271 research outputs found
Wake Geometry Effects on Rotor Blade-Vortex Interaction Noise Directivity
Acoustic measurements from a model rotor wind tunnel test are presented which show that the directionality of rotor blade vortex interaction (BVI) noise is strongly dependent on the rotor advance ratio and disk attitude. A rotor free wake analysis is used to show that the general locus of interactions on the rotor disk is also strongly dependent on advance ratio and disk attitude. A comparison of the changing directionality of the BVI noise with changes in the interaction locations shows that the strongest noise radiation occurs in the direction of motion normal to the blade span at the time of interaction, for both advancing and retreating side BVI. For advancing side interactions, the BVI radiation angle down from the tip-path plane appears relatively insensitive to rotor operating condition and is typically between 40 and 55 deg below the disk. However, the azimuthal radiation direction shows a clear trend with descent speed, moving towards the right of the flight path with increasing descent speed. The movement of the strongest radiation direction is attributed to the movement of the interaction locations on the rotor disk with increasing descent speed
Frequency response calibration of recess-mounted pressure transducers
A technique is described for measuring the frequency response of pressure transducers mounted inside a model, where a narrow pipette leads to an orifice at the surface. An acoustic driver is mounted to a small chamber which has an opening at the opposite end with an O-ring seal to place over the orifice. A 3.18 mm (1/8 inch) reference microphone is mounted to one side of the chamber. The acoustic driver receives an input of white noise, and the transducer and reference microphone outputs are compared to obtain the frequency response of the pressure transducer. Selected results are presented in the form of power spectra for both the transducer and the reference, as well as the amplitude variation and phase shift between the two signals as a function of frequency. The effect of pipette length and the use of this technique for identifying both blocked orifices and faulty transducers are described
Evaluation of plant derivatives of Meliaceae family as a source of nitrogen for trees
Soil application of fresh organic matter is a way to increase soil organic matter and provide nutrients to trees. The effect of application of organic matter depends on the interaction among soil, root and microbial biomass. The aim of this research was to evaluate the potential release of N for hybrid GF677 (P. persica x P. dulcis) uptake, of 6 neemcakes available on the Italian market compared with fresh leaves of Melia azedarach, an ornamental tree that grows in the area of investigation. The release of N, and consequently root uptake was related to C:N ratio, the lower the ratio the higher the N concentration in plant tissues and plant growth. Using the 15N isotope technique, we found that up to 30% of the N applied with fresh Melia leaves, was accumulated in the tree, however the mineral N concentration in soil and plant and plant growth was not affected by the application of plant derivatives
Gender‐specific Issues in Traumatic Injury and Resuscitation: Consensus‐based Recommendations for Future Research
Traumatic injury remains an unacceptably high contributor to morbidity and mortality rates across the United States. Gender‐specific research in trauma and emergency resuscitation has become a rising priority. In concert with the 2014 Academic Emergency Medicine consensus conference “Gender‐specific Research in Emergency Care: Investigate, Understand, and Translate How Gender Affects Patient Outcomes,” a consensus‐building group consisting of experts in emergency medicine, critical care, traumatology, anesthesiology, and public health convened to generate research recommendations and priority questions to be answered and thus move the field forward. Nominal group technique was used for the consensus‐building process and a combination of face‐to‐face meetings, monthly conference calls, e‐mail discussions, and preconference surveys were used to refine the research questions. The resulting research agenda focuses on opportunities to improve patient outcomes by expanding research in sex‐ and gender‐specific emergency care in the field of traumatic injury and resuscitation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110065/1/acem12536.pd
Scheduling reactivo de procesos make-and-pack operando en modo campaña: enfoque CP novedoso
Se presenta un modelo matemático de Constraint Programming (CP) para resolver el problema de scheduling de corto plazo en plantas industriales de tipo batch, multiproducto, multietapa; las cuales operan con procesos make-andpack.
Se trata de un enfoque novedoso, capaz de considerar, entre otros aspectos, la operación en modo campañas y tiempos de changeover dependientes de la secuencia y/o del equipo productivo involucrado. El mismo permitió resolver 20 instancias, de tamaño creciente en cuanto al número de lotes a agendar, correspondiente a un problema ampliamente abordado en la bibliografía (proceso de producción de helados). Los resultados obtenidos indican un buen desempeño (veloz y eficaz). Asimismo, se trata de una formulación cuyo tamaño no se incrementa exponencialmente con el crecimiento en el número de lotes considerados.Sociedad Argentina de Informática e Investigación Operativ
Ram pressure histories of cluster galaxies
Ram pressure stripping can remove significant amounts of gas from galaxies
that orbit in clusters and massive groups, and thus has a large impact on the
evolution of cluster galaxies. In this paper, we reconstruct the present-day
distribution of ram-pressure, and the ram pressure histories of cluster
galaxies. To this aim, we combine the Millennium Simulation and an associated
semi-analytic model of galaxy evolution with analytic models for the gas
distribution in clusters. We find that about one quarter of galaxies in massive
clusters are subject to strong ram-pressures that are likely to cause an
expedient loss of all gas. Strong ram-pressures occur predominantly in the
inner core of the cluster, where both the gas density and the galaxy velocity
are higher. Since their accretion onto a massive system, more than 64 per cent
of galaxies that reside in a cluster today have experienced strong
ram-pressures of dyn cm which most likely led to a
substantial loss of the gas.Comment: MNRAS accepte
The History of Galaxy Formation in Groups: An Observational Perspective
We present a pedagogical review on the formation and evolution of galaxies in
groups, utilizing observational information from the Local Group to galaxies at
z~6. The majority of galaxies in the nearby universe are found in groups, and
galaxies at all redshifts up to z~6 tend to cluster on the scale of nearby
groups (~1 Mpc). This suggests that the group environment may play a role in
the formation of most galaxies. The Local Group, and other nearby groups,
display a diversity in star formation and morphological properties that puts
limits on how, and when, galaxies in groups formed. Effects that depend on an
intragroup medium, such as ram-pressure and strangulation, are likely not major
mechanisms driving group galaxy evolution. Simple dynamical friction arguments
however show that galaxy mergers should be common, and a dominant process for
driving evolution. While mergers between L_* galaxies are observed to be rare
at z < 1, they are much more common at earlier times. This is due to the
increased density of the universe, and to the fact that high mass galaxies are
highly clustered on the scale of groups. We furthermore discus why the local
number density environment of galaxies strongly correlates with galaxy
properties, and why the group environment may be the preferred method for
establishing the relationship between properties of galaxies and their local
density.Comment: Invited review, 16 pages, to be published in ESO Astrophysics
Symposia: "Groups of Galaxies in the Nearby Universe", eds. I. Saviane, V.
Ivanov, J. Borissov
The Dynamical and Chemical Evolution of Dwarf Spheroidal Galaxies
We present a large sample of fully self-consistent hydrodynamical
Nbody/Tree-SPH simulations of isolated dwarf spheroidal galaxies (dSphs). It
has enabled us to identify the key physical parameters and mechanisms at the
origin of the observed variety in the Local Group dSph properties. The initial
total mass (gas + dark matter) of these galaxies is the main driver of their
evolution. Star formation (SF) occurs in series of short bursts. In massive
systems, the very short intervals between the SF peaks mimic a continuous star
formation rate, while less massive systems exhibit well separated SF bursts, as
identified observationally. The delay between the SF events is controlled by
the gas cooling time dependence on galaxy mass. The observed global scaling
relations, luminosity-mass and luminosity-metallicity, are reproduced with low
scatter. We take advantage of the unprecedentedly large sample size and data
homogeneity of the ESO Large Programme DART, and add to it a few independent
studies, to constrain the star formation history of five Milky Way dSphs,
Sextans, LeoII, Carina, Sculptor and Fornax. For the first time, [Mg/Fe] vs
[Fe/H] diagrams derived from high-resolution spectroscopy of hundreds of
individual stars are confronted with model predictions. We find that the
diversity in dSph properties may well result from intrinsic evolution. We note,
however, that the presence of gas in the final state of our simulations, of the
order of what is observed in dwarf irregulars, calls for removal by external
processes.Comment: 21 Pages, 19 figures ; Accepted for publication in A&A. Higher
resolution version may be downloaded here :
http://obswww.unige.ch/~revaz/publications/aa2009_1173
VLT/FLAMES-ARGUS observations of stellar wind--ISM cloud interactions in NGC 6357
We present optical/near-IR IFU observations of a gas pillar in the Galactic
HII region NGC 6357 containing the young open star cluster Pismis 24. These
observations have allowed us to examined in detail the gas conditions of the
strong wind-clump interactions taking place on its surface. We identify the
presence of a narrow (~20 km/s) and broad (50-150 km/s) component to the
H_alpha emission line, where the broadest broad component widths are found in a
region that follows the shape of the eastern pillar edge. These connections
have allowed us to firmly associate the broad component with emission from
ionized gas within turbulent mixing layers on the pillar's surface set up by
the shear flows of the O-star winds from the cluster. We discuss the
implications of our findings in terms of the broad emission line component that
is increasingly found in extragalactic starburst environments. Although the
broad line widths found here are narrower, we conclude that the mechanisms
producing both must be the same. The difference in line widths may result from
the lower total mechanical wind energy produced by the O stars in Pismis 24
compared to that from a typical young massive star cluster found in a starburst
galaxy. The pillar's edge is also clearly defined by dense (<5000 cm^-3), hot
(>20000 K), and excited (via [NII]/H_a and [SII]/H_a ratios) gas conditions,
implying the presence of a D-type ionization front propagating into the pillar
surface. Although there must be both photoevaporation outflows produced by the
ionization front, and mass-loss through mechanical ablation, we see no evidence
for any significant bulk gas motions on or around the pillar. We postulate that
the evaporated/ablated gas must be rapidly heated before being entrained.Comment: 9 pages, 5 figures (3 colour). Accepted for publication in MNRA
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