Zoom link available upon request- email sekhrn@missouri.edu

Abstract:

A new instrument is described that employs buffer gas cooling with mm-wave rotational
spectroscopy to probe molecules desorbed from interstellar ice analogues. The unique
combination of these tools has shown, for the first time, direct measurement of products formed
and desorbing from astrochemical ice analogues with both isomer and conformer specificity, and
determined their relative abundances under well-defined, astrochemically-relevant conditions.
Details of the technique, apparatus, and first results will be described in application to the
temperature-programmed desorption of n- and i-propyl cyanide with rotational spectroscopic
detection. This approach represents a new window into the emergence of chemical complexity in
star forming regions.

Abstract

         Steels have important applications in current and advanced nuclear reactors, however, their irradiation tolerance and mechanical properties need to be improved. Bulk ultrafine-grained and nanocrystalline metals possess drastically higher strength than their conventional coarse-grained counterparts due to significant grain boundary strengthening, and are anticipated to have significantly enhanced irradiation tolerance owing to the role of grain boundaries as sinks for irradiation-induced defects. In our 7-year-long and multi-million-dollar DOE project, ultrafine-grained and nanocrystalline austenitic and ferritic steels were manufactured by equal-channel angular pressing (ECAP) and high-pressure torsion (HPT), respectively. The microstructure and mechanical behavior of the steels manufactured by ECAP and HPT were carefully studied. The thermal stability of the ultrafine-grained and nanocrystalline steels was also investigated. For ferritic FeCrAl alloys with different ranges of grain sizes, thermal aging was conducted to study thermally induced α’ Cr precipitation, which typically causes embrittlement. Neutron irradiation was performed to study irradiation behavior of the steels. Ion irradiation was also conducted to compare with the neutron irradiation. Results indicate that the ultrafine-grained and nanocrystalline steels manufactured by ECAP and HPT possess significantly improved hardness/strength compared to their conventionally manufactured coarse-grained counterparts. In FeCrAl alloys, with decreasing grain size, thermally induced α’ Cr precipitation was reduced. In 304 and FeCrAl steels, smaller grains possess reduced irradiation-induced hardening, segregation and precipitation compared to larger grains. Ultrafine-grained and nanocrystalline 304 steels have enhanced phase stability during irradiation compared to the coarse-grained counterpart. These results indicate enhanced irradiation tolerance of ultrafine-grained and nanocrystalline steels.

Bio

          Dr. Wen is an Assistant Professor in Department of Materials Science and Engineering and Department of Nuclear Engineering and Radiation Science at Missouri S&T. He obtained his PhD from University of California – Davis in 2012, and subsequently held postdoctoral appointments at Northwestern University and Idaho National Laboratory. Prior to joining Missouri S&T, he was a Research Assistant Professor at Idaho State University and a staff scientist at Idaho National Laboratory. Dr. Wen has extensive experience in research and development of advanced materials, including those for nuclear applications. He has been leading multiple research projects funded by Department of Energy, National Science Foundation, and Nuclear Regulatory Commission. Dr. Wen has authored or coauthored more than 65 peer-reviewed journal publications, with citations >3,200 and an h-index of 24. He serves on the Editorial Board of the journal Materials Science and Engineering A, and has served as the lead guest-editor of a special issue in AIMS Materials Science. He regularly reviews manuscripts for many journals and research proposals for DOE and NSF.

Switching of control mechanisms during the rapid solidification of alloys

Abstract

The formation of complex solidification patterns is an intrinsic non-equilibrium phenomenon. It is the interplay between capillary and kinetic effects at the solidification front (solid-liquid interface) that produces the complex growth patterns we see in nature. In general, the solidification growth is solely controlled by diffusion. Pure metals are controlled by thermal diffusion, while alloys are controlled by solute diffusion.  However, in the rapid solidification of alloys, the solidification growth may undergo a change from solute diffusion-controlled to thermal diffusion-controlled. The switching of control mechanisms is found to cause the velocity jump and disrupt the microstructure development. In this work, we will investigate two rapid solidification processes, additive manufacturing (AM) and melt spinning (MS), using phase-field modeling. Specifically, the nucleation or the onset of the solidification of AM and MS will be explored. The resulting solidification pathway and the development of inhomogeneous microstructures will be elucidated.

Bio

Dr. Yijia Gu obtained his Ph.D. in Materials Science and Engineering (MSE) with a minor in Computational Science from the Pennsylvania State University in 2014. During his Ph.D., Dr. Gu performed thermodynamic and kinetic modeling work on semiconductor, metal, and ferroelectric materials mostly using the phase-field method. Then, he launched his career at Alcoa Technical Center (ATC, now Arconic Technology Center), where he was first a Senior Engineer and then Staff Engineer. At ATC, he did CALPHAD and kinetic modeling work for alloy design and processing optimization, including both conventional route and additive manufacturing. In 2019, he joined Missouri S&T as an Assistant Professor in the MSE department, where he has been collaborating with colleagues and continues to apply computational materials modeling to the studies of advanced steels, machine learning-assisted alloy design, as well as metal additive manufacturing

Abstract

Radiative cooling is a passive cooling technique featured with zero-energy consumption by emitting terrestrial heat to the universe in form of blackbody thermal radiation. Nocturnal radiative cooling is an ordinary phenomenon of radiative cooling effect happening during a clear and calm night, but day-time sub-ambient radiative cooling material, which can cool an object’s surface temperature below ambient air temperature, has never been found in nature. The first realization day-time radiative cooler has been demonstrated by optimizing spectroscopic property of its surface from ultra-violet to mid-infrared, and indicates the day-time sub-ambient radiative cooling material is a promising cooling solution to save energy from current cooling facilities, such as air conditioners. Therefore, a scalable, low-cost day-time sub-ambient radiative cooling material is demanded to mitigate energy demand in large-scale thermal management systems. In this talk, Dr. Zhai will introduce his research projects related to day-time sub-ambient radiative cooling materials and systems, including scalable-manufactured optical metamaterial, kilo-watt scale radiative cooling collection and storage system, as well as radiative cooling structural materials. He will also discuss potential applications of day-time sub-ambient radiative cooling materials in renewable energy generation, environment sustainability and space cooling in buildings.

Dr. Zhai is an assistant professor in the Department of Mechanical & Aerospace Engineering at the University of Missouri Columbia. Dr. Zhai received his PhD degree from the University of Colorado Boulder and continued his postdoc in the National Institute of Standards and Technology. Dr. Zhai’s research interests focus on investigating novel optical materials with unprecedented properties and developing advanced manufacturing technologies to transform these materials into practical solutions in real-world applications in energy, thermal management, environment sustainability.

Materials and Device Physics for Solid-State Lighting and Renewable Energy Generation

Peifen Zhu

Department of Electrical Engineering and Computer Science, University of Missouri

Abstract:

Efficient use of energy and renewable energy production are of paramount importance to society. Lighting accounts for one-eighth of total U.S. electricity consumption. Light-emitting diodes (LEDs) as a new generation lighting technology have extremely long-life spans and consume much less energy. They are penetrating our daily life and adoption of this technology is expected to reduce energy consumption by 40% in 2030.  Despite rapid advances, LED technology is still in its early stage, and continued innovation and breakthroughs are needed to achieve the full potential of this technology. The relatively higher initial cost of LED over incumbent light sources is hindering the widespread adoption of this technology. Therefore, the utilization of cost-effective approaches to achieve high-efficiency LED is instrumental in the application of this technology in the general illumination market. The periodic nanostructures by low-cost self-assembly process were implemented on both LED and OLED, which resulted in a significant enhancement in power efficiency. The key advantage of the self-assembly process is the ability for implementation of roll-to-roll printing method for large wafer-scale manufacturing processes. Developing efficient, stable, and narrow linewidth down-converter materials as well as engineering the properties of existing materials, which can combine with blue LED chips to generate white light with high color quality, will speed up the adoption of LED in the general illumination market. Both material development and additive manufacturing of white LEDs will be presented. Photocatalysis of CO2 is an environmentally friendly and promising technology to convert CO2 into value-added chemical fuels using solar energy. However, the conversion efficiency is low due to the complex reactions. The efforts to improve the CO2 adsorption capacity, light absorption, and charge separation will also be covered.

Quasiparticles with total angular momentum greater than j=1/2 can emerge in a solid state with strong spin-orbit interaction. While the existence of such high-spin quasiparticles has been known for decades, their implication has been largely overlooked. The possibility of superconductivity beyond spin-triplet in such solid states attracted substantial attention. In this talk, I will talk about unconventional quantum oscillations and superfluid response in half-Heusler YPtBi which is a topological semimetal with j=3/2 quasiparticles. The angle-dependent quantum oscillation exhibits striking anisotropy, and the London penetration depth varies as almost temperature-linear, both of which are not easily expected in a compound with cubic symmetry. These anomalous behaviors can be explained within j=3/2 Fermi surface and high-spin superconductivity.

Triangular magnetic structures have gained considerable interest due to their rich magnetic behavior and structural simplicity. These structures contain the motif of a triangle as the main structural feature, leading to geometric frustration and implicitly to degenerate magnetic ground states. Most of the previous work on triangular lattice structures was performed on simple transition metal halides or oxides. Therefore, it presents an interesting challenge for materials scientists to synthesize new class of materials that preserve the quasi-two dimensionality of the structures. This talk will feature two class of materials (1) triangular materials synthesized using high-pressure hydrothermal method (2) AREQ2 (A = Alkali metal, RE= rare earth, Q = O, S, Se) triangular magnetic materials. 

First, I will focus on synthesis, magnetism and use of neutron diffraction to characterize the magnetic phase diagram of several classes of hydrothermally synthesized oxy-anions based transition metal compound series (EOyx-, E = As, Mo, Se). These linking groups can lead to an enormous array of new structure types with great potential for exploring and characterizing new emergent phenomena. Here, I will focus the role of vanadate building blocks (VO43-) in magnetically interesting transition metal layered materials. The vanadates display a rich diversity of structural behavior including multiple bridging modes such as corner and edge sharing. In addition, the presence of vacant d-orbitals in the bridging center can have a significant effect on the magnetic coupling behavior. As the first example, SrM(VO4)(OH) (Mn, Co, Ni) possess on-dimensional magnetic lattice with totally different magnetic properties depending on the transition metal cation even though they crystallizes in same space group. Further, Na2BaM(VO4)2 (M = Mn2+, Fe2+, Co2+) series all have similar chemical structures and are members of the glaserite family, but each one displays dramatically different magnetic behavior between room temperature and 2 K. Another interesting system for discussion is the mixed vanadate carbonate material A2M3(VO4)2(CO3) where A = K, Rb and M = Mn2+, Co2+. The chemical structure is quite complex and has two unique layers, one built of corner sharing vanadates and one with the trigonal planar carbonates. The material also has a complex magnetic behavior and undergoes three magnetic phase transitions between 300-2 K. 

In the second part of my talk, I will focus on the synthesis of ARESe2 single crystal growth, magnetic properties and elastic and inelastic neutron scattering. These crystals crystallize in either trigonal (R-3m) or hexagonal (P63/mmc) crystal systems and associate with an ideal triangular RE3+ layers. The magnetic properties and heat capacity of these compounds were characterized down to 0.4 K. The Yb-compounds exhibit a broader peak in heat capacity ~10 K suggesting short range ordering. 

DNA is a new generation material for molecular data storage, with a potential storage capacity several orders of magnitude greater than current methods. Data stored in DNA can be encoded (written) and decoded (read) using sequencing technologies. Advantages of DNA data storage are (i) high data density, (ii) high stability, (iii) ease of copy, and (iv) low energy. Current methods rely on slow, expensive, complicated synthesis of long DNA to write, followed by costly, high error rate (10%) reads. We overcome these challenges with a low-cost, enzyme-free, mix-and-detect method for high fidelity DNA data reading, writing, and rewriting using nanopore technology and universal rewritable blank medium DNA without the need for nucleic acid synthesis. This technology has applications not only in DNA data storage, but also in DNA barcoding for high throughput screening of nucleic acid secondary structure and drug/ligand binding.

Claudio Mazzoli will present some opportunities of scientific investigation by micro-spectro-scattering in the soft X-ray regime of Resonant X-ray Scattering, as implemented and developed at CSX (the Coherent Soft X-ray scattering beamline of NSLS-II, BNL). The peculiarity of such an integrated approach in terms of space, time, energy scales, and correlations, allows revealing unique properties of materials from the microscopic point of view, and shining new light on a variety of interesting cases. Electronic orderings, inhomogeneities, self-organization, collective dynamics and interplay of degrees of freedom will be presented, together with some future ideas.

Metallic systems with magnetic ions embedded which have been prepared to undergo a second-order phase transition at zero Kelvin, namely the quantum critical systems, historically appear to fall into two distinct categories: (chemically) heavily-doped systems in which the unusual properties can be attributed to a disorder-induced distribution of Kondo shielding temperatures and (nearly) stoichiometric systems where the departures from Fermi-liquid theory have been attributed to intrinsic instabilities. We show that this historic distinction between doped and stoichiometric systems should be left to history: we find that magnetic clusters associated with a distribution of Kondo shielding temperatures found in heavily-doped quantum critical Ce(Fe0.755Ru0.245)2Ge2 are also present in CeRu2Si2, a stoichiometric system close to a quantum critical point. In both the doped and stoichiometric system, the response of these clusters that emerge upon cooling dominates the macroscopic response of these systems. This implies that the dominant physics that drives heavily doped systems, namely spontaneous formation of magnetic clusters, should also play a leading role in the response of homogeneous systems. This represents a notable departure of how the physics that governs quantum critical points has been described in the literature and it might even point the way towards a magnetic pairing mechanism in high Tc superconductors.

Convolutional neural network (CNN) and graph convolutional network (GCN) has gained huge success in various tasks, from image classification, video processing to speech recognition and natural language understanding. The success stems from both the well-designed neural network architecture and the increasing computing power in recent hardware. Many attempts have been made to extend these frameworks to biological problems, with varying success. In this talk, I will present the applications of using both CNN and GCN models to predict Mg2+/small molecule binding sites/modes in RNA molecules. These approaches exploit the information of the local binding environment and predict the most probable distribution of the Mg2+ sites or ligand binding modes. Further comparisons between our methods and various types of methods validate the machine-learning approaches.