bluuebunny/crossref_metadata_2025 huggingface dataset:
Influenza detection from emergency department reports using natural language processing and Bayesian network classifiers
Authors: Ye Ye , Tsui Fuchiang , Wagner Michael , Espino Jessi , Li Qi
Published: January 2014

Objectives To evaluate factors affecting performance of influenza detection, including accuracy of natural language processing (NLP), discriminative ability of Bayesian network (BN) classifiers, and feature selection.

Methods We derived a testing dataset of 124 influenza patients and 87 non-influenza (shigellosis) patients. To assess NLP finding-extraction performance, we measured the overall accuracy, recall, and precision of Topaz and MedLEE parsers for 31 influenza-related findings against a reference standard established by three physician reviewers. To elucidate the relative contribution of NLP and BN classifier to classification performance, we compared the discriminative ability of nine combinations of finding-extraction methods (expert, Topaz, and MedLEE) and classifiers (one human-parameterized BN and two machine-parameterized BNs). To assess the effects of feature selection, we conducted secondary analyses of discriminative ability using the most influential findings defined by their likelihood ratios.

Results The overall accuracy of Topaz was significantly better than MedLEE (with post-processing) (0.78 vs 0.71, p<0.0001). Classifiers using human-annotated findings were superior to classifiers using Topaz/MedLEE-extracted findings (average area under the receiver operating characteristic (AUROC): 0.75 vs 0.68, p=0.0113), and machine-parameterized classifiers were superior to the human-parameterized classifier (average AUROC: 0.73 vs 0.66, p=0.0059). The classifiers using the 17 ‘most influential’ findings were more accurate than classifiers using all 31 subject-matter expert-identified findings (average AUROC: 0.76>0.70, p<0.05).

Conclusions Using a three-component evaluation method we demonstrated how one could elucidate the relative contributions of components under an integrated framework. To improve classification performance, this study encourages researchers to improve NLP accuracy, use a machine-parameterized classifier, and apply feature selection methods.
Sensitisation to mites in a group of patients with asthma in Yaounde, Cameroon: a cross-sectional study
Authors: Pefura-Yone Eric Walter , Kengne André Pascal , Kuaban Christopher
Published: January 2014

Objectives

Sensitisation of asthmatic patients to mites in sub-Saharan Africa has been less described. The aim of this study was to assess the prevalence and determinants of sensitisation to mites in asthmatic adolescents and adults in Yaounde, Cameroon.

Design

This was a cross-sectional study. Logistic regression models were employed to investigate the determinants of sensitisation to mites.

Setting

This study was carried out at the Jamot Hospital and CEDIMER private centre, in Yaounde, capital city of Cameroon.

Participants

All asthmatic patients received in consultations from January 2012 to June 2013 and in whom prick-skin tests for perennial aeroallergens were performed were included.

Outcome measures

Prevalence of sensitisation to mites and associated factors.

Results

In total, 201 patients (132 being women, 65.7%), with a median age of 36 (25th–75th centiles: 20–54) years were included, with 135 (67.2%) having a positive skin test for mites. Sensitisation toDermatophagoïdes pteronyssinus,Dermatophagoides farinaeandBlomia tropicaliswas found in 53.2%, 49.8% and 47.8% of the patients, respectively. Intermittent rhinitis (16.3% vs 7.6%) and persistent rhinitis (43.0% vs 22.7%) were more frequent in sensitised patients than in the non-sensitised ones (p<0.010). Independent allergological determinants of sensitisation to mites were sensitisation toAlternaria alternata(adjusted OR 14.98 (95% CIs 1.96 to 114.4)) and sensitisation toBlattella germanica(3.48 (1.34 to 9.00)).

Conclusions

Sensitisation to mites was found in about two-thirds of asthmatic patients in this setting, with a frequent multiple sensitisations toA alternataandBlattella germanica. Systematically investigating asthmatic patients for mites' sensitisation and determinants will help optimising the care in this setting by combining the aetiological treatment for the allergy with symptomatic treatment for asthma, in order to modify the natural course of the disease.
Investigating the bundle compliance of IVIG delivery in the Greater Manchester Neuroscience centre
Authors: Patel Neena , Woodall Amanda , Gow David
Published: January 2014

Salford Royal Hospital is one of the largest users of IVIG for chronic neurological illnesses within the UK. The majority of patients are being treated for chronic inflammatory polyneuropathy and multifocal motor neuropathy. We hypothesised that the components of care being delivered to these patients differed to our stated standard of care (IVIG care bundle). We performed a service review exercise to identify shortcomings and improve quality of patient care. The aim was to measure overall bundle compliance being delivered to 75 patients with a view to improving the overall quality of care being delivered in the future. A retrospective case note study was carried out to measure compliance with the 17 areas of care, which constituted the IVIG bundle. Nine areas of care were being delivered to all 75 patients. This meant that all patients were receiving three monthly bloods, a documented cannula pathway, a filed prescription, a medical assessment, and the correct follow-up. Not all patients had a filed consent form, ECG or HAT assessment and an even smaller number of patients had a documented calculation for the amount of IVIG that needed to be given and few had a serum save. No patient in the group was receiving the intended complete bundle of care.

The results led to the development of an electronic treatment dashboard for the delivery of chronic IVIG therapy to this group. A re-audit has shown that rates of individual areas of care being delivered has increased markedly but overall compliance has only increased a slightly due to a lack of serum saves for patients.
Performance improvement through best practice team management: human factors in complex trauma
Authors: Mercer Simon , Arul G S , Pugh H E J
Published: January 2014

Human factors or non-technical skills are now commonplace in the medical literature, having taken the lead from the airline and nuclear industries and more recently Formula One motor racing. They have been suggested as playing a vital role in the success of the trauma teams in recent conflicts. This article outlines the background to human factors, referring to early papers and reports and also outlines high profile cases that highlight their importance. We then describe the importance of human factors in the deployed setting and some of the lessons that have been learnt from current conflicts.
Endovascular reconstruction for progressively worsening carotid artery dissection
Authors: Asif Kaiz S , Lazzaro Marc A , Teleb Mohamed S , Fitzsimmons Brian-Fred , Lynch John , Zaidat Osama
Published: January 2014

Background

Carotid artery dissection is an important cause of stroke in young patients. Selection criteria for endovascular repair have not been well defined and limited data exist on long-term outcomes of stent reconstruction.

Objective

To report the immediate and long-term clinical and radiographic outcomes of patients treated with stent placement for progressively worsening symptomatic carotid arterial dissection despite antithrombotic therapy.

Methods

A single institution neuro-endovascular database was accessed to identify consecutive cases in which carotid artery dissection was treated with endovascular repair between 2006 and 2012. Clinical, demographic, radiographic, and procedural data were obtained through chart review.

Results

A total of 22 patients were identified and included 27 carotid artery dissection repairs with stent implantation. The mean age was 43 years (±8.7) with 13 patients being women. Traumatic dissections were seen in 9 (40.9%) patients and spontaneous dissections in 13 (59.1%) patients. All patients were symptomatic and were started on antithrombotic therapy on diagnosis. Most common indications for treatment included recurrent ischemia despite antithrombotic therapy in 15 (55.5%) arteries and enlarging dissecting aneurysm in 4 (14.8%) arteries. Mean degree of stenosis was 79.1%. Mean number of stents used was 1.88 (range 1–4). There was 1 (4.5%) asymptomatic peri-procedural thromboembolic event. Median clinical follow-up was 14 months (range 3–40) and median imaging follow-up was 14 months (range 3–38). There was 1 (4.5%) case of recurrent transient ischemic attack. There was no death, significant restenosis or stroke in the territory of the treated vessel during the duration of the follow-up.

Conclusions

Endovascular stent reconstruction for the treatment of selected patients with progressively worsening carotid dissection despite medical management is feasible with acceptable immediate and long-term clinical and radiographic outcomes. To be able to draw more robust conclusions, further evaluation with larger number of patients and longer follow-up is needed.
Moisture barrier enhancement by spontaneous formation of silicon oxide interlayers in hot wire chemical vapor deposition of silicon nitride on poly(glycidyl methacrylate)
Authors: Spee D.A. , van der Werf C.H.M. , Rath J.K. , Schropp R.E.I.
Published: January 2014

We deposited a silicon nitride (SiNx)–polymer hybrid multilayer moisture barrier in a hot wire chemical vapor deposition (HWCVD) process, entirely below 100 °C. The polymer, poly(glycidyl methacrylate) (PGMA), was deposited by initiated chemical vapour deposition and the SiNx in a dedicated HWCVD reactor. Line profile investigation of our barrier structures by cross-sectional scanning transmission electron microscopy and energy dispersive X-ray spectrometry reveals that, upon deposition of SiNx on top of our polymer layer, an intermediate layer of silicon oxide (SiOx) like material is formed. X-ray photoelectron spectroscopy measurements confirm the presence of this material and indicate the epoxy rings in the PGMA material open upon heating (to 100 °C) and exposure to atomic hydrogen and amine species in the HWCVD process. The oxygen atoms subsequently react with silicon and nitrogen containing radicals to form SiOxNy. The interlayer turns out to be highly beneficial for interlayer adhesion and this is considered to be one of the reasons for the excellent barrier properties of our multilayer.
COMPUTATIONAL MODELING OF TRANSCRANIAL DIRECT CURRENT STIMULATION IN THE CHILD BRAIN: IMPLICATIONS FOR THE TREATMENT OF REFRACTORY CHILDHOOD FOCAL EPILEPSY
Authors: PARAZZINI MARTA , FIOCCHI SERENA , LIORNI ILARIA , PRIORI ALBERTO , RAVAZZANI PAOLO
Published: January 2014

Transcranial direct current stimulation (tDCS) was recently proposed for the treatment of epilepsy. However, the electrode arrangement for this case is debated. This paper analyzes the influence of the position of the anodal electrode on the electric field in the brain. The simulation shows that moving the anode from scalp to shoulder does influence the electric field not only in the cortex, but also in deeper brain regions. The electric field decreases dramatically in the brain area without epileptiform activity.
IMPROVED ADAPTIVE SPLITTING AND SELECTION: THE HYBRID TRAINING METHOD OF A CLASSIFIER BASED ON A FEATURE SPACE PARTITIONING
Authors: JACKOWSKI KONRAD , KRAWCZYK BARTOSZ , WOŹNIAK MICHAŁ
Published: January 2014

Currently, methods of combined classification are the focus of intense research. A properly designed group of combined classifiers exploiting knowledge gathered in a pool of elementary classifiers can successfully outperform a single classifier. There are two essential issues to consider when creating combined classifiers: how to establish the most comprehensive pool and how to design a fusion model that allows for taking full advantage of the collected knowledge. In this work, we address the issues and propose an AdaSS+, training algorithm dedicated for the compound classifier system that effectively exploits local specialization of the elementary classifiers. An effective training procedure consists of two phases. The first phase detects the classifier competencies and adjusts the respective fusion parameters. The second phase boosts classification accuracy by elevating the degree of local specialization. The quality of the proposed algorithms are evaluated on the basis of a wide range of computer experiments that show that AdaSS+ can outperform the original method and several reference classifiers.
CLASSIFICATION OF CERTAIN CONTINUOUS FIELDS OF KIRCHBERG ALGEBRAS
Authors: BENTMANN RASMUS
Published: January 2014

We show that the K-theory cosheaf is a complete invariant for separable continuous fields with vanishing boundary maps over a finite-dimensional compact metrizable topological space whose fibers are stable Kirchberg algebras with rational K-theory groups satisfying the universal coefficient theorem. We provide a range result for fields in this class with finite-dimensional K-theory. There are versions of both results for unital continuous fields.
RIGIDITY OF HOLOMORPHIC MAPS BETWEEN FIBER SPACES
Authors: BHARALI GAUTAM , BISWAS INDRANIL
Published: January 2014

In the study of holomorphic maps, the term "rigidity" refers to certain types of results that give us very specific information about a general class of holomorphic maps owing to the geometry of their domains or target spaces. Under this theme, we begin by studying when, given two compact connected complex manifolds X and Y, a degree-one holomorphic map f : Y → X is a biholomorphism. Given that the real manifolds underlying X and Y are diffeomorphic, we provide a condition under which f is a biholomorphism. Using this result, we deduce a rigidity result for holomorphic self-maps of the total space of a holomorphic fiber space. Lastly, we consider products X = X1 × X2 and Y = Y1 × Y2 of compact connected complex manifolds. When X1 is a Riemann surface of genus ≥ 2, we show that any non-constant holomorphic map F : Y → X is of a special form.
How to Use the New DSM-5 Somatic Symptom Disorder Diagnosis in Research and Practice: A Critical Evaluation and a Proposal for Modifications
Authors: Rief Winfried , Martin Alexandra
Published: January 2014

The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) changed the term “somatoform disorders” to “somatic symptom and related disorders” and further modified diagnostic labels and criteria. We review evidence for the validity of the new criteria, specifically of somatic symptom disorder (SSD), and present a critical discussion of unsolved and new problems. We also provide an update of mechanisms and interventions that have been empirically evaluated in somatoform disorders. For many mechanisms, it is unclear whether their role can be easily transposed to SSD. Therefore more research is needed on the similarities and differences between medically unexplained and medically explained conditions. To overcome the obvious shortcomings of the current classification, we offer a modification of this DSM-5 section as well as a crossover system to apply these criteria for somatic symptom and related disorders. This proposal allows working with DSM-5 but also continuing successful lines of research with concepts such as hypochondriasis/illness anxiety, chronic pain, and medically unexplained versus medically explained syndromes.
Soft Materials Deformation, Flow, and Lubrication Between Compliant Substrates: Impact on Flow Behavior, Mouthfeel, Stability, and Flavor
Authors: Selway Nichola , Stokes Jason R.
Published: January 2014

Foods are rationally designed to be semifluids or soft solids for optimal stabilization of the multiple phases they contain and to provide favorable textural properties. Although rheology provides a guide to physical stability and initial texture perception, measurements on intact foods do not enable predictions of the organoleptic properties experienced during oral processing. Oral processing includes lubrication between compliant oral substrates, and studies into soft lubrication/tribology are providing new insights into the physical processes experienced by soft foods in the mouth. We provide a review of the key rheological considerations for food product stability and texture, and we delve into how rheology and soft tribology, with consideration for oral physiology and saliva, are providing new insights into texture, mouthfeel, taste, and aroma.
Designing Food Structures for Nutrition and Health Benefits
Authors: Norton Jennifer E. , Wallis Gareth A. , Spyropoulos Fotis , Lillford Peter J. , Norton Ian T.
Published: January 2014

In addition to providing specific sensory properties (e.g., flavor or textures), there is a need to produce foods that also provide functionality within the gastrointestinal (GI) tract, over and above simple nutrition. As such, there is a need to understand the physical and chemical processes occurring in the mouth, stomach, small intestine, and large intestine, in addition to the food structure-physiology interactions. In vivo techniques and in vitro models have allowed us to study and simulate these processes, which aids us in the design of food microstructures that can provide functionality within the human body. Furthermore, it is important to be aware of the health or nutritional needs of different groups of consumers when designing food structures, to provide targeted functionality. Examples of three groups of consumers (elderly, obese, and athletes) are given to demonstrate their differing nutritional requirements and the formulation engineering approaches that can be utilized to improve the health of these individuals. Eating is a pleasurable process, but foods of the future will be required to provide much more in terms of functionality for health and nutrition.
Nanodelivery of Bioactive Components for Food Applications: Types of Delivery Systems, Properties, and Their Effect on ADME Profiles and Toxicity of Nanoparticles
Authors: Borel T. , Sabliov C.M.
Published: January 2014

Food bioactives are known to prevent aging, cancer, and other diseases for an overall improved health of the consumer. Nanodelivery provides a means to control stability, solubility, and bioavailability, and also provides controlled release of food bioactives. There are two main types of nanodelivery systems, liquid and solid. Liquid nanodelivery systems include nanoemulsions, nanoliposomes, and nanopolymersomes. Solid nanodelivery systems include nanocrystals, lipid nanoparticles, and polymeric nanoparticles. Each type of nanodelivery system offers distinct benefits depending on the compatibility of nanoparticle properties with the properties of the bioactive and the desired application. Physicochemical properties of nanoparticles such as size, charge, hydrophobicity, and targeting molecules affect the absorption, distribution, metabolism, and excretion (ADME) of nanodelivery systems. The fate of the bioactive depends on its physicochemical properties and the location of its release. The safety of nanodelivery systems for use in food applications is largely unknown. Toxicological studies consisting of a combination of in silico, in vitro, and in vivo studies are needed to reveal the safety of nanodelivery systems for successful applications in food and agriculture.
Strategies to Mitigate Peanut Allergy: Production, Processing, Utilization, and Immunotherapy Considerations
Authors: White Brittany L. , Shi Xiaolei , Burk Caitlin M. , Kulis Michael , Burks A. Wesley , Sanders Timothy H. , Davis Jack P.
Published: January 2014

Peanut (Arachis hypogaea L.) is an important crop grown worldwide for food and edible oil. The surge of peanut allergy in the past 25 years has profoundly impacted both affected individuals and the peanut and related food industries. In response, several strategies to mitigate peanut allergy have emerged to reduce/eliminate the allergenicity of peanuts or to better treat peanut-allergic individuals. In this review, we give an overview of peanut allergy, with a focus on peanut proteins, including the impact of thermal processing on peanut protein structure and detection in food matrices. We discuss several strategies currently being investigated to mitigate peanut allergy, including genetic engineering, novel processing strategies, and immunotherapy in terms of mechanisms, recent research, and limitations. All strategies are discussed with considerations for both peanut-allergic individuals and the numerous industries/government agencies involved throughout peanut production and utilization.
γδT Cells: First Line of Defense and Beyond
Authors: Chien Yueh-hsiu , Meyer Christina , Bonneville Marc
Published: January 2014

γδ T cells, αβ T cells, and B cells are present together in all but the most primitive vertebrates, suggesting that each population contributes to host immune competence uniquely and that all three are necessary for maintaining immune competence. Functional and molecular analyses indicate that in infections, γδ T cells respond earlier than αβ T cells do and that they emerge late after pathogen numbers start to decline. Thus, these cells may be involved in both establishing and regulating the inflammatory response. Moreover, γδ T cells and αβ T cells are clearly distinct in their antigen recognition and activation requirements as well as in the development of their antigen-specific repertoire and effector function. These aspects allow γδ T cells to occupy unique temporal and functional niches in host immune defense. We review these and other advances in γδ T cell biology in the context of their being the major initial IL-17 producers in acute infection.
Health Promotion in Smaller Workplaces in the United States
Authors: Harris Jeffrey R. , Hannon Peggy A. , Beresford Shirley A.A. , Linnan Laura A. , McLellan Deborah L.
Published: January 2014

Most American workplaces are smaller, with fewer than 1,000 employees. Many of these employees are low-wage earners and at increased risk for chronic diseases. Owing to the challenges smaller workplaces face to offering health-promotion programs, their employees often lack access to health-promotion opportunities available at larger workplaces. Many smaller employers do not offer health insurance, which is currently the major funding vehicle for health-promotion services. They also have few health-promotion vendors to serve them and low internal capacity for, and commitment to, delivery of on-site programs. The programs they offer, whether aimed at health promotion alone or integrated with health protection, are rarely comprehensive and are understudied. Research priorities for health promotion in smaller workplaces include developing programs feasible for the smallest workplaces with fewer than 20 employees. Policy priorities include incentives for smaller workplaces to implement comprehensive programs and an ongoing system for monitoring and evaluation.
Analysis of Vibrating Timoshenko Beams Using the Method of Differential Quadrature
Authors: Laura P.A.A. , Gutierrez R.H.
Published: January 2014

The main advantages of the differential quadrature method are its inherent conceptual simplicity and the fact that easily programmable algorithmic expressions are obtained. It was developed by Bellman in the 1970s but only recently has been applied in the solution of technically important problems. Essentially, it consists of the approximate solution of the differential system by means of a polynomial–collocation approach at a finite number of points selected by the analyst. This article reports some numerical experiments on vibrating Timoshenko beams of nonuniform cross-section.
Adaptivity in Crashworthiness Calculations
Authors: Belytschko Ted , Lee Sang-Ho , Yeh I-Sheng , Lin Jerry I. , Tsay Chen-Shyh , Kennedy James M.
Published: January 2014

h-Adaptive finite element methods for nonlinear transient analysis by explicit time integration are described. Examples are given of adaptive calculations for simple components and prototype calculations for a full car model. h-Adaptivity offers substantial reductions in data preparation costs and improvements in accuracy.
Neural Networks in Mechanical System Simulation, Identification, and Assessment
Authors: Paez Thomas L.
Published: January 2014

Artificial neural networks (ANNs) have been used in the solution of a variety of mechanical system design, analysis, and control problems. This paper describes the ANNs that have been most frequently used in mechanical system applications. It also summarizes some of the applications that have been developed for ANNs, and briefly reviews the literature where descriptions of the developments and applications can be found. Some recommendations regarding ANN applications in mechanical system simulation, identification, and assessment are provided.
Scaling for Shock Response of Equipment in Different Submarines
Authors: O’Hara G.J. , Cunniff P.F.
Published: January 2014

This article presents scaling rules developed to predict the response of submarine equipment subjected to underwater chemical explosions. The computer was used as a surrogate for shock tests. A simplified model of a hull section was used to contain frame-mounted single degree of freedom equipment. A general scaling rule has been developed to handle the spread in the shock response attributable to the charge weight, equipment weight, and equipment frequency, where the shock response is the absolute maximum acceleration of the equipment mass as a function of the shock factor for a given charge weight. The article also examines those cases where a new hull is derived from an original hull by the linear scaling law. The solution of the shock response is well known when the internal equipment has also been linearly scaled. A new general scaling rule is developed for those cases when the equipment is not linearly scaled, that is, the equipment and charge weight used with the original hull remains unchanged when installed in the linearly scaled hull or a completely different equipment and charge weight are used with the new hull. It is emphasized that the test sections were short and devoid of typical equipment present in a real compartment. The results, nevertheless, provide trends and ratios in shock design values, not necessarily absolute design numbers. The approach taken in developing these scaling rules could be useful for enhancing field data that may exist for a given class of boat to allow greater usage of these data for different equipment subject to a variety of charge weights, attack geometries, and other boats.
Calibration of a Hopkinson Bar with a Transfer Standard
Authors: Bateman Vesta I. , Leisher William B. , Brown Fred A. , Davie Neil T.
Published: January 2014

A program requirement for field test temperatures that are beyond the test accelerometer operational limits of −30° F and +150° F required the calibration of accelerometers at high shock levels and at the temperature extremes of −50° F and +160° F. The purposes of these calibrations were to insure that the accelerometers operated at the field test temperatures and to provide an accelerometer sensitivity at each test temperature. Because there is no National Institute of Standards and Technology traceable calibration capability at shock levels of 5,000–15,000 g for the temperature extremes of −50° F and +160° F, a method for calibrating and certifying the Hopkinson bar with a transfer standard was developed. Time domain and frequency domain results are given that characterize the Hopkinson bar. The National Institute of Standards and Technology traceable accuracy for the standard accelerometer in shock is ±5%. The Hopkinson bar has been certified with an uncertainty of 6%.
Pseudo Wigner–Ville Time-Frequency Distribution and Its Application to Machinery Condition Monitoring
Authors: Shin Young S. , Jeon Jae-Jin
Published: January 2014

Machinery operating in a nonstationary mode generates a signature that at each instant of time has a distinct frequency. A Time-frequency domain representation is needed to characterize such a signature. Pseudo Wigner–Ville distribution is ideally suited for portraying a nonstationary signal in the time-frequency domain and is carried out by adapting the fast Fourier transform algorithm. The important parameters affecting the pseudo Wigner–Ville distribution are discussed and sensitivity analyses are also performed. Practical examples of an actual transient signal are used to illustrate its dynamic features jointly in time and frequency.
Dynamic Stiffness Analysis of Curved Thin-Walled Beams
Authors: Leung A.Y.T. , Zhou W.E.
Published: January 2014

The natural vibration problem of curved thin-walled beams is solved by the dynamic stiffness method. The dynamic stiffness of a curved open thin-walled beam is given. The computed natural frequencies of the beam are compared with those obtained by a completely analytical method to show the high accuracy of the present method. The interaction of in-plane and out-of-plane modes is emphasized.
Excitation of Arch and Suspension Bridges by Subwires
Authors: Hiwatashi Noriaki , Mizuta Yoji , Ishihara Yutaka , Hirai Itio
Published: January 2014

A force generation method using a subwire for arch and suspension bridges is proposed. The subwire is connected to the arch or the cable of the bridge through rollers. The uniform force produced by pulling and releasing the pretensioned subwires acts on the bridge as an externalforce. A new device called “the resonance force generator” is also developed to excite the bridges by applying a small force. To verify the proposed concept, a stress ribbon bridge was excited with the resonance force generator.
Sensitivity of Eigenvalues to Nonsymmetrical, Dissipative Control Matrices
Authors: Neubert Vernon H.
Published: January 2014

Dissipation of energy in vibrating structures can be accomplished with a combination of passive damping and active, constant gain, closed loop control forces. The matrix equations areMz¨+Cz˙+Kz=−Gz˙. With conventional viscous damping, the damping force is proportional to relative velocity, withFi=Ciiz˙i−Cijz˙j, where Cii=Cij but the subscripts show the position of the number in the C matrix. For a dashpot connected directly to ground,Fi=Ciiz˙i. Thus there is a definite pattern to the positions of numbers in the ith and jth rows of theCmatrix, that is, a positive number on the diagonal is paired with an equal negative number, or zero, off the diagonal. With the control matrixG, it is here assumed that the positioning of individual controllers and sensors is flexible, withFi=Ciiz˙iorFi=Cijz˙j, the latter meaning that the control force at i is proportional to the velocity sensed at j. Thus the problem addressed herein is how the individual elements in theGmatrix affect the modal eigenvalues. Two methods are discussed for finding the sensitivities, the classical method based on the products of eigenvectors and a new method, derived during the present study, involving the derivatives of the invariants in the similarity transformation. Examples are presented for the sensitivities of the complex eigenvalues of the formλr=−ζrwr+iwDrto individual elements in theGmatrix, to combinations of elements, and to a combination of passive damping and active control. Systems with two, three, and eight degrees of freedom are investigated.
Specification of Modal Participation Factors in Acoustic Scattering Problems
Authors: Ettouney M. , Daddazio R. , DiMaggio F.
Published: January 2014

Using the wet modes of a submerged structure as expansion functions, it is shown how the scattered far-field pressures induced by an incident harmonic wave may be modified in a prescribed manner. This is done by applying forces directly to the structural surface, which superposes a radiated pressure field on the scattered one. By appropriate choice of the applied nodal forces, modal participation factors associated with any combination of mode shapes may be controlled. The method is illustrated by a numerical example.
Spectral Techniques for Nonlinear System Analysis and Identification
Authors: Bendat Julius S.
Published: January 2014

This article reviews some recent and current research work with emphasis on new recommended spectral techniques that can analyze and identify the optimum linear and nonlinear system properties in a large class of single-input/single-output nonlinear models by using experimentally measured input/output random data. This is done by showing how to replace these nonlinear models with equivalent multiple-input/single-output linear models that are solvable by well-established practical procedures. The input random data can have probability density functions that are Gaussian or non-Gaussian with arbitrary spectral properties. Results in this article prove that serious errors can occur when conventional linear model analysis procedures are used to determine the physical properties of nonlinear systems.
Modeling Accuracy in FEA of Vibrations of a Drumhead
Authors: Melosh Robert J.
Published: January 2014

The study of the problem of predicting values of Rayleigh’s quotient for a square drumhead provides a basis for assessing the relation between grid size, accuracy of analysis results, and efficiency of data processing in finite element analysis. The analysis data indicate that unacceptable grid sampling can occur even for the fine grids, that strictly monotonic convergence is attainable for vibration analysis, and that more efficient computer analysis associates with use of curve fitting analysis of conventional finite element analysis results.
A Frequency Domain Method for the Generation of Partially Coherent Normal Stationary Time Domain Signals
Authors: Smallwood David O. , Paez Thomas L.
Published: January 2014

A procedure for generating vectors of time domain signals that are partially coherent in a prescribed manner is described. The procedure starts with the spectral density matrix,[Gxx(f)], that relates pairs of elements of the vector random process{X(t)},−∞<t<∞. The spectral density matrix is decomposed into the form[Gxx(f)]=[U(f)][S(f)][U(f)]'where[U(f)]is a matrix of complex frequency response functions, and[S(f)]is a diagonal matrix of real functions that can vary with frequency. The factors of the spectral density matrix,[U(f)]and[S(f)], are then used to generate a frame of random data in the frequency domain. The data is transformed into the time domain using an inverse FFT to generate a frame of data in the time domain. Successive frames of data are then windowed, overlapped, and added to form a vector of normal stationary sampled time histories,{X(t)}, of arbitrary length.
Motion of a Rigid Body Supported at One Point by a Rotating Arm
Authors: Stoen Jeffrey D. , Kane Thomas R.
Published: January 2014

This article details a scheme for evaluating the stability of motions of a system consisting of a rigid body connected at one point to a rotating arm. The nonlinear equations of motion for the system are formulated, and a method for finding exact solutions representing motions that resemble a state of rest is presented. The equations are then linearized and roots of the eigensystem are classified and used to construct stability diagrams that facilitate the assessment of effects of varying the body's mass properties and system geometry, changing the position of the attachment joint, and adding energy dissipation in the joint.
On Maximum Energy of Mechanical Systems Under Shock Disturbances
Authors: Balandin Dimitry V.
Published: January 2014

In this article, we develop a method for estimating the maximum energy of a mechanical system subjected to disturbances whose integral absolute value is bounded. The conditions for this estimate to be exact are found. The method is demonstrated by calculating the maximal displacement in a second-order nonlinear system.
Optimum Resolution Bandwidth for Spectral Analysis of Stationary Random Vibration Data
Authors: Piersol Allan G.
Published: January 2014

This article presents a methodology for selecting the frequency resolution bandwidth for the spectral analysis of stationary random vibration signals in an optimum manner. Specifically, the resolution bandwidth that will produce power spectral density estimates with a minimum mean square error is determined for any given measurement duration (averaging time), and methods of approximating the optimum bandwidth using practical spectral analysis procedures are detailed. The determination of the optimum resolution bandwidth requires an estimate for the damping ratio of the vibrating structure that produced the measured vibration signal and the analysis averaging time. It is shown that the optimum resolution bandwidth varies approximately with the 0.8 power of the damping ratio and the bandwidth center frequency, and the −0.2 power of the averaging time. Also, any resolution bandwidth within ±50% of the optimum bandwidth will produce power spectral density (PSD) estimates with an error that is no more than 25% above the minimum achievable error. If a damping ratio of about 5% for structural resonances is assumed, a constant percentage resolution bandwidth of 1/12 octave, but no less than 2.5 Hz, will provide a near optimum PSD analysis for an averaging time of 2 seconds over the frequency range from 20 to 2000 Hz. A simple scaling formula allows the determination of appropriate bandwidths for other damping ratios and averaging times.
A New Algorithm for the Coupled Soil–Pore Fluid Problem
Authors: Zienkiewicz O.C. , Huang Maosong , Wu Jie , Wu Shiming
Published: January 2014

Two new semiexplicit algorithms for the coupled soil–pore fluid problem are developed in this article. The stability of the new algorithms is much better than that of the previous algorithm. The first new scheme (H*-scheme) based on operator splitting before spatial discretization can avoid the restriction of mixed formulation in the incompressible (zero permeability) limit. The steady-state formulation is discussed to verify this argument. Several examples illustrate the article.
Derivation of Equations for Flexible Multibody Systems in Terms of Quasi-Coordinates from the Extended Hamilton’s Principle
Authors: Meirovitch L.
Published: January 2014

Early derivations of the equations of motion for single rigid bodies, single flexible bodies, and flexible multibody systems in terms of quasi-coordinates have been carried out in two stages. The first consists of the use of the extended Hamilton’s principle to derive standard Lagrange’s equations in terms of generalized coordinates and the second represents a transformation of the Lagrange’s equations to equations in terms of quasi-coordinates. In this article, hybrid (ordinary and partial) differential equations for flexible multibody systems are derived in terms of quasi-coordinates directly from the extended Hamilton's principle. The approach has beneficial implications in an eventual spatial discretization of the problem.
Finite Dynamic Elements and Modal Analysis
Authors: Fergusson N.J. , Pilkey W.D.
Published: January 2014

A general modal analysis scheme is derived for forced response that makes use of high accuracy modes computed by the dynamic element method. The new procedure differs from the usual modal analysis in that the modes are obtained from a power series expansion for the dynamic stiffness matrix that includes an extra dynamic correction term in addition to the static stiffness matrix and the consistent mass matrix based on static displacement. A cantilevered beam example is used to demonstrate the relative accuracies of the dynamic element and the traditional finite element methods.
An Improved Finite Difference Type Numerical Method for Structural Dynamic Analysis
Authors: Kim Sung-Hoon , Park Youn-sik
Published: January 2014

An improved finite difference type numerical method to solve partial differential equations for one-dimensional (1-D) structure is proposed. This numerical scheme is a kind of a single-step, second-order accurate and implicit method. The stability, consistency, and convergence are examined analytically with a second-order hyperbolic partial differential equation. Since the proposed numerical scheme automatically satisfies the natural boundary conditions and at the same time, all the partial differential terms at boundary points are directly interpretable to their physical meanings, the proposed numerical scheme has merits in computing 1-D structural dynamic motion over the existing finite difference numeric methods. Using a numerical example, the suggested method was proven to be more accurate and effective than the well-known central difference method. The only limitation of this method is that it is applicable to only 1-D structure.
Feasibility of a Transient Dynamic Design Analysis Method
Authors: Cunniff Patrick F. , O’Hara George J.
Published: January 2014

This article addresses the degree of success that may be achieved by using simple equipment–vehicle models that produce time history responses whose equipment fixed base modal maximum response values are equivalent to those found in the U.S. Navy's dynamic design analysis method. The criteria of success is measured by a comparison of the results with typical interim shock design values. The equipment models reported are limited to two- degree and three degrees of freedom systems; the model of the vehicle to which the equipment is attached consists solely of a rigid mass and an elastic spring; and the shock excitation is produced by an ideal impulse that is applied to the vehicle mass.
Exact and Direct Modeling Technique for Rotor-Bearing Systems with Arbitrary Selected Degrees-of-Freedom
Authors: Chen Shilin , Géradin Michel
Published: January 2014

An exact and direct modeling technique is proposed for modeling of rotor-bearing systems with arbitrary selected degrees-of-freedom. This technique is based on the combination of the transfer and dynamic stiffness matrices. The technique differs from the usual combination methods in that the global dynamic stiffness matrix for the system or the subsystem is obtained directly by rearranging the corresponding global transfer matrix. Therefore, the dimension of the global dynamic stiffness matrix is independent of the number of the elements or the substructures. In order to show the simplicity and efficiency of the method, two numerical examples are given.
Plastic Deformation and Rupture of Ring-Stiffened Cylinders under Localized Pressure Pulse Loading
Authors: Fatt Michelle S. Hoo
Published: January 2014

An analytical solution for the dynamic plastic deformation of a ring-stiffened cylindrical shell subject to high intensity pressure pulse loading is presented. By using an analogy between a cylindrical shell that undergoes large plastic deformation and a rigid-plastic string resting on a rigid-plastic foundation, one derives closed-form solutions for the transient and final deflection profiles and fracture initiation of the shell. Discrete masses' and springs are used to describe the ring stiffeners in the stiffened shell. The problem of finding the transient deflection profile of the central bay is reduced to solving an inhomogeneous wave equation with inhomogeneous boundary conditions using the method of eigenfunction expansion. The overall deflection profile consists of both global (stiffener) and local (bay) components. This division of the shell deflection profile reveals a complex interplay between the motions of the stiffener and the bay. Furthermore, a parametric study on a ring-stiffened shell damaged by a succession of underwater explosions shows that the string-on-foundation model with ring stiffeners described by lumped masses and springs is a promising method of analyzing the structure.
Two Visually Meaningful Correlation Measures for Comparing Calculated and Measured Response Histories
Authors: Whang Benjamin , Gilbert William E. , Zilliacus Stephen
Published: January 2014

Two visually meaningful correlation measures are proposed for comparing calculated and measured response histories. One is an error index which is a simplification of RSS (root-sum-square) error factor, and the other is an inequality index that is a simplification of Theil’s inequality coefficient. The first compares the difference between the calculated and the measured histories to the measured history. The second compares the difference between the two histories to the sum of the two. The proposed correlation measures are compared to other existing measures, namely, Geers’ Error Factors, RSS Error Factor, and Theil's Inequality Coefficient for ease of interpretation and visualization.
Metallurgical Investigation of HSLA Steel Subjected to Underwater Explosion
Authors: Rao V. Bhujanga , Rajendran R. , Jaykumar A.V. , Satyanarayana K.H.B.S.
Published: January 2014

The metallurgical behaviour of HSLA steel subjected to underwater explosion is of prime importance because of its structural applications in underwater vehicles. HSLA steel plates 300 × 250 × 4 mm were subjected to single and repetitive shock loadings and the point of rupture was identified. Test plates exhibited mode-I (large ductile deformation) and mode-II (tensile tearing) macroscopic failures. Electron micrographic and fractographic examination showed that the initiation of fracture was due to adiabatic shearing and the microscopic mode of failure was ductile. Plates subjected to single shock showed an increase in residual hardness and at the point of rupture it was approximately one-third higher than the initial residual hardness.
Head Injury Reduction in Automobile Pedestrian Impact
Authors: Lemmon David R. , Wu Ming-yi , Huston Ronald L.
Published: January 2014

This article presents and discusses automobile hood/fender rail design to reduce head injury of pedestrians struck by the front of the vehicle. Fender seam designs are presented that reduce the head injury criterion values by over 50%. The procedures and analysis are conducted using a nonlinear dynamic finite element program for an Oldsmobile Ciera hood and a Ford Taurus hood/fender.
Nonlinear Vibrations of Thin-Walled Composite Frames
Authors: Noor Ahmed K. , Peters Jeanne M.
Published: January 2014

A reduced basis technique and a computational procedure are presented for generating the nonlinear vibrational response, and evaluating the first-order sensitivity coefficients of thin-walled composite frames. The sensitivity coefficients are the derivatives of the nonlinear frequency with respect to the material and lamination parameters of the frame. A mixed formulation is used with the fundamental unknowns consisting of both the generalized displacements and stress resultants in the frame. The flanges and webs of the frames are modeled by using geometrically nonlinear two-dimensional shell and plate finite elements. The computational procedure can be conveniently divided into three distinct steps. The first step involves the generation of various-order perturbation vectors, and their derivatives with respect to the material and lamination parameters of the frame, using the Linstedt–Poincaré perturbation technique. The second step consists of using the perturbation vectors as basis vectors, computing the amplitudes of these vectors and the nonlinear frequency of vibration, via a direct variational procedure. The third step consists of using the perturbation vectors, and their derivatives, as basis vectors and computing the sensitivity coefficients of the nonlinear frequency via a second application of the direct variational procedure. Numerical results are presented for semicircular thin-walled frames with I and J sections, showing the convergence of the nonlinear frequency and the sensitivity coefficients obtained by both the reduced-basis and perturbation techniques.