Effects of interedge scattering on the Wigner crystallization in graphene nanoribbons

We investigate the effects of coupling between the two zigzag edges of graphene nanoribbons on the Wigner crystallization of electrons and holes using a combination of tight-binding, mean field Hubbard and many-body configuration interaction methods. We show that the thickness of the nanoribbon plays a crucial role in the formation of Wigner crystal. For ribbon widths smaller than 16 \mbox{\AA}, increased kinetic energy overcomes the long-range Coulomb repulsion and suppresses the Wigner crystallization. For wider ribbons up to 38 \mbox{\AA} wide, strong Wigner localization is observed for even number of electrons, revealing an even-odd effect also found in Coulomb blockade addition spectrum. Interedge correlations are found to be strong enough to allow simultaneous crystallization on both edges, although an applied electric field can decouple the two edges. Finally, we show that Wigner crystallization can also occurs for holes, albeit weaker than for electrons.Comment: Accepted for publication in PR

fDETECT webserver: fast predictor of propensity for protein production, purification, and crystallization

Background: Development of predictors of propensity of protein sequences for successful crystallization has been actively pursued for over a decade. A few novel methods that expanded the scope of these predictions to address additional steps of protein production and structure determination pipelines were released in recent years. The predictive performance of the current methods is modest. This is because the only input that they use is the protein sequence and since the experimental annotations of these data might be inconsistent given that they were collected across many laboratories and centers. However, even these modest levels of predictive quality are still practical compared to the reported low success rates of crystallization, which are below 10%. We focus on another important aspect related to a high computational cost of running the predictors that offer the expanded scope. Results: We introduce a novel fDETECT webserver that provides very fast and modestly accurate predictions of the success of protein production, purification, crystallization, and structure determination. Empirical tests on two datasets demonstrate that fDETECT is more accurate than the only other similarly fast method, and similarly accurate and three orders of magnitude faster than the currently most accurate predictors. Our method predicts a single protein in about 120 milliseconds and needs less than an hour to generate the four predictions for an entire human proteome. Moreover, we empirically show that fDETECT secures similar levels of predictive performance when compared with four representative methods that only predict success of crystallization, while it also provides the other three predictions. A webserver that implements fDETECT is available at http://biomine.cs.vcu.edu/servers/ fDETECT/. Conclusions: fDETECT is a computational tool that supports target selection for protein production and X-ray crystallography-based structure determination. It offers predictive quality that matches or exceeds other state-ofthe-art tools and is especially suitable for the analysis of large protein sets

Protein-crystal growth experiment (planned)

To evaluate the effectiveness of a microgravity environment on protein crystal growth, a system was developed using 5 cubic feet Get Away Special payload canister. In the experiment, protein (myoglobin) will be simultaneously crystallized from an aqueous solution in 16 crystallization units using three types of crystallization methods, i.e., batch, vapor diffusion, and free interface diffusion. Each unit has two compartments: one for the protein solution and the other for the ammonium sulfate solution. Compartments are separated by thick acrylic or thin stainless steel plates. Crystallization will be started by sliding out the plates, then will be periodically recorded up to 120 hours by a still camera. The temperature will be passively controlled by a phase transition thermal storage component and recorded in IC memory throughout the experiment. Microgravity environment can then be evaluated for protein crystal growth by comparing crystallization in space with that on Earth

Computational Crystallization

Crystallization is a key step in macromolecular structure determination by crystallography. While a robust theoretical treatment of the process is available, due to the complexity of the system, the experimental process is still largely one of trial and error. In this article, efforts in the field are discussed together with a theoretical underpinning using a solubility phase diagram. Prior knowledge has been used to develop tools that computationally predict the crystallization outcome and define mutational approaches that enhance the likelihood of crystallization. For the most part these tools are based on binary outcomes (crystal or no crystal), and the full information contained in an assembly of crystallization screening experiments is lost. The potential of this additional information is illustrated by examples where new biological knowledge can be obtained and where a target can be sub-categorized to predict which class of reagents provides the crystallization driving force. Computational analysis of crystallization requires complete and correctly formatted data. While massive crystallization screening efforts are under way, the data available from many of these studies are sparse. The potential for this data and the steps needed to realize this potential are discussed.Comment: 9 pages, 3 figure

Recovery of Water and Salt from Hyper-Saline Mine Water using Freeze Crystallization

The Freezerbacks researched, designed, and economically evaluated a full-scale freeze crystallization process as well as two alternative full-scale processes: 5 stage multiple effect evaporation and reverse osmosis. All three processes were designed to treat hyper-saline mine water that was sent into evaporation pond systems. These systems were designed for Freeport-McMoRan’s mines that need to treat impacted water. The Freeport-McMoRan copper mine in Miami, Arizona was visited in order to gain insight about the problem. The mine is no longer actively mining copper and is in the process of reclaiming land used. An essential part of restoring the land is treating impacted water that is currently being recirculated throughout the process before discharging. Current methods, evaporation ponds, are neither time nor cost effective. Ultimately, the water needs to be purified to the EPA standard of the maximum concentration level of sulfates (250 mg/L). After the feed has been processed, a waste stream will be disposed of via existing evaporation ponds. The deciding factor between the processes is the economics and total recovery. Multiple effect evaporation can be modified to recover more than 50% of water therefore reducing the footprint for the evaporation ponds. Although the heat of vaporization for water is about six times greater (40.65 kJ/mol) than the heat of fusion for water (6.02 kJ/mol), the capital cost for freeze crystallization is greater, and the process is unused on an industrial scale. Reverse osmosis will purify 50% of the water with a simpler system and cheaper overall cost. All processes are being presented as viable, with preference for the reverse osmosis. A batch bench scale system was constructed to model freeze crystallization. It was designed to process one gallon of salt solution in a single vessel. The bench scale process overall recovered 72% of the water with a final salt composition that ranges from 1.44 wt.% to 5.10 wt.%. For full-scale design purposes, 2.5 wt.% recovery was assumed. Reverse osmosis further purified the melted ice to EPA standards. A thorough evaluation was conducted by generating a full-scale economic analysis for each process, taking into consideration the advantages and disadvantages of each. Important factors taken into consideration were capital and operating costs, complexity, total recovery of water, and concentration of sulfates in the water recovered. In the freeze crystallization process, impacted water is pumped through two units in a semi-batch process where ice is formed on concentric plate coils in vessels. A total of 75% water is first recovered by crystallization and then the recovered water is passed through a reverse osmosis membrane (RO) to recover 50% of the initial brine water at environmental specifications. The net present value (NPV) after 10 years of operation is $(21.4 million) with a 50$(9.44 million). The reverse osmosis process will require two stages and a total of 21 elements. Reverse osmosis proved to be the most economical with an NPV of $(2.96 million) and a 50% purified water recovery compared to the other two processes

Parametric, Optimization-Based Study on the Feasibility of a Multisegment Antisolvent Crystallizer for in Situ Fines Removal and Matching of Target Size Distribution

Peer reviewedPostprin