Higher twist effects in asymptotically free gauge theories

The anomalous dimensions of the flavor octet, three-body operators of twist four are evaluated at the one-loop level. The calculation is complicated due to the appearance of gauge non-invariant operators which are needed to renormalize gauge invariant operators. The mixing problem of these operators is resolved by using the Ward identities derived through the Becchi-Rouet-Stora transformations. Some comments on the evaluation of the coefficient functions are also made.     

Diffuse optical tomography: Present status and its future

Diffuse optical tomography (DOT) is one of the emerging modalities for the non-invasive imaging of thick biological tissues using near-infrared (NIR) light. This article reviews the fundamentals and development of DOT technology since its advent in the early 1990s, including the modeling of light propagation in biological tissues which strongly scatter and weakly absorb NIR light, the optical properties of biological tissues in the NIR wavelength range, three typical measurement methods, image reconstruction algorithms, and so forth. Then various studies are referred to for improvement of the DOT images, which are essentially low in quality due to the ill-conditioned and underdetermined problem. Studies and clinical applications presently attracting much attention are discussed in some detail. Finally, the expected future developments are summarized.     

Instability of vacuum arc in Ag-Cu contact alloys

To clarify the effect of contact material characteristics on the arc instability and chopping phenomena, the spectrum intensity of ionized and neutral vapor generated continuously during discharge is measured using contacts of Ag-Cu binary alloys. It is observed that arc instability and chopping are closely related to the behavior of the ionized vapor during discharge. The chopping current decreases with increased Ag content, while the instability-initiating current has a minimum value at 60 at.% Ag content. These effects are discussed from the viewpoint of the ion generation capability, including thermal properties, of contact materials     

Renormalized trajectory for non-linear sigma model and improved scaling behavior

We apply the block-spin renormalization group method to the O(N) Heisenberg spin model. Extending a previous work of Hirsch and Shenker, we find the renormalized trajectory for O(∞) in two dimensions. For finite N models, we choose a four-parameter action near the large-N renormalized trajectory and demonstrate a remarkable improvement in the approach to continuum limit by performing Monte Carlo simulation of O(3) and O(4) models.     

Finite-size scaling of the three-state Potts model on a simple cubic lattice

Finite-size scaling is studied for the three-state Potts model on a simple cubic lattice. We show that the specific heat and the magnetic susceptibility scale accurately as the volume. The correlation length exhibits behaviors expected for a genuine first-order transition; the one extracted from the unsubtracted correlation function shows a characteristic finite-size behavior, whereas the physical correlation length that characterizes the first excited state stays at a finite value and is discontinuous at the transition point.     

Light propagation for time-domain fluorescence diffuse optical tomography by convolution using lifetime function

Time-domain light propagation in biological tissue is studied by solving the forward problem for fluorescence diffuse optical tomography using a convolution of the zero-lifetime emission light and the exponential function for a finite lifetime. We firstly formulate the fundamental equations in a time-domain assuming that the fluorescence lifetime is equal to zero, and then the solution including the lifetime is obtained by convolving the emission light and the lifetime function. The model is a two-dimensional (2-D) 10 mm-radius circle with the optical properties simulating biological tissue for the near infrared light, and contains some inclusions with fluorophores. Temporal and spatial profiles of excitation and emission light are calculated and discussed for several models with different inclusions. The results are physically reasonable and will be used for the inverse problem of fluorescence diffuse optical tomography.