494 research outputs found
Cryogenic spectroscopy of ultra-low density colloidal lead chalcogenide quantum dots on chip-scale optical cavities towards single quantum dot near-infrared cavity QED
We present evidence of cavity quantum electrodynamics from a sparse density
of strongly quantum-confined Pb-chalcogenide nanocrystals (between 1 and 10)
approaching single-dot levels on moderately high-Q mesoscopic silicon optical
cavities. Operating at important near-infrared (1500-nm) wavelengths, large
enhancements are observed from devices and strong modifications of the QD
emission are achieved. Saturation spectroscopy of coupled QDs is observed at
77K, highlighting the modified nanocrystal dynamics for quantum information
processing.Comment: * new additional figures and text * 10 pages, 5 figure
Temperature-tuning of near-infrared monodisperse quantum dot solids at 1.5 um for controllable Forster energy transfer
We present the first time-resolved cryogenic observations of Forster energy
transfer in large, monodisperse lead sulphide quantum dots with ground state
transitions near 1.5 um (0.83 eV), in environments from 160 K to room
temperature. The observed temperature-dependent dipole-dipole transfer rate
occurs in the range of (30-50 ns)^(-1), measured with our confocal
single-photon counting setup at 1.5 um wavelengths. By temperature-tuning the
dots, 94% efficiency of resonant energy transfer can be achieved for donor
dots. The resonant transfer rates match well with proposed theoretical models
Demonstration of an air-slot mode-gap confined photonic crystal slab nanocavity with ultrasmall mode volumes
We demonstrate experimentally an air-slot mode-gap photonic crystal cavity
with quality factor of 15,000 and modal volume of 0.02 cubic wavelengths, based
on the design of an air-slot in a width-modulated line-defect in a photonic
crystal slab. The origin of the high Q air-slot cavity mode is the mode-gap
effect from the slotted photonic crystal waveguide mode with negative
dispersion. The high Q cavities with ultrasmall mode volume are important for
applications such as cavity quantum electrodynamics, nonlinear optics and
optical sensing.Comment: 12 pages, 4 figure
Deterministic integrated tuning of multi-cavity resonances and phase for slow-light in coupled photonic crystal cavities
We present the integrated chip-scale tuning of multiple photonic crystal
cavities. The optimized implementation allows effective and precise tuning of
multiple cavity resonances (up to ~1.60 nm/mW) and inter-cavity phase (~ 0.038
pi/mW) by direct local temperature tuning on silicon nanomembranes. Through
designing the serpentine metal electrodes and careful electron-beam alignment
to avoid cavity mode overlap, the coupled photonic crystal L3 cavities preserve
their high quality factors. The deterministic resonance and phase control
enables switching between the all-optical analogue of
electromagnetically-induced-transparency (EIT) to flat-top filter lineshapes,
with future applications of trapping photons/photonic transistors and
optoelectronic modulators
New distances to RAVE stars
Probability density functions are determined from new stellar parameters for
the distance moduli of stars for which the RAdial Velocity Experiment (RAVE)
has obtained spectra with S/N>=10. Single-Gaussian fits to the pdf in distance
modulus suffice for roughly half the stars, with most of the other half having
satisfactory two-Gaussian representations. As expected, early-type stars rarely
require more than one Gaussian. The expectation value of distance is larger
than the distance implied by the expectation of distance modulus; the latter is
itself larger than the distance implied by the expectation value of the
parallax. Our parallaxes of Hipparcos stars agree well with the values measured
by Hipparcos, so the expectation of parallax is the most reliable distance
indicator. The latter are improved by taking extinction into account. The
effective temperature absolute-magnitude diagram of our stars is significantly
improved when these pdfs are used to make the diagram. We use the method of
kinematic corrections devised by Schoenrich, Binney & Asplund to check for
systematic errors for general stars and confirm that the most reliable distance
indicator is the expectation of parallax. For cool dwarfs and low-gravity
giants tends to be larger than the true distance by up to 30 percent. The
most satisfactory distances are for dwarfs hotter than 5500 K. We compare our
distances to stars in 13 open clusters with cluster distances from the
literature and find excellent agreement for the dwarfs and indications that we
are over-estimating distances to giants, especially in young clusters.Comment: 20 pages accepted by MNRAS. Minor changes to the submitted versio
WISE/NEOWISE Observations of Comet 103P/Hartley 2
We report results based on mid-infrared photometry of comet 103P/Hartley 2 taken during 2010 May 4-13 (when the comet was at a heliocentric distance of 2.3 AU, and an observer distance of 2.0 AU) by the Wide-field Infrared Survey Explorer. Photometry of the coma at 22 Ī¼m and data from the University of Hawaii 2.2 m telescope obtained on 2010 May 22 provide constraints on the dust particle size distribution, d log n/d log m, yielding power-law slope values of alpha = ā0.97 Ā± 0.10, steeper than that found for the inbound particle fluence during the Stardust encounter of comet 81P/Wild 2. The extracted nucleus signal at 12 Ī¼m is consistent with a body of average spherical radius of 0.6 Ā± 0.2 km (one standard deviation), assuming a beaming parameter of 1.2. The 4.6 Ī¼m band signal in excess of dust and nucleus reflected and thermal contributions may be attributed to carbon monoxide or carbon dioxide emission lines and provides limits and estimates of species production. Derived carbon dioxide coma production rates are 3.5(Ā± 0.9) Ć 10^(24) molecules per second. Analyses of the trail signal present in the stacked image with an effective exposure time of 158.4 s yields optical-depth values near 9 Ć 10^(ā10) at a delta mean anomaly of 0.2 deg trailing the comet nucleus, in both 12 and 22 Ī¼m bands. A minimum chi-squared analysis of the dust trail position yields a beta-parameter value of 1.0 Ć 10^(ā4), consistent with a derived mean trail-grain diameter of 1.1/Ļ cm for grains of Ļ g cm^(ā3) density. This leads to a total detected trail mass of at least 4 Ć 10^(10) Ļ kg
A Century of Grading Research: Meaning and Value in the Most Common Educational Measure
Grading refers to the symbols assigned to individual pieces of student work or to composite measures of student performance on report cards. This review of over 100 years of research on grading considers five types of studies: (a) early studies of the reliability of grades, (b) quantitative studies of the composition of K-12 report card grades, (c) survey and interview studies of teachersā perceptions of grades, (d) studies of standards-based grading, and (e) grading in higher education. Early 20th century studies generally condemned teachersā grades as unreliable. More recent studies of the relationships of grades to tested achievement and survey studies of teachersā grading practices and beliefs suggest that grades assess a multidimensional construct containing both cognitive and non-cognitive factors reflecting what teachers value in student work. Implications for future research and for grading practices are discussed
1934: Abilene Christian College Bible Lectures - Full Text
INTRODUCTION
The theme for the Lectures for 1934, āThe New Testament Church in History,ā is a very timely one and follows naturally the theme of the 1933 Lectures, āThe Church We Read About in the New Testament.ā There is no subject that is so vital in our work as Christians today as a proper understanding of the great spiritual kingdom of our Savior, the church which was built by Jesus Christ. It is a hard lesson to teach because all people are so dull of hearing concerning things spiritual. Just as Nicodemus marveled when the Christ told him of the spiritual kingdom so do people today wonder and marvel when they are told that there is only one great church, the spiritual kingdom of our Lord and Savior Jesus Christ, and that all the saved of earth belong to that church and that belonging to anything else profits little, and is unnecessary. Not only are numbers of denominational churches and people who have no religious affiliation ignorant of the true meaning of the church, but even those who claim to be members of the one body are lacking in understanding concerning the kingdom of Christ. It is therefore the purpose of the Abilene College Lectures last year, this year and next year to arouse a greater interest in the study and the teaching of this very vital matter. In this particular volume much valuable information is brought together on the trials and struggles of the church from its foundations to the present. The speakers have made careful preparation on their subjects and have given lessons that should prove helpful to all who desire to have a better understanding of the church. Our prayer is that these Lectures may be read by many and that they may do much good in the name of the Christ.
Jas. F. Cox,President, Abilene Christian College.
Nov. 6, 1934
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