Toward a Numerical Error Bar in CFD

Abstract. The size-normalised weight (SNW) of planktic foraminifera, a measure of test wall thickness and density, is potentially a valuable palaeo-proxy for marine carbon chemistry. As increasing attention is given to developing this proxy it is important that methods are comparable between studies. Here, we compare SNW data generated using two different methods to account for variability in test size, namely (i) the narrow (50 μm range) sieve fraction method and (ii) the individually measured test size method. Using specimens from the 200–250 μm sieve fraction range collected in multinet samples from the North Atlantic, we find that sieving does not constrain size sufficiently well to isolate changes in weight driven by variations in test wall thickness and density from those driven by size. We estimate that the SNW data produced as part of this study are associated with an uncertainty, or error bar, of about ±11%. Errors associated with the narrow sieve fraction method may be reduced by decreasing the size of the sieve window, by using larger tests and by increasing the number tests employed. In situations where numerous large tests are unavailable, however, substantial errors associated with this sieve method remain unavoidable. In such circumstances the individually measured test size method provides a better means for estimating SNW because, as our results show, this method isolates changes in weight driven by variations in test wall thickness and density from those driven by size.

Download Full-text

STRUCTURAL AND ELECTRONIC PROPERTIES OF TRANSITION METAL DI-CHALCOGENIDES (MX2) M=(Mo, W) AND X=(S, Se) IN BULK STATE: A FIRST-PRINCIPLES STUDY

Journal of Institute of Science and Technology ◽

10.3126/jist.v22i1.17738 ◽

2017 ◽

Vol 22 (1) ◽

pp. 41-50

Author(s):

Ram Prasad Sedhain ◽

Gopi Chandra Kaphle

Keyword(s):

Transition Metal ◽

Electronic Properties ◽

Density Functional ◽

Tight Binding ◽

Calculated Data ◽

Modern Technology ◽

Fundamental Aspect ◽

Bulk State ◽

Error Bar ◽

Structural And Electronic Properties

Transition metal di-chalcogenides (MX2) M=(Mo, W) and X=(S, Se) in bulk state are of great interest due to their diverse applications in the field of modern technology as well as to understand the fundamental aspect of Physics. We performed structural and electronic properties of selected systems using density functional theory implemented in Tight Binding Linear Muffin- tin Orbital (TBLMTO) approach with subsequent refinement. The structural optimization is performed through energy minimization process and lattice parameters of optimized structures for MoS2, MoSe2, WS2 and WSe2 are found to be 3.20Å, 3.34Å, 3.27Å and 3.34Å respectively, which are within the error bar less than 5% with experimental values. The band gaps for all TMDCs are found to be of indirect types with semiconducting behaviours. The values of band gap of MoS2, MoSe2, WS2 and WSe2 in bulk state are found to be 1.16eV, 108eV, 1.50eV and 1.29eV respectively which are comparable with experimental and previously calculated data. Due to the symmetric nature of up spin and down spin channels of Density of States (DOS) all the systems selected are found to be non magnetic. However it fully supports the results obtained from band structure calculations. The potential and charge distributions plots support the results. The charge density plots reveals the covalent nature of bond in (100) plane. However (110) plane shows mixed types of bonding.Journal of Institute of Science and TechnologyVolume 22, Issue 1, July 2017, page: 41-50

Download Full-text