In vitro assessment of MRI issues at 3-Tesla for a breast tissue expander with a remote port

Objectives

A patient with a breast tissue expander may require a diagnostic assessment using magnetic resonance imaging (MRI). To ensure patient safety, this type of implant must undergo in vitro MRI testing using proper techniques. Therefore, this investigation evaluated MRI issues (i.e., magnetic field interactions, heating, and artifacts) at 3-Tesla for a breast tissue expander with a remote port.

Methods

A breast tissue expander with a remote port (Integra Breast Tissue Expander, Model 3612-06 with Standard Remote Port, PMT Corporation, Chanhassen, MN) underwent evaluation for magnetic field interactions (translational attraction and torque), MRI-related heating, and artifacts using standardized techniques. Heating was evaluated by placing the implant in a gelled-saline-filled phantom and MRI was performed using a transmit/receive RF body coil at an MR system reported, whole body averaged specific absorption rate of 2.9-W/kg. Artifacts were characterized using T1-weighted and GRE pulse sequences.

Results

Magnetic field interactions were not substantial and, thus, will not pose a hazard to a patient in a 3-Tesla or less MRI environment. The highest temperature rise was 1.7 °C, which is physiologically inconsequential. Artifacts were large in relation to the remote port and metal connector of the implant but will only present problems if the MR imaging area of interest is where these components are located.

Conclusions

A patient with this breast tissue expander with a remote port may safely undergo MRI at 3-Tesla or less under the conditions used for this investigation. These findings are the first reported at 3-Tesla for a tissue expander.     

The effect of angle on the strain of scarf lap joints subjected to tensile loads

In this paper, the mechanical behavior of the scarf lap joints (SLJs) bonded with adhesive (Vinylester Atlac 580) under a tensile load was analyzed. The effects of scarf angle at the interface strain distributions of SLJs were examined. The stress analyses were performed via three dimensional Finite Element Method (3D-FEM). The 3D-FEM code employed was Ansys (12.0). Experimental results were compared with the 3D-FEM results and were found quite reasonable. The results indicated that the maximum values of the normalized ε_x strain values were determined at θ = 60° in all joints.     

Stress field characteristics of eccentrically loaded aircraft spliced joints

The paper details the stress characteristics in eccentrically loaded aircraft spliced joints. It is shown that the hoop stress (σ_θθ) around each rivet is characterized by two peak values located at θ = (0°, 90°). The magnitude of (σ_θθ) is then reduced to a minimum value between these two peaks. A sharp increase in the axial stress component (σ_xx) along the vertical splice lines occurs in the vicinity of the rivet centerlines followed by a rapid decrease in the areas between the rivets. It is shown that stresses along the first interior rivet row is the most critical. The axial stress (σ_xx) profile along horizontal rivet lines has a “sinusoidal” pattern. It is observed that the transverse stress profile (σ_yy), along the horizontal lines, has different peak and minimum values between the rivets. The magnitude of the peak/minimum values depends upon the line location within the splice region. It is also shown the bending stress component varies significantly and must be accounted for the analysis of the eccentric aircraft joints. Experimental comparisons are made along several lines in the splice region. The numerical model is utilized for analysis of a full frame-bay/splice of aircraft fuselage. The paper provides valuable information that can be utilized by practicing engineers for analysis and design of joints with large number of rivets.     

二维正方晶格光子晶体禁带特性

基于平面波展开法,以碳化硅构成二维正方晶格光子晶体,数值模拟了TE模、TM模二维光子晶体的禁带特性,结果表明,TE模更容易形成光子禁带。同时设计了以碳化硅构成二维正方晶格光子晶体波导,数值模拟了TE模、TM模波导的传输特性和禁带特性,结果表明,TE模构成的波导电磁波能够较好的传播,它们的光子禁带都没有出现。研究结论为光子晶体波导器件的开发提供参考。     

Vibrational resonance in biological nonlinear maps

We investigate vibrational resonance in two different nonlinear maps driven by a biharmonic force: the Bellows and the Rulkov map. These two maps possess dynamical features of particular interest for the study of these phenomena. In both maps, the resonance occurs at the low-frequency of the biharmonic signal as the amplitude of the high-frequency signal is varied. We also consider an array of unidirectionally coupled maps with the forcing signal applied to the first unit. In this case, a signal propagation with several interesting features above a critical value of the coupling strength is found, while the response amplitude of the ith unit is greater than the first one. This response evolves in a sigmoidal fashion with the system number i, meaning that at some point the amplitudes saturate. The unidirectional coupling acts as a low-pass filter for distant units. Moreover, the analysis of the mean residence time of the trajectory in a given region of the phase space unveils a multiresonance mechanism in the coupled map system. These results point at the relevance of the discrete-time models for the study of resonance phenomena, since analyses and simulations are much easier than for continuous-time models.     

Expanding a Finite Blaschke Product

It is shown that a finite Blaschke product with finite poles, has a nonzero residue. The proofs for the two types of Blaschke products are essentially different.     

Understanding crack growth in fuselage lap joints

The problem of multi-site damage and multiple interacting cracks is one experienced by many aircraft manufacturers and operators. This paper focuses on understanding the phenomena, and on developing a predictive capability that can form the engineering framework for maintaining continued airworthiness. To this end the present paper uses a simple formulation based on the Frost–Dugdale crack growth law to study the problem of cracking at fastener holes in fuselage lap joints and shows that the predicted crack growth history is in good agreement with both experimental results and with fleet data.     

On prestress stiffness analysis of bolt-plate contact assemblies

Bolt connections are among the most important connections used in structures. The stiffnesses of the bolt and of the connected members are the primary qualities that control the lifetime of the connection. The stiffness of the bolt can be estimated rather easily, in contrast to the member stiffness, but with finite element (FE) and contact analysis, it is possible to find the stiffness of the member. In the case of many connections and for practical applications, it is not suitable to make a full FE analysis. The purpose of the present paper is to find simplified expressions for the stiffness of the member, including the case when the width of the member is limited. The calculation of the stiffness is based on the FE, including the solution to the contact problem, and we express the stiffness as a function of the elastic energy in the structure, whereby the definition of the displacements related to the stiffness is circumvented. The contact analysis is performed using a method where iterations are not necessary, and the results are compared to alternative available results. New practical formulas for the stiffnesses are suggested.     

膨胀聚合反应研究的进展

着重介绍膨胀聚合反应的类型和机理,讨论膨胀聚合反应研究中在的问题及今后的研究方向。