d-Hole localization and the suppression of superconductivity in YBa2(Cu1-xZnx)3O7?y

The temperature and Zn concentration dependence of the electrical resistivity, specific heat, magnetic susceptibility, and electron paramagnetic resonance (EPR) spectra of YBa₂(Cu_1–x Zn _x )₃O_7–y withy0.1 has been measured forx0.16. In addition, the temperature and field dependence of the magnetization has been measured for 2<T<300K and 0<H<9.0T, along with the temperature and quasihydrostatic pressure dependence of the electrical resistivity for selected samples for 0<P<13 GPa. The substitution of Zn for Cu in YBa₂Cu₃O_7–y causes a rapid and nearly linear depression of the superconducting transition temperature,T _c , withT _c going to 0 K forx 0.10. YBa₂(Cu_1–x Zn _x )₃O_7–y retains the YBa₂Cu₃O_7-y orthorhombic structure forx0.16 for both the superconducting and nonsuperconducting samples. Initially, the unit cell volume increases nearly linearly with Zn content; however, an abrupt change occurs in the vicinityx=0.8–0.10. Forx<0.10, the temperature dependence of the electrical resistivity,(T), is metallic-like (d/dT>0) and increases gradually with increasing Zn content. However, forx 0.10,(T) becomes semiconductor-like, with a very rapid increase of the resistivity with increasingx. The electrical resistivity, magnetic susceptibility, EPR spectra, and specific heat all indicate that thed-holes associated with the Cu ions become localized in the nonsuperconducting phase,x>-0.10.     

Re-evaluating genetic algorithm performance under coordinate rotation of benchmark functions. A survey of some theoretical and practical aspects of genetic algorithms

In recent years, genetic algorithms (GAs) have become increasingly robust and easy to use. Current knowledge and many successful experiments suggest that the application of GAs is not limited to easy-to-optimize unimodal functions. Several results and GA theory give the impression that GAs easily escape from millions of local optima and reliably converge to a single global optimum. The theoretical analysis presented in this paper shows that most of the widely-used test functions have n independent parameters and that, when optimizing such functions, many GAs scale with an O(n ln n) complexity. Furthermore, it is shown that the current design of GAs and its parameter settings are optimal with respect to independent parameters. Both analysis and results show that a rotation of the coordinate system causes a severe performance loss to GAs that use a small mutation rate. In case of a rotation, the GA's complexity can increase up to O(nn) = O(exp(n ln n)). Future work should find new GA designs that solve this performance loss. As long as these problems have not been solved, the application of GAs will be limited to the optimization of easy-to-optimize functions.     

Efficient linear scaling geometry optimization and transition-state search for direct wavefunction optimization schemes in density functional theory using a plane-wave basis

Two linear scaling schemes for the search of stationary points on the nuclear potential energy surface have been developed and implemented for density functional theory programs using plane waves: a geometry optimizer based on the limited-memory Broyden–Fletcher–Goldfarb–Shanno (L-BFGS) method and a linear scaling method for transition-state search based on the microiterative scheme using the partitioned rational function optimizer (P-RFO) and L-BFGS. These optimizers are written with parallelized execution in mind. It is shown that the electronic wavefunction does not need to be fully optimized in the earlier stages of geometry optimization. The reasons for the robustness and good performance of the proposed schemes are identified. Test calculations are presented that use our implementation in the CPMD code.     

The rheumatic forefoot

The prevalence of rheumatic forefoot arthritis is estimated at 85-95%. Early synovitis of the metatarsophalangeal (MTP) joints is frequently neglected or overlooked. The disease leads to depression of the forefoot arch, dislocation of the MTP joints and hallux valgus with severe metatarsalgia. Operative treatment may give good results in 77-91% of cases. Our preferred treatment consists of resection arthroplasties for the smaller toes and use of Swanson spacer for the big toe, extensive capsular and tendon release from the dorsal approach, reduction of the first metatarsal bone, relocation of the extensor hallucis tendon and postoperative corrective dressing for 6-12 weeks. With this technique, we obtained 36 good results out of 46 forefoot reconstructions, the mean observation period being 30 months.     

Tuberculosis in drug users

The rise in tuberculosis (TB) has disproportionately affected specific populations. Historically, many patients with TB became iatrogenic opiate addicts through therapeutic use of these drugs for symptom control. Demographic trends reshaped the relationship between drug use and TB into one in which drug use became a risk factor for tuberculosis as a result of the overlap of epidemiological and social factors associated with both drug use and TB. The spread of human immunodeficiency virus infection has amplified the spread of TB among drug users. We review the epidemiology of TB in drug users as well as the factors relevant to screening and compliance in drug-using populations. Drug users constitute a high-risk group for whom screening, prevention of infection, diagnosis, and treatment pose particular challenges. The development of TB services capable of engaging drug users (those both in and out of drug treatment programs) has potential for disrupting a significant chain of rapid TB transmission.     

Mutation of the RET ligand, neurturin, supports multigenic inheritance in Hirschsprung disease

Hirschsprung disease (HSCR) is a frequent neurocristopathy characterized by the absence of submucosal and myenteric plexuses in a variable length of the gastrointestinal tract. Pedigrees and segregation analyses suggested the involvement of one or several dominant genes with low penetrance in HSCR. Considering that RET and glial cell line-derived neurotrophic factor (GDNF) mutations have been reported in the disease, we regarded the other RET ligand, neurturin (NTN), as an attractive candidate gene, especially as it shares large homologies with GDNF. Here, we report on the finding of a heterozygous missense NTN mutation in a large non-consanguineous family including four children affected with a severe aganglionosis phenotype extending up to the small intestine. Interestingly, it appears that the NTN mutation reported here is not sufficient to cause HSCR, and this multiplex family also segregates a RET mutation. This cascade of independent and additive genetic events fits well with the multigenic pattern of inheritance expected in HSCR, and further support the role of RET ligands in development of the enteric nervous system.