1,628 research outputs found
Characterization of the South Atlantic marine boundary layer aerosol using an Aerodyne Aerosol Mass Spectrometer
International audienceMeasurements of the submicron fraction of the atmospheric aerosol in the marine boundary layer were performed from January to March 2007 (Southern Hemisphere summer) onboard the French research vessel Marion Dufresne in the Southern Atlantic and Indian Ocean (20° S?60° S, 70° W?60° E). For chemical composition measurements an Aerodyne High-Resolution-Time-of-Flight AMS was used to measure mass concentrations and species-resolved size distributions of non-refractory aerosol components in the submicron range. Within the "standard" AMS compounds (ammonium, chloride, nitrate, sulfate, organics) "sulfate" is the dominating species in the marine boundary layer reaching concentrations between 50 ng m?3 and 3 ?g m?3. Furthermore, what is seen as "sulfate" by the AMS seems to be mostly sulfuric acid. Another sulfur containing species that can ubiquitously be found in marine environments is methanesulfonic acid (MSA). Since MSA has not been directly measured before with an AMS, and is not part of the standard AMS analysis, laboratory experiments needed to be performed in order to be able to identify it within the AMS raw data and to extract mass concentrations for MSA from the field measurements. To identify characteristic air masses and their source regions backwards trajectories were used and averaged concentrations for AMS standard compounds were calculated for each air mass type. Sulfate mass size distributions were measured for these periods showing a distinct difference between oceanic air masses and those from African outflow. While the peak size in the mass distribution was roughly 250 nm in marine air masses it was shifted to 470 nm in African outflow air. Correlations between the mass concentrations of sulfate, organics and MSA were calculated which show a narrow correlation for MSA with sulfate/sulfuric acid coming from the ocean but not with continental sulfate
Analysis of chromosome positions in the interphase nucleus of Chinese hamster cells by laser-UV-microirradiation experiments
Unsynchronized cells of an essentially diploid strain of female Chinese hamster cells derived from lung tissue (CHL) were laser-UV-microirradiated (=257 nm) in the nucleus either at its central part or at its periphery. After 7â9 h postincubation with 0.5 mM caffeine, chromosome preparations were made in situ. Twenty-one and 29 metaphase spreads, respectively, with partial chromosome shattering (PCS) obtained after micro-irradiation at these two nuclear sites, were Q-banded and analyzed in detail. A positive correlation was observed between the frequency of damage of chromosomes and both their DNA content and length at metaphase. No significant difference was observed between the frequencies of damage obtained for individual chromosomes at either site of microirradiation. The frequency of joint damage of homologous chromosomes was low as compared to nonhomologous ones. Considerable variation was noted in different cells in the combinations of jointly shattered chromosomes. Evidence which justifies an interpretation of these data in terms of an interphase arrangement of chromosome territories is discussed. Our data strongly argue against somatic pairing as a regular event, and suggest a considerable variability of chromosome positions in different nuclei. However, present data do not exclude the possibility of certain non-random chromosomal arrangements in CHL-nuclei. The interphase chromosome distribution revealed by these experiments is compared with centromere-centromere, centromere-center and angle analyses of metaphase spreads and the relationship between interphase and metaphase arrangements of chromosomes is discussed
Investigating organic aerosol loading in the remote marine environment
Aerosol loading in the marine environment is investigated using aerosol composition measurements from several research ship campaigns (ICEALOT, MAP, RHaMBLe, VOCALS and OOMPH), observations of total AOD column from satellite (MODIS) and ship-based instruments (Maritime Aerosol Network, MAN), and a global chemical transport model (GEOS-Chem). This work represents the most comprehensive evaluation of oceanic OM emission inventories to date, by employing aerosol composition measurements obtained from campaigns with wide spatial and temporal coverage. The model underestimates AOD over the remote ocean on average by 0.02 (21 %), compared to satellite observations, but provides an unbiased simulation of ground-based Maritime Aerosol Network (MAN) observations. Comparison with cruise data demonstrates that the GEOS-Chem simulation of marine sulfate, with the mean observed values ranging between 0.22 ÎŒg mâ3 and 1.34 ÎŒg mâ3, is generally unbiased, however surface organic matter (OM) concentrations, with the mean observed concentrations between 0.07 ÎŒg mâ3 and 0.77 ÎŒg mâ3, are underestimated by a factor of 2â5 for the standard model run. Addition of a sub-micron marine OM source of approximately 9 TgC yrâ1 brings the model into agreement with the ship-based measurements, however this additional OM source does not explain the model underestimate of marine AOD. The model underestimate of marine AOD is therefore likely the result of a combination of satellite retrieval bias and a missing marine aerosol source (which exhibits a different spatial pattern than existing aerosol in the model)
Confinement effects on glass forming liquids probed by DMA
Many molecular glass forming liquids show a shift of the glass transition T-g
to lower temperatures when the liquid is confined into mesoporous host
matrices. Two contrary explanations for this effect are given in literature:
First, confinement induced acceleration of the dynamics of the molecules leads
to an effective downshift of T-g increasing with decreasing pore size. Second,
due to thermal mismatch between the liquid and the surrounding host matrix,
negative pressure develops inside the pores with decreasing temperature, which
also shifts T-g to lower temperatures. Here we present dynamic mechanical
analysis measurements of the glass forming liquid salol in Vycor and Gelsil
with pore sizes of d=2.6, 5.0 and 7.5 nm. The dynamic complex elastic
susceptibility data can be consistently described with the assumption of two
relaxation processes inside the pores: A surface induced slowed down relaxation
due to interaction with rough pore interfaces and a second relaxation within
the core of the pores. This core relaxation time is reduced with decreasing
pore size d, leading to a downshift of T-g proportional to 1/d in perfect
agreement with recent differential scanning calorimetry (DSC) measurements.
Thermal expansion measurements of empty and salol filled mesoporous samples
revealed that the contribution of negative pressure to the downshift of T-g is
small (<30%) and the main effect is due to the suppression of dynamically
correlated regions of size xi when the pore size xi approaches
Exchange Monte Carlo Method and Application to Spin Glass Simulations
We propose an efficient Monte Carlo algorithm for simulating a
``hardly-relaxing" system, in which many replicas with different temperatures
are simultaneously simulated and a virtual process exchanging configurations of
these replica is introduced. This exchange process is expected to let the
system at low temperatures escape from a local minimum. By using this algorithm
the three-dimensional Ising spin glass model is studied. The ergodicity
time in this method is found much smaller than that of the multi-canonical
method. In particular the time correlation function almost follows an
exponential decay whose relaxation time is comparable to the ergodicity time at
low temperatures. It suggests that the system relaxes very rapidly through the
exchange process even in the low temperature phase.Comment: 10 pages + uuencoded 5 Postscript figures, REVTe
The clinical effectiveness of transurethral incision of the prostate : a systematic review of randomised controlled trials
The original publication is available at www.springerlink.com.Peer reviewedPostprin
Qweak: A Precision Measurement of the Proton's Weak Charge
The Qweak experiment at Jefferson Lab aims to make a 4% measurement of the
parity-violating asymmetry in elastic scattering at very low of a
longitudinally polarized electron beam on a proton target. The experiment will
measure the weak charge of the proton, and thus the weak mixing angle at low
energy scale, providing a precision test of the Standard Model. Since the value
of the weak mixing angle is approximately 1/4, the weak charge of the proton
is suppressed in the Standard Model, making it
especially sensitive to the value of the mixing angle and also to possible new
physics. The experiment is approved to run at JLab, and the construction plan
calls for the hardware to be ready to install in Hall C in 2007. The
theoretical context of the experiment and the status of its design are
discussed.Comment: 5 pages, 2 figures, LaTeX2e, to be published in CIPANP 2003
proceeding
ifo Konjunkturprognose 2011/2012: Schuldenkrise bremst deutsche Wirtschaft aus
Am 14. Dezember 2011 stellte das ifo Institut im Rahmen seines vorweihnachtlichen PressegesprĂ€chs seine Prognose fĂŒr die Jahre 2011 und 2012 vor. In Deutschland ist das Bruttoinlandsprodukt bis zuletzt deutlich gestiegen. Der ifo GeschĂ€ftsklimaindex und andere FrĂŒhindikatoren zeigen jedoch an, dass der deutschen Konjunktur ein Abschwung bevorsteht. MaĂgeblich hierfĂŒr sind die sich abschwĂ€chende Weltwirtschaft und die europĂ€ische Schuldenkrise. Die AbhĂ€ngigkeit der Konjunkturentwicklung von den Entscheidungen der europĂ€ischen Politik erschwert die Prognose erheblich, denn es sind ganz unterschiedliche plausible Szenarien möglich. Unter der Annahme, dass sich die Eurokrise nicht weiter verschĂ€rft und sich insbesondere Italien weiter am Markt finanzieren kann, dĂŒrfte eine Rezession in Deutschland vermieden werden. Dennoch wird das deutsche Bruttoinlandsprodukt 2012 voraussichtlich nur um 0,4% zunehmen. Es ist daher zu erwarten, dass sich der BeschĂ€ftigungsaufbau deutlich verlangsamt. GestĂŒtzt von demographischen Faktoren dĂŒrfte die Arbeitslosenzahl aber noch um 140 000 auf rund 2,8 Mill. Personen zurĂŒckgehen. Dies entspricht einer Arbeitslosenquote von 6,7%. Im Gefolge der schwĂ€cheren Konjunktur wird sich das Tempo des Preisauftriebs abschwĂ€chen; im Jahresdurchschnitt 2012 ist mit einer Inflationsrate von 1,8% zu rechnen. Das staatliche Budgetdefizit in Relation zum nominalen Bruttoinlandsprodukt wird im nĂ€chsten Jahr voraussichtlich bei 0,9% liegen. Es muss betont werden, dass die makroökonomische Unsicherheit nicht zuletzt aus politischen GrĂŒnden derzeit extrem hoch ist. So könnten schon kleine Abweichungen Italiens vom geplanten Konsolidierungskurs zu neuen Verwerfungen an den ohnehin extrem angespannten FinanzmĂ€rkten und kaum abschĂ€tzbaren politischen Reaktionen fĂŒhren. Diese könnten die der Prognose zugrunde liegenden Annahmen schnell obsolet werden lassen. Aus technischer Sicht ist damit die Eintrittswahrscheinlichkeit des Basisszenarios deutlich geringer, als e
Contrasting organic aerosol particles from boreal and tropical forests during HUMPPA-COPEC-2010 and AMAZE-08 using coherent vibrational spectroscopy
We present the vibrational sum frequency generation spectra of organic particles collected in a boreal forest in Finland and a tropical forest in Brazil. These spectra are compared to those of secondary organic material produced in the Harvard Environmental Chamber. By comparing coherent vibrational spectra of a variety of terpene and olefin reference compounds, along with the secondary organic material synthesized in the environmental chamber, we show that submicron aerosol particles sampled in Southern Finland during HUMPPA-COPEC-2010 are composed to a large degree of material similar in chemical composition to synthetic α-pinene-derived material. For material collected in Brazil as part of AMAZE-08, the organic component is found to be chemically complex in the coarse mode but highly uniform in the fine mode. When combined with histogram analyses of the isoprene and monoterpene abundance recorded during the HUMPPA-COPEC-2010 and AMAZE-08 campaigns, the findings presented here indicate that if air is rich in monoterpenes, submicron-sized secondary aerosol particles that form under normal OH and O<sub>3</sub> concentration levels can be described in terms of their hydrocarbon content as being similar to α-pinene-derived model secondary organic aerosol particles. If the isoprene concentration dominates the chemical composition of organic compounds in forest air, then the hydrocarbon component of secondary organic material in the submicron size range is not simply well-represented by that of isoprene-derived model secondary organic aerosol particles but is more complex. Throughout the climate-relevant size range of the fine mode, however, we find that the chemical composition of the secondary organic particle material from such air is invariant with size, suggesting that the particle growth does not change the chemical composition of the hydrocarbon component of the particles in a significant way
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