Extremal transmission through a microwave photonic crystal and the observation of edge states in a rectangular Dirac billiard

This article presents experimental results on properties of waves propagating in an unbounded and a bounded photonic crystal consisting of metallic cylinders which are arranged in a triangular lattice. First, we present transmission measurements of plane waves traversing a photonic crystal. The experiments are performed in the vicinity of a Dirac point, i.e., an isolated conical singularity of the photonic band structure. There, the transmission shows a pseudodiffusive 1/L dependence, with $L$ being the thickness of the crystal, a phenomenon also observed in graphene. Second, eigenmode intensity distributions measured in a microwave analog of a relativistic Dirac billiard, a rectangular microwave billiard that contains a photonic crystal, are discussed. Close to the Dirac point states have been detected which are localized at the straight edge of the photonic crystal corresponding to a zigzag edge in graphene

Breeding Oats Resistant to Puccinia graminis avenae

A test of some three hundred oat varieties showed some susceptible and some resistant to Puccinia graminis avenae. A study of the inheritance of resistance has been made by determining the response of hybrids of resistant x susceptible varieties. In this study, Iowa 105 was found to possess a marked resistance in addition to maturing early and thus escaping stem rust. Green Russian and Raukura were both resistant. The F1 generation of Iowa 105 x Green Russian was resistant. The F2 generation gave a wide ratio of several hundred resistant plants to one susceptible. In the F1 progeny test the susceptible F2 plants bred true for susceptibility, while numerous progenies from the resistant F2 plants, segregated into resistant and susceptible plants. Such a wide ratio exists in the F2 generation it is impossible to determine the true factorial basis of inheritance without further work. It is probable, however, that several factors are responsible for the inheritance of resistance to stem rust of oats. These data were further confirmed by the Raukura x Green Russian crosses

Response of the Genus Rhamnus to Puccinia coronata Corda

All of the several species and varieties of Rhamnus exposed to infection with Puccinia coronata Corda show some degree of infection with some form of crown rust. Eleven species of Rhamnus produced aecidiospores which were able to infect oats, from teleutospores developed on oats. Of the susceptible buckthorn species, only Rhamnus cathartica, R. lanceolata and R. alnifolia occur in Iowa. The former is a cultivated species imported from Europe that has escaped from cultivation in many places. Rhamnus lanceolata is commonly found along the small streams and shaded dry runs throughout the southern half of this state and as far north as Sioux City on the Missouri river and McGregor on the Mississippi. Rhamnus alnifolia is confined to a few counties in extreme northeastern Iowa

Application of a trace formula to the spectra of flat three-dimensional dielectric resonators

The length spectra of flat three-dimensional dielectric resonators of circular shape were determined from a microwave experiment. They were compared to a semiclassical trace formula obtained within a two-dimensional model based on the effective index of refraction approximation and a good agreement was found. It was necessary to take into account the dispersion of the effective index of refraction for the two-dimensional approximation. Furthermore, small deviations between the experimental length spectrum and the trace formula prediction were attributed to the systematic error of the effective index of refraction approximation. In summary, the methods developed in this article enable the application of the trace formula for two-dimensional dielectric resonators also to realistic, flat three-dimensional dielectric microcavities and -lasers, allowing for the interpretation of their spectra in terms of classical periodic orbits.Comment: 13 pages, 12 figures, 1 tabl

Experimental Observation of Localized Modes in a Dielectric Square Resonator

We investigated the frequency spectra and field distributions of a dielectric square resonator in a microwave experiment. Since such systems cannot be treated analytically, the experimental studies of their properties are indispensable. The momentum representation of the measured field distributions shows that all resonant modes are localized on specific classical tori of the square billiard. Based on these observations a semiclassical model was developed. It shows excellent agreement with all but a single class of measured field distributions that will be treated separately.Comment: 6 pages, 5 figures, 1 tabl

Classical gravitational spin-spin interaction

I obtain an exact, axially symmetric, stationary solution of Einstein's equations for two massless spinning particles. The term representing the spin-spin interaction agrees with recently published approximate work. The spin-spin force appears to be proportional to the inverse fourth power of the coordinate distance between the particles.Comment: six pages, no figures, journal ref:accepted for Classical and Quantum Gravit

Static axisymmetric spacetimes with non-generic world-line SUSY

The conditions for the existence of Killing-Yano tensors, which are closely related to the appearance of non-generic world-line SUSY, are presented for static axisymmetric spacetimes. Imposing the vacuum Einstein equation, the set of solutions admitting Killing-Yano tensors is considered. In particular, it is shown that static, axisymmetric and asymptotically flat vacuum solutions admitting Killing-Yano tensors are only the Schwarzschild solution.Comment: 10 pages (RevTeX), TIT/HEP-253/COSMO-4

Scattering Experiments with Microwave Billiards at an Exceptional Point under Broken Time Reversal Invariance

Scattering experiments with microwave cavities were performed and the effects of broken time-reversal invariance (TRI), induced by means of a magnetized ferrite placed inside the cavity, on an isolated doublet of nearly degenerate resonances were investigated. All elements of the effective Hamiltonian of this two-level system were extracted. As a function of two experimental parameters, the doublet and also the associated eigenvectors could be tuned to coalesce at a so-called exceptional point (EP). The behavior of the eigenvalues and eigenvectors when encircling the EP in parameter space was studied, including the geometric amplitude that builds up in the case of broken TRI. A one-dimensional subspace of parameters was found where the differences of the eigenvalues are either real or purely imaginary. There, the Hamiltonians were found PT-invariant under the combined operation of parity (P) and time reversal (T) in a generalized sense. The EP is the point of transition between both regions. There a spontaneous breaking of PT occurs

Oak wilt—A serious disease in Iowa

In the past 5 years wilt has come to be recognized as the most important oak disease in the upper Mississippi valley. The disease has been reported from Iowa, Wisconsin, Minnesota, Missouri and Illinois. The fungus Chalara quercina Henry has been shown definitely to be the cause of the disease. Trees of the red oak group are killed quickly, usually within 30 to 60 days after wilt symptoms are apparent. Those of the white oak group may survive several years after infection with only a few branches being killed each year. All types of oak apparently are susceptible since all of the 28 species inoculated in the greenhouse were infected. The disease has been found on 9 of the 11 native species in Iowa. Infected trees have not been observed to recover from oak wilt. Prevention of spread of the disease has been attempted by various methods of sanitation. In general, removing diseased trees as soon as symptoms appear has been effective in stopping or retarding spread in state park and state forest test areas. Pruning experiments on trees that had only a few infected branches indicate that white oaks may often be saved by removal of such infected branches at a point well back of the latest symptoms. Frost injury, leaf blight and insect and rodent injury often result in leaf discoloration which from a distance may be mistaken for oak wilt