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ATLAS $b$-jet identification performance and efficiency measurement with $t{\bar{t}}$ events in $pp$ collisions at $\sqrt{s}=13$
The algorithms used by the ATLAS Collaboration during Run 2 of the Large Hadron Collider to identify jets containing b-hadrons are presented. The performance of the algorithms is evaluated in the simulation and the efficiency with which these algorithms identify jets containing b-hadrons is measured in collision data. The measurement uses a likelihood-based method in a sample highly enriched in $t\bar{t}$ events. The topology of the t → Wb decays is exploited to simultaneously measure both the jet flavour composition of the sample and the efficiency in a transverse momentum range from 20 to 600 GeV. The efficiency measurement is subsequently compared with that predicted by the simulation. The data used in this measurement, corresponding to a total integrated luminosity of 80.5 fb -1 , were collected in proton–proton collisions during the years 2015–2017 at a centre-of-mass energy $ \sqrt{s}$ = 13 TeV. By simultaneously extracting both the efficiency and jet flavour composition, this measurement significantly improves the precision compared to previous results, with uncertainties ranging from 1 to 8% depending on the jet transverse momentum.
Efficient design of random metasurfaces
Random media introduce large degrees of freedom in device design and can thus address challenges in manipulating optical waves. Wave shaping with metasurfaces has mainly utilized periodic or quasi-periodic grids, and the potential of random arrangement of particles for devices has only come under investigation recently. The main difficulty in pursuing random metasurfaces is the identification of the degrees of freedom that optimize their efficiencies and functions. They can also encode information using the statistics of particle distribution. We propose a phase-map that accounts for the statistical nature of random media. The method takes into account effects of random near-field couplings that introduce phase errors by affecting the phase shift of elements. The proposed approach increases the efficiency of our random metasurface devices by up to ~20%. Furthermore, this work paves the way toward the efficient design of random metasurfaces with potential applications in highly secure optical cryptography and information encoding.
Microstructure tuning facilitated photo-efficiency enhancement and environmental benign nature of HfO2/Mo/HfO2 multilayer films
Nano-layered, multilayered ?lms consisting of HfO2(dielectric)/Mo(metal)/HfO2(dielectric), (D/M/D archi-tecture) with controlled layer thickness, chemistry and microstructure were demonstrated for e?cient utiliza-tion of solar energy with well-designated spectral control. The e?ect of Mo metal interlayer on the energy performance and e?ciency of HfO2/Mo/HfO2 multilayer ?lms made by electron-beam deposition onto silicon and glass substrates has been evaluated. The Mo interlayer thickness [Mo(t)] was varied in the range of 5–25 nm while the top/bottom HfO2 layer thickness was kept constant at ~50 nm. Structural, morphological and optical characterization was performed to understand the e?ect of Mo(t) induced microstructure on mechanical dur-ability and optical behavior of the D/M/D multilayer ?lms. Structural studies revealed that D/M/D multilayer ?lms with relatively low Mo(t) were amorphous, while higher Mo(t) induces the amorphous-to-nanocrystalline microstructure transformation, which also induces surface roughening e?ects. The D/M/D multilayer ?lm with Mo(t) = 20 nm, where the nano-columnar morphology of the D-M-D layers are aligned perpendicular to the substrate surface and exhibits the optimum spectral selectivity. Such microstructure and morphological tailoring also facilitates the environmentally friendly (self-cleaning/stain repellent) nature of these multilayer ?lms by the high contact angle (~102°) achieved. Molybdenum interlayer facilitated higher contact angle leads to super-hydrophobic nature of the HfO2/Mo/HfO2 multilayered ?lm surfaces. The low surface roughness values (0.2–0.8 nm), which are primarily due to Mo at the interface, of the HfO2/Mo/HfO2 multilayered ?lms satisfy the general requirements of heat mirror applications. In addition, the microstructure of intermediate Mo layer and HfO2-Mo interfaces signi?cantly control the mechanical properties of D/M/D multilayer ?lms. Optimal me-chanical properties (hardness = 30 GPa, elastic modulus = 312 GPa, wear resistance = 0.094, adhesion strength = 2050 µN) have been obtained for Mo(t) = 20 nm D/M/D multilayer ?lm. The mechanical response strongly supports ?exible and wear resistive nature of HfO2/Mo/HfO2 multilayer ?lms.
Memory Seeds Enable High Structural Phase Purity in 2D Perovskite Films for High-Efficiency Devices
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Experimental study of the impact of scavenging efficiency on diesel combustion in an opposed-piston two-stroke engine
The opposed-piston two-stroke (OP2S) engine is a promising alternative powertrain technology that can offer thermal and brake efficiency improvements over conventional four-stroke engines. In recent years, many of the technical barriers of the OP2S engine architecture have been overcome. However, there is still a need for fundamental studies to provide insight into the scavenging and combustion processes of the OP2S engine to help design and operate the most efficient combustion systems using this engine architecture. This work aims to provide such insights by analyzing experimental data collected on a 3-cylinder, 4.9 L OP2S engine. Specifically, a scavenging efficiency sweep, an engine speed sweep with a constant scavenging efficiency, and an engine speed with a constant pressure differential across the engine were studied in detail. It was found that in diesel combustion, as the scavenging efficiency decreased, the increase in temperature of the hot, internal residuals resulted in a significant increase in heat transfer. Despite lowering pumping losses, this resulted in an overall decrease in brake efficiency. When the bulk thermodynamic conditions of two different scavenging efficiency cases (67% and 72%) were matched at port closing, the lower scavenging efficiency case still displayed a 0.7 percentage point penalty in net thermal efficiency and an increase in engine-out indicated specific emissions of NOx of 18% due to residual stratification in the cylinder. The results presented in this work show that the optimal breathing strategy in diesel combustion on an OP2S engine architecture is one that results in a slightly under-scavenged environment at port closing. However, the results did show potential system-level efficiency benefits of decreasing scavenging efficiency, meaning that alternative fuels and combustion strategies without the constraints of diesel combustion could achieve system-level efficiency gains by running significantly under-scavenged.
Performance of direct injected propane and gasoline in a high stroke-to-bore ratio SI engine: Pathways to diesel efficiency parity with ultra low soot
This work explores pathways to achieve diesel-like, high-efficiency combustion with stoichiometric 3-way catalyst compatible combustion in a single-cylinder spark ignition (SI) research engine. A unique high stroke-to-bore engine design (1.5:1) with cooled exhaust gas recirculation (EGR) and high compression ratio ( r c ) was used to improve engine efficiency by up to 30% compared with a production turbocharged gasoline direct injection spark ignition engine. Engine experiments were conducted with both 91 RON E10 gasoline and liquified petroleum gas (LPG) (i.e. autogas) and were compared to legacy gasoline data on the production engine. Geometric compression ratio ( r c ) of 13.3:1 was used for both fuels with additional experiments at 16.8:1 for LPG only. Measurements of exhaust soot particle size and number concentrations were made with both fuels. Significant reduction in soot particles across the whole particle size range were achieved with LPG due to the elimination of in-cylinder liquid films. The effects of EGR, late intake valve closing (IVC) and fuel characteristics were investigated through their effects on efficiency, combustion stability and soot production. Results of 47% gross thermal efficiency, and 45% net thermal efficiency at stoichiometric engine operation, at up to 17 bar IMEP and 2000 r/min with 16.8:1 r c were achieved with LPG. Estimated brake efficiency values were compared to a contemporary medium duty diesel engine illustrating the benefits of the chosen path for achieving diesel efficiency parity.
Over 11% Efficient Eco-Friendly Kesterite Solar Cell: Effects of S-Enriched Surface of Cu2ZnSn(S,Se)4 Absorber and Band Gap Controlled (Zn,Sn)O Buffer
For high efficiency kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cell, CdS thin film was usually used as a buffer layer. However, due to the toxicity of Cd and pollution problems involved from the solution-based chemical bath deposition, eco-friendly high efficiency CZTSSe solar cell with Cd-free buffer is necessary. As an Cd-free buffer layer, we investigated (Zn,Sn)O (ZTO) film deposited by sputtering method. In order to achieve high power conversion efficiency, we controlled energy band gaps of CZTSSe absorber as well as ZTO buffer, which was required to optimize conduction band offset (CBO) between the absorber and the buffer and to increase open circuit voltage (Voc) and fill factor (FF). The CBO was optimized by controlling the band gap of ZTO. By varying the Sn/(Zn + Sn) ratio and its deposition temperature, band gap of ZTO was successfully adjusted. Experimental and computational calculation results showed that solar cell performance was strongly affected by the CBO between absorber and buffer. Besides CBO matching, larger band gap of ZTO improved short circuit current density (Jsc) with enhanced external quantum efficiency value in blue photon spectrum range. As an additional way to improve power conversion efficiency of solar cell, band graded CZTSSe absorber was developed by using spray-based two-step process. The sprayed CZTSSe film was engineered to have S-enriched surface, which makes surface band gap widened and surface passivated, and resultantly increases Voc, Jsc and fill factor (FF). By controlling band gaps of both CZTSSe absorber and ZTO buffer, we obtained 11.22% environment-friendly CZTSSe solar cell without MgF2 anti-reflection coating.
Investigation of the combined efficiency of a solar/gas hybrid water heating system
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Highly Efficient Solar-Driven Carbon Dioxide Reduction on Molybdenum Disulfide Catalyst Using Choline Chloride-Based Electrolyte
Conversion of CO2 to energy-rich chemicals using renewable energy is of much interest to close the anthropogenic carbon cycle. However, the current photoelectrochemical systems are still far from being practically feasible. Here the successful demonstration of a continuous, energy efficient, and scalable solar-driven CO2 reduction process based on earth-abundant molybdenum disulfide (MoS2) catalyst, which works in synergy with an inexpensive hybrid electrolyte of choline chloride (a common food additive for livestock) and potassium hydroxide (KOH) is reported. The CO(2 )saturated hybrid electrolyte utilized in this study also acts as a buffer solution (pH approximate to 7.6) to adjust pH during the reactions. This study reveals that this system can efficiently convert CO(2 )to CO with solar-to-fuel and catalytic conversion efficiencies of 23% and 83%, respectively. Using density functional theory calculations, a new reaction mechanism in which the water molecules near the MoS(2 )cathode act as proton donors to facilitate the CO2 reduction process by MoS2 catalyst is proposed. This demonstration of a continuous, cost-effective, and energy efficient solar driven CO2 conversion process is a key step toward the industrialization of this technology.
Measurements of b -jet tagging efficiency with the ATLAS detector using $t\overline{t}$ events at $\sqrt{s}=13$ TeV
The efficiency to identify jets containing b-hadrons (b-jets) is measured using a high purity sample of dileptonic top quark-antiquark pairs ($t\bar{t}$) selected from the 36.1 fb -1 of data collected by the ATLAS detector in 2015 and 2016 from proton-proton collisions produced by the Large Hadron Collider at a centre-of-mass energy $\sqrt{s}=13$ TeV. Two methods are used to extract the efficiency from $t\bar{t}$ events, a combinatorial likelihood approach and a tag-and-probe method. A boosted decision tree, not using b-tagging information, is used to select events in which two b-jets are present, which reduces the dominant uncertainty in the modelling of the flavour of the jets. The efficiency is extracted for jets in a transverse momentum range from 20 to 300 GeV, with data-to-simulation scale factors calculated by comparing the efficiency measured using collision data to that predicted by the simulation. In conclusion, the two methods give compatible results, and achieve a similar level of precision, measuring data-to-simulation scale factors close to unity with uncertainties ranging from 2% to 12% depending on the jet transverse momentum.
Platform for Accurate Efficiency Quantification of > 35% Efficient Thermophotovoltaic Cells
Thermophotovoltaic (TPV) devices convert thermal radiation directly into electricity using semiconductor diodes and have a variety of uses from waste heat recovery to energy storage to primary power conversion. Recent results have demonstrated promising cells nearing and surpassing 30% conversion efficiency. As TPV cells continue to increase in efficiency, they become attractive for a wider range of applications. Their efficiencies must be quantified in a standardized fashion to compare results accurately across research groups. Here, we outline and quantify the most important characteristics of an accurate and precise TPV efficiency measurement. Using a custom-built measurement apparatus that takes these characteristics into account, we report 19 cells with greater than 30% conversion efficiency and 2 cells with greater than 35% conversion efficiency. This confirms that our reported cell efficiencies are not simply those of hero cells but rather of a distribution of cells that can be produced in a consistent, high-quality process.
Suppressed non-radiative loss and efficient hole transfer at a small highest occupied molecular orbital offset endows binary organic solar cells with 19.73% efficiency and a small efficiency-cost gap
Two novel acceptors are designed and synthesized, and the PTQ11:PEH-F binary system is highly promising for industrial cost-effective organic photovoltaics.
Edge Dislocations Induce Improved Photocatalytic Efficiency of Colored TiO2
Titanium oxide is the most widely used material for photocatalytic applications due to its low cost and environmental friendliness. One of the grand challenges to improve its energy conversion efficiency is to utilize more visible light while inhibiting the recombination of photo-generated electrons and holes. We use a one-step hydro-solvothermal method to obtain colored ultra-fine nanowires of rutile and nanoparticles of anatase with edge dislocations, which induced broadened visible solar absorption (400-900 nm) and improved photocatalytic efficiency up to 1.8 times that of rutile or anatase without defects. Enhanced photocatalytic activity of these structures is demonstrated by photodegrading methylene blue measurements under simulated solar light irradiation. Results show the existence of Ti3+, induced by edge dislocations, and subsequent electronic band structure-property relationships. This work highlights a strategy for generating sufficient desired defects in TiO2 nanostructures, leading to broadened visible solar absorption and improved photocatalytic efficiency under visible light irradiation.
Efficient Cytosolic Delivery Using Crystalline Nanoflowers Assembled from Fluorinated Peptoids
The design and synthesis of biocompatible nanomaterials as cargoes for the intracellular delivery of therapeutic proteins or genes have attracted intense attention because of their promise for use in therapeutics. Despite the advances in this area, very few nanomaterials can be efficiently delivered to the cytosol. To address these challenges, we designed and synthesized crystalline nanoflower-like particles from fluorinated sequence-defined peptoids; the crystallinity and fluorination of these particles enabled highly efficient cytosolic delivery with minimal cytotoxicity. We delivered these particles, 80% appear to diffuse in the cytosol. Furthermore, these nanocrystals can carry mRNA for instance and effectively delivered into cytosol for gene transfection, demonstrating the generality of our nanocrystals. Our results indicate that self-assembly of crystalline nanomaterials from fluorinated peptoids paves a new way toward development of nanocargoes with efficient cytosol gene delivery. Y. Song and M. Wang contributed equally to this work. This work was supported by start-up funds from Washington State University. Peptoid synthesis work was supported by the Materials Synthesis and Simulation Across Scales (MS3) Initiative through the LDRD fund at Pacific Northwest National Laboratory (PNNL). Assembly of peptoid particles and their structural characterizations were supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Biomolecular Materials Program at PNNL. XRD work was conducted at the Advanced Light Source with support from the Molecular Foundry, at Lawrence Berkeley National Laboratory, both of which are supported by the Office of Science, under Contrast No. DE-AC02-05CH11231. PNNL is multi-program national laboratory operated for Department of Energy by Battelle under Contract No. DE-AC05-76RL01830.
Impact of Measured Spectrum Variation on Solar Photovoltaic Efficiencies Worldwide
In photovoltaic power ratings, a single solar spectrum, AM1.5, is the de facto standard for record laboratory efficiencies, commercial module specifications, and performance ratios of solar power plants. More detailed energy analysis that accounts for local spectral irradiance, along with temperature and broadband irradiance, reduces forecast errors to expand the grid utility of solar energy. Here, ground-level measurements of spectral irradiance collected worldwide have been pooled to provide a sampling of geographic, seasonal, and diurnal variation. Applied to nine solar cell types, the resulting divergence in solar cell efficiencies illustrates that a single spectrum is insufficient for comparisons of cells with different spectral responses. Cells with two or more junctions tend to have efficiencies below that under the standard spectrum. Silicon exhibits the least spectral sensitivity: relative weekly site variation ranges from 1% in Lima, Peru to 14% in Edmonton, Canada.
A hot carrier perovskite solar cell with efficiency exceeding 27% enabled by ultrafast hot hole transfer with phthalocyanine derivatives
Illustration of hot hole transfer through interfacial S–Pb interactions, and a peak efficiency of 27.30% was achieved under 5.9 suns via ultrafast hot hole extraction.