2,085 research outputs found
Empirical metallicity-dependent calibrations of effective temperature against colours for dwarfs and giants based on interferometric data
We present empirical metallicity-dependent calibrations of effective
temperature against colours for dwarfs of luminosity classes IV and V and for
giants of luminosity classes II and III, based on a collection from the
literature of about two hundred nearby stars with direct effective temperature
measurements of better than 2.5 per cent. The calibrations are valid for an
effective temperature range 3,100 - 10,000 K for dwarfs of spectral types M5 to
A0 and 3,100 - 5,700 K for giants of spectral types K5 to G5. A total of
twenty-one colours for dwarfs and eighteen colours for giants of bands of four
photometric systems, i.e. the Johnson (), the Cousins
(), the Sloan Digital Sky Survey (SDSS, ) and the Two
Micron All Sky Survey (2MASS, ), have been calibrated. Restricted
by the metallicity range of the current sample, the calibrations are mainly
applicable for disk stars ([Fe/H]). The normalized percentage
residuals of the calibrations are typically 2.0 and 1.5 per cent for dwarfs and
giants, respectively. Some systematic discrepancies at various levels are found
between the current scales and those available in the literature (e.g. those
based on the infrared flux method IRFM or spectroscopy). Based on the current
calibrations, we have re-determined the colours of the Sun. We have also
investigated the systematic errors in effective temperatures yielded by the
current on-going large scale low- to intermediate-resolution stellar
spectroscopic surveys. We show that the calibration of colour ()
presented in the current work provides an invaluable tool for the estimation of
stellar effective temperature for those on-going or upcoming surveys.Comment: 28 pages, 19 figures, 8 tables, accepted for publication in MNRA
Amide Activation by Tf2O: Reduction of Amides to Amines by NaBH4 under Mild Conditions
An expeditious and practical method for the reduction of amides to amines is reported. The method is consisted of activation of amides with Tf2O followed by reduction with sodium borohydride in THF at room temperature. Various amides/lactams gave the corresponding amines in good to excellent yields, even with hindered amides and secondary amides. This method also presents other advantages such as TBDPS-group tolerance, short reaction time, simple workup and purification procedure.NSF of China [20832005]; National Basic Research Program (973 Program) of China [2010CB833200
Spiniform phase-encoded metagratings entangling arbitrary rational-order orbital angular momentum
Quantum entanglements between integer-order and fractional-order orbital angular momentums (OAMs) have been previously discussed.
However, the entangled nature of arbitrary rational-order OAM has long been considered a myth due to the absence of
an effective strategy for generating arbitrary rational-order OAM beams. Therefore, we report a single metadevice comprising a
bilaterally symmetric grating with an aperture, creating optical beams with dynamically controllable OAM values that are continuously
varying over a rational range. Due to its encoded spiniform phase, this novel metagrating enables the production of an
average OAM that can be increased without a theoretical limit by embracing distributed singularities, which differs significantly
from the classic method of stacking phase singularities using fork gratings. This new method makes it possible to probe the
unexplored niche of quantum entanglement between arbitrarily defined OAMs in light, which could lead to the complex manipulation
of microparticles, high-dimensional quantum entanglement and optical communication. We show that quantum coincidence
based on rational-order OAM-superposition states could give rise to low cross-talks between two different states that
have no significant overlap in their spiral spectra. Additionally, future applications in quantum communication and optical micromanipulation
may be found
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