635 research outputs found
Numerical Evaluation of Microwave Thermal Ablation to Treat Small Adrenocortical Masses
In this paper microwave thermal ablation is numerically evaluated in the context of a treatment for Connâs Syndrome. This condition is caused by a benign shallow tumour in the cortex of adrenal gland. The modelling and design of microwave applicator to deliver thermal ablation to the adrenal gland requires accurate tissue characterisation. Measuring the dielectric properties of the constituent tissues in the adrenal gland, i.e. cortex and medulla, enables more accurate numerical modelling for electromagnetic and thermal simulations. This study presents an anatomically and dielectrically realistic numerical model of the adrenal gland, and investigates the feasibility of applying controlled heating to small targets in the adrenal cortex. In addition, the use of dielectric contrast between the fat and the cortex of the adrenal gland to focus the thermal energy in the gland has also been studied. Being conscious of limitations of numerical simulation of complex multiphysics problems like the microwave ablative treatment, calculated results provide a preliminary description of the electromagnetic and thermal phenomena involved
Case report of a phantom pheochromocytoma
Plasma free metanephrines or urinary fractionated metanephrines are the biochemical tests of choice for the diagnosis of pheochromocytoma as
they have greater sensitivity and specificity than catecholamines for pheochromocytoma detection. This case highlights the preanalytical factors
which can influence metanephrine measurement and cause a false positive result. It describes a patient with a high pre-test probability of pheochromocytoma
due to hypertension and a past medical history of adrenalectomy for a purported pheochromocytoma in her home country. When
biochemical screening revealed grossly elevated urine normetanephrine in the presence of a previously identified right adrenal lesion, there was
high clinical suspicion of a pheochromocytoma. However, functional imaging did not support this view which prompted additional testing with
plasma metanephrines. Results for plasma and urine metanephrines were discordant and preanalytical drug interference was suspected. Patient
medications were reviewed and sulfasalazine, an anti-inflammatory drug was identified as the most likely analytical interferent. Urinary fractionated
metanephrines were re-analysed using liquid chromatography tandem mass spectrometry (LC-MS/MS) and all metanephrines were within their
reference intervals. This case illustrates how method-specific analytical drug interference prompted unnecessary expensive imaging, heightened
patient anxiety and resulted in lengthy investigations for what turned out to be a phantom pheochromocytoma
Spitzer-IRS Spectroscopy of the Prototypical Starburst Galaxy NGC7714
We present observations of the starburst galaxy NGC 7714 with the Infrared
Spectrograph IRS on board the Spitzer Space Telescope. The spectra yield a
wealth of ionic and molecular features that allow a detailed characterization
of its properties. NGC 7714 has an HII region-like spectrum with strong PAH
emission features. We find no evidence for an obscured active galactic nucleus,
and with [NeIII]/[NeII]~0.73, NGC7714 lies near the upper end of
normal-metallicity starburst galaxies. With very little slicate absorption and
a temperature of the hottest dust component of 340K, NGC 7714 is the perfect
template for a young, unobscured starburstComment: To appear in the special ApJSS issue on early results from Spitze
Models of the Morphology, Kinematics, and Star Formation History of the Prototypical Collisional Starburst System: NGC 7714/7715 = Arp 284
(abridged) We present new N-body, hydrodynamical simulations of the
interaction between the starburst galaxy NGC 7714 and its post-starburst
companion NGC 7715, focusing on the formation of the collisional features,
including: 1) the gas-rich star forming bridge, 2) the large gaseous loop (and
stellar tails) to the west of the system, 3) the very extended HI tail to the
west and north of NGC 7714, and 4) the partial stellar ring in NGC 7714. Our
simulations confirm the results of earlier work that an off-center inclined
collision between two disk galaxies is almost certainly responsible for the
peculiar morphologies of this system. However, we have explored a wider set of
initial galaxy and collisional encounter parameters than previously, and have
found a relatively narrow range of parameters that reproduce all the major
morphologies of this system. The simulations suggest specific mechanisms for
the development of several unusual structures. We find that the complex gas
bridge has up to four distinct components, with gas contributed from two sides
of NGC 7715, as well as from NGC 7714. The observed gas-star offset in this
bridge is accounted for in the simulations by the dissipative evolution of the
gas. The models also indicate that the low surface brightness HI tail to the
far west of NGC 7714 is the end of the NGC 7715 countertail, curved behind the
two galaxies. Spectral evolutionary models of the NGC 7714 core by Lan\c{c}on
et al. suggest the possibility of multiple starbursts in the last 300 Myr. Our
hydrodynamic models suggest that bursts could be triggered by induced ring-like
waves, and a post-collision buildup of gas in the core of the galaxy.Comment: 24 pages, 20 figures, accepted for ApJ Supp
Online leadership discourse in higher education: a digital multimodal discourse perspective
As leadership discourses in higher education are increasingly being mediated online, texts previously reserved for staff are now being made available in the public domain. As such, these texts become accessible for study, critique and evaluation. Additionally, discourses previously confined to the written domain are now increasingly multimodal. Thus, an approach is required that is capable of relating detailed, complex multimodal discourse analyses to broader sociocultural perspectives to account for the complex meaning-making practices that operate in online leadership discourses. For this purpose, a digital multimodal discourse approach is proposed and illustrated via a small-scale case study of the online leadership discourse of an Australian university. The analysis of two short video texts demonstrates how a digital multimodal discourse perspective facilitates the identification of key multimodal systems used for meaning-making in online communication, how meaning arises through combinations of semiotic choices (not individual choices), and how the results of multimodal discourse analysis using digital technology can reveal larger sociocultural patterns â in this case, divergent leadership styles and approaches as reflected in online discourse, at a time of immense change within the higher education sector
New Observations of Extra-Disk Molecular Gas in Interacting Galaxy Systems, Including a Two-Component System in Stephan's Quintet
We present new CO (1 - 0) observations of eleven extragalactic tails and
bridges in nine interacting galaxy systems, almost doubling the number of such
features with sensitive CO measurements. Eight of these eleven features were
undetected in CO to very low CO/HI limits, with the most extreme case being the
NGC 7714/5 bridge. This bridge contains luminous H II regions and has a very
high HI column density (1.6 X 10^21 cm^-2 in the 55" CO beam), yet was
undetected in CO to rms T(R)* = 2.4 mK. The HI column density is higher than
standard H2 and CO self-shielding limits for solar-metallicity gas, suggesting
that the gas in this bridge is metal-poor and has an enhanced N(H2)/I(CO) ratio
compared to the Galactic value. Only one of the eleven features in our sample
was unambiguously detected in CO, a luminous HI-rich star formation region near
an optical tail in the compact group Stephan's Quintet. We detect CO at two
widely separated velocities in this feature, at ~6000 km/s and ~6700 km/s. Both
of these components have HI and H-alpha counterparts. These velocities
correspond to those of galaxies in the group, suggesting that this gas is
material that has been removed from two galaxies in the group. The
CO/HI/H-alpha ratios for both components are similar to global values for
spiral galaxies.Comment: 39 pages, Latex, 15 figures, Astronomical Journal, in pres
Contribution of the cyclic nucleotide gated channel subunit, CNG-3, to olfactory plasticity in Caenorhabditis elegans.
In Caenorhabditis elegans, the AWC neurons are thought to deploy a cGMP signaling cascade in the detection of and response to AWC sensed odors. Prolonged exposure to an AWC sensed odor in the absence of food leads to reversible decreases in the animal's attraction to that odor. This adaptation exhibits two stages referred to as short-term and long-term adaptation. Previously, the protein kinase G (PKG), EGL-4/PKG-1, was shown necessary for both stages of adaptation and phosphorylation of its target, the beta-type cyclic nucleotide gated (CNG) channel subunit, TAX-2, was implicated in the short term stage. Here we uncover a novel role for the CNG channel subunit, CNG-3, in short term adaptation. We demonstrate that CNG-3 is required in the AWC for adaptation to short (thirty minute) exposures of odor, and contains a candidate PKG phosphorylation site required to tune odor sensitivity. We also provide in vivo data suggesting that CNG-3 forms a complex with both TAX-2 and TAX-4 CNG channel subunits in AWC. Finally, we examine the physiology of different CNG channel subunit combinations
ISO observations of Hickson Compact Group 31 with the central Wolf-Rayet galaxy NGC 1741
Hickson Compact Group (HCG) 31, consisting of the Wolf-Rayet galaxy NGC 1741
and its irregular dwarf companions, was observed using the Infrared Space
Observatory. The deconvolved ISOCAM maps of the galaxies using the 7.7 micron
and 14.3 micron (LW6 and LW3) filters are presented, along with ISOPHOT
spectrometry of the central starburst region of NGC 1741 and the nucleus of
galaxy HCG 31A. Strong mid-IR emission was detected from the central burst in
NGC 1741, along with strong PAH features and a blend of features including [S
IV] at 10.5 micron. The 14.3/6.75 micron flux ratio, where the 6.75 micron flux
was synthesized from the PHT-S spectrum, and 14.3/7.7 micron flux ratios
suggest that the central burst within NGC 1741 may be moving towards the
post-starburst phase. Diagnostic tools including the ratio of the integrated
PAH luminosity to the 40 to 120 micron infrared luminosity and the far-infrared
colours reveal that despite the high surface brightness of the nucleus, the
properties of NGC 1741 can be explained in terms of a starburst and do not
require the presence of an AGN. The Tycho catalogue star TYC 04758-466-1, with
m = 11.3 and spectral type F6, was detected at 7.7 and 14.3 microns.Comment: 27 pages, 7 figures. Accepted for publication in the Astrophysical
Journa
A nearby GRB host prototype for z~7 Lyman-break galaxies: Spitzer-IRS and X-shooter spectroscopy of the host galaxy of GRB031203
Gamma-ray burst (GRB) host galaxies have been studied extensively in optical
photometry and spectroscopy. Here we present the first mid-infrared spectrum of
a GRB host, HG031203. It is one of the nearest GRB hosts at z=0.1055, allowing
both low and high-resolution spectroscopy with Spitzer-IRS. Medium resolution
UV-to-K-band spectroscopy with the X-shooter spectrograph on the VLT is also
presented, along with Spitzer IRAC and MIPS photometry, as well as radio and
sub-mm observations. These data allow us to construct a UV-to-radio spectral
energy distribution with almost complete spectroscopic coverage from 0.3-35
micron of a GRB host galaxy for the first time, potentially valuable as a
template for future model comparisons. The IRS spectra show strong,
high-ionisation fine structure line emission indicative of a hard radiation
field in the galaxy, suggestive of strong ongoing star-formation and a very
young stellar population. The selection of HG031203 via the presence of a GRB
suggests that it might be a useful analogue of very young star-forming galaxies
in the early universe, and hints that local BCDs may be used as more reliable
analogues of star-formation in the early universe than typical local
starbursts. We look at the current debate on the ages of the dominant stellar
populations in z~7 and z~8 galaxies in this context. The nebular line emission
is so strong in HG031203, that at z~7, it can reproduce the spectral energy
distributions of z-band dropout galaxies with elevated IRAC 3.6 and 4.5 micron
fluxes without the need to invoke a 4000A break.Comment: Published in ApJ. 9 pages, 6 figures, emulateapj styl
The Link Between Star Formation and Accretion in LINERs: A Comparison with other AGN Subclasses
We present archival high resolution X-ray imaging observations of 25 nearby
LINERs observed by ACIS on board Chandra. This sample builds on our previously
published proprietary and archival X-ray observations, and includes the
complete set of LINERs with published black hole masses and FIR luminosities
that have been observed by Chandra. Of the 82 LINERs observed by Chandra, 41
(50%) display hard nuclear cores consistent with an AGN. The nuclear 2-10 keV
luminosities of these AGN-LINERs range from ~ 2 X 10^38 ergs s^-1 to ~ 1 X
10^44 ergs s^-1. Reinforcing our previous work, we find a significant
correlation between the Eddington ratio, L bol/LEdd, and the far-IR (FIR)
luminosity, LFIR, as well as the IR brightness ratio, LFIR/LB in the host
galaxy of AGN-LINERs that extends over seven orders of magnitude in Lbol/LEdd.
Combining our AGN-LINER sample with galaxies from other AGN subclasses, we find
that this correlation is reinforced in the full sample of 129 AGN, extending
over almost nine orders of magnitude in Lbol/LEdd. Using archival and
previously published observations of the 6.2 mm PAH feature from the Infrared
Space Observatory (ISO), we find that it is unlikely that dust heating by the
AGN dominates the FIR luminosity in our sample of AGN. Our results may
therefore imply a fundamental link between the mass accretion rate (Mdot), as
measured by the Eddington ratio, and the star formation rate (SFR), as measured
by the FIR luminosity.Comment: 22 pages, 11 figures. Paper excepted for publication by ApJ in
Novembe
- âŠ