324 research outputs found
Strategies in the direction of scaling-up aspects of microbial electrolysis cells
No full textBioelectrochemical systems (BESs) are evolving as modern hybrid technologies, with BES outputs being extensively used in the area of environmental remediation. Although biopower can donate electrons to provide bioelectroremediation of contaminants from BESs, the distribution of electrons is dependent on the close arrangement of electrodes, which is impractical in aquifers. Another type of the BES, namely, the microbial electrolysis cell (MEC), is a highly likely factor in H2 and CH4 synthesis formed by biodegradable organic compounds. Nonetheless, biogas produced by MECs can be used extensively in industry, such as in industrial chemical synthesis, purification, and/or upgrading to a single gas, which is extremely expensive and challenging. The introduction and fundamental principles of MECs that demonstrate their theoretical advantages are outlined in this chapter. The low formal cell voltage and energy yields are the essential advantages. Additional theoretical capabilities, like the development of CH4 and certain value-added chemicals, are explored. The biggest obstacle to this strategy is that the options mentioned above are still rather premature and need more insight. This impact may be damaging if the device is not well-built. Different constraints, perspectives, and facets of the MEC architecture are described in this chapter. Various factors are required for MECs to scale up reactors and other techniques to achieve a dynamic balance status can be problematic and can be solved in the scaling-up phase. The problem of low conductivity of electrolytes and how an increase can damage the main issue of anode acidification is highlighted. Finally, potential guidelines for the implementation of MECs are suggested
Enhanced Thermoelectric Properties By Embedding Fe Nanoparticles Into CrN Films For Energy Harvesting Applications
No full textNanostructured materials and nanocomposites have shown great promise for
improving the efficiency of thermoelectric materials. Herein, Fe nanoparticles
were imbedded into a CrN matrix by combining two physical vapor deposition
approaches, namely high-power impulse magnetron sputtering and a nanoparticle
gun. The combination of these techniques allowed the formation of
nanocomposites in which the Fe nanoparticles remained intact without
intermixing with the matrix. The electrical and thermal transport properties of
the nanocomposites were investigated and compared to a monolithic CrN film. The
measured thermoelectric properties revealed an increase in the Seebeck
coefficient, with a decrease of hall carrier concentration and an increase of
the electron mobility which could be explained by energy filtering by internal
phases created at the NP/matrix interface. The thermal conductivity of the
final nanocomposite was reduced from 4.8 W m-1K-1 to a minimum of 3.0 W m-1K-1
W. This study shows prospects for the nanocomposite synthesis process using
nanoparticles and its use in improving the thermoelectric properties of
coatings.Comment: 5 figures / 2 tabl
Second Malignant Neoplasms Following Radiotherapy
No full textMore than half of all cancer patients receive radiotherapy as a part of their treatment. With the increasing number of long-term cancer survivors, there is a growing concern about the risk of radiation induced second malignant neoplasm [SMN]. This risk appears to be highest for survivors of childhood cancers. The exact mechanism and dose-response relationship for radiation induced malignancy is not well understood, however, there have been growing efforts to develop strategies for the prevention and mitigation of radiation induced cancers. This review article focuses on the incidence, etiology, and risk factors for SMN in various organs after radiotherapy
Turbulent channel flow with stable stratification beyond the Oberbeck-Boussinesq assumptions: A DNS study
No full textStratified turbulent flows abound in environmental and industrial settings. Examples are atmospheric boundary layer flows, the transport of nutrients and organisms and the mixing of heat and salinity in the oceans, fluid flow in heat exchangers, and the transport of reactants and products in chemical reactions. These examples and many others consider stratified wall-bounded turbulence, in which the creation of turbulence by mechanical processes contends with its dissipation due to buoyancy effects. These flows are said to be stably stratified as these are inherently stable flows and are averse to mixing. The buoyancy effects alter the structure of the flow, and consequently the dynamics of mass, heat, and momentum transport. As density fluctuations become more severe, the Oberbeck-Boussinesq approximation becomes inaccurate and the resulting dynamics are not correctly predicted. In the current work, we developed and validated a numerical solver for direct numerical simulations (DNS) of turbulent flows featuring strong property variations. More precisely, we solve the Navier-Stokes equations in the limit of vanishing Mach number (so-called low-Mach number limit), with the fluid density given by the ideal gas law, and the dynamic viscosity and thermal conductivity also expressed as functions of temperature.Our numerical solver is used to study stably-stratified turbulent channel flow under non-Oberbeck-Boussinesq conditions. The simulations are carried out at friction Reynolds number of 180, Prandtl number of 0.71, and friction Richardson number of the O(10). These non-dimensional numbers are the governing parameters and are defined based on the prescribed pressure drop and properties of the fluid at the reference temperature. Stratification is achieved by imposing constant temperature boundary conditions, with a high upper-to-lower wall temperature ratio (larger than 2), resulting in strong density variations in the flow. We will vary the temperature ratios and adjust gravity to maintain a similar Richardson number between cases, thereby isolating the effects of strong property variations in the flow dynamics. We will analyze the dynamics of heat and momentum transport under strong stratification for these conditions, also in light of DNS data of the same system under the Oberbeck-Boussinesq regime.Mechanical Engineering | Energy, Flow and Process Technolog
Energy-efficient physical vapor deposition of transition metal nitride thin films
No full textThis thesis focuses on providing insights into energy-efficient ways of growing protective thin films using physical vapor deposition (PVD) by magnetron sputtering, specifically high-power impulse magnetron sputtering (HiPIMS). This technique involves ionizing the material to be deposited to a high degree. The properties of the film for applications such as protective coatings could thus be controlled by modulating the energy and guiding the ions using electric and magnetic fields, respectively. The multiprincipal element TiZrNbTa nitride system is of interest for its corrosion-resistant coating applications. This material system consists of refractory metals that exhibit different ionic charge states with significant mass contrast. Thus, when sputtered with HiPIMS, the properties of the films strongly depend on the mass and energy of the bombarding metal ions. The transport of these ions to the substrate is influenced by the magnetic field distribution in the chamber. To demonstrate the influence of the magnetron arrangement, the deposition is performed without external heating. Two magnetron arrangements were chosen: a tilted closed-field design with four magnetrons and a single magnetron. The films exhibited different properties depending on the magnetron design used. The single magnetron design induces changes in the preferred orientation of the films from 111 to 200 along with film composition and density. A reduction in residual stress was observed with only a ~6 % degradation in the hardness compared to the closed-field design. I also demonstrate epitaxial growth of TiZrNbTaNx films without external heating. The films were grown with a single magnetron design on single crystal sapphire substrate. Applying a pulsed substrate bias with a long pulse width instead of a constant bias, resulted in low argon (~1 at. %) and oxygen (0.5 at. %) content in the films. In addition, the films exhibited a higher optical absorbance in the near-infrared region than the high-temperature grown films. The total energy consumption for film deposition was reduced by approximately 50 % compared to dc magnetron sputtering (DCMS) at 400°C growth temperature. This reduction is without considering the substrate heating and stabilization phase, which is shorter compared to the industry standard where the entire chamber is heated up to ~500-600°C. These findings are beneficial in designing film growth conditions for energy-efficient processes without compromising film quality. This could also address the challenges of growing high-quality films on temperature-sensitive substrates. Funding: The work is supported financially by the VINNOVA Competence Centre FunMat-II (Grant No. 2022-03071), the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No. 2009 00971), the Knut and Alice Wallenberg foundation through the Wallenberg Academy Fellows program (KAW-2020.0196), the Swedish Research Council (VR) under Project No. 2021-03826, and the Swedish Energy Agency under Project No. 52740-1.</p
Fire Type Classification in the Brazilian Tropical Moist Forest Biome
No full textThe Brazilian Tropical Moist Forest Biome (BTMFB) is “Earth’s greatest biological treasure and a major component of the earth system” and forest degradation and deforestation by fire is a serious issue in this region. Fires in the BTMFB can be broadly classified as maintenance, deforestation and forest fire types. Spatially and temporally explicit information on the incidences of fire types are important as they have widely varying atmospheric emissions and ecological impacts. Satellite based remote sensing is a practical means of monitoring the BTMFB that spans almost 4 million km2. However, there has been no way to reliably classify satellite active fire type to date. In this work, methods to characterize MODIS active fire detections are developed using physically based and geographic context/proximity approaches. The research methodology is developed by addressing four hypotheses concerning differences among active fire type characteristics including factors that drive and mediate fire in the BTMFB. Differences in the active fire characteristics among different fire types are presented and discussed. The spatio-temporal distribution of fire types over 8 year (2003-2010) period is documented, analyzed and presented. This dissertation has, to date, resulted in one published, one in press, and one submitted paper
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Challenges in network-based classification of gene expression profiles
No full textClassification of gene expression profiles to distinguish one disease state from another is essential for the realization of personalized medicine. Recent approaches towards this problem use prior knowledge about interaction among bio-molecules to improve classification accuracy and the biological relevance of the predictive features. However, many such network-based methods do not significantly outperform their unconstrained counterparts in terms of sensitivity and specificity due to unexplained reasons. This behavior, observed across diverse datasets and methods, is a cause of concern as it implies that something is wrong with the data, the algorithms or both. This work focuses on understanding the reasons behind this problem through extensive simulation of gene expression profile to help the development of better classifiers in the future. We infer that when using networks whose interactions do not agree well with the patterns of gene expression, improvement in classification performance will not be significant. Because this improvement is dependent on the classifier also, future network-based methods need to understand their properties with respect to network noise and know the quality of actual network mapping to make meaningful inferences from the performance result
Excision Versus Fixation of the Radial Head: A Comparative Study of the Functional Outcomes of the Two Techniques
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