bluuebunny/crossref_metadata_2025_split huggingface dataset:
Noise Reduction Evaluation of Multi‐Layered Viscoelastic Infinite Cylinder under Acoustical Wave Excitation
Authors: Mofakhami M.R. , Toudeshky H. Hosseini , Hashemi Sh. Hosseini 
Published: January 2014

In this paper sound transmission through the multilayered viscoelastic air filled cylinders subjected to the incident acoustic wave is studied using the technique of separation of variables on the basis of linear three dimensional theory of elasticity. The effect of interior acoustic medium on the mode maps (frequency vs geometry) and noise reduction is investigated. The effects of internal absorption and external moving medium on noise reduction are also evaluated. The dynamic viscoelastic properties of the structure are rigorously taken into account with a power law technique that models the viscoelastic damping of the cylinder. A parametric study is also performed for the two layered infinite cylinders to obtain the effect of viscoelastic layer characteristics such as thickness, material type and frequency dependency of viscoelastic properties on the noise reduction. It is shown that using constant and frequency dependent viscoelastic material with high loss factor leads to the uniform noise reduction in the frequency domain. It is also shown that the noise reduction obtained for constant viscoelastic material property is subjected to some errors in the low frequency range with respect to those obtained for the frequency dependent viscoelastic material.Noise reduction analyses are also performed for the infinite cylinder subjected to the periodic incident wave with uniform and piecewise form.
Reliability Analysis of Electronic Equipment Subjected to Shock and Vibration – A Review
Authors: Amy Robin Alastair , Aglietti Guglielmo S. , Richardson Guy 
Published: January 2014

Increasingly modern electronic equipment is expected to provide more functionality whilst still being able to withstand shock and vibration loads. The process of reliability prediction has been hampered by the complicated response and failure characteristics of electronic equipment, with the currently available methods being a compromise between accuracy and cost. A process to quickly and confidently predict the reliability of proposed electronic equipment to dynamic loads would greatly benefit industry.This paper will illustrate the difficulties in predicting electronic equipment reliability, showing why progress has been slow, in addition to the difficulty in making a model that works across a broad range of equipment configurations. The four classes of reliability prediction methods (Handbook, Test data, Field data and Physics of Failure) will be contrasted before addressing the individual methods.It is pertinent to note that although the majority of failures in electronic equipment are due to thermal issues, this review focuses on shock and vibration induced failures.
Hybrid Secondary Suspension Systems
Authors: Vahdati Nader , Ahmadian Mehdi 
Published: January 2014

Passive fluid mounts are used in the fixed wing applications as engine mounts. The passive fluid mount is placed in between the engine and the fuselage to reduce the cabin's structure- borne noise and vibration generated by the engine.To investigate the benefits of passive fluid mounts used in conjunction with tuned vibration absorbers (TVA), a simple mathematical model is developed. This mathematical model includes the mathematical model of a passive fluid mount, a TVA, and a spring representing the fuselage structure. The simulation results indicate that when passive fluid mounts are used in conjunction with TVAs, an active suspension system behavior is nearly created.
Identification Methods and Test Results for Tilting Pad and Fixed Geometry Journal Bearing Dynamic Coefficients – A Review
Authors: Dimond T.W. , Sheth P.N. , Allaire P.E. , He M. 
Published: January 2014

Fluid film journal bearings (FFBs) are used to support high-speed rotors in turbomachinery which often operate above the rotor first bending critical speed. The FFBs provide both lateral support and dynamic coefficients: stiffness, damping, and mass terms, related to machine vibrations. Detailed numerical values of the bearing dynamic characteristics are necessary for proper design and operation of rotating machinery.The methods of the identification of fluid film journal bearing static and dynamic characteristics, particularly the bearing stiffness, damping, and mass coefficients, from measured data, obtained from different measurement systems, is reviewed. Many bearing tests have been performed to validate a number of different theoretical models, including the classical Reynolds isoviscous model. More advanced bearing models include the thermohydrodynamic (THD), and thermoelastohydrodynamic (TEHD) approaches. The advanced models also include turbulence effects which are important as rotor speeds continue to increase. The range of measured bearing data no longer includes current operational conditions.The various approaches to the bearing identification problem are discussed, including the different force excitation methods of incremental loading, sinusoidal, pseudorandom, impulse, known/additional unbalance, and non-contact excitation. Also bearing excitation and rotor excitation approaches are discussed. Data processing methods in the time and frequency domains are presented. Methods of evaluating the effects of measurement uncertainty on overall bearing coefficient confidence levels are reviewed.In this review, the relative strengths and weaknesses of bearing identification methods are presented, and developments and trends in improving bearing measurements are documented. Future trends in journal bearing identification improvement are discussed.
The NIHSS-Plus: Improving Cognitive Assessment with the NIHSS
Authors: Gottesman Rebecca F. , Kleinman Jonathan T. , Davis Cameron , Heidler-Gary Jennifer , Newhart Melissa , Hillis Argye E. 
Published: January 2014

Background:The National Institutes of Health Stroke Scale (NIHSS) has been criticized for limited representation of cognitive dysfunction and bias towards dominant hemisphere functions. Patients may therefore receive a low NIHSS score despite a fairly large stroke. A broader scale including simple cognitive tests would improve the clinical and research utility of the NIHSS.Methods:We studied 200 patients with acute non-dominant hemispheric stroke who underwent cognitive testing and had MRI with diffusion-weighted imaging (DWI) within 5 days of presentation. We measured DWI volumes and retrospectively calculated NIHSS scores. We used linear regression to determine the role of selected cognitive tests, when added to the NIHSS, in predicting DWI volume.Results:The NIHSS predicted DWI volume in a univariate analysis, as did total line cancellation and a visual perception task. In a multivariate model, using log-transformed variables, the NIHSS (p= 0.0002), line cancellation errors (p= 0.02) and visual perception (p= 0.004) each improved prediction of total infarct volume.Conclusion:The addition of line cancellation and visual perception tasks significantly adds to the model of NIHSS alone in predicting DWI volume. We propose that these two cognitive tests, which together can be completed in 2–3 minutes, could be combined with the NIHSS to create an “NIHSS-plus” that more accurately represents a patient’s ischemic tissue volume after a stroke. This scale requires further validation in a prospective study.
Prospective Memory in Patients with Severe Closed-Head Injury: Role of Concurrent Activity and Encoding Instructions
Authors: Carlesimo Giovanni A. , Formisano Rita , Bivona Umberto , Barba Lina , Caltagirone Carlo 
Published: January 2014

Objectives:To assess the sensitivity of patients who suffered a severe closed-head injury to the manipulation of attentional resources and encoding instructions during the execution of prospective memory tasks.Material and Methods:A group of patients with chronic sequelae of severe closed-head injury and a group of matched normal controls were given an experimental procedure for the assessment of time-based and event-based prospective memory. Availability of attentional resources at the time of intention recall and encoding conditions at the time of giving instructions were varied across experimental sessions.Results:The simultaneous execution of a concurrent task was more detrimental to accuracy in the spontaneous recall of the prospective intention in the post-traumatic than in the normal control group. Moreover, the instruction to encode more extensively by rehearsing aloud and mentally imaging the actions to be performed at the time of the study improved recall accuracy more in the post-traumatic than in the normal control group.Conclusions:Based on these data, we suggest that a prospective memory deficit in post-traumatic patients is due, among other things, to reduced availability of attentional resources and to poor encoding of actions to be performed.
Prediction of Modal Parameters of Linear Time-Varying Systems
Authors: Marchesiello S. , Bellino A. , Garibaldi L. 
Published: January 2014

Many engineering structures, such as cranes, traffic-excited bridges, flexible mechanisms and robotic devices exhibit characteristics that vary with time and are referred to as time-varying or nonstationary. In particular, linear time-varying (LTV) systems have been often dealt with on a case-by-case basis. Many concepts and analytic methods of linear time-invariant (LTI) systems cannot be applied to LTV systems, as for example the conventional definition of modal parameters. In fact, LTV systems violate one of the assumptions of the conventional modal analysis, which is stationarity.Subspace-based identification methods, proposed in the 1970s, have been attracting much attention due to their affinity to the modern control theory, which is based on the state space model. These methods are now successfully applied to many industrial cases and may be considered reference methods for identifying LTI systems.In this paper the use of a subspace-based method for identifying LTV systems is discussed and applied to both numerical and experimental systems. More precisely a modified version of the SSI method, referred to here as ST-SSI (Short Time Stochastic Subspace Identification) is introduced as well as a method for predicting time-varying stochastic systems using the angle variation between the subspaces; the latter is able to predict the system parameter in the “near” future.
Wavelet Approach for Vibration Analysis of Fast Moving Load on a Viscoelastic Medium
Authors: Koziol Piotr , Mares Cristinel 
Published: January 2014

This paper analyses theoretically the response of a solid for fast moving trains using models related to real situations: a load moving in a tunnel and a load moving on a surface. The mathematical model is described by Navier's elastodynamic equation of motion for the soil and Euler-Bernoulli equation for the beam with appropriate boundary conditions. Two modelling approaches are investigated: the model with half space under the beam and the model with finite thickness of supporting medium. The problem of singularities for displacements calculation is discussed in relation with boundary conditions and types of considered loads: harmonic and constant, point and distributed moving loads. The analysis in frequency-time and frequency-velocity domains is presented and discussed with regard to critical velocities.A wavelet approximation method based on application of coiflet filters is used for the derivation of displacements in physical domain. A new, modified filter is used in numerical calculations allowing to alleviate numerical difficulties related to the form of approximating sequences based on classical filters, formulated in previous publications. The effectiveness of the coiflet approach is discussed for filter coefficients with different order of accuracy. This methodology is very efficient for the analysis in the range of relatively high and low load frequencies (treated as an approximation of a constant load) which are especially important for the analysis of vibrations generated by trains moving with velocities near critical values.Results of numerical simulations are presented, demonstrating their utility for modelling and preliminary analysis of complex models.
Analytical Stationary Acoustic Wave in a Liquid over Which a Moving Pressure Runs
Authors: Langlet André , Renard Jérôme , Pennetier Olivier 
Published: January 2014

This paper presents an analytical study of the stationary response of a liquid loaded on its free surface by an ideal pressure step moving in a constant direction at a constant velocity. The acoustic pressure in the liquid is found, in four different examples, by means of the Fourier Transform. Two loading regimes are considered; subsonic and supersonic. Two configurations of liquid domains are also studied, the first one is a half infinite space while the second one is bounded by a rigid bottom at a finite depth. For the two supersonic cases, a simple reasoning based on the existence of a front of discontinuity in the liquid and on the property of reflection of waves confirms the result of the mathematical investigations. The results obtained for the steady state case are of intererest, even when the loading is not exactly stationary, such as the presure produced by an explosion occurring in the vicinity of the surface of a liquid. Two numerically resolved examples are presented, which confirm this assumption.For the two supersonic cases, a simple reasoning based on the existence of a front of discontinuity in the liquid and on the property of reflection of waves confirms the result of the mathematical investigations.The results obtained for the steady state case are of intererest, even when the loading is not exactly stationary, such as the presure produced by an explosion occurring in the vicinity of the surface of a liquid. Two numerically resolved examples are presented, which confirm this assumption.
A Study on the Hybrid Mount against Vibration and Shock for Naval Ships
Authors: Moon Seok-Jun , Kwak Jeong-Seok , Chung Jung-Hoon , Ji Yong-Jin , Yoon Jeong-Sik , Choi Seung-Bok , Lee Hyun-Yup , Jung Woo-Jin , Ki Dock-Jong 
Published: January 2014

In naval ships, some methods or devices are acquired both to cut off the transmission of vibration from shipboard machineries and to protect them from external shock loading. One of the approaches is to install the passive mountings between machinery and a flexible supporting structure. More advanced performance has become necessary recently so far as at high frequencies in order to retain the stealth function of certain types of naval vessels.For the purpose of this research, a novel hybrid mount for shipboard machinery installed on naval ships was developed. The mount is combined with a rubber mount and piezostack actuators. The rubber mount is one of the most popular and effective passive mounts to have been applied to various vibration systems to date. The piezostack actuator is featured by a fast response time, small displacement and low power consumption. Through a series of experimental tests conducted in accordance with MIL-M-17185A(SHIPS), MIL-M-17508F(SH), and MIL-S-901D which are US military specifications related to the performance requirements of the mount, it has been confirmed that the hybrid mount shows more effective performance for use in naval ships.
A Case Study of Analysis of Natural Frequency Variability Related to Manufacturing Process
Authors: Uhl T. , Lisowski W. 
Published: January 2014

One of the important challenges present nowadays in the automotive industry is minimizing of a car components design time. Traditional manufacturing of a prototype is usually a time and a cost consuming process. Alternatively, rapid prototyping techniques can be used in such a case. In the reported research a brake caliper was investigated, since it is an example of an element, which should have very strictly defined structural dynamic properties. As a technique of rapid prototyping of the considered caliper the 3D printing of a mould was selected. A process of the caliper casting with the use of the "prototype" mould is different than the one with the use of the metal form. Thus it is very likely that the both considered types of the caliper would possess different properties from the point of view of structural dynamics.Structural dynamic properties can be analyzed both numerically and experimentally. Simulation of the caliper FE model with uncertain parameters was used to analyze influence of various caliper parameters on its natural frequency values. Modal testing of the caliper was performed with the aim of investigation of applicability of Experimental Modal Analysis for determination of variability of natural frequencies resulting from the manufacturing process. In the course of this research, the natural frequencies of the prototype caliper and the standard caliper were compared.
Association between Hypotension, Low Ejection Fraction and Cognitive Performance in Cardiac Patients
Authors: Gottesman Rebecca F. , Grega Maura A. , Bailey Maryanne M. , Zeger Scott L. , Baumgartner William A. , McKhann Guy M. , Selnes Ola A. 
Published: January 2014

Background and Purpose:Impaired cardiac function can adversely affect the brain via decreased perfusion. The purpose of this study was to determine if cardiac ejection fraction (EF) is associated with cognitive performance, and whether this is modified by low blood pressure.Methods:Neuropsychological testing evaluating multiple cognitive domains, measurement of mean arterial pressure (MAP), and measurement of EF were performed in 234 individuals with coronary artery disease. The association between level of EF and performance within each cognitive domain was explored, as was the interaction between low MAP and EF.Results:Adjusted global cognitive performance, as well as performance in visuoconstruction and motor speed, was significantly directly associated with cardiac EF. This relationship was not entirely linear, with a steeper association between EF and cognition at lower levels of EF than at higher levels. Patients with low EF and low MAP at the time of testing had worse cognitive performance than either of these alone, particularly for the global and motor speed cognitive scores.Conclusions:Low EF may be associated with worse cognitive performance, particularly among individuals with low MAP and for cognitive domains typically associated with vascular cognitive impairment. Further care should be paid to hypotension in the setting of heart failure, as this may exacerbate cerebral hypoperfusion.
Does Diabetes Mellitus Alter the Onset and Clinical Course of Vascular Dementia?
Authors: Murthy Santosh B. , Jawaid Ali , Qureshi Salah U. , Kalkonde Yogeshwar , Wilson Andrew M. , Johnson Michael L. , Kunik Mark E. , Schulz Paul E. 
Published: January 2014

Background:Vascular dementia (VaD) is the second most common dementing illness. Multiple risk factors are associated with VaD, but the individual contribution of each to disease onset and progression is unclear. We examined the relationship between diabetes mellitus type 2 (DM) and the clinical variables of VaD.Methods:Data from 593 patients evaluated between June, 2003 and June, 2008 for cognitive impairment were prospectively entered into a database. We retrospectively reviewed the charts of 63 patients who fit the NINDSAIREN criteria for VaD. The patients were divided into those with DM (VaDDM, n = 29) and those without DM(VaD,n= 34). The groups were compared with regard to multiple variables.Results:Patients with DM had a significantly earlier onset of VaD (71.9 ± 6.54 vs. 77.2 ± 6.03,p< 0.001), a faster rate of decline per year on the mini mental state examination (MMSE; 3.60 ± 1.82 vs. 2.54 ± 1.60 points,p= 0.02), and a greater prevalence of neuropsychiatric symptoms at the time of diagnosis (62% vs. 21%,p= 0.02).Conclusions:A history of premorbid DM was associated with an earlier onset and faster cognitive deterioration in VaD. Moreover, DM was associated with neuropsychiatric symptoms in patients with VaD. A larger study is needed to verify these associations. It will be important to investigate whether better glycemic control will mitigate the potential effects of DM on VaD.
Eigenpath Following for Systems with Symmetric Complex-Valued Stiffness Matrices
Authors: Miller U. , Bograd S. , Schmidt A. , Gaul L. 
Published: January 2014

A vibration analysis of a structure with joints is performed. The simulation is conducted with finite element software capable of performing a numeric modal analysis with hysteretic damping assumption. The joints are modeled with thin layer elements, representing dissipation and stiffness of the joints. The matrices describing the system consist of the mass, as well as real and complex-valued stiffness matrices. If the eigenvalues of this system are found in one step, due to the mode crossing occurring for the closely spaced modes, it is difficult and time consuming to assign calculated modal damping factors to the corresponding undamped eigenvalues. In order to avoid this problem, an eigenvalue following method is used. The outcome of the solution is the graphical presentation of continuous eigenvalue paths, showing the change in the eigenvalues from the undamped to the fully damped case. For every undamped eigenvalue exists its equivalent eigenfrequency and damping factor that can be used for further numerical analysis.In scope of this article a Predictor-Corrector and a Rayleigh-Quotient Iteration algorithms are applied to the problem. The algorithms are tested specifically on the type of matrices resulting from the weakly damped hysteretic formulation arising from the simulation of metallic structures with joints.
Cognitive Impairment in Patients with Pseudotumor Cerebri Syndrome
Authors: Kharkar Siddharth , hernandez Robert , Batra Sachin , Metellus Philippe , Hillis Argye , Williams Michael A. , Rigamonti Daniele 
Published: January 2014

Introduction:Patients with Pseudotumor Cerebri Syndrome (PTCS) may complain of difficulty in thinking or concentrating; however there has been little formal cognitive evaluation in this population.Objective:To evaluate the characteristics and nature of cognitive impairment in patients with PTCS.Methods:We retrospectively reviewed records of 10 patients diagnosed with PTCS who were cognitively tested at presentation. In each cognitive test, “Borderline deficit” (BD) was defined as a score more than 1 standard deviation (SD) below and “Definite Deficit” (DD) as a score more than 2 SD below the mean for age, sex and education. In each cognitive domain, impairment was defined as a single test score more than 2 SD below the mean, or scores of more than 1 SD below the mean for age, sex and education in > 50% of tests.Results:Mean age of patients was 43.4 ± 13.5 years. 8/10(80%) patients were female. 3/10(30%) had papilledema; 3/10(30%) had significant cerebral venous outflow obstruction. Impairment was most commonly seen and was most severe in the WMS logical memory I (BD44%, DD44%), WMS logical memory II (BD37.5%, DD50%), RAVLT delayed recall (BD30%, DD40%) and RAVLT retention(BD40%, DD30%) tests. Evaluation of cognitive domains revealed impairment in memory and learning (80%), executive function (10%), visuospatial skills (30%), and language (30%).Conclusion:Our results indicate that patients with PTCS can have significant cognitive impairment, particularly in learning and memory. The prevalence needs to be studied in a larger cohort. The relationship of cognitive impairment with chronically elevated intracranial pressures and its role in contributing to patient morbidity needs to be investigated further.