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Defect-engineered metal-organic frameworks (MOF-808) towards the improved adsorptive removal of organic dyes and chromium (vi) species from water
Get PDFIn this work, two defective zirconium-based metal-organic frameworks (Zr-MOFs), MOF-808-OH and MOF-808-NH2, were synthesized by partially replacing the 1,3,5-benzenetricarboxylate building block with 5-hydroxyisophthalate and 5-aminoisophthalate, respectively. The structural features of the defective materials were analyzed by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), nitrogen physisorption at 77 K, and thermogravimetric analysis (TGA). Importantly, the number of defect sites determined via proton nuclear magnetic resonance (1H-NMR) analysis of the digested materials was approximately 7 mol% for MOF-808-OH and 3 mol% for MOF-808-NH2. The presence of the defect sites increased the number of acidic centers on Zr-clusters originating from missing-linker nodes which accounted for a remarkable adsorption capacity towards various anionic organic dyes and chromium (vi) species. Compared to standard MOF-808, the defect-engineered ones showed significant increments by 30-60% in trapping capacity for anionic contaminants including sunset yellow, quinoline yellow, methyl orange, and potassium dichromate, while they exhibited modest improvements by 5-15% in the removal of cationic dyes, namely malachite green and methylene blue
CRISPRi screen highlights chromatin regulation to be involved in formic acid tolerance in Saccharomyces cerevisiae
Get PDFFormic acid is one of the main weak acids in lignocellulosic hydrolysates that is known to be inhibitory to yeast growth even at low concentrations. In this study, we employed a CRISPR interference (CRISPRi) strain library comprising >9000 strains encompassing >98% of all essential and respiratory growth-essential genes, to study formic acid tolerance in Saccharomyces cerevisiae. To provide quantitative growth estimates on formic acid tolerance, the strains were screened individually on solid medium supplemented with 140 mM formic acid using the Scan-o-Matic platform. Selected resistant and sensitive strains were characterized in liquid medium supplemented with formic acid and in synthetic hydrolysate medium containing a combination of inhibitors. Strains with gRNAs targeting genes associated with chromatin remodeling were significantly enriched for strains showing formic acid tolerance. In line with earlier findings on acetic acid tolerance, we found genes encoding proteins involved in intracellular vesicle transport enriched among formic acid sensitive strains. The growth of the strains in synthetic hydrolysate medium followed the same trend as when screened in medium supplemented with formic acid. Strains sensitive to formic acid had decreased growth in the synthetic hydrolysate and all strains that had improved growth in the presence of formic acid also grew better in the hydrolysate medium. Systematic analysis of CRISPRi strains allowed identification of genes involved in tolerance mechanisms and provided novel engineering targets for bioengineering strains with increased resistance to inhibitors in lignocellulosic hydrolysates
Turbulent transport in tokamak plasmas: linear-, quasi- and non-linear simulations
Get PDFAn attractive energy source is nuclear fusion with its abundance of fuel, intrinsic safety and limited environmental impact. Although the concept of fusion energy was established in the 1920s, to develop fusion as an energy source has been challenging. The most developed concept for fusion is the tokamak, a torodial shaped chamber where a plasma, a hot ionized gas, is confined with a strong magnetic field. The feasibility and efficiency of the future fusion power plants depend critically on the energy confinement properties of the tokamaks which are mainly determined by micro turbulence.The turbulent transport is driven by different instabilities in the plasma, especially the Ion Temperature Gradient (ITG) mode, Trapped Electron Mode (TEM) and Electron Temperature Gradient (ETG) mode. The work presented in this thesis focuses on a number of key aspects of turbulent transport using advanced numerical modelling tools. In today\u27s experiments, measurements have shown the plasma\u27s densities to be peaked towards the centre of the plasma. Research into this peaking has uncovered two key mechanisms, a strong particle pinch from the turbulent transport and a particle source from Neutral Beam Injection which is used to heat plasma. In future tokamaks the source will be comparatively smaller, hence it is important to distinguish which of the two provides the dominant contribution. Which is one of the aspects analysed in the thesis. From basic considerations, the turbulent transport should exhibit so called gyro-Bohm scaling, i.e. the transport should increase with the ionic mass. However, this is not observed experimentally and the discrepancy is called the isotope effect. Several mechanism has been suggested as the cause, such as collisions, ExB shear, beta-effects, edge effects and contribution of the ETG mode. A number of JET discharges design to study this isotope effect have been analysed to asses the relative importance of these effects, Calculation of the turbulent transport can be computationally expensive, therefore reduced quasi-linear models that are computationally less intensive have been developed. These models use linear relations between perturbed quantities combined with a saturation rule for the electrostatic potential to determine the turbulent fluxes. A saturation rule adapted to a quasi-linear model has been developed and validated against non-linear gyro-kinetic simulations which are characterized by a high degree of physics fidelity
Dark matter-electron interactions in materials beyond the dark photon model
Get PDFThe search for sub-GeV dark matter (DM) particles via electronic transitions in underground detectors attracted much theoretical and experimental interest in the past few years. A still open question in this field is whether experimental results can in general be interpreted in a framework where the response of detector materials to an external DM probe is described by a single ionisation or crystal form factor, as expected for the so-called dark photon model. Here, ionisation and crystal form factors are examples of material response functions: interaction-specific integrals of the initial and final state electron wave functions. In this work, we address this question through a systematic classification of the material response functions induced by a wide range of models for spin-0, spin-1/2 and spin-1 DM. We find several examples for which an accurate description of the electronic transition rate at DM direct detection experiments requires material response functions that go beyond those expected for the dark photon model. This concretely illustrates the limitations of a framework that is entirely based on the standard ionisation and crystal form factors, and points towards the need for the general response-function-based formalism we pushed forward recently [1,2]. For the models that require non-standard atomic and crystal response functions, we use the response functions of [1,2] to calculate the DM-induced electronic transition rate in atomic and crystal detectors, and to present 90% confidence level exclusion limits on the strength of the DM-electron interaction from the null results reported by XENON10, XENON1T, EDELWEISS and SENSEI
Influence of iron nanopowder addition on the densification of chromium-prealloyed water-atomised powder metallurgy steel admixed with nickel
Get PDFHigh sintered density is desired for heavy-duty applications and there are different ways through which the sintered density can be improved. In the current study, nanopowder is blended to the conventionally used micrometre-sized water-atomised steel powder to evaluate its impact on sintering. Both the powder variants, without and with nanopowder, were subjected to thermogravimetry analysis, and uniaxially compacted to the same green density of 7.15 g/cc or 90% relative density and sintered at 1250\ub0C in pure hydrogen. A comparative analysis was performed with respect to the microstructural evolution between the micro and micro/nano bimodal powder compacts. JMatPro and electron backscattered diffraction was used to understand the microstructural evolution. An attempt was made to understand the improved linear shrinkage in the micro/nano bimodal powder compact using a combination of microstructure analysis and chemical analysis
Dynamics of Molecular Gas in the Central Region of the Quasar I Zwicky 1
Get PDFWe present a study of the molecular gas distribution and kinematics in the cicumnuclear region (radii ≲2 kpc) of the z ≈ 0.061 quasar I Zwicky 1 using a collection of available Atacama Large Millimeter/submillimeter Array observations of the carbon monoxide (CO) emission. With an angular resolution of ∼0.″36 (corresponding to ∼400 pc), the host-galaxy substructures including the nuclear molecular gas disk, spiral arms, and a compact bar-like component are resolved. We analyzed the gas kinematics based on the CO image cube and obtained the rotation curve and radial distribution of velocity dispersion. The velocity dispersion is about 30 km s−1 in the outer CO disk region and rises up to ≳100 km s−1 at radius ≲1 kpc, suggesting that the central region of the disk is dynamically hot. We constrain the CO-to-H2 conversion factor, α CO, by modeling the cold gas disk dynamics. We find that, with prior knowledge about the stellar and dark matter components, the α CO value in the circumnuclear region of this quasar host galaxy is 1.55 − 0.49 + 0.47 M ⊙ K km s − 1 pc 2 − 1 , which is between the value reported in ultraluminous infrared galaxies and in the Milky Way. The central 1 kpc region of this quasar host galaxy has significant star formation activity, which can be identified as a nuclear starburst. We further investigate the high-velocity dispersion in the central region. We find that the interstellar medium (ISM) turbulent pressure derived from the gas velocity dispersion is in equilibrium with the weight of the ISM. This argues against extra power from active galactic nuclei feedback that significantly affects the kinematics of the cold molecular gas
Characteristics and mechanisms of low-alloy high-strength steel corrosion behavior under barnacle adhesion based on a comparison experiment
No full textA comparative experiment was set up in a field site and laboratory to study the effect of barnacles (model organisms of macrofouling) on the corrosion behavior of a low-alloy high-strength steel. The results indicated that barnacle adhesion can slow the corrosion rate of steel in an immersion environment by hindering the diffusion of corrosive ions. It was found that barnacle adhesion had a significant promotion effect on localized corrosion. Due to steel’s high corrosion rate, the corrosion-impeding effect was improved, and the promotioneffect on localized corrosion was weakened. The study proposed a corrosion mechanism model influenced by barnacles
Scalable Fabrication of Edge Contacts to 2D Materials: Implications for Quantum Resistance Metrology and 2D Electronics
Get PDFWe report a reliable and scalable fabrication method for producing electrical contacts to two-dimensional (2D) materials based on the tri-layer resist system. We demonstrate the applicability of this method in devices fabricated on epitaxial graphene on silicon carbide (epigraphene) used as a scalable 2D material platform. For epigraphene, data on nearly 70 contacts result in median values of the one-dimensional (1D) specific contact resistances ρc ∼ 67 Ω\ub7μm and follow the Landauer quantum limit ρc ∼ n-1/2, consistently reaching values ρc < 50 Ω\ub7μm at high carrier densityn. As a proof of concept, we apply the same fabrication method to the transition metal dichalcogenide (TMDC) molybdenum disulfide (MoS2). Our edge contacts enable MoS2 field-effect transistor (FET) behavior with an ON/OFF ratio of >106 at room temperature (>109 at cryogenic temperatures). The fabrication route demonstrated here allows for contact metallization using thermal evaporation and also by sputtering, giving an additional flexibility when designing electrical interfaces, which is key in practical devices and when exploring the electrical properties of emerging materials
Flexible Mm-Wave Sigma-Delta-Over-Fiber MIMO Link
No full textMillimeter-wave and multiple-input-multiple-output (MIMO) technologies combine broad bandwidth with spatial diversity to offer a greater data rate. This paper investigates a flexible millimeter-wave sigma-delta-over-fiber based transmitter solution with digital beamforming MISO and MIMO functionality. Those functions are controlled by a central unit connecting a remote radio head with a standardized QSFP28 fiber link. The central unit generates binary encoded intermediate frequency signals using bandpass sigma-delta modulation. The QSFP28 based fiber link transmits the intermediate frequency bitstreams to the remote radio head. The remote radio head consists of a QSFP28 module, hybrids, and upconverters. The remote radio head feeds four parallel, independent, coherent, and central-unit controlled 28\ua0GHz signals to a linear array transmitting antenna. The transmitter performance is experimentally verified, demonstrating up to 800\ua0Msym/s at an EVM/NMSE of 6.7%/-23.5\ua0dB when tested with a 64 quadrature amplitude modulation (64-QAM) modulation scheme. Digital over-the-air beamforming MISO functionality is demonstrated up to 700\ua0Msym/s across 1\ua0m wireless distance. MIMO communication capabilities is demonstrated by over-the-air transmission of two independent 500\ua0Msym/s to two spatially separated receivers. The results show that the proposed link can be used for realization of scalable, low-cost and flexible transmitter solution for emerging distributed antenna systems
A Dual-Permanent-Magnet Machine with Asymmetric Stator Teeth-Tips
No full textDual-permanent-magnet machines (DPMMs) have attracted increasing attentions due to their merit of high torque density. Nevertheless, DPMMs suffer from low PM utilization ratio owing to large PM consumption. To improve the situation, this paper presents a DPMM with asymmetric stator teeth-tips, termed as AST-DPMM. The key of the proposed design is to arrange wide and narrow stator teeth-tips alternatively. By building an analytical model of the AST-DPMM, the impact of asymmetric stator teeth-tips is investigated. It is found the asymmetric stator teeth-tips can enhance the working harmonics by generating new magnetomotive force harmonics and permeance harmonics. Hence, it can achieve high torque density and improve PM utilization ratio simultaneously. The performance comparisons together with other machines are conducted to evaluate the investigated AST-DPMM. Finally, a prototype of the AST-DPMM is fabricated, and the experimental testing is conducted to verify the proposed ideas