Exploiting time for super-lensing
Imaging and focusing are subject to the diffraction barrier which limits
the resolution of images or equivalently the size of focal spots to at
best half a wavelength. In the past few years, the quest for a perfect
lens, which would break this barrier has attracted an enormous interest.
Various monochromatic approaches have been proposed, mainly based on
negative index materials. In this work we introduce a broadband lens, the
“resonant metalens”, whose resolution is no more limited by diffraction.
Its broadband mechanism permits it to capture the spatial profile of an
object, even very small compared to the wavelength, and code it into a
temporal signature. Then, owing to the resonant nature of the lens, this
signature is efficiently sent in the far-field of the object for imaging
beyond the diffraction limit. Our work demonstrates a forty fold
improvement over the smallest details that can be imaged using radio-waves
and antennas. This concept has many potential applications in medical
imaging or therapy, wireless communications or sensing. Furthermore, the
generality of the approach suggests that resonant metalenses can be
designed throughout the electromagnetic spectrum up to the visible,
opening up new avenues for diffraction free imaging and focusing systems.
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BNR1108
Structure giving the highest Tc in the elements
Successive structural transitions consisting of face-centered cubic (Ca-I) - body-centered cubic (Ca-II) - simple cubic (Ca-III) - P41212 (Ca-IV) - Cmca (Ca-V) have been reported in compressed calcium. The superconducting transition temperature Tc of calcium is only 2 K at 44 GPa, however, the Tc increases by pressure and reaches 25 K at 161 GPa, which is the highest record among all the elements. The relation between the high-Tc and the crystal structure has been of high interest. We performed x-ray diffraction measurements of calcium at pressure up to 172 GPa at room temperature and discovered another higher pressure phase "Ca-VI" above 158 GPa. The structure was determined to be an orthorhombic Pnma by a Rietveld analysis and confirmed the structure with a density-functional theory calculation. We claim that Ca-VI gives the highest Tc of 25 K.
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LK12505
Bands in Particle Tumblers Finally Explained
Over 70 years ago, an obscure Japanese researcher discovered that the harder one tries to mix granular particles of two different sizes in a long rotating tumbler, the more they unmix by forming bands of small and large particles. The explanation for this counter-intuitive phenomenon has eluded researchers for all this time. In this paper, we obtained detailed information on what all particles do at all times by applying Newton’s Second Law simultaneously to many thousands of particles in a computer simulation of the flow. Miniscule flows related to friction at the tumbler walls occur parallel to the axis of the tumbler. These flows cause larger particles near the surface to be carried to a different axial position than smaller particles that end up deeper in the flowing layer because they fall into spaces between large particles. This results in a band of large particles near each end of the tumbler, and these bands lead to more bands. Many practical situations for processing pharmaceuticals, minerals, grains, and polymers run into this effect. One may want to eliminate this effect or exploit it. Unmixing is problematic when mixing is desired but could be useful for separating particles in other applications.
