Thermoelectric waste heat recovery in automobile exhaust systems: Topological studies and performance analysis

The demand for improved fuel efficiency in automobiles has placed an emphasis on exhaust system waste heat recovery as a 40% of the fuel\u27s chemical energy is lost to the environment in modern spark ignition engines. To advance fuel economy, researchers are currently evaluating technologies to exploit exhaust stream thermal power using thermoelectric generators (TEGs) that operate using the Seebeck effect. Thermoelectric generators have the potential to recover some of this waste energy in the exhaust stream potentially improving fuel economy by as much as 5%. ^ Attempts are made to maximize the electrical power generation by optimizing the thermoelectric generator geometry for a prescribed volume. A plate-fin heat exchanger configuration is assumed and consideration is given to pressure drops associated with the fins placed in the exhaust flow path; and the cross-sectional changes across thermoelectric generator inlet-exit ports. Multiple filled skutterudites based thermoelectric modules are employed in the higher temperature regions and Bismuth Telluride modules are used at lower temperature regions of the device. Power is optimized for rectangular configurations featuring longitudinal and transverse flow through the device and for hexagonal and cylindrical topologies as well. Optimal designs that maximize power output for fixed volume and number of thermoelectric elements are obtained for all configurations. In general, the rectangular configuration with transverse flow has the best overall performance. ^ System modeling of thermoelectric (TE) components is performed to maximize thermoelectric power generation. One-dimensional heat flux and temperature variations across thermoelectric legs have been solved using iterative numerical approach as a tool to optimize both TE module and TEG designs. Design trades are explored assuming the use of skutterudite as thermoelectric material that has potential for application to automotive applications where exhaust gas and heat exchanger temperatures typically vary from 100°C to 600°C. Dependencies of parameters such as leg geometry, fill fractions, electric current, thermal boundary conditions, etc., on leg efficiency, thermal fluxes and electric power generation have been studied in detail. Optimal leg geometries are computed for various automotive exhaust conditions. ^ Axial conduction in the wall liner is further modeled numerically and its impact on temperature distribution in gas stream, wall liner, and temperature difference across thermoelectric junctions are presented. The developed model is simulated to establish TEG output sensitivity to liner materials and thicknesses for both zero and non-zero axial conduction cases. Further, the axial conduction sensitivity to inlet conditions is considered and the effect on TEG output statistics are presented

A single-server Markovian queuing system with discouraged arrivals and retention of reneged customers

Customer impatience has a very negative impact on the queuing system under investigation. If we talk from business point of view, the firms lose their potential customers due to customer impatience, which affects their business as a whole. If the firms employ certain customer retention strategies, then there are chances that a certain fraction of impatient customers can be retained in the queuing system. A reneged customer may be convinced to stay in the queuing system for his further service with some probability, say q and he may abandon the queue without receiving the service with a probability p(=1− q). A finite waiting space Markovian single-server queuing model with discouraged arrivals, reneging and retention of reneged customers is studied. The steady state solution of the model is derived iteratively. The measures of effectiveness of the queuing model are also obtained. Some important queuing models are derived as special cases of this model

Effects of Non-Motorized Vehicles on Traffic Flow Parameters

India, being a developing nation has a heterogeneous traffic. The traffic consists of vehicles which can broadly be divided into motorized vehicles and non-motorized vehicles.The motorized vehicles include all cars, motorcycles, trucks, etc. whereas the non-motorized vehicles include cycles, cycle-rickshaws, rickshaw-van, hand pulled or cycle driven trolleys,hand pulled rickshaws, etc.. There has been a significant impact of non-motorized transport on intersection capacity and roadway segments between intersections. But, as per study that had previously been done the proportion of bicycle and other non-motorized vehicle is veryless as compared to that of motorized vehicles. However the presence of non-motorized vehicles highly affects the traffic parameters such as flow, speed and density. Hence for urban heterogeneous Indian traffic the consideration of the effect of non-motorized vehicles is highly essential for design of traffic stream. The thesis has been divided into various parts like data collection, data extraction, data analysis, field observations and statistical analysis using hypothesis testing. The experimental analysis involved in study of fundamental variables and studying the effects of non-motorized vehicles on parameters like flow, speed, density, lateral occupancy and queue length. The effect of %age of non-motorized vehicles is also discussed. The distance from road edge and the type of shoulder or kerb in the section is also considered for field observation. The statistical analysis part was done using hypothesis testing which helped us understanding the comparison between the variables like flow of different years and hence the statistical relation was penned down. The results of the study involved in showing the characteristics and effects of non-motorized vehicles on Indian heterogeneous traffic which was done as per the above procedure. As discussed the non-motorized vehicles have a very significant impact on the traffic parameters

Identification of host-associated genomic determinants in Escherichia coli using Genome-wide Association Study (GWAS)

E. coli is a commensal bacterium, as well as a versatile pathogen. Its ability to colonize distinct environmental niches provides an evolutionary advantage to acquire and disseminate antibiotic resistance traits within or across the different populations. In this study, we analyzed a diverse collection of 1,198 strains of E. coli isolated from different hosts, and a microbial GWAS was applied to determine the host-associated genomic determinants leading to host-adaptation. The E. coli were randomly distributed over the whole phylogeny, but small host-associated clusters (enriched with specific STs) were observed based on the core-genome phylogeny and clustering of strains based on their accessory genes. GWAS identified a novel nan gene cluster associated with E. coli strains isolated from humans. These nan genes were predicted to be responsible for the metabolism of sialic acid. It is located on the chromosome as inferred from the RefSeq complete genome collections of E. coli and was predominantly found in ST131 and ST73 ExPEC lineages; both are known multidrug-resistant and highly virulent lineages. On the other hand, a significant association of the omptin family of proteases with chicken and cattle hosts is also intriguing. The genes encoding for ompP and arlC (ompTp) proteases were associated with cattle and chicken hosts, respectively, instead of chromosomally encoded ompT protease. Preference for omptin proteases seems to correlate with the fact that both cattle and chicken have differences in innate immunity responses. In addition to that, GWAS also revealed the bor gene’s (involved in increased serum resistance in animal serum) association with cattle and confirms the previous association of iroBCDEN gene cluster with chicken in contrast to humans or other hosts. Here, we observed that host-associated genes belong to accessory-genome and these genes were found in few lineages of associated host. These determinants might play an essential role in adaptation and provide a fitness advantage over others in different host environments. To confirm their role in influencing a strain’s AMR carrying ability and dissemination, additional in-vitro or in-vivo studies are required.E. coli ist sowohl ein kommensales Bakterium als auch ein vielseitiges Pathogen. Seine Fähigkeit, verschiedene Umweltnischen zu kolonisieren, bietet einen evolutionären Vorteil, um Antibiotikaresistenz-Merkmale innerhalb oder zwischen den verschiedenen Populationen zu erwerben und zu verbreiten. In dieser Studie haben wir eine vielfältige Sammlung von 1.198 E. coli Stämmen untersucht, die aus verschiedenen Wirten isoliert wurden. Eine genomweite Assoziationstudie (GWAS) speziell adaptiert auf den Einsatz in mikrobiellen Genomen wurde angewendet, um die wirtsassoziierten genomischen Determinanten zu bestimmen, die zur Anpassung an die unterschiedlichen Wirte führen. Die untersuchten E. coli Stämme waren weitgehend zufällig über die gesamte Phylogenie verteilt, es wurden jedoch kleine wirtsassoziierte Cluster (angereichert mit spezifischen STs) basierend auf der Kerngenom-Phylogenie und der Clusterung von Stämmen basierend auf ihrem akzessorischen Genom gefunden. Mit Hilfe der GWAS konnte ein neues nan-Gen-Cluster identifiziert werden, das mit von Menschen isolierten E. coli Stämmen assoziiert ist. Mittels in silico Vorhersage konnte gezeigt werden, dass diese nan-Gene wahrscheinlich für den Metabolismus von Sialinsäure verantwortlich sind. Eine Analyse der RefSeq-Gesamtgenomsammlungen von E. coli ergab, dass dieses nan Operon auf dem chromosomalen Genom der E. coli Stämme lokalisiert ist und vorwiegend in den ExPEC-Linien ST131 und ST73 gefunden wird. Diese beiden Linien sind sehr häufig mit Multiresistenz und Virulenz assoziiert. Auf der anderen Seite ist die Familie der Omptin Proteasen regelmäßig mit den Wirten Huhn und Rind assoziiert. Die Gene ompP und arlC (ompTp), die für die entsprechenden Proteasen kodieren, wurden oft in Stämmen gefunden, die aus Rindern und Hühnern isoliert wurden und ersetzen hier die im Chromosom häufig nicht vorhandene durch ompT kodierte Protease. Die Präferenz für Omptin-Proteasen scheint mit der Tatsache zu korrelieren, dass sowohl Rinder als auch Hühner Unterschiede in der angeborenen Immunantwort aufweisen. Darüber hinaus zeigte die GWAS auch die Assoziation des bor-Gens (beteiligt an der erhöhten Serumresistenz in tierischem Serum) mit Rindern und bestätigt auch die frühere Assoziation des iroBCDEN-Genclusters mit Hühnern im Gegensatz zu Menschen oder anderen Wirten. Wir konnten in dieser Arbeit zeigen, dass wirtsassoziierte Gene zum akzessorischen Genom gehören und diese Gene nur in einigen Linien der wirtsassoziierten Stämme gefunden werden konnten. Diese Determinanten könnten eine wesentliche Rolle bei der Anpassung spielen und einen Fitnessvorteil gegenüber anderen Linien in verschiedenen Wirtsumgebungen bieten. In wieweit diese wirtsadaptiven genomischen Faktoren einen Einfluss auf die Fähigkeit eines Stammes haben antimikrobielle Resistenzfaktoren zu enthalten und zu deren Verbreitung beizutragen, erfordert zusätzliche in-vitro oder in-vivo Studien

INVESTIGATION OF QUASI BI-SLANT RIEMANNIAN MAPS

Riemannian maps are generalization of well-known notions of isometric immersions and Riemannian submersions. In this paper, we defne and study a natural generalization of previously defned quasi bi-slant submersions [18] in the case of Riemannian maps. We mainly investigate fundamental results on quasi bi-slant Riemannian maps from almost Hermitian manifolds to Riemannian manifolds: the integrability of distributions, geometry of foliations, the condition for such maps to be totally geodesic, etc. At the end of the article, we give proper non-trivial examples for this notion

Spatially Resolved Conductivity of Rectangular Interconnects considering Surface Scattering -- Part II: Circuit-Compatible Modeling

Interconnect conductivity modeling is a critical aspect for modern chip design. Surface scattering -- an important scattering mechanism in scaled interconnects is usually captured using Fuchs-Sondheimer (FS) model which offers the average behavior of the interconnect. However, to support the modern interconnect structures (such as tapered geometries), modeling spatial dependency of conductivity becomes important. In Part I of this work, we presented a spatially resolved FS (SRFS) model for rectangular interconnects derived from the fundamental FS approach. While the proposed SRFS model offers both spatial-dependency of conductivity and its direct relationship with the physical parameters, its complex expression is not suitable for incorporation in circuit simulations. In this part, we build upon our SRFS model to propose a circuit-compatible conductivity model for rectangular interconnects accounting for 2D surface scattering. The proposed circuit-compatible model offers spatial resolution of conductivity as well as explicit dependence on the physical parameters such as electron mean free path (${\lambda}_0$), specularity ($p$) and interconnect geometry. We validate our circuit-compatible model over a range of interconnect width/height (and ${\lambda}_0$) and p values and show a close match with the physical SRFS model proposed in Part I (with error < 0.7%). We also compare our circuit-compatible model with a previous spatially resolved analytical model (appropriately modified for a fair comparison) and show that our model captures the spatial resolution of conductivity and the dependence on physical parameters more accurately. Finally, we present a semi-analytical equation for the average conductivity based on our circuit-compatible model.Comment: 10 pages, 8 figures in process to submit to IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems (TCAD

Valley-Spin Hall Effect-based Nonvolatile Memory with Exchange-Coupling-Enabled Electrical Isolation of Read and Write Paths

Valley-spin hall (VSH) effect in monolayer WSe2 has been shown to exhibit highly beneficial features for nonvolatile memory (NVM) design. Key advantages of VSH-based magnetic random-access memory (VSH-MRAM) over spin orbit torque (SOT)-MRAM include access transistor-less compact bit-cell and low power switching of perpendicular magnetic anisotropy (PMA) magnets. Nevertheless, large device resistance in the read path (RS) due to low mobility of WSe2 and Schottky contacts deteriorates sense margin, offsetting the benefits of VSH-MRAM. To address this limitation, we propose another flavor of VSH-based MRAM that (while inheriting most of the benefits of VSH-MRAM) achieves lower RS in the read path by electrically isolating the read and write terminals. This is enabled by coupling VSH with electrically-isolated but magnetically-coupled PMA magnets via interlayer exchange-coupling. Designing the proposed devices using object oriented micro magnetic framework (OOMMF) simulation, we ensure the robustness of the exchange-coupled PMA system under process variations. To maintain a compact memory footprint, we share the read access transistor across multiple bit-cells. Compared to the existing VSH-MRAMs, our design achieves 39%-42% and 36%-46% reduction in read time and energy, respectively, along with 1.1X-1.3X larger sense margin at a comparable area. This comes at the cost of 1.7X and 2.0X increase in write time and energy, respectively. Thus, the proposed design is suitable for applications in which reads are more dominant than writes

XNOR-VSH: A Valley-Spin Hall Effect-based Compact and Energy-Efficient Synaptic Crossbar Array for Binary Neural Networks

Binary neural networks (BNNs) have shown an immense promise for resource-constrained edge artificial intelligence (AI) platforms as their binarized weights and inputs can significantly reduce the compute, storage and communication costs. Several works have explored XNOR-based BNNs using SRAMs and nonvolatile memories (NVMs). However, these designs typically need two bit-cells to encode signed weights leading to an area overhead. In this paper, we address this issue by proposing a compact and low power in-memory computing (IMC) of XNOR-based dot products featuring signed weight encoding in a single bit-cell. Our approach utilizes valley-spin Hall (VSH) effect in monolayer tungsten di-selenide to design an XNOR bit-cell (named 'XNOR-VSH') with differential storage and access-transistor-less topology. We co-optimize the proposed VSH device and a memory array to enable robust in-memory dot product computations between signed binary inputs and signed binary weights with sense margin (SM) > 1 micro-amps. Our results show that the proposed XNOR-VSH array achieves 4.8% ~ 9.0% and 37% ~ 63% lower IMC latency and energy, respectively, with 4 % ~ 64% smaller area compared to spin-transfer-torque (STT)-MRAM and spin-orbit-torque (SOT)-MRAM based XNOR-arrays