Upshift In Frequency Research Articles

Influence of the Intracranial Contents on the Head Motion under Bone Conduction

Introduction: The mechanism of non-osseous bone conduction pathways, involving the intracranial contents (ICC) of the skull, is still not well understood. This study aimed to investigate the influence of the ICC on the skull bone wave propagation, including dependence on stimulation location and coupling. Methods: Three Thiel-embalmed whole-head cadaver specimens were studied before and after the removal of the ICC. Stimulation was via the electromagnetic actuators from commercial bone conduction hearing aids. Osseous pathways were sequentially activated by mastoid, forehead, and bone-anchored hearing aid location stimulation via a 5-Newton steel headband or percutaneously implanted screw. Non-osseous pathways were activated by stimulation on the eye and dura via a 5-Newton steel headband and a custom-made pneumatic holder, respectively. Under each test condition, the 3D motion of the superior skull bone was monitored at ∼200 points. Results: The averaged response of the skull surface showed limited differences due to the removal of the ICC. In some isolated cases, the modal pattern on the skull surface showed a trend for an upshift (∼1/2 octave) in the observed natural frequencies for drained heads. This was also consistent with an observed trend for an upshift in the transition frequency in the estimated deformation across the lateral surfaces of the temporal bones. Such changes were consistent with the expected reduction in mass and damping due to the absence of the ICC. Conclusion: Overall, the ICC affect to a limited extent the motion of the skull bone, with a limited trend for a reduction of its natural frequencies.

UV Light Detection Using Resonance Frequency of Piezoelectric Quartz Crystal

This article reported about the ultraviolet (UV) radiation effect on the resonance frequency response of a AT-cut piezoelectric quartz crystal. A large resonance frequency upshift was observed when the quartz crystal was irradiated by UV light of 355-nm wavelength using a Q-switched pulsed Nd:YVO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> UV laser. The dynamic frequency response behavior was systematically investigated by illuminating the quartz crystal with UV light in which the UV intensity was varied with time in staircase- and linear pulse-shaped patterns. From the experimental analysis, we measured the limit of detection and the sensitivity of the quartz crystal, which are about 0.5 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 0.706 Hz/(mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), respectively. For a constant UV irradiation, a moderate response (<;10 s) and recovery (<;10 s) times were achieved during the on and off cycles of the UV light. The short-term repeatability and maximum operating limit of AT-cut quartz crystal were also further studied upon exposure to UV light with different intensities. In this work, we not only demonstrate the impact of UV irradiation on quartz crystal but also discuss the mechanism of upshift in resonance frequency upon exposure to UV light. This study shows the applicability of quartz crystal for the detection of UV light.

Tunable Graphene Phononic Crystal.

In the field of phononics, periodic patterning controls vibrations and thereby the flow of heat and sound in matter. Bandgaps arising in such phononic crystals (PnCs) realize low-dissipation vibrational modes and enable applications toward mechanical qubits, efficient waveguides, and state-of-the-art sensing. Here, we combine phononics and two-dimensional materials and explore tuning of PnCs via applied mechanical pressure. To this end, we fabricate the thinnest possible PnC from monolayer graphene and simulate its vibrational properties. We find a bandgap in the megahertz regime within which we localize a defect mode with a small effective mass of 0.72 ag = 0.002 mphysical. We exploit graphene’s flexibility and simulate mechanical tuning of a finite size PnC. Under electrostatic pressure up to 30 kPa, we observe an upshift in frequency of the entire phononic system by ∼350%. At the same time, the defect mode stays within the bandgap and remains localized, suggesting a high-quality, dynamically tunable mechanical system.

Ultrawide Band Gap β-Ga2O3 Nanomechanical Resonators with Spatially Visualized Multimode Motion.

Beta gallium oxide (β-Ga2O3) is an emerging ultrawide band gap (4.5 eV-4.9 eV) semiconductor with attractive properties for future power electronics, optoelectronics, and sensors for detecting gases and ultraviolet radiation. β-Ga2O3 thin films made by various methods are being actively studied toward such devices. Here, we report on the experimental demonstration of single-crystal β-Ga2O3 nanomechanical resonators using β-Ga2O3 nanoflakes grown via low-pressure chemical vapor deposition (LPCVD). By investigating β-Ga2O3 circular drumhead structures, we demonstrate multimode nanoresonators up to the sixth mode in high and very high frequency (HF/VHF) bands, and also realize spatial mapping and visualization of the multimode motion. These measurements reveal a Young's modulus of EY = 261 GPa and anisotropic biaxial built-in tension of 37.5 MPa and 107.5 MPa. We find that thermal annealing can considerably improve the resonance characteristics, including ∼40% upshift in frequency and ∼90% enhancement in quality (Q) factor. This study lays a foundation for future exploration and development of mechanically coupled and tunable β-Ga2O3 electronic, optoelectronic, and physical sensing devices.

European Blackbirds Exposed to Aircraft Noise Advance Their Chorus, Modify Their Song and Spend More Time Singing

Noise pollution has a strong impact on wildlife by disrupting vocal communication or inducing physiological stress. Songbirds are particularly reliant on vocal communication as they use song during territorial and sexual interactions. Birds living in noisy environments have been shown to change the acoustic and temporal parameters of their song presumably to maximize signal transmissibility. Also, research shows that birds advance their dawn chorus in urban environments to avoid the noisiest hours, but little is known on the consequences of these changes in the time they spent singing at dawn. Here we present a comprehensive view of the European blackbird singing behaviour living next to a large airport in Madrid, using as a control a population living in a similar but silent forest. Blackbird song is composed of two parts: a series of loud low-frequency whistles (motif) and a final flourish (twitter). We found that airport blackbirds were more likely to sing songs without the twitter part. Also, when songs included a twitter part, airport blackbirds used a smaller proportion of song for the twitter than control blackbirds. Interestingly, our results show no differences in song frequency between airport and control populations. The most relevant finding of this study shows that airport blackbirds not only sang earlier but also increased the time they spent singing when chorus and aircraft traffic coincide on time. This effect disappeared as the season progressed and the chorus and the aircraft traffic day-time schedule were separated on time. We propose that the typical urban upshift in frequency might not be useful under the conditions of noise and landscape structure found near airports. We suggest that the modifications in singing behaviour induced by aircraft noise may be adaptive and that they are specific to airport acoustic habitat. Moreover, we found that adjustment of singing activity in relation to noise is plastic and possibly optimized to cope with aircraft traffic activity. In a soundscape characterised by intermittent and strong noise bursts, singing for longer could be more advantageous than modifying frequency parameters, although it is likely more costly.

Analytical theory of the shear Alfvén continuum in the presence of a magnetic island

The effect of a magnetic island chain on the shear Alfvén continuum is calculated analytically. Using a WKB approximation of the linearized ideal MHD equations, the island is shown to cause an upshift in the continuum accumulation point frequency. This minimum of the frequency spectrum is shifted from the rational surface to the island separatrix. The structure of the eigenmodes is also presented.

Monoxide carbon frequency shift as a tool for the characterization of TiO2 surfaces: Insights from first principles spectroscopy

The adsorption and vibrational frequency of CO on defective and undefective titanium dioxide surfaces is examined applying first-principles molecular dynamics simulations. In particular, the vibrational frequencies are obtained beyond the harmonic approximation, through the time correlation functions of the atomic trajectories. In agreement with experiments, at low CO coverages we find an upshift in the vibration frequency with respect to the free CO molecule, of 45 and 35 cm(-1) on the stoichiometric rutile (110) and anatase (101) faces, respectively. A band falling 8 cm(-1) below the frequency corresponding to the perfect face is observed for the reduced rutile (110) surface in the low vacancy concentration limit, where the adsorption is favored on Ti(4+) sites. At a higher density of defects, adsorption on Ti(3+) sites becomes more stable, accompanied by a downshift in the stretching band. In the case of anatase (101), we analyze the effect of subsurface oxygen vacancies, which have been shown to be predominant in this material. Interestingly, we find that the adsorption of CO on five coordinate Ti atoms placed over subsurface vacancies is favored with respect to other Ti(4+) sites (7.25 against 6.95 kcal/mol), exhibiting a vibrational redshift of 20 cm(-1). These results provide the basis to quantitatively assess the degree of reduction of rutile and anatase surfaces via IR spectroscopy, and at the same time allow for the assignment of characteristic bands in the CO spectra on TiO2 whose origin has remained ambiguous.

Electromechanical resonance behavior of suspended single-walled carbon nanotubes under high bias voltages

We characterize the nanoelectromechanical response of suspended individual carbon nanotubes under high voltage biases. An abrupt upshift in the mechanical resonance frequency of approximately 3 MHz is observed at high bias. While several possible mechanisms are discussed, this upshift is attributed to the onset of optical phonon emission, which results in a sudden contraction of the nanotube due to its negative thermal expansion coefficient. This, in turn, causes an increase in the tension in the suspended nanotube, which upshifts its mechanical resonance frequency. This upshift is consistent with Raman spectral measurements, which show a sudden downshift of the optical phonon modes at high bias voltages. Using a simple model for oscillations on a string, we estimate the effective change in the length of the nanotube to be ΔL/L ≈ −2 × 10−5 at a bias voltage of 1 V.

Measurements of spectral broadening and Doppler shift of backreflections from a fiber fuse using heterodyne detection

We report broadening in spectrum as light is backreflected from a propagating fiber fuse. The formation of micrometer-size voids results in periodic changes in Fresnel reflection occurring in the leading part of the fuse. High-resolution measurement of the optical spectrum via heterodyne detection revealed an upshift (Doppler shift) in the optical frequency and discrete frequency components that are characteristic of amplitude modulation due to periodic void formation.

Cross-phase modulation between lasers in a tunnel ionizing gas

The phase modulation of a low power long pulse probe laser beam in a rapidly tunnel ionizing gas (helium) under a relativistic short pulse laser is investigated. The relativistic pulse creates a fast increasing plasma density at its front, far ahead of the intensity peak. The probe pulse sees these changes as modulation in its phase and undergoes large frequency upshift. The spectral content of the blueshifted potion of the probe pulse is large when its intensity peak commoves with the ionization front. There are two ionization front created by first and second ionizations, and the separation between the two increases as laser propagates through the gas. The rate of density variation by first and second ionizations, however, is fairly the same and varies little as the spot size of the laser beam increases up to three times its initial value. The ionization front velocity, as well as the upshift in probe pulse frequency, is bigger for sharper laser pulse.

Effect of nanotube-nanotube coupling on the radial breathing mode of carbon nanotubes

We study the radial breathing mode (RBM) of resonant single walled carbon nanotubes within individual bundles. As strain is applied, significant debundling of the nanotubes occurs, causing an upshift in the RBM frequency. The RBM frequency is found to change irreversibly with strain, correlating more strongly with the total number of strains and relaxations than with absolute strain, indicating that debundling is the dominant cause of the observed changes. The RBM upshift of semiconducting nanotubes is 70% larger than that of metallic nanotubes. We also observe a large drop in the Raman intensity as the nanotubes are debundled. This drop is not due to a change in the resonant electronic transition energies of the nanotube and indicates that neighboring nanotubes within a bundle play an important role in the resonant nanotube's Raman signal.

Nature of the constant factor in the relation between radial breathing mode frequency and tube diameter for single-wall carbon nanotubes

Resonance Raman scattering is used to determine the radial breathing mode (RBM) frequency $({\ensuremath{\omega}}_{\text{RBM}})$ dependence on tube diameter $({d}_{t})$ for single-wall carbon nanotubes (SWNTs). We establish experimentally the ${\ensuremath{\omega}}_{\text{RBM}}=227.0/{d}_{t}$ as the fundamental relation for pristine SWNTs. All the other RBM values found in the literature can be explained by an upshift in frequency due mostly to van der Waals interaction between SWNTs and environment.

Ultrathin magnetic multilayer films for low-field microwave notch filters

Microwave filters that use thin films of ferromagnetic metals are now being established as a valuable option compared to yttrium iron garnet based filters due to their higher frequency response. In these filters the signal propagation is inhibited over a wide frequency band, depending on the applied dc magnetic field. However, the continuous application of an applied field to achieve an operating frequency in the higher gigahertz range increases the power consumption of the device. The main contribution of this article is to provide techniques which significantly boost the operating frequency of notch filters in zero or very low applied magnetic fields. To do this, the authors fabricated high quality epitaxial Fe films which are interlayer exchange coupled through nonmagnetic Si layer of different thicknesses. The films were used in flip-chip geometry on top of a Cu-coplanar waveguide to create band-stop filters. In contrast to filters based on Fe alone, the multilayer filters can operate above 25GHz with a very small applied magnetic field. The observed upshift in frequency is attributed to the induced interlayer exchange coupling energy mediated through the nonmagnetic Si layer between the two Fe layers. These frequency shifts are in good agreement with theoretical calculations of the ferromagnetic resonance modes taking into account anisotropy, exchange, and Zeeman energies.

The environmental effect on the radial breathing mode of carbon nanotubes in water

We investigate, using molecular dynamics, the effect on the radial breathing mode (RBM) frequency of immersion in water for a range of single-walled carbon nanotubes. We find that nanotube-water interactions are responsible for an upshift in the RBM frequency of the order of 4-10 wave numbers. The upshift is comprised of two components: increased hydrostatic pressure on the nanotube due to curvature effects, and the dynamic coupling of the RBM with its solvation shell. In contrast to much of the current literature, we find that the latter of the two effects is dominant. This could serve as an innovative tool for determining the interaction potential between nanotubes/graphitic surfaces and fluids.

Iron-based microstrip band-stop filters at higher microwave frequency range: Design optimization using shape anisotropy

Microwave filters that use thin films of ferromagnetic metals are now being established as an option compared to YIG based filters due to their higher frequency response at very small magnetic fields. The aim of the present investigation is to significantly boost the operating frequency of notch filters in very low applied magnetic fields. To do this, we fabricated a series of notch filters with Fe films of different thicknesses and shapes. The stop-band response of each of these filters cover four waveguide bands (X, KU, K and Ka) ranging from 8to40GHz with an applied magnetic field up to 4.5kOe. The frequency characteristics of these filters at zero field can be significantly changed by changing the geometry of the magnetic element. For example, an Fe film which is 7.5μm wide, 100nm thick, and 3mm long has a stop band centered at 9.5GHz, but this is increased to 22GHz for an 800nm thick Fe film. For narrower signal lines (4.5μm wide), we observed further increases in the frequencies: 11GHz for a 100nm Fe film increased to 25GHz for an 800nm thick Fe film. This upshift in frequency is due to the shape anisotropy of the Fe film. In addition, we investigated the temperature variations in the properties of the devices from room temperature to +85°C

Synthesis and Spectroscopic Identification of Ethylidyne Adsorbed on Ni(111)

The interaction of ethylene adsorbed on Ni(111) with gas-phase H atoms has been investigated. The major adsorbed reaction product is identified by high-resolution electron energy loss spectroscopy to be ethylidyne (C−CH3). This study is the first direct spectroscopic observation of a C−CH3 species adsorbed on Ni in an ultrahigh-vacuum environment. Spectra of four isotopomers, C−CH3, 13C−13CH3, C−CD3, and 13C−13CD3, are reported, and a complete and consistent vibrational assignment of their fundamental modes is presented. Based on this assignment, a force field is derived from the measured vibrational frequencies using a normal-modes analysis and is found to be in good agreement with that deduced from IR spectra of an ethylidyne species in an organometallic complex. Inspection of the eigenvectors of the normal-mode displacements reveals that substantial mixing of harmonic bond motions is the origin of the unusual upshift in frequency of the C−C stretching mode upon deuteration. A quantitative determination of the relative dynamic bond dipole moments demonstrates that the changes in intensity and dipole activity of the C−C stretching and symmetric CH3 deformation modes upon deuteration, phenomena common to all C−CD3 spectra, also arise from extensive mixing of bond motions. A detailed analysis of the spectra strongly suggests a C3v or C3 local environment for ethylidyne and a 3-fold hollow adsorption site.

Structural evolution of the heme group during the allosteric transition in hemoglobin: Insights from resonance raman spectra of isotopically labeled heme

Visible resonance Raman spectra in the low-frequency region (200–500 cm−1) are reported for hemoglobin (Hb) reconstituted with heme that is deuterated at the meso carbon atoms (meso-d4). Spectra were obtained in the deoxy form and in the immediate photoproduct of the carbonmonoxide adduct, HbCO. The isotope shifts permit assignment of two out-of-plane modes, γ6 and γ7, and the in-plane skeletal mode ν8, as well as the well-known iron-histidine [Fe-His] stretching vibration. Important differences between deoxyHb and the immediate photoproduct include 1) a large upshift in the Fe-His frequency, from 216 to 228 cm−1, 2) an upshift in γ6 (349 to 353 cm−1) together with substantial diminution of the ν8 (341 cm−1) intensity, and 3) collapse of two γ7 bands (305 and 296 cm−1) to a single band at 304 cm−1. This last observation implies subunit heterogeneity in deoxyHb but not in the photoproduct. When these bands are monitored in the time-resolved RR spectra following HbCO photolysis, it is seen that subunit heterogeneity is first detectable in the 0.5-μs transient [intermediate S], which has been associated with the initial rearrangement of the subunits to form the T-state contacts, on the basis of ultraviolet RR spectroscopy.1 However the intensification of ν8 does not occur until the 17-μs transient (intermediate T′), in which the T-state contacts are locked in and the Fe-His bond is strained. Implications for the mechanism of Hb allostery are discussed. © 1996 John Wiley & Sons, Inc.

Kinetic description of harmonic instabilities in a planar wiggler free-electron laser

The linearized Vlasov–Maxwell equations are used to investigate harmonic stability properties for a planar wiggler free-electron laser (FEL). The analysis is carried out in the Compton regime for a tenuous electron beam propagating in the z direction through the constant-amplitude planar wiggler magnetic field B0=−Bw cos k0zêx. Transverse spatial variations are neglected (∂/∂x =0=∂/∂y), and the case of an FEL oscillator (temporal growth) is considered. Assuming ultrarelativistic electrons and κ2=a2w/(γ20−1) ≪1, where a2w =e2B2w /m2c4k20 and γ0mc2 is the electron energy, the kinetic dispersion relation is derived in the diagonal approximation for perturbations about general beam equilibrium distribution function G+0(γ0). Because of the wiggler modulation of the axial electron orbits, strong wave–particle interaction can occur for ω≊[k+k0(1+2l)] βFc, where βFc is the axial velocity, ω and k are the wave oscillation frequency and wavenumber, respectively, and l=0, 1, 2, . . . are harmonic numbers corresponding to an upshift in frequency. The strength of the lth harmonic wave–particle coupling is proportional to Kl(b1) =[Jl (b1)−Jl+1 (b1)]2, where b1=(k/8k0)κ2. Assuming that G+0(γ0) is strongly peaked around γ0=γ̂≫1, detailed lth harmonic stability properties are investigated for (a) strong FEL instability corresponding to monoenergetic electrons (Δγ=0), and (b) weak resonant FEL instability corresponding to a sufficiently large energy spread that ‖Im ω/[k+k0(1+2l)] Δvz ‖≪1. For monoenergetic electrons the characteristic maximum growth rate scales as [Kl (b̂1)(1+2l)]1/3, which exhibits a relatively weak dependence on harmonic number l. Here, b̂1= 1/2 [a2w/(2+a2w)] (1+2l). On the other hand, for weak resonant FEL instability, the growth rate scales as Kl (b̂1)/(1+2l), which decreases rapidly for harmonic numbers l≥1.