1,143 research outputs found
Photothermal effects in ultra-precisely stabilized tunable microcavities
We study the mechanical stability of a tunable high-finesse microcavity under
ambient conditions and investigate light-induced effects that can both suppress
and excite mechanical fluctuations. As an enabling step, we demonstrate the
ultra-precise electronic stabilization of a microcavity. We then show that
photothermal mirror expansion can provide high-bandwidth feedback and improve
cavity stability by almost two orders of magnitude. At high intracavity power,
we observe self-oscillations of mechanical resonances of the cavity. We explain
the observations by a dynamic photothermal instability, leading to parametric
driving of mechanical motion. For an optimized combination of electronic and
photothermal stabilization, we achieve a feedback bandwidth of kHz and a
noise level of m rms
On the nature of the fast moving star S2 in the Galactic Center
We analyze the properties of the star S2 orbiting the supermassive black hole
at the center of the Galaxy. A high quality SINFONI H and K band spectrum
obtained from coadding 23.5 hours of observation between 2004 and 2007 reveals
that S2 is an early B dwarf (B0-2.5V). Using model atmospheres, we constrain
its stellar and wind properties. We show that S2 is a genuine massive star, and
not the core of a stripped giant star as sometimes speculated to resolve the
problem of star formation so close to the supermassive black hole. We give an
upper limit on its mass loss rate, and show that it is He enriched, possibly
because of the presence of a magnetic field.Comment: 4 pages, 5 figures, ApJ letters accepte
Comparative flame structure investigation of normal and inverse turbulent non-premixed oxy-fuel flames using experimentally recorded and numerically predicted Rayleigh and OH-PLIF signals
The structure and characteristics of a turbulent inverse and normal oxy-fuel diffusion flame are investigated. Previous investigations reported in the literature looked at flame characteristics of laminar inverse diffusion flames and their differences to normal diffusion flames. Only few investigations are reported for turbulent inverse diffusion flames and they did not compare the results to the corresponding normal configuration. The present study uses a combined experimental and numerical approach to compare and analyze a turbulent non-premixed inverse oxy-fuel and a corresponding normal flame, both are non-piloted. Measurements were conducted using simultaneously recorded planar Rayleigh scattering and OH-LIF signals. Due to the significant variation of the effective Rayleigh cross section in mixture fraction space and the unknown OH quenching contributions, a comparison of derived quantities such as temperature and OH mole fraction is not possible. Therefore, the Rayleigh and OH-LIF signals were incorporated in the LES flamelet/progress variable approach used here. This allows for a direct comparison of experimentally recorded and numerically predicted Rayleigh and OH-PLIF signals for the flame structure analysis, which includes the joint PDF of both quantities. The two flames are compared in terms of the local flame structure. In addition, differences in the mixing field and especially in the location of turbulent/non-turbulent interface are investigated
Caracterización térmica de placas de yeso con material de cambio de fase incorporado
En este trabajo se demuestra la idoneidad de incorporar materiales de cambio de fase en placas de yeso para incrementar su capacidad de almacenamiento térmico. Para ello se evalúa y se compara la capacidad de almacenamiento térmico, de diferentes elementos constructivos cuyo uso y aplicación es similar a la de las placas de yeso: trasdosado y tabique separador. Se ha disenado y puesto en funcionamiento una instalación experimental que simula las condiciones de contorno que se producen en una estancia donde estén instalados los diferentes materiales y sistemas constructivos. Se ha estudiado la influencia de diferentes para´metros y variables del sistema (temperatura de trabajo, velocidad del aire, presentación de los materiales de cambio de fase, ubicación en el edificio,…), para constituir un sistema de almacenamiento de calor latente, que, complementado con estrategias pasivas (captación solar, ventilación natural), reduzca las necesidades de consumo energético para la climatización de edificios. Se obtiene que las placas de yeso con un 45% en peso de material de cambio de fase es capaz de almacenar en 1,5 cm de espesor, 5 veces la energÃa térmica de un panel de yeso laminado con el mismo espesor, y la misma cantidad que 1/2 pie de fábrica ladrillo hueco sencillo, en el rango de temperaturas próximas a la de confort (20-30 ºC), manteniendo las propiedades fÃsicas y mecánicas exigidas en la normativa
Self-localization of magnon Bose-Einstein condensates in the ground state and on excited levels: from harmonic to box-like trapping potential
Long-lived coherent spin precession of 3He-B at low temperatures around 0.2
Tc is a manifestation of Bose-Einstein condensation of spin-wave excitations or
magnons in a magnetic trap which is formed by the order-parameter texture and
can be manipulated experimentally. When the number of magnons increases, the
orbital texture reorients under the influence of the spin-orbit interaction and
the profile of the trap gradually changes from harmonic to a square well, with
walls almost impenetrable to magnons. This is the first experimental example of
Bose condensation in a box. By selective rf pumping the trap can be populated
with a ground-state condensate or one at any of the excited energy levels. In
the latter case the ground state is simultaneously populated by relaxation from
the exited level, forming a system of two coexisting condensates.Comment: 4 pages, 5 figure
A microfabricated surface ion trap on a high-finesse optical mirror
A novel approach to optics integration in ion traps is demonstrated based on
a surface electrode ion trap that is microfabricated on top of a dielectric
mirror. Additional optical losses due to fabrication are found to be as low as
80 ppm for light at 422 nm. The integrated mirror is used to demonstrate light
collection from, and imaging of, a single 88 Sr+ ion trapped m
above the mirror.Comment: 4 pages, 3 figure
The Rigidly Rotating Magnetosphere of Sigma Ori E
We attempt to characterize the observed variability of the magnetic
helium-strong star sigma Ori E in terms of a recently developed rigidly
rotating magnetosphere model. This model predicts the accumulation of
circumstellar plasma in two co-rotating clouds, situated in magnetohydrostatic
equilibrium at the intersection between magnetic and rotational equators. We
find that the model can reproduce well the periodic modulations observed in the
star's light curve, H alpha emission-line profile, and longitudinal field
strength, confirming that it furnishes an essentially correct, quantitative
description of the star's magnetically controlled circumstellar environment.Comment: 4 pages, 3 figures, accepted by Ap
Cryogenic platform for coupling color centers in diamond membranes to a fiberbased microcavity
We operate a fiberbased cavity with an inserted diamond membrane containing
ensembles of silicon vacancy centers (SiV) at cryogenic temperatures K. The setup, sample fabrication and spectroscopic characterization is
described, together with a demonstration of the cavity influence by the Purcell
effect. This paves the way towards solid state qubits coupled to optical
interfaces as long-lived quantum memories.Comment: 10 pages, 6 figure
Cryogenic platform for coupling color centers in diamond membranes to a fiber-based microcavity
We operate a fiber-based cavity with an inserted diamond membrane containing ensembles of silicon vacancy centers (SiV) at cryogenic temperatures ≥4 K. The setup, sample fabrication and spectroscopic characterization are described, together with a demonstration of the cavity influence by the Purcell effect. This paves the way towards solid-state qubits coupled to optical interfaces as long-lived quantum memories
2009 wheat variety comparison
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