1,075 research outputs found
Iron single crystal growth from a lithium-rich melt
\alpha-Fe single crystals of rhombic dodecahedral habit were grown from a
melt of LiNFe. Crystals of several millimeter along a
side form at temperatures around C. Upon further cooling
the growth competes with the formation of Fe-doped LiN. The b.c.c.
structure and good sample quality of \alpha-Fe single crystals were confirmed
by X-ray and electron diffraction as well as magnetization measurements and
chemical analysis. A nitrogen concentration of 90\,ppm was detected by means of
carrier gas hot extraction. Scanning electron microscopy did not reveal any
sign of iron nitride precipitates.Comment: 13 pages, 4 figure
Sensitivity studies for a space-based methane lidar mission
Methane is the third most important greenhouse gas in the atmosphere after water vapour and carbon dioxide. A major handicap to quantify the emissions at the Earth's surface in order to better understand biosphere-atmosphere exchange processes and potential climate feedbacks is the lack of accurate and global observations of methane. Space-based integrated path differential absorption (IPDA) lidar has potential to fill this gap, and a Methane Remote Lidar Mission (MERLIN) on a small satellite in polar orbit was proposed by DLR and CNES in the frame of a German-French climate monitoring initiative. System simulations are used to identify key performance parameters and to find an advantageous instrument configuration, given the environmental, technological, and budget constraints. The sensitivity studies use representative averages of the atmospheric and surface state to estimate the measurement precision, i.e. the random uncertainty due to instrument noise. Key performance parameters for MERLIN are average laser power, telescope size, orbit height, surface reflectance, and detector noise. A modest-size lidar instrument with 0.45 W average laser power and 0.55 m telescope diameter on a 506 km orbit could provide 50-km averaged methane column measurement along the sub-satellite track with a precision of about 1% over vegetation. The use of a methane absorption trough at 1.65 μm improves the near-surface measurement sensitivity and vastly relaxes the wavelength stability requirement that was identified as one of the major technological risks in the pre-phase A studies for A-SCOPE, a space-based IPDA lidar for carbon dioxide at the European Space Agency. Minimal humidity and temperature sensitivity at this wavelength position will enable accurate measurements in tropical wetlands, key regions with largely uncertain methane emissions. In contrast to actual passive remote sensors, measurements in Polar Regions will be possible and biases due to aerosol layers and thin ice clouds will be minimised
Ferromagnetism or slow paramagnetic relaxation in Fe-doped LiN?
We report on isothermal magnetization, M\"ossbauer spectroscopy, and
magnetostriction as well as temperature-dependent alternating-current (ac)
susceptibility, specific heat, and thermal expansion of single crystalline and
polycrstalline Li(LiFe)N with and .
Magnetic hysteresis emerges at temperatures below K with
coercivity fields of up to T at K and magnetic
anisotropy energies of K (meV). The ac susceptibility is strongly
frequency dependent (--Hz) and reveals an effective energy
barrier for spin reversal of K. The relaxation times
follow Arrhenius behavior for K. For K, however, the
relaxation times of s are only weakly
temperature-dependent indicating the relevance of a quantum tunneling process
instead of thermal excitations. The magnetic entropy amounts to more than
J molK which significantly exceeds ln2, the
value expected for the entropy of a ground state doublet. Thermal expansion and
magnetostriction indicate a weak magneto-elastic coupling in accordance with
slow relaxation of the magnetization. The classification of
Li(LiFe)N as ferromagnet is stressed and contrasted with highly
anisotropic and slowly relaxing paramagnetic behavior.Comment: 12 pages, 10 figure
Learning within sustainable educational innovation:An analysis of teachers' perceptions and leadership practice
Innovative initiatives in education often have problems with their sustainability. The present study focuses on three educational innovations that have proved to be sustainable over time. We used a qualitative research approach to study and identify essential features of sustainable educational innovation. Two theoretical frameworks were used to guide the study: the integrated model for sustainable innovation (IMSI) and self-determination theory (SDT). Both frameworks take a different perspective upon learning; IMSI presents learning at the individual level, the team level and the organizational level to be the heart of sustainable innovation, and SDT presents how learning can be improved. The research question focused upon how the SDT concepts of autonomy, competence and relatedness were perceived within sustainable innovation, expressed by the IMSI framework, by teachers and school leaders. Based on our findings we demonstrate that the framework of IMSI and SDT can effectively be applied as a frame of analysis to identify essential features of sustainability in educational innovations and we discuss how concepts of SDT deepen the knowledge of sustainable educational innovation
Polarization observables of the gamma d --> PiNN reaction in the Delta(1232)-resonance region
Polarization observables of the three charge states of the pion for the
reaction with polarized photon beam and/or oriented
deuteron target are evaluated over the whole (1232)-resonance region
adopting a nonrelativistic model based on time-ordered perturbation theory.
Results for the -meson spectra, linear photon asymmetry, vector and tensor
target asymmetries are presented. Particular attention is given, for the first
time, to double polarization asymmetries for which we present results for
and . We found that all other double
polarization asymmetries of photon and deuteron target are vanished.Comment: 17 Pages, 8 Figures, accepted for publication in Int. J. Mod. Phys.
First airborne water vapor lidar measurements in the tropical upper troposphere and mid-latitudes lower stratosphere: accuracy evaluation and intercomparisons with other instruments
In the tropics, deep convection is the major source of uncertainty in water vapor transport to the upper troposphere and into the stratosphere. Although accurate measurements in this region would be of first order importance to better understand the processes that govern stratospheric water vapor concentrations and trends in the context of a changing climate, they are sparse because of instrumental shortcomings and observational challenges. Therefore, the Falcon research aircraft of the Deutsches Zentrum für Luft- und Raumfahrt (DLR) flew a zenith-viewing water vapor differential absorption lidar (DIAL) during the Tropical Convection, Cirrus and Nitrogen Oxides Experiment (TROCCINOX) in 2004 and 2005 in Brazil. The measurements were performed alternatively on three water vapor absorption lines of different strength around 940 nm. These are the first aircraft DIAL measurements in the tropical upper troposphere and in the mid-latitudes lower stratosphere. Sensitivity analyses reveal an accuracy of 5% between altitudes of 8 and 16 km. This is confirmed by intercomparisons with the Fast In-situ Stratospheric Hygrometer (FISH) and the Fluorescent Advanced Stratospheric Hygrometer (FLASH) onboard the Russian M-55 Geophysica research aircraft during five coordinated flights. The average relative differences between FISH and DIAL amount to −3%±8% and between FLASH and DIAL to −8%±14%, negative meaning DIAL is more humid. The average distance between the probed air masses was 129 km. The DIAL is found to have no altitude- or latitude-dependent bias. A comparison with the balloon ascent of a laser absorption spectrometer gives an average difference of 0%±19% at a distance of 75 km. Six tropical DIAL under-flights of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board ENVISAT reveal a mean difference of −8%±49% at an average distance of 315 km. While the comparison with MIPAS is somewhat less significant due to poorer comparison conditions, the agreement with the in-situ hygrometers provides evidence of the excellent quality of FISH, FLASH and DIAL. Most DIAL profiles exhibit a smooth exponential decrease of water vapor mixing ratio in the tropical upper troposphere to lower stratosphere transition. The hygropause with a minimum mixing ratio of 2.5 µmol/mol is found between 15 and 17 km. A high-resolution (2 km horizontal, 0.2 km vertical) DIAL cross section through the anvil outflow of tropical convection shows that the ambient humidity is increased by a factor of three across 100 km
The temporal nature of social context: Insights from the daily lives of patients with HIV
BACKGROUND: Patients\u27 life contexts are increasingly recognized as important, as evidenced by growing attention to the Social Determinants of Health (SDoH). This attention may be particularly valuable for patients with complex needs, like those with HIV, who are more likely to experience age-related comorbidities, mental health or substance use issues. Understanding patient perceptions of their life context can advance SDoH approaches.
OBJECTIVES: We sought to understand how aging patients with HIV think about their life context and explored if and how their reported context was documented in their electronic medical records (EMRs).
DESIGN: We combined life story interviews and EMR data to understand the health-related daily life experiences of patients with HIV. Patients over 50 were recruited from two US Department of Veterans Affairs HIV clinics. Narrative analysis was used to organize data by life events and health-related metrics.
KEY RESULTS: EMRs of 15 participants documented an average of 19 diagnoses and 10 medications but generally failed to include social contexts salient to patients. In interviews, HIV was discussed primarily in response to direct interviewer questions. Instead, participants raised past trauma, current social engagement, and concern about future health with varying salience. This led us to organize the narratives temporally according to past-, present-, or future-orientation. Past-focused narratives dwelled on unresolved experiences with social institutions like the school system, military or marriage. Present-focused narratives emphasized daily life challenges, like social isolation. Future-focused narratives were dominated by concerns that aging would limit activities.
CONCLUSIONS: A temporally informed understanding of patients\u27 life circumstances that are the foundation of their individualized SDoH could better focus care plans by addressing contextual concerns salient to patients. Trust-building may be a critical first step in caring for past-focused patients. Present-focused patients may benefit from support groups. Future-focused patients may desire discussing long term care options
Incoherent Photoproduction of -mesons from the Deuteron near Threshold
Incoherent photoproduction of the -meson on the deuteron is studied for
photon energies from threshold to 800 MeV. The dominant contribution, the
N-N amplitude, is described within an isobar model. The final
state interaction derived from the CD-Bonn potential is included and found to
be important for the description of the production cross section close to
threshold. Possible effects from the final state interaction are
discussed.Comment: 11 pages, revtex, including 6 figure
Small eta-N scattering lengths favour eta-d and eta-alpha states
Unstable states of the eta meson and the 3He nucleus predicted using the time
delay method were found to be in agreement with a recent claim of eta-mesic 3He
states made by the TAPS collaboration. Here, we extend this method to a
speculative study of the unstable states occurring in the eta-d and eta-4He
elastic scattering. The T-matrix for eta-4He scattering is evaluated within the
Finite Rank Approximation (FRA) of few body equations. For the evaluation of
time delay in the eta-d case, we use a parameterization of an existing Faddeev
calculation and compare the results with those obtained from FRA. With an eta-N
scattering length, fm, we find an eta-d unstable
bound state around -16 MeV, within the Faddeev calculation. A similar state
within the FRA is found for a low value of , namely, fm. The existence of an eta-4He unstable bound state close to
threshold is hinted by fm, but is ruled out by
large scattering lengths.Comment: 21 pages, LaTex, 7 Figure
Solar Flare Intermittency and the Earth's Temperature Anomalies
We argue that earth's short-term temperature anomalies and the solar flare
intermittency are linked. The analysis is based upon the study of the scaling
of both the spreading and the entropy of the diffusion generated by the
fluctuations of the temperature time series. The joint use of these two methods
evidences the presence of a L\'{e}vy component in the temporal persistence of
the temperature data sets that corresponds to the one that would be induced by
the solar flare intermittency. The mean monthly temperature datasets cover the
period from 1856 to 2002.Comment: 4 pages, 5 figure
- …