A physical approach to the automated classification of clinical percussion sounds.

Chest percussion is a traditional technique used for the physical examination of pulmonary injuries and diseases. It is a method of tapping body parts with fingers or small instruments to evaluate the size, consistency, borders, and presence of fluid/air in the lungs and abdomen. Percussion has been successfully used for the diagnosis of such potentially lethal conditions as traumatic and tension pneumothorax. This technique, however, has certain shortcomings, including limitations of the human ear and the subjectivity of the administrator, that lead to overall low sensitivity. Automation of the method by using a standardized percussion source and computerized classification of digitized signals would remove the subjective factor and other limitations of the technique. It would also enable rapid on-site diagnostics of pulmonary traumas when thorough clinical examination is impossible. This paper lays the groundwork for an objective signal classification approach based on a general physical model of a damped harmonic oscillator. Using this concept, critical parameters that effectively subdivide percussion signals into three main groups, historically known as "tympanic," "resonant," and "dull," are identified, opening the possibility for automated diagnostics of air/liquid inclusions in the thorax and abdomen. The key role of damping in forming the character of the percussion signal is investigated using a 3D thorax phantom. The contribution of the abdominal component into the complex multimode spectrum of chest percussion signals is demonstrated.

Fluctuations of the tensor order-parameter modes in a cholesteric liquid crystal.

We use a Landau-de Gennes free energy to calculate the fluctuations of the five independent modes of the tensor order parameter for a cholesteric liquid crystal. Our results include, as a limiting case, the two classical director modes, known as the twist mode and the "umbrella" mode. We find, however, in contrast to the classical director model, that there can be substantial temperature dependence to the umbrella mode, as well as three additional modes near the transition to the isotropic phase. We comment on a recent experiment that suggests that two of these additional modes may have already been detected.

Proposal for the temperature-electric-field phase diagram of a ferroelectric smectic-C* liquid crystal.

We report on the results of extensive optical measurements on the ferroelectric smectic-C* phase of the chiral liquid crystal 4-(2(') methyl butyl) phenyl 4(')-n-octylbiphenyl-4-carboxylate. We have explored the entire temperature-electric-field phase space searching for all possible phase transitions in the C* region and have characterized them both as to their character, including whether they are first or second order, and also whether they are of instability or nucleation type. Our results lead us to conclude that the experimental phase diagram is incompatible with all existing theoretical models for the C* phase transitions. We propose instead a phase diagram where two second-order lines and one first-order line meet at a triple point that we tentatively identify as a Lifshitz point.