227,396 research outputs found

    Mixing 4D-Equipped and Unequipped Aircraft in the Terminal Area

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    On-board 4D guidance systems, which predict and control the touchdown time of an aircraft to an accuracy of a few seconds throughout the descent, were developed and demonstrated in several flight test programs. However, in addition to refinements of the on board system, two important issues still need to be considered. First, in order to make effective use of these on-board systems, it is necessary to understand and develop the interactions of the airborne and air traffic control (ATC) system in the proposed advanced environment. Unless the total system is understood, the advanced on-board system may prove unusable from an ATC standpoint. Second, in planning for a future system in which all aircraft are 4D equipped, it is necessary to confront the transition situation in which some percentage of traffic must still be handled by conventional means. In terms of 4D, this means that some traffic must still be given radar vectors and speed clearances (that is, be spaced by conventional distance separation techniques), while the 4D-equipped aircraft need to be issued time assignments. These apparent differences are reconciled and efficient ATC operation is developed

    Superconducting energy gap in MgCNi3 single crystals: Point-contact spectroscopy and specific-heat measurements

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    Specific heat has been measured down to 600 mK and up to 8 Tesla by the highly sensitive AC microcalorimetry on the MgCNi3 single crystals with Tc ~ 7 K. Exponential decay of the electronic specific heat at low temperatures proved that a superconducting energy gap is fully open on the whole Fermi surface, in agreement with our previous magnetic penetration depth measurements on the same crystals. The specific-heat data analysis shows consistently the strong coupling strength 2D/kTc ~ 4. This scenario is supported by the direct gap measurements via the point-contact spectroscopy. Moreover, the spectroscopy measurements show a decrease in the critical temperature at the sample surface accounting for the observed differences of the superfluid density deduced from the measurements by different techniques

    Influence of Al doping on the critical fields and gap values in magnesium diboride single crystals

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    The lower (Hc1H_{c1}) and upper (Hc2H_{c2}) critical fields of Mg1−x_{1-x}Alx_{x}B2_2 single crystals (for x=0x = 0, 0.1 and ≳0.2\gtrsim 0.2) have been deduced from specific heat and local magnetization measurements, respectively. We show that Hc1H_{c1} and Hc2H_{c2} are both decreasing with increasing doping content. The corresponding anisotropy parameter ΓHc2(0)=Hc2ab(0)/Hc2c(0)\Gamma_{H_{c2}}(0) = H^{ab}_{c2}(0)/H^c_{c2}(0) value also decreases from ∌5\sim 5 in pure MgB2_2 samples down to ∌1.5\sim 1.5 for x≳0.2x \gtrsim 0.2 whereas ΓHc1(0)=Hc1c(0)/Hc1ab(0)\Gamma_{H_{c1}}(0)=H^c_{c1}(0)/H^{ab}_{c1}(0) remains on the order of 1 in all samples. The small and large gap values have been obtained by fitting the temperature dependence of the zero field electronic contribution to the specific heat to the two gap model for the three Al concentrations. Very similar values have also been obtained by point contact spectroscopy measurements. The evolution of those gaps with Al concentration suggests that both band filling and interband scattering effects are present

    Investigation of high energy radiation from a plasma focus

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    Included are seventeen topics covering the experimental setup, diagnostics, analyses and various applications of the plasma focus. An invention, a hypocycloidal-pinch apparatus, is also included
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