Ultrasound attenuation in ferrofluids

The absorption of acoustic energy by internal degrees of freedom of short chains is proposed as a new viable mechanism of ultrasound attenuation in ferrofluids. It is demonstrated that even though the volume fraction of the chains may be quite small, such an effect may reach the order of magnitude of viscous damping. In addition, by investigating the statistical properties of dimers in ferrofluids, it is shown that an applied magnetic field modifies the sound attenuation in a highly anisotropic manner. The proposed mechanism provides new insight into the fundamental issue of colloidal response, and, in particular, may lead to its utilization in novel experimental concepts.     

Multiple metamagnetic transitions in the magnetic refrigerant La(Fe,Si)13Hx

The effect of hydrostatic pressure on thermally and field-induced first-order magnetic phase transitions is studied in the La(Fe,Si)_(13)-type compounds. A peculiar series of consecutive field-induced transitions is realized using a distinct combination of hydrostatic pressure and negative pressure created by the interstitial insertion of hydrogen. The pressure-induced discontinuous magnetization jumps result in an enhanced cooling power, thus opening up the possibility to exploit in full the magnetocaloric potential of this compound class.     

Efficient, tunable, and coherent 0.18-5.27-THz source based on GaSe crystal

Continuously tunable and coherent radiation in the wide range 56.8-1618 mum (0.18-5.27 THz) has been achieved as a novel and promising terahertz source based on collinear phase-matched difference frequency generation in a GaSe crystal. This source has the advantages of high coherence, simplicity for tuning, simple alignment, and stable output. The peak output power for the terahertz radiation reaches 69.4 W at a wavelength of 196 mum (1.53 THz), which corresponds to a photon conversion efficiency of 3.3%. A simple optimization of the design can yield a compact terahertz source.     

Revisiting infinite lattice sums with the periodic fast multipole method

The evaluation of lattice sums as well as stress lattice sums encountered in the periodic fast multipole method is reinvestigated. Simple, accurate, and efficient recurrence expressions for such sums following the ideas of the renormalization method are derived. The first few nonzero lattice sum terms in a three-dimensional cubic lattice are computed and given in Tables. The practical considerations accompanying the computation of the sums such as convergence and accuracy are discussed.     

Common pathway for the red chromophore formation in fluorescent proteins and chromoproteins

The mechanism of the chromophore maturation in members of the green fluorescent protein (GFP) family such as DsRed and other red fluorescent and chromoproteins was analyzed. The analysis indicates that the red chromophore results from a chemical transformation of the protonated form of the GFP-like chromophore, not from the anionic form, which appears to be a dead-end product. The data suggest a rational strategy to achieve the complete red chromophore maturation utilizing substitutions to favor the formation of the neutral phenol in GFP-like chromophore. Our approach to detect the neutral chromophore form expands the application of fluorescent timer proteins to faster promoter activities and more spectrally distinguishable fluorescent colors. Light sensitivity found in the DsRed neutral form, resulting in its instant transformation to the mature red chromophore, could be exploited to accelerate the fluorescence acquisition.     

Superelectrophilic activation of polyfunctional organic compounds using zeolites and other solid acids

Zeolites and other available solid acids have been successfully applied to initiate reactions, which were earlier recognised to involve superelectrophilic intermediates and thus required excess of superacids to be carried out.     

Water and tris(5-acetyl-3-thienyl)methane (TATM) assemble into a one-dimensional channel compound

Tris(5-acetyl-3-thienyl)methane (TATM), a well known hydrophobic host compound, assembles with water molecules into a material with one-dimensional channels that also contain water.