bluuebunny/crossref_metadata_2025 huggingface dataset:
How the asymmetry of internal potential influences the shape of I-V characteristic of nanochannels
Authors: Kosińska I. D.
Published: July 2006

Ion transport in biological and synthetic nanochannels is characterized by such phenomena as ion current fluctuations, rectification, and pumping. Recently, it has been shown that the nanofabricated synthetic pores could be considered as analogous to biological channels with respect to their transport characteristics [P. Yu. Apel et al., Nucl. Instrum. Methods Phys. Res. B 184, 337 (2001); Z. Siwy et al., Europhys. Lett. 60, 349 (2002)]. The ion current rectification is analyzed. Ion transport through cylindrical nanopores is described by the Smoluchowski equation. The model is considering the symmetric nanopore with asymmetric charge distribution. In this model, the current rectification in asymmetrically charged nanochannels shows a diodelike shape of I-V characteristic. It is shown that this feature may be induced by the coupling between the degree of asymmetry and the depth of internal electric potential well. The role of concentration gradient is discussed.
Slow electron velocity-map imaging photoelectron spectra of the methoxide anion
Authors: Nee Matthew J. , Osterwalder Andreas , Zhou Jia , Neumark Daniel M.
Published: July 2006

High resolution anion photodetachment spectra are presented for the methoxide anion and its fully deuterated counterpart. The spectra were obtained with slow electron velocity-map imaging. Improved electron affinities are determined for CH3O as 1.5690±0.0019eV and for CD3O as 1.5546±0.0019eV. The spectra resolve many features associated with spin-orbit and vibronic coupling that were not seen in previous photodetachment studies. Photoelectron angular distributions taken as a function of detachment wavelength for the ground vibronic state transitions are recorded and are consistent with the removal of a nonbonding, p-type electron localized on the oxygen atom. Several hot bands and sequence bands are observed for the first time, providing insight into the vibrational structure of the methoxide anion. The results are compared to recent calculations of the anion photoelectron spectra that incorporate bilinear coupling terms among the methoxy vibrational modes and are found to be in reasonable agreement.
Epitaxial growth of GaN on copper substrates
Authors: Inoue S. , Okamoto K. , Matsuki N. , Kim Tae-Won , Fujioka H.
Published: July 2006

We have grown GaN films on Cu(111) substrates using pulsed laser deposition. We have found that GaN(0001) grows epitaxially on Cu(111) when employing low temperature grown AlN buffer layers with an in-plane epitaxial relationship of AlN[112¯0]‖Cu[11¯0] Reflection high-energy electron diffraction images have exhibited sharp streaky patterns, indicating that GaN grows with a flat surface. Electron backscattering diffraction observations have revealed that neither 30° rotational domains nor cubic phase domains exist in the GaN films. Spectroscopic ellipsometry measurements have shown that the heterointerfaces in the GaN∕AlN∕Cu structure are abrupt. The epitaxial growth of GaN on Cu substrates is likely to raise the power limit for future light emitting and electron devices due to the high thermal conductivity of Cu.
Electronic linearization of piezoelectric actuators and noise budget in scanning probe microscopy
Authors: Aloisi G. , Santucci A. , Carlà M. , Dolci D. , Lanzi L.
Published: July 2006

The maximum resolution achievable with a scanning probe microscope is limited by the probe size, by the mechanism of interaction with the sample, as is widely known, and by the electronic noise in the instrument. The evaluation of this noise for the three motion axes of a linearized high resolution scanning electrochemical microscope has been carried through and the intrinsic maximum resolution is discussed.
Dielectric and optical properties of epitaxial rare-earth scandate films and their crystallization behavior
Authors: Christen H. M. , Jellison G. E. , Ohkubo I. , Huang S. , Reeves M. E. , Cicerrella E. , Freeouf J. L. , Jia Y. , Schlom D. G.
Published: July 2006

Rare-earth scandates (ReScO3, with Re=Y, La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, i.e., the entire series for which the individual oxides are chemically stable in contact with Si) were deposited in a temperature-gradient pulsed laser deposition system onto LaAlO3 substrates. The crystallization temperature depends monotonically on the Re atomic number and the Goldschmidt tolerance factor, with crystallization temperatures as low as 650°C for LaScO3 and PrScO3. The dielectric constants of the crystalline films K≈30 (determined by microwave microscopy) are significantly larger than those of their amorphous counterparts. In combination with the large observed band gaps (Eg>5.5eV, determined by ellipsometry), these results indicate the potential of these materials as high-K dielectrics for field-effect transistor applications.
Broadband high-resolution elliptical crystal x-ray spectrometer for high energy density physics experiments
Authors: Anderson S. G. , Heeter R. F. , Booth R. , Emig J. , Fulkerson S. , McCarville T. , Norman D. , Young B. K. F.
Published: July 2006

The spectroscopic investigation of high temperature laser produced plasmas in general, and x-ray opacity experiments in particular, often requires instruments with both a broad coverage of x-ray energies and high spectral, spatial, and temporal resolution. We analyze the design, model the response, and report the commissioning of a spectrometer using elliptical crystals in conjunction with a large format, gated microchannel plate detector. Measurements taken with this instrument at the Janus laser facilities demonstrate the designed spectral range of 0.24–5.8keV and spectral resolution E∕ΔE>400, resulting in two to three times more spectral data than achieved by previous spectrometer designs. The observed 100ps temporal resolution and 35μm spatial resolution are consistent with the requirements of high energy density opacity experiments.
Apparatus for the imaging of infrared photoluminescence, transmittance, and phototransmittance with high spatial and spectral resolutions
Authors: Furstenberg Robert , Soares Julio A. , White Jeffrey O.
Published: July 2006

Photoluminescence is a widely used tool for the characterization of wide-gap semiconductor materials. However, most narrow-gap, infrared materials exhibit very weak, hard to detect photoluminescence. We report on the development of a sensitive, Fourier transform infrared (FTIR)-based apparatus capable of measuring and spatial imaging of weak infrared photoluminescence with diffraction limited resolution. The apparatus is also capable of measuring transmittance and phototransmittance. This is, to our knowledge, the first report of measuring infrared phototransmittance using an FTIR spectrometer.
Versatile optical manipulation system for inspection, laser processing, and isolation of individual living cells
Authors: Stuhrmann B. , Jahnke H.-G. , Schmidt M. , Jähn K. , Betz T. , Müller K. , Rothermel A. , Käs J. , Robitzki A. A.
Published: July 2006

Isolation of individual cells from a heterogeneous cell population is an invaluable step in the analysis of single cell properties. The demands in molecular and cellular biology as well as molecular medicine are the selection, isolation, and monitoring of single cells and cell clusters of biopsy material. Of particular interest are methods which complement a passive optical or spectroscopic selection with a variety of active single cell processing techniques such as mechanical, biochemical, or genetic manipulation prior to isolation. Sophisticated laser-based cell processing systems are available which can perform single cell processing in a contact-free and sterile manner. Until now, however, these multipurpose turnkey systems offer only basic micromanipulation and are not easily modified or upgraded, whereas laboratory situations often demand simple but versatile and adaptable solutions. We built a flexible laser micromanipulation platform combining contact-free microdissection and catapulting capabilities using a pulsed ultraviolet (337nm) laser with simultaneous generation of optical tweezing forces using a continuous wave infrared (1064nm) laser. The potential of our platform is exemplified with techniques such as local laser-induced injection of biomolecules into individual living cells, laser surgery, isolation of single cells by laser catapulting, and control of neuronal growth using optical gradient forces. Arbitrary dynamic optical force patterns can be created by fast laser scanning with acousto-optical deflectors and galvanometer mirrors, allowing multibeam contact-free micromanipulation, a prerequisite for reliable handling of material in laboratory-on-a-chip applications. All common microscopy techniques can be used simultaneously with the offered palette of micromanipulation methods. Taken together, we show that advanced optical micromanipulation systems can be designed which combine quality, cost efficiency, and adaptability.
Adjustable Wollaston-like prisms
Authors: Feldman M. , El-Amawy A. , Srivastava A. , Vaidyanathan R.
Published: July 2006

A combination of a polarizing beam splitter and two quarter wave plates is used to direct a beam of light into one of two directions, depending on its polarization. Its function is similar to that of a Wollaston prism, except that the angle between the two directions is adjustable and does not vary with wavelength. Three cascaded units have been used to deflect a beam of light into eight selectable directions.
Pulsed slit jet cavity ring-down spectroscopy with a midinfrared lead salt diode laser
Authors: Tam Wai Shun , Leonov Igor , Xu Yunjie
Published: July 2006

We report the design, construction, and evaluation of a midinfrared continuous wave cavity ring-down spectrometer based on a lead salt diode laser. A pulsed molecular beam assembly with a homemade slit nozzle was constructed and incorporated into the spectrometer. A computer program was developed to automate and to synchronize the timing of the cavity ring-down experiments with the pulsed molecular beam. To initiate a cavity ring-down event, a frequency detuning scheme is exploited to effectively block the laser from entering the ring-down cavity by rapidly shifting the laser frequency. The standard deviation of the experimental ring-down time, i.e., σ(τ)∕⟨τ⟩, was 0.63%, corresponding to a noise-equivalent absorption of 8.0×10−7 at a fixed laser frequency with an evacuated cavity with ten averaging cycles. A room temperature infrared spectrum of methane and a jet cooled infrared spectrum of propylene oxide at 3.3μm are presented.
Probehead operating at 35GHz for continuous wave and pulse electron paramagnetic resonance applications
Authors: Gromov Igor , Forrer Jörg , Schweiger Arthur
Published: July 2006

The design, construction, numerical modeling, and performance of a probehead for electron paramagnetic resonance (EPR) spectroscopy at 34–36GHz is described. A classical cylindrical cavity operating in the TE011 mode with adjustable frequency and coupling has been found to be well suited for continuous wave and pulse EPR studies of frozen solutions of transition metal complexes at low temperature. The highest attention is given to the probehead performance in the pulse mode. The implemented design has been analyzed in detail using numerical modeling. The distribution of the electromagnetic fields, eigenfrequencies, quality factors, coupling coefficients, and conversion factors are calculated and compared with experimental data. The results demonstrate the effectiveness of the design and can serve as a guide for probehead optimization.
Directional random lasing in dye-TiO2 doped polymer nanowire array embedded in porous alumina membrane
Authors: Shin Hee-Won , Cho Seung Yeon , Choi Kyong-Hoon , Oh Seung-Lim , Kim Yong-Rok
Published: July 2006

We have demonstrated the lasing in the porous alumina membrane filled with hybrid polymer nanowires which consisted of poly(N-vinylcarvazole), rhodamine 6G, and TiO2 nanoparticles. The angle-resolved photoluminescence measurement suggested that lasing had a strong directionality along the hybrid polymer nanowires which were embedded within the nanochannels of the membrane. Although wavelengths of the lasing peaks were not affected by excitation and detection angles, lasing behavior strongly depended on the pore diameters of the membranes utilized. It is suggested that the closed loops for lasing are formed via multiple scattering induced by TiO2 nanoparticles embedded in the hybrid polymer nanowires.
Injection of metallic elements into an electron-beam ion trap using a Knudsen cell
Authors: Yamada C. , Nagata K. , Nakamura N. , Ohtani S. , Takahashi S. , Tobiyama T. , Tona M. , Watanabe H. , Yoshiyasu N. , Sakurai M. , Kavanagh A. P. , Currell F. J.
Published: July 2006

A method of injecting metallic elements into an electron-beam ion trap (EBIT) is described. The method is advantageous over the conventional coaxial and pulsed injection methods in two ways: (a) complicated switching of injection and extraction beams can be avoided when extracting beams of highly charged ions from the EBIT and (b) a beam of stable intensity can be achieved. This method may be applicable to any metallic elements or metallic compounds that have vapor pressures of ∼0.1Pa at a temperature lower than 1900°C. We have employed this method for the extraction of highly charged ions of Bi, Er, Fe, and Ho.
At-wavelength figure metrology of hard x-ray focusing mirrors
Authors: Yumoto Hirokatsu , Mimura Hidekazu , Matsuyama Satoshi , Handa Soichiro , Sano Yasuhisa , Yabashi Makina , Nishino Yoshinori , Tamasaku Kenji , Ishikawa Tetsuya , Yamauchi Kazuto
Published: July 2006

We have developed an at-wavelength wave-front metrology of a grazing-incidence focusing optical systems in the hard x-ray region. The metrology is based on numerical retrieval from the intensity profile around the focal point. We demonstrated the at-wavelength metrology and estimated the surface figure error on a test mirror. An experiment for measuring the focusing intensity profile was performed at the 1-km-long beamline (BL29XUL) of SPring-8. The obtained results were compared with the profile measured using an optical interferometer and were confirmed to be in good agreement with it. This technique is a potential method of characterizing wave-front aberrations on elliptical mirrors for sub-10-nm focusing.
Machine vision and feedback control system allow the precise control of vascular deformation in vitro
Authors: Xu Jie , Zhou Xiaolin , Ge Haiyan , Yang Daping , Guo Tiefang
Published: July 2006

Mechanical environment significantly affects the growth of tissue-engineered vessels. Previous studies have focused on the effect of pressure, while the effect of deformation has not been thoroughly investigated due to the lack of precise deformation control technologies. In this study, we have developed a vascular deformation control system using machine vision and feedback control algorithms. The system continuously perfuses the tissue-engineered vessel with a peristaltic pump. The real-time image of deformed vessel in the processing chamber was captured by a video camera and then transmitted to a machine vision identifier to analyze the diameter of the vessel. The time series of diameters formed deformation ratios, which was compared with the deformation set point (from 1% to 15% in this study). The feedback value was converted into analog signal, driving a control valve to regulate the resistance of the vascular outlet port. In the pulsate perfusion process, the deformation of the tissue-engineered vessels were, respectively, controlled at 1%, 3%, 5%, 7%, 10%, and 15%, with an average variation of only 0.03%. A video camera aided by machine vision module can identify the diameter of tissue-engineered vessels in high resolution. A simple feedback control system is enough for keeping the vascular deformation at any set point between 1% and 15%. These findings will guide further investigations on deformation-based mechanical stimuli in vascular tissue engineering.
Real time multicomponent echo particle image velocimetry technique for opaque flow imaging
Authors: Zheng Hairong , Liu Lingli , Williams Logan , Hertzberg Jean R. , Lanning Craig , Shandas Robin
Published: July 2006

This letter reports on a contrast-based ultrasonic particle imaging technique (echo PIV) for measuring multicomponent velocity vectors in opaque flows with excellent temporal (up to 0.5ms) and spatial (up to 0.4mm) resolution. Ultrasound contrast microbubbles are used as flow tracers, and digitally acquired rf data are converted into B-mode images for PIV analysis. Here, velocity fields from various flow patterns (including rotating and transient vortex flows) that are difficult to measure using other opaque flow methods such as ultrasound Doppler or magnetic resonance imaging are measured using echo PIV. This nonintrusive technique should be a promising addition to opaque flow diagnostics.
Synchrotron x-ray powder diffraction studies in pulsed magnetic fields
Authors: Frings P. , Vanacken J. , Detlefs C. , Duc F. , Lorenzo J. E. , Nardone M. , Billette J. , Zitouni A. , Bras W. , Rikken G. L. J. A.
Published: July 2006

X-ray powder diffraction experiments under pulsed magnetic fields were carried out at the DUBBLE beamline (BM26B) at the ESRF. A mobile generator delivered 110kJ to the magnet coil, which was sufficient to generate peak fields of 30T. A liquid He flow cryostat allowed us to vary the sample temperature accurately between 8 and 300K. Powder diffraction patterns of several samples were recorded using 21keV monochromatic x-rays and an on-line image plate detector. Here we present the first results on the suppression of the Jahn-Teller structural distortion in TbVO4 by magnetic field. These data clearly demonstrate the feasibility of x-ray powder diffraction experiments under pulsed magnetic fields with relatively inexpensive instrumentation.
Observing the stereodynamics of chemical reactions using randomly oriented molecular beams
Authors: Gustafsson Magnus , Skodje Rex T. , Zhang Jianyang , Dai Dongxu , Harich Steven A. , Wang Xiuyan , Yang Xueming
Published: July 2006

A new method is demonstrated to study the stereodynamics of simple chemical reactions that does not require the use of oriented (or aligned) molecular beams or measurements of the orientation state of product molecules. Instead, it is shown that by numerically combining accurate measurements of the state-to-state differential cross section for two or more rotational states of the reagent molecule, the separate contribution from the individual helicity states can be extracted. New molecular beam experiments are conducted for the D+H2→HD+H reaction that confirm the validity of the method.
Nanoscale strain analysis of strained-Si metal-oxide-semiconductor field effect transistors by large angle convergent-beam electron diffraction
Authors: Liu H. H. , Duan X. F. , Qi X. Y. , Xu Q. X. , Li H. O. , Qian H.
Published: July 2006

In this letter we report the characterization of local compressive strain in p-type strained-silicon channel metal-oxide-semiconductor field effect transistors by large angle convergent-beam electron diffraction. The compressive strain was induced into the channel region of gate length of 80nm strained-Si p-type metal-oxide-semiconductor field effect transistor by Ge preamorphization implantation for source/drain extension. A method to distinguish between compressive strain and shear strain in the cross-sectional transmission electron microscopy specimens is proposed.
Long dephasing time in self-assembled InAs quantum dots at over 1.3μm wavelength
Authors: Ishi-Hayase J. , Akahane K. , Yamamoto N. , Sasaki M. , Kujiraoka M. , Ema K.
Published: July 2006

Excitonic dephasing is investigated in InAs self-assembled quantum dots fabricated by the strain-compensation technique. The exciton ground-state emission is centered at the wavelength of 1420nm at 5K. Transient four-wave mixing measurements under resonant excitation clearly demonstrate a long dephasing time of 1.09ns at 5K, corresponding to the homogeneous broadening of 1.2μeV. The extrapolated zero-temperature homogeneous broadening is limited only by the population lifetime of the exciton ground state. At slightly increased temperatures, the acoustic-phonon broadening becomes dominant on dephasing.
Plasma dynamics of water breakdown at a water surface induced by femtosecond laser pulses
Authors: Sarpe-Tudoran C. , Assion A. , Wollenhaupt M. , Winter M. , Baumert T.
Published: July 2006

Femtosecond laser pulse induced ultrafast plasma dynamics studies of water breakdown in the range up to 250ps are reported. We combine transient imaging techniques together with spectrally resolved reflection spectroscopy to monitor the early breakdown dynamics at the water surface with a laser intensity being 1.5 above threshold. We observe a 20ps delay before the plasma expands with an initial velocity of 5900m∕s. The transient electron density after formation of the plasma is 1.2×1021∕cm3. A recombination on a picosecond time scale with a rate of (1.6×10−9±0.3×10−9)cm3∕s is found.
p
-type behavior in nominally undoped ZnO thin films by oxygen plasma growth
Authors: Zeng Y. J. , Ye Z. Z. , Xu W. Z. , Lu J. G. , He H. P. , Zhu L. P. , Zhao B. H. , Che Y. , Zhang S. B.
Published: July 2006

We report on intrinsic p-type ZnO thin films by plasma-assisted metal-organic chemical vapor deposition. The optimal results give a resistivity of 12.7Ωcm, a Hall mobility of 2.6cm2∕Vs, and a hole concentration of 1.88×1017cm−3. The oxygen concentration is increased in the intrinsic p-type ZnO, compared with the n-type layer. Two acceptor states, with the energy levels located at 160 and 270meV above the valence band maximum, are identified by temperature-dependent photoluminescence. The origin of intrinsic p-type behavior has been ascribed to the formation of zinc vacancy and some complex acceptor center.
High tunnel magnetoresistance in fully epitaxial magnetic tunnel junctions with a full-Heusler alloy Co2Cr0.6Fe0.4Al thin film
Authors: Marukame Takao , Ishikawa Takayuki , Matsuda Ken-Ichi , Uemura Tetsuya , Yamamoto Masafumi
Published: July 2006

Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated with a Co-based full-Heusler alloy Co2Cr0.6Fe0.4Al (CCFA) thin film, whose composition was close to the stoichiometric one, and a MgO tunnel barrier. Cross-sectional high-resolution transmission electron microscope observations indicated that all layers of the CCFA∕MgO∕Co50Fe50 MTJ layer structure were grown epitaxially and were single crystalline. The microfabricated CCFA∕MgO∕Co50Fe50 MTJs exhibited high tunnel magnetoresistance (TMR) ratios of 90% at room temperature and 240% at 4.2K. A high tunneling spin polarization of 0.79 at 4.2K was obtained for the epitaxial CCFA films from the TMR ratios.
Passivation of boron emitters on n-type silicon by plasma-enhanced chemical vapor deposited silicon nitride
Authors: Chen Florence W. , Li Tsu-Tsung A. , Cotter Jeffrey E.
Published: July 2006

A well-passivated emitter is crucial to making high efficiency solar cells. With several reported potential benefits in using n-type silicon compared to p-type silicon for solar cell applications, there is a need to investigate silicon nitride passivation on boron-diffused emitters. The passivation of plasma-enhanced chemical vapor deposited silicon nitride with different refractive indices on a variety of boron doping profiles on 1Ωcm, float zoned, n-type silicon is studied. Contrary to the general perceptions that silicon nitride provides relatively poor passivation on boron-diffused surfaces, our results show that for some diffusion sheet resistances and with sufficient annealing, silicon nitride can be particularly well suited for passivating boron emitters. One-sun implied open circuit voltages of 663 and 718mV and dark saturation current densities of 25 and 13fA∕cm2 per side are achieved by silicon nitride passivation on moderately doped boron emitters (100Ω∕sq) and lightly doped boron emitters (240Ω∕sq), respectively.
Field-mediated self-assembly and actuation of highly parallel microfluidic devices
Authors: Bleil S. , Marr D. W. M. , Bechinger C.
Published: July 2006

We present a macroscopic approach for the fabrication and actuation of microscale pumps in microfluidic environments. By applying a combination of rotating and static magnetic fields we overcome two fundamental issues preventing development of nanoscale systems: how does one assemble components in situ and how does one power these devices once in place? By using macroscopic fields we avoid the need for individual particle micromanipulation allowing for both scale down to the nanoscale and “scale up” to the simultaneous assembly and control of highly parallel device networks.
Effects of As and Mn doping on microstructure and electrical conduction in ZnO films
Authors: Lord K. , Williams T. M. , Hunter D. , Zhang K. , Dadson J. , Pradhan A. K.
Published: July 2006

We report the synthesis of epitaxial As-doped ZnO and Mn-doped (ZnAs)O films by pulsed-laser deposition technique. The grain size in (ZnAs)O films decreases from 40 to less than 10nm upon Mn doping, illustrating that Mn acts as a potential catalyst to create nanosize grains. Temperature dependent electrical resistance shows metal-insulator transition and metal-semiconductor transition (MST) at 165 and 115K, respectively, in (ZnAs)O, although Mn doping suppresses MST completely. Both ionization efficiency on oxygen vacancies and percolation of charge carriers may be responsible for such transitions. In addition, electrical conduction in these films shows strong aging effects.
Alternative precursor metal-organic chemical vapor deposition of InGaAs∕GaAs quantum dot laser diodes with ultralow threshold at 1.25μm
Authors: Strittmatter A. , Germann T. D. , Kettler Th. , Posilovic K. , Pohl U. W. , Bimberg D.
Published: July 2006

Laser diodes based on InGaAs quantum dots (QDs) operating at 1250nm with ultralow threshold current densities of 66A∕cm2, transparency current densities of 10A∕cm2 per quantum dot layer, and high internal quantum efficiencies of 94% have been realized using alternative precursor metal-organic chemical vapor deposition. Photoluminescence of the active QD stacks clearly indicates the requirement of varying growth parameters for subsequently deposited QD layers. The excellent performance of the QD lasers was obtained by adjusting the number of stacked QD layers to a limit given by the In content of the InGaAs strain-reducing layers grown on the QDs and individual durations of the growth interruption after deposition for each QD layer.
Modified atomic force microscope for high-rate dynamic force spectroscopy
Authors: Ptak A. , Kappl M. , Butt H.-J.
Published: July 2006

Usually adhesion forces between interfaces increase with the rate of separating the interfaces. One of the most popular instruments for such rate-dependent adhesion experiments (also called dynamic force spectroscopy) is the atomic force microscope (AFM). A limitation of this as well as that of other experimental techniques is the maximum loading rate that can be applied. We extended the range of loading rates of a commercial AFM by up to three orders of magnitude by integration of a small additional piezoactuator with high resonance frequency. Performance of the instrument is demonstrated for a model system of self-assembled monolayers of thiols.
Thermal conductivity enhancement in water-in-FC72 nanoemulsion fluids
Authors: Yang B. , Han Z. H.
Published: July 2006

The strategy of adding solid particles to fluids for improving thermal conductivity has been pursued for nearly a century. In this work, a concept of using liquid nanodroplets for enhancing thermal conductivity has been developed and was demonstrated in water-in-FC72 suspensions, called “nanoemulsion fluids.” The thermal conductivity of FC72 is found to be increased by up to 52% for a nanoemulsion fluid containing 12vol% water nanodroplets of radius 9.8nm. Such types of nanoemulsion fluids possess long-term stability and can be mass produced because of no needs for solid nanoparticles. The development of nanoemulsion fluids would open a direction for thermal fluids studies.
Scalings of steady state Hall magnetohydrodynamic reconnection in high-beta plasmas
Authors: Wang Xiaogang , Yang Hong-Ang , Jin Shu-Ping
Published: July 2006

Scalings of Hall magnetohydrodynamics reconnection in high-β plasmas has been studied in steady states. It again confirms previous temporal evolution reconnection results that while the width of the reconnection layer is scaled by ωA∕Ωci=di∕Lc, where ωA is the Alfvén frequency, Ωci is the ion gyrofrequency, Lc is the typical system length scale, and di=c∕ωpi is the ion inertial length, the length of the layer should be scaled by (ωA∕Ωci)1∕2Lc=(diLc)1∕2 [X. Wang and A. Bhattacharjee, Phys. Rev. Lett. 70, 1627 (1993)], to yield the fast reconnection rate of (di∕Lc)1∕2VA with VA as the Alfvén velocity [X. Wang, A. Bhattacharjee, and Z. Ma, Phys. Rev. Lett. 87, 265003 (2001)]. It is also shown that the reconnection rate is proportional to the perturbed boundary flow. Furthermore it is found that in the high-β plasmas, the reconnection keeps constant in the regime β<2, and decays as β−1∕2 for β⩾2.
HERC5 is an IFN-induced HECT-type E3 protein ligase that mediates type I IFN-induced ISGylation of protein targets
Authors: Wong Joyce Jing Yi , Pung Yuh Fen , Sze Newman Siu-Kwan , Chin Keh-Chuang
Published: July 2006

Type I IFNs induce the expression of IFN-stimulated gene 15 (ISG15) and its conjugation to cellular targets. ISGylation is a multistep process involving IFN-inducible Ube1L, UbcH8, and a yet-to-be identified E3 ligase. Here we report the identification of an IFN-induced HECT-type E3 protein ligase, HERC5/Ceb1, which mediates ISGylation. We also defined a number of proteins modified by ISG15 after IFN triggering or HERC5 overexpression. A reduction in endogenous HERC5 by small interfering RNA inhibition blocks the IFN-induced ISG15 conjugation. Conversely, HERC5 coexpression with Ube1L and UbcH8 induces the ISG15 conjugation
in vivo
independent of IFN stimulation. A targeted substitution of Cys-994 to Ala in the HECT domain of HERC5 completely abrogates its E3 protein ligase activity. Therefore, this study demonstrates that HERC5/Ceb1 is involved in the conjugation of ISG15 to cellular proteins.
Cryptic sex and many-to-one coevolution in the fungus-growing ant symbiosis
Authors: Mikheyev Alexander S. , Mueller Ulrich G. , Abbot Patrick
Published: July 2006

The fungus-growing ants have long provided a spectacular example of coevolutionary integration. Their ecological success is thought to depend largely on the evolutionary alignment of reproductive interests between ants and fungi after vertical transmission and the ancient suppression of fungal sexuality. In the present study we test these assumptions and provide the first evidence of recombination in attine cultivars, contradicting widely held perceptions of obligate clonality. In addition, we document long-distance horizontal transmission of symbionts between leaf-cutter ant species on mainland Central America and South America and those endemic to Cuba, suggesting both lack of pairwise coevolutionary specificity in ant/cultivar interactions and dispersal of symbionts independent of their ant hosts. The coevolution between leaf-cutters and their fungal symbionts is thus not reciprocally pairwise. Rather, a single widespread and sexual fungal symbiont species is engaged in multiple interactions with divergent ant lineages. Strict fungal clonality and vertical transmission evidently have not played a critical role in the long-term evolutionary or ecological success of this well known mutualism.
Discrete steps in sensing of β-lactam antibiotics by the BlaR1 protein of the methicillin-resistant
Staphylococcus aureus
bacterium
Authors: Thumanu Kanjana , Cha Jooyoung , Fisher Jed F. , Perrins Richard , Mobashery Shahriar , Wharton Christopher
Published: July 2006

Chemical sensing by cell-surface receptors to effect signal transduction is a ubiquitous biological event. Despite extensive structural biochemical study, detailed knowledge of how signal transduction occurs is largely lacking. We report herein a kinetic and structural study, obtained by stopped-flow IR spectroscopy, of the activation of the BlaR1 receptor of the
Staphylococcus aureus
bacterium by β-lactam antibiotics. The cell-surface BlaR1 receptor alerts the bacterium to the presence of β-lactam antibiotics, resulting in expression of the gene for a β-lactamase enzyme. This enzyme hydrolytically destroys the remaining β-lactam antibiotics. IR spectroscopic interrogation of the β-lactam–BlaR1 receptor reaction has allowed the simultaneous measurement of the chemical events of receptor recognition of the β-lactam and the characterization of the conformational changes in the BlaR1 receptor that result. The key chemical events in β-lactam recognition are serine acylation and subsequent irreversible decarboxylation of the BlaR1 active site lysine carbamate. Both events are observed by stopped-flow IR kinetics and
13
C isotope-edited IR spectroscopy. The secondary structural changes in the BlaR1 receptor conformation that occur as a consequence of this acylation/decarboxylation are predicted to correlate to the signal transduction event accomplished by this receptor.
A sensor for intracellular ionic strength
Authors: Biemans-Oldehinkel Esther , Mahmood Nik A. B. N. , Poolman Bert
Published: July 2006

Cystathionine-β-synthase (CBS) domains are found in >4,000 proteins in species from all kingdoms of life, yet their functions are largely unknown. Tandem CBS domains are associated with membrane transport proteins, most notably members of the ATP-binding cassette (ABC) superfamily; voltage-gated chloride channels and transporters; cation efflux systems; and various enzymes, transcription factors, and proteins of unknown function. We now show that tandem CBS domains in the osmoregulatory ABC transporter OpuA are sensors for ionic strength that control the transport activity through an electrostatic switching mechanism. The on/off state of the transporter is determined by the surface charge of the membrane and the internal ionic strength that is sensed by the CBS domains. By modifying the CBS domains, we can control the ionic strength dependence of the transporter: deleting a stretch of C-terminal anionic residues shifts the ionic strength dependence to higher values, whereas deleting the CBS domains makes the system largely independent of ionic strength. We present a model for the gating of membrane transport by ionic strength and propose a new role for CBS domains.
Aberrant Wnt/β-catenin signaling can induce chromosomal instability in colon cancer
Authors: Hadjihannas Michel V. , Brückner Martina , Jerchow Boris , Birchmeier Walter , Dietmaier Wolfgang , Behrens Jürgen
Published: July 2006

Chromosomal instability (CIN), a hallmark of most colon tumors, may promote tumor progression by increasing the rate of genetic aberrations. CIN is thought to arise as a consequence of improper mitosis and spindle checkpoint activity, but its molecular basis remains largely elusive. The majority of colon tumors develop because of mutations in the tumor suppressor APC that lead to Wnt/β-catenin signaling activation and subsequent transcription of target genes, including conductin/AXIN2. Here we demonstrate that Wnt/β-catenin signaling causes CIN via up-regulation of conductin. Human colon tumor samples with CIN show significantly higher expression of conductin than those without. Conductin is up-regulated during mitosis, localizes along the mitotic spindles of colon cancer cells, and binds to polo-like kinase 1. Ectopic expression of conductin or its up-regulation through small interfering RNA-mediated knock-down of APC leads to CIN in chromosomally stable colon cancer cells. High conductin expression compromises the spindle checkpoint, and this requires localized polo-like kinase 1 activity. Knock-down of conductin by small interfering RNA in colon carcinoma cells or gene ablation in mouse embryo fibroblasts enforces the checkpoint.
The Relationship Between Somatic Growth and In Vivo Esophageal Segmental and Sphincteric Growth in Human Neonates
Authors: Gupta Alankar , Jadcherla Sudarshan Rao
Published: July 2006

Background:

Measurement of aerodigestive tract length is an important determinant for accurate placement of esophageal probes and gavage tubes at the desired location. The relationship of esophageal body, upper esophageal sphincter (UES) and lower esophageal sphincter (LES) lengths with somatic growth in neonates is not well understood.

Objectives:

Our objectives were to (1) evaluate a relationship between segmental esophageal lengths and somatic growth parameters and (2) ascertain the relationship between segmental esophageal lengths and gestational age (GA) and postmenstrual age (PMA) in preterm and full‐term born human neonates.

Design/Methods:

One hundred esophageal manometry studies were performed in 75 infants (30‐60 weeks PMA) and the high‐pressure zones of LES and UES identified. The distance from nares to LES and from nares to UES, esophageal body length, length of UES and LES derived from the manometry studies were correlated with somatic growth parameters. Growth rate of different esophageal segments was also determined in 26 subjects that underwent longitudinal studies. Analysis of variance and linear regression analysis were performed.

Results:

Seventy‐five neonates of 23.0‐40.6 weeks gestational age (0.6‐4.4 kg) were studied at 29.1‐58.6 weeks PMA (1.0‐6.4 kg). Significant correlation (P < 0.001) of PMA and physical growth parameters with the growth of nares‐LES (R2 = 0.8), esophageal body length (R2 = 0.6) and nares‐UES (R2 = 0.4) were noted. Nares‐to‐LES length increased at a rate of 0.25 cm/wk PMA during 33.0‐36.0 weeks of age.

Conclusions:

In vivo esophageal segmental lengths correlated strongly with somatic growth parameters and PMA in neonates. We speculate that this approach has many practical applications with the use of esophageal probes and catheters.
Nutritional Approach to Restore Impaired Intestinal Barrier Function and Growth After Neonatal Stress in Rats
Authors: García‐Ródenas Clara L. , Bergonzelli Gabriela E. , Nutten Sophie , Schumann Alexandra , Cherbut Christine , Turini Marco , Ornstein Kurt , Rochat Florence , Corthésy‐Theulaz Irène
Published: July 2006

Objectives:

Psychological stress during the neonatal period results in intestinal barrier dysfunction and growth alterations later in life. We aimed to restore impaired barrier function and growth rate by a nutritional intervention.

Methods:

Male rat pups (n = 84) were assigned to 1 of 2 rearing conditions from postnatal day (PND) 2 to PND14: S, separated 3 h/d from their mothers, or H, 15 min/d handled controls. From PND15 to PND35, rats received a control diet or a similar diet adapted to contain arachidonic and docosahexaenoic acids, galacto‐ and fructo‐oligosaccharides and Lactobacillus paracasei NCC2461.

Results:

Maternal separation had only a minor impact on the measured gut barrier parameters at PND15, whereas it severely affected them at PND35. At this age, intestinal permeability to macromolecules was higher, mucin content in small intestinal tissues was lower and microbiota composition was altered in S compared with H animals. Feeding the adapted diet normalized the intestinal permeability, although it did not restore intestinal mucin content or microbiota. In addition, the adapted diet improved the growth rate recovery of the S animals after weaning and resulted in increased villus length in small intestine.

Conclusion:

Our results suggest that an adapted diet containing specific long‐chain polyunsaturated fatty acids, prebiotics and probiotics can revert the negative imprinting of neonatal stress on both intestinal barrier function and growth.
Impact of Pretransplant Growth Retardation in Pediatric Liver Transplantation
Authors: Barshes Neal R. , Chang I‐Fen , Karpen Saul J. , Carter Beth A. , Goss John A.
Published: July 2006

Objective:

Malnutrition frequently complicates end‐stage liver disease and orthotopic liver transplantation (OLT) in pediatric patients. Pretransplant malnutrition has been associated with increased post‐OLT mortality and length of stay in adults. The relationship between pre‐OLT nutritional status and post‐OLT outcomes in pediatric liver transplant recipients, however, is not well studied.

Methods:

The records of 65 pediatric patients who underwent OLT at a single institution were reviewed. Univariate analyses were used to investigate the relationship between anthropomorphic data (expressed as z‐scores) and post‐OLT hospital length‐of‐stay, hospital costs and clinical outcomes. A multivariate model was then used to identify peri‐OLT variables independently correlated with post‐OLT length‐of‐stay.

Results:

A decreased height z‐score was correlated with an increased post‐OLT hospital length‐of‐stay (r = −0.30; P = 0.015) and increased hospital costs (r = −0.49; P = 0.0004). The mean length‐of‐stay was 20.5 days for patients with a height z‐score of <−1.5 and 10.7 days for patients with a height z‐score of >1.5 (P = 0.038). Likewise, hospital costs were about $40,000 higher (25% increased) for patients with growth retardation. A weak direct correlation was seen between weight z‐score and post‐OLT length‐of‐stay (r = 0.18; P = 0.15). Height z‐score, biliary atresia and pre‐OLT protime were independently and significantly correlated with post‐OLT length‐of‐stay in a multivariate model.

Conclusions:

Height z‐score is a better indicator of pretransplant malnutrition than weight z‐score. Pretransplant growth retardation is associated with increased post‐OLT hospital length‐of‐stay and increased hospitalization costs.

Abbreviations: OLT, orthotopic liver transplantation‐PELD, Pediatric End‐Stage Liver Disease Model.
Ileal Lymphonular Hyperplasia Is Not Associated With NOD2/CARD15 Mutations
Authors: Shaoul Ron , Eliakim Rami , Tamir Ada , Karban Amir
Published: July 2006

Introduction:

Lymphonodular hyperplasia (LNH) is a mass of lymphoid tissue that has been described in the terminal ileum, colon and duodenum mainly in children. Controversy exists regarding the benign nature of LNH. The combination of chronic abdominal pain and hematochezia leads many of these patients to undergo investigations for inflammatory bowel diseases. NOD2/CARD15 on chromosome 16 has been identified as a susceptibility gene for Crohn disease (CD). No study has yet examined the possible association of NOD2/CARD15 mutations with patients with LNH. The purpose of this study was to investigate the presence of NOD2/CARD15 mutations in patients with clinically proven LNH.

Methods:

Children and young adults with gastrointestinal symptoms diagnosed as having terminal ileum LNH were eligible for the study.

Results:

The study group consisted of 32 patients (15 males and 17 females), age range 3‐23 years, mean 13.1 ± 5 years. Twenty‐seven (84%) had abdominal pain, 3 (9%) had rectal bleeding. The duration of symptoms ranged from 1‐60 months (17.9 ± 14.5). Only 2 patients (6.2%) were found to be heterozygote for the NOD2/CARD15 mutation (1007 fs), whereas all of the others did not carry any of the 3 common mutant alleles. This number is significantly lower (P < 0.001) than the mutation prevalence demonstrated in both pediatric and adult Israeli CD patients.

Conclusions:

NOD2/CARD15 mutations are not associated with LNH. This may strengthen the lack of association between CD and LNH that has been previously reported. We suggest that genotyping NOD2/CARD15 may help to distinguish LNH from inflammatory bowel diseases in selected patients.
Plasma Zinc and Growth Status in Preadolescent Children with Cystic Fibrosis
Authors: Maqbool Asim , Schall Joan I. , Zemel Babette S. , Garcia‐Espana J. Felipe , Stallings Virginia A.
Published: July 2006

Objective:

To investigate plasma zinc status in relation to dietary and supplemental zinc intake, growth and pulmonary status in preadolescent children with cystic fibrosis (CF) and pancreatic insufficiency (PI).

Methods:

Fasting plasma zinc was assessed in children (age, 8‐11 years) with CF and PI. Food (7‐day weighed records) and supplemental zinc intake, serum alkaline phosphatase and albumin, pulmonary function (spirometry), coefficient of fat absorption (%COA, 72‐hour fecal fat) and growth status [height adjusted for genetic potential (AHAZ), weight (WAZ) and BMI Z scores (BMIZ)] were assessed.

Results:

For the 62 children (32 males), mean plasma zinc (±SD) was 16.8 ± 3.1 μmol/L (110 ± 20 ug/dL). Sixty‐five percent of the subjects had levels above the study reference range of 9.2 to 15.3 μmol/L (60‐100 ug/dL); no subjects had low zinc levels. Median (range) total daily zinc intake was 279% (83‐988%) recommended dietary allowance, growth status was suboptimal (mean ± SD: AHAZ, −0.8 ± 1.0; WAZ, −0.5 ± 1.2; BMIZ, −0.2 ± 1.1), and forced expiratory volume at 1 second (FEV1) was 92 ± 13% predicted. Plasma zinc was not correlated with growth, pulmonary or alkaline phosphatase status. Plasma zinc was correlated with serum albumin (r = 0.25, P < 0.05) and was inversely correlated with coefficient of fat absorption (as %; r = −0.30, P = 0.02).

Conclusions:

Under current patterns of care in CF Centers, total zinc intake and plasma zinc status were adequate. These findings suggest that zinc was not a limiting micronutrient for preadolescent children with CF and PI and mild‐to‐moderate lung disease, and not likely contributing to their suboptimal growth status.
Characteristics of Persistent Diarrhea in a Community‐Based Cohort of Young US Children
Authors: Vernacchio Louis , Vezina Richard M. , Mitchell Allen A. , Lesko Samuel M. , Plaut Andrew G. , Acheson David W.K.
Published: July 2006

Objective:

The objective of the study was to define the characteristics and microbiology of persistent diarrhea (PD) in US children.

Methods:

Six‐month prospective cohort study of a convenience sample of 604 healthy 6‐ to 36‐month‐old children recruited by the Slone Center Office‐based Research Network.

Results:

Of 611 diarrhea episodes, 50 (8.2%) lasted ≤ 14 days. The incidence of PD was 0.18 episodes per person‐year, and the median duration of episodes was 22.0 days (range, 14‐64 days). PD episodes were more likely than acute episodes to result in a medical visit (28.0% vs 8.2%; P = 0.0001). The most commonly used treatments were oral rehydration solution (12.0% of episodes) and antibiotics (6.0%). No bacterial or parasitic pathogens were associated with PD; but norovirus, rotavirus and sapovirus were each significantly more prevalent in PD stools compared with baseline stools, with relative risks of 12.4, 6.9 and 6.2, respectively. Fifty‐nine per cent of the PD specimens tested were negative for all studied pathogens.

Conclusions:

PD occurs with a frequency of approximately 1 case per 5 person‐years in US infants and young children. It seems to be a generally benign illness, with only 28% of cases presenting to medical care. Although viral pathogens seem to cause a minority of PD episodes in this population, most are not due to currently known infectious agents.