1,129 research outputs found
Organic semiconductors in the limit of a few monolayers : molecular surface doping of pentacene thin film transistors
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Use of the KlADH4 promoter for ethanol-dependent production of recombinant human serum albumine in Kluyveromyces lactis
Get PDFKlADH4 is a gene of Kluyveromyces lactis encoding a mitochondrial alcohol dehydrogenase activity which is specifically induced by ethanol. The promoter of this gene was used for the expression of heterologous proteins in K. lactis, a very promising organism which can be used as an alternative host to Saccharomyces cerevisiae due to its good secretory properties. In this paper we report the ethanol-driven expression in K. lactis of the bacterial beta-glucuronidase and of the human serum albumin (HSA) genes under the control of the KlADH4 promoter. In particular, we studied the extracellular production of recombinant HSA (rHSA) with integrative and replicative vectors and obtained a significant increase in the amount of the protein with multicopy vectors, showing that no limitation of KlADH4 trans-acting factors occurred in the cells. By deletion analysis of the promoter, we identified an element (UASE) which is sufficient for the induction of KlADH4 by ethanol and, when inserted in the respective promoters, allows ethanol-dependent activation of other yeast genes, such as PGK and LAC4. We also analyzed the effect of medium composition on cell growth and protein secretion. A clear improvement in the production of the recombinant protein was achieved by shifting from batch cultures (0.3 g/liter) to fed-batch cultures (1 g/liter) with ethanol as the preferred carbon source
Representing Roomates' Preferences with Symmetric Utilities
Get PDFIn the context of the stable roommates problem, it is shown that acyclicity of preferences is equivalent to the existence of symmetric utility functions, i.e. the utility of agent i when matched with j is the same as j 's utility when matched with i .
Electronic transport, field effect and doping in pentacene nanorods and monolayer thin film prepared by combination of nano-fabrication and self-assembly
Get PDFThe transport in organic semiconductors is investigated on the nanometer scale. Field effect transistor with device-active layers in the monolayer (ML) range are characterized in-situ right after the controlled deposition of pentacene. By using a bottom contact geometry, the thickness of the channel is varied in several steps and the thin film transistors (TFTs) are characterized after each additional deposition. The mobility is found to saturate at a channel thickness of 3-4 ML. This allows for the operation ofML TFT, where the effect of dopant molecules deposited on top of the channel is studied. Fluorinated tetracyanoquinodimethane (F4 TCNQ) is found to increase the charge carrier concentration by a charge transfer process with pentacene without degradation of the mobility. For a separation of contact effects from bulk effects, TFTs with channel length between 20 µm and 200 µm have been processed in parallel. The contact resistance Rc and the contact free mobility µcf have been extracted and analyzed by the transmission line method (TLM). In temperature dependent studies, an approximately linear log(µ) vs. 1/T relation describes the experimental results. The fit is slightly better for the undoped TFT compared to the doped TFT. This is consistent with the accepted theoretical models based on a disordered Gaussian density of states (DOS). In fact, the experimental determination
of the DOS in doped TFTs shows an additional broad peak
at 0.14 eV above the HOMO edge caused by the dopant molecules.
A second pronounced effect of doping is the reduction of the
Rc by a factor 20 between the gold electrode and pentacene. The
gate field dependent decrease of Rc in undoped TFTs is related to
a lowering of the Schottky barrier at the interface. In doped TFTs,
the opposite effect is observed. This demonstrates the influence of
the dopant molecules on the interface barrier. The injection process
determining Rc is found to change from a thermionic emission
mechanism to a tunneling regime.
For the investigation of the injection properties at the interface,
a new manufacturing method to produce metallic nanojunction is
presented. In combination with a self-assembly process leading to
pentacene rod-like islands connecting the two electrodes right through
their growth, the transport in the 10-nm scale is investigated. At this
scale length, the current-voltage (I-V) characteristics of pentacene is
changing from rectifying Schottky-like behavior to fully linear behavior
upon F4TCNQ doping. Variable temperature investigations show
that the conduction in the doped pentacene nanojunction is thermally
activated, with an activation energy very close to the energy
position of the dopant induced peak in the DOS and to the thermal
activation energy of Rc
The Effect of Bid-Ask Prices on Brazilian Options Implied Volatility: A Case Study of Telemar Call Options
Get PDFAlthough not explicitly reported, option traders on the Bovespa exchange pay an implicit bid-ask spread on each trade. Reported transaction prices that comprise the databases previously used to study the Brazilian options markets do not reflect actual option values at the time of the trades, but actual values plus (for purchases) or minus (for sales) the bid-ask spread. We use a chooser American option model to estimate Telemar call options bid-ask spreads, and to create a database of spread-adjusted trade prices. We find that the bid-ask spreads explain several previously reported puzzles regarding asset price volatility.
Balance Sheet Effects in Currency Crises: Evidence from Brazil
Get PDF"Third-generation currency crises models" argue that capital losses from exchange-rate depreciation propagate the crises to the productive sector. To test these models, we use a firm-level dataset that allows us to measure currency mismatches around the 2002 Brazilian currency crisis. We find that, between 2001 and 2003, firms that shortly before the crisis had large currency mismatches decreased their investment rates by 8.1 percentual points, relatively to other public firms. Moreover, we show that the currency depreciation implied large competitive gains for the exporters, and yet the investment of exporters with large currency mismatches fell by 12.5 percentual points, relatively to other exporters. The estimated falls in investment are economically very relevant, thereby corroborating the relevance of third generation models negative balance sheet effects.
Miradas Al Sur: a criação mitológica do bairro sur na obra de Jorge Luis Borges
Get PDFDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Comunicação e Expressão, Programa de Pós-Graduação em Literatura, Florianópolis, 2014Este estudo investiga como Jorge Luis Borges constrói o Sur como espaço mítico, em seus três primeiros livros de poesia. Para tanto, analisou-se de que forma a representação de tal espaço torna-o simbólico e, posteriormente, mítico, tanto no conjunto da obra do autor, como também, a partir desse movimento individual de Borges, no imaginário coletivo da cidade. Estudou-se ainda como a memória própria e o imaginário criaram espaços afetivos, que permeiam a totalidade dos textos do autor.Abstract: This study investigates how Jorge Luis Borges builds Sur neighborhood as mythic space in his first three books of poetry. To this end, we analyzed how the representation of such a space make of it a symbolic and later a mythical space, both in the overall work of the author, but also that individual movement of Borges that achieve the collective imagination of the city. Still we have studied how the personal memory and the imagery is able to create emotional spaces, which constitute the totality of texts by the author
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