Recent studies indicate that PEM fuel cell performance may be strongly influenced by in-plane permeability of the gas diffusion layer (GDL). The current study employs a radial flow technique for ...obtaining in-plane permeability of GDLs, using either gas or liquid as the impregnating fluid. A model has been developed and experimentally verified to account for compressibility effects when permeability measurements are conducted using a gas. Permeability experiments are performed on samples of woven, non-woven, and carbon fiber-based GDL at various levels of compression using air as the impregnating fluid. Woven and non-woven samples are measured to have significantly higher in-plane permeability compared to carbon fiber paper at similar solid volume fractions.
Demands for allowing audio and visual recordings during sessions of parliamentary inquiry committees to ensure better public information have been brought forward not only since the introduction of ...legislation on these commission some 20 years ago . While the law— with high legal hurdles—introduced the possibility during these sessions, actual recordings have only been allowed in very few cases . In the previous parliamentary term of the Bundestag, media reports stressed the demand for visual and audio recordings during the “Wirecard” inquiry . Making use of such recordings raises three fundamental issues with the conformity of inquiry proceedings: complying with important procedural principles, balancing competing rights of relevant parties as well as avoiding possible contradictions of the inquiry committee´s mandate . None of these three questions can be answered in a way that would support the general authorization of audio and visual documentation . Findings in psychology even suggest that there is an insolvable conflict between the unwanted influence of the mere knowledge about of television coverage on witnesses and the facts based mandate of the committee .
Colorless distributed combustion (CDC) is a novel method to enhance flame stability and thermal field uniformity, increase combustion efficiency and reduce pollutants emission, including noise. CDC ...is achieved through the use of a carefully prepared oxidizer mixture of reduced oxygen concentration through added high temperature reactive species. In this study, a partially premixed, swirl assisted cylindrical combustor utilized a propane-air flame with either nitrogen or carbon dioxide gas in order to reduce the oxygen concentration of the oxidizer. OH* chemiluminescence signatures were used to determine transition to distributed combustion condition. The results showed transition to CDC at approximately 15% using N2, and 17% using CO2 dilution. Emission of NO and CO were determined under conditions approaching CDC. NO levels of only 2 or 1 ppm were achieved using N2 or CO2 dilution, respectively under CDC condition. In order to determine how the flow velocity structure and eddy size effect the stability and emissions a high speed (3 kHz) particle image velocimetry (PIV) system was used. Increase in dilution enhanced both the radial and axial mean and fluctuating velocities under CDC that foster mixing. Additionally, the Kolmogorov length decreased with increase in dilution resulting in smaller eddy size particularly in the swirl lobe region, which enhanced turbulent dissipation that resulted in lower peak temperatures and reduced thermal NOx emission. Investigation of Reynolds stress showed that dilution with CO2 provided stronger impact on stress than N2 due to the increased density and reduced viscosity of CO2.
Renewable biofuels offer good performance characteristics as fossil liquid fuels while reducing the emission of pollutants and greenhouse gases helping promote sustainability. Colorless distributed ...combustion (CDC) for gas turbine applications offers robust means of providing understanding of performance and emissions characteristics using liquid biofuels. In this study, performance and emission characteristics are reported from the combustion of a liquid biofuel, hydroprocessed esters and fatty acids synthetic paraffinic kerosene (HEFA-SPK), derived from camelina oil. Currently HEFA-SPK is approved in up to a 50% blend with jet fuel (JP-8) for commercial and military applications. Experiments conducted on various blended ratios of HEFA-SPK to JP-8 are reported, ranging from 100% JP-8 to 100% HEFA-SPK. Experiments were carried out on a swirl-assisted burner at thermal intensity of 5.7 MW/m-atm, with oxidizer preheated and fuel pre-vaporized to 600 K. Distributed combustion conditions were achieved by reducing the oxygen concentration in the oxidizer through adding diluent gases of N2 and CO2 simulating internal entrainment of hot reactive gases. The effect of blended fuel properties on flame structure (through OH* chemiluminescence) and emissions are reported here. HEFA-SPK and JP-8 showed ultra-low NO emission under CDC, ranging between 2 and 2.5 ppm. HEFA-SPK showed significant reduction in CO of up to 50% compared to JP-8 fuel. This study revealed that camelina oil derived fuel produced from biomass can be used as a mixture component with JP-8, maintaining high combustion performance while providing ultra-low CO emission. The biofuels also help support reduction of lifecycle CO2 emission.
As digital technology becomes increasingly available in education, educational researchers around the globe increasingly have to confront how it may affect school students’ academic success. The use ...and potential benefits of AI-based chatbots such as ChatGPT within high school (STEM) education is a novel area of educational research with a broad variety of research gaps. To the best of my knowledge, this is especially true when it comes to parents’ views in this regard. Therefore, it is plausible to assume that delving into an in-depth inquiry of parents’ attitudes, perspectives, and concerns about the use of such chatbots in educational settings would substantially contribute to bridging some crucial voids in our understanding of the overall impact of these digital technologies on high school (STEM) education and thus may be a particularly promising area for future research.
•Distributed combustion studied for hydrogen enriched methane fuel.•Distributed mode alleviates hot-spot zones for mitigating high thermal NOx.•Flame stability enhancement provided for high hydrogen ...content fuel.•Demonstrated less than 1 PPM NO under favorable distributed conditions.
Controlled entrainment of hot reactive gases into the fresh oxidizer mixture prior to ignition is critical for achieving colorless distributed combustion (CDC) condition that results in a uniform thermal field, ultra-low emissions, enhanced flame stability, low noise and mitigation of combustion instability. This paper examines the fuel flexibility of colorless distributed combustion in a swirl-stabilized burner using hydrogen enriched methane gas. Distributed combustion condition was achieved by reducing the oxygen concentration in the oxidizer through addition of either N2 or CO2. Three different gas fuel compositions were investigated. Hydrogen enriched methane in various concentrations in the presence of CO2 and N2 represented coke oven gas. Results on the effect of fuel properties on global flame structure and emissions are reported here. The effect of equivalence ratio on flame stability and emissions was also investigated to determine the impact of air dilution with no change in oxygen concentration. The results showed that for the different gas compositions investigated, transition to distributed combustion conditions occurred at oxygen concentrations of 10–12% with N2 and 13–15% with CO2 as the diluent gas. Increase in hydrogen concentration (or decrease in methane concentration) in the gas mixture resulted in transition to distributed condition at reduced oxygen concentration. The NO emission decreased considerably (to less than 1 ppm) as compared to normal air combustion under the distributed combustion condition for all the gas compositions examined using the different diluents. The emission of CO decreased gradually when approaching distributed conditions, and then increased slightly when the condition moved toward the lower flammability limit. Single digit ppm CO levels were achieved with CDC under nitrogen dilution while carbon dioxide dilution resulted in slightly higher CO emission that was attributed to the dissociation of CO2 at high temperatures. The propensity for flashback with high hydrogen content gas was eliminated under distributed condition and provide wider flame stability limits. These results demonstrate fuel flexibility of diluted hydrogen rich methane gas (akin to coke oven gas) under distributed combustion that provided enhanced stability and ultra-low emissions.
Global atmospheric reanalyses have become a common tool for both validation of climate models and diagnostic studies, such as assessing climate variability and long-term trends. Presently, the ...Twentieth Century Reanalysis (20CR), which assimilates only surface pressure reports, sea ice, and sea surface temperature distributions, represents the longest global reanalysis dataset available covering the period from 1871 to the present. Currently the 20CR dataset is extensively used for the assessment of climate variability and trends. Here, the authors compare the variability and long-term trends in northeast Atlantic storminess derived from 20CR and from observations. A well-established storm index derived from pressure observations over a relatively densely monitored marine area is used. It is found that both variability and long-term trends derived from 20CR and from observations are inconsistent. In particular, both time series show opposing trends during the first half of the twentieth century: both storm indices share a similar behavior only for the more recent periods. While the variability and long-term trend derived from the observations are supported by a number of independent data and analyses, the behavior shown by 20CR is quite different, indicating substantial inhomogeneities in the reanalysis, most likely caused by the increasing number of observations assimilated into 20CR over time. The latter makes 20CR likely unsuitable for the identification of trends in storminess in the earlier part of the record, at least over the northeast Atlantic. The results imply and reconfirm previous findings that care is needed in general when global reanalyses are used to assess long-term changes.
Recombinant engineering for protein production commonly employs plasmid-based gene templates for introduction and expression of genes in a candidate cell system in vitro. Challenges to this approach ...include identifying cell types that can facilitate proper post-translational modifications and difficulty expressing large multimeric proteins. We hypothesized that integration of the CRISPR/Cas9-synergistic activator mediator (SAM) system into the human genome would be a powerful tool capable of robust gene expression and protein production. SAMs are comprised of a "dead" Cas9 (dCas9) linked to transcriptional activators viral particle 64 (VP64), nuclear factor-kappa-B p65 subunit (p65), and heat shock factor 1 (HSF1) and are programmable to single or multiple gene targets. We integrated the components of the SAM system into human HEK293, HKB11, SK-HEP1, and HEP-g2 cells using
and
as proof of concept. We observed upregulation of mRNA in each cell type with concomitant protein expression. Our findings demonstrate the capability of human cells stably expressing SAM for user-defined singleplex and multiplex gene targeting and highlight their broad potential utility for recombinant engineering as well as transcriptional modulation across networks for basic, translational, and clinical modeling and applications.
More power to pyroelectrics Feser, Joseph P; Ravichandran, Jayakanth
Nature materials,
05/2018, Letnik:
17, Številka:
5
Journal Article
Recenzirano
Using a thin-film geometry and electric-field-driven enhancement of pyroelectric response, a relaxor ferroelectric is shown to display superior power densities for thermal harvesting.
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