Entropic Tightening of Vibrated Chains

We investigate experimentally the distribution of configurations of a ring with an elementary topological constraint, a ``figure-8'' twist. Using vibrated granular chains, which permit controlled preparation and direct observation of such a constraint, we show that configurations where one of the loops is tight and the second is large are strongly preferred. This agrees with recent predictions for equilibrium properties of topologically-constrained polymers. However, the dynamics of the tightening process weakly violate detailed balance, a signature of the nonequilibrium nature of this system.Comment: 4 pages, 4 figure

Опыт применения контраст-усиленного ультразвукового исследования при наиболее часто встречающихся злокачественных новообразованиях печени

Aim. To study the features of contrast enhancement of malignant neoplasms of the liver in patients with and without cirrhosis (LC), to study the differences in the dynamics of contrast enhancement of liver are metastatic lesions (MTS) and hepatocellular carcinoma (HCC).Material and methods. A retrospective analysis results 58 patients with HCC (group 1) and 51 patients with liver metastases (group 2) was carried out based on morphological data. According to the criterion for the presence of LC, group 1 was divided into two subgroups. The main method of radiological diagnostics was contrast enhancement ultrasound (CEUS).Results. The indicators of the dynamics of the Wash-in of an ultrasound contrast agent into the HCC node and the dynamics of the drug WASH-OUT from the focus in patients with LC did not significantly differ from those in patients without cirrhosis. HCC is characterized by the onset of leaching of the ultrasound contrast agent after 62 seconds from the beginning of the study, which significantly differs from MTS (p <0.05). The parameters in predicting the G3 stage of the tumor were as follows: the parameter “onset of WASH-OUT” of the from the focus <79 sec, the parameter “time of maximum WASH-OUT” of the ultrasound contrast agent <270 seconds. In our opinion, certain difficulties are presented by the diagnosis of highly differentiated carcinomas due to the absence of the WASH-OUT phenomenon in 50% of patients. Differential diagnosis of metastases should be based on a combination of a number of signs, the most important of which, in our opinion, are: early onset of elution of ultrasound contrast agent, “black hole” symptom, peripheral ring-shaped enhancement in arterial phase.Conclusion. The data obtained with the help of CEUS confirm the effect of “arterialization of hepatic blood flow” in patients with LC. Differences in the parameters of contrasting HCC nodes in subgroups of patients with and without LC are not statistically significant. The polymorphism of the signs detected in MTS in the liver is due to the morphology of the primary tumor and the size of the neoplasms. Differential diagnosis should be based on a combination of signs of the dynamics of ultrasound contrast agents.Цель исследования: изучение особенностей контрастирования злокачественных новообразований печени у пациентов с циррозом печени (ЦП) и без, изучение отличий динамики контрастирования метастазов печени (МТС) и гепатоцеллюлярной карциномы (ГЦК).Материал и методы. На основании морфологических данных проведен ретроспективный анализ обследования 58 пациентов с ГЦК (группа 1) и 51 пациента с МТС печени (группа 2). По критерию наличия ЦП группа 1 была разделена на две подгруппы. Основным методом лучевой диагностики в обеих группах было контраст-усиленное ультразвуковое исследование (КУУЗИ).Результаты. Показатели динамики поступления ультразвукового контрастного препарата (УЗКП) в узел ГЦК и динамики вымывания препарата из очага у пациентов с ЦП достоверно не отличались от показателей у пациентов без цирроза. Для ГЦК характерно начало вымывания УЗКП после 62-й секунды от начала исследования, чем она достоверно отличается от МТС (р < 0,05). Параметры в прогнозировании G3 стадии опухоли были следующими: параметр “начало вымывания” УЗКП из очага <79 с, параметр “время максимального вымывания” УЗКП < 270 с. На наш взгляд, определенные сложности представляет диагностика высокодифференцированных карцином ввиду отсутствия феномена WASH-OUT у 50% пациентов. Дифференциальная диагностика метастазов должна строиться на комбинации ряда признаков, наиболее важными из них, на наш взгляд, являются: раннее начало вымывания УЗКП, симптом “черной дыры”, периферическое кольцевидное усиление в артериальную фазу.Выводы. Полученные при помощи КУУЗИ данные подтверждают эффект “артериализации печеночного кровотока” у больных с ЦП. Различия показателей параметров контрастирования узлов ГЦК в подгруппах пациентов с ЦП и без статистически недостоверны. Для очаговых поражений характерны различные рисунки контрастирования, которые являются основой определения их злокачественности. Полиморфизм признаков, выявляемых при МТС в печени, обусловлен морфологией первичной опухоли и размерами новообразований. Дифференциальная диагностика должна строиться на комбинации признаков динамики УЗКП

Helical Chirality: a Link between Local Interactions and Global Topology in DNA

DNA supercoiling plays a major role in many cellular functions. The global DNA conformation is however intimately linked to local DNA-DNA interactions influencing both the physical properties and the biological functions of the supercoiled molecule. Juxtaposition of DNA double helices in ubiquitous crossover arrangements participates in multiple functions such as recombination, gene regulation and DNA packaging. However, little is currently known about how the structure and stability of direct DNA-DNA interactions influence the topological state of DNA. Here, a crystallographic analysis shows that due to the intrinsic helical chirality of DNA, crossovers of opposite handedness exhibit markedly different geometries. While right-handed crossovers are self-fitted by sequence-specific groove-backbone interaction and bridging Mg2+ sites, left-handed crossovers are juxtaposed by groove-groove interaction. Our previous calculations have shown that the different geometries result in differential stabilisation in solution, in the presence of divalent cations. The present study reveals that the various topological states of the cell are associated with different inter-segmental interactions. While the unstable left-handed crossovers are exclusively formed in negatively supercoiled DNA, stable right-handed crossovers constitute the local signature of an unusual topological state in the cell, such as the positively supercoiled or relaxed DNA. These findings not only provide a simple mechanism for locally sensing the DNA topology but also lead to the prediction that, due to their different tertiary intra-molecular interactions, supercoiled molecules of opposite signs must display markedly different physical properties. Sticky inter-segmental interactions in positively supercoiled or relaxed DNA are expected to greatly slow down the slithering dynamics of DNA. We therefore suggest that the intrinsic helical chirality of DNA may have oriented the early evolutionary choices for DNA topology