41,073 research outputs found
A Transverse Lattice QCD Model for Mesons
QCD is analysed with two light-front continuum dimensions and two transverse
lattice dimensions. In the limit of large number of colours and strong
transverse gauge coupling, the contributions of light-front and transverse
directions factorise in the dynamics, and the theory can be analytically solved
in a closed form. An integral equation is obtained, describing the properties
of mesons, which generalises the 't Hooft equation by including spin degrees of
freedom. The meson spectrum, light-front wavefunctions and form factors can be
obtained by solving this equation numerically. These results would be a good
starting point to model QCD observables which only weakly depend on transverse
directions, e.g. deep inelastic scattering structure functions.Comment: Lattice 2003 (theory), 3 page
Measuring brand image: Shopping centre case studies
'Branding' is well known for consumer products but power has shifted from manufacturers' brands towards retailers'. The term 'image' is more common than 'brand' in the context of shopping centres, but 'branding' may become more important. In this study, the authors first investigated qualitatively, asking shoppers to describe centres in 'personality' terms and eliciting clear descriptive differences between centres. For example, one in-town centre was 'dull, boring and old-fashioned . . . not exciting, just OK'; a larger regional centre was 'trendy, prestigious . . . strong, vibrant, big and colourful'. Second, the authors evaluated six UK shopping centres quantitatively using a questionnaire survey (n = 287). The 'strong and vibrant' centre scored significantly higher than the 'dull and boring' one. Despite 'branding' being little used by shopping centres, those with the better 'brand images' tended to have larger catchment areas, sales and rental incomes. The authors contend that brand management could pay rewards in terms of customer numbers, sales turnover and rental income
A derivation of Regge trajectories in large-N transverse lattice QCD
Large-N QCD is analysed in light-front coordinates with a transverse lattice
at strong coupling. The general formalism can be looked up on as a d+n
expansion with a stack of d-dimensional hyperplanes uniformly spaced in n
transverse dimensions. It can arise by application of the renormalisation group
transformations only in the transverse directions. At leading order in strong
coupling, the gauge field dynamics reduces to the constraint that only colour
singlet states can jump between the hyperplanes. With d=2, n=2 and large-N, the
leading order strong coupling results are simple renormalisations of those for
the 't Hooft model. The meson spectrum lies on a set of parallel trajectories
labeled by spin. This is the first derivation of the widely anticipated Regge
trajectories in a regulated systematic expansion in QCD.Comment: Lattice 2000 (spectrum), 5 pages, to appear in the proceeding
The ART of IAM: The Winning Strategy for the 2006 Competition
In many dynamic open systems, agents have to interact with one another to achieve their goals. Here, agents may be self-interested, and when trusted to perform an action for others, may betray that trust by not performing the actions as required. In addition, due to the size of such systems, agents will often interact with other agents with which they have little or no past experience. This situation has led to the development of a number of trust and reputation models, which aim to facilitate an agent's decision making in the face of uncertainty regarding the behaviour of its peers. However, these multifarious models employ a variety of different representations of trust between agents, and measure performance in many different ways. This has made it hard to adequately evaluate the relative properties of different models, raising the need for a common platform on which to compare competing mechanisms. To this end, the ART Testbed Competition has been proposed, in which agents using different trust models compete against each other to provide services in an open marketplace. In this paper, we present the winning strategy for this competition in 2006, provide an analysis of the factors that led to this success, and discuss lessons learnt from the competition about issues of trust in multiagent systems in general. Our strategy, IAM, is Intelligent (using statistical models for opponent modelling), Abstemious (spending its money parsimoniously based on its trust model) and Moral (providing fair and honest feedback to those that request it)
From fields to a super-cluster: the role of the environment at z=0.84 with HiZELS
At z=0, clusters are primarily populated by red, elliptical and massive
galaxies, while blue, spiral and lower-mass galaxies are common in low-density
environments. Understanding how and when these differences were established is
of absolute importance for our understanding of galaxy formation and evolution,
but results at high-z remain contradictory. By taking advantage of the widest
and deepest H-alpha narrow-band survey at z=0.84 over the COSMOS and UKIDSS UDS
fields, probing a wide range of densities (from poor fields to rich groups and
clusters, including a confirmed super-cluster with a striking filamentary
structure), we show that the fraction of star-forming galaxies falls
continuously from ~40% in fields to approaching 0% in rich groups/clusters. We
also find that the median SFR increases with environmental density, at least up
to group densities - but only for low and medium mass galaxies, and thus such
enhancement is mass-dependent at z~1. The environment also plays a role in
setting the faint-end slope (alpha) of the H-alpha luminosity function. Our
findings provide a sharper view on galaxy formation and evolution and reconcile
previously contradictory results at z~1: stellar mass is the primary predictor
of star formation activity, but the environment also plays a major role.Comment: 5 pages, 4 figures, to appear in the proceedings of JENAM 2010 S2:
`Environment and the Formation of Galaxies: 30 years later', ASSP, Springe
Activation of the P2Y2 receptor regulates bone cell function by enhancing ATP release
Bone cells constitutively release ATP into the extracellular environment where it acts locally via P2 receptors to regulate bone cell function. Whilst P2Y2 receptor stimulation regulates bone mineralisation, the functional effects of this receptor in osteoclasts remain unknown. This investigation used the P2Y2 receptor knockout (P2Y2R−/−) mouse model to investigate the role of this receptor in bone. MicroCT analysis of P2Y2R−/− mice demonstrated age-related increases in trabecular bone volume (≤48%), number (≤30%) and thickness (≤17%). In vitro P2Y2R−/− osteoblasts displayed a 3-fold increase in bone formation and alkaline phosphatase activity, whilst P2Y2R−/− osteoclasts exhibited a 65% reduction in resorptive activity. Serum cross-linked C-telopeptide levels (CTX, resorption marker) were also decreased (≤35%). The resorption defect in P2Y2R−/− osteoclasts was rescued by the addition of exogenous ATP, suggesting that an ATP deficit could be a key factor in the reduced function of these cells. In agreement, we found that basal ATP release was reduced up to 53% in P2Y2R−/− osteoclasts. The P2Y2 receptor agonists, UTP and 2-thioUTP, increased osteoclast activity and ATP release in wild-type but not in P2Y2R−/− cells. This indicates that the P2Y2 receptor may regulate osteoclast function indirectly by promoting ATP release. UTP and 2-thioUTP also stimulate ATP release from osteoblasts suggesting that the P2Y2 receptor exerts a similar function in these cells. Taken together, our findings are consistent with the notion that the primary action of P2Y2 receptor signalling in bone is to regulate extracellular ATP levels
Algorithms to automatically quantify the geometric similarity of anatomical surfaces
We describe new approaches for distances between pairs of 2-dimensional
surfaces (embedded in 3-dimensional space) that use local structures and global
information contained in inter-structure geometric relationships. We present
algorithms to automatically determine these distances as well as geometric
correspondences. This is motivated by the aspiration of students of natural
science to understand the continuity of form that unites the diversity of life.
At present, scientists using physical traits to study evolutionary
relationships among living and extinct animals analyze data extracted from
carefully defined anatomical correspondence points (landmarks). Identifying and
recording these landmarks is time consuming and can be done accurately only by
trained morphologists. This renders these studies inaccessible to
non-morphologists, and causes phenomics to lag behind genomics in elucidating
evolutionary patterns. Unlike other algorithms presented for morphological
correspondences our approach does not require any preliminary marking of
special features or landmarks by the user. It also differs from other seminal
work in computational geometry in that our algorithms are polynomial in nature
and thus faster, making pairwise comparisons feasible for significantly larger
numbers of digitized surfaces. We illustrate our approach using three datasets
representing teeth and different bones of primates and humans, and show that it
leads to highly accurate results.Comment: Changes with respect to v1, v2: an Erratum was added, correcting the
references for one of the three datasets. Note that the datasets and code for
this paper can be obtained from the Data Conservancy (see Download column on
v1, v2
Investigating the intrinsic noise limit of Dayem bridge NanoSQUIDs
NanoSQUIDs made from Nb thin films have been produced with nanometre loop sizes down to 200 nm, using weak-link junctions with dimensions less than 60 nm. These composite (W/Nb) single layer thin film devices, patterned by FIB milling, show extremely good low-noise performance ∼170 nΦ0 at temperatures between 5 and 8.5 K and can operate in rather high magnetic fields (at least up to 1 T). The devices produced so far have a limited operating temperature range, typically only 1–2 K. We have the goal of achieving operation at 4.2 K, to be compatible with the best SQUID series array (SSA) preamplifier available. Using the SSA to readout the nanoSQUIDs provides us with a means of investigating the intrinsic noise of the former. In this paper we report improved white noise levels of these nanoSQUIDs, enabling potential detection of a single electronic spin flip in a 1-Hz bandwidth. At low frequencies the noise performance is already limited by SSA preamplifier noise
Free surface cusp formation as a failure mechanism for hard disk drives with fluid dynamic bearings
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