The axisymmetric response of a fluid-filled spherical shell to a local radial impulse--A model for head injury

This investigation is concerned with determination of the dynamic response of a fluid-filled spherical shell subjected to a local radial impulsive load. From the application point of view, such a fluid-shell system is considered to be a simple, but to date, the most improved theoretical model representing the human head when subjected to impulsive external loads. Analysis is based on linear shell theory which includes both membrane and bending effects. The motion of the fluid is assumed to be governed by the wave equation. Laplace transform technique is used in obtaining the transient axisymmetric response of the system to a local radial impulsive load. The solutions thus obtained for the velocity potential of the fluid and the displacement components of the shell mid-surface are the Green's functions of the problem with respect to time. Some numerical results for the theoretical model are obtained for a set of appropriate data. The comparison is made for the stress distributions at various times in the shell for both the empty and the fluid-filled cases. In the fluid-filled case the excess pressure propagation in the fluid is also discussed. The possible locations of brain damage and skull injury are indicated on the basis of the numerical computations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32940/1/0000323.pd

A mathematical model to determine viscoelastic behavior of in vivo primate brain

Determination of mechanical properties of the constituents of the head is very essential for the construction of various theoretical and experimental head injury models. This paper represents a mathematical model for the evaluation of viscoelastic behavior of in vivo primate brain. From a theoretical mechanics point of view, the problem being considered is that of the steady state response characteristics of a solid sphere of linear viscoelastic material whose mating surface with the rigid container is free from shear stresses. The external load is taken to be a local radial harmonic excitation. First, the response of the elastic material is determined; later the elastic response solution is converted to viscoelastic response solution through the use of the correspondence principle applicable to steady state oscillations. The paper is concluded with a discussion of a method which enables the determination of the complex dynamic shear modulus of in vivo primate brain.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32763/1/0000134.pd

Two Functions Used in the Analysis of Crossflow Exchangers, Regenerators and Related Equipment

a response exhibits a step when t = P and thus t' = t a . The first cross-sectional fluid a lamina that enters at time zero with a temperature of unity sees fluid b at zero temperature. (The wall is "transparent" when its thermal capacitance is zero.) This lamina therefore has a temperature of exp(-AOc). When it reaches its exit plane {x -1) at time /" its temperature is exp (-N), which is the magnitude of the jumps seen in The solution with zero core capacitance is much easier and faster to compute than the Spiga and Spiga solution. It is therefore of interest to estimate the upper range of V a or V b that is reasonable for an exchanger. Suppose that fluid a flows inside tubes. Then for thin wall tubes V a -£>y/(4A) in which D and A are the tube diameter and wall thickness and v is the ratio of the volummetric heat capacities of the fluid and tube materials. This ratio has the exceptionally large value of 1.7 for water and aluminum. Using this material combination gives V a -0.4D/A. Thus an aluminum tube with 25 mm diameter and 1 mm wall thickness gives V a = 10. The parameters V a and V b can, of course, vary over a wide range, but this illustration indicates that the simplicity of the zero core capacitance solution can sometimes be enjoyed with acceptable accuracy. References Anzelius, A., 1926 Introduction This note focuses on the transport in aiding laminar mixed convection flow adjacent to a vertical isothermal surface. The direction of forced flow is taken to be upward for the heated surface. This situation causes the flow to be predominantly forced at the leading edge, primarily natural far downstream, and mixed in the middle. In the intermediate region of mixed convection Merkin (1969) reported a finite difference solution for Pr = 1

Axisymmetric response of a fluid-filled spherical shell in free vibrations

this paper is concerned with a theoretical model of the head. Neuroanatomical and analytical considerations lead to a fluid-filled spherical shell as a first-generation model. The shell is considered thin, elastic, homogeneous, and isotropic. The shell equations include both membrane and bending effects in axisymmetric torsionless motion. The motion of the fluid is governed by the wave equation. A free vibration analysis of the fluid-shell system is obtained in the form of a frequency equation. Compared with a fluid-filled rigid shell and an elastic shell in vacuo, the frequency spectrum of the fluid-shell system is almost a `superposition' of the spectra of the two special cases. The exceptions appear as slight distortions in the neighborhood of the `curve' intersections.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32824/1/0000199.pd

A Review of Fiber-Reinforced Injection Molding: Flow Kinematics and Particle Orientation

The existing flow and particle orientation models applicable to fiber- reinforced injection molding are reviewed. After a brief description of injection molding, previous studies on the flow kinematics and fiber reinforcement are presented. Basics of Hele-Shaw flows are described Including the commonly used viscosity models and foun tain flow effects. Some of the existing models for particle orientation are analyzed with particular emphasis on the amsotropic description of the material system. Concentration regions for short fiber suspensions are defined and relevant constitutive equations are dis cussed. A few example solutions are also given which describe the three-dimensional ori entation field for the filling of a sudden expansion cavity, depicting skin-core orientation structure.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Über die Bewegung der anisotropen Flussigkeiten.

LEIDSSTELSELDiss. Uppsala.OPLADEN-RUG0

The optic tectum of the salmon:site of interaction of neurohormonal photoperiodic and neural visual signals. The GABAergic neuronal system and melatonin receptors.

Melatonin is a neurohormone which mediates photoperiodic signals from the pineal organ to the brain. GABA (g-aminobutyric acid) is the major inhibitory transmitter in the central nervous system. It has previously been suggested that functional interaction exists between central binding sites for GABA/benzodiazepines (GABAA/bzd receptors) and melatonin in the central nervous system, and that GABA and benzodiazepines may be involved in circadian responses to light. To investigate if there is a structural basis for interactions between the neurohormone melatonin and GABA in the primary visual center, the optic tectum of the brain of the Atlantic salmon (Salmo salar) I compared the distribution of the GABAA/benzodiazepine receptor complex(GABAA/bzd receptor) to that of melatonin receptors, using immunohistochemistry (for GABAA/bzd receptors) and quantitative autoradiography (for melatonin receptors). I also investigated if there is any difference in the binding of 2-[125I]iodomelatonin at day compared to at night. I was also interested to know which transmitter substance that mediates the light-/dark message from the retina to the optic tectum via the optic tract. By using immunohistochemistry I studied the distribution of GABA in the retina and in the optic tectum. The ganglion cells in the retina showed no GABA immunoreactivity indicating that GABA is not the transmitter mediating the light-/dark message to the optic tectum. An overlap in the distribution of GABAA/bzd receptors, melatonin receptors, and GABAergic neurons and fibers in the retinorecipient layers of the optic tectum was observed. Thus, there is a structural basis for interactions between GABA and melatonin in the optic tectum of the Atlantic salmon. It is likely that GABA is involved in the intrinsic processing of the light-/dark message in the optic tectum. The 2-[125I]iodomelatonin was found to be specific, saturable, displaceable and of high affinity, with a dissociation constant (Kd) 85±14 pM and a maximum number of binding sites (Bmax) 58±7 fmol/mg protein. The Hill plot coefficient (nH) was 2.0 which indicates the presence of two types of binding sites. The presence of two binding sites could, however, not be statistically verified using MACLIGAND. No significant differences were found when comparing the 2-[125I]iodomelatonin at night to that at day