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Throughout the international railway community, there are many different designs of elastic fastening systems that have been developed to meet a variety of design specifications and performance expectations. Historically, in North America, the most common types of fastening systems used for concrete crossties are the Safelok I or e-clip systems. In recent years railroads have begun implementing the Skl-style (W) fastening system with concrete crossties in existing and new heavy haul freight railroad mainlines. The magnitude of lateral force applied to the Skl-style fastening system is important information for both design and application purposes. Despite this importance, the lateral force applied to the Skl-style fastening system in a heavy haul freight railroad environment has never been quantified to date. To better understand how the Skl-style system performs under the magnitude of lateral loads observed on heavy haul freight railroads, research was conducted by the Rail Transportation and Engineering Center (RailTEC) at the University of Illinois at Urbana-Champaign (UIUC). The focus of this paper is on laboratory characterization of the lateral load path through the Skl-style fastening system using novel instrumentation techniques that are subjected to heavy haul freight railroad loading conditions. The investigation of fastening system performance included an evaluation of lateral load distribution through the track superstructure, and a single fastening system. Laboratory experimentation concluded that lateral wheel load is primarily distributed to three crossties, the relationship between lateral wheel load and lateral force resisted by field side angled guide plate is non-linear, and that the design of the Skl-style fastening system allows lateral force to be transferred into the crosstie below the worst case concrete compressive fatigue strength. The observations from this study will assist the rail industry in improving fastening system design and developing mechanistic track structure design method.

A compact linearly polarized dual-band patch antenna with low cross-polarization and independent band control is presented. Miniaturization was achieved through a combination of shorting, subsequently folding, and by replacing the standard slot loading with a slot that is featured by a meander line. By replacing the standard straight slot with an interdigitated slot loading, the resonance condition was shifted to the lower operating band, facilitating significant antenna miniaturization and resulting in an element size equal to or smaller than $0.1\lambda _{ {0}}$ in all three dimensions. The antenna design procedure is outlined and a prototype for WiFi applications was fabricated and measured for impedance matching, radiation pattern, and broadside gain. A simulated parametric analysis was performed on the interdigitated slot geometry to determine how the antenna performance is controlled. Then, based on the parametric analysis, it was further demonstrated that the two operational bands of the antenna element could be independently controlled by changing only the geometrical dimensions of the interdigitated slot, leaving the base of the antenna entirely unaltered. As a result, the lower operating band could be fixed while the upper operating band could be shifted by up to 10%. Lastly, the effect of utilizing a small ground plane, in an effort to achieve a small antenna footprint, is discussed.

Consistent increases in cumulative freight tonnages, combined with the move towards increased higher-speed intercity passenger rail operation, have placed greater demands on North American railroad infrastructure. Concrete sleepers and fastening system components are known to fail at a wide range of life cycle intervals when subjected to demanding loading environments. Such failures can cause track geometry defects, require repetitive maintenance procedures, and present critical engineering challenges. Rail seat deterioration, the degradation of the concrete material beneath the rail, has been identified through a survey of North American Class I railroads to be the most-critical engineering challenge for concrete sleepers. Shoulder/fastener wear or fatigue was identified by the same survey as the second-most-critical engineering challenge related to concrete sleepers. Lateral forces transferred through the fastening system are thought to be a primary cause of degradation of insulators. The objective of this study is to quantify the demands on the insulator through analysis of the transfer of lateral wheel loads into the fastening system by measuring the magnitude of the lateral forces entering the shoulder, a component of the fastening system adjacent to the insulator. The lateral load evaluation device (LLED) was developed at the University of Illinois in Urbana Champaign to quantify these forces. Data captured by the LLED will assist the rail industry in moving towards the mechanistic design of future fastening systems, by quantifying the lateral forces in the fastening system under representative loading conditions. Information gained through this study will also lead to a better understanding of the frictional forces at key interfaces in the fastening system. Preliminary results show that the transfer of lateral wheel loads into the fastening system is highly dependent on the magnitude of the lateral wheel loads and the frictional characteristics of the fastening system.

The underground-mining environment can affect radio-signal propagation in various ways. Understanding these effects is especially critical in evaluating communications systems used during normal mining operations and during mine emergencies. One of these types of communications systems relies on medium-frequency (MF) radio frequencies. This paper presents the simulation and measurement results of recent National Institute for Occupational Safety and Health (NIOSH) research aimed at investigating MF coupling between a transmission line (TL) and a loop antenna in an underground coal mine. Two different types of measurements were completed: 1) line-current distribution and 2) line-to-antenna coupling. Measurements were taken underground in an experimental coal mine and on a specially designed surface test area. The results of these tests are characterized by current along a TL and voltage induced in the loop from a line. This paper concludes with a discussion of issues for MF TLs. These include electromagnetic fields at the ends of the TL, connection of the ends of the TL, the effect of other conductors underground, and the proximity of coal or earth. These results could help operators by providing examples of these challenges that may be experienced underground and a method by which to measure voltage induced by a line.

The theoretical basis for an ultra-thin broadband absorber is established which is comprised of a mushroom-type high impedance surface (HIS) and a pixelized frequency selective surface (FSS). The latter is engineered to exhibit a prescribed series $RLC$ circuit response and it is placed at an electrically small distance above the HIS. Through a transmission line analysis, it is demonstrated that the admittances of the two structures cancel each other, resulting in an almost zero input reactance and a resistance that fluctuates around that of free space within the frequency range of interest. The resulting structure has a total thickness that does not exceed 2 mm while a $ - 10~\hbox{dB}$ return loss is achieved for normal incidence from $9 - 13~\hbox{GHz}$ .

An efficient procedure for modeling medium frequency (MF) communications in coal mines is introduced. In particular, a hybrid approach is formulated and demonstrated utilizing ideal transmission line equations to model MF propagation in combination with full-wave sections used for accurate simulation of local antenna-line coupling and other near-field effects. This work confirms that the hybrid method accurately models signal propagation from a source to a load for various system geometries and material compositions, while significantly reducing computation time. With such dramatic improvement to solution times, it becomes feasible to perform large-scale optimizations with the primary motivation of improving communications in coal mines both for daily operations and emergency response. Furthermore, it is demonstrated that the hybrid approach is suitable for modeling and optimizing large communication networks in coal mines that may otherwise be intractable to simulate using traditional full-wave techniques such as moment methods or finite-element analysis.

Electromagnetic absorbers based on frequency-selective surfaces have been explored for many applications. It is often useful to represent these devices using a circuit equivalence, which provides a physical insight into underlying performance capabilities and limitations. Yet, absorbers tend to deviate from their ideal circuit representations for ultra-thin implementations where coupling between layers becomes significant. To date, there has been little investigation into the corrective measures required to compensate for parasitic coupling associated with ultra-thin absorbers. In the paper, a circuit model is proposed for a broadband absorber comprised of a single-resonance FSS cascaded with a PEC-backed substrate. The thin nature of the absorber is shown to introduce undesirable coupling between the FSS and PEC layers, resulting in non-ideal performance. Two corrective measures are outlined with the goal of retuning the absorber for maximum bandwidth.

We propose a compact conformal wearable antenna that operates in the 2.36-2.4 GHz medical body-area network band. The antenna is enabled by placing a highly truncated metasurface, consisting of only a two by two array of I-shaped elements, underneath a planar monopole. In contrast to previously reported artificial magnetic conducting ground plane backed antenna designs, here the metasurface acts not only as a ground plane for isolation, but also as the main radiator. An antenna prototype was fabricated and tested, showing a strong agreement between simulation and measurement. Comparing to previously proposed wearable antennas, the demonstrated antenna has a compact form factor of 0.5 λ 0 ×0.3 λ 0 ×0.028 λ 0 , all while achieving a 5.5% impedance bandwidth, a gain of 6.2 dBi, and a front-to-back ratio higher than 23 dB. Further numerical and experimental investigations reveal that the performance of the antenna is extraordinarily robust to both structural deformation and human body loading, far superior to both planar monopoles and microstrip patch antennas. Additionally, the introduced metal backed metasurface enables a 95.3% reduction in the specific absorption rate, making such an antenna a prime candidate for incorporation into various wearable devices.

A low-profile high-gain unidirectional antenna is proposed and demonstrated using both metamaterial (MM) and substrate-integrated waveguide (SIW) technologies. First, the leaky modes supported by a grounded anisotropic slab are studied. These investigations reveal that a grounded slab consisting of an anisotropic zero/low index material can provide an extremely low value for the real part of the propagation constant of the leaky mode, thereby facilitating stable unidirectional broadside radiation over a wide frequency range. The truncation effect of the slab is then investigated through full-wave simulations, which is found to be beneficial for a practical implementation of dispersive metamaterials. Finally, to validate the proposed concept, a subwavelength end-loaded dipole array is designed to realize the required anisotropic zero-index property and is applied to a SIW fed longitudinal slot antenna for the 5.8 GHz wireless local area network (WLAN) band. Measurements of the fabricated antenna prototype are shown to be in strong agreement with simulation results, thus confirming the proposed antenna design. The resulting antenna is only 0.12 λ thick, all while accomplishing a broadside gain of more than 10 dBi and a front-to-back ratio larger than 26 dB, which is ~ 7 dB and ~ 10 dB higher than that of the SIW fed slot alone, respectively. The -10 dB impedance bandwidth is more than 9% both with and without the presence of the MM coating. The proposed technique offers a means for realizing low-cost and low-profile unidirectional antennas with moderate bandwidth.

Transformation electromagnetics (TE) has been used to predict many unconventional and potentially game-changing electromagnetic devices, but they are often left unimplemented due to the complexity of the required material properties. Restricting transformations to quasi-conformal mappings allows all-dielectric gradient-index (GRIN) lens implementations using approaches familiar to optical system designers. We demonstrate spherical-aberration-corrected lenses with spherical surface profiles by mimicking the optical behavior of aspherical lenses using quasi-conformal mappings. Several approaches for mapping aspherical to spherical contours are described and contrasted, including the use of bulk GRIN regions throughout the entire lens as well as layered designs where the GRIN profiles are restricted to thin laminar layers at the surface of the otherwise homogeneous lens. Hence, the proposed methodology provides engineers with a powerfully intuitive means to design, compare, and contrast various equivalently performing GRIN lenses, adding new modeling capabilities to the existing, well-known remedies for optical system optimization. Furthermore, such an approach facilitates straightforward monitoring and manipulation of material gradients and overall change in refractive index.

While historically limited by a lack of suitable materials, rapid advancements in manufacturing techniques, including 3D printing, have caused renewed interest in gradient-index (GRIN) optics in recent years. Further increasing the desire for GRIN devices has been the advent of Transformation Optics (TO) which provides the mathematical framework for representing the behavior of electromagnetic radiation in a given geometry by “transforming” it to an alternative, usually more desirable, geometry through an appropriate mapping of the constituent material parameters. These transformations generally result in 3D GRIN lenses which often possess better performances than traditional radial GRINs. By decomposing TO-GRIN solutions into a 2D-polynomial basis to analyze their behavior, it can be determined which terms govern their performance improvements. However, TO is a computationally intensive evaluation and a comprehensive study of this sort could take weeks to perform. But, by training a surrogate model to approximate the TO calculation, the procedure can be greatly accelerated, dramatically reducing the time of this study from weeks to hours. Moreover, the obscure GRIN terms present in the TO solutions can be mapped to specific aberrations by decomposing the resulting wavefronts into a Zernike polynomial basis and performing multivariate regression analyses. This yields a surrogate model which approximates the full numerical ray-trace and offers an avenue for rapid GRIN lens design and optimization. Meanwhile, to aid in the GRIN construction, we employ advanced multi-objective optimization algorithms which allow the designer to explicitly view the trade-offs between all design objectives such as spot size, field-of-view, and Δn.

GRadient INdex (GRIN) optics has revolutionized the field of lens design by providing an unparalleled amount of design freedom, resulting in high-performance optical systems. Unfortunately, this design freedom leads to a large number of parameters in multi-element systems, since the GRIN distributions need to be described in addition to the lens geometries. This can lead to slow convergence and stagnation for even the most robust numerical optimizers. This paper proposes a modular, black-box design paradigm which allows for the optimization of each element in the system independently. This leads to an efficient strategy to design all-GRIN systems from scratch, or to replace existing homogeneous doublets and triplets in a system with GRIN singlets.

A low-frequency coupling model consisting of a multi-conductor transmission line (TL) system and a small circular loop antenna is presented. The TL system is composed of N perfect electrical conductor (PEC) wires above a lossy ground. An approximate and computationally efficient analytical method is proposed to predict the current distribution on each wire. The total electromagnetic (EM) fields produced by the small circular loop antenna above the lossy half-space are calculated by employing a discrete complex image method (DCIM). The resulting induced current distributions are subsequently calculated and validated with a commercially available moment method code.

Transformation optics is applied to interpret the dispersive nature of materials via changes in geometry, providing an alternative methodology for dispersion correction. An example is proposed and analyzed to demonstrate the effectiveness of the proposed technique.

A radial-axial hybrid GRIN theory is developed in order to explore the solution space of an achromatic GRIN singlet. With the achromatic hybrid GRIN theory in hand, the tradeoffs between thickness, curvature, and GRIN type can be directly studied in the context of SWaP (size, weight, and power) reduction. Finally, the achromatic solution space of a Silicon-Germanium based material system is explored.

An analytical method based on paraxial ray-tracing equations is proposed for designing gradient-index (GRIN) metamaterial lenses with dispersion-correction. An instructive example is considered to demonstrate the effectiveness.

A low-frequency coupling model from a small circular loop antenna to a multi-conductor transmission line (TL) system composed of N perfect electric conductor (PEC) wires above a PEC ground is presented. The telegrapher's equations for the model are presented, and a computationally efficient analytical solution for the induced current distributions is formulated for each wire. An example is constructed in FEKO and the induced currents are compared with the proposed method, showing excellent agreement.

GRadient-INdex (GRIN) lenses have long been of interest due to their potential for providing levels of performance unachievable with traditional homogeneous lenses. While historically limited by a lack of suitable materials, rapid advancements in manufacturing techniques, including 3D printing, have recently kindled a renewed interest in GRIN optics. Further increasing the desire for GRIN devices has been the advent of Transformation Optics (TO), which provides the mathematical framework for representing the behavior of electromagnetic radiation in a given geometry by “transforming” it to an alternative, usually more desirable, geometry through an appropriate mapping of the constituent material parameters. Using TO, aspherical lenses can be transformed to simpler spherical and flat geometries or even rotationally-asymmetric shapes which result in true 3D GRIN profiles. Meanwhile, there is a critical lack of suitable design tools which can effectively evaluate the optical wave propagation through 3D GRIN profiles produced by TO. Current modeling software packages for optical lens systems also lack advanced multi-objective global optimization capability which allows the user to explicitly view the trade-offs between all design objectives such as focus quality, FOV, unand focal drift due to chromatic aberrations. When coupled with advanced design methodologies such as TO, wavefront matching (WFM), and analytical achromatic GRIN theory, these tools provide a powerful framework for maximizing SWaP (Size, Weight and Power) reduction in GRIN-enabled optical systems. We provide an overview of our advanced GRIN design tools and examples which minimize the presence of mono- and polychromatic aberrations in the context of reducing SWaP.

In 2013, there were 14 killer tornadoes in the United States that caused a total of 55 fatalities. The most severe tornado in this group was an Enhanced Fujita (EF) 5 storm that occurred on May 20 in Moore, Oklahoma. Because of the severity of this storm, a field investigation was undertaken to observe and document damaged commercial and residential structures so that a better appreciation of their structural and nonstructural performance could be developed. Both low-rise engineered commercial buildings and single-family homes were surveyed. Most of the commercial buildings sustained severe nonstructural damage and limited damage to the primary structural system. However, some instances of global structural collapse and local collapse of structural elements around building entrances were also observed in commercial buildings. Residential construction exhibited extensive damage to brick veneer and failure of garage doors and subsequent roof damage. These failures illustrate the importance of an ade...

The underground mining environment can affect radio signal propagation in various ways. Understanding these effects is especially critical in evaluating communications systems used during normal mining operations and during mine emergencies. One of these types of communications systems relies on Medium Frequency radio frequencies. This paper presents the simulation and measurement results of recent National Institute for Occupational Safety and Health (NIOSH) research aimed at investigating medium frequency coupling between a transmission line and a loop antenna in an underground coal mine. Two different types of measurements were completed: line current distribution and line to antenna coupling. Measurements were taken underground in an experimental coal mine and on a specially designed surface test area. The results of these tests are characterized by current along a transmission line and voltage induced in the loop from a line. The paper concludes with a discussion of issues for medium frequency transmission lines. These include magnetic fields at the ends of the transmission line, connection of the ends of the transmission line, the effect of other conductors underground, and the proximity of coal or earth. These results could help operators by providing examples of these challenges that may be experienced underground.

Transformation Optics (TO) provides the mathematical framework for representing the behavior of electromagnetic radiation in a given geometry by “transforming” it to an alternative, usually more desirable, geometry through an appropriate mapping of the constituent material parameters. Using a quasi-conformal mapping, the restrictions on the required material parameters can be relaxed allowing isotropic inhomogeneous all-dielectric materials to be employed. This approach has led to the development of a new and powerful design tool for gradient-index (GRIN) optical systems. Using TO, aspherical lenses can be transformed to simpler spherical and flat geometries or even rotationally-asymmetric shapes which result in true 3D GRIN profiles. TO can also potentially be extended to collapse an entire lens system into a representative GRIN profile thus reducing its physical dimensions while retaining the optical performance of the original system. However, dispersion effects of the constituent materials often limit the bandwidth of metamaterial and TO structures thus restricting their potential applicability. Nonetheless, with the proper pairing of GRIN profile and lens geometry to a given material system, chromatic aberrations can be minimized. To aid in the GRIN construction, we employ advanced multi-objective optimization algorithms which allow the designer to explicitly view the trade-offs between all design objectives such as RMS spot size, field-of-view (FOV), lens thickness, 𝛥𝑛, and focal drift due to chromatic aberrations. We present an overview of our TO-enabled GRIN lens design process and analysis techniques while demonstrating designs which minimize the presence of mono- and poly-chromatic aberrations and discuss their requisite material systems.

The ability to correct for monochromatic aberrations without the need for complex geometry has made gradient-index optics an attractive area of research, but manufacturing challenges have limited their application to a select few areas. In this study, a novel method for fabricating gradient-index lenses using inkjet solid free form three-dimensional printed optical polymers is proposed. A flat gradient-index lens based on the fabrication constraints is optimized using a powerful customized design synthesis tool. Cross-sectional views of its continuous index profile and a representative binary pixel-map are shown.

Gradient-index (GRIN) lenses are predicted by many to have superior performance compared with lens systems using conventional homogeneous material compositions. Namely, the complexity of classic (i.e. homogeneous) multi-lens sequences required for high performance optical systems can be instead manifested into GRIN profile complexity, allowing for refraction throughout the volume of a lens and not just at the hard surface boundaries. As GRIN material technologies continue to evolve, facilitating more practical GRIN lens implementations, the knowledgebase and design tools to optimize GRIN lens systems must be simultaneously built. In this paper, one of the more unknown, yet crucially important, challenges of GRIN lens design is considered: dispersion. Dispersion and its effects on GRIN lenses are considered and a method to minimize its impact on the performance of GRIN lenses is outlined. Finally, a GRIN focusing lens based on the mixing of Germanium (Ge) and Silicon (Si) is proposed and designed to have minimal focal drift.

A low-frequency coupling model from a small circular loop antenna to a transmission line (TL) composed of a single perfect electrical conductor (PEC) wire above a lossy half-space is presented. Instead of using Sommerfeld integrals, a discrete complex images method (CIM) is utilized to calculate the electromagnetic fields produced by a horizontal magnetic dipole (HMD). The resulting currents induced on the TL are subsequently calculated and are validated with a commercial moment method code which uses numerical solutions to the Sommerfeld integral.

Recent developments in transformation optics have led to burgeoning research on gradient index lenses for novel optical systems. Such lenses hold great potential for the advancement of complex optics for a wide range of applications. Despite the plethora of literature on gradient index lenses, previous works have not yet considered the application of anti-reflective coatings to these systems. Reducing system reflections is crucial to the development of this technology for highly sensitive optical applications. Here, we present effective anti-reflective-coating designs for gradient index lens systems. Conventional anti-reflective-design methodologies are leveraged in conjunction with transformation optics to develop coatings that significantly reduce reflections of a flat gradient index lens. Finally, the resulting gradient-index anti-reflective coatings are compared and contrasted with conventional homogeneous anti-reflective coatings.

Many new, high-performance antenna designs have employed optimization strategies to tune their geometric parameters for optimal electromagnetic properties such as return loss and gain. Several antenna designs are presented here that demonstrate the ability of these optimization strategies to competently fulfill the designer's performance criteria. Designs such as the anisotropic zero-index and low-index metamaterial-enabled antennas illustrate the benefits of applying evolutionary strategies to create metamaterials for integration into classical antennas as well as tune the final, integrated antenna system. The folded meander-slot and embedded-element stacked patch antenna designs illustrate how the algorithms can be used to directly optimize antenna geometries for wide-band and multi-band purposes.

An ultra-thin wideband absorber is proposed comprised of two cascaded layers. The first layer is a pixelized Frequency Selective Surface (FSS) engineered to exhibit the response of a series RLC circuit. The FSS is placed at a small but useful distance above a mushroom-type artificial magnetic conductor (AMC). The admittances of the two structures cancel each other resulting in an almost zero input reactance within the frequency range of interest. A -10dB return loss is achieved for normal incidence from 9-13 GHz, while the total thickness of the structure does not exceed 2 mm.

Transformation Optics (TO) has enabled new methodologies for the design and specification of gradient-index (GRIN) lenses for radio-frequency and optical applications by linking refractive index gradients to a mathematically equivalent change in geometry in another dimension. With the new mathematical design tools, there have been many interesting devices introduced in the literature, such as optical collimators and absorbers (optical “black holes”), GRIN couplers and bends for optical waveguides, and compressed or flattened collimating lenses for imaging and non-imaging applications. Many of the most interesting TO designs are not feasible for implementation, however, due to the complex anisotropic, inhomogeneous material parameters required by the full TO formulation. Instead, restricting the geometric transformations to be mathematically conformal or quasi-conformal (qTO) eliminates the anisotropic material requirements and allows implementation with an isotropic 2D or 3D GRIN profile, for which multiple fabrication methods exist in the RF and IR wavelength ranges and are under development for the complete optical spectrum. We present an overview of the usefulness of combining TO, qTO, and GRIN optics for energy concentration along with the associated design and analysis techniques. Moving away from traditional lenses to GRIN and TO optics for which, in general, no analytical geometric optics or full-wave solution exists, involves the development of new design strategies for individual lenses and systems of lenses. We demonstrate results obtained using advanced, multivariate optimizations that are tightly coupled to a fast, advanced inhomogeneous ray tracing engine for electrically-large lenses, and to an efficient body-of-revolution solver for electrically-small cylindrically-symmetric lenses.

Quasi-conformal Transformation Optics (QCTO) has been proposed as a design technique for flattened or compressed optical and RF lenses. QCTO devices may be realized using all-dielectric gradient-index structures, which simplifies implementation and improves bandwidth for structures at optical wavelengths by avoiding the requirement for metamaterial design and fabrication. However, replacing one or more conventional homogeneous optical lenses by a QCTO equivalent is not as simple as a single-step design from performance specification to a drop-in replacement lens. Optimizations must be performed over the QCTO transformation in order to achieve equivalent optical performance under index and fabrication constraints. This abstract presents an optimization procedure for QCTO lenses that makes use of a ray tracing tool that supports arbitrary numerically-specified GRIN profiles for electrically large structures.

This work presents research in the development of medium frequency communications systems that the National Institute for Occupational Safety and Health (NIOSH) is performing in support of the 2006 MINER Act. In this work, a 280-m twin-lead (30-cm separation, 725-ohm) transmission line (TL) was constructed and used to measure complex input impedance and line currents resulting from open and shorted terminations at medium frequencies (MF). The line was placed in free space and positioned close to a lossy earth surface. This 3-conductor system (two wires and earth) was chosen to be a starting point to investigate the multimodal nature TLs may possess inside a coal mine. Although the TL was constructed to be physically isolated from the ground, measurements indicate the existence of common mode (CM) currents which are characteristic of a three-conductor system; hence, the ground affected the MF propagation characteristics. In this paper, full-wave computational models using moment methods are compared with the experimental measurements as a way to determine the origin of the CM currents. In the future, related experiments will be performed in underground mines in an effort to predict how multimodal MF signals will propagate in the presence of similar multiple-conductor systems.

By analyzing the limitations that achromatic gradient-index (GRIN) lens solutions in the radial and axial extremes place on lens thickness and surface curvature, a radial-axial hybrid GRIN theory is developed in order to overcome these restrictions and expose a larger solution space. With the achromatic hybrid GRIN theory, the trade-offs between thickness, curvature, and GRIN type can be directly studied in the context of size, weight, and power (SWaP) reduction. Finally, the achromatic solution space of a silicon-germanium-based material system is explored, and several designs are verified with ray tracing.

This paper proposes a new design paradigm which allows for a modular approach to replacing a homogeneous optical lens system with a higher-performance GRadient-INdex (GRIN) lens system using a WaveFront Matching (WFM) method. In multi-lens GRIN systems, a full-system-optimization approach can be challenging due to the large number of design variables. The proposed WFM design paradigm enables optimization of each component independently by explicitly matching the WaveFront Error (WFE) of the original homogeneous component at the exit pupil, resulting in an efficient design procedure for complex multi-lens systems.

Recent advances in the field of transformation optics (TO) have renewed interest in gradient-index (GRIN) optical systems. By transforming a classically inspired aspherical lens to a flat geometry using TO, one can achieve a design with better field-of-view (FOV) performance than traditional radial GRIN lenses. In order to understand the underlying physics of this performance improvement, TO-derived solutions of various designs are decomposed into a 2D-polynomial basis to analyze their behavior and to determine which terms improve optical performance. A comprehensive study of this sort involves thousands of iterations of numerical TO and ray tracing. By training a surrogate model to approximate the TO calculation, the procedure can be greatly accelerated, dramatically reducing the time of this study from weeks to hours. The accuracy of the surrogate model approximation is verified against the original TO solution, and its usefulness in a system-by-design procedure is tested in a series of single- and multi-objective optimizations.

This work presents research in the development of medium frequency communications systems that the National Institute of Occupational Safety and Health (NIOSH) is performing in support of the 2006 MINER Act. In this work, a 280 m twin-lead transmission line (TL) is used to measure complex input impedance and line currents resulting from open and shorted terminations at medium frequencies (MF). The line is placed in free space and positioned close to a lossy earth surface such that two line configurations can be chosen in order to control the extent to which the ground's presence affects MF propagation. In this way, the effects of the earth return may be characterized and modeled. Further, full-wave computational models using moment methods are used to compare with the experimental measurements as a way to determine the material properties of the ground medium. In the future, these experiments will be conducted in underground mines in an effort to develop and improve MF communication systems for mining operations and emergency response.

In this paper, we experimentally demonstrate an artificial perfect magnetic mirror constructed from an array of cross-shaped dielectric resonators in the optical range. The TM 01δ mode of the cross-shaped dielectric resonator was exploited to provide a near-unity reflectivity and a near-zero reflection phase, mimicing a theoretical perfect magnetic conductor. A sample of the artificial mirror was fabricated using standard e-beam lithography and was further characterized, showing a strong agreement with simulated predictions.

This work presents a hybrid approach using transmission line (TL) equations in conjunction with commercial method of moment (MoM) codes, to aid in efficient modeling of medium frequency (MF) propagation in coal mines. All local electromagnetic phenomena can be accurately modeled by strategic placement of full wave MoM sections near transmitting and receiving antennas. Meanwhile, ideal TL models are used to calculate loading and excitation of those MoM sections. In this way, communication networks can be modeled using a hybrid approach. The TL geometry of specific interest for this work is a single wire conductor positioned much less than one wavelength away from the floor/ceiling/wall of a mine. Previous work related to this geometry is summarized for approximate solutions of TL parameters. Examples are considered to demonstrate the capacity of the hybrid approach to optimize TL networks with significantly improved speeds.

A method to analyze and optimize medium frequency (MF) wave propagation in coal mines is introduced. Specifically, a hybrid approach using ideal transmission line (TL) models in conjunction with strategically placed full-wave sections is demonstrated. This hybrid approach provides for a computationally efficient and accurate alternative to typical numerical methods. Specifically, this work demonstrates that conduction paths between transmitter and receiver can be accurately modeled with the hybrid approach, resulting in significantly improved computation speeds relative to full-wave simulations. With this hybrid approach, the complex propagation networks of coal mines can be analyzed, facilitating the optimization of conductor and/or antenna placement for improved performance of MF communication systems.

Pregnant rats were subjected to nutritional stress, environmental stress (immobilization-illumination-heat), or injections of adrenocorticotropic hormone (ACTH) during the third trimester of gestation. Masculine and feminine behavior potentials of the male offspring were determined in adulthood. Compared to control males, male copulatory behavior was severely impaired in all three experimental groups. The prenatally stressed animals showed a significant reduction in the cumulative percent ejaculating and an increase in the number of intromissions prior to the first ejaculation compared to control animals. When tested for female behavior, all three treatment groups displayed a significantly greater lordosis quotient than the control males. Gestation length was increased in the mothers exposed to environmental stress and ACTH injections but not in the nutritional stress animals. At birth, offspring from all experimental groups showed a significant reduction in body weight when compared with control offspring. These results confirm and extend earlier data which indicate that exposure of the mother to stress during the period of fetal sexual differentiation may impair masculine and feminine sexual behavior of the male offspring.

Eighteen food-deprived pigeons were divided into three groups and either hand-shaped or autoshaped to peck a response key illuminated with red or green light. Group 1 was autoshaped using a procedure that employed a 30-sec intertrial interval (ITI); the other two groups were hand shaped by the method of successive approximations, one (Group 2) with a 30-sec ITI, the other (Group 3) without. In subsequent discrimination training, the subjects in Groups 1 and 2 emitted significantly fewer errors than those in Group 3. The role of the ITI was explained with reference to the Rescorla-Wagner model of associative learning, modified to account for stimulus generalization. Implications of the data for the study of errorless learning and the comparison between hand shaping and autoshaping are discussed.

The relationships between five dimensions of complex stimuli and the latency, waveform, and amplitude of the visually evoked potential (VEP) were investigated in three experiments. One stimulus variable, contour density, emerged as the most consistent predictor of VEP amplitude. Contrary to earlier reports, changes in either latency or waveform were not observed, and linearity was the most frequent form of the relationship between the stimuli and amplitude measures.

Human occipital responses evoked by trains of four consecutive pulses of light varying in rate of presentation and pulse-to-cycle fraction were recorded from scalp. Perceptual reports were simultaneously obtained. Electrical responses were computer-averaged, and peak delays and amplitudes of consistent wave components were analyzed. At 5 and 10 c/s a distinct complex was recorded to each light pulse, while at 20 and 30 c/s a single complex was recorded to the entire stimulus train. For the two main wave components analyzed, highest amplitudes were recorded in the second pulse response, with amplitude generally greater at 10 than at 5 c/s. Pulse-to-cycle fraction significantly affected peak delay values, with briefest latencies at PCF 0.03, and briefer latencies at 10 than at 5 c/s. Correlations between verbal reports of number of flashes seen and evoked potential record were demonstrated for all 5 and 30 c/s conditions.

Photically evoked cortical potentials (VERs) were recorded from four subjects under conditions of systematically varied background intermittent stimulation. Cortical responses recorded when the subjects' pupils were mobile were compared with those obtained with pupillary mydriasis. VER amplitude was reliably greater when responses were recorded with mydriatic pupils than with mobile pupils. Under either condition, response amplitude was reliably diminished by increasing the frequency of background intermittent stimulation. With mobile pupils, VER diminution was partitioned between the results of pupillary constriction and light adaptation produced by the intermittent stimulation. Under conditions of mydriasis, VER diminution was related singularly to light adaptive processes in the visual system.

Inclusion bodies isolated from Spo − Cr + mutants of Bacillus thuringiensis were toxic for larvae of the European corn borer. Probit analysis revealed comparable toxicity between wild-type crystals (isolated from B. thuringiensis subsp. kurstaki ) and crystals produced from two spore-free mutants of the same subspecies. Death of the larvae was due to starvation, presumably through δ-endotoxin-induced gut paralysis. Inclusion bodies pretreated with α-chymotrypsinogen were equally as toxic as native crystals for the insect larvae.

Photically evoked afterdischarge (AD) parameters were examined in albino rats during the time course of 1 h of iterative photic stimulation (515 light flashes). It was observed that percentage of AD elicitation, duration of AD activity, and number of spindle waves per AD increased and then subsequently decreased over time. The amplitude of the largest peak-to-peak wave per AD was unaffected by time. Greatest AD elicitation took place during the 5- to 15-min time segment following the initiation of iterative photic stimulation. Likewise, the last 5 min of iterative stimulation yielded the lowest AD elicitation scores. These data suggest the operations of an arousal continuum in the process of AD elicitation. It was also observed that spontaneous AD-like waves occurred in the visual cortex at irregular intervals that were not specifically correlated with the light flashes.

Pregnant rats were subjected to environmental stress (immobilization, illumination, heat) during the last trimester of gestation. Copulatory behavior of prenatally stressed and control male offspring was determined during seven weekly 30-min tests. At the conclusion of the 7-week testing period, prenatally stressed and control males that were sexually inactive were injected intraperitoneally with 10 mg/kg of naloxone hydrochloride 30-min prior to retesting for copulatory behavior. Fifty-five percent (10/18) of the control males became sexually active and ejaculated during a single 30-min testing period, whereas 0% (0/32) of the prenatally stressed males became sexually active. It is concluded that prenatal stress renders male offspring unresponsive to opiate-antagonist induction of copulatory behavior.

Two groups of rats (the recovery groups) were fed on a synthetic thiamine-deficient diet, and another group (the supplemented group) was fed on the same diet but received supplemental thiamine in their water so as not to become deficient. Following a 6-day recovery period during which all rats were given a novel-flavored thiamine-enriched diet, one recovery group and the supplemented group received injections of lithium chloride, and the remaining recovery group received injections of saline. Although all groups consumed similar amounts of the chocolate-enriched diet during the recovery period (i.e., all groups were approximately equally familiar with the enriched diet), only the supplemented/poisoned rats showed a marked taste aversion. These results confirm the existence of a “familiar-positive” class of foods and suggest that the context in which a rat is made familiar with dietary choice may overshadow the role of familarity per se as the determining factor in the development of food aversions and preferences.

Summary Lightly restrained albino rats were administered dipropylacetic acid, trimethadione, diphenylhydantoin, saline, and a pentylenetetrazol challenge. The results were attributed to the locus of action of the anticonvulsants and strongly support the usefulness of the photically evoked afterdischarge as a model for the evaluation of thalamically active drugs, with particular reference to those useful in the control of petit mal epilepsy. RESUME Chez des rats albinos, on a administre de l'acide dipropylacetique, de la trimethadione, de la diphenylhydantoine, une solution saline, et du pentylenetetrazol. Les resultats ont ete consideres en fonction du lieu d'action des anticonvulsivants et indiquent d'une facon tres evidente que la postdecharge par stimulation lumineuse est un modele utile pour juger de l'efficacite de substances qui agissent au niveau thalamique et en particulier de celles utiles dans le traitement de l'epilepsie de type petit mal. RESUMEN A varias ratas albinas se administraron acido dipropilacetico, trimetadiona, difenilhidantoina, suero salino y una prueba de pentilentetrazol. Los resultados se atribuyeron al lugar de accion de los anticonvulsivantes y confirman el valor de la utilizacion de los potenciales post-descarga, foticamente evocados, como modelo para la evaluacion de drogas talamicamente activas y, en especial, las que se consideran utiles en el tratamiento de la epilepsia petit mal. ZUSAMMENFASSUNG Albinoratten erhielten Dipropylacetat, Trimethadion, Diphenylhydantoin, Salzlosung und einen Pentylentetrazolreiz. Die Ergebnisse wurden dem Wirkungsort der Antikonvulsiva zugeordnet und unterstutzen wesentlich die Nutzlichkeit der durch Fotostimulation evozierten Nachentladungen als Modell fur die Bewertung thalamisch aktiver Medikamente, speziell solcher die in der Kontrolle der Petit-Mal-Epilepsie von Nutzen sind.