1,467 research outputs found
Internet-Supported Multi-User Virtual and Physical Prototypes for Architectural Academic Education and Research
Architectural Engineering +Technolog
Self diffusion of particles in complex fluids: temporary cages and permanent barriers
We study the self diffusion of individual particles in dense (non-)uniform
complex fluids within dynamic density functional theory and explicitly account
for their coupling to the temporally fluctuating background particles. Applying
the formalism to rod-like particles in uniaxial nematic and smectic liquid
crystals, we find correlated diffusion in different directions: The temporary
cage formed by the neighboring particles competes with permanent barriers in
periodic inhomogeneous systems such as the lamellar smectic state and delays
self diffusion of particles even in uniform systems. We compare our theory with
recent experimental data on the self diffusion of fluorescently labelled
filamentous virus particles in aqueous dispersions in the smectic phase and
find qualitative agreement. This demonstrates the importance of explicitly
dealing with the time-dependent self-consistent molecular field that every
particle experiences.Comment: submitte
Feasiblity study for a 34 GHz (Ka band) gyroamplifier
The feasibility of using a gyroklystron power tube as the final amplifier in a 400 kW CW 34 GHz transmitter on the Goldstone Antenna is investigated. A conceptual design of the gyroklystron and the transmission line connecting it with the antenna feed horn is presented. The performance characteristics of the tube and transmission line are compared to the transmitter requirements for a deep space radar system. Areas of technical risk for a follow-on hardware development program for the gyroklystron amplifier and overmoded transmission line components are discussed
Involvement of an SCF(Slmb) complex in timely elimination of E2F upon initiation of DNA replication in Drosophila
BACKGROUND: Cul1 is a core component of the evolutionarily conserved SCF-type ubiquitin ligases that target specific proteins for destruction. SCF action contributes to cell cycle progression but few of the key targets of its action have been identified. RESULTS: We found that expression of the mouse Cul1 (mCul1) in the larval wing disc has a dominant negative effect. It reduces, but does not eliminate, the function of SCF complexes, promotes accumulation of Cubitus interruptus (a target of SCF action), triggers apoptosis, and causes a small wing phenotype. A screen for mutations that dominantly modify this phenotype showed effective suppression upon reduction of E2F function, suggesting that compromised downregulation of E2F contributes to the phenotype. Partial inactivation of Cul1 delayed the abrupt loss of E2F immunofluorescence beyond its normal point of downregulation at the onset of S phase. Additional screens showed that mild reduction in function of the F-box encoding gene slimb enhanced the mCul1 overexpression phenotype. Cell cycle modulation of E2F levels is virtually absent in slimb mutant cells in which slimb function is severely reduced. This implicates Slimb, a known targeting subunit of SCF, in E2F downregulation. In addition, Slimb and E2F interacted in vitro in a phosphorylation-dependent manner. CONCLUSION: We have used genetic and physical interactions to identify the G1/S transcription factor E2F as an SCF(Slmb )target in Drosophila. These results argue that the SCF(Slmb )ubiquitin ligase directs E2F destruction in S phase
Information and flux in a feedback controlled Brownian ratchet
We study a feedback control version of the flashing Brownian ratchet, in
which the application of the flashing potential depends on the state of the
particles to be controlled. Taking the view that the ratchet acts as a
Maxwell's demon, we study the relationship that exists between the performance
of the demon as a rectifier of random motion and the amount of information
gathered by the demon through measurements. In the context of a simple
measurement model, we derive analytic expressions for the flux induced by the
feedback ratchet when acting on one particle and a few particles, and compare
these results with those obtained with its open-loop version, which operates
without information. Our main finding is that the flux in the feedback case has
an upper bound proportional to the square-root of the information. Our results
provide a quantitative analysis of the value of information in feedback
ratchets, as well as an effective description of imperfect or noisy feedback
ratchets that are relevant for experimental applications.Comment: LaTeX, 13 pages, 2 figure
Irreversible and reversible modes of operation of deterministic ratchets
We discuss a problem of optimization of the energetic efficiency of a simple
rocked ratchet. We concentrate on a low-temperature case in which the
particle's motion in a ratchet potential is deterministic. We show that the
energetic efficiency of a ratchet working adiabatically is bounded from above
by a value depending on the form of ratchet potential. The ratchets with
strongly asymmetric potentials can achieve ideal efficiency of unity without
approaching reversibility. On the other hand we show that for any form of the
ratchet potential a set of time-protocols of the outer force exist under which
the operation is reversible and the ideal value of efficiency is also achieved.
The mode of operation of the ratchet is still quasistatic but not adiabatic.
The high values of efficiency can be preserved even under elevated
temperatures
Multiple current reversals in forced inhomogeneous ratchets
Transport properties of overdamped Brownian paricles in a rocked thermal
ratchet with space dependent friction coefficient is studied. By tuning the
parameters, the direction of current exhibit multiple reversals, both as a
function of the thermal noise strength as well as the amplitude of rocking
force. Current reversals also occur under deterministic conditions and exhibits
intriguing structure. All these features arise due to mutual interplay between
potential asymmetry,noise, driving frequency and inhomogeneous friction.Comment: 6 figure
The Use of Variable Stiffness Joints in Adaptive Structures
Adaptive structures are defined here as structures capable of counteracting actively the effect of external loads via controlled shape changes and redirection of the internal load path. These structures are integrated with sensors (e.g. strain, vision), control intelligence and actuators. This paper investigates the use of variable stiffness joints in adaptive structures to achieve large shape changes. Large shape changes are employed as a structural adaptation strategy to counteract the effect of the external load. The structure is designed to ‘morph’ into optimal shapes as the load changes. This way the stress can be homogenized avoiding peak demands that occur rarely. Numerical results show that when large shape changes are considered, material mass (and thus embodied energy) reduction is achieved with respect to both adaptive structures limited to small shape changes and optimised passive structures. Embodied energy savings become substantive when shape changes are allowed to go beyond conventional deflection limits. However, large shape changes require significant flexibility of the joints because their fixity can affect load-path and shape control. To address this problem, a variable stiffness joint is proposed. During shape/load-path control, the joint reduces its stiffness so that required deformation patterns can be achieved with low actuation energy. After shape control the joint recovers rigidity. Experimental studies are presented to show the potential for application of joints with variable stiffness in adaptive structures
Untersuchung des Stroemungsverlaufs von He/Ar- und He/SF₆-Gemischen in der Trennduese mit molekular angestroemten Drucksonden
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