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相关概念视频

Rocket Propulsion In Empty Space - II01:12

Rocket Propulsion In Empty Space - II

The motion of a rocket is governed by the conservation of momentum principle. A rocket's momentum changes by the same amount (with the opposite sign) as the ejected gases. As time goes by, the rocket's mass (which includes the mass of the remaining fuel) continuously decreases, and its velocity increases. Therefore, the principle of conservation of momentum is used to explain the dynamics of a rocket's motion. The ideal rocket equation gives the change in velocity that a rocket experiences by...
Rocket Propulsion in Gravitational Field - I01:20

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Rockets range in size from small fireworks that ordinary people use to the enormous Saturn V that once propelled massive payloads toward the Moon. The propulsion of all rockets, jet engines, deflating balloons, and even squids and octopuses are explained by the same physical principle: Newton's third law of motion. The matter is forcefully ejected from a system, producing an equal and opposite reaction on what remains.
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Rocket Propulsion in Gravitational Field - II01:03

Rocket Propulsion in Gravitational Field - II

A rocket's velocity in the presence of a gravitational field is decreased by the amount of force exerted by Earth's gravitational field, which opposes the motion of the rocket. If we consider thrust, that is, the force exerted on a rocket by the exhaust gases, then a rocket's thrust is greater in outer space than in the atmosphere or on a launch pad. In fact, gases are easier to expel in a vacuum.
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Atomic Nuclei: Larmor Precession Frequency01:11

Atomic Nuclei: Larmor Precession Frequency

The earth's gravitational field produces a 'twisting force' perpendicular to the angular momentum of a spinning mass (such as a spinning top) that causes the mass to 'wobble' around the gravitational field axis in a phenomenon called precession. Similarly, the magnetic moment (μ) of a spinning nucleus precesses due to an external magnetic field directed along the z-axis. The precession of the magnetic moment vector about the magnetic field is called Larmor precession, and the angular frequency...
Momentum And Radiation Pressure01:20

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Investigation of Early Plasma Evolution Induced by Ultrashort Laser Pulses
11:20

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Published on: July 2, 2012

一个可变的原星中的脉冲积累.

James Muzerolle1, Elise Furlan, Kevin Flaherty

  • 1Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA. muzerol@stsci.edu

Nature
|January 4, 2013
PubMed
概括
此摘要是机器生成的。

年轻的原星表现出脉冲积累,这种现象是由于可变的积累速率,光度定期增加. 这项研究观察到一个原恒星,它的红外发光度每25.34天增加10倍,这是令人惊的.

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20 mJ, 1 ps Yb:YAG Thin-disk Regenerative Amplifier
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科学领域:

  • 天体物理学 天体物理学
  • 恒星进化 恒星进化
  • 太阳系外行星研究

背景情况:

  • 主序前的密切的双星从环双星盘中积聚物质.
  • 脉冲积累,其特点是周期性增加的亮度,影响二进制进化和行星形成.
  • 在年轻的恒星中,积累变性是常见的,但在年轻的双星中很少观察到周期性脉冲积累信号.

研究的目的:

  • 为了研究一个年轻的原星的周期性亮度变化.
  • 确定观察到的变化是否与脉冲增积相一致.
  • 了解在非常年轻的恒星系统中强烈,规律的脉冲积累的含义.

主要方法:

  • 一个年轻的原星的多时代红外观测.
  • 分析随时间变化的亮度变化.
  • 观察到的模式与脉冲积累的理论模型的比较.

主要成果:

  • 一个年轻的原恒星 (年龄约为105年) 在大约一周的时间内显示红外发光量增加了十倍.
  • 这种亮度的增加每25.34天就会以惊人的规律重复.
  • 观察到的现象归因于来自一个看不见的二进制伴侣的脉冲积累.

结论:

  • 观察到的脉冲积累信号对于这个年轻的系统来说,异常强大且规律.
  • 这一发现表明脉冲积累可能在接近的双星的早期进化中发挥了重要作用.
  • 与以前研究的系统相比,信号的规律性和强度可能与原星的非常年轻年龄有关.