Micromagnetic Domain Structures in Cylindrical Nickel Dots

The magnetic domain structures of cylindrical nickel dots (diameters from 40 nm to 1700 nm) with anisotropy parallel to the cylinder axis is predicted by the ratio of the dot diameter to the stripe period of unpatterned films with the same perpendicular anisotropy. The dominant domain structure for a given ratio increases in complexity as the ratio increases. We present evidence for the full micromagnetic domain structure for the simplest cases

Dynamical Arrest in Attractive Colloids: The Effect of Long-Range Repulsion

We study gelation in suspensions of model colloidal particles with short-ranged attractive and long-ranged repulsive interactions by means of three-dimensional fluorescence confocal microscopy. At low packing fractions, particles form stable equilibrium clusters. Upon increasing the packing fraction the clusters grow in size and become increasingly anisotropic until finally associating into a fully connected network at gelation. We find a surprising order in the gel structure. Analysis of spatial and orientational correlations reveals that the gel is composed of dense chains of particles constructed from face-sharing tetrahedral clusters. Our findings imply that dynamical arrest occurs via cluster growth and association.Comment: Final version: Phys. Rev. Lett. 94, 208301 (2005

Bright Source of Cold Ions for Surface-Electrode Traps

We produce large numbers of low-energy ions by photoionization of laser-cooled atoms inside a surface-electrode-based Paul trap. The isotope-selective trap loading rate of $4\times10^{5}$ Yb$^{+}$ ions/s exceeds that attained by photoionization (electron impact ionization) of an atomic beam by four (six) orders of magnitude. Traps as shallow as 0.13 eV are easily loaded with this technique. The ions are confined in the same spatial region as the laser-cooled atoms, which will allow the experimental investigation of interactions between cold ions and cold atoms or Bose-Einstein condensates.Comment: Paper submitted to PRL for review on 2/1/0

Peak-ratio analysis method for enhancement of LOM protection using M class PMUs

A novel technique for loss of mains (LOM) detection, using Phasor Measurement Unit (PMU) data, is described in this paper. The technique, known as the Peak Ratio Analysis Method (PRAM), improves both sensitivity and stability of LOM protection when compared to prevailing techniques. The technique is based on a Rate of Change of Frequency (ROCOF) measurement from M-class PMUs, but the key novelty of the method lies in the fact that it employs a new “peak-ratio” analysis of the measured ROCOF waveform during any frequency disturbance to determine whether the potentially-islanded element of the network is grid connected or not. The proposed technique is described and several examples of its operation are compared with three competing LOM protection methods that have all been widely used by industry and/or reported in the literature: standard ROCOF, Phase Offset Relay (POR) and Phase Angle Difference (PAD) methods. It is shown that the PRAM technique exhibits comparable performance to the others, and in many cases improves upon their abilities, in particular for systems where the inertia of the main power system is reduced, which may arise in future systems with increased penetrations of renewable generation and HVDC infeed

Jamming and unjamming of concentrated colloidal dispersions in channel flow

We investigated the pressure driven flow of concentrated colloidal dispersions in a converging channel geometry. Optical microscopy and image analysis were used to track tracer particles mixed into dispersions of sterically stabilized poly(methyl methacrylate) (PMMA) spheres. The dispersions were drawn into a round \unit[0.5]{mm} capillary at one of two pump speeds ($\equiv$ applied pressure): v_1=\unit[0.245]{ml\,\, min^{-1}} and v_2=\unit[0.612]{ml\,\, min^{-1}}. We observed that the dispersions at particle volume fractions $\phi\leqslant0.50$ followed Hagen-Poiseuille flow for a simple fluid; i.e. the mean flow rate $\langle V\rangle$ is approximately proportional to pressure drop (pump speed) and inversely proportional viscosity $\eta$. Above this concentration ($\phi\geqslant0.505$), the dispersions exhibit granular-like jamming behavior with $\langle V\rangle$ becoming independent of the pressure drop. However, at the highest applied pressure ($v_2$), the dispersions are able to unjam and switch from granular-like behaviour back to a simple hard-sphere liquid like system, due to the formation of rotating vortices in the spatial flow pattern. This mechanism is consistent with computer simulations of granular systems and supports for example proposed explanations of anomalously low friction in earthquake faults

The initiator methionine tRNA drives cell migration and invasion leading to increased metastatic potential in melanoma

The cell's repertoire of transfer RNAs (tRNAs) has been linked to cancer. Recently, levels of the initiator methionine tRNA (tRNAiMet) in stromal fibroblasts have been shown to influence extracellular matrix (ECM) secretion to drive tumour growth and angiogenesis. Here we show that increased tRNAiMet within cancer cells does not influence tumour growth, but drives cell migration and invasion via a mechanism that is independent from ECM synthesis and dependent on α5β1 integrin and levels of the translation initiation ternary complex. In vivo and ex vivo migration (but not proliferation) of melanoblasts is significantly enhanced in transgenic mice which express additional copies of the tRNAiMet gene. We show that increased tRNAiMet in melanoma drives migratory, invasive behaviour and metastatic potential without affecting cell proliferation and primary tumour growth, and that expression of RNA polymerase III-associated genes (which drive tRNA expression) are elevated in metastases by comparison with primary tumours. Thus specific alterations to the cancer cell tRNA repertoire drive a migration/invasion programme that may lead to metastasis

Subversion of allocation concealment in a randomised controlled trial : a historical case study

BACKGROUND: If the randomisation process within a trial is subverted, this can lead to selection bias that may invalidate the trial's result. To avoid this problem, it is recommended that some form of concealment should be put into place. Despite ongoing anecdotal concerns about their susceptibility to subversion, a surprising number of trials (over 10%) still use sealed opaque envelopes as the randomisation method of choice. This is likely due in part to the paucity of empirical data quantifying the potential effects of subversion. In this study we report a historical before and after study that compares the use of the sealed envelope method with a more secure centralised telephone allocation approach in order to provide such empirical evidence of the effects of subversion. METHODS: This was an opportunistic before and after study set within a multi-centre surgical trial, which involved 654 patients from 28 clinicians from 23 centres in the UK and Ireland. Two methods of randomly allocating subjects to alternative treatments were adopted: (a) a sealed envelope system administered locally, and (b) a centralised telephone system administered by the trial co-ordination centre. Key prognostic variables were compared between randomisation methods: (a) age at trial entry, a key prognostic factor in the study, and (b) the order in which 'randomisation envelopes' were matched to subjects. RESULTS: The median age of patients allocated to the experimental group with the sealed envelope system, was significantly lower both overall (59 vs 63 years, p < 0.01) and in particular for three clinicians (57 vs 72, p < 0.01; 33 vs 69, p < 0.001; 47 vs 72, p = 0.03). No differences in median age were found between the allocation groups for the centralised system. CONCLUSIONS: Due to inadequate allocation concealment with the sealed envelope system, the randomisation process was corrupted for patients recruited from three clinicians. Centralised randomisation ensures that treatment allocation is not only secure but seen to be secure. Where this proves to be impossible, allocation should at least be performed by an independent third party. Unless it is an absolute requirement, the use of sealed envelopes should be discontinued forthwith

Strategy for Mapping Quantitative Trait Loci (QTL) by Using Human Metapopulations

Aim: To present a novel strategy for mapping quantitative trait loci (QTL), using human metapopulations. The strategy is based on the expectation that in geographic clusters of small and distinct human isolates, a combination of founder effect and genetic drift can dramatically increase population frequency of rare QTL variants with large effect. In such cases, the distribution of QT measurements in an “affected” isolate is expected to deviate from that observed in neighboring isolates. Methods: We tested this hypothesis in 9 villages from a larger Croatian isolate resource, where 7 Mendelian disorders have been previously reported. The values of 10 physiological and biochemical QTs were measured in a random sample of 1001 individuals (100 inhabitants of each of 9 villages and 101 immigrant controls). Results: Significant over- or under- representation of individuals from specific villages in extreme ends of standardized QT measurement distribution was found 10 times more frequently than expected by chance. The large majority of such clusters of individuals with extreme QT values (34/36, 94.4%) originated from the 6 villages with the most pronounced geographic isolation and endogamy. Conclusion: Early epidemiological assessment supports the feasibility of the proposed strategy. Clusters of individuals with extreme QT values responsible for over-representation of single villages can usually be linked to a larger pedigree and may be useful for further QTL mapping, using linkage analysis

Use of an inertia-less virtual synchronous machine within future power networks with high penetrations of converters

Conventional converter models for wind turbines and Voltage Source HVDC links, as submitted to System Operators, typically use dq-axis controllers with current injection (DQCI). Recent work carried out by the authors has proven that for DQCI converter-interfaced sources there are overall penetration limits, i.e. the 'tipping points' beyond which the system will become unstable. Initial investigations of this "tipping point", based on a reduced model of the transmission system of Great Britain using phasor simulation within DIgSILENT PowerFactory, are reviewed briefly in this paper. The 'tipping points' relating to maximum penetration of DQCI converter-interfaced sources are subsequently investigated in this paper using a higher fidelity three-phase dynamic power system model in Matlab Simulink. Additionally, a new converter controller, termed here as Virtual Synchronous Machine Zero Inertia (VSM0H), is described and implemented in the model. It is shown that, in principle, it is possible to significantly increase the penetration of converter based generation (up to 100% of installed capacity) without reaching a stability constraint

Distinguishing coherent and thermal photon noise in a circuit QED system

In the cavity-QED architecture, photon number fluctuations from residual cavity photons cause qubit dephasing due to the AC Stark effect. These unwanted photons originate from a variety of sources, such as thermal radiation, leftover measurement photons, and crosstalk. Using a capacitively-shunted flux qubit coupled to a transmission line cavity, we demonstrate a method that identifies and distinguishes coherent and thermal photons based on noise-spectral reconstruction from time-domain spin-locking relaxometry. Using these measurements, we attribute the limiting dephasing source in our system to thermal photons, rather than coherent photons. By improving the cryogenic attenuation on lines leading to the cavity, we successfully suppress residual thermal photons and achieve $T_1$-limited spin-echo decay time. The spin-locking noise spectroscopy technique can readily be applied to other qubit modalities for identifying general asymmetric non-classical noise spectra