Non-perturbative running of the average momentum of non-singlet parton densities

We determine non-perturbatively the anomalous dimensions of the second moment of non-singlet parton densities from a continuum extrapolation of results computed in quenched lattice simulations at different lattice spacings. We use a Schr\"odinger functional scheme for the definition of the renormalization constant of the relevant twist-2 operator. In the region of renormalized couplings explored, we obtain a good description of our data in terms of a three-loop expression for the anomalous dimensions. The calculation can be used for exploring values of the coupling where a perturbative expansion of the anomalous dimensions is not valid a priori. Moreover, our results provide the non-perturbative renormalization constant that connects hadron matrix elements on the lattice, renormalized at a low scale, with the experimental results, renormalized at much higher energy scales.Comment: Latex2e file, 6 figures, 25 pages, Corrected errors on linear fit in table 2 and discussion on anomalous dimension of f_

FPT is Characterized by Useful Obstruction Sets

Many graph problems were first shown to be fixed-parameter tractable using the results of Robertson and Seymour on graph minors. We show that the combination of finite, computable, obstruction sets and efficient order tests is not just one way of obtaining strongly uniform FPT algorithms, but that all of FPT may be captured in this way. Our new characterization of FPT has a strong connection to the theory of kernelization, as we prove that problems with polynomial kernels can be characterized by obstruction sets whose elements have polynomial size. Consequently we investigate the interplay between the sizes of problem kernels and the sizes of the elements of such obstruction sets, obtaining several examples of how results in one area yield new insights in the other. We show how exponential-size minor-minimal obstructions for pathwidth k form the crucial ingredient in a novel OR-cross-composition for k-Pathwidth, complementing the trivial AND-composition that is known for this problem. In the other direction, we show that OR-cross-compositions into a parameterized problem can be used to rule out the existence of efficiently generated quasi-orders on its instances that characterize the NO-instances by polynomial-size obstructions.Comment: Extended abstract with appendix, as accepted to WG 201

Injection and detection of spin in a semiconductor by tunneling via interface states

Injection and detection of spin accumulation in a semiconductor having localized states at the interface is evaluated. Spin transport from a ferromagnetic contact by sequential, two-step tunneling via interface states is treated not in itself, but in parallel with direct tunneling. The spin accumulation induced in the semiconductor channel is not suppressed, as previously argued, but genuinely enhanced by the additional spin current via interface states. Spin detection with a ferromagnetic contact yields a weighted average of the spin accumulation in the channel and in the localized states. In the regime where the spin accumulation in the localized states is much larger than that in the channel, the detected spin signal is insensitive to the spin accumulation in the localized states and the ferromagnet probes the spin accumulation in the semiconductor channel.Comment: 7 pages, 2 figures. Theory onl

Thermal spin current and magnetothermopower by Seebeck spin tunneling

The recently observed Seebeck spin tunneling, the thermoelectric analog of spin-polarized tunneling, is described. The fundamental origin is the spin dependence of the Seebeck coefficient of a tunnel junction with at least one ferromagnetic electrode. Seebeck spin tunneling creates a thermal flow of spin-angular momentum across a tunnel barrier without a charge tunnel current. In ferromagnet/insulator/semiconductor tunnel junctions this can be used to induce a spin accumulation (\Delta \mu) in the semiconductor in response to a temperature difference (\Delta T) between the electrodes. A phenomenological framework is presented to describe the thermal spin transport in terms of parameters that can be obtained from experiment or theory. Key ingredients are a spin-polarized thermoelectric tunnel conductance and a tunnel spin polarization with non-zero energy derivative, resulting in different Seebeck tunnel coefficients for majority and minority spin electrons. We evaluate the thermal spin current, the induced spin accumulation and \Delta\mu/\Delta T, discuss limiting regimes, and compare thermal and electrical flow of spin across a tunnel barrier. A salient feature is that the thermally-induced spin accumulation is maximal for smaller tunnel resistance, in contrast to the electrically-induced spin accumulation that suffers from the impedance mismatch between a ferromagnetic metal and a semiconductor. The thermally-induced spin accumulation produces an additional thermovoltage proportional to \Delta\mu, which can significantly enhance the conventional charge thermopower. Owing to the Hanle effect, the thermopower can also be manipulated with a magnetic field, producing a Hanle magnetothermopower.Comment: 10 pages, 3 figures, 1 tabl

Molecular Lines as Diagnostics of High Redshift Objects

Models are presented for CO rotational line emission by high redshift starburst galaxies. The influence of the cosmic microwave background on the thermal balance and the level populations of atomic and molecular species is explicitly included. Predictions are made for the observability of starburst galaxies through line and continuum emission between z=5 and z=30. It is found that the Millimeter Array could detect a starburst galaxy with ~10^5 Orion regions, corresponding to a star formation rate of about 30 Mo yr^{-1}, equally well at z=5 or z=30 due to the increasing cosmic microwave background temperature with redshift. Line emission is a potentially more powerful probe than dust continuum emission of very high redshift objects.Comment: 15 pages LaTex, uses aasms4.sty, Accepted by ApJ

Non-perturbative renormalization of moments of parton distribution functions

We compute non-perturbatively the evolution of the twist-2 operators corresponding to the average momentum of non-singlet quark densities. The calculation is based on a finite-size technique, using the Schr\"odinger Functional, in quenched QCD. We find that a careful choice of the boundary conditions, is essential, for such operators, to render possible the computation. As a by-product we apply the non-perturbatively computed renormalization constants to available data of bare matrix elements between nucleon states.Comment: Lattice2003(Matrix); 3 pages, 3 figures. Talk by A.

The recognition of Customary Marriages Act: many women still left out in the cold

This paper focuses on the position of women in monogamous customary marriages concluded before the commencement of The Recognition of Customary Marriages Act, 120 of 1998. This Act alleviated (on appearances) the subordination and inferior status of women in cutomary law. Sec 6 specifically stipulates that a wife in a customary marriage has, on the basis of equality with her husband and subject to the matrimonial system governing the marriage, full status and capacity. According to sec 7 the proprietary consequences of marriages entered into before the commencement of the Act continue to be governed by customary law. However, the question arises – what is the point of sec 6 granting a wife equality with her husband and the capacity to acquire assets, but still subject to the customary law which places the marital property under the control and almost complete discretion of her husband? Many of the sections of the Divorce Act and the Matrimonial Property Act (which was introduced mainly to improve the postion of women) are also only applicable to customary marriages entered into after the commencement of the Act. It is submitted that arguments which supported a retrospective change to proprietary regimes, should have been adopted in the legislation. Sec 7(1) of th Act should be amended to provide that a monogamous customary marriage entered into before the commencement of the Act, is a marriage in community of property and of profit and loss

Multiple marriages, burial rights and the role of lobolo at the dissolution of the marriage

This paper highlights three aspects which have an impact on both customary and common law that came to the fore in the Thembisile case. An evaluation of the way in which the court dealt with the different aspects is made. Regarding multiple marriages, where a civil marriage is also involved, it is suggested that the courts should be hesitant to simply declare either the civil or the customary marriage a nullity and should consider the different options available first. Where a funeral is marred by feuds about burial rights, it is suggested that a flexible approach should be followed. Strict adherence to common law principles could lead to unreasonable and inequitable results, especially in traditional communities. Lastly, there seems to be conflict between the official customary law and the living law regarding the return of the lobolo at the dissolution of a customary marriage. Empirical research should be undertaken to determine whether lobolo is in fact still returned

Hospital disclaimers: Afrox Health Care v Strydom

From text: In Afrox Healthcare v Strydom the Supreme Court of Appeal had to adjudicate on the enforceability of hospital disclaimers. The question arose as to whether a clause contained in the hospital’s admission form, which exempted the hospital from liability for the negligence of its staff, was enforceable against an aggrieved party. Most of the private hospitals in South Africa include this type of clause in their admission forms. According to Strauss, the reason for this is that our society is becoming increasingly litigious

Phonon-assisted tunneling in the quantum regime of Mn12-ac

Longitudinal or transverse magnetic fields applied on a crystal of Mn12-ac allows to observe independent tunnel transitions between m=-S+p and m=S-n-p (n=6-10, p=0-2 in longitudinal field and n=p=0 in transverse field). We observe a smooth transition (in longitudinal) from coherent ground-state to thermally activated tunneling. Furthermore two ground-state relaxation regimes showing a crossover between quantum spin relaxation far from equilibrium and near equilibrium, when the environment destroys multimolecule correlations. Finally, we stress that the complete Hamiltonian of Mn12 should contain odd spin operators of low order