An integrated superconductive magnetic nanosensor for high-sensitivity nanoscale applications

An integrated magnetic nanosensor based on a niobium dc SQUID (superconducting quantum interference device) for nanoscale applications is presented. The sensor, having a washer shape with a hole of 200?nm and two Josephson-Dayem nanobridges of 80?nm × 100?nm, consists of a Nb(30?nm)/Al(30?nm) bilayer patterned by electron beam lithography (EBL) and shaped by lift-off and reactive ion etch (RIE) processes. The presence of the niobium coils, integrated on-chip and tightly coupled to the SQUID, allows us to easily excite the sensor in order to get the voltage-flux characteristics and to flux bias the SQUID at its optimal point. The measurements were performed at liquid helium temperature. A voltage swing of 75?μV and a maximum voltage-flux transfer coefficient (responsivity) as high as 1?mV/Φ(0) were directly measured from the voltage-flux characteristic. The noise measurements were performed in open loop mode, biasing the SQUID with a dc magnetic flux at its maximum responsivity point and using direct-coupled low-noise readout electronics. A white magnetic flux noise spectral density as low as 2.5?μΦ(0)?Hz(-1/2) was achieved, corresponding to a magnetization or spin sensitivity in units of the Bohr magneton of 100?spin?Hz(-1/2). Possible applications of this nanosensor can be envisaged in magnetic detection of nanoparticles and small clusters of atoms and molecules, in the measurement of nanoobject magnetization, and in quantum computing.     

Dual-detector for simultaneous time and energy measurements with superconductive detectors

The development of a superconductive detector for simultaneous measurement of energy and arrival time is reported. The detector consists of two superconducting tunnel junctions coupled through a passive network. The first junction operates in the quasi-particle regime and measures the energy absorbed by counting the total charge that tunnels. The second junction uses the DC Josephson effect to act as a fast discriminator for the onset of surplus current in the first junction. The feasibility of the detector is demonstrated through simultaneous time and energy measurements of 6 keV X-rays. A model of the detector is presented and numerical simulations show good correspondence with experimental data.     

High-pin density feedthrough for superfluid helium applications

A vacuum tight high-pin density feedthrough for use in superfluid helium has been developed. The design and construction based on commercially available Framatome connectors is described.     

Large size optical windows for superfluid helium applications

We report on a technique to seal large size optical windows on metal cryostats for He II applications.     

On the activation energy of vacancies in solid helium

Contrary to existing theories, we have taken into account the fact that the effective potential between a pair of particles will be affected by the presence of a vacancy. This charge gives rise to a contribution to the activation energy which is of the same order of magnitude as the contribution due to the vacancy nonlocalization.     

JACEE emulsion chambers for studying the energy spectra of high energy cosmic ray protons and helium

Emulsion chambers are being used in a series of stratospheric balloon flights to study nuclear interactions, charge composition, and energy spectra of cosmic ray nuclei over the energy range 10¹²–10¹⁵ eV. Charge identification involves grain, gap, and/or delta-ray counting in emulsion plates having different sensitivities on two sides of an acrylic base. Electromagnetic cascade energies are measured with resolutions of about 25% by the three-dimensional track counting method. This report describes the apparatus, the measurement techniques, and the analysis methods used to determine the primary proton and helium spectra.     

Submicrometer gratings for solar energy applications

Diffractive optical structures for increasing the efficiency of crystalline silicon solar cells are discussed. As a consequence of the indirect band gap, light absorption becomes very ineffective near the band edge. This can be remedied by use of optimized diffraction gratings that lead to light trapping. We present blazed gratings that increase the optically effective cell thickness by approximately a factor of 5. In addition we present a wideband antireflection structure for glass that consists of a diffraction grating with a dielectric overcoat, which leads to an average reflection of less than 0.6% in the wavelength range between 300 and 2100 nm.     

Polymer-based nanopiezoelectric generators for energy harvesting applications

Abstract

Energy harvesting from ambient vibrations originating from sources such as moving parts of machines, fluid flow and even body movement, has enormous potential for small power applications, such as wireless sensors, flexible, portable and wearable electronics, and bio-medical implants, to name a few. Nanoscale piezoelectric energy harvesters, also known as nanogenerators (NGs), can directly convert small scale ambient vibrations into electrical energy. Scavenging power from ubiquitous vibrations in this way offers an attractive route to provide power to small devices, which would otherwise require direct or indirect connection to electrical power infrastructure. Ceramics such as lead zirconium titanate and semiconductors such as zinc oxide are the most widely used piezoelectric energy harvesting materials. This review focuses on a different class of piezoelectric materials, namely, ferroelectric polymers, such as polyvinlyidene fluoride (PVDF) and its copolymers. These are potentially superior energy harvesting materials as they are flexible, robust, lightweight, easy and cheap to fabricate, as well as being lead free and biocompatible. We review some of the theoretical and experimental aspects of piezoelectric energy recovery using Polymer-based NGs with a novel emphasis on coupling to mechanical resonance, which is relevant for efficient energy harvesting from typically low frequency (<1 kHz) ambient vibrations. The realisation of highly efficient and low cost piezoelectric polymer NGs with reliable energy harvesting performance could lead to wide ranging energy solutions for the next generation of autonomous electronic and wireless devices.     

Metal oxide nanoparticles for advanced energy applications

Hot-wire chemical vapor deposition (HWCVD) has been employed as an economically scalable method for the deposition of crystalline molybdenum oxide nanoparticles at high density. Under optimal synthesis conditions, only crystalline nanostructures with a smallest dimension of ~ 3-50 nm are observed with extensive transmission electron microscopy analyses. The incorporation of crystalline molybdenum oxide nanoparticles into battery electrodes has led to profound advancements in state-of-the-art negative electrodes (anodes) in lithium-ion batteries. The nanoparticle materials exhibit a high rate capability as anticipated for the reduced solid-state Li-ion diffusion length.     

氦低温系统螺杆压缩机组运行分析及节能优化

主要分析了EAST全超导托卡马克可控核聚变装置低温系统的喷油螺杆压缩机组,对其运行状况做了一些分析研究,并分析导致压机等温效率偏低的原因;最后提出一些节能优化措施,改善螺杆压缩机组的运行状况.     

Superconductivity applications in high energy physics

During the past five years, several very large superconducting bubble chamber and spark chamber magnets have become operational. The economic and other factors which have led to the construction of large superconducting solenoid magnets for high energy physics research are discussed, and the technological development which made these magnets possible is summarized. Much of the recent development work on superconducting magnets for high energy physics has been directed toward the next generation of accelerators and beam storage rings. Here the goal is to develop dipole and quadrupole magnets of high field precision, low cost, high reliability, capability for slow pulsing, and minimal sensitivity to radiation heating. The status of this work and its application to future accelerators is described. Also, the application of superconducting rf cavities for linear accelerators and particle separation is reviewed briefly.     

Ionic liquids for electrochemical energy storage devices applications

Ionic liquids, defined here as room-temperature molten salts, composed mainly of organic cations and (in)organic anions ions that may undergo almost unlimited structural variations with melting points below 100?°C. They offer a unique series of physical and chemical properties that make them extreme important candidates for several energy applications, especially for clean and sustainable energy storage and conversion materials and devices. Ionic liquids exhibit high thermal and electrochemical stability coupled with low volatility, create the possibility of designing appropriate electrolytes for different type batteries and supercapacitors. Herein, varieties of ionic liquids applications are reviewed on their utilization as electrolytes for Li-ion batteries, Na-ion batteries, Li-O₂(air) batteries, Li-Sulfur (Li-S) batteries, supercapacitors and as precursors to prepare and modify the electrode materials, meanwhile, some important research results in recent years are specially introduced, and the perspective on novel application of ionic liquids is also discussed.     

Advanced polymeric dielectrics for high energy density applications

This article provides an overview of the present state-of-the-art pertaining to polymer capacitor dielectrics appropriate for high electrostatic energy density applications. The challenges and opportunities surrounding capacitor materials development/discovery in a practical context are reviewed. It is pointed out that several hierarchical considerations ranging from dielectric, electronic, morphological, processing, reliability and electrical characteristics need to be confronted and addressed adequately before one can progress from “standard” materials (such as biaxially oriented polypropylene) toward next generation materials. Nevertheless, it is argued that the prospects for systematic approaches toward polymer dielectrics discovery appear to be strong, especially given recent successes and evidence that a cooperative computation-synthesis-processing-characterization paradigm can bear fruit. It is hoped that this article will be particularly useful for a new researcher entering the field as it presents a snapshot of various critical aspects of this emerging field in one comprehensive narrative.     

Integration of design systems for energy related applications

An EPSRC funded Engineering Design Centre (EDC) has been established at The Queen's University of Belfast to develop integrated design software for energy related applications. Software is being developed for the design of two-stroke engines, power station controllers and wave power stations. These ‘real’ design problems are highly complex with a large number of interrelated variables resulting in a wide range of design permutations. Although at an early state of application, the advantages of using object orientated design/programming methodologies is being demonstrated in the development of ‘structured’ design software. It is concluded that a balance must be struck between the complexity and the accuracy of the analytic models describing the interrelationship between the variables. This depends on the stage of the design optimization process. It is argued that complex optimization routines can only be justified when the process is well-defined and accurately modelled. Modelling of many systems includes approximations which have a more significant effect on the design optimization process than some of the variables.     

Bioinspired nanoscale materials for biomedical and energy applications

The demand for green, affordable and environmentally sustainable materials has encouraged scientists in different fields to draw inspiration from nature in developing materials with unique properties such as miniaturization, hierarchical organization and adaptability. Together with the exceptional properties of nanomaterials, over the past century, the field of bioinspired nanomaterials has taken huge leaps. While on the one hand, the sophistication of hierarchical structures endows biological systems with multi-functionality, the synthetic control on the creation of nanomaterials enables the design of materials with specific functionalities. The aim of this review is to provide a comprehensive, up-to-date overview of the field of bioinspired nanomaterials, which we have broadly categorized into biotemplates and biomimics. We discuss the application of bioinspired nanomaterials as biotemplates in catalysis, nanomedicine, immunoassays and in energy, drawing attention to novel materials such as protein cages. Furthermore, the applications of bioinspired materials in tissue engineering and biomineralization are also discussed.     

Solid helium. II. Exchange energy in solid3He

The problem of exchange energy in solid³He is investigated, and the exchange integral for bcc³He is calculated. Results are obtained from reaction-matrix elements calculated by means of a modified Brueckner theory developed earlier, and the calculations are repeated for several values of the molar volume and the parameter ² defining the unperturbed wave functions. The final results indicate an antiferromagnetic and strongly density-dependent exchange integral with the absolute value decreasing rapidly with increasing density or decreasing molar volume. The calculations are made for two different two-body potentials, an Yntema-Schneider potential given by Brueckner and Gammel, and a Frost-Musulin potential given by Bruch and McGee. Theoretical results for the exchange integral are approximately –0.13 to –0.16 mK at a molar volume of 22 cm³/mole, and –0.44 to –0.57 mK at a molar volume of 24 cm³/mole. The corresponding experimental results are approximately –0.135 and –0.655 mK, respectively, i.e., the difference is generally within a factor of 1.5. The agreement with experimental results is reasonably good since the theoretical value is given by a small difference between several large terms of opposite sign almost canceling each other, and the results are also very sensitive to the choice of the parameter value ² for each molar volume.     

Effect of rotation on the flow behaviour in a high-speed cryogenic microturbine used in helium applications

The complex flow characteristics in a high-speed helium microturbine used in cryogenic refrigeration and liquefaction cycles are highly influenced by the effects of rotation. In order to enhance the turbine performance and to improve the preliminary design process of the turboexpander, the flow characteristics within the turbine blade passage need to be investigated at different rotational speeds. Here, three-dimensional unsteady flow analysis of a high speed cryogenic microturbine used in helium applications was carried out using Ansys CFX^®. The loss generated by the various secondary and vortical flows for the different cases was quantified in terms of entropy loss coefficient. The loss generating mechanism was also assessed by analysing the velocity vectors, entropy contours and the behaviour of the vortex cores. With change in speed the influence of scraping flow due to relative casing motion and the blade loading on the flow characteristics was found to vary significantly. At lower speeds, the scraping flow decreases and thus augments the tip leakage flow which in turn interacts with the suction side leg of the leading edge vortex to form a single large vortex. This combined vortex increases the velocity defect and thus leads to increased loss generation. The analysis of the vortex core velocity and the blade loading diagram revealed the need for modifications in blade profile for improved turbine performance. Furthermore, the comparison of the CFD results with the Balje's n_sd_s chart showed remarkable variations, the results of which can be used to modify the chart for the design of efficient cryogenic microturbines for helium applications.     

Advanced pyroelectric materials for energy harvesting and sensing applications

Heat energy is among the most wasted energy in the environment which is available in an ample quantity. So, developing new technology for harvesting and detecting wasted thermal energy to produce electrical energy which may be used as reliable energy sources for ultra-low power devices like nanogenerators and self-powered sensor applications. In this approach, pyroelectric energy harvesting technology has gained a huge attraction for application in power generation and sensing systems. Currently, a class of pyroelectric and piezoelectric materials has drawn enormous attraction because of its pyroelectric effect caused by spontaneous polarization and successful thermal energy harvesting for producing electrical energy for application in many sensor networks. This review makes a comprehensive summary of the significance and physical application of pyroelectric materials including single crystal, inorganic films, ceramics, organic materials, polymers, and composites as energy harvesting devices for scavenging thermal energy from surrounding for sensing devices. Finally, the perspective for next-generation self-powered sensor technologies is described.