Working within the stochastic series expansion framework, we introduce and characterize a new quantum cluster algorithm for quantum Monte Carlo simulations of transverse field Ising models with frustrated Ising exchange interactions. As a demonstration of the capabilities of this new algorithm, we show that a relatively small, ferromagnetic next-nearest neighbour coupling drives the transverse field Ising antiferromagnet on the triangular lattice from an antiferromagnetic threesublattice ordered state at low temperature to a ferrimagnetic three-sublattice ordered state.

The Global Precipitation Measurement (GPM) mission Core Observatory is equipped with a dual-frequency precipitation radar (DPR) with capability of measuring precipitation simultaneously at frequencies of 13.6 GHz (Ku-band) and 35.5 GHz (Ka-band). Since the GPM-DPR cannot use information from polarization diversity, radar reflectivity factor is the most important parameter used in all retrievals. In this study, GPM's observations of reflectivity at dual-frequency and instantaneous rainfall products are compared quantitatively against dual-polarization ground-based NEXRAD radars from the GPM Validation Network (VN). The ground radars, chosen for this study, are located in the southeastern plains of the U.S.A. with altitudes varying from 5 to 210 m. It is a challenging task to quantitatively compare measurements from space-based and ground-based platforms due to their difference in resolution volumes and viewing geometry. To perform comparisons on a point-to-point basis, radar observations need to be volume matched by averaging data in common volume or by re-sampling data to a common grid system. In this study, a 3-D volume matching technique first proposed by Bolen and Chandrasekar (2003) and later modified by Schwaller and Morris (2011) is applied to both radar data. DPR and ground radar observations and products are cross validated against each other with a large data set. Over 250 GPM overpass cases at 5 NEXRAD locations, starting from April 2014 to June 2018, have been considered. Analysis shows that DPR Ku-and Ka-Band reflectivities are well matched with ground radar with correlation coefficient as high as 0.9 for Ku-band and 0.85 for Ka-band. Ground radar calibration is also checked by observing variation in mean biases of reflectivity between DPR and GR over time. DPR rainfall products are also evaluated. Though DPR underestimates higher rainfall rates in convective cases, its overall performance is found to be satisfactory.

We identify the low energy effective Hamiltonian that is expected to describe the low temperature properties of the frustrated magnet Ca10Cr7O28. Motivated by the fact that this effective Hamiltonian has S = 3/2 effective moments as its degrees of freedom, we use semiclassical spinwave theory to study the T = 0 physics of this effective model and argue that singular spinwave fluctuations destabilize the spiral order favoured by the exchange couplings of this effective Hamiltonian. We also use a combination of classical Monte-Carlo simulations and molecular dynamics, as well as analytical approximations, to study the physics at low, nonzero temperatures. The results of these nonzero temperature calculations capture the liquid-like structure factors observed in the temperature range accessed by recent experiments. Additionally, at still lower temperatures, they predict that a transition to nematic order in the bond energies reflects itself in the spin channel in the form of a crossover to a regime with large but finite correlation length for spiral spin correlations and a corresponding slowing down of spin dynamics.

We develop a formalism for computing the nonlinear response of interacting integrable systems. Our results are asymptotically exact in the hydrodynamic limit where perturbing fields vary sufficiently slowly in space and time. We show that spatially resolved nonlinear response distinguishes interacting integrable systems from noninteracting ones, exemplifying this for the Lieb–Liniger gas. We give a prescription for computing finite-temperature Drude weights of arbitrary order, which is in excellent agreement with numerical evaluation of the third-order response of the XXZ spin chain. We identify intrinsically nonperturbative regimes of the nonlinear response of integrable systems.

A transverse magnetic field Γ is known to induce antiferromagnetic three-sublattice order of the Ising spins σ z in the triangular lattice Ising antiferromagnet at low enough temperature. This lowtemperature order is known to melt on heating in a two-step manner, with a power-law ordered intermediate temperature phase characterized by power-law correlations at the three-sublattice wavevector Q:with the temperature-dependent power-law exponent η(T ) ∈ (1/9, 1/4). Here, we use a newly developed quantum cluster algorithm to study the ferromagnetic easy-axis susceptibility χu(L) of an L × L sample in this power-law ordered phase. Our numerical results are consistent with a recent prediction of a singular L dependence χu(L) ∼ L 2−9η when η(T ) is in the range (1/9, 2/9). This finite-size result implies, via standard scaling arguments, that the ferromagnetic susceptibility χu(B) to a uniform field B along the easy axis is singular at intermediate temperatures in the small B limit, χu(B) ∼ |B| − 4−18η 4−9η for η(T ) ∈ (1/9, 2/9), although there is no ferromagnetic long-range order in the low temperature state.