Co-linear Array Research Articles

Orbits of a system of three point vortices and the associated chaotic mixing.

We study the general periodic motion of a set of three point vortices in the plane, as well as the potentially chaotic motion of one or more tracer particles. While the motion of three vortices is simple in that it can only be periodic, the actual orbits can be surprisingly complex and varied. This rich behavior arises from the existence of both co-linear and equilateral relative equilibria (steady motion in a rotating frame of reference). Here, we start from a general (unsteady) co-linear array with arbitrary vortex circulations. The subsequent motion may take the vortices close to a distinct co-linear relative equilibrium or to an equilateral one. Both equilibrium states are necessarily unstable, as we demonstrate by a linear stability analysis. We go on to study mixing by examining Poincaré sections and finite-time Lyapunov exponents. Both indicate widespread chaotic motion in general, implying that the motion of three vortices efficiently mixes the nearby surrounding fluid outside of small regions surrounding each vortex.

Geo-electrical anisotropy corrections derived from square array data to improve Earth resistivity models of the Shale Hills' critical zone

Geo-electric anisotropy in the shallow subsurface, often expressed as the “paradox of anisotropy”, is seldom accounted for in colinear array resistivity models of the critical zone. The paradox of anisotropy can be observed in areas of inclined bedding planes or fractures where longitudinal apparent resistivities are greater than transverse apparent resistivities, which is opposite of the true resistivities. In this study, we illustrate the paradox of anisotropy for fractured shale bedrock in Pennsylvania's Susquehanna Shale Hills Critical Zone Observatory (Shale Hills) using square and Wenner array data, and derive an anisotropy correction from the square array data, which is not influenced by the anisotropy. Square array measurements were made around a center point near the middle of a planar slope on the north-facing side of the Shale Hills watershed at four a-spacings (5, 10, 25, and 50 m), each rotated at 15° increments until a full rotation (0° to 165°) of measurements were collected. Coefficients of anisotropy, estimated from the square array data, were then applied to Wenner array data collected at the same location in the watershed to correct the anisotropic flow of current affecting the colinear (i.e., Wenner) array data. Correction of Wenner array data for profiles parallel and orthogonal to bedding strike yield favorable model results when compared to expected resistivity ranges with respect to bedding strike. We further demonstrate that application of the anisotropy corrections to several Wenner array profiles, followed by a pseudo 3D inversion of the profiles, yields a resistivity model of the subsurface providing new insights into groundwater flow through the Shale Hills' critical zone.

A Dual-Frequency Colinear Array for Acoustic Angiography in Prostate Cancer Evaluation.

Approximately 80% of men who reach 80 years of age will have some form of prostate cancer. The challenge remains to differentiate benign and malignant lesions. Based on recent research, acoustic angiography, a novel contrast-enhanced ultrasound imaging technique, can provide high-resolution visualization of tissue microvasculature and has demonstrated the ability to differentiate vascular characteristics between healthy and tumor tissue in preclinical studies. We hypothesize that transrectal acoustic angiography may enhance the assessment of prostate cancer. In this paper, we describe the development of a dual frequency, dual-layer colinear array transducer for transrectal acoustic angiography. The probe consists of 64 transmitting (TX) elements with a center frequency of 3 MHz and 128 receiving (RX) elements with a center frequency of 15 MHz. The dimensions of the array are 18 mm in azimuth and 9 mm in elevation. The pitch is [Formula: see text] for TX elements and 140 [Formula: see text] for RX elements. Pulse-echo tests of TX/RX elements and aperture acoustic field measurements were conducted, and both results were compared with the simulation results. Real-time contrast imaging was performed using a Verasonics system and a tissue-mimicking phantom. Nonlinear acoustic responses from microbubble contrast agents at a depth of 35 mm were clearly observed. In vivo imaging in a rodent model demonstrated the ability to detect individual vessels underneath the skin. These results indicate the potential use of the array described herein for acoustic angiography imaging of prostate tumor and identification of regions of neovascularization for the guidance of prostate biopsies.

Crack Detection of Propeller Shaft on board Marine Ship using Microphone Array

Vibration due to rotation of a shaft of a ship propeller may cause crack due to lack of proper maintenance. It is considered to be hazardous area to conduct a direct measurement on rotating shaft using accelerometer. In this paper, acoustic emission using linear microphone array is proposed to collect acoustical data emitted from the rotation of the shaft. In a semi-anechoic chamber, the proposed technique using single microphone may have detected a crack in propeller shaft by observing the peak of the main spectrum. In engine room on a ship with highly noisy background, we propose microphone co-linear array to increase microphone sensitivity. First, the normal shaft sound was recorded using single sensor, thereafter used as baseline. The cracks were intentionally introduced to the shaft with depth 0.25, 0.5, and 0.75 diameter of the shaft respectively. The sound mixture was separated using frequency domain independent component analysis (TFICA) and then, compared to the accelerometer. The results showed that the measurement accuracy was increased from one sensor to the array and comparable to the direct measurement. These results suggest that the proposed technique may be used as an easy-to-deploy vibration monitoring in a noisy and hazardous engine room.

Design, Fabrication, and Characterization of a Bifrequency Colinear Array

Design, Fabrication, and Characterization of a Bifrequency Colinear Array

Design, Fabrication, and Characterization of a Bifrequency Colinear Array.

Ultrasound imaging with high resolution and large penetration depth has been increasingly adopted in medical diagnosis, surgery guidance, and treatment assessment. Conventional ultrasound works at a particular frequency, with a [Formula: see text] fractional bandwidth of [Formula: see text], limiting the imaging resolution or depth of field. In this paper, a bifrequency colinear array with resonant frequencies of 8 and 20 MHz was investigated to meet the requirements of resolution and penetration depth for a broad range of ultrasound imaging applications. Specifically, a 32-element bifrequency colinear array was designed and fabricated, followed by element characterization and real-time sectorial scan (S-scan) phantom imaging using a Verasonics system. The bifrequency colinear array was tested in four different modes by switching between low and high frequencies on transmit and receive. The four modes included the following: 1) transmit low, receive low; 2) transmit low, receive high; 3) transmit high, receive low; and 4) transmit high, receive high. After testing, the axial and lateral resolutions of all modes were calculated and compared. The results of this study suggest that bifrequency colinear arrays are potential aids for wideband fundamental imaging and harmonic/subharmonic imaging.

Noninvasive thermometry assisted by a dual-function ultrasound transducer for mild hyperthermia

Mild hyperthermia is increasingly important for the activation of temperature-sensitive drug delivery vehicles. Noninvasive ultrasound thermometry based on a 2-D speckle tracking algorithm was examined in this study. Here, a commercial ultrasound scanner, a customized co-linear array transducer, and a controlling PC system were used to generate mild hyperthermia. Because the co-linear array transducer is capable of both therapy and imaging at widely separated frequencies, RF image frames were acquired during therapeutic insonation and then exported for off-line analysis. For in vivo studies in a mouse model, before temperature estimation, motion correction was applied between a reference RF frame and subsequent RF frames. Both in vitro and in vivo experiments were examined; in the in vitro and in vivo studies, the average temperature error had a standard deviation of 0.7°C and 0.8°C, respectively. The application of motion correction improved the accuracy of temperature estimation, where the error range was 1.9 to 4.5°C without correction compared with 1.1 to 1.0°C following correction. This study demonstrates the feasibility of combining therapy and monitoring using a commercial system. In the future, real-time temperature estimation will be incorporated into this system.

A sensitive TLRH targeted imaging technique for ultrasonic molecular imaging

The primary goals of ultrasound molecular imaging are the detection and imaging of ultrasound contrast agents (microbubbles), which are bound to specific vascular surface receptors. Imaging methods that can sensitively and selectively detect and distinguish bound microbubbles from freely circulating microbubbles (free microbubbles) and surrounding tissue are critically important for the practical application of ultrasound contrast molecular imaging. Microbubbles excited by low-frequency acoustic pulses emit wide-band echoes with a bandwidth extending beyond 20 MHz; we refer to this technique as transmission at a low frequency and reception at a high frequency (TLRH). Using this wideband, transient echo, we have developed and implemented a targeted imaging technique incorporating a multifrequency colinear array and the Siemens Antares imaging system. The multifrequency colinear array integrates a center 5.4-MHz array, used to receive echoes and produce radiation force, and 2 outer 1.5-MHz arrays used to transmit low-frequency incident pulses. The targeted imaging technique makes use of an acoustic radiation force subsequence to enhance accumulation and a TLRH imaging subsequence to detect bound microbubbles. The radiofrequency (RF) data obtained from the TLRH imaging subsequence are processed to separate echo signatures between tissue, free microbubbles, and bound microbubbles. By imaging biotin-coated microbubbles targeted to avidin-coated cellulose tubes, we demonstrate that the proposed method has a high contrast-to-tissue ratio (up to 34 dB) and a high sensitivity to bound microbubbles (with the ratio of echoes from bound microbubbles versus free microbubbles extending up to 23 dB). The effects of the imaging pulse acoustic pressure, the radiation force subsequence, and the use of various slow-time filters on the targeted imaging quality are studied. The TLRH targeted imaging method is demonstrated in this study to provide sensitive and selective detection of bound microbubbles for ultrasound molecularly targeted imaging.

Resistivity and IP arrays, optimised for data collection and inversion

The advent of 3D inversion packages for Resistivity and Induced Polarization has meant that geophysicists are no longer constrained by survey arrays designed to produce data to be plotted manually and interpreted by eye. 3D inversion processing means that there is no longer a need to place receiver and transmitter electrodes in a co-linear array. Electrode arrays can now be designed to optimise target definition and data collection efficiency.The double offset pole–dipole array offers a way to collect large amounts of data efficiently and has superior inversion sensitivity and depth of investigation to standard arrays.

Relation of tensile strength-porosity effects in ceramics to porosity dependence of Young's modulus and fracture energy, porosity character and grain size

Abstract The dependence of tensile strength σ on the porosity P of ceramics is considered, based on recent theories and observations of failure from pores and emanating microstructural cracks. Extensions of a model for such failure based on a colinear array of pore-crack combinations is used to evaluate such σ dependence and its relationship to the porosity dependence of Young's modulus E and fracture energy γ as well as the dependence of strength on the grain size G. It is shown that the porosity dependences of σ, E and γ should usually be similar, as is generally observed. It is also shown that the dependences of σ on both P and G are generally separable even if the sizes of the cracks surrounding the pores are related to G. The concept of pore linkage due to connection by cracks following preferred (mainly grain boundary) paths is introduced, and is suggested to be much more common than pore linkage due to cracking from overlapping stress fields of closely spaced pores.

Hybrid phase-shift/time-delay digital beamforming

Digital phase-shift beamforming of narrow-band signals from uniform colinear hydrophone arrays may be accomplished by computationally efficient algorithms which exploit the functional regularity of the required phase-shift operations. However, phase-shift beamforming is a valid approximation to delay-and-sum steering over only a limited bandwidth whose value depends on array aperture and steering angle. This paper describes a multiple-beam digital beamforming structure which is a phase-shift/time-delay hybrid and which an be designed for operating bandwidths in excess of the phase-shift limit. Much of the computational efficiency of colinear array phase-shift beamforming is retained in this approach, and it can offer substantial advantage over the alternative of delay steering by digital interpolation. This will be demonstrated by examples.

Orientation of the genetic and physical map of Rhizobium meliloti temperate phage 16-3

The attachment site, the C cistron of Rhizobium meliloti temperate phage 16-3, and the insertion of the host cys46+ gene in the phage genome were localized on the HindIII and EcoRJ restriction endonuclease maps, as well as mapped genetically. The strategy employed included restriction analysis and Southern in situ hybridization of plasmid pGY1, which carries the bacterial chromosome region containing the integration site of 16-3, plasmid pGY2, which carries the 16-3 prophage, deletion and inversion mutants, and the cys46+ transducing 16-3 particles. The colinear array of genetic and physical data was possible. The possibility of isolation of a replacement phage vector for Rhizobium is discussed.

Distribution of Humpback Whales (Megaptera novaeangliae) in the Caribbean Determined by a Rapid Acoustic Method

Humpback whale (Megaptera novaeangliae) distribution in the eastern Caribbean Sea was studied by means of solitary sonobuoys deployed from an oceanographic aircraft. Humpback whale sounds were detected on 33 of 82 sonobuoys deployed. It is estimated that 62 whales were detected in an area of 22 140 km2 by this method with whale density calculated at 2.8 × 10−3 whales/km2. For further experiments in selected areas we used a colinear array to obtain accurate counts of humpbacks. A total of 18 humpbacks were detected in this manner with a mean of 2.6 whales per array deployment. Combined acoustic and visual detections indicate a minimum of 119 humpbacks in the area surveyed. This rapid acoustic method could also be applied to detection of almost all odontocete cetaceans and to other marine mammals with distinctive vocal patterns. Key words: cetaceans, whales, acoustic detection, distribution, density, humpbacks, aircraft detectors, sonobuoys

Experiments on heat transfer and pressure drop for a pair of colinear, interrupted plates aligned with the flow

Experiments have been performed to determine the heat-transfer characteristics for each plate of a two-plate colinear array aligned parallel to the flow direction and situated in an airflow in a flat rectangular duct. The pressure drop associated with the plates was also determined. The plate thickness and the interplate spacing were parametrically varied (for a fixed plate length), as was the Reynolds number. It was found that while the Nusselt number may either increase or decrease with plate thickness, depending on the operating conditions, it should increase for conditions corresponding to those commonly encountered in an interrupted-plate heat exchanger. The pressure drop increase caused by increasing plate thickness is greater than the largest thickness-related increase of the Nusselt number. The presence of the inter-plate gap affects the Nusselt numbers for both the first and second plates, but to a greater extent for the latter. In many cases, the curves of Nusselt number vs spacing attain a local maximum and indicate that the conventional spacing-to-length ratio of unity is not necessarily optimal.

Antiferromagnetism in Au5Mn2

The intermetallic compound Au5Mn2 has been investigated by neutron diffraction and x-ray techniques and the temperature variations of the magnetic susceptibility, electrical resistivity and Young's modulus have been measured. The compound is shown to be antiferromagnetic with a Neel temperature of 353 °K, and to have identical chemical and magnetic unit cells. Each contains four manganese atoms with ionic moments of spin S = fraction five-twos arranged in a co-linear antiferromagnetic array. Above the Neel temperature the magnetic susceptibility showed Curie-Weiss behaviour, with a Curie temperature of +100 °K. Characteristic antiferromagnetic anomalies were also observed in the temperature variation of resistivity and Young's modulus.

Geochronology of the Keweenawan rocks, White Pine, Michigan

Age determinations by the total-rock Rb-Sr method of several suites of felsite from the White Pine area of Michigan indicate dates ranging from 978 + or - 40 m.y. to 1,100 + or - 25 m.y. A single specimen of felsite from Government Peak of the Porcupine Mountains was dated at 1,042 + or - 32 m.y. Assuming that the Porcupine Mountains are an anticline, this date sets an upper limit to the time of deposition of the overlying Nonesuch Shale. Another upper limit is provided by dates of 1,107 and 1,180 m.y. for two felsite pebbles from the lower sandstone unit of the Parting Shale member exposed in the old Nonesuch Mine.Nine samples of mineralized and unmineralized rock from the basal section of the Nonesuch Shale exposed in the mine workings of the White Pine Mine were analyzed. These samples form a good co-linear array in coordinates of Rb 87 /Sr 86 and Sr 87 /Sr 86 . The apparent age, calculated from the slope of the isochron, is 1,075 + or - 50 m.y. The initial Sr 87 /Sr 86 ratio is 0.7080 + or - 0.0008. The apparent age of the Nonesuch Shale is interpreted to be slightly greater than the time of deposition because of the probable incorporation of inherited Sr 87 into the sediment at the time of deposition.The isotope composition of three lead samples extracted from chalcocite of the ore body at White Pine was found to be anomalous. This suggests that the lead in the ore was mixed with radiogenic lead and favors an epigenetic or late diagenetic rather than a syngenetic origin for the copper sulfide in the basal portion of the Nonesuch Shale.

A broadband 160-MC colinear array

The design of a 3-element colinear array is described. Over the 152-162 MC band, the array has a minimum gain of 4 db over a half-wavelength dipole and VSWR less than 1.5. The circularity of its horizontal pattern is ± 1/4 db. The array elements are covered and supported by a Fiberglas tube, DC grounds are provided for these radiating elements for lightning protection and reduction in static noise.

Mutual and Self-Impedance for Colinear Antennas

In Part I a two-element colinear array, consisting of identical center-driven antennas of finite radius, is discussed as a boundary-value problem. A formulation is given for the distribution of current when the antennas are driven symmetrically and antisymmetrically. From these data the impedance properties of the array may be deduced. In Part II a simplified, but much less rigorous investigation of the same problem is presented. The more important results include curves and tables for mutual and self-impedance.

Coupled Antennas and Transmission Lines

The problem of coupled antennas is reviewed; unbalanced currents in and radiation from transmission lines are discussed briefly and resolved into transmission line and antenna problems. The use of sections of transmission line as coupling links between antennas is discussed qualitatively and illustrated in terms of a colinear array. The principles of phase reversing and of detuning stubs and sleeves are explained in terms of coupled circuits in which a section of transmission line may carry transmission-line currents, antenna currents, or both. Methods of driving transmission lines and of feeding antennas using transmission lines are discussed from the point of view of minimizing unbalanced currents on the line.