29,874 research outputs found
Mitigating performance limitations of single beam-pipe circular e+e- colliders
Renewed interest in circular e+e- colliders has spurred designs of single
beam-pipe machines, like the CEPC in China, and double beam pipe ones, such as
the FCC-ee effort at CERN. Single beam-pipe designs profit from lower costs but
are limited by the number of bunches that can be accommodated in the machine.
We analyse these performance limitations and propose a solution that can
accommodate O(1000) bunches while keeping more than 90% of the ring with a
single beam pipe.Comment: Poster presented at IPAC'15, Richmond, VA, USA, May 201
The gravitational wave spectrum of non-axisymmetric, freely precessing neutron stars
Evidence for free precession has been observed in the radio signature of
several pulsars. Freely precessing pulsars radiate gravitationally at
frequencies near the rotation rate and twice the rotation rate, which for
rotation frequencies greater than Hz is in the LIGO band. In older
work, the gravitational wave spectrum of a precessing neutron star has been
evaluated to first order in a small precession angle. Here we calculate the
contributions to second order in the wobble angle, and we find that a new
spectral line emerges. We show that for reasonable wobble angles, the
second-order line may well be observable with the proposed advanced LIGO
detector for precessing neutron stars as far away as the galactic center.
Observation of the full second-order spectrum permits a direct measurement of
the star's wobble angle, oblateness, and deviation from axisymmetry, with the
potential to significantly increase our understanding of neutron star
structure.Comment: 22 pages, 1 figure. Minor changes in the text, typos correcte
The broad-band radio spectrum of LSI+61303 in outburst
Aims: Our aim is to explore the broad-band radio continuum spectrum of
LSI+61303 during its outbursts by employing the available set of secondary
focus receivers of the Effelsberg 100 m telescope. Methods: The clear
periodicity of the system LSI+61303 allowed observations to be scheduled
covering the large radio outburst in March-April 2012. We observed LSI+61303 on
14 consecutive days at 2.6, 4.85, 8.35, 10.45, 14.3, 23, and 32 GHz with a
cadence of about 12 hours followed by two additional observations several days
later. Based on these observations we obtained a total of 24 quasi-simultaneous
broad-band radio spectra. Results: During onset, the main flare shows an almost
flat broad-band spectrum, most prominently seen on March 27, 2012, where - for
the first time - a flat spectrum (alpha=0.00+/-0.07, S nu^alpha) is observed up
to 32 GHz (9 mm wavelength). The flare decay phase shows superimposed
'sub-flares' with the spectral index oscillating between -0.4 and -0.1 in a
quasi-regular fashion. Finally, the spectral index steepens during the decay
phase, showing optically thin emission with values alpha -0.5 to -0.7.
Conclusions: The radio characteristics of LSI+61303 compare well with those of
the microquasars XTE J1752-223 and Cygnus X-3. In these systems the flaring
phase is actually also composed of a sequence of outbursts with clearly
different spectral characteristics: a first outburst with a flat/inverted
spectrum followed by a bursting phase of optically thin emission.Comment: 4 pages, 3 figures, accepted for publication in A&
Modeling microwave/electron-cloud interaction
Starting from the separate codes BI-RME and ECLOUD or PyECLOUD, we are
developing a novel joint simulation tool, which models the combined effect of a
charged particle beam and of microwaves on an electron cloud. Possible
applications include the degradation of microwave transmission in
tele-communication satellites by electron clouds; the microwave-transmission
tecchniques being used in particle accelerators for the purpose of
electroncloud diagnostics; the microwave emission by the electron cloud itself
in the presence of a magnetic field; and the possible suppression of
electron-cloud formation in an accelerator by injecting microwaves of suitable
amplitude and frequency. A few early simulation results are presented.Comment: 3 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Ital
On the recombination in high-order harmonic generation in molecules
We show that the dependence of high-order harmonic generation (HHG) on the
molecular orientation can be understood within a theoretical treatment that
does not involve the strong field of the laser. The results for H_2 show
excellent agreement with time-dependent strong field calculations for model
molecules, and this motivates a prediction for the orientation dependence of
HHG from the N_2 3s_g valence orbital. For both molecules, we find that the
polarization of recombination photons is influenced by the molecular
orientation. The variations are particularly pronounced for the N_2 valence
orbital, which can be explained by the presence of atomic p-orbitals.Comment: 6 pages 7 figure
Evaluation of the importance of spin-orbit couplings in the nonadiabatic quantum dynamics with quantum fidelity and with its efficient "on-the-fly" ab initio semiclassical approximation
We propose to measure the importance of spin-orbit couplings (SOCs) in the
nonadiabatic molecular quantum dynamics rigorously with quantum fidelity. To
make the criterion practical, quantum fidelity is estimated efficiently with
the multiple-surface dephasing representation (MSDR). The MSDR is a
semiclassical method that includes nuclear quantum effects through interference
of mixed quantum-classical trajectories without the need for the Hessian of
potential energy surfaces. Two variants of the MSDR are studied, in which the
nuclei are propagated either with the fewest-switches surface hopping or with
the locally mean field dynamics. The fidelity criterion and MSDR are first
tested on one-dimensional model systems amenable to numerically exact quantum
dynamics. Then, the MSDR is combined with "on-the-fly" computed electronic
structure to measure the importance of SOCs and nonadiabatic couplings (NACs)
in the photoisomerization dynamics of CH2NH2+ considering 20 electronic states
and in the collision of F + H2 considering six electronic states.Comment: 9 pages, 3 figures, submitted to J. Chem. Phy
Leadership Structure and Corporate Governance in Switzerland
The question of whether the CEO should also serve as chairman of the board is one of the most hotly debated issues in the recent corporate governance discussion. While agencytheoretic arguments advocate a separation of decision and control functions, the empirical evidence focusing on U.S. companies is not conclusive. In this context evidence from a country with a different practice of CEO succession may provide important new insights with respect to the question of whether one leadership structure should generally be preferred to the other one. This article fills this gap by investigating the valuation effects of leadership structure in Switzerland where â in contrast to the U.S. â a separation of the CEO and chairman functions is common. Consistent with the majority of prior research focusing on the U.S., the authors found no evidence of a systematic and significant difference in valuation between firms with combined and firms with separated functions. They also investigated whether leadership structure is related to firm-level corporate governance characteristics and found a similar curvilinear relationship between leadership structure and managerial shareholdings as is observed between firm value and managerial shareholdings. An implication is that possible agency costs associated with a combined function are mitigated by a higher incentive alignment of the CEO/chairman through an adequate level of managerial shareholdings. Over the last few years corporate governance became an important investment criterion, which is for example reflected in the emergence of various corporate governance ratings. The authors of this article additionally investigated whether firm value is significantly related to firm level corporate governance as measured by a broad survey-based index for a representative sample of Swiss firms. They documented a positive and significant relationship between the corporate governance index and firm valuation. This finding is robust to controlling for a series of additional governance mechanisms related to ownership structure, board characteristics, and leverage as well as a potential endogeneity of these mechanisms.Leadership structure; Firm valuation; Corporate governance; Managerial shareholdings
Evolution of Cooperative Networks and the Emergence of Leadership
A generic property of biological, social and economical networks is their ability to evolve in time, creating or supressing links. We model this situation with an adaptive network of agents playing a Prisoner's Dilemma game. Each agent plays with its local neighbors, collects an aggregate payoff and imitates the strategy of its best neighbor. Furthermore we allow the agents adapt their local neighborhood according to their satisfaction level and the strategy played. Therefore each agent will have diverse environments that induces an interesting dynamics in the cooperation fraction of the whole network. In the absence of noise, a steady state is always reached, where the strategies and the neighborhoods remain stationary, and where for a wide range of parameter values, an almost full cooperative outcome is obtained. The topology of the network in these states reveals that cooperators with a large number of connections emerges. These "leaders" are shown to be very important in understanding the global stability of the final steady state. If the "leaders" are perturbated, then global cascades arise and the system oscillates between the nearly full defection network and the fully cooperative outcome, before settling again in a nearly fully cooperative outcome.Cooperation -- Evolutionary Game Theory -- Stochastic Networks -- Prisoner Dilemma
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