Configuration Transformation Research Articles

Tailoring a gradient nanostructured age-hardened aluminum alloy using high-gradient strain and strain rate

Microstructural evolution of Al2024 alloy, consisting of precipitates, subjected to surface mechanical grinding treatment (SMGT) was investigated to reveal the role of strain and strain rate in structural refinement. Following SMGT, a gradient nanostructure was formed on the coarse-grained substrate, with a significant increase in nanohardness to over 1 GPa at the top surface. At low strains, the presence of particles and increasing strain rate stimulated the rapid transformation of dislocation configurations. However, at larger strains, increasing strain rate effectively stabilized the fine nanoscale structure. Strain gradient from the deformed layers and near the particles significantly promoted the development of microstructure by increasing the boundary misorientations, which was more significant at high strain rates. In particular, at very high rates and large strain gradients, extreme grain sizes may be induced. The presence of minority grains with size below 10 nm in the top 20-μm layers revealed that dislocation processes still operated at sub-nanoscale level. The dislocation-governed ductility was expected to be improved in the nanostructured materials.

Characteristics of ZnO nanorods-based ammonia gas sensors with a cross-linked configuration

Cross-linked ZnO nanorods (NRs)-based ammonia gas sensors have been fabricated and investigated. The influences of interdigitated electrode spacing d and working temperature on ammonia sensing performance are studied. It is found that when the electrode spacing d is reduced, the ammonia sensor response S would be increased due to the configuration transformation of ZnO NRs. The optimal working temperature is about 573K due to the temperature dependence on reactions of oxygen species. The studied sensor with an electrode spacing d of 2μm shows a maximum ammonia sensor response S of 81.6 under exposing to a 1000ppm NH3/air gas at 573K. Also, a lower detection limit of 10ppm NH3/air is achieved. The improved ammonia detecting capability could be attributed to the formation of more cross-linked configurations. The adsorption-time (τa) and desorption-time (τb) constants of the studied sensor with an electrode spacing d of 2μm, at 573K, are 74 and 29s, respectively. Finally, the studied sensor exhibits good gas sensing response and repeatability toward NH3 gas. Thus, the studied sensor with a cross-linked configuration gives a promise for high-performance ammonia sensing applications.

Maneuvering thermal conductivity of magnetic nanofluids by tunable magnetic fields

We report an experimental investigation of magnetic field dependent thermal conductivity of a transformer oil base magnetic fluid as a function of volume fractions. In the absence of magnetic field, thermal conductivity increases linearly with an increase in volume fraction, and magnitude of thermal conductivity thus obtained is lower than that predicted by Maxwell's theory. This reveals the presence of clusters/oligomers in the system. On application of magnetic field, it exhibits a non-monotonous increase in thermal conductivity. The results are interpreted using the concept of a two-step homogenization method (which is based on differential effective medium theory). The results show a transformation of particle cluster configuration from long chain like prolate shape to the aggregated drop-like structure with increasing concentration as well as a magnetic field. The aggregated drop-like structure for concentrated system is supported by optical microscopic images. This shape change of clusters reduces thermal conductivity enhancement. Moreover, this structure formation is observed as a dynamic phenomenon, and at 226 mT field, the length of the structure extends with time, becomes maximum, and then reduces. This change results in the increase or decrease of thermal conductivity.

The Synergic Relationship Between Xylan Removal and Enhanced Cellulose Digestibility for Bioethanol Production: Reactive Area, Crystallinity, and Inhibitation

Hemicellulosic fraction is thought to act as a barrier, preventing the access of cellulase to cellulose. The impact of xylan removal, by both of the chemical and biological processes, on the cellulose accessibility was comparatively studied. Poplar holocellulose with 24.7 % xylan was taken as the starting material, and the gradual removal of xylan was achieved by successive treatments with increasing NaOH concentration. The data indicated that partial removal of hemicelluloses, not complete, favored the crystal configuration transformation of cellulose and then the lignocellulose/biomass enzymatic digestibility/saccharification. The maximum enzymatic efficiency (94.6 %) was achieved when cellulose II was formed as the NaOH concentration higher than 2.0 M. With the supplement of xylanase, the inhibitory effect from oligosaccharides was probably reduced, but the accumulation of xylose still negatively affected the cellulase cocktails. From the economic perspective, the xylanase loading of 5.0 IU/g xylan was proposed and 1.2-fold increment of cellulose hydrolysis was final obtained.

Autonomous Pose Detection and Alignment of Suction Modules of a Biped Wall-Climbing Robot

Vacuum adsorption is a simple but effective attaching method widely used in many fields including robotic wall climbing. It is required that the sucker is aligned well with the target surface to form airtight chamber for vacuum generation. For applications in biped wall-climbing robots, automatically aligning the sucker with the wall is beneficial and important to enhance the efficiency and effectiveness of vacuum adsorption. Especially, such a function is essential for autonomous intelligent climbing. To this end, we propose a novel and low-cost approach to perform autonomous alignment of a sucker (suction module) based on noncontact sensors. We first develop a sensing system to detect the configuration of the swinging suction module with respect to the target surface, and then present an algorithm to compute the configuration transformation and control the robot to drive the suction cups toward the target surface with a well-aligned configuration for adherence. In this paper, the basic theory for autonomous pose detection and alignment of the suction module for wall climbing with a biped robot is presented. Specifically, the key configuration of the swinging suction module for adsorption is analyzed, and the pose detection model, the conditions for forming airtight chamber, and the autonomous alignment algorithm are introduced. Calibration of the sensing system and experiments with our biped wall-climbing robot W-Climbot is conducted. The results have verified the feasibility, effectiveness and applicability of the proposed sensing system, theoretical analysis and the algorithm for autonomous pose detection and alignment of the suction modules.

Theoretical prediction of the host-guest interactions between novel photoresponsive nanorings and C60: a strategy for facile encapsulation and release of fullerene.

A series of photoresponsive-group-containing nanorings hosts with 12∼14 Å in diameter is designed by introducing different number of azo groups as the structural composition units. And the host-guest interactions between fullerene C60 and those nanoring hosts were investigated theoretically at M06-2X/6-31G(d)//M06-L/MIDI! and wB97X-D/6-31G(d) levels. Analysis on geometrical characteristics and host-guest binding energies revealed that the designed nanoring molecule (labeled as 7) which is composed by seven azo groups and seven phenyls is the most feasible host for encapsulation of C60 guest among all candidates. Moreover, inferring from the simulated UV-vis-NIR spectroscopy, the C60 guest could be facilely released from the cavity of the host 7 via configuration transformation between trans-form and cis-form of the host under the 563 nm photoirradiation. Additionally, the frontier orbital features, weak interaction regions, infrared, and NMR spectra of the C60@7 host-guest complex have also been investigated theoretically.

Nitrogen Configuration of Polybenzoxazine Carbide

AbstractCarbon materials should have specific centers for its functionalities. In this study, the specific centers of polybenzoxazine carbides were studied for the first time. Three classical benzoxazine monomers were chose as the object. The transformation of nitrogen configuration of polybenzoxazines carbides was characterized via pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and X-ray photoelectron spectroscopy (XPS). The results showed that the tertiary amine nitrogen converted to pyridinic nitrogen and pyrrolic nitrogen incorporated in graphene residuals during the carbonization, which were the specific centers for the functionality.

A soluble cryogenic thermometer with high sensitivity based on excited-state configuration transformations.

Cryogenic temperature detection plays an irreplaceable role in exploring nature. Developing high sensitivity, accurate, observable and convenient measurements of cryogenic temperature is not only a challenge but also an opportunity for the thermometer field. The small molecule 9-(9,9-dimethyl-9H-fluoren-3yl)-14-phenyl-9,14-dihydrodibenzo[a,c]phenazine (FIPAC) in 2-methyl-tetrahydrofuran (MeTHF) solution is utilized for the detection of cryogenic temperature with a wide range from 138 K to 343 K. This system possesses significantly high sensitivity at low temperature, which reaches as high as 19.4% K(-1) at 138 K. The temperature-dependent ratio of the dual emission intensity can be fitted as a single-exponential curve as a function of temperature. This single-exponential curve can be explained by the mechanism that the dual emission feature of FIPAC results from the excited-state configuration transformations upon heating or cooling, which is very different from the previously reported mechanisms. Here, our work gives an overall interpretation for this mechanism. Therefore, application of FIPAC as a cryogenic thermometer is experimentally and theoretically feasible.

Design and Analysis of a Novel Parallel Metamorphic Mechanism

3-UPU parallel mechanisms, whose axes of hooke joint on base plate and moving plate fit different geometric constraints, can have translational or orientational output. A configuration-switch mechanism for 3-UPU parallel mechanism is designed based on the theory of metamorphic that change the orientations of kinematic pairs can lead to configuration transformation. This mechanism consists of two identical kinematic chains fixed on base plate and moving plate respectively. In order to change output and design a novel parallel metamorphic mechanism, the joint of two identical kinematic chains transforms to make axes of hooke joints change between parallel and jointed. A proper configuration-switch position affects the working performance of consequent configuration, since metamorphic mechanisms have multigroup couple relationship. Screw theory is adopted to calculate the DOF of this parallel metamorphic mechanism in different configuration respectively. Taking the mechanisms' workspace for example, the effect of the configuration-switch position on working performance of mechanisms in different configuration is analyzed.

Modeling and experimental validation of cutting forces in five-axis ball-end milling based on true tooth trajectory

The accurate prediction of cutting forces plays an important role in high performance cutting of free-form surfaces which are widely used in automotive, die/mold, and aerospace industries. The purpose of this paper is to present a novel model of cutting forces in five-axis ball-end milling based on true tooth trajectory. The model can be implemented in three steps. First, the representation of the five-axis machine configuration and kinematic transformations is given as the basis of the geometry analysis of five-axis milling operations. Second, through analysis of the true tooth trajectories during the five-axis ball-end milling process, the bisection method can be applied to calculate the true instantaneous undeformed chip thickness. Meanwhile, the start and exit rotation immersion angles and the two limit axial positions can be modeled to determine the exact engagement region. Finally, a method to identify cutting force coefficients is proposed, and the model is then utilized to predict the cutting forces. All experiments carry out under different cutting parameters and cutter positions to prove its effectiveness. Comparisons of the predicted cutting forces and the experimental results show the reliability of the proposed model.

A novel photo-responsive azobenzene-containing nanoring host for fullerene-guest facile encapsulation and release.

Azobenzenes in particular have been proved to have a robust photo-response, in which their configuration can transform between the trans- and cis-form upon UV-visible irradiation. Accordingly, azobenzene-containing molecules are frequently applied in the design of the guests, involving so-called host-guest chemistry. In this paper, a novel photo-responsive nanoring host molecule ([4]AB) has been designed by introducing four azobenzene groups onto the ring, and interactions between the designed nanoring host and fullerenes C60 and C70 guests were investigated at both the M06-L/MIDI! as well as M06-2X/6-31G(d) level of theory. By analyzing the geometric characteristics and host-guest binding energies, it is revealed that the designed [4]AB with diameter ca. 13.4 Å is an ideal host molecule for the encapsulation of guests C60 and C70 fullerene. Meanwhile, inferred from UV-vis-NIR spectroscopy, the guest C60 and C70 could be facilely released from the cavity of the [4]AB via configuration transformation between trans- and cis-form of the host under 474 and 506 nm photo-irradiation, respectively. Frontier orbital features, weak interaction regions, infrared spectroscopy and (1)H NMR spectra have also been theoretically simulated. The present work would provide a new strategy for facile reversible encapsulation and release of fullerene guest by a novel nanoring host.

Design and Principle Analysis of Wheel-Tracked Robot’s Mobile Mechanism

Integrating the merits of wheeled and tracked mechanism, a robot’s mobile mechanism may have more adaptability in field environments. A kind of metamorphic mechanism with three configurations was proposed, which configuration transformation was analyzed and metamorphic equations on configuration transformations were put forward. Based on them, a wheel-tracked robot’s mobile mechanism was brought forward. The key component of the structure, locomotion-mode-changing unit, was synthesized. The robot’s prototype was made and the principle test was finished. The result shows that the built prototype can run by wheels or tracks, and transform itself successfully.

Analysis of some basic approaches to finite strain elasto-plasticity in view of reference change

There is a large variety of concepts used to generalize the classical Prandtl–Reuss relations of infinitesimal elasto-plasticity to finite strains. In this work, some basic approaches are compared in a qualitative way with respect to a certain invariance property. These basic approaches include the additive hypoelasto-plasticity with corotational stress rates, additive plasticity in the logarithmic strain space, and multiplicative hyperelasto-plasticity.The notion of weak invariance is introduced in this study. Roughly speaking, a material model is weakly invariant under a certain transformation of the local reference configuration if this reference change can be neutralized by a suitable transformation of initial conditions, leaving the remaining constitutive relations intact. We analyse the basic models in order to find out if they are weakly invariant under arbitrary volume-preserving transformations of the reference configuration.It is shown that the weak invariance property corresponds to a generalized symmetry which provides insights into underlying constitutive assumptions. This property can be used for a systematic study of different frameworks of finite strain elasto-plasticity. In particular, it can be used as a classification criterion.

Direct coordinate-free derivation of the compatibility equation for finite strains

The compatibility equation for the Cauchy-Green tensor field (squared tensor of pure extensionwith respect to the reference configuration) is directly derived from the well-known relation expressing this tensor via the vector field determining the mapping (transformation) of the reference configuration into the actual one. The derivation is based on the use of the apparatus of coordinatefree tensor calculus and does not apply any notions and relations of Riemannian geometry at all. The method is illustrated by deriving the well-known compatibility equation for small strains. It is shown that when the obtained compatibility equation for finite strains is linearized, it becomes the compatibility equation for small strains which indirectly confirms its correctness.

The role of Nx–Si–Oy bonding configuration in acquiring strong blue to red photoluminescence from amorphous SiNxOy film

We report the acquisition of strong blue to red photoluminescence (PL) from a-SiNxOy thin film that was prepared by plasma enhanced chemical vapor deposition at room temperature. By increasing the flow rate ratio (R) of silane (SiH4) to ammonia (NH3), the luminescent peak position can be tunable in the visible range from 440 to 590 nm, and shown to be independent of temperature as revealed by temperature-dependent PL investigation. The Fourier transform infrared (FTIR) spectra and X-ray photoelectron spectra (XPS) were employed to clarify the relationship between the bonding configuration and PL characteristics. Based on the existence of N–Si–O bond arrangement evidenced in FTIR spectra, the deconvolution of the Si 2p peak was carried out to yield five component peaks corresponding to Si–N4, N3–Si–O, N2–Si–O2, N–Si–O3, and Si–O4. The increase of PL intensity is suggested to be closely related to increased concentration of Nx–Si–Oy bonds. All the results obtained from temperature-dependent PL spectra, FTIR spectra, and XPS spectra disclosed that the light emission from a-SiNxOy film can be originated from recombination via luminescent centers associated with Nx–Si–Oy bonding configuration, and the redshift of PL peak with the increase of R may arise from integral effect of Nx–Si–Oy bonding configuration transformation and valence band maximum upward shift.

An off–on–off electrochemiluminescence approach for ultrasensitive detection of thrombin

This work demonstrates an aptasensor for ultrasensitive electrochemiluminescence (ECL) detection of thrombin based on an “off–on–off” approach. The system is composed of an Eu3+-doped CdS nanocrystals (CdS:Eu NCs) film on glassy carbon electrode (GCE) as ECL emitter. Then gold nanoparticles (AuNPs) labeled hairpin-DNA probe (ssDNA1) containing thrombin-binding aptamer (TBA) sequence was linked on the NCs film, which led to ECL quenching (off) as a result of Förster-resonance energy transfer (FRET) between the CdS:Eu NC film and the proximal AuNPs. Upon the occurrence of hybridization with its complementary DNA (ssDNA2), an ECL enhancement (on) occurred owing to the interactions of the excited CdS:Eu NCs with ECL-induced surface plasmon resonance (SPR) in AuNPs at large separation. Thrombin could induce ssDNA1 forming a G-quadruplex and cause the AuNPs to be close to CdS:Eu NCs film again, which resulted in an enhanced ECL quenching (off). This “off–on–off” system showed a maximum 7.4-fold change of ECL intensity due to the configuration transformation of ssDNA1 and provides great sensitivity for detection of thrombin in a wide detection range from 50aM to 1pM.

Research on Lower-Order Body Matrix Method and the Configuration Transformation of Planar Metamorphic Mechanism

The lower-order body matrix method is proposed as to topological configuration issue of planar metamorphic mechanism. Through combining lower-order operator and type code of kinematic pair, the lower-order body matrix is built to describe the information of adjacent body and kinematic pair. In the research on configuration transformation of planar metamorphic mechanism, step-description method is put forward which adapts to the analysis of various planar metamorphic ways. Step mathematical equation is established based on the generalized operational rule of lower-order body matrix. Application example shows that the lower-order matrix built with lower-order body matrix method is simpler and more informative, which has many advantages over the adjacency matrix and the correlation matrix that cannot be combined with the kinematics and dynamics equations, and solve the issue that the low-order sequences can only describe the open chain metamorphic mechanism. Step-description method can describe various planar metamorphic configuration transformation process comprehensively, which the EU matrix method cannot complete, providing a new method on the research of planar metamorphic mechanism.

Stabilization and transformation of asymmetric configurations in small-mismatch alloy nanoparticles: the role of coordination dependent energetics

Chemical order in platinum-iridium truncated-octahedron nanoparticles as a model system was studied using coordination-dependent bond-energy variations (CBEV) and the statistical-mechanical free-energy concentration expansion method (FCEM) adapted for handling axially symmetric structures. Pt-Ir side-separated ("Quasi-Janus", QJ) configurations are found to be stabilized at low temperatures mainly due to CBEV-related preferential strengthening of Pt-surface-Ir-subsurface bonds, and the greatly reduced number of hetero-atomic bonds. In comparison, the roles of local strain (by only ~2% atomic mismatch), short-range-order and vibrational entropy are minor. At higher temperatures, the QJ configuration is transformed into a partially disordered central-symmetric onion-like structure, and the sharp transition is accompanied by extensive pre-transition atomic exchange processes, reflected in a lambda-type heat capacity curve. The nanoparticle composition and size dependent transition temperatures, which are well below the bulk miscibility gap, furnish the first Pt-Ir nanophase diagram, which is likely to represent a distinct class of asymmetrically phase-separated nanoalloys having negligible mismatch but large preferential bond strengthening at the near-surface region.

Topological Analysis of Configuration Evolution and Biological Modeling of a Novel Type of Electric Loading Mechanism with Metamorphic Functions

Metamorphic mechanism is a class of mechanism which possesses the characteristics such as multi-stage, multi-topology, multi-degree of freedom(DOF) changes. A novel type of electric loading mechanism is proposed by employing the concepts of the mechanism to the innovative design of loaders, which can change its topological structures to adjust various kinds of demands during the working process. One driving motor can finish multiple tasks such as shoveling, loading, lifting, and dumping. The motor is placed on the frame, problems of traditional serial manipulators such as low stiffness, high inertia of the linkages can be avoided. The source-metamorphic mechanism of the newly invented mechanism is introduced, as well as its metamorphic ways. The adjacent matrix and topological graphs are used to describe the topological changes of each sub-phase of the mechanism, based on which the working principles and characteristics of configuration changing are analyzed. The characteristics during the evolutionary process are obtained. Configuration transformation and its degeneration ways during the genetic growth are studied. The representation of source-metamorphic mechanism is given after generation operations.

Energy barrier for configurational transformation of graphene nanoribbon on nanotube

A graphene nanoribbon (GNR) has two basic configurations when winding on the outer surface of a carbon nanotube (CNT): helix and scroll. Here the transformation between the two configurations is studied utilizing molecular dynamics simulations. The energy barrier during the transformation as well as its relationship with the interfacial energy and the radius of CNT are investigated. Our work offers further insights into the formation of desirable helix/scroll of GNR winding on nanotubes or nanowires, and thus can enable novel design of potential graphene-based electronics.