HEMI Graduate Student Suhas Eswarappa Prameela Featured in Science Working Life

Suhas Eswarappa Prameela, a graduate student in HEMI, has been featured in Science Magazine’s Working Life section with an essay about finding his voice on Twitter.

His essay describes how he found value in sharing his experiences on the science side of Twitter. In the beginning, he only tweeted about his research results. One day, out of frustration, he tweeted about the “importance of properly naming research files.” Prameela was retweeted by a high-profile academic account and went viral overnight.

Prameela initially had apprehensions about sharing his experiences online. He said, “Who was I to offer advice? I’m just a PhD student doing my best; I didn’t know whether I was doing anything right myself!” However, after falling into his new-found Twitter fame, he began tweeting regularly about his personal experiences as a PhD student: from navigating authorship conflicts to giving presentations and more.

As a result of his efforts, other students on Twitter have reached out to him, thanking him for his tweets and asking questions. Prameela says that although sometimes he feels “uncomfortable and vulnerable sharing my experiences on a massive global platform, I’ve found it is well worth it. I’ve learned that we are all stronger if we authentically share and connect with one another.”

Science Magazine’s Working Life section features articles that discuss the professional side of science and research, with topics ranging from mentorship to mental health struggles and more. Click here to read the full text of Prameela’s essay.

You can follow Prameela on Twitter (@suhas_prameela) here.

Simulations offer new approach for designing high strength metals under high rate loading

Jaafar El-Awady, HEMI Fellow and associate professor of mechanical engineering, has co-authored research that reveals more clues about the microscopic mechanisms that govern the strength of metals.

In the paper recently published in Nature Communications, titled “Strain rate dependency of dislocation plasticity,” El-Awady and team present a new understanding of the effects of strain rate and dislocation density on the deformation behavior of aluminum and cooper.

Metals like aluminum and cooper are commonly used engineering materials, thanks in part to their strength and damage tolerance. Why, then, do metals sometimes deform or break unexpectedly due to stress? Understanding why metal components fail will inform the design of stronger metals, improving their performance in a broad range of applications.

In materials research, the flow strength refers to a material’s ability to resist deformation under an applied load. Metal properties are loading rate sensitive, meaning they react differently across various rates of loading. Dislocations, or line defects, in metals also move and localize under loading, which is a precursor to crack initiation and failure. Thus, researchers hypothesize that dislocation density, or the number of dislocations per unit area in a material, may affect the loading rate sensitivity of the material. However, the relationship between the two mechanisms is still not well understood.

To solve this problem, the team performed a large set of three-dimensional discrete dislocation plasticity simulations to predict the metal yield strength at different initial dislocation densities and strain rates. The simulation results showed that the material response can be divided into two regimes. In one regime, dislocation-dislocation interactions control the material flow strength; in the other, strain rate induced hardening dominates. Additionally, the transition between both regimes is mainly controlled by the dislocation density in the material.

Based on their observations, the team was able to develop a unified law that correlates the material flow strength with the loading strain rate and the initial dislocation density in the material. This unified law is shown to be in excellent agreement with a large set of experimental results from previous studies.

The study provides a fundamental understanding of the co-interaction of different mechanisms in materials and how they influence the material strength, said El-Awady. These findings could help researchers design metals better suited for high strain rate loading applications, by tailoring the initial dislocation density in the material to achieve a desired strength.

In addition to El-Awady, the research team includes first author Haidong Fan, a former Johns Hopkins postdoc and current professor at Sichuan University, Qingyuan Wang, Dierk Raabe, and Michael Zaiser.

Excerpted from the Department of Mechanical Engineering >>

HEMI Fellow Sung Hoon Kang Highlights Applications for Microactuators in Science Robotics Article

Sung Hoon Kang, HEMI Fellow, assistant professor in the Department of Mechanical Engineering, and associate researcher at the Institute for NanoBioTechnology, has written a focus article about the fabrication of and potential applications for an electrically-controlled shape-memory microactuator that operates in a solution matching the ion concentration of the human body. The article was published in Science Robotics and includes contributions by Kang’s graduate students Mostafa Omar and Bohan Sun.

Titled “Good reactions for low-power shape-memory microactuators,” the article details the mechanism of the microactuator and its potential versatile applications. The microactuator has two configurations: bent and flat. When the bent microactuator is exposed to an electrochemical oxidation reaction, an oxide layer grows on its surface, expanding and flattening the device into its flat configuration. The oxide layer stays after the reaction, which allows the device to maintain its shape without applying voltage. As such, it is especially useful for robots operating with limited power supplies.

The article showcases the versatility of microactuators in extreme environments. For example, in medicine, applications can include: controlled drug delivery, temporary clamps in place of stitches, and fast-response devices against blood clots in arteries. Other applications include use as a microvalve to control flow in microfluidics and reconfigurable optical metamaterials/metaservices. Its potential for application can be further increased by improving energy efficiency, speed, actuation range, and durability.

Read the focus article here.


HEMI Fellow Jaafar El-Awady Identifies New Method to Predict Cracks in Metal Before They Are Visible

Congratulations to Jaafar El-Awady, HEMI Fellow and associate professor in the Department of Mechanical Engineering, for discovering a new method to predict cracks in metal before they appear. His results were published in Science.

His paper, titled “The heterogeneity of persistent slip band nucleation and evolution in metals at the micrometer scale,” identifies a new method to test metals and predict vulnerabilities before visible cracks are formed. This has implications in understanding and predicting the life of a metal mechanism, especially to help prevent fatigue failure and to avoid discarding parts that may still be useful.

“We’re able now to have a more fundamental understanding about what leads up to cracks,” El-Awady said. “The practical implication is that it will allow us to understand and predict when or how the material is going to fail.”

Read El-Awady’s paper here.

HEMI Fellow Ryan Hurley Leads Research Team to Determine How Forces Control Granular Material Properties

Understanding the way a wave moves through granular materials—after an earthquake, for example—has vast implications for modern science. After all, scientists use stress wave propagation through granular materials to detect the magnitude of earthquakes, locate oil and gas reservoirs, design acoustic insulation, and develop materials for compacting powders.

Using X-ray measurements and analyses, a team of researchers led by a Johns Hopkins mechanical engineering professor have shown that velocity scaling and dispersion in wave transmission is based on particle arrangements and chains of force between them, while reduction of wave intensity is caused mainly from particle arrangements alone. The research appeared yesterday in the online edition of the journal Proceedings of the National Academy of Sciences.

“Our study provides a better understanding of how the fine-scale structure of a granular material is related to the behavior of waves propagating through them,” said Ryan Hurley, assistant professor of mechanical engineering at Johns Hopkins Whiting School of Engineering and fellow of the Hopkins Extreme Materials Institute. “This knowledge is of fundamental importance in the study of seismic signals from landslides and earthquakes, in the nondestructive evaluation of soils in civil engineering, and in the fabrication of materials with desired wave properties in materials science.”

Hurley conceived of this line of research while a postdoc at Lawrence Livermore National Laboratory, collaborating with a team that included physicist Eric Herbold. The experiments and analysis were later performed by Hurley and Whiting School postdoc Chongpu Zhai after Hurley moved to JHU, with experimental assistance and continued discussions with Herbold.

Structure-property relations of granular materials are governed by the arrangement of particles and the chains of forces between them. These relations enable the design of wave damping materials and non-destructive testing technologies. Wave transmission in granular materials has been extensively studied and demonstrates unique features: power-law velocity scaling, dispersion, and attenuation (the reduction of the amplitude of a signal, electric current, or other oscillation).

Earlier research dating back to the late 1950s described what may be happening to material underlying wave propagation, but the new research provides evidence for “why.”

“The novel experimental aspect of this work is the use of in-situ X-ray measurements to obtain packing structure, particle stress, and inter-particle forces throughout a granular material during the simultaneous measurement of ultrasound transmission,” said Hurley. “These measurements are the highest fidelity dataset to-date investigating ultrasound, forces, and structure in granular materials.”

“These experiments, along with the supporting simulations, allow us to reveal why wave speeds in granular materials change as a function of pressure and to quantify the effects of particular particle-scale phenomena on macroscopic wave behavior,” said Zhai, who led the data analysis efforts and was that paper’s first author.

The research provides new insight into time- and frequency-domain features of wave propagation in randomly packed grainy materials, shedding light on the fundamental mechanisms controlling wave velocities, dispersion, and attenuation in these systems.

This story was originally posted on the Hub in June 2020.

The image is a combination of two sets of data from X-ray scans of single crystal sapphire spheres.
The image is a combination of two sets of data from X-ray scans of single crystal sapphire spheres. The reconstructed X-ray Computed Tomography (XRCT) data defines the surface of all 621 grains in the load frame. The far-field X-ray Diffraction (ff-XRD or 3DXRD) data provides a strain tensor that is mapped to each grain center. The combination and colorization of this data shows the distribution of stresses for each grain under load. This information was used as initial conditions for ultrasonic transmission measurements, where structure-property relationships were measured in-situ.

This research was funded by the Johns Hopkins Whiting School of Engineering and LLNL’s Laboratory Directed Research and Development program, and was carried out at the Advanced Photon Source, an Office of Science User Facility, operated by Argonne National Laboratory.

HEMI Fellow Sarah Hörst Published in Sky and Telescope Magazine

Congratulations to HEMI Fellow Sarah Hörst, an assistant professor in the Dept. of Earth and Planetary Sciences whose article, “Titan’s Veil,” is featured in the February issue of Sky & Telescope magazine.

The eight-page article details the chemical ingredients found within the each region of atmosphere of Saturn’s largest moon, Titan, and likens that complex atmospheric makeup to that of early Earth.  In doing so, Hörst makes a point that, by studying Titan, we might learn enough to identify markers that will allow us to recognize habitable planets surrounding other stars.

Hörst’s primary research interest is atmospheric chemistry. She is particularly interested in the complex organic chemistry occurring in the atmosphere of Titan, but is also interested in complex organics elsewhere in the solar system and universe, whether they are produced in an atmosphere or on a surface.

Sky & Telescope is the essential guide to astronomy, showcasing each month a wide array of celestial events and astronomy news to a highly-engaged audience that includes astronomy practitioners of all levels – from novices with their first telescope, to intermediate and advanced backyard astronomers, to professionals.



HEMI Fellow June Wicks Authors Paper Containing Record-breaking Data for Use in Simulating Core Conditions for ‘Super-Earth’ Exoplanets

Congratulations to June K. Wicks, a HEMI Fellow and an assistant professor in the Department of Earth and Planetary Sciences, who published a paper today in Science Advances reporting X-ray diffraction data on iron-silicon alloys at core conditions of “super-Earth” exoplanets.

Using high-powered laser beams, Wicks and her colleagues at Princeton University, Lawrence Livermore National Laboratory, and the University of Rochester have developed techniques to extend X-ray diffraction of solid materials to TPa pressures (1 TPa = 10 million atmospheres). This work represents the highest-pressure X-ray diffraction data ever reported.

With the continued discovery of thousands of planets outside our solar system, an effort that will be extended with instruments such as the James Webb Space Telescope, scientists are eager to learn more about interior structures of these exoplanets. However, in this quest researchers have encountered two major limitations: they have no direct measurements of our own planetary core from which to extrapolate, and interior pressures in super-Earths can reach more than 10 times the pressure at the center of the Earth, well beyond the range of conventional experimental techniques. By using groundbreaking techniques, Wicks and her colleagues have generated the first experimental data on likely constituent core materials at pressures exceeding 1.3 TPa, about three times higher than previous experiments. These data are directly useful for modeling the interior structure of large, rocky exoplanets, which in turn provides insights into the types of planetary architectures that may exist in our galaxy.

Wicks and her colleagues directed a short but intense laser beam onto two iron samples: one alloyed with 7 weight-percent silicon, similar to the modeled composition of Earth’s core, and another with 15 weight-percent silicon, relevant to more silicon-rich planets. They compressed these samples for only a few billionths of a second, but it was just long enough to probe the atomic structure using a pulse of bright X-rays. The resulting diffraction pattern provided information on the density and crystal structure of the iron-silicon alloys, revealing that the crystal structure changed with higher silicon content.

The researchers found that at ultrahigh pressures, the lower-silicon alloy organized into a hexagonal close-packed crystal structure, while the higher-silicon alloy adopted body-centered cubic packing.

“This atomic difference has enormous implications,” said Wicks. “Knowledge of the crystal structure is the most fundamental piece of information about the material making up the interior of a planet, as all other physical and chemical properties follow from the crystal structure.”

Future research will investigate how other light elements, such as carbon or sulfur, affect the structure and density of iron at ultrahigh pressure conditions. The researchers also hope to measure other key physical properties of iron alloys, to further constrain models of exoplanets’ interiors.

Crystal structure and equation of state of Fe-Si alloys at super-Earth core conditions,” by June Wicks, Raymond Smith, Dayne Fratanduono, Federica Coppari, Richard Kraus, Matthew Newman, J. Ryan Rygg, Jon Eggert and Thomas Duffy was published April 25 in Science Advances. The research was funded by the National Nuclear Security Administration through the National Laser Users’ Facility Program (contract nos. DE-NA0002154 and DE-NA0002720) and the Laboratory Directed Research and Development Program at Lawrence Livermore National Laboratory (project no. 15-ERD-012).

HEMI Fellow June Wicks Contributes to the Formulation of New Mass-Radius Relationship for a Hypothetical Pure Iron Planet at Super-Earth Core Conditions

Congratulations to HEMI Fellow June K. Wicks (Dept. of Earth and Planetary Sciences), who, along with collaborators from Lawrence Livermore National Laboratories, Princeton, and the University of Rochester, has published the first experimentally-based mass radius relationship for a hypothetical pure iron planet at super-Earth core conditions.

The discovery, published earlier this week by Nature Astronomy, is hoped to be used to evaluate plausible composition of large, rocky exoplanets and aid with the formation of interior planetary models.

They measured the first absolute equation of state of iron to 1.4 TPa (14 million atmospheres) on the National Ignition Facility, the world’s largest and most energetic laser.

“The high-pressure behavior of iron metal is the anchor point for interpreting exoplanet observations,” Prof. Wicks says. “Now that we know the equation of state of iron, we can probe the effect of light element alloying on observable properties and explore the diversity of planetary cores in our universe.”

To read the paper in its entirety, visit www.nature.com/articles/s41550-018-0437-9.

Harvesting Wind Energy with a Piezo-Flag: Kang Group Published in Applied Energy

HEMI fellow Sung Hoon Kang and his team were recently published in Applied Energy, a journal  focusing on the modern state of research and development for energy conversion and conservation. Titled “Harvesting Ambient Wind Energy With an Inverted Piezoelectric Flag,” the publication showcases a novel way to enhance the wind-harvesting capabilities of piezoelectric materials.

Pictured above, HEMI postdoctoral fellow Santiago Orrego demonstrates the technology; optimizing the flexible and conductive properties of piezoelectric material to make a nano-generator that could provide energy for time-spans extending over months, and even years. Dr. Kang’s group has since refined this innovative energy source by changing the flag orientation, allowing the “piezo-flag” to be tuned to the most efficient flapping direction for ambient wind conditions.


The paper describes an experimental study of wind energy harvesting by self-sustained oscillations (flutter) of a flexible piezoelectric membrane fixed in a novel orientation called the ‘‘inverted flag.”


The flutter and piezo-leaf design was experimentally tested using a wind tunnel simulator, as shown in the video here. The design was also mounted onto the roof of Garland Hall at Johns Hopkins University to test ambient wind conditions on the nano-generator. In this case, the generator powered a sustainable temperature sensor.

Orrego is working on this project in conjunction with Assistant Professor Sung Hoon Kang from the The Kang Group and the Department of Mechanical Engineering and mechanical engineering Professor Rajat Mittal from the Flow Physics & Computational Lab.

To read the full abstract and publication, click here.

Follow the project and check out a sustainable temperature reading: https://www.youtube.com/channel/UCDxonH3QS1GNzysYly6hsTw/live