6,567 research outputs found
Two Social Worlds: Social Correlates and Stability of Adolescent Status Groups
Examined adolescents\u27 peer group status in high school using self-report, peer nominations, and archival data collected during 2 consecutive school yrs. 408 students participated in the 1st yr, and 404 students participated in the 2nd yr. 60% of the 2nd yr Ss had also participated in the 1st yr. Higher status students (popular and controversial) had more close friends, engaged more frequently in peer activities, and self-disclosed more than lower status students (rejected and neglected). They were also more involved in extracurricular school activities and received more social honors from their schoolmates. Although the higher status students were more alike than different, controversial adolescents did report more self-disclosure and dating behavior than popular students. Lower status students were also highly similar, although rejected students reported lower grades
Hyperelastic cloaking theory: Transformation elasticity with pre-stressed solids
Transformation elasticity, by analogy with transformation acoustics and
optics, converts material domains without altering wave properties, thereby
enabling cloaking and related effects. By noting the similarity between
transformation elasticity and the theory of incremental motion superimposed on
finite pre-strain it is shown that the constitutive parameters of
transformation elasticity correspond to the density and moduli of
small-on-large theory. The formal equivalence indicates that transformation
elasticity can be achieved by selecting a particular finite (hyperelastic)
strain energy function, which for isotropic elasticity is semilinear strain
energy. The associated elastic transformation is restricted by the requirement
of statically equilibrated pre-stress. This constraint can be cast as \tr
{\mathbf F} = constant, where is the deformation gradient,
subject to symmetry constraints, and its consequences are explored both
analytically and through numerical examples of cloaking of anti-plane and
in-plane wave motion.Comment: 20 pages, 5 figure
Flame Holder System
A flame holder system includes a modified torch body and a ceramic flame holder. Catch pin(s) are coupled to and extend radially out from the torch body. The ceramic flame holder has groove(s) formed in its inner wall that correspond in number and positioning to the catch pin(s). Each groove starts at one end of the flame holder and is can be shaped to define at least two 90 degree elbows. Each groove is sized to receive one catch pin therein when the flame holder is fitted over the end of the torch body. The flame holder is then manipulated until the catch pin(s) butt up against the end of the groove(s)
870 micron continuum observations of the bubble-shaped nebula Gum 31
We are presenting here a study of the cold dust in the infrared ring nebula
Gum 31. We aim at deriving the physical properties of the molecular gas and
dust associated with the nebula, and investigating its correlation with the
star formation in the region, that was probably triggered by the expansion of
the ionization front. We use 870 micron data obtained with LABOCA to map the
dust emission. The obtained LABOCA image was compared to archival IR,radio
continuum, and optical images. The 870 micron emission follows the 8 micron
(Spitzer), 250 micron, and 500 micron (Herschel) emission distributions showing
the classical morphology of a spherical shell. We use the 870 micron and 250
micron images to identify 60 dust clumps in the collected layers of molecular
gas using the Gaussclumps algorithm. The clumps have effective deconvolved
radii between 0.16 pc and 1.35 pc, masses between 70 Mo and 2800 Mo, and volume
densities between 1.1x10^3 cm^-3 and 2.04x10^5 cm^-3. The total mass of the
clumps is 37600 Mo. The dust temperature of the clumps is in the range from 21
K to 32 K, while inside the HII region reaches ~ 40 K. The clump mass
distribution is well-fitted by a power law dN/dlog(M/Mo) proportional to
M^(-alpha), with alpha=0.93+/-0.28. The slope differs from those obtained for
the stellar IMF in the solar neighborhood, suggesting that the clumps are not
direct progenitors of single stars/protostars. The mass-radius relationship for
the 41 clumps detected in the 870 microns emission shows that only 37% of them
lie in or above the high-mass star formation threshold, most of them having
candidate YSOs projected inside. A comparison of the dynamical age of the HII
region with the fragmentation time, allowed us to conclude that the collect and
collapse mechanism may be important for the star formation at the edge of Gum
31, although other processes may also be acting.Comment: 15 pages, 10 figures. Accepted for publication in A&
Dissipative Dynamics of Collisionless Nonlinear Alfven Wave Trains
The nonlinear dynamics of collisionless Alfven trains, including resonant
particle effects is studied using the kinetic nonlinear Schroedinger (KNLS)
equation model. Numerical solutions of the KNLS reveal the dynamics of Alfven
waves to be sensitive to the sense of polarization as well as the angle of
propagation with respect to the ambient magnetic field. The combined effects of
both wave nonlinearity and Landau damping result in the evolutionary formation
of stationaryOA S- and arc-polarized directional and rotational
discontinuities. These waveforms are freqently observed in the interplanetary
plasma.Comment: REVTeX, 6 pages (including 5 figures). This and other papers may be
found at http://sdphpd.ucsd.edu/~medvedev/papers.htm
Molecular gas and star formation towards the IR dust bubble S24 and its environs
We present a multi-wavelength analysis of the infrared dust bubble S24, and
its environs, with the aim of investigating the characteristics of the
molecular gas and the interstellar dust linked to them, and analyzing the
evolutionary status of the young stellar objects (YSOs) identified there. Using
APEX data, we mapped the molecular emission in the CO(2-1), CO(2-1),
CO(2-1), and CO(3-2) lines in a region of about 5'x 5' in size
around the bubble. The cold dust distribution was analyzed using ATLASGAL and
Herschel images. Complementary IR and radio data were also used.The molecular
gas linked to the S24 bubble, G341.220-0.213, and G341.217-0.237 has velocities
between -48.0 km sec and -40.0 km sec. The gas distribution
reveals a shell-like molecular structure of 0.8 pc in radius bordering
the bubble. A cold dust counterpart of the shell is detected in the LABOCA and
Herschel images.The presence of extended emission at 24 m and radio
continuum emission inside the bubble indicates that the bubble is a compact HII
region. Part of the molecular gas bordering S24 coincides with the extended
infrared dust cloud SDC341.194-0.221. A cold molecular clump is present at the
interface between S24 and G341.217-0.237. As regards G341.220-0.213, the
presence of an arc-like molecular structure at the northern and eastern
sections of this IR source indicates that G341.220-0.213 is interacting with
the molecular gas. Several YSO candidates are found to be linked to the IR
extended sources, thus confirming their nature as active star-forming regions.
The total gas mass in the region and the H ambient density amount to 10300
M and 5900 cm, indicating that G341.220-0.213, G341.217-0.237,
and the S24 HII region are evolving in a high density medium. A triggering star
formation scenario is also investigated.Comment: 17 pages, 16 figures. Submitted to A&A. Revised according to the
referee repor
Hybrid stars with reactive interfaces: analysis within the Nambu-Jona-Lasinio model
It has been shown recently that quark-hadron conversions at the interface of
a hybrid star may have a key role on the dynamic stability of the compact
object. In this work we perform a systematic study of hybrid stars with
reactive interfaces using a model-agnostic piecewise-polytropic hadronic
equation of state and the Nambu-Jona-Lasinio model for three-flavor quark
matter. For the hadronic phase we use a soft, an intermediate and a stiff
parametrization that match at {with predictions} based on chiral
effective field theory (cEFT) interactions. In the NJL Lagrangian we include
scalar, vector and 't Hooft interactions. The vector coupling constant
is treated as a free parameter. We also consider that there is a split between
the deconfinement and the chiral phase transitions which is controlled by
changing the conventional value of the vacuum pressure in the NJL
thermodynamic potential by , being
a free parameter. We analyze the mass-radius (-)
relation in the case of rapid () and slow () conversions, being the reaction timescale. In the
case of slow interface reactions we find - curves with a cusp at the
maximum mass point where a pure hadronic branch and a slow-stable hybrid star
(SSHS) branch coincide. We find that the length of the slow-stable branch grows
with the increase of the transition density and the energy density jump at the
hadron-quark interface. We calculate the tidal deformabilities of SSHSs and
analyse them in the light of the GW170817 event.Comment: 12 pages, 4 figures, to be published in Physical Review
Controlling the exchange interaction using the spin-flip transition of antiferromagnetic spins in NiFe / -FeO
We report studies of exchange bias and coercivity in ferromagnetic
NiFe layers coupled to antiferromagnetic (AF) (0001),
(110), and (112) -FeO layers. We show that AF
spin configurations which permit spin-flop coupling give rise to a strong
uniaxial anisotropy and hence a large coercivity, and that by annealing in
magnetic fields parallel to specific directions in the AF we can control either
coercivity or exchange bias. In particular, we show for the first time that a
reversible temperature-induced spin reorientation in the AF can be used to
control the exchange interaction.Comment: 15 pages, 5 figures, submitted to Phys. Rev. Let
- …