779 research outputs found

    Combustion waves in a model with chain branching reaction and their stability

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    In this paper the travelling wave solutions in the adiabatic model with two-step chain branching reaction mechanism are investigated both numerically and analytically in the limit of equal diffusivity of reactant, radicals and heat. The properties of these solutions and their stability are investigated in detail. The behaviour of combustion waves are demonstrated to have similarities with the properties of nonadiabatic one-step combustion waves in that there is a residual amount of fuel left behind the travelling waves and the solutions can exhibit extinction. The difference between the nonadiabatic one-step and adiabatic two-step models is found in the behaviour of the combustion waves near the extinction condition. It is shown that the flame velocity drops down to zero and a standing combustion wave is formed as the extinction condition is reached. Prospects of further work are also discussed.Comment: pages 32, figures 2

    Variation in Flame Temperature with Burner Stabilization in 1D Premixed Dimethyl Ether/Air Flames Measured by Spontaneous Raman Scattering

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    The flame temperatures in flat, laminar premixed dimethyl ether (DME)/air flames with varying degrees of burner stabilization were measured by spontaneous Raman scattering in a range of equivalence ratio (phi) from 0.6 to 2.0. Three commonly used mechanisms to describe DME oxidation were evaluated by comparing the calculated variation of flame temperature derived from one-dimensional flame calculations as a function of DME/air exit velocity with those obtained from the measurements. The results showed the necessity of incorporating radiative heat losses in the flame calculations. The three mechanisms yield similar results at phi = 0.6 and 2.0, underpredicting the temperatures more than 30 K. Differences between the measured and predicted temperatures for burner-stabilized flames are seen to indicate whether a free-flame burning velocity (S-L) is too high or too low. The results suggest a free-flame burning velocity of similar to 14 cm/s at phi = 0.6, 2 cm/s lower than the mechanisms predicted, and burning velocities closer to 49 and 40 cm/s for phi = 1.0 and 1.4, respectively. Sensitivity analysis of the DME/air flame temperature as a function of exit velocity shows that the DME decomposition reaction and H abstraction from DME become important in the rich flames at phi = 1.7 and 2.0

    Spectroscopy of free radicals and radical containing entrance-channel complexes in superfluid helium nano-droplets

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    The spectroscopy of free radicals and radical containing entrance-channel complexes embedded in superfluid helium nano-droplets is reviewed. The collection of dopants inside individual droplets in the beam represents a micro-canonical ensemble, and as such each droplet may be considered an isolated cryo-reactor. The unique properties of the droplets, namely their low temperature (0.4 K) and fast cooling rates (∼1016\sim10^{16} K s−1^{-1}) provides novel opportunities for the formation and high-resolution studies of molecular complexes containing one or more free radicals. The production methods of radicals are discussed in light of their applicability for embedding the radicals in helium droplets. The spectroscopic studies performed to date on molecular radicals and on entrance / exit-channel complexes of radicals with stable molecules are detailed. The observed complexes provide new information on the potential energy surfaces of several fundamental chemical reactions and on the intermolecular interactions present in open-shell systems. Prospects of further experiments of radicals embedded in helium droplets are discussed, especially the possibilities to prepare and study high-energy structures and their controlled manipulation, as well as the possibility of fundamental physics experiments.Comment: 25 pages, 12 figures, 4 tables (RevTeX

    Primary vs. Secondary Antibody Deficiency: Clinical Features and Infection Outcomes of Immunoglobulin Replacement

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    <div><p>Secondary antibody deficiency can occur as a result of haematological malignancies or certain medications, but not much is known about the clinical and immunological features of this group of patients as a whole. Here we describe a cohort of 167 patients with primary or secondary antibody deficiencies on immunoglobulin (Ig)-replacement treatment. The demographics, causes of immunodeficiency, diagnostic delay, clinical and laboratory features, and infection frequency were analysed retrospectively. Chemotherapy for B cell lymphoma and the use of Rituximab, corticosteroids or immunosuppressive medications were the most common causes of secondary antibody deficiency in this cohort. There was no difference in diagnostic delay or bronchiectasis between primary and secondary antibody deficiency patients, and both groups experienced disorders associated with immune dysregulation. Secondary antibody deficiency patients had similar baseline levels of serum IgG, but higher IgM and IgA, and a higher frequency of switched memory B cells than primary antibody deficiency patients. Serious and non-serious infections before and after Ig-replacement were also compared in both groups. Although secondary antibody deficiency patients had more serious infections before initiation of Ig-replacement, treatment resulted in a significant reduction of serious and non-serious infections in both primary and secondary antibody deficiency patients. Patients with secondary antibody deficiency experience similar delays in diagnosis as primary antibody deficiency patients and can also benefit from immunoglobulin-replacement treatment.</p></div

    Time-delayed spread of viruses in growing plaques

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    The spread of viruses in growing plaques predicted by classical models is greater than that measured experimentally. There is a widespread belief that this discrepancy is due to biological factors. Here we show that the observed speeds can be satisfactorily predicted by a purely physical model that takes into account the delay time due to virus reproduction inside infected cells. No free or adjustable parameters are used

    Diagnostic testing for interstitial lung disease in common variable immunodeficiency: a systematic review

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    INTRODUCTION: Common variable immunodeficiency related interstitial lung disease (CVID-ILD, also referred to as GLILD) is generally considered a manifestation of systemic immune dysregulation occurring in up to 20% of people with CVID. There is a lack of evidence-based guidelines for the diagnosis and management of CVID-ILD. AIM: To systematically review use of diagnostic tests for assessing patients with CVID for possible ILD, and to evaluate their utility and risks. METHODS: EMBASE, MEDLINE, PubMed and Cochrane databases were searched. Papers reporting information on the diagnosis of ILD in patients with CVID were included. RESULTS: 58 studies were included. Radiology was the investigation modality most commonly used. HRCT was the most reported test, as abnormal radiology often first raised suspicion of CVID-ILD. Lung biopsy was used in 42 (72%) of studies, and surgical lung biopsy had more conclusive results compared to trans-bronchial biopsy (TBB). Analysis of broncho-alveolar lavage was reported in 24 (41%) studies, primarily to exclude infection. Pulmonary function tests, most commonly gas transfer, were widely used. However, results varied from normal to severely impaired, typically with a restrictive pattern and reduced gas transfer. CONCLUSION: Consensus diagnostic criteria are urgently required to support accurate assessment and monitoring in CVID-ILD. ESID and the ERS e-GLILDnet CRC have initiated a diagnostic and management guideline through international collaboration. SYSTEMATIC REVIEW REGISTRATION: https://www.crd.york.ac.uk/prospero/, identifier CRD42022276337
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