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Hydrodynamics of Insects. Part 1. Jetting of the Dragonfly Larvae. Part 2. Honeybee at the Air-water Interface: Surfing with the Capillary Wave
Get PDFThis thesis presents the study on the hydrodynamics of two insects commonly known for their aerial adaptation: the dragonfly and the honeybee.
Part 1: Anisopteran dragonflies live underwater in their larval stages. The key factor for their aquatic adaptation is the modified hindgut chamber that is used as a pump. The two main functions of this biological pump are jet propulsion and respiration. Both functions involve jetting and refilling of the chamber through an orifice guard by a tri-leaflet anal valve. Despite it being a unique machinery among insects, associated hydrodynamic studies are limited thus far. In the first part of this thesis, various aspects of the hydrodynamics of the dragonfly larvae’s ventilatory flow are studied. The flow visualization showed that the respiratory flow is laminar but the propulsion flow is turbulent. The hydrodynamic force analysis showed that jetting and refilling phase forces are dominated by quasi-steady momentum flux and unsteady acceleration, respectively. Finally, simultaneous measurement of the anal valve kinematics and jet flow showed that the larvae could influence the direction and magnitude of the jet by controlling the anal valve leaflets.
Part 2: Water-collecting honeybees often fall onto water surfaces. However, bees trapped by the “stickiness” of the water can propel by vibrating their wings, often making it to shore. In the second part of this thesis, the honeybee’s propulsion mechanisms at the air–water interface is studied. The result shows that the bees can achieve three body-lengths per second propulsion speed. High-speed video of their wing motion shows that honeybee’s propulsion involves pulling blobs of water with the underside of the wing, while pushing on a surface wave with its trailing edge. This propulsion mechanism resembles surfing on a self-generated capillary wave. Moreover, their wing vibration generates complicated surface waves and flows, below which the deeper water flow shows a single jet stream. From the wave and flow field measurements, the average force imparted to the surrounding fluid is estimated and compared to the average force calculated from the bee’s body motion. The resulting average forces are of the same order of magnitude, which means that generating wave and flow are both important for the bee’s propulsion.</p
Robotically Assembled Space Telescopes with Deployable Modules: Concepts and Design Methodologies
Get PDFThis thesis first presents a novel architecture for robotically assembled optical telescopes with apertures between 20 m and 100 m, that utilizes only currently available technology. In this architecture, the primary mirror consists of two layers: a reflective layer and a truss backplane layer. The reflective layer is divided into mirror modules, or groups of mirror segments and actuators. The truss backplane layer is divided into truss modules that fold compactly for launch and are deployed in space by the robot. In this thesis, the design methodology of the mirror modules and truss modules is detailed. The ability of the designed truss layer to maintain precision requirements in the presence of typical space environment loads is demonstrated.
This architecture requires the deployment of many truss modules, and thus the deployment must be reliable despite errors introduced during manufacturing. In this thesis, a new simulation-based toolkit for estimating deployment reliability is described, including the experimental validation of the deployment simulation and the Monte Carlo-style method for repeating deployment simulations with different distributions of random fabrication errors to statistically estimate reliability. Using the toolkit, a set of reliability trade studies are then presented, revealing how different types of errors and design parameters affect reliability. Finally, the manufacturing tolerances and design modifications required to ensure high reliability are proposed.
Even if all modules deploy successfully, fabrication errors will still be present and may affect the assembly process. In this thesis, a new simulation method is presented that can model the step-by-step assembly of flexible modules with errors. The method is used to reveal that overall shape errors grow with the number of connections, resulting in significantly decreased surface precision and large-scale deformations from the nominal backplane shape as the size of the backplane increases. The misalignment at each individual connection does not increase as the backplane increases, but can still be much larger than the applied manufacturing tolerances simply due to random combinations. A simple design for the interconnects between modules is then tested, with simulation results demonstrating that it is unlikely to fully engage when the expected errors are present. With this information, a requirement on the complexity of the interconnect design is inferred, and potential modifications that may increase its efficacy are suggested.</p
Development and Applications of Opposed Migration Aerosol Classifiers (OMACs)
Get PDFParticle electrical mobility classification has made important contributions in atmospheric and climate science, public health and welfare policy, and nanotechnology. The measurement of the particle size distribution is integral to characterization of the sub-micrometer aerosol particle population. The differential mobility analyzer (DMA) has been the primary instrument for such measurements. Aerosol particles are transmitted through the DMA on the condition that their migration time across an electrode separation distance is approximately equal to the advective transport time from the inlet to the outlet; these two travel times are induced by an electric field between the electrodes and an orthogonal particle-free carrier gas flow. However, scientific interest has increasingly shifted toward both the nanometer-scale particle size distribution and the miniaturization of instruments. The classical DMA suffers from severe resolution degradation and diffusional losses of nanometer-scale particles, as well as being ill-suited for lightweight, low-power applications. It is relatively recently that miniaturization of DMAs for portable applications has appeared in the scientific literature. Additionally, an abundance of efforts on DMA design have yielded instruments that can probe the nanometer-scale particle size regime, though their use is restricted to the laboratory as they require powerful pumps and operate at near-turbulent flow conditions.
The opposed migration aerosol classifier (OMAC) is a novel concept for particle electrical mobility classification introduced about a decade ago. In contrast to the DMA, the OMAC transmits particles on the condition that their migration velocity in an electric field is approximately equal to the advective transport velocity by a particle-free flow; the migration velocity is induced by an electric field between two porous electrodes, through which a particle-free cross-flow moves in an anti-parallel direction to the electric field. Because of this flow field arrangement, the length scale over which diffusion must act to affect resolution is the entire electrode separation distance in the OMAC, whereas in the DMA it is smaller by about a factor of the sample-to-carrier gas flow rate ratio. As a result, resolution degradation due to diffusion occurs at a lower operating voltage in the OMAC compared to the DMA. Not only does this suggest a larger dynamic range for the OMAC, but also the capability to classify nanometer-scale particles with greater resolution and lower operating voltages and flow rates.
Motivated by the theoretical advantages of an OMAC compared to a DMA, this thesis details the design and characterization of OMAC classifiers to verify the performance of realized OMACs. The capabilities of prototype radial geometry OMACs were first investigated. They demonstrated sub-20 nm particle diameter classification at high resolution using modest flow rates, making them amenable to non-laboratory applications. Additionally, the delayed resolution degradation of OMACs was validated by the maintenance of resolution at operating voltages below those at which a DMA would have experienced severely degraded resolution.
Various applications were then carried out to validate the use of OMACs in both nanometer-scale and sub-micrometer particle size regimes. The first OMAC application was in the field of biomolecule analysis, in which the radial OMAC was operated as an ion mobility spectrometer coupled to a mass spectrometer to resolve conformations of sub-2 nm biomolecules. The resolving power of the radial OMAC was high enough to differentiate peptide stereoisomers and populations of thermally-induced biomolecule conformations.
In the aerosol measurement field, aerosol particle size distributions are typically obtained by passing the sample through an ionization source to impart charges on the sample particles, before mobility separation and detection. The detected signal must be inverted, using detector efficiencies, classifier transfer functions, and charge distributions, to obtain the true particle size distribution. While detector efficiencies and classifier transfer functions are typically well-quantified for the specific instruments used in the measurement, the charge distribution is almost never calculated for the specific measurement conditions. This is due both to the computational expense of, as well as the present impracticability of obtaining all the information needed for carrying out such calculations. Aerosol scientists typically use one parameterization of the charge distribution, regardless of the measurement conditions. Thus, the charge distribution represents the greatest source of bias in particle size distribution measurements. Having demonstrated high resolution of sub-2 nm ions, the radial OMAC was then used to obtain mobility distributions of gas ions formed in a bipolar aerosol charger. These ion mobility distributions were then used to quantify the particle size distribution bias due to the use of the common charge distribution parameterization.
In atmospheric nucleation field, the radial OMAC was deployed as part of an airborne particle detection payload over a large cattle feedlot. Again, the radial OMAC demonstrated the ability to obtain nanometer-scale particle size distributions, that, when paired with a concurrently-deployed DMA, allowed for the measurement of ambient particle size distributions over the entire sub-micrometer size range. A spatially-dense set of such particle size distributions allowed for the calculation of particle growth rates from a clear nucleation event from cattle feedlot emissions.
Finally, OMACs were evaluated for their performance at low-flow rate operation to obtain sub-micron particle size distribution for deployment as portable exposure monitors, distributed network area monitors, and unmanned aerial vehicle instrumentation. The radial OMAC showed high fidelity to a reference instrument in reported ambient particle size distributions for nearly 48 hours of unattended operation. A planar geometry OMAC prototype was designed and characterized as well, indicating design and construction issues that caused deviations from ideal behavior. The planer OMAC qualitatively agreed with a reference instrument in reported ambient particle size distributions for about 12 hours of unattended operation. Both radial and planar OMACs were more compact, lower in weight, and less demanding in power consumption than a classical DMA, showing high potential for further miniaturized instrumentation development.</p
New Techniques for Noble Gas Geochronometry and Thermochronometry
Get PDFNoble gases were among the first species measured by mass spectrometry and interrogated for geochemical information about the solid Earth. The analytical challenge of measuring them has driven technological development in the field, and new applications have in turn followed from new developments. In the first chapter, I present developments that bolster an existing technique, the (U–Th)/Ne system, by verifying the theoretical underpinnings of the method and by exploring its application in several minerals. In the second chapter, I show that the hematite (U–Th)/Ne system is a sound geochronometer for use in the upper crust and a potent thermochronometer for exploring mid-crustal processes. In the third chapter I show significant advances toward using a quadrupole ion trap as a noble gas mass spectrometer, including the first static vacuum measurements. This technique provides new opportunities for low abundance noble gas measurements through its ultra low dark noise time of flight measurement approach and its high resolution, high mass range scanning capabilities. The quadrupole ion trap can measure lower concentrations of rare species like 3He and 21Ne on Earth, allowing us to make more precise determinations of cosmogenic exposure ages, and it can measure species with much higher resolution than is currently possible on most spaceflight instruments, allowing us to perform measurements on planetary surfaces and in deep space that are currently reserved to terrestrial laboratories. Finally, in the fourth chapter I demonstrate that an old, largely abandoned technique, (U–Th)/He geochronometry, has useful applications now that we fully understand its limitations
Essays on Timing and Economic Behavior
Get PDFEconomic activities unfold over time. How does timing influence our choices? How do we control our timing? Economic agents are considered to satisfy their preferences in an optimal fashion subject to constraints. Each chapter in this thesis tackles a different one of these three elements where the timing of behavior is central.
In the first chapter, I study the impact of loss aversion on preferences for labor versus leisure. In a real-effort lab experiment, I show that a worker's willingness to persevere in a task is influenced by information about task completion time. To directly assess the location and impact of reference dependence, I structurally estimate labor-leisure preferences with a novel econometric approach drawing on computational neuroscience. Once participants exceed an expectations-based reference point, their subjective values of time rise sharply, and they speed up at the cost of reduced work quality and forgone earnings.
In the second chapter, I propose and implement a method to test the optimality of individual deliberative time allocation. I also conduct experiments to study perceptual decision making in both simple decisions, where the difference in values between better and worse choices is known, and complex decisions, where this value difference is uncertain. The test reveals significant departures from optimality when task difficulty and monetary incentives are varied. However, a recently developed model based on optimality provides an improvement in fit over its predecessor.
In the third chapter, I investigate the effects of memory constraints on choice over sequentially presented options. In a study that combines experimental paradigms used to analyze memory and judgment separately, I find a close link between order effects in choice and in memory. I show that cognitive load stemming from either an externally-imposed distractor or naturally-occuring fatigue substantially weakens primacy effects. Thus disrupting memory encoding and consolidation can potentially alleviate bias in judgment.</p
Concentration Inequalities of Random Matrices and Solving Ptychography with a Convex Relaxation
Get PDFRandom matrix theory has seen rapid development in recent years. In particular, researchers have developed many non-asymptotic matrix concentration inequalities that parallel powerful scalar concentration inequalities. In this thesis, we focus on three topics: 1) estimating sparse covariance matrix using matrix concentration inequalities, 2) constructing the matrix phi-entropy to derive matrix concentration inequalities, 3) developing scalable algorithms to solve the phase recovery problem of ptychography based on low-rank matrix factorization.
Estimation of covariance matrix is an important subject. In the setting of high dimensional statistics, the number of samples can be small in comparison to the dimension of the problem, thus estimating the complete covariance matrix is unfeasible. By assuming that the covariance matrix satisfies some sparsity assumptions, prior work has proved that it is feasible to estimate the sparse covariance matrix of Gaussian distribution using the masked sample covariance estimator. In this thesis, we use a new approach and apply non-asymptotic matrix concentration inequalities to obtain tight sample bounds for estimating the sparse covariance matrix of subgaussian distributions.
The entropy method is a powerful approach in developing scalar concentration inequalities. The key ingredient is the subadditivity property that scalar entropy function exhibits. In this thesis, we construct a new concept of matrix phi-entropy and prove that matrix phi-entropy also satisfies a subadditivity property similar to the scalar form. We apply this new concept of matrix phi-entropy to derive non-asymptotic matrix concentration inequalities.
Ptychography is a computational imaging technique which transforms low-resolution intensity-only images into a high-resolution complex recovery of the signal. Conventional algorithms are based on alternating projection, which lacks theoretical guarantees for their performance. In this thesis, we construct two new algorithms. The first algorithm relies on a convex formulation of the ptychography problem and on low-rank matrix recovery. This algorithm improves traditional approaches' performance but has high computational cost. The second algorithm achieves near-linear runtime and memory complexity by factorizing the objective matrix into its low-rank components and approximates the first algorithm's imaging quality.</p
Spatial Profiles in the Singular Solutions of the 3D Euler Equations and Simplified Models
Get PDFThe partial differential equations (PDE) governing the motions of incompressible ideal fluid in three dimensional (3D) space are among the most fundamental nonlinear PDEs in nature and have found a lot of important applications. Due to the presence of super-critical non-linearity, the fundamental question of global well-posedness still remains open and is generally viewed as one of the most outstanding open questions in mathematics. In this thesis, we investigate the potential finite-time singularity formation of the 3D Euler equations and simplified models by studying the self-similar spatial profiles in the potentially singular solutions.
In the first part, we study the self-similar singularity of two 1D models, the CKY model and the HL model, which approximate the dynamics of the 3D axisymmtric Euler equations on the solid boundary of a cylindrical domain. The two models are both numerically observed to develop self-similar singularity. We prove the existence of a discrete family of self-similar profiles for the CKY model, using a combination of analysis and computer-aided verification. Then we employ a dynamic rescaling formulation to numerically study the evolution of the spatial profiles for the two 1D models, and demonstrate the stability of the self-similar singularity. We also study a singularity scenario for the HL model with multi-scale feature.
In the second part, we study the self-similar singularity for the 3D axisymmetric Euler equations. We first prove the local existence of a family of analytic self-similar profiles using a modified Cauchy-Kowalevski majorization argument. Then we use the dynamic rescaling formulation to investigate two types of initial data with different leading order properties. The first initial data correspond to the singularity scenario reported by Luo and Hou. We demonstrate that the self-similar profiles enjoy certain stability, which confirms the finite-time singularity reported by Luo and Hou. For the second initial data, we show that the solutions develop singularity in a different manner from the first case, which is unknown previously. The spatial profiles in the solutions become singular themselves, which means that the solutions to the Euler equations develop singularity at multiple spatial scales.
In the third part, we propose a family of 3D models for the 3D axisymmetric Euler and Navier-Stokes equations by modifying the amplitude of the convection terms. The family of models share several regularity results with the original Euler and Navier-Stokes equations, and we study the potential finite-time singularity of the models numerically. We show that for small convection, the solutions of the inviscid model develop self-similar singularity and the profiles behave like travelling waves. As we increase the amplitude of the velocity field, we find a critical value, after which the travelling wave self-similar singularity scenario disappears. Our numerical results reveal the potential stabilizing effect the convection terms.</p
Seismogeodetic Imaging of Active Crustal Faulting
Get PDFMonitoring microseismicity is important for illuminating active faults and for improving our understanding earthquake physics. These tasks are difficult in urban areas where the SNR is poor, and the level of background seismicity is low. One example is the Newport-Inglewood fault (NIFZ), an active fault that transverses the city of Long-Beach (LB). The catalog magnitude of completeness within this area is M=2, about one order of magnitude larger than along other, less instrumented faults in southern California. Since earthquakes obey a power-law distribution according to which for each unit drop in magnitude the number of events increases by a tenfold, reducing the magnitude of completeness along the NIFZ will significantly decrease the time needed for effective monitoring. The LB and Rosecrans experiments provides a unique opportunity for studying seismicity along the NIFZ. These two array contain thousands of vertical geophones deployed for several-months periods along the NIFZ for exploration purposes. The array recordings are dominated by noise sources such as the local airport, highways, and pumping in the nearby oil fields. We utilize array processing techniques to enhance the SNR.We downward continue the recorded wave field to a depth of a few kilometers, which allows us to detect signals whose amplitude is a few percent of the average surface noise. The migrated wave field is back-projected onto a volume beneath the arrays to search for seismic events. The new catalog illuminates the fault structure beneath LB, and allows us to study the depth-dependent transition in earthquake scaling properties.
Deep aseismic transients carry valuable information on the physical conditions that prevail at the roots of seismic faults. However, due the limited sensitivity of geodetic networks, details of the spatiotemporal evolution of such transients are not well resolved. To address this problem, we have developed a new technique to jointly infer the distribution of aseismic slip from seismicity and strain data. Our approach relies on Dieterich (1994)'s aftershock model to map observed changes in seismicity rates into stress changes. We apply this technique to study a three month long transient slip event on the Anza segment of the San Jacinto Fault (SJF), triggered by the remote Mw7.2, 2010 El Mayor-Cucapah (EMC) mainshock.
The EMC sequence in Anza initiated with ten days of rapid (≈100 times the longterm slip rate), deep (12-17 km) slip, which migrated along the SJF strike. During the following 80 days afterslip remained stationary, thus significantly stressing a segment hosting the impending Mw5.4 Collins Valley mainshock. Remarkably, the cumulative moment due to afterslip induced by the later mainshock is about 10 times larger than the moment corresponding to the mainshock and its aftershocks. Similar to sequences of large earthquakes rupturing fault gaps, afterslip generated by the two mainshocks is spatially complementary. One interpretation is that the stress field due to afterslip early in the sequence determined the spatial extent of the late slip episode. Alternatively, the spatial distribution is the result of strong heterogeneity of frictional properties within the transition zone. Our preferred model suggests that Anza seismicity is primarily induced due to stress transfer from an aseismically slipping principal fault to adjacent subsidiary faults, and that the importance of earthquake interactions for generating seismicity is negligible.</p
The Catalytic and Mechanical Properties of Lithium Battery Electrodes
Get PDFThe mass adoption of electric vehicles warrants higher energy densities at lower costs. Novel chemistries such as Li-S or Li-air, high energy density anodes such as lithium (Li) metal are some of the ways to address the aforementioned issue. However, many scientific challenges must be overcome in order to achieve the successful commercialization of these batteries. For Li-air, poor cyclability and low coulumbic efficiency are key obstacles. The search for cathode materials that exhibit high capacity, low discharge/charge overpotential and chemical stability over many cycles is a major area of interest in the field. On the anode side, the application of Li metal is stumped by uncontrollable dendrite growth during the charging, and existing methods such as pulsed charging, physical suppression, and additives in the electrolyte have only had alleviating effects.
The first part of this thesis investigates the suitability of various materials as Li-air cathodes. We fabricated 3-dimensional architected electrodes using a variety of materials including Au, Ni, Ti, LaCoO3 (LCO), LaNiO3 (LNO), and LaNi0.5Co0.5O3 (LNCO). Their performances in capacity, overpotential, and cyclability were assessed using galvanostatic battery testing methods. The reaction products were investigated using spectroscopic techniques such as FTIR and Raman. Our experiments corroborated recent findings that even trace moisture contamination can dramatically influence discharge product composition and morphology. Furthermore, Ni nanoparticles may serve as a carbon substitute in investigating the properties of non-conductive catalysts under specific potential windows. By incorporation the perovskites into a Ni based conductive mesh, we found the oxygen reduction reaction capability of the three materials to be ranked as LCO>LNCO>LNO, and the chemical stability ranked as LCO>LNO>LNCO. The instability of DMSO due to chemical reactions with discharge products is observed and discussed in the context of the solution-mediated mechanism of Li2O2 growth. The second part of the thesis investigates the nano-mechanical properties of Li (bcc), as a function of size, temperature, and crystal grain orientation. At room temperature the power law exponent of the strength vs. size log-log plot is -0.68, while at 90°C this value is increased to -1.00. A factor of 3 decrease in the yield strength at 90°C is observed, and the morphology of deformation was found to transition from localized slip planes to homogeneous barreling. Our collaborators at Carnegie Mellon University calculated the elastic constants of Li from 78 K to 440 K (melting temperature of Li is 453 K), and is found to be within reasonable agreement with existing experimental data where applicable (78 -300 K). We proceeded to calculate the elastic and shear moduli of single crystal Li as a function of temperature and orientation. We found that due to the extreme anisotropy of Li, there is a factor of ~4 difference between the strongest and weakest orientation of both the elastic and shear moduli. Our findings are discussed in the context of Li anodes, where we highlight the importance of taking into consideration the size-effect and anisotropy when designing solid electrolytes, or modeling dendrite growth behavior. </p
Constant Stress and Pressure Rheology of Dense Colloidal Suspensions
Get PDFThis thesis is a computational investigation on several aspects of the constant stress and pressure rheology of dense polydisperse colloidal suspensions. Using bidisperse suspensions as a model, we first study the influences of size polydispersity on short-time transport properties. The hydrodynamic interactions are calculated using a polydisperse implementation of Stokesian Dynamics (SD) via a Monte-Carlo approach. We carefully compare the SD computations with existing theoretical and numerical results, and critically assess the strengths and weaknesses of the SD algorithm. For suspensions, we find that the Pairwise Additive (PA) approximations with the Percus-Yevick structural input is valid up to volume fraction φ=0.1. We also develop an semi-analytical approximation scheme to predict the wavenumber-dependent partial hydrodynamic functions based on the δγ-scheme of Beenakker & Mazur [Physica 120A (1983) 388 & 126A (1984) 349], which is shown to be valid up to φ=0.4.
To meet the computation requirements of dynamic simulations, we then developed the Spectral Ewald Accelerated Stokesian Dynamics (SEASD) based on the framework of SD with extension to compressible solvents. The SEASD uses the Spectral Ewald (SE) method [Lindbo & Tornberg, J. Comput. Phys. 229 (2010) 8994] for mobility computation with flexible error control, a novel block-diagonal preconditioner for the iterative solver, and the Graphic Processing Units (GPU) acceleration. For further speedup, we developed the SEASD-nf, a polydisperse extension of the mean-field Brownian approximation of Banchio & Brady [J. Chem. Phys. 118 (2003) 10323]. The SEASD and SEASD-nf are extensively validated with static and dynamic computations, and are found to scale as O(NlogN) with N the system size. The SEASD and SEASD-nf agree satisfactorily over a wide range of parameters for dynamic simulations.
Next, we investigate the colloidal film drying processes to understand the structural and mechanical implications when the constant pressure constraint is imposed by confining boundaries. The suspension is sandwiched between a stationary substrate and an interface moving either at a constant velocity or with constant imposed stress. Using Brownian Dynamics (BD) simulations without hydrodynamic interactions, we find that both fast and slow interface movement promote crystallization via distinct mechanisms. The most amorphous suspension structures occur when the interface moves at a rate comparable to particle Brownian motion. Imposing constant normal stresses leads to similar suspension behaviors, except that the interface stops moving when the suspension osmotic pressure matches the imposed stress. We also compare the simulation results with a continuum model. This work reveals the critical role of interface movement on the stress and structure of the suspension.
Finally, we study the constant shear stress and pressure rheology of dense colloidal suspensions using both BD and SEASD-nf to identify the role of hydrodynamic interactions. The constant pressure constraint is imposed by introducing a compressible solvent. We focus on the rheological, structural, and dynamical characteristics of flowing suspensions. Although hydrodynamic interactions profoundly affect the suspension structure and dynamics, they only quantitatively influence the behaviors of amorphous suspensions. The suspension becomes glassy, i.e., exhibits flow-arrest transitions, when the imposed pressure is high, and reveals the Shear Arrest Point (SAP) in the non-Brownian limit. From a granular perspective, we find that the suspensions move away from the arrested state in a universal fashion regardless of the imposed pressure, suggesting the critical role of the jamming physics. The hydrodynamic simulations quantitatively agree with the experiments of Boyer et al. [Phys. Rev. Lett. 107 (2011) 188301] with a volume fraction shift. The results at all imposed stresses and pressures reveal a generalized Stokes-Einstein-Sutherland relation with an effective temperature proportional to the pressure. We develop a model that accurately describes the rheology and diffusion of glassy suspensions. Our results show the critical role of pressure on the behaviors of dense colloidal suspensions.</p