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Molecular clouds have power-law probability distribution functions

Lombardi, Marco; Alves, João; Lada, Charles J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/02/2015 Português
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In this Letter we investigate the shape of the probability distribution of column densities (PDF) in molecular clouds. Through the use of low-noise, extinction-calibrated \textit{Herschel}/\textit{Planck} emission data for eight molecular clouds, we demonstrate that, contrary to common belief, the PDFs of molecular clouds are not described well by log-normal functions, but are instead power laws with exponents close to two and with breaks between $A_K \simeq 0.1$ and $0.2\,\mathrm{mag}$, so close to the CO self-shielding limit and not far from the transition between molecular and atomic gas. Additionally, we argue that the intrinsic functional form of the PDF cannot be securely determined below $A_K \simeq 0.1\,\mathrm{mag}$, limiting our ability to investigate more complex models for the shape of the cloud PDF.; Comment: Letter to the Editor, to appear in A&A

Joint resonant CMB power spectrum and bispectrum estimation

Meerburg, P. Daniel; Münchmeyer, Moritz; Wandelt, Benjamin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We develop the tools necessary to assess the statistical significance of resonant features in the CMB correlation functions, combining power spectrum and bispectrum measurements. This significance is typically addressed by running a large number of simulations to derive the probability density function (PDF) of the feature-amplitude in the Gaussian case. Although these simulations are tractable for the power spectrum, for the bispectrum they require significant computational resources. We show that, by assuming that the PDF is given by a multi-variate Gaussian where the covariance is determined by the Fisher matrix of the sine and cosine terms, we can efficiently produce spectra that are statistically close to those derived from full simulations. By drawing a large number of spectra from this PDF, both for the power spectrum and the bispectrum, we can quickly determine the statistical significance of candidate signatures in the CMB, considering both single frequency and multi-frequency estimators. We show that for resonance models, cosmology and foreground parameters have little influence on the estimated amplitude, which allows to simplify the analysis considerably. A more precise likelihood treatment can then be applied to candidate signatures only. We also discuss a modal expansion approach for the power spectrum...

The probability distribution for non-Gaussianity estimators constructed from the CMB trispectrum

Smith, Tristan L.; Kamionkowski, Marc
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/03/2012 Português
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Considerable recent attention has focussed on the prospects to use the cosmic microwave background (CMB) trispectrum to probe the physics of the early universe. Here we evaluate the probability distribution function (PDF) for the standard estimator tau_nle for the amplitude tau_nl of the CMB trispectrum both for the null-hypothesis (i.e., for Gaussian maps with tau_nl = 0) and for maps with a non-vanishing trispectrum (|tau_nl|>0). We find these PDFs to be highly non-Gaussian in both cases. We also evaluate the variance with which the trispectrum amplitude can be measured, , as a function of its underlying value, tau_nl. We find a strong dependence of this variance on tau_nl. We also find that the variance does not, given the highly non-Gaussian nature of the PDF, effectively characterize the distribution. Detailed knowledge of these PDFs will therefore be imperative in order to properly interpret the implications of any given trispectrum measurement. For example, if a CMB experiment with a maximum multipole of lmax = 1500 (such as the Planck satellite) measures tau_nle = 0 then at the 95% confidence our calculations show that we can conclude tau_nl < 1005; assuming a Gaussian PDF but with the correct tau_nl-dependent variance we would incorrectly conclude tau_nl < 4225; further neglecting the tau_nl-dependence in the variance we would incorrectly conclude tau_nl < 361.; Comment: 9 pages...

The Evolution of Optical Depth in the Ly-alpha Forest: Evidence Against Reionization at z~6

Becker, George D.; Rauch, Michael; Sargent, Wallace L. W.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/07/2006 Português
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We examine the evolution of the IGM Ly-alpha optical depth distribution using the transmitted flux probability distribution function (PDF) in a sample of 63 QSOs spanning absorption redshifts 1.7 < z < 5.8. The data are compared to two theoretical optical depth distributions: a model distribution based on the density distribution of Miralda-Escude et al. (2000) (MHR00), and a lognormal distribution. We assume a uniform UV background and an isothermal IGM for the MHR00 model, as has been done in previous works. Under these assumptions, the MHR00 model produces poor fits to the observed flux PDFs at redshifts where the optical depth distribution is well sampled, unless large continuum corrections are applied. However, the lognormal optical depth distribution fits the data at all redshifts with only minor continuum adjustments. We use a simple parametrization for the evolution of the lognormal parameters to calculate the expected mean transmitted flux at z > 5.4. The lognormal optical depth distribution predicts the observed Ly-alpha and Ly-beta effective optical depths at z > 5.7 while simultaneously fitting the mean transmitted flux down to z = 1.6. If the evolution of the lognormal distribution at z < 5 reflects a slowly-evolving density field...

Parton Distributions in the Higgs Boson Era

Rojo, Juan
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/05/2013 Português
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Parton distributions are an essential ingredient of the LHC program. PDFs are relevant for precision Standard Model measurements, for Higgs boson characterization as well as for New Physics searches. In this contribution I review recent progress in the determination of the parton distributions of the proton during the last year. Important developments include the impact of new LHC measurements to pin down poorly known PDFs, studies of theoretical uncertainties, higher order calculations for processes relevant for PDF determinations, PDF benchmarking exercises with LHC data, as well as methodological and statistical improvements in the global analysis framework. I conclude with some speculative considerations about future directions in PDF determinations from the theory point of view.; Comment: 11 pages, 5 figures, write-up of the plenary talk at the XXI International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2013), Marseille, 22-26 April 2013

Structure, morphology and reaction mechanisms of novel electrode materials for lithium-ion batteries

Hua, Xiao
Fonte: University of Cambridge; Department of Chemistry; St Edmund?s College Publicador: University of Cambridge; Department of Chemistry; St Edmund?s College
Tipo: Thesis; doctoral; PhD
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For the Li1+xV1-xO2 materials, the amount of excess Li does not change the average crystal structure; however, it alters the cycling performance greatly. This suggests that the local structure governs the electrochemical behaviour. This motivated us to employ the pair distribution function (PDF) technique to probe the local structure. The analyses show the displacements of V3+ form trimers. A structure model for the stoichiometric LiVO2 incorporating the V3+ distortion was constructed and refined, to assist in the assignment of the Li sites revealed by the 6Li nuclear magnetic resonance (NMR) results. For the TiO2-B materials, previous investigations of nanostructured phases suggested the Li insertion mechanism of these materials has a morphological dependence. However, the morphology of the nanoparticles, which to date shows the best cycling performance among all the TiO2 phases with various morphologies, has not been well studied due to the technical challenges which arise from the nature of the diffraction technique and the limited particle sizes. We therefore employed techniques including small-angle X-ray scattering (SAXS) and PDF analyses, to provide an accurate description of the morphology for these nanoparticles. Combining advanced structure modelling...

Interaction between the BDNF gene Val/66/Met polymorphism and morning cortisol levels as a predictor of depression in adult women

Herbert, Joe; Ban, M.; Brown, G. W.; Harris, T. O.; Ogilvie, A.; Uher, R.; Craig, T. K. J.
Fonte: Royal College of Psychiatrists Publicador: Royal College of Psychiatrists
Tipo: Article; published version
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This is the published version. It has been published by the Royal College of Psychiatrists in The British Journal of Psychiartry and can be found here: http://bjp.rcpsych.org/content/201/4/313.full.pdf+html. Information about the licence this work falls under can be found here: http://www.rcpsych.ac.uk/pdf/Wellcome%20Trust%20licence.pdf.; Background Common genetic variants, such as the brain-derived neurotrophic factor (BDNF) Val/66/Met polymorphism (rs6265), are known to interact with environmental factors such as early adversity to increase the risk of subsequent major depression. Much less is known about how they interact with individual differences in cortisol, although these also represent a risk for major depression. Aims To determine whether this BDNF variant moderated the risk represented by higher levels of morning salivary cortisol in adult women. Method We recruited 279 premenopausal women who were at high risk of major depressive disorder because of either negative self-evaluation, unsupportive core relationship or chronic subclinical symptoms of depression or anxiety. Morning salivary cortisol was measured daily for up to 10 days at entry. Participants were followed up for about 12 months by telephone calls at 3?4 monthly intervals. Major depression and severe life events were assessed through interviews at baseline and follow-up; DNA was obtained from the saliva. Results There were 53 onsets (19%) of depressive episodes during follow-up. There was a significant U-shaped relationship between adjusted morning cortisol levels at baseline and the probability of depression onset during follow-up. In total...

Extracting and re-using research data from chemistry e-theses: the SPECTRa-T project

Morgan, Peter; Downing, Jim; Murray-Rust, Peter; Stewart, Diana; Tonge, Alan; Townsend, Joseph A; Harvey, Matt; Rzepa, Henry S
Fonte: 11th International Symposium on Electronic Theses and Dissertations Publicador: 11th International Symposium on Electronic Theses and Dissertations
Tipo: Article; accepted version
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Scientific e-theses are data-rich resources, but much of the information they contain is not readily accessible. For chemistry, the SPECTRa-T project has addressed this problem by developing data-mining techniques to extract experimental data, creating RDF (Resource Description Framework) triples for exposure to sophisticated Semantic Web searches. We used OSCAR3, an Open Source chemistry text-mining tool, to parse and extract data from theses in PDF, and from theses in Office Open XML document format. Theses in PDF suffered data corruption and a loss of formatting that prevented the identification of chemical objects. Theses in .docx yielded semantically rich SciXML that enabled the additional extraction of associated data. Chemical objects were placed in a data repository, and RDF triples deposited in a triplestore. Data-mining from chemistry e-theses is both desirable and feasible; but the use of PDF, the de facto format standard for deposit in most repositories, prevents the optimal extraction of data for semantic querying. In order to facilitate this, we recommend that universities also require deposition of chemistry e-theses in an XML document format. Further work is required to clarify the complex IPR issues and ensure that they do not become an unwarranted barrier to data extraction and re-use.

Consciousness and the Physical World

Josephson, Brian D; Ramachandran, Vilayanur S
Fonte: Pergamon Press Publicador: Pergamon Press
Tipo: Book or Book Chapter; published version
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The main file in this deposition is a pdf file containing the scanned pages of the Proceedings. Additional files OCR.txt and OCR.pdf (the latter having the same pagination as the book) are included to simplify search, etc. Because of their automated creation using software, the accuracy of the OCR files cannot be guaranteed, though some checking has been carried out. In the scanned version, entering 'go to page n' in a pdf reader will access the pair of pages 2n and 2n+1. Alternatively, go to the contents pages (accessible via 'go to page', entering 'contents' at the prompt) for the numbers to use with 'go to' for specific chapters. ? By arrangement with the publishers, the editors (Brian D Josephson and Vilayanur S Ramachandran) are the present copyright holders. They grant permission for the use of the material in this book in accord with the terms of the CC licence below.; Edited proceedings of an interdisciplinary symposium on consciousness held at the University of Cambridge in January 1978, including a foreword by Freeman J. Dyson. Chapter authors: G. Vesey, R.L. Gregory, H.C. Longuet-Higgins, N.K. Humphrey, H.B. Barlow, D.M. MacKay, B.D. Josephson, M. Roth, V.S. Ramachandran, S. Padfield, and (editorial summary only) E. Noakes.; The conference was supported by a grant from Research Corporation of New York.

Differential vulnerability to the punishment of cocaine related behaviours: effects of locus of punishment, cocaine taking history and alternative reinforcer availability

Pelloux, Yann; Murray, Jennifer E.; Everitt, Barry J.
Fonte: Springer Publicador: Springer
Tipo: Article; published version
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This is the final published version, which can also be found on the publisher's website here: http://download.springer.com/static/pdf/914/art%253A10.1007%252Fs00213-014-3648-5.pdf?auth66=1404987650_ca63ac8614a2994c56b0f619563ee6af&ext=.pdf; Background: The availability of alternative reinforcement has been shown to reduce drug use, but it remains unclear whether it facilitates a reduction or cessation of drug seeking or taking. Objectives: We compared the effects of punishment of cocaine seeking or taking behaviour after brief or extended cocaine-taking histories when behavioural reallocation was facilitated or not by making available an alternative ingestive reinforcer (sucrose). Methods: In the first experiment, punishment of either seeking or taking responses was introduced immediately after training on the seeking-taking chained schedule. In the second experiment, punishment of cocaine seeking was introduced after 12 additional days of either 1 or 6 h daily access to cocaine self-administration. In both experiments, beginning 1 week before the introduction of punishment, a subset of rats had concurrent nose poke access to sucrose while seeking or taking cocaine. Results: The presence of an alternative source of reinforcement markedly facilitated behavioural reallocation from punished cocaine taking after acquisition. It also facilitated punishment-induced suppression of cocaine seeking after an extensive cocaine self-administration history likely by prompting goal-directed motivational control over drug use. However...

Galactic substructure and direct detection of dark matter

Kamionkowski, Marc; Koushiappas, Savvas M.
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 15/05/2008 Português
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We study the effects of substructure in the Galactic halo on direct detection of dark matter, on searches for energetic neutrinos from weakly interacting massive particles (WIMP) annihilation in the Sun and Earth, and on the enhancement in the WIMP annihilation rate in the halo. Our central result is a probability distribution function (PDF) P(rho) for the local dark-matter density. This distribution must be taken into account when using null dark-matter searches to constrain the properties of dark-matter candidates. We take two approaches to calculating the PDF. The first is an analytic model that capitalizes on the scale-invariant nature of the structure-formation hierarchy in order to address early stages in the hierarchy (very small scales; high densities). Our second approach uses simulation-inspired results to describe the PDF that arises from lower-density larger-scale substructures which formed in more recent stages in the merger hierarchy. The distributions are skew positive, and they peak at densities lower than the mean density. The local dark-matter density may be as small as 1/10th the canonical value of ~=0.4 GeV cm^-3, but it is probably no less than 0.2 GeV cm^-3.

Characteristics of transitional multicomponent gaseous and drop-laden mixing layers from direct numerical simulation: Composition effects

Selle, L. C.; Bellan, J.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /06/2007 Português
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Transitional states are obtained by exercising a model of multicomponent-liquid (MC-liquid) drop evaporation in a three-dimensional mixing layer at larger Reynolds numbers, Re, than in a previous study. The gas phase is followed in an Eulerian frame and the multitude of drops is described in a Lagrangian frame. Complete dynamic and thermodynamic coupling between phases is included. The liquid composition, initially specified as a single-Gamma (SG) probability distribution function (PDF) depending on the molar mass, is allowed to evolve into a linear combination of two SGPDFs, called the double-Gamma PDF (DGPDF). The compositions of liquid and vapor emanating from the drops are calculated through four moments of their PDFs, which are drop-specific and location-specific, respectively. The mixing layer is initially excited to promote the double pairing of its four initial spanwise vortices, resulting into an ultimate vortex in which small scales proliferate. Simulations are performed for four liquids of different compositions, and the effects of the initial mass loading and initial free-stream gas temperature are explored. For reference, simulations are also performed for gaseous multicomponent mixing layers for which the effect of Re is investigated in the direct-numerical-simulation–accessible regime. The results encompass examination of the global layer characteristics...

Distributed space-time coding for two-way wireless relay networks

Cui, Tao; Gao, Feifei; Ho, Tracey; Nallanathan, Arumugam
Fonte: IEEE Publicador: IEEE
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /02/2009 Português
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In this paper, we consider distributed space-time coding for two-way wireless relay networks, where communication between two terminals is assisted by relay nodes. Relaying protocols using two, three, and four time slots are proposed. The protocols using four time slots are the traditional amplify-and-forward (AF) and decode-and-forward (DF) protocols, which do not consider the property of the two-way traffic. A new class of relaying protocols, termed as partial decode-and-forward (PDF), is developed for the two time slots transmission, where each relay first removes part of the noise before sending the signal to the two terminals. Protocols using three time slots are proposed to compensate the fact that the two time slots protocols cannot make use of direct transmission between the two terminals. For all protocols, after processing their received signals, the relays encode the resulting signals using a distributed linear dispersion (LD) code. The proposed AF protocols are shown to achieve the diversity order of min{N,K}(1- (log log P/log P)), where N is the number of relays, P is the total power of the network, and K is the number of symbols transmitted during each time slot. When random unitary matrix is used for LD code, the proposed PDF protocols resemble random linear network coding...

Improved Estimation of Discrete Probability Density Functions Using Multirate Models

Yoon, Byung-Jun; Vaidyanathan, P. P.
Fonte: IEEE Publicador: IEEE
Tipo: Book Section; PeerReviewed Formato: application/pdf
Publicado em 04/05/2004 Português
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For many decades, the problem of estimating a pdf based on measurements has been of interest to many researchers. Even though much work has been done in the area of pdf estimation, most of it was focused on the continuous case. In this paper, we propose a new model based approach for estimating a discrete probability density function. This approach is based on multirate dsp theory, and it has several advantages over the traditional histogram method. It is shown that this method yields an unbiased pdf estimate with small variance, which is guaranteed to have a smaller estimation error than the histogram. Simulation results are given, which show the merit of the proposed method.

Reconstruction subgrid models for nonpremixed combustion

Mellado, J. P.; Sarkar, S.; Pantano, C.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /11/2003 Português
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Large-eddy simulation of combustion problems involves highly nonlinear terms that, when filtered, result in a contribution from subgrid fluctuations of scalars, Z, to the dynamics of the filtered value. This subgrid contribution requires modeling. Reconstruction models try to recover as much information as possible from the resolved field Z, based on a deconvolution procedure to obtain an intermediate field ZM. The approximate reconstruction using moments (ARM) method combines approximate reconstruction, a purely mathematical procedure, with additional physics-based information required to match specific scalar moments, in the simplest case, the Reynolds-averaged value of the subgrid variance. Here, results from the analysis of the ARM model in the case of a spatially evolving turbulent plane jet are presented. A priori and a posteriori evaluations using data from direct numerical simulation are carried out. The nonlinearities considered are representative of reacting flows: power functions, the dependence of the density on the mixture fraction (relevant for conserved scalar approaches) and the Arrhenius nonlinearity (very localized in Z space). Comparisons are made against the more popular beta probability density function (PDF) approach in the a priori analysis...

Probability distribution for non-Gaussianity estimators constructed from the CMB trispectrum

Smith, Tristan L.; Kamionkowski, Marc
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Article; PeerReviewed Formato: application/pdf; application/pdf
Publicado em 15/09/2012 Português
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Considerable recent attention has focussed on the prospects to use the cosmic microwave background (CMB) trispectrum to probe the physics of the early universe. Here we evaluate the probability distribution function (PDF) for the standard estimator τ̂_nl for the amplitude τ_nl of the CMB trispectrum both for the null hypothesis (i.e., for Gaussian maps with τnl=0) and for maps with a nonvanishing trispectrum (τ_nl≠0). We find these PDFs to be highly non-Gaussian in both cases. We also evaluate the variance with which the trispectrum amplitude can be measured, ⟨Δτ̂^(2)_(nl)⟩, as a function of its underlying value, τnl. We find a strong dependence of this variance on τ_nl. We also find that the variance does not, given the highly non-Gaussian nature of the PDF, effectively characterize the distribution. Detailed knowledge of these PDFs will therefore be imperative in order to properly interpret the implications of any given trispectrum measurement. For example, if a CMB experiment with a maximum multipole of l_max=1500 (such as the Planck satellite) measures τ̂_nl=0 then at the 95% confidence level our calculations show that we can conclude τ_nl≤1005; assuming a Gaussian PDF but with the correct τnl-dependent variance we would incorrectly conclude τ_nl≤4225; further neglecting the τ_nl-dependence in the variance we would incorrectly conclude τ_nl≤361.

An Experimental study of differences in reading photo books by presentation media: print vs. screen

Tsai, Ya-Fang
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
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As photography technology changes, the penetration of digital cameras is increasing, especially among young users. Compared to conventional camera users who print most of their images, digital camera users print about one-third of their digital images (PMA, 2009b, p. 10). Moreover, only 5 percent of camera phone users make photo prints (Henning, 2008, p. 4). One popular photo-finishing product is the photo book. The objective of this research was to determine whether people interacted differently with photographic content presented in print versus on screen. This research was focused on: 1. Time spent interacting with photo books. 2. Differences of recall and recognition by presentation modality. 3. Choices of medium preference. An experimental study was administered at RIT with 64 participants. Half were shown the printed book, and half were shown the PDF displayed on a computer monitor. The results showed that: 1. The average time spent interacting with the book was approximately 5 minutes for both printed book and screen views. There were no differences in the amount of time spent interacting with photographic content presented in print versus on screen. 2. There were no differences in how much participants remembered with photographic content presented on print versus on screen. 3. Overall...

CCD speckle observations of binary stars from the Southern Hemisphere

Horch, Elliott; Ninkov, Zoran; Slawson, Robert
Fonte: University of Chicago Press Publicador: University of Chicago Press
Tipo: Artigo de Revista Científica Formato: 1823538 bytes; application/pdf
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We present 119 position angle and separation measures of 86 double stars observed by way of speckle interferometry with the University of Toronto Southern Observatory 60 cm telescope at Las Campanas, Chile. Speckle interferograms are recorded with a bare (unintensified) front-illuminated CCD in a fast subarray-readout mode. Position angles and separations are determined by a weighted least-squares fitting algorithm applied to the binary power spectra, and the 180-degree ambiguity in the position angle inherent in this approach is resolved by bispectral analysis. In this configuration the 60 cm telescope exhibits near-diffraction-limited performance. Initial results indicate that our separation measures have a root-mean-square (rms) deviation of 6.6 +/- 1.0 milliarcsecond (mas) and our position angles have an rms deviation of 1.73 +/- 0.26 degrees when judged against the ephemeris positions of a small sample of binaries with previously well-determined orbits (Refer to PDF file for exact formulas).; This article may also be accessed from the publisher's website at: http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1997AJ....114.2117H&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf; We would like to thank the University of Toronto Southern Observatory for observing time...

Deep CCD photometry and the initial mass function of the core of the OB cluster Berkeley 86

Deeg, Hans; Ninkov, Zoran
Fonte: The European Southern Observatory (ESO) Publicador: The European Southern Observatory (ESO)
Tipo: Artigo de Revista Científica Formato: 1800831 bytes; application/pdf
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Based on photometry of deep CCD frames of the central region of the OB cluster Berkeley 86, we derive the cluster mass function. The absence of current star formation, and the cluster's young age of about 6Myrs, leads to the conclusion that the initial mass function (IMF) and the current mass function are identical for stars with m<10msun_. In the range of 1.2-20msun_, an IMF with a slope of {GAMMA}=-1.3+/-0.3 is found. This value agrees well with other recent determinations of young clusters IMFs which are close to the classical Salpeter IMF with {GAMMA}=-1.35. Sections of the IMF of Berkeley 86 that are significantly steeper, or flatter, are most likely the result of a dip in the star's mass distribution in the range of 3.5-10msun_. Similar dips may have led to steep IMFs over narrow mass ranges, as reported in the literature for some other clusters. No sign for a low mass turn-over in the IMF of Berkeley 86 is found for masses extending down to 0.85 msun _ (Refer to PDF file for exact formulas).; This article may also be accessed on the publisher's website at: http://www.edpsciences.org/articles/aas/pdf/1996/14/ds4506.pdf?access=ok; The CCD sensor development was supported by an NSF IUCRC and a New York State CAT grant to the Center for Electronic Imaging Systems and a FAR Theodore Dunham Jr. Grant.

Imaging of the central region of IC 1805

Ninkov, Zoran; Bretz, David; Easton, Roger
Fonte: The University of Chicago Press Publicador: The University of Chicago Press
Tipo: Artigo de Revista Científica Formato: 3221178 bytes; application/pdf
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The central regions of OB Associations are suitable for the study of the initial mass function since the constituent stars have not had sufficient time to migrate far from their formation site or to evolve from the main sequence. This paper reports on CCD observations of the central 7'x7' region of the OB cluster Ocl 352, locatied in the H _ region IC 1805, that is within the association Cas OB6, which is in turn part of the molecular cloud W4. Colors were determined for 160 stars in IC 1805 and this information allowed the initial mass function for the region to be determined. A weighted linear least-squares fit to this mass function in the mass range 2.5-30 M_, yields a slope of _ = -1.38 +/- 0.19. This is similar to the slope (-1.25 +/- 0.17) determined using the brighter stars identified in a larger region (50'x50') of IC 1805 by Joshi & Sagar [JRASC, 77, 40 (1983)]. It is also close to the slope of the IMF determined by other modern studies of select OB clusters. A roll off in the number of low-mass stars is observed but this is attributed to incompleteness in this study's inventory of stars of mass less than 2.5 M_ (Refer to PDF file for exact formulas).; This article may also be accessed on the publisher's website at: http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1995AJ....110.2242N&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf; The detector development effort at RIT is supported by NSF IUCRC and New York State Science and Technology Foundation CAT grants. The analysis of the CCD data was made possible by a NASA JOVE grant and a FAR Theodore Dunham Jr. grant. This research made use of the Simbad database operated at CDS...