Theory of Single Electron Spin Relaxation in Si/SiGe Lateral Coupled Quantum Dots

We investigate the spin relaxation induced by acoustic phonons in the presence of spin-orbit interactions in single electron Si/SiGe lateral coupled quantum dots. The relaxation rates are computed numerically in single and double quantum dots, in in-plane and perpendicular magnetic fields. The deformation potential of acoustic phonons is taken into account for both transverse and longitudinal polarizations and their contributions to the total relaxation rate are discussed with respect to the dilatation and shear potential constants. We find that in single dots the spin relaxation rate scales approximately with the seventh power of the magnetic field, in line with a recent experiment. In double dots the relaxation rate is much more sensitive to the dot spectrum structure, as it is often dominated by a spin hot spot. The anisotropy of the spin-orbit interactions gives rise to easy passages, special directions of the magnetic field for which the relaxation is strongly suppressed. Quantitatively, the spin relaxation rates in Si are typically 2 orders of magnitude smaller than in GaAs due to the absence of the piezoelectric phonon potential and generally weaker spin-orbit interactions.Comment: 10 pages, 9 figure

Perceiving the Value of Business Planning

The value of business planning has been subject to much controversy over the past years. In-deed, there appears to be an escalation in empirical research, with opposing implications and diverging approaches to teaching entrepreneurship. Most empirical studies have taken an ex-post, comparative view of the relationship between planning and performance. In this paper, we introduce an ex-ante perspective by formally characterizing the decision of the nascent entrepreneur whether or not to start a business and whether or not to plan beforehand. We focus on the evaluative function of business planning, define the information value of busi-ness planning, identify its influencing factors, and show how costs of business planning de-termine the quality of planning. We find as the crucial aspect of good evaluative business planning that it helps to identify and to sort out poor business ideas before they reach the mar-ket. We contrast our results with conclusions drawn from empirical studies that have been critical of planning. In a setting in which, by construction, planning has a positive value, we question several popular negative implications by showing how they result from an incom-plete sample of entrepreneurs.Business plan, Start-ups, Entrepreneurship, Decision Making, Uncertainty

A-coupled-expanding and distributional chaos

The concept of A-coupled-expanding map, which is one of the more natural and useful ideas generalized the horseshoe map, is well known as a criterion of chaos. It is well known that distributional chaos is one of the concepts which reflect strong chaotic behaviour. In this paper, we focus the relations between A-coupled-expanding and distributional chaos. We prove two theorems that give sufficient conditions for a strictly A-coupled-expanding map to be distributionally chaotic in the senses of two kinds, where A is an irreducible transition matrix.Comment: 10 page

The U-shaped Investment Curve: Theory and Evidence

This paper examines how the investment of financially constrained firms varies with their level of internal funds. We develop a theoretical model of optimal investment under financial constraints. Our model endogenizes the costs of external funds and allows for negative levels of internal funds. We show that the resulting relationship between internal funds and investment is U-shaped. In particular, when a firm's internal funds are negative and sufficiently low, a further decrease leads to an increase in investment. This effect is driven by the investor's participation constraint: when part of any loan must be used to close a financing gap, the investor will provide funds only if the firm invests at a scale large enough to generate the revenue that enables the firm to repay. We test our theory using a data set with close to 100,000 firm-year observations. The data strongly support our predictions. Among other results, we find a negative relationship between measures of internal funds and investment for a substantial share of financially constrained firms. Our results also help to explain some contrasting findings in the empirical investment literature.Financial constraints, capital market imperfections, financial contracts, investment, internal funds, investment-cash flow sensitivity

Theory of Spin Relaxation in Two-Electron Lateral Coupled Quantum Dots

A global quantitative picture of the phonon-induced two-electron spin relaxation in GaAs double quantum dots is presented using highly accurate numerical calculations. Wide regimes of interdot coupling, magnetic field magnitude and orientation, and detuning are explored in the presence of a nuclear bath. Most important, the unusually strong magnetic anisotropy of the singlet-triplet relaxation can be controlled by detuning switching the principal anisotropy axes: a protected state becomes unprotected upon detuning, and vice versa. It is also established that nuclear spins can dominate spin relaxation for unpolarized triplets even at high magnetic fields, contrary to common belief. These findings are central to designing quantum dots geometries for spin-based quantum information processing with minimal environmental impact.Comment: 8 pages, 8 figure

Computer Simulation of Tooth Mobility using Varying Material Properties

Tooth mobility is the major cause of stress on a tooth implant or partial denture and often results in the damage of the device. For many prosthetic devices like dental bridges, a partial denture used for a person who is missing a tooth to give the appearance and function of a tooth, mobility can cause up to double the amount of stress in comparison to a fixed model. Creating a computer simulation of tooth mobility using Finite Element Analysis allows one to understand and predict this movement in order to improve future dental prosthetic devices. The main cause of tooth mobility within the mouth is the periodontal ligament (PDL). This ligament is a soft biological tissue that surrounds the roots of teeth. The tooth moves when a force like mastication, or chewing, causes the ligament to deform. This deformation is due to the small Young’s Modulus of the ligament. The Young’s Modulus determines the stiffness of a material. In the case of the PDL, the Young’s Modulus is sometimes noted to be 30,000 times smaller than that of dentin, this is the material that makes up the majority of the tooth, and of the alveolar bone, this is the bone in which the tooth lies. The deformation of the PDL is also due to the viscoelastic nature of the ligament. The major elastic component of the ligament is collagen, this material allows the PDL to stretch to a certain limit, and the major viscous component of the ligament is the interstitial fluid between the cells, this allows the material to have a fluid-like nature (4)

Monetary and fiscal policy interaction and government debt stabilization

In many developing and developed countries, government debt stabilization is an important policy issue. This paper models the strategic interaction between the monetary authorities who control monetization and the fiscal authorities who control primary fiscal deficits. Government debt dynamics are driven by the interest payments on outstanding debt and the part of the primary fiscal deficits that is not monetized. Modelling the interaction as a differential game, we compare the cooperative equilibrium and the non-cooperative Nash open-loop equilibrium. The well-known unpleasant monetarist arithmetic is reinterpreted in this differential game framework. We consider also the effects of making the Central Bank more independent.Game Theory;Central Banks;Monetary Policy;National Debt;Fiscal Policy;monetary economics

Interactions Between Soft Nanoparticles and Mammalian Cells

Nanoparticles have been of interest to the pharmaceutical industry since the 1980s. The first FDA approved nanoparticle-based therapies included liposomal anesthesia agents. Since then, the amount of FDA-approved nanoparticle therapies remains low. This is because nanoparticle-patient interactions can be very complex and are not well understood. Complicating factors also include increasing obesity rates among the patient population and many small animal pre-clinical trials are completed with healthy, lean animals. The biochemical differences between lean and obese patients prevents early studies from accurately predicting nanoparticle clinical behaviors. Many nanoparticles fail in trails. In this thesis, I aimed to uncover how nanoparticles interact with cells in an obesity-like environment. I focused mainly on nanoparticles made from PEO-PBD di-block polymers (synthesized by Jimmy Mays’s group in chemistry). The di-block polymers form into long, flexible cylinders (“filomicelles” or more generally, cylindrical nanoparticles (CNPs)). CNPs have been previously shown to have favorable circulation times compared to spherical nanoparticles, but I wanted to know how CNP enter cells. Surprisingly, this mechanism is not well-known for any nanoparticle. I focused on the potential interaction between CNPs and the major HDL receptor SR-BI. This was done with in vitro experiments involving the small molecule inhibition and binding site competition of SR-BI. In vivo experiments were also conducted with SR-BI deficient mice and co-injection of CNPs and HDL. I then wanted to study the effects obesity would have on the pharmokinetics profile and biodistribution of CNPs and liposomal nanoparticles (LNPs). LNPs are the most used NPs in the clinic, so they provide a good control to evaluate the possibility of using CNPs in the clinic. I used a combination of controlled diet and leptin deficiency in mice to conduct this study. Interestingly, obesity caused CNPs to localize to the liver faster than lean controls. LNPs had the opposite effect. Further experimentation suggested this was due to different destination cell types within the liver for CNP vs LNP. In the third study, I developed a nucleic acid therapy that can trigger the lipolysis (breakdown) of neutral lipids in mammalian cells using a split-intein technology that I learned as an undergraduate