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

Search for neutron dark decay: n → χ + e⁺e⁻

In January, 2018, Fornal and Grinstein proposed that a previously unobserved neutron decay branch to a dark matter particle (χ) 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 χ along with an e⁺e⁻ 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 ∼ 4π 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 → p + e⁻ + ν̅_e decays. The summed kinetic energy (E_(e⁺e⁻)) from such events is reconstructed and used to set limits, as a function of the χ mass, on the branching fraction for this decay channel

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 $\mu$m has been achieved, which is equivalent to an UCN energy resolution below 2 pico-electron-volts through the relation $\delta E = m_0g \delta x$. Here, the symbols $\delta E$, $\delta x$, $m_0$ and $g$ 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

Surface State Recombination and Passivation in Nanocrystalline TiO₂ 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 Al₂O₃-coated TiO₂ photoanode achieved through atomic layer deposition (ALD). Electrochemical characterization, performed through impedance measurements and intensity modulated photovoltage spectroscopy (IMVS), data showed that the Al₂O₃ 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 Al₂O₃ 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 core–shell 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