803 research outputs found
Effect of modeled reduced gravity conditions on bacterial morphology and physiology
<p>Abstract</p> <p>Background</p> <p>Bacterial phenotypes result from responses to environmental conditions under which these organisms grow; reduced gravity has been demonstrated in many studies as an environmental condition that profoundly influences microorganisms. In this study, we focused on low-shear stress, modeled reduced gravity (MRG) conditions and examined, for <it>Escherichia coli and Staphlyococcus aureus</it>, a suite of bacterial responses (including total protein concentrations, biovolume, membrane potential and membrane integrity) in rich and dilute media and at exponential and stationary phases for growth. The parameters selected have not been studied in <it>E. coli </it>and <it>S. aureus </it>under MRG conditions and provide critical information about bacterial viability and potential for population growth.</p> <p>Results</p> <p>With the exception of <it>S. aureus </it>in dilute Luria Bertani (LB) broth, specific growth rates (based on optical density) of the bacteria were not significantly different between normal gravity (NG) and MRG conditions. However, significantly higher bacterial yields were observed for both bacteria under MRG than NG, irrespective of the medium with the exception of <it>E. coli </it>grown in LB. Also, enumeration of cells after staining with 4',6-diamidino-2-phenylindole showed that significantly higher numbers were achieved under MRG conditions during stationary phase for <it>E. coli </it>and <it>S. aureus </it>grown in M9 and dilute LB, respectively. In addition, with the exception of smaller <it>S. aureus </it>volume under MRG conditions at exponential phase in dilute LB, biovolume and protein concentrations per cell did not significantly differ between MRG and NG treatments. Both <it>E. coli </it>and <it>S. aureus </it>had higher average membrane potential and integrity under MRG than NG conditions; however, these responses varied with growth medium and growth phase.</p> <p>Conclusions</p> <p>Overall, our data provides novel information about <it>E. coli </it>and <it>S. aureus </it>membrane potential and integrity and suggest that bacteria are physiologically more active and a larger percentage are viable under MRG as compared to NG conditions. In addition, these results demonstrate that bacterial physiological responses to MRG conditions vary with growth medium and growth phase demonstrating that nutrient resources are a modulator of response.</p
QCD corrections to the electric dipole moment of the neutron in the MSSM
We consider the QCD corrections to the electric dipole moment of the neutron
in the Minimal Supersymmetric Standard Model. We provide a master formula for
the Wilson coefficients at the low energy scale including for the first time
the mixing between the electric and chromoelectric operators and correcting
widely used previous LO estimates. We show that, because of the mixing between
the electric and chromoelectric operators, the neutralino contribution is
always strongly suppressed. We find that, in general, the effect of the QCD
corrections is to reduce the amount of CP violation generated at the high
scale. We discuss the perturbative uncertainties of the LO computation, which
are particularly large for the gluino-mediated contribution. This motivates our
Next-to-Leading order analysis. We compute for the first time the order alpha_s
corrections to the Wilson coefficients for the gluino contributions, and
recompute the two-loop anomalous dimension for the dipole operators. We show
that the large LO uncertainty disappears once NLO corrections are taken into
account.Comment: 23 pages, 5 figures, added references, corrected typo
Irreversible and reversible modes of operation of deterministic ratchets
We discuss a problem of optimization of the energetic efficiency of a simple
rocked ratchet. We concentrate on a low-temperature case in which the
particle's motion in a ratchet potential is deterministic. We show that the
energetic efficiency of a ratchet working adiabatically is bounded from above
by a value depending on the form of ratchet potential. The ratchets with
strongly asymmetric potentials can achieve ideal efficiency of unity without
approaching reversibility. On the other hand we show that for any form of the
ratchet potential a set of time-protocols of the outer force exist under which
the operation is reversible and the ideal value of efficiency is also achieved.
The mode of operation of the ratchet is still quasistatic but not adiabatic.
The high values of efficiency can be preserved even under elevated
temperatures
Kaon mixing and the charm mass
We study contributions to the Delta S=2 weak Chiral Lagrangian producing
K0-K0bar mixing which are not enhanced by the charm mass. For the real part,
these contributions turn out to be related to the box diagram with up quarks
but, unlike in perturbation theory, they do not vanish in the limit m_u->0.
They increase the leading contribution to the K_L-K_S mass difference by ~10%.
This means that short distances amount to (90+-15)% of this mass difference.
For the imaginary part, we find a correction to the lambda_c^2 m_c^2 term of
-5% from the integration of charm, which is a small contribution to epsilon_K.
The calculation is done in the large-Nc limit and we show explicitly how to
match short and long distances.Comment: 20 pages, 5 figures. Typos fixe
The Role of Animal Models for Research on Severe Malaria
The Role of Animal Models for Research on Severe Malari
Generalized stochastic Schroedinger equations for state vector collapse
A number of authors have proposed stochastic versions of the Schr\"odinger
equation, either as effective evolution equations for open quantum systems or
as alternative theories with an intrinsic collapse mechanism. We discuss here
two directions for generalization of these equations. First, we study a general
class of norm preserving stochastic evolution equations, and show that even
after making several specializations, there is an infinity of possible
stochastic Schr\"odinger equations for which state vector collapse is provable.
Second, we explore the problem of formulating a relativistic stochastic
Schr\"odinger equation, using a manifestly covariant equation for a quantum
field system based on the interaction picture of Tomonaga and Schwinger. The
stochastic noise term in this equation can couple to any local scalar density
that commutes with the interaction energy density, and leads to collapse onto
spatially localized eigenstates. However, as found in a similar model by
Pearle, the equation predicts an infinite rate of energy nonconservation
proportional to , arising from the local double commutator in
the drift term.Comment: 24 pages Plain TeX. Minor changes, some new references. To appear in
Journal of Physics
KK Parity in Warped Extra Dimension
We construct models with a Kaluza-Klein (KK) parity in a five- dimensional
warped geometry, in an attempt to address the little hierarchy problem present
in setups with bulk Standard Model fields. The lightest KK particle (LKP) is
stable and can play the role of dark matter. We consider the possibilities of
gluing two identical slices of 5D AdS in either the UV (IR-UV-IR model) or the
IR region (UV-IR-UV model) and discuss the model-building issues as well as
phenomenological properties in both cases. In particular, we find that the
UV-IR-UV model is not gravitationally stable and that additional mechanisms
might be required in the IR-UV-IR model in order to address flavor issues.
Collider signals of the warped KK parity are different from either the
conventional warped extra dimension without KK parity, in which the new
particles are not necessarily pair-produced, or the KK parity in flat universal
extra dimensions, where each KK level is nearly degenerate in mass. Dark matter
and collider properties of a TeV mass KK Z gauge boson as the LKP are
discussed.Comment: 35 pages, 11 figure
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