bluuebunny/crossref_metadata_2025 huggingface dataset:
SPATIAL DISTRIBUTION OF POPULATION OF LISTERIA MONOCYTOGENES DURING MANUFACTURING AND RIPENING OF CAMEMBERT CHEESE
Authors: LIU S. , PURI V.M. , DEMIRCI A.
Published: January 2007

The spatial distribution of the survival and growth of Listeria monocytogenes during manufacturing and ripening of Camembert cheese was studied. All cheeses were artificially inoculated with L. monocytogenes and ripened in three stages: room temperature (∼20C) and relative humidity (RH) of 60% for 36 h, 13C and RH of 93% for 2 weeks, and 7C and RH of 85% for 3 weeks. During ripening, different locations were analyzed for population of L. monocytogenes. The data were collected on days 1, 5, 10, 15, 20, 25, 30 and 35 of ripening. Results showed that the population of L. monocytogenes on day 1 was 6.06 log10 cfu/g, which was 1.96 log10 cfu/g increasing over the initial inoculation of 4.08 log10 cfu/g. For the subsequent 20 days, the L. monocytogenes population declined to 5.33 log10 cfu/g. Thereafter, the L. monocytogenes population increased to 6.07 log10 cfu/g on day 35 of ripening. Generally, the growth of L. monocytogenes is faster in locations near the surface than in the center. There were no significant differences between batches and sections of cheese, whereas the ripening time and locations had a significant effect on the survival and growth of L. monocytogenes. The survival and growth data for L. monocytogenes during ripening of Camembert cheese can be used to develop dynamic predictive models for possible use in risk assessment and Hazard Analysis and Critical Control Point implementation.
DETECTION OF CENTRAL NERVOUS SYSTEM TISSUES AS BOVINE SPONGIFORM ENCEPHALOPATHY SPECIFIED RISK MATERIAL IN PROCESSED AND RAW MEAT PRODUCTS IN TURKEY
Authors: KALE M. , KURŞUN Ö. , PEHLİVANOĞLU F.
Published: January 2007

Spinal cord and brain tissues have the highest importance in the transfer of bovine spongiform encephalopathy to humans. The European Union issued the complete removal of spinal cord and brain tissues from meat products. In Turkey, regulation on meat products is applied by government veterinarians. But there are some questions on the effective application of the regulation, especially in some private slaughterhouses. This study was designed to reveal the mixing of these tissues to meat products sold in the Akdeniz region of Turkey. For this purpose, a total of 471 meat product samples were tested. Two semiquantitative enzyme‐linked immunosorbent assay kits (Ridascreen Risk Material and Risk Material 10/5 [R‐biofarm GmbH, Darmstadt, Germany]), which detect glial fibrillary acidic protein as marker, were used. In the tests, standard controls 0, 0.2, 1.0 and 2.0%, and 0, 0.1, 0.2 and 0.5% were practiced, respectively. Of the 220 processed meat sampled, 33 samples (15.0%) gave an optical density (OD) equal to or higher than standard 0.2%. Of the 251 raw meat sampled, 54 samples (21.51%) gave an OD equal to or higher than standard 0.1%. It was concluded that mixing of central nervous system tissue to the meat products still happens, and more effective control measurements need to be developed and applied in Turkey.
HYGIENIC PRACTICES BY VENDORS OF THE STREET FOOD “DOUBLES” AND PUBLIC PERCEPTION OF VENDING PRACTICES IN TRINIDAD, WEST INDIES
Authors: BENNY‐OLLIVIERRA CHANDRA , BADRIE NEELA
Published: January 2007

This study investigated the hygienic practices by vendors of street food “doubles” and the public perception of these practices. Doubles is an East Indian‐originated food comprised of two “baras” with a filling of curried “channa”/chickpea (Cicer arietinum). A structured questionnaire was administered to 120 street vendors and 115 public members in Trinidad, West Indies. Most vendors are male (61.7%), had been vending for 5 years (81.7%) and received primary level of education (72.5%). Preparation of doubles was mainly by family (84.2%) in the morning of vending (81.7%). Vendors were appropriately dressed (99.2%), used forks/spoons (100%) and tongs (81.7%) for serving. At vending sites, containers with faucets supplied water (85.7%) and toilets were not close (97.5%). Most respondents (86.1%) consumed doubles. Some (30.6%) felt ill from eating doubles, but only 2.7% reported to a medical doctor/health authority. Significant associations were found for vending practices and sanitation of vending environment.
FATE OF AFLATOXIN M1 IN KASHAR CHEESE
Authors: ORUC H. HUSEYIN , CIBIK RECEP , YILMAZ ENGIN , GUNES ERTAN
Published: January 2007

The distribution and stability of aflatoxin M1 (AFM1) in Kashar cheese were investigated. Raw milk samples were spiked with AFM1 at the levels of 50, 250 and 750 ng/L. Distribution of toxin in milk, cheese curd, whey, kneading brine and cheese, and its stability during ripening were determined by high‐performance liquid chromatography. Concentrations of AFM1 in curds for each contamination level were 2.93, 3.19 and 3.37 times higher than those in milk. After syneresis, the percentage distribution of AFM1 was 40–46% in curds and 53–58% in whey indicating that relatively higher concentration of toxin passed to whey. Moreover, by the kneading process approximately 2–5% of AFM1 passed to kneading brine. Compared to the initial spiking level, the percentage of toxin in cheeses varied between 35–42%. Over a 60‐day storage period, there was no decrease in the concentration of AFM1, suggesting that the toxin was stable during ripening.
ANTIFUNGAL ACTIVITIES OF THYME, CLOVE AND OREGANO ESSENTIAL OILS
Authors: VIUDA‐MARTOS M. , RUIZ‐NAVAJAS Y. , FERNÁNDEZ‐LÓPEZ J. , PÉREZ‐ÁLVAREZ J.A.
Published: January 2007

The antifungal potential of essential oils of oregano (Origanum vulgare), thyme (Thymus vulgaris) and clove (Syzygium aromaticum) was determined. To establish this antifungal potential, two molds related to food spoilage, Aspergillus niger and Aspergillus flavus, were selected. The agar dilution method was employed for the determination of antifungal activities. The three essential oils analyzed presented inhibitory effects on both molds tested. Oregano essential oil showed the highest inhibition of mold growth, followed by clove and thyme. Aspergillus flavus was more sensitive to thyme essential oil than A. niger. Clove essential oil was a stronger inhibitor against A. niger than against A. flavus.
DO CUSTOMER COMPLAINTS PREDICT POOR RESTAURANT INSPECTION SCORES? THE EXPERIENCE IN ALEXANDRIA, VIRGINIA, 2004–2005
Authors: GOODIN AMANDA KATE , KLONTZ KARL C.
Published: January 2007

Routine inspections of retail food service facilities by public health authorities serve as a major method of ensuring food sanitation. The objectives were to determine whether customer complaints received by restaurants in Alexandria, VA, during 2004 predicted the number of critical violations issued on subsequent food safety inspections. Using a retrospective cohort study design, we defined “exposed” restaurants as those that received ≥1 complaints from January 1 to December 31 of 2004 and “unexposed” restaurants as those that received none. We then counted the number of critical violations cited on food safety inspections conducted immediately after receipt of customer complaints (exposed restaurants) or on the first inspection conducted in 2005 (unexposed restaurants). A total of 144 exposed and 233 unexposed restaurants were enrolled in the study. Compared with unexposed restaurants, exposed restaurants were less likely to have received one or more critical violations (relative risk = 0.84, 95% confidence interval of 0.74–0.96, P = 0.01). Restaurant inspections conducted specifically in response to customer complaints may not identify critical violations any more often than inspections conducted at restaurants free from such complaints.
Presidential Address: Go to the Principal's Office: Toward a Social History of the School Principal in North America
Authors: Rousmaniere Kate
Published: January 2007

Of the many organizational changes that took place in public education in North America at the turn of the last century, few had greater impact on the school than the development of the principal. The creation of the principal's office revolutionized the internal organization of the school from a group of students supervised by one teacher to a collection of teachers managed by one administrator. In its very conception, the appointment of a school-based administrator who was authorized to supervise other teachers significantly restructured power relations in schools, realigning the source of authority from the classroom to the principal's office. Just as significant was the role that the principal played as a school based representative of the central educational office.
The Choctaw Nation: Changing the Appearance of American Higher Education, 1830-1907
Authors: Crum Steven
Published: January 2007

In September 1830 the U.S. government negotiated the Treaty of Dancing Rabbit Creek with some leaders of the Choctaw Nation. The treaty reinforced the congressional Indian Removal Act of 1830, which paved the way for the large-scale physical removal of tens of thousands of tribal people of the southeast, including many of the Choctaw. It provided for the “removal” of the Choctaw from their traditional homeland in Mississippi to Indian Territory. Over a two-year period, from 1831 to 1833, roughly thirteen thousand to fifteen thousand Choctaw, or about half of the tribe, moved to the region we now call southeastern Oklahoma
Education and Marginality: Race and Gender in Higher Education, 1940–1955
Authors: Crocco Margaret Smith , Waite Catty L.
Published: January 2007

Whether it be my religion, my aesthetic taste, my economic opportunity, my educational desire, whatever the craving is, I find a limitation because I suffer from the greatest known handicap, a Negro — a Negro woman. (Mary McLeod Bethune, “Closed Doors,” 1936).
Component Mode Synthesis of a Vehicle System Model Using the Fictitious Mass Method
Authors: Karpel M. , Moulin B. , Feldgun V.
Published: January 2007

A new procedure for dynamic analysis of complex structures, based on the fictitious-mass component mode synthesis method, is presented. Normal modes of separate components are calculated by finite-element analysis with the interface coordinates loaded with fictitious masses that generate local boundary deformations in the low-frequency modes. The original fictitious-mass method is extended to include three types of component interconnections: displacement constraints, connection elements, and structural links. The connection elements allow the introduction of springs and dampers between the interface points without adding structural degrees of freedom. The structural links facilitate the inclusion the discrete finite-element representation of typically small components in the coupling equations. This allows a convenient treatment of loose elements and the introduction of nonlinear effects and parametric studies in subsequent analyses. The new procedure is demonstrated with the structural model of a typical vehicle with four major substructures and a relatively large number of interface coordinates. High accuracy is obtained in calculating the natural frequencies and modes of the assembled structure and the separate components with the fictitious masses removed. Dynamic response analysis of the vehicle travelling over a rough road, performed by modal coupling, is in excellent agreement with that performed for the full model.
Towards Rapid Redesign: Pattern-based Redesign Planning for Large-Scale and Complex Redesign Problems
Authors: Li Simon , Chen Li
Published: January 2007

We have developed a decomposition-based rapid redesign methodology for large and complex computational redesign problems. While the overall methodology consists of two general steps: diagnosis and repair, in this paper we focus on the repair step in which decomposition patterns are utilized for redesign planning. Resulting from design diagnosis, a typical decomposition pattern solution to a given redesign problem indicates the portions of the design model necessary for recomputation as well as the interaction part within the model accountable for design change propagation. Following this, in this paper we suggest repair actions with an approach derived from an input pattern solution, to generate a redesign road map allowing for taking a shortcut in the redesign solution process. To do so, a two-stage redesign planning approach from recomputation strategy selection to redesign road map generation is proposed. An example problem concerning the redesign of a relief valve is used for illustration and validation.
Coupling Vibrations in Rotating Shaft-Disk-Blades System
Authors: Yang Chia-Hao , Huang Shyh-Chin
Published: January 2007

Applications that have coupling among shaft, disk, and blades are investigated. A shaft-disk-blades unit often seen in engineering is presented. The governing relations for shaft torsion, disk bending, and blade bending are derived. Free vibration is then studied and the results show that shaft-blade (SB), shaft-disk-blades (SDB), disk-blades (DB), and blade-blade (BB) type coupling modes exist. The SDB and DB modes are observed to be evolved from the original SB and BB modes in a previously studied case of a rigid disk case. The effects of stagger angle (β) on the coupling of the components are also examined. In the two extremes at β=0, the disk is uncoupled, and at β=π∕2, the shaft is uncoupled. In between, the three components are coupled. As β increases, the disk participates more strongly, but the shaft behaves in exactly the opposite way. A SB mode at β=0 will transfer into a SDB mode as β increases, eventually becoming a DB mode at β=π∕2. Basically, as β increases, the disk flexibility contributes more and reduces the natural frequencies. The effect of rotation is the last to be discussed and the results show that frequency bifurcation and loci veering occur as the rotation rate increases because of disk flexibility. For SD and SDB modes, the frequency loci veer and merge at certain rotational speeds. In these regions, there exist mode exchange and instability problems.
An Adaptive Sequential Linear Programming Algorithm for Optimal Design Problems With Probabilistic Constraints
Authors: Chan Kuei-Yuan , Skerlos Steven J. , Papalambros Panos
Published: January 2007

Optimal design problems with probabilistic constraints, often referred to as reliability-based design optimization problems, have been the subject of extensive recent studies. Solution methods to date have focused more on improving efficiency rather than accuracy and the global convergence behavior of the solution. A new strategy utilizing an adaptive sequential linear programming (SLP) algorithm is proposed as a promising approach to balance accuracy, efficiency, and convergence. The strategy transforms the nonlinear probabilistic constraints into equivalent deterministic ones using both first order and second order approximations, and applies a filter-based SLP algorithm to reach the optimum. Simple numerical examples show promise for increased accuracy without sacrificing efficiency.
Active Helmholtz Resonator With Positive Real Impedance
Authors: Yuan Jing
Published: January 2007

The impedance of a passive noise control device is strictly positive real, if the device is installed in noise fields with weak mean flows. Passive noise control devices are, therefore, more reliable than active ones. Active control may be applied to a Helmholtz resonator to introduce electronic resonance. It will affect the impedance Zact of the resonator. A controller may be designed such that (a) Zact is small and resistive at some tunable frequencies; and (b) Re{Zact}⩾0 in the entire frequency range of interest. If criterion (a) is satisfied, the active resonator can suppress duct noise at tunable frequencies. It is difficult to design a controller to satisfy criterion (b) because parameters of the controller depend on acoustic parameters of the noise field. A new method is proposed here to design an active controller to meet both criteria simultaneously. The satisfaction of criterion (b) implies a positive real Zact and a robust active resonator with respect to parameter variation in the noise field. Experimental results are presented to verify the performance of the active resonator.
Structured Vibration Modes of General Compound Planetary Gear Systems
Authors: Kiracofe Daniel R. , Parker Robert G.
Published: January 2007

This paper extends previous analytical models of simple, single-stage planetary gears to compound, multi-stage planetary gears. This model is then used to investigate the structured vibration mode and natural frequency properties of compound planetary gears of general description, including those with equally spaced planets and diametrically opposed planet pairs. The well-defined cyclic structure of simple, single-stage planetary gears is shown to be preserved in compound, multi-stage planetary gears. The vibration modes are classified into rotational, translational, and planet modes and the unique properties of each type are examined and proved for general compound planetary gears. All vibration modes fall into one of these three categories. For most cases, both the properties of the modes and the modes themselves are shown to be insensitive to relative planet positions between stages of a multi-stage system.
The Influence of Same-Sign Cross-Coupled Stiffness on Rotordynamics
Authors: Ertas Bugra , Vance John
Published: January 2007

The following paper focuses on same-sign stiffness cross coupling from several viewpoints. First, the influence on rotordynamics is analyzed and discussed, followed by a discussion of how past experiments measuring cross-coupled forces on rotating components may have been in error due to an incomplete testing procedure. Finally, experimental tests are presented on a partitioned damper seal and the correct and complete experimental procedure for determining cross-coupled coefficients is described.
Modeling of Nonlinear Oscillations for Viscoelastic Moving Belt Using Generalized Hamilton’s Principle
Authors: Chen L. H. , Zhang W. , Liu Y. Q.
Published: January 2007

In this paper, the nonlinear governing equations of motion for viscoelastic moving belt are established by using the generalized Hamilton’s principle for the first time. Two kinds of viscoelastic constitutive laws are adopted to describe the relation between the stress and strain for viscoelastic materials. Moreover, the correct forms of elastic strain energy, kinetic energy, and the virtual work performed by both external and viscous dissipative forces are given for the viscoelastic moving belt. Using the generalized Hamilton’s principle, the nonlinear governing equations of three-dimensional motion are established for the viscoelastic moving belt. Neglecting the axial deformation, the governing equations of in-plane motion and transverse nonlinear oscillations are also derived for the viscoelastic moving belt. Comparing the nonlinear governing equations of motion obtained here with those obtained by using the Newton’s second law, it is observed that the former completely agree with the latter.
Active Vibration Damping Using an Inertial, Electrodynamic Actuator (DETC2005-84632)
Authors: Paulitsch Christoph , Gardonio Paolo , Elliott Stephen J.
Published: January 2007

Active vibration damping using a shunted inertial actuator is advantageous if external sensors cannot be collocated with the actuators, or these sensors would add too much weight or cost. When electrodynamic actuators are used, damping can be directly added to the structure where they are attached without the need of electronic integrators or differentiators. Inertial actuators have also the advantage that they do not need to react relative to a fixed base. In this paper, control with a shunted resistor, current feedback, and induced voltage feedback, with and without inductance compensation, are all investigated in simulations and experiments. Experiments with a lightweight, inertial actuator on a clamped plate show that vibration amplitude is decreased between 6 and 13dB and control bandwidth is doubled when the internal actuator inductance is compensated.
A Truncated Low Approach of Intrinsic Linear and Nonlinear Damping in Thin Structures
Authors: Gourinat Yves , Belloeil Victorien
Published: January 2007

An adaptive approach of vibrating thin structures is proposed here. The method consists in applying an equivalent adimensional damping ratio to each potential resonance. This ratio is deduced from experimental data obtained in vacuum facility, in relation with frequencies, for several structural technologies. Consequently, it is possible to calculate the structure in a linear nondissipative context, valid out of resonance bands, and truncated in those bands. Thus, the equivalent damping ratio is directly used to define adimensional resonance truncation bandwith and level. The contribution consists in tested and applied modal methodology and algebraic representations of damping including several dissipations—viscous and internal microfrictions—inducing a nonmonotonous model. The here aim is to provide realistic recommendations for simple vibrational analysis of aerospace thin structures—panels and stiffeners.
Nanostructuring Borosilicate Glass With Near-Field Enhanced Energy Using a Femtosecond Laser Pulse
Authors: Heltzel Alex , Battula Arvind , Howell J. R. , Chen Shaochen
Published: January 2007

A model based on the evolution of electron density derived from the Fokker-Planck equation has been built to describe ablation of dielectrics during femtosecond laser pulses. The model is verified against an experimental investigation of borosilicate glass with a 200fs laser pulse centered at 780nm wavelength in a range of laser energies. The ablation mechanisms in dielectrics include multi-photon ionization (MPI) and avalanche ionization. MPI dominates the ionization process during the first stages of the laser pulse, contributing seed electrons which supply avalanche ionization. The avalanche process initiates and becomes responsible for the majority of free-electron generation. The overall material removal is shown to be highly dependent upon the optical response of the dielectric as plasma is formed. The ablation model is employed to predict the response of borosilicate glass to an enhanced electromagnetic field due to the presence of microspheres on the substrate surface. It is shown that the diffraction limit can be broken, creating nanoscale surface modification. An experimental study accompanies the model, with AFM and SEM characterizations that are consistent with the predicted surface modifications.
Vibration of Delaminated Composite Laminates: A
Review
Authors: Della Christian N. , Shu Dongwei
Published: January 2007

Fiber reinforced composite laminates are increasingly replacing traditional metallic materials. The manufacturing process and service of the composite laminates frequently lead to delamination. Vibration analysis is an integral part of most engineering structures. In the present article we provide a relevant survey on the various analytical models and numerical analyses for the free vibration of delaminated composites. A basic understanding of the influence of the delamination on the natural frequencies and the mode shapes of composite laminates is presented. In addition, other factors affecting the vibration of the delaminated composites are discussed. Particular attention is given to composite laminates having piezoelectric sensors and actuators, and ones subjected to axial loadings.
Electroelasticity Relations and Fracture Mechanics of Piezoelectric Structures
Authors: Bogomol’nyi V. M.
Published: January 2007

Three-dimensional (3D) constitutive equations of piezoelectric (PZ) plates and shells are considered for inverse linear and electrostrictive (quadratic) piezoeffects. Prestressed multilayer PZ shells reinforced with metal including the case of uneven thickness polarization are studied. Asymptotic and variational methods to solve the governing differential equations of PZ shells are considered. Concentrations of electrical and mechanical fields near structure imperfections and external local loading are investigated. The electrothermoviscoelastic heating of PZ shells is considered at harmonic excitation. From numerical analysis and the experimental data of energy dissipation and the temperature behavior of PZ shell the conditions of optimal transformation of electric energy into mechanical deformations are defined. Thus, the geometrical parameters and working frequencies are determined with due account of dielectric relaxation processes. The following nonlinear phenomena are studied: acoustoelectronic wave amplification; electron injection into metalized polar dielectric; resonance growth by 5–20 times of internal electrical field strength in the PZ shells and plates; and autothermostabilization of ferroelectric resonators. For a better understanding of R.D. Mindlin’s gradient theory of polarization in view of electron processes in thin metal-dielectric-metal structures, use was made of solid state physics interpretations as well as experimental data. High concentration of mechanical stresses and temperature and electrical fields near structure defects (first of all, near boundary between various materials) defines the main properties of polar dielectrics. An unknown domain of electrode rough surface influence was estimated, and as result an uneven polarization distribution was found. A theory of nonlinear autowave systems with energy dissipation was used in a physical model of the electrothermal fracture of dielectrics (contacting with metal electrodes), and as a result a nondestructive testing method to study the microstructure defect formation has been suggested.
Effect of Varus/Valgus Malalignment on Bone Strains in the Proximal Tibia After TKR: An Explicit Finite Element Study
Authors: Perillo-Marcone A. , Taylor M.
Published: January 2007

Malalignment is the main cause of tibial component loosening. Implants that migrate rapidly in the first two post-operative years are likely to present aseptic loosening. It has been suggested that cancellous bone stresses can be correlated with tibial component migration. A recent study has shown that patient-specific finite element (FE) models have the power to predict the short-term behavior of tibial trays. The stresses generated within the implanted tibia are dependent on the kinematics of the joint; however, previous studies have ignored the kinematics and only applied static loads. Using explicit FE, it is possible to simultaneously predict the kinematics and stresses during a gait cycle. The aim of this study was to examine the cancellous bone strains during the stance phase of the gait cycle, for varying degrees of varus/valgus eccentric loading using explicit FE. A patient-specific model of a proximal tibia was created from CT scan images, including heterogeneous bone properties. The proximal tibia was implanted with a commercial total knee replacement (TKR) model. The stance phase of gait was simulated and the applied loads and boundary conditions were based on those used for the Stanmore knee simulator. Eccentric loading was simulated. As well as examining the tibial bone strains (minimum and maximum principal strain), the kinematics of the bone-implant construct are also reported. The maximum anterior–posterior displacements and internal–external rotations were produced by the model with 20mm offset. The peak minimum and maximum principal strain values increased as the load was shifted laterally, reaching a maximum magnitude for −20mm offset. This suggests that when in varus, the load transferred to the bone is shifted medially, and as the bone supporting this load is stiffer, the resulting peak bone strains are lower than when the load is shifted laterally (valgus). For this particular patient, the TKR design analyzed produced the highest cancellous bone strains when in valgus. This study has provided an insight in the variations produced in bone strain distribution when the axial load is applied eccentrically. To the authors’ knowledge, this is the first time that the bone strain distribution of a proximal implanted tibia has been examined, also accounting for the kinematics of the tibio–femoral joint as part of the simulation. This approach gives greater insight into the overall performance of TKR.
Finite Element Modeling for Strain Rate Dependency of Fracture Resistance in Compact Bone
Authors: Charoenphan S. , Polchai A.
Published: January 2007

Crack growths in compact bones driven by various strain rate levels were studied using finite element modeling. The energy resistance curves in bovine femur cortical bones were characterized, whereas the orthotropic viscoelasticity in bone materials was accounted for to assess the effect of strain rate on the energy resistance curve. The models were also used to justify the anticipated plane strain response as a result of rather thick specimens used in experiments. Similarities were found between the experimental and model results when crack resistance ability exhibited in bones with slow loading rates, while unstable crack growth existed in bones with rapid loading rates. The critical energy release rates slightly decreased with the increase in strain rates. The hybrid experimental and computational method introduced in this study could be beneficial for application in fracture study in which standard experiments cannot be validly performed.
Thermally Induced Convective Movements in a Standard Experimental Model for Characterization of Lesions Prior to Radiofrequency Functional Neurosurgery
Authors: Wren Joakim , Loyd Dan , Andersson Urban , Karlsson Rolf
Published: January 2007

Experimental exploration of equipment for stereotactic functional neurosurgery based on heating induced by radio-frequency current is most often carried out prior to surgery in order to secure a correct function of the equipment. The experiments are normally conducted in an experimental model including an albumin solution in which the treatment electrode is submerged, followed by a heating session during which a protein clot is generated around the electrode tip. The clot is believed to reflect the lesion generated in the brain during treatment. It is thereby presupposed that both the thermal and electric properties of the model are similar to brain tissue. This study investigates the presence of convective movements in the albumin solution using laser Doppler velocimetry. The result clearly shows that convective movements that depend on the time dependent heating characteristics of the equipment arise in the solution upon heating. The convective movements detected show a clear discrepancy compared with the in vivo situation that the experimental model tries to mimic; both the velocity (maximum velocity of about 5mm∕s) and mass flux are greater in this experimental setting. Furthermore the flow geometry is completely different since only a small fraction of the tissue surrounding the electrode in vivo consists of moving blood, whereas the entire surrounding given by the albumin solution in the experimental model is moving. Earlier investigations by our group (Eriksson et al., 1999, Med. Biol. Eng. Comput. 37, pp. 737–741; Wren, 2001, Ph.D. thesis; and Wren et al., 2001, Med. Biol. Eng. Comput. 39, pp. 255–262) indicate that the heat flux is an essential parameter for the lesion growth and final size, and that presence of convective movements in the model might substantially increase the heat flux. Thus, convective movements of the magnitude presented here will very likely underestimate the size of the brain lesion, a finding that definitely should be taken into consideration when using the model prior to patient treatment.
Thermal Detection of Embedded Tumors Using Infrared Imaging
Authors: Mital Manu , Scott E. P.
Published: January 2007

Breast cancer is the most common cancer among women. Thermography, also known as thermal or infrared imaging, is a procedure to determine if an abnormality is present in the breast tissue temperature distribution. This abnormality in temperature distribution might indicate the presence of an embedded tumor. Although thermography is currently used to indicate the presence of an abnormality, there are no standard procedures to interpret these and determine the location of an embedded tumor. This research is a first step towards this direction. It explores the relationship between the characteristics (location and power) of an embedded heat source and the resulting temperature distribution on the surface. Experiments were conducted using a resistance heater that was embedded in agar in order to simulate the heat produced by a tumor in the biological tissue. The resulting temperature distribution on the surface was imaged using an infrared camera. In order to estimate the location and heat generation rate of the source from these temperature distributions, a genetic algorithm was used as the estimation method. The genetic algorithm utilizes a finite difference scheme for the direct solution of the Pennes bioheat equation. It was determined that a genetic algorithm based approach is well suited for the estimation problem since both the depth and the heat generation rate of the heat source were accurately predicted.
Turbulence Modeling in Three-Dimensional Stenosed Arterial Bifurcations
Authors: Banks J. , Bressloff N. W.
Published: January 2007

Under normal healthy conditions, blood flow in the carotid artery bifurcation is laminar. However, in the presence of a stenosis, the flow can become turbulent at the higher Reynolds numbers during systole. There is growing consensus that the transitional k−ω model is the best suited Reynolds averaged turbulence model for such flows. Further confirmation of this opinion is presented here by a comparison with the RNG k−ϵ model for the flow through a straight, nonbifurcating tube. Unlike similar validation studies elsewhere, no assumptions are made about the inlet profile since the full length of the experimental tube is simulated. Additionally, variations in the inflow turbulence quantities are shown to have no noticeable affect on downstream turbulence intensity, turbulent viscosity, or velocity in the k−ϵ model, whereas the velocity profiles in the transitional k−ω model show some differences due to large variations in the downstream turbulence quantities. Following this validation study, the transitional k−ω model is applied in a three-dimensional parametrically defined computer model of the carotid artery bifurcation in which the sinus bulb is manipulated to produce mild, moderate, and severe stenosis. The parametric geometry definition facilitates a powerful means for investigating the effect of local shape variation while keeping the global shape fixed. While turbulence levels are generally low in all cases considered, the mild stenosis model produces higher levels of turbulent viscosity and this is linked to relatively high values of turbulent kinetic energy and low values of the specific dissipation rate. The severe stenosis model displays stronger recirculation in the flow field with higher values of vorticity, helicity, and negative wall shear stress. The mild and moderate stenosis configurations produce similar lower levels of vorticity and helicity.
Two Mathematical Models for Predicting Dispersion of Particles in the Human Lung
Authors: Ganser G. H. , Christie I. , McCawley M. A.
Published: January 2007

The dispersion of particles in the human lung is modeled as a series of virtual mixing tanks. Using the experimental results of Scherer et al. (1975, J. Appl. Physiol., 38(4), pp. 719–723) for a five-generation glass lung model, it is shown that each generation of the glass lung behaves like an independent virtual mixing tank. The corresponding resident time distribution is shown to have a variance approximately equal to the square of the average time a particle spends in the generation. By assuming that each generation of the human lung behaves as an independent virtual mixing tank, the realistic lung data provided by Weibel (1963, Morphometry of the Human Lung, Spinger-Verlag, New York) are used to validate this assumption in two ways. First, the half-width of the exhaled particle concentration profile is obtained. Second, a system of differential equations, with the concentration of particles in each mixing tank as its solution, is derived and solved numerically. This gives the exhaled concentration profile. Both techniques yield similar results to each other, and both give excellent agreement with the experimental data. The virtual mixing tank approach allows the complex mixing that occurs in the branching pathways of the lung to be more simply modeled. The model, thereby derived, is simple to change and could lead to enhancements in the understanding of the underlying processes contributing to the ventilation of the lung in health and disease.
Support Force Measures of Midsized Men in Seated Positions
Authors: Bush Tamara Reid , Hubbard Robert P.
Published: January 2007

Two areas not well researched in the field of seating mechanics are the distribution of normal and shear forces, and how those forces change with seat position. The availability of these data would be beneficial for the design and development of office, automotive and medical seats. To increase our knowledge in the area of seating mechanics, this study sought to measure the normal and shear loads applied to segmental supports in 12 seated positions, utilizing three inclination angles and four levels of seat back articulation that were associated with automotive driving positions. Force data from six regions, including the thorax, sacral region, buttocks, thighs, feet, and hand support were gathered using multi-axis load cells. The sample contained 23 midsized subjects with an average weight of 76.7kg and a standard deviation of 4.2kg, and an average height of 1745mm with a standard deviation of 19mm. Results were examined in terms of seat back inclination and in terms of torso articulation for relationships between seat positions and support forces. Using a repeated measures analysis, significant differences (p<0.05) were identified for normal forces relative to all inclination angles except for forces occurring at the hand support. Other significant differences were observed between normal forces behind the buttocks, pelvis, and feet for torso articulations. Significant differences in the shear forces occurred under the buttocks and posterior pelvis during changes in seat back inclination. Significant differences in shear forces were also identified for torso articulations. These data suggest that as seat back inclination or torso articulation change, significant shifts in force distribution occur.
Electromyography of Superficial and Deep Neck Muscles During Isometric, Voluntary, and Reflex Contractions
Authors: Siegmund Gunter P. , Blouin Jean-Sébastien , Brault John R. , Hedenstierna Sofia , Inglis J. Timothy
Published: January 2007

Increasingly complex models of the neck neuromusculature need detailed muscle and kinematic data for proper validation. The goal of this study was to measure the electromyographic activity of superficial and deep neck muscles during tasks involving isometric, voluntary, and reflexively evoked contractions of the neck muscles. Three male subjects (28-41years) had electromyographic (EMG) fine wires inserted into the left sternocleidomastoid, levator scapulae, trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus muscles. Surface electrodes were placed over the left sternohyoid muscle. Subjects then performed: (i) maximal voluntary contractions (MVCs) in the eight directions (45deg intervals) from the neutral posture; (ii) 50N isometric contractions with a slow sweep of the force direction through 720deg; (iii) voluntary oscillatory head movements in flexion and extension; and (iv) initially relaxed reflex muscle activations to a forward acceleration while seated on a sled. Isometric contractions were performed against an overhead load cell and movement dynamics were measured using six-axis accelerometry on the head and torso. In all three subjects, the two anterior neck muscles had similar preferred activation directions and acted synergistically in both dynamic tasks. With the exception of splenius capitis, the posterior and posterolateral neck muscles also showed consistent activation directions and acted synergistically during the voluntary motions, but not during the sled perturbations. These findings suggest that the common numerical-modeling assumption that all anterior muscles act synergistically as flexors is reasonable, but that the related assumption that all posterior muscles act synergistically as extensors is not. Despite the small number of subjects, the data presented here can be used to inform and validate a neck model at three levels of increasing neuromuscular–kinematic complexity: muscles generating forces with no movement, muscles generating forces and causing movement, and muscles generating forces in response to induced movement. These increasingly complex data sets will allow researchers to incrementally tune their neck models’ muscle geometry, physiology, and feedforward/feedback neuromechanics.
The Relation Between Collagen Fibril Kinematics and Mechanical Properties in the Mitral Valve Anterior Leaflet
Authors: Liao Jun , Yang Lin , Grashow Jonathan , Sacks Michael S.
Published: January 2007

We have recently demonstrated that the mitral valve anterior leaflet (MVAL) exhibited minimal hysteresis, no strain rate sensitivity, stress relaxation but not creep (Grashow et al., 2006, Ann Biomed Eng., 34(2), pp. 315–325;Grashow et al., 2006, Ann Biomed. Eng., 34(10), pp. 1509–1518). However, the underlying structural basis for this unique quasi-elastic mechanical behavior is presently unknown. As collagen is the major structural component of the MVAL, we investigated the relation between collagen fibril kinematics (rotation and stretch) and tissue-level mechanical properties in the MVAL under biaxial loading using small angle X-ray scattering. A novel device was developed and utilized to perform simultaneous measurements of tissue level forces and strain under a planar biaxial loading state. Collagen fibril D-period strain (εD) and the fibrillar angular distribution were measured under equibiaxial tension, creep, and stress relaxation to a peak tension of 90N∕m. Results indicated that, under equibiaxial tension, collagen fibril straining did not initiate until the end of the nonlinear region of the tissue-level stress-strain curve. At higher tissue tension levels, εD increased linearly with increasing tension. Changes in the angular distribution of the collagen fibrils mainly occurred in the tissue toe region. Using εD, the tangent modulus of collagen fibrils was estimated to be 95.5±25.5MPa, which was ∼27 times higher than the tissue tensile tangent modulus of 3.58±1.83MPa. In creep tests performed at 90N∕m equibiaxial tension for 60min, both tissue strain and εD remained constant with no observable changes over the test length. In contrast, in stress relaxation tests performed for 90minεD was found to rapidly decrease in the first 10min followed by a slower decay rate for the remainder of the test. Using a single exponential model, the time constant for the reduction in collagen fibril strain was 8.3min, which was smaller than the tissue-level stress relaxation time constants of 22.0 and 16.9min in the circumferential and radial directions, respectively. Moreover, there was no change in the fibril angular distribution under both creep and stress relaxation over the test period. Our results suggest that (1) the MVAL collagen fibrils do not exhibit intrinsic viscoelastic behavior, (2) tissue relaxation results from the removal of stress from the fibrils, possibly by a slipping mechanism modulated by noncollagenous components (e.g. proteoglycans), and (3) the lack of creep but the occurrence of stress relaxation suggests a “load-locking” behavior under maintained loading conditions. These unique mechanical characteristics are likely necessary for normal valvular function.
Nonlinear Anisotropic Stress Analysis of Anatomically Realistic
Cerebral Aneurysms
Authors: Ma Baoshun , Lu Jia , Harbaugh Robert E , Raghavan Madhavan L.
Published: January 2007

Background. Static deformation analysis and estimation of wall stress distribution of patient-specific cerebral aneurysms can provide useful insights into the disease process and rupture. Method of Approach. The three-dimensional geometry of saccular cerebral aneurysms from 27 patients (18 unruptured and nine ruptured) was reconstructed based on computer tomography angiography images. The aneurysm wall tissue was modeled using a nonlinear, anisotropic, hyperelastic material model (Fung-type) which was incorporated in a user subroutine in ABAQUS. Effective material fiber orientations were assumed to align with principal surface curvatures. Static deformation of the aneurysm models were simulated assuming uniform wall thickness and internal pressure load of 100mmHg. Results. The numerical analysis technique was validated by quantitative comparisons to results in the literature. For the patient-specific models, in-plane stresses in the aneurysm wall along both the stiff and weak fiber directions showed significant regional variations with the former being higher. The spatial maximum of stress ranged from as low as 0.30MPa in a small aneurysm to as high as 1.06MPa in a giant aneurysm. The patterns of distribution of stress, strain, and surface curvature were found to be similar. Sensitivity analyses showed that the computed stress is mesh independent and not very sensitive to reasonable perturbations in model parameters, and the curvature-based criteria for fiber orientations tend to minimize the total elastic strain energy in the aneurysms wall. Within this small study population, there were no statistically significant differences in the spatial means and maximums of stress and strain values between the ruptured and unruptured groups. However, the ratios between the stress components in the stiff and weak fiber directions were significantly higher in the ruptured group than those in the unruptured group. Conclusions. A methodology for nonlinear, anisotropic static deformation analysis of geometrically realistic aneurysms was developed, which can be used for a more accurate estimation of the stresses and strains than previous methods and to facilitate prospective studies on the role of stress in aneurysm rupture.
Regional Multiaxial Mechanical Properties of the Porcine Anterior Lens Capsule
Authors: David G. , Pedrigi R. M. , Heistand M. R. , Humphrey J. D.
Published: January 2007

The lens capsule of the eye plays fundamental biomechanical roles in both normal physiological processes and clinical interventions. There has been modest attention given to the mechanical properties of this important membrane, however, and prior studies have focused on 1-D analyses of the data. We present results that suggest that the porcine anterior lens capsule has a complex, regionally dependent, nonlinear, anisotropic behavior. Specifically, using a subdomain inverse finite element method to analyze data collected via a new biplane video-based test system, we found that the lens capsule is nearly isotropic (in-plane) near the pole but progressively stiffer in the circumferential compared to the meridional direction as one approaches the equator. Because the porcine capsule is a good model of the young human capsule, there is strong motivation to determine if similar regional variations exist in the human lens capsule for knowledge of such complexities may allow us to improve the design of surgical procedures and implants.