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At least 19 recordsLinked to original sources

arXiv2008

A Novel Temperature-Induced Magnetization Transition in Pt/Co/Pt Sandwiches

It is found in the Pt/Co/Pt(111) sandwiches that perpendicular magnetic anisotropy weakens associated with the dramatic magnetization enhancement as the temperature decreases below a critical temperature, T_cri, which increases with the Pt overlayer thickness t_Pt. For the sandwich with enough thick Pt overlayer, it trends to an unusual state with weak perpendicular magnetic anisotropy in the absence of obvious easy direction behavior at low temperature. It suggests that Pt is more significantly polarized in the film with thicker Pt overlayer. The results reveal the strong influence of both thick nonmagnetic coverage and temperature on the electronic structure of the Pt/Co/Pt(111) sandwich.

cond-mat.mtrl-sci↗

arXiv2014

A modified Michelson interferometer type Raman laser system for atom interferometers

We have developed a modified Michelson interferometer type Raman laser system to manipulate cold 87 Rb atoms to interfere. A frequency modulated continuous wave technique was introduced to determine the optical path difference, thus compensating it to zero to minimize the effects of common mode noise. The linewidth (full width at half maximum) of the beat signal at 6.834 GHz was measured to 1Hz limited by the resolution bandwidth of the spectral analyzer. The measured rms phase variance of the phase noise at 166 MHz was 0.015 rad2, mainly restricted by our poor performance radio frequency microwave source. With modest improvements, we plan to apply this laser system to form an atom interferometer for acceleration and rotation measurements.

physics.atom-ph↗

arXiv2016

A novel flexible and modular energy storage system for near future Energy Banks

We considered a novel energy storage system based on the compression of air through pumped water. Differently from CAES on trial, the proposed indirect compression leaves the opportunity to choose the kind of compression from adiabatic to isothermal. The energy storage process could be both fast or slow leading to different configuration and applications. These novel storage system are modular and could be applied in different scales for different locations and applications, being very flexible in charge and discharge process. The system may offer an ideal energy buffer for wind and solar storage with no (or negligible) environment hazard. The main features of this novel energy storage system will be showed together with overall energy and power data.

physics.flu-dyn↗

arXiv2019

Three-dimensional electromagnetic modeling of practical superconductors for power applications

HTS are feasible for hight power applications because of the smaller consumption demand of the cooling system in comparison to the whole power device. Real industral devices contain superconductors with 2D and 3D geometry (coated conductors tapes represent an example of 2D geometry, since the superconducting layer is very thin). In order to know the feasibility and the optimum design of a certain device, there is a need of software tools. These Numerical tools have hight requirements like fast computation, a physical model for any E(J) relation of the superconductor and any complex geometry such as coils, motors and generators, where E is the electric field and J is the current density. In this work we present a 3D variational model based on a functional that restricts the problem in the superconductor volume. We show the magnetization process of a thin film and a 3D bulk sample. We compare our model of the thin film geometry with the thin film formula, reaching a good agreement. We also compare a striated tape, where the filaments are connected by linear material, with a FEM model. We present several results for a thin film with constant critical current density, Jc, magnetic-field dependent Jc, and an anisotropic E(J) relation. For the latter, E is not parallel to J when the magnetic flux density is not perpendicular to J (force free situation). The last studied situation is the 3D cubic sample. We find the time dependence of the current density and AC loss for each situation. In the cubic bulk sample, we found a non-negligible component of the current density in the direction of the applied field. The presented numerical method is very promising for 3D modeling of superconducting samples and power applications.

cond-mat.supr-con↗

arXiv2017

Amorphous Alloys, Degradation Performance of Azo Dyes: Review

Today freshwater is more important than ever before and it is contaminated from textile industry. Removal of dyes from effluent of textile using amorphous alloys has been studied extensively by many researchers. In this review article it is presented up to date development on the azo dye degradation performance of amorphous alloys, a new class of catalytic materials. Numerous amorphous alloys have been developed for increasing higher degradation efficiency in comparison to conventional ones for the removal of azo dyes in wastewater. One of the objectives of this review article is to organize the scattered available information on various aspects on a wide range of potentially effective in the removal of dyes by using amorphous alloys. This study comprises the affective removal factors of azo dye such as solution pH, initial dye concentration, and adsorbent dosage. It was concluded that Fe, Mg, Co, Al and Mn-based amorphous alloys with wide availability have appreciable for removing several types of azo dyes from wastewater. Concerning amorphous alloys for future research, some suggestions are proposed and conclusions have been drawn.

physics.app-ph↗

arXiv2017

Optimizing Thermochromism of Solution-Processed VO$_2$ Nanocomposite Films for Chromogenic Fenestration

Vanadium (IV) oxide is one of the most promising materials for thermochromic films due to its unique, reversible crystal phase transition from monoclinic (M1) to rutile (R) at its critical temperature (T$_c$) which corresponds to a change in optical properties: above T$_c$, VO$_2$ films exhibit a decreased transmittance for wavelengths of light in the near-infrared region. However, a high transmittance modulation often sacrifices luminous transmittance which is necessary for commercial and residential applications of this technology. In this study, we explore the potential for synthesis of VO$_2$ films in a matrix of metal oxide nanocrystals, using In$_2$O$_3$, TiO$_2$, and ZnO as diluents. We seek to optimize the annealing conditions to yield desirable optical properties. Although the films diluted with TiO$_2$ and ZnO failed to show transmittance modulation, those diluted with In$_2$O$_3$ exhibited strong thermochromism. Our investigation introduces a novel window film consisting of a 0.93 metal ionic molar ratio VO$_2$-In$_2$O$_3$ nanocrystalline matrix, demonstrating a significant increase in luminous transmittance without any measurable impact on thermochromic character. Furthermore, solution-processing mitigates costs, allowing this film to be synthesized 4x-7x cheaper than industry standards. This study represents a crucial development in film chemistry and paves the way for further application of VO$_2$ nanocomposite films in chromogenic fenestration.

physics.app-ph↗

arXiv2017

Diffusion-limited Reactions in Nanoscale Electronics

A partial differential equation (PDE) was developed to describe time-dependent ligand-receptor interactions for applications in biosensing using field effect transistors (FET). The model describes biochemical interactions at the sensor surface (or biochemical gate) located at the bottom of a solution-well, which result in a time-dependent change in the FET conductance. It was shown that one can exploit the disparate length scales of the solution-well and biochemical gate to reduce the coupled PDE model to a single nonlinear integrodifferential equation (IDE) that describes the concentration of reacting species. Although this equation has a convolution integral with a singular kernel, a numerical approximation was constructed by applying the method of lines. The need for specialized quadrature techniques was obviated and numerical evidence strongly suggests that this method achieves first-order accuracy. Results reveal a depletion region on the biochemical gate, which non-uniformly alters the surface potential of the semiconductor.

math.AP↗

arXiv2017

Kirigami-based Elastic Metamaterials with Anisotropic Mass Density for Subwavelength Flexural Wave Control

A novel design of an elastic metamaterial with anisotropic mass density is proposed to manipulate flexural waves at a subwavelength scale. The three-dimensional metamaterial is inspired by kirigami, which can be easily manufactured by cutting and folding a thin metallic plate. By attaching the resonant kirigami structures periodically on the top of a host plate, a metamaterial plate can be constructed without any perforation that degrades the strength of the pristine plate. An analytical model is developed to understand the working mechanism of the proposed elastic metamaterial and the dispersion curves are calculated by using an extended plane wave expansion method. As a result, we verify an anisotropic effective mass density stemming from the coupling between the local resonance of the kirigami cells and the global flexural wave propagations in the host plate. Finally, numerical simulations on the directional flexural wave propagation in a two-dimensional array of kirigami metamaterial as well as super-resolution imaging through an elastic hyperlens are conducted to demonstrate the subwavelength-scale flexural wave control abilities. The proposed kirigami-based metamaterial has the advantages of no-perforation design and subwavelength flexural wave manipulation capability, which can be highly useful for engineering applications including non-destructive evaluations and structural health monitoring.

physics.app-ph↗

arXiv2017

Graphene oxide dielectric permittivity at GHz and its applications for wireless humidity sensing

Graphene oxide relative dielectric permittivity, both its real and imaginary parts, have been measured under various humidity conditions at GHz. It is demonstrated that the relative dielectric permittivity increases with increasing humidity due to water uptake. This electrical property of graphene oxide was used to create a battery-free wireless radio-frequency identification (RFID) humidity sensor by coating printed graphene antenna with the graphene oxide layer. The resonance frequency as well as the backscattering phase of such graphene oxide/graphene antenna become sensitive to the surrounding humidity and can be detected by the RFID reader. This enables batteryless wireless monitoring of the local humidity with digital identification attached to any location or item and paves the way for low-cost efficient sensors for Internet of Things applications.

physics.app-ph↗

arXiv2017

Single crystal diamond membranes for nanoelectronics

Single crystal, nanoscale diamond membranes are highly sought after for a variety of applications including nanophotonics, nanoelectronics and quantum information science. However, so far, the availability of conductive diamond membranes remained an unreachable goal. In this work we present a complete nanofabrication methodology for engineering high aspect ratio, electrically active single crystal diamond membranes. The membranes have large lateral directions, exceeding 500x500 um2 and are only several hundreds of nanometers thick. We further realize vertical single crystal p-n junctions, made from the diamond membranes that exhibit onset voltages of ~ 10V and a current of several mA. Moreover, we deterministically introduce optically active color centers into the membranes, and demonstrate for the first time a single crystal nanoscale diamond LED. The robust and scalable approach to engineer the electrically active single crystal diamond membranes, offers new pathways for advanced nanophotonics, nanoelectronics and optomechanics devices employing diamond.

physics.app-ph↗

arXiv2017

An optical micro-comb with a 50GHz free spectral range for photonic microwave true time delays

We demonstrate significantly improved performance of a microwave true time delay line (TTDL) based on an integrated micro-ring resonator (MRR) Kerr optical comb source with a channel spacing of 49GHz, corresponding to 81 channels over the C-band. The broadband microcomb, with a record low free spectral range of 49GHz, results in a large number of comb lines for the TTDL, greatly reducing the size, cost, and complexity of the system. The large channel count results in a high angular resolution and wide beam steering tunable range of the phased array antenna (PAA). The enhancement of PAA performance matches well with theory, corroborating the feasibility of our approach as a competitive solution towards implementing compact low-cost TTDL in radar and communications systems.

physics.app-ph↗

arXiv2017

Elastic metasurfaces for splitting SV- and P-waves in elastic solids

Although recent advances have made it possible to manipulate electromagnetic and acoustic wavefronts with sub-wavelength metasurface slabs, the design of elastodynamic counterparts remains challenging. We introduce a novel but simple design approach to control SV-waves in elastic solids. The proposed metasurface can be fabricated by cutting an array of aligned parallel cracks in a solid such that the materials between the cracks act as plate-like waveguides in the background medium. The plate array is capable of modulating the phase change of SV-wave while keeping the phase of P-wave unchanged. An analytical model for SV-wave incidence is established to calculate the transmission coefficient and the transmitted phase through the plate-like waveguide explicitly. A complete $2π$ range of phase delay is achieved by selecting different thicknesses for the plates. An elastic metasurface for splitting SV- and P-waves is designed and demonstrated using full wave finite element (FEM) simulations. Two metasurfaces for focusing plane and cylindrical SV-waves are also presented.

physics.app-ph↗

arXiv2017

Demonstration of a 2x2 programmable phase plate for electrons

First results on the experimental realisation of a 2x2 programmable phase plate for electrons are presented. The design consists of an array of electrostatic einzel lenses that influence the phase of electron waves passing through 4 separately controllable aperture holes. This functionality is demonstrated in a conventional transmission electron microscope operating at 300~kV and results are in very close agreement with theoretical predictions. The dynamic creation of a set of electron probes with different phase symmetry is demonstrated, thereby bringing adaptive optics in TEM one step closer to reality. The limitations of the current design and how to overcome these in the future are discussed. Simulations show how further evolved versions of the current proof of concept might open new and exciting application prospects for beam shaping and aberration correction.

physics.app-ph↗

arXiv2017

Detection Limit for Optically Sensing Specific Protein Interactions in Free-solution

Optical molecular sensing techniques are often limited by the refractive index change associated with the probed interactions. In this work, we present a closed form analytical model to estimate the magnitude of optical refractive index change arising from protein-protein interactions. The model, based on the Maxwell Garnett effective medium theory and first order chemical kinetics serves as a general framework for estimating the detection limits of optical sensing of molecular interactions. The model is applicable to situations where one interacting species is immobilized to a surface, as commonly done, or to emerging techniques such as Back-Scattering Interferometry (BSI) where both interacting species are un-tethered. Our findings from this model point to the strong role of as yet unidentified factors in the origin of the BSI signal resulting in significant deviation from linear optical response.

physics.app-ph↗

arXiv2017

Comprehensive Modeling of Graphene Resistivity

Since the first graphene layer was fabricated in the early 2000's, graphene properties have been studied extensively both experimentally and theoretically. However, when comparing the many resistivity models reported in literature, several discrepancies can be found, as well as a number of inconsistencies between formulas. In this paper, we revise the main scattering mechanisms in graphene, based on theory and goodness of fit to in-house experimental data. In particular, a step-by-step evaluation of the interaction between electrons and optical phonons is carried out, where we demonstrate that the process of optical phonon emission scattering is completely suppressed for all low-field applications and all temperatures in the range of interest, as opposed to what is often reported in literature. Finally, we identify the best scattering models based on the goodness of fit to experimental data.

physics.app-ph↗

arXiv2018

Chip-based Brillouin processing for carrier recovery in coherent optical communications

Modern fiber-optic coherent communications employ advanced spectrally-efficient modulation formats that require sophisticated narrow linewidth local oscillators (LOs) and complex digital signal processing (DSP). Here, we establish a novel approach to carrier recovery harnessing large-gain stimulated Brillouin scattering (SBS) on a photonic chip for up to 116.82 Gbit/sec self-coherent optical signals, eliminating the need for a separate LO. In contrast to SBS processing on-fiber, our solution provides phase and polarization stability while the narrow SBS linewidth allows for a record-breaking small guardband of ~265 MHz, resulting in higher spectral-efficiency than benchmark self-coherent schemes. This approach reveals comparable performance to state-of-the-art coherent optical receivers without requiring advanced DSP. Our demonstration develops a low-noise and frequency-preserving filter that synchronously regenerates a low-power narrowband optical tone that could relax the requirements on very-high-order modulation signaling and be useful in long-baseline interferometry for precision optical timing or reconstructing a reference tone for quantum-state measurements.

physics.app-ph↗

arXiv2017

An Electrochemical Technique for Measurements of Electrical Conductivity of Aqueous Electrolytes

The technique presented here for the measurement of electrical conductivity is based on the principle that the current converges on a small disk electrode. Most of the ohmic resistance therefore lies within a narrow region surrounding the disk. If the reference electrode is kept outside this zone, the potential difference between the working and the reference electrode includes practically all ohmic potential drops occurring in the solution. Moreover, this ohmic drop can be related to the conductivity of the solution by an analytical expression derived by Newman. At sufficiently high overpotentials, the rate of charge transfer is limited by the conduction of current from the bulk solution to the electrode. In this regime, the current varies linearly with the electrode potential and the conductivity of the solution can be estimated from the slope of the voltammogram using Newman's expression. The electrochemical reaction used for measuring conductivity of solutions of salts is the cathodic reduction of water and that used for aqueous acids is the cathodic reduction of hydrogen ions. The technique has been used to measure conductivity of several common aqueous electrolytes. A good agreement is found between the present technique and the conventional technique based on AC impedance analysis.

physics.chem-ph↗

arXiv2018

Nondestructive in-line sub-picomolar detection of magnetic nanoparticles in flowing complex fluids

Over the last decades, the use of magnetic nanoparticles in research and commercial applications has increased dramatically. However, direct detection of trace quantities remains a challenge in terms of equipment cost, operating conditions and data acquisition times, especially in flowing conditions within complex media. Here we present the in-line, non-destructive detection of magnetic nanoparticles using high performance atomic magnetometers at ambient conditions in flowing media. We achieve sub-picomolar sensitivities measuring $\sim$30 nm ferromagnetic iron and cobalt nanoparticles that are suitable for biomedical and industrial applications, under flowing conditions in water and whole blood. Additionally, we demonstrate real-time surveillance of the magnetic separation of nanoparticles from water and whole blood. Overall our system has the merit of inline direct measurement of trace quantities of ferromagnetic nanoparticles with so far unreached sensitivities and could be applied in the biomedical field (diagnostics and therapeutics) but also in the industrial sector.

physics.app-ph↗