bluuebunny/crossref_metadata_2025 huggingface dataset:
Longitudinal assessment of lung area measurements by two‐dimensional ultrasound in fetuses with isolated left‐sided congenital diaphragmatic hernia
Authors: Ruano R. , Britto I. S. W. , Sangi‐Haghpeykar H. , Bussamra L. C. S. , Da Silva M. M. , Belfort M. A. , Deter R. L. , Lee W. , Tannuri U. , Zugaib M.
Published: May 2014

Objective

To evaluate lung growth in healthy fetuses and those with congenital diaphragmatic hernia (CDH) using two‐dimensional (2D) ultrasound.

Methods

Fetal right lung measurements obtained by 2D ultrasound between 19 and 37 weeks' gestation were evaluated longitudinally in 66 healthy fetuses and 52 fetuses with isolated left‐sided CDH. Right lung areas were determined by the ‘tracing’ and ‘longest‐diameters’ methods and, subsequently, lung area‐to‐head circumference ratios (LHRs) were calculated. Functions fitted to these size parameters with respect to gestational age were evaluated for three sets of group‐wise comparisons: (1) healthy vs CDH fetuses; (2) different degrees of severity of CDH; and (3) CDH fetuses that survived vs those that died by 6 months postpartum.

Results

There was a significantly slower increase in right lung areas and LHRs with advancing gestational age in CDH fetuses than in healthy individuals (P < 0.05). Compared to those with milder forms of CDH, lung areas and LHRs of fetuses with more severe forms displayed a smaller increase (P < 0.05) and LHRs of fetuses with severe CDH did not increase during pregnancy (P > 0.05). Individuals who died postpartum did not show any increase in LHR (P > 0.05) throughout gestation.

Conclusions

The right lung area and LHR, calculated using either the longest‐diameters or tracing method, display reduced growth rates during gestation in cases of isolated left‐sided CDH as compared with healthy fetuses. The growth curve characteristics of fetal lung areas and LHRs may be useful for predicting neonatal mortality. Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.
Fish Oil Supplementation Decreases Oxidative Stress but Does Not Affect Platelet‐Activating Factor Bioactivity in Lungs of Asthmatic Rats
Authors: Zanatta A. L. , Miranda D. T. S. Z. , Dias B. C. L. , Campos R. M. , Massaro M. C. , Michelotto P. V. , West A. L. , Miles E. A. , Calder P. C. , Nishiyama A.
Published: May 2014

Dietary fish oil supplementation increases the content of n‐3 polyunsaturated fatty acids (PUFA) in cellular membranes. The highly unsaturated nature of n‐3 PUFA could result in an enhanced lipid peroxidation in the oxidative environment characteristic of asthma. The oxidative reaction cascade culminates in an increased production of components associated to oxidative stress and of an important proinflammatory mediator platelet‐activating factor (PAF)‐like lipid. We evaluated the effect of fish oil supplementation in asthmatic rats upon the PAF bioactivity and parameters related to oxidative stress in the lung. Fish oil supplementation of asthmatic rats resulted in lower concentrations of nitrite (1.719 ± 0.137 vs. 2.454 ± 0.163 nmol/mL) and lipid hydroperoxide (72.190 ± 7.327 vs. 120.200 ± 11.270 nmol/mg protein). In asthmatic animals, fish oil increased the activities of superoxide dismutase (EC 1.15.1.1) (33.910 ± 2.325 vs. 24.110 ± 0.618 U/mg protein) and glutathione peroxidase (EC 1.11.1.9) (164.100 ± 31.250 vs. 12.590 ± 5.234 U/mg protein). However, fish oil did not affect PAF bioactivity in lung tissue of asthmatic rats (0.545 ± 0.098 340/380 vs. 0.669 ± 0.101 340/380 nm ratio). Considering the two‐step process—oxidative stress and PAF bioactivity—fish oil exhibited a divergent action on these aspects of asthmatic inflammation, since the supplement lowered oxidative stress in the lungs of asthmatic rats, presenting an antioxidant effect, but did not affect PAF bioactivity. This suggests a dual effect of fish oil on oxidative stress and inflammation in asthma.
Intrinsic Lipschitz graphs in Heisenberg groups and continuous solutions of a balance equation
Authors: Serra Cassano F. , Bigolin F. , Caravenna L.
Published: May 2014

We provide a characterization of intrinsic Lipschitz graphs in the sub-Riemannian Heisenberg groups in terms of their distributional gradients. Moreover, we prove the equivalence of different notions of continuous weak solutions to the equation

\frac{\partial \phi }{\partial z} + \frac{\partial }{\partial t}[\phi ^{2}/ 2] = w

, where
w
is a bounded measurable function.
Senescence marker protein‐30/superoxide dismutase 1 double knockout mice exhibit increased oxidative stress and hepatic steatosis
Authors: Kondo Yoshitaka , Masutomi Hirofumi , Noda Yoshihiro , Ozawa Yusuke , Takahashi Keita , Handa Setsuko , Maruyama Naoki , Shimizu Takahiko , Ishigami Akihito
Published: May 2014

Superoxide dismutase 1 (SOD1) is an antioxidant enzyme that converts superoxide anion radicals into hydrogen peroxide and molecular oxygen. The senescence marker protein‐30 (SMP30) is a gluconolactonase that functions as an antioxidant protein in mammals due to its involvement in ascorbic acid (AA) biosynthesis. SMP30 also participates in Ca2+ efflux by activating the calmodulin‐dependent Ca2+‐pump. To reveal the role of oxidative stress in lipid metabolism defects occurring in non‐alcoholic fatty liver disease pathogenesis, we generated SMP30/SOD1‐double knockout (SMP30/SOD1‐DKO) mice and investigated their survival curves, plasma and hepatic lipid profiles, amounts of hepatic oxidative stress, and hepatic protein levels expressed by genes related to lipid metabolism. While SMP30/SOD1‐DKO pups had no growth retardation by 14 days of age, they did have low plasma and hepatic AA levels. Thereafter, 39% and 53% of male and female pups died by 15–24 and 89 days of age, respectively. Compared to wild type, SMP30‐KO and SOD1‐KO mice, by 14 days SMP30/SOD1‐DKO mice exhibited: (1) higher plasma levels of triglyceride and aspartate aminotransferase; (2) severe accumulation of hepatic triglyceride and total cholesterol; (3) higher levels of superoxide anion radicals and thiobarbituric acid reactive substances in livers; and (4) decreased mRNA and protein levels of Apolipoprotein B (ApoB) in livers – ApoB is an essential component of VLDL secretion. These results suggest that high levels of oxidative stress due to concomitant deficiency of SMP30 and/or AA, and SOD1 cause abnormal plasma lipid metabolism, hepatic lipid accumulation and premature death resulting from impaired VLDL secretion.
Response to Early Intensive Behavioral Intervention for autism—An umbrella approach to issues critical to treatment individualization
Authors: Fava Leonardo , Strauss Kristin
Published: May 2014

Integrating knowledge across the disciplines of genetics, neurological, and behavioral science targets, so far, early identification of children with autism and thus early access to intervention. Cross‐discipline collaboration might be substantially improve treatment efficacy via individualized treatment based on the child and family needs, consistency across treatment providers and careful planning of skill curricula, setting and techniques. This paper documents the current state of five main issues critical to treatment individualization where cross‐discipline collaboration is warranted: (1) developmental timing, (2) treatment intensity, (3) heterogeneity in treatment response, (4) program breath and flexibility, and (5) formats of treatment provision.
Perinatal α‐linolenic acid availability alters the expression of genes related to memory and to epigenetic machinery, and the Mecp2 DNA methylation in the whole brain of mouse offspring
Authors: He Fuli , Lupu Daniel S. , Niculescu Mihai D.
Published: May 2014

Many animal and human studies indicated that dietary ω‐3 fatty acids could have beneficial roles on brain development, memory, and learning. However, the exact mechanisms involved are far from being clearly understood, especially for α‐linolenic acid (ALA), which is the precursor for the ω‐3 elongation and desaturation pathways. This study investigated the alterations induced by different intakes of flaxseed oil (containing 50% ALA), during gestation and lactation, upon the expression of genes involved in neurogenesis, memory‐related molecular processes, and DNA methylation, in the brains of mouse offspring at the end of lactation (postnatal day 19, P19). In addition, DNA methylation status for the same genes was investigated. Maternal flaxseed oil supplementation during lactation increased the expression of Mecp2, Ppp1cc, and Reelin, while decreasing the expression of Ppp1cb and Dnmt3a. Dnmt1 expression was decreased by postnatal flaxseed oil supplementation but this effect was offset by ALA deficiency during gestation. Mecp2 DNA methylation was decreased by maternal ALA deficiency during gestation, with a more robust effect in the lactation‐deficient group. In addition, linear regression analysis revealed positive correlations between Mecp2, Reelin, and Ppp1cc, between Gadd45b, Bdnf, and Creb1, and between Egr1 and Dnmt1, respectively. However, there were no correlations, in any gene, between DNA methylation and gene expression. In summary, the interplay between ALA availability during gestation and lactation differentially altered the expression of genes involved in neurogenesis and memory, in the whole brain of the offspring at the end of lactation. The Mecp2 epigenetic status was correlated with ALA availability during gestation. However, the epigenetic status of the genes investigated was not associated with transcript levels, suggesting that either the regulation of these genes is not necessarily under epigenetic control, or that the whole brain model is not adequate for the exploration of epigenetic regulation in the context of this study.
Catastrophic Acute Ischemic Stroke After Crotalidae Polyvalent Immune Fab (Ovine)-Treated Rattlesnake Envenomation
Authors: Bush Sean P. , Mooy Graham G. , Phan Tammy H.
Published: May 2014

We report 2 cases of catastrophic ischemic stroke after Crotalidae polyvalent immune Fab (ovine)-treated rattlesnake envenomation, 1 fatal and the other resulting in significant permanent disability. It is possible these serious adverse events may have been related to venom factor(s), an interaction between venom and antivenom, occult patient blood dyscrasia, or to random unrelated events. We present the rationale for each possibility, and submit the experiences to elicit alternate postulation and communication of similar presentations.
Human Attacks by Large Felid Carnivores in Captivity and in the Wild
Authors: Shepherd Suzanne M. , Mills Angela , Shoff William H.
Published: May 2014

Whereas those who live in the native ranges of the large feline carnivores are well aware of the risks of cat and human encounters, North Americans and Europeans are increasingly exposed to exotic animals through travel, ecotourism, leisure pursuits in rural areas, occupational exposure, zoo and animal park visits, wild habitat encroachment at the urban-wildlands interface, and contact with exotic pets. In encounters during which persons have been severely injured, lapses in animal management protocols, lack of appropriate adult supervision, and intoxication have been reported. Unlike common domestic pets that have lived in close association with humans for thousands of years, no matter where individual large felines may have been raised, they remain wild carnivores with strong prey-drive and territorial instincts. The emergency management of large felid attacks is similar to that of other major trauma: stabilization; management of significant orthopedic, neurologic, vascular, and soft tissue injuries; antibiotic coverage provided for the number of organisms that inhabit their mouths and the potential for tetanus and rabies; and early management in survivors of likely posttraumatic stress disorder. We must actively explore responsible measures globally that can be taken to ensure biologically appropriate, ethical, safe, and sustainable conservation of these large carnivores in both their natural habitats and captivity.
Molecular ageing: Free radical initiated epimerization of thymopentin – A case study
Authors: Sheykhkarimli Dayag , Choo Ken-Loon , Owen Michael , Fiser Béla , Jójárt Balázs , Csizmadia Imre G. , Viskolcz Béla
Published: May 2014

The epimerization of amino acid residues increases with age in living organisms. In the present study, the structural consequences and thermodynamic functions of the epimerization of thymopentin (TP-5), the active site of the thymic hormone thymopoietin, were studied using molecular dynamics and density functional theory methods. The results show that free radical-initiated D-amino acid formation is energetically favoured (−130 kJmol−1) for each residue and induces significant changes to the peptide structure. In comparison to the wild-type (each residue in the L-configuration), the radius of gyration of the D-Asp3 epimer of the peptide decreased by 0.5 Å, and disrupted the intramolecular hydrogen bonding of the native peptide. Beyond establishing important structural, energetic and thermodynamic benchmarks and reference data for the structure of TP-5, these results disseminate the understanding of molecular ageing, the epimerization of amino acid residues.
Growth-substrate induced performance degradation in chemically synthesized monolayer MoS2 field effect transistors
Authors: Amani Matin , Chin Matthew L. , Mazzoni Alexander L. , Burke Robert A. , Najmaei Sina , Ajayan Pulickel M. , Lou Jun , Dubey Madan
Published: May 2014

We report on the electronic transport properties of single-layer thick chemical vapor deposition (CVD) grown molybdenum disulfide (MoS2) field-effect transistors (FETs) on Si/SiO2 substrates. MoS2 has been extensively investigated for the past two years as a potential semiconductor analogue to graphene. To date, MoS2 samples prepared via mechanical exfoliation have demonstrated field-effect mobility values which are significantly higher than that of CVD-grown MoS2. In this study, we will show that the intrinsic electronic performance of CVD-grown MoS2 is equal or superior to that of exfoliated material and has been possibly masked by a combination of interfacial contamination on the growth substrate and residual tensile strain resulting from the high-temperature growth process. We are able to quantify this strain in the as-grown material using pre- and post-transfer metrology and microscopy of the same crystals. Moreover, temperature-dependent electrical measurements made on as-grown and transferred MoS2 devices following an identical fabrication process demonstrate the improvement in field-effect mobility.
Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy
Authors: Wilkinson Iain , Boguslavskiy Andrey E. , Mikosch Jochen , Bertrand Julien B. , Wörner Hans Jakob , Villeneuve David M. , Spanner Michael , Patchkovskii Serguei , Stolow Albert
Published: May 2014

The excited state dynamics of isolated sulfur dioxide molecules have been investigated using the time-resolved photoelectron spectroscopy and time-resolved photoelectron-photoion coincidence techniques. Excited state wavepackets were prepared in the spectroscopically complex, electronically mixed (${\tilde{\rm B}}$B̃)1B1/(Ã)1A2, Clements manifold following broadband excitation at a range of photon energies between 4.03 eV and 4.28 eV (308 nm and 290 nm, respectively). The resulting wavepacket dynamics were monitored using a multiphoton ionisation probe. The extensive literature associated with the Clements bands has been summarised and a detailed time domain description of the ultrafast relaxation pathways occurring from the optically bright (${\tilde{\rm B}}$B̃)1B1 diabatic state is presented. Signatures of the oscillatory motion on the (${\tilde{\rm B}}$B̃)1B1/(Ã)1A2 lower adiabatic surface responsible for the Clements band structure were observed. The recorded spectra also indicate that a component of the excited state wavepacket undergoes intersystem crossing from the Clements manifold to the underlying triplet states on a sub-picosecond time scale. Photoelectron signal growth time constants have been predominantly associated with intersystem crossing to the (${\tilde{\rm c}}$c̃)3B2 state and were measured to vary between 750 and 150 fs over the implemented pump photon energy range. Additionally, pump beam intensity studies were performed. These experiments highlighted parallel relaxation processes that occurred at the one- and two-pump-photon levels of excitation on similar time scales, obscuring the Clements band dynamics when high pump beam intensities were implemented. Hence, the Clements band dynamics may be difficult to disentangle from higher order processes when ultrashort laser pulses and less-differential probe techniques are implemented.
Non-adiabatic and intersystem crossing dynamics in SO2. II. The role of triplet states in the bound state dynamics studied by surface-hopping simulations
Authors: Mai Sebastian , Marquetand Philipp , González Leticia
Published: May 2014

The importance of triplet states in the photorelaxation dynamics of SO2 is studied by mixed quantum-classical dynamics simulations. Using the SHARC method, standing for Surface Hopping including ARbitrary Couplings, intersystem crossing (ISC) processes caused by spin-orbit coupling are found occurring on an ultrafast time scale (few 100 fs) and thus competing with internal conversion. While in the singlet-only dynamics only oscillatory population transfer between the 1B1 and 1A2 states is observed, in the dynamics including singlet and triplet states we find additionally continuous ISC to the 3B2 state and to a smaller extent to the 3B1/3A2 coupled states. The populations obtained from the dynamics are discussed with respect to the overall nuclear motion and in the light of recent TRPEPICO studies [I. Wilkinson, A. E. Boguslavskiy, J. Mikosch, D. M. Villeneuve, H.-J. Wörner, M. Spanner, S. Patchkovskii, and A. Stolow, “Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy,” J. Chem. Phys. 140, 204301 (2014)].
Excited state dynamics in SO2. III. An ab initio quantum study of single- and multi-photon ionization
Authors: Lévêque Camille , Köppel Horst , Taïeb Richard
Published: May 2014

We present an ab initio quantum study of the photoelectron spectra of sulfur dioxide, based on wavepacket propagations on manifolds of ionic, and excited/Rydberg states. We obtain excellent agreement for two different cases. First, the one photon ionization case where we can reproduce all details of the experimental spectrum and demonstrate the influence of the conical intersection between two of the ionic states. Then the multiphoton ionization regime, in which the dynamics of the wave packet on the two lowest singlet states is directly mapped in the spectra via a pump-probe scheme, as proposed in the experimental companion paper [I. Wilkinson et al., J. Chem. Phys. 140, 204301 (2014)].
Covalent bonds are created by the drive of electron waves to lower their kinetic energy through expansion
Authors: Schmidt Michael W. , Ivanic Joseph , Ruedenberg Klaus
Published: May 2014

An analysis based on the variation principle shows that in the molecules H2+, H2, B2, C2, N2, O2, F2, covalent bonding is driven by the attenuation of the kinetic energy that results from the delocalization of the electronic wave function. For molecular geometries around the equilibrium distance, two features of the wave function contribute to this delocalization: (i) Superposition of atomic orbitals extends the electronic wave function from one atom to two or more atoms; (ii) intra-atomic contraction of the atomic orbitals further increases the inter-atomic delocalization. The inter-atomic kinetic energy lowering that (perhaps counter-intuitively) is a consequence of the intra-atomic contractions drives these contractions (which per se would increase the energy). Since the contractions necessarily encompass both, the intra-atomic kinetic and potential energy changes (which add to a positive total), the fact that the intra-atomic potential energy change renders the total potential binding energy negative does not alter the fact that it is the kinetic delocalization energy that drives the bond formation.
Effect of orientation anisotropy on calculating effective electrical conductivities
Authors: Myles Timothy D. , Peracchio Aldo A. , Chiu Wilson K. S.
Published: May 2014

This paper develops an analytical effective medium theory (EMT) equation for calculating the effective conductivity of a mixture based on Maxwell's and Maxwell-Garnett’s theories, extended to higher volume fractions using Bruggeman's unsymmetrical treatment (BUT), with a long term goal of extending the treatment to mixtures more representative of real materials in order to calculate their effective electrical conductivity. The development accounts for spheroid shaped inclusions of varying degrees of anisotropic orientation. The orientation is described by the introduction of a distribution function. Two methodologies valid for the inclusion dilute limit were used to evaluate the effective conductivity: one based on Maxwell's far field approach, and the other based on the Maxwell-Garnett in the matrix approach. It was found that while the dilute limit equations for the effective conductivity were different, the final EMT equations derived by applying BUT collapsed to the same formula which was generalized for anisotropic orientation based on the distribution function presented.
Improving the hot-spot pressure and demonstrating ignition hydrodynamic equivalence in cryogenic deuterium–tritium implosions on OMEGA
Authors: Goncharov V. N. , Sangster T. C. , Betti R. , Boehly T. R. , Bonino M. J. , Collins T. J. B. , Craxton R. S. , Delettrez J. A. , Edgell D. H. , Epstein R. , Follett R. K. , Forrest C. J. , Froula D. H. , Yu. Glebov V. , Harding D. R. , Henchen R. J. , Hu S. X. , Igumenshchev I. V. , Janezic R. , Kelly J. H. , Kessler T. J. , Kosc T. Z. , Loucks S. J. , Marozas J. A. , Marshall F. J. , Maximov A. V. , McCrory R. L. , McKenty P. W. , Meyerhofer D. D. , Michel D. T. , Myatt J. F. , Nora R. , Radha P. B. , Regan S. P. , Seka W. , Shmayda W. T. , Short R. W. , Shvydky A. , Skupsky S. , Stoeckl C. , Yaakobi B. , Frenje J. A. , Gatu-Johnson M. , Petrasso R. D. , Casey D. T.
Published: May 2014

Reaching ignition in direct-drive (DD) inertial confinement fusion implosions requires achieving central pressures in excess of 100 Gbar. The OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] is used to study the physics of implosions that are hydrodynamically equivalent to the ignition designs on the National Ignition Facility (NIF) [J. A. Paisner et al., Laser Focus World 30, 75 (1994)]. It is shown that the highest hot-spot pressures (up to 40 Gbar) are achieved in target designs with a fuel adiabat of α ≃ 4, an implosion velocity of 3.8 × 107 cm/s, and a laser intensity of ∼1015 W/cm2. These moderate-adiabat implosions are well understood using two-dimensional hydrocode simulations. The performance of lower-adiabat implosions is significantly degraded relative to code predictions, a common feature between DD implosions on OMEGA and indirect-drive cryogenic implosions on the NIF. Simplified theoretical models are developed to gain physical understanding of the implosion dynamics that dictate the target performance. These models indicate that degradations in the shell density and integrity (caused by hydrodynamic instabilities during the target acceleration) coupled with hydrodynamics at stagnation are the main failure mechanisms in low-adiabat designs. To demonstrate ignition hydrodynamic equivalence in cryogenic implosions on OMEGA, the target-design robustness to hydrodynamic instability growth must be improved by reducing laser-coupling losses caused by cross beam energy transfer.
Phase behaviour of liquid-crystal monolayers of rod-like and plate-like particles
Authors: Martínez-Ratón Yuri , Varga Szabolcs , Velasco Enrique
Published: May 2014

Orientational and positional ordering properties of liquid crystal monolayers are examined by means of Fundamental-Measure Density Functional Theory. Particles forming the monolayer are modeled as hard parallelepipeds of square section of size σ and length L. Their shapes are controlled by the aspect ratio κ = L/σ (>1 for prolate and <1 for oblate shapes). The particle centers of mass are restricted to a flat surface and three possible and mutually perpendicular orientations (in-plane and along the layer normal) of their uniaxial axes are allowed. We find that the structure of the monolayer depends strongly on particle shape and density. In the case of rod-like shapes, particles align along the layer normal in order to achieve the lowest possible occupied area per particle. This phase is a uniaxial nematic even at very low densities. In contrast, for plate-like particles, the lowest occupied area can be achieved by random in-plane ordering in the monolayer, i.e., planar nematic ordering takes place even at vanishing densities. It is found that the random in-plane ordering is not favorable at higher densities and the system undergoes an in-plane ordering transition forming a biaxial nematic phase or crystallizes. For certain values of the aspect ratio, the uniaxial-biaxial nematic phase transition is observed for both rod-like and plate-like shapes. The stability region of the biaxial nematic phase enhances with decreasing aspect ratios for plate-like particles, while the rod-like particles exhibit a reentrant phenomenon, i.e., a sequence of uniaxial-biaxial-uniaxial nematic ordering with increasing density if the aspect ratio is larger than 21.34. In addition to this, packing fraction inversion is observed with increasing surface pressure due to the alignment along the layers normal. At very high densities the nematic phase destabilizes to a nonuniform phases (columnar, smectic, or crystalline phases) for both shapes.
Investigation and optimization of low-frequency noise performance in readout electronics of dc superconducting quantum interference device
Authors: Zhao Jing , Zhang Yi , Lee Yong-Ho , Krause Hans-Joachim
Published: May 2014

We investigated and optimized the low-frequency noise characteristics of a preamplifier used for readout of direct current superconducting quantum interference devices (SQUIDs). When the SQUID output was detected directly using a room-temperature low-voltage-noise preamplifier, the low-frequency noise of a SQUID system was found to be dominated by the input current noise of the preamplifiers in case of a large dynamic resistance of the SQUID. To reduce the current noise of the preamplifier in the low-frequency range, we investigated the dependence of total preamplifier noise on the collector current and source resistance. When the collector current was decreased from 8.4 mA to 3 mA in the preamplifier made of 3 parallel SSM2220 transistor pairs, the low-frequency total voltage noise of the preamplifier (at 0.1 Hz) decreased by about 3 times for a source resistance of 30 Ω whereas the white noise level remained nearly unchanged. Since the relative contribution of preamplifier's input voltage and current noise is different depending on the dynamic resistance or flux-to-voltage transfer of the SQUID, the results showed that the total noise of a SQUID system at low-frequency range can be improved significantly by optimizing the preamplifier circuit parameters, mainly the collector current in case of low-noise bipolar transistor pairs.
Multi-band polarization-insensitive metamaterial absorber based on Chinese ancient coin-shaped structures
Authors: Mao Zhiwen , Liu Shaobin , Bian Borui , Wang Beiyin , Ma Ben , Chen Lin , Xu Junyi
Published: May 2014

In this paper, the design, simulation, fabrication, and measurement of the five-band metamaterial absorber (MMA) based on Chinese ancient coin-shaped structure are proposed. Simulation results show that the proposed absorber has five distinctive absorption peaks at frequencies of 2.538 GHz, 7.092 GHz, 9.702 GHz, 13.302 GHz, and 15.588 GHz with the absorptivity of 0.99, 0.99, 0.99, 0.98, and 0.99, respectively. Experiment results matches well with the simulation. Both simulation and experiment results exhibit that the MMA sample is polarization insensitive for transverse electric and transverse magnetic incident wave. It also shows that high absorption for wide angle of incidence is up to 60°. Finally, the current distribution for the MMA is presented to gain an insight into the physics behind the multiple absorption mechanism. The five-band absorber is promising candidates as absorbing elements in scientific and technical applications because of its multiband absorption, polarization insensitive, and wide angle incidence.
Energy relaxation of hot electrons in Si-doped GaN
Authors: Zhang J.-Z.
Published: May 2014

Energy relaxation of the hot electrons in Si-doped bulk GaN is studied theoretically, taking into account non-equilibrium polar optical phonons, electron degeneracy, and screening from the mobile electrons. The electron power dissipation and energy relaxation time are calculated as functions of the electron temperature Te, the hot-phonon effect (HPE) is examined by varying the optical phonon lifetime values, and the results are compared with previous calculations for typical GaN-based heterostructures. Particular attention is paid to the distinct temperature Te dependences of the power loss and the energy relaxation time τE at the low and high electron temperatures. At low electron temperatures (Te<500 K), the exponential rise of phonon generation number, fast weakened screening and HPE result in a rapid increase of power loss and sharp drop of relaxation time with Te. At high electron temperatures (Te>1500 K), the power loss increases slowly with Te due to the decrease in phonon generation rate, and the temperature-dependence of the energy relaxation time depends on the polar optical phonon lifetime—saturation in energy relaxation occurs when the phonon lifetime increases or varies little with Te. Our calculated temperature dependences of the energy relaxation time are in good agreement with experimental findings [Liberis et al., Appl. Phys. Lett. 89, 202117 (2006); Matulionis et al., Phys. Status Solidi C 2, 2585 (2005)]. With no HPE, the electron energy relaxation is much faster in bulk GaN (τE∼ several tens femtoseconds) than in the GaN-based heterostructures. However, stronger hot-phonon re-absorption occurs in bulk GaN due to rapid polar-optical phonon emission compared to phonon decay. Therefore, including HPE yields very close power loss and energy relaxation times in bulk and heterostructures with similar densities of electrons (τE∼ several tenths of a picosecond). Transparent expressions for energy relaxation are obtained in the Boltzmann approximation, which are very useful for resolving the temperature dependences of the energy relaxation in the low- and high-Te regions.
Interaction between magnetic vortex cores in a pair of nonidentical nanodisks
Authors: Sinnecker J. P. , Vigo-Cotrina H. , Garcia F. , Novais E. R. P. , Guimarães A. P.
Published: May 2014

The coupling of two nonidentical magnetic nanodisks, i.e., with different vortex gyrotropic frequencies, is studied. From the analytical approach, the interactions between the nanodisks along x and y directions (the coupling integrals) were obtained as a function of distance. From the numerical solution of Thiele's equation, we derived the eigenfrequencies of the vortex cores as a function of distance. The motion of the two vortex cores and, consequently, the time dependence of the total magnetization M(t) were derived both using Thiele's equation and by micromagnetic simulation. From M(t), a recently developed method, the magnetic vortex echoes, analogous to the Nuclear Magnetic Resonance spin echoes, was used to compute the distance dependence of the magnetic coupling strength. The results of the two approaches differ by approximately 10%; using one single term, a dependence with distance found is broadly in agreement with studies employing other techniques.
Low-current-density spin-transfer switching in Gd22Fe78-MgO magnetic tunnel junction
Authors: Kinjo Hidekazu , Machida Kenji , Matsui Koichi , Aoshima Ken-ichi , Kato Daisuke , Kuga Kiyoshi , Kikuchi Hiroshi , Shimidzu Naoki
Published: May 2014

Magnetization switching of a relatively thick (9 nm) Gd-Fe free layer was achieved with a low spin injection current density of 1.0 × 106 A/cm2 using MgO based magnetic tunnel junction devices, fabricated for light modulators. At about 560 × 560 nm2 in size, the devices exhibited a tunneling magnetoresistance ratio of 7%. This low-current switching is mainly attributed to thermally assisted spin-transfer switching in consequence of its thermal magnetic behavior arising from Joule heating.
Temperature distributions at the surface of functionally graded materials containing a cylindrical defect
Authors: Ma Xiao-Bo , Wang Fei , Chen De-Zhen
Published: May 2014

The recognition of subsurface defects is an important aspect of inverse heat transfer problems. The solution of direct problems is the basis of the inverse problems. In this paper, based on the non-Fourier heat conduction equation and using the image method and the wave function expansion method, an analytical method to study the multiple scattering of thermal waves and temperatures from the subsurface defect in semi-infinite functionally graded materials (FGMs) is presented. A general solution of the scattered fields of thermal waves is obtained. Without loss of generality, the incidence of thermal waves excited by the periodically modulated laser and the subsurface defect are treated as the line heat source and a cylindrical cavity with thermal insulation in the modelling, respectively. The amplitude of the changes in temperature at the frontal surface in the cylindrical defect due to different physical and geometrical parameters is analysed, discussed, and presented graphically using the analytical method. The significant changes in the temperature were found to occur at the frontal surface because of the existence of conducting defects. In addition, the influence of the defect state on the temperature was found to also be related to the nonhomogeneous parameters of FGMs, the wavenumber, the frequency of the thermal waves, and the depth of the buried defects. The numerical results and method proposed in this paper are expected to be applied for the analysis of infrared thermal waves in non-destructive evaluations of functionally graded materials and inverse problems of mathematical physics.
The development of a portable ultrahigh vacuum chamber via silicon block
Authors: Chuang Ho-Chiao , Huang Chia-Shiuan
Published: May 2014

This paper describes a nonmetallic, light weight portable chamber for ultra-high vacuum (UHV) applications. The chamber consists of a processed silicon block anodically bonding five polished Pyrex glass windows and a Pyrex glass adapter, without using any screws, bolts or vacuum adhesives. The design features provide an alternative chamber for UHV applications which require nonmetallic components. We have cyclically baked the chamber up to 180 °C for 160 h and have achieved an ultimate pressure of 1.4 × 10−9 Torr (limited by our pumping station), with no leak detected. Both Pyrex glass windows and Pyrex glass adapter have been used successfully.
Chemical, electronic, and magnetic structure of LaFeCoSi alloy: Surface and bulk properties
Authors: Lollobrigida V. , Basso V. , Borgatti F. , Torelli P. , Kuepferling M. , Coïsson M. , Olivetti E. S. , Celegato F. , Tortora L. , Stefani G. , Panaccione G. , Offi F.
Published: May 2014

We investigate the chemical, electronic, and magnetic structure of the magnetocaloric LaFeCoSi compound with bulk and surface sensitive techniques. We put in evidence that the surface retains a soft ferromagnetic behavior at temperatures higher than the Curie temperature of the bulk due to the presence of Fe clusters at the surface only. This peculiar magnetic surface effect is attributed to the exchange interaction between the ferromagnetic Fe clusters located at the surface and the bulk magnetocaloric alloy, and it is used here to monitor the magnetic properties of the alloy itself.
Suppression of activation energy and superconductivity by the addition of Al2O3 nanoparticles in CuTl-1223 matrix
Authors: Jabbar Abdul , Qasim Irfan , Mumtaz M. , Zubair M. , Nadeem K. , Khurram A. A.
Published: May 2014

Low anisotropic (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (CuTl-1223) high Tc superconducting matrix was synthesized by solid-state reaction and Al2O3 nanoparticles were prepared separately by co-precipitation method. Al2O3 nanoparticles were added with different concentrations during the final sintering cycle of CuTl-1223 superconducting matrix to get the required (Al2O3)y/CuTl-1223, y = 0.0, 0.5, 0.7, 1.0, and 1.5 wt. %, composites. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive X-ray, and dc-resistivity (ρ) measurements. The activation energy and superconductivity were suppressed with increasing concentration of Al2O3 nanoparticles in (CuTl-1223) matrix. The XRD analysis showed that the addition of Al2O3 nanoparticles did not affect the crystal structure of the parent CuTl-1223 superconducting phase. The suppression of activation energy and superconducting properties is most probably due to weak flux pinning in the samples. The possible reason of weak flux pinning is reduction of weak links and enhanced inter-grain coupling due to the presence of Al2O3 nanoparticles at the grain boundaries. The presence of Al2O3 nanoparticles at the grain boundaries possibly reduced the number of flux pinning centers, which were present in the form of weak links in the pure CuTl-1223 superconducting matrix. The increase in the values of inter-grain coupling (α) deduced from the fluctuation induced conductivity analysis with the increased concentration of Al2O3 nanoparticles is a theoretical evidence of improved inter-grain coupling.
Effect of a rigid wall on the vortex induced vibration of two staggered circular cylinders
Authors: Derakhshandeh Javad Farrokhi , Arjomandi Maziar , Cazzolato Benjamin S. , Dally Bassam
Published: May 2014

Vortex Induced Vibrations (VIVs) play a key role in a wide range of engineering applications including the extraction of renewable energy. In this paper, numerical studies of the phenomenon of VIV were conducted to investigate the flow behaviour around two identical circular cylinders. The upstream cylinder was located in the vicinity of a rigid wall and downstream one was mounted on an elastic support with one degree of freedom. The Reynolds number based on the cylinder's diameter was kept constant at 8700, while the separation between the upstream cylinder and the wall was varied. The results show that this separation distance known as the gap ratio has a significant effect on the dynamic behaviour of the upstream and downstream cylinders. Accordingly, the interaction of shear layers between the upstream cylinder and the rigid wall has a strong influence on the vortex dynamics of both cylinders, in particular, when the upstream cylinder was mounted close to the wall. In this arrangement, a jet flow produced in the wake of the upstream cylinder significantly affects the vortex shedding frequency, and the lift and drag coefficients of both cylinders. This can alter the dynamic response of the downstream cylinder and theoretical efficiency of the VIV power.
A non-invasive beam profile monitor for charged particle beams
Authors: Tzoganis Vasilis , Welsch Carsten P.
Published: May 2014

Non-interceptive beam profile monitors are highly desirable in almost all particle accelerators. Such techniques are especially valuable in applications where real time monitoring of the beam properties is required while beam preservation and minimal influence on the vacuum are of the greatest importance. This applies to many kinds of accelerators such as high energy machines where the normal diagnostics cannot withstand the beam's power, medical machines where treatment time is valuable and cannot be allocated to diagnostics and also low energy, low intensity accelerators where the beam's properties are difficult to measure. This paper presents the design of a gas-jet based beam profile monitor which was developed and commissioned at the Cockcroft Institute and can operate in a very large background pressure range from 10−7 down to below 10−11 millibars. The functioning principle of the monitor is described and the first experimental results obtained using a 5 keV electron beam are discussed.
Tensile-strained InxGa1−xP membranes for cavity optomechanics
Authors: Cole Garrett D. , Yu Pen-Li , Gärtner Claus , Siquans Karoline , Moghadas Nia Ramon , Schmöle Jonas , Hoelscher-Obermaier Jason , Purdy Thomas P. , Wieczorek Witlef , Regal Cindy A. , Aspelmeyer Markus
Published: May 2014

We investigate the optomechanical properties of tensile-strained ternary InxGa1−xP nanomembranes grown on GaAs. This material system combines the benefits of highly strained membranes, similar to those based on stoichiometric silicon nitride, with the unique properties of thin-film semiconductor single crystals, as previously demonstrated with suspended GaAs. Here, we employ lattice mismatch in epitaxial growth to impart an intrinsic tensile strain to a monocrystalline thin film (approximately 30 nm thick). These structures exhibit mechanical quality factors of 2 × 106 or beyond at room temperature and 17 K for eigenfrequencies up to 1 MHz, yielding Q × f products of 2 × 1012 Hz for a tensile stress of ∼170 MPa. Incorporating such membranes in a high-finesse Fabry-Perot cavity, we extract an upper limit to the total optical loss (including both absorption and scatter) of 40 ppm at 1064 nm and room temperature. Further reductions of the In content of this alloy will enable tensile stress levels of 1 GPa, with the potential for a significant increase in the Q × f product, assuming no deterioration in the mechanical loss at this composition and strain level. This materials system is a promising candidate for the integration of strained semiconductor membrane structures with low-loss semiconductor mirrors and for realizing stacks of membranes for enhanced optomechanical coupling.
Negative refraction imaging of acoustic metamaterial lens in the supersonic range
Authors: Han Jianning , Wen Tingdun , Yang Peng , Zhang Lu
Published: May 2014

Acoustic metamaterials with negative refraction index is the most promising method to overcome the diffraction limit of acoustic imaging to achieve ultrahigh resolution. In this paper, we use localized resonant phononic crystal as the unit cell to construct the acoustic negative refraction lens. Based on the vibration model of the phononic crystal, negative quality parameters of the lens are obtained while excited near the system resonance frequency. Simulation results show that negative refraction of the acoustic lens can be achieved when a sound wave transmiting through the phononic crystal plate. The patterns of the imaging field agree well with that of the incident wave, while the dispersion is very weak. The unit cell size in the simulation is 0.0005 m and the wavelength of the sound source is 0.02 m, from which we show that acoustic signal can be manipulated through structures with dimensions much smaller than the wavelength of incident wave.
Density functional theory study on bond dissociation enthalpies for lignin dimer model compounds
Authors: Huang Jinbao , Liu Chao , Jin Qiujing , Tong Hong , Li Weimin , Wu Dan
Published: May 2014

In order to enhance understanding of the mechanism of lignin pyrolysis, homolytic bond dissociation enthalpies (BDEs) in ten lignin dimer model compounds were calculated by using density functional theory methods at B3LYP/6-31G++(d,p) level and B3P86/6-31G++(d,p) level. The BDE values calculated at B3LYP/6-31G(d,p) level are about 20 kJ/mol lower than that at B3P86/6-31G(d,p) level, but the variation trends of BDE values at two levels are the same and the B3P86 functional was found to yield accurate BDEs. The calculation results show that the order of the BDE values for the β-O-4 type of linkage is as follows: Cβ-O < Cα-Cβ < C4-O < C1-Cα, and the substituents (methoxyl, carbonyl, and hydroxyl) on both the aromatic and alkyl groups in model compounds 1 have an important effect on the BDEs. It is found that the BDEs of Caromatic(1,4,5)-C(or O) in lignin model compounds are higher, but the BDEs of Calkyl(α, β)-Calkyl(α, β)(or O) are lower. Therefore, the initial step in pyrolysis of lignin is the homolytic cleavage of the Calkyl(α, β)-Calkyl(α, β)(or O) bond. The possible formation pathways of major products in the pyrolysis process of model compounds have been analysed.
Femtosecond Two-Photon Detachment of Cu− Studied By Photoelectron Imaging
Authors: Liu Ben-kang , Wang Yan-qiu , Wang Li
Published: May 2014

The wavelength dependence of photoelectron angular distributions (PADs) of two-photon detachment of Cu− has been directly studied by using the photoelectron map imaging. Results show that for the laser field intensity of 6.0×1010 W/cm2, PADs exhibit dramatic change with the external field wavelength. Comparison between the experimental observation and the lowest-order perturbation theory prediction indicates that the pattern of PADs can be explained by the interference of the s and d partial waves in the final state. Relative contributions of s and d partial waves in the two-photon detachment at different laser wavelengths are obtained.
Surface-enhanced Raman Scattering of Aflatoxin B1 on Silver by DFT Method
Authors: Gao Si-min , Wang Hong-yan , Lin Yue-xia
Published: May 2014

The structure, electrostatic properties, and Raman spectra of aflatoxin B1 (AFB1) and AFB1-Ag complex are studied by density functional theory with B3LYP/6-311G(d,p)/Lanl2dz basis set. The results show that the surface-enhanced Raman scattering (SERS) and pre-resonance Raman spectra of AFB1-Ag complex strongly depend on the adsorption site and the excitation wavelength of the incident light. The SERS factors are found to enhance 102−103 order compared to normal Raman spectrum of AFB1 molecule due to the larger static polarizabilities of the AFB1-Ag complex, which directly results in the stronger chemical enhancement in SERS spectra. The pre-resonance Raman spectra of AFB1-Ag complex are explored at 266, 482, 785, and 1064 nm incident light wavelength, in which the enhancement factors are about 102−104, mainly caused by the charge-transfer excitation resonance. The vibrational modes are analyzed to explain the relationship between the vibrational direction and the enhanced Raman intensities.
Insight into Capture of Greenhouse Gas (CO2) based on Guanidinium Ionic Liquids
Authors: Liu He-xiu , Man Rui-lin , Zheng Bai-shu , Wang Zhao-xu , Yi Ping-gui
Published: May 2014

Quantum mechanics and molecular dynamics are used to simulate guanidinium ionic liquids. Results show that the stronger interaction exists between guanidine cation and chlorine anion with interaction energy about 109.216 kcal/mol. There are two types of spatial distribution for the title system: middle and top. Middle mode is a more stable conformation according to energy and geometric distribution. It is also verified by radial distribution function. The continuous increase of carbon dioxide (CO2) does not affect the structure of ionic liquids, but CO2 molecules are always captured by the cavity of ionic liquids.
Theoretical Study on Dissociation Mechanisms of Di-ethyl Berylliums and Di-t-butyl Berylliums
Authors: Meng Ling-biao , Zhao Yan , Zhang Ji-qiang , Zhang Ji-cheng , Wu Wei-dong , Wang Zhuo
Published: May 2014

The potential energy surfaces (PES) of unimolecular dissociation reactions for di-ethyl beryllium and di-t-butyl beryllium are investigated by B3LYP, CCSD(T), and G3B3 approaches. Possible reaction pathways through either the radical or transition state (TS) of the molecules are considered. The geometries, vibrational frequencies and relative energies for various stationary points are determined. From the study of energetics, the TS pathways arising from concerted molecular eliminations are indicated to be the main dissociation pathways for both molecules. The PES differences of the dissociation reactions are investigated. The activation energies and rate constants will be helpful for investigating the predictive ability of the reaction in further theoretical and experimental research.