Electron crystallography as a complement to X-ray powder diffraction techniques

Electron microscopy techniques yield information for crystal structure analysis that is remarkably complementary to that obtained from X-ray powder diffraction data. Structures of polycrystalline materials that resist solution by either method alone can sometimes be solved by combining the two. For example, the intensities extracted from an X-ray powder diffraction pattern are kinematical and can be interpreted easily, while those obtained from a typical selected area electron diffraction (SAED) or precession electron diffraction (PED) pattern are at least partially dynamical and therefore more difficult to use directly. On the other hand, many reflections in a powder diffraction pattern overlap and only the sum of their intensities can be measured, while those in an electron diffraction pattern are from a single crystal and therefore well separated in space. Although the intensities obtained from either SAED or PED data are less reliable than those obtained with X-rays, they can be used to advantage to improve the initial partitioning of the intensities of overlapping reflections. However, it is the partial crystallographic phase information that can be extracted either from high-resolution transmission electron microscopy (HRTEM) images or from PED data that has proven to be particularly useful in combination with high-resolution X-ray powder diffraction data. The dual-space (reciprocal and real space) structure determination programs Focus and Superflip have been shown to be especially useful for combining the two different types of dat

Amplification of Molecular Traffic Control in catalytic grains with novel channel topology design

We investigate the conditions for reactivity enhancement of catalytic processes in porous solids by use of molecular traffic control (MTC). With dynamic Monte-Carlo simulations and continuous-time master equation theory applied to the high concentration regime we obtain a quantitative description of the MTC effect for a network of intersecting single-file channels in a wide range of grain parameters and for optimal external operating conditions. Implementing the concept of MTC in models with specially designed alternating bimodal channels we find the efficiency ratio (compared with a topologically and structurally similar reference system without MTC) to be enhanced with increasing grain diameter, a property verified for the first time for an MTC system. Even for short intersection channels, MTC leads to a reactivity enhancement of up to approximately 65%. This suggests that MTC may significantly enhance the efficiency of a catalytic process for small as well as large porous particles with a suitably chosen binary channel topology.Comment: 15 pages, 12 figure

Optimized Synthesis and Structural Characterization of the Borosilicate MCM-70

A structure analysis of the borosilicate zeolite MCM-70, whose synthesis had been patented in 2003, was reported in 2005. Unfortunately, that structure analysis was somewhat ambiguous. Anisotropic line broadening made it difficult to model the peak shape, some peaks in the electron density map could not be interpreted satisfactorily, the framework geometry was distorted, and MAS NMR results were partially contradictory. In an attempt to resolve some of these points, an optimization of the synthesis was undertaken, and the structure was reinvestigated. The structure was solved from synchrotron powder diffraction data collected on an as-synthesized sample (Pmn2_1, a = 13.3167(1) Å, b = 4.6604(1) Å, c = 8.7000(1) Å) using a powder charge-flipping algorithm. The framework topology, with a 1-dimensional, 10-ring channel system, is identical to the one previously reported. However, the B in this new sample was found to be ordered in the framework, fully occupying one of the four tetrahedral sites. Two extra-framework K^+ ion positions, each coordinated to five framework O atoms and one water molecule, were also found. The solid state ^(29)Si, ^(11)B and ^1H NMR results are fully consistent with this ordered structure

The northern flying squirrel (Glaucomys sabrinus) as a vector for inoculation of red spruce (Picea rubens) seedlings with ectomycorrhizal fungi

Mycophagous mammals excavate and ingest fruiting bodies (ascomata) of hypogeous ectomycorrhizal fungi and produce faeces containing numerous spores. To evaluate the significance of mycophagy to plant hosts we compared inoculation rate and degree of fungal development on red spruce (Picea rubens) seedlings treated with (1) faeces of the northern flying squirrel (Glaucomys sabrinus) against seedlings treated with (2) ascospores of Elaphomyces granulatus, and (3) those grown in natural forest soil or (4) forest soil that had been rendered sterile. No seedlings grown in sterilised soil showed fungal colonization. Significantly more seedlings were colonized in natural forest soil (97.5 %) than in sterile soil treated with squirrel faeces (69.2 %) or fruiting body spores (27.5 %). Treatment with squirrel faeces produced significantly more colonization than treatment with fruiting body spores. Fungal development was significantly greater on seedlings grown in forest soil compared with other treatments, but did not differ significantly between squirrel faeces and fruiting body treatments. These results demonstrate that passage through the digestive tract of flying squirrels may enhance germination and inoculation potential of fruiting body spores, although actively growing mycelium in forest soil may be the primary and most effective means by which seedlings develop mycorrhizae under natural conditions

International medical graduates (IMGs) needs assessment study: comparison between current IMG trainees and program directors

<p>Abstract</p> <p>Background</p> <p>International Medical Graduates (IMGs) training within the Canadian medical education system face unique difficulties. The purpose of this study was to explore the challenges IMGs encounter from the perspective of trainees and their Program Directors.</p> <p>Methods</p> <p>Program Directors of residency programs and IMGs at the University of Toronto were anonymously surveyed and asked to rate (using a 5-point Likert scale; 1 = least important – 5 = most important) the extent to which specific issues were challenging to IMGs and whether an orientation program (in the form of a horizontal curriculum) should be implemented for incoming IMGs prior to starting their residency.</p> <p>Results</p> <p>Among the IMGs surveyed, Knowledge of the Canadian Healthcare System received the highest mean score (3.93), followed by Knowledge of Pharmaceuticals and Hospital formularies (3.69), and Knowledge of the Hospital System (3.69). In contrast, Program Directors felt that Communication with Patients (4.40) was a main challenge faced by IMGs, followed by Communication with Team Members (4.33) and Basic Clinical Skills (4.28).</p> <p>Conclusion</p> <p>IMGs and Program Directors differ in their perspectives as to what are considered challenges to foreign-trained physicians entering residency training. Both groups agree that an orientation program is necessary for incoming IMGs prior to starting their residency program.</p

Myelosuppression in Patients Treated with the Telomerase Inhibitor Imetelstat Is Not Mediated through Activation of Toll-Like Receptors.

Imetelstat sodium (GRN163L; hereafter, imetelstat) is a first-in-class telomerase inhibitor that has demonstrated activity in patients with myeloproliferative neoplasms (MPNs). Treatment with imetelstat has been associated with thrombocytopenia and other hematologic adverse effects that were manageable and reversible. Toll-like receptors (TLRs) are proteins that recognize pathogen-associated molecular patterns and stimulate innate immune and pro-apoptotic responses. Because imetelstat is an oligonucleotide, and some oligonucleotides can activate TLRs, we conducted an in vitro study to rule out the possibility of imetelstat-associated thrombocytopenia by off-target effects through activation of TLRs. We used HEK293 cell lines stably co-expressing a human TLR gene and an NFκB-inducible reporter to investigate whether imetelstat can activate TLR signaling. We treated the cells with imetelstat or control oligonucleotides for 20 h, and used absorbance of the culture media to calculate the reporter activity. Treatment with imetelstat within or beyond the clinically relevant concentrations had no stimulatory effect on TLR2, TLR3, TLR4, TLR5, TLR7, or TLR9. This result was not surprising since the structure of imetelstat does not meet the reported minimal structural requirements for TLR9 activation. Furthermore, imetelstat treatment of the MPN cell line HEL did not impact the expression of TLR signaling pathway target genes that are commonly induced by activation of different TLRs, whereas it significantly reduced its target gene hTERT, human telomerase reverse transcriptase, in a dose- and time-dependent manner. Hence, cytopenias, especially thrombocytopenia observed in some patients treated with imetelstat, are not mediated by off-target interactions with TLRs

Perception of Radiation Exposure and Risk Among Patients, Medical Students, and Referring Physicians at a Tertiary Care Community Hospital

AbstractBackgroundIt is important for physicians to be aware of the radiation doses as well as the risks associated with diagnostic imaging procedures that they are ordering.MethodsA survey was administered to patients, medical students, and referring physicians from a number of specialties to determine background knowledge regarding radiation exposure and risk associated with commonly ordered medical imaging tests.ResultsA total of 127 patients, 32 referring physicians, and 30 medical students completed the survey. The majority of patients (92%) were not informed of the radiation risks associated with tests that they were scheduled to receive and had false perceptions about the use of radiation and its associated risks. Physicians and medical students had misconceptions about the use of ionizing radiation in a number of radiologic examinations; for example, 25% and 43% of physicians and medical students, respectively, were unaware that interventional procedures used ionizing radiation, and 28% of physicians were unaware that mammography used ionizing radiation. Computed tomographies and barium studies were thought to be associated with the least ionizing radiation among physicians.ConclusionThere is a need for educating the public, medical students, and referring physicians about radiation exposure and associated risk so that (1) patients receiving multiple medical imaging tests are aware of the radiation that they are receiving and (2) physicians and future physicians will make informed decisions when ordering such tests to limit the amount of radiation that patients receive and to promote informed consent among patients

Essays on human capital and economic development

In this dissertation I discuss how the allocation of human capital, in the form of education, across groups and sectors impacts economic development. Particularly, in Chapter 2, I provide evidence that improvements in life expectancy achieved along the 20th century impeded countries from moving toward more market-oriented labor regulations. First, using declines in predicted mortality from medical advances in the 1940s and 1950s as an instrument for improvements in life expectancy, the chapter shows that improvements in health cause an decrease in the share of the skilled labor force. These low-skilled workers increase the political support for labor regulation since they can bargain for higher wages when the cost of worker replacement is higher. Cross-country data shows that countries with a larger share of low-skilled workers failed to make their labor regulation more flexible. Lastly, I show that health improvements in the 1940s and 1950s have a positive long-run effect on the index of labor regulation. In Chapter 3, exploiting heterogeneity across Brazilian micro-regions over the 1970-2000 period, Parente, Rios-Neto and I examine whether the demographic dividend extends beyond a pure accounting effect. Using a Sys-GMM approach, we find evidence that changes in age structure have only pure accounting effects after controlling for human capital. Therefore, in the case of Brazilian micro-regions, there is a second demographic dividend, which is associated with education. This second dividend is the far more important of the two dividends in terms of economic growth. In a counterfactual exercise, we show that the accounting effect is responsible for less that 10% of the income gap between the poorest and richest regions in Brazil. In Chapter 4, I show that large governments hinder economic development by reducing competition in the private sector. The model features a public sector that uses human capital to provide public goods that reduce costs in the private sector, increasing competition. However, large governments reduce market competition by reducing the supply of human capital in the private sector. The model produces the empirical finding that government size has an inverted-U relationship with economic growth. The model also stresses the importance of public sector productivity. Using data from European countries, a calibrated version of the model shows that the average gap in income to the US in 30 years would be 87% instead of 74% if all countries in the sample had the same public sector productivity of Finland, the country with highest public efficiency

Stent implantation and balloon angioplasty for treatment of branch pulmonary artery stenosis in children

Objectives: Comparison of the results of branch pulmonary artery stenosis treated with balloon angioplasty (BA) or stent implantation (SI) in children. Background: Branch pulmonary artery stenosis may be treated with BA or SI. Methods: We compared the results of 147 interventions of branch pulmonary artery stenosis in 87 children (median age 3.6 years). Patients were treated during 1989-2000 with BA and during 2001-2004 with SI. Primary endpoints were acute complications and reintervention during follow up. Secondary variables were age, vessel diameter increase, acute success rate, balloon/vessel diameter ratio, pulmonary artery hypoplasia indices, and procedure related factors. Results: The acute vessel diameter increase with BA (4.31 ± 1.98 vs. 7.15 ± 2.31 mm) and SI (3.71 ± 1.58 vs. 6.97 ± 2.68 mm) was significant within both groups (P < 0.001), but not between both groups. The reintervention rate was comparable between both groups, but median time to reintervention was shorter after SI in infants compared to BA. The balloon/vessel diameter ratio was on average higher in BA than the stent/vessel diameter ratio in SI (3.49 ± 2.16 vs. 2.42 ± 0.56; P < 0.05) and was a significant risk factor (P < 0.01) for the higher complication rate after BA (BA: 14.1% vs. SI: 4.8%). No mortality occurred in both groups. Conclusion: BA and SI are safe interventional catheter therapies of branch pulmonary artery stenosis. The immediate results of BA and SI are comparable. The higher complication rate after BA, especially in infants, was associated with a higher balloon/vessel diameter ratio. SI seems to be a safe permanent alternative with foreign material, but requires more reinterventions in infants due to its therapeutic strateg