Changing resonator geometry to boost sound power decouples size and song frequency in a small insect

Despite their small size, some insects, such as crickets, can produce high amplitude mating songs by rubbing their wings together. By exploiting structural resonance for sound radiation, crickets broadcast species-specific songs at a sharply tuned frequency. Such songs enhance the range of signal transmission, contain information about the signaler's quality, and allow mate choice. The production of pure tones requires elaborate structural mechanisms that control and sustain resonance at the species-specific frequency. Tree crickets differ sharply from this scheme. Although they use a resonant system to produce sound, tree crickets can produce high amplitude songs at different frequencies, varying by as much as an octave. Based on an investigation of the driving mechanism and the resonant system, using laser Doppler vibrometry and finite element modeling, we show that it is the distinctive geometry of the crickets' forewings (the resonant system) that is responsible for their capacity to vary frequency. The long, enlarged wings enable the production of high amplitude songs; however, as a mechanical consequence of the high aspect ratio, the resonant structures have multiple resonant modes that are similar in frequency. The drive produced by the singing apparatus cannot, therefore, be locked to a single frequency, and different resonant modes can easily be engaged, allowing individual males to vary the carrier frequency of their songs. Such flexibility in sound production, decoupling body size and song frequency, has important implications for conventional views of mate choice, and offers inspiration for the design of miniature, multifrequency, resonant acoustic radiators.

Monotonic and low cycle fatigue behavior of an O+B2 alloy at high temperatures

Low cycle fatigue behavior of an O+B2 alloy was evaluated at 650 degrees C in ambient atmosphere under fully reversed total axial strain controlled mode. Three different microstructures, namely equiaxed O plus aged B2 (fine O plates in B2 matrix), lenticular O laths plus aged B2 and a pancake composite microstructure comprising equiaxed alpha 2, lenticular O and aged B2, were selected to study the effect of microstructure on low cycle fatigue behavior in this class of alloys. Distinct well-defined trends were observed in the cyclic stress-strain response curves depending on the microstructure. The cyclic stress response was examined in terms of softening or hardening and correlated with microstructural features and dislocation behavior. Fatigue life was analyzed in terms of standard Coffin-Manson and Basquin plots and for all microstructures a prevailing elastic strain regime was identified, with a single slope for microstructures equiaxed and composite and a double slope for lenticular O laths. (c) 2014 Elsevier B.V. All rights reserved.

Stable and low resistive zinc contacts for SnS based optoelectronic devices

The contact behavior of tin mono sulfide (SnS) nanocrystalline thin films with zinc (Zn) and silver (Ag) contacts was studied. SnS films have been deposited on glass substrates by thermal evaporation technique at a growth temperature of 300 degrees C. The as-grown SnS films composed of vertically aligned nanocrystallites with a preferential orientation along the < 010 > direction. SnS films exhibited excellent chemical stoichiometry and direct optical band gap of 1.96 eV. These films also exhibited excellent Ohmic characteristics and low electrical resistivity with Zn contacts. The observed electrical resistivity of SnS films with Zn contacts is 22 times lower than that of the resistivity with Ag contacts. The interfacing analysis reveals the formation of conductive Zn-S layer between SnS and Zn as interfacial layer. (C) 2014 Elsevier B. V. All rights reserved.

Ferrimagnetism and magnetic phase separation in Nd1-xYxMnO3 studied by magnetization and high frequency electron paramagnetic resonance

Ferrimagnetism and metamagnetic features tunable by composition are observed in the magnetic response of Nd1-xYxMnO3, for x=0.1-0.5. For all values of x in the series, the compound crystallizes in orthorhombic Pbnm space group similar to NdMnO3. Magnetization studies reveal a phase transition of the Mn-sublattice below T-N(Mn) approximate to 80 K for all compositions, which, decreases up on diluting the Nd-site with Yttrium. For x=0.35, ferrimagnetism is observed. At 5 K, metamagnetic transition is observed for all compositions x < 0.4. The evolution of magnetic ground states and appearance of ferrimagnetism in Nd1-xYxMnO3 can be accounted for by invoking the scenario of magnetic phase separation. The high frequency electron paramagnetic resonance measurements on x=0.4 sample, which is close to the critical composition for phase separation, revealed complex temperature dependent lineshapes clearly supporting the assumption of magnetic phase separation. (C) 2014 Elsevier B.V. All rights reserved.

A unique strategy towards high dielectric constant and low loss with multiwall carbon nanotubes anchored onto graphene oxide sheets

Multiwall carbon nanotubes (MWNTs) were anchored onto graphene oxide sheets (GOs) via diazonium and C-C coupling reactions and characterized by spectroscopic and electron microscopic techniques. The thus synthesized MWNT-GO hybrid was then melt mixed with 50/50 polyamide6-maleic anhydride-modified acrylonitrile-butadiene-styrene (PA6-mABS) blend to design materials with high dielectric constant (30) and low dielectric loss. The phase morphology was studied by SEM and it was observed that the MWNT-GO hybrid was selectively localized in the PA6 phase of the blend. The 30 scales with the concentration of MWNT-GO in the blends, which interestingly showed a very low dielectric loss (< 0.2) making them potential candidate for capacitors. In addition, the dynamic storage modulus scales with the fraction of MWNT-GO in the blends, demonstrating their reinforcing capability as well.

Synthesis, characterization and low temperature electrical conductivity of Polyaniline/NiFe2O4 nanocomposites

Conducting polymer/ferrite nanocomposites with an organized structure provide a new functional hybrid between organic and inorganic materials. The most popular among the conductive polymers is the polyaniline (PANI) due to its wide application in different fields. In the present work nickel ferrite (NiFe2O4) nanoparticles were prepared by sol-gel citrate-nitrate method with an average size of 21.6nm. PANI/NiFe2O4 nanoparticles were synthesized by a simple general and inexpensive in-situ polymerization in the presence of NiFe2O4 nanoparticles. The effects of NiFe2O4 nanoparticles on the dc-electrical properties of polyaniline were investigated. The structural components in the nanocomposites were identified from Fourier Transform Infrared (FTIR) spectroscopy. The crystalline phase of nanocomposites was characterized by X-Ray Diffraction (XRD). The Scanning Electron Micrograph (SEM) reveals that there was some interaction between the NiFe2O4 particles and polyaniline and the nanocomposites are composed of polycrystalline ferrite nanoparticles and PANI. The dc conductivity of polyaniline/NiFe2O4 nanocomposites have been measured as a function of temperature in the range of 80K to 300K. It is observed that the room temperature conductivity sigma(RT) decreases with increase in the relative content of NiFe2O4. The experimental data reveals that the resistivity increases for all composites with decrease of temperature exhibiting semiconductor behaviour.

Generalized Partial Response Equalization and Data-Dependent Noise Predictive Signal Detection Over Media Models for TDMR

Two-dimensional magnetic recording (2-D TDMR) is an emerging technology that aims to achieve areal densities as high as 10 Tb/in(2) using sophisticated 2-D signal-processing algorithms. High areal densities are achieved by reducing the size of a bit to the order of the size of magnetic grains, resulting in severe 2-D intersymbol interference (ISI). Jitter noise due to irregular grain positions on the magnetic medium is more pronounced at these areal densities. Therefore, a viable read-channel architecture for TDMR requires 2-D signal-detection algorithms that can mitigate 2-D ISI and combat noise comprising jitter and electronic components. Partial response maximum likelihood (PRML) detection scheme allows controlled ISI as seen by the detector. With the controlled and reduced span of 2-D ISI, the PRML scheme overcomes practical difficulties such as Nyquist rate signaling required for full response 2-D equalization. As in the case of 1-D magnetic recording, jitter noise can be handled using a data-dependent noise-prediction (DDNP) filter bank within a 2-D signal-detection engine. The contributions of this paper are threefold: 1) we empirically study the jitter noise characteristics in TDMR as a function of grain density using a Voronoi-based granular media model; 2) we develop a 2-D DDNP algorithm to handle the media noise seen in TDMR; and 3) we also develop techniques to design 2-D separable and nonseparable targets for generalized partial response equalization for TDMR. This can be used along with a 2-D signal-detection algorithm. The DDNP algorithm is observed to give a 2.5 dB gain in SNR over uncoded data compared with the noise predictive maximum likelihood detection for the same choice of channel model parameters to achieve a channel bit density of 1.3 Tb/in(2) with media grain center-to-center distance of 10 nm. The DDNP algorithm is observed to give similar to 10% gain in areal density near 5 grains/bit. The proposed signal-processing framework can broadly scale to various TDMR realizations and areal density points.

Unusual dielectric response in B-site size-disordered hexagonal transition metal oxides

We discover that hexagonal holmium copper titanate (Ho2CuTiO6), has a unique and highly desirable combination of high dielectric constant, low losses, very small temperature coefficient, and low frequency dependence. Our first-principles calculations indicate that these exceptional properties result from a size-difference at the Cu/Ti B-site that suppresses the expected ferroelectric transition, combined with the dominance of intermediate-frequency polar vibrational modes in the dielectric response. Our results suggest that the use of such B-site disorder in alloys of hexagonal transition-metal oxides should generally result in similar robust dielectrics.

A unified model for auxiliary switch commutated DC-DC converters

A novel ZVS auxiliary switch commutated variation for all DGDC converter topologies has been proposed in 2006. With proper designation of the circuit variables (throw current I and the pole voltage V), all these converters are seen to be governed by an identical set of equations. With idealized switches, the steady-state performance is obtainable in an analytical form. The conversion ratio of the converter topologies is obtained. A generalized equivalent circuit emerges for all these converters from the steady-state conversion ratio. It also provides a dynamic model as well. With these generalized steady-state equivalent circuits, small signal analysis of these converters may be carried out readily. It enables one to use the familiar state space averaged results of the standard PWM DGDC converters for the resonant counterparts. Th dc and ac models reveals that dc and low frequency behaviour of the proposed family of converters is similiar to that of its PWM parent

Characterization of cast irons for optimum performance by overall rating method

An experimental investigation was carried out to Characterise the performance of four types of cast iron under adhesive wear, erosive wear, cavitation erosion and low frequency thermal cycling. Results indicate that vermicular graphite iron has the best rating among the cast irons investigate,based on the overall performance as well as cost consideration.

Optimal Power and Noise for Analog and Digital Sections of a Low Power Radio Receiver

We determine the optimal allocation of power between the analog and digital sections of an RF receiver while meeting the BER constraint. Unlike conventional RF receiver designs, we treat the SNR at the output of the analog front end (SNRAD) as a design parameter rather than a specification to arrive at this optimal allocation. We first determine the relationship of the SNRAD to the resolution and operating frequency of the digital section. We then use power models for the analog and digital sections to solve the power minimization problem. As an example, we consider a 802.15.4 compliant low-IF receiver operating at 2.4 GHz in 0.13 μm technology with 1.2 V power supply. We find that the overall receiver power is minimized by having the analog front end provide an SNR of 1.3dB and the ADC and the digital section operate at 1-bit resolution with 18MHz sampling frequency while achieving a power dissipation of 7mW.