7,579 research outputs found
On Estimating the High-Energy Cutoff in the X-ray Spectra of Black Holes via Reflection Spectroscopy
The fundamental parameters describing the coronal spectrum of an accreting
black hole are the slope of the power-law continuum and the energy
at which it rolls over. Remarkably, this parameter can be accurately
measured for values as high as 1 MeV by modeling the spectrum of X-rays
reflected from a black hole accretion disk at energies below 100 keV. This is
possible because the details in the reflection spectrum, rich in fluorescent
lines and other atomic features, are very sensitive to the spectral shape of
the hardest coronal radiation illuminating the disk. We show that fitting
simultaneous NuSTAR (3-79 keV) and low-energy (e.g., Suzaku) data with the most
recent version of our reflection model RELXILL, one can obtain reasonable
constraints on at energies from tens of keV up to 1 MeV, for a source
as faint as 1 mCrab in a 100 ks observation.Comment: Accepted for publication in ApJL, 6 pages, 5 figure
HAAS AUTOMATION UMC750 5AXIS MILL ASSEMBLY PROCESS IMPROVEMENT
The improvement of the current assembly of the motor and casting components for the Haas UMC-750 5-Axis vertical CNC mill includes the evaluation, development and proposal of a new pair of material handling carts. To meet these deliverables, a student team began by assessing the assembly workstation, defining the problem to be solved, researching ergonomics in material handling equipment and drafting the final design of the improved cart models using SolidWorks. The final design considered the initial improvement request from the client, as well as better ergonomic features to enhance the safety of the operators. It was estimated that the new design can provide Haas Automation with savings in material cost and production of the cart. At the same time, by improving the design, the new carts reduce risk of employee injury by decreasing the use of an overhead crane for assembling the motor components. The SolidWorks models and engineering drawings will be presented to Haas Automation in the hope of a future implementation
The dispersive self-dual Einstein equations and the Toda lattice
The Boyer-Finley equation, or -Toda equation is both a reduction
of the self-dual Einstein equations and the dispersionlesslimit of the
-Toda lattice equation. This suggests that there should be a dispersive
version of the self-dual Einstein equation which both contains the Toda lattice
equation and whose dispersionless limit is the familiar self-dual Einstein
equation. Such a system is studied in this paper. The results are achieved by
using a deformation, based on an associative -product, of the algebra
used in the study of the undeformed, or dispersionless,
equations.Comment: 11 pages, LaTeX. To appear: J. Phys.
Improvement of convective drying of carrot by applying power ultrasound. Influence of mass load density
[EN] Power ultrasound is considered to be a novel and promising
technology with which to improve heat and mass transfer phenomena
in drying processes. The aim of this work was to contribute to the
knowledge of ultrasound application to air drying by addressing
the influence of mass load density on the ultrasonically assisted air
drying of carrot. Drying kinetics of carrot cubes were carried out
(in triplicate) with or without power ultrasound application (75 W,
21.7 kHz) at 40 C, 1 m/s, and several mass load densities: 12, 24,
36, 42, 48, 60, 72, 84, 96, 108, and 120 kg/m3
. The experimental
results showed a significant (p < 0.05) influence of both factors, mass
load density and power ultrasound application, on drying kinetics. As
expected, the increase of mass load density did not affect the effective
moisture diffusivity (De, m2
/s) but produced a reduction of the
mass transfer coefficient (k, kg water/m2
/s). This was explained by
considering perturbations in the air flow through the drying chamber
thus creating preferential pathways and, as a consequence, increasing
external mass transfer resistance. On the other hand, it was
found that the power ultrasound application increased the mass
transfer coefficient and the effective moisture diffusivity regardless
of the mass load density used. However, the influence of power ultrasound
was not significant at the highest mass load densities tested
(108 and 120 kg/m3
), which may be explained from the high ratio
(acoustic energy/sample mass) found under those experimental
conditions. Therefore, the application of ultrasound was considered
as a useful technology with which to improve the convective drying,
although its effects may be reduced at high mass load densities.The authors acknowledge the financial support of the Spanish Ministry of Science and Technology (DPI2009-14549-C04-04) and the Universidad Politecnica de Valencia (PAID-06-08-3180).Cárcel Carrión, JA.; García Pérez, JV.; Riera, E.; Mulet Pons, A. (2011). Improvement of convective drying of carrot by applying power ultrasound. Influence of mass load density. Drying Technology. 29(2):174-182. https://doi.org/10.1080/07373937.2010.483032S17418229
Testing the Unification Model for AGN in the Infrared: are the obscuring tori of Type 1 and 2 Seyferts different?
We present new mid-infrared (MIR) imaging data for three Type-1 Seyfert
galaxies obtained with T-ReCS on the Gemini-South Telescope at subarcsecond
resolution. Our aim is to enlarge the sample studied in a previous work to
compare the properties of Type-1 and Type-2 Seyfert tori using clumpy torus
models and a Bayesian approach to fit the infrared nuclear spectral energy
distributions (SEDs). Thus, the sample considered here comprises 7 Type-1, 11
Type-2, and 3 intermediate-type Seyferts. The unresolved IR emission of the
Seyfert 1 galaxies can be reproduced by a combination of dust heated by the
central engine and direct AGN emission, while for the Seyfert 2 nuclei only
dust emission is considered. These dusty tori have physical sizes smaller than
6 pc radius, as derived from our fits. Unification schemes of AGN account for a
variety of observational differences in terms of viewing geometry. However, we
find evidence that strong unification may not hold, and that the immediate
dusty surroundings of Type-1 and Type-2 Seyfert nuclei are intrinsically
different. The Type-2 tori studied here are broader, have more clumps, and
these clumps have lower optical depths than those of Type-1 tori. The larger
the covering factor of the torus, the smaller the probability of having direct
view of the AGN, and vice-versa. In our sample, Seyfert 2 tori have larger
covering factors and smaller escape probabilities than those of Seyfert 1. All
the previous differences are significant according to the Kullback-Leibler
divergence. Thus, on the basis of the results presented here, the
classification of a Seyfert galaxy as a Type-1 or Type-2 depends more on the
intrinsic properties of the torus rather than on its mere inclination towards
us, in contradiction with the simplest unification model.Comment: 21 pages, 14 figures, Appendix including supplementary figures.
Accepted by Ap
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Spectroscopic studies of ketones as a marker for patients with diabetes
Acetone in human breath has been established as a biomarker for diabetes. The application of UV spectroscopy for the study of biomedical compounds has been developed over recent years but is often limited by the lack of absolute data for calibration of the instrumentation. By measuring high resolution absolute VUV photoabsorption cross sections of acetone, we are able to provide calibration values at several wavelengths with special attention to 4.661 eV (266 nm). Results are compared with recent published data [C Wang, A Mbi, Meas. Sci. Technol., 2007, 18, 2731–2741]. The acetone spectrum is here revisited from a recent contribution [Nobre M, et al, Phys Chem Chem Phys, 2008 (in press)] where the absolute cross sectional values are obtained in the 3.7–10.8 eV energy region. Future medical units working in close link with synchrotron radiation facilities can make use of the VUV spectra wavelength region to trace acetone in diabetic patients
Spectroscopic and physical parameters of Galactic O-type stars. I. Effects of rotation and spectral resolving power in the spectral classification of dwarfs and giants
The modern-era spectral classification of O-stars relies on either the
Walborn or the Conti-Mathys scheme. Since both of these approaches have been
developed using low-quality photographic data, their application to
high-quality digital data might not be straightforward and be hampered by
problems and complications that have not yet been appreciated. Using
high-resolution spectra obtained with the ESO/MPG 2.2\,m telescope in La Silla
and following the premises of the Walborn and Conti classification schemes, we
determined the spectral types and luminosity classes of 19 Galactic O-type
stars and compared them to those attributed by Walborn and Mathys based on
low-quality data. Our analysis reveals that the morphological spectral types
assigned using high-resolution data are systematically later (by up to 1.5
subtypes) then those attributed by Walborn. By means of line-profile
simulations, we show that part of this discrepancy is more likely caused by the
combined effect of stellar rotation and high spectral resolution on the depth
of helium lines used as spectral type indicators. In addition, we demonstrate
that at least for narrow-lined stars the "rotational effect" does not disappear
when the high-resolution spectra are degraded to the resolution of the Walborn
standards. We also find evidence of a systematic difference between our
high-resolution quantitative spectral types and those assigned by Mathys.
Rotation and spectral resolution are important third parameters in the spectral
classification of O-type stars. To obtain reliable spectral classes within the
Walborn approach, the unknown and the standard spectra must be compared at the
same resolution and \vsini. Owing to resolution effects, the Conti approach
might also need to be updated.Comment: paper accepted for publication in A&
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Fbxl17 is rearranged in breast cancer and loss of its activity leads to increased global O -GlcNAcylation
Funder: Wildy Fellowship Department of PathologyFunder: Addenbrooke's Charitable Trust, Cambridge University Hospitals; doi: http://dx.doi.org/10.13039/501100002927Funder: The Mark FoundationAbstract: In cancer, many genes are mutated by genome rearrangement, but our understanding of the functional consequences of this remains rudimentary. Here we report the F-box protein encoded by FBXL17 is disrupted in the region of the gene that encodes its substrate-binding leucine rich repeat (LRR) domain. Truncating Fbxl17 LRRs impaired its association with the other SCF holoenzyme subunits Skp1, Cul1 and Rbx1, and decreased ubiquitination activity. Loss of the LRRs also differentially affected Fbxl17 binding to its targets. Thus, genomic rearrangements in FBXL17 are likely to disrupt SCFFbxl17-regulated networks in cancer cells. To investigate the functional effect of these rearrangements, we performed a yeast two-hybrid screen to identify Fbxl17-interacting proteins. Among the 37 binding partners Uap1, an enzyme involved in O-GlcNAcylation of proteins was identified most frequently. We demonstrate that Fbxl17 binds to UAP1 directly and inhibits its phosphorylation, which we propose regulates UAP1 activity. Knockdown of Fbxl17 expression elevated O-GlcNAcylation in breast cancer cells, arguing for a functional role for Fbxl17 in this metabolic pathway
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Efficient incorporation of channel cross-section geometry uncertainty into regional and global scale flood inundation models
This paper investigates the challenge of representing structural differences in river channel cross-section geometry for regional to global scale river hydraulic models and the effect this can have on simulations of wave dynamics. Classically, channel geometry is defined using data, yet at larger scales the necessary information and model structures do not exist to take this approach. We therefore propose a fundamentally different approach where the structural uncertainty in channel geometry is represented using a simple parameterization, which could then be estimated through calibration or data assimilation. This paper first outlines the development of a computationally efficient numerical scheme to represent generalised channel shapes using a single parameter, which is then validated using a simple straight channel test case and shown to predict wetted perimeter to within 2% for the channels tested. An application to the River Severn, UK is also presented, along with an analysis of model sensitivity to channel shape, depth and friction. The channel shape parameter was shown to improve model simulations of river level, particularly for more physically plausible channel roughness and depth parameter ranges. Calibrating channel Manning’s coefficient in a rectangular channel provided similar water level simulation accuracy in terms of Nash-Sutcliffe efficiency to a model where friction and shape or depth were calibrated. However, the calibrated Manning coefficient in the rectangular channel model was ~2/3 greater than the likely physically realistic value for this reach and this erroneously slowed wave propagation times through the reach by several hours. Therefore, for large scale models applied in data sparse areas, calibrating channel depth and/or shape may be preferable to assuming a rectangular geometry and calibrating friction alone
The short term debt vs. long term debt puzzle: a model for the optimal mix
This paper argues that the existing finance literature is inadequate with respect to its coverage of capital structure of small and medium sized enterprises (SMEs). In particular it is argued that the cost of equity (being both conceptually ill defined and empirically non quantifiable) is not applicable to the capital structure decisions for a large proportion of SMEs and the optimal capital structure depends only on the mix of short and long term debt. The paper then presents a model, developed by practitioners for optimising the debt mix and demonstrates its practical application using an Italian firm's debt structure as a case study
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