363 research outputs found
Historic rammed earth structures in Spain : construction techniques and a preliminary classification.
Conservation and repair of historic rammed earth sites should only be undertaken if there is a good understanding of the consequences of any intervention technique. Until recently there has been little interest in the characterisation of historic rammed earth construction, yet it is only with this understanding that successful conservation strategies can be adopted.
A survey of around 60 historic rammed earth sites in Spain constructed between 967AD and 1837AD has recently been undertaken. While all the sites are built primarily in rammed earth, the construction techniques and state of repair vary greatly. The high density of historic rammed earth structures in the Iberian peninsula is likely due to the Muslim presence there from the 8th century onwards. Initial expansion, a period of civil war and eventual defeat by Christians led to the construction of a large number of fortifications, many constructed in rammed earth. A famous example is the Alhambra at Granada, but there are hundreds of smaller sites throughout Spain. By the end of the 15th century Christians had replaced Muslims through most of Spain, but rammed earth continued to be used in both vernacular and monumental architecture.
Examples of historic construction techniques are presented and common features of historic rammed earth construction are identified. A classification is outlined and a clear development of the rammed earth technique is observed
Atomic Scale Depth Profile of Space Weathering in an Itokawa Olivine Grain
No abstract available
Parameterized Inapproximability of Target Set Selection and Generalizations
In this paper, we consider the Target Set Selection problem: given a graph
and a threshold value for any vertex of the graph, find a minimum
size vertex-subset to "activate" s.t. all the vertices of the graph are
activated at the end of the propagation process. A vertex is activated
during the propagation process if at least of its neighbors are
activated. This problem models several practical issues like faults in
distributed networks or word-to-mouth recommendations in social networks. We
show that for any functions and this problem cannot be approximated
within a factor of in time, unless FPT = W[P],
even for restricted thresholds (namely constant and majority thresholds). We
also study the cardinality constraint maximization and minimization versions of
the problem for which we prove similar hardness results
Atomic Scale Depth Profile of Space Weathering in an Itokawa Olivine Grain
No abstract available
Demonstrating the Feasibility of Line Intensity Mapping Using Mock Data of Galaxy Clustering from Simulations
Visbal & Loeb (2010) have shown that it is possible to measure the clustering
of galaxies by cross correlating the cumulative emission from two different
spectral lines which originate at the same redshift. Through this cross
correlation, one can study galaxies which are too faint to be individually
resolved. This technique, known as intensity mapping, is a promising probe of
the global properties of high redshift galaxies. Here, we test the feasibility
of such measurements with synthetic data generated from cosmological dark
matter simulations. We use a simple prescription for associating galaxies with
dark matter halos and create a realization of emitted radiation as a function
of angular position and wavelength over a patch of the sky. This is then used
to create synthetic data for two different hypothetical instruments, one aboard
the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) and another
consisting of a pair of ground based radio telescopes designed to measure the
CO(1-0) and CO(2-1) emission lines. We find that the line cross power spectrum
can be measured accurately from the synthetic data with errors consistent with
the analytical prediction of Visbal & Loeb (2010). Removal of astronomical
backgrounds and masking bright line emission from foreground contaminating
galaxies do not prevent accurate cross power spectrum measurements.Comment: 12 pages, 6 figures, Submitted to JCA
Characterizations and comparison of low sulfur fuel oils compliant with 2020 global sulfur cap regulation for international shipping
The International Marine Organization 2020 Global Sulfur Cap requires ships to burn fuels with <0.50% S and some countries require <0.10% S in certain Sulfur Emission Control Areas but little is known about these new types of fuels. Using both traditional GCâMS and more advanced chromatographic and mass spectrometry techniques, plus stable isotopic, ÎŽ13C and ÎŽ2H, analyses of pristane, phytane and n-alkanes, the organic components of a suite of three 0.50% S and three 0.10% S compliant fuels were characterized. Two oils were found to be near identical but all of the remaining oils could be forensically distinguished by comparison of their molecular biomarkers and by the profiles of the heterocyclic parent and alkylated homologues. Oils could also be differentiated by their ÎŽ13C and ÎŽ2H of n-alkanes and isoprenoids. This study provides important forensic data that may prove invaluable in the event of future oil spills
UV-continuum slopes at z~4-7 from the HUDF09+ERS+CANDELS observations: Discovery of a well-defined UV-color magnitude relationship for z>=4 star-forming galaxies
Ultra-deep ACS and WFC3/IR HUDF+HUDF09 data, along with the wide-area
GOODS+ERS+CANDELS data over the CDF-S GOODS field, are used to measure UV
colors, expressed as the UV-continuum slope beta, of star-forming galaxies over
a wide range in luminosity (0.1L*(z=3) to 2L*(z=3)) at high redshift (z~7 to
z~4). Beta is measured using all ACS and WFC3/IR passbands uncontaminated by
Ly_alpha and spectral breaks. Extensive tests show that our beta measurements
are only subject to minimal biases. Using a different selection procedure,
Dunlop et al. recently found large biases in their beta measurements. To
reconcile these different results, we simulated both approaches and found that
beta measurements for faint sources are subject to large biases if the same
passbands are used both to select the sources and to measure beta.
High-redshift galaxies show a well-defined rest-frame UV color-magnitude (CM)
relationship that becomes systematically bluer towards fainter UV luminosities.
No evolution is seen in the slope of the UV CM relationship in the first 1.5
Gyr, though there is a small evolution in the zero-point to redder colors from
z~7 to z~4. This suggests that galaxies are evolving along a well-defined
sequence in the L(UV)-color (beta) plane (a "star-forming sequence"?). Dust
appears to be the principal factor driving changes in the UV color (beta) with
luminosity. These new larger beta samples lead to improved dust extinction
estimates at z~4-7 and confirm that the extinction is still essentially zero at
low luminosities and high redshifts. Inclusion of the new dust extinction
results leads to (i) excellent agreement between the SFR density at z~4-8 and
that inferred from the stellar mass density, and (ii) to higher SSFRs at z>~4,
suggesting the SSFR may evolve modestly (by factors of ~2) from z~4-7 to z~2.Comment: 39 pages, 26 figures, 8 tables, accepted for publication in ApJ,
updated to include results from the full CANDELS data set over the CDF South
and also to use the most recent WFC3/IR zeropoint determination
Atom scale element and isotopic investigation of 25Mg-rich stardust from a H-burning supernova
We have discovered a presolar olivine from ALH 77307 with the highest 25Mg isotopic composition measured in a silicate to date (ÎŽ25Mg = 3025.1Ⱐ± 38.3â°). Its isotopic compositions challenge current stellar models, with modeling of magnesium, silicon, and oxygen showing a closest match to formation in a supernova (SN) where hydrogen ingestion occurred in the pre-SN phase. Presolar grains within primitive astromaterials retain records of processes and environmental changes throughout stellar evolution. However, accessing these records has proved challenging due to the average grain size (âŒ150 nm) of presolar silicates, their sensitivity to extraction agents, and instrumental restrictions, limiting the range of isotopic and chemical signatures which can be studied per grain volume. Here, we present the first known detailed geochemical study of a presolar silicate from a hydrogen-burning SN, studied in 3D without contributions to the analysis volume and at unprecedented spatial resolutions (<1 nm), essential for constraining physical and chemical processes occurring within this recently proposed stellar environment. From our results, we infer either (i) condensation within an environment depleted of heavy elements compatible with the olivine lattice under the pressure and temperature conditions during condensation, or (ii) during periods of limited mixing either near the end of the pre-SN phase or from a collapse so rapid localized pockets of different gas compositions formed
Abundances of the elements in the solar system
A review of the abundances and condensation temperatures of the elements and
their nuclides in the solar nebula and in chondritic meteorites. Abundances of
the elements in some neighboring stars are also discussed.Comment: 42 pages, 11 tables, 8 figures, chapter, In Landolt- B\"ornstein, New
Series, Vol. VI/4B, Chap. 4.4, J.E. Tr\"umper (ed.), Berlin, Heidelberg, New
York: Springer-Verlag, p. 560-63
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