Beam Propagation Through Atmospheric Turbulence Using an Altitude-Dependent Structure Profile with Non-Uniformly Distributed Phase Screens

Modeling the effects of atmospheric turbulence on optical beam propagation is a key element in the design and analysis of free-space optical communication systems. Numerical wave optics simulations provide a particularly useful technique for understanding the degradation of the optical field in the receiver plane when the analytical theory is insufficient for characterizing the atmospheric channel. Motivated by such an application, we use a split-step method modeling the turbulence along the propagation path as a series of thin random phase screens with modified von Karman refractive index statistics using the Hufnagel-Valley turbulence profile to determine the effective structure constant for each screen. In this work, we employ a space-to-ground case study to examine the irradiance and phase statistics for both uniformly and non-uniformly spaced screens along the propagation path and compare to analytical results. We find that better agreement with the analytical theory is obtained using a non-uniform spacing with the effective structure constant for each screen chosen to minimize its contribution to the scintillation in the receiver plane. We evaluate this method as a flexible alternative to other standard layered models used in astronomical imaging applications

Beam Propagation Through Atmospheric Turbulence Using an Altitude-Dependent Structure Profile with Non-Uniformly Distributed Phase Screens

For free-space optical communication systems, numerical wave optics simulations provide a useful technique for modeling turbulence-induced beam degradation when the analytical theory is insufficient for characterizing the atmospheric channel. Motivated by such applications we use a split-step method modeling the turbulence as a series of random phase screens using the Hufnagel-Valley turbulence profile. We employ a space-to-ground case study to examine the irradiance and phase statistics for uniformly and non-uniformly located screens and find better agreement with theory using a non-uniform discretization minimizing the contribution of each screen to the total scintillation. In this poster, we summarize the method and the results of the case study including a comparison to layered models used in astronomical imaging applications

Comparing loneliness in England and the United States, 2014-2016: Differential item functioning and risk factor prevalence and impact

The purpose of this study is to compare mean levels of loneliness, and correlates of loneliness, among older adults in the U.S. and England. Comparisons are conducted after attending to comparability of the loneliness measure between countries based on tests for discriminatory capacity and differential item functioning of the 3-item UCLA Loneliness Scale. Cross-sectional data from the 2015-16 wave of the National Social Life, Health and Aging Project (NSHAP) and the 2014-2015 wave of the English Longitudinal Study on Ageing (ELSA) were analyzed using graded item response models and multiple indicators and multiple causes (MIMIC) models. Risk factors included demographic variables, health characteristics, and social characteristics that were harmonized across surveys. Because of differences in the racial-ethnic composition of the U.S. and England, analyses were limited to white respondents (N = 2624 in NSHAP; N = 6639 in ELSA). Only respondents born 1925-1965 were included in analyses. Discriminatory capacity was evident in each item being able to distinguish a lonely from a nonlonely individual. Differential item functioning (DIF) was evident in country differences in the likelihood of endorsing the "lack companionship" item at a given level of trait loneliness, and in DIF among marital status, education, and gender subgroups that were comparable across countries. Overall loneliness levels are equivalent in England and the U.S. Risk factor impact did not differ between countries, but differences in risk factor prevalence between countries combined to produce a net result of slightly lower mean levels of loneliness in older adults in England than in the U.S. after risk factor adjustment. The fact that the impact of risk factors were similar across countries suggests that evidence of successful interventions in one country could be leveraged to accelerate development of effective interventions in the other

Demonstration Advanced Avionics System (DAAS) function description

The Demonstration Advanced Avionics System, DAAS, is an integrated avionics system utilizing microprocessor technologies, data busing, and shared displays for demonstrating the potential of these technologies in improving the safety and utility of general aviation operations in the late 1980's and beyond. Major hardware elements of the DAAS include a functionally distributed microcomputer complex, an integrated data control center, an electronic horizontal situation indicator, and a radio adaptor unit. All processing and display resources are interconnected by an IEEE-488 bus in order to enhance the overall system effectiveness, reliability, modularity and maintainability. A detail description of the DAAS architecture, the DAAS hardware, and the DAAS functions is presented. The system is designed for installation and flight test in a NASA Cessna 402-B aircraft

Transition from Baryon- to Meson-Dominated Freeze Out -- Early Decoupling around 30 A GeV?

The recently discovered sharp peak in the excitation function of the K+/pi+ ratio around 30 A GeV in relativistic heavy-ion collisions is discussed in the framework of the Statistical Model. In this model, the freeze-out of an ideal hadron gas changes from a situation where baryons dominate to one with mainly mesons. This transition occurs at a temperature T = 140 MeV and baryon chemical potential mu(B) = 410 MeV corresponding to an energy of sqrt(s) = 8.2 GeV. The calculated maximum in the K+/pi+ ratio is, however, much less pronounced than the one observed by the NA49 Collaboration. The smooth increase of the K-/pi- ratio with incident energy and the shape of the excitation functions of the Lambda/pi+, Xi-/pi+ and Omega/pi ratios all exhibiting maxima at different incident energies, is consistent with the presently available experimental data. The measured K+/pi+ ratio exceeds the calculated one just at the incident energy when the freeze-out condition is changing. We speculate that at this point freeze-out might occur in a modified way. We discuss a scenario of an early freeze-out which indeed increases K+/pi+ ratio while most other particle ratios remain essentially unchanged. Such an early freeze-out is supported by results from HBT studies.Comment: 8 pages, 5 figures, SQM2006 conference, Los Angeles, March 200

Strangeness Production at RHIC in the Perturbative Regim

We investigate strange quark production in Au-Au collisions at RHIC in the framework of the Parton Cascade Model(PCM). The yields of (anti-) strange quarks for three production scenarios -- primary-primary scattering, full scattering, and full production -- are compared to a proton-proton baseline. Enhancement of strange quark yields in central Au-Au collisions compared to scaled p-p collisions increases with the number of secondary interactions. The centrality dependence of strangeness production for the three production scenarios is studied as well. For all production mechanisms, the strangeness yield increases with $(N_{\rm part})^{4/3}$. The perturbative QCD regime described by the PCM is able to account for up to 50% of the observed strangeness at RHIC.Comment: 10 pages, 4 figures, IOP forma

Strange Particle Production from SIS to LHC

>1A review of meson emission in heavy ion collisions at incident energies from SIS up to collider energies is presented. A statistical model assuming chemical equilibrium and local strangeness conservation (i.e. strangeness conservation per collision) explains most of the observed features. Emphasis is put onto the study of $K^+$ and $K^-$ emission at low incident energies. In the framework of this statistical model it is shown that the experimentally observed equality of $K^+$ and $K^-$ rates at ``threshold-corrected'' energies $\sqrt{s} - \sqrt{s_{th}}$ is due to a crossing of two excitation functions. Furthermore, the independence of the $K^+$ to $K^-$ ratio on the number of participating nucleons observed between SIS and RHIC is consistent with this model. It is demonstrated that the $K^-$ production at SIS energies occurs predominantly via strangeness exchange and this channel is approaching chemical equilibrium. The observed maximum in the $K^+/\pi^+$ excitation function is also seen in the ratio of strange to non-strange particle production. The appearance of this maximum around 30 $A\cdot$GeV is due to the energy dependence of the chemical freeze-out parameters $T$ and $\mu_B$.Comment: Presented at the International Workshop "On the Physics of the Quark-Gluon Plasma", Palaiseau, France, September 2001. 10 pages, 8 figure

Labyrinth seals flow field evaluation with optical methods

This work aims to perform the detailed experimental investigation of the flow field in labyrinth seal specimen using optical methods: LDA (Laser Doppler Anemometry) and schlieren visualization. Preliminary tests were performed on a stationary (rotor model with labyrinth does not move), linear – where the curvature of the specimen is omitted – measuring stand supplied by a vacuum pump. The installation makes it possible to achieve critical pressure ratios, up to two. This investigation was also supported by CFD (Computational Fluid Dynamics) calculations performed using the Ansys CFX v.17 commercial code with a flow model based on the RANS equations. Prediction scheme simulated the experimental campaign parameters. In CFD study, different types of mesh resolution were tested, with variable volume discretization in the area of labyrinth fin tip. Presented study shows challenges as well as the possibilities of flow field visualization including three-dimensional vortexes and strong jets occurring downstream the fin tips. Some limitations of LDA method application were pointed out, especially in areas of rapid fluid expansion. Moreover paper presented that schlieren method is a very efficient way of giving the turbulence structures in linear labyrinth seal fins. In the end, experimental results were compared with CFD study, which reviled the best method for labyrinth seal structures flow field simulation. Comparison of experimental and computed results showed some agreement between those two approaches. Flow visualization also allowed to understand better the flow behavior in cavities, which is crucial for design tools development.Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .International centre for heat and mass transfer.American society of thermal and fluids engineers

Strange prospects for LHC energies

Strange quark and hadron production will be studied at the Large Hadron Collider (LHC) energies in order to explore the properties of both pp and heavy-ion collisions. The ALICE experiment will be specifically efficient in the strange sector with the identification of baryons and mesons over a wide range of transverse momentum. Dedicated measurements are proposed for investigating chemical equilibration and bulk properties. Strange particles can also help to probe kinematical regions where hard processes and pQCD dominate. We try to anticipate here several ALICE analyses to be performed as the first Pb--Pb and pp data will be available.Comment: 5 pages, 2 figures. To appear in the proceedings of Hot Quarks 2006, Villasimius, Italy, 15-20 May 200