BOR-FDTD subgridding based on finite element principles

In this paper a recently developed provably passive and stable 3D FDTD subgridding technique, based on finite elements principles, is extended to body-of-revolution (BOR) FDTD. First, a suitable choice of basis functions is presented together with the mechanism to assemble them into an overall mesh consisting of coarse and fine mesh cells. Invoking appropriate mass-lumping concepts then leads to an explicit leapfrog time stepping algorithm for the amplitudes of the basis functions. Attention is devoted to provide the reader with insight into the updating equations, in particular at a subgridding boundary. Stability, grid reflection and dispersion are also discussed. Finally, some numerical examples for toroidal and cylindrical cavities demonstrate the stability and accuracy of the method.     

Dynamic solubility limits in nanosized olivine LiFePO4

Because of its stability, nanosized olivine LiFePO(4) opens the door toward high-power Li-ion battery technology for large-scale applications as required for plug-in hybrid vehicles. Here, we reveal that the thermodynamics of first-order phase transitions in nanoinsertion materials is distinctly different from bulk materials as demonstrated by the decreasing miscibility gap that appears to be strongly dependent on the overall composition in LiFePO(4). In contrast to our common thermodynamic knowledge, that dictates solubility limits to be independent of the overall composition, combined neutron and X-ray diffraction reveals strongly varying solubility limits below particle sizes of 35 nm. A rationale is found based on modeling of the diffuse interface. Size confinement of the lithium concentration gradient, which exists at the phase boundary, competes with the in bulk energetically favorable compositions. Consequently, temperature and size diagrams of nanomaterials require complete reconsideration, being strongly dependent on the overall composition. This is vital knowledge for the future nanoarchitecturing of superior energy storage devices as the performance will heavily depend on the disclosed nanoionic properties.     

Coupled commensurate cation and charge modulation in the tunneled structure, Na(0.40(2))MnO(2)

Na(0.40(2))MnO(2) belongs to a family of mixed Mn(3+) and Mn(4+) porous oxides that contains both octahedral and square pyramidal Mn-O units. Neutron and synchrotron radiation studies identify the presence of both sodium ordering (T(Na) ≈ 310 K) and Mn charge and orbital ordering. Below T(Na), the centrosymmetric Pbam structure adopts an (ab 4c) supercell of Pnnm symmetry that accommodates a coupled commensurate modulation down the c-axis channels of both Na position and occupancy with Mn valence.     

Precision Compton polarimetry for the Q Weak experiment at Jefferson Lab

The Q _Weak experiment, scheduled to run in 2010?C2012 in Hall?C at Jefferson?Lab, will measure the parity-violating asymmetry in elastic electron-proton scattering at 1.1?GeV to determine the weak charge of the proton, $Q^p_{\rm Weak} = 1 - 4 \sin^2 \theta_W$ . The dominant experimental systematic uncertainty will be the knowledge of the electron beam polarization. With a new Compton polarimeter we aim to measure the beam polarization with a statistical precision of 1% in one hour and a systematic uncertainty of 1%. A low-gain Fabry?CP??rot cavity laser system provides the circularly polarized photons. The scattered electrons are detected in radiation-hard diamond strip detectors, and form the basis for a coincidence trigger using distributed logic boards. The photon detector uses a fast, undoped CsI crystal with simultaneous sampling and integrating read-out. Coincident events are used to cross-calibrate the photon and electron detectors.     

Tribenzotriquinacene Receptors for C60 Fullerene Rotors: Towards C3 Symmetrical Chiral Stators for Unidirectionally Operating Nanoratchets

The synthesis of a stereochemically pure concave tribenzotriquinacene receptor ( 7 ) for C₆₀ fullerene, possessing C₃ point group symmetry, by threefold condensation of C₂‐symmetric 1,2‐diketone synthons ( 5 ) and a hexaaminotribenzotriquinacene core ( 6 ) is described. The chiral diketone was synthesized in a five‐step reaction sequence starting from C_2h‐symmetric 2,6‐di‐tert‐butylanthracene. The highly diastereo‐discriminating Diels–Alder reaction of 2,6‐di‐tert‐butylanthracene with fumaric acid di(?)menthyl ester, catalyzed by aluminium chloride, is the relevant stereochemistry introducing step. The structure of the fullerene receptor was verified by ¹H and ¹³C NMR spectroscopy, mass spectrometry and single crystal X‐ray diffraction. VCD and ECD spectra were recorded, which were corroborated by ab initio DFT calculations, establishing the chiral nature of 7 with about 99.7 % ee, based on the ee (99.9 %) of the chiral synthon ( 1 ). The absolute configuration of 7 could thus be established as all‐S [(2S,7S,16S,21S,30S,35S)‐( 7 )]. Spectroscopic titration experiments reveal that the host forms 1:1 complexes with either pure fullerene (C₆₀) or fullerene derivatives, such as rotor 1′‐(4‐nitrophenyl)‐3′‐(4‐N,N‐dimethylaminophenyl)‐pyrazolino[4′,5′:1,2][60]fullerene ( R ). The complex stability constants of the complexes dissolved in CHCl₃/CS₂ (1:1 vol. %) are K([ C₆₀ ? 7 ])=319(±156) M ^?1 and K([ R ? 7 ])=110(±50) M ^?1. With molecular dynamics simulations using a first‐principles parameterized force field the asymmetry of the rotational potential for [ R ? 7 ] was shown, demonstrating the potential suitability of receptor 7 to act as a stator in a unidirectionally operating nanoratchet.     

Total Synthesis of Five Lipoteichoic acids of Clostridium difficile

The emergence of hypervirulent resistant strains have made Clostridium difficile a notorious nosocomial pathogen and has resulted in a renewed interest in preventive strategies, such as vaccines based on (synthetic) cell wall antigens. Recently, the structure of the lipoteichoic acid (LTA) of this species has been elucidated. Additionally, this LTA was found to induce the formation of protective antibodies against C. difficile in rabbits and mice. The LTA from C. difficile is isolated as a microheterogenous mixture, differing in size and composition, impeding any structure–activity relationship studies. To ensure reliable biological results, pure and well‐defined synthetic samples are required. In this work the total synthesis of LTAs from C. difficile with defined chain length is described and the initial biological results are presented.     

Lactate biosensors: current status and outlook

Many research efforts over the last few decades have been devoted to sensing lactate as an important analytical target in clinical care, sport medicine, and food processing. Therefore, research in designing lactate sensors is no longer in its infancy and now is more directed toward viable sensors for direct applications. In this review, we provide an overview of the most immediate and relevant developments toward this end, and we discuss and assess common transduction approaches. Further, we critically describe the pros and cons of current commercial lactate sensors and envision how future sensing design may benefit from emerging new technologies.     

Double cation adduction in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of electron deficient anthraquinone derivatives

Six anthraquinone derivatives were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS). Clear (pseudo) molecular ions were observed for all the compounds. Interestingly, for some derivatives, strong ions with double cation adduction were also recorded in the positive mode. It is remarkable that all these ions are singly charged. In this work, possible mechanisms for the double cation adduction were investigated and discussed. It appears that the double cation adduction was due to the electron deficient nature of the derivatives, and formed by taking up two singly charged cations and one electron. Substituents on the anthraquinone ring were found to have a significant effect on the double cation adduction. In contrast, no considerable influence of the acidity of MALDI matrix/solution was observed, even on the double proton adduction. Furthermore, it was demonstrated that double cation adduction might occur in the MALDI gas-phase plume. In addition to the anthraquinones, three more electron deficient compounds of different types, i.e. a perylene bisimide derivative (PB), 3,7-decanoylamino-4,8-dihydrobenzo[1,2-b:4,5-b']dithiophene-4,8-dione (TQ) and 6,6-phenyl C61-butyric acid methyl ester (PCBM), were also analyzed with MALDI TOF MS. The results indicate that the 'abnormal' double cation adduction might be a 'normal' phenomenon in the MALDI TOF MS analysis of many electron deficient compounds.     

Message Passing-Based Inference for Time-Varying Autoregressive Models

Time-varying autoregressive (TVAR) models are widely used for modeling of non-stationary signals. Unfortunately, online joint adaptation of both states and parameters in these models remains a challenge. In this paper, we represent the TVAR model by a factor graph and solve the inference problem by automated message passing-based inference for states and parameters. We derive structured variational update rules for a composite “AR node” with probabilistic observations that can be used as a plug-in module in hierarchical models, for example, to model the time-varying behavior of the hyper-parameters of a time-varying AR model. Our method includes tracking of variational free energy (FE) as a Bayesian measure of TVAR model performance. The proposed methods are verified on a synthetic data set and validated on real-world data from temperature modeling and speech enhancement tasks.