35 research outputs found
Cavallo's Multiplier for in situ Generation of High Voltage
A classic electrostatic induction machine, Cavallo's multiplier, is suggested
for in situ production of very high voltage in cryogenic environments. The
device is suitable for generating a large electrostatic field under conditions
of very small load current. Operation of the Cavallo multiplier is analyzed,
with quantitative description in terms of mutual capacitances between
electrodes in the system. A demonstration apparatus was constructed, and
measured voltages are compared to predictions based on measured capacitances in
the system. The simplicity of the Cavallo multiplier makes it amenable to
electrostatic analysis using finite element software, and electrode shapes can
be optimized to take advantage of a high dielectric strength medium such as
liquid helium. A design study is presented for a Cavallo multiplier in a
large-scale, cryogenic experiment to measure the neutron electric dipole
moment.Comment: 9 pages, 10 figure
An offloading method using decentralized P2P-enabled mobile edge servers in edge computing
Edge computing has emerged as a promising infrastructure for providing elastic resources in the proximity of mobile users. Owing to resource limitations in mobile devices, offloading several computational tasks from mobile devices to mobile edge servers is the main means of improving the quality of experience of mobile users. In fact, because of the high speeds of moving vehicles on expressways, there would be numerous candidate mobile edge servers available for them to offload their computational workload. However, the selection of the mobile edge server to be utilized and how much computation should be offloaded to meet the corresponding task deadlines without large computing bills are topics that have not been discussed much. Furthermore, with the increasing deployment of mobile edge servers, their centralized management would cause certain performance issues. In order to address these challenges, we firstly apply peer-to-peer networks to manage geo-distributed mobile edge servers. Secondly, we propose a new deadline-aware and cost-effective offloading approach, which aims to improve the offloading efficiency for vehicles and allows additional tasks to meet their deadlines. The proposed approach was validated for its feasibility and efficiency by means of extensive experiments, which are presented in this paper
Position-sensitive detection of ultracold neutrons with an imaging camera and its implications to spectroscopy
Position-sensitive detection of ultracold neutrons (UCNs) is demonstrated
using an imaging charge-coupled device (CCD) camera. A spatial resolution less
than 15 m has been achieved, which is equivalent to an UCN energy
resolution below 2 pico-electron-volts through the relation . Here, the symbols , , and are the
energy resolution, the spatial resolution, the neutron rest mass and the
gravitational acceleration, respectively. A multilayer surface convertor
described previously is used to capture UCNs and then emits visible light for
CCD imaging. Particle identification and noise rejection are discussed through
the use of light intensity profile analysis. This method allows different types
of UCN spectroscopy and other applications.Comment: 12 figures, 28 pages, accepted for publication in NIM
Search for neutron dark decay: nāāāĻā+āeāŗeā»
In January, 2018, Fornal and Grinstein proposed that a previously unobserved neutron decay branch to a dark matter particle (Ļ) could account for the discrepancy in the neutron lifetime observed in two different types of experiments. One of the possible final states discussed includes a single Ļ along with an eāŗeā» pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with ā¼ 4Ļ acceptance using a pair of detectors that observe a volume of stored Ultracold Neutrons (UCNs). We use the timing information of coincidence events to select candidate dark sector particle decays by applying a timing calibration and selecting events within a physically-forbidden timing region for conventional n ā p + eā» + Ī½Ģ
_e decays. The summed kinetic energy (E_(eāŗeā»)) from such events is reconstructed and used to set limits, as a function of the Ļ mass, on the branching fraction for this decay channel
Surface State Recombination and Passivation in Nanocrystalline TiO<sub>2</sub> Dye-Sensitized Solar Cells
The
relative role of surface state recombination in dye-sensitized solar
cells is not fully understood, yet reductions in the recombination
rate are frequently attributed to the passivation of surface states.
We have investigated reports of trap state passivation using an Al<sub>2</sub>O<sub>3</sub>-coated TiO<sub>2</sub> photoanode achieved through
atomic layer deposition (ALD). Electrochemical characterization, performed
through impedance measurements and intensity modulated photovoltage
spectroscopy (IMVS), data showed that the Al<sub>2</sub>O<sub>3</sub> deposition successfully blocked electron recombination and that
the chemical capacitance of the film was unchanged after the ALD treatment.
A theoretical model outlining the recombination kinetics was applied
to the experimental data to obtain charge transfer rates from conduction
band states, exponentially distributed traps, and monoenergetic traps.
The determined electron transfer rates showed that the deposited Al<sub>2</sub>O<sub>3</sub> coating did not selectively passivate trap states
at the nanoparticle surface but reduced recombination rates equally
from both conduction band states and surface states. These results
imply that the reduction in the recombination rates reported in coreāshell
structured photoanodes cannot be attributed to a modification of surface
traps, but rather to the weakened electronic coupling between electrons
in the film and the electrolyte species