Narrow Phase Research Articles

Breathing Effect via Solvent Inclusions on the Linker Rotational Dynamics of Functionalized MIL-53.

The breathing effects of functionalized MIL-53-X (X=H, CH3 , NH2 , OH, and NO2 ) induced by the inclusions of water, methanol, acetone, and N,N-dimethylformamide solvents were comprehensively investigated by solid-state NMR spectroscopy. 2D homo-nuclear correlation NMR provided direct experimental evidence for the host-guest interaction between the guest solvents and the MOF frameworks. The variations of the 1 H and 13 C NMR chemical shifts in functionalized MIL-53 from the narrow pore phase transitions to large pore forms due to solvent inclusions were clearly identified. The influence of functionalized linkers and their host-guest interactions with the confined solvents on the rotational dynamics of the linkers was examined by separated-local-field MAS NMR experiments in conjunction with DFT theoretical calculations. It is found that the linker rotational dynamics of functionalized MIL-53 in narrow pore form is closely related to the computational rotational energy barrier. The BDC-NO2 linker of activated MIL-53-NO2 undergoes relatively faster rotation, whereas the BDC-NH2 and BDC-OH linkers of activated MIL-53-NH2 and MIL-53-OH exhibit relatively slower rotation. The host-guest interactions between confined solvents and MIL-53-NO2 , MIL-53-CH3 would significantly induce an increase of the order parameters of unsubstituted carbon and reduce the rotational frequency of linkers. This study provides a spectroscopic approach for the investigation of linker rotation in functionalized MOFs at natural abundance with solvents inclusions.

Performance analysis of packed bed latent heat storage system for high-temperature thermal energy storage using pellets composed of micro-encapsulated phase change material

High temperature latent heat storage has gained increasing attention owing to its potential in the integration of renewable energy sources. This study is a novel experimental investigation on the heat storage performance of a horizontal packed bed containing composites comprising Al-Si-based microencapsulated phase change material in a high-temperature air heating system. The pellet type composites with 3 mm is tested here in a 1L scale packed bed heat exchanger at airflow rates between 75 and 150 L min−1. The composite exhibited a narrow phase change temperature range and high heat storage/release characteristics. As the airflow increased, the phase change time of the composite decreased, and the heat exchanging rate increased. The heat exchange efficiency during charging and discharging ranged from 71.0 % to 98.3 % and 69.0 %–90.2 %, respectively. In the discharging mode, although supercooling which comes from the microencapsulated phase change material, was observed, this did not noticeable effect on the heat transfer.

Inkjet-Printed Full-Color Matrix Quasi-Two-Dimensional Perovskite Light-Emitting Diodes.

Full-color matrix devices based on perovskite light-emitting diodes (PeLEDs) formed via inkjet printing are increasingly attractive due to their tunable emission, high color purity, and low cost. A key challenge for realizing PeLED matrix devices is achieving high-quality perovskite films with a favorable emission structure via inkjet printing techniques. In this work, a narrow phase distribution, high-quality quasi-two-dimensional (quasi-2D) perovskite film without a "coffee ring" was obtained via the introduction of a phenylbutylammonium cation into the perovskite and the use of a vacuum-assisted quick-drying process. Relatively efficient emissions of red, green, and blue (RGB) uniform quasi-2D perovskite films with high photoluminescence quantum yields were cast by the inkjet printing technique. The RGB monochrome perovskite matrix devices with 120 pixel-per-inch resolution exhibited electroluminescence, with maximum external quantum efficiencies of 3.5, 3.4, and 1.0% (for red, green, and blue light emissions, respectively). Furthermore, a full-color perovskite matrix device with a color gamut of 102% (NTSC 1931) was realized. To the best of our knowledge, this is the first report of a full-color perovskite matrix device formed by inkjet printing.

Intersection-free rigid body dynamics

We introduce the first implicit time-stepping algorithm for rigid body dynamics, with contact and friction, that guarantees intersection-free configurations at every time step. Our algorithm explicitly models the curved trajectories traced by rigid bodies in both collision detection and response. For collision detection, we propose a conservative narrow phase collision detection algorithm for curved trajectories, which reduces the problem to a sequence of linear CCD queries with minimal separation. For time integration and contact response, we extend the recently proposed incremental potential contact framework to reduced coordinates and rigid body dynamics. We introduce a benchmark for rigid body simulation and show that our approach, while less efficient than alternatives, can robustly handle a wide array of complex scenes, which cannot be simulated with competing methods, without requiring per-scene parameter tuning.

Insights in the Thermal Volume Transition of Poly(2‐oxazoline) Hydrogels

AbstractPolymers with a lower or an upper critical solution temperature (LCST or UCST) can precipitate in a very narrow temperature range. Cross‐linking of such polymers and adding them to suited solvent results in smart gels that are capable of greatly changing their dimensions with changing temperature. This transition occurs very often in a broad temperature range, which limits the applicability of smart materials. To shed some light into the design of thermo‐responsive hydrogels with a narrow phase transition, poly(2‐ethyl‐2‐oxazoline) (PEtOx), poly(2‐isopropyl‐2‐oxazoline), and statistical copolymers of 2‐butyl‐2‐oxazoline and 2‐ethyl‐2‐oxazoline, respectively, are synthesized and the concentration‐dependent cloud point temperatures (Tcp) of the free polymers in aqueous media are determined in relation to the thermo‐responsive swelling behavior of the respective hydrogels. A narrow thermal transition of the hydrogels can only be achieved when the Tcp of the free polymers in water is independent on the concentration. Aqueous salt solutions can render even PEtOx into a concentration independent LCST polymer. However, this salt effect does not work for hydrogels.

Progress and perspective in Dion-Jacobson phase 2D layered perovskite optoelectronic applications

2D organic-inorganic halide perovskites have recently become the “next big thing” as promising candidates in optoelectronics. They possess higher moisture stability and lower ion migration compared to 3D perovskites due to the incorporation of bulky organic spacers. Compared to 2D Ruddlesden-Popper (RP) phase with two monoammoniums, 2D Dion-Jacobson (DJ) phase containing one diammonium has achieved a tighter connection between inorganic sheets due to formation of hydrogen bonds, resulting in higher crystal stability and more favorable charge transfer. RP phase solar cell has increased from 4.73% to 18.24% within six years, whereas DJ phase device shows a steep efficiency rise from 7.32% to 17.9% within only one year. Herein, this review provides in-depth understandings on optical property, orientation and charge transport, and energy band alignment of DJ phase perovskites, and raise perspectives that how they are affected by n value and diammoniums characteristics. The recent advances in solar cells, light-emitting diodes, and photodetectors have also been summarized. Finally, we discuss the remaining challenges of boosting device efficiency and try to answer the key scientific question that how to narrow phase distribution and engineer vertical orientation achieving the favorable energy alignment.

Effects of different electrical stimulation currents and phase durations on submaximal and maximum torque, efficiency, and discomfort: a randomized crossover trial

BackgroundNeuromuscular electrical stimulation (NMES) is an important therapeutic tool for rehabilitation. However, best stimulation parameters remain to be determined. ObjectiveTo determine the influence of different electrical stimulation currents and phase durations on torque, efficiency, and discomfort. MethodsUsing a cross-over design, kHz frequency alternating currents (KFAC) and pulsed currents (PC) with narrow (200 µs) or wide (500 µs) phase durations were randomly applied on knee extensor muscles of healthy participants with a minimum of seven days between sessions. The NMES-evoked torque, NMES-efficiency, and discomfort (visual 0−10 cm analogue scale) were measured for each stimulation intensity increments (10 mA). Statistics were conducted using a three-way analysis of variances (phase duration x current x intensity), followed by Tukey post-hoc. ResultsTwenty-four males (age 22.3 ± 3.5years) were included. No effect of NMES current was observed for torque, efficiency, and discomfort. For wide phase durations (500 µs), torque significantly increased for all stimulation intensities. For narrow phase durations (200 µs) evoked torque significantly increased only after 40% of maximal stimulation intensity. Phase durations of 500 µs produced greater torque than 200 µs. Discomfort was greater with 500 µs when compared to 200 µs. Submaximal relative torque, for example 40% of maximum voluntary contraction (MVC), was obtained with ∼ 60% and ∼ 80% of the maximal current intensity for 500 µs and 200 µs, respectively. ConclusionKFAC and PC current applied with the same phase duration induced similar relative submaximal and maximum evoked-torque, efficiency, and perceived discomfort. However, currents with 500 µs induced higher evoked-torque, current efficiency, and perceived discomfort.

Molecular Sieving Properties of Nanoporous Mixed-Linker ZIF-62: Associated Structural Changes upon Gas Adsorption Application

The evaluation of the flexibility in zeolitic imidazolate frameworks (ZIFs) has been very useful to understand their performance in gas adsorption and separation applications. Here, we have evaluated the adsorption properties of a nanoporous mixed-linker ZIF-62 using a combination of gas adsorption measurements, grand canonical Monte Carlo simulations, and synchrotron X-ray powder diffraction under operando conditions. While adsorption studies in nanoporous ZIF-62 at 77 K and atmospheric pressure predict a large O2/N2 separation ability, computational studies anticipate that the observed differences must be attributed to kinetic restrictions of N2 to access the internal porosity at cryogenic temperatures. Interestingly, upon a small increase in the adsorption temperature (90 K vs 77 K), both N2 and O2 are able to access the inner porous structure through the promotion of a phase transition (ca. 3.8% volume expansion) upon gas adsorption. This narrow phase (np) to expanded phase (ep) structural transition in ZIF-62 is completely suppressed above 150 K. Based on the excellent molecular sieve properties of nanoporous ZIF-62 for O2/N2 at cryogenic temperatures, we extended our study to the adsorption of linear and branched hydrocarbons. This study predicts the preferential adsorption of alkanes over alkenes in ZIF-62 for small hydrocarbons (C2), while in the case of C3 hydrocarbons and above, the adsorption process is mainly defined by kinetic restrictions.

Quasi-2D bromide perovskite nanocrystals with narrow phase distribution prepared using ternary organic cations for sky-blue light-emitting diodes

Quasi-2D perovskite semiconductors can be created by introducing organic interlayer cations into 3D perovskites and possess large binding energy, superior stability, high luminance efficiency, and tunable bandgap, holding promising applications in blue-light emitting devices. Compared with mixed halide perovskites, quasi-2D bromide perovskites emit blue light with high color stability. However, multiple-phases usually co-exist in quasi-2D bromide perovskites, resulting in low color purity. In this work, three ammonium bromides, namely, 3-(trifluoromethyl)phenyltrimethylammonium bromide (F-PTABr), benzyltributylammonium bromide (BTBABr), and phenethylammonium bromide (PEABr), are employed to fabricate quasi-2D perovskite films with narrow phase distribution. PEA serves as the scaffold to stabilize the quasi-2D PEA2Csn-1PbnBr3n+1 perovskite structure and provides enough space to allow the F-PTA cation entering the interlayer, which further triggers the entrance of a larger BTBA cation into the interlayer. The large F-PTA and BTBA cations reduce the crystal size of the perovskite and narrow the phase distribution to n = 2. As a result, the photoluminescence spectrum of the PEA0.9F-PTA0.05BTBA0.05-based perovskite film becomes unimodal and blue-shifts from 498 to 484 nm compared with the film using the PEA1.0 cation. A sky-blue light-emitting diode with an external quantum efficiency of 0.6% is achieved using the PEA0.9F-PTA0.05BTBA0.05-based perovskite as the emitter. We, therefore, demonstrate a strategy to prepare phase narrow quasi-2D perovskites with improved color purity by introducing ternary organic cations into the quasi-2D perovskites and envisage that promising device performance can be achieved with a further dedicated structure design of the ammonium cations.

Synthesis of heterovalently substituted slab perovskites Sr 2–xLnxBIV1–xBxIIIO4(BIV = Sn, Ti, BIII = Sc, In)

The possibility of the heterovalent substitution of A- and B-positions atoms in a single-layer slab perovskitelike structure of strontium titanate and stannate Sr2BIVO4 (BIV = Ti, Sn) by type Sr2–xLnxBIV1–xBxIIIO4 (Ln = La – Tb, BIV = Ti, Sn, BIII = Sc, In) has been established by X-ray powder diffraction methods. The boundaries of the heterovalent substitution of A- and B-positions atoms and the crystallographic parameters of the synthesized Sr2–xLnxBIV1–xBxIIIO4 phases with a single-layer structure are determined. The continuous phase area formation with a single-layer structure has been observed in 10 systems: Sr2–xLnxTi1–xScxO4 (Ln = La, Pr, Nd, Sm, Eu), Sr2–xLnxTi1–xInxO4 (Ln = La, Pr), Sr2–xLaxSn1–xScxO4, Sr2–xLnxSn1–xInxO4 (Ln = La, Pr). Increasing the degree of heterovalent substitution of atoms in these systems leads to a reduction of the sym metry of the crystal lattice of phases from the tetragonal (space group I4/mmm) to the interconnected rhombic one. In the rest of the studied Sr2–xLnxBIV1–xBxIIIO4 systems, the existence of a narrow (x value significantly less than 1) phase region with a single-layer structure based on Sr3BIVO7 is observed. The character of the phase relations in the Sr2–xLnxBIV1–xBxIIIO4 systems (Ln = La – Tb, BIII = Sc, In) (BIV = Sn, Ti) and the linear type of concentration dependences of the parameters of the reduced tetragonal unit cells of Sr2–xLnxBIV1–xBxIIIO4 phases with a single-layer structure indicate that, by their nature, these phases are series of solid solutions in the pseudobinary systems Sr2BIVO4 – SrLnBIIIO4 (BIV = Ti, Sn, BIII = Sc, In). The obtained data can be used to regulate the functional properties of titanates and stannates Sr2BIVO4 and materials based on them, as well as to solve the problem of a purposeful search for new compounds of the type An+1BnO3n+1 with a slab perovskite-like structure.

Active illumination uniformity with narrow spectrum laser based on ladderlike phase modulation

<sec>Active illumination is a crucial technology for active imaging, active tracking and aiming system. But the atmosphere turbulence distributed over the entire path causes the intensity to fluctuate, which reduces the illumination uniformity seriously. Therefore, it is desirable to find ways to reduce the intensity fluctuation and improve the uniformity of active illumination. It has been revealed that one can improve illumination uniformity by using multi-beam laser illuminator. Another effective approach is partially coherent beam illumination.</sec><sec>In this paper, a novel method is suggested to improve the illumination uniformity. Phase disturbance is induced by a ladder-like phase modulator (LPM) and the transmitting field of narrow spectrum laser is confused, and thus the atmosphere turbulence will be compensated and the illumination uniformity will be improved. The physical models of narrow spectrum laser phase modulation and atmosphere propagation are deduced, and the expression of the facular distribution is obtained. The active-illumination experimental setup with a laser propagation distance of 1.8 km through horizontal atmosphere is established. Based on the facular distribution of illumination laser at 1.8 km, the uniformity and stabilization are achieved. The experimental results indicate that the illumination uniformity and stabilization are both improved. The spatial and central time scintillation indexes are improved from 0.73 to 0.33 and from 0.38 to 0.14, respectively.</sec>

Current harmonic suppression for permanent magnet synchronous motor based on phase compensation resonant controller

Permanent magnet synchronous motor always suffers from air gap field distortion and inverter nonlinearity, which lead to the harmonic components in motor currents. A resonant controller is a remarkable control method to eliminate periodic disturbance, whereas the conventional resonant controller is limited by narrow bandwidth and phase lag. This article presents a novel resonant controller with a precise phase compensation method for a permanent magnet synchronous motor to suppress the current harmonics. Based on the analysis of the current harmonic characteristics, the proposed resonant controller for rejecting a set of selected current harmonic components is plugged in the current loop, and it is parallel to the traditional proportional–integral controller. Furthermore, the stability analysis of the proposed resonant controller is investigated, and the parameters are tuned to get a satisfactory performance. Compared with the conventional resonant controller, the proposed resonant controller can achieve good steady-state performance, dynamic performance, and frequency adaptivity performance, simultaneously. Finally, the experimental results demonstrate the effectiveness of the proposed suppression scheme.

Controlling Metal-Insulator Transitions in Vanadium Oxide Thin Films by Modifying Oxygen Stoichiometry.

Vanadium oxides are strongly correlated materials which display metal-insulator transitions (MITs) as well as various structural and magnetic properties that depend heavily on oxygen stoichiometry. Therefore, it is crucial to precisely control oxygen stoichiometry in these materials, especially in thin films. This work demonstrates a high-vacuum gas evolution technique which allows for the modification of oxygen concentrations in VOX thin films by carefully tuning the thermodynamic conditions. We were able to control the evolution between VO2, V3O5, and V2O3 phases on sapphire substrates, overcoming the narrow phase stability of adjacent Magnéli phases. A variety of annealing routes were found to achieve the desired phases and eventually control the MIT. The pronounced MIT of the transformed films along with the detailed structural investigations based on X-ray diffraction measurements and X-ray photoelectron spectroscopy show that optimal stoichiometry is obtained and stabilized. Using this technique, we find that the thin-film V-O phase diagram differs from that of the bulk material because of strain and finite size effects. Our study demonstrates new pathways to strategically tune the oxygen stoichiometry in complex oxides and provides a road map for understanding the phase stability of VOX thin films.

Two-phase real-time rendering method for realistic water refraction

BackgroundRealistic rendering has been an important goal of several interactive applications, which requires an efficient virtual simulation of many special effects that are common in the real world. However, refraction is often ignored in these applications. Rendering the refraction effect is extremely complicated and time-consuming. MethodsIn this study, a simple, efficient, and fast rendering technique of water refraction effects is proposed. This technique comprises a broad and narrow phase. In the broad phase, the water surface is considered flat. The vertices of underwater meshes are transformed based on Snell's Law. In the narrow phase, the effects of waves on the water surface are examined. Every pixel on the water surface mesh is collected by a screen-space method with an extra rendering pass. The broad phase redirects most pixels that need to be recalculated in the narrow phase to the pixels in the rendering buffer. ResultsWe analyzed the performances of three different conventional methods and ours in rendering refraction effects for the same scenes. The proposed method obtains higher frame rate and physical accuracy comparing with other methods. It is used in several game scene, and realistic water refraction effects can be generated efficiently. ConclusionsThe two-phase water refraction method produces a tradeoff between efficiency and quality. It is easy to implementin modern game engines, and thus improve the quality of rendering scenes in video games or other real-time applications.

2D Perovskites: Coordination Engineering of Single‐Crystal Precursor for Phase Control in Ruddlesden–Popper Perovskite Solar Cells (Adv. Energy Mater. 16/2020)

In article number 1904050, Chaochao Qin, Alex K.-Y. Jen, Kai Yao and co-workers describe a generic guideline for fine tuning colloidal properties of 2D perovskites via coordination engineering of the single-crystal precursor solution. In nonpolar co-solvent media, the derived colloidal templates prefer to grow along the vertical direction with a narrow phase variation, elucidating the critical role of colloidal chemistry in low-dimensional perovskite solar cells.

Channel narrowing by inset floodplain formation of the lower Green River in the Canyonlands region, Utah

AbstractThe lower Green River episodically narrowed between the mid-1930s and present day through deposition of new floodplains within a wider channel that had been established and/or maintained during the early twentieth century pluvial period. Comparison of air photos spanning a 74-yr period (1940–2014) and covering a 61 km study area shows that the channel narrowed by 12% from 138 ± 3.4 m to 122 ± 2.1 m. Stratigraphic and sedimentologic analysis and tree ring dating of a floodplain trench corroborates the air photo analysis and suggests that the initial phase of floodplain formation began by the mid-1930s, approximately the same time that the flow regime decreased in total annual and peak annual flow. Tamarisk, a nonnative shrub, began to establish in the 1930s as well. Narrowing from the 1940s to the mid-1980s was insignificant, because floodplain formation was approximately matched by bank erosion. Air photo analysis demonstrates that the most significant episode of narrowing was underway by the late 1980s, and analysis of the trench shows that floodplain formation had begun in the mid-1980s during a multi-year period of low peak annual flow. Air photo analysis shows that mean channel width decreased by ∼7% between 1993 and 2009. A new phase of narrowing may have begun in 2003, based on evidence in the trench. Comparison of field surveys made in 1998 and 2015 in an 8.5 km reach near Fort Bottom suggests that narrowing continues and demonstrates that new floodplain formation has been a very small proportion of the total annual fine sediment flux of the Green River. Vertical accretion of new floodplains near Fort Bottom averaged 2.4 m between 1998 and 2015 but only accounted for ∼1.5% of the estimated fine sediment flux during that period. Flood control by Flaming Gorge Dam after 1962 significantly influenced flow regime, reducing the magnitude of the annual snowmelt flood and increasing the magnitude of base flows. Though narrowing was initiated by changes in flow regime, native and nonnative riparian vegetation promoted floodplain formation and channel narrowing especially through establishment on channel bars and incipient floodplains during years of small annual floods.

QPSK Demodulator Based on Wideband Acquisition System

The paper describes the design of the QPSK demodulator based satellite base station. The most important requirement of the design process is to have wide band acquisition range of 100 kHz under narrow Phase Lock Loop (PLL) bandwidth and low input Signal to Noise Ratio (SNR). The efficiency of the technique is verified with extensive simulations in MATLAB.

Coordination Engineering of Single‐Crystal Precursor for Phase Control in Ruddlesden–Popper Perovskite Solar Cells

Abstract2D Ruddlesden–Popper perovskites (RPPs) have recently drawn significant attention because of their structural variability that can be used to tailor optoelectronic properties and improve the stability of derived photovoltaic devices. However, charge separation and transport in 2D perovskite solar cells (PSCs) suffer from quantum well barriers formed during the processing of perovskites. It is extremely difficult to manage phase distributions in 2D perovskites made from the stoichiometric mixtures of precursor solutions. Herein, a generally applicable guideline is demonstrated for precisely controlling phase purity and arrangement in RPP films. By visually presenting the critical colloidal formation of the single‐crystal precursor solution, coordination engineering is conducted with a rationally selected cosolvent to tune the colloidal properties. In nonpolar cosolvent media, the derived colloidal template enables RPP crystals to preferentially grow along the vertically ordered alignment with a narrow phase variation around a target value, resulting in efficient charge transport and extraction. As a result, a record‐high power conversion efficiency (PCE) of 14.68% is demonstrated for a (TEA)2(MA)2Pb3I10 (n = 3) photovoltaic device with negligible hysteresis. Remarkably, superior stability is achieved with 93% retainment of the initial efficiency after 500 h of unencapsulated operation in ambient air conditions.

Magnetic flux density measurements from grain boundary phase in 0.1 at% Ga-doped Nd–Fe–B sintered magnet

The magnetism of a narrow (~1.6 nm) grain boundary phase produced in a 0.1 at% Ga-doped Nd–Fe–B sintered magnet was examined using electron holography. The magnetic flux density was determined to be 0.8 ± 0.1 T, which was smaller than that for a commercial magnet free from Ga doping (~1.0 T). The presence of a ferromagnetic grain boundary phase reasonably explained the functionality of the 0.1 at% Ga-doped system, such as the improvement in the squareness of the demagnetization curve. The observations provide useful information for deeper understanding of the coercivity mechanism in Ga-doped Nd–Fe–B sintered magnets.

Giant enhancement of the skyrmion stability in a chemically strained helimagnet

We employed small-angle neutron scattering to demonstrate that the magnetic skyrmion lattice can be realized in bulk chiral magnets as a thermodynamically stable state at temperatures much lower than the ordering temperature of the material. This is in the regime where temperature fluctuations become completely irrelevant to the formation of the topologically non-trivial magnetic texture. In this attempt we focused on the model helimagnet MnSi, in which the skyrmion lattice was previously well characterized and shown to exist only in a very narrow phase pocket close to the Curie temperature of 29.5~K. We revealed that large uniaxial distortions caused by the crystal-lattice strain in MnSi result in stabilization of the skyrmion lattice in magnetic fields applied perpendicular to the uniaxial strain at temperatures as low as 5~K. To study the bulk chiral magnet subjected to a large uniaxial stress, we have utilized $\mu$m-sized single-crystalline inclusions of MnSi naturally found inside single crystals of the nonmagnetic material Mn$_{11}$Si$_{19}$. The reciprocal-space imaging allowed us to unambiguously identify the stabilization of the skyrmion state over the competing conical spin spiral.