621 research outputs found
Weak Gravity Conjecture and Holographic Dark Energy Model with Interaction and Spatial Curvature
In the paper, we apply the weak gravity conjecture to the holographic
quintessence model of dark energy. Three different holographic dark energy
models are considered: without the interaction in the non-flat universe; with
interaction in the flat universe; with interaction in the non-flat universe. We
find that only in the models with the spatial curvature and interaction term
proportional to the energy density of matter, it is possible for the weak
gravity conjecture to be satisfied.Comment: 14 pages, 7 figures, typographical errors are corrected; conclusin is
unchange
Simulation of the thermally induced austenitic phase transition in NiTi nanoparticles
The reverse martensitic ("austenitic") transformation upon heating of
equiatomic nickel-titanium nanoparticles with diameters between 4 and 17 nm is
analyzed by means of molecular-dynamics simulations with a semi-empirical model
potential. After constructing an appropriate order parameter to distinguish
locally between the monoclinic B19' at low and the cubic B2 structure at high
temperatures, the process of the phase transition is visualized. This shows a
heterogeneous nucleation of austenite at the surface of the particles, which
propagates to the interior by plane sliding, explaining a difference in
austenite start and end temperatures. Their absolute values and dependence on
particle diameter are obtained and related to calculations of the surface
induced size dependence of the difference in free energy between austenite and
martensite.Comment: 6 pages, 4 figures, accepted for publication in "The European
Physical Journal B
Wideband THz time domain spectroscopy based on optical rectification and electro-optic sampling
We present an analytical model describing the full electromagnetic propagation in a THz time-domain spectroscopy (THz-TDS) system, from the THz pulses via Optical Rectification to the detection via Electro Optic-Sampling. While several investigations deal singularly with the many elements that constitute a THz-TDS, in our work we pay particular attention to the modelling of the time-frequency behaviour of all the stages which compose the experimental set-up. Therefore, our model considers the following main aspects: (i) pump beam focusing into the generation crystal; (ii) phase-matching inside both the generation and detection crystals; (iii) chromatic dispersion and absorption inside the crystals; (iv) Fabry-Perot effect; (v) diffraction outside, i.e. along the propagation, (vi) focalization and overlapping between THz and probe beams, (vii) electro-optic sampling. In order to validate our model, we report on the comparison between the simulations and the experimental data obtained from the same set-up, showing their good agreement
Fast Photon Detection for Particle Identification with COMPASS RICH-1
Particle identification at high rates is an important challenge for many
current and future high-energy physics experiments. The upgrade of the COMPASS
RICH-1 detector requires a new technique for Cherenkov photon detection at
count rates of several per channel in the central detector region, and a
read-out system allowing for trigger rates of up to 100 kHz. To cope with these
requirements, the photon detectors in the central region have been replaced
with the detection system described in this paper. In the peripheral regions,
the existing multi-wire proportional chambers with CsI photocathode are now
read out via a new system employing APV pre-amplifiers and flash ADC chips. The
new detection system consists of multi-anode photomultiplier tubes (MAPMT) and
fast read-out electronics based on the MAD4 discriminator and the F1-TDC chip.
The RICH-1 is in operation in its upgraded version for the 2006 CERN SPS run.
We present the photon detection design, constructive aspects and the first
Cherenkov light in the detector.Comment: Proceedings of the Imaging 2006 conference, Stockholm, Sweden, 27-30
June 2006, 5 pages, 6 figures, to appear in NIM A; corrected typo in caption
of Fig.
Fast photon detection for the COMPASS RICH detector
The COMPASS experiment at the SPS accelerator at CERN uses a large scale Ring
Imaging CHerenkov detector (RICH) to identify pions, kaons and protons in a
wide momentum range. For the data taking in 2006, the COMPASS RICH has been
upgraded in the central photon detection area (25% of the surface) with a new
technology to detect Cherenkov photons at very high count rates of several 10^6
per second and channel and a new dead-time free read-out system, which allows
trigger rates up to 100 kHz. The Cherenkov photons are detected by an array of
576 visible and ultra-violet sensitive multi-anode photomultipliers with 16
channels each. The upgraded detector showed an excellent performance during the
2006 data taking.Comment: Proceeding of the IPRD06 conference (Siena, Okt. 06
Variability in organ-specific EGFR mutational spectra in tumour epithelium and stroma may be the biological basis for differential responses to tyrosine kinase inhibitors
Organ-specific differences in epidermal growth factor receptor (EGFR) mutational spectra and frequencies were found in lung cancer and sporadic and BRCA1/2-related breast cancers. Additionally, we found a high frequency of EGFR mutations in the tumour stroma of these invasive breast carcinomas. Those organ-specific mutational spectra and potential targets in the cancer-associated stroma might influence the efficacy of TKI therapy
First Measurement of Chiral Dynamics in \pi^- \gamma -> \pi^- \pi^- \pi^+
The COMPASS collaboration at CERN has investigated the \pi^- \gamma -> \pi^-
\pi^- \pi^+ reaction at center-of-momentum energy below five pion masses,
sqrt(s) < 5 m(\pi), embedded in the Primakoff reaction of 190 GeV pions
impinging on a lead target. Exchange of quasi-real photons is selected by
isolating the sharp Coulomb peak observed at smallest momentum transfers, t' <
0.001 (GeV/c)^2. Using partial-wave analysis techniques, the scattering
intensity of Coulomb production described in terms of chiral dynamics and its
dependence on the 3\pi-invariant mass m(3\pi) = sqrt(s) were extracted. The
absolute cross section was determined in seven bins of with an
overall precision of 20%. At leading order, the result is found to be in good
agreement with the prediction of chiral perturbation theory over the whole
energy range investigated.Comment: 10 pages, 5 figure
The Fast Read-out System for the MAPMTs of COMPASS RICH-1
A fast readout system for the upgrade of the COMPASS RICH detector has been
developed and successfully used for data taking in 2006 and 2007. The new
readout system for the multi-anode PMTs in the central part of the photon
detector of the RICH is based on the high-sensitivity MAD4
preamplifier-discriminator and the dead-time free F1-TDC chip characterized by
high-resolution. The readout electronics has been designed taking into account
the high photon flux in the central part of the detector and the requirement to
run at high trigger rates of up to 100 kHz with negligible dead-time. The
system is designed as a very compact setup and is mounted directly behind the
multi-anode photomultipliers. The data are digitized on the frontend boards and
transferred via optical links to the readout system. The read-out electronics
system is described in detail together with its measured performances.Comment: Proceeding of RICH2007 Conference, Trieste, Oct. 2007. v2: minor
change
- …