Temperature behavior of the magnon modes of the square lattice antiferromagnet

A spin-wave theory of short-range order in the square lattice Heisenberg antiferromagnet is formulated. With growing temperature from T=0 a gapless mode is shown to arise simultaneously with opening a gap in the conventional spin-wave mode. The spectral intensity is redistributed from the latter mode to the former. For low temperatures the theory reproduces results of the modified spin-wave theory by M.Takahashi, J.E.Hirsch et al. and without fitting parameters gives values of observables in good agreement with Monte Carlo results in the temperature range 0 <= T < 0.8J where J is the exchange constant.Comment: 12 pages, 2 figure

High resolution Ge/Li/ spectrometer reduces rate-dependent distortions at high counting rates

Modified spectrometer system with a low-noise preamplifier reduces rate-dependent distortions at high counting rates, 25,000 counts per second. Pole-zero cancellation minimizes pulse undershoots due to multiple time constants, baseline restoration improves resolution and prevents spectral shifts

Tight Bounds for MIS in Multichannel Radio Networks

Daum et al. [PODC'13] presented an algorithm that computes a maximal independent set (MIS) within $O(\log^2 n/F+\log n \mathrm{polyloglog} n)$ rounds in an $n$-node multichannel radio network with $F$ communication channels. The paper uses a multichannel variant of the standard graph-based radio network model without collision detection and it assumes that the network graph is a polynomially bounded independence graph (BIG), a natural combinatorial generalization of well-known geographic families. The upper bound of that paper is known to be optimal up to a polyloglog factor. In this paper, we adapt algorithm and analysis to improve the result in two ways. Mainly, we get rid of the polyloglog factor in the runtime and we thus obtain an asymptotically optimal multichannel radio network MIS algorithm. In addition, our new analysis allows to generalize the class of graphs from those with polynomially bounded local independence to graphs where the local independence is bounded by an arbitrary function of the neighborhood radius.Comment: 37 pages, to be published in DISC 201

Low-frequency incommensurate magnetic response in strongly correlated systems

It is shown that in the t-J model of Cu-O planes at low frequencies the dynamic spin structure factor is peaked at incommensurate wave vectors (1/2+-delta,1/2)$, (1/2,1/2+-delta). The incommensurability is connected with the momentum dependencies of the magnon frequency and damping near the antiferromagnetic wave vector. The behavior of the incommensurate peaks is similar to that observed in La_{2-x}(Ba,Sr)_xCuO_{4+y} and YBa_2Cu_3O_{7-y}: for hole concentrations 0.02<x<=0.12 we find that delta is nearly proportional to x, while for x>0.12 it tends to saturation. The incommensurability disappears with increasing temperature. Generally the incommensurate magnetic response is not accompanied by an inhomogeneity of the carrier density.Comment: 4 pages, 4 figure

Detectability of Excitatory versus Inhibitory Drive in an Integrate-and-Fire-or-Burst Thalamocortical Relay Neuron Model

Although inhibitory inputs are often viewed as equal but opposite to excitatory inputs, excitatory inputs may alter the firing of postsynaptic cells more effectively than inhibitory inputs. This is because spike cancellation produced by an inhibitory input requires coincidence in time, whereas an excitatory input can add spikes with less temporal constraint. To test for such potential differences, especially in the context of the function of thalamocortical (TC) relay nuclei, we used a stochastic “integrate-and-fire-or-burst” TC neuron model to quantify the detectability of excitatory and inhibitory drive in the presence and absence of the low-threshold Ca 2+ current, IT, and the hyperpolarization-activated cation conductance, Isag. We find that excitatory inputs are generally superior drivers compared with inhibitory inputs in part because spontaneous activity of a postsynaptic neuron is not required in the case of excitatory drive. Interestingly, the presence of the low-threshold Ca 2+ current, IT in a postsynaptic neuron allows the robust detection of inhibitory drive over a certain range of spontaneous and driven activity, a range that can be extended by the presence of the hyperpolarization-activated cation conductance, Isag. These simulations suggest a possible reinterpretation of the role of inhibitory inputs, such as those to the thalamus

Acanthocephala of Cichlids (Pisces) in Lake Malawi, Africa, with a Description of \u3ci\u3eAcanthogyrus (Acanthosentis} malawiensis\u3c/i\u3e sp. n. (Quadrigyridae) from \u3ci\u3eLabeo cylindricus\u3c/i\u3e Peters, 1852 (Cyprinidae)

Two species of acanthocephalans are reported from fishes collected during the summer of 1996 in the southeast arm of Lake Malawi (Lake Nyasa), East Africa. The common Acanthogyrus (Acanthosentis) tilapiae (Baylis, 1948) had infected 18 cichlid and 1 bagrid host species (all new host records) netted by divers wearing scuba gear around Harbor Island or caught by hook and line in deep water. The specimens of this parasite were some of the smallest ever reported for that species. Two males of a new species, Acanthogyrus (Acanthosentis) malawiensis, are described from 2 male Labeo cylindricus (Cyprinidae). This is the fifth species of this genus and subgenus described in Africa. It is distinguished from the other 4 African and 33 mostly Asian species in that the proboscis hooks of the middle circle are longer than those of the anterior circle. The new species further differs from the other African species in proboscis and hook size, posterior hook root, trunk spination, and lemniscal form. Observations on host and geographical distribution, prevalence, and developmental stages of A. (A.) tilapiae are also reported