1,348 research outputs found
The initial temporal evolution of a feedback dynamo for Mercury
Various possibilities are currently under discussion to explain the observed
weakness of the intrinsic magnetic field of planet Mercury. One of the possible
dynamo scenarios is a dynamo with feedback from the magnetosphere. Due to its
weak magnetic field Mercury exhibits a small magnetosphere whose subsolar
magnetopause distance is only about 1.7 Hermean radii. We consider the magnetic
field due to magnetopause currents in the dynamo region. Since the external
field of magnetospheric origin is antiparallel to the dipole component of the
dynamo field, a negative feedback results. For an alpha-omega-dynamo two
stationary solutions of such a feedback dynamo emerge, one with a weak and the
other with a strong magnetic field. The question, however, is how these
solutions can be realized. To address this problem, we discuss various
scenarios for a simple dynamo model and the conditions under which a steady
weak magnetic field can be reached. We find that the feedback mechanism
quenches the overall field to a low value of about 100 to 150 nT if the dynamo
is not driven too strongly
The Magnetic Sun: Reversals and Long-Term Variations
A didactic introduction to current thinking on some aspects of the solar
dynamo is given for geophysicists and planetary scientists.Comment: 17 pages, 9 figures; Space Science Rev., in pres
Observation of B_s to phi gamma and Search for B_s to gamma gamma Decays at Belle
We search for the radiative penguin decays B_s to phi gamma and B_s to gamma
gamma in a 23.6 fb-1 data sample collected at the Upsilon(5S) resonance with
the Belle detector at the KEKB e+e- asymmetric-energy collider. We observe for
the first time a radiative penguin decay of the B_s meson in the B_s to phi
gamma mode. No significant B_s to gamma gamma signal is observed.Comment: 5 pages, 3 figures, accepted by Physics Review Letter
Identification of 2,4-Disubstituted Imidazopyridines as Hemozoin Formation Inhibitors with Fast-Killing Kinetics and In Vivo Efficacy in the Plasmodium falciparum NSG Mouse Model
A series of 2,4-disubstituted imidazopyridines, originating from a SoftFocus Kinase library, was identified from a high throughput phenotypic screen against the human malaria parasite Plasmodium falciparum. Hit compounds showed moderate asexual blood stage activity. During lead optimization, several issues were flagged such as cross-resistance against the multidrug-resistant K1 strain, in vitro cytotoxicity, and cardiotoxicity and were addressed through structure–activity and structure–property relationship studies. Pharmacokinetic properties were assessed in mice for compounds showing desirable in vitro activity, a selectivity window over cytotoxicity, and microsomal metabolic stability. Frontrunner compound 37 showed good exposure in mice combined with good in vitro activity against the malaria parasite, which translated into in vivo efficacy in the P. falciparum NOD-scid IL-2Rγnull (NSG) mouse model. Preliminary mechanistic studies suggest inhibition of hemozoin formation as a contributing mode of action
Measurement of Inclusive Radiative B-meson Decays with a Photon Energy Threshold of 1.7 GeV
Using 605/fb of data collected at the Upsilon(4S) resonance we present a
measurement of the inclusive radiative B-meson decay channel, B to X_s gamma.
For the lower photon energy thresholds of 1.7, 1.8, 1.9 and 2.0GeV, as defined
in the rest frame of the B-meson, we measure the partial branching fraction and
the mean and variance of the photon energy spectrum. At the 1.7GeV threshold we
obtain the partial branching fraction BF(B to X_s gamma) = (3.45 +/- 0.15 +/-
0.40) x 10^-4, where the errors are statistical and systematic.Comment: 9 pages, 3 figures, 2 table
Evidence for B to K eta' gamma Decays at Belle
We present the results of a search for the radiative decay (B -> K eta'
gamma) and find evidence for (B^+ -> K^+ eta' gamma) decays at the 3.3 standard
deviation level with a partial branching fraction of (3.6 +/- 1.2 +/- 0.4) x
10e-6, where the first error is statistical and the second systematic. This
measurement is restricted to the region of combined (K eta') invariant mass
less than 3.4GeVc^2. A 90% confidence level upper limit of 6.4 x 10e-6 is
obtained for the decay (B^0 -> K^0 eta' gamma) in the same (K eta') invariant
mass region. These results are obtained from a 605 fb^-1 data sample containing
657 x 10e6 B anti-B pairs collected at the Upsilon(4S) resonance with the Belle
detector at the KEKB asymmetric-energy e^+e^- collider.Comment: 5 pages, 4 figures. Submitted to PRD-RC on 6/8/0
Evidence of time-dependent CP violation in the decay B0 to D*+D*-
We report a measurement of the CP-odd fraction and the time-dependent CP
violation in B0 to D*+D*- decays, using 657.10^6 BBbar events collected at the
Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy
e+e- collider. We measure a CP-odd fraction of
Rperp=0.125+/-0.043(stat)+/-0.023(syst). From the distributions of the
proper-time intervals between a B0to D*+D*- decay and the other B meson in the
event, we obtain evidence of CP violation with measured parameters
AD*+D*-=0.15+/-0.13(stat)+/-0.04(syst) and
SD*+D*-=-0.96+/-0.25(stat)-0.16+0.13(syst).Comment: Published in PR
Measurements of exclusive B_s^0 decays at the Y(5S) resonance
Several exclusive decays are studied using a 1.86 fb-1 data sample
collected at the Y(5S) resonance with the Belle detector at the KEKB asymmetric
energy e^+ e^- collider. In the decay mode we find 10
candidates and measure the corresponding branching fraction. Combining
the B_s^0 -> D_s^{(*)-} \pi^+, B_s^0 -> D_s^{(*)-} \rho^+, B_s^0 -> J/\psi \phi
and B_s^0 -> J/\psi \eta decay modes, a significant signal is observed.
The ratio \sigma (e^+ e^- -> B_s^* \bar{B}_s^*) / \sigma (e^+ e^- -> B_s^{(*)}
\bar{B}_s^{(*)}) = (93^{+7}_{-9} \pm 1)% is obtained at the Y(5S) energy,
indicating that meson production proceeds predominantly through the
creation of pairs. The and meson masses are
measured to be M(B_s^0)=(5370 \pm 1 \pm 3)MeV/c^2 and M(B_s^*)=(5418 \pm 1 \pm
3)MeV/c^2. Upper limits on the B_s^0 -> \gamma \gamma, B_s^0 -> \phi \gamma,
B_s^0 -> K^+ K^- and B_s^0 -> D_s^{(*)+} D_s^{(*)-} branching fractions are
also reported.Comment: 9 pages, 5 figures, published in Phys. Rev. D76, 012002 (2007
Observation of b --> d gamma and Determination of |V_td/V_ts|
We report the observation of the flavor-changing neutral current process b
--> d gamma using a sample of 386*10^6 B meson pairs accumulated by the Belle
detector at the KEKB e+ e- collider. We measure branching fractions for the
exclusive modes B- --> rho- gamma, B0bar --> rho0 gammaand B0bar --> omega
gamma. Assuming that these three modes are related by isospin, we find Br(B -->
(rho,omega) gamma) = (1.32 +0.34-0.31(stat.) +0.10-0.09(syst.)) * 10^-6 with a
significance of 5.1 sigma. This result is used to determine the ratio of CKM
matrix elements |V_td/V_ts| to be 0.199 +0.026-0.025(exp.) +0.018-0.015(theo.).Comment: 5 pages, 2 figures, submitted to Physical Review Letter
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