Radar cross section of symmetric parabolic reflectors withcavity-backed dipole feeds

The monostatic radar cross section (RCS) of a symmetric parabolic reflector antenna with a cavity-backed dipole feed is computed using the method of moments. At frequencies below the operating frequency band of the antenna the dipole contribution is not significant; in the operating band the dipole terminal load condition only affects the RCS near boresight. The f/D ratio of the antenna is shown to have a significant effect on the RCS. By adjusting the focal length, the cavity and paraboloid scattering contributions can be made to partially cancel, yielding a reduction in RCS near boresight     

Derivation and application of the equivalent paraboloid forclassical offset Cassegrain and Gregorian antennas

The equivalent paraboloid is derived for classical offset Cassegrain and Gregorian antennas. The important practical case of systems with circular exit apertures is discussed in detail, and a condition for a symmetric equivalent paraboloid is derived. For such systems, diffraction effects are investigated using tapered and scanned feeds to illuminate the equivalent paraboloid and the two-reflector system     

A design procedure for classical offset dual reflector antennaswith circular apertures

A geometrical optics procedure for designing electrically optimized classical offset dual reflector antennas with circular apertures is presented. Equations are derived that allow the size and spacing of the main and subreflectors of the antenna system, along with the feed horn subintended angle, to be used as input variables of the design procedure. The procedure, together with these equations, yields an optimized design, starting from general system requirements. The procedure is demonstrated by designing both an offset Cassegrain and an offset Gregorian antenna, and is validated by analyzing their radiation patterns using physical optics surface current integration on both the main and subreflectors     

The STR system hTPO: population and segregation data

A population study was carried out on a random sample of 164 individuals from North Portugal using the short tandem repeat (STR) system hTPO (locus: 2p23-2pter). After electrophoresis, 7 alleles were identified of which 6 had been previously described and a new one, estimated to be 134 bp long. The observed genotype distribution is in Hardy-Weinberg equilibrium. In order to assess the forensic applicability of the system, namely for paternity investigations, 109 mother-child pairs were analysed. No exclusions were found and the observed distribution did not deviate from the expected. Since hTPO has a relatively high information content (PIC = 0.60; H = 0.65) this system can be very useful in paternity investigations.     

GO Shaping of Omnidirectional Dual-Reflector Antennas for a Prescribed Equi-Phase Aperture Field Distribution

A formulation is presented for shaping dual-reflector antennas designed to offer an omnidirectional coverage. The shaping procedure is based on geometrical optics (GO) principles and assumes a uniform phase distribution for the aperture field. Two distinct dual-reflector arrangements, based on the axis-displaced Cassegrain (ADC) and ellipse (ADE) configurations, are investigated. The GO shaping results are validated using the accurate analysis provided by the method-of-moments technique     

Biodegradable starch particles for controlled release applications: Swelling and leaching mechanisms

Starch-extruded particles have only found infrequent use as delivery systems for active ingredients. We have previously shown that these particles are attractive for releasing hydrophobic compounds in water media. Here, we cover a range of amylose–amylopectin ratios and evaluate the presence of the thyme essential oil (TEO) as active compound to understand the dominant release mechanism in relation to the physicochemical properties of the starch matrices. Starch blends with high amylopectin content (1.8 and 15% amylose) could not be shaped into regular particles. For amylose contents higher than 28%, the equilibrium degree of swelling in water decreased with increasing amylose contents, from nearly 300% for an amylose content of 28–90% at an amylose content of 70%. For both lowest amylose contents, 1.8 and 15%, leaching of solids and disintegration of the particles resulted in a low apparent degree of swelling. The presence of TEO reduces the degree of swelling of the gelatinized starch matrix. This is explained by the formation of thymol–amylose complexes, which is confirmed by Fourier transform infrared spectroscopy analysis and X-ray diffraction.     

A Branch-and-Bound Algorithm for Optimal Pump Scheduling in Water Distribution Networks

Nowadays water distribution operation systems are accomplished with the aid of qualified professionals who use their experience in order to achieve a satisfactory performance of the several hydromechanical devices, which are part of the system, such as boosters and valves. In general, these operational rules are empirical and the main goal is to assure the availability of water for the population, with no special concerns about saving energy used in pumping systems. Besides, these empirical rules often disregard hours of lower energy rates. There are several research works concerning the developments of operational rules optimization applied to specific water distribution systems. However, in this work, a general optimization routine integrated with EPANET is presented, which allows the determination of strategic optimal rules of operation for any type of water distribution system. Moreover, a Branch-and-Bound algorithm is also used, where finding the global optimal solution is guaranteed, in admissible computational times. The water distribution system used in this work corresponds to a hypothetical network proposed in the specialized literature.     

Analytical and CFD modeling of the fluid flow in an eccentric-tube centrifugal oil pump for hermetic compressors

A model is presented for calculating the volume flow rate in an eccentric-tube centrifugal oil pump for reciprocating compressors. The oil pump assembly consists of a pick-up tube with an inclined inlet that is mounted off-center with the crankshaft symmetry axis. The pick-up tube is connected to the shaft channel, a helical groove machined on the crankshaft that facilitates the supply of lubricant to the bearings. The analytical models for the pick-up tube and shaft channel were developed independently and were coupled via a numerical procedure to determine the steady-state volume flow rate in the assembly. The steady-state results were verified against a CFD model, which was also used to evaluate the fluid flow in the oil pump assembly during a start-up transient. A parametric analysis was conducted to quantify the influence of some oil pump geometric parameters, such as the pick-up tube diameter and the shaft eccentricity.     

The design of classical offset Dragonian reflector antennas with circular apertures

The vector aperture field of classical offset Dragonian dual-reflector antennas is derived using geometrical-optics concepts. This field then yields the equivalent paraboloid of the geometry. From these results, the conditions for an axially symmetric equivalent paraboloid, when a circular aperture is assumed, are obtained. A complete step-by-step geometrical-optics-based design procedure for optimum classical offset Dragonian antennas with circular apertures is then presented (i.e., zero geometrical-optics cross-polarization and minimum spillover). This procedure is demonstrated by two design examples.