4D In-Situ Microscopy of Aerosol Filtration in a Wall Flow Filter.

The transient nature of the internal pore structure of particulate wall flow filters, caused by the continuous deposition of particulate matter, makes studying their flow and filtration characteristics challenging. In this article we present a new methodology and first experimental demonstration of time resolved in-situ synchrotron micro X-ray computed tomography (micro-CT) to study aerosol filtration. We directly imaged in 4D (3D plus time) pore scale deposits of TiO2 nanoparticles (nominal mean primary diameter of 25 nm) with a pixel resolution of 1.6 µm. We obtained 3D tomograms at a rate of ∼1 per minute. The combined spatial and temporal resolution allows us to observe pore blocking and filling phenomena as they occur in the filter's pore space. We quantified the reduction in filter porosity over time, from an initial porosity of 0.60 to a final porosity of 0.56 after 20 min. Furthermore, the penetration depth of particulate deposits and filtration rate was quantified. This novel image-based method offers valuable and statistically relevant insights into how the pore structure and function evolves during particulate filtration. Our data set will allow validation of simulations of automotive wall flow filters. Evolutions of this experimental design have potential for the study of a wide range of dry aerosol filters and could be directly applied to catalysed automotive wall flow filters.

Exploiting Hydrazones To Improve the Efficiency of 6π-Electrocyclization Reactions of 1-Azatrienes.

The greater geometric lability of hydrazones compared to that of oxime ethers is used as a basis to overcome the reluctance of Z-oxime ether azatrienes to undergo electrocyclization toward the synthesis of borylated (heteroaromatic) pyridines and ring-fused analogues. Such hydrazones now allow access to previously inaccessible tri- and tetrasubstituted 3-borylpyridines in high yields.

Synthetic and Mechanistic Investigation of an Oxime Ether Electrocyclization Approach to Heteroaromatic Boronic Acid Derivatives.

A range of functionalized heteroaromatic boronic acid derivatives are readily accessed by a diboration/6π-electrocyclization sequence. This study revealed the surprising observation that there is a direct relationship between oxime ether stereochemistry and reactivity towards electrocyclization. Specifically, E-oxime ethers are found to be significantly more reactive than their Z-counterparts (stereochemistry relative to azatriene scaffold). In contrast, the configuration at the azatriene alkene terminus has little impact on reaction rates. Computational analysis offers a rationale for this observation; a Nlone pair →C=C π* orbital interaction lowers the energy of the transition state in the electrocyclization of E-oxime ethers. Finally, unreactive Z-oxime ethers can be converted to the corresponding heterocyclic products by a photolytically promoted E→Z isomerization and electrocyclization sequence.

Alkynyl Thioethers in Gold-Catalyzed Annulations To Form Oxazoles.

Non-oxidative, regioselective, and convergent access to densely functionalized oxazoles is realized in a functional-group tolerant manner using alkynyl thioethers. Sulfur-terminated alkynes provide access to reactivity previously requiring strong donor-substituted alkynes such as ynamides. Sulfur does not act in an analogous donor fashion in this gold-catalyzed reaction, thus leading to complementary regioselective outcomes and addressing the limitations of using ynamides.

Tunable cw UV laser with <35 kHz absolute frequency instability for precision spectroscopy of Sr Rydberg states.

We present a solid-state laser system that generates over 200 mW of continuous-wave, narrowband light, tunable from 316.3 nm - 317.7 nm and 318.0 nm - 319.3 nm. The laser is based on commercially available fiber amplifiers and optical frequency doubling technology, along with sum frequency generation in a periodically poled stoichiometric lithium tantalate crystal. The laser frequency is stabilized to an atomic-referenced high finesse optical transfer cavity. Using a GPS-referenced optical frequency comb we measure a long term frequency instability of < 35 kHz for timescales between 10(-3) s and 10(3) s. As an application we perform spectroscopy of Sr Rydberg states from n = 37 - 81, demonstrating mode-hop-free scans of 24 GHz. In a cold atomic sample we measure Doppler-limited linewidths of 350 kHz.

Aphasia and swallowing problems in subjects with incident stroke in rural northern Tanzania: a case-control study.

OBJECTIVES: This study was carried out to quantify the degree of cognitive impairment and the extent of speech, language, and swallowing problems in a representative cohort of Swahili-speaking people with stroke in Tanzania. METHODS: A case-control design was used, comparing people with and without stroke on a screening test for aphasia (spoken comprehension and expression), a water swallow test, and the Community Screening Instrument for Dementia (CSI-D). RESULTS: Fifty-eight persons between 6 and 60 months (median 36) post stroke and 58 age- and gender-matched control subjects were assessed. Twenty-eight strokes were left hemisphere; 25, right; 2, posterior circulation; and 3, undetermined. Forty-nine of 58 (84%) control subjects scored 19 to 20 (maximum) on the language screen compared with 26 of 56 (46%) persons with stroke who completed the assessment. Higher age and lower educational attainment, but not gender or time since stroke, were associated with poorer performance on language and swallow assessments. Poorer CSI-D score was significantly correlated with all items. Greater disability (Barthel Index score) was significantly correlated with poorer performance in all items except rate of drinking water. Those with a left hemisphere stroke performed less well on understanding and expression items but better than other subjects with stroke on the water swallow task. CONCLUSIONS: This is the first attempt to describe aphasia incidence in a sub-Saharan African language. Further work on the psychometric properties of the screening instrument is warranted. Given that it delivers a relatively coarse indication of language disturbance, it is likely that incidence of aphasia in the current cohort is underestimated.

A cross-sectional study of quality of life in incident stroke survivors in rural northern Tanzania.

The aim of this study was to evaluate changes to, and predictors of, quality of life (QOL) in a community-based cohort of stroke survivors from an earlier stroke incidence study in rural northern Tanzania. Patients were assessed 1-5 years after their incident stroke. The study cohort was compared with an age- and sex-matched control group from the same rural district within a cross-sectional design. Patients and controls were asked a series of questions relating to their QOL [World Health Organization quality of life, abbreviated version (WHOQOL-BREF)], levels of anxiety and depression [hospital anxiety and depression (HAD) scale], cognitive function [community screening instrument for dementia (CSI-D) screening tool], socioeconomic status and demographic characteristics (e.g. age, sex, education and abode). Patients were further assessed for functional outcome and disability (Barthel index, modified Rankin scale), post-stroke care and psychosocial functioning. Patients (n = 58) were found to have significantly lower QOL than controls (n = 58) in all six domains of the WHOQOL-BREF. Gender, socioeconomic status, cognitive function and time elapsed since stroke were not associated with QOL. Older patients and those with more impaired motor function and disability (Barthel index, modified Rankin score) had significantly poorer physical health-related QOL. Greater anxiety and depression, reduced muscle power and less involvement in social events were significantly correlated with lower physical and psychological health-related QOL. To our knowledge, this is the first long-term study of QOL in survivors of incident stroke in Sub-Saharan Africa (SSA). Poorer QOL was associated with greater levels of physical disability, anxiety and depression and reduced social interaction. Demographic factors appear to be much less significant. Modifying these QOL predictors could be important in planning effective post-stroke care within a stretched healthcare system.

Chemistry of 4-alkylaryloxenium ion "precursors": sound and fury signifying something?

Quinol esters 2b, 2c, and 3b and sulfonamide 4c were investigated as possible precursors to 4-alkylaryloxenium ions, reactive intermediates that have not been previously detected. These compounds exhibit a variety of interesting reactions, but with one possible exception, they do not generate oxenium ions. The 4-isopropyl ester 2b predominantly undergoes ordinary acid- and base-catalyzed ester hydrolysis. The 4-tert-butyl ester 2c decomposes under both acidic and neutral conditions to generate tert-butanol and 1-acetyl-1,4-hydroquinone, 8, apparently by an SN1 mechanism. This is also a minor decomposition pathway for 2b, but the mechanism in that case is not likely to be SN1. Decomposition of 2c in the presence of N3- leads to formation of the explosive 2,3,5,6-tetraazido-1,4-benzoquinone, 14, produced by N3--induced hydrolysis of 8, followed by a series of oxidations and nucleophilic additions by N3-. No products suggestive of N3--trapping of an oxenium ion were detected. The 4-isopropyl dichloroacetic acid ester 3b reacts with N3- to generate the two adducts 2-azido-4-isopropylphenol, 5b, and 3-azido-4-isopropylphenol, 11b. Although 5b is the expected product of N3- trapping of the oxenium ion, kinetic analysis shows that it is produced by a kinetically bimolecular reaction of N3- with 3b. No oxenium ion is involved. The sulfonamide 4c predominantly undergoes a rearrangement reaction under acidic and neutral conditions, but a minor component of the reaction yields 4-tert-butylcresol, 17, and 2-azido-4-tert-butylphenol, 5c, in the presence of N3-. These products may indicate that 4c generates the oxenium ion 1c, but they are generated in very low yields (ca. 10%) so it is not possible to definitively conclude that 1c has been produced. If 1c has been generated, the N3--trapping data indicate that it is a very short-lived and reactive species in H2O. Comparisons with similarly reactive nitrenium ions indicate that the lifetime of 1c is ca. 20-200 ps if it is generated, so it must react by a preassociation process. Density functional theory calculations at the B3LYP/6-31G*//HF/6-31G* level coupled with kinetic correlations also indicate that the aqueous solution lifetimes of 1a-c are in the picosecond range.

4'-substituted-4-biphenylyloxenium ions: reactivity and selectivity in aqueous solution.

Azide trapping shows that the 4'-substituted-4-biphenylyloxenium ions 1b-d are generated during hydrolysis of 4-aryl-4-acetoxy-2,5-cyclohexadienones, 2c and 2d, and O-(4-aryl)phenyl-N-methanesulfonylhydroxylamines, 3b and 3c. In addition, the 4'-bromo-substituted ester, 2d, undergoes a kinetically second-order reaction with N3- that accounts for a fraction of the azide adduct, 5d. Since both first-order and second-order azide trapping occurs simultaneously in 2d, the second-order reaction is not enforced by the short lifetime of 1d, which has similar azide/solvent selectivity to the unsubstituted ion, 1a. In contrast the 4'-CN and 4'-NO2 ions 1e and 1f cannot be detected by azide trapping during the hydrolysis of the dichloroacetic acid esters 2e' and 2f' even though 18O labeling experiments show that a fraction of the hydrolysis of both esters occurs through C(alkyl)-O bond cleavage. These esters exhibit only second-order trapping by azide. Correlations of the azide/solvent selectivities of 1a-d with the calculated relative driving force for hydration of the ions (DeltaE of eq 4) determined at the pBP/DN//HF/6-31G and BP/6-31G//HF/6-31G levels of theory suggest that 1e and 1f have lifetimes in the 1-100 ps range. Ions with these short lifetimes are not in diffusional equilibrium with nonsolvent nucleophiles, and must be trapped by such nucleophiles via a preassociation mechanism. The second-order trapping that is observed in these two cases is enforced by the short lifetime of the cations, and may occur by a concerted S(N)2' mechanism or by internal azide trapping of an ion sandwich produced by azide-assisted ionization. Comparison of azide/solvent selectivities of the oxenium ions 1a-c with the corresponding biphenylylnitrenium ions 8a-c shows that 4'-substituent effects on reactivity in both sets of ions are similar in magnitude, although the nitrenium ions are ca. 30-fold more stable in an aqueous environment than the corresponding oxenium ions. The magnitude of the 4'-substituent effects for electron-donating substituents suggest that both sets of ions are more accurately described as 4-aryl-1-imino-2,5-cyclohexadienyl or 4-aryl-1-oxo-2,5-cyclohexadienyl carbocations. Calculated structures of the oxenium ions are also consistent with this interpretation.