212 research outputs found
The Cell Wall of Seagrasses: Fascinating, Peculiar and a Blank Canvas for Future Research
Seegrasses are a polyphyletic group of angiosperm plants, which evolved from early monocotyledonous land plants and returned to the marine environment around 140 million years ago. Today, seagrasses comprise the five families Zosteraceae, Hydrocharitaceae, Posidoniaceae, Cymodoceaceae, and Ruppiaceae and form important coastal ecosystems worldwide. Despite of this ecological importance, the existing literature on adaption of these angiosperms to the marine environment and especially their cell wall composition is limited up to now. A unique feature described for some seagrasses is the occurrence of polyanionic, low-methylated pectins mainly composed of galacturonic acid and apiose (apiogalacturonans). Furthermore, sulfated galactans have been detected in some species. Recently, arabinogalactan-proteins (AGPs), highly glycosylated proteins of the cell wall of land plants, have been isolated for the first time from a seagrass of the baltic sea. Obviously, seagrass cell walls are characterized by new combinations of structural polysaccharide and glycoprotein elements known from macroalgae and angiosperm land plants. In this review, current knowledge on cell walls of seagrasses is summarized and suggestions for future investigations are given
Hamilton Geometry - Phase Space Geometry from Modified Dispersion Relations
Quantum gravity phenomenology suggests an effective modification of the
general relativistic dispersion relation of freely falling point particles
caused by an underlying theory of quantum gravity. Here we analyse the
consequences of modifications of the general relativistic dispersion on the
geometry of spacetime in the language of Hamilton geometry. The dispersion
relation is interpreted as the Hamiltonian which determines the motion of point
particles. It is a function on the cotangent bundle of spacetime, i.e. on phase
space, and determines the geometry of phase space completely, in a similar way
as the metric determines the geometry of spacetime in general relativity. After
a review of the general Hamilton geometry of phase space we discuss two
examples. The phase space geometry of the metric Hamiltonian
and the phase space geometry of the first order q-de
Sitter dispersion relation of the form which is suggested from quantum gravity phenomenology. We
will see that for the metric Hamiltonian the geometry of phase space is
equivalent to the standard metric spacetime geometry from general relativity.
For the q-de Sitter Hamiltonian the Hamilton equations of motion for
point particles do not become autoparallels but contain a force term, the
momentum space part of phase space is curved and the curvature of spacetime
becomes momentum dependent.Comment: 6 page
Hamilton geometry: Phase space geometry from modified dispersion relations
We describe the Hamilton geometry of the phase space of particles whose
motion is characterised by general dispersion relations. In this framework
spacetime and momentum space are naturally curved and intertwined, allowing for
a simultaneous description of both spacetime curvature and non-trivial momentum
space geometry. We consider as explicit examples two models for Planck-scale
modified dispersion relations, inspired from the -de Sitter and
-Poincar\'e quantum groups. In the first case we find the expressions
for the momentum and position dependent curvature of spacetime and momentum
space, while for the second case the manifold is flat and only the momentum
space possesses a nonzero, momentum dependent curvature. In contrast, for a
dispersion relation that is induced by a spacetime metric, as in General
Relativity, the Hamilton geometry yields a flat momentum space and the usual
curved spacetime geometry with only position dependent geometric objects.Comment: 32 pages, section on quantisation of the theory added, comments on
additin of momenta on curved momentum spaces extende
Coupled Rotary and Oscillatory Motion in a Second-Generation Molecular Motor Pd Complex
Molecular machines offer many opportunities for the development of responsive materials and introduce autonomous motion in molecular systems. While basic molecular switches and motors carry out one type of motion upon being exposed to an external stimulus, the development of molecular systems capable of performing coupled motions is essential for the development of more advanced molecular machinery. Overcrowded alkene-based rotary molecular motors are an ideal basis for the design of such systems as they undergo a controlled rotation initiated by light allowing for excellent spatio-temporal precision. Here, we present an example of a Pd complex of a second-generation rotary motor whose Pd center undergoes a coupled oscillatory motion relative to the motor core upon rotation of the motor. We have studied this phenomenon by UV-vis, NMR, and density functional theory calculations to support our conclusions. With this demonstration of a coupled rotation-oscillation motion powered by a light-driven molecular motor, we provide a solid basis for the development of more advanced molecular machines integrating different types of motion in their operation
Direct laser-written optomechanical membranes in fiber Fabry-Perot cavities
Integrated micro and nanophotonic optomechanical experiments enable the
manipulation of mechanical resonators on the single phonon level. Interfacing
these structures requires elaborate techniques limited in tunability,
flexibility, and scaling towards multi-mode systems. Here, we demonstrate a
cavity optomechanical experiment using 3D-laser-written polymer membranes
inside fiber Fabry-Perot cavities. Vacuum coupling strengths of ~ 30 kHz to the
fundamental megahertz mechanical mode are reached. We observe optomechanical
spring tuning of the mechanical resonator by tens of kHz exceeding its
linewidth at cryogenic temperatures. The extreme flexibility of the laser
writing process allows for a direct integration of the membrane into the
microscopic cavity. The direct fiber coupling, its scaling capabilities to
coupled resonator systems, and the potential implementation of dissipation
dilution structures and integration of electrodes make it a promising platform
for fiber-tip integrated accelerometers, optomechanically tunable multi-mode
mechanical systems, or directly fiber-coupled systems for microwave to optics
conversion.Comment: 10 pages, 5 figure
Ecological and Economic Feasibility of Inductive Heating for Sustainable Press Hardening Processes
Press hardening is an established process for the production of high-strength lightweight structural automotive parts, like the B-pillar. While lightweight design is an important aspect of emission reduction during the use phase, emissions arising in other phases of the automotive lifecycle also need to be considered. Roller-hearth-furnaces, as used during the press hardening process, present a non-negligible source of greenhouse gas emissions in part production processes. Alternative heating methods, such as inductive heating, may pose a possibility to reduce emissions during the manufacturing process, while also offering additional advantages in high process flexibility, high energy efficiency and low space requirements. However, there are multiple challenges when it comes to inductive heating of sheet metal for industrial processes, such as homogeneity of heating and resulting material properties. Therefore, various investigation on the usability of inductive heating for press hardening process have been conducted. Recently, an inductive heating process utilizing a longitudinal field inductor for industrial press hardening has been developed, showing good results in regard to process homogeneity, heating times and material properties. This process is used as a baseline for an ecological and economical assessment of inductive heating for industrial press hardening processes in comparison to traditional gas-fired furnaces. The reference values for a comparison on cost and emission are based on a gas-fired conveyor furnace with constant speed used for the heating of sheet metal for press hardening. The share of furnace operation modes, like standby and production with varying good-mass flows, as well as resulting natural gas demands are provided. From this data, specific energy requirements of heated sheet metal can be derived for various material mass flows and utilization scenarios, which serve as a baseline for the cost and emission comparison.
The objective of this study is to determine the emissions and costs for inductive heating compared to conventional gas-fired roller-hearth furnaces for different parameter-set of boundary conditions like product mass flow, energy prices, emission factors depending on energy transition scenarios. Based on this evaluation matrix, break-even conditions favoring inductive heating can be identified.&nbs
Planck-scale-modified dispersion relations in homogeneous and isotropic spacetimes
The covariant understanding of dispersion relations as level sets of Hamilton functions on phase space enables us to derive the most general dispersion relation compatible with homogeneous and isotropic spacetimes. We use this concept to present a Planck-scale deformation of the Hamiltonian of a particle in Friedman-Lemaître-Robertson-Walker (FLRW) geometry that is locally identical to the κ-Poincaré dispersion relation, in the same way as the dispersion relation of point particles in general relativity is locally identical to the one valid in special relativity. Studying the motion of particles subject to such a Hamiltonian, we derive the redshift and lateshift as observable consequences of the Planck-scale deformed FLRW universe. © 2017 American Physical Society
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