Bulk dynamics of Brownian hard disks: Dynamical density functional theory versus experiments on two-dimensional colloidal hard spheres

Using dynamical density functional theory (DDFT), we theoretically study Brownian self-diffusion and structural relaxation of hard disks and compare to experimental results on quasi two-dimensional colloidal hard spheres. To this end, we calculate the self and distinct van Hove correlation functions by extending a recently proposed DDFT-approach for three-dimensional systems to two dimensions. We find that the theoretical results for both self- and distinct part of the van Hove function are in very good quantitative agreement with the experiments up to relatively high fluid packing fractions of roughly 0.60. However, at even higher densities, deviations between experiment and the theoretical approach become clearly visible. Upon increasing packing fraction, in experiments the short-time self diffusive behavior is strongly affected by hydrodynamic effects and leads to a significant decrease in the respective mean-squared displacement. In contrast, and in accordance with previous simulation studies, the present DDFT which neglects hydrodynamic effects, shows no dependence on the particle density for this quantity

Structure and Dynamics of Model Fluids with Anisotropic Interactions

In dieser Promotionsarbeit wird die statistische Physik von kolloidalen Flüssigkeiten mit stark-richtungsabhängigen Teilchenwechselwirkungen untersucht, was Relevanz für viele reale Systeme hat. So spielen auf der molekularen Ebene anisotrope Teilchenwechselwirkungen zum Beispiel in Wasser eine entscheidende Rolle, wohingegen auf der Skala der weichen und biologischen Materie anisotrope Wechselwirkungen insbesondere das Phasenverhalten von Proteinen in wässriger Lösung bestimmen. Ein wichtiges Fundament zur theoretischen Beschreibung von Systemen mit starkrichtungsabhängigen Wechselwirkungen bilden sogennante Patchy Particles. Dieses Modell beschreibt harte Kugeln, welche über attraktive Wechselwirkungszentren (patches) auf ihren Oberflächen miteinander interagieren können. Interessanterweise kann dieses einfache Modell bereits sehr viele Eigenschaften von realen Flüssigkeiten mit anisotropen Wechselwirkungen beschreiben. Diese Dissertation fußt auf einem erfolgreichen theoretischen Modell für patchy particles, welches von Wertheim in den 1980er Jahren im Rahmen der Statistischen Mechanik formuliert wurde. Die Wertheim’sche Theorie kann das Phasenverhalten von Patchy Particles in vielen Facetten äußerst erfolgreich beschreiben. Die Beschreibung von strukturellen Eigenschaften wie der Dichteverteilung in einem externen Feld oder die Berechnung von Korrelationsfunktionen stellt die statistische Physik jedoch vor Herausforderungen. In dieser Arbeit nutzen wir klassische Dichtefunktionaltheorie (DFT) sowie Computersimulationen um Paarkorrelationsfunktionen und deren asymptotischen Zerfall, oder die Adsorptionseigenschaften von Patchy Particles an einer Oberfläche (z.B. einer harte Wand) zu berechnen. Weiterhin werden wir auch dynamischen Eigenschaften wie z.B. das Diffusionsverhalten untersuchen. Neben grundlegenden und fundamentalen Betrachtungen aus dem Blickwinkel der theoretischen statistischen Physik werden wir auch ein experimentelles System in welchem stark-richtungsabhängigeWechselwirkungen auftreten ausführlicher behandeln: Protein- Salz-Mischungen. In diesen Systemen können Salzionen stark-richtungsabhängige Wechselwirkungen zwischen den Proteinen hervorrufen. Aufbauend auf einem einfachen Modell, welches Proteine als Patchy Particles basierend auf der Wertheim’schen Theorie beschreibt, zeigen wir mithilfe von DFT-Rechnungen, dass das experimentelle Adsoprtionsverhalten von Proteinen an festen Oberflächen verstanden werden kann, was für viele interdisziplinäre Gebiete wie der Biotechnologie oder Humanmedizin von Relevanz ist.In this thesis we investigate the statistical physics of model fluids with anisotropic particle interactions, i.e. interactions that depend on the relative orientation of the fluid particles to each other. In the fields of soft matter and biophysics, anisotropic interactions occur for instance in many protein solutions or can explicitly be designed in colloidal fluids in order to achieve certain desired material properties. Orientationdepend interparticle forces arise also in many atomic fluids; for instance, the directional interactions between the oxygen and hydrogen atoms in water are responsible for many of its anomalies, most notably the fact that the liquid phase is denser than the solid. A widely employed framework to describe directional interactions is the model of patchy particles, which consists of hard spheres decorated with a specific number of attractive interaction sites (patches). If two sites of distinct particles overlap, a bond between the latter is formed. Detailed studies based on theoretical considerations and computer simulations have revealed that this rather simple model is capable of describing many features of the thermodynamic phase behavior, structure and dynamics of real fluids with anisotropic interactions. Seminal work by Wertheim has paved the way towards a theoretical understanding of the rich bulk phase behavior of uniform patchy fluids. Determining structural properties, such as correlation functions, however, is still a challenge for liquid-state theories. In this work we employ classical density functional theory (DFT) and computer simulations in order to investigate structural properties of patchy fluids, which includes bulk pair correlation functions or density profiles in the vicinity of solid surfaces such as a hard planar wall. In addition, we also put attention to the dynamic properties of patchy fluids. Besides fundamental considerations from the perspective of liquid-state theory, we shall focus explicitly on an experimental system in which patchy interactions are believed to play a crucial role: protein solutions in the presence of multivalent metal ions. In these systems, the latter can bind to the protein surfaces and thereby act as mediator of a highly-directional interaction between the proteins. Building up on an existing simple model for the protein bulk phase behavior, we for instance demonstrate that experimentally observed protein adsorption at substrates attracting the proteins can successfully be understood with a DFT formulation of this protein model. The results are relevant for many interdisciplinary fields such as biology and medical sciences

On the decay of the pair correlation function and the line of vanishing excess isothermal compressibility in simple fluids

We re-visit the competition between attractive and repulsive interparticle forces in simple fluids and how this governs and connects the macroscopic phase behavior and structural properties as manifest in pair correlation functions. We focus on the asymptotic decay of the total correlation function $h(r)$ which is, in turn, controlled by the form of the pair direct correlation function $c(r)$. The decay of $r h(r)$ to zero can be either exponential (monotonic) if attraction dominates repulsion and exponentially damped oscillatory otherwise. The Fisher-Widom (FW) line separates the phase diagram into two regions characterized by the two different types of asymptotic decay. We show that there is a new and physically intuitive thermodynamic criterion which approximates well the actual FW line. This new criterion defines a line where the isothermal compressibility takes its ideal gas value $\chi_T=\chi_T^\text{id}$. We test our hypothesis by considering four commonly used models for simple fluids. In all cases the new criterion yields a line in the phase diagram that is close to the actual FW line for the thermodynamic state points that are most relevant. We also investigate (Widom) lines of maximal correlation length, emphasizing the importance of distinguishing between the true and Ornstein-Zernike correlation length

Wine and other alcohol consumption and risk of ovarian cancer in the California Teachers Study cohort

OBJECTIVE: Whether alcohol consumption influences ovarian cancer risk is unclear. Therefore, we investigated the association between alcohol intake at various ages and risk of ovarian cancer. METHODS: Among 90,371 eligible members of the California Teachers Study cohort who completed a baseline alcohol assessment in 1995–1996, 253 women were diagnosed with epithelial ovarian cancer by the end of 2003. Multivariate Cox proportional hazards regression analysis was performed to estimate relative risks (RRs) and 95% confidence intervals (CIs). RESULTS: Consumption of total alcohol, beer, or liquor in the year prior to baseline, at ages 30–35 years, or at ages 18–22 years was not associated with risk of ovarian cancer. Consumption of at least one glass per day of wine, compared to no wine, in the year before baseline was associated with increased risk of developing ovarian cancer: RR = 1.57 (95% CI 1.11–2.22), P(trend) = 0.01. The association with wine intake at baseline was particularly strong among peri-/post-menopausal women who used estrogen-only hormone therapy and women of high socioeconomic status. CONCLUSIONS: Alcohol intake does not appear to affect ovarian cancer risk. Constituents of wine other than alcohol or, more likely, unmeasured determinants of wine drinking were associated with increased risk of ovarian cancer

Studio de factibilidad para la creación de una empresa de consultorías para créditos de la Corporación Financiera Nacional en Esmeraldas

Tesis previa obtención del título de Ingeniero/a en Administración de Empresas Mención ProductividadActualmente Ecuador experimenta un cambio del manejo económico, dando protagonismo y apoyo tanto al empresario ya establecido, como al emprendedor y sus ideas de inversión. Este nuevo impulso e interés expresado en las nuevas políticas comerciales que pretende establecer el estado, mediante medidas económicas amigables con el empresario y que además invita a nuevas inversiones y emprendimientos, se queda a medio camino de su verdadero fin, ya que sin una adecuada difusión y socialización de los mecanismos de acción y financiamiento que ofrece la banca pública, muchos emprendedores y empresarios no llegan a conocer de este tipo de oportunidades. El presente trabajo pretende demostrar la factibilidad de crear una empresa de consultoría y asesorías administrativas, comerciales, productivas y económicas-financieras, capaz de cubrir la demanda por este servicio, tomando en cuenta la encuesta realizada a una muestra determinada de los sectores productivos de la provincia de Esmeraldas, se logró identificar los principales factores que inciden en el mercado y analizarlas desde el estudio de mercado. Por otra parte, para complementar este estudio y para el desarrollo del estudio técnico identificado para conocer los requerimientos de la empresa consultora, en la investigación bibliográfica y en los argumentos obtenidos en la entrevista realizada al funcionario de la CFN, se identificaron las diversas líneas de crédito, condiciones, políticas y características del servicio que oferta la CFN, se demostró, que el actual mercado posee condiciones favorables para la implementación de una empresa consultora, bajo criterios como; falta de pericia y conocimientos al desarrollar y completar los procesos de crédito, desconocimiento de las ofertas de crédito, características, condiciones y políticas. En base a los resultados obtenidos tanto en el estudio de mercado y estudio técnico, se determinó en el estudio financiero que la creación de una empresa de consultorías para créditos de la CFN en Esmeraldas es viable y económicamente rentable