On the efficient numerical solution of lattice systems with low-order couplings

We apply the Quasi Monte Carlo (QMC) and recursive numerical integration methods to evaluate the Euclidean, discretized time path-integral for the quantum mechanical anharmonic oscillator and a topological quantum mechanical rotor model. For the anharmonic oscillator both methods outperform standard Markov Chain Monte Carlo methods and show a significantly improved error scaling. For the quantum mechanical rotor we could, however, not find a successful way employing QMC. On the other hand, the recursive numerical integration method works extremely well for this model and shows an at least exponentially fast error scaling

The 25 October 2010 Mentawai tsunami earthquake (M_w 7.8) and the tsunami hazard presented by shallow megathrust ruptures

The 25 October 2010 Mentawai, Indonesia earthquake (M_w 7.8) ruptured the shallow portion of the subduction zone seaward of the Mentawai islands, off-shore of Sumatra, generating 3 to 9 m tsunami run-up along southwestern coasts of the Pagai Islands that took at least 431 lives. Analyses of teleseismic P, SH and Rayleigh waves for finite-fault source rupture characteristics indicate ∼90 s rupture duration with a low rupture velocity of ∼1.5 km/s on the 10° dipping megathrust, with total slip of 2–4 m over an ∼100 km long source region. The seismic moment-scaled energy release is 1.4 × 10^(−6), lower than 2.4 × 10^(−6) found for the 17 July 2006 Java tsunami earthquake (M_w 7.8). The Mentawai event ruptured up-dip of the slip region of the 12 September 2007 Kepulauan earthquake (M_w 7.9), and together with the 4 January 1907 (M 7.6) tsunami earthquake located seaward of Simeulue Island to the northwest along the arc, demonstrates the significant tsunami generation potential for shallow megathrust ruptures in regions up-dip of great underthrusting events in Indonesia and elsewhere

THE INFLUENCE OF WATER ON THE DEGRADATION AND WEAR OF AL2O3 SURFACES

As alumina plays ever more important roles in advanced technologies, such as substrates for in vivo biological sensors, catalysts for water purification and components of novel fuel devices, it is exposed to various environments. These environments lead to wear and degradation due to chemical and mechanical forces. Macroscale tribological tests including the scratch test and indentation are unable to analyze nanoscale properties due to their limited sensitivity. Today, nanotribologists incorporate three main tools to analyze nanoscale tribological properties: atomic force microscopy (AFM), the nanoindentor and surface force apparatus. Of these, AFM is the instrument of choice due to the sensitivity to and diversity of surface properties analyzed in a single setting. Through adhesion measurements and scratch testing under known loads the AFM was used to analyze the effect of OH- on the degradation of the alumina surface. Fourier transform infrared spectroscopy (FTIR) and AFM were also used to analyze the stability of self-assembled monolayers (SAMs) on the alumina surface. Through scanning a region of the surface with a defined force in an aqueous environment, the tribochemical surface properties were found. The pressure required to induce degradation of the first O-Al layer (~2 �) ranged from 3.10 GPa at a pH 3 to 1.58 GPa at pH 10. Further analysis of adhesion across the surface and within a defect region exposed significant changes in the forces of adhesion as the alumina surface experienced wear. At pH 3, 5, 7, and 10 the adhesion was approximately double that of the defect free surface. Two well known molecules were examined for their ability to protect the surface from bond rupture due to the catalytic effect of OH-. SAMs of octadyclephosphonic acid (OPA) and Octadycletrichlorosilane (OTS) were assembled on the alumina surface. FTIR spectra indicated well ordered monolayers formed from each molecule. The exposure of OPA to aqueous environments of pH >7 lead to the degradation of the SAM. OTS, on the other hand, demonstrated significantly more resilience to degradation as indicated through FTIR and AFM analysis

Holographic Flavor Transport in Arbitrary Constant Background Fields

We use gauge-gravity duality to compute a new transport coefficient associated with a number Nf of massive N=2 supersymmetric hypermultiplet fields propagating through an N=4 SU(Nc) super-Yang-Mills theory plasma in the limits of large Nc and large 't Hooft coupling, with Nf << Nc. We introduce a baryon number density as well as arbitrary constant electric and magnetic fields, generalizing previous calculations by including a magnetic field with a component parallel to the electric field. We can thus compute all components of the conductivity tensor associated with transport of baryon number charge, including a component never before calculated in gauge-gravity duality. We also compute the contribution that the flavor degrees of freedom make to the stress-energy tensor, which exhibits divergences associated with the rates of energy and momentum loss of the flavor degrees of freedom. We discuss two currents that are free from these divergences, one of which becomes anomalous when the magnetic field has a component parallel to the electric field and hence may be related to recent study of charge transport in the presence of anomalies.Comment: 27 page

Reducing Detrimental Defects for High‐Performance Metal Halide Perovskite Solar Cells

In several photovoltaic (PV) technologies, the presence of electronic defects within the semiconductor band gap limit the efficiency, reproducibility, as well as lifetime. Metal halide perovskites (MHPs) have drawn great attention because of their excellent photovoltaic properties that can be achieved even without a very strict film‐growth control processing. Much has been done theoretically in describing the different point defects in MHPs. Herein, we discuss the experimental challenges in thoroughly characterizing the defects in MHPs such as, experimental assignment of the type of defects, defects densities, and the energy positions within the band gap induced by these defects. The second topic of this Review is passivation strategies. Based on a literature survey, the different types of defects that are important to consider and need to be minimized are examined. A complete fundamental understanding of defect nature in MHPs is needed to further improve their optoelectronic functionalities

Application of the density matrix renormalization group method to finite temperatures and two-dimensional systems

The density matrix renormalization group (DMRG) method and its applications to finite temperatures and two-dimensional systems are reviewed. The basic idea of the original DMRG method, which allows precise study of the ground state properties and low-energy excitations, is presented for models which include long-range interactions. The DMRG scheme is then applied to the diagonalization of the quantum transfer matrix for one-dimensional systems, and a reliable algorithm at finite temperatures is formulated. Dynamic correlation functions at finite temperatures are calculated from the eigenvectors of the quantum transfer matrix with analytical continuation to the real frequency axis. An application of the DMRG method to two-dimensional quantum systems in a magnetic field is demonstrated and reliable results for quantum Hall systems are presented.Comment: 33 pages, 18 figures; corrected Eq.(117

Household food insecurity positively associated with increased hospital charges for infants

Objective: To test whether household food insecurity (HFI) was associated with total annual hospitalization charges, annual days hospitalized, and charges per day, among low-income infants (months) with any non-neonatal hospital stays. Methods: Administrative inpatient hospital charge data were matched to survey data from infants\u27 caregivers interviewed 1998-2005 in emergency departments in Boston and Little Rock. All study infants had been hospitalized at least once since birth; infants whose diagnoses were not plausibly related to nutrition were excluded from both groups. Log-transformed hospitalization charges were analyzed, controlling for site fixed effects. Results: 24% of infants from food-insecure households and 16% from food-secure households were hospitalized \u3e2 times (P=0.02). Mean annual inpatient hospital charges ($6,707 vs$5,735; P Conclusion: HFI was positively associated with annual inpatient charges among hospitalized low income infants. Average annual inpatient charges were almost $2,000 higher (inflation adjusted) for infants living in food-insecure households. Reducing or eliminating food insecurity could reduce health services utilization and expenditures for infants in low-income families, most of whom are covered by public health insurance

Efficiency of symmetric targeting for finite-T DMRG

Two targeting schemes have been known for the density matrix renormalization group (DMRG) applied to non-Hermitian problems; one uses an asymmetric density matrix and the other uses symmetric density matrix. We compare the numerical efficiency of these two targeting schemes when they are used for the finite temperature DMRG.Comment: 4 pages, 3 Postscript figures, REVTe

Non-Equilibrium Field Dynamics of an Honest Holographic Superconductor

Most holographic models of superconducting systems neglect the effects of dynamical boundary gauge fields during the process of spontaneous symmetry-breaking. Usually a global symmetry gets broken. This yields a superfluid, which then is gauged "weakly" afterwards. In this work we build (and probe the dynamics of) a holographic model in which a local boundary symmetry is spontaneously broken instead. We compute two-point functions of dynamical non-Abelian gauge fields in the normal and in the broken phase, and find non-trivial gapless modes. Our AdS3 gravity dual realizes a p-wave superconductor in (1+1) dimensions. The ground state of this model also breaks (1+1)-dimensional parity spontaneously, while the Hamiltonian is parity-invariant. We discuss possible implications of our results for a wider class of holographic liquids.Comment: 32 pages, 12 figures; v3: string theory derivation of setup added (section 3.1), improved presentation, version accepted by JHEP; v2: paragraph added to discussion, figure added, references added, typos correcte