Fabrication mechanism of friction-induced selective etching on Si(100) surface

As a maskless nanofabrication technique, friction-induced selective etching can easily produce nanopatterns on a Si(100) surface. Experimental results indicated that the height of the nanopatterns increased with the KOH etching time, while their width increased with the scratching load. It has also found that a contact pressure of 6.3 GPa is enough to fabricate a mask layer on the Si(100) surface. To understand the mechanism involved, the cross-sectional microstructure of a scratched area was examined, and the mask ability of the tip-disturbed silicon layer was studied. Transmission electron microscope observation and scanning Auger nanoprobe analysis suggested that the scratched area was covered by a thin superficial oxidation layer followed by a thick distorted (amorphous and deformed) layer in the subsurface. After the surface oxidation layer was removed by HF etching, the residual amorphous and deformed silicon layer on the scratched area can still serve as an etching mask in KOH solution. The results may help to develop a low-destructive, low-cost, and flexible nanofabrication technique suitable for machining of micro-mold and prototype fabrication in micro-systems.     

Exact formulations and algorithm for the train timetabling problem with dynamic demand

In this paper we study the design and optimization of train timetabling adapted to a dynamic demand environment. This problem arises in rapid train services which are common in most important cities. We present three formulations for the problem, with the aim of minimizing passenger average waiting time. The most intuitive model would consider binary variables representing train departure times but it yields to non-linear objective function. Instead, we introduce flow variables, which allow a linear representation of the objective function. We provide incremental improvements on these formulations, which allows us to evaluate and compare the benefits and disadvantages of each modification. We present a branch-and-cut algorithm applicable to all formulations. Through extensive computational experiments on several instances derived from real data provided by the Madrid Metropolitan Railway, we show the advantages of designing a timetable adapted to the demand pattern, as opposed to a regular timetable. We also perform an extensive computational comparison of all linear formulations in terms of size, solution quality and running time.     

New simplified approach for obtaining a reliable plateau value in fatigue analysis of bituminous materials

The Plateau Value (PV) based on the Ratio of Dissipated Energy Change (RDEC) approach has been proven to provide a unique relationship with the fatigue life, N_f, independent of loading mode, temperature and frequency. In this paper, a new simplified approach is proposed to compute the unique energy parameter PV. The results of this study show that applying the proposed method allows a unique fatigue power law to be produced and eliminates the ambiguity and variability in calculating PV. However, the study also shows that the PV-N_f fatigue curves for bituminous materials are dependent on material type which is contradictory to other studies dealing with PV. The study also highlights the importance of appropriately identifying the fatigue failure point prior to commencing any fatigue analysis.     

Facile preparation of Gd3+ doped carbon quantum dots: Photoluminescence materials with magnetic resonance response as magnetic resonance/fluorescence bimodal probes

There are a few bimodal molecular imaging probes constructed by gadolinium (3+) ions in combination with carbon quantum dots (CQDs), and the reported ones show such obvious drawbacks as low luminous efficiency and weak MRI contrast. In the paper, a kind of CQDs photoluminescence materials with magnetic resonance response was prepared by hydrothermal method and employing gadopentetate monomeglumine (GdPM) as a precusor. Here, the GdPM plays a role of not only carbon source, but also gadolinium (3+) sources. When the GdPM aqueous solution with a concentration of 4 mg mL⁻¹ was pyrolyzed under 220 °C and 2.0 MPa for 8 h, an optimal CQDs was obtained which are doped with gadolinium (3+) ions in both chelates and Gd₂O₃ (named as Gd³⁺-CQDs). The average diameter of the Gd³⁺-CQDs is about 1.6 nm, which show a high photoluminescence quantum yield of 7.1%, as well as high longitudinal relaxivity (r₁) of 9.87 mM⁻¹ s⁻¹. And owing to the unconspicuous cell toxicity, the Gd³⁺-CQDs show big possibility for clinical application in magnetic resonance/fluorescence bimodal molecular imaging.     

Hierarchical Particle Swarm Optimization with Ortho-Cyclic Circles

Cloud computing is an emerging technology which deals with real world problems that changes dynamically. The users of dynamically changing applications in cloud demand for rapid and efficient service at any instance of time. To deal with this paper proposes a new modified Particle Swarm Optimization (PSO) algorithm that work efficiently in dynamic environments. The proposed Hierarchical Particle Swarm Optimization with Ortho Cyclic Circles (HPSO-OCC) receives the request in cloud from various resources, employs multiple swarm interaction and implements cyclic and orthogonal properties in a hierarchical manner to provide the near optimal solution. HPSO-OCC is tested and analysed in both static and dynamic environments using seven benchmark optimization functions. The proposed algorithm gives the best solution and outperforms in terms of accuracy and convergence speed when compared with the performance of existing PSO algorithms in dynamic scenarios. As a case study, HPSO-OCC is implemented in remote health monitoring application for optimal service scheduling in cloud. The near optimal solution from HPSO-OCC and Dynamic Round Robin Scheduling algorithm is implemented to schedule the services in healthcare.     

A physical mechanism based constitutive model for temperature-dependent transformation ratchetting of NiTi shape memory alloy: One-dimensional model

In this paper, the effect of test temperature on the transformation ratchetting of super-elastic NiTi shape memory alloy was first investigated in the cyclic tension-unloading tests. It is shown that all the residual strain, dissipation energy, the start stress of martensite transformation and their evolutions during the cyclic loading depend greatly upon the test temperature. Based on the experimental observations, a new one-dimensional constitutive model is constructed by considering two different inelastic deformation mechanisms (i.e., martensite transformation and transformation-induced plasticity). The proposed model employs a new evolution rule of transformation-induced plasticity which considers the physical mechanism of the plastic deformation, i.e., the dislocation slipping in the austenite phase near the austenite–martensite interfaces. Furthermore, the interaction between dislocation and martensite transformation is also taken into account in the proposed model. The capability of the proposed model to predict the uniaxial temperature-dependent transformation ratchetting of NiTi shape memory alloy is verified by comparing the predictions with the experimental data.     

Influence of laser dispersed treatment on rolling contact wear and fatigue behavior of railway wheel steel

The aim of this paper is to improve the rolling contact wear and fatigue resistance of ferrite–pearlite railway wheel steel by laser dispersed treatment. Such treatment creates isolated glazed regions on the surface layer of railway wheel steel, which are composed of fine martensite and retained austenite and have an average hardness of 762HV_0.3. The wear rate and rolling contact fatigue life of treated and untreated railway wheel steel were evaluated and compared by Amsler twin-disc testing machines in dry and lubricated condition, respectively. The test results show that laser dispersed treatment improves the rolling contact wear and fatigue resistance of railway wheel steel. The stable wear rate of the laser treated railway wheel steel is about 0.3 times that of untreated railway wheel steel and the average rolling contact life of treated railway wheel steel is about double that of the untreated steel. Further investigations show that the glazed regions suppress the plastic deformation of railway wheel steel. This inhibits the treated railway wheel steel from delamination wear and delays the formation of fatigue crack initiation.     

Multilevel resistive memory switching in graphene sandwiched organic polymer heterostructure

A novel multilevel resistive switching was observed in trilayer stacked geometry composed of graphene nano flakes sandwiched between polyvinylidene fluoride layers fabricated by spin coating method, which are expected to fulfill the need of high density data storage memories. External parameters such as current compliance and induced voltage pulse imposed on the devices provided an aid to tune the inherent resistance states. As fabricated devices exhibited multi level switching with stable resistance ratios between different resistance states having excellent data retention and endurance. Space charge limited conduction and Fowler–Nordheim (F–N) tunneling were found to be responsible for the switching mechanism. Graphene enriched with trapping sites provides the adequate environment for F–N tunneling process to occur, resulting in multi-bit resistance states.     

Comparison between two model-based algorithms for Li-ion battery SOC estimation in electric vehicles

Accurate battery State of Charge (SOC) estimation is of great significance for safe and efficient energy utilization for electric vehicles. This paper presents a comparison between a novel robust extended Kalman filter (REKF) and a standard extended Kalman filter (EKF) for Li-ion battery SOC indication. The REKF-based method is formulated to explicitly compensate for the battery modeling uncertainty and linearization error often involved in EKF, as well as to provide robustness against the battery system noise to some extent. Evaluation results indicate that both filters have a good average performance, given appropriate noise covariances, owing to a small average modeling error. However, in contrast, the REKF-based SOC estimation method possesses slightly smaller root-mean-square (RMS) error. In the worst case, the robustness characteristics of the REKF result in an obviously smaller error bound (around by 1%). Additionally, the REKF-based approach shows superior robustness against the noise statistics, leading to a better tolerance to inappropriate tuning of the process and measurement noise covariances.     

Carbody hunting investigation of a high speed passenger car

This paper describes the low frequency carbody hunting problem of a high speed passenger car emerged in the process of tests and service operations. It causes a significant deterioration of lateral comfort. First, the vehicle model is established as a multiple rigid body system. Using root locus analysis, the effect of system parameters on the carbody hunting stability has been studied. It shows that carbody hunting instability has something to do with suspension parameters and wheel/rail conditions. To find the causes of this carbody hunting problem, component tests have been carried out. Based on the theoretical hunting stability analysis and component tests, solutions are proposed and then validated in the field test.