41 research outputs found
Variable Switching Point Predictive Current Control for Multi-Phase Permanent Magnet Synchronous Drives
Finite control set model predictive control (FCS-MPC) is a promising method for the control of multi-phase machines, due to its capability to directly account for nonlinearities and multiple controlled variables. To overcome the drawback of high current ripples and excitation of harmonic currents in the so-called xy-subsystem, several methods have been proposed in the literature so far. This paper proposes an MPC-based method that achieves high granularity of switching by not only switching at the discrete time steps, but also within the sampling interval. In doing so, the discussed algorithm, referred to as variable switching point current control (VSP2CC), produces low current distortions, while still keeping the advantages of conventional FCS-MPC, such as fast dynamic behavior during transients. To highlight the above, VSP2CC is applied to a six-phase permanent magnet synchronous machine (PMSM) and compared with conventional FCS-MPC and MPC that employs virtual voltage vectors (VV-MPC).acceptedVersionPeer reviewe
Small Scale Structure at High Redshift: II. Physical Properties of the CIV Absorbing Clouds
Keck HIRES spectra were obtained of the separate images of three
gravitationally lensed QSOs (UM 673, Q1104-1804, and Q1422+2309). We studied
the velocity and column density differences in CIV doublets in each QSO. Unlike
the low ionization gas clouds typical of the interstellar gas in the Galaxy or
damped Ly alpha galaxies, the spatial density distribution of CIV absorbing gas
clouds turns out to be mostly featureless on scales up to a few hundred
parsecs, with column density differences rising to 50 percent or more over
separations beyond a few kpc. Similarly, velocity shear becomes detectable only
over distances larger than a few hundred pc, rising to 70 km/s at a few kpc.
The energy transmitted to the gas is substantially less than in present day
star-forming regions, and the gas is less turbulent on a given spatial scale
than, e.g., local HII regions. The quiescence of CIV clouds, taken with their
probable low density, imply that these objects are not internal to galaxies.
The CIV absorbers could be gas expelled recently to large radii and raining
back onto its parent galaxy, or pre-enriched gas from an earlier (population
III) episode of star formation, falling into the nearest mass concentration.
However, while the metals in the gas may have been formed at higher redshifts,
the residual turbulence in the clouds and the minimum coherence length measured
here imply that the gas was stirred more recently, possibly by star formation
events recurring on a timescale on the order of 10-100 Million years (abstract
abbreviated).Comment: latex file plus 15 postscript figures (45 pages in total); to be
published in the ApJ, June 20, 2001 issu
Modeling of an Interleaved DC-DC Boost Converter for a Direct Model Predictive Control Strategy
This paper presents a model predictive control (MPC) algorithm for interleaved dc-dc boost converters with coupled inductors. The prediction model covers the switching nature of the converter and all possible operating states. The MPC algorithm is realized in MATLAB and designed such to facilitate its real-time implementation on a field programmable gate array (FPGA) using the MATLAB HDL Coder. Open-loop measurement results demonstrate the accuracy of the system model, while the effectiveness of the controller is validated in simulation.acceptedVersionPeer reviewe
Microglia-mediated demyelination protects against CD8+ T cell-driven axon degeneration in mice carrying PLP defects
Axon degeneration and functional decline in myelin diseases are often attributed to loss of myelin but their relation is not fully understood. Perturbed myelinating glia can instigate chronic neuroinflammation and contribute to demyelination and axonal damage. Here we study mice with distinct defects in the proteolipid protein 1 gene that develop axonal damage which is driven by cytotoxic T cells targeting myelinating oligodendrocytes. We show that persistent ensheathment with perturbed myelin poses a risk for axon degeneration, neuron loss, and behavioral decline. We demonstrate that CD8(+) T cell-driven axonal damage is less likely to progress towards degeneration when axons are efficiently demyelinated by activated microglia. Mechanistically, we show that cytotoxic T cell effector molecules induce cytoskeletal alterations within myelinating glia and aberrant actomyosin constriction of axons at paranodal domains. Our study identifies detrimental axon-glia-immune interactions which promote neurodegeneration and possible therapeutic targets for disorders associated with myelin defects and neuroinflammation. Demyelination is often suggested to cause axonal degeneration. Here, the authors study mice carrying distinct PLP defects and reveal how persistent ensheathment with perturbed myelin poses a risk for CD8+T cell-driven axon loss and behavioral decline
The Benefits and Harms of Transmitting Into Space
Deliberate and unintentional radio transmissions from Earth propagate into
space. These transmissions could be detected by extraterrestrial watchers over
interstellar distances. Here, we analyze the harms and benefits of deliberate
and unintentional transmissions relevant to Earth and humanity. Comparing the
magnitude of deliberate radio broadcasts intended for messaging to
extraterrestrial intelligence (METI) with the background radio spectrum of
Earth, we find that METI attempts to date have much lower detectability than
emissions from current radio communication technologies on Earth. METI
broadcasts are usually transient and several orders of magnitude less powerful
than other terrestrial sources such as astronomical and military radars, which
provide the strongest detectable signals. The benefits of radio communication
on Earth likely outweigh the potential harms of detection by extraterrestrial
watchers; however, the uncertainty regarding the outcome of contact with
extraterrestrial beings creates difficulty in assessing whether or not to
engage in long-term and large-scale METI.Comment: Published in Space Polic
Comparison of <i>Ab-initio</i> Solute-Boundary Binding Energies and Experimental Recrystallization Data in Austenite for Solute Nb and Other Elements
LTPP Data Analysis, Phase I: Validation of Guidelines for K-Value Selection and Concrete Pavement Performance Prediction
DTFH61-94-C-00218Several important issues concerning the effect of slab support on concrete pavement performance were studied in a National Cooperative Highway Research Program project, "Support Under Concrete Pavements" (NCHRP 1-30). The results were promising, however, the data that were available for analysis were limited. This study was conducted to further field-verify and develop the improved support guidelines proposed in NCHRP 1-30, using the Long-Term Pavement Performance (LTPP) database, in order to establish their practicality and appropriateness for use in concrete pavement design nationwide. This study was also conducted to further field-verify the proposed revised American Association of State Highway and Transportation Officials (AASHTO) performance model to the fullest extent possible using the design, materials, climate, traffic, and performance data available in the LTPP database for General Pavement Section 3 (GPS-3) (jointed plain concrete pavement), GPS-4 (jointed reinforced concrete pavement), and GPS-5 (continuously reinforced concrete pavement). Guidelines, revised on the basis of the results of this field verification study, are presented in the appendix in the form of a proposed addendum to the AASHTO Design Guide. The documentation of these field verification efforts using the LTPP database is provided in this report