Atomic Temperature Research Articles

Analysis of wall catalytic effects on magnetohydrodynamic control of high-temperature non-quilibrium flow field

In the re-entry process of the vehicle into the atmosphere, the high-temperature environment, induced by the compression of the strong shock wave and viscous retardation, is created around the head of a vehicle. These generate a conductive plasma flow field, which provides a direct working environment for the application of magnetohydrodynaimic (MHD) control technology. Numerical simulations based on thermochemical non-equilibrium MHD model are adopted to analyze the surface heat flux of an orbital reentry experiment (OREX) vehicle. The influences of wall catalytic conditions on the aerothermal environment under different flight conditions are discussed. In addition, the control mechanism of an external magnetic field on high-temperature thermochemical non-equilibrium flow field is analyzed. The results show that the distribution of surface heat flux monotonically increases with the catalytic recombination coefficient increasing, and the surface heat flux rises and then drops with the flight altitude decreasing. Moreover, the wall catalytic properties significantly affect the efficiency of MHD control technology, and the total heat flux is closely related to the accumulation of atomic components, diffusion gradient and temperature gradient near the wall region. With an external magnetic field applied, the accumulation of oxygen atoms and nitrogen atoms near the wall can be reduced. Moreover, the Lorentz force can increase the shock standoff distance, and then reduce the component diffusion gradient and wall temperature gradient. Under three different wall catalytic conditions, the ability to control the surface heat flux MHD is ranked from strong to weak as fully catalyzed, partially catalyzed and non-catalyzed.

Chemical heat derived from rocket-borne WADIS-2 experiment

AbstractChemical heating rates were derived from three of the most significant reactions based on the analysis of common volume rocket-borne measurements of temperature, atomic oxygen densities, and neutral air densities. This is one of the first instances of the retrieval of nighttime chemical heat through the utilization of non-emissive observations of atomic oxygen concentrations, obtained through in situ measurements, performed at the Andøya Space Center (69°N, 16°E) at 01:44:00 UTC on 5 March 2015. Furthermore, we determine the heating efficiency for one of the most significant reactions of atomic hydrogen with ozone and illustrate the methodology for such calculations based on known atomic oxygen and temperature. Subsequently, using ozone values obtained from satellite observations, we retrieved odd-hydrogens and total chemical heat. Finally, we compared the retrieved chemical heat with the heat from turbulent energy dissipation. Our findings reveal that the vertically averaged chemical heat is greater than the heat from turbulent energy dissipation throughout the entire mesopause region during nocturnal conditions. The heating rates of turbulent energy dissipation may exceed the chemical heating rates only in narrow peaks, several hundred meters wide. Graphical Abstract

Enhancing quantum coherence in hybrid optomechanical systems with coherent feedback, atomic ensembles, and optical parametric amplifier

Abstract We theoretically investigate quantum coherence in a hybrid optomechanical system with a fixed mirror, mechanical oscillators, two-level atoms, and an optical parametric amplifier (OPA) within the cavity. A coherent feedback loop is created by redirecting part of the cavity's output field back into the cavity via an asymmetric beam splitter. Using numerical solutions of the Lyapunov equation and steady-state mean values, we quantify the Gaussian quantum coherence of the system. Our results show that the OPA, coherent feedback, atomic ensembles, and strong laser power significantly enhance quantum coherence, while higher atomic decay rates, relative phase, and temperatures reduce it. This approach not only boosts quantum coherence but also improves resilience to temperature fluctuations, providing a robust foundation for quantum information processing.

Comparison and analysis of methods for measuring the spin transverse relaxation time of rubidium atomic vapor

The spin transverse relaxation time (T2) of atoms is an important indicator for magnetic field precision measurement. Especially in optically-pumped atomic magnetometer, the linewidth of the magnetic resonance signal is one of the most important parameters of sensitivity, which is inversely correlated with T2 of atoms. In this paper, we propose four methods, namely spin noise spectroscopy signal fitting, radio-frequency free induction decay (RF-FID) signal fitting, ω m (modulation frequency)-broadening fitting, and magnetic resonance broadening fitting, for in-situ measurement T2 of atomic vapor cells based on light-atom interactions. Meanwhile, T2 of three Rubidium (Rb) atomic vapor cells with different parameters are measured and discussed by using these four methods. A comparative analysis visualizes the characteristics of the different methods and the effects of buffer gas on T2 of Rb atoms. Through theoretical and experimental analysis, we assess the applicability of each method and concluded that the RF-FID signal fitting method provides the most accurate measurements due to the timing sequence control system, which results in a cleaner measurement environment. Furthermore, we demonstrate and qualitatively analyze the relationship between temperature and T2 of Rb atoms. This work may offer valuable insights into the selection of atomic vapor cells and it is also applicable for the spin-exchange relaxation-free region.

Fiber laser system for Rb atomic fountain clock

A compact and robust all-fiber laser system comprising fiber-optical components for a Rb atomic fountain clock is demonstrated. The laser sources were based on the frequency doubling of two seed lasers at a wavelength of 1560 nm, which were locked using digital frequency locking and modulation transfer spectroscopy. During the Sisyphus cooling period, the PZT control voltage of the fiber laser was ramped to detune the laser frequency to 170 MHz, and we get an atomic temperature of 1.9 □K. A series of customized optical fiber splitters, acousto-optic modulators (AOMs), and shutters were integrated into two 2U enclosures as cooling and repumping light modules. The entire laser system was integrated into a 22U cabinet and was characterized via polarization, power, and frequency stability measurements over 100 days. Apply the laser system to the Rb atomic fountain clock, which exhibited a frequency stability of less than 4.5 × 10-16 at the interval of 24 h.

Molecular dynamics study on the enhancement of high‐temperature friction and mechanical properties of perfluoroelastomers by carbon nanomaterials

AbstractThe mechanical and frictional properties of pure perfluoroelastomer, graphene (GN)/perfluoroelastomer, and carbon nanotube (CNT)/perfluoroelastomer composite systems were investigated using molecular dynamics simulations. The influence of carbon nanomaterials on the glass transition temperature, mechanical properties, and frictional behavior of perfluoroelastomers at various temperatures was evaluated. The simulation results demonstrated that the addition of GN and CNTs increased the glass transition temperature of perfluoroelastomers to varying extents. CNTs enhanced the mechanical properties of perfluoroelastomers more effectively than GN, whereas GN provided superior improvement in frictional properties compared to CNTs. Analysis of stress–strain distribution, atomic motion trajectory, interaction energy, mass density, and temperature distribution, bond orientation parameters, radial distribution function (RDF), mean square displacement (MSD), and diffusion coefficients revealed the mechanisms and differences by which GN and CNTs enhance the mechanical and frictional properties of perfluoroelastomers.Highlights Carbon nanomaterials enhance perfluoroelastomer's high‐temperature performance. CNTs provide higher mechanical strength but lower wear resistance. GN nanosheets outperform CNTs in reducing friction and wear. Molecular dynamics simulations reveal distinct enhancement mechanisms.

Thermal Melting of a Vortex Lattice in a Quasi-Two-Dimensional Bose Gas.

We report the observation of the melting of a vortex lattice in a fast rotating quasi-two dimensional Bose gas, under the influence of thermal fluctuations. We image the vortex lattice after a time-of-flight expansion, for increasing rotation frequency at constant atom number and temperature. We detect the vortex positions and study the order of the lattice using the pair correlation function and the orientational correlation function. We evidence the melting transition by a change in the decay of orientational correlations, associated with a proliferation of dislocations. Our findings are consistent with the hexatic to liquid transition in the Kosterlitz, Thouless, Halperin, Nelson, and Young scenario for two-dimensional melting.

Influences of ultrasonic vibration directions, amplitudes, and frequencies on sapphire polishing studied by molecular dynamics

The sapphire surface morphology, atom removal rate, temperature, polishing force, subsurface damage, dislocation, and stress were explored under different ultrasonic directions, frequencies and amplitudes through molecular dynamics (MD). For both vertical and horizontal vibration, the rising ultrasonic frequency and amplitude will reduce the tangential and normal force, and increase the subsurface temperature and the material removal rate (MRR). Higher frequencies promote the basal dislocation, thus reducing the subsurface damage. Higher amplitudes cause thinner subsurface damage layer under horizontal vibration. However, it is opposite at vertical vibration. The horizontal vibration can obtain a flatter polished surface and a thinner subsurface damage layer due to the longer trajectory and less impact on sapphire surface. This study can provide reference for sapphire high-quality polishing.

Atom number fluctuations in Bose gases—statistical analysis of parameter estimation

Abstract The investigation of atom number fluctuations in quantum gases at finite temperatures showcases the ongoing challenges in understanding complex quantum systems. Recently, the microcanonical nature of atom number fluctuations in weakly interacting Bose-Einstein condensates was observed. This motivates an investigation of the thermal component of partially condensed Bose gases, due to the conservation of the total atom number.

Here, we present a combined analysis of both components, including a comprehensive analysis of the uncertainties in the preparation and parameter extraction of partially condensed quantum gases. This enables a complementary observation of the thermal atom number fluctuations and yields and improved value of the peak BEC atom number fluctuations $\Delta N_\mathrm{p,0}^2 =(3.7\pm7)\times10^5$ close to the critical temperature. This corresponds to a reduction by \SI{41}{\percent} with respect to previous analysis and corroborates the microcanonical nature of the fluctuations.

The analysis of noise contributions due to the preparation and evaluation of partially condensed Bose gases is based on Monte Carlo simulations of optical density profiles. Importantly, this allows for an estimation of the technical noise contributions to the atom number and temperature, which is generally applicable in the field of ultracold atoms.

Investigating the Discoloration of Leaves of Dioscorea polystachya Using Developed Atomic Absorption Spectrometry Methods for Manganese and Molybdenum.

The Chinese yam (Dioscorea polystachya, DP) is promising for the food and pharmaceutical industries due to its nutritional value and pharmaceutical potential. Its proper cultivation is therefore of interest. An insufficient supply of minerals necessary for plant growth can be manifested by discoloration of the leaves. In our earlier study, magnesium deficiency was excluded as a cause. As a follow-up, this work focused on manganese and molybdenum. To quantify both minerals in leaf extracts of DP, analytical methods based on atomic absorption spectrometry (AAS) using the graphite furnace sub-technique were devised. The development revealed that the quantification of manganese works best without using any of the investigated modifiers. The optimized pyrolysis and atomization temperatures were 1300 °C and 1800 °C, respectively. For the analysis of molybdenum, calcium proved to be advantageous as a modifier. The optimum temperatures were 1900 °C and 2800 °C, respectively. Both methods showed satisfactory linearity for analysis. Thus, they were applied to quantify extracts from normal and discolored leaves of DP concerning the two minerals. It was found that discolored leaves had higher manganese levels and a lower molybdenum content. With these results, a potential explanation for the discoloration could be found.

Stabilization of natural antioxidants from Chillangua (Eryngium foetidum) by encapsulation

The Chillangua (Eryngium foetidum) is 4a species of significant scientific interest due to its history and traditional uses throughout the world. Therefore, the focus of this research was on stabilizing the functional and antioxidant components of Chillangua through encapsulation with maltodextrin and Arabic gum. A central composite experimental design was used to evaluate the variables: type of encapsulant (maltodextrin and Arabic gum), encapsulant concentration (3% and 10%), and atomization temperature (130 and 160°C). The results showed that the fresh plant contained 1.34% fat, 17.47% protein, 22.90% fiber, 14.24% ash, and a pH of 6.88. Additionally, concentrations of 3,883.77 μg/g of chlorophyll a, 1,761.72 μg/g of chlorophyll b, 889.19 μg/g of carotenoids, 61.21 mg/g of total polyphenols, 0.02 mg/g of flavonoids, 1.29 mg/g of ascorbic acid, 40 µmol Trolox Eq/g, and 91.60 µmol Trolox/g of antioxidant activity by 2´2´-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-difenil-1-picrilhidrazilo (DPPH), respectively, were identified. When encapsulating Chillangua, it is identified that a reduction occurs in its functional components, as well as its antioxidant activity. The maximum process optimization was achieved at 160°C with 3% maltodextrin and 3% Arabic gum. The irregular morphology of the particles contained C, O, K, Zn, Cl, Al, Ca, and Na.

Study of Size Effect on Ni60Nb40 Amorphous Particles and Thin Films by Molecular Dynamic Simulations

Ni60Nb40 amorphous particles (APs) and amorphous thin films (ATFs) with various sizes were investigated by molecular dynamic simulations. It is revealed that sample size has effects on both Ni60Nb40 APs and ATFs composed of shell or surface and core components. Ni60Nb40 APs have an average bond length of 2.57 Å with major fivefold-symmetry atomic packing and low bond-orientation orders of Q6 and Q4 in both core and shell components. Ni atoms in Ni60Nb40 APs and ATFs prefer to segregate to the shell and surface regions, respectively. Atomic packing structure differences between various-sized Ni60Nb40 APs and ATFs affect their glass transition temperatures Tg, i.e., Tg decreases as the particle size or the film thickness decreases in Ni60Nb40 APs and ATFs, respectively. Our obtained results for Ni60Nb40 APs and ATFs clearly reveal a size effect on atomic packing and glass transition temperature in low-dimensional metallic glass systems.

A Community Ionosphere‐Thermosphere Observing System Simulation Experiment (OSSE) Tool: Geospace Dynamics Constellation Example

AbstractObserving System Simulation Experiments (OSSEs) provide an effective way to evaluate the impact of assimilating data from a specific observing system on hindcasting, nowcasting, and forecasting of environmental systems. The NSF NCAR's Data Assimilation (DA) Research Testbed/Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (DART/TIEGCM) tool, to be hosted at the NASA Community Coordinated Modeling Center, serves as a valuable and accessible community resource for quantitatively evaluating the impact of observations from both current and future ionosphere‐thermosphere (IT) observing systems. This study demonstrates the utility of DART/TIEGCM as an IT OSSE tool, using synthetic observations simulated using a currently planned NASA Geospace Dynamics Constellation (GDC) observing system design. Five sets of OSSEs are carried out to compare the effects of assimilating various combinations of prospective GDC observations (e.g., neutral temperature, neutral wind, neutral composition, atomic oxygen ion density, and ion and electron temperature) during a major geomagnetic storm period of the St Patrick's Day Storm on 17 March 2013. The maximum error reduction in neutral temperature and atomic ion oxygen density is 24.6% and 43.3% compared to the control experiment. These OSSEs indicate the benefits of coupled IT DA approaches implemented in DART/TIEGCM to maximize the impact of multi‐parameter IT observations, such as those expected from the GDC mission. Although more work is required to draw any definitive conclusion on the GDC data impact, the study provides an illustrative example of how the DART/TIEGCM community tool can be used to evaluate observational impacts of planned or existing missions for geospace research and applications.

Molecular dynamics simulations and analyzation of Cu deposited on stainless steel substrate surfaces

Copper (Cu) is used in integrated circuits and microdevices and has the potential to replace aluminum alloys due to its low resistivity, strong electromigration properties, and affordability. However, a significant factor that influences the performance of devices at the micro and nano scales is the surface roughness of the deposits. LAMMPS software is employed to simulate the deposition Cu on an ideal state for a stainless-steel substrate. The deposition process and deformation behavior of Cu on the surface and the roughness of the deposition surface are analyzed. Taking the deposition process of Cu atoms as an object, the effects of different atomic numbers, different temperatures, different velocities, and different heights on the surface roughness of the deposits were investigated. The atomic structure composition of the deposition velocity is analyzed, and the radial distribution function is analyzed to reveal the microscopic mechanism of action. The results of the theoretical deposition and analysis show that the surface roughness increases with the number of atoms deposited and decreases with increasing substrate temperature. The surface roughness first decreases and then, after some fluctuation, stays constant at a particular level with increasing velocity. Additionally, as the deposition height increases, the surface roughness reduces. There is a nonlinear relationship between the various components and the deposited surface roughness. The surface quality of deposits can be improved during the deposition process by optimizing the deposition parameters of deposition atoms, substrate temperature, deposition velocity, and deposition height.

Research on key factors of pulsed CO2 laser annealing of Ge core fiber

The germanium (Ge) core fiber with a core diameter of 29–32 μm and a cladding diameter of 158–162 μm was annealed by pulsed CO2 laser, exploring the key factors determining the properties of annealed Ge core fiber. The experimental results shown that the single pulse energy and the laser scanning speed are key factors of pulsed CO2 laser annealing of Ge core fibers. The reasons for experimental results were preliminarily analyzed from the perspectives of Ge atomic instantaneous kinetic energy and temperature field of Ge core during annealing. For different frequencies of laser annealing, optimal samples with similar properties can be obtained by adjusting the single pulse energy and laser scanning speed. For the samples annealed by 30 kHz, 50 kHz, 60 kHz, and 70 kHz lasers, the optimal Raman frequency average value is 301.191 cm−1, 301.107 cm−1, 301.153 cm−1, and 301.174 cm−1; the lowest propagation loss is 2.174 dB/cm, 2.596 dB/cm, 2.387 dB/cm, and 2.312 dB/cm respectively, which were measured using a quantum cascade laser with the wavelength range from 4.7 to 4.9 μm.

Effect of crystal orientation on surface/subsurface damage characteristics of nano-cutting Ni-based single crystal superalloy

In ultra-precision machining, material anisotropy has an essential impact on surface generation and subsurface damage. In this work, the molecular dynamics method is applied to create the diamond nano-cutting models of Ni-based single crystal (NBSX) superalloy workpieces with different crystal orientations, and the surface/subsurface damage characteristics, crystal structure changes, cutting force, and atomic temperature and stress are discussed. The results show significant differences in surface/subsurface quality, crystal structure transformation, cutting force, atomic temperature and stress distributions and dislocation density obtained from nano-cutting workpieces along different crystal orientations. In four groups of workpieces, the surface/subsurface quality is used as an evaluation index, which shows that the [110](001) crystal orientation has the best cutting effect, and the [111](1‾ 10) crystal orientation is the worst cutting direction. This work reveals the damage generation mechanism of the machined surface/subsurface of NBSX superalloy on an atomic scale, which provides technical support for improving machining quality and optimizing machining parameters.

Atomistic analysis on implantation effects of hydrogen ions and copper ions into 4H-SiC

The microstructure evolution of 4H-SiC under the implantation of hydron ions and copper ions was investigated using molecular dynamics (MD) simulations and experimental analysis. MD models were developed to simulate the implantation of single Cu2+ and H+ ions into SiC, analyzing lattice damage, amorphous defects, and temperature distribution. H+ ion implantation resulted in a higher number of amorphous atoms compared to Cu2+ ions. The maximum atomic temperature during Cu2+ ion implantation was significantly higher (1635 K) than during H+ ion implantation (950 K), although the volume of the temperature rise region was larger in the H+ model. Cu2+ ions induced more severe lattice vibrations than H+ ions. Atom movement along regions of weak lattice binding energy was observed. The study also examined overlapping multiple ion implantations, considering ion type, initial energy, and incident angle. Cu2+ ions exhibited smaller sputtering yield, projection range, number of amorphous atoms, and energy increment compared to H+ ions. A 0° incident angle resulted in higher sputtering yield and increased amorphous structure formation due to the channeling effect, which was more pronounced in the H+ model. The experimental results demonstrate that compared to Cu2+ ions, H+ ions have a greater impact on the surface peak roughness, sub-surface damage depth, and surface damage of SiC samples. It can provide a reliable guidance for selecting process parameters and the types of ions to implant.

The study of ideal/defected graphene nanosheet roughness after atomic deposition process: Molecular dynamics simulation

In this work, molecular dynamics (MD) approach was performed to study the surface roughness of ideal/defected graphene nanosheet after carbon atoms deposition at various temperatures and pressures. In our calculations, the atomic interactions of nanostructures are based on TERSOFF and Lennard-Jones potential functions. The results show that the temperature of simulated structure is an important parameter in atomic deposition process and initial temperature enlarges, intensifies atomic deposition ratio. Numerically, by temperature increasing to 15 K, the surface roughness amplitude increase to 0.98 Å/0.83 Å after atomic deposition in ideal/defected structure. The roughness power in MD simulations converges to 0.64/0.55 in ideal/defected sample at maximum temperature. Furthermore, the pressure effects on dynamical behavior of simulated samples were reported in our study. We conclude that, by increasing initial pressure from 0 to 2 bar, the surface roughness amplitude in ideal/defected atomic arrangement increases to 1.01 Å/0.84 Å after deposition process and the roughness power of simulated structures reaches to larger value. Numerically, by initial pressure setting at 2 bar, the roughness power value converged to 0.72/0.56 in ideal/defected graphene. Reported numeric results in various temperature and pressures predicted the initial condition can be manipulated the atomic deposition process in ideal/defected graphene nanostructures.

Qualitative ab initio theory of magnetic and atomic ordering in FeNi

Magnetic and atomic ordering in equiatomic FeNi alloy is studied by different techniques and methods based on density functional theory in order to clarify the main driving forces and their interplay behind these transitions and possibility of their accurate description within standard density functional theory calculations. The Curie temperature is obtained in Monte Carlo simulations using magnetic exchange interactions obtained by applying the magnetic force theorem within multiple scattering theory for different magnetic and atomic configurational states, including account for the thermal atomic displacements and exchange-correlation potential. The calculations show a very strong sensitivity of the results upon exchange-correlation potential, atomic order, and thermal atomic displacements. The calculated Curie temperature of a completely random alloy with the account of thermal lattice displacement is at least about 200 K below the known experimental data (780–800 K) depending on the above mentioned factors. The atomic order-disorder transition temperature is determined from effective chemical interactions, which apart from the chemical contribution (on the ideal fcc lattice) include contributions from lattice thermal vibrations and local lattice relaxations. The effective chemical interactions are strongly affected by the magnetic state, so the order-disorder transition temperature changes between 1000 and 140 K in the fully ordered ferromagnetic and paramagnetic states, respectively. For the reduced magnetization 0.7 (close to the experimental order-disorder transition temperature at 600 K), the order-disorder transition temperature varies between 550 and 700 K depending mostly on the exchange-correlation potential. The latter effect is the uncertainty in the choice of the exchange-correlation approximation in density functional theory calculations. Published by the American Physical Society 2024

Tritium storage and release mechanism in nuclear graphite using first-principles combined thermal desorption theory

Nuclear graphite (NG) is widely applied in nuclear facilities, and its strong interaction with tritium is an essential factor for tritium transport behavior in various reactors and the treatment of radioactive NG waste. Given that NG is a polycrystalline and porous material, interactions between tritium and NG exist in various microstructures, including graphite edges, graphene basal planes, and amorphous structures. In this study, density functional theory which is integrated in Vienna ab initio simulation package (VASP) was combined with thermal desorption theory to elucidate the underlying mechanism of hydrogen isotope storage corresponding to the experimentally observed desorption peaks in NG. The four desorption temperature peaks, ranging from low to high, were mainly attributed to hydrogen isotope desorption from the graphite basal plane surface, amorphous carbon surface, unsaturated armchair and zigzag edges, respectively. The interaction between hydrogen isotopes and carbon nanostructures provides deeper insights into the understanding of tritium enrichment on the NG surface, which is primarily attributed to the adsorption of tritium on graphite basal plane-like surfaces at relatively low temperatures. This study provides a practical method to bridge the gap between the atomic binding structure and desorption temperature peaks from a kinetic perspective, providing insights into temperature-dependent hydrogen desorption in typical carbon structures and deepening our understanding of tritium transport behaviors in advanced nuclear energy systems.