Context. Circumstellar disks surrounding young stars are known to be the birthplaces of planetary systems, and the innermost astronomical unit is of particular interest. Near-infrared interferometric ...studies have revealed a complex morphology for the close environment surrounding Herbig Ae stars. Aims. We present new long-baseline spectro-interferometric observations of the Herbig Ae star, HR 5999, obtained in the H and K bands with the AMBER instrument at the VLTI, and aim to produce near-infrared images at the sub-AU spatial scale. Methods. We spatially resolve the circumstellar material and reconstruct images in the H and K bands using the MiRA algorithm. In addition, we interpret the interferometric observations using models that assume that the near-infrared excess is dominated by the emission of a circumstellar disk. We compare the images reconstructed from the VLTI measurements to images obtained using simulated model data. Results. The K-band image reveals three main elements: a ring-like feature located at ~0.65 AU, a low surface brightness region inside 0.65 AU, and a central spot. At the maximum angular resolution of our observations (B/λ ~ 1.3 mas), the ring is resolved while the central spot is only marginally resolved, preventing us from revealing the exact morphology of the circumstellar environment. We suggest that the ring traces silicate condensation, i.e., an opacity change, in a circumstellar disk around HR 5999. We build a model that includes a ring at the silicate sublimation radius and an inner disk of low surface brightness responsible for a large amount of the near-infrared continuum emission. The model successfully fits the SED, visibilities, and closure phases in the H and K bands, and provides evidence of a low surface brightness region inside the silicate sublimation radius. Conclusions. This study provides milli-arcsecond resolution images of the environment of HR 5999 and additional evidence that in Herbig Ae stars, there is material in a low surface brightness region, probably a low optical depth region, located inside the silicate sublimation radius and of unknown nature. The possibility that the formation of such a region in a thick disk is related to disk evolution should be investigated.
Purpose: This study evaluated the measurement accuracy of three-dimensional (3D) volumetric images from spiral computed tomography (CT) in vitro.
Materials and Methods: The study sample consisted of ...nine cadaver heads that were submitted to an impact force by a special device to promote blunt traumatic craniofacial fractures. The heads were subsequently scanned by a spiral CT scanner (Toshiba Xpress S/X). The archived CT data were transferred to networked computer workstations (Sun Microsystems with Cemax VIP version 1.4 software) to generate 3D volumetric images. The visualization software was used to make interactive linear measurements on the 3D images. Measurements were made on the images twice by two observers, based on conventional craniofacial anatomic landmarks. The soft tissues were subsequently removed, and the same measurements were repeated on the cadaver heads with an electromagnetic digitizer (3 Space, Polhemus, Colchester, VT).
Results: The results showed no statistically significant differences between the 3D-CT and the physical measurements, with
P > .05 for all measurements. The mean difference between the image and real measurements was less than 2 mm in all instances.
Conclusions: It is concluded that measurement of the skull and facial bone landmarks by 3D reconstruction is quantitatively accurate for surgical planning and treatment evaluation of craniofacial fractures.
Lysosomal cysteine proteases from mammalian cells and plants are regulated by endogenous tight-binding inhibitors from the cystatin superfamily. The presence of cystatin-like inhibitors in lower ...eukaryotes such as protozoan parasites has not yet been demonstrated, although these cells express large quantities of cysteine proteases and may also count on endogenous inhibitors to regulate cellular proteolysis. Trypanosoma cruzi, the causative agent of Chagas' heart disease, is a relevant model to explore this possibility because these intracellular parasites rely on their major lysosomal cysteine protease (cruzipain) to invade and multiply in mammalian host cells. Here we report the isolation, biochemical characterization, developmental stage distribution and subcellular localization of chagasin, an endogenous cysteine protease inhibitor in T. cruzi. We used high temperature induced denaturation to isolate a heat-stable cruzipain-binding protein (apparent molecular mass, 12 kDa) from epimastigote lysates. This protein was subsequently characterized as a tight-binding and reversible inhibitor of papain-like cysteine proteases. Immunoblotting indicated that the expression of chagasin is developmentally regulated and inversely correlated with that of cruzipain. Gold-labeled antibodies localized chagasin to the flagellar pocket and cytoplasmic vesicles of trypomastigotes and to the cell surface of amastigotes. Binding assays performed by probing living parasites with fluorescein (FITC)-cruzipain or FITC-chagasin revealed the presence of both inhibitor and protease at the cell surface of amastigotes. The intersection of chagasin and cruzipain trafficking pathways may represent a checkpoint for downstream regulation of proteolysis in trypanosomatid protozoa.
Spiral (helical) CT Heiken, J P; Brink, J A; Vannier, M W
Radiology,
12/1993, Letnik:
189, Številka:
3
Journal Article
Recenzirano
Spiral (helical) computed tomography (CT) involves continuous patient translation during x-ray source rotation and data acquisition. As a result, a volume data set is obtained in a relatively short ...period of time. For chest or abdominal scanning, an entire examination can be completed in a single breath hold of the patient or in several successive short breath holds. The data volume may be viewed as conventional transaxial images or with multiplanar and three-dimensional methods. The authors review the technologic aspects of spiral CT, as well as its advantages, limitations, and current clinical applications.
Trypanosoma cruzi is the etiological agent of American trypanosomiasis. Most of the available data on trypanosomatid parasites were obtained from African trypanosomes. Parasitic protozoa polyamine ...metabolism and transport pathways comprise valuable targets for chemotherapy. T. cruzi cannot synthesize putrescine, but its uptake from the extracellular milieu can promote parasite survival. Nevertheless, little is known about the cell biology of this diamine in T. cruzi. Here we notice that the putrescine analogue 1,4-diamino-2-butanone (DAB) inhibited T. cruzi epimastigotes' in vitro proliferation and produced remarkable mitochondrial destruction and cell architecture disorganization, as assessed by transmission electron microscopy. Mitochondrial damage was confirmed by MTT reduction. We decided to analyze the oxidative stress undergone by DAB-treated parasites. Thiobarbituric-acid-reactive substances were measured to assess lipid peroxidation. Analogue effects were dose-dependent; 5 mM DAB only slightly enhanced peroxidation, whereas 10 mM DAB significantly (P < 0.05) diminished it. These data indicate that putrescine uptake by this diamine auxotrophic parasite may be important for epimastigote axenic growth and cellular organization.
Aims. Performed in November 2007 as a part of the MIDI Guaranteed Time Observation Exoplanet Programme, the observation of Gliese 86b constituted the first attempt at an exoplanet detection with the ...VLTI instrument MIDI. It is also a technical achievement since it motivated the first VLTI observation using AMBER and MIDI simultaneously. Methods. Fringes were obtained for both instruments with the aim of reaching sufficient precision on the low differential phase signal of Gliese 86b. The principle is to correct the phase measured in N-band from the water vapour dispersion using the fringes in K-band. In N-band, the source, Gliese 86, has an estimated magnitude of 3.8. With a separation of 0.11 AU, a flux ratio of about 10-3 is expected between the planet and the star. According to the measurement principle and the planet signal signature, the effective expected interferometric phase is a curved-like function of the wavelength with a mean amplitude of about 0.03°. Results. Based on the MIDI phase measurements of the calibrator HD 9362, our study shows that a precision on the curvature measurement of about 0.33° is currently reached. Consequently, we stand at a factor 10 above the phase signal from the planet. The AMBER data, obtained in parallel, were too noisy to extrapolate and to remove the corresponding dispersion in N band at the required level of precision. However, we report the set of data obtained, we discuss the calibration process involved, and we estimate its theoretical efficiency.
Structured
Author –
Vannier MW
Objectives – Craniofacial imaging in three dimensions depends on computed tomography (CT) and related technologies. This paper explains the state‐of‐the‐art for medical ...and dedicated craniofacial cone‐beam CT scanners.
Method – Current medical CT scanners are surveyed, especially the recently announced 16 simultaneous slice models with subsecond source–detector rotation times and spiral/helical third generation geometry. The medical scanner technology is contrasted with dedicated low‐cost craniofacial cone‐beam CT scanners to delineate the relevant technologies and clarify the differences.
Results – CT scanners performance in any task is determined by their detectors and reconstruction algorithm primarily and to a lesser extent by the X‐ray source, dose utilization, computational and display electronics, and software for post‐processing. Each of these components differs between medical and low‐cost cone‐beam scanners, and the differences are tabulated and explained.
Conclusion – Low‐cost craniofacial CT scanners are significantly different from general purpose medical CT scanners, with compromises in technical performance. Despite their limitations, these instruments are remarkably useful for their intended application domain and should improve as computers continue to increase their performance.
We present the high angular resolution technique of colour-differential interferometry for direct detection of extrasolar giant planets (EGPs). The measurement of differential phase with ...long-baseline ground-based interferometers in the near-infrared could allow the observation of several hot giant extrasolar planets in tight orbit around the nearby stars, and thus yield their low- or mid-resolution spectroscopy, complete orbital data set and mass. Estimates of potentially achievable signal-to-noise ratios are presented for a number of planets already discovered by indirect methods. The limits from the instrumental and atmospheric instability are discussed, and a subsequent observational strategy is proposed.
Context. The triple stellar system δ Vel (composed of two A-type and one F-type main-sequence stars) is particularly interesting because it contains one of the nearest and brightest eclipsing ...binaries. It therefore presents a unique opportunity to determine independently the physical properties of the three components of the system, as well as its distance. Aims: We aim at determining the fundamental parameters (masses, radii, luminosities, rotational velocities) of the three components of δ Vel, as well as the parallax of the system, independently from the existing Hipparcos measurement. Methods: We determined dynamical masses from high-precision astrometry of the orbits of Aab-B and Aa-Ab using adaptive optics (VLT/NACO) and optical interferometry (VLTI/AMBER). The main component is an eclipsing binary composed of two early A-type stars in rapid rotation. We modeled the photometric and radial velocity measurements of the eclipsing pair Aa-Ab using a self-consistent method based on physical parameters (mass, radius, luminosity, rotational velocity). Results: From our self-consistent modeling of the primary and secondary components of the δ Vel A eclipsing pair, we derive their fundamental parameters with a typical accuracy of 1%. We find that they have similar masses, 2.43 ± 0.02 M⊙ and 2.27 ± 0.02 M⊙. The physical parameters of the tertiary component (δ Vel B) are also estimated, although to a lower accuracy. We obtain a parallax π = 39.8 ± 0.4 mas for the system, in satisfactory agreement (-1.2 σ) with the Hipparcos value (πHip = 40.5 ± 0.4 mas). Conclusions: The physical parameters we derive represent a consistent set of constraints for the evolutionary modeling of this system. The agreement of the parallax we measure with the Hipparcos value to a 1% accuracy is also an interesting confirmation of the true accuracy of these two independent measurements. Based on observations made with ESO telescopes at Paranal Observatory, under ESO programs 076.D-0782(B), 081.D-0109(B), 081.D-0109(C), 282.D-5006(A) and Arcetri GTO program 084.C-0170(C).
Aims.We report on spectrally dispersed interferometric AMBER/VLTI observations of the recurrent nova RS Oph five days after the discovery of its outburst on 2006 Feb. 12. Methods.Using three ...baselines ranging from 44 to 86 m, and a spectral resolution of $\lambda/\delta\lambda=1500$, we measured the extension of the milliarcsecond-scale emission in the K band continuum and in the Brγ and He I $2.06~\mu$m lines, allowing us to get an insight into the kinematics of the line forming regions. The continuum visibilities were interpreted by fitting simple geometric models consisting of uniform and Gaussian ellipses, ring and binary models. The visibilities and differential phases in the Brγ line were interpreted using skewed ring models aiming to perform a limited parametric reconstruction of the extension and kinematics of the line forming region. Results.The limited uv coverage does not allow discrimination between filled models (uniform or Gaussian ellipses) and rings. Binary models are discarded because the measured closure phase in the continuum is close to zero. The visibilities in the lines are at a low level compared to their nearby continuum, consistent with a more extended line forming region for He I $2.06~\mu$m than Brγ. The ellipse models for the continuum and for the lines are highly flattened ($b/a\sim0.6$) and share the same position angle (${\rm PA}\sim140^{\circ}$). Their typical Gaussian extensions are $3.1\times1.9~{\rm mas}$, $4.9\times2.9~{\rm mas}$ and $6.3\times3.6~{\rm mas}$ for the continuum, Brγ and He I $2.06~\mu$m lines, respectively. Two radial velocity fields are apparent in the Brγ line: a slow expanding ring-like structure ($v_{\rm rad}\leq1800~{\rm km\,s}^{-1}$), and a fast structure extended in the E-W direction ($v_{\rm rad}\sim 2500{-}3000~{\rm km\,s}^{-1}$), a direction that coincides with the jet-like structure seen in the radio. These results confirm the basic fireball model, contrary to the conclusions of other interferometric observations conducted by Monnier et al. (2006a, ApJ, 647, L127).
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