Thermomechanical Nanocutting of 2D Materials

Atomically thin materials, such as graphene and transition metal dichalcogenides, are promising candidates for future applications in micro/nanodevices and systems. For most applications, functional nanostructures have to be patterned by lithography. Developing lithography techniques for 2D materials is essential for system integration and wafer-scale manufacturing. Here, a thermomechanical indentation technique is demonstrated, which allows for the direct cutting of 2D materials using a heated scanning nanotip. Arbitrarily shaped cuts with a resolution of 20 nm are obtained in monolayer 2D materials, i.e., molybdenum ditelluride (MoTe₂), molybdenum disulfide (MoS₂), and molybdenum diselenide (MoSe₂), by thermomechanically cleaving the chemical bonds and by rapid sublimation of the polymer layer underneath the 2D material layer. Several micro/nanoribbon structures are fabricated and electrically characterized to demonstrate the process for device fabrication. The proposed direct nanocutting technique allows for precisely tailoring nanostructures of 2D materials with foreseen applications in the fabrication of electronic and photonic nanodevices.     

Model reduction in the presence of uncertainty in model parameters

This short note describes how to extend a certain class of existing model reduction techniques to take into account uncertainty in model parameters. The key idea of this extension is that the reduced-order model should not only contain the model parameters, but that the reduction procedure itself has to be geared for dealing with parametric uncertainty. This goal is achieved by augmenting the vector of inputs to the system with the uncertain parameters and by performing model reduction on the augmented system. It is shown that error bounds for the reduced-order model can be computed if the underlying system is linear with respect to the states, parameters, and inputs. A comparison between the presented technique and a conventional approach is made via two examples.     

High-performance deep-ultraviolet optics for free-electron lasers

Working with wavelengths shorter than the deep ultraviolet involves the development of dedicated optics for free-electron lasers with devoted coating techniques and characterizations. High-performance deep-ultraviolet optics are specially developed to create low-loss, high-reflectivity dielectric mirrors with long lifetimes in harsh synchrotron radiation environments. In February 2001, lasing at 189.7 nm, the shortest wavelength obtained so far with free-electron-laser oscillators, was obtained at the European Free-electron-laser project at ELETTRA Synchrotron Light Laboratory, Trieste, Italy. In July 2001, 330-mW extracted power at 250 nm was measured with optimized transmission mirrors. Research and development of coatings correlated to lasing performance are reported.     

Snow-cover variability in central Asia between 2000 and 2011 derived from improved MODIS daily snow-cover products

In this study, the daily snow-cover time series has been analysed for the whole of central Asia after cloud coverage was removed. Snow-cover duration (SCD), snow-cover start (SCS), and snow-cover melt (SCM) have been derived for each hydrological year from 2000/2001 to 2010/2011 and mean conditions were extracted that identify a distinct north–south gradient of these parameters. The snow-cover index (SCI), which depicts a moderate variability with maximum deviations of ～20%, has been included for major hydrological catchments. The hydrological year 2001/2002 stands out due to minimum SCD caused by late SCS and early SCM while 2002/2003 constitutes maximum SCD initiated by late SCM. Although the time series of 11 years of data is too short to calculate possible trends of snow-cover characteristics, the results can be used to describe the average snow-cover conditions and compare single years against these values. Large divergences can indicate deficits or excesses of snow, which may lead to abnormal run-off situations, including natural disasters such as floods, landslides, or droughts. The latter, especially, can have severe negative economic impacts in a region.     

Dye and polymer based light sensor for tag integration

In this work we present a light sensor for tag integration based on the principle of a dye sensitized solar cell, using a flexible substrate and a polymer electrolyte. These features make an integration of the light sensor into current smart label fabrication processes possible. A printable light sensor combined with novel conductive polymers could solve reliability issues resulting from bonding processes. The components of the light sensor were chosen in a way to enable screen print production. The dye Ruthenium 535-bis-TBA has been used as active dye and Iodolyte AN-50 by Solaronix and PEDOT/PSS by H.C. Starck have been used as liquid and polymer electrolyte respectively. In order to prepare the liquid electrolyte for tag integration it has been gelatinized by addition of silica gel. Depending on the amount of silica gel different stiffness levels have been achieved. The functional layers have been deposited first on glass substrate and then on KAPTON foil by Du Pont. The polymer has been used as flexible substrate. Special care has been taken regarding the preparation of the transparent electrode. The transparent conductive oxide (TCO) indium tin oxide (ITO), which has been used as transparent electrode, has to be cured at elevated temperatures on the polymer substrate. A complete process flow for an integrated light sensor is being described in this work.     

On the use of bifurcation analysis for robust controller tuning for nonlinear systems

This paper presents a new approach to robust controller tuning for nonlinear systems. The main idea is to apply numerical bifurcation analysis to the closed-loop process, using the controller tuning parameters, the set points, and parameters describing model uncertainty (parametric as well as unmodeled dynamics) as bifurcation parameters. By analyzing the Hopf bifurcation and saddle-node bifurcation loci, bounds on the controller parameters are identified. These bounds depend upon the type as well as the degree of mismatch that exists between the plant and the model used for controller design.The method is illustrated by tuning a state feedback linearizing controller for an unstable reactor as well as by comparing a proportional-integral (PI) controller and a state feedback linearizing controller applied to a continuously operated fermenter. The feedback linearizing controller can result in better performance than the PI controller if a very accurate model of the process is known and if the operating conditions vary over a significant range. However, stability properties of systems controlled by feedback linearizing controllers can degrade significantly as the mismatch between the plant and the model increases. This is illustrated in the fermenter example by showing that bounds on the tuning parameter of the feedback linearizing controller are significantly tighter than the ones for the PI controller.     

Groundwater Circulation Well for Controlling Saltwater Intrusion in Coastal aquifers: Numerical study with Experimental Validation

Saltwater intrusion into coastal aquifers has become a prominent environmental concern worldwide. As such, there is a need to prepare and implement proper remediation techniques with careful planning of freshwater withdrawal systems for controlling saltwater intrusion in coastal marine and estuarine environments. This paper investigates the performance of groundwater circulation well (GCW) in controlling saltwater intrusion problems in unconfined coastal aquifers. The GCWs have been established as a promising in-situ remedial technique of contaminated groundwater. The GCW system creates vertical circulation flow by extracting groundwater from an aquifer through a screen in a single well and injecting back into the aquifer through another screen. The circulation flow induced by GCW force water in a circular pattern between abstraction and recharge screens and can be as a hydraulic barrier for controlling saltwater intrusion problem in coastal aquifers. In this study, an effort has been made to investigate the behavior of saltwater intrusion dynamics under a GCW. An experiment has been conducted in a laboratory-scale flow tank model under constant water head boundary conditions, and the variable-density flow and transport model FEMWATER is used to simulate the flow and transport processes for the experimental setup. The evaluation of the results indicates that there is no further movement of saltwater intrusion wedge towards the inland side upon implementation of GCW, and the GCW acts as a hydraulic barrier in controlling saltwater intrusion in coastal aquifers. The present study reveals the GCWs system can effectively mitigate the saltwater intrusion problem in coastal regions and could be considered as one of the most efficient management strategies for controlling the problem.

     

A comparison of adaptive and adaptable automation under different levels of environmental stress

The effectiveness of different forms of adaptive and adaptable automation was examined under low- and high-stress conditions, in the form of different levels of noise. Thirty-six participants were assigned to one of the three types of variable automation (adaptive event-based, adaptive performance-based and adaptable serving as a control condition). Participants received 3 h of training on a simulation of a highly automated process control task and were subsequently tested during a 4-h session under noise exposure and quiet conditions. The results for performance suggested no clear benefits of one automation control mode over the other two. However, it emerged that participants under adaptable automation adopted a more active system management strategy and reported higher levels of self-confidence than in the two adaptive control modes. Furthermore, the results showed higher levels of perceived workload, fatigue and anxiety for performance-based adaptive automation control than the other two modes. PRACTITIONER SUMMARY: This study compared two forms of adaptive automation (where the automated system flexibly allocates tasks between human and machine) with adaptable automation (where the human allocates the tasks). The adaptable mode showed marginal advantages. This is of relevance, given that this automation mode may also be easier to design.     

Metallo-porphyrin zinc as gas sensitive material for colorimetric gas sensors on planar optical waveguides

The presented work focuses on the investigations of a metallo-porphyrin and its gasochromic behavior to different gases. Gasochromic materials change their color while they are exposed to a certain gas. So they offer the possibility to develop highly selective chemical gas sensors and gas sensing systems. The focus of this work is the characterization of the metallo-porphyrin 5, 10, 15, 20-tetraphenylporphyrin-zinc (ZnTPP). Nonetheless, there is a wide range of other possible metallo-porphyrins. When embedded into a polymeric matrix (PVC) a color change to the toxic gas NO₂ can be detected. To develop a stand-alone gas sensor, the porphyrin/PVC matrix is deposited onto a planar optical waveguide. The color change of the porphyrin dye can be detected in the evanescent field of the optical waveguide. Therefore, the light of a high power LED is coupled into the waveguide. The color change of the porphyrin is detectable with photodiodes as a variation of the out-coupled light intensity. The sensor shows no unwished sensitivities to CO₂ and CO and only low to NH₃. NO₂ is detectable with a resolution of 1?ppm.