Anomalous periodicity of magnetic interference patterns in encapsulated graphene Josephson junctions
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75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
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Peak effect and dynamics of stripe- and pattern-forming systems on a periodic one-dimensional substrate
Here we examine the ordering, pinning, and dynamics of two-dimensional pattern-forming systems interacting with a periodic one-dimensional substrate. In the absence of the substrate, particles with competing long-range repulsion and short-range attraction form anisotropic crystal, stripe, and bubble states. When the system is tuned across the stripe transition in the presence of a substrate, we find that there is a peak effect in the critical depinning force when the stripes align and become commensurate with the substrate. Under an applied drive, the anisotropic crystal and stripe states can exhibit soliton depinning and plastic flow. When the stripes depin plastically, they dynamically reorder into a moving stripe state that is perpendicular to the substrate trough direction. We also find that when the substrate spacing is smaller than the widths of the bubbles or stripes, the system forms pinned stripe states that are perpendicular to the substrate trough direction. The system exhibits multiple reentrant pinning effects as a function of increasing attraction, with the anisotropic crystal and large bubble states experiencing weak pinning but the stripe and smaller bubble states showing stronger pinning. We map out the different dynamic phases as a function of filling, the strength of the attractive interaction term, the substrate strength, and the drive, and demonstrate that the different phases produce identifiable features in the transport curves and particle orderings.
97 MATHEMATICS AND COMPUTING↗
The Faint "Heartbeats" of IGR J17091-3624: An Exceptional Black Hole Candidate
We report on the first 180 days of Rossi X-Ray Timing Explorer observations of the outburst of the black hole candidate IGR Jl7091-3624. This source exhibits a broad variety of complex light curve patterns including periods of strong flares alternating with quiet intervals. Similar patterns in the X-ray light curves have been seen in the (up to now) unique black hole system GRS 1915+105. In the context of the variability classes defined by Belloni et al. for GRS 1915+105, we find that JGR J17091-3624 shows the nu, rho, alpha, lambda, Beta, and mu classes as well as quiet periods which resemble the chi class, all occurring at 2-60 keY count rate levels which can be 10-50 times lower than observed in GRS 1915+\05. The so-called rho class "heartbeats" occur as fast as every few seconds and as slow as approx 100 s, tracing a loop in the hardness-intensity diagram which resembles that previously seen in GRS 1915+\05. However, while GRS 1915+105 traverses this loop clockwise, IGR Jl7091-3624 does so in the opposite sense. We briefly discuss our findings in the context of the models proposed for GRS 1915+105 and find that either all models requiring near Eddington luminosities for GRS 1915+105-like variability fail, or IGR Il7091-3624 lies at a distance well in excess of 20 kpc, or it harbors one of the least massive black holes known( <3 solar M).
Altamirano, D.↗
Periodic chiral magnetic domains in single-crystal nickel nanowires
We report here on experimental and computational investigations of the domain structure of single-crystal Ni nanowires (NWs). The ${\sim}200\times{}200\times{}8000\mathrm{n}{\mathrm{m}}^{3}$ Ni NWs were grown by a thermal chemical vapor deposition technique that results in single-crystal structures. Magnetoresistance measurements of individual NWs suggest the average magnetization points largely off the NW long axis at zero field. X-ray photoemission electron microscopy images obtained at room temperature show a well-defined periodic magnetization pattern along the surface of the nanowires with a period of ${{\lambda}}_{\mathrm{avg}}=239\pm{}37\mathrm{nm}$. Finite element micromagnetic simulations reveal that when the material parameters of the modeled system match those of nickel crystal at $T=10\mathrm{K}$, an oscillatory magnetization configuration with a period closely matching experimental observation (${\lambda}=222\mathrm{nm}$) is obtainable at remanence. This magnetization configuration involves a periodic array of alternating chirality vortex domains distributed along the length of the NW. Vortex formation is attributable to the relatively high cubic anisotropy of the single crystal Ni NW system at $T=10\mathrm{K}$ and its reduced structural dimensions. The periodic alternating chirality vortex state is a topologically protected metastable state, analogous to an array of 360° domain walls in a thin strip. Simulations show that other remanent states are also possible, depending on the field history. At room temperature ($T=273\mathrm{K}$), simulations show vortices are no longer stable due to the expected reduced cubic anisotropy of the system, suggesting a disparity between the fabricated and modeled nanowires. Negative uniaxial anisotropy and magnetoelastic effects in the presence of compressive biaxial strain are shown to promote and restore formation of vortices at room temperature.
36 MATERIALS SCIENCE↗
Electrodynamic patterns in the polar region during periods of extreme magnetic quiescence
Using data from the DE 2 satellite, the electrodynamic patterns in the polar region during periods of extreme magnetic and auroral quiescence are analyzed for the existence of region-1 and region-2 field-aligned current systems, convection patterns, and electron-precipitation boundaries. The large-scale region-1 and region-2 currents were found to be usually absent during quiet periods, except in the cusp region. Field-aligned currents continue to be present, but as small-scale structures distributed through the auroral oval and over the entire polar cap. Convection patterns were always found in the summer hemisphere, but not always in the winter hemisphere, while structured electron precipitation was found to extend over the entire polar region independent of season.
Hoffman, R. A.↗
Electron-Beam Induced Emergence of Mesoscopic Ordering in Layered MnPS 3
Ordered mesoscale structures in 2D materials induced by small misorientations have allowed for a wide variety of electronic, ferroelectric, and quantum phenomena to be explored. Until now, the only mechanism to induce this periodic ordering was via mechanical rotations between the layers, with the periodicity of the resulting moiré pattern being directly related to twist angle. Here we report a fundamentally distinct mechanism for emergence of mesoscopic periodic patterns in multilayer sulfur-containing metal phosphorus trichalcogenide, MnPS3, induced by the electron beam. The formation under the beam of periodic hexagonal patterns with several characteristic length scales, nucleation and transitions between the phases, and local dynamics are demonstrated. The associated mechanisms are attributed to the relative contraction of the layers caused by beam-induced sulfur vacancy formation with subsequent ordering and lattice parameter change. As a result, the plasmonic response of the system is locally altered, suggesting an element of control over plasmon resonances by electron beam patterning. To conclude, we pose that harnessing this phenomenon provides both insight into fundamental physics of quantum materials and enables device applications by enabling controlled periodic potentials on the atomic scale.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Unsteady Phenomena During Operation of the SSME Fuel Flowmeter
This report describes a part of the analysis carried in support of the SSME (Space Shuttle Main Engine) Fuel Flowmeter redesign, addressing an intensely researched phenomenon known as "shifting" of the flowmeter constant value. It consists of a sudden change in the flowmeter indication, which occurs simultaneously with the onset of an oscillatory variation of the rotor speed. The change in the flowmeter indications does not correspond to a real change in the volumetric flow through the device. Several causes have been investigated in detail, in the past, without conclusive evidence towards a cause of this phenomenon. The present analysis addresses the flow physics through the flowmeter by assembling results from 3-D CFD (computational fluid dynamics) calculations, airfoil C(sub D)/C(sub L) performance curves and mass moment of inertia characteristics of the rotor into a synergistic calculation which simulates the unsteady regime of the flowmeter operation. The results show that the 4-bladed rotor interacts with the periodic flow pattern created behind the flow straightener upstream in a manner that generates a steady, periodic fluctuation in the rotor's speed. The amplitude of this fluctuation is significantly smaller than the 0.5% of mean speed threshold which constitutes a flight operational limit. When manufacturing errors occur, however, the fluctuations are amplified and can generate a significant apparent change in the flowmeter indication. Two types of possible fabrication errors-which can occur even for parts fabricated within the accepted tolerances for the blade airfoil-are presented, together with their effect on the flowmeter operation.
Marcu, Bogdan↗
Effects of human presence on African mammal waterhole attendance and temporal activity patterns
Abstract Human impacts on the environment and wildlife populations are increasing globally, threatening thousands of species with extinction. While wildlife‐based tourism is beneficial for educating tourists, generating income for conservation efforts, and providing local employment, more information is needed to understand how this industry may impact wildlife. In this study, we used motion‐activated cameras at 12 waterholes on a private game reserve in northern Namibia to determine if the presence of humans and permanent infrastructure affected mammal visits by examining their (1) number of visits, (2) time spent, and (3) diel activity patterns. Our results revealed no differences in the number of visits based on human presence for any of the 17 mammal species studied. However, giraffes ( Giraffe camelopardalis ) spent more time at waterholes before observer presence compared to during. Additionally, several species changed diel activity patterns when human observers were present. Notably, several carnivore and ungulate species increased overlap in their activity patterns during periods while humans were present relative to when humans were absent. These modifications of mammal temporal activity patterns due to human presence could eventually lead to changes in community structure and trophic dynamics because of altered predator–prey interactions. As humans continue to expand into wildlife habitats, and wildlife‐based tourism increases globally, it is imperative that we fully understand the effects of anthropogenic pressures on mammal behavior. Monitoring of wildlife behavioral changes in response to human activity is crucial to further develop wildlife tourism opportunities in a way that optimizes the impact of conservation goals.
Patterson, J. R. [Savannah River Ecology Lab, Warn↗
Temporal studies of compact galactic X-ray sources
Advances in X-ray astronomy due to temporal studies are discussed. Attention is given to X-ray temporal variability categorized into periodic, quasi-periodic, and chaotic. Approximately 95% of all known X-ray sources exhibit chaotic variability, in which there is no apparent pattern or periodicities. The orbits of seven binary X-ray sources are presented, along with empirical findings of neutron star masses. In addition, the interior structure of a supergiant star, HD 77581, is investigated by attempting to measure its apsidal motion. Graphs are provided for the power density spectrum of 4U 1626-67, GX301-2 Doppler delay data, and empirically determined error contours for the mass and radius of four companions stars in X-ray binary systems.
Rappaport, S.↗
Seasonal and nonseasonal variability of satellite-derived surface pigment concentration in the California Current
The large-scale patterns of satellite-derived surface pigment concentration off the west coast of North America are presented and are averaged into monthly mean surface wind fields over the California Current system (CCS) for the July 1979 to June 1986 period. The patterns are discussed in terms of both seasonal and nonseasonal variability for the indicated time period. The large-scale seasonal characteristics of the California Current are summarized. The data and methods used are described, and the problems known to affect the satellite-derived pigment concentrations and the wind data used in the study are discussed. The statistical analysis results are then presented and discussed in light of past observations and theory. Details of the CZCS data processing are described, and details of the principal estimator pattern methodology used here are given.
Strub, P. Ted↗
Microgravity Flow Boiling Experiments With Liquid-Vapor Mixture Inlet Onboard the International Space Station
This article is part of a series of studies culminating from the multi-objective Flow Boiling and Condensation Experiment (FBCE) onboard the International Space Station, which utilized the Flow Boiling Module (FBM) for experiments between February and July 2022. This study investigates microgravity flow boiling of n-Perfluorohexane with liquid-vapor mixture (two-phase) inlet conditions to the FBM with either one or two opposite walls heated. The FBM’s channel has a rectangular cross-sectional area of 5.0 × 2.5 mm 2 and a heated length of 114.6 mm. Key parameters of interest include mass velocity (180 – 2400 kg/m 2 s), inlet quality (-0.01 – 0.87), inlet pressure (120 – 200 kPa), and heat flux (1.8 W/cm 2 to critical heat flux), and a large database is amassed. The flow is visualized via a high-speed video camera and photographs are recorded at each heating increment to assess the periodic flow patterns within the channel and the near-wall interfacial behavior. Flow patterns are complex and mainly characterized by high- and low-density fronts alternately traversing the channel to yield high- and low-density-dominant periods of boiling. At all operating conditions, high-density fronts are faster during high-density-dominant periods. At low inlet qualities, the flow is annular near the channel inlet with a central vapor core surrounded by an annular liquid layer. Each high-density front having a high liquid fraction leaves a thin liquid layer sheared onto the heated walls. Boiling occurs within the liquid layer and a vapor layer is formed next to the heated wall. Inlet quality and mass velocity most dictate the overall flow patterns followed by heating configuration, and to a much lesser extent, heat flux and inlet pressure. Heat transfer characteristics are assessed via averaged boiling curves, streamwise profiles of wall temperature and heat transfer coefficient, and parametric curves of local and averaged heat transfer coefficients. Inlet pressure has an insignificant effect on heat transfer. At similar operating conditions, both the heating configurations yield similar trends and values of heat transfer coefficient and critical heat flux (CHF, slightly higher for single-sided) even though double-sided heating adds twice the heat to the fluid and doubly raises local quality. The heat fluxes required for both onset of nucleate boiling degradation and CHF are larger at high mass velocities and low inlet qualities. For a fixed inlet quality, high mass velocities yield higher average heat transfer coefficients at both lower and higher heat fluxes, while the nucleate boiling regime at intermediate heat fluxes is unaffected. For a fixed mass velocity, higher inlet qualities yield higher and lower average heat transfer coefficients at lower and higher heat fluxes, respectively.
Microgravity↗
False lock in quadriphase receivers with unequal I- and Q-channel data rates
Results are presented concerning the noise-free false-lock problem in quadriphase receivers with unequal I-channel and Q-channel data rates. It is shown that false lock may occur when the incoming carrier frequency and the loop VCO (voltage-controlled oscillator) frequency differ by an amount that is a linear combination of a quarter of I-channel and Q-channel data rates. General expressions for the false-lock performance of quadriphase receivers are given for random as well as periodic data patterns. Specific closed-form expressions for the false-lock margin are are derived when the arm filters of the quadriphase receivers are single-pole Butterworth filters, and the format of the random data is NRZ (nonreturn-to-zero). Numerical evaluations of false-lock margin as a function of the product of 3-dB arm-filter bandwidth and symbol duration are carried out for random data using various arm filters and for different periodic I-chanel and Q-channel data patterns.
Cideciyan, Roy D.↗
Intradomain Textures in Block Copolymers: Multizone Alignment and Biaxiality
Block copolymer (BCP) melt assembly has been studied for decades, focusing largely on self-organized spatial patterns of periodically ordered segment density. Here, we demonstrate that underlying the well-known composition profiles (i.e., ordered lamella, cylinders, spheres, and networks) are generic and heterogeneous patterns of segment orientation that couple strongly to morphology, even in the absence of specific factors that promote intra or interchain segment alignment. We employ both self-consistent field theory and coarse-grained simulation methods to measure polar and nematic order parameters of segments in a freely jointed chain model of diblock melts. We show that BCP morphologies have a multizone texture, with segments predominantly aligned normal and parallel to interdomain interfaces in the respective brush and interfacial regions of the microdomain. Further, morphologies with anisotropically curved interfaces (i.e., cylinders and networks) exhibit biaxial order that is aligned to the principal curvature axes of the interface.
42 ENGINEERING↗
Modeling a Propagating Sawtooth Flare Ribbon Structure as a Tearing Mode in the Presence of Velocity Shear
On 2014 April 18 (SOL2014-04-18T13:03), an M-class flare was observed by IRIS. The associated flare ribbon contained a quasi-periodic sawtooth pattern that was observed to propagate along the ribbon, perpendicular to the IRIS spectral slit, with a phase velocity of ∼15 km s{sup −1}. This motion resulted in periodicities in both intensity and Doppler velocity along the slit. These periodicities were reported by Brannon et al. to be approximately ±0.″5 in position and ±20 km s{sup −1} in velocity and were measured to be ∼180° out of phase with one another. This quasi-periodic behavior has been attributed by others to bursty or patchy reconnection and slipping occurring during three-dimensional magnetic reconnection. Though able to account for periodicities in both intensity and Doppler velocity, these suggestions do not explicitly account for the phase velocity of the entire sawtooth structure or the relative phasing of the oscillations. Here we propose that the observations can be explained by a tearing mode (TM) instability occurring at a current sheet across which there is also a velocity shear. Using a linear model of this instability, we reproduce the relative phase of the oscillations, as well as the phase velocity of the sawtooth structure. We suggest a geometry and local plasma parameters for the April 18 flare that would support our hypothesis. Under this proposal, the combined spectral and spatial IRIS observations of this flare may provide the most compelling evidence to date of a TM occurring in the solar magnetic field.
79 ASTRONOMY AND ASTROPHYSICS↗
Twisted bilayered graphenes at magic angles and Casimir interactions: correlation-driven effects
Twisted bilayered graphenes (TBGs) at magic angles are systems housing long ranged periodicity of moiré patterns together with short ranged periodicity associated with the individual graphenes. Such materials are a fertile ground for novel states largely driven by electronic correlations. Here we find that the ubiquitous Casimir force can serve as a platform for macroscopic manifestations of the quantum effects stemming from the magic angle bilayered graphenes properties and their phases determined by electronic correlations. In conclusion, by utilizing comprehensive calculations for the electronic and optical response, we find that Casimir torque can probe anisotropy from the Drude conductivities in nematic states, while repulsion in the Casimir force can help identify topologically nontrivial phases in magic angle TBGs.
36 MATERIALS SCIENCE↗
Method and apparatus for ultra-high-sensitivity, incremental and absolute optical encoding
An absolute optical linear or rotary encoder which encodes the motion of an object (3) with increased resolution and encoding range and decreased sensitivity to damage to the scale includes a scale (5), which moves with the object and is illuminated by a light source (11). The scale carries a pattern (9) which is imaged by a microscope optical system (13) on a CCD array (17) in a camera head (15). The pattern includes both fiducial markings (31) which are identical for each period of the pattern and code areas (33) which include binary codings of numbers identifying the individual periods of the pattern. The image of the pattern formed on the CCD array is analyzed by an image processor (23) to locate the fiducial marking, decode the information encoded in the code area, and thereby determine the position of the object.
Leviton, Douglas B.↗
Climate Conditions During a Rift Valley Fever Post-epizootic Period in Free State, South Africa, 2014–2019
Rift Valley fever virus (RVFV) activity in Southern Africa tends to occur during periods of sustained elevated rainfall, cooler than normal conditions, and abundant vegetation cover creating ideal conditions for the increase and propagation of populations of RVFV mosquito vectors. These climatic and ecological conditions are modulated by large-scale tropical-wide El Niño–Southern Oscillation (ENSO) phenomena. The aim of this 5-year study was to investigate climatic conditions during Rift Valley fever “post-epizootic” period in Free State province of the Republic of South Africa, which historically experienced the largest RVF outbreaks in this country. We collected satellite-derived rainfall, land surface temperature (LST), and normalized difference vegetation index (NDVI) data since 2014 to understand broad environmental conditions in the years following a period of sustained and widespread large RVF outbreaks (2008–2011) in the region. We found this post-epizootic/interepizootic period to be characterized by below-normal rainfall (~-500 mm), above LSTs (~+12°C), depressed NDVI (60% below normal), and severe drought as manifested particularly during the 2015–2016 growing season. Such conditions reduce the patchwork of appropriate habitats available for emergence of RVFV vectors and diminish chances of RVFV activity. However, the 2016–2017 growing season saw a marked return to somewhat wetter conditions without any reported RVFV transmission. In general, the aggregate vector collections during this 5-year period follow patterns observed in climate measurements. During the 2017–2018 growing season, late and seasonally above average rainfall resulted in a focal RVF outbreak in one location in the study region. This unanticipated event is an indicator of cryptic RVF activity during post-epizootic period and may be a harbinger of RVFV activity in the coming years.
climate variability↗
High frequency scattering from corrugated stratified cylinders
Interest in applying radar remote sensing for the study of forested areas led to the development of a model for scattering from corrugated stratified dielectric cylinders. The model is used to investigate the effect of bark and its roughness on scattering from tree trunks and branches. The outer layer of the cylinder (bark) is assumed to be a low-loss dielectric material and to have a regular (periodic) corrugation pattern. The inner layers are treated as lossy dielectrics with smooth boundaries. A hybrid solution based on the moment method and the physical optics approximation is obtained. In the solution, the corrugations are replaced with polarization currents that are identical to those of the local tangential periodic corrugated surface, and the stratified cylinder is replaced with equivalent surface currents. New expressions for the equivalent physical-optics currents are used which are more convenient than the standard ones. It is shown that the bark layer and its roughness both reduce the radar cross-section. It is also demonstrated that the corrugations can be replaced by an equivalent anisotropic layer.
Sarabandi, Kamal↗