bluuebunny/crossref_metadata_2025 huggingface dataset:
Annealing effects on InGaAsN∕GaAs quantum wells analyzed using thermally detected optical absorption and ten band k−p calculations
Authors: Bouragba T. , Mihailovic M. , Reveret F. , Disseix P. , Leymarie J. , Vasson A. , Damilano B. , Hugues M. , Massies J. , Duboz J. Y.
Published: April 2007

The effects of thermal annealing for In0.25Ga0.75As1−yNy∕GaAs multiquantum wells (MQWs) have been investigated through thermally detected optical absorption. The QW transition energies have been calculated by using a ten-band k−p model including the band anticrossing model for the description of the InGaAsN band gap variation. The modification of the In concentration profile due to In-Ga interdiffusion during thermal annealing is taken into account through the Fick law. A good agreement is obtained between calculated and experimental energies of optical transitions. Our results show that the In-Ga interdiffusion phenomenon observed in a nitrogen free sample is moderately enhanced by the introduction of nitrogen. The blueshift of optical transitions induced by the annealing process is the result of both In-Ga interdiffusion and rearrangement of local nitrogen environment.
Oscillatory interlayer exchange coupling in epitaxial Co2MnSi∕Cr∕Co2MnSi trilayers
Authors: Wang H. , Sato A. , Saito K. , Mitani S. , Takanashi K. , Yakushiji K.
Published: April 2007

Interlayer exchange coupling (IEC) in trilayers, which consist of a full Heusler Co2MnSi (CMS) phase as ferromagnetic layers separated by a Cr spacer layer, has been investigated. The shape of magnetization loops shows unusual oscillatory behavior with the thickness of Cr. The oscillation period is about 3.3–3.5nm. The charecteristics of magnetization curves show that 90° coupling plays a dominant role in IEC between CMS layers. Moreover, the strength of 90° coupling turns out to be very high (up to −1.85ergs∕cm2) around the first oscillation peak.
Technique for tilting GaAs photonic crystal nanocavities out of plane
Authors: Meier Cedrik , Hennessy Kevin
Published: April 2007

The authors demonstrate a technique to mechanically tilt GaAs membranes out of the substrate plane by an arbitrary angle. Tilting is achieved by dosing a thin line of a perforated membrane with Ga ions using a focused ion beam. The change in material properties at the dosing site initiates a tilt about this axis that is monitored in situ to achieve the desired angle. The authors apply this technique to modify the emission direction of photonic crystal cavity, quantum dot light sources.
Nanoscale zoom tomography with hard x rays using Kirkpatrick-Baez optics
Authors: Mokso R. , Cloetens P. , Maire E. , Ludwig W. , Buffière J.-Y.
Published: April 2007

To overcome the limitations in terms of spatial resolution and field of view of existing tomography techniques, a hard x-ray projection microscope is realized based on the sub-100-nm focus produced by Kirkpatrick-Baez optics. The sample is set at a small distance downstream of the focus and Fresnel diffraction patterns with variable magnification are recorded on a medium-resolution detector. While the approach requires a specific phase retrieval procedure and correction for mirror imperfections, it allows zooming nondestructively into bulky samples. Quantitative three-dimensional nanoscale microscopy is demonstrated on an aluminum alloy in local tomography mode.
Si-based electromagnetic noise suppressors integrated with a magnetic thin film
Authors: Sohn Jaecheon , Han S. H. , Yamaguchi Masahiro , Lim S. H.
Published: April 2007

Electromagnetic noise suppressors on Cu transmission lines and oxidized Si substrate integrated with a SiO2 dielectric and a Co–Fe–Al–O magnetic layer are presented. Extremely large signal attenuation is achieved (−90dB at 20GHz) while the signal reflection is relatively small, being below −10dB. These characteristics are attributed to the distributed capacitance (C) formed by the Cu and the oxidized Si substrate and the Cu∕SiO2∕Co–Fe–Al–O and the distributed inductance (L) due to the magnetic thin film. The main loss mechanism is the L-C resonance and this emphasizes the role of the magnetic thin film providing the inductance.
In situ stress evolution during sputter deposition of Cu∕Co bilayers and multilayers
Authors: Pletea M. , Brückner W. , Wendrock H. , Thomas J. , Kaltofen R. , Koch R.
Published: April 2007

The stress evolution of Cu∕Co bilayers and multilayers sputtered onto oxidized Si(100) (SiOx) substrates has been studied by in situ substrate curvature measurements with the thickness of the individual layers ranging from 3 to 10 nm. In order to understand the stress developing during deposition, we investigated the microstructure of single layers and bilayers by scanning electron microscopy as well as of the multilayers by cross-section transmission electron microscopy. The growth of Cu and Co on SiOx substrates proceeds by the Volmer-Weber mechanism. Due to the lower mobility, Co layers exhibit a finer grain morphology compared to Cu. The stress evolution and morphology of the first Cu∕Co or Co∕Cu bilayer are still influenced by the SiOx substrates and differ from that of subsequent bilayers. The metal on metal growth of subsequent bilayers is discussed in terms of the surface energies of Cu and Co, respectively. Accordingly, Cu wets Co and Co forms three-dimensional (3D) islands on Cu. After a transition region of 5−10 bilayers, a steady state with respect to the evolution of stress and morphology is reached. In both, the Cu and Co layers, the lattice mismatch gives rise to stress during deposition of the first monolayers.
Electrospun dye-doped polymer nanofibers emitting in the near infrared
Authors: Camposeo A. , Di Benedetto F. , Stabile R. , Cingolani R. , Pisignano D.
Published: April 2007

The authors report on the fabrication and characterization of near infrared fluorescent nanofibers. The nanofibers are composed by an organic dye dispersed in a poly(methylmethacrylate) inert matrix and realized by electrospinning. They exhibit diameters down to 70nm, with average values in the range of 170–480nm, depending on the process parameters, and photoluminescence emission peaked at 865nm. The temporal behavior of the emission under ultraviolet excitation in air can be described by an oxygen diffusion model with a characteristic time τ in the range of 400–1200s, depending on the fiber size, which correspond to a photostability longer than (0.4–1.2)×105 excitation laser pulses. These results open the way for large volume and cost-effective realization of infrared-emitting nanofibers, which are promising candidates as nanoscale infrared light sources.
Nanovoid nature and compression effects in organic light emitting diode
Authors: Kim Jong H. , Seo Soon-min , Lee Hong H.
Published: April 2007

Compressing the organic layers in organic light emitting diode (OLED) is introduced as an effective process for improving the performance of organic electroluminescent devices. This process involves applying physical pressure to the organic layers of the device. The OLED fabricated by this method shows a notable increase in luminance intensity and current efficiency when compared with compression-free device, the current efficiency almost doubling. The organic layers have nanovoids and the compression results in a denser packing of organic molecules, leading to a better charge transport.
Distributed Bragg reflector consisting of high- and low-refractive-index thin film layers made of the same material
Authors: Schubert Martin F. , Xi J.-Q. , Kim Jong Kyu , Schubert E. Fred
Published: April 2007

A conductive distributed Bragg reflector (DBR) composed entirely of a single material—indium tin oxide (ITO)—is reported. The high- and low-refractive-index layers of the DBR are deposited by oblique-angle deposition and consist of ITO thin films with low and high porosities, which yield an index contrast of Δn=0.4. A single-material DBR with three periods achieves a reflectivity of 72.7%, in excellent agreement with theory.
Slow-light enhancement of Beer-Lambert-Bouguer absorption
Authors: Mortensen Niels Asger , Xiao Sanshui
Published: April 2007

The authors theoretically show how slow light in an optofluidic environment facilitates enhanced light-matter interactions, by orders of magnitude. The proposed concept provides strong opportunities for improving existing miniaturized chemical absorbance cells for Beer-Lambert-Bouguer absorption measurements widely employed in analytical chemistry.
Comment on the use of calcium as a dopant in X8R BaTiO3-based ceramics
Authors: Zhang Lei , Thakur Om Prakash , Feteira Antonio , Keith Gillian M. , Mould Andrew G. , Sinclair Derek C. , West Anthony R.
Published: April 2007

Ba Ti 1 − x Ca x O 3 − x ceramics, where 0⩽x⩽0.04, prepared by the mixed oxide route at 1500°C display a strong suppression of the Curie temperature and a significant increase in grain conductivity with increasing x. The ramifications of these results on the applicability of using Ca2+ as a dopant to achieve X8R specification in BaTiO3-based formulations are discussed.
Single shot method for a quantitative spatially resolved investigation of the homogeneity of the birefringence of nonlinear optical crystals
Authors: Frieß L. K. , Wesemann V. , Robertson A. , L’huillier J. A.
Published: April 2007

This letter reports on a single shot method for the spatially resolved investigation of the homogeneity of the birefringence of nonlinear optical crystals. Using the same method the wavelength acceptance and the wavelength for phase-matched second harmonic generation are measured. The method is based on a single shot measurement of the sinc2 wavelength dependence of the second harmonic conversion efficiency. This dependence is detected by converting the broad spectrum of femtosecond-laser pulses generated by a Ti:sapphire laser. The spatial resolution of these measurements is 80μm. The accuracy exceeds 2.5% for the determination of the homogeneity of the birefringence.
Systematic study of contact annealing: Ambipolar silicon nanowire transistor with improved performance
Authors: Byon K. , Tham D. , Fischer J. E. , Johnson A. T.
Published: April 2007

High performance ambipolar silicon nanowire (SiNW) transistors were fabricated. SiNWs with uniform oxide sheath thicknesses of 6–7nm were synthesized via a gas-flow-controlled thermal evaporation method. Field effect transistors (FETs) were fabricated using as-grown SiNWs. A two step annealing process was used to control contacts between SiNW and metal source and drain in order to enhance device performance. Initially p-channel devices exhibited ambipolar behavior after contact annealing at 400°C. Significant increases in on/off ratio and channel mobility were also achieved by annealing.
Valence band tunneling model for charge transfer of redox-active molecules attached to n- and p-silicon substrates
Authors: Gowda Srivardhan , Mathur Guru , Misra Veena
Published: April 2007

In this work, monolayers of the redox-active molecules, with cationic- accessible states, were incorporated on p- and n-type silicons of varying doping concentrations. The redox voltages and kinetics were found to be strongly dependent on the silicon doping concentrations, and ambient light in case of n-Si substrate, while there was no significant impact of substrate doping concentration or ambient light in case of p-Si substrate. These results suggest the redox energy states in the molecule align within the valence band of the silicon substrate. Based on this, a model for electronic coupling and charge transfer at the molecule-semiconductor interfaces is proposed.
Hot electron transport in Au–HfO2–SiO2–Si structures studied by ballistic electron emission spectroscopy
Authors: Zheng Yi , Wee Andrew T. S. , Pey K. L. , Troadec Cedric , O’Shea S. J. , Chandrasekhar N.
Published: April 2007

Hot electron transport in Au–HfO2–SiO2–Si structures with 4nm HfO2 and 1.5nm SiO2 interfacial layer have been investigated by ballistic electron emission spectroscopy (BEES). By controlling the hot electron kinetic energy and injection current, distinctly different barrier heights can be measured. BEES sweeping below −5V with 1nA injection current yields high barrier heights (∼3.8eV), attributable to the interfacial SiO2 layer. BEES sweeping from −6V with high injection current (5nA and above) induced localized breakdown of the SiO2 interfacial layer, allowing the barrier height of the HfO2 layer to be measured (∼1.9eV). The energy-dependent effective mass of electrons in HfO2 is also determined by fitting oscillations in the BEES current.
Nitride-based near-ultraviolet light emitting diodes with meshed p-GaN
Authors: Kuo C. H. , Feng H. C. , Kuo C. W. , Chen C. M. , Wu L. W. , Chi G. C.
Published: April 2007

This investigation presents nitride-based near ultraviolet light emitting diodes (LEDs) with a meshed p-GaN layer. With 20mA injection current, it was found that forward voltages were 3.33 and 3.39V while output powers were 9.0 and 10.6mW for the meshed indium-tin-oxide (ITO) LED and meshed p-GaN LED, respectively. The larger LED output power is attributed to increased light extraction efficiency.
Highly efficient electron gun with a single-atom electron source
Authors: Ishikawa Tsuyoshi , Urata Tomohiro , Cho Boklae , Rokuta Eiji , Oshima Chuhei , Terui Yoshinori , Saito Hidekazu , Yonezawa Akira , Tsong Tien T.
Published: April 2007

The authors have demonstrated highly collimated electron-beam emission from a practical electron gun with a single-atom electron source; ∼80% of the total emission current entered the electron optics. This ratio was two or three orders of magnitude higher than those of the conventional electron sources such as a cold field emission gun and a Zr∕O∕W Schottky gun. At the pressure of less than 1×10−9Pa, the authors observed stable emission of 20nA, which generates the specimen current of 5pA required for scanning electron microscopes.
Enhancement of Curie temperature under low electric fields in Mn selectively δ-doped GaAs∕AlGaAs wide quantum wells
Authors: Lv Bin , Wang Jiqing , Yu Jianguo , Mao Huibing , Shen Ye , Zhu Ziqiang , Xing Huaizhong
Published: April 2007

A prominent improvement of Curie temperature under low electric fields through Mn δ-doped GaAs∕p-AlGaAs wide quantum wells is presented theoretically. The electric-field-controlled Curie temperature for different δ-doping positions and well widths has been investigated by means of the numerical self-consistent calculation. For quantum wells with 40nm well width, an applied electric field of 0.3meV∕nm enhances TC up to five times than ones without the applied field. Our results indicate that wide quantum wells (>20nm) have more advantage than narrow quantum wells in the electric-field-controlled low dimensional ferromagnetic systems.
Vertical surround-gated silicon nanowire impact ionization field-effect transistors
Authors: Björk M. T. , Hayden O. , Schmid H. , Riel H. , Riess W.
Published: April 2007

One of the fundamental limits in the scaling of metal oxide semiconductor field-effect transistor technology is the room-temperature (RT) limit of ∼60mV/decade in the inverse subthreshold slope. Here, the authors demonstrate vertical integration of a single surround-gated silicon nanowire field-effect transistor with an inverse subthreshold slope as low as 6mV/decade at RT that spans four orders of magnitude in current. Operation of the device is based on avalanche breakdown in a partially gated vertical nanowire, epitaxially grown using the vapor-liquid-solid method. Low-power logic based on impact ionization field-effect transistors in combination with a vertical architecture is very promising for future high-performance ultrahigh-density circuits.
Two-dimensional space-charge-limited flows in a crossed-field gap
Authors: Koh W. S. , Ang L. K.
Published: April 2007

This letter presents a two-dimensional (2D) model of space-charge-limited current in a planar crossed-field gap with a magnetic strength of B∕BH=0–3, where BH is the Hull cutoff magnetic field. The electrons are emitted from an infinite length strip of finite width W comparable to the gap spacing D. It is found that the 2D enhancement of the crossed-field limiting current is 1+F×4D∕(πW), where F (=0.05–0.5) is a normalized mean-position factor, and it is a function of B∕BH. Good agreement has been obtained in comparisons with particle-in-cell simulation.
Hole-initiated multiplication in back-illuminated GaN avalanche photodiodes
Authors: McClintock R. , Pau J. L. , Minder K. , Bayram C. , Kung P. , Razeghi M.
Published: April 2007

Avalanche p-i-n photodiodes were fabricated on AlN templates for back illumination. Structures with different intrinsic layer thicknesses were tested. A critical electric field of 2.73MV∕cm was estimated from the variation of the breakdown voltage with thickness. From the device response under back and front illumination and the consequent selective injection of holes and electrons in the junction, ionization coefficients were obtained for GaN. The hole ionization coefficient was found to be higher than the electron ionization coefficient as predicted by theory. Excess multiplication noise factors were also calculated for back and front illumination, and indicated a higher noise contribution for electron injection.
Pressure control model for transport of liquid mercury in carbon nanotubes
Authors: Zhang H. W. , Zhang Z. Q. , Wang L. , Zheng Y. G. , Wang J. B. , Wang Z. K.
Published: April 2007

Carbon nanotubes have a significant application in nanotechnology as nanopipes conveying fluids. In this letter, a pressure control model for transport of liquid mercury through carbon nanotubes using classical molecular dynamics simulations in conjunction with an atomistic model is presented. Wetting of single-walled carbon nanotubes by mercury occurs above a threshold pressure of liquid mercury. The liquid mercury can be transported through carbon nanotubes with the continuous increase of its internal pressure. Also, the authors show that single-walled carbon nanotubes can transport liquid mercury discontinuously when a periodical pressure is applied on the liquid.
Resistance switching memory device with a nanoscale confined current path
Authors: Ogimoto Yasushi , Tamai Yukio , Kawasaki Masashi , Tokura Yoshinori
Published: April 2007

The impact of a nanoscale confined current path is demonstrated on a resistance switching memory device. The memory element consists of a Ti layer constricted by an insulating self-assembly nanogap oxide, in which a redox reaction is anticipated for the resistance change without an aid of a forming process. The device exhibits a resistance ratio greater than 100, a data retention longer than 3.7×106s, an endurance of more than 2000cycles, and a switching operation temperature up to 125°C at an operation condition of ±2.5V with 50–100ns duration, evidencing an essential role of the nanostructure on the device performance.
Negative small-signal impedance of nanoscale GaN diodes in the terahertz frequency regime
Authors: Sokolov V. N. , Kim K. W. , Kochelap V. A. , Muntiian P. M.
Published: April 2007

A physical mechanism of electrical instability in the terahertz frequency range is explored in a nanoscale two-terminal configuration of nitride-based structures under a high-field transport regime. The investigated instability utilizes the negative differential resistance effect that is known to occur in bulk group-III nitride semiconductors. A distinctive feature of the proposed mechanism for terahertz generation is that the diode steady-state I-V characteristics maintain a positive differential resistance for a stable operation, while the small-signal response provides negative impedance within the desired frequency range. An additional advantage is that the frequency window of negative small-signal impedance can be tuned electrically.
Room temperature observation of negative differential resistance effect using ZnO nanocrystal structure with double Schottky barriers
Authors: Ito Daisuke , Tomita Takashi , Hatazawa Tsuyonobu
Published: April 2007

A varistic nonlinear I-V characteristic caused by a tunneling effect was observed in two-dimensional nanopolycrystal ZnO (NPC-ZnO) with double Schottky barriers (DSBs). Id-Vd characteristic of a NPC-ZnO field effect transistor showed a negative differential resistance characteristic at room temperature. The Id-Vg showed clear current peaks and valleys although this characteristic has an asymmetric hysteresis. An ultraviolet irradiation on the Id-Vg showed the increase of current peaks and disappearance of the hysteresis. These results could be related to the tunneling effect via DSBs and quasibound states that were caused by the internal defect of ZnO dots or the grain boundary.
Anisotropy compensation and magnetostriction in TbxNd1−xFe1.9 cubic Laves alloys
Authors: Shi Y. G. , Tang S. L. , Huang Y. J. , Lv L. Y. , Du Y. W.
Published: April 2007

Polycrystalline TbxNd1−xFe1.9 (0⩽x⩽0.8) cubic Laves phase alloys with MgCu2-type structure were prepared by high-pressure synthesis and subsequent low-temperature annealing. The crystal structure, magnetic properties, and magnetostriction have been investigated. The change of easy magnetic direction from ⟨100⟩ to ⟨111⟩ with increasing x up to 0.1 is detected by Mössbauer spectra. In accordance with Mössbauer effect study, both magnetization and magnetostriction analyses show that TbxNd1−xFe1.9 is an anisotropy compensation system and the compensation point is close to x=0.1. The present work may open an avenue in searching magnetostrictive materials with inexpensive Nd.
Characterizing tumor-promoting T cells in chemically induced cutaneous carcinogenesis
Authors: Roberts Scott J. , Ng Bernice Y. , Filler Renata B. , Lewis Julia , Glusac Earl J. , Hayday Adrian C. , Tigelaar Robert E. , Girardi Michael
Published: April 2007

There is a longstanding but poorly understood epidemiologic link between inflammation and cancer. Consistent with this, we previously showed that αβ T cell deficiency can increase resistance to chemical carcinogenesis initiated by 7,12-dimethylbenz[
a
]anthracene and promoted by phorbol 12-myristate 13-acetate. This provoked the hypothesis that αβ T cell deficiency removed T regulatory cells that limit the anti-tumor response or removed a specific tumor-promoting (T-pro) T cell population. Here we provide evidence for the latter, identifying a novel CD8
+
subset that is a candidate for T-pro cells. We demonstrate that CD8 cell-deficient mice show substantially less tumor incidence and progression to carcinoma, whereas susceptibility is restored by CD8
+
cell reconstitution. To characterize the putative T-pro cells, tumor-infiltrating lymphocytes were isolated from normal and CD4
−/−
mice, revealing an activated population of T cell receptor αβ
+
CD8
+
CD44
+
CD62L
−
cells expressing the inflammatory mediators IFNγ, TNFα, and cyclooxygenase-2, but deficient in perforin, relative to recirculating cells of equivalent phenotype. This novel population of CD8
+
T cells has intriguing similarities with other lymphocytes that have been associated with tissue growth and invasiveness and has implications for inflammation-associated carcinogenesis, models of cancer immunosurveillance, and immunotherapeutic strategies.
Exotic modes of excitation in atomic nuclei far from stability
Authors: Paar Nils , Vretenar Dario , Khan Elias , Colò Gianluca
Published: April 2007

We review recent studies of the evolution of collective excitations in atomic nuclei far from the valley of β-stability. Collective degrees of freedom govern essential aspects of nuclear structure, and for several decades the study of collective modes such as rotations and vibrations has played a vital role in our understanding of complex properties of nuclei. The multipole response of unstable nuclei and the possible occurrence of new exotic modes of excitation in weakly bound nuclear systems, present a rapidly growing field of research, but only few experimental studies of these phenomena have been reported so far. Valuable data on the evolution of the low-energy dipole response in unstable neutron-rich nuclei have been gathered in recent experiments, but the available information is not sufficient to determine the nature of observed excitations. Even in stable nuclei various modes of giant collective oscillations had been predicted by theory years before they were observed, and for that reason it is very important to perform detailed theoretical studies of the evolution of collective modes of excitation in nuclei far from stability. We therefore discuss the modern theoretical tools that have been developed in recent years for the description of collective excitations in weakly bound nuclei. The review focuses on the applications of these models to studies of the evolution of low-energy dipole modes from stable nuclei to systems near the particle emission threshold, to analyses of various isoscalar modes, those for which data are already available, as well as those that could be observed in future experiments, to a description of charge-exchange modes and their evolution in neutron-rich nuclei, and to studies of the role of exotic low-energy modes in astrophysical processes.
Intense ultrasonic clicks from echolocating toothed whales do not elicit anti–predator responses or debilitate the squid
Loligo pealeii
Authors: Wilson Maria , Hanlon Roger T , Tyack Peter L , Madsen Peter T
Published: April 2007

Toothed whales use intense ultrasonic clicks to echolocate prey and it has been hypothesized that they also acoustically debilitate their prey with these intense sound pulses to facilitate capture. Cephalopods are an important food source for toothed whales, and there has probably been an evolutionary selection pressure on cephalopods to develop a mechanism for detecting and evading sound–emitting toothed whale predators. Ultrasonic detection has evolved in some insects to avoid echolocating bats, and it can be hypothesized that cephalopods might have evolved similar ultrasound detection as an anti–predation measure. We test this hypothesis in the squid
Loligo pealeii
in a playback experiment using intense echolocation clicks from two squid–eating toothed whale species. Twelve squid were exposed to clicks at two repetition rates (16 and 125 clicks per second) with received sound pressure levels of 199–226 dB re 1 μPa (pp) mimicking the sound exposure from an echolocating toothed whale as it approaches and captures prey. We demonstrate that intense ultrasonic clicks do not elicit any detectable anti–predator behaviour in
L. pealeii
and that clicks with received levels up to 226 dB re 1 μPa (pp) do not acoustically debilitate this cephalopod species.
Control of reproductive dominance by thethelytokygene in honeybees
Authors: Lattorff H. Michael G , Moritz Robin F.A , Crewe Robin M , Solignac Michel
Published: April 2007

Differentiation into castes and reproductive division of labour are a characteristics of eusocial insects. Caste determination occurs at an early stage of larval development in social bees and is achieved via differential nutrition irrespective of the genotype. Workers are usually subordinate to the queen and altruistically refrain from reproduction. Workers of the Cape honeybee (Apis mellifera capensis) do not necessarily refrain from reproduction. They have the unique ability to produce female offspring parthenogenetically (thelytoky) and can develop into ‘pseudoqueens’. Although these are morphologically workers, they develop a queen-like phenotype with respect to physiology and behaviour. Thelytoky is determined by a single gene (th) and we show that this gene also influences other traits related to the queen phenotype, including egg production and queen pheromone synthesis. Using 566 microsatellite markers, we mapped this gene to chromosome 13 and identified a candidate locusthelytoky, similar tograiny head(a transcription factor), which has been shown to be highly expressed in queens of eusocial insects. We therefore suggest that this gene is not only important for determining the pseudoqueen phenotype inA. m. capensisworkers, but is also of general importance in regulating the gene cascades controlling reproduction and sterility in female social bees.
Can predation by invasive mice drive seabird extinctions?
Authors: Wanless Ross M , Angel Andrea , Cuthbert Richard J , Hilton Geoff M , Ryan Peter G
Published: April 2007

The house mouse,
Mus musculus
, is one of the most widespread and well-studied invasive mammals on islands. It was thought to pose little risk to seabirds, but video evidence from Gough Island, South Atlantic Ocean shows house mice killing chicks of two IUCN-listed seabird species. Mouse-induced mortality in 2004 was a significant cause of extremely poor breeding success for Tristan albatrosses,
Diomedea dabbenena
(0.27 fledglings/pair), and Atlantic petrels,
Pterodroma incerta
(0.33). Population models show that these levels of predation are sufficient to cause population decreases. Unlike many other islands, mice are the only introduced mammals on Gough Island. However, restoration programmes to eradicate rats and other introduced mammals from islands are increasing the number of islands where mice are the sole alien mammals. If these mouse populations are released from the ecological effects of predators and competitors, they too may become predatory on seabird chicks.
Natural origin biodegradable systems in tissue engineering and regenerative medicine: present status and some moving trends
Authors: Mano J.F , Silva G.A , Azevedo H.S , Malafaya P.B , Sousa R.A , Silva S.S , Boesel L.F , Oliveira J.M , Santos T.C , Marques A.P , Neves N.M , Reis R.L
Published: April 2007

The fields of tissue engineering and regenerative medicine aim at promoting the regeneration of tissues or replacing failing or malfunctioning organs, by means of combining a scaffold/support material, adequate cells and bioactive molecules. Different materials have been proposed to be used as both three-dimensional porous scaffolds and hydrogel matrices for distinct tissue engineering strategies. Among them, polymers of natural origin are one of the most attractive options, mainly due to their similarities with the extracellular matrix (ECM), chemical versatility as well as typically good biological performance. In this review, the most studied and promising and recently proposed naturally derived polymers that have been suggested for tissue engineering applications are described. Different classes of such type of polymers and their blends with synthetic polymers are analysed, with special focus on polysaccharides and proteins, the systems that are more inspired by the ECM. The adaptation of conventional methods or non-conventional processing techniques for processing scaffolds from natural origin based polymers is reviewed. The use of particles, membranes and injectable systems from such kind of materials is also overviewed, especially what concerns the present status of the research that should lead towards their final application. Finally, the biological performance of tissue engineering constructs based on natural-based polymers is discussed, using several examples for different clinically relevant applications.
Viscoelastic nanoscale properties of cuticle contribute to the high-pass properties of spider vibration receptor (Cupiennius saleiKeys)
Authors: McConney Michael E , Schaber Clemens F , Julian Michael D , Barth Friedrich G , Tsukruk Vladimir V
Published: April 2007

Atomic force microscopy (AFM) and surface force spectroscopy were applied in live spiders to their joint pad material located distal of the metatarsal lyriform organs, which are highly sensitive vibration sensors. The surface topography of the material is sufficiently smooth to probe the local nanomechanical properties with nanometre elastic deflections. Nanoscale loads were applied in the proximad direction on the distal joint region simulating the natural stimulus situation. The force curves obtained indicate the presence of a soft, liquid-like epicuticular layer (20–40 nm thick) above the pad material, which has much higher stiffness. The Young modulus of the pad material is close to 15 MPa at low frequencies, but increases rapidly with increasing frequencies approximately above 30 Hz to approximately 70 MPa at 112 Hz. The adhesive forces drop sharply by about 40% in the same frequency range. The strong frequency dependence of the elastic modulus indicates the viscoelastic nature of the pad material, its glass transition temperature being close to room temperature (25±2 °C) and, therefore, to its maximized energy absorption from low-frequency mechanical stimuli. These viscoelastic properties of the cuticular pad are suggested to be at least partly responsible for the high-pass characteristics of the vibration sensor's physiological properties demonstrated earlier.
The fundamental axioms of structural health monitoring
Authors: Worden Keith , Farrar Charles R , Manson Graeme , Park Gyuhae
Published: April 2007

Based on the extensive literature that has developed on structural health monitoring over the last 20 years, it can be argued that this field has matured to the point where several fundamental axioms, or gen eral principles, have emerged. The intention of this paper is to explicitly state and justify these axioms. In so doing, it is hoped that two subsequent goals are facilitated. First, the statement of such axioms will give new researchers in the field a starting point that alleviates the need to review the vast amounts of literature in this field. Second, the authors hope to stimulate discussion and thought within the community regarding these axioms.
Mitochondrial DNA analysis shows a Near Eastern Neolithic origin for domestic cattle and no indication of domestication of European aurochs
Authors: Edwards Ceiridwen J , Bollongino Ruth , Scheu Amelie , Chamberlain Andrew , Tresset Anne , Vigne Jean-Denis , Baird Jillian F , Larson Greger , Ho Simon Y.W , Heupink Tim H , Shapiro Beth , Freeman Abigail R , Thomas Mark G , Arbogast Rose-Marie , Arndt Betty , Bartosiewicz László , Benecke Norbert , Budja Mihael , Chaix Louis , Choyke Alice M , Coqueugniot Eric , Döhle Hans-Jürgen , Göldner Holger , Hartz Sönke , Helmer Daniel , Herzig Barabara , Hongo Hitomi , Mashkour Marjan , Özdogan Mehmet , Pucher Erich , Roth Georg , Schade-Lindig Sabine , Schmölcke Ulrich , Schulting Rick J , Stephan Elisabeth , Uerpmann Hans-Peter , Vörös István , Voytek Barbara , Bradley Daniel G , Burger Joachim
Published: April 2007

The extinct aurochs (Bos primigenius primigenius) was a large type of cattle that ranged over almost the whole Eurasian continent. The aurochs is the wild progenitor of modern cattle, but it is unclear whether European aurochs contributed to this process. To provide new insights into the demographic history of aurochs and domestic cattle, we have generated high-confidence mitochondrial DNA sequences from 59 archaeological skeletal finds, which were attributed to wild European cattle populations based on their chronological date and/or morphology. All pre-Neolithic aurochs belonged to the previously designated P haplogroup, indicating that this represents the Late Glacial Central European signature. We also report one new and highly divergent haplotype in a Neolithic aurochs sample from Germany, which points to greater variability during the Pleistocene. Furthermore, the Neolithic and Bronze Age samples that were classified with confidence as European aurochs using morphological criteria all carry P haplotype mitochondrial DNA, suggesting continuity of Late Glacial and Early Holocene aurochs populations in Europe. Bayesian analysis indicates that recent population growth gives a significantly better fit to our data than a constant-sized population, an observation consistent with a postglacial expansion scenario, possibly from a single European refugial population. Previous work has shown that most ancient and modern European domestic cattle carry haplotypes previously designated T. This, in combination with our new finding of a T haplotype in a very Early Neolithic site in Syria, lends persuasive support to a scenario whereby gracile Near Eastern domestic populations, carrying predominantly T haplotypes, replaced P haplotype-carrying robust autochthonous aurochs populations in Europe, from the Early Neolithic onward. During the period of coexistence, it appears that domestic cattle were kept separate from wild aurochs and introgression was extremely rare.
The human amygdala and orbital prefrontal cortex in behavioural regulation
Authors: Dolan R.J
Published: April 2007

Survival in complex environments depends on an ability to optimize future behaviour based on past experience. Learning from experience enables an organism to generate predictive expectancies regarding probable future states of the world, enabling deployment of flexible behavioural strategies. However, behavioural flexibility cannot rely on predictive expectancies alone and options for action need to be deployed in a manner that is responsive to a changing environment. Important moderators on learning-based predictions include those provided by context and inputs regarding an organism's current state, including its physiological state. In this paper, I consider human experimental approaches using functional magnetic resonance imaging that have addressed the role of the amygdala and prefrontal cortex (PFC), in particular the orbital PFC, in acquiring predictive information regarding the probable value of future events, updating this information, and shaping behaviour and decision processes on the basis of these value representations.
Beyond the sentence given
Authors: Hagoort Peter , van Berkum Jos
Published: April 2007

A central and influential idea among researchers of language is that our language faculty is organized according to Fregean compositionality, which states that the meaning of an utterance is a function of the meaning of its parts and of the syntactic rules by which these parts are combined. Since the domain of syntactic rules is the sentence, the implication of this idea is that language interpretation takes place in a two-step fashion. First, the meaning of a sentence is computed. In a second step, the sentence meaning is integrated with information from prior discourse, world knowledge, information about the speaker and semantic information from extra-linguistic domains such as co-speech gestures or the visual world. Here, we present results from recordings of event-related brain potentials that are inconsistent with this classical two-step model of language interpretation. Our data support a one-step model in which knowledge about the context and the world, concomitant information from other modalities, and the speaker are brought to bear immediately, by the same fast-acting brain system that combines the meanings of individual words into a message-level representation. Underlying the one-step model is the immediacy assumption, according to which all available information will immediately be used to co-determine the interpretation of the speaker's message. Functional magnetic resonance imaging data that we collected indicate that Broca's area plays an important role in semantic unification. Language comprehension involves the rapid incorporation of information in a ‘single unification space’, coming from a broader range of cognitive domains than presupposed in the standard two-step model of interpretation.
Function and localization within rostral prefrontal cortex (area 10)
Authors: Burgess Paul W , Gilbert Sam J , Dumontheil Iroise
Published: April 2007

We propose that rostral prefrontal cortex (PFC; approximating area 10) supports a cognitive system that facilitates either stimulus-oriented (SO) or stimulus-independent (SI) attending. SO attending is the behaviour required to concentrate on current sensory input, whereas SI attending is the mental processing that accompanies self-generated or self-maintained thought. Regions of medial area 10 support processes related to the former, whilst areas of lateral area 10 support processes that enable the latter. Three lines of evidence for this ‘gateway hypothesis’ are presented. First, we demonstrate the predicted patterns of activation in area 10 during the performance of new tests designed to stress the hypothetical function. Second, we demonstrate area 10 activations during the performance of established functions (prospective memory, context memory), which should hypothetically involve the proposed attentional system. Third, we examine predictions about behaviour–activation patterns within rostral PFC that follow from the hypothesis. We show with meta-analysis of neuroimaging investigations that these predictions are supported across a wide variety of tasks, thus establishing a general principle for functional imaging studies of this large brain region. We then show that while the gateway hypothesis accommodates a large range of findings relating to the functional organization of area 10 along a medial–lateral dimension, there are further principles relating to other dimensions and functions. In particular, there is a functional dissociation between the anterior medial area 10, which supports processes required for SO attending, and the caudal medial area 10, which supports processes relating to mentalizing.
Contextual-specificity of short-delay extinction in humans: Renewal of fear-potentiated startle in a virtual environment
Authors: Alvarez Ruben P. , Johnson Linda , Grillon Christian
Published: April 2007

A recent fear-potentiated startle study in rodents suggested that extinction was not context dependent when extinction was conducted after a short delay following acquisition, suggesting that extinction can lead to erasure of fear learning in some circumstances. The main objective of this study was to attempt to replicate these findings in humans by examining the context specificity of short-delay extinction in an ABA renewal procedure using virtual reality environments. A second objective was to examine whether renewal, if any, would be influenced by context conditioning. Subjects underwent differential aversive conditioning in virtual context A, which was immediately followed by extinction in virtual context B. Extinction was followed by tests of renewal in context A and B, with the order counterbalanced across subjects. Results showed that extinction was context dependent. Evidence for renewal was established using fear-potentiated startle as well as skin conductance and fear ratings. In addition, although contextual anxiety was greater in the acquisition context than in the extinction context during renewal, as assessed with startle, context conditioning did not influence the renewal effect. These data do not support the view that extinction conducted shortly after acquisition is context independent. Hence, they do not provide evidence that extinction can lead to erasure of a fear memory established via Pavlovian conditioning.
Neural correlates of conceptual implicit memory and their contamination of putative neural correlates of explicit memory
Authors: Voss Joel L. , Paller Ken A.
Published: April 2007

During episodic recognition tests, meaningful stimuli such as words can engender both conscious retrieval (explicit memory) and facilitated access to meaning that is distinct from the awareness of remembering (conceptual implicit memory). Neuroimaging investigations of one type of memory are frequently subject to the confounding influence of the other type of memory, thus posing a serious impediment to theoretical advances in this area. We used minimalist visual shapes (squiggles) to attempt to overcome this problem. Subjective ratings of squiggle meaningfulness varied idiosyncratically, and behavioral indications of conceptual implicit memory were evident only for stimuli given higher ratings. These effects did not result from perceptual-based fluency or from explicit remembering. Distinct event-related brain potentials were associated with conceptual implicit memory and with explicit memory by virtue of contrasts based on meaningfulness ratings and memory judgments, respectively. Frontal potentials from 300 to 500 msec after the onset of repeated squiggles varied systematically with perceived meaningfulness. Explicit memory was held constant in this contrast, so these potentials were taken as neural correlates of conceptual implicit memory. Such potentials can contaminate putative neural correlates of explicit memory, in that they are frequently attributed to the expression of explicit memory known as familiarity. These findings provide the first neural dissociation of these two memory phenomena during recognition testing and underscore the necessity of taking both types of memory into account in order to obtain valid neural correlates of specific memory functions.
The function of the glutamate–nitric oxide–cGMP pathway in brain in vivo and learning ability decrease in parallel in mature compared with young rats
Authors: Piedrafita Blanca , Cauli Omar , Montoliu Carmina , Felipo Vicente
Published: April 2007

Aging is associated with cognitive impairment, but the underlying mechanisms remain unclear. We have recently reported that the ability of rats to learn a Y-maze conditional discrimination task depends on the function of the glutamate–nitric oxide–cGMP pathway in brain. The aims of the present work were to assess whether the ability of rats to learn this task decreases with age and whether this reduction is associated with a decreased function of the glutamate–nitric oxide–cGMP pathway in brain in vivo, as analyzed by microdialysis in freely moving rats. We show that 7-mo-old rats need significantly more (192 ± 64%) trials than do 3-mo-old rats to learn the Y-maze task. Moreover, the function of the glutamate–nitric oxide–cGMP pathway is reduced by 60 ± 23% in 7-mo-old rats compared with 3-mo-old rats. The results reported support the idea that the reduction in the ability to learn the Y-maze task (and likely other types of learning) of mature compared with young rats would be a consequence of reduced function of the glutamate–nitric oxide–cGMP pathway.
Sonodynamic therapy of cancer using a novel porphyrin derivative, DCPH‐P‐Na(I), which is devoid of photosensitivity
Authors: Hachimine Ken , Shibaguchi Hirotomo , Kuroki Motomu , Yamada Hiromi , Kinugasa Tetsushi , Nakae Yoshinori , Asano Ryuji , Sakata Isao , Yamashita Yuichi , Shirakusa Takayuki , Kuroki Masahide
Published: April 2007

To improve the efficacy of sonodynamic therapy of cancer using photosensitizers, we developed a novel porphyrin derivative designated DCPH‐P‐Na(I) and investigated its photochemical characteristics and sonotoxicity on tumor cells. DCPH‐P‐Na(I) exhibited a minimum fluorescent emission by excitation with light, compared with a strong emission from ATX‐70, which is known to reveal both photo‐ and sonotoxicity. According to this observation, when human tumor cells were exposed to light in the presence of DCPH‐P‐Na(I) in vitro, the least phototoxicity was observed, in contrast to the strong phototoxicity of ATX‐70. However, DCPH‐P‐Na(I) exhibited a potent sonotoxicity on tumor cells by irradiation with ultrasound in vitro. This sonotoxicity was reduced by the addition of L‐histidine, but not D‐mannitol, thus suggesting that singlet oxygen may be responsible for the sonotoxicity of DCPH‐P‐Na(I). DCPH‐P‐Na(I) demonstrated significant sonotoxicity against a variety of cancer cell lines derived from different tissues. In addition, in a mouse xenograft model, a potent growth inhibition of the tumor was observed using sonication after the administration of DCPH‐P‐Na(I) to the mouse. These results suggest that sonodynamic therapy with DCPH‐P‐Na(I) may therefore be a useful clinical treatment for cancers located deep in the human body without inducing skin sensitivity, which tends to be a major side‐effect of photosensitizers. (Cancer Sci 2007; 98: 916–920)