105 research outputs found
Kahvede Osmanlı parmağı
Taha Toros Arşivi, Dosya No: 134/B-KahveUnutma İstanbul projesi İstanbul Kalkınma Ajansı'nın 2016 yılı "Yenilikçi ve Yaratıcı İstanbul Mali Destek Programı" kapsamında desteklenmiştir. Proje No: TR10/16/YNY/010
Josephson effect in hybrid superconductor-normal metal structures
Ankara : Department of Physics and the Institute of Engineering and Science of Bilkent Univ., 2000.Thesis (Master's) -- Bilkent University, 2000.Includes bibliographical references leaves 67-69.The clean SNS junction, with a phase difference x across the normal metal
barrier and without Fermi level mismatch between the components, is modeled
by a step like pair potential. The quasiclassical equations are obtained from the
Gorkov equations by the elimination of crystal momenta and are valid in the
existence of only the off-diagonal potential(pair potential). Then for the SNS
junction, the quasiclassical Green functions are obtained. At zero temperature, in
the long barrier limit(d ^ ^o)> the current is found to have a sawtooth dependence
on the phase difference, the amplitude of which is inversely proportional to the
thickness of the normal layer. At finite temperatures in the limits d and
Tc T, the current is found to have exponential dependence on the thickness of
the normal layer, T exp(—d/^7’) sin y, .where = vfI2ttT.
An extension of single SNS structures is the periodic SNS structure which
may as well exhibit Josephson effect. It is simulated by a periodic step-wise pair
potential, where the phase of the pair potential changes by some constant value
in subsequent superconducting islands. Bogoliubov equations in the semicla.ssical limit are employed, yielding the density of states(DOS). In the DOS, there
appears some forbidden energy regions, which point out to a band structure.Çakır, ÖzgürM.S
Robust entanglement in atomic systems
Cataloged from PDF version of article.Various models for generation of robust atomic entangled states and their
implementation with current accessible technologies are proposed and worked out.
Deterministic creation of long living Bell states with respect to metastable states
in three-level Λ type systems is studied. Strong atom-field coupling drives atoms
into a transient entangled state followed by an irreversible evolution towards a
long-living maximally entangled state featuring robustness against dipole-allowed
transitions. First, generation of pairwise atomic entanglement in cavities in ideal
case is discussed, extension to multi-party entangled states is made. Observation
of photons emitted from the system signals the generation of a Bell state.
The interaction of multi-level atoms with body-assisted electro-magnetic field
in the presence of dispersing and absorbing media is studied and these results are
applied to the description of a pair of Λ type atoms passing by a microsphere.
Microspheres give rise to resonances of well defined height and width with easy
access to strong and weak coupling regimes for atom-field interaction, thus enabling
realization of the proposed scheme of ”robust entanglement of three-level
atoms”. Even in realistic settings it is possible to obtain quite high amount of
entanglement at spatially well separated distances.
Then we focus on steady state entanglement between atomic dipoles. It is
shown that two dipoles in free space driven by a classical driving field become
entangled in the steady state. The crucial point is that, this entanglement is
irrespective of the initial state and may be preserved as long as the engineered
system is kept intact.
Absorption effects in real cavities are studied, and an input-output relation is
formulated in the presence of a source in the cavity. Extraction of non-classical photon states from a cavity is investigated.Çakır, ÖzgürPh.D
Quantum dynamics in electron-nuclei coupled spin system in quantum dots: Bunching, revival, and quantum correlation in electron-spin measurements
We investigate quantum dynamics in the electron-nuclei coupled spin system in
quantum dots and clarify the fundamental features of quantum correlation
induced via successive electron spin measurements. This quantum correlation
leads to interesting phenomena such as the bunching of outcomes in the electron
spin measurements and the revival of an arbitrary initial electron spin state.
The nuclear spin system is also affected by the quantum correlation and is in
fact squeezed via conditional measurements or postselection. This squeezing is
confirmed by calculating the increase in the purity of the nuclear spin system.
Thus the successive electron spin measurements provide a probabilistic method
to squeeze the nuclear spin system. These new features are predicted not only
for the case of a double quantum dots occupied by a pair of electrons but also
for the case of a single quantum dot occupied by a single electron or a pair of
electrons.Comment: 21 pages, to be published in Phys. Rev.
Quantum Dynamics of Electron-Nuclei Coupled System in Quantum Dots
We have investigated the dynamics of the electron-nuclei coupled system in
quantum dots. The bunching of results of the electron spin measurements and the
revival in the conditional probabilities are salient features of the nuclear
spin memory. The underlying mechanism is the squeezing of the nuclear spin
state and the correlations between the successive electron spin measurements.
Further we make a proposal for the preparation and detection of superposition
states of nuclear spins merely relying on electron spin measurements. For
unpolarized, completely random nuclear spin state one can still trace the
quantum interference effects. We discuss the realization of these schemes for
electron spins on both single and double QDs.Comment: 4 pages,3 figure
Do the Age of Implantation, the Widths of Internal Acoustic Canal and Bony Cochlear Nerve Canal Affect the Auditory Performance of Primary School Children with Bilateral Cochlear Implants?
Objective:To reveal the correlation between implantation age, the internal acoustic canal (IAC) width, bony cochlear nerve canal (BCNC) width, and auditory performance in primary school children with bilateral cochlear implantation (CI).Methods:Preoperative IAC and BCNC widths of 57 pre-lingually deaf children aged 7–11 years who had previously undergone bilateral CI in our institution were reviewed and cut-off values were calculated. Twenty-four patients who had additional problems and could not attend school and those who refused to participate in the study were excluded. The remaining 33 were invited to the hospital, and their speech perception tests, and language development scores were analyzed (16 of 33 patients had been operated on before the age of 24 months).Results:The cut-off values calculated from the 114 ears of 57 patients were 3.86 mm for IAC width and 1.56 mm for BCNC width. The auditory performances of the 33 patients after CI were not significantly different in the narrow and normal width groups. However, speech perception test results, and language development scores of patients implanted before the age of 24 months were significantly higher.Conclusion:There are some studies showing that children with bilateral sensorineural hearing loss have narrower IAC and BCNC widths. However, we concluded that the widths of the IAC and the bone cochlear nerve canal did not affect auditory performance. We found that implantation age is the single most important determinant of speech-language development after CI
Factors Affecting Optimal Titration Pressure of Continuous Positive Airway Pressure Device in Patients with Obstructive Sleep Apnea Syndrome
Objective: To assess the effects of anatomical, clinical parameters, and pulmonary respiratory function on the therapeutic titration pressure of continuous positive airway pressure (CPAP) device in obstructive sleep apnea syndrome (OSAS).Methods: The study comprised 41 OSAS patients whose optimum CPAP titration pressures were measured. Each patient underwent an otorhinolaryngologic and thoracic examination, and data was recorded for height, weight, body mass index, neck-waist circumferences, Mallampati classification, tonsillar hypertrophy, hypopharyngeal collapse, soft palate-tongue base obstruction scores, peak nasal inspiratory flow and acoustic rhinometry measures, and CPAP device therapeutic pressures. Forced vital capacity, forced expiratory volume, FEV1/FVC ratio and peak expiratory flow values were noted.Results: Median CPAP optimal pressure cut-off value was determined as 9 mmH2O. Statistical analysis was made in two groups as CPAP titration optimal pressure ≤9 and >9 mmH2O. In the optimal pressure >9 group, neck and waist circumferences, hypopharyngeal collapse score, retropalatal and retrolingual lateral wall collapse scores were significantly higher (p<0.05). In multivariate and univariate model analysis, neck and waist circumferences, hypopharyngeal collapse score, retropalatal and retrolingual lateral wall collapse scores were observed to be significant in predicting high and low pressures in univariate model.Conclusion: For the prediction of optimal CPAP titration pressure in OSAS treatment, wide neck and waist circumferences, high hypopharyngeal collapse score and retropalatal and retrolingual lateral wall collapse grades may be determinative
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