17,776 research outputs found
Gated rotation mechanism of site-specific recombination by ÏC31 integrase
Integrases, such as that of the Streptomyces temperate bacteriophage ÏC31, promote site-specific recombination between DNA sequences in the bacteriophage and bacterial genomes to integrate or excise the phage DNA. ÏC31 integrase belongs to the serine recombinase family, a large group of structurally related enzymes with diverse biological functions. It has been proposed that serine integrases use a âsubunit rotationâ mechanism to exchange DNA strands after double-strand DNA cleavage at the two recombining att sites, and that many rounds of subunit rotation can occur before the strands are religated. We have analyzed the mechanism of ÏC31 integrase-mediated recombination in a topologically constrained experimental system using hybrid âphesâ recombination sites, each of which comprises a ÏC31 att site positioned adjacent to a regulatory sequence recognized by Tn3 resolvase. The topologies of reaction products from circular substrates containing two phes sites support a right-handed subunit rotation mechanism for catalysis of both integrative and excisive recombination. Strand exchange usually terminates after a single round of 180° rotation. However, multiple processive â360° rotationâ rounds of strand exchange can be observed, if the recombining sites have nonidentical base pairs at their centers. We propose that a regulatory âgatingâ mechanism normally blocks multiple rounds of strand exchange and triggers product release after a single round
Continuous maintenance and the future â Foundations and technological challenges
High value and long life products require continuous maintenance throughout their life cycle to achieve required performance with optimum through-life cost. This paper presents foundations and technologies required to offer the maintenance service. Component and system level degradation science, assessment and modelling along with life cycle âbig dataâ analytics are the two most important knowledge and skill base required for the continuous maintenance. Advanced computing and visualisation technologies will improve efficiency of the maintenance and reduce through-life cost of the product. Future of continuous maintenance within the Industry 4.0 context also identifies the role of IoT, standards and cyber security
Beltrami state in black-hole accretion disk: A magnetofluid approach
Using the magnetofluid unification framework, we show that the accretion disk
plasma (embedded in the background geometry of a blackhole) can relax to a
class of states known as the Beltrami-Bernoulli (BB) equilibria. Modeling the
disk plasma as a Hall MHD system, we find that the space-time curvature can
significantly alter the magnetic/velocity decay rate as we move away from the
compact object; the velocity profiles in BB states, for example, deviate
substantially from the predicted corresponding geodesic velocity profiles.
These departures imply a rich interplay of plasma dynamics and general
relativity revealed by examining the corresponding Bernoulli condition
representing "homogeneity" of total energy. The relaxed states have their
origin in the constraints provided by the two helicity invariants of Hall MHD.
These helicities conspire to introduce a new oscillatory length scale into the
system that is strongly influenced by relativistic and thermal effects.Comment: 8 figure
Steam storage systems for flexible biomass CHP plants - Evaluation and initial model based calculation
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Within the present study a novel concept for the demand-oriented power generation of a solid-biomass fueled combined heat and power (CHP) plant is investigated. The integration of a steam storage system into the plants process enables a decoupling of the steam (boiler) and the power generation (steam turbine). By buffering the steam, the power output of the turbine can be adjusted without changing the rated thermal capacity of the plant. Various available storage systems are selected and comparatively evaluated applying the adapted analytic hierarchy process (AHP). The technology assessment revealed that the combination of a steam accumulator and solid concrete storage represents the best suiting option. An initial model based simulation study is performed to identify the fundamental behaviour of this system, integrated in a biomass CHP plant. The operation principle is has proved their technical feasibility and seems to be applicable at a commercial scale. According to the modelling results flexible short term power generation in a time range of up to fifteen minutes is applicable. A load-range of almost the plants rated capacity can be achieved
Anti-aliasing with stratified B-spline filters of arbitrary degree
A simple and elegant method is presented to perform anti-aliasing in raytraced images. The method uses stratified
sampling to reduce the occurrence of artefacts in an image and features a B-spline filter to compute the final
luminous intensity at each pixel. The method is scalable through the specification of the filter degree. A B-spline
filter of degree one amounts to a simple anti-aliasing scheme with box filtering. Increasing the degree of the B-spline generates progressively smoother filters. Computation of the filter values is done in a recursive way, as part of a sequence of Newton-Raphson iterations, to obtain the optimal sample positions in screen space. The proposed method can perform both anti-aliasing in space and in time, the latter being more commonly known as motion blur. We show an application of the method to the ray casting of implicit procedural surfaces
Extraction and tribological investigation of top piston ring zone oil from a gasoline engine
With tightening emission regulations, increased expected fuel economy, and longer drain intervals impacting on lubricant formulation, greater understanding of how oil degrades in an automotive engine is becoming ever more important. Equally significant is the effect that this degraded lubricant has on the tribological operation of the engine, particularly its overall internal friction and component wear. In a previous paper, four tests to degrade oil in a single cylinder engine were reported [1]. These tests were set up such that the lubricating oil was degraded in the ring pack before returning to the sump, where it was sampled and chemical and rheological analysis undertaken. This paper reports the extension of this work using the same Hydra engine and describes how oil has additionally been extracted from the rear of the top piston ring during engine operation. This extracted oil has then been subjected to similar analysis as the sump oil samples in the previous tests, along with additional analysis to look at the tribological properties of the oil using tribometers. The results clearly show significant differences in the rheological, tribological, and chemical properties of the fresh oil and used sump oil samples when compared with the top ring zone (TRZ) oil samples, particularly the effect of load on the levels of volatiles present in the TRZ samples and their effect on traction and friction coefficient values during tribological testing
Decelerating microdynamics can accelerate macrodynamics in the voter model
For the voter model, we study the effect of a memory-dependent transition
rate. We assume that the transition of a spin into the opposite state decreases
with the time it has been in its current state. Counter-intuitively, we find
that the time to reach a macroscopically ordered state can be accelerated by
slowing-down the microscopic dynamics in this way. This holds for different
network topologies, including fully-connected ones. We find that the ordering
dynamics is governed by two competing processes which either stabilize the
majority or the minority state. If the first one dominates, it accelerates the
ordering of the system. The conclusions of this Letter are not restricted to
the voter model, but remain valid to many other spin systems as well.Comment: See http://www.sg.ethz.ch for related publication
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