Simplex solid states of SU(N) quantum antiferromagnets

I define a set of wavefunctions for SU(N) lattice antiferromagnets, analogous to the valence bond solid states of Affleck, Kennedy, Lieb, and Tasaki (AKLT), in which the singlets are extended over N-site simplices. As with the valence bond solids, the new simplex solid (SS) states are extinguished by certain local projection operators, allowing us to construct Hamiltonians with local interactions which render the SS states exact ground states. Using a coherent state representation, we show that the quantum correlations in each SS state are calculable as the finite temperature correlations of an associated classical model, with N-spin interactions, on the same lattice. In three and higher dimensions, the SS states can spontaneously break SU(N) and exhibit N-sublattice long-ranged order, as a function of a discrete parameter which fixes the local representation of SU(N). I analyze this transition using a classical mean field approach. For N>2 the ordered state is selected via an "order by disorder" mechanism. As in the AKLT case, the bulk representations fractionalize at an edge, and the ground state entropy is proportional to the volume of the boundary.Comment: 14 pages, 8 figures, minor typos correcte

Evaluation of Three Rapid Tests for Diagnosis of P. Falciparum and P. Vivax Malaria in Colombia.

The diagnostic capacity of three malaria rapid diagnostic tests (RDTs), NOW-Malaria-ICT, OptiMAL-IT, and Paracheck-Pf, was evaluated against expert microscopy in Colombia. We tested 896 patients, of whom microscopy confirmed 139 P. falciparum, 279 P. vivax, and 13 mixed P.f/P.v infections and 465 negatives. Paracheck-Pf and NOW-malaria-ICT were more accurate in detecting P. falciparum (sensitivities 90.8% and 90.1%, respectively) in comparison with Optimal-IT (83.6%). NOW showed an acceptable Pf detection rate at low densities (< 500/microL), but resulted in a higher proportion of false positives. For P. vivax diagnosis, Optimal-IT had a higher sensitivity than NOW (91.0% and 81.4%, respectively). The choice between the two Pf/Pv detecting RDTs balances P. falciparum and P. vivax detection rates. Considering some degree of P. falciparum overtreatment and failure to detect all P. vivax cases as more acceptable than missing some cases of P. falciparum, we recommend careful implementation of NOW-malaria-ICT in areas where microscopy is lacking. The price is however still a constraint

Unraveling DNA tori under tension

Motivated by recent experiments, we develop a model for DNA toroids under external tension. We find that tori are the equilibrium states for our model up to a critical tension, above which they become only metstable. Above this tension, we find a cascade of transitions between discrete toroid states that successively lowers the winding number, until the ground state (rod) is reached. In this process, this model predicts a nearly constant force plateau as a function of extension, in agreement with experiment.Comment: 9 pages, 11 figure

Эффективность комбинированных криоконсервантов, содержащих глицерин или 1,2-пропандиол, при замораживании эритроцитов

Исследовали осмотические свойства эритроцитов, замороженных в комбинированных криоконсервантах, содержащих полимерные непроникающие (декстран, полиэтиленгликоль) и проникающие (глицерин, 1,2-пропандиол) криопротекторы. Установлено, что в эритроцитах, замороженных-отогретых в среде с полимерами, отмечается повышение скорости потока ионов Н+ и осмотической хрупкости в среде, содержащей 0,45–0,9% NaCl. Для сохранения осмотических свойств замороженных- отогретых клеток достаточно включить в среду глицерин или 1,2-пропандиол (1,2-ПД) в концентрации 5%. Полученные результаты позволяют предположить, что криопротекторная эффективность комбинированных криоконсервантов, содержащих непроникающие и проникающие криопротекторы, определяется вкладом различных по механизму действия криозащитных компонентов в суммарную защитную эффективность при замораживании и ослаблением постгипертонического стресса на клетки при размораживании.Досліджували осмотичні властивості еритроцитів, заморожених-відігрітих у комбінованих кріоконсервантах, які містять полімерні непроникаючі (декстран, поліетиленгліколь) і проникаючі (гліцерин, 1,2-пропандіол) кріопротектори. Встановлено, що в еритроцитах, заморожених-відігрітих у середовищі з полімерами, визначається зростання швидкості потоку іонів Н+ і осмотичної крихкості в середовищі, яке містить 0,45–0,9% NaCl. Для збереження осмотичних властивостей заморожених- відігрітих клітин достатньо включити в середовище гліцерин або 1,2-пропандіол в концентрації 5%. Отримані результати дозволяють припустити, що кріопротекторна ефективність комбінованих кріоконсервантів, які містять непроникаючі і проникаючі кріопротектори, визначається внеском різноманітних за механізмом дії кріозахисних компонентів у сумарну захисну ефективність при заморожуванні та послабленням постгіпертонічного стресу на клітини при розморожуванні.The osmotic properties of erythrocytes frozen-thawed in combined cryopreservatives, containing polymeric non-penetrating (dextran, polyethylene glycol) and penetrating (glycerol, 1,2-propane diol) cryoprotectants were studied. It was established that in erythrocytes frozen-thawed in the presence of polymers the increasing of H+ ion flow rate and osmotic fragility in the environment with 0.45–0.9% NaCl was observed. It is sufficient to add 5% glycerol or 1,2-propane diol (1,2-PD) to the medium to preserve osmotic properties of frozen-thawed cells. The obtained results enable to suggest that cryoprotective efficiency of combined cryopreservatives, containing non-penetrating and penetrating cryoprotectants is determined both by the contribution of cryoprotective components differing by action mechanism into th

Endoscopic tri-modal imaging for surveillance in ulcerative colitis: randomised comparison of high-resolution endoscopy and autofluorescence imaging for neoplasia detection; and evaluation of narrow-band imaging for classification of lesions

Background: Endoscopic tri-modal imaging (ETMI) incorporates white light endoscopy (WLE), autofluorescence imaging (AFI) and narrow-band imaging (NBI). Aims: To assess the value of ETMI for the detection and classification of neoplasia in patients with longstanding ulcerative colitis. Design: Randomised comparative trial of tandem colonoscopies. Setting: Academic Medical Centre Amsterdam, Netherlands. Patients and methods: Fifty patients with ulcerative colitis underwent surveillance colonoscopy with ETMI. Each colonic segment was inspected twice, once with AFI and once with WLE, in random order. All detected lesions were inspected by NBI for Kudo pit pattern analysis and additional random biopsies were taken. Main outcome measures: Neoplasia miss-rates of AFI and WLE, and accuracy of the Kudo classification by NBI. Results: Among patients assigned to inspection with AFI first (n = 25), 10 neoplastic lesions were primarily detected. Subsequent WLE detected no additional neoplasia. Among patients examined with WLE first (n = 25), three neoplastic lesions were detected; subsequent inspection with AFI added three neoplastic lesions. Neoplasia miss-rates for AFI and WLE were 0% and 50% (p = 0.036). The Kudo classification by NBI had a sensitivity and specificity of 75% and 81%; however, all neoplasia was coloured purple on AFI (sensitivity 100%). No additional patients with neoplasia were detected by random biopsies. Conclusion: Autofluorescence imaging improves the detection of neoplasia in patients with ulcerative colitis and decreases the yield of random biopsies. Pit pattern analysis by NBI has a moderate accuracy for the prediction of histology, whereas AFI colour appears valuable in excluding the presence of neoplasia. Trial registration number: ISRCTN0527274

Geographical distribution of selected and putatively neutral SNPs in Southeast Asian malaria parasites.

Loci targeted by directional selection are expected to show elevated geographical population structure relative to neutral loci, and a flurry of recent papers have used this rationale to search for genome regions involved in adaptation. Studies of functional mutations that are known to be under selection are particularly useful for assessing the utility of this approach. Antimalarial drug treatment regimes vary considerably between countries in Southeast Asia selecting for local adaptation at parasite loci underlying resistance. We compared the population structure revealed by 10 nonsynonymous mutations (nonsynonymous single-nucleotide polymorphisms [nsSNPs]) in four loci that are known to be involved in antimalarial drug resistance, with patterns revealed by 10 synonymous mutations (synonymous single-nucleotide polymorphisms [sSNPs]) in housekeeping genes or genes of unknown function in 755 Plasmodium falciparum infections collected from 13 populations in six Southeast Asian countries. Allele frequencies at known nsSNPs underlying resistance varied markedly between locations (F(ST) = 0.18-0.66), with the highest frequencies on the Thailand-Burma border and the lowest frequencies in neighboring Lao PDR. In contrast, we found weak but significant geographic structure (F(ST) = 0-0.14) for 8 of 10 sSNPs. Importantly, all 10 nsSNPs showed significantly higher F(ST) (P < 8 x 10(-5)) than simulated neutral expectations based on observed F(ST) values in the putatively neutral sSNPs. This result was unaffected by the methods used to estimate allele frequencies or the number of populations used in the simulations. Given that dense single-nucleotide polymorphism (SNP) maps and rapid SNP assay methods are now available for P. falciparum, comparing genetic differentiation across the genome may provide a valuable aid to identifying parasite loci underlying local adaptation to drug treatment regimes or other selective forces. However, the high proportion of polymorphic sites that appear to be under balancing selection (or linked to selected sites) in the P. falciparum genome violates the central assumption that selected sites are rare, which complicates identification of outlier loci, and suggests that caution is needed when using this approach