Low Power Conditions Research Articles

Plasma-Assisted Combustor Dynamics Control at Realistic Gas Turbine Conditions

ABSTRACT This study investigated the effectiveness of implementing a plasma discharge to improve combustor dynamics and flame stability. Specifically, a nano-second pulsed plasma discharge (NSPD) was applied to a premixed gaseous fuel/air dump combustor for mitigation of dynamic combustion instabilities with a minimal NOX penalty. As a result, a significant reduction of pressure fluctuation level (2X to 4X) was observed at realistic low-power conditions of aero-engine combustors. The plasma power required for the reduction increased with increasing combustor inlet velocity and pressure. The change of fuel from methane to propane required significantly (2X) higher plasma power to achieve a similar noise reduction. The lean blowout limit was significantly extended due to the plasma; however, substantial incomplete combustion occurred in the extended regime. The incremental NOX production in the presence of the plasma was low (~ < 1EINOX); however, it increased with decreasing velocity and pressure, and increasing temperature.

A Si/SiC Hybrid Five-Level Active NPC Inverter With Improved Modulation Scheme

Compared with full-silicon-carbide (SiC) mosfet converters, the hybrid utilization of Si/SiC converters is an alternative approach to achieve the tradeoff between performance and cost. In this article, a 2-SiC hybrid five-level active neutral-point-clamped (5L-ANPC) full-bridge inverter is proposed. The proposed inverter is constructed by combining a 2-SiC hybrid 3L-ANPC half-bridge inverter and a two-level half-bridge arm. The operation principle of the proposed inverter by using the conventional modulation scheme is analyzed in detail. Furthermore, a dedicated modulation scheme is proposed to lower the conduction losses. The calculated power losses of the 2-SiC hybrid 5L-ANPC full-bridge inverter with the conventional modulation scheme and the proposed modulation scheme are addressed and compared. The proposed modulation scheme exhibits higher efficiencies under high-power conditions. But the conventional modulation scheme shows efficiency superiority under low-power conditions. Therefore, a hybrid modulation scheme is also proposed to achieve an overall high efficiency performance. A 4-kW prototype is built to evaluate the proposed topology and its modulation scheme at conversion efficiency. Experimental results and analysis show that comparing to the conventional modulation scheme, the hybrid modulation scheme can reduce power loss without increasing the hardware cost.

Low-damaged p-type doping of MoS2 using direct nitrogen plasma modulated by toroidal-magnetic-field

Low damaged doping of two-dimensional (2D) materials proves to be a significant obstacle in realizing fundamental devices such as p–n junction diodes and transistors due to its atom layer thickness. In this work, the defect formation energy and p-type conduction behavior of nitrogen plasma doping are investigated by first principle calculation. Low damaged substitutional p-type doping in MoS2 using low energy nitrogen plasma composed of N+ and N2+ is achieved by a novel toroidal magnetic field (TMF). The TMF helps to raise the concentration of N2+ ions at low RF power condition. The electrical characteristics of double-layer MoS2 field-effect transistors (FETs) clearly show an efficient p-type doping behavior. Atomic force microscope is applied to verify the slight damage in MoS2. X-ray photoelectron spectroscopy, photoluminescence and Raman spectroscopy confirm the effective p-type doping characteristic with weak damage. These findings provide a low damage technology for efficient carrier modulation of MoS2 and other homogeneous TMDC materials, which overcomes barriers in developing 2D electronic and optoelectronic devices.

Positive self-perception and corticospinal excitability: Recalling positive behavior expands peripersonal space boundaries

Converging evidence suggests that peripersonal space has dynamic properties, that can be influenced by motor and cognitive factors. Here, we investigated whether changes in self-perception may impact upon peripersonal representation. Specifically, employing non-invasive brain stimulation, we tested whether corticospinal excitability elicited by objects placed in the vertical peripersonal vs extrapersonal space can be influenced by changes in self-perception after recalling a personal experience inducing the feeling of high power (vs. positivity vs. low power).In a preliminary study (Study 1, N = 39) participants were presented with an object, whose position was manipulated in the horizontal vs vertical space. We assessed corticospinal excitability by measuring Motor Evoked Potentials (MEPs) using Transcranial Magnetic Stimulation with Electromyography co-registration (TMS-EMG). In the horizontal condition, we replicated the well-known motor facilitation induced by objects falling in the peri vs extrapersonal space, while in the vertical dimension MEPs were higher in the extrapersonal space.In the main experiment (Study 2), participants (N = 55) were randomly assigned to feel high power, low power, or a general positive emotion and were asked to observe the same object positioned either in the peripersonal or in the extrapersonal vertical space. Results showed that in the low power condition MEPs were higher in the extrapersonal vs peripersonal, as in Study 1, while in high power and positive conditions MEPs were not influenced by distance.Taken together, our findings suggest a dissociable pattern of motor facilitation underlying vertical vs horizontal space perception and, crucially, that changes in self-perception can influence such a representation.

Low Noise Amplifier Design for IoT Wireless Communication Systems

In the era of Internet of Things (IoT), the Internet has evolved from a simple Internet function of web information access to intelligent functions of identification, position, monitoring, and management of things. Devices in the IoT must transmit data between the devices and equipment connecting to cloud. As a fog computing architecture is established proximally at the local ends of the IoT, the data transmission volume and transmission delay can be effectively reduced. IoT wireless communication is one of the essential items for complete data transmission between the devices and on-line equipment. This paper proposes the low noise amplifier (LNA) design that can be applied to the RF front-end receiver of a 2.45-GHz wireless communication system for IoT applications. The LNA is required to have characteristics of low noise factor and high signal gain in order to amplify weak signals received by the antenna. In this study, the design of 2.45-GHz LNA adopts an architecture of power-constrained simultaneous noise and input matching on the basis of the 0.18-μm CMOS process technology in order to achieve simultaneous noise and input matching at low power conditions. Both the architectures of push-pull and forward substrate bias are also utilized. The LNA demonstrates the characteristics of low noise factor, high gain, and good 1-dB gain compression. The LNA shows good potential for IoT wireless communication system applications.

Influence of processing parameters on internal porosity and types of defects formed in Ti6Al4V lattice structure fabricated by selective laser melting

Ti6Al4V lattice structures were fabricated using selective laser melting with a wide range of processing parameters, namely laser power and scan speed, in order to study their effect on strut diameter and internal porosity morphology. Hence, identifying the optimum processing condition. Scanning electron microscopy (SEM) and optical microscopy (OM) were used to investigate the influence of these parameters on the strut size and internal porosity within the struts. The results show that at low laser power conditions the strut size decreased with increasing the scan speed. At intermediate laser power (200 W) the strut size decreased until it reached 2400 mm/s, beyond which no pattern was observed. Fluctuations in strut size values were found at different scan speeds using high laser power (250 W, 300 W). The micrographs of the sectioned lattice structures showed various morphologies of the internal porosity, from which a process map was developed to pinpoint the various types of defects at the different processing conditions. Five zones were formed which are: gas porosity, keyholing, irregular defects, balling, and lack of fusion defects. SLM processing condition of 100 W–1600 mm/s was selected to be the best condition from the studied samples for producing the lattice structure with strut size closest to the design and with minimum internal porosity. Mechanical and microstructural analysis were performed for this condition.

Surface quality and kerf width prediction in abrasive water jet machining of metal-composite stacks

Machinability of stacked Titanium (Ti6Al4V) and CFRP was evaluated using Abrasive Water Jet (AWJ) machining process. The experimental study was conducted using three pressure levels – 200, 275 and 350 MPa. Traverse speed was varied between 1 and 10 mm/s for two stacking configurations (Ti/CFRP, and CFRP/Ti). The erosion characteristics, kerf width and surface roughness was studied as a function of process parameters. Surface roughness and kerf width variation was high at low jet power conditions, as described by lumped parameters (E˙/u and E˙/hu). The minimum average roughness Ra for Ti and CFRP was less than 3.5 μm and 4.5 μm respectively for both the stacking sequence. The kerf width increased significantly, especially when Ti6Al4V is at top in which case low-energy, turbulent jet diverges at the exit from Ti6Al4V. Mathematical regression models were developed to predict kerf width. An energy based, semi-analytical model was proposed to predict the kerf geometry with R2=92.26%.

Ultra-low-power sub-photon-voltage high-efficiency light-emitting diodes

Conventional light-emitting diodes (LEDs) face an efficiency droop at low current due to non-radiative recombination overtaking radiative recombination at low carrier density. To overcome this universal problem, we develop LEDs with high efficiency at ultralow current and voltage, using a novel quantum well design and high-quality interfaces to suppress non-radiative recombination and enhance radiative recombination. The device exhibits close to unity internal quantum efficiency at a low current density of <1 × 10−4 A cm−2, more than three orders of magnitude lower than conventional LEDs. The LED bias voltage is reduced to ~30% below the photon voltage (hν/q). Wireless communication is demonstrated at these low-power conditions, which enables new applications in smart dust and sensor networks 1–6 , low-cost block chain and authentication 7–9 , medical applications 10,11 and wherever high efficiency at low power is needed. New phenomena such as high-efficiency electroluminescent cooling becomes possible as the LED unity internal quantum efficiency extends to smaller voltage and current. By using a single-quantum-well active region with a unique well–cladding design to suppress non-radiative recombination and enhance radiative recombination, light-emitting diodes with close to unity internal quantum efficiency at a low current density of <10−4 A cm−2 are demonstrated.

Induced Social Power Improves Visual Working Memory.

The possibility that social power improves working memory relative to conditions of powerlessness has been invoked to explain why manipulations of power improve performance in many cognitive tasks. Yet, whether power facilitates working memory performance has never been tested directly. In three studies, we induced high or low sense of power using the episodic recall task and tested participants' visual working memory capacity. We found that working memory capacity estimates were higher in the high-power than in the low-power condition in the standard change-detection task (Study 1), in a variation of the task that introduced distractors alongside the targets (Study 2), and in a variation that used real-world objects (Study 3). Studies 2 and 3 also tested whether high power improved working memory relative to low power by enhancing filtering efficiency, but did not find support for this hypothesis. We discuss implications for theories of both power and working memory.

Thermal performance enhancement of an oscillating heat pipe with external expansion structure for thermal energy recovery and storage

In this paper, an oscillating heat pipe (OHP) with external expansion structure and compact layout for thermal energy recovery and storage was designed and fabricated. The thermal performance of the OHP with different filling ratios (FRs) of self-rewetting fluid under continuous heating mode was tested at first. Then pulsing heating mode and alternate heating mode were explored to enhance the heat transport performance. The temperature fluctuation characteristic and the thermal resistance under different heating modes and heating periods were compared and analyzed. The result showed that the OHP can function well and sustain large heating power under appropriate range of FR. The pulsing mode and alternate mode are both helpful to increase the fluctuation frequency and amplitude of evaporator temperature. For the condition of relative low heating power and short heating period, the enhancement effect is more obvious. The thermal resistance at 100 W can be reduced by more than 10% when the heating period varies from 2 s to 10 s. Under short heating period of 0.4 s, the thermal resistance of the OHP under pulsing heating mode at 200 W can be even reduced by over 30%.

Investigating the ablation depth and surface roughness of laser-induced nano-ablation of CVD diamond material

The CVD diamond material with high wear resistant has been frequently used as the material of micro mills. The laser-based pre-treatment of CVD diamond has been identified as a favorable technique for subsequent precision machining in terms of efficiency and surface quality. This study is aimed to investigate the effect of CVD diamond material on the ablation depth and surface roughness (Sa and Sz) in laser-based machining, so as to improve the overall machined surface quality. Controlling ablation depth and high surface finish are the key indicator for the follow-up accurate treatment. In addition, the energy density distribution (EDD) model was established to better explain the microstructural changes in CVD diamond material after performing the laser machining. Through EDD model, the variation in ablation depth and surface roughness were evaluated at different laser parametric levels. The results showed that the ablation depth and surface roughness of EDD model are basically consistent with the experimental values. Moreover, at the same total energy density, the ablation depth and surface roughness Sa and Sz values are lower under the condition of low average laser power, large filling pitch and small laser scanning speed. In a nutshell, minimum surface roughness and a controlled ablation depth are achieved on CVD diamond by adjusting laser parameters.

Dipole saturated absorption modeling in frequency modulation spectroscopy: Dealing with a Gaussian beam, resonance narrowing

Quantitative, nonlinear sub-Doppler sensitive spectroscopy requires reliable formalism for optimizing the detection of weak molecular absorption patterns. Phase modulation spectroscopy (FMS) is a common technique used to challenge the ultimate photon-shot-noise limit. In addition, nonlinear spectroscopy can exhibit surprising effects like resonance narrowing, i.e., resonance width below the transit-time rate, like it has been pointed out in the seventies. Here, by extending our previous work, we propose an analytical development associated with numerical integration to simulate the equivalent Lamb-dip under Gaussian beam conditions. Simulations of nonlinear profiles of two transitions belonging to the polyad ΔP11 of acetylene are discussed, and analyzed by fitting with standard functions. The respective roles of the transit-time, of the collision rate, and of the Rabi frequency (including the power broadening) are carefully discussed and reviewed. It shows “super-narrowing” effects under specific low pressure and low power conditions. A reviewing introduction states previous experimental reports as well about previous modeling.

Application of two alternative shutdown severe accident management guideline (SSAMG) entry conditions for CPR1000

Abstract Recently, with the development and application of full-scope level 2 probabilistic safety assessment (PSA) method around the world, severe accident phenomena during shutdown and low power conditions have aroused extensive attention in nuclear industry. And the shutdown severe accident management guideline (SSAMG) is claimed to be developed, and the verification of the traditional and alternative entry conditions is the first consideration in this procedure. Thus in this paper, the feasibility of the hot leg pipe temperature and the modified jakob number are analyzed based on a SBO sequence firstly. Subsequently, verification work is conducted under a SBO sequence with pressurizer manhole open and a SBO sequence along with SBLOCA. The results proved the excellent effectiveness of the two parameters to be used as alternative SSAMG entry conditions. Also, a relational figure is constructed based on the results of diverse sequences with various primary system pressure to provide visualized guidance for operators. What's more, the value of modified jakob number which indicates the SSAMG entry is thought to be in the range of 0.5–1.

Fundamental plasma diagnostic study for guiding TIG arc phenomenon by laser beam irradiation

ABSTRACT Laser-arc hybrid welding is divided into laser-based and arc-based welding. In the arc-based welding, the laser beam irradiation provides the guiding effect to the arc plasma. Some studies have reported that an unstable arc plasma becomes stable due to this guiding effect. This is considered as the influence of metal vapour generation by laser beam irradiation; however, there are few reports on the measurement of metal vapour and arc plasma state during the guiding process. Therefore, the mechanism has been still not fully understood. In this study, the fundamental study of the guiding arc phenomenon was conducted in TIG arc welding (60 A) with laser beam irradiation (170 W) under relatively low-power condition. When the base metal was stainless steel, the guiding arc by the laser beam irradiation was observed which did not happen with mild steel. Spectroscopic measurement for the guiding arc phenomenon in stainless steel showed that the metal vapour was composed of manganese and chromium, and was widely distributed near the irradiation point, but not concentrated. We also observed a reduction of plasma temperature, thought to be caused by distributed metal vapour and the resultant reduction of the current density.

Design and Implementation of Low Power High-Efficient Transceiver for Body Channel Communications.

Body channel communications (BCC) have been researched while an allowing technology to improve necessities for the low power and high reconfiguration power in wireless telemetry systems used at wireless communication purpose. Conventional features on BCC are concentrated mostly on modeling of channels by using of an efficient measurement technique, wireless transceiver design and then by means of a transmission technique. Particularly, the wireless digital transmitting, developed as a personalized method intended for the body channel, offers wanted to develop flexible and low power BCC systems. With the developing level of wearable communication protocol and applications, there may be an increasingly reliable on an adaptable BCC transmitter that helps both data reconfigure power and power reduction condition. In this paper, an extremely reconfigurable Hamming Encoding Digital Transmitter (HEDT) which works with both reconfigurable data and power reduction condition that supports from two innovative operation conditions is suggested. In a HEDT device, the overall data rate is controlled by the level of Hamming codes designed to make use of in the perfect BCC band of 20-100MHz. The proposed Hamming Encoded Transmission method achieves seven times improved data rate when compared with conventional BCC processors. The next unique implementation technique is based on the usage of Frequency Shift Keying (FSK) of a Hamming encoded HEDT approach. This approach permits the BCC transceiver to use the perfect channel with bandwidth among 40-100MHz. Thereby half the clock rate reduces 40% of overall power utilization. The HEDT system is completely designed in a 65nm CMOS procedure. It uses a primary area of 0.14 × 0.2mm. When functioning below a data-rate of 60Mb/s (low power) condition, the BCC transmitter utilizes only 1.00mW.

Analysis of IPWR neutronic-thermohydraulic operation characteristics under low power condition

In nuclear industry, using coupling of different best estimate 3-D neutron kinetic (N-K) and thermal hydraulic (T-H) codes to analyze neutronic-thermohydraulic features of reactor core is one of the most concerned research areas, which could help improve simulation fidelity and optimize nuclear design. In this paper, to further understand low power operation features of Integral PWR-200 (IP200), the coupled code combining RELAP5 and 3-D two-group neutron diffusion code had been developed. This paper reported the detailed processing of synchronizing different time steps explicitly and spatial mapping between T-H and N-K codes. To verify and validate the coupled code, the benchmark test results showed good agreement with the existing Qinshan nuclear power plant (NPP) operation data. IP200′s entire system and reactor core were modeled using the coupled code. The simulation tasks gave descriptions of different scenarios of operation strategies, including rated power, natural circulation (NC) and once-through steam generators’ (OTSGs) group operation under low power conditions. For forced circulation (FC) operation, reactor power, coolant flow and temperature features were mainly influenced by fuel assembly enrichment, control rods configuration and pumps’ thrust. Under 25%FP low power operation, NC showed different coupled effects with that of FC, whose above core features were mainly influenced by loss of pumps’ driven force. Besides, 25%FP OTSGs group operation transient conquered secondary-side flow instability, but also characterized by a strongly asymmetric behavior of the primary system which was caused by non-uniform coolant temperature distribution at the core inlet. The coupled code improved simulation precision of different low power operation strategies under the premise that it could fully generalize characteristics and performance of the whole system. Furthermore, the obtained knowledge of coupled code provided a better understanding of integral pressurized water reactor (IPWR) operation features with strong neutronic-thermohydraulic coupling effects, which would be beneficial to improve coupling other codes in future work.

Design and Measurement of 3D Flexible Antenna Diversity for Ambient RF Energy Scavenging in Indoor Scenarios

Ambient radiofrequency (RF) energy scavenging has been recently addressed with a wide range of studies to provide alternative powering for low-power applications. However, due to the low power level of the ambient electromagnetic field, the efficiency of the latter systems is still below expectations. Multipath in the environment may be considered and antenna diversity is then a solution for quasi-omnidirectional RF reception to reach a higher probability of receiving energy in a realistic situation. A 3D flexible antenna diversity, which can be integrated into the rectangular packaging, is proposed in order to take advantage of system packaging form. The angle and polarization diversity antenna was designed on flexible substrate in order to achieve the flexibility and low-cost. This design overcomes the low performance of the substrate while maintaining a compact, high isolation, and good radiation efficiency of the antenna. An indoor experimental setup was carried out to compare different rectenna configurations. The measurement results validate the principle and demonstrate the performance of the 3D flexible diversity system. The probability measurements were carried out under precise conditions in indoor scenarios and the results in comparison with statistic models confirmed the performance of the system in such low power conditions.

A dual-stage low-power converter driving for piezoelectric actuator applied in micro robot

In this article, a dual-stage converter driving for a piezoelectric actuator based on flyback circuit was designed and implemented, which could be applied in a micro robot. A low-voltage direct current could be converted to a high-voltage alternating current through flyback circuit and direct current/alternating current circuit in low-power condition. In the direct current/direct current stage, the charging and discharging process was realized to generate a high voltage bias from a low voltage directly supplied by battery. Then, the high voltage was converted into alternating waveform by an energy recovery circuit in direct current/alternating current stage. Experiments were conducted to verify the ability of the proposed converter to drive a 100-V-input piezoelectric bimorph actuator using a prototype 108 mg (excluding printed circuit board mass), 169 (13 × 13) mm2, and 500-mW converter. According to the experimental results, this converter could be used for driving piezoelectric actuator applied in micro robot.

Cooperative Spectrum Sharing on SWIPT-Based DF Relay: An Energy-Aware Retransmission Approach

In this paper, cooperative cognitive radio networks are considered, in which a primary user (PU) and an off-the-grid secondary user (SU) co-exist by exploiting simultaneous wireless information and power transfer. Based on a two-phase relaying model, adaptive power splitting is performed at the SU for information decoding while collecting the energy remaining in the first phase. The energy harvested is then used to forward the decoded primary signal, with the secondary signal superimposed in the second phase. To enhance the utilization of both the spectrum and energy, an energy-aware retransmission approach is proposed for enabling successful decoding at the SU while collecting a reasonable amount of energy for relaying. The outage probability and throughput are theoretically analyzed for both the PU and the SU. To provide more analytical insights, tight performance upper and lower bounds are obtained in closed forms. Our results demonstrate that a mutually beneficial relationship can be built between the PU and the SU under proper parameter configurations. Furthermore, a performance tradeoff with respect to the number of retransmissions is demonstrated, where additional performance gains can be achieved by the proposed retransmission approach under unfavorable conditions of high rate, low power, and weak channels.

Highly Sensitive Charge Sensor Based on Atom-Assisted High-Order Sideband Generation in a Hybrid Optomechanical System.

Realizing highly sensitive charge sensors is of fundamental importance in physics, and may find applications in metrology, electronic tunnel imaging, and engineering technology. With the development of nanophotonics, cavity optomechanics with Coulomb interaction provides a powerful platform to explore new options for the precision measurement of charges. In this work, a method of realizing a highly sensitive charge sensor based on atom-assisted high-order sideband generation in a hybrid optomechanical system is proposed. The advantage of this scheme is that the sideband cutoff order and the charge number satisfy a monotonically increasing relationship, which is more sensitive than the atom-free case discussed previously. Calculations show that the sensitivity of the charge sensor in our scheme is improved by about 25 times. In particular, our proposed charge sensor can operate in low power conditions and extremely weak charge measurement environments. Furthermore, phase-dependent effects between the sideband generation and Coulomb interaction are also discussed in detail. Beyond their fundamental scientific significance, our work is an important step toward measuring individual charge.