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Miniaturized Optical Neuroimaging Systems
Published in Francesco S. Pavone, Shy Shoham, Handbook of Neurophotonics, 2020
Hang Yu, Janaka Senarathna, Betty M. Tyler, Nitish V. Thakor, Arvind P. Pathak
An elegant example of utilizing a miniaturized two-photon microscope for imaging awake, freely moving animals was demonstrated by Sawinski et al. (2009). As shown in Figure 1.4a–c, the head-mounted unit weighed 5.5 g, which could be carried by an adult or even an adolescent rat. A custom-designed 0.9 numerical aperture (NA) objective lens provided better fluorescence excitation and detection than a regular GRIN lens pair. A large core multi-mode plastic fiber was used to deliver the fluorescent signals to a benchtop detector. The compact fiber scanner in the headpiece achieved a 10.9 Hz frame rate with 64 × 128 pixels scanning. This miniaturized microscope could resolve individual soma from layer 2/3 of the visual cortex with a penetration depth of more than 200 μm. For their experiment, the primary visual cortex was stained with two fluorescent dyes, a calcium indicator (Oregon green BAPTA-1, OGB), and sulforhodamine 101 (SR101) for labeling astrocytes. The experiment was conducted on a semicircular track on which the animal could move freely, and visual stimuli were delivered by three monitors placed at the ends and apex of the track. Four infrared LEDs placed on the headpiece allowed the animal’s position and head orientation to be monitored with a synchronized infrared camera. The authors observed robust Ca2+ transients from the labeled neurons, comparable to results from benchtop two-photon microscopy in both anesthetized and awake animals (Stosiek et al., 2003; Greenberg et al., 2008). A significant increase in Ca2+ transients was observed when the animal swept its gaze across different monitors with some neurons showing preferential firing to a certain monitor location.
The Challenge to Measure Single-phase Convective Heat Transfer Coefficients in Microchannels
Published in Heat Transfer Engineering, 2019
The common aspect of these techniques is that they are based on the observation of tracers which are able to change their properties (i.e., fluorescence intensity, hue, or color) if the local temperature varies. In the case of Laser Induced Fluorescence (LIF) technique, the fluid is typically seeded with a fluorescent dye (i.e., fluorescein or rhodamine B) that changes its fluorescence intensity as a function of the local temperature (Crimaldi [33]). The exciting light is delivered from a laser system but in some cases an arc mercury lamp can be equally used (Ross et al. [34]). The main drawback of this method is that the accuracy of this technique is strongly affected by the intensity and uniformity of the light excitation as well as by the concentration of the seeding. An improvement of the LIF technique is given by the dual-emission LIF method (DeLIF), also known as two-color or radiometric LIF method [35]–[38]. In the DeLIF method two different dyes are involved: one dye shows a temperature-dependent behavior (i.e., rhodamine B, fluorescein, Kiton Red), while the second one is a temperature-insensitive dye (i.e., rhodamine 110, sulforhodamine 101) and it is used for the normalization of the signal given by the temperature-sensitive one. The sensitivity of DeLIF can be further improved by using two temperature-sensitive species with inverted temperature sensitivities. In this case the couple of tracers employed are Fluorescein and sulforhodamine B (Shafii et al. [39]) or fluorescein 27 and rhodamine B (Sutton et al. [40]).
Two-Stage Impinging-Jet Injector Flow Dynamics and Mixing: Kerosene and Hydrogen Peroxide Propellants
Published in Combustion Science and Technology, 2023
The patternator and photographic techniques were commonly adopted to determine mass distribution and spray angle, respectively (Gadgil et al. 2006; Tate 1960). Since the patternator technique has relatively low spatial resolution and the photographic method has high uncertainty, in the present study, planar laser-induced fluorescence (PLIF) technique is employed to perform detailed observations of individual spray structure in a multi-spray setting (Jung, Yoon, and Hwang 2000; Notaro, Khare, and Lee 2019). Yuan et al. (2009) conducted a comparison between the hot-fire and cold-flow observations of NTO/MMH impinging spray. By analyzing the mass distribution in the cold-flow experiment using simulants, they were able to predict the temperature distribution of the impinging combustion of NTO/MMH. Figure 7 shows the PLIF experimental setup. A 1 mm × 50 mm laser sheet from a second-harmonic (532 nm) Nd-YAG laser is aligned to cross the spray cone to excite the laser dye (Sulforhodamine 101) that is dissolved uniformly in either fuel simulant (ethanol) or oxidizer simulant (water). The fluorescence of the laser dye is between 619 and 673 nm, with the peak efficiency near 628 nm. A 600 nm high-pass filter is used to attenuate the Mie scattering from droplets at the laser frequency. A 1600 × 1200 pixel pseudo-color CCD camera at 30° depression angle is used to acquire the fluorescence images with a spatial resolution of 0.02 mm per pixel. The images are recorded and distortion corrected by means of affine transformation. Figure 8 shows the data analysis procedure for PLIF experiments. Since the fluorescence, as measured by PLIF, is emitted by the excitable molecules present in the droplets, its intensity is directly proportional to the liquid mass. Rather than attempting to determine the absolute mass distribution of liquid droplets from the intensity profile of a PLIF image, the spray structure was described using the probability distribution of mass. The 2-D spray probability distribution of mass is determined by