12,433 research outputs found
Opening the Treasure Chest in Carina
We have mapped the G287.84-0.82 cometary globule (with the Treasure Chest
cluster embedded in it) in the South Pillars region of Carina (i) in [CII],
63micron [OI], and CO(11-10) using upGREAT on SOFIA and (ii) in J=2-1
transitions of CO, 13CO, C18O and J=3-2 transitions of H2CO using the APEX
telescope in Chile. We probe the morphology, kinematics, and physical
conditions of the molecular gas and the photon dominated regions (PDRs) in
G287.84-0.82. The [CII] and [OI] emission suggest that the overall structure of
the pillar (with red-shifted photo evaporating tails) is consistent with the
effect of FUV radiation and winds from eta-Car and O stars in Trumpler 16. The
gas in the head of the pillar is strongly influenced by the embedded cluster,
whose brightest member is an O9.5V star, CPD-59 2661. The emission of the [CII]
and [OI] lines peak at a position close to the embedded star, while all other
tracers peak at another position lying to the north-east consistent with gas
being compressed by the expanding PDR created by the embedded cluster. The
molecular gas inside the globule is probed with the J=2-1 transitions of CO and
isotopologues as well as H2CO, and analyzed using a non-LTE model
(escape-probability approach), while we use PDR models to derive the physical
conditions of the PDR. We identify at least two PDR gas components; the diffuse
part (~10^4 cm^-3) is traced by [CII], while the dense (n~ 2-8x10^5 cm^-3) part
is traced by [CII], [OI], CO(11-10). Using the F=2-1 transition of [13CII]
detected at 50 positions in the region, we derive optical depths (0.9-5),
excitation temperatures of [CII] (80-255 K), and N(C+) of 0.3-1x10^19 cm^-2.
The total mass of the globule is ~1000 Msun, about half of which is traced by
[CII]. The dense PDR gas has a thermal pressure of 10^7-10^8 K cm^-3, which is
similar to the values observed in other regions.Comment: Accepted for publication in Astronomy and Astrophysics (abstract
slightly abridged
Origin of positive magnetoresistance in small-amplitude unidirectional lateral superlattices
We report quantitative analysis of positive magnetoresistance (PMR) for
unidirectional-lateral-superlattice samples with relatively small periods
(a=92-184 nm) and modulation amplitudes (V_0=0.015-0.25 meV). By comparing
observed PMR's with ones calculated using experimentally obtained mobilities,
quantum mobilities, and V_0's, it is shown that contribution from streaming
orbits (SO) accounts for only small fraction of the total PMR. For small V_0,
the limiting magnetic field B_e of SO can be identified as an inflection point
of the magnetoresistance trace. The major part of PMR is ascribed to drift
velocity arising from incompleted cyclotron orbits obstructed by scatterings.Comment: 12 pages, 9 figures, REVTe
Applications of polymer optical fibre grating sensors to condition monitoring of textiles
Fibre Bragg gratings (FBGs) in polymer optical fibres (POFs) have been used to measure the strain in a woven textile.
FBGs in both POFs and silica optical fibres were attached to a woven textile specimen, and their performance
characterised. It was demonstrated that the POF FBGs provide improved strain transfer coefficients and reduce local
structural reinforcement compared to silica FBGs and therefore make a more suitable proposition for textile monitoring
Ligation of protease-activated receptor 1 enhances alpha(v)beta(6) integrin-dependent TGF-beta activation and promotes acute lung injury
Activation of latent TGF-beta by the alpha(v)beta(6) integrin is a critical step in the development of acute lung injury. However, the mechanism by which a alpha(v)beta(6)-mediated TGF-beta activation is regulated has not been identified. We show that thrombin, and other agonists of protease-activated receptor 1(PAR1), activate TGF-beta in an alpha(v)beta(6) integrin-specific manner. This effect is PART specific and is mediated by RhoA and Rho kinase. Intratracheal instillation of the PART-specific peptide TFLLRN increases lung edema during high-tidal-volume ventilation, and this effect is completely inhibited by a blocking antibody against the alpha(v)beta(6) integrin. Instillation of TFLLRN during high-tidal-volume ventilation is associated with increased pulmonary TGF-beta activation; however, this is not observed in Itgb6(-/-) mice. Furthermore, Itgb6(-/-) mice are also protected from ventilator-induced lung edema. We also demonstrate that pulmonary edema and TGF-beta activity are similarly reduced in Par1(-/-) mice following bleomycin-induced lung injury. These results suggest that PART-mediated enhancement of a alpha(v)beta(6)-dependent TGF-beta activation could be one mechanism by which activation of the coagulation cascade contributes to the development of acute lung injury, and they identify PART and the alpha(v)beta(6) integrin as potential therapeutic targets in this condition
Connected and disconnected quark contributions to hadron spin
By introducing an external spin operator to the fermion action, the quark
spin fractions of hadrons are determined from the linear response of the hadron
energies using the Feynman-Hellmann (FH) theorem. At our SU(3)-flavour
symmetric point, we find that the connected quark spin fractions are
universally in the range 55-70\% for vector mesons and octet and decuplet
baryons. There is an indication that the amount of spin suppression is quite
sensitive to the strength of SU(3) breaking. We also present first preliminary
results applying the FH technique to calculations of quark-line disconnected
contributions to hadronic matrix elements of axial and tensor operators. At the
SU(3)-flavour symmetric point we find a small negative contribution to the
nucleon spin from disconnected quark diagrams, while the corresponding tensor
matrix elements are consistent with zero.Comment: 7 pages, 5 figures, 32nd International Symposium on Lattice Field
Theor
Einstein Cluster Alignments Revisited
We have examined whether the major axes of rich galaxy clusters tend to point
toward their nearest neighboring cluster. We have used the data of Ulmer,
McMillan, and Kowalski, who used position angles based on X-ray morphology. We
also studied a subset of this sample with updated positions and distances from
the MX Northern Abell Cluster Survey (for rich clusters () with well
known redshifts). A Kolmogorov-Smirnov (KS) test showed no significant signal
for nonrandom angles on any scale Mpc. However, refining the
null hypothesis with the Wilcoxon rank-sum test, we found a high confidence
signal for alignment. Confidence levels increase to a high of 99.997% as only
near neighbors which are very close are considered. We conclude there is a
strong alignment signal in the data, consistent with gravitational instability
acting on Gaussian perturbations.Comment: Minor revisions. To be published in Ap
Applications of the Feynman-Hellmann theorem in hadron structure
The Feynman-Hellmann (FH) relation offers an alternative way of accessing
hadronic matrix elements through artificial modifications to the QCD
Lagrangian. In particular, a FH-motivated method provides a new approach to
calculations of disconnected contributions to matrix elements and high-momentum
nucleon and pion form factors. Here we present results for the total nucleon
axial charge, including a statistically significant non-negative total
disconnected quark contribution of around at an unphysically heavy pion
mass. Extending the FH relation to finite-momentum transfers, we also present
calculations of the pion and nucleon electromagnetic form factors up to
momentum transfers of around 7-8 GeV. Results for the nucleon are not able
to confirm the existence of a sign change for the ratio , but
suggest that future calculations at lighter pion masses will provide
fascinating insight into this behaviour at large momentum transfers
The Paradoxical Forces for the Classical Electromagnetic Lag Associated with the Aharonov-Bohm Phase Shift
The classical electromagnetic lag assocated with the Aharonov-Bohm phase
shift is obtained by using a Darwin-Lagrangian analysis similar to that given
by Coleman and Van Vleck to identify the puzzling forces of the Shockley-James
paradox. The classical forces cause changes in particle velocities and so
produce a relative lag leading to the same phase shift as predicted by Aharonov
and Bohm and observed in experiments. An experiment is proposed to test for
this lag aspect implied by the classical analysis but not present in the
currently-accepted quantum topological description of the phase shift.Comment: 8 pages, 3 figure
Spinning Down a Black Hole With Scalar Fields
We study the evolution of a Kerr black hole emitting scalar radiation via the
Hawking process. We show that the rate at which mass and angular momentum are
lost by the black hole leads to a final evolutionary state with nonzero angular
momentum, namely .Comment: 4 pages (including 3 postscript figures), Revtex, uses epsf.tex,
twocolumn.sty and header.sty (included). Submitted to Physical Review Letter
Disconnected contributions to the spin of the nucleon
The spin decomposition of the proton is a long-standing topic of much
interest in hadronic physics. Lattice QCD has had much success in calculating
the connected contributions to the quark spin. However, complete calculations,
which necessarily involve gluonic and strange-quark contributions, still
present some challenges. These "disconnected" contributions typically involve
small signals hidden against large statistical backgrounds and rely on
computationally intensive stochastic techniques. In this work we demonstrate
how a Feynman-Hellmann approach may be used to calculate such quantities, by
measuring shifts in the proton energy arising from artificial modifications to
the QCD action. We find a statistically significant non-zero result for the
disconnected quark spin contribution to the proton of about -5% at a pion mass
of 470 MeV
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