Anomalous Increase Research Articles

Temperature driven anomalous unit-cell c-axis shifts in highly oriented pyrolytic graphite measured at the magic-angle

Small misfit-angles in the grain boundary of HOPG interfaces have been recently reported to act as a source of unusual superconductive effects, with significant changes in the electronic-band-structure. These observations may imply that possible structural-transitions can exist with the variation of the temperature. In this letter we report the presence of temperature driven structural-transitions in the temperature range from 298.15 to 673.15 K measured under magic-angle HOPG (0.8°,±0.2°, first magic-angle). Novel memory effects consisting in an anomalous reversible linear increase of the c-axis unit cell values of HOPG with the increase of the temperature are described.

Structure and Transport Properties in Itinerant Antiferromagnet RE2(Ni1- xCu x)5As3O2 (RE = Ce, Sm).

We report the crystal structure and physical properties of two Ni5As3-based compounds RE2Ni5As3O2 (RE = Ce, Sm). The former exhibits structural phase transition from tetragonal (space group I4/ mmm, 139) to orthorhombic (space group Immm, 71) symmetry at 230 K, while the latter undergoes a charge-density-wave-like structural distortion with abrupt change of Ni-As bond length. Both compounds show antiferromagnetic transitions due to RE3+ ions ordering at 4.4 and 3.4 K, accompanying with the large enhancement of Sommerfeld coefficients comparing to the nonmagnetic La analogue. Although the Cu substitution for Ni induces structural anomalies and suppression of structural transition like the behaviors in La/Pr/Nd analogues, the superconductivity is not observed in both Cu-doped RE2Ni5As3O2 (RE = Ce, Sm) above 0.25 K. Our structural refinements reveal that the lacking of superconductivity in RE2(Ni1- xCu x)5As3O2 might relate to the anomalous increase of As height, h1.

Polyamorphic transition in a transition metal based metallic glass under high pressure

Pressure-induced glass-glass transition (GGT) has been reported in a few rare-earth based and main-group metallic glasses (MGs), a process during which the compressibility decreases with the transformation from a low-density to a high-density amorphous state. Herein, we report an unexpected GGT behavior in Pd-based MGs under pressure, which is characterized by an anomalous increase in the compressibility with the pressure. State-of-the-art high-energy synchrotron technique, coupled with theoretical simulations, reveals that this unique GGT behavior is primarily caused by the change in bonding characteristics, i.e., some covalentlike atomic bonds in the as-prepared state change to metallic ones under high pressure, which also leads to the increase in the compressibility. Our current findings shed light on the understanding of the nature of polyamorphic transitions in MGs.

Anomalous damping dependence of the switching time in Fe/FePt bilayer recording media

Gilbert damping plays a significant role in magnetic reversal processes, and it determines the timescale of the switching. Here we investigate the properties of exchange-coupled composite media and the dependence of the switching time on the damping constant of the soft layer using atomistic spin dynamics. For a bilayer Fe/FePt medium, we find an anomalous increase of the switching time with increasing soft layer damping constant. The reversal occurs via a high-temperature exchange spring, and we show that the increase in the switching time is related to a corresponding increase in the time to establish the exchange spring. This phenomenon is delicately balanced in that the switching time increase occurs only in fields close to the coercivity.

Origin of the anomalous size-dependent increase of capacitance in boron nitride-graphene nanocapacitors.

The anomalous size-dependent increase in capacitance in boron nitride–graphene nanocapacitors is a puzzle that has been initially attributed to the negative quantum capacitance exhibited by this particular materials system. However, we show in this work that the anomalous nanocapacitance of this system is not due to quantum effects but has pure electrostatic origin and can be explained by a parallel-plate (square) nanocapacitor model filled with a dielectric film characterized by a size/thickness-dependent relative permittivity. The model presented here is in excellent agreement with the experimentally measured capacitance values of recently fabricated graphene and hexagonal boron nitride nanocapacitors. The results obtained seem to suggest that the size-dependent increase of capacitance in the above-mentioned family of nanocapacitors can be explained by classical finite-size geometric electrostatic effects.

Исследование неоднородности электрохимического электрода со смешанной проводимостью

AbstractThe ionic resistance of membrane–electrode assemblies of oxygen–hydrogen fuel cell electrodes containing platinum nanoparticles on carbon black, carbon nanofibers, and proton-conducting Nafion polymer in a wide range of compositions (10–80 wt %) are studied in situ by the methods of current–voltage characteristics, electrochemical impedance spectroscopy, and simulation of the impedance hodograph. Conditions that make it possible to correctly determine the ionic resistance of the electrode on the basis of an analysis of the linear approximation of the high-frequency region of the impedance hodograph are found. It is shown that the occurrence of inhomogeneities and an anomalous increase in the ionic resistance with an increase in the content of Nafion in the electrode are associated with a decrease in the volume fraction of water-generation centers (particles of electrochemically active platinum), which leads to incomplete wetting of Nafion.

Микрокристаллические алмазные порошки как перспективные объекты для генерации многочастотного вынужденного комбинационного рассеяния-=SUP=-*-=/SUP=-

The laws of Raman scattering in microcrystalline diamond powders are investigated depending on the size of diamond microresonators in the range of 1–600 mkm. The observed effect of the anomalously high intensity of spontaneous Raman scattering in diamond microresonators is explained by the “trapping” of electromagnetic radiation in them, the wavelength of which is smaller than the size of diamond microcrystals. Due to the "trapping" of photons in diamond microresonators, the density of electromagnetic energy for excitation and secondary radiation increases. The high quality factor of the fundamental optical mode in the vibrational spectrum of diamond and the anomalous increase in the intensity of Raman scattering in diamond microresonators open up possibilities for observing low-threshold stimulated multifrequency Raman scattering in microcrystalline diamond powders. The use of the generation lines of a pulsed solid-state YAG: Nd3+ laser (λ = 1064 nm) and its optical harmonics (λ = 1064, 532, 354, 266 nm) as exciting radiation makes it possible to create a line of laser-frequency oscillators from the ultraviolet region that are equidistant in frequency shift to the terahertz range, promising for the study of biological and medical objects.

Влияние фазового перехода второго рода на электропроводность структуры металл/полупроводник

AbstractThe properties of the Cr– p -Si potential barrier near the temperature of the antiferromagnetic–paramagnetic phase transition in chromium are investigated. A significant change in the potential barrier and an anomalous increase in the conductivity in the Cr– p -Si–Au structure are observed near the temperature of the second-order antiferromagnetic–paramagnetic phase transition in chromium. It is established that current fluctuations in the structure are enhanced when approaching the phase-transition point. The experimental results are interpreted based on the assumption that the observed change in the electron-transport properties of the Cr–Si interface is due to a shift of the Fermi quasi-level in chromium as a result of the second-order phase transition.

THE INFLUENCE OF γ-IRRADIATION ON ELECTRICAL PROPERTIES OF CdIn2Te4 CRYSTALS

The influence of γ-irradiation on the basic electrical parameters of CdIn2Te4 crystals in the temperature range of 240-410 K has been investigated. It was established that the noticeable changes in the parameters of the irradiated samples take place under irradiation doses D > 1·108 Roentgen. It was shown that under dose D = 1.2·108 Roentgen and additional dose D = 4·108 Roentgen the parameters change slightly at high temperature T > 350 K and at T < 350 K the changes of parameters increase with rising γ-irradiation dose. The anomalous increase of the Hall mobility in the irradiated samples was found and the explanation of the obtained effect nature was proposed. It was shown that the main cause of the changes of the electrical parameters under the influence of γ-irradiation is the Fermi-level displacement within the energy gap of CdIn2Te4 crystals.

Влияние фазового перехода второго рода на электропроводность структуры Cr-полимер-Cu

The results of the study of an anomalous increase in conductivity in the Cr / polymer / Cu structure near the phase transition temperature of an antiferromagnet / paramagnet in chromium are presented. Polydiphenylenephthalide was used as a polymer. In thin films of this polymer, the effect of charge instability was previously observed. It was found that as the phase transition temperature in the structure approaches, an increase in current fluctuations is observed, which in the phase transition area switch the structure's conductivity to a highly conductive state with anomalously low resistance. The interpretation of the presented results is carried out taking into account the change in charge carrier injection near the phase transition temperature in chromium.

Drain Conductance Oscillations in Poly-Si Junctionless Nanowire Thin-Film Transistors

The drain conductance oscillations are simultaneously observed in the trigated and double-gated poly-Si junctionless (JL) nanowire thin-film transistors (TFTs). The strongest oscillations appear at ${V} _{\text {GS}}$ of 1 V and $V_{\text {DS}}$ of 4–5 V/6–7 V in 0.35- $\mu \text{m}$ /5- $\mu \text{m}$ poly-Si JL nanowire TFTs. To explain the drain conductance oscillations, in addition to the separated sub-bands and Coulomb blockade effect, the space-charge-potential barrier/grain boundary (GB) potential barrier in the channel and the kink effect in the output characteristics should be considered. The space-charge-potential barrier is affected by the unstable trapped electrons at GB and leads to the drain conductance oscillations. Due to the kink effect, an anomalous increase of the current in the output characteristics can enhance the conductance oscillations. Moreover, the channel of the double-gated device shows higher degree of crystallinity by solid-phase crystallization. Compared with the trigated device without solid-phase crystallization, less GB potential barriers in the channel of the double-gated device lead to a higher mobility in the channel, and these electrons can easily destroy the stability of the trapped electrons at the GBs, resulting in the stronger drain conductance oscillations. Therefore, the physical mechanisms are proposed to understand the drain conductance oscillations well in poly-Si JL nanowire TFTs.

Filtration performance of novel microfibrous media embedded with nanofiber flocs for aerosol particle removal

Ingestion and accumulation of sea salt and other impurities is a major challenge for high speed vessels, turbine engines, and other air breathing systems. The performance and reliability of filters are anticipated to be improved significantly after the rate of performance degradation is reduced via enhanced filtration media and well-designed filtration approaches. This study proposes to apply anionic surfactant to disperse the nanofibers thoroughly and employ cationic surfactant to flocculate the dispersed nanofibers into numerous small groups of nanofiber flocs. Using the wet-lay procedure in the lab, the novel porous microfiber media was then fabricated with small groups of nanofiber flocs together with activated carbon and polyester fibers. The unique nanofiber filter media was then evaluated for filtration performance using face velocity, pressure drop, and filtration efficiency parameters. Due to nanoflocced fiber inclusion, an anomalous region in the filtration efficiency versus pressure drop regime was observed where wall slip occurring at the nanostructured surface provided an unusually high level of filtration efficiency near the most penetrating particle size (MPPS) region of 0.1–0.4 μm with a concomitant reduction in the normally encountered levels of pressure drop. This anomalous increase in the filtration efficiency versus pressure drop is a novel phenomenon and it is highly beneficial to aerosol filtration. The enhanced filtration reveals that the quality factor near the MPPS region increases significantly due to the inclusion of nanofiber flocs. The unique porous filtration media is expected to increase the dirt holding capacity and prolong the lifecycle of the turbine air filter systems.

The energy cascade associated with daily variability of the North Atlantic Oscillation

An analysis of anomalies of the energy cascade associated with daily fluctuations of the North Atlantic Oscillation (NAO) is presented here. The analysis consists of a detailed version of the Lorenz energy cycle, which decomposes the energy flows into baroclinic and barotropic terms and into zonal mean and eddy components, and was applied to the 6‐hourly ERA‐Interim reanalysis for the period of 1979–2016. The obtained results show that the positive NAO phase is preceded by a significant increase of synoptic baroclinic eddy activity. The eddy available potential energy is converted into kinetic energy and transferred to barotropic synoptic eddies. Then, the kinetic energy is transferred upscale into the barotropic planetary waves, which produce the NAO pattern. Immediately after the positive NAO peak, there is a significant reduction of baroclinic activity, and no indication of an anomalous increase of the global‐mean baroclinic eddy activity in the 10‐day period after the peak was found. At longer lags, between 10 and 20 days, the kinetic energy of barotropic eddies shows positive anomalies consistent with the eddy–zonal mean flow feedback. We conclude that the synoptic baroclinic eddy activity forces the NAO variability, and no modulating role of the NAO in the global‐mean baroclinic eddy activity (storminess) occurs.

Temperature Behavior of Plasma Reflection Spectra of (Bi2–xSbx)Te3 (0 &lt; х &lt; 1) Crystals in the Temperature Interval 80–300 K

A decrease in the resonant frequency ωр of plasma fluctuations of free charge carriers with increasing temperature observed in all Bi2-xSbx (0 < х < 1) crystals can be explained only partly by the increased polarization background e∞ of the crystal. An analysis of the experimental data allows us to state that the change of ωр and of the electrical conductivity σ is also caused by the decrease of the ratio of the free carrier concentration to their effective mass r/m* (by a factor of 1.47) whose value almost coincides with the anomalous increase in the Hall coefficient in the temperature interval from 80 to 300 K.

Charge transport in confined concentrated solutions: A minireview

Abstract This Minireview summarizes several recent experiments clouding over prevailing theoretical understanding of charge transport behaviors in electrochemical systems; they are nonlinear concentration dependence of ionic conductivity, ultra-long Debye length in ionic liquids, nonmonotonic double layer charging behavior, and anomalous increase in area specific capacitance with decreasing nanopore size. Theoretical activities reveal that nanoconfinement and high concentration exert strong influence on charge distribution and transport via strong ion-ion correlations and ion-wall interactions. By exemplifying where and why classical theories of charge transport fail, we defy the popular point of view that theoretical electrochemistry is well-established and we are left with applications of these theories only.

Experimental thermal energy assessment of a liquid metal eutectic in a microchannel heat exchanger equipped with a (10 Hz/50 Hz) resonator

In the present work, an experimental investigation was conducted on the fluid flow and heat transfer characteristics of gallium-indium eutectic flowing in the microchannel passages. The overall heat transfer coefficient, pressure drop, friction factor and the thermo-hydraulic performance of the microchannel was experimentally quantified for various compositions of indium in the eutectic mixture. Influence of low-frequency vibration at two frequencies and amplitudes on the overall heat transfer coefficient and thermo-hydraulic performance of the microchannel was also studied and discussed. Results showed that the eutectic mixture has a higher thermal performance in comparison with gallium (78% enhancement in thermo-hydraulic performance). Also, the vibration increased the heat transfer coefficient of the microchannel such that at a frequency of 50 Hz and an amplitude of 10 m/s2, the highest heat transfer coefficient and thermal performance of the microchannel was registered. However, the effect of the frequency was more tangible for the eutectic mixtures with lower viscosities such as 95%Ga-5%In and pure gallium. Also, neither the frequency nor the amplitude changed the pressure drop value of the system. Interestingly, the presence of the indium in the eutectic mixture enhanced the heat transfer coefficient, which was attributed to the enhancement in the thermal conductivity of the eutectic mixture. The augmentation in the value of the pressure drop was also compensated with the anomalous increase in the heat transfer coefficient. This study revealed the plausible application of Ga-In mixture in high heat flux cooling systems inside the microchannel heat exchangers.

Oscillations Accompanying a He i 10830 Å Negative Flare in a Solar Facula

On September 21, 2012, we carried out spectral observations of a solar facula in the Si I 10827 {\AA}, He I 10830 {\AA}, and H{\alpha} spectral lines. Later, in the process of analyzing the data, we found a small-scale flare in the middle of the time series. Due to an anomalous increase in the absorption of the He I 10830 {\AA} line, we identified this flare as a negative flare. The aim of this paper is to study the influence of the negative flare on the oscillation characteristics in the facular photosphere and chromosphere. We measured line-of-sight (LOS) velocity and intensity of all the three lines as well as half-width of the chromospheric lines. We also used SDO/HMI magnetic field data. The flare caused modulation of all the studied parameters. In the location of the negative flare, the amplitude of the oscillations increased four times on average. In the adjacent magnetic field local maxima, the chromospheric LOS velocity oscillations appreciably decreased during the flare. The facula region oscillated as a whole with a 5-minute period before the flare, and this synchronicity was disrupted after the flare. The flare changed the spectral composition of the line-of-sight magnetic field oscillations, causing an increase in the low-frequency oscillation power.

Impacts of Diabatic Heating on the Genesis and Development of an Inner Tibetan Plateau Vortex

AbstractA short‐lived (less than 2 days) inner Tibetan Plateau vortex (TPV) with heavy precipitation was simulated using the Weather Research and Forecasting model, and the sensitivity experiments with and without surface diabatic heating and atmospheric latent heating released by precipitation were conducted to investigate the roles of surface and atmospheric diabatic heating on the genesis and development of TPV. Results show that before the genesis of the TPV, there is an anomalous increase of surface heating flux; while a disturbance of potential vorticity (PV) at 500 hPa moves over this region, the PV is enhanced and induces the generation of TPV. The precipitation in turn reduces the surface heating flux. The release of condensation latent heating by precipitation during the development of TPV does not further contribute to its reinforcement. Instead, it is more likely a result of precipitation, tending to stabilize the atmosphere and conducive to the decay of TPV. The PV diagnoses further reveal that in the early phase, the strong diabatic heating in the lower levels associated with the increasing surface heating flux has a significantly positive contribution to the generation of the TPV. The precipitation results in the decrease of positive diabatic heating contribution at low levels. Inversely, the diabatic heating in the middle levels associated with the released latent heating of precipitation condensation tends to have the negative contribution to TPV, resulting in the decay of TPV. The study of this case can deepen our understanding on the mechanism of TPV and its precipitation.

The anomalous increase in tunability in Ba0.55Sr0.45TiO3‐MgO‐Mg2SiO4 composite ceramics

AbstractThe Ba0.55Sr0.45TiO3–Mg2SiO4–MgO composite ceramics were prepared via solid‐stated method and the dielectric tunable properties of composite ceramics were investigated. With the increase in dielectrics content, the tunability of composites ceramics increased abnormally first and then decreased, while the anharmonic coefficient increased monotonously. A simple 3D Finite Element model was developed to simulate the dielectric response and an anomalous increase in tunability when increasing the dielectrics content in composites was obtained. The simulation indicated that adding dielectrics into ferroelectrics causes the redistribution of the electric field. Increasing dielectrics content, the average electric field strength in the enhanced area of ferroelectrics increases, which lead to the increase in the tunability. The abnormal increase in tunability originates from the enhancement of the electric field on a fraction of the ferroelectrics around dielectrics.

The anisotropic effect of hexagonal warping on the transport

In the presence of hexagonal warping (HW), the surface state of a topological insulator (TI) exhibits anisotropic Fermi surface. In this work, we study the transport properties of a TI junction, focusing on the influence of anisotropic effect of the HW on the scattering. We establish general expressions for calculating the scattering with an arbitrary angle between TI surface and the potential step, and find that the transmission probability and conductance have a strong dependence on the angle, making TI junction a promising platform for studying the geometry control of transport. Remarkably, we find that the HW can induce a triple refraction, which gives rise to an anomalous increase of the transmission probability when varying incident angle. The general expressions here for calculating the scattering can be extended to the systems with trigonally and tetragonally warped Fermi surface.