INVESTMENT RISK AND THE TRANSITION INTO HOMEOWNERSHIP*

ABSTRACT This paper investigates the extent to which house–price uncertainty affects the transition of renter households into homeownership. Using a 14‐year household panel from the Panel Study of Income Dynamics during the years 1984–1997 and measures of the time‐varying risk and return to owner‐occupied housing, we estimate a Cox proportional hazard model of the effect of house–price volatility on the transition into homeownership. Results indicate that house–price uncertainty has a negative and dramatic impact on transitions into homeownership. In addition, we find that the low‐wealth renters are particularly sensitive to house–price risk.     

Detection of parasite eggs from a moat encircling the royal palace of Silla, the ancient Korean Kingdom

We conducted a paleo-parasitological study on soil samples from the ancient moat ruins of Weolseong palace, of the Silla Dynasty (BC 57–AD 935) of Korea. Based on the cultural remains found in the mud-soil layer, the layer was precipitated onto the floor of a moat between the 5th and 8th centuries AD. We found Trichuris trichiura eggs only in that mud-soil layer, whereas no parasite eggs were identified in the other archaeological strata of the ruins. As T. trichiura eggs are shed only in human feces, we speculated that palace toilet contents were continually drained into the moat; therefore, at a certain point in time after construction, the moat finally became a ditch around the palace. Structures in the stone embankments of the moat, possibly designed to make the water flow continuously in one direction, might reflect the Silla people's efforts to alleviate the ever-increasing problems inherent in a moat.     

Amplification and sequencing of Trichuris trichiura ancient DNA extracted from archaeological sediments

Despite high prevalence of Trichuris trichiura infection, PCR-based analysis on T. trichiura from archaeological samples has not been established so far. In the present study, we sought to perform PCR-based amplification of T. trichiura aDNA using the sediments from medieval tomb of Korea. The presence of Trichuris eggs were first detected by microscopic observation; then confirmed by PCR-based aDNA analysis. Obtained sequence showed 100% homology to that of the small subunit ribosomal RNA (SSUrRNA) gene of T. trichiura but distinct from that of other Trichuris species. PCR-based aDNA analysis in this study can serve as effective method to confirm the presence of T. trichiura eggs in the soils or coprolites collected from archaeological sites.     

Ectopic paragonimiasis from 400-year-old female mummy of Korea

Of the parasite eggs discovered in ancient samples from Korean archaeological sites, Paragonimus spp. are of particular importance in that they are regarded as one of the most insidious trematode infection sources. Although their infection prevalence decreased rapidly in the early 20th century, archaeoparasitological studies on the species are still required, as historical knowledge of paragonimiasis remains far from comprehensive. Fortunately, we recently were given a chance to examine a medieval Korean mummy in a good state of preservation. Using morphological techniques, we discovered evidence of ectopic paragonimiasis in the sample from the 17th-century female. When the ITS 2 gene was extracted, amplified and sequenced from Paragonimus eggs, it showed 100% homology to the sequences of modern Paragonimus westermani reported from Korea and Japan, forming a cluster distinct from South Asian P. westermani. Our report is the first-ever analysis of ancient Paragonimus DNA from any archaeological field in the world. The ectopic paragonimiasis diagnosis made in this study, especially involving the liver sample, also is the first of its kind in archaeoparasitology.     

Nonlinear Structural Response to Low-Cut Filtered Ground Acceleration Records

Ground acceleration records obtained from instruments in the field are often filtered to reduce noise in both low and high frequency bands before being used for structural response analyses. The structural analysis using a filtered acceleration record may elongate the fundamental period of a structure which will potentially lead to an underestimation of the nonlinear response.

The nonlinear response of single-degree-of-freedom systems to low-cut filtered ground acceleration records is investigated. Based on the results of this study, a simple criterion for selecting ground acceleration records for seismic response analyses is proposed to avoid underestimating the nonlinear structural response.     

Ancient DNA analysis on Clonorchis sinensis eggs remained in samples from medieval Korean mummy

In the present study, Clonorchis sinensis (C. sinensis) ancient DNA (aDNA) was successfully extracted from human remains discovered in a tomb dating to the medieval Joseon dynasty of Korea. The presence of C. sinensis eggs was confirmed by microscopic observation, after which a PCR-based aDNA analysis was performed using primer sets designed for the amplification of nuclear ribosomal internal transcribed spacer 1 (ITS1), 2 (ITS2) and mitochondrial cytochrome c oxidase 1 (CO1) genes. The sequences obtained were 100% homologous to some contemporary C. sinensis gene sequences reported from Korea and other East Asian countries. We believe that the results of our analysis expand the temporal and geographical scopes of research on the history of C. sinensis infection in different human populations.     

REVERSE COMMUTATION IN A MONOCENTRIC CITY*

ABSTRACT. A general equilibrium multiperiod linear programming model of urban land use is used to identify reverse commutation as a rational response to economic change. Information about future economic conditions is complete, and capital is replaceable at finite cost. Export mixes are defined exogenously, and temporal shifts between activities of different land intensities are shown to induce reverse commutes as one way of avoiding the cost of land use change.     

Paleo-parasitological study on the soils collected from archaeological sites in old district of Seoul City

A paleo-parasitological study was performed on soil samples from archaeological sites in the old district of Seoul Metropolitan City (Old Seoul City) where the capital of the Joseon Kingdom was constructed about 600 years ago. The sampling sites were the original locations of the Royal Palace Wall, Yukjo Street and the Royal Arsenal. Microscopic examinations showed that parasite eggs of Clonorchis sinensis, Diphyllobothrium latum, Ascaris sp. and Trichuris sp. remained in the soil strata, which were estimated to represent the 14th-19th centuries. We suspect that the medieval citizens of Old Seoul City, numbering around 200,000, might have been made vulnerable to parasite infection by a combination of bad hygiene, inadequate sewer system and seasonal flooding.