Imaging and Nulling with the Space Interferometry Mission

We present numerical simulations for a possible synthesis imaging mode of the Space Interferometer Mission (SIM). We summarize the general techniques that SIM offers to perform imaging of high surface brightness sources, and discuss their strengths and weaknesses. We describe an interactive software package that is used to provide realistic, photometrically correct estimates of SIM performance for various classes of astronomical objects. In particular, we simulate the cases of gaseous disks around black holes in the nuclei of galaxies, and zodiacal dust disks around young stellar objects. Regarding the first, we show that a Keplerian velocity gradient of the line-emitting gaseous disk -- and thus the mass of the putative black hole -- can be determined with SIM to unprecedented accuracy in about 5 hours of integration time for objects with H_alpha surface brigthness comparable to the prototype M 87. Detections and observations of exo-zodiacal dust disks depend critically on the disk properties and the nulling capabilities of SIM. Systems with similar disk size and at least one tenth of the dust content of beta Pic can be detected by SIM at distances between 100 pc and a few kpc, if a nulling efficiency of 1/10000 is achieved. Possible inner clear regions indicative of the presence of massive planets can also be detected and imaged. On the other hand, exo-zodiacal disks with properties more similar to the solar system will not be found in reasonable integration times with SIM.Comment: 28 pages, incl. 8 postscript figures, excl. 10 gif-figures Submitted to Ap

Consumer-Directed Health Insurance vs. Managed Care: Analysis of Health Care Utilization and Expenditure Incurred by Employees in a Rural Area

Consumer-Directed Health Plans (CDHPs) are proposed as an option to control healthcare costs. No research has addressed their applicability in rural settings. This study analyzes three years (2003–2005) of healthcare expenditure and utilization incurred by two employers and a national carrier providing data from a rural state, Kentucky. The study included two measures of expenditures (health care and prescription drugs) and three measures of utilization (physician visits, hospital admissions, and hospital inpatient days). In general, the CDHP successfully controlled the growth of medical costs. These findings suggest that CDHPs may be a viable alternative benefit structure for rural employers

Odd-Order Aberration-Cancellation in Correlated-Photon Imaging

We discuss a correlated two-photon imaging apparatus that is capable of producing images that are free of the effects of odd-order aberration introduced by the optical system. We show that both quantum-entangled and classically correlated light sources are capable of producing the desired spatial-aberration cancelation

A single-column model intercomparison of a heavily drizzling stratocumulus-topped boundary layer

This study presents an intercomparison of single-column model simulations of a nocturnal heavily drizzling marine stratocumulus-topped boundary layer. Initial conditions and forcings are based on nocturnal flight observations off the coast of California during the DYCOMS-II field experiment. Differences in turbulent and microphysical parameterizations between models were isolated by slightly idealizing and standardizing the specification of surface and radiative fluxes. For most participating models, the case was run at both typical operational vertical resolution of about 100 m and also at high vertical resolution of about 10 m. As in prior stratocumulus intercomparisons, the simulations quickly develop considerable scatter in liquid water path (LWP) between models. However, the simulated dependence of cloud base drizzle fluxes on LWP in most models is broadly consistent with recent observations. Sensitivity tests with drizzle turned off show that drizzle substantially decreases LWP for many models. The sensitivity of entrainment rate to drizzle is more muted. Simulated LWP and entrainment are also sensitive to the inclusion of cloud droplet sedimentation. Many models underestimate the fraction of drizzle that evaporates below cloud base, which may distort the simulated feedbacks of drizzle on turbulence, entrainment, and LWP

Astrometric Methods and Instrumentation to Identify and Characterize Extrasolar Planets: A Review

I present a review of astrometric techniques and instrumentation utilized to search for, detect, and characterize extra-solar planets. First, I briefly summarize the properties of the present-day sample of extrasolar planets, in connection with predictions from theoretical models of planet formation and evolution. Next, the generic approach to planet detection with astrometry is described, with significant discussion of a variety of technical, statistical, and astrophysical issues to be faced by future ground-based as well as space-borne efforts in order to achieve the required degree of measurement precision. After a brief summary of past and present efforts to detect planets via milli-arcsecond astrometry, I then discuss the planet-finding capabilities of future astrometric observatories aiming at micro-arcsecond precision. Lastly, I outline a number experiments that can be conducted by means of high-precision astrometry during the next decade, to illustrate its potential for important contributions to planetary science, in comparison with other indirect and direct methods for the detection and characterization of planetary systems.Comment: 61 pages, 8 figures, PASP, accepted (October 2005 issue

The PreVOCA experiment: modeling the lower troposphere in the Southeast Pacific

The Preliminary VOCALS Model Assessment (PreVOCA) aims to assess contemporary atmospheric modeling of the subtropical South East Pacific, with a particular focus on the clouds and the marine boundary layer (MBL). Models results from fourteen modeling centers were collected including operational forecast models, regional models, and global climate models for the month of October 2006. Forecast models and global climate models produced daily forecasts, while most regional models were run continuously during the study period, initialized and forced at the boundaries with global model analyses. Results are compared in the region from 40° S to the equator and from 110° W to 70° W, corresponding to the Pacific coast of South America. Mean-monthly model surface winds agree well with QuikSCAT observed winds and models agree fairly well on mean weak large-scale subsidence in the region next to the coast. However they have greatly differing geographic patterns of mean cloud fraction with only a few models agreeing well with MODIS observations. Most models also underestimate the MBL depth by several hundred meters in the eastern part of the study region. The diurnal cycle of liquid water path is underestimated by most models at the 85° W 20° S stratus buoy site compared with satellite, consistent with previous modeling studies. The low cloud fraction is also underestimated during all parts of the diurnal cycle compared to surface-based climatologies. Most models qualitatively capture the MBL deepening around 15 October 2006 at the stratus buoy, associated with colder air at 700 hPa

Doppelheterodyn-Interferometrie für hochgenaue Vermessung im Nahbereich

In diesem Aufsatz wurde ein Meßsystem vorgestellt, welches sich aus der Kombination der Zweiwellenlängen-Interferometrie mit dem intensitätsunabhängigen Heterodyn-Verfahren zusammensetzt. Die resultierende Doppelheterodyn-Interferometrie vereinigt die Vorteile der beiden Verfahren. Ein großer Eindeutigkeitsbereich entsprechend der effektiven Wellenlänge A entsteht, darüberhinaus sind optisch rauhe Oberflächen als Meßobjekte zulässig; reduzierte Empfindlichkeit gegenüber Vibrationen und Umwelteinflüssen, hohe Auflösung infolge elektronischer Phasenbestimmung sowie hochgenaue Abstandsmessung in Echtzeit sind weitere Vorteile. Das Doppelheterodyn-Interferometer wird in Zukunft zu einem effektiven und dynamischen Meßinstrument zur hochgenauen Entfernungsmessung im Mikrometerbereich bis hin zu Meßdistanzen von 100 m entwickelt werden, für das sich schon jetzt zahlreiche Einsatzmöglichkeiten abzeichnen

Submillimetric GPS distance measurement over short baselines: case study in inner consistency

Distance determination in the open air with submillimetric accuracy is a challenging task usually carried out with the use of submillimetric distancemeters and costly observation campaigns. The present paper represents a first step in the research of the potential use of GPS for submillimetric distance determination for distances up to a few hundred metres consisting in the evaluation of GPS distance determination reproducibility. As will be concluded, reliable submillimetric precision is attainable after some hours of observation if the same equipment in both baseline ends is used, even considering that there still remain some long-term systematic effects of a few tenths of a millimetre. The need for precise absolute antenna calibration values is also shown to be critical for submillimetric distance reproducibility.This research is funded by the Spanish Ministry of Science and Innovation (AYA2011-23232). The authors are grateful to the editor and the anonymous reviewers for their valuable suggestions, corrections and comments that helped improve the original manuscript.Baselga Moreno, S.; García-Asenjo Villamayor, L.; Garrigues Talens, P. (2013). Submillimetric GPS distance measurement over short baselines: case study in inner consistency. Measurement Science and Technology. 24(7):750011-750018. https://doi.org/10.1088/0957-0233/24/7/075001S750011750018247Amiri-Simkooei, A. R., & Tiberius, C. C. J. M. (2006). Assessing receiver noise using GPS short baseline time series. GPS Solutions, 11(1), 21-35. doi:10.1007/s10291-006-0026-8Bruyninx, C., Altamimi, Z., Boucher, C., Brockmann, E., Caporali, A., Gurtner, W., … Weber, G. (2009). The European Reference Frame: Maintenance and Products. International Association of Geodesy Symposia, 131-136. doi:10.1007/978-3-642-00860-3_20Doloca, N. R., Meiners-Hagen, K., Wedde, M., Pollinger, F., & Abou-Zeid, A. (2010). Absolute distance measurement system using a femtosecond laser as a modulator. Measurement Science and Technology, 21(11), 115302. doi:10.1088/0957-0233/21/11/115302Dow, J. M., Neilan, R. E., & Rizos, C. (2009). The International GNSS Service in a changing landscape of Global Navigation Satellite Systems. Journal of Geodesy, 83(3-4), 191-198. doi:10.1007/s00190-008-0300-3Firuzabadì, D., & King, R. W. (2011). GPS precision as a function of session duration and reference frame using multi-point software. GPS Solutions, 16(2), 191-196. doi:10.1007/s10291-011-0218-8Hyun, S., Kim, Y.-J., Kim, Y., Jin, J., & Kim, S.-W. (2009). Absolute length measurement with the frequency comb of a femtosecond laser. Measurement Science and Technology, 20(9), 095302. doi:10.1088/0957-0233/20/9/095302Koivula, H., Häkli, P., Jokela, J., Buga, A., & Putrimas, R. (2011). GPS Metrology: Bringing Traceable Scale to a Local Crustal Deformation GPS Network. International Association of Geodesy Symposia, 105-112. doi:10.1007/978-3-642-20338-1_13Ray, J., Altamimi, Z., Collilieux, X., & van Dam, T. (2007). Anomalous harmonics in the spectra of GPS position estimates. GPS Solutions, 12(1), 55-64. doi:10.1007/s10291-007-0067-7Schuhler, N., Salvadé, Y., Lévêque, S., Dändliker, R., & Holzwarth, R. (2006). Frequency-comb-referenced two-wavelength source for absolute distance measurement. Optics Letters, 31(21), 3101. doi:10.1364/ol.31.003101Snay, R. A., & Soler, T. (2008). Continuously Operating Reference Station (CORS): History, Applications, and Future Enhancements. Journal of Surveying Engineering, 134(4), 95-104. doi:10.1061/(asce)0733-9453(2008)134:4(95

Clouds, aerosols, and precipitation in the marine boundary layer: an ARM Mobile Facility Deployment

The Clouds, Aerosol, and Precipitation in the Marine Boundary Layer (CAP-MBL) deployment at Graciosa Island in the Azores generated a 21-month (April 2009–December 2010) comprehensive dataset documenting clouds, aerosols, and precipitation using the Atmospheric Radiation Measurement Program (ARM) Mobile Facility (AMF). The scientific aim of the deployment is to gain improved understanding of the interactions of clouds, aerosols, and precipitation in the marine boundary layer. Graciosa Island straddles the boundary between the subtropics and midlatitudes in the northeast Atlantic Ocean and consequently experiences a great diversity of meteorological and cloudiness conditions. Low clouds are the dominant cloud type, with stratocumulus and cumulus occurring regularly. Approximately half of all clouds contained precipitation detectable as radar echoes below the cloud base. Radar and satellite observations show that clouds with tops from 1 to 11 km contribute more or less equally to surface-measured precipitation at Graciosa. A wide range of aerosol conditions was sampled during the deployment consistent with the diversity of sources as indicated by back-trajectory analysis. Preliminary findings suggest important two-way interactions between aerosols and clouds at Graciosa, with aerosols affecting light precipitation and cloud radiative properties while being controlled in part by precipitation scavenging. The data from Graciosa are being compared with short-range forecasts made with a variety of models. A pilot analysis with two climate and two weather forecast models shows that they reproduce the observed time-varying vertical structure of lower-tropospheric cloud fairly well but the cloud-nucleating aerosol concentrations less well. The Graciosa site has been chosen to be a permanent fixed ARM site that became operational in October 2013

The clinical features of the piriformis syndrome: a systematic review

Piriformis syndrome, sciatica caused by compression of the sciatic nerve by the piriformis muscle, has been described for over 70 years; yet, it remains controversial. The literature consists mainly of case series and narrative reviews. The objectives of the study were: first, to make the best use of existing evidence to estimate the frequencies of clinical features in patients reported to have PS; second, to identify future research questions. A systematic review was conducted of any study type that reported extractable data relevant to diagnosis. The search included all studies up to 1 March 2008 in four databases: AMED, CINAHL, Embase and Medline. Screening, data extraction and analysis were all performed independently by two reviewers. A total of 55 studies were included: 51 individual and 3 aggregated data studies, and 1 combined study. The most common features found were: buttock pain, external tenderness over the greater sciatic notch, aggravation of the pain through sitting and augmentation of the pain with manoeuvres that increase piriformis muscle tension. Future research could start with comparing the frequencies of these features in sciatica patients with and without disc herniation or spinal stenosis