Intermediate Contact Research Articles

Development of Innovative Thermoplastic Foam Materials Using Two Additive Manufacturing Technologies for Application in Evaporative Cooling Systems.

Evaporative cooling systems have emerged as low-energy consumption alternatives to traditional vapor compression systems for building air conditioning. This study explored the feasibility of utilizing polymeric foamed materials produced through additive manufacturing as wetting materials in evaporative cooling systems. Specifically, two different commercial polylactic acid filaments, each containing a percentage of a chemical blowing agent, were studied. Experiments were designed to evaluate the influence of critical process parameters (line width, flow rate, speed, and layer height) on the performance of the resulting foamed materials in terms of evaporative cooling by conducting water absorption, capillarity, porosity, and wettability tests. Considering that high water absorption, capillarity, and porosity, coupled with an intermediate contact angle, are advantageous for evaporative cooling effectiveness, a low flow rate was found to be the most important parameter to improve these properties' values. The results showed that the appropriate combination of polymer and process parameters allowed the production of foamed polymer-based materials processed by additive manufacturing technology with optimal performance.

Interplay of pore geometry and wettability in immiscible displacement dynamics and entry capillary pressure

Recent studies highlight the significant role of pore geometry and wettability in determining fluid–fluid interface dynamics in two-phase flow in porous media. However, current entry capillary pressure equations, rooted in the Young–Laplace equation, consider only cross-sectional details and apply wettability data measured on flat surfaces to complex three-dimensional (3D) pore structures, overlooking the coupled effect of contact angle and pore morphologies along the flow direction. This study employs the volume-of-fluid method to investigate the following: (a) How do combined effects of pore geometry and wettability control capillary pressure change, displacement efficiency, and residual saturations? (b) Can continuous two-phase flow be achieved at the pore scale? Through direct numerical simulations in constricted idealized-geometry capillary tubes and real pore structures, we vary the contact angle to characterize its impact on fluid–fluid interface morphology, entry capillary pressure (pce), and displacement efficiency. Our results show that during the drainage, pce temporarily decreases/turns negative under intermediate wettability conditions due to forced curvature rearrangement/reversal in the converging section. Local orientation angles along the flow direction are important in controlling the interface morphology and pce evolution. Moreover, intermediate contact angles enhance displacement efficiency due to curvature reversal, while insufficient corner flow during imbibition causes pore snap-off of the receding fluid, leading to higher residual saturation. The results challenge conventional methods in predicting entry capillary pressure, highlighting the need for incorporating 3D geometry in predictive models. Eventually, the insights underscore the importance of considering corner flow in controlling displacement efficiency within constricted geometries in pore network modelling studies.

High-Performance p-Type Quasi-Ohmic of WSe2 Transistors Using Vanadium-Doped WSe2 as Intermediate Layer Contact.

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs), such as tungsten diselenide (WSe2), hold immense potential for applications in electronic and optoelectronic devices. However, a significant Schottky barrier height (SBH) at the metal-semiconductor (MS) interface reduces the electronic device performance. Here, we present a unique 2D/2D contact method for minimizing contact resistance and reducing the SBH. This approach utilizes vanadium-doped WSe2 (V-WSe2) as the drain and source contacts. The fabricated transistor exhibited a stable operation with p-type quasi-ohmic contact and a high on/off current ratio surpassing 108 at room temperature, reaching 1011 at 10 K. The device achieved an on-current of 68.87 μA, a high mobility of 103.80 cm2 V-1 s-1, a low contact resistance of 0.92 kΩ, and remarkably low SBH values of 1.51 meV for holes at VGS = -120 V with fixed VDS = 1 V. Furthermore, a Schottky photodiode has been fabricated, utilizing V-WSe2 and Cr as the asymmetric contact platform, showing a responsivity of 116 mA W1-. The findings of this study suggest a simple and efficient method for improving the performance of TMDC-based transistors.

Progressive Collapse Behavior of a Precast Reinforced Concrete Frame System with Layered Beams

A possible way to improve the structural safety and robustness of precast building structures is to develop effective precast frame systems with layered beams, which combine prefabricated parts with cast-in situ ordinary concrete, high-performance concrete, fiber concrete, or FRP. The paper provides a new type of precast reinforced concrete frame system with layered beams for rapidly erected multi-story buildings resistant to accidental actions. Using a combination of the variational method and two-level design schemes, a simplified analytical model has been developed for structural analysis of the precast reinforced concrete frame system, both for serviceable and ultimate limit states as well as for accidental actions. The proposed model allows for determining shear deformations and the formation and opening of longitudinal cracks in the intermediate contact zone between precast and monolithic parts of reinforced concrete structural elements of the frame, as well as the formation and opening of normal cracks because of the action of axial tensile force or bending moment in these elements. The design model was validated by comparing the calculated and experimental data obtained from testing scaled models of the precast reinforced concrete frame system with layered beams. The paper investigates and thoroughly analyzes the factors affecting the stiffness and bearing capacity of the intermediate contact zone, discusses the criteria for the formation of shear cracks along the contact zone of precast and monolithic concrete, and examines the change in the stiffness and dissipative properties of layered elements at different stages of their static–dynamic loading. The robustness of the experimental models of the structural system was not ensured under the specified load, section dimensions, and reinforcement scheme. Following an accidental action, longitudinal cracks were observed in the contact joint between the monolithic and prefabricated parts in the layered beams. This occurred almost simultaneously with the opening of normal cracks in adjacent sections. A comprehensive analysis of the results indicated a satisfactory degree of agreement between the proposed semi-analytical model and the test data.

Electrical characterization of multi-gated WSe2/MoS2 van der Waals heterojunctions

Vertical stacking of different two-dimensional (2D) materials into van der Waals heterostructures exploits the properties of individual materials as well as their interlayer coupling, thereby exhibiting unique electrical and optical properties. Here, we study and investigate a system consisting entirely of different 2D materials for the implementation of electronic devices that are based on quantum mechanical band-to-band tunneling transport such as tunnel diodes and tunnel field-effect transistors. We fabricated and characterized van der Waals heterojunctions based on semiconducting layers of WSe2 and MoS2 by employing different gate configurations to analyze the transport properties of the junction. We found that the device dielectric environment is crucial for achieving tunneling transport across the heterojunction by replacing thick oxide dielectrics with thin layers of hexagonal-boronnitride. With the help of additional top gates implemented in different regions of our heterojunction device, it was seen that the tunneling properties as well as the Schottky barriers at the contact interfaces could be tuned efficiently by using layers of graphene as an intermediate contact material.

Uniform Lithium Plating for Dendrite-Free Lithium Metal Batteries: Role of Dipolar Channels in Poly(vinylidene fluoride) and PbZrxTi1-xO3 Interface.

Conventional polymer/ceramic composite solid-state electrolytes (CPEs) have limitations in inhibiting lithium dendrite growth and fail to meet the contradictory requirements of anodes and cathodes. Herein, an asymmetrical poly(vinylidene fluoride) (PVDF)-PbZrxTi1-xO3 (PZT) CPE was prepared. The CPE incorporates high dielectric PZT nanoparticles, which enrich a dense thin layer on the anode side, making their dipole ends strongly electronegative. This attracts lithium ions (Li+) at the PVDF-PZT interface to transport through dipolar channels and promotes the dissociation of lithium salts into free Li+. Consequently, the CPE enables homogeneous lithium plating and suppresses dendrite growth. Meanwhile, the PVDF-enriched region at the cathode side ensures intermediate contact with positive active materials. Therefore, Li/PVDF-PZT CPE/Li symmetrical cells exhibit a stable cycling performance exceeding 1900 h at 0.1 mA cm-2 at 25 °C, outperforming Li/PVDF solid-state electrolyte/Li cells that fail after 120 h. The LiNi0.8Co0.1Mo0.1O2/PVDF-PZT CPE/Li cells show low interfacial impedances and maintain stable cycling performance for 500 cycles with a capacity retention of 86.2% at 0.5 C and 25 °C. This study introduces a strategy utilizing dielectric ceramics to construct dipolar channels, providing a uniform Li+ transport mechanism and inhibiting dendrite growth.

A force–displacement relation based on the JKR theory for DEM simulations of adhesive particles

Studying the collective behavior of adhesive particles with the discrete element method (DEM) requires well-founded force–displacement relations (force models). While the Johnson–Kendall–Roberts (JKR) theory reliably predicts the dependence of the contact radius a on the force F, it has remained a challenge in this framework to obtain a straightforward force–displacement relation F(δ) with physically meaningful parameters to calculate the force F from the displacement δ. We derive a novel force–displacement relation from the JKR theory as a composition of functions F(δ)=(F∘a∘λ)(δ), with the intermediate functions contact radius a(λ) and effective adhesive contact radius λ(δ). We also analyze contact geometry errors in the Hertz and JKR models, derive the exact contact centroid to accurately calculate contact torques and relative tangential velocities, and propose a smoothed JKR model to avoid discontinuities in force and energy. We find that incorrect torques and relative tangential velocities are obtained when the stiffness quotient is neglected because it affects the exact location of the contact centroid. We also find that contact geometry errors can become non-negligible for nanoparticles due to their large relative contact size. In addition, we show from bouncing ball simulations that the JKR models with a nominal coefficient of restitution derived for the Hertz model result in higher damping and thus reduced actual coefficients of restitution. Our analysis serves as a foundation for contact-mechanics-based force models for DEM simulations of adhesive particles to investigate their collective behavior in the future.

Tuberculosis in 0-5-year-old children following TB contact investigations: a retrospective study in a low burden setting.

We assessed the risk of tuberculosis (TB), the management and the outcomes of 0-5-year-old children after TB contact investigations in a low-burden setting. All 0-5-year-old children who attended the TB clinic of Robert Debre Hospital, Paris, France, for a TB contact investigation between June 2016 and December 2019 were included in this retrospective study. The risk factors for TB were assessed using univariate and multivariate analyses. A total of 261 children were included. Forty-six (18%) had TB, including 37 latent tuberculosis infections (LTBIs) and 9 active TB diseases. The prevalence of TB was 21% among high-risk contacts, i.e., household or close contacts and regular or casual contacts. There was no TB among intermediate- or low-risk contacts (0/42). Living under the same roof with (OR: 19.8; 95% CI: 2.6-153), the BCG vaccine (OR: 3.2; 95% CI: 1.2-8.3), contact duration >40 h (OR: 7.6; 95% CI: 2.3-25.3) and sleeping in the room of the index case (OR: 3.9; 95% CI: 1.3-11.7) were independently associated with TB. The BCG vaccine was no longer associated when the analysis was restricted to interferon gamma release assay results. Among children without initial LTBI, antibiotic prophylaxis was not prescribed for 2-5-year-old children or for 32/36 (89%) of 0-2-year-old children who had intermediate- or low-risk contact. Overall, none of these children experienced TB. In our low prevalence setting, the risk of TB in 0-5-year-old children following a household or close contact was high. Further studies are needed to better assess prophylaxis recommendations in intermediate or low risk contact.

INTEGRATED CALCULATION AND EXPERIMENTAL TECHNOLOGY FOR ANALYSIS OF CONTACT INTERACTION WITH ACCOUNT OF ELASTIC INTERMEDIATE LAYER

The work delivers solution to a relevant scientific problem of solid mechanics. It consists in developing theoretical basis for computational and experimental research of contact interaction of complex-shaped bodies with account for micromechanical models of roughness and other intermediate or surface layers. New methods and models have been developed for the analysis of contact interaction of complex-shaped bodies with account for the micromechanical properties of surface and intermediate layers characterized by nonlinear local contact stiffness. The developed methods and models as well as the numerical analysis tools have been applied to a series of model and applied problems. The deformation behaviour of novel materials with network microstructures of one-dimensional elements has been determined. Macroscopical properties of these materials have been evaluated based on the special microscopic models and the homogenization methods. Regularities in contact distribution and its dependence on geometrical and physical factors have been determined for various complexshaped bodies. New design solutions for machine elements that improve their strength and durability have been justified. The developed methods and analysis tools have been introduced into the design of new engineering products. Their implementation resulted in improved technical characteristics of protection, structural and functional elements of transport vehicles of special purpose, gear transmissions, technical equipment, hydrovolumetric drives and so on. The conducted computational and experimental studies showed good agreement with the real response of network materials and the observed behavior of interacting elastic bodies with intermediate contact layer. Keywords: solid mechanics, complex-shaped body, contact interaction, contact pressure, intermediate layer

Widespread reticulate evolution in an adaptive radiation.

A fundamental assumption of evolutionary biology is that phylogeny follows a bifurcating process. However, hybrid speciation and introgression are becoming more widely documented in many groups. Hybrid inference studies have been historically limited to small sets of taxa, while exploration of the prevalence and trends of reticulation at deep time scales remains unexplored. We study the evolutionary history of an adaptive radiation of 109 gemsnakes in Madagascar (Pseudoxyrhophiinae) to identify potential instances of introgression. Using several network inference methods, we find 12 reticulation events within the 22-million-year evolutionary history of gemsnakes, producing 28% of the diversity for the group, including one reticulation that resulted in the diversification of an 18 species radiation. These reticulations are found at nodes with high gene tree discordance and occurred among parental lineages distributed along a north-south axis that share similar ecologies. Younger hybrids occupy intermediate contact zones between the parent lineages showing that post-speciation dispersal in this group has not eroded the spatial signatures of introgression. Reticulations accumulated consistently over time, despite drops in overall speciation rates during the Pleistocene. This suggests that while bifurcating speciation rates may decline as the result of species accumulation and environmental change, speciation by hybridization may be more robust to these processes.

Investigation of III-V GaP solar cell on silicon substrate

The best solar conversion efficiencies have been reached thanks to multijunction solar based on III-V semiconductors on GaAs or Ge substrates. While displaying high conversion efficiencies, these solar cells suffer from the high cost of such substrates. To benefit from both the low cost and technological maturity of silicon cells, III-V tandem cells on silicon seem a good compromise to overpass the theoretical efficiency limit of the Si single cells. To study the GaP/Si interface effect on the solar cell characteristic, a GaP n-i-p solar cell has been grown on silicon substrate. Two types of electrical contacts configurations have been processed: a top-top configuration in which the current does not see the GaP/Si interface and the top-bottom configuration where the electric current crosses the interface. A comparison of dark I-V, I-V under solar illumination, and EQE measurements on both configurations is performed. The top-bottom contacts configuration shows an EQE a little bit lower than the top-top contact one, likely due to lower carrier diffusion length or recombination at the lower interface. However, the result on the EQE of the top-bottom configuration is encouraging for the future development of the GaP-based/Si tandem solar cells, and any other tandem cell on silicon using GaP as an intermediate selective contact.

Intestinal helminthiasis survey withemphasison schistosomiasis in Koga irrigation scheme environs, northwest Ethiopia.

BackgroundDistribution of schistosomiasis is more focal due to spatial heterogeneities in intermediate host snail dynamics and water contact behavior of humans. This makes the search for new transmission foci of schistosomiasis and its connection with malacologically receptive water bodies essential for effective control of its transmission. This study was intended to assess the prevalence of intestinal helminth infections among schoolchildren and Schistosoma mansoni transmission in Koga irrigation scheme surroundings, northwest Ethiopia.Materials and methodsCross-sectional parasitological and malacological surveys were conducted in three schools and nearby water bodies, respectively around Koga irrigation scheme. Stool specimens were collected from 421 randomly selected schoolchildren and microscopically examined using Kato-Katz and formol-ether concentration methods. Malacological surveys were carried out and the identified Biomphalaria pfeifferi snails were screened for schistosome infection. Swiss albino mice were exposed to schistosome cercariae shed by Biomphalaria pfeifferi for definite identification of Schistosoma species.ResultsAmong the examined schoolchildren, 22.6% (95% CI: 18.7%-26.9%) were positive for at least one intestinal helminths species. Ascaris lumbricoides was the most frequent intestinal helminth detected among forty (9.5%) children. Schistosoma mansoni was detected among 4.8% (95% CI: 2.9%-7.2%) of children and its prevalence was significantly higher among male children (p = 0.038) and those attending in Mengesha Jemberie Primary School (p = 0.044). Biomphalaria pfeifferi snails were identified in water bodies in close proximity to Mengesha Jemberie and Wotete Abay Primay schools. Schistosoma mansoni adult worms were harvested after exposure of mice to cercariae shed from Biomphalaria pfeifferi snails collected from water bodies nearby Mengesha Jemberie Primary School.ConclusionsSchistosoma mansoni infection of schoolchildren, findings of schistosome infected snails and establishment of mice infection confirm that transmission is taking place in the study areas. Hence, snail control and other measures such as provision of sanitary facilities and health education are recommended.

A photo-sensitive BiVO4@Bi2O3@g-C3N4 sensor for the detection of dopamine

Dopamine (DA) plays an important biological role in cardiovascular, renal, hormone, central nervous systems and human metabolism. Photo-sensitive sensors studies are gained great importance in recent years due to some problems in enzyme-based sensors. In this study, photo-sensitive BiVO4@Bi2O3@g-C3N4 based sensor is fabricated for DA determination. The semiconductors use in this sensor system have important functions; g-C3N4 is a photosensitive material, δ-Bi2O3 is a stable electrode responsible for intermediate contact, and BiVO4 is a good electron conduction material due to its stable structure. DA is analyzed by BiVO4@Bi2O3@g-C3N4 photo-sensitive sensor in 0.1 M PBS medium at solutions with different concentrations. In this study, for the first time, a calibration curve is constructed from Tafel curves of solutions of different concentrations. The DA sensor is worked in a linear range of 25–750 µM. In addition, in this developed sensor, limit of detection (LOD), limit of quantification (LOQ) and sensitivity values are 0.046, 0.154 µM and 0.011 μA µM−1 cm−2, respectively. Our strategy opens a new pathway to determination of some neurotransmitter via photo-sensitive materials.

Silica deposition on zirconia via room-temperature atomic layer deposition (RT-ALD): Effect on bond strength to veneering ceramic

PurposeTo develop and to characterize a hybrid interface between yttria-stabilized zirconia (Y-TZP) transformed layer and silica-based nanofilm to enable a better bonding between Y-TZP and a veneering ceramic. Material and methodsSixty-six fully-sintered rectangular Y-TZP specimens were distributed into 6 groups, according to the surface treatment applied: C (control): no treatment; Al: 27 μm-alumina particle abrasion; Ht: hydrothermal treatment in autoclave for 15h; Si20: 20 cycles of silica deposition using room-temperature atomic layer deposition (RT-ALD); Si40: 40 cycles of RT-ALD; Ht + Si40: hydrothermal treatment followed by 40 cycles of RT-ALD. RT-ALD was performed by the sequential exposure of specimens to vapor of tetramethoxysilane orthosilicate (TMOS) and ammonium hydroxide (NH4OH). Y-TZP surface wettability and shear bond strength (SBS) between Y-TZP and the veneering ceramic were analyzed for all groups after surface treatments. One-way ANOVA and Tukey's HSD test were used for data analysis (p ≤ 0.05). ResultsThe highest contact angle was observed for the control group (64.46 ± 6.09 θ), while the lowest values (p < 0.001) were presented after Si20 (29.85 ± 4.23 θ) and Si40 (30.37 ± 5.51 θ) treatments. Hydrothermal treatment (49.3 ± 2.69 θ) and alumina abrasion (45.84 ± 4.12 θ) resulted in intermediate contact angle values. The highest SBS values were observed for Al (16.74 ± 1.68 MPa) and Ht (15.27 ± 2.11 MPa) groups (p < 0.018). Groups Si20 (9.66 ± 1.22 MPa), Si40 (9.33 ± 2.11 MPa), Ht + Si40 (9.37 ± 1.02 MPa) and C (12.54 ± 2.64 MPa) all resulted in similar SBS results (p > 0.998). ConclusionThe experimental treatments proposed enhanced surface wettability, but shear bond strength between Y-TZP and veneering ceramic was not improved. Alumina particle-abrasion improved SBS values while a decrease in wettability was observed.

Organic foams stabilized by Biphenyl-bridged organosilica particles

HypothesisCan surface-active particles be designed à la carte just by incorporating functional groups mimicking the structure of the solvent and gas? This is based on the idea that, to achieve good foamability, the particle wettability needs to be finely tuned to adjust the liquid-particle and gas-particle surface tensions. In practice, could particles containing phenyl rings and alkyl chains assemble at the air–liquid interface and stabilize foams based on aromatic solvents? ExperimentsA library of organosilica particles was prepared by sol–gel synthesis using aromatic organosilane precursors. The particles were characterized by TGA, FTIR and 13C/29Si MAS NMR. The foaming properties were studied after hand shaking and high-speed homogenization. The influence of particle wettability and solvent properties on foam formation was systematically investigated. A comparison was carried out between biphenyl-bridged particles and various stabilizers on foamability in benzyl alcohol. FindingsBiphenyl-bridged particles could stabilize foams in aromatic solvents with a high foam volume fraction up to 96% using Ultra-Turrax. The presence of biphenyl rings and short alkyl chains was crucial for foamability. Organic foams were prepared for aromatic solvents with intermediate surface tension (35–44 mN m−1) and contact angle in the range 32–53°. Biphenyl-bridged particles outperformed polytetrafluoroethylene and fluorinated surfactants in benzyl alcohol.

Hymecromone Administration in Real Clinical Practice: Results of the Prospective Multicentre Observational Study in the Republic of Kazakhstan

Introduction. This multicentre prospective non-interventional observational study was conducted to obtain additional data about Odeston efficacy and safety in routine clinical practice. The objectives of the study included collection of clinical characteristics of patients, evaluation of Odeston effects in treatment of biliary pain and changes in the gallbladder emptying, evaluation of compliance to therapy, and treatment effect satisfaction.Materials and methods. The study was conducted from July 2020 to April 2021 at the premises of 60 study sites in 4 cities of the Republic of Kazakhstan. Patients having indications for Odeston administration according to the patient leaflet were enrolled. The study included 2 patient visits and an intermediate telephone contact. A visual analogue scale and RAPID questionnaire were used to characterise biliary pain; severity of associated symptoms, bowel habit and a quality of life according the SF-12 were also assessed. A rate of a ≥50 % reduction in symptom severity was used as a primary efficacy criterion; a rate of a ≥10 improvement in the SF-12 quality of life score was used as a secondary efficacy criterion. Compliance to treatment was evaluated using a number of days on Odeston. Treatment satisfaction was assessed using 5 grades.Results. 877 patients, 68.2 % of females and 31.8 % of males, were included in the study; the mean age was 46.0 ± 14.9 years. Primary functional biliary disorder was diagnosed in 65.3 % of patients, chronic non-calculous cholecystitis — 51.4 %, uncomplicated gallbladder disease — in 8.9 %, biliary sludge — 38.4 %, sphincter of Oddi functional disorder — 5.3 % of patients. A dose of Odeston was prescribed at the discretion of the physician. Group A patients received 600 mg (n = 89), group B received 1200 mg of Odeston a day (n = 788). In group B, an incidence of pronounced pain interference with daily living activities was higher. In both groups, the mean VAS scores were reduced to 1 point on treatment, a primary efficacy criterion was achieved in 77.3 % of patients in group A and in 79.8 % of patients in group B, р &lt; 0.05. In both groups, a reduction in the incidence of constipation and diarrhea (р &lt; 0,001) and an increase in the mean scores of physical and mental functioning were noted (р &lt; 0.001, though a secondary efficacy criterion was not achieved (a ≥10 change in the SF-12 score). A prevalence of ultrasonographic sings of biliary sludge was reduced, and an increased gallbladder emptying was observed (p &lt; 0.001). 77.4 % of patients in a total group of patients reported about drug administration for 21 days. A number of patients who were completely satisfied with treatment was higher in group B (p = 0.027).Conclusions. It was found that biliary pain interfered with daily living activities and commonly accompanied by other symptoms of gastrointestinal dysmotility. Odeston effectively reduces the severity of biliary pain, corrects dyspeptic disorders and normalizes stool pattern in patients with functional and organic diseases of the biliary system. Treatment satisfaction was higher with a dose of 1200 mg a day, particularly in more pronounced interference of pain with daily living activities.

Primary Caregiver Retention and Perceptions of Retention Strategies in a 36-Month Prospective Childhood Caries Study.

Introduction/Objectives:This paper reports on participant retention from an ongoing prospective, multi-site cohort caries risk study involving parent/infant pairs. The objectives were to: (1) compare the retention rates at each intermediate contact (every 4 months) and dental visit (every 18 months) across the 3 clinical sites, (2) assess primary caregivers’ perceptions at the end of the study about the retention efforts used in this longitudinal study, and (3) determine whether primary caregiver baseline demographic characteristics and child’s baseline caries experience were associated with retention.Methods:1325 primary caregiver-child pairs recruited at the child’s first birthday were followed for 36 months at 3 sites. Dental visits occurred at children’s ages of approximately 12, 30, and 48 months. Telephone/email intermediate contacts with the primary caregiver occurred 6 times between dental visits. The outcome variable was the retention rates at each dental visit and each intermediate contact. Primary caregivers’ perceptions of intermediate contacts were evaluated. Retention rates were compared by maternal age, race, ethnicity, Medicaid status, yearly household income, baseline caries experience (defined as decayed, missing due to caries, or filled tooth surfaces) at 12 months, and the number of teeth erupted.Results:1325 primary caregiver/infant pairs were enrolled and completed the first in-person dental visit, 1062 pairs (80%) completed the second visit and 985 (74%) completed the third. Most primary caregivers were female (94%), with a mean age of 29 years and 667 (50%) self-identified as White, 544 (41%) as Black, and 146 (11%) as Hispanic. The percentages of successful intermediate contacts were 95% at 4 months decreasing to 82% at 34 months. Almost all 964 (98%) of 985 primary caregivers reported at the last visit that they were comfortable/very comfortable with 4-month intermediate contacts. The multivariable analysis showed that primary caregivers who were older (OR = 1.07; 95% CI, 1.04-1.09) and White (OR = 1.52; 95% CI, 1.12-2.06) were more likely to complete the study.Conclusions:Retention strategies were focused on frequent routine contact and increasing monetary incentives. Those strategies may have resulted in retention exceeding the proposed goals. At the end of the study, primary caregivers were comfortable with the 4-month intermediate contacts.

Synergistic effects between anionic and amphoteric surfactants on promoting spontaneous imbibition in ultra-low permeability reservoirs: Study of mechanism and formula construction

Faster spontaneous imbibition in ultra-low permeability reservoirs ensures higher productivity. Surfactants can promote spontaneous imbibition by creating a strong water-wet condition while keeping the oil-water interfacial tension (IFT) at an intermediate level. In this paper, A surfactant mixture composed of Alpha Olefin Sulfonate (AOS, an anionic surfactant) and Cocoamidopropyl-Hydroxysulfobetaine (CHSB-35, an amphoteric surfactant)CHSB-35 was proposed to promote the spontaneous imbibition rate of Chang 9 reservoir, a sandstone reservoir with high salinity, and ultra-low permeability. The synergistic effects between AOS and CHSB-35 as well as the functional mechanisms were clarified by conducting spontaneous imbibition tests. Experimental results show that when the total surfactant concentration locates in the range of 0.20–0.35 wt%, the oil-water IFT can be lowered to an ultra-low level at a salinity of 11.2 wt%. However, the spontaneous imbibition rate was found to be higher at a total surfactant concentration around 0.10–0.15 wt% with intermediate IFTs and contact angles around 35°. Our results indicated that once surfactant changes the rock wettability from an oil-wet state to a water-wet state, ultra-low IFTs are unnecessary or should be avoided in ultra-low permeability reservoirs. Spontaneous imbibition tests show that the oil production rate of AOS-CHSB-35 mixture is four times faster than simulated water and two times faster than each single surfactant.

Aging brine-dependent deposition of crude oil components onto mica substrates, and its consequences for wettability

While wettability alteration is widely accepted as the dominant mechanism underlying enhanced oil recovery (EOR) in sandstone reservoirs under low salinity water flooding (LSWF) conditions, the effectiveness of LSWF still varies substantially between laboratory experiments and the field indicating our incomplete understanding and control of the process. We use simple mica substrates to investigate the impact of aging conditions on the macroscopic contact angle and the microscopic properties (morphology, composition, stiffness, surface charge) of the surface. Mica samples pre-aged in brines of variable salt content prior to aging in crude oil at elevated temperature displayed macroscopic wettabilities ranging from complete water wetting to intermediate contact angles around 90° in ambient brines of variable salinity. Compared to the macroscopic wettability, variations of the microscopic properties as probed by Atomic Force Microscopy and Confocal Raman microscopy were found to be rather subtle. Clear signatures of asphaltenic deposits were observed ubiquitously, usually consisting of a combination of a thin film and larger aggregates. The deposits typically displayed a salinity-dependent elasticity and (predominantly negative) surface charge. Selective removal of ions from the pre-aging brine lead to strong variations of both macroscopic wettability and microscopic properties, including the response to low ambient salinity: For the same crude oil, reducing the salinity of the ambient brine can either increase or decrease the macroscopic oil contact angle, depending on the composition of the formation brine used to pre-age the mineral surface. These results clearly highlight the complex balance of interactions during brine-oil-rock aging and the subtle role of the connate water composition in extracting and binding different types of crude oil components and thereby setting the initial and boundary conditions for the oil recovery process.

Phase Selection in Self-catalyzed GaAs Nanowires.

Crystal phase switching between the zincblende and wurtzite structures in III-V nanowires is crucial from the fundamental viewpoint as well as for electronic and photonic applications of crystal phase heterostructures. Here, the results of in situ monitoring of self-catalyzed vapor-liquid-solid growth of GaAs nanowires by molecular beam epitaxy inside a transmission electron microscope are presented. It is demonstrated that the occurrence of the zincblende or wurtzite phase in self-catalyzed nanowires is determined by the sole parameter, the droplet contact angle, which can be finely tuned by changing the group III and V fluxes. The zincblende phase forms at small (<100°) and large (>125°) contact angles, whereas pure wurtzite phase is observed for intermediate contact angles. Wurtzite nanowires are restricted by vertical sidewalls, whereas zincblende nanowires taper or develop the truncated edge at their top. These findings are explained within a dedicated model for the surface energetics. These results give a clear route for the crystal phase control in Au-free III-V nanowires. On a more general note, in situ growth monitoring with atomic resolution and at the technological-relevant growth rates is shown to be a powerful tool for the fine-tuning of material properties at the nanoscale.