Hoon Cho

Unsmoothing Commercial Property Returns: A Revision to Fisher-Geltner-Webb's Unsmoothing Methodology

Fisher, Geltner, and Webb (1993), in a highly influential paper, develop a procedure to recover the underlying market values from a smoothed valuation-based commercial property return index, without assuming that the underlying property market is informationally efficient. Many papers since then have used the Fisher–Geltner–Webb unsmoothing technique to desmooth commercial property returns. We show, however, that there is an inherent bias in Fisher–Geltner–Webb unsmoothing technique and propose a simple extension of their model to correct for this bias. We then compare the performance of our improved specification to that of the Fisher–Geltner–Webb model.

Abnormal behavior of midgap electron trap in HB‐GaAs during thermal annealing

The behavior of the EL2 family in horizontal Bridgman‐(HB) grown GaAs by two thermal annealing methods, furnace annealing and rapid thermal annealing, was studied through deep level transient spectroscopy (DLTS) measurements, and a similar behavior of another group of electron traps was observed. As the annealing time is increased, the EL2 trap (Ec‐0.81 eV) is transformed to the new trap, EX2 (Ec‐0.73 eV), and finally to the other new trap, EX1 (Ec‐0.86 eV). Also the EL6 group (Ec‐0.18, 0.22, 0.27, and 0.35 eV) varied similarly to the EL2 family as a trap (Ec‐0.27 eV) is transformed to the first trap (Ec‐0.18 eV) and then the second trap (Ec‐0.22 eV). This result revealed that the EL2 family is related to the EL6 group. From the study of photocapacitance quenching, the existence of metastable states of the EL2 family is identified. These results suggest that the atomic structure of the EL2 trap may be an arsenic antisite with an interstitial arsenic and a double vacancy, such as VAsAsIVGaAsGa or its complex.

Creation of deep levels in horizontal Bridgman‐grown GaAs by hydrogenation

The effect of hydrogen plasma exposure on the deep levels in GaAs grown by the horizontal Bridgman method was studied. After hydrogenation at 250 °C for 3 h, the concentrations of the electron deep levels, such as the EL2 trap (Ec‐0.81 eV), the EL3 trap (Ec−0.63 eV), and the EL6 trap (Ec−0.35 eV), decrease by one order of magnitude. On the other hand, three new electron traps at Ec −0.42 eV, Ec −0.54 eV, and Ec −0.94 eV are created. After rapid thermal annealing up to 550 °C for 10 s, these created traps are reduced and the deep levels decreased by hydrogenation recover nearly completely. This result reveals that the passivation and creation of deep levels by hydrogenation may be explained as the interaction of atomic hydrogen with an unsaturated bond of native defects.

Valuing Retail Shopping Center Lease Contracts

In this article we set up a real option model of retail shopping center leases. The model incorporates the effects of stochastic sales externalities and the possibility of tenant default, and in the presence of these effects, we derive and solve a partial differential equation that can be used to price a lease transaction. The model then sums across all tenants to determine the value of the shopping center. The model generates a number of new predictions, including why a Jorgensonian user cost of capital may overestimate shopping center values, why the general industry practice is to ignore percentage rent payments and tenant default risk in commercial mortgage underwriting and why shopping center owners may not act opportunistically as most observers seem to think they do.

A relation between EL2 (Ec−0.81 eV) and EL6 (Ec−0.35 eV) in annealed HB‐GaAs by hydrogen plasma exposure

We present annealing and hydrogenation behaviors for EL2 (Ec−0.81 eV) and EL6 (Ec−0.35 eV) as dominant deep levels in GaAs. During rapid thermal annealing and the hydrogenation process, a relation has been identified between a midgap level group (the EL2 group) at 0.73, 0.81, and 0.87 eV, and a deep‐level group (the EL6 group) at 0.27, 0.18, and 0.22 eV below the conduction band. We then discuss a relation between the two groups and their origins.

Isothermal capacitance transient spectroscopy (ICTS) study for midgap levels in Hb-GaAs by rapid thermal annealing

We studied the midgap levels by using isothermal capacitance transient spectroscopy (ICTS) in Hb-GaAs which had been processed by rapid thermal annealing (RTA). As the annealing time at 850 °C increased, the EL2 trap (Ec−0.81 eV) was transformed to the EX2 trap (Ec−0.73 eV) and eventually to the EX1 trap (Ec−0.87 eV). The diffusivity of the EL2 trap obtained from the experimental result of the heat treatment was about 1.02·10−8cm2/s at 850 °C. This result indicate that the EL2 trap contains an interstitial arsenic atom. The result of the transformation to the EX1 and EX2 traps suggests that, when the EL2 trap is VAsASiVGaAsGa, the EX2 trap may be VAsVGaAsGa, which Asi is diffused out during a thermal annealing.

Hydrogenation effects on n+‐p InP solar cell

The hydrogenation effects on the solar cell property have been investigated in the sulfur (S) diffused n+‐p solar cell. In the plasma‐hydrogenated n+‐p junction at 150 °C for 30 min, the carrier concentration of p‐type substrate (Zn doped) decreased by one order of magnitude as the distance from the junction region becomes 0.7 μm. This indicates that the hydrogen passivation by atomic hydrogen is due to the form of the neutral hydrogen‐Zn acceptor complex near the junction region. The InP solar cell properties, especially the conversion efficiency and the short circuit current of the solar cell, were remarkably improved by 150 °C hydrogenation. The mechanism for the hydrogen passivation effects on the InP solar cell is also discussed. It is shown that the increase of the solar cell efficiency and short circuit current after hydrogenation may be due to the formation of the n+‐p−‐p structure by the hydrogen‐defect incorporation and adequate control of the carrier density in the p‐type substrate.

Schottky diode characteristics and deep levels on hydrogenated n-type GaAs

Schottky diode characteristics and deep levels of Si-doped n-type GaAs after hydrogen plasma exposure have been investigated as a function of substrate temperature during hydrogenation. The barrier height and reverse breakdown voltage of Au Schottky diodes on Si-doped GaAs increased during hydrogen plasma exposure. The ideality factor of the hydrogenated samples was lowered to 1.11 at substrate temperatures between 150 and 250 degrees C, and deep levels in these samples were effectively passivated at these temperatures. These properties of n-GaAs can be related to hydrogen redistribution in an electrically passivated surface layer. Good diode characteristics and the most effective passivation of deep levels in GaAs could be achieved at a substrate temperature of about 200 degrees C and a power density of 0.06 W cm-2.

Development of Algal Bloom Removal System Using Unmanned Aerial Vehicle and Surface Vehicle

Recently, owing to changes in weather conditions, cyanobacterial blooms, also known as harmful algal blooms (HABs), have caused serious damage to the ecosystems of rivers and lakes by producing cyanotoxins. In this paper, for the removal of HABs, an algal bloom removal robotic system (ARROS) is proposed. The ARROS has been designed with a catamaran-type unmanned surface vehicle (USV) and an algae-removal device attached below. In addition, electrical control systems and a guidance, navigation, and control (GNC) system are implemented on the ARROS to remove the algal bloom autonomously. Moreover, to increase the efficiency of the work, an unmanned aerial vehicle (UAV) is utilized and the system detects algal blooms with an image-based detection algorithm, which is known as a local binary pattern. The overall mission begins with a command from a server when the UAV detects an algal bloom, and the USV follows the given path autonomously generated by a coverage path planning algorithm. Subsequently, with an electrocoagulation and floatation reactor under the USV, HABs are removed. The performance of the algal bloom detection and HABs removal is verified through outdoor field tests in Daecheong Dam, South Korea.

Do Higher Land Values Cause Higher House Prices, or Vice Versa?

This paper is a study of the dynamic relationship between residential land values and house prices. Little agreement exists regarding the direction of causality between house prices and residential land values. One could argue that causality is unidirectional, running from house prices to residential land values, but not vice versa. One could also argue that causality could go the other way, from high residential land values to high house prices. Still further one could argue that causality goes both ways. To examine which of these hypotheses is most likely, tests of Granger causality are applied. The tests are applied to US data from 1985-2004 for 27 MSAs. The data strongly support the view that the causality between residential land values and house prices is bidirectional. Our findings also indicate that the causality from house prices to residential land values increases in proportion to land use regulations. Finally, we find that our results are robust to employing the level of house prices to take account of the option to develop in the future.