arXiv subjects

W. Cai

Publications and source records attributed to W. Cai.

22 records · Page 2Linked to original sources

arXiv2004

Multiple passages of light through an absorption inhomogeneity in optical imaging of turbid media

The multiple passages of light through an absorption inhomogeneity of finite size deep within a turbid medium is analyzed for optical imaging using the ``self-energy'' diagram. The nonlinear correction becomes more important for an inhomogeneity of a larger size and with greater contrast in absorption with respect to the host background. The nonlinear correction factor agrees well with that from Monte Carlo simulations for CW light. The correction is about $50%-75%$ in near infrared for an absorption inhomogeneity with the typical optical properties found in tissues and of size of five times the transport mean free path.

cond-mat.soft↗

arXiv2004

Electrical transport and magnetic properties of nanostructured La0.67Ca0.33MnO3

Nanostructured La0.67Ca0.33MnO3 (NS-LCMO) was formed by pulsed-laser deposition on the surface of porous Al2O3. The resistance peak temperature (Tp) of the NS-LCMO increases with increasing average thickness of the films, while their Curie temperatures (Tc) remain unchanged. The coercive field of the samples increases with decreasing film thickness and its temperature dependence can be well described by Hc(T) = Hc(0)[1-(T/TB)1/2]. A large magnetoresistance and strong memory effect were observed for the NS-LCMO. The results are discussed in terms of the size effect, Coulomb blockade and magnetic tunneling effect. This work also demonstrates a new way to get nanostructured manganites.

cond-mat.mtrl-sci↗

arXiv2004

Stochastic View of Photon Migration in Turbid Media

Light propagation in an infinite uniform turbid medium is treated as a Markov stochastic process of photons to provide an intuitive framework for photon migration. The macroscopic physical quantities of photon migration are shown to be completely determined by the microscopic statistics of the photon propagation direction in direction space and a generalized Poisson distribution of the number of scattering events that includes an exponential decay absorption factor. A proper diffusion solution is derived with an exact time-dependent central position and half width of photon migration in this framework. The diffusion coefficient is found to be absorption-independent.

cond-mat.dis-nn↗

arXiv1994

Measure Factors, Tension, and Correlations of Fluid Membranes

We study two geometrical factors needed for the correct construction of statistical ensembles of surfaces. Such ensembles appear in the study of fluid bilayer membranes, though our results are more generally applicable. The naive functional measure over height fluctuations must be corrected by these factors in order to give correct, self-consistent formulas for the free energy and correlation functions of the height. While one of these corrections -- the Faddeev-Popov determinant -- has been studied extensively, our derivation proceeds from very simple geometrical ideas, which we hope removes some of its mystery. The other factor is similar to the Liouville correction in string theory. Since our formulas differ from those of previous authors, we include some explicit calculations of the effective frame tension and two-point function to show that our version indeed secures coordinate-invariance and consistency to lowest nontrivial order in a temperature expansion.

cond-mat↗