A conceptual model for changes in finger photoplethysmograph signals caused by hand posture and isothermic regulation

Objective. To observe changes in baseline and pulsatile light absorbance (photoplethysmograph, PPG) in the finger-tip, by raising the hand above the horizontal plane in recumbent subjects. We applied current knowledge of the circulation to the finger-tip, particularly arteriovenous anastomoses (AVAs), and the physiology of the venous circulation. Approach. We studied healthy young volunteers in a quiet thermoneutral environment. A finger plethysmograph on the non-dominant hand recorded transmission of red and infra-red light, and the values were converted into absorbance to allow comparisons within and between subjects. Breathing movements were recorded unobtrusively to assess any effect on absorbance and the pulse amplitude of the signals. All body movements were passive: the study arm was elevated in a trough to about 40° above the horizontal plane. The following conditions were studied, each for 15 minutes, using the last 10 minutes for analysis: recumbent, study arm elevated, study arm horizontal, and both legs elevated by 40°. Main results. There was a substantial time-related effect, and considerable variation between subjects. Arm elevation reduced red light absorbance and increased the range of amplitudes of the PPG waveform: only in subjects with large absorbances, did waveform amplitude increase. The other main effect was that spontaneous, thermoregulatory decreases in absorbance were associated with decreases in waveform amplitude. Significance. Finger-tip vessels distend with blood when AVAs open. The vessels pulsate more strongly if venous collapse allows the vessels to become more compliant. The postcapillary circulation is likely to be an important source of pulsation.

Evaluation of Stereolithography-Based Additive Manufacturing Technology for BaTiO3 Ceramics at 465 nm

A piezoceramic BaTiO3 material that is difficult for 3D printing was tested with a homemade laser-based stereolithography (SLA) setup. The high light absorbance of BaTiO3 in the spectral range of 350–410 nm makes this material hardly usable with most commercial SLA 3D printers. The typical polymerization depth of BaTiO3 ceramic pastes in this spectral range hardly reaches 30–50 µm for 40 vol % powder loading. A spectral change to 465 nm was realized in this work via a robot-based experimental SLA setup to improve the 3D printing efficiency. The ceramic paste was prepared from a preconditioned commercial BaTiO3 powder and used for 3D printing. The paste’s polymerization was investigated with variation of powder fraction (10–55 vol %), speed of a laser beam (1–10 mm/s, at constant laser power), and a hatching spacing (100–1000 µm). The polymerization depths of over 100 µm were routinely reached with the 465 nm SLA for pastes having 55 vol % powder loading. The spectral shift from 350–410 nm spectral region to 465 nm reduced the light absorption by BaTiO3 and remedied the photopolymerization process, emphasizing the importance of comprehensive optical analysis of prospective powders in SLA technology. Two multi-layered objects were 3D-printed to demonstrate the positive effect of the spectral shift.

EXTRACTION CONCENTRATING OF SCANDIUM (III) IN COMPLEX FORM WITH 2-HYDROXY-5-T-BUTYLPHENOL-4-METOXYAZOBENZENE AND ITS DETERMINATION BY ATOMIC-ABSORPTION SPECTROMETRY

Complexation of scandium 2-hydroxy-5-T-butylphenol-4-metoxyazobenzene (HR) was studied by atomic-absorption and spectrophotometric methods. Optimum conditions of formation and extraction of the complex were found. Maximum light absorbance of a complex in n-butanol is in the range of 470÷480 nm. Molar absorption coefficient equals to (2.2–3.0).104. Stability constant of scandium in n-butanol is л=2.8·1010. Selective and sensitive techniques of extraction-atomic absorption determination of scandium in soils were developed

A Field-Deployable Diagnostic Assay for the Visual Detection of Misfolded Prions

Diagnostic tools for the detection of protein-misfolding diseases (i.e., proteopathies) are limited. Gold nanoparticles (AuNPs) facilitate sensitive diagnostic techniques via visual color change for the detection of a variety of targets. In parallel, recently developed quaking-induced conversion (QuIC) assays leverage protein-amplification and fluorescent signaling for the accurate detection of misfolded proteins. Here, we combine AuNP and QuIC technologies for the visual detection of amplified misfolded prion proteins from tissues of wild white-tailed deer infected with chronic wasting disease (CWD), a prion disease of cervids. Our newly developed assay, MN-QuIC™, enables both naked-eye and light-absorbance measurements for detection of misfolded prions. MN-QuIC™ leverages basic laboratory equipment that is cost-effective and portable, thus facilitating real-time prion diagnostics across a variety of settings. To test the portability of our assay, we deployed to a rural field-station in southeastern Minnesota and tested for CWD on site. We successfully demonstrated that MN-QuIC™ is functional in a non-traditional laboratory setting by performing a blinded analysis in the field and correctly identifying all CWD positive and CWD not detected deer at the field site in less than 24 hours, thus documenting the portability of the assay. Additionally, we show that electrostatic forces help govern the AuNP/prion interactions. Importantly, all of our white-tailed deer (n=37) were independently tested using ELISA, IHC, and/or RT-QuIC technologies and results secured with MN-QuIC™ were 100% consistent with these tests. We conclude that hybrid AuNP and QuIC assays, such as MN-QuIC™, have great potential for sensitive, field-deployable diagnostics of a variety of protein misfolding diseases.

Optimization of photovoltaic conversion performance of a TiO2 based dye sensitized solar cells (DSSCs)

Combined theoretical and experimental investigations are carried out to achieve an optimum photovoltaic (PV) conversion performance (η) of a DSSC. All theoretical studies are done in tiberCAD software, wherein simulated parameters are calibrated and correlated with the measured experimental parameters of a DSSC fabricated using nearly spherical shape nanosize TiO2 working electrode. For two types of dye molecules, theoretically optimized electrode’s thicknesses were 6 µm (η~6.45%) and 18 µm (η~7.51%) for DB and LEG4 dyes, respectively. Relatively a better short-circuit photocurrent density (JSC) was found for a LEG4 dye although it had a lower light absorbance compared to a DB dye. The theoretical investigation revealed that charge recombination of a DB dye is 7 times higher than that of a LEG4 dye, and this high recombination becomes one of the most critical factors affecting the overall incident photon to current conversion efficiency.

Study on Optical Properties of Milk based on Light Propagation Theory

The light propagation in milk based on experimental and theoretical analysis is reviewed. The review is done on light propagation theory which consists of light absorbance, reflection, and scattering. The study covers on types of milk, milk quality and modelling methods based on Mie scattering and Monte Carlo algorithm. The experiments consist of spectrometry methods where visible (VIS) and near infra-red (NIR) are used. Many spectrometry experiments and theoretical modelling are discussed to observe and analyse optical properties of milk.

Simultaneous Absorbance and Fluorescence Measurements Using an Inlaid Microfluidic Approach

A novel microfluidic optical cell is presented that enables simultaneous measurement of both light absorbance and fluorescence on microlitre volumes of fluid. The chip design is based on an inlaid fabrication technique using clear and opaque poly(methyl methacrylate) or PMMA to create a 20.2 mm long optical cell. The inlaid approach allows fluid interrogation with minimal interference from external light over centimeter long path lengths. The performance of the optical cell is evaluated using a stable fluorescent dye: rhodamine B. Excellent linear relationships (R2 > 0.99) are found for both absorbance and fluorescence over a 0.1–10 µM concentration range. Furthermore, the molar attenuation spectrum is accurately measured over the range 460–550 nm. The approach presented here is applicable to numerous colorimetric- or fluorescence-based assays and presents an important step in the development of multipurpose lab-on-chip sensors.

Forecasting Young Apple Tree Bud Status with a Visible/Near-Infrared Spectrometer

Being able to ascertain the physiological condition of the buds on a young apple tree before bud burst could help farmers manage their orchards more efficiently, especially if they could do so without destroying the buds in the process. The experiments carried out in this study were conducted with the aim of distinguishing shoot from non-shoot buds before bud burst using a visible/near-infrared spectrometer, a device that does not destroy the buds being tested. Tests on spring-planted (April 30, 2021) trees were conducted to check shoot and non-shoot bud physiology and the winter dormancy of young ‘Jonagold’, ‘Miyabi Fuji’ and ‘Orin’ apple trees. The light absorbance of the shoot buds before bud burst was much lower than the light absorbance of the non-shoot buds as checked on the visible/near-infrared spectrometer. The highest first factor effect was determined by a PCA test conducted on shoot and non-shoot ‘Jonagold’ buds (99.9%) at a range of 640-652 nm, ‘Miyabi Fuji’ buds (99.7%) at 654-680 nm and ‘Orin’ buds (99.6%) at 704-766 nm seven days before bud burst. We also found that the highest level of accuracy, using the Classifier analysis, between shoot and non-shoot ‘Jonagold’ buds (76.6%) was one day before bud burst, for ‘Miyabi Fuji’ buds (82.1%) it was three days before and for ‘Orin’ buds (76.3%) it was two days before. These findings suggest that growers can more effectively manage the development of the young trees in their orchards with a visible/near-infrared spectrometer.

Correlating light absorbance parameters in peach skin with susceptibility to streaking and association with rainwater components

Since first observed in 2003, peach skin streaking (PSS) has increasingly affected fruit production in the Southeast. Since 2017 we have documented the occurrence of peach skin streaking on 21 cultivars in South Carolina and symptoms have also been reported in Maryland and Pennsylvania. PSS seems to be linked to an unidentified causal agent mediated in rainwater with susceptibility closely related to the ripening status of maturing fruit. Over the course of the 2019 peach growing season, we collected rainwater at a South Carolina peach farm with a history of PSS and analyzed samples for chemical and physical property. Five cultivars were monitored for occurrence of PSS to associate specific rain events with symptom development in the field. PSS was observed in the field on one of the monitored and three additional cultivars between May and June, and five rain events coincided in time with symptom development. However, chemical, and physical properties from these rainwater samples were not significantly different from samples not associated with PSS in that time frame. Fruit of the five cultivars were also collected at 21, 14, 7 and 0 days before harvest, to determine light absorbance parameters, ΔA and color space, and to induce symptoms under laboratory conditions by treatment with ClO2. There were significant correlations between symptom development and light absorbance parameters illustrating how proneness to PSS increases during fruit maturation.