Phonon assisted intersubband transitions in step quantum well structures

We evaluate effects of heterointerfaces on optical phonon modes and phonon assisted electron intersubband transition rates in step quantum well structures for intersubband lasers. Various phonon modes and electron–phonon interaction Hamiltonians, including the interface modes, confined longitudinal-optical modes, and half space modes in the quantum well structures are calculated based on the macroscopic dielectric continuum model and microscopic analysis. The transfer matrix method is used to calculate the interface modes. The intersubband transition rates due to electron–phonon scattering by these phonon modes are evaluated using Fermi’s golden rule, with the electron wave functions obtained by solving the Schrödinger equation for the heterostructures under investigation. Our results show that, compared with the transition rates in the same structures calculated using the bulk phonon modes and the bulk Fröhlich interaction Hamiltonian, the electron interface–phonon interactions give significantly larger transition rates up to an order of magnitude. Therefore, the effects of localized phonon modes, especially the interface modes, must be taken into consideration for optimal device design. © 1998 American Institute of Physics.  Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71224/2/JAPIAU-84-4-2155-1.pd

Managing (Un)certainty in the Japanese Antique Art Trade - How Economic and Social Factors Shape a Market

Market actors are commonly faced with solving three distinct coordination problems as sources of uncertainty. How should they value the objects of their trade, how can they shield themselves from the competition, and with whom and how do they cooperate? This article investigates how Japanese antique art dealers confront these issues. While offering a rich description and analysis of a hitherto understudied Japanese market, the article shows how economic and social issues are closely intertwined. It contributes to our understanding of behaviour in a Japanese market in three ways: Firstly, it underscores how inclusion/exclusion, status, reputation, networks and hierarchies constitute a field that allows market exchanges to exist in the first place, while also channelling, and being impacted by these market exchanges. Secondly, contrary to neoclassical economic theory, where the idea of value has largely been abandoned, the findings highlight the importance of distinguishing between notions of value and price in the understanding of markets. Thirdly, the article shows how market actors actively shape market arrangements to address the specific challenges of their domain. In the case of the Japanese antique art market these challenges include high risks of fakes, a limited quantity of high quality material, market outsiders, and dealers with deep pockets

Is the incidence of meningiomas underestimated? A regional survey

We assessed the undercount of meningiomas in a population-based cancer registry. A comprehensive material was formed by compiling hospital sources with the Finnish Cancer Registry database. The completeness of each source ranged 62–69%. The corrected age-standardised meningioma incidence was 2.9/100 000 for men and 13.0/100 000 for women, a third higher than the cancer registry figures

The genera Melanothamnus Bornet & Falkenberg and Vertebrata S.F. Gray constitute well-defined clades of the red algal tribe Polysiphonieae (Rhodomelaceae, Ceramiales).

Polysiphonia is the largest genus of red algae, and several schemes subdividing it into smaller taxa have been proposed since its original description. Most of these proposals were not generally accepted, and currently the tribe Polysiphonieae consists of the large genus Polysiphonia (190 species), the segregate genus Neosiphonia (43 species), and 13 smaller genera (< 10 species each). In this paper, phylogenetic relationships of the tribe Polysiphonieae are analysed, with particular emphasis on the genera Carradoriella, Fernandosiphonia, Melanothamnus, Neosiphonia, Polysiphonia sensu stricto, Streblocladia and Vertebrata. We evaluated the consistency of 14 selected morphological characters in the identified clades. Based on molecular phylogenetic (rbcL and 18S genes) and morphological evidence, two speciose genera are recognized: Vertebrata (including the type species of the genera Ctenosiphonia, Enelittosiphonia, Boergeseniella and Brongniartella) and Melanothamnus (including the type species of the genera Fernandosiphonia and Neosiphonia). Both genera are distinguished from other members of the Polysiphonieae by synapomorphic characters, the emergence of which could have provided evolutionarily selective advantages for these two lineages. In Vertebrata trichoblast cells are multinucleate, possibly associated with the development of extraordinarily long, photoprotective, trichoblasts. Melanothamnus has 3-celled carpogonial branches and plastids lying exclusively on radial walls of the pericentral cells, which similarly may improve resistance to damage caused by excessive light. Other relevant characters that are constant in each genus are also shared with other clades. The evolutionary origin of the genera Melanothamnus and Vertebrata is estimated as 75.7-95.78 and 90.7-138.66 Ma, respectively. Despite arising in the Cretaceous, before the closure of the Tethys Seaway, Melanothamnus is a predominantly Indo-Pacific genus and its near-absence from the northeastern Atlantic is enigmatic. The nomenclatural implications of this work are that 46 species are here transferred to Melanothamnus, six species are transferred to Vertebrata and 13 names are resurrected for Vertebrata

Prostaglandin E2 Promotes Endothelial Differentiation from Bone Marrow-Derived Cells through AMPK Activation

Prostaglandin E2 (PGE2) has been reported to modulate angiogenesis, the process of new blood vessel formation, by promoting proliferation, migration and tube formation of endothelial cells. Endothelial progenitor cells are known as a subset of circulating bone marrow mononuclear cells that have the capacity to differentiate into endothelial cells. However, the mechanism underlying the stimulatory effects of PGE2 and its specific receptors on bone marrow-derived cells (BMCs) in angiogenesis has not been fully characterized. Treatment with PGE2 significantly increased the differentiation and migration of BMCs. Also, the markers of differentiation to endothelial cells, CD31 and von Willebrand factor, and the genes associated with migration, matrix metalloproteinases 2 and 9, were significantly upregulated. This upregulation was abolished by dominant-negative AMP-activated protein kinase (AMPK) and AMPK inhibitor but not protein kinase, a inhibitor. As a functional consequence of differentiation and migration, the tube formation of BMCs was reinforced. Along with altered BMCs functions, phosphorylation and activation of AMPK and endothelial nitric oxide synthase, the target of activated AMPK, were both increased which could be blocked by EP4 blocking peptide and simulated by the agonist of EP4 but not EP1, EP2 or EP3. The pro-angiogenic role of PGE2 could be repressed by EP4 blocking peptide and retarded in EP4+/− mice. Therefore, by promoting the differentiation and migration of BMCs, PGE2 reinforced their neovascularization by binding to the receptor of EP4 in an AMPK-dependent manner. PGE2 may have clinical value in ischemic heart disease