M.A. in Physics

New York City traffic jams tend to begin with clusters of tie-ups within a network of streets before expanding rapidly and chaotically to surrounding areas, according to a paper published by two professors in the Katz School’s M.A. in Physics.

Read the entire story in the Katz blog.

Katz School researchers are developing an advanced method for examining how ice crystallizes and how antifreeze proteins inhibit the crystallization process.

Dr. Ran Drori, assistant professor of chemistry in YU’s Stern College for Women and the Katz School’s M.A. in Physics, is  studying the unique ability of ice-binding proteins, or antifreeze proteins, to both accelerate and inhibit the growth of ice using a microscope-mounted cold stage, which holds a temperature-controlled sample and is 10 times more powerful than the industry standard.

Read the entire story in the Katz blog.

A Katz School of Science and Health paper that devises a theoretical framework for studying the quantum origins of flexoelectricity, a phenomenon in which electric charges scatter within a material after it has been bent, has been published in the Journal of Applied Physics.

Flexoelectricity occurs when an ordinary object, which is normally uncharged, is significantly changed in size and shape—or deformed—by mechanical or other forces. The result is that positive and negative charge regions inside the object are rearranged due to the migration of electrons.

“The net charge is still zero,” said Dr. Fredy Zypman, professor and chair of the M.A. in physics program who authored the article “Quantum Flexoelectric Nanobending.” “But the fact that you can separate the charges will have an effect via the electric field induced by that dissociation.”

Most people have experienced charge migration on a dry winter day when they feel a shock at the touch of a metallic doorknob. The spark is a violent manifestation of a fast electric charge transfer. While charge relocation is ubiquitous in nature, its manifestation is usually, unlike the spark, subtle to common observation. In the case of flexoelectricity, the effect is so well concealed that it shows up in extremely tiny objects that can only be monitored with very delicate instrumentation.

Flexoelectricity is present in all materials, but it’s virtually imperceptible in everyday events. Still, it’s prevalent at submicroscopic scales. Researchers have recently become more interested in experimentally validating this phenomenon, which has been a point of speculation since the 1950s, as the trend toward the miniaturization of electronics and microchips has accelerated.

“Flexoelectricity has tantalizing implications in a wide range of areas, ranging from biotechnology to energy harvesting,” said Dr. Zypman. “Most important, all materials display this property, making the menu of flexoelectric materials unlimited in practice, a most desirable quality in scientific, engineering and commercial spheres.”

Flexoelectric materials can be used as sensors and actuators at the nanometer scale; by comparison, a sheet of paper is about 100,000 nanometers thick. Sensors can monitor small movements by direct measurement of the voltage created by a charge separation. Conversely, in an actuator, the input is a voltage—or charge—and the output is motion. It could be linear motion, said Dr. Zypman, or angular motion, like a twist.

“These two aspects have vast practical applications,” he said. “For example, a submicroscopic autonomous robot—a micro-cyborg—can use actuators to move and sensors to decide how to move.”

These flexoelectric sensors can also be used to monitor the structural integrity of a building by measuring its vibrations with great precision. Pacemakers implanted in human hearts and utilizing lithium batteries could instead be self-powered as natural movement generates electrical power. Human bones are flexoelectric. When microfractures occur during exercise, the behavior of cells that form new bone is dictated by the fracture’s flexoelectric field.

“While flexoelectricity is a property of all materials, it is necessary to continue finding unambiguous foundational connections between theory and experiments to be able to assess real systems,” said Dr. Zypman. “This is important as applications of flexoelectricity in nanodevices grow. It is still a very exciting work in progress.”

Three Katz School mathematics and physics researchers have developed a theoretical framework for predicting the possible shapes and gravitational fields of asteroids.

The results, published in the international journal Astrophysics and Space Science in March 2021, can be useful for spacecraft engineers developing landing designs for irregularly shaped celestial objects. The research was funded by a $412,000 grant from the National Science Foundation.

“One of the paper’s central challenges was to find mathematical expressions for representing gravity on the surface of an irregularly shaped asteroid, understanding that, unlike on Earth, gravity on these objects isn’t constant,” said Dr. Fredy Zypman, a professor of physics and co-author of the paper “Surface Gravity of Rotating Dumbbell Shapes” with Dr. Marian Gidea, professor and chair of the M.S. and Ph.D. mathematics programs, and Dr. Wai-Ting Lam, a doctoral alum in mathematics and now a member of the faculty at Yeshiva University’s Stern College for Women.

Asteroids in the solar system can take on a variety of shapes. They are of particular interest to scientists and explorers because they’re rich in minerals. “The exploration of the irregular gravity fields is compelling,” said Dr. Lam. “In particular, dumbbell shapes are among those that have been observed for comets and asteroids.”

The Katz School researchers focused on dumbbell-shaped, or peanut-shaped, asteroids whose gravitational fields can vary widely on their surfaces because their mass is unevenly distributed, as opposed to Earth, a nearly rounded object that produces a relatively constant gravitational field.

“Dumbbells are among the shapes that have been observed for comets and asteroids, making them both astronomically and mathematically interesting,” said Dr. Gidea. “Because the gravitational field of an asteroid is complicated, more irregular, spacecrafts have to be very careful on their approach.”

Examples of oddly shaped asteroids include Hektor, the largest Jupiter Trojan asteroid that has its own moon; the Comet Hartley 2, which was the target of a flyby in 2010 by NASA’s Deep Impact spacecraft; and the trans-Neptunian Arrokoth, or Ultima Thule, located in the Kuiper Belt, which was the target of the New Horizons space probe’s flyby in 2019.

“In addition to the general results for gravity on peanut-shaped objects, we also created a model for the shape of Hektor that can be described by simple equations. This formula gives us a possible family of shapes for this type of asteroid,” said Dr. Gidea. “The peanut-shaped asteroids aren’t all identical. We had to figure out how many exist and the family of shapes, and then we figured out the gravity at any point in the vicinity of these shapes.”

Dr. Zypman said the researchers also studied how the shape of an asteroid changes depending on its rotation. “This knowledge is relevant for understanding how the asteroid formed initially, when the object was still malleable and approaching its current shape.”

Dr. Lea Ferreira dos Santos, professor of physics and chair of the physics department at Stern College for Women, has received two major awards that will significantly help her advance the computational study of many-body quantum systems.

In 2019, Dr. Santos received a $400,000 National Science Foundation grant to study “Nonequilibrium Quantum Matter: Timescales and Self-Averaging.” The grant is a collaboration between the NSF and the U.S.-Israel Binational Science Foundation (BSF) that reduced barriers to working internationally. Using a lead agency model, U.S. and Israeli researchers can submit a single collaborative proposal that will undergo a single review process at NSF, which will be the lead agency.

“This collaboration,” noted Dr. Santos, “will allow for the combination of complementary skills and will significantly expand the NSF-PI’s group size and computer resources.” A further benefit of the collaboration will be that “the undergraduate students of Yeshiva University will have the opportunity to experience research at a Ph.D.-granting institution in Israel.”

This award supports computational and theoretical studies of the evolution of systems that have many interacting particles and which are described by quantum mechanics. These so-called many-body quantum systems are so complex that it is often impossible to describe their evolution analytically, which forces us to resort to numerical methods. But even numerically, the problem is challenging. Because the number of states that need to be considered grows exponentially with system size, existing computers soon run out of memory. As a result, despite being ubiquitous, these systems are still little understood. Understanding the properties of many-body quantum systems out of equilibrium is a fundamental problem of great interest to a wide range of fields, from atomic, molecular, and condensed matter physics to quantum information and cosmology. These studies may also lead to practical applications.

Dr. Santos also received notice that she had been selected as a Simons Fellows in Theoretical Physics by the Simons Foundation, an organization dedicated to “advancing the frontiers of research in mathematics and the basic sciences.” The selection includes a $100,000 grant to support “sabbatical research leaves from classroom teaching and administrative obligations” and is based on “the applicant’s scientific accomplishments in the five-year period preceding the application and on the potential scientific impact of the work to be done during the leave period.”

Dr. Santos’ project will be “Nonequilibrium Quantum Dynamics of Many-Body Systems,” and as she explained it, the grant will give her the time and space to expand her current program of studying nonequilibrium quantum dynamics by allowing her to “initiate a new research line, develop computer codes, strengthen current collaborations and establish new ones, and write proposals.”

Of course, Dr. Santos is thrilled by these awards, not only for the way they help her advance her career but also for the positive notice they bring to Yeshiva University. “I’m especially pleased,” she noted, “that the NSF grant will help my undergraduate students at Stern College work with leaders in the field and across the two countries. The Simons fellowship is a very prestigious award, and I’m humbled by being included in the exceptional company of the past awardees.”

Both Dr. Selma Botman, provost and vice president for academic affairs, and Dr. Karen Bacon, the Mordecai D. Katz and Dr. Monique C. Katz Dean of the Undergraduate Faculty of Arts and Sciences, were both thrilled to hear the news. “We are so very, very proud of her achievements,” said Dr. Bacon, “as well as of this recognition of her as an exceptional scientist and scholar.”

Yeshiva University ranks 68th among Best National Universities and 33rd in Best Value Schools in the 2022 edition of U.S. News & World Report’s Best Colleges.

Read more about Yeshiva University's U.S. News & World Report rankings.