Angle Spread Research Articles

Resonant Scattering of Radiation Belt Electrons at Saturn by Ion Cyclotron Waves

AbstractBy constructing an empirical model of the spectral and latitudinal distribution of ion cyclotron waves on the basis of Cassini datasets, we investigate the resonant interactions between ion cyclotron waves and radiation belt electrons at Saturn. Calculations based on quasi‐linear bounce‐averaged diffusion coefficients show that at Saturn ion cyclotron waves can efficiently pitch angle scatter >∼1 MeV to tens of MeV electrons into the loss cone thereby inducing precipitation loss, while the mixed and momentum scattering effects are typically negligible. The resultant electron loss timescales range from a few to tens of minutes, which in fact decrease significantly with increasing L‐shell at L = 4–6. We also find that the kinetic effects introduced by pick‐up ring particles cause distinct changes in pitch angle scattering efficiency for lower energy electrons (<3 MeV at L = 5). Our results demonstrate that ion cyclotron waves play a significant role in the dynamics of Saturn's radiation belt electrons.

Introduction of Research Work on Laser Proton Acceleration and Its Application Carried out on Compact Laser–Plasma Accelerator at Peking University

Laser plasma acceleration has made remarkable progress in the last few decades, but it also faces many challenges. Although the high gradient is a great potential advantage, the beam quality of the laser accelerator has a certain gap, or it is different from that of traditional accelerators. Therefore, it is important to explore and utilize its own features. In this article, some recent research progress on laser proton acceleration and its irradiation application, which was carried out on the compact laser plasma accelerator (CLAPA) platform at Peking University, have been introduced. By combining a TW laser accelerator and a monoenergetic beamline, proton beams with energies of less than 10 MeV, an energy spread of less than 1%, and with several to tens of pC charge, have been stably produced and transported in CLAPA. The beamline is an object–image point analyzing system, which ensures the transmission efficiency and the energy selection accuracy for proton beams with large initial divergence angle and energy spread. A spread-out Bragg peak (SOBP) is produced with high precision beam control, which preliminarily proved the feasibility of the laser accelerator for radiotherapy. Some application experiments based on laser-accelerated proton beams have also been carried out, such as proton radiograph, preparation of graphene on SiC, ultra-high dose FLASH radiation of cancer cells, and ion-beam trace probes for plasma diagnosis. The above applications take advantage of the unique characteristics of laser-driven protons, such as a micron scale point source, an ultra-short pulse duration, a wide energy spectrum, etc. A new laser-driven proton therapy facility (CLAPA II) is being designed and is under construction at Peking University. The 100 MeV proton beams will be produced via laser–plasma interaction by using a 2-PW laser, which may promote the real-world applications of laser accelerators in malignant tumor treatment soon.

Evaluation of a GNSS for wave measurement and directional wave spectrum analysis

Wave buoys are important devices to monitor and analyze wave data for ocean and coastal engineering. A GNSS wave buoy is briefly introduced in the paper, which has high resolution to measure the buoy motion by vertical, north-south and west-east displacements and independent velocities in above three directions. Based on the displacements and velocities, statistical results, frequency spectra and directional spectra are analyzed, and results based on the displacements are compared with that from Waverider with a distance less than 6m deployed in the special sea water with the GNSS buoy. Wave profiles comparison show that GNSS buoy presented slightly large significant wave height and mean wave height due to its high sampling frequency, and resulted in smaller mean wave period than that from Waverider. Statisticaly, between the analyzing result of the GNSS and wave rider, the maximum error of wave height is about 5.5%; and the maximum difference of wave period is about 0.5s, when sampling frequency is similar. The energy spectra were basically consistent from these two devices. The peaks of directional spectra were similar but the spreading angle was smaller from GNSS. Results mean the GNSS device presents almost similar wave information to that from Waverider.

Harmonic structure of wave loads on a surface piercing column in directionally spread and unidirectional random seas

We investigate the harmonic structure of wave-induced loads on vertical cylinders with dimensions comparable to those used to support offshore wind turbines. Many offshore wind turbines are designed, so the structural resonance is two or three times the fundamental wave loading period, which may be excited by higher harmonics of wave loading. The suitability of a ‘Stokes-type’ model for force is examined. We analyse experimental data for unidirectional and directionally spread sea-states. We demonstrate that approximate harmonic components may be extracted from a random time series, using a novel signal processing method. The extracted harmonics are shown to follow a ‘Stokes-like’ model, where the higher harmonics in frequency are proportional to the n-th power of the linear inline force component and its Hilbert transform. Results show that the third harmonic component of force is fitted less well by this model, which is consistent with the literature. A key new result is that the harmonic coefficients for spread and unidirectional seas are nearly identical when fitted as powers of the linear inline force and its Hilbert transform. This finding has the potential to greatly simplify the process of generating harmonic data for new wavelength to cylinder and wavelength to depth ratios. This also implies that the size of the inline component of the ntextrm{th} harmonic for force in a directional sea relative to the same component in a unidirectional sea scales as cos ^n sigma _theta , where sigma _theta is the rms directional spreading angle of the incident wave field. Hence, higher harmonics will be of less importance in directionally spread seas than unidirectional ones. We show that the computationally fast harmonic decomposition approach taken here can reproduce the shape and magnitude of the loading from non-breaking waves waves in a wide range of realistic unidirectional and directionally spread sea-states. The proposed force model has potential as an engineering tool for computationally fast prediction of nonlinear wave loads.

The influence of particle size on the spread distance and angle of friction of granular materials

To produce a hazard map and thus provide mitigation measures against natural catastrophic events such as landslides, avalanches, and debris flows, it is necessary to determine the spread distance of such flows. There is a well-documented relationship between the angle of friction and the debris flow volume, allowing one to determine the possible distance a debris flow can travel. However, the effect of mean particle size (d50) and the sorting coefficient (Sc) on the final spread distance (Df) has received mere attention. In this study, a mini conical-shaped mould was used to measure the final spread distance (Df) and angle of friction (αf) for various dry granular material samples both in air and in water. Experimental results indicated that a granular material sample with a smaller d50 travel a longer distance compared to a sample with a higher d50. However, a sample with a smaller d50 results in a smaller angle of friction than the one with a higher d50. Conversely, a well-sorted sample has a smaller spread distance and larger angle of friction. Results also indicated that the spread distance in air is slightly larger and the angle of friction is slightly smaller than in water.

A sui generis whipping-instability-based self-sequencing multi-monodisperse 2D spray from an anisotropic microfluidic liquid jet device

Well-defined aerosols pave the way for versatile basic and applied research. Here, we demonstrate a unique whipping instability that generates from a high-aspect-ratio microfluidic device resulting in a unique steady-state gas-focused whipping jet (WJ) without any need for electrification. This WJ device emanates a multi-monodisperse whipping spray jet with a two-dimensional (2D) profile. We demonstrate this phenomenon based on various fluidic parameters theoretically and experimentally. The 2D WJ’s unique behavior is derived using analytical fluid dynamics to explain jet diameter, whipping regime, and spreading angle. The phenomenon is further characterized experimentally by measuring the angle with respect to the flow rate, the distances between droplets, the droplet shapes, and the reproducibility of these parameters. We also explain the precise fabrication of such inexpensive devices. Lastly, we highlight these devices’ potential use as sample environments in versatile applications ranging from cryoelectron microscopy over mass spectrometry to drug formulation and structural studies at X-ray free-electron lasers.

Theoretical Corrections of Instrumental Broadening Effect and Surface Property Measurement of Fluid at Low Scattering Angle by Surface Light Scattering Method

Theoretical Corrections of Instrumental Broadening Effect and Surface Property Measurement of Fluid at Low Scattering Angle by Surface Light Scattering Method

Precision Small Scattering Angle Measurements of Proton–Proton and Proton–Nucleus Analyzing Powers at the RHIC Hydrogen Jet Polarimeter

Precision Small Scattering Angle Measurements of Proton–Proton and Proton–Nucleus Analyzing Powers at the RHIC Hydrogen Jet Polarimeter

Investigation of Driver Lane Visibility According to Geometry of Road and Headlight Spread Angle

Investigation of Driver Lane Visibility According to Geometry of Road and Headlight Spread Angle

Wave-By-Wave Prediction in Narrowly Spread Seas Using Fixed- and Drifting-Point Wave Records: Validation Using Physical Measurements

Abstract Accurate and reliable phase-resolved prediction of ocean surface waves is crucial for many offshore operations in ocean engineering and marine science. One important application is in optimal control of a power take-off in a wave energy converter, leading to significantly higher power production. Our interest is forecasting wave fields based on measurements obtained from multiple upwave locations in moderate seas with small directional spreading angles, as occurs along the south coast of Australia. The prediction model, based on FFTs and propagation of waves according to the linear dispersion relation, is applied to both wave groups and irregular wave fields generated in a wave basin and, additionally, to ocean waves measured with drifting wave buoys. To account for spreading, the model numerically advances linear, plane (i.e., long-crested) waves in space at an optimum offset angle equal to the underlying sea-state root mean square spreading angle. Averaging predictions from a few slightly separated measurement locations, each weighted according to its estimated variance, results in more accurate predictions than from any single location. We also assess in detail the effect of drifting buoy measurements in both long-crested and short-crested seas using synthetic wave records and show that it is possible to satisfactorily reconstruct the signal at fixed points based on the Doppler shift felt by the drifting buoy. The reconstructed signals give much better predictions compared to those completely neglecting the effect of even rather slow drift due to current.

Scattering angles in Kerr metrics

Scattering angles for probes in Kerr metrics are derived for scattering in the equatorial plane of the black hole. We use a method that naturally resums all orders in the spin of the Kerr black hole, thus facilitating comparisons with scattering-angle computations based on the Post-Minkowskian expansion from scattering amplitudes or worldline calculations. We extend these results to spinning black-hole probes up to and including second order in the probe spin and any order in the Post- Minkowskian expansion, for probe spins aligned with the Kerr spin. When truncating to third Post-Minkowskian order, our results agree with those obtained by amplitude and worldline methods.

Phase-resolved wave prediction in highly spread seas using optimised arrays of buoys

In many offshore operations, including the operation of wave energy converters, phase-resolved wave prediction is essential for safety and efficiency. However, for sea-states with large directional spreading angles, wave prediction becomes increasingly difficult. This study investigates the benefit of exploiting concurrent surface-displacement time histories measured by a buoy in three degrees of freedom (DoF) to facilitate prediction in such highly spread sea-states. A direct comparison is made with arrays of sensors measuring in a single DoF using the same formulation. The arrays considered are extensively optimised along with multiple sets of representative angles used to describe wave propagation, which is assumed to be normally distributed. The performance of the scheme is tested on a range of synthetically generated, realistic sea-states comprising single and crossing swells prevalent along the south coast of Australia. Additional tests involve wind-sea and swell waves described using Ewans models. Accurate predictions are obtained for times up to three wave periods into the future, in typical cases. With the multiple sets of optimal angles obtained for each optimal array, we further enhance the capability of the scheme by aggregating and averaging the different predictions from these sets. We observe a marked increase in both performance with large spreading and tolerance to possible variation in mean wave directions.

Birch plywood as gusset plates in glulam frame via mechanical connectors: A combined experimental and numerical study

Birch is a short-lived hardwood species widespread in the Northern Hemisphere. Plywood made from birch has superior mechanical properties compared with that made from most softwoods, which makes it suitable for structural application. In this study, the feasibility of using birch plywood as gusset plates in timber-timber connections is presented. Test frames consisting of birch plywood gussets and glulam beams connected by nails were built and tested. A 2D analytical model based on truss theory and a 3D finite element model were proposed and constructed. Both models showed satisfactory agreements with the test results in terms of stiffness and strength. Tensile failure on the birch plywood gussets along the outermost row of nail holes was observed in the experiment. The observed failure modes and the stress distributions in the 3D numerical model suggest that the spreading angle (Whitmore effective width) theory should be considered in the design phase of birch plywood gusset plates. Besides, a modified spreading angle theory is proposed to both approximate the stress distribution and predict the load-bearing capacity.

An Experimental Investigation of Supercritical Methane Injection Characteristics in a CO2 Environment

Abstract Clean energy generation is gaining significant attention from industries, academia, and governments across the globe. The Allam cycle is one such technology that has been under focus due to its efficiency, environmental friendliness, and economics. This is a direct-fired cycle operating at supercritical conditions using carbon dioxide as a working fluid. Fuel or oxidizer jet mixing with CO2 is a vital phenomenon that governs combustion efficiency, and it is not well understood for the Allam cycle conditions. This paper experimentally investigated the jet characteristics of a methane jet injected into a subcritical to supercritical carbon dioxide environment. A wide range of injection pressures and temperatures were targeted between subcritical to supercritical conditions. Unlike previous studies, the current work focused on injecting lower-density (methane) jets into higher-density (carbon dioxide) environments. Schlieren imaging and methane absorption measurements were simultaneously performed with a CMOS high-speed camera and a 3.39 μm infrared laser. Specifically, we looked at the classical injection parameter of jet spreading angle, which was classically established to be mainly a density ratio function. Here, the jet cone angle was obtained from the postprocessed schlieren imaging. The jet cone angle is a critical characteristic parameter that describes the entrainment rate in a jet; thus, it is a crucial parameter in understanding the nature of the jet. The laser measurements were only used as an additional check to confirm the entry time of methane into the chamber filled with carbon dioxide. Notably, this paper makes a detailed comparison between the jet cone angles of jets with a density ratio. The result showed that the classical correlations, such as Abramovich's theory applied to submerged turbulent gas jets developed for low-density ratio jets, were unsuitable for higher-density ratio jets. It was also observed that the divergence angles were dependent not only on density ratio but also on other parameters such as pressure ratios and reduced pressures.

Interplay of temperature and calcium content in beta-casein solutions: From controlled self-aggregation of micelles in bulk to the design of stable foams

We describe in this study the aggregation behaviour of β-casein micelles from milk in bulk aqueous solution as function of both temperature and calcium content, and its influence on the foaming properties, in order to test if the different aggregation states of β-casein makes possible the design of proteins-based thermoresponsive foams. First, we characterized the morphology of the self-assembled β-casein molecules in solution by coupling turbidity measurements, Dynamic Light Scattering and Small Angle Neutron Scattering. They self-organize into individual micelles at low temperature (20°C) whatever the calcium content, and transit in a reversible way into aggregates of micelles at large temperature in presence of calcium, with a threshold transition that depend both on temperature and calcium content. The micelles aggregation is driven by the calcium through association with serine phosphate groups localized on the hydrophilic part of the β-casein. In the micelles regime, we demonstrated that the addition of calcium tunes the aggregation number of unimers per micelle in the same way than an increase of temperature through a change of hydrophobic interactions. The hydrophilic chains of the corona are however in a good solvent and interact through excluded volume interactions, even when the β-casein micelles aggregates themselves. The internal molecular structure of the micelles is thus not modified by calcium bridges, which explains the complete reversibility of the aggregation process over temperature cycling. Second, we studied the foam stability versus time as a function of the temperature and calcium content by measuring the kinetic evolution of both the foam volume and the liquid fraction. Foams produced by solutions containing only β-casein micelles were stable in terms of foam volume on a timescale of 1 h at 20°C but drained quickly. However, foams become unstable when the temperature was increased above 20°C. In presence of calcium, the aggregation of β-casein micelles inside the foam liquid channels enabled to increase foam stability at larger temperature by acting as a cork, which slows down the drainage. The increase of foam stability by such aggregates is however not sufficient on the long term to allow the design of thermoresponsive foams.

Bioinspired Meta‐Reflection‐Splitter for Near‐Infrared Laser Stealth with Large Scattering Angle

AbstractMetasurface based phase manipulation has shown great capable of controlling anomalous reflection for low observability against laser active detection. However, current meta‐based designs for laser stealth in near‐infrared (NIR) range suffer from small scattering angles and complex fabrication process, and this hinders their mass productivity and flexible application in actual environments. Here, a bioinspired strategy is proposed to design a meta‐reflection‐splitter with a large scattering angle and strongly extinct specular reflection for NIR laser stealth, motivated by the color splitting effect on the green scale of butterfly Diaethria clymena. The biological reflection splitting is demonstrated to originate from the 180° phase difference of reflection created by the unsymmetrical laminae on densely arranged ridges. A simple etching‐free approach is further developed to generate large‐scale meta‐reflector‐splitter by self‐assembly of colloidal particles. This large‐area meta‐reflector‐splitter shows high‐efficient low observability (ultralow specular reflectance <1%) accompanied by a scattering angle of nearly 50° under the 1064 nm laser detection as well as a low mid‐infrared emissivity. This work sheds light on the phase manipulation of biophotonic structures and thus benefits the innovation in advanced optical materials and devices.

Dynamic Light Scattering Plus Scanning Electron Microscopy: Usefulness and Limitations of a Simplified Estimation of Nanocellulose Dimensions

Measurements of nanocellulose size usually demand very high-resolution techniques and tedious image processing, mainly in what pertains to the length of nanofibers. Aiming to ease the process, this work assesses a relatively simple method to estimate the dimensions of nanocellulose particles with an aspect ratio greater than 1. Nanocellulose suspensions, both as nanofibers and as nanocrystals, are subjected to dynamic light scattering (DLS) and to field-emission scanning electron microscopy (FE-SEM). The former provides the hydrodynamic diameter, as long as the scatter angle and the consistency are adequate. Assays with different angles and concentrations compel us to recommend forward scattering (12.8°) and concentrations around 0.05-0.10 wt %. Then, FE-SEM with magnifications of ×5000-×20,000 generally suffices to obtain an acceptable approximation for the actual diameter, at least for bundles. Finally, length can be estimated by a simple geometric relationship. Regardless of whether they are collected from FE-SEM or DLS, size distributions are generally skewed to lower diameters. Width distributions from FE-SEM, in particular, are well fitted to log-normal functions. Overall, while this method is not valid for the thinnest fibrils or for single, small nanocrystals, it can be useful in lieu of very high-resolution techniques.

Mantle Tomography of Central‐Eastern USA: Influence of Inversion Volume Size

AbstractTeleseismic tomography is a powerful tool to study the 3‐D structure of the upper mantle beneath a local seismic network, but the robustness of its images has been challenged by the increasing size of the study volume in recent studies. This is because teleseismic tomography uses relative travel‐time residuals (RTTRs) that are contaminated more by the whole‐mantle heterogeneity for a larger study region. In this work, we correct the RTTRs of teleseismic events for the mantle heterogeneities outside the study volume using two global tomographic models. Our results show that the whole‐mantle correction is necessary when a study region is wider than ∼10°, and the maximum outside residual reaches 1.2 s for a study region of ∼35° wide. After the whole‐mantle correction, those teleseismic events with a large ray spread angle are still useful for tomographic imaging. Applying this approach to teleseismic travel‐time data recorded by the USArray, we obtain a high‐resolution 3‐D P‐wave velocity (Vp) model beneath the central and eastern United States. It shows three low‐velocity anomalies beneath the New Madrid Seismic Zone, the East Tennessee Seismic Zone, and the South Carolina Seismic Zone, suggesting that lithospheric weakness induced by fluids may play an important role in reactivating the intraplate seismic zones. The passage of the Bermuda hotspot and remnants of the subducted Farallon slab in the lower mantle might be responsible for the fluid release and lithospheric weakening, which reactivated ancient rifts and suture zones in the crust and facilitated the formation of the intraplate seismic zones.

Effect of high temperature on nanopores in cokes

Small Angle Neutron Scattering and Ultra Small Angle Neutron Scattering were used to study the effect of annealing at temperatures of 1400 and 1600 °C, in an inert atmosphere, on the pore size distribution of three cokes prepared from Australian coals. The pore size range investigated was 1 nm to 2 µm. It was found that annealing substantially changed the size distribution of these pores in similar ways for all three cokes examined, despite the difference in rank and maceral composition of the starting coals. The pore sizes at which the greatest percentage changes in numbers occurred on heating was around 10 nm, with an increase in the number of both open and closed pores, by up to a factor of four after annealing at 1600 °C. For pores in the size range 100 nm to 2 µm, the number of closed pores decreased slightly and the number of open pores increased substantially; new open pores were created. The percentage increase in pore numbers introduced by annealing decreased with increasing pore size above 100 nm, but even at 2 µm pore radius, some samples showed a 50 % increase in total pore numbers. Annealing at greater temperature or longer time had a greater effect on pore numbers.

Quantifying structure and dynamics of bound and bulk polymer in tailor-made rubber-silica nanocomposites

The dynamics of long polymer chains in the presence of nanoparticles have been investigated. The nanocomposites of interest were inspired by tire industry-like rubber materials and consisted of entangled polyisoprene linear chains mixed with chemically pre-treated silica nanoparticles. Combining rheology, dielectric spectroscopy, and neutron spin echo measurements, we measured the modification of the polymer chain dynamics from bulk state to high filler concentration over a broad range of time and length scales. We show that the end-to-end relaxation does not seem to be impacted, whereas the polymer dynamics is significantly slowed down at a very local scale in the presence of nano-fillers. In addition to this length scale dependent different dynamics, additional Neutron Spin Echo spectroscopy experiments and Small Angle Scattering on labelled polymer chains, irreversibly bound to the filler surface and re-dispersed in a fully deuterated matrix, revealed a negligible dynamical behavior of this particular population of localized chains in the rubber layer. The conformational statistics of these chains is that of self-avoiding walk train within a shell that is thinner than the size of the chain. To the best of our knowledge, this work is the first of its kind which measures the single chain form factor in the bound layer of chemically multi-linked chains to the filler surface.