1,535 research outputs found
S15RS SGFB No. 10 (Union Seating)
A FINANCE BILL
To allocate a maximum of seven thousand seven hundred fifty-seven dollars and ninety-three cents ($7,757.93) from the Student Government Senate General Contingency Account to fund nine new round tables and thirty new chairs for the LSU Student Union
The Effect of Common-Mode Voltage Elimination on the Iron Loss in Machine Core Laminations of Multilevel Drives
This paper studies the effect of common-mode voltage elimination (CMVE) on the iron loss of electrical machine core laminations under multilevel converter supply. Three identical magnetic ring cores are excited by either a three-level converter or a five-level voltage source converter to study the behavior of CMVE on a three-phase system. Both multilevel converters are controlled by using a space vector pulse width modulation as it is one of the most often used techniques for CMVE. These experimental results are confirmed numerically with a dynamic iron loss model. In addition, the effect of CMVE, at different switching frequencies, on the core loss of a synchronous machine is numerically studied. The results presented in this paper show that the core loss is considerably increased when the CMVE is implemented. However this iron loss increase in five-level drive systems is lower compared to the three-level ones. Therefore, it is important that the designers of drive systems take such effects into consideration.Peer reviewe
Effect of Multilevel Inverter Supply on Core Losses in Magnetic Materials and Electrical Machines
The effect of multilevel inverter supply on power losses in magnetic cores and electrical machines is studied. A dynamic numerical model for the hysteresis, eddy current, and excess losses in a core lamination is first developed. By both measurements and simulations for a ring-core inductor, we demonstrate how increasing the number of inverter voltage levels decreases the iron losses when compared with traditional two-level supply. Although the switching frequency has a significant impact on the iron losses in the case of a traditional two-level inverter, using three or five voltage levels makes the losses almost independent of the switching. Finally, finite-element simulations show that simi-lar reductions are also possible for the core losses of 150-kVA and 12.5-MW wound-field synchronous machines, in which rather low switching frequencies are typically used. Calorimetric loss measurements are also presented for the 150-kVA machine in order to confirm the significant effect of switching frequency on the core losses with two-level inverter supply.Peer reviewe
Closure to Discussion on “Effect of Multilevel Inverter Supply on Core Losses in Magnetic Materials and Electrical Machines”
Peer reviewe
Symmetries of Electrostatic Interaction between DNA Molecules
We study a model for pair interaction of DNA molecules generated by the
discrete dipole moments of base-pairs and the charges of phosphate groups, and
find noncommutative group of eighth order of symmetries that leave
invariant. We classify the minima using group and employ
numerical methods for finding them. The minima may correspond to several
cholesteric phases, as well as phases formed by cross-like conformations of
molecules at an angle close to , "snowflake phase". The results
depend on the effective charge of the phosphate group which can be modified
by the polycations or the ions of metals. The snowflake phase could exist for
above the threshold . Below there could be several cholesteric
phases. Close to the snowflake phase could change into the cholesteric
one at constant distance between adjacent molecules.Comment: 13 pages, 4 figure
A twist in chiral interaction between biological helices
Using an exact solution for the pair interaction potential, we show that
long, rigid, chiral molecules with helical surface charge patterns have a
preferential interaxial angle ~((RH)^1/2)/L, where L is the length of the
molecules, R is the closest distance between their axes, and H is the helical
pitch. Estimates based on this formula suggest a solution for the puzzle of
small interaxial angles in a-helix bundles and in cholesteric phases of DNA.Comment: 7 pages, 2 figures, PDF file onl
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New mechanism for lightning initiation
This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). To distinguish radio-frequency (rf) signals generated by lightning from the electromagnetic pulse produced by a nuclear explosion, it is necessary to understand the fundamental nature of thunderstorm discharges. The recent debate surrounding the origin of transionospheric pulse pairs (TIPPs) detected by the BLACKBEARD experiment aboard the ALEXIS satellite illustrates this point. We have argued that TIPP events could originate from the upward propagating discharges recently identified by optical images taken from the ground, from airplanes, and from the space shuttle. In addition, the Gamma Ray Observatory (GRO) measurements of x-ray bursts originating from thunderstorms are almost certainly associated with these upward propagating discharges. When taken together, these three measurements point directly to the runaway electron mechanism as the source of the upward discharges. The primary goal of this research effort was to identify the specific role played by the runaway-air-breakdown mechanism in the general area of thunderstorm electricity and in so doing develop lightning models that predict the optical, rf, and x-ray emissions that are observable from space
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