2,116 research outputs found
Calculation of the Phase Behavior of Lipids
The self-assembly of monoacyl lipids in solution is studied employing a model
in which the lipid's hydrocarbon tail is described within the Rotational
Isomeric State framework and is attached to a simple hydrophilic head.
Mean-field theory is employed, and the necessary partition function of a single
lipid is obtained via a partial enumeration over a large sample of molecular
conformations. The influence of the lipid architecture on the transition
between the lamellar and inverted-hexagonal phases is calculated, and
qualitative agreement with experiment is found.Comment: to appear in Phys.Rev.
Spin- and angle-resolved photoemission studies of the electronic structure of Si(110)"16x2" surfaces
The electronic structure of Si(110)"16 x 2" double-domain, single-domain and
1 x 1 surfaces have been investigated using spin- and angle-resolved
photoemission at sample temperatures of 77 K and 300 K. Angle-resolved
photoemission was conducted using horizontally- and vertically-polarised 60 eV
and 80 eV photons. Band-dispersion maps revealed four surface states ( to
) which were assigned to silicon dangling bonds on the basis of measured
binding energies and photoemission intensity changes between horizontal and
vertical light polarisations. Three surface states (, and ),
observed in the Si(110)"16 x 2" reconstruction, were assigned to Si adatoms and
Si atoms present at the edges of the corrugated terrace structure. Only one of
the four surface states, , was observed in both the Si(110)"16 x 2" and 1
x 1 band maps and consequently attributed to the pervasive Si zigzag chains
that are components of both the Si(110)"16 x 2" and 1 x 1 surfaces. A state in
the bulk-band region was attributed to an in-plane bond. All data were
consistent with the adatom-buckling model of the Si(110)"16 x 2" surface.
Whilst room temperature measurements of and were statistically
compatible with zero, measurements of the enantiomorphic A-type and
B-type Si(110)"16 x 2" surfaces gave small average polarisations of around
1.5\% that were opposite in sign. Further measurements at 77 K on A-type
Si(110)"16 x 2" surface gave a smaller value of +0.3\%. An upper limit of
may thus be taken for the longitudinal polarisation.Comment: Main paper: 12 pages and 11 figures. Supplemental information: 5
pages and 2 figure
Long-term trends in diatom diversity and palaeoproductivity: a 16 000-year multidecadal record from Lake Baikal, southern Siberia
Biological diversity is inextricably linked to community stability and
ecosystem functioning, but our understanding of these relationships in
freshwater ecosystems is largely based on short-term observational,
experimental, and modelling approaches. Using a multidecadal diatom record
for the past ca. 16 000 years from Lake Baikal, we investigate how diversity
and palaeoproductivity have responded to climate change during periods of
both rapid climate fluctuation and relative climate stability. We show
dynamic changes in diatom communities during the past 16 000 years, with
decadal shifts in species dominance punctuating millennial-scale seasonal
trends. We describe for the first time in Lake Baikal a gradual shift from
spring to autumnal diatom communities that started during the Younger Dryas
and peaked during the Late Holocene, which likely represents orbitally driven
ecosystem responses to long-term changes in seasonality. Using a
multivariate classification tree, we show that trends in planktonic and
tychoplanktonic diatoms broadly reflect both long-term climatic changes
associated with the demise of Northern Hemisphere ice sheets and abrupt
climatic changes associated with, for example, the Younger Dryas stadial.
Indeed, diatom communities are most different before and after the boundary
between the Early and Middle Holocene periods of ca. 8.2 cal kyr BP, associated
with the presence and demise of Northern Hemisphere ice sheets respectively.
Diatom richness and diversity, estimated using Hill's species numbers, are
also shown to be very responsive to periods characterized by abrupt climate
change, and using knowledge of diatom autecologies in Lake Baikal, diversity
trends are interpreted in terms of resource availability. Using diatom
biovolume accumulation rates (BVARs; µm3 cm−2 yr−1), we
show that spring diatom crops dominate palaeoproductivity for nearly all of
our record, apart from a short period during the Late Holocene, when
autumnal productivity dominated between 1.8–1.4 cal kyr BP.
Palaeoproductivity was especially unstable during the Younger Dryas,
reaching peak rates of 18.3 × 103 µm3 cm−2 yr−1 at
ca. 12.3 cal kyr BP. Generalized additive models (GAMs), which explore
productivity–diversity relationships (PDRs) during pre-defined climate
periods, reveal complex relationships. The strongest statistical evidence for
GAMs were found during the Younger Dryas, the Early Holocene, and the Late
Holocene, i.e. periods of rapid climate change. We account for these
differences in terms of climate-mediated resource availability, and the
ability of endemic diatom species in Lake Baikal to adapt to extreme forms
of living in this unique ecosystem. Our analyses offer insight into how
productivity–diversity relationships may develop in the future under a
warming climate
Characterisation of ferroelectric domains in magnetite (Fe3O4)
Magnetite has long been investigated across many disciplines due to the
interplay between its ferroic order parameters, namely its ferrimagnetism,
ferroelasticity and ferroelectricty. Despite this, the experimental difficulty
in measuring low temperature real space images of the ferroelectric domains has
meant that the local behaviour of ferroelectric domains emergent below the 38 K
phase transition have yet to be realised. This work presents real space images
of the ferroelectric domains, and uses piezo force microscopy to, as a function
of temperature, probe the onset of piezoelectricty and ferroelectricity across
the 38 K transitionComment: 6 Pages, 3 figure
Pressure Induced Hydration Dynamics of Membranes
Pressure-jump initiated time-resolved x-ray diffraction studies of dynamics
of the hydration of the hexagonal phase in biological membranes show that (i)
the relaxation of the unit cell spacing is non-exponential in time; (ii) the
Bragg peaks shift smoothly to their final positions without significant
broadening or loss in crystalline order. This suggests that the hydration is
not diffusion limited but occurs via a rather homogeneous swelling of the whole
lattice, described by power law kinetics with an exponent .Comment: REVTEX 3, 10 pages,3 figures(available on request),#
rs5888 Variant of SCARB1 Gene Is a Possible Susceptibility Factor for Age-Related Macular Degeneration
Major genetic factors for age-related macular degeneration (AMD) have recently been identified as susceptibility risk factors, including variants in the CFH gene and the ARMS2 LOC387715/HTRA1locus. Our purpose was to perform a case-control study in two populations among individuals who did not carry risk variants for CFHY402H and LOC387715 A69S (ARMS2), called “study” individuals, in order to identify new genetic risk factors. Based on a candidate gene approach, we analyzed SNP rs5888 of the SCARB1 gene, coding for SRBI, which is involved in the lipid and lutein pathways. This study was conducted in a French series of 1241 AMD patients and 297 controls, and in a North American series of 1257 patients with advanced AMD and 1732 controls. Among these individuals, we identified 61 French patients, 77 French controls, 85 North American patients and 338 North American controls who did not carry the CFH nor ARMS2 polymorphisms. An association between AMD and the SCARB1 gene was seen among the study subjects. The genotypic distribution of the rs5888 polymorphism was significantly different between cases and controls in the French population (p<0.006). Heterozygosity at the rs5888 SNP increased risk of AMD compared to the CC genotypes in the French study population (odds ratio (OR) = 3.5, CI95%: 1.4–8.9, p<0.01) and after pooling the 2 populations (OR = 2.9, 95% CI: 1.6–5.3, p<0.002). Subgroup analysis in exudative forms of AMD revealed a pooled OR of 3.6 for individuals heterozygous for rs5888 (95% CI: 1.7–7.6, p<0.0015). These results suggest the possible contribution of SCARB1, a new genetic factor in AMD, and implicate a role for cholesterol and antioxidant micronutrient (lutein and vitamin E) metabolism in AMD
Capitals and commitment. The case of a local learning and employment network.
This article draws on research undertaken with a Local Learning and Employment Network (LLEN) in the state of Victoria, Australia. LLEN are networks that were implemented by the state government in 2001 to undertake community capacity building through which the outcomes of young people aged 15-19 in education, training and employment would be enhanced. In 2008, in the context
of an enhanced federal commitment to social inclusion through ‘joining-up’, the Victorian experience provides insights on the implications of such policy initiatives. Drawing on Bourdieu’s discussion of the forms of capital and
Granovetter’s notion of the strength of weak ties, I argue that stores of economic, cultural and social capital as outlined by Bourdieu were necessary, but insufficient, for LLEN to achieve the objectives with which they were charged
given the failure of government to follow through on the implications of its policies. I argue for a commitment on the part of all stakeholders to realise the potential of ‘joining-up’
YPTB3816 of 'Yersinia pseudotuberculosis' strain IP32953 is a virulence-related metallo-oligopeptidase
Background: although bacterial peptidases are known to be produced by various microorganisms, including pathogenic bacteria, their role in bacterial physiology is not fully understood. In particular, oligopeptidases are thought to be mainly involved in degradation of short peptides e.g. leader peptides released during classical protein secretion pathways. The aim of this study was to investigate effects of inactivation of an oligopeptidase encoding gene opdA gene of Yersinia pseudotuberculosis on bacterial properties in vivo and in vitro, and to test dependence of the enzymatic activity of the respective purified enzyme on the presence of different divalent cations.
Results: in this study we found that oligopeptidase OpdA of Yersinia pseudotuberculosis is required for bacterial virulence, whilst knocking out the respective gene did not have any effect on bacterial viability or growth rate in vitro. In addition, we studied enzymatic properties of this enzyme after expression and purification from E. coli. Using an enzyme depleted of contaminant divalent cations and different types of fluorescently labelled substrates, we found strong dependence of its activity on the presence of particular cations. Unexpectedly, Zn2+ showed stimulatory activity only at low concentrations, but inhibited the enzyme at higher concentrations. In contrast, Co2+, Ca2+ and Mn2+ stimulated activity at all concentrations tested, whilst Mg2+ revealed no effect on the enzyme activity at all concentrations used.
Conclusions: the results of this study provide valuable contribution to the investigation of bacterial peptidases in general, and that of metallo-oligopeptidases in particular. This is the first study demonstrating that opdA in Yersinia pseudotuberculsosis is required for pathogenicity. The data reported are important for better understanding of the role of OpdA-like enzymes in pathogenesis in bacterial infections. Characterisation of this protein may serve as a basis for the development of novel antibacterials based on specific inhibition of this peptidase activity
Effect of vessel wettability on the foamability of "ideal" surfactants and "real-world" beer heads
The ability to tailor the foaming properties of a solution by controlling its chemical composition is highly desirable and has been the subject of extensive research driven by a range of applications. However, the control of foams by varying the wettability of the foaming vessel has been less widely reported. This work investigates the effect of the wettability of the side walls of vessels used for the in situ generation of foam by shaking aqueous solutions of three different types of model surfactant systems (non-ionic, anionic and cationic surfactants) along with four different beers (Guinness Original, Banks’s Bitter, Bass No 1 and Harvest Pale). We found that hydrophilic vials increased the foamability only for the three model systems but increased foam stability for all foams except the model cationic system. We then compared stability of beer foams produced by shaking and pouring and demonstrated weak qualitative agreement between both foam methods. We also showed how wettability of the glass controls bubble nucleation for beers and champagne and used this effect to control exactly where bubbles form using simple wettability patterns
- …