Yury Gogotsi

Bio: Yury Gogotsi is an academic researcher from Drexel University. The author has contributed to research in topics: MXenes & Carbon. The author has an hindex of 171, co-authored 956 publications receiving 144520 citations. Previous affiliations of Yury Gogotsi include Qatar Airways & Clemson University.

Prof. Millie Dresselhaus (1930–2017), Carbon Nanomaterials Pioneer

Abstract: Nanomaterials Pioneer We join the world of science and engineering in mourning the loss last month of Prof. Millie Dresselhaus, an international treasure, a scientific leader, and a mentor to many of us. Prof. Dresselhaus had an inspiring life and career; she broadcast her enthusiasm for science and was a role model and champion for scientists around the world with her creativity, insight, intelligence, and persistence. She was an early supporter of and advisor to us at ACS Nano, offering advice on how we could impact the world, and actively joining that effort. At conferences, she was always up front, paying close attention to all the presentations, and was frequently called upon to capture the sense of the meeting and where the field was going. We were happy to capture those thoughts in writing a number of times. We had planned to have additional such pieces in the near future. Typical of the reactions to our community’s loss were comments from our editors and readers such as “but she is coming to Philadelphia to receive the Franklin Medal this May.” We all thought that we had her with us for the foreseeable future, and it is difficult to imagine that future without her. At the annual nanotube conference, one of several where she regularly summarized the meeting, the conference has been renamed “NT17 in honor of Millie Dresselhaus.” Many of us around the world relied on her wisdom. Prof. Riichiro Saito of Tohoku University in Sendai, Japan, who has collaborated with Prof. Dresselhaus since 1991 and coauthored more than 170 papers, recalled that, “Whenever I sent the draft of a paper or book by email before going home for the evening, I had it back in the morning; she would take advantage of the time difference between Boston and Japan to edit when I was sleeping.” Prof. Gang Chen, her colleague at MIT, with whom she collaborated for 20 years, said, “Warm and open, she is always receptive, ready to work, and willing to help. She earned respect all over the world and made friends both old and young.” Many others have sent us their comments and warm thoughts on all that she did both for the scientific community and for a worldwide cohort of individuals, including each of us.

In-situ TEM Study of Thermal Stabilities of Metastable Silicon Phases

Abstract: The cubic diamond structure of silicon (Si-I) undergoes a phase transformation to a tetragonal structure (Si-II) at a pressure level of 11.2~12 GPa. This transition is not reversible; a mixture of body-centered cubic Si-III (bc8) and rhombohedral Si-XII (r8) structures or amorphous silicon (a-Si) may form during pressure release [1]. In the last decade, depth-sensing indentation has proven to be a powerful tool for studying phase transformations in silicon under highly deviatoric stresses. However, the transmission electron microscopy (TEM) analysis of various Si structures formed during nanoindentation has been largely inhibited by the difficulties involved in sample preparation. Recently, with the aid of focused ion beam and other advanced TEM sample preparation techniques, a few groups have performed successful TEM studies on residual silicon indentations [2-6]. However, the structures formed under load and the exact transformation mechanisms between different phases are still not fully understood. Furthermore, the thermal stabilities of metastable phases (such as Si-III and Si-XII) formed within nanoindentations have not been reported. In this paper, a plan-view TEM work on silicon nanoidentations is presented. This work is then used to discuss phase transformation mechanisms during unloading and to investigate the stability of metastable silicon phases during heating in TEM.

Removal and Recovery of Ammonia from Wastewater using Ti$_3$C$_2$T$_x$ MXenes in Flow Electrode Capacitive Deionization

Abstract: Flow electrode CDI systems (FE-CDI) have recently garnered attention because of their ability to prevent cross contamination, and operate in uninterrupted cycles ad infinitum. Typically, FE-CDI electrodes suffer from low conductivity, which reduces deionization performance. Higher mass loading to combat low conductivity leads to poor rheological properties, which prevent the process from being continuous and scalable. Herein, Ti3C2Tx MXenes were introduced as 1 mg/mL slurry electrodes in an FE-CDI system for the removal and recovery of ammonia from stimulated wastewater. The electrode performance was evaluated by operating the FE-CDI system with a feed solution of 500 mg/L NH4Cl running in batch mode at a constant voltage of 1.2 and -1.2 V in charging and discharging modes respectively. Despite low loading compared to activated carbon solution, Ti3C2Tx flowing electrodes showed markedly improved performance by achieving 60% ion removal efficiency in a saturation time of 115 minutes, and an unprecedented adsorption capacity of 460 mg/g. The system proved to be a green technology by exhibiting satisfactory charge efficiency of 58-70% while operating at a relatively low energy consumption of 0.45 kWh/kg when compared to the current industry standard nitrification-denitrification ammonia stripping process. A 92% regeneration efficiency showed that the electrodes were stable and suitable for long term and scalable usage. The results demonstrate that MXenes hold great potential in improving the FE-CDI process for energy-efficient removal and recovery of ammonium ions from wastewater.

Exploring nanotechnology with electrospinning: Design, experiment, and discover!

Abstract: Nanotechnology is a challenging concept to teach. The length scales involved are difficult to visualize, the products are invisible to the human eye and in most cases the fabrication and characterization of nano-scale materials are prohibitively expensive for high school science programs. Moreover, the inaccessibility of nanotechnology in the classroom reduces the student’s experience to factual recall of a list of properties and advantages of materials at the nanometer scale. This situation does nothing to alleviate the perception that science/engineering is boring and does not engage students in the actual work patterns and discourse of practicing Science Technology Engineering and Mathematics (STEM) professionals. To redress this situation, students need not only to acquire the fundamental principles of nanotechnology, but participate in activities designed to encourage the habitus that will make it more likely they will pursue higher education in STEM fields. Electrospinning was chosen as a vehicle to explore nanofabrication because it is not only simple, but inexpensive. The physics, chemistry, and engineering principals used in electrospinning were attainable for high school students and the materials used to produce the nanofibers are safe for a classroom. In this project, the students built K’NEX electrospinning stations, and identified the process variables and material’s properties that control the resulting fiber diameters and product yield. They wrote a short proposal positing their hypothesis and a detailed experimental plan to optimize the fiber diameters and yield using their electrospinning station. The students implemented their experiment, trouble shot equipment failures, and collected their nanofibers. In collaboration with a local university their nanofibers were imaged using an SEM and the students analyzed the fiber diameter distributions with Image J software and a statistical package in Excel. The electrospinning activity was supported through a series of short lectures and inquirybased activities designed to provide a working knowledge of nanotechnology in general and the physics and chemistry employed in nanofiber production specifically. Additionally several modes of assessment were used through out the activity. In particular, an attitudes inventory was administered pre and post activity to evaluate change in perceptions about pursuing STEM careers. Summative assessments were used to gage student’s learning and performance based assessments were used to enhance student’s internalization of the subject matter. The students demonstrated an improved understanding of nanotechnology across the board and girls performed better than the boys on the summative assessment. As a capstone on the project the students produced posters to communicate their findings to their peers and compete in local and regional science fairs. This project was a joint effort between high school teachers who participated in the 2011 Research Experience for Teachers in Nanotechnology (RET-Nano), students in the 2011 Research Experience for Undergraduates (REU), their graduate mentors and faculty. The RET-Nano teachers and REU students/mentors worked together to develop lesson plans and activities to scaffold the high school student’s learning experience. The REU students P ge 25617.2 designed, built the tested the experimental hardware for the electrospinning traveling kit. And the graduate mentor travelled to all of the schools to demonstrate the electrospinning equipment and talk about her research. Introduction: Preparing the next generation of scientists and engineers for an increasingly global technology-based economy is a challenge faced by many STEM (Science, Technology, Engineering, and Mathematics) educators in the US. Although organizations such as the National Nanotechnology Initiative focus their efforts on preparing the nation for the estimated need for 2 million in the field of nanotechnology by 2015, many of our students are not measuring up 1 . For example, the National Assessment of Educational Progress (NAEP) reports that only 30% of eighth-graders and 21% of twelfth-graders ranked at or above the Proficient level in science. Similarly, only sixty-three percent of eighth-graders and 60% of twelfth-graders performed at or above the Basic level in science in 2009. Such reports clearly indicate that the US is quickly falling behind other world leaders in educating the next generation of scientists and engineers. Nanotechnology is the study of materials and their properties at the nanoscale, approximately sizes between 1 and 100 nanometers. At this scale, many materials exhibit properties and behaviors unique to the nanoscale. The applications of nanotechnology are becoming increasingly incorporated into modern life. For example, materials such as tennis rackets, makeup, and paint all utilize nanotechnology to make materials stronger, lighter and more energy efficient. Due to the high demand of a technical workforce versed in the area of nanotechnology, this field is becoming increasingly incorporated into the K-12 curriculum. While there is no doubt that the study and understanding of materials on the nanoscale is vital to the manufacturing preparedness of our country. For example, Cornell University in NY has established a “Nano World” traveling exhibit to educate students in the K-12 system about nanobiotechnology through engaging hands on activities 2 . Currently there had been an increased effort to incorporate hands – on activities in the science classroom through traveling kits such as the NISENET kits 3 . Research has shown that multi-modal approach not only addresses learning styles but scaffolds students learning to develop problem solving skills, inquiry based learning, and intellectual development 4 . Therefore a group of teachers in collaboration with Drexel University have developed a novel electrospinning lecture series and hands-on activity to be implemented into high school classrooms. The purpose of this project is three fold: 1) to encourage high school students to pursue careers in STEM fields 2) Introduce the field of nanotechnology and its applications to high school students 3) to provide a hands-on nanotechnology activity that involves the following elements: design, experimentation, analysis and reporting of results. This project was a joint effort between three high school teachers from the Greater Philadelphia Region (GPR) who participated in the 2011 NSF Research Experience for Teachers in Nanotechnology (RET-Nano), students in the 2011 NSF Research Experience for Undergraduates (REU), their graduate mentors and faculty. P ge 25617.3 Materials: Polyethelene Oxide (PEO) (MW: 300,000g/mol) was purchased from Sigma Aldrich and used as received. A VWR scale (Model: SLW302-US) was used to weigh dry PEO. All solutions were prepared with tap water mixed with a magnetic stir bar on a stir-plate in labeled 200 ml beakers. Solutions were contained in a small, rectangular reservoir for each setup. Various K’NEX pieces were provided and assembled to form a housing for the PEO reservoir and attachments for the K’NEX motor, axle, spindle holder and collection plate. (Appendix A) A high voltage power supply (Model: ES40P-10W/DAM) from Gamma HV Power Supplies was attached to custom breakout boxes built from electrical wall housings and wired to each female RCA plug in series on a face plate. Each electrospinning setup was connected to the breakout box via two RCA-Alligator cables; positive to the spindle wires, and ground to the collector plate. Electrical tape was used to insulate exposed connections. The K’NEX motors were powered by K’NEX battery packs containing two AA batteries. A collection plate of aluminum foil was wrapped around a 3X3 inch piece of copper screen attached to the common ground. Optionally, collection plates were visualized under classroom microscopes following each experiment to confirm the presence of polymer. Each foil collection plate was carefully placed into a plastic sandwich bag for transport to a local University and inspected under Scanning Electron Microscope (SEM). A Ziess VP 5 Supra scanning electron microscope (SEM) was used to image the fibrous mats. The SEM samples were prepared by sputter coating, Denton Vacuum, with Pt target at 40 milli amps for 35 s resulting in a 7-8 nm conductive film. The SEM was run at 3.5 KV at a 11mm working distance in high vacuum. Image results were sent via email to students for fiber diameter analysis with Image J. Methods: The schools that participated in this project were from three different regions in the Greater Philadelphia Region and reflect three different learning environments: An upperclassmen Physics course in a rural high school, two sophomore honors chemistry classes in an all male parochial school and two freshmen general science classes in an urban charter school. Reduced/free lunch data were not available from administration for these schools. All the teachers participated in a NSF RET-Nano summer program and the graduate student was a NSF REU Sensors mentor and the undergraduate was her NSF REU Sensors student. The RET-Nano teachers and REU students/mentors worked together to develop lesson plans and activities to scaffold the high school student’s learning experience. The REU student and mentor designed, built, and tested the experimental hardware for the electrospinning traveling kit shown in Figure 1 (a-d). And the graduate mentor travelled to all of school sites to demonstrate the electrospinning equipment and talk about her research. The electrospinning kit rotated to all three schools starting in the early fall with the physics class, then to the general science class finishing at the honors chemistry class. Page 25617.4 At each school the students were introduced to nanotechnology and its applications through a series of short lectures and inquiry-based activities designed to support the central c

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Materials for electrochemical capacitors

Abstract: Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices.