In The Physics Teacher, co-published by AIP Publishing and the American Association of Physics Teachers, researcher T. Ryan Rogers designed a hand-held model to demonstrate the concept of entropy for students. Using everyday materials, Rogers’ approach allows students to confront the topic with new intuition — one that takes specific aim at the confusion between entropy and disorder.

“It’s a huge conceptual roadblock,” Rogers said. “The good news is that we’ve found that it’s something you can correct relatively easily early on. The bad news is that this misunderstanding gets taught so early on.”

While many classes opt for the imperfect, qualitative shorthand of calling entropy “disorder,” it’s defined mathematically as the number of ways energy can be distributed in a system. Such a definition merely requires students to understand how particles store energy, formally known as “degrees of freedom.”

To tackle the problem, Rogers developed a model in which small objects such as dice and buttons are poured into a box, replicating a simple thermodynamic system. Some particles in the densely filled box are packed in place, meaning they have fewer degrees of freedom, leading to an overall low-entropy system.

As students shake the box, they introduce energy into the system, which loosens up locked-in particles. This increases the overall number of ways energy can be distributed within the box.

“You essentially zoom in on entropy so students can say, ‘Aha! There is where I saw the entropy increase,'” Rogers said.

As students shake further, the particles settle into a configuration that more evenly portions out the energy among them. The catch: at this point of high entropy, the particles fall into an orderly alignment.

“Even though it looks more orientationally ordered, there’s actually higher entropy,” Rogers said.

All the students who participated in the lesson were able to reason to the correct definition of entropy after the experiment.

Next, Rogers plans to extend the reach of the model by starting a conversation about entropy with other educators and creating a broader activity guide for ways to use the kits for kindergarten through college. He hopes his work inspires others to clarify the distinction in their classrooms, even if by DIY means.

“Grapes and Cheez-It crackers are very effective, as well,” Rogers said.

The findings, published today in the journal Science Advances, shed new light on genomic imprinting, a fundamental, biological process in which a gene from one parent is switched off while the copy from the other parent remains active. Errors in imprinting are linked to a host of diseases, such as the rare disease Silver-Russell syndrome along with certain cancers and diabetes.

“Proper imprinting is crucial for lifelong health but, despite its importance, we still lack a full understanding of the factors that regulate this vital process,” said VAI Associate Professor Piroska Szabó, Ph.D., the study’s corresponding author. “Our findings reveal an RNA mechanism that governs establishment of imprinting and illuminates why it differs between fathers and mothers.”

Our genetic information is encoded in DNA, a long, winding molecule that is tightly packed to form 23 pairs of chromosomes, half of which come from one’s father and half from one’s mother. Sperm and eggs only contain 23 single chromosomes — half of the genetic material required for life. During fertilization, they each contribute their half, resulting in a zygote with a full set of 23 pairs of chromosomes.

But not all instructions in DNA are needed at the same time or in the same places. That’s where epigenetics come in. Epigenetic mechanisms annotate DNA with special chemical tags called methyl groups, which tell certain genes when to be active and when to be silent — all without changing the sequence of DNA itself.

Imprinting occurs when methyl groups are added to certain genes during either sperm or egg formation. This, in turn, is important for determining which parental copy of that gene is expressed in the offspring.

To better understand the processes that govern imprinting, Szabó and colleagues focused on an imprinting control region in the DNA that regulates the Igf2 gene. Igf2 plays key roles in fetal growth and only is active in the chromosome inherited from the father. Too little methylation in the IGF2 control region in humans can result in Silver-Russell syndrome, which is marked by reduced growth and increased risk of metabolic disease.

“If the IGF2 gene’s imprinting control region from one’s father is not methylated, it can result in disease,” Szabó said.

Using genetic models and in-depth genetic sequencing, the team found that the methylation of the Igf2 control region in paternally inherited DNA is governed by an underlying RNA-based process in the male germline.

“We found earlier that RNA similarly runs through other paternally marked imprinted domains in the male germ cells, suggesting that this same process is generally true for paternal imprinting,” Szabó said. “These results suggest a more broadly applicable process, which is exciting and will need to be confirmed in subsequent studies.”

Other authors include Ji Liao, Ph.D., Zhen Fu, Ph.D., Ivan VanderKolk, Brianna M. Busscher and Kin H. Lau, Ph.D., of VAI; Sangmin Song of City of Hope Cancer Center; and Samuel Gusscott, Ph.D., and Julie Brind’Amour, Ph.D., of Université de Montréal.

“These findings indicate that even people with traumatic brain injuries in earlier life who appear to have fully recovered from them may still be at increased risk of cognitive problems and dementia later in life,” said study author Marianne Chanti-Ketterl, PhD, MSPH, of Duke University in Durham, North Carolina. “Among identical twins, who share the same genes and many of the same exposures early in life, we found that the twin who had a concussion had lower test scores and faster decline than their twin who had never had a concussion.”

The study involved 8,662 men who were World War II veterans. The participants took a test of thinking skills at the start of the study when they were an average age of 67 and then again up to three more times over 12 years. Scores for the test can range from zero to 50. The average score for all participants at the beginning of the study was 32.5 points.

A total of 25% of the participants had experienced a concussion in their life.

Twins who had experienced a concussion were more likely to have lower test scores at age 70, especially if they had a concussion where they lost consciousness or were older than 24 when they had their concussion. Those twins with traumatic brain injury with loss of consciousness, more than one traumatic brain injury and who had their injuries after age 24 were more likely to have faster cognitive decline than those with no history of traumatic brain injury.

For example, a twin who experienced a traumatic brain injury after age 24 scored 0.59 points lower at age 70 than his twin with no traumatic brain injury, and his thinking skills declined faster, by 0.05 points per year.

These results took into account other factors that could affect thinking skills, such as high blood pressure, alcohol use, smoking status and education.

“Although these effect sizes are modest, the contribution of TBI on late life cognition, in addition to numerous other factors with a detrimental effect on cognition, may be enough to trigger an evaluation for cognitive impairment,” Chanti-Ketterl said. “With the trend we are seeing with increased emergency room visits due to sports or recreation activity injuries, combined with the estimated half million members of the military who suffered a TBI between 2000 and 2020, the potential long-term impact of TBI cannot be overlooked. These results may help us identify people who may benefit from early interventions that may slow cognitive decline or potentially delay or prevent dementia.”

A limitation of the study was that traumatic brain injuries were reported by the participants, so not all injuries may have been remembered or reported accurately.

The study was supported by the National Institute on Aging and the U.S. Department of Defense.