388 research outputs found
TELECTR User's Manual
This Working Paper was written in response to requests for a telectr reference manual that does not have to be read from cover to cover to be useful. We hope the command-by-command format and expanded table of contents permit users to quickly locate and master commands of interest. In a similar vein, we offer a "Quick Reference" sheet on the next two pages of this preface. It shows a sample interaction on telectr that users can imitate when sending their first messages. We suggest tearing out and retaining this sheet as a summary of how to log in and send a message.
Although both internal and external users can refer to this manual, it is geared mainly for people accessing telectr from outside the Institute. IIASA-based users can refer to IIASA Working Paper WP-80-109 for information specific to IIASA's video terminals. For more general information about computerized conferencing as a concept, see IIASA Working Paper WP-80-72
Confirming Bank Liability in Letter of Credit Transactions: Whose Bank Is It Anyway?
Context. The abundance of deuterated molecules in a star-forming region is sensitive to the environment in which they are formed. Deuteration fractions, in other words the ratio of a species containing D to its hydrogenated counterpart, therefore provide a powerful tool for studying the physical and chemical evolution of a star-forming system. While local low-mass star-forming regions show very high deuteration ratios, much lower fractions are observed towards Orion and the Galactic centre. Astration of deuterium has been suggested as a possible cause for low deuteration in the Galactic centre. Aims. We derive methanol deuteration fractions at a number of locations towards the high-mass star-forming region NGC 6334I, located at a mean distance of 1.3 kpc, and discuss how these can shed light on the conditions prevailing during its formation. Methods. We use high sensitivity, high spatial and spectral resolution observations obtained with the Atacama Large Millimeter/ submillimeter Array to study transitions of the less abundant, optically thin, methanol-isotopologues: 13CH3OH, CH318OH, CH2DOH and CH3OD, detected towards NGC 6334I. Assuming local thermodynamic equilibrium (LTE) and excitation temperatures of ~120–330 K, we derive column densities for each of the species and use these to infer CH2DOH/CH3OH and CH3OD/CH3OH fractions. Results. We derive column densities in a range of (0.8–8.3) × 1017 cm−2 for 13CH3OH, (0.13–3.4) × 1017 cm−2 for CH318OH, (0.03–1.63) × 1017 cm−2 for CH2DOH and (0.15–5.5) × 1017 cm−2 for CH3OD in a ~1″ beam. Interestingly, the column densities of CH3OD are consistently higher than those of CH2DOH throughout the region by factors of 2–15. We calculate the CH2DOH to CH3OH and CH3OD to CH3OH ratios for each of the sampled locations in NGC 6334I. These values range from 0.03% to 0.34% for CH2DOH and from 0.27% to 1.07% for CH3OD if we use the 13C isotope of methanol as a standard; using the 18 O-methanol as a standard, decreases the ratios by factors of between two and three. Conclusions. All regions studied in this work show CH2DOH/CH3OH as well as CH2DOH/CH3OD values that are considerably lower than those derived towards low-mass star-forming regions and slightly lower than those derived for the high-mass star-forming regions in Orion and the Galactic centre. The low ratios indicate a grain surface temperature during formation ~30 K, for which the efficiency of the formation of deuterated species is significantly reduced. Therefore, astration of deuterium in the Galactic centre cannot be the explanation for its low deuteration ratio but rather the high temperatures characterising the region
Constraining slow-roll inflation with WMAP and 2dF
We constrain slow-roll inflationary models using the recent WMAP data
combined with data from the VSA, CBI, ACBAR and 2dF experiments. We find the
slow-roll parameters to be and . For inflation models
we find that at the 2 and levels,
indicating that the model is under very strong pressure from
observations. We define a convergence criterion to judge the necessity of
introducing further power spectrum parameters such as the spectral index and
running of the spectral index. This criterion is typically violated by models
with large negative running that fit the data, indicating that the running
cannot be reliably measured with present data.Comment: 8 pages RevTeX4 file with six figures incorporate
Annual radiocarbon record indicates 16th century BCE date for the Thera eruption
The mid-second millennium BCE eruption of Thera (Santorini) offers a critically important marker horizon to synchronize archaeological chronologies of the Aegean, Egypt, and the Near East and to anchor paleoenvironmental records from ice cores, speleothems, and lake sediments. Precise and accurate dating for the event has been the subject of many decades of research. Using calendar-dated tree rings, we created an annual resolution radiocarbon time series 1700–1500 BCE to validate, improve, or more clearly define the limitations for radiocarbon calibration of materials from key eruption contexts. Results show an offset from the international radiocarbon calibration curve, which indicates a shift in the calibrated age range for Thera toward the 16th century BCE. This finding sheds new light on the long-running debate focused on a discrepancy between radiocarbon (late 17th–early 16th century BCE) and archaeological (mid 16th–early 15th century BCE) dating evidence for Thera
WMAP constraints on inflationary models with global defects
We use the cosmic microwave background angular power spectra to place upper
limits on the degree to which global defects may have aided cosmic structure
formation. We explore this under the inflationary paradigm, but with the
addition of textures resulting from the breaking of a global O(4) symmetry
during the early stages of the Universe. As a measure of their contribution, we
use the fraction of the temperature power spectrum that is attributed to the
defects at a multipole of 10. However, we find a parameter degeneracy enabling
a fit to the first-year WMAP data to be made even with a significant defect
fraction. This degeneracy involves the baryon fraction and the Hubble constant,
plus the normalization and tilt of the primordial power spectrum. Hence,
constraints on these cosmological parameters are weakened. Combining the WMAP
data with a constraint on the physical baryon fraction from big bang
nucleosynthesis calculations and high-redshift deuterium abundance, limits the
extent of the degeneracy and gives an upper bound on the defect fraction of
0.13 (95% confidence).Comment: 10pp LaTeX/RevTeX, 6 eps figs; matches accepted versio
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum
P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in
combination with WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when
dropping prior assumptions about curvature, neutrinos, tensor modes and the
equation of state. Our results are in substantial agreement with the joint
analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive
consistency check with independent redshift survey data and analysis
techniques. In this paper, we place particular emphasis on clarifying the
physical origin of the constraints, i.e., what we do and do not know when using
different data sets and prior assumptions. For instance, dropping the
assumption that space is perfectly flat, the WMAP-only constraint on the
measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running
tilt, neutrino mass and equation of state in the list of free parameters, many
constraints are still quite weak, but future cosmological measurements from
SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm
Dark Energy and Gravity
I review the problem of dark energy focusing on the cosmological constant as
the candidate and discuss its implications for the nature of gravity. Part 1
briefly overviews the currently popular `concordance cosmology' and summarises
the evidence for dark energy. It also provides the observational and
theoretical arguments in favour of the cosmological constant as the candidate
and emphasises why no other approach really solves the conceptual problems
usually attributed to the cosmological constant. Part 2 describes some of the
approaches to understand the nature of the cosmological constant and attempts
to extract the key ingredients which must be present in any viable solution. I
argue that (i)the cosmological constant problem cannot be satisfactorily solved
until gravitational action is made invariant under the shift of the matter
lagrangian by a constant and (ii) this cannot happen if the metric is the
dynamical variable. Hence the cosmological constant problem essentially has to
do with our (mis)understanding of the nature of gravity. Part 3 discusses an
alternative perspective on gravity in which the action is explicitly invariant
under the above transformation. Extremizing this action leads to an equation
determining the background geometry which gives Einstein's theory at the lowest
order with Lanczos-Lovelock type corrections. (Condensed abstract).Comment: Invited Review for a special Gen.Rel.Grav. issue on Dark Energy,
edited by G.F.R.Ellis, R.Maartens and H.Nicolai; revtex; 22 pages; 2 figure
The PHENIX Experiment at RHIC
The physics emphases of the PHENIX collaboration and the design and current
status of the PHENIX detector are discussed. The plan of the collaboration for
making the most effective use of the available luminosity in the first years of
RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program
available at http://www.rhic.bnl.gov/phenix
Brane inflation revisited after WMAP five-year results
In this paper, we revisit brane inflation models with the WMAP five-year
results. The WMAP five-year data favor a red-tilted power spectrum of
primordial fluctuations at the level of two standard deviations, which is the
same as the WMAP three-year result qualitatively, but quantitatively the
spectral index is slightly greater than the three-year value. This result can
bring impacts on brane inflation models. According to the WMAP five-year data,
we find that the KKLMMT model can survive at the level of one standard
deviation, and the fine-tuning of the parameter can be alleviated to a
certain extent at the level of two standard deviations.Comment: 23 pages, 11 figure
An interlaboratory study of TEX86 and BIT analysis of sediments, extracts and standard mixtures.
Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility ±3-4°C when translated to temperature) but a large spread in BIT measurements (reproducibility ±0.41 on a scale of 0-1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0°C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the "true" (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values
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