3,396 research outputs found
Asymptotically maximal families of hypersurfaces in toric varieties
A real algebraic variety is maximal (with respect to the Smith-Thom
inequality) if the sum of the Betti numbers (with coefficients)
of the real part of the variety is equal to the sum of Betti numbers of its
complex part. We prove that there exist polytopes that are not Newton polytopes
of any maximal hypersurface in the corresponding toric variety. On the other
hand we show that for any polytope there are families of hypersurfaces
with the Newton polytopes that are
asymptotically maximal when tends to infinity. We also show that
these results generalize to complete intersections.Comment: 18 pages, 1 figur
Consideration of unresolved binaries with evaluation of the mass of star clusters
При различных предположениях о функции масс компонент двойных систем оценивается, как наличие неразрешенных двойных систем влияет на определение массы скопления.An influence of the presence of unresolved binaries onto star cluster mass estimation is evaluated with different assumptions on the mass function of binary components.Часть работ проведена при финансовой поддержке государства в лице Министерства образования и науки Российской Федерации (базовая часть госзадания, РК №AAAA-A17-117030310283-7), а также при финансовой поддержке Правительства РФ (постановление № 211, контракт № 02.A03.21.0006)
Radio-frequency Bloch-transistor electrometer
A quantum-limited electrometer based on charge modulation of the Josephson
supercurrent in the Bloch transistor inserted into a superconducting ring is
proposed. As this ring is inductive coupled to a high-Q resonance tank circuit,
the variations of the charge on the transistor island (input signal) are
converted into variations of amplitude and phase of radio-frequency
oscillations in the tank. These variations are amplified and then detected. The
output noise, the back-action fluctuations and their cross-correlation are
computed. It is shown that our device enables measurements of the charge with a
sensitivity which is determined by the energy resolution of its amplifier, that
can be reduced down to the standard quantum limit of \hbar/2. On the basis of
this setup a "back-action-evading" scheme of the charge measurements is
proposed.Comment: 5 pages incl. 2 figure
Unresolved Multiple Stars and Galactic Clusters' Mass Estimates
If not properly accounted for, unresolved binary stars can induce a bias in the photometric determination of star cluster masses inferred from star counts and the luminosity function. A correction factor close to 1.15 (for a binary fraction of 0.35) was found in Borodina et al., which needs to be applied to blind photometric mass estimates. This value for the correction factor was found to be smaller than literature values. In an attempt to lift this discrepancy, in this work the focus is on higher order multiple stars with the goal of investigating the effect of triple and quadruple systems adopting the same methodology and data set as in the quoted work. The result is that when triple and quadruple, together with binary, systems are properly accounted for, the actual cluster mass (computed as all stars were single) should be incremented by a factor of 1.18-1.27, depending on the cluster and when the binary fraction α is 0.35. Fitting formulae are provided to derive the increment factor for different binary star percentages. © 2021. The American Astronomical Society. All rights reserved.
Acceleration of the precession frequency for optically-oriented electron spins in ferromagnetic/semiconductor hybrids
Time-resolved Kerr rotation measurements were performed in InGaAs/GaAs
quantum wells nearby a doped Mn delta layer. Our magneto-optical results show a
typical time evolution of the optically-oriented electron spin in the quantum
well. Surprisingly, this is strongly affected by the Mn spins, resulting in an
increase of the spin precession frequency in time. This increase is attributed
to the variation in the effective magnetic field induced by the dynamical
relaxation of the Mn spins. Two processes are observed during electron spin
precession: a quasi-instantaneous alignment of the Mn spins with photo-excited
holes, followed by a slow alignment of Mn spins with the external transverse
magnetic field. The first process leads to an equilibrium state imprinted in
the initial precession frequency, which depends on pump power, while the second
process promotes a linear frequency increase, with acceleration depending on
temperature and external magnetic field. This observation yields new
information about exchange process dynamics and on the possibility of
constructing spin memories, which can rapidly respond to light while retaining
information for a longer period.Comment: 7 pages, 5 figure
Consistent alpha-cluster description of the 12C (0^+_2) resonance
The near-threshold 12C (0^+_2) resonance provides unique possibility for fast
helium burning in stars, as predicted by Hoyle to explain the observed
abundance of elements in the Universe. Properties of this resonance are
calculated within the framework of the alpha-cluster model whose two-body and
three-body effective potentials are tuned to describe the alpha - alpha
scattering data, the energies of the 0^+_1 and 0^+_2 states, and the
0^+_1-state root-mean-square radius. The extremely small width of the 0^+_2
state, the 0_2^+ to 0_1^+ monopole transition matrix element, and transition
radius are found in remarkable agreement with the experimental data. The
0^+_2-state structure is described as a system of three alpha-particles
oscillating between the ground-state-like configuration and the elongated chain
configuration whose probability exceeds 0.9
КВАНТОВО-ХИМИЧЕСКОЕ МОДЕЛИРОВАНИЕ СИН-АНТИ - ИЗОМЕРИЗАЦИИ В МЕТИЛЗАМЕЩЕННЫХ АЛЛИЛЬНЫХ КОМПЛЕКСАХ НИКЕЛЯ(II)
The syn-anti isomerization of bis-(η3 -allyl)nickel complexes (allyl – C3H5, 2-CH3C3H4, 1-CH3C3H4) has been studied using the density functional theory (DFT-PBE). Calculations indicated that in all cases isomerization goes through 3 steps according to η3 -η1 -η3 -mechanism. The rate-limiting step of that is vinyl fragment rotation in η1 -allyl ligand.Методом функционала плотности DFT-PBE проведено моделирование син-анти-изомеризации в бис-η3-аллильных комплексах никеля (аллил - C3H5, 2-CH3C3H4, 1-CH3C3H4). Расчеты показали, что во всех рассмотренных случаях изомеризация протекает в три стадии по η3-η1-η3-механизму с лимитирующей стадией поворота винильного фрагмента в η1-аллильном интермедиате
Optically controlled spin-polarization memory effect on Mn delta-doped heterostrucutres
We investigated the dynamics of the interaction between spin-polarized
photo-created carriers and Mn ions on InGaAs/GaAs:Mn structures. The carriers
are confined in an InGaAs quantum well and the Mn ions come from a Mn
delta-layer grown at the GaAs barrier close to the well. Even though the
carriers and the Mn ions are spatially separated, the interaction between them
is demonstrated by time-resolved spin-polarized photoluminescence measurements.
Using a pre-pulse laser excitation with an opposite circular-polarization
clearly reduces the polarization degree of the quantum-well emission for
samples where a strong magnetic interaction is observed. The results
demonstrate that the Mn ions act as a spin-memory that can be optically
controlled by the polarization of the photocreated carriers. On the other hand,
the spin-polarized Mn ions also affect the spin-polarization of the
subsequently created carriers as observed by their spin relaxation time. These
effects fade away with increasing time delays between the pulses as well as
with increasing temperatures.Comment: 12 pages, 5 figure
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