1,935 research outputs found
Optimal symmetric Tardos traitor tracing schemes
For the Tardos traitor tracing scheme, we show that by combining the
symbol-symmetric accusation function of Skoric et al. with the improved
analysis of Blayer and Tassa we get further improvements. Our construction
gives codes that are up to 4 times shorter than Blayer and Tassa's, and up to 2
times shorter than the codes from Skoric et al. Asymptotically, we achieve the
theoretical optimal codelength for Tardos' distribution function and the
symmetric score function. For large coalitions, our codelengths are
asymptotically about 4.93% of Tardos' original codelengths, which also improves
upon results from Nuida et al.Comment: 16 pages, 1 figur
Oxidation of AlInAs for current blocking in a photonic crystal laser
To make an electrically pumped photonic crystal membrane laser is a challenging task. One of the problems is how to avoid short circuiting between the p- and n-doped parts of the laser diode, when the membrane thickness is limited to 200-300nm. We propose to use the oxide of AlInAs to realize a current blocking function. In this way, based on submicron selective area re-growth, we aim for electrically injected photonic crystal lasers with high output power, small threshold currents and low power consumption. Here results are presented on the oxidation of AlInAs. The results show that it is feasible to use the oxide of AlInAs for current blocking in an InP-based membrane photonic crystal laser
3D-to-2D Transition of Anion Vacancy Mobility in CsPbBr<sub>3</sub>under Hydrostatic Pressure
We study the effects of hydrostatic pressure in the range 0.0--2.0 GPa on
anion mobility in the orthorhombic phase of CsPbBr. Using density
functional theory and the climbing nudged elastic band method, we calculate the
transition states and activation energies for anions to migrate both within and
between neighbouring PbBr octahedra. The results of those calculations
are used as input to a kinetic model for anion migration, which we solve in the
steady state to determine the anion mobility tensor as a function of applied
pressure. We find that the response of the mobility tensor to increasing
pressure is highly anisotropic, being strongly enhanced in the lattice
plane and strongly reduced in the direction normal to it at elevated pressure.
These results demonstrate the potentially significant influence of pressure and
strain on the magnitude and direction of anion migration in lead--halide
perovskites.Comment: 25 pages, 3 figure
Force balance in canonical ensembles of static granular packings
We investigate the role of local force balance in the transition from a
microcanonical ensemble of static granular packings, characterized by an
invariant stress, to a canonical ensemble. Packings in two dimensions admit a
reciprocal tiling, and a collective effect of force balance is that the area of
this tiling is also invariant in a microcanonical ensemble. We present
analytical relations between stress, tiling area and tiling area fluctuations,
and show that a canonical ensemble can be characterized by an intensive
thermodynamic parameter conjugate to one or the other. We test the equivalence
of different ensembles through the first canonical simulations of the force
network ensemble, a model system.Comment: 9 pages, 9 figures, submitted to JSTA
Origin and emergence of entrepreneurship as a research field
This paper seeks to map out the emergence and evolution of entrepreneurship as an independent field in the social science literature from the early 1990s to 2009. Our analysis indicates that entrepreneurship has grown steadily during the 1990s but has truly emerged as a legitimate academic discipline in the latter part of the 2000s. The field has been dominated by researchers from Anglo-Saxon countries over the past 20 years, with particularly strong representations from the US, UK, and Canada. The results from our structural analysis, which is based on a core document approach, point to five large knowledge clusters and further 16 sub-clusters. We characterize the clusters from their cognitive structure and assess the strength of the relationships between these clusters. In addition, a list of most cited articles is presented and discussed
Fluorescence resonance energy transfer sensors for quantitative monitoring of pentose and disaccharide accumulation in bacteria
<p>Abstract</p> <p>Background</p> <p>Engineering microorganisms to improve metabolite flux requires detailed knowledge of the concentrations and flux rates of metabolites and metabolic intermediates <it>in vivo</it>. Fluorescence resonance energy transfer sensors represent a promising technology for measuring metabolite levels and corresponding rate changes in live cells. These sensors have been applied successfully in mammalian and plant cells but potentially could also be used to monitor steady-state levels of metabolites in microorganisms using fluorimetric assays. Sensors for hexose and pentose carbohydrates could help in the development of fermentative microorganisms, for example, for biofuels applications. Arabinose is one of the carbohydrates to be monitored during biofuels production from lignocellulose, while maltose is an important degradation product of starch that is relevant for starch-derived biofuels production.</p> <p>Results</p> <p>An <it>Escherichia coli </it>expression vector compatible with phage λ recombination technology was constructed to facilitate sensor construction and was used to generate a novel fluorescence resonance energy transfer sensor for arabinose. In parallel, a strategy for improving the sensor signal was applied to construct an improved maltose sensor. Both sensors were expressed in the cytosol of <it>E. coli </it>and sugar accumulation was monitored using a simple fluorimetric assay of <it>E. coli </it>cultures in microtiter plates. In the case of both nanosensors, the addition of the respective ligand led to concentration-dependent fluorescence resonance energy transfer responses allowing quantitative analysis of the intracellular sugar levels at given extracellular supply levels as well as accumulation rates.</p> <p>Conclusion</p> <p>The nanosensor destination vector combined with the optimization strategy for sensor responses should help to accelerate the development of metabolite sensors. The new carbohydrate fluorescence resonance energy transfer sensors can be used for <it>in vivo </it>monitoring of sugar levels in prokaryotes, demonstrating the potential of such sensors as reporter tools in the development of metabolically engineered microbial strains or for real-time monitoring of intracellular metabolite during fermentation.</p
Translating climate beliefs into action in a changing political landscape
Political leaders can influence public beliefs about climate change, and climate beliefs can influence climate actions. But, much is still unknown about (1) whether changes in political landscapes influence public's climate beliefs and (2) the psychological process through which climate beliefs influence pro-environmental sentiments and actions. Achieving a better understanding these influences are the dual purposes of this paper, we investigated during the unique setting of the 2016 US presidential elections. First, we explored to what extent the American public's belief in the anthropogenic origins and negative impacts of climate change were influenced by the 2016 US presidential election and earliest administrative days of a climate-skeptical political leader, Donald Trump. We found Trump's influence on public climate beliefs may have increased after his election in such a way that may have polarized public climate beliefs. Compared with pre-election levels, supporters' climate beliefs grew weaker and, further, opponents' climate beliefs grew stronger after his election. Second, we tested a novel conditional mediation model that proposes climate beliefs interact to exert their influence on climate actions via moral behavioral sentiments. Specifically, we found people's origin and impact climate beliefs interact to influence climate actions by activating moral sentiments about their own environmental behavior (i.e., guilt, striving to be a better person), with the particularly weak moral sentiments reported by those with both weak belief in climate change's anthropogenic origins and its negative impacts. Moral sentiments, in turn, predicted respondents' willingness to save energy to reduce climate change and their support for the Paris Climate Agreement. These results suggest the election of climate-skeptical political leaders can impact the public's climate beliefs. Moreover, climate beliefs interact to influence the moral sentiments people feel about their own behavior, and consequently, influence their climate-friendly behavioral intentions and policy preferences
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Producing Crack-Free, High Density M2 HSS Parts by Selective Laser Melting: Pre-Heating the Baseplate
Cracks and delamination, resulting from residual stresses are a barrier in the world of Additive
Manufacturing and Selective Laser Melting (SLM) that prohibits the use of many metals in this field. By preheating the baseplate, thermal gradients are lowered and stresses can be reduced. In this work, some initial tests
were performed with M2 Tool Steel. Results show that pre-heating enables the production of dense M2 parts.
The influence of pre-heating on density and mechanical and physical properties is investigated. The paper
shows many promising results for the production of SLM parts in materials that are very sensitive to crack
formation and delamination. When using a pre-heating of 200°C, crack-free parts were produced with a relative
density of 99.8%.Mechanical Engineerin
Complex response of dinoflagellate cyst distribution patterns to cooler early Oligocene oceans
Previous studies have made extensive use of dinoflagellate cysts to reconstruct past sea surface temperature (SST). Analysis of associations of dinoflagellate cysts using two new ocean datasets for the mid Eocene (Bartonian) and early Oligocene (Rupelian) reveals clear latitudinally constrained distributions for the Bartonian, but unexpected changes in their Rupelian distribution; a significant number of species with low and mid latitude northern hemisphere occurrences in the Bartonian extend their northward ranges in the Rupelian, including some forms characterised as ‘warm water’ by previous studies. This suggests either that dinoflagellates are faithfully tracking a complex oceanographic response to Rupelian cooling, or that dinoflagellate sensitivity/adaptability to a range of ecological variables means that at a global scale their distributions are not primarily controlled by sea surface temperature-variability.
Previous use of dinoflagellate cysts for palaeoclimate work has relied on rather subjective and inconsistent identification of ‘warm’ and ‘cold’ water forms, rather than comprehensive analysis of community associations at the global-scale. It is clear from this study that a better understanding of the (palaeo-)ecology of dinoflagellates and their cysts is required.
Rupelian dinoflagellate cyst distribution may reflect changes in a range of environmental variables linked to early Oligocene climate-cooling, for example changes in nutrient fluxes triggered by glacially-induced base-level fall; complex reorganisation of ocean current systems between the Bartonian and Rupelian, or muted changes to Rupelian summer SSTs in the northern hemisphere that have previously been reported. Many extant dinoflagellate species also exhibit relatively broad temperature tolerance. Moreover, they have potentially extensive cryptic diversity, and are able to produce dormant cysts during short-lived environmental deterioration, all of which may act to limit the value of undifferentiated dinoflagellate cyst assemblages for identifying climate signals
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