Determining the muscle forces that underlie some experimentally observed human motion, is a challenging biomechanical problem,
both from an experimental and a computational point of view. No non-invasive method is currently available for experimentally
measuring muscle forces. The alternative of computing them from the observed motion is complicated by the inherent overactuation
of the human body: it has many more muscles than strictly needed for driving all the degrees of freedom of the skeleton. As
a result, the skeleton’s equations of motion do not suffice to determine the muscle forces unambiguously. Therefore, muscle
force determination is often reformulated as a (large-scale) optimization problem.
Generally, the optimization approaches are classified according to the formalism, inverse or forward, adopted for solving
the skeleton’s equations of motion. Classical inverse approaches are fast but do not take into account the constraints imposed
by muscle physiology. Classical forward approaches, on the other hand, do take the muscle physiology into account but are
extremely costly from a computational point of view.
The present paper makes a double contribution. First, it proposes a novel inverse approach that results from including muscle
physiology (both activation and contraction dynamics) in the inverse dynamic formalism. Second, the efficiency with which
the corresponding optimization problem is solved is increased by using convex optimization techniques. That is, an approximate
convex program is formulated and solved in order to provide a hot-start for the exact nonconvex program. The key element in
this approximation is a (global) linearization of muscle physiology based on techniques from experimental system identification.
This approach is applied to the study of muscle forces during gait. Although the results for gait are promising, experimental
study of faster motions is needed to demonstrate the full power and advantages of the proposed methodology, and therefore
is the subject of subsequent research. 相似文献
Bacteria colonizing BAC filters used in drinking water purification from lake water were characterized by morphology, physiological tests, whole cell protein profiles and PLFA (phospholipid fatty acid) composition, and identified by partial 16S rRNA gene sequencing. Epifluorescence revealed prothecate bacteria to dominate in BAC. The majority of the isolates belonged to order Burkholderiales of β-Proteobacteria, a few to Comamonadaceae but the majority to an undescribed family and the related sequences belonged mainly to uncultured bacteria. Among the less common α-Proteobacteria the genus Sphingomonas and the genera Afipia, Bosea or Bradyrhizobium of the Bradyrhizobiaceae family were detected. The majority of cultured bacteria persisting in the BAC biofilter were Burkholderiales, which according to ecological information are efficient in the mineralisation of dissolved organic matter in BAC. The biotechnical potential of the previously uncultured dominant bacteria warrants to be further studied. 相似文献
Position control of robot manipulators using a novel PID control configuration derived from modeling error compensation ideas is introduced. The PID control law stability depends only on the inertial parameters of the robot. A simple proof of semiglobal PID stabilization of robot manipulators is provided. It is shown that the performance of the inverse dynamics control can be recovered by the PID control in the high-gain limit. Simple tuning guidelines derived from the proposed PID control configuration and closed-loop stability analysis are presented. 相似文献
Cancers affecting the gastrointestinal system are highly prevalent and their incidence is still increasing. Among them, gastric and pancreatic cancers have a dismal prognosis (survival of 5–20%) and are defined as difficult-to-treat cancers. This reflects the urge for novel therapeutic targets and aims for personalised therapies. As a prerequisite for identifying targets and test therapeutic interventions, the development of well-established, translational and reliable preclinical research models is instrumental. This review discusses the development, advantages and limitations of both patient-derived organoids (PDO) and patient-derived xenografts (PDX) for gastric and pancreatic ductal adenocarcinoma (PDAC). First and next generation multicellular PDO/PDX models are believed to faithfully generate a patient-specific avatar in a preclinical setting, opening novel therapeutic directions for these difficult-to-treat cancers. Excitingly, future opportunities such as PDO co-cultures with immune or stromal cells, organoid-on-a-chip models and humanised PDXs are the basis of a completely new area, offering close-to-human models. These tools can be exploited to understand cancer heterogeneity, which is indispensable to pave the way towards more tumour-specific therapies and, with that, better survival for patients. 相似文献
The thermal stability of nitroxide capped polystyrene is examined by TGA and pyrolysis-GC/MS. As opposed to technical polystyrene, these polymers (Mn > 30000 g mol–1) show a characteristic decomposition step at 230–250°C. The volatile product of this step is mainly styrene, which results from retropolymerization. For some PS-N adducts terminator fragments can be identified. Prolonged isothermal treatment of PS-N adducts at their step temperature yields polystyrene without nitroxides. The loss of molecular weight is in the range of technical PS by the same treatment, but the polymers keep a narrow molecular weight distribution. 相似文献
A method is presented for in-flight validation of space-based polarization measurements based on approximation of the direction of polarization of scattered sunlight by the Rayleigh single-scattering value. This approximation is verified by simulations of radiative transfer calculations for various atmospheric conditions. The simulations show locations along an orbit where the scattering geometries are such that the intensities of the parallel and orthogonal polarization components of the light are equal, regardless of the observed atmosphere and surface. The method can be applied to any space-based instrument that measures the polarization of reflected solar light. We successfully applied the method to validate the Global Ozone Monitoring Experiment (GOME) polarization measurements. The error in the GOME's three broadband polarization measurements appears to be approximately 1%. 相似文献
Accountability and responsibility are key concepts in the academic and societal debate on Autonomous Weapon Systems, but these notions are often used as high-level overarching constructs and are not operationalised to be useful in practice. “Meaningful Human Control” is often mentioned as a requirement for the deployment of Autonomous Weapon Systems, but a common definition of what this notion means in practice, and a clear understanding of its relation with responsibility and accountability is also lacking. In this paper, we present a definition of these concepts and describe the relations between accountability, responsibility, control and oversight in order to show how these notions are distinct but also connected. We focus on accountability as a particular form of responsibility—the obligation to explain one’s action to a forum—and we present three ways in which the introduction of Autonomous Weapon Systems may create “accountability gaps”. We propose a Framework for Comprehensive Human Oversight based on an engineering, socio-technical and governance perspective on control. Our main claim is that combining the control mechanisms at technical, socio-technical and governance levels will lead to comprehensive human oversight over Autonomous Weapon Systems which may ensure solid controllability and accountability for the behaviour of Autonomous Weapon Systems. Finally, we give an overview of the military control instruments that are currently used in the Netherlands and show the applicability of the comprehensive human oversight Framework to Autonomous Weapon Systems. Our analysis reveals two main gaps in the current control mechanisms as applied to Autonomous Weapon Systems. We have identified three first options as future work for the design of a control mechanism, one in the technological layer, one in the socio-technical layer and one the governance layer, in order to achieve comprehensive human oversight and ensure accountability over Autonomous Weapon Systems.
The N-nitrosopiperidine (NPIP) formation in blends of spices and nitrite curing salt was investigated in relation with the piperine and piperidine contents in spices. Firstly, two analytical methods were developed. Piperine was extracted with dichloromethane by means of accelerated solvent extraction (ASE) and determined by high-performance liquid chromatography (HPLC)–diode array detector (λ = 343 nm). A selective hydroextraction of piperidine using ASE and its quantification by HPLC–ELSD was applied. Both methods were sufficiently sensitive and accurate (limit of detection, limit of quantification, and recovery: 0.28, 0.84 μg, and 98.9 ± 2.6 % for piperine, and 5.76, 17.45 μg, and 95.9 ± 2.9 % for piperidine, respectively). Secondly, both compounds were quantified in commercial samples (black and white pepper, paprika, chili pepper, allspice, and nutmeg). The maximum amount of piperine (21.12 mg g?1) was found in pepper, while the other spices contained only traces. Piperidine was detected mainly in the pepper samples, whereby the highest concentration was found in the white pepper extract (11.42 mg g?1). Thirdly, during the storage of spices blended with nitrite curing salt, the NPIP content was determined, using a gas chromatograph coupled with a thermal energy analyzer. Against our expectations, no NPIP formation was observed in the curing mixture which contained white pepper extract. This result remains in contrast with the white pepper mixture, in which the NPIP content significantly increased from not detected to 9.80 ± 0.41 ng g?1 after the 2 months storage period. In conclusion, high amounts of piperine or piperidine in spices do not systematically result in the formation of NPIP, when blended with nitrite curing salt . 相似文献
Ceramic filters are used to avoid slag and impurities in foundry applications. When not properly applied, the presence of these filters may have a significant influence on mould filling. 3-D casting simulation has been applied to study the effects of the use of a ceramic filter on the metal flow in a gating system. Instead of using a pressure drop model to represent the behaviour of a fluid metal flow passing through a filter, a real exact filter geometry, which is created by a high resolution CT-scan and a non-destructive imaging technique, in the gating system is applied in the simulation. In this research, nodular cast iron is poured into a block casting. A depressurized gating system is used. After a choke, a filter with different orientations is placed in the system. Mould filling coupled with temperature is simulated. Geometries using different orientations of the filter, and without the filter have been researched. The simulated results show that the filter has no influence on the pouring time of the casting if the choke section is small enough compared to the effective section of the filter. Although the filter has no significant influence on the flow patterns in the block casting itself, the flow patterns in the filter zone are different. When the liquid metal passes a horizontal filter, it will be broken into many small streams and show a shower effect. After the part under the filter is full, the shower effect disappears. When the filter is located at the vertical position, due to the gravity, the shower effect is less. If no filter presents on the system, the liquid metal passes through the filter zone with a high speed and causes surface turbulence. 相似文献