14,542 research outputs found
Spherical solid-propellant rocket motor Patent
Spherical solid propellant rocket engine desig
Ground-based NIR emission spectroscopy of HD189733b
We investigate the K and L band dayside emission of the hot-Jupiter HD
189733b with three nights of secondary eclipse data obtained with the SpeX
instrument on the NASA IRTF. The observations for each of these three nights
use equivalent instrument settings and the data from one of the nights has
previously reported by Swain et al (2010). We describe an improved data
analysis method that, in conjunction with the multi-night data set, allows
increased spectral resolution (R~175) leading to high-confidence identification
of spectral features. We confirm the previously reported strong emission at
~3.3 microns and, by assuming a 5% vibrational temperature excess for methane,
we show that non-LTE emission from the methane nu3 branch is a physically
plausible source of this emission. We consider two possible energy sources that
could power non-LTE emission and additional modelling is needed to obtain a
detailed understanding of the physics of the emission mechanism. The validity
of the data analysis method and the presence of strong 3.3 microns emission is
independently confirmed by simultaneous, long-slit, L band spectroscopy of HD
189733b and a comparison star.Comment: ApJ accepte
Molecular Signatures in the Near Infrared Dayside Spectrum of HD 189733b
We have measured the dayside spectrum of HD 189733b between 1.5 and 2.5
microns using the NICMOS instrument on the Hubble Space Telescope. The emergent
spectrum contains significant modulation, which we attribute to the presence of
molecular bands seen in absorption. We find that water (H2O), carbon monoxide
(CO), and carbon dioxide (CO2) are needed to explain the observations, and we
are able to estimate the mixing ratios for these molecules. We also find
temperature decreases with altitude in the ~0.01 < P < ~1 bar region of the
dayside near-infrared photosphere and set an upper limit to the dayside
abundance of methane (CH4) at these pressures.Comment: 13 pages, 3 figures. accepted in Astrophysical Journal Letter
Late Holocene Pollen Stratigraphy in Four Northeastern United States Lakes
Four pollen diagrams from Maine, New York, and Pennsylvania provide fine resolution (40 or 80 years) records of vegetation change in northeastern United States during the past 2000 years. A long term increase in pollen accumulation rates (PAR) of Picea occurred at the three sites in Maine and New York. Around 1100 years ago, Tsuga and Fagus decreased and Quercus and Castanea increased at Ely Lake in northeastern Pennsylvania. Around 500 years ago, Tsuga and Fagus greatly decreased in Maine and northern New York, while in northeastern Pennsylvania there was an increase in Tsuga and Fagus and a decrease in Quercus and Castanea pollen. Non-arboreal PAR were negligible prior to the European settlement of the area, after which there was an abrupt increase in non-arboreal pollen types.Quatre diagrammes polliniques des Ă©tats du Maine, de New York et de Pennsylvanie illustrent de maniĂšre dĂ©taillĂ©e (40 ou 80 ans) les changements survenus dans la vĂ©gĂ©tation du nord-est des Ătats-Unis sur une pĂ©riode de 2000 ans. Les trois diagrammes des Ă©tats du Maine et de New York enregistrent un accroissement continu de l'influx pollinique (PAR) de Picea. Il y a environ 1100 ans, Tsuga et Fagus ont subi une diminution, tandis que Quercus et Castanea ont augmentĂ© Ă Ely Lake, dans le nord-est de la Pennsylvanie. Il y a 500 ans, Tsuga et Fagus ont considĂ©rablement diminuĂ© dans les Ă©tats du Maine et de New York, alors que leur reprĂ©sentation pollinique augmentait dans le nord-est de la Pennsylvanie et que Quercus et Castanea diminuaient. Les influx polliniques des herbacĂ©s Ă©taient minimes avant l'arrivĂ©e des EuropĂ©ens dans la rĂ©gion, aprĂšs quoi ces taxons ont connu une augmentation subite.Vier Pollen-Diagramme von Maine, New York und Pennsylvania geben detaillierte AuflĂŽsungs-Nachweise der Vegetationswechsel im Nordosten der Vereinigten Staaten wĂ hrend der letzten 2000 Jahre. Ein langfristiges Anwachsen der Pollen-Akkumulationsraten (PAR) von Picea trat an den drei Fundstellen in Maine und im Staat New York auf. Vor ungefĂ hr 11000 Jahren, nahmen am Ely-See in Nordost-Pennsylvania Tsuga and Fagus ab und Quercus und Castanea zu. Vor ungefĂ hr 500 Jahren nahmen in Maine und im Norden des staats New York Tsuga und Fagus stark ab, wĂ hrend in Nordost-Pennsylvania Tsuga und Fagus zunahmen und Quercus und Casfanea-Pollen abnahmen. Die nicht von BĂ umen stammenden PAR waren gering, bevor das Gebiet von EuropĂ ern besiedelt wurde, wĂ hrend danach die nicht von BĂ umen stammenden Pollenarten plĂŽtzlich anwuchsen
High-Calcium Limestone Deposits of Cumberland Valley, Pennsylvania
Author Institution: University of Minnesota, Minneapolis, MinnesotaHigh-calcium limestones occur in the upper part of the New Market Formation, of Lower Middle Ordovician age, in Franklin and Cumberland Counties, Pennsylvania. The high-calcium facies of the New Market Formation is represented by sublithographic limestone or vaughanite, which probably formed in quiet water, low-energy environments such as intershoal lagoons, or in protected bays similar to the present-day Florida Bay environment. Rapid facies changes are characteristic of the strata.
The better grade of stone lies in the upper 100 to 125 feet of the New Market Formation and averages 95-97% calcium carbonate. Silica and magnesia are about equal in amount as impurities.
One high-calcium belt extends from the Maryland state line through Chambersburg and Newville to beyond Carlisle. The strata in this belt are structurally complex, which requires careful field study and core-drilling prior to exploitation.
Stone suitable for blast-furnace flux is present in relatively large amounts, but stone for open-hearth use or portland cement requires more selective quarrying
Phase-dependent spectra in a driven two-level atom
We propose a method to observe phase-dependent spectra in resonance
fluorescence, employing a two-level atom driven by a strong coherent field and
a weak, amplitude-fluctuating field. The spectra are similar to those which
occur in a squeezed vacuum, but avoid the problem of achieving squeezing over a
solid angle. The system shows other interesting features, such as
pronounced gain without population inversion.Comment: 4 pages and 4 figures. Submitted to Phys. Rev. Let
The First Data Release of the KODIAQ Survey
We present and make publicly available the first data release (DR1) of the
Keck Observatory Database of Ionized Absorption toward Quasars (KODIAQ) survey.
The KODIAQ survey is aimed at studying galactic and circumgalactic gas in
absorption at high-redshift, with a focus on highly-ionized gas traced by OVI,
using the HIRES spectrograph on the Keck-I telescope. KODIAQ DR1 consists of a
fully-reduced sample of 170 quasars at 0.29 < z_em < 5.29 observed with HIRES
at high resolution (36,000 <= R <= 103,000) between 2004 and 2012. DR1 contains
247 spectra available in continuum normalized form, representing a sum total
exposure time of ~1.6 megaseconds. These co-added spectra arise from a total of
567 individual exposures of quasars taken from the Keck Observatory Archive
(KOA) in raw form and uniformly processed using a HIRES data reduction package
made available through the XIDL distribution. DR1 is publicly available to the
community, housed as a higher level science product at the KOA. We will provide
future data releases that make further QSOs, including those with pre-2004
observations taken with the previous-generation HIRES detectors.Comment: 14 pages, 9 figures, Submitted to AJ. All data products available at
the Keck Observatory Archive beginning May 15, 2015. URL:
https://koa.ipac.caltech.edu/applications/KODIA
No effect of arm exercise on diaphragmatic fatigue or ventilatory constraint in Paralympic athletes with cervical spinal cord injury
Cervical spinal cord injury (CSCI) results in a decrease in the capacity of the lungs and chest wall for pressure, volume, and airflow generation. We asked whether such impairments might increase the potential for exercise-induced diaphragmatic fatigue and mechanical ventilatory constraint in this population. Seven Paralympic wheelchair rugby players (mean ± SD peak oxygen uptake = 16.9 ± 4.9 ml·kgâ1·minâ1) with traumatic CSCI (C5âC7) performed arm-crank exercise to the limit of tolerance at 90% of their predetermined peak work rate. Diaphragm function was assessed before and 15 and 30 min after exercise by measuring the twitch transdiaphragmatic pressure (Pdi,tw) response to bilateral anterolateral magnetic stimulation of the phrenic nerves. Ventilatory constraint was assessed by measuring the tidal flow volume responses to exercise in relation to the maximal flow volume envelope. Pdi,tw was not different from baseline at any time after exercise (unpotentiated Pdi,tw = 19.3 ± 5.6 cmH2O at baseline, 19.8 ± 5.0 cmH2O at 15 min after exercise, and 19.4 ± 5.7 cmH2O at 30 min after exercise; P = 0.16). During exercise, there was a sudden, sustained rise in operating lung volumes and an eightfold increase in the work of breathing. However, only two subjects showed expiratory flow limitation, and there was substantial capacity to increase both flow and volume (<50% of maximal breathing reserve). In conclusion, highly trained athletes with CSCI do not develop exercise-induced diaphragmatic fatigue and rarely reach mechanical ventilatory constraint
Quantum interference in optical fields and atomic radiation
We discuss the connection between quantum interference effects in optical
beams and radiation fields emitted from atomic systems. We illustrate this
connection by a study of the first- and second-order correlation functions of
optical fields and atomic dipole moments. We explore the role of correlations
between the emitting systems and present examples of practical methods to
implement two systems with non-orthogonal dipole moments. We also derive
general conditions for quantum interference in a two-atom system and for a
control of spontaneous emission. The relation between population trapping and
dark states is also discussed. Moreover, we present quantum dressed-atom models
of cancellation of spontaneous emission, amplification on dark transitions,
fluorescence quenching and coherent population trapping.Comment: To be published in Journal of Modern Optics Special Issue on Quantum
Interferenc
- âŠ