1,828 research outputs found
Spatially resolved mid-infrared observations of the triple system T Tauri
To enhance our knowledge of the characteristics and distribution of the
circumstellar dust associated with the individual components of the young
hierarchical triple system T Tau, observations in the N-band with MIDI at the
VLTI were performed. Our study is based on both the interferometric and the
spectrophotometric measurements and is supplemented by new visual and infrared
photometry. Also, the phases were investigated to determine the dominating
mid-infrared source in the close southern binary. The data were fit with the
help of a sophisticated physical disc model. This model utilises the radiative
transfer code MC3D that is based on the Monte-Carlo method. Extended
mid-infrared emission is found around all three components of the system.
Simultaneous fits to the photometric and interferometric data confirm the
picture of an almost face-on circumstellar disc around T Tau N. Towards this
star, the silicate band is seen in emission. This emission feature is used to
model the dust content of the circumstellar disc. Clear signs of dust
processing are found. Towards T Tau S, the silicate band is seen in absorption.
This absorption is strongly pronounced towards the infrared companion T Tau Sa
as can be seen from the first individual N-band spectra for the two southern
components. Our fits support the previous suggestion that an almost edge-on
disc is present around T Tau Sa. This disc is thus misaligned with respect to
the circumstellar disc around T Tau N. The interferometric data indicate that
the disc around T Tau Sa is oriented in the north-south direction, which
favours this source as launching site for the east-western jet. We further
determine from the interferometric data the relative positions of the
components of the southern binary.Comment: 24 pages, 19 figures, accepted for publication in A&
Properties of small molecular drug loading and diffusion in a fluorinated PEG hydrogel studied by ^1H molecular diffusion NMR and ^(19)F spin diffusion NMR
R_f-PEG (fluoroalkyl double-ended poly(ethylene glycol)) hydrogel is potentially useful as a drug delivery depot due to its advanced properties of sol–gel two-phase coexistence and low surface erosion. In this study, ^1H molecular diffusion nuclear magnetic resonance (NMR) and ^(19)F spin diffusion NMR were used to probe the drug loading and diffusion properties of the R_f-PEG hydrogel for small anticancer drugs, 5-fluorouracil (FU) and its hydrophobic analog, 1,3-dimethyl-5-fluorouracil (DMFU). It was found that FU has a larger apparent diffusion coefficient than that of DMFU, and the diffusion of the latter was more hindered. The result of ^(19)F spin diffusion NMR for the corresponding freeze-dried samples indicates that a larger portion of DMFU resided in the R_f core/IPDU intermediate-layer region (where IPDU refers to isophorone diurethane, as a linker to interconnect the R_f group and the PEG chain) than that of FU while the opposite is true in the PEG–water phase. To understand the experimental data, a diffusion model was proposed to include: (1) hindered diffusion of the drug molecules in the R_f core/IPDU-intermediate-layer region; (2) relatively free diffusion of the drug molecules in the PEG-water phase (or region); and (3) diffusive exchange of the probe molecules between the above two regions. This study also shows that molecular diffusion NMR combined with spin diffusion NMR is useful in studying the drug loading and diffusion properties in hydrogels for the purpose of drug delivery applications
Multi-wavelength analysis of high energy electrons in solar flares: a case study of August 20, 2002 flare
A multi-wavelength spatial and temporal analysis of solar high energy
electrons is conducted using the August 20, 2002 flare of an unusually flat
(gamma=1.8) hard X-ray spectrum. The flare is studied using RHESSI, Halpha,
radio, TRACE, and MDI observations with advanced methods and techniques never
previously applied in the solar flare context. A new method to account for
X-ray Compton backscattering in the photosphere (photospheric albedo) has been
used to deduce the primary X-ray flare spectra. The mean electron flux
distribution has been analysed using both forward fitting and model independent
inversion methods of spectral analysis. We show that the contribution of the
photospheric albedo to the photon spectrum modifies the calculated mean
electron flux distribution, mainly at energies below 100 keV. The positions of
the Halpha emission and hard X-ray sources with respect to the current-free
extrapolation of the MDI photospheric magnetic field and the characteristics of
the radio emission provide evidence of the closed geometry of the magnetic
field structure and the flare process in low altitude magnetic loops. In
agreement with the predictions of some solar flare models, the hard X-ray
sources are located on the external edges of the Halpha emission and show
chromospheric plasma heated by the non-thermal electrons. The fast changes of
Halpha intensities are located not only inside the hard X-ray sources, as
expected if they are the signatures of the chromospheric response to the
electron bombardment, but also away from them.Comment: 26 pages, 9 figures, accepted to Solar Physic
The T Tauri star RY Tau as a case study of the inner regions of circumstellar dust disks
We study the inner region of the circumstellar disk around the TTauri star RY
Tau. Our aim is to find a physical description satisfying the available
interferometric data, obtained with the mid-infrared interferometric instrument
at the Very Large Telescope Interferometer, as well as the spectral energy
distribution. We also compare the findings with the results of similar studies,
including those of intermediate-mass stars. Our analysis is done within the
framework of a passive circumstellar disk, which is optionally supplemented by
the effects of accretion and an added envelope. To achieve a more consistent
and realistic model, we used our continuum transfer code MC3D. In addition, we
studied the shape of the 10um silicate emission feature in terms of the
underlying dust population, both for single-dish and for interferometric
measurements. We show that a modestly flaring disk model with accretion can
explain both the observed spectral energy distribution and the mid-infrared
visibilities obtained with the mid-infrared infrared instrument. We found an
interesting ambiguity: a circumstellar active disk model with an added
envelope, and a lower accretion rate than in the active disk model without
envelope, could represent the observations equally as well. This type of model
with the envelope should be considered a viable alternative in future models of
other TTauri stars. The approach of a disk with a puffed-up inner rim wall and
the influence of a stellar companion is also discussed. From the study of the
silicate emission feature we see evidence for dust evolution in a TTauri star,
with a decreasing fraction of small amorphous and an increasing fraction of
crystalline particles closer to the star.Comment: 19 pages, 23 figures; accepted by Astronomy & Astrophysic
Testing Bergmann's rule in marine copepods
Macroecological relationships provide insights into rules that govern ecological systems. Bergmann's rule posits that members of the same clade are larger at colder temperatures. Whether temperature drives this relationship is debated because several other potential drivers covary with temperature. We conducted a near-global comparative analysis on marine copepods (97 830 samples, 388 taxa) to test Bergmann's rule, considering other potential drivers. Supporting Bergmann's rule, we found temperature better predicted size than did latitude or oxygen, with body size decreasing by 43.9% across the temperature range (-1.7 to 30ºC). Body size also decreased by 26.9% across the range in food availability. Our results provide strong support for Bergman's rule in copepods, but emphasises the importance of other drivers in modifying this pattern. As the world warms, smaller copepod species are likely to emerge as ‘winners', potentially reducing rates of fisheries production and carbon sequestration
Boundary Conditions for Elastohydrodynamics of Circular Point Contacts
The paper presents the solution of an elastohydrodynamic point contact condition using inlet and outlet lubricant entrainment with partial counter-flow. The inlet and outlet boundaries are determined using potential flow analysis for the pure rolling of contiguous surfaces. This shows that Swift–Stieber boundary conditions best conform to the observed partial counter-flow at the inlet conjunction, satisfying the compatibility condition. For the outlet region, the same is true when Prandtl–Hopkins boundary conditions are employed. Using these boundary conditions, the predictions conform closely to the measured pressure distribution using a deposited pressure-sensitive micro-transducer in a ball-to-flat race contact. Furthermore, the predicted conjunctional shape closely conforms to the often observed characteristic keyhole conjunction through optical interferometry. The combined numerical–experimental analysis with realistic boundary conditions described here has not hitherto been reported in the literature
The feasibility and results of a population-based approach to evaluating prostate-specific antigen screening for prostate cancer in men with a raised familial risk
The feasibility of a population-based evaluation of screening for prostate cancer in men with a raised familial risk was investigated by studying reasons for non-participation and uptake rates according to postal recruitment and clinic contact. The levels of prostate-specific antigen (PSA) and the positive predictive values (PPV) for cancer in men referred with a raised PSA and in those biopsied were analysed. First-degree male relatives (FDRs) were identified through index cases (ICs): patients living in two regions of England and diagnosed with prostate cancer at age ⩽65 years from 1998 to 2004. First-degree relatives were eligible if they were aged 45–69 years, living in the UK and had no prior diagnosis of prostate cancer. Postal recruitment was low (45 of 1687 ICs agreed to their FDR being contacted: 2.7%) but this was partly due to ICs not having eligible FDRs. A third of ICs in clinic had eligible FDRs and 49% (192 out of 389) agreed to their FDR(s) being contacted. Of 220 eligible FDRs who initially consented, 170 (77.3%) had a new PSA test taken and 32 (14.5%) provided a previous PSA result. Among the 170 PSA tests, 10% (17) were ⩾4 ng ml−1 and 13.5% (23) tests above the age-related cutoffs. In 21 men referred, five were diagnosed with prostate cancer (PPV 24%; 95% CI 8, 47). To study further the effects of screening, patients with a raised familial risk should be counselled in clinic about screening of relatives and data routinely recorded so that the effects of screening on high-risk groups can be studied
Loss of oxidative defense and potential blockade of satellite cell maturation in the skeletal muscle of patients with cancer but not in the healthy elderly
Purpose: Muscle wasting in old age or cancer may result from failure of myofibre regeneration and /or accelerated apoptosis both of which may be up-regulated by oxidative stress or inflammation. The aim of this study was to determine from the transcriptome in human skeletal muscle whether there is evidence for oxidative stress and its relationship with satellite cell differentiation or apoptosis in the muscle of patients with cancer (weight-stable: CWS or weight-losing: CWL) or healthy elderly (HE) when compared with healthy middle aged controls (HMAC) .
Design: 28 patients with resectable upper GI/pancreatic cancer (CWS: 14 and CWL14), 17 HE and 22 HMAC underwent biopsy of the quadriceps muscle. Markers of muscle regeneration, inflammation, oxidative stress and apoptosis were measured by qPCR.
Results: The expression of transcription factors responsible for muscle regeneration (Pax3, Pax7 and MyoD) were increased in the skeletal muscle of CWS and HE when compared with HMAC (P<0.001). In contrast, the expression of myogenic differentiation markers (MyoG and Myh2) was reduced in CWS and CWL but increased in HE when compared with HMAC (P<0.0001). The expression of the pro-apoptotic gene Bax was significantly increased in CWS, CWL and HE compared with HMAC (P<0.0001). Pro-inflammatory cytokine expression was variable with increased expression of TNF in CWS and HE, increased Il-6 in CWS and increased Il-1 in CWL when compared with HMAC. Expression of the oxidative defense genes SOD2, GCLM, and NRF2 was decreased in CWS and CWL but increased in HE when compared with HMA (P<0.0001).
Conclusion: There is evidence for blockade of satellite cell maturation, upregulation of apoptosis and reduced oxidative defense in the skeletal muscle of cancer patients. In contrast, in muscle from healthy elderly the potential for myotube differentiation and oxidative defense is maintained
Spatio-Temporal Variation in Length-Weight Relationships and Condition of the Ribbonfish Trichiurus lepturus (Linnaeus, 1758): Implications for Fisheries Management
Knowledge of length-weight relationships for commercially exploited fish is an important tool for assessing and managing of fish stocks. However, analyses of length-weight relationship fisheries data typically do not consider the inherent differences in length-weight relationships for fish caught from different habitats, seasons, or years, and this can affect the utility of these data for developing condition indices or calculating fisheries biomass. Here, we investigated length-weight relationships for ribbonfish Trichiurus lepturus in the waters of the Arabian Sea off Oman collected during three periods (2001-02, 2007-08, and 2014-15) and showed that a multivariate modelling approach that considers the areas and seasons in which ribbonfish were caught improved estimation of length-weight relationships. We used the outputs of these models to explore spatio-temporal variations in condition indices and relative weights among ribbonfish, revealing fish of 85-125 cm were in the best overall condition. We also found that condition differed according to where and when fish were caught, with condition lowest during spring and pre-south-west monsoon periods and highest during and after the south-west monsoons. We interpret these differences to be a consequence of variability in temperature and food availability. Based on our findings, we suggest fishing during seasons that have the lowest impact on fish condition and which are commercially most viable; such fishery management would enhance fisheries conservation and economic revenue in the region
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