A. Burrows  D. Vartanyan  J. C. Dolence  M. A. Skinner  D. Radice 《Space Science Reviews》2018,214(1):33

We explore with self-consistent 2D Fornax simulations the dependence of the outcome of collapse on many-body corrections to neutrino-nucleon cross sections, the nucleon-nucleon bremsstrahlung rate, electron capture on heavy nuclei, pre-collapse seed perturbations, and inelastic neutrino-electron and neutrino-nucleon scattering. Importantly, proximity to criticality amplifies the role of even small changes in the neutrino-matter couplings, and such changes can together add to produce outsized effects. When close to the critical condition the cumulative result of a few small effects (including seeds) that individually have only modest consequence can convert an anemic into a robust explosion, or even a dud into a blast. Such sensitivity is not seen in one dimension and may explain the apparent heterogeneity in the outcomes of detailed simulations performed internationally. A natural conclusion is that the different groups collectively are closer to a realistic understanding of the mechanism of core-collapse supernovae than might have seemed apparent.  相似文献   

    

B. Williams  P. Antreasian  E. Carranza  C. Jackman  J. Leonard  D. Nelson  B. Page  D. Stanbridge  D. Wibben  K. Williams  M. Moreau  K. Berry  K. Getzandanner  A. Liounis  A. Mashiku  D. Highsmith  B. Sutter  D. S. Lauretta 《Space Science Reviews》2018,214(4):69

OSIRIS-REx is the first NASA mission to return a sample of an asteroid to Earth. Navigation and flight dynamics for the mission to acquire and return a sample of asteroid 101955 Bennu establish many firsts for space exploration. These include relatively small orbital maneuvers that are precise to ～1 mm/s, close-up operations in a captured orbit about an asteroid that is small in size and mass, and planning and orbit phasing to revisit the same spot on Bennu in similar lighting conditions. After preliminary surveys and close approach flyovers of Bennu, the sample site will be scientifically characterized and selected. A robotic shock-absorbing arm with an attached sample collection head mounted on the main spacecraft bus acquires the sample, requiring navigation to Bennu’s surface. A touch-and-go sample acquisition maneuver will result in the retrieval of at least 60 grams of regolith, and up to several kilograms. The flight activity concludes with a return cruise to Earth and delivery of the sample return capsule (SRC) for landing and sample recovery at the Utah Test and Training Range (UTTR).  相似文献   

    

Auston  D. H. 《IEEE transactions on aerospace and electronic systems》1967,(3):441-446

A new resonant quasi-optic interferometer has been developed which has a unique capability to deduce spatial information about perturbing plasma media. The fundamental property of the resonator is that it is multiply degenerate. Its geometry consists of four spherical mirrors arranged in a confocal ring configuration such that the transverse modes are simultaneously resonant. Energy is coupled into and out of the resonator by thin dielectric film beam splitters. When perturbed, it is found that the resonant frequency of the system depends on the point at which the field is measured and this dependence is directly related to the geometry of the perturbation. The results of a theoretical analysis of the perturbation of the resonator are presented and preliminary experimental measurements of a 4-mm system are discussed.  相似文献   

    

De Couvreur  G. A. Ludwig  D. 《IEEE transactions on aerospace and electronic systems》1967,(4):731-731

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Atlas  D. Srivastava  R.C. 《IEEE transactions on aerospace and electronic systems》1971,(1):179-187

A method is described whereby a conventional non-Doppler radar may be used in the measurement and detection of atmospheric turbulence. The technique involves the measurement of the average echo power and the variance of the fluctuation spectrum in each of two separated pulse volumes, and corresponding measure ments of echo power and variance of the detected signals in a channel representing the predetection sum of the signals from those two volumes. It is shown that the variance of the sum channel is the power-weighted sum of the variances in the independent channels plus a term dependent upon the difference in mean radial velocity of the associated pulse volumes. Accordingly, the difference in mean radial velocity can be measured. When the spacing of the sampled volumes is adjusted to represent distance along an aircraft flight plan, the measurement is a measure of the turbulence to be experienced in traversing the space between those volumes. Specific systems for accomplishing the measure ment are discussed.  相似文献   

    

T. Koryu Ishii Aggarwal  D. Combs  V.P. 《IEEE transactions on aerospace and electronic systems》1972,(2):191-195

Comparative utilization of a limited amount of energy for continuous and pulse operations was investigated. Under a restriction that the amount of available energy was limited, general equations for operational hours of the energy source for given power output were derived for both continuous and pulse mode operations. This paper points out that due to various adjustable parameters available for pulse mode operation, if properly designed pulse mode operation produces longer utilization of available energy for required output power than continuous mode operation.  相似文献   

  总被引：1，自引：0，他引：1  

Wangsness  D.L. 《IEEE transactions on aerospace and electronic systems》1973,(6):959-960

A method of locating radio emitters anywhere on the surface of the Earth, by using bearing measurements, is presented. The method associates planes of bearing with the measured bearings, and characterizes these planes by their unit normals. The emitter is located by finding the unit vector from the Earth's center that minimizes the sum of squares of its inner product with the normal vectors. The solution is found in terms of the eigenvalues and eigenvectors of a 3 × 3 matrix.  相似文献   

    

Urkowitz  H. Geisler  J.D. Ricciardi  N.A. 《IEEE transactions on aerospace and electronic systems》1973,(4):486-494

The Doppler sidelobes of a received pulse burst may be partially controlled by varying the amplitudes of the pulses in the burst or sequence upon transmission and/or reception. When there is a peak power limitation, weighting the amplitudes produces a loss in signal-to-noise ratio. A general expression is derived for the loss factor under the peak power limitation, and loss factor formulas are given for the following cases: Case A: Full nominal weights upon reception. Uniform weights on transmission. Case B: Square roots of the nominal weights on both transmission and reception. Case C: Full nominal weights on both transmission and reception. These cases are listed in order of increasing loss. Numerical results are tabulated for regular spacings and for the following nominal weights: 1) Dolph-Tchebycheff, 2) Taylor, 3) Hamming, and 4) Hann.  相似文献   

    

Beste  D.C. 《IEEE transactions on aerospace and electronic systems》1978,(3):466-473

A satellite-borne sensor can view a region at or above the Earth's surface. The size of this region depends on the satellite's altitude, the maximum range and scan angle of the sensor, the minimum above-the-horizon viewing angle required, the extent in altitude of the region to be viewed, and the maximum altitude of sensor obscuration by the atmosphere. Except for geosynchronous satellites this region moves relative to the Earth, so that constellations of satellites are generally necessary for continuous coverage. Satellite constellations which minimize the number of satellites required for continuous coverage are derived as a function of the angle subtended at the Earth's center by the coverage of a single satellite. This is done for single and triple continuous coverage of the entire Earth and of the polar regions extending to arbitrary latitude. Simple, cogent approximations for the configurations and numbers of satellites are found. Expressions which relate sensor capabilities and surveillance requirements to are presented. Examples are given to illustrate the use and accuracy of the results.  相似文献   

    

P. J. Christiansen  M. P. Gough  G. Martelli  J. J. Bloch  N. Cornilleau  J. Etcheto  R. Gendrin  C. Beghin  P. Decreau  D. Jones 《Space Science Reviews》1978,22(4):383-400

In this paper we describe and discuss the occurrence of natural wave emissions detected by GEOS-1 at frequencies above the electron gyrofrequency. The bulk of the data presented comes from the first six months of satellite operation and thus concerns mainly dayside phenomena. The paper is arranged as follows:After some general remarks, a classification of the wave phenomena is developed in Section 2, and experimental evidence and morphological information relevant to this classification are contained in Section 3. Section 4 includes some preliminary comments on nightside observations. The results are discussed in Section 5, where it is argued that they can be understood as manifestations of electron cyclotron harmonic (Bernstein) wave emission in a plasma parameter range which has only very recently received any theoretical examinations. This theme is further developed in a comparison paper (Ronnmark et al., 1978).  相似文献