963 research outputs found
Influence of Lipid Heterogeneity and Phase Behavior on Phospholipase A2 Action at the Single Molecule Level
We monitored the action of phospholipase A2 (PLA2) on L- and
D-dipalmitoylphosphatidylcholine (DPPC) Langmuir monolayers by mounting a
Langmuir-trough on a wide-field fluorescence microscope with single molecule
sensitivity. This made it possible to directly visualize the activity and
diffusion behavior of single PLA2 molecules in a heterogeneous lipid
environment during active hydrolysis. The experiments showed that enzyme
molecules adsorbed and interacted almost exclusively with the fluid region of
the DPPC monolayers. Domains of gel state L-DPPC were degraded exclusively from
the gel-fluid interface where the build-up of negatively charged hydrolysis
products, fatty acid salts, led to changes in the mobility of PLA2. The
mobility of individual enzymes on the monolayers was characterized by single
particle tracking (SPT). Diffusion coefficients of enzymes adsorbed to the
fluid interface were between 3 mu m^2/s on the L-DPPC and 4.6 mu m^/s on the
D-DPPC monolayers. In regions enriched with hydrolysis products the diffusion
dropped to approx. 0.2 mu m^2/s. In addition, slower normal and anomalous
diffusion modes were seen at the L-DPPC gel domain boundaries where hydrolysis
took place. The average residence times of the enzyme in the fluid regions of
the monolayer and on the product domain were between approx. 30 and 220 ms. At
the gel domains it was below the experimental time resolution, i.e. enzymes
were simply reflected from the gel domains back into solution.Comment: 10 pages, 10 figure
Light absorption by marine cyanobacteria affects tropical climate mean state and variability
Observations indicate that positively buoyant marine cyanobacteria, which are abundant
throughout the tropical and subtropical ocean, have a strong local heating effect due to
light absorption at the ocean surface. How these local changes in radiative heating
affect the climate system on the large scale is unclear. We use the Max Planck Institute
Earth System Model (MPI-ESM), include light absorption by cyanobacteria, and find a
considerable cooling effect on tropical sea surface temperature (SST) in the order of
0.5 K on a climatological timescale. This cooling is caused by local shading of
subtropical subsurface water by cyanobacteria that is upwelled at the Equator and in
eastern boundary upwelling systems. Implications for the climate system include a
westward shift of the Walker circulation and a weakening of the Hadley circulation. The
amplitude of the seasonal cycle of SST is increased in large parts of the tropical ocean
by up to 25 %, and the tropical Pacific interannual variability is enhanced by
approx. 20 %. This study emphasizes the sensitivity of the tropical climate system to
light absorption by cyanobacteria due to its regulative effect on tropical SST.
Generally, including phytoplankton-dependent light attenuation instead of a globally
uniform attenuation depth improves some of the major model temperature biases, indicating
the relevance of taking this biophysical feedback into account in climate models.</p
Bell inequalities for entangled kaons and their unitary time evolution
We investigate Bell inequalities for neutral kaon systems from Phi resonance
decay to test local realism versus quantum mechanics. We emphasize the unitary
time evolution of the states, that means we also include all decay product
states, in contrast to other authors. Only this guarantees the use of the
complete Hilbert space. We develop a general formalism for Bell inequalities
including both arbitrary "quasi spin" states and different times; finally we
analyze Wigner-type inequalities. They contain an additional term, a correction
function h, as compared to the spin 1/2 or photon case, which changes
considerably the possibility of quantum mechanics to violate the Bell
inequality. Examples for special "quasi spin" states are given, especially
those which are sensitive to the CP parameters epsilon and epsilon'.Comment: REVTeX, 22 page
Beyond Prejudice as Simple Antipathy: Hostile and Benevolent Sexism Across Cultures
The authors argue that complementary hostile and benevolent componen:s of sexism exist ac ro.ss
cultures. Male dominance creates hostile sexism (HS). but men's dependence on women fosters
benevolent sexism (BS)-subjectively positive attitudes that put women on a pedestal but reinforce their
subordination. Research with 15,000 men and women in 19 nations showed that (a) HS and BS are
coherenl constructs th at correlate positively across nations, but (b) HS predicts the ascription of negative
and BS the ascription of positive traits to women, (c) relative to men, women are more likely to reject
HS than BS. especially when overall levels of sexism in a culture are high, and (d) national averages on
BS and HS predict gender inequal ity across nations. These results challenge prevailing notions of
prejudice as an antipathy in that BS (an affectionate, patronizing ideology) reflects inequality and is a
cross-culturally pervasive complement to HS
Diverse soil carbon dynamics expressed at the molecular level
The stability and potential vulnerability of soil organic matter (SOM) to global change remains incompletely understood due to the complex processes involved in its formation and turnover. Here we combine compound-specific radiocarbon analysis with fraction-specific and bulk-level radiocarbon measurements in order to further elucidate controls on SOM dynamics in a temperate and sub-alpine forested ecosystem. Radiocarbon contents of individual organic compounds isolated from the same soil interval generally exhibit greater variation than those among corresponding operationally-defined fractions. Notably, markedly older ages of long-chain plant leaf wax lipids (n-alkanoic acids) imply that they reflect a highly stable carbon pool. Furthermore, marked 14C variations among shorter- and longer-chain n-alkanoic acid homologues suggest that they track different SOM pools. Extremes in SOM dynamics thus manifest themselves within a single compound class. This exploratory study highlights the potential of compound-specific radiocarbon analysis for understanding SOM dynamics in ecosystems potentially vulnerable to global change
N2O isotopocule measurements using laser spectroscopy:analyzer characterization and intercomparison
For the past two decades, the measurement of nitrous oxide (N2O) isotopocules – isotopically substituted molecules 14N15N16O, 15N14N16O and 14N14N18O of the main isotopic species 14N14N16O – has been a promising technique for understanding N2O production and consumption pathways. The coupling of non-cryogenic and tuneable light sources with different detection schemes, such as direct absorption quantum cascade laser absorption spectroscopy (QCLAS), cavity ring-down spectroscopy (CRDS) and off-axis integrated cavity output spectroscopy (OA-ICOS), has enabled the production of commercially available and field-deployable N2O isotopic analyzers. In contrast to traditional isotope-ratio mass spectrometry (IRMS), these instruments are inherently selective for position-specific 15N substitution and provide real-time data, with minimal or no sample pretreatment, which is highly attractive for process studies.
Here, we compared the performance of N2O isotope laser spectrometers with the three most common detection schemes: OA-ICOS (N2OIA-30e-EP, ABB – Los Gatos Research Inc.), CRDS (G5131-i, Picarro Inc.) and QCLAS (dual QCLAS and preconcentration, trace gas extractor (TREX)-mini QCLAS, Aerodyne Research Inc.). For each instrument, the precision, drift and repeatability of N2O mole fraction [N2O] and isotope data were tested. The analyzers were then characterized for their dependence on [N2O], gas matrix composition (O2, Ar) and spectral interferences caused by H2O, CO2, CH4 and CO to develop analyzer-specific correction functions. Subsequently, a simulated two-end-member mixing experiment was used to compare the accuracy and repeatability of corrected and calibrated isotope measurements that could be acquired using the different laser spectrometers.
Our results show that N2O isotope laser spectrometer performance is governed by an interplay between instrumental precision, drift, matrix effects and spectral interferences. To retrieve compatible and accurate results, it is necessary to include appropriate reference materials following the identical treatment (IT) principle during every measurement. Remaining differences between sample and reference gas compositions have to be corrected by applying analyzer-specific correction algorithms. These matrix and trace gas correction equations vary considerably according to N2O mole fraction, complicating the procedure further. Thus, researchers should strive to minimize differences in composition between sample and reference gases. In closing, we provide a calibration workflow to guide researchers in the operation of N2O isotope laser spectrometers in order to acquire accurate N2O isotope analyses. We anticipate that this workflow will assist in applications where matrix and trace gas compositions vary considerably (e.g., laboratory incubations, N2O liberated from wastewater or groundwater), as well as extend to future analyzer models and instruments focusing on isotopic species of other molecules.ISSN:1867-1381ISSN:1867-854
NO isotopocule measurements using laser spectroscopy: analyzer characterization and intercomparison
For the past two decades, the measurement of nitrous oxide (N2O) isotopocules – isotopically substituted molecules NNO, NNO and NNO of the main isotopic species NNO – has been a promising technique for understanding N2O production and consumption pathways. The coupling of non-cryogenic and tuneable light sources with different detection schemes, such as direct absorption quantum cascade laser absorption spectroscopy (QCLAS), cavity ring-down spectroscopy (CRDS) and off-axis integrated cavity output spectroscopy (OA-ICOS), has enabled the production of commercially available and field-deployable NO isotopic analyzers. In contrast to traditional isotope-ratio mass spectrometry (IRMS), these instruments are inherently selective for position-specific N substitution and provide real-time data, with minimal or no sample pretreatment, which is highly attractive for process studies.
Here, we compared the performance of NO isotope laser spectrometers with the three most common detection schemes: OA-ICOS (NOIA-30e-EP, ABB – Los Gatos Research Inc.), CRDS (G5131-i, Picarro Inc.) and QCLAS (dual QCLAS and preconcentration, trace gas extractor (TREX)-mini QCLAS, Aerodyne Research Inc.). For each instrument, the precision, drift and repeatability of NO mole fraction [NO] and isotope data were tested. The analyzers were then characterized for their dependence on [NO], gas matrix composition (O, Ar) and spectral interferences caused by HO, CO, CH and CO to develop analyzer-specific correction functions. Subsequently, a simulated two-end-member mixing experiment was used to compare the accuracy and repeatability of corrected and calibrated isotope measurements that could be acquired using the different laser spectrometers.
Our results show that NO isotope laser spectrometer performance is governed by an interplay between instrumental precision, drift, matrix effects and spectral interferences. To retrieve compatible and accurate results, it is necessary to include appropriate reference materials following the identical treatment (IT) principle during every measurement. Remaining differences between sample and reference gas compositions have to be corrected by applying analyzer-specific correction algorithms. These matrix and trace gas correction equations vary considerably according to NO mole fraction, complicating the procedure further. Thus, researchers should strive to minimize differences in composition between sample and reference gases. In closing, we provide a calibration workflow to guide researchers in the operation of NO isotope laser spectrometers in order to acquire accurate NO isotope analyses. We anticipate that this workflow will assist in applications where matrix and trace gas compositions vary considerably (e.g., laboratory incubations, NO liberated from wastewater or groundwater), as well as extend to future analyzer models and instruments focusing on isotopic species of other molecules
Measurements of the Generalized Electric and Magnetic Polarizabilities of the Proton at Low Q2 Using the VCS Reaction
The mean square polarizability radii of the proton have been measured for the
first time in a virtual Compton scattering experiment performed at the
MIT-Bates out-of-plane scattering facility. Response functions and
polarizabilities obtained from a dispersion analysis of the data at Q2=0.06
GeV2/c2 are in agreement with O(p3) heavy baryon chiral perturbation theory.
The data support the dominance of mesonic effects in the polarizabilities, and
the increase of beta with increasing Q2 is evidence for the cancellation of
long-range diamagnetism by short-range paramagnetism from the pion cloud
Investigation of the conjectured nucleon deformation at low momentum transfer
We report new precise H measurements at the
resonance at (GeV/c) using the MIT/Bates
out-of-plane scattering (OOPS) facility. The data reported here are
particularly sensitive to the transverse electric amplitude () of the
transition. Analyzed together with previous data yield
precise quadrupole to dipole amplitude ratios and and
for . They give credence to the conjecture of
deformation in hadronic systems favoring, at low , the dominance of
mesonic effects.Comment: 4 pages, 1figur
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