Large Modifications Research Articles

Dependence of SAS particle morphologies on the ternary phase equilibria

In this work, the precipitation of a model compound (cefonicid) from DMSO by Supercritical Antisolvent (SAS) was performed. Various morphologies; i.e., expanded microparticles, microparticles, and nanoparticles were obtained, varying operating conditions. In order to explain these results, high-pressure vapor–liquid phase equilibria (VLEs) of the binary system DMSO-CO2 and of the ternary system DMSO-CO2-cefonicid were investigated, using a static analytic method.At 313K and low concentrations, the presence of the solute had a negligible effect on VLEs with respect to the binary system solvent-CO2. At concentrations up to 90mg/mL (at 313K) or increasing temperature at 333K (at 30mg/mL), a large modification of the VLEs was observed.The changes in phase behavior were successfully correlated to the powder morphologies, considering the position of the SAS operating point with respect to the ternary mixture critical point. The given explanations can be readily extended to other compounds.

Searching for some natural orbits to observe the double asteroid 2002CE26

Knowledge of the Solar System is increasing with data coming from space missions to small bodies. A mission to those bodies offers some problems, because they have several characteristics that are not well known, like their shapes, sizes and masses. The present research has the goal of searching for trajectories around the double asteroid 2002CE26, a system of Near-Earth Asteroids (NEAs) of the Apollo type. For every trajectory of the spacecraft, the evolution of the distances between the spacecraft and the two bodies that compose the system is crucial, due to its impact in the quality of the observations made from the spacecraft. Furthermore, this study has a first objective of searching for trajectories that make the spacecraft remain as long as possible near the two bodies that compose the asteroid system, without the use of orbital maneuvers. The model used here assumes elliptical orbits for the asteroids. The effect of the solar radiation pressure is also included, since it is a major perturbing force acting in spacecrafts traveling around small bodies. The natural orbits found here are useful for the mission. They can be used individually or combined in several pieces by orbital maneuvers. Another point considered here is the importance of the errors in the estimation of the physical parameters of the bodies. This task is very important, because there are great uncertainties in these values because the measurements are based on observations made from the Earth. It is shown that a variation of those parameters can make very large modifications in the times that the spacecraft remains close to the bodies of the system (called here “observational times”). Those modifications are large enough to make the best trajectories obtained under nominal conditions to be useless under some errors in the physical parameters. So, a search is made to find trajectories that have reasonable observation times for all the assumed error scenarios for the two bodies, because those orbits can be used as initial parking orbits for the spacecraft. We called these orbits “quasi-stable orbits”, in the sense that they do not collide with any of the primaries nor travel to large distances from them. From these orbits, it is possible to make better observations of the bodies in any scenario, and a more accurate estimation of their sizes and masses is performed, so giving information to allow for other choices for the orbit of the spacecraft.

Uniformly Thin and Large Surface Modification of Lithium Anode for Improving Cycling Performance of Lithium Metal Batteries

Rechargeable lithium batteries using lithium metal as a negative electrode are attractive candidates for high energy density power sources, because the lithium metal offers a high specific capacity and possesses a low electrochemical potential.1,2 However, the development of rechargeable lithium metal batteries has been hindered for several decades by the high reactivity of lithium metal toward liquid electrolytes and the occurrence of dendrite growth during charge and discharge cycles. The formation and growth of lithium dendrites result in safety and cycle life problems. Additionally, continuous generation of the new solid electrolyte interphase (SEI) layer on lithium metal causes uncontrolled reductive decomposition of the organic electrolyte and gradual loss in capacity and cycling efficiency with repeated cycling. Therefore, protection of lithium metal and the formation of a stable SEI layer on the lithium electrode are very important for developing lithium metal batteries with good capacity retention and enhanced safety. In this work, a prospective approach for protecting a lithium metal is presented by spray coating with a conductive poly(3,4-ethylenedioxythiohene)-co-poly(ethylene glycol) (PEDOT-co-PEG) and inorganic particles (AlF3), which allows for lithium ion diffusion and restricts the access of the reactive solvents to the lithium surface. The protective composite layer played a positive role in reducing the reductive decomposition of the electrolyte and suppressing the dendrite growth of lithium during cycling. As a result, the surface modification of lithium electrode with PEDOT-co-PEG and AlF3 significantly improved the cycling stability of the lithium metal batteries.

Generation of light in spatially dispersive materials

Spatial dispersion makes optical properties of materials depend on the direction of light propagation. The effect can be applied to control optical emission by sources embedded in such media. We propose a method to determine the radiation pattern of essentially any emitter located in a general spatially dispersive and optically anisotropic medium. The method is based on a decomposition of the source into waves of electric current, each creating optical plane waves whose properties are determined by the wave parameters, the refractive index, and impedance. The method is computationally fast and very accurate even in strongly spatially dispersive plasmonic metamaterials. In particular, we observe large modification of dipole emission in a bifacial and a diffraction-compensating metamaterial. The method is applicable to a large variety of nanostructured materials and, therefore, we believe that it can find numerous applications in nano-optics.

Oil tea shell derived porous carbon with an extremely large specific surface area and modification with MnO2 for high-performance supercapacitor electrodes

Activated carbon (AC) with an extremely large specific surface area (2851m2/g) and large pore volume (2.68cm3/g) was derived from bio-waste oil tea shells by using ZnCl2 as the activation agent. The porous carbon had a high amount of CO2 adsorption (3.61mmol/g) at ambient conditions (25°C, 1bar). Comprehensive characterizations including XRD, Raman, SEM, TEM, and TGA proved graphite existed in the AC samples. However, the capacitance (146F/g @ 0.5A/g) was in the normal range of carbon materials. By coating with a thin layer of MnO2, the capacitance of MnO2/AC was enhanced significantly (1126F/g @ 0.5A/g) without sacrificing the rate capability and cycle stability, even though the surface area was reduced to 23m2/g and pore volume reduced to 0.05cm3/g. A two-electrode (MnO2/AC//AC) supercapacitor cell was set up, the energy density reached 24Wh/kg with a power density of 275W/kg.

NucTools: analysis of chromatin feature occupancy profiles from high-throughput sequencing data

BackgroundBiomedical applications of high-throughput sequencing methods generate a vast amount of data in which numerous chromatin features are mapped along the genome. The results are frequently analysed by creating binary data sets that link the presence/absence of a given feature to specific genomic loci. However, the nucleosome occupancy or chromatin accessibility landscape is essentially continuous. It is currently a challenge in the field to cope with continuous distributions of deep sequencing chromatin readouts and to integrate the different types of discrete chromatin features to reveal linkages between them.ResultsHere we introduce the NucTools suite of Perl scripts as well as MATLAB- and R-based visualization programs for a nucleosome-centred downstream analysis of deep sequencing data. NucTools accounts for the continuous distribution of nucleosome occupancy. It allows calculations of nucleosome occupancy profiles averaged over several replicates, comparisons of nucleosome occupancy landscapes between different experimental conditions, and the estimation of the changes of integral chromatin properties such as the nucleosome repeat length. Furthermore, NucTools facilitates the annotation of nucleosome occupancy with other chromatin features like binding of transcription factors or architectural proteins, and epigenetic marks like histone modifications or DNA methylation. The applications of NucTools are demonstrated for the comparison of several datasets for nucleosome occupancy in mouse embryonic stem cells (ESCs) and mouse embryonic fibroblasts (MEFs).ConclusionsThe typical workflows of data processing and integrative analysis with NucTools reveal information on the interplay of nucleosome positioning with other features such as for example binding of a transcription factor CTCF, regions with stable and unstable nucleosomes, and domains of large organized chromatin K9me2 modifications (LOCKs). As potential limitations and problems we discuss how inter-replicate variability of MNase-seq experiments can be addressed.

Multiple-site fragment deletion, insertion and substitution mutagenesis by modified overlap extension PCR

ABSTRACTIntroducing various mutations at multiple specific sites within a gene requires multiple steps of DNA manipulation, which is the initial, but limiting step of protein structure–function studies. In the present work, we standardized a simple and fast procedure to perform site-directed mutagenesis, multiple-site fragment deletion, insertion and substitution mutagenesis by a modified version of overlap extension polymerase chain reaction (PCR). In this procedure, target genes divided into several fragments based on the site of mutagenesis are amplified and annealed with their complementary overhanging, followed by extension and amplification to full-length gene with expected mutation(s) by PCR. Vectors inserted with the modified target gene are screened by colony PCR. By using the standardized procedure, we have easily generated single-site mutations, replaced/deleted DNA fragment into/from a target gene and engineered a cysteine-free protein. Practically, the standardized procedure provides an efficient choice for almost all kinds of mutagenesis, especially for multiple-site and large DNA fragment modification mutagenesis. Therefore, this method can be utilized to analyze protein structure and function, to optimize codons of genes for protein expression and to assemble genes of interest.

Evolution of hydraulic properties and wettability of organic growing media during cultivation according to irrigation strategies

Recent studies have shown that growth period largely affected physical properties of growing media, and therefore irrigation management has to be revised according to these changes in order to avoid poor irrigation. Decreases in pore tortuosity but also in wettability have been identified as the most relevant parameters explaining these evolutions with time, as a result of combined effects of root growth and irrigation regimes. So, this study aimed to analyse the respective effects of root development and irrigation strategies on the physical and hydraulic properties of four different growing media (peat, pine bark, coir and wood fiber) within a culture of Rosa×hybrida “Radrazz” grown with and without plants during four months, for which watering was managed in three different ways: (1) water potential always maintained at −1kPa, (2) irrigation triggered when water potential reached −10kPa or (3) −30kPa.Root volume, total volume, air and water retention properties, hydraulic conductivity, relative gas diffusivity, and wettability were evaluated at the beginning and at the end of the experiment. The study showed important changes over time, mainly due to the hydric history, leading to large and higher modifications of pore size distribution, tortuosity and wettability as a function of the intensity of the drying/wetting cycles. Changes in wettability, and notably, more hydrophobic properties of the coarser porosity due to its drainage during the drying processes were suggested for explaining the general physical/hydraulic behaviour of growing media, and the decrease in shoot dry mass and root content with the intensity of irrigation regimes. Although they were with smaller amplitude to those resulting of the hydric history, positive effects of the root system were shown, increasing pore connectivity, relative gas diffusivity and limiting the decrease in total pore volume, and moreover, limiting the degradation in wettability.

Development and Implementation of a Successful Northern Bobwhite Translocation Program in Georgia

Gamebird translocations have been used for many years to establish or re-establish populations in North America. A long-term severe decline of northern bobwhites (Colinus virginianus) over much of their range has brought this issue to the forefront for this species as well. Field studies in Georgia over the last decade have documented site fidelity, high survival, reproductive success, and population response from bobwhites translocated into large blocks of well-managed habitat. The Georgia Department of Natural Resources/ Wildlife Resources Division developed an official wild quail translocation policy in 2006. Five translocation projects have been permitted and conducted since the policy was established. Extensive large scale habitat modifications were required on the recipient sites while donor sites were required to have existing high density bobwhite populations. These projects have resulted in translocation of . 800 bobwhites and the establishment of 7,480 ha of new wild quail population centers thereby contributing to the National Bobwhite Conservation Initiative (NBCI) recovery goals. Average fall densities on completed projects have increased from , 0.5 birds/ha to . 1.25 birds/ha.

Basic evaluation of typical nanoporous silica nanoparticles in being drug carrier: Structure, wettability and hemolysis

Herein, the present work devoted to study the basic capacity of nanoporous silica nanoparticles in being drug carrier that covered structure, wettability and hemolysis so as to provide crucial evaluation. Typical nanoporous silica nanoparticles that consist of nanoporous silica nanoparticles (NSN), amino modified nanoporous silica nanoparticles (amino-NSN), carboxyl modified nanoporous silica nanoparticles (carboxyl-NSN) and hierachical nanoporous silica nanoparticles (hierachical-NSN) were studied. The results showed that their wettability and hemolysis were closely related to structure and surface modification. Basically, wettability became stronger as the amount of OH on the surface of NSN was higher. Both large nanopores and surface modification can reduce the wettability of NSN. Furthermore, NSN series were safe to be used when they circulated into the blood in low concentration, while if high concentration can not be avoided during administration, high porosity or amino modification of NSN were safer to be considered. It is believed that the basic evaluation of NSN can make contribution in providing scientific instruction for designing drug loaded NSN systems.

Shape optimization of microstructural designs subject to local stress constraints within an XFEM-level set framework

The present paper investigates the tailoring of bimaterial microstructures minimizing their local stress field exploiting shape optimization. The problem formulation relies on the extended finite element method (XFEM) combined with a level set representation of the geometry, to deal with complex microstructures and handle large shape modifications while working on fixed meshes. The homogenization theory, allowing extracting the behavior of periodic materials built from the repetition of a representative volume element (RVE), is applied to impose macroscopic strain fields and periodic boundary conditions to the RVE. Classical numerical homogenization techniques are adapted to the selected XFEM-level set framework. Following previous works by the authors on analytical sensitivity analysis (Noel et al. (2016)), the scope of the developed approach is extended to tackle the problem of stress objective or constraint functions. Finally, the method is illustrated by revisiting 2D classical shape optimization examples: finding the optimal shapes of single or multiple inclusions in a microstructure while minimizing its local stress field.

Clostridium difficile colonization and antibiotics response in PolyFermS continuous model mimicking elderly intestinal fermentation.

Background Clostridium difficile (CD), a spore-forming and toxin-producing bacterium, is the main cause for antibiotic-associated diarrhea in the elderly. Here we investigated CD colonization in novel in vitro fermentation models inoculated with immobilized elderly fecal microbiota and the effects of antibiotic treatments.MethodsTwo continuous intestinal PolyFermS models inoculated with different immobilized elder microbiota were used to investigate selected factors of colonization of CD in proximal (PC, model 1) and transverse-distal (TDC, model 1 and 2) colon conditions. Colonization of two CD strains of different PCR ribotypes, inoculated as vegetative cells (ribotype 001, model 1) or spores (ribotypes 001 and 012, model 2), was tested. Treatments with two antibiotics, ceftriaxone (daily 150 mg L−1) known to induce CD infection in vivo or metronidazole (twice daily 333 mg L−1) commonly used to treat CD, were investigated in TDC conditions (model 2) for their effects on gut microbiota composition (qPCR, 16S pyrosequencing) and activity (HPLC), CD spore germination and colonization, and cytotoxin titer (Vero cell assay).ResultsCD remained undetected after inoculating vegetative cells in PC reactors of model 1, but was shown to colonize TDC reactors of both models, reaching copy numbers of up to log10 8 mL−1 effluent with stable production of toxin correlating with CD cell numbers. Ceftriaxone treatment in TDC reactors showed only small effects on microbiota composition and activity and did not promote CD colonization compared to antibiotic-free control reactor. In contrast, treatment with metronidazole after colonization of CD induced large modifications in the microbiota and decreased CD numbers below the detection limit of the specific qPCR. However, a fast CD recurrence was measured only 2 days after cessation of metronidazole treatment.ConclusionsUsing our in vitro fermentation models, we demonstrated that stable CD colonization in TDC reactors can be induced by inoculating CD vegetative cells or spores without the application of ceftriaxone. Treatment with metronidazole temporarily reduced the counts of CD, in agreement with CD infection recurrence in vivo. Our data demonstrate that CD colonized an undisturbed microbiota in vitro, in contrast to in vivo observations, thus suggesting an important contribution of host-related factors in the protection against CD infection.Electronic supplementary materialThe online version of this article (doi:10.1186/s13099-016-0144-y) contains supplementary material, which is available to authorized users.

Temporal gradient-domain path tracing

We present a novel approach to improve temporal coherence in Monte Carlo renderings of animation sequences. Unlike other approaches that exploit temporal coherence in a post-process, our technique does so already during sampling. Building on previous gradient-domain rendering techniques that sample finite differences over the image plane, we introduce temporal finite differences and formulate a corresponding 3D spatio-temporal screened Poisson reconstruction problem that is solved over windowed batches of several frames simultaneously. We further extend our approach to include second order, mixed spatio-temporal differences, an improved technique to compute temporal differences exploiting motion vectors, and adaptive sampling. Our algorithm can be built on a gradient-domain path tracer without large modifications. In particular, we do not require the ability to evaluate animation paths over multiple frames. We demonstrate that our approach effectively reduces temporal flickering in animation sequences, significantly improving the visual quality compared to both path tracing and gradient-domain rendering of individual frames.

Ionospheric storm effects and equatorial plasma irregularities during the 17–18 March 2015 event

AbstractThe intense magnetic storm on 17–18 March 2015 caused large disturbances of the ionosphere. Based on the plasma density (Ni) observations performed by the Swarm fleet of satellites, the Gravity Recovery and Climate Experiment mission, and the Communications/Navigation Outage Forecasting System satellite, we characterize the storm‐related perturbations at low latitudes. All these satellites sampled the ionosphere in morning and evening time sectors where large modifications occurred. Modifications of plasma density are closely related to changes of the solar wind merging electric field (Em). We consider two mechanisms, prompt penetration electric field (PPEF) and disturbance dynamo electric field (DDEF), as the main cause for the Ni redistribution, but effects of meridional wind are also taken into account. At the start of the storm main phase, the PPEF is enhancing plasma density on the dayside and reducing it on the nightside. Later, DDEF takes over and causes the opposite reaction. Unexpectedly, there appears during the recovery phase a strong density enhancement in the morning/prenoon sector and a severe Ni reduction in the afternoon/evening sector, and we suggest a combined effect of vertical plasma drift, and meridional wind is responsible for these ionospheric storm effects. Different from earlier studies about this storm, we also investigate the influence of storm dynamics on the initiation of equatorial plasma irregularities (EPIs). Shortly after the start of the storm main phase, EPIs appear in the postsunset sector. As a response to a short‐lived decline of Em, EPI activity appears in the early morning sector. Following the second start of the main phase, EPIs are generated for a few hours in the late evening sector. However, for the rest of the storm main phase, no more EPIs are initiated for more than 12 h. Only after the onset of recovery phase does EPI activity start again in the postmidnight sector, lasting more than 7 h. This comprehensive view of ionospheric storm effects and plasma irregularities adds to our understanding of conditions that lead to ionospheric instabilities.

Large range modification of exciton species in monolayer WS2.

Unconventional emissions from excitons and trions in monolayer WS2 are studied by photoexcitation. When excited by a 532 nm laser beam, the carrier species in the monolayer WS2 are affected by the excess electrons escaping from photoionization of donor impurity, the concentration of which varies with different locations of the sample. Simply by increasing the excitation power at room temperature, the excess electrons and, thus, the intensity ratio of excited trions and excitons can be continuously tuned over a large range from 0.1 to 7.7. Furthermore, this intensity ratio can also be manipulated by varying temperature. However, in this way, the resonance energy of the excitons and trions shows redshifts with increasing temperature due to electron-phonon coupling. The binding energy of the trion is determined to be ∼26 meV and independent of temperature, indicating strong Coulomb interaction of carriers in such 2D materials.

CSculpt

Collaborative systems are well established solutions for sharing work among people. In computer graphics these workflows are still not well established, compared to what is done for text writing or software development. Usually artists work alone and share their final models by sending files. In this paper we present a system for collaborative 3D digital sculpting. In our prototype, multiple artists concurrently sculpt a polygonal mesh on their local machines by changing its vertex properties, such as positions and material BRDFs. Our system shares the artists' edits automatically and seamlessly merges these edits even when they happen on the same region of the surface. We propose a merge algorithm that is fast-enough for seamless collaboration, respects users' edits as much as possible, can support any sculpting operation, and works for both geometry and appearance modifications. Since in sculpting artists alternatively perform fine adjustments and large scale modifications, our algorithm is based on a multiresolution edit representation that handles concurrent overlapping edits at different scales. We tested our algorithm by modeling meshes collaboratively in different sculpting sessions and found that our algorithm outperforms prior works on collaborative mesh editing in all cases.

Large fragment deletion using a CRISPR/Cas9 system in Saccharomyces cerevisiae

Large chromosomal modifications have been performed in natural and laboratory evolution studies and hold tremendous potential for use in foundational research, medicine, and biotechnology applications. Recently, the type II bacterial Clustered Regularly Interspaced Short Palindromic Repeat and CRISPR-associated (CRISPR/Cas9) system has emerged as a powerful tool for genome editing in various organisms. In this study, we applied the CRISPR/Cas9 system to preform large fragment deletions in Saccharomyces cerevisiae and compared the performance activity to that of a traditional method that uses the Latour system. Here we report in S. Cerevisiae the CRIPR/Cas9 system has been used to delete fragments exceeding 30 kb. The use of the CRISPR/Cas9 system for generating chromosomal segment excision showed some potential advantages over the Latour system. All the results indicated that CRISPR/Cas9 system was a rapid, efficient, low-cost, and versatile method for genome editing and that it can be applied in further studies in the fields of biology, agriculture, and medicine.

Variational Contrast Enhancement of Gray-Scale and RGB Images

The aim of this paper is twofold. First, we propose a new method for enhancing the contrast of gray-value images. We use the difference of the average local contrast measures between the original and the enhanced images within a variational framework. This enables the user to intuitively control the contrast level and the scale of the enhanced details. Moreover, our model avoids large modifications of the original image histogram. Thereby it preserves the global illumination of the scene and it can cope with large areas having similar gray values. The minimizer of the proposed functional is computed by a gradient descent algorithm in connection with a polynomial approximation of the average local contrast measure. The polynomial approximation is computed via Bernstein polynomials. In the second part, the approach is extended to a variational enhancement method for color images. The model approximately preserves the hue of the original image and additionally includes a total variation term to correct the possible noise. The method requires no post- or preprocessing. The minimization problem is solved with a hybrid primal---dual algorithm. Experiments demonstrate the efficiency and the flexibility of the proposed approaches in comparison with state-of-the-art methods.

Study on the Lithiation Mechanism in Micro-Grain Structured Amorphous Silicon Anodes in Lithium-Ion Batteries with the Aid of Impedance Spectroscopy

It is well known that silicon presents one of the most important anode materials for the improvement of lithium-ion cells in terms of energy density. Indeed, silicon’s high theoretical specific capacity to lithium (more than 3800 mAh/g at room temperature), environmental friendliness, low potential compared to lithium and material abundance turn silicon to a strong candidate for the replacement of carbon-based anodes [1,2]. However, one of the main drawbacks of silicon’s application to the lithium-ion technology is its poor electrochemical cycling stability over several galvanostatic cycles, mainly due to silicon’s huge volume change (around 300%) during lithiation and delithiation that leads to high internal mechanical stress and therefore to film fracturing and delamination [3]. Many alternatives have been proposed that alleviate this mechanical expansion issue either through the use of nanostructured silicon sometimes combined with carbon-based materials or with special coatings and binders with the current collector [1,4]. Even though many years ago in 1999 amorphous silicon (a-Si) was initially proposed by Bourdereau et al. [5], it is quite recently that it has been found that a-Si can be more resistive to fractures and pulverisation upon lithiation [6] than crystalline silicon (c-Si). It has been demonstrated by McDowell et al., that amorphous silicon compared to the crystalline can resist more efficiently the large volume modifications at least for spheres with 870 nm of diameter and this has been attributed to the different lithiation mechanism [7]. Recently, Farmakis et al. [8] have demonstrated micro-grain structured amorphous silicon anodes delivering specific capacity of more than 2000 mAh/g and 2.0 mAh/cm2for more than 50 cycles. As a goal to comprehend the performance of the silicon and the related lithium kinetics, this contribution attempts to study the lithiation mechanism at micro-grain structures amorphous silicon structures with the aid of impedance spectroscopy. For this purpose, silicon/metal Lithium half cells were prepared with silicon being previously deposited by DC sputtering on rough copper foil and electrochemical characterization including impedance spectroscopy was conducted. After the application of a two semi-circle fitting model, the charge transfer and the Solid Electrolyte Interphase impedances are extracted. It is shown that the charge transfer resistance is highly dependent on the State Of Charge (SOC) and consequently on the charging rate. It is observed that the charge transfer resistance is highly increased (5-6 times) when silicon anode lithiation exceeds 80% of SOC and not. The results can be explained by considering that lithiation of amorphous silicon strongly depends on x at LixSi alloy throughout the silicon bulk material.

Theoretical Insights into the Biophysics of Protein Bi-stability and Evolutionary Switches.

Deciphering the effects of nonsynonymous mutations on protein structure is central to many areas of biomedical research and is of fundamental importance to the study of molecular evolution. Much of the investigation of protein evolution has focused on mutations that leave a protein’s folded structure essentially unchanged. However, to evolve novel folds of proteins, mutations that lead to large conformational modifications have to be involved. Unraveling the basic biophysics of such mutations is a challenge to theory, especially when only one or two amino acid substitutions cause a large-scale conformational switch. Among the few such mutational switches identified experimentally, the one between the GA all-α and GB α+β folds is extensively characterized; but all-atom simulations using fully transferrable potentials have not been able to account for this striking switching behavior. Here we introduce an explicit-chain model that combines structure-based native biases for multiple alternative structures with a general physical atomic force field, and apply this construct to twelve mutants spanning the sequence variation between GA and GB. In agreement with experiment, we observe conformational switching from GA to GB upon a single L45Y substitution in the GA98 mutant. In line with the latent evolutionary potential concept, our model shows a gradual sequence-dependent change in fold preference in the mutants before this switch. Our analysis also indicates that a sharp GA/GB switch may arise from the orientation dependence of aromatic π-interactions. These findings provide physical insights toward rationalizing, predicting and designing evolutionary conformational switches.