476 research outputs found
ROLE OF THE HISTONE DEMETHYLASE LSD1 IN THE REGULATION OF DIFFERENTIATION OF ACUTE PROMYELOCYTIC LEUKEMIA CELLS
Acute promyelocytic leukemia (APL) is characterized by the appearance of blasts,
insensitive to physiological retinoic acid (RA)-dependent differentiation and in the
majority of the cases, expressing PML-RAR fusion protein. PML-RAR works as a
dominant negative counterpart of retinoic acid receptor (RAR) and represses its target
genes by cooperating with many epigenetic regulators. Some of the known epigenetic
enzymes involved in the APL pathogenesis also interact with LSD1 in other systems.
LSD1 is a demethylase involved in transcriptional regulation, mainly acting on
dimethylated lysine 4 of Histone H3 (H3K4me2). We showed that LSD1 inhibition
sensitizes an APL cell line to physiological RA concentration. Here we characterize
for the first time mechanistic insights of LSD1 activity in PML-RAR expressing APL
cells. We determined the genomic distribution of LSD1, in particular LSD1 binds
both promoters and candidate enhancer regions. We found that LSD1 works as
finetuners of genes involved in differentiation and cell growth control as assessed by
gene ontology analysis. Moreover, LSD1 modulates H3K4me2 levels at regions
enriched in binding sites of master regulators of the myeloid/monocytic lineage,
suggesting their regulatory potential. We also described a previously unknown large
fraction of genomic loci bound by LSD1 and PR. Commonly bound regions show a
peculiar H3K4me2 enrichment and a subset of them resulted dynamically regulated
upon differentiation, suggesting a functional interplay between the two proteins in
reshaping the local chromatin environment. Overall, our findings contribute to the
mechanistic understanding of the role of LSD1 in the sensitization of APL cells to
differentiation
Etude des transformations structurales et minéralogiques provoquées par compactage avec ou sans addition de chaux à des argiles latéritiques brésiliennes
Electrochemical properties and electrochemical impedance spectroscopy of polypyrrole-coated platinum electrodes
Polypyrrole (PPy) films of different thickness were characterized by electrochemical impedance spectroscopy (EIS) measurements in acetonitrile and aqueous solutions, containing 0.1 M NaClO4 or sodium dodecylsulfate as the dopant. The PPy films were electrochemically deposited on Pt, and their electrochemical properties studied by cyclic voltammetry. Impedance spectra were obtained at potentials ranging from 0 to 0.8 V/SCE. The EIS data were fitted using two different equivalent electrical circuits (depending on the nature of the dopant). They involve a diffusive capacitance, which increased with the passing charge during electrosynthesis (i.e. film thickness) for ClO4--doped PPy, but was practically unaffected by the film thickness in the case of SDS-doped PPy. Also, a double-layer capacitance was found only in the circuit of ClO4--doped PPy. It increased with the film thickness, and showed a minimum near the open-circuit potential. Finally the charge-transfer resistance (Rct) obtained with SDS is nearly 200-fold higher than that obtained with ClO4- in the same solvent (H2O). With the same dopant (ClO4-), Rct is about five times higher in acetonitrile relative to water. All these EIS results of the different types of PPy suggest a relation with the wettability of the polymer.KEY WORDS: Conducting polymers, Polypyrrole, Electrochemical impedance spectroscopy, Equivalent-electrical circuit, Micellar mediaBull. Chem. Soc. Ethiop. 2006, 20(2), 279-293
Stability and collisions of moving semi-gap solitons in Bragg cross-gratings
We report results of a systematic study of one-dimensional four-wave moving
solitons in a recently proposed model of the Bragg cross-grating in planar
optical waveguides with the Kerr nonlinearity; the same model applies to a
fiber Bragg grating (BG) carrying two polarizations of light. We concentrate on
the case when the system's spectrum contains no true bandgap, but only
semi-gaps (which are gaps only with respect to one branch of the dispersion
relation), that nevertheless support soliton families. Solely zero-velocity
solitons were previously studied in this system, while current experiments
cannot generate solitons with the velocity smaller than half the maximum group
velocity. We find the semi-gaps for the moving solitons in an analytical form,
and demonstrated that they are completely filled with (numerically found)
solitons. Stability of the moving solitons is identified in direct simulations.
The stability region strongly depends on the frustration parameter, which
controls the difference of the present system from the usual model for the
single BG. A completely new situation is possible, when the velocity interval
for stable solitons is limited not only from above, but also from below.
Collisions between stable solitons may be both elastic and strongly inelastic.
Close to their instability border, the solitons collide elastically only if
their velocities c1 and c2 are small; however, collisions between more robust
solitons are elastic in a strip around c1=-c2.Comment: 16 pages, 7 figures, Physics Letters A, in pres
Dust Devil Tracks
Dust devils that leave dark- or light-toned tracks are common on Mars and they can also be found on the Earth’s surface. Dust devil tracks (hereinafter DDTs) are ephemeral surface features with mostly sub-annual lifetimes. Regarding their size, DDT widths can range between ∼1 m and ∼1 km, depending on the diameter of dust devil that created the track, and DDT lengths range from a few tens of meters to several kilometers, limited by the duration and horizontal ground speed of dust devils. DDTs can be classified into three main types based on their morphology and albedo in contrast to their surroundings; all are found on both planets: (a) dark continuous DDTs, (b) dark cycloidal DDTs, and (c) bright DDTs. Dark continuous DDTs are the most common type on Mars. They are characterized by their relatively homogenous and continuous low albedo surface tracks. Based on terrestrial and martian in situ studies, these DDTs most likely form when surficial dust layers are removed to expose larger-grained substrate material (coarse sands of ≥500 μm in diameter). The exposure of larger-grained materials changes the photometric properties of the surface; hence leading to lower albedo tracks because grain size is photometrically inversely proportional to the surface reflectance. However, although not observed so far, compositional differences (i.e., color differences) might also lead to albedo contrasts when dust is removed to expose substrate materials with mineralogical differences. For dark continuous DDTs, albedo drop measurements are around 2.5 % in the wavelength range of 550–850 nm on Mars and around 0.5 % in the wavelength range from 300–1100 nm on Earth. The removal of an equivalent layer thickness around 1 μm is sufficient for the formation of visible dark continuous DDTs on Mars and Earth. The next type of DDTs, dark cycloidal DDTs, are characterized by their low albedo pattern of overlapping scallops. Terrestrial in situ studies imply that they are formed when sand-sized material that is eroded from the outer vortex area of a dust devil is redeposited in annular patterns in the central vortex region. This type of DDT can also be found in on Mars in orbital image data, and although in situ studies are lacking, terrestrial analog studies, laboratory work, and numerical modeling suggest they have the same formation mechanism as those on Earth. Finally, bright DDTs are characterized by their continuous track pattern and high albedo compared to their undisturbed surroundings. They are found on both planets, but to date they have only been analyzed in situ on Earth. Here, the destruction of aggregates of dust, silt and sand by dust devils leads to smooth surfaces in contrast to the undisturbed rough surfaces surrounding the track. The resulting change in photometric properties occurs because the smoother surfaces have a higher reflectance compared to the surrounding rough surface, leading to bright DDTs. On Mars, the destruction of surficial dust-aggregates may also lead to bright DDTs. However, higher reflective surfaces may be produced by other formation mechanisms, such as dust compaction by passing dust devils, as this may also cause changes in photometric properties. On Mars, DDTs in general are found at all elevations and on a global scale, except on the permanent polar caps. DDT maximum areal densities occur during spring and summer in both hemispheres produced by an increase in dust devil activity caused by maximum insolation. Regionally, dust devil densities vary spatially likely controlled by changes in dust cover thicknesses and substrate materials. This variability makes it difficult to infer dust devil activity from DDT frequencies. Furthermore, only a fraction of dust devils leave tracks. However, DDTs can be used as proxies for dust devil lifetimes and wind directions and speeds, and they can also be used to predict lander or rover solar panel clearing events. Overall, the high DDT frequency in many areas on Mars leads to drastic albedo changes that affect large-scale weather patterns
Differential cross section and recoil polarization measurements for the gamma p to K+ Lambda reaction using CLAS at Jefferson Lab
We present measurements of the differential cross section and Lambda recoil
polarization for the gamma p to K+ Lambda reaction made using the CLAS detector
at Jefferson Lab. These measurements cover the center-of-mass energy range from
1.62 to 2.84 GeV and a wide range of center-of-mass K+ production angles.
Independent analyses were performed using the K+ p pi- and K+ p (missing pi -)
final-state topologies; results from these analyses were found to exhibit good
agreement. These differential cross section measurements show excellent
agreement with previous CLAS and LEPS results and offer increased precision and
a 300 MeV increase in energy coverage. The recoil polarization data agree well
with previous results and offer a large increase in precision and a 500 MeV
extension in energy range. The increased center-of-mass energy range that these
data represent will allow for independent study of non-resonant K+ Lambda
photoproduction mechanisms at all production angles.Comment: 22 pages, 16 figure
Measurement of the nuclear multiplicity ratio for hadronization at CLAS
The influence of cold nuclear matter on lepto-production of hadrons in
semi-inclusive deep inelastic scattering is measured using the CLAS detector in
Hall B at Jefferson Lab and a 5.014 GeV electron beam. We report the
multiplicity ratios for targets of C, Fe, and Pb relative to deuterium as a
function of the fractional virtual photon energy transferred to the
and the transverse momentum squared of the . We find that the
multiplicity ratios for are reduced in the nuclear medium at high
and low , with a trend for the transverse momentum to be
broadened in the nucleus for large .Comment: Submitted to Phys. Lett.
Coherent Photoproduction of pi^+ from 3^He
We have measured the differential cross section for the
He reaction. This reaction was studied using
the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. Real photons
produced with the Hall-B bremsstrahlung tagging system in the energy range from
0.50 to 1.55 GeV were incident on a cryogenic liquid He target. The
differential cross sections for the He
reaction were measured as a function of photon-beam energy and pion-scattering
angle. Theoretical predictions to date cannot explain the large cross sections
except at backward angles, showing that additional components must be added to
the model.Comment: 11 pages, 16 figure
Demonstration of a novel technique to measure two-photon exchange effects in elastic scattering
The discrepancy between proton electromagnetic form factors extracted using
unpolarized and polarized scattering data is believed to be a consequence of
two-photon exchange (TPE) effects. However, the calculations of TPE corrections
have significant model dependence, and there is limited direct experimental
evidence for such corrections. We present the results of a new experimental
technique for making direct comparisons, which has the potential to
make precise measurements over a broad range in and scattering angles. We
use the Jefferson Lab electron beam and the Hall B photon tagger to generate a
clean but untagged photon beam. The photon beam impinges on a converter foil to
generate a mixed beam of electrons, positrons, and photons. A chicane is used
to separate and recombine the electron and positron beams while the photon beam
is stopped by a photon blocker. This provides a combined electron and positron
beam, with energies from 0.5 to 3.2 GeV, which impinges on a liquid hydrogen
target. The large acceptance CLAS detector is used to identify and reconstruct
elastic scattering events, determining both the initial lepton energy and the
sign of the scattered lepton. The data were collected in two days with a
primary electron beam energy of only 3.3 GeV, limiting the data from this run
to smaller values of and scattering angle. Nonetheless, this measurement
yields a data sample for with statistics comparable to those of the
best previous measurements. We have shown that we can cleanly identify elastic
scattering events and correct for the difference in acceptance for electron and
positron scattering. The final ratio of positron to electron scattering:
for GeV and
Measurement of the Nucleon Structure Function F2 in the Nuclear Medium and Evaluation of its Moments
We report on the measurement of inclusive electron scattering off a carbon
target performed with CLAS at Jefferson Laboratory. A combination of three
different beam energies 1.161, 2.261 and 4.461 GeV allowed us to reach an
invariant mass of the final-state hadronic system W~2.4 GeV with four-momentum
transfers Q2 ranging from 0.2 to 5 GeV2. These data, together with previous
measurements of the inclusive electron scattering off proton and deuteron,
which cover a similar continuous two-dimensional region of Q2 and Bjorken
variable x, permit the study of nuclear modifications of the nucleon structure.
By using these, as well as other world data, we evaluated the F2 structure
function and its moments. Using an OPE-based twist expansion, we studied the
Q2-evolution of the moments, obtaining a separation of the leading-twist and
the total higher-twist terms. The carbon-to-deuteron ratio of the leading-twist
contributions to the F2 moments exhibits the well known EMC effect, compatible
with that discovered previously in x-space. The total higher-twist term in the
carbon nucleus appears, although with large systematic uncertainites, to be
smaller with respect to the deuteron case for n<7, suggesting partial parton
deconfinement in nuclear matter. We speculate that the spatial extension of the
nucleon is changed when it is immersed in the nuclear medium.Comment: 37 pages, 15 figure
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