Luminosity is the key quantity characterizing the performance of charged particle colliders. Precise luminosity determination is an important task in collider physics. Part of this task is the proper ...calibration of detectors dedicated for luminosity measurements. The wide-used experimental method of calibration is the van-der-Meer scan, which is the beam separation scan performed at specifically optimized beam conditions. This work is devoted to modeling this scan with the q-Gaussian distribution of particles in colliding beams. Because of its properties, the q-Gaussian distribution is believed to describe the density closer to reality than regular Gaussian-based models. In this work, the q-Gaussian model is applied for van-der-Meer scan modeling, and the benefits of this model for luminosity calibration task are demonstrated.
Phase transitions in 2D Potts models with the number of spin states
q
= 4 and 5 have been studied by computer simulation. Systems with linear sizes
L
= 21–180 have been considered. As follows from ...numerical data, the 2D Potts model on the hexagonal lattice demonstrates a first-order phase transition for the number of spin states
q
= 5 and a second-order phase transition for
q
= 4.
Computer simulation of the three-component Potts model on a hexagonal lattice was carried out using the Monte Carlo method. Systems with linear dimensions
L
×
L
=
N
,
L
= 20–320 in units of ...interatomic distances are considered. Based on the theory of finite-size scaling, the static critical exponents of heat capacity α, susceptibility γ, magnetization β, and correlation radius ν are calculated. The data we obtained confirm that in the considered Potts model on a hexagonal lattice, a second-order phase transition is observed with critical exponents corresponding to the universality class of the three-component Potts model.
Using computer-based simulation methods, phase transitions in the three-dimensional weakly diluted Potts model with the spin state number
q
= 5 are studied. Systems with linear dimensions
L
×
L
×
L
... =
N
,
L
= 10–40, at spin concentrations
p
= 1.00 and 0.90 are considered. The obtained numerical data indicate that introduction of a minor disorder in the form of nonmagnetic impurities (
p
= 0.90) into the three-dimensional Potts model with
q
= 5 is not significant for the first-order phase transition.
The influence of a weak disorder in the form of quenched nonmagnetic impurities on the phase transitions (PTs) in a three-dimensional 5-state Potts model is studied using the cluster Wolff algorithm ...of the Monte Carlo method. Systems with linear sizes
L
= 10–120 at spin concentrations
p
= 1.00 and 0.80 are considered. Using the fourth-order Binder cumulant method and histogram analysis, we show that the introduction of a weak quenched disorder (
p
= 0.80) in the form of nonmagnetic impurities changes a first-order PT into a second-order PT.
At the Large Hadron Collider (LHC), absolute luminosity calibrations obtained by the van der Meer (
vdM
) method are affected by the mutual electromagnetic interaction of the two beams. The colliding ...bunches experience relative orbit shifts, as well as optical distortions akin to the dynamic-
β
effect, that both depend on the transverse beam separation and must therefore be corrected for when deriving the absolute luminosity scale. In the
vdM
regime, the beam–beam parameter is small enough that the orbit shift can be calculated analytically. The dynamic-
β
corrections to the luminometer calibrations, however, had until the end of Run 2 been estimated in the linear approximation only. In this report, the influence of beam–beam effects on the
vdM
-based luminosity scale is quantified, together with the associated systematic uncertainties, by means of simulations that fully take into account the non-linearity of the beam–beam force, as well as the resulting non-Gaussian distortions of the transverse beam distributions. Two independent multiparticle simulations, one limited to the weak-strong approximation and one that models strong-strong effects in a self-consistent manner, are found in excellent agreement; both predict a percent-level shift of the absolute
pp
-luminosity values with respect to those assumed until recently in the physics publications of the LHC experiments. These results also provide guidance regarding further studies aimed at reducing the beam–beam-related systematic uncertainty on beam–beam corrections to absolute luminosity calibrations by the van der Meer method.
Hypoxia causes depression of synaptic plasticity, hyperexcitation of neuronal networks, and the death of specific populations of neurons. However, brief episodes of hypoxia can promote the adaptation ...of cells. Hypoxic preconditioning is well manifested in glutamatergic neurons, while this adaptive mechanism is virtually suppressed in GABAergic neurons. Here, we show that brain-derived neurotrophic factor (BDNF) overexpression in neurons enhances the preconditioning effect of brief episodes of hypoxia. The amplitudes of the NMDAR- and AMPAR-mediated Ca
2+
responses of glutamatergic and GABAergic neurons gradually decreased after repetitive brief hypoxia/reoxygenation cycles in cell cultures transduced with the (AAV)-Syn-BDNF-EGFP virus construct. In contrast, the amplitudes of the responses of GABAergic neurons increased in non-transduced cultures after preconditioning. The decrease of the amplitudes in GABAergic neurons indicated the activation of mechanisms of hypoxic preconditioning. Preconditioning suppressed apoptotic or necrotic cell death. This effect was most pronounced in cultures with BDNF overexpression. Knockdown of BDNF abolished the effect of preconditioning and promoted the death of GABAergic neurons. Moreover, the expression of the anti-apoptotic genes Stat3, Socs3, and Bcl-xl substantially increased 24 h after hypoxic episodes in the transduced cultures compared to controls. The expression of genes encoding the pro-inflammatory cytokines IL-10 and IL-6 also increased. In turn, the expression of pro-apoptotic (Bax, Casp-3, and Fas) and pro-inflammatory (IL-1β and TNFα) genes decreased after hypoxic episodes in cultures with BDNF overexpression. Inhibition of vesicular BDNF release abolished its protective action targeting inhibition of the oxygen-glucose deprivation (OGD)-induced Ca
2+
i
increase in GABAergic and glutamatergic neurons, thus promoting their death. Bafilomycin A1, Brefeldin A, and tetanus toxin suppressed vesicular release (including BDNF) and shifted the gene expression profile towards excitotoxicity, inflammation, and apoptosis. These inhibitors of vesicular release abolished the protective effects of hypoxic preconditioning in glutamatergic neurons 24 h after hypoxia/reoxygenation cycles. This finding indicates a significant contribution of vesicular BDNF release to the development of the mechanisms of hypoxic preconditioning. Thus, our results demonstrate that BDNF plays a pivotal role in the activation and enhancement of the preconditioning effect of brief episodes of hypoxia and promotes tolerance of the most vulnerable populations of GABAergic neurons to hypoxia/ischemia.
The relative variances of the magnetization
R
m
, heat capacity
R
c
, and susceptibility
R
χ
are calculated by the Monte Carlo method in the spin lattice four-component weakly diluted Potts model on ...a square lattice at a spin density
p
= 0.80. It is shown that introducing a disorder in the form of nonmagnetic impurities into the 2D Potts model leads to nonzero values of
R
m
,
R
c
, and
R
χ
at the critical point. It has been found that these values decrease noticeably for systems with linear sizes
L
≥ 120 interatomic distances.
The phase transitions in the two-dimensional diluted Potts model with the number of spin states
q
= 3 are studied by computer simulation method. The systems with linear sizes
L
×
L = N
,
L
= 10–160 ...at spin concentrations
p
= 1.00, 0.80 are considered. The obtained numerical data show that the second-order phase transition takes place in the pure Potts model with the number of spin states
q
= 3, according to the theory. The introduction of a disorder in the form of nonmagnetic impurities (
p
= 0.80) in the Potts model with
q
= 3 conserves the second-order phase transition.
PDF
