Accurate Density Measurements Research Articles

Optical fiber interferometer application for high electron density measurements on compact torus plasmas.

An optical fiber Mach-Zehnder interferometer at a wavelength of 1.55 µm has been developed for measurements of high electron density on compact torus (CT) plasmas with a high time resolution of 0.1 µs and high phase resolution of 6.4 × 10-4 rad. To improve density measurement accuracy, the phase noise of the interferometer has been investigated in detail and optimized. In the bench test, the interferometer was calibrated using a piezoelectric ceramic actuator with known stroke. Initial results on CT plasma show that the optical fiber interferometer provides reliable density measurements at two spatial locations and the bulk velocity of plasma can be determined by the method of time of flight.

Prediction of Liquid Density by Gamma-Ray Measurement for Materials with Low Atomic Number

A new method has been developed and evaluated for density measurement of liquid materials based on conventional gamma density meter, whether a low strength gamma radioactive source as the backscatter technique with collimated detector cannot be properly used for density measurement. In this comparative study, proposed method aimed to improve the linearity of the density measurement without using time consuming spectroscopy. Both transmission and backscatter methods for density measurement were used together in a combined model. The whole measurement system was designed, constructed and simulated for nuclear gamma–gamma density measurement. MCNP modeling results were benchmarked with experimental data, showing a good correlation between combined density measurement method and conventional transmission density measurement while values of MRE(%), RMSE and MAE(%) are lower in combined model. This study shows that, MRE(%) in combined model, and for both experimental and simulation results, is improved with the average of about 41% in comparison with the conventional density measurement. Also in this comparative study, RMSE decreased significantly about 56%. Additionally, average MAE (%) reduced about 36%. Furthermore, R-square values were also improved in both experimental and simulation results. Evaluating different methods of nuclear density measurements led us to propose an innovative formula, to investigate an accurate density measurement. This paper discusses advantages of proposed model in comparison with the conventional transmission method for gamma interaction with lower percentage errors and better calibration curve fitting.

Two-photon absorption laser induced fluorescence: rate and density-matrix regimes for plasma diagnostics

Two-photon absorption laser induced fluorescence (TALIF) technique employing nanosecond lasers is often used to measure space- and time-resolved distributions of key atomic and molecular radicals in reactive environments such as plasmas and combustions. Although the technique was applied for about four decades, particularly in high pressure non-equilibrium plasmas accurate measurements of species densities remain challenging. With atomic oxygen as an example, central aspects of the technique including the role of photon statistics and line profiles on the two-photon absorption rates, selection rules, spatial and temporal resolutions, photolytic and quenching effects, and absolute calibration methods are discussed. Simulations using rate equations which include non-depletion regime, three-level and six-level models are compared and criteria for non-saturation regimes are given for low- and high-pressure plasmas. Solutions of the density-matrix model, which include coherent excitation and Stark detuning phenomena, and the rate equation model are compared. The validity criteria for non-depletion and photolytic-free regimes and rate models are given. The nanosecond TALIF quench-free regime at high laser intensities is investigated using the density-matrix model. The two-photon cross-sections for O, H and N atomic radicals and their ratio with Kr and Xe rare gases used for calibrations are revisited and recommendations are proposed. For TALIF applying ultrafast lasers, the appropriate model for the fluorescence probability is discussed.

A Reliable Flow-Based Method for the Accurate Measure of Mass Density, Size and Weight of Live 3D Tumor Spheroids

Gathering precise information on mass density, size and weight of cells or cell aggregates, is crucial for applications in many biomedical fields with a specific focus on cancer research. Although few technical solutions have been presented for single-cell analysis, literature does not cover this aspect for 3D models such as spheroids. Since the research interest on such samples is notably rising, here we describe a flow-apparatus, and the associated physical method and operative protocol for the accurate measurements of mass density, size and weight. The technique is based on the detection of the terminal velocity of a free-falling sample into a specifically conceived analysis flow-channel. Moreover, in order to demonstrate the accuracy and precision of the presented flow-device, analyses were initially carried out on standardized polystyrene beads. Finally, to display the application of the proposed system for biological samples, mass density, size and weight of live SW620 tumor spheroids were analyzed. The combined measurements of such parameters can represent a step toward a deeper understanding of 3D culture models.

Sampling to determine density of arthropods in intensively grazed grasslands

AbstractArthropod population field studies undertaken to understand the impacts and population dynamics of the target organism rely on sampling methods that provide accurate measurements of population density. Unsuitable methods may underestimate or provide widely variable measures of population density. The suitability of three vacuum sampling methods: a domestic vacuum cleaner, Vortis™, and blower‐vac (G‐vac), plus heat extraction of turves were compared for sampling common species in an intensively grazed irrigated dairy pasture. Each method used a different approach to sampling with the number of samples per method based on protocols that had been used in grasslands. Overall, for adults of the weevil Listronotus bonariensis, no method provided a consistently high mean density, while for adults of the weevil Sitona obsoletus, the vacuum cleaner and turf heat extraction methods gave generally higher mean densities. For predatory beetles and lacewings, heat extraction was the most effective for density measurements, while for ladybirds and spiders, the Vortis™ provided the best estimate of mean density. Increasing pasture dry matter (kg Dm/ha) generally had a significant negative effect on S. obsoletus density but not for L. bonariensis. While no method was consistently superior than another, the vacuum cleaner and heat extraction methods generally provided higher mean densities. The G‐vac generally produced the lowest density estimates, but the sampling protocol meant a larger collection area per unit effort and therefore the probability of detection was higher compared with the three other methods. In conclusion, the study showed that the optimal sampling method depends on the taxa targeted, and more than one method may be required to measure density and diversity of species in both natural and modified grasslands.

Measurements and modelling of the viscosity of (methane + ethane) mixtures at temperatures from (253.15 to 473.15) K with pressures up to 2 MPa

We present viscosity measurements of three (methane + ethane) gas mixtures as well as of the pure fluids methane and ethane over the temperature range from (253.15 to 473.15)K at pressures between (0.1 and 2.0)MPa; the relative expanded combined uncertainty (k = 2) in viscosity ranges between (0.16 and 0.49)%. Measurements were carried out relative to helium using a rotating-body viscometer. The composition of the commercially purchased gas mixtures was verified in-house through highly accurate density measurements utilizing a well-proven two-sinker magnetic-suspension densimeter. We compare our experimental viscosities to experimental literature data, recent ab initio calculated values and correlations. Around ambient conditions, the new pure fluid data do not differ more than 0.1 % from reference and ab initio calculated values. At the highest temperature of the present study, deviations of the new data to ab initio data increase to 0.20 % and 0.33 % for methane and ethane, respectively. For an appropriate evaluation of the binary mixture data and for the purpose of data comparison, a second-order viscosity virial correlation for the present mixture was fitted to the experimental data for the pure fluids and for one mixture. The correlation is based on the modified Enskog theory for hard sphere mixtures. As a result, the relative deviations of the pure fluid data do not exceed 0.15 %, and the maximum relative deviation of all viscosity data from the model was 0.22 %. This implies that all experimental viscosity data are reproduced or predicted, respectively, within their experimental uncertainties.

Density-Based Measurement and Manipulation via Magnetic Levitation Enhanced by the Dual-Halbach Array

This work explores the design of a magnetic levitation configuration enhanced by a dual-Halbach array that enables density-based measurement and manipulation in a flexible, open-plan space. The two-parallel arranged Halbach arrays with concentrated magnetic flux allow the use of magnetic gradients parallel to the faces of the magnets to levitate samples in paramagnetic solutions. Compared to the commonly used MagLev device in which a sample container remains obscured by the magnets, the dual-Halbach array places no physical barriers to physical sampling while levitating in the magnetic field, gaining easy access to specific populations of samples in paramagnetic solutions. The strength of the linear gradient in density can be tuned by setting the gap between the two arrays, enabling accurate and convenient density measurement with tunable sensitivity. The access to manipulate specific populations of samples and ability to tune measurement sensitivity provide an operationally simple method for iterative separation and purification procedures. The design of the magnetic levitation configuration enhanced by the dual-Halbach array provides an accurate, inexpensive and easy-to-operate method that would be useful for analysis, quality control, purification in the fields of agriculture science, pharmaceutical industry and materials science.

About ecology around industrial areas of Mariupol

The oxygen content in the atmospheric air of cities, as well as in residential, office and industrial premises is the most important factor in the health and well-being of citizens. With high temperature and high absolute humidity of the surface air, the oxygen content in ambient air is minimal, and people may experience signs of hypoxia. In the industrial southern cities to which the city of Mariupol (Ukraine) belongs, there are additional factors that impede human breathing: higher (relative to the territory surrounding the city) air temperature and pollution of the atmosphere, including carbon monoxide and suspended particles. This results in conditions of abnormal heat and industrial emissions to an increase in the morbidity and mortality of the urban population. Accurate measurements of partial pressure and partial density of oxygen require special equipment and techniques, since the percentage of oxygen in ambient air is large enough, and its changes are relatively small. Most modern instruments used by urban atmospheric monitoring services are focused on measuring significant deviations of oxygen content from the norm. Air quality monitoring services do not usually measure the density of oxygen, apparently due to the implicit assumption of the negligible effect of changes in weather conditions on its content. In addition, the measurement of small changes in the oxygen content in the surface air is a rather complicated technical task. The paper presents an attempt to analytically determine the distribution of oxygen concentrations in the surface layers of the atmosphere around the places of oxygen runoff from the atmosphere at metallurgical enterprises of Mariupol, provides an analytical model based on the theory of "reverse flow" in a one-dimensional formulation of oxygen flow from the surface layer. The corresponding concentration contour lines were obtained at various distances from the oxygen sink sites. At the same time, the oxygen concentration decreases inversely with the distance from the drain, which makes it quite easy to estimate the distribution of concentrations in the surface layer of the atmosphere around the metallurgical enterprises at known coordinates of its drain points in calm weather. The spatial variability and episodes of anomalous oxygen content in the surface air are analyzed in the context of their possible effect on people's well-being.

Dew Points, Dielectric Permittivities, and Densities for (Hydrogen + Carbon Dioxide) Mixtures Determined with a Microwave Re-Entrant Cavity Resonator

Accurate dew-point, dielectric permittivity, and density measurements of two binary (H2 + CO2) mixtures with CO2 mole fractions of 0.94638 and 0.74576 were carried out utilizing an apparatus that employs a microwave re-entrant cavity resonator. Isochoric dew-point measurements were conducted at pressures up to 7.1 MPa and temperatures from T = (249.55 to 296.61) K for the (0.05362 H2 + 0.94638 CO2) mixture and between T = (251.63 and 280.44) K for the (0.25424 H2 + 0.74576 CO2) mixture. The combined expanded uncertainty with a level of confidence of approximately 95% (k = 2) in dew-point temperature and pressure ranged between (0.016 and 0.065) K and (0.0041 and 0.0177) MPa, respectively. Within 2.5%, the new data were consistent with the predictions of the GERG-2008 equation of state. Measurements of dielectric permittivity in the single-phase vapor region over the temperature range from (273.06 to 313.18) K at pressures up to 8.2 MPa and in the vicinity of the phase boundary were conducted to determine mixture molar densities by applying a method based on the polarizability mixing rule developed by Harvey and Prausnitz. The microwave-determined mixture densities near 5 MPa agree within 0.33% of reported values measured with a precision two-sinker magnetic suspension densimeter; mixture densities near 8 MPa agree within 1.33% of values calculated with the GERG-2008 equation of state.

On the ecological state of the atmosphere around the industrial areas of Mariupol

The oxygen content in the atmospheric air of cities, as well as in residential, office and industrial premises is the most important factor in the health and well-being of citizens. With high temperature and high absolute humidity of the surface air, the oxygen content in ambient air is minimal, and people may suffer hypoxia. In the industrial southern cities to which the city of Mariupol (Ukraine) belongs, there are additional factors that impede human breathing: higher (relative to the territory surrounding the city) air temperature and pollution of the atmosphere, including carbon monoxide and suspended particles. This results in an increase in the morbidity and mortality of the urban population under the conditions of abnormal heat and industrial emissions. Accurate measurements of partial pressure and partial density of oxygen require special equipment and techniques, since the percentage of oxygen in ambient air is large enough, and its changes are relatively small. Most modern instruments used by urban atmospheric monitoring services are focused on measuring significant deviations of oxygen content from the norm. Air quality monitoring services do not usually measure the density of oxygen, apparently due to the implicit assumption of the negligible effect of weather conditions changes on its content. In addition, the measurement of small changes in the oxygen content in the surface air is a rather complicated technical task. The paper presents an attempt to analytically determine the distribution of oxygen concentrations in the surface layers of the atmosphere around the places of oxygen runoff from the atmosphere at metallurgical enterprises of Mariupol, provides an analytical model based on the theory of «reverse flow» in a one-dimensional formulation of oxygen flow from the surface layer. The corresponding concentration contour lines were obtained at various distances from the oxygen sink sites. In doing so, the oxygen concentration decreases inversely with the distance from the drain, which makes it quite easy to estimate the distribution of concentrations in the surface layer of the atmosphere around the metallurgical enterprises at known coordinates of its drain points in calm weather. The spatial variability and episodes of anomalous oxygen content in the surface air have been analyzed from considerations of their possible effect on people’s well-being

Impact of photoelectric effect on X-ray density logging and its correction

This paper studied the impact of the photoelectric effect of X-ray density logging in order to improve the accuracy of X-ray measurement density. Firstly, the laws governing the changes of the Compton scattering and photoelectric effect of X-rays in the formation were analyzed based on the principle of X-ray attenuation in the formation and using the XCOM program. Secondly, the impact of photoelectric effect on X-ray density logging was studied on the basis thereof. Thirdly, a method for correcting photoelectric effect by calculating the formation bulk density using the counts in both lithology window and density window was proposed. Finally, the proposed method was verified through MCNP simulation. The results indicate that photoelectric effect was an important factor affecting the accuracy of X-ray density measurement, and the lower the X-ray energy was, the greater the impact of photoelectric effect on X-ray density measurement would be and the lower the accuracy of density measurement would be. As the γ-rays released from a Cs-137 source were at a high energy level, the impact of photoelectric effect was basically negligible when the formation bulk density was calculated using the counts in density window; on the contrary, the X-rays released from the X-ray source was at a low energy level, the impact of photoelectric effect could not be neglected when the formation bulk density was measured using X-ray. The method for calculating the formation bulk density proposed in this paper can effectively eliminate the impact of photoelectric effect and reach up to a measurement accuracy level of about 0.01g/cm3, providing a theoretical foundation for accurate density measurement during X-ray density logging.

Experimental Study for Measuring Density of slag melts by An Established Archimedean Double-bob Method

The apparatus of Archimedean double-bob method for practicing accurate was established for density measurements of slag melts. The accuracy of density measurements at room temperature to establish measurements was determined in the following ways. Firstly, the densities of water were measured at 25, 30, 35, and 40 °C. Secondly, the densities of silicone fluids with the viscosities 0.01, 0.999, 4.850, and 29.44 Pa·s were measured at 25 °C. The measured densities have good agreement with the data of water standards with a precision of 0.07% and silicone fluid standards with a precision of 0.16%. The densities of Na2O–SiO2 slag melts with 60, 70 and 80 mol % SiO2 were measured in the temperature range from 1350 to 1500 °C. The density decreases with increasing temperature and increases with increasing SiO2 contents for all compositions. The reproducibility of this work is within the error estimation of density measurements. The density results of Na2O–SiO2 melts with 60, 70 and 80 mol % at 1400 °C show that the measurements data are within 0.23 % of the density values.

An expectation-maximization algorithm enables accurate ecological modeling using longitudinal microbiome sequencing data

BackgroundThe dynamics of microbial communities is driven by a range of interactions from symbiosis to predator-prey relationships, the majority of which are poorly understood. With the increasing availability of high-throughput microbiome taxonomic profiling data, it is now conceivable to directly learn the ecological models that explicitly define microbial interactions and explain community dynamics. The applicability of these approaches is severely limited by the lack of accurate absolute cell density measurements (biomass).MethodsWe present a new computational approach that resolves this key limitation in the inference of generalized Lotka-Volterra models (gLVMs) by coupling biomass estimation and model inference with an expectation-maximization algorithm (BEEM).ResultsBEEM outperforms the state-of-the-art methods for inferring gLVMs, while simultaneously eliminating the need for additional experimental biomass data as input. BEEM’s application to previously inaccessible public datasets (due to the lack of biomass data) allowed us to construct ecological models of microbial communities in the human gut on a per-individual basis, revealing personalized dynamics and keystone species.ConclusionsBEEM addresses a key bottleneck in “systems analysis” of microbiomes by enabling accurate inference of ecological models from high throughput sequencing data without the need for experimental biomass measurements.

Study of a novel density well-logging tool using A position-sensitive detector

Density well-logging tool is an essential instrument used in the petroleum industry for determining formation density, porosity, and lithology of subsurface strata. To improve the vertical resolution and accuracy of density measurements in thin-bedded sedimentary rocks, we proposed an innovative density well-logging tool in which the traditional short- and long-spacing detectors are replaced with a position-sensitive detector (PSD). This replacement enables the measurement of the continuous gamma-ray flux in the area near the PSD. To demonstrate the feasibility of this new tool, we first simulated the performance of a PSD with NaI(Tl) crystal by using the Monte Carlo simulation method (GEANT4). The outcome shows that both gamma-ray deposited energy and interaction position can be determined by the photoelectron yield at each end of the detector, and the resolutions for energy and position are 19.0% and 1.3 cm, respectively, when the gamma-ray energy is 100 keV. Next, we created a Monte Carlo model of a density well-logging tool using such a PSD and simulated its response in a geologic model of thin-bedded strata. The result proves that the proposed tool can yield a good density evaluation when the thickness of the layer is 5 cm, which is significantly better than that obtained with the 16 cm-thick layer of traditional density tools. This study confirms the feasibility of using a PSD in density well-logging tool in theory and indicates that the proposed tool has a promising application in measuring the density of thin-bedded strata.

An accurate low-redshift measurement of the cosmic neutral hydrogen density

ABSTRACT Using a spectral stacking technique, we measure the neutral hydrogen (H i) properties of a sample of galaxies at z < 0.11 across 35 pointings of the Westerbork Synthesis Radio Telescope. The radio data contain 1895 galaxies with redshifts and positions known from the Sloan Digital Sky Survey. We carefully quantified the effects of sample bias, aperture used to extract spectra, sidelobes and weighting technique and use our data to provide a new estimate for the cosmic H i mass density. We find a cosmic H i mass density of $\Omega _{\rm H\,{\small I}} = (4.02 \pm 0.26)\times 10^{-4} h_{70}^{-1}$ at 〈z〉 = 0.066, consistent with measurements from blind H i surveys and other H i stacking experiments at low redshifts. The combination of the small interferometer beam size and the large survey volume makes our result highly robust against systematic effects due to confusion at small scales and cosmic variance at large scales. Splitting into three sub-samples with 〈z〉 = 0.038, 0.067, and 0.093 shows no significant evolution of the H i gas content at low redshift.

Relative density and isobaric expansivity of cold and supercooled heavy water from 254 to 298 K and up to 100 MPa.

A dual-capillary apparatus was developed for highly accurate measurements of density of liquids, including the supercooled liquid region. The device was used to determine the density of supercooled heavy water in the temperature range from 254 K to 298 K at pressures ranging from atmospheric to 100 MPa, relative to density at reference isotherm 298.15 K. The measurements of relative density were reproducible within 10 ppm, and their expanded (k = 2) uncertainty was within 50 ppm. To obtain absolute values of density, thermodynamic integration was performed using recent accurate speed of sound measurements in the stable liquid region. An empirical equation of state (EoS) was developed, giving specific volume as a rational function of pressure and temperature. The new experimental data are represented by EoS within their experimental uncertainty. Gibbs energy was obtained by EoS integration allowing computation of all thermodynamic properties of heavy water using Gibbs energy derivatives. Although based on data in relatively narrow temperature and pressure ranges, the developed EoS shows an excellent agreement with literature data for densities, isothermal compressibilities, and isobaric expansivities of deeply supercooled heavy water. The curvature of the thermodynamic surface steeply increases toward low temperatures and low pressures, thus supporting the existence of the hypothesized liquid-liquid coexistence boundary in a close vicinity of existing experimental data.

Numerical simulation and analysis of the characteristics of spatial distribution of induced γ-ray source used for D-D source density measurement

Abstract D-D source has a promising prospect of application in the field of controllable source density logging. However, the spatial distribution of a D-D ‘induced γ-ray source’ varies significantly and such a source is more susceptible to the influence of various formation factors, resulting in relatively low accuracy of density measurement. This study researched the spatial distribution of an induced γ-ray source. First, the principle of D-D controllable source density measurement was analyzed. Second, the generation process of a D-D induced γ-ray source and the spatial distribution under different formation conditions were simulated and studied. Finally, the associated influential factors were summarized. The results indicate that the spatial position and intensity of the induced γ-ray source were susceptible to the influence of various formation factors, such as HI, lithology and salinity. Among these factors, HI had greatest impact on the spatial position of induced γ-ray source and, particularly, when formation HI varied within the range of 0–0.1, the spatial positions of capture γ-rays changed significantly. In addition, as HI increased, the intensity of γ-rays also increased gradually. Formation lithology and salinity had a greater impact on the intensity of induced γ-rays than on the spatial distribution of these γ-rays. For formations of different lithologies, as the types and contents of main elements were different, the intensity of capture γ-rays also varied. This research provides the basic data for correcting the effects on a D-D induced γ-ray source and establishing a method of density measurement using a D-D controllable source.

The study protocol for the China Health Big Data (China Biobank) project.

Osteoporosis, obesity, and fatty liver are increasingly common chronic diseases that seriously threaten people's health. Low-dose chest computed tomography (LDCT) scan is frequently used for lung cancer screening in health screenings and checkups. Quantitative computed tomography (QCT) enables the accurate measurement of volumetric bone mineral density (vBMD), liver fat content, and abdominal fat area using the existing LDCT data without extra radiation. We initiated a new project, the China Health Big Data (China Biobank), which combines the LDCT scan images from lung cancer screening of participants in health checkup with QCT to investigate the added value of QCT to LDCT, in order to establish the normative reference database and diagnosis criteria for the three aforementioned conditions. The China Biobank project is a prospective nationwide multicenter cohort study that will combine QCT technology with LDCT scans to measure bone mineral density (BMD), intra-abdominal fat distribution, and liver fat content of the generally healthy checkup participants. Mindways QCT calibration phantom (Mindways Software Inc., Austin, TX, USA) and analysis software QCT PRO v6.0 will be used for all centers. Before data collection begins, the European Spine Phantom (ESP) will be used for quality control analysis at each collaborating center. The inclusion criteria are a healthy checkup participant aged 30-90 years, with LDCT as a part of his/her health checkup protocol. Exclusion criteria are pregnant women or participants with a metal implant in the CT scan area. The LDCT images will be transferred to the Mindways workstation for analysis, and vBMD in the L1 and L2 vertebrae, visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), and liver fat content will be measured. As part of the health checkup, the demographic, anthropometric parameters, blood pressure, and a routine blood laboratory test will be collected. The estimated sample size will be about 30,000. The combination of QCT with LDCT of the chest was validated in this project. The vBMD of spine, visceral fat and liver fat can be measured with a LDCT chest scan. The China Biobank project will assess the added value of QCT to LDCT, and enable accurate evaluation of the prevalence of osteoporosis, obesity, and fatty liver disease in a very large Chinese cohort.

An accurate and versatile density measurement device: Magnetic levitation

This study presents a magnetic levitation device for measuring density with high accuracy and versatility, and of low cost. Samples that are immersed in paramagnetic medium can be levitated at some equilibrium positions between two identical NdFeB magnets with like-poles facing each other. The method measures density without acquiring the sample’s volume, therefore it can be used to deal with tiny particles (<1 mL) which the existing methods, such as densitometer and pycnometer, cannot handle. The correlations between levitated positions and densities are mathematically modelled, in which the density can be determined based on the equilibrium position of the sample and the magnetic field. The model of the device is verified through a series of experiments on standard density glass beads and various materials of different phases and scales, i.e., PCL particles, microcrystalline cellulose powder, and corn oil droplets. The accuracy of the device reaches 0.0009 g cm−3. This approach has implications in multiple density-based applications such as cell manipulation and material separation.

Thickness dependence of the physical properties of atomic-layer deposited Al2O3

Inspired by nature, we investigate the short-range order effect on the physical properties of amorphous materials. Amorphous Al2O3 thin films exhibit a higher proportion of their 4-coordinated Al sites close to the surface, causing variations in the average short-range order of the film. Below some thickness, the density of these films changes with size. In this work, we address the short-range order effect, through the thickness, on the electronic and optical properties of atomic layer deposited Al2O3 thin films. Both the refractive index and the permittivity were found to vary with size. The refractive index increased with thickness, and for thick films (∼50 nm), it was comparable to that of bulk amorphous Al2O3. The permittivity values increased with thickness as well, but did not reach those of the bulk material. Our experimental design circumvents the unpredictable Al2O3–Si interface, allowing new insights into the permittivity–thickness relations. By combining this design with accurate thickness and density measurements, we systematically correlate the refractive index and permittivity with the density and short-range order. These results shed light on the size effects in thin amorphous oxides and may guide the design of electronic and optical components and devices.