2,145 research outputs found
Hankel determinants, Pad\'e approximations, and irrationality exponents
The irrationality exponent of an irrational number , which measures the
approximation rate of by rationals, is in general extremely difficult to
compute explicitly, unless we know the continued fraction expansion of .
Results obtained so far are rather fragmentary, and often treated case by case.
In this work, we shall unify all the known results on the subject by showing
that the irrationality exponents of large classes of automatic numbers and
Mahler numbers (which are transcendental) are exactly equal to . Our classes
contain the Thue--Morse--Mahler numbers, the sum of the reciprocals of the
Fermat numbers, the regular paperfolding numbers, which have been previously
considered respectively by Bugeaud, Coons, and Guo, Wu and Wen, but also new
classes such as the Stern numbers and so on. Among other ingredients, our
proofs use results on Hankel determinants obtained recently by Han.Comment: International Mathematics Research Notices 201
Ab initio study of the giant ferroelectric distortion and pressure induced spin-state transition in BiCoO3
Using configuration-state-constrained electronic structure calculations based
on the generalized gradient approximation plus Hubbard U method, we sought the
origin of the giant tetragonal ferroelectric distortion in the ambient phase of
the potentially multiferroic material BiCoO3 and identified the nature of the
pressure induced spin-state transition. Our results show that a strong Bi-O
covalency drives the giant ferroelectric distortion, which is further
stabilized by an xy-type orbital ordering of the high-spin (HS) Co3+ ions. For
the orthorhombic phase under 5.8 GPa, we find that a mixed HS and low-spin (LS)
state is more stable than both LS and intermediate-spin (IS) states, and that
the former well accounts for the available experimental results. Thus, we
identify that the pressure induced spin-state transition is via a mixed HS+LS
state, and we predict that the HS-to-LS transition would be complete upon a
large volume decrease of about 20%.Comment: 6 pages, 6 figures, 2 table
LAMDA-SSL: Semi-Supervised Learning in Python
LAMDA-SSL is open-sourced on GitHub and its detailed usage documentation is
available at https://ygzwqzd.github.io/LAMDA-SSL/. This documentation
introduces LAMDA-SSL in detail from various aspects and can be divided into
four parts. The first part introduces the design idea, features and functions
of LAMDA-SSL. The second part shows the usage of LAMDA-SSL by abundant examples
in detail. The third part introduces all algorithms implemented by LAMDA-SSL to
help users quickly understand and choose SSL algorithms. The fourth part shows
the APIs of LAMDA-SSL. This detailed documentation greatly reduces the cost of
familiarizing users with LAMDA-SSL toolkit and SSL algorithms
Stochastic bifurcation characteristics of cantilevered piezoelectric energy harvester
Stochastic bifurcation characteristics of cantilevered piezoelectric energy harvester were studied in this paper. Von de Pol differencial item was introduced to interpret the hysteretic phenomena of piezoelectric ceramics, and then the nonlinear dynamic model of piezoelectric cantilever beam subjected to axial stochastic excitation was developed. The stochastic stability of the system was analyzed, and the steady-state probability density function and the joint probability density function of the dynamic response of the system were obtained, and then the conditions of stochastic Hopf bifurcation were analyzed. Numerical simulation shows that stochastic Hopf bifurcation appears when bifurcation parameter varies, which can increase vibration amplitude of cantilever beam system and improve the efficiency of piezoelectric energy harvester. Finally, the theoretical and numerical results were proved by experiments. The results of this paper are helpful to application of cantilevered piezoelectric energy harvester in engineering fields
Characterization of Microbial Diversity and Community Structure in Fermentation Pit Mud of Different Ages for Production of Strong-Aroma Baijiu
2-(4-Bromophenyl)quinoxaline
In the title compound, C14H9BrN2, the benzene and quinoxaline rings are almost coplanar [r.m.s. deviation = 0.0285 (3) Å and dihedral angle = 2.1 (2)°]
1,1′-(4-Oxoheptane-1,7-diyl)bis(2-methyl-1H-benzimidazole) pentahydrate
The title compound, C23H26N4O·5H2O, has noncrystallographic twofold rotation symmetry in the solid state. It crystallizes with five solvent water molecules in the asymmetric unit. Four of these water molecules are connected with each other via hydrogen-bonding interactions to form two types of centrosymmetric hexameric (H2O)6 rings. Via edge sharing of the hexamers, the water clusters thus build infinite chains that stretch parallel to the a axis. The fifth water molecule provides an additional connection between the two hexameric (H2O)6 units via hydrogen bonds to both rings. The water molecules in the channels along the a axis are also bonded via O—H⋯N hydrogen bonds to the organic units, and face-to-face π–π interactions [with centroid-to-centroid distances of 3.656 (1) Å and average face-to-face distances of 3.431 (5) Å] between the aromatic rings of adjacent molecules complete the intermolecular interactions in this structure
Knowledge-driven Meta-learning for CSI Feedback
Accurate and effective channel state information (CSI) feedback is a key
technology for massive multiple-input and multiple-output systems. Recently,
deep learning (DL) has been introduced for CSI feedback enhancement through
massive collected training data and lengthy training time, which is quite
costly and impractical for realistic deployment. In this article, a
knowledge-driven meta-learning approach is proposed, where the DL model
initialized by the meta model obtained from meta training phase is able to
achieve rapid convergence when facing a new scenario during target retraining
phase. Specifically, instead of training with massive data collected from
various scenarios, the meta task environment is constructed based on the
intrinsic knowledge of spatial-frequency characteristics of CSI for meta
training. Moreover, the target task dataset is also augmented by exploiting the
knowledge of statistical characteristics of wireless channel, so that the DL
model can achieve higher performance with small actually collected dataset and
short training time. In addition, we provide analyses of rationale for the
improvement yielded by the knowledge in both phases. Simulation results
demonstrate the superiority of the proposed approach from the perspective of
feedback performance and convergence speed.Comment: arXiv admin note: text overlap with arXiv:2301.1347
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