3,057 research outputs found
Apparatus to control and visualize the impact of a high-energy laser pulse on a liquid target
We present an experimental apparatus to control and visualize the response of
a liquid target to a laser-induced vaporization. We use a millimeter-sized drop
as target and present two liquid-dye solutions that allow a variation of the
absorption coefficient of the laser light in the drop by seven orders of
magnitude. The excitation source is a Q-switched Nd:YAG laser at its
frequency-doubled wavelength emitting nanosecond pulses with energy densities
above the local vaporization threshold. The absorption of the laser energy
leads to a large-scale liquid motion at timescales that are separated by
several orders of magnitude, which we spatiotemporally resolve by a combination
of ultra-high-speed and stroboscopic high-resolution imaging in two orthogonal
views. Surprisingly, the large-scale liquid motion at upon laser impact is
completely controlled by the spatial energy distribution obtained by a precise
beam-shaping technique. The apparatus demonstrates the potential for accurate
and quantitative studies of laser-matter interactions.Comment: Submitted to Review of Scientific Instrument
Near-to mid-IR spectral purity transfer with a tunable frequency comb: methanol frequency metrology over a record frequency span
We report the development and operation of a frequency-comb-assisted
high-resolution mid-infrared molecular spectrometer combining high spectral
purity, SI-traceability, wide tunability and high sensitivity. An optical
frequency comb is used to transfer the spectral purity of a SI-traceable 1.54
m metrology-grade frequency reference to a 10.3 m quantum cascade
laser (QCL). The near-infrared reference is operated at the French
time/frequency metrology institute, calibrated there to primary frequency
standards, and transferred to Laboratoire de Physique des Lasers via the
REFIMEVE fiber network. The QCL exhibits a sub-10 --15 frequency stability from
0.1 to 10 s and its frequency is traceable to the SI with a total uncertainty
better than 4 x 10 --14 after 1-s averaging time. We have developed the
instrumentation allowing comb modes to be continuously tuned over 9 GHz
resulting in a QCL of record spectral purity uninterruptedly tunable at the
precision of the reference over an unprecedented span of 1.4 GHz. We have used
our apparatus to conduct sub-Doppler spectroscopy of methanol in a multi-pass
cell, demonstrating state-of-art frequency uncertainties down to the few
kilohertz level. We have observed weak intensity resonances unreported so far,
resolved subtle doublets never seen before and brought to light discrepancies
with the HITRAN database. This demonstrates the potential of our apparatus for
probing subtle internal molecular processes, building accurate spectroscopic
models of polyatomic molecules of atmospheric or astrophysical interest, and
carrying out precise spectroscopic tests of fundamental physics
Causes of early death and treatment-related death in newly diagnosed pediatric acute myeloid leukemia:Recent experiences of the Dutch Childhood Oncology Group
Background: With the current more effective treatment regimens for pediatric acute myeloid leukemia (AML), research on early death (ED), treatment-related mortality (TRM), and toxicity becomes increasingly important. The aim of this study was to give an overview of the frequency, clinical features, and risk factors associated with ED and TRM in first complete remission (CR1) during the last three consecutive treatment protocols of the Dutch Childhood Oncology Group (DCOG) between 1998 and 2014. Methods: Incidence and risk factors associated with ED and TRM in CR1 were retrospectively studied in 245 patients treated according to the Dutch ANLL-97/AML-12 (n = 118), AML-15 (n = 60), or DB AML-01 (n = 67) protocols. Results: The incidence of ED was, respectively, 5.1%, 6.7%, and 3.0% excluding deaths before treatment (P = NS), and 7.4%, 11.1%, and 4.4% including deaths before the onset of treatment. Severe underweight at initial diagnosis was significantly associated with more frequent ED. When relapse was included as a competing risk, cumulative incidence of death in CR1 were 5.9%, 5.0%, and 4.6% for ANLL97, AML15, and DB01, respectively (P = NS). The most important cause of TRM included infectious and SCT-related complications. Conclusion: We report relatively stable rates of ED and TRM in CR1 in the latest completed DCOG protocols for newly diagnosed AML patients. The most important causes of TRM were SCT- or infection-related, warranting further evaluation and awareness
Generalized eigenvalue-counting estimates for the Anderson model
We generalize Minami's estimate for the Anderson model and its extensions to
eigenvalues, allowing for arbitrary intervals and arbitrary single-site
probability measures with no atoms. As an application, we derive new results
about the multiplicity of eigenvalues and Mott's formula for the
ac-conductivity when the single site probability distribution is H\"older
continuous.Comment: Minor revisio
Possible Evidence for MeV Dark Matter In Dwarf Spheroidals
It has been recently proposed that the observed 511 keV emission from the
Galactic bulge could be the product of very light (1-100 MeV) annihilating dark
matter particles. Other possible explanations for this signal are associated
with stellar objects, such as hypernovae. In order to distinguish between
annihilating light dark matter scenario and more conventional astrophysical
sources for the bulge emission, we here propose the study of dwarf spheroidals
such as Sagittarius. These galaxies have typical luminosities of
but mass-to-light ratios of . As there are comparatively few stars,
the prospects for 511 keV emission from standard astrophysical scenarios are
minimal. The dwarf spheroidals do, however, contain copious amounts of dark
matter. INTEGRAL/SPI has observed the Sagittarius region. Analysis of this data
for 511 keV emission will provide a test of MeV dark matter which can
distinguish between annihilating dark matter and more standard astrophysics.
The observation of such a signal from Sagittarius should be a ``smoking gun''
for MeV dark matter.Comment: 4 pages, no figures. Version accepted by Physical Review Letter
Comparison of Pittsburgh compound B and florbetapir in cross-sectional and longitudinal studies.
IntroductionQuantitative in vivo measurement of brain amyloid burden is important for both research and clinical purposes. However, the existence of multiple imaging tracers presents challenges to the interpretation of such measurements. This study presents a direct comparison of Pittsburgh compound B-based and florbetapir-based amyloid imaging in the same participants from two independent cohorts using a crossover design.MethodsPittsburgh compound B and florbetapir amyloid PET imaging data from three different cohorts were analyzed using previously established pipelines to obtain global amyloid burden measurements. These measurements were converted to the Centiloid scale to allow fair comparison between the two tracers. The mean and inter-individual variability of the two tracers were compared using multivariate linear models both cross-sectionally and longitudinally.ResultsGlobal amyloid burden measured using the two tracers were strongly correlated in both cohorts. However, higher variability was observed when florbetapir was used as the imaging tracer. The variability may be partially caused by white matter signal as partial volume correction reduces the variability and improves the correlations between the two tracers. Amyloid burden measured using both tracers was found to be in association with clinical and psychometric measurements. Longitudinal comparison of the two tracers was also performed in similar but separate cohorts whose baseline amyloid load was considered elevated (i.e., amyloid positive). No significant difference was detected in the average annualized rate of change measurements made with these two tracers.DiscussionAlthough the amyloid burden measurements were quite similar using these two tracers as expected, difference was observable even after conversion into the Centiloid scale. Further investigation is warranted to identify optimal strategies to harmonize amyloid imaging data acquired using different tracers
The helicity amplitudes A and A for the D resonance obtained from the reaction}
The helicity dependence of the reaction
has been measured for the first time in the photon energy range from 550 to 790
MeV. The experiment, performed at the Mainz microtron MAMI, used a
4-detector system, a circularly polarized, tagged photon beam, and a
longitudinally polarized frozen-spin target. These data are predominantly
sensitive to the resonance and are used to determine its
parameters.Comment: 5 pages, 4 figure
Analysis of host responses to Mycobacterium tuberculosis antigens in a multi-site study of subjects with different TB and HIV infection states in sub-Saharan Africa.
BACKGROUND: Tuberculosis (TB) remains a global health threat with 9 million new cases and 1.4 million deaths per year. In order to develop a protective vaccine, we need to define the antigens expressed by Mycobacterium tuberculosis (Mtb), which are relevant to protective immunity in high-endemic areas. METHODS: We analysed responses to 23 Mtb antigens in a total of 1247 subjects with different HIV and TB status across 5 geographically diverse sites in Africa (South Africa, The Gambia, Ethiopia, Malawi and Uganda). We used a 7-day whole blood assay followed by IFN-γ ELISA on the supernatants. Antigens included PPD, ESAT-6 and Ag85B (dominant antigens) together with novel resuscitation-promoting factors (rpf), reactivation proteins, latency (Mtb DosR regulon-encoded) antigens, starvation-induced antigens and secreted antigens. RESULTS: There was variation between sites in responses to the antigens, presumably due to underlying genetic and environmental differences. When results from all sites were combined, HIV- subjects with active TB showed significantly lower responses compared to both TST(-) and TST(+) contacts to latency antigens (Rv0569, Rv1733, Rv1735, Rv1737) and the rpf Rv0867; whilst responses to ESAT-6/CFP-10 fusion protein (EC), PPD, Rv2029, TB10.3, and TB10.4 were significantly higher in TST(+) contacts (LTBI) compared to TB and TST(-) contacts fewer differences were seen in subjects with HIV co-infection, with responses to the mitogen PHA significantly lower in subjects with active TB compared to those with LTBI and no difference with any antigen. CONCLUSIONS: Our multi-site study design for testing novel Mtb antigens revealed promising antigens for future vaccine development. The IFN-γ ELISA is a cheap and useful tool for screening potential antigenicity in subjects with different ethnic backgrounds and across a spectrum of TB and HIV infection states. Analysis of cytokines other than IFN-γ is currently on-going to determine correlates of protection, which may be useful for vaccine efficacy trials
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