Direct Energy Flux Research Articles

GPCR Signaling: A Study of the Interplay Between Structure, Energy, and Function.

G protein-coupled receptors (GPCRs) exemplify sophisticated allosteric communication, transducing extracellular signals through ligand-induced structural rearrangements that resonate through the molecular scaffold. Despite extensive study, the biophysical underpinnings of how conformational changes spread remain unclear. This work employs a novel physics-based framework to characterize the role of energy dissipation in directing intramolecular signaling pathways. By modeling each residue as a network of coupled oscillators, we generate a localization landscape depicting the vibrational energy distribution throughout the protein scaffold. Quantifying directional energy flux between residues reveals distinct pathways for energy and information transfer, illuminating sequences of allosteric communication. Our analysis of CB1 and CCR5 crystal structures unveils an anisotropic pattern of energy dissipation aligning with key functional dynamics, such as activation-related conformational changes. These anisotropic patterns of vibrational energy flow constitute pre-configured channels for allosteric signaling. Elucidating the relationship between structural topology and energy dissipation patterns provides key insights into the thermodynamic drivers of conformational signaling. This methodology significantly advances our mechanistic understanding of allostery in GPCRs and presents a broadly applicable approach for rationally dissecting allosteric communication pathways, with potential implications for structure-based drug design targeting these critical receptors.

An approach to assess the potential of wave energy resources based on directional energy flux

Estimating the total available wave energy surrounding islands holds significant importance in accessing the hosting capacity of wave energy. This study proposes a novel method for estimating the total available wave energy resources around islands using directional wave energy flux as a key parameter. By introducing the concept of directional across section, this method incorporates the directionality into the total resource calculation. A case study of the northern Zhoushan Archipelago was conducted to demonstrate the practical application of this method. The wave conditions were computed using the SWAN wave model for a 10-year period and validated against 7 months of buoy observations near Shengshan island. Basic wave energy resource characteristics were analyzed and the spatiotemporal features were analyzed using various indices. Subsequently, the proposed method was applied to calculated the total available wave energy around islands at various extend distances from the coastline. The wave energy potential of the islands in the study area stands at 349 MW, 302 MW, 318 MW, and 387 MW respectively, at extend distances of 5 km, 7.5 km, 10 km, and 12.5 km from the shoreline. These values represent approximately 25.1%–42.2% of the total energy obtained using existing methods.

On the impact of canopy model complexity on simulated carbon, water, and solar-induced chlorophyll fluorescence fluxes

Abstract. Lack of direct carbon, water, and energy flux observations at global scales makes it difficult to calibrate land surface models (LSMs). The increasing number of remote-sensing-based products provide an alternative way to verify or constrain land models given their global coverage and satisfactory spatial and temporal resolutions. However, these products and LSMs often differ in their assumptions and model setups, for example, the canopy model complexity. The disagreements hamper the fusion of global-scale datasets with LSMs. To evaluate how much the canopy complexity affects predicted canopy fluxes, we simulated and compared the carbon, water, and solar-induced chlorophyll fluorescence (SIF) fluxes using five different canopy complexity setups from a one-layered canopy to a multi-layered canopy with leaf angular distributions. We modeled the canopy fluxes using the recently developed land model by the Climate Modeling Alliance, CliMA Land. Our model results suggested that (1) when using the same model inputs, model-predicted carbon, water, and SIF fluxes were all higher for simpler canopy setups; (2) when accounting for vertical photosynthetic capacity heterogeneity, differences between canopy complexity levels increased compared to the scenario of a uniform canopy; and (3) SIF fluxes modeled with different canopy complexity levels changed with sun-sensor geometry. Given the different modeled canopy fluxes with different canopy complexities, we recommend (1) not misusing parameters inverted with different canopy complexities or assumptions to avoid biases in model outputs and (2) using a complex canopy model with angular distribution and a hyperspectral radiation transfer scheme when linking land processes to remotely sensed spectra.

Is it necessary to manage falling number in the field?

AbstractWheat (Triticum aestivum L.)‐growing areas of the U.S. Pacific Northwest, particularly eastern Washington and northern Idaho, are hillier than other wheat‐producing areas in the country. This may produce microclimate variation within a field due to differences in elevation and solar exposure thus causing corresponding variation in yield at harvest. It is unknown whether falling number (FN), an indirect indicator of endogenous α‐amylase activity and hence end‐product quality, is also affected. The aim of this study was to determine the utility of using local (subfield) topographical data to make decisions on segregating potentially low FN wheat produced from susceptible regions within a field. In two consecutive seasons, six large fields in commercial production were studied to reveal effects of elevation and solar exposure on FN. Elevation, slope, and aspect were determined through referencing land coordinates to U.S. Geological Survey (USGS) elevation datasets and ArcMap tools. Theoretical direct solar radiation flux energy increments were summed over the growing period. Findings indicate that for five of the six fields an elevation effect on FN was not significant despite a variation by as much as 50 m within a field. Direct energy flux was positively correlated with FN for two fields (r = .469 and .704) in the first season, but negatively correlated for one field in the second season (r = –.507). However, even in cases when energy flux or elevation trends were significant, these effects were minor. Thus, in‐field segregation of wheat during harvest is not necessary in favorable seasons.

Efficient dip‐angle angle‐domain common‐image gather estimation using Poynting vector in acoustic reverse time migration and its application in noise suppression

ABSTRACTIn reverse time migration, we can produce angle‐domain common‐imaging gathers in either the scattering‐angle domain or the dip‐angle domain. The latter, although not used as widely as the former, still provides a unique view to look into seismic imaging. The reverse time migration dip‐angle angle‐domain common‐image gather can be computed via the subsurface offset extension, which is a bit costly in storage. We here obtain dip‐angle angle‐domain common‐imaging gathers efficiently in acoustic reverse time migration by using the normalized Poynting vectors. Poynting vector, an indicator of the directional energy flux, is easy to compute during wavefield propagation. Similar to the subsurface‐offset method, our method also has dip‐angle angle‐domain common‐imaging gathers of blocky horizontal coherence. In the theory of local semblance analysis, the signal with better horizontal coherence has a higher semblance score, and vice versa. Based on the estimated semblance scores, we can thus design a specularity filter to preserve valid signals and suppress noises. We validate our method with two data sets. Both the Marmousi data and the real data show that our method works effectively in eliminating noises and enhancing resolution in the acoustic reverse time migration imaging.

Air temperature feedback and its contribution to global warming

Air temperature feedback results from the thermal-radiative coupling between the atmosphere and the surface and plays an important role in surface energy balance. This paper reveals the contribution of air temperature feedback to the global warming from 1980 to 2000. The air temperature feedback kernel, evaluated using the ERA-Interim reanalysis data, is used to discuss the physical mechanism for air temperature feedback, the dependency of the strength of air temperature feedback on the climatological spatial distributions of air temperature, water vapor and cloud content, and the contributions of air temperature feedback to rapid global warming. The coupling between temperature feedback and each of the external forcings and individual feedback processes will amplify the anomaly of direct energy flux convergence at the surface induced by the external forcings and individual processes. The air temperature feedback amplifies the initial surface warming due to the increase in CO2 concentration, ice and snow melting, increase in water vapor, and change in ocean heat storage. It also amplifies the surface warming due to the longwave radiaitve forcing associated with the increase in cloud cover, which acts to suppress the cooling of the shortwave effect of cloud forcing. Overall, temperature feedback plays an important role in the global warming from 1980 to 2000, as the net positive contribution to the perturbation of global mean energy flux at the surface from the air temperature feedback is larger than the net negative contribution from external forcing and all non-temperature feedbacks.

The dynamically correct Poynting vector formulation for acoustic media with application in calculating multidirectional propagation vectors to produce angle gathers from reverse time migration

The Poynting vector (PV) has been widely used to calculate propagation vectors of a pressure field (PF) in acoustic media. The most widely used acoustic PV formula is the negative of a product of the time and space derivatives. These two derivatives result in a phase shift between the PF and its PV; particularly, for a PF at a local magnitude peak, the PV modulus is zero and thus the propagation direction there is undefined. This “zero-modulus” issue is not consistent with the physical definition of the PV, which is the directional energy flux density of a PF because this definition indicates that the variation of the PV modulus should be consistent with the PF magnitude. This PV is only considered as kinematically correct and defined as K-PV. We derive the dynamically correct PV (D-PV) formula for acoustic media, which is the negative of the product of the reciprocal of the density, the PF itself, and a factor that is obtained by applying a time integration and a space derivative to the PF. There are two derivations. One uses the slowness vector, and the other is by simplifying the elastic PV. This D-PV does not suffer from the zero-modulus problem, and we also use it to update the multidirectional PV (MPV), which produces a D-MPV. Two strategies are provided to reduce the computational complexity of the time integration in the D-PV formula. Because the MPV already involves Fourier transforms between the time and frequency domains (which facilitates implementation of the time integration), its updated version causes only a very minor increase in the computational complexity of the original one. Numerical examples indicate that the D-PV provides more reliable propagation vectors than the K-PV, and the D-MPV provides more accurate angle-domain common-image gathers from reverse time migration of acoustic media than the K-MPV.

Formation of the bi-directional energy cascade in low-frequency damped wave-turbulent systems

We demonstrate that in wave-turbulent systems, an inverse energy flux can be formed in addition to the conventional direct energy flux if large-scale wave damping is present. Such a bi-directional energy cascade can be understood in terms of the wave energy transfer on the temperature wave background. The formation of the bi-directional cascade provides an effective mechanism for global coupling between the scales where the turbulent fluctuations at small scales are affected by the wave distribution at large scales due to the total energy conservation. We discuss physical systems where this scenario is realized.

Slow translation speed causes rapid collapse of northeast Pacific Hurricane Kenneth over cold core eddy

AbstractCategory 4 Hurricane Kenneth (HK) experienced unpredicted rapid weakening when it stalled over a cold core eddy (CCE) on 19–20 September 2005, 2800 km SE of Hawaii. Maximum sea surface temperature (SST) cooling of 8–9°C and a minimum aerially averaged SST of 18.3°C (over 8750 km2) characterized its cool wake. A 3‐D mixed‐layer model enabled estimation of enthalpy fluxes (latent and sensible heat), as well as the relative importance of slow translation speed (Uh) compared with the preexisting CCE. As Uh dropped below 1.5 m s−1, enthalpy fluxes became negative, cutting off direct ocean energy flux to HK. Although HK's weakening was attributed to wind shear, our results indicate that slow Uh and consequent intense SST cooling were the main causes. The tropical cyclone‐intensified CCE experienced rapid growth in magnitude (−6 to −40 cm), increased diameter (60 to 350 km), elevated chlorophyll a for 4 months, and 12 month longevity.

On Induction Heating - Conductor Excited by External Field

Electromagnetic field in a banded strip conductor excited by external AC voltage driven coil is analyzed. Inhomogeneous wave equation describing this axis-symmetrical configuration is deduced and solved to find the induced current density and the directional energy flux density (Poynting vector) in the conductor.

On energetics and inertial-range scaling laws of two-dimensional magnetohydrodynamic turbulence

AbstractWe study two-dimensional magnetohydrodynamic turbulence, with an emphasis on its energetics and inertial-range scaling laws. A detailed spectral analysis shows that dynamo triads (those converting kinetic into magnetic energy) are associated with a direct magnetic energy flux while anti-dynamo triads (those converting magnetic into kinetic energy) are associated with an inverse magnetic energy flux. As both dynamo and anti-dynamo interacting triads are integral parts of the direct energy transfer, the anti-dynamo inverse flux partially neutralizes the dynamo direct flux, arguably resulting in relatively weak direct energy transfer and giving rise to dynamo saturation. This result is consistent with a qualitative prediction of energy transfer reduction due to Alfvén wave effects by the Iroshnikov–Kraichnan theory (which was originally formulated for magnetohydrodynamic turbulence in three dimensions). We numerically confirm the correlation between dynamo action and direct magnetic energy flux and investigate the applicability of quantitative aspects of the Iroshnikov–Kraichnan theory to the present case, particularly its predictions of energy equipartition and ${k}^{\ensuremath{-} 3/ 2} $ spectra in the energy inertial range. It is found that for turbulence satisfying the Kraichnan condition of magnetic energy at large scales exceeding total energy in the inertial range, the kinetic energy spectrum, which is significantly shallower than ${k}^{\ensuremath{-} 3/ 2} $, is shallower than its magnetic counterpart. This result suggests no energy equipartition. The total energy spectrum appears to depend on the energy composition of the turbulence but is clearly shallower than ${k}^{\ensuremath{-} 3/ 2} $ for $r\approx 2$, even at moderate resolutions. Here $r\approx 2$ is the magnetic-to-kinetic energy ratio during the stage when the turbulence can be considered fully developed. The implication of the present findings is discussed in conjunction with further numerical results on the dependence of the energy dissipation rate on resolution.

On the measurement of energy fluxes in plasmas using a calorimetric probe and a thermopile sensor

Two different diagnostics for the determination of the energy influx in plasma processes were used to characterize an ion beam source and an asymmetric RF discharge. The related energy fluxes were measured in dependence on the ion energy and on the RF power, respectively. The first sensor, called HFM (Heat Flux Microsensor) is a thermopile which allows for direct energy flux measurements. With the second sensor, a calorimetric probe, the energy influx has been calculated from the temporal temperature evolution preliminarily registered. Although the working principle of both sensors is different, the obtained results are in good agreement. In the ion beam (<1.5 keV)) rather high energy influxes are achieved (up to 700 mW cm−2), whereas the values measured in the asymmetric RF discharge were lower than 50 mW cm−2 for discharge powers in the range 10–100 W. The performances and limitations of both sensors are compared and discussed.

Structure and decay of rotating homogeneous turbulence

Navier–Stokes turbulence subject to solid-body rotation is studied by high-resolution direct numerical simulations (DNS) of freely decaying and stationary flows. Setups characterized by different Rossby numbers are considered. In agreement with experimental results strong rotation is found to lead to anisotropy of the direct nonlinear energy flux, which is attenuated primarily in the direction of the rotation axis. In decaying turbulence the evolution of kinetic energy follows an approximate power law with a distinct dependence of the decay exponent on the rotation frequency. A simple phenomenological relation between exponent and rotation rate reproduces this observation. Stationary turbulence driven by large-scale forcing exhibits k⊥−2-scaling in the rotation-dominated inertial range of the one-dimensional energy spectrum taken perpendicularly to the rotation axis. The self-similar scaling is shown to be the cumulative result of individual spectral contributions which, for low rotation rate, display k⊥−3-scaling near the k∥ = 0 plane. A phenomenology which incorporates the modification of the energy cascade by rotation is proposed. In the observed regime the nonlinear turbulent interactions are strongly influenced by rotation but not suppressed. Longitudinal two-point velocity structure functions taken perpendicularly to the axis of rotation indicate weak intermittency of the k∥ = 0 (2D) component of the flow while the intermittent scaling of k∥ ≠ 0 (3D) fluctuations is well captured by a modified She–Lévêque intermittency model which yields the expression ζp = p/6 + 2(1 − (2/3)p/2) for the structure function scaling exponents.

Directional wave measurement at Haifa, Israel, and sediment transport along the Nile littoral cell

Results of three years of directional wave measurement at the Eastern Mediterranean coast of Haifa, Israel are presented. The wave-height and energy-flux distributions reveal a moderately high-energy coast with a bimodal annual cycle. The rate of wave-induced longshore sediment transport is estimated from the directional energy flux distributions. It describes an annual cycle with a maximum northward transport of 75 ± 14 × 10 3 m 3/month in midwinter and a southward transport of 26 ± 5 × 10 3 m 3/month in summer. The net annual transport is northward and computed at 110 ± 100 × 10 3 m 3/yr. We show that a wave-induced transport is sufficient in explaining the apparent transport of sediments in the Nile Littoral Cell, from the Nile Delta source to the Haifa Bay sink.

On the low-temperature region of chromospheric flares

Most of the energy of particles accelerated in a flare is used for the creation of a high-temperature flare region, the structure of which is determined by the heat conduction (Shmeleva and Syrovatskii, 1973). However, as the temperature drops with the depth in the chromosphere, the heat flux decreases quickly and in the low-temperature part of a flare may appear to be lower than the direct energy flux carried to these depths by the most energetic of the accelerated particles. In the latter case the radiation from the low-temperature region will be determined by the direct input of energy by energetic particles (Hudson, 1972; Brown, 1973a). Here we consider conditions under which one of the above-mentioned types of heating dominates. Correspondingly we may consider two types of flares: penetrating flares, when heating is produced by non-thermal particles, and thermal ones, when the heat conduction dominates. The conditions of occurrence of one of these types depend mainly on the particle energy spectrum: the heat conduction dominates for the soft spectra and for the high enough temperature of the hot (coronal) part of a flare, as is usual for X-ray flares. It is essential that for both the heating mechanisms the radiation from the low-temperature regions gives as a rule only a small part of the total flare radiation. In the case of conductive heating the temperature run in the cold part of a flare depends essentially on the mode of hydrogen ionization in this region. It is shown that the optical depth effects in hydrogen ionization can be neglected for flares in the upper chromosphere with unperturbed temperature T ∼- 10000 K. The absorption of radiation begins to play a role for lower boundary temperatures T = 6000–8000 K.

Explorer 12 observations of the magnetospheric boundary and the associated solar plasma on September 13, 1961

Phenomena at and near the boundary of the magnetosphere during the prolonged initial phase of a mild magnetic storm on September 13, 1961, were observed with a variety of magnetic field and particle detectors in Explorer 12. There was an abrupt termination of the regular geomagnetic field and a coincident discontinuity in the intensity of trapped particles at a geocentric radial distance of 8.2 earth radii. A mean directional energy flux of the order of tens of ergs (cm/sup 2/ sec ster)/sup -1/ was observed outside the boundary. This energy flux is interpreted as being due to an omnidirectional intensity of the order of 10/sup 10/ (cm/sup 2/ sec)/sup -1/ of electrons having energies of a few kev. From the Chapman- Ferraro point of view, these electrons are believed to be the observable component of a piston' of quasi-thermalized plasma, of the order of 10,000 km thick, which acted as the pressuretransmitting agent between the directional solar wind and the geomagnetic field. Possible relationships between these observations and the third radiation belt' of Gringauz are considered. 29 references. (auth)