Estimation of properties of low-lying excited states of Hubbard models : a multi-configurational symmetrized projector quantum Monte Carlo approach

We present in detail the recently developed multi-configurational symmetrized projector quantum Monte Carlo (MSPQMC) method for excited states of the Hubbard model. We describe the implementation of the Monte Carlo method for a multi-configurational trial wavefunction. We give a detailed discussion of issues related to the symmetry of the projection procedure which validates our Monte Carlo procedure for excited states and leads naturally to the idea of symmetrized sampling for correlation functions, developed earlier in the context of ground state simulations. It also leads to three possible averaging schemes. We have analyzed the errors incurred in these various averaging procedures and discuss and detail the preferred averaging procedure for correlations that do not have the full symmetry of the Hamiltonian. We study the energies and correlation functions of the low-lying excited states of the half-filled Hubbard model in 1-D. We have used this technique to study the pair-binding energies of two holes in $4n$ and $4n+2$ systems, which compare well the Bethe ansatz data of Fye, Martins and Scalettar. We have also studied small clusters amenable to exact diagonalization studies in 2-D and have reproduced their energies and correlation functions by the MSPQMC method. We identify two ways in which a multiconfigurational trial wavefunction can lead to a negative sign problem. We observe that this effect is not severe in 1-D and tends to vanish with increasing system size. We also note that this does not enhance the severity of the sign problem in two dimensions.Comment: 29 pages, 2 figures available on request, submitted to Phys. Rev.

Effect of atrazine (Herbicide) on blood parameters of common carp Cyprinus carpio (Actinopterygii: Cypriniformes)

In the present study an attempt was made to investigate the acute toxicity of atrazine (ATR) a herbicide on an economically important fish, Cyprinus carpio. In which, 24 h median lethal concentration (24 h LC50) of herbicide, atrazine to C. carpio was 18.5 ppm. Due to fish exposure to 24 h LC50 of atrazine for 24 h, red blood cells (RBCs) count (-63.17%), hemoglobin (-27.35%), plasma glucose (-6.78%) and plasma protein (-18.73%) levels were decreased; whereas white blood cells (WBCs) count (+3.73%) was enhanced. The differences in haematological and biochemical values were statistically significant (p < 0.05). However, WBC count was not significantly changed. The alterations of the above parameters could be used as an important tool for the assessment of pathological conditions of fish

Flutter and forced response of mistuned rotors using standing wave analysis

A standing wave approach is applied to the analysis of the flutter and forced response of tuned and mistuned rotors. The traditional traveling wave cascade airforces are recast into standing wave arbitrary motion form using Pade approximants, and the resulting equations of motion are written in the matrix form. Applications for vibration modes, flutter, and forced response are discussed. It is noted that the standing wave methods may prove to be more versatile for dealing with certain applications, such as coupling flutter with forced response and dynamic shaft problems, transient impulses on the rotor, low-order engine excitation, bearing motion, and mistuning effects in rotors