682 research outputs found
Characterization of the aerosol produced by infrared femtosecond laser ablation of polyacrylamide gels for the sensitive inductively coupled plasma mass spectrometry detection of selenoproteins
A 2D high repetition rate femtosecondlaserablation strategy (2-mm wide lane) previously developed for the detection of selenoproteins in gel electrophoresis by inductively coupled plasma mass spectrometry was found to increase signal sensitivity by a factor of 40 compared to conventional nanosecond ablation (0.12-mm wide lane) [G. Ballihaut, F. Claverie, C. PĂ©cheyran, S. Mounicou, R. Grimaud and R. Lobinski, Sensitive Detection of Selenoproteins in Gel Electrophoresis by High Repetition Rate FemtosecondLaserAblation-Inductively Coupled Plasma Mass Spectrometry, Anal. Chem. 79 (2007) 6874â6880]. Such improvement couldn't be explained solely by the difference of amount of material ablated, and then, was attributed to the aerosol properties. In order to validate this hypothesis, the characterization of the aerosolproduced by nanosecond and high repetition rate femtosecondlaserablation of polyacrylamidegels was investigated. Our 2D high repetition rate femtosecondlaserablation strategy of 2-mm wide lane was found to produce aerosols of similar particle size distribution compared to nanosecond laserablation of 0.12-mm wide lane, with 38% mass of particles < 1 ”m. However, at high repetition rate, when the ablated surface was reduced, the particle size distribution was shifted toward thinner particle diameter (up to 77% for a 0.12-mm wide lane at 285 ”m depth). Meanwhile, scanning electron microscopy was employed to visualize the morphology of the aerosol. In the case of larger ablation, the fine particles ejected from the sample were found to form agglomerates due to higher ablation rate and then higher collision probability. Additionally, investigations of the plasma temperature changes during the ablation demonstrated that the introduction of such amount of polyacrylamidegel particles had very limited impact on the ICP source (ÎT~ 25 ± 5 K). This suggests that the cohesion forces between the thin particles composing these large aggregates were weak enough to have negligible impact on the ICPMS detection
Cambios en la heterogeneidad del paisaje y organizaciĂłn espacial de bosques nativos en Patagonia, Argentina
Native forests in Patagonia have been influenced by human activities since the beginning of the past century. Nevertheless, the availability of aerial photographs to conduct analysis of changes at a landscape level due to anthropic factors is generally restricted to the last decades. Therefore this study was aimed to detect changes of the forest landscape heterogeneity during the last thirty years in the northwest region of Chubut, the middle-located Patagonian province, and to study spatial patterning of forest landscapes. For the first goal, we focused on a 2,000 ha landscape unit with prevailing Austrocedrus chilensis forests. In 466 ha covered by these forests, 41% of this area was negatively affected by forest fires, timber logging followed by livestock grazing and substitution with pine plantations. In contrast, growth of young Austrocedrus forests was verified in 9% of the forest area. Spatial patterns were studied on an area of 10,000 ha showing a high heterogeneity of the distinctive landscape configurations.Los bosques nativos en Patagonia han estado influidos por la acción del hombre desde principios del siglo pasado. Sin embargo, la disponibilidad de fotografías aéreas para efectuar análisis de cambios debidos a factores antrópicos a escala de paisaje está generalmente restringida a las últimas décadas. En consecuencia, este estudio estuvo orientado a detectar y analizar los cambios de la heterogeneidad del paisaje forestal durante los últimos treinta años en la región noroeste de Chubut, la provincia central de Patagonia en Argentina, y a estudiar la organización espacial de paisajes forestales. Para el primer objetivo, nos concentramos en una unidad de paisaje de 2.000 ha con predominancia de bosques de Austrocedrus chilensis. En 466 ha cubiertas con estos bosques, 41% de esta área fue negativamente afectado por incendios forestales, extracciones forestales seguidas de pastoreo y reemplazo de bosques nativos por plantaciones de pinos. En contraste, el crecimiento de bosques jóvenes de Austrocedrus se verificó en el 9% del área forestal. Los patrones espaciales se estudiaron en un área de 10.000 ha y mostraron una alta heterogeneidad de las configuraciones distintivas del paisaje
Determination of strongly overlapping signaling activity from microarray data
BACKGROUND: As numerous diseases involve errors in signal transduction, modern therapeutics often target proteins involved in cellular signaling. Interpretation of the activity of signaling pathways during disease development or therapeutic intervention would assist in drug development, design of therapy, and target identification. Microarrays provide a global measure of cellular response, however linking these responses to signaling pathways requires an analytic approach tuned to the underlying biology. An ongoing issue in pattern recognition in microarrays has been how to determine the number of patterns (or clusters) to use for data interpretation, and this is a critical issue as measures of statistical significance in gene ontology or pathways rely on proper separation of genes into groups. RESULTS: Here we introduce a method relying on gene annotation coupled to decompositional analysis of global gene expression data that allows us to estimate specific activity on strongly coupled signaling pathways and, in some cases, activity of specific signaling proteins. We demonstrate the technique using the Rosetta yeast deletion mutant data set, decompositional analysis by Bayesian Decomposition, and annotation analysis using ClutrFree. We determined from measurements of gene persistence in patterns across multiple potential dimensionalities that 15 basis vectors provides the correct dimensionality for interpreting the data. Using gene ontology and data on gene regulation in the Saccharomyces Genome Database, we identified the transcriptional signatures of several cellular processes in yeast, including cell wall creation, ribosomal disruption, chemical blocking of protein synthesis, and, criticially, individual signatures of the strongly coupled mating and filamentation pathways. CONCLUSION: This works demonstrates that microarray data can provide downstream indicators of pathway activity either through use of gene ontology or transcription factor databases. This can be used to investigate the specificity and success of targeted therapeutics as well as to elucidate signaling activity in normal and disease processes
Elemental fractionation effects in high repetition rate IR femtosecond laser ablation ICP-MS analysis of glasses
An IR-femtosecond laser ablation ICPMS coupling was used to investigate the influence of the high repetition rate on elemental fractionation effects for the analysis of silicate glass SRM NIST 610. First, elemental fractionation inherent to the ICP was minimised by working on wet plasma conditions which had greater tolerance to mass loading and demonstrated a higher robustness compared to dry plasma conditions. Because of the use of a narrow laser beam producing small craters (17 ”m in diameter), a special arrangement of pulses was used to perform resulting craters of 100 ”m diameter. The ablation strategy developed in this work consisted in a series of concentric circle trajectories ablated at high repetition rates by moving the laser beam rapidly thanks to a scanning beam device. Two scanner speeds (0.25 mm sâ1 and 1.5 mm sâ1), five laser repetition rates (from 0.1 kHz to 10 kHz) and three fluence values (5 J cmâ2, 14 J cmâ2, and 25 J cmâ2) were investigated in detail. For this purpose, critical elemental ratios (namely 238U/232Th, 208Pb/238U, and 66Zn/65Cu) of aerosols produced by fs-LA of silicate glass were studied to evaluate the impact of the different laser parameters on elemental fractionation . No heating zones or preferential evaporation of elements were found depending on the repetition rate employed. However, particle-size-fractionation was measured during the ablation of the sample surface, and this effect was reduced by using a high repetition rate as well as a high scanner speed which allow the dilution of the large particles coming from the surface layer with finer particles coming to deeper levels. Additionally, the ablation rate induced by the selected ablation strategy had a low influence on fractionation effects due to the high robustness of the ICP plasma and, on the other hand, fractionation indices were not particularly affected by the laser repetition rate although they could be improved by the use of high fluence values. Finally, it could be stressed that no differences on the structure of the aerosol particles collected on membrane filters were found depending on the ablation parameters
Phytoplankton primary production in Chascomus pond (Provincia de Buenos Aires, Argentina)
In situ phytoplankton primary production in ChascomĂșs pond (eutrophic Pampasic âlagunaâ) was studied by the oxygen method (light and dark bottle) between.January 1984-January 1985. ValĂșes obtained ranged from37,9 to 981,6 mg C âą m-1 âą d-1. Factors influencing it, as suspended particulate matter and hydrological changes, are discussed. Parallel determinations of the artificial light photosynthesis response proved to be useful,almostqualitatively under the experimental conditions applied, to follow the behaviour obtained by incubations in natural environment.In situ phytoplankton primary production in ChascomĂșs pond (eutrophic Pampasic âlagunaâ) was studied by the oxygen method (light and dark bottle) between.January 1984-January 1985. ValĂșes obtained ranged from37,9 to 981,6 mg C âą m-1 âą d-1. Factors influencing it, as suspended particulate matter and hydrological changes, are discussed. Parallel determinations of the artificial light photosynthesis response proved to be useful,almostqualitatively under the experimental conditions applied, to follow the behaviour obtained by incubations in natural environment
A self-consistent perturbative evaluation of ground state energies: application to cohesive energies of spin lattices
The work presents a simple formalism which proposes an estimate of the ground
state energy from a single reference function. It is based on a perturbative
expansion but leads to non linear coupled equations. It can be viewed as well
as a modified coupled cluster formulation. Applied to a series of spin lattices
governed by model Hamiltonians the method leads to simple analytic solutions.
The so-calculated cohesive energies are surprisingly accurate. Two examples
illustrate its applicability to locate phase transition.Comment: Accepted by Phys. Rev.
Low energy measurement of the 7Be(p,gamma)8B cross section
We have measured the cross section of the 7Be(p,gamma)8B reaction for E_cm =
185.8 keV, 134.7 keV and 111.7 keV using a radioactive 7Be target (132 mCi).
Single and coincidence spectra of beta^+ and alpha particles from 8B and 8Be^*
decay, respectively, were measured using a large acceptance spectrometer. The
zero energy S factor inferred from these data is 18.5 +/- 2.4 eV b and a
weighted mean value of 18.8 +/- 1.7 eV b (theoretical uncertainty included) is
deduced when combining this value with our previous results at higher energies.Comment: Accepted for publication in Phys. Rev. Let
Depictions of Thailand in Australian and Thai writings:Reflections of the Self and Other
This thesis offers both an examination of the depiction of Thailand in Australian novels, short stories and poems written in the 1980s and after, and an analysis of modern Thai novels and short stories that reflect similar themes to those covered in the Australian literature. One Australian film is also examined as the film provides an important framework for the analysis of some of the short stories and novels under consideration. The thesis establishes a dialogue between Thai and Australian literatures and demonstrates that the comparison of Australian representations of Thailand with Thai representations challenges constructively certain dominant political and social ideologies that enhance conservatism and the status quo in Thailand. The author acknowledges that the discussion of the representations of Thailand in contemporary Australian novels and short stories needs to take into account the colonial legacy and the discourse of Orientalism that tends to posit the âEastâ as the âWestââs âOtherâ. Textual analysis is thus informed by post-colonial and cross-cultural theories, starting from Edward Saidâs powerful and controversial critique of Western representation of the East in Orientalism. The first part of the thesis examines Australian crime stories and shows how certain Orientalist images and perceptions persist and help reinforce the image of the East and its people as the antithesis of the West. From Chapters Three through Six, however, more literary works by Australian authors are examined. The important finding is that most of the Australian authors under consideration attempt, though not always successfully, to resist and challenge the Eurocentric stereotypes of Asia and Asians that dominated Australian literature in earlier periods. This difference between contemporary Australian authors and their predecessors seems to reflect modern Australiaâs endeavor to distinguish itself from the rest of the Western world and to redefine its relationship with Asia. As literary representations cannot be separated from socio-political contexts, the thesis also includes discussion of the Thai social and political history and, where appropriate, shows how colonialism and neo-colonialism exert their impact on modern Thailand
The role of dynamical polarization of the ligand to metal charge transfer excitations in {\em ab initio} determination of effective exchange parameters
The role of the bridging ligand on the effective Heisenberg coupling
parameters is analyzed in detail. This analysis strongly suggests that the
ligand-to-metal charge transfer excitations are responsible for a large part of
the final value of the magnetic coupling constant. This permits to suggest a
new variant of the Difference Dedicated Configuration Interaction (DDCI)
method, presently one of the most accurate and reliable for the evaluation of
magnetic effective interactions. This new method treats the bridging ligand
orbitals mediating the interaction at the same level than the magnetic orbitals
and preserves the high quality of the DDCI results while being much less
computationally demanding. The numerical accuracy of the new approach is
illustrated on various systems with one or two magnetic electrons per magnetic
center. The fact that accurate results can be obtained using a rather reduced
configuration interaction space opens the possibility to study more complex
systems with many magnetic centers and/or many electrons per center.Comment: 7 pages, 4 figure
Stochastic optics: A local realistic analysis of optical tests of Bell inequalities
Stochastic optics may be considered as simply a local realistic interpretation of quantum optics and, in this sense, it is a first step in the reinterpretation of the whole of quantum theory. However, as it is not possible to interpret all the details of quantum theory in a local realistic manner, as shown by Bellâs theorem, minor changes are introduced in the formalism with the consequence that the new theory makes different predictions in some special cases. In stochastic optics, the quantum-operator formalism is simply considered a formal way of dealing with stochastic fields. In particular, the quantum zero point is taken as a real random electromagnetic radiation filling the whole of space. This radiation noise has the same nature as light signals, the only difference being the greater intensity of the latter. We assume that photon detectors have an intensity threshold just above the level of the noise, thus detecting only signals. Transmission of radiation through polarizers follows Malusâs law, but the interplay of signal and noise leads quite naturally to the prediction that the detection probability of some signals is enhanced, which is known to be a necessary condition for the violation of the empirically tested Bell inequalities. In our view, correlated photon pairs are pairs of light signals supercorrelated in polarization, in the sense that, as well as the signal, the accompanying noise is also correlated. Thus stochastic optics allows predictions for the empirical correlations very close, but not identical, to the quantum ones. The theory is applied to the analysis of all experiments designed to test the Bell inequalities by measuring polarization correlations of photon pairs. The predictions agree with quantum optics and experiments within statistical errors, except for the Holt-Pipkin experiment. In this case, the experimental results agree with stochastic optical predictions within two standard deviations while violating quantum optics by four
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