Showing papers by "University of Notre Dame published in 2001"

Statistical mechanics of complex networks

Abstract: The emergence of order in natural systems is a constant source of inspiration for both physical and biological sciences. While the spatial order characterizing for example the crystals has been the basis of many advances in contemporary physics, most complex systems in nature do not offer such high degree of order. Many of these systems form complex networks whose nodes are the elements of the system and edges represent the interactions between them. Traditionally complex networks have been described by the random graph theory founded in 1959 by Paul Erdohs and Alfred Renyi. One of the defining features of random graphs is that they are statistically homogeneous, and their degree distribution (characterizing the spread in the number of edges starting from a node) is a Poisson distribution. In contrast, recent empirical studies, including the work of our group, indicate that the topology of real networks is much richer than that of random graphs. In particular, the degree distribution of real networks is a power-law, indicating a heterogeneous topology in which the majority of the nodes have a small degree, but there is a significant fraction of highly connected nodes that play an important role in the connectivity of the network. The scale-free topology of real networks has very important consequences on their functioning. For example, we have discovered that scale-free networks are extremely resilient to the random disruption of their nodes. On the other hand, the selective removal of the nodes with highest degree induces a rapid breakdown of the network to isolated subparts that cannot communicate with each other. The non-trivial scaling of the degree distribution of real networks is also an indication of their assembly and evolution. Indeed, our modeling studies have shown us that there are general principles governing the evolution of networks. Most networks start from a small seed and grow by the addition of new nodes which attach to the nodes already in the system. This process obeys preferential attachment: the new nodes are more likely to connect to nodes with already high degree. We have proposed a simple model based on these two principles wich was able to reproduce the power-law degree distribution of real networks. Perhaps even more importantly, this model paved the way to a new paradigm of network modeling, trying to capture the evolution of networks, not just their static topology.

Lethality and centrality in protein networks

Abstract: The most highly connected proteins in the cell are the most important for its survival. Proteins are traditionally identified on the basis of their individual actions as catalysts, signalling molecules, or building blocks in cells and microorganisms. But our post-genomic view is expanding the protein's role into an element in a network of protein–protein interactions as well, in which it has a contextual or cellular function within functional modules1,2. Here we provide quantitative support for this idea by demonstrating that the phenotypic consequence of a single gene deletion in the yeast Saccharomyces cerevisiae is affected to a large extent by the topological position of its protein product in the complex hierarchical web of molecular interactions.

The Population Biology of Invasive Species

Abstract: ■ Abstract Contributions from the field of population biology hold promise for understanding and managing invasiveness; invasive species also offer excellent opportunities to study basic processes in population biology. Life history studies and demographic models may be valuable for examining the introduction of invasive species and identifying life history stages where management will be most effective. Evolutionary processes may be key features in determining whether invasive species establish and spread. Studies of genetic diversity and evolutionary changes should be useful for

Progress in invasion biology: predicting invaders

Abstract: Predicting which species are probable invaders has been a long-standing goal of ecologists, but only recently have quantitative methods been used to achieve such a goal. Although restricted to few taxa, these studies reveal clear relationships between the characteristics of releases and the species involved, and the successful establishment and spread of invaders. For example, the probability of bird establishment increases with the number of individuals released and the number of release events. Also, the probability of plant invasiveness increases if the species has a history of invasion and reproduces vegetatively. These promising quantitative approaches should be more widely applied to allow us to predict patterns of invading species more successfully.

What do proactive people do? a longitudinal model linking proactive personality and career success

Abstract: We developed and tested a model linking proactive personality and career success through a set of four behavioral and cognitive mediators. A 2-year longitudinal design with data from a sample of 180 full-time employees and their supervisors was used. Results from structural equation modeling showed that proactive personality measured at Time 1 was positively related to innovation, political knowledge, and career initiative, but not voice; all measured at Time 2. Innovation, political knowledge, and career initiative in turn had positive relationships with career progression (salary growth and the number of promotions during the previous 2 years) and career satisfaction. Interestingly, voice had a negative relationship with career progression. We discuss practical implications and future research directions for proactive personality, extra-role behavior, and careers.

High-Pressure Phase Behavior of Ionic Liquid/CO2 Systems

Abstract: This work presents the high-pressure phase behavior of CO2 with six ionic liquids: 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1-n-octyl-3-methylimidazolium hexafluorophosphate ([C8-mim][PF6]), 1-n-octyl-3-methylimidazolium tetrafluoroborate ([C8-mim][BF4]), 1-n-butyl-3-methylimidazolium nitrate ([bmim][NO3]), 1-ethyl-3-methylimidazolium ethyl sulfate ([emim][EtSO4]), and N-butylpyridinium tetrafluoroborate ([N-bupy][BF4]). We explored the effect of systematically changing the anionic and cationic components of the ionic liquid on the CO2−ionic liquid phase behavior. For all of the ionic liquids tested, large quantities of CO2 dissolved in the ionic liquid phase, but no appreciable amount of ionic liquid solubilized in the CO2 phase. In addition, the liquid phase volume expansion with the introduction of even large amounts of CO2 is negligible, in dramatic contrast to the large volume expansion observed for neutral organic liquids. Our results seek to elucidate the underlying physica...

Semiconductor−Metal Composite Nanostructures. To What Extent Do Metal Nanoparticles Improve the Photocatalytic Activity of TiO2 Films?

Abstract: Noble metal particles of Au, Pt, and Ir were deposited on nanostructured TiO2 film using an electrophoretic approach. The nanocomposite films were characterized by UV-absorption and atomic force microscopy (AFM). The deposition of tetraoctylammonium bromide (TOAB)-capped metal nanoparticles on TiO2 films improved the photocurrent generation and induced a shift in the apparent flat band potential. The TiO2 films modified with TOAB-capped metal nanoparticles were less prone to the electron scavenging by the oxygen in solution. Improved photoelectrochemical performance of semiconductor−metal composite film is attributed to the shift in quasi-Fermi level of the composite to more negative potentials. Continuous irradiation of the composite films over a long period causes photocurrent to decrease as the semiconductor−metal interface undergoes chemical changes. The role of semiconductor−metal composite films in improving the rate of photocatalytic degradation of an azo dye is also discussed.

Competition and multiscaling in evolving networks

Abstract: The rate at which nodes in a network increase their connectivity depends on their fitness to compete for links. For example, in social networks some individuals acquire more social links than others, or on the www some webpages attract considerably more links than others. We find that this competition for links translates into multiscaling, i.e. a fitness- dependent dynamic exponent, allowing fitter nodes to overcome the more connected but less fit ones. Uncovering this fitter-gets-richer phenomenon can help us understand in quantitative terms the evolution of many competitive systems in nature and society.

Ecological forecasts: an emerging imperative.

Abstract: Planning and decision-making can be improved by access to reliable forecasts of ecosystem state, ecosystem services, and natural capital. Availability of new data sets, together with progress in computation and statistics, will increase our ability to forecast ecosystem change. An agenda that would lead toward a capacity to produce, evaluate, and communicate forecasts of critical ecosystem services requires a process that engages scientists and decision-makers. Interdisciplinary linkages are necessary because of the climate and societal controls on ecosystems, the feedbacks involving social change, and the decision-making relevance of forecasts.

Objectives, Characteristics and Outcomes of University Licensing: A Survey of Major U.S. Universities

Abstract: This paper describes results of our survey of licensing at 62 research universities. We consider ownership, income splits, stage of development, marketing, license policies and characteristics, goals of licensing and the role of the inventor in licensing. Based on these results we analyze the relationship between licensing outcomes and both the objectives of the TTO and the characteristics of the technologies. Patent applications grow one-to-one with disclosures, while sponsored research grows similarly with licenses executed. Royalties are typically larger the higher the quality of the faculty and the higher the fraction of licenses that are executed at latter stages of development. Sponsored research is more likely to be included in a license if the new technology is at an early stage of development or if the TTO evaluates it as important. We find that additional disclosures generate smaller percentage increases in licenses, and those increases in licenses generate smaller percentage increases in royalties.

Machine Dreams Economics Becomes a Cyborg Science

Abstract: Acknowledgements 1 Cyborg agonistes 2 Some cyborg genealogies or, how the demon got its bots 3 John von Neumann and the cyborg incursion into economics 4 The military, the scientists and the revised rules of the game 5 Do cyborgs dream of efficient markets? 6 The empire strikes back 7 Core wars 8 Machines who think versus machines that sell Envoi References Index

Bose-Einstein Condensation in Complex Networks

Abstract: The evolution of many complex systems, including the World Wide Web, business, and citation networks, is encoded in the dynamic web describing the interactions between the system's constituents. Despite their irreversible and nonequilibrium nature these networks follow Bose statistics and can undergo Bose-Einstein condensation. Addressing the dynamical properties of these nonequilibrium systems within the framework of equilibrium quantum gases predicts that the "first-mover-advantage," "fit-get-rich," and "winner-takes-all" phenomena observed in competitive systems are thermodynamically distinct phases of the underlying evolving networks.

Solution Thermodynamics of Imidazolium-Based Ionic Liquids and Water

Abstract: This work presents the vapor−liquid equilibrium and the liquid−liquid equilibrium phase behavior and associated thermodynamic properties of water with three ionic liquids: 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1-n-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]), and 1-n-octyl-3-methylimidazolium tetrafluoroborate ([C8mim][BF4]). Although water stable, these compounds are hygroscopic, so the uptake of water vapor is an important issue. Due to the negligible volatility of ionic liquids, we were able to measure vapor−liquid equilibrium using a gravimetric microbalance, which was designed to measure adsorption on solids. The Henry's law constants range from 0.033 to 0.45 bar, with infinite dilution activity coefficients ranging from slight positive deviations from Raoult's law to as high as 8.62. The enthalpies and entropies of absorption are similar to those for the absorption of water into alcohols. In addition, we present water/ionic liquid liquid−liquid equilibria,...

Stability analysis of switched systems with stable and unstable subsystems: An average dwell time approach

Abstract: We study the stability properties of switched systems consisting of both Hurwitz stable and unstable linear time-invariant subsystems using an average dwell time approach. We propose a class of switching laws so that the entire switched system is exponentially stable with a desired stability margin. In the switching laws, the average dwell time is required to be sufficiently large, and the total activation time ratio between Hurwitz stable subsystems and unstable subsystems is required to be no less than a specified constant. We also apply the result to perturbed switched systems where nonlinear vanishing or non-vanishing norm-bounded perturbations exist in the subsystems, and we show quantitatively that, when norms of the perturbations are small, the solutions of the switched systems converge to the origin exponentially under the same switching laws.

Recovery of Organic Products from Ionic Liquids Using Supercritical Carbon Dioxide

Abstract: Ionic liquids (ILs) hold great potential as replacements for traditional volatile organic solvents and have been shown to be a viable medium for numerous types of reactions. This work investigates the feasibility of using supercritical carbon dioxide, another environmentally benign solvent, for the separation of organic solutes from an ionic liquid. Recovery rates of aromatic and aliphatic solutes from 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) are given. Supercritical fluid extraction is shown to be a viable separation technique with the additional benefits of environmental sustainability and pure product recovery.

Disturbance Attenuation Properties of Time-Controlled Switched Systems

Abstract: In this paper, we investigate the disturbance attenuation properties of time-controlled switched systems consisting of several linear time-invariant subsystems by using an average dwell time approach incorporated with a piecewise Lyapunov function. First, we show that when all subsystems are Hurwitz stable and achieve a disturbance attenuation level smaller than a positive scalar γ0, the switched system under an average dwell time scheme achieves a weighted disturbance attenuation level γ0, and the weighted disturbance attenuation approaches normal disturbance attenuation if the average dwell time is chosen sufficiently large. We extend this result to the case where not all subsystems are Hurwitz stable, by showing that in addition to the average dwell time scheme, if the total activation time of unstable subsystems is relatively small compared with that of the Hurwitz stable subsystems, then a reasonable weighted disturbance attenuation level is guaranteed. Finally, a discussion is made on the case for which nonlinear norm-bounded perturbations exist in the subsystems.

Modulating charge separation and charge recombination dynamics in porphyrin-fullerene linked dyads and triads: Marcus-normal versus inverted region.

Abstract: Photoinduced charge separation (CS) and charge recombination (CR) processes have been examined in various porphyrin−fullerene linked systems (i.e., dyads and triads) by means of time-resolved transient absorption spectroscopy and fluorescence lifetime measurements. The investigated compounds comprise a homologous series of rigidly linked, linear donor−acceptor arrays with different donor−acceptor separations and diversified donor strength: freebase porphyrin−C60 dyad (H2P-C60), zincporphyrin−C60 dyad (ZnP-C60), ferrocene−zincporphyrin−C60 triad (Fc-ZnP-C60), ferrocene−freebase porphyrin−C60 triad (Fc-H2P-C60), and zincporphyrin−freebase porphyrin−C60 triad (ZnP-H2P-C60). Most importantly, the lowest lying charge-separated state of all the investigated systems, namely, that of ferrocenium ion (Fc+) and the C60 radical anion (C60•-) pair in the Fc-ZnP-C60 triad, has been generated with the highest quantum yields (close to unity) and reveals a lifetime as long as 16 μs. Determination of CS and CR rate const...

Elliptic flow in Au + Au collisions at √SNN = 130 GeV

Abstract: Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at √(sNN) = 130 GeV using the STAR Time Projection Chamber at the Relativistic Heavy Ion Collider. The elliptic flow signal, v₂, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.

Antifreeze and ice nucleator proteins in terrestrial arthropods.

Abstract: ▪ Abstract Terrestrial arthropods survive subzero temperatures by becoming either freeze tolerant (survive body fluid freezing) or freeze avoiding (prevent body fluid freezing). Protein ice nucleators (PINs), which limit supercooling and induce freezing, and antifreeze proteins (AFPs), which function to prevent freezing, can have roles in both freeze tolerance and avoidance. Many freeze-tolerant insects produce hemolymph PINs, which induce freezing at high subzero temperatures thereby inhibiting lethal intracellular freezing. Some freeze-tolerant species have AFPs that function as cryoprotectants to prevent freeze damage. Although the mechanism of this cryoprotection is not known, it may involve recrystallization inhibition and perhaps stabilization of the cell membrane. Freeze-avoiding species must prevent inoculative freezing initiated by external ice across the cuticle and extend supercooling abilities. Some insects remove PINs in the winter to promote supercooling, whereas others have selected against...

Spectra of “real-world” graphs: Beyond the semicircle law

Abstract: results on the spectra of adjacency matrices corresponding to models of real-world graphs. We find that when the number of links grows as the number of nodes, the spectral density of uncorrelated random matrices does not converge to the semicircle law. Furthermore, the spectra of real-world graphs have specific features, depending on the details of the corresponding models. In particular, scale-free graphs develop a trianglelike spectral density with a power-law tail, while small-world graphs have a complex spectral density consisting of several sharp peaks. These and further results indicate that the spectra of correlated graphs represent a practical tool for graph classification and can provide useful insight into the relevant structural properties of real networks.

Partial differential equations in several complex variables

Abstract: This book is intended as both an introductory text and a reference book for those interested in studying several complex variables in the context of partial differential equations. In the last few decades, significant progress has been made in the study of Cauchy-Riemann and tangential Cauchy-Riemann operators; this progress greatly influenced the development of PDEs and several complex variables. After the background material in complex analysis is developed in Chapters 1 to 3, the next three chapters are devoted to the solvability and regularity of the Cauchy-Riemann equations using Hilbert space techniques. The authors provide a systematic study of the Cauchy-Riemann equations and the \bar\partial-Neumann problem, including Hormander's L2 existence progress on the global regularity and irregularity of the \bar\partial-Neumann operators. The second part of the book gives a comprehensive study of the tangential Cauchy-Riemann equations, another important class of equations in several complex variables first studied by Lewy. An up-to-date account of the L2 theory for \bar\partial_b operator is given. Explicit integral solution representations are constructed both on the Heisenberg groups and on strictly convex boundaries with estimates in Holder and L2 spaces. Embeddability of abstract CR structures is discussed in detail here for the first time. Titles in this series are co-published with International Press, Cambridge, MA.

Charge separation in a novel artificial photosynthetic reaction center lives 380 ms.

Abstract: An extremely long-lived charge-separated state has been achieved successfully using a ferrocene−zincporphyrin−freebaseporphyrin−fullerene tetrad which reveals a cascade of photoinduced energy transfer and multistep electron transfer within a molecule in frozen media as well as in solutions. The lifetime of the resulting charge-separated state (i.e., ferricenium ion−C60 radical anion pair) in a frozen benzonitrile is determined as 0.38 s, which is more than one order of magnitude longer than any other intramolecular charge recombination processes of synthetic systems, and is comparable to that observed for the bacterial photosynthetic reaction center. Such an extremely long lifetime of the tetrad system has been well correlated with the charge-separated lifetimes of two homologous series of porphyrin−fullerene dyad and triad systems.

Inter‐biome comparison of factors controlling stream metabolism

Abstract: 'SUMMARY 1. We studied whole-ecosystem metabolism in eight streams from several biomes in North America to identify controls on the rate of stream metabolism over a large geographic range. The streams studied had climates ranging from tropical to cool-temperate and from humid to arid and were all relatively uninfluenced by human disturbances. 2. Rates of gross primary production (GPP), ecosystem respiration (R) and net ecosystem production (NEP) were determined using the open-system, two-station diurnal oxygen change method. 3. Three general patterns in metabolism were evident among streams: (1) relatively high GPP with positive NEP (i.e. net oxygen production) in early afternoon, (2) moderate primary production with a distinct peak in GPP during daylight but negative NEP at all times and (3) little or no evidence of GPP during daylight and a relatively constant and negative NEP over the entire day. ', 4. Gross primary production was most strongly correlated with photosynthetically active radiation (PAR). A multiple regression model that included log PAR and stream water soluble reactive phosphorus (SRP) concentration explained 90% of the variation in log GPP. 5. Ecosystem respiration was significantly correlated with SRP concentration and size of the transient storage zone and, together, these factors,explained 73% of the variation in R. The rate of R was poorly correlated with the rate of GPP. 6. Net ecosystem production was significantly correlated only with PAR, with 53% of the variation in log NEP explained by log PAR. Only Sycamore Creek, a desert stream in Arizona, had positive NEP (GPP: R > I), supporting the idea that streams are generally net sinks rather than net sources of organic matter.

Deterministic scale-free networks

Abstract: Scale-free networks are abundant in nature and society, describing such diverse systems as the world wide web, the web of human sexual contacts, or the chemical network of a cell. All models used to generate a scale-free topology are stochastic, that is they create networks in which the nodes appear to be randomly connected to each other. Here we propose a simple model that generates scale-free networks in a deterministic fashion. We solve exactly the model, showing that the tail of the degree distribution follows a power law.

End point of the rp process on accreting neutron stars

Abstract: We calculate the rapid proton ( rp) capture process of hydrogen burning on the surface of an accreting neutron star with an updated reaction network that extends up to Xe, far beyond previous work. In both steady-state nuclear burning appropriate for rapidly accreting neutron stars (such as the magnetic polar caps of accreting x-ray pulsars) and unstable burning of type I x-ray bursts, we find that the rp process ends in a closed SnSbTe cycle. This prevents the synthesis of elements heavier than Te and has important consequences for x-ray burst profiles, the composition of accreting neutron stars, and potentially galactic nucleosynthesis of light p nuclei.

Ethnic Conflict and Civil Society: India and Beyond

Abstract: Scholars have worked either on civil society or on ethnic conflict, but no systematic attempt has yet been made to connect the two. In an attempt to explore the possible links, this article makes two interconnected arguments. First, interethnic and intraethnic networks of civic engagement play very different roles in ethnic conflict. Because they build bridges and manage tensions, interethnic networks are agents of peace. But if communities are organized only along intraethnic lines and the interconnections with other communities are very weak (or do not exist), ethnic violence is then quite likely. Second, civic networks, both intra- and interethnic, can also be broken down into two other types: associational forms of engagement and everyday forms of engagement. This distinction is based on whether civic interaction is formal or not. Both forms of engagement, if robust, promote peace: contrariwise, their absence or weakness opens up space for ethnic violence. Of the two, however, the associational forms turn out to be sturdier than everyday engagement, especially when confronted with attempts by politicians to polarize the people along ethnic lines. Both arguments have significance for theories of ethnic conflict and social capital.

The Influence of Activism by Institutional Investors on R&D

Abstract: Researchers have assumed that large ownership stakes held by institutional investors grant them power to influence R&D investments. We found that ownership alone was insufficient and that instituti...

“Total Synthesis” Supramolecular Style: Design and Hydrogen-Bond-Directed Assembly of Ternary Supermolecules

Abstract: Getting the right balance between intermolecular interactions is crucial for the synthesis of supermolecules in a preconceived manner. The three-component supermolecule in the ternary cocrystal of 3,5-dinitrobenzoic acid, isonicotinamide, and 4-(dimethylamino)benzoic acid (1:1:1) assembles through a "primary" (between the stronger acid and pyridine) and a "secondary" hydrogen-bonding interaction (between the weaker acid and amide).