Hierarchically Micro- and Nanostructured Polymer via Crystallinity Alteration for Sustainable Environmental Cooling.

Cooling environments are a pervasive need in our society, with conventional air conditioners being the most popular approach. However, air conditioners rely heavily on electricity and Freon, a chemical that depletes ozone and contributes to greenhouse gas effects. To address this issue, passive daytime radiative coolers (PDRCs) have been proposed to achieve cooling by simultaneously reflecting sunlight and allowing internal heat to escape without electricity. Despite their potential, most high-performance PDRCs are composed of thick polymer films, which increases material costs during PDRC preparation and limits thermal transport. In this work, we introduced an economical and scalable solvent evaporation-based method to prepare a relatively thin hierarchically micro- and nanostructured poly(vinylidene fluoride-trifluoroethylene) via crystallinity alteration. Particularly, we find that the key to generating nanosized pores is to remove the water residual within the film without sample annealing, which significantly enhances the scattering efficiency across the solar spectrum. With our design, we demonstrate effective cooling of the outdoor environment, achieving a cooling temperature of Δ2.5 °C, with a film thickness of only 215 µm. Furthermore, our model suggested that applying this material could lead to annual energy savings of up to ∼39% in warmer climates across the country and up to 715 GJ nationwide. Developing effective PDRCs with reduced material thickness, such as the one discussed here, is imperative for implementing sustainable cooling solutions and reducing our carbon footprint.

Knowledge extraction and transfer in data-driven fracture mechanics.

Data-driven approaches promise to usher in a new phase of development in fracture mechanics, but very little is currently known about how data-driven knowledge extraction and transfer can be accomplished in this field. As in many other fields, data scarcity presents a major challenge for knowledge extraction, and knowledge transfer among different fracture problems remains largely unexplored. Here, a data-driven framework for knowledge extraction with rigorous metrics for accuracy assessments is proposed and demonstrated through a nontrivial linear elastic fracture mechanics problem encountered in small-scale toughness measurements. It is shown that a tailored active learning method enables accurate knowledge extraction even in a data-limited regime. The viability of knowledge transfer is demonstrated through mining the hidden connection between the selected three-dimensional benchmark problem and a well-established auxiliary two-dimensional problem. The combination of data-driven knowledge extraction and transfer is expected to have transformative impact in this field over the coming decades.

Redox-couple investigations in Si-doped Li-rich cathode materials.

In this investigation, the improved electrochemical behavior in Si-doped Li-rich cathodes is studied with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). Z-contrast images show a layered structure that develops a thin, spinel-like surface layer after the first charge cycle. Si-doping increases discharge capacity by ∼25% and appears to retard the surface phase transformation. Based on electron energy loss spectra, the surface layer in the doped material has an altered oxygen electronic environment, which supports the STEM findings. Furthermore, Si-doping changes the redox behavior during the activation cycle. Density functional theory calculations indicate that Si-doping can increase oxygen vacancy formation, and change the sequence of the redox couples by introducing more oxygen vacancies before or during the typical high voltage activation process. The results of this work indicate that the type of doping employed here is an effective strategy for controlling the complex charge compensation mechanisms in lithium-rich cathodes.

Anisotropic chemical strain in cubic ceria due to oxygen-vacancy-induced elastic dipoles.

Accurate characterization of chemical strain is required to study a broad range of chemical-mechanical coupling phenomena. One of the most studied mechano-chemically active oxides, nonstoichiometric ceria (CeO2-δ), has only been described by a scalar chemical strain assuming isotropic deformation. However, combined density functional theory (DFT) calculations and elastic dipole tensor theory reveal that both the short-range bond distortions surrounding an oxygen-vacancy and the long-range chemical strain are anisotropic in cubic CeO2-δ. The origin of this anisotropy is the charge disproportionation between the four cerium atoms around each oxygen-vacancy (two become Ce3+ and two become Ce4+) when a neutral oxygen-vacancy is formed. Around the oxygen-vacancy, six of the Ce3+-O bonds elongate, one of the Ce3+-O bond shorten, and all seven of the Ce4+-O bonds shorten. Further, the average and maximum chemical strain values obtained through tensor analysis successfully bound the various experimental data. Lastly, the anisotropic, oxygen-vacancy-elastic-dipole induced chemical strain is polarizable, which provides a physical model for the giant electrostriction recently discovered in doped and non-doped CeO2-δ. Together, this work highlights the need to consider anisotropic tensors when calculating the chemical strain induced by dilute point defects in all materials, regardless of their symmetry.

Role of grain size on redox induced compositional stresses in Pr doped ceria thin films.

In constrained geometries and in varying oxygen partial pressures and operating temperatures, exchange of oxygen ions between non-stoichiometric oxide thin films (for example, doped and undoped ceria systems) and the gas phase can lead to stresses. In this study, these compositional stresses were investigated in thin films of nanocrystalline 10% praseodymium doped ceria (PCO), as a function of average grain size. In situ wafer curvature measurements, along with High Temperature X-Ray Diffraction (HTXRD), were employed to measure stresses and strains, respectively on the PCO films during oxidation-reduction cycling, over the pO2 range of 10-1-10-5 atm at 750 °C. For relatively large grain sizes, the stress values agree well with the amount of expansion induced by oxygen non-stoichiometry (chemical expansion) predicted by a thin film defect equilibria model that was developed previously. The compositional stresses were found to increase with decreasing grain size. The origin of this effect, including the role of space charge effects near surfaces and interfaces are discussed in this paper. To our knowledge, this is the first time that such comparisons are reported by simultaneously employing high temperature in situ wafer curvature and HTXRD measurements on doped ceria systems.

Synergetic Effects of Inorganic Components in Solid Electrolyte Interphase on High Cycle Efficiency of Lithium Ion Batteries.

The solid electrolyte interphase (SEI), a passivation layer formed on electrodes, is critical to battery performance and durability. The inorganic components in SEI, including lithium carbonate (Li2CO3) and lithium fluoride (LiF), provide both mechanical and chemical protection, meanwhile control lithium ion transport. Although both Li2CO3 and LiF have relatively low ionic conductivity, we found, surprisingly, that the contact between Li2CO3 and LiF can promote space charge accumulation along their interfaces, which generates a higher ionic carrier concentration and significantly improves lithium ion transport and reduces electron leakage. The synergetic effect of the two inorganic components leads to high current efficiency and long cycle stability.

Improved spatial resolution and lower-dose pediatric CT imaging: a feasibility study to evaluate narrowing the X-ray photon energy spectrum.

This feasibility study has shown that improved spatial resolution and reduced radiation dose can be achieved in pediatric CT by narrowing the X-ray photon energy spectrum. This is done by placing a hafnium filter between the X-ray generator and a pediatric abdominal phantom. A CT system manufactured in 1999 that was in the process of being remanufactured was used as the platform for this study. This system had the advantage of easy access to the X-ray generator for modifications to change the X-ray photon energy spectrum; it also had the disadvantage of not employing the latest post-imaging noise reduction iterative reconstruction technology. Because we observed improvements after changing the X-ray photon energy spectrum, we recommend a future study combining this change with an optimized iterative reconstruction noise reduction technique.

Li segregation induces structure and strength changes at the amorphous Si/Cu interface.

The study of interfacial properties, especially of their change upon lithiation, is a fundamentally significant and challenging topic in designing heterogeneous nanostructured electrodes for lithium ion batteries. This issue becomes more intriguing for Si electrodes, whose ultrahigh capacity is accompanied by large volume expansion and mechanical stress, threatening with delamination of silicon from the metal current collector and failure of the electrode. Instead of inferring interfacial properties from experiments, in this work, we have combined density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations with time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements of the lithium depth profile, to study the effect of lithiation on the a-Si/Cu interface. Our results clearly demonstrate Li segregation at the lithiated a-Si/Cu interface (more than 20% compared to the bulk concentration). The segregation of Li is responsible for a small decrease (up to 16%) of the adhesion strength and a dramatic reduction (by one order of magnitude) of the sliding resistance of the fully lithiated a-Si/Cu interface. Our results suggest that this almost frictionless sliding stems from the change of the bonding nature at the interface with increasing lithium content, from directional covalent bonding to uniform metallic. These findings are an essential first step toward an in-depth understanding of the role of lithiation on the a-Si/Cu interface, which may contribute in the development of quantitative electrochemical mechanical models and the design of nonfracture-and-always-connected heterogeneous nanostructured Si electrodes.

Dual-Interface-Reinforced Flexible Perovskite Solar Cells for Enhanced Performance and Mechanical Reliability.

Two key interfaces in flexible perovskite solar cells (f-PSCs) are mechanically reinforced simultaneously: one between the electron-transport layer (ETL) and the 3D metal-halide perovskite (MHP) thin film using self-assembled monolayer (SAM), and the other between the 3D-MHP thin film and the hole-transport layer (HTL) using an in situ grown low-dimensional (LD) MHP capping layer. The interfacial mechanical properties are measured and modeled. This rational interface engineering results in the enhancement of not only the mechanical properties of both interfaces but also their optoelectronic properties holistically. As a result, the new class of dual-interface-reinforced f-PSCs has an unprecedented combination of the following three important performance parameters: high power-conversion efficiency (PCE) of 21.03% (with reduced hysteresis), improved operational stability of 1000 h T90 (duration at 90% initial PCE retained), and enhanced mechanical reliability of 10 000 cycles n88 (number of bending cycles at 88% initial PCE retained). The scientific underpinnings of these synergistic enhancements are elucidated.

Space charge induced surface stresses: implications in ceria and other ionic solids.

Volume changes associated with point defects in space charge layers can produce strains that substantially alter thermodynamic equilibrium near surfaces in ionic solids. For example, near-surface compressive stresses exceeding -10 GPa are predicted for ceria. The magnitude of this effect is consistent with anomalous lattice parameter increases that occur in ceria nanoparticles. These stresses should significantly alter defect concentrations and key transport properties in a wide range of materials (e.g., ceria electrolytes in fuel cells).

Farm-scale evaluation of ozonation for mitigating ammonia concentrations in broiler houses.

This study evaluated the effectiveness of in-house ozonation within the public health standard limit (0.1 parts per million [ppm]) for mitigating ammonia (NH3) concentrations inside commercial broiler houses. The project was conducted in four identical tunnel-ventilated houses. Two houses served as treatment and the other two served as control units. The experiment was replicated in five consecutive flocks. Except for ozonation treatment, all other operational parameters including feed, broiler strain, age and number of broilers, and ventilation system were the same among four houses. NH3 and carbon dioxide (CO2) concentrations in the treatment and control houses were measured for a minimum of 48 hr/week throughout the five flocks of 8 or 9 weeks each. The gas measurements were conducted using portable multigas units (PMUs). House temperatures were recorded with data loggers in each flock. Comparison of temperatures and CO2 concentrations among houses indicated no significant differences in ventilation rates among treatment and control houses in any of the five flocks. As a result, comparisons of NH3 concentrations inside houses were used to evaluate the effectiveness of house ozonation for NH3 emission mitigation. Statistical test of mean NH3 concentrations for each flock separated by house indicated that the house-to-house variation was significantly smaller than the flock-to-flock variation. There was a substantial variation in NH3 concentrations across different flocks, but no house had consistently higher or lower mean NH3 concentrations than any other. Evaluations for differences in mean NH3 from week to week, between treatment groups, and differences in week-to-week variations between treatment groups suggested that ozone effect was not uniform for each week and the effect was not statistically significant for any week. Tests of overall ozone treatment effect and treatment-week interaction indicated there was no difference in mean NH3 between the control and ozone treatment groups (P = 0.25), nor was the week effect different for control and treatment groups (P = 0.46). The results of this field evaluation indicate that there was no statistical evidence to suggest that the ozone treatment has any effect on average NH3 concentrations in these chicken houses.

Stress Bearing Mechanism of Reduced Graphene Oxide in Silicon-Based Composite Anodes for Lithium Ion Batteries.

Despite the significant research that has been carried out to improve cycling performance of lithium ion batteries (LIB) with silicon (Si) based composite electrodes, limited studies have been performed on these materials to evaluate the effects of internal microstructural changes and stress evolution on the electrochemical performance. Here, combined ex situ and in situ investigations on the accommodation of volume expansion in Si-based nanocomposite electrodes are reported. This work emphasizes the importance of conductive agents in light of the poor electronic conductivity of Si. A detailed comparison between commonly used carbon black (CB) and reduced graphene oxide (rGO) shows that these materials have substantial effects on microstructural evolution and internal stress in Si based composite electrodes that are employed in lithium ion cells. This study provides the first monitoring of stress evolution in Si-rGO based composite electrode during electrochemical cycling using in situ wafer curvature measurements. The prepared Si-rGO based electrode exhibits almost 10 times lower stress generation and consequently higher cycling performance in electrochemical cells. The resulting 3D networked structure not only acts as an electronic conduit to the encapsulated active materials but also serves as a mini-electrochemical reaction chamber which hinders the formation of the solid electrolyte interphase (SEI) and limits the pulverization of active material and the evolution of severe stress during cycling. Moreover, investigations of the microstructural changes and internal charge transfer resistance in the electrodes after cycling provide further evidence that rGO produces superior structures for energy storage.

Metal oxide coated cell culture arrays for rapid biological screening.

The biointerface of metallic alloy implants is a spontaneously formed metal oxide layer. This study presents a novel method for creating titanium oxide xerogel coated microplates for high-throughput biological screening that overcomes several limitations of using bulk metal samples to study oxides. Metal-organic precursors were used to evaluate the influence of Al, V, Ca, and P doped smooth and textured titanium oxide xerogel coatings on the bioresponse of human fibroblasts to increase understanding of the soft tissue sealing around transepithelial devices. Coatings made of titanium n-butoxide were characteristically smooth, while those of titanium isopropoxide were micro- and nanofeatured. Screening consisted of WST-1 proliferation assay, calcein AM cell number and viability assay, and a modified cell seeding efficiency and centrifugation adhesion assay. Small variations in initial attachment and centrifugation adhesion of human fibroblasts were observed among the coatings and comparable to tissue-culture treated polystyrene. Proliferation and viability at 24 and 48 h were reduced by the 10 and 20% vanadium additions. Metal oxide coated microplates are adaptable to the investigation of a wide range of metal-organic derived chemistries and the influence of oxide texture, and level of oxide crystallinity and oxide grain size on the biological responses of cells.

Strain-Induced Lithium Losses in the Solid Electrolyte Interphase on Silicon Electrodes.

The chemical and mechanical stability of SEI layers are particularly important for high capacity anode materials such as silicon, which undergoes large volume changes (∼300%) during cycling. In this work, we present a novel approach for applying controlled strains to SEI films with patterned Si electrodes to systematically investigate the impact of large volume changes on SEI formation and evolution. Comparisons between patterned silicon islands and continuous silicon thin films make it possible to correlate the irreversible capacity losses due to expansion and contraction of underlying silicon. The current work demonstrates that strain in the SEI layer leads to more lithium consumption. The combination of in situ AFM and electrochemical lithium loss measurements provides further information on SEI layer growth. These experiments indicate that in-plane strains in the SEI layer lead to substantial increases in the amount of inorganic phase formation, without significantly affecting the overall SEI thickness. These observations are further supported with EIS and TOF-SIMS results. A map of irreversible capacity evolution with strain in the SEI is obtained from the experimental results.

Identifying the components in eggshell membrane responsible for reducing the heat resistance of bacterial pathogens.

The biological activity (D-value determination) of eggshell membrane (ESM) was examined to determine the membrane components and mechanisms responsible for antibacterial activity. Biological and enzymatic activities (i.e., beta-N-acetylglucosaminidase [beta-NAGase], lysozyme, and ovotransferrin) of ESM denatured with trypsin, lipases, or heat were compared with those of untreated ESM. Trypsin-treated ESM lost all biological activity (D-values at 54 degrees C were 5.12 and 5.38 min for immobilized and solubilized trypsin, respectively) but showed no significant loss of enzymatic activities. Treatments with porcine lipase and a lipase cocktail did not impact biological or enzymatic activities. Heat denaturation of ESM (at 80 and 100 degrees C for 15 min) resulted in significant decreases in biological activity (D-values of 3.99 and 4.43 min, respectively) and loss of beta-NAGase activity. Lysozyme and ovotransferrin activities remained but were significantly reduced. Purified ESM and hen egg white components (i.e., beta-NAGase, lysozyme, and ovotransferrin) were added to Salmonella Typhimurium suspensions (in 0.1% peptone water) at varying concentrations to evaluate their biological activity. D-values at 54 degrees C were 4.50 and 3.68 min for treatment with lysozyme or beta-NAGase alone, respectively, and 2.44 min for ovotransferrin but 1.47 min for a combination of all three components (similar to values for ESM). Exposure of Salmonella Typhimurium cells to a mixture of ovotransferrin, lysozyme, and beta-NAGase or ESM resulted in significant increases in extracellular concentrations of Ca2+, Mg2+, and K+. Transmission electron microscopic examination of Salmonella Typhimurium cells treated with a combination of ovotransferrin, lysozyme, and beta-NAGase revealed membrane disruption and cell lysis. The findings of this study demonstrate that ovotransferrin, lysozyme, and beta-NAGase are the primary components responsible for ESM antibacterial activity. The combination of these proteins and perhaps other ESM components interferes with interactions between bacterial lipopolysaccharides, sensitizing the outer bacterial membrane to the lethal affects of heat and possibly pressure and osmotic stressors.

Ab initio diffuse-interface model for lithiated electrode interface evolution.

The study of chemical segregation at interfaces, and in particular the ability to predict the thickness of segregated layers via analytical expressions or computational modeling, is a fundamentally challenging topic in the design of novel heterostructured materials. This issue is particularly relevant for the phase-field (PF) methodology, which has become a prominent tool for describing phase transitions. These models rely on phenomenological parameters that pertain to the interfacial energy and thickness, quantities that cannot be experimentally measured. Instead of back-calculating these parameters from experimental data, here we combine a set of analytical expressions based on the Cahn-Hilliard approach with ab initio calculations to compute the gradient energy parameter κ and the thickness λ of the segregated Li layer at the Li_{x}Si-Cu interface. With this bottom-up approach we calculate the thickness λ of the Li diffuse interface to be on the order of a few nm, in agreement with prior experimental secondary ion mass spectrometry observations. Our analysis indicates that Li segregation is primarily driven by solution thermodynamics, while the strain contribution in this system is relatively small. This combined scheme provides an essential first step in the systematic evaluation of the thermodynamic parameters of the PF methodology, and we believe that it can serve as a framework for the development of quantitative interface models in the field of Li-ion batteries.

Use of time-temperature integrators and predictive modeling to evaluate microbiological quality loss in poultry products.

The purpose of this study was to characterize the kinetics of the spoilage process of chicken drumsticks in order to evaluate the application of an enzyme process-based time-temperature integrator (TTI) as a continuous quality monitor of poultry products. Shelf life studies were conducted at several temperatures (3 to 20 degrees C) to characterize (i) the poultry spoilage process as a function of total aerobic bacteria and Pseudomonas species populations and (ii) the TTI chroma response function. Two types of poultry products were examined: ice-packed and chill-packed drumsticks. An enzyme-based TTI with a color change response from green to yellow was used. Activation energies for each of the poultry products and each of the bacterial populations were as follows: 21.8 +/- 1.6 kcal/mol (ca. 91.2 +/- 6.7 kJ/mol) for ice-packed drumsticks and total aerobic population, 18.8 +/- 4.5 kcal/mol ca. 78.7 +/- 18.8 kJ/mol) for ice-packed drumsticks and Pseudomonas spp., 17.0 +/- 2.3 kcal/mol (ca. 71.1 +/- 9.6 kJ/mol) for chill-packed drumsticks and total aerobic population, and 14.1 +/- 3.6 kcal/mol (ca. 59.0 +/- 15.1 kJ/mol) for chill-packed drumsticks and Pseudomonas spp. The activation energy calculated for the TTI, 19.1 +/- 1.8 kcal/mol (ca. 79.9 +/- 7.5 kJ/mol), was determined to be adequately close to that of the poultry spoilage process to make effective quality predictions possible. Initial bacteria levels on the chicken drumsticks were uniform and not judged as important limiting factors in the application of TTIs to poultry products. Because the poultry spoilage process was reasonably characterized on the basis of Arrhenius kinetics, there is further need to conduct validation studies to determine the ability of TTIs to provide a continuous quality monitoring system.

Evaluation of time-temperature integrators for tracking poultry product quality throughout the chill chain.

The goal of this study was to evaluate the application of one type of time-temperature integrator (TTI) to monitor the microbiological quality of ice-packed raw chicken drumsticks as a function of temperature exposure. A kinetics-based model was used to correlate the TTI chroma response to the number of bacteria on the drumstick surface under constant- and variable-temperature conditions. Two constant-temperature studies (4 and 15 degrees C) and one variable-temperature study (4 degrees C for 24 h, 15 degrees C for 24 h, 4 degrees C constant) were conducted to evaluate the applicability of the TTI under ideal and worst-case situations. During the constant-temperature studies, quality predictions made at the midpoint of the product shelf life were accurate within 15% for the observed bacterial populations. The accuracy of the TTI was marginal in the initial and final stages of the response period. During the variable-temperature study, the TTI response demonstrated positive history effects, whereby the observed rate constant is affected by previous temperature exposure. After the TTIs had been held at 15 degrees C for 24 h, the TTI response rate constant observed during subsequent storage at 4 degrees C was higher than what would be predicted for 4 degrees C. Further work will be needed to develop a continuous TTI-based quality monitoring system. However, because the microbiological quality of fresh poultry could be reliably predicted with kinetic models, fresh poultry products would be excellent candidates for a TTI-based quality monitoring system.

Inhibition of Listeria monocytogenes in pH-adjusted pasteurized liquid whole egg.

Although the transmission of L. monocytogenes to humans via pasteurized egg products has not been documented, L. monocytogenes and other Listeria species have been isolated from commercially broken raw liquid whole egg (LWE) in both the United States and Ireland. Recent Listeria thermal inactivation studies indicate that conventional minimal egg pasteurization processes would effect only a 2.1- to 2.7-order-of-magnitude inactivation of L. monocytogenes in LWE; thus, the margin of safety provided by conventional pasteurization processes is substantially smaller for L. monocytogenes than for Salmonella species (a 9-order-of-magnitude process). The objective of this study was to evaluate the inhibitory effects of nisin on the survival and growth of L. monocytogenes in refrigerated and pH-adjusted (pH 6.6 versus pH 7.5) ultrapasteurized LWE and in a liquid model system. The addition of nisin (1,000 IU/ml) to pH-adjusted ultrapasteurized LWE reduced L. monocytogenes populations by 1.6 to > 3.3 log CFU/ml and delayed (pH 7.5) or prevented (pH 6.6) the growth of the pathogen for 8 to 12 weeks at 4 and 10 degrees C. Bioactive nisin was detected in LWE at both pH values for 12 weeks at 4 degrees C. In subsequent experiments, Listeria reductions of > 3.0 log CFU/ml were achieved within 24 h in both LWE and broth plus nisin (500 IU/ml) at pH 6.6 but not at pH 7.5, and antilisterial activity was enhanced when nisin was added as a solution rather than in dry form.

Transfer of Salmonella and Campylobacter from stainless steel to romaine lettuce.

The degree of transfer of Campylobacter jejuni and Salmonella enterica serovar Typhimurium was evaluated from a stainless steel contact surface to a ready-to-eat food (lettuce). Stainless steel coupons (25 cm2) were inoculated with a 20-microl drop of either C. jejuni or Salmonella Typhimurium to provide an inoculum level of approximately 10(6) CFU/28 mm2. Wet and dry lettuce (Lactuca sativa var. longifolia) pieces (9 cm2) were placed onto the inoculated stainless steel surface for 10 s after the designated inoculum drying time (0 to 80 min for C. jejuni; 0 to 120 min for Salmonella Typhimurium), which was followed by the recovery and enumeration of transferred pathogens (lettuce) and residual surface pathogens (stainless steel coupons). For transfers of Salmonella Typhimurium to dry lettuce, there was an increase from 36 to 66% in the percent transfer of the initial inoculum load during the first 60 min of sampling and then a precipitous drop from 66 to 6% in percent transfer. The transfer of Salmonella Typhimurium to wet lettuce ranged from 23 to 31%, with no statistically significant difference between recoveries over the entire 120-min sampling period. For C. jejuni, the mean percent transfer ranged from 16 to 38% for dry lettuce and from 15 to 27% for wet lettuce during the 80-min sampling period. The results of this study indicate that relatively high numbers of bacteria may be transferred to a food even 1 to 2 h after surface contamination. These findings can be used to support future projects aimed at estimating the degree of risk associated with poor handling practices of ready-to-eat foods.