269 research outputs found
A novel fast gas chromatography method for higher time resolution measurements of speciated monoterpenes in air
Biogenic emissions supply the largest fraction of non-methane volatile
organic compounds (VOC) from the biosphere to the atmospheric boundary
layer, and typically comprise a complex mixture of reactive terpenes. Due to
this chemical complexity, achieving comprehensive measurements of biogenic
VOC (BVOC) in air within a satisfactory time resolution is analytically
challenging. To address this, we have developed a novel, fully automated
Fast Gas Chromatography (Fast-GC) based technique to provide higher time
resolution monitoring of monoterpenes (and selected other C<sub>9</sub>-C<sub>15</sub>
terpenes) during plant emission studies and in ambient air. To our
knowledge, this is the first study to apply a Fast-GC based separation
technique to achieve quantification of terpenes in ambient air. Three
chromatography methods have been developed for atmospheric terpene analysis
under different sampling scenarios. Each method facilitates chromatographic
separation of selected BVOC within a significantly reduced analysis time
compared to conventional GC methods, whilst maintaining the ability to
quantify individual monoterpene structural isomers. Using this approach, the
C<sub>9</sub>-C<sub>15</sub> BVOC composition of single plant emissions may be
characterised within a 14.5 min analysis time. Moreover, in-situ
quantification of 12 monoterpenes in unpolluted ambient air may be achieved
within an 11.7 min chromatographic separation time (increasing to 19.7 min
when simultaneous quantification of multiple oxygenated C<sub>9</sub>-C<sub>10</sub>
terpenoids is required, and/or when concentrations of anthropogenic VOC are
significant). These analysis times potentially allow for a twofold to fivefold
increase in measurement frequency compared to conventional GC methods. Here we outline the technical
details and analytical capability of this chromatographic approach, and
present the first in-situ Fast-GC observations of 6 monoterpenes and the
oxygenated BVOC (OBVOC) linalool in ambient air. During this field
deployment within a suburban forest ~30 km west of central
Tokyo, Japan, the Fast-GC limit of detection with respect to monoterpenes
was 4–5 ppt, and the agreement between Fast-GC and PTR-MS derived total
monoterpene mixing ratios was consistent with previous GC/PTR-MS
comparisons. The measurement uncertainties associated with the Fast-GC
quantification of monoterpenes are ≤ 12%, while larger uncertainties
(up to ~25%) are associated with the OBVOC and
sesquiterpene measurements
A global disorder of imprinting in the human female germ line
Imprinted genes are expressed differently depending on whether they are carried by a chromosome of maternal or paternal origin. Correct imprinting is established by germline-specific modifications; failure of this process underlies several inherited human syndromes. All these imprinting control defects are cis-acting, disrupting establishment or maintenance of allele-specific epigenetic modifications across one contiguous segment of the genome. In contrast, we report here an inherited global imprinting defect. This recessive maternal-effect mutation disrupts the specification of imprints at multiple, non-contiguous loci, with the result that genes normally carrying a maternal methylation imprint assume a paternal epigenetic pattern on the maternal allele. The resulting conception is phenotypically indistinguishable from an androgenetic complete hydatidiform mole, in which abnormal extra-embryonic tissue proliferates while development of the embryo is absent or nearly so. This disorder offers a genetic route to the identification of trans-acting oocyte factors that mediate maternal imprint establishment
Molar pregnancy and childhood cancer: a population-based linkage study from Denmark
We observed a relative risk of 1.40 (95% confidence interval; 0.86–2.16) for cancers diagnosed under the age 20 in 6192 offspring of 3431 mothers with a molar pregnancy, indicating it is not a major determinant of childhood cancer
Technical Note: Formal blind intercomparison of HO<sub>2</sub> measurements in the atmosphere simulation chamber SAPHIR during the HOxComp campaign
Hydroperoxy radical (HO<sub>2</sub>) concentrations were measured during the formal blind intercomparison campaign HOxComp carried out in Jülich, Germany, in 2005. Three instruments detected HO<sub>2</sub> via chemical conversion to hydroxyl radicals (OH) and subsequent detection of the sum of OH and HO<sub>2</sub> by laser induced fluorescence (LIF). All instruments were based on the same detection and calibration scheme. Because measurements by a MIESR instrument failed during the campaign, no absolute reference measurement was available, so that the accuracy of individual instruments could not be addressed. Instruments sampled ambient air for three days and were attached to the atmosphere simulation chamber SAPHIR during the second part of the campaign. Six experiments of one day each were conducted in SAPHIR, where air masses are homogeneously mixed, in order to investigate the performance of instruments and to determine potential interferences of measurements under well-controlled conditions. Linear correlation coefficients (<i>R</i><sup>2</sup>) between measurements of the LIF instruments are generally high and range from 0.82 to 0.98. However, the agreement between measurements is variable. The regression analysis of the entire data set of measurements in SAPHIR yields slopes between 0.69 to 1.26 and intercepts are smaller than typical atmospheric daytime concentrations (less than 1 pptv). The quality of fit parameters improves significantly, when data are grouped into data subsets of similar water vapor concentrations. Because measurements of LIF instruments were corrected for a well-characterized water dependence of their sensitivities, this indicates that an unknown factor related to water vapor affected measurements in SAPHIR. Measurements in ambient air are also well-correlated, but regression parameters differ from results obtained from SAPHIR experiments. This could have been caused by differences in HO<sub>2</sub> concentrations in the sampled air at the slightly different locations of instruments
Does community-based education increase students' motivation to practice community health care? - a cross sectional study
<p>Abstract</p> <p>Background</p> <p>Community-based education has been introduced in many medical schools around the globe, but evaluation of instructional quality has remained a critical issue. Community-based education is an approach that aims to prepare students for future professional work at the community level. Instructional quality should be measured based on a program's outcomes. However, the association between learning activities and students' attitudes is unknown. The purpose of this study was to clarify what learning activities affect students' attitudes toward community health care.</p> <p>Methods</p> <p>From 2003 to 2009, self-administered pre- and post-questionnaire surveys were given to 693 fifth-year medical students taking a 2-week clinical clerkship. Main items measured were student attitudes, which were: "I think practicing community health care is worthwhile" ("worthwhile") and "I am confident about practicing community health care" ("confidence") using a visual analogue scale (0-100). Other items were gender, training setting, and learning activities. We analyzed the difference in attitudes before and after the clerkships by paired <it>t </it>test and the factors associated with a positive change in attitude by logistic regression analysis.</p> <p>Results</p> <p>Six hundred forty-five students (93.1%), 494 (76.6%) male and 151(23.4%) female, completed the pre- and post-questionnaires. The VAS scores of the students' attitudes for "worthwhile" and "confidence" after the clerkship were 80.2 ± 17.4 and 57.3 ± 20.1, respectively. Both of the scores increased after the clerkship. Using multivariate logistic regression analysis, "health education" was associated with a positive change for both attitudes of "worthwhile" (adjusted RR: 1.71, 95% CI: 1.10-2.66) and "confidence" (1.56, 1.08-2.25).</p> <p>Conclusions</p> <p>Community-based education motivates students to practice community health care. In addition, their motivation is increased by the health education activity. Participating in this activity probably produces a positive effect and improves the instructional quality of the program based on its outcomes.</p
First direct measurements of formaldehyde flux via eddy covariance: implications for missing in-canopy formaldehyde sources
We report the first observations of formaldehyde (HCHO) flux measured via eddy covariance, as well as HCHO concentrations and gradients, as observed by the Madison Fiber Laser-Induced Fluorescence Instrument during the BEACHON-ROCS 2010 campaign in a rural, Ponderosa Pine forest northwest of Colorado Springs, CO. A median noon upward flux of ~80 &mu;g m<sup>&minus;2</sup> h<sup>&minus;1</sup> (~24 ppt<sub>v</sub> m s<sup>&minus;1</sup>) was observed with a noon range of 37 to 131 &mu;g m<sup>&minus;2</sup> h<sup>&minus;1</sup>. Enclosure experiments were performed to determine the HCHO branch (3.5 &mu;g m<sup>-2</sup> h<sup>&minus;1</sup>) and soil (7.3 &mu;g m<sup>&minus;2</sup> h<sup>&minus;1</sup>) direct emission rates in the canopy. A zero-dimensional canopy box model, used to determine the apportionment of HCHO source and sink contributions to the flux, underpredicted the observed HCHO flux by a factor of 6. Simulated increases in concentrations of species similar to monoterpenes resulted in poor agreement with measurements, while simulated increases in direct HCHO emissions and/or concentrations of species similar to 2-methyl-3-buten-2-ol best improved model/measurement agreement. Given the typical diurnal variability of these BVOC emissions and direct HCHO emissions, this suggests that the source of the missing flux is a process with both a strong temperature and radiation dependence
Missing peroxy radical sources within a summertime ponderosa pine forest
Organic peroxy (RO<sub>2</sub>) and hydroperoxy (HO<sub>2</sub>) radicals are key
intermediates in the photochemical processes that generate ozone, secondary
organic aerosol and reactive nitrogen reservoirs throughout the troposphere.
In regions with ample biogenic hydrocarbons, the richness and complexity of
peroxy radical chemistry presents a significant challenge to
current-generation models, especially given the scarcity of measurements in
such environments. We present peroxy radical observations acquired within a
ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere
interactions of Energy, Aerosols, Carbon, H<sub>2</sub>O, Organics and Nitrogen –
Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total peroxy radical
mixing ratios reach as high as 180 pptv (parts per trillion by volume) and are among the highest yet
recorded. Using the comprehensive measurement suite to constrain a
near-explicit 0-D box model, we investigate the sources, sinks and
distribution of peroxy radicals below the forest canopy. The base chemical
mechanism underestimates total peroxy radicals by as much as a factor of 3.
Since primary reaction partners for peroxy radicals are either measured (NO)
or underpredicted (HO<sub>2</sub> and RO<sub>2</sub>, i.e., self-reaction), missing
sources are the most likely explanation for this result. A close comparison
of model output with observations reveals at least two distinct source
signatures. The first missing source, characterized by a sharp midday
maximum and a strong dependence on solar radiation, is consistent with
photolytic production of HO<sub>2</sub>. The diel profile of the second missing
source peaks in the afternoon and suggests a process that generates RO<sub>2</sub>
independently of sun-driven photochemistry, such as ozonolysis of reactive
hydrocarbons. The maximum magnitudes of these missing sources
(~120 and 50 pptv min<sup>−1</sup>, respectively) are consistent
with previous observations alluding to unexpectedly intense oxidation within
forests. We conclude that a similar mechanism may underlie many such
observations
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