277 research outputs found
Crystallisation effects on rare earth dopants in oxyfluoride glass ceramics
No full textTransparent oxyfluoride glass-ceramic materials are of significant interest for the production of new optoelectronic devices. In this paper we report measurements of the detailed spectroscopy of rare earth dopants in both an oxyfluoride transparent glass ceramic and its glass precursor. We show that several spectroscopically different sites exist for the rare earth even in the glass precursor material, where a significant amount of the rare earth is already coordinated with fluorine. In the glass-ceramic material, these glassy fluorine-coordinated sites are replaced with crystalline sites, but a significant fraction of the rare earth ions are still within the glass phase. The fraction of rare earth ion that is incorporated into the crystalline phase is estimated from the rare earth spectroscopy, and the role of the rare earth coordination in the precursor glass is discussed
Laser-induced incandescence for soot-particle sizing at elevated pressure
No full textThis paper describes the applicability of laser-induced incandescence (LII) as a measurement technique for primary soot particle sizes at elevated pressure. A high-pressure burner was constructed that provides stable, laminar, sooting, premixed ethylene/air flames at 1-10 bar. An LII model was set up that includes different heat-conduction sub-models and used an accommodation coefficient of 0.25 for all pressures studied. Based on this model experimental time-resolved LII signals recorded at different positions in the flame were evaluated with respect to the mean particle diameter of a log-normal particle-size distribution. The resulting primary particle sizes were compared to results from TEM images of soot samples that were collected thermophoretically from the high-pressure flame. The LII results are in good agreement with the mean primary particle sizes of a log-normal particle-size distribution obtained from the TEM-data for all pressures, if the LII signals are evaluated with the heat-conduction model of Fuchs combined with an aggregate sub-model that describes the reduced heat conduction of aggregated primary soot particles. The model, called LIISim, is available online via a web interface
Numerical study on the temperature dependence of soot formation in acetylene pyrolysis blended with methane, formaldehyde, methanol, and dimethyl ether
No full textAbstract
This paper addresses the combined effects of varying C/H and C/O ratios as well as of the molecular structure of the fuels selected on the normalized soot volume fraction
f
V
. For the simulations, an already existing and validated reaction mechanism for the pyrolysis of C
2
H
2
in argon, Aghsaee et al. (
Combust. Flame
2014,
161
, 2263–2269), was used in the current work. It was extended with PAH reactions from coronene (C
24
H
12
) up to ovalene (C
32
H
14
), whereas general principles for the rapid build-up of
large
PAHs were presented. Soot formation was modeled according to Appel et al. (
Combust. Flame
2000,
121
, 122–136) by applying the method of moments. A validation of the extended reaction model was carried out for shock-wave-induced O
2
/C
2
H
2
mixtures from literature. In the following, the influence of blends of methane (CH
4
), formaldehyde (CH
2
O), methanol (CH
3
OH), and dimethyl ether (CH
3
)
2
O on soot formation during C
2
H
2
pyrolysis diluted in Ar was studied. Special emphasis was laid on the inception chemistry of soot formation. The role of intermediates, such as the propargyl radical (C
3
H
3
), leading towards benzene and polyaromatic hydrocarbon (PAH) formation and their interplay with hydrogen molecules (H
2
) to H atoms (H) ratio was examined. All blends increased the ratio of the concentrations of H
2
and H leading thus to reduced soot inception and soot formation. However, soot suppressing effects were overrun by supporting ones when the additives provided suitable molecular groups, such as methyl radicals (CH
3
), in sufficient high concentrations for early aromatic ring formation. Thus, a prominent synergistic effect on soot formation was found for the CH
4
/C
2
H
2
mixture only. Besides, species able to mirror characteristics of the soot formation process, such as the peak value of the normalized soot volume fraction, are presented. The findings of this work indicate the synergistic effect of H
2
/H and C/O ratios as well as of methyl radicals on the PAHs’ production of appropriate size able to initiate soot inception process in an aliphatic fuel
Remote Laboratory Testing Demonstration
No full textThe complexity of a smart grid with a high share of renewable energy resources introduces several issues in testing power equipment and controls. In this context, real-time simulation and Hardware in the Loop (HIL) techniques can tackle these problems that are typical for power system testing. However, implementing a convoluted HIL setup in a single infrastructure can be physically impossible or can increase the time required to test a smart grid application in detail. This paper introduces the Joint Test Facility for Smart Energy Networks with Distributed Energy Resources (JaNDER) that allows users to exchange data in real-time between two or more infrastructures. This tool enables the integration of infrastructures, exploiting the synergies between them, and creating a virtual infrastructure that can perform more experiments using a combination of the resources installed in each infrastructure. In particular, JaNDER can extend a HIL setup. In order to validate this new testing concept, a coordinated voltage controller has been tested in a Controller HIL setup where JaNDER was used to interact with an actual On Load Tap Changer (OLTC) controller located in a remote infrastructure. The results show that the latency introduced by JaNDER is not critical; hence, under certain circumstances, it can be used to expand the real-time testing without affecting the stability of the experiment
Fig. 1 a in Susceptibility of Chrysoperla externa (Hagen, 1861) (Neuroptera: Crysopidae) to insecticides used in coffee crops
No full textFig. 1 a Percentage of adults emergence of Chrysoperla externa from pupae exposed to insecticides (df = 4, F = 7.3237, p> 0.05). b Duration of the pupal stage in days, when insects exposed to insecticides while pupae of C. externa (ns = the means do not differ from each other, df = 4, F = 1.3462, p> 0.05)Published as part of <i>Souza, Jander Rodrigues, Moreira, Luciano Bastos, Lima, Lucas Lorenzon Resende, Silva, Túlio Guimarães, Braga, Pedro Paulo Malfitano & Carvalho, Geraldo Andrade, 2020, Susceptibility of Chrysoperla externa (Hagen, 1861) (Neuroptera: Crysopidae) to insecticides used in coffee crops, pp. 1306-1314 in Ecotoxicology (London, England) 29 (9)</i> on page 2008, DOI: 10.1007/s10646-020-02261-w, <a href="http://zenodo.org/record/8431508">http://zenodo.org/record/8431508</a>
Fibrous Cap Thickness and Smooth Muscle Cell Apoptosis in High-grade Carotid Artery Stenosis
No full textAbstractObjectiveThere is growing evidence that, in high-grade internal carotid artery (ICA) stenosis, continuous fibrous cap thinning is not mandatory for plaque rupture and symptom development. The possibility that smooth muscle cell (SMC) apoptosis is involved in loss of fibrous cap volume has only been examined in a limited number of patients with high grade carotid artery stenosis.MethodsEndarterectomy specimens from n=38 consecutive patients undergoing surgery for high-grade ICA stenosis (≥70%) were transversely sectioned at 2mm intervals. Plaque instability was defined clinically, by a history of recent ischemic symptoms (<60 days before surgery; n=19) attributable to the stenosis, or histopathologically by the presence of plaque rupture (n=14). Detailed morphometric analyses of the fibrous cap was based on routine stains; for DNA in situ end labeling the TUNEL technique was used. SMCs were identified by immunostaining for SMC actin.ResultsWe found no significant difference between symptomatic/asymptomatic or ruptured/unruptured plaque with respect to various morphometric measures of the fibrous cap (i.e. mean area, number of plaque sections with fibrous cap, necrotic core-to-lumen distance at its thinnest or thickest part). The mean (±SD) apoptotic SMCs per thousand within the fibrous cap was significantly higher in symptomatic vs. asymptomatic (64.53±77.3 vs. 6.71±11.9; P<0.001) but not in ruptured plaques (43.3±64.4 vs. 30.1±60.9; P=0.117).ConclusionsThese data suggest that continuous thinning of the fibrous cap is not an essential prerequisite for plaque rupture in ICA stenosis. Symptomatic, but not ruptured plaque, were associated with the highest number of apoptotic SMC. Thus, it seems unlikely that SMC apoptosis promotes plaque rupture by fibrous cap thinning
Fig. 4 in Susceptibility of Chrysoperla externa (Hagen, 1861) (Neuroptera: Crysopidae) to insecticides used in coffee crops
No full textFig. 4 Reproductive parameters of Chrysoperla externa exposed to insecticides used in coffee crop. a Mean number of eggs oviposited by females (SE) exposed to insecticides when pupae (df = 3, Χ² = 247.3, p <0.05) and adults (df = 2, F = 8.1353, p <0.05. b Total eggs layed by females exposed to insecticides when pupae (df = 3, F = 29.756, p <0.05) and adults (df = 2, F = 53.006, p <0.05). c Egg viability (SE) of females exposed to insecticides when pupae (df = 3, F = 3.4328, p <0.05) and adults (ns = the means do not differ from each other, df = 2, F = 1.5769, p> 0.05)Published as part of <i>Souza, Jander Rodrigues, Moreira, Luciano Bastos, Lima, Lucas Lorenzon Resende, Silva, Túlio Guimarães, Braga, Pedro Paulo Malfitano & Carvalho, Geraldo Andrade, 2020, Susceptibility of Chrysoperla externa (Hagen, 1861) (Neuroptera: Crysopidae) to insecticides used in coffee crops, pp. 1306-1314 in Ecotoxicology (London, England) 29 (9)</i> on page 2009, DOI: 10.1007/s10646-020-02261-w, <a href="http://zenodo.org/record/8431508">http://zenodo.org/record/8431508</a>
Jander, Rosa (Birth, 1875-11-23)
No full textAddress: 271 Main St.5136/Pg. 187/1875/F W/City/Barbara Bryan, Mid.Original record filed in drawer labeled 'Jameson-Johnson'
Recommended from our members
1/f noise of GaAs resistors on semi-insulating substrates, and 1/f noise due to temperature fluctuations in heat conduction
No full textThis research work focuses on the mechanism of 1/f noise in GaAs
resistors on semi-insulating substrates and 1/f noise due to temperature
fluctuations in heat conduction in resistors, diodes, and bipolar transistors. The
goal of this research is to generate accurate models to explain physical origin of 1/f
noise in semi-insulating substrate and semiconductor devices dissipating high
power.
The model is based on a distributed equivalent circuit representation of the
substrate, and shows that 1/f noise bulk phenomena associated with high resistivity
substrates. One consequence of the theory is that in this particular instance
Hooge's parameter is given by a formula and it is not an empirical parameter.
Power dissipation at high currents and voltages in semiconductor devices
results in significant heat generation and heat conduction towards the heat sink.
The device temperature is only an average value and there are as a consequence of
the diffusion equation for heat flow itself temperature fluctuations about this
average value. It will be shown that these temperature fluctuations can result in 1/f
noise at moderately low frequencies where these frequencies are determined by the
physical dimensions over which the heat flows and the diffusion transit time. The
results are then related to the shot noise or white noise due to the collector current
allowing a determination of the 1/f noise corner frequency
- …
