692 research outputs found
Travelling Waves of a Delayed SIR Epidemic Model with Nonlinear Incidence Rate and Spatial Diffusion
This paper is concerned with the existence of travlelling waves to a SIR epidemic model with nonlinear incidence rate, spatial diffusion and time delay. By analyzing the corresponding characteristic equations, the local stability of a disease-free steady state and an endemic steady state to this system under homogeneous Neumann boundary conditions is discussed. By using the cross iteration method and the Schauder's fixed point theorem, we reduce the existence of travelling waves to the existence of a pair of upper-lower solutions. By constructing a pair of upper-lower solutions, we derive the existence of a travelling wave connecting the disease-free steady state and the endemic steady state. Numerical simulations are carried out to illustrate the main results
NGTS-13b: A hot 4.8 Jupiter-mass planet transiting a subgiant star
We report the discovery of the massive hot Jupiter NGTS-13b by the Next
Generation Transit Survey (NGTS). The V = 12.7 host star is likely in the
subgiant evolutionary phase with log g = 4.04 0.05, T =
5819 73 K, M = 1.30 M, and R =
1.79 0.06 R. NGTS detected a transiting planet with a period of
P = 4.12 days around the star, which was later validated with the Transiting
Exoplanet Survey Satellite (TESS; TIC 454069765). We confirm the planet using
radial velocities from the CORALIE spectrograph. Using NGTS and TESS full-frame
image photometry combined with CORALIE radial velocities we determine NGTS-13b
to have a radius of R = 1.142 0.046 R, mass of M =
4.84 0.44 M and eccentricity e = 0.086 0.034. Some previous
studies suggest that 4 M may be a border between two separate
formation scenarios (e.g., core accretion and disk instability) and that
massive giant planets share similar formation mechanisms as lower-mass brown
dwarfs. NGTS-13b is just above 4 M making it an important addition to
the statistical sample needed to understand the differences between various
classes of substellar companions. The high metallicity, [Fe/H] = 0.25
0.17, of NGTS-13 does not support previous suggestions that massive giants are
found preferentially around lower metallicity host stars, but NGTS-13b does
support findings that more massive and evolved hosts may have a higher
occurrence of close-in massive planets than lower-mass unevolved stars
NGTS-5b: A highly inflated planet offering insights into the sub-Jovian desert
Context: Planetary population analysis gives us insight into formation and
evolution processes. For short-period planets, the subJovian desert has been
discussed in recent years with regard to the planet population in the
mass/period and radius/period parameter space without taking stellar parameters
into account. The Next Generation Transit Survey (NGTS) is optimised for
detecting planets in this regime, which allows for further analysis of the
sub-Jovian desert.
Aims: With high-precision photometric surveys (e.g. with NGTS and TESS),
which aim to detect short period planets especially around M/K-type host stars,
stellar parameters need to be accounted for when empirical data are compared to
model predictions. Presenting a newly discovered planet at the boundary of the
sub-Jovian desert, we analyse its bulk properties and use it to show the
properties of exoplanets that border the sub-Jovian desert.
Methods: Using NGTS light curve and spectroscopic follow-up observations, we
confirm the planetary nature of planet NGTS-5b and determine its mass. Using
exoplanet archives, we set the planet in context with other discoveries.
Results: NGTS-5b is a short-period planet with an orbital period of 3.3569866
+- 0.0000026 days. With a mass of 0.229 +- 0.037 MJup and a radius of 1.136 +-
0.023 RJup, it is highly inflated. Its mass places it at the upper boundary of
the sub-Jovian desert. Because the host is a K2 dwarf, we need to account for
the stellar parameters when NGTS-5b is analysed with regard to planet
populations.
Conclusions: With red-sensitive surveys (e.g. with NGTS and TESS), we expect
many more planets around late-type stars to be detected. An empirical analysis
of the sub-Jovian desert should therefore take stellar parameters into account
NGTS discovery of a highly inflated Saturn-mass planet and a highly irradiated hot Jupiter: NGTS-26 b and NGTS-27 b
We report the discovery of two new transiting giant exoplanets NGTS-26 b and NGTS-27 b by the Next Generation Transit Survey (NGTS). NGTS-26 b orbits around a G6-type main sequence star every 4.52 days. It has a mass of 0.29-0.06+0.07 MJup and a radius of 1.33-0.05+0.06 RJup making it a Saturn-mass planet with a highly inflated radius. NGTS-27 b orbits around a slightly evolved G3-type star every 3.37 days. It has a mass of 0.59-0.07+0.10 MJup and a radius of 1.40±0.04 RJup, making it a relatively standard hot Jupiter. The transits of these two planetary systems were re-observed and confirmed in photometry by the SAAO 1.0-m telescope, 1.2-m Euler Swiss telescope as well as the TESS spacecraft, and their masses were derived spectroscopically by the CORALIE, FEROS and HARPS spectrographs. Both giant exoplanets are highly irradiated by their host stars and present an anomalously inflated radius, especially NGTS-26 b which is one of the largest objects among peers of similar mass
Utilisation of an operative difficulty grading scale for laparoscopic cholecystectomy
Background
A reliable system for grading operative difficulty of laparoscopic cholecystectomy would standardise description of findings and reporting of outcomes. The aim of this study was to validate a difficulty grading system (Nassar scale), testing its applicability and consistency in two large prospective datasets.
Methods
Patient and disease-related variables and 30-day outcomes were identified in two prospective cholecystectomy databases: the multi-centre prospective cohort of 8820 patients from the recent CholeS Study and the single-surgeon series containing 4089 patients. Operative data and patient outcomes were correlated with Nassar operative difficultly scale, using Kendall’s tau for dichotomous variables, or Jonckheere–Terpstra tests for continuous variables. A ROC curve analysis was performed, to quantify the predictive accuracy of the scale for each outcome, with continuous outcomes dichotomised, prior to analysis.
Results
A higher operative difficulty grade was consistently associated with worse outcomes for the patients in both the reference and CholeS cohorts. The median length of stay increased from 0 to 4 days, and the 30-day complication rate from 7.6 to 24.4% as the difficulty grade increased from 1 to 4/5 (both p < 0.001). In the CholeS cohort, a higher difficulty grade was found to be most strongly associated with conversion to open and 30-day mortality (AUROC = 0.903, 0.822, respectively). On multivariable analysis, the Nassar operative difficultly scale was found to be a significant independent predictor of operative duration, conversion to open surgery, 30-day complications and 30-day reintervention (all p < 0.001).
Conclusion
We have shown that an operative difficulty scale can standardise the description of operative findings by multiple grades of surgeons to facilitate audit, training assessment and research. It provides a tool for reporting operative findings, disease severity and technical difficulty and can be utilised in future research to reliably compare outcomes according to case mix and intra-operative difficulty
NGTS-11 b (TOI-1847 b): A Transiting Warm Saturn Recovered from a TESS Single-transit Event
We report the discovery of NGTS-11 b (=TOI-1847 b), a transiting Saturn in a
35.46-day orbit around a mid K-type star (Teff=5050 K). We initially identified
the system from a single-transit event in a TESS full-frame image light-curve.
Following seventy-nine nights of photometric monitoring with an NGTS telescope,
we observed a second full transit of NGTS-11 b approximately one year after the
TESS single-transit event. The NGTS transit confirmed the parameters of the
transit signal and restricted the orbital period to a set of 13 discrete
periods. We combined our transit detections with precise radial velocity
measurements to determine the true orbital period and measure the mass of the
planet. We find NGTS-11 b has a radius of 0.817+0.028-0.032 , a mass of
0.344+0.092-0.073 , and an equilibrium temperature of just 435+34-32 K,
making it one of the coolest known transiting gas giants. NGTS-11 b is the
first exoplanet to be discovered after being initially identified as a TESS
single-transit event, and its discovery highlights the power of intense
photometric monitoring in recovering longer-period transiting exoplanets from
single-transit events
Polymorphic Variation in TIRAP Is Not Associated with Susceptibility to Childhood TB but May Determine Susceptibility to TBM in Some Ethnic Groups
Host recognition of mycobacterial surface molecules occurs through toll like receptors (TLR) 2 and 6. The adaptor protein TIRAP mediates down stream signalling of TLR2 and 4, and polymorphisms in the TIRAP gene (TIRAP) have been associated with susceptibility and resistance to tuberculosis (TB) in adults. In order to investigate the role of polymorphic variation in TIRAP in childhood TB in South Africa, which has one of the highest TB incidence rates in the world, we screened the entire open reading frame of TIRAP for sequence variation in two cohorts of childhood TB from different ethnic groups (Xhosa and mixed ancestry). We identified 13 SNPs, including seven previously unreported, in the two cohorts, and found significant differences in frequency of the variants between the two ethnic groups. No differences in frequency between individual SNPs or combinations were found between TB cases and controls in either cohort. However the 558C→T SNP previously associated with TB meningitis (TBM) in a Vietnamese population was found to be associated with TBM in the mixed ancestry group. Polymorphisms in TIRAP do not appear to be involved in childhood TB susceptibility in South Africa, but may play a role in determining occurrence of TBM
[18F]FBEM-ZHER2:342–Affibody molecule—a new molecular tracer for in vivo monitoring of HER2 expression by positron emission tomography
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