Critical Power Level Research Articles

Ultrasonic irrigation flows in root canals: effects of ultrasound power and file insertion depth

Ultrasonic irrigation during root canal treatment can enhance biofilm disruption. The challenge is to improve the fluid flow so that the irrigant reaches areas inaccessible to hand instrumentation. The aim of this study is to experimentally investigate how the flow field and hydrodynamic forces induced by ultrasonic irrigation are influenced by the ultrasound power and file insertion depth. A root canal phantom was 3D printed and used as a mold for the fabrication of a PDMS channel. An ultrasonic instrument with a #15K-file provided the irrigation. The flow field was studied by means of Particle Image Velocimetry (PIV). The time averaged velocity and shear stress distributions were found to vary significantly with ultrasound power. Their maximum values increase sharply for low powers and up to a critical power level. At and above this setting, the flow pattern changes, from the high velocity and shear stress region confined in the vicinity of the tip, to one covering the whole root canal domain. Exceeding this threshold also induces a moderate increase in the maximum velocities and shear stresses. The insertion depth was found to have a smaller effect on the measured velocity and shear stresses. Due to the oscillating nature of the flow, instantaneous maximum velocities and shear stresses can reach much higher values than the mean, especially for high powers. Ultrasonic irrigation will benefit from using a higher power setting as this does produce greater shear stresses near the walls of the root canal leading to the potential for increased biofilm removal.

An optimization framework for RIS-based energy-efficient multi-cell NOMA systems

Non-orthogonal multiple access (NOMA) is a highly promising multiple access strategy for wideband communication systems due to its high spectral efficiency. However, in multi-cell multi-band systems, interference issues can arise from resource sharing among multiple users, which limits the potential of NOMA. To tackle these issues, in this paper, we study a NOMA system where reconfigurable intelligent surfaces (RIS) are employed across multiple cells with multiple users clusters. Specifically, we propose an optimization framework to maximize the system energy efficiency (EE) through jointly designing the transmission beamformer at each base station, the RIS phase shifts and the corresponding binary selection matrix indicating which elements of the RIS should be used to serve a specific cell. Our optimization framework takes into account the minimum rate requirements of users, the successive interference cancellation (SIC) decoding-based rate constraint, fairness among users as well as the maximum allowed transmission power. The resulting non-convex problem is solved by using an alternating optimization algorithm, wherein semidefinite programming (SDP), successive convex approximation (SCA), and penalty-based difference-of-convex (DC) programming are used to reach a solution. Simulation results show that the proposed system outperforms conventional orthogonal access in terms of EE performance, the achievable rate, and power consumption. Also, the results revealed the critical transmission power level for NOMA beyond which the EE starts decaying. Moreover, the proposed NOMA system shows a limited EE performance compared to the conventional orthogonal access as the number of clusters exceeds a certain limit.

Numerical characterization of heat transfer deterioration in supercritical natural circulation loop and role of loop inclination

Thermalhydraulics of any supercritical natural circulation loop (sNCL) is strongly influenced by the choice of operating conditions and geometric configurations, and can experience severe deterioration in heat transfer characteristics and circulation rate under certain situations. Present study focuses on systematic identification of a quantifiable criterion for prior identification of such deterioration in a carbon dioxide-driven rectangular loop, subjected to a wide range of operating conditions and also with particular emphasis on loop inclination. Four distinct regimes of operation have been identified, primarily based on the temperature levels in the adiabatic arms. Operation is desirable to be restricted within the enhanced heat transfer regime, which offers large heat transfer rate and moderate level of fluid temperature. Inclination to vertical lowers the driving potential, thereby reducing the flow rate and forcing an early induction into the deteriorated heat transfer regime. Highest circulation rate corresponds to the heater power capable of equating the average loop temperature to the pseudocritical value at that pressure. Strong thermal asymmetry and density stratification has been observed in the horizontal sections, with local recirculation and non-uniform radial velocity profiles. Buoyancy parameter has been identified as a capable dimensionless quantity to predict the appearance of deterioration a priori. It can also be coupled with the average friction factor to quantify the critical power level, and a correlation has been suggested for the same.

A low-complexity, energy-efficient data securing model for wireless sensor network based on linearly complex voice encryption mechanism of GSM technology

A wireless sensor network is the formation of a temporary network of sensor nodes equipped with limited resources working in an ad hoc environment. Routing protocol is one of the key challenges while designing a wireless sensor network, which requires optimum use of limited resources of a sensor node, such as power and so on. Similarly, data security and integrity is another open issue that has emerged as a flash point in research community in the last decade. This article proposes a secure model for routing data from source to destination named as secure and energy-efficient routing. The proposed secure and energy-efficient routing is inherited from authentication and voice encryption scheme developed for Global System for Mobile Communications. Necessary modifications have been carried out in order to fit the Global System for Mobile Communications technology in a wireless sensor network ad hoc environment. Due to its low complexity, the secure and energy-efficient routing consumes lesser battery power both during encryption/decryption and for routing purposes. It is due to the XoR operation used in the proposed scheme which is considered as the most inexpensive process with respect to time and space complexity. It is observed through simulations that secure and energy-efficient routing can work effectively even in critical power level in a sensor network. The article also presents a simulation-based comparative analysis of the proposed secure and energy-efficient routing with two notable existing secure routing protocols. We proved that the proposed secure and energy-efficient routing helps to achieve the desired performance under dynamically changing network conditions with various numbers of malicious nodes. Moreover, in Global System for Mobile Communications, generally three linear feedback shift registers are used to fragment the key in data encryption mechanism. In this article, a mathematical model is proposed to increase the number of possible combinations of shift register in order to make the data encryption mechanism more secure which has never been done before. Due to its liner complexity, lesser power consumption, and more dynamic route updating, the secure and energy-efficient routing can easily find its use in the emerging Internet-of-Things systems.

High-Throughput Triggered Merging of Surfactant-Stabilized Droplet Pairs Using Traveling Surface Acoustic Waves.

We present an acoustofluidic device for fluorescently triggered merging of surfactant-stabilized picoliter droplet pairs at high throughput. Droplets that exceed a preset fluorescence threshold level are selectively merged by a traveling surface acoustic wave (T-SAW) pulse. We characterize the operation of our device by analyzing the merging efficiency as a function of acoustic pulse position, duration, and acoustic pressure amplitude. We probe droplet merging at different droplet rates and find that efficient merging occurs above a critical acoustic power level. Our results indicate that the efficiency of acoustically induced merging of surfactant stabilized droplets is correlated with acoustic streaming velocity. Finally, we discuss how both time-averaged and instantaneous acoustic pressure fields can affect the integrity of surfactant layers. Our technique, by allowing the merging of up to 105 droplets per hour, shows great potential for integration into microfluidic systems for high-throughput and high-content screening applications.

Topical Problems Concerned with the Thermophysical Characteristics of New-Generation Light Water Reactors: Comprehensive Study Results

The article presents and analyses the results from first-priority thermophysical investigations aimed at assessing the characteristics and safety of water-cooled reactors, including enhancement of the nuclear fuel technical and economic characteristics, design solutions for passive safety features, and stable operation of the passive heat removal system (PHRS) air-cooled heat exchangers under extreme meteorological conditions. It is shown that the fuel assembly (FA) critical power level depends both on the type and number of spacer and mixing grids and on the burnout occurrence spot. The critical heat fluxes that occur when the coolant flowrate drops by 4% are higher in unsteady modes than they are in steady modes of operation at the same flow parameters. Information about the upgraded base of estimated experimental data on the critical heat fluxes in the new FA designs is given. The article also presents data on pressure variations in the main components of the RU-ZO experimental bench (containing the reactor plant and containment models) in the experiment modeling an accident involving reactor coolant pipeline (RCPL) rupture at the reactor inlet (scenario 1) and decrease of the steam generator (SG) model condensing power in the bench (scenario 2). It is found that the drop of SG condensing power is approximately 30% of its level at the onset of the SG condensing operation mode during accidents according to both the scenarios. However, the remaining condensing power level is sufficient for reliably cooling the VVER-1200 reactor core for no less than 24 h with joint operation of the second-stage hydro accumulators (HA-2) and PHRS. Experimental investigations of the external aerodynamic characteristics of the Novovoronezh-2 NPP (NVNPP-2) main building aimed at checking if proper operation of the PHRS is secured independently of the wind load have shown that extreme meteorological conditions, including hurricane winds and dust storms, may manifest themselves in a decreased capacity of part of the PHRS air-cooled heat exchangers. Studies carried out for assessing the design of a water-cooled nuclear power facility (NPF) for an electrical power capacity of 1700 MW operating at supercritical parameters and the experimental VVER-SKD-30 reactor with a thermal power capacity of 30 MW are mentioned. The problems that have to be solved in carrying out further thermophysical investigations of water-cooled reactors for supercritical parameters are listed.

Influence of laser doping on nanocrystalline ZnO thin films gas sensors

The effect of laser doping of Al on the gas sensing behavior of nanocrystalline ZnO thin films is reported. The doping of Al was carried out by the spin-coating of Al-precursors on nanocrystalline ZnO films followed by a pulsed laser irradiation. The laser-doped films were characterized as a function of laser power density by measuring the optical, structural, electrical, morphological and gas sensing properties of ZnO films. It was found that the laser doping process resulted in an increase of electrical conductivity of ZnO films. The performance of gas sensor was investigated for different concentrations of H2 and NH3 in the air. The results indicate that the laser doping process can be utilized to improve the sensor characteristics such as sensitivity and response time by optimization of laser power density. The optimum laser power is interpreted as the critical power level required to compete the effective doping versus developing the effective grain boundaries. Also, the selectivity of laser-doped ZnO sensors for H2 was studied for a likelihood practical gas mixture composed of H2, NH3 and CH4. It is found that these films can be optimized to develop H2 and NH3 sensors in PPM level with a higher selectivity over other reducing gases.

Dissipative rogue waves induced by soliton explosions in an ultrafast fiber laser.

We reported on the observation of dissipative rogue waves (DRWs) induced by soliton explosions in an ultrafast fiber laser. It was found that the soliton explosions could be obtained in the fiber laser at a critical pump power level. During the process of the soliton explosion, the high-amplitude waves that fulfill the rogue wave criteria could be detected. The appearance of the DRWs was identified by characterizing the intensity statistics of the time-stretched soliton profile based on the dispersive Fourier-transform method. Our findings provide the first experimental demonstration that the DRWs could be observed in the soliton explosion regime and further enhance the understanding of the physical mechanism of optical RW generation.

Broadening of Diffraction Peak Widths and Temperature Nonuniformity During Flash Experiments

Thermal expansion arising from Joule heating produces shifts in the diffraction peaks. The shifts are calibrated against the platinum standard to determine the specimen temperature during in ‐situ experiments at the Advanced Photon Source. Temperature gradients within the specimen cause the peaks to shift differently from different parts of the specimen. If the beam travels through the specimen the diffraction peak would broaden as a result of the nonuniform temperature. We report extensive measurements of peak widths in flash experiments over power dissipation levels that range from 300 to 2500 mW/mm3. Peak broadening occurs only above a critical power level. The broadening is transient, occurring only near the spike in power dissipation when the power supply is switched from voltage to current control (Stage II); it is estimated to arise from a nonuniformity of ~100°C within the specimen. The broadening subsides in the ensuing state of steady‐state flash under current control (Stage III).

The influence of marketing from a power perspective

PurposeBased on the widely held view that influence is exercised power, and in light of the suitability of power theory to studies of marketing's relative influence within the firm, this paper seeks to explore marketing's level of influence from a power perspective. The paper proposes and empirically tests a model in which the marketing function's four key types of power (bureaucratic power, critical contingencies power, network power, and psychological power) act as antecedents to marketing's influence within the firm. The model also aims to consider the contingency effect of market turbulence.Design/methodology/approachThe study employs data drawn from a sample of senior managers in medium and large manufacturing firms. The model is tested using hierarchical ordinary least squares regression analysis.FindingsThe findings provide support for a link between all types of power and marketing's influence, with the exception of psychological power. Market turbulence is also found to strengthen the positive link between marketing's critical contingencies power and marketing's level of influence.Practical implicationsThe study identifies and discusses power mechanisms that may be employed by marketing subunits to maintain or strengthen their influence within the firm.Originality/valueEmpirical evidence has shown that strong marketing functions are still needed, yet are slowly disappearing. This study approaches the question of how marketing departments can protect or regain their influence by adopting a power perspective. The findings suggest that marketing departments can tap into different types of power to further their influence. The study discusses the key theoretical and managerial implications and proposes some directions for future research.

Transparency powers levels in Yb 3+-doped fiber due to temperature changes

The critical power level provides an objective tool for the determination of the maximum power available in a fiber laser based on physical parameters such as core diameter, temperature, and absorption and emission cross section for both the pump and laser wavelengths. This work presents a theoretical study of critical power levels when Ytterbium-doped fibers are exposed to changes of temperatures. We found that critical power curves extend their wavelength dependence, ranging from 1 μm to 1.2-μm when fibers were heated up 300 K. However, critical power values were rather high compared to the values obtained at room temperature. Nevertheless, low critical powers were obtained at low temperatures as 77 K in a reduced interval of wavelengths, i.e., from 1-μm to 1.1-μm.

Time and frequency domain measurements of solitons in subwavelength silicon waveguides using a cross-correlation technique

We report time domain measurements of the group-velocity-dispersion-induced and nonlinearity-induced chirping of femtosecond pulses in subwavelength silicon-on-insulator waveguides. We observe that at a critical input power level, these two effects compensate each other leading to soliton formation. Formation of the fundamental optical soliton is observed at a peak power of a few Watts inside the waveguide. Interferometric cross-correlation traces reveal compression of the soliton pulses, while spectral measurements show pronounced dispersive waves emitted by solitons into the wavelength range of normal group velocity dispersion.

Thermal Degradation of Electroplated Nickel Thermal Microactuators

In this paper, the thermal degradation of laterally operating thermal actuators made from electroplated nickel has been studied. The actuators investigated delivered a maximum displacement of ca. 20 mum at an average temperature of ~ 450degC , which is much lower than that of typical silicon-based microactuators. However, the magnitude of the displacement strongly depended on the frequency and voltage amplitude of the pulse signal applied. Back bending was observed at maximum temperatures as low as 240degC. Both forward and backward displacements increase as the applied power was increased up to a value of 60 mW; further increases led to reductions in the magnitudes of both displacements. Scanning electron microscopy clearly showed that the nickel beams began to deform and change their shape at this critical power level. Compressive stress is responsible for nickel pileup, while tensile stresses, generated upon removing the current, are responsible for necking at the hottest section of the hot arm of the device. Energy dispersive X-ray diffraction analysis also revealed the severe oxidation of Ni structure induced by Joule heating. The combination of plastic deformation and oxidation was responsible for the observed thermal degradation. Results indicate that nickel thermal microactuators should be operated below 200degC to avoid thermal degradation.

High stability of atmospheric pressure plasmas containing carbon tetrafluoride and sulfur hexafluoride

The properties of electronegative discharges operating at atmospheric pressure have been investigated. The plasma source consisted of two parallel metal electrodes into which helium was fed with 0.5–8.0 Torr carbon tetrafluoride or sulfur hexafluoride. It was found that the ionization mechanism changed from the α- to the γ-mode at a critical RF power level. In pure helium, this resulted in an abrupt drop in the voltage with increasing current, whereas for the fluorine-containing plasmas, a smooth, continuous transition was observed along the I–V curve. The electron densities in the plasmas fed with 4.0 Torr CF4 and SF6 were calculated to be 7.0± 2.0 × 1011 cm−3, or about 30 times lower than that estimated for the pure helium case. Free electrons were consumed by electron attachment to the gas molecules, which boosted the density of negative ions to ∼1013 cm−3. Compared with pure He, the lower electron density in the fluorine-containing plasmas removed the ionization instabilities encountered in the γ -mode and made it possible to sustain these discharges over substantially larger areas.

The microwave heating of three-dimensional blocks: semi-analytical solutions

The microwave heating of three-dimensional blocks, by the transverse magnetic waveguide mode TM 11 , is considered in a long rectangular waveguide. The governing equations are the forced heat equation and a steady-state version of Maxwell's equations, while the boundary conditions take into account both convective and radiative heat loss. Semi-analytical solutions, valid for small thermal absorptivity, are found using the Galerkin method. The electrical conductivity and the thermal absorptivity are assumed to be temperature dependent, while both the electrical permittivity and magnetic permeability are taken to be constant. Both a quadratic relation and an Arrhenius-type law are used for the temperature dependency. As the Arrhenius-type law is not amenable analytically, it is approximated by a rational-cubic function. A multivalued steady-state temperature versus power relationship is found to be possible for both types of temperature dependency. At the critical power level thermal runaway occurs when the temperature jumps from the lower (cool) temperature branch to the upper (hot) temperature branch of the solution. The semi-analytical solutions are compared with numerical solutions of the governing equations for various special cases such as the limits of small and large heat loss at the edges of the block. An excellent comparison is obtained between the semi-analytical and numerical solutions, on both temperature branches for the Arrhenius-type law. For the quadratic temperature dependency the comparison is excellent on the low branch but the semi-analytical theory significantly underpredicts the temperature on the upper solution branch.

On the heating of a two-dimensional slab in a microwave cavity: aperture effects

AbstractThe steady-state heating of a two-dimensional slab by the TE10 mode in a microwave cavity is considered. The cavity contains an iris with a variable aperture and is closed by a short. Resonance can occur in the cavity, which is dependent on the short position, the aperture width and the temperature of the heated slab.The governing equations for the slab are steady-state versions of the forced heat equation and Maxwell's equations while fixed-temperature boundary conditions are used. An Arrhenius temperature dependency is assumed for both the electrical conductivity and the thermal absorptivity. Semi-analytical solutions, valid for small thermal absorptivity, are found for the steady-state temperature and the electric-field amplitude in the slab using the Galerkin method.With no-iris (a semi-infinite waveguide) the usual S-shaped power versus temperature curve occurs. As the aperture width is varied however, the critical power level at which thermal runaway occurs and the temperature response on the upper branch of the S-shaped curve are both changed. This is due to the interaction between the radiation, the cavity and the heated slab. An example is presented to illustrate these aperture effects. Also, it is shown that an optimal aperture setting and short position exists which minimises the input power needed to obtain a given temperature.

Observations on changes in ultrasonically treated waste-activated sludge

This work experimentally elucidates the effects of ultrasonic treatment on the physical, chemical, and biological characteristics of a waste-activated sludge. A critical ultrasonic power level exists above which, accompanied with the release of divalent cations from the sludge body, the floc structure effectively disintegrated, microbial level acceptably disinfected, and particulate organic compounds sufficiently transformed into soluble state. Both ultrasonic vibration and bulk temperature rise contribute to the treatment efficiency. Possible mechanisms of ultrasonic treatment are discussed.

Microwave characterization of HgBa 2CaCu 2O 6+δ thin films

We assessed the potential of Hg-based high-T c superconducting thin films for microwave applications by measuring its microwave surface resistance R s and microwave power handling capability. HgBa 2CaCu 2O 6+δ (Hg-1212) epitaxial thin films were fabricated using cation-exchange. They are c-axis oriented with thickness of about 0.3 μm. Their T c s are typically ∼ 120 K. On un-patterned films, we obtained an R s of 0.3 mΩ at 10 GHz and 100 K using Nb cavity perturbation technique. For power handling measurements, we fabricated Hg-1212 microstrip structure and determined the maximum power it could handle at 1 GHz. At 100 K, output power was very stable up to 19 dBm (critical operating power level) and above that level, non-linearity between input and output power was observed. When temperature was increased to 112 K, critical power level dropped to 16 dBm. These microwave properties suggest that Hg-1212 films are very promising for microwave device applications above 100 K.

Intermodulation measurements in Nb superconducting microstrip resonators

The issue of intermodulation distortion in superconducting devices for rf and microwave applications is discussed. The classical frequency conversion theory for nonlinear two-port devices in the small signal limit is shown to apply to microstrip resonators regardless of their geometry and material. Two tone, third order intermodulation measurements allow more sensitive detection of nonlinearity compared to surface impedance measurements, provided a low noise, spurious free experimental setup is adopted. Measurements carried out on high quality Nb meanderline microstrip resonators show that at very low power level nonlinearity is dominated by intrinsic device properties. Film defects start to play a predominant role above a critical power level that strongly depends on the defect’s nature.

Stationary states of a low-pressure inductively coupled RF discharge near the quenching threshold

A refined self-consistent volume-averaged model of a low-pressure inductively coupled RF discharge is proposed. It is demonstrated that taking into account finite dimensions of the near-electrode space-charge region leads to a double-valued dependence of the equilibrium electron temperature on the discharge pressure and power. There is a critical power level, dependent on the pressure and working chamber geometry, below which no stationary inductively coupled discharge can exist in the system. The theoretical results show good agreement with experiment.