Narrow Transition Research Articles

Mixing brain cerebrosides with brain ceramides, cholesterol and phospholipids

The properties of bilayers composed of pure brain cerebroside (bCrb) or of binary mixtures of bCrb with brain ceramide, cholesterol, egg phosphatidylcholine or brain sphingomyelin have been studied using a combination of physical techniques. Pure bCrb exhibits a rather narrow gel-fluid transition centred at ≈65 °C, with a half-width at half-height T1/2 ≈ 3 °C. bCrb mixes well with both fluid and gel phospholipids and ceramide, and it rigidifies bilayers of egg phosphatidylcholine or brain sphingomyelin when the latter are in the fluid state. Cholesterol markedly widens the bCrb gel-fluid transition, while decreasing the associated transition enthalpy, in the manner of cholesterol mixtures with saturated phosphatidylcholines, or sphingomyelins. Laurdan and DPH fluorescence indicate the formation of fluid ordered phases in the bCrb:cholesterol mixtures. Macroscopic phase separation of more and less fluid domains is observed in giant unilamellar vesicles consisting of bCrb:egg phosphatidylcholine or bCrb:sphingomyelin. Crb capacity to induce bilayer permeabilization or transbilayer (flip-flop) lipid motion is much lower than those of ceramides. The mixtures explored here contained mostly bCrb concentrations >50 mol%, mimicking the situation of cell membranes in Gaucher’s disease, or of the Crb-enriched microdomains proposed to exist in healthy cell plasma membranes.

Cyclic response and fatigue failure of Nitinol under tension–tension loading

Abstract

Asymptotics of the Solution of a Differential Equation in a Saddle–Node Bifurcation

A second-order semilinear differential equation with slowly varying parameters is considered. With frozen parameters, the corresponding autonomous equation has fixed points: a saddle point and stable nodes. Upon deformation of the parameters, the saddle–node pair merges. An asymptotic solution near such a dynamic bifurcation is constructed. It is found that, in a narrow transition layer, the principal terms of the asymptotics are described by the Riccati and Kolmogorov–Petrovsky–Piskunov equations. An important result is finding the dragging out of the stability: the moment of disruption significantly shifts from the moment of bifurcation. The exact assertions are illustrated by the results of numerical experiments.

Numerical Implementation of High-Order Vold–Kalman Filter Using Python Arbitrary-Precision Arithmetic Library

The Vold–Kalman (VK) order tracking filter plays a vital role in the order analysis of noise in various fields. However, owing to the limited accuracy of double-precision floating-point data type, the order of the filter cannot be too high. This problem of accuracy makes it impossible for the filter to use a smaller bandwidth, meaning that the extracted order signal has greater noise. In this paper, the Python mpmath arbitrary-precision floating-point arithmetic library is used to implement a high-order VK filter. Based on this library, a filter with arbitrary bandwidth and arbitrary difference order can be implemented whenever necessary. Using the proposed algorithm, a narrower transition band and a flatter passband can be obtained, a good filtering effect can still be obtained when the sampling rate of the speed signal is far lower than that of the measured signal, and it is possible to extract narrowband signals from signals with large bandwidth. Test cases adopted in this paper show that the proposed algorithm has better filtering effect, better frequency selectivity, and stronger anti-interference ability compared with double-precision data type algorithm.

Low computation digital down converter using polyphase IIR filter

PurposeThe digital down converter (DDC) is a principal component in modern communication systems. The DDC process traditionally entails quadrature down conversion, bandwidth reducing filters and commensurate sample rate reduction. To avoid group delay, distortion linear phase FIR filters are used in the DDC. The filter performance specifications related to deep stopband attenuation, small in-band ripple and narrow transition bandwidth lead to filters with a large number of coefficients. To reduce the computational workload of the filtering process, filtering is often performed as a two-stage process, the first stage being a down sampling Hoegenauer (or cascade-integrated comb) filter and a reduced sample rate FIR filter. An alternative option is an M-Path polyphase partition of a band cantered FIR filter. Even though IIR filters offer reduced workload to implement a specific filtering task, the authors avoid using them because of their poor group delay characteristics. This paper aims to propose the design of M-path, approximately linear phase IIR filters as an alternative option to the M-path FIR filter.Design/methodology/approachTwo filter designs are presented in the paper. The first approach uses linear phase IIR low pass structure to reduce the filter’s coefficient. Whereas the second approach uses multipath polyphase structure to design approximately linear phase IIR filter in DDC.FindingsThe authors have compared the performance and workload of the proposed polyphase structured IIR filters with state-of-the-art filter design used in DDC. The proposed design is seen to satisfy tight design specification with a significant reduction in arithmetic operations and required power consumption.Originality/valueThe proposed design is an alternate solution to the M-path polyphase FIR filter offering very less number of coefficients in the filter design. Proposed DDC using polyphase structured IIR filter satisfies the requirement of linear phase with the least number of computation cost in comparison with other DDC structure.

Background and Review of Cavity-Enhanced Spontaneous Parametric Down-Conversion.

Spontaneous parametric down-conversion (SPDC) in a nonlinear crystal has been a workhorse for the generation of entangled and correlated single-photon pairs used for quantum communications applications for nearly three decades. However, as a naturally broadband process, the ability of SPDC to interface with the very narrow energy transitions in atomic ensembles for implementing quantum memories, which are needed for quantum repeaters to extend the reach of quantum communications, was initially limited. To overcome this limitation, the process was enhanced by placing the nonlinear crystal inside a resonating cavity. This modified process has some important advantages, including narrowing the spectral linewidth of generated photons into brighter resonant modes of the cavity, and the ability to lock the desired mode of the cavity to the targeted transition frequency of the atomic ensemble. This paper presents an overview of the principle of cavity-enhanced SPDC, a review of works to date using this technique, and an example of one of these implementations.

Folding and Dynamics Are Strongly pH-Dependent in a Psychrophile Frataxin.

Protein dynamics, folding, and thermodynamics represent a central aspect of biophysical chemistry. pH, temperature, and denaturant perturbations inform our understanding of diverse contributors to stability and rates. In this work, we performed a thermodynamic analysis using a combined experimental and computational approach to gain insights into the role of electrostatics in the folding reaction of a psychrophile frataxin variant from Psychromonas ingrahamii. This folding reaction is strongly modulated by pH with a single, narrow, and well-defined transition state with ∼80% compactness, ∼70% electrostatic interactions, and ∼60% hydration shell compared to the native state (αD = 0.82, αH = 0.67, and αΔCp = 0.59). Our results are best explained by a two-proton/two-state model with very different pKa values of the native and denatured states (∼5.5 and ∼8.0, respectively). As a consequence, the stability strongly increases from pH 8.0 to 6.0 (|ΔΔG°| = 5.2 kcal mol-1), mainly because of a decrease in the TΔS°. Variation of ΔH° and ΔS° at pH below 7.0 is dominated by a change in ΔHf⧧ and ΔSf⧧, while at pH above 7.0, it is governed by ΔHu⧧ and ΔSu⧧. Molecular dynamics simulations showed that these pH modulations could be explained by the fluctuations of two regions, rich in electrostatic contacts, whose dynamics are pH-dependent and motions are strongly correlated. Results presented herein contribute to the understanding of the stability and dynamics of this frataxin variant, pointing to an intrinsic feature of the family topology to support different folding mechanisms.

Global Transcriptomic Profiling of the Bone Marrow Stromal Microenvironment During Postnatal Development, Aging and Inflammation

Bone marrow (BM) stromal cells provide the structural and regulatory framework for hematopoiesis and contribute to developmental-stage specific niches, such as those preserving hematopoietic stem cell (HSCs). Despite recent advances in our understanding of stromal composition and function, little is known on the dynamic transcriptional remodeling that this compartment undergoes over time and during adaptation to stress. Similarly, how molecular changes in stroma are linked to age-related modulation of hematopoiesis is poorly understood. Using RNA-sequencing, we performed a longitudinal comparison of the transcriptional profile of four principal mesenchymal and endothelial stromal subsets, namely CXCL12-abundant reticular (CARc), PDGFR-α+Sca-1+, sinusoidal (SECs) and arterial endothelial cells (AECs), isolated from early postnatal, adult and aged mice. Our data i) provide molecular fingerprints defining novel, cell-specific anatomical and functional features ii) reveal radical reprogramming of pro-hematopoietic, immune and matrisomic transcriptional programs during the narrow temporal transition from juvenile to adult stages iii) demonstrate that homeostatic aging is characterized by a progressive and pronounced upregulation of pro-inflammatory gene-expression and loss of stromal cell fitness. By profiling in vivo responses of stromal cells to infection-mimicking agents, we finally demonstrate that transcriptomic pathways elicited by sterile inflammation are largely recapitulated during aging, thereby supporting the inflammatory basis of aging-related adaptations of BM hematopoietic function.

Control of the Exciton Radiative Lifetime in van der Waals Heterostructures.

Optical properties of atomically thin transition metal dichalcogenides are controlled by robust excitons characterized by a very large oscillator strengths. Encapsulation of monolayers such as MoSe_{2} in hexagonal boron nitride (hBN) yields narrow optical transitions approaching the homogenous exciton linewidth. We demonstrate that the exciton radiative rate in these van der Waals heterostructures can be tailored by a simple change of the hBN encapsulation layer thickness as a consequence of the Purcell effect. The time-resolved photoluminescence measurements show that the neutral exciton spontaneous emission time can be tuned by one order of magnitude depending on the thickness of the surrounding hBN layers. The inhibition of the radiative recombination can yield spontaneous emission time up to 10ps. These results are in very good agreement with the calculated recombination rate in the weak exciton-photon coupling regime. The analysis shows that we are also able to observe a sizable enhancement of the exciton radiative decay rate. Understanding the role of these electrodynamical effects allows us to elucidate the complex dynamics of relaxation and recombination for both neutral and charged excitons.

Some Results of Designing an IIR Smoothing Filter with P- Splines

Requirements for modern digital filters are high and depend on some selective properties of such filters. IIR filters can ensure the narrowest transition width of signal omission and suppression with the same DF order. This study proposes to design and analyze a software-based IIR filter, a digital filter (DF) that is based on simple mathematical basis facilitates subsequent interpretation of data (estimation of derivatives, trends, forecast of time series, etc.). A modified penalty spline has been used as a model for such digital software-based IIR filter. A recurrent form of the P-spline computation has been created for the the IIR spline filter. The new modified recurrent P-spline can be used for stand-alone or group data. The recurrent spline filter has been investigated by the methods of linear dynamic systems. The obtained difference equation of the spline transform corresponds to a linear recursive DF with constant parameters. Frequency and time characteristics of the DF, being the main characteristics system and instrument functions, have been obtained analytically. The system function has been used to investigate the frequency characteristics of the spline filter and it has been found out that the spline filter is low frequency throughout the entire variation range of the spline parameters. Such filter characteristics correspond to a second-order aperiodic segment or a system with delay, which is typical for grouped data processing. The selective properties of the spline filter are clearly illustrated with the width of the instrument function, which depends on the spline parameters. Studies have shown that the passband bandwidth is mostly influenced by the group data size (the number of non-recursive terms of the difference equation). The stability of the recursive spline filter has been also estimated analytically based on the characteristic equation and the Hurwitz criterion. DF is always stable only when the conjugation of recurrent coefficients occurs at the beginning of a spline segment. Frequency characteristics of the spline filter have been confirmed in the time domain by histograms of the remainders of two recovered model functions.

The anomalous behaviour of aliphatic fatty diamides: Chain length and hydrogen bonding interactions

A series of five linear aliphatic diamides were synthesised via facile direct coupling of stearic acid (C18) with diamines of varying carbon number (18-n-18, n = 2, 4, 6, 8 and 10) in a catalyst-free neat reaction. The compounds were investigated as potential renewable phase change materials (PCMs) for latent heat thermal energy storage. The thermal properties of the diamides were predictably related to the diamine chain length. TGA measurements indicated that the diamides evaporated before decomposition, with evaporation onsets increasing from 325 °C for 18-2-18 to plateau at 337 °C for the longer-chain diamides. The diamides display negligible supercooling and melt and crystallize at 140 °C–150 °C within a narrow transition span (<5 °C). Notably, both their melting and crystallization temperatures versus n present a maximum at n = 4, explained by peak hydrogen bonding and chain length considerations. As the distance between the amide groups increases, the transition temperatures decrease exponentially owing to the subsequent decrease in intermolecular hydrogen bond strength. The latent heat of the diamides presented a sharp increase from 165 J/g for 18-2-18 to plateau at ~210 J/g for the other amides (n ≥ 4). XRD measurements support the thermal transition behaviour; it shows that all the diamides crystallize from the melt into the β-phase, except for 18-2-18 in which the β-phase co-existed with the less stable β′-phase. Overall, the study shows that the diamides are suitable alternatives to classical petrochemical derived PCMs, expanding the currently limited library of organic PCMs.

Low-Complexity Channelizer Based on FRM for Passive Radar Multi-channel Wideband Receiver

The low-complexity channelizer is essential in passive radar multi-channel wideband receiver using array antennas. The digital filter bank is usually used to realize the channelizer. In the paper, a low-complexity channelizer based on frequency response masking (FRM) is proposed to reduce the high computational complexity of the narrow transition bandwidth filter bank. A half-band filter is used to design the prototype filter of the proposed low-complexity channelizer based on FRM. Compared to the maximally decimated filter bank, the decimation coefficient of the non-maximally decimated filter bank can be different from the number of channels, which makes the low-complexity channelizer more flexible. The low-complexity channelizer based on FRM can be directly applied to a wideband receiver without the limit of the sampling rate. The simulation and complexity analysis results show that the proposed low-complexity channelizer is correct and significantly reduces computational and hardware complexities. The proposed low-complexity channelizer makes it possible to implement passive radar multi-channel wideband receiver on a single hardware processor; thus, it is suitable to applied in passive radar multi-channel wideband receiver using array antennas.

Laser cooling with adiabatic transfer on a Raman transition

Sawtooth Wave Adiabatic Passage (SWAP) laser cooling was recently demonstrated using a narrow-linewidth single-photon optical transition in atomic strontium and may prove useful for cooling other atoms and molecules. However, many atoms and molecules lack the appropriate narrow optical transition. Here we use such an atom, 87Rb, to demonstrate that two-photon Raman transitions with arbitrarily-tunable linewidths can be used to achieve 1D SWAP cooling without significantly populating the intermediate excited state. Unlike SWAP cooling on a narrow transition, Raman SWAP cooling allows for a final 1D temperature well below the Doppler cooling limit (here, 25 times lower); and the effective excited state decay rate can be modified in time, presenting another degree of freedom during the cooling process. We also develop a generic model for Raman Landau–Zener transitions in the presence of small residual free-space scattering for future applications of SWAP cooling in other atoms or molecules.

Effect of post annealing on properties of N-doped TiO2 films deposited by reactive magnetron sputtering

The paper studies the effect of annealing on the structure and properties of N-doped TiO2 films, deposited by reactive magnetron sputtering. An increase in the annealing temperature results in a reduction of the film thickness and a rise of the refractive index. The post annealing induces the anatase-rutile phase transition and also leads to band gap narrowing and wettability transition.

Topological superfluidity with repulsive alkaline-earth atoms in optical lattices

We discuss a realization of topological superfluidity with fermionic atoms in an optical lattice. We consider a situation where atoms in two internal states experience different lattice potentials: one species is localized and the other itinerant, and show how quantum fluctuations of the localized fermions give rise to an attraction and spin–orbit coupling in the itinerant band. At low temperature, these effects stabilize a topological superfluid of mobile atoms even if their bare interactions are repulsive. This emergent state can be engineered with alkaline-earth atoms in a superlattice with a dimerized unit cell. To probe its unique properties we describe protocols that use high spectral resolution and controllability of a narrow clock transition, such as momentum-resolved spectroscopy and supercurrent response to a synthetic (laser-induced) magnetic field.

Influence of different sputtering conditions on superconductivity of ultra-thin epitaxial niobium nitride film

Superconductors are used in military and commercial applications due to the full diamagnetic and zero resistance properties. Hereinto, niobium nitride (NbN) has been extensively studied for its excellent superconducting properties, such as high transition temperature ( T c), large superconducting energy gap, narrow transition width and good stability. Superconducting NbN films are widely used in low temperature superconducting devices, for instance, hot electron bolometer, superconducting quantum interference devices and rapid single flux quantum. Especially, in 2001 Gol’tsman has successfully detected a single photon response of 810 nm near-infrared using an ultra-thin superconducting NbN, which proved that the high-quality growth of ultra-thin NbN film was the key step for high resolution and sensitivity of the superconducting detector. Up to now, atomic layer deposition (ALD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD) and magnetron sputtering have been successfully used to grow NbN thin films. However, T c is decreasing gradually as the reduced of thickness. Therefore, there is still a challenge to grow ultra-thin superconducting NbN film with high performance. In this work, 5 nm thickness of superconducting epitaxial NbN film has been grown on MgO substrate by magnetron sputtering. We systematically study the effect of different sputtering parameters on the superconductivity properties of the NbN film. The experiment results show that the high vacuum, high sputtering temperature and low working pressure are positively correlated with the superconducting transition temperature of NbN film under the premise of suitable argon-nitrogen ratio or magnetron power. The analyses of physical property measurement system (PPMS) indicate that as-grown 5 nm-thick NbN film has high performance with a superconducting transition temperature as high as 12.5 K under the optimum condition. Morphologic characterizations show that the ultra-thin NbN films have high density and smoothness with 0.116 nm of the surface roughness. Microstructural measurements also illustrate the epitaxial growth of NbN on MgO substrate. This work demonstrates the ultra-thin NbN films can be well controllably grown with high quality and offers a platform to fabricate the ultra-thin superconducting devices in the coming future.

High quality NbTiN films fabrication and rapid thermal annealing investigation**Project supported by the Chinese Academy of Sciences Strategic Priority Research Program B (Grant No. XDB07010300) and the National Natural Science Foundation of China (Grant No. 11674376).

NbTiN thin films are good candidates for applications including single-photon detector, kinetic inductance detector, hot electron bolometer, and superconducting quantum computing circuits because of their favorable characteristics, such as good superconducting properties and easy fabrication. In this work, we systematically investigated the growth of high-quality NbTiN films with different thicknesses on Si substrates by reactive DC-magnetron sputtering method. After optimizing the growth conditions, such as the gas pressure, Ar/N2 mixture ratio, and sputtering power, we obtained films with excellent superconducting properties. A high superconducting transition temperature of 15.5 K with narrow transition width of 0.03 K was obtained in a film of 300 nm thickness with surface roughness of less than 0.2 nm. In an ultra-thin film of 5 nm thick, we still obtained a transition temperature of 7.6 K. In addition, rapid thermal annealing (RTA) in atmosphere of nitrogen or nitrogen and hydrogen mixture was studied to improve the film quality. The results showed that Tc and crystal size of the NbTiN films were remarkably increased by RTA. For ultrathin films, the annealing in N2/H2 mixture had better effect than that in pure N2. The Tc of 10 nm films improved from 9.6 K to 10.3 K after RTA in N2/H2 mixture at 450 °C.

Design of Low-Complexity IFRM-UMFB Architecture for Wideband Digital Receivers

Modulated filter bank with low complexity is the key to realize the engineering applications for speech signal processing, multicarrier communication, and wideband digital receivers. The frequency response masking (FRM) technology is an effective method to design finite impulse response filters with narrow transition band (NTB). In this paper, an interpolation FRM unified modulated filter bank (IFRM-UMFB) architecture with NTB is proposed to reduce the computational complexity of the modulated filter bank architecture. The IFRM approach increases the transition band of two masking filters by the interpolation of N and reduces the computational complexity of two masking filters compared with classic FRM approach. The proposed IFRM-UMFB architecture with NTB is suitable for different odd-stacked or even-stacked, maximally decimated or non-maximally decimated structures. The proposed IFRM-UMFB architecture with NTB is verified to be correct through simulation. The complexity comparison result shows that the proposed IFRM-UMFB architecture offers multipliers reduction of 77.4% over the directly design approach and 26.5% over the classic FRM approach. Moreover, the proposed IFRM-UMFB architecture with NTB also can be directly applied to wideband digital receivers with high sampling rate.

Electron Spin Coherence in Optically Excited States of Rare-Earth Ions for Microwave to Optical Quantum Transducers.

Efficient and reversible optical to microwave transducers are required for entanglement transfer between superconducting qubits and light in quantum networks. Rare-earth-doped crystals with narrow optical and spin transitions are a promising system for enabling these devices. Current resonant transduction approaches use ground-state electron spin transitions that have coherence lifetimes often limited by spin flip-flop processes and spectral diffusion, even at very low temperatures. We investigate spin coherence in an optically excited state of an Er^{3+}: Y_{2}SiO_{5} crystal at temperatures from 1.6 to 3.5K for a low 8.7mT magnetic field compatible with superconducting resonators. Spin coherence and population lifetimes of up to 1.6 μs and 1.2ms, respectively, are measured by optically detected spin echo experiments. Analysis of decoherence processes suggest that ms coherence can be reached at lower temperatures for the excited-state spins, whereas ground-state spin coherence would be limited to a few μs due to resonant interactions with other Er^{3+} spins in the lattice and greater instantaneous spectral diffusion from the radio-frequency control pulses. We propose a quantum transducer scheme with potential for close to unity efficiency that exploits the advantages offered by spin states of the optically excited electronic energy levels.

Design of Narrow Transition Band Digital Filter: An Analytical Approach

Frequency response masking (FRM) approach, is widely used to reduce the transition width of FIR filter which includes several advantages like lower coefficient sensitivity, higher computation speed and low power consumption. This paper proposes a novel interpolated bandpass method (IBM) for the synthesis of linear phase, narrow transition band FIR filter with less complexity. Simulation results have shown the magnitude response of several lowpass FIR filters with narrow transition bandwidth, as designed with the aid of proposed approach. Supremacy of the proposed algorithm has also been established in terms of frequency response characteristics and hardware complexity over a number of state-of-the-art techniques of recent interest. Simulation results have identified an improvement of ∼18.89%, 44.62%, 38.75%, 41.2% and 29.5% in terms of transition bandwidth when compared with several example filters under consideration. In addition to this, hardware cost resulting from the proposed narrow-band FIR filter is analyzed by implementing it on Artix field programmable gate array (FPGA) chip and consequently power consumption of the resulting filter has been estimated using Xilinx Power Estimator (XPE)-2018.1. Finally, the designed narrow transition band FIR filter is used in filtered-orthogonal frequency division multiplexing (F-OFDM) based quadrature amplitude modulated (QAM) system and the resultant bit error rate (BER) performance has been studied.