Comment to the paper : Collapse of the vortex-lattice inductance and shear modulus at the melting transition in untwinned YBa2_2Cu3_3O7_7, by Matl \QTR{em}{et al.}

In a recent paper, Matl et al present a high-frequency study of the complex resistivity of a pinned vortex lattice in YBaCuO . They focus on the inductive-to-resistive transition which is investigated as a function of temperature at a constant field $B_0=2$ T, so that the transition is associated with the vanishing of vortex pinning strength. To our view, their conclusions rely on a rather brittle experimental body and the collapse of C66 results from an involved analysis of the finite frequency corrections to $\rho (\omega)$. These corrections are not necessary since the complex frequency spectrum has been previously interpreted by the two modes model, first proposed for low Tc materials. We think that it is more adequate to interpret the present data and should be at least considered.Comment: 4pages tex. submitted to PR

The vortex depinning transition in untwinned YBaCuO using complex impedance measurements

We present surface impedance measurement of the vortex linear response in a large untwinned YBCO crystal. The depinning spectra obtained over a broad frequency range (100 Hz- 30 MHz) are those of a surface pinned vortex lattice with a free flux flow resistivity (two modes response). The critical current in the "Campbell" like regime and the flux flow resistivity in the dissipative regime are extracted. Those two parameters are affected by the first order transition, showing that this transition may be related to the electronic state of vortices.Comment: to be published in the proceedings of M2S RI

rf-studies of vortex dynamics in isotropic type-II superconductors

We have measured the surface impedance of thick superconductors in the mixed state over a broad 2 kHz - 20 MHz frequency range. The depinning cross-over is observed; but it is much broader than expected from classical theories of pinning. A striking result is the existence of size effects which invalidate the common interpretation of the low-frequency surface inductance in terms of a single penetration depth. Instead, a two-mode description of vortex dynamics, assuming free vortex flow in the bulk and surface pinning, accounts quantitatively for the spectrum of the complex apparent penetration depth.Comment: 20 pages, 6 figures, 28 reference

Depinning transition in type-II superconductors

The surface impedance Z(f) of conventional isotropic materials has been carefully measured for frequencies f ranging from 1 kHz to 3 MHz, allowing a detailed investigation of the depinning transition. Our results exhibit the irrelevance of classical ideas to the dynamics of vortex pinning. We propose a new picture, where the linear ac response is entirely governed by disordered boundary conditions of a rough surface, whereas in the bulk vortices respond freely. The universal law for Z(f) thus predicted is in remarkable agreement with experiment, and tentatively applies to microwave data in YBaCuO films.Comment: 4 pages, 4 figures, 14 reference

Phase-Sensitive Impurity Effects in Vortex Core of Moderately Clean Chiral Superconductors

We study impurity effects in vortex core of two-dimensional moderately clean su perconductors within the quasiclassical theory. The impurity scattering rate \G amma(E) of the Andreev bound states in vortex core with +1 vorticity of p-wav e superconductors with {\mib d}=\hat{\mib z}(p_x+\iu p_y) is suppre ssed, compared to the normal state scattering rate $\Gamma_{\rm n}$ in the energ y region \Gamma_{\rm n}^3/E_\delta^2\ll E\ll E_\delta\equiv |\delta_0|\Delta_\i nfty with scattering phase shift $\delta_0$ $(|\delta_0|\ll 1)$ and the pair-po tential in bulk $\Delta_\infty$. Further we find that $\Gamma(E)/\Gamma_{\rm n}$ for p-wave superconductors with {\mib d}=\hat{\mib z}(p_x-\iu p_y) is at most {\cal O}(E/\Delta_\i nfty). These results are in marked contrast to the even-parity case (s,d-wave), where $\Gamma(E)/\Gamma_{\rm n}$ is known to be proportional to \ln(\Delta_\i nfty/E) . Parity- and chirality-dependences of impurity effects are attributed to the Andr eev reflections involved in the impurity-induced scattering between bound states . Implications for the flux flow conductivity is also discussed. Novel enhanceme nt of flux flow conductivity is expected to occur at $T\ll E_\delta$ for {\mib d}=\hat{\mib z}(p_x+\iu p_y) and at $T\ll \Delta_\infty$ for {\mib d}=\hat{\mib z}(p_x-\iu p_y).Comment: 9 pages, No figures, To appear in JPSJ Vol. 69, No. 10 (2000

Supporting Engineering Processes Utilizing Service-Oriented Grid Technology

Speeding up knowledge-intensive core processes in engineering and increas-ing the quality of their results is becoming more and more decisive, since economic pressure from national and international competitors and customers is rising. In particular, these demands exceed the organizational and infrastructural capacities of small and medium-sized enterprises (SME) by far. Hence, combining complementary core competencies across organizational boundaries is crucial for an enterprise's continuing success. Efficient and economically reasonable support of knowledge-intensive core processes in virtual organisations is therefore a predominant requirement for future IT infrastructures. The paradigm shift to service-orientation in Grid middleware opens the possibility to provide such support along the product lifecycle by employing a flexible software development approach, namely to compose applications from standard components, promising easier development and modification of Grid applications. In this paper, a service-oriented Grid computing approach is presented which aims at supporting distributed business processes in industry (see section 2 for industrial scenarios) from top level modelling, workflow design and exe-cution to actual Grid service code (presented in section 3). Parts of this gap between processes and code can be bridged by semi-automatically generated Grid service code. Orchestration of these Grid services is also automated by using a Grid-enabled workflow engine (see section 3). The feasibility of the proposed approach is demonstrated by presenting an exemplary process chain from the casting industry (see full paper)

Coenzyme A-transferase-independent butyrate re-assimilation in Clostridium acetobutylicum - evidence from a mathematical model

The hetero-dimeric CoA-transferase CtfA/B is believed to be crucial for the metabolic transition from acidogenesis to solventogenesis in Clostridium acetobutylicum as part of the industrial-relevant acetone-butanol-ethanol (ABE) fermentation. Here, the enzyme is assumed to mediate re-assimilation of acetate and butyrate during a pH-induced metabolic shift and to faciliate the first step of acetone formation from acetoacetyl-CoA. However, recent investigations using phosphate-limited continuous cultures have questioned this common dogma. To address the emerging experimental discrepancies, we investigated the mutant strain Cac-ctfA398s::CT using chemostat cultures. As a consequence of this mutation, the cells are unable to express functional ctfA and are thus lacking CoA-transferase activity. A mathematical model of the pH-induced metabolic shift, which was recently developed for the wild type, is used to analyse the observed behaviour of the mutant strain with a focus on re-assimilation activities for the two produced acids. Our theoretical analysis reveals that the ctfA mutant still re-assimilates butyrate, but not acetate. Based upon this finding, we conclude that C. acetobutylicum possesses a CoA-tranferase-independent butyrate uptake mechanism that is activated by decreasing pH levels. Furthermore, we observe that butanol formation is not inhibited under our experimental conditions, as suggested by previous batch culture experiments. In concordance with recent batch experiments, acetone formation is abolished in chemostat cultures using the ctfa mutant

Genome sequence of the bioplastic-producing ‘‘Knallgas’’ bacterium Ralstonia eutropha H16

The H2-oxidizing lithoautotrophic bacterium Ralstonia eutropha H16 is a metabolically versatile organism capable of subsisting, in the absence of organic growth substrates, on H2 and CO2 as its sole sources of energy and carbon. R. eutropha H16 first attracted biotechnological interest nearly 50 years ago with the realization that the organism’s ability to produce and store large amounts of poly[R-(–)-3-hydroxybutyrate] and other polyesters could be harnessed to make biodegradable plastics. Here we report the complete genome sequence of the two chromosomes of R. eutropha H16. Together, chromosome 1 (4,052,032 base pairs (bp)) and chromosome 2 (2,912,490 bp) encode 6,116 putative genes. Analysis of the genome sequence offers the genetic basis for exploiting the biotechnological potential of this organism and provides insights into its remarkable metabolic versatility

New East Manchester: urban renaissance or urban opportunism?

In this paper we ask how a shrinking city responds when faced with a perforated urban fabric. Drawing on Manchester’s response to its perforated eastern flank - and informed by a parallel study of Leipzig - we use the city’s current approach to critique urban regeneration policy in England. Urban renaissance holds out the promise of delivering more sustainable - that is more compact, more inclusive and more equitable - cities. However, the Manchester study demonstrated that the attempt to stem population loss from the city is at best fragile, despite a raft of policies now in place to support urban renaissance in England. It is argued here that Manchester like Leipzig is likely to face an ongoing battle to attract residents back from their suburban hinterlands. This is especially true of the family market that we identify as being an important element for long-term sustainable population growth in both cities. We use the case of New East Manchester to consider how discourses linked to urban renaissance – particularly those that link urbanism with greater densities - rule out some of the options available to Leipzig, namely, managing the long-term perforation of the city. We demonstrate that while Manchester is inevitably committed to the urban renaissance agenda, in practice New East Manchester demonstrates a far more pragmatic – but equally unavoidable – approach. This we attribute to the gap between renaissance and regeneration described by Amin et al (2000) who define the former as urbanism for the middle class and the latter as urbanism for the working class. While this opportunistic approach may ultimately succeed in producing development on the ground, it will not address the fundamental, and chronic, problem; the combination of push and pull that sees families relocating to suburban areas. Thus, if existing communities in East Manchester are to have their area buoyed up – or sustained - by incomers, and especially families, with greater levels of social capital and higher incomes urban policy in England will have to be challenged