@misc{WagnerKrenkelDoenitzetal., author = {Wagner, Thomas and Krenkel, Lars and D{\"o}nitz, Christian and Brawanski, Alexander}, title = {Influence of CFD Strategy on WSS and OSI Determination for Intracranial Aneurysm Rupture Assessment}, series = {25th Congress of the European Society of Biomechanics, July 7-10, 2019, Vienna, Austria}, journal = {25th Congress of the European Society of Biomechanics, July 7-10, 2019, Vienna, Austria}, language = {en} } @misc{Krenkel, author = {Krenkel, Lars}, title = {Relevanz von Aerosolen im klinischen Kontext}, series = {Innovationstag Hygiene 2021, Continental Arena, Regensburg, Deutschland}, journal = {Innovationstag Hygiene 2021, Continental Arena, Regensburg, Deutschland}, language = {de} } @article{TauwaldErzingerQuadrioetal., author = {Tauwald, Sandra Melina and Erzinger, Florian and Quadrio, Maurizio and R{\"u}tten, Markus and Stemmer, Christian and Krenkel, Lars}, title = {Tomo-PIV in a patient-specific model of human nasal cavities: a methodological approach}, series = {Measurement Science and Technology}, volume = {35}, journal = {Measurement Science and Technology}, number = {5}, publisher = {IOP Publishing}, doi = {10.1088/1361-6501/ad282c}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-70393}, abstract = {The human nose serves as the primary gateway for air entering the respiratory system and plays a vital role in breathing. Nasal breathing difficulties are a significant health concern, leading to substantial healthcare costs for patients. Understanding nasal airflow dynamics is crucial for comprehending respiratory mechanisms. This article presents a detailed study using tomo-Particle Image Velocimetry (PIV) to investigate nasal airflow dynamics while addressing its accuracy. Embedded in the OpenNose project, the work described aims to provide a validation basis for different numerical approaches to upper airway flow. The study includes the manufacturing of a transparent silicone model based on a clinical CT scan, refractive index matching to minimize optical distortions, and precise flow rate adjustments based on physiological breathing cycles. This method allows for spatial high-resolution investigations in different regions of interest within the nasopharynx during various phases of the breathing cycle. The results demonstrate the accuracy of the investigations, enabling detailed analysis of flow structures and gradients. This spatial high-resolution tomo-PIV approach provides valuable insights into the complex flow phenomena occurring during the physiological breathing cycle in the nasopharynx. The study's findings contribute to advancements in non-free-of-sight experimental flow investigation of complex cavities under nearly realistic conditions. Furthermore, reliable and accurate experimental data is crucial for properly validating numerical approaches that compute this patient-specific flow for clinical purposes.}, language = {en} } @misc{AuerKrutschRenkawitzetal., author = {Auer, Simon and Krutsch, Werner and Renkawitz, Tobias and Kubowitsch, Simone and S{\"u}ß, Franz and Dendorfer, Sebastian}, title = {Effect of mental demand on leg loading in highly dynamic motion}, series = {AnyBody online Webinar, Oct 2020}, journal = {AnyBody online Webinar, Oct 2020}, abstract = {Football players have a high risk of leg muscle injuries, especially when exposed to mental stress. Injuries to muscles of the thigh are common in amateur and professional football, representing almost a third of all injuries. These injuries occur primarily in non-contact situations and from overuse. They can lead to a range of costs, including financial costs associated with treatment as well as those associated with long-term recovery, and absence from training and/or competition. Further, there is a high risk of injury recurrence and subsequent injury.}, language = {en} } @article{LingelHausPaschkeetal., author = {Lingel, Maximilian P. and Haus, Moritz and Paschke, Lukas and Foltan, Maik and Lubnow, Matthias and Gruber, Michael and Krenkel, Lars and Lehle, Karla}, title = {Clinical relevance of cell-free DNA during venovenous extracorporeal membrane oxygenation}, series = {Artificial organs}, volume = {47}, journal = {Artificial organs}, number = {11}, publisher = {Wiley}, issn = {1525-1594}, doi = {10.1111/aor.14616}, pages = {1720 -- 1731}, abstract = {BACKGROUND: Thrombosis remains a critical complication during venovenous extracorporeal membrane oxygenation (VV ECMO). The involvement of neutrophil extracellular traps (NETs) in thrombogenesis has to be discussed. The aim was to verify NETs in the form of cell-free DNA (cfDNA) in the plasma of patients during ECMO. METHODS: A fluorescent DNA-binding dye (QuantifFluor®, Promega) was used to detect cell-free DNA in plasma samples. cfDNA concentrations from volunteers (n = 21) and patients (n = 9) were compared and correlated with clinical/technical data before/during support, ECMO end and time of a system exchange. RESULTS: Before ECMO, patients with a median (IQR) age of 59 (51/63) years, SOFA score of 11 (10/15), and ECMO run time of 9.0 (7.0/19.5) days presented significantly higher levels of cfDNA compared to volunteers (6.4 (5.8/7.9) ng/μL vs. 5.9 (5.4/6.3) ng/μL; p = 0.044). Within 2 days after ECMO start, cfDNA, inflammatory, and hemolysis parameters remained unchanged, while platelets decreased (p = 0.005). After ECMO removal at the end of therapy, cfDNA, inflammation, and coagulation data (except antithrombin III) remained unchanged. The renewal of a system resulted in known alterations in fibrinogen, d-dimers, and platelets, while cfDNA remained unchanged. CONCLUSION: Detection of cfDNA in plasma of ECMO patients was not an indicator of acute and circuit-induced thrombogenesis.}, language = {en} } @article{FoltanDinhGruberetal., author = {Foltan, Maik and Dinh, D. and Gruber, Michael and M{\"u}ller, Thomas and Hart, C. and Krenkel, Lars and Schmid, C. and Lehle, Karla}, title = {Incidence of neutrophil extracellular traps (NETs) in different membrane oxygenators: pilot in vitro experiments in commercially available coated membranes}, series = {Journal of artificial organs : the official journal of the Japanese Society for Artificial Organs}, journal = {Journal of artificial organs : the official journal of the Japanese Society for Artificial Organs}, doi = {10.1007/s10047-024-01486-4}, abstract = {Neutrophil extracellular traps (NETs) were detected in blood samples and in cellular deposits of oxygenator membranes during extracorporeal membrane oxygenation (ECMO) therapy and may be responsible for thrombogenesis. The aim was to evaluate the effect of the base material of gas fiber (GF, polymethylpentene) and heat exchange (HE) membranes and different antithrombogenic coatings on isolated granulocytes from healthy volunteers under static culture conditions. Contact of granulocytes with membranes from different ECMO oxygenators (with different surface coatings) and uncoated-GFs allowed detection of adherent cells and NETotic nuclear structures (normal, swollen, ruptured) using nuclear staining. Flow cytometry was used to identify cell activation (CD11b/CD62L, oxidative burst) of non-adherent cells. Uncoated-GFs were used as a reference. Within 3 h, granulocytes adhered to the same extent on all surfaces. In contrast, the ratio of normal to NETotic cells was significantly higher for uncoated-GFs (56-83\%) compared to all coated GFs (34-72\%) (p < 0.001) with no difference between the coatings. After material contact, non-adherent cells remained vital with unchanged oxidative burst function and the proportion of activated cells remained low. The expression of activation markers was independent of the origin of the GF material. In conclusion, the polymethylpentene surfaces of the GFs already induce NET formation. Antithrombogenic coatings can already reduce the proportion of NETotic nuclei. However, it cannot be ruled out that NET formation can induce thrombotic events. Therefore, new surfaces or coatings are required for future ECMO systems and long-term implantable artificial lungs.}, language = {en} } @article{SteigerFoltanPhilippetal., author = {Steiger, Tamara and Foltan, Maik and Philipp, Alois and M{\"u}ller, Thomas and Gruber, Michael and Bredthauer, Andre and Krenkel, Lars and Birkenmaier, Clemens and Lehle, Karla}, title = {Accumulations of von Willebrand factor within ECMO oxygenators: Potential indicator of coagulation abnormalities in critically ill patients?}, series = {Artificial Organs}, volume = {43}, journal = {Artificial Organs}, number = {11}, publisher = {Wiley}, address = {Hoboken}, issn = {1525-1594}, doi = {10.1111/aor.13513}, pages = {1065 -- 1076}, abstract = {Clot formation within membrane oxygenators (MOs) remains a critical problem during extracorporeal membrane oxygenation (ECMO). The composition of the clots-in particular, the presence of von Willebrand factor (vWF)-may be an indicator for prevalent nonphysiological flow conditions, foreign body reactions, or coagulation abnormalities in critically ill patients. Mats of interwoven gas exchange fibers from randomly collected MOs (PLS, Maquet, Rastatt, Germany) of 21 patients were stained with antibodies (anti-vWF and anti-P-selectin) and counterstained with 4 ',6-diamidino-2-phenylindole. The extent of vWF-loading was correlated with patient and technical data. While 12 MOs showed low vWF-loadings, 9 MOs showed high vWF-loading with highest accumulations close to crossing points of adjacent gas fibers. The presence and the extent of vWF-fibers/"cobwebs," leukocytes, platelet-leukocyte aggregates (PLAs), and P-selectin-positive platelet aggregates were independent of the extent of vWF-loading. However, the highly loaded MOs were obtained from patients with a significantly elevated SOFA score, severe thrombocytopenia, and persistent liver dysfunction. The coagulation abnormalities of these critically ill patients may cause an accumulation of the highly thrombogenic and elongated high-molecular-weight vWF multimers in the plasma which will be trapped in the MOs during the ECMO therapy.}, language = {en} } @misc{KrenkelMichelKeiletal., author = {Krenkel, Lars and Michel, Johanna and Keil, Niklas and Daschner, Jan}, title = {Experimental Investigation of Logitudinal Folds in Endotracheal Tube Cuffs and their Correlation to Silent Breathing}, series = {23. DGLR Fach-Symposium Str{\"o}mungen mit Abl{\"o}sung, 09./10. November 2022, Berlin, Deutschland}, journal = {23. DGLR Fach-Symposium Str{\"o}mungen mit Abl{\"o}sung, 09./10. November 2022, Berlin, Deutschland}, address = {G{\"o}ttingen}, organization = {Deutsche Gesellschaft f{\"u}r Luft- und Raumfahrt e.V. / Arbeitsgemeinschaft Str{\"o}mungen mit Abl{\"o}sung, AG STAB}, abstract = {Air leakage past High-Volume-Low-Pressure (HVLP) endotracheal tube (ETT) cuffs creates a potential infection risk for health care professionals during ventilation of patients suffering from contagious airborne diseases. However, unlike silent aspiration, a phenomenon where fluids enter the airways of intubated patients, the aspect of aerosol emergence through cuff folds -what we called accordingly "silent breathing" (SB)- has not been investigated in detail so far. This study investigates air leakage past HVLP cuffs with varying cuff pressures under realistic artificial breathing scenarios experimentally and in addition numerically. The focus was laid on the parametric investigation of the occurrence and furthermore on different influencing factors of silent breathing. The morphology of the folds responsible for the leakage was captured using high-resolution 3D microcomputed tomography (μCT). For the numerical investigations (Com-putational Fluid Dynamics - CFD), the commercial CFD Software package FLUENT 2021 R2 (ANSYS, Inc., Canonsburg, PA, US), as well as the DLR in-house research code THETA has been used.}, language = {en} } @article{HausFoltanPhilippetal., author = {Haus, Moritz and Foltan, Maik and Philipp, Alois and M{\"u}ller, Thomas and Lingel, Maximilian P. and Krenkel, Lars and Gruber, Michael and Lehle, Karla}, title = {Neutrophil extracellular traps -a potential trigger for the development of thrombocytopenia during extracorporeal membrane oxygenation}, volume = {15}, publisher = {frontiers}, doi = {10.3389/fimmu.2024.1339235}, abstract = {Neutrophil extracellular traps (NETs) have recently emerged as a potential link between inflammation, immunity, and thrombosis, as well as other coagulation disorders which present a major challenge in the context of extracorporeal membrane oxygenation (ECMO). By examining blood from ECMO patients for NETs and their precursors and correlating them with clinical and laboratory biomarkers of coagulation and inflammation, this study aims to evaluate the association between the presence of NETs in the bloodstream of ECMO patients and the development of potentially severe coagulation disorders during ECMO therapy. Therefore, blood samples were collected from healthy volunteers (n=13) and patients receiving veno-venous (VV) ECMO therapy (n=10). To identify NETs and their precursors, DNA and myeloperoxidase as well as granulocyte marker CD66b were visualized simultaneously by immunofluorescence staining in serial blood smears. Differentiation of DNA-containing objects and identification of NETs and their precursors was performed semiautomatically by a specific algorithm using the shape and size of DNA staining and the intensity of MPO and CD66b signal. Neutrophil extracellular traps and their precursors could be detected in blood smears from patients requiring VV ECMO. Compared to volunteers, ECMO patients presented significantly higher rates of NETs and NET precursors as well as an increased proportion of neutrophil granulocytes in all detected nucleated cells. A high NET rate prior to the initiation of ECMO therapy was associated with both increased iL-6 and TNF-α levels as an expression of a high cytokine burden. These patients with increased NET release also presented an earlier and significantly more pronounced decrease in platelet counts and ATIII activity following initiation of therapy compared with patients with less elevated NETs. These findings provide further indications for the development of immune-mediated acquired thrombocytopenia in ECMO patients.}, language = {en} } @article{DeuterHajBrawanskietal., author = {Deuter, Daniel and Haj, Amer and Brawanski, Alexander and Krenkel, Lars and Schmidt, Nils Ole and Doenitz, Christian}, title = {Fast simulation of hemodynamics in intracranial aneurysms for clinical use}, series = {Acta Neurochirurgica}, volume = {167}, journal = {Acta Neurochirurgica}, publisher = {Springer}, doi = {10.1007/s00701-025-06469-9}, pages = {14}, abstract = {BACKGROUND: A widely accepted tool to assess hemodynamics, one of the most important factors in aneurysm pathophysiology, is Computational Fluid Dynamics (CFD). As current workflows are still time consuming and difficult to operate, CFD is not yet a standard tool in the clinical setting. There it could provide valuable information on aneurysm treatment, especially regarding local risks of rupture, which might help to optimize the individualized strategy of neurosurgical dissection during microsurgical aneurysm clipping. METHOD: We established and validated a semi-automated workflow using 3D rotational angiographies of 24 intracranial aneurysms from patients having received aneurysm treatment at our centre. Reconstruction of vessel geometry and generation of volume meshes was performed using AMIRA 6.2.0 and ICEM 17.1. For solving ANSYS CFX was used. For validational checks, tests regarding the volumetric impact of smoothing operations, the impact of mesh sizes on the results (grid convergence), geometric mesh quality and time tests for the time needed to perform the workflow were conducted in subgroups. RESULTS: Most of the steps of the workflow were performed directly on the 3D images requiring no programming experience. The workflow led to final CFD results in a mean time of 22 min 51.4 s (95\%-CI 20 min 51.562 s-24 min 51.238 s, n = 5). Volume of the geometries after pre-processing was in mean 4.46\% higher than before in the analysed subgroup (95\%-CI 3.43-5.50\%). Regarding mesh sizes, mean relative aberrations of 2.30\% (95\%-CI 1.51-3.09\%) were found for surface meshes and between 1.40\% (95\%-CI 1.07-1.72\%) and 2.61\% (95\%-CI 1.93-3.29\%) for volume meshes. Acceptable geometric mesh quality of volume meshes was found. CONCLUSIONS: We developed a semi-automated workflow for aneurysm CFD to benefit from hemodynamic data in the clinical setting. The ease of handling opens the workflow to clinicians untrained in programming. As previous studies have found that the distribution of hemodynamic parameters correlates with thin-walled aneurysm areas susceptible to rupture, these data might be beneficial for the operating neurosurgeon during aneurysm surgery, even in acute cases.}, language = {en} } @inproceedings{RuettenKrenkelQuadrio, author = {R{\"u}tten, Markus and Krenkel, Lars and Quadrio, Maurizio}, title = {Simulation and Analyis of the Unsteady Flow within Nasal Airways}, series = {9th European Congress on Computational Methods in Applied Sciences and Engineering - ECCOMAS Congress, 3-7 June 2024, Lisbon, Portugal}, booktitle = {9th European Congress on Computational Methods in Applied Sciences and Engineering - ECCOMAS Congress, 3-7 June 2024, Lisbon, Portugal}, language = {en} } @inproceedings{KrenkelWagnerWolfetal., author = {Krenkel, Lars and Wagner, Claus and Wolf, Ursula and Scholz, Alexander-Wigbert K. and Terekhov, Maxim and Rivoire, Julien and Schreiber, W.}, title = {Protective Artificial Lung Ventilation: Impact of an Endotracheal Tube on the Flow in a Generic Trachea}, series = {New Results in Numerical and Experimental Fluid Mechanics VII : Contributions to the 16th STAB/DGLR Symposium Aachen, Germany 2008}, booktitle = {New Results in Numerical and Experimental Fluid Mechanics VII : Contributions to the 16th STAB/DGLR Symposium Aachen, Germany 2008}, editor = {Hirschel, Ernst Heinrich and Schr{\"o}der, Wolfgang and Fujii, Kozo and Haase, Werner and Leer, Bram and Leschziner, Michael A. and Pandolfi, Maurizio and Periaux, Jacques and Rizzi, Arthur and Roux, Bernard and Shokin, Yurii I. and Dillmann, Andreas and Heller, Gerd and Klaas, Michael and Kreplin, Hans-Peter and Nitsche, Wolfgang}, publisher = {Springer Berlin Heidelberg}, address = {Berlin, Heidelberg}, isbn = {978-3-642-14242-0}, doi = {10.1007/978-3-642-14243-7_62}, pages = {505 -- 512}, abstract = {Computational Fluid Dynamics (CFD) and experimental investigations on a generic model of the trachea have been carried out focusing on the impact of an endotracheal tube (ETT) on the resulting flow regime. It could be shown that detailed modelling of the airway management devices is essential for proper flow prediction, but secondary details as Murphy Eyes can be neglected. Models with bending and connector promote the formation of stronger secondary flows and disturbances which persist for a longer time.}, language = {en} } @misc{FriedrichRivoireScholzetal., author = {Friedrich, Janet and Rivoire, Julien and Scholz, Alexander-Wigbert K. and Wiegbert, and Terekov, Maxim and Kbrich, Rainer and Krenkel, Lars and Wagner, Claus and Schreiber, Laura Maria}, title = {Exploration of Gas Flow During High Frequency Oscillated Ventilation by 19F-Gas-MRI}, series = {Proceedings of the International Society for Magnetic Resonance in Medicine}, volume = {18}, journal = {Proceedings of the International Society for Magnetic Resonance in Medicine}, abstract = {To detect convective gas flow inside the large airways during high frequency oscillated ventilation (HFOV) the fluorinated contrast gas Heptafluoropropane was used for 19F-MRI. In a first study the comparison between constant flow measurements and Computational Fluid Dynamics (CFD) simulations provided a good agreement. In a following experiment oscillated flow was applied to a lung phantom consisting of ventilation bag and long pipe. The pressure wave inside the pipe was explored point-by-point and corresponding velocities were determined. With these experiments it could be shown for the first time that flow measurement during HFOV using fluorinated contrast gas is feasible.}, language = {en} } @article{LehlePhilippKrenkeletal., author = {Lehle, Karla and Philipp, Alois and Krenkel, Lars and Gruber, Michael and Hiller, Karl-Anton and M{\"u}ller, Thomas and Lubnow, Matthias}, title = {Thrombocytopenia During Venovenous Extracorporeal Membrane Oxygenation in Adult Patients With Bacterial, Viral, and COVID-19 Pneumonia}, series = {ASAIO Journal}, journal = {ASAIO Journal}, publisher = {Wolters Kluwer}, issn = {1058-2916}, doi = {10.1097/MAT.0000000000002383}, abstract = {Contact of blood with artificial surfaces triggers platelet activation. The aim was to compare platelet kinetics after venovenous extracorporeal membrane oxygenation (V-V ECMO) start and after system exchange in different etiologies of acute lung failure. Platelet counts and coagulation parameters were analyzed from adult patients with long and exchange-free (≥8 days) ECMO runs (n = 330) caused by bacterial (n = 142), viral (n = 76), or coronavirus disease 2019 (COVID-19) (n = 112) pneumonia. A subpopulation requiring a system exchange and with long, exchange-free runs of the second oxygenator (≥7 days) (n = 110) was analyzed analogously. Patients with COVID-19 showed the highest platelet levels before ECMO implantation. Independent of the underlying disease and ECMO type, platelet counts decreased significantly within 24 hours and reached a steady state after 5 days. In the subpopulation, at the day of a system exchange, platelet counts were lower compared with ECMO start, but without differences between underlying diseases. Subsequently, platelets remained unchanged in the bacterial pneumonia group, but increased in the COVID-19 and viral pneumonia groups within 2-4 days, whereas D-dimers decreased and fibrinogen levels increased. Thus, overall platelet counts on V-V ECMO show disease-specific initial dynamics followed by an ongoing consumption by the ECMO device, which is not boosted by new artificial surfaces after a system exchange.}, language = {en} } @article{PointnerKranzWagneretal., author = {Pointner, Daniel and Kranz, Michael and Wagner, Maria Stella and Haus, Moritz and Lehle, Karla and Krenkel, Lars}, title = {Automated deep learning based detection of cellular deposits on clinically used ECMO membrane lungs}, series = {Frontiers in Bioinformatics}, volume = {6}, journal = {Frontiers in Bioinformatics}, publisher = {Frontiers}, doi = {10.3389/fbinf.2026.1771574}, pages = {18}, abstract = {Introduction: Despite the promising application of extracorporeal membrane oxygenation (ECMO) in the treatment of critically ill patients, coagulation-associated technical complications, primarily clot formation and critical bleeding, remain a major challenge during ECMO therapy. The deposition of nucleated cells on the surface has been shown, yet the role of these cells towards complication development is still matter of ongoing research. In particular, the membrane lung (MemL) is prone to clot formation. Therefore, the investigation of nuclear deposits on its hollow-fibers may provide insights for a better understanding of the cellular mechanisms involved in the development of ECMO complications. Methods: To support current research, this study aimed to develop a deep learning-based tool for the automated detection and quantitative analysis of nuclear depositions on MemL hollow-fiber mats. A customized fluorescence microscopy workflow, combined with a semi-automated iterative labeling strategy, was used to generate a high-quality dataset for model training. Results: Six configurations of instance segmentation models were evaluated, with a Mask R-CNN with ResNet 101 backbone using dilated convolution providing the most balanced performance in both nuclei count and area accuracy. Compared with U-Net-based approaches such as Cellpose or StarDist, the proposed model demonstrated superior segmentation of overlapping and low-intensity nuclei, maintaining accuracy even in densely packed cellular regions. Discussion: We present an automated image analysis tool for clinically used MemLs, which exhibit complex three-dimensional hollow-fiber architectures and irregular cellular deposits that challenge conventional tools. A dedicated graphical user interface enables streamlined detection, morphometric analysis, and spatial clustering of nuclei, establishing a reproducible workflow for high-throughput analysis of fluorescence microscopy images. This approach eliminates labor-intensive manual counting and facilitates large-scale studies on cell-fiber interactions and disease-related correlations.}, language = {en} } @inproceedings{MichelKrenkel, author = {Michel, Johanna and Krenkel, Lars}, title = {Towards Experimental Validation of Models of Shear-Induced Aerosol Generation in the Human Respiratory System}, series = {New Results in Numerical and Experimental Fluid Mechanics XV : Contributions to the 24th STAB/DGLR Symposium, Regensburg, Germany, 2024}, booktitle = {New Results in Numerical and Experimental Fluid Mechanics XV : Contributions to the 24th STAB/DGLR Symposium, Regensburg, Germany, 2024}, editor = {Dillmann, Andreas and Heller, Gerd and Kr{\"a}mer, Ewald and Breitsamter, Christian and Wagner, Claus and Krenkel, Lars}, publisher = {Springer Nature}, address = {Cham}, isbn = {978-3-032-11114-2}, doi = {10.1007/978-3-032-11115-9_13}, pages = {135 -- 144}, abstract = {Numerical modeling is a valuable tool to research shear-induced aerosol generation inside the human respiratory system. While the volume of fluid method and Eulerian wall film models have been used to predict the stripping of particles from the mucus film, sufficient validation data is lacking. Here, we present an experimental method to create such validation data. A film of mucus mimetic hydrogel with an initial thickness of 1 mm covering the floor of a rectangular channel (75.5 mm 25.5 mm 3 mm) was exposed to an airflow with a flow rate of 9.5 and 21.6 L/min. The number of created particles and the emergence of waves on the mucus surface were measured. Shear-induced aerosol generation was triggered successfully and caused an increase of mean particle flow. Different wave profiles were observed at varying film depths.}, language = {en} }