Complete Understanding Of Physics Research Articles

Optimal finite-time processes in weakly driven overdamped Brownian motion

The complete physical understanding of the optimization of the thermodynamic work still is an important open problem in stochastic thermodynamics. We address this issue using the Hamiltonian approach of linear response theory in finite time and weak processes. We derive the Euler–Lagrange equation associated and discuss its main features, illustrating them using the paradigmatic example of driven Brownian motion in overdamped regime. We show that the optimal protocols obtained either coincide, in the appropriate limit, with the exact solutions by stochastic thermodynamics or can be even identical to them, presenting the well-known jumps. However, our approach reveals that jumps at the extremities of the process are a good optimization strategy in the regime of fast but weak processes for any driven system. Additionally, we show that fast-but-weak optimal protocols are time-reversal symmetric, a property that has until now remained hidden in the exact solutions far from equilibrium.

Magnetic Imprints of Eruptive and Noneruptive Solar Flares as Observed by Solar Dynamics Observatory

Abstract The abrupt and permanent changes of the photospheric magnetic field in the localized regions of active regions during solar flares, called magnetic imprints (MIs), have been observed for nearly the past three decades. The well-known coronal implosion model is assumed to explain such flare-associated changes but the complete physical understanding is still missing and debatable. In this study, we made a systematic analysis of flare-related changes of the photospheric magnetic field during 21 flares (14 eruptive and seven noneruptive) using the 135 s cadence vector magnetogram data obtained from the Helioseismic and Magnetic Imager. The MI regions for eruptive flares are found to be strongly localized, whereas the majority of noneruptive events (>70%) have scattered imprint regions. To quantify the strength of the MIs, we derived the integrated change of horizontal field and the total change of Lorentz force over an area. These quantities correlate well with the flare strength, irrespective of whether flares are eruptive or not, or have a short or long duration. Further, the free energy (FE), determined from virial theorem estimates, exhibits a statistically significant downward trend that starts around the flare time and is observed in the majority of flares. The change of FE during flares does not depend on eruptivity but has a strong positive correlation (≈0.8) with the Lorentz force change, indicating that part of the FE released would penetrate the photosphere. While these results strongly favor the idea of significant feedback from the corona on the photospheric magnetic field, the characteristics of MIs are quite indistinguishable from flares being eruptive or not.

The Newtonian gravity of irregular shapes using STL files and 3D printing

The gravitational interactions of irregular shapes are rarely discussed in the compulsory schooling system and sometimes even ignored at the university level. This omission is due to the complexities encountered in extending Newton's law of gravitation to bodies that are not spherical. However, a deep understanding of the link between the gravity and the shape is quite important to interpret some basic facts of nature. In this paper, we show how simple concepts can be used to create a more general algorithm that has been implemented in matlab to compute the gravity of irregular bodies. Shapes are described in terms of Standard Tessellation Language files, the standard format for 3D printing. This approach to teaching allows students to model physical bodies, and the 3D representation of complex problems can help students acquire a more complete understanding of physics.

Study of a Nonequilibrium Plasma Model of Surface Discharge and the Influencing Factors

The ultrafast mechanical switch is one of the core technologies in hybrid high-voltage direct current breakers. However, the insulation between contacts may suffer surface insulation failure at moments of large current interruption. Studies show that surface charges play an important role in surface insulation failure. To date, there is still a lack of complete physical understanding of the rules governing the generation, migration, and accumulation of surface charges. In this paper, we present a nonequilibrium plasma model to investigate the development rules of stage transformation (corona discharge, streamer discharge, and spark discharge) of surface discharge. Surface charge distributions considering the effects of voltage amplitude and insulation materials are also discussed. The results show that the stages of surface discharge can be identified from the discharge current. The surface charge will increase under a continuous voltage, and most of the surface charge density is within 100 μC/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Increasing the voltage amplitude is not conducive to the accumulation of positive charges. However, the surface charge density and discharge current increase along with the voltage amplitude. The discharge current variations of different materials are basically consistent. The surface charge density may be positively associated with the relative dielectric constant, whereas it is difficult to judge the direct relationship between the surface charges and discharge current.

Bayesian calibration for electrochemical thermal model of lithium-ion cells

Pseudo-two dimensional electrochemical thermal (P2D-ECT) model contains many parameters that are difficult to evaluate experimentally. Estimation of these model parameters is challenging due to computational cost and the transient model. Due to lack of complete physical understanding, this issue gets aggravated at extreme conditions like low temperature (LT) operations. This paper presents a Bayesian calibration framework for estimation of the P2D-ECT model parameters. The framework uses a matrix variate Gaussian process representation to obtain a computationally tractable formulation for calibration of the transient model. Performance of the framework is investigated for calibration of the P2D-ECT model across a range of temperatures (333 K263 K) and operating protocols. In the absence of complete physical understanding, the framework also quantifies structural uncertainty in the calibrated model. This information is used by the framework to test validity of the new physical phenomena before incorporation in the model. This capability is demonstrated by introducing temperature dependence on Bruggeman's coefficient and lithium plating formation at LT. With the incorporation of new physics, the calibrated P2D-ECT model accurately predicts the cell voltage with high confidence. The accurate predictions are used to obtain new insights into the low temperature lithium ion cell behavior.

Acoustic metamaterials for sound mitigation

We provide theoretical and numerical analyses of the behavior of a plate-type acoustic metamaterial considered in an air-borne sound environment in view of sound mitigation application. Two configurations of plate are studied, a spring-mass one and a pillar system-based one. The acoustic performances of the considered systems are investigated with different approaches and show that a high sound transmission loss (STL) up to 82 dB is reached with a metamaterial plate with a thickness of 0.5 mm. The physical understanding of the acoustic behavior of the metamaterial partition is discussed based on both air-borne and structure-borne approaches. Confrontation between the STL, the band structure, the displacement fields and the effective mass density of the plate metamaterial is made to have a complete physical understanding of the different mechanisms involved. Dans ce travail, nous présentons des études théoriques et numériques sur le comportement physique de métamatériaux acoustiques en plaque dans un environnement sonique dans le but de développer des systèmes pour l'isolation acoustique. Deux configurations sont analysées, une à base d'un système masse-ressort et une à base d'un système à piliers. Les performances acoustiques des systèmes en question ont été étudiées suivant différentes approches et ont montré l'obtention d'une perte en transmission (STL) allant jusqu'à 82 dB pour un métamatériau en plaque ayant une épaisseur de 0.5 mm. L'interprétation physique des performances acoustiques de ces métamatériaux est analysée à la base des deux approches sonique et vibratoire considérées dans ce travail. Une confrontation entre les résultats des pertes en transmission, la structure de bande, les champs de déplacement et la densité de masse effective du métamatériau est réalisée afin de comprendre les mécanismes physiques mis en jeu.

Local conformal symmetry: The missing symmetry component for space and time

Local conformal symmetry is usually considered to be an approximate symmetry of nature, which is explicitly and badly broken. Arguments are brought forward here why it has to be turned into an exact symmetry that is spontaneously broken. As in the BEH mechanism in Yang–Mills theories, we then will have a formalism for disclosing the small-distance structure of the gravitational force. The symmetry could be as fundamental as Lorentz invariance, and guide us towards a complete understanding of physics at the Planck scale.

(Invited) Direct Physical Understanding in Memristive Devices and Corresponding Device Models

Nanoscale devices composed of transition metal-oxide layers exhibiting a prominent resistance change (memristors) have been extensively researched for their technological potential. The mechanism for the reversible resistance change in these systems involves an interaction of many physical effects including electrochemistry, ion motion driven by electric fields and concentration gradients, and interactions with thermal effects. While a complete physical understanding is still in development, I will describe some of the insights gained from direct measurements using structurally and chemically-sensitive techniques with nanoscale resolution such as x-ray spectromicroscopy. Specifically, I will show recent studies utilizing scanning transmission x-ray microscopy (STXM) to observe oxygen migration in a working tantalum oxide memristor device. I will also describe ongoing work utilizing hard x-rays to probe the local bonding of Ta atoms within a memristor device. These studies will aid in developing a microscopic switching model, essential for guiding material selection, device engineering, and effective design of driving circuits. Ultimately, any utilization of this technology depends critically on predictive and microphysically accurate device models, and I will describe our work in this area.

Transient Analysis of the Thin-Wire Equiangular Spiral Antenna

The study of large antenna structures, compared to the duration of the input pulse times the speed of light, allows a better understanding of the pulse propagation and reflection by the antenna structure. Identifying which part of the antenna geometry contributes to radiation makes it possible to identify the relationship between the radiated field impulse response and the acceleration of charges due to the antenna geometry. To this end, this paper analyzes the thin-wire equiangular spiral antenna from a time-domain perspective and shows the role of the centripetal acceleration on its radiated field. An analytical expression for the time-domain radiated field is also presented with good match with the simulation results. This approach leads to a more complete physical understanding of the radiation process and, thus, to a more guided design process of thin-wire antennas in general.

Dry Sliding Contact Between Rough Surfaces at the Atomistic Scale

Although, a lot is known about the factors contributing to friction, a complete physical understanding of the origins of friction is still lacking. At the macroscale several laws have long since described the relation between load (Amontons, Coulomb), apparent and real area of contact (Bowden and Tabor), and frictional forces. But it is not yet completely understood if these laws of friction extend all the way down to the atomistic level. Some current research suggests that a linear dependence of friction on the real contact area is observed at the atomistic level, but only for specific cases (indentors and rigid substrates). Because continuum models are not applicable at the atomic scale, other modeling techniques (such as molecular dynamics simulations) are necessary to elucidate the physics of friction at the small scale. We use molecular dynamics simulations to model the friction of two rough deformable surfaces, while changing the surface roughness, the sliding speed, and the applied normal load. We find that friction increases with roughness. Also all sliding cases show considerable surface flattening, reducing the friction close to zero after repetitive sliding. This questions the current view of (static) roughness at the atomistic scale, and possibly indicates that the macroscopic laws of friction break down several orders of magnitude before reaching the atomic scale.

Physical interpretation of the Schott energy of an accelerating point charge and the question of whether a uniformly accelerating charge radiates

A core topic in graduate courses in electrodynamics is the description of radiation from an accelerated charge and the associated radiation reaction. However, contemporary papers still express a diversity of views on the question of whether or not a uniformly accelerating charge radiates suggesting that a complete physical understanding of the energy content of the fields surrounding an accelerating charge is still missing. It is argued in this paper that the missing insight is the precise physical meaning of the somewhat mysterious ‘Schott energy’ which is shown to be simply the difference between the energy in the bound electromagnetic fields of the accelerating charge and the amount of energy in the bound fields of a uniformly moving charge which has the same instantaneous velocity. This difference arises because the bound fields of a charge cannot respond ‘rigidly’ when the state of motion of a charge is changed by an external force. During uniform acceleration, the rate of change of this difference is just the negative of the rate at which radiation energy is created, and hence the power needed to accelerate a charged particle uniformly is just that which is required to accelerate a neutral particle with the same rest mass even though the charge is radiating. The errors in other analyses are also identified.

Physical Mechanisms Linking the Winter Pacific–North American Teleconnection Pattern to Spring North American Snow Depth

Abstract The wintertime Pacific–North American (PNA) teleconnection pattern has previously been shown to influence springtime snow conditions over portions of North America. This paper develops a more complete physical understanding of this linkage across the continent, using a recently released long-term, continental-scale gridded North American snow depth dataset and the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis data. An empirical orthogonal function–based filtering process is used to identify and isolate the interannual snow depth variations associated with PNA. Then linear and partial correlations are employed to investigate the physical mechanisms that link winter PNA with spring snow depth. In the positive phase of PNA, the enhanced PNA pressure centers lead to warmer temperatures over northwestern North America and less precipitation at midlatitudes. The temperature and precipitation pathways act independently and in distinct geographical regions, and together they serve to reduce winter snow depth across much of North America. Winter anomalies in the snow depth field then tend to persist into spring. Dynamic mechanisms responsible for the PNA-influenced North American precipitation and temperature anomalies, involving moisture transport and cold air intrusions, are confirmed in this study and also extended to continental snow depth anomalies.

The energization of relativistic electrons in the outer Van Allen radiation belt

The origin and dynamics of the Van Allen radiation belts is one of the longest-standing questions of the space age, and one that is increasingly important for space applications as satellite systems become more sophisticated, smaller and more susceptible to radiation effects. The precise mechanism by which the Earth’s magnetosphere is able to accelerate electrons from thermal to ultrarelativistic energies (E≫0.5 MeV) has been particularly difficult to definitively resolve. The traditional explanation is that large-scale, fluctuating electric and magnetic fields energize particles through radial diffusion1. More recent theories2,3 and observations4,5 have suggested that gyro-resonant wave–particle interactions may be comparable to or more important than radial diffusion. Using data collected simultaneously by multiple satellites passing through the magnetosphere at different distances from the Earth, we demonstrate that the latter of these is the dominant mechanism responsible for relativistic electron acceleration. Specifically, we identify frequent and persistent peaks in equatorial electron phase space density near or inside geosynchronous orbit that provide unambiguous evidence for local wave–particle acceleration. These observations represent an important step towards a more complete physical understanding of radiation belt dynamics and to the development of space-weather models.

Statistical analysis of hydroclimatic time series: Uncertainty and insights

Today, hydrologic research and modeling depends largely on climatological inputs, whose physical and statistical behavior are the subject of many debates in the scientific community. A relevant ongoing discussion is focused on long‐term persistence (LTP), a natural behavior identified in several studies of instrumental and proxy hydroclimatic time series, which, nevertheless, is neglected in some climatological studies. LTP may reflect a long‐term variability of several factors and thus can support a more complete physical understanding and uncertainty characterization of climate. The implications of LTP in hydroclimatic research, especially in statistical questions and problems, may be substantial but appear to be not fully understood or recognized. To offer insights on these implications, we demonstrate by using analytical methods that the characteristics of temperature series, which appear to be compatible with the LTP hypothesis, imply a dramatic increase of uncertainty in statistical estimation and reduction of significance in statistical testing, in comparison with classical statistics. Therefore we maintain that statistical analysis in hydroclimatic research should be revisited in order not to derive misleading results and simultaneously that merely statistical arguments do not suffice to verify or falsify the LTP (or another) climatic hypothesis.

The Complex Scaling Method for Many-Body Resonances and Its Applications to Three-Body Resonances

Resonance phenomena in quantum physics are very familiar in many fields of physics, but we have not yet obtained a complete physical understanding, mathematical description or computational treatment, especially in the case of many-body resonances. Recently, in experimental developments concerning unstable nuclear physics and heavy-ion nuclear reactions, much interest has been concentrated on many-body resonance problems. In the last quarter century, theoretical and mathematical treatments of many-body resonances have experienced great development through application of the complex scaling method (CSM). We can now treat resonant states of three-body systems in the same way as those of twobody systems. In this article, starting from the definition of a resonant state and discussion of its norm, we present a summary of recent studies of CSM to treat many-body resonances and applications to three-body resonant states in two-neutron halo nuclei and three-cluster systems.

On the dynamics of a slender rod

The moment equation for the space rotation of a slender rod about a fixed point on its axis is developed with the aid of a visual vector approach and is shown to have the same form as the moment equation for the plane rotation of a slender rod. Also, an analogy between the general rotation of the rod and the plane motion of a point expressed in polar coordinates is presented as an aid to the more complete physical understanding of the motion.