Condensation of helium in nanoscopic alkali wedges at zero temperature

We present a complete calculation of the structure of liquid 4He confined to a concave nanoscopic wedge, as a function of the opening angle of the walls. This is achieved within a finite-range density functional formalism. The results here presented, restricted to alkali metal substrates, illustrate the change in meniscus shape from rather broad to narrow wedges on weak and strong alkali adsorbers, and we relate this change to the wetting behavior of helium on the corresponding planar substrate. As the wedge angle is varied, we find a sequence of stable states that, in the case of cesium, undergo one filling and one emptying transition at large and small openings, respectively. A computationally unambiguous criterion to determine the contact angle of 4He on cesium is also proposed.

Determining the effect of asymmetric data on the variogram. II. Outliers

Asymmetry in a distribution can arise from a long tail of values in the underlying process or from outliers that belong to another population that contaminate the primary process. The first paper of this series examined the effects of the former on the variogram and this paper examines the effects of asymmetry arising from outliers. Simulated annealing was used to create normally distributed random fields of different size that are realizations of known processes described by variograms with different nugget:sill ratios. These primary data sets were then contaminated with randomly located and spatially aggregated outliers from a secondary process to produce different degrees of asymmetry. Experimental variograms were computed from these data by Matheron's estimator and by three robust estimators. The effects of standard data transformations on the coefficient of skewness and on the variogram were also investigated. Cross-validation was used to assess the performance of models fitted to experimental variograms computed from a range of data contaminated by outliers for kriging. The results showed that where skewness was caused by outliers the variograms retained their general shape, but showed an increase in the nugget and sill variances and nugget:sill ratios. This effect was only slightly more for the smallest data set than for the two larger data sets and there was little difference between the results for the latter. Overall, the effect of size of data set was small for all analyses. The nugget:sill ratio showed a consistent decrease after transformation to both square roots and logarithms; the decrease was generally larger for the latter, however. Aggregated outliers had different effects on the variogram shape from those that were randomly located, and this also depended on whether they were aggregated near to the edge or the centre of the field. The results of cross-validation showed that the robust estimators and the removal of outliers were the most effective ways of dealing with outliers for variogram estimation and kriging. (C) 2007 Elsevier Ltd. All rights reserved.

Measurement of thermal neutron cross section and resonance integral for the (165)Ho(n, gamma)(166g)Ho reaction

The ground state thermal neutron cross section and the resonance integral for the (165)Ho(n, gamma)(166)Ho reaction in thermal and 1/E regions, respectively, of a thermal reactor neutron spectrum have been measured experimentally by activation technique. The reaction product, (166)Ho in the ground state, is gaining considerable importance as a therapeutic radionuclide and precisely measured data of the reaction are of significance from the fundamental point of view as well as for application. In this work, the spectrographically pure holmium oxide (Ho(2)O(3)) powder samples were irradiated with and without cadmium covers at the IEA-RI reactor (IPEN, Sao Paulo), Brazil. The deviation of the neutron spectrum shape from 1/E law was measured by co-irradiating Co, Zn, Zr and Au activation detectors with thermal and epithermal neutrons followed by regression and iterative procedures. The magnitudes of the discrepancies that can occur in measurements made with the ideal 1/E law considerations in the epithermal range were studied. The measured thermal neutron cross section at the Maxwellian averaged thermal energy of 0.0253 eV is 59.0 +/- 2.1 b and for the resonance integral 657 +/- 36b. The results are measured with good precision and indicated a consistency trend to resolve the discrepant status of the literature data. The results are compared with the values in main libraries such as ENDF/B-VII, JEF-2.2 and JENDL-3.2, and with other measurements in the literature.

Plato's legacy : How to do philosophy

Although it has its origins earlier, philosophy as we know it in the West took its shape from the Socrates of Plato's Dialogues. It is not implausible to regard the Dialogues as heuristic devices designed for engaging in philosophical inquiry. As such, they would model the process of philosophical inquiry as well as illustrate the common pitfalls or errors to avoid when engaging in such inquiry. So it will not be surprising to see Socrates, the character of the Dialogues, modeling questionable, even poor, inquiry techniques as well as good; admonishing other characters for poor technique and reminding them of lessons they should have learned earlier in their tuition. Plato presumably would expect students reading and role-playing a Dialogue to recognise when and where such instances occur. It is instructive then to take a close look at one of the longer dialogues featuring Socrates engaging in such inquiry, not with an untutored interlocutor, but with a professional, the sophist Protagoras, in order to identify the features of the inquiry itself. For this will reveal something of what Plato conceived to be the activity of philosophy to which we are the heirs. The Protagoras can be read as an illustration (not a definition) of how to do philosophy. And to aid this reading, I propose to focus on the logical form of the inquiry, the moves made by the characters and the techniques displayed, rather than the adequacy of the substantive arguments they mount.

An experimental investigation of yarn tension in simulated ring spinning

Yarn tension is a key factor that affects the efficiency of a ring spinning system. In this paper, a specially constructed rig, which can rotate a yarn at a high speed without inserting any real twist into the yarn, was used to simulate a ring spinning process. Yarn tension was measured at the guide-eye during the simulated spinning of different yarns at various balloon heights and with varying yarn length in the balloon. The effect of balloon shape, yarn hairiness and thickness, and yarn rotating speed, on the measured yarn tension, was examined. The results indicate that the collapse of balloon shape from single loop to double loop, or from double loop to triple etc, lead to sudden reduction in yarn tension. Under otherwise identical conditions, a longer length of yarn in the balloon gives a lower yarn tension at the guide-eye. In addition, thicker yarns and/or more hairy yarns generate a higher tension in the yarn, due to the increased air drag acting on the thicker or more hairy yarns.

Numerical investigation of ramp and constant pressurization system during tube crushing process

The requirement for the automotive industry at present and even more so in the future is to simultaneously develop materials, economic forming processes and techniques for weight reduction of the component. To fulfil this need steel manufacturers have developed Advanced High Strength Steels which have high strength and good formability. Due to high strength, material thickness can be reduced without compromising the function of the component. High pressure hydro forming is one process that can be used to produce complex components from these materials. However, reduction in material thickness of these steels does not result in a large decrease of internal fluid pressure and die closing force during tube hydro forming and hence the higher strengths of these steels will require higher pressures. Tube crushing is a process in which the component can be formed with low pressures. In this paper numerical comparison of ramp and constant pressurization system during tube crushing for a TRIP steel is studied. It is proposed that ramp pressure is the best option to obtain a part with accurate geometrical shape from tube crushing with less die closing force. The stress and thickness distribution of the part during tube crushing were critically analysed.

Comparison of fracture surface and plane section analysis for ceramic grain size characterisation

A method has been developed to obtain quantitative information about grain size and shape from fractured surfaces of ceramic materials. One elaborated a routine to split intergranular and transgranular grains facets of ceramic fracture surfaces by digital image processing. A commercial ceramic (ALCOA A-16, Al2O3-1.5% of CrO) was used to test the proposed method. Microstructural measurements of grain shape and size taken from fracture surfaces have been compared through descriptive statistics of distributions, with the corresponding measurements from polished and etched surfaces. The agreement between results, with the expected bias on grain size values from fractures, obtained for both types of surfaces allowed to infer that this new technique can be used to extract the relevant microstructural information from fractured surfaces, thus minimising the time consuming steps of sample preparation. (C) 2003 Elsevier Ltd. All rights reserved.

Ultramorphological characteristics of Chrysomya megacephala (Diptera, Calliphoridae) eggs and its eclosion

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

CRANIOMETRIC VARIATION AND SUBSPECIFIC DIFFERENTIATION IN THRICHOMYS APEREOIDES IN NORTHEASTERN BRAZIL (RODENTIA, ECHIMYIDAE)

Thrichomys apereoides is an echimyid rodent which ranges in distribution from northeastern and central Brazil into Paraguay. Five subspecies are recognized, although each form is not well characterized and diagnosis is based primarily in pelage color variation. In this study we employed procedures from multivariate statistics to assess the systematic status of subspecies described from northeastern Brazil. The results of the craniometric analysis cannot be reconciled with the subspecies currently recognized for northeastern Brazil. Populations assigned to T. a. laurentius and T. a. inermis form a continuum of variation in cranial size, although they differ in cranial shape from a population from the locality of Bodoco in the state of Pernambuco. The implications of these findings for the systematics of T. apereoides are discussed.

Cranial differentiation and evolution in Thrichomys apereoides (Rodentia: Echimyidae)

Thrichomys apereoides is an echimyid rodent which ranges in distribution from north-eastern and central Brazil into Paraguay, and currently five subspecies are recognized. Recent morphometric analyses of population samples formally assignable to T. a. laurentius and T. a. inermis, which occur in north-eastern Brazil, have shown that a major group of populations including both subspecies differ in cranial shape from a single population allocated to T. a. laurentius. In this study we employed mathematical models of evolutionary quantitative genetics to assess the role that random drift and selection may have played in the evolution of cranial shape differences in T. apereoides. The hypothesis of evolution due to drift was rejected and the selective forces necessary to account for shape differences were estimated. Minimum selective mortalities of the order of 10(-3) per generation were sufficient to explain the observed morphologic differentiation.

Evolution of caste in neotropical swarm-founding wasps (Hymenoptera : Vespidae; Epiponini)

Reproductive castes are compared in species of swarming wasps representing all currently recognized genera of Epiponini (Polistinae). New morphometric data for nine measures of body parts and ovarian data are presented for 13 species. These are integrated with all similarly conducted available studies, giving a total of 30 species. Analysis reveals several syndromes relating reproductive and nonreproductive individuals: no meaningful distinction, physiological differences only, reproductives larger than nonreproductives with intermediate individuals present, reproductives different in shape from nonreproductives with no intermediates, and reproductives smaller in some aspects than nonreproductives. Distribution of these syndromes among species is consistent with phylogenetic relationships derived from other data. Optimizing these syndromes on the cladogram indicates that the basal condition of Epiponini is a casteless society that is not comparable to the primitively social genus Polistes where dominant queens control reproduction. Castes originate several times in Epiponini, with different results in different lineages. The best documented evolutionary sequence passes from casteless societies, to those with reproductives larger, to those with reproductives differing in shape from nonreproductives, to those with reproductives smaller in some measures. This sequence is consistent with Wheeler's theory of the origin of caste through developmental switches, and represents the most thorough test of that theory to date.

Capital flows to Latin America: fourth quarter 2002

Includes bibliography

Considerações sobre a anatomia funcional e adptativa de alguns sigmodontinae (Mammalia : Rodentia : Muridae)

Entre os mamíferos, os pequenos roedores compõem um grupo singular. Devido sua grande capacidade reprodutiva e adaptabilidade aos diferentes hábitats tornaram-se animais em plena explosão evolutiva. Filogeneticamente, o grupo ainda não está bem caracterizado e apresenta fortes similaridades morfológicas para os roedores Sigmodontinae da Serra dos Carajás. Através de estudos das características externas e de alguns ossos do pós-crânio relacionados ao hábito locomotor observamos que: 1) a preferência de habitat dentro da região da Serra dos Carajás entre os roedores estudados, parece não está relacionada a um padrão filogenético; 2) não foi possível estabelecer uma correlação entre as características ecológicas e as principais feições morfológicas do pós-- crânio ligadas ao desenho corporal entre os Sigmodontinae; 3) a morfologia do úmero e fêmur contém forte sinal filogenético característico de subfamília Sigmodontinae 4) os índices intermembral, crural e braquial não foram eficazes na caracterização dos vários modos de locomoção entre os roedores Sigmodontinae.

Tensid- und Interpolyelektrolytkomplexe semiflexibler Polyelektrolyte

Hochgeladene semiflexible kationische und anionische Polyelektrolyte wurden mit niedermolekularen Tensiden zu Polyelektrolyt-Tensid-Komplexen (PETK) umgesetzt und in organischen Lösungsmitteln mit Streumethoden und Rasterkraftmikroskopie charakterisiert. Die synthetisierten PETK wurden anschließend, mit dem Ziel einer strukturkontrollierten Komplexbildung, für die Bildung von Interpolyelektrolytkomplexen (IPEK) in organischen Lösungsmitteln verwendet und anhand ihres Komplexbildungsverhaltens mit wässrigen Systemen verglichen. Die Umsetzung von zylindrischen Polymerbürsten mit Poly(styrolsulfonat)-, bzw. Poly(2-vinylpyridinium)-Seitenketten mit entgegengesetzt geladenen Tensiden verlief, trotz einer Graftingdichte von eins, quantitativ. Mit Streumethoden konnte gezeigt werden, dass die gebildeten PETK in Lösung als molekulare Zylinder vorliegen. Die Synthese von pUC19-DNA-Tensidkomplexen (DNA-TK), die sich in Alkoholen gut lösen, ist nur in stark basischer Lösung gelungen. Während der Charakterisierung der DNA-TK mit Streumethoden zeigte sich eine starke Abhängigkeit des Trägheitsradius von dem Verhältnis DNA-/Salz+. Die Bildung von IPEK aus hochgeladenen Polyelektrolyt-Bürsten bzw. PETK-Bürsten wurde an verschiedenen Beispielen in Wasser und DMF durchgeführt und mit Streumethoden verfolgt. Alle Systeme zeigten ein zu der IPEK-Bildung von linearen Polyelektrolyten analoges Komplexbildungsverhalten. Bei der Komplexierung von Poly(styrolsulfonat)-Bürsten-Tensidkomplexen mit kommerziellen Polyamidoamin-G5-Dendrimeren (PAMAM) oder Poly(ethylenoxid) modifizierten Poly(ethylenimin)-Bürsten hingegen wurden über den gesamten Gewichtsbruchbereich mit Streumethoden und AFM zylindrische Aggregate gefunden, die den Dimensionen der Poly(styrolsulfonat)-Bürsten-Tensidkomplexe entsprechen. Durch statistische Höhenanalyse der AFM-Bilder wurde ein linearer Zusammenhang zwischen der Komplexhöhe und dem Gewichtsbruch an PAMAM, bzw. PEI-PEO gefunden, der auf die Zunahme der Molmasse der Komplexe durch Wachstum entlang des Zylinderdurchmessers hindeutet. Die Bildung von Aggregaten, mit mehr als einem Polyanion, wurde nicht beobachtet.

Thermal excitations of optical nanofibers measured with a fiber-integrated Fabry-Pérot cavity

Efficient coupling of light to quantum emitters, such as atoms, molecules or quantum dots, is one of the great challenges in current research. The interaction can be strongly enhanced by coupling the emitter to the eva-nescent field of subwavelength dielectric waveguides that offer strong lateral confinement of the guided light. In this context subwavelength diameter optical nanofibers as part of a tapered optical fiber (TOF) have proven to be powerful tool which also provide an efficient transfer of the light from the interaction region to an optical bus, that is to say, from the nanofiber to an optical fiber. rnAnother approach towards enhancing light–matter interaction is to employ an optical resonator in which the light is circulating and thus passes the emitters many times. Here, both approaches are combined by experi-mentally realizing a microresonator with an integrated nanofiber waist. This is achieved by building a fiber-integrated Fabry-Pérot type resonator from two fiber Bragg grating mirrors with a stop-band near the cesium D2-line wavelength. The characteristics of this resonator fulfill the requirements of nonlinear optics, optical sensing, and cavity quantum electrodynamics in the strong-coupling regime. Together with its advantageous features, such as a constant high coupling strength over a large volume, tunability, high transmission outside the mirror stop band, and a monolithic design, this resonator is a promising tool for experiments with nanofiber-coupled atomic ensembles in the strong-coupling regime. rnThe resonator's high sensitivity to the optical properties of the nanofiber provides a probe for changes of phys-ical parameters that affect the guided optical mode, e.g., the temperature via the thermo-optic effect of silica. Utilizing this detection scheme, the thermalization dynamics due to far-field heat radiation of a nanofiber is studied over a large temperature range. This investigation provides, for the first time, a measurement of the total radiated power of an object with a diameter smaller than all absorption lengths in the thermal spectrum at the level of a single object of deterministic shape and material. The results show excellent agreement with an ab initio thermodynamic model that considers heat radiation as a volumetric effect and that takes the emitter shape and size relative to the emission wavelength into account. Modeling and investigating the thermalization of microscopic objects with arbitrary shape from first principles is of fundamental interest and has important applications, such as heat management in nano-devices or radiative forcing of aerosols in Earth's climate system. rnUsing a similar method, the effect of the TOF's mechanical modes on the polarization and phase of the fiber-guided light is studied. The measurement results show that in typical TOFs these quantities exhibit high-frequency thermal fluctuations. They originate from high-Q torsional oscillations that couple to the nanofiber-guided light via the strain-optic effect. An ab-initio opto-mechanical model of the TOF is developed that provides an accurate quantitative prediction for the mode spectrum and the mechanically induced polarization and phase fluctuations. These high-frequency fluctuations may limit the ultimate ideality of fiber-coupling into photonic structures. Furthermore, first estimations show that they may currently limit the storage time of nanofiber-based atom traps. The model, on the other hand, provides a method to design TOFs with tailored mechanical properties in order to meet experimental requirements. rn