N′-(5-Chloro-2-hydroxy­benzyl­idene)nicotinohydrazide

There are two independent Schiff base mol­ecules in the asymmetric unit of the title compound, C13H10ClN3O2. The dihedral angles between the benzene and pyridine rings are 12.8 (2) and 1.9 (2)° in the two mol­ecules. Intra­molecular O—H⋯N hydrogen bonds are observed. Mol­ecules are linked into centrosymmetric R 4 4(26) motifs by N—H⋯O and N—H⋯N inter­actions

Intelligent Reflecting Surface Aided Multigroup Multicast MISO Communication Systems

Intelligent reflecting surface (IRS) has recently been envisioned to offer unprecedented massive multiple-input multiple-output (MIMO)-like gains by deploying large-scale and low-cost passive reflection elements. By adjusting the reflection coefficients, the IRS can change the phase shifts on the impinging electromagnetic waves so that it can smartly reconfigure the signal propagation environment and enhance the power of the desired received signal or suppress the interference signal. In this paper, we consider downlink multigroup multicast communication systems assisted by an IRS. We aim for maximizing the sum rate of all the multicasting groups by the joint optimization of the precoding matrix at the base station (BS) and the reflection coefficients at the IRS under both the power and unit-modulus constraint. To tackle this non-convex problem, we propose two efficient algorithms. Specifically, a concave lower bound surrogate objective function has been derived firstly, based on which two sets of variables can be updated alternately by solving two corresponding second-order cone programming (SOCP) problems.Then, in order to reduce the computational complexity, we further adopt the majorization—minimization (MM) method for each set of variables at every iteration, and obtain the closed form solutions under loose surrogate objective functions. Finally, the simulation results demonstrate the benefits of the introduced IRS and the effectiveness of our proposed algorithms

The energy spectrum symmetry of Heisenberg model in Fock space

We prove strictly that one dimension spin 1/2 Heisenberg model has a symmetry of energy spectrum between its subspace $n$ and the subspace $L-n$ of the Fock space. Our proof is completed by introducing two general quantum operations. One is a flip operation of spin direction and another is a mirror reflection of spin sites.Comment: Revising version, 7 preprint pages, no figures; Published version contains some revisions in Languag

China's uncertain demographic present and future

This paper applies methods of probabilistic population forecasting to assess the range of uncertainty of China’s future population trends. Unlike previous applications of probabilistic population projections that consider stochastic future fertility, mortality and migration, this paper will also account for the significant uncertainty of China’s current fertility level (with published figures ranging from 1.2 to 2.3) and the related uncertainties about the sex ratio at birth (with estimates from 1.06 to above 1.2) and the size of the youngest cohorts in the 2000 census. The model applied in this paper will be based on assumed uncertainty ranges for current conditions, in addition to the probabilistic treatment of future trends. Given the sheer size of China’s population, these significant uncertainties about current conditions are of high importance not only for the future population of China but also for considerations on a global scale.