Non-uniform Phase Research Articles

Composite pulse combinations for chirp excitation

Composite pulses are the efficient method for broadband excitation to get control of the limitations of high field NMR, such as resonance offset effects with constraints on rf power that leads to signal intensity distortion. Phase-modulated chirp pulses are used as ordered composite pulse sequences in this paper as CHORUS sequence in a high-field NMR spectrometer (BRUKER 750 MHz) for broadband excitation. The composite pulse sequence applies chirp pulses with the forward and the reverse sweep mechanisms. A single excitation pulse combines adiabatic and non-adiabatic rotation, explained as a three-phase rotation, which leaves the magnetizing vectors to a non-uniform phase dispersion as a function of the offset frequency. One adiabatic refocusing pulse of the double sweep rate after the excitation pulse cannot satisfactorily compensate for the phase dispersion. Hence, composite self-refocussing CHORUS excitation pulse, with forward, reverse, and their combinations are used to remove the non-uniform phase dispersion generated due to offset resonance frequency. Four such combinations of composite pulses are produced with analytical explanation in this paper. MATLAB simulation results and experimental verification on the BRUKER 750 MHz NMR spectrometer of the composite pulses are also presented in this paper.

Modeling Deformation and Fracture of Boron-Based Ceramics with Nonuniform Grain and Phase Boundaries and Thermal-Residual Stress

A phase field framework of elasticity, inelasticity, and fracture mechanics is invoked to study the behavior of ceramic materials. Mechanisms addressed by phase field theory include deformation twinning, dislocation slip, amorphization, and anisotropic cleavage fracture. Failure along grain and phase boundaries is resolved explicitly, whereWeibull statistics are used to characterize the surface energies of such boundaries. Residual stress incurred by mismatching coefficients of thermal expansion among phases is included. Polycrystalline materials of interest are the ultra-hard ceramics boron carbide (B4C) and boron carbide-titanium diboride (B4C-TiB2), the latter a dual-phase composite. Recent advancements in processing technology enable the production of these materials via spark-plasma sintering (SPS) at nearly full theoretical density. Numerical simulations invoking biaxial loading (e.g., pure shear) demonstrate how properties and mechanisms at the scale of the microstructure influence overall strength and ductility. In agreement with experimental inferences, simulations show that plasticity is more prevalent in the TiB2 phase of the composite and reduces the tendency for transgranular fracture. The composite demonstrates greater overall strength and ductility than monolithic B4C in both simulations and experiments. Toughening of the more brittle B4C phase from residual stress, in addition to crack mitigation from the stronger and more ductile TiB2 phase are deemed advantageous attributes of the composite.

Non-uniform phase change material strategy for directional mitigation of battery thermal runaway propagation

Thermal runaway propagation of the power battery pack is an essential factor affecting the safety of electric vehicles. The commonly adopted propagation inhibition methods mainly include adding heat insulation materials and enlarging battery spacing, which could cause problematic heat dissipation and lower the system energy density. Herein, an innovative battery thermal management system composed of non-uniform thermal conductivity phase change materials and assisted liquid cooling is proposed. Combining the phase change materials with high and low thermal conductivity balances heat transfer and heat insulation requirements. The cooling performance and the ability of thermal runaway propagation mitigation of the proposed schemes are numerically studied. The results show that the proposed strategy can meet the heat dissipation requirements under normal operation and control the thermal runaway in a safe range by transferring the heat generated from the battery thermal runaway in the set direction. The maximum battery temperature and the temperature difference are 38.1 °C and 2.1 °C, respectively, under 3C discharge. Under thermal runaway conditions, the strategy successful confines the thermal runaway propagation within the middle row. The maximum battery temperature in other rows can be controlled under the irreversible thermal runaway reaction temperature of 200 °C. Further study found that increased thermal conductivity benefits the battery heat dissipation and reduces the risk of thermal runaway. However, it propagates faster and broader once the thermal runaway is triggered. In comparison, the decrease of thermal conductivity is beneficial to the mitigation of propagation but may reduce the overall heat dissipation of the battery module. This study can provide a new way to solve the contradiction between battery temperature control and thermal runaway spread suppression.

Structural phase stability and homogeneity enhancement of electrochemically synthesized Mn2V2O7 by nanocarbon networks

Structural phase stability and homogeneity of the electrochemically synthesized Mn 2 V 2 O 7 (MVO) on nanocarbon network structures are investigated. The cup-stacked multi-walled carbon nanotubes (CNTs) and electrolytic graphene oxide (eGO) are the networks exploited in present work. It is shown that co-electrodeposition of carbonaceous network and V 2 O 5 .nH 2 O followed by electro-insertion of Mn 2 + cations results in the formation of intermixed β -Mn 2 V 2 O 7 nano-structures. The morphology and surface chemistry of the synthesized nano-structures is studied via high-resolution electron transmission and scanning X-ray photo-emission microscopies as well as Raman spectroscopy. The synthesized MVO on carbon fiber surface in the absence of the nanocarbon network shows a non-uniform phase formation and uneven coating distribution. The nanocarbon networks assisted MVO demonstrate uniform phase formation and distribution. The dominant MVO structural phase product present in these samples differs with different type of carbonaceous networks. The possible effect of the catalytic activity of the carbonaceous network as well as their hydrophilicity on the final structural and phase formation is discussed. The present study establishes new possibilities on catalytic assisted metal alloy oxide deposition for advanced applications.

Longitudinally Miniaturized H-Plane Horn Antenna With −30 dB Sidelobes Realized by Simple Blocks Redistributing the Aperture Field

A longitudinally miniaturized H-plane horn antenna with suppressed sidelobes by redistributing the field on the radiating aperture is proposed by loading a few rectangular blocks. The substantial longitudinal length reduction (around 50% of an optimal horn) will cause a nonuniform phase and nontapering magnitude distributions of the electric fields on the horn aperture, resulting in high sidelobes and decreased gain. Four pairs of rectangular blocks perturbing the fields are loaded near the radiating aperture, realizing a field redistribution for a tapered magnitude distribution and relatively uniform phase distribution on the aperture. Thus, the sidelobes are noticeably reduced to lower than −30 dB, and 10.6 dBi average gain in the frequency band of 10.5–15 GHz is achieved. A prototype of the proposed miniaturized H-plane horn antenna is manufactured and measured, and good agreements between the measured and simulated results are obtained. The proposed miniaturized H-plane horn has two advantages over other reported miniaturized horn antennas: 1) simple geometry resulting in easy fabrication and low cost and 2) −30 dB ultralow sidelobe level (SLL).

Bright Light Increases Alertness and Not Cortisol in Healthy Men: A Forced Desynchrony Study Under Dim and Bright Light (I).

Light-induced improvements in alertness are more prominent during nighttime than during the day, suggesting that alerting effects of light may depend on internal clock time or wake duration. Relative contributions of both factors can be quantified using a forced desynchrony (FD) designs. FD designs have only been conducted under dim light conditions (<10 lux) since light above this amount can induce non-uniform phase progression of the circadian pacemaker (also called relative coordination). This complicates the mathematical separation of circadian clock phase from homeostatic sleep pressure effects. Here we investigate alerting effects of light in a novel 4 × 18 h FD protocol (5 h sleep, 13 h wake) under dim (6 lux) and bright light (1300 lux) conditions. Hourly saliva samples (melatonin and cortisol assessment) and 2-hourly test sessions were used to assess effects of bright light on subjective and objective alertness (electroencephalography and performance). Results reveal (1) stable free-running cortisol rhythms with uniform phase progression under both light conditions, suggesting that FD designs can be conducted under bright light conditions (1300 lux), (2) subjective alerting effects of light depend on elapsed time awake but not circadian clock phase, while (3) light consistently improves objective alertness independent of time awake or circadian clock phase. Reconstructing the daily time course by combining circadian clock phase and wake duration effects indicates that performance is improved during daytime, while subjective alertness remains unchanged. This suggests that high-intensity indoor lighting during the regular day might be beneficial for mental performance, even though this may not be perceived as such.

DNN-assisted phase distance tuned PSK modulation for PAM4-to-QPSK format conversion gateway node.

This paper proposes an optical gateway that converts pulse amplitude modulation (PAM) format to phase shift keying (PSK) modulation format, enabling flexible intensity-to-phase mapping without relying on optical-electrical-optical data conversion at heterogenous network connections. A proof-of-principle experiment shows that optically converted PSK signals from regular PAM signals will induce non-uniform irregular phase noise distortion. The proposed optical gateway is designed to provide an optimized phase distance for PSK signals such that an achievable information rate is maximized by a deep learning-based decision on the receiver side. The phase distance-tuned PSK signals offer performance improvement of about 4 dB gain at a target generalized mutual information by making use of a digital neural network recovery.

Evaluation of structure and mechanical properties of TiZrNi coatings under annealing

The effect of annealing temperature on the structure and mechanical properties of Ti41Zr39Ni20 coatings was examined. Coatings were deposited on stainless-steel substrates via magnetron sputtering and then annealed in a vacuum under temperatures from 200 to 850 °C. Evaluation of structure and mechanical properties under annealing was performed using cross-sectional transmission electron microscopy, X-ray diffraction analysis, and ultra-nano indentation. Further, mechanical durability was assessed by reciprocating sliding tests. The relationships between the mechanical properties and structural-phase characteristics of the coatings were established. Results suggested that the mechanical properties of the 2/1 approximant phase were better than those of the quasicrystal phase, probably due to the peculiarity of the atomic-crystal structure of the 2/1 approximant phase. In addition, the formation of layered structure caused by non-uniform phase transitions was observed for coatings annealed at 600 °C. The nanocrystalline structure of the top layer and high concentration of the 2/1 approximant phase resulted in the highest values of hardness (25 GPa) and hardness/elasticity ratio (0.14).

Microstructural evolution during multiple scans in laser polishing of Ti6Al4V

Consecutive thermal cycles during laser polishing lead the complex microstructural changes. It is more difficult for modeling microstructural evolution in multiple thermal cycles compared to the single thermal cycle of heat treatment. In the present work, a thermo-microstructural model is established to investigate the temperature history and microstructural evolution during multiple scans in laser polishing of Ti6Al4V (TC4). The temperature history of the present model is validated the temperature data recorded by the thermal camera. The phase transformation involved α phase and β phase, martensitic transformation and decomposition, as well as the reservation of β phase is considered in the microstructural model. The numerical results show that the non-uniform phase distribution is attributed to the reservation of β phase and the multiple thermal cycles.

Anti-aliasing phase reconstruction via a non-uniform phase-shifting technique.

The conventional phase-shifting techniques commonly suffer from frequency aliasing because of their number of phase shifts below the critical sampling rate. As a result, fringe harmonics induce ripple-like artifacts in their reconstructed phase maps. For solving this issue, this paper presents an anti-aliasing phase-measuring technique. Theoretical analysis shows that, with phase-shifting, the harmonics aliased with the fundamental frequency component of a fringe signal depend on the greatest common divisor (GCD) of the used phase shifts. This fact implies a possibility of removing such aliasing effects by selecting non-uniform phase shifts that together with 2π have no common divisors. However, even if we do so, it remains challenging to separate harmonics from the fundamental fringe signals, because the systems of equations available from the captured fringe patterns are generally under-determined, especially when the number of phase shifts is very few. To overcome this difficulty, we practically presume that all the points over the fringe patterns have an identical characteristic of harmonics. Under this constraint, using an alternate iterative least-squares fitting procedure allows us to estimate the fringe phases and the harmonic coefficients accurately. Simulation and experimental results demonstrate that this proposed method enables separating high order harmonics from as few as 4 fringe patterns having non-uniform phase shifts, thus significantly suppressing the ripple-like phase errors caused by the frequency aliasing.

Alternate Iterative Least-Squares Algorithm Based on Nonuniform Phase Shifting for Suppressing Nonlinearity Errors in Fringe Projection Profilometry

In fringe projection technique, nonlinearities of used devices are recognized as major factors inducing phase errors, especially when the used camera and projector simultaneously have nonlinear features. In this case, ripple artifacts appear to be unevenly distributed over the reconstructed surface depending on the local reflectivity. For suppressing these errors, this paper suggests a phase-measuring technique which is characterized by two critical steps including anti-aliasing phase-shifting and iterative least-squares phase estimation. Anti-aliasing phase-shifting requires the selected phase shifts to be nonuniform and to have no common divisors. It provides a possibility of accurately recovering phases from few to four fringe patterns and eliminating influence of high order harmonics on the measurement results. By expanding the fringe signals from projector into harmonics and modeling the camera response as a polynomial, we derive a least-squares algorithm based on alternate iterations to calculate the fringe phase map and the related nonlinearity coefficients simultaneously. Through practical experiments, it has been demonstrated that this technique allows us to decrease artifacts caused by the simultaneous nonlinearities of the camera and the projector, thus improving measurement accuracy significantly.

Mechanism of chirp excitation

In design of a chirp inversion pulse, we keep the sweep rate a≪ω12, where ω1 is the amplitude of the pulse. This is the adiabaticity condition for the inversion to work. We can convert a chirp inversion pulse to an excitation pulse by keeping the chirp rate high, with a>ω12. To be precise a=2.8ω12. The analysis of such a pulse breaks the evolution into three phases. The first and third phase are adiabatic phases while the second phase is non-adiabatic. Starting from north pole such a pulse brings the magnetization to equator, however there is a nonuniform phase which depends on the resonance offsets. We show how by following this pulse with a chirp inversion pulse at twice the sweep rate of excitation pulse, we can refocus this uniform phase. We find there is still some phase dispersion. This can be further eliminated by bringing in a second inversion pulse. The combination of these three chirp pulses allows us to excite arbitrary large bandwidth without increasing the peak amplitude of the pulse. Refocusing properties of pair of chirp has been studied before but our description is very different.

Phase Statistics of Light/Photonic Wave Reflected from One-Dimensional Optical Disordered Media and Its Effects on Light Transport Properties

Light wave reflection intensity from optical disordered media is associated with its phase, and the phase statistics influence the reflection statistics. A detailed numerical study is reported for the statistics of the reflection coefficient |R(L)|2 and its associated phase θ for plane electromagnetic waves reflected from one dimensional Gaussian white-noise optical disordered media, ranging from weak to strong disordered regimes. The full Fokker–Planck (FP) equation for the joint probability distribution in the |R(L)|2−(θ) space is simulated numerically for varying length and disorder strength of the sample; and the statistical optical transport properties are calculated. Results show the parameter regimes of the validation of the random phase approximations (RPA) or uniform phase distribution, within the Born approximation, as well as the contribution of the phase statistics to the different reflections, averaging from nonuniform phase distribution. This constitutes a complete solution for the reflection phase statistics and its effect on light transport properties in a 1D Gaussian white-noise disordered optical potential.

First-order dissipative phase transition in an exciton-polariton condensate

We investigate the phase diagram of a two-dimensional driven-dissipative system of polaritons coupled to the excitonic reservoir. We find that two critical points exists. The first corresponds to the quasi-condensation and the second to a first-order phase transition from the non-uniform state with spatially modulated density to a uniform state. The latter is related to the modulational instability of a homogeneous state due to the repulsive interactions with the non-condensed reservoir. The first-order character of the transition is evidenced by a discontinuity in the density and the correlation length as well as the phase coexistence and metastability. Moreover, we show that a signature of a Berezinskii-Kosterlitz-Thouless-like transition can be observed in the non-uniform phase.

A Modified ABC-PTS with Non-Uniform Phase Factor for OFDM Signal

A Modified ABC-PTS with Non-Uniform Phase Factor for OFDM Signal

Macroporous Al2O3 with three-dimensionally interconnected structure: Catalytic performance of hydrodemetallization for residue oil

Three-dimensionally interconnected macroporous (3DM) Al2O3 was prepared by phase separation. Macropore size of the obtained Al2O3 is 250 nm with a bimodal pore distribution (at about 21 and 250 nm, respectively) and the BET specific surface area of 174 m2/g, as well as the crushing strength of 16.5 N/mm. Ni and Mo on the 3DM catalyst are uniformly dispersed on the surface of the support. The active phases of sulfurized catalyst possess length of 3–10 nm and stacking layers of 1–7. The stacking distribution of active phase more than 4 layers is about 40%, forming a non-uniform active phase structure. Compared with the industrial catalysts, the hydrodemetallization (HDM) rate, hydrodesulfurization (HDS) rate and hydrodecarbonization (HDCCR) rate of the 3DM catalyst increased by 6.2%, 6.0% and 6.8%, respectively. The pore structure, surface properties, active phase structure and their synergistic effect may be the main reasons for the excellent catalytic performance of the 3DM catalyst.

Intraparticle Model for Non-Uniform Active Phase Distribution Catalysts in a Batch Reactor

The study and the understanding of the importance of the morphological properties of heterogeneous catalysts can pave the way for important improvements in the performance of catalytic systems. Non-uniform active phase distribution catalysts are normally adopted for consecutive reactions to improve the selectivity to the desired intermediate product. Attributes on which minor attention is paid, such as the distribution and thickness of the active phase, can be decisive in the final rationale of the catalyst synthesis strategy. Starting from a previous work, where a single non-uniform active phase model for catalyst particles was developed, a key step to control the entire system is to include the bulk-phase equations and related transport phenomena. For this purpose, this work proposes a modeling approach of a biphasic reactive system in a batch reactor in the presence of three different kinds of catalytic particles (egg shell, egg white, and egg yolk) whose distinction lies in the localization of the active zone. The reactive network consists of a couple of reactions in series, which take place exclusively on the solid surface, and the intermediate component is the main product of interest. To reveal the influence related to the type of catalyst, an extensive parametric study was conducted, varying several structural coefficients to highlight the changes in the intraparticle and bulk concentration profiles of the different chemical species. The main results can be considered of wide interest for the chemical reaction engineering community, as it was demonstrated that mass and heat transfer limitations affect the catalyst performance. For the chosen system, the egg shell catalyst normally led to better catalytic performances.

Ionization of carbon at 10-100 times the diamond density and in the 10^{6}K temperature range.

The behavior of partially ionized hot compressed matter is critical to the study of planetary interiors as well as nuclear fusion studies. A recent quantum study of carbon in the 10-70 Gbar range and at a temperature of 100eV used N-atom density functional theory (DFT) with N∼32-64 and molecular dynamics (MD). This involves band-structure-type electronic calculations and averaging over many MD-generated ion configurations. The calculated average number of free electrons per ion, viz., Z[over ¯], was systematically higher than from a standard average-atom quantum calculation. To clarify this offset, we examine the effect of the self-interaction error in such estimates and the possibility of carbon being in a granular plasma state containing Coulomb crystals with a magic number. The electrical conductivity, pressure, and compressibility of the carbon system are examined. The very low conductivity and the high-Z[over ¯] results of DFT MD point to the existence of carbon in a complex, nonuniform, low-conducting dispersed phase, possibly containing magic-number Coulomb crystals. The neutral pseudoatom estimate of Z[over ¯], conductivity, compressibility, and pressure reported here pertain to the uniform liquid.

Energy storage performance of Na0.5Bi0.5TiO3 based lead-free ferroelectric ceramics prepared via non-uniform phase structure modification and rolling process

With the rapid growth of electronic devices towards to miniaturization and integration, the Pb-free ceramic materials with excellent recoverable energy storage density and efficiency are extremely required for the real application of pulse power capacitors. Moreover, it is also a huge challenge to sustain excellent energy storage performance in a dynamic temperature. The paper proposed a design strategy for building the co-existence of polymorphic PNRs through phase structure control. Based on the strategy, (1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xBiMg2/3Nb1/3O3 ((BNT-BT)-xBMN) solid-solution was engineered and synthesized to achieve co-existence of tetragonal and rhombohedral phase PNRs in the perovskite structure. The pinch phenomenon of the P-E loops is linked with the phase transition caused by the electrical field. High polarization with limited hysteresis has been achieved, taking advantage of ample hybridization between O2– 2p and Bi3+ 6p orbitals for polarization and increased structural disorder caused by composition modification. With the further enhancement of the electrical breakdown strength by the rolling process, an ultra-high energy density of 6.3 J/cm3, an improved energy efficiency of 79.6% and an excellent temperature stability (Wrec > 5.03 J/cm3, η > 82%, and a small variation of Wrec (less than 10%) in the temperature range of 30 to 170 °C) were achieved. The current work shows that this strategy is very important and successful in the design of high-performance Pb-free dielectric capacitors for real applications in the future.

Gain and AR Improvements of the Wideband Circularly Polarized Fabry-Perot Resonator Antenna

A method to improve the performance of a wideband circularly polarized (CP) Fabry–Perot resonator antenna (FPRA) is presented in this communication. First, a wideband CP FPRA composed of a partially reflective surface (PRS) with a positive reflection phase gradient and a wideband CP patch antenna is proposed. Then, a transmission metasurface (MS) with a high transmission magnitude and tunable transmission phase in a broadband range is proposed to correct the electric field phase above the antenna. This MS has the ability to independently tune the transmission phases of two orthogonally polarized waves. On the one hand, the nonuniform phase distribution on the aperture field of the antenna can be transmitted to be nearly uniform, so the gain of the antenna will be enhanced. On the other hand, the transmission phases of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula> -polarized waves are corrected to maintain a 90° phase difference at every position, which leads to a wider axial ratio (AR) bandwidth. Therefore, after the phase correction of the MS, the gain and AR performances of the antenna are both improved significantly. The measured results suggest that the overlap of the 10 dB return loss bandwidth, 3 dB gain bandwidth, and 3 dB AR bandwidth of the antenna is 9–11.1 GHz (21%). The peak gain of 18.3 dBic is achieved at 10.2 GHz. The results indicate that the proposed MS can achieve excellent performance improvement of the CP FPRA.