Collective charge density wave motion through an ensemble of Aharonov-Bohm rings

We investigate theoretically the collective charge density wave motion through an ensemble of small disordered Aharonov-Bohm rings. It is shown that the magnetic flux modulates the threshold field and the magnetoresistance with a half flux quantum periodicity $\Phi_{0}/2=h/2e$, resulting from ensemble averaging over random scattering phases of multiple rings. The magnitude of the magnetoresistance oscillations decreases rapidly with increasing bias. This is consistent with recent experiments on $NbSe_3$ in presence of columnar defects [Phys. Rev. Lett. 78, 919 (1997)].Comment: 4 pages Revtex, 2 figures. Submitted to Phys. Rev. Let

Density-orbital embedding theory

In the article density-orbital embedding (DOE) theory is proposed. DOE is based on the concept of density orbital (DO), which is a generalization of the square root of the density for real functions and fractional electron numbers. The basic feature of DOE is the representation of the total supermolecular density ρs as the square of the sum of the DO φa, which represents the active subsystem A and the square root of the frozen density ρf of the environment F. The correct ρs is obtained with φa being negative in the regions in which ρf might exceed ρs. This makes it possible to obtain the correct ρs with a broad range of the input frozen densities ρf so that DOE resolves the problem of the frozen-density admissibility of the current frozen-density embedding theory. The DOE Euler equation for the DO φa is derived with the characteristic embedding potential representing the effect of the environment. The DO square φa2 is determined from the orbitals of the effective Kohn-Sham (KS) system. Self-consistent solution of the corresponding one-electron KS equations yields not only φa2, but also the DO φa itself. © 2010 The American Physical Society

Calculation of electronic excitations using wave-function in wave-function frozen-density embedding

Recently, a general framework suitable for general frozen-density embedding (FDE) methods was published [S. Höfener, A. S. P. Gomes, and L. Visscher, J. Chem. Phys. 136, 044104 (2012)]10.1063/1.3675845. In the present article, we report the fragmentation of a supermolecule while treating all subsystems with coupled-cluster theory and the interaction of the subsystems with density-functional theory. This variant is denoted wave-function theory in wave-function theory FDE, or coupled-cluster theory in coupled-cluster theory FDE. Main target of this approach is not the embedding of a single molecule in large solvation shells, but rather the possibility to divide a complex system consisting of several molecules when all subsystems are to be treated with, e.g., coupled-cluster methods to provide a balanced and unbiased description. We present numerical results for hydrogen-bonded complexes which exhibit rather strong interactions. Cases with weakly interacting subsystems are expected to exhibit even higher accuracy. This facilitates the study of properties of larger complexes such as DNA base pairs with coupled-cluster methods. © 2012 American Institute of Physics

Exopolymeric substances (EPS) from Bacillus subtilis: polymers and genes encoding their synthesis

Bacterial exopolymeric substances (EPS) are molecules released in response to the physiological stress encountered in the natural environment. EPS are structural components of the extracellular matrix in which cells are embedded during biofilm development. The chemical nature and functions of these EPS are dependent on the genetic expression of the cells within each biofilm. Although some bacterial matrices have been characterized, understanding of the function of the EPS is relatively limited, particularly within the Bacillus genus. Similar gaps of knowledge exist with respect to the chemical composition and specific roles of the macromolecules secreted by Bacillus subtilis in its natural environment. In this review, the different EPS from B. subtilis were classified into four main functional categories: structural (neutral polymers), sorptive (charged polymers), surface-active and active polymers. In addition, current information regarding the genetic expression, production and function of the main polymers secreted by B. subtilis strains, particularly those related to biofilm formation and its architecture, has been compiled. Further characterization of these EPS from B. subtilis remains a challenge

Calculating energy derivatives for quantum chemistry on a quantum computer

Modeling chemical reactions and complicated molecular systems has been proposed as the `killer application' of a future quantum computer. Accurate calculations of derivatives of molecular eigenenergies are essential towards this end, allowing for geometry optimization, transition state searches, predictions of the response to an applied electric or magnetic field, and molecular dynamics simulations. In this work, we survey methods to calculate energy derivatives, and present two new methods: one based on quantum phase estimation, the other on a low-order response approximation. We calculate asymptotic error bounds and approximate computational scalings for the methods presented. Implementing these methods, we perform the world's first geometry optimization on an experimental quantum processor, estimating the equilibrium bond length of the dihydrogen molecule to within 0.014 Angstrom of the full configuration interaction value. Within the same experiment, we estimate the polarizability of the H2 molecule, finding agreement at the equilibrium bond length to within 0.06 a.u. (2% relative error).Comment: 19 pages, 1 page supplemental, 7 figures. v2 - tidied up and added example to appendice

Estimation of linkage disequilibrium in a sample of the United Kingdom dairy cattle population using unphased genotypes

The association between genetic marker alleles was estimated for two regions of the bovine genome from a random sample of 50 young dairy bulls born in the United Kingdom between 1988 and 1995. Microsatellite marker genotypes were obtained for six markers on chromosome 2 and seven markers on chromosome 6, spanning 38 and 20 cM, respectively. Two different methods, which do not require family information, were used to estimate population haplotype frequencies. Haplotype frequencies were estimated for pairs of loci using the expectation-maximization algorithm and for all linked loci using a Bayesian approach via a Markov chain-Monte Carlo algorithm. Significant (P = 0.0007) linkage disequilibrium was detected between pairs of loci in syntenic groups (that is, loci in the same linkage group), extending to about 10 cM. No significant linkage disequilibrium was detected between markers in nonsyntenic regions. Given the observed level of linkage disequilibrium, mapping methods based on population-wide association might provide a better resolution than traditional quantitative trait loci mapping methods in the U.K. dairy cattle population and may reduce the required sample sizes of the experiments

Het FOCUS-project: OpbrengstGericht Werken op basis van prestatie-feedback

In het FOCUS-project is een tweeejarige training ‘OpbrengstGericht Werken’ voor complete basisschoolteams ontwikkeld. Het is de bedoeling dat basisscholen door de training allereerst leren om de mogelijkheden van het leerlingvolgsysteem dat ze bezitten beter te benutten. De praktijk leert namelijk dat veel scholen maar een klein deel van die mogelijkheden gebruiken. Dat is zonde, omdat onderzoek duidelijk heeft aangetoond dat het goed benutten van feedback waarvan je over de kwaliteit van je eigen handelen leert sterk prestatieverbeterende effecten kan hebben. De training gaat echter verder. Scholen leren vervolgens namelijk om op basis van het inzicht in hun prestaties doelen te stellen die voldoen aan de principes van de goal setting theorie (uitdagende, haalbare en evalueerbare doelen). Daarnaast bieden we rekendidactische informatie aan evenals informatie over de kenmerken van rekensterke scholen, die scholen kunnen gebruiken om hun onderwijs zo aan te passen dat de kans op het behalen van de gestelde doelen groot wordt. In het artikel worden de ontwikkeling en inhoud van de training, evenals de ervaringen met scholen die de training volgden, nader beschreven