159 research outputs found
Differential diffusive instabilities of miscible two-layer stratifications in porous media and Hele-Shaw cells
No full textIn porous media, a stratification of a given solution on top of another miscible solution can be buoyantly unstable because of an unstable density stratification or because of differential diffusive effects. The former is the well known Rayleigh–Taylor (RT) mechanism wherein the interface is destabilized by the denser solution overlying a less dense one in the gravity field. Whereas the latter is of particular interest in the field of oceanography, when the upper solution is less dense than the lower one with the lower component diffusing faster than the upper one, resulting in a double diffusive (DD) instability. Similarly, a diffusive-layer convection (DLC) instability has also been observed for a stable density stratification with the upper solute diffusing faster than the lower one. Though the literature on differential diffusion effects is pretty vast, very few studies have managed to establish a connection, both qualitatively and quantitatively, between numerical simulations and experimental observations, which is the basis of the present study. We report our findings in a broad parameter range where the instability mechanism could be triggered by an unstable density stratification or due to differential diffusive effects, or even both, resulting in mixed modes
Federated file systems for clusters with remote memory communication
No full textWe present the design, prototype implementation and initial evaluation of FedFS - a novel cluster file system architecture that provides a global file space by aggregating the local file systems of the cluster nodes into a loose federation. The federated file system (FedFS) is created ad-hoc for a distributed application that runs on the cluster, and its lifetime is limited by the lifetime of the distributed application. FedFS provides location-independent global file naming, load balancing, and file migration and replication. It relies on the local file systems to perform the file I/O operations. The local file systems retain their autonomy, in the sense that their structure and content do not change to support the federated file system. Other applications may run on the local file systems without realizing that the same file system is part of one or multiple FedFS. If the distributed application permits, nodes can dynamically join or leave the federation anytime, with no modifications required to the local file system organization. FedFS is implemented as an I/O library over VIA, which supports remote memory operations. The applicability and performance of the federated file system architecture is evaluated by building a distributed NFS file server.Technical report DCS-TR-47
Federated DAFS: scalable cluster-based direct access file servers
No full textProtocols like the Direct Access File System (DAFS) leverage user-level memory-mapped communication to enable low overhead access to network-attached storage for applications. DAFS offers significant improvement in application performance using features like direct data transfer and RDMA. Our goal is to build high performance network file servers using DAFS. The benefits of the DAFS protocol can be extended to cluster-based servers, using low overhead user-level communication within the cluster. In this paper, we present Federated DAFS, a scalable and efficient cluster-based direct access file server. Federated DAFS combines an efficient user-space DAFS implementation with a low overhead clustering layer to present a scalable clustering solution for DAFS servers. Federated DAFS uses a portable mechanism for distribution and handling of client requests across the servers in the cluster. Federated DAFS also minimizes the intra-cluster communication by caching data blocks and by matching the file placement on the servers with the distribution of requests from the clients. Our results show that reasonable speedups(2.6 on four nodes and 4.5 on eight nodes) can be achieved using Federated DAFS on server clusters of up to eight nodes.Technical report DCS-TR-51
Effect of temperature on NH3 sensing by ZnO: Mg thin film grown by radio frequency magnetron sputtering technique
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Capacitance meters and transistor tester
No full textThe author briefly describes a capacitor meter based on a 555 timer in astable mode which directly measures capacitor values in microfarads. The author also describes a capacitance meter based on a 555 timer in monostable mode. The author also describes a transistor tester based on a 555 timer in astable mode with dual supply. Circuit diagrams for each meter are give
The Psychology Underlying Pregnancy: Investigation of Social Comparison Processes and Their Projection in Natural Language
No full textIn addition to the physiological alterations that occur relatively predictably during pregnancy, psychological transformations also occur at the same time. The baby is developing, but so are a mother's fears and imaginations about her unborn child. Such imaginations about the unborn child and parenting methods are sure to evoke a range of emotions, including happiness, excitement, curiosity, anxiety, frustration, and maybe depression. Social comparison and intense emotional expression are two of the numerous opportunities offered by social networking platforms. Social comparison is a personality characteristic. Individuals who are highly social comparison-oriented make excessive social comparisons and are more affected by the outcomes. Social comparisons can be done intentionally, but more frequently they are done involuntarily. Social networking sites play a key role in the contemporary digital age in terms of personal experience sharing and constructive debate. However, research has found that the need for social comparison increases at times of stress, uncertainty, or adjustment. As a result, in unexpected and upsetting settings like pregnancy, social comparison may become more significant. The social comparison, psychology, and linguistics aspects of pregnancy had all previously been the subject of very few research, however, they had been done so independently. The objective of this research is to jointly comprehend the social, psychological, and linguistic aspects of pregnancy. In this research, a survey that was published on Reddit communities collected responses based on three questionnaires (Iowa-Netherlands Comparison Orientation Measure, Gratitude During Pregnancy Scale, and Tilburg Pregnancy Distress Scale), as well as a textual question on using social media while being pregnant. A correlation and linear regression analysis were used in this study to investigate the association between the three sub-scales and the selected LIWC (Linguistic Inquiry and Word Count) categories. In conclusion, considering the general inadequacy of information in the domain of pregnancy care and the imminent transition to digital care, the findings of this study could make a significant contribution to social and psychological research.Management of Technology (MoT
Appropriation of water: Exploring the impacts of global supply chain of cotton virtual water in Central India (Marathwada)
No full textThe phenomenon of ‘globalisation of water’ (A. Y. Hoekstra & Hung, 2005) talks about the importance of recognizing the adverse effects on local freshwater resources from a global perspective. The trade of water through the export and import of products results in ‘virtual water flows’ (Arjen Y. Hoekstra & Mekonnen, 2012), which leads to many counties externalizing their water footprint with serious consequences leading to water stress, scarcity and pollution elsewhere. Lenzen et, al. talks about the trade of scarce water through water-intensive crops and their consequences on water stress in exporting regions (Lenzen et al., 2013). This leads to a vicious circle of water stress which has several impacts on the environment and society. However, the extent of these impacts is not fully researched. This thesis hopes to investigate the spatial, socio-economic, and environmental impacts that are associated with the virtual water trade of cotton from India, and how they can be improved to obtain a sustainable and balanced water footprint in water-scarce regions.Architecture, Urbanism and Building Sciences | Urbanis
Fabrication of bifacial poly-Si solar cells with copper-plating metallization
No full textCarrier-selective passivating contacts (CSPC) have been proven to be effective in suppressing recombination losses at metal-silicon interface in high-efficiency crystalline silicon solar cells. The poly-Si-based CSPCs consisting of SiOX/poly-Si stacks are used in this thesis due to their compatibility with high thermal budgets. CSPCs with thin poly-Si layers are preferred since thicker poly-Si layers induce significant parasitic absorption at device level. The bifacial solar cell design could provide a higher energy yield than monofacial solar cells and largely reduce the consumption of metals such as silver, indium due to the contribution of reflected light. The objective of this thesis is to fabricate double-side textured copper (Cu)-plated bifacial poly-Si solar cells. It is achieved by developing thin poly-Si contacts, addressing the TCO sputtering-induced passivation damage, and optimizing the Cu-plating processes.Firstly, the passivation of the poly-Si symmetric samples and solar cells was optimized. 16 nm-thick n+ poly-Si and 16 nm-thick p+ poly-Si symmetric samples with intrinsic layer grown through PECVD demonstrated good passivation quality indicated by their iVOC of 713 mV and 665 mV respectively. To further improve the passivation quality of the p+ poly-Si, the layer thickness and the doping gas flow ratios were varied. Best passivation was achieved for a solar cell precursor with 42 nm-thick p+ poly-Si layers. The optimum doping gas flow ratio was found to be SiH4-B2H6=20/15 sccm. The highest iVOC achieved was 692 mV. TCO sputtering caused a severe passivation drop of ~90 mV in solar cell precursors. Post-deposition annealing treatments and 2-step TCO sputtering techniques were used to reduce such a passivation loss. However, it was challenging to reproducibly obtain solar cell precursors with good passivation quality before metallization step. The initial solar cell with double side TCO use showed cell parameters were: VOC 398 mV, FF 56.22%, JSC 30.55 mA/cm2 and η 6.85% (from n-side illumination).To maintain a good passivation quality of the solar cell precursor, an 8 nm-thick MoOX buffer layer was introduced on top of the p+ poly-Si layer. This approach effectively reduced the passivation drop from 91 mV to 12 mV. However, the MoOX layer was observed to strongly react with the solution which was used for silver seed layer removal in Cu-plating metallization procedure. Different approaches were tested to obtain a well-plated p+ poly-Si side. As for the n+ poly-Si side, a TCO-free design was deployed. To ensure a good adhesion of the plated Cu fingers, a Ti/Ag (8 nm/192 nm) seed layer was employed before Cu-plating step. Moreover, an additional SiOX layer, which acts as the anti-reflection coating, was deposited on the n-side of a complete solar cell. With these adjustments, the solar cell performance was improved to: VOC 610 mV, FF 64.98%, JSC 36.95 mA/cm2 and η 14.64% (from n-side illumination). Furthermore, with reducing the Ti thickness in the metal seed layer to 2 nm. The solar cell performance was further improved to VOC 611 mV, FF 69.58%, JSC 36.16 mA/cm2 and η 15.38% (from n-side illumination). The bifaciality factor is 89%. Electrical Engineering | Sustainable Energy Technolog
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