bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoelectric properties of hot-pressed skutterudite CoSb3
Authors: He Zeming , Stiewe Christian , Platzek Dieter , Karpinski Gabriele , Müller Eckhard , Li Shanghua , Toprak Muhammet , Muhammed Mamoun
Published: March 2007

In the present work, skutterudite CoSb3 were fabricated by hot pressing at different sintering temperatures under vacuum and argon. For the prepared compacts, the phase, the microstructure, and the temperature dependent thermoelectric properties were characterized. The correlation of the materials factors: density, grain size, Sb content, with the thermoelectric variables: Seebeck coefficient, electrical conductivity, thermal conductivity, and dimensionless figure of merit (ZT), is presented. The achieved ZT values are also compared with those reported in the literature. The investigated samples show larger electrical conductivity due to existence of metallic Sb and smaller thermal conductivity because of fine-grained structure. A maximal ZT of 0.11 was achieved for the samples sintered at 853 K under vacuum and at 773 K under argon. A moderate improvement on ZT for pure CoSb3 is shown in the present work.
Effects of a constant electric field on the diffusional instability of cubic autocatalytic reaction fronts
Authors: D’Hernoncourt J. , De Wit A. , Merkin J. H.
Published: March 2007

An electric field applied in the direction of propagation of a chemical reaction-diffusion front can affect the stability of this front with regard to diffusive instabilities. The influence of an applied constant electric field is investigated by a linear stability analysis and by nonlinear simulations of a simple chemical system based on the cubic autocatalytic reaction A−+2B−→3B−. The diffusional stability of the front is seen to depend on the intensity E and sign of the applied field, and D, the ratio diffusion coefficients of the reactant species. Depending on E, the front can become more or less diffusively unstable for a given value of D. Above a critical value of E, which depends on D, electrophoretic separation of the two fronts is observed.
Quasi-Fourier-transform limited, scannable, high energy titanium-sapphire laser source for high resolution spectroscopy
Authors: Dupré Patrick , Miller Terry A.
Published: March 2007

A tunable injection seeded Ti:sapphire laser source has been developed and tested. Slave-master tandem cavity and ramp-lock-and-fire concepts have been implemented and fully controlled by a digital signal processor. A Fourier-transform-based analysis, as well as direct measurements, have demonstrated spectral linewidths in the range of 3.5–15 MHz (HWHM), with potential tunability over the entire Ti:sapphire lasing range. A quasi-Fourier-transform limited spectral linewidth is demonstrated assuming a secant hyperbolic shape of the electromagnetic field. Output energies >100 mJ have been reached with ∼300 mJ of pump energy. The highest spectral purity is obtained using the quadruple pumping scheme.
Influence of quantum-well-barrier composition on gain and threshold current in AlGaN lasers
Authors: Chow W. W. , Kneissl M. , Northrup J. E. , Johnson N. M.
Published: March 2007

In an AlGaN quantum-well laser, the presence of Al affects the optical properties of the gain-generating active region partly because of the distinct difference in the band structure between AlN and GaN or InN. The intricate connection between band structure and internal-electric-field effects leads to a noticeably stronger influence of barrier composition on optical gain, lasing polarization, and threshold current than in conventional near-infrared III-V lasers.
Interpolating moving least-squares methods for fitting potential energy surfaces: An application to the H2CN unimolecular reaction
Authors: Guo Yin , Harding Lawrence B. , Wagner Albert F. , Minkoff Michael , Thompson Donald L.
Published: March 2007

Classical trajectories have been used to compute rates for the unimolecular reaction H2CN→H+HCN on a fitted ab initio potential energy surface (PES). The ab initio energies were obtained from CCSD(T)/aug-cc-pvtz electronic structure calculations. The ab initio energies were fitted by the interpolating moving least-squares (IMLS) method. This work continues the development of the IMLS method for producing ab initio PESs for use in molecular dynamics simulations of many-atom systems. A dual-level scheme was used in which the preliminary selection of data points was done using a low-level theory and the points used for fitting the final PES were obtained at the desired higher level of theory. Classical trajectories were used on various low-level IMLS fits to tune the fit to the unimolecular reaction under study. Procedures for efficiently picking data points, selecting basis functions, and defining cutoff limits to exclude distant points were investigated. The accuracy of the fitted PES was assessed by comparing interpolated values of quantities to the corresponding ab initio values. With as little as 330 ab initio points classical trajectory rate constants were converged to 5%–10% and the rms error over the six-dimensional region sampled by the trajectories was a few tenths of a kcal/mol.
High-redshift supernovae indicate that dark energy has been around for 10 billion years
Authors: Schwarzschild Bertram
Published: March 2007

A puzzling dark energy is presumed to be driving the present acceleration of the Hubble expansion. But what was it doing before it became the dominant component of the cosmos?
The early days of precision laser spectroscopy
Authors: Brewer Richard G. , Mooradian Aram , Stoicheff Boris P.
Published: March 2007

In the 1960s and 1970s, spectroscopists developed a host of nonlinear techniques to measure the interaction of light and matter with a resolution fine enough to test quantum electrodynamics and optically detect weak interactions in atoms.
Low-loss planar and stripe waveguides in Nd3+-doped silicate glass produced by oxygen-ion implantation
Authors: Wang Lei , Chen Feng , Wang Xue-Lin , Wang Ke-Ming , Jiao Yang , Wang Liang-Ling , Li Xi-Shan , Lu Qing-Ming , Ma Hong-Ji , Nie Rui
Published: March 2007

We report on the fabrication and characterization of low-loss planar and stripe waveguides in a Nd3+-doped glass by 6MeV oxygen-ion implantation at a dose of 1×1015ions∕cm2. The dark mode spectroscopy of the planar waveguide was measured using a prism coupling arrangement. The refractive index profile of the planar waveguide was reconstructed from a code based on the reflectivity calculation method. The results indicate that a refractive index enhanced region as well as an optical barrier have been created after the ion beam processing. The near-field mode profiles of the stripe waveguide were obtained by an end-fire coupling arrangement, by which three quasitransverse electric modes were observed. After annealing, the propagation losses of the planar and stripe waveguides were reduced to be ∼0.5 and ∼1.8dB∕cm, respectively.
Role of the electric dipole moment in positron binding to the ground and excited states of the BeO molecule
Authors: Buenker Robert J. , Liebermann Heinz-Peter , Pichl Lukáš , Tachikawa Masanori , Kimura Mineo
Published: March 2007

Self-consistent-field and multireference single- and double-excitation configuration interaction (CI) calculations have been carried out for various electronic states of the beryllium oxide molecule and their positron-attached counterparts. Particular emphasis is placed on the correlation between the polarity of a given BeO state and the magnitude of the positron binding energy as the internuclear distance is varied. Potential curves are computed for all BeO states that correlate with the first three atomic limits for this system and good agreement is found between the experimental and calculated spectroscopic constants in all cases. The present level of CI treatment is known to underestimate the positron affinities of atoms by at least several tenths of an eV, and this fact needs to be taken into account in evaluating the results for positron binding to molecules. The lowest BeO excited states (Π3,1) are not found to bind with a positron in the Franck-Condon region due to their comparatively small dipole moments caused by O to Be charge transfer relative to the XΣ+1 ground state, which in turn does have a fairly sizeable positron affinity. The situation changes significantly as dissociation proceeds, however, with both Π4,2 and Σ+2 positronic states lying several tenths of an eV lower than their neutral counterparts over a broad range of internuclear distance.
Charge-induced wettability modification
Authors: Aronov D. , Molotskii M. , Rosenman G.
Published: March 2007

Electric charges deposited on a liquid droplet, located on a solid surface, strengthen the wetting effect. Here, the authors report on the opposite phenomenon—a decrease of wettability induced by a low-energy electron irradiation of solids. They provide evidence that the electron-induced surface charge decreases solid/liquid and solid/vapor interfacial energies when reduction of the latter is always higher. This explains the observed dependence of the droplet shape on the incident electron charge and energy, as well as on a liquid origin. This phenomenon is reversible when the charged material is subjected to ultraviolet illumination, which restores its initial state.
Improvement of photovoltages in organic dye-sensitized solar cells by Li intercalation in particulate TiO2 electrodes
Authors: Harima Y. , Kawabuchi K. , Kajihara S. , Ishii A. , Ooyama Y. , Takeda K.
Published: March 2007

Photovoltages of nanoporous TiO2 solar cells sensitized by organic dyes are found to be improved by up to 200mV with a negligible decrease in photocurrent by treating TiO2 electrodes with intercalation of Li. The enhancement in photovoltage is explained in terms of the formation of a dipole layer due to adsorption of Li ions on the TiO2 surface generated by the reaction of intercalated Li atoms with moisture in air.
Positronium formation as a three-body reaction. I. The second-order positron-electron interaction amplitude
Authors: Bolorizadeh M. A. , Brunger M. J. , Maddern T. , Ghanbari Adivi E.
Published: March 2007

We derive the exact analytic form for the second-order positron-electron interaction term in the Faddeev three-body approach which is applicable in the nonrelativistic high energy region. Although there is no nonintegrable singularity in the six-dimensional integral form of this amplitude, here the basic difficulty arises from the presence of complex nonintegral exponents in the components included in the integrand. Consequently, three brunch cuts must be handled simultaneously. However, by using an integral representation of the gamma function, these brunch cuts are removed from the integrand. Expanding the radial parts of the initial and final wave functions further reduces the second-order positron-electron interaction term to a one-variable integral in terms of Bessel functions of the third kind. The different final closed expressions are ultimately derived in terms of the generalized hypergeometric functions for different regions of the scattering angle.
Direct evidence on magnetic-field-induced phase transition in a NiCoMnIn ferromagnetic shape memory alloy under a stress field
Authors: Wang Y. D. , Ren Yang , Huang E. W. , Nie Z. H. , Wang G. , Liu Y. D. , Deng J. N. , Zuo L. , Choo H. , Liaw P. K. , Brown D. E.
Published: March 2007

The magnetoelasticity and magnetoplasticity behaviors of a Ni–Co–Mn–In ferromagnetic shape memory alloy (FSMA) induced by the reverse phase transformation interplayed under multiple (temperature, magnetic, and stress) fields were captured directly by high-energy synchrotron x-ray diffraction technique. The experiments showed the direct experimental evidence of that a stress (∼50MPa) applied to this material made a complete recovery of the original orientations of the martensite variants, showing a full shape memory effect. This finding offers the in-depth understanding the fundamental properties and applications of the Ni–Co–Mn–In FSMA with the magnetic-field-induced reverse transformation.
Implementation of diffractive optical element in four-wave mixing scheme for ex situ characterization of hydride vapor phase epitaxy-grown GaN layers
Authors: Jarasiunas K. , Aleksiejunas R. , Malinauskas T. , Gudelis V. , Tamulevicius T. , Tamulevicius S. , Guobiene A. , Usikov A. , Dmitriev V. , Gerritsen H. J.
Published: March 2007

A holographic beam splitter has been integrated into a picosecond four-wave mixing (FWM) scheme. This modification significantly simplified the procedure of dynamic grating recording, thus making the FWM technique an easy-to-use tool for the holographic characterization of wide band gap materials. The novel FWM scheme was applied for characterization of hydride vapor phase epitaxy-grown undoped GaN layers of different thickness. It allowed the determination of carrier lifetime, diffusion coefficient, and carrier diffusion length by optical means, as well as the study of carrier recombination peculiarities with respect to dislocation and excess carrier density.
A lead-free piezoelectric transformer in radial vibration modes
Authors: Guo Mingsen , Lin D. M. , Lam K. H. , Wang S. , Chan Helen L. W. , Zhao X. Z.
Published: March 2007

In this study, a disk-shaped piezoelectric transformer was fabricated using lead-free (K,Na)NbO3-based ceramics with high mechanical quality factor. The transformer can operate in the fundamental or the third radial vibration mode. The transformer is poled along the thickness direction. The top surface is covered by ring/dot silver electrodes separated by an annular gap which serve as the input and output parts of the transformer, respectively. The bottom surface, fully covered with a silver electrode, is grounded as a common electrode. The dimensions of the top ring/dot electrodes are designed such that the third radial vibration mode can be strongly excited. The electrical properties of the transformer with diameter of 34.2mm and thickness of 1.9mm were measured. For a temperature rise of 35°C, the transformer has a maximum output power of 12W. With the matching load, its maximum efficiency is >95%, and maximum voltage gains are 6.5 and 3.9 for the fundamental and the third radial vibration modes, respectively. It has potential to be used in power supply units and other electronic circuits.
Synthesis and optical properties of InN nanowires and nanotubes
Authors: Xu H. Y. , Liu Z. , Zhang X. T. , Hark S. K.
Published: March 2007

InN nanowires and faceted hexagonal InN nanotubes are synthesized by catalyst-free chemical vapor deposition at different temperatures. Both have the single crystalline wurtzite structure and grow along the c axis. Different growth dynamics are suggested for the difference in morphology. Observations of phonon-plasmon coupled modes in their Raman scattering suggest of high electron concentrations. Absorption edges in their optical spectra have energies slightly higher than 1eV, showing blueshifts from the fundamental band gap of ∼0.7eV, recently observed in epitaxial films. The shifts are argued to be the result of the Burstein-Moss effect.
High temperature stability of lanthanum silicate dielectric on Si (001)
Authors: Jur J. S. , Lichtenwalner D. J. , Kingon A. I.
Published: March 2007

Integration of a high-κ dielectric into complementary metal-oxide-semiconductor devices requires thermal stability of the amorphous dielectric phase and chemical compatibility with silicon. The stability of amorphous lanthanum silicate on Si (001) is investigated by means of metal-insulator-semiconductor capacitor measurements, back side secondary ion mass spectrometry (SIMS) depth profiling, and high-resolution transmission electron microscopy (HRTEM) after a 1000°C, 10s anneal in nitrogen ambient. Back side SIMS depth profiling of the TaN∕LaSiOx∕Si gate stack reveals no detectable lanthanum in the silicon substrate, and HRTEM shows stability of the amorphous LaSiOx. An effective work function near 4.0eV is obtained for these gate stacks, making the stack design ideal for n-type metal-oxide-semiconductor device fabrication.
Transient photoconductivity measurements of carrier lifetimes in an InAs∕In0.15Ga0.85As dots-in-a-well detector
Authors: Matthews Mary R. , Steed Robert J. , Frogley Mark D. , Phillips Chris C. , Attaluri Ram S. , Krishna Sanjay
Published: March 2007

A pulsed midinfrared photoconductivity study of electron recapture in dot-in-a-well infrared photodetectors yields bias-dependent electron-capture lifetimes in the range of 3–600ns and photoconductive gain factors of ∼104–105. The dependence of the lifetimes on temperature and electric field argues for these surprisingly long values being due to electron intervalley transfer. Under normal device operating conditions, photoexcited electrons transfer efficiently out of the central GaAs Γ minimum into the high energy L and X valleys, where they couple only weakly to the Γ-like confined states in the InAs dots.
High performance temperature controlled UHV sample holder
Authors: Marques Hugo P. , Alves David C. , Canário Ana R. , Moutinho Augusto M. C. , Teodoro Orlando M. N. D.
Published: March 2007

A requirement of many surface science studies is the capability to alter a sample temperature in a controlled mode. Sample preparation procedures such as heating or cooling ramps, high temperature spikes, fast annealing, or simply maintaining a sample at a very high, or very low, temperature are common. To address these issues, we describe the design and the construction of a multipurpose sample holder. Key points of this design are operation in an extended temperature range from liquid nitrogen (LN2) temperature to ∼1300K, temperature control during heating and cooling, low thermal inertia with rates up to 50Ks−1 (heating) and −20Ks−1 (cooling), and small heated volume to minimize background problems in thermal desorption spectroscopy (TDS) spectra. With this design the sample can be flash heated from LN2 temperature to 1300K and cooled down again in less than 100s. This sample holder was mounted and tested in a multitechnique apparatus and adds a large number of sample preparation procedures as well as TDS to the list of already available surface analysis techniques.
Self-assembled formation of ZnO hexagonal micropyramids with high luminescence efficiency
Authors: Kim DaeGwi , Wakaiki Shuji , Komura Shingo , Nakayama Masaaki , Mori Yukimasa , Suzuki Kazuyo
Published: March 2007

The authors have found the self-assembled formation of ZnO hexagonal micropyramids after the growth of a sufficiently thick ZnO layer on a (0001) Al2O3 substrate by rf-magnetron sputtering deposition. It was confirmed by scanning electron microscopy that the orientations of the micropyramids are well arranged. The reflection and photoluminescence spectra at 10K demonstrate that optical properties of the total growth layer are of high quality. The noticeable discovery with the use of cathodoluminescence spectroscopy is that the luminescence intensity of the micropyramids is 30 times stronger than that of the underlying layer; namely, strong enhancement of luminescence is realized in the self-assembled micropyramids.
Low threshold current density and negative characteristic temperature 1.3μm InAs self-assembled quantum dot lasers
Authors: Badcock T. J. , Royce R. J. , Mowbray D. J. , Skolnick M. S. , Liu H. Y. , Hopkinson M. , Groom K. M. , Jiang Q.
Published: March 2007

By combining optimized growth of the GaAs spacer layers and p-type modulation doping of the quantum dots, a 1.3μm emitting self-assembled quantum dot laser exhibiting both a low threshold current density and negative-T0 temperature behavior at room temperature is achieved. Spontaneous emission measurements provide no evidence for enhanced Auger recombination in doped devices. The negative T0 exhibited by the doped device is consistent with a delayed thermalization of carriers within the quantum dot ensemble.
Changes in microbubble dynamics near a boundary revealed by combined optical micromanipulation and high-speed imaging
Authors: Garbin V. , Cojoc D. , Ferrari E. , Di Fabrizio E. , Overvelde M. L. J. , van der Meer S. M. , de Jong N. , Lohse D. , Versluis M.
Published: March 2007

The authors report optical observations of the change in the dynamics of one and the same ultrasound contrast agent microbubble due to the influence of interfaces and neighboring bubbles. The bubble is excited by a 2.25MHz ultrasound burst and its oscillations are recorded with an ultrahigh-speed camera at 15 million frames per second. The position of an individual bubble relative to a rigid wall or second bubble is precisely controlled using optical tweezers based on Laguerre-Gaussian laser beams [P. Prentice et al., Opt. Express 12, 593 (2004); V. Garbin et al., Jpn. J. Appl. Phys. 44, 5773 (2005)]. This allows for repeated experiments on the very same bubble and for a quantitative comparison of the effect of boundaries on bubble behavior.
Single-electron transistors with wide operating temperature range
Authors: Dubuc C. , Beauvais J. , Drouin D.
Published: March 2007

Single-electron transistors are fabricated with a planar self-aligned process using chemical mechanical polishing. The method is demonstrated with Ti∕TiOx junctions and resistless lithography. The device characterization showed Coulomb blockade up to 433K. High temperature data allowed one to calculate the impact of the process variations on the charging energy and thus on a realistic operating temperature. It is found that single electron devices can have an operating temperature range similar to conventional silicon transistors, opening the door to hybrid designs. These approaches are promising because advanced functionality is created by an optimal combination of both technology strengths.
Aging-induced dielectric relaxation in barium titanate ceramics
Authors: Ahmad Mohamad M. , Yamada Koji , Meuffels Paul , Waser Rainer
Published: March 2007

In this letter the authors report on the aging effect on the phase transitions and dielectric properties of 1mol% Mn-doped BaTiO3 ceramics. Aging the ceramics in the ferroelectric state stimulates a resistance for the orthorhombic-tetragonal and tetragonal-cubic phase transitions, which leads to stabilization of the tetragonal phase over a wider temperature range. The dielectric constant of the aged sample shows dispersion, associated with a dielectric loss relaxation peak near the 100kHz frequency region, in contrast to the unaged one. The present results are discussed in light of the existing models for ferroelectric domain stabilization.
Relation between photoluminescence emission and local order-disorder in the CaTiO3 lattice modifier
Authors: de Lazaro Sergio , Milanez Juliana , de Figueiredo Alberthmeiry T. , Longo Valéria M. , Mastelaro Valmor R. , De Vicente Fabio S. , Hernandes Antônio C. , Varela José A. , Longo Elson
Published: March 2007

In this letter, the authors propose that photoluminescence emission in CaTiO3 is affected not only by disorder in the lattice former but also by structural disorder in the lattice modifier. Structural disorder was evaluated by Ti, Ca K-edge x-ray absorption near-edge structure experiments and by photoluminescence emission. The preedge feature of the Ca K edge was related to the intensity of photoluminescence emission. The results of the preedge feature of the Ca K-edge x-ray absorption near-edge structure confirm the presence of different Ca coordination numbers, namely, Ca–O11 and Ca–O12.
Image enhanced polymer-based multimode interference coupler covering C and L bands using deeply etched air trenches
Authors: Wang Xiaolong , Chen Ray T.
Published: March 2007

A design of multimode interference coupler with deeply etched air trenches at the boundary of the multimode section is proposed for photonic integrated circuitry on low-index-contrast materials. The device length decreases from 820to750μm for a 1×8 polymer multimode interference coupler. Due to the enhanced optical confinement, the optimized coupler with air trenches experimentally achieved 0.28∕0.23dB reduced insertion loss, 2.16∕2.34dB improved contrast ratio for transverse-electric and transverse-magnetic polarization, compared with conventional multimode interference coupler. The device entirely covers the wavelength range of both C and L bands, which is sufficient for broadband communications.
Origin of the drain current bistability in polymer ferroelectric field-effect transistors
Authors: Naber R. C. G. , Massolt J. , Spijkman M. , Asadi K. , Blom P. W. M. , de Leeuw D. M.
Published: March 2007

The authors present measurements that elucidate the mechanism behind the observed drain current bistability in ferroelectric field-effect transistors based on the ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene) as the gate dielectric. Capacitance-voltage measurements on metal-insulator-semiconductor diodes demonstrate that the bistability originates from switching between two states in which the ferroelectric gate dielectric is either polarized or depolarized. Pulsed charge displacement measurements on these diodes enable a direct measurement of the accumulated charge in the polarized state of 40±3mC∕m2.
Physics and the Information Revolution
Authors: Birnbaum Joel , Williams R. Stanley
Published: March 2007

In the fourth century BC, a young man named Pythias was condemned to death by Dionysius, the tyrant of Syracuse, for plotting against him, but Pythias was granted three days’ leave to go home to settle his family's affairs after his friend Damon agreed to take his place and be executed should Pythias not return. Pythias encountered many problems but managed to return just in time to save Damon. Dionysius was so struck by this remarkable and honorable friendship that he released them both.
Survey Halves Estimated Population of Big Near-Earth Asteroids
Authors: Schwarzschild Bertram
Published: March 2007

On 1 January 1801, reckoned by sticklers to be the first day of the 19th century, the Sicilian astronomer Giuseppe Piazzi discovered Ceres, the first of the asteroids. With a diameter of almost 1000 km, Ceres remains by far the largest of the known asteroids. Piazzi was searching the region between the orbits of Mars and Jupiter where Bode's law, an empirical formula of the day, said there ought to be an undiscovered planet.
The Quantum Hall Effect—in Pentacene?
Authors: Levi Barbara Goss
Published: March 2007

Organic materials have long held promise as possible inexpensive semiconductors in field-effect transistors (FETs) for electronic circuits. No one, however, had dreamed that one might use them to create a two-dimensional gas of electrons or holes and with it to study fundamental electronic behavior. Thus, Bertram Batlogg of Bell Laboratories, Lucent Technologies, stunned an audience at the March Meeting of the American Physical Society in Minneapolis by showing textbook curves of the fractional and integer quantum Hall effects and of an apparent metal-insulator transition—all seen in FETs made with tetracene and pentacene (chains of four and five benzene rings, respectively).

The following news story reports on work that has since been discredited. An independent committee commissioned by Bell Laboratories, Lucent Technologies, found evidence of scientific misconduct in the papers on which it was based (see Physics Today, November 2002, page 15 http://dx.doi.org/10.1063/1.1534995 ). The authors have withdrawn the papers in questions.
Career Opportunities in Optics
Authors: Johnson Anthony M. , Breck Hitz C.
Published: March 2007

It's the bandwidth, stupid! That's the most concise explanation of the explosive growth in interest in optical communications. This year's Optical Fiber Communications conference drew a record 17 300 people, an astounding 70% increase over an already robust attendance last year. The number of exhibitors at the meeting, which was held in Baltimore in March, was up by 25%. More than 3400 jobs were posted for consideration by a record 300 job seekers—11 jobs per seeker. Similarly, the Photonics West conference, held in San Jose in January, drew a record attendance of 12 141, surpassing the previous year's attendance by nearly a thousand.
Rho GTPase Cdc42 coordinates hematopoietic stem cell quiescence and niche interaction in the bone marrow
Authors: Yang Linda , Wang Lei , Geiger Hartmut , Cancelas Jose A. , Mo Jun , Zheng Yi
Published: March 2007

Adult hematopoietic stem cells (HSCs) exist in a relatively quiescent state in the bone marrow (BM) microenvironment to fulfill long-term self-renewal and multilineage differentiation functions, an event that is tightly regulated by extrinsic and intrinsic cues. However, the mechanism coordinating the quiescent state of HSCs and their retention in the BM microenvironment remains poorly understood. In a conditional-knockout mouse model, we show that Cdc42
−/−
HSCs enter the active cell cycle, resulting in significantly increased number and frequency of the stem/progenitor cells in the BM. Cdc42 deficiency also causes impaired adhesion, homing, lodging, and retention of HSCs, leading to massive egress of HSCs from BM to distal organs and peripheral blood and to an engraftment failure. These effects are intrinsic to the HSCs and are associated with deregulated c-Myc, p21
Cip1
, β1-integrin, and N-cadherin expressions and defective actin organization. Thus, Cdc42 is a critical coordinator of HSC quiescence maintenance and interaction with the BM niche.
Smad4 is critical for self-renewal of hematopoietic stem cells
Authors: Karlsson Göran , Blank Ulrika , Moody Jennifer L. , Ehinger Mats , Singbrant Sofie , Deng Chu-Xia , Karlsson Stefan
Published: March 2007

Members of the transforming growth factor β (TGF-β) superfamily of growth factors have been shown to regulate the in vitro proliferation and maintenance of hematopoietic stem cells (HSCs). Working at a common level of convergence for all TGF-β superfamily signals, Smad4 is key in orchestrating these effects. The role of Smad4 in HSC function has remained elusive because of the early embryonic lethality of the conventional knockout. We clarify its role by using an inducible model of Smad4 deletion coupled with transplantation experiments. Remarkably, systemic induction of Smad4 deletion through activation of MxCre was incompatible with survival 4 wk after induction because of anemia and histopathological changes in the colonic mucosa. Isolation of Smad4 deletion to the hematopoietic system via several transplantation approaches demonstrated a role for Smad4 in the maintenance of HSC self-renewal and reconstituting capacity, leaving homing potential, viability, and differentiation intact. Furthermore, the observed down-regulation of notch1 and c-myc in Smad4−/− primitive cells places Smad4 within a network of genes involved in the regulation HSC renewal.
A palindrome-driven complex rearrangement of 22q11.2 and 8q24.1 elucidated using novel technologies
Authors: Gotter Anthony L. , Nimmakayalu Manjunath A. , Jalali G. Reza , Hacker April M. , Vorstman Jacob , Conforto Duffy Danielle , Medne Livija , Emanuel Beverly S.
Published: March 2007

Constitutional translocations at the same 22q11.21 low copy repeat B (LCR-B) breakpoint involved in the recurrent t(11;22) are relatively abundant. A novel 46,XY,t(8;22)(q24.13;q11.21) rearrangement was investigated to determine whether the recurrent LCR-B breakpoint is involved. Investigations demonstrated an inversion of the 3Mb region typically deleted in patients with the 22q11.2 deletion syndrome. The 22q11.21 inversion appears to be mediated by low copy repeats, and is presumed to have taken place prior to translocation with 8q24.13. Despite predictions based on inversions observed in other chromosomes harboring low copy repeats, this 22q11.2 inversion has not been observed previously. The current studies utilize novel laser microdissection and MLPA (multiplex ligation-dependent probe amplification) approaches, as adjuncts to FISH, to map the breakpoints of the complex rearrangements of 22q11.21 and 8q24.21. The t(8;22) occurs between the recurrent site on 22q11.21 and an AT-rich site at 8q24.13, making it the fifth different chromosomal locus characterized at the nucleotide level engaged in a translocation with the unstable recurrent breakpoint at 22q11.21. Like the others, this breakpoint occurs at the center of a palindromic sequence. This sequence appears capable of forming a perfect 145 bp stem–loop. Remarkably, this site appears to have been involved in a previously reported t(3;8) occurring between 8q24.13 and FRA3B on 3p14.2. Further, the fragile site-like nature of all of the breakpoint sites involved in translocations with the recurrent site on 22q11.21, suggests a mechanism based on delay of DNA replication in the initiation of these chromosomal rearrangements.
Angiotensin-(1-7)-induced plasticity changes in the lateral amygdala are mediated by COX-2 and NO
Authors: Albrecht Doris
Published: March 2007

It is known from studies outside the brain that upon binding to its receptor, angiotensin-(1-7) elicits the release of prostanoids and nitric oxide (NO). Cyclooxygenase (COX) is a key enzyme that converts arachidonic acid to prostaglandins. Since there are no data available so far on the role of COX-2 in the amygdala, in a first step we demonstrated that the selective COX-2 inhibitor NS-398 significantly reduced the probability of long-term potentiation (LTP) induction in the lateral nucleus of the amygdala. Similarly, in COX-2−/−mice, LTP induced by external capsule (EC) stimulation was impaired. Second, we evaluated the action of angiotensin-(1-7) in the amygdala. In wild-type mice, angiotensin-(1-7) increased LTP. This LTP-enhancing effect of Ang-(1-7) was not observed in COX-2+/−mice. However, in COX-2−/−mice, Ang-(1-7) caused an enhancement of LTP similar to that in wild-type mice. The NO synthetase inhibitor L-NAME blocked this angiotensin-(1-7)-induced increase in LTP in COX-2−/−mice. Low-frequency stimulation of external capsule fibers did not cause long-term depression (LTD) in drug-free and angiotensin-(1-7)-treated brain slices in wild-type mice. In contrast, in COX-2−/−mice, angiotensin-(1-7) caused stable LTD. Increasing NO concentration by the NO-donor SNAP also caused LTD in wild-type mice. Our study shows for the first time that LTP in the amygdala is dependent on COX-2 activity. Moreover, COX-2 is involved in the mediation of angiotensin-(1-7) effects on LTP. Finally, it is recognized that there is a molecular cross-talk between COX-2 and NO that may regulate synaptic plasticity.
Implicit probabilistic sequence learning is independent of explicit awareness
Authors: Song Sunbin , Howard James H. , Howard Darlene V.
Published: March 2007

Studies into interactions between explicit and implicit motor sequence learning have yielded mixed results. Some of these discrepancies have been attributed to difficulties in isolating implicit learning. In the present study, the effect of explicit knowledge on implicit learning was investigated using a modified version of the Alternating Serial Response Time (ASRT) task, a probabilistic sequence learning paradigm that yields continuous and relatively pure measures of implicit learning. Results revealed that implicit learning occurred to the same extent, whether or not subjects had explicit knowledge. Some evidence, however, indicated that explicit knowledge could interfere with the expression of implicit learning early in training. In addition, there were dissociations between learning measures, in that reaction time and accuracy were differentially affected by explicit knowledge. These findings indicate that implicit sequence learning occurs independently of explicit knowledge, and help to explain previous discrepant findings.
Medial auditory thalamic stimulation as a conditioned stimulus for eyeblink conditioning in rats
Authors: Campolattaro Matthew M. , Halverson Hunter E. , Freeman John H.
Published: March 2007

The neural pathways that convey conditioned stimulus (CS) information to the cerebellum during eyeblink conditioning have not been fully delineated. It is well established that pontine mossy fiber inputs to the cerebellum convey CS-related stimulation for different sensory modalities (e.g., auditory, visual, tactile). Less is known about the sources of sensory input to the pons that are important for eyeblink conditioning. The first experiment of the current study was designed to determine whether electrical stimulation of the medial auditory thalamic nuclei is a sufficient CS for establishing eyeblink conditioning in rats. The second experiment used anterograde and retrograde tract tracing techniques to assess neuroanatomical connections between the medial auditory thalamus and pontine nuclei. Stimulation of the medial auditory thalamus was a very effective CS for eyeblink conditioning in rats, and the medial auditory thalamus has direct ipsilateral projections to the pontine nuclei. The results suggest that the medial auditory thalamic nuclei and their projections to the pontine nuclei are components of the auditory CS pathway in eyeblink conditioning.
LTP induction modifies functional relationship among hippocampal neurons
Authors: Yun Sung H. , Lee Deok S. , Lee Hyunjung , Baeg Eun H. , Kim Yun B. , Jung Min W.
Published: March 2007

To obtain evidence linking long-term potentiation (LTP) and memory, we examined whether LTP induction modifies functional relationship among neurons in the rat hippocampus. In contrast to neurons in low-frequency stimulated or AP5-treated slices, LTP induction altered ‘functional connectivity,’ as defined by the degree of synchronous firing, among simultaneously recorded neurons in the CA3 region. Interestingly, functional connectivity changed bidirectionally so that the total sum of functional connectivity remained constant. These results demonstrate LTP-induced changes in neuronal functional connectivity and suggest the existence of a normalization mechanism for the total sum of functional connectivity.
The influence of visual ability on learning and memory performance in 13 strains of mice
Authors: Brown Richard E. , Wong Aimée A.
Published: March 2007

We calculated visual ability in 13 strains of mice (129SI/Sv1mJ, A/J, AKR/J, BALB/cByJ, C3H/HeJ, C57BL/6J, CAST/EiJ, DBA/2J, FVB/NJ, MOLF/EiJ, SJL/J, SM/J, and SPRET/EiJ) on visual detection, pattern discrimination, and visual acuity and tested these and other mice of the same strains in a behavioral test battery that evaluated visuo-spatial learning and memory, conditioned odor preference, and motor learning. Strain differences in visual acuity accounted for a significant proportion of the variance between strains in measures of learning and memory in the Morris water maze. Strain differences in motor learning performance were not influenced by visual ability. Conditioned odor preference was enhanced in mice with visual defects. These results indicate that visual ability must be accounted for when testing for strain differences in learning and memory in mice because differences in performance in many tasks may be due to visual deficits rather than differences in higher order cognitive functions. These results have significant implications for the search for the neural and genetic basis of learning and memory in mice.
Context preexposure prevents forgetting of a contextual fear memory: Implication for regional changes in brain activation patterns associated with recent and remote memory tests
Authors: Biedenkapp Joseph C. , Rudy Jerry W.
Published: March 2007

Contextual fear conditioning was maintained over a 15-day retention interval suggesting no forgetting of the conditioning experience. However, a more subtle generalization test revealed that, as the retention interval increased, rats showed enhanced generalized fear to an altered context. Preexposure to the training context prior to conditioning, however, prevented this enhanced generalized fear from developing. These results support the hypothesis that the memory representation of the context degrades as the memory ages and is responsible for enhanced generalization. The implications of these results for systems consolidation versus forgetting interpretations of regional changes in neural activation patterns that occur as memories age are discussed.
Magnaporthe griseaInfection Triggers RNA Variation and Antisense Transcript Expression in Rice
Authors: Gowda Malali , Venu R.-C. , Li Huameng , Jantasuriyarat Chatchawan , Chen Songbiao , Bellizzi Maria , Pampanwar Vishal , Kim HyeRan , Dean Ralph A. , Stahlberg Eric , Wing Rod , Soderlund Cari , Wang Guo-Liang
Published: March 2007

Rice blast disease, caused by the fungal pathogen Magnaporthe grisea, is an excellent model system to study plant-fungal interactions and host defense responses. In this study, comprehensive analysis of the rice (Oryza sativa) transcriptome after M. grisea infection was conducted using robust-long serial analysis of gene expression. A total of 83,382 distinct 21-bp robust-long serial analysis of gene expression tags were identified from 627,262 individual tags isolated from the resistant (R), susceptible (S), and control (C) libraries. Sequence analysis revealed that the tags in the R and S libraries had a significant reduced matching rate to the rice genomic and expressed sequences in comparison to the C library. The high level of one-nucleotide mismatches of the R and S library tags was due to nucleotide conversions. The A-to-G and U-to-C nucleotide conversions were the most predominant types, which were induced in the M. grisea-infected plants. Reverse transcription-polymerase chain reaction analysis showed that expression of the adenine deaminase and cytidine deaminase genes was highly induced after inoculation. In addition, many antisense transcripts were induced in infected plants and expression of four antisense transcripts was confirmed by strand-specific reverse transcription-polymerase chain reaction. These results demonstrate that there is a series of dynamic and complex transcript modifications and changes in the rice transcriptome at the M. grisea early infection stages.
The Mi-1-Mediated Pest Resistance Requires Hsp90 and Sgt1
Authors: Bhattarai Kishor K. , Li Qi , Liu Yule , Dinesh-Kumar Savithramma P. , Kaloshian Isgouhi
Published: March 2007

The tomato (Solanum lycopersicum) Mi-1 gene encodes a protein with putative coiled-coil nucleotide-binding site and leucine-rich repeat motifs. Mi-1 confers resistance to root-knot nematodes (Meloidogyne spp.), potato aphids (Macrosiphum euphorbiae), and sweet potato whitefly (Bemisia tabaci). To identify genes required in the Mi-1-mediated resistance to nematodes and aphids, we used tobacco rattle virus (TRV)-based virus-induced gene silencing (VIGS) to repress candidate genes and assay for nematode and aphid resistance. We targeted Sgt1 (suppressor of G-two allele of Skp1), Rar1 (required for Mla12 resistance), and Hsp90 (heat shock protein 90), which are known to participate early in resistance gene signaling pathways. Two Arabidopsis (Arabidopsis thaliana) Sgt1 genes exist and one has been implicated in disease resistance. Thus far the sequence of only one Sgt1 ortholog is known in tomato. To design gene-specific VIGS constructs, we cloned a second tomato Sgt1 gene, Sgt1-2. The gene-specific VIGS construct TRV-SlSgt1-1 resulted in lethality, while silencing Sgt1-2 using TRV-SlSgt1-2 did not result in lethal phenotype. Aphid and root-knot nematode assays of Sgt1-2-silenced plants indicated no role for Sgt1-2 in Mi-1-mediated resistance. A Nicotiana benthamiana Sgt1 VIGS construct silencing both Sgt1-1 and Sgt1-2 yielded live plants and identified a role for Sgt1 in Mi-1-mediated aphid resistance. Silencing of Rar1 did not affect Mi-1-mediated nematode and aphid resistance and demonstrated that Rar1 is not required for Mi-1 resistance. Silencing Hsp90-1 resulted in attenuation of Mi-1-mediated aphid and nematode resistance and indicated a role for Hsp90-1. The requirement for Sgt1 and Hsp90-1 in Mi-1-mediated resistance provides further evidence for common components in early resistance gene defense signaling against diverse pathogens and pests.
Management of incomplete regional anaesthesia in Germany: results of a nation‐wide survey
Authors: Heid F. , Jage B. , Piepho T. , Jage J.
Published: March 2007

Background:  Regional anaesthesia (RA) provides well‐defined benefits with known attendant risks. However, incomplete blockade may introduce unanticipated risks depending on the compensatory measures employed. Until now, no data were available characterizing the pattern of response of German anaesthesiologists in this situation. This study analyses interventions in response to incomplete RA in a nation‐wide setting.

Methods:  A questionnaire was sent to every German anaesthesia department (n= 1381). Questions focused on interventions coping with an incomplete RA and differentiated between a pre‐ and a peri‐surgical setting and measures to face pain outside the surgical field. If systemic supplementation was administered, we analysed the substances and characterized their influence on subsequent patient care.

Results:  Six hundred and sixty‐seven questionnaires were returned anonymously, representing a return rate of 48.3%. If RA was incomplete before surgery, 56.8% of anaesthesiologists repeated peripheral blocks, 48.5% repeated epidural (EDA) and 60.4% repeated spinal anaesthesia (SPA). 56.9% of clinicians preferred an early switch to general anesthesia (GA). If RA was incomplete during surgery, 49.5% tended to switch early to GA, 13.9% made attempts to avoid this by intensive systemic supplementation. Benzodiazepines and opioids were the most commonly used substances. Pain or discomfort outside the surgical field was widely managed by intravenous supplementation (67.7%) and only 10.6% were willing to switch to general anaesthesia.

Conclusions:  In Germany, anaesthesiologists manage incomplete RA using a widespread spectrum of measures. Some might introduce specific risks, which potentially outweigh the benefits of RA in comparison to GA techniques.
The effects of single‐dose tramadol on post‐operative pain and morphine requirements after coronary artery bypass surgery
Authors: But A. K. , Erdil F. , Yucel A. , Gedik E. , Durmus M. , Ersoy M. O.
Published: March 2007

Aim:  To investigate the effects of a single dose of tramadol administered prior to extubation on post‐operative pain and morphine consumption after coronary artery bypass surgery.

Methods:  Patients were randomized post‐operatively into two groups (group T, n= 30; group P, n= 30). The technique of anaesthesia was standardized for all patients. The patients in group T received intravenous tramadol, 1 mg/kg, and the patients in group P received 2 ml of saline 0.9%, both approximately 1 h before extubation. After extubation, all patients were allowed to use the morphine patient‐controlled analgesia (PCA) device for 24 h post‐operatively. Post‐operative data were recorded in the cardiac intensive care unit at 30 min, 1 h, 2 h, 4 h, 12 h and 24 h after extubation by the same anaesthesiologist, who had no knowledge of the groups, and the side‐effects were also evaluated.

Results:  In group P, the visual analogue scale (VAS) scores were found to be higher 30 min (P < 0.01), 1 h (P < 0.01), 2 h (P < 0.01) and 4 h (P < 0.05) after extubation. The patient comfort scores were higher in group T 30 min (P < 0.01), 1 h (P < 0.05), 2 h (P < 0.01) and 4 h (P < 0.01) after extubation. The total morphine consumption was higher in group P at all evaluation times (P < 0.01), and the numbers of PCA demands and boluses were also higher in group P (P < 0.01).

Conclusions:  The study demonstrated that a single dose of tramadol administered prior to extubation following coronary artery bypass surgery is associated with a decrease of up to 25% in morphine consumption, a decrease in the VAS scores and an improvement in patient comfort within the first 4 h post‐operatively.