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Local and average structures of BaTiO[subscript 3]-Bi(Zn[subscript 1/2]Ti[subscript 1/2])O[subscript 3]
Abstract not provided
Structure of the lutein-binding domain of human StARD3 at 1.74 Å resolution and model of a complex with lutein
A crystal structure of the lutein-binding domain of human StARD3 (StAR-related lipid-transfer protein 3; also known as MLN64) has been refined to 1.74 Å resolution. A previous structure of the same protein determined to 2.2 Å resolution highlighted homology with StARD1 and shared cholesterol-binding character. StARD3 has since been recognized as a carotenoid-binding protein in the primate retina, where its biochemical function of binding lutein with specificity appears to be well suited to recruit this photoprotective molecule. The current and previous structures correspond closely to each other (r.m.s.d. of 0.25 Å), especially in terms of the helix-grip fold constructed around a solvent-filled cavity. Regions of interest were defined with alternate conformations in the current higher-resolution structure, including Arg351 found within the cavity and Ω1, a loop of four residues found just outside the cavity entrance. Models of the complex with lutein generated by rigid-body docking indicate that one of the ionone rings must protrude outside the cavity, and this insight has implications for molecular interactions with transport proteins and enzymes that act on lutein. Interestingly, models with the ϵ-ionone ring characteristic of lutein pointing towards the bottom of the cavity were associated with fewer steric clashes, suggesting that steric complementarity and ligand asymmetry may play a role in discriminating lutein from the other ocular carotenoids zeaxanthin and meso -zeaxanthin, which only have β-ionone rings.
Hydrodynamics of the rivulet flow over corrugated sheet used in structured packings
Not Available
Crystal Structure of PKG I:cGMP Complex Reveals a cGMP-Mediated Dimeric Interface that Facilitates cGMP-Induced Activation
Abstract not provided
Structure, Function, and Dynamics of the Gα Binding Domain of Ric-8A
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Odd–Even Structural Sensitivity on Dynamics in Network-Forming Ionic Liquids
As a compelling case of sensitive structure–property relationship, an odd–even effect refers to the alternating trend of physical or chemical properties on odd/even number of repeating structural units. In crystalline or semicrystalline materials, such odd–even effects emerge as manifestations of differences in the periodic packing patterns of molecules. Therefore, due to the lack of long-range order, such an odd–even phenomenon is not expected for dynamic properties in amorphous state. Herein, we report the discovery of a remarkable odd–even effect of dynamical properties in the liquid phase. In a class of glass-forming diammonium citrate ionic liquids, using incoherent quasi-elastic neutron scattering measurements, we measured the dynamical properties including diffusion coefficient and rotational relaxation time. These directly measured molecular dynamics showed pronounced alternating trends with increased number of methylene (-CH2-) groups in the backbone. Meanwhile, the structure factor S(Q) showed no long-range periodic packing of molecules, while the pair distribution function G(r) revealed subtle differences in the local molecular morphology. The observed dynamical odd–even phenomenon in liquids showed that profound dynamical changes originate from subtle local structural differences.
A comparative study on the oxidation of two-dimensional Ti 3 C 2 MXene structures in different environments
The oxidation of two-dimensional Ti 3 C 2 MXene structures has been recognized as a promising method for the formation of hybrid structures of carbon supported nanotitania. Here, we studied the oxidation of Ti 3 C 2 MXene structures using reactive force field (ReaxFF) based molecular dynamics simulations. To investigate the effect of oxidizing agent, we used three different environments including dry air (oxygen molecules), wet air (oxygen and water molecules) and hydrogen peroxide (H 2 O 2 molecules). Oxidation simulations were performed at different temperatures of 1000, 1500, 2000, 2500 and 3000 K. We found that by controlling the temperature, carbon supported titania can be formed by diffusion of Ti atoms to the surface of MXene structures during the oxidation. These results were confirmed by the increase in the average bond orders of C–C and Ti–O and decrease in the average bond orders of Ti–C. Moreover, it was revealed that by increasing the temperature, the oxidation rate increases, and the rate depends on the oxidant according to the following order: H 2 O 2 > wet air > dry air. This was validated by heating the MXene in wet air and dry air followed by examining the products using X-ray diffraction and Raman spectroscopy. To investigate the effect of the presence of the oxidant, the MXene structure was also heated under vacuum, and it was found that in this case the MXene structure was converted to cubic TiC. Furthermore, it was indicated that during the heating process of the MXene structure in a vacuum, the average bond orders for C–C, Ti–C and Ti–O do not change significantly due to the lack of oxidants in the environment, leaving room for only topotactic transformation of atoms during the heating. In conclusion, the formation of the TiC structure by heating the MXene in an inert environment was confirmed experimentally as well.
R -Nb 2 O 5 has an ‘idealized’ V 2 O 5 structure and Wadsley–Roth-like structural stability during Li-ion battery cycling
The adoption of batteries across diverse applications requires electrode materials with a wider range of performance metrics, such as cost, safety, and material availability. Along the path to discovering new commercially viable materials, a fundamental understanding of chemical and atomic structure features that provide structural stability and effective ion transport is essential. In support of new understanding, we report the cycling behavior of metastable R-Nb 2 O 5 . R-Nb 2 O 5 adopts an ‘idealized’ V 2 O 5 structure, in which [NbO 6 ] octahedra alternate in edge- and corner-sharing resulting in ReO 3 -like slabs, whereas Wadsley–Roth materials have ReO 3 -like blocks, linked through edge-sharing octahedra at intersecting crystallographic shear planes. We find that this slab structure is stable during cycling, with minor atomic structure changes and cycling curves that are symmetric on discharge and charge, resembling the behavior of Wadsley–Roth materials more than other related materials, such as ReO 3 , V 2 O 5 , or Nb 3 O 7 F. Based on our findings, R-Nb 2 O 5 can serve as a ‘structural bridge’ between Wadsley–Roth block structures and V 2 O 5 , through which we can relate inter- and intra-polyhedral structures to cycling behavior and structural stability during cycling.
Crystal structure of an atypical cobalamin riboswitch reveals RNA structural adaptability as basis for promiscuous ligand binding
Cobalamin riboswitches encompass a structurally diverse group of cis-acting, gene regulatory elements found mostly in bacterial messenger RNA and are classified into subtypes based on secondary and tertiary characteristics. An unusual variant of the cobalamin riboswitch with predicted structural features was identified in Bacillus subtilis over a decade ago, but its structure and mechanisms of cobalamin selectivity and translational control have remained unsolved. We present the crystal structure of the aptamer domain of this atypical cobalamin riboswitch and a model for the complete riboswitch, including its expression platform domain. We demonstrate that this riboswitch binds to multiple cobalamin derivatives and correlate its promiscuous behavior to its structure and unique arrangement of peripheral elements. Comparative structural analyses between conventional cobalamin riboswitches and the B. subtilis cobalamin riboswitch reveal that the likely basis for this promiscuous ligand binding is intrinsic structural adaptability encoded in the RNA structure. It suggests that cobalamin selectivity might ultimately be viewed as existing on a spectrum of affinity for each derivative rather than as belonging to distinct types based on ligand specificities. Our work provides an interesting and notable example of functional coupling of ligand-sensing and adaptive folding by a structured RNA molecule.
User's guide to computer program CIVM-JET 4B to calculate the transient structural responses of partial and/or complete structural rings to engine-rotor-fragment impact
A user-oriented computer program CIVM-JET 4B is described to predict the large-deflection elastic-plastic structural responses of fragment impacted single-layer: (a) partial-ring fragment containment or deflector structure or (b) complete-ring fragment containment structure. These two types of structures may be either free or supported in various ways. Supports accommodated include: (1) point supports such as pinned-fixed, ideally-clamped, or supported by a structural branch simulating mounting-bracket structure and (2) elastic foundation support distributed over selected regions of the structure. The initial geometry of each partial or complete ring may be circular or arbitrarily curved; uniform or variable thicknesses of the structure are accommodated. The structural material is assumed to be initially isotropic; strain hardening and strain rate effects are taken into account.
Recent results on structural control of an active precision structure
This paper describes recent results in structural control of an active precision truss structure at JPL. The goal is to develop practical control methodology and to apply to active truss structures intended for high precision space-based optics applications. The active structure considered incorporates piezoelectric active members which apply control forces internal to the structure and thereby improve the structure's dimensional stability. Two approaches to structural control system design were investigated. The first approach uses only noncollocated measurements of acceleration at the location of a simulated optical component to achieve structural stabilization. The second approach is essentially the same as the first one except that a viscous damper was used in place of a truss member on the structure to improve the dampings of selected flexible modes. The corresponding experimental closed-loop results are presented in this paper.
Vibration attenuation of the NASA Langley evolutionary structure experiment using H(sub infinity) and structured singular value (micron) robust multivariable control techniques
The use is studied of active control to attenuate structural vibrations of the NASA Langley Phase Zero Evolutionary Structure due to external disturbance excitations. H sub infinity and structured singular value (mu) based control techniques are used to analyze and synthesize control laws for the NASA Langley Controls Structures Interaction (CSI) Evolutionary Model (CEM). The CEM structure experiment provides an excellent test bed to address control design issues for large space structures. Specifically, control design for structures with numerous lightly damped, coupled flexible modes, collocated and noncollocated sensors and actuators and stringent performance specifications. The performance objectives are to attenuate the vibration of the structure due to external disturbances, and minimize the actuator control force. The control design problem formulation for the CEM Structure uses a mathematical model developed with finite element techniques. A reduced order state space model for the control design is formulated from the finite element model. It is noted that there are significant variations between the design model and the experimentally derived transfer function data.
Effects of Piezoelectric (PZT) Sensor Bonding and the Characteristics of the Host Structure on Impedance Based Structural Health Monitoring
This study was conducted to investigate the effects of certain factors on the impedance signal in structural health monitoring. These factors were: the quality of the bond between the sensor and the host structure, and the characteristics of the host structure, such as geometry, mass, and material properties. This work was carried out to answer a set of questions, related to these factors, that were developed by the project team. The project team was comprised of Dr. Doug Ramers and Dr. Abdul Jalloh of the Summer Faculty Fellowship Program, Mr. Arnaldo Colon- Perez, a student intern from the University of Puerto Rico of Turabo, and Mr. John Lassiter and Mr. Bob Engberg of the Structural and Dynamics Test Group at NASA Marshall Space Flight Center (MSFC). This study was based on a review of the literature on structural health monitoring to investigate the factors referred to above because there was not enough time to plan and conduct the appropriate tests at MSFC during the tenure of the Summer Faculty Fellowship Program project members. The surveyed literature documents works on structural health monitoring that were based on laboratory tests that were conducted using bolted trusses and other civil engineering type structures for the most part. These are not the typical types of structures used in designing and building NASA s space vehicles and systems. It was therefore recommended that tests be conducted using NASA type structures, such as pressure vessels, to validate the observations made in this report.
Elastomeric Structural Attachment Concepts for Aircraft Flap Noise Reduction - Challenges and Approaches to Hyperelastic Structural Modeling and Analysis
Airframe noise is a significant part of the overall noise of transport aircraft during the approach and landing phases of flight. Airframe noise reduction is currently emphasized under the Environmentally Responsible Aviation (ERA) and Fixed Wing (FW) Project goals of NASA. A promising concept for trailing-edge-flap noise reduction is a flexible structural element or link that connects the side edges of the deployable flap to the adjacent main-wing structure. The proposed solution is distinguished by minimization of the span-wise extent of the structural link, thereby minimizing the aerodynamic load on the link structure at the expense of increased deformation requirement. Development of such a flexible structural link necessitated application of hyperelastic materials, atypical structural configurations and novel interface hardware. The resulting highly-deformable structural concept was termed the FLEXible Side Edge Link (FLEXSEL) concept. Prediction of atypical elastomeric deformation responses from detailed structural analysis was essential for evaluating feasible concepts that met the design constraints. The focus of this paper is to describe the many challenges encountered with hyperelastic finite element modeling and the nonlinear structural analysis of evolving FLEXSEL concepts. Detailed herein is the nonlinear analysis of FLEXSEL concepts that emerged during the project which include solid-section, foamcore, hollow, extended-span and pre-stressed concepts. Coupon-level analysis performed on elastomeric interface joints, which form a part of the FLEXSEL topology development, are also presented.
Structural Certification of Human-Rated Inflatable Space Structures
This paper details the results of an initial study to develop a certification plan for human-rated inflatable space structures, including guidelines for qualification testing. Habitable softgoods inflatables are multi-layered shell structures that use high-strength webbing, cordage and broadcloth fabric to carry the skin loads of a variety of volumetric shapes and structural architectures. The primary objectives of this study are to define the key parameters that affect these structures and propose a statistically robust approach to defining safety and knockdown factors based on test and analysis. Current NASA standards for habitable inflatable space structures use a factor of safety of 4, which was inherited from airship design criteria. An updated approach to defining a design factor, taking into account material strength variability, load variability in the article, number of test samples, and damage and degradation effects is specified. Accurate analytical modeling of these structures is hindered by the difficulty of obtaining accurate and consistent material data due to load-history- dependent, nonlinear load versus strain behavior. A building block approach to certification is detailed that uses stochastic modeling and statistical test design and analysis to address the unique challenges these high-strength softgoods structures present. Human-rated inflatable modules are a transformative capability for launching much larger habitable volumes into space than is possible with rigid shell structures. This research aims to provide the framework for certifying these structures for future human space exploration missions.
Aircraft Conceptual Structural Design Using the AMMIT Structural Analysis Tool
Aircraft conceptual structural design is the process of developing and refining an idea for an aircraft into a feasible structural design. The process typically involves multiple evaluations of a single configuration and can require designers to examine thousands of concepts. Standard approaches to conducting structural analyses in this phase are either based on the use of historical or empirical data or often require significant expertise in structural analysis to perform these rapid assessments. The AMMIT structural analysis tool includes structural line models and handbook methods wrapped in a simple to use interface that can enable rapid, physics-based structural designs without requiring extensive structural expertise. The objectives of the present paper are to introduce AMMIT, describe the methods used in AMMIT, and present the results of the validation effort. Validation of the AMMIT methodology was performed on nine aircraft to determine the accuracy of the methods, highlight features of AMMIT, and guide future development of the methodology. Results of the validation effort indicated that AMMIT provides a prediction of primary structural weight for each aircraft with an acceptable level of error during the preliminary design phase with a minimal expenditure of computational resources.
Click-chemistry compatible structures, click-chemistry functionalized structures, and materials and methods for making the same
According to various embodiments, systems, methods, and computer program products for click-chemistry compatible structures, additive manufacturing resins for forming the same, and method of formation of such structures and resins, as well as techniques for functionalizing click-chemistry compatible structures are disclosed. The inventive structures generally include a plurality of photo polymerized molecules structurally arranged according to a three-dimensional pattern, while surfaces of the structure are functionalized with one or more click-chemistry compatible molecules each having one or more click-chemistry compatible functional groups. The structures may be formed from single- or dual-component resins, each having unique synthetic pathways. The resulting structures may be functionalized for utility in a wide range of applications by leveraging click chemistry to further functionalize the structure with organic additives also compatible with click-chemistry reaction schemes.