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AMinkowski fractal-shaped patch is proposed for the design of a reduced-size reflectarray element. The intrinsic miniaturization capability of the fractal geometry is fully exploited by leaving unchanged the patch length, while using the fractal scaling factor to obtain a good reflectarray phase agility. The achieved size reduction effect allows to choose array grids with smaller interelement spacing, thus offering the opportunity to have wide-angle scanning capabilities. As validation test, a fractal-shaped X-band reflectarray element, embedded into a0.3λ×0.3λ cell, is designed to give a high phase agility range, greater than 300°. Furthermore, the design and the experimental validation of a15×15 reflectarray prototype are presented to prove the fixed-beam large angle pointing ability. [ABSTRACT FROM AUTHOR]

An electronically tunable reflectarray element is proposed in this work to design beam-steering antennas useful for radar applications. A reduced size reflectarray unit cell is properly synthesized in order to extend the antenna beam scanning capabilities within a wider angular region. The radiating structure is accurately optimized to provide a full phase tuning range by adopting a single varactor load as phase shifter element. A 0.46λ-reflectarray cell is designed at the frequency of 11.5GHz, obtaining a phase agility of about 330°. The cell is successfully adopted for the design of a 21 X 21 reconfigurable reflectarray. The antenna is numerically tested for different configurations of the varactors capacitance values, and good beam-steering performances are demonstrated within a wide angular range. [ABSTRACT FROM AUTHOR]

The bandwidth features of reflectarray antennas are analyzed by examining in detail the phase errors due to the compensation mechanism for spatial phase delays. A bandwidth estimation rule is defined, taking into account the combined effects due to the overall antenna geometry and the frequency response of the single reflectarray element. An aperture-coupled reflectarray configuration with reduced interelement spacing is considered as broadband solution for the implementation of small reflectarrays. A 20GHz aperture-coupled element is synthesized for the design of a 12? diameter reflectarray, showing a simulated 1 dB gain bandwidth of 23%. [ABSTRACT FROM AUTHOR]

A single varactor-tuned element is investigated as effective solution for the realization of reconfigurable reflectarray antennas. The proposed configuration is successfully implemented for the design of an X-band reflectarray prototype of 3 × 15 radiators. A dedicated electronic control board is designed as an integral part of the antenna. Good performances in terms of beam-scanning capabilities are obtained from measurements. [ABSTRACT FROM AUTHOR]

Benzocyclobutene (BCB) polymer is proposed in this study as an innovative and versatile substrate material for millimetre-wave reflectarrays. The excellent material features in terms of low loss, low dielectric constant and strong dielectric stability against frequency and temperature are highlighted. The design, realisation and test of a 60 GHz reflectarray with 21×21 variable-sized patches giving a focused boresight beam pattern are fully described. The BCB thickness is chosen on the basis of a parametric analysis performed on the unit cell to optimise the performances in terms of dielectric losses and radiation bandwidth. The in-house fabrication process able to assemble multi-layered BCB substrates is described in detail. Experimental results on the radiation pattern and the boresight gain are used to validate both the synthesis and the manufacturing process. [ABSTRACT FROM AUTHOR]

An extensive analysis is performed on the aperture-coupled reflectarray configuration to highlight and quantify the bandwidth enhancement due to the use of reduced inter-element spacings. Bandwidth extension is directly evaluated on the phase curves relative to the reflection coefficient against frequency for different lengths of the tuning line. The operating frequency range computed with the proposed approach is numerically validated on the gain patterns of synthesized reflectarrays and a strong broadband behavior is demonstrated for reflectarrays of moderate aperture dimensions and reduced unit cell size. [ABSTRACT FROM AUTHOR]

The design of microstrip reflect arrays requires the use of a design curve to correlate the phase of the reradiated field and the size of the elements. In this Letter this parameter has been evaluated by analyzing the field scattered from an isolated reflect-array unit cell. As a test case a microstrip reflect array has been designed with the use of these data. Even if this approach neglects the mutual coupling effects, the measured reflect-array radiation pattern shows that the main beam steering agrees with the design requirements. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 411–414, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10479 [ABSTRACT FROM AUTHOR]

The effects of radiation emission on the dynamic development of a neon seeded dense plasma focus are observed. The radiative cooling of the discharge is found to be responsible for the >10 times the increase in density of the pinch. [ABSTRACT FROM AUTHOR]

The dispersive analysis of the x-ray continuum is employed to determine the electron temperature of a dense pinched plasma. A curved crystal spectrometer was used to obtain the desired dispersion, and two or more p-i-n (doubly diffused silicon) diodes were used to monitor the time-resolved emission. The dispersive technique is inherently more accurate than filtering techniques and simpler to implement than laser scattering techniques. In an experimental verification of the technique, the time-resolved temperature of a plasma focus pinch was measured under various conditions, and was found to be consistent with density observations and MHD calculations. It was possible to observe the cooling effect of radiation emission from seeded plasma focus discharges. The elliptical crystal spectrometer is shown to be well suited to the analysis of the x-ray emission from a pinched plasma source. [ABSTRACT FROM AUTHOR]

Several widely endorsed solutions to the long‐term disposition of weapons plutonium and other waste fissile nuclear material involve placement of batches of the material underground in subcritical concentrations. It is pointed out here that such concentrated subcritical fissile material underground might reach criticality that is autocatalytic or self‐enhancing. This criticality could come about upon dispersion into the surrounding medium by either natural or unnatural processes, or by the fissile material being carried to other sites where it can collect into different autocatalytic critical configurations. Underground, where the material is confined and there is an abundance of moderating medium around it, the results of such supercritical excursions could range from modest energy releases to the several hundred gigajoules range from a single event. Without water, 50–100 kg of fissile material is required to reach autocatalytic criticality. Amounts as small as 2 kg can reach autocatalytic criticality with water present. In varying degrees, all categories of waste containing fissile actinide appear to be susceptible to these criticality excursions, including vitrified weapons plutonium, research reactor and DOE spent fuel, commercial, and MOX spent fuel. [ABSTRACT FROM PUBLISHER]

Portal thrombosis is a rare complication of splenectomy. We performed 12 laparoscopic splenectomies and observed this complication only in one patient with idiopathic thrombocytopenia (ITP). The right branch of the portal vein presented a partial thrombosis, while the left branch was completely obstructed by thrombi. Abdominal ultrasonography and an ultrasound doppler exam allowed us to diagnose this event and a retrograde angiography performed afterward confirmed our diagnosis. A 48-h intravenous heparin treatment was promptly begun, followed by anticoagulant drugs (dicumarol). The patient was dismissed 5 days afterward, presenting a steady-state ultrasound doppler pattern and a complete normalization of liver parameters. An ultrasound doppler exam performed 1 month after anticoagulant therapy showed a complete resolution of portal thrombosis. We believe that early diagnosis of this rare complication, prompt beginning of anticoagulant therapy, and care in surgical procedures may reduce patient life-threatening risks and assure complete remission. [ABSTRACT FROM AUTHOR]

An aperture-coupled reflectarray element with a reduced inter-element spacing is proposed. Bandwidth improvements are demonstrated by a smooth and similar behaviour of the phase design curves when properly decreasing the unit cell size. Experimental validations are reported for the measured radiation patterns of two reflectarray propotypes with different element spacings. [ABSTRACT FROM AUTHOR]

A magnetically stabilized plasma focus with controlled modulations has been demonstrated for the first time. A 3-mm-diam plasma focus with two wiggler periods of 1 cm each was kept stable for about 30 ns. Similar configurations with shorter periods could be used as intense wigglers for short-wavelength free-electron lasers. [ABSTRACT FROM AUTHOR]

A reconfigurable aperture-coupled reflectarray element offering a continuous tuning of the reflection phase is presented. A single varactor load is demonstrated to be sufficient for a full tuning range. Experimental validations are reported for the measured reflection phase of an X-band reflectarray element. [ABSTRACT FROM AUTHOR]

Proposes the use of printed reflectarrays as planar scatterers for SAR interferometry. Application of a phase-only synthesis to obtain a scattered field in a prescribed direction; Simulation of a reflectarray working at EERS1/2 frequency to validate the method; Performance of measurements on a 10GHz size-reduced prototype.

The determination of the phase of the field scattered from microstrip patches is a key factor in the design of reflect-array antennas. Although the problem has been treated in a number of theoretical articles, an experimental characterization of a such an important parameter has never been considered. In this Letter an experimental study of the phase of the field reradiated from small arrays of patches is presented. As a result a diagram of the phase of the scattered field versus the size of the patches is obtained. Results have been compared with the ones obtained with a commercial MoM package. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 163–164, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10403 [ABSTRACT FROM AUTHOR]

To meet world power demands, the use of nuclear power must continue to grow as a safe, emission-free, reliable, and economical source of energy. However, at the rate waste is produced by the existing fleet of nuclear reactors in the US, new repository capacity equal to the statutory capacity of the yet-to-open Yucca Mountain would be needed about every 20 years. Therefore, the ability to expand, or even maintain the nuclear power capacity in the US will be limited, unless either additional disposal capacity is identified, or waste volume, proliferation risk, and toxicity dose are significantly reduced. A preferred option for the destruction (transmutation) of waste from reactors is based on the use of thermal modular helium reactor systems (MHRs). This paper gives a brief outline of the MHR-based transmutation concept and its attendant advantages. [ABSTRACT FROM AUTHOR]