University of Maryland, College Park
  • College Park, MD, United States
Recent publications
We have measured temporal fluctuations in the energy relaxation time T <sub xmlns:mml="" xmlns:xlink="">1</sub> of a series of 3D transmon qubits. At 20 mK, the relaxation times of the devices have average values between 2 and 190 μs, with standard deviations as large as 20% of the averages. Over the different devices, this fluctuation magnitude roughly scales as a power law in the average T <sub xmlns:mml="" xmlns:xlink="">1</sub> , with an exponent near 1.5. With increasing temperature, T <sub xmlns:mml="" xmlns:xlink="">1</sub> decreases due to a higher density of thermally-generated quasiparticles. For an individual device measured up to 250 mK, the fluctuation magnitude appears to be proportional to T <sub xmlns:mml="" xmlns:xlink="">1</sub> . We present a model of quasiparticle dissipation channels that reproduces both of the observed scaling relationships.
We have fabricated and characterized asymmetric gap-engineered junctions and transmon devices. To create Josephson junctions with asymmetric gaps, Ti was used to proximitize and lower the superconducting gap of the Al counter-electrode. DC IV measurements of these small, proximitized Josephson junctions show a reduced gap and larger excess current for voltage biases below the superconducting gap when compared to standard Al/AlO $\mathrm{_{x}}$ /Al junctions. The energy relaxation time constant for an Al/AlO $\mathrm{_{x}}$ /Al/Ti 3D transmon was $T_{1}= 1\ \mu s$ , over two orders of magnitude shorter than the measured $T_{1} = 134\ \mu s$ of a standard Al/AlO $\mathrm{_{x}}$ /Al 3D transmon. Intentionally adding disorder between the Al and Ti layers reduces the proximity effect and subgap current while increasing the relaxation time to $T_{1} = 32\ \mu s$ .
At NASA Goddard Space Flight Center, we have previously demonstrated a kilo-pixel array of transition-edge sensor (TES) microcalorimeters capable of meeting the energy resolution requirements of the future X-ray Integral Field Unit (X-IFU) instrument that is being developed for the Advanced Telescope for High ENergy Astrophysics (ATHENA) observatory satellite. The TES design in this array was a square device with side length of $50 \,\mathrm{\upmu }\mathrm{m}$ . Here, we describe studies of TES designs with small variations of the dimensions, exploring lengths, parallel to the current direction, ranging from $75 \,\mathrm{\upmu }\mathrm{m}$ to $50 \,\mathrm{\upmu }\mathrm{m}$ and widths, perpendicular to the current direction, ranging from $50 \,\mathrm{\upmu }\mathrm{m}$ to $15 \,\mathrm{\upmu }\mathrm{m}$ . We describe how these changes impact transition properties, thermal conductance and magnetic field sensitivity. In particular, we show that using a TES with a length of $50 \,\mathrm{\upmu }\mathrm{m}$ and width of $30 \,\mathrm{\upmu }\mathrm{m}$ may be a promising route to reduce the maximum time-derivative of the TES current in an X-ray pulse and reduce the sensitivity of the TES to magnetic field.
Increased thermal resistance of Salmonella at low water activity (aw) is a significant food safety concern in low-moisture foods (LMFs). We evaluated whether trans-cinnamaldehyde (CA, 1000 ppm) and eugenol (EG, 1000 ppm), which can accelerate thermal inactivation of Salmonella Typhimurium in water, can show similar effect in bacteria adapted to low aw in different LMF components. Although CA and EG significantly accelerated thermal inactivation (55 °C) of S. Typhimurium in whey protein (WP), corn starch (CS) and peanut oil (PO) at 0.9 aw, such effect was not observed in bacteria adapted to lower aw (0.4). The matrix effect on bacterial thermal resistance was observed at 0.9 aw, which was ranked as WP > PO > CS. The effect of heat treatment with CA or EG on bacterial metabolic activity was also partially dependent on the food matrix. Bacteria adapted to lower aw had lower membrane fluidity and unsaturated to saturated fatty acids ratio, suggesting that bacteria at low aw can change its membrane composition to increase its rigidity, thus increasing resistance against the combined treatments. This study demonstrates the effect of aw and food components on the antimicrobials-assisted heat treatment in LMF and provides an insight into the resistance mechanism.
This paper presents a high-rejection, thin-film HTS, microstrip bandstop filter to prevent a local and high-power RFI source from interfering with NASA GGAO's VGOS cryogenic receiver. This filter has an excellent 2.7%, 50-dB-fractionalbandwidth and a center stop-band frequency of 9.41 GHz. It does not contain any narrow or interdigital features as found in some designs, which reduces the fringing electric fields and improves its power handling capability. The YBCO films were grown on 435-μm-thick R-plane sapphire substrate and the anisotropic behavior was modeled and simulated with a high degree of accuracy. The device was tested while cooled to 77 K and the measurements agree well with simulation.
All‐solid‐state batteries (ASSBs) have piqued global research interest because of their unprecedented safety and high energy density. Significant advances have been made in achieving high room‐temperature ionic conductivity and good air stability of solid‐state electrolytes (SSEs), mitigating the challenges at the electrode‐electrolyte interface, and developing feasible manufacturing processes. Along with the advances in fundamental study, all‐solid‐state pouch cells using inorganic SSEs have been widely demonstrated, revealing their immense potential for industrialization. This Review provides an overview of inorganic all‐solid‐state pouch cells, focusing on ultrathin solid‐state electrolyte membranes, sheet‐type thick solid‐state electrodes, and bipolar stacking. Moreover, several critical parameters directly influencing the energy density of all‐solid‐state Li‐ion and Li‐S pouch cells are outlined. Finally, perspectives on all‐solid‐state pouch cells are provided and specific metrics to meet certain energy density targets are specified. With this Review, we look to facilitate the development of inorganic all‐solid‐state pouch cells with high energy density and excellent safety. This article is protected by copyright. All rights reserved
There are various definitions of fidelity in non-Hermitian systems, leading to confusion among researchers on which definition to use and the potential for different results. The present study proposes metricized fidelity, which has many desirable general properties. In PT-symmetric non-Hermitian systems, the PT-unbroken state is characterized by a real fidelity, while for PT-broken states, the real part of the fidelity susceptibility approaches negative infinity as the parameter approaches the exceptional point. Furthermore, the study proves that the real part of the fidelity between PT-unbroken and PT-broken states is always 1/2 at the second-order exceptional point. This definition provides clarity and consistency in the study of non-Hermitian systems, potentially enabling more accurate and comprehensive investigations of non-Hermitian systems in the future.
Particles measured in large gradual solar energetic particle events are believed to be predominantly accelerated at shocks driven by coronal mass ejections (CMEs). Ion charge state and composition analyses suggest that the origin of the seed particle population for the mechanisms of particle acceleration at CME‐driven shocks is not the bulk solar wind thermal material, but rather a suprathermal population present in the solar wind. This suprathermal population could result from remnant material accelerated in prior solar flares and/or preceding CME‐driven shocks. In this work, we examine the distribution of this suprathermal particle population in the inner heliosphere by combining a magnetohydrodynamic simulation of the solar wind and a Monte Carlo simulation of particle acceleration and transport. Assuming that the seed particles are uniformly distributed near the Sun by solar flares of various magnitudes, we study the longitudinal distribution of the seed population at multiple heliocentric distances. We consider a nonuniform background solar wind, consisting of fast and slow streams that lead to compression and rarefaction regions within the solar wind. Our simulations show that the seed population at a particular location (e.g., 1 au) is strongly modulated by the underlying solar wind configuration. Corotating interaction regions and merged interactions regions can strongly alter the energy spectra of the seed particle populations. In addition, cross‐field diffusion plays an important role in mitigating strong variations of the seed population in both space and energy.
Low mucus penetration ability and cellular uptake seriously limit the effectiveness of local vaginal drug administration because of the rapid foreign particulate and pathogen removal property of the mucus layer. Our previous work proved that nanoparticles with a highly dense polyethylene glycol (PEG) coating can penetrate mucus rapidly (mucus-penetrating nanoparticles, MPPs) and improve drug distribution and retention at mucosal surfaces. However, the "stealth-effect" of the PEG coating also restricts cellular uptake of MPPs. In this work, we designed pH-responsive mucus-penetrating nanoparticles (pMPPs) with hydrazone bonds as the linker to conjugate a dense PEG surface coating, which enabled the pMPPs to rapidly penetrate through the mucus layer. More importantly, the acidic environment of the vaginal mucus induces slow shedding of the PEG layer, leading to a positive charge exposure to facilitate cellular uptake. Overall, pMPPs demonstrate potential as an effective delivery platform for the prophylactic and therapeutic treatment of female reproductive diseases.
Understanding and controlling chirality in inorganic crystalline materials at the nanoscale is crucial in elucidating fundamental chirality-dependent physical and chemical processes as well as advancing new technological prospects, but significant challenges remain due to the lack of material control. Here, we have developed a facile and general bottom-up synthetic strategy for achieving chiral plasmonic Au nanostructures, including nanocubes and nanorods with fine chirality control. The underlying chiral mechanism enabled by the chiral boundary morphology is substantiated by theoretical modeling and finite element method (FEM) simulation. Because of the robustness of induced handedness and their small size, these as-synthesized chiral nanostructures can be further employed as building blocks toward the formation of complex chiral nanostructures. We have demonstrated a new class of chiral hybrid metal-semiconductor nanostructures that can allow integration of chirality with other properties and functionalities. All of these together have paved the way to engineer nanoscale inorganic chirality and thus study various emerging chirality-entangled effects with practical technological applications.
It has been hypothesized that liquid polyamorphism, the existence of multiple amorphous states in a single-component substance, may be caused by molecular or supramolecular interconversion. A simple microscopic model [Caupin and Anisimov, Phys. Rev. Lett. 2021, 127, 185701] introduces interconversion in a compressible binary lattice to generate various thermodynamic scenarios for fluids that exhibit liquid polyamorphism and/or water-like anomalies. Using this model, we demonstrate the dramatic effects of interconversion on the interfacial properties. In particular, we find that the liquid-vapor surface tension exhibits either an inflection point or two extrema in its temperature dependence. Correspondingly, we observe anomalous behavior of the interfacial thickness and a significant shift in the location of the concentration profile with respect to the location of the density profile.
Accurately predicting future ocean acidification (OA) conditions is crucial for advancing OA research at regional and global scales, and guiding society's mitigation and adaptation efforts. This study presents a new model-data fusion product covering 10 global surface OA indicators based on 14 Earth System Models (ESMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6), along with three recent observational ocean carbon data products. The indicators include fugacity of carbon dioxide, pH on total scale, total hydrogen ion content, free hydrogen ion content, carbonate ion content, aragonite saturation state, calcite saturation state, Revelle Factor, total dissolved inorganic carbon content, and total alkalinity content. The evolution of these OA indicators is presented on a global surface ocean 1° × 1° grid as decadal averages every 10 years from preindustrial conditions (1750), through historical conditions (1850–2010), and to five future Shared Socioeconomic Pathways (2020–2100): SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5. These OA trajectories represent an improvement over previous OA data products with respect to data quantity, spatial and temporal coverage, diversity of the underlying data and model simulations, and the provided SSPs. The generated data product offers a state-of-the-art research and management tool for the 21st century under the combined stressors of global climate change and ocean acidification. The gridded data product is available in NetCDF at the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information:, and global maps of these indicators are available in jpeg at:
Athletic shoes that induce dorsiflexion in standing can improve jump height compared to traditional athletic shoes that induce plantarflexion, but it is unknown if dorsiflexion shoes (DF) also affect landing biomechanics associated with lower extremity injury risk. Thus, the purpose of this study was to investigate if DF adversely affect landing mechanics related to patellofemoral pain and anterior cruciate ligament injury risk compared to neutral (NT) and plantarflexion (PF) shoes. Sixteen females (21.65 ± 4.7 years, 63.69 ± 14.3 kg, 1.60 ± 0.05 m) performed three maximum vertical countermovement jumps in DF (−1.5°), NT (0°) and PF (8°) shoes as 3D kinetics and kinematics were recorded. One-way repeated-measures ANOVAs revealed peak vertical ground reaction force, knee abduction moment and total energy absorption were similar between conditions. At the knee, peak flexion and joint displacement were lower in DF and NT, while relative energy absorption was greater in PF (all p < .01). Conversely, relative ankle energy absorption was greater in DF and NT compared to PF (p < .01). Both DF and NT induce landing patterns that may increase strain on passive structures in the knee, emphasising the need for landing mechanics to be considered when testing footwear as gains in performance could come at the cost of injury risk.
Many demographic problems require models for partnership formation. We consider a model for matchings within a bipartite population where individuals have utility for people based on observed and unobserved characteristics. It represents both the availability of potential partners of different types and the preferences of individuals for such people. We develop an estimator for the preference parameters based on sample survey data on partnerships and population composition. We conduct simulation studies based on the Survey of Income and Program Participation showing that the estimator recovers preference parameters that are invariant under different population availabilities and has the correct confidence coverage.
The density profiles of dark matter haloes contain rich information about their growth history and physical properties. One particularly interesting region is the splashback radius, Rsp, which marks the transition between particles orbiting in the halo and particles undergoing first infall. While the dependence of Rsp on the recent accretion rate is well established and theoretically expected, it is not clear exactly what parts of the accretion history Rsp responds to, and what other halo properties might additionally influence its position. We comprehensively investigate these questions by correlating the dynamically measured splashback radii of a large set of simulated haloes with their individual growth histories as well as their structural, dynamical, and environmental properties. We find that Rsp is sensitive to the accretion over one crossing time but largely insensitive to the prior history (in contrast to concentration, which probes earlier epochs). All secondary correlations are much weaker, but we discern a relatively higher Rsp in less massive, older, more elliptical, and more tidally deformed haloes. Despite these minor influences, we conclude that the splashback radius is a clean indicator of a halo’s growth over the past dynamical time. We predict that the magnitude gap should be a promising observable indicator of a halo’s accretion rate and splashback radius.
Cold gas in galaxies provides a crucial test to evaluate the realism of cosmological hydrodynamical simulations. To extract the atomic and molecular hydrogen properties of the simulated galaxy population, postprocessing methods taking the local UV field into account are required. We improve upon previous studies by calculating realistic UV fields with the dust radiative transfer code SKIRT to model the atomic-to-molecular transition in TNG50, the highest-resolution run of the IllustrisTNG suite. Comparing integrated quantities such as the H i mass function, we study to what detail the UV field needs to be modelled in order to calculate realistic cold gas properties. We then evaluate new, spatially resolved comparisons for cold gas in galaxies by exploring synthetic maps of atomic hydrogen at redshift zero and compare them to 21-cm observations of local galaxies from the WHISP survey. In terms of non-parametric morphologies, we find that TNG50 H i maps are less concentrated than their WHISP counterparts (median ΔC ≈ 0.3), due in part to central H i deficits related to the ejective character of supermassive black hole feedback in TNG. In terms of the H i column density distribution function, we find discrepancies between WHISP and IllustrisTNG that depend on the total H i abundance in these datasets as well as the postprocessing method. To fully exploit the synergy between cosmological simulations and upcoming deep H i /H2 data, we advocate the use of accurate methods to estimate the UV radiation field and to generate mock maps.
Young adults may benefit from civic engagement as a health promotion tool, as civic engagement is generally associated with positive well-being. However, more information is needed to examine civic engagement among lesser-educated young adults who are least likely to civically engage, and more likely to demonstrate mental health needs. We surveyed noncollege young adults (N = 621) to measure their civic engagement, meaning, civic efficacy, well-being, and sociodemographic factors. Using an a priori model, direct, indirect, and full effects path analyses were conducted across men and women, and then the entire sample. The full effects model best fit the data with mediation by civic efficacy and meaning (χ2 (2) = 0.59, p = 0.74; comparative fit index = 1.0; root mean square error of approximation = 0.00, 90% confidence interval [0.00-0.06]; R2 = 0.42). Types of engagement (civic, electoral, activism, and online) demonstrated differing relationships with well-being. Stakeholders should resource young adults with civic skills and coping strategies to address the many challenges that civic experiences often elicit.
Background: The COVID-19 pandemic had a global impact on health systems and the delivery of health services, including for chronic conditions such as HIV. In South Africa, impacts on HIV services have widely been quantitatively described. Across different health settings, patients have also qualitatively described numerous negative impacts to their HIV care. However, patient perspectives on COVID-19 impacts to HIV care in South Africa, the largest HIV care system in the world, have been little explored to date. Methods: We conducted 29 semi-structured individual interviews with people living with HIV (n = 24) and providers (n = 5) in Cape Town, South Africa. Results: While most patient participants reported continued access to HIV treatment during the pandemic, many described perceiving that the quality of their care declined. Increased structural barriers were described as one contributing factor to this change. Additionally, patients described that reduced privacy in clinical interactions was a key factor negatively influencing their experience of receiving care. Conclusion: Findings underscore the importance of ensuring patient privacy for HIV services even during the rearrangement of services in emergencies. It is also important to continue developing models to integrate community mental health services within HIV care delivery in South Africa.
Alternative splicing of pre-mRNAs is crucial for plant growth and development. Serine/arginine-rich (SR) proteins are a conserved family of RNA binding proteins that are critical for both constitutive and alternative splicing. However, how phosphorylation of SR proteins regulates gene transcription and alternative splicing during plant development is poorly understood. We found that the Arabidopsis thaliana L. SR protein-specific kinase II family proteins (SRPKIIs) play an important role in plant development, including flowering. SRPKIIs regulate the phosphorylation status of a subset of specific SR proteins, including SR45 and SC35, which subsequently mediates their subcellular localization. A phospho-dead SR45 mutant inhibits the assembly of the ASAP (apoptosis-and splicing-associated protein) complex and thereby upregulates the expression of FLC (FLOWERING LOCUS C) via epigenetic modification. The splicing efficiency of FLC introns was significantly increased in the shoot apex of the srpkii mutant. Transcriptomic analysis revealed that SRPKIIs regulate the alternative splicing of approximately four hundred genes, which largely overlap with those regulated by SR45 and SC35-SCL family proteins. In summary, we found that Arabidopsis SRPKIIs specifically affect the phosphorylation status of a subset SR proteins and regulate the expression and alternative splicing of FLC to control flowering time.
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William Rand
  • Marketing, Information Systems and Computer Science
Prabhat Koner
  • Earth System Science Interdisciplinary Center
Greg Bissonette
  • Department of Psychology
Jiuzhou Song
  • Department of Animal and Avian Sciences
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