Miracle-dz/UniFAR-FTUs huggingface dataset:
DISCOVERING THE POSITRON (II)*

THIS remark is often repeated in textbooks and manuals on modem physics. It is singled out here for several reasons: (i) Its innocent, matter-of-fact tone conceals one of the most intricate and interesting chapters in the history of scientific discovery; (2) it encourages an analogy between discoveries within microphysics, and quite noncomparable discoveries within, e.g., natural history; and (3) the actual discovery of the positron, in all its dimensions, constitutes an instructive example of the interplay of theory and experiment within physical science, one of the best a historian, or logician, of science could ever hope for. The positron packet can be dipped into in three different ways. The physicist reaches into this complex of concepts to facilitate his thinking within e.g. quantum field theory, or the experimental study of cosmic rays. The historian of physics attends to the exciting interplay of ideas within the microphysics of the 1920s--the better to perceive the initial resistance to the positron-idea, as well as to trace the theoretical evolution which resulted in the claim that positive electrons exist. The logician will focus upon the internal structure of the arguments and concepts actually employed, and still being employed, by those physicists who have played major roles in this story. In the history of science the positron discovery constitutes at once one of the richest, and yet one of the most neglected, areas of inquiry. The discovery of the positive electron was a discovery of three different particles. I choose to put the matter this way, rather than to
Three‐dimensional numerical ray tracing on a phenomenological ionospheric model

In this paper we present a numerical and step by step ray‐tracing method on a phenomenological ionospheric electron density (Ne) model, the TaiWan Ionospheric Model (TWIM), which is constructed from the FormoSat3/Constellation Observing System for Meteorology, Ionosphere and Climate (FS3/COSMIC) ionospheric radio occultation data. With the Earth's magnetic field and horizontal Ne gradient effects included, efficient methods for calculating ray parameters such as the ground range, reflection height, phase path, and group path are presented. The three‐dimensional TWIM consists of vertically fitted α‐Chapman‐type layers, with distinct F2, F1, E, and D layers, for which the layer parameters such as peak density, peak density height, and scale height are represented by surface spherical harmonics. This way the continuity of Ne and its derivatives is maintained. This is important for practical schemes for providing reliable radio propagation predictions. The methodology is successfully applied to a practical high‐frequency transmitter for oblique incidence ray tracing and further evaluated by comparing synthetic vertical ionograms generated by the method with experimental ionosonde observations.
Ternary vector cross products

Ternary vector cross products are studied in their own right. Results include a new proof of Hurwitz's theorem and a 'principle of duplicity'. Upon breaking the symmetry in eight dimensions, by choosing a preferred axis, this last principle implies the well known triality principle for octonions and SO(8) transformations. In displaying canonical forms it helps to put the eight basis vectors in correspondence with the eight points of the three-dimensional affine geometry over F2.
Air mass transformation processes over the Southwestern region of the ice-covered Sea of Okhotsk during cold air outbreaks

Radio sounding and in-situ observations at land-based (26 January-11 February 1998) and ship stations (4-11 February 1998) were performed over the southwestern Sea of Okhotsk covered with sea ice to estimate turbulent heat flux and investigate characteristics of thermodynamic air mass transformation processes during cold-air outbreaks. Surface heat flux estimations were carried out using two indirect methods; an atmospheric heat budget analysis using the radio sounding data at three stations and a bulk method utilizing meteorological and sea ice thickness data obtained by the ship observations. The estimated total upward turbulent heat flux over the analyzed area was approximately 100 Wm-2 even within the intense cold-air outbreak period. The height of the mixing layer associated with this small amount of the heat flux is only about 1 km, which implies that sea ice acts as an insulating material between the ocean and atmosphere and thus significantly reduces the turbulent heat fluxes. Nevertheless, the upward turbulent heat flux from the ice surface was found to be non-negligible during cold-air outbreaks and it is suggested that the sea ice grows through the sea or ice surface cooling.
A physical model for the hysteresis phenomenon of the ultrathin ZrO2 film

This work studies and presents an inner-interface trapping physical model for the ultra-thin (effective oxide thickness=15 A) zirconium oxide (ZrO2) film to explain its hysteresis phenomenon. The shift of the capacitance–voltage characteristics swept from accumulation to inversion and then swept back with light illumination is about 110 mV, which is larger than the shift without light illumination (∼45 mV). The mobile ion effect is obviated using bias-temperature stress measurement. The proposed model successfully explains not only the phenomenon but also the thickness effect for the capacitance–voltage characteristics and the different turn-around voltages of the current density–voltage characteristics of the zirconium dielectrics.
Jovian Orbit Capture and Eccentricity Reduction Using Electrodynamic Tether Propulsion

The use of electrodynamic tethers for propulsion and power generation is attractive for missions to the outer planets, which are traditionally handicapped by large propellant requirements, large times of flight, and a scarcity of power available. In this work, the orbital dynamics of a spacecraft using electrodynamic tether propulsion during the mission phases of capture, apojove pump down and perijove pump up, in the Jovian system are investigated. The main result is the mapped design space involving mission duration, tether length, and minimum perijove radius. Phase-free flyby sequences are also included, which provide performance upper bounds for a given mission architecture. It is found to be advantageous to use inbound-only flybys of the Galilean moons during capture. Flybys during the apojove pump down phase are only useful in conjunction with a perijove-raising mechanism at apoapse such as solar perturbations or a small propulsive maneuver. The electrodynamic tether system is also shown to be capab.
Asymmetric rotational axis reconstruction of grating-based x-ray phase contrast tomography of the human cerebellum

The brain has an outstanding functional importance in the human organism. Therefore, there is a strong need for three-dimensional brain imaging modalities. Magnetic resonance imaging provides deep insights but its spatial resolution is insufficient to study the structure on the cellular level. X-ray absorption microtomography yields the necessary spatial resolution, but shows only marginal contrast between the different types of brain tissue. Alternatively, differential X-ray phase contrast obtained with grating interferometry, which is known for much better differentiations between soft tissues can be used for the visualization of the human brain. As important structures of the human brain such as the human thalamus have dimensions of several centimeters, a large field of view is required. In the present communication, we report an evaluation of grating-based X-ray phase contrast microtomography in the off-axis modus which allows to expand the field of view up to a factor of two but may reduce the image quality. We demonstrate that tomograms with comparable contrast-to-noise values, about 10%, and 50% inferior spatial resolution can be generated with off-axis measurements. As one can reduce the effective pixel size up to a factor of two, the choice of an asymmetrical rotation axis can give rise to an improvement of the spatial resolution by 20%.
ON THE ENERGY DECAY OF TWO COUPLED STRINGS THROUGH A JOINT DAMPER

Abstract The stabilization of two coupled strings with fixed boundaries attached to a linear damper at their joint of connection is studied. The transformation used in a previous approach to convert the second order hyperbolic equations into a first order system results in a loss of equivalence. It is shown that when the ratio of the wave speeds of the two strings is an irrational number, the system is asymptotically, but not exponentially, stable. The method is applied to the other cases with different joint and boundary conditions.
Comparison and Analysis of Heat Transfer in Aluminum Foam Using Local Thermal Equilibrium or Nonequilibrium Model

Aluminum foams are favorable in modern thermal engineering applications because of the high thermal conductivity and the large specific surface area. The present study aims to investigate an application of porous aluminum foam by using the local thermal equilibrium (LTE) and local thermal nonequilibrium (LTNE) heat transfer models. Three-dimensional simulations of laminar flow (porous foam zone), turbulent flow (open zone), and heat transfer are performed by a computational fluid dynamics approach. In addition, the Forchheimer extended Darcy's law is employed to evaluate the fluid characteristics. By comparing and analyzing the average and local Nusselt numbers, it is found that the LTNE and LTE models can reach the same Nusselt numbers inside the aluminum foam when the air velocity is high, meaning that the aluminum foam is in a thermal equilibrium state. Besides, a high interfacial heat transfer coefficient is required for the aluminum foam to reach a thermal equilibrium state as the height of the aluminum foam is reduced. This study suggests that the LTE model can be applied to predict the thermal performance at high fluid velocities or for the case with a large height.
Quantum wells to quantum dots: 640x512 pixels Long-Wavelength Infrared (LWIR) Quantum Dot Infrared Photodetector (QDIP) imaging focal plane array

We have exploited the artificial atom-like properties of epitaxially grown self-assembled quantum dots (QDs) for the development of high operating temperature long wavelength infrared (LWIR) focal plane arrays (FPAs). QD infrared photodetectors (QDIPs) are expected to outperform quantum well infrared detectors (QWIPs) and are expected to offer significant advantages over II-VI material based FPAs. We have used molecular beam epitaxy (MBE) technology to grow multi-layer LWIR Dot-in-a-Well (DWELL) structures based on the InAs/InGaAs/GaAs material system. This hybrid quantum dot/quantum well device offers additional control in wavelength tuning via control of dot-size and/or quantum well sizes. DWELL QDIPs were also experimentally shown to absorb both 45o and normally incident light. Thus we have employed a reflection grating structure to further enhance the quantum efficiency. The most recent devices exhibit peak responsivity out to 8.1 microns. Peak detectivity of the 8.1 μm devices has reached ~ 1 x 1010 Jones at 77 K. Furthermore, we have fabricated the first long-wavelength 640x512 pixels QDIP imaging FPA. This QDIP FPA has produced excellent infrared imagery with noise equivalent temperature difference of 40 mK at 60K operating temperature.
Flow beneath a stagnant film on water: the Reynolds ridge

Surface-active material is present in most naturally occurring water samples, and it naturally diffuses steadily to free surfaces, where it both reduces the surface tension and gives the surface elastic properties which enable it to resist compression. When the water flows so that the surface layer is trapped and compressed against a fixed shallow-draught barrier the film material makes the surface incompressible, and flow beneath the barrier forms a viscous boundary layer under the film. The stresses associated with this boundary layer are found to distort the surface in the region of the leading edge of the film, giving rise to a phenomenon which is commonly observed in nature and which has been called the Reynolds ridge. This paper describes experimental work on the measurement of the ridge, and compares the results with a theoretical model due to Harper & Dixon. Good agreement is indicated.
A priori estimates for prescribing scalar curvature equations

We obtain a priori estimates for solutions to the prescribing scalar curvature equation (1) R(x)n-2 on Sn for n > 3. There have been a series of results in this respect. To obtain a priori estimates people required that the function R(x) be positive and bounded away from 0. This technical assumption has been used by many authors for quite a few years. It is due to the fact that the standard blowing-up analysis fails near R(x) = 0. The main objective of this paper is to remove this well-known assumption. Using the method of moving planes, we are able to control the growth of the solutions in the region where R is negative and in the region where R is small, and thus obtain a priori estimates on the solutions of (1) for a general function R which is allowed to change signs.
Numerical Simulation of Fully Passive Flapping Foil Power Generation

A fully passive flapping foil turbine was simulated using a two-dimensional Navier–Stokes solver with two-way fluid-structure interaction at a Reynolds number based on freestream flow Re=1100 and 1.1×106 with a NACA 0012 foil. Both pitch angle and angle-of-attack control methodologies were investigated. Efficiencies of up to 30% based on the Betz criterion were found using pitch control, which is commensurate with values reported in the literature for prescribed motion studies. Nonsinusoidal foil pitching motions were found to be superior to sinusoidal motions. Efficiencies exceeding 41% were found using angle-of-attack control, and nonsinusoidal angle-of-attack profiles were found to be superior. The key to improving the efficiency of energy extraction from the flow is to control the timing of the formation and location of the leading-edge vortex at crucial times during the flapping cycle and the interaction of the vortex with the trailing edge. Simulations using Reynolds-averaged Navier–Stokes turbulenc.
Evidence of Kelvin Waves in California's Marine Layer and Related Eddy Generation

Abstract Evidence suggests that an internal solitary Kelvin wave exists in the marine layer along California. The marine layer is lifted over the central coast by a weak cyclonic circulation. This “bump,” initially 850 m high, moves to the north along the coast at 6 m s−1. The undisturbed layer depth is 100–200 m thick. The crest height of the wave decreases to 500 m farther north. Winds under the raised marine layer are southerly. The leading edge of the wave is easily followed by satellite as the thickened marine layer is marked by overcast stratus. A greatly curved offshore leading edge indicates that nonlinear effects are important. Offshore scale in the overcast is about 300 km in the south and 50 km in the north. Surface pressure gradient alongshore is closely related to the marine layer depth. The surface wind shifts when the leading and trailing edge of the wave passes. Northerly wave progression ceases at the sharp bend formed by Cape Mendocino. At this time, a vortex is formed in the marine laye.
Controlling mesoscopic phase separation near electronic topological transitions via quenched disorder in ternary diborides

A phase separation driven by the negative compressibility of the electron gas, near electronic topological transitions (ETT), could drive the system at the verge of a catastrophe. We show here that the metastable phases very close to the ETT transition are observed in a mesoscopic phase separation (MePhS) driven by the quenched lattice disorder. By using high resolution synchrotron radiation x-ray powder diffraction we have identified the MePhS for the intermetallic ternary Mg1−xAlxB2 in the proximity of two ETTs: the first at x1 = 0.1 and the second at x2 = 0.3. We have identified the competition between a first ‘relaxed’ (R) hole poor and a second ‘tense’ (T) hole rich phase, and by micro-Raman we observe the splitting of the in-plane phonon E2g mode in the proximity of the first ETT at x = 0.1. The anisotropic quenched disorder due to a random distribution of Al3+ and Mg2+ ions both in the axial (c axis) direction and planar (ab plane) direction, probed by x-ray diffraction and Raman data, is proposed to be the physical variable that allows the formation of metastable phases near the critical points of electronic topological transitions, where Feshbach shape resonances in interband pairing amplifies the superconducting critical temperature.
Picosecond time‐resolved measurements of crystallization in noble metals

Crystallization rates in pure metals have been measured by monitoring changes in reflectivity on a picosecond time scale during pulsed laser quenching. Multilayered films were used to establish that the transient decreases in reflectivity correspond to melting. Depth profiling with Auger electron spectroscopy on laser‐irradiated areas showed complete mixing of the layers, which could only have occurred by melting. Crystallization velocities as high as 100 m/s were measured. These growth speeds are too large to be the result of a crystallization process governed by liquid state diffusion. The results of computer simulations based on a collision‐limited growth model for crystallization were consistent with the measurements.
Modeling Mesoscale Cellular Structures and Drizzle in Marine Stratocumulus. Part I: Impact of Drizzle on the Formation and Evolution of Open Cells

Abstract A new modeling framework is used to investigate aerosol–cloud–precipitation interactions and dynamical feedbacks at the mesoscale. The focus is on simulation of the formation and evolution of cellular structures that are commonly seen in satellite images of marine stratocumulus clouds. Simulations are performed at moderate resolution in a 60 × 60 km2 domain for 16 h to adequately represent the mesoscale organization associated with open cells and precipitation. Results support the emerging understanding that precipitation plays a critical role in the formation and evolution of open cells. Evaporation of raindrops generates a dynamic response that manifests itself in cellular organization of updrafts and downdrafts and promotes and sustains the formation of an open cellular structure in cloud fields. Vertical motion in open-cell centers with thin clouds is minimal. It is shown that a mean surface rain rate as low as 0.02 mm day−1 is, for the case considered, sufficient to promote the formation of .
Inner-shell excitation energy and autoionization rates for Li-, Be-, B-like ions with Z = 6–54

Absolute energies of the autoionization states 1s2s22pn [LSJ] with n = 0–2, 1s2s2pn [LSJ] with n = 1–3 and 1s2pn [LSJ] with n = 2–4 and non-autoionizing states 1s22s22pn [LSJ] with n = 0–1, 1s22s2pn [LSJ] with n = 0–2 and 1s22pn [LSJ] with n = 1–3 were calculated for ions with nuclear charge Z = 6–54 by using the 1/Z perturbation theory method. Relativistic corrections were taken into account in the frame of the Breit operators. The autoionization rates for the above-mentioned autoionization states for ions with Z = 6–54 were computed as well. These data are very important for modelling the satellite spectra produced by high-temperature plasma with thermal and non-thermal electrons.
Particle paths in wavy vortices

The authors study the paths of individual fluid particles moving in velocity fields which model Taylor vortices close to the onset of the wavy instability. In particular, they consider the possibility of particle transport between vortices. By studying the flow in the context of dynamical systems theory, they show that this arises through the destruction of invariant surfaces which form the vortex boundaries in the absence of the wave. Particles able to pass between vortices follow chaotic trajectories (in the sense of showing sensitive dependence on initial conditions). This results in a mixing process that has some properties in common with diffusion.
GROSS PROPERTIES OF FIVE Scd GALAXIES AS DETERMINED FROM 21-CENTIMETER OBSERVATIONS.

Abstract : Neutral hydrogen studies of the five Scd galaxies M33, NGC 2403, IC342, M101 and NGC6946 have revealed substantial similarities in their hydrogen distributions and rotation curves. It is found that about 80% of the observable HI lies within the boundary defined by the Holmberg diameter for each galaxy. The ratio of the HI mass to the total mass contained within this same boundary has a mean value of about 0.11. The central HI surface density is also nearly a constant within the Scd classification. We find that all the HI global properties and ratios are nearly constant or scale approximately with Holmberg radius or total mass. An observed correlation of maximal rotation velocity with Holmberg radius allows characterization of the total mass with only one parameter. Because of the very flat rotation curves observed for thse Scd galaxies, total masses extrapolated to infinite radius are not known. Surface mass-luminosities ratios must reach values of about 20 at the Holmberg radius. (Author)
Theoretical Analysis of Shape Transformations of Liposomes Caused by Microtubule Assembly

When a cytoskeletal protein, tubulin, is enclosed inside a liposome and the tubulin molecules assemble to form microtubules, a spherical liposome transforms into a rugby-ball shape due to the mechanical force generated by the microtubule assembly. Tubular projections of membrane then grow from both ends of the rugby-ball liposome, and finally the liposome transforms into a characteristic shape consisting of a central ellipsoid and straight tubes. Here we investigate mechanical aspects of the shape transformation of liposomes caused by microtubule assembly. We calculate the liposome shape using a mathematical model based on the notion of the minimum bending energy of the liposome membrane. The force generated by the microtubule assembly is incorporated in the model by considering the local force balance of the membrane. Numerical analysis of the model gives a series of shapes which are similar to the shapes observed in experiments. The force-transformation relationship obtained in our model predicts the ex.
Sensitivity of gyre-scale marine connectivity estimates to fine-scale circulation

Abstract. We investigated the connectivity properties of an idealized western boundary current system separating two ocean gyres, where the flow is characterized by a well-defined mean circulation as well as energetic fine-scale features (i.e., mesoscale and submesoscale currents). We used a time-evolving 3D flow field from a high-resolution (HR-3D) ocean model of this system. In order to evaluate the role of the fine scales in connectivity estimates, we computed Lagrangian trajectories in three different ways: using the HR-3D flow, using the same flow but filtered on a coarse-resolution grid (CR-3D), and using the surface layer flow only (HR-SL). We examined connectivity between the two gyres along the western boundary current and across it by using and comparing different metrics, such as minimum and averaged values of transit time between 16 key sites, arrival depths, and probability density functions of transit times. We find that when the fine-scale flow is resolved, the numerical particles connect pairs of sites faster (between 100 to 300 d) than when it is absent. This is particularly true for sites that are along and near the jets separating the two gyres. Moreover, the connectivity is facilitated when 3D instead of surface currents are resolved. Finally, our results emphasize that ocean connectivity is 3D and not 2D and that assessing connectivity properties using climatologies or low-resolution velocity fields yields strongly biased estimates.