633 research outputs found
Picropodophyllin causes mitotic arrest and catastrophe by depolymerizing microtubules via Insulin-like growth factor-1 receptor-independent mechanism
Picropodophyllin (PPP) is an anticancer drug undergoing clinical development in NSCLC. PPP has been shown to suppress IGF-1R signaling and to induce a G2/M cell cycle phase arrest but the exact mechanisms remain to be elucidated. The present study identified an IGF-1-independent mechanism of PPP leading to pro-metaphase arrest. The mitotic block was induced in human cancer cell lines and in an A549 xenograft mouse but did not occur in normal hepatocytes/mouse tissues. Cell cycle arrest by PPP occurred in vitro and in vivo accompanied by prominent CDK1 activation, and was IGF-1R-independent since it occurred also in IGF-1R-depleted and null cells. The tumor cells were not arrested in G2/M but in mitosis. Centrosome separation was prevented during mitotic entry, resulting in a monopolar mitotic spindle with subsequent prometaphase-arrest, independent of Plk1/Aurora A or Eg5, and leading to cell features of mitotic catastrophe. PPP also increased soluble tubulin and decreased spindle-associated tubulin within minutes, indicating that it interfered with microtubule dynamics. These results provide a novel IGF-1R-independent mechanism of antitumor effects of PPP
Observations of whistler mode waves with nonlinear parallel electric fields near the dayside magnetic reconnection separatrix by the Magnetospheric Multiscale mission
We show observations from the Magnetospheric Multiscale (MMS) mission of whistler mode waves in the Earth's low-latitude boundary layer (LLBL) during a magnetic reconnection event. The waves propagated obliquely to the magnetic field toward the X line and were confined to the edge of a southward jet in the LLBL. Bipolar parallel electric fields interpreted as electrostatic solitary waves (ESW) are observed intermittently and appear to be in phase with the parallel component of the whistler oscillations. The polarity of the ESWs suggests that if they propagate with the waves, they are electron enhancements as opposed to electron holes. The reduced electron distribution shows a shoulder in the distribution for parallel velocities between 17,000 and 22,000âkm/s, which persisted during the interval when ESWs were observed, and is near the phase velocity of the whistlers. This shoulder can drive Langmuir waves, which were observed in the high-frequency parallel electric field data
Electron scale structures and magnetic reconnection signatures in the turbulent magnetosheath
Collisionless space plasma turbulence can generate reconnecting thin current
sheets as suggested by recent results of numerical magnetohydrodynamic
simulations. The MMS mission provides the first serious opportunity to check if
small ion-electron-scale reconnection, generated by turbulence, resembles the
reconnection events frequently observed in the magnetotail or at the
magnetopause. Here we investigate field and particle observations obtained by
the MMS fleet in the turbulent terrestrial magnetosheath behind quasi-parallel
bow shock geometry. We observe multiple small-scale current sheets during the
event and present a detailed look of one of the detected structures. The
emergence of thin current sheets can lead to electron scale structures where
ions are demagnetized. Within the selected structure we see signatures of ion
demagnetization, electron jets, electron heating and agyrotropy suggesting that
MMS spacecraft observe reconnection at these scales
The Effects of Alfven Waves and Radiation Pressure in Dust Winds of Late-type Stars
In the present study, we analyze the effects of a flux of Alfven waves acting
together with radiation pressure on grains as an acceleration mechanism of the
wind of late-type stars. In the wind model we simulate the presence of grains
through a strong damping of the waves, we used a non-isothermal profile for
temperature, coherent with grain formation theories. We examine the changes in
the velocity profile of the wind and we show that if the grains are created in
the region 1.1 < r/r_0 < 2.0 their presence will affect the mass loss and
terminal velocity. The model is applied to a K5 supergiant star and for
Betelgeuse (alpha Ori).Comment: 6 pages, 3 figures, accepted in ApJ (Sep, 2002
First 230 GHz VLBI Fringes on 3C 279 using the APEX Telescope
We report about a 230 GHz very long baseline interferometry (VLBI) fringe
finder observation of blazar 3C 279 with the APEX telescope in Chile, the
phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory
(ARO). We installed VLBI equipment and measured the APEX station position to 1
cm accuracy (1 sigma). We then observed 3C 279 on 2012 May 7 in a 5 hour 230
GHz VLBI track with baseline lengths of 2800 M to 7200 M and
a finest fringe spacing of 28.6 micro-arcseconds. Fringes were detected on all
baselines with SNRs of 12 to 55 in 420 s. The correlated flux density on the
longest baseline was ~0.3 Jy/beam, out of a total flux density of 19.8 Jy.
Visibility data suggest an emission region <38 uas in size, and at least two
components, possibly polarized. We find a lower limit of the brightness
temperature of the inner jet region of about 10^10 K. Lastly, we find an upper
limit of 20% on the linear polarization fraction at a fringe spacing of ~38
uas. With APEX the angular resolution of 230 GHz VLBI improves to 28.6 uas.
This allows one to resolve the last-photon ring around the Galactic Center
black hole event horizon, expected to be 40 uas in diameter, and probe radio
jet launching at unprecedented resolution, down to a few gravitational radii in
galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in
detail, follow-up observations with APEX and five other mm-VLBI stations have
been conducted (March 2013) and are being analyzed.Comment: accepted for publication in A&
Microhabitat use by the white-clawed crayfish in a Tuscan stream.
Habitat modification, pollution, overfishing, poaching, competition from nonindigenous
species, and diseases have led to the extinction in Europe of many
populations of indigenous crayfish. Under the rationale that any programme of
reintroduction should be preceded by a thorough understanding of habitat
requirements of the species of concern, we studied the microhabitat use of an
Austropotamobius pallipes population in Tuscany, central Italy. Microhabitat use
was assessed for water depth, current velocity, substrate, percentages of boulders,
underwater tree roots, and in-stream vegetation cover. Results show that A.
pallipesâ habitat use is size-partitioned. Smaller individuals mostly occupy stream
edges in shallow waters with submerged roots, whereas larger individuals use
deeper waters, often associated with boulders. Crayfish spatial distribution is
restricted mostly to the microhabitats characterised by extensive cover and slow
current velocity. The study highlights the importance of habitat heterogeneity and
cover elements for the protection of this indigenous species
Improved retrievals of carbon dioxide from Orbiting Carbon Observatory-2 with the version 8 ACOS algorithm
Since September 2014, NASA's Orbiting Carbon Observatory-2 (OCO-2)
satellite has been taking measurements of reflected solar spectra and using
them to infer atmospheric carbon dioxide levels. This work provides details
of the OCO-2 retrieval algorithm, versions 7 and 8, used to derive the
column-averaged dry air mole fraction of atmospheric CO2
(XCO2) for the roughly 100 000Â cloud-free measurements recorded
by OCO-2 each day. The algorithm is based on the Atmospheric Carbon
Observations from Space (ACOS) algorithm which has been applied to
observations from the Greenhouse Gases Observing SATellite (GOSAT) since
2009, with modifications necessary for OCO-2. Because high accuracy,
better than 0.25 %, is required in order to accurately infer carbon
sources and sinks from XCO2, significant errors and regional-scale
biases in the measurements must be minimized. We discuss efforts to filter
out poor-quality measurements, and correct the remaining good-quality
measurements to minimize regional-scale biases. Updates to the radiance
calibration and retrieval forward model in version 8 have improved many
aspects of the retrieved data products. The version 8 data appear to have
reduced regional-scale biases overall, and demonstrate a clear improvement
over the version 7 data. In particular, error variance with respect to TCCON
was reduced by 20 % over land and 40 % over ocean between versions 7
and 8, and nadir and glint observations over land are now more consistent.
While this paper documents the significant improvements in the ACOS
algorithm, it will continue to evolve and improve as the CO2 data
record continues to expand.</p
Large enhancement of deuteron polarization with frequency modulated microwaves
We report a large enhancement of 1.7 in deuteron polarization up to values of
0.6 due to frequency modulation of the polarizing microwaves in a two liters
polarized target using the method of dynamic nuclear polarization. This target
was used during a deep inelastic polarized muon-deuteron scattering experiment
at CERN. Measurements of the electron paramagnetic resonance absorption spectra
show that frequency modulation gives rise to additional microwave absorption in
the spectral wings. Although these results are not understood theoretically,
they may provide a useful testing ground for the deeper understanding of
dynamic nuclear polarization.Comment: 10 pages, including the figures coming in uuencoded compressed tar
files in poltar.uu, which also brings cernart.sty and crna12.sty files neede
Spin Structure of the Proton from Polarized Inclusive Deep-Inelastic Muon-Proton Scattering
We have measured the spin-dependent structure function in inclusive
deep-inelastic scattering of polarized muons off polarized protons, in the
kinematic range and . A
next-to-leading order QCD analysis is used to evolve the measured
to a fixed . The first moment of at is .
This result is below the prediction of the Ellis-Jaffe sum rule by more than
two standard deviations. The singlet axial charge is found to be . In the Adler-Bardeen factorization scheme, is
required to bring in agreement with the Quark-Parton Model. A
combined analysis of all available proton and deuteron data confirms the
Bjorken sum rule.Comment: 33 pages, 22 figures, uses ReVTex and smc.sty. submitted to Physical
Review
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