The diamagnetism above the superconducting transition in underdoped La(1.9)Sr(0.1)CuO(4) revisited: Chemical disorder or phase incoherent superconductivity?

The interplay between superconducting fluctuations and inhomogeneities presents a renewed interest due to recent works supporting an anomalous [beyond the conventional Gaussian-Ginzburg-Landau (GGL) scenario] diamagnetism above Tc in underdoped cuprates. This conclusion, mainly based in the observation of new anomalies in the low-field isothermal magnetization curves, is in contradiction with our earlier results in the underdoped La(1.9)Sr(0.1)CuO(4) [Phys. Rev. Lett. 84, 3157 (2000)]. These seemingly intrinsic anomalies are being presented in various influential works as a 'thermodynamic evidence' for phase incoherent superconductivity in the pseudogap regime, this last being at present a central and debated issue of the cuprate superconductors' physics. Here we have extended our magnetization measurements in La(1.9)Sr(0.1)CuO(4) to two samples with different chemical disorder, in one of them close to the one associated with the random distribution of Sr ions. For this sample, the corresponding Tc-distribution may be approximated as symmetric around the average Tc, while in the most disordered sample is strongly asymmetric. The comparison between the magnetization measured in both samples provides a crucial check of the chemical disorder origin of the observed diamagnetism anomalies, which are similar to those claimed as due to phase fluctuations by other authors. This conclusion applies also to the sample affected only by the intrinsic-like chemical disorder, providing then a further check that the intrinsic diamagnetism above the superconducting transition of underdoped cuprates is not affected by the opening of a pseudogap in the normal state. It is also shown here that once these disorder effects are overcome, the remaining precursor diamagnetism may be accounted at a quantitative level in terms of the GGL approach under a total energy cutoff.Comment: 13 pages, 7 figures. Minor corrections include

A Method for Solving Distributed Service Allocation Problems

We present a method for solving service allocation problems in which a set of services must be allocated to a set of agents so as to maximize a global utility. The method is completely distributed so it can scale to any number of services without degradation. We first formalize the service allocation problem and then present a simple hill-climbing, a global hill-climbing, and a bidding-protocol algorithm for solving it. We analyze the expected performance of these algorithms as a function of various problem parameters such as the branching factor and the number of agents. Finally, we use the sensor allocation problem, an instance of a service allocation problem, to show the bidding protocol at work. The simulations also show that phase transition on the expected quality of the solution exists as the amount of communication between agents increases

Fluctuation diamagnetism around the superconducting transition in a cuprate crystal with a reduced Meissner fraction

The magnetization around the superconducting transition was measured in a Tl$_{0.5}$Pb$_{0.5}$Sr$_2$CaCu$_2$O$_7$ crystal affected by a considerable reduction ($\sim$55%) of its effective superconducting volume fraction but still with a relatively sharp low-field Meissner transition, a behaviour that may be attributed to the presence of structural inhomogeneities. By taking into account these inhomogeneities just through the Meissner fraction, the observed diamagnetism may still be explained, consistently above and below the superconducting transition, in terms of the conventional Ginzburg-Landau approach with fluctuations of Cooper pairs and vortices.Comment: 4 pages, 4 figure

Comment on "High Field Studies of Superconducting Fluctuations in High-Tc Cuprates. Evidence for a Small Gap distinct from the Large Pseudogap"

By using high magnetic field data to estimate the background conductivity, Rullier-Albenque and coworkers have recently published [Phys.Rev.B 84, 014522 (2011)] experimental evidence that the in-plane paraconductivity in cuprates is almost independent of doping. In this Comment we also show that, in contrast with their claims, these useful data may be explained at a quantitative level in terms of the Gaussian-Ginzburg-Landau approach for layered superconductors, extended by Carballeira and coworkers to high reduced-temperatures by introducing a total-energy cutoff [Phys.Rev.B 63, 144515 (2001)]. When combined, these two conclusions further suggest that the paraconductivity in cuprates is conventional, i.e., associated with fluctuating superconducting pairs above the mean-field critical temperature.Comment: 9 pages, 1 figur

Diamagnetism around the Meissner transition in a homogeneous cuprate single crystal

The in-plane diamagnetism around the Meissner transition was measured in a Tl$_2$Ba$_2$Ca$_2$Cu$_3$O$_{10}$ single crystal of high chemical and structural quality, which minimizes the inhomogeneity and disorder rounding effects on the magnetization. When analyzed quantitatively and consistently above and below the transition in terms of the Ginzburg-Landau (GL) approach with fluctuations of Cooper pairs and vortices, these data provide a further confirmation that the observed Meissner transition is a conventional GL superconducting transition in a homogeneous layered superconductor.Comment: 5 pages, including 3 figure

Exposure to “real life” professional experiences through a shadowing scheme that matches penultimate and final year students with employers

This paper reports on a learning development project undertaken during 2010 – 2011. The Work-Shadowing Scheme (WSS) was primarily developed in response to feedback following the National Student Survey (NSS). The NSS brought to light the apparent discrepancy between, the number of structured programmes City University London host that offer exposure within professional environments (for example, formal placement schemes) and the number of students looking for experience within a professional context. In an attempt to bridge this gap, the Career and Skills Development Service began thinking about how to implement a scheme that would provide City students with a unique opportunity to gain professional experience across a variety of industries. The WSS project was designed to provide students with the opportunity to shadow a guide from a sector of their choice. Typically, students requested to shadow guides in industries associated with their course, however an additional benefit of the WSS was the potential to shadow a guide within a sector that was not traditionally associated with their degree. On completion of a shadowing experience, students were given the option to shadow two more employers. This aspect of the scheme was further commended, and students reiterated the benefits of gaining „snapshots‟ of multiple sectors before making crucial career decisions

Pointwise universal consistency of nonparametric linear estimators

This paper presents sufficient conditions for pointwise universal consistency of nonparametric delta estimators. We show the applicability of these conditions for some classes of nonparametric estimators

A generalization of Bohr's Equivalence Theorem

Based on a generalization of Bohr's equivalence relation for general Dirichlet series, in this paper we study the sets of values taken by certain classes of equivalent almost periodic functions in their strips of almost periodicity. In fact, the main result of this paper consists of a result like Bohr's equivalence theorem extended to the case of these functions.Comment: Because of a mistake detected in one of the references, the previous version of this paper has been modified by the authors to restrict the scope of its application to the case of existence of an integral basi

A universal quantum circuit for two-qubit transformations with three CNOT gates

We consider the implementation of two-qubit unitary transformations by means of CNOT gates and single-qubit unitary gates. We show, by means of an explicit quantum circuit, that together with local gates three CNOT gates are necessary and sufficient in order to implement an arbitrary unitary transformation of two qubits. We also identify the subset of two-qubit gates that can be performed with only two CNOT gates.Comment: 3 pages, 7 figures. One theorem, one author and references added. Change of notational conventions. Minor correction in Theorem

Bohr's equivalence relation in the space of Besicovitch almost periodic functions

Based on Bohr's equivalence relation which was established for general Dirichlet series, in this paper we introduce a new equivalence relation on the space of almost periodic functions in the sense of Besicovitch, $B(\mathbb{R},\mathbb{C})$, defined in terms of polynomial approximations. From this, we show that in an important subspace $B^2(\mathbb{R},\mathbb{C})\subset B(\mathbb{R},\mathbb{C})$, where Parseval's equality and Riesz-Fischer theorem holds, its equivalence classes are sequentially compact and the family of translates of a function belonging to this subspace is dense in its own class.Comment: Because of a mistake detected in one of the references, the equivalence relation which is inspired by that of Bohr is revised to adapt correctly the situation in the general case. arXiv admin note: text overlap with arXiv:1801.0803