Triangular Pulse Research Articles

Intrinsically Switchable Ferroelectric Scandium Aluminum Nitride Lamb-Mode Resonators

This letter reports intrinsically switchable ultra- and super-high-frequency Lamb-mode resonators based on the use of ferroelectricity in scandium aluminum nitride (ScxAl1−xN) films. Highly crystalline 200nm-thick Sc0.22Al0.78N film is sputtered using segmented-target reactive magnetron sputtering, and interdigitated electrodes are patterned to create one-port resonators operating in symmetric Lamb modes. The resonators are intrinsically switched using the ferroelectric behavior in Sc0.22Al0.78N film and through polarization switching at one of the terminals, resulting in a zero-sum electromechanical coupling factor ( ${k}_{t}^{2}$ ). Resonators with frequencies over 0.45 – 6 GHz, frequency $\times $ quality factor product ( ${f}_{s}\times {Q}$ ) as high as $4\times 10^{12}$ , and and $k_{t}^{2} \times Q$ product exceeding29 aredemonstrated. The intrinsic switchability of resonators is characterized using 100ms triangular monopolar pulses, resulting in an admittance switching isolation as high as 15dB.

Mechanical behaviour of bonded joints including viscoelasticity for the adhesive under triangular pulse loading and harmonic loading

The constitutive law of the interface is a prime issue when evaluating the strength of adhesively bonded joints. The polymer-based adhesives exhibit loading rate sensitivity and damping properties owing to their viscous nature, especially at high temperatures or under water. This paper aims to establish a shear-lag model to elucidate the mechanical behaviour of adhesively bonded joints under triangular pulse loading and harmonic loading. The extended shear-lag model is focused on improving the previous shear-lag models by including viscoelastic behaviour using the Kelvin model for the adhesive. Analytical expressions of the slip and interfacial shear stress distribution have been respectively presented for pull-push joint and pull-pull joint under triangular pulse loading. Compared with finite element simulation, the predictive model shows an excellent agreement with the FEA results. The damping properties including the storage modulus, loss modulus and loss factor for these two bonded joints subjected to harmonic loading are theoretically derived. Finally, results obtained from the predictive model are presented to illustrate how the bond length, loading rate and loading frequency affect the behaviour of such bonded joints.

Unexpected Scaling of Peak Acceleration for a Yielding Mass-Spring System Subjected to a Triangular Base Acceleration Pulse

Abstract The use of bounding scenarios is a common practice that greatly simplifies the design and qualification of structures. However, this approach implicitly assumes that the quantities of interest increase monotonically with the input to the structure, which is not necessarily true for nonlinear structures. This paper surveys the literature for observations of nonmonotonic behavior of nonlinear systems and finds such observations in both the earthquake engineering and applied mechanics literature. Numerical simulations of a single degree-of-freedom mass-spring system with an elastic–plastic spring subjected to a triangular base acceleration pulse are then presented, and it is shown that the relative acceleration of this system scales nonmonotonically with the input magnitude in some cases. The equation of motion for this system is solved symbolically and an approximate expression for the relative acceleration is developed, which qualitatively agrees with the nonmonotonic behavior seen in the numerical results. The nonmonotonicity is investigated and found to be a result of dynamics excited by the discontinuous derivative of the base acceleration pulse, the magnitude of which scales nonmonotonically with the input magnitude due to the fact that the first yield of the spring occurs earlier as the input magnitude is increased. The relevance of this finding within the context of defining bounding scenarios is discussed, and it is recommended that modeling be used to perform a survey of the full range of possible inputs prior to defining bounding scenarios.

Switching strategies for a multi-level inverter

The article examines the methods of switching the stages of a multi-level inverter in order to reduce the harmonic factor of the output voltage of the inverter. These methods use pulse-width modulation for switching, which is obtained by comparing a reference sinusoidal signal and a sequence of triangular pulses. The article describes the algorithms for obtaining the control sequence of pulses and simulates each of the strategies. The dependence of the nonlinear distortion factor on the frequency of the carrier wave for different switching strategies is obtained based on the simulation results. The influence of the LPF on the quality of the output voltage of the inverter is also investigated. In addition, an experimental study of a six-level inverter was carried out. The waveforms and spectrograms of the inverter were obtained using the Fluke 434-II electrical energy analyzer. The harmonics of the output voltage, which are distinguished by power from the entire spectrum, were identified.

A Digitally Controlled Multichannel Spectrally Efficient Low-Power Transceiver for Ultra-Wideband Cognitive Radio Applications

A multichannel transceiver design with low hardware complexity, flexibility and efficient spectrum use intended for Impulse Radio (IR) Ultra-Wideband (UWB) apertures, is proposed in this paper. The transceiver supports 14 channels and is implemented in TSMC CMOS process. The transmitter adopts a symmetrical triangular narrow pulse generator, a multiband LC-VCO, a mixer and a Variable-Gain Amplifier. A digital control of transmitter output power and carrier frequency is achieved by a current-steering Digital-to-Analog Converter (CS-DAC). The receiver follows the noncoherent Energy Detection (ED) scheme including Low-Noise Amplifier (LNA) which takes the benefits of the body biasing technique to further reduce power consumption, squarer and comparator. The LNA achieves high gain of up to 30[Formula: see text]dB allowing to enhance the receiver sensitivity which is [Formula: see text]83.7[Formula: see text]dBm at 25[Formula: see text]Mbps. The transmitter provides output pulses with a width of 3[Formula: see text]ns, a pulse repetition rate of 20[Formula: see text]ns and a maximum Power Spectral Density (PSD) of [Formula: see text]42[Formula: see text]dBm/MHz. The power consumptions of transmitter and receiver are 35.6[Formula: see text]pJ/bit and 0.207[Formula: see text]nJ/bit at 25[Formula: see text]Mbps, respectively. Maximizing utilization of the scarce wireless spectrum, enhancing spectral flexibility and efficiency and reducing power consumption are the main contributions brought by this work, enabling this transceiver to be able to deal with the current debate on producing single multifunctional Cognitive Radio (CR) UWB systems.

Propagation of stress pulses in a Rayleigh-Love elastic rod

In this paper, the longitudinal wave propagation in an elastic rod is studied based on the 1D Rayleigh-Love rod theory considering the lateral inertia effect. The Laplace transform method is applied to solve the initial boundary value problem. After conducting the inverse transform, a kernel function in form of integral is obtained, which reveals the essential dispersion characteristics of the wave propagation in a Rayleigh-Love rod. Then the general solution of stress is expressed as the convolution of the kernel function and the boundary loading. Specific examples are given for the problems of typical boundary pulses, i.e. the rectangular, trapezoidal, triangular, and two-stage pulses. Moreover, the dispersive waveforms from our analysis compare nicely with those from the finite element simulation, which indicates that our analytical solution can be used for the dispersion correction in the Hopkinson bar tests.

Transient Analysis of Laminated composite Plate using New Higher-Order Shear Deformation Theory

This work develops transient analysis using a new higher-order displacement function for simply supported cross-ply laminated plates. Muntari’s higher-order shear deformation method for elastic composite plates is used to investigate the composite laminated thick and thin plate’s transient response. The current theory accounts for an approximately parabolic distribution of the transverse shear strains on the plate boundary surface through the thickness and tangential stress-free boundary conditions. The governing equations and boundary conditions are derived by employing the principle of virtual work. These equations are solved using closed-form solutions of a Navier’s type, plates are subjected to a different distribution of transient loadings such as step pulse, triangular pulse, and sinusoidal pulse, and many design parameters are studied, as expected minimum deflection is obtained for thick, antisymmetric, and has high orthotropy ratio laminated plate. The results obtained theoretically are compared with those available in various literature and showed a high agreement.

Selective Surface Electrostimulation of the Denervated Zygomaticus Muscle.

: ObjectiveThis article describes a first attempt to generate a standardized and safe selective surface electrostimulation (SES) protocol, including detailed instructions on electrode placement and stimulation parameter choice to obtain a selective stimulation of the denervated zygomaticus muscle (ZYG), without unwanted simultaneous activation of other ipsilateral or contralateral facial muscles. Methods: Single pulse stimulation with biphasic triangular and rectangular waveforms and pulse widths (PW) of 1000, 500, 250, 100, 50, 25, 15, 10, 5, 2, 1 ms, at increasing amplitudes between 0.1 and 20 mA was performed. Stimulations delivered in trains were assessed at a PW of 50 ms only. The stimulation was considered successful exclusively if it drew the ipsilateral corner of the mouth upwards and outwards, without the simultaneous activation of other ipsilateral or contralateral facial muscles. I/t curves, accommodation quotient, rheobase, and chronaxie were regularly assessed over 1-year follow-up. Results: 5 facial paralysis patients were assessed. Selective ZYG response in absence of discomfort and unselective contraction of other facial muscle was reproducibly obtained for all the assessed patients. The most effective results with single pulses were observed with PW ≥ 50 ms. The required amplitude was remarkably lower (≤5 mA vs. up to 15 mA) in freshly diagnosed (≤3 months) than in long-term facial paralysis patients (>5 years). Triangular was more effective than rectangular waveform, mostly because of the lower discomfort threshold of the latter. Delivery of trains of stimulation showed similar results to the single pulse setting, though lower amplitudes were necessary to achieve the selective ZYG response. Initial reinnervation signs could be detected effectively by needle-electromyography (n-EMG). Conclusion: It is possible to define stimulation parameters able to elicit an effective selective stimulation of a specific facial muscle, in our case, of the ZYG, without causing discomfort to the patient and without causing unwanted unspecific reactions of other ipsilateral and/or contralateral facial muscles. We observed that the SES success is strongly conditioned by the correct electrode placement, which ideally should exclusively interest the area of the target muscles and its immediate proximity.

Effective Activation by Kynurenic Acid and Its Aminoalkylated Derivatives on M-Type K+ Current.

Kynurenic acid (KYNA, 4-oxoquinoline-2-carboxylic acid), an intermediate of the tryptophan metabolism, has been recognized to exert different neuroactive actions; however, the need of how it or its aminoalkylated amide derivative N-(2-(dimethylamino)ethyl)-3-(morpholinomethyl)-4-oxo-1,4-dihydroquinoline-2-carboxamide (KYNA-A4) exerts any effects on ion currents in excitable cells remains largely unmet. In this study, the investigations of how KYNA and other structurally similar KYNA derivatives have any adjustments on different ionic currents in pituitary GH3 cells and hippocampal mHippoE-14 neurons were performed by patch-clamp technique. KYNA or KYNA-A4 increased the amplitude of M-type K+ current (IK(M)) and concomitantly enhanced the activation time course of the current. The EC50 value required for KYNA- or KYNA-A4 -stimulated IK(M) was yielded to be 18.1 or 6.4 μM, respectively. The presence of KYNA or KYNA-A4 shifted the relationship of normalized IK(M)-conductance versus membrane potential to more depolarized potential with no change in the gating charge of the current. The voltage-dependent hysteretic area of IK(M) elicited by long-lasting triangular ramp pulse was observed in GH3 cells and that was increased during exposure to KYNA or KYNA-A4. In cell-attached current recordings, addition of KYNA raised the open probability of M-type K+ channels, along with increased mean open time of the channel. Cell exposure to KYNA or KYNA-A4 mildly inhibited delayed-rectifying K+ current; however, neither erg-mediated K+ current, hyperpolarization-activated cation current, nor voltage-gated Na+ current in GH3 cells was changed by KYNA or KYNA-A4. Under whole-cell, current-clamp recordings, exposure to KYNA or KYNA-A4 diminished the frequency of spontaneous action potentials; moreover, their reduction in firing frequency was attenuated by linopirdine, yet not by iberiotoxin or apamin. In hippocampal mHippoE-14 neurons, the addition of KYNA also increased the IK(M) amplitude effectively. Taken together, the actions presented herein would be one of the noticeable mechanisms through which they modulate functional activities of excitable cells occurring in vivo.

Influence of Cu Doping in Si–Te-Based Chalcogenide Glasses and Thin Films: Electrical Switching, Morphological and Raman Studies

To understand the electrical switching behavior of Si15Te $_{85-{x}}$ Cu x ( $1\le {x} \le10$ ) series, ${I}$ – ${V}$ characterization has been performed on bulk as well as amorphous thin films of the as-prepared samples. Both the bulk glasses and amorphous thin films are found to manifest memory-type switching behavior. The threshold voltages of thin-film devices are found to be much lower than the bulk counterparts and hence could find application for phase change memory (PCM). The composition analyses of both have divulged the existence of intermediate phase (IP) in the composition range of $2 \le {x} \le6$ . To examine the probability of the given glass for PCM application, Set–Reset studies have been performed on the glasses with a triangular pulse of 6 mA for set operation and rectangular pulse of 12 mA for the reset operation. The study has revealed a continuous repetition of few Set–Reset cycle by the Si–Te–Cu series. Raman studies carried out on the bulk glasses report the occurrence of blue shift over the composition in a regular manner. Further, SEM studies have been carried out on Si–Te–Cu samples to understand the morphological changes that would have occurred during switching. Additionally, thickness dependence of threshold voltage of representative Si15Te80Cu5 and Si15Te76Cu9 glasses has been carried out to reveal the relationship between threshold voltage and thickness.

Effectiveness of Columbianadin, a Bioactive Coumarin Derivative, in Perturbing Transient and Persistent INa.

Columbianadin (CBN) is a bioactive coumarin-type compound with various biological activities. However, the action of CBN on the ionic mechanism remains largely uncertain, albeit it was reported to inhibit voltage-gated Ca2+ current or to modulate TRP-channel activity. In this study, whole-cell patch-clamp current recordings were undertaken to explore the modifications of CBN or other related compounds on ionic currents in excitable cells (e.g., pituitary GH3 cells and HL-1 atrial cardiomyocytes). GH3-cell exposure to CBN differentially decreased peak or late component of voltage-gated Na+ current (INa) with effective IC50 of 14.7 or 2.8 µM, respectively. The inactivation time course of INa activated by short depolarization became fastened in the presence of CBN with estimated KD value of 3.15 µM. The peak INa diminished by 10 µM CBN was further suppressed by subsequent addition of either sesamin (10 µM), ranolazine (10 µM), or tetrodotoxin (1 µM), but it was reversed by 10 µM tefluthrin (Tef); however, further application of 10 µM nimodipine failed to alter CBN-mediated inhibition of INa. CBN (10 µM) shifted the midpoint of inactivation curve of INa to the leftward direction. The CBN-mediated inhibition of peak INa exhibited tonic and use-dependent characteristics. Using triangular ramp pulse, the hysteresis of persistent INa enhanced by Tef was noticed, and the behavior was attenuated by subsequent addition of CBN. The delayed-rectifier or erg-mediated K+ current was mildly inhibited by 10 µM CBN, while it also slightly inhibited the amplitude of hyperpolarization-activated cation current. In HL-1 atrial cardiomyocytes, CBN inhibited peak INa and raised the inactivation rate of the current; moreover, further application of 10 µM Tef attenuated CBN-mediated decrease in INa. Collectively, this study provides an important yet unidentified finding revealing that CBN modifies INa in electrically excitable cells.

Zero-dimensional numerical simulation of dry reforming of methane in atmospheric pressure non-equilibrium plasma

Recently, atmospheric non-equilibrium plasma has been proposed as a potential and novel type of “reaction carrier” for the activation and conversion of greenhouse gases (methane and carbon dioxide) into value-added chemicals, due to its unique non-equilibrium characteristics. In this paper, a zero-dimensional plasma chemical reaction kinetic model in CH<sub>4</sub>/CO<sub>2</sub> gas mixture is constructed, with an emphasis on reaction mechanism for plasma dry reforming of methane to syngas and oxygenates. Especially, the effect of the CH<sub>4</sub> molar fraction (5%–95%) on plasma dry reforming of methane is investigated. First, the time evolution of electron temperature and density with initial methane content is presented, and the results show that both the electron temperature and electron density vary periodically with the applied triangular power density pulse, and the higher initial methane content in gas mixture is favored for a larger electron temperature and density. Subsequently, the time evolution of number densities of free radicals, ions and molecules at different CH<sub>4</sub>/CO<sub>2</sub> molar fraction are given. The higher the initial methane content, the greater the number densities of H, H<sup>–</sup>, H<sub>2</sub>, and CH<sub>3</sub>, leading to insufficient oxygen atoms to participate in the reaction for oxygenates synthesis. The conversions of inlet gases, the selectivities of syngas and important oxygenates are also calculated. The conversion rate of carbon dioxide increases with the increasing methane content, but the conversion rate of methane is insensitive to the variation of methane content. As methane mole fraction is increased from 5% to 95%, the selectivities of important oxygenates (CH<sub>3</sub>OH and CH<sub>2</sub>O) are relatively low (<5%), and the selectivity of H<sub>2</sub> gradually increases from 13.0% to 24.6%, while the selectivity of CO significantly decreases from 58.9% to 9.7%. Moreover, the dominant reaction pathways governing production and destruction of H<sub>2</sub>, CO, CH<sub>2</sub>O and CH<sub>3</sub>OH are determined, and CH<sub>3</sub> and OH radicals are found to be the key intermediate for the production of valuable oxygenates. Finally, a schematic overview of the transformation relationship between dominant plasma species is summarized and shown to clearly reveal intrinsic reaction mechanism of dry reforming of methane in atmospheric non-equilibrium plasma.

Investigations into machining accuracy and quality in wire electrochemical micromachining under sinusoidal and triangular voltage pulse condition

• Application and optimization of novel pulsed voltage waveforms for improving the process accuracy in Wire-ECMM. • A mathematical analysis of the evolution of machining gap with time under the application of different voltage waveforms. • Finite element modelling for the visualization of current density distribution in the machining zone. • Evaluation of machining quality using three dimensional optical profilometer and SEM images of machined features. • Optimization of triangular pulsed voltage waveform by varying its rise and fall time for improving the process accuracy. Since the past two decades, improving machining accuracy, precision, and quality of machining in Wire-ECMM has been a prime focus of researchers across the globe. Application of high frequency pulse voltage for machining has served the purpose to a large extent. However, with high frequency pulse voltage, machining rate is compromised. Often, the use of very high frequency also necessitates the application of high voltage amplitude which consequently, leads to increased power consumption. To solve this problem, this research proposes the use of sinusoidal voltage waveform (SVW) and triangular voltage waveform (TVW) instead of a conventionally used rectangular voltage waveform (RVW) for machining. A mathematical analysis of the machining gap in the process using a mechanistic approach suggests that accuracy in terms of kerf width improves significantly when SVW and TVW are used for machining. Experiments are conducted to investigate the impact of pulse voltage waveform on different characteristic features of a kerf profile which are kerf width, edge fillet radius, corner radius, and taper angle. These waveforms are generated using a function generator with the help of a rectification cum amplification electronic circuit. Roughness of the surface machined using these three waveforms are also measured using optical profilometer. Experimental results suggest that the percent reduction in the kerf width for the three waveforms considered by changing the frequency of voltage pulse from 100 kHz to 200 kHz is significantly lower than that obtained by switching from RVW to TVW and keeping other pulse parameters such as frequency, amplitude, and duty ratio same. Using a wire (tool) made of tungsten and a diameter of 30 μm, minimum kerf width of 60 ± 2 μm, edge fillet radius of 11 ± 1 μm, and a negligible corner radius is obtained when TVW is used for machining. For the above stated parameters, profile roughness (R a ) & area surface roughness (S a ) of machined kerf are 1.43 μm and 1.55 μm respectively for RVW, which are reduced to 0.44 μm and 0.57 μm respectively, for TVW. To understand the reason behind the reduction of kerf width, corner radius, and edge fillet radius in case of TVW, as indicated by the experimental observations, numerical simulations are performed. For a comparative study, current density distribution pattern over the workpiece surface is plotted for the three waveforms. Later, TVW is further optimized by varying its ‘rise’ and ‘fall’ time. For this, a factor termed as Pulse Rise Factor (PRF) is defined and is varied in 5 steps. Experimental results suggest that kerf width is minimum 55.4 μm when PRF is zero and is maximum 71.8 μm when PRF is one. In the end, different micro features are machined using the optimal machining conditions.

An Efficient Asymmetric Direct Current (DC) Source Configured Switched Capacitor Multi-level Inverter

This paper is dealing about Switched Capacitor Multi-Level Inverter (SCMLI) circuit which is controlled by triangular multicarrier Sinewave Pulse Width Modulation (SPWM) technique. The proposed SCMLI is powered from asymmetric DC source configuration to obtain multi-level output voltage by applying switching pulse to the main circuit from control circuit for switching operation. Fourteen switches and four capacitors are employing to do the proposed inversion operation in an effective way. Switching capacitors can perform boost operation to enhance voltage from the source level to the required level. Input DC from the asymmetric sources is converted to AC voltage for the application of consumers. This proposed conversion system is applicable for mainly in industrial and renewable energy-based energy conversion system because it can carry high output voltages. This proposed method gives about more efficiency. Also reduces switching losses in lower value, low conduction losses and capacitor ripple losses. The simulation model is analyzed in MATLAB/SIMULINK platform and the same validated in hardware results. The developed SCMLI structure is witness over other topologies for the power inversion process in the multi-level.

Efficient generation of triangular optical pulses in an erbium-doped chalcogenide fiber amplifier by exploiting the time transformation technique.

The time transformation (TT) technique is used to study the nonlinear pulse reshaping towards triangular pulse (TP) generation by efficiently optimizing the pulse parameters in an erbium-doped chalcogenide fiber amplifier (EDCFA), for the first time, to the best of our knowledge. The effects of input chirp parameter, optical gain, and dipole relaxation time are also depicted in the context of TP generation. The results obtained from the TT approach when compared with that from the nonlinear Schrodinger equation show excellent agreement. The study also reveals that spectral pulse doubling can be achieved at a shorter length when a pre-chirped Gaussian pulse is propagated through the proposed EDCFA.

Transient dynamic response of doubly curved laminated composite shells under pulse loading

Transient response behavior of laminated doubly curved shells with varying geometry and boundary conditions subjected to various time-dependent pulse loads is investigated using Higher order Shear Deformation Theory (HSDT) in the present study. The ratio of thickness co-ordinate to radius of shell (z/R) is incorporated in the mathematical formulation based on HSDT. The condition of zero transverse shear stresses at free surfaces of laminated shell is also included in the displacement function. A C0 finite element formulation using eight noded isoparametric shell element with seven degrees of freedom per node is applied to evaluate the dynamic response of shells. Three types of pulse loading such as sine, triangular and rectangular pulses are considered for the present investigation. Newmark's β method is applied to solve the dynamic equilibrium equation of the shells. The accuracy of the present analysis is examined by comparing the results obtained with those available in the published literature. Several numerical examples are illustrated to show the effects of pulse loading and boundary condition on the central displacement and stresses of laminated composite shells.

Safety of Oil/Gas Offshore Platforms Designed According to European Provisions under the Action of Pulse-Like Ground Motions

Oil and gas offshore platforms are important civil constructions, which are loaded by various types of environmental actions such as wave loads and wind forces. These actions usually govern the platforms’ structural design, while seismic action appears to have minor influence. Nonetheless, numerous offshore structures have been founded in earthquake-prone regions where the structural design can be strongly affected by earthquake action. Many studies have investigated the seismic behaviour of oil and gas offshore platforms examining traditional seismic records. This study investigates the application of simple pulses, i.e., exponential, triangular, rectangular and sinusoidal pulse waveforms, as an earthquake excitation for offshore platforms. To the best of the authors’ knowledge, this is the first time that the aforementioned set of simplified ground motions have been applied to assess the nonlinear seismic behaviour of offshore oil/gas platform. It should be mentioned that pulses could make important information concerning the dynamic response available considering that many intense seismic events enclose actually an acceleration pulse, which can lead to a nonlinear structural response. It is worth noticing that a small number of works have examined the nonlinear response of the platform and most of the previous works assumed fixed boundary conditions ignoring the soil-structure interaction. On the contrary, this study investigates the structural response of 3-D platforms under the action of simplified pulses, considering also the soil-pile-platform interaction. It should be mentioned that the structural design of these special structures fulfils the Eurocode 8 standards. Finally, this work investigates the effect of angle of earthquake waves incidence.

Numerical Simulation of Sub-Terahertz Thermal Emission: RADYN Code

The temporal evolution of thermal bremsstrahlung in the sub-terahertz range is calculated for F-CHROMA models of the flare chromosphere and transition region ( https://www.fchroma.org ). These models are calculated based on the numerical solution of the system of equations of radiation hydrodynamics with the RADYN code, which describes the response of chromospheric plasma to the flux of accelerated electrons in the form of a triangular pulse. It is found that the positive slope of the spectrum in the frequency range of 93–400 GHz is formed during the entire burst. The sub-THz radiation peak can be both ahead and behind the maximum of the function of the injection of energetic electrons depending on the number and index of the spectrum of precipitating particles. In some cases, the time profile of the sub-THz radiation is quite complex and pulsating due to gas-dynamic phenomena in the chromosphere and transition region.

Effectiveness in Block by Dexmedetomidine of Hyperpolarization-Activated Cation Current, Independent of Its Agonistic Effect on α2-Adrenergic Receptors.

Dexmedetomidine (DEX), a highly selective agonist of α2-adrenergic receptors, has been tailored for sedation without risk of respiratory depression. Our hypothesis is that DEX produces any direct perturbations on ionic currents (e.g., hyperpolarization-activated cation current, Ih). In this study, addition of DEX to pituitary GH3 cells caused a time- and concentration-dependent reduction in the amplitude of Ih with an IC50 value of 1.21 μM and a KD value of 1.97 μM. A hyperpolarizing shift in the activation curve of Ih by 10 mV was observed in the presence of DEX. The voltage-dependent hysteresis of Ih elicited by long-lasting triangular ramp pulse was also dose-dependently reduced during its presence. In continued presence of DEX (1 μM), further addition of OXAL (10 μM) or replacement with high K+ could reverse DEX-mediated inhibition of Ih, while subsequent addition of yohimbine (10 μM) did not attenuate the inhibitory effect on Ih amplitude. The addition of 3 μM DEX mildly suppressed the amplitude of erg-mediated K+ current. Under current-clamp potential recordings, the exposure to DEX could diminish the firing frequency of spontaneous action potentials. In pheochromocytoma PC12 cells, DEX was effective at suppressing Ih together with a slowing in activation time course of the current. Taken together, findings from this study strongly suggest that during cell exposure to DEX used at clinically relevant concentrations, the DEX-mediated block of Ih appears to be direct and would particularly be one of the ionic mechanisms underlying reduced membrane excitability in the in vivo endocrine or neuroendocrine cells.

Seismic Design of Offshore Structures under Simplified Pulse-Like Earthquakes

Oil and gas offshore structures are essential infrastructures which are subjected to several categories of environmental loads such as wave and wind actions. These loads commonly designate the structural design of offshore platforms. Additionally, several offshore platforms are founded in earthquake-prone areas and the design of them is intensely affected by seismic ground motions. To be sure, various investigations have studied the earthquake response of offshore structures under the action of far-field seismic events. However, the inelastic behavior of platforms under the action of simple pulses has not been examined yet, where the latter loads can successfully simulate near-fault earthquakes. This work investigates, for the first time to our knowledge, the dynamic inelastic response of offshore platforms subjected to triangular, exponential, sinusoidal, and rectangular pulses. Thus, three-dimensional offshore structures are examined also considering the dynamic soil-pile-platform interaction effects, satisfying all the pertinent provisions of European Codes and taking into account geometric and material nonlinearities as well as the effects of the different angles of incidence of seismic waves on the overall/global response of offshore platforms.