Diffusion Measurements Research Articles

Impact of specific ion effects and electrostatic interactions on a polyelectrolyte-polyampholyte complex

A complex overlay of interactions governs the conformations of polymers in solution. Among them, electrostatic interactions are the dominating factor for governing the dynamics of charged macromolecules. Salt ions further impact the conformations by inducing screening of the electrostatic interactions of the polymers. Polyelectrolytes and polyampholytes are two majorly used charged polymers for engineering hydrogels. These polymers form a complex when added together in a solution. This article emphasises the effect of salts on the polyelectrolyte-polyampholyte complex. The interactions have been analysed through the viscosity and diffusivity measurements. The in-depth analysis of the specific ion effect along with the viscous effect induced by the polymer has been carried out. It was concluded that the viscous effect tends to reverse the impact of salts on the electrostatic-dominated conformations of the polymers. The ‘Shear Dependent Generalised Intrinsic Viscosity’ (SDGIV) have been used to gain insights into the interactions between the polymers. Finally, the scaling of the viscosity with respect to the polymer concentration and the impact of the salts on the same has also been studied. It is concluded that the viscous effect of the polymers should also be considered for analysing the specific ion effects of the salts on the charged polymers.Graphical

First measurements of radon-220 diffusion in mice tumors, towards treatment planning in diffusing alpha-emitters radiation therapy.

Diffusing alpha-emitters radiation therapy ("Alpha-DaRT") is a new method for treating solid tumors with alpha particles, relying on the release of the short-lived alpha-emitting daughter atoms of radium-224 from interstitial sources inserted into the tumor. Alpha-DaRT tumor dosimetry is governed by the spread of radium's progeny around the source, as described by an approximate framework called the "diffusion-leakage model". The most important model parameters are the diffusion lengths of radon-220 and lead-212, and their estimation is therefore essential for treatmentplanning. Previous works have provided initial estimates for the dominant diffusion length, by measuring the activity spread inside mice-borne tumors several days after the insertion of an Alpha-DaRT source. The measurements, taken when lead-212 was in secular equilibrium with radium-224, were interpreted as representing the lead-212 diffusion length. The aim of this work is to provide first experimental estimates for the diffusion length of radon-220, using a newmethodology. The diffusion length of radon-220 was estimated from autoradiography measurements of histological sectionstaken from 24 mice-borne subcutaneous tumors of five different types. Unlike previous studies, the source dwell time inside the tumor was limited to 30 min, to prevent the buildup of lead-212. To investigate the contribution of potential non-diffusive processes, experiments were done in two sets: fourteen in vivo tumors, where during the treatment the tumors were still carried by the mice with active blood supply, and 10 ex-vivo tumors, where the tumors were excised before source insertion and kept in a medium at with the sourceinside. The measured diffusion lengths of radon-220, extracted by fitting the recorded activity pattern up to 1.5mm from the source, lie in the range , with no significant difference between the average values measured in in-vivo and ex-vivo tumors: versus . However, in-vivo tumors display an enhanced spread of activity 2-3mm away from the source. This effect is not explained by the current model and is much less pronounced in ex-vivotumors. The average measured radon-220 diffusion lengths in both in-vivo and ex-vivo tumors are consistent with published data on the diffusion length of radon in water and lie close to the upper limit of the previously estimated range of . The observation that close to the source there is no apparent difference between in-vivo and ex-vivo tumors, and the good agreement with the theoretical model in this region suggest that the spread of radon-220 is predominantly diffusive in this region. The departure from the model prediction in in-vivo tumors at large radial distances may hint at potential vascular contribution, which will be the subject of futureworks.

Quantitative Assessment of Breast Tumor: Comparison of Four Methods of Positioning Region of Interest for Synthetic Relaxometry and Diffusion Measurement

ObjectivesTo compare the differences in apparent diffusion coefficient (ADC) and synthetic magnetic resonance (MR) measurements of four region of interest (ROI) placement methods for breast tumor and to investigate their diagnostic performance. Methods110 (70 malignant, 40 benign) newly diagnosed breast tumors were evaluated. The patients underwent 3.0T MR examinations including diffusion-weighted imaging and synthetic MR. Two radiologists independently measured ADCs, T1 relaxation time (T1), T2 relaxation time (T2), and proton density (PD) using four ROI methods: round, square, freehand, and whole-tumor volume (WTV). The interclass correlation coefficient (ICC) was used to assess their measurement reliability. Diagnostic performance was evaluated using multivariate logistic regression analysis and the receiver operating characteristic (ROC) curves. ResultsThe mean values of all ROI methods showed good or excellent interobserver reproducibility (0.79~0.99) and showed the best diagnostic performance compared to the minimum and maximum values. The square ROI exhibited superior performance in differentiating between benign from malignant breast lesions, followed by the freehand ROI. T2, PD, and ADC values were significantly lower in malignant breast lesions compared to benign ones for all ROI methods (p < 0.05). Multiparameters of T2 + ADC demonstrated the highest AUC values (0.82~0.95), surpassing the diagnostic efficacy of ADC or T2 alone (p < 0.05). ConclusionsROI placement significantly influences ADC and synthetic MR values measured in breast tumors. Square ROI and mean values showed superior performance in differentiating benign and malignant breast lesions. The multiparameters of T2 + ADC surpassed the diagnostic efficacy of a single parameter.

Diffusing Wave Spectroscopy Measurements of Colloidal Suspension Dynamics.

Diffusing wave spectroscopy (DWS) is used to measure the dynamics of charged silica particles between the volume fractions 0.065 ≤ ϕ ≤ 0.352 (weight percentages from 12.7 to 55.8 wt %). The short-time diffusivity averaged over the scattering vectors sampled by DWS (ϕ) decreases with an increasing concentration. An effective hard-sphere model that accounts for hydrodynamic interactions and a double-layer repulsion fits the values up to an effective volume fraction , where is the excluded shell radius normalized by the particle radius = b/a = 1.3. While DWS measurements of diffusivity are sensitive to repulsive interactions, we show that they are relatively insensitive to attraction, such as those due to secondary minima in the interaction potential or weak depletion interaction.

Refractive index measurement of pharmaceutical powders in the short-wave infrared range using index matching assisted with phase imaging

Refractive index is a fundamental optical property of powder that is used as an important input in light scattering measurements of the size distribution and diffuse reflectance spectroscopy measurements of the absorption and scattering coefficients. In this work, we demonstrate a method that combines index matching with phase imaging to determine the refractive index of complex powder particles at high accuracy without relying on any assumptions. Index matching is robust, but the accuracy is not high by relying on ocular observation of the interface. Phase imaging using interferometry improves the accuracy of determining the match by an order of magnitude. Using the proposed method, we determine the refractive index of four types of pharmaceutical powder in the short-wave infrared range of 1100–1650 nm.

Global Basic Reproduction Number of African Swine Fever in Wild Boar and a Mental Model to Explore the Disease Dynamics

Basic reproduction number (R0) is a mathematical expression used in epidemiology to address expected number of secondary cases. R0 helps to predict outbreak diffusion and preventive measures. As African swine fever (ASF) is a viral infectious disease, there are significant studies related to R0 of the ASF outbreak, but most of them are investigated in a zonal and geospecific boundary. This study explores the general overview of African swine fever virus (ASFV) R0 based on existing literature and examines for the global scale using a doubling time approach using wild boar outbreaks. Further, a qualitative mental model is developed to explore the ASF disease dynamics. It was found that the average R0 was 3.56 from existing literature. Based on the global scenario, ASFV spread in wild boar was above the threshold line (R0≥1). The recent growth trend (R0=5.87) flagging the very high risk. ASFV is threatening the world. The qualitative mental model highlighted the veterinary services as awareness and R&amp;D support are highlighted as the control measures. This study provides a reference to researchers and veterinarians in setting strategies of developing preventive measures and highlights the importance of awareness programs and R&amp;D support for mitigating the ASFV spread.

In-plane oxygen diffusion measurements in polymer films using time-resolved imaging of programmable luminescent tags

Oxygen diffusion properties in thin polymer films are key parameters in industrial applications from food packaging, over medical encapsulation to organic semiconductor devices and have been continuously investigated in recent decades. The established methods have in common that they require complex pressure-sensitive setups or vacuum technology and usually do not come without surface effects. In contrast, this work provides a low-cost, precise and reliable method to determine the oxygen diffusion coefficient D in bulk polymer films based on tracking the phosphorescent pattern of a programmable luminescent tag over time. Our method exploits two-dimensional image analysis of oxygen-quenched organic room-temperature phosphors in a host polymer with high spatial accuracy. It avoids interface effects and accounts for the photoconsumption of oxygen. As a role model, the diffusion coefficients of polystyrene glasses with molecular weights between 13k and 350k g/mol are determined to be in the range of (0.8–1.5) × 10–7 cm2/s, which is in good agreement with previously reported values. We finally demonstrate the reduction of the oxygen diffusion coefficient in polystyrene by one quarter upon annealing above its glass transition temperature.

Analysis of cold island effect in city parks from the perspectives of maximum and cumulative values – a case study of Xi'an City

The continuous process of urbanization and climate change has led to severe urban heat island (UHI) effects. Constructing parks with cooling capabilities is considered an effective measure to alleviate UHI effects. However, most studies only quantify the cooling effect from a maximum value perspective, lacking a measure of temperature diffusion in space. This study combines the perspectives of maximum value and accumulation to define a cold island index, quantifying the cooling effect of 40 urban parks in the main urban area of Xi'an city. The results show that, on average, urban parks can reduce the surrounding environment by approximately 2.3℃, with a cooling range of about 127.1ha, which is three times the park area. Different factors drive the measurement of the cooling effect using different cold island indexes, but all indexes are highly correlated with green space area. There are significant differences in the cooling effect among different types of parks, and overall, ecological parks have the best cooling effect. The directional spread of internal cold islands in parks is most related to park shape, while external spread is related to surrounding green spaces. The research results have practical value in the construction of parks with cooling effects and the sustainable development of cities in urban planning processes..

Ion and Water Dynamics in the Transition from Dry to Wet Conditions in Salt-Doped PEG.

The influence of the water content on ion and water transport mechanisms in polymer membranes under low to moderate hydration conditions remains poorly understood. In this study, we combine ion and water diffusivity (PFG-NMR) measurements with atomistic molecular dynamics simulations to better understand transport processes in hydrated salt-doped poly(ethylene glycol). Above the water percolation threshold, the experimental and simulated diffusivities are in good agreement with the free volume transport models. At low hydration levels, unlike dry systems, ion diffusion cannot be described by polymer segmental dynamics alone. We rationalize such observations by the interplay between ion-water and ion-polymer solvation of cations and between ion-water and cation-anion interactions for anions. Further, we demonstrate that a two-state model combining ion-water solvation and free volume transport can describe water dynamics across the entire hydration range of interest. Our findings provide a more encompassing analysis of ion and water transport in hydrated polyelectrolytes, specifically in the low hydration regime.

Connection Between Weighted Tail, Orlicz, Grand Lorentz And Grand Lebesgue Norms

We prove that the norm of functions in a suitable Grand Lorentz space built on a measure space, equipped with sigma finite diffuse measure, coincides with the norm in a suitable exponential Grand Lebesgue Space space as well as coincides with the so-called exponential tail norm, which may be quite described as norm in a suitable Banach rearrangement invariant space. We also exhibit comparisons with exponential Orlicz norms.

Structured Excitation Energy Transfer: Tracking Exciton Diffusion below Sunlight Intensity.

With the increasing demand for new materials for light-harvesting applications, spatiotemporal microscopy techniques are receiving increasing attention as they allow direct observation of the nanoscale diffusion of excitons. However, the use of pulsed and tightly focused laser beams generates light intensities far above those expected under sunlight illumination, leading to photodamage and nonlinear effects that seriously limit the accuracy and applicability of these techniques, especially in biological or atomically thin materials. In this work, we present a novel spatiotemporal microscopy technique that exploits structured excitation in order to dramatically decrease the excitation intensity, up to 10,000-fold when compared with previously reported spatiotemporal photoluminescence microscopy experiments. We tested our method in two different systems, reporting the first exciton diffusion measurement at illumination conditions below sunlight, both considering average power and peak exciton densities in an organic photovoltaic sample (Y6), where we tracked the excitons for up to five recombination lifetimes. Next, nanometer-scale energy transport was directly observed for the first time in both space and time in a printed monolayer of the light-harvesting complex 2 from purple bacteria.

The investigation of synthesis and textured properties of in situ formed hBN with spark plasma sintering

Hexagonal boron nitride (hBN) exhibits high thermal conductivity within the in-plane direction and significantly lower thermal conductivity in the cross-plane direction because of its anisotropic nature. When the texture properties of bulk hBN are strong, it is a potentially promising application area for the insulating heat spreaders and heat sinks. In this study, hBN was synthesized in situ with the spark plasma sintering (SPS) technique and the effects of sintering temperature on the orientation of hBN grains were investigated. The precursor was prepared by chemically reacting urea and boric acid in heat treatment at 850 °C. The hBN was produced using the previous precursor in a SPS at 1500, 1700, and 1900 °C. The samples were characterized using XRD, FTIR, SEM and Raman spectroscopy. The properties of the samples were further determined through measurements of density, DSC and thermal diffusivity. The hBN samples obtained through the SPS process have nano and micron-size grains. The hBN was highly crystalline and homogeneous, as determined by the XRD pattern, Raman spectra and Raman maps. The orientation of hBN grains has been revealed in the c-axis of hBN crystallites and was preferably arranged within a plane parallel to the SPS pressing direction. The hBN orientation preference index (IOP) value of −19925.5 at 1700 °C indicates the highest quality texture orientation. Increasing the temperature to 1900 °C decreased the orientation in the direction parallel to the pressing direction. The highest thermal conductivity calculated according to the thermal diffusivity perpendicular to the sintering pressure direction was 8.86 W m−1K−1 at 1900 °C.

The evaluation of microbubble concentration using the techniques of optical spectroscopy

We present an accurate and low-cost method for the evaluation of concentration of ultrasound contrast agents, microbubbles (MBs) by utilizing light-scattering properties of MBs. Illuminated by near-infrared light, MBs act as Mie scattering particles. We used absorption spectroscopy to detect the optical density immediately after the preparation of Sonovue MBs, and after MB insonification for total of 187 MB samples. Strong linear correlation (r = 0.97) was determined between optical density of MB suspension, evaluated at 790 nm, and MB concentration in vitro (measured by hematocytometer, up to 3.3 × 107 MBs/ml).Optical density of MB suspension was assessed by simultaneously performing diffuse reflectance spectroscopy and absorption spectroscopy measurements in vitro. Further we aimed to assess MB optical density in tibialis cranialis muscles of C57Bl/CBA mice. The results of diagnostic B-scan imaging and diffuse reflectance spectroscopy shows that optical techniques are excellent for monitoring the changes in MB concentration both in vitro and in vivo.

Quantitative measurement of mammographic density in breast-tissue explants using portable NMR: Precision and accuracy.

Single-sided portable NMR (pNMR) has previously been demonstrated to be suitable for quantification of mammographic density (MD) in excised breast tissue samples. Here we investigate the precision and accuracy of pNMR measurements of MD ex vivo as compared with the gold standards. Forty-five breast-tissue explants from 9 prophylactic mastectomy patients were measured. The relative tissue water content was taken as the MD-equivalent quantity. In each sample, the water content was measured using some combination of three pNMR techniques (apparent T2, diffusion, and T1 measurements) and two gold-standard techniques (computed microtomography [μCT] and hematoxylin and eosin [H&E] histology). Pairwise correlation plots and Bland-Altman analysis were used to quantify the degree of agreement between pNMR techniques and the gold standards. Relative water content measured from both apparent T2 relaxation spectra, and diffusion decays exhibited strong correlation with the H&E and μCT results. Bland-Altman analysis yielded average bias values of -0.4, -2.6, 2.6, and 2.8 water percentage points (pp) and 95% confidence intervals of 13.1, 7.5, 11.2, and 11.8 pp for the H&E - T2, μCT - T2, H&E - diffusion, and μCT - diffusion comparison pairs, respectively. T1-based measurements were found to be less reliable, with the Bland-Altman confidence intervals of 27.7 and 33.0 pp when compared with H&E and μCT, respectively. Apparent T2-based and diffusion-based pNMR measurements enable quantification of MD in breast-tissue explants with the precision of approximately 10 pp and accuracy of approximately 3 pp or better, making pNMR a promising measurement modality for radiation-free quantification of MD.

The Effect of an Er:YAG Laser Combined with a 755 nm Picosecond Laser on Tattoo Removal in a Rat Model

Laser tattoo removal is an effective technique, but multiple rounds of treatment are required to eliminate tattoos, which can be a challenge for patients who do not have the time. Additionally, there is relatively limited research on the mechanisms of laser tattoo removal, necessitating further in-depth studies. This study aimed to investigate the efficacy of an Er:YAG laser combined with a 755-picosecond laser for tattoo removal and the changes in skin diffuse reflection, pigment particle size, macrophage recruitment, and inflammatory factor levels during combined laser treatment. Our experiments used three sets of lasers—an Er:YAG laser, a 755 nm picosecond laser, and an Er:YAG laser combined with a 755 nm picosecond laser—for tattoo removal. The effects of tattoo removal at different time points were evaluated. Moreover, the mechanisms were explored using HE staining, immunohistochemistry, diffuse reflectance measurements, in vitro gel tests, mass spectrometry, and ELISA experiments. The combined treatment was more effective for tattoo removal in rats. The combined laser treatment effectively reduced diffuse reflection from the skin, thereby increasing the effective laser power, reducing the size of the pigment particles, allowing for easier removal of the pigment, and increasing the recruitment of dermal macrophages and the release of inflammatory factors, thus increasing the rate of tattoo removal in vivo.

The effects of biological crowders on fibrillization, structure, diffusion, and conformational dynamics of α-synuclein.

α-synuclein is an intrinsically disordered protein (IDP) whose aggregation in presynaptic neuronal cells is a pathological hallmark of Lewy body formation and Parkinson's disease. This aggregation process is likely affected by the crowded macromolecular cellular environment. In this study, α-synuclein was studied in the presence of both a synthetic crowder, Ficoll70, and a biological crowder composed of lysed cells that better mimics the biocomplexity of the cellular environment. 15 N-1 H HSQC NMR results show similar α-synuclein chemical shifts in non-crowded and all crowded conditions implying that it remains similarly unstructured in all conditions. Nevertheless, both HSQC NMR and fluorescence measurements indicate that, only in the cell lysate, α-synuclein forms aggregates over a timescale of 48 h. 15 N-edited diffusion measurements indicate that all crowders slow down the α-synuclein's diffusivity. Interestingly, at high concentrations, α-synuclein diffuses faster in cell lysate than in Ficoll70, possibly due to additional soft (e.g., electrostatic or hydrophobic) interactions. 15 N-edited relaxation measurements show that some residues are more mobile in cell lysate than in Ficoll70; the rates that are most different are predominantly in hydrophobic residues. We thus examined cell lysates with reduced hydrophobicity and found slower dynamics (higher relaxation rates) in several α-synuclein residues. Taken together, these experiments suggest that while cell lysate does not substantially affect α-synuclein structure (HSQC spectra), it does affect chain dynamics and translational diffusion, and strongly affects aggregation over a timescale of days, in a manner that is different from either no crowder or an artificial crowder: soft hydrophobic interactions are implicated.

White matter diffusion estimates in obsessive-compulsive disorder across 1653 individuals: machine learning findings from the ENIGMA OCD Working Group

White matter pathways, typically studied with diffusion tensor imaging (DTI), have been implicated in the neurobiology of obsessive-compulsive disorder (OCD). However, due to limited sample sizes and the predominance of single-site studies, the generalizability of OCD classification based on diffusion white matter estimates remains unclear. Here, we tested classification accuracy using the largest OCD DTI dataset to date, involving 1336 adult participants (690 OCD patients and 646 healthy controls) and 317 pediatric participants (175 OCD patients and 142 healthy controls) from 18 international sites within the ENIGMA OCD Working Group. We used an automatic machine learning pipeline (with feature engineering and selection, and model optimization) and examined the cross-site generalizability of the OCD classification models using leave-one-site-out cross-validation. Our models showed low-to-moderate accuracy in classifying (1) “OCD vs. healthy controls” (Adults, receiver operator characteristic-area under the curve = 57.19 ± 3.47 in the replication set; Children, 59.8 ± 7.39), (2) “unmedicated OCD vs. healthy controls” (Adults, 62.67 ± 3.84; Children, 48.51 ± 10.14), and (3) “medicated OCD vs. unmedicated OCD” (Adults, 76.72 ± 3.97; Children, 72.45 ± 8.87). There was significant site variability in model performance (cross-validated ROC AUC ranges 51.6–79.1 in adults; 35.9–63.2 in children). Machine learning interpretation showed that diffusivity measures of the corpus callosum, internal capsule, and posterior thalamic radiation contributed to the classification of OCD from HC. The classification performance appeared greater than the model trained on grey matter morphometry in the prior ENIGMA OCD study (our study includes subsamples from the morphometry study). Taken together, this study points to the meaningful multivariate patterns of white matter features relevant to the neurobiology of OCD, but with low-to-moderate classification accuracy. The OCD classification performance may be constrained by site variability and medication effects on the white matter integrity, indicating room for improvement for future research.

Proline-Tyrosine Ring Interactions in Black Widow Dragline Silk Revealed by Solid-State Nuclear Magnetic Resonance and Molecular Dynamics Simulations.

Selective one-dimensional 13C-13C spin-diffusion solid-state nuclear magnetic resonance (SSNMR) provides evidence for CH/π ring packing interactions between Pro and Tyr residues in 13C-enriched Latrodectus hesperus dragline silk. The secondary structure of Pro-containing motifs in dragline spider silks consistently points to an elastin-like type II β-turn conformation based on 13C chemical shift analysis. 13C-13C spin diffusion measurements as a function of mixing times allow for the measurement of spatial proximity between the Pro and Tyr rings to be ∼0.5-1 nm, supporting strong Pro-Tyr ring interactions that likely occur through a CH/π mechanism. These results are supported by molecular dynamics (MD) simulations and analysis and reveals new insights into the secondary structure and Pro-Tyr ring stacking interactions for one of nature's toughest biomaterials.

Positive Effects of Uric Acid on White Matter Microstructures and Treatment Response in Patients With Schizophrenia.

Schizophrenia involves microstructural changes in white matter (WM) tracts. Oxidative stress is a key factor causing WM damage by hindering oligodendrocyte development and myelin maturation. Uric acid (UA), an endogenous antioxidant, may protect against oxidative stress. We investigated the effect of UA on WM connectivity in antipsychotic-naive or -free patients with early- or chronic-stage schizophrenia. A total of 192 patients with schizophrenia (122 recent-onset [ROS] and 70 chronic [CS]) and 107 healthy controls (HCs) participated in this study. Diffusion tensor imaging data and serum UA levels at baseline were obtained. Fractional anisotropy was lower in the widespread WM regions across the whole brain, and diffusivity measures were higher in both schizophrenia groups than in HCs. The CS group showed lower diffusivity in some WM tracts than the ROS or HC groups. The linear relationship of serum UA levels with axial and mean diffusivity in the right frontal region was significantly different between schizophrenia stages, which was driven by a negative association in the CS group. WM diffusivity associated with serum UA levels correlated with 8-week treatment responses only in patients with CS, suggesting UA to be protective against long-term schizophrenia. UA may protect against the WM damage associated with the progression of schizophrenia by reducing oxidative stress and supporting WM repair against oxidative damage. These results provide insights into the positive role of UA and may facilitate the development of novel disease-modifying therapies.

Dynamic Changes in Long-Standing Multiple Sclerosis Revealed by Longitudinal Structural Network Analysis Using Diffusion Tensor Imaging.

DTI can be used to derive conventional diffusion measurements, which can measure WM abnormalities in multiple sclerosis. DTI can also be used to construct structural brain networks and derive network measurements. However, few studies have compared their sensitivity in detecting brain alterations, especially in longitudinal studies. Therefore, in this study, we aimed to determine which type of measurement is more sensitive in tracking the dynamic changes over time in MS. Eighteen patients with MS were recruited at baseline and followed up at 6 and 12 months. All patients underwent MR imaging and clinical evaluation at 3 time points. Diffusion and network measurements were derived, and their brain changes were evaluated. None of the conventional DTI measurements displayed statistically significant changes during the follow-up period; however, the nodal degree, nodal efficiency, and nodal path length of the left middle frontal gyrus and bilateral inferior frontal gyrus, opercular part showed significant longitudinal changes between baseline and at 12 months, respectively. The nodal degree, nodal efficiency, and nodal path length of the left middle frontal gyrus and bilateral inferior frontal gyrus, opercular part may be used to monitor brain changes over time in MS.