bluuebunny/crossref_metadata_2025 huggingface dataset:
Organic Ferroelectric Field-Effect Transistor Memory Using Flat Poly(vinylidene fluoride–tetrafluoroethylene) and Pentacene Thin Films
Authors: Kanashima Takeshi , Yabe Kazuki , Okuyama Masanori
Published: February 2012

Organic ferroelectric field-effect transistor (FET) memories have been fabricated using pentacene as the semiconductor and a flat poly(vinylidene fluoride–tetrafluoroethylene) [P(VDF–TeFE)] thin film as the ferroelectric gate. The P(VDF–TeFE) film is prepared by spin coating, and it was cooled slowly with a flattening process after annealing. The polarization–electric field (P–E) hysteresis of the P(VDF–TeFE) thin film prepared by slow cooling is larger than that in the case of quick cooling. Moreover, the flattening process does not have a negative effect on ferroelectric properties. The obtained remanent polarization (P
r) of 5.2 µC/cm2 is sufficient for controlling the pentacene surface potential. Good memory characteristics are obtained in the P(VDF–TeFE) gate FET with pentacene deposited on the flat P(VDF–TeFE). The maximum drain current is about twice larger than that deposited on the rough P(VDF–TeFE) prepared by quick cooling, and the memory retention is over 1 week.
Two-Step Polarization Reversal Process in Pentacene/Poly(vinylidene fluoride–trifluoroethylene) Double-Layer Capacitor: Reduced Coercive Field
Authors: Li Jun , Taguchi Dai , Manaka Takaaki , Iwamoto Mitsumasa
Published: February 2012

The coercive field E
c of ferroelectric poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)] has been studied by observing the displacement current due to polarization reversal. Unlike in a metal–insulator–metal device, the polarization reversal in a metal–insulator–semiconductor diode (pentacene as the semiconductor) is a two-step process. We used modified current–voltage measurements to intentionally avoid the second-step polarization reversal and observed a reduced E
c. The reduction of E
c is interpreted to be a result of the reduced local dipole-induced field, on the basis of the optical electric-field-induced second-harmonic generation measurements.
Characterization on Improved Effective Mobility of Pentacene Organic Field-Effect Transistors Using Graphene Electrodes
Authors: Lee Sangchul , Jo Gunho , Kang Seok-Ju , Park Woojin , Kahng Yung Ho , Kim Dong-Yu , Lee Byoung Hun , Lee Takhee
Published: February 2012

Pentacene organic field-effect transistors (OFETs) with multilayer graphene (MLG) films as the source and drain electrodes were fabricated. Pentacene OFETs with MLG electrodes showed significantly enhanced electrical property compared to devices with typically used Au electrodes because MLG electrode yields lower contact resistance and lower barrier height. Specifically, the pentacene OFETs with graphene electrodes exhibited increased output current by more than tenfold, high mobility as 0.4 cm2V-1s-1, and high on/off current ratio of 107. Our study may be useful for the development of organic transistors that are capable of producing improved performances.
Thermal Annealing Effects on Optical Anisotropy of Aligned Thiophene-Based π-Conjugated Polymer Films Fabricated by Capillary Action
Authors: Higashi Takuya , Yamasaki Naoyuki , Utsumi Hideyuki , Yoshida Hiroyuki , Fujii Akihiko , Ozaki Masanori
Published: February 2012

Thermal annealing effects of the aligned thiophene-based polymer films were studied. Aligned poly2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene (pBTTT) and poly2,5-bis(3-alkylthiophene-2-yl)thieno[2,3-b]thiophene (pBTCT) films were fabricated by utilizing capillary actions of polymer solutions. The optical anisotropies of the aligned films were enhanced by thermal annealing at temperatures below the phase transition. The differences in the optical anisotropies between pBTTT and pBTCT were discussed by taking the lamellar stacking structures in the aligned films and phase transition into consideration.
Photovoltaic Properties of 1,4,8,11,15,18,22,25-Octaalkylphthalocyanine Doped Polymer Bulk Heterojunction Solar Cells
Authors: Masuda Tetsuya , Hori Tetsuro , Fukumura Kaoru , Miyake Yasuo , Duy Dao Quang , Hayashi Takeshi , Kamikado Toshiya , Yoshida Hiroyuki , Fujii Akihiko , Shimizu Yo , Ozaki Masanori
Published: February 2012

The effects of doping a liquid crystalline phthalocyanine derivative, 1,4,8,11,15,18,22,25-octaalkylphthalocyanine (CnPcH2,n= 6, 7), into bulk heterojunction organic thin-film solar cells based on poly(3-hexylthiophene) (P3HT) and 1-(3-methoxy-carbonyl)-propyl-1-1-phenyl-(6,6)C61 (PCBM) were studied. The absorbance spectra and external quantum efficiency spectra in the near-infrared region corresponding to the Q-band of CnPcH2were improved by doping C6PcH2or C7PcH2. On the basis of the characteristics of CnPcH2, obtained optical properties, and results of analysis of X-ray diffraction of the composite films of P3HT:CnPcH2:PCBM, we discussed the photovoltaic properties of solar cells with CnPcH2by taking the micro phase separation in the active layers into consideration.
Complementary Metal–Oxide–Semiconductor Image Sensor with Microchamber Array for Fluorescent Bead Counting
Authors: Sasagawa Kiyotaka , Ando Keisuke , Kobayashi Takuma , Noda Toshihiko , Tokuda Takashi , Kim Soo Hyeon , Iino Ryota , Noji Hiroyuki , Ohta Jun
Published: February 2012

We fabricated a complementary metal–oxide–semiconductor image sensor with a femtoliter microchamber array. The microchamber array plate is used for trapping microbeads and limiting the incident angle of light detected by the sensor. The sensor has an interference filter for fluorescent microbeads imaging. We detected fluorescent and nonfluorescent microbead with this sensor and showed its capability for counting the number of fluorescent chambers.
Recovery Based Nanowire Field-Effect Transistor Detection of Pathogenic Avian Influenza DNA
Authors: Lin Chih-Heng , Chu Chia-Jung , Teng  , Su Yi-Jr , Chen Chii-Dong , Tsai Li-Chu , Yang Yuh-Shyong
Published: February 2012

Fast and accurate diagnosis is critical in infectious disease surveillance and management. We proposed a DNA recovery system that can easily be adapted to DNA chip or DNA biosensor for fast identification and confirmation of target DNA. This method was based on the re-hybridization of DNA target with a recovery DNA to free the DNA probe. Functionalized silicon nanowire field-effect transistor (SiNW FET) was demonstrated to monitor such specific DNA–DNA interaction using high pathogenic strain virus hemagglutinin 1 (H1) DNA of avian influenza (AI) as target. Specific electric changes were observed in real-time for AI virus DNA sensing and device recovery when nanowire surface of SiNW FET was modified with complementary captured DNA probe. The recovery based SiNW FET biosensor can be further developed for fast identification and further confirmation of a variety of influenza virus strains and other infectious diseases.
Photoresist Spray Coating Using a Shield Plate with an Aperture for Uniform Deposition onto Trench-Type Three-Dimensional Microdevice Structures
Authors: Kumagai Shinya , Fukuda Naoya , Tajima Hisayoshi , Sasaki Minoru
Published: February 2012

The spray coating of a photoresist using a shield plate with an aperture is carried out for uniform deposition onto three-dimensional (3D) trench structures. The shield plate set over a sample blocks resist deposition onto the sample, except in the aperture area. Numerical analysis reveals that the vertical velocity component of gas flow is enhanced in the aperture area. In experiments on spray coating, the difference between the thicknesses of resist films deposited on top and bottom trench surfaces is decreased. On the trench sidewall, resist bump formation, which is frequently observed in spray coating, is suppressed. The profile of the resist film becomes conformal and uniform. Such resist deposition is necessary to realize 3D microdevices. In microfluidic devices using dielectrophoresis, aside from the top and bottom trench surfaces, the trench sidewall can be used for preparing device structures such as electrode. Electric interaction is enhanced for controlling the transport of micro-/nano-scale objects in micro-trench structures.
Fabrication of High Performance Ion-Sensitive Field-Effect Transistors Using an Engineered Sensing Membrane for Bio-Sensor Application
Authors: Jang Hyun-June , Cho Won-Ju
Published: February 2012

We propose a SiO2/HfO2/Al2O3 (OHA)-engineered sensing membrane fabricated by stacking high-k materials in order to improve the electrical and chemical stability of ion-sensitive field effect transistors (ISFETs). The sensing properties of the OHA layer were compared with SiO2/HfO2 (OH) and SiO2/Al2O3 (OA) layers. As a result, the OHA layer revealed a high on/off current ratio of 1.05 ×1010, a low subthreshold swing of 62 mV/dec as gate insulator of the metal–oxide–semiconductor field-effect transistors (MOSFETs) and an excellent pH sensitivity of 57.1 mV/pH, a small drift rate of 0.23 mV/h and a low hysteresis voltage of 1.85 mV as the sensing membrane of the ISFET pH sensors. These improvements could be explained by the rigid band structure of the tri-stacked engineered sensing layer. Consequently, the OHA sensing membrane looks promising for bio-sensor application with improved signal-to-noise ratio.
Effect of MgO Barrier Insertion on Spin-Dependent Transport Properties of CoFe/n-GaAs Heterojunctions
Authors: Akiho Takafumi , Uemura Tetsuya , Harada Masanobu , Matsuda Ken-ichi , Yamamoto Masafumi
Published: February 2012

The effect of MgO barrier insertion on a spin-valve signal in a four-terminal non-local geometry and on tunneling anisotropic magnetoresistance (TAMR) characteristics in a three-terminal geometry was investigated in Co50Fe50/n-GaAs heterojunctions. Inserting a MgO barrier significantly enhanced the spin-valve signal amplitude by a factor of 38, and the sign of spin polarization was opposite that of a sample without a MgO barrier. The TAMR effect was suppressed in the case of a Co50Fe50/MgO/n-GaAs junction. This suppression of the TAMR effect can be explained by the suppression of Fermi-level pinning and the lowering of Schottky barrier height.
Fabrication of MgAl2O4Thin Films on Ferromagnetic Heusler Alloy Fe2CrSi by Reactive Magnetron Sputtering
Authors: Fukatani Naoto , Inagaki Keima , Mari Kenichiro , Fujita Hirohito , Miyawaki Tetsuta , Ueda Kenji , Asano Hidefumi
Published: February 2012

Epitaxial MgAl2O4thin films were grown on Heusler alloy Fe2CrSi by reactive magnetron sputtering of a MgAl2target in an O2+Ar atmosphere. To grow MgAl2O4on Fe2CrSi, we inserted a protective layer of MgAl2between Fe2CrSi and MgAl2O4to prevent Fe2CrSi from being oxidized. Growth of MgAl2O4was found to be very sensitive to the MgAl2thickness andPO2during deposition of MgAl2O4. A strong XRD peak of MgAl2O4(004) was observed with an ultrathin (0.2 nm) MgAl2layer. The saturation magnetic moment of Fe2CrSi was measured to be 370 emu/cm3(1.84 µB/f.u.) at room temperature and it is expected to have a high spin polarization. The Fe2CrSi/MgAl2O4heterostructure is promising for use in future spintronic devices.
MgO Layer Thickness Dependence of Structure and Magnetic Properties of L10-FePt/MgO/GaAs Structures
Authors: Ohsugi Rento , Kohda Makoto , Seki Takeshi , Ohtsu Akihiko , Mizuguchi Masaki , Takanashi Koki , Nitta Junsaku
Published: February 2012

We investigated the MgO layer thickness dependences of the structure and magnetic properties of L10-FePt/MgO/GaAs structures. To examine how the crystallinity and growth morphology of the MgO layer affect the L10-FePt layer, two kinds of preparation method were employed for MgO deposition: electron beam (EB) evaporation and sputter deposition. The MgO layer deposited by EB evaporation included a large strain because of the cube-on-cube epitaxial relationship despite a large lattice mismatch between MgO and GaAs. For the MgO layer prepared by sputtering, on the other hand, an amorphous MgO layer was initially grown on the GaAs substrate. Subsequently, a crystalline MgO layer was grown in the (001) direction. In the case of the EB-deposited MgO, as the MgO layer thickness increased, the degree of chemical order of the L10-FePt layer increased from 55 to 81% owing to the improvement of the crystallinity of the MgO layer. The improvement of chemical order also led to the increase in the remanent magnetization of L10-FePt from 84 to 98%.
Design of a Nine-Transistor/Two-Magnetic-Tunnel-Junction-Cell-Based Low-Energy Nonvolatile Ternary Content-Addressable Memory
Authors: Matsunaga Shoun , Katsumata Akira , Natsui Masanori , Endoh Tetsuo , Ohno Hideo , Hanyu Takahiro
Published: February 2012

Towards a low search-energy nonvolatile ternary content-addressable memory (TCAM), we propose a novel nine-transistor/two-magnetic-tunnel-junction (9T–2MTJ) nonvolatile TCAM cell circuit with a high-speed accessibility. Since critical path for switching in the TCAM cell circuit is only a single metal-oxide-semiconductor (MOS) transistor, switching delay of the TCAM word circuit is minimized. As a result, the worst-case switching delay of 0.22 ns is achieved in a 144-bit word circuit under a 90 nm complementary MOS (CMOS)/MTJ technology, which is about 2.6 times faster than that of a conventional CMOS-based TCAM. In order to minimize the active power dissipation in the proposed TCAM, a multi-level segmented match-line scheme that maximally brings inessential cells to standby state is also applied to the 9T–2MTJ-cell-based word circuit. Finally, low search-energy of 0.73 fJ/bit/search is achieved in a 144-bit × 256-word nonvolatile TCAM together with eliminating standby power using nonvolatility.
Fabrication and Characterization of InP Nanowire Light-Emitting Diodes
Authors: Maeda Satoshi , Tomioka Katsuhiro , Hara Shinjiroh , Motohisa Junichi
Published: February 2012

We fabricated nanowire light-emitting diodes (LEDs) using InP nanowires (NWs). Indium phosphide NWs with axial p–n junction were grown by selective-area metalorganic vapor phase epitaxy. The results of secondary-electron-microscopy (SEM) observation and photoluminescence measurement showed the formation of wurtzite InP NWs with some mixture of zincblende crystal phase, as expected from the used growth conditions. NW-LEDs were fabricated by sputtering indium tin oxide (ITO) after a planarization process for the top contact and AuZn evaporation for the backside contact. Current–voltage characterisitics showed clear rectifying characteristics with a small leakage current, and fairly linear current–light output characteristics were observed. By designing the pitch of the NW array, emission from individual NWs was confirmed, which opens the possibility for realizing a single NW-LED applicable to single-photon emitters.
Tunable Magnetic Properties of Rhombohedral Graphite Thin Films: Effects of Insulating Substrate on Magnetic Properties
Authors: Cuong Nguyen Thanh , Otani Minoru , Okada Susumu
Published: February 2012

First-principles total energy calculations are performed to investigate the electronic and magnetic properties of rhombohedral graphite thin films on hexagonal boron nitride (h-BN) substrate. We find that the ferrimagnetic spin ordering of graphite thin films on h-BN substrate is robust irrespective of the adsorption arrangement. However, by enhancing the interaction between the graphite thin film and the substrate, the interaction suppresses the electron spin polarization of the bottommost graphene layer situated at the interface with the substrate. The electron spin polarization emerges at the second subsurface graphene layer in the thin film. We also find that the magnetic property of the graphite thin film on the insulating substrate is tunable by applying an external pressure.
Observation of In-Plane Asymmetric Strain Relaxation during Crystal Growth and Growth Interruption in InGaAs/GaAs(001)
Authors: Sasaki Takuo , Shimomura Kenichi , Suzuki Hidetoshi , Takahasi Masamitu , Kamiya Itaru , Ohshita Yoshio , Yamaguchi Masafumi
Published: February 2012

In-plane asymmetric strain relaxation in lattice-mismatched InGaAs/GaAs(001) heteroepitaxy is studied by in situ three-dimensional X-ray reciprocal space mapping. Repeating crystal growth and growth interruptions during measurements allows us to investigate whether the strain relaxation is limited at a certain thickness or saturated. We find that the degree of relaxation during growth interruption depends on both the film thickness and the in-plane directions. Significant lattice relaxation is observed in rapid relaxation regimes during interruption. This is a clear indication that relaxation is kinetically limited. In addition, relaxation along the [110] direction can saturate more readily than that along the [1̄10] direction. We discuss this result in terms of the interaction between orthogonally aligned dislocations.
Effect of Thermal Stress on a N-Related Recombination Center in GaAsN Grown by Chemical Beam Epitaxy
Authors: Bouzazi Boussairi , Kojima Nobuaki , Ohshita Yoshio , Yamaguchi Masafumi
Published: February 2012

Isochronal and isothermal annealing treatments were carried out on GaAsN films grown by chemical beam epitaxy to clarify the evolution of a nonradiative recombination center, at an average energy level of 0.33 eV below the conduction band minimum of the alloy. This lattice defect showed a strong persistence during post-thermal annealing even under critical annealing conditions. By considering as-grown samples as references and after optimizing the temperature and time of annealing, the trapping density of this recombination center could be reduced to one-half. Since the origin of this N-related recombination center was tentatively considered as the split interstitial (N–As)As, we suggest that the evolution of its density could be explained in great part to the diffusion behavior of As atoms during thermal stress.
Two-Dimensional Mapping of Power Consumption Due to Series Resistance Evaluated by Simulator for Concentrator Photovoltaic Module
Authors: Ota Yasuyuki , Nishioka Kensuke
Published: February 2012

Under concentration conditions, it is important to optimize the design of electrodes and cell structures, because high-density energy is emitted to the cell and photocurrent with high density is generated by each subcell of a multijunction solar cell. The in-plane distributions of power consumption by the each resistance component were calculated using a total three-dimensional (3D) simulator. In the case of optical design without a homogenizer, high power consumption at the electrode and top layer was observed in part of the cell. In the middle and bottom layers, power consumption was also observed, though it was slight in comparison with the upper layers. On the other hand, in the case of the optical design with a homogenizer, the power consumption was considerably reduced. This technique can be applied to the structural optimization of solar cells for concentration.
Photovoltaic Property of Wide-Gap Nanocrystalline Silicon Layers
Authors: Mentek Romain , Gelloz Bernard , Koshida Nobuyoshi
Published: February 2012

Nanocrystalline porous silicon (nc-PSi), a material already widely studied for application in photonics, optoelectronics and sensing devices, is currently under investigation as an active element in photodetection and photovoltaic application as well. Thanks to its unusual properties such as a band gap widening compare to bulk Silicon and its relatively simple and cheap fabrication method, the material could potentially be used as an active top-cell material in multi-junction cells structures. In order to confirm the availability of nc-PSi material as a wide gap absorber for solar cells, free standing layers of the material were fabricated and the results of their optical and photovoltaic characterization are presented in this paper.
CO2 Conversion with Light and Water by GaN Photoelectrode
Authors: Yotsuhashi Satoshi , Deguchi Masahiro , Zenitani Yuji , Hinogami Reiko , Hashiba Hiroshi , Yamada Yuka , Ohkawa Kazuhiro
Published: February 2012

Light illumination on a photoelectrode creates separate electron and hole pairs that lead to an oxidation and reduction reaction. Here, we show that CO2 reduction by means of water and light is realized by a gallium nitride (GaN) photoelectrode in which excited electrons drive CO2 conversion at the counterelectrode. A copper (Cu) plate was chosen as the counterelectrode. With this system, the generation of formic acid (HCOOH) with 9% Faradic efficiency was confirmed by light illumination alone with the help of NiO co-catalysts.
Impact of Light-Element Impurities on Crystalline Defect Generation in Silicon Wafer
Authors: Tachibana Tomihisa , Sameshima Takashi , Kojima Takuto , Arafune Koji , Kakimoto Koichi , Miyamura Yoshiji , Harada Hirofumi , Sekiguchi Takashi , Ohshita Yoshio , Ogura Atsushi
Published: February 2012

In multi-crystalline silicon grown by unidirectional solidification, there are many origins of crystalline defects. In this study, we investigated the effect of light-element impurities on the generation of crystalline imperfections during crystal growth. In order to control the interfusion of impurities, we regulate the Ar gas flow in the atmosphere on the basis of a computer simulation. The etch pit densities in the sample fabricated without and with Ar gas flow control in the atmosphere were 1.5×105–7.0×107 and 5.0×103–4.0×105 cm-2, respectively. In the sample fabricated without Ar gas flow control, the precipitates consisting of light-elements were observed in the region where the etch pit density markedly increased. In the region with the highest etch pit density, there were small-angle grain boundaries consisting of dislocations. We believed that the precipitates consisting of light-element impurities were the potential origins of small-angle grain boundaries. The light-element impurities should affect the crystalline defect generation induced during crystal growth, and thereby should be controlled.
Hydrothermal Synthesis of TiO2 Porous Hollow Nanospheres for Coating on the Photoelectrode of Dye-Sensitized Solar Cells
Authors: Mohan Varishetty Madhu , Murakami Kenji
Published: February 2012

Various sizes of TiO2 hollow nanosphers were synthesized by a hydrolysis followed by the hydrothermal treatment using different water content and titanium isopropoxide (TTIP) while the remaining components such as methylamine, ethanol and acetonitrile were kept as a constant. We synthesized the various sizes of spheres, 150, 250, 400, 450, and 600 nm in diameter; those are represented as SP150, SP250, SP400, SP450, and SP600. The prepared spheres diameters were confirmed by scanning electron microscopy (SEM). These spheres were coated by using a simple spray technique with the TiO2 colloidal solution as a scattering layer for the TiO2 photoelectrode of dye-sensitized solar cells. Optical absorption measurements did not find a difference in the dye adsorption amount with and without the scattering layer. The scattering effect was observed by incident photon to current conversion efficiency (IPCE) measurements especially in the wavelength region of 550–700 nm. The current–voltage (I–V) measurements show that the scattering layer with 450 nm spheres coated on the photoelectrode gave the improved photovoltaic performances compared to other diameters of the spheres. In the present study, the best energy conversion efficiency of 9.56% was obtained for the photoelectrode with the scattering layer, while the pure photoelectrode without the layer gave 8.4%.
Estimation of Surface Recombination Velocity from Thickness Dependence of Carrier Lifetime in n-Type 4H-SiC Epilayers
Authors: Kato Masashi , Yoshida Atsushi , Ichimura Masaya
Published: February 2012

For the fabrication of very high voltage SiC devices, it is essential to know the surface recombination velocity to accurately control the carrier lifetime. This study shows experimental results on the carrier lifetime in free-standing n-type 4H-SiC epilayers with several thicknesses and under two surface conditions to estimate the surface recombination velocity. The surface with chemical–mechanical polishing (CMP) was found to have lower surface recombination velocities than the as-grown epilayer surface. Similarly, the surface recombination velocity after CMP was low on the Si-face compared with that on the C-face. In addition, the surface recombination velocities on Si- and C-faces after CMP were quantitatively evaluated by comparison of experimental results with numerical calculations.
Strain waveform dependence of stress fiber reorientation in cyclically stretched osteoblastic cells: effects of viscoelastic compression of stress fibers
Authors: Nagayama Kazuaki , Kimura Yuki , Makino Narutaka , Matsumoto Takeo
Published: February 2012

Actin stress fibers (SFs) of cells cultured on cyclically stretched substrate tend to reorient in the direction in which a normal strain of substrate becomes zero. However, little is known about the mechanism of this reorientation. Here we investigated the effects of cyclic stretch waveform on SF reorientation in osteoblastic cells. Cells adhering to silicone membranes were subjected to cyclic uniaxial stretch, having one of the following waveforms with an amplitude of 8% for 24 h: triangular, trapezoid, bottom hold, or peak hold. SF reorientation of these cells was then analyzed. No preferential orientation was observed for the triangular and the peak-hold waveforms, whereas SFs aligned mostly in the direction with zero normal strain (∼55°) with other waveforms, especially the trapezoid waveform, which had a hold time both at loaded and unloaded states. Viscoelastic properties of SFs were estimated in a quasi-in situ stress relaxation test using intact and SF-disrupted cells that maintained their shape on the substrate. The dynamics of tension FSFs acting on SFs during cyclic stretching were simulated using these properties. The simulation demonstrated that FSFs decreased gradually during cyclic stretching and exhibited a compressive value (FSFs < 0). The magnitude and duration time of the compressive forces were relatively larger in the group with a trapezoid waveform. The frequency of SF orientation had a significant negative correlation with the applied compressive forces integrated with time in a strain cycle, and the integrated value was largest with the trapezoid waveform. These results may indicate that the applied compressive forces on SFs have a significant effect on the stretch-induced reorientation of SFs, and that SFs realigned to avoid their compression. Stress relaxation of SFs might be facilitated during the holding period in the trapezoid waveform, and depolymerization and reorientation of SFs were significantly accelerated by their viscoelastic compression.
Regulation of cell proliferation of human induced pluripotent stem cell-derived mesenchymal stem cells via ether-à-go-go 1 (hEAG1) potassium channel
Authors: Zhang Jiao , Chan Yau-Chi , Ho Jenny Chung-Yee , Siu Chung-Wah , Lian Qizhou , Tse Hung-Fat
Published: February 2012

The successful generation of a high yield of mesenchymal stem cells (MSCs) from human induced pluripotent stem cells (iPSCs) may represent an unlimited cell source with superior therapeutic benefits for tissue regeneration to bone marrow (BM)-derived MSCs. We investigated whether the differential expression of ion channels in iPSC-MSCs was responsible for their higher proliferation capacity than BM-MSCs. The expression of ion channels for K+, Na+, Ca2+, and Cl− was examined by RT-PCR. The electrophysiological properties of iPSC-MSCs and BM-MSCs were then compared by patch-clamp experiments to verify their functional roles. Significant mRNA expression of ion channel genes including KCa1.1, KCa3.1, KCNH1, Kir2.1, SCN9A, CACNA1C, and Clcn3 was observed in both human iPSC-MSCs and BM-MSCs, whereas Kir2.2 and Kir2.3 were only detected in human iPSC-MSCs. Five types of currents [big-conductance Ca2+-activated K+ current (BKCa), delayed rectifier K+ current ( IKDR), inwardly rectifying K+ current ( IKir), Ca2+-activated K+ current ( IKCa), and chloride current ( ICl)] were found in iPSC-MSCs (83%, 47%, 11%, 5%, and 4%, respectively) but only four of them (BKCa, IKDR, IKir, and IKCa) were identified in BM-MSCs (76%, 25%, 22%, and 11%, respectively). Cell proliferation was examined with MTT or bromodeoxyuridine assay, and doubling times were 2.66 and 3.72 days for iPSC-MSCs and BM-MSCs, respectively, showing a 1.4-fold discrepancy. Blockade of IKDR with short hairpin RNA or human ether-à-go-go 1 (hEAG1) channel blockers, 4-AP and astemizole, significantly reduced the rate of proliferation of human iPSC-MSCs. These treatments also decreased the rate of proliferation of human BM-MSCs albeit to a lesser extent. These findings demonstrate that the hEAG1 channel plays a crucial role in controlling the proliferation rate of human iPSC-MSCs and to a lesser extent in BM-MSCs.
Influence of acetaminophen consumption and exercise on Achilles tendon structural properties in male Wistar rats
Authors: Carroll Chad C. , Whitt Jamie A. , Peterson Amity , Gump Brian S. , Tedeschi Jamie , Broderick Tom L.
Published: February 2012

Chronic consumption of acetaminophen (APAP) during exercise training leads to a reduction in tendon stiffness and modulus compared with a placebo. We explored whether this effect could be due to a reduction in tendon collagen content or cross-linking. Ten-week-old male Wistar rats ( n = 50) were divided into placebo or APAP groups and into sedentary or treadmill-exercised groups. APAP (200 mg/kg) or saline was administered once daily by oral gavage. Rats in the exercise groups ran on a treadmill 5 days per week for 8 wk with progression to 60 min per day, 20 m/min, and 8° incline. After 8 wk, lyophilized Achilles tendon samples were assayed for the collagen-specific amino acid hydroxyproline and cross-linking [hydroxylyslpyridinoline (HP)] content by high-performance liquid chromatrography. Collagen content was not influenced by exercise or APAP ( P > 0.05). Compared with placebo, tendon water content was 7% ( P = 0.006, main effect) lower in animals consuming APAP (placebo: 54.79 ± 0.8%, APAP: 50.89 ± 1.2%). HP in the Achilles tendon was 36% greater (sedentary: 141 ± 15, exercise: 204 ± 26 mmol/mol collagen) in the exercise-trained rats independent of drug treatment ( P = 0.020, main effect). Independent of exercise, HP content was 33% lower ( P = 0.032, main effect) in the animals consuming APAP (placebo: 195 ± 21, APAP: 140 ± 19 mmol/mol collagen). Our data suggests that chronic consumption of APAP results in a reduction in collagen cross-linking and a loss of tissue water independent of chronic exercise. This reduction in cross-linking and water content could contribute to the decrease in tendon stiffness noted in humans chronically consuming APAP.
Control of cardiovascular variability during undisturbed wake-sleep behavior in hypocretin-deficient mice
Authors: Silvani Alessandro , Bastianini Stefano , Berteotti Chiara , Martire Viviana Lo , Zoccoli Giovanna
Published: February 2012

The central neural mechanisms underlying differences in cardiovascular variability between wakefulness, non-rapid-eye-movement sleep (NREMS), and rapid-eye-movement sleep (REMS) remain poorly understood. These mechanisms may involve hypocretin (HCRT)/orexin signaling. HCRT signaling is linked to wake-sleep states, involved in central autonomic control, and impaired in narcoleptic patients. Thus, we investigated whether HCRT signaling plays a role in controlling cardiovascular variability during spontaneous behavior in HCRT-deficient mice. HCRT-ataxin3 transgenic mice lacking HCRT neurons (TG), knockout mice lacking HCRT peptides (KO), and wild-type controls (WT) were instrumented with electrodes for sleep recordings and a telemetric blood pressure transducer. Fluctuations of systolic blood pressure (SBP) and heart period (HP) during undisturbed wake-sleep behavior were analyzed with the sequence technique, cross-correlation functions, and coherent averaging of SBP surges. During NREMS, all mice had lower SBP variability, greater baroreflex contribution to HP control at low frequencies, and greater amplitude of the central autonomic and baroreflex changes in HP associated with SBP surges than during wakefulness. During REMS, all mice had higher SBP variability and depressed central autonomic and baroreflex HP controls relative to NREMS. HP variability during REMS was higher than during NREMS in WT only. TG and KO also had lower amplitude of the cardiac baroreflex response to SBP surges during REMS than WT. These results indicate that chronic lack of HCRT signaling may cause subtle alterations in the control of HP during spontaneous behavior. Conversely, the integrity of HCRT signaling is not necessary for the occurrence of physiological sleep-dependent changes in SBP variability.
Effects of ibuprofen treatment on the developing preterm baboon kidney
Authors: Sutherland Megan R. , Yoder Bradley A. , McCurnin Donald , Seidner Steven , Gubhaju Lina , Clyman Ronald I. , Black M. Jane
Published: February 2012

Preterm neonates are commonly exposed postnatally to pharmacological treatments for a patent ductus arteriosus. Exposure of the developing kidney to nephrotoxic medications may adversely impact renal development. This study aimed to determine the effect of early postnatal ibuprofen treatment, both alone and in combination with a nitric oxide synthase inhibitor (NOSi), on renal development and morphology. Baboon neonates were delivered prematurely at 125-day (125d) gestation (term = 185d) and were euthanized at birth or postnatal day 6. Neonates were divided into four groups: 125d gestational controls ( n = 8), Untreated ( n = 8), Ibuprofen ( n = 6), and ibuprofen (Ibu)+NOSi ( n = 4). Animals in the Ibuprofen and Ibu+NOSi groups received five doses of ibuprofen, with the Ibuprofen+NOSi animals additionally administered a NOS inhibitor ( NG-monomethyl-l-arginine). There was no difference among groups in body weight, kidney weight, or glomerular generation number. Nephrogenic zone width was significantly reduced in the Ibuprofen group (123.5 ± 7.4 μm) compared with the 125d gestational control (176.1 ± 6.9 μm) and Untreated animals (169.7 ± 78.8 μm). In the Ibu+NOSi group, nephrogenic zone width averaged 152.7 ± 3.9 μm, which was not significantly different from any other group. Morphologically abnormal glomeruli were present at a range of 0.0–22.9% in the Untreated group, 0.0–6.1% in the Ibuprofen group, and 0.0–1.4% in the Ibu+NOSi group. In conclusion, early postnatal ibuprofen exposure is associated with a reduced nephrogenic zone width, which may suggest the early cessation of nephrogenesis following treatment. Ultimately, this may impact the number of nephrons formed in the preterm kidney.
Modulation of spontaneous activity in the overactive bladder: the role of P2Y agonists
Authors: Fry C. H. , Young J. S. , Jabr R. I. , McCarthy C. , Ikeda Y. , Kanai A. J.
Published: February 2012

Spinal cord transection (SCT) leads to an increase in spontaneous contractile activity in the isolated bladder that is reminiscent of an overactive bladder syndrome in patients with similar damage to the central nervous system. An increase in interstitial cell number in the suburothelial space between the urothelium and detrusor smooth muscle layer occurs in SCT bladders, and these cells elicit excitatory responses to purines and pyrimidines such as ATP, ADP, and UTP. We have investigated the hypothesis that these agents underlie the increase in spontaneous activity. Rats underwent lower thoracic spinal cord transection, and their bladder sheets or strips, with intact mucosa except where specified, were used for experiments. Isometric tension was recorded and propagating Ca2+ and membrane potential ( Em) waves were recorded by fluorescence imaging using photodiode arrays. SCT bladders were associated with regular spontaneous contractions (2.9 ± 0.4/min); ADP, UTP, and UDP augmented the amplitude but not their frequency. With strips from such bladders, a P2Y6-selective agonist (PSB0474) exerted similar effects. Fluorescence imaging of bladder sheets showed that ADP or UTP increased the conduction velocity of Ca2+/ Em waves that were confined to regions of the bladder wall with an intact mucosa. When transverse bladder sections were used, Ca2+/ Em waves originated in the suburothelial space and propagated to the detrusor and urothelium. Analysis of wave propagation showed that the suburothelial space exhibited properties of an electrical syncitium. These experiments are consistent with the hypothesis that P2Y-receptor agonists increase spontaneous contractile activity by augmenting functional activity of the cellular syncitium in the suburothelial space.
The transcription factor ETS-1 regulates angiotensin II-stimulated fibronectin production in mesangial cells
Authors: Hua Ping , Feng Wenguang , Rezonzew Gabriel , Chumley Phillip , Jaimes Edgar A.
Published: February 2012

Angiotensin II (ANG II) produced as result of activation of the renin-angiotensin system (RAS) plays a critical role in the pathogenesis of chronic kidney disease via its hemodynamic effects on the renal microcirculation as well as by its nonhemodynamic actions including the production of extracellular matrix proteins such as fibronectin, a multifunctional extracellular matrix protein that plays a major role in cell adhesion and migration as well as in the development of glomerulosclerosis. ETS-1 is an important transcription factor essential for normal kidney development and glomerular integrity. We previously showed that ANG II increases ETS-1 expression and is required for fibronectin production in mesangial cells. In these studies, we determined that ANG II induces phosphorylation of ETS-1 via activation of the type 1 ANG II receptor and that Erk1/2 and Akt/PKB phosphorylation are required for these effects. In addition, we characterized the role of ETS-1 on the transcriptional activation of fibronectin production in mesangial cells. We determined that ETS-1 directly activates the fibronectin promoter and by utilizing gel shift assays and chromatin immunoprecipitation assays identified two different ETS-1 binding sites that promote the transcriptional activation of fibronectin in response to ANG II. In addition, we identified the essential role of CREB and its coactivator p300 on the transcriptional activation of fibronectin by ETS-1. These studies unveil novel mechanisms involved in RAS-induced production of the extracellular matrix protein fibronectin in mesangial cells and establish the role of the transcription factor ETS-1 as a direct mediator of these effects.
Event-related potentials elicited by errors during the stop-signal task. II: Human effector-specific error responses
Authors: Reinhart Robert M. G. , Carlisle Nancy B. , Kang Min-Suk , Woodman Geoffrey F.
Published: February 2012

Although previous research with human and nonhuman primates has examined the neural correlates of performance monitoring, discrepancies in methodology have limited our ability to make cross-species generalizations. One major obstacle arises from the use of different behavioral responses and tasks across different primate species. Specifically, it is unknown whether performance-monitoring mechanisms rely on different neural circuitry in tasks requiring oculomotor vs. skeletomotor responses. Here, we show that the human error-related negativity (ERN) elicited by a saccadic eye-movement response relative to a manual response differs in several critical ways. The human saccadic ERN exhibits a prolonged duration, a broader frontomedial voltage distribution, and different neural source estimates than the manual ERN in exactly the same stop-signal task. The human saccadic error positivity (Pe) exhibited a frontomedial voltage distribution with estimated electrical sources in supplementary motor area and rostral anterior cingulate cortex for saccadic responses, whereas the manual Pe showed a posterior scalp distribution and potential origins in the superior parietal lobule. These findings constrain models of the cognitive mechanisms indexed by the ERN/Pe complex. Moreover, by paralleling work with nonhuman primates performing the same saccadic stop-signal task ( Godlove et al. 2011 ), we demonstrate a cross-species homology of error event-related potentials (ERPs) and lay the groundwork for definitively localizing the neural sources of performance-monitoring ERPs.
Fast corrective responses are evoked by perturbations approaching the natural variability of posture and movement tasks
Authors: Crevecoeur F. , Kurtzer I. , Scott S. H.
Published: February 2012

A wealth of studies highlight the importance of rapid corrective responses during voluntary motor tasks. These studies used relatively large perturbations to evoke robust muscle activity. Thus it remains unknown whether these corrective responses (latency 20–100 ms) are evoked at perturbation levels approaching the inherent variability of voluntary control. To fill this gap, we examined responses for large to small perturbations applied while participants either performed postural or reaching tasks. To address multijoint corrective responses, we induced various amounts of single-joint elbow motion with scaled amounts of combined elbow and shoulder torques. Indeed, such perturbations are known to elicit a response at the unstretched shoulder muscle, which reflects an internal model of arm intersegmental dynamics. Significant muscle responses were observed during both postural control and reaching, even when perturbation-related joint angle, velocity, and acceleration overlapped in distribution with deviations encountered in unperturbed trials. The response onsets were consistent across the explored range of perturbation loads, with short-latency onset for the muscles spanning the elbow joints (20–40 ms), and long-latency for shoulder muscles (onset > 45 ms). In addition, the evoked activity was strongly modulated by perturbation magnitude. These results suggest that multijoint responses are not specifically engaged to counter motor errors that exceed a certain threshold. Instead, we suggest that these corrective processes operate continuously during voluntary motor control.
Exercise training normalizes an increased neuronal excitability of NTS-projecting neurons of the hypothalamic paraventricular nucleus in hypertensive rats
Authors: Stern Javier E. , Sonner Patrick M. , Son Sook Jin , Silva Fabiana C. P. , Jackson Keshia , Michelini Lisete C.
Published: February 2012

Elevated sympathetic outflow and altered autonomic reflexes, including impaired baroreflex function, are common findings observed in hypertensive disorders. Although a growing body of evidence supports a contribution of preautonomic neurons in the hypothalamic paraventricular nucleus (PVN) to altered autonomic control during hypertension, the precise underlying mechanisms remain unknown. Here, we aimed to determine whether the intrinsic excitability and repetitive firing properties of preautonomic PVN neurons that innervate the nucleus tractus solitarii (PVN-NTS neurons) were altered in spontaneously hypertensive rats (SHR). Moreover, given that exercise training is known to improve and/or correct autonomic deficits in hypertensive conditions, we evaluated whether exercise is an efficient behavioral approach to correct altered neuronal excitability in hypertensive rats. Patch-clamp recordings were obtained from retrogradely labeled PVN-NTS neurons in hypothalamic slices obtained from sedentary (S) and trained (T) Wistar-Kyoto (WKY) and SHR rats. Our results indicate an increased excitability of PVN-NTS neurons in SHR-S rats, reflected by an enhanced input-output function in response to depolarizing stimuli, a hyperpolarizing shift in Na+ spike threshold, and smaller hyperpolarizing afterpotentials. Importantly, we found exercise training in SHR rats to restore all these parameters back to those levels observed in WKY-S rats. In several cases, exercise evoked opposing effects in WKY-S rats compared with SHR-S rats, suggesting that exercise effects on PVN-NTS neurons are state dependent. Taken together, our results suggest that elevated preautonomic PVN-NTS neuronal excitability may contribute to altered autonomic control in SHR rats and that exercise training efficiently corrects these abnormalities.
Passive resting state and history of antagonist muscle activity shape active extensions in an insect limb
Authors: Ache Jan M. , Matheson Thomas
Published: February 2012

Limb movements can be driven by muscle contractions, external forces, or intrinsic passive forces. For lightweight limbs like those of insects or small vertebrates, passive forces can be large enough to overcome the effects of gravity and may even generate limb movements in the absence of active muscle contractions. Understanding the sources and actions of such forces is therefore important in understanding motor control. We describe passive properties of the femur-tibia joint of the locust hind leg. The resting angle is determined primarily by passive properties of the relatively large extensor tibiae muscle and is influenced by the history of activation of the fast extensor tibiae motor neuron. The resting angle is therefore better described as a history-dependent resting state. We selectively stimulated different flexor tibiae motor neurons to generate a range of isometric contractions of the flexor tibiae muscle and then stimulated the fast extensor tibiae motor neuron to elicit active tibial extensions. Residual forces in the flexor muscle have only a small effect on subsequent active extensions, but the effect is larger for distal than for proximal flexor motor neurons and varies with the strength of flexor activation. We conclude that passive properties of a lightweight limb make substantial and complex contributions to the resting state of the limb that must be taken into account in the patterning of neuronal control signals driving its active movements. Low variability in the effects of the passive forces may permit the nervous system to accurately predict their contributions to behavior.
Physiological and molecular characterization of connexin hemichannels in zebrafish retinal horizontal cells
Authors: Sun Ziyi , Risner Michael L. , van Asselt Jorrit B. , Zhang Dao-Qi , Kamermans Maarten , McMahon Douglas G.
Published: February 2012

Connexin channels mediate electrical synaptic transmission when assembled as cell-to-cell pores at gap junctions and can mediate transmembrane currents when expressed in plasma membranes as hemichannels. They are widely expressed in the vertebrate retina where in electrical synapses they are critical for transmission of visual signals. While the roles of connexins in electrical synapses are well-studied, the function and roles of connexin hemichannels in the nervous system are less well understood. Genetic deletion in zebrafish of connexin (Cx) 55.5 alters horizontal cell feedback to cones, spectral responses, and visual behavior. Here, we have characterized the properties of hemichannel currents in zebrafish retinal horizontal cells and examined the roles of two connexin isoforms, Cx55.5 and Cx52.6, that are coexpressed in these cells. We report that zebrafish horizontal cells express hemichannel currents that conduct inward current at physiological negative potentials and Ca2+ levels. Manipulation of Cx55.5 and Cx52.6 gene expression in horizontal cells of adult zebrafish revealed that both Cx55.5 and Cx52.6 contribute to hemichannel currents; however, Cx55.5 expression is necessary for high-amplitude currents. Similarly, coexpression of Cx55.5 with Cx52.6 in oocytes increased hemichannel currents in a supra-additive manner. Taken together these results demonstrate that zebrafish horizontal cell hemichannel currents exhibit the functional characteristics necessary to contribute to synaptic feedback at the first visual synapse, that both Cx55.5 and Cx52.6 contribute to hemichannel currents, and that Cx55.5 may have an additional regulatory function enhancing the amplitude of hemichannel currents.