How to characterize the nonlinear amplifier?

The conception of the amplification of the coherent field is formulated. The definition of the coefficient of the amplification as the relation between the mean value of the field at the output to the value at the input and the definition of the noise as the difference between the number of photons in the output mode and square of the modulus of the mean value of the output amplitude are considered. Using a simple example it is shown that by these definitions the noise of the nonlinear amplifier may be less than the noise of the ideal linear amplifier of the same amplification coefficient. Proposals to search another definition of basic parameters of the nonlinear amplifiers are discussed. This definition should enable us to formulate the universal fundamental lower limit of the noise which should be valid for linear quantum amplifiers as for nonlinear ones

Wavelike Structures in the Turbulent Layer During the Morning Development of Convection at Dome C, Antarctica

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Progress in observing and modelling the urban boundary layer

The urban boundary layer (UBL) is the part of the atmosphere in which most of the planet’s population now lives, and is one of the most complex and least understood microclimates. Given potential climate change impacts and the requirement to develop cities sustainably, the need for sound modelling and observational tools becomes pressing. This review paper considers progress made in studies of the UBL in terms of a conceptual framework spanning microscale to mesoscale determinants of UBL structure and evolution. Considerable progress in observing and modelling the urban surface energy balance has been made. The urban roughness sub-layer is an important region requiring attention as assumptions about atmospheric turbulence break down in this layer and it may dominate coupling of the surface to the UBL due to its considerable depth. The upper 90% of the UBL (mixed and residual layers) remains under-researched but new remote sensing methods and high resolution modelling tools now permit rapid progress. Surface heterogeneity dominates from neighbourhood to regional scales and should be more strongly considered in future studies. Specific research priorities include humidity within the UBL, high-rise urban canopies and the development of long-term, spatially extensive measurement networks coupled strongly to model development

Wind and turbulence in the urban boundary layer analysis from acoustic remote sensing data and fit to analytical relations

Mittlere saisonale Profile der Windgeschwindigkeit, Standardabweichung der Vertikalgeschwindigkeit und der Turbulenzintensität aus SODAR-Messungen in drei unterschiedlich großen Städten, Moskau, Hannover und Linz, werden mit analytischen Annäherungen für die Prandtl- und die Ekman Schicht verglichen. Typische Eigenschaften für diese Profile in Städten sind eine stärkere Zunahme desWindgeschwindigkeitsprofils mit der Höhe, höhere Turbulenzintensitäten und die Zunahme der Turbulenz mit der Höhe. Der analytische Ansatz, welcher von ETLING (2002) für die Beschreibung des Windprofils in der gesamten Grenzschicht vorgeschlagen wird, wird in der Prandtl Schicht durch eine Korrekturfunktion zur Berücksichtigung der atmosphärischen Stabilität erweitert. Die erweiterte Profilbeschreibung ermöglicht die beste Annäherung an städtische Windprofile in den untersten 500 m über Grund

Stable Surface-Based Turbulent Layer During the Polar Winter at Dome C, Antarctica: Sodar and In Situ Observations

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