2,995 research outputs found
Experimental studies on the reaction kinetics of 1,1-dimethylhydrazine and oxygen
Measurements behind shock waves in highly diluted 1,1 dimethylhydrazine-O2-Ar mixtures clearly showed a two-stage reaction. In the first stage, UDMH decomposes via a unimolecular step; in the second stage, clearly separated from the first one, the decay products react further with O2. Values for the rate constant of unimolecular decomposition were obtained
Roche volume filling and the dissolution of open star clusters
From direct N-body simulations we find that the dynamical evolution of star
clusters is strongly influenced by the Roche volume filling factor. We present
a parameter study of the dissolution of open star clusters with different Roche
volume filling factors and different particle numbers. We study both Roche
volume underfilling and overfilling models and compare with the Roche volume
filling case. We find that in the Roche volume overfilling limit of our
simulations two-body relaxation is no longer the dominant dissolution mechanism
but the changing cluster potential. We call this mechnism "mass-loss driven
dissolution" in contrast to "two-body relaxation driven dissolution" which
occurs in the Roche volume underfilling regime. We have measured scaling
exponents of the dissolution time with the two-body relaxation time. In this
experimental study we find a decreasing scaling exponent with increasing Roche
volume filling factor. The evolution of the escaper number in the Roche volume
overfilling limit can be described by a log-logistic differential equation. We
report the finding of a resonance condition which may play a role for the
evolution of star clusters and may be calibrated by the main periodic orbit in
the large island of retrograde quasiperiodic orbits in the Poincar\'e surfaces
of section. We also report on the existence of a stability curve which may be
of relevance with respect to the structure of star clusters.Comment: 14 pages, 10+1 figures, accepted by Astronomische Nachrichte
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Modulation of sterol homeostasis by the Cdc42p effectors Cla4p and Ste20p in the yeast Saccharomyces cerevisiae
This article is available open access through the publisher’s website at the link below. Copyright @ 2009 The Authors.The conserved Rho-type GTPase Cdc42p is a key regulator of signal transduction and polarity in eukaryotic cells. In the yeast Saccharomyces cerevisiae, Cdc42p promotes polarized growth through the p21-activated kinases Ste20p and Cla4p. Previously, we demonstrated that Ste20p forms a complex with Erg4p, Cbr1p and Ncp1p, which all catalyze important steps in sterol biosynthesis. CLA4 interacts genetically with ERG4 and NCP1. Furthermore, Erg4p, Ncp1p and Cbr1p play important roles in cell polarization during vegetative growth, mating and filamentation. As Ste20p and Cla4p are involved in these processes it seems likely that sterol biosynthetic enzymes and p21-activated kinases act in related pathways. Here, we demonstrate that the deletion of either STE20 or CLA4 results in increased levels of sterols. In addition, higher concentrations of steryl esters, the storage form of sterols, were observed in cla4Δ cells. CLA4 expression from a multicopy plasmid reduces enzyme activity of Are2p, the major steryl ester synthase, under aerobic conditions. Altogether, our data suggest that Ste20p and Cla4p may function as negative modulators of sterol biosynthesis. Moreover, Cla4p has a negative effect on steryl ester formation. As sterol homeostasis is crucial for cell polarization, Ste20p and Cla4p may regulate cell polarity in part through the modulation of sterol homeostasis.Deutsche Forschungsgemeinschaft and the Austrian FWF
Optimization of Master Alloy Amount and Gating System Design for Ductile Cast Iron Obtain in Lost Foam Process
The paper presents the optimization of master alloy amount for the high nodular graphite yield (80-90%) in cast iron obtain in lost foam process. The influence of the gating system configuration and the shape of the reaction chamber, the degree of spheroidisation cast iron was examined. Research has shown that the, optimal of master alloy amount of 1.5% by mass on casting iron. The degree of spheroidisation is also influenced by the gating system configuration. The best spheroidisation effect was obtained for liquid cast iron was fed into the reaction chamber from the bottom and discharged from the top
Continued-fraction expansion of eigenvalues of generalized evolution operators in terms of periodic orbits
A new expansion scheme to evaluate the eigenvalues of the generalized
evolution operator (Frobenius-Perron operator) relevant to the
fluctuation spectrum and poles of the order- power spectrum is proposed. The
``partition function'' is computed in terms of unstable periodic orbits and
then used in a finite pole approximation of the continued fraction expansion
for the evolution operator. A solvable example is presented and the approximate
and exact results are compared; good agreement is found.Comment: CYCLER Paper 93mar00
The X-ray Properties of the Most-Luminous Quasars from the Sloan Digital Sky Survey
Utilizing 21 new Chandra observations as well as archival Chandra, ROSAT, and
XMM-Newton data, we study the X-ray properties of a representative sample of 59
of the most optically luminous quasars in the Universe (M_i~~-29.3 to -30.2)
spanning a redshift range of z~~1.5-4.5. Our full sample consists of 32 quasars
from the Sloan Digital Sky Survey (SDSS) Data Release 3 (DR3) quasar catalog,
two additional objects in the DR3 area that were missed by the SDSS selection
criteria, and 25 comparably luminous quasars at z>~4. This is the largest X-ray
study of such luminous quasars to date. By jointly fitting the X-ray spectra of
our sample quasars, excluding radio-loud and broad absorption line (BAL)
objects, we find a mean X-ray power-law photon index of
Gamma=1.92^{+0.09}_{-0.08} and constrain any neutral intrinsic absorbing
material to have a mean column density of N_H<~2x10^{21} cm^{-2}. We find,
consistent with other studies, that Gamma does not change with redshift, and we
constrain the amount of allowed Gamma evolution for the most-luminous quasars.
Our sample, excluding radio-loud and BAL quasars, has a mean X-ray-to-optical
spectral slope of a_ox=-1.80+/-0.02, as well as no significant evolution of
a_ox with redshift. We also comment upon the X-ray properties of a number of
notable quasars, including an X-ray weak quasar with several strong narrow
absorption-line systems, a mildly radio-loud BAL quasar, and a well-studied
gravitationally lensed quasar.Comment: 18 pages (emulateapj), 11 figures. Accepted for publication in The
Astrophysical Journa
Movimientos verticales diarios de larvas de peces en estadÃo pre-flexión asociados a las praderas de Posidonia oceanica
Habitat complexity is a strong determinant of fish assemblage structure. Enhanced food resources and protection from predators are generally considered the main benefits of vegetated areas. We investigated the diel and vertical movements of preflexion fish larvae within and above the leaf canopy of Posidonia oceanica to determine if it acts as an important habitat for larval stage fish. Samples were taken with moored plankton nets during the night and day at two depths (13 and 15 m) over five consecutive days in July 2000 in the Marine Protected Area off Tabarca Island (Spain, SW Mediterranean Sea). In total, 353 fish larvae were captured. The most abundant taxa were Sardinella aurita, Sparidae, Engraulis encrasicolus and Gobiidae. Sparidae were more abundant within the leaf canopy during the day but increased in waters 2 m above the canopy at night. In contrast, Sardinella aurita were present throughout the entire water column during both the day and night. We conclude that the P. oceanica leaf canopy is important as a transitional shelter for the early stage larvae of some demersal fish species.El tipo de hábitat determina la estructura del poblamiento larvario de peces. Los principales beneficios que proporciona un hábitat con vegetación son el incremento de las fuentes de alimento y una mayor protección frente a los predadores. Este estudio se ha centrado en praderas de Posidonia oceanica para evaluar su papel como zonas de refugio, función que ha sido poco estudiada. Este trabajo se ha llevado a cabo en la Reserva Marina de Tabarca (España, SW Mar Mediterráneo). Las muestras se recolectaron con redes de plancton fijas en periodos diurnos y nocturnos, y a dos profundidades (13 y 15 m), durante 5 dÃas consecutivos en el mes de Julio de 2000. Se capturaron 353 larvas y 256 fueron identificadas. Los taxones más abundantes fueron S. aurita, Sparidae, Engraulis encrasicolus y Gobiidae. Sparidae dominó al nivel de las hojas de la pradera durante el dÃa, incrementando su presencia en la columna de agua durante la noche; mientras que la S. aurita se encontró a lo largo de toda la columna de agua en los dos periodos estudiados. Nuestro estudio confirma el papel de las praderas de P. oceanica como zona de refugio transitoria para los primeros estadios de larvas de de peces, aunque limitado a algunas especies demersales.
Matrix change of bone grafting substitute after implantation into guinea pig bulla
Background: Many different surgical techniques have been developed to remove
open mastoid cavities. In addition to autologous materials, alloplastic substances
have been used. A very slow absorption of these materials and extrusion reactions
have been reported. We investigated a newly developed, highly porous bone grafting
material to eliminate open mastoid cavities, in an animal model. To characterise
the transformation process, the early tissue reactions were studied in relation
to the matrix transformation of the bone material.
Material and methods: NanoBone (NB), a highly porous bone grafting material
based on calcium phosphate and silica, was filled into the open bullae
from 20 guinea pigs. The bullae were examined histologically. Energy dispersive
X-ray spectroscopy (EDX) was used to investigate the change in the elemental
composition at different sampling times. The surface topography of the
sections was examined by electron microscopy.
Results: After 1 week, periodic acid-Schiffs (PAS) staining demonstrated accumulation
of glycogen and proteins, particularly in the border area of the NB particles.
After 2 weeks, the particles were evenly coloured after PAS staining. EDX analysis
showed a rapid absorption of the silica in the bone grafting material.
Conclusions: NanoBone showed a rapid matrix change after implantation in the
bullae of guinea pigs. The absorption of the silica matrix and replacement by PAS-positive substances like glycoproteins and mucopolysaccharides seems to play
a decisive role in the degradation processes of NB. This is associated with the good
osteoinductive properties of the material
Time--delay autosynchronization of the spatio-temporal dynamics in resonant tunneling diodes
The double barrier resonant tunneling diode exhibits complex spatio-temporal
patterns including low-dimensional chaos when operated in an active external
circuit. We demonstrate how autosynchronization by time--delayed feedback
control can be used to select and stabilize specific current density patterns
in a noninvasive way. We compare the efficiency of different control schemes
involving feedback in either local spatial or global degrees of freedom. The
numerically obtained Floquet exponents are explained by analytical results from
linear stability analysis.Comment: 10 pages, 16 figure
Low satisfaction and failed relational coordination among relevant stakeholders in Spanish Mediterranean marine protected areas
Marine protected areas (MPAs) are a conservation tool that are increasingly commonplace around the world. MPAs have the potential to benefit both ecosystems and human communities if well-designed and implemented. Achieving effective implementation and governance of MPAs, however, is complicated because they deal with systems that overlap with both non-human environments and human economies and societies. As a result, MPA success is thought to be primarily dependent on socioeconomic factors, particularly the behavior of stakeholder groups involved in the MPAs. Using the theory of relational coordination, we designed surveys that we delivered to members of four stakeholder groups implicated in five MPAs in the Spanish Mediterranean to investigate their habits of inter- and intra-group communication and relations. Relational coordination posits that high-quality communication and relations results in positive stakeholder behaviors and an effective system, which makes it a useful tool to investigate the effectiveness of the MPAs involved in this study. Our results demonstrate that a high degree of relational coordination leads to higher satisfaction on the part of the participants in the system. The exploratory model constructed here also supports the notion that each stakeholder group adopts particular beliefs and behaves in particular ways in terms of relational coordination and satisfaction. We found patterns that indicated poor communication and relations amongst the four stakeholder groups, which in turn has grave implications for management outcomes of these MPAs. Cumulatively, these conditions could precipitate management failure. To remedy these concerns, we recommend establishing channels of communication between the four stakeholder groups, and investigating means to cultivate good relations amongst these groups. Doing so will help assure management success
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