149 research outputs found
Columnar Molecular Aggregation In The Aqueous Solutions Of Disodium Cromoglycate
Stack, chimneylike, and threadlike assemblies have previously been proposed for the structure of disodium cromoglycate (DSCG) aggregates in aqueous solutions. The results of the synchrotron x-ray scattering investigations reported here reveal the formation of simple columnar assemblies with pi-pi stacking at a separation of 3.4 angstrom between the DSCG molecules. Lateral separation between the assemblies is concentration and temperature dependent, varying from similar to 35 to 42 angstrom in the orientationally ordered nematic (N) phase and from 27 to 32 angstrom in the columnar or middle (M) phase having long range lateral positional order. The assemblies\u27 length depends on concentration and consists of similar to 23 molecules in the N phase, becoming three to ten times larger in the M phase. The scission energy is concentration dependent in the N phase with values similar to 7.19 +/- 0.14 k(B)T (15 wt%), 2.73 +/- 0.4 k(B)T (20 wt%), and 3.05 +/- 0.2 k(B)T (25 wt%). Solutions of all concentrations undergo a spinodal decomposition at temperatures above similar to 40 degrees C, resulting in DSCG-rich regions with the M phase and water-rich regions in the N and isotropic phases
Measurement of the conductance of a hydrogen molecule
Recent years have shown steady progress in research towards molecular
electronics [1,2], where molecules have been investigated as switches [3-5],
diodes [6], and electronic mixers [7]. In much of the previous work a Scanning
Tunnelling Microscope was employed to address an individual molecule. As this
arrangement does not provide long-term stability, more recently
metal-molecule-metal links have been made using break junction devices [8-10].
However, it has been difficult to establish unambiguously that a single
molecule forms the contact [11]. Here, we show that a single H2 molecule can
form a stable bridge between Pt electrodes. In contrast to results for other
organic molecules, the bridge has a nearly perfect conductance of one quantum
unit, carried by a single channel. The H2-bridge provides a simple test system
and a fundamental step towards understanding transport properties of
single-molecule devices.Comment: 6 pages, 4 figure
Algorithm Engineering in Robust Optimization
Robust optimization is a young and emerging field of research having received
a considerable increase of interest over the last decade. In this paper, we
argue that the the algorithm engineering methodology fits very well to the
field of robust optimization and yields a rewarding new perspective on both the
current state of research and open research directions.
To this end we go through the algorithm engineering cycle of design and
analysis of concepts, development and implementation of algorithms, and
theoretical and experimental evaluation. We show that many ideas of algorithm
engineering have already been applied in publications on robust optimization.
Most work on robust optimization is devoted to analysis of the concepts and the
development of algorithms, some papers deal with the evaluation of a particular
concept in case studies, and work on comparison of concepts just starts. What
is still a drawback in many papers on robustness is the missing link to include
the results of the experiments again in the design
Radio continuum observations of Class I protostellar disks in Taurus: constraining the greybody tail at centimetre wavelengths
We present deep 1.8 cm (16 GHz) radio continuum imaging of seven young
stellar objects in the Taurus molecular cloud. These objects have previously
been extensively studied in the sub-mm to NIR range and their SEDs modelled to
provide reliable physical and geometrical parametres.We use this new data to
constrain the properties of the long-wavelength tail of the greybody spectrum,
which is expected to be dominated by emission from large dust grains in the
protostellar disk. We find spectra consistent with the opacity indices expected
for such a population, with an average opacity index of beta = 0.26+/-0.22
indicating grain growth within the disks. We use spectra fitted jointly to
radio and sub-mm data to separate the contributions from thermal dust and radio
emission at 1.8 cm and derive disk masses directly from the cm-wave dust
contribution. We find that disk masses derived from these flux densities under
assumptions consistent with the literature are systematically higher than those
calculated from sub-mm data, and meet the criteria for giant planet formation
in a number of cases.Comment: submitted MNRA
Combined ship routing and inventory management in the salmon farming industry
We consider a maritime inventory routing problem for Norway's largest salmon farmer both producing the feed at a production factory and being responsible for fish farms located along the Norwegian coast. The company has bought two new ships to transport the feed from the factory to the fish farms and is responsible for the routing and scheduling of the ships. In addition, the company has to ensure that the feed at the production factory as well as at the fish farms is within the inventory limits. A mathematical model of the problem is presented, and this model is reformulated to improve the efficiency of the branch-and-bound algorithm and tightened with valid inequalities. To derive good solutions quickly, several practical aspects of the problem are utilized and two matheuristics developed. Computational results are reported for instances based on the real problem of the salmon farmer
School dropout, problem behaviour and poor academic achievement : a longitudinal view of portuguese male offenders
This study examines school drop outs from the perspective of male adults
themselves through interviews with offenders currently serving sentences. Participants
were 10 Portuguese male inmates, between the ages of 19 and 46 years of age,
incarcerated in two prison facilities of the Azores. Qualitative and interpretative methods
were carried out using a semi-structured in-depth individual interview that was audiorecorded
and conducted on the basis of a list of topics. Interview transcripts and thematic
analysis were used in data treatment and analysis. The findings primarily indicate that
poor academic achievement and emotional and behavioural difficulties of participants
played a particular role in early school drop out. The trajectories these individuals
followed within the education system presented problem behaviour, learning disabilities,
and/or foster care interventions. While school drop out circumstances were apparently
various, analysis showed that they were underpinned by three distinct sets of conditions
generally not addressed by the education system. The analysis of the triggering factors
and the maintenance dynamics of school drop outs indicated three distinct types:
retention/absenteeism, life turning points and positive resolution. Implications for
secondary prevention and screening practices are discussed.FCT (SFRH/ BD/ 44245/ 2008)CIEC - unidade de investigação 317 da FC
Controlling Clusters of Colloidal Platelets:The Effects of Edge and Face Surface Chemistries on the Behaviour of Montmorillonite Suspensions
Grain growth across protoplanetary discs: 10-micron silicate feature versus millimetre slope
Young stars are formed within dusty discs. The grains in the disc are
originally of the same size as interstellar dust. Models predict that these
grains will grow in size through coagulation. Observations of the silicate
features at micron wavelengths are consistent with growth to micron sizes
whereas the slope of the SED at longer wavelengths traces growth up to mm
sizes. We here look for a correlation between these two grain growth
indicators. A large sample of T-Tauri and Herbig-Ae/Be stars was observed with
the Spitzer Space Telescope at 5-13 micron; a subsample was observed at mm
wavelengths. We complement this subsample with data from the literature to
maximise the overlap between micron and mm observations and search for
correlations. Synthetic spectra are produced to determine which processes may
produce the dust evolution. Dust disc masses in the range <1 to 7 x 10^-4 MSun
are obtained. Most sources have a mm spectral slope consistent with grain
growth. There is a tentative correlation between the 10-micron silicate feature
and the mm slope of the SED. The observed sources seem to be grouped per
star-forming region in the micron-vs-mm diagram. The modelling results show
that the 10-micron feature becomes flatter and subsequently the mm slope
becomes shallower. Grain size distributions shallower than that of the ISM
and/or bright central stars are required to explain specific features. Settling
of larger grains towards the disc midplane affects the 10-micron feature, but
hardly the mm slope. The tentative correlation between the strength of the
10-micron feature and the mm slope suggests that the inner and outer disc
evolve simultaneously. Dust with a mass dominated by mm-sized grains is
required to explain the shallowest mm slopes. Other processes besides grain
growth may also be responsible for the removal of small grains.Comment: 23 pages, 14 figures, accepted by A&
Effect of SGLT2 inhibitors on stroke and atrial fibrillation in diabetic kidney disease: Results from the CREDENCE trial and meta-analysis
BACKGROUND AND PURPOSE: Chronic kidney disease with reduced estimated glomerular filtration rate or elevated albuminuria increases risk for ischemic and hemorrhagic stroke. This study assessed the effects of sodium glucose cotransporter 2 inhibitors (SGLT2i) on stroke and atrial fibrillation/flutter (AF/AFL) from CREDENCE (Canagliflozin and Renal Events in Diabetes With Established Nephropathy Clinical Evaluation) and a meta-Analysis of large cardiovascular outcome trials (CVOTs) of SGLT2i in type 2 diabetes mellitus. METHODS: CREDENCE randomized 4401 participants with type 2 diabetes mellitus and chronic kidney disease to canagliflozin or placebo. Post hoc, we estimated effects on fatal or nonfatal stroke, stroke subtypes, and intermediate markers of stroke risk including AF/AFL. Stroke and AF/AFL data from 3 other completed large CVOTs and CREDENCE were pooled using random-effects meta-Analysis. RESULTS: In CREDENCE, 142 participants experienced a stroke during follow-up (10.9/1000 patient-years with canagliflozin, 14.2/1000 patient-years with placebo; hazard ratio [HR], 0.77 [95% CI, 0.55-1.08]). Effects by stroke subtypes were: ischemic (HR, 0.88 [95% CI, 0.61-1.28]; n=111), hemorrhagic (HR, 0.50 [95% CI, 0.19-1.32]; n=18), and undetermined (HR, 0.54 [95% CI, 0.20-1.46]; n=17). There was no clear effect on AF/AFL (HR, 0.76 [95% CI, 0.53-1.10]; n=115). The overall effects in the 4 CVOTs combined were: Total stroke (HRpooled, 0.96 [95% CI, 0.82-1.12]), ischemic stroke (HRpooled, 1.01 [95% CI, 0.89-1.14]), hemorrhagic stroke (HRpooled, 0.50 [95% CI, 0.30-0.83]), undetermined stroke (HRpooled, 0.86 [95% CI, 0.49-1.51]), and AF/AFL (HRpooled, 0.81 [95% CI, 0.71-0.93]). There was evidence that SGLT2i effects on total stroke varied by baseline estimated glomerular filtration rate (P=0.01), with protection in the lowest estimated glomerular filtration rate (45 mL/min/1.73 m2]) subgroup (HRpooled, 0.50 [95% CI, 0.31-0.79]). CONCLUSIONS: Although we found no clear effect of SGLT2i on total stroke in CREDENCE or across trials combined, there was some evidence of benefit in preventing hemorrhagic stroke and AF/AFL, as well as total stroke for those with lowest estimated glomerular filtration rate. Future research should focus on confirming these data and exploring potential mechanisms
Evaluation of genotoxic and cytotoxic effects of hydroalcoholic extract of Euphorbia tirucalli (Euphorbiaceae) in cell cultures of human leukocytes
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