Cooling a mechanical resonator via coupling to a tunable double quantum dot

We study the cooling of a mechanical resonator (MR) that is capacitively coupled to a double quantum dot (DQD). The MR is cooled by the dynamical backaction induced by the capacitive coupling between the DQD and the MR. The DQD is excited by a microwave field and afterwards a tunneling event results in the decay of the excited state of the DQD. An important advantage of this system is that both the energy level splitting and the decay rate of the DQD can be well tuned by varying the gate voltage. We find that the steady average occupancy, below unity, of the MR can be achieved by changing both the decay rate of the excited state and the detuning between the transition frequency of the DQD and the microwave frequency, in analogy to the laser sideband cooling of an atom or trapped ion in atomic physics. Our results show that the cooling of the MR to the ground state is experimentally implementable.Comment: 10 pages, 5 figure

The Effect of Current Expected Variance of Return on Future Trading Optimal Strategy

Due to the presence of transaction cost, most investors do not keep changing their portfolio to an optimal portfolio over time. This paper adopts a new approach to investigate the linkages between current optimal portfolio variance and the expected future portfolios variances. It is given a closed-form solution for optimal dynamic portfolio selection with trading cost; considering the minimum variance of the utility function as an optimal or selected portfolio by an investor for any period of time based on Gârleanu & Pedersen (2013) framework. Finally, we introduce the multi-period portfolio model based on CRRA preference utility function. Keywords: multiperiod portfolio selection, higher-order moments, CRRA utility function, optimal wealth change

A Novel Approach to Construct Portfolio that Addresses Variance of Utility Function

Many studies in the area of portfolio selection have done based on trade-off among various moments especially between mean and risk of sample returns. Merton (1980) argued that the instability of portfolio weights and sampling errors are due more to estimate the amount of mean. Indeed, it is difficult to estimate the expected return from time series of realized expected return. By this paper, we first answer to this question how to eliminate the wrong effect of mean sample returns instead of ignoring it from calculating portfolio weights and how would be the relation of other moments after this consideration. Second, the substantial evidence from experiments shows that hide information exposes ambiguity aversion to investor’s behavior, and hence decision making under ambiguity for portfolio choice has led to improving tractability of the main features of asset returns. By considering the volatility of utility preferences as ambiguity then individuals prefer to stabilize their utility preferences to maximize their expected utility. Keywords: utility function, portfolio selection, risk aversion, ambiguity aversio

Operating and maintenance cost reduction using probabilistic risk assessment (PRA)

"January 1992."Includes bibliographical references (pages 129-132)Final report, "Operating and maintenance cost reduction using probabilistic risk assessment (PRA)"This study quantifies the change in one measure of plant risk, the frequency of loss of long-term decay heat removal, due to changes in maintenance at the James A. Fitzpatrick (JAF) plant. Quantification is accomplished in two steps. First, the effects of maintenance are quantified in terms of changes in: a) the frequency of common cause failure of residual heat removal (RHR) pumps and b) the frequency with which operators fail to correctly restore the RHR system following maintenance. These parameters are selected as the result of an importance analysis for the plant. Second, the changes in these two parameters are propagated through a simple plant model to obtain the associated change in plant risk. Based on this study's assessment of the current maintenance program at JAF, it appears that the potential for significant risk reduction due to improved maintenance is not extremely large; an optimal program might lead to an 80% reduction. The optimal program would place a stronger emphasis on predictive maintenance, and would employ improved procedures for RHR pump maintenance. There is potential for significant risk increase (around a factor of 70) if the maintenance program is significantly degraded (e.g., if post-maintenance is deemphasized). This study shows how, at a simple level, maintenance program changes can be quantified without explicit modeling of the details of a plant's management and organizational structure. However, such modeling may be required: a) to more strongly justify the quantitative factors used in the analysis and b) to quantify the effect of other program changes not yet treated (e.g., the strengthening of program elements ensuring feedback of information to organization). In addition, failure data specific to the JAF plant are also needed to increase the confidence in the quantitative results of this study.Sponsored by New York Power Authority, White Plains, NY under contract no. S-90-0019

Turing Instability in a Boundary-fed System

The formation of localized structures in the chlorine dioxide-idodine-malonic acid (CDIMA) reaction-diffusion system is investigated numerically using a realistic model of this system. We analyze the one-dimensional patterns formed along the gradients imposed by boundary feeds, and study their linear stability to symmetry-breaking perturbations (Turing instability) in the plane transverse to these gradients. We establish that an often-invoked simple local linear analysis which neglects longitudinal diffusion is inappropriate for predicting the linear stability of these patterns. Using a fully nonuniform analysis, we investigate the structure of the patterns formed along the gradients and their stability to transverse Turing pattern formation as a function of the values of two control parameters: the malonic acid feed concentration and the size of the reactor in the dimension along the gradients. The results from this investigation are compared with existing experiments.Comment: 41 pages, 18 figures, to be published in Physical Review

An Essential Role of the Forkhead-Box Transcription Factor Foxo1 in Control of T Cell Homeostasis and Tolerance

SummaryMembers of the Forkhead box O (Foxo) family of transcription factors are key regulators of cellular responses, but their function in the immune system remains incompletely understood. Here we showed that T cell-specific deletion of Foxo1 gene in mice led to spontaneous T cell activation, effector T cell differentiation, autoantibody production, and the induction of inflammatory bowel disease in a transfer model. In addition, Foxo1 was critical for the maintenance of naive T cells in the peripheral lymphoid organs. Transcriptome analyses of T cells identified Foxo1-regulated genes encoding, among others, cell-surface molecules, signaling proteins, and nuclear factors that control gene expression. Functional studies validated interleukin-7 receptor-α as a Foxo1 target gene essential for Foxo1 maintenance of naive T cells. These findings reveal crucial functions of Foxo1-dependent transcription in control of T cell homeostasis and tolerance

Preliminary study of a radiantly heated fluidized bed for the production of high purity silicon

The preparation of very pure silicon from silane (SIH4) using radiant heating of the hot silicon particles of a fluidized bed is discussed. The fraction of electrical energy supplied to the heater which is actually absorbed by the particles and the heat transfer coefficient between the hot bed and the cool distributor plate were investigated. The experimental design is presented and the results of the study are summarized

Branes and fluxes in special holonomy manifolds and cascading field theories

We conduct a study of holographic RG flows whose UV is a theory in 2+1 dimensions decoupled from gravity, and the IR is the N=6,8 superconformal fixed point of ABJM. The solutions we consider are constructed by warping the M-theory background whose eight spatial dimensions are manifolds of special holonomies sp(1) times sp(1) and spin(7). Our main example for the spin(7) holonomy manifold is the A8 geometry originally constructed by Cvetic, Gibbons, Lu, and Pope. On the gravity side, our constructions generalize the earlier construction of RG flow where the UV was N=3 Yang-Mills-Chern-Simons matter system and are simpler in a number of ways. Through careful consideration of Page, Maxwell, and brane charges, we identify the discrete and continuous parameters characterizing each system. We then determine the range of the discrete data, corresponding to the flux/rank for which the supersymmetry is unbroken, and estimate the dynamical supersymmetry breaking scale as a function of these data. We then point out the similarity between the physics of supersymmetry breaking between our system and the system considered by Maldacena and Nastase. We also describe the condition for unbroken supersymmetry on class of construction based on a different class of spin(7) manifolds known as B8 spaces whose IR is different from that of ABJM and exhibit some interesting features.Comment: 51 pages, 12 figures. Update in quantization of G4 on B8 in equations (5.12) and (5.13

Computational Study of Tunneling Transistor Based on Graphene Nanoribbon

Tunneling field-effect transistors (FETs) have been intensely explored recently due to its potential to address power concerns in nanoelectronics. The recently discovered graphene nanoribbon (GNR) is ideal for tunneling FETs due to its symmetric bandstructure, light effective mass, and monolayer-thin body. In this work, we examine the device physics of p-i-n GNR tunneling FETs using atomistic quantum transport simulations. The important role of the edge bond relaxation in the device characteristics is identified. The device, however, has ambipolar I-V characteristics, which are not preferred for digital electronics applications. We suggest that using either an asymmetric source-drain doping or a properly designed gate underlap can effectively suppress the ambipolar I-V. A subthreshold slope of 14mV/dec and a significantly improved on-off ratio can be obtained by the p-i-n GNR tunneling FETs