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Flame Photometry: Lab01:16

Flame Photometry: Lab

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In a flame photometer, when a solution like potassium chloride is aspirated into the flame, the solvent evaporates, leaving behind dehydrated salt. This salt dissociates into free gaseous atoms in their ground state. Some of these atoms absorb energy from the flame, leading to their excitation. The excited atoms return to the ground state, emitting photons at characteristic wavelengths. Because only electronic transitions are involved, the resulting emission lines are very narrow. The intensity...
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Flame Photometry: Overview01:02

Flame Photometry: Overview

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Flame photometry, also known as flame emission spectrometry, is a technique used for the qualitative and quantitative analysis of elements present in a sample using a flame as the source of excitation energy. The concept of flame photometry was realized in the early 1860s by Kirchhoff and Bunsen, who discovered that specific elements emit characteristic radiation when excited in flames. The first instrument developed for this purpose was used to measure sodium (Na) in plant ash using a Bunsen...
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Steady, Laminar Flow in Circular Tubes01:23

Steady, Laminar Flow in Circular Tubes

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Hagen-Poiseuille flow describes a viscous fluid's steady, incompressible flow through a cylindrical tube with a constant radius R. This flow profile is often applied to understand fluid transport in narrow channels, such as capillaries. It serves as a foundational example of laminar flow. In this model, cylindrical coordinates (r,θ,z) are used to describe the radial (r), angular (θ), and axial (z) dimensions within the tube. For Hagen-Poiseuille flow, the velocity profile is purely...
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Steady Flow of a Fluid Stream01:27

Steady Flow of a Fluid Stream

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Consider a control volume, such as a pipe with solid boundaries, through which fluid flows and changes direction due to the impulse exerted by the resulting force from the pipe walls. In steady flow, the mass of fluid entering the control volume at a given time, t, with velocity v1, is equal to the mass leaving after infinitesimal time dt, with velocity v2.
During this process, the momentum of the fluid within the control volume remains constant over the time interval dt. By applying the...
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Bernoulli's Equation for Flow Along a Streamline01:30

Bernoulli's Equation for Flow Along a Streamline

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Bernoulli's equation relates the energy conservation in a fluid moving along a streamline. The equation applies to incompressible and inviscid fluids under steady flow. For such a flow, Newton's second law is applied to a small fluid element, which experiences forces due to pressure differences, gravity, and velocity variations. The force balance leads to the following form of Bernoulli's equation:
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Couette Flow01:22

Couette Flow

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Couette flow represents the flow of fluid between two parallel plates, with one plate fixed and the other moving with a constant velocity. This configuration allows for a simplified analysis using the Navier-Stokes equations, which govern fluid motion under conditions of viscosity and incompressibility. For Couette flow, the assumptions include a steady, laminar, incompressible flow with a zero-pressure gradient in the flow direction. This flow type is beneficial for understanding shear-driven...
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Updated: Apr 16, 2026

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NGC 5253の非常に効率的な恒星形成は,おそらくストリームに供給された蓄積によるものです.

J L Turner1, S C Beck2, D J Benford3

  • 1Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, California 90095-1547, USA.

Nature
|March 20, 2015
PubMed
まとめ

銀河の恒星形成は非効率ですが,NGC 5253の密集した,塵に満ちたガス雲は,50%以上の効率を示しています. この高い速度は,膨らむガスが燃料となり,古代の大量恒星群の形成を説明している可能性がある.

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Formation of Thick Dense Yttrium Iron Garnet Films Using Aerosol Deposition
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科学分野:

  • 天文学 (astronomy) 天文学 (astronomy) とは,天文学 (astronomy) とは,天文学 (astronomy) とは,天文学 (astronomy) とは
  • 天体物理学 天体物理学
  • 銀河の進化 銀河の進化 銀河の進化

背景:

  • 銀河の恒星形成効率は一般的に低いため,銀河の進化と星団の生存に影響を与えます.
  • 古代球状星団の存在は,初期の宇宙におけるより高い恒星形成効率を示唆しています.
  • 矮星銀河NGC 5253は,若くて巨大な恒星群をホストし,効率的な恒星形成のための潜在的なケーススタディを提供します.

研究 の 目的:

  • 矮星銀河NGC 5253の巨大な若い恒星群に関連したガス雲の性質を調査する.
  • この特定のガス雲内の恒星形成効率を決定するために.
  • 高効率の恒星形成につながる可能性のある条件を理解する.

主な方法:

  • 放射天文学を用いた一酸化炭素 (CO) のJ = 3→2の回転転移の検出.
  • ガス雲の物理的性質の分析:温度,密度,および塵の含有量.
  • ガスと塵の比率を,天の川の比率と比較した.

主要な成果:

  • ガス雲の特徴は,高温,密度,極度の塵の含有量である.
  • ガスと塵の比率は銀河の平均より著しく低く,おそらくは埋め込まれた星団からの塵の濃縮によるものです.
  • この雲内の星形成効率は50%を超え,典型的な銀河の値の約10倍です.

結論:

  • NGC 5253のガス雲で観測された高い恒星形成効率は,高密度と塵含有量を含むユニークな物理条件に起因する.
  • 低いガスと塵の比率は,若い巨大な恒星群による濃縮を示唆しています.
  • 流入するガス流 ("フォースフィーディング") は,この強化された星形成を駆動するメカニズムとして提案されており,初期の宇宙の条件を潜在的に反映しています.