6,880 research outputs found
Squeezed K^+ K^- correlations in high energy heavy ion collisions
The hot and dense medium formed in high energy heavy ion collisions may
modify some hadronic properties. In particular, if hadron masses are shifted
in-medium, it was demonstrated that this could lead to back-to-back squeezed
correlations (BBC) of particle-antiparticle pairs. Although well-established
theoretically, the squeezed correlations have not yet been discovered
experimentally. A method has been suggested for the empirical search of this
effect, which was previously illustrated for phi-phi pairs. We apply here the
formalism and the suggested method to the case of K^+ K^- pairs, since they may
be easier to identify experimentally. The time distribution of the emission
process plays a crucial role in the survival of the BBC's. We analyze the cases
where the emission is supposed to occur suddenly or via a Lorentzian
distribution, and compare with the case of a Levy distribution in time. Effects
of squeezing on the correlation function of identical particles are also
analyzed.Comment: 9 pages and 6 figures (figures 2 to 6 contain 4 plots each).
Paragraph added to text, figures 2 to 6 revised for improving visualizatio
Squeezed correlations of strange particle-antiparticles
Squeezed correlations of hadron-antihadron pairs are predicted to appear if
their masses are modified in the hot and dense medium formed in high energy
heavy ion collisions. If discovered experimentally, they would be an
unequivocal evidence of in-medium mass shift found by means of hadronic probes.
We discuss a method proposed to search for this novel type of correlation,
illustrating it by means of D_s-mesons with in-medium shifted masses. These
particles are expected to be more easily detected and identified in future
upgrades at RHIC.Comment: 6 pages, 3 figures with parts a) and b), SQM 2009 contribution; added
acknowledgmen
Screening tests, information, and the health-education gradient
The association between health outcomes and education - the health-education gradient - is widely documented but little is known about its source. Using microeconomic data on a sample of individuals aged 50+ in eight European countries, we find that education and cognitive skills (such as verbal fluency) are associated with a greater propensity for standard screening tests (mammography and colonoscopy). In order to study the role of information on the decision to screen, we test whether the health-education gradient varies with the quality of the information provided by the health care system, as proxied by the quality of the General Practitioner. Using an Instrumental Variable approach to control for the potential endogeneity of the GP quality score, we find evidence of a strong and significant complementarity between education and quality of primary care. We interpret this result as evidence that health-education gradient can be explained, at least in part, by the fact that better educated individuals are more able to process and internalize health related information as provided by GPs
Integrated Thermal-structural-electromagnetic Design Optimization of Large Space Antenna Reflectors
The requirements for low mass and high electromagnetic (EM) performance in large, flexible space antenna structures is motivating the development of a systematic procedure for antenna design. In contrast to previous work which concentrated on reducing rms distortions of the reflector surface, thereby indirectly increasing antenna performance, the current work involves a direct approach to increasing electromagnetic performance using mathematical optimization. The thermal, structural, and EM analyses are fully integrated in the context of an optimization procedure, and consequently, the interaction of the various responses is accounted for directly and automatically. Preliminary results are presented for sizing cross-sectional areas of a tetrahedral truss reflector. The results indicate potential for this integrated procedure from the standpoint of mass reduction, performance increase, and efficiency of the design process
Integrated structure electromagnetic optimization of large space antenna reflectors
The requirements for extremely precise and powerful large space antenna reflectors have motivated the development of a procedure for shape control of the reflector surface. A mathematical optimization procedure has been developed which improves antenna performance while minimizing necessary shape correction effort. In contrast to previous work which proposed controlling the rms distortion error of the surface thereby indirectly improving antenna performance, the current work includes electromagnetic (EM) performance calculations as an integral of the control procedure. The application of the procedure to a radiometer design with a tetrahedral truss backup structure demonstrates the potential for significant improvement. The results indicate the benefit of including EM performance calculations in procedures for shape control of large space antenna reflectors
Advanced turboprop noise prediction: Development of a code at NASA Langley based on recent theoretical results
The development of a high speed propeller noise prediction code at Langley Research Center is described. The code utilizes two recent acoustic formulations in the time domain for subsonic and supersonic sources. The structure and capabilities of the code are discussed. Grid size study for accuracy and speed of execution on a computer is also presented. The code is tested against an earlier Langley code. Considerable increase in accuracy and speed of execution are observed. Some examples of noise prediction of a high speed propeller for which acoustic test data are available are given. A brisk derivation of formulations used is given in an appendix
The phylogeography and population genetic structure of least cisco (Coregonus sardinella) in Alaska
Thesis (M.S.) University of Alaska Fairbanks, 2013The least cisco (Coregonus sardinella) is a whitefish species broadly distributed across the Arctic regions of Russia, Alaska, and Canada, and little is known about the genetic relationships among groups within this species. We investigated the genetic relationships among least cisco on two landscape scales. On a broader landscape scale, we investigated the relationships among populations across the state of Alaska by comparing mitochondria) DNA (mtDNA) sequences. On a finer landscape scale, we investigated the relationships among least cisco populations in closely located lakes on the Arctic Coastal Plain by comparing microsatellite DNA haplotypes. Data from mtDNA suggest that least cisco are relatively diverse across Alaska, with 68 unique haplotypes found in 305 individuals and a large proportion of genetic variation is shared across Alaska, but this variation is not homogeneously distributed across all regions and for all haplotype groups. Interpretation of microsatellite data was limited. Overall, the data suggest that least cisco populations are currently isolated from one another. Isolation also occurred historically, accounting for divergence among major Glades. But general recontact events occurred as isolated populations migrated and colonized new habitats, accounting for the heterogeneity found across Alaska. Ultimately, Alaskan least cisco may have functioned as a metapopulation historically, but present populations are too isolated to be considered a metapopulation today
Search for Squeezed-Pair Correlations at RHIC
Squeezed correlations of particle-antiparticle pairs, also called
Back-to-Back Correlations, are predicted to appear if the hadron masses are
modified in the hot and dense hadronic medium formed in high energy
nucleus-nucleus collisions. Although well-established theoretically, the
squeezed-particle correlations have not yet been searched for experimentally in
high energy hadronic or heavy ion collisions, clearly requiring optimized forms
to experimentally search for this effect. Within a non-relativistic treatment
developed earlier we show that one promising way to search for the BBC signal
is to look into the squeezed correlation function of pairs of phi-mesons at
RHIC energies, plotted in terms of the average momentum of the pair,
K12=(k1+k2)/2. This variable's modulus, 2|K12|, is the non-relativistic limit
of the variable Q_bbc, introduced herewith. The squeezing effects on the HBT
correlation function are also discussed.Comment: 4 pages, 2 figures. To be published in the Proceedings of Quark
Matter 2008, Jaipur, Indi
Testing the Resolving Power of 2-D K^+ K^+ Interferometry
Adopting a procedure previously proposed to quantitatively study
two-dimensional pion interferometry, an equivalent 2-D chi^2 analysis was
performed to test the resolving power of that method when applied to less
favorable conditions, i.e., if no significant contribution from long lived
resonances is expected, as in kaon interferometry. For that purpose, use is
made of the preliminary E859 K^+ K^+ interferometry data from Si+Au collisions
at 14.6 AGeV/c. As expected, less sensitivity is achieved in the present case,
although it still is possible to distinguish two distinct decoupling
geometries. The present analysis seems to favor scenarios with no resonance
formation at the AGS energy range, if the preliminary K^+ K^+ data are
confirmed. The possible compatibility of data with zero decoupling proper time
interval, conjectured by the 3-D experimental analysis, is also investigated
and is ruled out when considering more realistic dynamical models with
expanding sources. These results, however, clearly evidence the important
influence of the time emission interval on the source effective transverse
dimensions. Furthermore, they strongly emphasize that the static Gaussian
parameterization, commonly used to fit data, cannot be trusted under more
realistic conditions, leading to distorted or even wrong interpretation of the
source parameters!Comment: 11 pages, RevTeX, 4 Postscript figures include
Retirement expectations, pension reforms, and their effect on private wealth accumulation
We estimate the effect of pension reforms on households’ expectations of retirement outcomes and private wealth accumulation decisions exploiting a decade of intense Italian pension reforms as a source of exogenous variation in expected pension wealth. The Survey of Household Income and Wealth, a large random sample of the Italian population, elicits expectations of the age at which workers expect to retire and of the ratio of pension benefits to pre-retirement income between 1989 and 2002. We find that workers have revised expectations in the direction suggested by the reform and that there is substantial offset between private wealth and perceived pension wealth, particularly by workers that are better informed about their pension wealth
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