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Videos de Conceptos Relacionados

Specific Heat01:16

Specific Heat

The specific heat capacity of a substance refers to the energy required to increase the temperature of one gram of that substance by one degree Celcius. Specific heat capacity is often represented in calories (cal), grams (g), and degrees Celsius (oC), but can also be expressed in joules (J), kilograms (kg), and Kelvin (K), among other units.
For example, increasing the temperature of one gram of water by 1°C requires one calorie of heat energy and can be written as 1 cal/g-°C, or 4186 J/kg/K.
Le Chatelier's Principle: Changing Temperature02:19

Le Chatelier's Principle: Changing Temperature

Consistent with the law of mass action, an equilibrium stressed by a change in concentration will shift to re-establish equilibrium without any change in the value of the equilibrium constant, K. When an equilibrium shifts in response to a temperature change, however, it is re-established with a different relative composition that exhibits a different value for the equilibrium constant.
To understand this phenomenon, consider the elementary reaction:
Entropy02:39

Entropy

Salt particles that have dissolved in water never spontaneously come back together in solution to reform solid particles. Moreover, a gas that has expanded in a vacuum remains dispersed and never spontaneously reassembles. The unidirectional nature of these phenomena is the result of a thermodynamic state function called entropy (S). Entropy is the measure of the extent to which the energy is dispersed throughout a system, or in other words, it is proportional to the degree of disorder of a...
Effects of Temperature on Free Energy02:11

Effects of Temperature on Free Energy

The spontaneity of a process depends upon the temperature of the system. Phase transitions, for example, will proceed spontaneously in one direction or the other depending upon the temperature of the substance in question. Likewise, some chemical reactions can also exhibit temperature-dependent spontaneities. To illustrate this concept, the equation relating free energy change to the enthalpy and entropy changes for the process is considered:
Effect of Temperature Change on Reaction Rate02:28

Effect of Temperature Change on Reaction Rate

The Arrhenius equation,
Atomic Spectroscopy: Effects of Temperature01:27

Atomic Spectroscopy: Effects of Temperature

Atomization, converting samples into gas-phase atoms and ions, is essential for atomic spectroscopy. The flame temperature required for atomization affects the efficiency of the atomic spectroscopic methods by increasing the atomization efficiency and the relative population of the excited and ground states.
At thermal equilibrium, the relative populations of excited and ground state atoms can be estimated using the Maxwell–Boltzmann distribution. For example, an increase in temperature from...

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Characterization of Thermal Transport in One-dimensional Solid Materials
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Published on: January 26, 2014

El efecto Hall cuántico de temperatura ambiente en el grafeno.

K S Novoselov1, Z Jiang, Y Zhang

  • 1Department of Physics, University of Manchester, Manchester M13 9PL, UK.

Science (New York, N.Y.)
|February 17, 2007
PubMed
Resumen

Los investigadores demuestran el efecto Hall cuántico en el grafeno a temperatura ambiente, superando las limitaciones anteriores de temperaturas extremadamente bajas. Este avance permite una mayor accesibilidad a los estándares de resistencia cuántica Hall.

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Área de la Ciencia:

  • Física de la materia condensada Física de la materia condensada Física de la materia condensada Física de la materia condensada Física de la materia condensada
  • La mecánica cuántica es la mecánica cuántica.
  • Ciencia de los materiales ciencia de los materiales.

Sus antecedentes:

  • El efecto Hall cuántico (QHE) es un fenómeno cuántico macroscópico crucial para la comprensión de la física cuántica.
  • QHE ha llevado al desarrollo del estándar de resistencia cuántica.
  • Históricamente, el QHE se ha limitado a las temperaturas criogénicas (helio líquido).

Objetivo del estudio:

  • Investigar la posibilidad de observar el efecto Hall cuántico a temperatura ambiente.
  • Explorar el potencial del grafeno para superar las limitaciones de temperatura en las mediciones QHE.
  • Evaluar la viabilidad de hacer que los estándares de resistencia QHE sean más ampliamente accesibles.

Principales métodos:

  • Utilizando grafeno de una sola capa (un material 2D) para experimentos QHE.
  • Realizar mediciones en condiciones que permitan el funcionamiento a temperatura ambiente.
  • Medición confiable del efecto Hall cuántico en el rango de materiales y temperaturas especificados.

Principales resultados:

  • El efecto Hall cuántico se midió de manera confiable en grafeno a temperatura ambiente.
  • Este logro elimina la necesidad de enfriamiento extremo previamente requerido para las observaciones de QHE.
  • Demostró el potencial para aplicaciones prácticas de QHE a temperatura ambiente.

Conclusiones:

  • El grafeno permite la observación del efecto Hall cuántico a temperatura ambiente, un avance significativo.
  • Este hallazgo allana el camino para la adopción generalizada de estándares de resistencia basados en QHE.
  • La investigación amplía la accesibilidad de la metrología cuántica más allá de laboratorios especializados.