Efficient Energy Transport Research Articles

Effects of Oscillatory Deformations on the Coherent and Incoherent Quantum Transport

Inspired by the works of [F. Caruso, New J. Phys. 16, 055015 (2014)] and [T. Scholak et al, J. Phys. B: At. Mol. Opt. Phys. 44 184012 (2011)], which state that for a large class of complex noisy networks, the optimal efficiency of quantum transport is universally obtained by mixing coherent (Hamiltonian) and incoherent (noisy) parts where the contribution of the coherent part is strictly more than incoherent one, we examine the effect of oscillatory deformations on two simple prototypes in order to study their effects on the efficiency of coherent and incoherent energy transport. The prototypes are interchangeable to each other only by a simple phase modulation, such that the dynamics for the first type is only coherent, while for the second one the coherent evolution is completely suppressed and the evolution of the system is only incoherent (noisy). In this regard, it is shown that there exist a special deformation by which the efficiency of incoherent transport becomes better than the coherent one. This result suggests that in the noisy networks with collective harmonic motions, the optimality of transport can be occurred in such a way that the contribution of incoherent term is more than the coherent one.

Plasmon canalization and tunneling over anisotropic metasurfaces

We discuss the possibility of plasmon canalization, collimation, and tunneling over ultrathin metasurfaces, enabled by extreme anisotropy in their complex conductivity dyadic. The interplay between anisotropy, conductivity-near-zero, and loss is exploited here to derive general conditions for plasmon canalization and efficient energy transport. We also demonstrate how the intrinsic in-plane anisotropy of black phosphorus can provide a natural platform to engineer these conditions, exhibiting important advantages over isotropic plasmonic materials. Our findings have implications for plasmonic sensors, planar hyperlenses, and plasmon steering over a surface, and they highlight the potential of two-dimensional materials beyond graphene.

Suppressing Excimers in H-Aggregates of Perylene Bisimide Folda-Dimer: Role of Dimer Conformation and Competing Assembly Pathways.

Long-lived excitons in H-aggregates hold great promise for efficient transport of excitation energy, provided they are not scavenged by structurallly relaxed excimers. We report solution self-assembly of a perylene bisimide (PBI) folda-dimer that exhibits two distinct kinetic stages: an initial fast assembly leads to metastable aggregates with large excimer contribution that is followed by a slower growth of stable, extended H-aggregates free of excimers. Mechanistic investigations reveal an interplay of two competing aggregation pathways, where suppression of excimers is directly linked to the crossover from an isodesmic to cooperative aggregation. How the comeptition between two self-assembly pathways is influenced by the conformational flexibility of the folda-dimer is also discussed.

Structure-Dynamics Relation in Physically-Plausible Multi-Chromophore Systems.

We study a large number of physically-plausible arrangements of chromophores, generated via a computational method involving stochastic real-space transformations of a naturally-occurring "reference" structure, illustrating our methodology using the well-studied Fenna-Matthews-Olson complex (FMO). To explore the idea that the natural structure has been tuned for efficient energy transport, we use an atomic transition charge method to calculate the excitonic couplings of each generated structure and a Lindblad master equation to study the quantum transport of an exciton from a "source" to a "drain" chromophore. We find significant correlations between structure and transport efficiency: High-performing structures tend to be more compact and, among those, the best structures display a certain orientation of the chromophores, particularly the chromophore closest to the source-to-drain vector. We conclude that, subject to reasonable, physically motivated constraints, the FMO complex is highly attuned to the purpose of energy transport, partly by exploiting these structural motifs.

Mars's magnetotail: Nature's current sheet laboratory

AbstractThe configuration and stability of an important kinetic plasma structure, the current sheet, determine the efficiency of magnetic energy storage, release, and transport in surrounding plasmas. These properties depend on β (the ratio of plasma pressures to magnetic field pressures) and Mach number M (the ratio of bulk velocities to magnetosonic velocities). For the most investigated current sheet, the near‐Earth magnetotail current sheet, these parameters fall within a relatively narrow range of values (high β, low M). To investigate current sheet behavior for a wider range of parameters, we explore current sheets in the magnetotail of Mars using Mars Atmosphere and Volatile Evolution (MAVEN) mission observations. We find that low‐β, high‐M current sheets are abundant in Mars's magnetotail, but high‐β, low‐M current sheets can also be found there. Low‐β current sheets are nearly force‐free, whereas high‐M current sheets are balanced by a plasma flow gradient along the tail. We compare current sheet distributions in a (β,M) space for the Martian magnetotail, the near‐Earth magnetotail (using Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission), and the distant magnetotail (using Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission). We also find that the pressure balance in the Martian magnetotail current sheet can occur by contributions from a wide range of ion species, or, in low beta cases, from field‐aligned currents generation of a force‐free magnetic field configuration. The Martian magnetotail is a natural laboratory where current sheet of various types can be found and investigated.

Coupled energy patterns in zigzag molecular chains

The contribution of both longitudinal and transversal nonlinear oscillations to energy localization is investigated in a zigzag molecular chain, which include simultaneously nearest- and next-nearest neighbor interactions. Coupled amplitude equations are found in the form of discrete nonlinear Schrödinger equations, whose plane wave solutions are found to be subjected to some instabilities. They are shown to be very sensitive to transverse and longitudinal couplings, which is confirmed via direct numerical simulations. The two available modes are found to be alternatively responsible for energy localization and transport. Thermal fluctuations effects bring about highly localized modes, along with narrow structures for efficient energy transport.

Can Excited State Electronic Coherence Be Tuned via Molecular Structural Modification? A First-Principles Quantum Electronic Dynamics Study of Pyrazolate-Bridged Pt(II) Dimers.

Materials and molecular systems exhibiting long-lived electronic coherence can facilitate coherent transport, opening the door to efficient charge and energy transport beyond traditional methods. Recently, signatures of a possible coherent, recurrent electronic motion were identified in femtosecond pump-probe spectroscopy experiments on a binuclear platinum complex, where a persistent periodic beating in the transient absorption signal's anisotropy was observed. In this study, we investigate the excitonic dynamics that underlie the suspected electronic coherence for a series of binuclear platinum complexes exhibiting a range of interplatinum distances. Results suggest that the long-lived coherence can only result when competitive electronic couplings are in balance. At longer Pt-Pt distances, the electronic couplings between the two halves of the binuclear system weaken, and exciton localization and recombination is favored on short time scales. For short Pt-Pt distances, electronic couplings between the states in the coherent superposition are stronger than the coupling with other excitonic states, leading to long-lived coherence.

Nanostructured Oxide Thin Films for Sustainable Development

In the effort to emancipate mankind from fossil fuels dependence and minimize the CO2 emissions, efficient transport and conversion of energy is required. Advanced materials such as superconductors and thermoelectrics are expected to play an important role in sustainable science and development. We propose an overview of our recent progress on nanostructured thin films of superconducting and thermoelectric oxides. Superconducting properties of YBa2Cu3Ox and thermoelectric properties of Al-doped ZnO are described in relation to preparation techniques, experimental conditions, substrates used, structure and morphology. We especially discuss a nanoengineering approach for the enhancement of energy transport and energy conversion efficiency of oxide thin films compared to their corresponding counterpart of bulk materials.

Design of a multilayer-based collimated plane-grating monochromator for tender X-ray range.

Collimated plane-grating monochromators (cPGMs), consisting of a plane mirror and plane diffraction grating, are essential optics in synchrotron radiation sources for their remarkable flexibility and good optical characteristics in the soft X-ray region. However, the poor energy transport efficiency of a conventional cPGM (single-layer-coated) degrades the source intensity and leaves reduced flux at the sample, especially for the tender X-ray range (1-4 keV) that covers a large number of K- and L-edges of medium-Z elements, and M-edges of high-Z elements. To overcome this limitation, the use of a multilayer-based cPGM is proposed, combining a multilayer-coated plane mirror with blazed multilayer gratings. With this combination, the effective efficiency of cPGMs can be increased by an order of magnitude compared with the conventional single-layer cPGMs. In addition, higher resolving power can be achieved with improved efficiency by increasing the blaze angle and working at higher diffraction order.

Basic dynamic and scale study of quasi-spherical Z-pinch implosion

Unlike cylindrical Z pinch, a quasi-spherical implosion enables load plasma to implode inward spherically and concentrate its kinetic energy toward the center. This helps to improve the energy-transport efficiency and increase the shock-induced radiation intensity of the foam convertor, when the quasi-spherical implosion is used to drive a dynamic hohlraum (DH). In previous work, it has been proved that a spherical metal shell with an exact mass-distribution can implode spherically by the nonuniform magnetic field, whose magnitude increases with the load latitude, Bφ~cos-1θ. However, this ‘mass-redistribution’ method is hard to realize on the fast pulse power generator widely used in today's Z-pinch study. The rise time of the facility is only ~100 ns, and the load is wire arrays with typical weight about 1 mg/cm. We develop a method of gaining quasi-spherical implosion with wire arrays by adjusting their initial shape, and it proves feasible on the 1.5 MA Qiangguang-I facility. Recently, we try to realize the quasi-spherical dynamic hohlraum (QSDH) implosion on generator with higher current, such as the 4.5 MA Angara5-I or the 8 MA PTS facility, and to make a direct compare with its cylindrical equivalence. But first of all, a basic but relatively comprehensive study on the quasi-spherical implosion dynamics is necessary and useful for the future QSDH load design and optimization.#br#Comparing with the device for classical cylindrical Z-pinch implosions, the load and electrodes structures of quasi-spherical implosions are complex, which leads to distinct implosion dynamics and scale rules. In this paper, we develop a thin shell model for the quasi-spherical implosion, from which the movement equation, as well as the energy scale relation is derived analytically. It is found that under the same drive condition, the implosion velocity and total kinetic energy of cylindrical load are higher than those of quasi-spherical one. However, as we expected, the quasi-spherical implosion has larger kinetic energy density, which is important for the applications such as driving a dynamic holhraum. Besides the peak current, the kinetic energy of quasi-spherical implosion also depends on the initial size of the load. By increasing the initial radius and maximum latitude angle moderately, one can obtain higher kinetic energy and energy density of the implosion, which is crucial for the load design. The theoretical study is supported by simulation results. It is found that under a drive condition close to that of the ZR facility, a quasi-spherical load with an initial radius of 5 cm will reach a peak kinetic energy density of 3.2 MJ/cm, which is about 3 times those from the cylindrical ones.

Emission of magnetosound from MHD‐unstable shear flow boundaries

AbstractThe emission of propagating MHD waves from the boundaries of flow channels that are unstable to the Kelvin‐Helmholtz Instability (KHI) in magnetized plasma is investigated. The KHI and MHD wave emission are found to be two competing processes. It is shown that the fastest growing modes of the KHI surface waves do not coincide with efficient wave energy transport away from a velocity shear boundary. MHD wave emission is found to be inefficient when growth rates of KHI surface waves are maximum, which corresponds to the situation where the ambient magnetic field is perpendicular to the flow channel velocity vector. The efficiency of wave emission increases with increasing magnetic field tension, which in Earth's magnetosphere likely dominates along the nightside magnetopause tailward of the terminator, and within earthward Bursty Bulk Flows (BBFs) in the inner plasma sheet. MHD wave emission may also dominate in Supra‐Arcade Downflows (SADs) in the solar corona. Our results suggest that efficient emission of propagating MHD waves along BBF and SAD boundaries can potentially explain observations of deceleration and stopping of BBFs and SADs.

The effects of Ekman pumping on quasi-geostrophic Rayleigh–Bénard convection

Numerical simulations of three-dimensional rapidly rotating Rayleigh–Bénard convection are performed by employing an asymptotic quasi-geostrophic model that incorporates the effects of no-slip boundaries through (i) parametrized Ekman pumping boundary conditions and (ii) a thermal wind boundary layer that regularizes the enhanced thermal fluctuations induced by pumping. The fidelity of the model, obtained by an asymptotic reduction of the Navier–Stokes equations that implicitly enforces a pointwise geostrophic balance, is explored for the first time by comparisons of simulations against the findings of direct numerical simulations (DNS) and laboratory experiments. Results from these methods have established Ekman pumping as the mechanism responsible for significantly enhancing the vertical heat transport. This asymptotic model demonstrates excellent agreement over a range of thermal forcing for Prandtl number $Pr\approx 1$ when compared with results from experiments and DNS at maximal values of their attainable rotation rates, as measured by the Ekman number ($E\approx 10^{-7}$); good qualitative agreement is achieved for $Pr>1$. Similar to studies with stress-free boundaries, four spatially distinct flow morphologies exists. Despite the presence of frictional drag at the upper and/or lower boundaries, a strong non-local inverse cascade of barotropic (i.e. depth-independent) kinetic energy persists in the final regime of geostrophic turbulence and is dominant at large scales. For mixed no-slip/stress-free and no-slip/no-slip boundaries, Ekman friction is found to attenuate the efficiency of the upscale energy transport and, unlike the case of stress-free boundaries, rapidly saturates the barotropic kinetic energy. For no-slip/no-slip boundaries, Ekman friction is strong enough to prevent the development of a coherent dipole vortex condensate. Instead, vortex pairs are found to be intermittent, varying in both time and strength. For all combinations of boundary conditions, a Nastrom–Gage type of spectrum of kinetic energy is found, where the power-law exponent changes from ${\approx}-3$ to ${\approx}-5/3$, i.e. from steep to shallow, as the spectral wavenumber increases.

FORMATION OF OVERHEATED REGIONS AND TRUNCATED DISKS AROUND BLACK HOLES: THREE-DIMENSIONAL GENERAL RELATIVISTIC RADIATION-MAGNETOHYDRODYNAMICS SIMULATIONS

ABSTRACT Using three-dimensional general relativistic radiation-magnetohydrodynamics simulations of accretion flows around stellar mass black holes, we report that the relatively cold disk ( ) is truncated near the black hole. Hot and less dense regions, of which the gas temperature is and more than 10 times higher than the radiation temperature (overheated regions), appear within the truncation radius. The overheated regions also appear above as well as below the disk, sandwiching the cold disk, leading to the effective Compton upscattering. The truncation radius is for , where are the gravitational radius, mass accretion rate, Eddington luminosity, and light speed, respectively. Our results are consistent with observations of a very high state, whereby the truncated disk is thought to be embedded in the hot rarefied regions. The truncation radius shifts inward to with increasing mass accretion rate , which is very close to an innermost stable circular orbit. This model corresponds to the slim disk state observed in ultraluminous X-ray sources. Although the overheated regions shrink if the Compton cooling effectively reduces the gas temperature, the sandwich structure does not disappear at the range of . Our simulations also reveal that the gas temperature in the overheated regions depends on black hole spin, which would be due to efficient energy transport from black hole to disks through the Poynting flux, resulting in gas heating.

Electromagnetic Field Propagation in the One-Dimensional Silver Nanoparticle Dimer Chains: Hotspots and Energy Transport

Strong local electromagnetic (EM) fields and efficient EM energy transport in metallic nanostructures are two important issues in their applications in quantum computations/communications. We investigate the propagation characteristics of the hotspots in one-dimensional silver nanoparticle dimer chains, which combine the functions of the gap field enhancement and the waveguide. The near field and the far field induced interplay among the local field enhancement, the radiative interaction, and the dissipation affects significantly the EM field transport efficiency. Moreover, the correlation between local structure and global structure leads to the structure-dependent excitation. With the help of the combined effects of the structure-dependent excitation, the field confinement and the propagation, the efficient EM field excitation, and long-range propagation can be obtained by tuning the structure of our systems. With suitable geometric parameters (dimer orientations, dimer gap sizes) of our system, the electric field intensity at the position 5000 nm away from the starting point (exciting point) is about 50 times of the corresponding field intensity in a silver nanoparticle chain.

Stabilization of solitons in coupled nonlinear pendulums with simultaneous external and parametric excitations

The influence of an external harmonic excitation on the intrinsic localized modes of a chain of nonlinear pendulums is numerically investigated. We show, in particular, how the existence and stability domains of solitons are modified when the coupled pendulums are simultaneously subjected to external and parametric excitations. This stabilization mechanism opens the way towards the control of the energy localization phenomena in damped nonlinear periodic lattices for efficient energy transport applications.

Evolution and magnitudes of candidate Planet Nine

The recently renewed interest in a possible additional major body in the outer solar system prompted us to study the thermodynamic evolution of such an object. We assumed that it is a smaller version of Uranus and Neptune. We modeled the temporal evolution of the radius, temperature, intrinsic luminosity, and the blackbody spectrum of distant ice giant planets. The aim is also to provide estimates of the magnitudes in different bands to assess whether the object might be detectable. Simulations of the cooling and contraction were conducted for ice giants with masses of 5, 10, 20, and 50 Mearth that are located at 280, 700, and 1120 AU from the Sun. The core composition, the fraction of H/He, the efficiency of energy transport, and the initial luminosity were varied. The atmospheric opacity was set to 1, 50, and 100 times solar metallicity. We find for a nominal 10 Mearth planet at 700 AU at the current age of the solar system an effective temperature of 47 K, much higher than the equilibrium temperature of about 10 K, a radius of 3.7 Rearth, and an intrinsic luminosity of 0.006 Ljupiter. It has estimated apparent magnitudes of Johnson V, R, I, L, N, Q of 21.7, 21.4, 21.0, 20.1, 19.9, and 10.7, and WISE W1-W4 magnitudes of 20.1, 20.1, 18.6, and 10.2. The Q and W4 band and other observations longward of about 13 microns pick up the intrinsic flux. If candidate Planet 9 has a significant H/He layer and an efficient energy transport in the interior, then its luminosity is dominated by the intrinsic contribution, making it a self-luminous planet. At a likely position on its orbit near aphelion, we estimate for a mass of 5, 10, 20, and 50 Mearth a V magnitude from the reflected light of 24.3, 23.7, 23.3, and 22.6 and a Q magnitude from the intrinsic radiation of 14.6, 11.7, 9.2, and 5.8. The latter would probably have been detected by past surveys.

Förster Energy Transport in Metal-Organic Frameworks Is Beyond Step-by-Step Hopping.

Metal-organic frameworks (MOFs) with light-harvesting building blocks designed to mimic photosynthetic chromophore arrays in green plants provide an excellent platform to study exciton transport in networks with well-defined structures. A step-by-step exciton random hopping model made of the elementary steps of energy transfer between only the nearest neighbors is usually used to describe the transport dynamics. Although such a nearest neighbor approximation is valid in describing the energy transfer of triplet states via the Dexter mechanism, we found it inadequate in evaluating singlet exciton migration that occurs through the Förster mechanism, which involves one-step jumping over longer distance. We measured migration rates of singlet excitons on two MOFs constructed from truxene-derived ligands and zinc nodes, by monitoring energy transfer from the MOF skeleton to a coumarin probe in the MOF cavity. The diffusivities of the excitons on the frameworks were determined to be 1.8 × 10(-2) cm(2)/s and 2.3 × 10(-2) cm(2)/s, corresponding to migration distances of 43 and 48 nm within their lifetimes, respectively. "Through space" energy-jumping beyond nearest neighbor accounts for up to 67% of the energy transfer rates. This finding presents a new perspective in the design and understanding of highly efficient energy transport networks for singlet excited states.

Integration of Microalgae-Based Bioenergy Production into a Petrochemical Complex: Techno-Economic Assessment

The rapid development of modern society has resulted in an increased demand for energy, mainly from fossil fuels. The use of this source of energy has led to the accumulation of carbon dioxide (CO2) in the atmosphere. In this context, microalgae culturing may be an effective solution to reduce the CO2 concentration in the atmosphere, since these microorganisms can capture CO2 and, simultaneously, produce bioenergy. This work consists of a techno-economic assessment of a microalgal production facility integrated in a petrochemical complex, in which established infrastructure allows efficient material and energy transport. Seven different scenarios were considered regarding photosynthetic, lipids extraction and anaerobic digestion efficiencies. This analysis has demonstrated six economically viable scenarios able to: (i) reduce CO2 emissions from a thermoelectric power plant; (ii) treat domestic wastewaters (which were used as culture medium); and (iii) produce lipids and electrical and thermal energy. For a 100-ha facility, considering a photosynthetic efficiency of 3%, a lipids extraction efficiency of 75% and an anaerobic digestion efficiency of 45% (scenario 3), an economically viable process was obtained (net present value of 22.6 million euros), being effective in both CO2 removal (accounting for 1.1 × 104 t per year) and energy production (annual energy produced was 1.6 × 107 kWh and annual lipids productivity was 1.9 × 103 m3).

Long-Range Energy Transport via Plasmonic Propagation in a Supramolecular Organic Waveguide.

Energy transport in organic materials is dependent on the coherent migration of optically induced excited states. For instance, in active organic waveguides, the tight packing of dye molecules allows delocalization of excitons over a distance generally limited to at most several hundred nanometers. Here, we demonstrate an alternative mechanism of energy transport in a triarylamine-based supramolecular organic waveguide that is plasmonic in nature and results in coherent energy propagation superior to 10 μm. The optical, electric, and magnetic properties of the doped material support the presence of metallic electrons that couple with and transport incident light. These results show that organic metals constitute a novel class of materials with efficient energy transport and are of potential interest for optoelectronics, plasmonics, and artificial light-energy harvesting systems.

Defect Luminescence from Wurtzite CuInS2 Nanocrystals: Combined Experimental and Theoretical Analysis

CuInS2 nanocrystals with the wurtzite structure show promise for applications requiring efficient energy transport due to their anisotropic crystal structure. We investigate the source of photoluminescence in the near-infrared spectral region recently observed from these nanocrystals. Spectroscopic studies of both wurtzite CuInS2 itself and samples alloyed with Cd or Zn allow the assignment of this emission to a radiative point defect within the nanocrystal structure. Further, by varying the organic passivation layer on the material, we are able to determine that the atomic species responsible for nonradiative decay paths on the nanocrystal surface are Cu- or S-based. Density functional theory calculations of defect states within the material allow identification of the likely radiative species. Understanding both the electronic structure and optical properties of wurtzite CuInS2 nanocrystals is necessary for their efficient integration into potential biological, photovoltaic, and photocatalytic applications.