Clarkson University
  • Potsdam, New York, United States
Recent publications
The stochasticity of grid-connected renewable energies, such as wind farms, is challenging the deterministic engineering practices of power system operation. In this paper, a stochastic transient energy function (STEF) model based on the Lyapunov theory is proposed to evaluate the stability of the power system with doubly-fed-induction generator (DFIG). Based on the STEF, the methodology for construction of the stable region is proposed. And the stability degree of each bus under the different fault types and locations are evaluated by the bus stable nominal value (BSNV). To this end, the STEF is derived first from the operation mechanism of synchronous generators and DFIGs. Sequentially, the stable region of the power system with DFIG is constructed by using the stable region theory; the operation locations of every buses are marked on the stable region by the stochastic matrix theory. Case study based on the New England 9-Bus System with DFIG demonstrates the robustness of the proposed STEF to determine the stable region and the results show its potential applications for transient stability incorporating stochasticity of the wind farms based power grid.
Lateral migration is of significant importance to fiber deposition in wall-bounded flows, especially when other active external physical transport mechanisms are absent. Due to great technical difficulty, investigation on this phenomenon is limited to fundamental derivations, and the implication to particle deposition has not been fully explored. To fill the gap, this study investigated the shear-induced lift and rotation on microfiber transport and deposition in low Reynolds number flows. Transport and deposition of non-neutrally buoyant ellipsoidal fibers in Poiseuille flow in horizontal and vertical channels is systematically examined, and various lateral migration scenarios are carefully investigated. It was found out that, in absence of the sideway gravity, shear-induced lift and rotation cause the fibers to drift across main streamlines in the vertical channel. This lateral movement is either the driving force for fiber deposition in a downward flow or pushes the particles toward channel center in an upward flow configuration. Lateral migration velocity in the vertical channel is found to correlate positively with fiber length and shear rate. Lateral migration is negligible in a horizontal channel where the sideway gravity is dominant. Current study clearly identified the presence of fiber transport scenarios where lateral migration driven by the shear-induced lift and rotation is the major contributor for fiber deposition in wall-bounded flows. The finding is of particular significance to practical applications, as frequently, they involve a combination of these transport scenarios either actively or passively. The study also provided additional insights to examine the equivalency of spheres to fiber dynamics.
Despite extensive research, the relationship between the progression of alkali-silica reaction (ASR) and the cement hydration mechanism, particularly the influence of the pore solution composition on the nature of reaction products is not thoroughly understood. A multi-analytical approach was applied to study ASR mechanism under accelerated conditions using a mortar system comprising of fused silica aggregates. For the first time, large field SEM mapping was used to correlate physical expansion with the composition, distribution and amount of ASR reaction products produced over time. A three-stage behavioral model was proposed to explain the dynamic relationship between ASR progression and pore solution composition. The results confirmed the co-existence of two phases within the ASR products: a CSH- type gel and an ASR-type gel. The relative abundance of one gel type over the other was dictated by their accessibility to the pore solution, which in turn influences how ASR propagates through the microstructure.
We propose a decision tree model that considers reverse and forward flows in a closed-loop supply chain (CLSC). Based on observations of three CLSCs, the model considers an environment where there is uncertainty in the quantity of returned used components (and new components from suppliers) with the decision being the incentive offered to each return source. Given that there are multiple suppliers, one must determine which supplier(s) to use and the corresponding capacity to reserve, in order to minimise total system costs. An example and a sensitivity analysis are presented to illustrate the model and to investigate multiple scenarios under various conditions. The analysis demonstrates that the supplier portfolio and returner incentive decisions are strongly linked to the supplier reliability, returned quantities, and the costs of not meeting the demand. Furthermore, the analysis suggests that understanding the behaviour of return sources relative to incentives is the most critical variable to implement the model.
Microfinance institutions (MFIs) must balance financial and social goals. When these coopetitive goals are under threat, which goals do MFIs prefer? Based on the theory of myopic loss aversion, our study aims to assess the immediate effect of the 2016 demonetization in India on MFIs and their loan portfolio performance and on unintended social outcomes. Using the 2016 demonetization in India as a quasi-experiment, we find that MFIs had a lower 30-day and 90-day portfolio at risk (PAR) and implemented better client protection terms. In addition, demonetization had a small but positive effect on developing start-up enterprises and serving more clients below the poverty line. Last, we find that MFIs investing in female client education presented a lower PAR after demonetization. Overall, our study sheds light on the unintended consequences on MFIs as a result of the demonetization event, and it provides policy implications for MFIs.
The paper studies the impact of ethnocentrism and cultural intelligence on employee outcome during corporate restructuring or expansion. The authors propose a theoretical model to test this relationship. In-depth interviews of 122 professionals in Northern India who have either been a part of an international assignment or have expanded their businesses were conducted and analysed for testing the proposed model. Key findings suggest that an ethnocentric person finds it difficult to perform well at his workplace as he is constantly faced with dilemmas of cultural fitness. A culturally intelligent person easily adapts oneself to the new environment without any adverse effect on performance. To provide a smooth transition during restructuring, mangers should take measures to encourage cultural intelligence and promote ethno-relativism among the employees.
Thyroid hormones are key regulators of development and metabolism in vertebrates. During the nestling period, young of altricial species transition from an ectothermic phenotype to an endothermic phenotype. Red-winged blackbirds are an altricial species that exhibit an increase in plasma 3,3’, 5-triiodo-L-thyronine (T 3 ) levels during the first 5 days post-hatch (dph), begin to develop endothermic metabolic responses by 7 dph, and fledge within 10 days of hatching. We propose that thyroid hormones play an important role in regulating development of endothermy during the nestling period in altricial birds. To better understand the effects of thyroid hormones on endothermic metabolic development in an altricial species, we treated nestling red-winged blackbirds on 2, 3, and 5 dph with either methimazole (MMI) to induce hypothyroidism or supplemental T 3 to induce hyperthyroidism. We then measured on 5, 7, and 9 dph morphology and whole animal O 2 consumption ( V ˙ o 2 ) and ventilation in the thermal neutral zone and during gradual cooling. Treatment of nestlings with MMI resulted in lower plasma T 3 levels on 5 dph that recovered by 7 dph, while supplementing with T 3 did not affect plasma T 3 levels on 5, 7 and 9 dph. Treatment with MMI resulted in smaller nestlings with smaller hearts and structural characters such as wing chord and femur length, but larger lungs and kidneys. Treatment with T 3 produced smaller nestlings with smaller body masses and shorter femur and tarsus lengths. The development of V ˙ o 2 and ventilation endothermic responses to gradual cooling in MMI treated nestlings were delayed when compared with control nestlings. In 9 dph nestlings, hypothyroidism resulted in alterations in the responses of ventilation frequency and tidal volume to cooling when compared with the control nestlings. Supplemental T 3 had no effect on the development of V ˙ o 2 and ventilation in the thermal neutral zone or in response to cooling. Our data suggest plasma thyroid hormone levels play an active role in the systemic development of endothermic capacity and the development of ventilatory control. In the nestling avian, multiple systems develop in concert to produce an endothermic phenotype, but reduced thyroid hormone delays maturation of endothermic capacity.
The effects of climate change are being felt around the world, and the calls to mitigate are growing louder. In hopes of responding to this call, we examine strategic compensation practices as innovative solutions for tackling climate change. We employ a fixed panel analysis and examine organizational data from an array of global fossil fuel organizations—arguably the principal climate change contributors. Our findings suggest that executive stock-option compensation oriented around a 3-year or more vesting period will enhance organizational green behaviors. The contributions of this study add to the green human resource management literature in offering new perspectives on how compensation practices can enhance green behaviors and clarify key misconceptions related to linking sustainability targets to firm-level compensation schemes.
Regenerative medicine aims to repair degenerate tissue through cell refurbishment with minimally invasive procedures. Adipose tissue (FAT)-derived stem or stromal cells are a convenient autologous choice for many regenerative cell therapy approaches. The intervertebral disc (IVD) is a suitable target. Comprised of an inner nucleus pulposus (NP) and an outer annulus fibrosus (AF), the degeneration of the IVD through trauma or aging presents a substantial socio-economic burden worldwide. The avascular nature of the mature NP forces cells to reside in a unique environment with increased lactate levels, conditions that pose a challenge to cell-based therapies. We assessed adipose and IVD tissue-derived stromal cells through in vitro transcriptome analysis in 2D and 3D culture and suggested that the transcription factor Glis1 and metabolite oxaloacetic acid (OAA) could provide NP cells with survival tools for the harsh niche conditions in the IVD. Keywords: 3D culture; adipose; annulus fibrosus; intervertebral disc; nucleus pulposus; regenerative medicine; stromal cell; transcriptome analysis.
Precision analysis of the key biological metabolites such as L-lactate has great practical importance for many technological processes in food technology, including beverage production. Here we describe a new, highly selective, and sensitive biosensor for accurate L-lactate assay based on a combination of peroxidase-mimetic nanozymes with microbial lactate oxidase (LOx) immobilized onto the surface of a graphite-rod electrode (GE). The peroxidase-like nanozymes were synthesized using the debris of carbon microfibers (CFs) functionalized with hemin (H) and modified with gold nanoparticles (AuNPs) or platinum microparticles (PtMPs). The nanozyme formed with PtMPs as well as corresponding bioelectrodes based on it (LOx-CF-H-PtMPs/GE) is characterized by preferable catalytic and operational characteristics, so it was selected for the analysis of L-lactate content in real samples of grape must and red wine. The results of the L-lactate analysis obtained by the developed biosensors are highly correlated with a very selective spectrophotometric approach used as a reference. The developed biosensor, due to its high selectivity and sensitivity, is very prospective not only for the beverage industry and food technology, but also for clinical diagnostics and medicine, as well as in other applications where the accurate analysis of L-lactate is highly important.
This themed collection includes a collection of articles on molecular simulation of chemistry and physics in external electric fields.
The Laurentian Great Lakes region in North America is experiencing climate-driven disturbances that threaten the public safety of the region and is forcing communities to respond. Communities vary in their ability to respond to these disturbances based on their existing capacities and access to resources, but responses in the region are uneven and create vulnerabilities to disasters. A virtual workshop was conducted to understand the community responses to climate-driven disturbances in the Great Lakes and identify the essential capacities for effective responses. Results show that the region as a whole has not responded adequately, and although the resources exist to respond, they are not adequately organized, and inequalities between urban and rural communities can exacerbate these challenges. Community capacities identified as critical for resilience include leadership, scientific knowledge, and connection to broader regional networks to access additional resources, but there are challenges with the complacency of some communities and deficiencies in mental health services.
Saws are common tools used in postmortem dismemberment to alter human remains. Dismemberment may coincide with other concealment methods such as disposal in aquatic environments, so forensic anthropologists must recognize how taphonomy affects saw mark preservation. This study focuses on exposure of saw cut bone to a fluvial environment. Cross sections from pig humeri cut by a 7 TPI saw were evaluated on all cut surfaces for tooth hop (TH), exit chipping, and breakaway spurs. Pre-fluvial exposure, features were measured by two observers using a stereomicroscope while a one-dimensional profilometer was used to define surface roughness. Bones were randomly assigned to control or experimental groups and within each divided by duration of exposure (24, 48, 72, and 96 h). Control groups (four cross sections) were exposed to water in a 3-meter-long hydraulic channel; experimental groups (20 cross sections) were exposed to water and sediment in a 12-meter-long sediment-recirculating hydraulic channel. Velocity was maintained at 0.45 m/s. All measurements were repeated post-exposure. Observer A recorded 268 TH (mean: 3.70 ± 0.34 mm); post-exposure, count increased by 16.79% (mean: 3.71 ± 0.29 mm). Observer B recorded 247 TH (mean: 3.46 ± 0.42 mm); post-exposure, count decreased by 29.15% (mean: 3.36 ± 0.33 mm). All TPI estimates calculated include the 7 TPI saw. Exit chipping lost flakiness (in both channels), but was still visible. Breakaway spurs were not visibly altered. Surface staining was limited to bones exposed to sediment. Roughness was significantly lower in experimental groups post-fluvial exposure (W = 5705, p < 0.05). Overall, this fluvial environment did not obliterate saw mark evidence from bone.
The eastern Australia coastline is characterized by impressive coastal landforms and an extensive northward-moving longshore drift system that have been influenced by a stable, long-term tectonic history over the Quaternary period. However, the timing and drivers of the formation of two conspicuous landscape features—Fraser Island (K’gari) and the Great Barrier Reef—remain poorly understood. Here we use optically stimulated luminescence and palaeomagnetic dating to constrain the formation of the extensive dunes that make up Fraser Island, the world’s largest sand island, and adjacent Cooloola Sand Mass in southeastern Queensland. We find that both formed between 1.2 Ma and 0.7 Ma, during a global climate reconfiguration across the Middle Pleistocene transition. They formed as a direct result of increased amplitude of sea-level fluctuations associated with increasing global ice volume that redistributed previously stored sediment across the continental shelf. The development of Fraser Island dramatically reduced sediment supply to the continental shelf north of the island. This facilitated widespread coral reef formation in the southern and central Great Barrier Reef and was a necessary precondition for its development. This major reorganization of the coastal sedimentary system is probably not unique to eastern Australia and should be investigated in other passive-margin coastlines.
Since early March 2020, government agencies have utilized a wide variety of non-pharmaceutical interventions to mitigate the spread of COVID-19 and have struggled to determine when it is appropriate to return to in-person activities after an outbreak is detected. At many universities, fundamental issues related to understanding the spread of the disease (e.g. the transmission rate), the ability of administrators to respond quickly enough by closing when there is a sudden rise in cases, and how to make a decision on when to reopen remains a concern. Surveillance testing strategies have been implemented in some places, and those test outcomes have dictated whether to reopen, to simultaneously monitor community spread, and/or to isolate discovered cases. However, the question remains as to when it is safe to reopen and how much testing is required to remain safely open while keeping infection numbers low. Here, we propose an extension of the classic SIR model to investigate reopening strategies for a fixed testing strategy, based on feedback from testing results. Specifically, we close when a predefined proportion of the population becomes infected, and later reopen when that infected proportion decreases below a predefined threshold. A valuable outcome of our approach is that our reopening strategies are robust to variation in almost all model parameters, including transmission rates, which can be extremely difficult to determine as they typically differ between variants, location, vaccination status, etc. Thus, these strategies can be, in theory, translated over to new variants in different regions of the world. Examples of robust feedback strategies for high disease transmission and a fixed testing capacity include (1) a single long lock down followed by a single long in-person period, and (2) multiple shorter lock downs followed by multiple shorter in-person periods. The utility of this approach of having multiple strategies is that administrators of universities, schools, business, etc. can use a strategy that is best adapted for their own functionality.
Structured granular materials exhibit strongly anisotropic mechanical behaviours resulting from the directional properties of their microstructural components such as grain shape, cement topology and contact orientation. Here, a fabric-enriched continuum breakage-damage framework is proposed to examine and simulate the evolution of anisotropy in granular rock with evolving internal structure. Fabric tensors for both grains and cement are embedded in the expression of the elastic free energy potential. To reflect the influence of anisotropic strain energy storage on inelastic mechanisms, such free energy function is then incorporated within a continuum breakage-damage formulation. The performance of the model is evaluated against experimental data for a high porosity granular rock tested at different orientations of its bedding planes. It is shown that the proposed model can accurately predict the yielding and stress–strain responses by accounting for the microstructure of cement and grains. Parametric analyses indicate that the evolution of the degree and the orientation of anisotropy is controlled by the independent fabric tensors of the two solid phases (i.e., grains and cement), as well as by the competition between grain crushing and cement disintegration. As a result, the model is able to capture naturally that a higher volume fraction of cement can enhance the stiffness and augment the softening behavior of the granular rock.
Despite their central importance to a variety of endeavors and despite widespread use in both industry and academia, version control systems (software for tracking versions of files) have not been extensively studied in fields related to technical communication, rhetoric, and communication design. Git, by far the most dominant version control system today, is largely absent. This study theorizes Git as boundary infrastructure---infrastructure used to facilitate collaboration across disciplines and domains. The unique characteristics of boundary infrastructure explain how something as prominent as Git can be so invisible and help identify dangers posed by boundary infrastructure. Drawing on modes of resistance developed in feminist rhetorics, this article concludes with suggestions to ameliorate the negatives effects such infrastructure might have on collaborative knowledge work.
The safe operation, control, and stability of standalone microgrids (MGs) are highly dependent on their coordination with the MG control center (MGCC). Due to the open communication channel between the MG and the MGCC, the measurement signals are vulnerable to cyber attacks that can compromise the stability of the system. In this article, a false data injection (FDI) attack on the frequency measurement of a standalone MG is considered to disrupt the stable operation of the MG. Therefore, an attack detection and identification method are proposed to protect the MG against the impacts of this attack. The proposed method is based on a dynamic state estimation technique that uses an unknown input observer (UIO) to estimate the MG states and generate a residual function that detects the presence of an FDI attack and triggers a detection alarm for attack isolation and mitigation. The robustness and practicability of the proposed method are demonstrated with real-time simulation results of a real-world MG system.
We consider functional differential equations (FDEs) which are perturbations of smooth ordinary differential equations (ODEs). The FDE can involve multiple state-dependent delays, distributed delays, or implicitly defined delays (forward or backward). We show that, under some mild assumptions on the perturbation, if the ODE has a nondegenerate periodic orbit, then the FDE has a smooth periodic orbit. Moreover, when the perturbation depends on some parameters, we get smooth dependence of the periodic orbit and its frequency on the parameters with high regularity. The method can also be applied to treat equations with small delays appearing in electrodynamics and FDEs which are perturbations of some evolutionary partial differential equations (PDEs). The proof consists in solving functional equations satisfied by the parameterization of the periodic orbit and the frequency using a fixed-point approach. We do not need to consider the smoothness of the evolution or even the phase space of the FDEs.
Magnetic properties of root, bark, and leaf of mangrove (Avicenna marina) and sediment were determined for pollution assessment at three locations in the northern coast of the Persian Gulf. The study revealed that the sources of the particles deposited on leaf surfaces can be discriminated via saturation isothermal remanent magnetization (SIRM) values and heavy metal. However, different factors including wind direction, size of the magnetic particles and crown density, play a role using SIRM for biomonitoring of atmospheric particulate matter. For leaves, the significant correlations between SIRM and leaf elemental contents indicated that the deposited particles on their surface mainly have geogenic sources. The magnetic analyses revealed that leaves are more suitable than bark for monitoring atmospheric pollution using mangrove trees due to the effect of different factors including dense crown of trees, washing of tree trunk by sea waves, and elements translocation from roots and sediments. Instead, the positive and significant correlation between the SIRM values for sediments and mangrove roots, and no or negative correlation between sediments and roots with barks and leaves indicates that the magnetic properties of the sediments and mangrove roots are suitable indicators of pollution in aquatic environment.
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1,717 members
Costel Darie
  • Department of Chemistry & Biomolecular Science, Biochemistry & Proteomics Group
Robert Frantisek Holub
  • Department of Chemical and Biomolecular Engineering Coulter School
Sitaraman Krishnan
  • Department of Chemical and Biomolecular Engineering
Don Rasmussen
  • Department of Chemical and Biomolecular Engineering Coulter School
Oleh Smutok
  • Department of Chemistry & Biomolecular Science
8 Clarkson Avenue, 13699, Potsdam, New York, United States
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