Formation and characterization of FeLV iscoms.

Immunostimulating complexes (ISCOMs) have been prepared from feline leukaemia virus (FeLV) envelope proteins. The ISCOMs were characterized biochemically in SDS-polyacrylamide gel electrophoresis showing the presence of proteins of estimated molecular weights of 15,000, 27,000 and 70,000. Immunoblotting showed that both the transmembrane protein p15E and the external glycoprotein gp70 (making up the gp85 protein) were present in the ISCOM. Furthermore, a degradation product of gp70 with an estimated molecular weight of 32,000 was identified in the immunoblot. The FeLV ISCOM was shown by electron microscopy to have the characteristic cage-like structure of an ISCOM with a mean diameter of 37 nm. About 10% of the total amount of gp70 in the culture fluid was recovered in the ISCOMs. The largest loss was encountered during the sedimentation of the virus. In a preliminary immunization experiment in mice the FeLV ISCOMs elicited after a booster gave a clear-cut immune response against gp70

Gauge Thresholds and Kaehler Metrics for Rigid Intersecting D-brane Models

The gauge threshold corrections for globally consistent Z2 x Z2' orientifolds with rigid intersecting D6-branes are computed. The one-loop corrections to the holomorphic gauge kinetic function are extracted and the Kaehler metrics for the charged chiral multiplets are determined up to two constants.Comment: 22 pages, 1 figure; v2: minor modifications, version to appear in JHE

Comparative study of elemental mercury flux measurement techniques over a Fennoscandian boreal peatland

Quantitative estimates of the land-atmosphere exchange of gaseous elemental mercury (GEM) are biased by the measurement technique employed, because no standard method or scale in space and time are agreed upon. Here we present concurrent GEM exchange measurements over a boreal peatland using a novel relaxed eddy accumulation (REA) system, a rectangular Teflon (R) dynamic flux chamber (DFC) and a DFC designed according to aerodynamic considerations (Aero-DFC). During four consecutive days the DFCs were placed alternately on two measurement plots in every cardinal direction around the REA sampling mast. Spatial heterogeneity in peat surface characteristics (0-34 cm) was identified by measuring total mercury in eight peat cores (57 +/- 8 ng g(-1), average SE), vascular plant coverage (32-52%), water table level (4.5-14.1 cm) and dissolved gaseous elemental mercury concentrations (28-51 pg L-1) in the peat water. The GEM fluxes measured by the DFCs showed a distinct diel pattern, but no spatial difference in the average fluxes was detected (ANOVA, alpha = 0.05). Even though the correlation between the Teflon DFC and Aero-DFC was significant (r = 0.76, p < 0.05) the cumulative flux of the Aero-DFC was a factor of three larger. The average flux of the Aero-DFC (1.9 ng m(-2) h(-1)) and REA (2 ng m(-2) h(-1)) were in good agreement. The results indicate that the novel REA design is in agreement for cumulative flux estimates with the Aero-DFC, which incorporates the effect of atmospheric turbulence. The comparison was performed over a fetch with spatially rather homogenous GEM flux dynamics under fairly consistent weather conditions, minimizing the effect of weather influence on the data from the three measurement systems. However, in complex biomes with heterogeneous surface characteristics where there can be large spatial variability in GEM gas exchange, the small footprint of chambers ( < 0.2 m(2)) makes for large coefficients of variation. Thus many chamber measurement replications are needed to establish a credible biome GEM flux estimate, even for a single point in time. Dynamic flux chambers will, however, be able to resolve systematic differences between small scale features, such as experimentally manipulated plots or small scale spatial heterogeneity

Stringy Instantons and Cascading Quivers

D-brane instantons can perturb the quantum field theories on space-time filling D-branes by interesting operators. In some cases, these D-brane instantons are novel "stringy" effects (not interpretable directly as instanton effects in the low-energy quantum field theory), while in others the D-brane instantons can be directly interpreted as field theory effects. In this note, we describe a situation where both perspectives are available, by studying stringy instantons in quivers which arise at simple Calabi-Yau singularities. We show that a stringy instanton which wraps an unoccupied node of the quiver, and gives rise to a non-perturbative mass in the space-time field theory, can be reinterpreted as a conventional gauge theory effect by going up in an appropriate renormalization group cascade. Interestingly, in the cascade, the contribution of the stringy instanton does not come from gauge theory instantons but from strong coupling dynamics.Comment: 17 pages, 6 figures, harvma

Dynamical supersymmetry breaking from unoriented D-brane instantons

We study the non-perturbative dynamics of an unoriented Z_5-quiver theory of GUT kind with gauge group U(5) and chiral matter. At strong coupling the non-perturbative dynamics is described in terms of set of baryon/meson variables satisfying a quantum deformed constraint. We compute the effective superpotential of the theory and show that it admits a line of supersymmetric vacua and a phase where supersymmetry is dynamically broken via gaugino condensation.Comment: 24 pages, 1 figur

Unoriented D-brane Instantons vs Heterotic worldsheet Instantons

We discuss Fermi interactions of four hyperini generated by ``stringy'' instantons in a Type I / Heterotic dual pair on T^4/Z_2.Comment: Minor corrections and clarifications. Added reference

Instanton Induced Neutrino Majorana Masses in CFT Orientifolds with MSSM-like spectra

Recently it has been shown that string instanton effects may give rise to neutrino Majorana masses in certain classes of semi-realistic string compactifications. In this paper we make a systematic search for supersymmetric MSSM-like Type II Gepner orientifold constructions admitting boundary states associated with instantons giving rise to neutrino Majorana masses and other L- and/or B-violating operators. We analyze the zero mode structure of D-brane instantons on general type II orientifold compactifications, and show that only instantons with O(1) symmetry can have just the two zero modes required to contribute to the 4d superpotential. We however discuss how the addition of fluxes and/or possible non-perturbative extensions of the orientifold compactifications would allow also instantons with $Sp(2)$ and U(1) symmetries to generate such superpotentials. In the context of Gepner orientifolds with MSSM-like spectra, we find no models with O(1) instantons with just the required zero modes to generate a neutrino mass superpotential. On the other hand we find a number of models in one particular orientifold of the Gepner model $(2,4,22,22)$ with $Sp(2)$ instantons with a few extra uncharged non-chiral zero modes which could be easily lifted by the mentioned effects. A few more orientifold examples are also found under less stringent constraints on the zero modes. This class of $Sp(2)$ instantons have the interesting property that R-parity conservation is automatic and the flavour structure of the neutrino Majorana mass matrices has a simple factorized form.Comment: 68 pages, 2 figures; v2. typos corrected, refs adde

Holomorphic variables in magnetized brane models with continuous Wilson lines

We analyze the action of the target-space modular group in toroidal type IIB orientifold compactifications with magnetized D-branes and continuous Wilson lines. The transformation of matter fields agree with that of twisted fields in heterotic compactifications, constituting a check of type I/heterotic duality. We identify the holomorphic N = 1 variables for these compactifications. Matter fields and closed string moduli are both redefined by open string moduli. The redefinition of matter fields can be read directly from the perturbative Yukawa couplings, whereas closed string moduli redefinitions are obtained from D-brane instanton superpotential couplings. The resulting expressions reproduce and generalize, in the presence of internal magnetic fields, previous results in the literature.Comment: 9 pages, no figures; v2: conventions for Wilson lines changed, major simplifications in expressions, discussions extended, typos corrected, some references adde

FCNC Processes from D-brane Instantons

Low string scale models might be tested at the LHC directly by their Regge resonances. For such models it is important to investigate the constraints of Standard Model precision measurements on the string scale. It is shown that highly suppressed FCNC processes like K0- bar K^0 oscillations or leptonic decays of the D0-meson provide non-negligible lower bounds on both the perturbatively and surprisingly also non-perturbatively induced string theory couplings. We present both the D-brane instanton formalism to compute such amplitudes and discuss various possible scenarios and their constraints on the string scale for (softly broken) supersymmetric intersecting D-brane models.Comment: 28 pages, 13 figures, reference added, 1 typo corrected, style file adde

Lifting D-Instanton Zero Modes by Recombination and Background Fluxes

We study the conditions under which D-brane instantons in Type II orientifold compactifications generate a non-perturbative superpotential. If the instanton is non-invariant under the orientifold action, it carries four instead of the two Goldstone fermions required for superpotential contributions. Unless these are lifted, the instanton can at best generate higher fermionic F-terms of Beasley-Witten type. We analyse two strategies to lift the additional zero modes. First we discuss the process of instantonic brane recombination in Type IIA orientifolds. We show that in some cases charge invariance of the measure enforces the presence of further zero modes which, unlike the Goldstinos, cannot be absorbed. In other cases, the instanton exhibits reparameterisation zero modes after recombination and a superpotential is generated if these are lifted by suitable closed or open string couplings. In the second part of the paper we address lifting the extra Goldstinos of D3-brane instantons by supersymmetric three-form background fluxes in Type IIB orientifolds. This requires non-trivial gauge flux on the instanton. Only if the part of the fermionic action linear in the gauge flux survives the orientifold projection can the extra Goldstinos be lifted.Comment: 38 pages, 3 figures, 5 tables; v2: Appendix B slightly expanded, minor rewordin