Total synthesis of (-)-ratjadone.
[reaction in text] A convergent asymmetric synthesis of (-)-ratjadone (1) has been achieved, confirming the assignments of stereochemistry for the naturally occurring antifungal metabolite.
Antifungal Agents↗
Biomedical subjects
D R Williams
Publications and source records attributed to D R Williams.
The use of inverse phase gas chromatography to study the change of surface energy of amorphous lactose as a function of relative humidity and the processes of collapse and crystallisation.
The purpose of this study was to assess the effect of relative humidity (RH) on the surface energy of amorphous lactose. Two samples of amorphous lactose were investigated; a spray dried 100% amorphous material and a ball milled sample of crystalline lactose. The milled sample had less than 1% amorphous content by mass, but on investigation at 0% RH, yielded surface energies comparable to those obtained from the 100% amorphous material, indicating that the surface was amorphous. The effect of increasing humidity was to reduce the dispersive surface energy of the two samples from 36.0 +/- 0.14 and 41.6 +/- 1.4 mJ m(-2) at 0% RH for the spray dried and milled samples respectively, to a value comparable to that obtained for the crystalline alpha-lactose monohydrate of 31.3 +/- 0.41 mJ m(-2). The change in surface energy due to water sorption was only reversible up to 20% RH; after exposure to higher RH values subsequent drying did not result in a return to the original surface energy of the amorphous form. This shows that the surface is reorganising as the glass transition temperature (Tg) is reduced, even though the sample has not collapsed or crystallised. It was possible to follow the collapse behaviour in the column with ease, using a number of different methods.
Absorption↗
Total synthesis of (+)-amphidinolide K.
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Antineoplastic Agents↗
Toroidal condensates of semiflexible polymers in poor solvents: adsorption, stretching, and compression.
When a semiflexible polymer chain is placed in a poor solvent, or in the presence of condensing agents, a toroidal condensate can result. In typical experiments, these condensates are adsorbed to surfaces. Here we examine the changes that can occur when a toroid is adsorbed. We then examine the behavior of a toroid when stretched and identify two regimes: a weak stretching regime where the toroid deforms from a circle to an ellipse, and a strong stretching regime where a tether is pulled from the toroid. In the weak stretching regime, the force increases linearly with separation whereas in the strong stretching regime, the applied force is a constant. We then look at the case of a toroid compressed in the plane of the toroid. In this case the form of the force law depends on how strongly the toroid wets the surfaces. In general, an inverse square force law is found.
Biophysical Phenomena↗
Characterization and use of a digital light projector for vision research.
For creating stimuli in the laboratory, digital light projection (DLP) technology has the potential to overcome the low output luminance, lack of pixel independence, and limited chromaticity gamut of the cathode ray tube (CRT). We built a DLP-based stimulator for projecting patterns on the in vitro primate retina. The DLP produces high light levels and has good contrast. Spatial performance was similar to that of a CRT. Temporal performance was limited by the refresh rate (63 Hz). The chromatic gamut was modestly larger than that of a CRT although the primary spectra varied to a small degree with light output and numerical aperture.
Analog-Digital Conversion↗
Packing arrangement of the three cone classes in primate retina.
We describe a detailed analysis of the spatial arrangement of L, M and S cones in the living eyes of two humans and one monkey. We analyze the cone mosaics near 1 degrees eccentricity using statistical methods that characterize the arrangement of each type of cone in the mosaic of photoreceptors. In all eyes, the M and L cones are arranged randomly. This gives rise to patches containing cones of a single type. In human, but not in monkey, the arrangement of S-cones cannot be distinguished from random.
Animals↗
Socioeconomic disparities in health change in a longitudinal study of US adults: the role of health-risk behaviors.
This study investigated the hypothesis that socioeconomic differences in health status change can largely be explained by the higher prevalence of individual health-risk behaviors among those of lower socioeconomic position. Data were from the Americans' Changing Lives study, a longitudinal survey of 3,617 adults representative of the US non-institutionalized population in 1986. The authors examined associations between income and education in 1986, and physical functioning and self-rated health in 1994, adjusted for baseline health status, using a multinomial logistic regression framework that considered mortality and survey nonresponse as competing risks. Covariates included age, sex, race, cigarette smoking, alcohol consumption, physical activity, and Body Mass Index. Both income and education were strong predictors of poor health outcomes. The four health-risk behaviors under study statistically explained only a modest portion of the socioeconomic differences in health at follow-up. For example, after adjustment for baseline health status, those in the lowest income group at baseline had odds of moderate/severe functional impairment in 1994 of 2.11 (95% C.I.: 1.40, 3.20) in an unadjusted model and 1.89 (95% C.I.: 1.23, 2.89) in a model adjusted for health-risk behaviors. The results suggest that the higher prevalence of major health-risk behaviors among those in lower socioeconomic strata is not the dominant mediating mechanism that can explain socioeconomic disparities in health status among US adults.
Adult↗
Chemical speciation used to assess [S,S']-ethylenediaminedisuccinic acid (EDDS) as a readily-biodegradable replacement for EDTA in radiochemical decontamination formulations.
Preliminary investigations into the replacement of widely used chelating agents for industrial cleansing of radionuclide contaminated items using readily biodegradable alternatives which have equivalent effectiveness, have been made using chemical speciation simulation programs and databases such as the JESS system. The chelation of radionuclide cations by [S,S']-EDDS has been compared with traditional decontamination agents, EDTA and citrate. Models indicate that in many respects, [S,S']-EDDS compares favourably with EDTA.
Americium↗
Extraterrestrial resuscitation of hemorrhagic shock: fluids.
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Aerospace Medicine↗
Prospective evaluation of thoracic ultrasound in the detection of pneumothorax.
BACKGROUND: Thoracic ultrasound may rapidly diagnose pneumothorax when radiographs are unobtainable; the accuracy is not known. METHODS: We prospectively evaluated thoracic ultrasound detection of pneumothorax in patients at high suspicion of pneumothorax. The presence of "lung sliding" or "comet tail" artifacts were determined in patients by ultrasound before radiologic verification of pneumothorax by residents instructed in thoracic ultrasound. Results were compared with standard radiography. RESULTS: There were 382 patients enrolled; the cause of injury was blunt (281 of 382), gunshot wound (22 of 382), stab wound (61 of 382), and spontaneous (18 of 382). Pneumothorax was demonstrated on chest radiograph in 39 patients and confirmed by ultrasound in 37 of 39 patients (95% sensitivity); two pneumothoraces could not be diagnosed because of subcutaneous air; the true-negative rate was 100%. CONCLUSION: Thoracic ultrasound reliably diagnoses pneumothorax. Expansion of the focused abdominal sonography for trauma (FAST) examination to include the thorax should be investigated for terrestrial and space medical applications.
Humans↗
Child literacy promotion in the emergency department.
INTRODUCTION: Studies using primary health care settings to promote literacy have demonstrated success. Since socioeconomically disadvantaged children have less access to primary care, obtaining much of their medical care episodically in emergency departments (ED), the purpose of this study is to investigate the effectiveness of a simple literacy promotion program conducted in the ED and to determine its efficacy and if there is a difference in promoting literacy with a brochure alone versus a brochure plus a children's book. METHODS: Medical student study investigators enrolled patients aged 20 months to 7 years undergoing acute care treatment and evaluation in an ED. Subjects were randomized to a literacy promotion brochure versus a brochure plus a children's book. Phone follow-up interviews were conducted to survey the degree of parental reading taking place at home. RESULTS: Fifty-one families were enrolled, 8 could not be contacted for follow-up, which left 43 families. Twenty-eight were randomized to book + handout and 15 were randomized to handout alone. On follow-up phone interviews, no significant change in reading was demonstrated regardless of whether a brochure alone was given or a book was given with the brochure. CONCLUSION: Literacy promotion in the ED was not associated with any measurable improvement in parent-child reading. This could mean that the ED is not an effective place to promote literacy or confounding factors in this study are responsible for failing to demonstrate a measurable benefit.
Child↗
Food insufficiency and the physical and mental health of low-income women.
Poor women with children are disproportionately represented among the food insufficient. Recent research has linked food insufficiency with dietary deficiencies, but further research linking this problem to health and mental health problems is needed to inform health and social policy. We analyzed the relationship between food insufficiency and physical and mental health in a random sample of 724 single women who were welfare recipients in February, 1997. Food insufficiency was significantly associated with poor or fair self-rated health and physical limitations, and with respondents' meeting DSM-III-R criteria for recent major depression. Although the cross-sectional design of this study precludes causal inference, these findings add to a growing body of evidence that food insufficiency is associated with serious adverse physical and mental health consequences.
Adult↗
Dynamics of the eye's wave aberration.
It is well known that the eye's optics exhibit temporal instability in the form of microfluctuations in focus; however, almost nothing is known of the temporal properties of the eye's other aberrations. We constructed a real-time Hartmann-Shack (HS) wave-front sensor to measure these dynamics at frequencies as high as 60 Hz. To reduce spatial inhomogeneities in the short-exposure HS images, we used a low-coherence source and a scanning system. HS images were collected on three normal subjects with natural and paralyzed accommodation. Average temporal power spectra were computed for the wave-front rms, the Seidel aberrations, and each of 32 Zernike coefficients. The results indicate the presence of fluctuations in all of the eye's aberration, not just defocus. Fluctuations in higher-order aberrations share similar spectra and bandwidths both within and between subjects, dropping at a rate of approximately 4 dB per octave in temporal frequency. The spectrum shape for higher-order aberrations is generally different from that for microfluctuations of accommodation. The origin of these measured fluctuations is not known, and both corneal/lenticular and retinal causes are considered. Under the assumption that they are purely corneal or lenticular, calculations suggest that a perfect adaptive optics system with a closed-loop bandwidth of 1-2 Hz could correct these aberrations well enough to achieve diffraction-limited imaging over a dilated pupil.
Accommodation, Ocular↗
Effect of rotation and translation on the expected benefit of an ideal method to correct the eye's higher-order aberrations.
An ideal correcting method, such as a customized contact lens, laser refractive surgery, or adaptive optics, that corrects higher-order aberrations as well as defocus and astigmatism could improve vision. The benefit achieved with this ideal method will be limited by decentration. To estimate the significance of this potential limitation we studied the effect on image quality expected when an ideal correcting method translates or rotates with respect to the eye's pupil. Actual wave aberrations were obtained from ten human eyes for a 7.3-mm pupil with a Shack-Hartmann sensor. We computed the residual aberrations that appear as a result of translation or rotation of an otherwise ideal correction. The model is valid for adaptive optics, contact lenses, and phase plates, but it constitutes only a first approximation to the laser refractive surgery case where tissue removal occurs. Calculations suggest that the typical decentrations will reduce only slightly the optical benefits expected from an ideal correcting method. For typical decentrations the ideal correcting method offers a benefit in modulation 2-4 times higher (1.5-2 times in white light) than with a standard correction of defocus and astigmatism. We obtained analytical expressions that show the impact of translation and rotation on individual Zernike terms. These calculations also reveal which aberrations are most beneficial to correct. We provided practical rules to implement a selective correction depending on the amount of decentration. An experimental study was performed with an aberrated artificial eye corrected with an adaptive optics system, validating the theoretical predictions. The results in a keratoconic subject, also corrected with adaptive optics, showed that important benefits are obtained despite decentrations in highly aberrated eyes.
Eye↗
Ultrasound evaluation of the magnitude of pneumothorax: a new concept.
Pneumothorax is commonly seen in trauma patients; the diagnosis is confirmed by radiography. The use of ultrasound where radiographic capabilities are absent, is being investigated by the National Aeronautics and Space Administration. We investigated the ability of ultrasound to assess the magnitude of pneumothorax in a porcine model. Sonography was performed on anesthetized pigs in both ground-based laboratory (n = 5) and microgravity conditions (0 x g) aboard the KC-135 aircraft during parabolic flight (n = 4). Aliquots of air (50-100 cm3) were introduced into the chest to simulate pneumothorax. Results were videorecorded and digitized for later interpretation. Several distinct sonographic patterns of partial lung sliding were noted including the combination of a sliding zone with a still zone and a "segmented" sliding zone. These "partial lung sliding" patterns exclude massive pneumothorax manifested by a complete separation of the lung from the parietal pleura. In 0 x g, the sonographic picture is more diverse; one x g differences between posterior and anterior aspects are diminished. Modest pneumothorax can be inferred by the ultrasound sign of "partial lung sliding." This finding, which increases the negative predictive value of thoracic ultrasound, may be attributed to intermittent pleural contact, small air spaces, or alterations in pleural lubricant. Further studies of these phenomena are warranted.
Animals↗
The yawning reflex: an upper motor neuron sign in amyotrophic lateral sclerosis.
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Amyotrophic Lateral Sclerosis↗
Construction of 4-hydroxy-2-pyridinones. Total synthesis of (+)-sambutoxin.
Total synthesis of (+)-sambutoxin has been achieved, establishing the relative and absolute stereochemistry of the naturally occurring mycotoxin. Efforts feature methodology for enantiocontrolled construction of 1,3-anti-dimethyl arrays and a novel Saegusa oxidation to provide a pyridinone methide leading to formation of the central dihydropyran ring.
Fusarium↗
Synthetic studies toward phorboxazole A. stereoselective synthesis of the C(28)-C(46) side chain fragment.
A stereoselective synthesis of the C(28)-C(46) fragment (3) of phorboxazole A is described. Key advances include an enantioselective allylation to establish the stereochemistry of the tetrahydropyran unit and a useful SmI(2)-mediated modification of the Barbier reaction of iodomethyloxazole 15 with aldehyde 14.
Animals↗