We study quantum measurement with preselection and postselection, and derive the precise expressions of the measurement results without any restriction on the coupling strength between the system and the measuring device. For a qubit system, we derive the maximum pointer shifts by choosing appropriate initial and finial states. A significant amplification effect is obtained when the interaction between the system and the measuring device is very weak, and typical ideal quantum measurement results are obtained when the interaction is strong. The improvement of the signal-tonoise ratio (SNR) and the enhancement of the measurement sensitivity (MS) by weak measurements are studied. Without considering the probability decrease due to postselection, the SNR and the MS can be both significantly improved by weak measurements; however, neither SNR nor MS can be effectively improved when the probability decrease is considered.Comment: 9 pages, 4 figure

By ab initio calculation, Au, Cu, Fe, Ni and Pt adatoms were proposed for modulating the electronic property of graphdiyne naoribbons (GDNRs). GDNRs of 1~4 nm in width were found to be stable at room temperature, and the thermal rates of Au, Cu, Fe, Ni and Pt adatoms escaping from GDNR are slower than 0.003 atoms per hour even at 900 K. According to the calculation, Au and Cu-decorated GDNRs are metallic with carrier concentrations close to that of graphene at room temperature, while Fe, Ni and Pt-decorated GDNRs are n-type semiconductors with impurity states below Fermi energy. Heterojunction composed by doping Au, Cu or Fe atom on one side of GDNR was proposed as metal-semiconductor rectifier with rectification ratio of 2.8, 1.5 or 2.5 at 1.0 V, respectively

A generalization of the Dirac's canonical quantization theory for a system with second-class constraints is proposed as the fundamental commutation relations that are constituted by all commutators between positions, momenta and Hamiltonian so they are simultaneously quantized in a self-consistent manner, rather than by those between merely positions and momenta so the theory either contains redundant freedoms or conflicts with experiments. The application of the generalized theory to quantum motion on a torus leads to two remarkable results: i) The theory formulated purely on the torus, i.e., based on the so-called the purely intrinsic geometry, conflicts with itself. So it provides an explanation why an intrinsic examination of quantum motion on torus within the Schrödinger formalism is improper. ii) An extrinsic examination of the torus as a submanifold in three dimensional flat space turns out to be self-consistent and the resultant momenta and Hamiltonian are satisfactory all around.

As a fast-developing technique for in situ multi-element analysis method, laser induced breakdown spectroscopy - LIBS is, however, developing slowly on liquid analysis due to some technical difficulties. We propose a new method, namely capillary mode, to quantify the concentrations of the elements in solution using LIBS. A Nd:YAG laser with repetition of 10 Hz were used to analyze the solution of NaCrO and no any sample preparation in measurements. The experimental results show that the splashing of liquid induced by laser pulses is decreased significantly and the pollution of mirrors is avoided effectively using liquid capillary mode. The results of quantitative analysis for liquid are also improved than other method. The calibration curves of Cr and Na are well characterized by straight lines and the regression coefficient values of the linear fit are better than 0.998. The limits of detection (LODs) of Cr and Na are determined to be 28.9 mg/L and 1.0 mg/L in this work, respectively. The experimental results show that the liquid capillary mode provides a more practical and very simple approach to improve accuracy of quantitative element analysis in liquids by LIBS technique.