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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Stent-Retriever Thrombectomy and Rescue Treatment of M1 Occlusions Due to Underlying Intracranial Atherosclerotic Stenosis: Cohort Analysis and Review of the Literature

Background and Purpose: Data on the management of large vessel occlusion in patients with anterior circulation acute ischemic stroke (AIS) due to underlying intracranial stenosis are scarce. The aim of this retrospective study was to compare endovascular treatment and outcome in AIS patients with and without underlying stenosis of the M1 segment. Materials and Methods: A total of 533 acute stroke patients with an isolated M1 occlusion who underwent mechanical thrombectomy between 02/2010 and 08/2017 were included. Underlying intracranial atherosclerotic stenosis (ICAS) was present in 10 patients (1.9%), whereas 523 patients (98.1%) had an embolic occlusion without stenosis. Results: There was no difference in age, admission National Institutes of Health Stroke Scale, risk factors, Alberta stroke program early CT score or collaterals between the groups. Procedure time (155 vs 40 min, P = 0.001) was significantly longer in the ICAS group where rescue stent-angioplasty was performed in all patients. There was no statistical difference in final modified thrombolysis in cerebral infarction score between both groups (70 vs 88%, P = 0.115). Favorable outcome (modified Rankin Scale ≤ 2) at 90 days was less frequent in patients with ICAS than in the embolic group (0 vs 49.4%, P = 0.004). The mortality rate tended to be higher in the ICAS group (44.4 vs 19.4%, P = 0.082). Conclusion: In patients with AIS, rescue therapy with stent placement to treat underlying ICAS of the M1 segment is technically feasible; however, in our study, a significantly lower rate of favorable outcome was observed in these patients compared to those with thromboembolic M1 occlusions. Level of Evidence: Level 3, non-randomized controlled study.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

SU-F-J-49: IGRT Credentialing in NCTN Trials

Purpose: To make Image Guided Radiation Therapy (IGRT) credentialing a more unified, consistent and efficient process across the entire National Clinical Trial Network (NCTN). Methods: IGRT plays a role in several advanced NCTN trials. Previously an institution had to be IGRT credentialed for each protocol. When institutions were allowed to use previous credentials for new protocols it was limited to the same disease site as the original credentialing. The credentialing was analyzed by the physics PI of the protocol. We consulted with several of these physicists to determine what is important to consider when reviewing submissions and to learn ways to apply credentialing more broadly. Results: For trials open in 2016, IGRT credentialing can be simplified to cover either boney anatomy or soft tissue. This revised credentialing will cover all disease sites based on the type of anatomy, unless otherwise stated within the protocol. Institutions will submit will complete an online questionnaire about their IGRT procedures. Boney anatomy requirements will include submission of data from 2 sequential fraction of both a patient aligned with boney anatomy and pelvic patient. Soft tissue will require similar submissions for a patient aligned using soft tissue and a pelvic patient. Institutions will only be required to submit the pelvic patient once. Data should be in DICOM format and includes planning CT set, RT structure set, RT plan file, RT dose file, localization images and spatial registration file (if available). Reviews will be done by IROC-Houston staff who will continue to provide feedback to the sites. Conclusion: This revised IGRT credentialing process will bring consistency, a savings in time and effort for both the IROC Houston QA office and to those institutions wanting to be credentialed to participate in NCTN Trials. Sponsored by NIH/NCI CA10953.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Steady state effects in a two-pulse diffusion-weighted sequence

In conventional nuclear magnetic resonance (NMR) diffusion measurements a significant amount of experimental time is used up by magnetization recovery, serving to prevent the formation of the steady state, as in the latter case the manifestation of diffusion is modulated by multiple applications of the pulse sequence and conventional diffusion coefficient inference procedures are generally not applicable. Here, an analytical expression for diffusion-related effects in a two-pulse NMR experiment (e.g., pulsed-gradient spin echo) in the steady state mode (with repetition times less than the longitudinal relaxation time of the sample) is derived by employing a Fourier series expansion within the solution of the Bloch-Torrey equations. Considerations are given for the transition conditions between the full relaxation and the steady state experiment description. The diffusion coefficient of a polymer solution (polyethylene glycol) is measured by a two-pulse sequence in the full relaxation mode and for a range of repetition times, approaching the rapid steady state experiment. The precision of the fitting employing the presented steady state solution by far exceeds that of the conventional fitting. Additionally, numerical simulations are performed yielding results strongly supporting the proposed description of the NMR diffusion measurements in the steady state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Applying a predictive modeling methodology to a radiation transport inverse problem - 25588

In this paper, the predictive modeling of coupled multiphysics systems (PM-CMPS) procedure, developed by Cacuci and embodied in the software package MULTIPRED, has been applied to determine unknown parameters of a radioactive system from its gamma-ray and neutron signature. PM-CMPS has been integrated in two different ways with the inverse transport code INVERSE to determine the parameters. The first uses PM-CMPS in the inverse mode to directly estimate the parameters while the second mode uses a traditional nonlinear optimization routine and has PMCMPS complete a final iteration to estimate the uncertainty in the parameter best estimates. A test problem has been created and used to test both methods for varying numbers and types of responses and parameters. The first method was capable of accurately determining parameters but had a number of drawbacks. The second method functioned well at determining the correct parameter values in cases with limited numbers of parameters. (authors)

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

The Effect of Stent Cell Geometry on Carotid Stenting Outcomes

PurposeThe aim of this study was to investigate the effect of stent cell geometry on midterm results of carotid artery stenting (CAS).Materials and MethodOne hundred fifty-five patients underwent CAS between February 2010 and December 2012. Ninety-one open- and 84 closed-cell stents were used in this non-randomized, retrospective study. Periprocedural complications were defined as the ones happened during the procedure or within 30 days afterwards. Starting from the 6th month after the procedure, in-stent restenosis was detected with multidetector computed tomography angiography and classified into four groups from focal restenosis to occlusion.ResultsEleven complications were encountered in the periprocedural period (four on the open- and seven on the closed-cell group). Total complication rate was 6.3 % (11/175). No significant difference was detected in terms of periprocedural complications between two groups (p = 0.643). There was statistically significant difference between stent design groups in regard to radiological findings (p = 0.002). Sixteen of open-cell stents and three of closed-cell stents had focal restenosis. One closed-cell stent had diffuse proliferative restenosis and one open-cell stent had total occlusion.ConclusionIn-stent restenosis was more common in open-cell stent group, which have larger free cell area than closed-cell stents. Although our radiologic findings promote us to use closed-cell design if ‘possible’, no difference was detected in terms of clinical outcomes.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

GPU accelerated flow solver for direct numerical simulation of turbulent flows

Graphical processing units (GPUs), characterized by significant computing performance, are nowadays very appealing for the solution of computationally demanding tasks in a wide variety of scientific applications. However, to run on GPUs, existing codes need to be ported and optimized, a procedure which is not yet standardized and may require non trivial efforts, even to high-performance computing specialists. In the present paper we accurately describe the porting to CUDA (Compute Unified Device Architecture) of a finite-difference compressible Navier–Stokes solver, suitable for direct numerical simulation (DNS) of turbulent flows. Porting and validation processes are illustrated in detail, with emphasis on computational strategies and techniques that can be applied to overcome typical bottlenecks arising from the porting of common computational fluid dynamics solvers. We demonstrate that a careful optimization work is crucial to get the highest performance from GPU accelerators. The results show that the overall speedup of one NVIDIA Tesla S2070 GPU is approximately 22 compared with one AMD Opteron 2352 Barcelona chip and 11 compared with one Intel Xeon X5650 Westmere core. The potential of GPU devices in the simulation of unsteady three-dimensional turbulent flows is proved by performing a DNS of a spatially evolving compressible mixing layer.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

UAVs for Radiological Monitoring: Determining Ideal Operational Parameters From GEANT4 Simulations - 18025

Owing in no small part to the enormous advances in radiation detector technology (size, sensitivity and spectral-resolution), there has been an increased drive and requirement to accurately map both the spatial extent and magnitude of radiological contamination at the greatest possible spatial resolutions. To undertake this, a range of different methods have been devised and include the use of cars and human, but also planes (and more recently) unmanned aerial vehicles (UAVs). However, critical to the remote sensing using such UAVs in contrast to ground-based sensing, is (i) the selection of the ideal operational parameters to attain the best on-ground resolution in addition to, (ii) understanding the correct normalisation procedures and other influences on results that surveys at these reduced altitudes might present. Resulting from earlier works, through employing combined modelling and experimental data, the optimal height for a UAV survey using the more realistic 'area' radioactive source term (opposed to an infinitely-small 'point-source') is determined to be approximately 5 m - suitably maximizing cross detector counts. At greater altitudes than this, the influence of variations in neighboring topology / topography and nearby structures are observed to be negligible. However, at this and further-reduced altitudes (where optimal count-rates exists), small height-related variations are observed to result, and impact considerably on the complexity of the data normalisation. Whilst not occurring as a tool to entirely replace ground-based surveys, UAV systems are able to perform in challenging or dangerous environments, inadvisable or problematic to send humans. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2014

Sci—Thur PM: Imaging — 06: Canada's National Computed Tomography (CT) Survey

The value of computed tomography (CT) in medical imaging is reflected in its' increased use and availability since the early 1990's; however, given CT's relatively larger exposures (vs. planar x-ray) greater care must be taken to ensure that CT procedures are optimised in terms of providing the smallest dose possible while maintaining sufficient diagnostic image quality. The development of CT Diagnostic Reference Levels (DRLs) supports this process. DRLs have been suggested/supported by international/national bodies since the early 1990's and widely adopted elsewhere, but not on a national basis in Canada. Essentially, CT DRLs provide guidance on what is considered good practice for common CT exams, but require a representative sample of CT examination data to make any recommendations. Canada's National CT Survey project, in collaboration with provincial/territorial authorities, has collected a large national sample of CT practice data for 7 common examinations (with associated clinical indications) of both adult and pediatric patients. Following completion of data entry into a common database, a survey summary report and recommendations will be made on CT DRLs from this data. It is hoped that these can then be used by local regions to promote CT practice optimisation and support any dose reduction initiatives.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Percutaneous Radiofrequency Ablation of Lung Cancer Presenting as Ground-Glass Opacity

PurposeWe retrospectively evaluated the outcomes of lung cancer patients presenting with ground-glass opacity (GGO) who received radiofrequency ablation (RFA).MethodsSixteen patients (5 men and 11 women; mean age, 72.6 years) with 17 lung cancer lesions showing GGO (mean long axis diameter, 1.6 cm) underwent a total of 20 percutaneous computed tomography (CT) fluoroscopy-guided RFA sessions, including three repeated sessions for local progression. Lung cancer with GGO was defined as a histologically confirmed malignant pulmonary lesion with a GGO component accounting for >50 % of the lesion on high-resolution CT. Procedure outcomes were evaluated.ResultsThere were no major complications. Pneumothorax occurred in 15 of 20 treatment sessions: 14 were asymptomatic, and 1 required chest tube placement but resolved satisfactorily within 48 h. Minor pulmonary hemorrhage occurred in two and mild pneumonitis in one. The median tumor follow-up period was 61.5 (range 6.1–96.6) months. The effectiveness rates of the primary and secondary techniques were 100 and 100 % at 1 year, 93.3 and 100 % at 2 years, and 78.3 and 92.3 % at 3 years, respectively. The median patient follow-up period was 65.6 (range 6.1–96.6) months. One patient died owing to recurrent other cancer 11.7 months after RFA, whereas the other 15 remained alive. Overall survival and disease-specific survival rates were 93.3 and 100 % at 1 year and 93.3 and 100 % at 5 years, respectively.ConclusionsRFA for lung cancer with GGO was safe and effective, and resulted in promising survival rates.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Long-Term Evaluation of Percutaneous Groin Access for EVAR

Background: Percutaneous endovascular aneurysm repair (PEVAR) has been shown to have high success rates, shorter operating times and length of stay compared to open access. However, there exists a lack of long-term follow-up data on these patients, and questions remain regarding longer-term outcomes. This study aims to assess the long-term complications and evolution of accessed vessels post-PEVAR. Methods: Sixty-one cases of bilateral PEVAR (122 groins) with > 36 months follow-up were analysed. Vessel diameter, calcification, dissection, lymphocele, pseudoaneurysm and thrombus formation were reviewed at 30th day and at the most recent follow-up CT. Notes were reviewed for groin infections, haematomas and nerve injury. Complications were considered ‘major’ if they required intervention or treatment. Results: Mean follow-up time from procedure to most recent scan was 49.9 months. There were no major short- or long-term complications. The early complication rate was 9.8%, with six pseudoaneurysms, four dissections, one thrombus, one nerve injury and no lymphoceles, haematomas or groin infections. The long-term complication rate was 0.8%, with only one pseudoaneurysm. The remainder of early complications resolved naturally without intervention. Accessed vessel showed significantly (P ≤ 0.05) increased diameter and calcification between 30th day and last follow-up scan. Conclusion: This study provides the largest clinical cohort and the longest mean follow-up time reported in the literature and demonstrates the long-term safety of PEVAR. PEVAR has a very low long-term complication rate, without any major complications in our cohort. The accessed common femoral arteries do not show stenosis or thrombosis. Minor short-term complications appear to gradually resolve without intervention. Larger multi-centre studies are recommended.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Acoustic radiation force on a rigid elliptical cylinder in plane (quasi)standing waves

The acoustic radiation force on a 2D elliptical (non-circular) cylinder centered on the axis of wave propagation of plane quasi-standing and standing waves is derived, based on the partial-wave series expansion (PWSE) method in cylindrical coordinates. A non-dimensional acoustic radiation force function, which is the radiation force per unit length, per characteristic energy density and per unit cross-sectional surface of the ellipse, is defined in terms of the scattering coefficients that are determined by applying the Neumann boundary condition for an immovable surface. A system of linear equations involving a single numerical integration procedure is solved by matrix inversion. Numerical simulations showing the transition from the quasi-standing to the (equi-amplitude) standing wave behaviour are performed with particular emphasis on the aspect ratio a/b, where a and b are the ellipse semi-axes, as well as the dimensionless size parameter kb (where k is the wavenumber), without the restriction to a particular range of frequencies. It is found that at high kb values > 1, the radiation force per length with broadside incidence is larger, whereas the opposite situation occurs in the long-wavelength limit (i.e., kb < 1). The results are particularly relevant in acoustic levitation of elliptical cylinders, the acoustic stabilization of liquid columns in a host medium, acousto-fluidics devices, and other particle dynamics applications to name a few. Moreover, the formalism presented here may be effectively applied to compute the acoustic radiation force on other 2D surfaces of arbitrary shape such as super-ellipses, Chebyshev cylindrical particles, or other non-circular geometries.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Does Drug-Eluting Bead TACE Enhance the Local Effect of IRE? Imaging and Histopathological Evaluation in a Porcine Model

Objectives: We conducted an in vivo trial on swine to compare the ablation volumes of irreversible electroporation (IRE) followed by drug-eluting beads transarterial chemoembolization (DEB-TACE) versus IRE only. Materials and Methods: Nine swine underwent CT-guided IRE in one liver lobe and IRE immediately followed by DEB-TACE in a different liver lobe. For DEB-TACE, 100–300 µm beads (DC-Beads{sup ®}) were loaded with 50 mg doxorubicin. For IRE, the NanoKnife{sup ®} was used employing two electrodes according to the vendor’s protocol. Imaging follow-up was performed including CT-based lesion volume assessment using contrast-enhanced CT (venous phase) on days 1, 3, and 7 after the procedure. Three animals were killed for histopathological analysis after each follow-up. Results: Ablation volumes in CT in the IRE + DEB-TACE group were 15.4 ± 10.5 ml on day 1, 8.7 ± 5.6 ml on day 3, and 1.6 ± 0.7 ml on day 7. In the IRE group, the corresponding values were 5.2 ± 5.2 ml on day 1, 1.0 ± 1.2 ml on day 3, and 0.1 ± 0.1 ml on day 7. On day 1 and day 3, ablation volumes of IRE + TACE group were significantly larger than in the IRE group (p < 0.05). 96% of beads were depicted in or around ablative lesions. 69% of these beads were found in the surrounding hemorrhagic infiltration and 31% within the ablative lesion itself. Conclusions: Combination of IRE immediately followed by DEB-TACE resulted in larger ablation volumes compared to IRE alone, suggesting that local efficacy of IRE can be enhanced by post-IRE DEB-TACE.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Morphometric Atlas Selection for Automatic Brachial Plexus Segmentation

Purpose: The purpose of this study was to determine the effects of atlas selection based on different morphometric parameters, on the accuracy of automatic brachial plexus (BP) segmentation for radiation therapy planning. The segmentation accuracy was measured by comparing all of the generated automatic segmentations with anatomically validated gold standard atlases developed using cadavers. Methods and Materials: Twelve cadaver computed tomography (CT) atlases (3 males, 9 females; mean age: 73 years) were included in the study. One atlas was selected to serve as a patient, and the other 11 atlases were registered separately onto this “patient” using deformable image registration. This procedure was repeated for every atlas as a patient. Next, the Dice and Jaccard similarity indices and inclusion index were calculated for every registered BP with the original gold standard BP. In parallel, differences in several morphometric parameters that may influence the BP segmentation accuracy were measured for the different atlases. Specific brachial plexus-related CT-visible bony points were used to define the morphometric parameters. Subsequently, correlations between the similarity indices and morphometric parameters were calculated. Results: A clear negative correlation between difference in protraction-retraction distance and the similarity indices was observed (mean Pearson correlation coefficient = −0.546). All of the other investigated Pearson correlation coefficients were weak. Conclusions: Differences in the shoulder protraction-retraction position between the atlas and the patient during planning CT influence the BP autosegmentation accuracy. A greater difference in the protraction-retraction distance between the atlas and the patient reduces the accuracy of the BP automatic segmentation result.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Role and Effectiveness of Percutaneous Arterial Embolization in Hemodynamically Unstable Patients with Ruptured Splanchnic Artery Pseudoaneurysms

PurposeTo assess the role and effectiveness of percutaneous arterial embolization (TAE) in patients with hemodynamic instability due to hypovolemic shock secondary to ruptured splanchnic artery pseudoaneurysms (SAPA).Materials and MethodsSeventeen patients (11 men, 6 women; mean age, 53 years) with hemodynamic instability (systolic blood pressure <90 mmHg) due to hypovolemic shock secondary to ruptured SAPA were treated by TAE. Clinical files, multidetector row computed tomography angiography, and angiographic examinations along with procedure details were reviewed.ResultsSeventeen SAPAs were present, predominantly located on gastroduodenal or pancreatic arteries (9/17; 53 %). Angiography showed extravasation of contrast medium from SAPA in 15/17 patients (88 %). Technical success rate of TAE was 100 %. TAE was performed using metallic coils in all patients (100 %), in association with gelatin sponge in 5/17 patients (29 %). TAE allowed controlling the bleeding and returning to normal hemodynamic status in 16/17 patients (94 %). In 1/17 patient (6 %), surgery was needed to definitively control the bleeding. The mortality and morbidity rate of TAE at 30 days were 0 and 12 %, respectively. Morbidity consisted in coil migration in 1/17 patient (6 %) and transient serum liver enzyme elevation in 1/17 patient (6 %).ConclusionTAE is an effective and safe treatment option for ruptured SAPA in hemodynamically unstable patients, with a success rate of 94 %. Our results suggest that TAE should be the favored option in patients with hemodynamic instability due to ruptured SAPA.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2019

Comparative Analysis of Intra-arterial Cone-Beam Versus Conventional Computed Tomography During Hepatic Arteriography for Transarterial Chemoembolization Planning

Purpose: To compare the imaging characteristics of intra-arterial cone-beam computed tomography during hepatic arteriography (CBCTHA) versus intra-arterial computed tomography during hepatic arteriography (CTHA) for intraprocedural transarterial chemoembolization (TACE) planning. Materials and Methods: This single-institution retrospective study included 144 patients (96 men, mean age 67.9 years; 48 women, mean age 62.3 years) who underwent 181 TACE sessions between January 2015 and July 2017. Intraprocedural CBCTHA (111 procedures) or CTHA (70 procedures) was performed for TACE planning. Reformatted maximum intensity projection CBCTHA and CTHA images were reviewed by two radiologists and classified using an ordinal scoring system (for tumor identification, tumor feeder vessel identification, and streaking artifact) and a binary scoring system (for the presence of breathing motion artifact and field of view encompassing the entire liver). Data were analyzed using an F test and a z-score test. Results: There were no significant differences in demographic and tumor characteristics between the CBCTHA and CTHA patient cohorts. CTHA was superior to CBCTHA for tumor identification (P < .0001), tumor feeder vessel identification (P < .05), streaking artifact (P < .0001), and field of view encompassing the entire liver (P < .0001). There was a trend toward a lower frequency of breathing motion artifact with CTHA than with CBCTHA (1.4% vs. 10%; P = .057). Conclusion: CTHA provides improved clinical relevant imaging information compared to CBCTHA for intraprocedural TACE planning. Level of Evidence: Level III, retrospective comparative study.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Procedure design of F and B operation and its impact on the risk of a nuclear power plant - 168

A feed and bleed (F and B) operation is an operator's emergency task to remove core heat from a reactor coolant system by bleeding coolant from the pressurizer, and feeding makeup water through safety injection systems under the loss of all feedwater condition. Even though the F and B operation is an important task having a significant impact on the risk of a nuclear power plant, there is a high uncertainty regarding its modeling and analysis in a PSA. This paper introduces a study on the design of an operational strategy for an F and B operation and its impact on the risk of a nuclear power plant in Korea. An intensive support analysis was conducted to understand the plant behavior and revise the success criteria for the HRA of the F and B operation. A human performance analysis on the emergency tasks was also conducted using a training simulator to generate the operator's performance time for the F and B operation. We revised the PSA model and updated the risk of the reference plant, which shows that the risk of the revised model is much higher than that of the existing model. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2016

Composite vibrational spectroscopy of the group 12 difluorides: ZnF{sub 2}, CdF{sub 2}, and HgF{sub 2}

The vibrational spectra of group 12 difluorides, MF{sub 2} (M = Zn, Cd, Hg), were investigated via coupled cluster singles, doubles, and perturbative triples, CCSD(T), including core correlation, with a series of correlation consistent basis sets ranging in size from triple-zeta through quintuple-zeta quality, which were then extrapolated to the complete basis set (CBS) limit using a variety of extrapolation procedures. The explicitly correlated coupled cluster method, CCSD(T)-F12b, was employed as well. Although exhibiting quite different convergence behavior, the F12b method yielded the CBS limit estimates closely matching more computationally expensive conventional CBS extrapolations. The convergence with respect to basis set size was examined for the contributions entering into composite vibrational spectroscopy, including those from higher-order correlation accounted for through the CCSDT(Q) level of theory, second-order spin-orbit coupling effects assessed within four-component and two-component relativistic formalisms, and vibrational anharmonicity evaluated via a perturbative treatment. Overall, the composite results are in excellent agreement with available experimental values, except for the CdF{sub 2} bond-stretching frequencies compared to spectral assignments proposed in a matrix isolation infrared and Raman study of cadmium difluoride vapor species [Loewenschuss et al., J. Chem. Phys. 50, 2502 (1969); Givan and Loewenschuss, J. Chem. Phys. 72, 3809 (1980)]. These assignments are called into question in the light of the composite results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

THE EFFECTS OF PATCHY REIONIZATION ON SATELLITE GALAXIES OF THE MILKY WAY

We combine the high-resolution Aquarius simulations with three-dimensional models of reionization based on the initial density field of the Aquarius parent simulation, Millennium-II, to study the impact of patchy reionization on the faint satellite population of Milky Way halos. Because the Aquarius suite consists of zoom-in simulations of halos in the Millennium-II volume, we follow the formation of substructure and the growth of reionization bubbles due to the larger environment simultaneously, and thereby determine the reionization redshifts of satellite candidates. We do this for four different reionization models and also compare results to instantaneous reionization. Using a simple procedure for selecting satellites and assigning luminosities in the simulations, we compare the resulting satellite populations. We find that the overall number of satellites depends sensitively on the reionization model, with a factor of 3-4 variation between the four models for a given host halo, although the difference is entirely in the population of faint satellites (M{sub V} > -10). In addition, we find that for a given reionization model the total number of satellites differs by 10%-20% between the patchy and homogeneous scenarios, provided that the redshift is chosen appropriately for the instantaneous case. However, the halo-halo scatter from the six Aquarius halos is large, up to a factor of 2-3, and so is comparable to the difference between reionization scenarios. In order to use the population of faint dwarf galaxies around the Milky Way as a probe of the local reionization history, it is necessary to first better understand the general distribution of substructure around Milky Way-mass halos.

79 ASTRONOMY AND ASTROPHYSICS↗