Magnetoelliptic Instabilities

We consider the stability of a configuration consisting of a vertical magnetic field in a planar flow on elliptical streamlines in ideal hydromagnetics. In the absence of a magnetic field the elliptical flow is universally unstable (the ``elliptical instability''). We find this universal instability persists in the presence of magnetic fields of arbitrary strength, although the growthrate decreases somewhat. We also find further instabilities due to the presence of the magnetic field. One of these, a destabilization of Alfven waves, requires the magnetic parameter to exceed a certain critical value. A second, involving a mixing of hydrodynamic and magnetic modes, occurs for all magnetic-field strengths. These instabilities may be important in tidally distorted or otherwise elliptical disks. A disk of finite thickness is stable if the magnetic fieldstrength exceeds a critical value, similar to the fieldstrength which suppresses the magnetorotational instability.Comment: Accepted for publication in Astrophysical Journa

Inhibitors of SARS-CoV entry--identification using an internally-controlled dual envelope pseudovirion assay.

Severe acute respiratory syndrome-associated coronavirus (SARS-CoV) emerged as the causal agent of an endemic atypical pneumonia, infecting thousands of people worldwide. Although a number of promising potential vaccines and therapeutic agents for SARS-CoV have been described, no effective antiviral drug against SARS-CoV is currently available. The intricate, sequential nature of the viral entry process provides multiple valid targets for drug development. Here, we describe a rapid and safe cell-based high-throughput screening system, dual envelope pseudovirion (DEP) assay, for specifically screening inhibitors of viral entry. The assay system employs a novel dual envelope strategy, using lentiviral pseudovirions as targets whose entry is driven by the SARS-CoV Spike glycoprotein. A second, unrelated viral envelope is used as an internal control to reduce the number of false positives. As an example of the power of this assay a class of inhibitors is reported with the potential to inhibit SARS-CoV at two steps of the replication cycle, viral entry and particle assembly. This assay system can be easily adapted to screen entry inhibitors against other viruses with the careful selection of matching partner virus envelopes

Inhibition of a viral enzyme by a small-molecule dimer disruptor.

We identified small-molecule dimer disruptors that inhibit an essential dimeric protease of human Kaposi's sarcoma-associated herpesvirus (KSHV) by screening an alpha-helical mimetic library. Next, we synthesized a second generation of low-micromolar inhibitors with improved potency and solubility. Complementary methods including size exclusion chromatography and 1H-13C HSQC titration using selectively labeled 13C-Met samples revealed that monomeric protease is enriched in the presence of inhibitor. 1H-15N HSQC titration studies mapped the inhibitor binding site to the dimer interface, and mutagenesis studies targeting this region were consistent with a mechanism where inhibitor binding prevents dimerization through the conformational selection of a dynamic intermediate. These results validate the interface of herpesvirus proteases and other similar oligomeric interactions as suitable targets for the development of small-molecule inhibitors

Observation of the suppressed ADS modes B± → [π±K-/+ π+π-]D K± and B± → [π± K-/+π+π-]Dπ±

An analysis of and B± → DK± and B± → Dπ± decays is presented where the D meson is reconstructed in the four-body final state K± π-/+π+π-. Using LHCb data corresponding to an integrated luminosity of 1.0 fb-1, first observations are made of the suppressed ADS modes B± →[π± K-/+π+π-]DK± and B± → [π± K-/+π+π-]Dπ± with a significance of 5.1 sigma and greater than 10 sigma, respectively. Measurements of CP asymmetries and CP-conserving ratios of partial widths from this family of decays are also performed. The magnitude of the ratio between the suppressed and favoured B± → DK ± amplitudes is determined to be rKB = 0.097 ± 0.011

First observation of the decay B0s→ϕK∗0

The first observation of the decay B0s→ϕK∗0 is reported. The analysis is based on a data sample corresponding to an integrated luminosity of 1.0 fb−1 of pp collisions at s√=7 TeV, collected with the LHCb detector. A yield of 30 ± 6 B0s→(K+K−)(K−π+) decays is found in the mass windows 1012.5 < M (K + K −) < 1026.5 MeV/c 2 and 746 < M(K − π +) < 1046 MeV/c 2. The signal yield is found to be dominated by B0s→ϕK∗0 decays, and the corresponding branching fraction is measured to be B(B0s→ϕK∗0) = (1.10 ± 0.24 (stat) ± 0.14 (syst) ± 0.08 (f d /f s )) × 10−6, where the uncertainties are statistical, systematic and from the ratio of fragmentation fractions f d /f s which accounts for the different production rate of B 0 and B0s mesons. The significance of B0s→ϕK∗0 signal is 6.1 standard deviations. The fraction of longitudinal polarization in B0s→ϕK∗0 decays is found to be f 0 = 0.51 ± 0.15 (stat) ± 0.07 (syst)

Study of beauty hadron decays into pairs of charm hadrons

First observations of the decays Λb 0 → Λc +D(s) - are reported using data corresponding to an integrated luminosity of 3fb-1 collected at 7 and 8 TeV center-of-mass energies in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction B(Bs 0→D+Ds -) is made and a search is performed for the decays B(s) 0→Λc +Λc -. The results obtained are B(Λb 0→Λc +D-)/ B(Λb 0→Λc +D s -)=0.042±0.003(stat)±0.003(syst), [B(Λb 0→Λc +D s -)/B(B̄0→D+D s -)]/[B(Λb 0→Λ c +π-)/B(B̄0→D +π-)]=0.96±0.02(stat)±0.06(syst),B(B s 0→D+Ds -)/ B(B̄0→D+Ds -)=0. 038±0.004(stat)±0.003(syst),B(B̄0→Λ c +Λc -)/B(B̄ 0→D+Ds -)<0.0022[95%C.L.], B(Bs 0→Λc +Λ c -)/B(Bs 0→D+D s -)<0.30[95%C.L.]. Measurement of the mass of the Λb 0 baryon relative to the B̄0 meson gives M(Λb 0)-M(B̄0)=339. 72±0.24(stat)±0.18(syst)MeV/c2. This result provides the most precise measurement of the mass of the Λb 0 baryon to date

Effective lifetime measurements in the B-s(0) -> K+K-, B-0 -> K+pi(-) and B-s(0) -> pi K-+(-) decays

Measurements of the effective lifetimes in the View the MathML source, B0→K+π− and View the MathML source decays are presented using 1.0 fb−1 of pp collision data collected at a centre-of-mass energy of 7 TeV by the LHCb experiment. The analysis uses a data-driven approach to correct for the decay time acceptance. This is the most precise determination to date of the effective lifetime in the View the MathML source decay and provides constraints on contributions from physics beyond the Standard Model to the View the MathML source mixing phase and the width difference ΔΓs

Search for the doubly charmed baryon Xi+cc

A search for the doubly charmed baryon Ξ+ cc in the decay mode Ξ+ cc→ Λ + c K−π + is performed with a data sample, corresponding to an integrated luminosity of 0.65 fb−1 , of pp collisions recorded at a centre-of-mass energy of 7 TeV. No significant signal is found in the mass range 3300–3800 MeV/c2 . Upper limits at the 95% confidence level on the ratio of the Ξ+ cc production cross-section times branching fraction to that of the Λ + c , R, are given as a function of the Ξ+ cc mass and lifetime. The largest upper limits range from R < 1.5×10−2 for a lifetime of 100 fs to R < 3.9 × 10−4 for a lifetime of 400 fs