2,394 research outputs found
Antimatter research in Space
Two of the most compelling issues facing astrophysics and cosmology today are
to understand the nature of the dark matter that pervades the universe and to
understand the apparent absence of cosmological antimatter. For both issues,
sensitive measurements of cosmic-ray antiprotons and positrons, in a wide
energy range, are crucial. Many different mechanisms can contribute to
antiprotons and positrons production, ranging from conventional reactions up to
exotic processes like neutralino annihilation. The open problems are so
fundamental (i.e.: is the universe symmetric in matter and antimatter ?) that
experiments in this field will probably be of the greatest interest in the next
years. Here we will summarize the present situation, showing the different
hypothesis and models and the experimental measurements needed to lead to a
more established scenario.Comment: 10 pages, 7 figures, Invited talk at the 18th European Cosmic Ray
Symposium, Moscow, July 2002, submitted to Journal of Physics
Crowd-Centric Counting via Unsupervised Learning
Counting targets (people or things) within a moni-tored area is an important task in emerging wireless applications,including those for smart environments, safety, and security.Conventional device-free radio-based systems for counting targetsrely on localization and data association (i.e., individual-centric information) to infer the number of targets present in an area(i.e., crowd-centric information). However, many applications(e.g., affluence analytics) require only crowd-centric rather than individual-centric information. Moreover, individual-centric approaches may be inadequate due to the complexity of data association. This paper proposes a new technique for crowd-centric counting of device-free targets based on unsupervised learning, where the number of targets is inferred directly from a low-dimensional representation of the received waveforms. The proposed technique is validated via experimentation using an ultra-wideband sensor radar in an indoor environment.RYC-2016-1938
The primordial environment of super massive black holes: large scale galaxy overdensities around QSOs with LBT
We investigated the presence of galaxy overdensities around four
QSOs, namely SDSS J1030+0524 (z = 6.28), SDSS J1148+5251 (z = 6.41), SDSS
J1048+4637 (z = 6.20) and SDSS J1411+1217 (z = 5.95), through deep -, -
and - band imaging obtained with the wide-field () Large
Binocular Camera (LBC) at the Large Binocular Telescope (LBT). We adopted
color-color selections within the vs plane to identify samples of
-band dropouts at the QSO redshift and measure their relative abundance and
spatial distribution in the four LBC fields, each covering
physical Mpc at . The same selection criteria were then applied to
-band selected sources in the 1 deg Subaru-XMM Newton Deep Survey
to derive the expected number of dropouts over a blank LBC-sized field
(0.14 deg). The four observed QSO fields host a number of candidates
larger than what is expected in a blank field. By defining as -band dropouts
objects with and undetected in the -band, we found
16, 10, 9, 12 dropouts in SDSS J1030+0524, SDSS J1148+5251, SDSS J1048+4637,
and SDSS J1411+1217, respectively, whereas only 4.3 such objects are expected
over a 0.14 deg blank field. This corresponds to overdensity significances
of 3.3, 1.9, 1.7, 2.5, respectively. By considering the total number of
dropouts in the four LBC fields and comparing it with what is expected in four
blank fields of 0.14 deg each, we find that high-z QSOs reside in overdense
environments at the level. This is the first direct and unambiguous
measurement of the large scale structures around QSOs. [shortened]Comment: 12 pages, 8 figures. Accepted for publication in A&
The Thermal Diffusivity of Biochar Coating Deposited on a Heat Exchanger †
Biochar is a charcoal-like material obtained by burning organic wastes, coming from agricultural and forestry, in a controlled pyrolysis process. In this application, it is deposited on an aluminum foil of thickness 100 μm, which is used as a part of an heat exchanger. The thickness of the deposition of biochar on the aluminum foil ranges from 75 to 250 μm. The result coating is rough and, therefore, it is supposed to improve the heat exchange with the ambient environment, depending on the granulometry of the deposit. One key feature of the deposit is its thermal conductivity. In this work, it is determined by means of IR thermography used as a detector in a Laser Flash configuration. This allows us to evaluate the out-of-plane thermal diffusivity. Such measurements are complemented by density obtained by hydrostatic balance and specific heat by a differential scanning calorimeter
Domestic heating: Can hemp-hurd derived pellet be an alternative?
Among the renewable sources, residual woody biomass from agricultural crops is becoming of great interest due to its lower environmental impact and one of the most growing agricultural sector, of the last decade, is the hemp industry which generates several kind of byproducts. In this paper, a blend of 50% of hemp-hurd and 50% of fir sawdust was pulverized and pelletized. The pellets were burned into a domestic pellet stove (9 kWth maximum nominal thermal power output) at different biomass flowrates. To compare results with a commercial-grade pellet, the tests were repeated by fueling the same stove with A2-grade pellets. Results shown that the pellet mixture 50/50 of fir sawdust and hemp-hurd is suitable for the commercial pellet stove used and that the slightly higher amount of ashes (2.7%), compared to pellet A2 (<1.2%), can be handled by the self-cleaning fire chamber. Comparable results were also obtained in regards with the stove global efficiency which ranged from 90.8-92.3% for the hemp pellets and 91-94% for the A2. A significant difference was noted in the biomass flowrate where, during the tests with hemp-hurd pellets a lower value was obtained (-20%) compared to A2. This resulted into lower power input in the stove and lower performances at the same nominal power output
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