Página 1 dos resultados de 804 itens digitais encontrados em 0.301 segundos

- ACADEMIC PRESS INC ELSEVIER SCIENCE
- Biblioteca Digitais de Teses e Dissertações da USP
- The Rockefeller University Press
- Springer-Verlag
- Public Library of Science
- Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Ensino de Ciências Naturais e Matemática; Ensino de Ciências Naturais e Matemática
- Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em PROFMAT (RC); Regional de Catalão (RC)
- Universidade de Tubinga
- European University Institute
- Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Educação; Educação
- American Physical Society; College Park
- Universidade Cornell
- National Academy of Sciences
- Institute of Physics Publishing
- Mais Publicadores...

## Micellar properties of surface active ionic liquids: A comparison of 1-hexadecyl-3-methylimidazolium chloride with structurally related cationic surfactants

Fonte: ACADEMIC PRESS INC ELSEVIER SCIENCE
Publicador: ACADEMIC PRESS INC ELSEVIER SCIENCE

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

55.27%

#Surface active ionic liquids#Conductivity of cationic micelles#Isothermal titration calorimetry of cationic micelles#Light scattering#Polarity of interfacial water#1-Hexadecyl-3-methylimidazolium chloride#1-Hexadecylpyridinium chloride#Benzyl(3-hexadecanoylaminoethyl)dimethylammonium chloride#SODIUM DODECYL-SULFATE#ENTHALPY-ENTROPY COMPENSATION#CETYL PYRIDINIUM CHLORIDE

Ionic liquids, ILs, carrying long-chain alkyl groups are surface active, SAIIs. We investigated the micellar properties of the SAIL 1-hexadecyl-3-methylimidazolium chloride, C(16)MeImCl, and compared the data with 1-hexadecylpyridinium chloride, C(16)PYCl, and benzyl (3-hexadecanoylaminoethyl)dimethylammonium chloride, C(15)AEtBzMe(2)Cl. The properties compared include critical micelle concentration, cmc; thermodynamic parameters of micellization; empirical polarity and water concentrations in the interfacial regions. In the temperature range from 15 to 75 degrees C, the order of cmc in H(2)O and in D(2)O is C(16)PYCl > C(16)MeImCl > C(15)AEtBzMe(2)Cl. The enthalpies of micellization, Delta H(mic)(degrees), were calculated indirectly from by use of the van`t Hoff treatment; directly by isothermal titration calorimetry, ITC. Calculation of the degree of counter-ion dissociation, alpha(mic), from conductivity measurements, by use of Evans equation requires knowledge of the aggregation numbers, N(agg), at different temperatures. We have introduced a reliable method for carrying out this calculation, based on the volume and length of the monomer, and the dependence of N(agg) on temperature. The N(agg) calculated for C(16)PyCl and C(16)MeImCl were corroborated by light scattering measurements. Conductivity- and ITC-based Delta H(mic)(degrees) do not agree; reasons for this discrepancy are discussed. Micelle formation is entropy driven: at all studied temperatures for C(16)MeImCl; only up to 65 degrees C for C(16)PyCl; and up to 55 degrees C for C(15)AEtBzMe(2)Cl. All these data can be rationalized by considering hydrogen-bonding between the head-ions of the monomers in the micellar aggregate. The empirical polarities and concentrations of interfacial water were found to be independent of the nature of the head-group. (C) 2010 Elsevier Inc. All rights reserved.; FAPESP (State of Sao Paulo Research Foundation); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq (National Council for Scientific and Technological Research)

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## Simulação de fluxo de água e transporte de solutos na zona não-saturada do solo pelo método de elementos finitos adaptativo; Simulation of water flow and solute transport in the unsaturated zone of the soil by adaptative finite element method

Fonte: Biblioteca Digitais de Teses e Dissertações da USP
Publicador: Biblioteca Digitais de Teses e Dissertações da USP

Tipo: Tese de Doutorado
Formato: application/pdf

Publicado em 02/10/2009
PT

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55.41%

#Advection-dispersion equation#Aterro sanitário#Chorume#Equação de advecção-dispersão#Equação de Richards#Finite element method#Leachate#Método de elementos finitos#Modelo numérico#Numerical modeling#Richards equation

Devido aos riscos de contaminação dos recursos naturais solo e água, ao alto custo, ao tempo e ao esforço humano nas investigações de campo, os modelos matemáticos, aliados às técnicas numéricas e aos avanços computacionais, constituem uma ferramenta importante na previsão do deslocamento de solutos, contribuindo assim, para o controle de alterações ambientais. No Brasil, a modelação de fluxo e transporte de solutos na zona não-saturada é voltada, quase que exclusivamente, aos problemas relacionados às atividades agrícolas. Entretanto, tão importante quanto a problemática dos produtos químicos nas atividades agrícolas é a questão de poluição e contaminação do solo e da água por chorume, gerado pelos resíduos sólidos domiciliares. Neste trabalho, é desenvolvido e validado um modelo computacional unidimensional para simulação de fluxo e transporte de solutos na zona não-saturada do solo. O modelo matemático é dado pela equação diferencial parcial não-linear de Richards, que rege o movimento de água no solo, e a equação diferencial parcial linear de advecção-dispersão, do transporte de solutos, acompanhadas das condições iniciais e de contorno. A equação de Richards é dada em função do potencial matricial da água e a equação de transporte de solutos estima a evolução temporal da concentração de solutos no perfil do solo. Devido à dificuldade de se obter soluções analíticas destas equações...

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## THE RESPONSES OF THE PUPIL OF GEKKO GEKKO TO EXTERNAL LIGHT STIMULUS

Fonte: The Rockefeller University Press
Publicador: The Rockefeller University Press

Tipo: Artigo de Revista Científica

Publicado em 20/11/1956
EN

Relevância na Pesquisa

55.28%

1. The responses of the pupil of a nocturnal gecko (Gekko gekko) to external light stimulus were studied. 2. The responses of the pupil are determined by light entering the pupil and not by light acting directly on the iris. 3. The responses of the pupil are very uniform in sensitivity including spectral sensitivity for light coming in different directions to the eye. 4. The possible change in area of the pupil is more than 300-fold and probably represents an effort to shield the pure rod retina from saturating light intensities. 5. The pupil continues to contract sharply for changes in external light intensity which give retinal illuminations corresponding to 106 quanta/sec. striking a retinal rod. 6. There is a large degree of spatial summation of the response; circular external light fields subtending 5 and 140° giving the same illumination at the pupil give approximately the same pupil response. 7. The spectral sensitivity curve agrees with the absorption curve of an extracted pigment from a closely related gecko described by Crescitelli in the followig paper. It is similar to the human scotopic curve but its maximum is displaced about 20 to 30 mµ towards the red end of the spectrum. The fall in sensitivity towards the red end of the spectrum is described by the equation See PDF for Equation

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## Comparative evaluation of the degree of indomethacin crystallinity by chemoinfometrical fourie-transformed near-infrared spectroscopy and conventional powder X-ray diffractiometry

Fonte: Springer-Verlag
Publicador: Springer-Verlag

Tipo: Artigo de Revista Científica

Publicado em 23/03/2000
EN

Relevância na Pesquisa

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A chemoinfometrical method for evaluating the degree of crystallinity based on fourie-transformed near-infrared (FT-NIR) spectroscopy was established and compared with the conventional powder X-ray diffraction method. Powder X-ray diffraction profiles and FT-NIR spectra were recorded for 11 kinds of standard materials with various degrees of crystallinity obtained by physically mixing crystalline and amorphous indomethacin (IMC). Chemoinfometric analysis was performed on the FT-NIR spectral data sets by multiple linear regression (MLR) (MLR-Set-Up Search program). The crystalline and amorphous forms showed significant NIR spectral peaks. MLR analysis was performed based on normalized NIR spectra sets for standard samples of known crystallinity. A calibration equation was determined to minimize the root mean square error of prediction. The predicted crystallinity values were reproducible and had a smaller standard deviation. The values of crystallinity predicted by X-ray powder diffractometry and FT-NIR spectrometry suggested a satisfactory correlation between the 2 techniques. The results indicated that FT-NIR spectroscopy provides for an accurate quantitative analysis of crystallinity compared with conventional X-ray diffractometry.

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## Estimating Competition between Wildlife and Humans–A Case of Cormorants and Coastal Fisheries in the Baltic Sea

Fonte: Public Library of Science
Publicador: Public Library of Science

Tipo: Artigo de Revista Científica

Publicado em 30/12/2013
EN

Relevância na Pesquisa

55.28%

Cormorants and other wildlife populations have come in real or perceived conflicts with humans over exploited fish stocks. From gut contents of cormorants, and using an extension of the Catch equation, we estimated the degree of short term competition between great cormorants and coastal fisheries in two areas along the Swedish Baltic Sea. Cormorants consumed 10 and 44%, in respective area, of the fish biomass of six fish species harvested by humans; eel, flounder, herring, perch, pike, and whitefish. On average, cormorants consumed smaller individuals than harvested in fisheries. But for perch, cod and flounder, cormorants consumed harvestable sized fish corresponding >20% of human catches. Our competition model estimated the direct decrease in fisheries catches due to cormorant predation to be <10% for all species except flounder (>30%) and perch (2–20%). When also including the indirect effects of cormorant predation on smaller fish that never reached harvestable size, the estimated decrease in fisheries catches at least doubled for perch (13–34%) and pike (8–19%). Despite large uncertainties, our model indicates that cormorants may locally have a direct impact on human catches of at least flounder, and when incorporating indirect effects also on perch and pike. The study indicates that the degree of competition between cormorants and humans varies substantially between areas. We also included economical values in the model and concluded that for the commercially most important species...

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## Investigação histórica nas aulas de matemática: avaliação de duas experiências

Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Ensino de Ciências Naturais e Matemática; Ensino de Ciências Naturais e Matemática
Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Ensino de Ciências Naturais e Matemática; Ensino de Ciências Naturais e Matemática

Tipo: Dissertação
Formato: application/pdf

POR

Relevância na Pesquisa

75.38%

#Investigação Matemática#Atividades de Investigação#História da Matemática#Equação do 2º grau#Licenciatura em Matemática#Mathematics Research#Activities of Research#History of Mathematics#Equation 2 of the degree#Degree in Mathematics#CNPQ::CIENCIAS EXATAS E DA TERRA::MATEMATICA

This study reflects on some procedural aspects about the development of mathematics learning from the experience with investigative activities concerning the
resolution of second degree equation, which was tested a proposal for education, supported the use of texts in history of mathematics. The survey was conducted in two
stages, taking the first-served basis for the second, which was carried out with a study group remainder of the first experiment. The intention was to investigate how the group
participant, known as the study group, involved in the implementation of activities of research in mathematics, supported the use of the history of mathematics. Based on the
results achieved during the study, it was possible to understand that the activities of research enable the development of students, range of learning mathematics and the development of skills and expertise for research as a vehicle for construction of their mathematical knowledge. This approach proposed research into the classroom is important, both for prospective teachers of mathematics and for students from elementary school, bringing a new phase for mathematical education that will come to schools; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior; O presente estudo reflete sobre alguns aspectos processuais acerca do desenvolvimento da aprendizagem matemática a partir da experiência com atividades investigativas...

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## Técnica de perturbação utilizada para solução numérica de equações do 2º e 3º graus; Perturbation tecnhique used for numerical solution of the 2nd and 3nd degree equations

Fonte: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em PROFMAT (RC); Regional de Catalão (RC)
Publicador: Universidade Federal de Goiás; Brasil; UFG; Programa de Pós-graduação em PROFMAT (RC); Regional de Catalão (RC)

Tipo: Dissertação
Formato: application/pdf

POR

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55.33%

#Sistemas dinâmicos não lineares#Método da expansão#Equações algébricas#Raízes de equações#Nonlinear dynamical systems#Expansion method#Algebraic equations#Roots of equations#CIENCIAS EXATAS E DA TERRA::MATEMATICA

Phenomenon that occur in the nature are essentially nonlinear and the
dynamical systems theory aims to obtain a mathematical model that best represents
the real physical systems, then nothing more coherent than the description or
analysis of these natural phenomenon using models and techniques. In this
dissertation, the technique of direct expansion for the development of two differential
equations order to solve a nonlinear equation and the approximate determination of
the roots of order algebraic equation higher or equal to two, was used. For this
purpose, it was initially shown the development of a differential equation of motion
subjected to a nonlinear damping, which is represented by the equation of Duffing –
Van der Pol. Generally, it’s not easy to obtain an approximated analytical solution for
this type equation, but this study was done with the purpouse of illustrating the
technique used in the work, solving type solving a problem in which these techniques
are routinely used to obtain a solution. Studied for application in basic education, it
presents a way to obtain the approximate roots of equations of second and third
degrees, using the technique of direct expansion for the sake of comparison. Since
there are formulas for resolving this...

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## Spherical Quasihomogeneous SL(2)-Varieties; Sphärische Quasihomogeneous SL(2)-Varietät

Fonte: Universidade de Tubinga
Publicador: Universidade de Tubinga

Tipo: Dissertação

DE_DE

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55.41%

Man kann den n-dimensionalen projektiven Raum P^n über C als den
folgenden Quotienten: (Cn+1{0})C* defnieren. Eine ähnliche Quotientenkonstruktion für eine beliebige torische Varietät X wurde von David Cox vorgeschlagen [Cox95]. Sei
X eine n-dimensionale torische Varietät mit einem rationalen polyhedralen
Fächer Delta. Sei Delta(1) die Menge aller 1-dimensionaler Kegel von
4 und sei Cl(X) die Divisorenklassengruppe von X. Dann wirkt die
algebraische Gruppe (Quasitorus):
T := HomZ(Cl(X),C*)
auf natürliche Weise auf dem a nen Raum C^Delta(1), so dass der kategorische
Quotient (C^Delta(1) ) / T existiert und isomorph ist zu X. Hierbei
ist Z eine Zariski abgeschlossene Menge, die durch ein homogenes
Ideal im Koordinatenring C[x_0,..,x_n] definiert ist.
Eine quasihomogene SL(2)-Varietät ist eine normale 3-dimensionale
algebraische Varietät X über einem algebraisch abgeschlossenen Körper
k zusammen mit einer regulären SL(2)-Wirkung, so dass X eine offene
dichte Bahn hat. Zur Vereinfachung betrachten wir den Fall k = C.
In dieser Arbeit geben wir eine geometrische Methode zur Konstruktion
einer speziellen Klasse von SL(2)-Varietäten X als kategorische
Quotienten an.
Als ersten Schritt haben wir den affinen Fall von SL(2)-Varietäten
betrachtet [BH08]. Diese Varietäten wurden von Popov [P73] klassifiziert. Jede affine SL(2)-Varietät E ist durch zwei Zahlen eindeutig bestimmt; einer rationalen Zahl h = p/q (gcd(p...

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## Sample Kurtosis, GARCH-t and the Degrees of Freedom Issue

Fonte: European University Institute
Publicador: European University Institute

Tipo: Trabalho em Andamento
Formato: application/pdf; digital

EN

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Econometric modeling based on the Student’s t distribution introduces an
additional parameter — the degree of freedom. In this paper we use a simulation
study to investigate the ability of (i) the GARCH-t model (Bollerslev, 1987)
to estimate the true degree of freedom parameter and (ii) the sample kurtosis
coefficient to accurately determine the implied degrees of freedom. Simulation
results reveal that the GARCH-t model and the sample kurtosis coefficient
provide biased and inconsistent estimates of the degree of freedom parameter.
Moreover, by varying σ2, we find that only the constant term in the conditional
variance equation is affected, while the other parameters remain unaffected.

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## Utilizando processos geométricos da história da matemática para o ensino de equações do 2º grau

Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Educação; Educação
Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Educação; Educação

Tipo: Dissertação
Formato: application/pdf

POR

Relevância na Pesquisa

55.36%

#matemática ensino fundamental-equação do 2º grau#ensino construtivo#história da matemática#elementary education - mathematics - equation of the 2nd degree#construtivist teaching#history of the mathematics#CNPQ::CIENCIAS HUMANAS::EDUCACAO

The present work had as principal objective to analyze the, 9th grade students understanding about the solutions of an equation of the 2° degree, using geometric processes of the History of the Mathematics. To do so, the research had as base the elaboration and application of a group of teaching activities, based on Jean Piaget's construtivism. The research consisted of a methodological intervention, that has as subjects the students of a group of 9th grade of the State School José Martins de Vasconcelos, located in the municipal district of Mossoró, Rio Grande do Norte. The intervention was divided in three stages: application of an initial evaluation; development of activities‟ module with emphasis in constructive teaching; and the application of the final evaluation. The data presented in the initial evaluation revealed a low level of the students' understanding with relationship to the calculation of areas of rectangles, resolution of equations of the 1st and 2nd degrees, and they were to subsidize the elaboration of the teaching module. The data collected in the initial evaluation were commented and presented under descriptive statistics form. The results of the final evaluation were analyzed under the qualitative point of view...

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## Determination of the critical coupling of explosive synchronization transitions in scale-free networks by mean-field approximations

Fonte: American Physical Society; College Park
Publicador: American Physical Society; College Park

Tipo: Artigo de Revista Científica

ENG

Relevância na Pesquisa

55.28%

An explosive synchronization can be observed in scale-free networks when Kuramoto oscillators have natural frequencies equal to their number of connections. The present paper reports on mean-field approximations to determine the critical coupling of such explosive synchronization. It has been verified that the equation obtained for the critical coupling has an inverse dependence on the network average degree. This expression differs from those whose frequency distributions are unimodal and even. In this case, the critical coupling depends on the ratio between the first and second statistical moments of the degree distribution. Numerical simulations were also conducted to verify our analytical results.; CNPq [305940/2010-4]; FAPESP [2010/19440-2]

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## OSMOTIC PROPERTIES OF THE EGG CELLS OF THE OYSTER (OSTREA VIRGINICA)

Fonte: The Rockefeller University Press
Publicador: The Rockefeller University Press

Tipo: Artigo de Revista Científica

Publicado em 20/11/1941
EN

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Investigations of the osmotic properties of oyster eggs by a diffraction method for measuring volumes have led to the following conclusions: 1. The product of cell volume and osmotic pressure is approximately constant, if allowance is made for osmotically inactive cell contents (law of Boyle-van't Hoff). The space occupied by osmotically inactive averages 44 per cent of cell volume. 2. Volume changes over a wide range of pressures are reversible, indicating that the semipermeability of the cell during such changes remains intact. 3. The kinetics of endosmosis and of exosmosis are described by the equation, See PDF for Equation, where dV is rate of volume change; S, surface area of cell, (P-Pe), the difference in osmotic pressure between cell interior and medium, and K, the permeability of the cell to water. 4. Permeability to water during endosmosis is 0.6µ3 of water per minute, per square micron of cell surface, per atmosphere of pressure. The value of permeability for exosmosis is closely the same; in this respect the egg cell of the oyster appears to be a more perfect osmometer than the other marine cells which have been studied. Permeability to water computed by the equation given above is in good agreement with computations by the entirely different method devised by Jacobs. 5. Permeability to diethylene glycol averages 27.2...

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## Spectral Dependence of Degree of Localization of Eigenfunctions of the 1D Schrodinger Equation with a Peacewise-Constant Random Potential

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 13/05/2011

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The perturbation theory is developed for joint statistics of the advanced and
retarded Green's functions of the 1D Schrodinger equation with a
piecewise-constant random potential. Using this method, analytical expressions
are obtained for spectral dependence of the degree of localization and for the
limiting (at $t\rightarrow\infty$) probability to find the particle at the
point it was located at $t = 0$ (Andeson criterion). Definition of the
localization length is introduced. The computer experiments confirming
correctness of the calculations are described.; Comment: 18 pages, 2 figures

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## On determining absolute entropy without quantum theory or the Third Law of thermodynamics

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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#Condensed Matter - Statistical Mechanics#Physics - Chemical Physics#Physics - History and Philosophy of Physics

We employ classical thermodynamics to gain information about absolute
entropy, without recourse to statistical methods, quantum mechanics or the
Third Law of thermodynamics. The Gibbs-Duhem equation yields various simple
methods to determine the absolute entropy of a fluid. We also study the entropy
of an ideal gas and the ionization of a plasma in thermal equilibrium. A single
measurement of the degree of ionization can be used to determine an unknown
constant in the entropy equation, and thus determine the absolute entropy of a
gas. It follows from all these examples that the value of entropy at absolute
zero temperature does not need to be assigned by postulate, but can be deduced
empirically.; Comment: 16 pages, 2 figures; minor clarifications in v.2

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## Hydrodynamic limit of the Gross-Pitaevskii equation

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 16/10/2013

Relevância na Pesquisa

55.34%

We study dynamics of vortices in solutions of the Gross-Pitaevskii equation
$i \partial_t u = \Delta u + \varepsilon^{-2} u (1 - |u|^2)$ on $\mathbb{R}^2$
with nonzero degree at infinity. We prove that vortices move according to the
classical Kirchhoff-Onsager ODE for a small but finite coupling parameter
$\varepsilon$. By carefully tracking errors we allow for asymptotically large
numbers of vortices, and this lets us connect the Gross-Pitaevskii equation on
the plane to two dimensional incompressible Euler equations through the work of
Schochet [21].

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## Characterization of large energy solutions of the equivariant wave map problem: I

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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We consider 1-equivariant wave maps from 1+2 dimensions to the 2-sphere. For
wave maps of topological degree zero we prove global existence and scattering
for energies below twice the energy of harmonic map, Q, given by stereographic
projection. We deduce this result via the concentration compactness/rigidity
method developed by the second author and Merle. In particular, we establish a
classification of equivariant wave maps with trajectories that are pre-compact
in the energy space up to the scaling symmetry of the equation. Indeed, a wave
map of this type can only be either 0 or Q up to a rescaling. This gives a
proof in the equivariant case of a refined version of the threshold conjecture
adapted to the degree zero theory where the true threshold is 2E(Q), not E(Q).
The aforementioned global existence and scattering statement can also be
deduced by considering the work of Sterbenz and Tataru in the equivariant
setting.
For wave maps of topological degree one, we establish a classification of
solutions blowing up in finite time with energies less than three times the
energy of Q. Under this restriction on the energy, we show that a blow-up
solution of degree one is essentially the sum of a rescaled Q plus a remainder
term of topological degree zero of energy less than twice the energy of Q. This
result reveals the universal character of the known blow-up constructions for
degree one...

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## On the birational geometry of the parameter space for codimension 2 complete intersections

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 19/12/2012
EN

Relevância na Pesquisa

55.36%

Codimension 2 complete intersections in P^N have a natural parameter space
\bar{H}: a projective bundle over a projective space given by the choice of the
lower degree equation and of the higher degree equation up to a multiple of the
first. Motivated by the question of existence of complete families of smooth
complete intersections, we study the birational geometry of \bar{H}. In a first
part, we show that the first contraction of the MMP for \bar{H} always exists
and we describe it. Then, we show that it is possible to run the full MMP for
\bar{H}, and we describe it, in two degenerate cases. As an application, we
prove the existence of complete curves in the punctual Hilbert scheme of
complete intersection subschemes of A^2.; Comment: 33 pages, in english

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## Condensate fragmentation as a sensitive measure of the quantum many-body behavior of bosons with long-range interactions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 17/02/2015

Relevância na Pesquisa

55.32%

The occupation of more than one single-particle state and hence the emergence
of fragmentation is a many-body phenomenon universal to systems of spatially
confined interacting bosons. In the present study, we investigate the effect of
the range of the interparticle interactions on the fragmentation degree of one-
and two-dimensional systems. We solve the full many-body Schr\"odinger equation
of the system using the recursive implementation of the multiconfigurational
time-dependent Hartree for bosons method, R-MCTDHB. The dependence of the
degree of fragmentation on dimensionality, particle number, areal or line
density and interaction strength is assessed. It is found that for contact
interactions, the fragmentation is essentially density independent in two
dimensions. However, fragmentation increasingly depends on density the more
long-ranged the interactions become. The degree of fragmentation is increasing,
keeping the particle number $N$ fixed, when the density is decreasing as
expected in one spatial dimension. We demonstrate that this remains,
nontrivially, true also for long-range interactions in two spatial dimensions.
We, finally, find that within our fully self-consistent approach, the
fragmentation degree, to a good approximation...

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## The osmotic pressure of the ions and of the undissociated molecules of salts in aqueous solution

Fonte: National Academy of Sciences
Publicador: National Academy of Sciences

Tipo: Article; PeerReviewed
Formato: application/pdf

Publicado em /06/1915

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65.23%

The concentration of the ions (Ci) and that of the undissociated molecules (CU) are involved in the equation, Ci^2 / Cu = K, expressing the application of the law of mass-action to solutions of electrolytes. Hence the large divergence from this law which strong electrolytes exhibit may be due to the behavior of the ions, to that of the undissociated molecules, or to that of both. This so called anomalous behavior may be simply expressed by saying that for one or for both of these molecular species van't Hoff's law, II = CRT, where II is the osmotic pressure, C is the concentration in mols per unit-volume, R is the gas-constant, and T is the absolute temperature, does not hold; for, if all of the molecular species entering into an equilibrium obey this law, the law of mass-action is a thermodynamic necessity. [1]
In this paper is outlined and applied a method for determining the extent to which the ions and the undissociated molecules deviate from van't Hoff's law, that is, for determining the relation between the osmotic pressure of the ions or of the undissociated molecules and their concentration. The significance of the results, particularly as applied to the calculation of the degree of ionization and to the validity of the law of mass-action...

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## Some fundamental questions concerning the kinetic theory of electrons in molecular gases and the e-H 2 vibrational cross section controversy

Fonte: Institute of Physics Publishing
Publicador: Institute of Physics Publishing

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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#Keywords: Approximation theory#Diffusion#Electrons#Gases#Hydrogen#Kinetic theory#Molecular dynamics#Molecular orientation#Molecular vibrations#Quantum theory#Collisional excitation

We commence a fundamental re-examination of the kinetic theory of charged particle swarms in molecular gases, focusing on collisional excitation of molecular rotational and ro-vibrational states by electrons. Modern day analysis of electron swarms has been based upon the kinetic equation of Wang-Chang et al, which simply treats all processes as scalar energy excitations, and ignores angular momentum conservation and the vector dynamics associated with rotational excitation. It is pointed out that there is no alternative, more exact kinetic equation readily available for electrons which enables one to directly ascertain the degree of error introduced by this approximation. Thus in this preliminary study, we approach the problem indirectly, from the standpoint of the neutral molecules, using the Waldmann-Snider quantum kinetic equation, and insist that an electron-molecule collision must look the same from the perspective of both electron and molecule. We give a formula for quantitatively assessing the importance of scalar versus vectorial treatments of rotational excitation by looking at the post-collisional 'echo' produced by an electron swarm as it passes through the gas. It is then pointed out that in order to remedy any deficiency...

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