[Accumulation and Pollution Risks of Heavy Metals in Soils and Agricultural Products from a Typical Black Shale Region with High Geological Background].

Soil polluted by heavy metals (HMs) is an important environmental issue in China, and regional geological background is a vital factor that influences the enrichment of HMs in soils. Previous studies have shown that soils derived from black shales are commonly enriched in HMs and present high potential eco-environmental risks. However, few studies have investigated the HMs in different agricultural products, which inhibit the safe use of land and safe production of food crops in black shale regions. This study investigated the concentrations, pollution risks, and speciation of HMs in soils and agricultural products from a typical black shale region in Chongqing. The results showed that the study soils were enriched in Cd, Cr, Cu, Zn, and Se but not in Pb. Approximately 98.7% of total soils exceeded the risk screening values, and 47.3% of total soils exceeded the risk intervention values. Cd had the highest pollution level and potential ecological risks and was the primary pollutant in soils of the study area. Most of the Cd resided in ion-exchangeable fractions (40.6%), followed by residual fractions (19.1%) and weak organic matter combined fractions (16.6%), whereas Cr, Cu, Pb, Se, and Zn were dominated by residual fractions. Additionally, organic combined fractions contributed to Se and Cu, and Fe-Mn oxide combined fractions contributed to Pb. These results indicated that Cd had higher mobility and availability than those of other metals. The agricultural products presented a weak ability to accumulate HMs. Approximately 18.7% of the collected samples with Cd exceeded the safety limit, but the enrichment factor was relatively low, indicating low pollution risks of the heavy metals. The findings of this study could provide guidelines for safe use of land and safe production of food crops in black shale regions with high geological background.

A novel ultrasound probe calibration method for multimodal image guidance of needle placement in cervical cancer brachytherapy.

PURPOSE: Interstitial needles placement is a critical component of combined intracavitary/interstitial (IC/IS) brachytherapy (BT). To ensure precise placement of interstitial needles, we proposed a novel ultrasonic (US) probe calibration method to accurately register the US image in the magnetic resonance imaging (MRI) image and provide multimodal image guidance for needle placement. METHODS: A wire-based calibration phantom combined with the stylus was developed for the calibration of US probe. The calibration phantom helps to quickly align the imaging plane of the US probe with the fiducial points to obtain US images of these points. The coordinates of fiducial points in US images were located automatically by feature extraction algorithms and were further corrected by the proposed correction method. Ingenious structures were designed on both sides of the calibration phantom to accurately obtain the coordinates of the fiducial points relative to the tracking device. Marker validation and pelvic phantom study were performed to evaluate the accuracy of the proposed calibration method. RESULTS: In the marker validation, the US probe calibration method with corrected transformation achieves a registration accuracy of 0.694 ± 0.014 mm, and the uncorrected one is 0.746 ± 0.018 mm. In the pelvic phantom study, the needle tip difference was 1.096 ± 0.225 mm and trajectory difference was 1.416 ± 0.284 degrees. CONCLUSION: The proposed US probe calibration method is helpful to achieve more accurate multimodality image guidance for needle placement.

Deep reinforcement learning for treatment planning in high-dose-rate cervical brachytherapy.

PURPOSE: High-dose-rate (HDR) brachytherapy (BT) is an effective cancer treatment method in which the radiation source is placed within the body. Treatment planning is a critical component for a successful outcome. Almost all currently proposed treatment planning methods are built on stochastic heuristic algorithms, which limits the generation of higher quality plans. This study proposed a novel treatment planning method to adjust dwell times in a human-like fashion to improve the quality of the plan. METHODS: We built an intelligent treatment planner network (ITPN) based on deep reinforcement learning (DRL). The network architecture of ITPN is Dueling Double-Deep Q Network. The state is the dwell time of each dwell position and the action is which dwell time to adjust and how to adjust it. A hybrid equivalent uniform dose objective function was established and assigned corresponding rewards according to its changes. Experience replay was performed with the epsilon greedy algorithm and SumTree data structure. RESULTS: In the evaluation of ITPN using 20 patient cases, D90, D100 and V100 showed no significant difference compared with inverse planning simulated annealing (IPSA) optimization. However, D2cc of bladder, rectum and sigmoid, V150 and V200 were significant reduced, and homogeneity index and conformity index were significantly increased. CONCLUSION: The proposed ITPN was able to generate higher quality plans based on the learned dwell time adjustment policy than IPSA. This is the first artificial intelligence system that can directly determine the dwell times of HDR BT, which demonstrated the potential feasibility of solving optimization problems via DRL.

Water evaporation on highly viscoelastic polymer surfaces.

Results are reported for a study on the evaporation of water droplets from a highly viscoelastic acrylic polymer surface. These are contrasted with those collected for the same measurements carried out on polydimethylsiloxane (PDMS). For PDMS, the evaporation process involves the expected multistep process including constant drop area, constant contact angle, and finally a combination of these steps until the liquid is gone. In contrast, water evaporation from the acrylic polymer shows a constant drop area mode throughout. Furthermore, during the evaporation process, the drop area actually expands on the acrylic polymer. The single mode evaporation process is consistent with formation of wetting structures, which cannot be propagated by the capillary forces. Expansion of the drop area is attributed to the influence of the drop capillary pressure. Furthermore, the rate of drop area expansion is shown to be dependent on the thickness of the polymer film.

Drop behavior on a thermally-stripped acrylic polymer: influence of surface tension induced wetting ridge formation on retention and running.

Results are reviewed from a study on retention and running of water and other liquids on tilted, polymer coated surfaces. The polymer is a thermally-stripped, solvent-borne acrylic composed primarily of the monomer 2-ethylhexyl acrylate, providing a soft and viscoelastic substrate absent of contaminants. It is shown that drop retention does not obey standard models, which assume dominance of capillary forces in offsetting drop weight for tilted plates. For these surfaces, maximum volumes correlate with capillary lengths, and distinct deformations, which vary in magnitude depending on location, are apparent over the entire drop perimeter. Deformation images indicate that running, which in real time appears to be continuous motion, actually proceeds through a series of steps beginning with the failure of the front edge wetting line. This produces a relatively large translation of the drop's front edge down the plate surface stretching the drop. This is followed by multiple failures at the rear edge producing a series of small translations, contracting the drop volume to a more spherical-like geometry. Repetition of this mechanism results in the appearance of propagation similar to that employed by an inchworm. The proposed mechanism is consistent with images of drop movement and deformations induced on polymer surfaces, which are apparent subsequent to the running process.

Characterization of dynamic stick-and-break wetting behavior for various liquids on the surface of a highly viscoelastic polymer.

A thermally stripped acrylic polymer was wet with a series of liquids possessing a broad range of properties. Previously, novel wetting behavior by water was reported for the polymer, which included the formation of a wetting ridge structure substantially larger than those reported elsewhere and the complete halting of the three-phase line. This allows metastable angles ranging from 0 degrees to greater than 150 degrees to be achieved through changes in the sessile drop volume. Greater advancing angles are prevented by the collapse of the drop, producing what has been described as stick-and-break propagation. In Wilhelmy plate experiments for metal plates coated with the polymer, this mechanism produces a quasi-periodic pattern of lines composed of ridge structures. Similar behavior was observed for all liquids tested. Differences were observed in the maximum force measured with a tensiometer (pinning force) and the average distance between ridges for the formed pattern (pinning distance). These quantities are shown to be related to the height of the ridge structures. The kinematic viscosity of the liquids appears to be an important variable for the wetting process. A comparison of pinning quantities at various rates with the master curve of the polymer indicate that its viscoelastic properties govern, to a great extent, the observed rate dependencies; i.e., higher rates produce greater elastic behavior and smaller ridge heights. Also important is the polymer's tendency for creep deformation. The ridge apex is shown to be displaced a significant distance through ridge deformation, which modifies its symmetry.

Mechanical pinning of liquids through inelastic wetting ridge formation on thermally stripped acrylic polymers.

A film composed of a thermal-stripped, solvent-borne acrylic polymer is shown to completely arrest motion of the three-phase line for water as a result of ridge structure formation. This mechanism produces anomalous wetting behavior including the arbitrary selection of contact angles, formation of quasi-periodic ridge structures on surfaces, and requirement of stick and break motion for wetting line advancement, a novel mechanism reported here. The ridges are retained by the polymer subsequent to wetting, which are 2 scales larger in height than those described previously. This allows for their characterization, which shows significant detail including the hierarchical apex structure where a cutoff area is used in theoretical treatment to avoid a singularity. Results of Wilhelmy plate experiments show a spatial connection between quasi-periodic variation in force-displacement curves and the wetting ridges on plate. These results are consistent with the dominance of the viscoelastic properties of the substrate in determining wetting behavior.

Collapse and shedding transitions in binary lipid monolayers coating microbubbles.

We report on a fluorescence microscopy study of the monolayer collapse and shedding behavior due to shell compression during the dissolution of air-filled, lipid-coated microbubbles in degassed media. The monolayer shell was comprised of saturated diacyl phosphatidylcholine (C12:0 to C22:0) and an emulsifier, poly(ethylene glycol)-40 stearate. The morphologies of monolayer collapse structures and shed particles were monitored as a function of phospholipid acyl chain length (n) and temperature. The two components formed a single miscible phase when the phospholipid was near or above its main phase transition temperature, and collapse occurred via suboptical particles to vesicles (both were shed) and tubes as chain length increased. Conversely, two-phase coexistence was observed when the lipid was below its main phase transition temperature. For these bubbles, a transition from primary collapse to secondary collapse was observed. Primary collapse was observed as a loss of expanded phase due to vesiculation. Secondary collapse involved the rapid propagation of monolayer folds and simultaneous deformation. For very rigid monolayers, we observed substantial surface buckling with simultaneous nucleation and growth of folds. The folds merged at a single point or region, providing a conduit for the entire excess lipid to shed in a single event, and the bubble smoothed and became more spherical. These results are discussed in the context of general binary phospholipid collapse behavior, microbubble dissolution behavior, medical applications, and the dissolution behavior of natural microbubbles.

Effect of microstructure on molecular oxygen permeation through condensed phospholipid monolayers.

A method is presented that allows novel measurement of the effect of microstructure on the oxygen permeability of highly condensed, polycrystalline phospholipid monolayers. Oxygen permeability of the polycrystalline shell coating a stationary microbubble is measured directly using an apposing microelectrode in the induced transfer mode and modeling oxygen flux through the shell and intervening aqueous medium. Varying cooling rate through the phospholipid main phase transition permits control of shell microstructure by manipulation of crystalline domain size and shape. Domain boundary density, defined as the ratio of the mean domain perimeter to the mean domain area, of the microbubble shell is determined by fluorescence microscopy. Oxygen permeability was shown to increase linearly with domain boundary density at a constant phospholipid acyl chain length and, accordingly, was shown to decrease exponentially with increasing chain length at a constant domain boundary density. Modification of the energy barrier theory to account for microstructural effects, in terms of the domain boundary density, provides a general equation to model passive transport through polycrystalline monolayer films. Results from this method show promise in determining the gas transport kinetics of medical microbubbles and the gas exchange characteristics of biological monolayers.

Surface phase behavior and microstructure of lipid/PEG-emulsifier monolayer-coated microbubbles.

Langmuir trough methods and fluorescence microscopy were combined to investigate the phase behavior and microstructure of monolayer shells coating micron-scale bubbles (microbubbles) typically used in biomedical applications. The monolayer shell consisted of a homologous series of saturated acyl chain phospholipids and an emulsifier containing a single hydrophobic stearate chain and polyethylene glycol (PEG) head group. PEG-emulsifier was fully miscible with expanded phase lipids and phase separated from condensed phase lipids. Phase coexistence was observed in the form of dark condensed phase lipid domains surrounded by a sea of bright, emulsifier-rich expanded phase. A rich assortment of condensed phase area fractions and domain morphologies, including networks and other novel structures, were observed in each batch of microbubbles. Network domains were reproduced in Langmuir monolayers under conditions of heating-cooling followed by compression-expansion, as well as in microbubble shells that underwent surface flow with slight compression. Domain size decreased with increased cooling rate through the phase transition temperature, and domain branching increased with lipid acyl chain length at high cooling rates. Squeeze-out of the emulsifier at a surface pressure near 35 mN/m was indicated by a plateau in Langmuir isotherms and directly visualized with fluorescence microscopy, although collapse of the solid lipid domains occurred at much higher surface pressures. Compression of the monolayer past the PEG-emulsifier squeeze-out surface pressure resulted in a dark shell composed entirely of lipid. Under certain conditions, the PEG-emulsifier was reincorporated upon subsequent expansion. Factors that affect shell formation and evolution, as well as implications for the rational design of microbubbles in medical applications, are discussed.