Verification in Staged Tile Self-Assembly

We prove the unique assembly and unique shape verification problems, benchmark measures of self-assembly model power, are $\mathrm{coNP}^{\mathrm{NP}}$-hard and contained in $\mathrm{PSPACE}$ (and in $\mathrm{\Pi}^\mathrm{P}_{2s}$ for staged systems with $s$ stages). En route, we prove that unique shape verification problem in the 2HAM is $\mathrm{coNP}^{\mathrm{NP}}$-complete.Comment: An abstract version will appear in the proceedings of UCNC 201

Graduate Student Perceptions of Cohort Delivery and Problem-Based Learning in Online Principal Certification Courses

This qualitative study examined graduate/post-graduate student perceptions regarding the use of a cohort model and Project-Based Learning (PBL) in a completely online principal certification preparation classes. As part of a TEA funded grant, two districts (a cohort of 17 students) completed 24-semester hours of principal certification courses. All classes were online and emphasized PBL to engage the students in higher-level thinking skills. Participants responded to an open-ended survey regarding their perceptions of cohort and PBL experiences. Findings indicate graduate/post-graduate student perceptions were positive concerning both the cohort model and the PBL learning experiences. However, participants provided valuable feedback for improvements related to cohort organization, communication, and PBL introduction or presentation. Three themes emerged from the thematic analysis and peer debriefings: Theme One (T1)-Cohort Experience, Theme Two (T2)-PBL Experience, and Theme Three (T3)-the Interaction between Cohort and PBL Experiences

Using a Flow Through device to reconstruct the thermal gradient in the water column based on G. inflata Mg/Ca

We present Mg/Ca analyses performed via a Flow Through sequential dissolution device connected to an ICP-OES on the planktonic foraminifer Globorotalia inflata. The aim of the study is to explore the possibility to reconstruct the thermal gradient in the water column by separating non-crusted and crusted calcite phases in the tests of G. inflata using the difference between their Mg/Ca ratios as a measure of the thermal gradient. An important assumption is that the non-crusted part of the tests is calcified in shallow, warmer water than the crusted part. For analyses a range of different preparation steps were used to determine the ideal way of separating the phases. Foraminifer tests were (not) cleaned, (not) crushed, and (not) pulverized before online analysis with the FT device. To analyze samples with a FT device the foraminifer tests are placed on a filter with a mesh of 0.45 μm preventing clay minerals to wash through. A sequential dissolution protocol first rinses the samples with buffered Seralpur water before QD HNO3 is added in small steps to create a ramp of increasing acid strength. As acid is kept constant at each concentration for several minutes, dissolution of a specific calcite phase can take place. Initial results show that it is most effective to slightly crush the tests without applying standard cleaning procedures, but rather analyze them without cleaning. Samples were selected from the South Atlantic (core tops and specific downcore samples) and the Mediteterranean (plankton tows). All samples were chosen based on previous work on them to provide comparison with routinely analysed Mg/Ca ratios. The South Atlantic samples have been analyzed extensively as bulk samples separated in difference size fractions and crusted vs. non-crusted (Groeneveld and Chiessi). The Mediterranean samples were not only analyzed as bulk samples but also by Laser Ablation ICP-MS (von Raden et al.). Results show that bulk analyses are reliably reproduced by the FT method, especially for samples which are dominated by crusted calcite. Samples which were uncrusted often gave much higher Mg/Ca ratios than the bulk analyses. These higher Mg/Ca ratios mainly occur in the plankton tow samples and were also identified with Laser Ablation ICP-MS. A possible reason for this could be the presence of a high Mg amorphous calcite layer on the outside of foraminifer tests which have not completed their calcification yet as was recently also pointed out in several other studies. Identification of the crusted and uncrusted phases, and therewith a thermal gradient, seems to give the expected differences but a more rigorous statistical treatment is needed to pinpoint singular dissolution phases

Optimality program in segment and string graphs

Planar graphs are known to allow subexponential algorithms running in time $2^{O(\sqrt n)}$ or $2^{O(\sqrt n \log n)}$ for most of the paradigmatic problems, while the brute-force time $2^{\Theta(n)}$ is very likely to be asymptotically best on general graphs. Intrigued by an algorithm packing curves in $2^{O(n^{2/3}\log n)}$ by Fox and Pach [SODA'11], we investigate which problems have subexponential algorithms on the intersection graphs of curves (string graphs) or segments (segment intersection graphs) and which problems have no such algorithms under the ETH (Exponential Time Hypothesis). Among our results, we show that, quite surprisingly, 3-Coloring can also be solved in time $2^{O(n^{2/3}\log^{O(1)}n)}$ on string graphs while an algorithm running in time $2^{o(n)}$ for 4-Coloring even on axis-parallel segments (of unbounded length) would disprove the ETH. For 4-Coloring of unit segments, we show a weaker ETH lower bound of $2^{o(n^{2/3})}$ which exploits the celebrated Erd\H{o}s-Szekeres theorem. The subexponential running time also carries over to Min Feedback Vertex Set but not to Min Dominating Set and Min Independent Dominating Set.Comment: 19 pages, 15 figure

Direct path from microscopic mechanics to Debye shielding, Landau damping, and wave-particle interaction

The derivation of Debye shielding and Landau damping from the $N$-body description of plasmas is performed directly by using Newton's second law for the $N$-body system. This is done in a few steps with elementary calculations using standard tools of calculus, and no probabilistic setting. Unexpectedly, Debye shielding is encountered together with Landau damping. This approach is shown to be justified in the one-dimensional case when the number of particles in a Debye sphere becomes large. The theory is extended to accommodate a correct description of trapping and chaos due to Langmuir waves. Shielding and collisional transport are found to be two related aspects of the repulsive deflections of electrons, in such a way that each particle is shielded by all other ones while keeping in uninterrupted motion.Comment: arXiv admin note: substantial text overlap with arXiv:1310.3096, arXiv:1210.154

Les organisations paysannes et rurales. Des acteurs du développement en Afrique sub-saharienne

Dans tous les pays, les organisations paysannes et rurales sont à la fois le lieu d'expression des intérêts de paysans et un moyen d'atteindre les objectifs qu'ils se fixent. Au-delà de leurs multiples finalités, évoquées tout au long de ce document, les OPR devraient s'orienter vers la construction d'un pouvoir paysan, certes multiforme, capable à la fois de peser sur la définition et la mise en oeuvre des politiques concernant le monde rural, et de préciser la place des agriculteurs dans des sociétés en construction. Chacun, depuis le paysan jusqu'à l'homme politique en passant par le chercheur, le technicien, le représentant d'un organisme de coopération, possède une vision de ce que sont les organisations paysannes et de ce qu'elles devraient être. C'est un peu l'objet de ce document que de contribuer à faire s'exprimer ces visions différentes, à les confronter pour, au bout du compte, donner aux principaux acteurs, les paysans et ceux qui les accompagnent, des moyens pour mieux exprimer leur vision des chose