Modeling, Stability Analysis, and Testing of a Hybrid Docking Simulator

A hybrid docking simulator is a hardware-in-the-loop (HIL) simulator that includes a hardware element within a numerical simulation loop. One of the goals of performing a HIL simulation at the European Proximity Operation Simulator (EPOS) is the verification and validation of the docking phase in an on-orbit servicing mission.....Comment: 30 papge

Analytical and experimental stability investigation of a hardware-in-the-loop satellite docking simulator

The European Proximity Operation Simulator (EPOS) of the DLR-German Aerospace Center is a robotics-based simulator that aims at validating and verifying a satellite docking phase. The generic concept features a robotics tracking system working in closed loop with a force/torque feedback signal. Inherent delays in the tracking system combined with typical high stiffness at contact challenge the stability of the closed-loop system. The proposed concept of operations is hybrid: the feedback signal is a superposition of a measured value and of a virtual value that can be tuned in order to guarantee a desired behavior. This paper is concerned with an analytical study of the system's closed-loop stability, and with an experimental validation of the hybrid concept of operations in one dimension (1D). The robotics simulator is modeled as a second-order loop-delay system and closed-form expressions for the critical delay and associated frequency are derived as a function of the satellites' mass and the contact dynamics stiffness and damping parameters. A numerical illustration sheds light on the impact of the parameters on the stability regions. A first-order Pade approximation provides additional means of stability investigation. Experiments were performed and tests results are described for varying values of the mass and the damping coefficients. The empirical determination of instability is based on the coefficient of restitution and on the observed energy. There is a very good agreement between the critical damping values predicted by the analysis and observed during the tests...Comment: 16 page

The reasons for the collapse of the Tacoma Narrows Bridge and the lessons for the classroom

On 7 November 1940, a historical event occurred for suspension bridge construction and aerodynamic engineering around suspension bridges. Engineers investigating the event concluded the bridge collapsed due to high winds but did not explain how. Later lab tests by other engineers and scientists demonstrated that the collapse happened either due to forced oscillations with Resonance or aeroelastic flutter. Forced oscillations with Resonance treated the bridge as an object being periodically pushed by the winds in Resonance with its natural frequency. And aeroelastic flutter treats the bridge as a wingspan in a fluid stream where the winds would alternate the pushing of the bridge span as it enters above and under the plate. Due to historical similarities, some believed the collapse occurred due to Resonance. However, later articles would discuss the aeroelastic flutter and criticize the resonance argument. One of these articles would be written by Billah and Scanlan, criticizing the use of the bridge as an example of Resonance in physics books and showing an alternative interpretation of the collapse. After discussing the collapse with an expert in aerodynamics on bridges from the University of Stavanger, we were informed that the Billah and Scanlan article is considered the modern explanation by the professional community. However, there are still physics books today that still misrepresent the circumstances around the collapse. We, as teaching students, agree with the Billah and Scanlan article and the opinion of the professional community that the collapse was most likely due to aeroelastic flutter. And that the collapse being represented as Resonance simplifies and misrepresents a more complicated and comprehensive problem around the Tacoma Narrows Bridge.On 7 November 1940, a historical event occurred for suspension bridge construction and aerodynamic engineering around suspension bridges. Engineers investigating the event concluded the bridge collapsed due to high winds but did not explain how. Later lab tests by other engineers and scientists demonstrated that the collapse happened either due to forced oscillations with Resonance or aeroelastic flutter. Forced oscillations with Resonance treated the bridge as an object being periodically pushed by the winds in Resonance with its natural frequency. And aeroelastic flutter treats the bridge as a wingspan in a fluid stream where the winds would alternate the pushing of the bridge span as it enters above and under the plate. Due to historical similarities, some believed the collapse occurred due to Resonance. However, later articles would discuss the aeroelastic flutter and criticize the resonance argument. One of these articles would be written by Billah and Scanlan, criticizing the use of the bridge as an example of Resonance in physics books and showing an alternative interpretation of the collapse. After discussing the collapse with an expert in aerodynamics on bridges from the University of Stavanger, we were informed that the Billah and Scanlan article is considered the modern explanation by the professional community. However, there are still physics books today that still misrepresent the circumstances around the collapse. We, as teaching students, agree with the Billah and Scanlan article and the opinion of the professional community that the collapse was most likely due to aeroelastic flutter. And that the collapse being represented as Resonance simplifies and misrepresents a more complicated and comprehensive problem around the Tacoma Narrows Bridge

Studies on the radiation preservation of fish I. The Effect on Certain Vitamins in Fresh Fillets of Cod and Dogfish and in Smoked Fillets of Cod and Herring

The effect of radiopasteurization (0.3 Mrad) and radiosterilization (3.0 Mrad) on certain vitamins in canned fresh fillets of cod and dogfish and in vacuum packed smoked cod and herring, were studied. The effect of post-irradiation storage of the samples at appropriate temperatures on the vitamin contents was determined. Some differences between vitamin sensitivity to irradiation and storage among the various fish samples studied were noted. Thiamine was found to be most sensitive to both irradiation and storage of non irradiated samples. Irradiated samples lost little or no thiamine upon storage. Riboflavin was more sensitive to storage than to irradiation. Niacin and vitamin B12 were not appreciably affected by irradiation or storage. Vitamin A appeared to be more radiosensitive in smoked than in fresh fish. Thus a sample of dogfish retained 50 percent of the vitamin A content after irradiation with 3.0 Mrad. Vitamin E was not affected by the radiation doses employed in the fish samples investigated

FLEET: Butterfly Estimation from a Bipartite Graph Stream

We consider space-efficient single-pass estimation of the number of butterflies, a fundamental bipartite graph motif, from a massive bipartite graph stream where each edge represents a connection between entities in two different partitions. We present a space lower bound for any streaming algorithm that can estimate the number of butterflies accurately, as well as FLEET, a suite of algorithms for accurately estimating the number of butterflies in the graph stream. Estimates returned by the algorithms come with provable guarantees on the approximation error, and experiments show good tradeoffs between the space used and the accuracy of approximation. We also present space-efficient algorithms for estimating the number of butterflies within a sliding window of the most recent elements in the stream. While there is a significant body of work on counting subgraphs such as triangles in a unipartite graph stream, our work seems to be one of the few to tackle the case of bipartite graph streams.Comment: This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version was published in Seyed-Vahid Sanei-Mehri, Yu Zhang, Ahmet Erdem Sariyuce and Srikanta Tirthapura. "FLEET: Butterfly Estimation from a Bipartite Graph Stream". The 28th ACM International Conference on Information and Knowledge Managemen

Highly sensitive and specific protein detection via combined capillary isoelectric focusing and proximity ligation

Detection and quantification of proteins and their post-translational modifications are crucial to decipher functions of complex protein networks in cell biology and medicine. Capillary isoelectric focusing together with antibody-based detection can resolve and identify proteins and their isoforms with modest sample input. However, insufficient sensitivity prevents detection of proteins present at low concentrations and antibody cross-reactivity results in unspecific detection that cannot be distinguished from bona fide protein isoforms. By using DNA-conjugated antibodies enhanced signals can be obtained via rolling circle amplification (RCA). Both sensitivity and specificity can be greatly improved in assays dependent on target recognition by pairs of antibodies using in situ proximity ligation assays (PLA). Here we applied these DNA-assisted RCA techniques in capillary isoelectric focusing to resolve endogenous signaling transducers and isoforms along vascular endothelial growth factor (VEGF) signaling pathways at concentrations too low to be detected in standard assays. We also demonstrate background rejection and enhanced specificity when protein detection depended on binding by pairs of antibodies using in situ PLA, compared to assays where each antibody preparation was used on its own.</p

Highly sensitive and specific protein detection via combined capillary isoelectric focusing and proximity ligation

Detection and quantification of proteins and their post-translational modifications are crucial to decipher functions of complex protein networks in cell biology and medicine. Capillary isoelectric focusing together with antibody-based detection can resolve and identify proteins and their isoforms with modest sample input. However, insufficient sensitivity prevents detection of proteins present at low concentrations and antibody cross-reactivity results in unspecific detection that cannot be distinguished from bona fide protein isoforms. By using DNA-conjugated antibodies enhanced signals can be obtained via rolling circle amplification (RCA). Both sensitivity and specificity can be greatly improved in assays dependent on target recognition by pairs of antibodies using in situ proximity ligation assays (PLA). Here we applied these DNA-assisted RCA techniques in capillary isoelectric focusing to resolve endogenous signaling transducers and isoforms along vascular endothelial growth factor (VEGF) signaling pathways at concentrations too low to be detected in standard assays. We also demonstrate background rejection and enhanced specificity when protein detection depended on binding by pairs of antibodies using in situ PLA, compared to assays where each antibody preparation was used on its own.</p

Interpreting Attoclock Measurements of Tunnelling Times

Resolving in time the dynamics of light absorption by atoms and molecules, and the electronic rearrangement this induces, is among the most challenging goals of attosecond spectroscopy. The attoclock is an elegant approach to this problem, which encodes ionization times in the strong-field regime. However, the accurate reconstruction of these times from experimental data presents a formidable theoretical challenge. Here, we solve this problem by combining analytical theory with ab-initio numerical simulations. We apply our theory to numerical attoclock experiments on the hydrogen atom to extract ionization time delays and analyse their nature. Strong field ionization is often viewed as optical tunnelling through the barrier created by the field and the core potential. We show that, in the hydrogen atom, optical tunnelling is instantaneous. By calibrating the attoclock using the hydrogen atom, our method opens the way to identify possible delays associated with multielectron dynamics during strong-field ionization.Comment: 33 pages, 10 figures, 3 appendixe

A Radiomics Model Based on Synthetic MRI Acquisition for Predicting Neoadjuvant Systemic Treatment Response in Triple-Negative Breast Cancer

Purpose To determine if a radiomics model based on quantitative maps acquired with synthetic MRI (SyMRI) is useful for predicting neoadjuvant systemic therapy (NAST) response in triple-negative breast cancer (TNBC). Materials and Methods In this prospective study, 181 women diagnosed with stage I–III TNBC were scanned with a SyMRI sequence at baseline and at midtreatment (after four cycles of NAST), producing T1, T2, and proton density (PD) maps. Histopathologic analysis at surgery was used to determine pathologic complete response (pCR) or non-pCR status. From three-dimensional tumor contours drawn on the three maps, 310 histogram and textural features were extracted, resulting in 930 features per scan. Radiomic features were compared between pCR and non-pCR groups by using Wilcoxon rank sum test. To build a multivariable predictive model, logistic regression with elastic net regularization and cross-validation was performed for texture feature selection using 119 participants (median age, 52 years [range, 26–77 years]). An independent testing cohort of 62 participants (median age, 48 years [range, 23–74 years]) was used to evaluate and compare the models by area under the receiver operating characteristic curve (AUC). Results Univariable analysis identified 15 T1, 10 T2, and 12 PD radiomic features at midtreatment that predicted pCR with an AUC greater than 0.70 in both the training and testing cohorts. Multivariable radiomics models of maps acquired at midtreatment demonstrated superior performance over those acquired at baseline, achieving AUCs as high as 0.78 and 0.72 in the training and testing cohorts, respectively. Conclusion SyMRI-based radiomic features acquired at midtreatment are potentially useful for identifying early NAST responders in TNBC

Multiparametric MRI-Based Radiomic Models for Early Prediction of Response to Neoadjuvant Systemic Therapy in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is often treated with neoadjuvant systemic therapy (NAST). We investigated if radiomic models based on multiparametric Magnetic Resonance Imaging (MRI) obtained early during NAST predict pathologic complete response (pCR). We included 163 patients with stage I-III TNBC with multiparametric MRI at baseline and after 2 (C2) and 4 cycles of NAST. Seventy-eight patients (48%) had pCR, and 85 (52%) had non-pCR. Thirty-six multivariate models combining radiomic features from dynamic contrast-enhanced MRI and diffusion-weighted imaging had an area under the receiver operating characteristics curve (AUC) \u3e 0.7. The top-performing model combined 35 radiomic features of relative difference between C2 and baseline; had an AUC = 0.905 in the training and AUC = 0.802 in the testing set. There was high inter-reader agreement and very similar AUC values of the pCR prediction models for the 2 readers. Our data supports multiparametric MRI-based radiomic models for early prediction of NAST response in TNBC