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Hubbard ladders in a magnetic field
The behavior of a two leg Hubbard ladder in the presence of a magnetic field is studied by means of Abelian bosonization. We predict the appearance of a new (doping dependent) plateau in the magnetization curve of a doped 2-leg spin ladder in a wide range of couplings. We also discuss the extension to N-leg Hubbard ladders
Ultrafast all-optical wavelength conversion in silicon waveguides using femtosecond pump-probe pulses
Experimental results on ultrafast all-optical wavelength conversion in silicon-on-insulator waveguides are presented. Red and blue shifts of 10nm have been observed in femtosecond pump-probe experiments. Alloptical switching and the importance of waveguide dispersion are discussed
Evolution of SU(4) Transport Regimes in Carbon Nanotube Quantum Dots
We study the evolution of conductance regimes in carbon nanotubes with doubly
degenerate orbitals (``shells'') by controlling the contact transparency within
the same sample. For sufficiently open contacts, Kondo behavior is observed for
1, 2, and 3 electrons in the topmost shell. As the contacts are opened more,
the sample enters the ``mixed valence'' regime, where different charge states
are strongly hybridized by electron tunneling. Here, the conductance as a
function of gate voltage shows pronounced modulations with a period of four
electrons, and all single-electron features are washed away at low temperature.
We successfully describe this behavior by a simple formula with no fitting
parameters. Finally, we find a surprisingly small energy scale that controls
the temperature evolution of conductance and the tunneling density of states in
the mixed valence regime.Comment: 4 pages + supplementary info. The second part of the original
submission is now split off as a separate paper (0709.1288
Extra care : viable for couples living with dementia?
Purpose: The perspectives of people with dementia and their care partners regarding ‘extra care’ housing are currently unknown. This paper will report findings of a consultation study exploring the perceived barriers and facilitators of a relocation to extra care housing, from the perspective of people living with dementia, and their care partners.
Design/methodology/approach: Fieldwork consisted of paired or 1-1 interviews and small focus groups with potential users of an alternative model of extra care support for people living with dementia in the South of England. The consultation took place between June and August 2013. The interviews and focus groups were audio recorded, transcribed verbatim. The transcripts were analysed thematically.
Findings: Benefits of extra care were identified as the opportunity for couples to remain living together for longer, creating a supportive, dementia-friendly community, and a reduction in the strain experienced by the care partners. Barriers centred on a sense of loss, stress and uncertainty. Living and caring at home was perceived as preferable to shared care.
Research limitations/implications: The findings presented here have limited generalizability for two reasons. First the shared care approach consulted on was very specific. Second our participants form a purposive sample and as such are not representative of a wider population. Despite best intentions the voice of people with dementia are under reported in this consultation. Only one person with early on-set dementia was interviewed and the remaining two people with dementia were interviewed alongside their care partner.
Practical implications: The findings cast doubt on the viability of extra care facilities, designed for couples living with dementia, if extra care continues to be conceptualised and marketed as a preventative lifestyle choice. The findings indicate the value of consulting with people with dementia, and their care partners, when designing new forms of housing with care specifically for people living with dementia.
Originality/value: This paper contributes to the body of literature, exploring the feasibility of new and innovative alternative care and housing options, for people with dementia. This paper is one of the first to explore extra care as a housing and social care option for couples with dementia
Effects of Self-field and Low Magnetic Fields on the Normal-Superconducting Phase Transition
Researchers have studied the normal-superconducting phase transition in the
high- cuprates in a magnetic field (the vortex-glass or Bose-glass
transition) and in zero field. Often, transport measurements in "zero field"
are taken in the Earth's ambient field or in the remnant field of a magnet. We
show that fields as small as the Earth's field will alter the shape of the
current vs. voltage curves and will result in inaccurate values for the
critical temperature and the critical exponents and , and can
even destroy the phase transition. This indicates that without proper screening
of the magnetic field it is impossible to determine the true zero-field
critical parameters, making correct scaling and other data analysis impossible.
We also show, theoretically and experimentally, that the self-field generated
by the current flowing in the sample has no effect on the current vs. voltage
isotherms.Comment: 4 pages, 4 figure
Electron transport in semiconducting carbon nanotubes with hetero-metallic contacts
We present an atomistic self-consistent study of the electronic and transport
properties of semiconducting carbon nanotube in contact with metal electrodes
of different work functions, which shows simultaneous electron and hole doping
inside the nanotube junction through contact-induced charge transfer. We find
that the band lineup in the nanotube bulk region is determined by the effective
work function difference between the nanotube channel and source/drain
electrodes, while electron transmission through the SWNT junction is affected
by the local band structure modulation at the two metal-nanotube interfaces,
leading to an effective decoupling of interface and bulk effects in electron
transport through nanotube junction devices.Comment: Higher quality figures available at http://www.albany.edu/~yx15212
Normal-Superconducting Phase Transition Mimicked by Current Noise
As a superconductor goes from the normal state into the superconducting
state, the voltage vs. current characteristics at low currents change from
linear to non-linear. We show theoretically and experimentally that the
addition of current noise to non-linear voltage vs. current curves will create
ohmic behavior. Ohmic response at low currents for temperatures below the
critical temperature mimics the phase transition and leads to incorrect
values for and the critical exponents and . The ohmic response
occurs at low currents, when the applied current is smaller than the
width of the probability distribution , and will occur in both the
zero-field transition and the vortex-glass transition. Our results indicate
that the transition temperature and critical exponents extracted from the
conventional scaling analysis are inaccurate if current noise is not filtered
out. This is a possible explanation for the wide range of critical exponents
found in the literature.Comment: 4 pages, 2 figure
Optical conductivity of wet DNA
Motivated by recent experiments we have studied the optical conductivity of
DNA in its natural environment containing water molecules and counter ions. Our
density functional theory calculations (using SIESTA) for four base pair B-DNA
with order 250 surrounding water molecules suggest a thermally activated doping
of the DNA by water states which generically leads to an electronic
contribution to low-frequency absorption. The main contributions to the doping
result from water near DNA ends, breaks, or nicks and are thus potentially
associated with temporal or structural defects in the DNA.Comment: 4 pages, 4 figures included, final version, accepted for publication
in Phys. Rev. Let
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