Phase Curvature Research Articles

Controlled Self‐Assembly of Vesicles by Electrospray Deposition

The self‐assembly of amphiphilic molecules produces structures of diverse dimensions, encompassing micelles, tubules, lamellae, and vesicles. This study focuses on elucidating the controllability of amphiphilic lipid molecule self‐assembly in size and uniformity to facilitate our understanding of the molecular characteristics that correlate with the functions and attributes of the assembled structures. Electrospray deposition allows micropatterning of lipid molecules in conjunction with a conductive–nonconductive patterned substrate. The solvent in the sprayed mist undergoes evaporation during flight, leading to the deposition of dry lipids exclusively on the conductive regions of the substrate. This process enables homogeneous lipid micropatterning, effectively circumventing the coffee‐ring effect. Subsequent hydration of the lipid pattern triggers the spontaneous formation of a size‐controlled, unilamellar vesicle array on the substrate, spanning an area of a few square millimeters. The vesicles exhibits monodispersity, with a coefficient of variation below 8% for sizes ranging from 5 to 20 μm. The size‐controlled self‐assembly process is adaptable to various lipid compositions, thereby demonstrating that the molecular characteristics manifest in the morphological features appear as phase separation, budding, and curvature of vesicle membranes. The approach further validates its suitability for conducting time‐resolved analyses of molecular transport and ligand binding on the monodispersed vesicle array.

Automatic and accurate compensation for phase aberrations in digital holographic microscopy based on iteratively reweighted least squares fitting

Phase aberrations must be precisely compensated for phase-contrast imaging in digital holographic microscopy. In this paper, an automatic and accurate phase aberration compensation method is proposed based on iteratively reweighted least squares fitting. Instead of selecting the known-to-be-flat region with manual operation or image segmentation, this method starts from conventional least squares fitting in the whole image and attributes lower weights to the pixels with higher fitting residuals in an iterative reweighting procedure, during which the influence of specimen and noise is automatically reduced. Both phase curvature and high-order aberrations could be corrected without extra operation. Numerical simulation demonstrates that the proposed method is more accurate than the state-of-the-art numerical methods. Experimental result proves that this method is robust and fast enough for dynamic imaging of living cells.

Stability of Individual Phases in the Elastic Matrix of a Composite

A methodology for analytical stability assessment of individual compressed flexible phases of discretely heterogeneous composite elements of engineering structures is proposed to ensure their reliable safe operation and minimise the consequences of emergencies. Based on the energy balance equation for the proportional forces of a normal resistance of the medium to the phase displacement, expressions are obtained for determining the critical force, taking into account the possible initial curvature (non-rectilinearity) of a single phase in the elastic medium of the matrix for three possible cases of stability loss. The approbation of the results of the study on the example of deformation features of reinforcing bars in a compressed reinforced concrete column is presented.

Thermodynamic geometry of STU black holes

This work investigates the phase structure of STU black holes with uniform charges by utilizing the New Thermodynamic Geometry (NTG) approach. The study explores the intriguing relationship between heat capacity phase transitions and curvature singularities, employing the NTG formalism. The analysis encompasses an examination of phase transitions along the T − S and Q − Φ planes, a study of critical exponents, and an assessment of black hole stability. The NTG geometry is applied in both the normal and extended phase spaces, revealing valuable insights into the thermodynamic behavior and stability of STU black holes. Meanwhile, a closer examination of NTG geometry shows a positive correlation in the sign between the extrinsic curvature and the heat capacity, which is incompatible with the curvature singularity. Overall, this study contributes to our understanding of the phase transitions and thermodynamic properties of STU black holes, shedding light on the intricate interplay between curvature singularities and the stability of black holes in diverse thermodynamic scenarios.

Composite Spin Hall Conductivity from Non-Collinear Antiferromagnetic Order.

Non-collinear antiferromagnets (AFMs) are an exciting new platform for studying intrinsic spin Hall effects (SHEs), phenomena that arise from the materials' band structure, Berry phase curvature, and linear response to an external electric field. In contrast to conventional SHE materials, symmetry analysis of non-collinear antiferromagnets does not forbid non-zero longitudinal and out-of-plane spin currents with polarization and predicts an anisotropy with current orientation to the magnetic lattice. Here, multi-component out-of-plane spin Hall conductivities are reported in L12 -ordered antiferromagnetic PtMn3 thin films that are uniquely generated in the non-collinear state. The maximum spin torque efficiencies (ξ = JS /Je ≈ 0.3) are significantly larger than in Pt (ξ ≈ 0.1). Additionally, the spin Hall conductivities in the non-collinear state exhibit the predicted orientation-dependent anisotropy, opening the possibility for new devices with selectable spin polarization. This work demonstrates symmetry control through the magnetic lattice as a pathway to tailored functionality in magnetoelectronic systems.

Action Potential Morphology Accurately Predicts Proarrhythmic Risk for Drugs With Potential to Prolong Cardiac Repolarization.

Drug-induced or acquired long QT syndrome occurs as a result of the unintended disruption of cardiac repolarization due to drugs that block cardiac ion channels. These side effects have been responsible for the withdrawal of a range of drugs from market and are a common reason for termination of the development of new drugs in the preclinical stage. Existing approaches to risk prediction are expensive and overly sensitive meaning that recently there have been renewed efforts, largely driven by the comprehensive proarrhythmic assay initiative, to develop more accurate methods for allocation of proarrhythmic risk. In this study, we aimed to quantify changes in the morphology of the repolarization phase of the cardiac action potential as an indicator of proarrhythmia, supposing that these shape changes might precede the emergence of ectopic depolarizations that trigger arrhythmia. To do this, we describe a new method of quantifying action potential morphology by measuring the radius of curvature of the repolarization phase both in simulated action potentials, as well as in action potentials measured from induced pluripotent stem cell-derived cardiomyocytes. Features derived from the curvature signal were used as inputs for logistic regressions to predict proarrhythmic risk. Optimal risk classifiers based on morphology were able to correctly classify risk to drugs in the comprehensive proarrhythmic assay initiative panels with very high accuracy (0.9375) and outperformed conventional metrics based on action potential duration at 90% repolarization, triangulation, and charge movement (qNet). Analysis of action potential morphology in response to proarrhythmic drugs improves prediction of torsadogenic risk. Furthermore, morphology metrics can be measured directly from the action potential, potentially eliminating the burden of undertaking complex screens of potency and drug-binding kinetics against multiple cardiac ion channels. As such, this method has the potential to improve and streamline regulatory assessment of proarrhythmia in preclinical drug development.

Modeling the mechanisms through which protein phase separation induces membrane curvature.

Membrane curvature is an essential component of life. Many cellular processes, such as endocytosis, exocytosis, and cell motility induce curvature in membranes to carry out their functions. Though it is traditionally thought that structured proteins drive curvature, recent work has shown that disordered proteins can also be potent drivers of curvature. In particular, liquid-like condensation of disordered proteins has recently been shown to produce concave membrane curvature, resulting in protein-lined buds and tubules of the membrane. However, the mechanism behind this phenomenon remains poorly understood. Here we seek to understand the protein-protein and protein-membrane interactions that give rise to these behaviors. We begin by using coarse grained molecular dynamics simulations to investigate the conformational preferences of disordered proteins under different conditions: in varying salt concentrations, in solution or tethered to a lipid membrane. Specifically, we examine the deviation of disordered protein behavior from that of a simple random walk, both in solution and on membrane surfaces. By comparing modeling results to experimental data, we separate the role of protein-protein and protein-membrane interactions to shed light on the role of each in both phase separation and curvature generation. Our work will provide insight on the role that disordered regions have in membrane complexes, particularly those which facilitate membrane curvature.

Characterization of the error of the speckle-based wavefront metrology device at Shanghai Synchrotron Radiation Facility.

A metrology device based on the near-field speckle technique was developed in the x-ray test beamline at the Shanghai Synchrotron Radiation Facility to meet the at-wavelength detection requirements of ultra-high-precision optical elements. Different sources of error that limit the uncertainty of the instrument were characterized. Two main factors that contribute to the uncertainty of the measurements were investigated: (1) noise errors introduced by the electronics and the errors introduced by the algorithm and (2) stability errors owing to environmental conditions. The results show that the high measurement stability of the device is realized because it is insensitive to the effect of the external environment. The repetition accuracy of the device achieved 9 nrad (rms) when measuring the planar mirror that produces weak phase curvature.

Machine learning techniques for positioning and characterization of particles in digital holography using the whole phase curvature

We propose a machine learning-based regression method with the whole phase curvature of a reconstructed wave along the optical axis as input data to obtain not only the precise axial position but also the radius and refractive index of particles. Experimental results using well-characterized particles showed that an axial position of a particle could be detected, with the mean signed deviation (MSD) and root mean squared error (RMSE) being 0.02% and 85% of the particle’s diameter, respectively. A radius of 29.3 ± 0.36 µm and a refractive index of 1.589 ± 0.002 agreed well with the manufacturer’s specifications. In comparison to our previous nonlinear optimization method, the method was validated for characterizing the distribution of particle characteristics and can be used with a factor of 10,000 faster calculations.

Uncertainties in Bistatic RCS Measurements

Radar Cross Section (RCS) is a far field parameter and limited test range length produces error in its measurements. RCS measured with co-located Tx and Rx antennas is termed as monostatic RCS and with spatially separated Tx and Rx antennas as Bistatic RCS (BRCS). Interest in BRCS measurements has grown due to increase in use of multi-static Radars for detecting low-observable targets. In literature BRCS measurement techniques explored are either horn antenna based far field setups or Compact Antenna Test Range (CATR) based setups. All the techniques have inherent limitations and errors, which need to be assessed as the information generated plays a decisive role in the design of military platforms. In the present paper, the errors in each measurement technique are obtained through extensive numerical computation and measurements on various canonical as well as complex shapes. The results highlight the effect of the phase curvature in either or both, Tx, and Rx paths, affect the measurement accuracies, thereby limiting the target size and highest frequency of operation of present techniques.

Topological electronic bands in crystalline solids

Topology is now securely established as a means to explore and classify electronic states in crystalline solids. This review provides a gentle but firm introduction to topological electronic band structure suitable for new researchers in the field. I begin by outlining the relevant concepts from topology, then give a summary of the theory of non-interacting electrons in periodic potentials. Next, I explain the concepts of the Berry phase and Berry curvature, and derive key formulae. The remainder of the article deals with how these ideas are applied to classify crystalline solids according to the topology of the electronic states, and the implications for observable properties. Among the topics covered are the role of symmetry in determining band degeneracies in momentum space, the Chern number and topological invariants, surface electronic states, two- and three-dimensional topological insulators, and Weyl and Dirac semimetals

Symmetry-enforced electronic nodal straight lines in CsNb3SBr7

We propose the quaternary-compounds CsNb3SBr7 is a nodal-straight-line semimetal candidate based on the first-principles calculations and symmetry analyses. There are a pair of nodal straight lines locate in the k z = 0 plane of Brillouin zone, which is protected by the crystal symmetry. The topological properties of nodal-straight-line state are characterized by the nontrivial Berry phase and Berry curvature. On the (001) surface of CsNb3SBr7, Fermi arcs form the belt-like surface state, connecting the nodal straight lines with opposite chirality. Furthermore, the Hofstadter’s butterfly and optical conductivity are investigated using a slab sample. These results not only reveal the symmetric protection mechanism of nodal straight lines, but also pave a way for exploring the electronic and optical properties of CsNb3SBr7 in further condensed matter physics experiments.

Topological monopole's gauge field‐induced anomalous Hall effect in artificial honeycomb lattice

AbstractVortex magnetic structure in artificial honeycomb lattice provides a unique platform to explore emergent properties due to the additional Berry phase curvature imparted by chiral magnetization to circulating electrons via direct interaction. We argue that while the perpendicularly aligned magnetic component leads to the quantized flux of monopole at the center of the Berry sphere, the in‐plane vortex circulation of magnetization gives rise to unexpected nontrivial topological Berry phase due to the gauge field transformation. The unprecedented effect signifies the importance of vector potential in multiply connected geometrical systems. Experimental confirmations to proposed hypotheses are obtained from Hall resistance measurements on permalloy honeycomb lattice. Investigation of the topological gauge transformation due to the in‐plane chirality reveals anomalous quasi‐oscillatory behavior in Hall resistance as a function of perpendicular field. The oscillatory nature of is owed to the fluctuation in equilibrium current as a function of Fermi wave‐vector , envisaged under the proposed new formulation in this article. Our synergistic approach suggests that artificially tunable nanostructured material provides new vista to the exploration of topological phenomena of strong fundamental importance.Key PointsDemonstration of gauge field flux due to vortex magnetism.Anomalous Hall effect in magnetic honeycomb lattice.Topological monopole‐induced magnetic flux.

Temporal integration contributes to the masking release by amplitude modulation

Modulated maskers produce less amount of masking than unmodulated maskers, an effect referred to as masking release (MR). Both listening in the temporal dips and fast cochlear compression have been suggested as underlying mechanisms. We addressed the role of dip listening by measuring temporal integration in simultaneous masking using Schroeder-phase harmonic complexes (SPHC) with various phase curvatures. In an experiment with six normal-hearing listeners, SPHC masker and pure-tone target stimuli were covaried in duration at a high masker level. The MR increased with stimulus duration, suggesting integration of target information across multiple masker dips. The duration dependence of the MR was predicted by a physiology-inspired model based on the temporal envelope modulation strength in the auditory periphery. The modeling analysis suggested that listeners detect the presence of the target by a reduction in fluctuation strength that results primarily from a decline of F0-based response peaks, an effect known as synchrony capture. The detailed pattern of masked thresholds across various masker phase curvatures was not predicted by the model, suggesting that its phase response does not well fit the human phase response. Overall, temporal integration across neural envelope features associated with the masker dips seems to contribute to the MR with SPHCs.

Physiological sensitivity to across-channel temporal patterns in response to Schroeder harmonic complexes, based on sequence rather than coincidence detection

The flat-envelope harmonic complexes devised by Schroeder (1970) contain a linear frequency sweep whose direction and speed depend on phase curvature C. Physiological studies have focused on responses at a given characteristic frequency (CF), which show only a subtle dependence on the sign and magnitude of C. The question arises whether CNS neurons are sensitive to the temporal pattern across nerve fibers differing in CF. Octopus cells in the cochlear nucleus receive convergent excitatory input from nerve fibers spanning a wide range of CFs and are thought to be monaural coincidence detectors. We studied their spike output and membrane responses to Schroeder complexes in anesthetized gerbils. Octopus cells were indeed tuned to a wide frequency range but showed discrete frequency “hotspots” of differing strength. Most cells showed marked sensitivity to C, with some neurons preferring upward and others downward frequency sweeps, which was broadly stable across SPL and fundamental frequency. The sensitivity to C arises not from coincidence detection, but from a sensitivity to the temporal sequence of activation of inputs tuned to different frequencies. We conclude that marked sensitivity to Schroeder phase exists at the first CNS processing stage and is based on temporal sequence detection across frequency channels.

Propagation-invariant high-dimensional orbital angular momentum states

Photonic states encoded in spatial modes of paraxial light fields provide a promising platform for high-dimensional quantum information protocols and related studies, where several pioneering theoretical and experimental demonstrations have paved the path for future technologies. Crucially, critical issues encountered in free-space propagation still represent a major challenge. This is the case of asynchronous diffraction between spatial modes with different modal orders, which experience variations in their transverse structure upon free-space propagation. Here we address this issue by proposing an encoding method based on the use of Laguerre–Gaussian modes of the same modal order N to define a N + 1 dimensional space. Noteworthy, such modes endowed with orbital angular momentum (OAM) experience the same propagation aberrations featuring an identical Gouy phase and wavefront curvature. We demonstrate our proposal experimentally by using time-correlated-single-photon imaging combined with a digital propagation technique. Importantly, our technique allows to eliminate, without the use of imaging systems, all issues related to asynchronous diffraction, providing an accessible way to generate propagation-invariant OAM qudits for quantum optical protocols.

The flow of the Berry curvature vector field

The concept of Berry phase and Berry curvature has become ubiquitous in solid state physics as it relates to variety of phenomena, such as topological insulators, polarization, and various Hall effects. It is well known that large Berry curvatures arise from close proximity of hybridizing bands, however, the vectorial nature of the Berry curvature is not utilized in current research. On bulk bcc Fe, we demonstrate the flow of the Berry curvature vector field which features not only monopoles but also higher dimensional structures with its own topological features. They can provide a novel unique view on the electronic structure in all three dimensions. This knowledge is also used to quantify particular contributions to the intrinsic anomalous Hall effect in a simple analytical form.

Role of Ionizable Lipids in SARS-CoV-2 Vaccines As Revealed by Molecular Dynamics Simulations: From Membrane Structure to Interaction with mRNA Fragments.

Recent advances in RNA-based medicine have provided new opportunities for the global current challenge, i.e., the COVID-19 pandemic. Novel vaccines are based on a messenger RNA (mRNA) motif with a lipid nanoparticle (LNP) vector, consisting of high content of unique pH-sensitive ionizable lipids (ILs). Here we provide molecular insights into the role of the ILs and lipid mixtures used in current mRNA vaccines. We observed that the lipid mixtures adopted a nonlamellar organization, with ILs separating into a very disordered, pH-sensitive phase. We describe structural differences of the two ILs leading to their different congregation, with implications for the vaccine stability. Finally, as RNA interacts preferentially with IL-rich phases located at the regions with high curvature of lipid phase, local changes in RNA flexibility and base pairing are induced by lipids. A proper atomistic understanding of RNA–lipid interactions may enable rational tailoring of LNP composition for efficient RNA delivery.

Tuning curvature and phase behavior of monoolein bilayers by epigallocatechin-3-gallate: Structural insight and cytotoxicity

The use of glyceryl monooleate (GMO)-based nanoparticles has not yet been explored in overcoming the low bioavailability of Epigallocatechin-3-gallate (EGCG), a green tea polyphenol with a known anticancer activity. Since the inclusion of a guest molecule can affect the curvature and the supramolecular structure of fully hydrated GMO-based phase, the phase behavior of bulk and dispersed liquid crystalline systems containing EGCG were explored by Small Angle Neutron Scattering and X-Ray Diffraction experiments. Molecular Dynamic Simulations showed how the interaction of EGCG with polar heads of GMO strongly affects the curvature and packing of GMO phase. The EGCG encapsulation efficiency was determined in the nanodispersions and their size studied by Dynamic Light Scattering and Atomic Force Microscopy. A nanodispersed formulation has been optimized with a cytotoxic effect more than additive of GMO and EGCG.

Sensitivity to Schroeder phase arising from sensitivity to temporal patterns across nerve fibers

The flat-envelope harmonic complexes devised by Schroeder (1970) have been extensively used in psychophysical studies. The stimuli contain a linear frequency sweep, whose direction and speed depend on phase curvature C. For a given characteristic frequency, basilar membrane and nerve responses show only a subtle dependence on the sign and magnitude of C. The question arises whether CNS neurons are sensitive to the temporal pattern across nerve fibers. We studied octopus cells in the cochlear nucleus, which receive a convergent excitatory input from nerve fibers and have been hypothesized to be monaural coincidence detectors. We studied both their spike output and nerve input using multiple recording techniques in anesthetized chinchillas. Octopus cells showed marked sensitivity to C, which was broadly stable across SPL and fundamental frequency. They were tuned to a wide frequency range, but with discrete frequency “hotspots” that generate major and minor inputs. The sensitivity to C arises not from coincidence detection, but from a sensitivity to the temporal sequence of activation of inputs tuned to different frequencies. We conclude that marked sensitivity to Schroeder phase is already present at the first CNS processing stage, based on temporal sequence detection across frequency channels rather than on coincidence detection.