Nanoscale magnetic ratchets based on shape anisotropy.

Controlling magnetization using piezoelectric strain through the magnetoelectric effect offers several orders of magnitude reduction in energy consumption for spintronic applications. However strain is a uniaxial effect and, unlike directional magnetic field or spin-polarized current, cannot induce a full 180° reorientation of the magnetization vector when acting alone. We have engineered novel 'peanut' and 'cat-eye' shaped nanomagnets on piezoelectric substrates that undergo repeated deterministic 180° magnetization rotations in response to individual electric-field-induced strain pulses by breaking the uniaxial symmetry using shape anisotropy. This behavior can be likened to a magnetic ratchet, advancing magnetization clockwise with each piezostrain trigger. The results were validated using micromagnetics implemented in a multiphysics finite elements code to simulate the engineered spatial and temporal magnetic behavior. The engineering principles start from a target device function and proceed to the identification of shapes that produce the desired function. This approach opens a broad design space for next generation magnetoelectric spintronic devices.

Modeling of magnetoelastic nanostructures with a fully coupled mechanical-micromagnetic model.

Micromagnetic simulations of magnetoelastic nanostructures traditionally rely on either the Stoner-Wohlfarth model or the Landau-Lifshitz-Gilbert (LLG) model, assuming uniform strain (and/or assuming uniform magnetization). While the uniform strain assumption is reasonable when modeling magnetoelastic thin films, this constant strain approach becomes increasingly inaccurate for smaller in-plane nanoscale structures. This paper presents analytical work intended to significantly improve the simulation of finite structures by fully coupling the LLG model with elastodynamics, i.e., the partial differential equations are intrinsically coupled. The coupled equations developed in this manuscript, along with the Stoner-Wohlfarth model and the LLG (constant strain) model are compared to experimental data on nickel nanostructures. The nickel nanostructures are 100 × 300 × 35 nm single domain elements that are fabricated on a Si/SiO2 substrate; these nanostructures are mechanically strained when they experience an applied magnetic field, which is used to generate M vs H curves. Results reveal that this paper's fully-coupled approach corresponds the best with the experimental data on coercive field changes. This more sophisticated modeling technique is critical for guiding the design process of future nanoscale strain-mediated multiferroic elements, such as those needed in memory systems.

Magnetoelectric control of superparamagnetism.

Here we demonstrate electric-field induced magnetic anisotropy in a multiferroic composite containing nickel nanocrystals strain coupled to a piezoelectric substrate. This system can be switched between a superparamagnetic state and a single-domain ferromagnetic state at room temperature. The nanocrystals show a shift in the blocking temperature of 40 K upon electric poling. We believe this is the first example of a system where an electric field can be used to switch on and off a permanent magnetic moment.

Developing 21st century models of care for seniors in challenged urban settings.

This is an account of the revitalization of an urban area as its hospital closed but was replaced by community involvement, business, and new healthcare services to meet the needs of the aging people in the surrounding community.

Inpatient Transition to Virtual Care During COVID-19 Pandemic.

Introduction: During the coronavirus disease 2019 (COVID-19) outbreak, novel approaches to diabetes care have been employed. Care in both the inpatient and outpatient setting has transformed considerably. Driven by the need to reduce the use of personal protective equipment and exposure for patients and providers alike, we transitioned inpatient diabetes management services to largely "virtual" or remotely provided care at our hospital. Methods: Implementation of a diabetes co-management service under the direction of the University of North Carolina division of endocrinology was initiated in July 2019. In response to the COVID-19 pandemic, the diabetes service was largely transitioned to a virtual care model in March 2020. Automatic consults for COVID-19 patients were implemented. Glycemic outcomes from before and after transition to virtual care were evaluated. Results: Data over a 15-week period suggest that using virtual care for diabetes management in the hospital is feasible and can provide similar outcomes to traditional face-to-face care. Conclusion: Automatic consults for COVID-19 patients ensure that patients with serious illness receive specialized diabetes care. Transitioning to virtual care models does not limit the glycemic outcomes of inpatient diabetes care and should be employed to reduce patient and provider exposure in the setting of COVID-19. These findings may have implications for reducing nosocomial infection in less challenging times and might address shortage of health care providers, especially in the remote areas.

Calibration approach for fluorescence lifetime determination for applications using time-gated detection and finite pulse width excitation.

Time-gated techniques are useful for the rapid sampling of excited-state (fluorescence) emission decays in the time domain. Gated detectors coupled with bright, economical, nanosecond-pulsed light sources like flashlamps and nitrogen lasers are an attractive combination for bioanalytical and biomedical applications. Here we present a calibration approach for lifetime determination that is noniterative and that does not assume a negligible instrument response function (i.e., a negligible excitation pulse width) as does most current rapid lifetime determination approaches. Analogous to a transducer-based sensor, signals from fluorophores of known lifetime (0.5-12 ns) serve as calibration references. A fast avalanche photodiode and a GHz-bandwidth digital oscilloscope is used to detect transient emission from reference samples excited using a nitrogen laser. We find that the normalized time-integrated emission signal is proportional to the lifetime, which can be determined with good reproducibility (typically <100 ps) even for data with poor signal-to-noise ratios ( approximately 20). Results are in good agreement with simulations. Additionally, a new time-gating scheme for fluorescence lifetime imaging applications is proposed. In conclusion, a calibration-based approach is a valuable analysis tool for the rapid determination of lifetime in applications using time-gated detection and finite pulse width excitation.

Distinct developmental expression of Drosophila retinoblastoma factors.

Retinoblastoma (RB) tumor suppressor proteins are important regulators of the cell cycle and are implicated in a wide variety of human tumors. Genetic analysis of RB mutations in humans and in model systems indicates that individual RB proteins also have distinct functions in development. Specific target genes or mechanisms of action of individual RB proteins in developmental contexts are not well understood, however. To better understand the developmental activities of the two RB family members in Drosophila, we have characterized endogenous expression patterns of Rbf1 and Rbf2 proteins and transcripts in embryos and imaginal discs. These gene products are coexpressed at several stages of development, however, spatial and temporal differences are evident, including partly complementary patterns of expression in the embryonic central nervous system.

Electrically driven magnetic domain wall rotation in multiferroic heterostructures to manipulate suspended on-chip magnetic particles.

In this work, we experimentally demonstrate deterministic electrically driven, strain-mediated domain wall (DW) rotation in ferromagnetic Ni rings fabricated on piezoelectric [Pb(Mg1/3Nb2/3)O3]0.66-[PbTiO3]0.34 (PMN-PT) substrates. While simultaneously imaging the Ni rings with X-ray magnetic circular dichroism photoemission electron microscopy, an electric field is applied across the PMN-PT substrate that induces strain in the ring structures, driving DW rotation around the ring toward the dominant PMN-PT strain axis by the inverse magnetostriction effect. The DW rotation we observe is analytically predicted using a fully coupled micromagnetic/elastodynamic multiphysics simulation, which verifies that the experimental behavior is caused by the electrically generated strain in this multiferroic system. Finally, this DW rotation is used to capture and manipulate micrometer-scale magnetic beads in a fluidic environment to demonstrate a proof-of-concept energy-efficient pathway for multiferroic-based lab-on-a-chip applications.

Application of fluid modeling to determine threshold leak size for liquid foods.

In this study, the mechanism by which a package defect converts to a leaker was examined in an effort to develop a relationship between threshold leak size and loss of package sterility. The threshold leak size is the hole size at which the onset of leakage occurs. The threshold pressure is the pressure required to initiate a leak. Leak initiation was studied in terms of the interaction between three components: liquid attributes of liquid food products, defect size, and pressures required to initiate liquid flow. Liquid surface tension, viscosity, and density values were obtained for 16 liquids. The imposed pressures required to initiate flow through microtubes with interior diameters of 0, 2, 5, 7, 10, 20, and 50 microm were measured with the use of 63 test cells filled with safranin red dye, tryptic soy broth, and distilled water with surface tensions of 18.69, 44.09, and 64.67 mN/m, respectively. Significant differences (P<0.05) between threshold pressures observed for safranin red dye, tryptic soy broth, and distilled water were found. Liquids with low surface tensions, such as safranin red dye, required significantly lower threshold imposed pressures than did liquids with high surface tensions, such as distilled water (P<0.05). An equation to quantify the relationship between liquid surface tension, threshold imposed pressure, and defect size was developed. Threshold pressures observed were not significantly different (P>0.05) from those predicted by the equation. Imposed pressures and vacuums generated within packages during random vibration and sweep resonance tests were measured for brick-style aseptic packages (250 ml), metal cans (76.2 by 114.3 mm [425 ml]), 1-qt gable-top packages (946 ml), 0.5-gal gable-top packages (1.89 liters), and 1-gal milk jugs (4.25 liters). Significant differences between packages were found with respect to observed generated pressures during vibration testing (P<0.05). An equation to calculate threshold size on the basis of liquid surface tension and imposed pressure was established.

Effect of microorganism characteristics on leak size critical to predicting package sterility.

The effects of microorganism size and motility on the leak size critical to the sterility of a package, along with the imposed pressure required to initiate liquid flow for the critical leak size, were measured. Pseudomonas fragi Lacy-1052, Bacillus atrophaeus ATCC 49337, and Enterobacter aerogenes ATCC 29007 were employed to assess package sterility. One hundred twenty-six 7-mm-long microtubes with interior diameters of 5, 10, and 20 microm were used to simulate package defects. Forty-two solid microtubes were used as controls. No significant differences were found between sizes or motility statuses of test organisms with respect to loss of sterility as a result of microbial ingress into test cells with microtube interior diameters of 5, 10, and 20 microm (P > 0.05). Interactions between the initiation of liquid flow as a result of applied threshold pressures and sterility loss for test cells were significant (P < 0.05).

Bioaerosol Exposure Method for Package Integrity Testing †.

Test organism motility, concentration, aerosol exposure time, hole diameter and length were evaluated to determine their influence on microbial ingress into a flexible plastic pouch. Microtubes with 10- and 20-µm hole diameters and of 5- and 10-mm lengths were used as defects in 128 flexible pouches. A bioaerosol with a 2.68-µm mean particle size comprised of 102 or 106 CFU/ml source concentrations of motile or nonmotile Pseudomonas fragi TM 849 was introduced into a 119,911-cm3 chamber for exposures of 15 or 30 minutes. Six pouches showed test organism growth after a 72-h incubation period. Microbial ingress was significant (P < .05) for motile test organisms with source concentrations of 106 CFU/ml.

Contamination of Flexible Pouches Challenged by Immersion Biotesting †.

Immersion biotesting has long been used to challenge packages, particularly cans, for pinholes and channel leaks. Such testing for all types of plastic packaging may not be appropriate because some packages (e.g., aseptic, hot fill) are not exposed to water. As the food-packaging industry develops alternative environmental biotests there is a need to benchmark them against traditional immersion testing. The purpose of this research was to examine the threshold of critical-defect dimensions using artifically created channel leaks of 10 and 20 µm and 5- and 10-mm lengths sealed into plastic pouches which were subsequently tested by immersion at 102 and 106 CFU of motile and nonmotile Pseudomonas fragi TM849 per ml. Forty-four percent (44%) of the pouches tested became contaminated, indicating the threshold defect value is below 10 µm. Microbial ingress was significant (P < .05) for motile test organisms with a concentration of 106 CFU/ml. The interaction of concentration and time was also significant at 102 CFU/ml at 30 min exposure and 106 CFU/ml at 15 min. Channel length was not statistically significant. The markedly greater contamination rate using immersion testing versus that of aerosol testing highlights the importance of using test methods that reflect environmental exposure conditions of the packages.