1,006 research outputs found
Non-rigid Shell Model and Correlational Mechanism of the Local Pairing
The Hartree-Fock states of the many-electron atomic system can be unstable
with respect to a static or dynamic shift of the electron shells. An
appropriate non-rigid shell model for atomic clusters is developed. It permits
to formulate a convenient approach to the semiempirical description of the
different correlation effects and to reveal some new effects.Comment: 3 pages, 2 ".gif" figures, LaTeX; will be published in Physica C in
Materials of Int.Conf. HTSC-V. (1997, Beijing, China
Meissner effect, Spin Meissner effect and charge expulsion in superconductors
The Meissner effect and the Spin Meissner effect are the spontaneous
generation of charge and spin current respectively near the surface of a metal
making a transition to the superconducting state. The Meissner effect is well
known but, I argue, not explained by the conventional theory, the Spin Meissner
effect has yet to be detected. I propose that both effects take place in all
superconductors, the first one in the presence of an applied magnetostatic
field, the second one even in the absence of applied external fields. Both
effects can be understood under the assumption that electrons expand their
orbits and thereby lower their quantum kinetic energy in the transition to
superconductivity. Associated with this process, the metal expels negative
charge from the interior to the surface and an electric field is generated in
the interior. The resulting charge current can be understood as arising from
the magnetic Lorentz force on radially outgoing electrons, and the resulting
spin current can be understood as arising from a spin Hall effect originating
in the Rashba-like coupling of the electron magnetic moment to the internal
electric field. The associated electrodynamics is qualitatively different from
London electrodynamics, yet can be described by a small modification of the
conventional London equations. The stability of the superconducting state and
its macroscopic phase coherence hinge on the fact that the orbital angular
momentum of the carriers of the spin current is found to be exactly ,
indicating a topological origin. The simplicity and universality of our theory
argue for its validity, and the occurrence of superconductivity in many classes
of materials can be understood within our theory.Comment: Submitted to SLAFES XX Proceeding
Soil organic matter and the extracellular microbial matrix show contrasting responses to C and N availability
AbstractAn emerging paradigm in soil science suggests microbes can perform ‘N mining’ from recalcitrant soil organic matter (SOM) in conditions of low N availability. However, this requires the production of extracellular structures rich in N (including enzymes and structural components) and thus defies stoichiometric expectation. We set out to extract newly synthesised peptides from the extracellular matrix in soil and compare the amino acid (AA) profiles, N incorporation and AA dynamics in response to labile inputs of contrasting C/N ratio. Glycerol was added both with and without an inorganic source of N (10% 15N labelled NH4NO3) to a soil already containing a large pool of refractory SOM and incubated for 10 days. The resulting total soil peptide (TSP) and extracellular pools were compared using colorimetric methods, gas chromatography, and isotope ratio mass spectrometry. N isotope compositions showed that the extracellular polymeric substance (EPS) contained a greater proportion of products formed de novo than did TSP, with hydrophobic EPS-AAs (leucine, isoleucine, phenylalanine, hydroxyproline and tyrosine) deriving substantially more N from the inorganic source provided. Quantitative comparison between extracts showed that the EPS contained greater relative proportions of alanine, glycine, proline, phenylalanine and tyrosine. The greatest increases in EPS-peptide and EPS-polysaccharide concentrations occurred at the highest C/N ratios. All EPS-AAs responded similarly to treatment whereas the responses of TSP were more complex. The results suggest that extracellular investment of N (as EPS peptides) is a microbial survival mechanism in conditions of low N/high C which, from an evolutionary perspective, must ultimately lead to the tendency for increased N returns to the microbial biomass. A conceptual model is proposed that describes the dynamics of the extracellular matrix in response to the C/N ratio of labile inputs
Solar Neutrino Masses and Mixing from Bilinear R-Parity Broken Supersymmetry: Analytical versus Numerical Results
We give an analytical calculation of solar neutrino masses and mixing at
one-loop order within bilinear R-parity breaking supersymmetry, and compare our
results to the exact numerical calculation. Our method is based on a systematic
perturbative expansion of R-parity violating vertices to leading order. We find
in general quite good agreement between approximate and full numerical
calculation, but the approximate expressions are much simpler to implement. Our
formalism works especially well for the case of the large mixing angle MSW
solution (LMA-MSW), now strongly favoured by the recent KamLAND reactor
neutrino data.Comment: 34 pages, 14 ps figs, some clarifying comments adde
Neutrino properties and the decay of the lightest supersymmetric particle
Supersymmetry with broken R-parity can explain the neutrino mass squared
differences and mixing angles observed in neutrino oscillation experiments. In
the minimal model, where R-parity is broken only by bilinear terms, certain
decay properties of the lightest supersymmetric particle (LSP) are correlated
with neutrino mixing angles. Here we consider charginos, squarks, gluinos and
sneutrinos being the LSP and calculate their decay properties in bilinear
R-parity breaking supersymmetry. Together with the decays of charged scalars
and neutralinos calculated previously this completes the proof that bilinear
R-parity breaking as the source of neutrino masses will be testable at future
colliders. Moreover, we argue that in case of GMSB, the decays of the NLSP can
be used to test the model.Comment: 15 pages, 8 figure
Reconstructing Neutrino Properties from Collider Experiments in a Higgs Triplet Neutrino Mass Model
We extend the minimal supersymmetric standard model with bilinear R-parity
violation to include a pair of Higgs triplet superfields. The neutral
components of the Higgs triplets develop small vacuum expectation values (VEVs)
quadratic in the bilinear R-parity breaking parameters. In this scheme the
atmospheric neutrino mass scale arises from bilinear R-parity breaking while
for reasonable values of parameters the solar neutrino mass scale is generated
from the small Higgs triplet VEVs. We calculate neutrino masses and mixing
angles in this model and show how the model can be tested at future colliders.
The branching ratios of the doubly charged triplet decays are related to the
solar neutrino angle via a simple formula.Comment: 19 pages, 4 figures; one formula corrected, two author's names
corrected; some explanatory comments adde
Probing neutrino properties with charged scalar lepton decays
Supersymmetry with bilinear R-parity violation provides a predictive
framework for neutrino masses and mixings in agreement with current neutrino
oscillation data. The model leads to striking signals at future colliders
through the R-parity violating decays of the lightest supersymmetric particle.
Here we study charged scalar lepton decays and demonstrate that if the scalar
tau is the LSP (i) it will decay within the detector, despite the smallness of
the neutrino masses, (ii) the relative ratio of branching ratios Br({tilde
tau}_1 --> e sum nu_i)/ Br({tilde tau}_1 --> mu sum nu_i) is predicted from the
measured solar neutrino angle, and (iii) scalar muon and scalar electron decays
will allow to test the consistency of the model. Thus, bilinear R-parity
breaking SUSY will be testable at future colliders also in the case where the
LSP is not the neutralino.Comment: 24 pages, 8 ps figs Report-no.: IFIC/02-33 and ZU-TH 11/0
Nonlinear analysis of a simple model of temperature evolution in a satellite
We analyse a simple model of the heat transfer to and from a small satellite
orbiting round a solar system planet. Our approach considers the satellite
isothermal, with external heat input from the environment and from internal
energy dissipation, and output to the environment as black-body radiation. The
resulting nonlinear ordinary differential equation for the satellite's
temperature is analysed by qualitative, perturbation and numerical methods,
which show that the temperature approaches a periodic pattern (attracting limit
cycle). This approach can occur in two ways, according to the values of the
parameters: (i) a slow decay towards the limit cycle over a time longer than
the period, or (ii) a fast decay towards the limit cycle over a time shorter
than the period. In the first case, an exactly soluble average equation is
valid. We discuss the consequences of our model for the thermal stability of
satellites.Comment: 13 pages, 4 figures (5 EPS files
The decays gluino -> stop_1 b-quark W and gluino -> stop_1 c-quark and phenomenological implications in supersymmetric theories
We show that the decay gluino -> stop_1 b-quark W is important and can even
be dominant in the region of parameter space where it is kinematically allowed.
We discuss phenomenological implications within the Minimal Supersymmetric
Standard Model and models with broken R-parity. We consider the flavour
diagonal case as well as a possible mixing between squarks of different
generations. In the latter case also the decay gluino -> stop_1 c-quark is
potentially important. We show that the decay gluino -> stop_1 b-quark W is
sensitive to the stop mixing angle. Furthermore we demonstrate that in
scenarios with a higgsino--like LSP the gluino decays mainly into final states
containing top quarks or a light stop if allowed by kinematics.Comment: LaTex, 15 pages, 8 figures, uses JHEP3.cls (included), v2, improved
discussion of gluino -> stop_1 c-quark, conclusions unchanged, version to
appear in JHE
The complex superstructure in Mg1-xAlxB2 at x~0.5
Electron diffraction and high resolution microscopy have been performed on
Mg1-xAlxB2 with x~0.5. This composition displays a superstructure with a repeat
period of exactly 2c along the c axis and about 10 nm in the a-b plane. The
superstructure results in ring-shaped superreflections in the diffraction
pattern. Irradiation by a strong electron beam results in a loss of the
superstructure and a decrease of about 1% in the c lattice parameter. In-situ
heating and cooling on the other hand showed that the superstructure is stable
from 100 K to 700 K. Possible origins for the superstructure are proposed
- …