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Fe-Mg and Ni Partitioning between Olivine and Silicate Melt
Get PDFThe mineral olivine is abundant in a wide range of mafic igneous rocks from around the solar system. The fractionation, or accumulation, of olivine often exerts a major control on the observed variations in magma and whole-rock compositions. We performed experiments on a synthetic Hawaiian picrite and examined the olivine (ol)-liquid (liq) partitioning of Mg and Fe2+. These experiments show that the exchange coefficient, KD, Fe2+-Mg=(FeO/MgO)ol/(FeO/MgO)liq , by weight, is 0.345±0.009 (1σ) and is independent of temperature and liquid composition. Using this result, we estimate that parental liquids for tholeiites from Kilauea, Mauna Loa, and Mauna Kea have approximately 19-21 wt. % MgO. Published experiments on model Martian compositions suggest that for the Fe-enriched and Al-depleted Martian basalts a slightly higher KD,Fe2+-Mg of 0.36 is more appropriate. Using this value we conclude that the olivine-phyric shergottites Y 980459, NWA 5789, 2990, and EETA 79001 are possible liquid compositions (others are not); if the canonical KD,Fe2+-Mg of 0.30 were used, we would have concluded that none of the bulk meteorites represent liquids.
The behavior of Ni is nearly unique among most other major and trace elements: it is compatible in olivine. This compatibility is useful in constraining the evolution of lavas, as their Ni contents will be very sensitive to the fractionation or accumulation of olivine. We performed experiments investigating the partitioning of Ni between a liquid and olivine of approximately constant composition over a range of temperatures and pressures. These experiments successfully separate the effects of composition from those of temperature and pressure, showing that, for our liquid with ~ 18 wt. % MgO, the ol-liq Ni partition coefficient (by wt.) decreases from 5.0 to 3.8 as the temperature and pressure increase from 1400 to 1550°C and 1-atm to 3.0 GPa, respectively. We show that this temperature and pressure effect may contribute to the generation of high-NiO olivines observed in Hawaiian and other ocean-island basalts.</p
Combining Rational and Evolutionary Approaches to Optimize Enzyme Activity in Saccharomyces cerevisiae
Get PDFMetabolic engineering has become an increasingly important tool for the production of bulk and fine chemicals. New biosynthetic pathways can be built in a tractable production host using enzymes from a wide variety of organisms. However, these enzymes did not evolve to function in their new host, and as a result their activity may be unacceptably low. Additionally, the host has not adapted to support this new pathway, and its response to any new stresses imposed by the pathway may further limit productivity. I describe two methods for optimizing the host-enzyme interface, using an evolutionary approach to adapt an enzyme to its new host and a rational approach to modify the host in response. Using a synthetic RNA switch to screen for improvements in enzymatic activity in vivo, I increased the activity of a model enzyme more than 30-fold. I then used a systems-level analysis of the host to identify a stress, heme depletion, that the enzyme placed on its host. Alleviating that stress increased the activity of an optimized enzyme by a further 2.3-fold. These results highlight the advantages of combining systems and synthetic biology during the construction of a metabolic pathway. I also consider options for extending the uses of synthetic RNA switches both earlier and later in the pathway development process. An RNA switch could first be used in a functional screen for enzyme discovery and then be used to adapt the newly discovered enzyme to its production host. Finally, a variant of that switch could be used to dynamically regulate a biosynthetic pathway and improve the pathway reliability
Symmetries in Three-Dimensional Superconformal Quantum Field Theories
Get PDFMany examples of gauge-gravity duality and quantum equivalences of different-looking three-dimensional Quantum Field Theories indicate the existence of continuous symmetries whose currents are not built from elementary, or perturbative, elds used to write down the Lagrangian. These symmetries are called hidden or nonperturbative.
We describe a method for studying continuous symmetries in a large class of three-dimensional supersymmetric gauge theories which, in particular, enables one to explore nonperturbative global symmetries and supersymmetries. As an application of the method, we prove conjectured supersymmetry enhancement in strongly coupled ABJM theory from N = 6 to N = 8 and nd additional nonperturbative evidence for its duality to the N = 8 U(N) SYM theory for the minimal value of the Chern-Simons coupling. Hidden supersymmetry is also shown to occur in N = 4 d = 3 SQCD with one fundamental and one adjoint hypermultiplets. An innite family of N = 6 d = 3 ABJ theories is proved to have hidden N = 8 superconformal symmetry and hidden parity on the quantum level. We test several conjectural dualities between ABJ theories and theories proposed by Bagger and Lambert, and Gustavsson by comparing superconformal indices of these theories. Comparison of superconformal indices is also used to test dualities between N = 2 d = 3 theories proposed by Aharony, the analysis of whose chiral rings teaches some general lessons about nonperturbative chiral operators of strongly coupled 3d supersymmetric gauge theories.
As another application of our method we consider examples of hidden global symmetries in a class of quiver three-dimensional N = 4 superconformal gauge theories. Finally, we point out to the relations between some basic properties of superconformal N = 6 theories
and their symmetries.
The results presented in this thesis were obtained in a series of papers [1, 2, 3, 4, 5].</p
Search for Signatures of Extra Dimensions in the Diphoton Mass Spectrum with the CMS Detector
Get PDFA search for signatures of extra dimensions in the diphoton invariant-mass spectrum has been performed with the Compact Muon Solenoid detector at the Large Hadron Collider. No excess of events above the standard model expectation is observed using a data sample collected in proton-proton collisions at √s = 7 TeV corresponding to an intergrated luminosity of 2.2 fb−1. In the context of the Randall–Sundrum model, lower limits are set on the mass of the first graviton excitation in the range of 0.86–1.84 TeV, for values of the associated coupling parameter k ̃between 0.01 and 0.10. Additionally, in the context of the large-extra-dimensions model, lower limits are set on the effective Planck scale in the range of 2.3–3.8 TeV at the 95% confidence level. These are the most restrictive bounds to date
One the P-Adic Local Invariant Cycle Theorem
Get PDFThe aim of this paper is to consider the -adic local invariant cycle theorem in the mixed characteristic case.
In the first part of the paper, via case-by-case discussion, we construct the -adic specialization map, and then write out the complete conjecture in -adic case. We proved the theorem in good reduction and semistable reduction cases.
In the second part of the paper, by using Berthelot, Esnault and R\"{u}lling's trace morphisms in [BER], we first prove the case of coherent cohomology, then we extend it to the Witt vector cohomology, and we then get a result on the Frobenius-stable part of the Witt vector cohomology, which corresponds the slope 0 part of the rigid cohomology, we then get the general -adic local invariant cycle theorem.
We also give another approach in the and cases in the general case.
In the last part of the paper, based on Flach and Morin's work on the weight filtration in the -adic case, we consider the -adic analogous result (which, together with the -adic's result, serves as a part to prove the compatibility of the Weil-etale cohomology with the Tamagawa number conjecture). This is a direct corollary of the local invariant cycle theorem by taking the weight filtration. And we also consider some typical examples that the weight filtration statement could be verified by direct computations.</p
Localization of Gauge Theories on the Three-Sphere
Get PDFWe describe the application of localization techniques to the path integral for supersymmetric gauge theories in three dimensions. The localization procedure reduces the computation of the expectation value of BPS observables to a calculation in a matrix model. We describe the ingredients of this model for a general quiver gauge theory and the incorporation of supersymmetric deformations and observables.
We use the matrix model expressions to test several duality conjectures for supersymmetric gauge theories. We perform tests of mirror symmetry of three-dimensional quiver gauge theories and of Seiberg-like dualities. Specifically, we explicitly show that the partition functions of the dual pairs, which are highly nontrivial functions of the deformations, agree. We describe extensions of these dualities which can be inferred from the form of the partition functions. We review the application of the matrix model to the study of renormalization group flow and the space of conformal field theories in three dimensions.</p
Discrete Differential Form Subdivision and Vector Field Generation over Volumetric Domain
Get PDFThis thesis presents a new method to construct smooth l- and 2-form subdivision schemes over the 3D volumetric domain. Based on the subdivided 1- and 2-form coefficient field, smooth vector fields can be constructed using Whitney forms. To obtain stencils in the regular setting, classical 0-form subdivision and linear 1- and 2-form subdivision over the octet mesh are introduced. Then, convoluting with a smooth operator, smooth 1- and 2-form subdivision schemes in the regular case can be determined up to one free parameter. This parameter can be determined by a novel technique based on spectrum and momentum considerations. However, artifacts exist in boundary regions because of the incomplete regular support and the shrinking feature of the original 0-form subdivision scheme. To address these problems, the projection-scaling method and the expansion method are introduced and compared. The former method projects arbitrary discrete differential forms to a subspace spanned by low-order potential fields. The algorithm subdivides these potential fields and reconstructs the discrete form in the refined level using linear combinations. Scaling is included for elements near the boundary to offset the effect of mesh shrinkage. Alternatively, for the expansion method, a compatible nonshrinking 0-form subdivision scheme is constructed first. Based on the new 0-form subdivision method, extending 1- and 2-forms beyond the boundary becomes natural. In the experiment, no noticeable artifacts, including attenuation, enlarging or undesirable bend, are found in practice
Investigations into the Conditions Necessary for Stochastic Eternal Inflation
No full textTheories of cosmological inflation, an early exponential expansion of the universe, have solved the
horizon, flatness, and monopole problems in addition to successfully predicting properties of the
fluctuations in the cosmic microwave background. Many of these theories have the property, known as
eternal inflation, where inflation never ends everywhere at the same time and where there are always
regions of exponentially expanding inflating space. The details of inflation are not known at this
time and it would be interesting to estimate how generic eternal inflation is in the space of possible
inflaton potentials. Of the several ways that inflation can be eternal, we focus here on the one, known
as stochastic eternal inflation, where inflation is prevented from ending everywhere by quantum
fluctuations in the inflaton field exceeding its classical motion. We argue that the conditions currently
used to classify a trajectory as stochastically eternal are inadequate for general trajectories where the
inflaton field may classically have a large velocity or be moving up its potential and are therefore illsuited
to studying how generic stochastic eternal inflation is. We propose an improved condition that
takes these possibilities into account as well as more accurately calculating the quantum fluctuations
using a perturbative Langevin method developed elsewhere. We investigate this condition in specific
inflaton potentials and find examples where this condition deviates significantly from the one usually
used in addition to finding examples where the mechanisms for eternal inflation are seemingly met
even though space is not inflating
Studies of Exciton Condensation and Transport in Quantum Hall Bilayers
Get PDFThis thesis is a report of the transport properties of bilayer two-dimensional electron systems found in GaAs/AlGaAs double quantum well semiconductor heterostructures. When a strong perpendicular magnetic field is applied so that the total Landau filling factor is equal to one and if the two layers are close enough together, a novel quantum Hall (QH) state with strong interlayer correlations can form. This QH state is often described as an excitonic condensate, in which electrons in one layer pair with holes in the other. As neutral particles, excitons feel no Lorentz force and are not confined to the edges of the bilayer system like charged quasiparticles are. Instead, excitons are expected to be able to move freely through the bulk and even flow without any dissipation under proper conditions (i.e.,~excitonic superfluidity). Counterflow studies that directly probe the bulk verify this exciton transport in the electrically insulating interior. We also report on studies of the phase boundary between the correlated and uncorrelated phases at total Landau filling factor one as the effective interlayer separation is tuned. When both phases are fully spin polarized at high Zeeman energy, the phase transition is much broader than when the uncorrelated phase is incompletely polarized at low Zeeman energy. This suggests a possible change in the nature of the phase transition in the regime of complete spin polarization
Wavelength-Scale Confinement of Light and Its Applications in On-Chip Photonic Devices
Get PDFWe present design and experimental work toward building room temperature, continuous-wave (CW) lasers with a cavity that confines light to a volume of ≤ (λ/n)3. We begin with the mechanisms of strong optical confinement using dispersive metals and photonic crystals. Finite-difference time-domain methods (FDTD) are used to simulate the behavior of electromagnetic fields in the cavity; fast Fourier transform from FDTD-generated near-field data calculates the far-field radiation pattern from the microcavity laser.
We then present our investigations into designs where metals are incorporated into microdisk and photonic crystal optical cavities to curb or redirect radiation loss. The significant effects of boundary conditions and substrate feedback on far-field radiation directionality are studied. We evaluate the threshold gain required to achieve room temperature lasing in these metallo-dielectric cavities.
While studying the confinement mechanism of photonic crystals on metal substrate, it became clear that room temperature lasing can be achieved in optically-thick photonic crystal cavities, where the thicker semiconductor layer would give us more freedom in designing the vertical p-i-n doping profile within, for a less resistive and leaky electrical path for current injection operation. We fabricate and demonstrate single-mode room temperature lasing by optical pumping in an optically- thick single-defect cavity.
We move on to present our design and characterization of coupled-cavity photonic crystal lasers operating with CW, high output power, and directional emission. Single-mode stable emission with output power on the order of 10 μW and linear polarization was achieved. Moreover, we switched from the commonly used InGaAsP quantum well material to the lesser-known InAsP quantum wells in InP cladding, and found that the large band-edge offset between InAsP and InP made a world of difference in achieving high power operation despite the large thermal resistance in the device.
For a microcavity laser with directional radiation, Purcell-enhanced spontaneous emission, and diminished effects due to feedback from surrounding structures such as the substrate, nanobeam photonic crystal lasers are analyzed, fabricated, and characterized. Despite thermal resistance an order of magnitude higher than their 2D counterparts, quasi-CW operation with a soft threshold turn-on was achieved.
Much work was done to optimize fabrication techniques in order to realize the optical cavity designs with little fabrication error. We detail the high-contrast hydrogen silsesquioxane (HSQ) electron-beam lithography and deep vertical dry etch procedures especially developed for this work.
Lastly, related projects on nonlinear silicon photonic devices are presented. Synthetic nonlinear polymer is integrated on to the silicon photonic platform to achieve low half-wave voltage electro-optic modulation. Causes and magnitude of the nonlinear loss particular to silicon waveguides with sub-μm2 cross-section are evaluated.</p