620 research outputs found
First-principles approach to rotational-vibrational frequencies and infrared intensity for H adsorbed in nanoporous materials
The absorption sites and the low-lying rotational and vibrational (RV) energy
states for H adsorbed within a metal-organic framework are calculated via
van der Waals density functional theory. The induced dipole due to bond
stretching is found to be accurately given by a first-principles driven
approximation using maximally-localized-Wannier-function analysis. The
strengths and positions of lines in the complex spectra of RV transitions are
in reasonable agreement with experiment, and in particular explain the
experimentally mysteriously missing primary line for para hydrogen
Analyzing the frequency shift of physiadsorbed CO2 in metal organic framework materials
Combining first-principles density functional theory simulations with IR and
Raman experiments, we determine the frequency shift of vibrational modes of CO2
when physiadsorbed in the iso-structural metal organic framework materials
Mg-MOF74 and Zn-MOF74. Surprisingly, we find that the resulting change in shift
is rather different for these two systems and we elucidate possible reasons. We
explicitly consider three factors responsible for the frequency shift through
physiabsorption, namely (i) the change in the molecule length, (ii) the
asymmetric distortion of the CO molecule, and (iii) the direct influence of
the metal center. The influence of each factor is evaluated separately through
different geometry considerations, providing a fundamental understanding of the
frequency shifts observed experimentally.Comment: 9 pages, 4 figure
Recovery from cesarean delivery at UIHC: a comparison to Enhanced Recovery Protocols
Enhanced Recovery After Surgery programs (ERAS) have been used by some specialties for years, and are now becoming popular for gynecologic and obstetrics surgeries. ERAS programs consist of evidence-based interventions during a patient’s hospital stay that are intended to promote early return to activities such as eating, ambulation, and voiding and to manage pain. These programs reduce the risk of complications post-operatively and shorten a patient’s hospital stay. The University of Iowa Hospitals and Clinics (UIHC) is developing an ERAS protocol for cesarean deliveries. Our goal was to determine how current practices and outcomes for cesarean deliveries at UIHC compare to established ERAS programs. We also sought to identify which patients would be appropriate candidates for an ERAS protocol at UIHC
Multiscale modeling of interaction of alane clusters on Al(111) surfaces: A reactive force field and infrared absorption spectroscopy approach
We have used reactive force field (ReaxFF) to investigate the mechanism of interaction of alanes on Al(111) surface. Our simulations show that, on the Al(111) surface, alanes oligomerize into larger alanes. In addition, from our simulations, adsorption of atomic hydrogen on Al(111) surface leads to the formation of alanes via H-induced etching of aluminum atoms from the surface. The alanes then agglomerate at the step edges forming stringlike conformations. The identification of these stringlike intermediates as a precursor to the bulk hydride phase allows us to explain the loss of resolution in surface IR experiments with increasing hydrogen coverage on single crystal Al(111) surface. This is in excellent agreement with the experimental works of Go et al. [ E. Go, K. Thuermer, and J. E. Reutt-Robey, Surf. Sci. 437, 377 (1999) ]. The mobility of alanes molecules has been studied using molecular dynamics and it is found that the migration energy barrier of Al_(2)H_6 is 2.99 kcal/mol while the prefactor is D_0 = 2.82 × 10^(−3) cm^2/s. We further investigated the interaction between an alane and an aluminum vacancy using classical molecular dynamics simulations. We found that a vacancy acts as a trap for alane, and eventually fractionates/annihilates it. These results show that ReaxFF can be used, in conjunction with ab initio methods, to study complex reactions on surfaces at both ambient and elevated temperature conditions
Theoretical and experimental analysis of H2 binding in a prototype metal organic framework material
Hydrogen adsorption by the metal organic framework (MOF) structure
Zn2(BDC)2(TED) is investigated using a combination of experimental and
theoretical methods. By use of the nonempirical van der Waals
density-functional (vdW-DF) approach, it is found that the locus of deepest H2
binding positions lies within two types of narrow channel. The energies of the
most stable binding sites, as well as the number of such binding sites, are
consistent with the values obtained from experimental adsorption isotherms and
heat of adsorption data. Calculations of the shift of the H-H stretch frequency
when adsorbed in the MOF give a value of approximately -30 cm-1 at the
strongest binding point in each of the two channels. Ambient temperature
infrared absorption spectroscopy measurements give a hydrogen peak centered at
4120 cm-1, implying a shift consistent with the theoretical calculations.Comment: 4 pages, 4 figure
‘Because it’s our culture!’ (Re)negotiating the meaning of lobola in Southern African secondary schools
Payment of bridewealth or lobola is a significant element of marriage among the Basotho of Lesotho and the Shona of Zimbabwe. However, the functions and meanings attached to the practice are constantly changing. In order to gauge the interpretations attached to lobola by young people today, this paper analyses a series of focus group discussions conducted among senior students at two rural secondary schools. It compares the interpretations attached by the students to the practice of lobola with academic interpretations (both historical and contemporary). Among young people the meanings and functions of lobola are hotly contested, but differ markedly from those set out in the academic literature. While many students see lobola as a valued part of ‘African culture’, most also view it as a financial transaction which necessarily disadvantages women. The paper then seeks to explain the young people’s interpretations by reference to discourses of ‘equal rights’ and ‘culture’ prevalent in secondary schools. Young people make use of these discourses in (re)negotiating the meaning of lobola, but the limitations of the discourses restrict the interpretations of lobola available to them
Securitization outside of the West:conceptualizing the securitization–neo-patrimonialism nexus in Africa
Film structure of epitaxial graphene oxide on SiC: Insight on the relationship between interlayer spacing, water content, and intralayer structure
Chemical oxidation of multilayer graphene grown on silicon carbide yields
films exhibiting reproducible characteristics, lateral uniformity, smoothness
over large areas, and manageable chemical complexity, thereby opening
opportunities to accelerate both fundamental understanding and technological
applications of this form of graphene oxide films. Here, we investigate the
vertical inter-layer structure of these ultra-thin oxide films. X-ray
diffraction, atomic force microscopy, and IR experiments show that the
multilayer films exhibit excellent inter-layer registry, little amount (<10%)
of intercalated water, and unexpectedly large interlayer separations of about
9.35 {\AA}. Density functional theory calculations show that the apparent
contradiction of "little water but large interlayer spacing in the graphene
oxide films" can be explained by considering a multilayer film formed by carbon
layers presenting, at the nanoscale, a non-homogenous oxidation, where
non-oxidized and highly oxidized nano-domains coexist and where a few water
molecules trapped between oxidized regions of the stacked layers are sufficient
to account for the observed large inter-layer separations. This work sheds
light on both the vertical and intra-layer structure of graphene oxide films
grown on silicon carbide, and more in general, it provides novel insight on the
relationship between inter-layer spacing, water content, and structure of
graphene/graphite oxide materials.Comment: 23 pages, 4 figure
Ab initio optical properties of Si(100)
We compute the linear optical properties of different reconstructions of the
clean and hydrogenated Si(100) surface within DFT-LDA, using norm-conserving
pseudopotentials. The equilibrium atomic geometries of the surfaces, determined
from self-consistent total energy calculations within the Car-Parrinello
scheme, strongly influence Reflectance Anisotropy Spectra (RAS), showing
differences between the p(2x2) and c(4x2)reconstructions. The Differential
Reflectivity spectrum for the c(4x2) reconstruction shows a positive peak at
energies < 1 eV, in agreement with experimental results.Comment: fig. 2 correcte
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