Estimating Microbial Population Data from Optical Density

The spectrophotometer has been used for decades to measure the density of bacterial populations using the turbidity expressed as optical density – OD. However, the OD alone is an unreliable metric and is only proportionately accurate to cell titers to about an OD of 0.6. The relationship between OD and cell titer depends on the configuration of the spectrophotometer, the length of the light path through the culture, the size of the bacterial cells, and the cell culture density. We demonstrate the importance of plate reader calibration to identify the exact relationship between OD and cells/ml. We use four bacterial genera and two sizes of micro-titer plates (96-well and 384-well) and show that the cell/ml per unit OD depends heavily on the bacterial cell size and plate size. We applied our calibration curve to real growth curve data and conclude the cells/ml – rather than OD – is a metric that can be used to directly compare results across experiments, labs, instruments, and species.

Mass Transfer Features of Wavy-Bottomed Cascade Photobioreactors

It has been suggested that the energy-efficient production of microalgae biomass can be more easily obtained in short light path photobioreactors that can be operated at high biomass concentration. On the downside, however, high biomass concentrations also require an efficient gas exchange rate to avoid metabolic growth limitation or inhibition. A cascade photobioreactor featuring a thin liquid layer flowing down a sloping, wavy-bottomed surface can be operated at a biomass concentration that is much higher compared to most usual open-type equipment. Liquid flow, upon investigation, proved to exhibit peculiar “local recirculation” hydrodynamics, potentially conducive to the mixing of superficial and deep zones of the photobioreactor. Mass transfer coefficient represents a useful parameter to optimize the performance of a microalgal photobioreactor and its scale-up. The aim of the present article is to discuss the experimental mass transfer features of this novel type of photobioreactor and highlight expected opportunities and issues entailed by different ways of installing and operating such novel types of photobioreactors.

The Influence of LightPath Length on the Color of Flame-Fusion Synthetic Ruby

Colorimetric studies of different light path lengths from a new perspective of UV-Vis spectroscopy. The corrected ultraviolet-visible light spectrum was used to calculate the color of flame-fusion synthetic ruby, and the influence of light path length and standard light source on the color of flame-fusion synthetic ruby was studied. The results show that the L*, C*, h° under the A light source are higher than those under the D65 light source. In the ultraviolet-visible light spectrum, the strong absorption band of Cr3+ at 545nm is the main cause of the color of the ruby. As the length of the light path increases, the absorption peak area at 545nm also increases, the lightness L* decreases, and the hue angle h° increases. The chroma C* first increases as the length of the light path increases, and then begins to decrease under the influence of the continuous decrease in lightness. The color difference ΔE*ab reaches the maximum when the light path length is around 10mm, and the standard light source has the greatest influence on the color difference ΔE*ab. As the length of the light path continues to increase, the influence of the standard light source on the color difference\(\)ΔE*ab decreases.

The opto-respiratory compromise: Balancing oxygen supply and light transmittance in the retina

The light-absorbing retina has an exceptionally high oxygen demand, which imposes two conflicting needs: high rates of blood perfusion and an unobstructed light path devoid of blood vessels. This review discusses mechanisms and physiological tradeoffs underlying retinal oxygen supply in vertebrates and examines how these physiological systems supported the evolution of vision.

Design of an 8X8 Optical Matrix Protection Device based on Electric Power Communication Network

In order to realize the fast establishment of power fiber circuitous channels, the reliability of power communication optical cable network is guaranteed. An optical matrix 8X8 protection device is designed by using all-optical switcher. The test results show that at the end of each input light path, any 8 paths can be switched, it can achieve 1:8 protection switch, realized the arbitrary switching of three modes and has the function of remote fiber route scheduling.

Simultaneous orientation and 3D localization microscopy with a Vortex point spread function

Estimating the orientation and 3D position of rotationally constrained emitters with localization microscopy typically requires polarization splitting or a large engineered Point Spread Function (PSF). Here we utilize a compact modified PSF for single molecule emitter imaging to estimate simultaneously the 3D position, dipole orientation, and degree of rotational constraint from a single 2D image. We use an affordable and commonly available phase plate, normally used for STED microscopy in the excitation light path, to alter the PSF in the emission light path. This resulting Vortex PSF does not require polarization splitting and has a compact PSF size, making it easy to implement and combine with localization microscopy techniques. In addition to a vectorial PSF fitting routine we calibrate for field-dependent aberrations which enables orientation and position estimation within 30% of the Cramér-Rao bound limit over a 66 μm field of view. We demonstrate this technique on reorienting single molecules adhered to the cover slip, λ-DNA with DNA intercalators using binding-activated localization microscopy, and we reveal periodicity on intertwined structures on supercoiled DNA.