Implications of the currency crisis for exchange rate arrangements in emerging East Asia

The authors examine the implications of the East Asian currency crisis for exchange rate arrangements in the region's emerging market economies. They focus on the roles of the U.S. dollar, the Japanese yen, and the euro in the emerging East Asian economies'exchange rate policies. They claim that these economies are particularly susceptible to large exchange rate fluctuations because they have been pursuing financial deregulation, opening markets, and liberalizing capital accounts, and becausethey face increased risk of sudden capital flow reversals, with attendant instability in their financial system and foreign exchange market. The authors find that the dollar's role as the dominant anchor currency in East Asia was reduced during the recent currency crisis but has become prominent again since late 1998. It is too early for conclusions, but the economies seem likely to maintain more flexible exchange rate arrangements, at least officially. At the same time, these economies presumably will continue to prefer to maintain exchange rate stability without fixed rate commitments. They are better off choosing a balanced currency basket system in which the yen and the euro play a more important role than before. The ASEAN countries have a special incentive to avoid harmful fluctuations in exchange rates within the region, which could suddenly alter their international price competitiveness and make prospective free trade agreements unsuitable. So they may stabilize their exchange rates against similar currency baskets, to ensure intraregional exchange rate stability.Economic Stabilization,Economic Theory&Research,Foreign Trade Promotion and Regulation,Fiscal&Monetary Policy,Macroeconomic Management

Quantum wells with atomically smooth interfaces

By a cleaved-edge overgrowth method with molecular beam epitaxy and a (110) growth-interrupt-anneal, we have fabricated a GaAs quantum well exactly 30 monolayers thick bounded by atomically smooth AlGaAs hetero-interfaces without atomic roughness. Micro-photoluminescence imaging of this quantum well indeed shows spatially uniform and spectrally sharp emission over areas of several tens of $\mu$m in extent. By adding a fractional GaAs monolayer to our quantum well we are able to study the details of the atomic step-edge kinetics responsible for flat interface formation.Comment: 4 pages, 3 figures, revTex

One-dimensional continuum and exciton states in quantum wires

High-quality T-shaped quantum wires are fabricated by cleaved-edge overgrowth with the molecular beam epitaxy on the interface improved by a growth-interrupt high-temperature anneal. Characterization by micro-photoluminescence (PL) and PL excitation (PLE) spectroscopy at 5 K reveals high uniformity, a sharp spectral width, and a small Stokes shift of one-dimensional (1-D) excitons. The PLE spectrum for 1-D states shows a large peak of ground-state excitons and a small absorption band ascribed to 1-D continuum states with an onset at 11 meV above the exciton peak.Comment: 4 pages, 4 figures, RevTe

Lasing from a single quantum wire

A laser with an active volume consisting of only a single quantum wire in the 1-dimensional (1-D) ground state is demonstrated. The single wire is formed quantum-mechanically at the T-intersection of a 14 nm Al_{0.07}Ga_{0.93}As quantum well and a 6 nm GaAs quantum well, and is embedded in a 1-D single-mode optical waveguide. We observe single-mode lasing from the quantum wire ground state by optical pumping. The laser operates from 5 to 60 K, and has a low threshold pumping power of 5 mW at 5 K.Comment: 4 pages including 4 figure

Strong photo-absorption by a single quantum wire in waveguide-transmission spectroscopy

We measured the absorption spectrum of a single T-shaped, 14x6 nm lateral-sized quantum wire embedded in an optical waveguide using waveguide-transmission spectroscopy at 5 K. In spite of its small volume, the one-dimensional-exciton ground state shows a large absorption coefficient of 80 /cm, or a 98 % absorption probability for a single pass of the 500-um-long waveguide.Comment: 4 pages, 3 figure

Room-temperature excitonic absorption in quantum wires

We measured absorption spectra of T-shaped quantum wires at room temperature using waveguide-transmission spectroscopy. Strong and narrow room-temperature one-dimensional-exciton absorption peak was observed, which shows peak modal absorption coefficient of 160 cm$^{-1}$ per 20 wires with $\Gamma$-factor of $4.3\times10^{-3}$, width of 7.2 meV, and strong polarization anisotropy.Comment: 3pages, 3figure, 1tabl

Imaging of emission patterns in a T-shaped quantum wire laser

Spatially and spectrally resolved microscopic images of spontaneous and stimulated emissions are imaged at the mirror facets of a GaAs T-shaped quantum wire laser with high uniformity. Laser emission from the one-dimensional ground state reveals a circular image located at the core of a T-shaped optical waveguide but significantly smaller in area than the low power spontaneous emission from the same waveguide. These images unambiguously allow assignment of all spontaneous and laser emissions to the wire ground state and respective intersecting wells in the structure.Comment: 4 pages, 3 figure

Intersubband absorption linewidth in GaAs quantum wells due to scattering by interface roughness, phonons, alloy disorder, and impurities

We calculate the intersubband absorption linewidth in quantum wells (QWs) due to scattering by interface roughness, LO phonons, LA phonons, alloy disorder, and ionized impurities, and compare it with the transport energy broadening that corresponds to the transport relaxation time related to electron mobility. Numerical calculations for GaAs QWs clarify the different contributions of each individual scattering mechanism to absorption linewidth and transport broadening. Interface roughness scattering contributes about an order of magnitude more to linewidth than to transport broadening, because the contribution from the intrasubband scattering in the first excited subband is much larger than that in the ground subband. On the other hand, LO phonon scattering (at room temperature) and ionized impurity scattering contribute much less to linewidth than to transport broadening. LA phonon scattering makes comparable contributions to linewidth and transport broadening, and so does alloy disorder scattering. The combination of these contributions with significantly different characteristics makes the absolute values of linewidth and transport broadening very different, and leads to the apparent lack of correlation between them when a parameter, such as temperature or alloy composition, is changed. Our numerical calculations can quantitatively explain the previously reported experimental results.Comment: 17 pages, including 15 figure

Stem cells in dentistry – Part I: Stem cell sources

AbstractStem cells can self-renew and produce different cell types, thus providing new strategies to regenerate missing tissues and treat diseases. In the field of dentistry, adult mesenchymal stem/stromal cells (MSCs) have been identified in several oral and maxillofacial tissues, which suggests that the oral tissues are a rich source of stem cells, and oral stem and mucosal cells are expected to provide an ideal source for genetically reprogrammed cells such as induced pluripotent stem (iPS) cells. Furthermore, oral tissues are expected to be not only a source but also a therapeutic target for stem cells, as stem cell and tissue engineering therapies in dentistry continue to attract increasing clinical interest. Part I of this review outlines various types of intra- and extra-oral tissue-derived stem cells with regard to clinical availability and applications in dentistry. Additionally, appropriate sources of stem cells for regenerative dentistry are discussed with regard to differentiation capacity, accessibility and possible immunomodulatory properties