bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of an acoustic levitation technique to obtain foam material properties
Authors: Liu Li 
Published: October 2003

Aqueous foam is an impermanent form of matter in which a kind of gas, often air, is dispersed as an agglomeration of bubbles that are separated from each other by films of liquid. Foams are of tremendous economical importance in industry. Foam material properties are sensitive functions of the void fraction. A “wet foam” is a bubbly liquid that cannot support shearing motion; inside the wet foam the individual bubbles are free to move around. A “transitional” or “critical foam” is composed of bubbles whose dynamics are strongly interacting and whose surfaces may be in mechanical contact with each other. Finally, a “dry foam” is composed of bubbles who have a fixed position in a lattice for low to moderate straining rates. An acoustic levitation technique is developed which provides a noncontact means of estimating the properties of the foam by acoustically levitating aqueous foam drops and exciting their spheroidal modes oscillation. Assuming linear oscillation of foam drops, experimental data for frequency and damping show good agreement with a bubble dynamics-based theoretical model.
Thesis advisor: R. Glynn Holt
Copies of this thesis may be obtained by contacting the advisor, Glynn Holt, Dept. of Aerospace and Mechanical Engineering, Boston University, 110 Cummington St., Boston, MA 02215. E-mail address: rgholt@bu.edu
Investigation of bubble dynamics and heating during focused ultrasound insonation in tissue-mimicking materials
Authors: Yang Xinmai 
Published: October 2003

The deposition of ultrasonic energy in tissue can cause tissue damage due to local heating. For pressures above a critical threshold, cavitation will occur in tissue and bubbles will be created. These oscillating bubbles can induce a much larger thermal energy deposition in the local region. The present work is an attempt to control and utilize this bubble-enhanced heating. First, by applying appropriate bubble dynamic models, limits on the asymptotic bubble size distribution are obtained for different driving pressures at 1 MHz. The size distributions are bounded by two thresholds: the bubble shape instability threshold and the rectified diffusion threshold. The growth rate of bubbles in this region is also given, and the resulting time evolution of the heating in a given insonation scenario is modeled. Experimental results have been obtained to investigate the bubble-enhanced heating in an agar and graphite based tissue-mimicking material. By fitting appropriate bubble densities in the ultrasound field, the peak temperature changes observed in experiments are simulated. Finally, a simple bubbly liquid model is presented to estimate shielding effects which may be important even for low void fraction during high intensity focused ultrasound (HIFU) treatment.
Thesis advisor: R. Glynn Holt
Copies of this thesis may be obtained by contacting the advisor, Glynn Holt, Dept. of Aerospace and Mechanical Engineering, Boston University, 110 Cummington St., Boston, MA 02215. E-mail address: rgholt@bu.edu
Sonoluminescence in varying acceleration environments
Authors: Wyatt Sean C. 
Published: October 2003

In order to prepare for experiments in variable-g environments, some of the multiple effects caused by the time-varying acceleration of acoustic resonators used in bubble levitation experiments are considered. The coupled effects of the induced changes in ambient pressure (due to a changing hydrostatic head) and bubble position (due to a change in buoyant body force) were modeled. Changing the ambient pressure, while holding the acoustic pressure amplitude constant, causes changes in the radial bubble response and diffusive equilibrium requirements. Changing the bubble levitation position causes both the local acoustic pressure amplitude and gradient to change, which will again impact bubble response. If the bubble remains in a stable diffusive equilibrium, both of these effects will force the bubble’s equilibrium radius to change. By using an empirical relation for emitted sonoluminescence intensity versus bubble response, the variation of emitted light intensity as a function of the changing ambient acceleration can be predicted. The predicted results are shown to agree quantitatively with existing experimental data from other research groups. An experiment was designed and built to fly onboard a KC-135 aircraft that has been reinforced for parabolic flight maneuvers to simulate micro and hyper gravity acceleration.
Thesis advisor: R. Glynn Holt
Copies of this thesis may be obtained by contacting the advisor, Glynn Holt, Dept. of Aerospace and Mechanical Engineering, Boston University, 110 Cummington St., Boston, MA 02215. E-mail address: rgholt@bu.edu
Design, fabrication and use of a KC-135 experiment for studying sonoluminescence
Authors: Thomas Charles Robert 
Published: October 2003

The effects of many external parameters on single-bubble sonoluminescence (SBSL) have been studied since its discovery 13 years ago in 1990. These studies include the effects due to host water temperature, dissolved gas, ambient pressure, and even magnetic fields. Because the stability of the bubble depends in part on gravity, through its buoyancy, it is natural to study SBSL in microgravity. This is the subject of this thesis: the design and fabrication of an experiment to study the effects of gravity on SBSL for use on the NASA KC-135 aircraft. The KC-135 aircraft flies in a parabolic trajectory to simulate weightlessness for about 20 s per parabolic maneuver, performing roughly 40 parabolas per flight. During those flights, the bubble’s size, position in the imposed sound field, and emitted light intensity were measured. The apparatus and techniques used to make these measurements, along with the constraints imposed by the unique environment afforded by experimentation aboard the KC-135, are discussed in detail. Preliminary results are reported, and a full uncertainty analysis is presented for each measurement.
Thesis advisor: R. Glynn Holt
Copies of this thesis may be obtained by contacting the advisor, Glynn Holt, Dept. of Aerospace and Mechanical Engineering, Boston University, 110 Cummington St., Boston, MA 02215. E-mail address: rgholt@bu.edu
Mechanical and psychosocial factors predict new onset shoulder pain: a prospective cohort study of newly employed workers
Authors: Harkness E F , Macfarlane G J , Nahit E S , Silman A J , McBeth J 
Published: October 2003

Aim:To test the hypothesis that work related mechanical and psychosocial factors predict new onset shoulder pain in newly employed workers.Methods:Two year prospective study of newly employed workers from 12 diverse occupational settings. At baseline, 1081 subjects provided information on work related mechanical and psychosocial risk factors, and current pain status.Results:In all, 803 (74%) subjects were free from shoulder pain at baseline. Of those, 638 (79%) responded at 12 months and 476 (88%) at 24 months. New onset shoulder pain was reported by 93 (15%) and 73 (15%) subjects respectively. An increased risk of symptom onset was found in subjects reporting mechanical exposures involving heavy weights including lifting with one or two hands, carrying on one shoulder, lifting at or above shoulder level, and pushing or pulling. Working with hands above shoulder level was also predictive of new onset shoulder pain. Of the psychosocial factors examined, the strongest predictor was monotonous work. Those individuals with any other previous pain also had an increased risk of new onset shoulder pain at follow up. In multivariate analysis, lifting heavy weights with one or two hands, pushing or pulling heavy weights, working with hands above shoulder level, and monotonous work were independently associated with new onset shoulder pain.Conclusions:This study supports the hypothesised relation between mechanical risk factors and shoulder pain. In general, work related psychosocial factors were modestly associated with new onset shoulder pain. However, monotonous work was a strong risk factor for new onset shoulder pain.
Risk factors for incident neck and shoulder pain in hospital nurses
Authors: Smedley J , Inskip H , Trevelyan F , Buckle P , Cooper C , Coggon D 
Published: October 2003

Aim:To assess the incidence and risk factors for neck and shoulder pain in nurses.Methods:A longitudinal study of neck and shoulder pain was carried out in female nurses at two hospitals in England. Personal and occupational risk factors were assessed at baseline. The self reported incidence of symptoms in the neck and shoulder region was ascertained at three-monthly intervals over two years. A Cox regression model was used to estimate hazard ratios (HRs) for incident neck/shoulder pain during follow up in nurses who had been pain free for at least one month at baseline.Results:The baseline response rate was 56%. Of 903 women who were pain free at baseline, 587 (65%) completed at least one follow up while still in the same job. During an average of 13 months, 34% of these (202 women) reported at least one episode of neck/shoulder pain. The strongest predictor of pain in the neck/shoulder was previous history of the symptom (HRs up to 3.3). For physical exposures at work, the highest risks (HRs up to 1.7) were associated with specific patient handling tasks that involved reaching, pushing, and pulling. Nurses who reported low mood or stress at baseline were more likely to develop neck/shoulder pain later (HR 1.5). Workplace psychosocial factors (including job demands, satisfaction, and control) were not associated with incident neck/shoulder symptoms.Conclusions:Neck/shoulder pain is common among hospital nurses, and patient handling tasks that involve reaching and pulling are the most important target for risk reduction strategies.
High local unemployment and increased mortality in Danish adults; results from a prospective multilevel study
Authors: Osler M , Christensen U , Lund R , Gamborg M , Godtfredsen N , Prescott E 
Published: October 2003

Aims:To examine the relation between unemployment rates in area of residence and all-cause mortality, taking the individuals’ unemployment experience and a number of social and behavioural factors into account.Methods:Prospective cohort study with record linkage to mortality and unemployment registers. Data were pooled data from two population studies conducted in Copenhagen, Denmark. The association between unemployment at parish level and mortality was examined in Cox proportional hazard analysis. A total of 15 980 men and women, aged 20–67 years and employed at 1 January 1980, were studied. All-cause mortality was followed from January 1981 to December 1998.Results:The unemployment rate in the area of residence was associated with increased mortality (hazard ratiohighestvlowest quartile1.35:0.14–1.60) even after adjustment for individuals’ unemployment experience in 1980, which was also a risk factor (hazard ratioyes/no1.38:1.16–1.64). These estimates attenuated somewhat when other social and behavioural covariates were taken into account. The effects were similar in men and women, but the influence of individuals’ unemployment experience during one and five years decreased gradually with increasing age.Conclusion:This prospective study suggests that high local unemployment and individuals’ experience of unemployment increase mortality risk, even after adjustment for other social and behavioural factors.
A Quantum Gauge Group Approach to the 2D SU(n) WZNW Model
Authors: Furlan Paolo , Hadjiivanov Ludmil K. , Todorov Ivan T. 
Published: October 2003

The cannonical quantization of the WZNW model provides a complete set of exchange relation in the enlarged chiral state spaces that include the Gauss components M±, [Formula: see text] of the monodromy matrices M, [Formula: see text]. Regarded as new dynamical variables, the elements of M and [Formula: see text] cannot be identified — they satisfy different exchange relations. Accordingly, the two dimensional theory expressed in terms of the left and right movers' fields does not automatically respect monodromy invariance. Continuing our recent work on the subject we show that the definition of the appropriate physical subspace of the SU(n) WZNW model involves an extended quantum group symmetry in a finite dimensional Fock space. In the simplest (n = 2) case we explicitly construct the subspace of Uq(sl(2)) ⊗ Uq(sl(2)) invariant vectors. Monodromy invariance is also restored in a weak sense.
Constrained KP Hierarchies: Additional Symmetries, Darboux–Bäcklund Solutions and Relations to Multi-Matrix Models
Authors: Aratyn H. , Nissimov E. , Pacheva S. 
Published: October 2003

This paper provides a systematic description of the interplay between a specific class of reductions denoted as cKP r,m(r,m ≥ 1) of the primary continuum integrable system — the Kadomtsev–Petviashvili (KP) hierarchy and discrete multi-matrix models. The relevant integrable cKP r,m structure is a generalization of the familiar r-reduction of the full KP hierarchy to the SL (r) generalized KdV hierarchy cKP r,0. The important feature of cKP r,m hierarchies is the presence of a discrete symmetry structure generated by successive Darboux–Bäcklund (DB) transformations. This symmetry allows for expressing the relevant tau-functions as Wronskians within a formalism which realizes the tau-functions as DB orbits of simple initial solutions. In particular, it is shown that any DB orbit of a cKP r,1 defines a generalized two-dimensional Toda lattice structure. Furthermore, we consider the class of truncated KP hierarchies (i.e. those defined via Wilson–Sato dressing operator with a finite truncated pseudo-differential series) and establish explicitly their close relationship with DB orbits of cKP r,m hierarchies. This construction is relevant for finding partition functions of the discrete multi-matrix models. The next important step involves the reformulation of the familiar nonisospectral additional symmetries of the full KP hierarchy so that their action on cKP r,m hierarchies becomes consistent with the constraints of the reduction. Moreover, we show that the correct modified additional symmetries are compatible with the discrete DB symmetry on the cKP r,m DB orbits.
The Geometry of the Master Equation and Topological Quantum Field Theory
Authors: Alexandrov M. , Schwarz A. , Zaboronsky O. , Kontsevich M. 
Published: October 2003

In Batalin–Vilkovisky formalism, a classical mechanical system is specified by means of a solution to the classical master equation. Geometrically, such a solution can be considered as a QP-manifold, i.e. a supermanifold equipped with an odd vector field Q obeying {Q, Q} = 0 and with Q-invariant odd symplectic structure. We study geometry of QP-manifolds. In particular, we describe some construction of QP-manifolds and prove a classification theorem (under certain conditions). We apply these geometric constructions to obtain in a natural way the action functionals of two-dimensional topological sigma-models and to show that the Chern–Simons theory in BV-formalism arises as a sigma-model with target space [Formula: see text]. (Here [Formula: see text] stands for a Lie algebra and Π denotes parity inversion.)
A New Approach to Turbulence
Authors: Canuto V. M. , Dubovikov M. S. 
Published: October 2003

We propose a closed set of dynamic equations to describe turbulence. The equations are the result of systematic and heuristic elements. Specifically, the UV part of the nonlinear interactions, represented by a dynamical viscosity, is computed for a stirring force of a particular nature. However, since the results exhibit a general structure, we suggest heuristically to extend them to arbitrary flows. Because of nonrenormalizable divergences, the IR part of the nonlinear interactions has constituted a serious problem. We suggest a heuristic model, the basic ingredient of which is that the transfer of energy among eddies is mostly a local process. We show that possible adjustable parameters are actually fixed by the model itself. Because of the heuristic nature of one part of the model, its overall validity rests largely on the accumulated evidence gathered from checking its predictions against data from a wide variety of flows. The model has been tested against more than seventy turbulence statistics for homogeneous isotropic and anisotropic flows (the Kolmogorov constant is predicted to be Ko = 5/3). The overall performance is good. Here, we first extend the model to inhomogeneous flows and test the predictions using the newest laboratory and DNS data on turbulent convection at large Ra (Rayleigh number). The model reproduces both types of data quite accurately. Second, we study the problem of the so-called "sweeping effect" and derive the relation between the ω and k-spectra. Third, we show that for shear driven flows the present model reproduces well the data at large strain rates while the widely used K - ∊ model does not.
A Nucleation Process Drives the Percolation Transition
Authors: Skal Asya S. 
Published: October 2003

The new "special" nodes — the nucleation nodes, which drive the percolation transition for kinetic coefficients are found by using the distribution functions of kinetic coefficients such as conductivity, the Hall and Seebeck coefficients for the resistor network. They belong to the component, opposite to the "special" nodes and create an infinite cluster below the threshold and destroy it above the threshold. We have divided the "backbone" of an infinite cluster into two parts: (1) the static part which is responsible for analytic background; and (2) the dynamic part or a "scaling region" which equals the volume of the "special" nodes and is responsible for the singular part of kinetic coefficients and probably also for thermodynamic functions.
Graph-Based Software Process Management
Authors: Heimann Peter , Krapp Carl-Arndt , Westfechtel Bernhard , Joeris Gregor 
Published: October 2003

Software process dynamics challenge the capabilities of process-centered software engineering environments. Dynamic task nets represent evolving software processes by hierarchically organized nets of tasks which are connected by control, data, and feedback flows. Project managers operate on dynamic task nets in order to assess the current status of a project, trace its history, perform impact analysis, handle feedback, adapt the project plan to changed product structures, etc. Developers are supported through task agendas and provision of tools and documents. Chained tasks may be executed in parallel (simultaneous engineering), and cooperation is controlled through releases of document versions. Dynamic task nets are formally specified by a programmed graph rewriting system. Operations on task nets are specified declaratively by graph rewrite rules at a high level of abstraction. Furthermore, editing, analysis, and execution steps on a dynamic task net, which may be interleaved seamlessly, are described in a uniform formalism.
Managing Software Projects by Structured Project Planning
Authors: Cimitile A. , Visaggio G. 
Published: October 2003

This study is based on the Structured Process Model formalism previously proposed by the same authors, and describes some techniques for scheduling an execution plan which conforms to the chosen process but adapts to all the potential changes in the value of specific variables of the project. The executive plan is generated by means of Incremental Refinements. Each increment is the consequence of one or more decisions taken by the manager. All the contingencies which can occur during the execution of the project are classified in a finite number of types of events which form the basis for the definition of all the transition laws between the possible states of the process. Naturally, the manager's decisions, and therefore the composition of the increment, take into account the changes in the value of the variables of the process and of the process model itself. In addition, the study proposes the handling of fuzzy activities, by means of which the problems of recycles and reprocessing are solved. These activities also provide a better management of the execution times of the project.
An Easy Way to Minimal Algebras
Authors: Kiss Emil W. 
Published: October 2003

A finite algebra C is called minimal with respect to a pair δ<θ of its congruences if every unary polynomial f of C is either a permutation, or f(θ)⊆δ. It is the basic idea of tame congruence theory developed by Ralph McKenzie and David Hobby [7] to describe finite algebras via minimal algebras that sit inside them. As shown in [7] minimal algebras have a very restricted structure. This paper presents a new tool, the Twin Lemma, which makes it possible to give short proofs of some of these structure theorems. This part can be read as an alternative introduction to the theory. Our method yields new information in the type 1 case, and is especially useful in describing E-minimal algebras (that is, algebras that are minimal with respect to every prime congruence quotient). We complete their theory given in [7] by proving a structure theorem for the type 1 case. Finally we show that if an algebra is minimal with respect to two quotients, then the two types are the same, and if this type is 2, 3, or 4, then the bodies are also equal.
Knowledge-Based Software Prototyping and Reuse
Authors: Rubin Stuart H. 
Published: October 2003

Models are executable prototypes. Modeling is closely tied to simulation, which refers to the exercise of a model over a variable parametric space. Model simulations not only provide the engineer with feedback pertaining to the validity of a proposed design, but additionally allow competing designs to be compared on one or more parameters (i.e., sensitivity analysis). Models are defined from a base of several hundred primitive constructs. These constructs can define additional constructs hierarchically. An expertn–system was constructed, which retrieves software for reuse. This expert system is itself reusable and consists of many sub-systems – any one of which can invoke any other. A key feature is that any expertn–system need never be modified, for purposes of reuse, once saved in a repository. Rather, it communicates all information back to the caller and lets the caller decide how and when to use it. Thus, blocks in an expertn–system have very low coupling (i.e., no off-model connections). In addition, expertn–systems are, as their name suggests, organized in a hierarchy. This means that very complex decision-making systems can be called into play with minimal effort. Growing the repository is equivalent to learning.
Solving the Processor Configuration Problems with a Mutation-Based Genetic Algorithm
Authors: Lau T. L. , Tsang E. P. K. 
Published: October 2003

The Processor Configuration Problem (PCP) is a real life Constraint Optimization Problem. The task is to link up a finite set of processors into a network, whilst minimizing the maximum distance between these processors. Since each processor has a limited number of communication channels, a carefully planned layout will help reduce the overhead for message switching. In this paper, we present a Genetic Algorithm (GA) approach to the PCP. Our technique uses a mutation-based GA, a function that produces schemata by analyzing previous solutions, and an efficient data representation. Our approach has been shown to out-perform other published techniques in this problem.