4,532 research outputs found
Hydrodynamic model for expansion and collisional relaxation of x-ray laser-excited multi-component nanoplasma
The irradiation of an atomic cluster with a femtosecond x-ray free-electron
laser pulse results in a nanoplasma formation. This typically occurs within a
few hundreds femtoseconds. By this time the x-ray pulse is over, and the direct
photoinduced processes no longer contributing. All created electrons within the
nanoplasma are thermalized. The nanoplasma thus formed is a mixture of atoms,
electrons and ions of various charges. While expanding, it is undergoing
electron impact ionization and three-body recombination. Below we present a
hydrodynamic model to describe the dynamics of such multi-component nanoplasma.
The model equations are derived by taking the moments of the corresponding
Boltzmann kinetic equations. We include the equations obtained, together with
the source terms due to electron impact ionization and three-body
recombination, in our hydrodynamic solver. Model predictions for a test case:
expanding spherical Ar nanoplasma are obtained. With this model we complete the
two-step approach to simulate x-ray created nanoplasmas, enabling
computationally efficient simulations of their picosecond dynamics. Moreover,
the hydrodynamic framework including collisional processes can be easily
extended for other source terms and then applied to follow relaxation of any
finite non-isothermal multi-component nanoplasma with its components relaxed
into local thermodynamic equilibrium.Comment: 12 pages, 4 figures. This article has been accepted by Physics of
Plasmas. After it is published, it will be found at
http://scitation.aip.org/content/aip/journal/po
Lessons from crossing symmetry at large N
20 pages, v2: Assumptions stated more clearly, version published in JHEPWe consider the four-point correlator of the stress tensor multiplet in N=4 SYM. We construct all solutions consistent with crossing symmetry in the limit of large central charge c ~ N^2 and large g^2 N. While we find an infinite tower of solutions, we argue most of them are suppressed by an extra scale \Delta_{gap} and are consistent with the upper bounds for the scaling dimension of unprotected operators observed in the numerical superconformal bootstrap at large central charge. These solutions organize as a double expansion in 1/c and 1/\Delta_{gap}. Our solutions are valid to leading order in 1/c and to all orders in 1/\Delta_{gap} and reproduce, in particular, instanton corrections previously found. Furthermore, we find a connection between such upper bounds and positivity constraints arising from causality in flat space. Finally, we show that certain relations derived from causality constraints for scattering in AdS follow from crossing symmetry.Peer reviewe
Hydrodynamic model for expansion and collisional relaxation of x-ray laser-excited multi-component nanoplasma
Clinical Fellowship for an Innovative, Integrated BSN-PhD Program: An Academic and Practice Partnership
Opportunities for research-focused doctoral education must be available to nurses early in their careers in order to ensure the further development of nursing science. Early entry into the research doctorate through an integrated BSN-PhD program is one innovative approach. This approach highlights the value of integrating post-licensure clinical training into the doctoral curriculum. To better prepare innovative nurse scientists early in their careers we developed a clinical nurse fellowship within an integrated BSN-PhD program in partnership with an affiliated health system. The aims of this clinical fellowship are to integrate post-licensure clinical experience with academic preparation, cultivate scholarly reflection on the connections between research and practice, educate nurse researchers to work effectively in interdisciplinary teams, and develop nurses\u27 contributions to health care innovation. Major considerations for the development of similar clinical training opportunities include clarifying and articulating the major aims of the fellowship, enlisting the support of executive clinical leadership, and placing fellows on nursing units with experienced and advanced nursing teams and management that supports the fellowship\u27s aims. We emphasize the fully integrated and collaborative activities, decision-making, and commitment required of both academic and health system partners to successfully implement similar clinical training opportunities
A study of the interacting binary V 393 Scorpii
We present high resolution J-band spectroscopy of V 393 Sco obtained with the
CRIRES at the ESO Paranal Observatory along with a discussion of archival IUE
spectra and published broad band magnitudes. The best fit to the spectral
energy distribution outside eclipse gives = 19000 500 for the
gainer, = 7250 300 for the donor, = 0.13 0.02
mag. and a distance of = 523 60 pc, although circumstellar material
was not considered in the fit. We argue that V 393 Sco is not a member of the
open cluster M7. The shape of the He I 1083 nm line shows orbital modulations
that can be interpreted in terms of an optically thick pseudo-photosphere
mimicking a hot B-type star and relatively large equatorial mass loss through
the Lagrangian L3 point during long cycle minimum. IUE spectra show several
(usually asymmetric) absorption lines from highly ionized metals and a narrow
L emission core on a broad absorption profile. The overall behavior of
these lines suggests the existence of a wind at intermediate latitudes. From
the analysis of the radial velocities we find = 0.24 0.02
and a mass function of = 4.76 0.24 M. Our observations favor
equatorial mass loss rather than high latitude outflows as the cause for the
long variability.Comment: 13 pages, 14 figures, 7 tables. Accepted for publication in MNRAS,
main journa
The Structure of the Large Magellanic Halo Stellar Halo Derived Using OGLE-III RR Lyr stars
We use the recently released OGLE-III catalog of 17692 fundamental mode RR
Lyr (RRab) stars in the Large Magellanic Cloud (LMC) to investigate the
structure of its stellar halo. We apply conservative cuts in period, amplitude
and magnitude to remove blends and other contamination. We use
period--luminosity and period--color relations to determine distance and
extinction of every star in our final sample of 9393 stars. In order to
determine the scatter of our method, we compare the distributions of distances
in two regions at the edges of the covered area with a central region. We
determine the intrinsic line-of-sight dispersion in the center to be 0.135 mag
or 3.21 kpc (FWHM of 0.318 mag or 7.56 kpc), assuming zero depth in one of the
edge regions. The conservative cuts we apply reduce the derived depth
significantly. Furthermore, we find that the distribution of RRab stars is
deformed in the sense that stars on the Eastern side are closer than on the
Western side. We model the RRab distribution as a triaxial ellipsoid and
determine its axes ratios to be 1:2.00:3.50 with the longest axis inclined by 6
degrees from the line of sight. Another result of our analysis is an extinction
map of the LMC and a map of internal reddening, which we make publicly
available.Comment: Accepted for publication in November 2009 issue of ApJ. 7 pages, 5
figures. Extinction map of the LMC available at
http://www.astronomy.ohio-state.edu/~pejcha/lmc_extma
Large spin systematics in CFT
20 pages; v2: version published in JHEPUsing conformal field theory (CFT) arguments we derive an infinite number of constraints on the large spin expansion of the anomalous dimensions and structure constants of higher spin operators. These arguments rely only on analiticity, unitarity, crossing-symmetry and the structure of the conformal partial wave expansion. We obtain results for both, perturbative CFT to all order in the perturbation parameter, as well as non-perturbatively. For the case of conformal gauge theories this provides a proof of the reciprocity principle to all orders in perturbation theory and provides a new "reciprocity" principle for structure constants. We argue that these results extend also to non-conformal theories.Peer reviewe
A Long Time Gone: Post-conflict Rural Property Restitution under Customary Law
Mass displacement of people due to violence poses a unique set of challenges for property restitution when people return to their homes after a long absence. This is particularly evident in rural areas where the dominant form of land holding is customary tenure. Violence-induced displacement, unlike voluntary migration, challenges both customary and public legaladministrative structures. The lack of written documentation of customary holdings and the importance of the support of community leaders means that incorporating returnees back into a community can be easier for those who choose to return, while reclaiming property without physical return is nearly impossible. This article seeks to make three contributions: 1) to note the diversity of return processes after long displacements in terms of timing and demographics; 2) to demonstrate that the nature of the claims people can make on customary tenure systems is at odds with international legal norms on property restitution after displacement; and 3) to introduce a set of observations and questions on how conflict can change customary law. The article is based on fieldwork conducted in Uganda, Liberia and Timor-Leste, all countries with extended displacement
Soft-Wall Stabilization
We propose a general class of five-dimensional soft-wall models with AdS
metric near the ultraviolet brane and four-dimensional Poincar\'e invariance,
where the infrared scale is determined dynamically. A large UV/IR hierarchy can
be generated without any fine-tuning, thus solving the electroweak/Planck scale
hierarchy problem. Generically, the spectrum of fluctuations is discrete with a
level spacing (mass gap) provided by the inverse length of the wall, similar to
RS1 models with Standard Model fields propagating in the bulk. Moreover two
particularly interesting cases arise. They can describe: (a) a theory with a
continuous spectrum above the mass gap which can model unparticles
corresponding to operators of a CFT where the conformal symmetry is broken by a
mass gap, and; (b) a theory with a discrete spectrum provided by linear Regge
trajectories as in AdS/QCD models.Comment: 27 pages, 6 figures, 1 table. v2: references added, version to appear
in NJP Focus Issue on Extra Dimension
Influence of energy balance on the somatotrophic axis and matrix metalloproteinase expression in the endometrium of the postpartum dairy cow
Postpartum dairy cows enter a period of negative energy balance (NEB) associated with low circulating IGF1, during which the uterus must undergo extensive repair following calving. This study investigated the effects of NEB on expression of IGF family members and related genes in the involuting uterus. Cows were allocated to two treatments using differential feeding and milking regimes to produce mild NEB or severe NEB (SNEB). Uterine endometrial samples collected 2 weeks post partum were analysed by quantitative PCR. The expression of IGF-binding protein 4 (IGFBP4) mRNA increased in the endometrium of SNEB cows, with trends towards increased IGFBP1 and reduced IGFBP6 expression. There were no significant differences between treatments in mRNA expression of IGF1, IGF2 or of any hormone receptor studied, but significant correlations across all cows in the expression levels of groups of receptors suggested common regulatory mechanisms: type 1 IGF receptor (IGF1R), IGF2R and insulin receptor (INSR); GHR with ESR1; and ESR2 with NR3C1. The expression of IGF1R and INSR also positively correlated with the circulating urea concentration. Matrix metalloproteinases (MMPs) are important in tissue remodelling and can affect IGF signalling via interaction with IGFBPs. The expression levels of MMP1, MMP3, MMP9 and MMP13 mRNAs all showed major upregulation in the endometrium of cows in SNEB and all except MMP9 were highly correlated with expression of IGFBP4. Alpha(2)-HS-glycoprotein (AHSG) and PDK4, two genes implicated in insulin resistance, were also highly expressed in SNEB. These results suggest that cows in SNEB experience alterations to the IGF and insulin signalling pathways in the postpartum endometrium. This may affect the rate of tissue repair with a possible negative impact on subsequent fertility
- …