212,920 research outputs found
On-orbit assembly using superquadric potential fields
The autonomous on-orbit assembly of a large space structure is presented using a method based on superquadric artificial potential fields. The final configuration of the elements which form the structure is represented as the minimum of some attractive potential field. Each element of the structure is then considered as presenting an obstacle to the others using a superquadric potential field attached to the body axes of the element. A controller is developed which ensures that the global potential field decreases monotonically during the assembly process. An error quaternion representation is used to define both the attractive and superquadric obstacle potentials allowing the final configuration of the elements to be defined through both relative position and orientation. Through the use of superquadric potentials, a wide range of geometric objects can be represented using a common formalism, while collision avoidance can make use of both translational and rotation maneuvers to reduce total maneuver cost for the assembly process
The Dynamics of Liquid Drops and their Interaction with Solids of Varying Wettabilites
Microdrop impact and spreading phenomena are explored as an interface
formation process using a recently developed computational framework. The
accuracy of the results obtained from this framework for the simulation of high
deformation free-surface flows is confirmed by a comparison with previous
numerical studies for the large amplitude oscillations of free liquid drops.
Our code's ability to produce high resolution benchmark calculations for
dynamic wetting flows is then demonstrated by simulating microdrop impact and
spreading on surfaces of greatly differing wettability. The simulations allow
one to see features of the process which go beyond the resolution available to
experimental analysis. Strong interfacial effects which are observed at the
microfluidic scale are then harnessed by designing surfaces of varying
wettability that allow new methods of flow control to be developed
Automated precision alignment of optical components for hydroxide catalysis bonding
We describe an interferometric system that can measure the alignment and separation of a polished face of a optical component and an adjacent polished surface. Accuracies achieved are ∼ 1μrad for the relative angles in two orthogonal directions and ∼ 30μm in separation. We describe the use of this readout system to automate the process of hydroxide catalysis bonding of a fused-silica component to a fused-silica baseplate. The complete alignment and bonding sequence was typically achieved in a timescale of a few minutes, followed by an initial cure of 10 minutes. A series of bonds were performed using two fluids - a simple sodium hydroxide solution and a sodium hydroxide solution with some sodium silicate solution added. In each case we achieved final bonded component angular alignment within 10 μrad and position in the critical direction within 4 μm of the planned targets. The small movements of the component during the initial bonding and curing phases were monitored. The bonds made using the sodium silicate mixture achieved their final bonded alignment over a period of ∼ 15 hours. Bonds using the simple sodium hydroxide solution achieved their final alignment in a much shorter time of a few minutes. The automated system promises to speed the manufacture of precision-aligned assemblies using hydroxide catalysis bonding by more than an order of magnitude over the more manual approach used to build the optical interferometer at the heart of the recent ESA LISA Pathfinder technology demonstrator mission. This novel approach will be key to the time-efficient and low-risk manufacture of the complex optical systems needed for the forthcoming ESA spaceborne gravitational waves observatory mission, provisionally named LISA
Approximation of tensor fields on surfaces of arbitrary topology based on local Monge parametrizations
We introduce a new method, the Local Monge Parametrizations (LMP) method, to
approximate tensor fields on general surfaces given by a collection of local
parametrizations, e.g.~as in finite element or NURBS surface representations.
Our goal is to use this method to solve numerically tensor-valued partial
differential equations (PDE) on surfaces. Previous methods use scalar
potentials to numerically describe vector fields on surfaces, at the expense of
requiring higher-order derivatives of the approximated fields and limited to
simply connected surfaces, or represent tangential tensor fields as tensor
fields in 3D subjected to constraints, thus increasing the essential number of
degrees of freedom. In contrast, the LMP method uses an optimal number of
degrees of freedom to represent a tensor, is general with regards to the
topology of the surface, and does not increase the order of the PDEs governing
the tensor fields. The main idea is to construct maps between the element
parametrizations and a local Monge parametrization around each node. We test
the LMP method by approximating in a least-squares sense different vector and
tensor fields on simply connected and genus-1 surfaces. Furthermore, we apply
the LMP method to two physical models on surfaces, involving a tension-driven
flow (vector-valued PDE) and nematic ordering (tensor-valued PDE). The LMP
method thus solves the long-standing problem of the interpolation of tensors on
general surfaces with an optimal number of degrees of freedom.Comment: 16 pages, 6 figure
Methods for eradication of the biofilms formed by opportunistic pathogens using novel techniques – A review
The inconvenient environmental conditions force microorganisms to colonize either abiotic surfaces or animal and plant tissues and, therefore, form more resistant structures – biofilms. The phenomenon of microbial adherence, opportunistic pathogens in particular, is of a great concern. Colonization of medical devices and biofilm formation on their surface, may lead to severe infections mainly in humans with impaired immune system. Although, current research consider various methods for prevention of microbial biofilms formation, still, once a biofilm is formed, its elimination is almost impossible. This study focuses on the overview of novel methods applied for eradication of mature opportunistic pathogens' biofilms. Among various techniques the following: cold plasma, electric field, ultrasounds, ozonated water treatment, phagotherapy, matrix targeting enzymes, bacteriocins, synthetic chemicals and natural origin compounds used for biofilm matrix disruption were briefly described
Plasma Nanoscience: from Nano-Solids in Plasmas to Nano-Plasmas in Solids
The unique plasma-specific features and physical phenomena in the
organization of nanoscale solid-state systems in a broad range of elemental
composition, structure, and dimensionality are critically reviewed. These
effects lead to the possibility to localize and control energy and matter at
nanoscales and to produce self-organized nano-solids with highly unusual and
superior properties. A unifying conceptual framework based on the control of
production, transport, and self-organization of precursor species is introduced
and a variety of plasma-specific non-equilibrium and kinetics-driven phenomena
across the many temporal and spatial scales is explained. When the plasma is
localized to micrometer and nanometer dimensions, new emergent phenomena arise.
The examples range from semiconducting quantum dots and nanowires, chirality
control of single-walled carbon nanotubes, ultra-fine manipulation of
graphenes, nano-diamond, and organic matter, to nano-plasma effects and
nano-plasmas of different states of matter.Comment: This is an essential interdisciplinary reference which can be used by
both advanced and early career researchers as well as in undergraduate
teaching and postgraduate research trainin
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