4,312 research outputs found
Recent trends, technical concepts and components of computer-assisted orthopedic surgery systems: A comprehensive review
Computer-assisted orthopedic surgery (CAOS) systems have become one of the most important and challenging types of system in clinical orthopedics, as they enable precise treatment of musculoskeletal diseases, employing modern clinical navigation systems and surgical tools. This paper brings a comprehensive review of recent trends and possibilities of CAOS systems. There are three types of the surgical planning systems, including: systems based on the volumetric images (computer tomography (CT), magnetic resonance imaging (MRI) or ultrasound images), further systems utilize either 2D or 3D fluoroscopic images, and the last one utilizes the kinetic information about the joints and morphological information about the target bones. This complex review is focused on three fundamental aspects of CAOS systems: their essential components, types of CAOS systems, and mechanical tools used in CAOS systems. In this review, we also outline the possibilities for using ultrasound computer-assisted orthopedic surgery (UCAOS) systems as an alternative to conventionally used CAOS systems.Web of Science1923art. no. 519
The Peculiar Debris Disk of HD 111520 as Resolved by the Gemini Planet Imager
Using the Gemini Planet Imager (GPI), we have resolved the circumstellar
debris disk around HD 111520 at a projected range of ~30-100 AU in both total
and polarized -band intensity. The disk is seen edge-on at a position angle
of ~165 along the spine of emission. A slight inclination or
asymmetric warping are covariant and alters the interpretation of the observed
disk emission. We employ 3 point spread function (PSF) subtraction methods to
reduce the stellar glare and instrumental artifacts to confirm that there is a
roughly 2:1 brightness asymmetry between the NW and SE extension. This specific
feature makes HD 111520 the most extreme examples of asymmetric debris disks
observed in scattered light among similar highly inclined systems, such as HD
15115 and HD 106906. We further identify a tentative localized brightness
enhancement and scale height enhancement associated with the disk at ~40 AU
away from the star on the SE extension. We also find that the fractional
polarization rises from 10 to 40% from 0.5" to 0.8" from the star. The
combination of large brightness asymmetry and symmetric polarization fraction
leads us to believe that an azimuthal dust density variation is causing the
observed asymmetry.Comment: 9 pages, 8 Figures, 1 table, Accepted to Ap
A Highly Ordered Faraday-Rotation Structure in the Interstellar Medium
We describe a Faraday-rotation structure in the Interstellar Medium detected
through polarimetric imaging at 1420 MHz from the Canadian Galactic Plane
Survey (CGPS). The structure, at l=91.8, b=-2.5, has an extent of ~2 degree,
within which polarization angle varies smoothly over a range of ~100 degree.
Polarized intensity also varies smoothly, showing a central peak within an
outer shell. This region is in sharp contrast to its surroundings, where
low-level chaotic polarization structure occurs on arcminute scales. The
Faraday-rotation structure has no counterpart in radio total intensity, and is
unrelated to known objects along the line of sight, which include a Lynds
Bright Nebula, LBN 416, and the star cluster M39 (NGC7092). It is interpreted
as a smooth enhancement of electron density. The absence of a counterpart,
either in optical emission or in total intensity, establishes a lower limit to
its distance. An upper limit is determined by the strong beam depolarization in
this direction. At a probable distance of 350 +/- 50 pc, the size of the object
is 10 pc, the enhancement of electron density is 1.7 cm-3, and the mass of
ionized gas is 23 M_sun. It has a very smooth internal magnetic field of
strength 3 microG, slightly enhanced above the ambient field. G91.8-2.5 is the
second such object to be discovered in the CGPS, and it seems likely that such
structures are common in the Magneto-Ionic Medium.Comment: 16 pages, 5 figures, ApJ accepte
Outflow - Core Interaction in Barnard 1
In order to study how outflows from protostars influence the physical and
chemical conditions of the parent molecular cloud, we have observed Barnard 1
(B1) main core, which harbors four Class 0 and three Class I sources, in the CO
(J=1-0), CH3OH (J_K=2_K-1_K), and the SiO (J=1-0) lines using the Nobeyama 45 m
telescope. We have identified three CO outflows in this region; one is an
elongated (~ 0.3 pc) bipolar outflow from a Class 0 protostar B1-c in the
submillimeter clump SMM 2, another is a rather compact (~ 0.1 pc) outflow from
a Class I protostar B1 IRS in the clump SMM 6, and the other is an extended
outflow from a Class I protostar in SMM 11. In the western lobe of the SMM 2
outflow, both the SiO and CH3OH lines show broad redshifted wings with the
terminal velocities of 25 km/s and 13 km/s, respectively. It is likely that the
shocks caused by the interaction between the outflow and ambient gas enhance
the abundance of SiO and CH3OH in the gas phase. The total energy input rate by
the outflows (1.1x10^{-3} Lsun) is smaller than the energy loss rate
(8.5x10^{-3} Lsun$) through the turbulence decay in B1 main core, which
suggests that the outflows can not sustain the turbulence in this region. Since
the outflows are energetic enough to compensate the dissipating turbulence
energy in the neighboring, more evolved star forming region NGC 1333, we
suggest that the turbulence energy balance depends on the evolutionary state of
the star formation in molecular clouds.Comment: 34 pages, 8 figures, accepted for the publication in Ap
Digital computer processing of X-ray photographs
Enhanced digital computer processing of X-ray photographs by image subtraction or filterin
The Origin of Nitrogen on Jupiter and Saturn from the N/N Ratio
The Texas Echelon cross Echelle Spectrograph (TEXES), mounted on NASA's
Infrared Telescope Facility (IRTF), was used to map mid-infrared ammonia
absorption features on both Jupiter and Saturn in February 2013. Ammonia is the
principle reservoir of nitrogen on the giant planets, and the ratio of
isotopologues (N/N) can reveal insights into the molecular
carrier (e.g., as N or NH) of nitrogen to the forming protoplanets, and
hence the source reservoirs from which these worlds accreted. We targeted two
spectral intervals (900 and 960 cm) that were relatively clear of
terrestrial atmospheric contamination and contained close features of
NH and NH, allowing us to derive the ratio from a single
spectrum without ambiguity due to radiometric calibration (the primary source
of uncertainty in this study). We present the first ground-based determination
of Jupiter's N/N ratio (in the range from to
), which is consistent with both previous space-based studies
and with the primordial value of the protosolar nebula. On Saturn, we present
the first upper limit on the N/N ratio of no larger than
for the 900-cm channel and a less stringent
requirement that the ratio be no larger than for the
960-cm channel ( confidence). Specifically, the data rule out
strong N-enrichments such as those observed in Titan's atmosphere and in
cometary nitrogen compounds. To the extent possible with ground-based
radiometric uncertainties, the saturnian and jovian N/N ratios
appear indistinguishable, implying that N-enriched ammonia ices could
not have been a substantial contributor to the bulk nitrogen inventory of
either planet, favouring the accretion of primordial N from the gas phase
or as low-temperature ices.Comment: 33 pages, 19 figures, manuscript accepted for publication in Icaru
LBT/MODS spectroscopy of globular clusters in the irregular galaxy NGC 4449
We present intermediate-resolution (R1000) spectra in the
3500-10,000 A range of 14 globular clusters in the magellanic irregular
galaxy NGC 4449 acquired with the Multi Object Double Spectrograph on the Large
Binocular Telescope. We derived Lick indices in the optical and the
CaII-triplet index in the near-infrared in order to infer the clusters' stellar
population properties. The inferred cluster ages are typically older than
9 Gyr, although ages are derived with large uncertainties. The clusters
exhibit intermediate metallicities, in the range
[Fe/H], and typically sub-solar []
ratios, with a peak at . These properties suggest that i) during the
first few Gyrs NGC 4449 formed stars slowly and inefficiently, with galactic
winds having possibly contributed to the expulsion of the -elements,
and ii) globular clusters in NGC 4449 formed relatively "late", from a medium
already enriched in the products of type Ia supernovae. The majority of
clusters appear also under-abundant in CN compared to Milky Way halo globular
clusters, perhaps because of the lack of a conspicuous N-enriched,
second-generation of stars like that observed in Galactic globular clusters.
Using the cluster velocities, we infer the dynamical mass of NGC 4449 inside
2.88 kpc to be M(2.88 kpc)=. We
also report the serendipitous discovery of a planetary nebula within one of the
targeted clusters, a rather rare event.Comment: Accepted for publication in MNRAS; corrected typo in author lis
The Peculiar Debris Disk of HD 111520 as Resolved by the Gemini Planet Imager
Using the Gemini Planet Imager, we have resolved the circumstellar debris disk around HD 111520 at a projected range of ~30–100 AU in both total and polarized H-band intensity. The disk is seen edge-on at a position angle of 165° along the spine of emission. A slight inclination and asymmetric warp are covariant and alter the interpretation of the observed disk emission. We employ three point-spread function subtraction methods to reduce the stellar glare and instrumental artifacts to confirm that there is a roughly 2:1 brightness asymmetry between the NW and SE extension. This specific feature makes HD 111520 the most extreme example of asymmetric debris disks observed in scattered light among similar highly inclined systems, such as HD 15115 and HD 106906. We further identify a tentative localized brightness enhancement and scale height enhancement associated with the disk at ~40 AU away from the star on the SE extension. We also find that the fractional polarization rises from 10% to 40% from 0.”5 to 0.”8 from the star. The combination of large brightness asymmetry and symmetric polarization fraction leads us to believe that an azimuthal dust density variation is causing the observed asymmetry
Stellar photometry with Multi Conjugate Adaptive Optics
We overview the current status of photometric analyses of images collected
with Multi Conjugate Adaptive Optics (MCAO) at 8-10m class telescopes that
operated, or are operating, on sky. Particular attention will be payed to
resolved stellar population studies. Stars in crowded stellar systems, such as
globular clusters or in nearby galaxies, are ideal test particles to test AO
performance. We will focus the discussion on photometric precision and accuracy
reached nowadays. We briefly describe our project on stellar photometry and
astrometry of Galactic globular clusters using images taken with GeMS at the
Gemini South telescope. We also present the photometry performed with DAOPHOT
suite of programs into the crowded regions of these globulars reaching very
faint limiting magnitudes Ks ~21.5 mag on moderately large fields of view (~1.5
arcmin squared). We highlight the need for new algorithms to improve the
modeling of the complex variation of the Point Spread Function across the field
of view. Finally, we outline the role that large samples of stellar standards
plays in providing a detailed description of the MCAO performance and in
precise and accurate colour{magnitude diagrams.Comment: 17 pages, 12 figures, SPIE 201
PROSAC: A Submillimeter Array Survey of Low-Mass Protostars. I. Overview of Program: Envelopes, Disks, Outflows and Hot Cores
This paper presents a large spectral line and continuum survey of 8 deeply
embedded, low-mass protostellar cores using the Submillimeter Array. Each
source was observed in high excitation lines of some of the most common
molecular species, CO, HCO+, CS, SO, H2CO, CH3OH and SiO. Line emission from 11
species originating from warm and dense gas have been imaged at high angular
resolution (1-3"; typically 200-600 AU) together with continuum emission at 230
GHz (1.3 mm) and 345 GHz (0.8 mm). Compact continuum emission is observed for
all sources which likely originates in marginally optically thick circumstellar
disks, with typical lower limits to their masses of 0.1 M_sun (1-10% of the
masses of their envelopes) and having a dust opacity law with beta
approximately 1. Prominent outflows are present in CO 2-1 observations in all
sources: the most diffuse outflows are found in the sources with the lowest
ratios of disk-to-envelope mass, and it is suggested that these sources are in
a phase where accretion of matter from the envelope has almost finished and the
remainder of the envelope material is being dispersed by the outflows. Other
characteristic dynamical signatures are found with inverse P Cygni profiles
indicative of infalling motions seen in the 13CO 2-1 lines toward
NGC1333-IRAS4A and -IRAS4B. Outflow-induced shocks are present on all scales in
the protostellar environments and are most clearly traced by the emission of
CH3OH in NGC1333-IRAS4A and -IRAS4B. These observations suggest that the
emission of CH3OH and H2CO from these proposed "hot corinos" are related to the
shocks caused by the protostellar outflows. Only one source, NGC1333-IRAS2A,
has evidence for hot, compact CH3OH emission coincident with the embedded
protostar.Comment: Accepted for publication in ApJ (52 pages; 9 figures). Abstract
abridge
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