132 research outputs found
Quantum effects in a superconducting glass model
We study disordered Josephson junctions arrays with long-range interaction
and charging effects. The model consists of two orthogonal sets of positionally
disordered parallel filaments (or wires) Josephson coupled at each crossing
and in the presence of a homogeneous and transverse magnetic field. The large
charging energy (resulting from small self-capacitance of the ultrathin wires)
introduces important quantum fluctuations of the superconducting phase within
each filament. Positional disorder and magnetic field frustration induce
spin-glass like ground state, characterized by not having long-range order of
the phases. The stability of this phase is destroyed for sufficiently large
charging energy. We have evaluated the temperature vs charging energy phase
diagram by extending the methods developed in the theory of infinite-range spin
glasses, in the limit of large magnetic field. The phase diagram in the
different temperature regimes is evaluated by using variety of methods, to wit:
semiclassical WKB and variational methods, Rayleigh-Schr\"{o}dinger
perturbation theory and pseudospin effective Hamiltonians. Possible
experimental consequences of these results are briefly discussed.Comment: 17 pages REVTEX. Two Postscript figures can be obtained from the
authors. To appear in PR
Challenges in radiotherapy planning : dose verification in the vicinity of the border of tissue-prosthesis medium
The success or failure of radiotherapy largely depends on the accuracy with which the dose will be delivered to a specific volume in the patient’s body. One of the problems associated with radiotherapy planning for patients with endoprostheses is the inaccuracy of the algorithm calculating the dose distribution in the treatment planning system for the area in the vicinity of the border of tissue–prosthesis medium. The aim of this study is verification of a planned dose on the border of hip prosthesis–acetabulum surface. At the examined energy — 6 MV — a dose results in decrease at the border of the medium, to achieve up to 10%. To verify this hypothesis, a water-filled phantom (soft tissue equivalent) was used with bone fragments (imitating hip joint) and metallic elements (hip joint endoprostheses) placed in a working stand. On acetabulum surface, thermoluminescent microdosimeters (TLD) based on lithium fluoride (LiF) was placed. The irradiation by medical linear accelerator was performed. The planned dose is higher compared with measured dose by approx. 9.8% (1.112 vs. 1.003 Gy for 2 Gy of fraction dose). It was confirmed that the treatment planning system overestimates the dose on the surface of acetabulum
Nexus between quantum criticality and the chemical potential pinning in high- cuprates
For strongly correlated electrons the relation between total number of charge
carriers and the chemical potential reveals for large Coulomb
energy the apparently paradoxical pinning of within the Mott gap, as
observed in high- cuprates. By unravelling consequences of the non-trivial
topology of the charge gauge U(1) group and the associated ground state
degeneracy we found a close kinship between the pinning of and the
zero-temperature divergence of the charge compressibility , which marks a novel quantum criticality governed by
topological charges rather than Landau principle of the symmetry breaking.Comment: 4+ pages, 2 figures, typos corrected, version as publishe
SO(5) superconductor in a Zeeman magnetic field: Phase diagram and thermodynamic properties
In this paper we present calculations of the SO(5) quantum rotor theory of
high-T superconductivity in Zeeman magnetic field. We use the spherical
approach for five-component quantum rotors in three-dimensional lattice to
obtain formulas for critical lines, free energy, entropy and specific heat and
present temperature dependences of these quantities for different values of
magnetic field. Our results are in qualitative agreement with relevant
experiments on high-T cuprates.Comment: 4 pages, 2 figures, to appear in Phys. Rev. B, see http://prb.aps.or
Three-dimensional Josephson-junction arrays in the quantum regime
We study the quantum phase transition properties of a three-dimensional
periodic array of Josephson junctions with charging energy that includes both
the self and mutual junction capacitances. We use the phase fluctuation algebra
between number and phase operators, given by the Euclidean group E_2, and we
effectively map the problem onto a solvable quantum generalization of the
spherical model. We obtain a phase diagram as a function of temperature,
Josephson coupling and charging energy. We also analyze the corresponding
fluctuation conductivity and its universal scaling form in the vicinity of the
zero-temperature quantum critical point.Comment: 9 pages, LATEX, three PostScript figures. Submitted to Phys. Rev.
Let
A generalized spherical version of the Blume-Emery-Griffits model with ferromagnetic and antiferromagnetic interactions
We have investigated analitycally the phase diagram of a generalized
spherical version of the Blume-Emery-Griffiths model that includes
ferromagnetic or antiferromagnetic spin interactions as well as quadrupole
interactions in zero and nonzero magnetic field. We show that in three
dimensions and zero magnetic field a regular paramagnetic-ferromagnetic (PM-FM)
or a paramagnetic-antiferromagnetic (PM-AFM) phase transition occurs whenever
the magnetic spin interactions dominate over the quadrupole interactions.
However, when spin and quadrupole interactions are important, there appears a
reentrant FM-PM or AFM-PM phase transition at low temperatures, in addition to
the regular PM-FM or PM-AFM phase transitions. On the other hand, in a nonzero
homogeneous external magnetic field , we find no evidence of a transition to
the state with spontaneous magnetization for FM interactions in three
dimensions. Nonethelesss, for AFM interactions we do get a scenario similar to
that described above for zero external magnetic field, except that the critical
temperatures are now functions of . We also find two critical field values,
, at which the reentrance phenomenon dissapears and
(), above which the PM-AFM transition temperature
vanishes.Comment: 21 pages, 6 figs. Title changed, abstract and introduction as well as
section IV were rewritten relaxing the emphasis on spin S=1 and Figs. 5 an 6
were improved in presentation. However, all the results remain valid.
Accepted for publication in Phys. Rev.
Critical charge instability on verge of the Mott transition and the origin of quantum protection in high- cuprates
The concept of topological excitations and the related ground state
degeneracy are employed to establish an effective theory of the superconducting
state evolving from the Mott insulator for high-Tc cuprates. Casting the
Coulomb interaction in terms of composite-fermions via the gauge flux
attachment facility, we show that instanton events in the Matsubara "imaginary
time," labeled by topological winding numbers, are essential configurations of
the phase field dual to the charge. In analogy to the usual phase transition
that is characterized by a sudden change of the symmetry, the topological phase
transitions are governed by a discontinuous change of the topological numbers
signaled by the divergence of the zero-temperature topological susceptibility.
This defines a quantum criticality ruled by topologically conserved numbers
rather than the Landau principle of the symmetry breaking. We show that in the
limit of strong correlations topological charge is linked to the average
electronic filling number and the topological susceptibility to the electronic
compressibility of the system. We exploit the impact of these nontrivial U(1)
instanton phase field configurations for the cuprate phase diagram which
displays the "hidden" quantum critical point covered by the superconducting
lobe in addition to a sharp crossover between a compressible normal "strange
metal" state and a region characterized by a vanishing compressibility, which
marks the Mott insulator. Finally, we argue that the existence of robust
quantum numbers explains the stability against small perturbation of the system
and attributes to the topological "quantum protectorate" as observed in
strongly correlated systems.Comment: 23 pages, 12 figure
History Dependent Phenomena in the Transverse Ising Ferroglass: the Free Energy Landscape
In this paper we investigate the relationship between glassy and
ferromagnetic phases in disordered Ising ferromagnets in the presence of
transverse magnetic fields, . Iterative mean field simulations probe
the free energy landscape and suggest the existence of a glass transition as a
function of which is distinct from the Curie temperature. New
experimental field-cooled and zero-field-cooled data on LiHoYF
provide support for our theoretical picture.Comment: 4 pages RevTex; 5 figure
From second to first order transitions in a disordered quantum magnet
We study the spin-glass transition in a disordered quantum model. There is a
region in the phase diagram where quantum effects are small and the phase
transition is second order, as in the classical case. In another region,
quantum fluctuations drive the transition first order. Across the first order
line the susceptibility is discontinuous and shows hysteresis. Our findings
reproduce qualitatively observations on LiHoYF. We also discuss
a marginally stable spin-glass state and derive some results previously
obtained from the real-time dynamics of the model coupled to a bath.Comment: 4 pages, 3 figures, RevTe
Mycobacterium chimaera as an Underestimated Cause of NTM Lung Diseases in Patients Hospitalized in Pulmonary Wards
Mycobacterium chimaera is the newly described species belonging to Mycobacterium avium complex (MAC), with morphology and growth characteristics closely related to Mycobacterium intracellulare. The aim of this retrospective study was to analyze the frequency and clinical significance of M. chimaera identification in the population of patients with previous positive respiratory cultures for M. intracellulare or MAC. 200 strains of M. intracellulare or MAC, isolated from respiratory specimens of patients hospitalized in pulmonary wards, between 2011 and 2020, were retrospectively analyzed with GenoType NTM-DR test. 88 (44%) of strains were re-classified to M. chimaera species. Analysis of clinical data in 30 patients with positive M. chimaera isolates revealed that they were diagnosed with chronic obstructive pulmonary disease (COPD) – 27%, past tuberculosis – 20%, or interstitial lung diseases – 17%, respectively. Non-tuberculous mycobacterial lung disease (NTMLD) caused by M. chimaera has been recognized in 53% of patients, most often in those presenting with post-tuberculous lung lesions. M. chimaera was almost exclusively isolated from respiratory specimens of patients with underlying lung diseases, especially those with COPD and/or past tuberculosis. NTMLD due to M. chimaera was diagnosed predominantly in patients with past tuberculosis
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