Extracts from the Internet

Testing relativity theory

Gravitational influence of the Sun on radio waves.

Delation of time.

Freezing K-mesons

When two heavy, high-energy ions collide, the so-called `fireball' appears in the collision region, in which various types of elementary particles are intensely created and then annihilate. As the ball expands and cools down, the number of the particles levels off (they are said to be freezing) and from then on can only decrease due to decays. Similar processes also occurred in the early Universe. If the properties of particles and antiparticles were identical (except for the sign of the charge), so would the freezing processes they undergo. However, the KaoS collaboration in Germany has now found that `freezing' K⁺ and K^- mesons differ in their distributions and energy spectra - in a way, specifically, which suggests that the freezing of K⁺ mesons precedes that of their K^- counterparts. Mesons were created in Ni- NI and Au-Au ion collisions at about 1.5 GeV at the GSI accelerator. The verification of this important result is clearly needed. Source: Phys. Rev. Lett. 91 152301 (2003)

Superfluidity and superconductivity at nanometer scales

In recent years, the microscopic analogue of Andronikashvili's experiment has been repeated a number of times to study the rotation of OCS molecules in macroscopic droplets of liquid helium cooled below 2.2 K - the temperature at which macroscopic volumes of helium become superfluid. In 2002, R McKellar and colleagues in Canada discovered that droplets consisting of about eight helium molecules do not possess superfluidity. Now in a new experiment by the same researchers - but with the rotating molecules of N₂O to study - it proved possible for the first time to trace the superfluid transition with increasing the droplet size (miniclusters) in the range from 3 to 12 helium molecules. Droplets of helium with N₂O molecules inside were created by passing the mixture of the gases through a cold nozzle. Spectroscopic methods allowed droplets of different sizes to be distinguished in the experiment. Exposure to infrared light and microwave radiation excited the vibrational and rotational degrees of freedom of N₂O molecules in the droplets. From the level of radiation absorption, the moment of inertia of N₂O molecules was determined. If helium is not superfluid, helium molecules are dragged into rotation with N₂O molecules, thus increasing the moment of inertia. It turned out that as the number of helium molecules in droplets increases from 3 to 6, the moment of inertia increases, but as this number is further increased from 7 to 12, the moment of inertia decreases, signaling the transition to the supefluidity regime. Source: Phys. Rev. Lett. 91 163401 (2003)

S. Reich and his colleagues in Israel have studied the magnetic susceptibility of lead grains 4 to 1000 nm in size cooled to a temperature of about 5 K. An abrupt disappearance of the Meissner effect upon transition to grain size of less than 30 nm is discovered. This critical size of superconducting grains is consistent with the Anderson criterion. Although the absence of superconductivity in small grains has been observed earlier, the team's experiment is the first to study a superconducting transition with increasing grain size. Source: Phys. Rev. Lett. 91 147001 (2003)

Ordinary crystals with a negative index of refraction

A theoretical study of materials with both a negative electric permittivity and a negative magnetic permeability was carried out in the 1960s by V Veselago of the P N Lebedev Physics Institute, RAS. In 2000, such materials, with a index of refraction n<0 in the microwave range, were created at the University of California in the form of an assembly of microscopic rings and wires (see Physics Uspekhi 43 520 (2000)). Now Y Zhang and colleagues in the USA have for the first time found that not only composite materials but also usual crystals can have a negative index of refraction. Two samples of an alloy containing yttrium, vanadium, and oxygen were brought into contact along a flat surface, with the samples' optical axes differently oriented. This double crystal has n<0 for light of any frequency passing through the interface, and even for a coherent beam of electrons (quantum electron waves). At the same time, at certain angles of incidence the same crystal has n>0 or transmits light completely, without reflection. The discovered property may find practical applications, in particular, in the manufacture of anti-reflection lenses. Source: Phys. Rev. Lett. 91 157404 (2003)

Pentagonal crystal symmetry

Unit cells of ideal solid crystals do not have a pentagonal symmetry because such symmetry cannot be translated along a crystal. The exception is quasicrystals, in which translation is not exact and pentagonal symmetry is observed. It has long been predicted, however, that pentagonal symmetry can arise in liquid crystals, which, as is known, are not completely chaotic and form crystalline structures at small scales. Earlier, pentagonal symmetry has been observed only in thin films of liquid metals. Now, for the first time, pentagonal symmetry in a volume of liquid copper has been found by A Di Cicco and his colleagues in Italy. The team studied the diffraction of X-rays obtained from an accelerating source. Unlike liquid film experiments, not only scattered X-ray photons but also electrons knocked out of atoms were observed, enabling the geometry of the crystal units to be determined with a sufficient accuracy. From these data, about 6% of the atomic clusters in the melt have a pentagonal crystal structure. Theory predicts that pentagonal symmetry can be found not only in copper but also in some other (liquid) metals - specifically, in silver, lead, and gold - which do not have this symmetry in the solid state. Source: Phys. Rev. Lett. 91 135505 (2003)