5,643 research outputs found
Spatio-temporal growth of disturbances in a boundary layer and energy based receptivity analysis
No full textIn fluid dynamical systems, it is not known a priori whether disturbances grow either in space or in time or as spatio-temporal structures. However, for boundary layers, it is customary to treat it as a spatial problem and some limited comparison between prediction and laboratory experiments exist. In the present work, the receptivity problem of a zero pressure gradient boundary layer excited by a localized harmonic source is investigated under the general spatio-temporal framework, using the Bromwich contour integral method. While this approach has been shown to be equivalent to the spatial study, for unstable systems excited by a single frequency source [T. K. Sengupta, M. Ballav, and S. Nijhawan, Phys. Fluids6, 1213 (1994)], here we additionally show, how the boundary layer behaves when it is excited (i) at a single frequency that corresponds to a stable condition (given by spatial normal-mode analysis) and (ii) by wideband frequencies, that shows the possibility of flow transition due to a spatio-temporally growing forerunner or wave front. An energy based receptivity analysis tool is also developed as an alternative to traditional instabilitytheory. Using this, we reinterpret the concept of critical layer that was originally postulated to explain the mathematical singularity of inviscid disturbance field in traditional instabilitytheory of normal modes
Intern experience at the Honeywell Test Instrument Division: an internship report
No full text"Submitted to the College of Engineering of Texas A&M University in partial
fulfillment of the requirements for the degree of Doctor of Engineering."Includes vita (leaf 42)Includes bibliographical referencesThis report documents the industrial experience accrued by the author
during a twelve month Doctor of Engineering internship served with Honeywell. The internship
was served at the Test Instrument Division, Denver, Colorado as a Biomedical Applications
Engineer between June 15, 1976 and June 30, 1977
Dynamics and control of satellite relative motion in a central gravitational field
No full textThe study of satellite relative motion has been of great historic interest, primarily
due to its application to rendezvous, intercept, and docking maneuvers, between
spacecraft in orbit about gravitational bodies, such as the Earth. Recent interest in
the problem of satellite formation flight has also led to renewed effort in understanding
the dynamics of relative motion. Satellite formations have been proposed for
various tasks, such as deep-space interferometry, and terrestrial observation, among
others. Oftentimes, the rich natural dynamics of the relative motion problem near a
gravitational body are exploited to design formations of a specific geometry.
Traditional analysis models relative motion under the assumptions of a circular
reference orbit, linearized differential gravity field (small relative distance), and
without environmental perturbations such as oblateness effects of the attracting body,
and atmospheric drag. In this dissertation, the dynamics of the relative motion
problem are studied when these assumptions are relaxed collectively. Consequently,
the combined effects of nonlinearity, eccentricity, and Earth oblateness effects on
relative motion, are studied. To this end, coupling effects between the various environmental perturbations are also accounted for. Five key problems are addressed
- the development of a state transition matrix that accounts for eccentricity,
nonlinearity, and oblateness effects; oblateness effects on averaged relative motion;
eccentricity effects on formation design and planning; new analytical expressions for
periodic relative motion that account for nonlinearity and eccentricity effects; and
a solution to the optimal rendezvous problem near an eccentric orbit. The most
notable feature of this dissertation, is that the solutions to the stated problems are
completely analytical, and closed-form in nature. Use has been made of a generalized
reversion of vector series, and several integral forms of Kepler��������s equations, without
any assumptions on the magnitude of the eccentricity of the reference orbit
A phosphate-selective sorbent for the REM NUT® process: field experience at Massafra Wastewater Treatment Plant
No full textAbstract
P-control technologies from municipal wastewater are based on ‘‘destructive’’ methods leading to formation of solidphases
(sludge) that are disposed-off in controlled landfills. Non-destructive methods, based on selective liquid–solid
separations allow for removal of pollutants and their recovery to the same and/or related productive lines. REM
NUT, an ion exchange based process, removes selectively nutrients (HPO2 4 , NHþ4
, Kþ) present in biologically oxidised
municipal effluents and recovery in the form of struvites (MgNH4PO4; MgKPO4), premium quality slow release
fertilisers. The main limitation, for the extensive application of the process, is the availability of specific anion exchangers
for selective removal of phosphates.
The paper illustrates laboratory and field experience carried-out at Massafra (S.E. Italy) Wastewater Treatment
Plant (MWTP) with a revisited ‘‘P-driven’’ version of the REM NUT scheme and the use of a new phosphate-selective
sorbent developed at Lehigh University, PA, USA.P-control technologies from municipal wastewater are based on “destructive” methods leading to formation of solid-phases (sludge) that are disposed-off in controlled landfills. Non-destructive methods, based on selective liquid–solid separations allow for removal of pollutants and their recovery to the same and/or related productive lines. REM NUT®, an ion exchange based process, removes selectively nutrients (HPO42−, NH4+, K+) present in biologically oxidised municipal effluents and recovery in the form of struvites (MgNH4PO4; MgKPO4), premium quality slow release fertilisers. The main limitation, for the extensive application of the process, is the availability of specific anion exchangers for selective removal of phosphates.
The paper illustrates laboratory and field experience carried-out at Massafra (S.E. Italy) Wastewater Treatment Plant (MWTP) with a revisited “P-driven” version of the REM NUT® scheme and the use of a new phosphate-selective sorbent developed at Lehigh University, PA, USA
Uniform Bounds on Product Sylvester-Gallai Configurations
No full textIn this work, we explore a non-linear extension of the classical Sylvester-Gallai configuration. Let be an algebraically closed field of characteristic zero, and let ℱ = {F_1, …, F_m} ⊂ [x_1, …, x_N] denote a collection of irreducible homogeneous polynomials of degree at most d, where each F_i is not a scalar multiple of any other F_j for i ≠ j. We define ℱ to be a product Sylvester-Gallai configuration if, for any two distinct polynomials F_i, F_j ∈ ℱ, the following condition is satisfied: ∏_{k≠i, j} F_k ∈ rad (F_i, F_j) .
We prove that product Sylvester-Gallai configurations are inherently low dimensional. Specifically, we show that there exists a function λ : ℕ → ℕ, independent of , N, and m, such that any product Sylvester-Gallai configuration must satisfy: dim(span_(ℱ)) ≤ λ(d).
This result generalizes the main theorems from (Shpilka 2019, Peleg and Shpilka 2020, Oliveira and Sengupta 2023), and gets us one step closer to a full derandomization of the polynomial identity testing problem for the class of depth 4 circuits with bounded top and bottom fan-in
Satellite relative motion propagation and control in the presence of J2 perturbations
No full textFormation flying is a new satellite mission concept that is concerned with clusters of satellites in neighboring orbits cooperating to perform a specific task. The tasks may be Earth observation or space-based interferometry where a cluster of small satellites is able to fulfill the same requirements as that of a larger, monolithic satellite.
There exist a variety of models for the study of relative motion between two satellites. These include models based upon differential orbital elements, and relative position and velocity coordinates. Extensive work has been done on such models, both in the absence and presence of the J2 perturbation arising from the aspherical nature of the Earth, which causes variations in the orbital elements that describe the orbit. The approximate relative motion can be obtained analytically by using mean elements. However, the true orbit can only be described by the instantaneous osculating elements.
An analytical method to propagate the relative motion between two satellites in highly elliptic orbits is the main focus of this thesis. The method is kinematically exact and it maintains a high degree of accuracy even in the presence of J2 perturbations. Mean orbital elements are used for orbit propagation, and expansions involving the powers of eccentricity are not utilized. The true anomaly of the reference satellite is treated as the independent variable, instead of time. The relative orbit kinematics are obtained by using a projection onto a unit sphere. This procedure allows the relative position variables to be treated as angles depending on the orbital element differences. The effect of adding short-period corrections due to J2 to the mean elements is also studied.
Finally, the problem of formation reconfiguration is studied. The reconfiguration of a formation may be achieved by using impulsive thrust (velocity increments) or continuous control. This thesis presents a method to obtain the optimal velocity increments through numerical optimization, utilizing the analytical technique developed for relative orbit propagation. A continuous control law is also developed using a candidate Lyapunov function, and the asymptotic stability of the closed-loop system is ascertained
Visualization techniques for statistical circuit design
No full textDue to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references.Not availabl
Colloquium: Nonequilibrium dynamics of closed interacting quantum systems
No full textThis Colloquium gives an overview of recent theoretical and experimental progress in the area of nonequilibrium dynamics of isolated quantum systems. There is particularly a focus on quantum quenches: the temporal evolution following a sudden or slow change of the coupling constants of the system Hamiltonian. Several aspects of the slow dynamics in driven systems are discussed and the universality of such dynamics in gapless systems with specific focus on dynamics near continuous quantum phase transitions is emphasized. Recent progress on understanding thermalization in closed systems through the eigenstate thermalization hypothesis is also reviewed and relaxation in integrable systems is discussed. Finally key experiments probing quantum dynamics in cold atom systems are overviewed and put into the context of our current theoretical understanding. © 2011 American Physical Society
The Relationship Between Supply Chain Integration And International Sourcing And Their Influence On Delivery Performance: Insights From A Survey
No full textSupply chain integration (SCI) is a pivotal issue in SCM literature. Our quantitative analysis based on the High Performance Manufacturing database investigates the influence of SCI on delivery performance and the moderating effect of international sourcing on this relationship. The results confirm the positive relationship between SCI and delivery performance and also highlight that the impact of SCI is positively moderated by the adoption of international suppliers
A sequence modeling approach for structured data extraction from unstructured text
No full textExtraction of structured information from unstructured text has always been a problem of interest for NLP community. Structured data is concise to store, search and retrieve; and it facilitates easier human & machine consumption. Traditionally, structured data extraction from text has been done by using various parsing methodologies, applying domain specific rules and heuristics. In this work, we leverage the developments in the space of sequence modeling for the problem of structured data extraction. Initially, we posed the problem as a machine translation problem and used the state-of-the-art machine translation model. Based on these initial results, we changed the approach to a sequence tagging one. We propose an extension of one of the attractive models for sequence tagging tailored and effective to our problem. This gave 4.4% improvement over the vanilla sequence tagging model. We also propose another variant of the sequence tagging model which can handle multiple labels of words. Experiments have been performed on Wikipedia Infobox Dataset of biographies and results are presented for both single and multi-label models. These models indicate an effective alternate deep learning technique based methods to extract structured data from raw text.</p
- …
