Advanced combustion processes induced by self-ignition mechanisms in piston engines, such as Homogeneous Charge Compression Ignition (HCCI), especially need an accurate spatio-temporal temperature ...information because their phenomenology therefore their performances highly depend on the thermal conditions. The objective of this study is to measure the temperature distribution inside a rapid compression machine (RCM) along the compression stroke using anisole planar laser induced fluorescence. The present paper gives a new insight into the interpretation of RCM autoignition data. It also brings useful information for kinetics-related combustion research and combustion modeling. The anisole planar laser-induced fluorescence (PLIF) technique is applied, in order to observe the formation and the evolution of temperature heterogeneities in the combustion chamber prior to the auto-ignition process. Anisole is used as a novel tracer species, and the fluorescence signal's dependence on parameters, such as temperature, pressure and bath gas composition, is quantified in a high-pressure, high-temperature facility. Calibration of the fluorescence signal is defined under RCM-related temperature and pressure conditions and a protocol is proposed for post-processing of the PLIF image sequences, allowing the quantitative field temperatures to be determined at successive instants following compression. In order to gain a better understanding of the mixture process, Particle Image Velocimetry (PIV) measurements are analysed under the same conditions. The correlation between thermal and aerodynamic phenomena is determined. The temperature field is found to be non-uniform, with hot and cold centre positions resulting from recirculation inside the chamber, combined with heat transfer effects from the chamber wall.
Archaeological mortars are more convenient and much more representative for the chronology of buildings than brick or wood constructions that can be re-used from older buildings. Before dating ...unknown samples of mortars, further investigation of OSL from mortars is required and the most efficient methodology needs to be established. In this study we compared the ages obtained by OSL dating of quartz extracted from mortars of the Roman amphitheatre Palais-Gallien in Bordeaux with independent age information.
Resetting of the OSL signal occurred during the preparation of mortar when grains of sand (quartz) were extracted and mixed with lime and water. The mortar was subsequently hidden from light by embedding within the structure which is the event to be dated.
Various factors contribute to uncertainties in the age determination. The frequency of measured equivalent doses reveals a large scattering. Optical bleaching of certain grains can be partial due to the short duration of the exposure to light. We worked with the single grain technique in order to find and select the grains that were sufficiently exposed to daylight. To determine the average equivalent dose, we tried three different approaches: a calculation of an arithmetic mean and one following either the central age model or the 3-parameter minimum age model, the latter turned out to be the only relevant way to evaluate the experimental data. The proportion of grains included in the calculation of the average equivalent dose represents 2.7–4.7 % of the overall analysed grains. The results obtained for the three out of four samples are approaching the expected age, however, the minimum doses and the corresponding ages are significantly over-estimated in case of two samples.
The studied material is very coarse, which causes heterogeneity of irradiation at the single grain scale, and contributes to a dispersion of equivalent doses. Different analytical methods (scanning electron microscopy with energy dispersive X-ray spectroscopy cartography, Beta-radiography imaging, inductively coupled plasma mass spectrometry) were employed to demonstrate the presence of this phenomenon.
Despite the extremely large proportion of high equivalent doses in equivalent dose distributions, there is an apparent presence of well-bleached grains at the beginning of equivalent dose distributions. The study shows the potential of dating mortars by single grain OSL.
•Fewer than 8% of all measured grains exhibited an OSL signal.•The heterogeneity of β-irradiation arises principally from variations of K-content.•Beta-imaging confirmed inhomogeneous distribution of beta sources in studied samples.•The samples are highly affected by heterogeneous bleaching.•Standard age models are not adapted for the studied series of samples.
Aromatic molecules are promising candidates for using as a fluorescent tracer for gas-phase scalar parameter diagnostics in a drastic environment like engines. Along with anisole turning out an ...excellent temperature tracer by Planar Laser-Induced Fluorescence (PLIF) diagnostics in Rapid Compression Machine (RCM), its fluorescence signal evolution versus pressure and temperature variation in a high-pressure and high-temperature cell have been reported in our recent paper on Applied Phys. B by Tran et al. Parallel to this experimental study, a photophysical model to determine anisole Fluorescence Quantum Yield (FQY) is delivered in this paper. The key to development of the model is the identification of pressure, temperature, and ambient gases, where the FQY is dominated by certain processes of the model (quenching effect, vibrational relaxation, etc.). In addition to optimization of the vibrational relaxation energy cascade coefficient and the collision probability with oxygen, the non-radiative pathways are mainly discussed. The common non-radiative rate (intersystem crossing and internal conversion) is simulated in parametric form as a function of excess vibrational energy, derived from the data acquired at different pressures and temperatures from the literature. A new non-radiative rate, namely, the equivalent Intramolecular Vibrational Redistribution or Randomization (IVR) rate, is proposed to characterize anisole deactivated processes. The new model exhibits satisfactory results which are validated against experimental measurements of fluorescence signal induced at a wavelength of 266 nm in a cell with different bath gases (N
2
, CO
2
, Ar and O
2
), a pressure range from 0.2 to 4 MPa, and a temperature range from 473 to 873 K.
Laser-induced fluorescence of anisole as tracer of isooctane at an excitation wavelength of 266 nm was investigated for conditions relevant to rapid compression machine studies and for more general ...application of internal combustion engines regarding temperature, pressure, and ambient gas composition. An optically accessible high pressure and high temperature chamber was operated by using different ambient gases (Ar, N
2
, CO
2
, air, and gas mixtures). Fluorescence experiments were investigated at a large range of pressure and temperature (0.2–4 MPa and 473–823 K). Anisole fluorescence quantum yield decreases strongly with temperature for every considered ambient gas, due to efficient radiative mechanisms of intersystem crossing. Concerning the pressure effect, the fluorescence signal decreases with increasing pressure, because increasing the collisional rate leads to more important non-radiative collisional relaxation. The quenching effect is strongly efficient in oxygen, with a fluorescence evolution described by Stern–Volmer relation. The dependence of anisole fluorescence versus thermodynamic parameters suggests the use of this tracer for temperature imaging in specific conditions detailed in this paper. The calibration procedure for temperature measurements is established for the single-excitation wavelength and two-color detection technique.
The effect of X-ray irradiation and thermal treatments on the radio-luminescence emission spectrum of both a natural pegmatitic quartz and a synthetic one was investigated. All the emission spectra ...could be deconvolved into the same set of five Gaussian components. Among the identified RL bands, a blue emission at 2.53eV (480nm) is enhanced under X-ray irradiation. A strong correlation with the sensitization of the so called “110°C” TSL peak (in our measurements seen at lower temperature due to the lower heating rate) was proved, suggesting that the recombination centers associated with the 2.53eV band are produced under X-ray irradiation and are involved in both RL and TSL luminescence mechanisms. When each irradiation was followed by heating up to 500°C a strong sensitization of the RL band emitting at 3.44eV and of the 110°C TSL peak were observed. A perfect correlation between the RL and TSL emissions suggests that the recombination centers involved in the RL and TSL emissions are the same.
► Same emission bands in the radioluminescence, RL, of natural and synthetic quartz. ► The blue RL emission at 2.53eV (480nm) is enhanced under X-ray irradiation, both in natural and in synthetic quartz. ► Strong correlation between the sensitivity growth of the 110°C TSL peak and the RL band emitting at 3.44eV (360nm).
New excavations have been undertaken at Diepkloof Rock Shelter (DRS; South Africa) since 1999. It is one of the very few sites where Howiesons Poort and Stillbay assemblages can be collected from the ...same archaeological sequence. These Middle Stone Age techno-complexes are particularly interesting for their affinities with the much younger Later Stone Age facies, and their association with evidence for symbolic behaviour. Establishing their chronology is therefore particularly important for the understanding of the apparition and the evolution of the so-called “modern” behaviours. Data already available suggest ages ranging from 55 to 80
ka for the Howiesons Poort and from 70 to 80
ka for the Stillbay techno-complexes in several South African sites. The thermoluminescence dating undertaken at DRS on 22 stone samples originating from the entire stratigraphic record indicates intervals starting 10–50
ka earlier for these techno-complexes in this site. Possible caveats in the dating process are examined but to the best of our current knowledge must be rejected.
Disequilibria in uranium series and their consequences on the annual dose determination in luminescence dating studies are now well-known, but only a few studies refer to the systematic research of ...this kind of phenomenon, and eventually to how the problem has been misguided. The present work aims at considering a new case study: anciently heated ferruginous sandstones from a Magdalenian archaeological site have been dated by thermoluminescence. In this work, uranium series disequilibrium has been detected both in samples and surrounding sediments, using high resolution low background gamma spectrometry measurements. Further investigations, in particular with alpha-spectrometry measurements and geochemical considerations, helped us to understand when and how the disequilibrium began, and it led us to propose a specific simple model, based on a continuous and regular enrichment in uranium, for the evaluation of the mean annual dose absorbed by the samples to be dated. This work deals with the results of gamma and alpha-spectrometry as well as the dose variation model proposed and the dating results obtained, in terms of annual dose determination and in terms of age obtained.
► A case study of disequilibria in U series in luminescence dating is presented. ► γ and α spectrometry allow understanding the history of the disequilibrium. ► A model is proposed. ► The consequences on the annual dose determination are evaluated.
Magnetically induced flame flickering Legros, G.; Gomez, T.; Fessard, M. ...
Proceedings of the Combustion Institute,
2011, 2011-00-00, 20110101, Letnik:
33, Številka:
1
Journal Article
Recenzirano
This paper addresses a still unknown effect of a high downward gradient of the square of the magnetic flux density on a laminar methane diffusion flame established over an axisymmetric co-flow ...burner. Because the magnetic force is expected to act mainly on paramagnetic oxygen, a parametric study varying the co-flowing stream oxygen content, the oxidizer velocity and the magnitude of the gradient of the square of the magnetic flux density was performed. CH∗ radicals spontaneous chemiluminescence was captured to track the flame sheets. Despite a low Reynolds number at the fuel exit and oxidizer flow velocities slightly larger than the fuel exit velocity, the flame flickering was triggered by downward gradients of the square of the magnetic flux density of magnitudes from 0.4 and 1.4T2/m for O2 contents of 0.75 and 0.55, respectively. This flickering is shown to result from an axisymmetric mode of a convective instability. Qualitative speculations based on previous works suggest that the magnetic body force may alternately strengthen buoyancy and shear stress, therefore hastening the instability onset. Indeed, at relatively low Grashof numbers, a region of flickering conditions shows up and grows with a magnetic Reynolds number. The sensitivities of the flickering frequency and amplitude are finally addressed, namely showing that over the investigated range of parameters the frequency spreads from 10.5 to 14Hz.
The objective of this study is to develop a quantitative measurement of temperature from fluoranthene fluorescence under conditions with elevated temperatures and pressures. Absorption and ...fluorescence of fluoranthene are studied in a pressure and temperature range of 0.1–4 MPa and 473–873 K for the two excitation wavelengths of 266 and 355 nm. The influence of thermodynamic parameters such as pressure, temperature and gas composition is characterized in a high-pressure and high-temperature facility. When increasing the pressure, the vibrational relaxation mechanisms are favored, which involves an increase of the fluorescence quantum yield. Concerning the temperature effect, the fluorescence decreases with increasing temperature, this is explained by efficient radiative mechanisms of intersystem crossing. The quenching effect is strongly efficient in air, with a fluorescence evolution described by the Stern–Volmer relation. Over the temperature range studied, the fluorescence quantum yield decreases exponentially by two orders of magnitude. From the temperature dependence of fluoranthene fluorescence in different ambient gases for 266 and 355 nm excitation, the potential temperature measurements in homogeneously and inhomogeneously seeded systems are suggested: the single-color detection technique, the single-excitation two-color detection technique and the dual-excitation wavelength technique.
Peritoneal carcinomatosis (pcm) in metastatic pancreatic ductal adenocarcinomas (mpdac) is frequently encountered in day-to-day practice, but rarely addressed in the literature. The objective of the ...present study was to describe the management and outcome of patients diagnosed with pcm.
Data for all consecutive patients with mpdac treated in our centre between 1 January 2014 and 31 August 2015 were analyzed retrospectively. Computed tomography imaging was centrally reviewed by a dedicated radiologist to determine the date of pcm diagnosis.
The analysis included 48 patients. Median age in the group was 61 years, and 41 patients had an Eastern Cooperative Oncology Group performance status (ecog ps) of 0-1. All patients presented with pcm either synchronously (group 1) or metachronously (group 2). Those groups differed significantly by baseline ecog ps and neutrophil-to-lymphocyte ratio (nlr), with ecog ps being poorer and nlr being higher in group 1. In addition to pcm, the main sites of metastasis were liver (62.5%) and lungs (31.3%). First-line chemotherapy in 36 patients (75%) was folfirinox (fluorouracil-irinotecan-leucovorin-oxaliplatin). The median overall survival for the entire population was 10.81 months 95% confidence interval (ci): 7.16 months to 14.16 months; it was 13.17 months (95% ci: 5.9 months to 15.4 months) for patients treated with folfirinox. Median overall survival was 7.13 months (95% ci: 4.24 months to 10.41 months) for patients in group 1 and 14.34 months (95% ci: 9.79 months to 19.91 months) for patients in group 2,
= 0.1296.
Compared with other metastatic sites, synchronous pcm seems to be a poor prognostic factor. It could be more frequently associated with a poor ecog ps and a nlr greater than 5 in this group of patients. In patients with mpdac and pcm, either synchronous or metachronous, folfirinox remains an efficient regimen.
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