The structure and possible origins of stacking faults in gamma-yttrium disilicate

Parallel stacking faults on (010) planes are frequently observed in hot-pressed Y2Si2O7. A combination of conventional dark-field imaging and high-resolution transmission electron microscopy was used to investigate the structure of these faults and it was found that they consist of the repeat of one layer of the two layer γ-Y2Si2O7 structure with an associated in-plane rigid body displacement. The resulting structure was confirmed by image simulation of high-resolution images from two perpendicular projections. A model for the formation of the stacking faults is proposed as a consequence of a transformation from β-Y2Si2O7 to γ-Y2Si2O7 in the hot pressing

Edge states in Open Antiferromagnetic Heisenberg Chains

In this letter we report our results in investigating edge effects of open antiferromagnetic Heisenberg spin chains with spin magnitudes $S=1/2, 1,3/2,2$ using the density-matrix renormalization group (DMRG) method initiated by White. For integer spin chains, we find that edge states with spin magnitude $S_{edge}=S/2$ exist, in agreement with Valence-Bond-Solid model picture. For half-integer spin chains, we find that no edge states exist for $S=1/2$ spin chain, but edge state exists in $S=3/2$ spin chain with $S_{edge}=1/2$, in agreement with previous conjecture by Ng. Strong finite size effects associated with spin dimmerization in half-integer spin chains will also be discussed.Comment: 4 pages, RevTeX 3.0, 5 figures in a separate uuencoded postscript file. Replaced once to enlarge the acknowlegement

Preferential mobilization and egress of Type 1 and Type 3 innate lymphocytes in response to exercise and hypoxia

The study examined the effect of exercise and hypoxia on the mobilization and egress of innate lymphocytes (ILCs) and adaptive T cell populations in the blood. The ILCs have emerged as a critical population of cells in immune regulation at mucosal surfaces in animals and humans. Eleven healthy male subjects performed (i) 45 min of exercise at 50% VO2 peak on a cycle ergometer under normoxia and (ii) hypoxia, or (iii) while resting in hypoxia. Blood samples were obtained pre-exercise, immediately post-exercise and 60 min post-exercise and were analyzed by flow cytometry to examine the type 1 and type 3 ILCs and CD4+ and CD8+ naive and memory cell populations. There was a significant increase in the number of type 1 (NK cells) and type 3 ILC22 cells in the blood in response to exercise under normal oxygen conditions followed by a significant egress of these cells following the cessation of exercise. Exercise performed under hypoxic conditions abrogated the mobilization response of NK cells and ILC22 cells. Type 3 LTi cells were mobilized into the blood only under hypoxic rest conditions. No significant changes were observed when we analysed total CD4+ and CD8+T cell populations or the naive and memory subsets. This study highlights that distinct innate populations are mobilised under different environmental conditions and types of stress

Contextual variety, Internet-of-Things and the choice of tailoring over platform: Mass customisation strategy in supply chain management

This is the final version. Available on open access from Elsevier via the DOI in this recordThis paper considers the implications for Supply Chain Management (SCM) from the development of the Internet of Things (IoT) or Internet Connected Objects (ICO). We focus on opportunities and challenges stemming from consumption data that comes from ICO, and on how this data can be mapped onto strategic choices of product variety. We develop a simple analytical framework that illustrates the underlying mechanisms of a product supplier/producer׳s choice between (i) producing multiple product varieties as a way of meeting consumer demand (a “tailoring strategy”), and (ii) offering a flexible and standardised platform which enables consumers׳ needs to be met by incorporating personal ICO data into various customisable applications (a “platform strategy”). Under a platform strategy, the ICO data is independently produced by other providers and can be called on in both use and context of use. We derive conditions under which each of the strategies may be profitable for the provider through maximising consumers’ value. Our findings are that the higher the demand for contextual variety, the more profitable the platform strategy becomes, relative to the tailoring strategy. Our study concludes by considering the implications for SCM research and practice with an extension to postponement taxonomies, including those where the customer, and not the supplier, is the completer of the product, and we show that this yields higher profits than the tailoring strategy.Engineering and Physical Sciences Research Council (EPSRC

Spin-Orbit Coupling and Symmetry of the Order Parameter in Strontium Ruthenate

Determination of the orbital symmetry of a state in spin triplet Sr$_2$RuO$_4$ superconductor is a challenge of considerable importance. Most of the experiments show that the chiral state of the $\hat{z} (k_x \pm ik_y)$ type is realized and remains stable on lowering the temperature. Here we have studied the stability of various superconducting states of Sr$_2$RuO$_4$ in the presence of spin-orbit coupling. Numerically we found that the chiral state is never the minimum energy. Alone among the five states studied it has $=0$ and is therefore not affected to linear order in the coupling parameter $\lambda$. We found that stability of the chiral state requires spin dependent pairing interactions. This imposes strong constraint on the pairing mechanism.Comment: 4 pages, 4 figure

Tilting instability and other anomalies in the flux-lattice in some magnetic superconductors

The flux-line lattice in the compound $ErNi_2B_2C$, which has a tendency to ferromagnetic order in the a-b plane is studied with external magnetic field direction close to the c-axis. We show the existence of an instability where the direction of flux-lines spontaneously tilts away from that of the applied field near the onset of ferromagnetic order. The enhanced fluctuations in the flux lattice and the square flux lattice recently observed are explained and further experiments suggested.Comment: 12 pages, Latex file, no figur

The Minimal Length and Large Extra Dimensions

Planck scale physics represents a future challenge, located between particle physics and general relativity. The Planck scale marks a threshold beyond which the old description of spacetime breaks down and conceptually new phenomena must appear. Little is known about the fundamental theory valid at Planckian energies, except that it necessarily seems to imply the occurrence of a minimal length scale, providing a natural ultraviolet cutoff and a limit to the possible resolution of spacetime. Motivated by String Theory, the models of large extra dimensions lower the Planck scale to values soon accessible. These models predict a vast number of quantum gravity effects at the lowered Planck scale, among them the production of TeV-mass black holes and gravitons. Within the extra dimensional scenario, also the minimal length comes into the reach of experiment and sets a fundamental limit to short distance physics. We review the status of Planck scale physics in these effective models.Comment: 18 pages, 5 figures, brief review to appear in Mod. Phys. Let.

Space-Time Foam may Violate the Principle of Equivalence

The interactions of different particle species with the foamy space-time fluctuations expected in quantum gravity theories may not be universal, in which case different types of energetic particles may violate Lorentz invariance by varying amounts, violating the equivalence principle. We illustrate this possibility in two different models of space-time foam based on D-particle fluctuations in either flat Minkowski space or a stack of intersecting D-branes. Both models suggest that Lorentz invariance could be violated for energetic particles that do not carry conserved charges, such as photons, whereas charged particles such electrons would propagate in a Lorentz-inavariant way. The D-brane model further suggests that gluon propagation might violate Lorentz invariance, but not neutrinos. We argue that these conclusions hold at both the tree (lowest-genus) and loop (higher-genus) levels, and discuss their implications for the phenomenology of quantum gravity.Comment: 20 pages, 4 figures, the version accepted for publication in the International Journal of Modern Physics

Benchmarking 2D hydraulic models for urban flood simulations

This paper describes benchmark testing of six two-dimensional (2D) hydraulic models (DIVAST, DIVASTTVD, TUFLOW, JFLOW, TRENT and LISFLOOD-FP) in terms of their ability to simulate surface flows in a densely urbanised area. The models are applied to a 1·0 km × 0·4 km urban catchment within the city of Glasgow, Scotland, UK, and are used to simulate a flood event that occurred at this site on 30 July 2002. An identical numerical grid describing the underlying topography is constructed for each model, using a combination of airborne laser altimetry (LiDAR) fused with digital map data, and used to run a benchmark simulation. Two numerical experiments were then conducted to test the response of each model to topographic error and uncertainty over friction parameterisation. While all the models tested produce plausible results, subtle differences between particular groups of codes give considerable insight into both the practice and science of urban hydraulic modelling. In particular, the results show that the terrain data available from modern LiDAR systems are sufficiently accurate and resolved for simulating urban flows, but such data need to be fused with digital map data of building topology and land use to gain maximum benefit from the information contained therein. When such terrain data are available, uncertainty in friction parameters becomes a more dominant factor than topographic error for typical problems. The simulations also show that flows in urban environments are characterised by numerous transitions to supercritical flow and numerical shocks. However, the effects of these are localised and they do not appear to affect overall wave propagation. In contrast, inertia terms are shown to be important in this particular case, but the specific characteristics of the test site may mean that this does not hold more generally