Elementary excitations in solid and liquid He-4 at the melting pressure.

Recent discovery of a nonclassical rotational inertia (NCRI) in solid He-4 below 0.2 K by Kim and Chan has revived great interest in the problem of supersolidity and initiated intensive study on the properties of solid He-4. A direct proof that the onset of NCRI corresponds to the supersolid transition would be the observation of a corresponding drop of the entropy of solid He-4 below the transition temperature. We have measured the melting pressure of ultrapure He-4 in the temperature range from 0.01 to 0.45 K with several single crystals grown at different pressures and with the accuracy of 0.5 mu bar. In addition, supplementary measurements of the pressure in liquid He-4 at constant volume have been performed, which allowed us to eliminate the contribution of the temperature-dependent properties of the pressure gauge from the measured melting pressure data. With the correction to the temperature-dependent sensitivity of the pressure gauge, the variation of the melting pressure of He-4 below 320 mK obeys the pure T-4 law due to phonons with the accuracy of 0.5 mu bar, and no sign of the transition is seen (Todoshchenko et al. in JETP Lett. 85:454, 2007). This sets the upper limit of similar to 5 center dot 10(-8) R for a possible excess entropy in high-quality He-4 crystals below 320 mK. At higher temperatures the contribution from rotons in the superfluid He-4 has been observed. The thermal expansion coefficient of the superfluid He-4 has been measured in the range from 0.01 to 0.7 K with the accuracy of similar to 10(-7) 1/K, or by two orders of magnitude better than in previous measurements. The roton contributions to the melting pressure and to the pressure in liquid at a constant volume are consistent and yield the value of 6.8 K for the roton gap, which is very close to the values obtained with other methods. As no contribution due to weakly interacting vacancies to the melting pressure of He-4 has been observed, the lower limit of about 5.5 K for their activation energy can be set

Pattern recognition by pentraxins

Pentraxins are a family of evolutionarily conserved pattern-recognition proteins that are made up of five identical subunits. Based on the primary structure of the subunit, the pentraxins are divided into two groups: short pentraxins and long pentraxins. C-reactive protein (CRP) and serum amyloid P-component (SAP) are the two short pentraxins. The prototype protein of the long pentraxin group is pentraxin 3 (PTX3). CRP and SAP are produced primarily in the liver while PTX3 is produced in a variery oftissues during inflammation. The main functions of short pentraxins are to recognize a variery of pathogenic agents and then to either eliminate them or neutralize their harmful effects by utilizing the complement pathways and macrophages in the host. CRP binds to modified low-densiry lipoproteins, bacterial polysaccharides, apoptotic cells, and nuclear materials. By virtue of these recognition functions, CRP participates in the resolution ofcardiovascular, infectious, and autoimmune diseases. SAP recognizes carbohydrates, nuclear substances, and amyloid fibrils and thus participates in the resolution of infectious diseases, autoimmuniry, and amyloidosis. PTX3 interacts with several ligands, including growth factors, extracellular matrix component and selected pathogens, playing a role in complement activation and facilitating pathogen recognition by phagoeytes. In addition, data in gene-targeted mice show that PTX3 is essential in female fertiliry, participating in the assembly of the cumulus oophorus extracellular matrix. PTX3 is therefore a nonredundant component ofthe humoral arm of innate immuniry as well as a tuner of inflammation. Thus, in conjunction with the other components ofinnate immuniry, the pentraxins use their pattern-recognition properry for the benefit of the host