128,002 research outputs found

### Analytical Estimation of the Beam-Beam Interaction Limited Dynamic Apertures and Lifetimes in e^+e^- Circular Colliders

Physically speaking, the delta function like beam-beam nonlinear forces at
interaction points (IPs) act as a sum of delta function nonlinear multipoles.
By applying the general theory established in ref. 1, in this paper we
investigate analytically the beam-beam interaction limited dynamic apertures
and the corresponding beam lifetimes for both the round and the flat beams.
Relations between the beam-beam limited beam lifetimes and the beam-beam tune
shifts are established, which show clearly why experimentally one has always a
maximum beam-beam tune shift, \xi_{y, max}, around 0.045 for e-^+e$^- circular
colliders, and why one can use round beams to double this value approximately.
Comparisons with some machine parameters are given. Finally, we discuss the
mechanism of the luminosity reduction due to a definite collision crossing
angle.Comment: 25 page

### An Analysis of Phase Transition in NK Landscapes

In this paper, we analyze the decision version of the NK landscape model from
the perspective of threshold phenomena and phase transitions under two random
distributions, the uniform probability model and the fixed ratio model. For the
uniform probability model, we prove that the phase transition is easy in the
sense that there is a polynomial algorithm that can solve a random instance of
the problem with the probability asymptotic to 1 as the problem size tends to
infinity. For the fixed ratio model, we establish several upper bounds for the
solubility threshold, and prove that random instances with parameters above
these upper bounds can be solved polynomially. This, together with our
empirical study for random instances generated below and in the phase
transition region, suggests that the phase transition of the fixed ratio model
is also easy

### Gravitational Lensing and Anisotropies of CBR on the Small Angular Scales

We investigate the effect of gravitational lensing, produced by linear
density perturbations, for anisotropies of the Cosmic Background Radiation
(CBR) on scales of arcminutes. In calculations, a flat universe ($\Omega=1$)
and the Harrison-Zel'dovich spectrum ($n=1$) are assumed. The numerical results
show that on scales of a few arcminutes, gravitational lensing produces only
negligible anisotropies in the temperature of the CBR. Our conclusion disagrees
with that of Cay\'{o}n {\it et al.} who argue that the amplification of $\Delta
T/T$ on scales $\le 3'$ may even be larger than 100\%.Comment: Accepted by MNRAS. 16 pages, 2 figures, tarred, compressed and
uuencoded Postscript file

### Design Studies for a High Current Bunching System for CLIC Test Facility (CTF3) Drive Beam

A bunching system is proposed for the initial stage of CTF3 which consists of
one (two) 3 GHz prebunchers and one 3 GHz travelling wave (TW) buncher with
variable phase velocities. The electron beam is emitted from a 140 KV DC gun.
Since the macropulse beam current (3.5 A) at the exit of the TW buncher is
rather high, inside the TW buncher one has to take the beam loading effect into
consideration. By using PARMELA, it is shown numerically that the bunching
system can provide the bunches whose properties satisfy the design requirement
of CTF3. The 0.8 m long TW buncher working at 2pi/3 mode has two phase
velocities, 0.75 and 1. The dimensions of the caities in the two phase velocity
regions are proposed considering the beam loading effect. The transient beam
loading effect and the multibunch transverse instabilities are studied
numerically, and it is concluded that higher order mode couplers should be
installed in the TW buncher with the loaded quality factor of the dipole mode
lower than 80.Comment: 5 figures, presented at the Linear Accelerator Conference 2000,
August 2000, US

### Next-to-leading order QCD predictions for graviton and photon associated production in the Large Extra Dimensions model at the LHC

We present the calculations of the complete next-to-leading order(NLO) QCD
corrections to the inclusive total cross sections for the Kaluza-Klein(KK)
graviton and photon associated production process $pp \to \gamma G_{KK} + X$ in
the large extra dimensions(LED) model at the LHC. We show that the NLO QCD
corrections in general enhance the total cross sections and reduce the
dependence of the total cross sections on the factorization and renormalization
scales. When jet veto is considered, the NLO corrections reduce the total cross
sections. We also calculate some important differential cross sections for this
process at NLO: the missing transverse momentum distribution, the transverse
momentum distribution and the pseudorapidity distribution of photon.Comment: 28 pages, 14 figures; minor changes, version published in Phys.Rev.

### On the Triality Theory for a Quartic Polynomial Optimization Problem

This paper presents a detailed proof of the triality theorem for a class of
fourth-order polynomial optimization problems. The method is based on linear
algebra but it solves an open problem on the double-min duality left in 2003.
Results show that the triality theory holds strongly in a tri-duality form if
the primal problem and its canonical dual have the same dimension; otherwise,
both the canonical min-max duality and the double-max duality still hold
strongly, but the double-min duality holds weakly in a symmetrical form. Four
numerical examples are presented to illustrate that this theory can be used to
identify not only the global minimum, but also the largest local minimum and
local maximum.Comment: 16 pages, 1 figure; J. Industrial and Management Optimization, 2011.
arXiv admin note: substantial text overlap with arXiv:1104.297

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