Nonequilibrium Approach to Bloch-Peierls-Berry Dynamics

We examine the Bloch-Peierls-Berry dynamics under a classical nonequilibrium dynamical formulation. In this formulation all coordinates in phase space formed by the position and crystal momentum space are treated on equal footing. Explicitly demonstrations of the no (naive) Liouville theorem and of the validity of Darboux theorem are given. The explicit equilibrium distribution function is obtained. The similarities and differences to previous approaches are discussed. Our results confirm the richness of the Bloch-Peierls-Berry dynamics

Global Theory of Quantum Boundary Conditions and Topology Change

We analyze the global theory of boundary conditions for a constrained quantum system with classical configuration space a compact Riemannian manifold $M$ with regular boundary $\Gamma=\partial M$. The space \CM of self-adjoint extensions of the covariant Laplacian on $M$ is shown to have interesting geometrical and topological properties which are related to the different topological closures of $M$. In this sense, the change of topology of $M$ is connected with the non-trivial structure of \CM. The space \CM itself can be identified with the unitary group \CU(L^2(\Gamma,\C^N)) of the Hilbert space of boundary data L^2(\Gamma,\C^N). A particularly interesting family of boundary conditions, identified as the set of unitary operators which are singular under the Cayley transform, \CC_-\cap \CC_+ (the Cayley manifold), turns out to play a relevant role in topology change phenomena. The singularity of the Cayley transform implies that some energy levels, usually associated with edge states, acquire an infinity energy when by an adiabatic change the boundary condition reaches the Cayley submanifold \CC_-. In this sense topological transitions require an infinite amount of quantum energy to occur, although the description of the topological transition in the space \CM is smooth. This fact has relevant implications in string theory for possible scenarios with joint descriptions of open and closed strings. In the particular case of elliptic self--adjoint boundary conditions, the space \CC_- can be identified with a Lagrangian submanifold of the infinite dimensional Grassmannian. The corresponding Cayley manifold \CC_- is dual of the Maslov class of \CM.Comment: 29 pages, 2 figures, harvma

Selective Enzymatic Oxidation of Silanes to Silanols

Compared to the biological world's rich chemistry for functionalizing carbon, enzymatic transformations of the heavier homologue silicon are rare. We report that a wild‐type cytochrome P450 monooxygenase (P450_(BM3) from Bacillus megaterium, CYP102A1) has promiscuous activity for oxidation of hydrosilanes to give silanols. Directed evolution was applied to enhance this non‐native activity and create a highly efficient catalyst for selective silane oxidation under mild conditions with oxygen as the terminal oxidant. The evolved enzyme leaves C−H bonds present in the silane substrates untouched, and this biotransformation does not lead to disiloxane formation, a common problem in silanol syntheses. Computational studies reveal that catalysis proceeds through hydrogen atom abstraction followed by radical rebound, as observed in the native C−H hydroxylation mechanism of the P450 enzyme. This enzymatic silane oxidation extends nature's impressive catalytic repertoire

Wafer-Scale Nanopatterning and Translation into High-Performance Piezoelectric Nanowires

The development of a facile method for fabricating one-dimensional, precisely positioned nanostructures over large areas offers exciting opportunities in fundamental research and innovative applications. Large-scale nanofabrication methods have been restricted in accessibility due to their complexity and cost. Likewise, bottom-up synthesis of nanowires has been limited in methods to assemble these structures at precisely defined locations. Nanomaterials such as PbZr_xTi_(1−x)O_3 (PZT) nanowires (NWs)—which may be useful for nonvolatile memory storage (FeRAM), nanoactuation, and nanoscale power generation—are difficult to synthesize without suffering from polycrystallinity or poor stoichiometric control. Here, we report a novel fabrication method which requires only low-resolution photolithography and electrochemical etching to generate ultrasmooth NWs over wafer scales. These nanostructures are subsequently used as patterning templates to generate PZT nanowires with the highest reported piezoelectric performance (d_(eff) ~ 145 pm/V). The combined large-scale nanopatterning with hierarchical assembly of functional nanomaterials could yield breakthroughs in areas ranging from nanodevice arrays to nanodevice powering

Incidence and public health burden of sunburn among beachgoers in the United States.

The beach environment creates many barriers to effective sun protection, putting beachgoers at risk for sunburn, a well-established risk factor for skin cancer. Our objective was to estimate incidence of sunburn among beachgoers and evaluate the relationship between sunburn incidence and sun-protective behaviors. A secondary analysis, of prospective cohorts at 12 locations within the U.S. from 2003 to 2009 (n = 75,614), were pooled to evaluate sunburn incidence 10-12 days after the beach visit. Behavioral and environmental conditions were cross-tabulated with sunburn incidence. Multivariable logistic regression was used to estimate the association between new sunburn and sun-protective behaviors. Overall, 13.1% of beachgoers reported sunburn. Those aged 13-18 years (16.5%), whites (16.0%), and those at beach locations along the Eastern Seaboard (16.1%), had the highest incidence of sunburn. For those spending ≥5 h in the sun, the use of multiple types of sun protection reduced odds of sunburn by 55% relative to those who used no sun protection (Odds Ratio = 0.45 (95% Confidence Interval:0.27-0.77)) after adjusting for skin type, age, and race. Acute health effects of sunburn tend to be mild and self-limiting, but potential long-term health consequences are more serious and costly. Efforts to encourage and support proper sun-protective behaviors, and increase access to shade, protective clothing, and sunscreen, can help prevent sunburn and reduce skin cancer risk among beachgoers

Sugarbeet Production Under Reduced Tillage Prospects And Problems

A study was initiated in the fall of 1977 to obtain base line data on the applicability of reduced tillage sugarbeet production in the Red River Valley. Three reduced tillage systems were compared to a conventional system which consisted of fall plow plus secondary tillage. Results indicated warmer early spring soil temperatures, better seedling emergence, lower ground-level wind speed and no significant yield loss under reduced tillage as compared to the conventional system

Optimal discrete stopping times for reliability growth tests

Often, the duration of a reliability growth development test is specified in advance and the decision to terminate or continue testing is conducted at discrete time intervals. These features are normally not captured by reliability growth models. This paper adapts a standard reliability growth model to determine the optimal time for which to plan to terminate testing. The underlying stochastic process is developed from an Order Statistic argument with Bayesian inference used to estimate the number of faults within the design and classical inference procedures used to assess the rate of fault detection. Inference procedures within this framework are explored where it is shown the Maximum Likelihood Estimators possess a small bias and converges to the Minimum Variance Unbiased Estimator after few tests for designs with moderate number of faults. It is shown that the Likelihood function can be bimodal when there is conflict between the observed rate of fault detection and the prior distribution describing the number of faults in the design. An illustrative example is provided

Enteropathogen antibody dynamics and force of infection among children in low-resource settings.

Little is known about enteropathogen seroepidemiology among children in low-resource settings. We measured serological IgG responses to eight enteropathogens (Giardia intestinalis, Cryptosporidium parvum, Entamoeba histolytica, Salmonella enterica, enterotoxigenic Escherichia coli, Vibrio cholerae, Campylobacter jejuni, norovirus) in cohorts from Haiti, Kenya, and Tanzania. We studied antibody dynamics and force of infection across pathogens and cohorts. Enteropathogens shared common seroepidemiologic features that enabled between-pathogen comparisons of transmission. Overall, exposure was intense: for most pathogens the window of primary infection was <3 years old; for highest transmission pathogens primary infection occurred within the first year. Longitudinal profiles demonstrated significant IgG boosting and waning above seropositivity cutoffs, underscoring the value of longitudinal designs to estimate force of infection. Seroprevalence and force of infection were rank-preserving across pathogens, illustrating the measures provide similar information about transmission heterogeneity. Our findings suggest antibody response can be used to measure population-level transmission of diverse enteropathogens in serologic surveillance

Using five-minute bird counts to study magpie (Gymnorhina tibicen) impacts on other birds in New Zealand

We used five-minute bird counts to investigate whether introduced Australian magpies (Gymnorhina tibicen) influence the abundance of other birds in rural New Zealand. Over 3 years, magpies were removed from five c. 900-ha study blocks, one in each of Northland, Waikato, Bay of Plenty, Wellington and Southland. Birds were counted in both the treatment blocks and paired non-treatment blocks for the 3 years of removal and also 1 year before. To minimise problems raised elsewhere with index counts we (1) selected treatment blocks and count stations using randomisation procedures, (2) used trained observers who spent equal time in paired treatment and non-treatment blocks, and (3) counted all blocks at the same time of year and only in good weather. On average, 548 magpies were removed from each treatment block each year, with magpie counts reduced by 76% relative to non-treatment blocks. Our results suggest magpies may restrict the movements of some birds (including kererū and tūī) in rural areas, but are less important than pest mammals at limiting population abundance at a landscape scale. We submit that five-minute bird counts were appropriate for our objectives, but that more research to examine their relationship to absolute densities is needed