1,765 research outputs found
Proton endor study of the photoexcited triplet state PT in Rps. sphaeroides R-26 photosynthetic reaction centres
The photoexcited triplet state PT of Rhodopseudomonas sphaeroides R-26 has been investigated by ENDOR measurements performed on frozen photosynthetic reaction centre solutions. For the first time hyperfine data could be obtained for PT. These data indicate a delocalisation of the triplet state over two bacteriochlorophyll a molecules
Fast two-layer two-photon imaging of neuronal cell populations using an electrically tunable lens
Functional two-photon Ca2+-imaging is a versatile tool to study the dynamics of neuronal populations in brain slices and living animals. However, population imaging is typically restricted to a single two-dimensional image plane. By introducing an electrically tunable lens into the excitation path of a two-photon microscope we were able to realize fast axial focus shifts within 15 ms. The maximum axial scan range was 0.7 mm employing a 40x NA0.8 water immersion objective, plenty for typically required ranges of 0.2–0.3 mm. By combining the axial scanning method with 2D acousto-optic frame scanning and random-access scanning, we measured neuronal population activity of about 40 neurons across two imaging planes separated by 40 μm and achieved scan rates up to 20–30 Hz. The method presented is easily applicable and allows upgrading of existing two-photon microscopes for fast 3D scanning
Evidence for ubiquitous carbon grain destruction in hot protostellar envelopes
Earth is deficient in carbon and nitrogen by up to orders of
magnitude compared with the Sun. Destruction of (carbon- and nitrogen-rich)
refractory organics in the high-temperature planet forming regions could
explain this deficiency. Assuming a refractory cometary composition for these
grains, their destruction enhances nitrogen-containing oxygen-poor molecules in
the hot gas (K) after the initial formation and sublimation of
these molecules from oxygen-rich ices in the warm gas (K). Using
observations of high-mass protostars with ALMA, we find that
oxygen-containing molecules (CHOH and HNCO) systematically show no
enhancement in their hot component. In contrast, nitrogen-containing,
oxygen-poor molecules (CHCN and CHCN) systematically show an
enhancement of a factor in their hot component, pointing to
additional production of these molecules in the hot gas. Assuming only thermal
excitation conditions, we interpret these results as a signature of destruction
of refractory organics, consistent with the cometary composition. This
destruction implies a higher C/O and N/O in the hot gas than the warm gas,
while, the exact values of these ratios depend on the fraction of grains that
are effectively destroyed. This fraction can be found by future chemical models
that constrain C/O and N/O from the abundances of minor carbon, nitrogen and
oxygen carriers presented here.Comment: Accepted for publication in ApJ Letter
Эффективность капецитабина по сравнению с 5-фторурацилом при раке толстой кишки и желудка: обновленный метаанализ выживаемости в шести клинических исследованиях
Оральный фторпиримидин — капецитабин — широко изучен в сравнительных исследованиях с вводимым внутривенно 5-фторурацилом как монотерапевтическое средство или в комплексном приме- нении при метастатическом колоректальном раке (МКРР) и метастатическом раке желудка (МРЖ). По рекомендации Европейских органов здравоохранения выполнен метаанализ эффективности применения капецитабина по сравнению с 5-фторурацилом при МКРР и МРЖ
IDLaS-NL – A platform for running customized studies on individual differences in Dutch language skills via the internet
We introduce the Individual Differences in Language Skills (IDLaS-NL) web platform, which enables users to run studies on individual differences in Dutch language skills via the internet. IDLaS-NL consists of 35 behavioral tests, previously validated in participants aged between 18 and 30 years. The platform provides an intuitive graphical interface for users to select the tests they wish to include in their research, to divide these tests into different sessions and to determine their order. Moreover, for standardized administration the platform provides an application (an emulated browser) wherein the tests are run. Results can be retrieved by mouse click in the graphical interface and are provided as CSV-file output via email. Similarly, the graphical interface enables researchers to modify and delete their study configurations. IDLaS-NL is intended for researchers, clinicians, educators and in general anyone conducting fundamental research into language and general cognitive skills; it is not intended for diagnostic purposes. All platform services are free of charge. Here, we provide a description of its workings as well as instructions for using the platform. The IDLaS-NL platform can be accessed at www.mpi.nl/idlas-nl
Imaging the water snowline in a protostellar envelope with HCO
Snowlines are key ingredients for planet formation. Providing observational
constraints on the locations of the major snowlines is therefore crucial for
fully connecting planet compositions to their formation mechanism.
Unfortunately, the most important snowline, that of water, is very difficult to
observe directly in protoplanetary disks due to its close proximity to the
central star. Based on chemical considerations, HCO is predicted to be a
good chemical tracer of the water snowline, because it is particularly abundant
in dense clouds when water is frozen out. This work maps the optically thin
isotopologue HCO () toward the envelope of the low-mass
protostar NGC1333-IRAS2A (observed with NOEMA at ~0.9" resolution), where the
snowline is at larger distance from the star than in disks. The HCO
emission peaks ~2" northeast of the continuum peak, whereas the previously
observed HO shows compact emission on source. Quantitative modeling
shows that a decrease in HCO abundance by at least a factor of six
is needed in the inner ~360 AU to reproduce the observed emission profile.
Chemical modeling predicts indeed a steep increase in HCO just outside the
water snowline; the 50% decrease in gaseous HO at the snowline is not
enough to allow HCO to be abundant. This places the water snowline at 225
AU, further away from the star than expected based on the 1D envelope
temperature structure for NGC1333-IRAS2A. In contrast, DCO observations
show that the CO snowline is at the expected location, making an outburst
scenario unlikely. The spatial anticorrelation of the HCO and
HO emission provide a proof of concept that HCO can be used
as a tracer of the water snowline.Comment: 10 pages, 8 figures, 3 tables. Accepted for publication in A&
Temperature structures of embedded disks: young disks in Taurus are warm
The chemical composition of gas and ice in disks around young stars set the
bulk composition of planets. In contrast to protoplanetary disks (Class II),
young disks that are still embedded in their natal envelope (Class 0 and I) are
predicted to be too warm for CO to freeze out, as has been confirmed
observationally for L1527 IRS. To establish whether young disks are generally
warmer than their more evolved counterparts, we observed five young (Class 0/I
and Class I) disks in Taurus with the Atacama Large Millimeter/submillimeter
Array (ALMA), targeting CO , HCO , HDO
and CHOH transitions at resolution. The different freeze-out temperatures
of these species allow us to derive a global temperature structure. CO
and HCO are detected in all disks, with no signs of CO freeze-out in the
inner 100 au, and a CO abundance close to 10. HCO
emission originates in the surface layers of the two edge-on disks, as
witnessed by the especially beautiful V-shaped emission pattern in
IRAS~04302+2247. HDO and CHOH are not detected, with column density upper
limits more than 100 times lower than for hot cores. Young disks are thus found
to be warmer than more evolved protoplanetary disks around solar analogues,
with no CO freeze-out (or only in the outermost part of 100 au disks)
or CO processing. However, they are not as warm as hot cores or disks around
outbursting sources, and therefore do not have a large gas-phase reservoir of
complex molecules.Comment: Accepted for publication in ApJ. 19 pages, 11 figures, 3 tables (+
appendix
STAIRS4WORDS: A new adaptive test for assessing receptive vocabulary size in English, Dutch, and German
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