The chemical and electronic properties of surfaces to a large extent are controlled by defects. Defects facilitate the adsorption of gases and serve as reactive sites for chemical reactions. ...Furthermore, surface defects are a key to the nucleation, growth, and stability of metal clusters on metal oxide surfaces. This paper summarizes recent studies to assess the role of defects on Au cluster nucleation, growth, and stability on SiO
2 and mixed TiO
x
–SiO
2 thin films. For a SiO
2 thin film, Au clusters sinter at elevated temperatures and pressures; however, introduction of defects on a SiO
2 surface as TiO
x
islands or as substitutional Ti dramatically decreases the rate of Au cluster sintering.
Gold clusters supported on titania and silica substrates (Au/TiO
2 and Au/SiO
2) sinter when exposed to high temperatures and reaction pressures. By synthesizing a mixed titania-silica thin film possessing small TiO
x islands, the sintering of gold clusters can be inhibited.
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Supported metal catalysts, particularly noble metals supported on SiO
2, have attracted considerable attention due to the importance of the silica–metal interface in heterogeneous catalysis and in ...electronic device fabrication. Several important issues, e.g., the stability of the metal–oxide interface at working temperatures and pressures, are not well-understood. In this review, the present status of our understanding of the metal–silica interface is reviewed. Recent results of model studies in our laboratories on Pd/SiO
2/Mo(1
1
2) using LEED, AES and STM are reported. In this work, epitaxial, ultrathin, well-ordered SiO
2 films were grown on a Mo(1
1
2) substrate to circumvent complications that frequently arise from the silica–silicon interface present in silica thin films grown on silicon.
The argument that women in stressful environments spontaneously abort their least fit fetuses enjoys wide dissemination despite the fact that several of its most intuitive predictions remain ...untested. The literature includes no tests, for example, of the hypothesis that these mechanisms select against small for gestational age (SGA) males.
METHODS
We apply time-series modeling to 4.9 million California male term births to test the hypothesis that the rate of SGA infants in 1096 weekly birth cohorts varies inversely with labor market contraction, a known stressor of contemporary populations.
RESULTS
We find support for the hypothesis that small size becomes less frequent among term male infants when the labor market contracts.
CONCLUSIONS
Our findings contribute to the evidence supporting selection in utero. They also suggest that research into the association between maternal stress and adverse birth outcomes should acknowledge the possibility that fetal loss may affect findings and their interpretation. Strengths of our analyses include the large number and size of our birth cohorts and our control for autocorrelation. Weaknesses include that we, like nearly all researchers in the field, have no direct measure of fetal loss.
In-situ polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) is used to study CO adsorption at elevated pressures and temperatures on Pd nanoclusters deposited on crystalline ...SiO2 thin films. The PM-IRAS data indicate that CO dissociates on the Pd nanoclusters at 185 mbar and at temperature >600 K. Combined STM and PM-IRAS data show that the Pd nanoclusters are three-dimensional and consist predominantly of 〈111〉 facets with an average diameter and height of 3.5 and 0.7 nm, respectively. STM data indicate no change in the morphology or sintering of the Pd nanoclusters between 300 and 650 K. For comparison, CO adsorption was investigated on a Pd(111) single-crystal surface using PM-IRAS under similar conditions (P CO = 133 mbar, T = 175−750 K). Comparison of the PM-IRAS data for CO adsorption on Pd(111) and Pd nanoclusters indicate that in contrast to the Pd nanoclusters, CO adsorbs molecularly on the Pd(111) surface in a reversible manner, i.e., no dissociation.
Scanning tunneling microscopy (STM), in conjunction with the nucleation and growth of Au clusters, has been used to identify and quantify various types of defects on ordered, SiO2 thin films grown on ...Mo(112). On a low-defect surface, Au clusters nucleate and grow at line defects with metal deposition at room temperature, whereas deposition at 850 K leads to cluster decoration primarily at step edges. On a highly defective surface, clusters nucleate and grow at point defects (oxygen vacancies and/or oxygen vacancy complexes) on the terraces, with some clusters grown on oxygen vacancy complexes remaining even after an 850 K anneal. The average cluster density for low Au coverages deposited at room temperature is identical to that obtained for the same Au coverage deposited at 850 K, consistent with complete titration of point defects by the nucleating clusters.
Ataxia telangiectasia (A-T) is a rare disorder with many distinctive neurologic features. Although there is substantial individual variation in the rate of progression of these features, their ...relationship to one another or to age has not been characterized.
We formulated and tested multiple elements that assess different neurologic functions known to be affected by A-T. The overall index was applied to 52 patients with A-T, 2 to 29 years of age.
Seven elements items proved to be informative, and three elements were added based on face validity. In a linear regression model of individuals under 19 years of age, controlled for correlation within sibships, age accounted for 87% of the variation in the A-T Index.
Despite substantial individual variability of the phenotypic elements of A-T, scores on this multidimensional index have a very high correlation with age, indicating that there is a characteristic rate of progression of the disease, although functional domains in the brain are differentially affected. The pattern of scores suggests that a severe and a mild form of A-T may be distinguished by this quantitative measure. With further development this index may become useful as an outcome measure for treatment studies and prognosis.
This study was designed to prospectively compare helical CT with pulmonary angiography in the detection of pulmonary embolism in patients with an unresolved clinical and scintigraphic diagnosis.
...Twenty patients with an unresolved suspicion of pulmonary embolism were evaluated with contrast-enhanced helical CT and with selective pulmonary angiography. An average of 11 hr separated the two studies. The CT scans were obtained during one 24-sec or two 12-sec breath-holds. CT scans were interpreted without knowledge of the results of scintigraphy or angiography. Selective pulmonary angiograms were obtained with knowledge of the findings on the ventilation/perfusion scan only. The sensitivity and specificity of CT were compared with those of angiography for central vessels (segmental and larger) only and for all vessels.
Eleven of the 20 patients had proved pulmonary embolism (seven in central vessels and four in subsegmental vessels only). When only central vessels were analyzed, CT sensitivity was 86%, specificity was 92%, and the likelihood ratio was 10.7. However, when subsegmental vessels were included, CT results were 63%, 89%, and 5.7, respectively.
In our subset of patients, helical CT was only 63% sensitive. Subsegmental emboli are difficult to diagnose. Pulmonary angiography remains the study of choice. CT has a limited role in the evaluation of acute pulmonary embolism.
Monoclonal B-cell lymphocytosis (MBL) is a hematologic condition wherein small B-cell clones can be detected in the blood of asymptomatic individuals. Most MBL have an immunophenotype similar to ...chronic lymphocytic leukemia (CLL), and 'CLL-like' MBL is a precursor to CLL. We used flow cytometry to identify MBL from unaffected members of CLL kindreds. We identified 101 MBL cases from 622 study subjects; of these, 82 individuals with MBL were further characterized. In all, 91 unique MBL clones were detected: 73 CLL-like MBL (CD5(+)CD20(dim)sIg(dim)), 11 atypical MBL (CD5(+)CD20(+)sIg(+)) and 7 CD5(neg) MBL (CD5(neg)CD20(+)sIg(neg)). Extended immunophenotypic characterization of these MBL subtypes was performed, and significant differences in cell surface expression of CD23, CD49d, CD79b and FMC-7 were observed among the groups. Markers of risk in CLL such as CD38, ZAP70 and CD49d were infrequently expressed in CLL-like MBL, but were expressed in the majority of atypical MBL. Interphase cytogenetics was performed in 35 MBL cases, and del 13q14 was most common (22/30 CLL-like MBL cases). Gene expression analysis using oligonucleotide arrays was performed on seven CLL-like MBL, and showed activation of B-cell receptor associated pathways. Our findings underscore the diversity of MBL subtypes and further clarify the relationship between MBL and other lymphoproliferative disorders.
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