Contagion of Sovereign Default Risk: the Role of Two Financial Frictions.

This paper develops a quantitative general equilibrium model of sovereign default with heterogeneous agents to account for spillover of default risk across countries. Borrowers (sovereign governments) and foreign lenders (investors) in the model face financial frictions, which endogenously determine each agent’s credit condition. Due to lack of enforcement in sovereign debt,borrowing constraints for the governments are endogenous to incentives to default for the governments. On the other hand, investors who hold a portfolio of sovereign debts face a collateral constraint that limits their leverage of investment in sovereign debts. When the collateral constraint for investors binds due to a decrease in the value of collateral, triggered by a high default risk for one country, credit constrained investors ask for liquidity premiums even to countries in which there is no worsening of domestic fundamentals. This increase in the cost of borrowing,in turn, increases incentives to default for other countries with normal fundamentals, further constraining investors in obtaining credit through a decrease in the value of collateral. The interplay of each agent’s credit condition generates a bad spiral through which we observe spread of default risk across countries. In a quantitative analysis, the model is calibrated to Greece and Spain, and predicts (1) that cross-county correlation in sovereign spreads between Greece and Spain increases significantly during a crisis period, and (2) that Spain’s default rate, conditional on Greece’ default, increases about three times compared to Spain’s unconditional default rate. The model’s predictions are consistent with the recent European debt crisis

Sovereign Default and Capital Accumulation

I introduce endogenous capital accumulation into an otherwise standard quantitative sovereign default model in the tradition of Eaton and Gersovitz (1981), and find that conditional on a level of debt, default incentives are U shaped in the capital stock: the economy with too small or too large amounts of capital is likely to default. In addition to an “excusable” motive for default in line with Grossman and Huyck (1989), our model also predicts an “opportunistic” motive for default in line with Kehoe and Levine (1993). The model predicts the “opportunistic” motive for default, because (1) capital is used as a consumption insurance vehicle during autarky after default, (2) installed capital within the border cannot be seized by foreign lenders, and (3) our model does not use an ad-hoc output cost of default which only penalizes default in high income states. The two different motives for default allow the calibrated model to generate defaults in “good” and “bad” times in simulation with a frequency of 38% and 62%, respectively. This is consistent with Tomz and Wright (2007)’s empirical finding that throughout history and across countries, around one third of sovereign defaults occurred in “good” times, when output is above trend, whereas most defaults occur in “bad” times. The model is calibrated to the business cycle moments of Argentina, and simulation results show that the model matches business cycle facts regarding emerging economies along other dimensions. Moreover, simulation results show that default in “good” times occurs (1) after the economy has accumulated a significantly large amount of capital and (2) when the economy faces a modestly good shock, both of which reduce the value of external borrowing but increase the value of staying in autarky. On the other hand, around defaults in “bad” times, the model economy displays typical “V” shape economic dynamics, with a collapse in absorption upon default, especially investment. Aggregating quarterly data from the model into annual frequency is found to overestimate the fraction of defaults in “good” times around twofold

Programmable spectral shaping to improve the measurement precision of frequency comb mode-resolved spectral interferometric ranging

Comb-mode resolved spectral domain interferometry (CORE-SDI), which is capable of measuring length of kilometers or more with precision on the order of nanometers, is considered to be a promising technology for next-generation length standards, replacing laser displacement interferometers. In this study, we aim to improve the measurement precision of CORE-SDI using programmable spectral shaping. We report the generation of effectively broad and symmetric light sources through the programmable spectral shaping. The light source used here was generated by the spectrally-broadened electro-optic comb with a repetition rate of 17.5 GHz. Through the programmable spectral shaping, the optical spectrum was flattened within 1 dB, resulting in a square-shaped optical spectrum. As a result, the 3-dB spectral width was extended from 1.15 THz to 6.7 THz. We performed a comparison between the measurement results of various spectrum shapes. We confirmed an improvement in the measurement precision from 69 nm to 6 nm, which was also corroborated by numerical simulations. We believe that this study on enhancing the measurement precision of CORE-SDI through the proposed spectral shaping will make a significant contribution to reducing the measurement uncertainty of future CORE-SDI systems, thereby advancing the development of next-generation length standards.Comment: 22 pages, 10 figure

Fast Terahertz Beam Training Via Frequency-dependent Precoding

Terahertz (THz) communications in the 0.1-10 THz band are envisaged as an attractive way to attain richer spectrum resources and surmount the bandwidth desert. To overcome the severe propagation loss suffered in THz communications and thus achieve high beamforming gain, massive multiple-input multiple-output (MIMO) technique has received much attention. To realize highly directional communications, beam training procedure is indispensable but the beam training schemes designed for narrowband systems result in severe performance loss caused by the wideband beam squint effect. To address this problem, we propose a beam training scheme using frequencydependent RF precoder. Specifically, we analyze the optimal phase shifts to obtain the frequency-dependent RF precoder and then propose a hierarchical beam training scheme using the frequency-dependent RF precoder. Numerical results including the achievable sum-rate and the beamforming gain are presented to demonstrate the effectiveness of the proposed scheme.N

Mid-to-late Holocene climate variability in coastal East Asia and its impact on ancient Korean societies

Abstract The sustainability of human societies is contingent upon our ability to accurately predict the effects of future climate change on the global environment and humanity. Wise responses to forthcoming environmental alterations require extensive knowledge from historical precedents. However, in coastal East Asia, a region with a long history of agriculture, it is challenging to obtain paleoenvironmental proxy data without anthropogenic disturbances that can be used to assess the impact of late Holocene climate change on local communities. This study introduces a high-resolution multi-proxy sedimentary record from an isolated crater in Jeju Island, Korea, to elucidate the mechanisms underlying mid-to-late Holocene climate change and its impacts on ancient societies. Our findings suggest that hydroclimate changes were predominantly governed by sea surface temperature fluctuations in the western tropical Pacific, with low-frequency variability in solar activity and a decrease in summer insolation identified as primary drivers of temperature change. Moreover, ancient societies on the Korean peninsula were significantly affected by recurring cooling events, including the 2.8 ka event, 2.3 ka event, Late Antique Little Ice Age, maunder minimum, and others

Mid-to-late Holocene climate variability in coastal East Asia and its impact on ancient Korean societies

Acknowledgements: This work was made possible by the support of the Ministry of Education of the Republic of Korea and the National Research Foundation of Korea (NRF-2021R1F1A1062495). We thank the editor and anonymous reviewers for their valuable comments and suggestions, which significantly improved the manuscript.The sustainability of human societies is contingent upon our ability to accurately predict the effects of future climate change on the global environment and humanity. Wise responses to forthcoming environmental alterations require extensive knowledge from historical precedents. However, in coastal East Asia, a region with a long history of agriculture, it is challenging to obtain paleoenvironmental proxy data without anthropogenic disturbances that can be used to assess the impact of late Holocene climate change on local communities. This study introduces a high-resolution multi-proxy sedimentary record from an isolated crater in Jeju Island, Korea, to elucidate the mechanisms underlying mid-to-late Holocene climate change and its impacts on ancient societies. Our findings suggest that hydroclimate changes were predominantly governed by sea surface temperature fluctuations in the western tropical Pacific, with low-frequency variability in solar activity and a decrease in summer insolation identified as primary drivers of temperature change. Moreover, ancient societies on the Korean peninsula were significantly affected by recurring cooling events, including the 2.8 ka event, 2.3 ka event, Late Antique Little Ice Age, maunder minimum, and others

A Hybrid Non-destructive Measuring Method of Three-dimensional Profile of Through Silicon Vias for Realization of Smart Devices

Abstract Smart devices have been fabricated based on design concept of multiple layer structures which require through silicon vias to transfer electric signals between stacked layers. Because even a single defect leads to fail of the packaged devices, the dimensions of the through silicon vias are needed to be measured through whole sampling inspection process. For that, a novel hybrid optical probe working based on optical interferometry, confocal microscopy and optical microscopy was proposed and realized for enhancing inspection efficiency in this report. The optical microscope was utilized for coarsely monitoring the specimen in a large field of view, and the other methods of interferometry and confocal microscopy were used to measure dimensions of small features with high speed by eliminating time-consuming process of the vertical scanning. Owing to the importance of the reliability, the uncertainty evaluation of the proposed method was fulfilled, which offers a practical example for estimating the performance of inspection machines operating with numerous principles at semiconductor manufacturing sites. According to the measurement results, the mean values of the diameter and depth were 40.420 µm and 5.954 µm with the expanded uncertainty of 0.050 µm (k = 2) and 0.208 µm (k = 2), respectively

Mid-to-late Holocene climate variability in coastal East Asia and its impact on ancient Korean societies.

Acknowledgements: This work was made possible by the support of the Ministry of Education of the Republic of Korea and the National Research Foundation of Korea (NRF-2021R1F1A1062495). We thank the editor and anonymous reviewers for their valuable comments and suggestions, which significantly improved the manuscript.The sustainability of human societies is contingent upon our ability to accurately predict the effects of future climate change on the global environment and humanity. Wise responses to forthcoming environmental alterations require extensive knowledge from historical precedents. However, in coastal East Asia, a region with a long history of agriculture, it is challenging to obtain paleoenvironmental proxy data without anthropogenic disturbances that can be used to assess the impact of late Holocene climate change on local communities. This study introduces a high-resolution multi-proxy sedimentary record from an isolated crater in Jeju Island, Korea, to elucidate the mechanisms underlying mid-to-late Holocene climate change and its impacts on ancient societies. Our findings suggest that hydroclimate changes were predominantly governed by sea surface temperature fluctuations in the western tropical Pacific, with low-frequency variability in solar activity and a decrease in summer insolation identified as primary drivers of temperature change. Moreover, ancient societies on the Korean peninsula were significantly affected by recurring cooling events, including the 2.8 ka event, 2.3 ka event, Late Antique Little Ice Age, maunder minimum, and others