Numerical Techniques for Scattering from Submerged Objects

To represent the final results in terms of matrices, one expands all appropriate physical quantities in terms of partial wave basis states. This includes expansions for the incident and scattered fields and the surface quantities. The method then utilizes the Huygen-Poincare integral representation for both the exterior and interior solutions, leading to the required matrix equations. One thus deals with matrix equations, the complexity of which depends on the nature of the problem. It is shown that in general a transition matrix T can be obtained relating the incident field A with the scattered field f having the form T = PQ(-1), where f = TA. The structure of Q can be quite complicated and can itself be composed of other matrix inversions such as arise from layered objects. Recent improvements in this method appropriate for a variety of physical problems are focused on, and on their implementation. Results are outlined from scattering simulations for very elongated submerged objects and resonance scattering from elastic solids and shells. The final improvement concerns eigenfunction expansions of surface terms, arising from solution of the interior problem, obtained via a preconditioning technique. This effectively reduces the problem to that of obtaining eigenvalues of a Hermitian operator. This formalism is reviewed for scattering from targets that are rigid, sound-soft, acoustic, elastic solids, elastic shells, and elastic layered objects. Two sets of the more interesting results are presented. The first concerns scattering from elongated objects, and the second to thin elastic spheroids

A high resolution ultrawideband wall penetrating radar

A high resolution ultra wideband radar prototype is developed for through the wall imaging. The frequency range of operation of the radar is selected to be 1.85 to 6 GHz in order to have high spatial resolution. Besides the hardware, we have also developed a custom image processing software which attacks the problem of false target recognition and rejection. In this paper, we present our prototype along with various experimental results such as detecting stationary targets and detecting respiratory activity of a human behind a 23 cm thick brick wall

Acoustic properties of colloidal crystals

We present a systematic study of the frequency band structure of acoustic waves in crystals consisting of nonoverlapping solid spheres in a fluid. We consider colloidal crystals consisting of polystyrene spheres in water, and an opal consisting of close-packed silica spheres in air. The opal exhibits an omnidirectional frequency gap of considerable width; the colloidal crystals do not. The physical origin of the bands are discussed for each case in some detail. We present also results on the transmittance of finite slabs of the above crystals.Comment: 7 pages, 9 figures, prb approve

Sound scattering by several zooplankton groups. II. Scattering models

Author Posting. © Acoustical Society of America, 1998. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 103 (1998): 236-253, doi:10.1121/1.421110.Mathematical scattering models are derived and compared with data from zooplankton from several gross anatomical groups—fluidlike, elastic shelled, and gas bearing. The models are based upon the acoustically inferred boundary conditions determined from laboratory backscattering data presented in part I of this series [Stanton et al., J. Acoust. Soc. Am. 103, 225–235 (1998)]. The models use a combination of ray theory, modal-series solution, and distorted wave Born approximation (DWBA). The formulations, which are inherently approximate, are designed to include only the dominant scattering mechanisms as determined from the experiments. The models for the fluidlike animals (euphausiids in this case) ranged from the simplest case involving two rays, which could qualitatively describe the structure of target strength versus frequency for single pings, to the most complex case involving a rough inhomogeneous asymmetrically tapered bent cylinder using the DWBA-based formulation which could predict echo levels over all angles of incidence (including the difficult region of end-on incidence). The model for the elastic shelled body (gastropods in this case) involved development of an analytical model which takes into account irregularities and discontinuities of the shell. The model for gas-bearing animals (siphonophores) is a hybrid model which is composed of the summation of the exact solution to the gas sphere and the approximate DWBA-based formulation for arbitrarily shaped fluidlike bodies. There is also a simplified ray-based model for the siphonophore. The models are applied to data involving single pings, ping-to-ping variability, and echoes averaged over many pings. There is reasonable qualitative agreement between the predictions and single ping data, and reasonable quantitative agreement between the predictions and variability and averages of echo data.This work was supported by the National Science Foundation Grant No. OCE-9201264, the U.S. Office of Naval Research Grant Nos. N00014-89-J-1729, N00014-95-1-0287, and N00014-94-1-0452, and the MIT/WHOI Joint Graduate Education Program

Analysis and Scenario Planning for Fairland and Briggs Chaney, Maryland

Final project for URSP708:Community Planning Studio (Fall 2021). University of Maryland, College Park.For additional PALS research on Fairland & Briggs Chaney scenario planning, see: http://hdl.handle.net/1903/28507 .This report is the output of the Fall 2021 Urban Studies and Planning studio at the University of Maryland, College Park. Through the Partnership for Action Learning in Sustainability (PALS), our class partnered with Montgomery County’s Planning Department to provide a planning sector analysis and scenario plans to aid in the development of the new Fairland and Briggs Chaney Master Plan, which is organized and guided by the draft general plan for the county, Thrive Montgomery 2050. The scope of work included analysis of existing conditions within the plan boundaries and the provision of three scenario plans ranging from no change to high levels of change. We concentrated our attention within three thematic areas of emphasis: climate change adaptation and mitigation, economic and community development, and housing. Moreover, our central guiding principle for this project was justice; it informs everything we present here, and we hope that our work will contribute to its achievement. The report is organized into two major parts. In part I, in analysis of existing conditions, we cover a wide range of planning topics, including the history of the plan-area and special considerations related to our thematic areas of emphasis. In Part II, we present three scenarios of alternative futures for the plan-area: status quo, reform, and revolution.Montgomery County Park

Wave vision

The basic applications of radio waves are communication an

Exploring factors influencing low back pain in people with non-dysvascular lower limb amputation: a national survey

Background: Chronic low back pain (LBP) is a common musculoskeletal impairment in people with lower limb amputation. Given the multifactorial nature of LBP, exploring the factors influencing the presence and intensity of LBP is warranted. Objective: To investigate which physical, personal, and amputee-specific factors predicted presence and intensity of low back pain (LBP) in persons with non-dysvascular transfemoral (TFA) and transtibial amputation (TTA). Design: A retrospective cross-sectional survey. Setting: A national random sample of people with non-dysvascular TFA and TTA. Participants: Participants (N = 526) with unilateral TFA and TTA due to non-dysvascular aetiology (i.e. trauma, tumours, and congenital causes) and a minimum prosthesis usage of one year since amputation were invited to participate in the survey. The data from 208 participants (43.4% response rate) were used for multivariate regression analysis Methods (Independent variables): Personal (i.e. age, body mass, gender, work status, and presence of comorbid conditions), amputee-specific (i.e. level of amputation, years of prosthesis use, presence of phantom limb pain, residual limb problems, and non-amputated limb pain), and physical factors (i.e. pain provoking postures including standing, bending, lifting, walking,sitting, sit-to stand, and climbing stairs). Main outcome measures (Dependent variables): LBP presence and intensity. Results: A multivariate logistic regression model showed that the presence of two or more comorbid conditions (prevalence odds ratio (POR) = 4.34, p = .01), residual limb problems (POR 22 = 3.76, p<.01), and phantom limb pain (POR = 2.46, p = .01) influenced the presence of LBP. Given the high LBP prevalence (63%) in the study, there is a tendency for overestimation of PORand the results must be interpreted with caution. In those with LBP, the presence of residual limb problems (beta = 0.21, p = .01), and experiencing LBP symptoms during sit-to-stand task (beta = 0.22, p = .03) were positively associated with LBP intensity, while being employed demonstrated a negative association (beta = - 0.18, p = .03) in the multivariate linear regression model. Conclusions: Rehabilitation professionals should be cognisant of the influence that comorbid conditions, residual limb problems, and phantom pain have on the presence of LBP in people with non-dysvascular lower limb amputation. Further prospective studies could investigate the underlying causal mechanisms of LBP