50175 research outputs found
Sort by
Acid digestion of carbonates using break seal method for clumped isotope analysis
No full textRationale Acid digestion of carbonates to release CO2 is a crucial and sensitive step in sample preparation for clumped isotope analysis. In addition to data reduction and instrumental artefacts, many other uncertainties in the clumped isotope analysis of carbonates arise from the method used for the preparation of CO2. We describe here an in-house-designed reaction vessel that circumvents degassing and contamination problems commonly associated with the McCrea-type digestion protocols. Methods We designed a leak-free break seal reaction vessel (made of Pyrex (TM)) suitable for prolonged acid digestion at 25 degrees C. Using this new vessel, several carbonate reference materials widely used in the clumped isotope community and other in-house laboratory standards were acid-digested and analysed for their delta C-13, delta O-18 and Delta(47) values with a dual inlet MAT 253 isotope ratio mass spectrometer following standard gas chromatography purification and data evaluation protocols. Results Long-term reproducibility in Delta(47) determination was established using international references and in-house working standards as follows (mean and SE): Carrara-1 (0.395 +/- 0.002 parts per thousand, n = 43), Carrara-2 (0.441 +/- 0.003 parts per thousand, n = 22), OMC (0.587 +/- 0.004 parts per thousand, n = 16), NBS 19 (0.393 +/- 0.005 parts per thousand, n = 10), NBS 18 (0.473 +/- 0.003 parts per thousand, n = 5), ETH 1 (0.271 +/- 0.005 parts per thousand, n = 7), ETH 3 (0.698 +/- 0.005 parts per thousand, n = 3), MZ (0.715 +/- 0.002 parts per thousand, n = 3) and several others. Conclusions A new method using a break seal tube was found to be efficient for the clumped isotope analysis of carbonates that require longer reaction time at 25 degrees C. This method yields good precision in Delta(47) analysis and was found to be suitable for acid digestions at any desired temperature
Shape memory effect, temperature distribution and mechanical properties of friction stir welded nitinol
No full textWelding of shape memory alloys without deterioration of shape memory effect could vastly extend their applications. To retain shape memory behavior, a solid-state welding technique called friction stir welding was employed in this study. Austenitic NiTi alloy sheets of thickness 1.2 mm were joined at tool rotational speeds of 800,1000, and 1200 rpm. Due to dynamic recrystallization, the grain refinement has occurred in the weld region. The tensile testing has shown superelastic plateau for the welds at 800 and 1000 rpm. The phase transformation behavior of different weld regions was studied in detail using differential scanning calorimeter. A marginal drift in transformation temperatures was observed in the weld. To understand the drift in phase transformation temperatures, finite element analysis was carried out with focus on temperature distribution during welding. Finally, time-dependent shape recovery of a FSW welded joint was studied and it was found that the original position was completely recovered after 27 s at a temperature of 65 degrees C. (C) 2018 Elsevier B.V. All rights reserved
Search for anomalous alignments of structures in Planck data using Minkowski Tensors
No full textMinkowski Tensors are tensorial generalizations of the scalar Minkowski Functionals. Due to their tensorial nature they contain additional morphological information of structures, in particular about shape and alignment, in comparison to the scalar Minkowski functionals. They have recently been used 39] to study the statistical isotropy of temperature and E mode data from the Planck satellite. The calculation in 39] relied on stereographic projection of the fields to extract the shape and alignment information. In this work, we calculate Minkowski Tensors directly on the sphere and compute the net alignment in the data, based on a recent work that extends the definition of Minkowski Tensors to random fields on curved spaces. This method circumvents numerical errors that can be introduced by the stereographic projection. We compare the resulting net alignment parameter values obtained from the frequency coadded CMB temperature data cleaned by the SMICA pipeline, 1 to those obtained from simulations that include instrumental beam effects and residual foreground and noise. We find very good agreement between the two within approximate to 1 sigma. We further compare the alignments obtained from the beam-convolved CMB maps at individual Planck frequencies to those in the corresponding simulations. We find no significant difference between observed data and simulations across all Planck frequencies, except for the 30 GHz channel. For the 30 GHz channel we find approximate to 2 sigma difference between the data and the simulations. This mild disagreement could originate from an inaccurate estimation of the instrumental beam at 30 GHz
Influence of filament distribution on transverse tow permeability: Model predictions and experimental validation
No full textIn the past, various analytical and semi-analytical permeability models have been implemented for process modeling of flow through single scale fabric with reasonable success. However, characterization of permeability for a dual scale fabric is relatively more complex requiring specification of permeability at tow and fabric length scales. In the current work, a semi-analytical model for transverse tow permeability is developed taking into consideration the details of microstructural filament arrangements within a single tow by conducting detailed scanning electron microscopy (SEM) of a cured tow cross-section. The current analysis indicates that by explicitly accounting for said local fiber volume fraction and its distribution, the transverse tow permeability predictions improve when compared to existing analytical results. In addition, a new experimental methodology for transverse tow permeability characterization has been developed and presented. The predictions considering locally varying fiber volume fractions were found to match well with the experimentally evaluated tow permeability
Three-dimensional nonlinear gravity assisted aiming point guidance
No full textA novel three dimensional aiming point guidance law is presented in this paper, which eliminates the need for gravity compensation, resulting in engagements occurring with zero acceleration commands, in turn leading to smaller overall control effort and an excellent zero effort miss behavior. The conditions necessary for collision in the presence of gravity are derived using model-based prediction and computationally efficient shooting method. This is followed by employing differential-geometric guidance philosophy for achieving collision with the target. The efficacy of the proposed guidance law is then verified using simulation studies for terminal phase ballistic missile interception, and is compared with proportional navigation, aiming point guidance and compensated-weave guidance. Results indicate that the proposed guidance law ensured collision with desired level of accuracy and outperformed the aforementioned guidance laws used for comparison, in terms of miss distance, zero effort miss behavior and control effort. (C) 2018 Elsevier Masson SAS. All rights reserved
Design approach for drainage layer in pavement subsurface drainage system considering unsaturated characteristics
No full textProviding adequate subsurface drainage feature in a pavement system to remove the infiltrated moisture in a minimum time is an important design consideration, which prevents the premature failure of the pavement system, and hence helps in achieving a significantly lower life-cycle cost. Various surface drainage measures are taken to minimize the ingress of moisture into the pavement gradually lose their efficiency with the aging of the pavement. The use of an appropriate open-graded aggregate course as a drainage layer in the pavement is the best way to minimize the time for which the pavement materials are exposed to saturated conditions. The current drainage guidelines have been developed on the basis of moisture flow under saturated condition. A better understanding and estimation of moisture movement in a drainage layer can only be achieved by using seepage analysis that adopts the principles of saturated as well as unsaturated flow conditions. State-of-art of mathematical tools such as finite difference and FEA methods permits a rigorous solution of Richard's equation for saturated and unsaturated moisture flow in a porous medium, the only major drawback is the need for rigorous modeling and computational tool for the simulations and the design of the drainage layer. This paper focuses on the development of an analytical model for estimating the time to drain considering the unsaturated characteristics of pavement base material and calibration of the developed model based on a mechanistic approach which is relatively inexpensive. The applicability of the approach is explained by using the four-standard aggregate gradations recommended by AASHTO for the drainage layer, as well as a dense graded aggregate layer, and the results are compared with those from the FHWA approach and finite element analysis. The study shows that the developed model performs as good as the finite element analysis, which requires rigorous numerical modeling, predicts drainage times that are significantly different from those obtained from the FHWA analysis, and that it is sensitive to key significant design parameters. Hence, the proposed model is recommended for regular use for the design of the drainage layer and for a parametric study of the complete drainage process
An Online Power System Stability Monitoring System Using Convolutional Neural Networks
No full textA continuous Online Monitoring System (OMS) for power system stability based on Phasor Measurements (PMU measurements) at all the generator buses is proposed in this paper. Unlike the state-of-the-art methods, the proposed OMS does not require information about fault clearance. This paper proposes a convolutional neural network, whose input is the heatmap representation of the measurements, for instability prediction. Through extensive simulations on standard IEEE 118-bus and IEEE 145-bus systems, the effectiveness of the proposed OMS is demonstrated under varying loading conditions, fault scenarios, topology changes, and generator parameter variations. Two different methods are also proposed to identify the set of critical generators that are most impacted in the unstable cases
Hydrogen bond-linked pathways of peptide units and polar groups of amino acid residues suitable for electron transfer in cytochrome c proteins
No full textElectron transfer occurs through heme-Fe across the cytochrome c protein. The current models of long range electron transfer pathways in proteins include covalent sigma-bonds, van der Waals forces, and through space jump. Hydrogen-bond-linked pathways of delocalized electron units in peptide units and polar side chains of amino acid residues in proteins and internal water molecules are better suited for intramolecular atom-to-atom electron transfer in proteins. Crystal structures of cytochrome c proteins from horse (1HRC), tuna (3CYT), rice (1CCR), and yeast (3CX5) were analyzed using pymol software for `Hydrogen Bonds' marking the polar atoms within the distance of 2.6-3.3 angstrom and tracing the atom-to-atom pathways linked by hydrogen bonds. Pathways of hydrogen-bond-linked peptide units, polar side chains of the amino acid residues, and buried water molecules connect heme-Fe through axially coordinated Met80-S and His18-N have been traced in cytochrome c proteins obtained from horse, tuna, rice and yeast with an identical hydrogen-bonded sequence around the heme-Fe: Asn-N-water-O-Tyr-O-Met-S-heme-Fe-His (HN-C=N)-Pro-Asn-Pro-Gly (peptide unit, HN-C=O)-water-O. More than half of the amino acid residues in these pathways are among the conserved list and delocalized electron units, internal water molecules and hydrogen bonds are conspicuous by their presence
Effects of superelasticity and plasticity on the spherical indentation response of shape memory alloys: a finite element analysis
No full textInstrumented indentation is particularly useful for characterizing the mechanical behavior of shape memory alloys (SMAs), which are often used as `small volume' elements such as thin films or wires. Deciphering the measured indentation response, which is as such difficult for elastic-plastic materials due to the inhomogeneous state of stress underneath the indenter, becomes more complex for SMAs owing to the simultaneous occurrence of stress induced martensite transformation (SIMT) in conjunction with plastic deformation. In this work, a constitutive model that is able to capture the coupled nature of phase transformation and plastic deformation is employed to study, through finite element analyses, the spherical indentation behavior of SMAs at a temperature above the austenite finish temperature, A(f). It is found that the concurrent development of plastic yielding and SIMT leads to slower evolution of martensite volume and a smaller transformed zone size. Also, in the absence of plastic yielding, the proportion of depth recovered by superelasticity is fairly constant. It is also observed, from a systematic comparison with a conventional elastic-plastic material, that the presence of the transformed zone significantly alters the stress distribution beneath the indenter
Performance Analysis of Full-Duplex Decode-and-Forward Relaying With Media-Based Modulation
No full textIn this paper, we introduce and analyze the performance of a two-hop three-node full-duplex (FD) relay network, where the source and relay nodes transmit using media-based modulation (MBM). An MBM is a promising new modulation scheme that conveys information bits by digitally controlling the parasitic elements (knownas radio frequencymirrors) placed near the transmit antenna. The relay uses decode-and-forward relaying protocol. We refer to this system as FD relaying system with MBM (FDR-MBM). We first derive an upper bound on the end-to-end average bit error probability of FDR-MBM with maximum-likelihood detection at the relay and destination nodes. The bound is increasingly tight with increasing signal-to-noise ratios. Numerical results show that, for the same spectral efficiency, FDR-MBM can perform better than FD relaying using conventional modulation schemes. We then derive the diversity order achieved in FDR-MBM. The analytically predicted diversity orders are validated through simulations. Finally, we derive lower and upper bounds on the achievable rate in FDR-MBM