27,523 research outputs found
Coulomb-blockade effect in nonlinear mesoscopic capacitors
We consider an interacting quantum dot working as a coherent source of single
electrons. The dot is tunnel coupled to a reservoir and capacitively coupled to
a gate terminal with an applied ac potential. At low frequencies, this is the
quantum analog of the RC circuit with a purely dynamical response. We
investigate the quantized dynamics as a consequence of ac pulses with large
amplitude. Within a Keldysh-Green function formalism we derive the
time-dependent current in the Coulomb blockade regime. Our theory thus extends
previous models that considered either noninteracting electrons in nonlinear
response or interacting electrons in the linear regime. We prove that the
electron emission and absorption resonances undergo a splitting when the
charging energy is larger than the tunnel broadening. For very large charging
energies, the additional peaks collapse and the original resonances are
recovered, though with a reduced amplitude. Quantization of the charge emitted
by the capacitor is reduced due to Coulomb repulsion and additional plateaus
arise. Additionally, we discuss the differential capacitance and resistance as
a function of time. We find that to leading order in driving frequency the
current can be expressed as a weighted sum of noninteracting currents shifted
by the charging energy.Comment: 13 pages, 9 figures. Minor changes. Published versio
Mechanical compatibility of sol–gel annealing with titanium for orthopaedic prostheses
Sol–gel processing is an attractive method for large-scale surface coating due to its facile and inexpensive preparation, even with the inclusion of precision nanotopographies. These are desirable traits for metal orthopaedic prostheses where ceramic coatings are known to be osteoinductive and the effects may be amplified through nanotexturing. However there are a few concerns associated with the application of sol–gel technology to orthopaedics. Primarily, the annealing stage required to transform the sol–gel into a ceramic may compromise the physical integrity of the underlying metal. Secondly, loose particles on medical implants can be carcinogenic and cause inflammation so the coating needs to be strongly bonded to the implant. These concerns are addressed in this paper. Titanium, the dominant material for orthopaedics at present, is examined before and after sol–gel processing for changes in hardness and flexural modulus. Wear resistance, bending and pull tests are also performed to evaluate the ceramic coating. The findings suggest that sol–gel coatings will be compatible with titanium implants for an optimum temperature of 500 °C
Automated knowledge capture in 2D and 3D design environments
In Life Cycle Engineering, it is vital that the engineering knowledge for the product is captured throughout its life cycle in a formal and structured manner. This will allow the information to be referred to in the future by engineers who did not work on the original design but are wanting to understand the reasons that certain design decisions were made. In the past, attempts were made to try to capture this knowledge by having the engineer record the knowledge manually during a design session. However, this is not only time-consuming but is also disruptive to the creative process. Therefore, the research presented in this paper is concerned with capturing design knowledge automatically using a traditional 2D design environment and also an immersive 3D design environment. The design knowledge is captured by continuously and non-intrusively logging the user during a design session and then storing this output in a structured eXtensible Markup Language (XML) format. Next, the XML data is analysed and the design processes that are involved can be visualised by the automatic generation of IDEF0 diagrams. Using this captured knowledge, it forms the basis of an interactive online assistance system to aid future users who are carrying out a similar design task
Gauge-Fixing and Residual Symmetries in Gauge/Gravity Theories with Extra Dimensions
We study compactified pure gauge/gravitational theories with gauge-fixing
terms and show that these theories possess quantum mechanical SUSY-like
symmetries between unphysical degrees of freedom. These residual symmetries are
global symmetries and generated by quantum mechanical N=2 supercharges. Also,
we establish new one-parameter family of gauge choices for higher-dimensional
gravity, and calculate as a check of its validity one graviton exchange
amplitude in the lowest tree-level approximation. We confirm that the result is
indeed -independent and the cancellation of the -dependence is
ensured by the residual symmetries. We also give a simple interpretation of the
vDVZ-discontinuity, which arises in the lowest tree-level approximation, from
the supersymmetric point of view.Comment: REVTeX4, 17 pages, 1 figur
Supporting reinterpretation in computer-aided conceptual design
This paper presents research that aims to inform the development of computational tools that better support design exploration and idea transformation - key objectives in conceptual design. Analyses of experimental data from two fields - product design and architecture - suggest that the interactions of designers with their sketches can be formalised according to a finite number of generalised shape rules defined within a shape grammar. Such rules can provide a basis for the generation of alternative design concepts and they have informed the development of a prototype shape synthesis system that supports dynamic reinterpretation of shapes in design activity. The notion of 'sub-shapes' is introduced and the significance of these to perception, recognition and the development of emergent structures is discussed. The paper concludes with some speculation on how such a system might find application in a range of design fields
Implementation of Fuzzy Logic in FPGA for Maze Tracking of a Mobile Robot Based on Ultrasonic Distance Measurement
This paper describes an application of fuzzy logic to solve the problem of an autonomous mobile robot in tracking the path within a maze. The robot equipped with ultrasonic transceivers to measure the distance between robot and the wall. The information of distance then will be processed using fuzzy-based algorithm and implemented in two chips FPGA. The FPGA has responsibility to formulize the rule of the fuzzy and generate the PWM signals for robot's motors as the result of fuzzy inference. Implementing all necessary fuzzy logic algorithms will require many FPGA resources. Therefore, we use two FPGAs: XC4010E and XC4005XL. The first one for the fuzzification and rule base evaluation, and it consumes 98% of its resources (CLBs). The second one for defuzzification and PWM output generation, which utilizes 78% of all its CLBs. By implementing fuzzy logic using FPGA, the robot achieves relatively safe tracking the path in real-time sense
Electron Temperature of Ultracold Plasmas
We study the evolution of ultracold plasmas by measuring the electron
temperature. Shortly after plasma formation, competition between heating and
cooling mechanisms drives the electron temperature to a value within a narrow
range regardless of the initial energy imparted to the electrons. In agreement
with theory predictions, plasmas exhibit values of the Coulomb coupling
parameter less than 1.Comment: 4 pages, plus four figure
1/m_b^2 correction to the left-right lepton polarization asymmetry in the decay B -> X_s mu^+ mu^-
Using a known result by Falk et al. for the 1/m_b^2 correction to the
dilepton invariant mass spectrum in the decay B \rightarrow X_s \mu^+ \mu^-, we
calculate the 1/m_b^2 correction to the left-right muon polarization asymmetry
in this decay. Employing an up-to-date range of values for the non-perturbative
parameter \lambda_1, we find that the correction is much smaller than it should
have been expected from the previous work by Falk et al.Comment: 8 pages, 2 figures included. Uses epsf.sty and rotate.sty. To appear
in Physical Review D. The complete postscript file is also available from URL
ftp://feynman.t30.physik.tu-muenchen.de/pub/preprints/ tum_t31_98_96.ps.g
Porting Decision Tree Algorithms to Multicore using FastFlow
The whole computer hardware industry embraced multicores. For these machines,
the extreme optimisation of sequential algorithms is no longer sufficient to
squeeze the real machine power, which can be only exploited via thread-level
parallelism. Decision tree algorithms exhibit natural concurrency that makes
them suitable to be parallelised. This paper presents an approach for
easy-yet-efficient porting of an implementation of the C4.5 algorithm on
multicores. The parallel porting requires minimal changes to the original
sequential code, and it is able to exploit up to 7X speedup on an Intel
dual-quad core machine.Comment: 18 pages + cove
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