Coulomb crystal mass spectrometry in a digital ion trap

We present a mass spectrometric technique for identifying the masses and relative abundances of Coulomb-crystallized ions held in a linear Paul trap. A digital radio-frequency wave form is employed to generate the trapping potential, as this can be cleanly switched off, and static dipolar fields are subsequently applied to the trap electrodes for ion ejection. Close to 100% detection efficiency is demonstrated for Ca+ and CaF+ ions from bicomponent Ca+ − CaF+ Coulomb crystals prepared by the reaction of Ca+ with CH3F. A quantitative linear relationship is observed between ion number and the corresponding integrated time-of-flight (TOF) peak, independent of the ionic species. The technique is applicable to a diverse range of multicomponent Coulomb crystals—demonstrated here for Ca+ − NH3+ − NH4+ and Ca+ − CaOH+ − CaOD+ crystals—and will facilitate the measurement of ion-molecule reaction rates and branching ratios in complicated reaction systems

Using a direct simulation Monte Carlo approach to model collisions in a buffer gas cell

A direct simulation Monte Carlo (DSMC) method is applied to model collisions between He buffer gas atoms and ammonia molecules within a buffer gas cell. State-tostate cross sections, calculated as a function of collision energy, enable the inelastic collisions between He and NH3 to be considered explicitly. The inclusion of rotationalstate-changing collisions affects the translational temperature of the beam, indicating that elastic and inelastic processes should not be considered in isolation. The properties of the cold molecular beam exiting the cell are examined as a function of the cell parameters and operating conditions; the rotational and translational energy distributions and are in accord with experimental measurements. The DSMC calculations show that thermalisation occurs well within the typical 10-20 mm length of many buffer gas cells, suggesting that shorter cells could be employed in many instances – yielding a higher flux of cold molecules

Zeeman deceleration beyond periodic phase space stability

In Zeeman deceleration, time-varying spatially-inhomogeneous magnetic fields are used to create packets of translationally cold, quantum-state-selected paramagnetic particles with a tuneable forward velocity, which are ideal for cold reaction dynamics studies. Here, the covariance matrix adaptation evolutionary strategy (CMA-ES) is adopted in order to optimise deceleration switching sequences for the operation of a Zeeman decelerator. Using the optimised sequences, a 40% increase in the number of decelerated particles is observed compared to standard sequences for the same final velocity, imposing the same experimental boundary conditions. Furthermore, we demonstrate that it is possible to remove up to 98% of the initial kinetic energy of particles in the incoming beam, compared to the removal of a maximum of 83% of kinetic energy with standard sequences. Three-dimensional particle trajectory simulations are employed to reproduce the experimental results and to investigate differences in the deceleration mechanism adopted by standard and optimised sequences. It is experimentally verified that the optimal solution uncovered by the evolutionary algorithm is not merely a local optimisation of the experimental parameters { it is a novel mode of operation that goes beyond the standard periodic phase stability approach typically adopted

UK greenhouse gas measurements at two new tall towers for aiding emissions verification

Abstract. Under the UK focused Greenhouse gAs and Uk and Global Emissions (GAUGE) project, two new tall tower greenhouse gas (GHG) observation sites were established in the 2013/2014 Northern Hemispheric winter. These sites were located at two existing telecommunications towers, Heathfield (HFD) and Bilsdale (BSD), utilised a combination of cavity ring-down spectroscopy (CRDS) and gas chromatography (GC) to measure key GHGs (CO2, CH4, CO, N2O and SF6). Measurements were made at multiple intake heights on each tower. The inclusion of the two additional tower stations within the existing UK Deriving Emissions linked to Climate Change (DECC) network of four stations was found to reduce the uncertainty of CH4 UK emission estimates by between 10–20 %. CO2 and CH4 dry mole fractions were calculated from either CRDS measurements of wet air which were post corrected with an instrument specific empirical correction or samples dried to between 0.05 and 0.3 % H2O using a Nafion dryer, with a smaller correction applied for the residual H2O. The impact of these two drying strategies was examined. Drying with a Nafion drier was not found to have a significant effect on the observed CH4 mole fraction; however, Nafion drying did cause a 0.02 µmol mol−1 CO2 bias. This bias was stable with sample CO2 mole fractions between 373 and 514 µmol mol−1 and for sample H2O up to 3.5 %. As the calibration and standard gases are treated in the same manner, this error is mostly calibrated out with the residual error below the World Meteorological Organization’s (WMO) reproducibility requirements. Of more concern was the error associated with both default factory and empirical instrument specific water correction algorithms. These corrections are relatively stable and reproducible for samples with H2O between 0.2 and 2.5 %, CO2 between 345 and 449 µmol mol−1 and CH4 between 1743 and 2145 nmol mol−1. However, the residual errors in these corrections increase to &gt; 0.05 µmol mol−1 for CO2 and &gt; 1 nmol mol−1 for CH4 (greater than the WMO internal reproducibility guidelines) at higher humidities and for samples with very low ( </jats:p

Early Target Cells of Measles Virus after Aerosol Infection of Non-Human Primates

Measles virus (MV) is highly infectious, and has long been thought to enter the host by infecting epithelial cells of the respiratory tract. However, epithelial cells do not express signaling lymphocyte activation molecule (CD150), which is the high-affinity cellular receptor for wild-type MV strains. We have generated a new recombinant MV strain expressing enhanced green fluorescent protein (EGFP), based on a wild-type genotype B3 virus isolate from Khartoum, Sudan (KS). Cynomolgus macaques were infected with a high dose of rMVKSEGFP by aerosol inhalation to ensure that the virus could reach the full range of potential target cells throughout the entire respiratory tract. Animals were euthanized 2, 3, 4 or 5 days post-infection (d.p.i., n = 3 per time point) and infected (EGFP+) cells were identified at all four time points, albeit at low levels 2 and 3 d.p.i. At these earliest time points, MV-infected cells were exclusively detected in the lungs by fluorescence microscopy, histopathology and/or virus isolation from broncho-alveolar lavage cells. On 2 d.p.i., EGFP+ cells were phenotypically typed as large mononuclear cells present in the alveolar lumen or lining the alveolar epithelium. One to two days later, larger clusters of MV-infected cells were detected in bronchus-associated lymphoid tissue (BALT) and in the tracheo-bronchial lymph nodes. From 4 d.p.i. onward, MV-infected cells were detected in peripheral blood and various lymphoid tissues. In spite of the possibility for the aerosolized virus to infect cells and lymphoid tissues of the upper respiratory tract, MV-infected cells were not detected in either the tonsils or the adenoids until after onset of viremia. These data strongly suggest that in our model MV entered the host at the alveolar level by infecting macrophages or dendritic cells, which traffic the virus to BALT or regional lymph nodes, resulting in local amplification and subsequent systemic dissemination by viremia

Using a direct simulation Monte Carlo approach to model collisions in a buffer gas cell - supporting material

The dataset includes results from our direct simulation Monte Carlo (DSMC) modelling of the collisions between buffer gas atoms and ammonia molecules within a buffer gas cell. Both elastic and inelastic collisions are considered, through the inclusion of energy-dependent state-to-state collision cross sections. The properties of the resulting molecular beam are examined as a function of cell parameters and operating conditions – yielding good agreement with available experimental measurements. This study represents an important extension of previous investigations into buffer-gas cooling. We demonstrate that thermalisation occurs well within the typical 10-20mm length of typical experimental buffer gas cells, suggesting that a shorter cell could be employed in many applications. Our DSMC calculations indicate that shorter cells would achieve comparable molecular beam properties (translational and rotational temperature) with the benefit of significantly increased molecular density. The data were created from 2015-2016 and are discussed in detail in the accompanying publication. The labelling of each data file corresponds to the labelling adopted for the associated figure in the publicatio

Using a direct simulation Monte Carlo approach to model collisions in a buffer gas cell - supporting material

The dataset includes results from our direct simulation Monte Carlo (DSMC) modelling of the collisions between buffer gas atoms and ammonia molecules within a buffer gas cell. Both elastic and inelastic collisions are considered, through the inclusion of energy-dependent state-to-state collision cross sections. The properties of the resulting molecular beam are examined as a function of cell parameters and operating conditions – yielding good agreement with available experimental measurements. This study represents an important extension of previous investigations into buffer-gas cooling. We demonstrate that thermalisation occurs well within the typical 10-20mm length of typical experimental buffer gas cells, suggesting that a shorter cell could be employed in many applications. Our DSMC calculations indicate that shorter cells would achieve comparable molecular beam properties (translational and rotational temperature) with the benefit of significantly increased molecular density. The data were created from 2015-2016 and are discussed in detail in the accompanying publication. The labelling of each data file corresponds to the labelling adopted for the associated figure in the publicatio

Simulating rotationally inelastic collisions using a direct simulation Monte Carlo method

A new approach to simulating rotational cooling using a Direct Simulation Monte Carlo (DSMC) method is described and applied to the rotational cooling of ammonia seeded into a helium supersonic jet. The method makes use of {\it ab initio} rotational state changing cross sections calculated as a function of collision energy. Each particle in the DSMC simulations is labelled with a vector of rotational populations that evolves with time. Transfer of energy into translation is calculated from the mean energy transfer for this population at the specified collision energy. The simulations are compared with a continuum model for the on-axis density, temperature and velocity; rotational temperature as a function of distance from the nozzle is in accord with expectations from experimental measurements. The method could be applied to other types of gas mixture dynamics under non-uniform conditions, such as buffer gas cooling of NH$_3$ by He. Cross sections for He NH3 rotationally inelastic collisions in text file format. Results from a direct simulation Monte Carlo simulation of a supersonic expansion in HDF5 format. Python scripts to generate paper figures from simulation results

IL-23 provides a limited mechanism of resistance to acute toxoplasmosis in the absence of IL-12.

Submitted by Ana Maria Fiscina Sampaio ([email protected]) on 2015-06-18T11:51:16Z No. of bitstreams: 1 Lieberman LA IL-23 provides....pdf: 929125 bytes, checksum: 6f9a33a870555fbaba0aeddd40ceb3a9 (MD5)Approved for entry into archive by Ana Maria Fiscina Sampaio ([email protected]) on 2015-06-18T12:03:24Z (GMT) No. of bitstreams: 1 Lieberman LA IL-23 provides....pdf: 929125 bytes, checksum: 6f9a33a870555fbaba0aeddd40ceb3a9 (MD5)Made available in DSpace on 2015-06-18T12:03:24Z (GMT). No. of bitstreams: 1 Lieberman LA IL-23 provides....pdf: 929125 bytes, checksum: 6f9a33a870555fbaba0aeddd40ceb3a9 (MD5) Previous issue date: 2004University of Pennsylvania. School of Veterinary Medicine. Department of Pathobiology. Philadelphia, PAFundação Oswaldo Cruz. Centro de Pesquisas Gonçalo Moniz. Salvador, BA, BrasilDNAX Research Institute. Discovery Research. Palo Alto, CADNAX Research Institute. Discovery Research. Palo Alto, CADNAX Research Institute. Discovery Research. Palo Alto, CADNAX Research Institute. Discovery Research. Palo Alto, CAUniversity of Pennsylvania. School of Veterinary Medicine. Department of Pathobiology. Philadelphia, PAIL-23 and IL-12 are heterodimeric cytokines which share the p40 subunit, but which have unique second subunits, IL-23p19 and IL-12p35. Since p40 is required for the development of the Th1 type response necessary for resistance to Toxoplasma gondii, studies were performed to assess the role of IL-23 in resistance to this pathogen. Increased levels of IL-23 were detected in mice infected with T. gondii and in vitro stimulation of dendritic cells with this pathogen resulted in increased levels of mRNA for this cytokine. To address the role of IL-23 in resistance to T. gondii, mice lacking the p40 subunit (common to IL-12 and IL-23) and mice that lack IL-12 p35 (specific for IL-12) were infected and their responses were compared. These studies revealed that p40 / mice rapidly succumbed to toxoplasmosis, while p35 / mice displayed enhanced resistance though they eventually succumbed to this infection. In addition, the administration of IL-23 to p40 / mice infected with T. gondii resulted in a decreased parasite burden and enhanced resistance. However, the enhanced resistance of p35 / mice or p40 / mice treated with IL-23 was not associated with increased production of IFN- . When IL-23p19 / mice were infected with T. gondii these mice developed normal T cell responses and controlled parasite replication to the same extent as wild-type mice. Together, these studies indicate that IL-12, not IL-23, plays a dominant role in resistance to toxoplasmosis but, in the absence of IL-12, IL-23 can provide a limited mechanism of resistance to this infection