Research and publications

Permanent URI for this collectionhttps://hdl.handle.net/10315/43417

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Now showing 1 - 13 of 13

Access status: Open Access ,
Ionization of the water molecule by electron and positron impact
(IOP Publishing, 2010-01-29) Tóth, István; Campeanu, Radu I.; Chiş, V.; Nagy, Ladislau
Theoretical cross-sections for the ionization of the water molecule by electron and positron impact are presented. The calculations were performed in the framework of the simpler CPE and two distorted-wave models, ES and TS, by employing Gaussian wavefunctions for the description of the target. We found good agreement with the experiment, especially for higher impact energies.
Access status: Open Access ,
Calculations on e⁺ - N₂ Ionization
(Babes-Bolyai University Cluj-Napoca, 2019-12-30) Campeanu, Radu I.; Tóth, István; Nagy, Ladislau
Positron impact direct ionization cross sections are calculated for molecular nitrogen using two distorted wave models. The results are compared with the latest experimental and theoretical data available.
Access status: Open Access ,
Distorted-wave models in positron impact ionization of atoms
(Elsevier, 2002-05) Campeanu, Radu I.; McEachran, R. P.; Stauffer, Allan Daniel
This paper compares the best distorted-wave model results with the most recent experimental data in positron ionization of atomic hydrogen and noble gases. The re-calibration of the experimental measurements yields good agreement with our DCPE5 model at high energies for all the target atoms studied.
Access status: Open Access ,
Few Body Effects in the Electron and Positron Impact Ionization of Atoms
(MDPI, 2021-06-09) Campeanu, Radu I.; Parkin, D. T.
Triple differential cross sections (TDCS) are presented for the electron and positron impact ionization of inert gas atoms in a range of energy sharing geometries where a number of significant few body effects compete to define the shape of the TDCS. Using both positrons and electrons as projectiles has opened up the possibility of performing complementary studies which could effectively isolate competing interactions that cannot be separately detected in an experiment with a single projectile. Results will be presented in kinematics where the electron impact ionization appears to be well understood and using the same kinematics positron cross sections will be presented. The kinematics are then varied in order to focus on the role of distortion, post collision interaction (pci), and interference effects.
Access status: Open Access ,
Electron and Positron Impact Ionization of Molecules
(MDPI, 2024-07-23) Nagy, Ladislau; Tóth, István; Campeanu, Radu I.
We review our group’s most significant results concerning the collision of positrons and electrons with small molecules. Total and triple differential cross sections for the ionization of these targets were calculated in the distorted wave Born approximation using Gaussian molecular orbitals. Different models were tested. The obtained theoretical results reproduced, in most cases, the features observed in the experimental data.
Access status: Open Access ,
Triple-Differential Cross-Section Calculations for Positron Impact Ionization of Argon
(MDPI, 2025-05-04) Campeanu, Radu I.; Bálint, Zsuzsánna; Nagy, Ladislau
Triple-differential cross-sections for the positron impact ionization of argon were calculated using a distorted-wave Born approximation (DWBA) convoluted to the experimental uncertainties. In almost all of the cases studied, our results agree well with the positions and heights of the experimental peaks.
Access status: Open Access ,
Electron Impact Ionization of Krypton at Intermediate Energies
(MDPI, 2026-07-17) Campeanu, Radu I.; Nagy, Ladislau
The distorted-wave approach is applied to electron impact single ionization of krypton. We find that our models CPE4 and DW2 give results which are in fair agreement with the experiments. Both models contain a final state representation which includes the electrostatic repulsion between the ejected electron and the scattered electron.
Access status: Open Access ,
Double differential ionization cross sections of positron impact on argon
(IOP Publishing, 2012-11-05) Campeanu, Radu I.; Alam, M.
The ionization of the 3p orbitals of argon by 100 eV incident positrons is studied with the DWBA approximation.
Access status: Open Access ,
Ionization of the water molecule by electron and positron impact
(IOP Publishing, 2010-01-29) Tóth, I.; Campeanu, Radu I.; Chiş, V.; Nagy, L.
Theoretical cross-sections for the ionization of the water molecule by electron and positron impact are presented. The calculations were performed in the framework of the simpler CPE and two distorted-wave models, ES and TS, by employing Gaussian wavefunctions for the description of the target. We found good agreement with the experiment, especially for higher impact energies.
Access status: Open Access ,
DWBA calculation of positron impact ionization of argon
(IOP Publishing, 2011-01-18) Campeanu, Radu I.; Alam, M.
The ionization of the 3p and 3s orbitals of argon by 200 eV incident positrons is studied with the DWBA approximation. Our TDCS results for the 3p orbital ionization are found to be in good agreement with recent CDW-EIS data.
Access status: Open Access ,
Vertebral compression Fracture Risk in Spinal Metastases Patients Following Stereotactic Body Radiotherapy Using Quantitative Imaging Data and Machine Learning
(Institute of Electrical and Electronics Engineers (IEEE), 2025-08-22) Gulta, Dawit; Chen, Stephen; Klein, Geoff; Ross, Tayler D; Rezkalla, Matthew; Palhares, Daniel M; Burgess, Laura; Detsky, Jay; Sahgal, Arjun; Whyne, Cari M; Hardisty, Michael
Vertebral compression fractures (VCFs) occur in approximately 14% of patients with spinal metastases following treatment with Stereotactic Body Radiotherapy (SBRT). The Spinal Instability Neoplastic Score (SINS) is the current clinical standard for assessing potential mechanical instability in these patients; however, it has several limitations such as it is manually assessed, has an inconsistent relationship with fracture risk and is only semi-quantitative. This study used quantitative CT imaging biomarkers derived from SBRT treatment planning imaging and machine learning models (Logistic Regression, Random Forest, XGBoost, SVM, Gradient Boosting, AdaBoost, Neural Network) to predict vertebral compression fractures (VCF) following SBRT in spinal metastases patients (in 300 thoraco-lumbar vertebrae from 179 patients). The Random Forest model achieved the best performance (sensitivity: 0.64, specificity: 0.76, F1-score: 0.47), showing a 36% improvement in balanced accuracy over SINS. Feature importance analysis identified the quantitative imaging biomarkers, spinal alignment and bone lesion composition (lytic or blastic disease) as the strongest predictors. ML models demonstrated meaningful improvements over existing SINS assessment.
Access status: Open Access ,
The effect of elitist fitness-based selection on the escape from local optima
(Elsevier, 2025-10-11) Chen, Stephen
Random Search is the baseline that a metaheuristic must improve upon to be worth its added complexity. Random Search, in the form of Hill Climbing, cannot escape from local optima. A key claim of many metaheuristics is that they are able to escape from local optima. However, these claims are poorly tested and often based on imprecise definitions of what it means to escape from a local optimum in continuous domain search spaces. A practical and precise definition for an escape from a local optimum is developed. It is then shown how elitist fitness-based selection can lead to the rejection of exploratory search solutions, and this can cause many popular metaheuristics to degrade into (localized) Random Search in their attempts to escape from local optima. The explosion of new metaheuristics has often been just a repeated re-invention of localized Random Search for the key task of escaping from local optima.
Access status: Open Access ,
Simulation Optimization of Operating Room Schedules for Elective Surgeries
(Springer, 2024-07-10) Maltseva, Daria; Chen, Stephen; Lex, Johnathan; Abbas, Aazad; Whyne, Cari
Our specific problem is to create daily schedules of elective surgeries in a multiple operating room setting with the goals of minimizing the amount of overtime incurred and maintaining patient volumes. While surgical durations cannot always be perfectly estimated and vary by procedure and surgeon, our approach relies on leveraging the stochastic nature of surgical durations to simulate each operating day and understand the probability of incurring overtime under a certain schedule of surgeries. The heuristic optimization component of our approach investigates the probabilistic evaluation and strategically re-schedules surgeries. Through experimentation with three optimization techniques, two showed promising results being able to reduce the total number of overtime surgeries by 12–15%, equivalent to approximately 1h of total monthly overtime. Compared to the literature, this approach serves solely as a tool for improving schedules and can be used for supporting decision making at the hospital. Our contribution involves introducing the simulation optimization model and describing the data-driven approach to analyzing the scheduling problem.

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