Asymmetric Phase Research Articles

Differences in visual quality with orientation of a rotationally asymmetric bifocal intraocular lens design

To evaluate visual and perceptual performance for different orientations of a rotationally asymmetric bifocal intraocular lens (IOL) (M-Plus) simulated optically using a simultaneous vision simulator. Instituto de Optica, Madrid, Spain. Prospective observational study. Perceptual quality and decimal high-contrast visual acuity (HCVA) was measured under cycloplegia for 8 orientations of the asymmetric bifocal IOL phase pattern at far, intermediate, and near distances simulated with a simultaneous vision simulator using face images and tumbling E targets. The preferred orientation at each distance was calculated as the centroid of the data for 8 orientations. The visual Strehl value was calculated using the subjects' ocular aberrations and multifocal pattern at each orientation. Optical predictions were obtained by implementing a differential visual Strehl values-based ideal observer model. The study comprised 20 subjects (aged 21 to 62years). Horizontal orientation (near segment at 0 or 180 degrees±45 [SD]) was preferred by 14 subjects and by 13 subjects at far and near distances, respectively; 8 subjects showed strong orientation preferences. The mean difference in preferred orientation between far and near was 27±22 degrees. No significant differences in HCVA were observed. Optical predictions correlated strongly and significantly with measurements (far r=0.71, near r=0.62; P<.0001). The mean difference between measurement and simulation in the preferred orientation was 28±29 degrees at far and 36±28 degrees at near. The perception varied for different orientations of an asymmetric bifocal IOL design tested using a simultaneous vision simulator. Optimum orientation was driven by interactions of the design with the eye's optical aberrations. None of the authors has a financial or proprietary interest in any material or method mentioned.

Ssnmr Studies of Li3V2(PO4)3/C Cathode Reactions: Structural Evolution, Dynamics and LVP-Carbon Interface

Monoclinic lithium vanadium phosphate Li3V2 (PO4)3(LVP) is a highly promising cathode material for lithium-ion batteries. In the past decades, extensive efforts have been made to improve the electrochemical performance of LVP by carbon coating and cation doping[1]. In-depth understanding of the local structures and charge-discharge mechanism of LVP can provide valuable information for the design of cation doping or surface modification. SSNMR has been demonstrated a powerful tool of local structure analysis and dynamics. However, due to sever line broadening and signal coalescence caused by the heating effect of carbon in the cathode composite, SSNMR study of LVP material was only limited to samples prepared by chemical delithiation[2], which cannot fully represent the real electrochemical process. We hereby present the first SSNMR study of LVP/C cathode reaction. The electrodes have been prepared in a binder free and carbon additive free fashion, in order to reduce the heating effect to a minimum during NMR spectra acquisition. A variety of SSNMR techniques have been combined to obtain structural information from different aspects. The structural changes of the polyhedron framework upon delithiation-lithiation were traced by 7Li and 31P NMR. The dynamic processes involving Li exchange and migration were monitored by variable temperature 7Li NMR and EIS technique. 13C-7Li REDOR NMR and HRTEM were performed to investigate Li-O-C connectivity and the short range structure at the LVP-carbon interface. The NMR results have elucidated the driving force of the asymmetric phase formation during charge-discharge within the voltage window of 4.3-4.8 volts and provided experimental evidence of direct chemical bonding between LVP and carbon coating. Our study helps the battery community to understand the (de)lithiation mechanism of LVP cathode, and more important, the role of carbon coating. [1]. Rui X, Yan Q, Skyllas-Kazacos M, et al. Li3V2(PO4)3 cathode materials for lithium-ion batteries: A review[J]. J. Power Sources , 2014, 258(21):19-38. [2]. Yin S C, Grondey H, Strobel P, et al. Charge ordering in lithium vanadium phosphates: electrode materials for lithium-ion batteries.[J]. J. Am. Chem. Soc. , 2003, 125(2):326-7.

Diffusion and Localization of Relative Strategy Scores in The Minority Game

We study the equilibrium distribution of relative strategy scores of agents in the asymmetric phase ($\alpha\equiv P/N\gtrsim 1$) of the basic Minority Game using sign-payoff, with $N$ agents holding two strategies over $P$ histories. We formulate a statistical model that makes use of the gauge freedom with respect to the ordering of an agent's strategies to quantify the correlation between the attendance and the distribution of strategies. The relative score $x\in\mathbb{Z}$ of the two strategies of an agent is described in terms of a one dimensional random walk with asymmetric jump probabilities, leading either to a static and asymmetric exponential distribution centered at $x=0$ for fickle agents or to diffusion with a positive or negative drift for frozen agents. In terms of scaled coordinates $x/\sqrt{N}$ and $t/N$ the distributions are uniquely given by $\alpha$ and in quantitative agreement with direct simulations of the game. As the model avoids the reformulation in terms of a constrained minimization problem it can be used for arbitrary payoff functions with little calculational effort and provides a transparent and simple formulation of the dynamics of the basic Minority Game in the asymmetric phase.

Asymmetric dynamic phase holographic grating in nematic liquid crystal**Project supported by the Science and Technology Programs of the Educational Committee of Heilongjiang Province, China (Grant No. 12541730) and the National Natural Science Foundation of China (Grant No. 61405057).

A new scheme for recording a dynamic phase grating with an asymmetric profile in C60-doped homeotropically aligned nematic liquid crystal (NLC) was presented. An oblique incidence beam was used to record the thin asymmetric dynamic phase holographic grating. The diffraction efficiency we achieved is more than 40%, exceeding the theoretical limit for symmetric profile gratings. Both facts can be explained by assuming that a grating with an asymmetric saw-tooth profile is formed in the NLC. Finally, physical mechanism and mathematical model for characterizing the asymmetric phase holographic grating were presented, based on the photo-refractive-like (PR-like) effect.

Analysis of a new five‐phase fault‐tolerant doubly salient brushless DC generator

The fault-tolerant ability of a multi-phase doubly salient electromagnetic generator (DSEG) makes it suitable for important applications. However, asymmetric phase windings are a drawback of the traditional five-phase DSEG. This study presents the design of a new five-phase brushless DSEG with symmetrical phases and a robust rotor. The proposed stator poles, rotor poles, and their pole arc criteria form a general design basis for the multiphase DSEG with minimum cogging torque. The proposed new winding configuration overcomes the phase asymmetry drawback of the traditional DSEG. An analysis of the characteristic of the no-load and the loading operation of the five-phase DSEG shows that the five-phase DSEG has fewer harmonics than the three-phase DSEG does. Additionally, the five-phase DSEG has high fault-tolerance ability because adjacent phases will take over the activity of the fault phase if there is an open-circuit fault. Simulated and experimental results of machine performance under the same working conditions offer verification of the design principles presented.

Pentanidium- and Bisguanidinium-Catalyzed Enantioselective Alkylations Using Silylamide as Brønsted Probase.

Most asymmetric phase transfer reactions are Brønsted base reactions, and the inorganic bases used greatly influenced the profile of the reaction. Alkoxide salts are able to activate substrates with high pKa values, but background reactions are often unavoidable. On the other hand, carbonate and phosphate salts are milder, but their low basicity limits the scope of their reactions. This presents a difficult situation whereby fragile substrates such as lactone will be hydrolyzed by a stronger base but will not be activated with a weaker one. Thus, a Brønsted probase strategy is devised, in which a strong base can be generated in situ from silylamide (probase) through the use of fluoride. In this approach, the strong base produced will be transient and not be in excess, thus reducing background and side reactions. We demonstrate this strategy using pentanidinium and bisguanidinium as catalysts; highly enantioselective phase transfer alkylation of several types of substrates including dihydrocoumarin (lactone) can be achieved. We found that the probase also acts as a silylation reagent, generating silyl enol ether or silyl ketene acetal, which are key intermediates in the reaction. We further propose that hypervalent silicates form ion-pairs with pentanidinium and bisguanidinium as intermediates in the reaction, and it is through these ion-pairs that the selective enantiofacial approach of the electrophile is determined.

Asymmetrical phase separation and gelation in binary mixtures of oppositely charged colloids.

Two types of colloidal particles, which are nearly the same in chemical composition but carry opposite surface charges, are mixed in water. Depending on the relative proportion of the oppositely charged particles, the process of aggregation leads to the formation of discrete clusters of various sizes in dilute dispersions, and to the development of particle gel networks in more concentrated systems. Due to the significant difference in the absolute values of surface charges (negative particle: -48 mV, positive particle: +24 mV), the phase separation and the gelation behaviors are asymmetric with respect to the mixing ratio. Mixtures with excess negative particles are more stable, while mixtures with excess positive particles are easily affected by phase separation. The hetero-aggregation triggered by the addition of microscopically large macro-ions is similar to what is often observed in a mono-component charged colloidal system, i.e., phase separation occurs through addition of small electrolyte ions. Within the concentration region investigated here, it is clear that the gel line is buried inside the phase separation region. Gelation occurs only when the number and size of the clusters are large and big enough to connect up into a space-spanning network. Our results indicate that, in this binary mixture of oppositely charged colloids, although the interaction between unlike species is attractive and that between like species is repulsive, the onset of gelation is in fact governed by the equilibrium phase separation, as in the case of purely attractive systems with short-range isotropic interaction.

Binary-tree encryption strategy for optical multiple-image encryption.

In traditional optical multiple-image encryption schemes, different images typically have almost the same encryption or decryption process. Provided that an attacker manages to correctly decrypt some image, the conventional attacks upon other images are much easier to be made. In this paper, a binary-tree encryption strategy for multiple images is proposed to resist the attacks in this case. The encryption schemes produced by this strategy can not only increase the security of multiple-image encryption, but also realize an authority management with high security among the users sharing a cipher image. For a simulation test, we devise a basic binary-tree encryption scheme, whose encryption nodes are based on an asymmetric double random phase encoding in the gyrator domain. The favorable simulation results about the tested scheme can testify to the feasibility of the strategy.

Dispersion-Managed Optical Links Combined with Asymmetrical Optical Phase Conjugation for Compensating for Distorted WDM Signals

The combination of dispersion management (DM) and midway optical phase conjugation (OPC) is one of the promising techniques for compensating for optical signal distortion due to group velocity dispersion and nonlinear fiber effects. However, in this combination technique, midway OPC restricts the flexible optical link configuration. Therefore, the possibility of implementing the flexible optical link configuration with non-midway OPC applied to complete inline DM links is investigated in this study. It is confirmed that although the compensation using non-midway OPC for the distorted WDM channels is less effective than that using midway OPC, when non-midway OPC is placed at positions closer to the transmitters, the deployment of precompensation (i.e., the sequence of DCF + SMF)–OPC–postcompensation (i.e., the sequence of SMF + DCF) is more advantageous for the compensation. On the other hand, inverse deployment with respect to OPC (i.e., postcompensation–OPC–precompensation) is more advantageous when non-midway OPC is placed at positions closer to the receivers.

Hypothetical biomolecular probe based on a genetic switch with tunable symmetry and stability.

BackgroundGenetic switches are ubiquitous in nature, frequently associated with the control of cellular functions and developmental programs. In the realm of synthetic biology, it is of great interest to engineer genetic circuits that can change their mode of operation from monostable to bistable, or even to multistable, based on the experimental fine-tuning of readily accessible parameters. In order to successfully design robust, bistable synthetic circuits to be used as biomolecular probes, or understand modes of operation of such naturally occurring circuits, we must identify parameters that are key in determining their characteristics.ResultsHere, we analyze the bistability properties of a general, asymmetric genetic toggle switch based on a chemical-reaction kinetic description. By making appropriate approximations, we are able to reduce the system to two coupled differential equations. Their deterministic stability analysis and stochastic numerical simulations are in excellent agreement. Drawing upon this general framework, we develop a model of an experimentally realized asymmetric bistable genetic switch based on the LacI and TetR repressors. By varying the concentrations of two synthetic inducers, doxycycline and isopropyl β-D-1-thiogalactopyranoside, we predict that it will be possible to repeatedly fine-tune the mode of operation of this genetic switch from monostable to bistable, as well as the switching rates over many orders of magnitude, in an experimental setting. Furthermore, we find that the shape and size of the bistability region is closely connected with plasmid copy number.ConclusionsBased on our numerical calculations of the LacI-TetR asymmetric bistable switch phase diagram, we propose a generic work-flow for developing and applying biomolecular probes: Their initial state of operation should be specified by controlling inducer concentrations, and dilution due to cellular division would turn the probes into memory devices in which information could be preserved over multiple generations. Additionally, insights from our analysis of the LacI-TetR system suggest that this particular system is readily available to be employed in this kind of probe.Electronic supplementary materialThe online version of this article (doi:10.1186/s12918-016-0279-y) contains supplementary material, which is available to authorized users.

Acoustic one-way metasurfaces: Asymmetric Phase Modulation of Sound by Subwavelength Layer.

We theoretically design and numerically demonstrate an acoustic one-way metasurface, which is a planar and acoustically subwavelength layer behaving like a nearly-reflectionless surface with arbitrary wave-steering capability for incident wave impinging on one side, while virtually blocking the reversed wave. The underlying mechanism is based on an asymmetric phase modulation by coupling a phase array and a near-zero-index medium. We exemplify a metastructure-based implementation by combining the hybrid metastuctures and labyrinthine structures. Moreover, the performance of the proposed implementation is demonstrated via three distinct phenomena of anomalous refraction, wave splitting and conversion of propagation wave to surface wave. Our findings may offer more possibilities for sound manipulation and improve the application potential of acoustic artificial devices in situations such as ultrasonic imaging and therapy.

A High-efficiency Method to Suppress Transformer Core Imbalance in Digitally Controlled Phase-shifted Full-bridge Converter

A high-efficiency method is proposed to suppress magnetic core imbalance in phase-shifted full-bridge (PSFB) converters. Compared with conventional solutions, such as controlling peak current mode (PCM) or adding DC blocking capacitance, the proposed method has several advantages, such as lower power loss and smaller size, because the additional current sensor or blocking capacitor is removed. A time domain model of the secondary side is built to analyze the relationship between transformer core imbalance and cathode voltage of secondary side rectifiers. An approximate control algorithm is designed to achieve asymmetric phase control, which reduces the effects of imbalance. A 60 V/15 A prototype is built to verify the proposed method. Experimental results show that the numerical difference of primary side peak currents between two adjacent cycles is suppressed from 2 A to approximately 0 A. Meanwhile, compared with the PCM solution, the efficiency of the PSFB converter is slightly improved from 93% to 93.2%.

Proposal for realizing the quantum spin Hall phase in a gapped graphene bilayer

Quantum spin Hall (QSH) insulators with gapless edge states have potential applications in designing low-dissipation devices. In spite of many predictions, to verify the QSH phase in graphene layered materials experimentally is still difficult due to the obstacle in achieving spin-orbit coupling strong enough. We propose a Rashba system of graphene bilayer gapped by dielectric layers and show it can host a valley-polarized QSH phase even when the Rashba interaction approached zero. Such a system exhibits asymmetric topological quantum phase transitions under opposite interlayer biases, due to the dielectric-potential induced inversion asymmetry in the absence of interlayer bias. Specifically, the quantum valley Hall phase exists in zigzag-edged nanoribbons under the bias in one direction but is absent under the reverse bias. These topological phenomena can be well understood by the competition among the dielectric-induced potential, Rashba interaction, and interlayer bias in modulating the bulk band gap. Moreover, the phase diagram is given and the corresponding phase boundaries are derived analytically. Our findings provide a possible way to detect the QSH-related asymmetric topological quantum phenomena in graphene bilayer based on the current experimental technology.

Spin-Flop Transition and a Tilted Canted Spin Structure in a Coupled Antiferromagnet

We study a uniaxial coupled Heisenberg antiferromagnet that consists of two subsystems of classical spins with small and large lengths and spin-flop transitions in a magnetic field parallel to the magnetic easy axis. It is proved that the anisotropy of inter-subsystem coupling stabilizes an asymmetric canted antiferromagnetic phase with a tilted direction of antiferromagnetism that is not perpendicular to the magnetic field. In contrast to the conventional first-order spin-flop transition, the spin-flop transition from the Neel phase to such a tilted canted antiferromagnetic (TCAF) phase is of the second order in the absence of simple anisotropic energies in the subsystems. The transition from the TCAF phase to the high-field saturated spin phase is of the second order in the strong coupling limit of the exchange interactions J1 between the small spins, whereas when J1 is finite, it becomes first-order. Therefore, in the former case, the TCAF phase converts the Neel phase continuously into the saturated p...

High-Performance Microchanneled Asymmetric Gd(0.1)Ce(0.9)O(1.95-δ)-La(0.6)Sr(0.4)FeO(3-δ)-Based Membranes for Oxygen Separation.

A microchanneled asymmetric dual phase composite membrane of 70 vol % Gd(0.1)Ce(0.9)O(1.95-δ)-30 vol % La(0.6)Sr(0.4)FeO(3-δ) (CGO-LSF) was fabricated by a "one step" phase-inversion tape casting. The sample consists of a thin dense membrane (100 μm) and a porous substrate including "finger-like" microchannels. The oxygen permeation flux through the membrane with and without catalytic surface layers was investigated under a variety of oxygen partial pressure gradients. At 900 °C, the oxygen permeation flux of the bare membrane was 1.6 (STP) ml cm(-2) min(-1) for the air/He-case and 10.10 (STP) ml cm(-2) min(-1) for the air/CO-case. Oxygen flux measurements as well as electrical conductivity relaxation show that the oxygen flux through the bare membrane without catalyst is limited by the oxygen surface exchange. The surface exchange can be enhanced by introduction of catalyst on the membrane surface. An increase of the oxygen flux of ∼1.49 (STP) mL cm(-2) min(-1) at 900 °C was observed when catalyst is added for the air/He-case. Mass transfer polarization through the finger-like support was confirmed to be negligible, which benefits the overall performance. A stable flux of 7.00 (STP) ml cm(-2) min(-1) was observed between air/CO/CO2 over 200 h at 850 °C. Partial surface decomposition was observed on the permeate side exposed to CO, in line with predictions from thermodynamic calculations. In a mixture of CO, CO2, H2, and H2O at similar oxygen activity the material will according to the calculation not decompose. The microchanneled asymmetric CGO-LSF membranes show high oxygen permeability and chemical stability under a range of technologically relevant oxygen potential gradients.

To enhance imaging performance of hybrid imaging systems by using two asymmetrical phase masks.

We propose the use of two asymmetrical phase masks combined with the subtracted imaging method to enhance the signal-to-noise ratio in wavefront coding systems. This subtracted imaging technique is similar to the variable pinhole diameter in confocal microscopy. Two different phase modulations of same phase masks are employed to promote the magnitude of the optical transfer function (OTF). The ratio factor is used to control the phase variation between two phase masks. The noise of decoded images is suppressed owing to the higher magnitude of the OTF than the wavefront coding systems with a phase mask. A tangent phase mask as an example is used to demonstrate our concept. Simulated results show that the performance promotion controls noise amplification of decoded images while maintaining a depth-of-field extension.

Irreversible phase transition between LiFePO4 and FePO4 during high-rate charge-discharge reaction by operando X-ray diffraction

LiFePO4 is a practically used cathode material for lithium-ion batteries due to a high theoretical capacity, high cycle capability and the high-rate performance. The metastable LixFePO4 (LxFP) phase with an intermediate composition appears in the non-equilibrium state at high-rate condition. However, the formation process of the metastable LxFP phase and its impact to the electrochemical property are still unclear. In order to elucidate these points, we directly observed the phase transition behavior by applying operando XRD during 10C charge-discharge. LxFP phase does not form in charge reaction but preferentially forms in discharge reaction. The phase transition from LxFP to Li-rich phase is less likely to proceed in the end of discharge reaction. The asymmetric phase transition between LiFePO4 and FePO4 results in decreasing the discharge capacity and increasing the irreversible capacity at high-rate conditions.

Cross-phase modulation-induced spectral broadening in silicon waveguides.

We analytically and experimentally investigate cross-phase modulation (XPM) in silicon waveguides. In contrast to the well known result in pure Kerr media, the spectral broadening ratio of XPM to self-phase modulation is not two in the presence of either two-photon absorption (TPA) or free carriers. The physical origin of this change is different for each effect. In the case of TPA, this nonlinear absorption attenuates and slightly modifies the pulse shape due to differential absorption in the pulse peak and wings. When free carriers are present two different mechanisms modify the dynamics. First, free-carrier absorption performs a similar role to TPA, but is additionally asymmetric due to the delayed free-carrier response. Second, free-carrier dispersion induces an asymmetric blue phase shift which competes directly with the symmetric Kerr-induced XPM red shift. We confirm this analysis with pump-probe experiments in a silicon photonic crystal waveguide.

Naphthalene Derivatives Induce Acyl Chain Interdigitation in Dipalmitoylphosphatidylcholine Bilayers.

The interdigitated phase of the lipid bilayer results when acyl chains from opposing monolayers fully interpenetrate such that the terminal methyl groups of the respective lipid chains are located at the interfacial region on the opposite sides of the bilayer. Usually, chain interdigitation is not encountered in a symmetric chain phosphatidylcholine (PC) membrane but can be induced under certain special conditions. In this article, we elucidate the contribution of small amphiphatic molecules in altering the physical properties of a symmetric chain PC bilayer membrane, which results in acyl chain interdigitation. Using small-angle X-ray scattering (SAXS), we have carried out a systematic investigation of the physical interactions of three naphthalene derivatives containing hydroxyl groups: β-naphthol, 2,3-dihydroxynaphthalene, and 2,7-dihydroxynaphthalene, with dipalmitoylphosphatidylcholine (DPPC) bilayers. On the basis of the diffraction patterns, we have determined the temperature-composition phase diagrams of these binary mixtures. The present study not only enables us to gain insight into the role played by small molecules in altering the packing arrangement of the acyl chains of the constituting PC lipids of the bilayer but also brings to light some important features that have not yet been reported hitherto. One such feature is the stabilization of the enigmatic asymmetric ripple phase over a wide temperature and concentration range. The results presented here strongly point toward a clear correlation between chain interdigitation and the stability of the ripple phase.

ChemInform Abstract: Contemporary Asymmetric Phase Transfer Catalysis: Large‐Scale Industrial Applications

AbstractReview: [70 refs.