Search results for "flu"

Negative differential resistance and threshold-switching in conical nanopores with KF solutions

2021

Negative differential resistance (NDR) phenomena are under-explored in nanostructures operating in the liquid state. We characterize experimentally the NDR and threshold switching phenomena observed when conical nanopores are immersed in two identical KF solutions at low concentration. Sharp current drops in the nA range are obtained for applied voltages exceeding thresholds close to 1 V and a wide frequency window, which suggests that the threshold switching can be used to amplify small electrical perturbations because a small change in voltage typically results in a large change in current. While we have not given a detailed physical mechanism here, a phenomenological model is also includ…

Parameter sensitivity of flux-linkage based sensorless control for permanent magnet synchronous motors

2017

Sensorless control can be utilized to reduce cost, size and total complexity of a motor drive or enhance reliability of the system. This paper first presents a sensorless control algorithm for a surface permanent-magnet synchronous motor (SPMSM) based on estimated flux linkages and stator currents. Within the algorithm, rotor position error can be predicted by comparing the estimated currents with measured stator currents. Performance of the sensorless control based on flux-linkages and the dependency of the algorithm on motor parameters is then numerically investigated via simulations. It is found from the investigation that the accuracy of the method depends on the motor working condition…

An Experimental Study of Waveguide Coupled Microwave Heating with Conventional Multicusp Negative Ion Source

2015

Negative ion production with conventional multicusp plasma chambers utilizing 2.45 GHz microwave heating is demonstrated. The experimental results were obtained with the multicusp plasma chambers and extraction systems of the RFdriven RADIS ion source and the filament driven arc discharge ion source LIISA. A waveguide microwave coupling system, which is almost similar to the one used with the SILHI ion source, was used. The results demonstrate that at least one third of negative ion beam obtained with inductive RF-coupling (RADIS) or arc discharge (LIISA) can be achieved with 1 kW of 2.45 GHz microwave power in CW mode without any modification of the plasma chamber. The co-extracted electro…

The role of radio frequency scattering in high-energy electron losses from minimum-B ECR ion source

2021

Abstract The measurement of the axially lost electron energy distribution escaping from a minimum-B electron cyclotron resonance ion source in the range of 4–800 keV is reported. The experiments have revealed the existence of a hump at 150–300 keV energy, containing up to 15% of the lost electrons and carrying up to 30% of the measured energy losses. The mean energy of the hump is independent of the microwave power, frequency and neutral gas pressure but increases with the magnetic field strength, most importantly with the value of the minimum-B field. Experiments in pulsed operation mode have indicated the presence of the hump only when microwave power is applied, confirming that the origi…

The biased disc of an electron cyclotron resonance ion source as a probe of instability-induced electron and ion losses

2019

International audience; Electron Cyclotron Resonance Ion Source (ECRIS) plasmas are prone to kinetic instabilities resulting in loss of electron and ion confinement. It is demonstrated that the biased disk of an ECRIS can be used as a probe to quantify such instability-induced electron and ion losses occurring in less than 10 µs. The qualitative interpretation of the data is supported by the measurement of the energy spread of the extracted ion beams implying a transient plasma potential >1.5 kV during the instability. A parametric study of the electron losses combined with electron tracking simulations allows for estimating the fraction of electrons expelled in each instability event to be…

Ion source research and development at University of Jyväskylä: Studies of different plasma processes and towards the higher beam intensities

2015

MonPS16; International audience; The long-term operation of high charge state electron cyclotron resonance ion sources fed withhigh microwave power has caused damage to the plasma chamber wall in several laboratories.Porosity, or a small hole, can be progressively created in the wall on a year time scale, which cancause a water leak from the cooling system into the plasma chamber vacuum. A burnout of theVENUS chamber is investigated. Information on the hole formation and on the necessary localhot electron power density is presented. Next, the hot electron flux to the wall is studied bymeans of simulations. First, the results of a simple model assuming that electrons are fullymagnetized and …

2020

Desulfurization of hydrocarbons is an important step in the processing of petroleum products, which requires an accurate and robust method for the sulfur-containing component evaluation. On the other hand, sulfur-containing heteroatomic hydrocarbon additives are harmful for people and the environment. Therefore, it is advantageous to conduct laboratory tests at low volumes to reduce doses of exposure of sulfur-containing vapors to the personnel. Microfluidics is an emerging platform that provides an advantage to operate with low volumes. The microfluidic dielectric spectroscopy approach is proposed in the current contribution as a platform for determination of the concentration of polar het…

Estimating ion confinement times from beam current transients in conventional and charge breeder ECRIS

2019

International audience; Cumulative ion confinement times are probed by measuring decaying ion current transients in pulsed material injection mode. The method is applied in a charge breeder and conventional ECRIS yielding mutually corroborative results. The cumulative confinement time estimates vary from approximately 2 ms–60 ms with a clear dependence on the ion charge-to-mass ratio—higher charges having longer residence times. The long cumulative confinement times are proposed as a partial explanation to recently observed unexpectedly high ion temperatures. The results are relevant for rare ion beam (RIB) production as the confinement time and the lifetime of stable isotopes can be used f…

Carbonyl-functionalized quaterthiophenes: a study of the vibrational Raman and electronic absorption/emission properties guided by theoretical calcul…

2011

This work investigates the evolution of the molecular, vibrational, and optical properties within a family of carbonyl-functionalized quaterthiophenes: 5,5'''-diheptanoyl-2,2':5',2'':5'',2'''-quaterthiophene (1), 5,5'''-diperfluorohexylcarbonyl-2,2':5',2'':5'',2'''-quaterthiophene (2), and 2,7-[bis(5-perfluorohexylcarbonylthien-2-yl)]-4H-cyclopenta[2,1-b:3,4-b']-dithiophene-4-one (3). The analysis is performed by Raman and UV/Vis absorption/excitation/fluorescence spectroscopy in combination with density functional calculations. Theoretical calculations show that substitution with carbonyl groups and perfluorohexyl chains induces progressive quinoidization of the π-conjugated backbone in co…

Structural, electronic and energetic effects in heterocyclic fluorene derivatives fused with a fulvene unit

2019

Abstract A set of 36 heterocyclic (B, N and O) fluorene (C) derivatives fused in nine ways with fulvene ring have been analyzed by means of different local aromaticity criteria. Molecular geometry of analyzed compounds were optimized at B3LYP/6-311++G(2d,2p) level of theory. The evaluation of the local aromaticity has been carried out through the use of the geometry-based harmonic oscillator model of aromaticity (HOMA) and the magnetism-based zz‐component of the nucleus independent chemical shifts calculated 1 A above the ring center (NICS1zz) indices as well as one aromaticity index derived from the Quantum Theory Atoms in Molecules (QTAIM), i.e. the para-delocalization index (PDI). Additi…