Decay Rate Of Field Research Articles

Ultrahigh-resolution atomic localization via superposition of standing waves

In this study we theoretically demonstrate ultrahigh-resolution two-dimensional atomic localization within a three-level λ-type atomic medium via superposition of asymmetric and symmetric standing wave fields. Our analysis provides an understanding of the precise spatial localization of atomic positions at the atomic level, utilizing advanced theoretical approaches and principles of quantum mechanics. The dynamical behavior of a three-level atomic system is thoroughly analyzed using the density matrix formalism within the realm of quantum mechanics. A theoretical approach is constructed to describe the interaction between the system and external fields, specifically a control field and a probe field. The absorption spectrum of the probe field is thoroughly examined to clarify the spatial localization of the atom within the proposed configuration. A theoretical investigation found that symmetric and asymmetric superposition phenomena significantly influence the localized peaks within a two-dimensional spatial domain. Specifically, the emergence of one and two sharp localized peaks was observed within a one-wavelength domain. We observed notable influences of the intensity of the control field, probe field detuning and decay rates on atomic localization. Ultimately, we have achieved an unprecedented level of ultrahigh resolution and precision in localizing an atom within an area smaller than λ/35 × λ/35. These findings hold promise for potential applications in fields such as Bose–Einstein condensation, nanolithography, laser cooling, trapping of neutral atoms and the measurement of center-of-mass wave functions.

Periodicity alters topological states in thermal diffusion system

Topological edge states are a ubiquitous phenomenon across diverse wave systems, including electromagnetic, acoustic and quantum systems. In contrast to wave systems, thermal transport is a kind of diffusion system characterized by pure dissipation. The imposition of different boundary conditions can significantly influence the evolution of thermal system, leading to the appearance of different topological states, which haven't been systematically analyzed yet, especially in practical heat transfer structures. In this work, via a non-Hermitian thermal diffusion lattice model, we discuss the periodicity-dependent topological states. Through rigorous theoretical analysis and numerical simulations of the temperature field, the Hamiltonian is obtained whose eigenvalues are purely imaginary corresponding to the decay rate of the temperature field. Our work paves the way for the investigation of how periodicity alters topological states in thermal diffusion systems, potentially revolutionizing the design of thermal metamaterials for topological thermal protection in thermal management.

Controllable optical effects in Landau-quantized graphene

This paper investigates the manipulation and control of optical properties in a Y-configured four-level Landau-Quantized Graphene system. Through a comprehensive analysis of the density matrix elements, we explore the influence of various system parameters, including control field intensities, detunings, and decay rates, on the optical response of the graphene sample. Our findings unveil compelling phenomena such as optical transparency, sub- and superluminal light propagation, and the emergence of multiple absorption peaks and transparency windows. Specifically, we examine the impact of decay rates on the absorption characteristics of graphene, revealing that higher decay rates diminish the effectiveness of Electromagnetically Induced Transparency (EIT) and slow light in the system. Furthermore, by systematically varying system parameters, we demonstrate the controllability of achieving either single or double EIT through manipulation of control field intensities and detunings. These results open promising avenues for applications in optical communications and quantum information processing, where precise control over graphene's optical properties is critical.

Shielded Cone Coil Array for Non-Invasive Deep Brain Magnetic Stimulation.

Non-invasive deep brain stimulation using transcranial magnetic stimulation is a promising technique for treating several neurological disorders, such as Alzheimer's and Parkinson's diseases. However, the currently used coils do not demonstrate the required stimulation performance in deep regions of the brain, such as the hippocampus, due to the rapid decay of the field inside the head. This study proposes an array that uses the cone coil method for deep stimulation. This study investigates the impact of magnetic core and shielding on field strength, focality, decay rate, and safety. The coil's size and shape effects on the electric field distribution in deep brain areas are also examined. The finite element method is used to calculate the induced electric field in a realistic human head model. The simulation results indicate that the magnetic core and shielding increase the electric field intensity and enhance focality but do not improve the field decay rate. However, the decay rate can be reduced by increasing the coil size at the expense of focality. By adopting an optimum cone structure, the proposed five-coil array reduces the electric field attenuation rate to reach the stimulation threshold in deep regions while keeping all other regions within safety limits. In vitro and in vivo experimental results using a head phantom and a dead pig's head validate the simulated results and confirm that the proposed design is a reliable and efficient candidate for non-invasive deep brain magnetic stimulation.

Spatial and Temporal Distribution of Northwest Cape Transmitter (19.8 kHz) Radio Signals Using Data Collected by the China Seismo-Electromagnetic Satellite

Very Low Frequency (VLF) waves radiated from ground-based transmitters are crucial for long-distance communication and underwater navigation. These waves can reflect between the Earth’s surface and the ionosphere for Earth–ionosphere waveguide propagation. Additionally, they can penetrate not only the ionosphere but also the magnetosphere, where they interact with high-energy particles in the radiation belt. Therefore, studying the spatial and temporal distribution of VLF radio signals holds significant importance. Such research enables us to understand the propagation characteristics of VLF signals, their interaction with radiation belt particles, and their response to space weather and lithospheric activity events. In this paper, we investigate the seasonal variations in the intensity of the Northwest Cape (NWC) transmitter (19.8 kHz) radio signals at satellite altitude and the displacement of the electric field’s peak center. Our analysis is based on the nightly China Seismo-Electromagnetic Satellite (CSES) data from 2019 to 2021. The results reveal the following: (1) There is no significant seasonal variation in the electric field strength within a small area (2.5° radius) around the NWC transmitter. However, a clear seasonal variation in the electric field strength is observed within a larger area (15° radius), with higher strength during winter compared with summer. (2) The power spectral density of the electric field remains constant within the peak central area (approximately 1~2° radius), but it decays with distance outside this region, showing a north–south asymmetry. Moreover, the decay rate of the radiation electric field is slower in the northern direction than in the southern direction. (3) The center of the electric field moves northward from summer to winter and southward from winter to summer. (4) In winter, VLF waves radiated by the NWC transmitter may predominantly propagate by being ducted toward the conjugate hemisphere.

Operation of Prototype Race-Track Closed-Loop HTS Coil With Metal-as-Insulation in Solid Nitrogen

The second generation (2G) high temperature superconductor (HTS) has excellent current-carrying density performance in strong magnetic field. Thus, the maglev system driven by 2G HTS magnets has been studied a lot. In the design of magnets, metal-as-insulation coil retains self-protection feature of the no-insulation coil, and it performs well in charging time. On the other hand, using solid nitrogen (SN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) as a “thermal battery” may effectively reduce the volume of on-board HTS magnets. In order to design on-board magnets with fast charging, small volume and self-protection, firstly a prototype coil was manufactured. Then the experiment apparatus was set up and experiments in the persistent current mode were carried out. It was obtained by fitting that the magnetic field decay rate of the prototype coil was about 0.24% per day. This paper provides a foundation for the production of real-scale on-board magnets cooled by SN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> .

Shock Corrugation to the Rescue of the Internal Shock Model in Microquasars: The Single-scale Magnetohydrodynamic View

Questions regarding the energy dissipation in astrophysical jets remain open to date, despite numerous attempts to limit the diversity of the models. Some of the most popular models assume that energy is transferred to particles via internal shocks, which develop as a consequence of the nonuniform velocity of the jet matter. In this context, we study the structure and energy deposition of colliding plasma shells, focusing our attention on the case of initially inhomogeneous shells. This leads to the formation of distorted (corrugated) shock fronts—a setup that has recently been shown to revive particle acceleration in relativistic magnetized perpendicular shocks. Our study shows that the radiative power of the far downstream of nonrelativistic magnetized perpendicular shocks is moderately enhanced with respect to the flat-shock cases. Based on the decay rate of the downstream magnetic field, we make predictions for multiwavelength polarization properties.

Effect of cavity leakage on time-dependent spectrum of two atoms Tavis-Cummings model

We study the atomic emission spectrum and cavity field spectrum of dipole–dipole coupled two atoms interacting with a single-mode radiation field in a non-ideal cavity. We solved the quantum master equation by a method that combined analytical analysis and numerical solution. The explicit expression of spectral peak position and numerical results of spectral structure are given for the atoms in entangled state and the field in vacuum initially. The results shown that the decay rate of cavity field has obvious influence on the intensity of spectra but a little effect on the spectral structure. The cavity dissipation makes also the measurement time an important factor in measuring spectral structure.

Study of turbulent dispersion of a concentration plume emitting from a line source over a rib‐roughened surface

Turbulent dispersion of a concentration plume emitting from a horizontal line source over a rib-roughened surface has been studied using direct numerical simulations (DNS). Four test cases have been compared to investigate the effects of the source elevation and location on the plume dispersion in a turbulent boundary layer. The transport process of the concentration is investigated in both physical and spectral spaces which includes analyses of statistical moments of the concentration field, decay rate, plume width, pre-multiplied spectra of the velocity and concentration fields, and the probability density function (PDF) of concentration fluctuations. It is observed that as the mean plume development enters the long-range dispersion stage, the decay rate of the mean concentration field begins to feature a constant slope of −3/2, while the vertical spread of the mean plume exhibits a constant slope of 1/3 in all four line source release cases in a ribbed wall flow. It is also observed that the profiles of both the mean concentration field and the RMS of concentration fluctuations exhibit a self-similarity pattern downstream of the line source in all four test cases. By comparing the characteristic length scales of the spanwise velocity and scalar fields, two distinct stages of the instantaneous plume development are observed, dominated by the turbulent convective and diffusive mechanisms. It is discovered that the transition from the turbulent convective stage to the turbulent diffusive stage occurs more rapidly for line sources placed near the wall and inside the cavities.

Effect of sidewall spacing on the temperature field of a three-dimensional heated turbulent wall jet

The effect of sidewalls on the temperature field of a three-dimensional heated turbulent wall jet is characterized by the temperature measurement inside the sidewall enclosure (SWE). The SWE is defined as the presence of sidewalls parallel to the vertical jet centerline plane on both the sides. The sidewalls are equally spaced from the vertical jet centerline plane, and the distance between the sidewall is termed as the width (W). Four different widths (W) 140 mm, 160 mm, 180 mm, and 200 mm SWE are considered at a Reynolds number of Re= 25,000. The temperature field decay rate is increased with an increase in the SWE width in the downstream locations after x/h= 35. The decay rate of the jet centerline temperature in 200 mm SWE is 4.6% higher than the 140 mm SWE. The lateral spread increases with a decrease in SWE width due to the accumulation of the thermal energy content in the lateral shear layers adjacent to the sidewalls. In the near field, thermal spread in the wall-normal direction increases with the increase in the SWE width, but in far-field locations (x/h= 30), the thermal spread increases with a decrease in the SWE width. The wall-normal thermal similarity is delayed with a decrease in the width of the SWE, and it is found at x/h= 25, 22, 19 and 15 for the 140 mm, 160 mm, 180 mm, and 200 mm SWEs, respectively. The temperature field shows the climbing effect over the sidewalls similar to the velocity field in the transverse plane (z−y). The spread of the temperature fields in the lateral direction increases with the increase in the width of the enclosure. The similarity of the temperature field gets distorted near the sidewall (λ=0.9, where λ=z/(W/2) and z= lateral location) due to thermal energy content in lateral shear layers. The one point temperature fluctuation shows the normal distribution of the probability density function along the jet centerline for all the cases of SWE. The probability density function is independent of the SWE width before the attachment (x/h≤ 10) of the flow stream at the sidewall, but after the attachment (x/h≥ 10) of the flow stream to the sidewalls, the probability density function deviated from the normal distribution curve. The skewness and flatness factors were also calculated based on the instantaneous temperature fluctuation inside the SWE.

Rotational effect on the asymptotic stability of the MHD system

In this paper, we consider the large time behavior of solutions of the incompressible rotational magnetohydrodynamics equations. First, we prove the unique existence of a global smooth solution in the Sobolev spaces Hs(R3) for 1/2<s<3/2, when the rotation is sufficiently rapid. Second, we establish the temporal decay estimates for the solution under additional assumptions. It is observed that the rotation affects the decay rate of the velocity field.

Oscillatory Reconnection of a 2D X-point in a Hot Coronal Plasma

Abstract Oscillatory reconnection (a relaxation mechanism with periodic changes in connectivity) has been proposed as a potential physical mechanism underpinning several periodic phenomena in the solar atmosphere, including, but not limited to, quasi-periodic pulsations (QPPs). Despite its importance, however, the mechanism has never been studied within a hot, coronal plasma. We investigate oscillatory reconnection in a one million Kelvin plasma by solving the fully-compressive, resistive MHD equations for a 2D magnetic X-point under coronal conditions using the PLUTO code. We report on the resulting oscillatory reconnection including its periodicity and decay rate. We observe a more complicated oscillating profile for the current density compared to that found for a cold plasma, due to mode-conversion at the equipartition layer. We also consider, for the first time, the effect of adding anisotropic thermal conduction to the oscillatory reconnection mechanism, and we find this simplifies the spectrum of the oscillation profile and increases the decay rate. Crucially, the addition of thermal conduction does not prevent the oscillatory reconnection mechanism from manifesting. Finally, we reveal a relationship between the equilibrium magnetic field strength, decay rate, and period of oscillatory reconnection, which opens the tantalising possibility of utilizing oscillatory reconnection as a seismological tool.

Microwave Soil Heating with Evanescent Fields from Slow-Wave Comb and Ceramic Applicators

Microwave soil heating deactivates weed seeds; however, in many modern agricultural settings, weed seeds are mostly found in the top 1–2 cm of the soil profile. Until recently, microwave soil heating has been achieved using various antennas, which project the microwave energy deeply into the soil. The aim of this research was to develop new microwave applicators that provide shallow heating (less than 50 mm). This paper presents two applicator designs, one based on a comb slow-wave structure and the other on the frustrated total internal reflection (FTIR) principle, which utilise evanescent microwave fields to restrict the depth of microwave heating. The background theory to their performance is presented, followed by experimental evidence of their constrained heating performance under different soil moisture scenarios. Experimental measurements of the heating performance of these applicators, in soils of varying moisture content, demonstrate that the evanescent microwave fields restrict the depth of heating, so that most of the energy is manifested in the top 50 mm of soil. The evanescent field decay rate for the FTIR applicator changes from 44.0 ± 0.7 m−1 to 30 ± 1.2 m−1 as the soil moisture changes from 32% to 174% (dry weight basis). This is higher than the evanescent field decay rate for the comb slow-wave applicator (17.6 ± 0.7 m−1 to 19.9 ± 1.5 m−1). The FTIR applicator has a wider and shallower heating pattern than the comb slow-wave applicator. Because of the double heating lobes of the FTIR applicator, the effective half temperature heating width is approximately 150 mm. This is wider than the half temperature heating width of the comb slow-wave applicator (95 mm).

High-Performance Magnetic-core Coils for Targeted Rodent Brain Stimulations.

Objective and Impact Statement. There is a need to develop rodent coils capable of targeted brain stimulation for treating neuropsychiatric disorders and understanding brain mechanisms. We describe a novel rodent coil design to improve the focality for targeted stimulations in small rodent brains. Introduction. Transcranial magnetic stimulation (TMS) is becoming increasingly important for treating neuropsychiatric disorders and understanding brain mechanisms. Preclinical studies permit invasive manipulations and are essential for the mechanistic understanding of TMS effects and explorations of therapeutic outcomes in disease models. However, existing TMS tools lack focality for targeted stimulations. Notably, there has been limited fundamental research on developing coils capable of focal stimulation at deep brain regions on small animals like rodents. Methods. In this study, ferromagnetic cores are added to a novel angle-tuned coil design to enhance the coil performance regarding penetration depth and focality. Numerical simulations and experimental electric field measurements were conducted to optimize the coil design. Results. The proposed coil system demonstrated a significantly smaller stimulation spot size and enhanced electric field decay rate in comparison to existing coils. Adding the ferromagnetic core reduces the energy requirements up to 60% for rodent brain stimulation. The simulated results are validated with experimental measurements and demonstration of suprathreshold rodent limb excitation through targeted motor cortex activation. Conclusion. The newly developed coils are suitable tools for focal stimulations of the rodent brain due to their smaller stimulation spot size and improved electric field decay rate.

7 T Niobium-Titanium-Based Persistent-Mode Superconducting Magnet for an Electron Beam Ion Source

A high field magnet is a key element of cryogenic electron beam ion sources (EBISs), which are known for generating highly charged ions through the magnetic compression of an electron beam. Herein, we report the design, fabrication, and evaluation of a 7 T niobium-titanium superconducting magnet capable of persistent-mode operation. The magnet was designed using finite element analysis by considering its magnetic, thermal, and mechanical properties. The designed magnet was then fabricated, assembled, and evaluated for various design parameters in a recondensing-type liquid helium cryostat. After several quench trainings, the magnet reached a target magnetic field of 7 T with an operating current of 200 A, a magnetic field uniformity of 0.24%, and an electron beam focusing length of 1.3 m inside the bore. The magnet was successfully operated in the persistent-mode for 9.5 days (228 hours) and achieved a field-decay rate of 0.42 ppm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot \text{h}^{-1}$ </tex-math></inline-formula> . The magnet evaluation results confirm that our superconducting magnet system can be applied to an EBIS to carry out stable and effective electron beam compression.

Transient electroosmotic-driven ionic current magnetic fields in a charged nano-capillary

Transient electrokinetic analysis can provide practical insights on the evolution of dynamic phenomena in micro and nano-capillaries, which are often ignored in a steady-state analysis. In this paper, a numerical model is proposed for the transient electrokinetic analysis of electroosmotic flows in a charged nanocapillary. In addition, the transient effects of ionic currents and the magnetic field generated both inside and outside the nanochannel were evaluated, and the results were compared with a simplified analytical model. Results showed that the peak of the magnetic field strength occurs in the vicinity of the charged walls at the outer surface of the nanochannel, which was associated with the distribution of the total current density flowing within the channel. The magnetic flux density was also compared at three different sections; entry, mid, and exit locations. This comparison proved that the nature of the longitudinal changes in the electric double layer distribution has significant effects on the decay rate of the magnetic field outside of the nanochannel walls. The obtained results confirm that the generated magnetic field, detected outside of the nanochannels, could be used as a secondary electromagnetic signal for biomolecules as a part of a sequencing technique.

Synchronization of polarization chaos in mutually coupled free-running VCSELs.

We numerically demonstrate and analyze polarization chaos synchronization between two free-running vertical cavity surface emitting semiconductor lasers (VCSELs) in the mutual coupling configuration under two scenarios: parallel injection and orthogonal injection. Specifically, we investigate the effect of external parameters (the bias current, frequency detuning and coupling coefficient) and internal parameters (the linewidth enhancement factor, spin-flip relaxation rate, field decay rate, carrier decay rate, birefringence and dichroism) on the synchronization quality. Finally simulation results confirm that in the parallel injection, chaotic synchronization can reach a cross-correlation coefficient of 0.99 within a range of parameter mismatch ±12%. On the other hand, the chaos synchronization for orthogonal injection only reaches a cross-correlation coefficient of 0.95 within a range of parameter mismatch ±3%.

Behaviour prediction of closed-loop HTS coils in non-uniform AC fields

Field decay rate is the key characteristic of superconducting magnets based on closed-loop coils. However, in Maglev trains or rotating machines, closed-loop magnets work in external AC fields and will exhibit an evidently accelerated field decay resulting from dynamic resistances, which are usually much larger than joint resistance. Nevertheless, there has not been a numerical model capable of systematically studying this behaviour, which is the main topic of this work. The field decay curves of a closed-loop high-temperature-superconducting (HTS) coil in various AC fields are simulated based on H-formulation. A non-uniform external field generated by armature coils is considered. Reasonable consistence is found between experimental and simulation results. In our numerical model, the impact of current relaxation, which is a historical challenge, is analysed and subsequently eliminated with acceptable precision. Our simulation results suggest that most proportion of the field decay rate is from the innermost and outermost turns. Based on this observation, a magnetic shielding pattern is designed to reduce the field decay rate efficiently. This work has provided magnet designers with an effective method to predict the field decay rate of closed-loop HTS coils in external AC fields, and explore various shielding designs.

Investigation of magneto‐thermal evolution of AXP 1E 2259 + 586

AbstractIn this work, we calculated the toroidal magnetic field decay rates and magnetic energy decay rates by considering the general relativity effect of AXP 1E2259 + 586 associated with the supernova remnant CTB 109. The results confirmed that the high thermal radiation on the surface of the star could be attributed to Joule heating caused by the dissipation of crustal magnetic field. We also investigated the effects of ultrastrong magnetic fields on magnetization parameter and thermal conductivity in the crust.

Search for the Relationship between the Velocity of a Coronal Mass Ejection and the Decay Rate of the Magnetic Field in the Region of Mass Emission Generation

In this paper, we search for the relationship between the Vlin linear projection velocity and the Vss velocity in the 3D space of coronal mass ejections (CMEs) recorded by LASCO coronagraphs with an “n” decay rate of the transverse component of the Bt magnetic field above the polarity inversion line (PIL) of the photospheric magnetic field in the active region (AR) in which the CME appeared. The Bt decay rate at an altitude h measured from the photosphere was calculated with the formula n(h) = –(h/Bt)(dBt/dh). Three-dimensional calculations of the magnetic field were performed in the potential approximation. The positive trend of the dependences 〈n〉(Vlin) and 〈n〉(Vss), however, does not have sufficient statistical significance: on average, the larger is 〈n〉, the higher are the determined Vlin and Vss CME velocities. Here, 〈n〉 includes the averaging of n over both the altitude and along the extended section of the PIL identified within each studied AR. The relationship between the quality of 〈n〉(Vlin) and 〈n〉(Vss) is shown to depend on the PIL section in the AR within which n is averaged. Based on the example of a fast CME on March 7, 2012, and a slow CME on October 22, 2013, it is shown that the difference in 〈n〉 for CMEs with different velocities is greater if the averaging of n along the PIL is performed within the CME initiation region, not along the entire extended PIL section in the AR.