A novel topology for a HEMT negative current mirror

A new solution for the implementation of a HEMT negative current source is presented. The topology can be also profitably employed as a current mirror and as an active load in high-gain MMICs voltage amplifiers. A small-signal model of the proposed circuit is developed which allows to find accurate expressions for the required transfer functions (i.e., the output impedance of the current source, and the current gain of the circuit when operated as a current mirror). Design examples using Philips PML ED02AH GaAs PHEMT process are provided. Spice simulations show that a 10- kW output impedance for the current source and a 35dB voltage gain for a differential pair loaded with the proposed current mirror are easily achieved

Angular correlation of scattered annihilation photons, to test the possibility of hidden variables in quantum theory

Angular correlations of the annihilation photons, Compton scattered by plastic scintillators and detected by means of NaI (T1) crystals, have been measured in order to test the possibility of deviations of the experimental results from the predictions of the quantum theory

The general exact solution for the many moments macroscopic approach to extended thermodynamics of polyatomic gases

A new model for Polyatomic and for Dense Gases has been proposed in literature in the last five years in the framework of Extended Thermodynamics. The case with an arbitrary but fixed number of moments has been recently studied, both with the kinetic approach than with the macroscopic approach; this last one is more general and includes the results of the kinetic approach only as a particular case. \\ Scope of the "closure problem" is to find the expression of some arbitrary functions which appear in the balance equations. Up to now only a recurrence procedure has been published which outlines how to find the solution of this problem with the macroscopic approach; by using this procedure, a numberable set of solutions has been found and written explicitly, while we find here the most general exact solution. It is determined except for some arbirary terms and it is interesting that these terms appear also in the 24 moments model; so we find here that they are transmitted from the model with 24 moments to those with an arbitrary number of moments, without any further arbitrary term

Genetic drift at expanding frontiers promotes gene segregation

Competition between random genetic drift and natural selection plays a central role in evolution: Whereas non-beneficial mutations often prevail in small populations by chance, mutations that sweep through large populations typically confer a selective advantage. Here, however, we observe chance effects during range expansions that dramatically alter the gene pool even in large microbial populations. Initially well-mixed populations of two fluorescently labeled strains of Escherichia coli develop well-defined, sector-like regions with fractal boundaries in expanding colonies. The formation of these regions is driven by random fluctuations that originate in a thin band of pioneers at the expanding frontier. A comparison of bacterial and yeast colonies (Saccharomyces cerevisiae) suggests that this large-scale genetic sectoring is a generic phenomenon that may provide a detectable footprint of past range expansions.Comment: Please visit http://www.pnas.org/content/104/50/19926.abstract for published articl

Extended Thermodynamics for Dense Gases up to Whatever Order and with Only Some Symmetries

Extended Thermodynamics of dense gases is characterized by two hierarchies of field equations, which allow one to overcome some restrictions on the generality of the previous models. This idea has been introduced by Arima, Taniguchi, Ruggeri and Sugiyama. In~the case of a 14-moment model, they have found the closure of the balance equations up to second order with respect to equilibrium. Here, the closure is obtained up to whatever order and imposing only the necessary symmetry conditions. It comes out that the first non-symmetric parts of the higher order fluxes appear only at third order with respect to equilibrium, even if Arima, Taniguchi, Ruggeri and Sugiyama found a non-symmetric part proportional to an arbitrary constant also at first order with respect to equilibrium. Consequently, this constant must be zero, as Arima, Taniguchi, Ruggeri and Sugiyama assumed in the applications and on an intuitive ground

An Exact Solution for the Macroscopic Approach to Extended Thermodynamics of Dense Gases with Many Moments

Extended Thermodynamics of Dense Gases with an arbitrary but fixed number of moments has been recently studied in literature; the arbitrariness of the number of moments is linked to a number N and the resulting model is called an (N)−Model. As usual in Extended Thermodynamics, in the field equations some unknown functions appear; restriction on their generalities are obtained by imposing the entropy principle, the Galilean relativity principle and some symmetry conditions. The solution of these conditions is called the ”closure problem” and it has not been written explicitly because an hard notation is necessary, but it has been shown how the theory is selfgenerating in the sense that, if we know the closure of the (N) −Model, than we will be able to find that of the (N + 1) − Model. Instead of this, we find here an exact solution which holds for every number N

Resident Perceptions of a Proposed Environmental Education Center and Demonstration Farm

To gauge community support for a proposed environmental education center and demonstration farm, we surveyed 514 local residents. Our intent was to assess community members\u27 support for the project and relevant programming interests and to determine the roles that level of community satisfaction, perceived economic impact, and demographics played with regard to project support. We found that most community members supported the development and that levels of community satisfaction, perceptions of economic impact, background, gender, and age were significantly associated with level of support. Our research also revealed that community members were most interested in programs about nature and growing and preserving food and were not interested in technology-based programming

Extracting the hierarchical organization of complex systems

Extracting understanding from the growing ``sea'' of biological and socio-economic data is one of the most pressing scientific challenges facing us. Here, we introduce and validate an unsupervised method that is able to accurately extract the hierarchical organization of complex biological, social, and technological networks. We define an ensemble of hierarchically nested random graphs, which we use to validate the method. We then apply our method to real-world networks, including the air-transportation network, an electronic circuit, an email exchange network, and metabolic networks. We find that our method enables us to obtain an accurate multi-scale descriptions of a complex system.Comment: Figures in screen resolution. Version with full resolution figures available at http://amaral.chem-eng.northwestern.edu/Publications/Papers/sales-pardo-2007.pd

Teaching mathematics at distance: A challenge for universities

The focus of this research is how Sicilian state university mathematics professors faced the challenge of teaching via distance education during the first wave of the COVID-19 pandemic. Since the pandemic entered our lives suddenly, the professors found themselves having to lecture using an e-learning platform that they had never used before, and for which they could not receive training due to the health emergency. In addition to the emotional aspects related to the particular situation of the pandemic, there are two aspects to consider when teaching mathematics at a distance. The first is related to the fact that at university level, lecturers generally teach mathematics in a formal way, using many symbols and formulas that they are used to writing. The second aspect is that the way mathematics is taught is also related to the students to whom the teaching is addressed. In fact, not only online, but also in face-to-face modality, the teaching of mathematics to students on the mathematics degree course involves a different approach to lessons (as well as to the choice of topics to explain) than teaching mathematics in another degree course. In order to investigate how the Sicilian State university mathematics professors taught mathematics at distance, a questionnaire was prepared and administered one month after the beginning of the lockdown in Italy. Both quantitative and qualitative analyses were made, which allowed us to observe the way that university professors have adapted to the new teaching modality: they started to appropriate new artifacts (writing tablets, mathematical software, e-learning platform) to replicate their face-to-face teaching modality, mostly maintaining their blackboard teacher status. Their answers also reveal their beliefs related to teaching mathematics at university level, noting what has been an advantageous or disadvantageous for them in distance teaching