223 research outputs found
Bifurcated polarization rotation in bismuth-based piezoelectrics
ABO3 perovskite-type solid solutions display a large variety of structural and physical properties, which can be tuned by chemical composition or external parameters such as temperature, pressure, strain, electric, or magnetic fields. Some solid solutions show remarkably enhanced physical properties including colossal magnetoresistance or giant piezoelectricity. It has been recognized that structural distortions, competing on the local level, are key to understanding and tuning these remarkable properties, yet, it remains a challenge to experimentally observe such local structural details. Here, from neutron pair-distribution analysis, a temperature-dependent 3D atomic-level model of the lead-free piezoelectric perovskite Na0.5Bi0.5TiO3 (NBT) is reported. The statistical analysis of this model shows how local distortions compete, how this competition develops with temperature, and, in particular, how different polar displacements of Bi3+ cations coexist as a bifurcated polarization, highlighting the interest of Bi-based materials in the search for new lead-free piezoelectrics
Femtoscopy in Relativistic Heavy Ion Collisions: Two Decades of Progress
Analyses of two-particle correlations have provided the chief means for
determining spatio-temporal characteristics of relativistic heavy ion
collisions. We discuss the theoretical formalism behind these studies and the
experimental methods used in carrying them out. Recent results from RHIC are
put into context in a systematic review of correlation measurements performed
over the past two decades. The current understanding of these results is
discussed in terms of model comparisons and overall trends.Comment: 49 pages, 16 figures; to appear in Annual Review of Nuclear and
Particle Science; final version includes minor updates in text, a few
references added, and two figures updated; Figures and numerical data tables
available at http://www.physics.ohio-state.edu/~lisa/FemtoscopyReview2005
Transport model analysis of the transverse momentum and rapidity dependence of pion interferometry at SPS energies
Based on the UrQMD transport model, the transverse momentum and the rapidity
dependence of the Hanbury-Brown-Twiss (HBT) radii , , as well
as the cross term at SPS energies are investigated and compared with
the experimental NA49 and CERES data. The rapidity dependence of the ,
, is weak while the is significantly increased at large
rapidities and small transverse momenta. The HBT "life-time" issue (the
phenomenon that the calculated value is larger than
the correspondingly extracted experimental data) is also present at SPS
energies.Comment: 17 pages, 11 figure
System-size dependence of the pion freeze-out volume as a potential signature for the phase transition to a Quark Gluon Plasma
Hanburry-Brown-Twiss (HBT) correlation functions and radii of negatively
charged pions from C+C, Si+Si, Cu+Cu, and In+In at lower RHIC/SPS energies are
calculated with the UrQMD transport model and the CRAB analyzing program. We
find a minimum in the excitation function of the pion freeze-out volume at low
transverse momenta and around GeV which can be related to
the transition from hadronic to string matter (which might be interpreted as a
pre-cursor of the QGP). The existence of the minimum is explained by the
competition of two mechanisms of the particle production, resonance decays and
string formation/fragmentation.Comment: 12 pages, 4 fig
Imaging Sources with Fast and Slow Emission Components
We investigate two-proton correlation functions for reactions in which fast
dynamical and slow evaporative proton emission are both present. In such cases,
the width of the correlation peak provides the most reliable information about
the source size of the fast dynamical component. The maximum of the correlation
function is sensitive to the relative yields from the slow and fast emission
components. Numerically inverting the correlation function allows one to
accurately disentangle fast dynamical from slow evaporative emission and
extract details of the shape of the two-proton source.Comment: 13 pages, 4 figure
Prediction of clinically significant cancer using radiomics features of pre-biopsy of multiparametric MRi in men suspected of prostate cancer
SIMPLE SUMMARY: Radiomics is the field of computer-based medical image analysis that incorporates various radiological imaging features, such as texture and shape parameters, from scans to derive algorithms. These mathematical algorithms have the potential to predict the biological characteristics of disease. In this study, we obtained quantitative imaging texture features of pre-biopsy multiparametric MRI of men suspected of prostate cancer and extracted from the T2WI and ADC images focusing on gray-level co-occurrence matrices (GLCM). These were correlated with the Gleason score of the histopathology of radical prostatectomy specimen, including the prediction of clinically significant prostate cancer. The knowledge gained through this prospective protocol-based study should facilitate establishing that GLCM texture features alone can be used as a biomarker for predicting the presence of clinically significant PCa. ABSTRACT: Background: Texture features based on the spatial relationship of pixels, known as the gray-level co-occurrence matrix (GLCM), may play an important role in providing the accurate classification of suspected prostate cancer. The purpose of this study was to use quantitative imaging parameters of pre-biopsy multiparametric magnetic resonance imaging (mpMRI) for the prediction of clinically significant prostate cancer. Methods: This was a prospective study, recruiting 200 men suspected of having prostate cancer. Participants were imaged using a protocol-based 3T MRI in the pre-biopsy setting. Radiomics parameters were extracted from the T2WI and ADC texture features of the gray-level co-occurrence matrix were delineated from the region of interest. Radical prostatectomy histopathology was used as a reference standard. A Kruskal–Wallis test was applied first to identify the significant radiomic features between the three groups of Gleason scores (i.e., G1, G2 and G3). Subsequently, the Holm–Bonferroni method was applied to correct and control the probability of false rejections. We compared the probability of correctly predicting significant prostate cancer between the explanatory GLCM radiomic features, PIRADS and PSAD, using the area under the receiver operation characteristic curves. Results: We identified the significant difference in radiomic features between the three groups of Gleason scores. In total, 12 features out of 22 radiomics features correlated with the Gleason groups. Our model demonstrated excellent discriminative ability (C-statistic = 0.901, 95%CI 0.859–0.943). When comparing the probability of correctly predicting significant prostate cancer between explanatory GLCM radiomic features (Sum Variance T2WI, Sum Entropy T2WI, Difference Variance T2WI, Entropy ADC and Difference Variance ADC), PSAD and PIRADS via area under the ROC curve, radiomic features were 35.0% and 34.4% more successful than PIRADS and PSAD, respectively, in correctly predicting significant prostate cancer in our patients (p < 0.001). The Sum Entropy T2WI score had the greatest impact followed by the Sum Variance T2WI. Conclusion: Quantitative GLCM texture analyses of pre-biopsy MRI has the potential to be used as a non-invasive imaging technique to predict clinically significant cancer in men suspected of having prostate cancer
Space-time evolution and HBT analysis of relativistic heavy ion collisions in a chiral SU(3) x SU(3) model
The space-time dynamics and pion-HBT radii in central heavy ion-collisions at
CERN-SPS and BNL-RHIC are investigated within a hydrodynamic simulation. The
dependence of the dynamics and the HBT-parameters on the EoS is studied with
different parametrisations of a chiral SU(3) sigma-omega model. The
selfconsistent collective expansion includes the effects of effective hadron
masses, generated by the nonstrange and strange scalar condensates. Different
chiral EoS show different types of phase transitions and even a crossover. The
influence of the order of the phase transition and of the difference in the
latent heat on the space-time dynamics and pion-HBT radii is studied. A small
latent heat, i.e. a weak first-order chiral phase transition, or even a smooth
crossover leads to distinctly different HBT predictions than a strong first
order phase transition. A quantitative description of the data, both at SPS
energies as well as at RHIC energies, appears difficult to achieve within the
ideal hydrodynamical approach using the SU(3) chiral EoS. A strong first-order
quasi-adiabatic chiral phase transition seems to be disfavored by the pion-HBT
data from CERN-SPS and BNL-RHIC
A new cross term in the two-particle Hanbury-Brown-Twiss correlation function
Using two specific models and a model-independent formalism, we show that in
addition to the usual quadratic ``side'', ``out'' and ``longitudinal'' terms, a
previously neglected ``out-longitudinal'' cross term arises naturally in the
exponent of the two-particle correlator. Since its effects can be easily
observed, such a term should be included in any experimental fits to
correlation data. We also suggest a method of organizing correlation data using
rapidity rather than longitudinal momentum differences since in the former
every relevant quantity is longitudinally boost invariant.Comment: 11 pages, RevTeX 3.0 and 2 postscript figure
Solution of the RHIC HBT puzzle with Gaussian initial conditions
It is argued that the consistent description of the transverse-momentum
spectra, elliptic flow, and the HBT radii in the relativistic heavy-ion
collisions studied at RHIC may be obtained within the hydrodynamic model if one
uses the Gaussian profile for the initial energy density in the transverse
plane. Moreover, we show that the results obtained in the scenario with an
early start of hydrodynamics (at the proper time tau0 = 0.25 fm) are
practically equivalent to the results obtained in the model where the
hydrodynamics is preceded by the free-streaming stage of partons (in the proper
time interval 0.25 fm < tau < 1 fm) which suddenly equilibrate and with the
help of the Landau matching conditions are transformed into the hydrodynamic
regime (at the proper time tau0 = 1 fm).Comment: talk presented by WF at SQM2008 Conferenc
Model-independent source imaging using two-pion correlations in 2 to 8A GeV Au + Au collisions
We report a particle source imaging analysis based on two-pion correlations
in high multiplicity Au + Au collisions at beam energies between 2 and 8A GeV.
We apply the imaging technique introduced by Brown and Danielewicz, which
allows a model-independent extraction of source functions with useful accuracy
out to relative pion separations of about 20 fm. The extracted source functions
have Gaussian shapes. Values of source functions at zero separation are almost
constant across the energy range under study. Imaging results are found to be
consistent with conventional source parameters obtained from a multidimensional
HBT analysis.Comment: 4 pages, 3 figure
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