1,107 research outputs found
Paediatric hepatoblastoma and hepatocellular carcinoma: retrospective study.
OBJECTIVES: To compare and contrast clinical characteristics and outcomes of hepatoblastoma or hepatocellular carcinoma in paediatric patients. DESIGN: Retrospective study. SETTING: University teaching hospital, Hong Kong. PATIENTS AND METHODS: Medical records of 22 paediatric patients with hepatoblastoma (n=11) or hepatocellular carcinoma (n=11) admitted to Queen Mary Hospital between 1989 and 2000 were reviewed. Data gathered included demographic data, results of liver function tests, hepatitis A, B, and C titres, and alpha-foetoprotein levels, and imaging studies including chest X-ray, ultrasound study, computed tomography scan, and magnetic resonance imaging/hepatic angiogram for tumour staging and resectability. RESULTS: The mean age of patients with hepatoblastoma was 18 months (range, 5 months to 3 years), while that of patients with hepatocellular carcinoma was 10.2 years (range, 2 to 16 years). Females predominated in the hepatoblastoma group (female:male, 8:3) and males in the hepatocellular carcinoma group (male:female, 10:1). None of the patients with hepatoblastoma were hepatitis B surface antigen positive, in contrast to 64% of the hepatocellular carcinoma group. Only 45% of the hepatocellular carcinomas were resectable at presentation and this figure remained unchanged following chemotherapy. A total of 91% of hepatoblastomas were resectable, four at presentation, and a further six after chemotherapy. Tumour rupture was more common in patients with hepatoblastoma than in those with hepatocellular carcinoma (36% versus 9% of cases, respectively). Mortality rates were considerably higher among the hepatocellular carcinoma group than the hepatoblastoma group in this series. CONCLUSION: Childhood hepatoblastoma and hepatocellular carcinoma differ with respect to age and tumour stage at presentation, hepatatis B surface antigen status, tendency to rupture, chemosensitivity, and prognosis.published_or_final_versio
Investigating planet formation in circumstellar disks: CARMA observations of RY Tau and DG Tau
(Abridged) We present CARMA observations of the thermal dust emission from
the circumstellar disks around the young stars RYTau and DGTau at wavelengths
of 1.3mm and 2.8mm. The angular resolution of the maps is as high as
0.15arcsec, or 20AU at the distance of the Taurus cloud, which is a factor of 2
higher than has been achieved to date at these wavelengths. The unprecedented
detail of the resulting disk images enables us to address three important
questions related to the formation of planets. (1) What is the radial
distribution of the circumstellar dust? (2) Does the dust emission show any
indication of gaps that might signify the presence of (proto-)planets? (3) Do
the dust properties depend on the orbital radius? We find that modeling the
disk surface density in terms of either a classical power law or the similarity
solution for viscous disk evolution, reproduces the observations well. The
1.3mm image from RYTau shows two peaks separated by 0.2arcsec with a decline in
the dust emission toward the stellar position, which is significant at about
2-4sigma. For both RYTau and DGTau, the dust emission at radii larger than 15
AU displays no significant deviation from an unperturbed viscous disk model. In
particular, no radial gaps in the dust distribution are detected. Under
reasonable assumptions, we exclude the presence of planets more massive than 5
Jupiter masses orbiting either star at distances between about 10 and 60 AU.
The radial variation of the dust opacity slope, beta, was investigated by
comparing the 1.3mm and 2.8mm observations. We find mean values of beta of 0.5
and 0.7 for DGTau and RYTau respectively. Variations in beta are smaller than
0.7 between 20 and 70 AU. These results confirm that the circumstellar dust
throughout these disks differs significantly from dust in the interstellar
medium.Comment: ApJ in press
Final report of the Construction Industry Institute, Hong Kong research project on reinventing the Hong Kong construction industry for its sustainable development
Author name used in this publication: Andrew N. BaldwinAuthor name used in this publication: Y. H. ChiangAuthor name used in this publication: Joyce W. S. CheungAuthor name used in this publication: Joanne W. S. NgConstruction Industry Institute-Hong Kong Report, no. 132008-2009 > Academic research: not refereed > Research book or monograph (author)Other Versio
Photoprocesses in protoplanetary disks
Circumstellar disks are exposed to intense ultraviolet radiation from the
young star. In the inner disks, the UV radiation can be enhanced by more than
seven orders of magnitude compared with the average interstellar field,
resulting in a physical and chemical structure that resembles that of a dense
photon-dominated region (PDR). This intense UV field affects the chemistry, the
vertical structure of the disk, and the gas temperature, especially in the
surface layers of the disk. The parameters which make disks different from
traditional PDRs are discussed, including the shape of the UV radiation field,
grain growth, the absence of PAHs, the gas/dust ratio and the presence of inner
holes. New photorates for selected species, including simple ions, are
presented. Also, a summary of available cross sections at Lyman alpha 1216 A is
made. Rates are computed for radiation fields with color temperatures ranging
from 4000 to 30,000 K, and can be applied to a wide variety of astrophysical
regions including exo-planetary atmospheres. The importance of photoprocesses
is illustrated for a number of representative disk models, including disk
models with grain growth and settling.Comment: A website with the final published version and all photodissociation
cross sections and rates can be found at
http://www.strw.leidenuniv.nl/~ewine/phot
Correlation functions quantify super-resolution images and estimate apparent clustering due to over-counting
We present an analytical method to quantify clustering in super-resolution
localization images of static surfaces in two dimensions. The method also
describes how over-counting of labeled molecules contributes to apparent
self-clustering and how the effective lateral resolution of an image can be
determined. This treatment applies to clustering of proteins and lipids in
membranes, where there is significant interest in using super-resolution
localization techniques to probe membrane heterogeneity. When images are
quantified using pair correlation functions, the magnitude of apparent
clustering due to over-counting will vary inversely with the surface density of
labeled molecules and does not depend on the number of times an average
molecule is counted. Over-counting does not yield apparent co-clustering in
double label experiments when pair cross-correlation functions are measured. We
apply our analytical method to quantify the distribution of the IgE receptor
(Fc{\epsilon}RI) on the plasma membranes of chemically fixed RBL-2H3 mast cells
from images acquired using stochastic optical reconstruction microscopy (STORM)
and scanning electron microscopy (SEM). We find that apparent clustering of
labeled IgE bound to Fc{\epsilon}RI detected with both methods arises from
over-counting of individual complexes. Thus our results indicate that these
receptors are randomly distributed within the resolution and sensitivity limits
of these experiments.Comment: 22 pages, 5 figure
Quantum-well states in ultrathin Ag(111) films deposited onto H-passivated Si(111)-(1x1) surfaces
Ag(111) films were deposited at room temperature onto H-passivated
Si(111)-(1x1) substrates, and subsequently annealed at 300 C. An abrupt
non-reactive Ag/Si interface is formed, and very uniform non-strained Ag(111)
films of 6-12 monolayers have been grown. Angle resolved photoemission
spectroscopy has been used to study the valence band electronic properties of
these films. Well-defined Ag sp quantum-well states (QWS) have been observed at
discrete energies between 0.5-2eV below the Fermi level, and their dispersions
have been measured along the GammaK, GammaMM'and GammaL symmetry directions.
QWS show a parabolic bidimensional dispersion, with in-plane effective mass of
0.38-0.50mo, along the GammaK and GammaMM' directions, whereas no dispersion
has been found along the GammaL direction, indicating the low-dimensional
electronic character of these states. The binding energy dependence of the QWS
as a function of Ag film thickness has been analyzed in the framework of the
phase accumulation model. According to this model, a reflectivity of 70% has
been estimated for the Ag-sp states at the Ag/H/Si(111)-(1x1) interface.Comment: 6 pages, 6 figures, submitted to Phys. Rev.
Structure and evolution of pre-main sequence circumstellar disks
We present new sub-arcsecond (0.7'') Combined Array for Research in
Millimeter-wave Astronomy (CARMA) observations of the 1.3 mm continuum emission
from circumstellar disks around 11 low and intermediate mass pre-main sequence
stars. High resolution observations for 3 additional sources were obtained from
literature. In all cases the disk emission is spatially resolved. We adopt a
self consistent accretion disk model based on the similarity solution for the
disk surface density and constrain the dust radial density distribution on
spatial scales of about 40 AU. Disk surface densities appear to be correlated
with the stellar ages where the characteristic disk radius increases from ~ 20
AU to 100 AU over about 5 Myr. This disk expansion is accompanied by a decrease
in the mass accretion rate, suggesting that our sample disks form an
evolutionary sequence. Interpreting our results in terms of the temporal
evolution of a viscous -disk, we estimate (i) that at the beginning of
the disk evolution about 60% of the circumstellar material was located inside
radii of 25--40 AU, (ii) that disks formed with masses from 0.05 to 0.4
M_{\sun} and (iii) that the viscous timescale at the disk initial radius is
about 0.1-0.3 Myr. Viscous disk models tightly link the surface density
with the radial profile of the disk viscosity . We find values of ranging from -0.8 to 0.8, suggesting
that the viscosity dependence on the orbital radius can be very different in
the observed disks. Adopting the parameterization for the viscosity,
we argue that must decrease with the orbital radius and that it may
vary between 0.5 and . (abridged)Comment: Accepted for publication in The Astrophysical Journal, 43 pages, 18
figures, Typo in the author name correcte
Gender-dependent differences in plasma matrix metalloproteinase-8 elevated in pulmonary tuberculosis.
Tuberculosis (TB) remains a global health pandemic and greater understanding of underlying pathogenesis is required to develop novel therapeutic and diagnostic approaches. Matrix metalloproteinases (MMPs) are emerging as key effectors of tissue destruction in TB but have not been comprehensively studied in plasma, nor have gender differences been investigated. We measured the plasma concentrations of MMPs in a carefully characterised, prospectively recruited clinical cohort of 380 individuals. The collagenases, MMP-1 and MMP-8, were elevated in plasma of patients with pulmonary TB relative to healthy controls, and MMP-7 (matrilysin) and MMP-9 (gelatinase B) were also increased. MMP-8 was TB-specific (p<0.001), not being elevated in symptomatic controls (symptoms suspicious of TB but active disease excluded). Plasma MMP-8 concentrations inversely correlated with body mass index. Plasma MMP-8 concentration was 1.51-fold higher in males than females with TB (p<0.05) and this difference was not due to greater disease severity in men. Gender-specific analysis of MMPs demonstrated consistent increase in MMP-1 and -8 in TB, but MMP-8 was a better discriminator for TB in men. Plasma collagenases are elevated in pulmonary TB and differ between men and women. Gender must be considered in investigation of TB immunopathology and development of novel diagnostic markers
Downregulation of Mcl-1 has anti-inflammatory pro-resolution effects and enhances bacterial clearance from the lung
Phagocytes not only coordinate acute inflammation and host defense at mucosal sites, but also contribute to tissue damage. Respiratory infection causes a globally significant disease burden and frequently progresses to acute respiratory distress syndrome, a devastating inflammatory condition characterized by neutrophil recruitment and accumulation of protein-rich edema fluid causing impaired lung function. We hypothesized that targeting the intracellular protein myeloid cell leukemia 1 (Mcl-1) by a cyclin-dependent kinase inhibitor (AT7519) or a flavone (wogonin) would accelerate neutrophil apoptosis and resolution of established inflammation, but without detriment to bacterial clearance. Mcl-1 loss induced human neutrophil apoptosis, but did not induce macrophage apoptosis nor impair phagocytosis of apoptotic neutrophils. Neutrophil-dominant inflammation was modelled in mice by either endotoxin or bacteria (Escherichia coli). Downregulating inflammatory cell Mcl-1 had anti-inflammatory, pro-resolution effects, shortening the resolution interval (R(i)) from 19 to 7 h and improved organ dysfunction with enhanced alveolar–capillary barrier integrity. Conversely, attenuating drug-induced Mcl-1 downregulation inhibited neutrophil apoptosis and delayed resolution of endotoxin-mediated lung inflammation. Importantly, manipulating lung inflammatory cell Mcl-1 also accelerated resolution of bacterial infection (R(i); 50 to 16 h) concurrent with enhanced bacterial clearance. Therefore, manipulating inflammatory cell Mcl-1 accelerates inflammation resolution without detriment to host defense against bacteria, and represents a target for treating infection-associated inflammation
Simulations of extensional flow in microrheometric devices
We present a detailed numerical study of the flow of a Newtonian fluid through microrheometric devices featuring a sudden contraction–expansion. This flow configuration is typically used to generate extensional deformations and high strain rates. The excess pressure drop resulting from the converging and diverging flow is an important dynamic measure to quantify if the device is intended to be used as a microfluidic extensional rheometer. To explore this idea, we examine the effect of the contraction length, aspect ratio and Reynolds number on the flow kinematics and resulting pressure field. Analysis of the computed velocity and pressure fields show that, for typical experimental conditions used in microfluidic devices, the steady flow is highly three-dimensional with open spiraling vortical structures in the stagnant corner regions. The numerical simulations of the local kinematics and global pressure drop are in good agreement with experimental results. The device aspect ratio is shown to have a strong impact on the flow and consequently on the excess pressure drop, which is quantified in terms of the dimensionless Couette and Bagley correction factors. We suggest an approach for calculating the Bagley correction which may be especially appropriate for planar microchannels
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