Detection of Steps in Single Molecule Data.

Over the past few decades, single molecule investigations employing optical tweezers, AFM and TIRF microscopy have revealed that molecular behaviors are typically characterized by discrete steps or events that follow changes in protein conformation. These events, that manifest as steps or jumps, are short-lived transitions between otherwise more stable molecular states. A major limiting factor in determining the size and timing of the steps is the noise introduced by the measurement system.

Robust control approach to force estimation in a constant position optical tweezers.

Feedback enhanced optical tweezers with position regulation capability enable detection and estimation of forces in the pico-Newton regime. In this article we delineate the fundamental limitations and challenges of existing approaches for regulating position and force estimation in an optical tweezer. A modern control systems approach is shown to improve the bandwidth of force estimation by three to four times which is corroborated experimentally.

Real-time nonlinear correction of back-focal-plane detection in optical tweezers.

Photodiode based detection of laser trapped beads using forward scattered light is a frequently employed technique for position measurement. There is a nonlinear relationship between photodiode outputs and bead position but for small displacements linear approximation holds well. Traditionally, the nonlinearity is compensated by normalizing the photodiode's position signal with the intensity signal and then using a polynomial fit in the range where voltage to position mapping is one to one.

Holocord intramedullary abscess.

Intramedullary spinal cord abscess secondary to dorsal dermal sinus is a rare entity and involvement of the entire length of spinal cord is even rarer. A thorough history with precise clinical localization, a high index of suspicion, Magnetic Resonance Imaging (MRI) of spine and prompt surgical drainage with appropriate antibiotic therapy are key to the eventual outcome and prognosis.