4,598 research outputs found
Large scale correlations in galaxy clustering from the Two degree Field Galaxy Redshift Survey
We study galaxy correlations from samples extracted from the 2dFGRS final
release. Statistical properties are characterized by studying the nearest
neighbor probability density, the conditional density and the reduced two-point
correlation function. The result is that the conditional density has a
power-law behavior in redshift space described by an exponent \gamma=0.8 \pm
0.2 in the interval from about 1 Mpc/h, the average distance between nearest
galaxies, up to about 40 Mpc/h, corresponding to radius of the largest sphere
contained in the samples. These results are consistent with other studies of
the conditional density and are useful to clarify the subtle role of
finite-size effects on the determination of the two-point correlation function
in redshift and real spaceComment: 11 pages, 14 figures. Accepted for publication in Astronomy and
Astrophysic
Materials Balance for Bromine, Chlorine, Sulfur, and Nitrogen in Europe
An understanding of the flow of toxic materials through industry and into the environment is one of the major tasks for the IIASA Study, "The Future Environments for Europe: Some Implications, of Alternative Development Paths". Toxic chemicals represent a great threat to the environment, and yet they are commonly used in industrial societies. A sustainable development path would require that usage and disposal of toxic chemicals be compatible with the long-term health of humans and the natural environment. Examining the current and past flows of these materials is a starting point for understanding options for management of their use and disposal, and the impact these options might have on the economy and society.
The method chosen to analyze this problem is a materials balance approach in which toxic chemicals are traced as they move through the industrial economy; from extraction to production to intermediate uses and finally to end uses. The methodology and its advantages and disadvantages are discussed in some detail in Chapter 2. The implementation of this approach will become apparent in Chapters 3 through 6 as four individual chemical elements are studied.
The four elements examined are bromine, chlorine, sulfur and nitrogen. These chemicals were chosen from a list of 15 which were of particular interest because of the exceptional biological activity of many of the compounds derived from them. The major goal of the project was to develop process-product flow diagrams for these elements showing their pathways through the industrial economy. Each of Chapters 3 through 6 contains a discussion of production processes, major uses, process-product flow diagram(s) and an Appendix with detailed information about the chemical transformations involved in each of the processes. In addition, further investigations including quantitative analysis and discussions of the applicability of this approach for a given element are included in some of the Chapters.
Chapter 3, Bromine, presents a detailed qualitative material balance and a more aggregated quantitative material balance for the Netherlands and the United States for 1978 and 1985. The selection of these two countries was based solely on available data. Although the U.S. is not formally part of the study, it is useful as it more closely represents the Western European consumption pattern on average than the Netherlands. While the quantitative analysis focuses only on two countries for two years, it does demonstrate both the qualitative and quantitative aspects of the material balance approach. Bromine consumption is an interesting case as it has been heavily impacted by the phase-out of leaded gasoline and strong market shifts are expected in the future.
Chapter 4, Chlorine, presents an in-depth qualitative materials balance and a look at the pathways of chlorine into the environment based on its pattern of end-use consumption. Currently, millions of tons of chlorine are produced each year for use as a disinfectant and in the organic and inorganic chemical industries. Many of the end-uses of chlorine result in eventual releases into the environment of various compounds which have a significant effect on environmental quality. Organic chlorine compounds are of great use to man because they are not readily biodegradable and they are chemically stable. However, because of these qualities they represent some of the most difficult disposal problems of any anthropogenic material.
Chapter 5, Sulfur, presents a thorough qualitative analysis of the industrial processes and an in-depth discussion of the applicability of the materials balance approach to sulfur. A large portion of anthropogenically mobilized sulfur is from the burning of fossil fuels and the smelting of ores, two processes where sulfur is not an intentional product, simply an unavoidable one. The bulk of scientific study of sulfur wastes is concentrated on these areas due to their contribution to the acid rain problem. The analysis presented here shows that over half of the total anthropogenic sulfur budget in Europe is from industrial sources other than fossil fuels and ore smelting. This is a fairly surprising result. Thus, the flow of sulfur through the industrial economy in Europe is significant and greater understanding of the eventual disposal of this sulfur is needed. In addition, sulfuric acid is the number one industrial chemical based on the tonnage of production. It is used in a myriad of industries where it is generally consumed in the process and not embodied in the end product. This presents difficulties in the implementation of the materials balance analysis for sulfur.
Chapter 6, Nitrogen, presents the process-product flow diagram for nitrogen. About 95% of the anthropogenically mobilized nitrogen is in the form of ammonia. Therefore, this chapter concentrates on the production and eventual end-uses of ammonia. While the process-product diagram is quite thorough, due to time constraints, further discussion and analysis of nitrogen is left as a future research topic.
This report is the first step toward completing the task of understanding the impact of toxic materials in Europe. Future analysts may use the process-product diagrams and the analysis presented in this report as a starting point for a historical reconstruction which then could be used for building future scenarios of chemical flows of toxic materials
Industrial Metabolism, the Environment, and Application of Materials-Balance. Principles for Selected Chemicals
This report provides an important step in our understanding of material flows for four widely used inorganic chemicals, bromine, chlorine, sulfur, and nitrogen.
Also, by invoking the concept of industrial metabolism, the authors provide a new vision for understanding how industrial sciences produce, process, use, and dispose of materials, and how these activities, taken as a whole, are linked to environmental change
High-pressure behaviour of GeO2: a simulation study
In this work we study the high pressure behaviour of liquid and glassy GeO2
by means of molecular dynamics simulations. The interaction potential, which
includes dipole polarization effects, was parameterized from first-principles
calculations. Our simulations reproduce the most recent experimental data to a
high degree of precision. The proportion of the various GeOn polyhedra is
determined as a function of the pressure: a smooth transition from tetrahedral
to octahedral network is observed. Finally, the study of high-pressure, liquid
germania confirms that this material presents an anomalous behaviour of the
diffusivity as observed in analog systems such as silica and water. The
importance of penta-coordinated germanium ions for such behaviour is stressed.Comment: 16 pages, 4 figures, accepted as a Fast Track Communication on
Journal of Physics: Condensed Matte
The Angular Momentum Evolution of 0.1-10 Msun Stars From the Birthline to the Main Sequence
(Abridged) Projected rotational velocities (vsini) have been measured for a
sample of 145 stars with masses between 0.4 and >10 Msun (median mass 2.1 Msun)
located in the Orion star-forming complex. These measurements have been
supplemented with data from the literature for Orion stars with masses as low
as 0.1 Msun. The primary finding from analysis of these data is that the upper
envelope of the observed values of angular momentum per unit mass (J/M) varies
as M^0.25 for stars on convective tracks having masses in the range ~0.1 to ~3
Msun. This power law extends smoothly into the domain of more massive stars (3
to 10 Msun), which in Orion are already on the ZAMS. This result stands in
sharp contrast to the properties of main sequence stars, which show a break in
the power law and a sharp decline in J/M with decreasing mass for stars with M
<2 Msun. A second result of our study is that this break is seen already among
the PMS stars in our Orion sample that are on radiative tracks, even though
these stars are only a few million years old. A comparison of rotation rates
seen for stars on either side of the convective-radiative boundary shows that
stars do not rotate as solid bodies during the transition from convective to
radiative tracks.Comment: to appear in Ap
Measuring galaxy segregation using the mark connection function
(abridged) The clustering properties of galaxies belonging to different
luminosity ranges or having different morphological types are different. These
characteristics or `marks' permit to understand the galaxy catalogs that carry
all this information as realizations of marked point processes. Many attempts
have been presented to quantify the dependence of the clustering of galaxies on
their inner properties. The present paper summarizes methods on spatial marked
statistics used in cosmology to disentangle luminosity, colour or morphological
segregation and introduces a new one in this context, the mark connection
function. The methods used here are the partial correlation functions,
including the cross-correlation function, the normalised mark correlation
function, the mark variogram and the mark connection function. All these
methods are applied to a volume-limited sample drawn from the 2dFGRS, using the
spectral type as the mark. We show the virtues of each method to provide
information about the clustering properties of each population, the dependence
of the clustering on the marks, the similarity of the marks as a function of
the pair distances, and the way to characterise the spatial correlation between
the marks. We demonstrate by means of these statistics that passive galaxies
exhibit stronger spatial correlation than active galaxies at small scales (r
<20 Mpc/h). The mark connection function, introduced here, is particularly
useful for understanding the spatial correlation between the marks.Comment: 6 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
Disruption of vitellogenin gene function in adult honeybees by intra-abdominal injection of double-stranded RNA
BACKGROUND: The ability to manipulate the genetic networks underlying the physiological and behavioural repertoires of the adult honeybee worker (Apis mellifera) is likely to deepen our understanding of issues such as learning and memory generation, ageing, and the regulatory anatomy of social systems in proximate as well as evolutionary terms. Here we assess two methods for probing gene function by RNA interference (RNAi) in adult honeybees. RESULTS: The vitellogenin gene was chosen as target because its expression is unlikely to have a phenotypic effect until the adult stage in bees. This allowed us to introduce dsRNA in preblastoderm eggs without affecting gene function during development. Of workers reared from eggs injected with dsRNA derived from a 504 bp stretch of the vitellogenin coding sequence, 15% had strongly reduced levels of vitellogenin mRNA. When dsRNA was introduced by intra-abdominal injection in newly emerged bees, almost all individuals (96 %) showed the mutant phenotype. An RNA-fragment with an apparent size similar to the template dsRNA was still present in this group after 15 days. CONCLUSION: Injection of dsRNA in eggs at the preblastoderm stage seems to allow disruption of gene function in all developmental stages. To dissect gene function in the adult stage, the intra-abdominal injection technique seems superior to egg injection as it gives a much higher penetrance, it is much simpler, and it makes it possible to address genes that are also expressed in the embryonic, larval or pupal stages
Superclusters of galaxies in the 2dF redshift survey. III. The properties of galaxies in superclusters
We use catalogues of superclusters of galaxies from the 2dF Galaxy Redshift
Survey to study the properties of galaxies in superclusters. We compare the
properties of galaxies in high and low density regions of rich superclusters,
in poor superclusters and in the field, as well as in groups, and of isolated
galaxies in superclusters of various richness. We show that in rich
superclusters the values of the luminosity density smoothed on a scale of 8
\Mpc are higher than in poor superclusters: the median density in rich
superclusters is , in poor superclusters . Rich superclusters contain high density cores with densities while in poor superclusters such high density cores are absent. The
properties of galaxies in rich and poor superclusters and in the field are
different: the fraction of early type, passive galaxies in rich superclusters
is slightly larger than in poor superclusters, and is the smallest among the
field galaxies. Most importantly, in high density cores of rich superclusters
() there is an excess of early type, passive galaxies in groups
and clusters, as well as among those which do not belong to groups or clusters.
The main galaxies of superclusters have a rather limited range of absolute
magnitudes. The main galaxies of rich superclusters have larger luminosities
than those of poor superclusters and of groups in the field. Our results show
that both the local (group/cluster) environments and global (supercluster)
environments influence galaxy morphologies and their star formation activity.Comment: 13 pages, 10 figures, submitted to Astronomy and Astrophysic
The emptiness of voids: yet another over-abundance problem for the LCDM model
We study the luminosity function, the peculiar velocities, and the sizes of
voids in the Local Volume (LV) in observational samples of galaxies which
contain galaxies down to MB=-10-12 within the distance 4-8Mpc. Comparing the
results with the predictions of the standard cosmological LCDM model, we find
that the theory faces a sever problem: it predicts a factor of ten more dwarf
haloes as compared with the observed number of dwarf galaxies. In the LV we
identify voids with sizes ranging from 1 to 4.5Mpc and compare the
observational distribution of void sizes with the voids in very high resolution
simulations of the LCDM model with WMAP1 and WMAP3 parameters. The theoretical
void function matches the observations remarkably well only if we use haloes
with circular velocities Vc larger than 40-45 km/s (Mvir=(1-2)e10msun) for
models with with sigma8 = 0.9 and Vc>35km/s (Mvir=(6-8)e9msun) for sigma8 =
0.75. We exclude the possibility that in the LCDM model haloes with circular
velocities < 35km/s can host galaxies as bright as MB=-12: there are too many
small haloes in the LCDM model resulting in voids being too small as compared
with the observations. The problem is that many of the observed dwarf galaxies
have HI rotational velocities below 25km/s that strictly contradicts the LCDM
predictions. Thus, the LCDM model faces the same overabundance problem, which
it had with the number of satellites in the LG. We also estimate the rms
deviations from the Hubble flow sigmaH and find that in most of our model
LV-candidates the rms peculiar velocities are consistent with observational
values sigmaH=50km/s for distances less than 3Mpc and sigmaH=80km/s for
distances less than 8Mpc. At distances 4 (8) Mpc, the observed overdensities of
galaxies are 3.5-5.5 (1.3-1.6) -- significantly larger than typically assumed.Comment: 10 pages, accepted to MNRA
Filaments in observed and mock galaxy catalogues
Context. The main feature of the spatial large-scale galaxy distribution is
an intricate network of galaxy filaments. Although many attempts have been made
to quantify this network, there is no unique and satisfactory recipe for that
yet. Aims. The present paper compares the filaments in the real data and in the
numerical models, to see if our best models reproduce statistically the
filamentary network of galaxies. Methods. We apply an object point process with
interactions (the Bisous process) to trace and describe the filamentary network
both in the observed samples (the 2dFGRS catalogue) and in the numerical models
that have been prepared to mimic the data.We compare the networks. Results. We
find that the properties of filaments in numerical models (mock samples) have a
large variance. A few mock samples display filaments that resemble the observed
filaments, but usually the model filaments are much shorter and do not form an
extended network. Conclusions. We conclude that although we can build numerical
models that are similar to observations in many respects, they may fail yet to
explain the filamentary structure seen in the data. The Bisous-built filaments
are a good test for such a structure.Comment: 13 pages, accepted for publication in Astronomy and Astrophysic
- …