We present a novel and compact design of a constant-pressure inlet (CPI) developed for use in airborne aerosol mass spectrometry. In particular, the inlet system is optimized for aerodynamic lenses ...commonly used in aerosol mass spectrometers, in which efficient focusing of aerosol particles into a vacuum chamber requires a precisely controlled lens pressure, typically of a few hectopascals. The CPI device can also be used in condensation particle counters (CPCs), cloud condensation nucleus counters (CCNCs), and gas-phase sampling instruments across a wide range of altitudes and inlet pressures. The constant pressure is achieved by changing the inner diameter of a properly scaled O-ring that acts as a critical orifice. The CPI control keeps air pressure and thereby mass flow rate (≈0.1 L min−1) upstream of an aerodynamic lens constant, deviating at most by only ±2 % from a preset value. In our setup, a pressure sensor downstream of the O-ring maintains control of the pinch mechanism via a feedback loop and setpoint conditions are reached within seconds. The device was implemented in a few instruments, which were successfully operated on different research aircraft covering a wide range of ambient pressures, from sea level up to about 55 hPa. Details of operation and the quality of aerosol particle transmission were evaluated by laboratory experiments and in-flight data with a single-particle mass spectrometer.
To understand the intrinsic properties of peptides, which are determined by factors such as intramolecular hydrogen bonding, van der Waals bonding and electrostatic interactions, the conformational ...landscape of isolated protein building blocks in the gas phase was investigated. Here, we present IR‐UV double‐resonance spectra of jet‐cooled, uncapped peptides containing a tryptophan (Trp) UV chromophore in the 1000–2000 cm−1 spectral range. In the series Trp, Trp‐Gly and Trp‐Gly‐Gly (where Gly stands for glycine), the number of detected conformers was found to decrease from six (Snoek et al., PCCP, 2001, 3, 1819) to four and two, respectively, which indicates a trend to relaxation to a global minimum. Density functional theory calculations reveal that the OH in‐plane bending vibration, together with the NH in‐plane bending and the peptide CO stretching vibrations, is a sensitive probe to hydrogen bonding and, thus, to the folding of the peptide backbone in these structures. This enables the identification of spectroscopic fingerprints for the various conformational structures. By comparing the experimentally observed IR spectra with the calculated spectra, a unique conformational assignment can be made in most cases. The IR‐UV spectrum of a Trp‐containing nonapeptide (Trp‐Ala‐Gly‐Gly‐Asp‐Ala‐Ser‐Gly‐Glu) was recorded as well and, although the IR spectrum is less well‐resolved (and it probably results from different isomers), groups of amide I (peptide CO stretching) and amide II (NH in‐plane bending) bands can still be recognised, in agreement with predictions at the AM1 level.
Folding of peptides: Infrared spectra of unprotected peptides containing tryptophan were measured in the gas phase. The number of detected conformers decreased with peptide size, which indicated a trend toward relaxation to a global minimum. The combination of IR data with theoretical calculations allowed the distinction between stretched and folded conformations of the peptides (see Figure).
The aim of this study is to show how a newly developed aerodynamic lens system (ALS), a delayed ion extraction (DIE), and better electric shielding improve the efficiency of the Aircraft-based Laser ...ABlation Aerosol MAss spectrometer (ALABAMA). These improvements are applicable to single-particle laser ablation mass spectrometers in general. To characterize the modifications, extensive size-resolved measurements with spherical polystyrene latex particles (PSL; 150–6000 nm) and cubic sodium chloride particles (NaCl; 400–1700 nm) were performed. Measurements at a fixed ALS position show an improved detectable particle size range of the new ALS compared to the previously used Liu-type ALS, especially for supermicron particles. At a lens pressure of 2.4 hPa, the new ALS achieves a PSL particle size range from 230 to 3240 nm with 50 % detection efficiency and between 350 and 2000 nm with 95 % detection efficiency. The particle beam divergence was determined by measuring the detection efficiency at variable ALS positions along the laser cross sections and found to be minimal for PSL at about 800 nm. Compared to measurements by single-particle mass spectrometry (SPMS) instruments using Liu-type ALSs, the minimum particle beam divergence is shifted towards larger particle sizes. However, there are no disadvantages compared to the Liu-type lenses for particle sizes down to 200 nm. Improvements achieved by using the DIE and an additional electric shielding could be evaluated by size-resolved measurements of the hit rate, which is the ratio of laser pulses yielding a detectable amount of ions to the total number of emitted laser pulses. In particular, the hit rate for multiply charged particles smaller than 500 nm is significantly improved by preventing an undesired deflection of these particles in the ion extraction field. Moreover, it was found that by using the DIE the ion yield of the ablation, ionization, and ion extraction process could be increased, resulting in up to 7 times higher signal intensities of the cation spectra. The enhanced ion yield results in a larger effective width of the ablation laser beam, which in turn leads to a hit rate of almost 100 % for PSL particles in the size range from 350 to 2000 nm. Regarding cubic NaCl particles the modifications of the ALABAMA result in an up to 2 times increased detection efficiency and an up to 5 times increased hit rate. The need for such instrument modifications arises in particular for measurements of particles that are present in low number concentrations such as ice-nucleating particles (INPs) in general, but also aerosol particles at high altitudes or in pristine environments. Especially for these low particle number concentrations, improved efficiencies help to overcome the statistical limitations of single-particle mass spectrometer measurements. As an example, laboratory INP measurements carried out in this study show that the application of the DIE alone increases the number of INP mass spectra per time unit by a factor of 2 to 3 for the sampled substances. Overall, the combination of instrument modifications presented here resulted in an increased measurement efficiency of the ALABAMA for different particle types and particles shape as well as for highly charged particles.
We analyse aerosol particle composition measurements from five research missions between 2014 and 2018 to assess the meridional extent of particles
containing meteoric material in the upper ...troposphere and lower stratosphere (UTLS). Measurements from the Jungfraujoch mountaintop site and a
low-altitude aircraft mission show that meteoric material is also present within middle- and lower-tropospheric aerosol but within only a very small
proportion of particles. For both the UTLS campaigns and the lower- and mid-troposphere observations, the measurements were conducted with single-particle laser ablation mass spectrometers with bipolar-ion detection, which enabled us to measure the chemical composition of particles in a diameter
range of approximately 150 nm to 3 µm. The five UTLS aircraft missions cover a latitude range from 15 to 68∘ N,
altitudes up to 21 km, and a potential temperature range from 280 to 480 K. In total, 338 363 single particles were analysed, of
which 147 338 were measured in the stratosphere. Of these total particles, 50 688 were characterized by high abundances of magnesium and iron,
together with sulfuric ions, the vast majority (48 610) in the stratosphere, and are interpreted as meteoric material immersed or dissolved within
sulfuric acid. It must be noted that the relative abundance of such meteoric particles may be overestimated by about 10 % to 30 % due to the
presence of pure sulfuric acid particles in the stratosphere which are not detected by the instruments used here. Below the tropopause, the observed
fraction of the meteoric particle type decreased sharply with 0.2 %–1 % abundance at Jungfraujoch, and smaller abundances
(0.025 %–0.05 %) were observed during the lower-altitude Canadian Arctic aircraft measurements. The size distribution of the meteoric sulfuric
particles measured in the UTLS campaigns is consistent with earlier aircraft-based mass-spectrometric measurements, with only 5 %–10 %
fractions in the smallest particles detected (200–300 nm diameter) but with substantial (> 40 %) abundance fractions for particles
from 300–350 up to 900 nm in diameter, suggesting sedimentation is the primary loss mechanism. In the tropical lower stratosphere, only a
small fraction (< 10 %) of the analysed particles contained meteoric material. In contrast, in the extratropics the observed fraction of
meteoric particles reached 20 %–40 % directly above the tropopause. At potential temperature levels of more than 40 K above the
thermal tropopause, particles containing meteoric material were observed in much higher relative abundances than near the tropopause, and, at these
altitudes, they occurred at a similar abundance fraction across all latitudes and seasons measured. Above 440 K, the observed fraction of meteoric
particles is above 60 % at latitudes between 20 and 42∘ N. Meteoric smoke particles are transported from the mesosphere into the
stratosphere within the winter polar vortex and are subsequently distributed towards low latitudes by isentropic mixing, typically below a potential temperature of 440 K. By contrast, the findings from the UTLS measurements show that meteoric material is found in stratospheric
aerosol particles at all latitudes and seasons, which suggests that either isentropic mixing is effective also above 440 K or that meteoric
fragments may be the source of a substantial proportion of the observed meteoric material.
Venous thromboembolism (VTE) is a leading cause of morbidity and mortality in elderly people. Increased expression of tumor suppressor protein 53 (p53) has been implicated in vascular senescence. ...Here, we examined the importance of endothelial p53 for venous thrombosis and whether endothelial senescence and p53 overexpression are involved in the exponential increase of VTE with age. Mice with conditional, endothelial-specific deletion of p53 (End.p53-KO) and their wild-type littermates (End.p53-WT) underwent subtotal inferior vena cava (IVC) ligation to induce venous thrombosis. IVC ligation in aged (12-month-old) End.p53-WT mice resulted in higher rates of thrombus formation and greater mean thrombus size vs adult (12-week-old) End.p53-WT mice, whereas aged End.p53-KO mice were protected from vein thrombosis. Analysis of primary endothelial cells from aged mice or human vein endothelial cells after induction of replicative senescence revealed significantly increased early growth response gene-1 (Egr1) and heparanase expression, and plasma factor Xa levels were elevated in aged End.p53-WT, but not in End.p53-KO mice. Increased endothelial Egr1 and heparanase expression also was observed after doxorubicin-induced p53 overexpression, whereas p53 inhibition using pifithrin-α reduced tissue factor (TF) expression. Importantly, inhibition of heparanase activity using TF pathway inhibitor-2 (TFPI2) peptides prevented the enhanced venous thrombus formation in aged mice and restored it to the thrombotic phenotype of adult mice. Our findings suggest that p53 accumulation and heparanase overexpression in senescent endothelial cells are critically involved in mediating the increased risk of venous thrombosis with age and that heparanase antagonization may be explored as strategy to ameliorate the prothrombotic endothelial phenotype with age.
•Deletion of p53 in endothelial cells prevents venous thrombosis in aged, but not in adult, mice.•Neutralization of heparanase in aged mice using TFPI2 peptides restores the thrombotic phenotype of adult mice.
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High-end infotainment units for the Automotive domain have to provide a huge set of features, implemented in complex software on distributed embedded system hardware. In order to analyse the ...computational resources necessary for such systems, abstract models can be created which are used as a starting point for simulation and static analysis methods. In this paper, a domain-specific modeling method and derived analysis methods will be presented. A real-world scenario will be shown which could also serve as a challenging example for future tools and formal methods.
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