64 research outputs found
Collective modes in the electronic polarization of double-layer systems in the superconducting state
Standard weak coupling methods are used to study collective modes in the
superconducting state of a double-layer system with intralayer and interlayer
interaction, as well as a Josephson-type coupling and single particle hopping
between the layers by calculating the electronic polarization function
perpendicular to the layers. New analytical results are derived for the mode
frequencies corresponding to fluctuations of the relative phase and amplitude
of the layer order parameters in the case of interlayer pairing and finite
hopping . A new effect is found for finite -dependent hopping: then the
amplitude and phase fluctuations are coupled. Therefore two collective modes
may appear in the dynamical c-axis conductivity below the threshold energy for
breaking Cooper pairs. With help of numerical calculations we investigate the
temperature dependence of the collective modes and show how a plasmon
corresponding to charge fluctuations between the layers evolves in the normal
state.Comment: 17 pages, latex, 8 ps figure
Diagnosis and neurosurgical treatment of glossopharyngeal neuralgia: clinical findings and 3-D visualization of neurovascular compression in 19 consecutive patients
Glossopharyngeal neuralgia is a rare condition with neuralgic sharp pain in the pharyngeal and auricular region. Classical glossopharyngeal neuralgia is caused by neurovascular compression at the root entry zone of the nerve. Regarding the rare occurrence of glossopharyngeal neuralgia, we report clinical data and magnetic resonance imaging (MRI) findings in a case series of 19 patients, of whom 18 underwent surgery. Two patients additionally suffered from trigeminal neuralgia and three from additional symptomatic vagal nerve compression. In all patients, ipsilateral neurovascular compression syndrome of the IX cranial nerve could be shown by high-resolution MRI and image processing, which was confirmed intraoperatively. Additional neurovascular compression of the V cranial nerve was shown in patients suffering from trigeminal neuralgia. Vagal nerve neurovascular compression could be seen in all patients during surgery. Sixteen patients were completely pain free after surgery without need of anticonvulsant treatment. As a consequence of the operation, two patients suffered from transient cerebrospinal fluid hypersecretion as a reaction to Teflon implants. One patient suffered postoperatively from deep vein thrombosis and pulmonary embolism. Six patients showed transient cranial nerve dysfunctions (difficulties in swallowing, vocal cord paresis), but all recovered within 1 week. One patient complained of a gnawing and burning pain in the cervical area. Microvascular decompression is a second-line treatment after failure of standard medical treatment with high success in glossopharyngeal neuralgia. High-resolution MRI and 3D visualization of the brainstem and accompanying vessels as well as the cranial nerves is helpful in identifying neurovascular compression before microvascular decompression procedure
Magnetic-Field-Induced Hybridization of Electron Subbands in a Coupled Double Quantum Well
We employ a magnetocapacitance technique to study the spectrum of the soft
two-subband (or double-layer) electron system in a parabolic quantum well with
a narrow tunnel barrier in the centre. In this system unbalanced by gate
depletion, at temperatures T\agt 30 mK we observe two sets of quantum
oscillations: one originates from the upper electron subband in the
closer-to-the-gate part of the well and the other indicates the existence of
common gaps in the spectrum at integer fillings. For the lowest filling factors
and , both the common gap presence down to the point of one- to
two-subband transition and their non-trivial magnetic field dependences point
to magnetic-field-induced hybridization of electron subbands.Comment: Major changes, added one more figure, the latest version to be
published in JETP Let
Correlation between the Josephson coupling energy and the condensation energy in bilayer cuprate superconductors
We review some previous studies concerning the intra-bilayer Josephson
plasmons and present new ellipsometric data of the c-axis infrared response of
almost optimally doped Bi_{2}Sr_{2}CaCu_{2}O_{8}. The c-axis conductivity of
this compound exhibits the same kind of anomalies as that of underdoped
YBa_{2}Cu_{3}O_{7-delta}. We analyze these anomalies in detail and show that
they can be explained within a model involving the intra-bilayer Josephson
effect and variations of the electric field inside the unit cell. The Josephson
coupling energies of different bilayer compounds obtained from the optical data
are compared with the condensation energies and it is shown that there is a
reasonable agreement between the values of the two quantities. We argue that
the Josephson coupling energy, as determined by the frequency of the
intra-bilayer Josephson plasmon, represents a reasonable estimate of the change
of the effective c-axis kinetic energy upon entering the superconducting state.
It is further explained that this is not the case for the estimate based on the
use of the simplest ``tight-binding'' sum rule. We discuss possible
interpretations of the remarkable agreement between the Josephson coupling
energies and the condensation energies. The most plausible interpretation is
that the interlayer tunneling of the Cooper pairs provides the dominant
contribution to the condensation energy of the bilayer compounds; in other
words that the condensation energy of these compounds can be accounted for by
the interlayer tunneling theory. We suggest an extension of this theory, which
may also explain the high values of T_{c} in the single layer compounds
Tl_{2}Ba_{2}CuO_{6} and HgBa_{2}CuO_{4}, and we make several experimentally
verifiable predictions.Comment: 16 pages (including Tables) and 7 figures; accepted for publication
in Physical Review
The anomaly of the oxygen bond-bending mode at 320 cm and the additional absorption peak in the c-axis infrared conductivity of underdoped YBaCuO single crystals revisited by ellipsometricmeasurements
We have performed ellipsometric measurements of the far-infrared c-axis
dielectric response of underdoped YBaCuO single
crystals. Here we report a detailed analysis of the temperature-dependent
renormalization of the oxygen bending phonon mode at 320 cm and the
formation of the additional absorption peak around 400-500 cm. For a
strongly underdoped YBaCuO crystal with T=52 K we
find that, in agreement with previous reports based on conventional reflection
measurements, the gradual onset of both features occurs well above T at
T*150 K. Contrary to some of these reports, however, our data establish
that the phonon anomaly and the formation of the additional peak exhibit very
pronounced and steep changes right at T. For a less underdoped
YBaCuO crystal with T=80 K, the onset temperature of
the phonon anomaly almost coincides with T. Also in contrast to some
previous reports, we find for both crystals that a sizeable fraction of the
spectral weight of the additional absorption peak cannot be accounted for by
the spectral-weight loss of the phonon modes but instead arises from a
redistribution of the electronic continuum. Our ellipsometric data are
consistent with a model where the bilayer cuprate compounds are treated as a
superlattice of intra- and inter-bilayer Josephson-junctions
Patterns and correlates of tobacco control behavior among american association of pediatric dentistry members: a cross-sectional national study
<p>Abstract</p> <p>Background</p> <p>To determine the tobacco-related knowledge, attitudes, and practice behaviors among US pediatric dentists.</p> <p>Methods</p> <p>A survey was conducted in 1998 among a national, random sample of 1500 American Academy of Pediatric Dentistry members. Chi-square tests and logistic regression with odds ratios (ORs) and 95% confidence intervals assessed factors related to pediatric dentists' tobacco control behaviors.</p> <p>Results</p> <p>Response was 65% for the survey. Only 12% of respondents had prior tobacco prevention/cessation training. Of those untrained, 70% were willing to be trained. Less than two-thirds correctly answered any of four tobacco-related knowledge items. Over one-half agreed pediatric dentists should engage in tobacco control behaviors, but identified patient resistance as a barrier. About 24% of respondents reported always/often asking their adolescent patients about tobacco use; 73% reported always/often advising known tobacco users to quit; and 37% of respondents always/often assisting with stopping tobacco use. Feeling prepared to perform tobacco control behaviors (ORs = 1.9–2.8), a more positive attitude score (4 points) from 11 tobacco-related items (ORs = 1.5–1.8), and a higher statewide tobacco use prevalence significantly predicted performance of tobacco control behaviors.</p> <p>Conclusion</p> <p>Findings suggest thatraining programs on tobacco use and dependence treatment in the pediatric dental setting may be needed to promote tobacco control behaviors for adolescent patients.</p
When public action undermines public health: A critical examination of antifluoridationist literature
Background: The addition of the chemical fluorine to the water supply, called water fluoridation, reduces dental caries by making teeth more resistant to demineralisation and more likely to remineralise when initially decayed. This process has been implemented in more than 30 countries around the world, is cost-effective and has been shown to be efficacious in preventing decay across a person's lifespan. However, attempts to expand this major public health achievement in line with Australia's National Oral Health Plan 2004–2013 are almost universally met with considerable resistance from opponents of water fluoridation, who engage in coordinated campaigns to portray water fluoridation as ineffective and highly dangerous. Discussion: Water fluoridation opponents employ multiple techniques to try and undermine the scientifically established effectiveness of water fluoridation. The materials they use are often based on Internet resources or published books that present a highly misleading picture of water fluoridation. These materials are used to sway public and political opinion to the detriment of public health. Despite an extensive body of literature, both studies and results within studies are often selectively reported, giving a biased portrayal of water fluoridation effectiveness. Positive findings are downplayed or trivialised and the population implications of these findings misinterpreted. Ecological comparisons are sometimes used to support spurious conclusions. Opponents of water fluoridation frequently repeat that water fluoridation is associated with adverse health effects and studies are selectively picked from the extensive literature to convey only claimed adverse findings related to water fluoridation. Techniques such as "the big lie" and innuendo are used to associate water fluoridation with health and environmental disasters, without factual support. Half-truths are presented, fallacious statements reiterated, and attempts are made to bamboozle the public with a large list of claims and quotes often with little scientific basis. Ultimately, attempts are made to discredit and slander scientists and various health organisations that support water fluoridation. Summary: Water fluoridation is an important public health initiative that has been found to be safe and effective. Nonetheless, the implementation of water fluoridation is still regularly interrupted by a relatively small group of individuals who use misinformation and rhetoric to induce doubts in the minds of the public and government officials. It is important that public health officials are aware of these tactics so that they can better counter their negative effectJason M Armfiel
- …