846 research outputs found
Constructing and Representing Territory in Late Medieval and Early Modern Europe: A Conclusion
Constructing and Representing Territory in Late Medieval and Early Modern Europe: An Introduction
Water-gas shift (WGS) Operation of Pre-combustion CO2 Capture Pilot Plant at the Buggenum IGCC
AbstractIn the Nuon/Vattenfall CO2 Catch-up project, a pre-combustion CO2 capture pilot plant was built and operated at the Buggenum IGCC power plant, the Netherlands. The pilot consist of sweet water-gas shift, physical CO2 absorption and CO2 compression. The technology performance was verified and validated models were obtained. This paper describes the validation of a WGS reactor model and the excellent catalyst resistance to carbiding at steam/CO=1.5 mol·mol-1 testing. Model-based optimization shows that compared to conventional operation at steam/CO=2.65, applying steam/CO=1.5 leads to a 10% lower CO2 capture of penalty of 1155 MJelectric·tCO2−1, albeit at a decreased optimum CO2 capture efficiency of 78.5% versus 87.5%
Spitzer Constraints on the Stellar Populations of Lyman-Alpha Emitting Galaxies at z = 3.1
We investigate the stellar populations of a sample of 162 Lyman-alpha
emitting galaxies (LAEs) at z = 3.1 in the Extended Chandra Deep Field South,
using deep Spitzer IRAC data available from the GOODS and SIMPLE surveys to
derive reliable stellar population estimates. We divide the LAEs according to
their rest-frame near-IR luminosities into IRAC-detected and IRAC-undetected
samples. About 70% of the LAEs are undetected in 3.6 micron down to [3.6] =
25.2 AB. Stacking analysis reveals that the average stellar population of the
IRAC-undetected sample has an age of ~ 200 Myr and a mass of ~ 3x10^8 solar
masses, consistent with the expectation that LAEs are mostly young and low-mass
galaxies. On the other hand, the IRAC-detected LAEs are on average
significantly older and more massive, with an average age > 1 Gyr and mass ~
10^10 solar masses. Comparing the IRAC colors and magnitudes of the LAEs to z ~
3 Lyman break galaxies (LBGs) shows that the IRAC-detected LAEs lie at the
faint blue end of the LBG color-magnitude distribution, suggesting that
IRAC-detected LAEs may be the low mass extension of the LBG population. We also
present tentative evidence for a small fraction (~ 5%) of obscured AGN within
the LAE sample. Our results suggest that LAEs posses a wide range of ages and
masses. Additionally, the presence of evolved stellar populations inside LAEs
suggests that the Lyman-alpha luminous phase of galaxies may either be a
long-lasting or recurring phenomenon.Comment: Accepted for publication in ApJ; 5 pages, 4 figure
Ultrafast pump-probe dynamics in ZnSe-based semiconductor quantum-wells
Pump-probe experiments are used as a controllable way to investigate the
properties of photoexcited semiconductors, in particular, the absorption
saturation. We present an experiment-theory comparison for ZnSe quantum wells,
investigating the energy renormalization and bleaching of the excitonic
resonances. Experiments were performed with spin-selective excitation and
above-bandgap pumping. The model, based on the semiconductor Bloch equations in
the screened Hartree-Fock approximation, takes various scattering processes
into account phenomenologically. Comparing numerical results with available
experimental data, we explain the experimental results and find that the
electron spin-flip occurs on a time scale of 30 ps.Comment: 10 pages, 9 figures. Key words: nonlinear and ultrafast optics,
modeling of femtosecond pump-probe experiments, electron spin-flip tim
Attitudes of Students at Sultan Qaboos University towards the Nursing Profession
Objectives: The aim of this study was to explore the attitudes of Sultan Qaboos University (SQU) students towards the nursing profession. Methods: A sample of 377 students (male = 130; female = 247) were selected from different colleges of SQU, including the College of Nursing. A questionnaire was constructed and validated to assess the attitudes of SQU students towards the nursing profession. Results: Findings revealed that both male and female students in all academic years and colleges had positive attitudes toward the nursing profession. The findings also revealed that gender and academic year created no significant differences (P <0.05) among the study participants, but that the students’ college affiliation did have a significant effect on their attitudes. In particular, nursing students had more positive attitudes than students of other colleges. Conclusion: Findings indicated that the attitudes of SQU students towards the nursing profession were positive, especially those of the nursing students. This means that serious efforts should be made to continue to promote the nursing profession and so ensure that it remains positively regarded by all concerned
Friction reducing ability of a poly-l-lysine and dopamine modified hyaluronan coating for polycaprolactone cartilage resurfacing implants
Frictional properties of cartilage resurfacing implants should be sufficiently low to limit damaging of the opposing cartilage during articulation. The present study determines if native lubricious molecule proteoglycan 4 (PRG4) can adsorb onto a layer-by-layer bioinspired coating composed of poly-l-lysine (PLL) and dopamine modified hyaluronic acid (HADN) and thereby can reduce the friction between implant and articular cartilage. An ELISA was developed to quantify the amount of immobilized human recombinant (rh)PRG4 after exposure to the PLL-HADN coating. The effect on lubrication was evaluated by comparing the coefficient of friction (CoF) of bare polycaprolactone (PCL) disks to that of PLL-HADN coated PCL disks while articulated against cartilage using a ring-on-disk geometry and a lubricant solution consisting of native synovial fluid components including rhPRG4. The PLL-HADN coating effectively immobilized rhPRG4. The surface roughness of PCL disks significantly increased while the water contact angle significantly decreased after application of the coating. The average CoF measured during the first minute of bare PCL against cartilage exceeded twice the CoF of the PLL-HADN coated PCL against cartilage. After 60 min, the CoF reached equilibrium values which were still significantly higher for bare PCL compared to coated PCL. The present study demonstrated that PCL can effectively be coated with PLL-HADN. Additionally, this coating reduces the friction between PCL and cartilage when a PRG4-rich lubricant is used, similar to the lubricating surface of native cartilage. This makes PLL-HADN coating a promising application to improve the clinical success of PCL-based cartilage resurfacing implants.</p
Eddington-limited X-ray Bursts as Distance Indicators. I. Systematic Trends and Spherical Symmetry in Bursts from 4U 1728-34
We investigate the limitations of thermonuclear X-ray bursts as a distance
indicator for the weakly-magnetized accreting neutron star 4U 1728-34. We
measured the unabsorbed peak flux of 81 bursts in public data from the Rossi
X-Ray Timing Explorer (RXTE). The distribution of peak fluxes was bimodal: 66
bursts exhibited photospheric radius expansion and were distributed about a
mean bolometric flux of 9.2e-8 erg/cm^2/s, while the remaining (non-radius
expansion) bursts reached 4.5e-8 erg/cm^2/s, on average. The peak fluxes of the
radius-expansion bursts were not constant, exhibiting a standard deviation of
9.4% and a total variation of 46%. These bursts showed significant correlations
between their peak flux and the X-ray colors of the persistent emission
immediately prior to the burst. We also found evidence for quasi-periodic
variation of the peak fluxes of radius-expansion bursts, with a time scale of
approximately 40 d. The persistent flux observed with RXTE/ASM over 5.8 yr
exhibited quasi-periodic variability on a similar time scale. We suggest that
these variations may have a common origin in reflection from a warped accretion
disk. Once the systematic variation of the peak burst fluxes is subtracted, the
residual scatter is only approximately 3%, roughly consistent with the
measurement uncertainties. The narrowness of this distribution strongly
suggests that i) the radiation from the neutron star atmosphere during
radius-expansion episodes is nearly spherically symmetric, and ii) the
radius-expansion bursts reach a common peak flux which may be interpreted as a
standard candle intensity.Adopting the minimum peak flux for the
radius-expansion bursts as the Eddington flux limit, we derive a distance for
the source of 4.4-4.8 kpc.Comment: 9 pages, 7 figures, accepted by ApJ. Minor referee's revisions, also
includes 9 newly public X-ray burst
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