State estimation and experimental verification of a robotic vehicle with six in-wheel drives using Kalman filter

Microsystem Technologies - In this research we present an algorithm for a six-wheeled robotic vehicle with articulated suspension (RVAS) to estimate the vehicle velocity and acceleration states,...     

Environmental and economic assessment of the chemical absorption process in Korea using the LEAP model

CO₂ emission from fossil fuels is a major cause for the global warming effect, but it is hard to remove completely in actuality. Moreover, energy consumption is bound to increase for the continuous economic development of a country that has an industrial formation requiring high-energy demand. Therefore, we need to consider not only a device for CO₂ mitigation but also its impact when a CO₂ mitigation device is applied. The device for CO₂ emission mitigation can be classified into three fields: energy consumption reduction, development of CO₂ removal and recovery technology, and development of alternative energy technology. Among these options, CO₂ removal and recovery technology has a merit that can be applied to a process in the near future. Therefore, research for CO₂ removal and recovery is actively progressing in Korea. In this study, environmental and economic assessment according to the energy policy change for climate change agreement and increase of CO₂ mitigation technology is accomplished, on the bases of operating data for the CO₂ chemical absorption pilot plant that is installed in the Seoul coal steam power plant. The Long-range Energy Alternatives Planning system (LEAP) was used to analyze the alternative scenario, and results were shown quantitatively.     

Highly Efficient Top-Emitting Infrared-to-Visible Up-Conversion Device Enabled by Microcavity Effect

Infrared (IR)-to-visible up-conversion device allows a low-cost, pixel-free IR imaging over the conventional expensive compound semiconductor-based IR image sensors. However, the external quantum efficiency has been low due to the integration of an IR photodetector and a light-emitting diode (LED). Herein, by inducing a strong micro-cavity effect, a highly efficient top-emitting IR-to-visible up-conversion device is demonstrated where PbS quantum dots IR-absorbing layer is integrated with a phosphorescent organic LED. By optimizing the optical cavity length between indium tin oxide (ITO)/thin Ag/ITO anode and semi-transparent Mg:Ag top cathode, the up-conversion device yields 15.7% of photon-to-photon conversion efficiency from the top-emission. The high efficiency can be achieved under a low IR transmission through the semi-reflective anode. Finally, pixel-free IR imaging is demonstrated using the up-conversion device, boosting the effect of micro-cavity on the brightness and the contrast of an IR image.     

Synthesis of Allylester Resin Tethered to Layered Silicates by <Emphasis Type="Italic">in-situ</Emphasis> Polymerization and Its Nanocomposite

Summary Allylester resin tethered to layered silicate was synthesized by in-situ polymerization method and was cured by tert-butylperbenzoate (TBPB) directly. We ascertained the existing of carbonyl and benzyl groups which come from diallyl terephtalate in the gallery of layered silicates using the thermogravimetric analysis (TGA) and FT-IR. The residual weight and new IR peaks of the clay, which is treated by in-situ polymerization, imply that the hydroxy group of intercalant takes part in the polymerization of allylester resin. Also, its nanocomposite was characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns and TEM photographs indicate that the basal spacing (d ₀₀₁ ) of the nanocomposite made by in-situ polymerization is larger than those of the nanocomposite made by a simple mixing. Received: 3 October 2002/Revised version: 2 December 2002/Accepted: 3 December 2002 Correspondence to Seok-Ho Hwang     

The effect of hydrodynamic flow regimes on the algal bloom in a monomictic reservoir

The effectiveness of a proposed curtain weir to be installed in the transitional zone of a eutrophic reservoir located in monsoon areas on the control of algal blooms in the lacustrine zone where drinking water withdrawals occur was assessed with various hydrodynamic flow regimes. A two-dimensional hydrodynamic and eutrophication model that can accommodate vertical displacement of the weir following the water surface changes was developed and validated using field data obtained from two distinctive hydrological years; drought (2001) and wet (2004). The model adequately reproduced the temporal and spatial variations of temperature, nutrients and phytoplankton concentrations in the reservoir. The efficacy of the curtain weir method found to be diverse for different hydrological conditions and dependent on the inflow densimetric Froude number (Fr(i)). Algal blooming was considerably mitigated by curtailing the transport of nutrients and algae from riverine zone to lacustrine epilimnion zone during the drought year as long as Fr(i) < 1.0. However, some flood events with Fr(i) > 1.0 transported nutrients and algae built upstream of the weir into the downstream euphotic zone by strong entrainments in 2004. Numerical experiments revealed that the efficiency of the weir on the control of algal blooming becomes marginal if the Fr(i) > 3.0.     

Monolithic Organic/Colloidal Quantum Dot Hybrid Tandem Solar Cells via Buffer Engineering

Monolithically integrated hybrid tandem solar cells (TSCs) that combine solution-processed colloidal quantum dot (CQD) and organic molecules are a promising device architecture, able to complement the absorption across the visible to the infrared. However, the performance of organic/CQD hybrid TSCs has not yet surpassed that of single-junction CQD solar cells. Here, a strategic optical structure is devised to overcome the prior performance limit of hybrid TSCs by employing a multibuffer layer and a dual near-infrared (NIR) absorber. In particular, a multibuffer layer is introduced to solve the problem of the CQD solvent penetrating the underlying organic layer. In addition, the matching current of monolithic TSCs is significantly improved to 15.2 mA cm⁻² by using a dual NIR organic absorber that complements the absorption of CQD. The hybrid TSCs reach a power conversion efficiency (PCE) of 13.7%, higher than that of the corresponding individual single-junction cells, representing the highest efficiency reported to date for CQD-based hybrid TSCs.     

A Tuned Alternating D–A Copolymer Hole-Transport Layer Enables Colloidal Quantum Dot Solar Cells with Superior Fill Factor and Efficiency

The need for optoelectronic and chemical compatibility between the layers in colloidal quantum dot (CQD) photovoltaic devices remains a bottleneck in further increasing performance. Conjugated polymers are promising candidates as new hole-transport layer (HTL) materials in CQD solar cells (CQD-SCs) owing to the highly tunable optoelectronic properties and compatible chemistries. A diketopyrrolopyrrole-based polymer with benzothiadiazole derivatives (PD2FCT-29DPP) as an HTL in these devices is reported. The energy level, molecular orientation, and hole mobility of this HTL are manipulated through molecular engineering. By levering the polymer's optical absorption spectrum complementary to that of the CQD active layer, EQE across the visible and near-infrared regions is maximized. As a result, a PD2FCT-29DPP-based device exhibits a fill factor of 70% and approximately 35% efficiency enhancement compared to a PTB7-based device.     

Sulfurized Colloidal Quantum Dot/Tungsten Disulfide Multi-Dimensional Heterojunction for an Efficient Self-Powered Visible-to-SWIR Photodetector

Emerging semiconducting materials show considerable promise for application in the development of next-generation optoelectronic devices. In particular, broadband light detection is crucial in various applications, including multispectral imaging and cognition. Therefore, tuning the physical properties of semiconductors and thereby building an efficient heterojunction are important for achieving a high-performance photodetection device. In this study, a heavy p-type colloidal quantum dot (CQD) is synthesized through solution-based sulfurization. The resulting cubic-shaped CQD exhibits broadband and strong absorption, which enable its broadband absorption. Further, a multidimensional 0D-2D heterojunction is developed using p-type CQD and n-type tungsten disulfide (WS₂). This efficient p-n junction is operated as a fully self-powered optical sensor and phototransistor under various light illumination conditions. Under the self-powered condition, the CQD/WS₂ heterojunction device exhibits 440- and 200-fold-higher responsivity and detectivity, respectively, than pristine WS₂.     

A Chemically Orthogonal Hole Transport Layer for Efficient Colloidal Quantum Dot Solar Cells

Colloidal quantum dots (CQDs) are of interest in light of their solution-processing and bandgap tuning. Advances in the performance of CQD optoelectronic devices require fine control over the properties of each layer in the device materials stack. This is particularly challenging in the present best CQD solar cells, since these employ a p-type hole-transport layer (HTL) implemented using 1,2-ethanedithiol (EDT) ligand exchange on top of the CQD active layer. It is established that the high reactivity of EDT causes a severe chemical modification to the active layer that deteriorates charge extraction. By combining elemental mapping with the spatial charge collection efficiency in CQD solar cells, the key materials interface dominating the subpar performance of prior CQD PV devices is demonstrated. This motivates to develop a chemically orthogonal HTL that consists of malonic-acid-crosslinked CQDs. The new crosslinking strategy preserves the surface chemistry of the active layer beneath, and at the same time provides the needed efficient charge extraction. The new HTL enables a 1.4× increase in charge carrier diffusion length in the active layer; and as a result leads to an improvement in power conversion efficiency to 13.0% compared to EDT standard cells (12.2%).     

Stabilizing Surface Passivation Enables Stable Operation of Colloidal Quantum Dot Photovoltaic Devices at Maximum Power Point in an Air Ambient

Colloidal quantum dots (CQDs) are promising materials for photovoltaic (PV) applications owing to their size-tunable bandgap and solution processing. However, reports on CQD PV stability have been limited so far to storage in the dark; or operation illuminated, but under an inert atmosphere. CQD PV devices that are stable under continuous operation in air have yet to be demonstrated—a limitation that is shown here to arise due to rapid oxidation of both CQDs and surface passivation. Here, a stable CQD PV device under continuous operation in air is demonstrated by introducing additional potassium iodide (KI) on the CQD surface that acts as a shielding layer and thus stands in the way of oxidation of the CQD surface. The devices (unencapsulated) retain >80% of their initial efficiency following 300 h of continuous operation in air, whereas CQD PV devices without KI lose the amount of performance within just 21 h. KI shielding also provides improved surface passivation and, as a result, a higher power conversion efficiency (PCE) of 12.6% compared with 11.4% for control devices.