Measurement of the ratio h/e with a photomultiplier tube and a set of LEDs

We propose a laboratory experience aimed at undergraduate physics students to understand the main features of the photoelectric effect and to perform a measurement of the ratio h/e, where h is the Planck's constant and e is the electron charge. The experience is based on the method developed by Millikan for his measurements on the photoelectric effect in the years from 1912 to 1915. The experimental setup consists of a photomultiplier tube (PMT) equipped with a voltage divider properly modified to set variable retarding potentials between the photocathode and the first dynode, and a set of LEDs emitting at different wavelengths. The photocathode is illuminated with the various LEDs and, for each wavelength of the incident light, the output anode current is measured as a function of the retarding potential applied between the cathode and the first dynode. From each measurement, a value of the stopping potential for the anode current is derived. Finally, the stopping potentials are plotted as a function of the frequency of the incident light, and a linear fit is performed. The slope and the intercept of the line allow respectively to evaluate the ratio h/e and the ratio W/e, where W is the work function of the photocathode.Comment: 14 pages, 4 figure

The evolution of the immune system: conservation and diversification

The Evolution of the Immune System: Conservation and Diversification is the first book of its kind that prompts a new perspective when describing and considering the evolution of the immune system. Its unique approach summarizes, updates, and provides new insights on the different immune receptors, soluble factors, and immune cell effectors. Helps the reader gain a modern idea of the evolution of the immune systems in pluricellular organisms Provides a complete overview of the most studied and hot topics in comparative and evolutionary immunology Reflects the organisation of the immune system (cell-based, humoral [innate], humoral [adaptive]) without introducing further and misleading levels of organization Brings concepts and ideas on the evolution of the immune system to a wide readership

The use of fuzzy logic and expert systems for rating and pricing firms: a new perspective on valuation.

This paper presents an expert system aimed at evaluating firms and business units. It makes use of fuzzy logic and integrates financial, strategic, managerial aspects, processing both quantitative and qualitative information. Twenty-nine value drivers are explicitly taken into account and combined together via “if-then” rules to produce an output. The output is a real number in the interval [0,1], representing the value-creation power of the firm. The system may be used for rating, ranking and pricing firms as well as for assessing the impact of managers’ decisions on value creation and as a tool of corporate governance.Firm valuation, fuzzy logic, expert system, acquisition, rating, pricing

Electronic and magnetic properties of local moment systems rare earth metals and oxides

The magnetic and electronic properties of Gd and Gd-oxide local moment systems have been investigated by means of spin and angular resolved photoemission with synchrotron radiation. The electronic band structure of the (5d6s)-valence states in ferromagnetic Gd(0001) has been experimentally determined. The spin analysis shows the importance of including the photoelectron lifetime broadening in the interpretation of the experimental band structure. The photoemission results are compared with spin-polarized LSDA calculations of the surface and bulk Gd band structure. The comparison demonstrates that the (5d6s)-band dispersion can be consistently described within single particle band theory if the effects of the photoelectron lifetime broadening are included. Contrary to previous investigations, these results reduce the importance of band narrowing due to correlation effects in the description of rare earths valence states. The valence band structure of ferromagnetic Gd films has been studied as a function of the temperature, revealing a clear deviation from the Stoner behaviour that was attributed so far to the bulk magnetism in rare earths. The spectra evolution shows that a decrease in exchange splitting of the bulk states with increase in temperature (as predicted by the Stoner model) is accompanied by a decrease of the spin polarization, which is expected for a Spin mixing-like behaviour. The two different behaviours are found to mix together in different way depending on the effective exchange coupling of the considered state. The finite temperature effects in rare earths cannot be described within the pure Stoner or Spin mixing models proposed until now in the literature. The effects of oxygen and hydrogen adsorption on Gd(0001) surface has been investigated. In the first stage both hydrogen and oxygen chemisorbs on the surface and can be efficiently removed due to a photon stimulated desorption. Further oxygen exposures (up to 1 L) give rise to a surface 2-dimensional Gdoxide on top of the ferromagnetic Gd film. This oxide is characterized by oxygen-induced states in the valence band, whose spin polarization has been studied by spin resolved photoemission, providing the first evidence of the magnetic order of the surface. While, at room temperature, the adsorption of hydrogen is limited to the surface of the Gd film, oxygen penetrates into the bulk. The oxidation of thin Gd films gives rise to oxides with semiconducting properties, showing a strong band bending, whose value is a function of the subsequent Gd and oxygen exposures. After the exposure to about 10 L of oxygen of thick (> 30 ML) Gd films the Gd$_{2}$O$_{3}$ sesquioxide is formed, which do not react with oxygen anymore. This insulating oxide grows epitaxially on Gd films, which in turn has been found to grgw epitaxially on the oxide films. This result opens the possibility to prepare and investigate an epitaxially ordered structure composed of two Gdferromagnetic- metal films with interposed sesquioxide insulating film. This structure corresponds to the basic TMR configuration and, being epitaxially ordered, can be easier studied from the theoretical point of view

A Problem of Minimum Area for Bodies with Constrains on Width and Curvature

In this paper we solve the problem of finding the convex plane body of minimum area with the hypothesis of having a limited radius of curvature, together with an assigned minimum width. This result allows us to give a new and mainly analytical proof of Pal’s Theorem

Continued fractions in function fields: polynomial analogues of McMullen's and Zaremba's conjectures

We examine the polynomial analogues of McMullen's and Zaremba's conjectures on continued fractions with bounded partial quotients. It has already been proved by Blackburn that if the base field is infinite, then the polynomial analogue of Zaremba's conjecture holds; we will prove this again with a different method and examine some known results for finite base fields. Translating to the polynomial setting a result of Mercat, we will prove that the polynomial analogue of McMullen's conjecture holds over infinite algebraic extensions of finite fields and that, over finite fields, it would be a consequence of the polynomial analogue of Zaremba's conjecture. We will then prove that the polynomial analogue of McMullen's conjecture holds over uncountable base fields, over $\overline{\mathbb Q}$ (thanks to the theory of reduction of a formal Laurent series modulo a prime) and over number fields. For this purpose, we will examine the connection between the continued fractions of polynomial multiples of $\sqrt D$ and pullbacks of generalized Jacobians of the hyperelliptic curve $U^2=D(T)$.Comment: Corrected typos in Chapter

As atividades de incentivo à leitura desenvolvidas pela bibliotecária da Escola Básica Adotiva Liberato Valentim: um estudo de caso

TCC (graduação em Biblioteconomia) - Universidade Federal de Santa Catarina, FlorianópolisEste trabalho relata as observações feitas sobre as atividades de incentivo à leitura na biblioteca escolar, realizadas pela bibliotecária e a auxiliar de biblioteca da Escola Básica Adotiva Liberato Valentim, no Bairro Costeira do Pirajubaé, Florianópolis # SC, junto as crianças de 1ª a 4ª do ensino fundamental, durante o primeiro trimestre de 2011. Evidencia a importância de incentivar o exercício e o prazer da leitura desde o início da formação escolar. Mostra que é na infância que o ser humano está mais apto a aprender e a tomar o gosto pela leitura. Aponta a biblioteca escolar como um espaço agradável, prazeroso e recreativo, capaz de criar laços com o imaginário e o real por meio da leitura. Constata que a leitura desenvolve a criatividade, a imaginação e permite a obtenção do conhecimento do mundo. Aponta a necessidade da interação entre professores e bibliotecários. Registra estudos teóricos sobre leitura e o ato de ler e atividades práticas de estímulo á leitura. Quanto aos objetivos da pesquisa, caracteriza-se como descritiva. Ressalta-se a importância da biblioteca escolar na formação escolar e da figura do bibliotecário como fomentador da leitura. Conclui que o profissional bibliotecário é capaz de despertar o gosto pela leitura nas crianças e de aumentar sua presença na biblioteca, se desenvolver atividades que instiguem essas práticas. Com base nos objetivos, se confirma como exploratória. Quanto à abordagem, a pesquisa é quali-quantitativa. Quanto aos procedimentos técnicos é bibliográfica, participante e estudo de caso

Effects of selenium biofortification on crop nutritional quality

Selenium (Se) at very low doses has crucial functions in humans and animals. Since plants represent the main dietary source of this element, Se-containing crops may be used as a means to deliver Se to consumers (biofortification). Several strategies have been exploited to increase plant Se content. Selenium assimilation in plants affects both sulphur (S) and nitrogen (N) metabolic pathways, which is why recent research has also focused on the effect of Se fertilization on the production of S- and N- secondary metabolites with putative health benefits. In this review we discuss the function of Se in plant and human nutrition and the progress in the genetic engineering of Se metabolism to increase the levels and bioavailability of this element in food crops. Particular attention is paid to Se biofortification and the synthesis of compounds with beneficial effects on health