The effect of rotation on the hydrodynamics of stellar collapse

Summary Using values of d, _min, and _max that Van Riper (1978) has found most promising for a hydrodynamic envelope ejection, we have shown that even a small amount of rotation in the initial core can stop its collapse before nuclear densities are reached. We expected _i > 0.02 to produce significant deviations from a spherically symmetric collapse, but have found that _i as much as ten times smaller than this will not allow the core to reach densities as high as in the spherical collapse. In no case, however, does the core flatten very much, nor does the value of become very large. Low final 's preclude the formation of an axisymmetric torus. They also indicate that deformation of an iron core into a triaxial configuration or fragmentation of the core during its collapse is an extremely unlikely event. (Note: Classically, must exceed 0.27 before a dynamic instability to non-axisymmetric perturbations is encountered.)The small degree of flattening of the core also suggests that the reduced moment of inertia I of the core will always be relatively small in magnitude and hence that the third time derivative of I, which is proportional to the energy emitted in gravity wave radiation, will not be very significant. Numerically calculated estimates of I- during some of these model evolutions supports this suspicion. If the _min and used here are found to be realistic values after the detailed physics of the core collapse is well understood, it is clear that gravitational radiation from a core collapse will be difficult to measure.Finally, we should point out that it is the relatively large values of Y_min (near 4/3) combined with values of d near unity that (a) prevented the core from flattening significantly in these models and (b) prevented the core from reaching high configurations. If realistic values of either one (or both) of these parameters are found to be much smaller in more complete models of the core collapse, then the core will have to become flatter (and denser) before pressure gradients will support it along the rotation axis. All of the conclusions drawn here would be modified accordingly under those circumstances. It should also be noted that in general relativistic models, the critical for spherical collapse is somewhat larger than 4/3 (Van Riper, 1979). Therefore, we predict that when fully general relativistic core collapses are performed including rotation, a given choice of _min and _i will produce a slightly flatter and slightly denser core than the corresponding model that has been presented here.     

Phase Detector Response to Noisy and Noisy Fading Signals

Transfer characteristics of sinusoidal, triangular, and sawtooth-type phase detectors in response to noisy and noisy fading signals have been studied in detail. A new analytical model of the swatooth-type phase detector has been suggested. Detailed experimental results have been supplemented in support of the theoretical findings. Both the theoretical findings and the experimental results clearly indicate that the superiority of a sawtooth-type phase detector over the other two varieties is completely lost in noisy and noisy fading environments.     

Emitter Location Independent of Systematic Errors in Direction Finders

A scheme is suggested for the passive location of radio emitter position by using a mobile direction finder. The vehicle carrying the direction finder is made to maneuver such that the apparent direction of arrival is held constant. The resulting trajectory of the vehicle is a logarithmic spiral. The true direction of arrival can be obtained by monitoring the parameters of the spiral trajectory without using the value of the direction fimder reading. Two specific algorithms to eliminate direction finder bias are presented and their sensitivity to random errors in measurement assessed.     

Dynamic tests with a switched reluctance motor drive

Starting and reversing times of less than 40 ms, torque ripple below ten percent and operational speeds over 5000 1/min. (rpm) can be achieved with our 6/4 prototype switched reluctance motor drive. The drive efficiency approaches 80 percent but it is currently limited by high switching frequency. Peak currents of 50 A are needed in the 4.2 kW machine. Experimental results of the prototype switched reluctance machine are shown     

RF band high resolution sounding of building structures and works

A subsurface radar using a multi-frequency signal has been developed. It is designated for surveying building structures and works. The characteristic feature of this device is the possibility of obtaining sounding plane radio images featuring a high resolution attaining 1…2 cm. The main applications of this device includes the survey of building structures to reveal their heterogeneities and defects and the investigation of premises to detect bugging devices     

The (r)evolution and stagnation of higher education in EE ever thepast decades

The current university education of electrical and electronics engineers has evolved from the well-established system of the 1950's to a wishy-washy mixture operating with lots of ill-motivated or less-qualified students, a process mostly accelerated by the growth in the telecommunications industry. External projects take staff time and the curriculum continues to threaten youngsters with de-focused mathematics. The computer age has reduced the interest in experimental research, and the continuation of science in the systems level may be in danger     

SAR image formation via semiparametric spectral estimation

A new algorithm, referred to as the SPAR (Semiparametric) algorithm, is presented herein for target feature extraction and complex image formation via synthetic aperture radar (SAR). The algorithm is based on a flexible data model that models each target scatterer as a two-dimensional (2-D) complex sinusoid with arbitrary unknown amplitude and constant phase in cross-range and with constant amplitude and phase in range. By attempting to deal with one corner reflector, such as one dihedral or trihedral, at a time, the algorithm can be used to effectively mitigate the artifacts in the SAR images due to the flexible data model. Another advantage of SPAR is that it can be used to obtain initial conditions needed by other parametric target feature extraction methods to reduce the total amount of computations needed. Both numerical and experimental examples are provided to demonstrate the performance of the proposed algorithm     

Trailing-edge scalloping effect on flat-plate membrane wing performance

This investigation studies the effect of trailing-edge scalloping on the lift and drag force coefficients of flat, membrane wings that vibrate at low Reynolds numbers (<61,000). A series of rigid, flat plate frames with moderate aspect ratio and repeating membrane cell structure were studied and compared to a rigid plate and a rigid scalloped plate. Lift and drag measurements were acquired using an external force-balance; flow fluctuation measurements were captured with a hot-wire. Results showed that the size and aspect ratio of the latex cell had a greater impact on lift than scalloping and that scalloping had a greater effect on drag than the cell aspect ratio. Compared to the solid wings, the membrane wings exhibited higher lift and drag coefficients, likely due to both effective cambering and dynamic interaction with the free shear layer. While trailing-edge scalloping decreased both the lift and drag coefficients relative to no scalloping, the greater effect was on drag, thus, increasing aerodynamic efficiency. The maximum lift-to-drag ratio was attained for a 25% scallop with a repeating cell aspect ratio of one. A unique nondimensional scaling of the membrane vibration peak frequency is also presented.     

ARTEMIS Science Objectives

NASA??s two spacecraft ARTEMIS mission will address both heliospheric and planetary research questions, first while in orbit about the Earth with the Moon and subsequently while in orbit about the Moon. Heliospheric topics include the structure of the Earth??s magnetotail; reconnection, particle acceleration, and turbulence in the Earth??s magnetosphere, at the bow shock, and in the solar wind; and the formation and structure of the lunar wake. Planetary topics include the lunar exosphere and its relationship to the composition of the lunar surface, the effects of electric fields on dust in the exosphere, internal structure of the Moon, and the lunar crustal magnetic field. This paper describes the expected contributions of ARTEMIS to these baseline scientific objectives.     

The Galactic Environment of the Sun: Interstellar Material Inside and Outside of the Heliosphere

Interstellar material (ISMa) is observed both inside and outside of the heliosphere. Relating these diverse sets of ISMa data provides a richer understanding of both the interstellar medium and the heliosphere. The galactic environment of the Sun is dominated by warm, low-density, partially ionized interstellar material consisting of atoms and dust grains. The properties of the heliosphere are dependent on the pressure, composition, radiation field, ionization, and magnetic field of ambient ISMa. The very low-density interior of the Local Bubble, combined with an expanding superbubble shell associated with star formation in the Scorpius-Centaurus Association, dominate the properties of the local interstellar medium (LISM). Once the heliosphere boundaries and interaction mechanisms are understood, interstellar gas, dust, pickup ions, and anomalous cosmic rays inside of the heliosphere can be directly compared to ISMa outside of the heliosphere. Our understanding of ISMa at the Sun is further enriched when the circumheliospheric interstellar material is compared to observations of other nearby ISMa and the overall context of our galactic environment. The IBEX mission will map the interaction region between the heliosphere and ISMa, and improve the accuracy of comparisons between ISMa inside and outside the heliosphere.