13,230 research outputs found
Radiolysis of ammonia-containing ices by energetic, heavy and highly charged ions inside dense astrophysical environments
Deeply inside dense molecular clouds and protostellar disks, the interstellar
ices are protected from stellar energetic UV photons. However, X-rays and
energetic cosmic rays can penetrate inside these regions triggering chemical
reactions, molecular dissociation and evaporation processes. We present
experimental studies on the interaction of heavy, highly charged and energetic
ions (46 MeV Ni^13+) with ammonia-containing ices in an attempt to simulate the
physical chemistry induced by heavy ion cosmic rays inside dense astrophysical
environments. The measurements were performed inside a high vacuum chamber
coupled to the heavy ion accelerator GANIL (Grand Accelerateur National d'Ions
Lourds) in Caen, France.\textit{In-situ} analysis is performed by a Fourier
transform infrared spectrometer (FTIR) at different fluences. The averaged
values for the dissociation cross section of water, ammonia and carbon monoxide
due to heavy cosmic ray ion analogs are ~2x10^{-13}, 1.4x10^{-13} and
1.9x10^{-13} cm, respectively. In the presence of a typical heavy cosmic
ray field, the estimated half life for the studied species is 2-3x10^6 years.
The ice compaction (micropore collapse) due to heavy cosmic rays seems to be at
least 3 orders of magnitude higher than the one promoted by (0.8 MeV) protons .
In the case of the irradiated H2O:NH3:CO ice, the infrared spectrum at room
temperature reveals five bands that were tentatively assigned to vibration
modes of the zwitterionic glycine (+NH3CH2COO-).Comment: Accepted to be published in Astronomy and Astrophysics; Number of
pages: 12; Number of Figures: 7; Number of Tables:
A calcareous nannofossil and organic geochemical study of marine palaeoenvironmental changes across the Sinemurian/Pliensbachian (early Jurassic, ~191Ma) in Portugal
The Sinemurian/Pliensbachian boundary (~ 191 Ma) is acknowledged as one of the most important steps in the radiation of planktonic organisms, especially primary producers such as dinoflagellates and coccolithophores. To date, there is no detailed study documenting changes in planktonic assemblages related to palaeoceanographic changes across this boundary. The aim of this study is to characterize the palaeoenvironmental changes occurring across the Sinemurian/Pliensbachian boundary at the São Pedro de Moel section (Lusitanian Basin, Portugal) using micropalaeontology and organic geochemistry approaches. Combined calcareous nannofossil assemblage and lipid biomarker data document for a decrease in primary productivity in relation to a major sea-level rise occurring above the boundary. The Lusitanian Basin was particularly restricted during the late Sinemurian with a relatively low sea level, a configuration that led to the recurrent development of black shales. After a sharp sea-level fall, the basin became progressively deeper and more open during the earliest Pliensbachian, subsequently to a major transgression. This sea-level increase seems to have been a global feature and could have been related to the opening of the Hispanic Corridor that connected the Tethys and palaeo-Pacific oceans. The palaeoceanographic and palaeoclimatic changes induced by this opening may have played a role in the diversification of coccolithophores with the first occurrence or colonization of Tethyan waters by placolith-type coccoliths
Aperture-free star formation rate of SDSS star-forming galaxies
Large area surveys with a high number of galaxies observed have undoubtedly
marked a milestone in the understanding of several properties of galaxies, such
as star-formation history, morphology, and metallicity. However, in many cases,
these surveys provide fluxes from fixed small apertures (e.g. fibre), which
cover a scant fraction of the galaxy, compelling us to use aperture corrections
to study the global properties of galaxies. In this work, we derive the current
total star formation rate (SFR) of Sloan Digital Sky Survey (SDSS) star-forming
galaxies, using an empirically based aperture correction of the measured flux for the first time, thus minimising the uncertainties associated
with reduced apertures. All the fluxes have been
extinction-corrected using the ratio free from aperture
effects. The total SFR for 210,000 SDSS star-forming galaxies has been
derived applying pure empirical and aperture
corrections based on the Calar Alto Legacy Integral Field Area (CALIFA) survey.
We find that, on average, the aperture-corrected SFR is 0.65dex higher
than the SDSS fibre-based SFR. The relation between the SFR and stellar mass
for SDSS star-forming galaxies (SFR--) has been obtained, together
with its dependence on extinction and equivalent width. We
compare our results with those obtained in previous works and examine the
behaviour of the derived SFR in six redshift bins, over the redshift range . The SFR-- sequence derived here is in
agreement with selected observational studies based on integral field
spectroscopy of individual galaxies as well as with the predictions of recent
theoretical models of disc galaxies
Aplicação da sequência ultra/nanofiltração para valorização e redução do impacto ambiental de lactossoro de quijo de ovelha
Proceedings of Renaissance of the regions of Southern Europe, University of Évora: july 10-11, 2014.The by‐products of agro‐industries, due to its high content of nutritive substances, in particular
proteins and carbohydrates, have been the subject of intense investigation with a view to their
recovery/reuse, towards sustainability. One of these by‐products is ovine cheese whey, that is mainly
produced in Southern European countries, as a result of the production of ovine cheeses of Protected
Designation of Origin. In most cases, that whey is disposed off into public sewage, causing problems in
conventional treatment plants, due to its high organic load. In some countries, e.g. Portugal, Spain and Italy,
part of the ovine cheese whey is further processed to obtain whey cheeses, designated by different names,
such as requeijão, requesón and ricotta. However, not all of these cheese whey can be transformed due to
the high volumes generated. Membrane technology has emerged as a significant innovation for recovery
and treatment, because it is more economical than other alternatives, require much less land area than
competing technologies and may produce water suitable for multiple proposes. In this work, an example of
using membrane processes in the recovery of ovine cheese whey is presented. The operations of
ultrafiltration (UF) and nanofiltration (NF) of ovine cheese whey were investigated with the objective of
producing added‐value products, such as protein concentrates by UF, lactose concentrates by NF and final
permeates with a very low organic load. UF experiments were performed with skimmed cheese whey, both
in total recirculation and concentration modes. The equipment used was a plate‐and‐frame unit (Lab Unit
M20). Ultrafiltration was performed with organic membranes ETNA 10PP with a surface area of 0,072 m2
and a cut‐off of 10 kDa. Ultrafiltration allowed a clear separation between the protein fraction and a fraction
rich in lactose and minerals. About 40% of organic matter, expressed as COD was retained. Nanofiltration of
UF permeates was done with membranes NFT50 with a membrane surface area of 0,072 m2..This operation
allowed a high retention of lactose (98.8%) and the production of a permeate with a very low organic load.
The retention of organic matter, in terms of COD was about 93%. The sequence of operations UF/NF allowed
to produce two added‐value products, reducing at the same time the organic pollution of the final stream.
Nevertheless, the quality of the final water should be assessed, according with the intended use.RESUMO. Os subprodutos das agro‐indústrias, devido ao seu elevado teor em substâncias nutritivas, em
particular proteínas e hidratos de carbono, têm sido objecto de uma intensa investigação com objectivos de
recuperação/reutilização, tendo em vista um desenvolvimento sustentável. Um destes subprodutos é o soro
de queijo de ovelha, produzido principalmente nos países do sul da Europa, como resultado da produção de
queijos de ovelha de Denominação de Origem Protegida. Na maioria dos casos, o soro produzido é lançado
nos esgotos municipais, causando problemas em estações de tratamento convencionais, devido à sua
elevada carga orgânica. Em alguns países, como Portugal, Espanha e Itália, parte do soro é processado para
obtenção de queijos de soro, designados por nomes diferentes, como requeijão, requesón e ricota. No
entanto, nem todo o soro produzido pode ser transformado, devido aos elevados volumes gerados. As
tecnologias de membranas surgiram como uma inovação significativa para a recuperação/tratamento de
vários produtos, dado que relativamente a outros processos alternativos, são mais económicas, podendo
produzir água de qualidade adequada para diversos fins. Neste trabalho, é apresentado um exemplo de
utilização de processos de membrana na recuperação de soro de queijo de ovelha. As operações de
ultrafiltração (UF) e nanofiltração (NF) foram investigadas com o objetivo de produzir produtos de valor
acrescentado, como concentrados proteicos por UF, concentrados de lactose por NF e permeados finais,
com cargas orgânicas baixas. Os ensaios de UF foram realizados com soro desnatado, em recirculação total e
em concentração. O equipamento utilizado foi um módulo de pratos planos (Lab Unidade M20). Na
ultrafiltração, foram usadas membranas orgânicas ETNA 10PP, de área superficial 0.072 m2 e com um peso
molecular de corte de 10 kDa. A ultrafiltração permitiu uma nítida separação entre a fração proteica e uma
fração rica em lactose e sais minerais. Cerca de 40% da matéria orgânica, expressa como CQO, foi retida. Na
nanofiltração dos permeados da UF utilizaram‐se membranas NFT50, com uma área de superfície de 0.072
m2. Esta operação permitiu uma elevada retenção de lactose (98.8%) e a obtenção de um permeado com
uma carga orgânica bastante reduzida. O factor de retenção da matéria orgânica, em termos de CQO, foi
cerca de 93%. A sequência de separações UF / NF permitiu produzir dois produtos de valor acrescentado,
reduzindo ao mesmo tempo a poluição orgânica da corrente final. No entanto, a qualidade da água final
deve ser avaliada, de acordo com o uso pretendido
Clone size distributions in networks of genetic similarity
We build networks of genetic similarity in which the nodes are organisms
sampled from biological populations. The procedure is illustrated by
constructing networks from genetic data of a marine clonal plant. An important
feature in the networks is the presence of clone subgraphs, i.e. sets of
organisms with identical genotype forming clones. As a first step to understand
the dynamics that has shaped these networks, we point up a relationship between
a particular degree distribution and the clone size distribution in the
populations. We construct a dynamical model for the population dynamics,
focussing on the dynamics of the clones, and solve it for the required
distributions. Scale free and exponentially decaying forms are obtained
depending on parameter values, the first type being obtained when clonal growth
is the dominant process. Average distributions are dominated by the power law
behavior presented by the fastest replicating populations.Comment: 17 pages, 4 figures. One figure improved and other minor changes. To
appear in Physica
On a generalised model for time-dependent variance with long-term memory
The ARCH process (R. F. Engle, 1982) constitutes a paradigmatic generator of
stochastic time series with time-dependent variance like it appears on a wide
broad of systems besides economics in which ARCH was born. Although the ARCH
process captures the so-called "volatility clustering" and the asymptotic
power-law probability density distribution of the random variable, it is not
capable to reproduce further statistical properties of many of these time
series such as: the strong persistence of the instantaneous variance
characterised by large values of the Hurst exponent (H > 0.8), and asymptotic
power-law decay of the absolute values self-correlation function. By means of
considering an effective return obtained from a correlation of past returns
that has a q-exponential form we are able to fix the limitations of the
original model. Moreover, this improvement can be obtained through the correct
choice of a sole additional parameter, . The assessment of its validity
and usefulness is made by mimicking daily fluctuations of SP500 financial
index.Comment: 6 pages, 4 figure
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