Matthew Semak

PhD, The University of New Mexico, 2000
Area of Study: Physics

MS, Clarkson University, 1991
Area of Study: Physics

Complex Systems Summer School, Santa Fe Institute, 1990

BS, Clarkson University, 1989
Area of Study: Physics

Associate Professor, University of Northern Colorado
(2020-present)

Assistant Professor, University of Northern Colorado
(2014-2019)

Instructor, Assistant Professor, University of Northern Colorado
(2013 – 2014)

Lecturer, University of Northern Colorado
(2000-2013)

An examination of the correlation between cognitive ability and achievement on the FCI

We administered a commercial, nonverbal intelligence test (GAMA) to students in introductory physics. We examined the scores to determine if the performance on the GAMA, or any of its subtests, can predict student achievement on the Force Concept Inventory (FCI) before and/or after instruction. Given that a gender gap in performance is often seen to exist, gender was also considered as a predictor. The items of the FCI were divided into two groups to be predicted for – one consisted of questions seen to be “difficult” and the other comprised the remaining items. Gender was found to be a significant predictor in all but one situation, and two subtests of the GAMA correlated positively with achievement given certain conditions. We discuss possible implications of these results.

Biomimicry: Building a Robotic Snake

The locomotion of a snake is being reproduced by a robot. Special attention will be given to the mathematics of the algorithm which controls steering as well as the structure that will be built that connects successive sections making up the snake. A variety of sensors will be incorporated to allow for autonomous navigation. Microcontrollers still need to be selected.

Characterizing the Complexity of Human Unipedal Balance

We would like to understand the dynamical nature of human unipedal balance. Time series typical of the anterior-postural (A-P, front to back) and medial-lateral (M-L, side to side) jerk during the balance process were studied. Our interest is to classify features found in these measurements as indicative of subjects experiencing certain medical conditions. New data taken with a higher sampling rate and a more restricted filtering scheme (to deal with machine noise) revisits our earlier work in this area [1]. Currently, our data is very limited but typical of our studies at lower resolution. We anticipate more data to be taken soon with a variety of subjects and consider this work as a pilot study to inform preprocessing of future trials. Our analysis suggests that these signals have a deterministic character with a temporally evolving autocorrelation structure and time-frequency spectrum. We will use the term “nonstationary” for this behavior. Finally, with the Lempel-Ziv complexity having mild but measurable fluctuations throughout the time series, we have been led to pursue a classification scheme that attempts to track the evolution of the complexity with time. The signals have been decomposed into modes using multiresolution analysis. Using the Lempel-Ziv complexity with its coarse-graining application can classify bulk features and find suggestions of determinism playing a role in the jerk. This allows us to pursue an examination of the more nuanced features contained in the signal.

Examining Human Unipedal Quiet Stance: Resolving Temporal Scaling using a Binary Record of the Jerk

We investigate the quality of smoothness, or control, for human unipedal balance. In this work, smoothness is quantified by the time rate of change of the accelerations, or jerks, associated with the motion of each foot’s center-of-pressure. The presence of sudden jerks during the process of balance is seen to indicate a certain lack of control. Data were collected via a force plate for individuals attempting to maintain upright posture using one leg (with eyes open). The medial-lateral (M-L) and anterior-posterior (A-P) components of the jerk were considered. Our past studies have suggested the jerk’s time series can be modeled as a (stationary) stochastic process and, with this, we took the jerk to be proportional to the increment of the force realizations. Also, these studies suggested the existence of temporal correlations with a range of scaling behavior. Elements of mutual information and multifractal analyses (MFA) were the primary tools used to further explore the validity of these previous findings. To gain awareness as to what can be learned by studying the simpler aspects of these data, the time series was formed into a binary string tracking the jerk’s sign. The processed data is seen to contain the information such that a quasiperiodic mutual information profile could be resolved – one not observed with the unprocessed data. Moreover, a simplified MFA of the binary sequence suggests the existence of a singularity spectrum.

Investigating the Effect of Geometric Modifications on Body Armor

Modern body armor is essential for US soldiers and law enforcement to perform their duties with less risk of injury or loss of life. However, can we improve modern body armor using geometric shapes to make it safer? This research aims to reduce the amount of force felt by the wearer of plates. This research was conducted by 3-D printing different designs of body armor plates and recording the force caused by dropping a steel ball from a predetermined height while the plate sits upon a force sensor. These data are then analyzed to see if different geometric modifications to the plates reduce the impulse transmitted to the force plate. Based on this analysis, promising modifications are then further analyzed using more trials and different sensor placements to determine their effect. As of now, we have seen a reduction in the amount of force going through the plate, and the effects vary depending on the material used with the modification. As this research continues with more materials, we hope for promising results in helping to improve the field of body armor and help save the lives and health of those who protect us.

Loudspeaker and port phase matching at resonance

The electromechanical system under study is a loudspeaker (subwoofer) mounted in a ported enclosure. An understanding and demonstration of the distribution of electrical and mechanical energy of a speaker system at resonance is sought.

Noise Analysis in Physical Systems

A topic that is absent in our undergraduate curriculum is the treatment of noise in experiments. I am looking at ways to incorporate noise analysis, including studying circuits that acquire biological signals. We purchased a Teachspin Noise Fundamentals apparatus in summer 2021 that can be used in undergraduate research projects. The goal is to develop at least one novel undergraduate experiment that can be presented at an AAPT conference and possibly published in The Physics Teacher or the American Journal of Physics. Dr. Semak is a collaborator on this project.

Noise in Biomedical Systems: De-noising an ECG Signal

Electrocardiogram signals play a critical role in the diagnosis and management of cardiac conditions. However, these signals are often contaminated by noise. In space environments, this noise is further exacerbated by cosmic radiation, which induces single event effects. To assess the impact of such signal contamination, it is essential to explore modern signal processing techniques that can be used to effectively remove this noise. In this study, we applied Empirical Mode Decomposition to decompose the electrocardiogram into Intrinsic Mode Functions (IMFs), which contain specific oscillatory features of the original signal. By analyzing histograms of certain IMFs, we identified the frequencies contributing to noise. Subsequently, we utilized notch and lowpass filters to smooth the signal while preserving its key characteristics. Our ongoing work involves developing a program to automate this methodology, after which we will evaluate its performance by comparing the denoised signals against an Electrocardiogram database. This approach will enable us to eventually assess the efficacy of our established noise removal technique with radiation-induced single event effects.

Object Tracking Autonomous Rover

A student is building a robot to demonstrate to the lay person simple robotic capabilities/autonomous behavior. This is a tracked mini-rover that can be transported and deployed easily for use at a variety of events. The chassis will be assembled with four independent track units each having their own suspension system. Also, a new suite of programming is being developed along with incorporation of sensors. We would like the rover to use detachable sensor packages to extend its demonstration capabilities. Simple environmental navigation is the immediate goal for this project.

Planetary Weather

An effort to understand atmospheric dynamics on other planets will be taken on by one student and faculty from the Departments of Physics and Astronomy and Earth and Atmospheric Sciences at UNC. This work will include understanding and simulating atmospheric models of various planets with the intent of informing our understanding of Earth’s weather.

Support of UNC’s involvement in the Colorado Space Grant Consortium (COSG).

Dr. Semak was the PI and Associate Director in the consortium; I served as Co-PI. I assisted in writing funding proposals and progress reports; created, tracked, and balanced budgets; aided in making purchase and student stipend decisions; purchased equipment and supplies; and helped to mentor student projects that led to internal and external presentations. Students gave presentations at the annual Colorado Space Grant symposium. I also attended consortium meetings and symposia. The funding received annually nearly doubled DPA’s non-personnel state budget and provided sustained support to our undergraduate research program. Funds received from 2022 to 2024 totaled $65,000.

Areas of Interest

Statistical mechanics of nonequilibrium nonlinear systems – temporal correlations in noisy systems, computer modeling of noisy systems with memory, computer/mathematical modeling of human unipedal balance, applying human balance strategies to robotics
Psychoacoustics – Intelligibility at high sound pressure levels, impedance characteristics of audio waveguides

• Semak, M. R., Swchartz, J., Heise, G. (2020). Examining Human Unipedal Quiet Stance: Characterizing Control through Jerk. Computational and Mathematical Methods in Medicine, 15.
• Semak, M., Dietz, R., Pearson, R. H., Willis, C. (2017). Examining Evolving Performance on the Force Concept Inventory using Factor Analysis. Physical Review: Physics Education Research, 13(1).
• Semak, M., Forgacs, G. (1991). Adsorption of a Directed Polymer-chain in the Presence of Monomer Attraction: Analytical Results. Journal of Physics A – Mathematical and General, 24(1), L779-L784.