1,196 research outputs found
NAO und Vorhersagbarkeit / NAO and predictability
Ein Ăberblick ĂŒber die GĂŒte heutiger NAO-Vorhersagen und Vorhersagbarkeit der NAO an sich wird gegeben.
Der Einfluss der wesentlichen Prozesse auf die VorhersagegĂŒte auf saisonal-interannualen und dekadischen Zeitskalen
wird zusammengetragen. Auf den saisonal-interannualen Zeitskalen ist vor allem die WÀrmekapazitÀt und
der WĂ€rmetransport der oberen Schichten des Nordatlantik von Bedeutung fĂŒr den Anstieg der NAO-VorhersagegĂŒte.
Statistische Modelle sowie gekoppelte AtmosphĂ€re-Ozean-Ensemble-Vorhersagesysteme weisen fĂŒr die
beiden letzten Dekaden des 20 Jahrhunderts eine VorhersagegĂŒte von etwa 15 % auf. Die VorhersagegĂŒte ĂŒber die
letzten 50 Jahre liegt jedoch unter 10 %. Auf dekadischen Zeitskalen bildet die atlantische meridionale UmwÀlzbewegung
eine Grundlage fĂŒr die Vorhersagen des dekadischen Klimas in der atlantischen Region.
A review of the NAO prediction and predictability is given. The impact of basic processes governing the NAO variability
and their feasibility to enhance prediction skill on seasonal-to-interannual and decadal timescales is investigated.
On seasonal-to-interannual timescales heat content and transport of the North Atlantic upper layer ocean
can be essential to increase winter NAO prediction skill. Statistical models and coupled atmosphere-ocean ensemble
prediction systems suggest a positive skill of about 15% for the latest decades in the 20th century. The prediction
skill for the last 50 years, however, is below 10%. On decadal timescales particularly the meridional overturning
circulation provides the basis for forecasts of the decadal climate over the North Atlantic region
Using Technology to Monitor Hearing Device Use and Linguistic Environments: Early Intervention Providersâ Perspectives
To optimize outcomes of children with hearing loss, early intervention professionals must work with families to optimize both childrenâs hearing device use and the linguistic and auditory features of their environments. Two technologies with potential use in monitoring these domains are data logging and Language Environment Analysis (LENA) technology. This study had two objectives: 1) to determine whether providersâ experiences, perspectives, and current practices indicate there is a need for tools to better monitor these domains, and 2) to gain a better understanding of providersâ experiences with and perspectives on use of data logging and LENA technology using an internet-based questionnaire. Providers used informal, subjective methods to monitor functioning in the two domains and felt confident that this allowed them to know how consistently children on their caseloads were wearing their hearing devices and what their environments were like between intervention visits. Providers had limited personal experience with accessing data logging information from hearing devices, but many were receiving that information from the childâs audiologist. Most providers reported limited personal experience with LENA technology. Most providers indicated that they believed access to the technologies may be beneficial, but only if coupled with proper funding for the technology, appropriate training, and supportive administrative policies
A comparative study of satellite and ground-based phenology
Long time series of ground-based plant phenology, as well as more than two decades of satellite-derived phenological metrics, are currently available to assess the impacts of climate variability and trends on terrestrial vegetation. Traditional plant phenology provides very accurate information on individual plant species, but with limited spatial coverage. Satellite phenology allows monitoring of terrestrial vegetation on a global scale and provides an integrative view at the landscape level. Linking the strengths of both methodologies has high potential value for climate impact studies. We compared a multispecies index from ground-observed spring phases with two types (maximum slope and threshold approach) of satellite-derived start-of-season (SOS) metrics. We focus on Switzerland from 1982 to 2001 and show that temporal and spatial variability of the multispecies index correspond well with the satellite-derived metrics. All phenological metrics correlate with temperature anomalies as expected. The slope approach proved to deviate strongly from the temporal development of the ground observations as well as from the threshold-defined SOS satellite measure. The slope spring indicator is considered to indicate a different stage in vegetation development and is therefore less suited as a SOS parameter for comparative studies in relation to ground-observed phenology. Satellite-derived metrics are, however, very susceptible to snow cover, and it is suggested that this snow cover should be better accounted for by the use of newer satellite sensor
A Fully Tunable Single-Walled Carbon Nanotube Diode
We demonstrate a fully tunable diode structure utilizing a fully suspended
single-walled carbon nanotube (SWNT). The diode's turn-on voltage under forward
bias can be continuously tuned up to 4.3 V by controlling gate voltages, which
is ~6 times the nanotube bandgap energy. Furthermore, the same device design
can be configured into a backward diode by tuning the band-to-band tunneling
current with gate voltages. A nanotube backward diode is demonstrated for the
first time with nonlinearity exceeding the ideal diode. These results suggest
that a tunable nanotube diode can be a unique building block for developing
next generation programmable nanoelectronic logic and integrated circuits.Comment: 14 pages, 4 figure
A Census of the Chamaeleon I Star-Forming Region
Optical spectroscopy has been obtained for 179 objects that have been
previously identified as possible members of the cluster, that lack either
accurate spectral types or clear evidence of membership, and that are optically
visible (I<18). I have used these spectroscopic data and all other available
constraints to evaluate the spectral classifications and membership status of a
total sample of 288 candidate members of Chamaeleon I that have appeared in
published studies of the cluster. The latest census of Chamaeleon I now
contains 158 members, 8 of which are later than M6 and thus are likely to be
brown dwarfs. I find that many of the objects identified as members of
Chamaeleon I in recent surveys are actually field stars. Meanwhile, 7 of 9
candidates discovered by Carpenter and coworkers are confirmed as members, one
of which is the coolest known member of Chamaeleon I at a spectral type of M8
(~0.03 M_sun). I have estimated extinctions, luminosities, and effective
temperatures for the members and used these data to construct an H-R diagram
for the cluster. Chamaeleon I has a median age of ~2 Myr according to
evolutionary models, and hence is similar in age to IC 348 and is slightly
older than Taurus (~1 Myr). The measurement of an IMF for Chamaeleon I from
this census is not possible because of the disparate methods with which the
known members were originally selected, and must await an unbiased,
magnitude-limited survey of the cluster.Comment: 59 pages, 22 figure
The Stellar Population of the Chamaeleon I Star-Forming Region
I present a new census of the stellar population in the Chamaeleon I
star-forming region. Using optical and near-IR photometry and followup
spectroscopy, I have discovered 50 new members of Chamaeleon I, expanding the
census of known members to 226 objects. Fourteen of these new members have
spectral types later than M6, which doubles the number of known members that
are likely to be substellar. I have estimated extinctions, luminosities, and
effective temperatures for the known members, used these data to construct an
H-R diagram for the cluster, and inferred individual masses and ages with the
theoretical evolutionary models of Baraffe and Chabrier. The distribution of
isochronal ages indicates that star formation began 3-4 and 5-6 Myr ago in the
southern and northern subclusters, respectively, and has continued to the
present time at a declining rate. The IMF in Chamaeleon I reaches a maximum at
a mass of 0.1-0.15 M_sun, and thus closely resembles the IMFs in IC 348 and the
Orion Nebula Cluster. In logarithmic units where the Salpeter slope is 1.35,
the IMF is roughly flat in the substellar regime and shows no indication of
reaching a minimum down to a completeness limit of 0.01 M_sun. The low-mass
stars are more widely distributed than members at other masses in the northern
subcluster, but this is not the case in the southern subcluster. Meanwhile, the
brown dwarfs have the same spatial distribution as the stars out to a radius of
3 deg (8.5 pc) from the center of Chamaeleon I
Working Memory Training Effects on White Matter Integrity in Young and Older Adults
Objectives: Working memory is essential for daily life skills like reading comprehension, reasoning, and problem-solving. Healthy aging of the brain goes along with working memory decline that can affect older people's independence in everyday life. Interventions in the form of cognitive training are a promising tool for delaying age-related working memory decline, yet the underlying structural plasticity of white matter is hardly studied.
Methods: We conducted a longitudinal diffusion tensor imaging study to investigate the effects of an intensive four-week adaptive working memory training on white matter integrity quantified by global and tract-wise mean diffusivity. We compared diffusivity measures of fiber tracts that are associated with working memory of 32 young and 20 older participants that were randomly assigned to a working memory training group or an active control group.
Results: The behavioral analysis showed an increase in working memory performance after the four-week adaptive working memory training. The neuroanatomical analysis revealed a decrease in mean diffusivity in the working memory training group after the training intervention in the right inferior longitudinal fasciculus for the older adults. There was also a decrease in mean diffusivity in the working memory training group in the right superior longitudinal fasciculus for the older and young participants after the intervention.
Conclusion: This study shows that older people can benefit from working memory training by improving their working memory performance that is also reflected in terms of improved white matter integrity in the superior longitudinal fasciculus and the inferior longitudinal fasciculus, where the first is an essential component of the frontoparietal network known to be essential in working memory
The First VLT FORS1 spectra of Lyman-break candidates in the HDF-S and AXAF Deep Field
We report on low-resolution multi-object spectroscopy of 30 faint targets (R
\~ 24-25) in the HDF-S and AXAF deep field obtained with the VLT Focal
Reducer/low dispersion Spectrograph (FORS1). Eight high-redshift galaxies with
2.75< z < 4 have been identified. The spectroscopic redshifts are in good
agreement with the photometric ones with a dispersion at z<2
and at z>2. The inferred star formation rates of the
individual objects are moderate, ranging from a few to a few tens solar masses
per year. Five out of the eight high-z objects do not show prominent emission
lines. One object has a spectrum typical of an AGN. In the AXAF field two
relatively close pairs of galaxies have been identified, with separations of
8.7 and 3.1 proper Mpc and mean redshifts of 3.11 and 3.93, respectively.Comment: 5 pages Latex, with 2 PostScript figures. Astronomy and Astrophysics,
in pres
Did Frédéric Chopin die from heart failure?
On October 17, 1849, Poland's greatest composer, FrĂ©dĂ©ric Chopin (1810â1849) died aged 39. His cause of death remains unknown. An investigation of the documental sources was performed to reconstruct the medical history of the artist. Since his earliest years, his life had been dominated by poor health. Recurrent episodes of cough, fever, headaches, lymphadenopathy- a series of symptoms that may be attributed to viral respiratory infections- manifested in his teens. Later in life, he had chest pain, hemoptysis, hematemesis, neuralgia, and arthralgia. Exhaustion and breathlessness characterized all his adult life. Coughing, choking, and edema of the legs and ankles manifested four months before his death. Several hypotheses ranging from cystic fibrosis to alpha-1 anti-trypsin deficiency and pulmonary tuberculosis have been proposed to explain Chopin's lifelong illness. We suggest that Chopin had dilated cardiomyopathy with consequent heart failure and cirrhosis that caused his death
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