6,307 research outputs found
Tests of a Novel Design of Resistive Plate Chambers
A novel design of Resistive Plate Chambers (RPCs), using only a single
resistive plate, is being proposed. Based on this design, two large size
prototype chambers were constructed and were tested with cosmic rays and in
particle beams. The tests confirmed the viability of this new approach. In
addition to showing an improved single-particle response compared to the
traditional 2-plate design, the novel chambers also prove to be suitable for
calorimetric applications
Measurements of the Rate Capability of Various Resistive Plate Chambers
Resistive Plate Chambers (RPCs) exhibit a significant loss of efficiency for
the detection of particles, when subjected to high particle fluxes. This rate
limitation is related to the usually high resistivity of the resistive plates
used in their construction. This paper reports on measurements of the
performance of three different glass RPC designs featuring a different total
resistance of the resistive plates. The measurements were performed with 120
GeV protons at varying beam intensitie
Waveform Optimization and Beam Focusing for Near-field Wireless Power Transfer with Dynamic Metasurface Antennas and Non-linear Energy Harvesters
Radio frequency (RF) wireless power transfer (WPT) is a promising technology
for future wireless systems. However, the low power transfer efficiency (PTE)
is a critical challenge for practical implementations. One of the main
inefficiency sources is the power consumption and loss introduced by key
components such as high-power amplifier (HPA) and rectenna, thus they must be
carefully considered for PTE optimization. Herein, we consider a near-field
RF-WPT system with the emerging dynamic metasurface antenna (DMA) at the
transmitter and non-linear energy harvesters. We provide a mathematical
framework to calculate the power consumption and harvested power from
multi-tone signal transmissions. Then, we propose an approach relying on
alternating optimization and successive convex approximation for waveform
optimization and beam focusing to minimize power consumption while meeting
energy harvesting requirements. Numerical results show that increasing the
transmit tones reduces the power consumption by leveraging the rectifier's
non-linearity. Moreover, it is demonstrated that increasing the antenna length
improves the performance, while both DMA and fully-digital architectures may be
favorable depending on the setup. Finally, our results verify that the
transmitter generates accurate energy beams pointed to devices located in the
near-field, while energy beams are formed in devices' direction in the
far-field region.Comment: 13 pages, 12 figure
An instrument to measure fast gas phase radical kinetics at hight temperatures and pressures
Fast radical reactions are central to the chemistry of planetary atmospheres and combustion systems. Laser-induced fluorescence is a highly sensitive and selective technique that can be used to monitor a number of radical species in kinetics experiments, but is typically limited to low pressure systems owing to quenching of fluorescent states at higher pressures. The design and characterisation of an instrument is reported using laser-induced fluorescence detection to monitor fast radical kinetics (up to 25,000 s-1) at high temperatures and pressures by sampling from a high pressure reaction region to a low pressure detection region. Kinetics have been characterised at temperatures reaching 740 K and pressures up to 2 atm, with expected maximum operational conditions of up to ~ 900 K and ~ 5 atm. The distance between the point of sampling from the high pressure region and the point of probing within the low pressure region is critical to the measurement of fast kinetics. The instrumentation described in this work can be applied to the measurement of kinetics relevant to atmospheric and combustion chemistry
TinyML: Tools, Applications, Challenges, and Future Research Directions
In recent years, Artificial Intelligence (AI) and Machine learning (ML) have
gained significant interest from both, industry and academia. Notably,
conventional ML techniques require enormous amounts of power to meet the
desired accuracy, which has limited their use mainly to high-capability devices
such as network nodes. However, with many advancements in technologies such as
the Internet of Things (IoT) and edge computing, it is desirable to incorporate
ML techniques into resource-constrained embedded devices for distributed and
ubiquitous intelligence. This has motivated the emergence of the TinyML
paradigm which is an embedded ML technique that enables ML applications on
multiple cheap, resource- and power-constrained devices. However, during this
transition towards appropriate implementation of the TinyML technology,
multiple challenges such as processing capacity optimization, improved
reliability, and maintenance of learning models' accuracy require timely
solutions. In this article, various avenues available for TinyML implementation
are reviewed. Firstly, a background of TinyML is provided, followed by detailed
discussions on various tools supporting TinyML. Then, state-of-art applications
of TinyML using advanced technologies are detailed. Lastly, various research
challenges and future directions are identified.Comment: 12 pags, 3 tables, 4 figure
Sustainable Radio Frequency Wireless Energy Transfer for Massive Internet of Things
Reliable energy supply remains a crucial challenge in the Internet of Things
(IoT). Although relying on batteries is cost-effective for a few devices, it is
neither a scalable nor a sustainable charging solution as the network grows
massive. Besides, current energy-saving technologies alone cannot cope, for
instance, with the vision of zero-energy devices and the deploy-and-forget
paradigm which can unlock a myriad of new use cases. In this context,
sustainable radio frequency wireless energy transfer emerges as an attractive
solution for efficiently charging the next generation of ultra low power IoT
devices. Herein, we highlight that sustainable charging is broader than
conventional green charging, as it focuses on balancing economy prosperity and
social equity in addition to environmental health. Moreover, we overview the
key enablers for realizing this vision and associated challenges. We discuss
the economic implications of powering energy transmitters with ambient energy
sources, and reveal insights on their optimal deployment. We highlight relevant
research challenges and candidate solutions.Comment: 12 pages, 6 figures, 2 tables, submitted to IEEE Internet of Things
Journa
A new method for atmospheric detection of the CH3O2 radical
A new method for measurement of the methyl peroxy (CH3O2) radical has been developed using the conversion of CH3O2 into CH3O by excess NO with subsequent detection of CH3O by fluorescence assay by gas expansion (FAGE) with laser excitation at ca. 298 nm. The method can also directly detect CH3O, when no nitric oxide is added. Laboratory calibrations were performed to characterise the FAGE instrument sensitivity using the conventional radical source employed in OH calibration with conversion of a known concentration of OH into CH3O2 via reaction with CH4 in the presence of O2. Detection limits of 3.8 × 108 and 3.0 × 108 molecule cm−3 were determined for CH3O2 and CH3O respectively for a signal-to-noise ratio of 2 and 5 min averaging time. Averaging over 1 h reduces the detection limit for CH3O2 to 1.1 × 108 molecule cm−3, which is comparable to atmospheric concentrations. The kinetics of the second-order decay of CH3O2 via its self-reaction were observed in HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry) at 295 K and 1 bar and used as an alternative method of calibration to obtain a calibration constant with overlapping error limits at the 1σ level with the result of the conventional method of calibration. The overall uncertainties of the two methods of calibrations are similar – 15 % for the kinetic method and 17 % for the conventional method – and are discussed in detail. The capability to quantitatively measure CH3O in chamber experiments is demonstrated via observation in HIRAC of CH3O formed as a product of the CH3O2 self-reaction
Temperature and Pressure Dependent Kinetics of QOOH Decomposition and Reaction with O2: Experimental and Theoretical Investigations of QOOH Radicals Derived from Cl + (CH3)3COOH
QOOH radicals are key species in autoignition, produced by internal isomerisations of RO2 radicals, and are central to chain branching reactions in low temperature combustion. The kinetics of QOOH radical decomposition and reaction with O2 have been determined as a function of temperature and pressure, using observations of OH radical production and decay following H-atom abstraction from tertiary-butyl hydroperoxide ((CH3)3COOH) by Cl atoms to produce QOOH (.CH2(CH3)2COOH) radicals. The kinetics of QOOH decomposition have been investigated as a function of temperature (251 to 298 K), and pressure (10 to 350 Torr), in helium and nitrogen bath gases, and those of the reaction between QOOH and O2 have been investigated as a function of temperature (251 to 304 K), and pressure (10 to 100 Torr) in He and N2. Decomposition of the QOOH radicals was observed to display temperature and pressure dependence, with a barrier height for decomposition of (44.7 ± 4.0) kJ mol-1 determined by master equation fitting to the experimental data. The rate coefficient for the reaction between QOOH and O2 was determined to be (5.6 ± 1.7) × 10-13 cm3 s-1 at 298 K, with no significant dependence on pressure, and can be described by the Arrhenius parameters A = (7.3 ± 6.8) × 10-14 cm3 s-1 and Ea = -(5.4 ± 2.1) kJ mol-1 in the temperature range 251 to 304 K. This work represents the first measurements of any QOOH radical kinetics as a function of temperature and pressure
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