Participant: PROMISE AGEP Research Symposium
Ashley Wayne Thomas
Department: Mechanical Engineering
Institution: University of Maryland Baltimore County (UMBC)
Development of an Improved Whole Body Heat Transfer Model for Determining Postmortem Interval in Forensic Science
Estimating postmortem interval is often inaccurate due to uncertainty of thermal resistance between the body and its environment. The goal of this study is to develop a whole body heat transfer model to simulate temperature decay in human bodies postmortem.The model is based on a female adult and consists of a head, internal organs, skin, fat, muscle and clothing. The Pennes Bioheat equation is used to determine the temperature distribution, and is solved using ANSYS Fluent. The thermal conductivity of the clothing with fixed thickness of 5 mm is adjusted to ensure that the has established a thermal equilibrium with its environment before death. Using the steady state field as the initial condition, a 24-hour transient simulation was completed for the body lying on cement with or without carpet. In this study, we focus on the temperature decrease in the center of the internal organs, a location often used in forensic science. Initially, the temperature of the internal organs is relatively steady; it then decays exponentially and is approximately 31°C at the end of the simulation. The larger thermal resistance of carpet results in a slower temperature decrease than when the body is lying on a cement alone. This model significantly improves our previous work by considering a realistic postmortem body position. Furthermore, it accurately models thermal resistance between the skin and air via an indirect approach assuming thermal equilibrium. We expect the model will be useful to predict postmortem interval under various environmental conditions and body positions.
Infant Skull Fracture Mechanics in Abusive Head Trauma Versus Accidental Falls
Head injuries are the leading cause of death in infants (Powell et al., 2013). In addition, crying is the most common triggering factor for abusive head trauma and the majority of cases are reported when an infant is 6-8 weeks old (Simonnet et al., 2014). Oftentimes, there are disparities in whether the head injury was caused by inflicted abuse or an accidental fall as skull fracture can occur in both cases. More literature on cranial fracture mechanics can help forensic pathologists determine whether a skull fracture is due to abuse or an accidental fall.
A study was conducted to compare the crack length of entrapped infant (2-17 days old) porcine skulls to controlled head drops. However, the majority of abuse cases typically occur when the infant is slightly older and this study did not consider whole body kinematics for force dissipation through the body (Powell et al., 2013). There is also a lack of scientific data on the variability in the causes of the head injury such as distance of fall and the nature of the surface the child falls on. Therefore, it is important to test a range of variables to better understand the mechanical behavior of infant skulls after accidental falls and abuse.
The central goal of this proposed study is to compare infant skull fracture mechanics of infants who experience accidental falls and abusive head impacts. Our hypothesis is that the crack length in the skull will be larger in abuse cases compared to accidents.
Ashley Wayne is a graduate student in the Mechanical Engineering Department at the University of Maryland, Baltimore County. In May of 2016 she earned a Bachelor of Science in Mechanical Engineering from The University of Virginia in Charlottesville, VA. Ashley currently works in the Bioheat Transfer Laboratory under the supervision of Dr. Liang Zhu. Her research focus is on developing a thermo-fluidic whole body model to estimate postmortem interval. While she is not in the lab, she enjoys spending her time at the gym, advancing her natural hair products business and playing softball.
GENERAL SUMMARY OF GRADUATE RESEARCH
The human body’s ability to thermoregulate has been studied for many centuries. Most recently, scientists have been focused on studying how bioheat transfer methods can be used to assist in therapeutic and diagnostic applications, estimating time of death, and analyzing the body’s thermoregulation during exercise. By using realistic numerical methods to model the human thermoregulatory system and its interaction with its surroundings, scientists have been able to estimate the time of death and contribute a wealth of information to forensics. Mathematical formulations have been developed to estimate time of death, however they are often inaccurate as they do not incorporate details such as type of clothing, body size, sex, and boundary conditions. My research focuses on developing a whole body computational model to estimate the time of death for not only simplified cases but cases in which the body environment has changed or the person has had a medically induced death. My research also focuses on realistically modeling the human body. Oftentimes, portions of the body such as the head are modeled as a lump body without focus on characteristics such as thermal conductivity, blood perfusion rate, and metabolic heat generation rate. My research focus is on determining how modeling specific parts of the body and boundary conditions more realistically contribute to a more accurate model for estimating the body core temperature which in turn helps estimate time of death.
SELECTED LIST OF PRESENTATIONS AND PUBLICATIONS
- Development of an Improved Whole Body Heat Transfer Model for Determining Time of Death in Forensic Science, World Congress of Biomechanics, 2018
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