264 research outputs found
Mesonic screening masses at high temperature and finite density
We compute the first perturbative correction to the static correlation
lengths of light quark bilinears in hot QCD with finite quark chemical
potentials. The correction is small and positive, with mu-dependence depending
on the relative sign of chemical potentials and the number of dynamical
flavors. The computation is carried out using a three-dimensional effective
theory for the lowest fermionic Matsubara mode. We also compute the full
correlator in free theory and find a rather complicated general mu-dependence
at shorter distances. Finally, rough comparisons with lattice simulations are
discussed.Comment: 24 pages, 5 figures, JHEP style. Minor corrections and
clarifications, version to appear in JHE
HYDJET++ heavy ion event generator and its applications for RHIC and LHC
The heavy ion event generator HYDJET++ is presented. HYDJET++ simulates
relativistic heavy ion AA collisions as a superposition of the soft, hydro-type
state and the hard state resulting from multi-parton fragmentation. This model
is the development and continuation of HYDJET event generator. The hard parts
of HYDJET and HYDJET++ are identical. The soft part of HYDJET++ contains the
following important additional features as compared with HYDJET: resonance
decays and more detailed treatment of thermal and chemical freeze-out
hypersurfaces. HYDJET++ is capable of reproducing the bulk properties of heavy
ion collisions at RHIC (hadron spectra and ratios, radial and elliptic flow,
femtoscopic momentum correlations), as well as high-pT hadron spectra. Some
applications of HYDJET++ at LHC are discussed.Comment: Talk given at 4th International Workshop on High-pT physics at LHC
(Prague, Czech Republic, February 4-7, 2009); 12 pages including 7 figures as
EPS-files; prepared using LaTeX package for publication in Proceedings of
Science (PoS
Heavy quark medium polarization at next-to-leading order
We compute the imaginary part of the heavy quark contribution to the photon
polarization tensor, i.e. the quarkonium spectral function in the vector
channel, at next-to-leading order in thermal QCD. Matching our result, which is
valid sufficiently far away from the two-quark threshold, with a previously
determined resummed expression, which is valid close to the threshold, we
obtain a phenomenological estimate for the spectral function valid for all
non-zero energies. In particular, the new expression allows to fix the overall
normalization of the previous resummed one. Our result may be helpful for
lattice reconstructions of the spectral function (near the continuum limit),
which necessitate its high energy behaviour as input, and can in principle also
be compared with the dilepton production rate measured in heavy ion collision
experiments. In an appendix analogous results are given for the scalar channel.Comment: 43 pages. v2: a figure and other clarifications added, published
versio
Bisphosphonate treatment in children with acute lymphoblastic leukemia and osteonecrosis - radiological and clinical findings in a national cohort
Background: Osteonecrosis (ON) is a recognized complication of childhood ALL, but its optimal management remains unestablished. This study evaluated the effect of bisphosphonate (BP) treatment on the evolution of ON lesions in childhood ALL. Material and Methods: We included a national cohort of ALL patients diagnosed with symptomatic ON before 18 years of age and treated with BPs (N = 10; five males). Patients were followed both clinically and with serial MRIs. ON lesions were graded according to the Niinimaki classification. Results: The 10 patients had a total of 55 ON lesions. The median age was 13.3 years at ALL diagnosis and 14.8 years at ON diagnosis. Four patients had received HSCT before the ON diagnosis. BPs used were pamidronate (N = 7), alendronate (N = 2) and ibandronate (N = 1). The duration of BP treatment varied between 4 months and 4 years. In 4/10 patients, BP treatment was given during the chemotherapy. BPs were well-tolerated, with no severe complications or changes in kidney function. At the end of follow up 13/55 (24%) ON lesions were completely healed both clinically and radiographically; all these lesions were originally graded 3 or less. In contrast, ON lesions originally classified as grade 5 (joint destruction; N = 4) remained at grade 5. All grade 5 hip joint lesions needed surgical treatment. During BP treatment, the pain was relieved in 7/10 patients. At the end of follow-up, none of the patients reported severe or frequent pain. Conclusion: BP treatment was safe and seemed effective in relieving ON-induced pain in childhood ALL. After articular collapse (grade 5) lesions did not improve with BP treatment. Randomized controlled studies are needed to further elucidate the role of BPs in childhood ALL-associated ON.Peer reviewe
Comparison of six approaches to predicting droplet activation of surface active aerosol – Part 2: Strong surfactants
Surfactants have been a focus of investigation in atmospheric sciences for decades due to their ability to modify the water uptake and cloud formation potential of aerosols. Surfactants adsorb at the surface and can decrease the surface tension of aqueous solutions. In microscopic aqueous droplets with finite amounts of solute, surface adsorption may simultaneously deplete the droplet bulk of the surfactant. While this mechanism is now broadly accepted, the representation in atmospheric and cloud droplet models is still not well constrained. We compare the predictions of five bulk–surface partitioning models documented in the literature to represent aerosol surface activity in Köhler calculations of cloud droplet activation. The models are applied to common aerosol systems, consisting of strong atmospheric surfactants (sodium myristate or myristic acid) and sodium chloride in a wide range of relative mixing ratios. For the same particles, the partitioning models predict similar critical droplet properties at small surfactant mass fractions, but differences between the model predictions increase significantly with the surfactant mass fraction in the particles. Furthermore, significantly different surface tensions are predicted for growing droplets at given ambient conditions along the Köhler curves. The inter-model variation for these strong surfactant particles is different than previously observed for moderately surface active atmospheric aerosol components. Our results highlight the importance of establishing bulk–surface partitioning effects in Köhler calculations for a wide range of conditions and aerosol types relevant to the atmosphere. In particular, conclusions made for a single type of surface active aerosol and surface activity model may not be immediately generalized.</p
The ultraviolet limit and sum rule for the shear correlator in hot Yang-Mills theory
We determine a next-to-leading order result for the correlator of the shear
stress operator in high-temperature Yang-Mills theory. The computation is
performed via an ultraviolet expansion, valid in the limit of small distances
or large momenta, and the result is used for writing operator product
expansions for the Euclidean momentum and coordinate space correlators as well
as for the Minkowskian spectral density. In addition, our results enable us to
confirm and refine a shear sum rule originally derived by Romatschke, Son and
Meyer.Comment: 16 pages, 2 figures. v2: small clarifications, one reference added,
published versio
Ultraviolet asymptotics of scalar and pseudoscalar correlators in hot Yang-Mills theory
Inspired by recent lattice measurements, we determine the short-distance (a
> omega >> pi T) asymptotics
of scalar (trace anomaly) and pseudoscalar (topological charge density)
correlators at 2-loop order in hot Yang-Mills theory. The results are expressed
in the form of an Operator Product Expansion. We confirm and refine the
determination of a number of Wilson coefficients; however some discrepancies
with recent literature are detected as well, and employing the correct values
might help, on the qualitative level, to understand some of the features
observed in the lattice measurements. On the other hand, the Wilson
coefficients show slow convergence and it appears uncertain whether this
approach can lead to quantitative comparisons with lattice data. Nevertheless,
as we outline, our general results might serve as theoretical starting points
for a number of perhaps phenomenologically more successful lines of
investigation.Comment: 27 pages. v2: minor improvements, published versio
Intermediate distance correlators in hot Yang-Mills theory
Lattice measurements of spatial correlation functions of the operators FF and
FF-dual in thermal SU(3) gauge theory have revealed a clear difference between
the two channels at "intermediate" distances, x ~ 1/(pi T). This is at odds
with the AdS/CFT limit which predicts the results to coincide. On the other
hand, an OPE analysis at short distances (x << 1/(pi T)) as well as effective
theory methods at long distances (x >> 1/(pi T)) suggest differences. Here we
study the situation at intermediate distances by determining the time-averaged
spatial correlators through a 2-loop computation. We do find unequal results,
however the numerical disparity is small. Apart from theoretical issues, a
future comparison of our results with time-averaged lattice measurements might
also be of phenomenological interest in that understanding the convergence of
the weak-coupling series at intermediate distances may bear on studies of the
thermal broadening of heavy quarkonium resonances.Comment: 31 page
Effects of the DAGIS randomized controlled trial on home environment and children's food consumption according to the degree of implementation
Background Combining process evaluation data with effectiveness data and examining the possible mediators of intervention effects elicits valuable knowledge about how and for whom these interventions are effective. The aim of this study was to examine whether the parental degree of implementation (DOI) of a home-involving preschool intervention affected children's food consumption via home mediators. Methods The five-month Increased Health and Wellbeing in Preschools (DAGIS) intervention involved 476 participating children aged 3-6 years and was conducted in 2017-2018. Parents reported children's food consumption (g/day) outside childcare hours, the availability of foods at home, role modelling of food consumption, and the norms related to food consumption. In addition, parents reported the extent to which they had implemented the intervention program at home. Mediation analyses were conducted to examine the effect of low and high DOI compared to control group on the change in children's consumption of fruit and vegetables (FV), sugary everyday foods, sugary treats, and sugar-sweetened beverages (SSB) via food availability in the home, parental role modelling and parental norms. Results Compared to the control group, there was a direct effect of a high DOI on diminishing consumption of SSB (B -27.71, 95% CI -49.05, -4.80). No indirect effects were detected. In the high DOI group, a change in parental norm was associated with increased FV consumption showing an indirect effect (B 4.31, 95% CI 0.23, 10.59). In the low DOI group, there was an indirect effect via decreased food availability leading to decreased sugary everyday food consumption (B -2.17, 95% CI -5.09, -0.09). Conclusions Combining process evaluation and effectiveness data revealed a decrease in children's SSB consumption only in the high DOI group, as well as indirect effects on children's consumption of FV and sugary everyday foods. In order to gain more intervention effects, further studies are required in order to examine parental facilitators and barriers to the implementation of interventions and how to impact effectively the determinants of the targeted behavior.Peer reviewe
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