674 research outputs found
Optimal parameter estimation of a depolarizing channel
We investigate strategies for estimating a depolarizing channel for a finite dimensional system. Our analysis addresses the double optimization problem of selecting the best input probe state and the measurement strategy that minimizes the Bayes cost of a quadratic function. In the qubit case, we derive the Bayes optimal strategy for any finite number of input probe particles when bipartite entanglement can be formed in the probe particles
Reconstruction of primordial tensor power spectra from B-mode polarization of the cosmic microwave background
Given observations of B-mode polarization power spectrum of the cosmic
microwave background (CMB), we can reconstruct power spectra of primordial
tensor modes from the early Universe without assuming their functional form
such as a power-law spectrum. Shape of the reconstructed spectra can then be
used to probe the origin of tensor modes in a model-independent manner. We use
the Fisher matrix to calculate the covariance matrix of tensor power spectra
reconstructed in bins. We find that the power spectra are best reconstructed at
wavenumbers in the vicinity of and , which correspond to the "reionization bump" at
and "recombination bump" at of the CMB B-mode
power spectrum, respectively. The error bar between these two wavenumbers is
larger because of lack of the signal between the reionization and recombination
bumps. The error bars increase sharply towards smaller (larger) wavenumbers
because of the cosmic variance (CMB lensing and instrumental noise). To
demonstrate utility of the reconstructed power spectra we investigate whether
we can distinguish between various sources of tensor modes including those from
the vacuum metric fluctuation and SU(2) gauge fields during single-field
slow-roll inflation, open inflation and massive gravity inflation. The results
depend on the model parameters, but we find that future CMB experiments are
sensitive to differences in these models. We make our calculation tool
available on-line.Comment: 9 pages, 2 figures, 4 tables; accepted version in Phys. Rev.
Analysis of the Image for Landscape of Port City
The purpose of this study is to obtain basic information available to make a new design concept at the first stage of landscape planning. Recently, with the large change of waterfront spaces, urban environments around port cities are getting more serious in Japan. So it is nesessary to begin planning to recreate the landscapes and facilities. However in this case we should consider the people's image and impression on curtural climate or environments to make fascinating townscapes. We sconsider two positions of people's image denned. One is the Media Image, and the other is the Residents' Image. Many current topics on tourist resorts or fascinating landscapes have been usually reported by visual and linguistic mass media in Japan. Many people form their images on townscapes without real experience. This image is called the Media Image and represents the external people's hope for spaces. On the other hand, the internal residents in the port city form their image by real experience or influence on their lives. This image is defined as the Residents' Image. Through a psychological experiment under the stimulus of visual media, this study specifies basic characteristics of the visual landscapes at representative port cities in Japan by comparing the two images
Room-Temperature Electron Spin Transport in a Highly Doped Si Channel
We report on the first demonstration of generating a spin current and spin
transport in a highly doped Si channel at room temperature (RT) using a
four-terminal lateral device with a spin injector and a detector consisting of
an Fe/MgO tunnel barrier. Spin current was generated using a nonlocal
technique, and spin injection signals and Hanle-type spin precession were
successfully detected at 300 K, thus proving spin injection with the
elimination of spurious signals. The spin diffusion length and its lifetime at
RT were estimated to be 0.6 \"im and 1.3 ns by the Hanle-type spin precession,
respectively.Comment: 14 pages, 4 Figure
A Road Network Design Model Considering Node Capacity
Optimal road network design models have been investigated in order to generate alternatives of road network planning. Most of the previous works assume that the decision variables of the planners are the attributes of the links. The actual road network, however, consists of links and nodes, and it is useful to distinguish links and nodes explicitly. Planning models should involve the attributes of nodes in decision variables as well as the link attributes. We formulate a road network design model considering the nodal capacity. The frame of the proposed model is interpreted as a two level optimal problem, which is a system optimizing problem including an optimal problem as its constraint. Before the formulation of a two level problem, the structure of a node is simplified, and a nodal passing time function is introduced, which represents the performance of a node. As a user equilibrium is the most relevant assumption for the description of road network flow, the lower problem is formulated as a fixed demand user equilibrium problem, using nodal passing time functions as well as link travel time functions. Given the total investment cost constraint, the higher problem decides the link and nodal capacities in order to optimize a measure of the whole network performance. The lower problem describes the traffic flow on a network for given capacities. The structure of the model is explained by using the frame of the Stackelberg differential game, whose players are planner (leader) and aggregate term of network user (follower). In order to solve the formulated problem, a heuristic algorithm is proposed. This is the input/outputiterativemethod, and it is expected to be effective for a normal size problem. The convergence of the algorithm is numerically confirmed through an example for simple and hypothetical datum. A sensitivity analysis for the value of the cost constraint is executed to determine the effective value of an investment. Remaining problems are extensively discussed for further research
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