10,370 research outputs found
Baryogenesis at the Electroweak Phase Transition for a SUSY Model with a Gauge Singlet
SUSY models with a gauge singlet easily allow for a strongly first order
electroweak phase transition (EWPT). We discuss the wall profile, in particular
transitional CP violation during the EWPT. We calculate CP violating source
terms for the charginos in the WKB approximation and solve the relevant
transport equations to obtain the generated baryon asymmetry.Comment: 5 pages, 6 figures. To appear in the Proceedings of Strong and
Electroweak Matter 2000 (SEWM2000), Marseilles; a reference adde
Quantum Nature of Edge Magnetism in Graphene
It is argued that the subtle crossover from decoherence-dominated classical
magnetism to fluctuation-dominated quantum magnetism is experimentally
accessible in graphene nanoribbons. We show that the width of a nanoribbon
determines whether the edge magnetism is on the classical side, on the quantum
side, or in between. In the classical regime, decoherence is dominant and leads
to static spin polarizations at the ribbon edges, which are well described by
mean-field theories. The quantum Zeno effect is identified as the basic
mechanism which is responsible for the spin polarization and thereby enables
the application of graphene in spintronics. On the quantum side, however, the
spin polarization is destroyed by dynamical processes. The great tunability of
graphene magnetism thus offers a viable route for the study of the
quantum-classical crossover.Comment: 5 pages, 3 figure
Pressure anisotropy effects on the stability of the guiding center model of the bumpy theta pinch
Effective models for strong electronic correlations at graphene edges
We describe a method for deriving effective low-energy theories of electronic
interactions at graphene edges. Our method is applicable to general edges of
honeycomb lattices (zigzag, chiral, and even disordered) as long as localized
low-energy states (edge states) are present. The central characteristic of the
effective theories is a dramatically reduced number of degrees of freedom. As a
consequence, the solution of the effective theory by exact diagonalization is
feasible for reasonably large ribbon sizes. The quality of the involved
approximations is critically assessed by comparing the correlation functions
obtained from the effective theory with numerically exact quantum Monte-Carlo
calculations. We discuss effective theories of two levels: a relatively
complicated fermionic edge state theory and a further reduced Heisenberg spin
model. The latter theory paves the way to an efficient description of the
magnetic features in long and structurally disordered graphene edges beyond the
mean-field approximation.Comment: 13 pages, 9 figure
Multiple mRNA isoforms of the transcription activator protein CREB
We have characterized cDNA clones representing mouse
CREB (cyclic AMP responsive element binding protein)
mRNA isoforms. These include CREBA and CREBa, of
which the rat and human homologues have been
previously identified. Both encode proteins with CREbinding
activity and identical transactivation potential.
The additional CREB mRNA isoforms potentially encode
CREB related proteins. From the structural organization
of the mouse CREB gene we conclude that the multiple
transcripts are generated by alternative splicing. Furthermore
we show that specific CREB mRNA isoforms are
expressed at a high level in the adult testis. Expression
of these isoforms is induced after commencement of
spermatogenesis. In situ hybridization suggests that this
expression occurs predominantly in the primary spermatocytes.
Comparison of the CREB gene with the recently
isolated CREM (cAMP responsive element modulator)
cDNAs illustrates that the two genes have arisen by gene
duplication and have diverged to encode transcriptional
activators and repressors of the cAMP signal transduction
pathway
High-Velocity Features in Type Ia Supernova Spectra
We use a sample of 58 low-redshift (z <= 0.03) Type Ia supernovae (SNe Ia)
having well-sampled light curves and spectra near maximum light to examine the
behaviour of high-velocity features (HVFs) in SN Ia spectra. We take advantage
of the fact that Si II 6355 is free of HVFs at maximum light in all SNe Ia,
allowing us to quantify the strength of HVFs by comparing the structure of
these two lines. We find that the average HVF strength increases with
decreasing light-curve decline rate, and rapidly declining SNe Ia (dm_15(B) >=
1.4 mag) show no HVFs in their maximum-light spectra. Comparison of HVF
strength to the light-curve colour of the SNe Ia in our sample shows no
evidence of correlation. We find a correlation of HVF strength with the
velocity of Si II 6355 at maximum light (v_Si), such that SNe Ia with lower
v_Si have stronger HVFs, while those SNe Ia firmly in the "high-velocity"
(i.e., v_Si >= 12,000 km/s) subclass exhibit no HVFs in their maximum-light
spectra. While v_Si and dm_15(B) show no correlation in the full sample of SNe
Ia, we find a significant correlation between these quantities in the subset of
SNe Ia having weak HVFs. In general, we find that slowly declining (low
dm_15(B)) SNe Ia, which are more luminous and more energetic than average SNe
Ia, tend to produce either high photospheric ejecta velocities (i.e., high
v_Si) or strong HVFs at maximum light, but not both. Finally, we examine the
evolution of HVF strength for a sample of SNe Ia having extensive pre-maximum
spectroscopic coverage and find significant diversity of the pre-maximum HVF
behaviour.Comment: Version accepted by MNRA
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