2,435 research outputs found
Re-parameterization Invariance in Fractional Flux Periodicity
We analyze a common feature of a nontrivial fractional flux periodicity in
two-dimensional systems. We demonstrate that an addition of fractional flux can
be absorbed into re-parameterization of quantum numbers. For an exact
fractional periodicity, all the electronic states undergo the
re-parameterization, whereas for an approximate periodicity valid in a large
system, only the states near the Fermi level are involved in the
re-parameterization.Comment: 4 pages, 1 figure, minor changes, final version to appear in J. Phys.
Soc. Jp
Quantum Transition between an Antiferromagnetic Mott Insulator and Superconductor in Two Dimensions
We consider a Hubbard model on a square lattice with an additional
interaction, , which depends upon the square of a near-neighbor hopping. At
half-filling and a constant value of the Hubbard repulsion, increasing the
strength of the interaction drives the system from an antiferromagnetic
Mott insulator to a superconductor. This conclusion is reached
on the basis of zero temperature quantum Monte Carlo simulations on lattice
sizes up to .Comment: 4 pages (latex) and 4 postscript figure
Transport properties of ferromagnet/d-wave superconductor/ferromagnet double junctions
We investigate transport properties of a trilayer made of a d-wave
superconductor connected to two ferromagnetic electrodes. Using Keldysh
formalism we show that crossed Andreev reflection and elastic cotunneling exist
also with d-wave superconductors. Their properties are controlled by the
existence of zero energy states due to the anisotropy of the d-wave pair
potential.Comment: 16 pages, 4 figures, revised versio
Exact non-equilibrium current from the partition function for impurity transport problems
We study the partition functions of quantum impurity problems in the domain
of complex applied bias for its relation to the non-equilibrium current
suggested by Fendley, Lesage and Saleur (cond-mat/9510055). The problem is
reformulated as a certain generalization of the linear response theory that
accomodates an additional complex variable. It is shown that the mentioned
relation holds in a rather generic case in the linear response limit, or under
certain condition out of equilibrium. This condition is trivially satisfied by
the quadratic Hamiltonians and is rather restrictive for the interacting
models. An example is given when the condition is violated.Comment: 10 pages, RevTex. Final extended versio
Improving the SDG energy poverty targets: residential cooling needs in the Global South
With growing health risks from rising temperatures in the Global South, the lack of essential indoor cooling is increasingly seen as a dimension of energy poverty and human well-being. Air conditioning (AC) is expected to increase significantly with rising incomes, but it is likely that many who need AC will not have it. We estimate the current location and extent of populations potentially exposed to heat stress in the Global South. We apply a variable degree days (VDD) method on a global grid to estimate the energy demand required to meet these cooling needs, accounting for spatially explicit climate, housing types, access to electricity and AC ownership.
Our results show large gaps in access to essential space cooling, especially in India, South-East Asia and sub-Saharan Africa. Between 1.8 to 4.1 billion, depending on the required indoor temperatures and days of exposure, may need AC to avoid heat related stresses under current climate and socio-economic conditions. This number far exceeds the energy poverty gap indicated by the Sustainable Development Goal for electricity access (SDG7). Covering this cooling gap would entail a median energy demand growth of 14% of current global residential electricity consumption, primarily for AC. Solutions beyond improved AC efficiency, such as passive building and city design, innovative cooling technologies, and parsimonious use of AC will be needed to ensure essential cooling for all with minimized environmental damage. Meeting the essential cooling gap, as estimated by this study, can have important interactions with achieving several of the SDGs
Decay Rate Ratios of Upsilon(5S) to B Bbar Reactions
We calculate the decay rate ratios for OZI allowed decays of Upsilon(5S) to
two B mesons by using the decay amplitudes which incorporate the wave function
of the Upsilon(5S) state. We obtain the results that the branching ratio of the
Upsilon(5S) decay to Bs* Bs*bar is much larger than the branching ratio to Bs
Bs*bar or Bsbar Bs*, in good agreement with recent experimental results of CLEO
and BELLE. This agreement with the experimental results is made possible since
the nodes of the Upsilon(5S) radial wave function induce the nodes of the decay
amplitude. We find that the results for the Upsilon(5S) decays to Bu(*)
Bu(*)bar or Bd(*) Bd(*)bar pairs are dependent on the parameter values used for
the potential between heavy quarks.Comment: 9 pages, 5 figure
Topological quenching of the tunnel splitting for a particle in a double-well potential on a planar loop
The motion of a particle along a one-dimensional closed curve in a plane is considered. The only restriction on the shape of the loop is that it must be invariant under a twofold rotation about an axis perpendicular to the plane of motion. Along the curve a symmetric double-well potential is present leading to a twofold degeneracy of the classical ground state. In quantum mechanics, this degeneracy is lifted: the energies of the ground state and the first excited state are separated from each other by a slight difference ÂżE, the tunnel splitting. Although a magnetic field perpendicular to the plane of the loop does not influence the classical motion of the charged particle, the quantum-mechanical separation of levels turns out to be a function of its strength B. The dependence of ÂżE on the field B is oscillatory: for specific discrete values Bn the splitting drops to zero, indicating a twofold degeneracy of the ground state. This result is obtained within the path-integral formulation of quantum mechanics; in particular, the semiclassical instanton method is used. The origin of the quenched splitting is intuitively obvious: it is due to the fact that the configuration space of the system is not simply connected, thus allowing for destructive interference of quantum-mechanical amplitudes. From an abstract point of view this phenomenon can be traced back to the existence of a topological term in the Lagrangian and a nonsimply connected configuration space. In principle, it should be possible to observe the splitting in appropriately fabricated mesoscopic rings consisting of normally conducting metal
Incontinence-associated dermatitis: reducing adverse events
Incontinence-associated dermatitis (IAD) is a common problem in patients with faecal and/or urinary incontinence. Urine alters the normal skin flora and increases permeability of the stratum corneum and faecal enzymes on the skin contribute to skin damage. Faecal bacteria can then penetrate the skin, increasing the risk of secondary infection. However, IAD can be prevented and healed with timely and appropriate skin cleansing and skin protection. This includes appropriate use of containment devices. This article also looks at HARTMANN incontinence pads that have been developed to absorb the fluids that cause IAD and maintain the skin's acidic pH. The acidic pH of the skin contributes to its barrier function and defence against infection. Therefore, maintaining an acidic pH will help protect the skin from damage
Sand in the wheels, or oiling the wheels, of international finance? : New Labour's appeal to a 'new Bretton Woods'
Tony Blairâs political instinct typically is to associate himself only with the future. As such, his explicit appeal to âthe pastâ in his references to New Labourâs desire to establish a ânew Bretton Woodsâ is sufficient in itself to arouse some degree of analytical curiosity (see Blair 1998a). The fact that this appeal was made specifically in relation to Bretton Woods is even more interesting. The resonant image of the international economic context established by the original Bretton Woods agreements invokes a style and content of policy-making which Tony Blair typically dismisses as neither economically nor politically consistent with his preferred vision of the future (see Blair 2000c, 2001b)
Temperature Derivative of the Superfluid Density in the Attractive Hubbard model
Based on extensions of the grand-canonical Quantum Monte-Carlo algorithm to
incorporate magnetic fields, we provide numerical data confirming the existence
of a Kosterlitz-Thouless transition in the attractive Hubbard model. Here, we
calculate the temperature derivative of the superfluid density, to pin down the
transition. Away from half-band filling, the above quantity, shows a response
which increases with lattice size at the transition temperature. In contrast,
such a signal is not observed for the case of a half-band filling.Comment: Latex 8 pages, 3 figures (in postscript format) appendded at the end
of the fil
- âŠ