University of Michigan
  • Ann Arbor, United States
Recent publications
A large-eddy simulation framework has been coupled with controller modules to systematically investigate the impacts of collective (CPC) and individual (IPC) pitch control strategies on utility-scale wind turbine energy production and fatigue loads. Wind turbine components were parameterized using an actuator surface model to simulate the rotor blades and the turbine nacelle. The baseline CPC and IPC algorithms, consisting of single-input single-output proportional–integral controllers and two integral controllers, respectively, were incorporated into the numerical framework. A series of simulations were carried out to investigate the relative performance of the two controllers under various turbulent inflow conditions, spanning hub-height velocities of 7 to 14 m/s. The numerical simulation results of this study showed that, in comparison to the CPC, the IPC controller could successfully reduce the damage equivalent loads of utility-scale turbines at regions 2 and 3 of turbine operation by about 3% and 40%, respectively, without any penalty on the power production of the turbine. It was also shown that, despite its minor impact on the turbulence kinetic energy of the wake, the IPC controller did not influence the recovery of the turbine wake.
A pressure-sensing system with a half-Wheatstone-bridge-to-digital converter (HBDC) is proposed for implantable intraocular pressure (IOP) monitoring systems. The half-Wheatstone-bridge (H-WhB) sensor uses an RC-delay comparison instead of direct bias of the pressure transducer, allowing it to self-limit the current for efficient operation. To overcome the limited sensitivity of the H-WhB, energy-efficient bit-level oversampling (OS) is introduced. The system achieves 0.24-mmHg (1 $\sigma )$ resolution with an 8.58-nJ $\cdot$ mmHg $^{2}$ FOM and 12.79- $\mu $ W power consumption with a 11.52-ms conversion time. This marks a 2.8 $\times$ improvement in measured system power, 56.24 $\times$ improvement in energy consumption, and 2.8 $\times$ improvement in resolution compared to the prior H-WhB-based pressure sensor. In addition, the HBDC overcomes the low sensitivity limitations of the H-WhB and achieves a resolution FOM comparable to that of Wheatstone-bridge (WhB) sensor-based pressure sensors.
Determining the maximum cut of large graphs may require impractically long time, necessitating approximate algorithms and/or specialized computing platforms. A heuristic by Burer, Monteiro and Zhang for max-cut has not only been shown to be advantageous in many respects, but is also applicable to other NP-complete problems. From the perspective of accelerated computing, the heuristic's implementational challenge lies in its gradient-descent dynamics, which could be reduced to several sinusoidal kernel operations applied to each edge of the graph. We had previously established the theoretical underpinnings of a relaxed dynamical heuristic for max-cut similar to the one proposed by Burer et al. but suited for accelerated computing on custom analog CMOS. In this work, we present the first fully custom analog integrated circuit implementing the dynamics of our heuristic on 130-nm CMOS technology. In an era of increasing specificity of computing machines, our algorithm-circuit co-design, originally for max-cut, introduces a versatile approach applicable to a diverse set of practical large-scale NP-complete problems.
Ambient ozone (O 3 ) concentrations in Southeast Michigan (SEMI) can exceed the U.S. National Ambient Air Quality Standard (NAAQS). Despite past efforts to measure O 3 precursors and elucidate reaction mechanisms, changing emission patterns and atmospheric composition in SEMI warrant new measurements and updated mechanisms to understand the causes of observed O 3 exceedances. In this study, we examine the chemical drivers of O 3 exceedances in SEMI, based on the Phase I MOOSE (Michigan‐Ontario Ozone Source Experiment) field study performed during May – June 2021. A zero‐dimensional (0‐D) box model is constrained with measurement data of meteorology and trace gas concentrations. Box model sensitivity simulations suggest that the formaldehyde to nitrogen dioxide ratio (HCHO/NO 2 ) for the transition between the volatile organic compounds (VOC)‐ and nitrogen oxides (NO x )‐limited O 3 production regimes is 3.0 ± 0.3 in SEMI. The midday (12:00‐16:00) averaged HCHO/NO 2 ratio during the MOOSE Phase I study is 1.62 ± 1.03, suggesting that O 3 production in SEMI is limited by VOC emissions. This finding implies that imposing stricter regulations on VOC emissions should be prioritized for the SEMI O 3 nonattainment area. This study, through its use of ground‐based HCHO/NO 2 ratios and box modeling to assess O 3 ‐VOC‐NO x sensitivities, has significant implications for air quality policy and the design of effective O 3 pollution control strategies, especially in O 3 nonattainment areas.
Candida auris is an emerging fungal pathogen responsible for health care-associated outbreaks that arise from persistent surface and skin colonization. We characterized the arsenal of adhesins used by C. auris and discovered an uncharacterized adhesin, Surface Colonization Factor (Scf1), and a conserved adhesin, Iff4109, that are essential for the colonization of inert surfaces and mammalian hosts. SCF1 is apparently specific to C. auris, and its expression mediates adhesion to inert and biological surfaces across isolates from all five clades. Unlike canonical fungal adhesins, which function through hydrophobic interactions, Scf1 relies on exposed cationic residues for surface association. SCF1 is required for C. auris biofilm formation, skin colonization, virulence in systemic infection, and colonization of inserted medical devices.
Genetic assimilation is the evolutionary process by which an environmentally induced phenotype becomes genetically encoded and constitutive. Genetic assimilation has been proposed as a concluding step in environmental adaptation, but its prevalence has not been systematically investigated. Analyzing transcriptomic data collected upon reciprocal transplant, we address this question in the experimental evolution, domestication, or natural evolution of seven diverse species. We find that genetic assimilation of environment-induced gene expression is the exception rather than the rule and that substantially more genes retain than lose their expression plasticity upon organismal adaptations to new environments. The probability of genetic assimilation of gene expression decreases with the expression level and number of transcription factors controlling the gene, suggesting that genetic assimilation results primarily from passive losses of gene regulations that are not mutationally robust. Hence, for gene expression, our findings argue against the purported generality or importance of genetic assimilation to environmental adaptation.
A fully integrated high-efficiency phase-locked sub-terahertz (THz) radiator is reported in this article, implemented in a 55-nm SiGe BiCMOS process. This radiator is capable of generating 192–210-GHz chirps, which can be used for the new generation automotive and imaging radar systems. It consists of a low-power millimeter-wave digital phase-locked loop (DPLL)-based chirp generator, a high-efficiency 6 $\times$ multiplier chain, and an on-chip folded slot antenna. By incorporating a 32-entry lookup table into the millimeter-wave DPLL, a fast back-to-lock feature is realized at the end of each chirp signal. In addition, this chirp generator prototype achieves $+$ 5.9/ $+$ 19.2-dBm sub-THz power/effective isotropic radiated power (EIRP), which is among the highest in all the phase-locked sources at this frequency range. Its 3.0% dc-to-THz efficiency is at least 5 $\times$ higher than all previously published works.
Background Daily oral pre-exposure prophylaxis (PrEP) can reduce HIV incidence in pregnant and breastfeeding women, but adherence is essential. Methods We conducted a pilot randomized trial to evaluate an intervention package to enhance antenatal and postnatal PrEP use in Lilongwe, Malawi. The intervention was based on patient-centered counseling adapted from prior PrEP studies, with the option of a participant-selected adherence supporter. Participants were locally eligible for PrEP and randomized 1:1 to intervention or standard counseling (i.e., control) and followed for six months. Participants received the intervention package or standard counseling at enrollment, one month, three months, and six months. Adherence was measured via plasma and intracellular tenofovir concentrations and scored using a published algorithm. Our primary outcome was retention in care with concentrations consistent with 4-7 doses/week. Results From June to November 2020, we enrolled 200 pregnant women with median gestational age of 26 (IQR:19-33) weeks. Study retention was high at three months (89.5%) and six months (85.5%). In contrast, across the two timepoints, 32.8% had adherence scores consistent with 2-5 doses/week and 10.3% had scores consistent with daily dosing. For the composite primary endpoint, no substantial differences were observed between the intervention and control groups at three months (28.3% vs. 29.0%, probability difference [PD]:-0.7%, 95%CI:-13.3%, 11.8%) or at six months (22.0% vs. 26.3%, PD:-4.3%, 95%CI:-16.1%, 7.6%). Conclusions In this randomized trial of PrEP adherence support, retention was high, but less than one-third of participants had pharmacologically confirmed adherence of > 4 doses/week. Future research should focus on antenatal and postnatal HIV prevention needs and their alignment across the PrEP continuum, including uptake, persistence, and adherence.
The hypothesis that ice-sheet evolution is only controlled by the long-term non-Newtonian viscous behavior of ice has been challenged by observations indicating that effects like brittle failure, stick-slip sliding, tides and wave action may affect ice-sheet evolution on sub-daily timescales. Over these timescales, the quasi-static-creep approximation is no longer appropriate and elastic effects become important. Simulating elastic effects in ice-sheet models over relevant timescales, however, remains challenging. Here, we show that by including a visco-elastic rheology and reintroducing the oft neglected acceleration term back into the ice-sheet stress balance, we can create a visco-elastic system where the velocity is locally determined and information propagates at the elastic wave speed. Crucially, the elastic wave speed can be treated like an adjustable parameter and set to any value to reproduce a range of phenomena, provided the wave speed is large compared to the viscous velocity. We illustrate the system using three examples. The first two examples demonstrate that the system converges to the steady-state viscous and elastic limits. The third example examines ice-shelf rifting and iceberg calving. This final example hints at the utility of the visco-elastic formulation in treating both long-term evolution and short-term environmental effects.
Premise Field images are important sources of information for research in the natural sciences. However, images that lack photogrammetric scale bars, including most iNaturalist observations, cannot yield accurate trait measurements. We introduce FieldPrism, a novel system of photogrammetric markers, QR codes, and software to automate the curation of snapshot vouchers. Methods and Results Our photogrammetric background templates (FieldSheets) increase the utility of field images by providing machine‐readable scale bars and photogrammetric reference points to automatically correct image distortion and calculate a pixel‐to‐metric conversion ratio. Users can generate a QR code flipbook derived from a specimen identifier naming hierarchy, enabling machine‐readable specimen identification for automatic file renaming. We also developed FieldStation, a Raspberry Pi–based mobile imaging apparatus that records images, GPS location, and metadata redundantly on up to four USB storage devices and can be monitored and controlled from any Wi‐Fi connected device. Conclusions FieldPrism is a flexible software tool designed to standardize and improve the utility of images captured in the field. When paired with the optional FieldStation, researchers can create a self‐contained mobile imaging apparatus for quantitative trait data collection.
Plain Language Summary Thermospheric composition and temperature are important variables for the thermosphere and can influence the orbits of low Earth orbit satellites. Before the launch of Global‐scale Observations of the Limb and Disk (GOLD) mission, limited observations are available. Due to this limitation, the spatial variations of this thermospheric composition and temperature have not been adequately investigated. In this work, we utilized the data from the GOLD mission to investigate the local time (LT), latitude, and seasonal variations of the hemispheric asymmetry in the thermosphere. It is found that (a) The hemispheric asymmetry of the thermosphere is weaker at lower latitudes; (b) The hemispheric asymmetry of the thermosphere is weaker toward the duskside; (c) The northern hemisphere has a longer duration of lower ΣO/N2 and higher temperature.
Historians and ethnographers have described biomedicine as a modernist project that imagines accumulating ever-more stable knowledge over time. This project broke down in heavily hit hospitals at the onset of the COVID-19 pandemic in the U.S., when bureaucratic, physical and knowledge structures collapsed. A combination of terror, a partially characterized disease entity and clinicians′ inability to operate without disease models drove them to draw on rapidly changing and contradictory information via social media, changing medical practice minute-to-minute. The result was a unique form of knowing described as “hallucination”: a hyperreal, unstable ecology of imagined viral particles distributed in physical spaces, transforming with each text message and tweet. The nature, experience and practice of this ecology sheds light on what happens when instability comes to otherwise stable places.
Abstract Introduction HIV stigma can impact couple relationships through stress or bring partners closer through shared experiences. Conversely, couple relationships may protect against the harms of stigma, including anticipated stigma on negative health outcomes. Yet few studies have assessed the potential link between HIV stigma, relationship dynamics, and antiretroviral therapy (ART) adherence. Using dyadic data from a cross-sectional study of Malawian couples living with HIV, we tested associations between anticipated stigma and: 1) relationship dynamics (e.g., trust, sexual satisfaction, communication) and partner support; and 2) self-reported ART adherence. Methods Heterosexual couples (211 couples, 422 individuals) with at least one partner on ART were recruited from clinics in Zomba, Malawi. Partners completed separate surveys on anticipated stigma, relationship dynamics, and ART adherence. Linear mixed models evaluated associations between anticipated stigma and relationship dynamics, and whether associations varied by gender. Generalized estimating equation models tested for associations between anticipated stigma and high ART adherence (90–100% vs.
Broken symmetries and electronic topology are well manifested together in the second-order nonlinear optical responses from topologically non-trivial materials. Although second-order nonlinear optical effects from the electric dipole contribution have been extensively explored in polar Weyl semimetals with broken spatial-inversion symmetry, they are rarely studied in centrosymmetric magnetic Weyl semimetals with broken time-reversal symmetry due to the complete suppression of the electric dipole contribution. Here we report the experimental demonstration of optical second-harmonic generation (SHG) in a magnetic Weyl semimetal Co3Sn2S2 from the electric quadrupole contribution. By tracking the temperature dependence of the rotational anisotropy of SHG, we capture two magnetic phase transitions, with both SHG intensity increasing and its rotational anisotropy pattern rotating at TC,1 = 175 K and TC,2 = 120 K subsequently. The fitted critical exponents for the SHG intensity and rotational anisotropy orientation near TC,1 and TC,2 suggest that the magnetic phase at TC,1 is a three-dimensional Ising-type out-of-plane ferromagnetism, whereas the other at TC,2 is a three-dimensional XY-type all-in–all-out in-plane antiferromagnetism. Our results show the success of the detection and exploration of electric quadrupole SHG in a centrosymmetric magnetic Weyl semimetal and hence open the pathway towards future investigations into its association with band topology.
The flavoenzyme nicotine oxidoreductase (NicA2) is a promising injectable treatment to aid in the cessation of smoking, a behavior responsible for one in ten deaths worldwide. NicA2 acts by degrading nicotine in the bloodstream before it reaches the brain. Clinical use of NicA2 is limited by its poor catalytic activity in the absence of its natural electron acceptor CycN. Without CycN, NicA2 is instead oxidized slowly by dioxygen (O2), necessitating unfeasibly large doses in a therapeutic setting. Here, we report a genetic selection strategy that directly links CycN-independent activity of NicA2 to growth of Pseudomonas putida S16. This selection enabled us to evolve NicA2 variants with substantial improvement in their rate of oxidation by O2. The encoded mutations cluster around a putative O2 tunnel, increasing flexibility and accessibility to O2 in this region. These mutations further confer desirable clinical properties. A variant form of NicA2 is tenfold more effective than the wild type at degrading nicotine in the bloodstream of rats.
Coronary artery calcification (CAC), a measure of subclinical atherosclerosis, predicts future symptomatic coronary artery disease (CAD). Identifying genetic risk factors for CAC may point to new therapeutic avenues for prevention. Currently, there are only four known risk loci for CAC identified from genome-wide association studies (GWAS) in the general population. Here we conducted the largest multi-ancestry GWAS meta-analysis of CAC to date, which comprised 26,909 individuals of European ancestry and 8,867 individuals of African ancestry. We identified 11 independent risk loci, of which eight were new for CAC and five had not been reported for CAD. These new CAC loci are related to bone mineralization, phosphate catabolism and hormone metabolic pathways. Several new loci harbor candidate causal genes supported by multiple lines of functional evidence and are regulators of smooth muscle cell-mediated calcification ex vivo and in vitro. Together, these findings help refine the genetic architecture of CAC and extend our understanding of the biological and potential druggable pathways underlying CAC.
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Shailender Kanwar
  • Bio-interfaces Institute, NCRC B20/301W-6D
Raghunath Azhwar
  • Department of Pediatrics and Communicable Diseases
Olga Grushko
  • Division of Cardiovascular Medicine
Ann Arbor, United States