Effect of backgating on the field distribution in planar thin-film GaAs structures

The distribution of the electric field in planar film–substrate GaAs structures under backgating is considered. It is shown that backgating can make the film exhibit a long-length region of a low-gradient electric field exceeding the threshold of N-type negative differential mobility, the magnitude of negative differential mobility in this region being high enough. At values of the film doping density and film thickness typical of GaAs transferred-electron devices, this region can be as long as several tens of micrometers. The underlying physical mechanism is discussed.     

Whence CRIPTO: The Reemergence of an Oncofetal Factor in ‘Wounds’ That Fail to Heal

There exists a set of factors termed oncofetal proteins that play key roles in ontogeny before they decline or disappear as the organism’s tissues achieve homeostasis, only to then re-emerge in cancer. Although the unique therapeutic potential presented by such factors has been recognized for more than a century, their clinical utility has yet to be fully realized1. This review highlights the small signaling protein CRIPTO encoded by the tumor derived growth factor 1 (TDGF1/Tdgf1) gene, an oft cited oncofetal protein whose presence in the cancer literature as a tumor promoter, diagnostic marker and viable therapeutic target continues to grow. We touch lightly on features well established and well-reviewed since its discovery more than 30 years ago, including CRIPTO’s early developmental roles and modulation of SMAD2/3 activation by a selected set of transforming growth factor β (TGF-β) family ligands. We predominantly focus instead on more recent and less well understood additions to the CRIPTO signaling repertoire, on its potential upstream regulators and on new conceptual ground for understanding its mode of action in the multicellular and often stressful contexts of neoplastic transformation and progression. We ask whence it re-emerges in cancer and where it ‘hides’ between the time of its fetal activity and its oncogenic reemergence. In this regard, we examine CRIPTO’s restriction to rare cells in the adult, its potential for paracrine crosstalk, and its emerging role in inflammation and tissue regeneration—roles it may reprise in tumorigenesis, acting on subsets of tumor cells to foster cancer initiation and progression. We also consider critical gaps in knowledge and resources that stand between the recent, exciting momentum in the CRIPTO field and highly actionable CRIPTO manipulation for cancer therapy and beyond.     

On the testing,characterization, and evaluation of PV inverters and dynamic MPPT performance under real varying operating conditions

The increasing number of photovoltaic inverters that are coming on to the PV market stresses the need to carry out a dynamic characterization of these elements and their maximum power point tracking (MPPT) algorithms under real operating conditions. In order to make these conditions repeatable at the laboratory, PV array simulators are used. However, actual simulators, including the commercial simulators, recreate only a single or small set of PV array characteristic curves in which quite commonly theoretical calculations are included in order to simulate irradiance and temperature artificial variations. This is far from being a recreation of the real and long dynamic behavior of a PV array or generator. The testing and evaluation of the performance of PV inverters and MPPT algorithms has to be carried out when the PV system moves dynamically according to real operating conditions, including processes such as rapidly changing atmospheric conditions, partial shadows, dawn, and nightfall. This paper tries to contribute to the analysis of this problem by means of an electronic system that both measures the real evolution of the characteristic curves of PV arrays at outdoor operation and then recreates them at the laboratory to test PV inverters. This way the equipment can highlight the different performances of PV inverters and MPPT techniques when they operate under real operating conditions. As an example, two commercial inverters are tested and analyzed under the recreated behavior of a PV generator during 2 singular days that include processes of partial shading and fast irradiance variations. Copyright © 2007 John Wiley & Sons, Ltd.     

The neural correlates of infant and adult goal prediction: Evidence for semantic processing systems.

The sequential nature of action ensures that an individual can anticipate the conclusion of an observed action via the use of semantic rules. The semantic processing of language and action has been linked to the N400 component of the event-related potential (ERP). The authors developed an ERP paradigm in which infants and adults observed simple sequences of actions. In one condition the conclusion of the sequence was anticipated, whereas in the other condition the conclusion was not anticipated. Adults and infants at 9 months and 7 months were assessed via the same neural mechanisms—the N400 component and analysis of the theta frequency. Results indicated that adults and infants at 9 months produced N400-like responses when anticipating action conclusions. The infants at 7 months displayed no N400 component. Analysis of the theta frequency provided support for the relation between the N400 and semantic processing. This study suggests that infants at 9 months anticipate goals and use similar cognitive mechanisms to adults in this task. In addition, this result suggests that language processing may derive from understanding action in early development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reduced Levels of ABCA1 Transporter Are Responsible for the Cholesterol Efflux Impairment in β-Amyloid-Induced Reactive Astrocytes: Potential Rescue from Biomimetic HDLs

The cerebral synthesis of cholesterol is mainly handled by astrocytes, which are also responsible for apoproteins’ synthesis and lipoproteins’ assembly required for the cholesterol transport in the brain parenchyma. In Alzheimer disease (AD), these processes are impaired, likely because of the astrogliosis, a process characterized by morphological and functional changes in astrocytes. Several ATP-binding cassette transporters expressed by brain cells are involved in the formation of nascent discoidal lipoproteins, but the effect of beta-amyloid (Aβ) assemblies on this process is not fully understood. In this study, we investigated how of Aβ_1-42-induced astrogliosis affects the metabolism of cholesterol in vitro. We detected an impairment in the cholesterol efflux of reactive astrocytes attributable to reduced levels of ABCA1 transporters that could explain the decreased lipoproteins’ levels detected in AD patients. To approach this issue, we designed biomimetic HDLs and evaluated their performance as cholesterol acceptors. The results demonstrated the ability of apoA-I nanodiscs to cross the blood–brain barrier in vitro and to promote the cholesterol efflux from astrocytes, making them suitable as a potential supportive treatment for AD to compensate the depletion of cerebral HDLs.     

Phase evolution in plasma sprayed Nb2O5 coatings

Nb₂O₅ polymorphism and defect chemistry depend on the temperature, pressure, atmosphere composition and the initial crystallography. Plasma spray of Nb₂O₅ is a pathway to form coatings with in-situ metastable and nonstoichiometric phases, however so far unexplored. This study aimed to understand the phase evolution of plasma sprayed Nb₂O₅ coatings, and its effect on their morphology and properties. Phase evolution from H-Nb₂O₅ in the feedstock, to T-Nb₂O₅, TT-Nb₂O₅, N-Nb₂O₅, H-Nb₂O₅, Nb₁₂O₂₉ and NbO₂ in the coatings depends on the plasma Ar/H₂ ratio and its related enthalpy. The microstructure shows a layered distribution of nonstoichiometric phases at the splat boundaries and splat cores composed of T-Nb₂O₅ or TT-Nb₂O₅. The presence and distribution of these phases are related to the thermomechanical and electrical properties. The mechanisms driving the formation of these coatings are based on the Nb₂O₅ incongruent vaporization which promote retention of nonstoichiometric phases and the rapid solidification of metastable phases.     

A new acousto-electro-optic improved resolution deflector for high frequency operation

The two main constrains on the characteristics of the acousto-optic deflector are the acoustic sound attenuation and velocity. These two parameters will determine the resolution and the radio frequency bandwidth. Due to a double degenerated phase matching condition on a specific acousto-optic deflector configuration, the possibility of an improvement on the resolution of the acousto optic deflector becomes evident. This degenerescence is the result of the action of a D.C. electric field by the electro-optic effect. This configuration presents several advantages upon the early related works based on optical activity of selected materials and enables a wideband interaction in such a way that the number of resolvable channels is kept high. This has implications on the acousto-optic spectrometers for wideband radio astronomy research.     

Test for a correlation between VΛ and the + y opponent-channel sensitivity

Rushtion and Baker have shown that the ratio of R to G cones varies between observers. We use this variability to ask if observers, say, who are rich in R-cone input to the flicker (VΛ) channel, are also likely to be rich in R-cone input to the long-wavelength half of the y-b channel. For the 8 observers tested, there is no correlation between cone inputs to +y and VΛ.     

A graphical approach to relational reasoning

Relational reasoning is concerned with relations over an unspecified domain of discourse. Two limitations to which it is customarily subject are: only dyadic relations are taken into account; all formulas are equations, having the same expressive power as first-order sentences in three variables. The relational formalism inherits from the Peirce-Schröder tradition, through contributions of Tarski and many others.Algebraic manipulation of relational expressions (equations in particular) is much less natural than developing inferences in first-order logic; it may in fact appear to be overly machine-oriented for direct hand-based exploitation.The situation radically changes when one resorts to a convenient representation of relations based on labeled graphs. The paper provides details of this representation, which abstracts w.r.t. inessential features of expressions.Formal techniques illustrating three uses of the graph representation of relations are discussed: one technique deals with translating first-order specifications into the calculus of relations; another one, with inferring equalities within this calculus with the aid of convenient diagram-rewriting rules; a third one with checking, in the specialized framework of set theory, the definability of particular set operations. Examples of use of these techniques are produced; moreover, a promising approach to mechanization of graphical relational reasoning is outlined.     

Accurate measure of laser irradiance threshold for near-infrared photo-oxidation with a modified confocal microscope

Femtosecond mode‐locked lasers are now being used routinely in multiphoton fluorescence and autofluorescence spectroscopy, are just beginning to be used in refractive surgery, and may be used in the future diagnosis of skin cancer. Pulses from these lasers induce non‐linear effects in resultant tissue interactions. Using a modified confocal microscope with dispersion compensation and accurate measurements of beam diameter, a very low threshold was measured for photochemical oxidation in cultured cells. The measured threshold showed non‐linear photo‐oxidation at a peak irradiance and photon‐flux density of 8.4 × 10⁸ W cm^?2 and 3.4 × 10²⁷ photons cm^?2 s^?1, respectively (90‐fs pulse). The impact of these findings is significant to those using ultrashort lasers because they provide a tangible reference point (microscope‐independent) for the generation of photo‐oxidative stress in laser‐exposed tissues, and because they highlight the importance of dispersion compensation in minimizing collateral tissue damage.