Surface vibrational modes in disk-shaped resonators

The natural frequencies and distributions of displacement components for the surface vibrational modes in thin isotropic elastic disks are calculated. In particular, the research is focused on even solutions for low-lying resonant vibrations with large angular wave numbers. Several families of modes are found which are interpreted as modified surface modes of an infinitely long cylinder and Lamb modes of a plate. The results of calculation are compared with the results of the experimental measurements of vibrational modes generated by means of resonant excitation in duraluminum disk with radius of ≈90 mm and thickness of 16 mm in the frequency range of 130–200 kHz. An excellent agreement between the calculated and measured frequencies is found. Measurements of the structure of the resonant peaks show splitting of some modes. About a half of the measured modes has splitting Δ_fsplit/_fmode$\mathrm{\Delta }{f}_{\mathrm{split}}/f_{\mathrm{mode}}$ at the level of the order of 10⁻⁵. The Q-factors of all modes measured in vacuum lie in the interval (2…3) × 10⁵. This value is typical for duraluminum mechanical resonators in the ultrasonic frequency range.     

Adjustment on subjective annoyance of low frequency noise by adding additional sound

Structure-borne noise originating from a heat pump unit was selected to study the influence on subjective annoyance of low frequency noise (LFN) combined with additional sound. Paired comparison test was used for evaluating the subjective annoyance of LFN combined with different sound pressure levels (SPL) of pink noise, frequency-modulated pure tones (FM pure tones) and natural sounds. The results showed that, with pink noise of 250-1000 Hz combined with the original LFN, the subjective annoyance value (SAV) first dropped then rose with increasing SPL. When SPL of the pink noise was 15-25 dB, SAV was lower than that of the original LFN. With pink noise of frequency 250-20,000 Hz added to LFN, SAV increased linearly with increasing SPL. SAV and the psychoacoustic annoyance value (PAV) obtained by semi-theoretical formulas were well correlated. The determination coefficient (R²) was 0.966 and 0.881, respectively, when the frequency range of the pink noise was 250-1000 and 250-20,000 Hz. When FM pure tones with central frequencies of 500, 2000 and 8000 Hz, or natural sounds (including the sound of singing birds, flowing water, wind or ticking clock) were, respectively, added to the original sound, the SAV increased as the SPL of the added sound increased. However, when a FM pure tone of 15 dB with a central frequency of 2000 Hz and a modulation frequency of 10 Hz was added, the SAV was lower than that of the original LFN. With SPL and central frequency held invariable, the SAV declined primarily when modulation frequency increased. With SPL and modulation frequency held invariable, the SAV became lowest when the central frequency was 2000 Hz. This showed a preferable correlation between SAV and fluctuation extent of FM pure tones.     

Effect of continuous layer in CGC perpendicular recording media

The effect of continuous layer on CoCrPt–SiO₂ granular layer is studied in coupled granular continuous (CGC) perpendicular recording media. In the cross-section transmission electron microscope (TEM) observation, magnetic grain in the granular layer shows columnar structure, while Co/Pd multilayer shows continuous layer. The plane-view TEM image of the granular layer shows well-isolated grain structure with average grain size of around 6 nm, and grain-to-grain separation width of around 2 nm. Therefore, the interactions among the grains are negligible (J∼0). By depositing a continuous layer on a CoCrPt–SiO₂ granular layer, the grains in the granular layer are magnetically coupled through capping layer that leads to the suppression of magnetic anisotropy dispersion. This CGC structure reduces the coercivity dispersion (Δ_Hc/_Hc$\mathrm{\Delta }{H}_{\mathrm{c}}/H_{\mathrm{c}}$) from 0.26 to 0.15 and saturation field (H_s) from 10.4 to 6.7 kOe. The reduction of H_s and Δ_Hc/_Hc$\mathrm{\Delta }{H}_{\mathrm{c}}/H_{\mathrm{c}}$ improves the OW by 21.3 dB. The small Δ_Hc/_Hc$\mathrm{\Delta }{H}_{\mathrm{c}}/H_{\mathrm{c}}$ also maintains SNR of CGC media with strong magnetic exchange coupling. Furthermore, the coupling of grains through continuous layer enlarges the magnetic nucleation field (H_n) from 0.4 to −1.7 kOe. Consequently, CGC media shows better thermal stability compared to non-CGC media.     

Effect of Co layer thickness on the magnetic properties of Tb30Co70/SiNx/Co thin films

The SiN_x (20 nm)/Tb₃₀Co₇₀ (90 nm)/SiN_x (5 nm)/Co (3–37 nm)/SiN_x (10 nm)/Si multilayer films are deposited on naturally oxidized Si wafer by magnetron sputtering. The saturation magnetization (M_s) of the multilayer films is increased with the thickness of high M_s ferromagnetic Co layer. The perpendicular coercivity (_Hc⊥$H_{{\mathrm{c}}^{\perp }}$) value is increased with Co layer thickness as the thickness of the Co layer is lower than 15 nm and then decreases drastically when the thickness of the Co layer further increased. The increase of the _Hc⊥$H_{{\mathrm{c}}^{\perp }}$ value is owing to the interlayer exchange effect [Li Zhang, Physica B 390 (2007) 373] between TbCo and Co layers. Co under-layer with in-plane magnetic anisotropy would pin the magnetic moment of the TbCo layer near by the Co layer and cause the value of _Hc⊥$H_{{\mathrm{c}}^{\perp }}$ to increase. However, as the Co layer is thicker than a critical thickness, the _Hc⊥$H_{{\mathrm{c}}^{\perp }}$ value of the multilayer film would decrease. Therefore, the Co layer with in-plane magnetic anisotropy and soft magnetic properties is expected to dominate the magnetic properties of the multilayer films.     

Magnetic and transport properties of single-crystal Yb3Cu4Ge4

The magnetic and transport properties of single-crystal Yb₃Cu₄Ge₄ with the Gd₃Cu₄Ge₄-type orthorhombic structure are presented. Magnetization along the b-axis at 2 K saturates to 2.8_μB/Yb$2.8{\mu }_{\mathrm{B}}/\mathrm{Yb}$ at 3 kOe, while that along the a- and c-axes at 2 K are gradually increasing to the value of 1.5_μB/Yb$1.5{\mu }_{\mathrm{B}}/\mathrm{Yb}$ and 0.39_μB/Yb$0.39{\mu }_{\mathrm{B}}/\mathrm{Yb}$ at 50 kOe, respectively. The electrical resistivity within the ab-plane shows a metallic behavior in contrast to a broad maximum at around 30 K for that along the c-axis. Each resistivity for the principal axis suddenly decreases below 8 K. The specific heat shows a λ-type$\lambda \mathrm{-}\mathrm{type}$ sharp peak at 7.8 K. The electronic specific heat coefficient is estimated to be 29.4 mJ/mol Yb K² by fitting the magnetic part of the specific heat below 3 K. The magnetic entropy released up to T_C is 68% of that of R ln 2, expected for the doublet ground state. It is revealed that Yb₃Cu₄Ge₄ is categorized to a weak heavy-fermion system showing a ferromagnetic transition at 7.8 K with uniaxial anisotropy along the b-axis.     

Microwave performance enhancement in Double and Single Gate HEMT with channel thickness variation

In Single Gate HEMT (SGHEMT) shortening of gate length (_Lg)$\left(L_g\right)$ below 100 nm leads to reduction in Transconductance (_gm)$\left(g_m\right)$, which reduces the unloaded voltage gain (_gm/_gd)$(g_m/g_d)$ of the device, thereby reducing the maximum frequency of oscillation (_fmax)$\left(f_{max}\right)$. The main reason for this reduction in _gm$g_m$ with _Lg$L_g$ in the Single Gate HEMT (SGHEMT) is its inability to maintain the desired channel aspect ratio (α$\alpha$). At such a miniaturization level, α$\alpha$ not only depends on the channel depth (d)$\left(d\right)$ but also on the channel thickness (_dc)$\left(d_c\right)$ of the device [5]. Moreover, the variation of _dc$d_c$ may switch the device characteristics from quantum regime to classical regime  and . The Double Gate HEMT (DGHEMT)  and  has emerged as a solution for further reduction in _Lg$L_g$ and provides enhancements over SGHEMT by virtue of its double gate and also for same _dc$d_c$ due to double heterojunctions, which virtually increases the value of α$\alpha$. In the present work, extensive simulation work has been carried out using ATLAS device simulator [35] in order to study the effect of _dc$d_c$ and _Lg$L_g$ on DGHEMT and SGHEMT. An analytical model has also been proposed for SGHEMT and DGHEMT to incorporate the effect of variation of _dc$d_c$ and _Lg$L_g$.     

Single-domain versus two-domain configuration in thin ferromagnetic prisms

Thin ferromagnetic elements in the form of rectangular prisms are theoretically investigated in order to study the transition from single-domain to two-domain state, with changing the in-plane aspect ratio p  . We address two main questions: first, how general is the transition; second, how the critical value _pc$p_{\mathrm{c}}$ depends on the physical parameters. We use two complementary methods: discrete-lattice calculations and a micromagnetic continuum approach. Ultrathin films do not appear to split in two domains. Instead, thicker films may undergo the above transition. We have used the continuum approach to analyze recent magnetic force microscopy observations in 30 nm-thick patterned permalloy elements, finding a good agreement for _pc$p_{\mathrm{c}}$.     

Local anodization of permalloy film by atomic force microscope

Local anodization on a permalloy (_Ni80Fe20)${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20})$ thin film by an atomic force microscope (AFM) in air was studied. Fabrication of uniform structure on the permalloy film was difficult in comparison with that on a Si(1 0 0) substrate. On the permalloy film, threshold voltage for the AFM anodization increased until 3 h after exposure to air. With passage of time, I–V$I–V$ curves on the permalloy film also changed from metallic behavior to insulating one. In addition, I–V$I–V$ curves varied at positions on the permalloy film. The oxide layer with time- and position-dependencies can induce non-uniform structure in AFM anodization. However, uniformity of structure was able to be improved by using method of fabrication of dots.     

Three phases of the minority game

We define three phases of the minority game according to the value ρ=2^M/N$\rho =2^M/N$, the ratio of the number of entries in a strategy to the number of agents. The time sequence of the population in one room has distinct feature in different phase. It shows quasi-periodic structure in the first phase where ρ<_ρc1$\rho <{\rho }_{c_1}$. In the second phase, _ρc1<ρ<_ρc2${\rho }_{c_1}<\rho <{\rho }_{c_2}$, agents coordinate better and better as ρ   gets larger. In the third phase, ρ$\rho$>_ρc2${\rho }_{c_2}$, the system is able to reach its best performance in reducing the population variance. The crucial factor, which hinders the system to reach its best performance in the first and second phases, is the number of agents who switch strategy at the same time. When ρ<_ρc2$\rho <{\rho }_{c_2}$, the constraint that bound 2^M predictions in a strategy is small, so that too many agents will switch to a better strategy simultaneously. As a result, they form a majority group and are more likely to lose. We give analytical approximate formulas for the population variance in the first and third phases. We have also determined the phase-changing point _ρc1${\rho }_{c_1}$.     

Shot noise in the hybrid triple-quantum-dot interferometer coupled to superconductor and normal terminals

The shot noise of a hybrid triple-quantum-dot (TQD) interferometer has been investigated by employing the nonequilibrium Green's function method, and the general shot noise formula has been derived. The oscillation behaviors of transmission coefficients and shot noise versus the Aharonov–Bohm phase ?   exhibit asymmetric Fano resonance structure and blockade effect. Sub-Poissonian and super-Poissonian behaviors of shot noise appear in different regimes of terminal bias e_Vγ$e{V}_{\gamma }$ contributed by the Andreev reflection, and correlation of Andreev tunneling with the normal electron transport. The inverse resonance and resonance structures emerge in the shot noise and Fano factor with respect to one of the gate voltages in different regimes of e_Vγ$e{V}_{\gamma }$. The asymmetric structure can be enhanced by modifying the energy levels and gate biases of the TQD. The self-correlation and cross-correlation of current components contribute to the enhancement and suppression of shot noise.     

Entanglement thresholds for displaying the quantum nature of teleportation

A protocol for transferring an unknown single qubit state evidences quantum features when the average fidelity of the outcomes is, in principle, greater than 2/3$2/3$. We propose to use the probabilistic and unambiguous state extraction scheme   as a mechanism to redistribute the fidelity in the outcome of the standard teleportation when the process is performed with an X$X$-state as a noisy quantum channel. We show that the entanglement of the channel is necessary but not sufficient in order for the average fidelity f_X$f_X$ to display quantum features, i.e., we find a threshold C_X$C_X$ for the concurrence of the channel. On the other hand, if the mechanism for redistributing fidelity is successful then we find a filterable outcome with average fidelity f_X,0$f_{X,0}$ that can be greater than f_X$f_X$. In addition, we find the threshold concurrence of the channel C_X,0$C_{X,0}$ in order for the average fidelity f_X,0$f_{X,0}$ to display quantum features and surprisingly, the threshold concurrence C_X,0$C_{X,0}$ can be less than C_X$C_X$. Even more, we find some special cases for which the threshold values become zero.     

Modal content of noise generated by a coaxial jet in a pipe

The problem investigated was that of noise generated by air flow through a coaxial obstruction in a long, straight pipe of inside diameter, D = 97 mm. Downstream modal pressure spectra in the 200–6000 Hz frequency range were measured by a new technique [1] for orifices and nozzles of diameter d where $\text{0·03 ? (}\text{d}\text{D}\text{) ? 0·52}$. The Mach numbers of the flow through the restrictions ranged from 0·15 to choked conditions. The shape of the modal frequency spectrum was found to be determined by the frequency ratio $\text{f}{}_{\mathrm{r}}\text{=}\text{He}\text{St}\text{=}\text{U}{}_{\mathrm{i}}\text{D}\text{a}{}_0\text{d}$, where U_i is the jet velocity and a₀ is the speed of sound in the gas downstream of the restriction. This parameter is the ratio of two non-dimensional frequencies: namely, He, which controls acoustic propagation inside circular ducts, and St, which scales the jet noise spectrum shape. At low f_r(<3) the higher modes dominate the noise spectrum above their cut-off frequencies, while for higher f_r all modes are approximately of equal amplitude. The nature of large scale turbulence structures in the region of the jet near the nozzle exit may be used to explain these phenomena. The measured modal pressure spectra were converted to modal power spectra and integrated over the frequency range 200–6000 Hz. The acoustic efficiency levels (acoustic power normalized by jet kinetic energy flow), when plotted vs. jet Mach number, depend strongly on the ratio of restriction diameter to pipe diameter ($\text{d}\text{D}$). Dividing the efficiency levels by the area ratio, $\text{(}\text{d}\text{D}\text{)}{}^2$, correlated the results over a moderate range of ($\text{d}\text{D}$).     

Thermodynamic geometry of a kagome Ising model in a magnetic field

We derived the thermodynamic curvature of the Ising model on a kagome lattice under the presence of an external magnetic field. The curvature was found to have a singularity at the critical point. We focused on the zero field case to derive thermodynamic curvature and its components near the criticality. According to standard scaling, scalar curvature R   behaves as |β−_βc|^α−2${|\beta -{\beta }_c|}^{\alpha -2}$ for α>0$\alpha >0$ where β is the inverse temperature and α is the critical exponent of specific heat. In the model considered here in which α is zero, we found that R   behaves as |β−_βc|^α−1${|\beta -{\beta }_c|}^{\alpha -1}$.     

Magnetic properties of two-dimensional charged spin-1 Bose gases

Within the mean-field theory, we investigate the magnetic properties of a charged spin-1 Bose gas in two dimensions. In this system the diamagnetism competes with paramagnetism, where the Landé factor g   is introduced to describe the strength of the paramagnetic effect. The system presents a crossover from diamagnetism to paramagnetism with the increasing of the Landé factor. _gc$g_c$ denotes the critical value of the Landé factor. We get the same value of _gc$g_c$ both in the low temperature and strong magnetic field limit. Our results also show that in very weak magnetic field no condensation happens in the two-dimensional charged spin-1 Bose gas.     

Pressure dependence of the irradiation-induced ferromagnetism in Fe–Ni invar alloys

Pressure dependence of the irradiation-induced ferromagnetism recently found in Fe–Ni invar alloys was investigated under hydrostatic pressures up to 7.5 GPa. A rectangular sheet of Fe–30.2 at% Ni invar alloy was irradiated with 80 MeV Xe ions. The range was much smaller than the thickness of the sample. The Curie temperature of the irradiated part increased by 63 K, and the absolute value of the pressure coefficient, dT_C/dp   was smaller than that of non-irradiated part. The relation p≈(_TC0-_TC)ⁿ$p\approx (T_{{\mathrm{C}}_0}-T_{\mathrm{C}}{)}^n$ holds with n=2$n=2$ for both non-irradiated and irradiated part. The itinerant character was not so much modified by irradiation.     

Emergence of helicity ±2 modes (gravitons) from qubit models

We construct two quantum qubit models (or quantum spin models) on three-dimensional lattice in space, L-type model and N-type model. We show that, under a controlled approximation, all   the low energy excitations of the L-type model are described by one set of helicity ±2 modes with ω∝k³$\omega \propto k^3$ dispersion. We also argue that all   the low energy excitations of the N-type model are described by one set of helicity ±2 modes with ω∝k$\omega \propto k$ dispersion. In both model, the low energy helicity ±2 modes can be described by a symmetric tensor field _hμν$h_{\mu \nu }$ in continuum limit, and the gaplessness of the helicity ±2 modes is protected by an emergent linearized diffeomorphism gauge symmetry _hμν→_hμν+_∂μfν+_∂νfμ$h_{\mu \nu }\to h_{\mu \nu }+{\partial }_{\mu }{f}_{\nu }+{\partial }_{\nu }{f}_{\mu }$ at low energies. Thus the linearized quantum gravity emerge from our lattice models  . It turns out that the low energy effective Lagrangian density of the L-type model is invariant under the linearized diffeomorphism gauge transformation. Such a property protects the gapless ω∝k³$\omega \propto k^3$ helicity ±2 modes. In contrast, the low energy effective Lagrangian of the N-type model changes by a boundary term under the linearized diffeomorphism gauge transformation. Such a property protects the gapless ω∝k$\omega \propto k$ helicity ±2 modes. From many-body physics point of view, the ground states of the our two qubit model represent new states of quantum matter, whose low energy excitations are all described by one set of gapless helicity ±2 modes.     

The Bethe lattice treatment of sound attenuation for a spin- 3/2 Ising model

The sound attenuation phenomena is investigated for a spin- 3/2 Ising model on the Bethe lattice in terms of the recursion relations by using the Onsager theory of irreversible thermodynamics. The dependencies of sound attenuation on the temperature (T$T$), frequency (w$w$), Onsager coefficient (γ$\gamma$) and external magnetic field (H$H$) near the second-order (_Tc)$\left(T_c\right)$ and first-order (_Tt)$\left(T_t\right)$ phase transition temperatures are examined for given coordination numbers q$q$ on the Bethe lattice. It is assumed that the sound wave couples to the order-parameter fluctuations which decay mainly via the order-parameter relaxation process, thus two relaxation times are obtained and which are used to obtain an expression for the sound attenuation coefficient (α)$\left(\alpha \right)$. Our investigations revealed that only one peak is obtained near _Tt$T_t$ and three peaks are found near _Tc$T_c$ when the Onsager coefficient is varied at a given constant frequency for q=3$q=3$. Fixing the Onsager coefficient and varying the frequency always leads to two peaks for q=3,4$q=3,4$ and 6 near _Tc$T_c$. The sound attenuation peaks are observed near _Tt$T_t$ at lower values of external magnetic field, but as it increases the sound attenuation peaks decrease and eventually disappear.     

The chiral phase transition of QED3 around the critical number of fermion flavors

At zero temperature and density, the nature of the chiral phase transition in QED₃ with N_f$N_f$ massless fermion flavors is investigated. To this end, in Landau gauge, we numerically solve the coupled Dyson–Schwinger equations for the fermion and boson propagator within the bare and simplified Ball–Chiu vertices separately. It is found that, in the bare vertex approximation, the system undergoes a high-order continuous phase transition from the Nambu–Goldstone phase into the Wigner phase when the number of fermion flavors N_f$N_f$ reaches the critical number N_f,c$N_{f,c}$, while the system exhibits a typical characteristic of second-order phase transition for the simplified Ball–Chiu vertex.