To determine which measurement of donor renal size on computed tomographic (CT) angiograms has the greatest correlation with renal function preoperatively in the donor and postoperatively in the ...transplant recipient.
Informed consent was waived for this retrospective HIPAA-compliant study approved by the institutional review board. Renal length, total volume, and cortical volume were measured on renal donor CT angiograms in 111 patients. Preoperative serum creatinine values for donors and postoperative creatinine values for recipients at hospital discharge and 6, 12, 24, and 36 months after transplant were collected, and estimated glomerular filtration rate (eGFR) was calculated. Correlation coefficients with 95% confidence intervals (CIs) were obtained for renal measures and donor eGFR and for renal measures adjusted to recipient body habitus and posttransplant creatinine level in the recipient. Thresholds were set for adjusted length and volumes, and the odds ratio (OR) for creatinine level less than 1.5 mg/dL at 36 months was calculated.
Renal volumes and length were correlated with donor eGFR (r=0.58 95% CI: 0.44, 0.69 for cortical volume, 0.56 95% CI: 0.42, 0.68 for total volume, and 0.43 95% CI: 0.27, 0.57 for renal length). All three measures, adjusted to recipient body habitus, were correlated with recipient renal function from discharge (r=-0.41 to -0.43) up to 36 months after transplantation (r=-0.33 to -0.41). By using a threshold of 1.5 for cortical volume to recipient weight, 2.25 for total volume to recipient weight, and 0.175 for renal length to recipient weight, the odds of creatinine level greater than 1.5 mg/dL were four times as great for smaller kidney-to-recipient weight ratios, a statistically significant pattern for cortical volume (OR, 4.07; 95% CI: 1.10, 15.09) but not total volume (OR, 4.24; 95% CI: 0.90, 20.01) or renal length (OR, 4.08; 95% CI: 0.48-34.29).
Renal length and volumes correlated with recipient renal function up to 36 months after transplant. A low ratio of cortical volume to recipient weight was associated with diminished renal function at 36 months after transplant.
ABSTRACT
The mechanical properties of a neutron star crust, such as breaking strain and shear modulus, have implications for the detection of gravitational waves from a neutron star as well as bursts ...from soft Gamma‐ray repeaters (SGRs). These properties are calculated here for three different crustal compositions for a non‐accreting neutron star that results from three different cooling histories, as well as for a pure iron crust. A simple shear is simulated using molecular dynamics to the crustal compositions by deforming the simulation box. The breaking strain and shear modulus are found to be similar in the four cases, with a breaking strain of ∼0.1 and a shear modulus of ∼1030 dyne cm−2 at a density of ρ = 1014 g cm−3 for simulations with an initially perfect body‐centred cubic (BCC) lattice. With these crustal properties and the observed properties of PSR J2124−3358, the predicted strain amplitude of gravitational waves for a maximally deformed crust is found to be greater than the observational upper limits from LIGO. This suggests that the neutron star crust in this case may not be maximally deformed or it may not have a perfect BCC lattice structure. The implications of the calculated crustal properties of bursts from SGRs are also explored. The mechanical properties found for a perfect BCC lattice structure find that crustal events alone cannot be ruled out for triggering the energy in SGR bursts.
We present the Kepler Object of Interest (KOI) catalog of transiting exoplanets based on searching 4 yr of Kepler time series photometry (Data Release 25, Q1-Q17). The catalog contains 8054 KOIs, of ...which 4034 are planet candidates with periods between 0.25 and 632 days. Of these candidates, 219 are new, including two in multiplanet systems (KOI-82.06 and KOI-2926.05) and 10 high-reliability, terrestrial-size, habitable zone candidates. This catalog was created using a tool called the Robovetter, which automatically vets the DR25 threshold crossing events (TCEs). The Robovetter also vetted simulated data sets and measured how well it was able to separate TCEs caused by noise from those caused by low signal-to-noise transits. We discuss the Robovetter and the metrics it uses to sort TCEs. For orbital periods less than 100 days the Robovetter completeness (the fraction of simulated transits that are determined to be planet candidates) across all observed stars is greater than 85%. For the same period range, the catalog reliability (the fraction of candidates that are not due to instrumental or stellar noise) is greater than 98%. However, for low signal-to-noise candidates between 200 and 500 days around FGK-dwarf stars, the Robovetter is 76.7% complete and the catalog is 50.5% reliable. The KOI catalog, the transit fits, and all of the simulated data used to characterize this catalog are available at the NASA Exoplanet Archive.
ABSTRACT The Kepler mission discovered 2842 exoplanet candidates with 2 yr of data. We provide updates to the Kepler planet candidate sample based upon 3 yr (Q1-Q12) of data. Through a series of ...tests to exclude false-positives, primarily caused by eclipsing binary stars and instrumental systematics, 855 additional planetary candidates have been discovered, bringing the total number known to 3697. We provide revised transit parameters and accompanying posterior distributions based on a Markov Chain Monte Carlo algorithm for the cumulative catalog of Kepler Objects of Interest. There are now 130 candidates in the cumulative catalog that receive less than twice the flux the Earth receives and more than 1100 have a radius less than 1.5 . There are now a dozen candidates meeting both criteria, roughly doubling the number of candidate Earth analogs. A majority of planetary candidates have a high probability of being bonafide planets, however, there are populations of likely false-positives. We discuss and suggest additional cuts that can be easily applied to the catalog to produce a set of planetary candidates with good fidelity. The full catalog is publicly available at the NASA Exoplanet Archive.
Light curves from the 4-year Kepler exoplanet hunting mission have been searched for transits by NASA's Kepler team and others, but there are still important discoveries to be made. We have searched ...the light curves of 400 Kepler Objects of Interest (KOIs) to find transit signals down to signal-to-noise ratio (S/N) ∼ 6, which is under the limit of S/N ∼ 7.1 that has been commonly adopted as a strict threshold to distinguish between a transit candidate and false alarm. We detect four new and convincing planet candidates ranging in radius from near-Mercury-size to slightly larger than Neptune. We highlight the discovery of KOI-408.05 (period = 637 days; radius = 4.9 R⊕; incident flux = 0.6 S⊕), a planet candidate within its host star's Habitable Zone. We dub this planet a "warm Neptune," a likely volatile-rich world that deserves closer inspection. KOI-408.05 joins 21 other confirmed and candidate planets in the current Kepler sample with semimajor axes a > 1.4 au. These discoveries are significant as a demonstration that the S/N threshold for detection used by the Kepler project is open to debate.
We have investigated the crustal properties of neutron stars without fallback accretion. We have calculated the chemical evolution of the neutron star crust in three different cases (a modified Urca ...process without the thermal influence of a crust, a thick crust and a direct Urca process with a thin crust) in order to determine the detailed composition of the envelope and atmosphere as the nuclear reactions freeze out. Using a nuclear reaction network up to technetium, we calculate the distribution of nuclei at various depths of the neutron star. The nuclear reactions quench when the cooling time-scale is shorter than the inverse of the reaction rate. Trace light elements among the calculated isotopes may have enough time to float to the surface before the layer crystallizes and form the atmosphere or envelope of the neutron star. The composition of the neutron star envelope determines the total photon flux from the surface, and the composition of the atmosphere determines the emergent spectrum. Our calculations using each of the three cooling models indicate that without accretion of fallback the neutron star atmospheres are dependent on the assumed cooling process of the neutron star. Each of the cooling methods has different elements composing the atmosphere: for the modified Urca process, the atmosphere is 28Si, the thick crust has an atmosphere of 50Cr and the thin crust has an atmosphere of 40Ca. In all the three cases, the atmospheres are composed of elements which are lighter than iron.
Neutron Star Crustal Mass Fractions Hoffman, Kelsey L; Heyl, Jeremy S
40 Years of Pulsars: Millisecond Pulsars, Magnetars and More (AIP Conference Proceedings Volume 983),
2008, Letnik:
983, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
We are investigating mass fractions on the crust of a neutron star which would remain after one year of cooling. We use cooling curves corresponding with various densities, or depths, of the neutron ...star just after its formation. We assume the modified Urca process dominates the energy budget of the outer layers of the star in order to calculate the temperature of the neutron star as a function of time. Using a nuclear reaction network up to technetium, we calculate how the distribution of nuclei quenches at various depths of the neutron star crust. The initial results indicate that 28Si is the lightest isotope to be optically thick on the surface after one year of cooling.
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