2,055 research outputs found
Analytic two-loop virtual corrections to
We compute the two-loop virtual corrections to the flavour changing neutral
current process . As calculation techniques integration by
parts identities and the method of differential equations are used. The result
is presented in closed form as a function of , where is the
invariant mass of the lepton pair and is the b-quark mass.Comment: 19 pages, 3 figures. Minor modifications, references adde
Leptonic decay of the Upsilon(1S) meson at third order in QCD
We present the complete next-to-next-to-next-to-leading order short-distance
and bound-state QCD correction to the leptonic decay rate
Gamma(Upsilon(1S)->l+l-) of the lowest-lying spin-1 bottomonium state. The
perturbative QCD prediction is compared to the measurement
Gamma(Upsilon(1S)->e+e-)=1.340(18) keV.Comment: 4 pages, 2 figure
The effect of multifocal contact lenses on the dynamic accommodation step response
Purpose: To measure the dynamic accommodation response (AR) to step stimuli with and without multifocal contact lenses (MFCLs), in emmetropes and myopes.Methods: Twenty-two adult subjects viewed alternating distance (0.25D) and near (3D) Maltese crosses placed in free space, through two contact lens types: single vision (SVCL) or centre-distance multifocal (MFCL; +2.50D add). The AR level was measured along with near to far (N–F) and far to near (F–N) step response characteristics: percentage of correct responses, magnitude, latency, peak velocity and duration of step response.Results: There was no difference between N–F and F–N responses, or between refractive groups in any aspect of the accommodation step response dynamics. The percentage of correct responses was unaffected by contact lens type. Through MFCLs, subjects demonstrated smaller magnitude, longer latency, shorter duration and slower peak velocity steps than through SVCLs. When viewing the near target, the AR through MFCLs was significantly lower than through SVCLs. When viewing the distance target with the MFCL, the focal points from rays travelling through the distance and near zones were approximately 0.004D behind and 2.50D in front of the retina, respectively. When viewing the near target, the respective values were approximately 1.89D behind and 0.61D in front of the retina.Conclusion: The defocus error required for accommodation control appears not to be solely derived from the distance zone of the MFCL. This results in reduced performance in response to abruptly changing vergence stimuli; however, these errors were small and unlikely to impact everyday visual tasks. There was a decrease in ocular accommodation during near tasks, which has previously been correlated with a reduced myopic treatment response through these lenses. With MFCLs, the estimated dioptric myopic defocus was the largest when viewing a distant stimulus, supporting the hypothesis that the outdoors provides a beneficial visual environment to reduce myopia progression
Two-phase flow experiments in a model of the hot leg of a pressurised water reactor
In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at FZD. The hot leg model is operated in the pressure chamber of the TOPFLOW test facility, which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the chamber. This technique makes it possible to visualise the two-phase flow through large windows, also at reactor-typical pressure levels. In order to optimise the optical observation possibilities, the test section was designed with a rectangular cross-section.
Experiments were performed with air and water at 1.5 and 3.0 bar at room temperature as well as with steam and water at 15, 30 and 50 bar and the corresponding saturation temperature (i.e. up to 264°C). The total of 194 runs are divided into 4 types of experiments covering stationary co-current flow, counter-current flow, flow without water circulation and transient counter-current flow limitation (CCFL) experiments.
This report provides a detailed documentation of the experiments including information on the experimental setup, experimental procedure, test matrix and on the calibration of the measuring devices. The available data is described and data sheets were arranged for each experiment in order to give an overview of the most important parameters. For the cocurrent flow experiments, water level histograms were arranged and used to characterise the flow in the hot leg. In fact, the form of the probability distribution was found to be sensitive to the boundary conditions and, therefore, is useful for the CFD comparison.
Furthermore, the flooding characteristics of the hot leg model plotted in terms of the classical Wallis parameter or Kutateladze number were found to fail to properly correlate the data of the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which takes the effect of viscosity into account
DnaK3 is involved in biogenesis and/or maintenance of thylakoid membrane protein complexes in the cyanobacterium Synechocystis sp. PCC 6803
DnaK3, a highly conserved cyanobacterial chaperone of the Hsp70 family, binds to cyanobacterial thylakoid membranes, and an involvement of dnak3 in the biogenesis of thylakoid membranes has been suggested. as shown here, light triggers synthesis of dnak3 in the cyanobacterium synechocystis sp. pcc 6803, which links dnak3 to the biogenesis of thylakoid membranes and to photosynthetic processes. in a dnak3 depleted strain, the photosystem content is reduced and the photosystem ii activity is impaired, whereas photosystem i is regular active. an impact of dnak3 on the activity of other thylakoid membrane complexes involved in electron transfer is indicated. in conclusion, dnak3 is a versatile chaperone required for biogenesis and/or maintenance of thylakoid membrane-localized protein complexes involved in electron transfer reactions. as mentioned above, hsp70 proteins are involved in photoprotection and repair of ps ii in chloroplasts
Physics, Stability and Dynamics of Supply Networks
We show how to treat supply networks as physical transport problems governed
by balance equations and equations for the adaptation of production speeds.
Although the non-linear behaviour is different, the linearized set of coupled
differential equations is formally related to those of mechanical or electrical
oscillator networks. Supply networks possess interesting new features due to
their complex topology and directed links. We derive analytical conditions for
absolute and convective instabilities. The empirically observed "bull-whip
effect" in supply chains is explained as a form of convective instability based
on resonance effects. Moreover, it is generalized to arbitrary supply networks.
Their related eigenvalues are usually complex, depending on the network
structure (even without loops). Therefore, their generic behavior is
characterized by oscillations. We also show that regular distribution networks
possess two negative eigenvalues only, but perturbations generate a spectrum of
complex eigenvalues.Comment: For related work see http://www.helbing.or
- …