We present measurements of the linear diameter of the emission region of the Vela pulsar at observing wavelength lambda=18 cm. We infer the diameter as a function of pulse phase from the distribution ...of visibility on the Mopra-Tidbinbilla baseline. As we demonstrate, in the presence of strong scintillation, finite size of the emission region produces a characteristic W-shaped signature in the projection of the visibility distribution onto the real axis. This modification involves heightened probability density near the mean amplitude, decreased probability to either side, and a return to the zero-size distribution beyond. We observe this signature with high statistical significance, as compared with the best-fitting zero-size model, in many regions of pulse phase. We find that the equivalent full width at half maximum of the pulsar's emission region decreases from more than 400 km early in the pulse to near zero at the peak of the pulse, and then increases again to approximately 800 km near the trailing edge. We discuss possible systematic effects, and compare our work with previous results.
We compare the noise in interferometric measurements of the Vela pulsar from ground- and space-based antennas with theoretical predictions. The noise depends on both the flux density and the ...interferometric phase of the source. Because the Vela pulsar is bright and scintillating, these comparisons extend into both the low and high signal-to-noise regimes. Furthermore, our diversity of baselines explores the full range of variation in interferometric phase. We find excellent agreement between theoretical expectations and our estimates of noise among samples within the characteristic scintillation scales. Namely, the noise is drawn from an elliptical Gaussian distribution in the complex plane, centered on the signal. The major axis, aligned with the signal phase, varies quadratically with the signal, while the minor axis, at quadrature, varies with the same linear coefficients. For weak signal, the noise approaches a circular Gaussian distribution. Both the variance and covariance of the noise are also affected by artifacts of digitization and correlation. In particular, we show that gating introduces correlations between nearby spectral channels.
The VIMOS-VLT Deep Survey Pollo, A.; Guzzo, L.; Le Fèvre, O. ...
Astronomy and astrophysics (Berlin),
05/2006, Letnik:
451, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We investigate the dependence of galaxy clustering on the galaxy intrinsic luminosity at high redshift, using the data from the First Epoch VIMOS-VLT Deep Survey (VVDS). The size (6530 galaxies) and ...depth ($I_{AB}<24$) of the survey allows us to measure the projected two-point correlation function of galaxies, $w_{\rm p}(r_{\rm p})$, for a set of volume-limited samples up to an effective redshift $\left<z\right>=0.9$ and median absolute magnitude $-19.6< M_B < -21.3$. Fitting $w_{\rm p}(r_{\rm p})$ with a single power-law model for the real-space correlation function $\xi(r)=(r/r_0)^{-\gamma}$, we measure the relationship of the correlation length r0 and the slope γ with the sample median luminosity for the first time at such high redshift. Values from our lower-redshift samples ($0.1<z<0.5$) are fully consistent with the trend observed by larger local surveys. In our high redshift sample ($0.5<z<1.2$), we find that the clustering strength suddenly rises around $M_B^*$, apparently with a sharper inflection than at low redshifts. Galaxies in the faintest sample ($\left<M_B\right>=-19.6$) have a correlation length $r_0=2.7^{+0.3}_{-0.3}$ h-1 Mpc, compared to $r_0=5.0^{+1.5}_{-1.6}$ h-1 Mpc at $\left<M_B\right>=-21.3$. The slope of the correlation function is observed to correspondingly steepen significantly from $\gamma=1.6^{+0.1}_{-0.1}$ to $\gamma=2.4^{+0.4}_{-0.2}$. This is not observed either by large local surveys or in our lower-redshift samples and seems to imply a significant change in the way luminous galaxies trace dark-matter halos at $z\sim 1$ with respect to $z\sim 0$. At our effective median redshift $z \simeq 0.9$ this corresponds to a strong difference of the relative bias, from $b/b* < 0.7$ for galaxies with $L < L*$ to $b/b* \simeq 1.4$ for galaxies with $L > L*$.
The VIMOS-VLT Deep Survey Pollo, A.; Guzzo, L.; Le Fèvre, O. ...
Astronomy and astrophysics (Berlin),
05/2006, Letnik:
451, Številka:
2
Journal Article
Objectives Near-infrared cerebral oximetry increasingly is used for monitoring during cardiac surgery. Nonetheless, the scientific basis for incorporating this technology into clinical practice, the ...indications for when to do so, and standard diagnostic and treatment algorithms for defining abnormal values are yet to be rigorously defined. The authors hypothesized that there would be (1) variation in clinical use and practices for near-infrared spectroscopy (NIRS), and (2) variation in management of patients when clinicians are provided with NIRS information. In order to test this hypothesis, they sought to assess the nature and strength of response heterogeneity among anesthesiologists and cardiac perfusionists when provided with cardiac surgery patient scenarios and cerebral oximetry data. Design A prospectively collected survey. Setting A hospital-based, multi-institutional, multinational study. Participants By e-mail, the authors surveyed the membership of the Society of Cardiovascular Anesthesiologists and the online Cardiovascular Perfusion Forum. Interventions This survey was focused on ascertaining what actions clinicians would take in each scenario, given case information and cerebral oximetry tracings. Questions were based on 11 patient scenarios selected to represent small, large, symmetric, or asymmetric decreases in measured regional cerebral oxygen saturation (rScO2 ) encountered during cardiac surgery. Information on the respondents’ (n = 796; 73% anesthesiologists) clinical practice, demography, and cerebral oximetry utilization was collected. An index of dispersion was used to assess response heterogeneity overall and within demographic subgroups. Measurements and Main Results The majority of respondents indicated that cerebral oximetry monitoring was either useful or an essential monitor, especially perfusionists and clinicians who used cerebral oximetry most frequently. There were marked differences in responses between perfusionists and anesthesiologists for 4 of the 6 scenarios (p<0.005 for each of these 4 scenarios) occurring during cardiopulmonary bypass. Scenarios having greatest rScO2 reduction or asymmetry in rScO2 were associated with the highest dispersion, indicating least agreement in management. Scenarios with mild or moderate rScO2 reduction were associated with the lowest dispersion, indicating greater agreement in management. Conclusions Although experimental data gradually are accumulating to support the role for cerebral oximetry monitoring during cardiac surgery, the results of the present survey support the view that its role remains poorly defined, and consensus for its appropriate use is lacking. Importantly, the authors observed marked variation in the use, perceived utility, and management of patients for 4 of the 6 CPB scenarios between perfusionists and anesthesiologists who share the management of CPB. These findings support the need for well-designed, adequately-powered clinical trials examining the value of this technology.
Chronic lunotriquetral (LT) injuries are less common than scapholunate ligament injuries and difficult to diagnose. They may be associated with positive ulnar variance. Clinical diagnostic tests ...elicit pain at the LT interval. Although radiographs are typically normal, MRI and wrist arthroscopy can help confirm the diagnosis. When conservative treatments fail, surgical options include LT ligament reconstruction, LT arthrodesis, and ulnar-shortening osteotomy (in patients with positive ulnar variance).
PDF
