36,175 research outputs found
Following the relaxation dynamics of photoexcited aniline in the 273-266 nm region using time-resolved photoelectron imaging
Scanning tunnelling microscopy (STM) and Auger electron spectroscopy (AES) have been used to investigate the growth morphology of ultra-thin Pb films on the Ni3Al(111) face at room temperature. A previous study [K. Miśków and A. Krupski Appl Surf Sci 273, 2013, 554] using low-energy electron diffraction (LEED) and real time Auger intensity recording has demonstrated that an initial two-dimensional growth of the first Pb monolayer thick ‘wetting layer’ takes place. With further deposition and for T = 300 K, flat three atomic-layer-high islands are grown. Above 350 K, the Stranski–Krastanov growth mode was observed. In the current study, the analysis of STM measurements indicate and confirm that for coverage θ = 1.0 ML two-dimensional growth of the first Pb monolayer took place. Above θ > 1.0 ML, a three-dimensional growth of the Pb islands was observed with a strongly preferred atomic-scale ‘magic height (N),’ hexagonal shape and flat-tops. At coverage θ = 3.5 ML, only islands containing N = 3, 5, 7 and 11 atomic layers of Pb are observed. At the higher coverage θ = 5.5 ML, three types of regular hexagonal islands with side lengths of 25, 30 and 45 nm are observed. Furthermore, three different island adsorption configurations rotated by 10° ± 1° and 30° ± 6° with respect to each other were observed. After an annealing at T = 400 K of 5.5 ML of lead deposited at RT on the Ni3Al(111) the morphology of the surface changes. Post-anneal, islands of Pb are observed above the ‘wetting layer’ with an estimated average size and diameter of 768 ± 291 nm2 and 38.17 ± 6.56 nm and constant uniform height of two atomic layers (N = 2)
Following the relaxation dynamics of photoexcited aniline in the 273-266 nm region using time-resolved photoelectron imaging
The Profitability of Currency Speculation
This paper presents the results of a post-sample simulation of a speculative strategy using a portfolio of foreign currency forward contracts.The main new features of the speculative strategy are (a)the use of Kalman filters to update the forecasting equation, (b) the allowance for transactions,costs and margin requirements and (c) the endogenous determination of the leveraging of the portfolio. While the forecasting model tended to overestimate profit and underestimate risk, the strategy was still profitable over a three year period and it was possible to reject the hypothesis that the sum of profits was zero. Furthermore, the currency portfolio was found to have an extremely low market risk. Combinations of the speculative currency portfolio with traditional portfolios of U.S. equities resulted in considerable improvements in risk-adjusted returns on capital.
THE CANADA-FRANCE REDSHIFT SURVEY V: Global Properties of the Sample
The photometric and spectroscopic data of the CFRS survey of objects with
17.5 < I_{AB} < 22.5 are combined and analysed. The overall completeness is
85%. The redshift histogram of the sample is presented for 591 field galaxies
with secure redshifts. The median redshift is z = 0.56, and the highest
redshift observed is z = 1.3; 25 galaxies have z > 1 The distributions of
magnitudes and colors demonstrate that galaxies at these high redshifts have
very similar colors to those observed locally. The survey thus represents a
major improvement in our knowledge of field galaxies at large look-back times.
Only ~1% of the galaxies are as compact as stars (on images with FWHM ~ 0.9")
and comparisons of the photometric and spectroscopic data show that only one
galaxy was initially incorrectly classified spectroscopically as a star, and
only two stars were misclassified as galaxies. It is demonstrated that the
redshift distributions in the five fields are statistically consistent with
each other, once the reduction in the effective number of independent galaxies
due to small-scale clustering in redshift is taken into account.
The photometric properties of the spectroscopically-unidentified objects
indicate that most are likely to be galaxies rather than stars. At least half
of these must have the same redshift distribution as the identified galaxies,
and a combination of magnitudes, colors and compactness of the remaining
unidentified galaxies is used to predict their redshifts. The majority are
probably ordinary galaxies at the high redshift end of our sample, including
some quiescent galaxies at z > 1.0, rather than some new or unusual population.Comment: 20 uuencoded postscript pages (first part) with 12 figures (second
part). Also available at http://www.dao.nrc.ca/DAO/SCIENCE/science.html and
coming soon on a CFRS homepage. Accepted June 19, scheduled for Dec 10 issue
of Ap
On the Magnitude of Dark Energy Voids and Overdensities
We investigate the clustering of dark energy within matter overdensities and
voids. In particular, we derive an analytical expression for the dark energy
density perturbations, which is valid both in the linear, quasi-linear and
fully non-linear regime of structure formation. We also investigate the
possibility of detecting such dark energy clustering through the ISW effect. In
the case of uncoupled quintessence models, if the mass of the field is of order
the Hubble scale today or smaller, dark energy fluctuations are always small
compared to the matter density contrast. Even when the matter perturbations
enter the non-linear regime, the dark energy perturbations remain linear. We
find that virialised clusters and voids correspond to local overdensities in
dark energy, with \delta_{\phi}/(1+w) \sim \Oo(10^{-5}) for voids,
\delta_{\phi}/(1+w) \sim \Oo(10^{-4}) for super-voids and
\delta_{\phi}/(1+w) \sim \Oo(10^{-5}) for a typical virialised cluster. If
voids with radii of exist within the visible Universe then
may be as large as . Linear overdensities of
matter and super-clusters generally correspond to local voids in dark energy;
for a typical super-cluster: \delta_{\phi}/(1+w) \sim \Oo(-10^{-5}). The
approach taken in this work could be straightforwardly extended to study the
clustering of more general dark energy models.Comment: 20 pages, 14 figures. Accepted by the Astrophys.
THE CANADA-FRANCE REDSHIFT SURVEY II: Spectroscopic Program; Data for the 0000-00 and 1000+25 Fields
This paper describes the methods used to obtain the spectroscopic data and
construct redshift catalogs for the Canada-France deep Redshift Survey (CFRS).
The full data set consists of more than one thousand spectra, of objects with
17.5 < I_{AB} < 22.5, obtained from deep multi-slit data with the MARLIN and
MOS-SIS spectrographs at the CFHT. The final spectroscopic catalog contains 200
stars, 591 galaxies with secure redshifts in the range 0 < z < 1.3, 6 QSOs, and
146 objects with very uncertain or unknown redshifts, leading to an overall
success rate of identification of 85%. Additionally, 67 objects affected by
observational problems have been placed in a supplemental list.
We describe here the instrumental set up, and the observing procedures used
to efficiently gather this large data set. New optimal ways of packing spectra
on the detector to significantly increase the multiplexing gain offered by
multi-slit spectroscopy are described. Dedicated data reduction procedures have
been developed under the IRAF environment to allow for fast and accurate
processing.
Very strict procedures have been followed to establish a reliable list of
final spectroscopic measurements. Fully independent processing of the data has
been carried out by three members of the team for each data set associated with
a multi-slit mask, and final redshifts were
assigned only after the careful comparison of the three independent
measurements. A confidence class scheme was established. We strongly emphasize
the benefits of such procedures.
Finally, we present the spectroscopic data obtained for 303 objects in the
0000-00 and 1000+25 fields. The success rate in spectroscopic identification isComment: 16 uuencoded postcript pages with figures 4,5,8,9 and 12. Other
(large) figures available from the authors. Large data table not yet
released. Also available at http://www.dao.nrc.ca/DAO/SCIENCE/science.html
and coming soon on a CFRS homepage. Accepted June 19, scheduled for the Dec
10 issue of Ap
The CANADA-FRANCE REDSHIFT SURVEY I: Introduction to the Survey, Photometric Catalogs and Surface Brightness Selection Effects
The Canada-France Redshift Survey has been undertaken to provide a large
well-defined sample of faint galaxies at high redshift in which the selection
criteria match as closely as possible those of samples of nearby galaxies. The
survey is designed to have a median redshift of z ~ 0.6 corresponding to a
look-back time of half the present age of the Universe for Omega ~ 1. Such a
survey can then be used for studying many different aspects of the evolution of
galaxies over the interval 0 < z < 1. In this paper we describe the selection
of the fields, the multicolor imaging observations and the construction and
validation of the photometric catalogs. Particular attention is paid to
quantifying the unavoidable selection effects in surface brightness and their
impact on the survey is assessed in the context of the properties of known
populations of galaxies. The photometric catalogs contain several thousand
objects brighter than I_{AB}< 22.5 and are essentially complete for central
surface brightnesses as faint as 24.5 mag arcsec.
This should be sufficient to include both normal surface brightness galaxies
and prototypes of extreme low surface brightness galaxies.Comment: 17 pages, 2 tables, 10 postscript figures (in 2 parts), uses
aaspp.sty Also available at http://www.dao.nrc.ca/DAO/SCIENCE/science.html
and coming soon on a CFRS homepag
Summary statement of the Asilomar conference on recombinant DNA molecules
This meeting was organized to review scientific progress in research on recombinant DNA molecules and to discuss appropriate ways to deal with the potential biohazards of this work. Impressive scientific achievements have already been made in this field and these techniques have a remarkable potential for furthering our understanding of fundamental biochemical processes in pro- and eukaryotic cells. The use of recombinant DNA methodology promises to revolutionize the practice of molecular biology. Although there has as yet been no practical application of the new techniques, there is every reason to believe that they will have significant practical utility in the future
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