Millimeter-Wave Diffraction by a Photo-Induced Plasma Grating

Optical gratings are used extensively for beamsteering in the visible and IR range of the spectrum. Change in the dielectric permittivity of a semiconductor medium resulting from the excitation of a nonequilibrium electron-hole plasma makes it possible to extend this technique to MMW frequencies. A photo-induced plasma grating (PIPG) can be easily rewritten by changing the illumination pattern. So this technique can be used in optically controllable MMW antennas. Initial experimental work studied the diffraction of MMW propagating along a dielectric waveguide containing a PIPG. This paper reports on the diffraction of MMW propagating in free space, steered by the PIPG

Are Particles Self-Organized Systems?

Elementary particles possess quantized values of charge and internal angular momentum or spin. These characteristics do not change when the particles interact with other particles or fields as long as they preserve their entities. Quantum theory does not explain this quantization. It is introduced into the theory a priori. An interacting particle is an open system and thus does not obey conservation laws. However, an open system may create dynamically stable states with unchanged dynamical variables via self-organization. In self-organized systems stability is achieved through the interplay of nonlinearity and dissipation. Can self-organization be responsible for particle formation? In this paper we develop and analyze a particle model based on qualitative dynamics and the Feigenbaum universality. This model demonstrates that elementary particles can be described as self-organized dynamical systems belonging to a wide class of systems characterized by a hierarchy of period-doubling bifurcations. This semi-qualitative heuristic model gives possible explanations for charge and action quantization, and the origination and interrelation between the strong, weak, and electromagnetic forces, as well as SU(2) symmetry. It also provides a basis for particle taxonomy endorsed by the Standard Model. The key result is the discovery that the Planck constant is intimately related to elementary charge.Comment: 11 pages, 10 figure

Superlattice in an interminiband resonance ac field

We discuss the properties of miniband electrons in a superlattice illuminated by a strong electromagnetic field. If the ac field is in resonance with a two-miniband superlattice, gaps in the quasienergy spectrum appear. The gap is proportional to the Bessel function and oscillates with the ac electric field. The resonant ac driving force makes the quasienergy spectrum tunable and may decrease the critical dc field for electrical domains to form.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87344/2/043505_1.pd

Connexin30.2:<i>In vitro</i> interaction with connexin36 in hela cells and expression in AII amacrine cells and intrinsically photosensitive ganglion cells in the mouse retina

Electrical coupling via gap junctions is an abundant phenomenon in the mammalian retina and occurs in all major cell types. Gap junction channels are assembled from different connexin subunits, and the connexin composition of the channel confers specific properties to the electrical synapse. In the mouse retina, gap junctions were demonstrated between intrinsically photosensitive ganglion cells and displaced amacrine cells but the underlying connexin remained undetermined. In the primary rod pathway, gap junctions play a crucial role, coupling AII amacrine cells among each other and to ON cone bipolar cells. Although it has long been known that connexin36 and connexin45 are necessary for the proper functioning of this most sensitive rod pathway, differences between homocellular AII/AII gap junctions and AII/ON bipolar cell gap junctions suggested the presence of an additional connexin in AII amacrine cells. Here, we used a connexin30.2-lacZ mouse line to study the expression of connexin30.2 in the retina. We show that connexin30.2 is expressed in intrinsically photosensitive ganglion cells and AII amacrine cells. Moreover, we tested whether connexin30.2 and connexin36 – both expressed in AII amacrine cells – are able to interact with each other and are deposited in the same gap junctional plaques. Using newly generated anti-connexin30.2 antibodies, we show in HeLa cells that both connexins are indeed able to interact and may form heteromeric channels: both connexins were co-immunoprecipitated from transiently transfected HeLa cells and connexin30.2 gap junction plaques became significantly larger when co-expressed with connexin36. These data suggest that connexin36 is able to form heteromeric gap junctions with another connexin. We hypothesize that co-expression of connexin30.2 and connexin36 may endow AII amacrine cells with the means to differentially regulate its electrical coupling to different synaptic partners

III-Nitride based superlattice sub-millimeter wave source.

In recent years, interest in the use of terahertz (THz) radiation in civilian and military applications, ranging from biomedical imaging to space-communications, has increased greatly. However, several roadblocks stand in the way of integration of the THz radiation into practical applications. One of the biggest challenges is the development of a compact coherent high-power THz source. In order to progress into the THz frequency range and higher power regions, researchers are looking for new materials such as GaN and meta-materials including superlattices and carbon nanotubes. In this thesis, I explore a high-power high-frequency source of radiation based on a new regime of operation of short-period III-Nitride superlattice devices. I begin by extending a simple analytical miniband transport model to include energy-dependent effective mass and momentum relaxation time, as well as polarization and strain related effects found in Stark III-Nitride material systems. Using this analytical framework, I investigate various modes of superlattice transport that can be utilized for generation of high-frequency signals. The most significant results presented in my thesis arise from the investigation of a new mode of operation: high-harmonic generation in low-mobility superlattices under below-critical bias. This regime is very important since it allows high-frequency generation in the III-Nitride material system, in which both Bloch oscillations and electrical domains are extremely difficult to achieve. Analysis of superlattice transport in a biharmonic field reveals the presence of high-harmonic instabilities with respect to current oscillations, related to negative absorption (gain). These instabilities along with a feedback circuit allow for fabrication of a THz source. In addition, I find that even simple frequency conversion, resulting from high-harmonic superlattice response, can produce high output power levels in III-Nitrides. For example, second harmonic response can generate output powers on the order of 10--100 kW/cm2 for the second harmonic at 1.6 THz with high intrinsic generation efficiency of nearly 50%. My experimental development of the two-terminal vertical III-Nitride source devices shows that bulk GaN Gunn-type devices, under the biasing conditions necessary for the onset of oscillations, dissipate powers that are prohibitive for device operation. On the other hand, III-Nitride superlattice sources may dissipate significantly smaller powers, since the energy scale of minibands is nearly an order of magnitude smaller than the relevant scale in bulk GaN devices. Therefore, I suggest that high-harmonic generation in III-Nitride superlattice devices is an excellent avenue for the development of a practical compact high-power high-frequency source.Ph.D.Applied SciencesCondensed matter physicsElectrical engineeringPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125703/2/3208504.pd