Analysis of AC link topologies in non-isolated DC/DC triple active bridge converter for current stress minimization

This paper presents analysis of the non-isolated DC/DC triple active bridge (TAB) converter under various purely inductor-based AC link topologies. The objective of the analysis is to find the topology that incorporates the least value of the AC link inductors which leads to reduced converter footprint in addition to minimum internal current stresses. Modelling of the TAB under each of the different topologies is presented in per unit expressions of power transfer and reactive power assuming fundamental harmonic analysis. The power expressions are used to calculate the inductor values necessary to achieve same rated power transfer of Dual Active Bridge (DAB) converter for the sake of standardizing comparison. On this basis, the topology requiring the least value of interface inductors, hence lowest footprint, is identified. Furthermore, based on phase shift control, particle swarm optimization (PSO) is used to calculate optimal phase shift ratios in each of the proposed topologies to minimize reactive power loss (hence current stress). The topology with minimum stresses is therefore identified and the results are substantiated using a Matlab-Simulink model to verify the theoretical analysis

Optical Spectroscopic Determination of the Zero-Field Splitting in Vibronic Levels of the Triplet State of Nitrite

We have used conventional high resolution optical spectroscopic methods to determine the principal values of the fine structure tensor for the lowest triplet state (3B1 at 18 959 cm^−1) of NO2 - in Na NO2 single crystals. From the intensities in the Zeeman spectrum we find [dformula D - E = 0.86 [plus-minus] 0.04cm[sup -1],] [dformula D + E = 0.40 [plus-minus] 0.04cm[sup -1],] where the z axis is taken as the twofold axis and E = (Z − X) / 2. From the measurement of line positions in the high-field Zeeman spectrum we find D − E = 0.84 ± 0.05cm−1,D + E = 0.41 ± 0.05cm−1. The values of D and E calculated for one-center spin–spin interaction are D − E = 0.42cm^−1 and D + E = 0.24cm^−1. The calculated ordering of the spin states is the same as that observed, but we suggest that there is significant second-order spin–orbit energy associated with the real splittings. Roughly the same splittings are seen for different vibronic levels of 3B1 associated with nu2[prime

Purely rotational coherence effect and time-resolved sub-Doppler spectroscopy of large molecules. I. Theoretical

In this and the accompanying paper we present a theoretical treatment and experimental study, respectively, of the phenomenon termed purely rotational coherence. This phenomenon has been demonstrated to be useful as a time domain means by which to obtain high resolution spectroscopic information on excited state rotational levels of large molecules [Felker et al., J. Phys. Chem. 90, 724 (1986); Baskin et al., J. Chem. Phys. 84, 4708 (1986)]. Here, the manifestations in temporally resolved, polarization-analyzed fluorescence of coherently prepared rotational levels in samples of isolated symmetric and asymmetric top molecules are considered. These manifestations, for reasonably large molecules at rotational temperatures characteristic of jet-cooled samples, take the form of polarization-dependent transients and recurrences with temporal widths of the order of tens of picoseconds or less. The transients, which arise from the thermal averaging of many single molecule coherences, are examined with respect to their dependences on molecular parameters (rotational constants, transition dipole directions) and experimental parameters (polarization directions and temperature). A physical picture of rotational coherence as a reflection of the time-dependent orientation of molecules in the sample is developed. And, the influence of rotational coherence in experiments designed to probe intramolecular energy flow is discussed. In the accompanying paper, we present experimental results for jet-cooled t-stilbene and anthracene. For t-stilbene we determine rotational constants for vibrational levels in the S1 electronic state (from the recurrences) and we monitor the trends in rotational coherence vs vibrational coherence as the total energy in the molecule increases

Studies of the 3455-Å Triplet State of s-Triazine

We present a confirmation of the assignment of the 28 935-cm^−1 triplet state, 3A1[double-prime], of s-triazine. The high-field Zeeman effect is used to make this assignment which is consistent with the fact the transition is polarized perpendicular to the molecular plane. The optical spectrum at low magnetic fields yields the zero-field splitting D=−0.058±0.024 cm^−1. The sign and magnitude of D is consistent with an npi* state in which one-center spin—spin interaction is a significant feature of the zero-field splitting

Generalized small-signal modelling of dual active bridge DC/DC converter

this paper presents a novel generalised approach of the small-signal modelling of dual active bridge (DAB) DC/DC converter. The adopted analysis is based on a per-unit fundamental frequency representation of the DAB. The outcome of the proposed modelling approach is a small signal, linearised, state-space DAB model; which is considered as a main building block for future control applications. The developed small signal DAB model includes all possible degrees of freedom affecting the performance of the DAB; this includes the voltage conversion ratio to allow the study of all DAB operation modes (i.e.: unity-gain and buck/boost modes.). Furthermore, since triple phase shift control (TPS) is used in this development work, the proposed model incorporates phase shift in addition to duty ratios. This feature allows for bridge voltage regulation, which is essential for efficient DAB operation in the case of buck/boost operation. Another key achievement is that the proposed small signal modelling methodology can be applied to any bidirectional DC-DC converter regardless of ratings, parameter values and number of ports. Extensive simulation is carried out to verify the proposed analysis

Assessment of seismic performance of adobe structures in Pakistan and Portugal

Adobe buildings exist in different parts of the world. The construction of these buildings can be carried out economically, using locally available materials and skills that do not require use of modern machinery. Therefore, adobe buildings provide an economic housing option. The construction of adobe structures is carried out based on traditional construction practices which vary from region to region. This paper presents the results of a study which was conducted to study the construction practices of adobe buildings in Pakistan and Portugal in the context of their seismic vulnerability. The adobe buildings in both these countries were found to be subjected to seismic hazard levels which, although is low in some regions, may cause significant damages. Lack of essential elements or details for the adequate seismic performance was found in the adobe buildings in both regions

Opportunistic Spectrum Sharing using Dumb Basis Patterns: The Line-of-Sight Interference Scenario

We investigate a spectrum-sharing system with non-severely faded mutual interference links, where both the secondary-to-primary and primary-to-secondary channels have a Line-of-Sight (LoS) component. Based on a Rician model for the LoS channels, we show, analytically and numerically, that LoS interference hinders the achievable secondary user capacity. This is caused by the poor dynamic range of the interference channels fluctuations when a dominant LoS component exists. In order to improve the capacity of such system, we propose the usage of an Electronically Steerable Parasitic Array Radiator (ESPAR) antenna at the secondary terminals. An ESPAR antenna requires a single RF chain and has a reconfigurable radiation pattern that is controlled by assigning arbitrary weights to M orthonormal basis radiation patterns. By viewing these orthonormal patterns as multiple virtual dumb antennas, we randomly vary their weights over time creating artificial channel fluctuations that can perfectly eliminate the undesired impact of LoS interference. Because the proposed scheme uses a single RF chain, it is well suited for compact and low cost mobile terminals

Structural ultrafast dynamics of macromolecules: diffraction of free DNA and effect of hydration

Of special interest in molecular biology is the study of structural and conformational changes which are free of the additional effects of the environment. In the present contribution, we report on the ultrafast unfolding dynamics of a large DNA macromolecular ensemble in vacuo for a number of temperature jumps, and make a comparison with the unfolding dynamics of the DNA in aqueous solution. A number of coarse-graining approaches, such as kinetic intermediate structure (KIS) model and ensemble-averaged radial distribution functions, are used to account for the transitional dynamics of the DNA without sacrificing the structural resolution. The studied ensembles of DNA macromolecules were generated using distributed molecular dynamics (MD) simulations, and the ensemble convergence was ensured by monitoring the ensemble-averaged radial distribution functions and KIS unfolding trajectories. Because the order–disorder transition in free DNA implies unzipping, coiling, and strand-separation processes which occur consecutively or competitively depending on the initial and final temperature of the ensemble, DNA order–disorder transition in vacuo cannot be described as a two-state (un)folding process