Values Of Kt Research Articles

Sound Field Distribution Research of Polymer Materials Ultrasonic Probe Chip Polymer Materials

Compared to the probe based on conventional piezoelectric ceramic, the high-performance ultrasonic probe made from polymer composite materials is much better, which has characteristics such as high sensitivity, wide bandwidth and good directional. And probe’s thickness electromechanical coupling coefficient KT value is up to 68%, which means it can reduce the crosstalk effectively to the phased array probe. In industrial, due to its high bandwidth, it has obvious advantages when used in coarse-grained materials testing and high-precision thickness measurement. In the medical field, ultrasound will reflex significantly at the impurities or the interfaces, and produce the Doppler effect in the flow of blood. Based on the sound field distribution comparative study of polymer materials ultrasonic probe chip, this paper proposed some polymer new applications in ultrasonic testing field.

How does Hemoglobin Create Such Diverse Functionality of Physiological Relevance?

Hemoglobin (Hb) without heterotropic effectors or stripped Hb, is an O2-carrier with a high-affinity (P50 100 mmHg, KR from 10 to 0.005 /mmHg, KT from 0.3 to 0.005 /mmHg, KR/KT from 1 to >500, and ΔH+ up to −4.4 H+/Hb. Such enhanced functionality of Hb of physiological relevance is accomplished through pH-dependent asymmetric binding of heterotropic effectors to R(oxy)- and T(deoxy)-quaternary structures of Hb, which cause pH-dependent differential modulations/reductions of KR and KT, respectively. No changes in high-resolution static crystallographic T(deoxy)- and R(oxy)-quaternary and tertiary structures of Hb and their heme environment, as well as the axial coordination structures of the deoxy-heme (νFe-His = 215 /cm) and the oxy-heme (νFe-O2 = 567/cm) in solution, are observed, despite KT and KR values are changed as much as 100- and 2,000-folds, respectively. Thus, the assumption that the low-affinity state is caused by the inter-dimeric salt-bridge-linked constraints, the out-of-plane shift of the heme Fe, and the allosteric core constraint in the T(deoxy)-Hb is no longer valid. Although these constraints are completely absent in R(oxy)-Hb, its O2-affinity is modulated as much as 2,000-folds by its interaction with heterotropic effectors. The effector-linked modulation of thermal fluctuation of the protein may be responsible.

Growth and electrical properties of 0.95Na0.5Bi0.5TiO3–0.05K0.5Bi0.5TiO3 lead-free piezoelectric crystal by the TSSG method

0.95Na0.5Bi0.5TiO3–0.05K0.5Bi0.5TiO3 lead-free piezoelectric single crystal with rhombohedral structure was grown by the top-seeded solution growth method. The temperature dependence of dielectric constant and loss, polarization hysteresis loops, the optimum poling condition and the electromechanical coupling property were investigated for the 〈100〉-oriented as-grown crystal. The curves ε(T) show two anomalies, which are related to the two phase transformations at the temperature range of 130–340°C. The piezoelectric constant d33 and electromechanical coupling coefficient kt for the 〈001〉-oriented crystal at room temperature reached 147pC/N and 0.52, respectively. The value of kt demonstrated a relatively stable thermal electromechanical coupling property over the temperature range of 15–130°C.

Determination of a large tilting pad thrust bearing angular stiffness

A finite difference procedure to solve the Reynolds' and energy equations for the pressure and temperature distribution across the film is described. The film temperature takes viscosity variation and hot oil carryover into consideration. A coupled finite element method using ANSYS determines the important pad deformation. Torques for pad positions 1and 2 are calculated. The angular stiffness pertaining to the 2–1 pair is calculated for 0.5–20% variation of ho. The values of Kt⁎ converge asymptotically. The novel interpolation of a single pad's angular stiffness results to determine the characteristics of the bearing are highlighted. Unlike in earlier studies this analysis is helpful in understanding the factors causing pad flutter and dynamics of the bearing elements in hydrogenerators.

The Appearance of Type Ia Supernova Progenitors: If Not SSSs, then What Do They Look Like?

Abstract“What do the progenitors of Type Ia supernovae (SNe Ia) look like? How can we hope to find them?” We focus on the epoch during which mass is incident on a white dwarf (WD) at high rates (> 10−7M⊙ yr−1). Such epochs are expected in single-degenerate (SD) progenitors, double-degenerate (DD) progenitors, and in a wide range of binaries with WDs that will not achieve the Chandrasekhar mass, MCh. High-rate accretion onto a WD produces high luminosities through accretion alone; in addition, most calculations show that quasisteady or episodic nuclear burning can occur, increasing the luminosity by more than an order of magnitude. If the photosphere is not much larger than the WD, the emission will have values of kT in the range of tens of eV, and the source will appear as a luminous supersoft x-ray source (SSS). Studies of local SSSs that are good candidates for nuclear-burning WDs (NBWDs) suggest that many have low duty cycles of SSS activity. This is consistent with the fact that binary WD models predict about 100 times as many SSSs in external galaxies of all types as are actually detected. Interstellar absorption does not appear to be the problem. Instead, it is likely that the ~1037−1038 erg s−1 emitted by NBWDs emerges in other wavebands. The challenge we face is to search for highly luminous systems within the Milky Way and nearby galaxies that have unusual properties consistent with NBWDs, and inconsistent with other physical models. Model tests can then be conducted for individual candidates, allowing us to identify large numbers of progenitors years before explosion.

Performance of the Wave Energy Dissipation of a Floating Breakwater with Truss Structures and the Quantification of Transmission Coefficients

The wave absorption performance of a new type of steel floating breakwater with truss (FBT), which is composed of a box-type pontoon and truss structures, has been investigated experimentally. The truss structures are attached to the front and the rear of the pontoon, and exaggerate wave energy dissipation due to wave breaking. Flow visualization has revealed that the front truss breaks the incident waves and effectively converts wave energy to turbulent energy. Image analysis of the motions of the FBT and determination of the transmission coefficient Kt showed efficient dissipation of wave energy resulting from the truss structure. Kt is also discussed and quantified with the aid of dimensional analysis. Values of Kt are plotted against the ratio of the water depth h to the wavelength of incident waves L, and the profiles obtained are normalized by introducing values of h/L at which Kt equals 0.5, i.e., (h/L)0.5. Normalization gives a universal empirical expression for Kt, and empirical expressions of (h/L)0.5 are also obtained by independently changing the shape parameters and the wave steepness. A graphic chart of (h/L)0.5 is provided so Kt of the FBT can be evaluated easily. This data-reduction method developed for the quantification of Kt may be applicable for other floating breakwaters as well as for this new type.

Growth and orientation dependence of electrical properties of 0.92Na0.5Bi0.5TiO3-0.08 K0.5Bi0.5TiO3 lead-free piezoelectric single crystal

A 0.92Na0.5Bi0.5TiO3-0.08 K0.5Bi0.5TiO3 (0.92NBT-0.08KBT) lead-free piezoelectric single crystal with dimensions of Φ 35 × 10 mm was successfully grown by the top-seeded solution growth method. The effective segregation coefficient for K was calculated to be 0.27. An x-ray powder diffraction measurement showed that the as-grown crystal possesses a rhombohedral perovskite structure at room temperature. The room-temperature dielectric constants for poled 〈001〉, 〈110〉, and 〈111〉 oriented crystal samples are found to be 683, 567, and 435 at 1 kHz, respectively. The (Tm, ɛm) values for 〈001〉, 〈110〉, and 〈111〉 oriented crystals are (316 °C, 4318), (317 °C, 4160), and (318 °C, 4348) at 1 kHz, which indicate that the dielectric parameters of the as-grown crystals show weaker anisotropy. The curves, ɛ(T), for the three crystallographic orientations show two anomalies at about 170 and 320 °C, respectively, relating to the ferroelectric-antiferroelectric phase and the antiferroelectric-paraelectric phase. There is a thermal hysteresis, ΔT ≈ 35 °C for the ferroelectric-antiferroelectric phase transformation between heating and cooling. The antiferroelectric phase, the thermal hysteresis, and the dielectric relaxor behavior around 170 °C can be attributed to the formation of an intermediate orthorhombic modulated phase at 170–320 °C. For the 〈001〉, 〈110〉, and 〈111〉 crystal samples, the room-temperature piezoelectric constants, d33, reach 175, 130, and 70 pC/N, respectively. The remanent polarization for the 〈001〉, 〈110〉, and 〈111〉 crystal samples are 8.1, 10.8, and 13.5 μC/cm2, respectively, and the ratio is 1:1.33:1.67, close to 1:2:3. The diffusive factors, α, are found to be 1.94, 1.91, and 1.50 for the 〈001〉, 〈110〉, and 〈111〉 oriented crystal samples, which indicate that the antiferroelectric-paraelectric phase transition of the as-grown 0.92NBT-0.08KBT crystal is a strong diffuse one. The electromechanical coupling coefficients for the 〈001〉, 〈110〉, and 〈111〉 oriented 0.92NBT-0.08KBT crystals at room temperature are 52, 50, and 48%, respectively. The values of kt for the three main crystallographic orientations change slightly with the increase of temperature from 15 to 140 °C, demonstrating a relatively stable thermal electromechanical coupling property.

Lead-Free BSZT/Epoxy 1-3 Composites for Ultrasonic Transducer Applications

With high piezoelectric coefficient (d33> 300 pC/N) and electromechanical coupling factor (kt = 0.45), lead-free barium strontium zirconium titanate ((Ba0.95Sr0.05) (Zr0.05Ti0.95) O3, abbreviated as BSZT)was used to fabricate BSZT/epoxy 1-3 composites with different volume fractions of BSZT ranging from 0.55 - 0.85. The electromechanical properties of the 1-3 composites were determined by the resonance technique. It was found that the theoretical modeling of the 1-3 composites matches quite well with the measured material properties.The 1-3 composite with f = 0.65 was chosen to be fabricated as a transducer due to its comparatively high value of kt. The BSZT/epoxy 1-3 composite transducer demonstrates large bandwidth with good sensitivity, suggesting high potential in biomedical applications.

Fabrication and Piezoelectric Anisotropy of PFCs

PZT fibers were fabricated by extruding a mixture of PZT powder and sol. 1-3 piezoelectric composites and AFC were fabricated by arranging-cast technique. The piezoelectric anisotropy of piezoelectric composites was characterized. For PZT ceramic disk, the value of kt<kp, the piezoelectric response was mainly in radial direction. For 1-3 composites, the value of kt>kp, the piezoelectric response was mainly in thickness direction. The sensing and actuating experiment of AFCs indicated that the anisotropy of piezoelectric response was also obvious. The signal intensity of piezoelectric response was stronger in the direction of fiber length in both sensing and actuating experiment.

The general behavior of NLO unintegrated parton distributions based on the single-scale evolution and the angular ordering constraint

To overcome the complexity of generalized two hard scale (kt,μ) evolution equation, well known as the Ciafaloni, Catani, Fiorani and Marchesini (CCFM) evolution equations, and calculate the unintegrated parton distribution functions (UPDF), Kimber, Martin and Ryskin (KMR) proposed a procedure based on (i) the inclusion of single-scale (μ) only at the last step of evolution and (ii) the angular ordering constraint (AOC) on the DGLAP terms (the DGLAP collinear approximation), to bring the second scale, kt into the UPDF evolution equations. In this work we intend to use the MSTW2008 (Martin et al.) parton distribution functions (PDF) and try to calculate UPDF for various values of x (the longitudinal fraction of parton momentum), μ (the probe scale) and kt (the parton transverse momentum) to see the general behavior of three-dimensional UPDF at the NLO level up to the LHC working energy scales (μ2). It is shown that there exits some pronounced peaks for the three-dimensional UPDF(fa(x,kt)) with respect to the two variables x and kt at various energies (μ). These peaks get larger and move to larger values of kt, as the energy (μ) is increased. We hope these peaks could be detected in the LHC experiments at CERN and other laboratories in the less exclusive processes.

Bioactivity of Argentinean Essential Oils Against Permethrin-Resistant Head Lice,Pediculus humanus capitis

Infestation with the head louse, Pediculus humanus capitis De Geer (Phthiraptera: Pediculidae), is one of the most common parasitic infestation of humans worldwide. Traditionally, the main treatment for control of head lice is chemical control that is based in a wide variety of neurotoxic synthetic insecticides. The repeated overuse of these products has resulted in the selection of resistant populations of head lice. Thus, plant-derived insecticides, such as the essential oils seem to be good viable alternatives as some have low toxicity to mammals and are biodegradable. We determined the insecticidal activity of 25 essential oils belonging to several botanical families present in Argentina against permethrin-resistant head lice. Significant differences in fumigant activity against head lice were found among the essential oils from the native and exotic plant species. The most effective essential oils were Cinnamomum porphyrium, followed by Aloysia citriodora (chemotype 2) and Myrcianthes pseudomato, with KT50 values of 1.12, 3.02 and 4.09; respectively. The results indicate that these essential oils are effective and could be incorporated into pediculicide formulations to control head lice infestations once proper formulation and toxicological tests are performed.

Dielectric, electromechanical coupling properties of Mn-doped Na0.5Bi0.5TiO3–BaTiO3 lead-free single crystal

Mn-doped 0.948Na0.5Bi0.5TiO3–0.052BaTiO3 (NBBT94.8/5.2) lead-free single crystal with excellent piezoelectric and electromechanical coupling properties was successfully grown by top-seeded solution growth method (TSSG). X-ray powder diffraction measurement showed that the as-grown crystal possesses rhombohedral perovskite structure. The Mn-doped NBBT94.8/5.2 single crystal exhibits apparent diffused dielectric behavior, in which the diffusiveness index α is 1.99 for the [001]-oriented crystal planes. A notable thermal hysteresis is disclosed for the rhombohedral-tetragonal phase transition between heating and cooling studies in the dielectric property. The electromechanical coupling coefficients of Mn-doped NBBT94.8/5.2 were determined experimentally using the resonance–antiresonance technique. The room-temperature electromechanical coupling coefficients k 31, k 31〈110〉, k 33, k t are 35.9%, 35.5%, 68.5%, 58.7%, respectively. The room-temperature piezoelectric constants d 33, d 31 reach as high as 457, 138 pC/N respectively. The value of k t increases slightly with the increase of temperature from −80 to 70°C, demonstrating a relatively stable thermal electromechanical coupling property.

New spot-on formulation containing chlorpyrifos for controlling horn flies on cattle: laboratory model of insecticide release and field trial

A highly viscous formulation containing chlorpyrifos (RET) was evaluated under laboratory, pre-field, and field conditions, and compared against ear tags with organophosphorus insecticides. Laboratory bioassays were performed using Musca domestica L. and a thin layer chromatography (TLC) plate of reversed phase silica gel modeling a lipophilic surface. Insects were exposed to the insecticide vapors of both formulations, directly and indirectly to test for lateral diffusion. Knockdown time 50% (KT(50)) values were determined as toxicological indicators of insecticide release. Minimum KT(50) values of the direct effect of both formulations on horn flies were reached 4 weeks after being applied. The KT(50) effect of migrated insecticides showed that RET formulation had a maximal effectiveness between the fourth and tenth last week. The KT(50) effect of the insecticide migrating from ear tags decreased during the last 2 weeks of the experiment, and the KT(50) effect of the laterally migrated insecticide was significantly higher for the RET formulation during this period. A pre-field bioassay was performed by exposing pieces of rabbit leather with both formulations and recording the KT(50). At the end of the experiment, the KT(50) effect of laterally migrated insecticide was significantly higher for the RET formulation. Regarding vapor emission, as a general trend the KT(50) effect of ear tags was greater than for the RET formulation. To evaluate the horn fly infestation in the field bioassays, photographs of the animal were taken. The results shows that RET provided significant control for 11 weeks while the ear tags provided protection until the 12th week.

Diaspore crystal structure and compressibility at high pressures and high temperature

We have determined the unit-cell parameters of diaspore α-AlO(OH) at high pressures (13.5–27.8 GPa) and at high temperature (1900 K). Experimental data are compared with the theoretically predicted crystal structure variations derived from density functional theory (DFT) calculations. The experimental analysis establishes that the a axial direction is more compressible than the b and c axial directions in the low-pressure range (13.5–18 GPa) and at 1900 K, whereas all three directions show similar behaviors in the high-pressure range (18–27.8 GPa). The diaspore isothermal bulk modulus KT values are 137.6 GPa, 124.8 GPa, and 141.3 GPa, respectively, at 300 K, at 1900 K, and again at 300 K after quenching. By comparison, the diaspore isothermal bulk modulus KT computed at 300 K and at ambient pressure in the framework of the plane-wave pseudopotential approach is equal to 129.3 GPa.

Relationship between installation torque and uplift capacity of deep helical piles in sand

The empirical torque correlation factor (KT), which relates the uplift capacity to the installation torque of helical piles, is routinely used as an on-site instrument for quality control with this type of foundation. This paper presents a theoretical relationship between uplift capacity and installation torque of deep helical piles in sand. An experimental program, including centrifuge and direct shear interface tests, was carried out to validate this expression. The experimental results were compared with the values predicted by the suggested approach and showed good agreement. As the developed model depends on the residual interface friction angle (δr) between the helix surface and the surrounding sand, results of δr, extracted from different sand samples, are presented for use in this suggested relationship on site. Also, the values of KT found in this work were compared with those of field and laboratory tests on helical piles in sand reported in the literature. From this analysis, it was found that the measured values of KT decrease with an increase in pile dimensions and, in most of cases, with an increase in sand friction angle. These results were explained by the presented model.

Temperature dependence of protein motions in a thermophilic dihydrofolate reductase and its relationship to catalytic efficiency

We report hydrogen deuterium exchange by mass spectrometry (HDX-MS) as a function of temperature in a thermophilic dihydrofolate reductase from Bacillus stearothermophilus (Bs-DHFR). Protein stability, probed with circular dichroism, established an accessible temperature range of 10 degrees C to 55 degrees C for the interrogation of HDX-MS. Although both the rate and extent of HDX are sensitive to temperature, the majority of peptides showed rapid kinetics of exchange, allowing us to focus on plateau values for the maximal extent of exchange at each temperature. Arrhenius plots of the ratio of hydrogens exchanged at 5 h normalized to the number of exchangeable hydrogens vs. 1/T provides an estimate for the apparent enthalpic change of local unfolding, DeltaH degrees (unf(avg)). Most regions in the enzyme show DeltaH degrees (unf(avg)) < or = 2.0 kcal/mol, close to the value of kT; by contrast, significantly elevated values for DeltaH degrees (unf(avg)) are observed in regions within the core of protein that contain the cofactor and substrate-binding sites. Our technique introduces a new strategy for probing the temperature dependence of local protein unfolding within native proteins. These findings are discussed in the context of the demonstrated role for nuclear tunneling in hydride transfer from NADPH to dihydrofolate, and relate the observed enthalpic changes to two classes of motion, preorganization and reorganization, that have been proposed to control the efficiency of hydrogenic wave function overlap. Our findings suggest that the enthalpic contribution to the heavy atom environmental reorganizations controlling the hydrogenic wave function overlap will be dominated by regions of the protein proximal to the bound cofactor and substrate.

Circadian control of permethrin-resistance in the mosquito Aedes aegypti

Daily fluctuation of permethrin-resistance was found in adult mosquito Aedes aegypti, the major vector of dengue viruses in Taiwan. We hypothesized there is a relationship between resistance and the circadian clock. To test our hypothesis we correlated changes in the knock-down time (KT 50) response to permethrin with the expression of the pyrethroid-resistant gene CYP9M9 and the clock gene period ( per) during a 12:12 h photoperiodic cycle. Rhythmic expression of per peaked at early scotophase of the light–dark cycle and at early subjective night in constant darkness. The values of KT 50 and the expression of CYP9M9 also exhibited circadian rhythms in both susceptible and permethrin-resistant mosquito strains, from which we inferred a link to the circadian clock. The KT 50 was significantly longer in the light than in the dark phase, and the level of CYP9M9 mRNA was maximal in early scotophase, dropped to a minimum in the midnight and then slowly increased through the photophase. Existence of a clock control over mosquito sensitivity to permethrin was further indicated by reduced expression of CYP9M9 and reduced mosquito resistance to permethrin after temporal silencing of the per gene. These data provide the first evidence on the circadian control of insect resistance to permethrin.

Fatigue strength of sharp notched plate of Zr-based bulk metallic glass

Fatigue strength of notched specimen and smooth specimen of Zr-based bulk metallic glass, Zr55Cu30Ni5Al10, were conducted under either plane-bending or axial-loading. Fatigue notch factor, Kf, for axial-loading was almost equal to the elastic stress concentration factor, Kt, and the value of Kf for plane-bending was 5% lower than the value of Kt. It indicates that the effect of stress gradient around notch root is negligible, and the fatigue limit of notched specimen is determined by the stress at the notch root. On the contrary, the fatigue strength and the fatigue limit were lower for axial-loading than plane-bending either for notched or smooth specimen. It is considered that the fatigue strength of BMG depends on the cooling rate in the casting pro cess of the material, which is different along the thickness direction, and the fatigue strength of plane-bending reflects the strength at the specimen surface while that of axial-loading is determined by the weakest strength in the thickness direction.

Termination Rate Coefficients for Radical Homopolymerization of Methyl Methacrylate and Styrene at Low Conversion

AbstractA comprehensive and systematic study of overall termination rate coefficients, kt, in low‐conversion radical (homo)polymerization of methyl methacrylate and styrene is presented. Values of kt were determined by gravimetric analysis of steady‐state experiments, employing 2,2′‐azoisobutyronitrile as initiator. The values delivered by this simple method were found to be in qualitative and quantitative agreement with those from more modern and sophisticated techniques for measuring kt. Accordingly, correlations for bulk, low‐conversion kt as a function of temperature are given for each monomer. The effects of initiator concentration, cI, and temperature on bulk kt were studied in a controlled way for both monomers. Additionally, ethyl benzene was used as solvent in order to investigate rigorously the effect of monomer concentration, cM, on styrene kt. The trends found by these systematic studies were considered in the light of what is known about the chain‐length dependence of termination. Styrene's behavior was always found to be qualitatively in accord with expectation, although the variations of kt with cI and cM were not as strong as should be the case. However its activation energy, 15 kJ · mol−1, is shown to be almost perfectly in agreement with theory. Methyl methacrylate, on the other hand, is recalcitrant in that its overall kt does not make manifest the chain‐length dependent termination that has been directly measured by other techniques. Possible reasons for these discrepancies are discussed, as are reasons for the difference in values between kt for the two monomers. On the latter topic it is concluded likely that the chain‐length dependence of termination at short chain lengths is primarily responsible for styrene having kt that is higher by a factor of about 3, with there also being a contribution that arises from styrene's slower propagation.magnified image

Fatigue Crack Initiation and Propagation at a Sharp Notch in Zr-Based Bulk Metallic Glass

Fatigue strength of notched specimen and smooth specimen of Zr-based bulk metallic glass, Zr55Cu30Ni5Al10, were conducted under either plane-bending or axial-loading. Fatigue notch factor, Kf, for axial-loading was almost equal to the elastic stress concentration factor, Kt, and the value of Kf for plane-bending was 5% lower than the value of Kt. It indicates that the effect of stress gradient around notch root is negligible, and the fatigue limit of notched specimen is determined by the stress at the notch root. On the contrary, the fatigue strength and the fatigue limit were lower for axial-loading than plane-bending either for notched or smooth specimen. It is considered that the fatigue strength of BMG depends on the cooling rate in the casting process of the material, which is different along the thickness direction, and the fatigue strength of plane-bending reflects the strength at the specimen surface while that of axial-loading is determined by the weakest strength in the thickness direction.