Self-mixing model of terahertz rectification in a metal oxide semiconductor capacitance

Metal oxide semiconductor (MOS) capacitance within field effect transistors are of great interest in terahertz (THz) imaging, as they permit high-sensitivity, high-resolution detection of chemical species and images using integrated circuit technology. High-frequency detection based on MOS technology has long been justified using a mechanism described by the plasma wave detection theory. The present study introduces a new interpretation of this effect based on the self-mixing process that occurs in the field effect depletion region, rather than that within the channel of the transistor. The proposed model formulates the THz modulation mechanisms of the charge in the potential barrier below the oxide based on the hydrodynamic semiconductor equations solved for the small-signal approximation. This approach explains the occurrence of the self-mixing process, the detection capability of the structure and, in particular, its frequency dependence. The dependence of the rectified voltage on the bias gate voltage, substrate doping, and frequency is derived, offering a new explanation for several previous experimental results. Harmonic balance simulations are presented and compared with the model results, fully validating the model’s implementation. Thus, the proposed model substantially improves the current understanding of THz rectification in semiconductors and provides new tools for the design of detectors

Comments on Ekino et al. Cloning and Characterization of a Unique Cytotoxic Protein Parasporin-5 Produced by Bacillus thuringiensis A1100 Strain. Toxins 2014, 6, 1882–1895

Ekino et al. [1] reported the cloning and characterization of a novel cytotoxic protein (Parasporin-5) produced by Bacillus thuringiensis strain A1100. The 33.8-kDa inactive precursor protein exhibited strong cytocidal activity upon proteinase K activation against several mammalian (cancer) cell lines, and showed slight homology with Cry and aerolysin-type -pore-forming toxins. Most research concerning parasporins has mainly been performed in order to demonstrate their use as potential therapeutic agents against cancer, but they are lacking additional research supporting the absence of activity against invertebrates; especially, taking into account that these toxins are not expected to evolve to kill cancer cells. Therefore, it is reasonable to think that they should have another (unknown) target in nature. Despite the fact that in this work, the authors demonstrated the toxic activity of this protein against several types of cancer cells, further complementary studies against a minimum number of insects would be of great interest in order to determine the potential insecticidal activity of this protein and understand its natural role. For example, Palma and collaborators [2] reported the molecular and insecticidal characterization of a novel Cry-related protein closely related to parasporins 2 and 4, (Cry41Aa1 and Cry41Ab1). This protein did not show any toxic activity against five species of Lepidoptera but, after more extensive testing, this protein was found to demonstrate a specific toxic activity against the green-peach aphid Myzus persicae. Nowadays, parasporin proteins are commonly known in the literature to be produced by “non-insecticidal” B. thuringiensis strains and because they exhibit significant and preferential cytocidal activity against cancer cells of various origins [3]. However, the absence of insecticidal activity deserves to be more deeply investigated since a single B. thuringiensis toxin has shown to have a narrow host range while, in general, they are active against a wide range of invertebrates [4,5]. Therefore, the determination of the activity against a minimum number of insects (preferably from different taxonomic orders) is highly desirable and might change the non-insecticidal concept we currently have about parasporins proteins produced by non-insecticidal B. thuringiensis strains.Fil: Palma, Leopoldo. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin

Why has productivity growth stagnated in most Latin-American countries since the neo-liberal reforms?

Latin America’s economic performance since the beginning of neo-liberal reforms has been poor; this not only contrasts with its own performance pre-1980, but also with what has happened in Asia since 1980. I shall argue that the weakness of the region’s new paradigm is rooted as much in its intrinsic flaws as in the particular way it has been implemented. Latin America’s economic reforms were undertaken primarily as a result of the perceived economic weaknesses of the region — i.e., there was an attitude of ‘throwing in the towel’ vis-à-vis the previous state-led import substituting industrialisation strategy, because most politicians and economists interpreted the 1982 debt crisis as conclusive evidence that it had led the region into a cul-de-sac. As Hirschman has argued, policymaking has a strong component of ‘path-dependency’; as a result, people often stick with policies after they have achieved their aims, and those policies have become counterproductive. This leads to such frustration and disappointment with existing policies and institutions that is not uncommon to experience a ‘rebound effect’. An extreme example of this phenomenon is post-1982 Latin America, where the core of the discourse of the economic reforms that followed ended up simply emphasising the need to reverse as many aspects of the previous development (and political) strategies as possible. This helps to explain the peculiar set of priorities, the rigidity and the messianic attitude with which the reforms were implemented in Latin America, as well as their poor outcome. Something very different happened in Asia, where economic reforms were often intended (rightly or wrongly) as a more targeted and pragmatic mechanism to overcome specific economic and financial constraints. Instead of implementing reforms as a mechanism to reverse existing industrialisation strategies, in Asia they were put into practice in order to continue and strengthen ambitious processes of industrialisation

The Wehrl entropy has Gaussian optimizers

We determine the minimum Wehrl entropy among the quantum states with a given von Neumann entropy, and prove that it is achieved by thermal Gaussian states. This result determines the relation between the von Neumann and the Wehrl entropies. The key idea is proving that the quantum-classical channel that associates to a quantum state its Husimi Q representation is asymptotically equivalent to the Gaussian quantum-limited amplifier with infinite amplification parameter. This equivalence also permits to determine the p->q norms of the aforementioned quantum-classical channel in the two particular cases of one mode and p=q, and prove that they are achieved by thermal Gaussian states. The same equivalence permits to prove that the Husimi Q representation of a one-mode passive state (i.e. a state diagonal in the Fock basis with eigenvalues decreasing as the energy increases) majorizes the Husimi Q representation of any other one-mode state with the same spectrum, i.e. it maximizes any convex functional.Comment: Proof extended to multimode state

Development of a mass spectrometer system for the measurement of inert gases in meteorites

The study of the inert gases in meteorites has provided many clues as to the origin and evolution of the solar system. Particularly crucial and complex are the gases krypton and xenon. To accurately measure the isotopic compositions of these gases requires a mass spectrometer of high sensitivity and resolution. A previously unused and largely untested mass spectrometer system was brought to the point where it was ready for routine sample analyses. This involved, among other things, focusing the ion beam for optimal peak shape and sensitivity, documenting the instrument's response to a series of characteristic tests such as multplier gain checks, and interfacing the instrument to a computer to run the sample analyses. Following this testing and setting up, three iron meteorite samples were to be analyzed for argon, krypton, and xenon. The three samples were shown in prior work to possibly contain primordial heavy inert gases. Although these analyses have not yet been carried out, it is anticipated that they will be completed in the near future