Our view of phytoplankton has historically revolved around their inability to control their location in space. The term phytoplankton itself underscores this particular difference between phytoplankton and their sessile terrestrial counterparts. Yet there are other differences between land plants and the phytoplankton that are perhaps equally important, beyond this sessile-planktonic dichotomy, to their growth, survival, and productivity. For example, phytoplankton are microbes and thus are short-lived, with generational scales on the order of days or less. An intriguing question to ask is how today���s pelagic ecology would differ, had this temporal difference between plants and phytoplankton been initially emphasized, perhaps by naming these microbes phytoephemera instead? This dissertation addresses certain aspects of the ecology of phytoplankton that result from their having short generational scales. Because they are so short lived, phytoplankton need to adjust their photosynthetic physiology to cope with more rapid changes in irradiance than may matter to longer-lived plants. Photoacclimation on the hours-plus time scales has been studied extensively in the phytoplankton, because its temporal scales match those of vertical mixing processes in the ocean. Yet most phytoplankton exhibit faster photosynthetic responses as well, down to the time scales of seconds. These photosynthetic responses have received considerably less attention in phytoplankton ecology. This dissertation specifically examines these rapid, seconds-to-hour scale photosynthetic responses in phytoplankton. First, the physiological bases of rapid photosynthetic regulation were examined using a numerical model that shows how specific physiological changes in phytoplankton photosystems either constrain or enhance light harvesting. This model is stochastic, and thus replicates certain nonlinear aspects of light harvesting better than equation-based analytical models. Also in this dissertation, a laboratory study is described that examined rapid photosynthetic regulation in three model phytoplankton. Results suggest that rapid photosynthetic regulation is not only constrained to higher eukaryotic phytoplankton, but also occurs in the two dominant marine photosynthetic prokaryotes, Synechococcus and Prochlorococcus. Finally, rapid photosynthetic responses were examined in field assemblages at Station ALOHA in the North Pacific. This ocean region experiences considerable cloud cover, which may result in a strong degree of rapid photosynthetic responses, even in near-surface assemblages. / Graduation date: 2007

Spin and charge density fluctuations are important excitations in the strongly correlated systems, especially in the recently discovered high temperature superconductors. Several different theories on high temperature superconductors have been proposed based on spin fluctuations. However, experiments have also shown the existence of strong charge fluctuations. It is, therefore, desirable to investigate the physical consequences of the coexistence of strong spin and charge density fluctuations. As a first step toward a full understanding of both spin and charge excitations, a self-consistent theory is established. In this self-consistent theory, there are three important quantities, the spin susceptibility, the charge susceptibility, and the phonon Green's function. These three quantities are coupled together by the electron-phonon and phonon-spin fluctuation interactions. The phonon-spin fluctuation interaction is derived by making use of the spin-orbital coupling. For a strongly correlated system, the spin and charge density excitations have to be considered self-consistently. They are intimately related. The effects of antiparamagnons on phonons are also investigated. Antiparamagnons can have dramatic effects on phononic properties. It is found that new modes are formed in the presence of antiferromagnetic spin fluctuations. The de Haas-van Alphen effect in marginal and nearly antiferromagnetic Fermi liquids is studied. It is found that the de Haas-van Alphen frequency is unaffected by the anomalous response functions of the marginal and nearly antiferromagnetic Fermi liquids due to the absence of real parts of self-energies on the imaginary frequency axis. / Graduation date: 1993

The prediction of linear viscoelasticity (LVE) of a polymer melts from the knowledge of their structure has received tremendous attention in recent years. Quite accurate quantitative predictions are obtained for linear polymers, including inverse predictions of molecular weight distributions from knowledge of rheological response. The situation for branched polymers is much more complicated for at least two reasons. First, because of the incredible variety of architectures that can be, and are actually, made in the lab or by industry. Second, because branched polymers are characterised by very broad distributions of relaxation times, which are very dependent on details of the architecture. The main objective of this work is to propose a model suitable for predicting LVE of arbitrary mixtures of (a)symmetric stars and linear molecules, where the interrelation of relaxation processes (as reptation, tube length fluctuations or constraint release process) cannot be predicted a priori. We validate it on a large set of experimental data taken from the literature, from our own experiments or from co-workers. Next, we use it to detect long chain branching (LCB) in sparsely branched polycarbonate samples. This characterization technique, based on the analysis of the relaxation moduli, is compared to solution characterization. A similar work is performed for polyethylene samples, on which we compare our method to classical methods based on the measurement of their intrinsic viscosity or on the analysis of their activation energies spectrum. The success of our model in describing the relaxation of an already broad range of polymer structures gives some hope for understanding the dynamics of more complex systems. Indeed, its structure allows us to easily extend it to H or comb polymers and then, to proceed to polymers always closer to the industrial polymers.

We present predictions for the statistical error due to finite sampling in the presence of thermal fluctuations in molecular simulation algorithms. Expressions for the fluid velocity, density and temperature are derived using equilibrium statistical mechanics. The results show that the number of samples needed to adequately resolve the flow-field scales as the inverse square of the Mach number. The theoretical results are verified for a dilute gas using direct Monte Carlo simulations. The agreement between theory and simulation verifies that the use of equilibrium theory is justified. / Singapore-MIT Alliance (SMA)

Density fluctuations in high temperature fusion plasmas have been a central challenge to the development of fusion power. They are the cause of excessive anomalous losses from the plasma and are still not fully understood. A microwave scattering experiment is performed on the Saskatchewan Torus-Modified (STOR-M) tokamak for the first time to study these density fluctuations with wave-numbers in the range <b><i>k</i></b> = 5 /cm to 10 /cm. The fluctuations are found to follow <i>k¦Ñ_s</i> scaling consistent with ion drift waves; signatures of the electron temperature gradient (ETG) mode connected with anomalous electron losses are not detected. The fluctuation level in the STOR-M is measured to be <i>n_tilda/n</i> ¡Ö 0.1 at a mean perpendicular wave-number of <b><i>k</b>_perp</b></i> ¡Ö 7 /cm and is reported for the first time. The fluctuation levels are inversely proportional to the energy confinement time suggesting that these fluctuations are driving anomalous particle and energy losses from the STOR-M. The system is now fully operational and this work paves the way for future experiments with this equipment.

Dry adhesion systems adhere via physical bonds without any significant contribution from a liquid medium. In nature, these systems are found among the footpads of spiders, lizards and many other small animals, with high adhesion force, low detachment force and elfcleaning properties. These features are highly interesting for biomimetic man-made adhesives. Heavy animals have an adhesion force much higher than its muscle force, and to enable detachment, they have evolved a functional surface with hair-like structures called setae. Each seta branches into numerous microcontact elements that interact with the contacting area. This thesis continue on previous work, analyzing the functional surface in terms of contact geometries and stress distribution, and considers, for the first time, the effect of thermal fluctuations. Numerical and analytical results show how the muscle force is concentrated to a small fraction of the adhesion area, where each microcontact element is trapped in a potential well. The rate of detachment depends on the maximal concentration of stress across the crocontacts. When a seta is axially loaded, the concentration of stress is minimized, whereas radial loading amplifies the concentration of stress by a factor of maximum 68 and enable detachment with the animal’s limited muscle force. The results give theoretical insight in the adhesion and detachment of a functional surface. This knowledge is valuable and can be considered when constructing man-made adhesives with inspiration from nature’s dry adhesion solutions.

Density fluctuations in high temperature fusion plasmas have been a central challenge to the development of fusion power. They are the cause of excessive anomalous losses from the plasma and are still not fully understood. A microwave scattering experiment is performed on the Saskatchewan Torus-Modified (STOR-M) tokamak for the first time to study these density fluctuations with wave-numbers in the range <b><i>k</i></b> = 5 /cm to 10 /cm. The fluctuations are found to follow <i>k¦Ñ_s</i> scaling consistent with ion drift waves; signatures of the electron temperature gradient (ETG) mode connected with anomalous electron losses are not detected. The fluctuation level in the STOR-M is measured to be <i>n_tilda/n</i> ¡Ö 0.1 at a mean perpendicular wave-number of <b><i>k</b>_perp</b></i> ¡Ö 7 /cm and is reported for the first time. The fluctuation levels are inversely proportional to the energy confinement time suggesting that these fluctuations are driving anomalous particle and energy losses from the STOR-M. The system is now fully operational and this work paves the way for future experiments with this equipment.

Noise and time-dependent fluctuations are usually undesirable signals. However, they have many applications. This dissertation deals with two kinds of sensing applications of fluctuation and noise: soil bulk density assessment and bacterium sensing. The measurement of Vibration-Induced Conductivity Fluctuations (VICOF) provides information about the bulk density and other parameters of soils. Bulk density is the physical property of soils that is important to both the agriculture and construction industries. The traditional measurements of soil bulk density are often time-consuming, expensive or destructive. To determine the soil bulk density without the above drawbacks, the VICOF measurement scheme was proposed. The research of VICOF in this dissertation includes two parts: the initial phase of study and the new methods and their theory. In the initial phase of study, the simple experiments, theory, and simulations of VICOF were tested for relations between the soil bulk density, wetness, salinity, and the VICOF data. Then, new measurement arrangements and their theoretical models were proposed to improve the weaknesses of the initial approach (such as large scattering of data due to loose and heavy contacts) and to calculate the relationship between the measured signals and the electromechanical transport parameters of the soils. The bacterium sensing study in this dissertation was proposed to explore simple, practical, rapid, sensitive, specific, portable, and inexpensive ways to detect and recognize bacteria by Fluctuation-Enhanced Sensing (FES). One such potential way of bacterium sensing is to analyze their odor. The research of bacterium sensing also includes two parts: the initial phase of study and the new methods and their theory. The initial phase study was proposed to explore the possibility of detecting and identifying bacteria by sensing their odor via FES with commercial Taguchi sensors. Then the subsequently developed new methods and their theory provide a simple way to generate binary patterns with perfect reproducibility based on the spectral slopes in different frequency ranges at FES. This new type of signal processing and pattern recognition is implemented at the block diagram level using the building elements of analog circuitries and a few logic gates with total power consumption in the microWatts range.

In retrospect, telecommunication technology and services have seen incessant renovation and development. The wave of liberalization is also the inexorable trend in the global telecommunications industry, the telecommunications industry in Taiwan can not be excluded itself from the trend. The telecommunications industry in Taiwan has been opened by degrees and sought to establish a fair competitive environment. In the meantime, there are several important changes no matter in facets of regulatory regimes, industrial structure, technology, or market demand, etc. The environment of telecommunications industry became more volatile than the monopoly one's. We extend the opinion of Noam (2006) who observed the long-term upturn and downturn in the American telecommunications industry and concluded that that volatility and cyclicality will be an inherent part of the telecommunication sector in the future. First, in our thesis we explore the cyclical behavior of Taiwan telecommunications industry. As the turning point of the telecommunications industry may be obscure, we adopt a Markov Regime-Switching model with two regimes representing contraction and expansion. This nonlinear, two states, regime-switching model shows that Taiwan telecommunications industry has suffered from the cyclic fluctuation since the liberalization had been followed out. We focus on the mobile phone industry thereafter in this study. Since three telecommunication-related laws passed in 1996, the mobile phone industry is the first industry implemented the liberalization policy. In the process of the mobile phone industry's evolution, the carriers in this industry all experience the rapid growth in the mobile phone penetration rate and the fierce competition. Hence, to identify the main explanatory factors of the mobile phone industry fluctuation and cycles we introduce an 11-variable vector autoregressive (VAR) model. The empirical results confirm that the mobile phone industry' output can be influenced by five factors mainly including the macroeconomic status, demand, network effect, relative equipment import price, and output price, and furthermore, the impetus of the liberalization policy and the progress of the technology also play an important role beyond the five main factors in terms of the separate carriers' analysis.

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