RCS CONTROL USING CASCADED CIRCULARLY POLARIZED FREQUENCY SELECTIVE SURFACES AND AN AMC STRUCTURE AS A SWITCHABLE TWIST POLARIZER

This article presents a cascaded arrangement comprising a double-layer frequency selective surface circularly polarizing (CPFSS) and a second screen that can be switched between artificial magnetic conduction (AMC) or perfect electric conducting. (PEC) states. The CPFSS consists of two stacked aluminium sheets patterned with periodic split ring structures While the AMC is a PCB sheet patterned with metallic squares interconnected by links By either open or short circuiting these links it is shown that the cascade of screens can be made to twist, or not to twist, an incident 45 degrees linearly polirized signal through 90 degrees upon reflection from the assembly The system was designed and optimized using CST software and predictions were validated experimentally and measured monostatic reflection loss results (C) 2010 Wiley Periodicals, Inc Microwave Opt Technol Lett 52 577-580, 2010. Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.24979

Twist localizes three-dimensional patterns

A mechanism or the localization of spatially periodic,self-oganized patterns in anisotropic media which requires systems extended in all three spatial dimensions is presented: When the anisotropy axis is twisted, the pattern becomes localized in planes parallel to the anisotropy axis. An analytical description of the effect is developed, and used to interpret recent experiments in the high-frequency regime of electroconvection by Bohatsch and Stannarius [Phys. Rev. E 60, 5591 (1999)]. The localization width is found to be of the order of magnitude of the geometrical average of the pattern wavelength and the inverse twist.

Regarding “Co-expression of SNAIL and TWIST determines prognosis in estrogen receptor-positive early breast cancer patients”

We read the interesting research article published by van Nes et al. [1], which described the use of Snail and TWIST together in the prognosis of breast cancer, and in particular in estrogen receptor (ER)-positive breast cancer patients.

A twist in the tale of γ-ray bursts

An unusually long burst of γ-rays zapped Earth in December 2011, lasting 4 hours. The cause of this burst is now proposed to be a peculiar supernova produced by a spinning magnetic neutron star. See Letter p.189

Ring-opening polymerisation of silver-diphosphine [M2L3] coordination cages to give [M2L3](infinity) coordination polymers

[M2L3] coordination cages and linear [M2L3]infinity polymers of the rigid, bridging diphosphines bis(diphenylphosphino)acetylene (dppa) and trans-1,2-bis(diphenylphosphino)ethylene (dppet) with silver(I) salts have been investigated in the solution and solid states. Unlike flexible diphosphines, 1:1 dppa/AgX mixtures do not selectively form discrete [Ag2(diphos)2(X)2] macrocycles; instead dynamic mixtures of one-, two- and three-coordinate complexes are formed. However, 3:2 dppa/AgX ratios (X = SbF6. BF4, O3SCF3 or NO3) do lead selectively to new [M2L3] triply bridged cage complexes [Ag2(dppa)3(X)2] 1a-d (X = SbF6 a, BF4 b, O3SCF3 c, NO3 d), which do not exhibit Ag-P bond dissociation at room temperature on the NMR time scale (121 MHz). Complexes la-d were characterised by X-ray crystallography and were found to have small internal cavities, helical conformations and multiple intramolecular aromatic interactions. The nucleophilicity of the anion subtly influences the cage shape: Increasing nucleophilicity from SbF6 (1a) through BF4 (1b) and O3SCF3 (1c) to NO3 (1d) increases the pyramidal distortion at the AgP3 centres, stretching the cage framework (with Ag...Ag distances increasing from 5.48 in 1a to 6.21 A in 1d) and giving thinner internal cavities. Crystal packing strongly affected the size of the helical twist angle, and no correlation between this parameter and the Ag-Ag distance was observed. When crystalline 1c was stored in its supernatant for 16 weeks, conversion occured to the isostoichiometric [M2L3]infinity coordination polymer [Ag(dppa)2Ag(dppa)(O3SCF3)2]infinity (1c'). X-ray crystallography revealed a structure with ten-membered Ag2(dppa)2 rings linked into infinite one-dimensional chains by a third dppa unit. The clear structural relationship between this polymer and the precursor cage 1c suggests a novel example of ring-opening polymerisation. With dppet, evidence for discrete [M2L3] cages was also found in solution, although 31P NMR spectroscopy suggested some Ag-P bond dissociation. On crystallisation, only the corresponding ring-opened polymeric structures [M2L3]infinity could be obtained. This may be because the greater steric bulk of dppet versus dppa destabilises the cage and favours the ring-opening polymerisation.

Twisting flux tubes as a cause of micro-flaring activity

High-cadence optical observations of an H-alpha blue-wing bright point near solar AR NOAA 10794 are presented. The data were obtained with the Dunn Solar Telescope at the National Solar Observatory/Sacramento Peak using a newly developed camera system, the RAPID DUAL IMAGER. Wavelet analysis is undertaken to search for intensity-related oscillatory signatures, and periodicities ranging from 15 to 370 s are found with significance levels exceeding 95%. During two separate microflaring events, oscillation sites surrounding the bright point are observed to twist. We relate the twisting of the oscillation sites to the twisting of physical flux tubes, thus giving rise to reconnection phenomena. We derive an average twist velocity of 8.1 km s(-1) and detect a peak in the emitted flux between twist angles of 180 degrees and 230 degrees.

Alfvén Waves in the Lower Solar Atmosphere

The flow of energy through the solar atmosphere and the heating of the Sun's outer regions are still not understood. Here, we report the detection of oscillatory phenomena associated with a large bright-point group that is 430,000 square kilometers in area and located near the solar disk center. Wavelet analysis reveals full-width half-maximum oscillations with periodicities ranging from 126 to 700 seconds originating above the bright point and significance levels exceeding 99%. These oscillations, 2.6 kilometers per second in amplitude, are coupled with chromospheric line-of-sight Doppler velocities with an average blue shift of 23 kilometers per second. A lack of cospatial intensity oscillations and transversal displacements rules out the presence of magneto-acoustic wave modes. The oscillations are a signature of Alfvén waves produced by a torsional twist of ±22 degrees. A phase shift of 180 degrees across the diameter of the bright point suggests that these torsional Alfvén oscillations are induced globally throughout the entire brightening. The energy flux associated with this wave mode is sufficient to heat the solar corona.