Properties of nuclei in the inner crusts of neutron stars in the relativistic mean-field theory

We study the properties of nuclei in the inner crusts of neutron stars based on the Boguta-Bodmer nonlinear model in the relativistic mean-field theory. We carefully determine the surface diffuseness of the nuclei as the density of matter increases. The imaginary time step method is used to solve the Euler-Lagrange equation derived from the variational principle applied to the semiclassical energy density. It is shown that with increasing density, the spherical nuclei become more neutron rich and eventually merge to form a uniform liquid of neutrons, protons, and electrons. We find that the smaller the value of the incompressibility K, the lower the density at which the phase transition to uniform matter occurs. The relativistic extended Thomas-Fermi method is generalized to investigate nonspherical nuclei. Our results show that the spherical nucleus phase is the only equilibrium state in the inner crusts of neutron stars.published_or_final_versio

Soft-switching vector control for resonant snubber based inverters

This paper gives a new classification of soft-switching inverters according to the principle of operation. After discussing the soft-switching phenomena in hard-switching inverters, the concept of soft-switching vector (SSV) is introduced. The proposed SSV is not only helpful in analyzing the changes of switching states, but also easily realized in control scheme. Theoretical analyses are conducted step by step for both with and without SSV control applied to resonant snubber based inverters (RSI). The experimental results closely agree with theoretical analyses and show the significant reduction in power loss after using SSV. Moreover, a modified version of SSV is also presented to achieve the better working condition at low load current with current ripple.published_or_final_versio

Nonlinear modeling and spectral analysis of Cuk converters

Being a fourth-order circuit, the Cuk converter certainly needs alone systematic studies of its nonlinear dynamics. In this paper, the investigation of the nonlinear dynamics of Cuk converters is carried out by deriving their nonlinear models and performing their spectral analyses. Nonlinear dynamics, including the additional dc offset, significant subharmonic and higher harmonic spectral contamination as well as the effects of self-intermodulation and cross-intermodulation, due to large-signal perturbations of both the duty ratio and source voltage, are investigated.published_or_final_versio

Personalized Pancreatic Tumor Growth Prediction via Group Learning

Tumor growth prediction, a highly challenging task, has long been viewed as a mathematical modeling problem, where the tumor growth pattern is personalized based on imaging and clinical data of a target patient. Though mathematical models yield promising results, their prediction accuracy may be limited by the absence of population trend data and personalized clinical characteristics. In this paper, we propose a statistical group learning approach to predict the tumor growth pattern that incorporates both the population trend and personalized data, in order to discover high-level features from multimodal imaging data. A deep convolutional neural network approach is developed to model the voxel-wise spatio-temporal tumor progression. The deep features are combined with the time intervals and the clinical factors to feed a process of feature selection. Our predictive model is pretrained on a group data set and personalized on the target patient data to estimate the future spatio-temporal progression of the patient's tumor. Multimodal imaging data at multiple time points are used in the learning, personalization and inference stages. Our method achieves a Dice coefficient of 86.8% +- 3.6% and RVD of 7.9% +- 5.4% on a pancreatic tumor data set, outperforming the DSC of 84.4% +- 4.0% and RVD 13.9% +- 9.8% obtained by a previous state-of-the-art model-based method

A novel soft-switching inverter using resonant inductor freewheeling

A novel topology of the voltage-source soft-switching inverter for induction motor drives is presented. The key of this topology is to employ two fractional-duty auxiliary switches and one resonant inductor per phase to provide a favorable zero-voltage turn-on condition for those main switches. By fully utilizing the inherent natural freewheeling of the inverter, the auxiliary switches need to operate in the resonant inductor freewheeling only in a fractional duty. Apart from providing a soft-switching environment with minimum voltage and current stresses, the distinct advantage of this topology is its capability to control the operation of each phase individually. Therefore, this inverter can readily adopt the well-established PWM techniques while possessing the advantages of soft switching-namely PWM-oriented soft switching. Moreover, a new concept of the zero-voltage soft-switching vector is introduced to determine whether the auxiliary circuit needs to operate to achieving soft switching. A theoretical analysis has been conducted and then verified by using both computer simulation and experimental results.published_or_final_versio

Switching characteristics and efficiency improvement with auxiliaryresonant snubber based soft-switching inverters

The auxiliary resonant snubber inverter (RSI) has demonstrated superiority in reduction of switching losses and dv/dt. It was found that the overall inverter system efficiency might not be improved if the resonant current was not controlled in accordance with the load current. This paper proposes an improved control scheme to minimize the operation of auxiliary circuit for efficiency improvement. The principle of this control scheme is to vary the resonant current with variable timing control based on the load current magnitude and to disable the auxiliary circuit operation when diode freewheeling occurs after switching. To illustrate the operation of this control scheme, this paper compares the switching characteristics and inverter power loss of hard-switching inverter, RSI with fixed-timing and variable-timing control and RSI with the proposed control scheme. Experimental results fully agree with the analyses and prove that the proposed control scheme is suitable for RSI to achieve better operating conditions.published_or_final_versio

Properties of neutron stars in the relativistic mean-field theory

We study the properties of dense matter in neutron stars and calculate the structure of the stars based on the Zimanyi & Moszkowski (ZM) model in the relativistic mean-field theory. We also compare these results with those based on the Boguta (BB) model with a recent satisfactory parameter set. The two models satisfy the requirements from the observations of the masses of binary radio pulsars, the rotation frequencies of millisecond pulsars, the redshifts of the e + annihilation lines of some y-ray bursts if they are neutron stars, and the crustal moment of inertia of neutron stars deduced from the glitch events. Other observations may provide a way to discriminate between the two models. We suggest that the most important observational discriminant between these two models is found by observing the surface radiation of neutron stars, since the BB model leads to a large photon fraction of neutron star matter and rapid cooling of neutron stars, but the ZM model does not. © 1996. The American Astronomical Society. All rights reserved.published_or_final_versio

Microbial fuel cells: a green and alternative source for bioenergy production

Microbial fuel cell (MFC) represents one of the green technologies for the production of bioenergy. MFCs using microalgae produce bioenergy by converting solar energy into electrical energy as a function of metabolic and anabolic pathways of the cells. In the MFCs with bacteria, bioenergy is generated as a result of the organic substrate oxidation. MFCs have received high attention from researchers in the last years due to the simplicity of the process, the absence in toxic by-products, and low requirements for the algae growth. Many studies have been conducted on MFC and investigated the factors affecting the MFC performance. In the current chapter, the performance of MFC in producing bioenergy as well as the factors which influence the efficacy of MFCs is discussed. It appears that the main factors affecting MFC’s performance include bacterial and algae species, pH, temperature, salinity, substrate, mechanism of electron transfer in an anodic chamber, electrodes materials, surface area, and electron acceptor in a cathodic chamber. These factors are becoming more influential and might lead to overproduction of bioenergy when they are optimized using response surface methodology (RSM)

Cu-Doping Effects in CdI2Nanocrystals: The Role of Cu-Agglomerates

Cu-doping effects in CdI2nanocrystals are studied experimentally. We use the photostimulated second harmonic generation (PSSHG) as a tool to investigate the effects. It is found that the PSSHG increases with increasing Cu content up to 0.6% and then decreases due to the formation of the Cu-agglomerates. The PSSHG for the crystal with Cu content higher than 1% reduces to that for the undoped CdI2crystal. The results suggest that a crucial role of the Cu-metallic agglomerates is involved in the processes as responsible for the observed effects