H. Çelik

Value of acoustic rhinometry for measuring nasal valve area

Objective To assess the validity of acoustic rhinometry for measuring nasal valve area in human subjects.

Well-width dependence of the in-plane effective mass and quantum lifetime of electrons in multiple quantum wells

The electronic properties of modulation-doped multiple quantum wells (MWQ) with well width in the range between 51 and 145 ? have been investigated by using the Shubnikov - de Haas (SdH) oscillations technique. The carrier density and the Fermi energy have been determined from the period of the SdH oscillations. The in-plane effective mass and the quantum lifetime of 2D electrons have been obtained from the temperature and magnetic field dependences of the SdH amplitude. For narrow MQW samples (, 75 and 78 ?), increases with decreasing ; for the samples with and 145 ?, is approximately equal to that of electrons in bulk GaAs. The values obtained for show no clear well-width dependence and suggest that interface roughness is the dominating scattering mechanism in MQWs.

Accuracy of Acoustic Rhinometry Measurements

Objectives To identify the factors that influence the accuracy of acoustic rhinometry measurements recorded with commercially available equipment.

Acoustic Rhinometry in Healthy Humans: Accuracy of Area Estimates and Ability to Quantify Certain Anatomic Structures in the Nasal Cavity

Objectives: We evaluated the accuracy of acoustic rhinometry (AR) measurements in healthy humans and assessed the ability of AR in quantifying the dimensions of the paranasal sinuses and certain anatomic structures in the nasal cavity. Methods: Twenty nasal passages of 10 healthy adults were examined by AR and computed tomography (CT) before and after decongestion. Actual cross-sectional areas of the nasal cavity and actual locations of the nasal valve, the head of the inferior turbinate, the head of the middle turbinate, the ostia of the frontal and maxillary sinuses, and the choana were determined from CT sections perpendicular to the curved acoustic axis of the nasal passage. Results: The AR-measured cross-sectional areas in the anterior nasal cavity were in reasonable agreement with the corresponding areas determined from CT, whereas AR consistently overestimated the passage areas at locations posterior to the paranasal sinus ostia. The nasal valve was identified as a pronounced minimum on the AR area-distance curve. However, AR did not discretely identify the head of the inferior turbinate, the head of the middle turbinate, or the choana. Conclusions: The local minima on the AR area-distance curve beyond the nasal valve are caused by acoustic resonances in the nasal cavity, and do not correspond to any anatomic structure. The AR area overestimation beyond the paranasal sinus ostia is due to the interaction between the nasal cavity and the paranasal sinuses, rather than to sound loss into the sinuses. Acoustic rhinometry provides no quantitative information on ostium size or sinus volume in either non-decongested or decongested nasal cavities.

Acoustic rhinometry: accuracy and ability to detect changes in passage area at different locations in the nasal cavity.

Objectives: To evaluate the accuracy of acoustic rhinometry (AR) measurements, and to assess how well AR detects obstructions of various sizes at specific sites in the nasal cavity, we created a cast model from an adult cadaver nasal cavity. Methods: The actual cross-sectional areas of the cast model nasal passage were determined by computed tomography and compared with the corresponding areas measured by AR. To assess how nasal obstruction affects the AR results, we placed small wax spheres of different diameters at specific sites in the model (nasal valve, head of the inferior turbinate, head of the middle turbinate, middle of the middle turbinate, choana, and nasopharynx). Results: The AR-derived cross-sectional areas in the first 6.5 cm of the cast model nasal cavity were very close to the corresponding areas calculated from computed tomographic sections perpendicular to the presumed acoustic axis. However, AR overestimated the passage areas at locations posterior to the 6.5-cm point. Acoustic rhinometry gave an accurate indication of the passage area of the nasal valve and its distance from the nostril. The nasal valve and the choana were indicated by significant dips on the AR area-distance curve, whereas the curve was smooth throughout the region that included the head of the inferior turbinate, the head of the middle turbinate, the middle of the middle turbinate, and the nasopharynx. In other words, AR did not discretely identify these latter sites. Acoustic rhinometry detected the different-sized inserts (obstructions) more accurately at the nasal valve than at sites posterior to this location. Conclusions: The results of the study show that AR is a valuable method for assessing the anterior nasal cavity. This technique is sensitive for detecting changes in passage area at the nasal valve region; however, the sensitivity is lower at sites posterior to this. The findings suggest that when there is substantial narrowing of the nasal valve, AR will not identify an obstruction at any location posterior to the nasal valve. In such situations, AR measurements beyond the abnormal nasal valve may easily lead to misinterpretation of the patients nasal anatomy or condition.

Effects of anatomical variations of the nasal cavity on acoustic rhinometry measurements: a model study.

Background The goal of this study was to assess how anatomic variations of the nasal cavity affect the accuracy of acoustic rhinometry (AR) measurements. Methods A cast model of a human nasal cavity was used to investigate the effects of the nasal valve and paranasal sinuses on AR measurements. A luminal impression of a cadaver nasal cavity was made, and a cast model was created from this impression. To simulate the nasal valve, inserts of varying inner diameter were placed in the model nasal passage. To simulate the paranasal sinuses, side branches with varying neck diameters and cavity volumes were attached to the model. Results The AR measurements of the anterior nasal passage were reasonably precise when the passage area of the insert was within the normal range. When the passage area of the insert was reduced, AR measurements significantly underestimated the cross-sectional areas beyond the insert. The volume of the paranasal sinus had limited effect on AR measurements when the sinus ostium was small. However, when the ostium size was large, increasing the volume of the sinus led to significant overestimation of AR-derived areas beyond the ostium. Conclusion The pathologies that narrow the anterior nasal passage result in the most significant AR error by causing area underestimation beyond the constriction. It also appears that increased paranasal sinus volume causes overestimation of areas posterior to the sinus ostium when the ostium size is large. If these physical effects are not considered, the results obtained during clinical examination with AR may be misinterpreted.

Ultrasonic quantum oscillations and the magnetic field dependence of the Fermi energy in semimetallic Bi1-xSbx alloys

Ultrasonic quantum oscillations in pure Bi and semimetallic Bi1-xSbx alloys (x=0.012, 0.019, 0.033) have been investigated. Experiments were carried out in the temperature range 1.2-4.2K using longitudinal ultrasonic waves of frequencies up to 90 MHz propagated along the trigonal axis. Magnetic fields between 0.05 and 2.3 T were applied in the yz and xz planes. The angular dependence of the peak positions was studied. The Landau and spin quantum numbers of the oscillation peaks were obtained from the experimentally measured periods and peak positions of the oscillations. The experimental data indicate that, for most orientations of the magnetic field in the yz plane, the magnetic energy levels of electrons in the alloys studied can be described successfully by the ellipsoidal non-parabolic (ENP) model. The magnetic field dependence of the Fermi energy and the carrier density were calculated in the framework of the ENP model for electrons and the parabolic band for holes, using the previously determined band parameters. The magnetic field values at which the electrons in each pocket enter the quantum limit were deduced from the magnetic field dependence of the carrier density. The quantum limit fields obtained from calculations agree with the experimentally predicted values. It is concluded that within the magnetic field range studied the variation of the Fermi energy with magnetic field has a negligible effect on the period of ultrasonic quantum oscillations from light electrons.

Hot electron energy relaxation via acoustic-phonon emission in GaAs/Ga1−xAlxAs multiple quantum wells: well-width dependence

The well-width dependence of the two-dimensional (2D) electron energy relaxation associated with acoustic-phonon emission in GaAs/Ga1−xAlxAs multiple quantum wells (MQWs) has been investigated using Shubnikov-de Haas (SdH) effect measurements in the temperature range of 3.3–15 K and at applied electric fields up to 300 V m−1. The modulation-doped MQW samples studied have quantum-well widths (Lz) in the range between 40 and 145 A; only the lowest subband in each sample is populated with a 2D carrier density in the range from 1.04 × 1016 m−2 to 1.38 × 1016 m−2. The power loss–electron temperature characteristics of the samples have been obtained from the lattice temperature and electric field dependences of the amplitude of the SdH oscillations. It is found that the power loss decreases markedly when Lz increases from 40 A to about 120 A and it increases for Lz > 120 A. The experimental results are compared with the current 2D and three-dimensional (3D) theoretical models for power loss, which include both piezoelectric and deformation-potential scattering. The electron-temperature dependence of power loss determined experimentally fits well to both the 2D and 3D theoretical models in the intermediate-temperature regime but with different values for the acoustic deformation potential. It is shown that for samples with Lz in the range of 40–120 A, the 2D model predicts a dependence of power loss on the well width, which is similar to that observed experimentally. The 3D model, however, predicts a power loss which increases with increasing well width and describes well the well-width dependence of the experimental power loss for wide wells (Lz ≥ 120 A). The results provide useful information about the relative magnitude of the deformation-potential and piezoelectric contributions to power loss.

Resistivity minimum in Ni76−xMn24Ptx and Ni72−xMn28Ptx amorphous alloys

Abstract The electrical resistivity ϱ as a function of temperature has been measured for amorphous thin films of Ni 76 − x Mn 24 P x ( x = 0, 2, 5) and Ni 72 − x Mn 28 Pt x ( x = 0, 4, 10) alloys in the temperature range 1.5–400 K. The resistivity for every sample exhibits a low-temperature minimum, T min , following the logarithmic dependence. The results show the presence of two effects: one of them, associated with Kondo-like scattering, exists for all samples, the other, the electron-localized spin-wave scattering mechanism is dominant for the samples with higher Mn concentrations. In addition, the resistivity shows quadratic temperature behaviour in the intermediate temperature range. The examination of the quadratic behaviours suggests that the scattering mechanism with magnetic origin is not negligible compared with that of the electron-structural disordered scattering. Furthermore, the present data permits us for the first time to compare the nature of the resistivity minimum at lower temperatures for each sample of amorphous Ni 76 − x Mn 24 P x and Ni 72 − x Mn 28 Pt x alloys with that of the corresponding alloys in the polycrystalline phase.

Acoustic rhinometry measurements in stepped-tube models of the nasal cavity

Stepped-tube models with a constriction in the anterior section were used to evaluate the effects that nasal valve passage area and nasal cavity shape have on acoustic rhinometry (AR) measurements. The AR-determined cross-sectional areas beyond a constriction of small passage area were consistently underestimated, and the corresponding area-distance curves showed pronounced oscillations. Also, the AR technique did not accurately reproduce abrupt changes in passage area. The results suggest that, regardless of the particular shape of the nasal cavity model, AR does not provide reliable information about cross-sectional areas posterior to a severe constriction. The experimental results are discussed in terms of theoretically calculated acoustic input impedance for the models studied, the physical limitations of AR, and assumptions made in AR algorithms. The study demonstrated that energy losses and sound wave attenuation due to air viscosity do not significantly affect AR measurements. It was also shown that passage area beyond a severe constriction is underestimated because the barrier created by the constriction reflects most of the incident sound power. The results also indicate that the oscillations in area-distance curves are due to low-frequency acoustic resonances in the nasal cavity model.