196,132 research outputs found
Characterization and calibration of a Fourier-transform spectrometer using a laser frequency comb
No full textWe have used a laser frequency comb with a repetition frequency of rep≈1 GHz to measure the drift and dispersion of a Fourier-transform spectrometer (FTS). We used the electronic measurements of rep and CEO to create a reference line list. We measured 28 interferograms and computed the phase and power spectra. The analysis of the interferograms and phase spectra allowed for compensation of several spectroscopic artifacts. In the computed power spectra, we detected ∼64.000 suitable lines in the near-infrared bandwidth Δ=308.79–374.74 THz. The residual dispersion of the FTS can be described by two factors, a linear dispersion and a constant offset. Both are highly correlated and need to be computed simultaneously. The factors were computed from the comparison of a reference with measured line lists. The linear dispersion factor is found to be varying on the order of 10−8 Hz/Hz, while the constant offset is of the order of 107 Hz. Using two factors for calibration, the difference between the reference and the measured line list can be removed completely with an uncertainty of ∼65 kHz corresponding to a precision of 0.5·10−9 Hz/Hz
A systematic approach to determining the properties of an iodine absorption cell for high-precision radial velocity measurements
No full textAbsorption cells filled with diatomic iodine are frequently employed as wavelength reference
for high-precision stellar radial velocity determination due to their long-term stability and
low cost. Despite their wide-spread usage in the community, there is little documentation on
how to determine the ideal operating temperature of an individual cell. We have developed a
new approach to measuring the effective molecular temperature inside a gas absorption cell
and searching for effects detrimental to a high-precision wavelength reference, utilizing the
Boltzmann distribution of relative line depths within absorption bands of single vibrational
transitions. With a high-resolution Fourier transform spectrometer, we took a series of 632
spectra at temperatures between 23 and 66◦C. These spectra provide a sufficient basis to test the
algorithm and demonstrate the stability and repeatability of the temperature determination via
molecular lines on a single iodine absorption cell. The achievable radial velocity precision σ RV
is found to be independent of the cell temperature and a detailed analysis shows a wavelength
dependence, which originates in the resolving power of the spectrometer in use and the signal-
to-noise ratio. Two effects were found to cause apparent absolute shifts in radial velocity, a
temperature-induced shift of the order of ∼1 m s−1 K−1 and a more significant effect resulting
in abrupt jumps of ≥50 m s−1 is determined to be caused by the temperature crossing the dew
point of the molecular iodin
A comparison between FTIR spectra from HUKE and SH-SY5Y cell lines grown on different substrates
No full textIn recent years, Fourier Transform Infrared (FTIR) micro-spectroscopy has shown promising potential in medical diagnostics at the cellular level. In fact, FTIR spectra can provide information related to DNA, protein, and lipid content and how such a content changes when a pathological state arises. Most of these information is included in the so-called fingerprint region (1000–1800 cm−1), consisting of several spectral peaks related to vibrational modes occurring inside cellular components. Unfortunately, the slides commonly used in cytology (as the glass microscopy slides and coverslips) are opaque to IR radiation in the fingerprint region, whereas they are transparent for wavenumber values larger than 2000 cm−1, where few and broad spectral absorption bands, mainly due to lipids and proteins, are present. Nonetheless, here we show that FTIR spectra performed in the high wavenumber range 2750–3000 cm−1 can be used to discriminate two different types of cells, one from a normal cell line (Human Keratinocyte, HUKE) and the other from a cancer one (SH-SY5Y). The spectra are discriminated by means of their Principal Component Analysis, according to the PC1 component, and by means of ratiometric analysis, according to the ratio of the intensity of the peak at 2956 cm−1 and that of the peak at 2924 cm−1. The PC1 score values of the HUKE are statistically different from the PC1 score values of SH-SY5Y, whereas the intensity ratio results larger for SH-SY5Y than for HUKE cells. Such results occur for different substrates over which the cells have been grown, including the thick glass slides used for cytological analysis. This result is a further step toward the application of FTIR microspectroscopy in the cytological routine diagnosis
Radial velocity observations of the 2015 Mar. 20 eclipse A benchmark Rossiter-McLaughlin curve with zero free parameters
No full textSpectroscopic observations of a solar eclipse can provide unique information for solar
and exoplanet research; the huge amplitude of the Rossiter-McLaughlin (RM) effect during
solar eclipse and the high precision of solar radial velocities (RVs) allow detailed
comparison between observations and RV models, and they provide information about the
solar surface and about spectral line formation that are otherwise difficult to obtain. On
March 20, 2015, we obtained 159 spectra of the Sun as a star with the solar telescope and
the Fourier Transform Spectrograph at the Institut für Astrophysik Göttingen, 76 spectra
were taken during partial solar eclipse. We obtained RVs using I2 as wavelength
reference and determined the RM curve with a peak-to-peak amplitude of almost
1.4 km s-1 at
typical RV precision better than 1 m s-1. We modeled the disk-integrated solar RVs using
well-determined parameterizations of solar surface velocities, limb darkening, and
information about convective blueshift from 3D magnetohydrodynamic simulations. We confirm
that convective blueshift is crucial to understand solar RVs during eclipse. Our best
model reproduced the observations to within a relative precision of 10% with residuals
lower than 30 m s-1. We cross-checked parameterizations of velocity fields
using a Dopplergram from the Solar Dynamics Observatory and conclude that disk-integration
of the Dopplergram does not provide correct information about convective blueshift
necessary for m s-1
RV work. As main limitation for modeling RVs during eclipses, we identified limited
knowledge about convective blueshift and line shape as functions of solar limb angle. We
suspect that our model line profiles are too shallow at limb angles larger than
μ =
0.6, resulting in incorrect weighting of the
velocities across the solar disk. Alternative explanations cannot be excluded, such as
suppression of convection in magnetic areas and undiscovered systematics during eclipse
observations. To make progress, accurate observations of solar line profiles across the
solar disk are suggested. We publish our RVs taken during solar eclipse as a benchmark
curve for codes calculating the RM effect and for models of solar surface velocities and
line profiles
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States" By M. Carey.
No full text"Reflections on the subject of Emigration from Europe with a view to Settlement in the United States: containing bried sketches of the moral and political character of those states.
By M. Carey, member of the American philosophical, and of the American Antiquarian Society, and author of The Olive Branch, Cindiciae Hibernicae, essays on banking, on political economy, and on internal improvement.
To which are now added the English editor's comments on the subject; together with Important Advice to Emigrants, and Cautions Against Impositions Practiced in the Outports
Validation of the ESPRESSO wavelength calibration using iodine absorption cell spectra
No full textABSTRACT High-quality wavelength calibration is crucial for science cases like radial-velocity studies of exoplanets, the search for a possible variation of fundamental constants, and the redshift drift experiment. However, for state-of-the-art spectrographs, it has become difficult to verify the wavelength calibration on sky because no astrophysical source provides spectra with sufficiently stable or accurate wavelength information. We therefore propose to use iodine absorption cells to validate the wavelength calibration. Observing a bright and featureless star through the iodine cell emulates an astrophysical target with exactly known spectral features that can be analysed like any other science target, allowing to verify the wavelength calibration derived from the internal calibration sources and to identify systematics in the data processing. As demonstration, we temporarily installed an absorption cell at ESPRESSO. Employing a full forward modelling approach of the spectrum, including the instrumental line-spread function, we demonstrate wavelength calibration accuracy at the level of a few . We also show that wavelength measurements do depend on the geometry of the light-injection into the spectrograph fibers. This highlights the importance of probing exactly the same light path as science targets, something not possible with internal calibration sources alone. We also demonstrate excellent radial-velocity stability at the {{< 20\, \mathrm{cm\,s^{-1}}}} level in a full end-to-end fashion, from sky to data product. Our study therefore showcases the great potential of absorption cells for the verification and long-term monitoring of the wavelength calibration as well as the unique insights they can provide
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Dr. Glendon Swarthout
No full textHosted by Roger M. Busfield, MSU Assistant Professor of Speech and Theater, Meet the Author is designed to introduce a general audience to a contemporary author and their work through in-depth interviews. This episode features a conversation between Dr. Glendon Swarthout, prolific author and English professor at MSU, and assistant professors Sam S. Baskett and Theodore B. Strandness
Simulation of thermal plant optimization and hydraulic aspects of thermal distribution loops for large campuses
No full textFollowing an introduction, the author describes Texas A&M University and its utilities system. After that, the author presents how to construct simulation models for chilled water and heating hot water distribution systems. The simulation model was used in a $2.3 million Ross Street chilled water pipe replacement project at Texas A&M University. A second project conducted at the University of Texas at San Antonio was used as an example to demonstrate how to identify and design an optimal distribution system by using a simulation model. The author found that the minor losses of these closed loop thermal distribution systems are significantly higher than potable water distribution systems. In the second part of the report, the author presents the latest development of software called the Plant Optimization Program, which can simulate cogeneration plant operation, estimate its operation cost and provide optimized operation suggestions. The author also developed detailed simulation models for a gas turbine and heat recovery steam generator and identified significant potential savings. Finally, the author also used a steam turbine as an example to present a multi-regression method on constructing simulation models by using basic statistics and optimization algorithms. This report presents a survey of the author??s working experience at the Energy Systems Laboratory (ESL) at Texas A&M University during the period of January 2002 through March 2004. The purpose of the above work was to allow the author to become familiar with the practice of engineering. The result is that the author knows how to complete a project from start to finish and understands how both technical and nontechnical aspects of a project need to be considered in order to ensure a quality deliverable and bring a project to successful completion. This report concludes that the objectives of the internship were successfully accomplished and that the requirements for the degree of Degree of Engineering have been satisfied
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