Recent developments in the application of micro- and nanosystems for drug administration include a diverse range of new materials and methods. New approaches include the on-demand activation of molecular interactions, novel diffusion-controlled delivery devices, nanostructured 'smart' surfaces and materials, and prospects for coupling drug delivery to sensors and implants. Micro- and nanotechnologies are enabling the design of novel methods such as radio-frequency addressing of individual molecules or the suppression of immune response to a release device. Current challenges include the need to balance the small scale of the devices with the quantities of drugs that are clinically necessary, the requirement for more stable sensor platforms, and the development of methods to evaluate these new materials and devices for safety and efficacy.

Small-scale systems for in vivo drug delivery.

This report presents information on the characterization of cementitiously stabilized layers and the properties that influence pavement performance. It also contains recommended performance-related procedures for characterizing these layers and performance-prediction models for incorporation into the mechanistic–empirical pavement analysis methods. Individual chapters highlight pavement distresses of hot-mix asphalt pavements and concrete pavements, laboratory tests and model development, and model calibration. The material contained in the report will be of immediate interest to state materials, pavement, and construction engineers and others involved in the different aspects of pavement design and construction.

Characterization of Cementitiously Stabilized Layers for Use in Pavement Design and Analysis

Aspects of the subject disclosure may include, for example, a method, includes coordinating relay transmission of a modulated signal via relay links of a distributed antenna system to reduce an accumulated forwarding delay in forwarding the modulated signal through the relay links. One of the relay links of the distributed antenna system reconverts the spectral segment of the modulated signal for transmission to a communication device to which the modulated signal is directed.

Distributed antenna system and methods for use therewith

Aspects of the subject disclosure may include, for example, a coupling module that includes a waveguide that guides a first electromagnetic wave conveying data from a transmitting device. A dielectric coupler receives the first electromagnetic wave from the waveguide to form a second electromagnetic wave, and that guides the second electromagnetic wave along the dielectric coupler adjacent to a transmission medium, and wherein the dielectric coupler has a length that supports a cancellation of at least one cancelled wave mode from a coupling of the second electromagnetic wave to the transmission medium.

Launcher and coupling system for guided wave mode cancellation

Aspects of the subject disclosure may include, for example, a launching device including a transmitter configured to generate a radio frequency signal in a microwave frequency band. A planar strip antenna is configured to launch the radio frequency signal as a guided electromagnetic wave that is bound to an outer surface of a transmission medium, wherein the guided electromagnetic wave propagates along the outer surface of the transmission medium without an electrical return path. Other embodiments are disclosed.

Launcher with planar strip antenna and methods for use therewith

The discrete longitudinal dielectric support bars for a TWT helical slow-wave structure of either of the circular and rectangular cross sections have been analyzed using the theoretical approach of smoothing out the supports azimuthally into a large number of dielectric tubes of their respective effective permittivity values. The number of such tubes is increased to a very large value in order to ensure converging results for better theoretical predictions. The method has been applied to study the dispersion characteristics of a helix in a metal envelope. The method has a special significance for better results for high-permittivity supports, large helix-to-envelope separation and high operating frequencies. The theoretical predictions are also compared with experimental values available elsewhere. The theoretical method suggested is general and is applicable to arbitrarily shaped support bars as well as to both glass/ceramic and metal envelopes.

The inhomogeneous loading effects of practical dielectric supports for the helical slow-wave structure of a TWT

Absorption of terahertz waves by a metasurface comprising a biperiodic array of pixellated meta-atoms on top of a dielectric substrate backed by a perfect electric conductor was simulated using commercial software, with either all or a few of the pixels in every meta-atom patched with graphene Absorptances as high as 099 over a 116-THz-wide spectral regime for normal incidence were found for a metasurface comprising meta-atoms with only a few pixels patched with graphene, regardless of the polarization state In comparison to metasurface absorbers comprising two graphene layers separated by an insulator mounted on a metal-backed substrate, graphene need was thereby reduced by two-thirds The number and dimensions of the pixels in a meta-atom can be altered to fit spectral requirements

Graphene pixel-based polarization-insensitive metasurface for almost perfect and wideband terahertz absorption

The inhomogeneously-loaded helical slow-wave structure is field analyzed by azimuthally smoothing out the discrete supports into a number of continuous dielectric tube regions of appropriate permittivity values. The analysis is made rigorous by removing the usual approximation of considering the radial propagation constant to be the same in the different structure regions; moreover, a tape-helix instead of a simpler sheath-helix model has been used to consider the space-harmonic effects. This renders the present analysis more general, accurate and capable of dealing with a wide range of structure parameters, and particularly makes it valid for large values of helix pitch angle, inhomogeneity and separation between the helix and the metal envelope of the structure. Further, structured expressions amenable to easy computation are presented with the help of the recurrence relations for various structure regions, and methods to use them effectively in an iterative cycle for the desired accuracy are suggested. The developed analytical expressions have also been checked by seeing that they pass on, as special cases, to those obtained earlier by making simplifying assumptions. In this comparison, care has been taken to account for the helix tape thickness by considering a free-space gap equal to the difference between the mean helix radius and the inner radius of the dielectric helix support. The results for the propagation characteristics of an inhomogeneously-loaded helical structure presented here are rather general and can readily be used for the structure design, performance evaluation, and control of any space harmonic of interest in a practical device.

Rigorous tape analysis of inhomogeneously-loaded helical slow-wave structures

A general cylindrical waveguiding interaction structure with a dielectric rod at its axis and a dielectric lining at its wall is field-analyzed to obtain a cold dispersion relation. The results of the cold analysis are combined with the hot dispersion relation of a dielectric-free gyro-traveling wave tube (TWT) to obtain the hot dispersion relation of the dielectric-loaded gyro-TWT. The dispersion relation is interpreted to obtain the conventional TWT-type, Pierce-form gain equation. The dielectric parameters are chosen for a wideband coalescence between the beam end the waveguide modes. For a TE/sub 0n/-mode gyro-TWT, the fundamental mode of operation (n=s=1, where s is the beam-harmonic mode number), gives a higher gain which reduces as one goes for higher values of n=s. The second harmonic operation (n=s=2), however, gives a larger bandwidth. The present analysis also suggests a method to select the values of the hollow beam radius relative to the waveguide wall radius for enhancing both the device gain and bandwidth. This study shows the feasibility of a wideband amplification in a gyro-TWT using dielectric loading, at higher gain values than those obtainable from other broadbanding schemes such as simultaneous profiling of the waveguide cross section and the background dc magnetic flux density.

Broadbanding of a gyro-TWT by dielectric-loading through dispersion shaping

The wide-band low-gain feature of a tapered smooth wall gyro-traveling wave tube (gyro-TWT) was combined with the low beam energy, low magnetic field, and high gain, though narrow band, feature of a vane loaded nontapered gyro-TWT, to propose a distributed, tapered vane loaded gyro-TWT for both high gains and wide bandwidths. The device was analyzed for the tapering of any one of the three parameters - the waveguide radius, the vane depth, and the vane angle keeping the remaining two as constant. The magnetic field was also synchronously tapered. The optimum taper and vane parameters were predicted for a large gain and bandwidth.

Pradip Kumar Jain

Papers

The inhomogeneous loading effects of practical dielectric supports for the helical slow-wave structure of a TWT

Graphene pixel-based polarization-insensitive metasurface for almost perfect and wideband terahertz absorption

Rigorous tape analysis of inhomogeneously-loaded helical slow-wave structures

Broadbanding of a gyro-TWT by dielectric-loading through dispersion shaping

Analysis of a tapered vane loaded broad-band gyro-TWT