceptual and motor mechanisms in the process of visuo-spatial extrapolation
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