Frequency invariant beamforming for two-dimensional and three-dimensional arrays

A novel method for the design of two-dimensional (2-D) and three-dimensional (3-D)arrays with frequency invariant beam patterns is proposed. By suitable substitu- tions, the beam pattern of a 2-D or 3-D arrays can be regarded as the 3-D or 4-D Fourier transform of its spatial and temporal parameters. Since frequency invariance can be easily imposed in the Fourier domain, a simple design method is derived. Design examples for the 2-D case are provided

Beef Cattle Production and Management Practices and Implications for Educators

Beef producers need to continually incorporate new information and adopt new technology to effectively manage production costs. Oklahoma State University began a Master Cattleman program with this need in mind. Understanding technology adoption by producers requires identifying current management practices. Data from a survey developed as part of the Master Cattleman program document current practices. Management practices were examined for two groups; producers with smaller herds who are less dependent on the beef enterprise for family income, and producers with larger herds who are more dependent on beef. Results clearly show that size and dependence on the beef enterprise matters when considering a broad spectrum of beef management practices.Livestock Production/Industries,

Near-Independent Capacities and Highly Constrained Output Orders in the Simultaneous Free Recall of Auditory-Verbal and Visuo-Spatial Stimuli

Three experiments examined the immediate free recall (IFR) of auditory-verbal and visuospatial materials from single-modality and dual-modality lists. In Experiment 1, we presented participants with between 1 and 16 spoken words, with between 1 and 16 visuospatial dot locations, or with between 1 and 16 words and dots with synchronized onsets. We found that for dual-modality lists (a) overall performance, initial recalls, and serial position curves were largely determined by the within-modality list lengths, (b) there was only a small degree of dual-task trade-off (that was limited to the visuospatial items), and © there were strongly constrained output orders: participants tended to alternate between words and dots from equivalent or neighboring serial positions. In Experiments 2 and 3, we compared lists of 6 single-modality items with dual-modality lists of 6 words and 6 dots with synchronous or alternating onsets (Experiment 2), or random but asynchronous onsets (Experiment 3). In all 3 dual-modality conditions, we again found only a small trade-off in visuospatial (but not verbal) IFR performance. There were similarly highly constrained output orders with the synchronous and alternating onsets, and these patterns were present but attenuated with the randomized onsets. We propose that both auditory-verbal and visuospatial list items are associated with a common temporal episodic context that is used to guide cross-modal retrieval, and we speculate that the limited, asymmetric interference could arise because the less variable representations of the dots share only a relatively small subset of features with the more variable representations of the words

GRAZING SELECTIVITY AND IN VIVO DIGESTIBILITY OF SWITCHGRASS STRAINS SELECTED FOR DIFFERING DIGESTIBILITY

Animal selectivity and digestibility differences among switchgrass strains selected for different in vitro dry matter digestibilities (IVDMD) were measured in a grazing trial with esophageally fistulated steers and a sheep digestion trial. Extrusa selected by esophageally fistulated steers grazing high-IVDMD (Trailblazer), Pathfinder and Iow-IVDMD strains of switchgrass were compared, as were top and whole plant hand-clipped samples from each strain. Trailblazer extrusa had higher (P \u3c .1) in vitro organic matter disappearance (IVOMD) and lower (P \u3c .1) NDF and ADF than Pathfinder extrusa. Extrusa from all three strains appeared to be of higher quality than top or whole plant hand-clipped samples. In vitro organic matter disappearance tended to be highest for Trailblazer top hand-clipped samples. Composition of hand-clipped samples among strains was not significantly different. Mature crossbred wethers were used to compare Trailblazer and P ~ switchgrass hay in a digestion trial. No differences (P \u3e .1) were detected between slrains for DMI or apparent digestibility of DM, NDF, ADF and CP. Extrusa from Trailblazer switchgrass that had been selected for whole plant IVDMD had higher IVOMD; however, there was no indication that steers selected a differentially higher IVOMD for one strain than another

Mathematical modelling of ethanol metabolism in normal subjects and chronic alcohol misusers

The time course of ethanol disappearance from the blood has been examined in normal males and females and in alcohol misusers. Blood alcohol estimations were made over a period of 3 hr, following an oral dose of ethanol (0.8 g/kg body weight) administered in the form of whisky. Attempts were made to fit the data to zero order, first order and mixed zero + first order kinetics. In the majority (75%) of normal females the blood ethanol concentration was still increasing at 30 min. This was only seen in 50% of normal males and in 50% of non-dependent alcohol misusers, but not in dependent alcohol misusers. In all of the normal females the disappearance of ethanol could be adequately described by zero order kinetics. However, in the normal male group only 20% could be described by zero order kinetics, 10% fitted first order kinetics and the remainder required a mixed model of zero + first order. The rate constant for the zero order component of the control male group was identical to zero order rate constant obtained for the female control group. In the female alcohol misuser group, 40% of the curves could not be described by zero order kinetics and fitted best to a mixed model. The zero order component of the entire group was significantly increased (by 35%) compared to that obtained for the female control group. In the male dependent and non-dependent alcohol misuser groups, all blood alcohol concentration curves fitted best to mixed zero and first order kinetics. However, no significant differences were noted in the values of the kinetic parameters when compared with the male control group. It is suggested that the zero order component of the blood alcohol concentration curves is due to the action of liver alcohol dehydrogenase and the first order component represents redistribution to the tissues. The presence or absence of a first order component is attributed to differences in absorption rates from the gut

Three-dimensional Calculations of High and Low-mass Planets Embedded in Protoplanetary Discs

We analyse the non-linear, three-dimensional response of a gaseous, viscous protoplanetary disc to the presence of a planet of mass ranging from one Earth mass (1 M$_e$) to one Jupiter mass (1 M$_J$) by using the ZEUS hydrodynamics code. We determine the gas flow pattern, and the accretion and migration rates of the planet. The planet is assumed to be in a fixed circular orbit about the central star. It is also assumed to be able to accrete gas without expansion on the scale of its Roche radius. Only planets with masses M \gsim 0.1 M$_J$ produce significant perturbations in the disc's surface density. The flow within the Roche lobe of the planet is fully three-dimensional. Gas streams generally enter the Roche lobe close to the disc midplane, but produce much weaker shocks than the streams in two-dimensional models. The streams supply material to a circumplanetary disc that rotates in the same sense as the planet's orbit. Much of the mass supply to the circumplanetary disc comes from non-coplanar flow. The accretion rate peaks with a planet mass of approximately 0.1 M$_J$ and is highly efficient, occurring at the local viscous rate. The migration timescales for planets of mass less than 0.1 M$_J$, based on torques from disc material outside the planets' Roche lobes, are in excellent agreement with the linear theory of Type I (non-gap) migration for three-dimensional discs. The transition from Type I to Type II (gap) migration is smooth, with changes in migration times of about a factor of 2. Starting with a core which can undergo runaway growth, a planet can gain up to a few M$_J$ with little migration. Planets with final masses of order 10 M$_J$ would undergo large migration, which makes formation and survival difficult.Comment: Accepted by MNRAS, 18 pages, 13 figures (6 degraded resolution). Paper with high-resolution figures available at http://www.astro.ex.ac.uk/people/mbate

Expression characteristics of the transfer-related kilB gene product of Streptomyces plasmid pIJ101: Implications for the plasmid spread function

Intermycelial transfer of Streptomyces plasmid pIJ101 occurs prior to cellular differentiation and is mediated by plasmid functions that are also required for production of zones of growth-inhibited recipient cells (i.e., pocks) that develop around individual donors during mating on agar medium. Several other pIJ101 functions, including that of the kilB gene, whose unregulated expression on pIJ101 is lethal, are required for normal pock size and so have been postulated to mediate intramycelial spread of the plasmid throughout recipient cells. Using antibodies raised against a KilB fusion protein expressed in Escherichia coli, native KilB protein was detected throughout development of pIJ101-containing Streptomyces lividans cells, with the concentration of KilB increasing dramatically and reaching a maximum during the final stages (i.e., sporulation and secondary metabolism) of cellular differentiation. Insertion of the kilB gene of pIJ101 into the S. lividans chromosome in cells lacking the pIJ101 KorB protein, which normally represses kilB gene transcription, resulted in elevated but still temporally increasing amounts of KilB. The increased expression or accumulation of the KilB spread protein throughout cellular differentiation of S. lividans, which leads to maximum KilB concentrations during developmental stages that occur far later than when intermycelial transfer of pIJ101 is mediated, supports the existence of a subsequent intramycelial component to the pIJ101 spread function. The results also suggest that intramycelial spread of pIJ101 molecules within the recipient extends beyond intercompartmental movements within the mycelia and includes undetermined steps within the spore-yielding aerial hyphae as well

How Observations of Circumstellar Disk Asymmetries Can Reveal Hidden Planets: Pericenter Glow and its Application to the HR 4796 Disk

Recent images of the disks of dust around the young stars HR 4796A and Fomalhaut show, in each case, a double-lobed feature that may be asymmetric (one lobe may be brighter than the other). A symmetric double-lobed structure is that expected from a disk of dust with a central hole that is observed nearly edge-on (i.e., close to the plane of the disk). This paper shows how the gravitational influence of a second body in the system with an eccentric orbit would cause a brightness asymmetry in such a disk by imposing a "forced eccentricity" on the orbits of the constituent dust particles, thus shifting the center of symmetry of the disk away from the star and causing the dust near the forced pericenter of the perturbed disk to glow. Dynamic modeling of the HR 4796 disk shows that its 5% brightness asymmetry could be the result of a forced eccentricity as small as 0.02 imposed on the disk by either the binary companion HR 4796B, or by an unseen planet close to the inner edge of the disk. Since it is likely that a forced eccentricity of 0.01 or higher would be imposed on a disk in a system in which there are planets, but no binary companion, the corresponding asymmetry in the disk's structure could serve as a sensitive indicator of these planets that might otherwise remain undetected.Comment: 61 pages, 10 figures, accepted for publication in the Astrophysical Journal (scheduled for January 10, 2000