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Related Concept Videos

Flow Sheet01:17

Flow Sheet

2.9K
Flowsheets are valuable tools in nursing documentation. They enable healthcare professionals to efficiently record and monitor various patient assessments and measurements in a consolidated format.
Here's a closer look at the examples of flowsheets commonly used by nurses:
Graphic Sheet Documentation:
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Proton (¹H) NMR: Chemical Shift01:07

Proton (¹H) NMR: Chemical Shift

3.5K
Organic molecules primarily contain carbon and hydrogen atoms. While all the hydrogen isotopes are NMR-active, protium or hydrogen-1 is the most abundant. It has a significant energy separation between its nuclear spin states due to its large gyromagnetic ratio. As per Boltzmann's distribution, an increase in the energy separation implies a greater excess population of nuclei available for excitation, resulting in a strong NMR absorption signal.
Absorption signals of all the protium nuclei...
3.5K
NMR Spectroscopy: Chemical Shift Overview01:15

NMR Spectroscopy: Chemical Shift Overview

3.3K
The position of the absorption signal of a sample is reported relative to the position of the signal of tetramethylsilane (TMS), which is added as an internal reference while recording spectra. The difference between the absorption frequencies of the sample and TMS (in Hz) is divided by the spectrometer operating frequency (in MHz) to obtain a dimensionless quantity called the chemical shift. It is reported on the δ (delta) scale and expressed in parts per million.
For instance, the proton...
3.3K
Inductive Effects on Chemical Shift: Overview01:27

Inductive Effects on Chemical Shift: Overview

2.2K
The protons in unsubstituted alkanes are strongly shielded with chemical shifts below 1.8 ppm. Methine, methylene, and methyl protons appear at approximately 1.7, 1.2 and 0.7 ppm, while the proton signal from methane appears at 0.23 ppm. An electronegative substituent, such as chlorine, withdraws the electron density from the protons, increasing their chemical shift. Progressive substitution of the hydrogens in methane by chlorine shifts the proton signals increasingly downfield, to 3.05 ppm in...
2.2K
Chemical Shift: Internal References and Solvent Effects01:17

Chemical Shift: Internal References and Solvent Effects

1.4K
In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
1.4K
π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

1.7K
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0,...
1.7K

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Assessment of Stress Effects on Cognitive Flexibility using an Operant Strategy Shifting Paradigm
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The paradigm shift in Antarctic ice sheet modelling.

Frank Pattyn1

  • 1Laboratoire de Glaciologie, Université libre de Bruxelles (ULB), Brussels, B-1050, Belgium. fpattyn@ulb.ac.be.

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|July 18, 2018
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Summary
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The Antarctic ice sheet significantly impacts future sea level rise. Ongoing advancements in physically-based ice sheet models are improving predictions of its behavior.

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Area of Science:

  • Glaciology
  • Climate Science
  • Earth System Science

Background:

  • The Antarctic ice sheet is a major factor in global sea level rise.
  • Accurate prediction of ice sheet dynamics is crucial for climate change adaptation.
  • Physically-based ice sheet models are essential tools for forecasting.

Purpose of the Study:

  • To highlight the challenges in predicting Antarctic ice sheet behavior.
  • To discuss recent progress in developing and utilizing ice sheet models.
  • To emphasize the importance of these models for understanding sea level rise.

Main Methods:

  • Utilizing physically-based ice sheet models.
  • Analyzing model performance and limitations.
  • Reviewing recent advancements in ice sheet modeling techniques.

Main Results:

  • Physically-based ice sheet models have historically presented prediction challenges.
  • Significant progress is being made in overcoming these modeling bottlenecks.
  • Improved models enhance our ability to forecast ice sheet contributions to sea level rise.

Conclusions:

  • Advances in ice sheet modeling are critical for accurate sea level rise projections.
  • Continued research is necessary to refine these complex models.
  • Better predictions will aid in mitigating the impacts of climate change.