17,528 research outputs found
Rapid evaporation at the superheat limit
In an experimental investigation of the transient processes that occur when a single
droplet of butane at the superheat limit vaporizes explosively, short-exposure photographs
and fast-response pressure measurements have been used to construct a
description of the complete explosion process. It is observed that only a single bubble
forms within the drop during each explosion, and that the growth proceeds on a microsecond
time scale. An interfacial instability driven by rapid evaporation has been
observed on the surface of the bubbles. It is suggested that the Landau mechanism of
instability, originally described in connection with the instability of laminar flames,
also applies to rapid evaporation at the superheat limit.
The photographic evidence and the pressure data are used to estimate the evaporative
mass flux across the liquid-vapour interface after the onset of instability. The
;ate of evaporation is shown to be two orders of magnitude greater than would be
predicted by conventional bubble-growth theories that do not account for the effects
of instability. An estimate of the mean density within the bubbles during the evaporative
stage indicates that it is more than one half of the critical density of butane.
Additional interesting dynamical effects that are observed include a series of toroidal
waves that form on the interface between the butane vapour and the external host
liquid in the bubble column apparatus after the bubble has grown large enough to
contact the outer edge of the drop, and violent oscillations of the bubble that occur on
a millisecond time scale, after evaporation of the liquid butane is complete, that cause
the disintegration of the bubble into a cloud of tiny bubbles by Rayleigh-Taylor
instability
Fluid thermal actuator
Operational characteristics of actuator for spacecraft thermal control syste
Bi-Directional Relativistic Jets of the Radio Galaxy 1946+708: Constraints on the Hubble Constant
We present measurements of bi-directional motions in the jets of the radio
galaxy 1946+708 at z=0.101. This is a Compact Symmetric Object with striking
S-symmetry. Sensitive 15 GHz observations reveal a compact component at the
center of symmetry with a strongly inverted spectrum, that we identify as the
core. From five 4.9 GHz observations spread over 4 years we have determined the
velocities of four compact jet components. If simple kinematic models can be
applied then the inclination of the source and the bulk jet velocity can be
directly determined for any assumed value of the Hubble constant. Conversely,
the measurements already place constraints on the Hubble constant, and we show
how further observations of 1946+708 can yield an increasingly accurate
determination of H_0.Comment: in press at ApJ Letters, 12 page LaTex document includes 5 postscript
figure
VLBA Polarization Observations of Markarian 421 After a Gamma-Ray High State
We present four high dynamic range, dual-circular polarization, Very Long
Baseline Array (VLBA) observations at 22 GHz of Markarian 421, taken throughout
the year following the source's unprecedented gamma-ray high state in early
2001. These four new VLBA observations are combined with data from our earlier
1999 paper and archival VLBA data-sets that have become available since 1999 to
produce a combined 28 epoch VLBA data-set on Mrk 421 spanning the years 1994 to
2002. No new component associated with the 2001 flares was seen on the total
intensity images, but the combined data-set allowed precise measurements of the
apparent speeds of the existing components. The peak measured apparent speed
was for component C5, which has an apparent speed of 0.1 +/- 0.02 c (H_0=71 km
s^{-1} Mpc^{-1}, Omega_m=0.27, and Omega_Lambda=0.73). No counterjet is seen
with a limit on the jet to counterjet brightness ratio J >~ 100. These observed
VLBI properties of Markarian 421 are consistent with a jet with a bulk Lorentz
factor of about 2 and an angle to the line-of-sight of about 1 degree,
suggesting a jet that decelerates between the gamma-ray producing region and
the parsec scale. The VLBI core and inner jet (component C7) have fractional
polarizations of about 5%, and an electric vector position angle (EVPA) aligned
with the jet axis. Component C5 (at 1.5 mas from the core) has a higher
fractional polarization of about 15%, and an EVPA nearly orthogonal to the jet
axis. Significant variability is detected in the EVPA of component C6, which at
two of the four epochs shows an EVPA aligned with the jet axis, possibly a sign
of propagating disturbances that are only visible on the polarization images.
If these propagating disturbances are linked to the 2001 gamma-ray high state,
then their inferred apparent speed is between 1 and 3 c.Comment: 11 pages, accepted to Ap
Spectral infrared hemispherical reflectance measurements for LDEF tray clamps
Infrared hemispherical reflectance measurements that were made on 58 chromic acid anodized tray clamps from LDEF are described. The measurements were made using a hemiellipsoidal mirror reflectometer with interferometer for wavelengths between 2-15 microns. The tray clamps investigated were from locations about the entire spacecraft and provided the opportunity for comparing the effects of atomic oxygen at each location. Results indicate there was essentially no dependence on atomic oxygen fluence for the surfaces studied, but there did appear to be a slight dependence on solar radiation exposure. The reflectances of the front sides of the tray clamps consistently were slightly higher than for the protected rear tray clamp surfaces
Restorative Practices in One Pacific Northwest Middle School: A Case Study of Multiple Stakeholders’ Perspectives and Experiences
The purpose of this qualitative case study was to explore restorative justice practices in one Pacific Northwest Middle School. The specific restorative practices used as well as staff and student experiences and perceptions explored. Data were collected from teacher surveys (n=22), staff interviews (n=6), student interviews (n=3), restorative circle observations (3 sessions) and a document analysis. Results included descriptions of seven distinct restorative practices as well as an in-depth account of a whole-class dialogue circle. Staff perspectives indicated the challenges, benefits, and recommendations for RJ implementation as well as key student viewpoints and experiences on the transformative power of restorative justice. Implications include the importance of the following: accountability within RJ, high levels of support from district leadership, developing staff commitment to RJ, and facilitating the culture shift needed to implement RJ successfully
First record of an Odontaspidid shark in Ascension Island waters
The occurrence of the poorly understood shark species Odontapsis ferox is reported at an oceanic seamount in the central south Atlantic, within the Exclusive Economic Zone of Ascension Island. The presence of the species at this location is confirmed by the discovery of a tooth embedded in scientific equipment, and footage of at least one animal on autonomous underwater video. The new record of this shark species at this location demonstrates the knowledge gaps which still exist at many remote, oceanic structures and their candidacy for status as important conservation areas.info:eu-repo/semantics/publishedVersio
A Commentary on the Book of the Twelve: The Minor Prophets
The books of the twelve Minor Prophets are some of the least studied by Christians today, but they contain some of the great themes of Scripture, such as God\u27s mercy and judgment, His covenant with Israel, the day of the Lord, and the coming of the Messiah. Arguing for a canonical unity that recognizes the Minor Prophets as one cohesive composition, Michael Shepherd explains the historical meaning of each verse of the twelve books and also provides guidance for application and preaching. Pastors, teachers, and serious students of Scripture will find a wealth of insights for understanding the Minor Prophets.https://digitalcommons.cedarville.edu/faculty_books/1200/thumbnail.jp
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