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Fabry–Perot interferometers have stimulated numerous scientific and technical applications ranging from high-resolution spectroscopy over metrology, optical filters, to interfaces of light and matter at the quantum limit and more. End facet machining of optical fibers has enabled the miniaturization of optical Fabry–Perot cavities. Integration with fiber wave guide technology allows for small yet open devices with favorable scaling properties including mechanical stability and compact mode geometry. These fiber Fabry–Perot cavities (FFPCs) are stimulating extended applications in many fields including cavity quantum electrodynamics, optomechanics, sensing, nonlinear optics and more. Here we summarize the state of the art of devices based on FFPCs, provide an overview of applications and conclude with expected further research activities. [ABSTRACT FROM AUTHOR]

We report experimental observations of polygon-shaped patterns formed in a vertically vibrated bed of circular cross-section. A phase map is determined, showing that the polygon pattern is established for Γ = A(2 πf)/ g ≳ 10 . The sensitivity of the polygon structure to bed parameters was tested by studying beds of different particle sizes and fill levels. It was hypothesized that the polygon pattern observed in cylindrical beds is the corresponding pattern to the formation of arches in square-shaped beds. The close relationship between these two patterns was demonstrated by two observations: i) the radii of the arches of a corresponding square bed and the inner radius of the cylindrical bed were found to be very similar and ii) the boundary lengths of the two patterns were in good agreement. [ABSTRACT FROM AUTHOR]

We report on the study of the momentum distribution of a one-dimensional Bose gas in an optical lattice. From the momentum distribution we extract the condensed fraction of the gas and thereby measure the depletion of the condensate and compare it with a theoretical estimate. We have measured the coherence length of the gas for systems with average occupation n¯>1 and n¯>1 per lattice site. [ABSTRACT FROM AUTHOR]

In this paper a new numerical method for the multifrequency analysis of the three-dimensional Helmholtz equation is introduced. The collocation boundary element method (BEM) is used for the discretisation of the problem. The identity of the Fourier transform with respect to the wave number is applied to the matrix of the resulting linear system. The analytical form and some important properties are derived. Some numerical examples for the solution are presented. [ABSTRACT FROM AUTHOR]

We describe the measurement of the line width of an atom laser beam extracted from a Bose–Einstein condensate. Using a novel magnetic resonance imaging technique, we find that the energy width of the atom laser beam is Fourier-limited by the duration of the output-coupling process. [ABSTRACT FROM AUTHOR]

The reactivity of (−)-ephedrine ( 2) and (+)-norpseudoephedrine ( 3) towards the amidacetals 1 a/b has been studied. Both 2 and 3 were acetylated resp. formylated at first at the amino group. Nevertheless, derivatives of 2 and 3 possessing a trisubstituted amino group react with 1 a in a [3.3] sigmatopic rearrangement to ortho substituted dimethylcarbamoylmethyl derivatives. By subsequent reduction with lithiumaluminiumhydride the aromatic compounds 8, 13, and 18 with two aminoethyl groups are easily available. In contrast to these results 1 b did not furnish any rearrangement products. [ABSTRACT FROM AUTHOR]

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We report an experimental investigation of two-particle correlations between neutral atoms in a Hanbury Brown and Twiss experiment. Both an atom laser beam and a pseudo-thermal atomic beam are extracted from a Bose–Einstein condensate and the atom flux is measured with a single atom counter. We determine the conditional and the unconditional detection probabilities for the atoms in the beam and find good agreement with the theoretical predictions. [ABSTRACT FROM AUTHOR]

The density of wood is a key indicator of the carbon investment strategies of trees, impacting productivity and carbon storage. Despite its importance, the global variation in wood density and its environmental controls remain poorly understood, preventing accurate predictions of global forest carbon stocks. Here we analyse information from 1.1 million forest inventory plots alongside wood density data from 10,703 tree species to create a spatially explicit understanding of the global wood density distribution and its drivers. Our findings reveal a pronounced latitudinal gradient, with wood in tropical forests being up to 30% denser than that in boreal forests. In both angiosperms and gymnosperms, hydrothermal conditions represented by annual mean temperature and soil moisture emerged as the primary factors influencing the variation in wood density globally. This indicates similar environmental filters and evolutionary adaptations among distinct plant groups, underscoring the essential role of abiotic factors in determining wood density in forest ecosystems. Additionally, our study highlights the prominent role of disturbance, such as human modification and fire risk, in influencing wood density at more local scales. Factoring in the spatial variation of wood density notably changes the estimates of forest carbon stocks, leading to differences of up to 21% within biomes. Therefore, our research contributes to a deeper understanding of terrestrial biomass distribution and how environmental changes and disturbances impact forest ecosystems., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)