Two-State Migration of DNA in a structured Microchannel

DNA migration in topologically structured microchannels with periodic cavities is investigated experimentally and with Brownian dynamics simulations of a simple bead-spring model. The results are in very good agreement with one another. In particular, the experimentally observed migration order of Lambda- and T2-DNA molecules is reproduced by the simulations. The simulation data indicate that the mobility may depend on the chain length in a nonmonotonic way at high electric fields. This is found to be the signature of a nonequilibrium phase transition between two different migration states, a slow one and a fast one, which can also be observed experimentally under appropriate conditions.Comment: Revised edition corresponding to the comments by the referees, submitted to Physical Review

Dynamical scaling of the DNA unzipping transition

We report studies of the equilibrium and the dynamics of a general set of lattice models which capture the essence of the force-induced or mechanical DNA unzipping transition. Besides yielding the whole equilibrium phase diagram in the force vs temperature plane, which reveals the presence of an interesting re-entrant unzipping transition for low T, these models enable us to characterize the dynamics of the process starting from a non-equilibrium initial condition. The thermal melting of the DNA strands displays a model dependent time evolution. On the contrary, our results suggest that the dynamical mechanism for the unzipping by force is very robust and the scaling behaviour does not depend on the details of the description we adopt.Comment: 6 pages, 4 figures, A shorter version of this paper appeared in Phys. Rev. Lett. 88, 028102 (2002

Stand-alone device for the electrolytic fabrication of scanning near-field optical microscopy aperture probes

Haumann C, Pelargus C, Frey HG, et al. Stand-alone device for the electrolytic fabrication of scanning near-field optical microscopy aperture probes. Review of scientific instruments. 2005;76(3): 033704.Near-field optical applications require the fast, stable, and reproducible fabrication of scanning near-field optical microscopy (SNOM) aperture probes in the submicrometer range. We have developed a stand-alone device for the electrolytic etching of nanoapertures with an integrated current and optical transmission monitoring and control. Probes with an aperture ranging from 50 to 100 nm were reproducibly fabricated with great reliability. With these probes, high resolution SNOM images of 100 nm test patterns and single dye molecules (Rhodamine 6G in poly(vinyl alcohol)) are measured and presented. Not requiring a SNOM setup, the stand-alone device is not only inexpensive and compact, but also insensitive to external disturbances

Origin and evolution of the Laguna Potrok Aike maar (Patagonia, Argentina)

Laguna Potrok Aike, a maar lake in southern-most Patagonia, is located at about 110 m a.s.l. in the Pliocene to late Quaternary Pali Aike Volcanic Field (Santa Cruz, southern Patagonia, Argentina) at about 52°S and 70°W, some 20 km north of the Strait of Magellan and approximately 90 km west of the city of Rio Gallegos. The lake is almost circular and bowl-shaped with a 100 m deep, flat plain in its central part and an approximate diameter of 3.5 km.Steep slopes separate the central plain from the lake shoulder at about 35 m water depth. At present, strong winds permanently mix the entire water column. The closed lake basin contains a sub saline water body and has only episodic inflows with the most important episodic tributary situated on the western shore. Discharge is restricted to major snowmelt events.Laguna Potrok Aike is presently located at the boundary between the Southern Hemispheric Westerlies and the Antarctic Polar Front. The sedimentary regime is thus influenced by climatic and hydrologic conditions related to the Antarctic Circumpolar Current, the Southern HemisphericWesterlies and sporadic outbreaks of Antarctic polar air masses. Previous studies demonstrated that closed lakes in southern South America are sensitive to variations in the evaporation/precipitation ratio and have experienced drastic lake level changes in the past causing for example the desiccation of the 75 m deep Lago Cardiel during the Late Glacial. Multiproxy environmental reconstruction of the last 16 ka documents that Laguna Potrok Aike is highly sensitive to climate change. Based on an Ar/Ar age determination, the phreatomagmatic tephra that is assumed to relate to the Potrok Aike maar eruption was formed around 770 ka. Thus Laguna Potrok Aike sediments contain almost 0.8 million years of climate history spanning several past glacial-interglacial cycles making it a unique archive for non-tropical and non-polar regions of the Southern Hemisphere. In particular, variations of the hydrological cycle, changes in eolian dust deposition, frequencies and consequences of volcanic activities and other natural forces controlling climatic and environmental responses can be tracked throughout time. Laguna Potrok Aike has thus become a major focus of the International Continental Scientific Drilling Program. Drilling operations were carried out within PASADO (Potrok Aike Maar Lake Sediment Archive Drilling Project) in late 2008 and penetrated ~100 m into the lacustrine sediment.Laguna Potrok Aike is surrounded by a series of subaerial paleo-shorelines of modern to Holocene age that reach up to 21 m above the 2003 AD lake level. An erosional unconformity which can be observed basin-wide along the lake shoulder at about 33 m below the 2003 AD lake level marks the lowest lake level reached during Late Glacial to Holocene times. A high- resolution seismic survey revealed a series of buried, subaquatic paleo-shorelines that hold a record of the complex transgressional history of the past approximately 6800 years, which was temporarily interrupted by two regressional phases from approximately 5800 to 5400 and 4700 to 4000 cal BP. Seismic reflection and refraction data provide insights into the sedimentary infill and the underlying volcanic structure of Laguna Potrok Aike. Reflection data show undisturbed, stratified lacustrine sediments at least in the upper ~100 m of the sedimentary infill. Two stratigraphic boundaries were identified in the seismic profiles (separating subunits I-ab, I-c and I-d) that are likely related to changes in lake level. Subunits I-ab and I-d are quite similar even though velocities are enhanced in subunit I-d. This might point at cementation in subunit I-d. Subunit I-c is restricted to the central parts of the lake and thins out laterally.A velocity-depth model calculated from seismic refraction data reveals a funnel-shaped structure embedded in the sandstone rocks of the surrounding Santa Cruz Formation. This funnel struc

Quark--anti-quark potential in N=4 SYM

We construct a closed system of equations describing the quark--anti-quark potential at any coupling in planar N=4 supersymmetric Yang-Mills theory. It is based on the Quantum Spectral Curve method supplemented with a novel type of asymptotics. We present a high precision numerical solution reproducing the classical and one-loop string predictions very accurately. We also analytically compute the first 7 nontrivial orders of the weak coupling expansion. Moreover, we study analytically the generalized quark--anti-quark potential in the limit of large imaginary twist to all orders in perturbation theory. We demonstrate how the QSC reduces in this case to a one-dimensional Schrodinger equation. In the process we establish a link between the Q-functions and the solution of the Bethe-Salpeter equation.Comment: 31 pages, 1 figure; v2: minor correcton

Lateral variations in the signature of earthquake‐generated deposits in Lake Iznik, NW Turkey

Using lake-sediment cores to document past seismicity requires a comprehen- sive understanding of possible lateral variations in depositional processes. This study aims to reveal the lateral variations in earthquake-induced event deposits throughout Lake Iznik, a large lake located on the middle strand of the North Anatolian Fault. Based on stratigraphic, sedimentological and geochemical anal- yses of 14 sediment cores from two subbasins across the lake, five different types of event deposits (T1–T5) were identified and characterised. One event deposit type (T5) is restricted to a delta mouth, characterised by the occurrence of au- thigenic Fe-Mn carbonates and interpreted to result from flood events. The four other types of event deposits are characterised by their synchronicity between cores and their age consistency with historical earthquakes and are interpreted to be likely generated by earthquakes. The locally prominent 1065 CE historical earthquake that ruptured the sub-lacustrine Iznik Fault produced at least three different types of event deposits. One deposit type (T2) is only observed for this very local earthquake, implying that the type of event deposit might also depend on ground-motion parameters. At the lake scale, the occurrence of various event deposits depends on the flow distance from the source of sediment destabilisa- tions to the coring site

The low-energy limit of AdS(3)/CFT2 and its TBA

We investigate low-energy string excitations in AdS3 × S3 × T4. When the worldsheet is decompactified, the theory has gapless modes whose spectrum at low energies is determined by massless relativistic integrable S matrices of the type introduced by Al. B. Zamolodchikov. The S matrices are non-trivial only for excitations with identical worldsheet chirality, indicating that the low-energy theory is a CFT2. We construct a Thermodynamic Bethe Ansatz (TBA) for these excitations and show how the massless modes’ wrapping effects may be incorporated into the AdS3 spectral problem. Using the TBA and its associated Y-system, we determine the central charge of the low-energy CFT2 to be c = 6 from calculating the vacuum energy for antiperiodic fermions — with the vacuum energy being zero for periodic fermions in agreement with a supersymmetric theory — and find the energies of some excited states

Ultrahigh ionic exclusion through carbon nanomembranes

The collective “single‐file” motion of water molecules through natural and artificial nanoconduits inspires the development of high‐performance membranes for water separation. However, a material that contains a large number of pores combining rapid water flow with superior ion rejection is still highly desirable. Here, a 1.2 nm thick carbon nanomembrane (CNM) made from cross‐linking of terphenylthiol (TPT) self‐assembled monolayers is reported to possess these properties. Utilizing their extremely high pore density of 1 sub‐nm channel nm−2, TPT CNMs let water molecules rapidly pass, while the translocation of ions, including protons, is efficiently hindered. Their membrane resistance reaches ≈104 Ω cm2 in 1 m Cl− solutions, comparable to lipid bilayers of a cell membrane. Consequently, a single CNM channel yields an ≈108 higher resistance than pores in lipid membrane channels and carbon nanotubes. The ultrahigh ionic exclusion by CNMs is likely dominated by a steric hindrance mechanism, coupled with electrostatic repulsion and entrance effects. The operation of TPT CNM membrane composites in forward osmosis is also demonstrated. These observations highlight the potential of utilizing CNMs for water purification and opens up a simple avenue to creating 2D membranes through molecular self‐assembly for highly selective and fast separations