Superconductivity of lanthanum revisited: enhanced critical temperature in the clean limit

The thickness dependence of the superconducting energy gap $\Delta_{\rm{La}}$ of double hexagonally close packed (dhcp) lanthanum islands grown on W(110) is studied by scanning tunneling spectroscopy, from the bulk to the thin film limit. Superconductivity is suppressed by the boundary conditions for the superconducting wavefunction at the surface and W/La interface, leading to a linear decrease of the critical temperature $T_c$ as a function of the inverse film thickness. For thick, bulk-like films, $\Delta_{\rm{La}}$ and $T_c$ are 40% larger as compared to literature values of dhcp La measured by other techniques. This finding is reconciled by examining the effects of surface contamination as probed by modifications of the surface state, suggesting that the large $T_c$ originates in the superior purity of the samples investigated here.Comment: 14 pages, 7 figure

Reply to \u27Do oceanic zooplankton aggregate at, or near, the deep chlorophyll maximum?\u27

We appreciate the time and attention given our paper by Longhurst and Herman and the opportunity to reply to their critique. Unfortunately, we believe their difficulties with the presentation of our data are more subjective than substantive. In fact, we believe a careful reading of our text will show that our conclusions are suitably conservative...

Purple Loosestrife: History, Management, and Biological Control in Iowa

Purple loosestrife (Lythrum salicaria) is an invasive plant species infesting wetlands in North America. Biodiversity and wetland habitat quality are reduced following purple loosestrife establishment. Several management tactics, including cultural, mechanical, and chemical controls, have had limited success in reducing the spread of purple loosestrife. Beginning in the 1990s, a biological control program has introduced several species of natural enemies from Europe that feed on purple loosestrife. Since 1994, Iowa State University has reared and released two species of beetles that feed on purple loosestrife, Galerucella calmariensis and G. pusilla. Biological control is one component of an integrated purple loosestrife management and education program that is needed to reduce the spread and densities of purple loosestrife

Symptoms of posttraumatic stress disorder in adolescents with conduct disorder: Sex differences and onset Patterns

Examined sex differences in the rate and symptoms of posttraumatic stress disorder (PTSD), trauma exposure, and onset patterns in youth with conduct disorder (CD). 45 male and 31 female 10–17 yr olds admitted to a clinical facility for severe behavior problems completed the Diagnostic Interview for Children and Adolescents—Revised (DICA-R) to assess the presence of CD and PTSD. Over one-half of CD youth reported exposure to trauma, yet only 17% met criteria for PTSD. PTSD was more frequent in CD girls (28%) than in boys (10%), and girls experienced greater symptom intensity and anhedonia, difficulty feeling love or affection, and disturbance of s1eep and concentration. Girls more frequently reported sexual assault, while boys were more likely to report accidents, physical assaults, and witnessing the death of a loved one. Retrospective reports indicated that PTSD tended to develop subsequent to CD

Ordering of Trotterization: impact on errors in quantum simulation of electronic structure

Trotter–Suzuki decompositions are frequently used in the quantum simulation of quantum chemistry. They transform the evolution operator into a form implementable on a quantum device, while incurring an error—the Trotter error. The Trotter error can be made arbitrarily small by increasing the Trotter number. However, this increases the length of the quantum circuits required, which may be impractical. It is therefore desirable to find methods of reducing the Trotter error through alternate means. The Trotter error is dependent on the order in which individual term unitaries are applied. Due to the factorial growth in the number of possible orderings with respect to the number of terms, finding an optimal strategy for ordering Trotter sequences is difficult. In this paper, we propose three ordering strategies, and assess their impact on the Trotter error incurred. Initially, we exhaustively examine the possible orderings for molecular hydrogen in a STO-3G basis. We demonstrate how the optimal ordering scheme depends on the compatibility graph of the Hamiltonian, and show how it varies with increasing bond length. We then use 44 molecular Hamiltonians to evaluate two strategies based on coloring their incompatibility graphs, while considering the properties of the obtained colorings. We find that the Trotter error for most for systems involving heavy atoms, using a reference magnitude ordering, is less than 1 kcal/mol. Relative to this, the difference between ordering schemes can be substantial, being approximately on the order of millihartrees. The coloring-based ordering schemes are reasonably promising—particularly for systems involving heavy atoms—however further work is required to increase dependence on the magnitude of terms. Finally, we consider ordering strategies based on the norm of the Trotter error operator, including an iterative method for generating the new error operator terms added upon insertion of a term into an ordered Hamiltonian