Periodic magnetic geodesics on Heisenberg manifolds

Annals of Global Analysis and Geometry - We study the dynamics of magnetic flows on Heisenberg groups, investigating the extent to which properties of the underlying Riemannian geometry are...     

Heat‐Flow‐Driven Oligonucleotide Gelation Separates Single‐Base Differences

DNA phase transitions are often induced by the addition of condensation agents or by dry concentration. Herein, we show that the non‐equilibrium setting of a moderate heat flow across a water‐filled chamber separates and gelates DNA strands with single‐base resolution. A dilute mix of DNA with two slightly different gel‐forming sequences separates into sequence‐pure hydrogels under constant physiological solvent conditions. A single base change in a 36 mer DNA inhibits gelation. Only sequences with the ability to form longer strands are concentrated, further elongated, and finally gelated by length‐dependent thermal trapping. No condensation agents, such as multivalent ions, were added. Equilibrium aggregates from dry concentration did not show any sequence separation. RNA is expected to behave identically owing to its equal thermophoretic properties. The highly sequence‐specific phase transition points towards new possibilities for non‐equilibrium origins of life.     

Synthese,Struktur und Reaktivität von funktionalisierten Stibanidokomplexen des Eisens und Rutheniums [(η5-C5Me5)(CO)2MSbR1R2] (M = Fe,Ru; R1, R2 = SiMe3, C(O)tBu,C(O)Ph,C(O)-1 Ad)

Synthesis, Structure, and Reactivity of Functionalized Stibanido Complexes of Iron and Ruthenium [(η⁵-C₅Me₅)(CO)₂MSbR¹R²] (M = Fe, Ru; R¹, R² = SiMe₃, C(O) t Bu, C(O)Ph, C(O)-1 Ad) The reaction of equimolar amounts of [(η⁵-C₅Me₅)(CO)₂RuSb(SiMe₃)₂] ( 1 b ) and the carboxylic chlorides RC(O)Cl (R = tBu, Ph, 1-adamantyl) afforded the acyl(trimethylsilyl)stibanido complexes [(η⁵-C₅Me₅)(CO)₂RuSb · {C(O)R}(SiMe₃)] 2 b (R = tBu), 4 b (R = Ph), and 6 b (R = 1-Ad). The treatment of 1 b with two molar equivalents of pivaloyl chloride and benzoyl chloride led to the diacylstibanido complexes [(η⁵-C₅Me₅)(CO)₂RuSb{C(O)R}₂] ( 3 b , 5 b ). Analogously, the iron complex [(η⁵-C₅Me₅)(CO)₂FeSb · (SiMe₃)₂] ( 1 a ) is converted into the corresponding diacylstibanido complexes 3 a (R = tBu), 5 a (R = Ph) and 7 a (R = 1-Ad) by an excess of acid chloride. The treatment of 1 a with equimolar amounts of RC(O)Cl gave inseparable mixtures of starting material and the monoacyl- and diacyl stibanido complexes. Oxalyl chloride reacted quantitatively with two equivalents of 1 a to give complex [{(η⁵-C₅Me₅) · (CO)₂FeSb(SiMe₃)C(O)}₂] ( 8 ). The molecular structures of 1 a , 2 b and 5 b were elucidated by single crystal X-ray analyses.     

Simulation of ultrasonic focus aberration and correction through human tissue

Ultrasonic focusing in two dimensions has been investigated by calculating the propagation of ultrasonic pulses through cross-sectional models of human abdominal wall and breast. Propagation calculations used a full-wave k-space method that accounts for spatial variations in density, sound speed, and frequency-dependent absorption and includes perfectly matched layer absorbing boundary conditions. To obtain a distorted receive wavefront, propagation from a point source through the tissue path was computed. Receive focusing used an angular spectrum method. Transmit focusing was accomplished by propagating a pressure wavefront from a virtual array through the tissue path. As well as uncompensated focusing, focusing that employed time-shift compensation and time-shift compensation after backpropagation was investigated in both transmit and receive and time reversal was investigated for transmit focusing in addition. The results indicate, consistent with measurements, that breast causes greater focus degradation than abdominal wall. The investigated compensation methods corrected the receive focus better than the transmit focus. Time-shift compensation after backpropagation improved the focus from that obtained using time-shift compensation alone but the improvement was less in transmit focusing than in receive focusing. Transmit focusing by time reversal resulted in lower sidelobes but larger mainlobes than the other investigated transmit focus compensation methods.     

Developing rapid detection of mycobacteria using microwaves

In this paper, we describe the development of a culture-based biochip device for rapid detection of mycobacteria in environmental samples. Individual biochips rely upon the unique paraffinophilic nature of mycobacteria to rapidly and selectively adhere to the surface of the device. We used prototype biochips to experimentally demonstrate the concept of rapid and selective detection of mycobacteria by testing pure cultures and using epifluorescence microscopy to visualize microorganisms on the surface. As an alternative, rapid approach for identifying the biomass on the biochip surface, we used microwaves in the 10 to 26 GHz frequency range. The results of this study indicate that different microorganisms are responsible for specific shifts in resonance frequencies of a microwave cavity. By combing the semi-selective paraffin surface of the biochip with the microorganism-specific response to the microwaves, we have developed an improved analytical system with the potential to rapidly identify and enumerate mycobacteria in environmental samples in as little as 2 h.     

Measurement uncertainties of size, shape, and surface measurements using transmission electron microscopy of near-monodisperse, near-spherical nanoparticles

Carbon nanotubes are currently one of the most important materials due to their strong mechanical resistance, light weight, and transport properties. Since the publication of Ijima’s paper on tubular carbon structures (Iijima, Nature 354:56–58, 1991), approximately 80,000 research articles have been published according to the ISI web of science (WOS) database, using “carbon nanotube*” as the search criterion in the search by topic option. In this work, the development and impact of nanoscience and nanotechnology (N&N) and carbon nanotubes on several research areas, journals, specific papers, and emerging research areas are analyzed and discussed. Considering the production of papers in these areas from 1997 to 2012, quantitatively speaking, the People’s Republic of China is emerging as the leading country in N&N and carbon nanotube research, passing the United States of America. WOS data analysis of nanoscience, nanotechnology, and carbon nanotube research in developed and developing countries is discussed, and some ideas for accelerating the progress in these important research areas are proposed.     

Rare earth metal initiated ring‐opening polymerization of lactones

The progress in the synthesis of organolanthanide complexes supports the exploration of these compounds as initiators for ring‐opening polymerization (ROP) of lactones. The performance of these initiators in terms of yield, molecular weight, polydispersity, stereoregularity is affected by the ligands and by the oxidation state of the respective rare earth metals. Several initiators are known to initiate living polymerization of lactones with excellent polydispersities of the thus obtained polymers. Differences in the performance of the initiators are caused by differences in the initiation mechanism, chain growth mechanism, or side reactions. ROP of lactones was extended to block‐ and graft copolymerization with polylactones, polylactides, and polyolefins either by simply utilizing living polymer chain ends, by transformation of living polymer chain ends, or by usage of polyinitiators.     

Mitigating kinematic locking in the material point method

The material point method exhibits kinematic locking when traditional linear shape functions are used with a rectangular grid. The locking affects both the strain and the stress fields, which can lead to inaccurate results and nonphysical behavior. This paper presents a new anti-locking approach that mitigates the accumulation of fictitious strains and stresses, significantly improving the kinematic response and the quality of all field variables. The technique relies on the Hu–Washizu multi-field variational principle, with separate approximations for the volumetric and the deviatoric portions of the strain and stress fields. The proposed approach is validated using a series of benchmark examples from both solid and fluid mechanics, demonstrating the broad range of modeling possibilities within the MPM framework when combined with appropriate anti-locking techniques and algorithms.