Range Of Optical Techniques Research Articles

A conceptual model of polyoxymethylene dimethyl ether 3 (PODE3) spray combustion under compression ignition engine-like conditions

As one of the most popular synthetic fuels (E-fuels), Polyoxymethylene dimethyl ethers(PODEX) have garnered significant attention among researchers in the compression ignition engine field. This work aims to provide an exhaustive analysis of the combustion characteristics of PODE3, which typically constitutes the primary component of PODEX. This research seeks to deepen our understanding of the flame structure of PODE3, particularly in relation to ambient temperature variation, and unravel the underlying mechanisms driving the observed trends. To achieve this aim, a range of optical techniques was employed within a high-temperature high-pressure combustion vessel to quantify various general combustion parameters and assess OH* chemiluminescence, formaldehyde, and soot distribution. Two additional reference fuels, pure n-dodecane and a blend of 50 % vol n-dodecane and 50 % vol PODE3 were also tested. Additionally, some analysis from chemical kinetics and 1D spray model calculations were used to substantiate the experimental observations. The findings reveal that the flame structure of PODE3 differs significantly from traditional diffusion flames associated with diesel-like sprays. The flame lift-off length (LOL) of PODE3 aligns closely with that of n-dodecane, and maintains the two-lobe structure under high-temperature conditions. In contrast, under low ambient temperatures, the LOL of PODE3 significantly extends, accompanied by a concentration of OH* radicals at the spray center. The notable sensitivity of PODE3 flames to temperature variation is related to the chemical kinetics of formaldehyde and CO. As a result of the analysis, conceptual models of PODE3 flames under varying temperatures were proposed in the end.

Special Issue “Neurophotonics—Optics for the Brain”

Light-tissue interactions allow for a multitude of possibilities to sense; image; and impact the brain at molecular, cellular, and tissue levels. The application of optical techniques to neuronal tissue is the essence of neurophotonics, to which this Special Issue is dedicated. The eleven articles in this Special Issue are representative of the broad scope of this field and of the wide range of optical techniques that it encompasses. In more detail, the articles cover basic neuroscience, neuroanatomy, functional imaging, cerebral hemodynamics, brain development and aging, brain–computer interfaces, and therapeutic treatments. The optical techniques considered include various types of optical microscopy, optical coherence tomography, photoacoustic imaging, diffuse optical spectroscopy and imaging, photobiomodulation, and optogenetics.

Hyperspectral imaging fluorescence excitation scanning (HIFEX) microscopy for live cell imaging.

In the past two decades, spectral imaging technologies have expanded the capacity of fluorescence microscopy for accurate detection of multiple labels, separation of labels from cellular and tissue autofluorescence, and analysis of autofluorescence signatures. These technologies have been implemented using a range of optical techniques, such as tunable filters, diffraction gratings, prisms, interferometry, and custom Bayer filters. Each of these techniques has associated strengths and weaknesses with regard to spectral resolution, spatial resolution, temporal resolution, and signal-to-noise characteristics. We have previously shown that spectral scanning of the fluorescence excitation spectrum can provide greatly increased signal strength compared to traditional emission-scanning approaches. Here, we present results from utilizing a Hyperspectral Imaging Fluorescence Excitation Scanning (HIFEX) microscope system for live cell imaging. Live cell signaling studies were performed using HEK 293 and rat pulmonary microvascular endothelial cells (PMVECs), transfected with either a cAMP FRET reporter or a Ca2+ reporter. Cells were further labeled to visualize subcellular structures (nuclei, membrane, mitochondria, etc.). Spectral images were acquired using a custom inverted microscope (TE2000, Nikon Instruments) equipped with a 300W Xe arc lamp and tunable excitation filter (VF-5, Sutter Instrument Co., equipped with VersaChrome filters, Semrock), and run through MicroManager. Timelapse spectral images were acquired from 350-550 nm, in 5 nm increments. Spectral image data were linearly unmixed using custom MATLAB scripts. Results indicate that the HIFEX microscope system can acquire live cell image data at acquisition speeds of 8 ms/wavelength band with minimal photobleaching, sufficient for studying moderate speed cAMP and Ca2+ events.

Thalamocortical and Intracortical Inputs Differentiate Layer-Specific Mouse Auditory Corticocollicular Neurons.

Long-range descending projections from the auditory cortex play key roles in shaping response properties in the inferior colliculus. The auditory corticocollicular projection is massive and heterogeneous, with axons emanating from cortical layers 5 and 6, and plays a key role in directing plastic changes in the inferior colliculus. However, little is known about the cortical and thalamic networks within which corticocollicular neurons are embedded. Here, laser scanning photostimulation glutamate uncaging and photoactivation of channelrhodopsin-2 were used to probe the local and long-range network differences between preidentified layer 5 and layer 6 auditory corticocollicular neurons from male and female mice in vitro Layer 5 corticocollicular neurons were found to vertically integrate supragranular excitatory and inhibitory input to a substantially greater degree than their layer 6 counterparts. In addition, all layer 5 corticocollicular neurons received direct and large thalamic inputs from channelrhodopsin-2-labeled thalamocortical fibers, whereas such inputs were less common in layer 6 corticocollicular neurons. Finally, a new low-calcium/synaptic blockade approach to separate direct from indirect inputs using laser photostimulation was validated. These data demonstrate that layer 5 and 6 corticocollicular neurons receive distinct sets of cortical and thalamic inputs, supporting the hypothesis that they have divergent roles in modulating the inferior colliculus. Furthermore, the direct connection between the auditory thalamus and layer 5 corticocollicular neurons reveals a novel and rapid link connecting ascending and descending pathways.SIGNIFICANCE STATEMENT Descending projections from the cortex play a critical role in shaping the response properties of sensory neurons. The projection from the auditory cortex to the inferior colliculus is a massive, yet poorly understood, pathway emanating from two distinct cortical layers. Here we show, using a range of optical techniques, that mouse auditory corticocollicular neurons from different layers are embedded into different cortical and thalamic networks. Specifically, we observed that layer 5 corticocollicular neurons integrate information across cortical lamina and receive direct thalamic input. The latter connection provides a hyperdirect link between acoustic sensation and descending control, thus demonstrating a novel mechanism for rapid "online" modulation of sensory perception.

The design and performance of a polymer ribbon‐reinforced transparent composite material

For the purpose of producing polymer ribbon/polymer‐matrix composites, we manufacture rectangular cross section ribbons directly by spinning from a rectangular die. A range of optical techniques, including the interferometric measurement of filament refractive index and characterization of composite optical performance through the modulation transfer function, are employed to quantify properties and guide system design. The interferometric measurements revealed that, compared with previous mechanically worked filaments, the die spun filaments have a more uniform optical path across the fiber. These measurements also enabled characterization of the filament's chromatic dispersion and allowed for matching the matrix refractive index across the visible spectrum. The results show that composites manufactured from rectangular die‐spun ribbons have excellent optical properties with a significant optical performance improvement over previous work. POLYM. COMPOS., 39:2523–2534, 2018. © 2016 Society of Plastics Engineers

Comparative review of interferometric detection of plasmonic nanoparticles

Noble metal nanoparticles exhibit enhanced scattering and absorption at specific wavelengths due to a localized surface plamson resonance. This unique property can be exploited to enable the use of plasmonic nanoparticles as contrast agents in optical imaging. A range of optical techniques have been developed to detect nanoparticles in order to implement imaging schemes. Here we review several different approaches for using optical interferometry to detect the presence and concentration of nanoparticles. The strengths and weaknesses of the various approaches are discussed and quantitative comparisons of the achievable signal to noise ratios are presented. The benefits of each approach are outlined as they relate to specific application goals.

Search for biaxiality in a shape-persistent bent-core nematic liquid crystal

Using a range of optical techniques, we have probed the nature of orientational order in a thermotropic bent-core liquid crystal, which features a shape-persistent molecular architecture designed to promote a biaxial nematic phase. In the upper range of the nematic phase (enantiotropic regime), dynamic light scattering reveals strong fluctuations attributable to the biaxial order parameter, in addition to the usual uniaxial director modes. Assuming a Landau-type expansion of the orientational free energy, we estimate the correlation length associated with these fluctuations to be ∼100 nm. At lower temperatures, and mainly in the monotropic regime of the nematic, we observe by optical conoscopy an apparently biaxial texture, which develops when the sample temperature is changed but then relaxes back to a uniaxial state over time scales much longer than observed in the light scattering measurements. A combination of fluorescence confocal polarizing microscopy and coherent anti-Stokes Raman scattering confirms that the conoscopic texture arises from a flow-induced reorientation of the molecules, associated with a large thermal expansion coefficient of the material, rather than from the spontaneous development of a macroscopic secondary optical axis. We discuss a model to account for the observed behavior at both high and low temperatures based on the temperature-dependent formation of nanoscale, biaxially ordered complexes among the bent-core molecules within a macroscopically uniaxial phase.

High-speed imaging for direct-injection gasoline engine research and development

In recent years, new laser and camera technology have enabled the development of high-speed imaging diagnostics for measurements at frame rates commensurate with the time scales of turbulent mixing, combustion, and emission formation in internal combustion engines. The ability to study the evolution of in-cylinder flow, fuel/air mixing, ignition, and combustion within individual cycles and for many consecutive cycles provides new insights into the physics and chemistry of internal combustion engine performance. Data for model development and device development are obtained with unprecedented access to the identification of random events such as cycle to cycle variation and ignition instabilities. This paper summarizes high-speed diagnostics developments with a focus on application to spark-ignition direct-injection gasoline engines. A range of optical techniques is described along with examples of applications in research and near-production engines. Measurements of in-cylinder velocities were conducted with particle image velocimetry. The spray evolution was followed with Mie scattering. Quantitative fuel distributions were recorded with laser-induced fluorescence. Fuel impingement on surfaces was quantified with refractive index matching. Combined velocity and fuel measurements were used to study ignition reliability. Chemiluminescence techniques provided insights into the evolution of the spark plasma as well as the growing flame kernel. Chemiluminescence and black body radiation imaging yielded insights into the formation and oxidation of soot.

Guided wave study of the optical tensor configuration in FLC cells

Abstract In the absence of a complete continuum theory to describe the director configuration within ferroelectric liquid crystal cells detailed optical tensor characterisation is vital. There are available a range of optical techniques to study this tensor arrangement, the most powerful being generally some form of resonance guided wave excitation. This study reviews the geometries used with guided wave excitation and shows how the recently utilised half-leaky guided wave technique is extremely powerful in unravelling in detail the optical tensor configuration in ferroelectric liquid crystal layers.

Linear and nonlinear optical properties of CdSe xS 1−x microcrystallites

Microcrystals of CdSe xS 1−x (x≈0.6) with nanometer dimensions have been investigated experimentally by a range of optical techniques. This system of ‘quantum dot’ consists of nanometer sized semiconductor particles embedded within an insulating glass matrix. The existence of microscopic CdSeS crystals within the glass matrix is demonstrated by the observation of Raman scattering from the ‘CdSe-like’ and ‘CdS-like’ LO phonons. The nature of the electronic states within these three dimensionally confined systems is investigated by linear absorption and photoluminescence spectroscopy. The photoluminescence spectra show features which are attributed to direct electron-hole recombination and recombination via states within the ‘blue shifted’ energy gap (which are possibly surface related). Carrier relaxation is also investigated by a pump-probe experiment whereby the absorption is partially bleached by a short pump pulse then probed some variable time later by a delayed probe pulse of much lower intensity. Fast and slow components in the carrier relaxation process are identified, and a relationship is suggested between the carrier relaxation and the features observed in the photoluminescence spectra. The well known ‘photodarkening’ properties of such materials are also investigated by the above techniques.