Electronic structures of B-2p and C-2p of boron-doped diamond film by soft X-ray absorption and emission spectroscopy

X-ray absorption (XAS) and emission (XES) spectroscopy near B-K and C-K edges have been performed on metallic (~1at%B, B-diamond) and semiconducting (~0.1at%B and N, BN-diamond) doped-diamond films. Both B-K XAS and XES spectra shows metallic partial density of state (PDOS) with the Fermi energy of 185.3 eV, and there is no apparent boron-concentration dependence in contrast to the different electric property. In C-K XAS spectrum of B-diamond, the impurity state ascribed to boron is clearly observed near the Fermi level. The Fermi energy is found to be almost same with the top of the valence band of non-doped diamond, E_V, 283.9 eV. C-K XAS of BN-diamond shows both the B-induced shallow level and N-induced deep-and-broad levels as the in-gap states, in which the shallow level is in good agreement with the activation energy (E_a=0.37 eV) estimated from the temperature dependence of the conductivity, namely the change in C-2p PDOS of impurity-induced metallization is directly observed. The electric property of this diamond is mainly ascribed to the electronic structure of C-2p near the Fermi level. The observed XES spectra are compared with the DVX-alpha cluster calculation. The DVX-alpha result supports the strong hybridization between B-2p and C-2p observed in XAS and XES spectra, and suggests that the small amount of borons (<1at%) in diamond occupy the substitutional site rather than interstitial site.Comment: submitted to Phys. Rev. B, 5 pages and 5 figure

Herbig Ae/Be Stars in the Magellanic Bridge

We have found Herbig Ae/Be star candidates in the western region of the Magellanic Bridge. Using the near infrared camera SIRIUS and the 1.4 m telescope IRSF, we surveyed about 3.0 deg x 1.3 deg (24 deg < RA < 36 deg, -75 deg < Dec. < -73.7 deg) in the J, H, and Ks bands. On the basis of colors and magnitudes, about 200 Herbig Ae/Be star candidates are selected. Considering the contaminations by miscellaneous sources such as foreground stars and early-type dwarfs in the Magellanic Bridge, we estimate that about 80 (about 40%) of the candidates are likely to be Herbig Ae/Be stars. We also found one concentration of the candidates at the young star cluster NGC 796, strongly suggesting the existence of pre-main-sequence (PMS) stars in the Magellanic Bridge. This is the first detection of PMS star candidates in the Magellanic Bridge, and if they are genuine PMS stars, this could be direct evidence of recent star formation. However, the estimate of the number of Herbig Ae/Be stars depends on the fraction of classical Be stars, and thus a more precise determination of the Be star fraction or observations to differentiate between the Herbig Ae/Be stars and classical Be stars are required.Comment: 22 pages, 6 figures. Accepted for publication in Ap

Quantifying epistatic interactions among the components constituting the protein translation system

In principle, the accumulation of knowledge regarding the molecular basis of biological systems should allow the development of large-scale kinetic models of their functions. However, the development of such models requires vast numbers of parameters, which are difficult to obtain in practice. Here, we used an in vitro translation system, consisting of 69 defined components, to quantify the epistatic interactions among changes in component concentrations through Bahadur expansion, thereby obtaining a coarse-grained model of protein synthesis activity. Analyses of the data measured using various combinations of component concentrations indicated that the contributions of larger than 2-body inter-component epistatic interactions are negligible, despite the presence of larger than 2-body physical interactions. These findings allowed the prediction of protein synthesis activity at various combinations of component concentrations from a small number of samples, the principle of which is applicable to analysis and optimization of other biological systems. Moreover, the average ratio of 2- to 1-body terms was estimated to be as small as 0.1, implying high adaptability and evolvability of the protein translation system

Boundary states in the Nappi-Witten model

We investigate D-branes in the Nappi-Witten model. Classically symmetric D-branes are classified by the (twisted) conjugacy classes of the Nappi-Witten group, which specify the geometry of the corresponding D-branes. Quantum description of the D-branes is given by boundary states, and we need one point functions of closed strings to construct the boundary states. We compute the one point functions solving conformal bootstrap constraints, and check that the classical limit of the boundary states reproduces the geometry of D-branes.Comment: 19 pages, no figure; minor changes, references adde

D-instantons and Closed String Tachyons in Misner Space

We investigate closed string tachyon condensation in Misner space, a toy model for big bang universe. In Misner space, we are able to condense tachyonic modes of closed strings in the twisted sectors, which is supposed to remove the big bang singularity. In order to examine this, we utilize D-instanton as a probe. First, we study general properties of D-instanton by constructing boundary state and effective action. Then, resorting to these, we are able to show that tachyon condensation actually deforms the geometry such that the singularity becomes milder.Comment: 24 pages, 1 figure, minor change

D-branes in a Big Bang/Big Crunch Universe: Nappi-Witten Gauged WZW Model

We study D-branes in the Nappi-Witten model, which is a gauged WZW model based on (SL(2,R) x SU(2)) / (U(1) x U(1)). The model describes a four dimensional space-time consisting of cosmological regions with big bang/big crunch singularities and static regions with closed time-like curves. The aim of this paper is to investigate by D-brane probes whether there are pathologies associated with the cosmological singularities and the closed time-like curves. We first classify D-branes in a group theoretical way, and then examine DBI actions for effective theories on the D-branes. In particular, we show that D-brane metric from the DBI action does not include singularities, and wave functions on the D-branes are well behaved even in the presence of closed time-like curves.Comment: 50 pages, 2 figures, minor change

D-branes in PP-Waves and Massive Theories on Worldsheet with Boundary

We investigate the supersymmetric D-brane configurations in the pp-wave backgrounds proposed by Maldacena and Maoz. We study the surviving supersymmetry in a D-brane configuration from the worldvolume point of view. When we restrict ourselves to the background with N=(2,2) supersymmetry and no holomorphic Killing vector term, there are two types of supersymmetric D-branes: A-type and B-type. An A-type brane is wrapped on a special Lagrangian submanifold, and the imaginary part of the superpotential should be constant on its worldvolume. On the other hand, a B-type brane is wrapped on a complex submanifold, and the superpotential should be constant on its worldvolume. The results are almost consistent with the worldsheet theory in the lightcone gauge. The inclusion of gauge fields is also discussed and found BPS D-branes with the gauge field excitations. Furthermore, we consider the backgrounds with holomorphic Killing vector terms and N=(1,1) supersymmetric backgrounds.Comment: 27 pages, LaTeX, no figure. v2: typos corrected, comments added, references added. v3: typos corrected, comments added, references added. v4:typos correcte

An initial event in insect innate immune response: structural and biological studies of interactions between β-1,3-glucan and the N-terminal domain of β-1,3-glucan recognition protein

In response to invading microorganisms, insect β-1,3-glucan recognition protein (βGRP), a soluble receptor in the hemolymph, binds to the surfaces of bacteria and fungi and activates serine protease cascades that promote destruction of pathogens by means of melanization or expression of antimicrobial peptides. Here we report on the NMR solution structure of the N-terminal domain of βGRP (N-βGRP) from Indian meal moth (Plodia interpunctella), which is sufficient to activate the prophenoloxidase (proPO) pathway resulting in melanin formation. NMR and isothermal calorimetric titrations of N-βGRP with laminarihexaose, a glucose hexamer containing β-1,3 links, suggest a weak binding of the ligand. However, addition of laminarin, a glucose polysaccharide (~ 6 kDa) containing β-1,3 and β-1,6 links that activates the proPO pathway, to N-βGRP results in the loss of NMR cross-peaks from the backbone 15N-1H groups of the protein, suggesting the formation of a large complex. Analytical ultra centrifugation (AUC) studies of formation of N-βGRP:laminarin complex show that ligand-binding induces sel-fassociation of the protein:carbohydrate complex into a macro structure, likely containing six protein and three laminarin molecules (~ 102 kDa). The macro complex is quite stable, as it does not undergo dissociation upon dilution to sub-micromolar concentrations. The structural model thus derived from the present studies for N-βGRP:laminarin complex in solution differs from the one in which a single N-βGRP molecule has been proposed to bind to a triple helical form of laminarin on the basis of an X-ray crystallographic structure of N-βGRP:laminarihexaose complex [Kanagawa, M., Satoh, T., Ikeda, A., Adachi, Y., Ohno, N., and Yamaguchi, Y. (2011) J. Biol. Chem. 286, 29158-29165]. AUC studies and phenoloxidase activation measurements carried out with the designed mutants of N-βGRP indicate that electrostatic interactions involving Asp45, Arg54, and Asp68 between the ligand-bound protein molecules contribute in part to the stability of N-βGRP:laminarin macro complex and that a decreased stability is accompanied by a reduced activation of the proPO pathway. Increased β-1,6 branching in laminarin also results in destabilization of the macro complex. These novel findings suggest that ligand-induced self-association of βGRP:β-1,3-glucan complex may form a platform on a microbial surface for recruitment of downstream proteases, as a means of amplification of the initial signal of pathogen recognition for the activation of the proPO pathway

Superstring Vacua of 4-dimensional PP-Waves with Enhanced Supersymmetry

We study the superstring vacua constructed from the conformal field theories of the type H_4 x M, where H_4 denotes the super Nappi-Witten model (super WZW model on the 4-dimensional Heisenberg group H_4) and M denotes an arbitrary N=2 rational superconformal field theory with c=9. We define (type II) superstring vacua with 8 supercharges, which are twice as many as those on the backgrounds of H_4 x CY_3. We explicitly construct as physical vertices the space-time SUSY algebra that is a natural extension of H_4 Lie algebra. The spectrum of physical states is classified into two sectors: (1) strings freely propagating along the transverse plane of pp-wave geometry and possessing the integral U(1)_R-charges in M sector, and (2) strings that do not freely propagate along the transverse plane and possess the fractional U(1)_R-charges in M. The former behaves like the string excitations in the usual Calabi-Yau compactification, but the latter defines new sectors without changing the physics in ``bulk'' space. We also analyze the thermal partition functions of these systems, emphasizing the similarity to the DLCQ string theory. As a byproduct we prove the supersymmetric cancellation of conformal blocks in an arbitrary unitary N=2 SCFT of c=12 with the suitable GSO projection.Comment: 37 pages, no figures, v2: typo corrected, references added, v3: minor change

Boundary States for D-branes with Traveling Waves

We construct boundary states for D-branes which carry traveling waves in the covariant formalism. We compute their vacuum amplitudes to investigate their interactions. In non-compact space, the vacuum amplitudes become trivial as is common in plane wave geometries. However, we found that if they are compactified in the traveling direction, then the amplitudes are affected by non-trivial time dependent effects. The interaction between D-branes with waves traveling in the opposite directions (`pulse-antipulse scattering') are also computed. Furthermore, we apply these ideas to open string tachyon condensation with traveling waves.Comment: 30 pages. 1 figure, Latex, minor corrections, references adde