STAIR: Practical AIMD Multirate Congestion Control

Existing approaches for multirate multicast congestion control are either friendly to TCP only over large time scales or introduce unfortunate side effects, such as significant control traffic, wasted bandwidth, or the need for modifications to existing routers. We advocate a layered multicast approach in which steady-state receiver reception rates emulate the classical TCP sawtooth derived from additive-increase, multiplicative decrease (AIMD) principles. Our approach introduces the concept of dynamic stair layers to simulate various rates of additive increase for receivers with heterogeneous round-trip times (RTTs), facilitated by a minimal amount of IGMP control traffic. We employ a mix of cumulative and non-cumulative layering to minimize the amount of excess bandwidth consumed by receivers operating asynchronously behind a shared bottleneck. We integrate these techniques together into a congestion control scheme called STAIR which is amenable to those multicast applications which can make effective use of arbitrary and time-varying subscription levels.National Science Foundation (CAREER ANI-0093296, ANI-9986397

Smooth Multirate Multicast Congestion Control

A significant impediment to deployment of multicast services is the daunting technical complexity of developing, testing and validating congestion control protocols fit for wide-area deployment. Protocols such as pgmcc and TFMCC have recently made considerable progress on the single rate case, i.e. where one dynamic reception rate is maintained for all receivers in the session. However, these protocols have limited applicability, since scaling to session sizes beyond tens of participants necessitates the use of multiple rate protocols. Unfortunately, while existing multiple rate protocols exhibit better scalability, they are both less mature than single rate protocols and suffer from high complexity. We propose a new approach to multiple rate congestion control that leverages proven single rate congestion control methods by orchestrating an ensemble of independently controlled single rate sessions. We describe SMCC, a new multiple rate equation-based congestion control algorithm for layered multicast sessions that employs TFMCC as the primary underlying control mechanism for each layer. SMCC combines the benefits of TFMCC (smooth rate control, equation-based TCP friendliness) with the scalability and flexibility of multiple rates to provide a sound multiple rate multicast congestion control policy.National Science Foundation (ANI-9986397, ANI-0092196

Quantification of Local Hemodynamic Alterations Caused by Virtual Implantation of Three Commercially Available Stents for the Treatment of Aortic Coarctation

Patients with coarctation of the aorta (CoA) are prone to morbidity including atherosclerotic plaque that has been shown to correlate with altered wall shear stress (WSS) in the descending thoracic aorta (dAo). We created the first patient-specific computational fluid dynamics (CFD) model of a CoA patient treated by Palmaz stenting to date, and compared resulting WSS distributions to those from virtual implantation of Genesis XD and modified NuMED CP stents, also commonly used for CoA. CFD models were created from magnetic resonance imaging, fluoroscopy and blood pressure data. Simulations incorporated vessel deformation, downstream vascular resistance and compliance to match measured data and generate blood flow velocity and time-averaged WSS (TAWSS) results. TAWSS was quantified longitudinally and circumferentially in the stented region and dAo. While modest differences were seen in the distal portion of the stented region, marked differences were observed downstream along the posterior dAo and depended on stent type. The Genesis XD model had the least area of TAWSS values exceeding the threshold for platelet aggregation in vitro, followed by the Palmaz and NuMED CP stents. Alterations in local blood flow patterns and WSS imparted on the dAo appear to depend on the type of stent implanted for CoA. Following confirmation in larger studies, these findings may aid pediatric interventional cardiologists in selecting the most appropriate stent for each patient, and ultimately reduce long-term morbidity following treatment for CoA by stenting

A Case Report of Coronavirus Disease 2019 Presenting with Tremors and Gait Disturbance

Introduction: Neurologic symptoms present as significant complications of coronavirus disease 2019 (COVID-19) infection. This report describes a novel manifestation of tremors triggered by severe acute respiratory syndrome coronavirus 2 infection.Case Presentation: We describe a case of a 46-year-old man with COVID-19 infection complicated by a bilateral intention tremor and wide-based gait. Although neurological manifestations have been reported related to COVID-19, tremulousness has not yet been described.Conclusion: Considering the evolving diversity of neurologic manifestations in this infection, emergency physicians should be vigilant of possible COVID-19 infection in patients presenting with unexplained neurologic symptoms

Investigation of the Influence of the Clay Seams Around an Underground Excavation in Rock Salt

The presence of clay seams in the roof is especially important for assessing the stability of the excavations in salt and potash mines, since they allow separation as well as horizontal slip. The deformational behavior at clay seams in the roof of excavations was investigated by using actual field measurements made at the Waste Isolation Pilot Plant (WlPP) site. From the in situ deformation measurements, the separation and separation rate across the clay seams in the roof and floor could be estimated by using the technique developed in this study. The horizontal displacement along the clay seams was determined from the deflection measurements and compared with the predictions from a computer simulation using FLAC and clastic beam theory

A Flattened Protostellar Envelope in Absorption around L1157

Deep Spitzer IRAC images of L1157 reveal many of the details of the outflow and the circumstellar environment of this Class 0 protostar. In IRAC band 4, 8 microns, there is a flattened structure seen in absorption against the background emission. The structure is perpendicular to the outflow and is extended to a diameter of 2 arcminutes. This structure is the first clear detection of a flattened circumstellar envelope or pseudo-disk around a Class 0 protostar. Such a flattened morphology is an expected outcome for many collapse theories that include magnetic fields or rotation. We construct an extinction model for a power-law density profile, but we do not constrain the density power-law index.Comment: ApJL accepte

Hydroxymethylation Influences on Intestinal Epithelial Cells in Health and Disease

Epigenetics describes modifications that affect gene expression that are not encoded within the DNA sequence. DNA methylation is the longest appreciated epigenetic modification and has been accepted to play a critical role in maintaining euchromatin and silencing genes. Recently, a separate and distinct covalent modification has been recognized; hydroxymethylation, which has been associated with increased gene expression as opposed to gene silencing. However, traditional methods to study DNA methylation also recognized hydroxymethylation and did not distinguish between these two distinct DNA covalent modifications. Furthermore, TET enzymes have been identified to play a critical role in active hydroxymethylation of previously methylated cytosine residues and may further result in conversion to cytosine. TET1 plays a critical role in intestinal epithelial differentiation and development, and this is also correlated with increased hydroxymethylation in terminally differentiated epithelial cells. Colon cancer, which arises from the colonic epithelium, exhibits decreased hydroxymethylation and altered gene expression

SimpleSSD: Modeling Solid State Drives for Holistic System Simulation

Existing solid state drive (SSD) simulators unfortunately lack hardware and/or software architecture models. Consequently, they are far from capturing the critical features of contemporary SSD devices. More importantly, while the performance of modern systems that adopt SSDs can vary based on their numerous internal design parameters and storage-level configurations, a full system simulation with traditional SSD models often requires unreasonably long runtimes and excessive computational resources. In this work, we propose SimpleSSD, a highfidelity simulator that models all detailed characteristics of hardware and software, while simplifying the nondescript features of storage internals. In contrast to existing SSD simulators, SimpleSSD can easily be integrated into publicly-available full system simulators. In addition, it can accommodate a complete storage stack and evaluate the performance of SSDs along with diverse memory technologies and microarchitectures. Thus, it facilitates simulations that explore the full design space at different levels of system abstraction.Comment: This paper has been accepted at IEEE Computer Architecture Letters (CAL