484 research outputs found
A study of a non-deepening tropical disturbance
Data from research vessel, instrumented research aircraft, and Tiros VI and Tiros VII SATELLITES to study nondeepening tropical disturbanc
La enseñanza de las Matemáticas en Inglaterra
Las matemáticas en Inglaterra se encontraban á nivel bastante bajo cuando Babbage Peacock, Herschel y otros, fundaron la Sociedad Analítica de Cambridge en el año 1813. Su propósito, como lo refiere Babbage, era: «inculcar los principios de puro (d- irm) como opuestos al (dot age) de la Universidad», ó en otras palabras, sustituir la numeración Continental por los puntos originales de Newton. La sociedad alcanzó su objeto llegando así á la creciente actividad que caracteriza á la Escuela de Cambridge, por mucho tiempo la admiración del país. El valor de la iniciativa y la cooperación está bien demostrado por la parte que ha desempeñado la Sociedad Analítica en la reforma de las matemáticas universitarias.Facultad de Ciencias Jurídicas y Sociale
Comments on ``The first detections of the Extragalactic Background Light at 3000, 5500, and 8000 A'' by Bernstein, Freedman and Madore
A critical discussion is presented of the data analysis applied by Bernstein,
Freedman and Madore (2002 ApJ, 571, 56; and ApJ 571, 85) in their measurement
of the Extragalactic Background Light. There are questionable assumptions in
the analysis of the ground-based observations of the Zodiacal Light. The
modeling of the Diffuse Galactic Light is based on an underestimated value of
the dust column density along the line of sight. Comparison with the previously
presented results from the same observations reveals a puzzling situation: in
spite of a large difference in the atmospheric scattered light corrections the
derived Extragalactic Background Light values are exactly the same. The claim
of the paper of a ``detection of the Extragalactic Background Light'' appears
premature.Comment: 6 pages, accepted for Ap
Optical and near infrared observations of SN 1998bu
Infrared and optical spectra of SN 1998bu at an age of one year after
explosion are presented. The data show evidence for the radioactive decay of
56Co to 56Fe, long assumed to be the powering source for the supernova light
curve past maximum light. The spectra provide direct evidence for at least 0.4
solar masses of iron being present in the ejecta of the supernova. The fits to
the data also show that the widths of the emission lines increase with time.
Photometric measurements in the H-band show that the supernova is not fading
during the observation period. This is consistent with theoretical
expectations.Comment: accepted A&A, 7 pages, 9 figure
Interventions to Improve Safer Sleep Practices in Families With Children Considered to Be at Increased Risk for Sudden Unexpected Death in Infancy:A Systematic Review
Background: Advice to families to follow infant care practices known to reduce the risks of Sudden Unexpected Death in Infancy (SUDI) has led to a reduction in deaths across the world. This reduction has slowed in the last decade with most deaths now occurring in families experiencing social and economic deprivation. A systematic review of the literature was commissioned by the National Child Safeguarding Practice Review Panel in England. The review covered three areas: interventions to improve engagement with support services, parental decision-making for the infant sleep environment, and interventions to improve safer sleep practices in families with infants considered to be at risk of SUDI. Aim: To describe the safer sleep interventions tested with families with infants at risk of SUDI and investigate what this literature can tell us about what works to reduce risk and embed safer sleep practices in this group. Methods: Eight online databases were systematically searched in December 2019. Intervention studies that targeted families with infants (0–1 year) at increased risk of SUDI were included. Studies were limited to those from Western Europe, North America or Australasia, published in the last 15 years. The Quality Assessment Tool for Studies with Diverse Designs was applied to assess quality. Data from included studies were extracted for narrative synthesis, including mode of delivery using Michie et al.'s Mode of Delivery Taxonomy. Results: The wider review returned 3,367 papers, with 23 intervention papers. Five types of intervention were identified: (1) infant sleep space and safer sleep education programs, (2) intensive or targeted home visiting services, (3) peer educators/ambassadors, (4) health education/raising awareness interventions, (5) targeted health education messages using digital media. Conclusion: Influencing behavior in families with infants at risk of SUDI has traditionally focused on “getting messages across,” with interventions predominantly using education and awareness raising mechanisms. This review found evidence of interventions moving from “information giving” to “information exchange” models using personalized, longer term relationship-building models. This shift may represent an improvement in how safer sleep advice is implemented in families with infants at risk, but more robust evidence of effectiveness is required. Systematic Review Registration: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/901091/DfE_Death_in_infancy_review.pdf, identifier: CRD42020165302
The FERRUM project: Transition probabilities for forbidden lines in [FeII] and experimental metastable lifetimes
Accurate transition probabilities for forbidden lines are important
diagnostic parameters for low-density astrophysical plasmas. In this paper we
present experimental atomic data for forbidden [FeII] transitions that are
observed as strong features in astrophysical spectra.
Aims: To measure lifetimes for the 3d^6(^3G)4s a ^4G_{11/2} and 3d^6(^3D)4s b
^4D_{1/2} metastable levels in FeII and experimental transition probabilities
for the forbidden transitions 3d^7 a ^4F_{7/2,9/2}- 3d^6(^3G)4s a ^4G_{11/2}.
Methods: The lifetimes were measured at the ion storage ring facility CRYRING
using a laser probing technique. Astrophysical branching fractions were
obtained from spectra of Eta Carinae, obtained with the Space Telescope Imaging
Spectrograph onboard the Hubble Space Telescope. The lifetimes and branching
fractions were combined to yield absolute transition probabilities.
Results: The lifetimes of the a ^4G_{11/2} and the b ^4D_{1/2} levels have
been measured and have the following values, 0.75(10) s and 0.54(3) s
respectively. Furthermore, we have determined the transition probabilities for
two forbidden transitions of a ^4F_{7/2,9/2}- a ^4G_{11/2} at 4243.97 and
4346.85 A. Both the lifetimes and the transition probabilities are compared to
calculated values in the literature.Comment: 5 pages, accepted for publication in A&
On the feasibility of cooling and trapping metastable alkaline-earth atoms
Metastability and long-range interactions of Mg, Ca, and Sr in the
lowest-energy metastable state are investigated. The calculated
lifetimes are 38 minutes for Mg*, 118 minutes for Ca*, and 17 minutes for Sr*,
supporting feasibility of cooling and trapping experiments. The
quadrupole-quadrupole long-range interactions of two metastable atoms are
evaluated for various molecular symmetries. Hund's case (c) 4_g potential
possesses a large 100-1000 K potential barrier. Therefore magnetic trap losses
can possibly be reduced using cold metastable atoms in a stretched M=2 state.
Calculations were performed in the framework of ab initio relativistic
configuration interaction method coupled with the random-phase approximation.Comment: 8 pages, 2 figures; to appear in PR
Properties of metastable alkaline-earth-metal atoms calculated using an accurate effective core potential
The first three electronically excited states in the alkaline-earth-metal
atoms magnesium, calcium, and strontium comprise the (nsnp) triplet P^o_J
(J=0,1,2) fine-structure manifold. All three states are metastable and are of
interest for optical atomic clocks as well as for cold-collision physics. An
efficient technique--based on a physically motivated potential that models the
presence of the ionic core--is employed to solve the Schroedinger equation for
the two-electron valence shell. In this way, radiative lifetimes, laser-induced
clock shifts, and long-range interaction parameters are calculated for
metastable Mg, Ca, and Sr.Comment: 13 pages, 9 table
[Fe IV] emission in ionized nebulae
This paper presents an analysis of [Fe IV] emission based on new
identifications and previous measurements of [Fe IV] lines in 30 Doradus, IC
4846, M42, SMC N88A, and SBS 0335-052. The Fe abundances obtained by adding the
abundances of the relevant Fe ions (mainly Fe^{++} and Fe^{3+}) are found to be
lower, by factors in the range 2.6-5.9, than the Fe abundances implied by [Fe
III] emission and an ionization correction factor derived from ionization
models. The most likely explanation of this discrepancy is that either the
collision strengths for [Fe IV] or the Fe ionization fractions predicted by
models are unreliable. The available data neither allow one to distinguish
between these two possibilities nor to exclude another possible explanation:
that the discrepancy implies the presence of a gradient in the Fe abundance
within the ionized gas. Further measurements of [Fe IV] lines and checks on the
Fe^{3+} atomic data and ionization models are needed to reach a definitive
conclusion. The discrepancy introduces an uncertainty in the determination of
Fe abundances in ionized nebulae. This uncertainty has implications for our
understanding of both the evolution of dust in ionized nebulae and the chemical
history of low metallicity galaxies.Comment: 23 pages, 3 figures, accepted for publication in ApJ, a new table and
several comments adde
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