462 research outputs found
Simulation Studies on Arrival Time Distributions of Cherenkov Photons in Extensive Air Showers
Atmospheric Cherenkov technique is an established methodology to study TeV
energy gamma rays. Here we carry out systematic monte carlo simulation studies
of the timing information of Cherenkov photons. Extensive studies have already
been carried out in this regard. Most of these are carried out at higher
energies with the aim of studying the elemental composition of cosmic rays.
However not much attention is paid to the species dependent signatures at TeV
energies. In this work, functional fits have been carried out to the spherical
Cherenkov shower fronts and the radii of curvature have been found to be equal
to the height of shower maximum irrespective of the species or the observation
level. Functional fits have also been carried out to describe the pulse shapes
at various core distances in terms of well known probability density
distribution functions (PDF). Two types of PDF's have been tried viz. gamma
function and lognormal function. The variation of the pulse shape parameters as
a function of primary energy, observation height and incident angles have been
studied. The possibility of deriving the pulse shape parameters like the rise &
decay times, full width at half maximum from the easily measurable quantities
like the mean and RMS variation of photon arrival times offers a very important
new technique which can be easily applied in an observation.Comment: 34 pages, 14 figures, accepted for publication in Astroparticle
Physic
Possible Discrimination between Gamma Rays and Hadrons using Cerenkov Photon Timing Measurements
Atmospheric \v{C}erenkov Technique is an established methodology to study
energy gamma rays. However the challenging problem has always been the
poor signal to noise ratio due to the presence of abundant cosmic rays. Several
ingenious techniques have been employed to alleviate this problem, most of
which are centred around the \v{C}erenkov image characteristics. However there
are not many techniques available for improving the signal to noise ratio of
the data from wavefront sampling observations. One such possible technique is
to use the \v{C}erenkov photon arrival times and identify the species dependent
characteristics in them. Here we carry out systematic monte carlo simulation
studies of the timing information of \v{C}erenkov photons at the observation
level. We have parameterized the shape of the \v{C}erenkov shower front as well
as the pulse shapes in terms of experimentally measurable quantities. We
demonstrate the sensitivity of the curvature of the shower front, pulse shape
parameters as well as the photon arrival time jitter to primary species and
show their efficiency in improving the signal to noise ratio. The effect of
limiting the \v{C}erenkov telescope opening angle by using a circular focal
point mask, onthe efficacy of the parameters has also been studied for each of
the parameters. Radius of the shower front, pulse decay time and photon arrival
time jitter have been found to be the most promising parameters which could be
used to discriminate ray events from the background. We also find
that the efficiency of the first two parameters increases with zenith angle and
efficiency of pulse decay time decreases with increasing altitude of
observation.Comment: 30 pages, 5 postscript figures, uses elsart.sty; To appear in
Astroparticle Physic
Immune-mediated effects of microplanar radiotherapy with a small animal irradiator
Spatially fractionated radiotherapy has been shown to have effects on the immune system that differ from conventional radiotherapy (CRT). We compared several aspects of the immune response to CRT relative to a model of spatially fractionated radiotherapy (RT), termed microplanar radiotherapy (MRT). MRT delivers hundreds of grays of radiation in submillimeter beams (peak), separated by non-radiated volumes (valley). We have developed a preclinical method to apply MRT by a commercial small animal irradiator. Using a B16-F10 murine melanoma model, we first evaluated the in vitro and in vivo effect of MRT, which demonstrated significant treatment superiority relative to CRT. Interestingly, we observed insignificant treatment responses when MRT was applied to Ragâ/â and CD8-depleted mice. An immuno-histological analysis showed that MRT recruited cytotoxic lymphocytes (CD8), while suppressing the number of regulatory T cells (Tregs). Using RT-qPCR, we observed that, compared to CRT, MRT, up to the dose that we applied, significantly increased and did not saturate CXCL9 expression, a cytokine that plays a crucial role in the attraction of activated T cells. Finally, MRT combined with anti-CTLA-4 ablated the tumor in half of the cases, and induced prolonged systemic antitumor immunity
The local adsorption geometry of benzenethiolate on Cu(1 0 0)
The local adsorption geometry of benzenethiolate in the ordered c(2 Ă 6) phase on Cu(1 0 0) has been investigated by a combination of S K-edge near-edge X-ray absorption fine structure (NEXAFS), normal incidence X-ray standing waves (NIXSW) and S 1s scanned-energy mode photoelectron diffraction (PhD). NEXAFS and PhD show that the molecular plane is tilted from the surface normal by 20 ± 15°, while NIXSW clearly identifies the S head-group as occupying the four-fold coordinated hollow sites. PhD shows the S atoms lies 1.34 ± 0.04 Ă
above the outermost Cu atomic layer, leading to a CuâS bondlength of 2.25 ± 0.02 Ă
. The combination of the PhD and NIXSW results shows the Cu surface layer has an outward relaxation of 0.15 ± 0.06 Ă
. Possible origins for this large adsorbate-induced relaxation are discussed
Re-Shape: A Method to Teach Data Ethics for Data Science Education
Data has become central to the technologies and services that human-computer interaction (HCI) designers make, and the ethical use of data in and through these technologies should be given critical attention throughout the design process. However, there is little research on ethics education in computer science that explicitly addresses data ethics. We present and analyze Re-Shape, a method to teach students about the ethical implications of data collection and use. Re-Shape, as part of an educational environment, builds upon the idea of cultivating care and allows students to collect, process, and visualizetheir physical movement data in ways that support critical reflection and coordinated classroom activities about data, data privacy, and human-centered systems for data science. We also use a case study of Re-Shape in an undergraduate computer science course to explore prospects and limitations of instructional designs and educational technology such as Re-Shape that leverage personal data to teach data ethics
Towards an interoperable ecosystem of AI and LT platforms : a roadmap for the implementation of different levels of interoperability
With regard to the wider area of AI/LT platform interoperability, we concentrate on two core aspects: (1) cross-platform search and discovery of resources and services; (2) composition of cross-platform service workflows. We devise five different levels (of increasing complexity) of platform interoperability that we suggest to implement in a wider federation of AI/LT platforms. We illustrate the approach using the five emerging AI/LT platforms AI4EU, ELG, Lynx, QURATOR and SPEAKER
Strange Hadronic Loops of the Proton: A Quark Model Calculation
Nontrivial sea effects have their origin in the low- dynamics
of strong QCD. We present here a quark model calculation of the contribution of
pairs arising from a {\it complete} set of OZI-allowed strong
hadronic loops to the net spin of the proton, to its charge radius,
and to its magnetic moment. The calculation is performed in an ``unquenched
quark model" which has been shown to preserve the spectroscopic successes of
the naive quark model and to respect the OZI rule. We speculate that an
extension of the calculation to the nonstrange sea will show that most of the
``missing spin" of the proton is in orbital angular momenta.Comment: revtex, 34 pages, 4 figure
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