Voluminous D2 source for intense cold neutron beam production at the ESS

The development of the flat moderator concept at ESS recently opened up the possibility that a single flat moderator above the target could serve all the scattering instruments, that rely on high brightness. This would allow for the introduction of a fundamentally different moderator below the target for the complementary needs of certain fundamental physics experiments. To facilitate experiments depending on the total number of neutrons in a sizable beam, the option of a voluminous D2 moderator, in a large cross-section extraction guide is discussed and its neutronic performance is assessed.Comment: 3 pages, 2 figure

A Reinforcement Learning Approach to Sensing Design in Resource-Constrained Wireless Networked Control Systems

In this paper, we consider a wireless network of smart sensors (agents) that monitor a dynamical process and send measurements to a base station that performs global monitoring and decision-making. Smart sensors are equipped with both sensing and computation, and can either send raw measurements or process them prior to transmission. Constrained agent resources raise a fundamental latency-accuracy trade-off. On the one hand, raw measurements are inaccurate but fast to produce. On the other hand, data processing on resource-constrained platforms generates accurate measurements at the cost of non-negligible computation latency. Further, if processed data are also compressed, latency caused by wireless communication might be higher for raw measurements. Hence, it is challenging to decide when and where sensors in the network should transmit raw measurements or leverage time-consuming local processing. To tackle this design problem, we propose a Reinforcement Learning approach to learn an efficient policy that dynamically decides when measurements are to be processed at each sensor. Effectiveness of our proposed approach is validated through a numerical simulation with case study on smart sensing motivated by the Internet of Drones.Comment: 8 pages, 4 figures, submitted to CDC 2022; fixed author name

To Compute or not to Compute? Adaptive Smart Sensing in Resource-Constrained Edge Computing

We consider a network of smart sensors for edge computing application that sample a signal of interest and send updates to a base station for remote global monitoring. Sensors are equipped with sensing and compute, and can either send raw data or process them on-board before transmission. Limited hardware resources at the edge generate a fundamental latency-accuracy trade-off: raw measurements are inaccurate but timely, whereas accurate processed updates are available after computational delay. Also, if sensor on-board processing entails data compression, latency caused by wireless communication might be higher for raw measurements. Hence, one needs to decide when sensors should transmit raw measurements or rely on local processing to maximize overall network performance. To tackle this sensing design problem, we model an estimation-theoretic optimization framework that embeds computation and communication delays, and propose a Reinforcement Learning-based approach to dynamically allocate computational resources at each sensor. Effectiveness of our proposed approach is validated through numerical simulations with case studies motivated by the Internet of Drones and self-driving vehicles.Comment: 14 pages, 14 figures; submitted to IEEE TNSM; revised versio

Parity Violation in Neutron Capture Reactions

In the last decade, the scattering of polarized neutrons on compound nucleus resonances proved to be a powerful experimental technique for probing nuclear parity violation. Longitudinal analyzing powers in neutron transmission measurements on p-wave resonances in nuclei such as $^{139}$La and $^{232}$Th were found to be as large as 10%. Here we examine the possibilities of carrying out a parallel program to measure asymmetries in the $(n,\gamma$) reaction on these same compound nuclear resonances. Symmetry-violating $(n,\gamma$) studies can also show asymmetries as large as 10%, and have the advantage over transmission experiments of allowing parity-odd asymmetries in several different gamma-decay branches from the same resonance. Thus, studies of parity violation in the $(n,\gamma)$ reaction using high efficiency germanium detectors at the Los Alamos Lujan facility, for example, could determine the parity-odd nucleon-nucleon matrix elements in complex nuclei with high accuracy. Additionally, simultaneous studies of the E1 and $V_{PNC}$ matrix elements invol ved in these decays could be used to help constrain the statistical theory of parity non-conservation in compound nuclei.Comment: 10 pages, 1 figur

Water/Ethanol and 13X Zeolite Pairs for Long-Term Thermal Energy Storage at Ambient Pressure

Thermal energy storage is a key technology to increase the global energy share of renewables - by matching energy availability and demand - and to improve the fuel economy of energy systems - by recovery and reutilization of waste heat. In particular, the negligible heat losses of sorption technologies during the storing period make them ideal for applications where long-term storage is required. Current technologies are typically based on the sorption of vapour sorbates on solid sorbents, requiring cumbersome reactors and components operating at below ambient pressure. In this work, we report the experimental characterization of working pairs made of various liquid sorbates (distilled water, ethanol and their mixture) and a 13X zeolite sorbent at ambient pressure. The sorbent hydration by liquid sorbates shows lower heat storage performance than vapour hydration; yet, it provides similar heat storage density to that obtainable by latent heat storage (40-50 kWh/m^3) at comparable costs, robustness and simplicity of the system, while gaining the long-term storage capabilities of sorption-based technologies. As a representative application example of long-term storage, we verify the feasibility of a sorption heat storage system with liquid sorbate, which could be used to improve the cold-start of stand-by generators driven by internal combustion engines. This example shows that liquid hydration may be adopted as a simple and low-cost alternative to more efficient - yet more expensive - techniques for long-term energy storage

Beamline Simulation for the NNBAR Experiment at the European Spallation Source

The HIBEAM and NNBAR experiments are a proposed fundamental science experiments at the European Spallation Source, performing high precision searches for neutron conversions in several baryon number violating (BNV) channels. For simulations of the NNBAR beamline, a new sampling method has been developed. The method is based on probability density evaluation and duct source biasing and enables the simulations of the entire NNBAR beamline with high statistics while also preserving correlations of the neutron tracks

In-Pile ⁴He Source for UCN Production at the ESS

ESS will be a premier neutron source facility. Unprecedented neutron beam intensities are ensured by spallation reactions of a 5 MW, 2.0 GeV proton beam impinging on a tungsten target equipped with advanced moderators. The work presented here aims at investigating possibilities for installing an ultra cold neutron (UCN) source at the ESS. One consequence of using the recently proposed flat moderators is that they take up less space than the moderators originally foreseen and thus leave more freedom to design a UCN source, close to the spallation hotspot. One of the options studied is to place a large He-4 UCN source in a through-going tube which penetrates the shielding below the target. First calculations of neutron flux available for UCN production are given, along with heat-load estimates. It is estimated that the flux can give rise to a UCN production at a rate of up to 1.5 . 10(8) UCN/s. A production in this range potentially allows for a number of UCN experiments to be carried out at unprecedented precision, including, for example, quantum gravitational spectroscopy with UCNs which rely on high phase-space density

RADICAL FORMATION ON CTMP FIBERS BY ARGON PLASMA TREATMENTS AND RELATED LIGNIN CHEMICAL CHANGES

The changes at molecular level induced by cold argon plasma treat-ments on fibers obtained from chemi-thermo-mechanical pulp (CTMP) fibers were investigated. The radicals formed on CTMP fibers after treatments were identified and quantified by Electron Paramagnetic Resonance (EPR) spectroscopy. The plasma conditions which maximize the formation of radicals on fibers were assessed: after treatment with 0.4 mbar Ar pressure and 75 W radiofrequency power, phenoxy radicals triple their concentration in only 60 s and reach a value 4 times higher than that reported for laccase-catalyzed lignin oxidation. It was found that in plasma-treated fibers, the formation of radicals competes with their coupling. This latter result leads to cross-linkages of the lignin mono-meric units and formation of new intermonomeric C-C and C-O bonds, for the first time assigned to specific molecular interactions through Heteronuclear Single Quantum Coherence (2D-HSQC) spectroscopy and Nuclear Magnetic Resonance spectroscopy of carbon (13C-NMR). These results were confirmed by Nuclear Magnetic Resonance spectros-copy of phosphorous (31P-NMR). The lack of evidences of inter-fiber bond interactions, deduced from Gel Permeation Chromatography (GPC) data, suggests the possible application of plasma treatments for the production of wood fiber-based composites