100,633 research outputs found
Energetics of Domain Walls in the 2D t-J model
Using the density matrix renormalization group, we calculate the energy of a
domain wall in the 2D t-J model as a function of the linear hole density
\rho_\ell, as well as the interaction energy between walls, for J/t=0.35. Based
on these results, we conclude that the ground state always has domain walls for
dopings 0 < x < 0.3. For x < 0.125, the system has (1,0) domain walls with
\rho_\ell ~ 0.5, while for 0.125 < x < 0.17, the system has a possibly
phase-separated mixture of walls with \rho_\ell ~ 0.5 and \rho_\ell =1. For x >
0.17, there are only walls with \rho_\ell =1. For \rho_\ell = 1, diagonal (1,1)
domain walls have very nearly the same energy as (1,0) domain walls.Comment: Several minor changes. Four pages, four encapsulated figure
Comment on ``Stripes and the t-J Model''
This is a comment being submitted to Physical Review Letters on a recent
letter by Hellberg and Manousakis on stripes in the t-J model.Comment: One reference correcte
Checkerboard patterns in the t-J model
Using the density matrix renormalization group, we study the possibility of
real space checkerboard patterns arising as the ground states of the t-J model.
We find that checkerboards with a commensurate (pi,pi) background are not low
energy states and can only be stabilized with large external potentials.
However, we find that striped states with charge density waves along the
stripes can form approximate checkerboard patterns. These states can be
stabilized with a very weak external field aligning and pinning the CDWs on
different stripes.Comment: 4 pages, 5 figure
Competition Between Stripes and Pairing in a t-t'-J Model
As the number of legs n of an n-leg, t-J ladder increases, density matrix
renormalization group calculations have shown that the doped state tends to be
characterized by a static array of domain walls and that pairing correlations
are suppressed. Here we present results for a t-t'-J model in which a diagonal,
single particle, next-near-neighbor hopping t' is introduced. We find that this
can suppress the formation of stripes and, for t' positive, enhance the
d_{x^2-y^2}-like pairing correlations. The effect of t' > 0 is to cause the
stripes to evaporate into pairs and for t' < 0 to evaporate into
quasi-particles. Results for n=4 and 6-leg ladders are discussed.Comment: Four pages, four encapsulated figure
Unique case of inverted papilloma of septum with nasopharyngeal carcinoma:Is it a metachronous tumour?
Inverted papilloma is a rare and benign tumour. It affects the nasal cavity and paranasal sinuses, has a high rate of recurrence and is associated with malignant transformation. Only few cases of a poorly differentiated carcinoma arising from inverted papilloma have been reported, none of which in the nasopharynx. We report a case of a 37-year-old female, who presented originally in 2012 with inverted papilloma of the nasal septum which was surgically resected. Nasopharyngeal biopsy from 2014 was reported as carcinoma in situ and treated with local endoscopic resection. Three years later she presented with a solitary lesion of the right Eustachian tube opening, confirmed as invasive poorly differentiated carcinoma. Imaging revealed T4 N2b M0 malignancy with skull base and prevertebral space invasion, likely extension into right temporal lobe and malignant adenopathy. Although rare, malignant transformation of inverted papilloma in unusual places should be considered during workup and monitoring of patients
On Deriving Space-Time From Quantum Observables and States
We prove that, under suitable assumptions, operationally motivated data
completely determine a space-time in which the quantum systems can be
interpreted as evolving. At the same time, the dynamics of the quantum system
is also determined. To minimize technical complications, this is done in the
example of three-dimensional Minkowski space.Comment: 19 pages, to appear in Communications in Mathematical Physics; minor
corrections mad
Variable dimension automatic synthesis programs (VASP)
Variable dimension FORTRAN 4 version of the Automatic Synthesis Program (ASP) compensates for limitations within the program itself. Improvements are versatile programming language, convenient input/output format, new subprograms, variable dimensioning, and efficient storage
Effect of the W-term for a t-U-W Hubbard ladder
Antiferromagnetic and d_{x2-y2}-pairing correlations appear delicately
balanced in the 2D Hubbard model. Whether doping can tip the balance to pairing
is unclear and models with additional interaction terms have been studied. In
one of these, the square of a local hopping kinetic energy H_W was found to
favor pairing. However, such a term can be separated into a number of simpler
processes and one would like to know which of these terms are responsible for
enhancing the pairing. Here we analyze these processes for a 2-leg Hubbard
ladder
NATO: the view from the East
Relations between Russia, Ukraine and Belarus and NATO have placed more emphasis on cooperation than confrontation since the Cold War, and Ukraine has begun to move towards membership. At the popular level, on the evidence of national surveys in 2004 and 2005, NATO continues to be perceived as a significant threat, but in Russia and
Ukraine it comes behind the United States (in Belarus the numbers are similar). There are few socioeconomic predictors of support for NATO membership that are significant across all three countries, but there are wide differences by region, and by attitudinal variables
such as support for a market economy and for EU membership. The relationship between popular attitudes and foreign policy is normally a distant one; but in Ukraine NATO
membership will require public support in a referendum, and in all three cases public attitudes on foreign policy issues can influence foreign policy in other ways, including the composition of parliamentary committees. In newly independent states whose international allegiances are still evolving, the associations between public opinion and foreign and security policy may often be closer than in the established democracies
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