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Aerodynamic versus Ballistic Flight

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Open Journal of Fluid Dynamics 2019年第4期9卷 346-400页

作者： jack Denur Electric & Gas Technology Inc. Rowlett TX USA

We consider, compare, and contrast various aspects of aerodynamic and ballistic flight. We compare the energy efficiency of aerodynamic level flight at a given altitude versus that of ballistic flight beginning and ending at this same altitude. We show that for flights short compared to Earth’s radius, aerodynamic level flight with lift-to-drag ratio L/D > 2?is more energy-efficient than ballistic flight, neglecting air resistance or drag in the latter. Smaller L/D suffices if air resistance in ballistic flight is not neglected. For a single circumnavigation of Earth, we show that aerodynamic flight with L/D > 4π is more energy-efficient than minimum-altitude circular-orbit ballistic spaceflight. We introduce the concept of gravitational scale height, which may in an auxiliary way be helpful in understanding this result. For flights traversing N circumnavigations of Earth, if then even minimum-altitude circular-orbit ballistic spaceflight is much more energy-efficient than aerodynamic flight because even at minimum circular-orbit spaceflight altitude air resistance is very small. For higher-altitude spaceflight air resistance is even smaller and the energy-efficiency advantage of spaceflight over aerodynamic flight traversing the same distance is therefore even more pronounced. We distinguish between the energy efficiency of flight per se and the energy efficiency of the engine that powers flight. Next we consider the effects of air density on aerodynamic level flight and provide a simplified view of drag and lift. We estimate the low-density/high-altitude limits of aerodynamic level flight (and for comparison also of balloons) in Earth’s and Mars’ atmospheres. Employing Mars airplanes and underwater airplanes on Earth (and hypo-thetically also on Mars) as examples, we consider aerodynamic level flight in rarefied and dense aerodynamic media, respectively. We also briefly discuss hydrofoils. We appraise the optimum range of air densities for aerodynamic level flight

关键词： Aerodynamic Flight Ballistic Flight Lift Drag Lift-to-Drag Ratio Air Density Energy Efficiency

MATHEMATICAL MODEL FOR THE ENTERpRISE COMpETITIVE ABILITY AND pERFORMANCE THROUGH A pARTICULAR EMDEN-FOWLER EQUATION u〞-n^(-q-1)u(n)~q=0

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Acta Mathematica Scientia 2018年第4期38卷 1311-1321页

作者： Yue-Loong CHANC Meng-Rong LI C. jack YUE Yong-Shiuan LEE Tsung-Jui CHIANG-LIN Department of phycology National Chengchi University Taipei China Department of Mathematical Sciences National Chengchi University Taipei China Department of Statisitics National Chengchi University Taipei China Graduate Institute of Finance National Taiwan University of Science and Technology Taipei China

In this article, we work with the ordinary equation u″-n-q-1u（n）q=0 and learn some interesting phenomena concerning the blow-up and the blow-up rate of solution to the equation.

关键词： estimate life-span blow-up blow-up rate competitive ability performance

Accept the Challenge of English

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疯狂英语（初中天地） 2003年第7期 6-7页

作者： jack

大家都知道:学习任何一种语文,离不开“四多”:多读、多听、多讲、多写,才能事半功倍,学有所成。在“四多”之中,“多写”更不能忽略,因为它是磨练大家功力的最好方法。现在,请尝试完成下面两篇短文。切记:你必须先把答案填写后,才能参... 详细信息

大家都知道:学习任何一种语文,离不开“四多”:多读、多听、多讲、多写,才能事半功倍,学有所成。在“四多”之中,“多写”更不能忽略,因为它是磨练大家功力的最好方法。现在,请尝试完成下面两篇短文。切记:你必须先把答案填写后,才能参阅答案。

关键词： In Accept the Challenge of English

pressure Gradient, power, and Energy of Vortices

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Open Journal of Fluid Dynamics 2018年第2期8卷 216-247页

作者： jack Denur Electric & Gas Technology Inc. Rowlett TX USA

We consider small vortices, such as tornadoes, dust devils, whirlpools, and small hurricanes at low latitudes, for which the Coriolis force can be neglected. Such vortices are (at least approximately) cylindrically symmetrical about a vertical axis through the center of a calm central region or eye of radius . In the region fluid (gas or liquid) circulates about the eye with speed . We take to be the outer periphery of the vortex, where the fluid speed is reduced to that of the surrounding wind field (in the cases of tornadoes, dust devils, and small hurricanes at low latitudes) or deemed negligible (in the case of whirlpools). If , angular momentum is conserved within the fluid itself;if , angular momentum must be exchanged with Earth to ensure conservation of total angular momentum. We derive the steepness and upper limit of the pressure gradients in vortices. We then discuss the power and energy of vortices. We compare the kinetic energy of atmospheric vortices and the power required to maintain them against frictional dissipation with the same quantities for Earth’s atmosphere as a whole. We explain why the kinetic energy of atmospheric vortices must be replaced on much shorter timescales than is the case for Earth’s atmosphere as a whole. Brief comparisons of cyclostrophic flow with geostrophic and friction-balanced flows are then provided. We then consider an analogy that might be drawn, at least to some extent, with gravitational systems, considering mainly spherically-symmetrical and cylindrically-symmetrical ones. Generation of kinetic energy at the expense of potential energy in fluid vortices, in geostrophic and friction-balanced flows, and in gravitational systems is then briefly discussed. We explain the variations of pressure and gravitational gradients corresponding to generation of kinetic energy exceeding, equaling, and falling short of frictional dissipation. In the Appendix, we describe a simple method for maximizing power extraction from environm

关键词： Vortex Cyclostrophic Flow Angular Momentum pressure Gradient Geostrophic Flow Friction-Balanced Flow power Energy Gravity

Never Sleep Beside phones

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新世纪智能 2018年第17期 78-80页

作者： jack 不详

For electronic devices like laptops, phones, anything with a LED or LCD display, the problem is that they produce a large amount of artificial blue light. Blue light is what1us to know what time of day it is. By exposing ourselves to large amounts of blue light late at night, we are giving our bodies a cue that it’s time actually to wake up instead of going to2. This can lead to the3in our circadian rhythm(昼夜节律), and it’s been shown that when we have our biological clock out of phase with the natural day-night cycle outside, that can lead to4in the rates of diabetes, cancer, heart disease.

关键词： Sleep circadian rhythm

Accept the Challenge of English

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疯狂英语（初中天地） 2003年第3期 24-25页

作者： jack

大家都知道学习任何一种语文,离不开“四多”:多读、多听、多讲、多写,只有这样做,才能事半功倍,学有所成。在“四多”之中,“多写”更不能忽略,因为它是磨练大家功力的最好方法。

关键词： Accept the Challenge of English

Aging and Migration： Micro and Macro Evidence from China

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Frontiers of Economics in China-Selected publications from Chinese Universities 2016年第4期11卷 548-580页

作者： Orn B. Bodvarsson jack W. Hou Kailing Shen College of Social Sciences & Interdisciplinary Studies California State University Sacramento California 95819 6109 USA Department of Economics California State University-Long Beach Long Beach CA 90840USA Henan University Wang Yanan Institute for Studies in Economics (WISE) Xiamen University Xiamen 361005 China Research School of Economics College of Business and Economics Australian National University Canberra 0200 Australia IZA Bonn Germany

post-reform China has been experiencing two major demographic changes： an increasingly aging population and an extraordinary surge of rural-urban migrants. The question we ask is： are these two demographic changes related？ If yes, then, how？ The standard view in the migration literature is that the older the migrant, the lower the likelihood of migration. This paper proposes a simple theory of temporary migration for unskilled labor to fit the context of China Motivated by our model, we then use both cross-sectional micro data and panel macro data to examine the potential impacts of aging on migration. We find that shifts in China＇s age distribution have generated significant changes in the country＇s migration patterns： migration will shift to closer provinces （probably switching from interprovincial migration to intra-provincial migration） and will concentrate to a few destination provinces.

关键词： internal migration age distribution reform

Never sleep beside phones

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新世纪智能 2019年第50期 34-36页

作者： jack 不详

For electronic devices like laptops,phones,anything with a LED or LCD display,the problem is that they produce a large amount of artificial blue *** light is what__us to know what time of day it *** exposing aurselves to large amounts of blue liaht late at night,we are giving our bodies a cue that it's time actually to wake up instead of going to__.

关键词： Never blue artificial

Let’s Take Some photos!

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空中英语教室（初级版．大家说英语） 2020年第6期 34-37,54,55页

作者： jack LSmith 不详

How do you take photos?Some people use a *** many people use their *** are good for *** poses can you make?You can try some fun *** can make some funny faces,too!Or you can just *** can take photos *** can take them a... 详细信息

关键词： some make What too