1,207 research outputs found
Risk Factors for Delayed Cerebral Ischemia in Good-Grade Patients With Aneurysmal Subarachnoid Hemorrhage
Peer reviewe
NASA GRC Compass Team Conceptual Point Design and Trades of a Hybrid Solar Electric Propulsion (SEP)/Chemical Propulsion Human Mars Deep Space Transport (DST) Vehicle
NASA has long been conducting studies which apply different in-space propulsion technology assumptions to the mission of sending humans to Mars. Two of the technologies under study that are considered to be the most near-term with respect to technology readiness level (TRL) are traditional chemical propulsion systems and high-power Solar Electric Propulsion (SEP) systems. The benefit of relatively low trip times inherent in using impulsive chemical propulsion systems to perform the full round-trip delta V is hampered by the large propellant mass required to perform these burns for human Mars missions. SEP systems offer the benefit of much lower propellant requirements to perform the same round-trip missions, at the cost of longer trip times. Traditionally, impulsive chemical systems are better suited than SEP when used in a gravity well, and SEP systems are more efficient than traditional impulsive systems when used in interplanetary space. A mission to Mars includes both of these scenarios, and thus several NASA architecture studies performed over the last few years have looked to combine the use of both SEP and chemical propulsion systems where they are the most beneficial to human Mars missions. This combined propulsion system concept has been referred to as a SEP/Chem hybrid Mars Transfer Vehicle and is currently shown as the concept Deep Space Transport (DST) in the March 2017 NASA presentation to the National Aerospace Council (NAC)
Several types of types in programming languages
Types are an important part of any modern programming language, but we often
forget that the concept of type we understand nowadays is not the same it was
perceived in the sixties. Moreover, we conflate the concept of "type" in
programming languages with the concept of the same name in mathematical logic,
an identification that is only the result of the convergence of two different
paths, which started apart with different aims. The paper will present several
remarks (some historical, some of more conceptual character) on the subject, as
a basis for a further investigation. The thesis we will argue is that there are
three different characters at play in programming languages, all of them now
called types: the technical concept used in language design to guide
implementation; the general abstraction mechanism used as a modelling tool; the
classifying tool inherited from mathematical logic. We will suggest three
possible dates ad quem for their presence in the programming language
literature, suggesting that the emergence of the concept of type in computer
science is relatively independent from the logical tradition, until the
Curry-Howard isomorphism will make an explicit bridge between them.Comment: History and Philosophy of Computing, HAPOC 2015. To appear in LNC
Informações de saĂşde mental on-line : o que aprendemos com as mĂ©tricas de mĂdias sociais na Semana de SaĂşde Mental do BuzzFeed
Introduction: The Internet has seen rapid growth in the number of websites focusing on mental health content. Considering the increased need for access to accurate information about mental health treatment, it is important to understand the promotion of this information online. Objective: To analyze BuzzFeed’s Mental Health Week (BFMHW) interactions on its own website and in related social media platforms (Facebook, Twitter and YouTube) using metrics of information delivery in mental health topics. Methods: We extracted social media metrics from the 20 posts with the highest number of BuzzFeed interactions on the BFMHW website and from 41 videos available on the BFMHW playlist created by the BuzzFeed Video profile on YouTube. We analyzed the format and content used in BuzzFeed’s publishing methods as well as the following social media metrics: exposure (presence online, views and time online), influence (likes) and engagement (comments, shares, replies and BuzzFeed interactions). Results: Analysis of the variables revealed that audience engagement is associated with the number of medias in which the content is published: views on YouTube and shares on Facebook (0.71, p<0.001), total interactions on Facebook (0.66, p<0.001) and BuzzFeed number of total interactions (0.56, p<0.001). Conclusions: Our results suggest that videos on YouTube may be an important information channel, including activity and engagement on other medias such as Facebook. Information may be more effective in reaching the audience if it is delivered in more than one media and includes personal experiences, some humor in content and detailed information about treatment.Introdução: O nĂşmero de sites com foco em conteĂşdo de saĂşde mental vem crescendo rapidamente. Considerando a necessidade crescente de acesso a informações precisas sobre tratamento em saĂşde mental, Ă© importante entender a promoção dessas informações on-line. Objetivo: Analisar as interações da Semana de SaĂşde Mental do BuzzFeed (BuzzFeed’s Mental Health Week – BFMHW) em seu prĂłprio site e em plataformas de mĂdia social relacionadas (Facebook, Twitter e YouTube) usando mĂ©tricas de entrega de informações em tĂłpicos de saĂşde mental. MĂ©todos: ExtraĂmos mĂ©tricas de mĂdias sociais das 20 postagens com o maior nĂşmero de interações no site da BFMHW e de 41 vĂdeos disponĂveis na playlist da BFMHW criada pelo perfil BuzzFeed Video no YouTube. Analisamos o formato e o conteĂşdo usados nos mĂ©todos de publicação do BuzzFeed, bem como as seguintes mĂ©tricas de mĂdias sociais: exposição (presença on-line, visualizações e tempo on-line), influĂŞncia (curtidas) e engajamento (comentários, compartilhamentos, respostas e interações do BuzzFeed). Resultados: A análise das variáveis revelou que o envolvimento do pĂşblico está associado ao nĂşmero de mĂdias em que o conteĂşdo Ă© publicado: visualizações no YouTube e compartilhamentos no Facebook (0,71, p <0,001), interações totais no Facebook (0,66, p <0,001) e nĂşmero de interações totais no BuzzFeed (0,56, p <0,001). Conclusões: Nossos resultados sugerem que o YouTube pode ser um importante canal de informações, incluindo atividades e envolvimento em outras mĂdias, como o Facebook. As informações podem alcançar o pĂşblico de forma mais eficaz se forem exibidas em mais de uma mĂdia e incluĂrem experiĂŞncias pessoais, algum humor no conteĂşdo e informações detalhadas sobre o tratamento
Performance of the LHC Pre-Injectors
The LHC pre-injector complex, comprising Linac 2, the PS Booster (PSB) and the PS, has undergone a major upgrade in order to meet the very stringent requirements of the LHC. Whereas bunches with the nominal spacing and transverse beam brightness were already available from the PS in 1999 [1], their length proved to be outside tolerance due to a debunching procedure plagued by microwave instabilities. An alternative scenario was then proposed, based on a series of bunch-splitting steps in the PS. The entire process has recently been implemented successfully, and beams whose longitudinal characteristics are safely inside LHC specifications are now routinely available. Variants of the method also enable bunch trains with gaps of different lengths to be generated. These are of interest for the study and possible cure of electron cloud effects in both the SPS and LHC. The paper summarizes the beam dynamics issues that had to be addressed to produce beams with all the requisite qualities for the LHC
A Cubesat Asteroid Mission: Propulsion Trade-offs
A conceptual design was performed for a 6-U cubesat for a technology demonstration to be launched on the NASA Space Launch System (SLS) test launch EM-1, to be launched into a free-return translunar trajectory. The mission purpose was to demonstrate use of electric propulsion systems on a small satellite platform. The candidate objective chosen was a mission to visit a Near-Earth asteroid. Both asteroid fly-by and asteroid rendezvous missions were analyzed. Propulsion systems analyzed included cold-gas thruster systems, Hall and ion thrusters, incorporating either Xenon or Iodine propellant, and an electrospray thruster. The mission takes advantage of the ability of the SLS launch to place it into an initial trajectory of C3=0
Measuring Controlled-NOT and two-qubit gate operation
Accurate characterisation of two-qubit gates will be critical for any
realisation of quantum computation. We discuss a range of measurements aimed at
characterising a two-qubit gate, specifically the CNOT gate. These measurements
are architecture-independent, and range from simple truth table measurements,
to single figure measures such as the fringe visibility, parity, fidelity, and
entanglement witnesses, through to whole-state and whole-gate measures achieved
respectively via quantum state and process tomography. In doing so, we examine
critical differences between classical and quantum gate operation.Comment: 10 pages (two-column). 1 figur
Direct and indirect control of the initiation of meiotic recombination by DNA damage checkpoint mechanisms in budding yeast
Meiotic recombination plays an essential role in the proper segregation of chromosomes at meiosis I in many sexually reproducing organisms. Meiotic recombination is initiated by the scheduled formation of genome-wide DNA double-strand breaks (DSBs). The timing of DSB formation is strictly controlled because unscheduled DSB formation is detrimental to genome integrity. Here, we investigated the role of DNA damage checkpoint mechanisms in the control of meiotic DSB formation using budding yeast. By using recombination defective mutants in which meiotic DSBs are not repaired, the effect of DNA damage checkpoint mutations on DSB formation was evaluated. The Tel1 (ATM) pathway mainly responds to unresected DSB ends, thus the sae2 mutant background in which DSB ends remain intact was employed. On the other hand, the Mec1 (ATR) pathway is primarily used when DSB ends are resected, thus the rad51 dmc1 double mutant background was employed in which highly resected DSBs accumulate. In order to separate the effect caused by unscheduled cell cycle progression, which is often associated with DNA damage checkpoint defects, we also employed the ndt80 mutation which permanently arrests the meiotic cell cycle at prophase I. In the absence of Tel1, DSB formation was reduced in larger chromosomes (IV, VII, II and XI) whereas no significant reduction was found in smaller chromosomes (III and VI). On the other hand, the absence of Rad17 (a critical component of the ATR pathway) lead to an increase in DSB formation (chromosomes VII and II were tested). We propose that, within prophase I, the Tel1 pathway facilitates DSB formation, especially in bigger chromosomes, while the Mec1 pathway negatively regulates DSB formation. We also identified prophase I exit, which is under the control of the DNA damage checkpoint machinery, to be a critical event associated with down-regulating meiotic DSB formation
Methods to Determine Neutrino Flux at Low Energies:Investigation of the Low Method
We investigate the "low-" method (developed by the CCFR/NUTEV
collaborations) to determine the neutrino flux in a wide band neutrino beam at
very low energies, a region of interest to neutrino oscillations experiments.
Events with low hadronic final state energy (of 1, 2 and 5 GeV)
were used by the MINOS collaboration to determine the neutrino flux in their
measurements of neutrino () and antineutrino (\nub_\mu) total cross
sections. The lowest energy for which the method was used in MINOS is
3.5 GeV, and the lowest \nub_\mu energy is 6 GeV. At these energies, the
cross sections are dominated by inelastic processes. We investigate the
application of the method to determine the neutrino flux for ,
\nub_\mu energies as low as 0.7 GeV where the cross sections are dominated by
quasielastic scattering and (1232) resonance production. We find that
the method can be extended to low energies by using values of 0.25
and 0.50 GeV, which is feasible in fully active neutrino detectors such as
MINERvA.Comment: 25 pages, 32 figures, to be published in European Physics Journal
Chemodynamics of Compact Stellar Systems in NGC 5128: How similar are Globular Clusters, Ultra-Compact Dwarfs, and Dwarf Galaxies?
Velocity dispersion measurements are presented for luminous GCs in NGC 5128
derived from high-res. UVES spectra. The measurements are made with the pPXF
code that parametrically recovers line-of-sight velocity dispersions. Combining
the measured velocity dispersions with surface photometry and structural
parameter data from HST enables both dynamical masses and M/L ratios to be
derived. The fundamental plane relations of these clusters are investigated in
order to fill the apparent gap between the relations of Local Group GCs and
more massive early-type galaxies. It is found that the properties of these
massive stellar systems match those of nuclear clusters in dwarf elliptical
galaxies and UCDs better than those of Local Group GCs, and that all objects
share similarly old (>8 Gyr) ages, suggesting a possible link between the
formation and evolution of dE,Ns, UCDs and massive GCs. We find a very steep
correlation between dynamical (M/L) ratio and dynamical mass of the form
(M/L)_dyn ~ M_dyn^(0.24+/-0.02) above M_dyn = 2x10^6 Msol. Formation scenarios
are investigated with a chemical abundance analysis using absorption line
strengths calibrated to the Lick/IDS index system. The results lend support to
two scenarios contained within a single general formation scheme. Old, massive,
super-solar [alpha/Fe] systems are formed on short (<100 Myr) timescales
through the merging of single-collapse GCs which themselves are formed within
single, giant molecular clouds. More intermediate- and old-aged (~3-10 Gyr),
solar- to sub-solar [alpha/Fe] systems are formed on much longer (~Gyr)
timescales through the stripping of dE,Ns in the 10^13-10^15 Msol potential
wells of massive galaxies and galaxy clusters.Comment: 12 pages (ApJ style) with 11 figures and 7 tables, accepted for
publication in Ap
- …