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

Growth Inhibitory Effect of Extracts from Milt (Testis) of Different Fishes and of Pure Protamines on Microorganisms

A method has been described for the isolation of protamine from the milt (testes) of fish, employing direct extraction of the organ with dilute sulfuric acid, followed by stepwise precipitation with ethanol. The growth inhibitory effect of different protamine preparations on Saccharomyces carlsbergensis have been studied. 0, 7-0,8 µg clupeine sulphate per ml medium gave complete growth inhibition. It has been pointed out that the type (origin) of the protamine should be given in studies on these substances. The growth inhibition of clupein sulphate on some microorganisms employed in vitamin assays have been tried. For L. plantarum and L. leichmannii growth inhibition was observed at about 5 µg per ml medium, for L. casei at 10 µg, for S. fæcalis at about 150 µg, and for Neurospora crassa at about 50 µg per ml medium Aspergillus niger showed growth promotion, probably caused by enzymatic breakdown of the polypeptide and utilization of the free amino acids

Further studies on Vitamins and the Reproductive Cycle of Ovaries In Cod (Gadus morrhua)

The relations between vitamin B6, vitamin B12, biotin and total dry matter and the reproductive cycle of the ovaries in cod has been investigated. The stage of maturation or regeneration was expressed as the percentage ovary of the fish weight, and the cycle divided into 8 groups from the juvenile stage to the pre-spawning stage. Vitamin B6 showed a strong increase in the first stages, from 0.04 to 2.5 µg per g fresh weight. It remained on this level until spawning. Calculated on the basis of dry matter, the trend was the same and the corresponding values 0.23 to 8.5 µg per g. Vitamin B12 showed a significant decrease from 0.359 µg per g fresh weight in juvenile to 0.266 in the first stage of maturation. It then decreased slowly but significantly to 0.139 to drop just before spawning to 0.092 µg per g fresh weight. The corresponding values calculated on total dry matter were 2.35, 1.63, 0.46 and 0.38 µg per g. Biotin showed an increase in the first stages from 0.119 to 0.220 µg per g fresh weight. Just before spawning the concentration decreased to 0.132 µg per g fresh weight. The trend is similar to the change in dry matter, and calculated on this basis the values remained about 0.75 µg per g until the time of spawning, when it decreased to 0.55 µg per g. Total dry matter increased significantly from 15.3 % to about 30 % to decrease significantly just before spawning

A Comparative Study of Amino Acids in the Muscle of Different Species of Fish

1. The complete amino acid composition in the muscles of ten common food fishes has been investigated by microbiological methods. Each amino acid was determined simultaneously in all samples, thus making a direct comparison of the contents in the different species possible. 2. The amino acid percentages of the protein (N x 6.25) were essentially the same in the muscle of the different fishes. The only exception was the value for histidine in mackerel, which was twice as high as the contents found in the remaining nine species. 3. The present values were generally of the same order as the averages of the data in the literature. 4. The total amino acid nitrogen compared with the total nitrogen of the samples, made it possible to calculate more exact conversion factors for the estimation of protein in fish muscle. This proble1n has been discussed. 5. Compared with FAO's "provisional pattern" for the nutritional requirement, tryptophan was the first limiting amino acid followed by the sulphur containing amino acid. Compared with BENDER's "target values", the sulphur containing amino acids were the only limiting factors

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

Vitaminer i Norsk fisk IV. Vitamin B6 og biotin i forskjellige organer fra torskefisker (Gadidae) fanget langs Norskekysten

The species cod (Gadus morrhua), coalfish (Gadus virens), ling (Molva molva) and torsk (Brosmus brosme) have been investigated. The samples were collected from newly caught fish and analysed fresh or after storage at below - 15°C. Vitamin B6 was determined microbiologically using Saccharomyces carlsbergensis as testorganism. Biotin was determined microbiologically with Lactobacillus plantarum. The results are summarized in Table 1-5, which have English subtitles. In general the filets were good sources for vitamin B6 and biotin. The white and red muscle contained about equal concentrations of vitamin B6, wheras the red muscle contained 6 to 22 times as much biotin as the white muscle. The liver is a fair source for vitamin B6 but a very rich source for biotin. The kidneys showed a difference between the front parts and the back parts, with about four times higher concentrations of both vitamin B6 and biotin in the latter. The results are briefly discussed

Risk factors for severe postoperative complications in dogs with cranial cruciate ligament disease-A survival analysis

Objective: To analyze the effect of surgical technique and other risk factors on severe postoperative complications in dogs with cranial cruciate ligament disease (CCLD). Materials and Methods: A cohort study of 255 dogs (287 stifles) surgically treated for CCLD at two veterinary university hospitals (2011 & ndash;2016) was performed. The electronic medical records were reviewed and dog owners and referring veterinarians contacted for additional information. The complications were classified as minor, major and catastrophic, where major and catastrophic were considered severe. A multivariable Cox proportional hazards model was applied to assess risk factors for severe postoperative complications.Results: Three surgical techniques were used; lateral fabellotibial suture (LFS, 141 stifles), tibial plateau leveling osteotomy (TPLO, 77 stifles) and tibial tuberosity advancement (TTA, 69 stifles). The most common severe postoperative complications were surgical site infections or complications related to the surgical implant. Severe postoperative complications occurred in 31 % of the stifles treated with TPLO, 22 % of the stifles treated with LFS and 25 % of the stifles treated with TTA. The multivariable Cox proportional hazards model identified surgical technique (p = 0.0258) as a risk factor for severe postoperative complications; TPLO had a significantly lower hazard than LFS (hazard ratio (HR) = 0.37, p = 0.007) when controlling for body weight and age, which also were identified as risk factors (HR = 1.05, p < 0.001 and HR = 0.91, p = 0.047, respectively).Conclusion and Clinical relevance: Although TPLO procedures had the highest occurrence of severe postoperative complications, the hazard was lower than for LFS after adjusting for body weight and age. This implies that it is important to consider potential effect-modifiers when comparing postoperative complications after CCLD surgery

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

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