Typical Loop Research Articles

The atypical binding mechanism of second calcium on phospholipase A2 group IIE

Secreted phospholipase A2s (sPLA2s) are calcium dependent enzymes involved in various biological events such as lipid metabolism and inflammation. We previously identified the second calcium (Ca2) binding site of human sPLA2 Group IIE (hGIIE) by structural study and suggested that Asn21 act as the switch of Ca2 binding to modulate the enzymatic activity, but the detailed Ca2 binding mechanism is still unclear. Combined with enzymatic assay, model analysis and calcium binding affinity data for mutated hGIIE proteins, we herein further demonstrate that the flexibly bound Ca2 is essential for the catalysis of hGIIE, unlike the stable binding of Ca2 in hGIIA that replenishes the calcium in the typical loop during the reaction. The atypical Ca2 binding feature of hGIIE will provide a better understanding on the catalytic mechanism of hGIIE.

Modulation the structural, magnetic and electrical properties of Ni‐Zn ferrites by lutetium substitution

Ni-Zn ferrites with a formula of Ni0.5Zn0.5LuxFe2−xO4 (x = 0.000, 0.004, 0.008, 0.012, 0.016 and 0.020) have been synthesized by ceramic sintering method. The effects of Lu3+ doping on structural, electrical and magnetic performances are investigated. X-ray powder diffraction results demonstrate that Lu3+ ions completely enter into the lattice of cubic spinel structure without formation impurity phases. By increasing Lu3+ content, the lattice parameter increases monotonously. The average crystallite size D and microstrain for all samples are estimated by Williamson-Hall (W-H) method. Fourier transform infrared spectroscopy (FTIR) and energy dispersive spectra (EDS) analyses confirm the cubic spinel phase and chemical composition of the as-synthesized Ni0.5Zn0.5LuxFe2−xO4, respectively. Scanning electron microscope (SEM) images indicate that the size of agglomerated particles is not uniform with a little bit of pores, and the grain boundaries become more ambiguous as increasing Lu3+ content. The permittivity indicates a normal dielectric behavior of Ni-Zn ferrites under the alternating electric field. However, when the frequency of applied electric field reaches a certain value, the dielectric loss tangent will appear a peak behavior. The typical ferromagnetic S-shape loops of these samples were collected by vibrating sample magnetometer (VSM), the saturation magnetization first increases and then decreases with increasing Lu3+ concentration, exhibiting a maximum value of 71.41 emu/g when x = 0.004.

Resonant absorption of kink MHD waves in inclined and asymmetric coronal loops

ABSTRACT This paper separately evaluates the effects of inclination and asymmetry of solar coronal loops on the resonant absorption of kink magnetohydrodynamic oscillations. We modelled a typical coronal loop by a straight and axisymmetric cylindrical magnetic flux tube filled with cold plasma. We solved the dispersion relation numerically for different values of the longitudinal mass density stratification. We show that, in inclined and asymmetric loops, the frequencies and their corresponding damping rates of the fundamental and first-overtone modes of kink oscillations are smaller in comparison with semi-circular uninclined loops with the same lengths. The results also indicate that, the period ratio P1/P2, increases with increasing the inclination of the loop, but it decreases less than $2{{\ \rm per\ cent}}$ while imposing the asymmetry to each loop side, up to $9.66{{\ \rm per\ cent}}$ of the loop length. The ratio of each mode frequency to its corresponding damping rate remain unchanged approximately while the inclination or the asymmetry imposed. Hence, we conclude that these ratios are reliable for inferring the physical parameters of coronal loops and coronal medium, regardless of the loop shape or the state of its inclination. In addition, in contrast with the effect of asymmetry, which is not significant on the period ratio P1/P2, when an observed oscillating loop has a smaller apex height, the state of its inclination is an important factor that should be considered, especially when the period ratio P1/P2, is taken into consideration for coronal seismology.

Structure, dielectricity and ferroelectricity measurement of new perovskite ceramics (1-x)BaTiO3-xBiMnO3 synthesized by solid-state reaction

The complex oxide of general form (1-x)BaTiO3-xBiMnO3 was synthesized by solid-state reaction route and characterized the structure, dielectricity, and ferroelectricity for the first time. The XRD pattern confirms the formation of perovskite structure and a phase transitions from the tetragonal to cubic phase corresponds to the composition x > 0.3 with a reasonable change in the lattice parameter. An optimum dielectric constant value of 14512 corresponds to a maximum temperature of 200 °C, and 100Hz frequency has been measured in 0.5BaTiO3-0.5BiMnO3 ceramic. In contrast, the PE-loop study of these ceramics exhibited a remanent polarization (Pr) 0.230 μC/cm2 at a coercive field electric field (Ec) of 2.8 kV/cm in 50BaTiO3–50BiMnO3 ceramic. The composition-dependent change in structure and properties shows a prospective existence of morphotropic phase boundary (MPB) at about the composition with x = 0.5. The typical dielectricity and PE loop measurement of the oxides, especially in the composition range with x = 0.1 to 0.5, seems to be promising materials for multilayer ceramic capacitor (MLCC) and device applications.

The Electron Acoustic Wave and Its Role in Solar Flaring Loops Heating

Abstract From soft X-ray emission, the solar flare temperatures are from several MK to dozens of times MK, which are higher than the preflare coronal temperatures. A combination of several heating mechanisms may contribute to the heating problem in solar flare loops. In this paper, we propose an important mechanism of solar flaring loops heating, in which the excited electron acoustic wave (EAW) by flare-accelerated fast electron beams can lead to electron heating via collisionless Landau damping effect produced by wave–particle resonant interaction. Taking account of the return-current effect of fast electron beams, by use of numerical and analytic solutions, the plasma wave instability driven by fast electron beams is investigated in typical solar flare loop plasma parameters. The results show that the EAW is the strongest unstable wave mode rather than other wave modes. The dissipation of EAW via collisionless Landau damping and its application to solar flaring loops heating are discussed in detail.

Dielectric and ferroelectric properties of (Bi0.5Na0.5)0.94-δBa0.06Ti1−xNbxO3 lead-free ceramics

Lead-free ceramics (Bi0.5Na0.5)0.94-δBa0.06Ti1−xNbxO3 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were prepared via a solid-state sintering method. The ceramics exhibit pure perovskite structure as x ≤ 0.04, while the ceramic with x = 0.05 has a secondary phase. The rhombohedral (R)–tetragonal (T) morphotropic phase boundary exists in all the samples. The relative content of the T phase increases due to the Nb5+ doping. The ceramics show dense microstructures with mean grain sizes around 1–2 μm. The changes of dielectric constant and dielectric loss as a function of temperature for the unpoled and poled samples were compared. Two dielectric anomalies appear on the dielectric curves around the temperatures denoted as TRE and Tm. With the increase of Nb5+ amount, the values of TRE decrease and Tm increase. The Nb5+-doped ceramics exhibit better temperature stability of dielectric constant during a wide high-temperature window. The polarization hysteresis (P–E) loops change from typical ferroelectric loops for the sample with x = 0 to constricted P–E loops with increasing Nb5+ amount. The ceramic with x = 0.03 shows a maximum strain (Smax) of 0.55% and piezoelectric strain constant (d33*) of 675 pm/V.

On the Coronal Temperature in Solar Microflares

Abstract We present a study of solar imaging and spectral observations of a microflare, focusing on the temperature diagnostics provided by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, and the Extreme-Ultraviolet Imaging Spectrometer (EIS) on board Hinode. Our data analysis, in particular from the emission in the 131 and 94 Å channels, indicates that the heated plasma reaches temperatures of ≳10 MK, at odds with a previous analysis of the same event, and we discuss the reason for the discrepancy. A particularly interesting aspect is the likely presence of the Fe xxiii 263.76 Å line, though weak, in EIS spectra in the early phases of the event, supporting the presence of high temperature plasma. Hydrodynamic 1D modeling of a single loop heated with a 3 minute pulse to 12–15 MK reproduces well most observed features along one of the brightening loops, including intensities in the AIA hot channels and their temporal variability, as well as the intensity, Doppler shift, and line width of the EIS Fe xxiii line, and its timing relative to the AIA emission. Overall, we obtain a coherent scenario of a typical microflaring loop system and provide constraints on the intensity of the energy release as well as its spatial and temporal distribution, both along and across the loop.

Turbulence in a Coronal Loop Excited by Photospheric Motions

Photospheric motions are believed to be the source of coronal heating and of velocity fluctuations detected in the solar corona. A numerical model, based on the shell technique applied on reduced magnetohydrodynamics equations, is used to represent energy injection due to footpoint motions, storage and dissipation of energy in a coronal loop. Motions at the loop bases are simulated by random signals whose frequency-wavenumber spectrum reproduces features of photospheric motions: the p-mode peak and the low-frequency continuum. Results indicate that a turbulent state develops, dominated by magnetic energy, where dissipation takes place in an intermittent fashion. The nonlinear cascade is mainly controlled by velocity fluctuations, where resonant modes are dominant at high frequencies. Low frequency fluctuations present a power-law spectra and a bump at p-mode frequency; similar features are observed in velocity spectra detected in the corona. For typical loop parameters the energy input flux is comparable with that necessary to heat the quiet-Sun corona.

GCN2-Like Kinase Modulates Stress Granule Formation During Nutritional Stress in Trypanosoma cruzi.

The integrated stress response in eukaryotic cells is an orchestrated pathway that leads to eukaryotic Initiation Factor 2 alpha subunit (eIF2α) phosphorylation at ser51 and ultimately activates pathways to mitigate cellular damages. Three putative kinases (Tck1, Tck2, and Tck3) are found in the Trypanosoma cruzi genome, the flagellated parasite that causes Chagas disease. These kinases present similarities to other eukaryotic eIF2α kinases, exhibiting a typical insertion loop in the kinase domain of the protein. We found that this insertion loop is conserved among kinase 1 of several T. cruzi strains but differs among various Kinetoplastidae species, suggesting unique roles. Kinase 1 is orthologous of GCN2 of several eukaryotes, which have been implicated in the eIF2α ser51 phosphorylation in situations that mainly affects the nutrients levels. Therefore, we further investigated the responses to nutritional stress of T. cruzi devoid of TcK1 generated by CRISPR/Cas9 gene replacement. In nutrient-rich conditions, replicative T. cruzi epimastigotes depleted of TcK1 proliferate as wild type cells but showed increased levels of polysomes relative to monosomes. Upon nutritional deprivation, the polysomes decreased more than in TcK1 depleted line. However, eIF2α is still phosphorylated in TcK1 depleted line, as in wild type parasites. eIF2α phosphorylation increased at longer incubations times, but KO parasites showed less accumulation of ribonucleoprotein granules containing ATP-dependent RNA helicase involved in mRNA turnover (DHH1) and Poly-A binding protein (PABP1). Additionally, the formation of metacyclic-trypomastigotes is increased in the absence of Tck1 compared to controls. These metacyclics, as well as tissue culture trypomastigotes derived from the TcK1 knockout line, were less infective to mammalian host cells, although replicated faster inside mammalian cells. These results indicate that GCN2-like kinase in T. cruzi affects stress granule formation, independently of eIF2α phosphorylation upon nutrient deprivation. It also modulates the fate of the parasites during differentiation, invasion, and intracellular proliferation.

Electrocaloric and electromechanical properties of (Pb,La)(Zr,Ti)O3 ceramics

The direct observation of temperature changes in (Pb,La)(Zr,Ti)O3 (PLZT) (4/90/10), (8/80/20), and (8/70/30) ceramics during cycle of applying and removing electric field were utilized to evaluate their electrocaloric effects. The temperature change under the electric field drew temperature-electric field (T-E) hysteresis loops peculiar to each material. PLZT(4/90/10) ceramics exhibited a double hysteresis peculiar to antiferroelectrics in polarization-electric field (P-E) loops. A temperature drop of −0.07 K due to the application of an electric field of 70 kV/cm was observed directly by measuring the T-E loop. This temperature drop is due to a negative electrocaloric effect. PLZT(8/80/20) and (8/70/30) ceramics exhibited slim P-E loops with constriction and typical ferroelectric loops, respectively. The temperature changes induced by a bipolar switching field of 40 kV/cm in the PLZT(8/80/20) and PLZT(8/70/30) ceramics were both positive 0.22 K. The measured T-E loops had shapes similar to those of the strain-electric field loops in samples of PLZT(8/80/20) and PLZT(8/70/30) ceramics. PLZT(8/80/20) ceramics exhibited their largest electromechanical properties at around 25 °C, and the properties then decreased with increasing temperature.

Hierarchy and decoupling

A large hierarchy between the electroweak scale and virtually any new scale of beyond-Standard-Model physics is often claimed to be unnatural. Sometimes, the apparent disparity between the measured Higgs mass and the size of the typical loop corrections encountered within such schemes is even interpreted as a profound indication that one should expect a remedy just behind the corner, probably in the form of a new physics such as low-scale supersymmetry, new strong dynamics etc. Without much of an aspiration to shed more light on the smallness of the electroweak scale we exploit the symmetry properties of the Coleman–Weinberg effective potential to make it very clear why to all orders in the perturbative expansion. With the method we present no inspection of the explicit form of the tadpole equations is required. These findings are exemplified on an extended series of specific simplified models in which the role of the heavy dynamics is played by all ‘reasonable’ types of fields (barring gravity), i.e. by a heavy scalar, a heavy (Majorana) fermion and a heavy vector. We show that the explicit dependence of mH on the heavy scale follows the expectation based on dynamical arguments such as the decoupling theorem.

Loop Shaping by Single-Resonant Controllers for Prescribed Tracking of Sinusoidal References

It is well-known that in ac-grid-connected or motor-driving converters, current behavior directly sets the exchange of power between the two. Moreover, in corresponding current plants, most of the disturbance (formed by grid voltage or back EMF and the dc-link voltage) may be measured/estimated and appropriately canceled, reducing the current regulation problem to tracking challenge only. The latter is still of extreme importance since the amount of active/reactive power exchanged is proportional to current magnitude and phase. Recently, a method for deriving proportional-resonant controller structure and coefficients according to desired tracking behavior of ac signal amplitude, applied to typical power converter current loop, was proposed based on the fact that if ac signal envelope is perceived as dc signal, its transient behavior may be easily shaped utilizing well-known approaches employed in dc systems loop shaping while keeping zero phase tracking error at all time. This paper extends the proposed methodology by introducing in-depth analysis of the resulting loop gain shaping, applying practical issues, such as actuator delay, damping, and finite word length to the system, yielding a closed set of hands-on design guidelines. Experimental results are also given, providing a two-fold value: successfully validating the presented material and demonstrating that some of the previously reported outcomes (based on simulations) cannot be achieved in practice due to the above mentioned real world constraints.

Gridding place recognition for fast loop closure detection on mobile platforms

Loop closure detection is an indispensable component to reduce the error accumulation in localisation applications, however, it is hard to be implemented as a real-time application with high accuracy on the mobile platform. A place recognition method called gridding place recognition (GPR) is proposed for ultra-fast loop closure detection with high accuracy maintained. The GPR splits the images into multiple grids for high parallelism and uses bags of word features to summarise each grid. The matching results for each grid are then retrieved and merged for further determination of loop closure under extra temporal and spatial constraints. The authors implement the method on a mobile platform, and the best accuracy and fastest execution time of 47 frames per second are achieved on several public benchmarks compared with other typical or fast loop closure algorithms.

Circuit Implementation of Nano-Scale TiO2 Memristor Using Only Metal-Oxide-Semiconductor Transistors

A metal-oxide-semiconductor (MOS)-based circuit model that emulates a TiO2 memristor is proposed in this study. First, a TiO2 (10-nm active layer thickness)-based memristor device was fabricated. The structural properties of the device were confirmed via energy dispersive X-ray spectroscopy. The memristive characteristics of the device were resolved by applying a time-dependent voltage. The typical pinched hysteresis memristive loops of the current-voltage curves were obtained. After physical implementation and characterization of the device, a circuit model was implemented using only four MOS transistors to emulate the fabricated TiO2 memristor. In addition to emulating the fabricated memristor, the proposed circuit model is suitable for use in general memristor-based applications. No active element or circuit blocks were used in the circuit to achieve memristive characteristics. The simulation and experimental results are in good agreement; moreover, the circuit is very simple compared to those presented in previous studies in the literature and it was able to emulate the fabricated memristor. All simulations were completed using 180 nm TSMC CMOS process parameters.

Seismic behavior of self-centering concrete-filled square steel tubular (CFST) Column Base

Traditional column base connections typically designed as fully restrained moment connections are questionable to be applied in self-centering seismic resisting structural systems. In this study, three types of self-centering concrete-filled square steel tubular (CFST) column base connections, i.e., Type I and Type II fabricated with post-tensioned (PT) strands and sandwiched energy dissipaters constructed in opposite and the same directions respectively and Type III fabricated PT strands and sandwiched energy dissipaters in orthogonal direction are proposed. Results shed light on the influence of these bases on seismic performance, beginning with a cyclic experimental investigation on three 3/4 scaled of Type I test specimens. Findings demonstrate that all test specimens exhibited typical flag-shaped hysteretic loops with the expected deformation mode, stable energy dissipated and good self-centering ability with 0.14% of the maximum recorded residual drift at 2% drift. Under 4% drift, the buckling restrained steel (BRS) plates yielded while the column and strands remained elastic, creating no damage to the main structural elements. Moreover, an analytical model of three types of self-centering CFST column base connections was developed, which are able to predict the column base connections moments reasonably.

Transient characteristics of a parabolic trough direct-steam-generation process

Solar-powered direct steam generation (DSG) is attractive for power generation and industrial utilization due to the combination of renewable-energy source and clean energy carrier. An improved SIMPLE algorithm ensuring the dual roles of pressure acting on velocity and density fields is developed to realize thermo-hydraulic completely-coupled modeling of a typical DSG loop with transient phase-change and multiple flow-patterns. The excitation-response characteristics of the loop were investigated under various step-variations of direct normal irradiance (DNI), inlet mass flowrate (min) and inlet temperature (tin). Increasing DNI (decreasing min) is found to narrow the preheating-evaporation regions and expand the superheating region, and vice versa. While under step-variations of tin, the evaporation region almost remains unchanged (about 403 m). The water slides to a lower temperature faster than climbs to a higher one under variations of DNI (up to 670s vs. 2960s) and min (up to 1184s vs. 4420s), simultaneously the outlet temperature (tout) staying a monotonical response-trend. However, under tin variations, tout holds a higher-order trait. The responses of both pressure and velocity are tightly coupled and always hold higher-order trait. The response time of the total mass in the loop is almost 2.5 to 5.5 times as fast as tout.

Enhanced Photocatalytic Activity by the Combined Influence of Ferroelectric Domain and Au Nanoparticles for BaTiO3 Fibers

Ferroelectric particles have been applied in the photocatalytic field because the spontaneous polarization results in the internal electric field, which can accelerate the separation and migration of photogenerated carriers. In this study, the BaTiO3 (BT) fibers are synthesized by electrospinning. The BT fibers calcined above 800[Formula: see text]C exhibit a strong ferroelectric property, which is verified by a typical butterfly-shaped displacement-voltage loop. It is found that the BT fibers with the single-domain structure exhibit better photocatalytic performance than that with the multi-domain configuration. When the single-domain transforms into multi-domain, the integrated internal electric field correspondingly breaks up, inducing that the internal electric field might cancel each other out and diminish the separation of photogenerated carriers. Also, the Au nanoparticles can improve the photocatalytic activity further on account of the surface plasmon resonance. Therefore, it is suggested that Au nanoparticles decorated on ferroelectric BT nanomaterials are promising photocatalysts.

Power Saving LED Luminance Fuzzy Control with IOT Network

To lower down illumination power consumption and enhance lighting effects, smart LED controller and luminance sensors were connected to a WIFI based IOT network, fuzzy luminance control was employed on the IOT net. The schematic topology of the IOT net was outlined. The smart LED controller used the dedicated IOT chip ESP 8266 as the main processor, which was connected to the WIFI network and drove LEDs with PWM signals. The luminance fuzzy control strategy was also implemented on ESP8266 in C language. The fuzzy control process was a typical feedback loop, which took the error (difference between the luminance measured value and the luminance set value) and error change as inputs and calculated the output (the PWM increment) according to fuzzy rules. To test system efficiency, step response experiment and power saving experiment were conducted, proving the system to have good control quality and capable of saving more power by means of intelligent control.

Swift observations of the bright uncatalogued X-ray transient MAXI J1535-571

The black hole candidate MAXI J1535-571 is a recently discovered X-ray transient. We report on the monitoring observations of Swift Gamma-Ray Burst Mission during outburst. The source transits from the hard state to the intermediate state, and reaches the soft state; near the end of the outburst, it returns to the hard state passing through the low intermediate state, following a typical Q-shaped loop in the hardness-intensity diagram. During the high intermediate state, detailed spectral analyses using a multi-temperature disk model reveal that the disk luminosity is flatter than the inner disk temperature to the fourth power, and the disk temperature profile varies as the disk radius raised to the power of -0.5, consistent with the behavior of a slim disk, implying that the disk structure has been modified due to the high luminosity of ~ 10^{39} erg/s. Meanwhile, the column density increases with the Eddington ratio, suggesting that the outflow matters are driven by radiation pressure due to the high accretion rate.

Inertia and Primary Frequency Provisions of PLL-Synchronized VSC HVDC When Attached to Islanded AC System

The islanded scenarios of voltage source converter (VSC) high-voltage DC (HVDC) directly supplying power to islanded loads or connecting to wind farm are becoming popular, in which some new issues are required to be further addressed. While several control strategies have been studied, to the authors’ best knowledge, few have investigated the potential capability of VSC HVDC using the typical phase-locked loop (PLL)-synchronized vector control (PLLSynVC) to address islanded operation issues. To explore the potential capability of the typical PLLSynVC in islanded system, this paper proposes a frequency regulation scheme (FRS), including inertia and primary frequency control, for the PLL-synchronized VSC HVDC based on the motion equation concept. By adding the FRS, the VSC HVDC using the PLLSynVC, similar to a synchronous generator from the view of the phase motion equation, not only can self-maintain the frequency stable in an islanded system, but also naturally avoids the transition of control operation modes without changing the basic control structure. Furthermore, based on the developed phase motion equation, the inertia characteristics of VSC HVDC with the FRS is studied, which synthetically considers the impact of different controllers and PLL, and makes VSC HVDC's manifested inertia clear. The effectiveness of FRS and inertia analysis results is verified by time-domain simulations.