49 research outputs found
Numerical crack growth study on porosity afflicted cast steel specimens
This paper deals with the fatigue assessment of cast steel defects in terms of macroscopic shrinkage porosity. Within preliminary studies, a generalized Kitagawa diagram GKD was established by numerical analyses of V-notched specimens with varying opening angles. It was experimentally verified by the application of the notch stress intensity factor (NSIF) concept on fatigue tests under rotating bending and axial loading. This paper continuous the work by an application of the GKD to real cast steel pores. At first, casting simulations are performed to design representative cast specimen geometries. The study focusses on macroscopic shrinkage pores with different spatial shapes. At second, fatigue tests under axial loading are conducted. Subsequent fracture surface analysis by light optical and scanning electron microscopy provides fracture mechanical based geometry parameters. Finally, the results of the experiments related to the failure relevant defect sizes are assessed by the GKD. In order to define an equivalent defect size of the complexly shaped defects, numerical crack growth analyses are performed demonstrating crack coalescence path tendencies. Summing up, the application of the NSIF approach based on a GKD shows a sound accordance to the experimental results and thus provides an engineering-feasible fatigue assessment method of cast steel components with macroscopic imperfections
Numerical crack growth study on porosity afflicted cast steel specimens
This paper deals with the fatigue assessment of cast steel defects in terms of macroscopic shrinkage porosity. Within preliminary studies, a generalized Kitagawa diagram GKD was established by numerical analyses of V-notched specimens with varying opening angles. It was experimentally verified by the application of the notch stress intensity factor (NSIF) concept on fatigue tests under rotating bending and axial loading. This paper continuous the work by an application of the GKD to real cast steel pores. At first, casting simulations are performed to design representative cast specimen geometries. The study focusses on macroscopic shrinkage pores with different spatial shapes. At second, fatigue tests under axial loading are conducted. Subsequent fracture surface analysis by light optical and scanning electron microscopy provides fracture mechanical based geometry parameters. Finally, the results of the experiments related to the failure relevant defect sizes are assessed by the GKD. In order to define an equivalent defect size of the complexly shaped defects, numerical crack growth analyses are performed demonstrating crack coalescence path tendencies. Summing up, the application of the NSIF approach based on a GKD shows a sound accordance to the experimental results and thus provides an engineering-feasible fatigue assessment method of cast steel components with macroscopic imperfections
Combined strong and weak lensing analysis of 28 clusters from the Sloan Giant Arcs Survey
We study the mass distribution of a sample of 28 galaxy clusters using strong
and weak lensing observations. The clusters are selected via their strong
lensing properties as part of the Sloan Giant Arcs Survey (SGAS) from the Sloan
Digital Sky Survey (SDSS). Mass modelling of the strong lensing information
from the giant arcs is combined with weak lensing measurements from deep
Subaru/Suprime-cam images to primarily obtain robust constraints on the
concentration parameter and the shape of the mass distribution. We find that
the concentration c_vir is a steep function of the mass, c_vir \propto
M_vir^-0.59\pm0.12, with the value roughly consistent with the
lensing-bias-corrected theoretical expectation for high mass (10^15 h^-1 M_sun)
clusters. However, the observationally inferred concentration parameters appear
to be much higher at lower masses (10^14 h^-1 M_sun), possibly a consequence of
the modification to the inner density profiles provided by baryon cooling. The
steep mass-concentration relation is also supported from direct stacking
analysis of the tangential shear profiles. In addition, we explore the
two-dimensional shape of the projected mass distribution by stacking weak
lensing shear maps of individual clusters with prior information on the
position angle from strong lens modelling, and find significant evidence for a
large mean ellipticity with the best-fit value of e = 0.47 \pm 0.06 for the
mass distribution of the stacked sample. We find that the luminous cluster
member galaxy distribution traces the overall mass distribution very well,
although the distribution of fainter cluster galaxies appears to be more
extended than the total mass.Comment: 29 pages, 15+9 figures, 7 tables, accepted for publication in MNRA
Bandwidth-controlled Mott transition in I. Optical studies of localized charge excitations
Infrared reflection measurements of the half-filled two-dimensional organic
conductors -(BEDT-TTF)Cu[N(CN)]BrCl were
performed as a function of temperature ( K) and
Br-substitution (, 40%, 73%, 85%, and 90%) in order to study the
metal-insulator transition. We can distinguish absorption processes due to
itinerant and localized charge carriers. The broad mid-infrared absorption has
two contributions: transitions between the two Hubbard bands and intradimer
excitations from the charges localized on the (BEDT-TTF) dimer. Since the
latter couple to intramolecular vibrations of BEDT-TTF, the analysis of both
electronic and vibrational features provides a tool to disentangle these
contributions and to follow their temperature and electronic-correlations
dependence. Calculations based on the cluster model support our interpretation.Comment: 12 pages, 12 figure
CLASH: Precise New Constraints on the Mass Profile of Abell 2261
We precisely constrain the inner mass profile of Abell 2261 (z=0.225) for the
first time and determine this cluster is not "over-concentrated" as found
previously, implying a formation time in agreement with {\Lambda}CDM
expectations. These results are based on strong lensing analyses of new 16-band
HST imaging obtained as part of the Cluster Lensing and Supernova survey with
Hubble (CLASH). Combining this with revised weak lensing analyses of Subaru
wide field imaging with 5-band Subaru + KPNO photometry, we place tight new
constraints on the halo virial mass M_vir = 2.2\pm0.2\times10^15 M\odot/h70
(within r \approx 3 Mpc/h70) and concentration c = 6.2 \pm 0.3 when assuming a
spherical halo. This agrees broadly with average c(M,z) predictions from recent
{\Lambda}CDM simulations which span 5 <~ 8. Our most significant
systematic uncertainty is halo elongation along the line of sight. To estimate
this, we also derive a mass profile based on archival Chandra X-ray
observations and find it to be ~35% lower than our lensing-derived profile at
r2500 ~ 600 kpc. Agreement can be achieved by a halo elongated with a ~2:1 axis
ratio along our line of sight. For this elongated halo model, we find M_vir =
1.7\pm0.2\times10^15 M\odot/h70 and c_vir = 4.6\pm0.2, placing rough lower
limits on these values. The need for halo elongation can be partially obviated
by non-thermal pressure support and, perhaps entirely, by systematic errors in
the X-ray mass measurements. We estimate the effect of background structures
based on MMT/Hectospec spectroscopic redshifts and find these tend to lower
Mvir further by ~7% and increase cvir by ~5%.Comment: Submitted to the Astrophysical Journal. 19 pages, 14 figure
Bayesian analysis of weak gravitational lensing and Sunyaev-Zel'dovich data for six galaxy clusters
We present an analysis of observations made with the Arcminute Microkelvin
Imager (AMI) and the Canada-France-Hawaii Telescope (CFHT) of six galaxy
clusters in a redshift range of 0.16--0.41. The cluster gas is modelled using
the Sunyaev--Zel'dovich (SZ) data provided by AMI, while the total mass is
modelled using the lensing data from the CFHT. In this paper, we: i) find very
good agreement between SZ measurements (assuming large-scale virialisation and
a gas-fraction prior) and lensing measurements of the total cluster masses out
to r_200; ii) perform the first multiple-component weak-lensing analysis of
A115; iii) confirm the unusual separation between the gas and mass components
in A1914; iv) jointly analyse the SZ and lensing data for the relaxed cluster
A611, confirming our use of a simulation-derived mass-temperature relation for
parameterizing measurements of the SZ effect.Comment: 22 pages, 12 figures, 12 tables, published by MNRA
Definition and validation of a radiomics signature for loco-regional tumour control in patients with locally advanced head and neck squamous cell carcinoma
Purpose: To develop and validate a CT-based radiomics signature for the prognosis of loco-regional tumour control (LRC) in patients with locally advanced head and neck squamous cell carcinoma (HNSCC) treated by primary radiochemotherapy (RCTx) based on retrospective data from 6 partner sites of the German Cancer Consortium - Radiation Oncology Group (DKTK-ROG).
Material and methods: Pre-treatment CT images of 318 patients with locally advanced HNSCC were col-lected. Four-hundred forty-six features were extracted from each primary tumour volume and then fil-tered through stability analysis and clustering. First, a baseline signature was developed from demographic and tumour-associated clinical parameters. This signature was then supplemented by CT imaging features. A final signature was derived using repeated 3-fold cross-validation on the discovery cohort. Performance in external validation was assessed by the concordance index (C-Index). Furthermore, calibration and patient stratification in groups with low and high risk for loco-regional recurrence were analysed.
Results: For the clinical baseline signature, only the primary tumour volume was selected. The final sig-nature combined the tumour volume with two independent radiomics features. It achieved moderatel
Detailed SZ study of 19 LoCuSS galaxy clusters: masses and temperatures out to the virial radius
We present 16-GHz AMI SZ observations of 19 clusters with L_X >7x10^37 W
(h50=1) selected from the LoCuS survey (0.142<z<0.295) and of A1758b, in the
FoV of A1758a. We detect 17 clusters with 5-23sigma peak surface brightnesses.
Cluster parameters are obtained using a Bayesian cluster analysis. We fit
isothermal beta-models to our data and assume the clusters are virialized (with
all the kinetic energy in gas internal energy). Our gas temperature, T_AMI, is
derived from AMI SZ data, not from X-ray spectroscopy. Cluster parameters
internal to r500 are derived assuming HSE. We find: (i) Different gNFW
parameterizations yield significantly different parameter degeneracies. (ii)
For h70 = 1, we find the virial radius r200 to be typically 1.6+/-0.1 Mpc and
the total mass M_T(r200) typically to be 2.0-2.5xM_T(r500).(iii) Where we have
found M_T X-ray (X) and weak-lensing (WL) values in the literature, there is
good agreement between WL and AMI estimates (with M_{T,AMI}/M_{T,WL}
=1.2^{+0.2}_{-0.3} and =1.0+/-0.1 for r500 and r200, respectively). In
comparison, most Suzaku/Chandra estimates are higher than for AMI (with
M_{T,X}/M_{T,AMI}=1.7+/-0.2 within r500), particularly for the stronger
mergers.(iv) Comparison of T_AMI to T_X sheds light on high X-ray masses: even
at large r, T_X can substantially exceed T_AMI in mergers. The use of these
higher T_X values will give higher X-ray masses. We stress that large-r T_SZ
and T_X data are scarce and must be increased. (v) Despite the paucity of data,
there is an indication of a relation between merger activity and SZ
ellipticity. (vi) At small radius (but away from any cooling flow) the SZ
signal (and T_AMI) is less sensitive to ICM disturbance than the X-ray signal
(and T_X) and, even at high r, mergers affect n^2-weighted X-ray data more than
n-weighted SZ, implying significant shocking or clumping or both occur even in
the outer parts of mergers.Comment: 45 pages, 33 figures, 13 tables Accepted for publication in MNRA
Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world
Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic.
Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality.
Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States.
Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis.
Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection