A search with the ATLAS detector is presented for the Standard Model Higgs boson produced by vector-boson fusion and decaying to a pair of bottom quarks, using 20.2 fb−1 of LHC proton-proton collision data at s=8" role="presentation" style="box-sizing: border-box; display: inline-table; line-height: normal; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative;">s√=8s=8 TeV. The signal is searched for as a resonance in the invariant mass distribution of a pair of jets containing b-hadrons in vector-boson-fusion candidate events. The yield is measured to be −0.8 ± 2.3 times the Standard Model cross-section for a Higgs boson mass of 125 GeV. The upper limit on the cross-section times the branching ratio is found to be 4.4 times the Standard Model cross-section at the 95% confidence level, consistent with the expected limit value of 5.4 (5.7) in the background-only (Standard Model production) hypothesis.
In the present study, the conversion performance of hydrogen sulfide (H2S) to elemental sulfur in ionic-liquid-incorporated transition metals (ILTMs) is predicted using a conductor-like screening model for realistic solvents (COSMO-RS). The predictions were made via the establishment of a correlation between the conversion performance and solubility of H2S in ionic liquids (ILs). All molecules involved were optimized at the DFT/TZVP/M06 computational level and imported on the COSMOtherm program at equimolar conditions. For validation purposes, the solubility of ILs was predicted at 1 bar pressure. Simple regression analysis was used to establish a relationship between the solubility and conversion performance of H2S. The results indicate that the solubility prediction of ILs is accurate (R-2 = 93.40%) with a p-value of 0.0000000777. Additionally, the conversion performance is generally found to be dependent on the solubility value. Furthermore, 1-butyl-3-methylimidazolium chloride [bmim][Cl] was chosen as the base IL for incorporating the transition metal, owing to its solubility and selectivity to H2S. The solubility trend of ILTMs is found to follow the following order: [bmim][NiCl3] > [bmim][FeCl4] > [bmim][CoCl3] > [bmim][CuCl3]. According to the viscosity measurements of ILTMs, [bmim][NiCl3] and [bmim][FeCl4] exhibited the highest and lowest viscosity values, respectively. Therefore, [bmim][FeCl4] is a promising ILTM owing to its higher solubility and low viscosity for the application studied.
Designing heterostructure materials at the nanoscale is a well-known method to enhance gas sensing performance. In this study, a mixed solution of zinc chloride and tin (II) chloride dihydrate, dissolved in ethanol solvent, was used as the initial precursor for depositing the sensing layer on alumina substrates using the ultrasonic spray pyrolysis (USP) method. Several ZnO/SnO2 heterostructures were grown by applying different ratios in the initial precursors. These heterostructures were used as active materials for the sensing of H2S gas molecules. The results revealed that an increase in the zinc chloride in the USP precursor alters the H2S sensitivity of the sensor. The optimal working temperature was found to be 450 °C. The sensor, containing 5:1 (ZnCl2: SnCl2·2H2O) ratio in the USP precursor, demonstrates a higher response than the pure SnO2 (∼95 times) sample and other heterostructures. Later, the selectivity of the ZnO/SnO2 heterostructures toward 5 ppm NO2, 200 ppm methanol, and 100 ppm of CH4, acetone, and ethanol was also examined. The gas sensing mechanism of the ZnO/SnO2 was analyzed and the remarkably enhanced gas-sensing performance was mainly attributed to the heterostructure formation between ZnO and SnO2. The synthesized materials were also analyzed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, transmission electron microscopy, and X-ray photoelectron spectra to investigate the material distribution, grain size, and material quality of ZnO/SnO2 heterostructures.
H2S gas is harmful for human health and environment, therefore novel gas sensors for real time and fast detection with high precision have been sought. Metal oxides are already known as promising candidate for this purpose. This article presents the performance of a gas sensor consists of a microheater and active layer formed on single alumina substrate for operating at high temperature applications. Ultrasonic spray pyrolysis deposition method was used to make both thick layer of SnO2 for microheater and thin and porous crystalline layer of SnO2 as sensing layer. The prepared sensor showed suitable dynamic response towards 10 to 50 ppm of H2S gas both in humid and dry conditions at 450 °C. In these experiments, the cross sensitivity of the sensor was also checked for other interfering gases e.g. CH4 and NO2.
Integrating machine learning techniques into medical diagnostic systems holds great promise for enhancing disease identification and treatment. Among the various options for training such systems, the extreme learning machine (ELM) stands out due to its rapid learning capability and computational efficiency. However, the random selection of input weights and hidden neuron biases in the ELM can lead to suboptimal performance. To address this issue, our study introduces a novel approach called modified Harris hawks optimizer (MHHO) to optimize these parameters in ELM for medical classification tasks. By applying the MHHO-based method to seven medical datasets, our experimental results demonstrate its superiority over seven other evolutionary-based ELM trainer models. The findings strongly suggest that the MHHO approach can serve as a valuable tool for enhancing the performance of ELM in medical diagnosis.
The so-called '3He-crisis' has motivated the neutron detector community to undertake an intense R&D programme in order to develop technologies alternative to standard 3He tubes and suitable for neutron detection systems in future spallation sources such as the European spallation source (ESS). Boron-based GEM (gas electron multiplier) detectors are a promising '3He-free' technology for thermal neutron detection in neutron scattering experiments. In this paper the evolution of boron-based GEM detectors from planar to 3D converters with an application in diffraction measurements is presented. The use of 3D converters coupled with GEMs allows for an optimization of the detector performances. Three different detectors were used for diffraction measurements on the INES instrument at the ISIS spallation source. The performances of the GEM-detectors are compared with those of conventional 3He tubes installed on the INES instrument. The conceptual detector with the 3D converter used in this paper reached a count rate per unit area of about 25% relative to the currently installed 3He tube. Its timing resolution is similar and the signal-to-background ratio (S/B) is 2 times lower.
We introduced an exfoliation method of MoS2 in a 3% solution of sodium dodecyl surfactant at high concentration (i.e. 2 g/L). The bulk MoS2 was thinned by mechanical exfoliation between sand papers and the resulting powder was used to prepare dispersions by liquid exfoliation through probe sonication. The resulting dispersion consisted of very thin MoS2 nanosheets in surfactant solution with average lateral size around 126 nm. This may be interesting for applications in inkjet printed electronics.
We have determined absolute dielectronic recombination rate coefficients for C II, using the CRYRING heavy-ions storage ring. The resonances due to 2s-2p (Delta n= 0) core excitations are detected in the center-of-mass energy range of 0-15 eV. The experimental results are compared with intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients are obtained from the DR spectrum by convoluting it with a Maxwell-Boltzmann energy distribution for temperatures in the range of 10(3)-10(6) K. The derived temperature-dependent plasma recombination rate coefficients are presented graphically and parameterized by using a fit formula for convenient use in plasma modeling codes. The experimental rate coefficients are also compared with the theoretical data available in literature. In the temperature range of 10(3)-2 x 10(4) K, our experimental results show that previous calculations severely underestimate the plasma rate coefficients and also our AUTOSTRUCTURE calculation does not reproduce the experimental plasma rate coefficients well. Above 2x10(4) K, the agreement between the experimental and theoretical rate coefficients is much better, and the deviations are smaller than the estimated uncertainties.
The adaptive gain integrating pixel detector (AGIPD) is a development of a collaboration between Deustsches Elektronen-Synchrotron (DESY), the Paul-Scherrer-Institute (PSI), the University of Hamburg and the University of Bonn. The detector is designed to cope with the demanding challenges of the European XFEL. Therefore it comes along with an adaptive gain stage allowing a high dynamic range, spanning from single photon sensitivity to 10(4) x 12.4 keV photons and 352 analogue memory cells per pixel. The aim of this report is to briefly explain the concepts of the AGIPD electronics and mechanics and then present recent experiments demonstrating the functionality of its key features.
The Adaptive Gain Integrating Pixel Detector (AGIPD) is a hybrid pixel X-ray detector for the European-XFEL. One of the detector's important parts is the radiation tolerant front end ASIC fulfilling the European-XFEL requirements: high dynamic range-from sensitivity to single 12.5keV-photons up to 104 photons. It is implemented using the dynamic gain switching technique with three possible gains of the charge sensitive preamplifier. Each pixel can store up to 352 images in memory operated in random-access mode at >= 4.5MHz frame rate. An external vetoing may be applied to overwrite unwanted frames.
The Adaptive Gain Integrating Pixel Detector (AGIPD) is an X-ray imager, custom designed for the European X-ray Free-Electron Laser (XFEL). It is a fast, low-noise integrating detector, with an adaptive gain amplifier per pixel. This has an equivalent noise of less than 1keV when detecting single photons and, when switched into another gain state, a dynamic range of more than 10(4)photons of 12keV. In burst mode the system is able to store 352 images while running at up to 6.5MHz, which is compatible with the 4.5MHz frame rate at the European XFEL. The AGIPD system was installed and commissioned in August 2017, and successfully used for the first experiments at the Single Particles, Clusters and Biomolecules (SPB) experimental station at the European XFEL since September 2017. This paper describes the principal components and performance parameters of the system.
The European XFEL is an extremely brilliant Free Electron Laser Source with a very demanding pulse structure: trains of 2700 X-ray pulses are repeated at 10Hz. The pulses inside the train are spaced by 220ns and each one contains up to 1012photons of 12.4keV, while being ≤100fs in length. AGIPD, the Adaptive Gain Integrating Pixel Detector, is a hybrid pixel detector developed by DESY, PSI, and the Universities of Bonn and Hamburg to cope with these properties. It is a fast, low noise integrating detector, with single photon sensitivity (for Eγ⪆6keV) and a large dynamic range, up to 104 photons at 12.4keV. This is achieved with a charge sensitive amplifier with 3 adaptively selected gains per pixel. 352 images can be recorded at up to 6.5MHz and stored in the in-pixel analogue memory and read out between pulse trains. The core component of this detector is the AGIPD ASIC, which consists of 64 × 64 pixels of 200µm×200µm. Control of the ASIC's image acquisition and analogue readout is via a command based interface. FPGA based electronic boards, controlling ASIC operation, image digitisation and 10GE data transmission interface AGIPD detectors to DAQ and control systems. An AGIPD 1Mpixel detector has been installed at the SPB1 experimental station in August 2017, while a second one is currently commissioned for the MID 2 endstation. A larger (4Mpixel) AGIPD detector and one to employ Hi-Z sensor material to efficiently register photons up to Eγ≈25keV are currently under construction.
This work aims the functionalization of reduced graphene oxide nanoplatelets with chitosan (G-chitosan) and also with poly(styrenesulfonic acid) (GPSS), thus forming stable, dispersed aqueous solutions. G-chitosan and GPSS solutions allowed the layer-by-layer (LbL) film formation with glucose oxidase (GOx), establishing multilayered nanostructures with elevated control in thickness and morphology. The graphene nanoplatelets were characterized by UV-vis and FTIR spectroscopies, resulting in good adherence and linear deposition of the graphene nanoplatelets with GOx in the LbL structures.Cyclic voltammetry shows an enlargement in the current intensity with increasing number of deposited LbL layers, possibly owing to the formation of conducting paths by the graphene nanoplatelets in the tailored multilayer nanomaterial formed
Due to the availability of X-ray imaging detectors, full-field X-ray fluorescence (FF-XRF) imaging technique has become achievable, which provides an alternative to scanning X-ray fluorescence imaging with a micro-focus X-ray beamline. In this paper, we present a setup based on straight capillary optics and an energy-dispersive hybrid pixel detector, which can perform simultaneous mapping of several chemical elements. The photon transmission efficiency and spatial resolution are compared between two X-ray collimation setups: one using pinhole optics and one using straight polycapillary optics. There is a tradeoff between the spatial resolution and transmission efficiency when considering X-ray optics. When optimizing the spatial resolution, using straight capillary optics achieved a higher intensity gain when comparing with the pinhole setup. Characterization of the polycapillary imaging setup is performed through analyzing various samples in order to investigate the spatial frequency response and the energy sensitivity. This developed setup is capable of FF-XRF imaging in characteristic energies below 20 keV, while for higher energies the spatial resolution is affected by photon transmission through the collimator. This work shows the potential of the FF-XRF instrument in the monitoring of toxic metal distributions in environmental mapping measurements.
The Multi-Grid detector technology has evolved from the proof-of-principle and characterisation stages. Here we report on the performance of the Multi-Grid detector, the MG.CNCS prototype, which has been installed and tested at the Cold Neutron Chopper Spectrometer, CNCS at SNS. This has allowed a side-by-side comparison to the performance of 3He detectors on an operational instrument. The demonstrator has an active area of 0.2 m2. It is specifically tailored to the specifications of CNCS. The detector was installed in June 2016 and has operated since then, collecting neutron scattering data in parallel to the He-3 detectors of CNCS. In this paper, we present a comprehensive analysis of this data, in particular on instrument energy resolution, rate capability, background and relative efficiency. Stability, gamma-ray and fast neutron sensitivity have also been investigated. The effect of scattering in the detector components has been measured and provides input to comparison for Monte Carlo simulations. All data is presented in comparison to that measured by the 3He detectors simultaneously, showing that all features recorded by one detector are also recorded by the other. The energy resolution matches closely. We find that the Multi-Grid is able to match the data collected by 3He, and see an indication of a considerable advantage in the count rate capability. Based on these results, we are confident that the Multi-Grid detector will be capable of producing high quality scientific data on chopper spectrometers utilising the unprecedented neutron flux of the ESS.
Hybrid printed electronics, in which printed structures and silicon-based components co-exist will likely be among the first commercial solutions. In this case the paper substrate acts much in the same way as circuit boards, containing conductive tracks and acting as a carrier for the electrical components. It is important to consider the contacting of the components to be able to produce low resistance electrical contacts to the conductive tracks. Supercapacitors are able to deliver a large amount of current in a short time and are a good option for short term energy storage and if the printed product is to be used only one, or a few times, it can be the only power source needed. When manufacturing printed electronics, the overall resistance of the printed tracks as well as the contact resistance of the mounted components will add up to the total resistance of the system. A high resistance will cause a voltage drop from the power source to the component. This will waste power that goes to Joule heating and also the voltage and current available to components may be too low to drive them. If the intention is to use a power supply such as batteries or solar cells this becomes a limitation. In this article have been tested several conductive adhesives used to contact paper based supercapacitors to ink jet printed silver tracks on paper. The best adhesive gives about 0.3 Ω per contact, a factor 17 better compared to the worst which gave 5 Ω. The peak power that is possible to take out from a printed system with a flexible battery and super capacitors is about 10 times higher than compared with the same system with only the battery.
Flexible electronics is a field gathering a growing interest among researchers and companies with widely varying applications, such as organic light emitting diodes, transistors as well as many different sensors. If the circuit should be portable or off-grid, the power sources available are batteries, supercapacitors or some type of power generator. Thermoelectric generators produce electrical energy by the diffusion of charge carriers in response to heat flux caused by a temperature gradient between junctions of dissimilar materials. As wearables, flexible electronics and intelligent packaging applications increase, there is a need for low-cost, recyclable and printable power sources. For such applications, printed thermoelectric generators (TEGs) are an interesting power source, which can also be combined with printable energy storage, such as supercapacitors. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), or PEDOT:PSS, is a conductive polymer that has gathered interest as a thermoelectric material. Plastic substrates are commonly used for printed electronics, but an interesting and emerging alternative is to use paper. In this article, a printed thermoelectric generator consisting of PEDOT:PSS and silver inks was printed on two common types of paper substrates, which could be used to power electronic circuits on paper.
Today’s society is currently performing an exit from fossilfuel energy sources. The change to sustainable alternativesrequires inexpensive and environmentally friendly energy storagedevices. However, most current devices contain expensive,rare or toxic materials. These materials must be replaced bylow-cost, abundant, nontoxic components.In this thesis, I suggest the production of paper-based electricdouble-layer capacitors (EDLCs) to meet the demand oflow-cost energy storage devices that provide high power density.To fulfill the requirements of sustainable and environmentallyfriendly devices, production of EDLCs that consist of paper,graphite and saltwater is proposed. Paper can be used as aseparator between the electrodes and as a substrate for theelectrodes. Graphite is suited for use as an active material in theelectrodes, and saltwater can be employed as an electrolyte.Westudied and developed different methods for the productionof nanographite and graphene from graphite. Composites containingthese materials and similar advanced carbon materialshave been tested as electrode materials in EDLCs. I suggest theuse of cellulose nanofibers (CNFs) or microfibrillated cellulose(MFC) as a binder in the electrodes. In addition to improvedmechanical stability, the nanocellulose improved the stabilityof graphite dispersions and the electrical performance of theelectrodes. The influence of the cellulose quality on the electricalproperties of the electrodes and EDLCs was investigated.The results showed that the finest nanocellulose quality is notthe best choice for EDLC electrodes; MFC is recommended forthis application instead. The results also demonstrated thatthe capacitance of EDLCs can be increased if the electrodemasses are adjusted according to the size of the electrolyte ions.Moreover, we investigated the issue of high contact resistancesat the interface between porous carbon electrodes and metalcurrent collectors. To reduce the contact resistance, graphitefoil can be used as a current collector instead of metal foils.Using the suggested low-cost materials, production methodsand conceptual improvements, it is possible to reduce the material costs by more than 90% in comparison with commercialunits. This confirms that paper-based EDLCs are apromising alternative to conventional EDLCs. Our findings andadditional research can be expected to substantially supportthe design and commercialization of sustainable EDLCs andother green energy technologies.
Supercapacitors are high performance energy storage devices that offer many advantages like high power densities, fast charge/discharge times and long lifetimes. Due to high purchase prices the use of supercapacitors is limited. Thus we introduced the concept of low cost paper-based supercapacitors. Paper serves as a carrier for the active electrode material, as ion conductor and as separator in the supercapacitor. Different carbon materials, like graphene, graphite and activated carbon are used as active material for the electrodes. We are developing a process to produce large quantities of inexpensive graphene by mechanical exfoliation of graphite. Both coated and filled electrode papers were prepared and tested in supercapacitors. Besides graphene we coated several graphene/graphite composites on paper. By adding small amounts of gold nanoparticles or nanofibrillated cellulose (NFC) the supercapacitors performance can be improved to a great extent. Specific capacitances of up to 100 F/g for coated paper electrodes and sheet-resistances as low as 0.5 Ω/sq could be obtained. Another advantage of this concept is that papermaking technologies can be used to prepare conducting electrodes, thin separators and manufacture the device itself. The paper industry has the ability to facilitate a large scale production of inexpensive supercapacitors.
The growing market of mobile electronic devices, renewable off-grid energy sources and electric vehicles requires high-performance energy storage devices. Rechargeable batteries are usually the first choice due to their high energy density. However, supercapacitors have a higher power density and longer life-time compared to batteries. For some applications supercapacitors are more suitable than batteries. They can also be used to complement batteries in order to extend a battery's life-time. The use of supercapacitors is, however, still limited due to their high costs. Most commercially available supercapacitors contain expensive electrolytes and costly electrode materials.
In this thesis I will present the concept of cost efficient, paper-based supercapacitors. The idea is to produce supercapacitors with low-cost, green materials and inexpensive production processes. We show that supercapacitor electrodes can be produced by coating graphite on paper. Roll-to-roll techniques known from the paper industry can be employed to facilitate an economic large-scale production. We investigated the influence of paper on the supercapacitor's performance and discussed its role as passive component. Furthermore, we used chemically reduced graphite oxide (CRGO) and a CRGO-gold nanoparticle composite to produce electrodes for supercapacitors. The highest specific capacitance was achieved with the CRGO-gold nanoparticle electrodes. However, materials produced by chemical synthesis and intercalation of nanoparticles are too costly for a large-scale production of inexpensive supercapacitor electrodes. Therefore, we introduced the idea of producing graphene and similar nano-sized materials in a high-pressure homogenizer. Layered materials like graphite can be exfoliated when subjected to high shear forces. In order to form mechanical stable electrodes, binders need to be added. Nanofibrillated cellulose (NFC) can be used as binder to improve the mechanical stability of the porous electrodes. Furthermore, NFC can be prepared in a high-pressure homogenizer and we aim to produce both NFC and graphene simultaneously to obtain a NFC-graphene composite. The addition of 10% NFC in ratio to the amount of graphite, increased the supercapacitor's capacitance, enhanced the dispersion stability of homogenized graphite and improved the mechanical stability of graphite electrodes in both dry and wet conditions. Scanning electron microscope images of the electrode's cross section revealed that NFC changed the internal structure of graphite electrodes depending on the type of graphite used. Thus, we discussed the influence of NFC and the electrode structure on the capacitance of supercapacitors.
Supercapacitor electrodes are often made of porous carbon materials such as activated carbon, but also graphene was frequently used as active electrode material. Graphene can be produced by mechanical exfoliation, chemical exfoliation, chemical vapor deposition or other elaborate methods. These techniques are relatively expensive and produce small quantities only. Recently we presented a method to produce nanographite and graphene by mechanical exfoliation of graphite in a high-pressure homogenizer. In our contribution “Large-scale production of graphene” by Nicklas Blomquist we suggest to optimize the geometry of the shear zone and increase the feeding pressure to obtain a higher yield.
In this study we evaluated the influence of these process optimizations on the structural and electrical properties of the nanographite-graphene mixture. The produced dispersions were characterized in terms of particle size and shape by using a particle size analyzer, a transmission electron microscope (TEM) and an atomic force microscope (AFM). In order to analyze the performance of the produced material as electrodes for supercapacitors, electrodes were produced by vacuum filtration. The electrodes were studied by sheet-resistance and capacitance measurements. Furthermore, the structure of the electrode surface and the cross section of the electrode were visualized by using a scanning electron microscope (SEM).
Comparisons with previously produced nanographite-graphene dispersions showed an increase in yield of the exfoliated nanomaterials. The optimized shear zone increased the production of nanosized particles and flakes and enhanced the material quality.
Cellulose derivatives are widely used as binders and dispersing agents in different applications. Binders composed of cellulose are an environmentally friendly alternative to oil-based polymer binding agents. Previously, we reported the use of cellulose nanofibers (CNFs) as binders in electrodes for electric double-layer capacitors (EDLCs). In addition to good mechanical stability, we demonstrated that CNFs enhanced the electrical performance of the electrodes. However, cellulose fibers can cover a broad range of length scales, and the quality requirements from an electrode perspective have not been thoroughly investigated. To evaluate the influence of fiber quality on electrode properties, we tested seven samples with different fiber dimensions that are based on the same kraft pulp. To capture the length scale from fibers to nanofibrils, we evaluated the performance of the untreated kraft pulp, refined fibers, microfibrillated cellulose (MFC) and CNFs. Electrodes with kraft pulp or refined fibers showed the lowest electrical resistivity. The specific capacitances of all EDLCs were surprisingly similar, but slightly lower for the EDLC with CNFs. The same electrode sample with CNFs also showed a slightly higher equivalent series resistance (ESR), compared to those of the other EDLCs. Graphite dispersions with MFC showed the best dispersion stability.
Symmetric electric double-layer capacitors (EDLCs) have equal masses of the same active material in both electrodes. However, having equal electrode masses may prevent the EDLC to have the largest possible specific capacitance if the sizes of the hydrated anions and cations in the electrolyte differ because the electrodes and the electrolyte may not be completely utilized. Here we demonstrate how this issue can be resolved by mass balancing. If the electrode masses are adjusted according to the size of the ions, one can easily increase an EDLC's specific capacitance. To that end, we performed galvanostatic cycling to measure the capacitances of symmetric EDLCs with different electrode mass ratios using four aqueous electrolytes-Na2SO4, H2SO4, NaOH, and KOH (all with a concentration of 1 M)-and compared these to the theoretical optimal electrode mass ratio that we calculated using the sizes of the hydrated ions. Both the theoretical and experimental values revealed lower-than-1 optimal electrode ratios for all electrolytes except KOH. The largest increase in capacitance was obtained for EDLCs with NaOH as electrolyte. Specifically, we demonstrate an increase of the specific capacitance by 8.6% by adjusting the electrode mass ratio from 1 to 0.86. Our findings demonstrate that electrode mass balancing is a simple and inexpensive method to increase the capacitance of EDLCs. Furthermore, our results imply that one can reduce the amount of unused material in EDLCs and thus decrease their weight, volume and cost.
Graphene and other porous carbon materials are widely used as electrodes in supercapacitors. In order to form mechanically stable electrodes, binders can be added to the conducting electrode material. However, most binders degrade the electrical performance of the electrodes. Here we show that by using nanobrillated cellulose (NFC) as binder the electrical properties, such as sheet-resistance, were enhanced. NFC is a good ion conductor and improves the access of ions to the electrodes. Thus electrodes made of a mixture of nanographite and NFC achieved larger capacitances in supercapacitors than electrodes with nanographite only. The lowest sheet-resistance and the highest capacitance were measured at NFC contents of 10-15% in ratio to the total amount of active material. Furthermore, NFC formed a network that improved the mechanical stability of the electrodes signicantly. Beside the mechanical stability, NFC stabilized the aqueous nanographite dispersion that was used to prepare the electrodes. NFC avoids the restacking of the delaminated graphene akes by forming a ber network between the graphene layers.
This paper presents research on the synergistic effects of nickel molybdate and reduced graphene oxide as a nanocomposite for further development of energy storage systems. An enhancement in the electrochemical performance of supercapacitor electrodes occurs by synthesizing highly porous structures and achieving more surface area. In this work, a chemical precipitation technique was used to synthesize the NiMoO4/3D-rGO nanocomposite in a starch media. Starch was used to develop the porosities of the nanostructure. A temperature of 350◦C was applied to transform graphene oxide sheets to reduced graphene oxide and remove the starch to obtain the NiMoO4/3D-rGO nanocomposite with porous structure. The X-ray diffraction pattern of the NiMoO4 nano particles indicated a monoclinic structure. Also, the scanning electron microscope observation showed that the NiMoO4 NPs were dispersed across the rGO sheets. The electrochemical results of the NiMoO4/3D-rGO electrode revealed that the incorporation of rGO sheets with NiMoO4 NPs increased the capacity of the nanocomposite. Therefore, a significant increase in the specific capacity of the electrode was observed with the NiMoO4/3D-rGO nanocomposite (450 Cg−1 or 900 Fg−1) when compared with bare NiMoO4 nanoparticles (350 Cg−1 or 700 Fg−1) at the current density of 1 A g−1. Our findings show that the incorporation of rGO and NiMoO4 NP redox reactions with a porous structure can benefit the future development of supercapacitors.
Although Graphene oxide (GO)-based materials is known as a favorable candidate for supercapacitors, its conductivity needs to be increased. Therefore, this study aimed to investigate the performance of GO-based supercapicitor with new methods. In this work, an ammonia solution has been used to remove the oxygen functional groups of GO. In addition, a facile precipitation method was performed to synthesis a NiMoO4/3D-rGO electrode with purpose of using synergistic effects of rGO conductivity properties as well as NiMoO4 pseudocapacitive behavior. The phase structure, chemical bands and morphology of the synthesized powders were investigated by X-ray diffraction (XRD), Raman spectroscopy, and field emission secondary electron microscopy (FE-SEM). The electrochemical results showed that the NiMoO4/3D-rGO(II) electrode, where ammonia has been used during the synthesis, has a capacitive performance of 932 Fg(-1). This is higher capacitance than NiMoO4/3D-rGO(I) without using ammonia. Furthermore, the NiMoO4/3D-rGO(II) electrode exhibited a power density of up to 17.5 kW kg(-1) and an energy density of 32.36 Wh kg(-1). These results showed that ammonia addition has increased the conductivity of rGO sheets, and thus it can be suggested as a new technique to improve the capacitance.
Accurate determination of the complex refractive index of SU-8 epoxy has significant for the wide variety of applications in optical sensor technology at IR range. The complex refractive index of SU-8 is determined by recording the transmission of light spectra for the wavelength range of 2.5 – 22.0 μm. The data analysis is based on the Kramers-Kronig dispersion relation method. The method has several merits, such as ease of operation, non-contact technique, measurement accuracy, and rapid measurement. The present method is not restricted to the case of SU-8 but it is also proposed to be applicable across a broad range of applications, such as assessment of the optical properties of paints and biomedical samples.
For as long as light and matter have partnered, impurities have played a role in optical system performance. This remains generally true for photonic heat engines and especially the case for optical refrigeration. Building on the history of light and glass, including the materials development of low loss telecom fibers, this paper briefly discusses the sources of heat generation in materials and all-material means for their reduction. Particularly attention will be paid to active optical fibers and connect thermal management to parasitic optical nonlinearities, both critical to high and low power amplifier and laser systems.
In this work we present a promising method for fabrication of conductive tracks on paper based substrates by laser assisted reduction of Graphene Oxide (GO). Printed electronics on paper based substrates is be coming more popular due to lower cost and recyclability. Fabrication of conductive tracks is of great importance where metal, carbon and polymer inks are commonly used. An emerging option is reduced graphene oxide (r-GO), which can be a good conductor. Here we have evaluated reduction of GO by using a 532 nm laser source, showing promising results with a decrease of sheet resistance from >100 M Ω/Sqr for unreduced GO down to 126 Ω/Sqr. without any observable damage to the paper substrates.
Development of printed electronics is increasing each year, where many electrical components such as transistors and sensors are now printable. The most commonly used substrate have been plastics, but there is an increasing interest in using paper as substrate. The paper industry is a very large and mature industry with large production capacity and well developed processes. It is therefore of interest to investigate how it would be possible to combine printed electronics and paper based products. This can for example be to print sensors on packages, to use large scale roll-to-roll production for solar cells. To be able to achieve such goals it is of importance to develop methods of applying electrically active materials in the large, high speed roll-to-roll processes used in the paper industry. In this article we discuss coating of graphene oxide (GO) on large areas after which it is selectively reduced into electrically conductive reduced graphene oxide (rGO) by laser processing. Graphene oxide is an inexpensive, carbon based material very suitable to be deposited as a coating, and the selective activation of makes it possible to fabricate conductive patterns at high speeds. We have evaluated several different paper substrates on which GO was coated. The reduction was performed using an 532 nm laser source and the results are promising, showing that it is possible to fabricate selectively conductive patterns on paper substrates by coating and reduction of GO.
Development of cost-effective and environmentally friendly manufacturing methods will enable important advances for the production of large-scale flexible electronics. Laser processing has shown to be a promising candidate that offers a fast and non-destructive way to produce highly conductive patterns on flexible substrates such as plastics. However, an emerging option with a lower environmental impact is instead the use of cellulose-based flexible substrates, such as paper. In this work we investigate the use of laser sintering of silver nanoparticle inks, which were inkjet-printed on three different types of paper. Patterns with a high conductivity could be manufactured where a special care was taken to prevent the substrates from damage by the intense laser light. We found that the best results was obtained for a photopaper, with a conductivity of 1.63 107 S/m corresponding to nearly 26% of the bulk silver conductivity. In addition, we demonstrate laser sintering to fabricate a fully functional near field communication tag printed on a photopaper. Our results can have an important bearing for the development of cost-effective and environmentally friendly production methods for flexible electronics on a large scale.
High-power, single-frequency, pulsed fiber amplifiers are required in light detection and ranging, coherent laser detection, and remote sensing applications to reach long range within a short acquisition time. However, the power-scaling of these amplifiers is limited by nonlinearities generated in the optical fibers, in particular by stimulated Brillouin scattering (SBS). In this regard, the use of multicomponent phosphate glasses maximizes the energy extraction and minimizes nonlinearities. Here, we present the development of a single-stage, hybrid, pulsed fiber amplifier using a custom-made multicomponent Yb-doped phosphate fiber. The performance of the phosphate fiber was compared to a commercial Yb-doped silica fiber. While the latter showed SBS limitation at nearly 6.5 kW for 40 cm length, the maximum achieved output peak power for the multicomponent Yb-doped phosphate fiber was 11.7 kW for 9 ns pulses using only 20 cm with no sign of SBS.
We report on a single-frequency fiber master oscillator power amplifier utilizing a polarization-maintaining step-index fiber with an Al/Ce/F core-glass composition doped with a very high Yb concentration (0.25 at.%). This design made it possible to use a very short fiber (~1 m) and to coil it in a tight radius (4 cm in the amplifier, while 2 cm gave similarly negligible bending loss) so that the packaged system is one of the most compact reported to date (~0.6 L). The use of a short fiber increased the threshold for stimulated Brillouin scattering well above 100 W while maintaining near-ideal beam quality. The fiber was pumped with a diode-pumped solid-state laser and cooled passively by spooling it on a grooved aluminum mandrel. The amplifier produced a strongly linearly polarized output at 1064 nm in the fundamental mode (M2 ≤ 1.2) with a 150 kHz linewidth and a power of 81.5 W for 107 W of launched pump power. No deleterious effects from the elevated thermal load were observed. The residual photodarkening loss resulting from the high Yb concentration, found to be small (~0.7 dB/m inferred at 1064 nm) with accelerated aging, reduced the output power by only ~20% after 150 h of operation.
Single‐frequency lasers are essential for high‐resolution spectroscopy and sensing applications as they combine high‐frequency stability with low noise and high output power stability. For many of these applications, there is increasing interest in power‐scaling single‐frequency sources, both in the near‐infrared and visible spectral range. We report the second‐harmonic generation of 670 μJ at 532 nm of a single‐frequency fiber amplifier signal operating in the quasi‐continuous‐wave mode in a 10‐mm periodically poled Mg‐doped lithium niobate (MgO:PPLN) crystal, while increasing compactness. To the best of our knowledge, this is the highest pulse energy generated in this crystal, which may find applications in the visible and UV such as remote Raman spectroscopy.
Interest in compact, single-frequency fiber amplifier has increased within many scientific and industrial applications. The main challenge is the onset of nonlinear effects, which limit their power scaling. Here we demonstrate a compact, high-power, single-frequency, polarization-maintaining, continous-wave fiber amplifier using only one amplification stage. We developed the fiber amplifier using a master oscillator fiber amplifier architecture, where a low-noise, single-frequency, solid-state laser operating at 1064 nm was used as a seed source. We evaluated the amplifier's performance by using several state-of-the-art, small-core, Ytterbium (yb)-doped fibers, as well as an in-house-made, highly Yb-doped fiber. An output power of 82 W was achieved with no sign of stimulated Brillouin scattering. A good beam quality and a polarization extinction ratio (PER) of > 25 dB were achieved. The compact fiber amplifier can be a competitive alternative to multi stage designed fiber amplifiers.
The focus of this study was the development of a second generation of fiber lasers internally cooled by anti-Stokes fluorescence. The laser consisted of a length of a single-mode fiber spliced to fiber Bragg gratings to form the optical resonator. The fiber was single-moded at the pump (1040 nm) and signal (1064 nm) wavelengths. Its core was heavily doped with Yb, in the initial form of CaF2 nanoparticles, and co-doped with Al to reduce quenching and improve the cooling efficiency. After optimizing the fiber length (4.1 m) and output-coupler reflectivity (3.3%), the fiber laser exhibited a threshold of 160 mW, an optical efficiency of 56.8%, and a radiation-balanced output power (no net heat generation) of 192 mW. On all three metrics, this performance is significantly better than the only previously reported radiation-balanced fiber laser, which is even more meaningful given that the small size of the single-mode fiber core (7.8-µm diameter). At the maximum output power (∼2 W), the average fiber temperature was still barely above room temperature (428 mK). This work demonstrates that with anti-Stokes pumping, it is possible to induce significant gain and energy storage in a small-core Yb-doped fiber while keeping the fiber cool.
This paper reports a second generation of radiation-balanced fiber laser and amplifier cooled internally using anti-Stokes fluorescence by pumping them at 1040 nm. In both devices the gain medium is a single-mode silica fiber with a core heavily doped with Yb<sup>3+</sup>, initially encapsulated in CaF<sub>2</sub> nanoparticles, and co-doped with Al to reduce quenching and increase the cooling efficiency. After optimization of its length (4.1 m) and its output coupler reflectivity (3.3%), the 1065- nm continuous-wave fiber laser has a threshold of 160 mW and a radiation-balanced (no net heat generation) output power of 192 mW, or nearly 70% higher than the previous radiation-balanced fiber laser. At its radiation-balanced point, its optical efficiency is 56.8%. The single-frequency, single-mode fiber amplifier, constructed with the same fiber, was optimum with a length of 6.8 m, and it had a radiation-balanced gain of 20 dB: it amplified an 800-μW signal to 84.2 mW with 433 mW of input pump power. The significance of this result is underscored by the small diameter of the single-mode fiber core (7.8 μm), which makes cooling more challenging. This study further demonstrates the viability of achieving substantial gain and energy extraction in a small-core Yb-doped silica fiber while effectively utilizing anti-Stokes fluorescence to keep it cool.
For applications such as laser cooling of doped fibers, where it is critical to measure accurately the temperature of a cooled fiber that is very close to room temperature, it is paramount to develop a reliable, very short (mm) fiber temperature sensor with millikelvin resolution and very little drift. We report a second generation of a unique slow-light fiber Bragg grating (FBG) temperature sensor that meets these stringent requirements. Experiments and modeling establish that its temperature response depends only on well-known material constants of the silica FBG and the response of the probe laser's wavelength controller. The response is independent of the linewidth of the slow-light resonance, hence different FBGs and/or resonances have the exact same response. Examples of measured cooling in optically pumped Yb-doped fibers show that more reliable thermal contact with the cooled fiber is obtained by wrapping the FBG and the cooled fiber.
A comprehensive study was performed to quantify anti-Stokes-fluorescence (ASF) cooling in fibers of various host compositions (telluride, fluorozirconates, fluorophosphates, phosphates, and chalcogenides) doped with Yb3+ or Er3+. Published expressions were used to calculate the maximum heat that can be extracted per unit length and time from a single-mode fiber in the limit of negligible absorptive loss, and the associated cooling efficiency. These expressions consider host- and ion-dependent parameters, namely the absorption and emission cross-section spectra, the radiative and nonradiative lifetimes, and the critical concentration for quenching. Using these expressions with published values for these parameters, the maximum extractable heat was calculated for a large-mode-area fiber (NA = 0.05) doped with either Yb3+ or Er3+ in a variety of hosts. The results show that for a given ion, the maximum heat that can be extracted depends strongly on the host due to the strong dependence of quenching on host composition. In contrast, the cooling efficiency (ratio of extracted heat to pump power absorbed) depends very weakly on the host. The cooling efficiency is also almost twice as high for Er3+ (average of 3.8%) than for Yb3+ (average of 2.2%) due to the larger gap between the pump and mean fluorescence energy in Er3+. Of the limited number of materials for which a full set of data was found in the literature, the highest extractable heat for Yb3+ is in phosphate (-51.5 mW/m), and for Er3+ is in chalcogenide (-10.3 mW/m). This work provides a simple methodology to evaluate the quantitative cooling performance of these and other rare-earth ions in any amorphous host, a procedure that should guide researchers in the selection of optimum materials for ASF cooling of fibers.
Antimicrobial resistance has reached alarming levels in many countries, thus leading to a search for new classes of antibiotics, such as antimicrobial peptides whose activity is exerted by interacting specifically with the microorganism membrane. In this study, we investigate the molecular-level mechanism of action for Labaditin (Lo), a 10-amino acid residue cyclic peptide from Jatropha multifida with known bactericidal activity againstStreptococcus mutans. We show that Lo is also effective against Staphylococcus aureus(S. aureus) but this does not apply to its linear analogue (L1). Using polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), we observed with that the secondary structure of Lo was preserved upon interacting with Langmuir monolayers from a phospholipid mixture mimicking S. aureus membrane, in contrast to L1. This structure preservation for the rigid, cyclic Lo is key for the self-assembly of peptide nanotubes that induce pore formation in large unilamellar vesicles (LUVs), according to permeability assays and dynamic light scattering measurements. In summary, the comparison between Labaditin (Lo) and its linear analogue L1 allowed us to infer that the bactericidal activity of Lo is more related to its interaction with the membrane. It does not require specific metabolic targets, which makes cyclic peptides promising for antibiotics without bacteria resistance.
There is great demand for energy-efficient, environmentally sustainable, and cost-effective electrical energy storage devices. One important aspect of this demand is the need for automotive electrification to achieve more energy-efficient transportation at a reasonable cost, thus supporting a fossil-fuel free society. Another important aspect is the requirement for energy storage in the growing field of renewable energy production from wind and solar sources, which generates an irregular supply of electricity due to weather conditions.Much of the research in this area has been conducted in the field of battery technology with impressive results, but the need for rapid storage devices such as supercapacitors is growing. Due to the excellent ability of supercapacitors to handle short peak power pulses with high efficiency along with their long lifetime and superior cyclability, their implementations range from small consumer electronics to electric vehicles and stationary grid applications. Supercapacitors also have the potential to complement batteries to improve pulse efficiency and lifetime of the system, however, the cost of supercapacitors is a significant issue for large-scale commercial use, leading to a demand for sustainable, low-cost materials and simplified manufacturing processes. An important way to address this need is to develop a cost-efficient and environment-friendly large-scale process to produce highly conductive nanographites, such as graphene and graphite nanoplatelets, along with methods to manufacture low-cost electrodes from large area coating.
In this thesis, I present a novel process to mechanically exfoliate industrial quantities of nanographite from graphite in an aqueous environment with low energy consumption and at controlled shear conditions. The process is based on hydrodynamic tube-shearing and can produce both multilayer graphene and nanometer-thick and micrometer-wide flakes of nanographite. I also describe the production of highly conductive and robust carbon composites based on the addition of nanocellulose during production; these are suitable as electrodes in applications ranging from supercapacitors and batteries to printed electronics and solar cells.Furthermore I demonstrate a scalable route for roll-to-roll coating of the nanographite-nanocellulose electrode material and propose a novel aqueous, low-cost, and metal-free supercapacitor concept with graphite foil functioning as the current collector. The supercapacitors possessedmore than half the specific capacitance of commercial units but achieved a material cost reduction of more than 90 %, demonstrating anenvironment-friendly, low-cost alternative to conventional supercapacitors.
High mobility has been a standard in the modern world for decades. This has resulted in high energy consumption, diminishing fossil energy reserves and rising levels of greenhouse gases.
By recovering the energy lost in deceleration of vehicles the total energy consumption can be decreased and exhaust emissions reduced. This can be done with a kinetic energy recovery system (KERS) that converts kinetic energy to electric energy during deceleration, which then can be used for acceleration.
KERS requires an electrical storage device with high power density, due to the high power levels generated at heavy braking. Batteries does not generally meet these requirements, especially in the cost-effective point of view, but different types of capacitors can be used to obtain a cheap and effective system. To get such an energy storage device small, lightweight and inexpensive while the technology is sustainable requires avoidance of rare metals and hazardous materials.
In this master thesis energy and power levels for KERS has been modelled, based on standardized measurements techniques and small paper-based supercapacitors have been built and tested in order to model size, weight and price for a full-scale energy storage device to a KERS-application.
The models showed that energy consumption in urban traffic could be reduced with 18% and with an electrode material for the energy storage device with a capacitance of about 1500 F/m2 a reasonable size and weight is obtained. To reach these values of capacitance in paper-based supercapacitors further testing is required on area and layer dependence and for different electrodes.
Industrially scalable methods for the production of graphene and other nanographites are needed to achieve cost-efficient commercial products. At present, there are several available routes for the production of these materials but few allow large-scale manufacturing and environmentally friendly low-cost solvents are rarely used. We have previously demonstrated a scalable and low-cost industrial route to produce nanographites by tube-shearing in water suspensions. However, for a deeper understanding of the exfoliation mechanism, how and where the actual exfoliation occurs must be known. This study investigates the effect of shear zone geometry, straight and helical coil tubes, on this system based on both numerical simulation and experimental data. The results show that the helical coil tube achieves a more efficient exfoliation with smaller and thinner flakes than the straight version. Furthermore, only the local wall shear stress in the turbulent flow is sufficient for exfoliation since the laminar flow contribution is well below the needed range, indicating that exfoliation occurs at the tube walls. This explains the exfoliation mechanism of water-based tube-shear exfoliation, which is needed to achieve scaling to industrial levels of few-layer graphene with known and consequent quality.