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An in-house self-held respiration monitoring device (SHRMD) was developed for providing deep inspiration breath hold (DIBH) radiotherapy. The use of SHRMD is evaluated in terms of reproducibility, stability and heart dose reduction.
Methods and materials:
Sixteen patients receiving radiotherapy of left breast cancer were planned for treatment with both a free breathing (FB) scan and a DIBH scan. Both FB and DIBH plans were generated for comparison of the heart, left anterior descending (LAD) artery and lung dose. All patients received their treatments with DIBH using SHRMD. Megavoltage cine images were acquired during treatments for evaluating the reproducibility and stability of treatment position using SHRMD.
Compared with FB plans, the maximum dose to the heart by DIBH technique with SHRMD was reduced by 29·9 ± 15·6%; and the maximum dose of the LAD artery was reduced by 41·6 ± 18·3%. The inter-fractional overall mean error was 0·01 cm and the intra-fractional overall mean error was 0·04 cm.
This study demonstrated the potential benefits of using the SHRMD for DIBH to reduce the heart and LAD dose. The patients were able to perform stable and reproducible DIBHs.
We review recent observations of molecular gas in nearby galaxies and their implications for the star formation law on large (> 1 kpc) scales. High-resolution data provided by millimetre interferometers are now adding to the basic understanding that has been provided by single-dish telescopes. In particular, they confirm the good correlation between star formation rate (SFR) and molecular gas surface densities, while at the same time revealing a greater degree of heterogeneity in the CO distribution. Galaxies classified as SAB or SB tend to show radial CO profiles that peak sharply in the inner ∼20″, indicative of bar-driven inflow. The observed Schmidt law index of ≍1.5 may result from a nearly linear relation between SFR and H2 mass coupled with a modest dependence of the molecular gas fraction on the total gas density. The normalisation of the Schmidt law, giving the characteristic timescale for star formation, may stem from the generic nature of interstellar turbulence.
It is well known that the radial distributions of atomic and molecular gas differ markedly in spiral galaxies, including our own (e.g. Burton & Gordon 1978, Sofue et al. 1995). We have recently begun a program to obtain multifrequency observations of several nearby galaxies in order to determine whether H I is needed to replenish the H2 consumed by star formation and, if so, how this might be accomplished. Here we present initial results on the nearby RSab galaxy NGC 4736, known for its bright ring of H II regions and recently shown to have a central stellar bar (Möllenhoff et al. 1995). We have mapped the distribution of CO (1-0) emission within r=1′ (1.8 kpc at D=6.2 Mpc) with the BIMA interferometer at ~5″ resolution, and added data from the NRAO 12-m telescope to recover zero-spacing information.
High-mass stars usually form in giant molecular clouds (GMCs) as part of a young stellar cluster, but some isolated O/B stars are observed. What are the initial conditions that lead to the formation of these objects? The aim of this study is to measure the distribution and basic physical properties of the neutral gas associated with isolated intermediate- and high-mass young stellar objects (YSOs) in the Large Magellanic Cloud.
As part of the SAGE Spitzer Legacy program for the LMC, we have identified and confirmed YSOs using Spitzer IRAC photometry and IRS spectroscopy. By examining the spatial coincidence between the YSOs and 12CO(1–0) emission detected by the NANTEN mapping survey, we identified more than one hundred intermediate/massive YSOs in the LMC that appear to be isolated, i.e. not associated with CO emission. Deeper follow-up CO observations by our team with the higher resolution by Mopra Telescope (beam=30”) detected CO emission at the YSO positions for ~80% of the isolated LMC YSOs. We obtained ALMA data of some of the targets during Cycle 2. We targeted a small but representative (in terms of their association with neutral gas tracers) sample of the isolated high-mass YSOs that we have been studying in the LMC. All of our 12 targets are separated by more than 200 pc from known CO clouds. Our analysis of the ALMA data shows that a compact molecular cloud whose mass is a few thousand solar masses or smaller is associated with most of the YSOs.
We present new results from a comparative analysis of the resolved giant molecular cloud (GMC) populations in six nearby galaxies. We show that the GMCs in denser environments–M51, the centre of NGC6946–have greater CO surface brightness and higher velocity dispersions relative to their size than GMCs in less dense environments. We find systematic differences in the GMC mass distribution among galaxies, such that more of the molecular gas in the low-mass galaxies (M33, the Large Magellanic Cloud) and the outer disk of M31 is located in low mass clouds. Using the number density of GMCs in the interarm regions of M51, we argue that GMC destruction in this region is regulated by shear, and that cloud lifetimes there are finite and short, ~20 to 30 Myr. Our results indicate the importance of galactic environment on the evolution of GMCs, and on a galaxy's global pattern of star formation.
We present data characterising the performance of the Mopra Radio Telescope during the period 2000–2004, including measurements of the beam size and shape, as well as the overall beam efficiency of the telescope. In 2004 the full width half maximum of the beam was measured to be 36 ± 3″ at 86 GHz, falling to 33 ± 2″ at 115 GHz. Based on our observations of Jupiter we measured the beam efficiency of the Gaussian main beam to be 0.49 ± 0.03 at 86 GHz and 0.42 ± 0.02 at 115 GHz. Sources with angular sizes of ∼80″ couple well to the main beam, while sources with angular sizes between ∼80″ and ∼160″ couple to the both the main beam and inner error beam. Measurements indicate that the inner error beam contains approximately one-third the power of the main beam. We also compare efficiency corrected spectra to measurements made at similar facilities and present standard spectra taken towards the molecular clouds Orion-KL and M17-SW.
With the ATNF Mopra telescope we are performing a survey in the 12CO(1–0) line to map the molecular gas in the Large Magellanic Cloud. For some regions we also obtained interferometric maps of the high density gas tracers HCO+ and HCN with the Australia Telescope Compact Array. Here we discuss the properties of the elongated molecular complex that stretches about 2 kpc southward from 30 Doradus. Our data suggest that the complex, which we refer to as the ‘molecular ridge’, is not a coherent feature but consists of many smaller clumps that share the same formation history. Likely triggers of molecular-cloud formation are shocks and shearing forces that are present in the surrounding south-eastern Hi overdensity region, a region influenced by strong ram pressure and tidal forces. The molecular ridge is at the western edge of the the overdensity region where a bifurcated velocity structure transitions into a single disk velocity component. We find that the 12CO(1–0) and Hi emission peaks in the molecular ridge are typically near each other but never coincide. A likely explanation is the conversion of warmer, low-opacity Hi to colder, high-opacity Hi from which H2 subsequently forms. On smaller scales we find that very dense molecular gas, as traced by interferometric HCO+ and HCN maps, is associated with star formation along shocked filaments and with rims of expanding shell-like structures, both created by feedback from massive stars.
We have mapped an extensive sample of molecular clouds in the Large Magellanic Cloud (LMC) at 11 pc resolution in the CO(1-0) line as part of the Magellanic Mopra Assessment (MAGMA). We identify clouds as regions of connected CO emission and determine their sizes, line widths, and fluxes. We find that GMCs are not preferentially located in regions of high Hi line width or velocity gradient, and that there is no clear Hi column density threshold for CO detection. The luminosity function of CO clouds is steeper than dN/dL ∝ L−2, suggesting a substantial fraction of mass in low-mass clouds. The correlation between size and linewidth, while apparent for the largest emission structures, breaks down when those structures are decomposed into smaller structures. The virial parameter (the ratio of a cloud's kinetic to gravitational energy) shows a wide range of values and exhibits no clear trends with the likelihood of hosting young stellar object (YSO) candidates, suggesting that this parameter is a poor reflection of the evolutionary state of a cloud. More massive GMCs are more likely to harbor a YSO candidate, and more luminous YSOs are more likely to be coincident with detectable CO emission, confirming GMCs as the principal sites of massive star formation.
We have performed a survey study of rotational excited-state H2 Lyman-Werner absorption lines in the entire FUSE Magellanic Clouds Legacy archive. These lines reflect the UV pumping and formation conditions of H2, enabling a more comprehensive study of H2 gas properties, e.g. J-level populations N(J) and b-values (generally indicating the velocity dispersion). Combining with our previous measurements of N(Hi) and N(H2), we derived H2 excitation temperatures, gas volume density n(H), and local UV radiation field strength IUV for each sight line. The results indicate a weaker correlation between n(H) and IUV in Magellanic Clouds than the Galactic sight lines. We also obtained N(H)/E(B − V) ratios from the Spitzer-SAGE and previous CO J = 1 − 0 / Hi 21 cm surveys at sight line locations, using dust modeling and standard line brightness-column density conversion factors. They show a roughly linear correlation with absorption-based N(H)/E(B − V) values, and have a similar scatter (∼0.7 dex) across the LMC and SMC.
We present a brief summary and description of the upcoming 12CO(1-0) Magellanic Mopra Assesment (MAGMA) SMC survey data release. The MAGMA-SMC survey has sampled 100% of the known CO in the SMC (at ∼33″ resolution; 12 pc at D = 60 kpc). Having explored 522 × 103 square parsecs throughout the SMC with 69 5′ × 5′ fields, to a sensitivity of ∼150 mK, we apply the cloudprops (Rosolowsky & Leroy 2006) cloud-search algorithm optimized for low S/N data, to detect more than 30 CO clouds with virial masses between 103–104 M⊙, mean radii ∼5 pc and 0.3–0.9 km s−1 velocity width. Typical brightness temperatures are ∼1 K Tmb. All detected molecular regions are associated with at least one 24 μm compact emission source. Smoothing rarely increases the total detected CO flux, implying the CO emission is typically confined to small spatial scales. As recent dust maps of the SMC imply extended H2 mass, the apparent compact nature of the CO population indicates some departures from the canonical Galactic XCO-factor in the low-metallicity and relatively un-evolved ISM of the SMC.
A previous study reported preliminary results of enhanced processing of simple visual information in the form of faster reaction times, in female fragile X premutation carriers (fXPCs). In this study, we assessed manual and oral motor reaction times in 30 female fXPCs and 20 neurotypical (NT) controls. Participants completed two versions of the reaction time task; one version required a manual motor response and the other version required an oral motor response. Results revealed that the female fXPCs displayed faster reaction times for both manual and oral motor responses relative to NT controls. Molecular measures including CGG repeat length, FMR1 mRNA levels, and age were not associated with performance in either group. Given previously reported age and CGG repeat modulated performance on a magnitude comparison task in this same group of premutation carriers, results from the current study seem to suggest that female fXPCs may have spared basic psychomotor functionality. (JINS, 2011, 17, 746–750)
The twenty-first century marks the point in history when the proportion of the world's population living in urban environments has surpassed those living in the rural environment, making the urban environment a critical focal point for Ecologically Sustainable Development (ESD) practices. The pursuit of sustainability has emerged in recent years as a progression from previous environmental protection endeavors. The ambition of sustainability and sustainable development is to have lifestyles, and their supporting infrastructure, that can endure indefinitely because they are neither depleting resources nor degrading environmental quality. Urban development impacts on the sustainability of the physical environment, including the health and amenity of water environments. As growing urban communities seek to minimise their impact on already stressed water resources, an emerging challenge is to design for resilience and adaptability to the impact of climate change, particularly in regards to ensuring secure water supplies and the protection of water environments.
Conventional approaches to the provision of urban water services were designed to collect, store, treat and then discharge water within a framework of expansion and efficiency. Despite the many benefits from conventional urban water management approaches – such as widespread access to clean drinking water, flood control, and the protection of public health through better management of sewage and industrial waste water – the seemingly unintended environmental costs associated with these modes of water services delivery are now emerging through a range of symptomatic phenomena, particularly chronic pollution of surface and sub-surface water environments, depleted water resources and biodiversity, and increased water resources vulnerability to the effects of climate change.
Ion beam synthesis of Si and Ge nanocrystals in an SiO2 Matrix is
performed by precipitation from supersaturated solid solutions created by
ion implantation. Films of SiO2 on (100) Si substrates are
implanted with Si and Ge at doses 1 × 1016/cm2 - 5 ×
1016/cm2. IMplanted samples are subsequently
annealed to induce precipitation of Si and Ge nanocrystals. Raman
spectroscopy and high-resolution transmission electron microscopy indicate a
correlation between visible room-temperature photoluminescence and the
formation of diamond cubic nanocrystals approximately 2–5 nm in diameter in
annealed samples. As-implanted but unannealed samples do not exhibit
luminescence. Rutherford backscattering spectra indicate a steepening of
implanted Ge profiles upon annealing. Photoluminescence spectra are
correlated with annealing temperatures, and compared with theoretical
predictions for various possible luminescence Mechanisms, such as radiative
recombination of quantum-confined excitons, as well as possible localized
state luminescence related to structural defects in SiO2
Potential optoelectronic device applications are also discussed.
Thermally-induced solid-phase epitaxial crystallisation (SPEC) and
ion-beam-induced epitaxial crystallisation (IBffiC) of amorphous
GexSi1−x alloy layers is examined for three
different starting structures: a) strain-relaxed alloy layers of uniform
composition, b) strained alloy layers of uniform composition, and c) Ge
implanted Si layers. Thermal annealing experiments show that the activation
energy for strain-relaxed alloys is higher than that expected from a simple
extrapolation between the activation energies of Si and Ge, and exceeds that
of Si for x ≤ 0.3. Experiments on thin strained layers show that MBE grown
strained layers which are stable during annealing at 1100°C for 60 s are
also fully strained after SPEC, whereas layers which relax during annealing
at 1100°C also relax during SPEC. Experiments on ion-implanted
GexSi1−x structures show that fully strained
Si/GexSi1−x/Si heterostructures can be fabricated
for ion fluences below a critical fluence, and as for uniform alloy layers
that this critical fluence is accurately predicted by equilibrium theory.
Strain relaxation during SPEC of uniform alloys and implanted structures is
shown to be correlated with a sudden reduction in crystallisation velocity
which is believed to be caused by stress-induced roughening or faceting of
the crystalline/amorphous interface. SPEC of thick (800 nm) implanted layers
is shown to be limited by competition from ion-beam induced random
crystallisation, while thin (120 nm) uniform alloys and implanted structures
are shown to crystallise epitaxially and to exhibit similar behaviour to
thermally annealed samples under certain conditions.
Solid-phase epitaxial growth (SPEG) of amorphous GeSi alloy layers has been
examined. It is shown that fully strained depth dependent GeSi alloy layers
can be produced by multiple ion-implantation and SPEG for implant doses
below critical values. For doses above these critical values strain
relaxation is shown to occur during SPEG at a well defined depth, and to be
correlated with a reduction in the SPEG velocity caused by roughening or
faceting of the crystalline/amorphous interface. The velocity reduction is
shown to be a reliable indicator of strain relaxation. Both the critical
dose and the depth at which strain relaxation occurs are shown to be in
excellent agreement with equilibrium critical thickness theory.
Nitrogen implantation can be used to control gate oxide thicknesses [1,2]. This study aims at studying the fundamental behavior of nitrogen diffusion in silicon. Nitrogen at sub-amorphizing doses has been implanted as N2+ at 40 keV and 200 keV into Czochralski silicon wafers. Furnace anneals have been performed at a range of temperatures from 650°C through 1050°C. The resulting annealed profiles show anomalous diffusion behavior. For the 40 keV implants, nitrogen diffuses very rapidly and segregates at the silicon/ silicon-oxide interface. Modeling of this behavior is based on the theory that the diffusion is limited by the time to create a mobile nitrogen interstitial.
This paper revisits a general optimal stopping problem that often appears as a special case in some finance applications. The problem is essentially of the same form as the investment-timing problem of McDonald and Siegel (1986) in which the underlying processes are two correlated geometric Brownian motions (GBMs) with drifts less than the discount rate. By contrast, we attempt to analyze the underlying optimal stopping problem to its full generality without imposing any restriction on the drifts of the GBMs. By extending the first passage time approach of Xia and Zhou (2007) to the current context, we manage to obtain a complete and explicit characterization of the solution to the problem on all possible drift domains. Our analysis leads to a new and interesting observation that the underlying optimal stopping problem admits a two-sided optimal continuation region on some certain parameter domains.
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