Orientia and Rickettsia: different flowers from the same garden

Recent discoveries of basal extracellular Rickettsiales have illuminated divergent evolutionary paths to host dependency in later-evolving lineages. Family Rickettsiaceae, primarily comprised of numerous protist- and invertebrate-associated species, also includes human pathogens from two genera, Orientia and Rickettsia. Once considered sister taxa, these bacteria form distinct lineages with newly appreciated lifestyles and morphological traits. Contrasting other rickettsial human pathogens in Family Anaplasmataceae, Orientia and Rickettsia species do not reside in host-derived vacuoles and lack glycolytic potential. With only a few described mechanisms, strategies for commandeering host glycolysis to support cytosolic growth remain to be discovered. While regulatory systems for this unique mode of intracellular parasitism are unclear, conjugative transposons unique to Orientia and Rickettsia species provide insights that are critical for determining how these obligate intracellular pathogens overtake eukaryotic cytosol

Tin telluride: a weakly co-elastic metal

We report resonant ultrasound spectroscopy (RUS), dilatometry/magnetostriction, magnetotransport, magnetization, specific heat, and $^{119}$Sn M\"ossbauer spectroscopy measurements on SnTe and Sn$_{0.995}$Cr$_{0.005}$Te. Hall measurements at $T=77$ K indicate that our Bridgman-grown single crystals have a $p$-type carrier concentration of $3.4 \times 10^{19}$ cm$^{-3}$ and that our Cr-doped crystals have an $n$-type concentration of $5.8 \times 10^{22}$ cm$^{-3}$. Although our SnTe crystals are diamagnetic over the temperature range $2\, \text{K} \leq T \leq 1100\, \text{K}$, the Cr-doped crystals are room temperature ferromagnets with a Curie temperature of 294 K. For each sample type, three-terminal capacitive dilatometry measurements detect a subtle 0.5 micron distortion at $T_c \approx 85$ K. Whereas our RUS measurements on SnTe show elastic hardening near the structural transition, pointing to co-elastic behavior, similar measurements on Sn$_{0.995}$Cr$_{0.005}$Te show a pronounced softening, pointing to ferroelastic behavior. Effective Debye temperature, $\theta_D$, values of SnTe obtained from $^{119}$Sn M\"ossbauer studies show a hardening of phonons in the range 60--115K ($\theta_D$ = 162K) as compared with the 100--300K range ($\theta_D$ = 150K). In addition, a precursor softening extending over approximately 100 K anticipates this collapse at the critical temperature, and quantitative analysis over three decades of its reduced modulus finds $\Delta C_{44}/C_{44}=A|(T-T_0)/T_0|^{-\kappa}$ with $\kappa = 0.50 \pm 0.02$, a value indicating a three-dimensional softening of phonon branches at a temperature $T_0 \sim 75$ K, considerably below $T_c$. We suggest that the differences in these two types of elastic behaviors lie in the absence of elastic domain wall motion in the one case and their nucleation in the other

Simulating acoustic emission: The noise of collapsing domains

EPSRCThis is the accepted version of an article which is published in 'Physical Review B' at https://journals.aps.org/prb/ - the link to the published version is http://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.06410

Effect of pores and grain size on the elastic and piezoelectric properties of quartz-based materials

The role of grain size and porosity in the piezoelectric and elastic properties of SiO2-based materials was investigated using resonant piezoelectric spectroscopy, RPS, and resonant ultrasound spectroscopy, RUS. RPS performed on agate revealed a piezoelectric effect comparable in magnitude to that in single crystal quartz. The observed strong piezoelectricity in agate requires preferential orientation of SiO2 during crystal growth. Similarly, in novaculite and sandstone finite (but weak) RPS signals were evident, suggesting that the expected randomization of the piezoelectric quartz grains is incomplete. On the other hand, Vycor, a silica glass with a porosity of 40%, showed no evidence of the piezoelectric effect. According to temperature dependent RPS and RUS measurements, the α-β transition temperature in quartz does not change in polycrystalline samples. Finally, the temperature dependence under heating of the elastic constants is reversible in quartz and agate and irreversible in sandstone and vycor.RUS facilities in Cambridge were established through grant no. NE/B505738/1 to MAC from the Natural Environment Research Council. EKHS is grateful to the Leverhulme Foundation (RPG-2012-564) and EPSRC (EP/K009702/1) for financial support.This is the final version. It was first published by De Gruyter at http://www.degruyter.com/view/j/ammin.2015.100.issue-5-6/am-2015-5180ccby/am-2015-5180ccby.xm

Interface Driven Pseudo-Elasticity in a-Fe Nanowires

Molecular dynamics simulations of bent [100] α-Fe nanowires show the nucleation of twins and nano-scale interfaces that lead to pseudo-elasticity during loading/unloading cycles. The new type of interfaces along {110} stems from the accumulation of individual /{112} twin boundaries and stores high interfacial energies. These nonconventional interfaces provide a large part of the driving force for shape recovery upon unloading, while the minimization of surface energy is no longer the dominant driving force. This new pseudo-elastic effect is not much affected by surface roughness, and can be extended over a wide range of wire diameters, if the sample is seeded with conventional twin boundaries, which will transform to the desired {110} interfaces under bending.X.D. and J.S. appreciate the support of NSFC (51171140, 51231008, 51320105014, 51321003), the 973 Programs of China (2012CB619402) and 111 project (B06025). E.K.H.S. is grateful to EPSRC (EP/K009702/1) for support.This is the final version of the article. It first appeared from Advanced Functional Materials via https://doi.org/10.1002/adfm.20150408

Statistical analysis of emission, interaction and annihilation of phonons by kink motion in ferroelastic materials

Our early work showed that the evolution of the twin boundary pattern exhibits an avalanche behavior upon external loading of ferroelastic materials [Salje et al., Phys. Rev. B 83, 104109 (2011)]. The distribution of “jerks” (singularities of potential energy change) was found to follow a power law distribution below a Vogel–Fulcher temperature, mainly related to the movement of kinks in domain boundaries. We use molecular dynamics simulations to study the nucleation, scattering, and annihilation of phonons that are generated by the nucleation and propagation of such kinks. The interaction and scattering of phonons are correlated over a short time period and gradually become uncorrelated before annihilation at large temperature intervals. The movement and interaction of phonons show avalanche behavior. The probability of finding energy jerks follows a power law with exponents around 2.5–3. The distribution of waiting times between jerks also follows a power law. At temperatures above the Vogel–Fulcher temperature, scattering with thermal phonons becomes predominant and no phononic avalanches were observed.</jats:p

Observation of a continuous phase transition in a shape-memory alloy

Elastic neutron-scattering, inelastic x-ray scattering, specific-heat, and pressure-dependent electrical transport measurements have been made on single crystals of AuZn and Au_{0.52}Zn_{0.48} above and below their martensitic transition temperatures (T_M=64K and 45K, respectively). In each composition, elastic neutron scattering detects new commensurate Bragg peaks (modulation) appearing at Q = (1.33,0.67,0) at temperatures corresponding to each sample's T_M. Although the new Bragg peaks appear in a discontinuous manner in the Au_{0.52}Zn_{0.48} sample, they appear in a continuous manner in AuZn. Surprising us, the temperature dependence of the AuZn Bragg peak intensity and the specific-heat jump near the transition temperature are in favorable accord with a mean-field approximation. A Landau-theory-based fit to the pressure dependence of the transition temperature suggests the presence of a critical endpoint in the AuZn phase diagram located at T_M*=2.7K and p*=3.1GPa, with a quantum saturation temperature \theta_s=48.3 +/- 3.7K.Comment: 6 figure

Low-temperature phase transformations of PZT in the morphotropic phase-boundary region

We present anelastic and dielectric spectroscopy measurements of PbZr(1-x)Ti(x)O(3) with 0.455 < x < 0.53, which provide new information on the low temperature phase transitions. The tetragonal-to-monoclinic transformation is first-order for x < 0.48 and causes a softening of the polycrystal Young's modulus whose amplitude may exceed the one at the cubic-to-tetragonal transformation; this is explainable in terms of linear coupling between shear strain components and tilting angle of polarization in the monoclinic phase. The transition involving rotations of the octahedra below 200 K is visible both in the dielectric and anelastic losses, and it extends within the tetragonal phase, as predicted by recent first-principle calculations.Comment: 4 pages, 4 figure