Loss Peak Research Articles

Electromagnetic wave absorption and bending properties of double-layer honeycomb 3D woven composites: experiment and simulation

In order to solve the problems of honeycomb sandwich structure electromagnetic wave absorbing composites with easy delamination, low strength, and a narrow absorption frequency band, a double-layer honeycomb 3D woven electromagnetic wave absorbing composite was designed and prepared. CST electromagnetic simulations and mechanical finite element simulations were combined with experimental analysis, respectively. The electromagnetic wave absorption properties and bending properties of the double-layer honeycomb 3D woven electromagnetic wave absorbing composite were revealed, and the electromagnetic wave absorption mechanism was elucidated. The results show that the lowest peak of reflection loss obtained from both simulation and experiment of electromagnetic wave absorption property occurs in the X-band with the values of 10.78 GHz and 9.28 GHz, respectively. The lowest reflection loss is −24.35 dB and −23.5 dB, respectively. The simulation results were in good agreement with the experimental results. The maximum loads obtained from simulation and experiment for the bending property were 2696.28 N and 2271.07 N, respectively. There is no obvious delamination damage to the yarn, and the material has good resistance to delamination. The structural-functional integration of load-bearing and electromagnetic wave absorption in double-layer honeycomb 3D woven electromagnetic wave absorbing composite will have great development potential in civil and military fields.

Magnetoelastic coupling and microstructure dynamics associated with spin-orbit coupling in the ferrimagnetic/ferroelastic ordered double perovskite Ba2FeReO6

Strain coupling and relaxation dynamics associated with the ferrimagnetic/ferroelastic phase transition at ${T}_{c}\ensuremath{\approx}310\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ in double perovskite ${\mathrm{Ba}}_{2}{\mathrm{FeReO}}_{6}$ with a high degree of Fe/Re order have been investigated with resonant ultrasound spectroscopy through the temperature interval $\ensuremath{\sim}5--600\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and with applied magnetic field of up to $\ifmmode\pm\else\textpm\fi{}2\phantom{\rule{0.28em}{0ex}}\mathrm{T}$. Strain analysis using diffraction data from the literature is consistent with a Landau model of the transition as $Fm\overline{3}m{1}^{\ensuremath{'}}\ensuremath{\rightarrow}I4/m{m}^{\ensuremath{'}}{m}^{\ensuremath{'}}$, improperly ferroelastic, driven by a magnetic order parameter with symmetry ${\mathrm{\ensuremath{\Gamma}}}_{4}^{+}$. Ferroelastic shear strain of up to $\ensuremath{\sim}0.0015$ arises from spin/orbit coupling and is smaller than is typical of coupling with octahedral tilting. It provides the underlying cause of softening of the shear modulus observed over an interval of $\ensuremath{\sim}100\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ below ${T}_{\mathrm{c}}$, though with order/disorder rather than displacive character for the transition. Hysteretic effects suggest that precursor microstructures and mixed magnetic/ferroelastic domains below ${T}_{\mathrm{c}}$ depend on the thermal history of the sample and can evolve on a timescale of hours and days at room temperature. Elasticity data collected as a function of external magnetic field reveal that poled samples are slightly softer than those with multiple magnetic domains at 4 K. At 300 K there is a time-dependent viscous component of the response to the field that relates to the bulk modulus and, hence, to volume changes associated with magnetic ordering. A loss peak seen $\ensuremath{\sim}20--50\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ below ${T}_{\mathrm{c}}$ in AC magnetic measurements made at frequencies of $0.2--1\phantom{\rule{0.28em}{0ex}}\mathrm{kHz}$ yielded an activation energy $\ensuremath{\sim}0.4\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ and has been attributed to freezing of magnetic/ferroelastic domain walls. No equivalent loss peak was seen in the acoustic data measured at $\ensuremath{\sim}100--500\phantom{\rule{0.28em}{0ex}}\mathrm{kHz}$, however, implying that these domain walls are mobile in response to a dynamic magnetic field on a timescale of $\ensuremath{\sim}{10}^{\ensuremath{-}2}\text{--}{10}^{\ensuremath{-}3}\phantom{\rule{0.28em}{0ex}}\mathrm{s}$ but immobile in response to a dynamic stress field applied on a timescale of $\ensuremath{\sim}{10}^{\ensuremath{-}5}\text{--}{10}^{\ensuremath{-}6}\phantom{\rule{0.28em}{0ex}}\mathrm{s}$. Debye-like acoustic loss peaks at temperatures below $\ensuremath{\sim}100\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ yielded activation energies of $\ensuremath{\sim}0.02--0.1\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ and are discussed in terms of pinning/freezing of polarons. ${\mathrm{Ba}}_{2}{\mathrm{FeReO}}_{6}$ is a material with magnetoelastic and magnetoelectric heterogeneities that might be tuned by choice of thermal history and cation order.

Experimental and numerical modeling of plasma start-up assisted by electron drift injection on J-TEXT

Start-up is one of the critical phases for tokamak discharge. The electron drift injection (EDI) system has been developed on J-TEXT for start-up studies. A breakdown experiment with EDI-assisted start-up has been conducted, which verified the effect of pre-ionization by EDI to achieve start-up at a lower ohmic field voltage. A zero-dimensional (0D) model has been developed to explain the effect of EDI quantitatively. The comparison between the experiment and simulation verified the credibility of this model. Based on this model, a comparison between pure ohmic heating start-up and EDI-assisted start-up was presented, showing that EDI improved ionization, causing a lower delay to the peak of hydrogen ionization and radiation losses and a smoother rise in the electron and ion energy. This result quantitatively verified the pre-ionization effect of EDI on start-up . The effects of injecting different currents and electron energy were investigated. A better pre-ionization effect was realized by increasing the injected current, which can be a reference for the upgrading of the EDI system.

First-principles calculations to investigate optical properties of topological semimetal MX compounds (M = Ti, Zr, Hf and X = S, Se, Te)

In this study, the first-principles calculation was used to explore the optical properties of MX (M = Ti, Zr, Hf, and X = S, Se, Te) compounds in light of their newly discovered unique electronic properties over a broad energy range. The influence of each orbital (s, p, and d) was studied by comparing the imaginary and real spectra of dielectric functions with the electronic properties of these compounds. The d-orbital of transition metals has a major impact on the absorption performance of all these compounds. In negative regions of the real spectra, a very high intensity of reflectivity was observed. The high peaks of energy loss along x, y, and z components are linked to plasmons and in good agreement with real (Reii (ω) =0) and imaginary (Imgii (ω)≈0) spectra values. For transition metal M (i.e., Ti, Zr, and Hf), when the X element is changed from S to Te, a significant shift from higher to lower energy has been observed in the imaginary, real, reflectivity, and energy loss spectra of the x, y, and z components, respectively.

Preparation of a Microwave-Absorbing UV Coating Using a BaFe12O19-Polypyrrole Nanocomposite Filler.

BaFe12O19-polypyrrolenanocomposites were prepared via the in situ chemical oxidative polymerization of pyrrole monomers in the presence of BaFe12O19 powder, with ammonium persulfate as an oxidant and sodium dodecyl benzene sulfonate as a dopant. X-ray diffraction measurements and Fourier-transform infrared spectroscopy indicated that there were no chemical interactions between BaFe12O19 and polypyrrole. In addition, scanning electron microscopy showed that the composites exhibited a core-shell structure. Subsequently, the prepared nanocomposite was used as a filler to prepare a coating suitable for ultraviolet curing. The performance of the coating was investigated by evaluating its hardness, adhesion, absorbance, and resistance to acids and alkalis. Importantly, the addition of BaFe12O19-polypyrrole nanocomposites not only improved the coating hardness and adhesion but also produced a coating with a good microwave absorption performance. The results suggested that BaFe12O19/PPy composite has a lower reflection loss peak and a larger effective bandwidth at the X band when the proportion of the absorbent sample is 5-7%, when the absorption performance is the best. The reflection loss is in the range of 8.88-10.92 GHz below -10 dB.

Dispersion of droplets due to the use of air purifiers during summer: Focus on the spread of COVID-19

Coronavirus disease (COVID-19), which emerged in 2019, has induced worldwide chaos. The main cause of COVID-19 mass infection indoors is the spread of virus-containing droplets via indoor airflow, which is affected by air conditioners and purifiers. Here, ten experimental cases were established to analyze how use of air purifiers affects the spread of virus-containing droplets. The experiments were conducted in a school classroom with an air conditioner in summer. In the droplet dispersion experiment, paraffin oil was used as the droplet substance. Two main scenarios were simulated: (1) an infected student was seated in the back of the classroom; and (2) the teacher, standing in the front of the classroom, was infected. The results were expressed using two parameters: peak concentration and loss rate, which reflect the degree of direct and indirect infection (airborne infection), respectively. The air purifier induced a peak concentration decrease of 42% or an increase of 278%, depending on its location in the classroom. Conversely, when the air purifier was operated in the high mode (flow rate = 500 CMH; cubic meters per hour), the loss rate showed that the amount of droplet nuclei only decreased by 39% and the droplet amount decreased by 22%. Thus, the airborne infection degree can be significantly reduced. Finally, the use of air purifiers in the summer may be helpful in preventing group infections by reducing the loss rate and peak concentration if the air purifier is placed in a strategic location, according to the airflow of the corresponding room.

Analysis of the D-shaped PCF-based SPR sensor using Resonance Electron Relaxation and Fourier domain method

Since the D-shaped photonic crystal fiber (PCF) based Surface Plasmon Resonance (SPR) sensor is an important tool in scientifical research and applications, a new concept of Resonance Electron Relaxation (RER) is defined to investigate its detection property. It successfully explains the ‘S-shape’ profile in the dispersion and the wavelength delay between the dispersion intersection and loss peak. The birefringence interference has also been analyzed with the RER phenomenon. Then we experimentally demonstrated the SPR sensing performance. A fast Fourier transform (FFT) algorithm is applied in the experiment to separate each component signal in the spatial frequency domain. Then using a band passing filter of 0.001–0.006 nm−1 together with inverse FFT algorithm, the distinguished SPR spectrum shows a significant agreement with theoretical simulations, with differences of only 14.3 nm and 1.48% in resonance wavelength and intensity. This study facilitates a high precision analysis and data process approach for the SPR sensor based on D-shaped PCF and presents greatly promising application prospects in SPR sensors.

Surface plasmon resonance sensor composed of microstructured optical fibers for monitoring of external and internal environments in biological and environmental sensing

To achieve simultaneous detection of analytes with different states in internal and external environments, A microstructured optical fibers (MOFs) biochemical sensor based on surface plasmon resonance (SPR) is proposed. The micro-polished dual-open-loop structure with anti-corrosive gold as the sensing layer is designed, which greatly improves the phase matching between fundamental mode and plasmonic mode to further stimulate SPR effect. Numerical simulation by the full-vector finite element method (FEM) reveals that the even mode for y-polarized state has better sensing properties due to the more eminent electric field distribution and shift of the confinement loss peak. In order to better evaluate and analyze the output characteristics of this sensor, the wavelength modulation and amplitude interrogation methods are adopted. The results manifest that the maximum wavelength sensitivity (WS) of 20,000 nm/RIU and amplitude sensitivity (AS) of 208.21 RIU−1 with resolution (R) of 10−6 order can be acquired in operable infrared region (900–2,750 nm). Furthermore, this sensor has realized a broad range of detection for gas and liquid analytes with RIs from 1.00 to 1.38. On account of its simple structure, low cost, and industrial compatibility, this sensor has large potential in environmental and biological applications such as atmospheric monitoring, sewage treatment, food safety, humoral regulation, and medical diagnosis.

Extended effective absorption bandwidth of Sendust/phosphate flaky particles by TiO2 insulation coating

How to obtain a wide effective absorption bandwidth is still a challenge for Sendust micro-powder as microwave absorber at 2–10 GHz range. Double shell-core structured composites are desirable to extend effective absorption bandwidth through optimizing impedance match degree in wider frequency and forming a broad dielectric loss peak. In this work, TiO2 layer is fabricated on surface of flaky Sendust/phosphate composites through the hydrolysis reaction for constructing double shell-core structured TiO2@phosphate@Sendust flaky composites. The synergistic effect of TiO2-phosphate interface and phosphate-Sendust interface induces a broad peak for dielectric loss, microwave absorption ratio and attenuation constant, resulting in wider effective absorption bandwidth of 3.2 GHz compared with that (2.4 GHz) of raw Sendust/phosphate composites. This work offers a facile and effective strategy for extending effective absorption bandwidth of micron-scale microwave absorber.

Silicon Oxy-Nitride for the Low Refractive Index Layers in the Mirror Coatings of the Cryogenic Laser Interferometer Gravitational Waves Detector.

The low refractive index layers in the mirror coatings of the room-temperature laser interferometer gravitational waves detectors are silica deposited by the ion beam sputter method. However, the silica film suffers from the cryogenic mechanical loss peak, hindering its application for the next generation detector operated at cryogenics. New low refractive index materials need to be explored. We study amorphous silicon oxy-nitride (SiON) films deposited using the method of plasma-enhanced chemical vapor deposition. By changing the N_{2}O/SiH_{4} flow rate ratio, we can tune the refractive index of the SiON smoothly from nitridelike to silicalike of ∼1.48 at 1064nm, 1550nm, and 1950nm. Thermal anneal reduced the refractive index down to ∼1.46 and effectively reduced the absorption and cryogenic mechanical loss; the reductions correlated with the N─H bond concentration decrease. Extinction coefficients of the SiONs at the three wavelengths are reduced down to 5×10^{-6}∼3×10^{-7} by annealing. Cryogenic mechanical losses at 10K and 20K (for ET and KAGRA) of the annealed SiONs are significantly lower than the annealed ion beam sputter silica. They are comparable at 120K (for LIGO-Voyager). Absorption from the vibrational modes of the N─H terminal-hydride structures dominates over the absorption from other terminal hydrides, the Urbach tail, and the silicon dangling bond states in SiON at the three wavelengths.

End-to-End Fluctuation of cis-Poly(isoprene) under Constraints from Slow Poly(tert-butyl styrene)

The properties of miscible polymer blends are strongly affected by the dynamic asymmetry of the components reflecting a contrast of their bulk Tg. This study focused on a blend of unentangled polyisoprene (PI3; M = 3.0 kg/mol) and poly(4-tert-butyl)styrene (PtBS27; M = 27.2 kg/mol) with a PI content of wPI = 50 wt % to examine this effect on viscoelastic and dielectric properties. The dielectric loss (ε″) peak characterizing the end-to-end fluctuation of PI chains emerged at an angular frequency ω much higher than that of the terminal viscoelastic relaxation, confirming that PI3 and PtBS27 were the fast and slow components in the blend. At low temperatures T, PI3 exhibited a very broad ε″ peak and its terminal relaxation frequency, much lower than the peak frequency, was close to the Rouse relaxation frequency of PtBS27 over a length scale identical to the end-to-end distance RPI of the PI3 chain. This dielectric relaxation narrowed at higher T, namely, on the reduction of the dynamic asymmetry between PI3 and PtBS27. These observations suggested a molecular scenario that the dynamic concentration heterogeneity of the PtBS chains was essentially frozen during the relaxation of PI3 and the PI3 chains experienced broad distributions in both friction and motional constraints to exhibit broadened and retarded relaxation at low T. This scenario was in harmony with the molecular dynamics simulation in both atomistic and coarse-grained (cg) levels. Specifically, the end-to-end vector autocorrelation function of PI obtained from the cg simulation showed stronger broadening in its higher-order modes, which cannot be attained without the distributions of the friction and motional constraint for PI. This result demonstrated the importance of the dynamic concentration heterogeneity of PtBS giving those distributions during the PI relaxation.

Pseudobrookite Fe2-2xCoxTi1-½xO5: Structural, magnetic phase transformation and reflection loss characteristic

Single-phase pseudobrookite Fe2-2xCoxTi1-½xO5 (x = 0, 0.1, 0.2, and 0.4) with an orthorhombic structure has been successfully synthesized using a solid reaction and sintering at 1000 °C. Pseudobrookite Fe2-2xCoxTi1-½xO5 is an element that is abundant on earth and is attracting rapidly growing interest as a very promising candidate for the application of microwave absorbing materials. This paper studies the performance of exchange coupling in addition to the structural properties and microwave absorption characteristics of pseudobrookite Fe2-2xCoxTi1-½xO5. Qualitative and quantitative analysis of the X-ray diffraction (XRD) pattern show that all samples were single-phase pseudobrookite Fe2TiO5 with a space group of C m c m. The presence of Co causes the expansion of the lattice parameter with an indicator of an increase in the value of the unit cell volume as the composition of Co in the structure increases. Particle morphology and elemental composition were also observed using a scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS). The presence of Co2+ dopant ions does not affect the shape and size of the particles, while the crystallite size increased with the increase in the content of Co2+ dopant ions in the structure and Co elements of 1.82, 2.81, and 5.69 at% have been detected, which are contained in the composition x = 0.1, 0.2, and 0.4, respectively. The presence of the Co2+ dopant ion it stimulates the rearrangement of the cationic distribution in both tetrahedral and octahedral sites which will have an impact on changes in the magnetic properties of this pseudobrookite. Magnetic properties were analyzed by measuring magnetization (M) against a magnetic field (H) at 300 K (RT). The spontaneous magnetization at room temperature in pseudobrookite Fe2-xCoxTi1-½xO5 is ∼2.55, 7.41 and 8.67 emu/g for compositions of x = 0.1, 0.2 and 0.4, respectively. The coercive field is ∼424, 356 and 284 Oe for compositions of x = 0.1, 0.2 and 0.4, respectively. The presence of Co in the structure causes a magnetic phase transformation from paramagnetic to ferromagnetic behavior at room temperature. This ferromagnetic behavior can be explained due to the strengthening of indirect exchange interactions of Ti/Co – O – Fe/Co in addition to the interactions of Fe/Co – O – Fe/Co and Ti/Co – O – Ti/Co, as well as changes in the degree of inversion of this pseudobrookite structure, due to the presence of magnetic ion dopants. Magnetic parameters both Ms, Mr, and Hc show an increase with increasing Co2+ ion content at room temperature. This magnetic parameter is very important at room temperature to determine the absorption characteristics of microwaves through the resonant frequency. Microwave absorption characteristics are measured in the 8–12 GHz frequency range. The best reflection loss (RL) peaks were obtained at composition x = 0.1 of -24 dB at 10.6 GHz frequency. The presence of Co2+ dopant ions can produce a very significant increase in RL almost 3 times at the same absorption frequency. This increase in reflection loss can be attributed to the effect of the magnetic phase transformation of this material which has been described accordance of the magnetic coupling exchange interaction, which in turn changes the magnitude of the relative permeability value of this material complex.

Effect of Shear Action on Structural and Electrical Insulation Properties of Polypropylene

Polypropylene undergoes permanent alterations during the processing and manufacture of cables due to shear effects, which in turn affect all of its qualities. There are currently few research papers on the modulation of material structure and many performance parameters by the shear stress field. In this study, we examined the impact of various shear levels on the structural, mechanical, and electrical properties of polypropylene, as well as their relationships. The results indicated that shear strength decreased the material’s viscosity and oxidation resistance. As shear duration increased, crystallinity began to diminish. In the meantime, the crystallinity improved as the shear temperature rose. The thermal elongations of the sheared samples were all about 5%. Short-term shearing boosted the material’s toughness, but as the degree of shear continued to increase, the material’s toughness and rigidity steadily decreased. The storage modulus of the material decreased with increasing shear, the loss peak initially increased and subsequently decreased, the peak position shifted from low to high temperature, and the loss factor was relatively small. In samples sheared for brief periods, an accumulation of space charge and an increase in its nonlinear threshold field strength were observed. With increasing shear time, the material’s space charge accumulation was repressed, the current density initially grew and then reduced, and the nonlinear threshold field strength initially fell and then increased. Under shearing, the electrical strength of the material increased by approximately 2%. In addition, the presence of an antioxidant improved all of the aforementioned features.

Experimental and Numerical Studies on the Hilbert Fractal Architecture as an Acoustic Metamaterial

Experiments and numerical methods were used to investigate the key parameters which affect the transmission loss behaviour of Hilbert fractal acoustic metamaterials. The tests were conducted using a four-microphone impedance tube, and the numerical simulation was performed using COMSOL Multiphysics software. Fractal order and cavity slot widths on Hilbert fractal metamaterials were investigated. 3D printing manufacturing techniques were used to make polylactic acid specimens. The COMSOL model developed utilised thermo-viscous and lossless domains with boundary layer mesh in the fractal cavities. The tests and simulations' frequency range were 0.2 kHz to 3.0 kHz, with parametric gap widths ranging from 0.5 mm to 3.0 mm. There is a reasonable agreement between the numerical models and the experimental results; the second-order Hilbert fractal had the most significant effect on transmission loss, with an experimental peak of nearly 50 dB around 1600 Hz. Moreover, multiple transmission loss peaks were observed as a function of the gap width in the five Hilbert fractal orders studied. The gap width is one of the critical parameters for optimising the performance of the Hilbert fractal as an acoustic metamaterial.

Numerical design of Helmholtz resonators with multiple necks for multi-tonal noise control

The reduction of multi-tonal noise at multiple frequencies simultaneously is a challenge in many industrial fields. Different solutions such as metamaterials consisting of periodic Helmholtz resonators embedded into a porous layer have been studied in the literature. Generally, a classical resonator made of a cavity connected to a neck provides only one resonant transmission loss peak. In this study, a design of acoustic metamaterials is proposed numerically using the finite element method for multi-tonal noise reduction. The resonator is made of multiple necks extended into the cavity and is periodically distributed within a porous material. The cylindrical global cavity of the resonator is partitioned into several sub-cavities, which are separated from one another by a rigid wall, and each sub-cavity is connected to one neck. Helmholtz resonators with 2, 3, 4, and 5 necks are presented, they exhibit multiple resonance transmission loss peaks which correspond respectively to the number of the resonator necks. The proposed acoustic metamaterial designs can be used to reduce multi-total noise at several frequencies simultaneously.

Modelling of acoustic metamaterial sound insulator using a transfer matrix method for aircraft cabin applications

The incorporation of acoustic metamaterials in the design of aircraft fuselage panels in order to reduce the low frequency noise inside the cabin is nowadays a major research subject in order to offer passengers a comfortable cabin environment. In this study, acoustic metamaterial made of Helmholtz resonators periodically embedded into a porous material is investigated using a transfer matrix approach combined with finite element calculations. This transfer matrix method is based on the two-load methods where the two loads in the numerical simulations are two different termination conditions (plane wave radiation and rigid wall) in order to retrieve the equivalent transfer matrix of the porous layer with embedded periodic Helmholtz resonators. The equivalent matrix is then coupled analytically in series with others analytical matrices to model complex multilayer metamaterials. The results of the transmission loss obtained exclusively using finite element method for single and double wall configurations are compared with the results of the proposed transfer matrix method and good agreements are obtained. It is observed that the frequency band of the transmission loss of the double wall configuration is larger than the one of the single wall configuration with higher transmission loss peak value. The investigated metamaterial can potentially be used in the design of aircraft cabin panels for low frequency noise reduction.

Temperature Dependence of AC Electrical Conduction in Plasma Polymerized Pyrrole-N,N,3,5 Tetramethylaniline Bilayer Composite Thin Films

The temperature dependence of alternating current (ac) electrical conduction in Plasma Polymerized Pyrrole-N,N,3,5 tetramethylaniline (PPPy-PPTMA) bilayer composite thin films have been discussed in this article. The thin films were deposited by using a parallel plate capacitively coupled glow discharge reactor. To study the temperature dependence of ac electrical conduction the variation of dielectric constant (<i>ε</i>′), the dielectric loss factor (<i>ε</i>"), and the ac conductivity (<i>σ_ac</i>) of the thin films were investigated in the frequency range 100 Hz to 10 MHz and in the temperature range 298K to 398K. The decrease of dielectric constant <i>ε</i>′ with increasing frequency was observed and was attributed to the dielectric relaxation process. The dielectric constant, however, is observed to be increased with temperature in all frequency regions which is due to greater freedom of movement of dipole molecular chain in polymer films at high temperature. The variation of dielectric loss factor <i>ε</i>" with frequency showed a loss minimum then rises to a sharp peak which was also attributed to the relaxation phenomena of polymer. It is, however, observed that the loss peaks have shifted towards the higher frequency side with the increase of temperature which is usually attributed to dipolar orientation. The dielectric loss factor is also observed to be increased with temperature in all frequency regions. At lower frequencies the increase of loss factor with temperature was attributed to the effective chain motion of polymer and at high frequencies this increase might indicate the orientational polarization due to chain motion in bilayer film. The linear behavior of the ac conductivity <i>σ_ac</i> with the frequency and the observed weak temperature dependence of <i>σ_ac</i> led to interpret the ac conduction mechanism as the hopping between localized states at the Fermi level.

Dual-band highly-sensitive SPR photonic crystal fiber sensor based on birefringence analysis

In this paper, a dual-band highly-sensitive D-shaped photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) is proposed and numerically analyzed. Au-TiO2 grating is deposited on the flat surface of D-shaped PCF, thus surface plasmon resonances are excited to detect the change of refractive index (RI) of analyte. Rabi-like splitting spectrum is achieved by the introduction of a small air hole in the fiber. Besides spectrum analysis, it is found that the resonance wavelengths can be located by the abnormal change of birefringence. Moreover, complete coupling and incomplete coupling of the guided mode and plasmonic mode can be distinguished from our simulation results. The influences of structural parameters are also analyzed systematically. Simulation results show that the two loss peaks have different RI detection ranges, and the maximum sensitivity reaches 26700 nm/RIU. The proposed sensor could be applied widely in biomedical and chemical fields.

Dissipation-induced recurrence of non-Hermitian edge burst

In quantum mechanics, the Hermitian Hamiltonian is generally used to describe the ideal closed quantum system, but in reality, the physical system is closely related to the environment, and the open quantum system coupled to the environment can be described by the equivalent non-Hermitian Hamiltonian to a certain extent. Among them, the dissipation intensity is closely related to the dynamic properties of non-Hermitian quantum systems. Therefore, it is of great practical significance to study how dissipation affects particle loss. In this paper, the dynamic law related to dissipation intensity in a one-dimensional non-Hermitian system under open boundary condition is studied, and it is found that dissipation can induce the recurrence of edge burst. After the time-dependent evolution of the particles in the one-dimensional non-Hermitian dissipative lattice system with open boundary condition, there is an edge burst in the system, that is, there is a large probability of particle loss at the edge, and the edge burst disappears after increasing the intracell hopping. It is found that if the dissipation intensity increases or decreases, the edge burst will reappear. This kind of reappearance is different from the original edge burst, which is mainly manifested in the loss probability distribution of particles from the edge distribution to the bulk distribution, which is due to the difference in probability of particle motion direction between the two cases. Under the re-induced edge burst, the particles move leftward and rightward from their initial positions, and rebound from the left after having reached the boundary, forming a more obvious loss probability at the edge and gradually decreasing to the body area. In the original edge burst, the particles only move to the left with a greater probability, and are ‘trapped’ at the edge to completely dissipated, forming a distribution with an independent loss peak at the edge. The movement to the left is due to the non-Hermitian skin effect. The deeper reason for different movement directions is related to parity-time symmetry. Under the parameter near the parity-time symmetry breaking point, the loss probability of the particle is of unilateral distribution, and the loss probability of the particle moving to both sides is of bilateral distribution when it is far away. This is the description of the dissipation-induced edge burst recurrence phenomenon and its characteristics. In addition, this paper also studies the influence of impurity barrier on the probability distribution of particle loss in non-Hermitian dynamics. The results show that placing a small barrier on the non-dissipative &lt;i&gt;A&lt;/i&gt;-site can obviously hinder the particle motion, and when the barrier increases to a certain height, its influence on the particle motion tends to be unchanged. And the barrier at the dissipative &lt;i&gt;B&lt;/i&gt; lattice has little effect on the dynamics.

Electron energy loss spectroscopy of K0.7Fe1.7Se2 superconductor

Electronic structure and microstructure of ternary selenide superconductor K0.7Fe1.7Se2 have been investigated by transmission electron microscopy (TEM) and energy band structure calculations. Electron energy-loss spectroscopy (EELS) was performed to study K0.7Fe1.7Se2 experimentally. The individual inter-bands transitions were identified through the comparison between the energy loss peak positions with the partial density of states (PDOS) obtained by first principle calculation. The electron energy-loss near-edge fine structure (ELNES) were analyzed, the core-hole effect was found to play a key role in the simulation of ELNES. The results can present some insight into the interaction between superconductivity and electronic structure in this group of iron-related superconductor.