The final velocity was put forward to study the water flow characteristics inside the building drainage system; however, it is more suitable for low-rise and multi-storey buildings, not for high-rise ...buildings. This study revealed the drainage transient characteristics of a double stack drainage system in high-rise residential buildings. Based on the final velocity, the air-water interaction mechanism and two-phase flow conditions in high-rise residential drainage stacks were discussed. An influence model of drainage system flow rate on pressure fluctuation under the change of state parameters such as ventilation rate, pipe wall roughness and building height was established. The pressure limit and flow rate data were obtained through full-scale experiments. The pressure limit and flow rate model were simplified to P
= A ċ Q
+ B ċ Q
+ C. After the data were verified, the fitting coefficients A, B and C were linear to the floor height.
The major topology for wireless power transfer is resonant converters, which use fundamental harmonic approximation as a general analysis method. The accuracy of fundamental harmonic approximation ...(FHA) is unsatisfactory in some wireless power transfer applications, as the current has distortions due to the non-linear diode-bridge rectifier. Some frequency-domain models also consider harmonics beside fundamental component and indeed have a higher resolution. However, due to the difficulty of modeling the non-linear rectifier, most models are oversimplified by assuming a voltage source on the output to eliminate the rectifier. Moreover, the value of the voltage source is often treated as a fixed given number, which is not true for a resistive load. To cover a general case, this paper proposes a frequency-domain analytical model for resonant converters in continuous current mode (CCM) with the capability of considering any load and source situations in kHz frequency range. In terms of computation complexity, the proposed model only involves matrix operation (first-order). A simple algorithm has been chosen to demonstrate the fast convergency and high accuracy of the proposed model. The main findings are verified by the comparison between the theoretical calculation, time-domain simulation and experimental results, where the estimation of output power has 10% improvement than the FHA method.
•Fundamental harmonic approximation is inaccurate in wireless power transfer.•Resonant converter models are limited on nonlinear diode-bridge rectifier.•An analytical model is developed for resonant converter in continuous conduction mode.•The analytical model has only one variable for fast computation of steady state.
Since functionally graded WC-Co (FG WC-Co) offers superior combinations of wear resistance, fracture toughness, and strength, and provides superior engineering performance over conventional ...homogeneous WC-Co, many processes have been developed to produce FG WC-Co, a few of which are commercialized today. However, with respect to the underlying principles on how the graded structures form in WC-Co, there are considerable gaps in understandings. Based on the most recent studies, the present authors examined the processes for making FG WC-Co and found that in most cases the formation of graded structure in WC-Co is achieved through liquid phase migration which can be induced by different techniques. Several representative FG WC-Co processes are reviewed and explained using the theory of liquid phase migration. A new process that induces liquid migration by carburizing fully sintered WC-Co is described.
► The phenomena and principle of liquid phase migration is described. ► Major parameters affecting liquid phase migration in WC-Co are summarized. ► Formation of cobalt gradient in WC-Co is found due to liquid phase migration. ► A novel carburizing process can economically produce graded WC-Co.
Topological Kondo insulators have been proposed as a new class of topological insulators in which non-trivial surface states reside in the bulk Kondo band gap at low temperature due to strong ...spin-orbit coupling. In contrast to other three-dimensional topological insulators, a topological Kondo insulator is truly bulk insulating. Furthermore, strong electron correlations are present in the system, which may interact with the novel topological phase. By applying spin- and angle-resolved photoemission spectroscopy, here we show that the surface states of SmB6 are spin polarized. The spin is locked to the crystal momentum, fulfilling time reversal and crystal symmetries. Our results provide strong evidence that SmB6 can host topological surface states in a bulk insulating gap stemming from the Kondo effect, which can serve as an ideal platform for investigating of the interplay between novel topological quantum states with emergent effects and competing orders induced by strongly correlated electrons.
This review paper provides a recent overview of current international research that is being conducted into the functional properties of cellulose as a nanomaterial. A particular emphasis is placed ...on fundamental and applied research that is being undertaken to generate applications, which are now becoming a real prospect given the developments in the field over the last 20 years. A short introduction covers the context of the work, and definitions of the different forms of cellulose nanomaterials (CNMs) that are most widely studied. We also address the terminology used for CNMs, suggesting a standard way to classify these materials. The reviews are separated out into theme areas, namely healthcare, water purification, biocomposites, and energy. Each section contains a short review of the field within the theme and summarizes recent work being undertaken by the groups represented. Topics that are covered include cellulose nanocrystals for directed growth of tissues, bacterial cellulose in healthcare, nanocellulose for drug delivery, nanocellulose for water purification, nanocellulose for thermoplastic composites, nanocellulose for structurally colored materials, transparent wood biocomposites, supercapacitors and batteries.
In this paper, three different inverters: conventional pulsewidth modulation (PWM) inverter, dc-dc boosted PWM inverter, and Z -source inverter were investigated and compared for fuel cell vehicle ...application. Total switching device power, passive components requirement, and constant power speed ratio of each of these inverters were calculated. For purposes of comparison, an example of the total switching device power, requirement of passive components, the constant power speed ratio, and the efficiencies of the different inverters for fuel cell vehicle powered by the same fuel cell were conducted. The comparisons show that the Z -source inverter is very promising in applications when the boost ratio is low (1-2).
Highly oriented polycrystalline ZnO films were deposited on Si substrate by rf reactive sputtering technique. X-ray diffraction (XRD), atomic force microscope (AFM) and the refractive index were ...employed to analyze the influence of the post-annealing treatment on the structural properties of ZnO thin films. It has been found that the grain size of ZnO thin films increases with increasing the annealing temperature, the shift of the diffraction peak position from its normal powder value was observed. AFM analysis shows that the surface roughness of ZnO films is very low at temperature between 250 and 600°C. The packing density investigation shows ZnO films can obtain high packing densities (above 0.973) in the annealing temperature rang from 450 to 600°C.
Pulsewidth modulation (PWM)-based power electronics inverters are being widely used for various applications, including motor drives. However, the common-mode voltage (CMV) resulting from switching ...operations in the PWM inverters causes significant performance degradation of the system and can cause potential damage to motors. Since the effects of the CMV can be more severe in wide bandgap (WBG) and high switching frequency-based converter systems, various methods have been proposed to mitigate the CM noise issues. This work presents a multi-level inverter system composed of a multi-level inverter with a proposed multi-level active power filter (APF). For attenuating the CMV in multi-level inverters using multi-carrier-based PWM methods, a novel PWM method is presented for the proposed multi-level APF. The three-phase five-level active-neutral-point-clamped (ANPC) II-type inverter using the apparent switching frequency doubling (ASFD) PWM is used as an example of the multi-level inverters and carrier-based PWM methods to analyze and verify the proposed CMV attenuation method. The APF generates and injects the APF voltage equal to the CMV to attenuate the CM noise accurately. Various key challenges, including the dead-time compensation, are addressed through the proposed advanced PWM techniques to improve the CMV attenuation performance. Simulation and experimental results are provided to verify the comparison and effectiveness of the proposed CMV attenuation method.
Abstract
Sleep consolidates memory for procedural motor skills, reflected by sleep-dependent changes in the hippocampal-striatal-cortical network. Other forms of procedural skills require the ...acquisition of a novel strategy to solve a problem, which recruit overlapping brain regions and specialized areas including the caudate and prefrontal cortex. Sleep preferentially benefits strategy and problem-solving skills over the accompanying motor execution movements. However, it is unclear how acquiring new strategies benefit from sleep. Here, participants performed a task requiring the execution of a sequence of movements to learn a novel cognitive strategy. Participants performed this task while undergoing fMRI before and after an interval of either a full night sleep, a daytime nap, or wakefulness. Participants also performed a motor control task, which precluded the opportunity to learn the strategy. In this way, we subtracted motor execution-related brain activations from activations specific to the strategy. The sleep and nap groups experienced greater behavioral performance improvements compared to the wake group on the strategy-based task. Following sleep, we observed enhanced activation of the caudate in addition to other regions in the hippocampal-striatal-cortical network, compared to wakefulness. This study demonstrates that sleep is a privileged time to enhance newly acquired cognitive strategies needed to solve problems.
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