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Showing papers by "National University of La Plata published in 2010"


Journal ArticleDOI
TL;DR: The nature of the molecule-gold interface, whose chemistry and structure remain elusive, the self-assembly process on planar and irregular surfaces, and on nanometre-sized objects, and the chemical reactivity and thermal stability of these systems in ambient and aqueous solutions are reviewed.
Abstract: Self-assembled monolayers (SAMs) of alkanethiols and dialkanethiols on gold are key elements for building many systems and devices with applications in the wide field of nanotechnology. Despite the progress made in the knowledge of these fascinating two-dimensional molecular systems, there are still several “hot topics” that deserve special attention in order to understand and to control their physical and chemistry properties at the molecular level. This critical review focuses on some of these topics, including the nature of the molecule–gold interface, whose chemistry and structure remain elusive, the self-assembly process on planar and irregular surfaces, and on nanometre-sized objects, and the chemical reactivity and thermal stability of these systems in ambient and aqueous solutions, an issue which seriously limits their technological applications (375 references).

1,177 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a method to solve the problem of single-input single-output (SISO) communication in the context of artificial neural networks (ANNs).

927 citations


Journal ArticleDOI
Georges Aad1, Brad Abbott2, Jalal Abdallah3, A. A. Abdelalim4  +3098 moreInstitutions (192)
TL;DR: In this article, the authors used the ATLAS detector to detect dijet asymmetry in the collisions of lead ions at the Large Hadron Collider and found that the transverse energies of dijets in opposite hemispheres become systematically more unbalanced with increasing event centrality, leading to a large number of events which contain highly asymmetric di jets.
Abstract: By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.

630 citations


Journal ArticleDOI
TL;DR: The measurement of the depth of maximum, X{max}, of the longitudinal development of air showers induced by cosmic rays is described and the interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.
Abstract: We describe the measurement of the depth of maximum, Xmax, of the longitudinal development of air showers induced by cosmic rays. Almost four thousand events above 10^18 eV observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/- 0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.

558 citations


Journal ArticleDOI
J. Abraham1, P. Abreu2, Marco Aglietta3, Eun-Joo Ahn4  +489 moreInstitutions (65)
TL;DR: In this article, the authors reported a measurement of the flux of cosmic rays with unprecedented precision and statistics using the Pierre Auger Observatory based on fluorescence observations in coincidence with at least one surface detector.

461 citations


Journal ArticleDOI
TL;DR: The best corrosion behaviour of the AZ31 alloy was obtained for the finest grain alloy associated with the highest transfer resistance value, after long periods of immersion in PBS.

422 citations


Journal ArticleDOI
P. Abreu1, Marco Aglietta2, Eun-Joo Ahn3, D. Allard  +492 moreInstitutions (68)
TL;DR: In this paper, anisotropy was measured by the fraction of arrival directions that are less than 3.1 degrees from the position of an active galactic nucleus within 75 Mpc (using the Veron-Cetty and Veron 12th catalog).

404 citations


Journal ArticleDOI
J. Abraham, P. Abreu1, Marco Aglietta2, C. Aguirre  +526 moreInstitutions (65)
TL;DR: The Pierre Auger Observatory is a hybrid detector for ultra-high energy cosmic rays as discussed by the authors, which combines a surface array to measure secondary particles at ground level together with a fluorescence detector to measure the development of air showers in the atmosphere above the array.
Abstract: The Pierre Auger Observatory is a hybrid detector for ultra-high energy cosmic rays. It combines a surface array to measure secondary particles at ground level together with a fluorescence detector to measure the development of air showers in the atmosphere above the array. The fluorescence detector comprises 24 large telescopes specialized for measuring the nitrogen fluorescence caused by charged particles of cosmic ray air showers. In this paper we describe the components of the fluorescence detector including its optical system, the design of the camera, the electronics, and the systems for relative and absolute calibration. We also discuss the operation and the monitoring of the detector. Finally, we evaluate the detector performance and precision of shower reconstructions.

363 citations


Journal ArticleDOI
TL;DR: A detailed review of the physics of white dwarfs can be found in this paper, with a focus on the physical processes that lead to the formation of the stars and the different energy sources responsible for chemical abundance changes that occur along their evolution.
Abstract: White dwarf stars are the final evolutionary stage of the vast majority of stars, including our Sun. Since the coolest white dwarfs are very old objects, the present population of white dwarfs contains a wealth of information on the evolution of stars from birth to death, and on the star formation rate throughout the history of our Galaxy. Thus, the study of white dwarfs has potential applications in different fields of astrophysics. In particular, white dwarfs can be used as independent reliable cosmic clocks, and can also provide valuable information about the fundamental parameters of a wide variety of stellar populations, such as our Galaxy and open and globular clusters. In addition, the high densities and temperatures characterizing white dwarfs allow these stars to be used as cosmic laboratories for studying physical processes under extreme conditions that cannot be achieved in terrestrial laboratories. Last but not least, since many white dwarf stars undergo pulsational instabilities, the study of their properties constitutes a powerful tool for applications beyond stellar astrophysics. In particular, white dwarfs can be used to constrain fundamental properties of elementary particles such as axions and neutrinos and to study problems related to the variation of fundamental constants. These potential applications of white dwarfs have led to renewed interest in the calculation of very detailed evolutionary and pulsational models for these stars. In this work, we review the essentials of the physics of white dwarf stars. We enumerate the reasons that make these stars excellent chronometers, and we describe why white dwarfs provide tools for a wide variety of applications. Special emphasis is placed on the physical processes that lead to the formation of white dwarfs as well as on the different energy sources and processes responsible for chemical abundance changes that occur along their evolution. Moreover, in the course of their lives, white dwarfs cross different pulsational instability strips. The existence of these instability strips provides astronomers with a unique opportunity to peer into their internal structure that would otherwise remain hidden from observers. We will show that this allows one to measure stellar masses with unprecedented precision and to infer their envelope thicknesses, to probe the core chemical stratification, and to detect rotation rates and magnetic fields. Consequently, in this work, we also review the pulsational properties of white dwarfs and the most recent applications of white dwarf asteroseismology.

354 citations


Journal ArticleDOI
TL;DR: In this short review the author analyzes recent literature on some of the most important dangers related to self-medication practices, particularly: polypharmacy and drug interactions, medications abuse or dependence, misdiagnosis and incorrect choice of treatment.
Abstract: Self-medication is defined as the selection and use of medicines by individuals (or a member of the individuals' family) to treat self-recognized or self-diagnosed conditions or symptoms. Several benefits have been linked to appropriate self-medication, among them: increased access to medication and relief for the patient, the active role of the patient in his or her own health care, better use of physicians and pharmacists skills and reduced (or at least optimized) burden of governments due to health expenditure linked to the treatment of minor health conditions However, self-medication is far from being a completely safe practice, in particular in the case of non-responsible self-medication. Potential risks of self-medication practices include: incorrect self-diagnosis, delays in seeking medical advice when needed, infrequent but severe adverse reactions, dangerous drug interactions, incorrect manner of administration, incorrect dosage, incorrect choice of therapy, masking of a severe disease and risk of dependence and abuse. In this short review the author analyzes recent literature on some of the most important dangers related to self-medication practices, particularly: polypharmacy and drug interactions, medications abuse or dependence, misdiagnosis and incorrect choice of treatment. The author also proposes measures that could be adopted in order to solve or improve these issues.

332 citations


Journal ArticleDOI
TL;DR: In this article, the development of browning in bakery products is a simultaneous heat and mass transfer process that occurs mostly in a non-ideal system under nonideal conditions.

Journal ArticleDOI
TL;DR: In this article, the authors presented full evolutionary calculations appropriate for the study of hydrogen-rich DA white dwarfs for a wide range of stellarmasses and for two different metallicities.
Abstract: We present full evolutionary calculations appropriate for the study of hydrogen-rich DA white dwarfs. This is done by evolving white dwarf progenitors from the zero-age main sequence, through the core hydrogen-burning phase, the helium-burning phase, and the thermally pulsing asymptotic giant branch phase to the white dwarf stage. Complete evolutionary sequences are computed for a wide range of stellarmasses and for two different metallicities, Z = 0.01, which is representative of the solar neighborhood, and Z = 0.001, which is appropriate for the study of old stellar systems, like globular clusters. During the white dwarf cooling stage, we self-consistently compute the phase in which nuclear reactions are still important, the diffusive evolution of the elements in the outer layers and, finally, we also take into account all the relevant energy sources in the deep interior of the white dwarf, such as the release of latent heat and the release of gravitational energy due to carbon–oxygen phase separation upon crystallization. We also provide colors and magnitudes for these sequences, based on a new set of improved non-gray white dwarf model atmospheres, which include the most up-to-date physical inputs like the Lyα quasi-molecular opacity. The calculations are extended down to an effective temperature of 2500 K. Our calculations provide a homogeneous set of evolutionary cooling tracks appropriate for mass and age determinations of old DA white dwarfs and for white dwarf cosmochronology of the different Galactic populations.

Journal ArticleDOI
13 May 2010-Nature
TL;DR: It is reported that, as theoretically anticipated, physical separation processes occur in the cores of white dwarfs, resolving the age discrepancy for NGC 6791.
Abstract: Fil: Garcia Berro, Enrique. Instituto de Estudios Espaciales de Cataluna; . Universidad Politecnica de Catalunya; Espana

Journal ArticleDOI
TL;DR: In this paper, the crosslinking capacity of tannic acid was studied by evaluating both the structural modification produced on chitosan films and its effect on physicochemical, barrier and mechanical properties.

Journal ArticleDOI
TL;DR: It is concluded that the anti‐inflammatory activity of Helichrysum italicum can be explained by multiple effects, including inflammatory enzyme inhibition, free‐radical scavenging activity and corticoid‐like effects.
Abstract: The anti-inflammatory and antioxidant activities of the aerial part of Helichrysum italicum extracts have been established in various in-vivo and in-vitro experimental models. The results obtained on the acute oedemas induced by 12-O-tetradecanoylphorbol 13-acetate (TPA) and ethyl phenylpropiolate in the mouse ear, by serotonin and phospholipase A2 (PLA2) in the mouse paw, on chronic inflammation induced by repeated application of TPA in the mouse ear and on the delayed-type hypersensitivity induced by sheep red blood cells suggest that said anti-inflammatory activity is due to the effects of compounds expressed via a corticoid-like mechanism. In addition, the antioxidant activity of the extracts seems to be implicated in this anti-inflammatory activity, as the former inhibits enzymatic and non-enzymatic lipid peroxidation and has free-radical scavenger properties. We conclude that the anti-inflammatory activity of Helichrysum italicum can be explained by multiple effects, including inflammatory enzyme inhibition, free-radical scavenging activity and corticoid-like effects.

Journal ArticleDOI
J. Abraham1, P. Abreu2, Marco Aglietta3, Marco Aglietta4  +560 moreInstitutions (66)
TL;DR: The surface detector array of the Pierre Auger Observatory consists of 1600 water-Cherenkov detectors, for the study of extensive air showers (EAS) generated by ultra-high-energy cosmic rays.
Abstract: The surface detector array of the Pierre Auger Observatory consists of 1600 water-Cherenkov detectors, for the study of extensive air showers (EAS) generated by ultra-high-energy cosmic rays. We describe the trigger hierarchy, from the identification of candidate showers at the level of a single detector, amongst a large background (mainly random single cosmic ray muons), up to the selection of real events and the rejection of random coincidences. Such trigger makes the surface detector array fully efficient for the detection of EAS with energy above 3 x 10(18) eV, for all zenith angles between 0 degrees and 60 degrees, independently of the position of the impact point and of the mass of the primary particle. In these range of energies and angles, the exposure of the surface array can be determined purely on the basis of the geometrical acceptance. (C) 2009 Elsevier B.V. All rights reserved.

Journal ArticleDOI
TL;DR: The simulation of transport conditions of the in vivo interface should become a focus of research interest in order to gain a better understanding of the influence of connecting processes on the degradation of the biomaterials.

Journal ArticleDOI
TL;DR: The results indicated that the ability to in vitro solubilize P is not necessarily associated to the promotion of plant growth.
Abstract: To identify plant growth promotion ability of phosphorus-solubilizing native bacteria, we have examined a collection of isolates representing the diversity of culturable phosphate-solubilizing bacteria from acid soils of the northeast of Argentina. Assays in growth medium supplemented with tricalcium phosphate revealed different phosphorus solubilization activity and temporal patterns of solubilization. Acidification of the broth medium coincided with phosphorus solubilization. The isolates were grouped according to their Rep fingerprinting profiles and phylogenetically classified by 16S rDNA and biochemical analyses. These isolates were assigned to the genera Enterobacter, Pantoea, Pseudomonas, Acinetobacter, Burkholderia, and Exiguobacterium. Four isolates showing high phosphorus solubilizing activity in in vitro assays were inoculated on common beans (Phaseolus vulgaris); some of them promoted plant growth and increased photosynthesis and the P and N content of leaves. The results indicated that the ability to in vitro solubilize P is not necessarily associated to the promotion of plant growth.

Journal ArticleDOI
Georges Aad1, Brad Abbott2, Jalal Abdallah3, A. A. Abdelalim4  +2565 moreInstitutions (176)
TL;DR: An overview of the Tile Calorimeter performance as measured using random triggers, calibration data, data from cosmic ray muons and single beam data and the determination of the global energy scale was performed with an uncertainty of 4%.
Abstract: The Tile hadronic calorimeter of the ATLAS detector has undergone extensive testing in the experimental hall since its installation in late 2005. The readout, control and calibration systems have been fully operational since 2007 and the detector has successfully collected data from the LHC single beams in 2008 and first collisions in 2009. This paper gives an overview of the Tile Calorimeter performance as measured using random triggers, calibration data, data from cosmic ray muons and single beam data. The detector operation status, noise characteristics and performance of the calibration systems are presented, as well as the validation of the timing and energy calibration carried out with minimum ionising cosmic ray muons data. The calibration systems’ precision is well below the design value of 1%. The determination of the global energy scale was performed with an uncertainty of 4%.

Journal ArticleDOI
TL;DR: In this article, the authors used the largest set of velocities obtained so far of any elliptical galaxy to revise and extend the previous investigations (Richtler et al. 2004) of the dynamics of NGC 1399, the central dominant galaxy of the nearby Fornax cluster of galaxies.
Abstract: Globular clusters (GCs) are tracers of the gravitational potential of their host galaxies. Moreover, their kinematic properties may provide clues for understanding the formation of GC systems and their host galaxies. We use the largest set of GC velocities obtained so far of any elliptical galaxy to revise and extend the previous investigations (Richtler et al. 2004) of the dynamics of NGC 1399, the central dominant galaxy of the nearby Fornax cluster of galaxies. The GC velocities are used to study the kinematics, their relation with population properties, and the dark matter halo of NGC 1399. We have obtained 477 new medium-resolution spectra (of these, 292 are spectra from 265 individual GCs, 241 of which are not in the previous data set). with the VLT FORS 2 and Gemini South GMOS multi-object spectrographs. We revise velocities for the old spectra and measure velocities for the new spectra, using the same templates to obtain an homogeneously treated data set. Our entire sample now comprises velocities for almost 700 GCs with projected galactocentric radii between 6 and 100 kpc. In addition, we use velocities of GCs at larger distances published elsewhere. Combining the kinematic data with wide-field photometric Washington data, we study the kinematics of the metal-poor and metal-rich subpopulations. We discuss in detail the velocity dispersions of subsamples and perform spherical Jeans modelling. The most important results are: the red GCs resemble the stellar field population of NGC 1399 in the region of overlap. The blue GCs behave kinematically more erratic. Both subpopulations are kinematically distinct and do not show a smooth transition. It is not possible to find a common dark halo which reproduces simultaneously the properties of both red and blue GCs. Some velocities of blue GCs are only to be explained by orbits with very large apogalactic distances, thus indicating a contamination with GCs which belong to the entire Fornax cluster rather than to NGC 1399. Also, stripped GCs from nearby elliptical galaxies, particularly NGC 1404, may contaminate the blue sample. We argue in favour of a scenario in which the majority of the blue cluster population has been accreted during the assembly of the Fornax cluster. The red cluster population shares the dynamical history of the galaxy itself. Therefore we recommend to use a dark halo based on the red GCs alone. The dark halo which fits best is marginally less massive than the halo quoted previously. The comparison with X-ray analyses is satisfactory in the inner regions, but without showing evidence for a transition from a galaxy to a cluster halo, as suggested by X-ray work.

Journal ArticleDOI
TL;DR: In this paper, a series of relationships between film properties based on gelatin was found, as well as between these properties and glycerol content of the films, which would allow better management of film formulations and an appropriate selection of plasticizer concentration in accordance with the specific requirements of potential users.
Abstract: The aims of this work were to develop gelatin films using glycerol as plasticizer (0–100% based on protein mass) and to establish relationships between glycerol content and structural, barrier, thermal and mechanical film properties. These correlations were established since WVP exhibited a minimum for films containing 20 g glycerol/100 g gelatin, while flexibility increased from 2.2% to 180.9% and T g shifted from 137.5 to 21.3 °C, for films without glycerol and plasticized films with 80 g glycerol/100 g gelatin, respectively. Furthermore, a satisfactory fit between T g experimental data and predicted values by Couchman and Karasz's equation was found, with glycerol ranging from 0 to 60 g/100 g gelatin. T g values correlated inversely with film moisture content, and both mechanical and thermal properties showed a strong dependence since elastic modulus and T g followed a similar trend. Films exhibited similar X-ray patterns regardless of the glycerol concentration, showing a displacement in the position of the peak located at around 2 θ = 8°, which shifted towards lower 2 θ values with glycerol content. The abovementioned correlations between film physical properties and glycerol content, would allow to select the optimum conditions to develop, process and manage gelatin films according to specific requirements. Industrial relevance The methodology used in this work is of considerable importance for the film development and could be used in industrial applications. The management of film formulations and the function that each component plays could allow to obtain tailormade films. A series of relationships between film properties based on gelatin was found, as well as between these properties and glycerol content of the films. An inflexion point in the behavior and microstructure of these materials was established due to glycerol concentration. The addition of higher quantities of glycerol than that corresponds to the abovementioned point, would not be recommendable since the properties are not modified and moreover, it is not profitable. These results would allow better management of film formulations and an appropriate selection of plasticizer concentration in accordance with the specific requirements of potential users.

Journal ArticleDOI
TL;DR: It is found that metformin causes an osteogenic effect both in vivo and in vitro, possibly mediated by Runx2/Cbfa1 and AMPK activation, suggesting a possible action of met formin in a shift toward the osteoblastic differentiation of BMPCs.
Abstract: Diabetes mellitus is associated with bone loss. Patients with type 2 diabetes are frequently treated with oral antidiabetic drugs such as sulfonylureas, biguanides, and thiazolidinediones. Rosiglitazone treatment has been shown to increase adipogenesis in bone marrow and to induce bone loss. In this study we evaluated the effect of in vivo and in vitro treatment with metformin on bone marrow progenitor cells (BMPCs), as well as the involvement of AMPK pathway in its effects. The in vitro effect of coincubation with metformin and rosiglitazone on the adipogenic differentiation of BMPCs also was studied. In addition, we evaluated the effect of in vivo metformin treatment on bone regeneration in a model of parietal lesions in nondiabetic and streptozotocin-induced diabetic rats. We found that metformin administration both in vivo and in vitro caused an increase in alkaline phosphatase activity, type I collagen synthesis, osteocalcin expression, and extracellular calcium deposition of BMPCs. Moreover, metformin significantly activated AMPK in undifferentiated BMPCs. In vivo, metformin administration enhanced the expression of osteoblast-specific transcription factor Runx2/Cbfa1 and activation of AMPK in a time-dependent manner. Metformin treatment also stimulated bone lesion regeneration in control and diabetic rats. In vitro, metformin partially inhibited the adipogenic actions of rosiglitazone on BMPCs. In conclusion, our results indicate that metformin causes an osteogenic effect both in vivo and in vitro, possibly mediated by Runx2/Cbfa1 and AMPK activation, suggesting a possible action of metformin in a shift toward the osteoblastic differentiation of BMPCs.

Journal ArticleDOI
TL;DR: This work proposes to use the complexity-entropy causality plane, a powerful tool for discriminating Gaussian from non-Gaussian process and different degrees of correlations, to distinguish the stage of stock market development.
Abstract: The complexity-entropy causality plane has been recently introduced as a powerful tool for discriminating Gaussian from non-Gaussian process and different degrees of correlations [O.A. Rosso, H.A. Larrondo, M.T. Martin, A. Plastino, M.A. Fuentes, Distinguishing noise from chaos, Phys. Rev. Lett. 99 (2007) 154102]. We propose to use this representation space to distinguish the stage of stock market development. Our empirical results demonstrate that this statistical physics approach is useful, allowing a more refined classification of stock market dynamics.

Journal ArticleDOI
TL;DR: It is shown that it is possible to perform a reliable time delay identification by using quantifiers derived from information theory, more precisely, permutation entropy and permutation statistical complexity.
Abstract: In this paper an approach to identify delay phenomena from time series is developed. We show that it is possible to perform a reliable time delay identification by using quantifiers derived from information theory, more precisely, permutation entropy and permutation statistical complexity. These quantifiers show clear extrema when the embedding delay τ of the symbolic reconstruction matches the characteristic time delay τ(S) of the system. Numerical data originating from a time delay system based on the well-known Mackey-Glass equations operating in the chaotic regime were used as test beds. We show that our method is straightforward to apply and robust to additive observational and dynamical noise. Moreover, we find that the identification of the time delay is even more efficient in a noise environment. Our permutation approach is also able to recover the time delay in systems with low feedback rate or high nonlinearity.

Journal ArticleDOI
Georges Aad1, Brad Abbott2, Jalal Abdallah3, A. A. Abdelalim4  +2627 moreInstitutions (185)
TL;DR: The ATLAS Inner Detector as mentioned in this paper is a composite tracking system consisting of silicon pixels, silicon strips and straw tubes in a 2 T magnetic field, which was completed in 2008 and the detector took part in data-taking with single LHC beams and cosmic rays.
Abstract: The ATLAS Inner Detector is a composite tracking system consisting of silicon pixels, silicon strips and straw tubes in a 2 T magnetic field. Its installation was completed in August 2008 and the detector took part in data-taking with single LHC beams and cosmic rays. The initial detector operation, hardware commissioning and in-situ calibrations are described. Tracking performance has been measured with 7.6 million cosmic-ray events, collected using a tracking trigger and reconstructed with modular pattern-recognition and fitting software. The intrinsic hit efficiency and tracking trigger efficiencies are close to 100%. Lorentz angle measurements for both electrons and holes, specific energy-loss calibration and transition radiation turn-on measurements have been performed. Different alignment techniques have been used to reconstruct the detector geometry. After the initial alignment, a transverse impact parameter resolution of 22.1 +/- 0.9 mu m and a relative momentum resolution sigma (p) /p=(4.83 +/- 0.16)x10(-4) GeV(-1)xp (T) have been measured for high momentum tracks.

Journal ArticleDOI
TL;DR: In this article, the authors obtained millimeter-wavelength photometry, high-resolution optical spectroscopy, and adaptive optics near-infrared imaging for a sample of 26 Spitzer-selected transition circumstellar disks.
Abstract: We have obtained millimeter-wavelength photometry, high-resolution optical spectroscopy, and adaptive optics near-infrared imaging for a sample of 26 Spitzer-selected transition circumstellar disks. All of our targets are located in the Ophiuchus molecular cloud (d ~ 125 pc) and have spectral energy distributions (SEDs) suggesting the presence of inner opacity holes. We use these ground-based data to estimate the disk mass, multiplicity, and accretion rate for each object in our sample in order to investigate the mechanisms potentially responsible for their inner holes. We find that transition disks are a heterogeneous group of objects, with disk masses ranging from <0.6 to 40 M JUP and accretion rates ranging from <10–11 to 10–7 M ☉ yr–1, but most tend to have much lower masses and accretion rates than full disks (i.e., disks without opacity holes). Eight of our targets have stellar companions: six of them are binaries and the other two are triple systems. In four cases, the stellar companions are close enough to suspect they are responsible for the inferred inner holes. We find that nine of our 26 targets have low disk mass (<2.5 M JUP) and negligible accretion (<10–11 M ☉ yr–1), and are thus consistent with photoevaporating (or photoevaporated) disks. Four of these nine non-accreting objects have fractional disk luminosities <10–3 and could already be in a debris disk stage. Seventeen of our transition disks are accreting. Thirteen of these accreting objects are consistent with grain growth. The remaining four accreting objects have SEDs suggesting the presence of sharp inner holes, and thus are excellent candidates for harboring giant planets.

Journal ArticleDOI
01 Jan 2010
TL;DR: The objective of this work was to obtain water-in-oil emulsions with polyglycerol polyricinoleate (PGPR) as emulsifier and to study the effect of the addition of calcium in the dispersed aqueous phase on the stability of these systems.
Abstract: The objective of this work was to obtain water-in-oil (w/o) emulsions with polyglycerol polyricinoleate (PGPR) as emulsifier and to study the effect of the addition of calcium in the dispersed aqueous phase on the stability of these systems. Emulsions were formulated with 0.2, 0.5 and 1.0% w/w PGPR and 10% w/w water containing calcium chloride at varied concentrations or other salts (calcium lactate or carbonate; sodium, magnesium or potassium chloride). The stability of these systems was studied with a vertical scan analyzer during 15 days; coalescence and sedimentation were observed as simultaneous destabilization processes. The increase of PGPR concentration and/or calcium chloride content gave more stable emulsions. The stabilizing effect of calcium salt was attributed to the diminution of the water droplets size, the decrease of the attractive force between water droplets and the increase of the adsorption density of the emulsifier. The viscoelastic parameters of the interfacial film were decreased with increasing calcium and PGPR concentrations. Calcium chloride produced a higher increase of stability than calcium salts with lower dissociation degree. The presence of any assayed salt in the aqueous phase also allowed the stabilization of w/o emulsions with higher water contents.

Journal ArticleDOI
TL;DR: A review of the most common numerical methods used to solve the partial differential equations describing wave propagation in fluid-saturated rocks, including finite-difference, pseudospectral, and finite-element methods, including the spectral-element technique, is provided in this paper.
Abstract: Computational physics has become an essential research and interpretation tool in many fields. Particularly in reservoir geophysics, ultrasonic and seismic modeling in porous media is used to study the properties of rocks and to characterize the seismic response of geologic formations. We provide a review of the most common numerical methods used to solve the partial differential equations describing wave propagation in fluid-saturated rocks, i.e., finite-difference, pseudospectral, and finite-element methods, including the spectral-element technique. The modeling is based on Biot-type theories of dynamic poroelasticity, which constitute a general framework to describe the physics of wave propagation. We explain the various techniques and discuss numerical implementation aspects for application to seismic modeling and rock physics, as, for instance, the role of the Biot diffusion wave as a loss mechanism and interface waves in porous media.

Journal ArticleDOI
TL;DR: Three methods for the automatic picking of first-break picks are developed, including Modified Coppens’s method, an entropy-based method, and a variogram fractal-dimension method, which show that accurate and consistent picks can be obtained in an automated manner even under the presence of correlated noise, bad traces, pulsechanges, andindistinct firstbreaks.
Abstract: We have developed three methods for the automatic pickingoffirstbreaksthatcanbeusedformarine,dynamite,orvibroseisshotrecords:amodifiedCoppens’smethod,anentropy-based method, and a variogram fractal-dimension method.Thetechniquesarebasedonthefactthatthetransitionbetweennoiseandnoiseplussignalcanbeautomaticallyidentified by detecting rapid changes in a certain attribute energy ratio, entropy, or fractal dimension, which we calculate withinmovingwindowsalongtheseismictrace.Theapplication of appropriate edge-preserving smoothing operators to enhancethesetransitionsallowedustodevelopanautomated strategy that can be used to easily signal the precise location ofthefirst-arrivalonset.Furthermore,weproposeamispickcorrectingtechniquetoexploitthebenefitsofthedatapresent in the entire shot record, which allows us to adjust the traceby-trace picks and to discard picks associated with bad or dead traces. As a result, the consistency of the first-break picks is significantly improved. The methods are robust under noisy conditions, computationally efficient, and easy to apply. Results using dynamite and vibroseis field data show that accurate and consistent picks can be obtained in an automated manner even under the presence of correlated noise, badtraces,pulsechanges,andindistinctfirstbreaks.

Journal ArticleDOI
Georges Aad, E. Abat, Brad Abbott, Jalal Abdallah  +3208 moreInstitutions (169)
TL;DR: The first measurements from proton-proton collisions recorded with the ATLAS detector at the LHC are presented in this paper, where the charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transversal momentum and charge multiplicity are measured for events with at least one charged particle in the kinematic range.