External Flux Research Articles

The forming mechanism of spontaneous emission noise flux radiated from hydrogen-like atoms by means of vibrational Hamiltonian

The main goal of this article is to investigate the origin of spontaneous emission radiation by applying a new method. In this method, the vibrational Hamiltonian of hydrogen-like atoms (HLAs) is first constructed in accordance with the Hamiltonian of a simple harmonic oscillator. The Hamiltonian is then used to derive the vibrational motion equations of HLAs in a Heisenberg picture. The Langevin equation will ultimately be formed by adding the dissipative term and fluctuating (Langevin) force according to the fluctuation–dissipation theorem. The solution of the Langevin equation provides the exact data on the fluctuations that occur for the electron position during its rather fast vibrational oscillations. On the other hand, the fluctuations in the position of the oscillating electron, in turn, lead to the fluctuations in its potential and kinetic energies so that the appearance of the potential and kinetic noise fluxes is vulnerable. It is finally demonstrated that the potential and kinetic noise fluxes commonly act as an internal source of producing the external noise flux emitted from HLAs in the form of spontaneous emission with a Lorentzian profile. In contrast with all previous procedures, no ambient effect has been involved to describe the forming mechanism of spontaneous emission for the first time.

Gain-induced topological response via tailored long-range interactions

The ability to tailor the hopping interactions between the constituent elements of a physical system could enable the observation of unusual phenomena that are otherwise inaccessible in standard settings1,2. In this regard, a number of recent theoretical studies have indicated that an asymmetry in either the short- or long-range complex exchange constants can lead to counterintuitive effects, for example, the possibility of a Kramer’s degeneracy, even in the absence of spin 1/2 or the breakdown of the bulk–boundary correspondence3,4,5,6,7,8. Here we show how such tailored asymmetric interactions can be realized in photonic integrated platforms by exploiting non-Hermitian concepts, enabling a class of topological behaviours induced by optical gain. As a demonstration, we implement the Haldane model, a canonical lattice that relies on asymmetric long-range hopping to exhibit quantum Hall behaviour without a net external magnetic flux. The topological response observed in this lattice is a result of gain and vanishes in a passive but otherwise identical structure. Our findings not only enable the realization of a wide class of non-trivial phenomena associated with tailored interactions, but also open up avenues to study the role of gain and nonlinearity in topological systems in the presence of quantum noise.

The Influence of Additives on the Rheological and Sedimentary Properties of Magnetorheological Fluid

In this research, the influence of additives on the rheological and sedimentary properties of the magnetorheological fluid (MRF) was tested and analyzed. The additives were stearic acid, sodium dodecyl sulfate (SDS), and their mixture, respectively. The MRF was composed of carbonyl iron particle, silicone oil, liquid paraffin, graphite particle, bentonite, stearic acid, and SDS. The results indicated that the rheological properties of the MRF were mainly influenced by the mass fraction of carbonyl iron particle. When the mass fractions of carbonyl iron particle and additive were the same, the shear stress of MRF with stearic acid was larger than that of MRF with SDS, and the maximum increment was 73.81%. When the mass fraction of carbonyl iron particle was 40–50%, the shear stress of MRF increased firstly and then decreased with the increase of the external magnetic flux density. When the mass fraction of carbonyl iron particle was 60–70%, the shear stress of MRF increased firstly and then was stable with the increase of the external magnetic flux density. The results indicated that the sedimentary property of MRF with the mixture was better than that of MRF with the stearic acid and SDS. The settling rate of MRF with the mixture increased 91.53% compared to other additives.

Internal positive feedback promotes water quality improvement for a recovering hyper-eutrophic lake: A three-dimensional nutrient flux tracking model

Nutrient dynamics in lakes are determined by the combined effects of external and internal nutrient fluxes. However, the feedback loop of nutrient fluxes and water quality changes is still an open question. An integrated three-dimensional flux tracking approach based on the Environmental Fluid Dynamics Code model was established to quantify the long-term dynamic changes in external and internal processes in Lake Dianchi (one of the three most hyper-eutrophic lakes in China), and to explore the potential causes of water quality improvement during 2012–2018. The long-term trends and relative influences of nutrient fluxes on water quality were identified. The results showed that the inflow flux was the largest input source and declined by 50% between 2003 and 2012, which was followed by a stable trend from 2012 to 2018. The second largest input source was benthic release, which exhibited a significant interannual reduction. Algae sedimentation was the largest removal process, and declined by 45% between 2012 and 2018. An integrated analysis demonstrated that, following an external loading reduction prior to 2012, the positive feedback of internal fluxes promoted water quality improvement during 2012–2018. Considering the long timescale of the nutrient-flux feedback mechanism, reducing external loading is still the top priority for a long-term virtuous cycle of water quality in the process of eutrophic lake restoration.

Destruction of a Star during the Evolution of a Star + Supermassive Black Hole System

Destruction of a Star during the Evolution of a Star + Supermassive Black Hole System

Electromagnetic instability of electromechanical nano-bridge incorporating surface energy and size dependency

The external magnetic field might affect the performances of electromechanical nano-bridges sensors and switches. While different physical phenomena on the behavior of nano-electromechanical systems have been addressed, few works have been done on the inspiration of the magnetic flux on the performance of these systems. Herein, the primary field equations necessary for dynamic instability analysis of electromechanical nano-bridges subjected to an external magnetic flux are extracted. The simultaneous effects of scale dependency and surface energies are considered in the proposed. To this end, the consistent couple stress theory is incorporated with the surface elasticity. Next, the system's nonlinearity is defined by using von-Karman nonlinear strains. Also, the impact of vacuum fluctuation is also considered in the developed model. A reduced-order procedure is designed to solve the constitutive equation, and the effects of the longitudinal magnetic field on the instability of nano-bridge are examined. The outcomes demonstrate that the longitudinal magnetic flux considerably increases the instability voltage of the nano-bridge. • The constitutive equations of electromechanical nano-bridges subjected to an external magnetic flux are extracted. • The coupled effect of size dependency and surface energies are considered in the developed model. • The effect of Casimir force is simulated in the proposed model. • The system's nonlinearity is defined by using von-Karman nonlinear strains.

Thermal Modelling of a Remote Sensing Satellite Panel in an Inclined Orbit

Satellites consist of different subsystems; one of them is the thermal control subsystem (TCS), which warranties the specified temperature settings of other subsystems and devices through satellite lifetime. Satellite Thermal modelling is performed by solving thermal budget equation, taking into consideration maximum and minimum external fluxes, and heat rejection from internal devices which fixed on the internal surface of the panel. To reach the optimum design for the thermal control of the panel (radiation surface areas and power of the electric heaters), the thermal analysis results should meet the design requirements, and the temperature ranges of each device or subsystem inside the satellite. Multilayer Insulation (MLI) is one of the most important passive elements of thermal control subsystem covered the satellite as a blanket consists of some layers from thin pressed Mylar or Kapton sheets. MLI is important to minimize the heat exchange between the inside (devices heat dissipation), and outside satellite (external heat fluxes). A parametric investigation is presented for an inclined satellite in Low Earth Orbit (LEO) at 650 km altitude, to study MLI covering area effect on panel thermal control design. Satellite thermal analysis is performed by Thermal desktop/SINDA FLUINT Software by decreasing and increasing MLI on the outer surfaces of the satellite, to ensure that the satellite electrical equipment temperatures maintained in the required ranges for normal operation.

Double-diffusive natural convection study in a shallow horizontal porous layer filled with a binary fluid and submitted to destabilized conditions in the presence of Soret effect

This paper reports an analytical and numerical study of thermosolutal convection in a Brinkman horizontal porous layer saturated with a binary mixture, destabilized by submitting it either to both heat and mass fluxes (a=0, with Soret effect) or only to a heat flux to recover the case of pure Soret effect (a=1). The analytical solution is derived based on the parallel flow approximation and validated numerically using a finite difference method. A good agreement is found between the predictions of the parallel flow approximation and the numerical results obtained by solving the full governing equations. The governing parameters of this study are the Lewis number, Le, the Rayleigh thermal, RT, the Soret number, Sr, and the buoyancy ratio, φ. The thresholds for the onset of convection and the generated heat and mass transfer rates are examined both in the presence (a=0) and in the absence (a=1) of an external mass flux. The influence of the governing parameters on the onset of motion and the resulting fluid flow, temperature and concentration fields is discussed. It was found that the onset of convection for a=0 and positive values of Sr is delayed compared to the case a=1 (pure Soret effect) and, for the latter case, the onset of convection is delayed compared to a=0 and negative values of the Soret number.

Electromagnetic instability analysis of nano-sensor

The enormous increase in the application of nano-electromechanical systems for biological purposes, as well as modern sensors in the particle accelerators, leads to new operation situations for these devices, such as an external magnetic field. While different physical phenomena on the behavior of nano-electromechanical systems have been addressed, few researchers have focused on the magnetic flux’s inspiration on the performance of electromechanical nano-sensors. In this paper, the dynamic electromagnetic instability of nano-sensors immersed in an external magnetic flux is simulated. As nano-structures have a considerable surface-to-volume ratio, the constitutive equation is developed by incorporating surface energies. The impact of finite dimensions is taken into account in the developed model by using corrected relations for electrical and van der Waals force. The nonlinear dynamic behavior of the system is investigated by employing the Galerkin method. We find that the magnetic flux can significantly reduce the dynamic instability threshold of the nano-sensors.

Modeling and optimization of the fabrication process of thin-film solar cells by multi-source physical vapor deposition

This work presents a mathematical model describing the thin film formation during the co-evaporation of elements by PVD process for the production of CIGS type thin film photovoltaic cells. We propose a one-dimensional system of cross-diffusion Partial Differential Equations (PDEs) defined in a time-dependent space domain and introduce a numerical scheme for the discretization of the system. We calibrate our model on true experimental measurements using a dual approach. Then, in order to achieve certain targeted final concentration profiles, we consider an optimization problem that allows controlling the external atomic fluxes injected during the process. Despite its simplicity, the proposed model shows promising results towards a quantitatively predictive model. For instance, novel atomic fluxes obtained as solutions of the optimization problem could represent alternatives to the classical three-stage process. In this paper, a mathematical model describing the thin film formation during the co-evaporation PVD process for the production of CIGS type thin film photovoltaic cells is proposed.

Solids flow patterns in large-scale circulating fluidised bed boilers: Experimental evaluation under fluid-dynamically down-scaled conditions

This work aims at gaining novel knowledge of the mechanisms governing the solids flow pattern in the furnace of large-scale Circulating Fluidised Bed (CFB) boilers. A fluid-dynamically down-scaled unit resembling an existing 200-MWth CFB boiler was built and validated against full-scale data. The extensive experimental campaign showed, among others, that the presence or absence of a dense bed governs the entrainment of solids from the bottom region of the furnace, and that the back-flow of solids at the exit region is negligible at low gas velocities although it quickly becomes significant with an increase in gas velocity. Thus, it is shown that the estimation of the external solids flux by the top flux in the furnace is not generally valid.

Composition and supply of inorganic and organic nitrogen species in dry and wet atmospheric deposition: Use of organic nitrogen composition to calculate the Ocean's external nitrogen flux from the atmosphere

Wet and dry depositions in the southern East China Sea (ECS) differ substantially in their relative proportion of high-molecular-weight organic nitrogen (HMW-ON) and low-molecular-weight organic nitrogen (LMW-ON). By distinguishing between ON with different molecular weights, this study proposes an improved calculation of the contributions of dry and wet depositions to the new production in surface seawater in the southern ECS. This study used 54 rainwater samples and 12 sets of size-fractionated atmospheric particles from the southern ECS, collected from January to December 2014. Dissolved or water-soluble samples were subjected to an ultrafiltration method to separate ON into HMW-ON and LMW-ON. The overall average concentration of ON was 56.5 ± 18.8 μM in wet deposition and 117.0 nmol m−3 in dry deposition. LMW-ON and HMW-ON constituted 82 ± 9% and 18 ± 9% of the total wet deposition, respectively; the respective percentages in dry deposition were 58 ± 11% and 42 ± 11%. In this study, we used C/N: 6.625 in the Redfield ratio, and assumed a HMW and LMW ON utilization rates of 20% and 80%, respectively. The new production potentially supported by the ocean's external nitrogen supply provided through atmospheric input was calculated to be equivalent to 17.5 g C m−2 yr−1; specifically, atmospheric deposition could contribute 26.6% of the total new production in the southern ECS.

The Gaia spectrophotometric standard stars survey – IV. Results of the absolute photometry campaign

ABSTRACT We present Johnson–Kron–Cousins BVRI photometry of 228 candidate spectrophotometric standard stars for the external (absolute) flux calibration of Gaia data. The data were gathered as part of a 10-yr observing campaign with the goal of building the external grid of flux standards for Gaia and we obtained absolute photometry, relative photometry for constancy monitoring, and spectrophotometry. Preliminary releases of the flux tables were used to calibrate the first two Gaia releases. This paper focuses on the imaging frames observed in good sky conditions (about 9100). The photometry will be used to validate the ground-based flux tables of the Gaia spectrophotometric standard stars and to correct the spectra obtained in non-perfectly photometric observing conditions for small zero-point variations. The absolute photometry presented here is tied to the Landolt standard stars system to ≃1 per cent or better, depending on the photometric band. Extensive comparisons with various literature sources show an overall ≃1 per cent agreement, which appears to be the current limit in the accuracy of flux calibrations across various samples and techniques in the literature. The Gaia photometric precision is presently of the order of 0.1 per cent or better, thus various ideas for the improvement of photometric calibration accuracy are discussed.

An Overview of Methods and a New Three-Dimensional FEA and Analytical Hybrid Technique for Calculating AC Winding Losses in PM Machines

This article proposes a new hybrid analytical and numerical finite element (FE) based method for calculating ac eddy current losses in wire windings and demonstrates its applicability for axial flux permanent magnet electric machines. The method takes into account three-dimensional (3-D) field effects in order to achieve accurate results and yet greatly reduce computational efforts. The new 3-D FE-based method is advantageous as it employs minimum simplifications and considers the end turns in the eddy current path, the magnetic flux density variation along the effective length of coils, and the field fringing and leakage, which ultimately increases the accuracy of simulations. This study is one of the first ones to compare meticulous 3-D finite element analysis (FEA) models with more approximate, but faster solution methods, which can be employed in the optimization process. The accuracy of the 3-D FEA calculations has been confirmed through tests on a prototype axial flux permanent magnet machine. The proposed method is applicable for cases with majority of ac copper losses induced due to external magnetic flux sources, such as permanent magnets. Examples of such machines designs are coreless or open slot PM machines with conductors sizes smaller than skin depth.

Thermal Properties and Magnetic Susceptibility of Hellmann Potential in Aharonov–Bohm (AB) Flux and Magnetic Fields at Zero and Finite Temperatures

In this research work, the Hellmann potential is studied in the presence of external magnetic and AB flux fields within the framework of Schrodinger equation using the Nikiforov–Uvarov functional analysis method. The energy equation and wave function of the system are obtained in closed form. The effect of the fields on the energy spectra of the system is examined in detail. It is found that the AB field performs better than the magnetic field in its ability to remove degeneracy. Furthermore, the magnetization and magnetic susceptibility of the system were discussed at zero and finite temperatures. We evaluate the partition function and use it to evaluate other thermodynamic properties of the system such as magnetic susceptibility, $$ \chi_{\text{m}} \left( {\vec{B},\varPhi_{\text{AB}} ,\beta } \right) $$ , Helmholtz free energy $$ F\left( {\vec{B},\varPhi_{\text{AB}} ,\beta } \right) $$ , entropy $$ S\left( {\vec{B},\varPhi_{\text{AB}} ,\beta } \right) $$ , internal energy $$ U\left( {\vec{B},\varPhi_{\text{AB}} ,\beta } \right) $$ and specific heat $$ C_{v} \left( {\vec{B},\varPhi_{\text{AB}} ,\beta } \right) $$ . A comparative analysis of the magnetic susceptibility of the system at zero and finite temperatures shows a similarity in the behavior of the system. A straightforward extension of our results to three dimensions shows that the present result is consistent with what is obtained in the literature.

Analysis and Simulation of Multi-Loop SQUID-Based Electric Circuits With Mesh-Current Method

Practical superconducting quantum interference devices (SQUIDs) have been developed into multiloop hybrid electric circuits with Josephson junctions and normal elements such as resistor, inductor and capacitor. To find a common circuit analysis and simulation method for different types of SQUID hybrid circuits consist of both superconducting and normal components, we introduce a mesh-current method, which can derive both the general system model and uniform circuit equations directly from the equivalent circuit. The mesh-current method is demonstrated in the simulation of a SQUID additional positive feedback circuit. The numerical simulation results are presented and verified with the measurements. Compared with the conventional nodal analysis method, the mesh-current method is excellent in dealing with the relations including external flux, self and mutual inductances in multiloop hybrid circuit analysis; its final circuit equations directly exhibit the physical theorems; its general system model reveals the quantum interference mechanism inside SQUID circuits, and is applicable for further dynamics studies.

Intrinsic Bulk Quantum Oscillations in a Bulk Unconventional Insulator SmB6.

SummaryThe finding of bulk quantum oscillations in the Kondo insulator SmB6 proved a considerable surprise. Subsequent measurements of bulk quantum oscillations in other correlated insulators including YbB12 lent support to our discovery of a class of bulk unconventional insulators that host bulk quantum oscillations. Here we perform a series of experiments to examine evidence for the intrinsic character of bulk quantum oscillations in floating zone-grown single crystals of SmB6 that have been the subject of our quantum oscillation studies. We present results of thermodynamic, transport, and composition analysis experiments on pristine floating zone-grown single crystals of SmB6 and compare quantum oscillations with metallic LaB6 and elemental aluminum. These results establish the intrinsic origin of quantum oscillations from the insulating bulk of floating zone-grown SmB6. The similarity of the Fermi surface in insulating SmB6 with the conduction-electron Fermi surface in metallic hexaborides is at the heart of a theoretical mystery.

External Magnetic Field Measurements in UME Kibble Balance

The new definition of kilogram in terms of the fixed value of Planck constant ensures the long-term stability of SI mass unit and enables traceability from more than one source. Kibble balance experiments offer an effective primary realization method for the new definition of kilogram. Kibble Balance apparatus operating at National Metrology Institute of Turkey is designed with a stationary coil and an oscillating magnet. In contradistinction to traditional moving coil Kibble balance experiments, external magnetic field brings an asymmetry between the Ampere’s law of force and the Faraday’s law of induction in moving magnet experiments. In this paper, we develop a method based on the external magnetic flux density difference measurements in vertical direction to take into account the effect of the external magnetic field on the realization of kilogram. The proposed model in this approach fits well with the data such that the kilogram realization requirement is met within the accuracy of the measuring instrument.

A Carbon-enhanced Lyman Limit System: Signature of the First Generation of Stars?

Abstract We present the study of a Lyman limit system (LLS) at z abs = 1.5441 toward quasar J134122.50+185213.9 observed with VLT X-shooter. This is a very peculiar system with strong C i absorption seen associated with a neutral hydrogen column density of log N(H i) (cm−2) = 18.10, too small to shield the gas from any external UV flux. The low-ionization absorption lines exhibit a simple kinematic structure consistent with a single component. Using CLOUDY models to correct for ionization, we find that the ionization parameter of the gas is in the range −4.5 < log U < –4.2 and the gas density –1.5 < log n(H) (cm−3) < –1.2. The models suggest that carbon is overabundant relative to iron, [C/Fe] > +2.2 at [Fe/H] ∼–1.6. Such a metal abundance pattern is reminiscent of carbon-enhanced metal-poor stars detected in the Galaxy halo. Metal enrichment by the first generation of supernovae provide a plausible explanation for the inferred abundance pattern in this system.

The superconducting quasicharge qubit.

The non-dissipative nonlinearity of Josephson junctions1 converts macroscopic superconducting circuits into artificial atoms2, enabling some of the best-controlled qubits today3,4. Three fundamental types of superconducting qubit are known5, each reflecting a distinct behaviour of quantum fluctuations in a Cooper pair condensate: single-charge tunnelling (charge qubit6,7), single-flux tunnelling (flux qubit8) and phase oscillations (phase qubit9 or transmon10). Yet, the dual nature of charge and flux suggests that circuit atoms must come in pairs. Here we introduce the missing superconducting qubit, 'blochnium', which exploits a coherent insulating response of a single Josephson junction that emerges from the extension of phase fluctuations beyond 2π (refs. 11-14). Evidence for such an effect has been found in out-of-equilibrium direct-current transport through junctions connected to high-impedance leads15-19, although a full consensus on the existence of extended phase fluctuations is so far absent20-22. We shunt a weak junction with an extremely high inductance-the key technological innovation in our experiment-and measure the radiofrequency excitation spectrum as a function of external magnetic flux through the resulting loop. The insulating character of the junction is manifested by the vanishing flux sensitivity of the qubit transition between the ground state and the first excited state, which recovers rapidly for transitions to higher-energy states. The spectrum agrees with a duality mapping of blochnium onto a transmon, which replaces the external flux by the offset charge and introduces a new collective quasicharge variable instead of the superconducting phase23,24. Our findings may motivate the exploration of macroscopic quantum dynamics in ultrahigh-impedance circuits, with potential applications in quantum computing and metrology.