Hysteresis in Experimental I–V Curves of Electron Hop Funnels

Electron hop funnels provide a method to integrate field emission arrays into microwave vacuum electron devices, to protect the arrays, and to provide a method to study the secondary electron characteristics of dielectrics. A hop funnel is a dielectric material with an electrode, known as the hop electrode, placed around the narrow end (exit) of the funnel to control the current transmitted through the device. Current is transmitted through the funnel via electron-hopping transport. This work investigates a hysteresis observed in the current–voltage characteristic of the device. The experimental results showing the observed hysteresis will be presented. This work will demonstrate that charging on the bottom of the hop funnel is not the fundamental cause of the hysteresis

Simulation of Electron Hop Funnels Using Version 9.2 of Lorentz-2E

Electron hop funnels have been simulated using the new version of the particle trajectory simulation software, Lorentz-2E. Simulations were conducted to determine the validity of the version 9.2 results and the consistency of the results to a previous version of the software, version 8.0. In addition, a new method of injecting a uniform current with all rays of equal charge is discussed, and the results of the method are presented. Version 9.2 of the software was successfully implemented and a new emission model tested. The transition of the software version will allow for faster simulation times of the electron hop funnel simulations to increase the understanding of the device

Simulation of a Crossed-Field Amplifier Using a Modulated Distributed Cathode

Current crossed-field amplifiers (CFAs) use a uniformly distributed electron beam, and in this work, the effects of using a spatially and temporally controlled electron source are simulated and studied. Spatial and temporal modulation of the electron source in other microwave vacuum electron devices have shown an increase in gain and efficiency over a continuous current source, and it is expected that similar progress will be made with CFAs. Experimentally, for accurate control over the electron emission profile, integration of gated field emitter arrays (GFEAs) as the distributed electron source in a crossed-field amplifier (CFA) is proposed. Two linear format, 600 and 900 MHz CFAs, which use GFEAs in conjunction with hop funnels as an electron source, were designed, modeled in VSim, and built at BSU. The hop funnels provide a way to control the energy of the electron beam separately from the sole potential and to protect the GFEA cathode. The dispersion of the meandering microstrip line slow wave circuit used in the device and the electron beam characteristics were measured and validated the simulation model, but experiments failed to show electron beam interaction with the electromagnetic wave due to insufficient current from the available cathode. To complete the research, a working CFA built at Northeastern University (NU) was modeled. The NU CFA was a linear format, device operating at 150 MHz, with 10 W of RF input power, and typically 150 mA of injected beam current. The electrically short device (6 slow wave wavelengths long) achieved 7 dB of gain. After validating the Vsim model against the experimental results, an electrically longer version (9 wavelengths) was simulated with both an injected beam and distributed cathode. To model the distributed cathode computationally efficiently, where the emitted electron energy can be controlled separately from the sole potential, a new electron injection method was developed, using a divergence-free region. Static electron emission profiles showed no improvement over the injected beam model but the temporally modulated cathode was found to significantly improve the performance. It was found that the temporal modulation could improve the small-signal-gain from 13 dB for an unmodulated source to 25 dB with an injected current of 150 mA and 0.1 W of RF drive power. This improvement is only likely to be observed for higher power devices (\u3e10 kW) because of the additional RF drive power required by the GFEA, however. For larger RF drive powers, the improvements to gain become much smaller. With an RF drive power of 10 W, the modulated cathode showed 9 dB of gain, and the injected beam variant showed 8 dB. The signal-to-noise ratio (SNR) using the modulated cathode was consistently at least 15 dB higher than the SNR of the unmodulated cathode. This reduces the likelihood of excitation of unwanted modes. Even though this device showed small improvements to gain at large RF drive powers, it is proposed here that improvements to maximum power in higher power devices are likely, due to the inherent mode-locking mechanism of the modulated cathode, but this still needs to be confirmed. Previous research studying the effects of a modulated cathode in a magnetron and the improvements to the SNR shown here, show promise in this regard

Simulation of a Time-Varying Distributed Cathode in a Linear Format Crossed-Field Amplifier

The effects of a temporally modulated, distributed cathode in a linear format crossed-field amplifier (CFA) are simulated in VSim and analyzed. A linear format, 150 MHz, low power (100 W), moderate gain (7 dB), meander line CFA is used as the basis for the simulation model. This paper describes simulations with different time-varying distributed cathodes in which electron injection is modulated at the RF frequency both in and out of phase with the RF input. At low RF input power the modulated electron injection dominates the operation. Injecting in phase with the RF input shows gain increases from 23 dB at 150 mA to 32 dB at 1 A for low cathode modulation power (\u3c 0.1 W). The CFA efficiency increased from 2-4% to 20-24% using the electron modulation. The simulation shows distinct cylindrically shaped electron bunches as opposed to spokes because of the synchronous injection. These results suggest that for high power magnetrons electron modulation could improve gain

Investigation of the Current Transmission Hysteresis in Electron Hop Funnels

To integrate field emitter arrays (FEAs) into microwave vacuum electron devices, the use of insulating funnels, called electron hop funnels, is proposed. Electrons are emitted into the wide end of the funnel, and utilizing secondary electron emission to sustain current, the electrons hop up the funnel walls. Eventually the electrons exit the funnel as a denser and more uniform electron beam. To pull the electrons up the funnel, an electrode, called the hop electrode, is placed around the exit of the funnel to generate an electric field between the funnel exit and the electron source. The current transmitted through the device depends directly on the hop voltage, and experimental work has found that there is hysteresis in the transmitted current vs. the hop voltage (I-V characteristic). The shape of the I-V curve changes when the voltage is ramped up or down. To characterize and explain the hysteresis, a model of the hop funnel was simulated in the particle trajectory code LORENTZ 2E. The results of the simulations show that hysteresis is a fundamental characteristic of hop funnels. Experimental data does not directly match the simulation results but confirms the general trend found in the simulations

Impact of the 2008 economic and financial crisis on child health: a systematic review

The aim of this study was to provide an overview of studies in which the impact of the 2008 economic crisis on child health was reported. Structured searches of PubMed, and ISI Web of Knowledge, were conducted. Quantitative and qualitative studies reporting health outcomes on children, published since 2007 and related to the 2008 economic crisis were included. Two reviewers independently assessed studies for inclusion. Data were synthesised as a narrative review. Five hundred and six titles and abstracts were reviewed, from which 22 studies were included. The risk of bias for quantitative studies was mixed while qualitative studies showed low risk of bias. An excess of 28,000–50,000 infant deaths in 2009 was estimated in sub-Saharan African countries, and increased infant mortality in Greece was reported. Increased price of foods was related to worsening nutrition habits in disadvantaged families worldwide. An increase in violence against children was reported in the U.S., and inequalities in health-related quality of life appeared in some countries. Most studies suggest that the economic crisis has harmed children’s health, and disproportionately affected the most vulnerable groups. There is an urgent need for further studies to monitor the child health effects of the global recession and to inform appropriate public policy responses

Targeting Iron Acquisition Blocks Infection with the Fungal Pathogens Aspergillus fumigatus and Fusarium oxysporum

Filamentous fungi are an important cause of pulmonary and systemic morbidity and mortality, and also cause corneal blindness and visual impairment worldwide. Utilizing in vitro neutrophil killing assays and a model of fungal infection of the cornea, we demonstrated that Dectin-1 dependent IL-6 production regulates expression of iron chelators, heme and siderophore binding proteins and hepcidin in infected mice. In addition, we show that human neutrophils synthesize lipocalin-1, which sequesters fungal siderophores, and that topical lipocalin-1 or lactoferrin restricts fungal growth in vivo. Conversely, we show that exogenous iron or the xenosiderophore deferroxamine enhances fungal growth in infected mice. By examining mutant Aspergillus and Fusarium strains, we found that fungal transcriptional responses to low iron levels and extracellular siderophores are essential for fungal growth during infection. Further, we showed that targeting fungal iron acquisition or siderophore biosynthesis by topical application of iron chelators or statins reduces fungal growth in the cornea by 60% and that dual therapy with the iron chelator deferiprone and statins further restricts fungal growth by 75%. Together, these studies identify specific host iron-chelating and fungal iron-acquisition mediators that regulate fungal growth, and demonstrate that therapeutic inhibition of fungal iron acquisition can be utilized to treat topical fungal infections

Concert recording 2013-03-31b

[Track 01]. Sweet Georgie fame / Blossom Dearie -- [Track 02]. Joy spring / Clifford Brown -- [Track 03]. Summer samba / Marcos Valle -- [Track 04]. Rhythm\u27ning / Thelonious Monk -- [Track 05]. One note samba / Antonio Carlos Jobim -- [Track 06]. In a sentimental mood / Duke Ellington -- [Track 07]. Recordame / Joe Henderson -- [Track 08]. Full house / Wes Montgomery -- [Track 09]. Cats and kittens / Peter Erskine -- [Track 10]. Primal prayer / Dan Haerle -- [Track 11]. Cookin\u27 Boox / Detroit Jackson

Updating the first CHIME/FRB catalog of fast radio bursts with baseband data

In 2021, a catalog of 536 fast radio bursts (FRBs) detected with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope was released by the CHIME/FRB Collaboration. This large collection of bursts, observed with a single instrument and uniform selection effects, has advanced our understanding of the FRB population. Here we update the results for 140 of these FRBs for which channelized raw voltage ('baseband') data are available. With the voltages measured by the telescope's antennas, it is possible to maximize the telescope sensitivity in any direction within the primary beam, an operation called 'beamforming'. This allows us to increase the signal-to-noise ratio (S/N) of the bursts and to localize them to sub-arcminute precision. The improved localization is also used to correct the beam response of the instrument and to measure fluxes and fluences with a ~10% uncertainty. Additionally, the time resolution is increased by three orders of magnitude relative to that in the first CHIME/FRB catalog, and, applying coherent dedispersion, burst morphologies can be studied in detail. Polarization information is also available for the full sample of 140 FRBs, providing an unprecedented dataset to study the polarization properties of the population. We release the baseband data beamformed to the most probable position of each FRB. These data are analyzed in detail in a series of accompanying papers