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相关概念视频

Sharpless Epoxidation02:57

Sharpless Epoxidation

The conversion of allylic alcohols into epoxides using the chiral catalyst was discovered by K. Barry Sharpless and is known as Sharpless epoxidation. The use of a chiral catalyst enables the formation of one enantiomer of the product in excess. This chiral catalyst is mainly a chiral complex of titanium tetraisopropoxide and tartrate ester (specific stereoisomer). The stereoisomer used in the chiral catalyst dictates the formation of the enantiomer of the product. In other words, the use of...
Rocket Propulsion in Empty Space - I01:13

Rocket Propulsion in Empty Space - I

The driving force for the motion of any vehicle is friction, but in the case of rocket propulsion in space, the friction force is not present. The motion of a rocket changes its velocity (and hence its momentum) by ejecting burned fuel gases, thus causing it to accelerate in the direction opposite to the velocity of the ejected fuel. In this situation, the mass and velocity of the rocket constantly change along with the total mass of ejected gases. Due to conservation of momentum, the rocket's...
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...
Atomic Emission Spectroscopy: Instrumentation01:22

Atomic Emission Spectroscopy: Instrumentation

The instrumentation of atomic emission spectrometry (AES) involves various components, including atomization devices that convert samples into gas-phase atoms and ions. There are two main types of atomization devices: continuous and discrete atomizers.  Continuous atomizers, like plasmas and flames, introduce samples in a constant stream, while discrete atomizers inject individual samples using syringes or autosamplers. The most common discrete atomizer is the electrothermal atomizer.
Atomic Emission Spectroscopy: Lab01:29

Atomic Emission Spectroscopy: Lab

AES is a powerful analytical technique, especially effective when used with plasma sources, producing abundant spectra in characteristic emission lines. The Inductively Coupled Plasma (ICP), in particular, yields superior quantitative analytical data due to its high stability, low noise, low background, and minimal interferences under optimal experimental conditions. However, newer air-operated microwave sources are emerging as promising alternatives that could be more cost-effective than...
Preparation of Epoxides03:00

Preparation of Epoxides

Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...

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相关实验视频

Updated: May 31, 2026

The Effect of Interfacial Chemical Bonding in TiO2-SiO2 Composites on Their Photocatalytic NOx Abatement Performance
11:47

The Effect of Interfacial Chemical Bonding in TiO2-SiO2 Composites on Their Photocatalytic NOx Abatement Performance

Published on: July 4, 2017

在哈特利2彗星上的EPOXI.

Michael F A'Hearn1, Michael J S Belton, W Alan Delamere

  • 1Department of Astronomy, University of Maryland, College Park, MD 20742-2421 USA. ma@astro.umd.edu

Science (New York, N.Y.)
|June 18, 2011
PubMed
概括
此摘要是机器生成的。

EPOXI任务研究了103P/哈特利2彗星,发现其活动是由二氧化碳排气驱动的. 这一过程喷射出冰块,并在小的活跃核中显示出多样化的挥发性成分.

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Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser
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Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser

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U2O5 Film Preparation via UO2 Deposition by Direct Current Sputtering and Successive Oxidation and Reduction with Atomic Oxygen and Atomic Hydrogen
12:05

U2O5 Film Preparation via UO2 Deposition by Direct Current Sputtering and Successive Oxidation and Reduction with Atomic Oxygen and Atomic Hydrogen

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Last Updated: May 31, 2026

The Effect of Interfacial Chemical Bonding in TiO2-SiO2 Composites on Their Photocatalytic NOx Abatement Performance
11:47

The Effect of Interfacial Chemical Bonding in TiO2-SiO2 Composites on Their Photocatalytic NOx Abatement Performance

Published on: July 4, 2017

Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser
09:00

Experimental Methods for Spin- and Angle-Resolved Photoemission Spectroscopy Combined with Polarization-Variable Laser

Published on: June 28, 2018

U2O5 Film Preparation via UO2 Deposition by Direct Current Sputtering and Successive Oxidation and Reduction with Atomic Oxygen and Atomic Hydrogen
12:05

U2O5 Film Preparation via UO2 Deposition by Direct Current Sputtering and Successive Oxidation and Reduction with Atomic Oxygen and Atomic Hydrogen

Published on: February 21, 2019

科学领域:

  • * 星球科学 星球科学
  • * 天文学 * 天文学
  • * 彗星科学 彗星科学

背景情况:

  • *了解彗星活动是研究早期太阳系的关键.
  • *彗星为原始太阳系材料提供了独特的见解.
  • * EPOXI任务的目标是彗星103P/哈特利2进行详细的观测.

研究的目的:

  • * 调查彗星活动的驱动因素在小,活跃的原子核.
  • *分析103P/哈特利2彗星的组成和行为.
  • * 了解核特性与排气之间的关系.

主要方法:

  • * EPOXI航天器对103P/哈特利2彗星进行了飞越.
  • *高分辨率成像捕捉了彗星的核和活动.
  • *光谱分析提供了有关彗星挥发性组成的数据.

主要成果:

  • *103P/哈特利2彗星的核异常小,但非常活跃.
  • *二氧化碳 (CO2) 排气是活动的主要驱动因素,与较大的彗星不同.
  • *二氧化碳升温会抛出冰和尘埃,产生喷气和活动.
  • *在核的不同区域观察到挥发性丰度的显著变化.

结论:

  • *小的,活跃的彗星核可能被二氧化碳排气所主导.
  • *彗星活动机制根据原子核的大小和组成而有所不同.
  • *这些发现增强了我们对彗星进化和早期太阳系状况的理解.