Flexible Polyelectrolytes with Monovalent Salt

We present a model for describing flexible polyelectrolytes in a good solvent a nd in the presence of monovalent salt . The molecule composed by $N$ monomers is characterized by the end to end distanc e $R_e=b (Z-1)^\gamma$ and the number of associated counterions $n$. At high tem peratures the polyelectrolyte behaves as a neutral polymer ($\gamma=0.588$). Dec reasing the temperature, the macromolecule changes from this extended configurat ion($\gamma=0.588$) to a stretched form ($\gamma\approx 1$). At even lower temp eratures, above the Manning condensation threshold, the polyelectrolyte collapse s ($\gamma\approx 0.3$). Our results show good agreement with simulations

Cavitation Event Rates and Nuclei Distributions

This paper examines the relationship between the cavitation event rates on axisymmetric headforms and the nuclei distributions in the incident flow. An analytical model is developed to relate these quantities and the results are compared with experimental cavitation event rates measured in the Large Cavitation Channel (LCC) at David Taylor Research Center (DTRC) on three different sizes of Schiebe body. The experiments were carried out at various cavitation numbers, tunnel velocities and air contents. Boundary layer, bubble screening and observable cavitation bubble size effects on the event rates are examined. The trends in the event rates with changing cavitation number and body size are consistent with those observed experimentally. However the magnitudes of the event rates are about an order of magnitude larger than the experimental data. Nevertheless it is shown that the cavitation inception values predicted using a certain critical event rate are consistent with those observed experimentally

Observations and scaling of travelling bubble cavitation

Recent observations of growing and collapsing bubbles in flows over axisymmetric headforms have revealed the complexity of the ‘micro-fluid-mechanics’ associated with these bubbles (van der Meulen & van Renesse 1989; Briancon-Marjollet et al. 1990; Ceccio & Brennen 1991). Among the complex features observed were the bubble-to-bubble and bubble-to-boundary-layer interactions which leads to the shearing of the underside of the bubble and alters the collapsing process. All of these previous tests, though, were performed on small headform sizes. The focus of this research is to analyse the scaling effects of these phenomena due to variations in model size, Reynolds number and cavitation number. For this purpose, cavitating flows over Schiebe headforms of different sizes (5.08, 25.4 and 50.8 cm in diameter) were studied in the David Taylor Large Cavitation Channel (LCC). The bubble dynamics captured using high-speed film and electrode sensors are presented along with the noise signals generated during the collapse of the cavities. In the light of the complexity of the dynamics of the travelling bubbles and the important bubble/bubble interactions, it is clear that the spherical Rayleigh-Plesset analysis cannot reproduce many of the phenomena observed. For this purpose an unsteady numerical code was developed which uses travelling sources to model the interactions between the bubble (or bubbles) and the pressure gradients in the irrotational flow outside the boundary layer on the headform. The paper compares the results of this numerical code with the present experimental results and demonstrates good qualitative agreement between the two

Cavitation scaling experiments with headforms : bubble dynamics

Utilizing some novel instrumentation which allowed detection and location of individual cavitation bubbles in flows around headforms. Ceccio and Brennen (1991 and 1989) recently examined the interaction between individual bubbles and the structure of the boundary layer and flow field in which the bubble is growing and collapsing. They were able to show that individual bubbles are often fissioned by the fluid shear and that this process can significantly effect the acoustic signal produced by the collapse. Furthermore they were able to demonstrate a relationship between the number of cavitation events and the nuclei number distribution measured by holographic methods in the upstream flow. More recently Kumar and Brenncn (1991-1992) have closely examined further statistical properties of the acoustical signals from individual cavitation bubbles on two different headformsm in order to learn more about the bubble/flow interactions. However the above experiments were all conducted in the same facility with the same size of headform (5.08cm in diameter) and over a fairly narrow range of flow velocities (around 9m/s). Clearly this raises the issue of how the phenomena identified in those earlier experiments change with changes of speed, scale and facility. The present paper will describe experiments conducted in order to try to answer some of these important qucstions regarding the scaling of the cavitation phenomena. We present data from experiments conducted in the Large Cavitation Channel of the David Taylor Research Center in Memphis, Tennessee, on similar headforms which are 5.08, 25.4 and 50.8cm in diameter for speeds ranging up to 15m/s and for a range of cavitation numbers. In this paper we focus on visual observations of the cavitation patterns and changes in these patterns with speed and headform size

Fear expression and return of fear following threat instruction with or without direct contingency experience

Prior research showed that mere instructions about the contingency between a conditioned stimulus (CS) and an unconditioned stimulus (US) can generate fear reactions to the CS. Little is known, however, about the extent to which actual CS US contingency experience adds anything beyond the effect of contingency instructions. Our results extend previous studies on this topic in that it included fear potentiated startle as an additional dependent variable and examined return of fear (ROF) following reinstatement. We observed that CS US pairings can enhance fear reactions beyond the effect of contingency instructions. Moreover, for all measures of fear, instructions elicited immediate fear reactions that could not be completely overridden by subsequent situational safety information. Finally, ROF following reinstatement for instructed CS+s was unaffected by actual experience. In summary, our results demonstrate the power of contingency instructions and reveal the additional impact of actual experience of CS US pairings

Cavitation Scaling Experiments with Axisymmetric Bodies

Several experiments by Ceccio and Brennen (1991, 1989) and Kumar and Brennen (1992, 1991) have closely examined the interaction between individual cavitation bubbles and the boundary layer, as well as statistical properties of the acoustical signals produced by the bubble collapse. All of these experiments were, however, conducted in the same facility with the same headform size (5.08cm in diameter) and over a fairly narrow range of flow velocities (around 9m/s). Clearly this raises the issue of how the phenomena identified change with speed, scale and facility. The present paper describes experiments conducted in order to try to answer some of these important questions regarding the scaling of the cavitation phenomena. The experiments were conducted in the Large Cavitation Channel of the David Taylor Research Center in Memphis Tennessee, on geometrically similar Schiebe headforms which are 5.08, 25.4 and 50.8cm in diameter for speeds ranging up to 15m/s and for a range of cavitation numbers

Além da legitimidade : as condições da estabilidade do corpo político frente à ameaça das emoções disruptivas

A relação entre a distribuição de bens e a estabilidade em uma sociedade é um tema recorrente na teoria política. John Rawls, como muitos antes dele, assume corretamente que uma distribuição equitativa de bens primários está no centro de uma sociedade legítima e estável. Ele propõe uma distribuição equitativa em termos liberais, respeitando o pluralismo. Rawls falha, entretanto, em discutir emoções disruptivas conectadas à distribuição: inveja e ciúme. Ele reivindica que os cidadãos em uma sociedade guiada pelos princípios de justiça, uma sociedade bem ordenada, não terão razões para sentir essas emoções. Seu engano está em pensar que, em nome da neutralidade, essas emoções não deveriam concernir diretamente as instituições políticas. As pessoas, entretanto, podem sentir inveja e ciúme mesmo quando a propriedade é bem distribuída, tornando a sociedade instável. Seres humanos nunca param de ser ambiciosos e, dado sua pouca capacidade de julgamento sobre o que merecem, seu sentimento pode se tornar um problema político. O objetivo do artigo é mostrar que essa lacuna previne o liberalismo político de Rawls de atingir seu fim. Valorizar o pluralismo significa não apenas celebrar a liberdade, mas também impedir que ela emerja como intolerância. Pluralismo e liberdade verdadeira, por exemplo, são enfraquecidos pelo discurso que advoga alguma intolerância religiosa. Portanto, se o liberalismo deseja verdadeiramente promover a liberdade, ele precisa tratar de forma séria a questão do desacordo moral e político. Thomas Hobbes não era um liberal; ele era, entretanto, um filósofo político profundamente interessado em como superar o desacordo. A solução de Hobbes, a educação civil dos cidadãos, não envolve o aprimoramento moral das pessoas. Hobbes justifica a educação civil em termos políticos e em uma estrutura de consentimento, na qual a liberdade é limitada com intuito de aprofundar a liberdade – um argumento discutido no artigo e que é de interesse dos liberais contemporâneos, especialmente John Rawls. A teoria do poder política de Thomas Hobbes é mais completa e consistente do que normalmente pensada. A chave para resolver algumas das supostas inconsistências está na percepção de que Hobbes, na verdade, conta com duas concepções distintas de poder que frequente estão fundidas em uma expressão em Inglês: “poder.” A versão latina do Leviatã nos permite ver esses tipos distintos de poder no vocabulário hobbesiano, pois lá ele se utiliza de dois termos: potentia e potestas. Potentia é o meio que alguém possui para um bem aparente – um poder real, de facto. Para Hobbes, potentia é um poder relativo a cada indivíduo e depende de “sinais” de poder para se manter. Por ser um poder relativo, a potentia é também instável: alguém pode ser poderoso apenas se outros possuírem menos poder e, portanto, haverá competição constante por sinais de poder. Em contraste, potestas é um poder normativo com ums obrigação equivalente e é constituído quando os súditos renunciam ao seu direito natural, isto é, à sua liberdade de usar sua potentia. É também um poder absoluto, diferentemente da potentia, que é poder relativo. Potestas é um poder supremos que não depende do reconhecimento de outros. É possível pensar que, quando a República instituída, a potestas absoluta e de iure substitui a potentia relativa, de facto. Para Hobbes, elas são, contudo, complementares. O poder para gerar obrigações e comandos não é suficiente para manter a integridade da República: a potentia é também necessária. Isso levanta algo como uma encruzilhada: como pode o poder da República ser estável se ele não é apenas absoluto (potestas), mas também relativo (potentia)? Naquilo que concerne a potentia, os sinais de poder do Estado são as imagens políticas que ele propaga sobre si, que são poderosas apenas até o ponto que seus súditos as veem com tal. Portanto, a potestas da República pode ser mantida apenas se ela possui também potenta: uma República é tão grande quanto seus súditos acreditam que ela seja.The relationship between distribution of goods and stability in a society is a recurrent theme in political theory. John Rawls, as did many others before him correctly assumes that a fair distribution of primary goods is at the core of a legitimate and stable society. He proposes a fair distribution in liberal terms, respecting pluralism. Rawls fails, however, to address politically disruptive emotions connected to distribution: envy and jealousy. He claims that citizens in a society guided by his principles of justice, a well-ordered society, will have no reason to feel these emotions. His mistake is in thinking that, in the name of neutrality, these emotions should not directly concern political institutions. People, however, may feel envious or jealous of others even when property is well distributed, making society unstable. Human beings never stop being ambitious and, given their poor judgment of what they deserve, their sentiment may become a political problem. My objective in this article is to show how this gap hinders Rawls’s political liberalism from achieving its ends. Valuing pluralism means not only cherishing freedom, but also preventing the last from emerging as intolerance. Pluralism and actual freedom are undermined, for instance, by speech advocating religious intolerance. Thus if liberalism wishes to truly promote freedom, it needs to seriously address the issue of moral and political disagreement. Thomas Hobbes was not a liberal himself; he was, however, a political philosopher deeply interested in how to overcome disagreement. Hobbes’s solution, civil educating citizens, does not involve improving people morally. Hobbes justifies civil education in political terms and within a framework of consent, where freedom is limited in order to further freedom – an argument discussed in the article which is of interest to contemporary liberals, especially John Rawls. Thomas Hobbes’s theory of political power is more complete and consistent than is normally thought. The key to resolving some of the supposed inconsistencies in Hobbes’s theory of power lies in noticing that Hobbes actually relies on two distinct conceptions of power that are often conflated in one English expression, “power.” The Latin version of the Leviathan enables us to see these distinct types of power in the Hobbesian vocabulary, because there he uses two expressions: potentia and potestas. Potentia is the means one has to an apparent good – an actual, de facto power. For Hobbes, potentia is a relative power: it is relative to each individual, and depends upon “signs” of power to maintain itself. Because it is a relative power, it is also unstable: one may be powerful only if others are less powerful, and thus there will be constant competition for signs of power. In contrast, potestas is a normative power with an equivalent obligation, and it is constituted when subjects renounce their natural right, that is, their liberty to use their potentia. It is also an absolute power, unlike potentia, which is a relative power. Potestas is a supreme power that does not depend on its acknowledgment by others. One might think that when the commonwealth is instituted, absolute, de jure potestas completely replaces relative, de facto potentia. To Hobbes, they are however complimentary. The power to generate obligations and commands is not sufficient to maintain the integrity of a commonwealth: it also requires potentia. This raises somewhat of a conundrum: how can a commonwealth be stable if its power is not just absolute (potestas), but also relative (potentia)? In what regards potentia, its signs of power are the political images it propagates about itself, which are powerful only to the extent which its subjects see those images of power as equivalent to power itself. Thus, the potestas of the commonwealth can be maintained only if it also has potentia: a commonwealth is only as great as its subjects believe it to be

Controlled photon transfer between two individual nanoemitters via shared high-Q modes of a microsphere resonator

We realize controlled cavity-mediated photon transfer between two single nanoparticles over a distance of several tens of micrometers. First, we show how a single nanoscopic emitter attached to a near-field probe can be coupled to high-Q whispering-gallery modes of a silica microsphere at will. Then we demonstrate transfer of energy between this and a second nanoparticle deposited on the sphere surface. We estimate the photon transfer efficiency to be about six orders of magnitude higher than that via free space propagation at comparable separations.Comment: accepted for publication in Nano Letter