229,927 research outputs found
Amplitude-Phase Detection for Power Converters Tied to Unbalanced Grids with Large X/R Ratios
Full text linkAmplitude-phase information of the voltage/current phasor, which is the prerequisite for grid-tied converter control and protection, can change almost instantaneously in low-voltage distribution systems with small X/R ratios. However, the equivalent impedances of high-voltage power systems are usually inductive (with large X/R ratios), and the power flow of pertinent grids generates decaying dc (DDC) components with large amplitude and long duration during large disturbances. Therefore, the X/R ratios and DDC components must be fully considered in amplitude-phase detection to achieve effective converter control and protection. To this end, the main components present in the transient voltage/current of a high-voltage power system after unbalanced disturbance are first analyzed, and the general transient model is obtained by synthesizing multimode DDC components. Then, by resorting to waveform characteristics of different components, an amplitude-phase detection algorithm is proposed based on the multicomponent parallel-detection structure. Compared to existing techniques, the detection time is reduced to half grid cycle. Finally, an iterative variable-interval integral algorithm is developed, improving the antinoise ability of detection algorithm and overcoming the computational burden issue. This enables the direct integration of algorithm into the converter's embedded processor. Experiment results verified the effectiveness and superiority of the proposed technique
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Enhanced colour encoding of materials discrimination information for multiple view dual-energy x-ray imaging
No full textThis thesis reports an investigation into dual-energy X-ray discrimination techniques. These techniques are designed to provide colour-coded materials discrimination information in a sequence of perspective images exhibiting sequential parallax. The methods developed are combined with a novel 3D imaging technique employing depth from motion or kinetic depth effect (KDE). This technique when applied to X-ray images is termed KDEX imaging and was developed previously by the university team for luggage screening applications at security checkpoints. A primary motivation for this research is that the dual-energy X-ray techniques, which are routinely incorporated into ‘standard’ 2D luggage scanners, provide relatively crude materials discrimination information. In this work it was critical that robust materials discrimination and colour encoding process was implemented as the sequential parallax exhibited by the KDEX imagery may introduce colour changes, due to the different X-ray beam paths associated with each perspective image. Any introduction of ‘colour noise’ into the resultant image sequences could affect the perception of depth and hinder the ongoing assessment of the potential utility of the dual-energy KDEX technique. Two dual-energy discrimination methods have been developed, termed K-II and W-E respectively. Employing the total amount of attenuation measured at each energy level and the weight fraction of layered structures, a combination of the K-II and the W-E techniques enables the computation and extraction of a target objects’ effective atomic number (Zeff) and its surface density (ρS) in the presence of masking layers
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Operando X-ray absorption spectroscopy investigations on NaxNi1/3Fe1/3Mn1/3O2 positive electrode materials for sodium and sodium ion batteries
No full textNaxMn1/3Fe1/3Ni1/3O2 (x = 2/3 and 1) layered oxides are synthesized and applied as positive electrode materials for sodium batteries. The crystal structure of the material changes from the O3 single phase to P2/O3 mixed phases as the Na content decreases from 1 to 2/3. The mixed-phases Na2/3Mn1/3Fe1/3Ni1/3O2 shows superior cycling performance compared to the single-phase NaMn1/3Fe1/3Ni1/3O2 due to different redox process and structural change that are demonstrated by operando X-ray absorption spectroscopy (XAS). The Na2/3Mn1/3Fe1/3Ni1/3O2 experiences redox reactions of Ni3+|Ni4+ and Fe3+|Fe4+ with inactive Mn ions during the charge/discharge processes, while the NaMn1/3Fe1/3Ni1/3O2 undergoes deeper redox reactions from Ni2+|Ni3+|Ni4+ and Fe3+|Fe4+ that Mn ions are irreversibly oxidized to Mn4+ in the 1st charge process. In addition, the mixed-phases material has smaller changes in the transition metal oxygen bond lengths during cycling, corresponding to less distortions of TMO6 units in the crystal structure. The better reversibility of the redox reactions and the occurrence of less structural changes are both responsible for the enhanced cycling performance obtained from the mixed-phases material compared to the single-phase material. These results strengthen the understanding of interactions of transition metals in the layered cathode and provide guidelines for designing positive electrode materials for sodium batteries
Observation of Electromagnetic Dalitz Decays to , and
No full textUsing a sample of about 10^{10} J/ψ events collected at a center-of-mass energy sqrt[s]=3.097 GeV with the BESIII detector, the electromagnetic Dalitz decays J/ψ→e^{+}e^{-}π^{+}π^{-}η^{'}, with η^{'}→γπ^{+}π^{-} and η^{'}→π^{+}π^{-}η, have been studied. The decay J/ψ→e^{+}e^{-}X(1835) is observed with a significance of 15σ, and also an e^{+}e^{-} invariant-mass dependent transition form factor of J/ψ→e^{+}e^{-}X(1835) is presented for the first time. The intermediate states X(2120) and X(2370) are also observed in the π^{+}π^{-}η^{'} invariant-mass spectrum with significances of 5.3σ and 7.3σ. The corresponding product branching fractions for J/ψ→e^{+}e^{-}X, X→π^{+}π^{-}η^{'} [X=X(1835), X(2120), and X(2370)] are reported
ZHANG, F. & LIU, X-W. (2009) A review of the subgenus Diestrammena (Gymnaeta) from China (Orthoptera: Rhaphidophoridae Aemodogryllinae). Zootaxa, 2272, 21-36.
No full textZhang, F., Liu, X-W. (2009): ZHANG, F. & LIU, X-W. (2009) A review of the subgenus Diestrammena (Gymnaeta) from China (Orthoptera: Rhaphidophoridae Aemodogryllinae). Zootaxa, 2272, 21-36. Zootaxa 2288 (1): 68, DOI: 10.11646/zootaxa.2288.1.5, URL: http://dx.doi.org/10.11646/zootaxa.2288.1.
Effects of Rate Adaption on the Throughput of Random Ad Hoc Networks
No full textThe capacity of wireless ad hoc networks has been studied in an excellent treatise by Gupta and Kumar [1], assuming a fixed transmission rate. By contrast, in this treatise we investigate the achievable throughput improvement of rate adaptation in the context of random ad hoc networks, which have been studied in conjunction with a fixed transmission rate in [1]. Our analysis shows that rate adaptation has the potential of improving the achievable throughput compared to fixed rate transmission, since rate adaptation mitigates the effects of link quality fluctuations. However, even perfect rate control fails to change the scaling law of the per-node throughput result given in [1], regardless of the absence or presence of shadow fading. This result is confirmed in the context of specific adaptive modulation aided design examples
Traces and shards of self-injury: Strange accounting with “Author X”
No full textIn this strange account autoethnography, three or four authors explore their lived experiences with self-injury. Strange accounting is both a post-modern style of text, and a method for keeping identities concealed when risks and secrets are in play. Author X, a post-modern place-keeper for an anonymous author who may or may not have contributed to this manuscript, introduces a new dimension and layer of concealment. With Author X in-play and under erasure, the reader will never be sure if there were three or four authors on this manuscript. Through strange accounting, a post-structuralist/postmodernist frame will be applied to understanding the self-injury experience. We frame self-injury as a social practice and, for some, an everyday norm, while remaining acutely aware of the stigma surrounding the topic of self-injury. Each of us, coupled with Author X, provide the others cover to trace stories of self-injury through the literature, our flesh, and our lives
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View synthesis for depth from motion 3D x-ray imaging.
No full textThe depth from motion or kinetic depth X-ray imaging (KDEX) technique is designed to enhance the luggage screening at airport checkpoints. The technique requires multiple views of the luggage to be obtained from an arrangement of linear X-ray detector arrays. This research investigated a solution to the unique problems defined when considering the possibility of replacing some of the X-ray sensor views with synthetic images. If sufficiently high quality synthetic images can be generated then intermediary X-ray sensors can be removed to minimise the hardware requirements and improve the commercial viability of the KDEX technique. Existing image synthesis algorithms are developed for visible light images. Due to fundamental differences between visible light and X-ray images, those algorithms are not directly applicable to the X-ray scenario. The conditions imposed by the X-ray images have instigated the original research and novel algorithm development and experimentation that form the body of this work. A voting based dual criteria multiple X-ray images synthesis algorithm (V-DMX) is proposed to exploit the potential of two matching criteria and information contained in a sequence of images. The V-DMX algorithm is divided into four stages
Irradiation effect of HfO2 MOS structure under gamma-ray
No full textthe effect of gamma irradiation upon Al/HfO2/SiO2/Si MOS structure under different doses of Co-60 is studied in this article as a function of total dosage. MOS capacitors with a stacked gate dielectric of 2.8nm thick SiO2 and 15nm thick HfO2 having electrode areas of 1mm*1mm are prepared on the p-Si substrate using thermal oxidation and atomic layer deposition respectively. The MOS capacitors are under zero bias during irradiation under Co-60 gamma ray with total dose of 100Krad (Si)/500Krad (Si)/1Mrad (Si) and dose rate of 50rad (Si)/s. The high frequency Capacitor-Voltage (C-V) and Current-Voltage (I-V) characteristic of each structure are measured at room temperature before and after irradiation. As well as the C-V and I-V property, Atomic Force Microscopy (AFM), Grazing Incidence X-ray Diffraction (GIXRD), and X-ray Photoelectron Spectroscopy (XPS) are also applied to determine the surface morphology, physical, and mechanical properties before and after different doses of radiation. The oxide trapped charge calculated from the high frequency C-V measurement is in the order of 10(12) cm(-2) and increases linearly with the increase of applied total dose. The XRD spectrum exhibits several phases of SiO2 and HfO2 variation under each total dose. The XPS result shows that each different total dosage leads to the binding energy peak drifting to a different degree demonstrating the influence of irradiation on the valence state of the elements, which can be attributed to the gamma-ray induced interface states
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