20,215 research outputs found
Guide for third and fourth year students
Advice complied by Boston University School of Medicine students for incoming first year students and third or fourth year students preparing for clinical rotations
A flexible scintillation light apparatus for rare event searches
Compelling experimental evidences of neutrino oscillations and their
implication that neutrinos are massive particles have given neutrinoless double
beta decay a central role in astroparticle physics. In fact, the discovery of
this elusive decay would be a major breakthrough, unveiling that neutrino and
antineutrino are the same particle and that the lepton number is not conserved.
It would also impact our efforts to establish the absolute neutrino mass scale
and, ultimately, understand elementary particle interaction unification. All
current experimental programs to search for neutrinoless double beta decay are
facing with the technical and financial challenge of increasing the
experimental mass while maintaining incredibly low levels of spurious
background. The new concept described in this paper could be the answer which
combines all the features of an ideal experiment: energy resolution, low cost
mass scalability, isotope choice flexibility and many powerful handles to make
the background negligible. The proposed technology is based on the use of
arrays of silicon detectors cooled to 120 K to optimize the collection of the
scintillation light emitted by ultra-pure crystals. It is shown that with a 54
kg array of natural CaMoO4 scintillation detectors of this type it is possible
to yield a competitive sensitivity on the half-life of the neutrinoless double
beta decay of 100Mo as high as ~10E24 years in only one year of data taking.
The same array made of 40CaMoO4 scintillation detectors (to get rid of the
continuous background coming from the two neutrino double beta decay of 48Ca)
will instead be capable of achieving the remarkable sensitivity of ~10E25 years
on the half-life of 100Mo neutrinoless double beta decay in only one year of
measurement.Comment: 12 pages, 4 figures. Prepared for submission to EPJ
The Fast and the Flexible: training neural networks to learn to follow instructions from small data
Learning to follow human instructions is a long-pursued goal in artificial
intelligence. The task becomes particularly challenging if no prior knowledge
of the employed language is assumed while relying only on a handful of examples
to learn from. Work in the past has relied on hand-coded components or manually
engineered features to provide strong inductive biases that make learning in
such situations possible. In contrast, here we seek to establish whether this
knowledge can be acquired automatically by a neural network system through a
two phase training procedure: A (slow) offline learning stage where the network
learns about the general structure of the task and a (fast) online adaptation
phase where the network learns the language of a new given speaker. Controlled
experiments show that when the network is exposed to familiar instructions but
containing novel words, the model adapts very efficiently to the new
vocabulary. Moreover, even for human speakers whose language usage can depart
significantly from our artificial training language, our network can still make
use of its automatically acquired inductive bias to learn to follow
instructions more effectively
LArPix: Demonstration of low-power 3D pixelated charge readout for liquid argon time projection chambers
We report the demonstration of a low-power pixelated readout system designed
for three-dimensional ionization charge detection and digital readout of liquid
argon time projection chambers (LArTPCs). Unambiguous 3D charge readout was
achieved using a custom-designed system-on-a-chip ASIC (LArPix) to uniquely
instrument each pad in a pixelated array of charge-collection pads. The LArPix
ASIC, manufactured in 180 nm bulk CMOS, provides 32 channels of
charge-sensitive amplification with self-triggered digitization and multiplexed
readout at temperatures from 80 K to 300 K. Using an 832-channel LArPix-based
readout system with 3 mm spacing between pads, we demonstrated low-noise
(500 e RMS equivalent noise charge) and very low-power (100
W/channel) ionization signal detection and readout. The readout was used
to successfully measure the three-dimensional ionization distributions of
cosmic rays passing through a LArTPC, free from the ambiguities of existing
projective techniques. The system design relies on standard printed circuit
board manufacturing techniques, enabling scalable and low-cost production of
large-area readout systems using common commercial facilities. This
demonstration overcomes a critical technical obstacle for operation of LArTPCs
in high-occupancy environments, such as the near detector site of the Deep
Underground Neutrino Experiment (DUNE).Comment: 19 pages, 10 figures, 1 ancillary animation. V3 includes minor
revisions based on referee comment
Assessment on the feasibility of future shepherding of asteroid resources
Most plausible futures for space exploration and exploitation require a large mass in Earth orbit. Delivering this mass requires overcoming the Earth's natural gravity well, which imposes a distinct obstacle to any future space venture. An alternative solution is to search for more accessible resources elsewhere. In particular, this paper examines the possibility of future utilisation of near Earth asteroid resources. The accessibility of asteroid material can be estimated by analysing the volume of Keplerian orbital element space from which Earth can be reached under a certain energy threshold and then by mapping this analysis onto an existing statistical near Earth asteroid (NEA) model. Earth is reached through orbital transfers defined by a series of impulsive manoeuvres and computed using the patched-conic approximation. The NEA model allows an estimation of the probability of finding an object that could be transferred with a given Îv budget. For the first time, a resource map provides a realistic assessment of the mass of material resources in near Earth space as a function of energy investment. The results show that there is a considerable mass of resources that can be accessed and exploited at relatively low levels of energy. More importantly, asteroid resources can be accessed with a entire spectrum of levels of energy, unlike other more massive bodies such as the Earth or Moon, which require a minimum energy threshold implicit in their gravity well. With this resource map, the total change of velocity required to capture an asteroid, or transfer its resources to Earth, can be estimated as a function of object size. Thus, realistic examples of asteroid resource utilisation can be provided
- âŠ