A direct calculation of critical exponents of two-dimensional anisotropic Ising model

Using an exact solution of the one-dimensional (1D) quantum transverse-field Ising model (TFIM), we calculate the critical exponents of the two-dimensional (2D) anisotropic classical Ising model (IM). We verify that the exponents are the same as those of isotropic classical IM. Our approach provides an alternative means of obtaining and verifying these well-known results.Comment: 3 pages, no figures, accepted by Commun. Theor. Phys.(IPCAS

A liénard oscillator resonant tunnelling diode-laser diode hybrid integrated circuit: model and experiment

We report on a hybrid optoelectronic integrated circuit based on a resonant tunnelling diode driving an optical communications laser diode. This circuit can act as a voltage controlled oscillator with optical and electrical outputs. We show that the oscillator operation can be described by Liénard's equation, a second order nonlinear differential equation, which is a generalization of the Van der Pol equation. This treatment gives considerable insight into the potential of a monolithic version of the circuit for optical communication functions including clock recovery and chaotic source applications

N=2 Superstrings with (1,2m) Spacetime Signature

We show that the $N=2$ superstring in $d=2D\ge6$ real dimensions, with criticality achieved by including background charges in the two real time directions, exhibits a ``coordinate-freezing'' phenomenon, whereby the momentum in one of the two time directions is constrained to take a specific value for each physical state. This effectively removes this time direction as a physical coordinate, leaving the theory with $(1,d-2)$ real spacetime signature. Norm calculations for low-lying physical states suggest that the theory is ghost free.Comment: 8 page

A note on W_{2,s} strings

BRST operators for two-dimensional theories with spin-2 and spin-$s$ currents, generalising the $W_3$ BRST operator of Thierry-Mieg, have previously been obtained. The construction was based on demanding nilpotence of the BRST operators, making no reference to whether or not an underlying $W$ algebra exists. In this paper, we analyse the known cases ($s=3$, 4, 5 and 6), showing that the two $s=4$ BRST operators are associated with the $W\!B_2$ algebra, and that two of the four $s=6$ BRST operators are associated with the $W\!G_2$ algebra. We discuss the cohomology of all the known higher-spin BRST operators, the Weyl symmetry of their physical states, and their relation with certain minimal models. We also obtain the BRST operator for the case $s=7$.Comment: 12 pages, CTP TAMU-8/94, LZU-TH-94/0

Anomaly Freedom and Realisations for Super-W3W_3 Strings

We construct new multi-field realisations of the $N=2$ super-$W_3$ algebra, which are important for building super-$W_3$ string theories. We derive the structure of the ghost vacuum for such theories, and use the result to calculate the intercepts. These results determine the conditions for physical states in the super-$W_3$ string theory.Comment: 22 page

Open su(4)-invariant spin ladder with boundary defects

The integrable su(4)-invariant spin-ladder model with boundary defect is studied using the Bethe ansatz method. The exact phase diagram for the ground state is given and the boundary quantum critical behavior is discussed. It consists of a gapped phase in which the rungs of the ladder form singlet states and a gapless Luttinger liquid phase. It is found that in the gapped phase the boundary bound state corresponds to an unscreened local moment, while in the Luttinger liquid phase the local moment is screened at low temperatures in analogy to the Kondo effect.Comment: Revtex 9 pages, published in PR

On Sibling and Exceptional W Strings

We discuss the physical spectrum for $W$ strings based on the algebras $B_n$, $D_n$, $E_6$, $E_7$ and $E_8$. For a simply-laced $W$ string, we find a connection with the $(h,h+1)$ unitary Virasoro minimal model, where $h$ is the dual Coxeter number of the underlying Lie algebra. For the $W$ string based on $B_n$, we find a connection with the $(2h,2h+2)$ unitary $N=1$ super-Virasoro minimal model.Comment: 16 page

The Interacting W3W_3 String

We present a procedure for computing gauge-invariant scattering amplitudes in the $W_3$ string, and use it to calculate three-point and four-point functions. We show that non-vanishing scattering amplitudes necessarily involve external physical states with excitations of ghosts as well as matter fields. The crossing properties of the four-point functions are studied, and it is shown that the duality of the Virasoro string amplitudes generalises in the $W_3$ string, with different sets of intermediate states being exchanged in different channels. We also exhibit a relation between the scattering amplitudes of the $W_3$ string and the fusion rules of the Ising model.Comment: (Revised version), 26 pages, Plain Tex, CTP TAMU-86/92, KUL-TF-92/4

Three-dimensional character of the deformation twin in magnesium

Deformation twins are three-dimensional domains, traditionally viewed as ellipsoids because of their two-dimensional lenticular sections. In this work, we performed statistical analysis of twin shapes viewing along three orthogonal directions: the ‘dark side’ (DS) view along the twin shear direction (η1), the twinning plane normal (TPN) view (k1) and the ‘bright side’ (BS) view along the direction λ(=k1 × η1). Our electron back-scatter diffraction results show that twins in the DS and BS views normally exhibit a lenticular shape, whereas they show an irregular shape in the TPN view. Moreover, the findings in the TPN view revealed that twins grow faster along λ the lateral direction than along η1 the forward propagation direction at the initial stages of twin growth. These twin sections are irregular, indicating that growth is locally controlled and the overall shape is not perfectly ellipsoidal. We explain these findings using atomistic models, and ascribe them to differences in the mobility of the edge and screw components of the twinning dislocations

Thermoeconomic assessment of a spectral-splitting hybrid PVT system in dairy farms for combined heat and power

We investigate the thermoeconomic potential of a solar-combined heat and power (S-CHP) system based on concentrating, spectral-splitting hybrid photovoltaic-thermal (PVT) collectors for the provision of electricity, steam and hot water for processing milk products in dairy applications. Transient simulations are conducted by using a system model with real-time demand and weather data as inputs, taking account of the spectrum-selective features of the PV cells as well as key heat transfer mechanisms that determine the electrical and thermal performance of the PVT collector. Economic performance is also assessed by considering the investment and savings enabled by the reduced electrical and fuel consumption. The results show that incorporating spectral beam-splitting technology into hybrid PVT collectors can be effective in maintaining the PV cells at low temperatures, while at the same time supplying thermal outputs (fluid streams) at temperatures significantly higher than then cell temperatures for steam generation and/or hot water provision. Based on a 15, 000-m2 installed area, it is found that 80% of the thermal demand for steam generation and 60% of the hot water demand can be satisfied by the PVT S-CHP system, along with a net electrical output amounting to 60% of the demand. Economic and environmental assessments show that the system has an excellent decarbonisation potential (1, 500 tCO2/year) and is economically viable if the investment cost of the spectrum splitter is lower than 0.85 of the cost of the parabolic concentrator (i.e., <2, 150 €/m2 spectrum splitter) in this application