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Driven by the recent improvement in additive manufacturing technologies, we designed a detector that can be fully printed with a standard and commercial 3D printer. The main goals of this research concern the marginal design and construction costs, the reproducibility/modularity of the products, and the reduced assembly time. During the first phase of this research, after determining the most suitable material, we produced 10 examples of detectors., Comment: 2 pages, 4 figures

Despite antidepressant treatment, some patients continue to experience significant symptoms of depression. Literature has demonstrated modest benefit of folate supplementation in treatment-resistant depression among adults, though evidence is lacking in the pediatric population. This case series describes 10 adolescents (mean age 14.4 ± 2.8 years) with treatment-resistant depression prescribed adjunctive l-methylfolate (LM). The patient population was predominantly female (80%), Caucasian (90%), with an average of three comorbid psychiatric diagnoses, and failures of three psychotropic medications before starting LM. The majority of patients (80%) had a single mutation among the two methylene tetrahydrofolate reductase (MTHFR) gene variants evaluated (50% A1298 AC; 30% C677 CT), indicating reduced MTHFR activity. Eighty percent of patients demonstrated improvement in depression, anxiety, and irritability. Overall, LM was well tolerated. These cases suggest that LM as an adjunct to antidepressant treatment may be a safe and effective strategy for managing treatment-resistant depression in pediatric patients.

Uniformly excited, equally spaced linear arrays have a sidelobe level larger than −13.3 dB, which is too high for many applications. This limitation can be remedied by nonuniform excitation of array elements. We present an efficient method for sidelobe reduction in equally spaced linear arrays with low penalty on the directivity. The method involves the following steps: construction of a periodic function containing only the sidelobes of the uniformly excited array, calculation of the Fourier series of this periodic function, subtracting the series from the array factor of the original uniformly excited array after it is truncated, and finally mitigating the truncation effects which yields significant increase in sidelobe level reduction. A sidelobe reduction factor is incorporated into element currents that makes much larger sidelobe reductions possible and also allows varying the sidelobe level incrementally. It is shown that such newly formed arrays can provide sidelobe levels that are at least 22.7 dB below those of the uniformly excited arrays with the same size and number of elements. Analytical expressions for element currents are presented. Radiation characteristics of the sidelobe-reduced arrays introduced here are examined, and numerical results for directivity, sidelobe level, and half-power beam width are presented for example cases. Performance improvements over popular conventional array synthesis methods, such as Chebyshev and linear current tapered arrays, are obtained with the new method.

Selected results from a Computerized Food Microbiological Data Collection program are presented. Data are generated by 11 Department of Defense (DoD) laboratories and forwarded to a central location, coded into computer language, and entered into an existing program. As designed, the program is quite flexible, and selected retrievals for special purposes are easily accomplished. The total file contains data from over 30,000 food samples. Presented in this report are data on 810 samples of comminuted beef products, 215 samples of luncheon meats, 653 prepared sandwiches, and 1,023 delicatessen salads. Data are compared with existing microbiological criteria, if applicable. The retrieval of data from the file on such products should be useful in establishing future standards or guidelines.

A class of nonuniformly excited, equally spaced linear arrays (ESLAs) that can meet design requirements for half-power beamwidth and sidelobe level (SLL) without any limitation is introduced. These arrays are constructed using the patterns of uniformly excited arrays as building blocks, thus lending themselves to simple analytical descriptions and analysis. A design procedure is presented, which can be used to determine the required number of elements and the excitation currents to achieve the specified radiation properties. For these arrays, the element currents always decrease monotonically from a maximum at the array center to a minimum value at edge elements. This property can be exploited to limit the current taper ratio (CTR) when the number of elements is very large. Simulation results indicate that these arrays can provide half-power beamwidths, directivities, and SLLs comparable to those of other desirable array choices, such as Chebyshev arrays, with the same number of elements and interelement spacings. It is shown that, in fact, when the number of elements is sufficiently large, the array introduced here outperforms the Chebyshev array by providing larger directivity and allowing a smaller CTR to be achieved. Numerical results for broadside and endfire arrays are given.

A new class of low side lobe, rectangular planar arrays with monotonically decreasing nonuniform excitations is examined. Simulation results for directivity, side lobe level, and half-power beamwidths, are presented and their variations with the new array parameters and the direction of the pattern main beam maximum are discussed.

John Kraus stands out among the giants in the history of the Antennas and Propagation Society. He made high-impact contributions in both education and research. In education, he authored three classic textbooks. In research, he was a pioneer in antennas and radio astronomy. He invented many antennas, most notably the axial mode helix antenna. He used the antennas he invented in measurement programs, many in radio astronomy. His impact on our profession is immense. This paper reviews his life accomplishments and his contributions to our field.

This paper addresses the importance of both antenna design aspects along with propagation effects in communication systems. As systems become more compact and deployed more widely into complex environments, co-design of the antenna and the communication system propagation elements increases in importance. Several important considerations will be emphasized. The history of communication systems along with that of antennas and propagation will be reviewed

A new technique for synthesis of planar rectangular arrays is presented. Using the specified design requirements for side lobe level and half-power beamwidths in the principal planes, the number of elements and element excitation currents are determined. These arrays are constructed using the patterns of uniformly excited rectangular arrays as building blocks. An important feature of these arrays is that their element currents decrease monotonically away from the array center.

Antennas are a key enabling technology for software-defined radio (SDR). Although software is extremely flexible, SDR's potential is limited by antenna size and performance. In this paper, we review typical antenna miniaturization techniques and fundamental theories that limit antenna size and performance including operational bandwidth, gain (or range), and radiation pattern. Possible antenna design strategies are discussed to meet the desired specifications in SDR based on observations from the limit theories. The application of strategies to enable multiband (resonant), continuous multiband (frequency independent), and instantaneous, ultra-wideband antennas are discussed qualitatively. Advantages, disadvantages, and design trade-off strategies for different types of antennas are compared from a system-level perspective. A design example for a compact ultra-wideband (UWB) antenna is presented for a software-defined platform. The example involves a direct-conversion radio developed in Wireless@VT that uses a Motorola RFIC having a 100 MHz---6 GHz operational frequency range with a 9 kHz---20 MHz channel bandwidth. The example antenna covers frequencies from 450 MHz to 6 GHz instantaneously with approximately 5-dBi realized gain over a finite-size ground plane, including return loss and omni-directional coverage.

All antenna books ever written in English are listed, along with publication information and current availability. The list is organized by technical area. As appropriate, comments are made on the books. Useful information is also included in the article on how to locate antenna books in the library, and how to locate antenna books to buy (new, used, and out-of-print).

With the introduction of digital cellular phones, hearing-aid users have experienced a severe buzzing noise caused by the interaction between digital cellular phones and hearing aids. The cellular-phone industry, the hearing-aid industry, and consumers have been seeking a solution for the interference issue. Efforts reported in the literature have focused on measurements, modeling, and evaluation of interference and RF emission, but not on methods to solve the problem. In this paper, we focus on the causes of the interference and an understanding of the problem. We also present a method to reduce near-field electromagnetic energy around a cellular phone, mitigating the interference between cellular phones and hearing aids. The theoretical investigation of both the radiation mechanisms and fundamental limits on antennas suggested that a low-g antenna, such as an ultra-wideband antenna, could reduce the near-field intensity. Simulations and measurements were performed at 900 and 1880 MHz, using both low- and high-Q test antennas mounted on a mock cellular phone. The results showed that the peak electric and magnetic near-field strengths of the low-g test antenna were lower than those of a high-Q test antenna by at least 5 dBV/m and 4 dBA/m, respectively. The improvement in the near-field performance for the low-g antenna was without any sacrifice in far-field performance. Furthermore, in the presence of a human head, the simulation results showed that the radiation efficiency of the low-Q test antenna was better than that of the high-Q test antenna.

This article describes the software WebPRAC (parabolic reflector analysis code for the web). The Internet version was written as a Java applet of PRAC for DOS [1] and PRAC for Windows [2]. PRAC is a user-friendly code designed for analyzing offset parabolic reflector antennas with high precision and accuracy. It has been extensively used over the past decade in teaching (currently, distributed with [3]), research, and industrial development. WebPRAC is intentionally designed for the Internet, running directly from within the Web browser on all usual operating systems (Windows, Linux, Macintosh, Solaris, etc.).

Uniformly excited, equally-spaced linear arrays do not provide side lobe levels below − 13.3 dB, and thus are less desirable in applications requiring lower side lobe levels. We present an efficient method for side lobe reduction in these arrays with little penalty on the directivity. The method involves the following steps: construction of a periodic function containing only the side lobes of the uniformly excited array, calculation of the Fourier series of this periodic function, and subtracting the series from the array factor of the original uniformly excited array after it is truncated. It is shown that such newly formed arrays can provide side lobe levels about 10 dB below those of the corresponding uniformly excited arrays, at the cost of nearly 0.5 dB drop in directivity.

A class of nonuniformly excited, equally-spaced linear arrays that can meet design requirements for half-power beamwidth and side lobe level without any limitation is introduced. These arrays are constructed using the patterns of uniformly excited arrays as building blocks. A design procedure is presented which can be used to determine the required number of elements and the excitation currents in order to achieve some specified radiation properties. Numerical results for broadside and endfire arrays are given.

Results of an experimental investigation of adaptive beamforming in the presence of interferers are presented. Measurements at 2.05 GHz were performed using six different four-element array configurations. Data were collected in urban and suburban environments with line-of-sight (LOS) and obstructed multipath channels for mobile (vehicular) and pedestrian speeds. Interference rejection performance is determined based on the increase in mean signal-to-interference-plus-noise ratio (SINR) using adaptive beamforming at 10% and 1% outage levels. Experimental results are presented for vehicle-mounted arrays to illustrate the dependence of interference rejection on: the separation of interferer in azimuth, orientation with respect to the array axis, vehicular speed, and the array element spacing. Interference cancellation of 24 to 28 dB was measured in urban and suburban LOS channels. Vehicle mounted arrays driven at a speed of 32-40 km/hr offered 15 to 28 dB interference rejection in the urban obstructed environment. The multitarget least-squares constant modulus beamforming algorithm (MT-LSCMA) used to process the measured data provided a progressive increase in interference rejection of 16, 26, and 35.2 dB, for update intervals of 10, 5, and 2.5 ms, respectively, for the vehicle-mounted arrays in suburban LOS scenario.

This work presents a near-field to far-field (NF-FF) transformation for antenna and scatterer radiation evaluation. The transformation allows practical computation by making use of a sampling surface in the near-field that is spheroidal in shape: namely a prolate or oblate spheroid. The resulting vector wave equation does not support orthogonal vector solutions in spheroidal coordinates and instead rectangular field components are solved for using the scalar wave equation in spheroidal coordinates. The new transformation only requires knowledge of the completely-specified near-field electric field along the spheroidal transformation surface and does not need any information associated with the corresponding magnetic field. The benefit of using a spheroidal near-field geometry is its ability to closely conform to both linear and planar radiating structures while still permitting evaluation of the full far-field radiation pattern. Our approach makes use of an eigenfunction expansion of spheroidal wave-harmonics to develop two distinct, yet closely related, NF-FF transformation algorithms for each type of spheroidal surface. The spheroidal NF-FF transformation is validated and performance assessed using a well-characterized radiation structure. By applying the prolate and oblate algorithms to a radiating structure with known analytical near- and far-field electric fields, viz., a filament dipole with sinusoidal current distribution, we are able to setup and conduct multiple numerical tests that serve as a proof-of-concept for the spheroidal NF-FF transformation.

This paper reports on an investigation of spherical, disc, and half-disc antennas in the frequency and time domains with the objective of developing small planar versions of the antennas. These antennas have an omni-directional impulse response in azimuth and a pulse duration of 0.5 - 0.65 nanoseconds. In addition, the measured data show a reasonable peak received signal in a pulse communication link using two identical antennas.

A new antenna, the planar inverted cone antenna (PICA), provides ultrawideband (UWB) performance with a radiation pattern similar to monopole disk antennas , but is smaller in size. Extensive simulations and experiments demonstrate that the PICA antenna provides more than a 10:1 impedance bandwidth (for VSWR

An analytical expression for the probability density function of the signal-to-noise ratio (SNR) at the output of a two-branch maximal ratio and selection diversity system is given. The two branches are assumed to be Rayleigh fading, correlated, as well as of unequal average SNRs. Measurements of the cumulative distribution functions after selection and maximal ratio combining were made in Rayleigh fading channels and compared with the analytical results. Also presented are the exact analytical average probabilities of symbol error for coherent binary phase-shift keying and coherent quaternary phase-shift keying before and after two-branch maximal ratio combining for a slow and flat fading correlated Rayleigh channel.

Commercial satellite communications began in 1965 with the launch of Intelsat I (Early Bird), which was a geostationary satellite operating at 4 and 6 GHz. C-band satellite communications (satcom) continues today. As higher frequency bands were explored to expand capacity, problems were encountered with weather effects on the earth-space links, mainly rain attenuation. Many years of research was required to understand the influence of weather on signals above 10 GHz and to develop techniques to mitigate the effects. X-band, Ku-band, and Ka-band satcom links are in wide use today.

This paper examines the antenna diversity configurations that improve the performance in handheld radios. Experiments using spatial, polarization, and pattern diversity were conducted for both line-of-sight (LOS) and obstructed outdoor and indoor multipath channels that experienced Ricean fading. Antenna separation, polarization, and pattern were varied independently to the extent possible. Envelope correlation, power imbalance, and diversity gain were calculated from the measurements. Diversity performance is measured by diversity gain, which is the difference in signal-to-noise ratio (SNR) between the output of a diversity combiner and the signal on a single branch, measured at a given probability level. Diversity gain increases with decreasing envelope correlation between the antenna diversity branches. However, diversity gain decreases as the power imbalance between diversity branches increases because a branch that has a weak signal has only a small contribution to the combined signal. Diversity gain values of 7-9 dB at the 99% reliability level were achieved in non-line-of-sight (NLOS) channels for all diversity configurations even with very small antenna spacings. The use of polarization diversity reduced polarization mismatches, improving SNR by up to 12 dB even in LOS channels.

The folded dipole is known to have a fourfold increase in input impedance over that of a dipole. However, the half-wavelength folded dipole also maintains a balanced radiation pattern when fed with an unbalanced transmission line. A numerical and experimental investigation of the folded dipole performance is reported in this paper. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 155–160, 2001.

Summary 1 A series of field and laboratory experiments was performed to test the possible influence of food limitation on UVR tolerance in the calanoid copepod Diaptomusminutus. 2 Food-limited animals incubated at 0.5 m in a clear-water lake for over three days showed no evidence for increased mortality compared to food-replete animals when exposed to UVR. 3 Animals exposed to artificial UVR in the laboratory showed high mortality. There was no evidence that feeding improved UVR tolerance. 4 The results of these experiments show that UVR tolerance is not affected by a short-term lack of energy or a lack of essential nutrients. However, effects of non-nutritive dietary components such as carotenoids and mycosporine-like amino acids cannot be excluded.

We review diversity and smart antenna research applied to both base-stations and terminals. To illustrate the performance gains possible, the paper describes research being conducted by the Smart Antenna Group at Virginia Tech, in both smart base-stations and smart handheld terminals.

A series of experiments was conducted to test the hypothesis that populations of Diaptomus minutus routinely experiencing high levels of ultraviolet radiation (UVR) are more tolerant of UVR than are those that routinely experience low levels of UVR. The relative degree of UVR tolerance was determined by monitoring mortality induced by either lamp or solar UVR. Diaptomus minutus from the low-dissolved organic carbon (DOC), high-UVR Lake Giles were consistently more tolerant of lamp and solar UVR than were those from the moderate-DOC, low-UVR Lake Lacawac. This differ- ence in UVR tolerance was apparent throughout the year in freshly collected animals, but it did not persist in cultured animals. The lamp UVR tolerances of cultured D.minutus were similar, except for those initiated from September collections. The September culture of Lake Giles animals was signifi- cantly more tolerant than the Lake Giles cultures initiated in December, May and June. The September culture of Lake Lacawac animals was significantly more tolerant than the June culture. The lamp UVR tolerance of freshly collected Lake Giles animals was greatest from late June through October, but the Lake Lacawac population was least tolerant in July and August. No differences in lamp UVR toler- ances were detected between animals collected from the surface and those collected from deeper water of either lake. It is concluded that the Lake Giles population was more tolerant than the Lake Lacawac population and that the period of greatest tolerance occurred several months after the time period with the highest ambient levels of solar UVR. Collectively, the experiments with both field and laboratory- cultured animals suggest that acclimation time plays a large role in UVR tolerance.

Gain is the most important performance parameter of an antenna. However, in many practical situations it is not possible to measure or calculate the gain of an antenna. Also, the interest in wireless applications has increased the need of system engineers to accurately estimate antenna gain. Many simple formulas are available for estimating gain. But, each formula has a range of applicability, and inappropriate use of these formulas will result in inaccurate gain values. This paper explains the process of gain evaluation, and gives several simple gain-estimation formulas, together with recommendations for their use.

This paper presents an evaluation of the electrical performance of the Green Bank Telescope (GBT) reflector antenna, operating as single- and dual-offset configurations, as well as a general overview of the GBT system. The GBT dual-offset Gregorian configuration is designed for low cross polarization (XPOL) using the dual-offset reflector antenna (DORA) synthesis package code developed by the authors. The procedure implemented in DORA to upgrade an existing main reflector to a low cross-polarized dual-offset Gregorian reflector antenna is also described in this paper. All computed patterns were obtained with the parabolic reflector analysis code (PRAC) program, also developed by the authors, and with the commercial code GRASP7. The GBT radiation patterns and performance values, which include original data not available anywhere else as far as the authors know, indicate that low XPOL performance can be achieved with a dual-offset configuration, provided that a low XPOL feed is used. The GBT configuration is employed as a case example for the aforementioned procedure. However, an effort is made to present the main conclusions as generically as possible.

Cross polarization (XPOL) and beam squint phenomena of reflector antennas are examined in detail. Emphasis is on the explanation of the absence of XPOL and the presence of beam squint in offset parabolic reflectors illuminated by a circularly polarized feed. Linearly polarized feeds are also considered for both the offset and axisymmetric configurations. Although many of these results are known, they are presented in a single coherent treatment. In addition, the results for polarization and beam squint characteristics of prime-focus offset parabolic reflector antennas are extended to dual offset configurations based on computed data using the physical optics code, GRASP7 (TICRA, 1988).

Many species of zooplankton are traditionally considered to be herbivores despite their ability to capture nonphotosynthetic microorganisms. Several recent studies indicate that protozoa are ingested by crustacean zooplankton, but an important aspect of these trophic interactions that has generally been overlooked is the contribution of heterotrophic food organisms to growth and(or) reproduction. We conducted a series of experiments to examine the ability of two crustacean zooplankters to supplement their diets with protozoa and to utilize these foods for reproduction. The cladoceran, Daphnia pulicaria, and the copepod, Diaptomus oregonensis, both ingested bacteria, ciliates, and heterotrophic nanoflagellates in the presence of algal food. Total young produced by D. pulicaria increased in treatments with added ciliates, heterotrophic nanoflagellates, bacteria, or algae relative to the baseline level of algal food. D. oregonensis females produced abundant young only in the treatments with ciliates or extra algae. The heterotrophic flagellates were ingested at high rates by both D. pulicaria and D. oregonensis, but did not contribute significantly to reproduction in the copepod. This suggests that some foods may be utilized (vs. just ingested) differently by these two common crustaceans. Reproduction was not significantly correlated with the total amounts of carbon, nitrogen, or phosphorus ingested by D. pulicaria or D. oregonensis, suggesting that nutrient content does not sufficiently

We report measurements of the resistivity and Hall effect on single- and multiple-domain thin films of PrBa{sub 2}Cu{sub 3}O{sub 7} from 0.05 to 500 K. The two types of samples show nearly identical transport properties above 300 K, including a resistivity minimum near 480 K. Below 50 K dramatic differences in the transport are evident as the resistivity is divergent in multiple-domain samples but nearly constant in single-domain samples. The results support an electronic structure where a dispersive lower-energy localized band competes for carriers with a higher-energy metallic band on the CuO{sub 2} planes. {copyright} {ital 1996 The American Physical Society.}

The water columns of lakes and oceans provide a diverse habitat gradient in which light, temperature, food, and predation risk all change with depth. Many planktonic organisms exhibit diel vertical migrations (DVM) in response to daily oscillations in many of these variables. DVM theory often assumes that surface waters are more food-rich than deeper, subsurface layers and proceeds to try to explain why zooplankton migrate out of these beneficial surface layers during the day. Here, we test the assumption that food is best in surface waters by feeding two common crustacean zooplankton with natural epilimnetic and metalimnetic food assemblages from a eutrophic lake and examining their egg production rates. Both Diaptomus and Daphnia showed greater reproductive rates in the metalimnetic water and significant food limitation in the epilimnetic water. Mass-specific ingestion rates were approximately three times higher in the metalimnion than in the epilimnion. In spite of the poorer food in the surface waters, these two crustaceans migrated into the epilimnion at night. These observations are contrary to the assumption that food is best in the surface water, and a review of the literature suggests that food frequently is not best in surface waters. The upward migrations at night are best explained by the warmer temperatures and reduced predation risk in the surface waters at night.

SUMMARY 1. The capacities of the gelatinous colonial chlorophytes Pandorina morum and Sphaerocystis schroeteri to sustain survival and reproduction in the calanoid copepod Diaptomus oregonensis and the cladoceran Daphnia pulicaria were evaluated quantitatively. Control groups of animals were fed equivalent biovolumes of Cryptomonas reflexa, which is known to favour high levels of survival and reproduction. 2. On a biovolume basis, all three algae sustained equal survival of Daphnia, but Cryptomonas and Pandorina allowed longer survival of Diaptomus than did Sphaerocystis. 3. Both animals produced significantly more offspring clutch−1 and more total offspring on Cryptomonas than on either chlorophyte. Both animals produced more total offspring on Pandorina than on Sphaerocystis. 4. The interclutch duration for Daphnia was significantly longer on Pandorina than the other algae, and the interclutch duration for Diaptomus was longer on Pandorina than on Cryptomonas. 5. Daphnia utilized the gelatinous chlorophytes more effectively than did Diaptomus.

The order-disorder transition of the p(2 × 2) phase of oxygen chemisorbed on Ni(111) has been studied using low-energy electron diffraction (LEED). The transition was found to be continuous, and the measured critical exponents are consistent with those predicted for the 4-state Potts model. These results agree with the theoretical predictions for this overlayer based on symmetry considerations, but disagree with two other experimental studies. These discrepancies are discussed.