Operation of pulsed dye laser with an intracavity phase step

Effects of an intracavity phase step on the spectral and spatial characteristics of pulsed dye laser radiation are studied. In the broadband operation regime of the dye laser, the lasing spectrum was strongly, periodically modulated. In the narrowband regime, periodic alteration between TEM₀₀ and TEM₀₁-like beam profiles is observed on tuning the laser wavelength. Two different spectral periods of these effects are recognized. The shorter period corresponds to double passage and the longer one to apparent single passage of intracavity light through the phase step on a cavity round trip. Depending on the position of the phase step along the laser cavity, single-passage period, double-passage period, or a superposition of both periods appeared in the broadband emission spectrum and in the beam profile alteration sequence. These observations demonstrate several possibilities for the control of spectral, spatial, and phase characteristics of laser beams by simple intracavity phase elements.     

Globally optimal superconducting magnets part II: symmetric MSE coil arrangement

A globally optimal superconducting magnet coil design procedure based on the Minimum Stored Energy (MSE) current density map is outlined. The method has the ability to arrange coils in a manner that generates a strong and homogeneous axial magnetic field over a predefined region, and ensures the stray field external to the assembly and peak magnetic field at the wires are in acceptable ranges. The outlined strategy of allocating coils within a given domain suggests that coils should be placed around the perimeter of the domain with adjacent coils possessing alternating winding directions for optimum performance. The underlying current density maps from which the coils themselves are derived are unique, and optimized to possess minimal stored energy. Therefore, the method produces magnet designs with the lowest possible overall stored energy. Optimal coil layouts are provided for unshielded and shielded short bore symmetric superconducting magnets.     

Will a large complex system with time delays be stable?

In 1972 May showed that for a large linear system with random coupling the system size and the average coupling strength must together satisfy a simple inequality to ensure the stability of the equilibrium point. Here we extend the analysis to delay coupled systems. Our calculations establish that the same inequality obtained by May constrains the stability for systems randomly coupled through discrete and distributed delays.     

Interaction of dinuclear ruthenium(II) supramolecular cylinders with DNA: sequence-specific binding, unwinding, and photocleavage

Metallosupramolecular chemistry was used to design a new class of synthetic agents, namely, tetracationic supramolecular cylinders, that bind strongly and noncovalently in the major groove of DNA. To gain additional information on interactions of the cylinders with DNA we explored DNA unwinding and sequence-specific binding properties, as well as DNA photonuclease activity of ruthenium(II) metallosupramolecular cylinder [Ru(2)L(3)](4+), where L is a bis-pyridylimine ligand. We found that [Ru(2)L(3)](4+) unwinds negatively supercoiled plasmid DNA and exhibits binding preference to regular alternating purine-pyrimidine sequences in a similar way to the [Fe(2)L(3)](4+) analogue. Photocleavage studies showed that, unlike [Fe(2)L(3)](4+), [Ru(2)L(3)](4+) induces single-strand breaks on irradiation by visible and UVA light and cleaves DNA mainly at guanine residues contained preferentially in regularly alternating purine-pyrimidine nucleotides. As [Ru(2)L(3)](4+) binds and cleaves DNA in a sequence-dependent manner, it may provide a useful tool for basic and applied biology, such as for controlled manipulation of the genome.     

Pimprinols A–C,from the terrestrial actinomycete,Streptomyces sp.

A Streptomyces sp. Lv3-13, isolated from the rhizosphere soil of the plant Mespilus germanica, has yielded three new pimprinine derivatives, named pimprinols A–C (1–3) and the unknown (2-aminophenyl)(2-ethyloxazol-5-yl) methanone (4) along with the known compounds 2-ethyl oxazole pimprinine and 2-propyl oxazole pimprinine. The structures of the compounds were elucidated based on spectroscopic methods including UV, HR-ESIMS and 1D, 2D NMR data. Compounds 1–4 were screened for antimicrobial and cytotoxic activities.     

Potassium 3‐cyano‐4‐(dicyanomethylene)‐5‐oxo‐4,5‐dihydro‐1H‐pyrrol‐2‐olate

The crystal structure of the title potassium salt, K⁺·C₈HN₄O₂⁻, of the organic anion 3‐cyano‐4‐(di­cyano­methyl­ene)‐5‐oxo‐4,5‐di­hydro‐1H‐pyrrol‐2‐olate shows that the di­cyano­methyl­ene moiety is able to accept an electron in the same way as does tetra­cyano­ethyl­ene, to yield the novel product. The organic anion is nearly planar, with deviations caused by steric crowding among the exocyclic cyano groups. The K⁺ cations lie within tricapped trigonal prisms that stack to form channels. The three‐dimensional structure is completed by the formation of hydrogen‐bonded chains by the anions.