1,419 research outputs found
Comparing galaxy populations in compact and loose groups of galaxies
We perform a comparison of the properties of galaxies in compact groups,
loose groups and in the field to deepen our understanding of the physical
mechanisms acting upon galaxy evolution in different environments. We select
samples of galaxies in compact groups identified by McConnachie et al., loose
groups identified by Zandivarez and Martinez, and field galaxies from the Sloan
Digital Sky Survey. We compare properties of the galaxy populations in these
different environments: absolute magnitude, colour, size, surface brightness,
stellar mass and concentration. We also study the fraction of red and early
type galaxies, the luminosity function, the colour-luminosity and
luminosity-size relations. The population of galaxies in compact groups differ
from that of loose groups and the field. The fraction of read and early type
galaxies is higher in compact groups. On average, galaxies in compact groups
are systematically smaller, more concentrated and have higher surface
brightness than galaxies in the field and in loose groups. For fixed absolute
magnitude, or fixed surface brightness, galaxies in compact groups are smaller.
The physical mechanisms that transform galaxies into earlier types could be
more effective within compact groups given the high densities and low velocity
dispersion that characterise that particular environment, this could explain
the large fraction of red and early type galaxies we found in compact groups.
Galaxies inhabiting compact groups have undergone a major transformation
compared to galaxies that inhabit loose groups.Comment: 12 pages, 14 figures, accepted for publication in Astronomy &
Astrophysics (A&A
Comprehensive characterization of molecular interactions based on nanomechanics
Molecular interaction is a key concept in our understanding of the biological mechanisms of life. Two physical properties change when one molecular partner binds to another. Firstly, the masses combine and secondly, the structure of at least one binding partner is altered, mechanically transducing the binding into subsequent biological reactions. Here we present a nanomechanical micro-array technique for bio-medical research, which not only monitors the binding of effector molecules to their target but also the subsequent effect on a biological system in vitro. This label-free and real-time method directly and simultaneously tracks mass and nanomechanical changes at the sensor interface using micro-cantilever technology. To prove the concept we measured lipid vesicle (approximately 748*10(6) Da) adsorption on the sensor interface followed by subsequent binding of the bee venom peptide melittin (2840 Da) to the vesicles. The results show the high dynamic range of the instrument and that measuring the mass and structural changes simultaneously allow a comprehensive discussion of molecular interactions
Leaching as a pretreatment process to complement torrefaction in improving co-firing characteristics of Jatropha curcas seed cake
The presence of certain inorganic elements in biomass causes issues such as slagging, fouling and corrosion when co-firing with coal for power generation. In this work, the efficacy of leaching to remove these elements from Jatropha curcas seed cake was investigated. Leaching of both untorrefied and torrefied seed cakes was carried out in Milli-Q water at temperatures of 20, 35 and 50 °C. At 20 °C, the two critical elements, potassium and chlorine, decreased by as much as 85 and 97 %, respectively. Leaching at higher temperatures was only beneficial for the more intensely torrefied biomass, since they were more resistant to leaching. The electrical conductivity and ion content of the leachates were measured, as were the inorganic elemental content, dry ash content, volatile matter content and higher heating value (HHV) of the solid seed cake. A secondary benefit of the leaching was an increase in the HHV by up to 10 %
Adsorption of mono- and multivalent cat- and anions on DNA molecules
Adsorption of monovalent and multivalent cat- and anions on a deoxyribose
nucleic acid (DNA) molecule from a salt solution is investigated by computer
simulation. The ions are modelled as charged hard spheres, the DNA molecule as
a point charge pattern following the double-helical phosphate strands. The
geometrical shape of the DNA molecules is modelled on different levels ranging
from a simple cylindrical shape to structured models which include the major
and minor grooves between the phosphate strands. The densities of the ions
adsorbed on the phosphate strands, in the major and in the minor grooves are
calculated. First, we find that the adsorption pattern on the DNA surface
depends strongly on its geometrical shape: counterions adsorb preferentially
along the phosphate strands for a cylindrical model shape, but in the minor
groove for a geometrically structured model. Second, we find that an addition
of monovalent salt ions results in an increase of the charge density in the
minor groove while the total charge density of ions adsorbed in the major
groove stays unchanged. The adsorbed ion densities are highly structured along
the minor groove while they are almost smeared along the major groove.
Furthermore, for a fixed amount of added salt, the major groove cationic charge
is independent on the counterion valency. For increasing salt concentration the
major groove is neutralized while the total charge adsorbed in the minor groove
is constant. DNA overcharging is detected for multivalent salt. Simulations for
a larger ion radii, which mimic the effect of the ion hydration, indicate an
increased adsorbtion of cations in the major groove.Comment: 34 pages with 14 figure
The European Union in the World — A Community of Values
These are momentous times in Europe. The Euro has been successfully introduced, the enlargement negotiations are approaching their climax, and the European Convention (“Convention”) is moving towards the drafting of a constitution for a new, continent-wide political entity. At the same time, unrest is manifest, particularly in two areas. On the one hand, many of our citizens, and not just the political elites, are dissatisfied with Europe\u27s performance on the world stage and are concerned about the maintenance of peace and security within the Union. In these areas they would like to see a strengthened, more effective entity-- “more Europe.” On the other hand, their disenchantment with the long reach of European Union (“EU” or “Union”) regulation in the first pillar area of economic policy is growing. The feeling of loss of local control over their destiny and a vague feeling of potential loss of identity within an ever more centralized polity is palpable. Here, they want “less Europe.” In the outside world, change is also the order of the day. The ice-sheet of bipolarity, which overlaid and hid the complexity of international relations during the Cold War, is breaking up at an ever-increasing speed and revealing a world in which two paradigms are competing to become the underlying ordering principles for the new century. The traditional paradigm of interacting Nation States, each pursuing its own separate interests, with alliances allowing the small to compete with the large, is alive and well, and its proponents like Machiavelli or Churchill continue to be in vogue in the literature of international relations and the rhetoric of world leaders. At the same time, there is a school of thought which points to the growing economic and ecological interdependence of our societies and the necessity for new forms of global governance to complement national action. It is also becoming abundantly clear that the concept of a “Nation State” is often a fiction, positing as it does an identity between the citizens of a State and the members of a culturally homogenous society. For both reasons, the concept of the Nation State as the principal actor on the world stage, is called into question. The experience of the Union with the sharing of State sovereignty is clearly related to the second paradigm and also to the EU\u27s firm support for the development of the United Nations (“U.N.”) as well as other elements of multilateral governance. It would hardly be wise to suggest that any foreign policy, and certainly not that of the EU, should be based only on this paradigm. Given the recurrent threats to security, which seem to be part of the human condition expressed by some as the “inevitability of war”--the defense of territorial integrity; action against threats of aggression; and resistance to crimes against humanity such as genocide--the ability to conduct a security policy based much more on the old paradigm of interacting interests will continue to be required. That the EU needs to develop such a capability will be taken here as a given. Such a crisis-management capability will be essential to the Union, but will be distinguished here from the more long-term elements of foreign policy, which can be thought of as being designed to reduce the need for crisis management in the context of a security policy to a minimum. The crisis-management area of policy will not be treated further here. The thesis of this Essay is that the same set of political concepts can serve as a guide to the future internal development of the EU and as the basis of such a long-term foreign policy. Furthermore, it suggests that neither should be seen in terms of the balancing of interests but rather, as the expression of a small list of fundamental values. The list is as follows: (1) the rule of law as the basis for relations between members of society; (2) the interaction between the democratic process and entrenched human rights in political decision-making; (3) the operation of competition within a market economy as the source of increasing prosperity; (4) the anchoring of the principle of solidarity among all members of society alongside that of the liberty of the individual; (5) the adoption of the principle of sustainability of all economic development; and (6) the preservation of separate identities and the maintenance of cultural diversity within society. These values can be seen as the answer to the question posed both, by citizens of the Union and by our fellow citizens of the world: “What does the EU stand for?” In exploring these values we should, however, remember that in the real world there will be occasions on which Realpolitik will intrude and the interest-based paradigm will prevail
Structural insight into SUMO chain recognition and manipulation by the ubiquitin ligase RNF4
The small ubiquitin-like modifier (SUMO) can form polymeric chains that are important signals in cellular processes such as meiosis, genome maintenance and stress response. The SUMO-targeted ubiquitin ligase RNF4 engages with SUMO chains on linked substrates and catalyses their ubiquitination, which targets substrates for proteasomal degradation. Here we use a segmental labelling approach combined with solution nuclear magnetic resonance (NMR) spectroscopy and biochemical characterization to reveal how RNF4 manipulates the conformation of the SUMO chain, thereby facilitating optimal delivery of the distal SUMO domain for ubiquitin transfer
Measurement of the Target-Normal Single-Spin Asymmetry in Quasi-Elastic Scattering from the Reaction He
We report the first measurement of the target single-spin asymmetry, ,
in quasi-elastic scattering from the inclusive reaction
He on a He gas target polarized normal to the
lepton scattering plane. Assuming time-reversal invariance, this asymmetry is
strictly zero for one-photon exchange. A non-zero can arise from the
interference between the one- and two-photon exchange processes which is
sensitive to the details of the sub-structure of the nucleon. An experiment
recently completed at Jefferson Lab yielded asymmetries with high statistical
precision at 0.13, 0.46 and 0.97 GeV. These measurements
demonstrate, for the first time, that the He asymmetry is clearly non-zero
and negative with a statistical significance of (8-10). Using measured
proton-to-He cross-section ratios and the effective polarization
approximation, neutron asymmetries of (1-3)% were obtained. The neutron
asymmetry at high is related to moments of the Generalized Parton
Distributions (GPDs). Our measured neutron asymmetry at GeV
agrees well with a prediction based on two-photon exchange using a GPD model
and thus provides a new, independent constraint on these distributions
A Precision Measurement of the Neutron Twist-3 Matrix Element : Probing Color Forces
Double-spin asymmetries and absolute cross sections were measured at large
Bjorken (0.25 0.90), in both the deep-inelastic and resonance
regions, by scattering longitudinally polarized electrons at beam energies of
4.7 and 5.9 GeV from a transversely and longitudinally polarized He target.
In this dedicated experiment, the spin structure function on He was
determined with precision at large , and the neutron twist-three matrix
element was measured at \left of 3.21 and 4.32
GeV/, with an absolute precision of about . Our results are
found to be in agreement with lattice QCD calculations and resolve the
disagreement found with previous data at \left = 5 GeV/.
Combining and a newly extracted twist-four matrix element, , the
average neutron color electric and magnetic forces were extracted and found to
be of opposite sign and about 30 MeV/fm in magnitude.Comment: Corrected a typo in the author list and Figure 1 legend. 6 pages, 2
figures, 2 table
Single Spin Asymmetries of Inclusive Hadrons Produced in Electron Scattering from a Transversely Polarized He Target
We report the first measurement of target single-spin asymmetries (A) in
the inclusive hadron production reaction,
+, using a transversely polarized
He target. The experiment was conducted at Jefferson Lab in Hall A using a
5.9-GeV electron beam. Three types of hadrons (,
and proton) were detected in the transverse hadron momentum range 0.54
0.74 GeV/c. The range of for pions was -0.29 -0.23 and for kaons
-0.25 -0.18. The observed asymmetry strongly depends on the type of
hadron. A positive asymmetry is observed for and . A
negative asymmetry is observed for . The magnitudes of the asymmetries
follow . The K and proton
asymmetries are consistent with zero within the experimental uncertainties. The
and asymmetries measured for the He target and
extracted for neutrons are opposite in sign with a small increase observed as a
function of .Comment: Updated version, submitted to Phys. Rev.
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