Energy Filtering Research Articles

Optimal power and efficiency of single quantum dot heat engines: Theory and experiment

Quantum dots (QDs) can serve as near perfect energy filters and are therefore of significant interest for the study of thermoelectric energy conversion close to thermodynamic efficiency limits. Indeed, recent experiments in [Nat. Nano. 13, 920 (2018)] realized a QD heat engine with performance near these limits and in excellent agreement with theoretical predictions. However, these experiments also highlighted a need for more theory to help guide and understand the practical optimization of QD heat engines, in particular regarding the role of tunnel couplings on the performance at maximum power and efficiency for QDs that couple seemingly weakly to electronic reservoirs. Furthermore, these experiments also highlighted the critical role of the external load when optimizing the performance of a QD heat engine in practice. To provide further insight into the operation of these engines we use the Anderson impurity model together with a Master equation approach to perform power and efficiency calculations up to co-tunneling order. This is combined with additional thermoelectric experiments on a QD embedded in a nanowire where the power is measured using two methods. We use the measurements to present an experimental procedure for efficiently finding the external load $R_P$ which should be connected to the engine to optimize power output. Our theoretical estimates of $R_P$ show a good agreement with the experimental results, and we show that second order tunneling processes and non-linear effects have little impact close to maximum power, allowing us to derive a simple analytic expression for $R_P$. In contrast, we find that the electron contribution to the thermoelectric efficiency is significantly reduced by second order tunneling processes, even for rather weak tunnel couplings.

Transparent dual band Wi‐Fi filter for double glazed energy saving window as a smart network

AbstractA transparent advanced electromagnetic structure is designed to be used in real‐world Wi‐Fi shielding applications. Concentric square loops as frequency selective surfaces (FSSs) are analytically presented with the Pyrex glass substrate based on the equivalent electric circuit model. The designed FSS window suppresses signals at both 2.5 and 5 GHz bands, and reflects back to the indoor medium. Visible light transmittance of the studied window is achieved as 87%. Accordingly, other electromagnetic communication links can transfer through the designed filter such as cell phone, and radio. The dependency of the proposed window to polarization and angular variations is examined numerically, which shows stable frequency response at 2.5 GHz and an acceptable one for 5 GHz. As a figure of merit, the proposed structure is a double glazed window with potential application for smart, secure, and energy‐saving buildings. Also, practical considerations regarding the deployment of FSS on window glass and the separation distance between the glass layers have been investigated. A prototype of the proposed design is fabricated and measured that a good agreement between measurement and simulation is demonstrated. Therefore, parametric circuit model analysis, deployment of transparent substrate, thin metallic parts on one layer, secure indoor communications, and energy‐saving are some of the advantages of the proposed window.

Full-field X-ray fluorescence microscope based on total-reflection advanced Kirkpatrick-Baez mirror optics.

A novel full-field X-ray fluorescence microscope based on total-reflection advanced Kirkpatrick-Baez mirror optics was developed. The total-reflection imaging mirror optics arrangement, with four reflections, has the advantage of being able to function both as a powerful low-pass energy filter, completely rejecting incident excitation X-rays, and as an achromatic optical imaging system. Isolated X-ray fluorescence signals can be imaged, avoiding imaging-detector saturation, with low background noise. A prototype fluorescence microscope constructed at SPring-8 demonstrated the capability to simultaneously image elemental distributions using various X-ray fluorescence signals (Ni, Cu, Zn, Ge, and Bi). A half-period spatial resolution of ~0.5-1 µm (1000-500 LP/mm) was achieved, owing to the achromaticity of the imaging mirrors and the photon-counting scheme of the CCD camera used for fluorescence detection.

Iterative Bayesian denoising based on variance stabilization using Contourlet Transform with Sharp Frequency Localization: application to EFTEM images

BackgroundDue to the presence of high noise level in tomographic series of energy filtered transmission electron microscopy (EFTEM) images, alignment and 3D reconstruction steps become so difficult. To improve the alignment process which will in turn allow a more accurate and better three dimensional tomography reconstructions, a preprocessing step should be applied to the EFTEM data series.ResultsExperiments with real EFTEM data series at low SNR, show the feasibility and the accuracy of the proposed denoising approach being competitive with the best existing methods for Poisson image denoising. The effectiveness of the proposed denoising approach is thanks to the use of a nonparametric Bayesian estimation in the Contourlet Transform with Sharp Frequency Localization Domain (CTSD) and variance stabilizing transformation (VST). Furthermore, the optimal inverse Anscome transformation to obtain the final estimate of the denoised images, has allowed an accurate tomography reconstruction.ConclusionThe proposed approach provides qualitative information on the 3D distribution of individual chemical elements on the considered sample.

CFGVF: An improved correlation filters based visual tracking algorithm

Visual tracking is a challenging task in computer vision. Correlation filter (CF) based visual tracking algorithm has become an attractive tracking technique, while there are still some limitations. Existing CF-based tracking algorithms are vulnerable to the influence of the surrounding background, and the usage of fixed scale template may easily lead to tracking failure. To overcome the above limitations, we propose a CFs-based visual tracking algorithm, CFs with Gabor energy filter, variable-scale template and features fusion (CFGVF). In CFGVF, the Gabor energy filter is firstly adopted to preprocess every frame of the image sequence, which largely eliminates the influence of illumination variation. Then, the Gabor energy, Histogram of Oriented Gradient and color naming features are integrated to enhance the ability of dealing with significant appearance variations such as deformation and motion blur. Furthermore, we propose a variable-scale template method to estimate the scale of the target object. Finally, an online updating schema is adopted to reduce the interference of surrounding background and occlusion. Experimental results on the visual tracking benchmark dataset OOTB show that the performance and robustness of the CFGVF tracker outperform those of several state-of-the-art trackers.

Optimal performance region of energy selective electron cooling devices consisting of three reservoirs

In this paper, a model of irreversible three-electron-reservoir energy selective electron (ESE) cooling device with heat leakage is established. By utilizing the finite time thermodynamics, the optimal performance of the cooling device is studied and the influences of chemical potential differences of electron reservoirs, center energy level of energy filters and heat leakage on the optimal performances are discussed. On the basis of cooling rate and coefficient of performance (COP) analyses, the exergy-based ecological function and figure of merit are proposed as objective functions. The operation properties of ESE cooling device with different objective functions are investigated and the optimal performance region is obtained. Higher cooling rate and COP can both be attained for the ESE cooling device when it is working in the optimal performance region.

Automatic optic disc segmentation using a 3D Morphologic Fuzzy Histon Roughness Index

Fundus images have become increasingly important due to the growing number of diabetics and their risk of developing diabetic retinopathy. Automated diagnosis of retinal images requires the separation and analysis of retinal elements. Among these elements, the optic nerve head is the most significant since it is used as a reference for detecting other anatomical structures such as the fovea and blood vessels. For this reason, optic disc segmentation is essential. This paper presents a method for locating and segmenting the optic disc using the circular Hough transform and the roughness index, respectively. We used a location algorithm based on the multiscale energy filter for fast location and the medial Hough transform as the decision criterion. Segmentation was performed with Atanassov’s Intuitionistic Fuzzy Set representation and an algorithm using the 3D roughness index and mathematical morphology to smoothly segmenting. This approach to automatic segmentation was tested on the MESSIDOR database, achieving 99.59% accuracy and 91.56% sensitivity. Other types of roughness indices were also evaluated; however, color correlation within the color space of the object itself produced better results for the proposed algorithm. We hope these findings contribute to the development of reliable automatic diagnostic tools for retinal images.

Modeling of hot carrier solar cell with semi-infinite energy filtering

Electrical parameters of a symmetrical hot carrier solar cell double heterostructure with metallic absorber layer and high-pass energy filters are calculated within thermionic emission theory. An efficiency limit of 73% is predicted for infinite characteristic cooling time and full solar concentration. Carrier cooling is treated within linear thermal conductivity model. Heat loss through carrier cooling in the absorber layer depends not only on the characteristic cooling time, but also on the specific volumetric heat capacity of the carrier gas and on the thickness of the absorber layer. Optimal absorption of light together with small thermal loss to the lattice require high carrier mobility in the absorber layer.

Energy, Phonon, and Dynamic Stability Criteria of Two-Dimensional Materials.

First-principles calculations have become a powerful tool to exclude the Edisonian approach in search of novel two-dimensional (2D) materials. However, no universal first-principles criteria to examine the realizability of hypothetical 2D materials have been established in the literature yet. Because of this, and as the calculations are always performed in an artificial simulation environment, one can unintentionally study compounds that do not exist in experiments. Although investigations of physics and chemistry of unrealizable materials can provide some fundamental knowledge, the discussion of their applications can mislead experimentalists for years and increase the gap between experimental and theoretical research. By analyzing energy convex hull, phonon spectra, and structure evolution during ab initio molecular dynamics simulations for a range of synthesized and recently proposed 2D materials, we construct energy, phonon, and dynamic stability filters that need to be satisfied before proposing novel 2D compounds. We demonstrate the power of the suggested filters for several selected 2D systems, revealing that some of them cannot be ever realized experimentally.

Porphyrin‑silver nanoparticles hybrids: Synthesis, characterization and antibacterial activity

The preparation of light-activated hybrid antibacterial agent combining the porphyrin molecules, bound to the silver nanoparticles (AgNPs) surface is reported. AgNPs were synthesized by N-methyl-2-pyrrolidone-initiated reduction without additional reducing agents. The chemical structure of protoporphyrin IX was modified with the aim to introduce thiol groups. The size distribution and shape features of AgNPs were checked using TEM and HRTEM microscopies. The introduction of thiol groups into the porphyrin was proved by IR spectroscopy. The AgNPs-porphyrin binding was performed in solution and confirmed by fluorescence quenching, Raman spectroscopy and energy-filtered transmission electron microscopy (EFTEM). The antibacterial tests were performed against S. epidermidis and E. coli upon to LED illumination and in the dark. The synergetic effect of AgNPs and porphyrin as well as light activation of the created antibacterial conjugates were observed.

A new cryo-EM system for single particle analysis

A new cryo-EM system has been investigated for single particle analysis of protein structures. The system provides parallel illumination of a highly-coherent 300 kV electron beam from a cold-field emission gun, and boosts image contrast with an in-column energy filter and a hole-free phase plate. It includes motorized cryo-sample loading and automated liquid-nitrogen filling for cooling multiple samples. In this study, we describe gun and electron beam characteristics, and demonstrate the suitability of this system for single particle reconstructions. The performance of the system is tested on two examples, a spherical virus and apoferritin. GUI programs have also been developed to control and monitor the system for correct illumination, imaging with less ellipticity and steady magnification, and timing of flashing and liquid-nitrogen filling. These programs are especially useful for efficient application of the system to single particle cryo-EM.

A new cryo-EM system for electron 3D crystallography by eEFD

A new cryo-EM system has been developed and investigated for use in protein electron 3D crystallography. The system provides parallel illumination of a coherent 300 kV electron beam to a sample, filters out energy-loss electrons through the sample with an in-column energy filter, and allows rotational data collection on a fast camera. It also possesses motorized cryo-sample loading and automated liquid-nitrogen filling for cooling of multiple samples. To facilitate its use, we developed GUI programs for efficient operation and accurate structure analysis. Here we report on the performance of the system and first results for thin 3D crystals of the protein complexes, catalase and membrane protein complex ExbBD. Data quality is remarkably improved with this approach, which we name eEFD (electron energy-filtered diffraction of 3D crystals), compared with those collected at 200 kV without energy filtration. Key advances include precise control of the microscope and recordings of lens fluctuations, which the programs process and respond to. We also discuss the merits of higher-energy electrons and filtration of energy-loss electrons in electron 3D crystallography.

Microstructural origins of the high mechanical damage tolerance of NbTaMoW refractory high-entropy alloy thin films

Refractory NbTaMoW thin films in close to equiatomic composition were deposited by ion beam sputter-deposition at room temperature. Energy-filtered transmission electron microscopy shows uniform distribution of all elements and electron diffraction patterns reveals unvarying body-centred cubic crystalline structure. Transmission electron microscopy images show large grains with columnar morphology. Ar bubbles with diameters around of 1.3 ± 0.4 nm were witnessed. The film growth mechanisms are discussed based on high-entropy film nature, general nucleation and growth theory and the Movchan-Demchishin-Thornton structure-zone growth models. Nanoindentation showed that the films have hardness of 22.8 ± 0.7 GPa. Nanoscratching demonstrated that such high hardness is also connected with high crack and delamination resistances. This indicates high mechanical damage tolerance (e.g. toughness). The results show that the combination of refractory metals with the intrinsic characteristics of high-entropy alloy systems in the NbTaMoW case can be considered as a hard coating candidate for future application in extreme environments.

Resolving the molecular gymnastics of the elusive herpes simplex fusion protein

Herpes Simplex Virus (HSV) afflicts ∼90 % of the population, causing a range of diseases from oral cold sores to encephalitis. Despite the widespread effects of HSV, current drugs cannot cure infection and there are no preventative vaccines. HSV infection requires entry into the host cell, which is mediated by the fusion protein, gB. Despite various structures being available for post-fusion gB, a high-resolution model for the pre-fusion state, required to understand the fundamental mechanism of HSV fusion, is still lacking. To elucidate this structure, full length gB was previously expressed on lipid vesicles and was shown via cryo-electron microscopy techniques to adopt the elusive pre-fusion state. Strikingly, two recent studies, one characterising such vesicles, generated two different pre-fusion gB models. The discrepancy between the models can be summarised by the position of the fusion loops: are they positioned facing away from the viral membrane or towards it in the pre-fusion state? Using the gB studded vesicle production method combined with a state-of-the-art Titan Krios cryo-electron microscope equipped with a Volta Phase Plate, a direct electron detector camera and an energy filter, all to increase contrast and signal-to-noise ratio, we aim to settle the dispute as to the structure of pre-fusion gB. Revealing the pre-fusion structure could lead to possible therapeutics to a disease that can have serious complications in newborns and the immunocompromised, a growing cohort in the modern world.

High-Contrast Imaging of Nanodiamonds in Cells by Energy Filtered and Correlative Light-Electron Microscopy: Toward a Quantitative Nanoparticle-Cell Analysis.

Fluorescent nanodiamonds (fNDs) represent an emerging class of nanomaterials offering great opportunities for ultrahigh resolution imaging, sensing and drug delivery applications. Their biocompatibility, exceptional chemical and consistent photostability renders them particularly attractive for correlative light-electron microscopy studies providing unique insights into nanoparticle-cell interactions. Herein, we demonstrate a stringent procedure to image and quantify fNDs with a high contrast down to the single particle level in cells. Individual fNDs were directly visualized by energy-filtered transmission electron microscopy, that is, inside newly forming, early endosomal vesicles during their cellular uptake processes as well as inside cellular organelles such as a mitochondrion. Furthermore, we demonstrate the unequivocal identification, localization, and quantification of individual fNDs in larger fND clusters inside intracellular vesicles. Our studies are of great relevance to obtain quantitative information on nanoparticle trafficking and their various interactions with cells, membranes, and organelles, which will be crucial to design-improved sensors, imaging probes, and nanotherapeutics based on quantitative data.

Master-slave wave farm systems based on energy filter with smoothed power output

Wave energy is an important renewable energy source. Previous studies of wave energy conversion (WEC) have focused on the maximum power take-off (PTO) techniques of a single machine. However, there is a lack of research on the energy and power quality of wave farm systems. Owing to the pulsating nature of ocean waves and popular PTO devices, the generated electrical power suffers from severe fluctuations. Existing solutions require extra energy storage and overrated power converters for wave power integration. In this study, we developed a master-slave wave farm system with rotor inertia energy storage; this system delivers self-smoothed power output to the grid and reduces the number of converters. Two control methods based on the moving average filter (MAF) and energy filter (EF) are proposed to smooth the output power of wave farms. RTDS simulations show that the proposed systems and control methods facilitate simple and smooth grid integration of wave energy.

4He irradiation of zircon, ZrSiO4, using a micro-patterned, Si-based energy filter

The quantitative evaluation of alpha-particle damage in the mineral zircon, ZrSiO4, using 4He irradiation experiments is difficult because the vast majority of atomic knock-ons in the target are concentrated in a narrow depth range near the ends of the He-ion trajectories. Here we present a new concept to overcome this problem, namely, tailoring the depth profile of damage by means of a micromechanically fabricated “energy filter”. Lamellae of 1.5 μm thickness, prepared from ZrSiO4 using the focused-ion-beam technique, were subjected to irradiation with 8.8 MeV 4He ions. Five irradiations with ion fluences in the range 2.5 × 1015–1 × 1017 cm−2 have resulted in mild to severe damage, as monitored by the broadening and downshift of SiO4-stretching Raman bands. Our results may provide a means for quantifying the contribution of alpha particles to the total self-irradiation damage in zircon.

Response of 14YWT alloys under neutron irradiation: A complementary study on microstructure and mechanical properties

Nanostructured ferritic alloys (NFAs) having sub-micron grain size with a high density of nano-oxides (NOs) (size of ∼2–3 nm) are one of the best candidates for structural components in Generation IV nuclear systems. In this study, 14YWT NFA cladding tubes were irradiated in BOR60 reactor up to 7 dpa at 360–370 °C. Detailed microstructural analysis has been conducted using bright field transmission electron microscopy, bright field scanning transmission electron microscopy, energy filtered transmission electron microscopy, energy dispersive X-ray spectroscopy, electron energy loss spectroscopy and transmission Kikuchi diffraction techniques. This revealed cavities, <100> and <111> type dislocation loops, and α′ precipitates forming after irradiation with relationships between cavities and NOs, and α′ precipitates and NOs. Cavities mostly form on the NOs; whereas, α′ precipitates form between the NOs where the point defect concentration is high. Moreover, α′ precipitates are distributed homogenously on and around the dislocation loops which is consistent with the observation that there is no Cr segregation on dislocation loops. Grain boundaries were found to be mostly depleted in Cr; however, the characteristics of each grain boundary determines the Cr behavior and the α′ denuded zone around the grain boundaries. Mechanical properties of the irradiated tubes have been determined by using both low force and high force nanoindentation techniques, resulting in 1.03 ± 0.33 GPa and 0.82 ± 0.20 GPa hardening, respectively. Dispersed barrier hardening calculations and nanoindentation measurements are in good agreement. In this study, 14YWT NFA has been systematically studied after neutron irradiation to better understand its superior performance: low α′ concentration, low swelling and low radiation-induced hardening.

Effect of drying process and calcination on the structural and magnetic properties of cobalt ferrite

Synthesis of CoFe2O4 nanoparticles was carried out using a co-precipitation method. The resulting precipitate was dried by using conventional method (oven), and spray drying process. The products obtained from the two drying processes were calcined at 500 and 700 °C; and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) transmission electron microscopy (TEM), and N2 gas adsorption technique. Magnetic measurements were performed on a SQUID magnetometer. The magnetic saturation value (76 emu g−1) of the spray dried cobalt ferrite calcined at 700 °C (SD-700) was higher than its corresponding oven-dried sample. The as-received spray dried CoFe2O4 nanoplates (SD-100) has the highest BET specific surface area (138 m2 g−1), while the oven-dried sample calcined at 700 °C (OD-700) has the lowest area (47 m2 g−1). Cobalt ferrite samples obtained from the two drying processes were briefly applied to adsorb methylene blue solution as a cationic dye model to know the effect of drying process on the adsorption of dye. The studies showed that all the spray dried samples performed better in adsorbing methylene blue (MB) solution. Energy-filtered TEM (EFTEM) analysis that was carried out on SD-700 ascertained the adsorption of MB on its surface.

Radiation of Dynamic Toroidal Moments.

Dynamic toroidal dipoles, a distinguished class of fundamental electromagnetic sources, receive increasing interest and participate in fascinating electrodynamic phenomena and sensing applications. As described in the literature, the radiative nature of dynamic toroidal dipoles is sometimes confounded, intermixing with static toroidal dipoles and plasmonic dark modes. Here, we elucidate this issue and provide proof-of-principle experiments exclusively on the radiation behavior of dynamic toroidal moments. Optical toroidal modes in plasmonic heptamer nanocavities are analyzed by electron energy loss spectroscopy and energy-filtered transmission electron microscopy supported by finite-difference time-domain numerical calculations. Additionally, their corresponding radiation behaviors are experimentally investigated by means of cathodoluminescence. The observed contrasting behaviors of a single dynamic toroidal dipole mode and an antiparallel toroidal dipole pair mode are discussed and elucidated. Our findings further clarify the electromagnetic properties of dynamic toroidal dipoles and serve as important guidance for the use of toroidal dipole moments in future applications.