33 research outputs found
Direct experimental evidence for substrate adatom incorporation into a molecular overlayer
While the phenomenon of metal substrate adatom incorporation into molecular
overlayers is generally believed to occur in several systems, the experimental
evidence for this relies on the interpretation of scanning tunnelling
microscopy (STM) images, which can be ambiguous and provides no quantitative
structural information. We show that surface X- ray diffraction (SXRD) uniquely
provides unambiguous identification of these metal adatoms. We present the
results of a detailed structural study of the Au(111)-F4TCNQ system, combining
surface characterisation by STM, low energy electron diffraction and soft X-ray
photoelectron spectroscopy with quantitative experimental structural
information from normal incidence X-ray standing waves (NIXSW) and SXRD,
together with dispersion corrected density functional theory (DFT)
calculations. Excellent agreement is found between the NIXSW data and the DFT
calculations regarding the height and conformation of the adsorbed molecule,
which has a twisted geometry rather than the previously supposed inverted bowl
shape. SXRD measurements provide unequivocal evidence for the presence and
location of Au adatoms, while the DFT calculations show this reconstruction to
be strongly energetically favoured.Comment: 38 pages, 10 figure
Establishing race-, gender- and age-specific reference intervals for pyridoxal 5â-phosphate in the NHANES population to better identify adult hypophosphatasia
Introduction
Bisphosphonate treatment in adults with hypophosphatasia (HPP) may increase fracture risk. PLP is a useful marker in biochemically differentiating HPP from osteoporosis in adults. In order to identify elevated PLP, robust reference intervals are needed which are calculated in a large, representative sample population.
Methods
Complete data from 9069 individuals (ages 20â80, 50.6% female) from two years of the NHANES Survey (2007â2008 and 2009â2010) were investigated. Differences in PLP in the presence of four factors; inflammation (CRP â„5.0 mg/L), low ALP (<36 IU/L), chronic kidney disease (eGFR <60 mL/min/1.732), and daily vitamin B6 supplementation, were investigated. Race, gender and age differences in PLP were then investigated; 95% reference intervals were calculated that reflected these differences.
Results
Inflammation and chronic kidney disease were associated with lower PLP (p < .0001 and p = .0005 respectively), while low ALP and vitamin B6 supplementation were associated with higher PLP (both p < .0001). Individuals were excluded based on the presence of these factors; a reference interval population (n = 4463) was established. There were significant differences in PLP depending on race and gender (p < .0001) Increasing age was correlated with decreasing PLP (spearman's rho â0.204, p < .0001). Race- and gender-specific 95% reference intervals were calculated. In male patients, these were also calculated according to age groups: young and older adults (ages 20â49 years and â„50 years respectively).
Conclusions
In order to identify adult hypophosphatasia based on elevated PLP, considerations must be made depending on the race, gender and age of the individual. Factors associated with significant differences in PLP must also be considered when assessing biochemical measurements
Direct experimental evidence for substrate adatom incorporation into a molecular overlayer
While the phenomenon of metal substrate adatom incorporation into molecular overlayers is generally believed to occur in several systems, the experimental evidence for this relies on the interpretation of scanning tunneling microscopy (STM) images, which can be ambiguous and provides no quantitative structural information. We show that surface X-ray diffraction (SXRD) uniquely provides unambiguous identification of these metal adatoms. We present the results of a detailed structural study of the Au(111)-F4TCNQ system, combining surface characterization by STM, low-energy electron diffraction, and soft X-ray photoelectron spectroscopy with quantitative experimental structural information from normal incidence X-ray standing wave (NIXSW) and SXRD, together with dispersion-corrected density functional theory (DFT) calculations. Excellent agreement is found between the NIXSW data and the DFT calculations regarding the height and conformation of the adsorbed molecule, which has a twisted geometry rather than the previously supposed inverted bowl shape. SXRD measurements provide unequivocal evidence for the presence and location of Au adatoms, while the DFT calculations show this reconstruction to be strongly energetically favored
Direct experimental evidence for substrate adatom incorporation into a molecular overlayer
While the phenomenon of metal substrate adatom incorporation into molecular overlayers is generally believed to occur in several systems, the experimental evidence for this relies on the interpretation of scanning tunneling microscopy (STM) images, which can be ambiguous and provides no quantitative structural information. We show that surface X-ray diffraction (SXRD) uniquely provides unambiguous identification of these metal adatoms. We present the results of a detailed structural study of the Au(111)-F4TCNQ system, combining surface characterization by STM, low-energy electron diffraction, and soft X-ray photoelectron spectroscopy with quantitative experimental structural information from normal incidence X-ray standing wave (NIXSW) and SXRD, together with dispersion-corrected density functional theory (DFT) calculations. Excellent agreement is found between the NIXSW data and the DFT calculations regarding the height and conformation of the adsorbed molecule, which has a twisted geometry rather than the previously supposed inverted bowl shape. SXRD measurements provide unequivocal evidence for the presence and location of Au adatoms, while the DFT calculations show this reconstruction to be strongly energetically favored
Churn flow in high viscosity oils and large diameter columns
Churn flow is an important intermediate flow regimoccurring in between slug and annular flow patterns in two-phase flow, with profound implications in chemical and petroleum industry. The majority of studies to date in churn flow has been carried out mainly using water or liquids of low viscosities and limited information exists regarding the behaviour of high viscosity liquids which resemble realistic process conditions. In this paper, a study that investigated churn flow and its characteristics in high viscosity oils (360 and 330 Pa.s) and large diameter columns (240 and 290mm) is presented for a first time. Transition to churn flow regime starts when the structure velocity, length and frequency of the liquid bridges, which appear at the end of slug flow, increase. In churn flow, gas flows at the core of the oil column with a wavy passage, leaving the top surface open to atmosphere with a possibility of creating a very long bubble. The average length of the bubbles seen to decrease with increasing the gas flow rate. While, no considerable change is observed in void fraction, structure velocity and film thickness at this flow pattern
Data for Structure of strained low-dimensional Sb by in situ surface X-ray diffraction
Antimony ultrathin films in tensile strain are grown on InAs(111)B substrates and studied in situ using surface Xâray diffraction. The detailed atomic structures of two highly crystalline Sb(0001) films are derived, with thicknesses of 19 and 4 bilayers. Features considered in structural modeling include interfacial intermixing, surface roughness, individual layer relaxations, and rotational twin domains (RTDs). The fourâbilayer film shows significant structural relaxation in every layer, while both films include RTDs. The results are discussed in relation to the topological properties of lowâdimensional Sb
Direct experimental determination of Ag adatom locations in TCNQ-Ag 2D metalâorganic framework on Ag(111)
A previous investigation of the structure of TCNQ adsorbed on Ag(111) using normal-incidence X-ray standing waves (NIXSW) and density functional theory (DFT) provided indirect evidence that Ag adatoms must be incorporated into the molecular overlayer. New surface X-ray diffraction (SXRD) results, presented here, provide direct evidence for the presence and location of these Ag adatoms and clearly distinguishes between two alternative models of the adatom registry favored by two different DFT studies
Influence of the lipid backbone on electrochemical phase behavior
Sphingolipids are an important class of lipids found in mammalian cell membranes with important structural and signaling roles. They differ from another major group of lipids, the glycerophospholipids, in the connection of their hydrocarbon chains to their headgroups. In this study, a combination of electrochemical and structural methods has been used to elucidate the effect of this difference on sphingolipid behavior in an applied electric field. N-Palmitoyl sphingomyelin forms bilayers of similar coverage and thickness to its close analogue di-palmitoyl phosphatidylcholine. Grazing incidence diffraction data show slightly closer packing and a smaller chain tilt angle from the surface normal. Electrochemical IR results at low charge density show that the difference in tilt angle is retained on deposition to form bilayers. The bilayers respond differently to increasing electric field strength: chain tilt angles increase for both molecules, but sphingomyelin chains remain tilted as field strength is further increased. This behavior is correlated with disruption of the hydrogen-bonding network of small groups of sphingomyelin molecules, which may have significance for the behavior of molecules in lipid rafts in the presence of strong fields induced by ion gradients or asymmetric distribution of charged lipids