123 research outputs found
Calcium and structural dynamics of the axonal endoplasmic reticulum in animal models of spinal cord injury and multiple sclerosis
Optogalvanic Spectroscopy of Metastable States in Yb^{+}
The metastable ^{2}F_{7/2} and ^{2}D_{3/2} states of Yb^{+} are of interest
for applications in metrology and quantum information and also act as dark
states in laser cooling. These metastable states are commonly repumped to the
ground state via the 638.6 nm ^{2}F_{7/2} -- ^{1}D[5/2]_{5/2} and 935.2 nm
^{2}D_{3/2} -- ^{3}D[3/2]_{1/2} transitions. We have performed optogalvanic
spectroscopy of these transitions in Yb^{+} ions generated in a discharge. We
measure the pressure broadening coefficient for the 638.6 nm transition to be
70 \pm 10 MHz mbar^{-1}. We place an upper bound of 375 MHz/nucleon on the
638.6 nm isotope splitting and show that our observations are consistent with
theory for the hyperfine splitting. Our measurements of the 935.2 nm transition
extend those made by Sugiyama et al, showing well-resolved isotope and
hyperfine splitting. We obtain high signal to noise, sufficient for laser
stabilisation applications.Comment: 8 pages, 5 figure
The assembly and alignment of the 4MOST Wide Field Corrector
The 4-metre Multi-Object Spectroscopic Telescope (4MOST) is a fibre-fed multi-object spectrograph for the VISTA telescope at the ESO Paranal Observatory in Chile. The goal of the 4MOST project is to create a general-purpose and highly efficient spectroscopic survey facility for astronomers in the 4MOST consortium and the ESO community. The instrument itself will record 2436 simultaneous spectra over a ∼4.2 square degree field of view and consists of an optical Wide-Field Corrector (WFC), a fibre positioner system based on a tilting spine design, and three spectrographs giving both high and low spectral dispersion. The WFC comprises of 6 lenses grouped into 4 elements, 2 of which are cemented doublets that act as an atmospheric dispersion corrector (ADC). The first lens element is 0.9m in diameter whilst the diameter of the other elements is 0.65m. For the instrument to meet its science goals, each lens needs to be aligned to ∼50µm – a major challenge. This is achieved using contact metrology methods supplemented by pencil beam laser probes. In particular, a novel off-axis laser beam system has been implemented to test the optics’ alignment before and after shipment. This paper details the alignment and assembly methods and presents the latest results on the achieved lens positioning and projected performance of the WF
Calcium Influx through Plasma-Membrane Nanoruptures Drives Axon Degeneration in a Model of Multiple Sclerosis
Axon loss determines persistent disability in multiple sclerosis patients. Here, we use in vivo calcium imaging in a multiple sclerosis model to show that cytoplasmic calcium levels determine the choice between axon loss and survival. We rule out the endoplasmic reticulum, glutamate excitotoxicity, and the reversal of the sodium-calcium exchanger as sources of intra-axonal calcium accumulation and instead identify nanoscale ruptures of the axonal plasma membrane as the critical path of calcium entry
Оценка факторов рабочей среды при производстве фосфорных удобрений
Сделана оценка факторов рабочей среды при производстве фосфорных удобрений в "Агрополихиме" АД – в цехе "Фосфорная кислота" и в цехе "Тройной фосфат". Ведущее место по своей выраженности занимают химические вредные факторы. Кроме этого, внимание направлено на физико- химический фактор пыли и физический фактор шума
Black Hole Mass Estimates Based on CIV are Consistent with Those Based on the Balmer Lines
Using a sample of high-redshift lensed quasars from the CASTLES project with
observed-frame ultraviolet or optical and near-infrared spectra, we have
searched for possible biases between supermassive black hole (BH) mass
estimates based on the CIV, Halpha and Hbeta broad emission lines. Our sample
is based upon that of Greene, Peng & Ludwig, expanded with new near-IR
spectroscopic observations, consistently analyzed high S/N optical spectra, and
consistent continuum luminosity estimates at 5100A. We find that BH mass
estimates based on the FWHM of CIV show a systematic offset with respect to
those obtained from the line dispersion, sigma_l, of the same emission line,
but not with those obtained from the FWHM of Halpha and Hbeta. The magnitude of
the offset depends on the treatment of the HeII and FeII emission blended with
CIV, but there is little scatter for any fixed measurement prescription. While
we otherwise find no systematic offsets between CIV and Balmer line mass
estimates, we do find that the residuals between them are strongly correlated
with the ratio of the UV and optical continuum luminosities. Removing this
dependency reduces the scatter between the UV- and optical-based BH mass
estimates by a factor of approximately 2, from roughly 0.35 to 0.18 dex. The
dispersion is smallest when comparing the CIV sigma_l mass estimate, after
removing the offset from the FWHM estimates, and either Balmer line mass
estimate. The correlation with the continuum slope is likely due to a
combination of reddening, host contamination and object-dependent SED shapes.
When we add additional heterogeneous measurements from the literature, the
results are unchanged.Comment: Accepted for publication in The Astrophysical Journal. 37 text pages
+ 8 tables + 23 figures. Updated with comments by the referee and with a
expanded discussion on literature data including new observation
An overview of the mid-infrared spectro-interferometer MATISSE: science, concept, and current status
MATISSE is the second-generation mid-infrared spectrograph and imager for the
Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric
instrument will allow significant advances by opening new avenues in various
fundamental research fields: studying the planet-forming region of disks around
young stellar objects, understanding the surface structures and mass loss
phenomena affecting evolved stars, and probing the environments of black holes
in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the
spectral domain of current optical interferometers by offering the L and M
bands in addition to the N band. This will open a wide wavelength domain,
ranging from 2.8 to 13 um, exploring angular scales as small as 3 mas (L band)
/ 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared
imaging - closure-phase aperture-synthesis imaging - with up to four Unit
Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE
will offer a spectral resolution range from R ~ 30 to R ~ 5000. Here, we
present one of the main science objectives, the study of protoplanetary disks,
that has driven the instrument design and motivated several VLTI upgrades
(GRA4MAT and NAOMI). We introduce the physical concept of MATISSE including a
description of the signal on the detectors and an evaluation of the expected
performances. We also discuss the current status of the MATISSE instrument,
which is entering its testing phase, and the foreseen schedule for the next two
years that will lead to the first light at Paranal.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June
2016, 11 pages, 6 Figure
Infrared Narrow-Band Tomography of the Local Starburst NGC 1569 with LBT/LUCIFER
We used the near-IR imager/spectrograph LUCIFER mounted on the Large
Binocular Telescope (LBT) to image, with sub-arcsec seeing, the local dwarf
starburst NGC 1569 in the JHK bands and HeI 1.08 micron, [FeII] 1.64 micron and
Brgamma narrow-band filters. We obtained high-quality spatial maps of HeI,
[FeII] and Brgamma emission across the galaxy, and used them together with
HST/ACS images of NGC 1569 in the Halpha filter to derive the two-dimensional
spatial map of the dust extinction and surface star formation rate density. We
show that dust extinction is rather patchy and, on average, higher in the
North-West (NW) portion of the galaxy [E_g(B-V) = 0.71 mag] than in the
South-East [E_g(B-V) = 0.57 mag]. Similarly, the surface density of star
formation rate peaks in the NW region of NGC 1569, reaching a value of about 4
x 10^-6 M_sun yr^-1 pc^-2. The total star formation rate as estimated from the
integrated, dereddened Halpha luminosity is about 0.4 M_sun yr^-1, and the
total supernova rate from the integrated, dereddened [FeII] luminosity is about
0.005 yr^-1 (assuming a distance of 3.36 Mpc). The azimuthally averaged
[FeII]/Brgamma flux ratio is larger at the edges of the central, gas-deficient
cavities (encompassing the super star clusters A and B) and in the galaxy
outskirts. If we interpret this line ratio as the ratio between the average
past star formation (as traced by supernovae) and on-going activity
(represented by OB stars able to ionize the interstellar medium), it would then
indicate that star formation has been quenched within the central cavities and
lately triggered in a ring around them. The number of ionizing hydrogen and
helium photons as computed from the integrated, dereddened Halpha and HeI
luminosities suggests that the latest burst of star formation occurred about 4
Myr ago and produced new stars with a total mass of ~1.8 x 10^6 M_sun.
[Abridged]Comment: accepted for publication in A
Large body size constrains dispersal assembly of communities even across short distances
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