Multiple Independent Paths Research Articles

Revisiting the small-world property of co-enrollment networks: A network analysis of hybrid course delivery strategies

Infectious disease outbreaks bring new challenges to campus operations at institutions of higher education (IHEs). At the beginning of the COVID-19 pandemic, as a precaution against COVID-19 transmission on their campuses, many IHEs shifted to entirely remote courses in the Spring 2020 semester. As these institutions prepared for the Fall 2020 semester, their administrations evaluated the extent to which remote courses should continue. While remote courses may reduce the number of students who interact on campus and thus mitigate the risk of disease spread, there may be academic and financial downsides. MethodologyUsing de-identified enrollment, course schedule, and student profile data from the Fall 2019 semester at Georgia Institute of Technology (Georgia Tech), we construct a co-enrollment network, which is a representation of student connections through courses. In this co-enrollment network, we observe the small-world property in which the average path length among reachable student pairs is short and nearly all students are connected to each other in the main component of the network through multiple independent paths. We also observe high connectivity between different majors. Then, we apply various hybrid instructional mode strategies to this co-enrollment network and use network connectivity and in-person instruction metrics to compare these strategies from health and academic perspectives, by their impacts on various groups of students, and based on the trade-off between reducing network connectivity and delivering in-person instruction. ResultsAlthough these strategies result in reduced network connectivity, they do not remove the small-world property. When comparing the strategies in terms of reducing network connectivity, we find three different strategy types to be the most favorable. Even under these strategies, the percentage of students with in-person courses that could be exposed rises quickly with initial infection rates. When comparing the strategies in terms of delivering in-person instruction, the most favorable strategies select a fixed percentage of courses for each subject to be delivered remotely. We then consider the impacts of these strategies on various groups of students to evaluate if there may be disparate impacts across these groups. In general, we find that strategies with more remote courses result in less disparate impacts on network connectivity and in-person instruction across these groups. In addition, we generally see less in-person instruction for lower-level students (i.e., first-year students and sophomores) compared to upper-level students. Regarding the trade-off between reducing network connectivity and delivering in-person instruction, the only strategy that is dominated under all scenarios in this study is the 1000s and 4000s only strategy, which keeps only the 1000- and 4000-level (i.e., first-year and senior level, respectively) courses in-person. The reason for this is that even though the university offers less in-person instruction due to this strategy's large quantity of remote courses, this strategy results in more connected networks because the 1000- and 4000-level courses tend to be large in size, the 1000-level courses are highly central, and the first-year students and seniors have high connectivity. ImportanceBy quantitatively comparing network connectivity and in-person instruction for these various strategies, campus administrators can weigh the physical health, academic performance, and mental health of students, along with the financial well-being of their academic institutions when responding to infectious disease outbreaks.

Mode-Insensitive Wired Communication Method Based on MIMO Using Multimode Transmission Lines

This letter proposes a novel mode-insensitive wired communication method based on multiple input multiple output (MIMO) using multimode transmission lines. First, multiple eigenmodes of the transmission line are equivalent to multiple independent paths, exempting the consideration of modes purity (the share of all power that the mode accounts for) in excitation and transmission and thus simpler structure designs. Second, the multimode transmission line, being a waveguide or any guided wave structure, can provide a time-invariant channel. As a result, low overhead is required. Benefiting from the features, the proposed method can effectively improve communication capacity and reduce mode sensitivity. To prove the concept, simulations are conducted with the dielectric-filled waveguide adopted as the multimode transmission line.

Transcriptome-wide association study coupled with eQTL analysis reveals the genetic connection between gene expression and flowering time in Arabidopsis.

Genome-wide association study (GWAS) has improved our understanding of complex traits, but challenges exist in distinguishing causation versus association caused by linkage disequilibrium. Instead, transcriptome-wide association studies (TWAS) detect direct associations between expression levels and phenotypic variations, providing an opportunity to better prioritize candidate genes. To assess the feasibility of TWAS, we investigated the association between transcriptomes, genomes, and various traits in Arabidopsis, including flowering time. The associated genes formerly known to regulate growth allometry or metabolite production were first identified by TWAS. Next, for flowering time, six TWAS-newly identified genes were functionally validated. Analysis of the expression quantitative trait locus (eQTL) further revealed a trans-regulatory hotspot affecting the expression of several TWAS-identified genes. The hotspot covers the FRIGIDA (FRI) gene body, which possesses multiple haplotypes differentially affecting the expression of downstream genes, such as FLOWERING LOCUS C (FLC) and SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1). We also revealed multiple independent paths towards the loss of function of FRI in natural accessions. Altogether, this study demonstrates the potential of combining TWAS with eQTL analysis to identify important regulatory modules of FRI-FLC-SOC1 for quantitative traits in natural populations.

The Butterfly Effect: How Academics and Practitioners’ Micro-Practices Shape Turning Points in Response to Paradox

One of the most frequent means of creating relationships between management research and practice is through collaboration. However, odds are that such arrangements will be filled with tensions that characterize the academic–practitioner gap. Against this background, our study investigates how academics and practitioners’ micro-practices shape turning points in response to paradox in six collaborations. We assume a process ontology and employ a comparative case study approach to explore the evolving relationships between academics and practitioners in collaborative settings through 34 semi-structured interviews conducted during the second year of joint work in a social program. Our findings demonstrate how small and seemingly mundane acts at the micro level can affect turning points during the collaborative process by shaping their trajectories. With their day-to-day actions, our informants created significant change in organizational settings characterized by paradox. We found that multiple independent paths to generative responses to paradox exist. However, cultures of impactful collaboration do not evolve quickly and are not attributable to single discrete events. We propose a process model of turning points in academic–practitioner collaborations and offer implications for both theory and practice.

1020 – HEMATOPOIETIC STEM CELL CLONAL TRACKING BY WHOLE GENOME SEQUENCING IDENTIFIES MULTIPLE INDEPENDENT SOMATIC GENETIC RESCUE MECHANISMS IN BONE MARROW FAILURE DISORDERS.

The congenital bone marrow failure syndrome Shwachman-Diamond Syndrome (SDS) is characterized by defective ribosome biogenesis, with a significant risk of developing a severe myelodysplastic syndrome or leukemia. The most common causal germ line mutations are in the SBDS gene. It remains unclear how the germline ribosomal dysfunction/stress affects individual hematopoietic stem cells and contributes to the aberrant population dynamics that drive specific clonal expansions and eventual leukemic transformation. To address this, we adopted a clonal tracking approach using whole genome sequencing of single hematopoietic stem and progenitor cell (HSPC)-derived colonies followed by phylogenetic tree construction to assess clonal relatedness in 9 SDS patients. The mean mutation burden in SDS HSPCs increased linearly with age and the majority of mutations were C >T variants, consistent with mutational signatures in ageing. Single nucleotide variants in annotated genes across patients were found in known drivers <i>TP53, EIF6</i> and other ribosomal proteins: all of which were mutually exclusive in different HSPC clones. Distinct mutations in the same genes were found within the same patients, demonstrating that individual clones must acquire independent genetic rescue mechanisms. Whole genome sequencing permitted us to uncover a high degree of intra-patient heterogeneity, charting multiple independent paths that individual cells can take to combat defective ribosome deficiency caused by SBDS loss. This study sets the stage for functional analysis of potential leukemia driver mutations and longitudinal tracking of clonal dynamics throughout disease progression and re-enforces the value of using whole genome sequencing to track individual stem cell clones in disease.

HyP-DESPOT: A hybrid parallel algorithm for online planning under uncertainty

Robust planning under uncertainty is critical for robots in uncertain, dynamic environments, but incurs high computational cost. State-of-the-art online search algorithms, such as DESPOT, have vastly improved the computational efficiency of planning under uncertainty and made it a valuable tool for robotics in practice. This work takes one step further by leveraging both CPU and GPU parallelization in order to achieve real-time online planning performance for complex tasks with large state, action, and observation spaces. Specifically, Hybrid Parallel DESPOT (HyP-DESPOT) is a massively parallel online planning algorithm that integrates CPU and GPU parallelism in a multi-level scheme. It performs parallel DESPOT tree search by simultaneously traversing multiple independent paths using multi-core CPUs; it performs parallel Monte Carlo simulations at the leaf nodes of the search tree using GPUs. HyP-DESPOT provably converges in finite time under moderate conditions and guarantees near-optimality of the solution. Experimental results show that HyP-DESPOT speeds up online planning by up to a factor of several hundred in several challenging robotic tasks in simulation, compared with the original DESPOT algorithm. It also exhibits real-time performance on a robot vehicle navigating among many pedestrians.

The Small-World Network of College Classes: Implications for Epidemic Spread on a University Campus

To slow the spread of the novel coronavirus, many universities shifted to online instruction and now face the question of whether and how to resume in-person instruction. This article uses transcript data from a medium-sized American university to describe three enrollment networks that connect students through classes and in the process create social conditions for the spread of infectious disease: a university-wide network, an undergraduate-only network, and a liberal arts college network. All three networks are 'small worlds' characterized by high clustering, short average path lengths, and multiple independent paths connecting students. Students from different majors cluster together, but gateway courses and distributional requirements create cross-major integration. Connectivity declines when large courses of 100 students or more are removed from the network, as might be the case if some courses are taught online, but moderately sized courses must also be removed before less than half of student-pairs are connected in three steps and less than two-thirds in four steps. In all simulations, most students are connected through multiple independent paths. Hybrid models of instruction can reduce but not eliminate the potential for epidemic spread through the small worlds of course enrollments.

AeroMRP: A Multipath Reliable Transport Protocol for Aeronautical Ad Hoc Networks

In order to support Internet of Things, an aeronautical ad hoc network (AANET) has been proposed to solve the problem of air information isolated island. AANET is a special type of heterogeneous ad hoc network between commercial aircraft to share data and in-flight Internet access. Today’s civil airliners are typically equipped with multiple advanced network interfaces, which can form multiple independent communication paths between the source and the destination nodes in AANETs. Thus, users expect to utilize multiple networking interfaces of airliners simultaneously to support data transfer services. In this paper, we present a multipath reliable transport protocol for AANETs, called AeroMRP, which exploits path diversity provided by heterogeneous aeronautical networks. AeroMRP takes advantage of raptor codes to restore from packet loss in the aeronautical network environments while reducing the impact of the head-of-line blocking issue in the networks with multiple paths. A redundancy rate selection algorithm is adopted to determine the redundancy on the fly by considering the characteristics of the target applications and the time-varying aeronautical networks. Moreover, AeroMRP implements feedback-based packet scheduling considering not only aeronautical network status but also the acknowledgment scheme in congestion control for better use of different paths. We evaluate the performance of AeroMRP by ns-3 under a variety of simulation scenarios. The simulations demonstrate that AeroMRP can provide efficient and reliable data transmission services in heterogeneous multipath AANETs.

Setting an Optimization Problem of Distributing Traffic Across Multiple Independent Paths

There appeared a need for developing a communication network for urgent need, which became world demand. The given article addresses at the solution of the problem of traffic engineering, using the mechanisms of multi-path routing within the developed algorithm, the optimal number of paths was defined. The proposed algorithm includes a multicriteria optimization procedure. The values of the maximum flow and multi-path delay are used as partial criteria. If necessary, a set of particular criteria can be extended. This allows to solve the problem of ensuring the required quality of service.

SID-1 Functions in Multiple Roles To Support Parental RNAi in Caenorhabditis elegans.

Systemic RNA interference (RNAi) in Caenorhbaditis elegans requires sid-1, sid-3, and sid-5 Injected, expressed, or ingested double-stranded RNA (dsRNA) is transported between cells, enabling RNAi in most tissues, including the germline and progeny (parental RNAi). A recent report claims that parental RNAi also requires the yolk receptor rme-2 Here, we characterize the role of the sid genes and rme-2 in parental RNAi. We identify multiple independent paths for maternal dsRNA to reach embryos and initiate RNAi. We showed previously that maternal and embryonic sid-1 contribute independently to parental RNAi. Here we demonstrate a role for embryonic sid-5, but not sid-2 or sid-3 in parental RNAi. We also find that maternal rme-2 contributes to but is not required for parental RNAi. We determine that parental RNAi by feeding occurs nearly exclusively in adults. We also introduce 5-ethynyluridine to densely internally label dsRNA, avoiding complications associated with other labeling strategies such as inhibition of normal dsRNA trafficking and separation of label and RNA. Labeling shows that yolk and dsRNA do not colocalize following endocytosis, suggesting independent uptake, and, furthermore, dsRNA appears to rapidly progress through the RAB-7 endocytosis pathway independently of sid-1 activity. Our results support the premise that although sid-1 functions in multiple roles, it alone is central and absolutely required for inheritance of silencing RNAs.

Project Atlantis

This paper explores the reach and use of subsea engineering. Subsea engineering presents many new challenges and opportunities for engineers from any discipline. The fundamental engineering challenges facing today’s ultra-deepwater oil and gas production reside under a new engineering discipline, the subsea engineer. Designing subsea systems for 30-year-long controllability, safety, maintenance, and real-time optimization are critical issues and present an open-ended problem. Safety is absolutely a primary focus on any subsea production system design. There must be multiple independent safety paths in place to isolate a producing well. The most common subsea safety system is located within the well. Pioneering work performed at the university of Houston provided mathematical relationships to predict the flow regime given gas and liquid velocities, including dispersed bubble flow, elongated bubble flow, slug flow, stratified flow, etc. There is an unexplored coupling between the transient multiphase flow and the heat transfer. The field of modeling multiphase transient transport is important to the subsea architecture design and real-time optimization of subsea production.

Estimating the Effects of Multipath Selection on Concurrent Multipath Transfer

Multi-mode device which combines multiple access technologies into a device will offer more cost-effective solution than a sole access implementation. Its concurrent multipath transfer (CMT) technology can transmit media flows over multiple end-to-end paths simultaneously, which is essential to select at least two paths from all available paths. At real networks, different paths are likely to overlap each other and even share bottleneck, which can weaken the path diversity gained through CMT. Spurred by this observation, it is necessary to select multiple independent paths as much as possible to avoid underlying shared bottleneck between topologically joint paths. Recent research in this context has shown that different paths with shared bottleneck can weaken the path diversity gained through CMT. In our earlier work, a grouping-based multipath selection (GMS) mechanism is introduced and developed. However, how to estimating the selection is still to be resolved. In this paper, we firstly introduce a Selection Correctness Index (SCI) to evaluate the correctness of selection results in actual CMT experiment. Therefore, this metric is helpful to discuss and validate the accuracy of the output paths. From extensive experiments with a realized prototype, the proposed scheme provides better evaluation tool and criterion in various network conditions.

Moving beyond Stylized Economic Network Models: The Hybrid World of the Indian Firm Ownership Network.

A central theme of economic sociology has been to highlight the complexity and diversity of real world markets, but many network models of economic social structure ignore this feature and rely instead on stylized one-dimensional characterizations. Here, the authors return to the basic insight of structural diversity in economic sociology. Using the Indian interorganizational ownership network as their case, they discover a composite-or "hybrid"-model of economic networks that combines elements of prior stylized models. The network contains a disconnected periphery conforming closely to a "transactional" model; a semiperiphery characterized by small, dense clusters with sporadic links, as predicted in "small-world" models; and finally a nested core composed of clusters connected via multiple independent paths. The authors then show how a firm's position within the mesolevel structure is associated with demographic features such as age and industry and differences in the extent to which firms engage in multiplex and high-value exchanges.

Cooperative schemes for path establishment in mobile ad-hoc networks under shadow-fading

The performance of routing protocols for multi-hop path-establishment in Mobile Ad-hoc NETworks (MANET) is examined when the individual radio links undergo shadow fading of parameterized severity. Such propagation modeling is typical of ground-level networking along with node mobility. The metrics of main interest are the probability of having a reliable multi-hop path plus the temporal statistics of such availability under a Markovian model. Such availability is an indicator for the suitability of the network to carry delay-sensitive applications (push-to-talk voice, streaming video) in uninterrupted manner. It is shown that high levels of diversity are necessary in such adverse environments, as obtained either by multiple independent paths or via concurrent cooperative transmission. Analytical and simulation comparisons of typical routing options are presented on the above metrics, plus on the required nodal engagement for supporting such diversity.

Introducing multipath selection for concurrent multipath transfer in the future internet

It is essential for the Future Internet to fully support multihoming and select most appropriate paths for Concurrent Multipath Transfer (CMT). In real complex networks, different paths are likely to overlap each other and even share bottlenecks which can weaken the path diversity gained through CMT. Spurred by this observation, it is necessary to select multiple independent paths insofar as possible. However, the path correlation lurks behind the IP/network layer topology, so we have to fall back to end-to-end probes to estimate this correlation by analyzing path delay characteristics. In this paper, we present the first step towards a new topic of correlation-aware multipath selection, with formal and systematic problem definition, modeling and solution. Based on a well-designed delay probing, a Grouping-based Multipath Selection (GMS) mechanism is developed to avoid underlying shared bottlenecks between topologically joint paths. In addition, we further propose a practical functionality framework and define a novel multihoming sublayer for the exchange of the multipath capabilities. Extensive simulations demonstrate that the GMS under different network conditions performs much better than other selection schemes, even with burst background traffic.

Path Diversity Over Packet Switched Networks: Performance Analysis and Rate Allocation

Path diversity works by setting up multiple parallel connections between the endpoints using the topological path redundancy of the network. In this paper, forward error correction (FEC) is applied across multiple independent paths to enhance the end-to-end reliability. We prove that the probability of irrecoverable loss ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</sub> ) decays exponentially with the number of paths. Furthermore, the rate allocation (RA) problem across independent paths is studied. Our objective is to find the optimal RA, i.e., the allocation that minimizes <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</sub> . The RA problem is solved for a large number of paths. Moreover, it is shown that in such asymptotically optimal RA, each path is assigned a positive rate iff its quality is above a certain threshold. Finally, using memoization technique, a heuristic suboptimal algorithm with polynomial runtime is proposed for RA over a finite number of paths. This algorithm converges to the asymptotically optimal RA when the number of paths is large. For a practical number of paths, the simulation results demonstrate the close-to-optimal performance of the proposed algorithm .

Exploiting Cooperative Advantages in Slotted ALOHA Random Access Networks

In cooperative systems, users achieve spatial diversity and multihop gains by transmitting packets over multiple independent fading paths provided by their partners. Most previous works on cooperative communications focus on the physical layer aspects such as coding, modulation, and transceiver signal processing techniques. In this work, we study the advantages of user cooperation from a MAC layer perspective and devise queueing strategies to exploit cooperative gains in random access networks. Based on the conventional slotted ALOHA protocol, we propose a simple cooperative transmission mechanism for a two-user cooperative pair. We derive the two-user stability region of the proposed system and show the improvements compared to noncooperative systems. The benefits can be attributed to both physical layer cooperation, where users with good channels may relay for those with bad channels, and MAC layer cooperation, where system parameters can be chosen to enhance cooperation and reduce competition. Then, we extend the proposed strategy to a finite-user system that consists of multiple cooperative pairs. By treating each pair as a single transmission entity, we derive inner bounds for the finite-user stability region and propose a ranking system to characterize the transmission entities' relative tendency of being stable (or unstable).

Exploiting path diversity to enhance aggregating throughput for multihomed wireless devices

Multi-homed wireless devices equipped with multiple network interfaces can transmit data over multiple access paths simultaneously for high-speed services. It is essential for data transmission to select suitable number of paths to use from all available paths. At real multihomed network, multiple paths are likely to overlap each other and share the same bottleneck, which will weaken path diversity drastically. Spurred by this observation, selection of multiple paths should consider path correlation to select multiple independent paths as much as possible. In this paper, we propose a multi-path selection scheme to avoid underlying shared bottleneck between topologically joint paths. The results demonstrate that our approach under different network conditions is more accurate than other selection schemes, even with burst background traffic.

Multiple Descriptions and Path Diversity for Voice Communications Over Wireless Mesh Networks

A key feature of wireless mesh networks is that multiple independent paths through the network are available. Multiple descriptions coding is often suggested as a source coding scheme to take advantage of this path diversity. We compare multiple description (MD) coding with path diversity (PD) against a full-rate single description (SD) coder without PD, and two simple PD methods of 1) repeating a half-rate SD coder over both paths and 2) repeating the full-rate parent SD coder over the two paths. We first present a theoretical analysis comparing the average distortion per symbol in packetized communication using the above mentioned MD and PD methods to transmit a memoryless Gaussian source over additive white Gaussian noise channels. Next, using two new MD speech coders with balanced side descriptions derived from the AMR-WB and G.729 standards, we evaluate delivered voice quality using PESQ-MOS and compare MD coding against the PD methods for random and bursty packet losses. Both the theoretical analyses and the speech coding experiments show that with packet overheads, the simple PD methods may be preferable to MD coding. A new performance measure that incorporates both quality and bit rate is shown to account for the tradeoffs more explicitly.

Multipath-Based Multicasting Strategies for Wormhole-Routed Star Graph Interconnection Networks

The star graph interconnection network has been recognized as an attractive alternative to the popular hypercube network. In this paper, we present a multipath-based multicast routing model for wormholerouted star graph networks, propose two efficient multipath routing schemes, and contrast the performance of the proposed schemes with the performance of the scheme presented in our previous work. Both of the two proposed schemes have been proven to be deadlock-free. The first scheme, simple multipath routing, uses multiple independent paths for concurrent multicasting. The second scheme, two-phase multipath routing, includes two phases: source-to-relay and relay-to-destination. For each phase, multicasting is carried out using simple multipath routing. Experimental results show that, for short and medium messages with small message startup latencies, the proposed schemes reduce multicast latency more efficiently than other schemes.