Classical Radiation Research Articles

Determination and evolution of fractal property of n-heptane pool fires caused by depressurization process in an aircraft cargo compartment

Fractality is one of the inherent characteristics to present the irregularity and self-similarity of an object. In this study, the fractal theory was applied to the fire scene under decreasing pressure in an aircraft cargo compartment, considering that the compartment is usually inaccessible in flight and flame images are a kind of convenient monitoring information compared to other detection methods. A series of n-heptane pool fires were performed under decreasing pressure with four depressurized rates. The flame image was captured by a video camera with fixed aperture and exposure time. The fractal dimension (FD) of flame images was computed via two approaches, i.e., the box-counting (BC) and differential box-counting (DBC) methods. The results show that n-heptane pool fires have a good fractal property for both binary and grayscale images. The FD via BC method shows little sensitivity with decreasing pressure. However, the FD via DBC method presents a significant linear relationship with a slope of 0.0016 in the range from 2.85 to 2.75 during the depressurization. The quantitative correlation was brought into the classical radiation modeling, and the exponential function between FD and MLR of n-heptane was established.

Quantum blackbody thermometry

Blackbody radiation sources are calculable radiation sources that are frequently used in radiometry, temperature dissemination, and remote sensing. Despite their ubiquity, blackbody sources and radiometers have a plethora of systematics. We envision a new, primary route to measuring blackbody radiation using ensembles of polarizable quantum systems, such as Rydberg atoms and diatomic molecules. Quantum measurements with these exquisite electric field sensors could enable active feedback, improved design, and, ultimately, lower radiometric and thermal uncertainties of blackbody standards. A portable, calibration-free Rydberg-atom physics package could also complement a variety of classical radiation detector and thermometers. The successful merger of quantum and blackbody-based measurements provides a new, fundamental paradigm for blackbody physics.

Ancient and recent introgression shape the evolutionary history of pollinator adaptation and speciation in a model monkeyflower radiation (Mimulus section Erythranthe).

Inferences about past processes of adaptation and speciation require a gene-scale and genome-wide understanding of the evolutionary history of diverging taxa. In this study, we use genome-wide capture of nuclear gene sequences, plus skimming of organellar sequences, to investigate the phylogenomics of monkeyflowers in Mimulus section Erythranthe (27 accessions from seven species). Taxa within Erythranthe, particularly the parapatric and putatively sister species M. lewisii (bee-pollinated) and M. cardinalis (hummingbird-pollinated), have been a model system for investigating the ecological genetics of speciation and adaptation for over five decades. Across >8000 nuclear loci, multiple methods resolve a predominant species tree in which M. cardinalis groups with other hummingbird-pollinated taxa (37% of gene trees), rather than being sister to M. lewisii (32% of gene trees). We independently corroborate a single evolution of hummingbird pollination syndrome in Erythranthe by demonstrating functional redundancy in genetic complementation tests of floral traits in hybrids; together, these analyses overturn a textbook case of pollination-syndrome convergence. Strong asymmetries in allele sharing (Patterson’s D-statistic and related tests) indicate that gene tree discordance reflects ancient and recent introgression rather than incomplete lineage sorting. Consistent with abundant introgression blurring the history of divergence, low-recombination and adaptation-associated regions support the new species tree, while high-recombination regions generate phylogenetic evidence for sister status for M. lewisii and M. cardinalis. Population-level sampling of core taxa also revealed two instances of chloroplast capture, with Sierran M. lewisii and Southern Californian M. parishii each carrying organelle genomes nested within respective sympatric M. cardinalis clades. A recent organellar transfer from M. cardinalis, an outcrosser where selfish cytonuclear dynamics are more likely, may account for the unexpected cytoplasmic male sterility effects of selfer M. parishii organelles in hybrids with M. lewisii. Overall, our phylogenomic results reveal extensive reticulation throughout the evolutionary history of a classic monkeyflower radiation, suggesting that natural selection (re-)assembles and maintains species-diagnostic traits and barriers in the face of gene flow. Our findings further underline the challenges, even in reproductively isolated species, in distinguishing re-use of adaptive alleles from true convergence and emphasize the value of a phylogenomic framework for reconstructing the evolutionary genetics of adaptation and speciation.

Interference caused by electromagnetic interactions

We consider interference fluxes of energy, momentum and angular momentum, describing the interaction of electric charges with constant and variable electromagnetic fields. Absorption and stimulated emission of atoms in the field of free and evanescent waves are described. It is shown that in the case of interaction with reactive fields, the momentum of an atom during absorption and stimulated emission does not change. A wave derivation of Planck’s formula based on the interference of the fields of classical thermal radiation and quantum zero-point oscillations is presented.

Relativity and radiation balance for the classical hydrogen atom in classical electromagnetic zero-point radiation

When teaching modern physics, every instructor must deal with the apparent failure of classical physics to prevent the radiation collapse of the nuclear atom. Here we review the understanding of the classical hydrogen atom in classical electromagnetic zero-point radiation, and emphasize the importance of special relativity. The crucial missing ingredient in earlier calculational attempts (both numerical and analytic) is the use of valid approximations to the full relativistic analysis. It is pointed out that the nonrelativistic time Fourier expansion coefficients given by Landau and Lifshitz are in error as the electromagnetic description of a charged particle in a Coulomb potential, and, because of this error, Marshall and Claverie’s conclusion regarding the failure of radiation balance is invalid. Rather, using Marshall and Claverie’s calculations, but restricted to lowest nonvanishing order in the orbital eccentricity (where the nonrelativistic orbit is a valid approximation to the fully relativistic electromagnetic orbit) radiation balance for classical electromagnetic zero-point radiation is shown to hold at the fundamental frequencies and associated first overtones.

Review of Filtered Rayleigh Scattering technique for mixing studies in supersonic air flow

Filtered Rayleigh Scattering or FRS is a non-intrusive laser diagnostic technique that is utilized to observe and quantify various flow properties in high-speed gas flows. In this technique, a laser beam is used to irradiate a portion of the gas under investigation. The receiving gas molecules scatter the incident laser beam in all the directions. The scattered radiation from a single molecule stems from the induced oscillations of the electron cloud that acts as a classical dipole radiator. The intensity of the net scattered radiation from all the molecules that are in random motion depend on the spatio-temporal fluctuations of the dielectric permittivity of the gas. The thermodynamic properties of the gas govern the nature of these variations and the resulting spectra of the scattered radiation is referred to as Rayleigh Brillouin spectrum. In high-speed gas flows applications, the bulk velocity of the gas molecules causes the entire scattered spectrum to be Doppler shifted from the lasing frequency. The extent of this shift is very significant in supersonic flows and this enables the isolation of the scattered spectrum from the laser reflections using a molecular notch filter. Measurement of flow properties can be made based on the intensity of the RBS signal that is collected by a charged coupled device. The FRS technique is also utilized to perform mixing measurements in binary mixture of gases in high-speed flows. In non-reacting mixing studies, helium is often used as a passive scalar and simulant gas for hydrogen fuel. Helium concentration measurements in supersonic flows based on the FRS technique require two independent experiments. The first experiment involves injection of helium gas and the second separate experiment requires air injection. The helium mole-fraction is retrieved from the FRS imaging data under the key assumptions that the total number density profiles and the extent of the Doppler shift that is associated with each one of the two independent experiments at the measuring plane are identically the same. In this review, the theory governing Rayleigh scattering and the FRS technique to retrieve helium mole-fraction in supersonic flow will be discussed in detail. Measurement results from recent FRS studies on complex vortex interactions in supersonic flow will be also presented and discussed as well as the impact on the results of a departure from the key assumptions in FRS mixing studies will be analyzed for a canonical parallel injection using strut injector in supersonic flow.

Quantum Electrodynamic Control of Matter: Cavity-Enhanced Ferroelectric Phase Transition

The light-matter interaction can be utilized to qualitatively alter physical properties of materials. Recent theoretical and experimental studies have explored this possibility of controlling matter by light based on driving many-body systems via strong classical electromagnetic radiation, leading to a time-dependent Hamiltonian for electronic or lattice degrees of freedom. To avoid inevitable heating, pump-probe setups with ultrashort laser pulses have so far been used to study transient light-induced modifications in materials. Here, we pursue yet another direction of controlling quantum matter by modifying quantum fluctuations of its electromagnetic environment. In contrast to earlier proposals on light-enhanced electron-electron interactions, we consider a dipolar quantum many-body system embedded in a cavity composed of metal mirrors, and formulate a theoretical framework to manipulate its equilibrium properties on the basis of quantum light-matter interaction. We analyze hybridization of different types of the fundamental excitations, including dipolar phonons, cavity photons, and plasmons in metal mirrors, arising from the cavity confinement in the regime of strong light-matter interaction. This hybridization qualitatively alters the nature of the collective excitations and can be used to selectively control energy-level structures in a wide range of platforms. Most notably, in quantum paraelectrics, we show that the cavity-induced softening of infrared optical phonons enhances the ferroelectric phase in comparison with the bulk materials. Our findings suggest an intriguing possibility of inducing a superradiant-type transition via the light-matter coupling without external pumping. We also discuss possible applications of the cavity-induced modifications in collective excitations to molecular materials and excitonic devices.

The relation between quantum and classical field theory with a classical source.

Classical field theory is about fields and how they behave in space-time. Quantum field theory, in practice, usually seems to be about particles and how they scatter. Nevertheless, classical fields must emerge from quantum field theory in appropriate limits, and Michael Duff showed how this happens for the Schwarzschild solution in perturbative quantum gravity. In a series of papers, we and others have shown how classical radiation from an accelerated charge emerges from quantum field theory when the Unruh thermal effect is taken into account. Here, we sharpen those conclusions by showing that, even at finite times, the quantum picture is meaningful and is in close agreement with the classical picture.

Spectral damping without quasiparticle decay: The dynamic structure factor of two-dimensional quantum Heisenberg antiferromagnets

Two-dimensional Heisenberg antiferromagnets play a central role in quantum magnetism, yet the nature of dynamic correlations in these systems at finite temperature has remained poorly understood for decades. We solve this long-standing problem by using a novel quantum-classical duality to calculate the dynamic structure factor analytically and, paradoxically, find a broad frequency spectrum despite the very long quasiparticle lifetime. The solution reveals new multi-scale physics whereby an external probe creates a classical radiation field containing infinitely-many quanta. Crucially, it is the multi-scale nature of this phenomenon which prevents a conventional renormalization group approach. We also challenge the common wisdom on static correlations and perform Monte Carlo simulations which demonstrate excellent agreement with our theory.

Stationary solutions of equations of motion for a radiating charged particle including a radiation reaction effect.

For a radiating charged particle, the radiation reaction force plays an important role in determining its motion. Several formulas have been proposed to describe the radiation reaction force. Stationary solutions of the Lorentz-Abraham-Dirac (LAD), Mo-Papas, Landau-Lifshitz, and Ford-O'Connell equations are obtained and compared for a charged particle under a static magnetic and a rotating electric field. The behaviors of the obtained solutions look quite similar. The relative differences of the Lorentz factor, calculating the values using the LAD equation compared to the other equations, are evaluated; these values are shown to be less than 10^{-6} in the regime where classical radiation reactions are applicable.

Control of interference and diffraction of a three-level atom in a double-slit scheme with cavity fields

A double-cavity with a quantum mechanical and a classical field is placed immediately behind a double-slit in order to analyze the wave-particle duality. Both fields have common nodes and antinodes through which a three-level atom passes after crossing the double-slit. The atom-field interaction is maximum when the atom crosses a common antinode and path information can be recorded on the phase of the quantum field. On the other hand, if the atom crosses a common node, the interaction is null and no path information is stored. A quadrature measurement on the quantum field can reveal the path followed by the atom, depending on its initial amplitude $\ensuremath{\alpha}$ and the classical amplitude $\ensuremath{\varepsilon}$. In this report we show that the classical radiation acts like a focusing element of the interference and diffraction patterns and how it alters the visibility and distinguishabilily. Furthermore, in our double-slit scheme the two possible paths are correlated with the internal atomic states, which allows us to study the relationship between concurrence and wave-particle duality considering different cases.

On the Schott Term in the Lorentz-Abraham-Dirac Equation

The equation of motion for a radiating charged particle is known as the Lorentz–Abraham–Dirac (LAD) equation. The radiation reaction force in the LAD equation contains a third time-derivative term, called the Schott term, which leads to a runaway solution and a pre-acceleration solution. Since the Schott energy is the field energy confined to an area close to the particle and reversibly exchanged between particle and fields, the question of how it affects particle motion is of interest. In here we have obtained solutions for the LAD equation with and without the Schott term, and have compared them quantitatively. We have shown that the relative difference between the two solutions is quite small in the classical radiation reaction dominated regime.

Semiclassical predictions regarding a preinflationary era and its effects on the power spectrum

An investigation is undertaken into the properties and effects of a preinflationary era during at least part of which semiclassical gravity was valid. It is argued that if the Universe (or our part of it) was approximately homogeneous and isotropic during that era, then the Universe was likely to have been radiation dominated. A simple model in which the Universe contains classical radiation and a cosmological constant is used to investigate potential effects of such a preinflationary era on the cosmic microwave background. The power spectrum is computed using the mode functions of a quantized massless minimally coupled scalar field. Various choices of state for this field are considered, including adiabatic vacuum states of various orders and the vacuum state that would naturally occur if the Universe made a sudden transition from being radiation dominated to de Sitter space. In all cases investigated, there is a suppression of the power spectrum at large angles, and, when plotted as a function of the momentum parameter, there are always oscillations with state-dependent amplitudes.

Gradient of Residual Stress and Lattice Parameter in Mechanically Polished Tungsten Measured Using Classical X-rays and Synchrotron Radiation

In this work, the stress gradient in mechanically polished tungsten sample was studied using X-ray diffraction methods. To determine in-depth stress evolution in the very shallow subsurface region (up to 10 μm), special methods based on reflection geometry were applied. The subsurface stresses (depth up to 1 μm) were measured using the multiple-reflection grazing incidence X-ray diffraction method with classical characteristic X-rays, while the deeper volumes (depth up to 10 μm) were investigated using energy-dispersive diffraction with white high energy synchrotron beam. Both complementary methods allowed for determining in-depth stress profile and the evolution of stress-free lattice parameter. It was confirmed that the crystals of tungsten are elastically isotropic, which simplifies the stress analysis and makes tungsten a suitable material for testing stress measurement methods. Furthermore, it was found that an important compressive stress of about − 1000 MPa was generated on the surface of the mechanically polished sample, and this stress decreases to zero value at the depth of about 9 μm. On the other hand, the strain-free lattice parameter does not change significantly in the examined subsurface region.

Super-Planckian near-field heat transfer between hyperbolic metamaterials

Heat transfer between closely-spaced objects may be greatly enhanced with efficiency far beyond than the classic blackbody radiation limit under the participation of evanescent waves. Metamaterials with high density of optical surface states have been particularly explored to improve the heat flux upper limit but mostly confined in theoretical discussions due to the experimental challenges. In the near-field context, the effective medium theory (EMT) as widely used in the discussions is also lack of practical inspections. In this work, we managed to fabricate two 2 × 2 cm2 sized high-quality infrared hyperbolic metamaterials made of silicon nanorod array and studied their near-field thermophotonic interaction using home-made setup. At the 500 nm vacuum gap, a strong heat flux density of 830 W/m2 is observed, which is 4.7 times larger than the blackbody value. A local uniaxial model with parameters retrieved from the full-wave simulation was built to reproduce the measured results, which unambiguously validated the widely-adopted semi-empirical condition on the relationship between vacuum gap and lattice constant for the application of the EMT in the near-field regime. These results are believed essential for the future development of metamaterials for novel thermophotonic devices.

Particle Brownian motion due to random classical radiation: superfluid-like behavior in the presence of classical zero-point radiation

Nonrelativistic classical mechanics allows no fundamental transition between low-velocity and high-velocity forms of behavior, nor between low-temperature and high-temperature forms. In contrast, classical electrodynamics, which is a relativistic theory, allows fundamental transitions in velocity. Furthermore, the inclusion within the classical theory of Lorentz-invariant classical zero-point radiation allows classical electrodynamics to distinguish high-temperature and low-temperature forms of behavior. Because electromagnetism is a relativistic theory, it may provide a thermal radiation bath which gives rise to phenomena in Brownian motion which are not included in a model with a thermal bath based upon nonrelativistic particles. Here we explore the Brownian motion of a classical electric-dipole particle in random classical radiation, making use of the calculations of Einstein and Hopf. The Brownian motion as a function of temperature is analyzed in terms of the mean-square velocity and the diffusion constant for four different classical radiation spectra: the Rayleigh–Jeans spectrum, the Planck spectrum without zero-point radiation, the zero-point radiation spectrum, and the Planck spectrum including zero-point radiation. We illustrate how the inclusion of classical electromagnetic zero-point radiation alters Brownian motion behavior between high-temperature and low-temperature forms. For the Planck spectrum with zero-point radiation, the high-temperature Brownian motion agrees with some aspects found from nonrelativistic mechanics, while the low-temperature behavior includes some aspects analogous to superfluid behavior. At sufficiently low temperatures, the Brownian particle has an increasing mean-square velocity and more rapid diffusion with decreasing temperature due to the increasing dominance of the classical electromagnetic zero-point radiation.

Dirac's classical-quantum analogy for the harmonic oscillator: Classical aspects in thermal radiation including zero-point radiation

Dirac's Poisson-bracket-to-commutator analogy for the transition from classical to quantum mechanics assures that for many systems, the classical and quantum systems share the same algebraic structure. The quantum side of the analogy (involving operators on Hilbert space with commutators scaled by Planck's constant ℏ) not only gives the algebraic structure but also dictates the average values of physical quantities in the quantum ground state. On the other hand, the Poisson brackets of nonrelativistic mechanics, which give only the classical canonical transformations, do not give any values for physical quantities. Rather, one must go outside nonrelativistic classical mechanics in order to obtain a fundamental phase space distribution for classical physics. We assume that the values of physical quantities in classical theory at any temperature depend on the phase space probability distribution that arises from thermal radiation equilibrium including classical zero-point radiation with the scale set by Planck's constant ℏ. All mechanical systems in thermal radiation will inherit the constant ℏ from thermal radiation. Here, we note the connections between classical and quantum theories (agreement and contrasts) at all temperatures for the harmonic oscillator in one and three spatial dimensions.

Spectral Analysis of Line Sources With Complex Longitudinal Wavenumbers in Planarly Layered Media

Spectral properties of line sources carrying electric or magnetic current placed in a planarly layered medium are analyzed. It is shown that when the current along the line varies in the longitudinal direction by an exponential function with a complex exponent, classical Sommerfeld radiation condition that ensures outgoing and decaying fields simultaneously cannot always be used. Instead, depending on the exponent and the material properties of the layered medium, outgoing and exponentially increasing or incoming and exponentially decreasing waves are generated. This property is not observed when the exponent is real where the classical Sommerfeld radiation condition is fulfilled. In this article, an in-depth analysis of layered media is first performed in spectral domain as a function of the longitudinal dependence of the line sources. Then, the fields generated by the line sources are obtained by Sommerfeld integrations using two different radiation conditions separately. The effect of the radiation condition on the fields are discussed both in the spectral and spatial domains. In addition, field patterns are compared with the results obtained by finite element method (FEM) combined with perfectly matched layers (PMLs) and several guidelines for increasing the efficiency of simulations by FEM are introduced.

Beyond the Formulations of the Fluctuation Dissipation Theorem Given by Callen and Welton (1951) and Expanded by Kubo (1966)

The quantum formula of the fluctuation dissipation theorem (FDT) was given by Callen and Welton in 1951 for the case of conductors, and then expanded by Kubo in 1966. The drawback of these quantum relations concerns with the appearance of a zero-point contribution, ${\hbar \omega}/{2}$ with $\hbar$ the reduced Planck constant and $\omega$ the angular frequency of the considered photon, which implies a divergence of the fluctuation spectrum at increasing frequencies. This divergence is responsible for a vacuum-catastrophe, to keep the analogy with the well-known ultraviolet catastrophe of the classical black-body radiation spectrum. As a consequence, the quantum formulation of the FDT as given by Callen-Welton and Kubo introduces a Field Grand Challenge associated with the existence or less of a vacuum-fluctuations catastrophe for the energy-density spectrum. Here we propose a solution to this challenge by taking into account of the Casimir energy that, in turns, is found to be responsible for a quantum correction of the Stefan-Boltzmann law.

A New Mechanism of Light-Induced Bubble Growth to Propel Microbubble Piston Engine.

Radiation pressure refers to the momentum transfer of photons during light "particles" impacting a surface. The force is too small to drive microengines. Different from the classical radiation pressure, the indirect radiation pressure (Fm ) is introduced, coming from the momentum change of light-induced bubble expansion. Fm is shown to obey Fm ∼ (I·rb )2 , behaving faster growth of indirect radiation pressure versus light intensity I and bubble radius rb . An effective bubble size range is identified for Fm to suppress other forces for bubble in liquid. The top laser irradiation on nanofluid is used in this experiment. A well-defined bubble pulsating flow, being a new principle of bubble piston engine, is demonstrated. During pulse on (≈ns scale), Fm exceeding other forces generates an extremely large acceleration, which is three to four orders larger than the gravity acceleration, propelling the bubble traveling downward. During pulse off, the bubble is floating upward due to the nonexistence of Fm . In such a way, the piston engine sustains the oscillating ranges of 38-347 µm for bubble diameters and 2.7-457.9 µm for traveling distances of piston. This work is useful to manipulate bubble dynamics in solar energy systems, and can find various applications in optofluidics.