86 research outputs found
Measurement of 1.7 to 74 MeV polarised gamma rays with the HARPO TPC
Current {\gamma}-ray telescopes based on photon conversions to
electron-positron pairs, such as Fermi, use tungsten converters. They suffer of
limited angular resolution at low energies, and their sensitivity drops below 1
GeV. The low multiple scattering in a gaseous detector gives access to higher
angular resolution in the MeV-GeV range, and to the linear polarisation of the
photons through the azimuthal angle of the electron-positron pair.
HARPO is an R&D program to characterise the operation of a TPC (Time
Projection Chamber) as a high angular-resolution and sensitivity telescope and
polarimeter for {\gamma} rays from cosmic sources. It represents a first step
towards a future space instrument. A 30 cm cubic TPC demonstrator was built,
and filled with 2 bar argon-based gas. It was put in a polarised {\gamma}-ray
beam at the NewSUBARU accelerator in Japan in November 2014. Data were taken at
different photon energies from 1.7 MeV to 74 MeV, and with different
polarisation configurations. The electronics setup is described, with an
emphasis on the trigger system. The event reconstruction algorithm is quickly
described, and preliminary measurements of the polarisation of 11 MeVphotons
are shown.Comment: Proceedings VCI201
One-dimensional Topological Edge States of Bismuth Bilayers
The hallmark of a time-reversal symmetry protected topologically insulating
state of matter in two-dimensions (2D) is the existence of chiral edge modes
propagating along the perimeter of the system. To date, evidence for such
electronic modes has come from experiments on semiconducting heterostructures
in the topological phase which showed approximately quantized values of the
overall conductance as well as edge-dominated current flow. However, there have
not been any spectroscopic measurements to demonstrate the one-dimensional (1D)
nature of the edge modes. Among the first systems predicted to be a 2D
topological insulator are bilayers of bismuth (Bi) and there have been recent
experimental indications of possible topological boundary states at their
edges. However, the experiments on such bilayers suffered from irregular
structure of their edges or the coupling of the edge states to substrate's bulk
states. Here we report scanning tunneling microscopy (STM) experiments which
show that a subset of the predicted Bi-bilayers' edge states are decoupled from
states of Bi substrate and provide direct spectroscopic evidence of their 1D
nature. Moreover, by visualizing the quantum interference of edge mode
quasi-particles in confined geometries, we demonstrate their remarkable
coherent propagation along the edge with scattering properties that are
consistent with strong suppression of backscattering as predicted for the
propagating topological edge states.Comment: 15 pages, 5 figures, and supplementary materia
The unprecedented optical outburst of the quasar 3C 454.3. The WEBT campaign of 2004-2005
The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting
more than 1 year and culminating in spring 2005. The maximum brightness
detected was R = 12.0, which represents the most luminous quasar state thus far
observed (M_B ~ -31.4). In order to follow the emission behaviour of the source
in detail, a large multiwavelength campaign was organized by the Whole Earth
Blazar Telescope (WEBT). Continuous optical, near-IR and radio monitoring was
performed in several bands. ToO pointings by the Chandra and INTEGRAL
satellites provided additional information at high energies in May 2005. The
historical radio and optical light curves show different behaviours. Until
about 2001.0 only moderate variability was present in the optical regime, while
prominent and long-lasting radio outbursts were visible at the various radio
frequencies, with higher-frequency variations preceding the lower-frequency
ones. After that date, the optical activity increased and the radio flux is
less variable. This suggests that the optical and radio emissions come from two
separate and misaligned jet regions, with the inner optical one acquiring a
smaller viewing angle during the 2004-2005 outburst. Moreover, the colour-index
behaviour (generally redder-when-brighter) during the outburst suggests the
presence of a luminous accretion disc. A huge mm outburst followed the optical
one, peaking in June-July 2005. The high-frequency (37-43 GHz) radio flux
started to increase in early 2005 and reached a maximum at the end of our
observing period (end of September 2005). VLBA observations at 43 GHz during
the summer confirm theComment: 7 pages, 4 figures, to be published in A&
The WEBT Campaign on the Blazar 3C279 in 2006
The quasar 3C279 was the target of an extensive multiwavelength monitoring
campaign from January through April 2006, including an optical-IR-radio
monitoring campaign by the Whole Earth Blazar Telescope (WEBT) collaboration.
In this paper we focus on the results of the WEBT campaign. The source
exhibited substantial variability of optical flux and spectral shape, with a
characteristic time scale of a few days. The variability patterns throughout
the optical BVRI bands were very closely correlated with each other. In
intriguing contrast to other (in particular, BL Lac type) blazars, we find a
lag of shorter- behind longer-wavelength variability throughout the RVB ranges,
with a time delay increasing with increasing frequency. Spectral hardening
during flares appears delayed with respect to a rising optical flux. This, in
combination with the very steep IR-optical continuum spectral index of ~ 1.5 -
2.0, may indicate a highly oblique magnetic field configuration near the base
of the jet. An alternative explanation through a slow (time scale of several
days) acceleration mechanism would require an unusually low magnetic field of <
0.2 G, about an order of magnitude lower than inferred from previous analyses
of simultaneous SEDs of 3C279 and other FSRQs with similar properties.Comment: Accepted for publication in Ap
Novel H6PDH mutations in two girls with premature adrenarche: 'apparent' and 'true' CRD can be differentiated by urinary steroid profiling.
Inactivating mutations in the enzyme hexose-6-phosphate dehydrogenase (H6PDH, encoded by H6PD) cause apparent cortisone reductase deficiency (ACRD). H6PDH generates cofactor NADPH for 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1, encoded by HSD11B1) oxo-reductase activity, converting cortisone to cortisol. Inactivating mutations in HSD11B1 cause true cortisone reductase deficiency (CRD). Both ACRD and CRD present with hypothalamic-pituitary-adrenal (HPA) axis activation and adrenal hyperandrogenism. To describe the clinical, biochemical and molecular characteristics of two additional female children with ACRD and to illustrate the diagnostic value of urinary steroid profiling in identifying and differentiating a total of six ACRD and four CRD cases. Clinical, biochemical and genetic assessment of two female patients presenting during childhood. In addition, results of urinary steroid profiling in a total of ten ACRD/CRD patients were compared to identify distinguishing characteristics. Case 1 was compound heterozygous for R109AfsX3 and a novel P146L missense mutation in H6PD. Case 2 was compound heterozygous for novel nonsense mutations Q325X and Y446X in H6PD. Mutant expression studies confirmed loss of H6PDH activity in both cases. Urinary steroid metabolite profiling by gas chromatography/mass spectrometry suggested ACRD in both cases. In addition, we were able to establish a steroid metabolite signature differentiating ACRD and CRD, providing a basis for genetic diagnosis and future individualised management. Steroid profile analysis of a 24-h urine collection provides a diagnostic method for discriminating between ACRD and CRD. This will provide a useful tool in stratifying unresolved adrenal hyperandrogenism in children with premature adrenarche and adult females with polycystic ovary syndrome (PCOS)
Observation of weak neutral current neutrino production of
Observation of \jpsi production by neutrinos in the calorimeter of the CHORUS detector exposed to the CERN SPS wide-band \numu beam is reported. A spectrum-averaged cross-section = (6.3 3.0) is obtained for 20 GeV 200 GeV. The data are compared with the theoretical model based on the QCD Z-gluon fusion mechanism
The CHORUS neutrino oscillation search experiment
The CHORUS experiment has successfully finished run I (320~000 recorded \numu\ CC in 94/95) and performed half of run II (225~000 \numu\ CC in 96). The analysis chain was exercised on a small data sample for the muonic \tdecay\ search using for the first time fully automatic emulsion scanning. This pilot analysis, resulting in a limit \sintth \leq 3 \cdot 10^{-2}, confirms that the CHORUS proposal sensitivity (\sintth \leq 3 \cdot 10^{-4}) is within reach in two years
Aspects of the encephalitis epidemic caused by arbovirus in the Ribeira Valley, S. Paulo, Brazil, during 1975-1978
In 1975, 1976, and 1977, arbovirus caused an encephalitis epidemic in the Ribeira Valley in the state of S. Paulo. The epidemic would peak when the temperature and pluvial levels were higher. From 1978 on the disease maintained low levels within a presumed endemic zone. The epidemic had swept from east to west and from east to southwest in a wave toward the neighboring coastal region. The mountain chain to the north and northwest acted as a barrier. It was only logical natural that the hypothesis that the etiological agent, arbovirus Rocio may have recently infected the human population be considered. Mosquitos must have transmitted the infection from birds and small mammals in nearby forests. Probable forms of transmission of arboviroses in the home are also discussed in this article as well as the fact that population groups that presented the worst forms of the disease were the very young, and the very old and those living in the worst conditions. The epidemiological perspective of the arboviroses is that it persists in this area because the area presents excellent conditions for the development of the etiological agent - reservoirs and biological vectors, with a continuous supply of susceptible people, migrants or tourists.Foi realizado estudo epidemiológico da encefalite por arbovirus na região do Vale do Ribeira, S. Paulo, Brasil. Uma epidemia da moléstia ocorreu em 1975, 1976 e 1977, com picos nas épocas de maior temperatura e pluviosidade. A partir de 1978 a moléstia manteve-se em níveis baixos numa presumível ende-micidade. A epidemia se deslocou em onda em direção leste-oeste e leste-sudoeste para a região litorânea vizinha. A cadeia montanhosa situada ao norte e noroeste atuou como barreira à propagação da moléstia. Considerou-se a hipótese que o agente etiológico, arbovirus Rocio, deva ter começado a infectar a população humana recentemente, tendo sido veiculado ao homem de reservatórios silvestres, aves e pequenos mamíferos, por culicídeos silvestres. Discutiu-se também prováveis formas de transmissão domiciliar. Verificou-se que os grupos populacionais que apresentaram as formas mais graves foram os de idades extremas e os que apresentavam piores condições de vida. Considerou-se que a perspectiva epidemiológica desta arbovirose é que ela persista na região, uma vez que a mesma apresenta condições ótimas para o desenvolvimento do agente etiológico, dos reservatórios e dos vetores biológicos, além de receber um contínuo afluxo de população suscetível, migrantes ou turistas
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