Newly emerged bumblebees are highly susceptible to gut parasite infection

One factor that can affect infection susceptibility is host age, the effects of which vary in a range of ways. For example, susceptibility may increase with age, due to senescence or decrease with age as a result of maturation of the immune system. If certain ages are more susceptible to infection, populations with contrasting demographics, such as same-age cohorts versus a mixture of ages, will exhibit differing disease prevalence. We use the bumblebee, Bombus terrestris, and its interaction with the gut trypanosome Crithidia sp. as a model system to investigate age-related susceptibility in a social insect. Crithidia sp. are widespread and prevalent parasites of bumblebees that are spread between colonies via faeces on flowers when foraging, and within colonies via contact with infected bees and contaminated surfaces and resources. In the field, Bombus spp. live for approximately three weeks. Here, we inoculated bumblebees at 0, 7, 14 and 21 days of age and measured their infection after one week. We also measured the level of gene expression of two antimicrobial peptides important in the defence against Crithidia bombi in bumblebees. We found that younger bumblebees are more susceptible to infection by Crithidia sp. than their older siblings. Specifically, individuals inoculated on their first day of emergence had infection intensities seven days later that were four-fold higher than bees inoculated at 21 days of age. In contrast, the gene expression of two AMPs known to protect against the trypanosome, abaecin and defensin, did not significantly vary with age. These results suggest that age does affect susceptibility to Crithidia sp. infection in B. terrestris. The higher susceptibility of callows may have implications for the susceptibility of colonies at different stages of their lifecycle, due to the contrasting age demography of workers in the colony

Gapped optical excitations from gapless phases: imperfect nesting in unconventional density waves

We consider the effect of imperfect nesting in quasi-one-dimensional unconventional density waves in the case, when the imperfect nesting and the gap depends on the same wavevector component. The phase diagram is very similar to that in a conventional density wave. The density of states is highly asymmetric with respect to the Fermi energy. The optical conductivity at T=0 remains unchanged for small deviations from perfect nesting. For higher imperfect nesting parameter, an optical gap opens, and considerable amount of spectral weight is transferred to higher frequencies. This makes the optical response of our system very similar to that of a conventional density wave. Qualitatively similar results are expected in d-density waves.Comment: 8 pages, 7 figure

Mixed-State Quasiparticle Spectrum for d-wave Superconductors

Controversy concerning the pairing symmetry of high-$T_c$ materials has motivated an interest in those measurable properties of superconductors for which qualitative differences exist between the s-wave and d-wave cases. We report on a comparison between the microscopic electronic properties of d-wave and s-wave superconductors in the mixed state. Our study is based on self-consistent numerical solutions of the mean-field Bogoliubov-de Gennes equations for phenomenological BCS models which have s-wave and d-wave condensates in the absence of a magnetic field. We discuss differences between the s-wave and the d-wave local density-of-states, both near and away from vortex cores. Experimental implications for both scanning-tunneling-microscopy measurements and specific heat measurements are discussed.Comment: 10 pages, REVTEX3.0, 3 figures available upon reques

D1-D5 on ALE Space

We construct a two-dimensional N=(0,4) quiver gauge theory on D1-brane probing D5-branes on ALE space, and study its IR behavior. This can be thought of as a gauged linear sigma model for the NS5-branes on ALE space.Comment: 17 pages, 1 figure, lanlmac; v2: reference adde

Half-quantum vortex and d-soliton in Sr2_2RuO4_4

Assuming that the superconductivity in Sr$_2$RuO$_4$ is described by a planar p-wave order parameter, we consider possible topological defects in Sr$_2$RuO$_4$. In particular, it is shown that both of the ${\hat d}$-soliton and half-quantum vortex can be created in the presence of the magnetic field parallel to the $a$-$b$ plane. We discuss how one can detect the ${\hat d}$-soliton and half-quantum vortex experimentally.Comment: 8 pages, 3 figure

Collective modes and sound propagation in a p-wave superconductor: Sr2_2RuO4_4

There are five distinct collective modes in the recently discovered p-wave superconductor Sr$_2$RuO$_4$; phase and amplitude modes of the order parameter, clapping mode (real and imaginary), and spin wave. The first two modes also exist in the ordinary s-wave superconductors, while the clapping mode with the energy $\sqrt{2} \Delta(T)$ is unique to Sr$_2$RuO$_4$ and couples to the sound wave. Here we report a theoretical study of the sound propagation in a two dimensional p-wave superconductor. We identified the clapping mode and study its effects on the longitudinal and transverse sound velocities in the superconducting state. In contrast to the case of $^3$He, there is no resonance absorption associated with the collective mode, since in metals $\omega/(v_F |{\bf q}|) \ll 1$, where $v_F$ is the Fermi velocity, {\bf q} is the wave vector, and $\omega$ is the frequency of the sound wave. However, the velocity change in the collisionless limit gets modified by the contribution from the coupling to the clapping mode. We compute this contribution and comment on the visibility of the effect. In the diffusive limit, the contribution from the collective mode turns out to be negligible. The behaviors of the sound velocity change and the attenuation coefficient near $T_c$ in the diffusive limit are calculated and compared with the existing experimental data wherever it is possible. We also present the results for the attenuation coefficients in both of the collisionless and diffusive limits at finite temperatures.Comment: RevTex, 12 pages, 2 figures, Replaced by the published versio

Wess-Zumino Term in Tachyon Effective Action

We show that the source of RR field computed from the boundary state describing the decay of a non-BPS brane is reproduced by a particular form of the Wess-Zumino term in the tachyon effective action. We also obtain a simple expression of the S-charge associated with rolling tachyons.Comment: 10 pages, lanlma

Anisotropic s-wave superconductivity in MgB_2

It has recently been observed that MgB_2 is a superconductor with a high transition temperature. Here we propose a model of anisotropic s-wave superconductivity which consistently describes the observed properties of this compound, including the thermodynamic and optical response in sintered MgB_2 wires. We also determine the shape of the quasiparticle density of states and the anisotropy of the upper critical field and the superfluid density which should be detectable once single-crystal samples become available.Comment: RevTex, 10 pages with 4 eps figure

Angular position of nodes in the superconducting gap of YBCO

The thermal conductivity of a YBCO single crystal has been studied as a function of the relative orientation of the crystal axes and a magnetic field rotating in the Cu-O planes. Measurements were carried out at several temperatures below T_c and at a fixed field of 30 kOe. A four-fold symmetry characteristic of a superconducting gap with nodes at odd multiples of 45 degrees in k-space was resolved. Experiments were performed to exclude a possible macroscopic origin for such a four-fold symmetry such as sample shape or anisotropic pinning. Our results impose an upper limit of 10% on the weight of the s-wave component of the essentially d-wave superconducting order parameter of YBCO.Comment: 10 pages, 4 figure

Moyal Representation of the String Field Star Product in the Presence of a B-background

In this paper we show that in the presence of an anti-symmetric tensor $B$-background, Witten's star algebra for open string fields persists to possess the structure of a direct product of commuting Moyal pairs. The interplay between the noncommutativity due to three-string overlap and that due to the $B$-background is our main concern. In each pair of noncommutative directions parallel to the $B$-background, the Moyal pairs mix string modes in the two directions and are labeled, in addition to a continuous parameter, by {\it two} discrete values as well. However, the Moyal parameters are $B$-dependent only for discrete pairs. We have also demonstrated the large-$B$ contraction of the star algebra, with one of the discrete Moyal pairs dropping out while the other giving rise to the center-of-mass noncommutative function algebra.Comment: minor notation chang