Highlights
Abstract +
Ultrafast differential scanning calorimetry is the third-generation technique of differential thermal-analysis. It can fast heat up to 60000 K/s or fast cool down to 40000 K/s, so its temperature-changing rate spans five orders of magnitude, and permit repeating experiments on compounds or materials with a melting point lower than 1000 ℃. The unique rate of temperature change allows it to record structural changes of sample in milliseconds, producing a significant number of data. A “top-view” graph is suggested in this study for data analysis. It basically projects the heat flow onto a plane of variables such as temperature, rate or time and uses color contrast to describe the intensity change of heat flow. The issues with “side-view” graphs, where it is a challenge to discern rate or time from several curves, are successfully resolved by this novel technique. It can also realize a comparison of the kinetics among several co-existing physical events. Using an Au-based metallic glass as an example material, this work collects the data from four “side-view” graphs in literature, replots the data on “top-view” graphs, and compares pros and cons. Any substance or material to be examined by utilizing fast differential scanning calorimetry can be examined through using the “top-view” approach. It is useful not only for data analysis but also for constructing processing maps for novel materials, finding new structural transitions, and examining the kinetic behaviors of physical phenomena. All the data presented in this paper are openly available at https://doi.org/ 10.57760/sciencedb.j00213.00012.
The 90th Anniversary of Acta Physica Sinica
EDITOR'S SUGGESTION
2024, 73 (7): 070301.
doi: 10.7498/aps.73.20240222
Abstract +
The Landau Fermi liquid theory and the Ginzburg-Landau phase transition theory stand as two pivotal cornerstones in traditional condensed matter physics, achieving significant success in addressing crucial physical phenomena such as BCS superconductors and liquid helium superfluids. However, marked by the discoveries of the quantum Hall effect and high-temperature superconductivity in the 1980s, it gradually became evident that for a broad class of novel quantum states, such as fractional quantum Hall states and quantum spin liquids, their properties transcend the Landau Fermi liquid theory and Ginzburg-Landau phase transition theory. Topological order and its related concepts of long-range many-body quantum entanglement and fractionalized excitation have become the key concepts to understand these exotic quantum states. Designing and identifying topologically ordered states of matter in quantum materials and quantum simulation systems, and probing and manipulating their fractionalized excitations, are important research directions in modern condensed matter physics. In recent years, great progress has been made in the quantum simulation and manipulation of topological order on highly controllable quantum simulation platforms, such as Rydberg atomic systems, superconducting quantum processors, and two-dimensional moiré superlattices. This article provides a brief overview of recent research advances and challenges in the study of topological order in traditional condensed matter systems and quantum simulation experimental platforms. It also provides prospects for the future developments of this field.
SPECIAL TOPIC—Heat conduction and its related interdisciplinary areas
EDITOR'S SUGGESTION
2024, 73 (7): 070702.
doi: 10.7498/aps.73.20240150
Abstract +
Triboelectric nanogenerator (TENG), as a micro-nano power source or self-powered sensor, has shown great prospects in various industries in recent years. The TENG output performance is closely related to the contact electrification characteristics of the triboelectric dielectric material. Herein, we first introduce the relevant fundamental theory and models of TENG and tribo-dielectrics. Then, we introduce the material selection, modification method (including surface modification and bulk modification) and structural design strategy of TENG dielectric material. Surface and bulk modification mainly involve surface roughness control, surface functional group regulation, and optimization of dielectric parameters. In terms of dielectric structural design, the principle of charge transport, trapping, and blocking layers as well as typical techniques to improve the dielectric properties of TENGs through multi-layer structures are highlighted. Finally, challenges and directions for future research are discussed, which is conducive to the fabricating of high-performance TENG dielectric materials.
SPECIAL TOPIC—Heat conduction and its related interdisciplinary areas
EDITOR'S SUGGESTION
2024, 73 (7): 078801.
doi: 10.7498/aps.73.20240201
Abstract +
Cross-linked polyethylene (XLPE) has been widely used in the field of power cables due to its excellent mechanical properties and insulating properties. However, during the manufacturing of high voltage cables, XLPE will inevitably be affected by electrical aging, thermal aging and electro-thermal combined aging, which makes the resistance and life of the material decline. Therefore, it is necessary to enhance the aging resistance of XLPE without affecting its mechanical properties and insulating properties, so as to extend its service life. In this work, the structural characteristics and cross-linking mechanism of XLPE are introduced, the aging process and influencing mechanism are systematically analyzed, and the life decay problems of XLPE due to aging are explored by using methods such as the temperature Arrhenius equation and the inverse power law of voltage. The improvement strategies such as grafting, blending, and nanoparticle modification can be used to enhance the thermal stability, antioxidant properties, and thermal aging resistance of XLPE, thereby extending its service life. Finally, the strategies of adjusting and controlling the service life of XLPE cable insulation materials in the future are discussed, which provide theoretical guidance for further improving long-term stable operation of XLPE cable insulation materials.
SPECIAL TOPIC—Heat conduction and its related interdisciplinary areas
EDITOR'S SUGGESTION
2024, 73 (7): 070701.
doi: 10.7498/aps.73.20231869
Abstract +
During the long-term operation of a cable, the electrical field, high temperature, and interface stress may age or deteriorate the silicon rubber (SIR) insulation of the cable accessories, affecting the combined electrical-thermal-force performance of the accessories, and easily causing discharge faults. In this work, the electrical-thermal-force properties of silicone rubber for cable accessories under thermal aging and combined force-thermal aging are studied experimentally and numerically. The changes and mechanisms of physical and chemical properties, electrical properties, thermal properties and mechanical properties of silicone rubber are tested and compared before and after aging. The changes of electric, thermal and force field of cable accessories, caused by the change of SIR material parameters under different aging time and aging form, are further simulated. The experimental results show that the crosslinking degree and molecular motion system of SIR will change with the deepening of the aging degree, which will change the electrical-thermal-force properties of the material to different degree. After aging, large agglomeration protrudes and small cavities appear in SIR section, and the damage is more serious under force-thermal aging. The relative dielectric constant first decreases and then increases with the aging time increasing. The volume resistivity, breakdown strength and flashover voltage all first increase and then decrease. The thermal conductivity first increases and then decreases with aging time increasing. In addition, with the increase of aging time, the tensile strength and elongation at break decrease gradually. Considering the change of properties after aging, the destruction of SIR material by force-thermal aging is more serious. The simulation results show that under the two aging modes, the maximum electric field strength at the stress cone root of the cable accessories first increases and then decreases with the increase of time. The electric field strength at the stress cone root of the cable accessories, caused by the force-thermal aging, changes little, maintaining about 2.2 kV/mm. The difference in temperature between the inside and the outside of the insulation layer is obvious under different aging degree, and the temperature difference shows a first decreasing and then increasing trend under both aging modes, and the maximum temperature gradient is 9.15 ℃. The interface stress at the stress cone root decreases from 0.263 to 0.230 MPa, which is about 12.5% lower. This work has guiding significance in evaluating the insulation performance and analyzing the fault of distribution cable accessories.
EDITOR'S SUGGESTION
2024, 73 (7): 072801.
doi: 10.7498/aps.73.20231957
Abstract +
Neutron capture reaction is one of the neutron reactions and plays an important role in using reactor control rods and shell materials, designing nuclear device structures, and studying nuclear astrophysics S processes and element origins. The 4π BaF2 detection device has advantages such as high time resolution, low neutron sensitivity, and high detection efficiency, thus making it suitable for measuring neutron radiation capture reaction cross-section data. In order to fill the gap in our neutron capture reaction data in the keV energy range and improve their accuracy, the Key Laboratory of Nuclear Data at the Chinese Institute of Atomic Energy (CIAE) has established a Gamma Total Absorption Facility (GTAF), which consists of 28 hexagonal BaF2 crystals and 12 pentagonal BaF2 crystals to form a spherical shell with an external diameter of 25 cm and an internal diameter of 10 cm, covering 95.2% of the solid angles. The Back-n beam line of the Chinese Spallation Neutron Source (CSNS) is a back-streaming white beam line that covers neutron energy ranging from a few eV to several hundred MeV, making it suitable for measuring neutron capture cross-sections. The reaction cross-section data of 197Au is measured by using GTAF on the Back-n beam line. The measurement data are preliminarily background deducted through energy screening, PSD method, and crystal multiplicity screening. Subsequently, the background is analyzed and deducted based on the measurement data of natC and empty samples, and the yield of 197Au capture reaction is obtained. Resonance parameters are a set of parameters extracted from experimental data to describe the resonance curve, which can eliminate the influence of experimental conditions on resonance data and are more important than the cross-section obtained from experiments. The resonance energy, neutron resonance width, and gamma resonance width parameters of 197Au at 1–100 eV are fitted by using the SAMMY program. From the comparison between the resonance curves obtained from experimental measurements and the resonance parameters obtained from fitting with the ENDF/B-VIII.0 database, it can follow that the experimental measurement results are in good agreement with the database, nevertheless, there exist some differences in the resonance parameter, which may be due to the GTAF energy resolution, Back-n neutron spectrum measurement accuracy, and the experimental background deduction method. Our next work is to identify the sources of difference.
EDITOR'S SUGGESTION
2024, 73 (7): 078702.
doi: 10.7498/aps.73.20231990
Abstract +
Nucleolus and mitochondria play an important role in maintaining cell balance, and studying their physiological processes is helpful in understanding the biological functions. In this work, a red fluorescent pyrene rhodamine probe is used to target and label cell mitochondria and nucleolus under different conditions, and the binding mode of probe and RNA is also clarified by bio-computational simulation results. Confocal laser scanning microscopy is used to analyze the morphological changes of apoptosis in HeLa cells under the action of laser light, paclitaxel and colchicine, and the changes of microenvironment between mitochondria and nucleolus are quantitatively analyzed by fluorescence lifetime imaging phase map. It is determined that the average fluorescence lifetime of the probe labeled mitochondria in steady-state HeLa cells is about 3.65 ns. The mitochondrial viscosity is about 66×10–3 Pa·s. After laser irradiation, mitochondrial fracture and fusion occur, the fluorescence lifetime of the probe decreases to 3.61 ns and the mitochondrial viscosity increases to about 131×10–3 Pa·s. The mean fluorescence lifetime of the probe labeled nucleolus of HeLa cells increases from 4.23 ns to 4.32 ns, indicating that the changes of the nucleolus microenvironment is induced by prolonging laser irradiation. Apoptosis is induced by paclitaxel and colchicine, and the nucleolus moves out of the nucleus and into the cytoplasm. Meanwhile, the fluorescence lifetime of the probe labeled nucleolus first increases and then decreases. The treatment time of paclitaxel increases from 0.5 h to 4 h, and the average lifetime of the probe labeled nucleolus of HeLa cells increases from 4.19 ns to 4.47 ns, and finally decreases to 4.42 ns, reflecting the differences in nucleolar microenvironment of HeLa cells induced by different treatment times of paclitaxel. Comparing with the blank HeLa cell, the average lifetime of the probe increases from 4.10 ns to 4.34 ns after 1 h treatment with colchicine at low concentration (10 nmol/L), and continuously increases to 4.47 ns after 1 h treatment with high concentration (100 nmol/L) colchicine. The microenvironments of nucleolus and mitochondria induced by apoptosis induced by colchicine at different concentrations are shown. The above three ways of inducing injury or apoptosis, i.e. by laser light, paclitaxel and colchicine, prove that the changes of nucleolar and mitochondrial microenvironment and functional changes of HeLa cells under the condition of cell instability provide a new method of studying the dynamic process of apoptosis induced by different pathways and the diseases related to nucleolar and mitochondrial dysfunction as well.
EDITOR'S SUGGESTION
2024, 73 (7): 070201.
doi: 10.7498/aps.73.20231778
Abstract +
The high polarizability of Rydberg atoms enables the multi-parameters measurement of electromagnetic fields. In this paper, we report on an atomic antenna based on Rydberg atoms in a room temperature vapor cell. The EIT is a destructive interference spectroscopy with a narrow linewidth and can be used to detect small electric fields through Autler-Townes splitting or Stark shifts. In our experiments, we employ cascade-type two-photon excitation electromagnetically induced transparency (EIT) spectroscopy to measure the shift of the Rydberg energy level. We introduce a low-frequency electric field (~kHz frequency) using a built-in electrode technique in the cesium cell. The interaction between the Rydberg atom and electric field induces the Stark shifts, where the amplitude of the electric field is converted into corresponding two-photon detuning by the EIT effect. Furthermore, the amplitude of the low-frequency electric field is converted into an intensity signal of EIT probe beam. Under weak field conditions, it is an approximate linear relationship between EIT transmission signal and input electric field amplitude, enabling measurement of waveform, amplitude, and frequency. We have demonstrated optical measurements of low-frequency electric field using Rydberg atoms. By increasing the power of probe beam and coupling beam, the EIT can increase the response bandwidth from ~MHz to hundreds of MHz. This provides a scalable approach for measuring high-frequency electric fields.
Abstract +
Positron annihilation technique is an atomic-scale characterization method used to analyze the defects and microstructure of materials, which is extremely sensitive to open volume defects. By examining the annihilation behaviour of positrons and electrons in open volume defects, local electron density and atomic structure information around the annihilation site can be obtained, such as the size and concentration of vacancies, and vacancy clusters. In recent years, positron annihilation spectroscopy has evolved into a superior tool for characterizing features of material compared with conventional methods. The coincident Doppler broadening technique provides unique advantages for examining the local electronic structure and chemical environment (elemental composition) information about defects due to its effectiveness describing high momentum electronic information. The low momentum portion of the quotient spectrum indicates the Doppler shift generated by the annihilation of valence electrons near the vacancy defect. Changes in the peak amplitudes and positions of the characteristic peaks in the high momentum region can reveal elemental information about the positron annihilation point. The physical mechanism of element segregation, the structural features of open volume defects and the interaction between interstitial atoms and vacancy defects are well investigated by using the coincidence Doppler broadening technology. In recent years, based on the development of Doppler broadening technology, the sensitivity of slow positron beam coincidence Doppler broadening technology with adjustable energy has been significantly enhanced at a certain depth. It is notable that slow positron beam techniques can offer surface, defect, and interface microstructural information as a function of material depth. It compensates for the fact that the traditional coincidence Doppler broadening technique can only determine the overall defect information. Positron annihilation technology has been applied to the fields of second phase evolution in irradiated materials, hydrogen/helium effect, and free volume in thin films, as a result of the continuous development of slow positron beam and the improvement of various experimental test methods based on slow positron beam. In this paper, the basic principles of the coincidence Doppler broadening technique are briefly discussed, and the application research progress of the coincidence Doppler broadening technique in various materials is reviewed by combining the reported developments: 1) the evolution behaviour of nanoscale precipitation in alloys; 2) the interaction between lattice vacancies and impurity atoms in semiconductors; 3) the changes of oxygen vacancy and metal cation concentration in oxide material. In addition, coincident Doppler broadening technology has been steadily used to estimate and quantify the sizes, quantities, and distributions of free volume holes in polymers.
EDITOR'S SUGGESTION
2024, 73 (7): 073401.
doi: 10.7498/aps.73.20231736
Abstract +
Partially ionized plasma contains the bound electrons, which have an effect on the instability of the plasma. The evolution process of bound electron density cannot be obtained by using the existing optical method used for diagnosing the free electron density. In this work, we carry out a high-precision experiment: the energy loss of a 100 keV proton beam penetrating through the partially ionized hydrogen plasma target is measured on the platform of ion beam-plasma interaction at the Institute of Modern Physics, Chinese Academy of Sciences. The bound electron density is obtained according to the energy loss model of Bethe theory. The free electron density is measured by laser interferometry and the electron tempercture is obtained from the measured spectrum (Te = 0.68 eV; nfe = 2.41×1017 cm–2). It is found that the bound electron density decreases during plasma lifetime. The diagnosis of bound electron density by measuring energy loss of ion beam has the advantages of on-line, in-situ and high resolution, thus providing a new way to solve the problem about measuring the bound electron density in partially ionized plasma. A COMSOL simulation reveals that the high-temperature free electrons will be ejected quickly out of the plasma area through a mechanical diaphragm, thus reducing the total number of free electrons. In order to maintain a relatively high degree of ionization in this plasma, in principle, more and more bound electrons are ionized into free electrons, the density of bound electrons decreases correspondingly. The simulation result accords well with our experimental data. Based on this finding, more detailed plasma target parameter is obtained, which is helpful in deepening the understanding of the interaction process between ion beam and plasma. In future, more researches of low low-energy highly-charged ions-plasma interaction will be conducted.
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