4,974 research outputs found
Perturbation theory for O(3) topological charge correlators
To check the consistency of positivity requirements for the two-point
correlation function of the topological charge density, which were identified
in a previous paper, we are computing perturbatively this two-point correlation
function in the two-dimensional O(3) model. We find that at the one-loop level
these requirements are fulfilled.Comment: v1: 27 pages, 7 figures; v2: 28 pages, 8 figures, matches published
versio
Towards Kaluza-Klein Dark Matter on Nilmanifolds
We present a first study of the field spectrum on a class of
negatively-curved compact spaces: nilmanifolds or twisted tori. This is a case
where analytical results can be obtained, allowing to check numerical methods.
We focus on the Kaluza-Klein expansion of a scalar field. The results are then
applied to a toy model where a natural Dark Matter candidate arises as a stable
massive state of the bulk scalar.Comment: 32 pages, 8 figures; v2: few additions, published versio
A kinetics and mechanistic study of the atmospherically relevant reaction between molecular chlorine and dimethyl sulfide (DMS)
A gas-phase kinetics study of the atmospherically important reaction between Cl2 and dimethyl sulfide (DMS)Cl2 + CH3SCH3 → products has been made using a flow-tube interfaced to a photoelectron spectrometer. The rate constant for this reaction has been measured at 1.6 and 3.0 torr at T = (294 ± 2) K as (3.4 ± 0.7) × 10–14 cm3 molecule–1 s–1. Reaction (1) has been found to proceed via an intermediate, (CH3)2SCl2, to give CH3SCH2Cl and HCl as the products. The mechanism of this reaction and the structure of the intermediate were investigated using electronic structure calculations. A comparison of the mechanisms of the reactions between Cl atoms and DMS, and Cl2 and DMS has been made and the relevance of the results to atmospheric chemistry is discussed
Renormalization and topological susceptibility on the lattice: SU(2) Yang-Mills theory
The renormalization functions involved in the determination of the
topological susceptibility in the SU(2) lattice gauge theory are extracted by
direct measurements, without relying on perturbation theory. The determination
exploits the phenomenon of critical slowing down to allow the separation of
perturbative and non-perturbative effects. The results are in good agreement
with perturbative computations.Comment: 12 pages + 4 figures (PostScript); report no. IFUP-TH 10/9
A multi-physics approach to simulate the RF heating 3D power map induced by the proton beam in a beam intercepting device
The project High Luminosity Large Hadron Collider (HL-LHC) calls for a streaking beam intensity and brightness in the LHC machine. In such a scenario, beam-environment electromagnetic interactions are a crucial topic: they could lead to uneven power deposition in machine equipment. The resulting irregular temperature distribution would generate local thermal gradients, this would create mechanical stresses which could lead to cracks and premature failure of accelerator devices. This work presents a method to study this phenomenon by means of coupled electro-thermomechanical simulations. Further, an example of application on a real HL-LHC device is also discussed
Transparency and Oversight of the Council’s Budget: Council executive powers. CEPS Research Report No. 2017/11, July 2017
This briefing introduces the challenges that have been faced in delivering a discharge
of the Council’s budget over the last decade, with particular regard to the Council’s
executive activities. The authors analyse the institutional and legal constraints and
put forward a number of recommendations aimed at achieving more accountability
regarding the Council’s budget and executive expenditure without resorting to treaty
reform
Effects of rail dynamics and friction characteristics on curve squeal
Curve squeal in railway vehicles is an instability mechanism that arises in tight curves under certain running and environmental conditions. In developing a model the most important elements are the characterisation of friction coupled with an accurate representation of the structural dynamics of the wheel. However, the role played by the dynamics of the rail is not fully understood and it is unclear whether this should be included in a model or whether it can be safely neglected. This paper makes use of previously developed time domain and frequency domain curve squeal models to assess whether the presence of the rail and the falling characteristics of the friction force can modify the instability mechanisms and the final response. For this purpose, the time-domain model has been updated to include the rail dynamics in terms of its state space representation in various directions. Frequency domain and time domain analyses results show that falling friction is not the only reason for squeal and rail dynamics can play an important role, especially under constant friction conditions
Sound power and vibration levels for two different piano soundboards
This paper compares the sound power and vibration levels for two different soundboards for upright pianos. One of them is made of laminated spruce and the other of solid spruce (tone-wood). These differ also in the number of ribs and manufacturing procedure. The methodology used is defined in two major steps: (i) acoustic power due to a unit force is obtained reciprocally by measuring the acceleration response of the piano soundboards when excited by acoustic waves in reverberant field; (ii) impact tests are adopted to measure driving point and spatially-averaged mean-square transfer mobility. The results show that, in the mid-high frequency range, the soundboard made of solid spruce has a greater vibrational and acoustic response than the laminated soundboard. The effect of string tension is also addressed, showing that is only relevant at low frequencies
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