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This experiment was motivated by the need to understand the impacts of delaying the first colostrum feeding on the prevalence of failed transfer of passive immunity (FTPI). A cohort of 216 kids was stratified into groups based on the colostrum feeding delay postbirth: 0–4 h, 4–8 h, 8–12 h, and 12–16 h. All kids received a single colostrum meal of 300 mL, and blood samples were collected approximately 36 h after feeding. Serum immunoglobulin G (SIgG) was measured using ELISA, and serum total protein (STP) was assessed using the Bradford method and refractometry (STPb and STPr). Statistical methods like Pearson correlations, Bland-Altman plots, and Lin’s concordance coefficient were employed to assess associations and agreements between SIgG, STPb and STPr. Receiver operator characteristic analysis was employed to determine optimal STPb and STPr thresholds for predicting FTPI (SIgG < 12 g/L). Subsequently, areas under the curve, sensitivity, and specificity were examined to assess the accuracy of these thresholds. Our results showed that for each hour’s delay from birth to colostrum intake (up to 16 h), IgG apparent efficiency of absorption (AEA) decreases at an approximate rate of 2.0% per hour, and SIgG decreases at an approximate rate of 1.0 g/L per hour. However, this decline is not constant over time but intensifies progressively with increased feeding delay. Specifically, reductions in IgG AEA were 1.3, 2.9, and 5.9% per hour, and decreases in SIgG were 0.2, 0.3, and 0.7 g per hour for SIgG across the time intervals of 0–4 to 4–8 h, 4–8 to 8–12 h, and 8–12 to 12–16 h, respectively. Additionally, there was an increase in SIgG of 1.2 g/dL but a decrease in IgG AEA of 1.9% for each gram per kg of BW increase in IgG intake. The correlations between SIgG and STPr and STPb were 0.62, and 0.36, respectively. Optimal STPr and STPb thresholds predicting FTPI were determined to be 4.6 and 6.2 g/dL. The prevalence of FTPI, according to SIgG, STPr, and STPb thresholds were 63, 62, and 45%. Overall, STPr showed higher values for key performance metrics (i.e., sensitivity, likelihood ratio of positive tests, overall accuracy, and Youden’s index), indicating better prediction ability than STPb. Our findings corroborate the critical importance of swift colostrum administration, ideally occurring no later than 12 h postbirth. Moreover, our research validates the effectiveness of Brix refractometry as a practical, on-farm method for assessing FTPI in goat kids.

ABSTRACT Objective: To study vertex-optical distance variation and estimate its impact on manifest refraction. Methods: Prospective study in a private clinic using the Vision-S™ 700 with five forehead positions. Forehead on the third position showed the closest vertex-optical distance of 12mm. Results: Analysis of 52 eyes from 26 patients revealed mean differences in vertex-optical distance of 12.25mm (right eye) and 11.75mm (left eye). A 2mm change in vertex-optical distance resulted in a 0.05D change for a 5D spherical equivalent and 0.20D for a 10D equivalent. Conclusion: Vertex-optical distance varies among patients and is influenced by forehead adjustment. These variations impact refraction accuracy and treatment evaluation. Adjusting the forehead to the third position on the Vision-S™ 700 is recommended.

A minimally invasive needle refractometer is presented for sugar content measurements within produce. A passive sampling cap structure was developed that improves the reliability of the device by avoiding interfering back reflections from the flesh of the produce. It is explained that factory calibration may not be needed for this type of refractometer, potentially reducing production costs. Also demonstrated is an iterative method to correct for temperature variations without the need for an integrated model for how the refractive index changes with temperature for different levels of sugar concentration. The sensor showed a typical standard deviation of 0.4 °Bx for a 10-s-long measurement and was validated against a prism refractometer, showing an average offset of (0.0±0.1) °Bx. In addition, the potential for using the device to investigate sugar distributions within a single fruit sample is demonstrated.

The paper proposes a modified method for measuring the refractive index of a triangular prism using an autocollimation angle measuring system designed to measure angles formed by flat surfaces of objects. The method involves using a fixed mirror to reflect the refracted beam, measurement of the angles of incidence of the beam on the face of the prism corresponding to the autocollimation positions and calculating the refractive index of the prism material using the solution of a system of equations. The paper presents the experimental study results for a triangular prism made of K8 optical glass using the proposed method, and a comparison of the results with the readings obtained using the State Primary Standard of the Refractive Index Unit GET 138-2021. The proposed method makes it possible to simplify the process of measuring the refractive index since there is no need to measure the angle of deviation of the beam.

Methods for measuring the refractive index of optically transparent dielectric materials are considered. Modified methods based on the methods of minimum deviation and constant deviation are proposed and allow determining the refractive index of triangular prisms with unknown apex angles. In the proposed methods, the angles of light deviation on three faces of the prism are measured, and the refractive index of the material and the prism angles are determined from the solution of a system of equations. To implement the proposed methods, a goniometric system is used. That system was designed to measure angles between the flat surfaces of objects in manual and automated modes. Reference prism samples made of N-SF 1 optical glass, and a hollow prism filled with distilled water are studied. The proposed methods are compared and the measurement error is estimated. It is shown that the modified methods can be used for high-precision measurements of the refractive index in cases where the angles of the prism are unknown, or their measurement is associated with technical difficulties.

We propose a refractometric sensor based on hollow silicon Mie resonators of a toroidal magnetic dipole mode. This mode has a pair of antiparallel electric dipoles perpendicular to the silica substrate; thus, the radiation of the mode is suppressed, resulting in an ultra-narrow reflection peak linewidth of 0.35 nm. In addition, the hollow structure enhances the interaction between the enhanced electric field and the surrounding medium, thus improving the sensitivity. The proposed Mie resonators achieve a sensitivity of 486 nm RIU ^−1 and a figure of merit up to 1389 RIU ^−1 , which are ideal for refractometric sensing.

ABSTRACT: It is critical that bovine maternal colostrum is fed to newborn calves during their first hours of life. Colostrum is the secretion a cow produces after mammary involution that is rich in various nutrients. In addition to the nutritive value for newborn calves, immunoglobulins are of interest due to their role in developing the naïve immune system of calves at birth. The process by which a calf acquires immunity via absorption of immunoglobulins is defined as passive immunity. When calves consume an adequate amount of immunoglobulins, they are classified as having successful passive immunity (SPI). In contrast, if they are deprived of adequate colostrum, they are considered to have had a failure of transfer of passive immunity (FPI). Transfer of passive immunity is assessed by measuring serum IgG concentrations at 24 to 48 h of age. The major factors that influence whether a calf has SPI or FPI are colostrum IgG concentration, quantity fed, and age of calf at colostrum feeding. Monitoring apparent efficiency of immunoglobulin absorption in calves is often recommended to evaluate overall colostrum management practices. Serum IgG analyses can be determined with direct (radial immunodiffusion) or indirect (refractometry) methods and used to assess SPI or FPI prevalence.

The present study aims to perform a comparative analysis of vegetable oils and their two-component blends using infrared spectroscopy and refractometry. The study was conducted in Almaty (Kazakhstan) in 2020. Three samples of 44 vegetable oils and their blends made from two components were examined. Fractometry and infrared spectroscopy were used to investigate the properties of blended vegetable oils. To this end, the fatty acid fraction (in percentage), iodine number, and index of refraction (IOR) were calculated. Afterward, the spectrograms obtained for the blends were analyzed. It was found that the difference between the intensities of weak bands and the band expansion of 722 cm−1 indicates greater expressiveness. When low-intensity bands (1653 cm−1) become more distinct due to vibrations of double carbon bonds (C-bonds), the level of unsaturated fatty acids in the blend increases as well.

The research had in view to evaluate and compare two instrumental techniques used for the determination of milk lactose. Refractometric and polarimetric measurements were carried out on milk serum obtained after precipitation of casein by two different methods: by acidification of milk to its isoelectric point (E1), and by using copper sulphate and potassium ferrocyanide (E2). The average lactose content measured by refractometry was 5.469±0.256 g% for method E1 and 5.852±0.218 g% for method E2. The obtained average lactose values measured by polarimetry were higher both for E1 (5.613±0.253 g%) and E2 (5.910±0.224 g%) methods, due to the interference with other optically active components. The experimental data revealed a high correlation between the results obtained by refractometry and polarimetry (r=0.8712) when casein precipitation was performed by potentiometric titration until pH=4.6, at 25°C with 2N acetic acid (method E1).

Optical pressure standards (OPS) using Fabry-Perot (FP) cavities can measure a wide pressure range with high accuracy. National metrology institute of Japan (NMIJ) is developing an OPS for the pressure range of 1 Pa–100 kPa. In this study, the target uncertainty of the OPS, the challenges for measuring below 100 Pa, and its current specifications in the range from 10 Pa to 120 kPa are reported. In addition, the methods for solving the challenges to achieve the target uncertainty is considered.

When developing oil fields, there is an urgent task to quickly determine the type of pumped formation fluid, which includes formation gas, formation oil and formation water. In this paper, we propose a new type of a sensor element designed for flow refractometry of formation fluid based on the effect of total internal reflection. The sensor element is a taper tip of a conical shape made of sapphire and is 20 mm in length and 20 mm in diameter. The original shape of the sensor element is determined by a modified ray tracing method, taking into account analytical relations that determine the conditions for providing a larger dynamic range of measurements under specified physical, technological and design constraints. The conversion dependence of the tip is obtained for the wavelengths of 405 nm, 1064 nm and 3300 nm and allows determining the type of formation fluid (gas/water/oil). The proposed method enables the development of conical sensor elements based on the total internal reflection for downhole monitoring systems and optical threshold sensors of the refractive index.

Honey is a naturally occurring material made by bees from the sweet, fragrant nectar of flowers. More than 200 substances have been identified in honey, the majority of which are sugars and water. Certain physical characteristics of honey, such as crystallization and viscosity, are substantially affected by moisture. The honey may be stored for a longer period of time because of the low water content, which shields it from microbial activity. Honey from around Pozarevac, the place in Serbia with the largest production of honey, was controlled. A refractometer from A. KRÜSS Optronic GmbH was used for this research. In the period from 2019 to 2021, 99 samples of acacia honey and 114 samples of meadow honey were analyzed. The average values of water percentage in the indicated period in both types of honey were between 16 % and 17 %. Based on this research, it can be concluded that the percentage of water in acacia and meadow honey was below the maximum allowed values according to national and European regulations. Below 17 % water content, honey fermentation is inhibited. Honey with a water percentage above 17 % is sensitive to fermentation, while honey with a water content above 19 % is extremely vulnerable.

Medium polarity plays a crucial role in charge-transfer processes and electrochemistry. The added supporting electrolyte in electrochemical setups, essential for attaining the needed electrical conductivity, sets challenges for estimating medium polarity. Herein, we resort to Lippert–Mataga–Ooshika (LMO) formalism for estimating the Onsager polarity of electrolyte organic solutions pertinent to electrochemical analysis. An amine derivative of 1,8-naphthalimide proves to be an appropriate photoprobe for LMO analysis. An increase in electrolyte concentration enhances the polarity of the solutions. This effect becomes especially pronounced for low-polarity solvents. Adding 100 mM tetrabutylammonium hexafluorophosphate to chloroform results in solution polarity exceeding that of neat dichloromethane and 1,2-dichloroethane. Conversely, the observed polarity enhancement that emerges upon the same electrolyte addition to solvents such as acetonitrile and N,N-dimethylformamide is hardly as dramatic. Measured refractive indices provide a means for converting Onsager to Born polarity, which is essential for analyzing medium effects on electrochemical trends. This study demonstrates a robust optical means, encompassing steady-state spectroscopy and refractometry, for characterizing solution properties important for charge-transfer science and electrochemistry.

In this work, the splitting of resonance lines in a Fabry-Perot resonator formed by a section of a standard curved single-mode fiber with metal-coated ends is investigated numerically and experimentally. It is shown that this splitting is similar to the Autler-Townes splitting and results from a strong coupling between the fundamental mode of the core and the whispering gallery mode of the cladding of the curved fiber. The influence of all basic parameters of the curved resonator on the splitting of its resonance lines in the reflection and transmission spectra is considered. Prospects for the practical application of the effects studied for high-resolution optical refractometry, as well as the direction of further research are outlined.

Delayed gastric emptying contributes to complications as aspiration or malnutrition. Among patients suffering from acute neurological diseases, motility disorders are prevalent but poorly understood. Thus, methods to measure gastric emptying are required to allow for appropriate adaptions of individual enteral nutrition algorithms. For enterally fed patients repetitive concentration measurements of gastric content have been proposed to assess gastric emptying. This approach can be used to calculate the gastric residual volume (GRV) and transport of nutrition formula (NF), but it has not yet been implemented in clinical routine. The aim of this study was to investigate whether refractometry or other likewise straightforward analytical approaches produce the best results under in vitro conditions mimicking the gastric milieu. We measured NF in different known concentrations, either diluted in water or in simulated gastric fluid (SGF), with each of the following methods: refractometer, handheld glucose meter, and Bradford protein assay. Then, in enterally fed patients suffering from acute neurological disease, we calculated GRVs and nutrition transport and tested possible associations with clinical parameters. In water dilution experiments, NF concentrations could be assessed with the readout parameters of all three methods. Refractometry yielded the most precise results over the broadest range of concentrations and was biased least by the presence of SGF (detection range for Fresubin original fibre, given as volume concentration/normalized error of regression slope after incubation with water or SGF: 0–100 vs. 0–100%/0.5 vs. 3.9%; glucose-measurement: 5–100 vs. 25–100%/7.9 vs. 6.1%; Bradford-assay: 0–100 vs. 0–100%/7.8 vs. 15.7%). Out of 28 enterally fed patients, we calculated significant slower nutrition transport in patients with higher blood glucose (Rho −0.391; p = 0.039) and in patients who received high-dose sufentanil (Rho −0.514; p = 0.005). Also, the calculated nutrition transport could distinguish patients with and without feeding intolerance (Median 6 vs. 17 ml/h; Mann-Whitney test: p = 0.002). The results of our study prove that serial refractometry is a suitable and cost-effective method to assess gastric emptying and to enhance research on gastrointestinal complications of stroke.

This study investigated the interrelationships between the parameters of density, optical refraction, the volume fraction of ethanol and the total extract, using model solutions and samples of wine materials. The regularities of changes in refractometer readings in the process of alcoholic fermentation have been studied. The functional dependence of the value of the volume fraction of ethanol in the finished wine products on the density and scale of refractometer values has been established. A technique is proposed for controlling the process of alcoholic fermentation of grape must, based on the use of refractometry. Finally, we present an algorithm to calculate the composition (volume fraction of ethanol, mass concentration of the total extract) of the fermentation product from its physical properties (density, refractive index), the coefficient of determination was R2 = 0.975.

Optical pressure standards (OPS) using Fabry-Perot (FP) cavities can measure a wide pressure range with high accuracy. National metrology institute of Japan (NMIJ) is developing an OPS for a pressure range of 1 Pa–100 kPa. In this study, the target uncertainty of the OPS, its current specifications in the range from 40 kPa to 120 kPa, and the challenges for measuring below 100 Pa are reported. In addition, the methods for solving the challenges to achieve the target uncertainty is considered.

Lab-on-a-chip systems are currently one of the most promising areas in the development of ultra-compact sensor systems, used primarily for gas and liquid analysis to determine the concentration of impurities. Integrated photonics is an ideal basis for designing “lab-on-a-chip” systems, advantageous for its compactness, energy efficiency, and low cost in mass production. This paper presents a solution for “lab-on-a-chip” device realization, consisting of a sensor and an interrogator based on a silicon-on-insulator (SOI) integrated photonics platform. The sensor function is performed by an all-pass microring resonator (MRR), installed as a notch filter in the feedback circuit of an optoelectronic oscillator based on an electro-optic phase modulator. This structure realizes the frequency interrogation of the sensor with high accuracy and speed using a conventional single-mode laser source. The system sensitivity for the considered gases is 13,000 GHz/RIU. The results show that the use of frequency interrogation makes it possible to increase the intrinsic LoD by five orders. The proposed solution opens an opportunity for fully integrated implementation of a photonic “laboratory-on-a-chip” unit.

The design of a refractometric sensing system for liquids analysis with a sensor and the scheme for its intensity interrogation combined on a single photonic integrated circuit (PIC) is proposed. A racetrack microring resonator with a channel for the analyzed liquid formed on the top is used as a sensor, and another microring resonator with a lower Q-factor is utilized to detect the change in the resonant wavelength of the sensor. As a measurement result, the optical power at its drop port is detected in comparison with the sum of the powers at the through and drop ports. Simulations showed the possibility of registering a change in the analyte refractive index with a sensitivity of 110 nm per refractive index unit. The proposed scheme was analyzed with a broadband source, as well as a source based on an optoelectronic oscillator using an optical phase modulator. The second case showed the fundamental possibility of implementing an intensity interrogator on a PIC using an external typical single-mode laser as a source. Meanwhile, additional simulations demonstrated an increased system sensitivity compared to the conventional interrogation scheme with a broadband or tunable light source. The proposed approach provides the opportunity to increase the integration level of a sensing device, significantly reducing its cost, power consumption, and dimensions.

Global navigation satellite system (GNSS) refractometry enables automated and continuous in situ snow water equivalent (SWE) observations. Such accurate and reliable in situ data are needed for calibration and validation of remote sensing data and could enhance snow hydrological monitoring and modeling. In contrast to previous studies which relied on post-processing with the highly sophisticated Bernese GNSS processing software, the feasibility of in situ SWE determination in post-processing and (near) real time using the open-source GNSS processing software RTKLIB and GNSS refractometry based on the biased coordinate Up component is investigated here. Available GNSS observations from a fixed, high-end GNSS refractometry snow monitoring setup in the Swiss Alps are reprocessed for the season 2016/17 to investigate the applicability of RTKLIB in post-processing. A fixed, low-cost setup provides continuous SWE estimates in near real time at a low cost for the complete 2021/22 season. Additionally, a mobile, (near) real-time and low-cost setup was designed and evaluated in March 2020. The fixed and mobile multi-frequency GNSS setups demonstrate the feasibility of (near) real-time SWE estimation using GNSS refractometry. Compared to state-of-the-art manual SWE observations, a mean relative bias below 5% is achieved for (near) real-time and post-processed SWE estimation using RTKLIB.

Cervico-vaginal mucus (CVM) is a viscoelastic substance continuously produced by secretory cells of the endocervix and the vagina of cows. Its physicochemical composition varies depending on the hormonal status of the estrous cycle. In veterinary medicine refractometry is a widely diffused technique to determine total solids (TS) content of biological samples, but there are not published data of CVM total solids from refractometric measures. Refractometric TS determination contributes to the qualitative constituents analysis of CVM, additionally it is an easier and more inexpensive technique than gravimetric TS determination. The main goal of the present paper was to validate a refractometric method to estimate TS concentration of the soluble fraction of CVM samples. Samples were collected from seventy-three Holando Argentino cows of Santa Fe province farms in Argentina. Cows were classified in three experimental groups: healthy, subclinical (SE) and clinical endometritis (CE) group. To achieve a solubilisation protocol for CVM samples, four Triton™ X-100 concentrations were tested. Refractive index (RI) and gravimetric total solid (gTS) concentration of solubilised samples were determined for the three experimental groups. A mathematical equation was determined with the experimental data from the healthy group, in order to obtain calculated total solid concentration (cTS) from refractivity (R) values. To validate the RI method for CVM samples, cTS concentrations were compared with gTS concentrations from endometritis group samples. Triton™ X-100 0.01% (V/V) improved CVM samples handling and did not change physicochemical parameters (gTS, Na+ and K+ concentration, and RI values). The linear regression equation obtained was: cTS (g/dL) = (R – 0.67)/16.2, r2 = 0.91. Correlation between gTS and cTS concentration was: r = 0.97 for SE group and r = 0.97 for CE group. The homogenization protocol allowed the measurement of physicochemical parameters without altering their values. A high correlation coefficient between cTS and gTS postulates refractometry as an accurate method to determine TS concentration for solubilised CVM samples.

Morphological and physico-chemical properties of erythrocytes encapsulated by terpenoindol alkaloids (TIA) by nephelometry and osmotic resistance of erythrocytes in a medium with low concentrations of sodium chloride have been studied. Changes in the morphological and physico-chemical parameters of TIA-loaded erythrocyte carriers and freshly isolated erythrocytes have been studied. It was found that during the process of encapsulation of TIA by a modified hypotonic swelling method, the morphological and physicochemical parameters of erythrocytes change insignificantly in comparison with the control.

Background: The main drawbacks of zirconia are its high refractive index and opacity. This study aimed to assess the effect of sintering temperature on the translucency of Ivoclar e. max ZirCAD (IEZ), and White Peaks Symphony (WPS) zirconia blocks. Materials and Methods: In this in vitro experimental study, 30 IEZ and 30 WPS zirconia blocks measuring 10 mm × 10 mm × 1 mm were prepared and underwent sintering in three subgroups at 1440°C, 1500°C, and 1530°C. The specimens were then photographed against a black and a white background with a standard digital camera. The L*, a*, and b* color parameters were measured using Adobe Photoshop software, and translucency was calculated. Data were analyzed using one-way ANOVA and Tukey's test (P < 0.05). Results: In both the IEZ and WPS groups, the maximum and minimum translucency parameters were recorded in 1530°C and 1440°C subgroups, respectively. The difference in the mean translucency was significant among the three subgroups of each zirconia group (P < 0.001). The mean translucency of WPS zirconia was significantly higher than that of IEZ zirconia (P < 0.01), and maximum difference was noted at 1500°C sintering temperature. Conclusion: Increasing the sintering temperature from 1440°C to 1530°C can significantly increase the translucency of IEZ and WPS zirconia blocks, and can be considered to improve the quality of zirconia restorations.

The determination of salinity values from SI traceable densimetry and refractometry measurement results enable SI traceability of the former. In this work, a short study of the metrological compatibility of salinity determinations via these two methods for sodium chloride in ultrapure water solutions and two different standard seawaters (OSIL and ERM) solutions, in the [35.0; 215.0] g kg−1 interval, is presented. It evidenced the metrological compatibility of the salinity determinations in the referred interval. The largest salinity values enabled to test the matrix effect upon the determinations and concluded the preferable use of densimetry technique, when occurring.

Refractometry is a powerful technique for pressure assessments that, due to the recent redefinition of the SI system, also offers a new route to realizing the SI unit of pressure, the Pascal. Gas modulation refractometry (GAMOR) is a methodology that has demonstrated an outstanding ability to mitigate the influences of drifts and fluctuations, leading to long-term precision in the 10−7 region. However, its short-term performance, which is of importance for a variety of applications, has not yet been scrutinized. To assess this, we investigated the short-term performance (in terms of precision) of two similar, but independent, dual Fabry–Perot cavity refractometers utilizing the GAMOR methodology. Both systems assessed the same pressure produced by a dead weight piston gauge. That way, their short-term responses were assessed without being compromised by any pressure fluctuations produced by the piston gauge or the gas delivery system. We found that the two refractometer systems have a significantly higher degree of concordance (in the 10−8 range at 1 s) than what either of them has with the piston gauge. This shows that the refractometry systems under scrutiny are capable of assessing rapidly varying pressures (with bandwidths up to 2 Hz) with precision in the 10−8 range.

The study of Medical activity of antibiotics is gaining momentum now a days owing to the importance of their curative values. The Medical Activity correlated to molecular interactions,can be studied by various physical techniques, at present optical methods like Refractometry and Polarization are used to study the activity of a few antibiotics like Penicillin. The Refractive Indices Mean Molecular Polarizability Diamagnetic Susceptibilities and Electron Ionisation Cross Section are interpreted in terms of dosages and the toxic effects if any due to over dosages are discussed critically.

Abstract Background Tunic is a cellulosic, integumentary matrix found in tunicates (Subphylum Tunicata or Urochordata). The tunics of some ascidian species and pelagic tunicates, such as salps, are nearly transparent, which is useful in predator avoidance. Transparent materials can be detected visually using light reflected from their surfaces, with the different refractive indices between two media, i.e., tunic and seawater, being the measure of reflectance. A larger difference in refractive indices thus provides a larger measure of reflectance. Results We measured the refractive indices of the transparent tunic of Thetys vagina (salp: Thaliacea) and Rhopalaea sp. (ascidian: Ascidiacea) using an Abbe refractometer and an ellipsometer to estimate the light reflection at the tunic surface and evaluate the anti-reflection effect of the nipple array structure on the tunic surface of T. vagina. At D-line light (λ = 589 nm), the refractive indices of the tunics were 0.002–0.004 greater than seawater in the measurements by Abbe refractometer, and 0.02–0.03 greater than seawater in the measurements by ellipsometer. The refractive indices of tunics were slightly higher than that of seawater. According to the simulation of light reflection based on rigorous coupled wave analysis (RCWA), light at a large angle of incidence will be completely reflected from a surface when its refractive indices are smaller than seawater. Therefore, the refractive index of integument is important for enabling transparent organisms to remain invisible in the water column. Conclusion In order to minimize reflectance, the refractive index should be similar to, but never smaller than, that of the surrounding seawater. The simulation also indicated that the presence or absence of a nipple array does not cause significant difference in reflectance on the surface. The nipple array on the tunic of the diurnal salp may have another function, such as bubble repellence, other than anti-reflection.

ABSTRACT Total serum protein is a significant indicator of health condition in animals. The aim of this study was to analyze the precision of the portable refractometer in determining the concentration of total serum proteins in Podocnemis expansa and Phrynops geoffroanus. A total of 26 animals were used. The blood samples were collected from the supraoccipital sinus and stored in tubes without anticoagulant. Total serum protein was determined using both the biuret reaction and refractometry. The total serum protein mean concentration (g dL-1) with biuret method and refractometry for P. expansa were 3.16 and 3.2; and for P. geoffroanus were 3.56 and 2.72, respectively. These results indicate that total serum protein values can be determined with precision in P. expansa and P. geoffroanus using a portable refractometer.

Background: Accumulation of pleural and peritoneal fluid is seen in some diseases. In order to diagnose the disease and start the treatment, one of the most important actions will be to differentiate between exudates and transudates. The objective of this study was to determine the diagnostic value of measuring the specific gravity of the fluid through refractometer and strip in differentiation of exudates from transudates. Methods: The serum of patients was evaluated for protein, LDH, cholesterol, bilirubin and albumin. The fluid was evaluated for the number of white blood cells, protein, LDH, cholesterol, bilirubin and albumin. Then the fluids were divided into exduate and transudate categories based on Light and Gradient criteria. Finally, the specific gravity of the fluids was measured by refractometer, Erma, Japan and Medi-Test Combi II. The categorized fluids were compared with Gold Standards (final diagnosis) so that the sensitivity and specificity of Light and Gradient criteria in the transudate-exudate differentiation were specified. Results: In comparison with Light criteria, the cut off level of 1022 specific gravity measured by refractometer for pleural effusion has sensitivity, specificity of 92.1%, 68.1%respectively. In evaluation of peritoneal fluid considering cut off point 1023, measured by refractometer has reliable sensitivity 92.4%, specificity 70.4 compared with standard gradient method. Conclusion: Differentiating transudate from exudates by measuring its special gravity by refractometer will have acceptable sensitivity and specificity, and when rapidity is necessary or access to lab equipment is limited, this method could be used.

Objectives: To research the repeatability and intercompatibility of keratometry values measured with Potec PRK-6000 autorefractometer, IOL Master, and Pentacam. Materials and Methods: In this prospective study, consecutive measurements were performed in two different sessions with the mentioned three devices on 110 eyes of 55 subjects who had no additional ocular pathology except for refraction error. The consistency of flat and steep keratometry, average keratometry, and corneal astigmatism values obtained in both sessions was compared by using intraclass correlation coefficient (ICC). The measurement differences between the devices were statistically compared as well. Results: The mean age of the study subjects was 23.05±3.01 (18-30) years. ICC values of average keratometry measurements obtained in the sessions were 0.996 for Potec PRK-6000 autorefractometer, 0.997 for IOL Master, and 0.999 for Pentacam. There was high compatibility between the three devices in terms of average keratometry values in Bland-Altman analysis. However, there were statistically significant differences between the devices in terms of parameters other than corneal astigmatism. Conclusion: The repeatability of the three devices was found considerably high in keratometry measurements. However, it is not appropriate for these devices to be substituted for each other in keratometry measurements. (Turk J Ophthalmol 2014; 44: 179-83)

A review of the surface plasmon resonance (SPR) transducers based on tapered fibers that have been developed in the last years is presented. The devices have proved their good performance (specifically, in terms of sensitivity) and their versatility and they are a very good option to be considered as basis for any kind of chemical and biological sensor. The technology has now reached its maturity and here we summarize some of the characteristics of the devices produced.

At a critical angle of incidence, Fresnel reflectance at an interface between a fronttransparent and a rear lossy medium exhibits sensitive dependencies on the complex refractiveindex of the latter. This effect facilitates the design of optical sensors exploiting single (or multiple)reflections inside a prism (or a parallel plate). We determine an empirical framework that capturesperformance specifications of this sensing scheme, including sensitivity, detection limit, range oflinearity and—what we define here as—angular acceptance bandwidth. Subsequently, we developan optimization protocol that accounts for all relevant optical or geometrical variables and that canbe utilized in any application.

Methods of tissue-simulative phantoms and capillaries fabrication from PVC-plastisol and silicone for application as test-objects in optical coherence tomography (OCT) and skin and capillary emulation are considered. Comparison characteristics of these materials and recommendations for their application are given. Examples of phantoms visualization by optical coherence tomography method are given. Possibility of information using from B-scans for refractive index evaluation is shown.

We present an interferometric technique based on a differential interferometry setup for measurement under atmospheric conditions. The key limiting factor in any interferometric dimensional measurement are fluctuations of the refractive index of air representing a dominating source of uncertainty when evaluated indirectly from the physical parameters of the atmosphere. Our proposal is based on the concept of an over-determined interferometric setup where a reference length is derived from a mechanical frame made from a material with a very low thermal coefficient. The technique allows one to track the variations of the refractive index of air on-line directly in the line of the measuring beam and to compensate for the fluctuations. The optical setup consists of three interferometers sharing the same beam path where two measure differentially the displacement while the third evaluates the changes in the measuring range, acting as a tracking refractometer. The principle is demonstrated in an experimental setup.

The influence of the refractive index of air has proven to be a major problem on the road to improvement of the uncertainty in interferometric displacement measurements. We propose an approach with two counter-measuring interferometers acting as a combination of tracking refractometer and a displacement interferometer referencing the wavelength of the laser source to a mechanical standard made of a material with ultra-low thermal expansion. This technique combines length measurement within a specified range with measurement of the refractive index fluctuations in one axis. Errors caused by different position of the interferometer laser beam and air sensors are thus eliminated. The method has been experimentally tested in comparison with the indirect measurement of the refractive index of air in a thermal controlled environment. Over a 1 K temperature range an agreement on the level of 5 × 10−8 has been achieved.

Refractometry is a classic analytical method in analytical chemistry and biosensing. By integrating advanced micro- and nano-optical systems with well-developed microfluidics technology, optofluidics are shown to be a powerful, smart and universal platform for refractive index sensing applications. This paper reviews recent work on optofluidic refractometers based on different sensing mechanisms and structures (e.g., photonic crystal/photonic crystal fibers, waveguides, whisper gallery modes and surface plasmon resonance), and traces the performance enhancement due to the synergistic integration of optics and microfluidics. A brief discussion of future trends in optofluidic refractometers, namely volume sensing and resolution enhancement, are also offered.

We discuss the detection limit for refractometric sensors relying on high-Q optical cavities and show that the ultimate classical detection limit is given by min {Δn} ≳ η with n + iη being the complex refractive index of the material under refractometric investigation. Taking finite Q factors and filling fractions into account, the detection limit declines. As an example we discuss the fundamental limits of silicon-based high-Q resonators, such as photonic crystal resonators, for sensing in a bio-liquid environment, such as a water buffer. In the transparency window (λ ≳ 1100 nm) of silicon the detection limit becomes almost independent on the filling fraction, while in the visible, the detection limit depends strongly on the filling fraction because the silicon absorbs strongly.

The course of wort fermentation is most often monitored by measuring density by immersion saccharometer or digital densitometer; other methods include classical analysis or automatic analyzers. Another possibility is the measurement of refraction in the course of fermentation. When the original refraction or wort extract is known, refraction unambiguously determines the apparent extract or degree of attenuation. A refractometer with a scale in Brix degrees can be used similarly as a saccharometer having a scale in mass percent of sucrose. In the range of 0-16 mass % sucrose and 0-8% ethanol refraction is a linear function of concentration; this allows us to calculate concentration of ethanol, real extract and also an apparent extract in the course of fermentation from the values of actual and original refraction. Examples are given of measurement and instrument calibration. The measurements can be done with simple and inexpensive refractometers with computing compensation of the effect of temperature.The course of wort fermentation is most often monitored by measuring density by immersion saccharometer or digital densitometer; other methods include classical analysis or automatic analyzers. Another possibility is the measurement of refraction in the course of fermentation. When the original refraction or wort extract is known, refraction unambiguously determines the apparent extract or degree of attenuation. A refractometer with a scale in Brix degrees can be used similarly as a saccharometer having a scale in mass percent of sucrose. In the range of 0-16 mass % sucrose and 0-8% ethanol refraction is a linear function of concentration; this allows us to calculate concentration of ethanol, real extract and also an apparent extract in the course of fermentation from the values of actual and original refraction. Examples are given of measurement and instrument calibration. The measurements can be done with simple and inexpensive refractometers with computing compensation of the effect of temperature.

This paper describes the development of a novel microfluidic platform for multifactorial analysis integrating four label-free detection methods: electrical impedance, refractometry, optical absorption and fluorescence. We present the rationale for the design and the details of the microfabrication of this multifactorial hybrid microfluidic chip. The structure of the platform consists of a three-dimensionally patterned polydimethylsiloxane top part attached to a bottom SU-8 epoxy-based negative photoresist part, where microelectrodes and optical fibers are incorporated to enable impedance and optical analysis. As a proof of concept, the chip functions have been tested and explored, enabling a diversity of applications: (i) impedance-based identification of the size of micro beads, as well as counting and distinguishing of erythrocytes by their volume or membrane properties; (ii) simultaneous determination of the refractive index and optical absorption properties of solutions; and (iii) fluorescence-based bead counting.

Lipoprotein electrophoresis on agarose gel has been modified to allow estimation of the absolute quantity of each fraction. The reproducibility of the method is illustrated by 12 determinations in a single day on serum from one normal subject: mean total dye uptake was 302 ± (sd) “corrected dye units,” and the percentages of β-, pre-β, and α-lipoprotein were 56.1 ± 0.9, 29.1 ± 0.4, and 14.8 ± 0.7, respectively. Reproducibility over a period of 8 months was also demonstrated.Serum lipoproteins of five normal and 15 hyperlipidemic individuals determined by this technique were compared with values obtained by analytical ultracentrifugation. The correlation coefficients were: 0.993 for pre-²-LP vs. VLDL, 0.978 for ²-LP vs. LDL, and 0.867 for ±-LP vs. HDL. Lipoprotein values obtained by paper electrophoresis were also correlated with those of the analytical ultracentrifuge, but to a lesser degree (r = 0.956, 0.691, and 0.786, respectively). Values for LDL and VLDL which were measured by refractometry after preparative ultracentrifugation were very similar to those obtained from the analytical ultracentrifuge. Serum triglyceride concentration was highly correlated (r = 0.972) with the agarose values for pre-²-LP; serum cholesterol concentration was correlated (r = 0.673) with ²-LP. It is proposed that the standard curves of the comparisons with the analytical ultracentrifugal values be used to convert the corrected dye units of electrophoresis on agarose gel to mg/100 ml of specific lipoprotein.