15 research outputs found
Bridging the gap between stellar-mass black holes and ultraluminous X-ray sources
The X-ray spectral and timing properties of ultraluminous X-ray sources
(ULXs) have many similarities with the very high state of stellar-mass black
holes (power-law dominated, at accretion rates greater than the Eddington
rate). On the other hand, their cool disk components, large characteristic
inner-disk radii and low characteristic timescales have been interpreted as
evidence of black hole masses ~ 1000 Msun (intermediate-mass black holes). Here
we re-examine the physical interpretation of the cool disk model, in the
context of accretion states of stellar-mass black holes. In particular, XTE
J1550-564 can be considered the missing link between ULXs and stellar-mass
black holes, because it exhibits a high-accretion-rate, low-disk-temperature
state (ultraluminous branch). On the ultraluminous branch, the accretion rate
is positively correlated with the disk truncation radius and the bolometric
disk luminosity, while it is anti-correlated with the peak temperature and the
frequency of quasi-periodic-oscillations. Two prototypical ULXs (NGC1313 X-1
and X-2) also seem to move along that branch. We use a phenomenological model
to show how the different range of spectral and timing parameters found in the
two classes of accreting black holes depends on both their masses and accretion
rates. We suggest that ULXs are consistent with black hole masses ~ 50-100
Msun, moderately inefficiently accreting at ~20 times Eddington.Comment: 11 pages, accepted for publication in Astrophysics and Space Science.
Based on work presented at the Fifth Stromlo Symposium, Australian National
University, Dec 200
Impact of farm size on milk quality in the Brazilian dairy industry according to the seasons of the year
Intoxicação por Senecio spp. em bovinos no Rio Grande do Sul: condiçÔes ambientais favoråveis e medidas de controle
Composição e diversidade da fauna de aranhas (Arachnida, Araneae) da Fazenda Nazareth, MunicĂpio de JosĂ© de Freitas, PiauĂ, Brasil
Repositioning of the global epicentre of non-optimal cholesterol
High blood cholesterol is typically considered a feature of wealthy western countries1,2. However, dietary and behavioural determinants of blood cholesterol are changing rapidly throughout the world3 and countries are using lipid-lowering medications at varying rates. These changes can have distinct effects on the levels of high-density lipoprotein (HDL) cholesterol and non-HDL cholesterol, which have different effects on human health4,5. However, the trends of HDL and non-HDL cholesterol levels over time have not been previously reported in a global analysis. Here we pooled 1,127 population-based studies that measured blood lipids in 102.6 million individuals aged 18 years and older to estimate trends from 1980 to 2018 in mean total, non-HDL and HDL cholesterol levels for 200 countries. Globally, there was little change in total or non-HDL cholesterol from 1980 to 2018. This was a net effect of increases in low- and middle-income countries, especially in east and southeast Asia, and decreases in high-income western countries, especially those in northwestern Europe, and in central and eastern Europe. As a result, countries with the highest level of non-HDL cholesterolâwhich is a marker of cardiovascular riskâchanged from those in western Europe such as Belgium, Finland, Greenland, Iceland, Norway, Sweden, Switzerland and Malta in 1980 to those in Asia and the Pacific, such as Tokelau, Malaysia, The Philippines and Thailand. In 2017, high non-HDL cholesterol was responsible for an estimated 3.9 million (95% credible interval 3.7 millionâ4.2 million) worldwide deaths, half of which occurred in east, southeast and south Asia. The global repositioning of lipid-related risk, with non-optimal cholesterol shifting from a distinct feature of high-income countries in northwestern Europe, north America and Australasia to one that affects countries in east and southeast Asia and Oceania should motivate the use of population-based policies and personal interventions to improve nutrition and enhance access to treatment throughout the world.</p
Polymerization shrinkage and push-out bond strength of different composite resins for sealing the screw-access hole on implant-supported crowns
Purpose: To evaluate the effect of composite resin polymerization shrinkage stress on the stress distribution in the implant-supported crown-access hole, and on the bond strength between the ceramic and composite resin. Materials and Methods: A 3D model of a ceramic crown, in which the access hole was filled with composite resin (conventional or bulk-fill), was used to evaluate the stress distribution in the access hole using finite element analysis. The contacts were considered bonded and the polymerization shrinkage was simulated based on the coefficient of linear thermal expansion of each resin. The push-out test (1 mm/min, 100 kgf) was performed on perforated lithium disilicate samples filled with conventional or bulk-fill resins to validate the stress data of the bond strength. One-way ANOVA and Tukey's test were used to analyze the bond strength data, with α set at 5%. Results: Conventional resin showed the worst stress distribution and highest displacement values, von Mises stress, maximum principal strain, maximum principal stress, and maximum shear stress vs the bulk-fill resin. Statistically significantly greater bond strength was observed for bulk-fill (13.40 ± 5.59 MPa) than the conventional resin (8.70 ± 3.02 MPa). Conclusion: Comparing both materials tested in the present study, the use of bulk-fill composite resin to seal the screw-access hole is suggested to reduce the stress concentration and increase bond strength to the ceramic crown