266 research outputs found
Measurement of polarization-transfer to bound protons in carbon and its virtuality dependence
We measured the ratio of the transverse to longitudinal
components of polarization transferred from electrons to bound protons in
by the process at the
Mainz Microtron (MAMI). We observed consistent deviations from unity of this
ratio normalized to the free-proton ratio,
, for both -
and -shell knocked out protons, even though they are embedded in averaged
local densities that differ by about a factor of two. The dependence of the
double ratio on proton virtuality is similar to the one for knocked out protons
from and , suggesting a universal behavior.
It further implies no dependence on average local nuclear density
Fine tuning of surface CRLF2 expression and its associated signaling profile in childhood B-cell precursor acute lymphoblastic leukemia
Components of polarization-transfer to a bound proton in a deuteron measured by quasi-elastic electron scattering
We report the first measurements of the transverse ( and ) and
longitudinal () components of the polarization transfer to a bound
proton in the deuteron via the reaction,
over a wide range of missing momentum. A precise determination of the electron
beam polarization reduces the systematic uncertainties on the individual
components, to a level that enables a detailed comparison to a state-of-the-art
calculation of the deuteron that uses free-proton electromagnetic form factors.
We observe very good agreement between the measured and the calculated
ratios, but deviations of the individual components. Our results
cannot be explained by medium modified electromagnetic form factors. They point
to an incomplete description of the nuclear reaction mechanism in the
calculation
Comparison of recoil polarization in the process for protons extracted from and shell
We present first measurements of the double ratio of the polarization
transfer components for knock-out protons from and
shells in measured by the reaction in quasi-elastic kinematics. The data are
compared to theoretical predictions in relativistic distorted-wave impulse
approximation. Our results show that differences between - and -shell
protons, observed when compared at the same initial momentum (missing momentum)
largely disappear when the comparison is done at the same proton virtuality. We
observe no density-dependent medium modifications for protons from and
shells with the same virtuality in spite of the large differences in the
respective nuclear densities
The influence of Fermi motion on the comparison of the polarization transfer to a proton in elastic and quasi-elastic scattering
A comparison between polarization-transfer to a bound proton in quasi-free
kinematics by the A knockout reaction and that in elastic
scattering off a free proton can provide information on the characteristics of
the bound proton. In the past the reported measurements have been compared to
those of a free proton with zero initial momentum. We introduce, for the first
time, expressions for the polarization-transfer components when the proton is
initially in motion and compare them to the H data measured at the Mainz
Microtron (MAMI). We show the ratios of the transverse () and longitudinal
() components of the polarization transfer in , to those of elastic scattering off a "moving proton", assuming
the proton's initial (Fermi) momentum equals the negative missing momentum in
the measured reaction. We found that the correction due to the proton motion is
up to 20\% at high missing momentum.
However the effect on the double ratio
is largely canceled out, as
shown for both H and C data. This implies that the kinematics is not
the primary cause for the deviations between quasi-elastic and elastic
scattering reported previously
Combination Early-Phase Trials of Anticancer Agents in Children and Adolescents
PURPOSEThere is an increasing need to evaluate innovative drugs for childhood cancer using combination strategies. Strong biological rationale and clinical experience suggest that multiple agents will be more efficacious than monotherapy for most diseases and may overcome resistance mechanisms and increase synergy. The process to evaluate these combination trials needs to maximize efficiency and should be agreed by all stakeholders.METHODSAfter a review of existing combination trial methodologies, regulatory requirements, and current results, a consensus among stakeholders was achieved.RESULTSCombinations of anticancer therapies should be developed on the basis of mechanism of action and robust preclinical evaluation, and may include data from adult clinical trials. The general principle for combination early-phase studies is that, when possible, clinical trials should be dose- and schedule-confirmatory rather than dose-exploratory, and every effort should be made to optimize doses early. Efficient early-phase combination trials should be seamless, including dose confirmation and randomized expansion. Dose evaluation designs for combinations depend on the extent of previous knowledge. If not previously evaluated, limited evaluation of monotherapy should be included in the same clinical trial as the combination. Randomized evaluation of a new agent plus standard therapy versus standard therapy is the most effective approach to isolate the effect and toxicity of the novel agent. Platform trials may be valuable in the evaluation of combination studies. Patient advocates and regulators should be engaged with investigators early in a proposed clinical development pathway and trial design must consider regulatory requirements.CONCLUSIONAn optimized, agreed approach to the design and evaluation of early-phase pediatric combination trials will accelerate drug development and benefit all stakeholders, most importantly children and adolescents with cancer.</p
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Triplication of a 21q22 region contributes to B cell transformation through HMGN1 overexpression and loss of histone H3 lysine 27 trimethylation
Down syndrome confers a 20-fold increased risk of B cell acute lymphoblastic leukemia (B-ALL)1 and polysomy 21 is the most frequent somatic aneuploidy amongst all B-ALLs2. Yet, the mechanistic links between chr.21 triplication and B-ALL remain undefined. Here we show that germline triplication of only 31 genes orthologous to human chr.21q22 confers murine progenitor B cell self-renewal in vitro, maturation defects in vivo, and B-ALL with either BCR-ABL or CRLF2 with activated JAK2. Chr.21q22 triplication suppresses H3K27me3 in progenitor B cells and B-ALLs, and âbivalentâ genes with both H3K27me3 and H3K4me3 at their promoters in wild-type progenitor B cells are preferentially overexpressed in triplicated cells. Strikingly, human B-ALLs with polysomy 21 are distinguished by their overexpression of genes marked with H3K27me3 in multiple cell types. Finally, overexpression of HMGN1, a nucleosome remodeling protein encoded on chr.21q223â5, suppresses H3K27me3 and promotes both B cell proliferation in vitro and B-ALL in vivo
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