Transient and asymptotic properties of robust adaptive controllers in the presence of non-coercive Lyapunov functions

— Adaptive control architectures often make use of Lyapunov functions to design adaptive laws. We are specifically interested in adaptive control methods, such as the well-known L1 adaptive architecture, which employ a parameter observer for this purpose. In such architectures, the observation error plays a critical role in determining analytical bounds on the tracking error as well as robustness. In this paper, we show how the non-existence of coercive Lyapunov operators can impact the analytical bounds, and with it the performance and the robustness of such adaptive systems

Angular-momentum-based sizing of control moment gyro cluster for an agile spacecraft

The sizing of a control moment gyro (CMG) cluster is covered sparsely in literature, but it is of considerable interest 2 to a practicing engineer. In this paper, the sizing of a cluster of four control moment gyros is investigated based on the mission angular momentum requirement of a typical agile spacecraft. The CMG skew angle β and individual CMG angular momentum h are determined as part of the sizing. The work focuses on the sizing of a minimally redundant cluster of four CMGs in a pyramid and roof-type arrangement considering their external angular momentum surfaces. Two approaches are discussed: the first considers maximum angular momentum about individual axis separately, and the second considers the momentum requirement about two axes simultaneously. The internal momentum surfaces of the CMG clusters are analyzed. Gimbal angle desaturation and the fuel consumed for it by the roof-type and pyramid configurations are also examined. Both the four CMG clusters are able to meet the maximum nonspherical angular momentum demanded by a typical mission about each axes. However, using method 1, the cluster is able to generate only 88% of the two-axis mission demand. The clusters meet the mission demand completely with method 2 using 20% more angular momentum per CMG and an increase in skew angle by 8–11° compared to method 1. The 20% increase in momentum increases power consumption by 11%. For a typical gimbal angle desaturation, the roof-type cluster uses 8.5% more fuel than the pyramid arrangement. However, the former has only one major internal singular surface in contrast with seven for the latter. This makes the roof-type arrangement very desirable to keep the singularity avoidance algorithm simple and amenable with the CMGs 3 operating within the momentum capability, and achieve the required spacecraft agility

Modeling and simulation for the spread of Covid-19 in an Indian city: a case study

We present a case study on modeling and predicting the course of Covid-19 in the Indian city of Pune. The results presented in this paper are concerned primarily with the wave of infections triggered by the Delta variant during the period between February and June 2021. Our work demonstrates the necessity for bringing together compartmental stock-and-flow and agent-based models and the limitations of each approach when used individually. Some of the work presented here was carried out in the process of advising the local city administration and reflects the challenges associated with employing these models in a real-world environment with its uncertainties and time pressures. Our experience, described in the paper, also highlights the risks associated with forecasting the course of an epidemic with evolving variants

Real-time motion planning with a fixed-wing UAV using an agile maneuver space

Small fixed-wing unmanned aerial vehicles (UAVs) are becoming increasingly capable of flying at low altitudes and in constrained environments. This paper addresses the problem of automating the flight of a fixed-wing UAV through highly constrained environments. The main contribution of this paper is the development of a maneuver space, integrating steady and transient agile maneuvers for a class of fixed-wing aircraft. The maneuver space is integrated into the rapidly-exploring random trees (RRT) algorithm. The RRT-based motion planner, together with a flight control system, is demonstrated in simulations and flight tests to efficiently generate and execute a motion plan through highly constrained 3D environments in real-time. The flight experiments—which effectively demonstrated the usage of three highly agile maneuvers—were conducted using only on-board sensing and computing

Defective Interfering Viral Particles in Acute Dengue Infections

While much of the genetic variation in RNA viruses arises because of the error-prone nature of their RNA-dependent RNA polymerases, much larger changes may occur as a result of recombination. An extreme example of genetic change is found in defective interfering (DI) viral particles, where large sections of the genome of a parental virus have been deleted and the residual sub-genome fragment is replicated by complementation by co-infecting functional viruses. While most reports of DI particles have referred to studies in vitro, there is some evidence for the presence of DI particles in chronic viral infections in vivo. In this study, short fragments of dengue virus (DENV) RNA containing only key regulatory elements at the 3′ and 5′ ends of the genome were recovered from the sera of patients infected with any of the four DENV serotypes. Identical RNA fragments were detected in the supernatant from cultures of Aedes mosquito cells that were infected by the addition of sera from dengue patients, suggesting that the sub-genomic RNA might be transmitted between human and mosquito hosts in defective interfering (DI) viral particles. In vitro transcribed sub-genomic RNA corresponding to that detected in vivo could be packaged in virus like particles in the presence of wild type virus and transmitted for at least three passages in cell culture. DENV preparations enriched for these putative DI particles reduced the yield of wild type dengue virus following co-infections of C6–36 cells. This is the first report of DI particles in an acute arboviral infection in nature. The internal genomic deletions described here are the most extensive defects observed in DENV and may be part of a much broader disease attenuating process that is mediated by defective viruses

Isosteviol Has Beneficial Effects on Palmitate-Induced α-Cell Dysfunction and Gene Expression

BACKGROUND: Long-term exposure to high levels of fatty acids impairs insulin secretion and exaggerates glucagon secretion. The aim of this study was to explore if the antihyperglycemic agent, Isosteviol (ISV), is able to counteract palmitate-induced α-cell dysfunction and to influence α-cell gene expression. METHODOLOGY/PRINCIPAL FINDINGS: Long-term incubation studies with clonal α-TC1-6 cells were performed in the presence of 0.5 mM palmitate with or without ISV. We investigated effects on glucagon secretion, glucagon content, cellular triglyceride (TG) content, cell proliferation, and expression of genes involved in controlling glucagon synthesis, fatty acid metabolism, and insulin signal transduction. Furthermore, we studied effects of ISV on palmitate-induced glucagon secretion from isolated mouse islets. Culturing α-cells for 72-h with 0.5 mM palmitate in the presence of 18 mM glucose resulted in a 56% (p<0.01) increase in glucagon secretion. Concomitantly, the TG content of α-cells increased by 78% (p<0.01) and cell proliferation decreased by 19% (p<0.05). At 18 mM glucose, ISV (10(-8) and 10(-6) M) reduced palmitate-stimulated glucagon release by 27% (p<0.05) and 27% (p<0.05), respectively. ISV (10(-6) M) also counteracted the palmitate-induced hypersecretion of glucagon in mouse islets. ISV (10(-6) M) reduced α-TC1-6 cell proliferation rate by 25% (p<0.05), but ISV (10(-8) and 10(-6) M) had no effect on TG content in the presence of palmitate. Palmitate (0.5 mM) increased Pcsk2 (p<0.001), Irs2 (p<0.001), Fasn (p<0.001), Srebf2 (p<0.001), Acaca (p<0.01), Pax6 (p<0.05) and Gcg mRNA expression (p<0.05). ISV significantly (p<0.05) up-regulated Insr, Irs1, Irs2, Pik3r1 and Akt1 gene expression in the presence of palmitate. CONCLUSIONS/SIGNIFICANCE: ISV counteracts α-cell hypersecretion and apparently contributes to changes in expression of key genes resulting from long-term exposure to palmitate. ISV apparently acts as a glucagonostatic drug with potential as a new anti-diabetic drug for the treatment of type 2 diabetes

NF90 Binds the Dengue Virus RNA 3′ Terminus and is a Positive Regulator of Dengue Virus Replication

Background Viral RNA translation and replication are regulated by sequence and structural elements in the 5′ and 3′ untranslated regions (UTR) and by host cell and/or viral proteins that bind them. Dengue virus has a single-stranded RNA genome with positive polarity, a 5′ m7GpppG cap, and a conserved 3′-terminal stem loop (SL) that is linked to proposed functions in viral RNA transcription and translation. Mechanisms explaining the contributions of host proteins to viral RNA translation and replication are poorly defined, yet understanding host protein-viral RNA interactions may identify new targets for therapeutic intervention. This study was directed at identifying functionally significant host proteins that bind the conserved dengue virus RNA 3′ terminus. Methodology/Principal Findings Proteins eluted from a dengue 3′ SL RNA affinity column at increasing ionic strength included two with double-strand RNA binding motifs (NF90/DRBP76 and DEAH box polypeptide 9/RNA helicase A (RHA)), in addition to NF45, which forms a heterodimer with NF90. Although detectable NF90 and RHA proteins localized to the nucleus of uninfected cells, immunofluorescence revealed cytoplasmic NF90 in dengue virus-infected cells, leading us to hypothesize that NF90 has a functional role(s) in dengue infections. Cells depleted of NF90 were used to quantify viral RNA transcript levels and production of infectious dengue virus. NF90 depletion was accompanied by a 50%-70% decrease in dengue RNA levels and in production of infectious viral progeny. Conclusions/Significance The results indicate that NF90 interacts with the 3′ SL structure of the dengue RNA and is a positive regulator of dengue virus replication. NF90 depletion diminished the production of infectious dengue virus by more than 50%, which may have important significance for identifying therapeutic targets to limit a virus that threatens more than a billion people worldwide.Ruth L. Kirschstein National Research Service Award (NIH-NRSA GM64985)UNCF-Merck Postdoctoral FellowshipNational Institute of Allergy and Infectious Diseases (U.S.)Ellison Medical Foundatio

Southern Ocean pteropods at risk from ocean warming and acidification

Early life stages of marine calcifiers are particularly vulnerable to climate change. In the Southern Ocean aragonite undersaturation events and areas of rapid warming already occur and are predicted to increase in extent. Here, we present the first study to successfully hatch the polar pteropod Limacina helicina antarctica and observe the potential impact of exposure to increased temperature and aragonite undersaturation resulting from ocean acidification (OA) on the early life stage survival and shell morphology. High larval mortality (up to 39%) was observed in individuals exposed to perturbed conditions. Warming and OA induced extensive shell malformation and dissolution, respectively, increasing shell fragility. Furthermore, shell growth decreased, with variation between treatments and exposure time. Our results demonstrate that short-term exposure through passing through hotspots of OA and warming poses a serious threat to pteropod recruitment and long-term population viability