bluuebunny/crossref_metadata_2025 huggingface dataset:
Negative differential resistance and electrical bistability in nanocrystal organic memory devices
Authors: Tu Chia-Hsun , Kwong Dim-Lee , Lai Yi-Sheng
Published: December 2006

The authors observed a unique phenomenon in the Si∕SiO2∕Au∕organiclayer∕Al devices in regard to negative differential resistance (NDR) and bistability. Bistability was found to be transited from the NDR by annealing the gold film before the deposition of the organic layer. Meanwhile, the on/off current ratio in the NDR region could be tuned by as much as up to six orders. By suitable manipulation, the device exhibited repeatable electrical switching behavior. The observed NDR/bistability transition behavior is speculated to have resulted from the formation of discrete gold crystals. These crystals provide more trapping sites, which collect more charges, resulting in the repulsive Coulomb interaction.
Enhancement of critical current density of MgB2 by doping Ho2O3
Authors: Cheng C. , Zhao Y.
Published: December 2006

Mg 1 − x ( Ho 2 O 3 ) x B 2 alloys were prepared by in situ solid state reaction to study the effect of magnetic Ho2O3 dopant on flux pinning behavior of MgB2. Crystal structure, Tc, and Hc2 were not affected by Ho2O3 doping; however, Jc and Hirr were significantly enhanced. In 5T field, the best sample (x=3%) reached Jc of 1.0×103, 2.0×104, and 1.2×105A∕cm2 at 20, 10, and 5K, respectively, much higher than those achieved by nonmagnetic impurity, such as Ti-, Zr-, and Y2O3-doped MgB2. The observed magnetic HoB4 nanoparticles were attributed to be the source for the enhanced flux pinning effects.
Top-gate defined double quantum dots in InAs nanowires
Authors: Pfund A. , Shorubalko I. , Leturcq R. , Ensslin K.
Published: December 2006

The authors present low temperature transport measurements on double quantum dots in InAs nanowires grown by metal-organic vapor phase epitaxy. Two dots in series are created by lithographically defined top gates with a procedure involving no extra insulating layer. The authors demonstrate the full tunability from strong to weak coupling between the dots. The quantum mechanical nature of the coupling leads to the formation of a molecular state extending over both dots. The excitation spectra of the individual dots are observable by their signatures in the nonlinear transport.
Bond nature of oxygen-deficient HfO2∕Si(100) film
Authors: Cho Deok-Yong , Min C.-H. , Kim Jungho , Oh S.-J. , Kim Min Gyu
Published: December 2006

The authors investigate the bonding environment of an oxygen-deficient HfO2∕Si film grown by means of pulsed laser deposition, by analyzing the Hf L3-edge extended x-ray absorption fine structure. The local characteristics around the Hf atom, such as the bond length or the number of nearest neighbors, are found to depend on the oxygen supply during film growth. The chemical states of these samples are also probed in situ by x-ray/ultraviolet photoelectron spectroscopies. The core-level binding energy and the work function for each sample are found to be correlated with the mean Hf–O bond length, implying a close connection between the chemical environment and bond nature.
Dominant mode in closed photonic crystal microcavity filled with high scattering irregular gain medium
Authors: Long X. T. , Dai Q. F. , Fan H. H. , Wei Z. C. , Wu M. M. , Wang H. Z.
Published: December 2006

The experimental results demonstrate a dominant vertical cavity mode oscillation in a closed microcavity filled with high scattering and irregular structure gain medium. The mechanisms are (A) ultralow loss in a closed microcavity, (B) strong feedback from the microcavity causes light to be dominant in the vertical cavity mode, and (C) the dominant light in the vertical cavity mode synchronizes light in random directions and localization state.
Interlayer coupling in ferromagnetic epitaxial Fe3Si∕FeSi2 superlattices
Authors: Yoshitake T. , Ogawa T. , Nakagauchi D. , Hara D. , Itakura M. , Kuwano N. , Tomokiyo Y. , Takeda K. , Kajiwara T. , Ohashi M. , Oomi G. , Nagayama K.
Published: December 2006

Ferromagnetic epitaxial B2-type Fe3Si∕FeSi2 superlattices were prepared on Si(111) at room temperature by facing target direct-current sputtering. The bilinear and biquadratic coupling constants J1 and J2 of the antiferromagnetically coupled superlattice were comparable to those of the similar superlattices using Fe layers although the saturation magnetization of Fe3Si is approximately half as large as that of Fe. The authors believe that this is due to the formation of a well-ordered quantum well in the spacers, which is mainly caused by the regular accumulation of highly oriented Fe3Si layers.
Effects of phonon coupling and free carriers on band-edge emission at room temperature in n-type ZnO crystals
Authors: Giles N. C. , Xu Chunchuan , Callahan M. J. , Wang Buguo , Neal J. S. , Boatner L. A.
Published: December 2006

Room-temperature photoluminescence has been studied in n-type bulk ZnO crystals representing three different growth methods and having free-carrier concentrations (n) ranging from 1013to1018cm−3. The near-band-edge emission has both free-exciton and free-exciton-phonon contributions, with the strength of the phonon coupling dependent on sample defect concentrations. Band-gap shrinkage effects are used to explain a decrease in emission energy for the higher n values. Band filling and band nonparabolicity are predicted to be important for n>1019cm−3. At 300K, in the absence of free carriers, the free-exciton energy is 3.312±0.004eV.
Dielectric functions of densely stacked Si nanocrystal layer embedded in SiO2 thin films
Authors: Ding L. , Chen T. P. , Wong J. I. , Yang M. , Liu Y. , Ng C. Y. , Liu Y. C. , Tung C. H. , Trigg A. D. , Fung S.
Published: December 2006

A densely stacked silicon nanocrystal layer embedded in a SiO2 thin film is synthesized with Si ion implantation. The dielectric functions of the nanocrystal layer are determined with spectroscopic ellipsometry. The dielectric functions show a significant suppression as compared to that of bulk crystalline Si. Thermal annealing leads to an evolution of the dielectric functions from the amorphous towards crystalline state. For an insufficient annealing, the dielectric functions present a single broad peak, being similar to that of amorphous Si. However, a sufficient annealing leads to the emergence of the two-peak structure which is similar to that of bulk crystalline Si. In addition, the dielectric functions increase with annealing with a trend towards bulk Si.
InGaN-light emitting diode with high density truncated hexagonal pyramid shaped p-GaN hillocks on the emission surface
Authors: Park Eun-Hyun , Ferguson Ian T. , Jeon Soo-Kun , Park Joong-Seo , Yoo Tae-Kyung
Published: December 2006

To increase the light extraction efficiency, high density truncated hexagonal pyramid shaped submicron p-GaN hillocks were formed on the emission surface of an InGaN∕GaN multiple quantum well light emitting dicode (LED) using an in situ silicon carbon nitride self-masking layer. The self-assembled hillock density was raised up to a low 109cm−2 using several nanometers of a Si0.4C0.6N1 self-masking layer. The self-assembled hillock LED resulted in the optical power improvement up to 80% with similar electrical properties as a normal LED. This device showed a higher electrostatic discharge pass yield at over 1000V reverse stress voltage.
High efficiency thin-film CuIn1−xGaxSe2 photovoltaic cells using a Cd1−xZnxS buffer layer
Authors: Bhattacharya R. N. , Contreras M. A. , Egaas B. , Noufi R. N. , Kanevce A. , Sites J. R.
Published: December 2006

The authors have fabricated 19.52% thin-film CuIn1−xGaxSe2 (CIGS)-based photovoltaic devices using single layer chemical bath deposited Cd1−xZnxS (CdZnS) buffer layer. The efficiency equals the world record for any thin-film solar cell and is achieved with reduced optical absorption in the window layer. Using current-voltage, quantum efficiency, and capacitance-voltage measurements, the CIGS/CdZnS device parameters are directly compared with those of CIGS/CdS devices fabricated with equivalent absorbers.
Polarizing neutron monochromator with reduced higher-order contributions
Authors: Padiyath J. , Stahn J. , Horisberger M. , Ay M. , Böni P.
Published: December 2006

Polarized neutron reflectivity experiments have been performed to investigate polarizing multilayer monochromators. The neutron monochromators have been sputtered with Ti and Fe–Co–V as layer materials with a nominal period of 11nm. For more than two layers per period, the bulk magnetization of 2.35μB is reduced to 1.6μB. With 22 layers per period and 15 periods the higher-order contributions are decreased to below 0.6% of the first-order Bragg peak intensity (reflectivity of 0.21) at qz=0.06Å−1. The polarization efficiency for the final monochromator is 95.5%.
Extremely low voltage organic light-emitting diodes with p-doped alpha-sexithiophene hole transport and n-doped phenyldipyrenylphosphine oxide electron transport layers
Authors: Matsushima Toshinori , Adachi Chihaya
Published: December 2006

Organic light-emitting diodes with p-doped alpha-sexithiophene and n-doped phenyldipyrenylphosphine oxide carrier transport layers are fabricated. In the doped diodes, the authors demonstrate an extremely low driving voltage of 2.9V at a current density of 100mA∕cm2 and very high luminance at a low driving voltage: 1000cd∕m2 at 2.4V, 10000cd∕m2 at 2.8V, and 920000cd∕m2 at 4.5V. Such lowered driving voltages and enhanced luminance characteristics are attributed to the generation of free charge carriers by charge transfer from matrix to dopant molecules, resulting in an increase in electrical conductivities and formation of Ohmic contacts at metal/organic interfaces.
Fermi-level pinning and charge neutrality level in germanium
Authors: Dimoulas A. , Tsipas P. , Sotiropoulos A. , Evangelou E. K.
Published: December 2006

The Schottky barrier height in metal/Ge contacts shows weak dependence on the metal work function indicating strong Fermi-level pinning close to the Bardeen limit. The pinning factor S is about 0.05 and the charge neutrality level (CNL) is only about 0.09eV above the top of the valence band. Because of this, the Fermi level in Ge lies higher than CNL in most cases of interest so that unpassivated acceptorlike gap states at the interface are easily filled, building up a net negative fixed charge. This could prevent efficient inversion of a p-type Ge surface in a metal-oxide-semiconductor structure.
Experimental energy difference between heavy- or light-hole valence band and crystal-field split-off-hole valence band in AlxGa1−xN
Authors: Kawanishi Hideo , Niikura Eiichiro , Yamamoto Mao , Takeda Shoichiro
Published: December 2006

The energy difference between heavy- or light-hole (HH or LH) and crystal-field split-off-hole (CH) valence bands of m- and c-plane AlxGa1−xN was experimentally investigated as the peak-energy difference between (E⊥C)- and (E‖C)-polarized emissions. The energy difference was zero at x≈0.73–0.78. However, this value was significantly larger than x≈0.36–0.41, at which the spontaneous surface-emission intensities of E⊥C and E‖C polarizations from the AlxGa1−xN were equal. These results suggest a shorter carrier lifetime (larger optical gain) in the CH than in the HH and/or LH.
Catalyst-seeded synthesis and field emission properties of flowerlike Si-doped AlN nanoneedle array
Authors: Tang Y. B. , Cong H. T. , Wang Z. M. , Cheng H.-M.
Published: December 2006

Flowerlike Si-doped AlN nanoneedle array is grown from cobalt particles seeded on Si substrate by evaporating AlCl4 and SiCl4 in NH3 atmosphere. The nanoneedles are several microns in length, and their base and tip diameters are in the range of 50–150 and 5–30nm, respectively. Field emission (FE) measurements show that the Si-doped AlN nanoneedle array has a low turn-on field (∼1.8V∕μm) and a high field enhancement factor (∼3271), indicating that it is a promising candidate for FE applications. In addition, this catalyst-seeded and Si-doped method may facilitate the development of efficient AlN nanostructure FE devices.
Sol-gel-derived double-layered nanocrystal memory
Authors: Ko Fu-Hsiang , You Hsin-Chiang , Lei Tan-Fu
Published: December 2006

The authors have used the sol-gel spin-coating method to fabricate a coexisting hafnium silicate and zirconium silicate double-layered nanocrystal (NC) memories. From transmission electron microscopic and x-ray photoelectron spectroscopic analyses, the authors determined that the hafnium silicate and zirconium silicate NCs formed after annealing at 900°C for 1min. When using channel hot electron injection for charging and band-to-band tunneling-induced hot hole injection for discharging, the NC memories exhibited superior Vth shifting because of the higher probability for trapping the charge carrier.
Current degradation mechanism of single wall carbon nanotube emitters during field emission
Authors: Lee J. H. , Lee S. H. , Kim W. S. , Lee H. J. , Heo J. N. , Jeong T. W. , Baik C. W. , Park S. H. , Yu SeGi , Park J. B. , Jin Y. W. , Kim J. M. , Lee H. J. , Moon J. W. , Yoo M. A. , Nam J. W. , Cho S. H. , Ha J. S. , Yoon T. I. , Park J. H. , Choe D. H.
Published: December 2006

Electron emission current degradation is often observed from printed single wall carbon nanotube emitters during field emission process. After a highly imposed emission, structural deformation of emitters from thin crystalline nanotube bundle to thick amorphous-type carbon fiber was observed. This deformation seems to relate to the current degradation, deteriorating the efficiency of field emission either by increasing the resistance of emitters or by decreasing the field enhancement factor of emitter tips. Two possible mechanisms of structural deformation are internal structural transformation by Joule heating under excessively imposed emission current and continuous adsorption of carbon particles on actively working emitters.
Phonon-bottleneck enhanced magnetic hysteresis in a molecular paddle wheel complex of Ru25+
Authors: Chen L. , Ramsey C. M. , Dalal N. S. , Ren T. , Cotton F. A. , Wernsdorfer W. , Chiorescu I.
Published: December 2006

The ruthenium based molecular magnet [Ru2(D(3,5-Cl2Ph)F)4Cl(0.5H2O)∙C6H14] (hereafter Ru2) behaves as a two-level system at sufficiently low temperatures. The authors performed spin detection by means of single-crystal measurements and obtained magnetic hysteresis loops around zero bias as a function of field sweeping rate. Compared to other molecular systems, Ru2 presents an enhanced irreversibility as shown by “valleys” of negative differential susceptibility in the hysteresis curves. Simulations based on phonon-bottleneck model are in good qualitative agreement and suggest an abrupt spin reversal combined with insufficient thermal coupling between sample and cryostat phonon bath.
Manipulation of dielectric particles using photonic crystal cavities
Authors: Barth Michael , Benson Oliver
Published: December 2006

The authors present a theoretical study of the optical trapping forces on dielectric particles occurring in the highly localized evanescent field of planar photonic crystal (PC) cavities. These forces are evaluated by means of finite element simulations for particle sizes ranging from several nanometers to micrometers, and characteristic size-dependent changes of the trapping behavior are found. The authors introduce the phenomenon of self-induced trapping due to the resonance shift of the cavity and propose a transport mechanism based on alternating excitation of different cavity modes. Thus, PC cavities are promising candidates for applications involving the manipulation and arrangement of dielectric particles.
Near-ideal magnetoelectricity in high-permeability magnetostrictive/piezofiber laminates with a (2-1) connectivity
Authors: Dong Shuxiang , Zhai Junyi , Li Jiefang , Viehland D.
Published: December 2006

Theoretically, the two-phase laminated configurations should have even much higher magnetoelectric (ME) effects—however, prior experimental studies have failed to find such an enhancement. Here, the authors report the unleashing of the potential of the (2-1) connectivity configuration: a piezofiber (one-dimension connectivity) layer laminated between two high-permeability magnetostrictive FeBSiC alloy ones (two-dimension connectivity) has near-ideal ME coupling. Very high ME effects of up to 22V∕cmOe (4×10−7s∕m) at 1Hz—an order of magnitude higher than the giant ones—have been found.
Energy difference between electron subbands in AlInN∕GaInN quantum wells studied by contactless electroreflectance spectroscopy
Authors: Motyka M. , Kudrawiec R. , Cywiński G. , Siekacz M. , Skierbiszewski C. , Misiewicz J.
Published: December 2006

Contactless electroreflectance (CER) spectroscopy has been applied to study the energy difference between electron subbands in AlInN∕GaInN multiquantum wells (MQWs). Due to the strong built-in electric field, which is typical for III-nitrides, interband transitions between all QW subbands have been clearly observed. The energy difference between electron subbands has been found analyzing the interband transitions between the first hole subband and electron subbands. It has been shown that this difference is consistent with the results obtained by using photoinduced absorption of intersubband transitions. It shows that CER is an excellent method to study the energy difference between electron subbands in Al(In)N∕Ga(In)N QWs.
Lateral migration of dislocations in oxygen-doped GaN grown by molecular beam epitaxy
Authors: Hawkridge M. , Cherns D. , Myers T.
Published: December 2006

Threading dislocations in gallium nitride epilayers intermittently doped with oxygen were examined using transmission electron microscopy. Dislocations of all types were observed to incline away from the [0001] growth direction at the first introduction of oxygen, remaining inclined through subsequently doped layers. The type and the sign of the Burgers vector of inclined dislocations were characterized by large angle convergent beam electron diffraction, which revealed that the direction of inclination was not primarily driven by misfit stresses. In contrast, dislocations were observed to incline towards pronounced surface pits. It is concluded that the inclination is driven by surface roughening induced by oxygen doping, in contrast to previously published results.
175% tunnel magnetoresistance at room temperature and high thermal stability using Co2FeAl0.5Si0.5 full-Heusler alloy electrodes
Authors: Tezuka N. , Ikeda N. , Sugimoto S. , Inomata K.
Published: December 2006

The authors have fabricated epitaxially grown spin-valve-type magnetic tunnel junctions with L21-Co2FeAl0.5Si0.5 full-Heusler alloys for top and bottom electrodes and a MgO barrier. For MgO thickness tMgO=1.5nm, tunnel magnetoresistance (TMR) ratio and resistance and area product (RA) initially increase up to around 350°C and then decrease by annealing, while for tMgO=2.0 and 2.5nm, the TMR ratio increases with annealing temperature and peaks around 500°C. The TMR ratio up to 175% at RT and thermal stability up to 500°C have been achieved for tMgO=2.0nm, suggesting the large tunneling spin polarization and high thermal stability for Co2FeAl0.5Si0.5 with L21 structure.
Higher-k LaYOx films with strong moisture resistance
Authors: Zhao Yi , Kita Koji , Kyuno Kentaro , Toriumi Akira
Published: December 2006

The permittivities and the moisture resistance of LaYOx films annealed at 600°C with different Y concentrations are investigated. The permittivities of 40%Y–LaYOx and 70%Y–LaYOx films are higher than 25. The high permittivities come from the well crystallized hexagonal phase of LaYOx films, since the hexagonal phase rare earth oxides show higher permittivity than the cubic phase ones due to the smaller molar volume of the hexagonal phase. Furthermore, the high permittivity LaYOx films (40%Y–LaYOx and 70%Y–LaYOx) show a strong resistance to the moisture due to the introduction of Y2O3.
Electronic structure of the Mott insulator LaVO3 in a quantum well geometry
Authors: Hotta Y. , Wadati H. , Fujimori A. , Susaki T. , Hwang H. Y.
Published: December 2006

We used x-ray photoemission spectroscopy to investigate the electronic structure of one to five unit cell thick layers of the Mott insulator LaVO3 embedded in LaAlO3. By limiting the upper layer of LaAlO3 to three unit cells, the underlying LaVO3 could be probed. The V 2p core-level spectra had both V3+ and V4+ components, and above two unit cell thick LaVO3, the structures exhibited spectra similar to bulk samples. The atomically flat surfaces enabled the study of the emission angle dependence, which indicates that the V4+ is localized to the topmost layer. These results demonstrate the potential for probing interface electronic structure in oxide ultrathin films by surface spectroscopy.
Scanning transmission x-ray microscopy with a configurable detector
Authors: Gianoncelli A. , Morrison G. R. , Kaulich B. , Bacescu D. , Kovac J.
Published: December 2006

A configurable charge-coupled-device (CCD) detector is used in a scanning transmission x-ray microscope to record the transmitted intensity distribution for every pixel in a raster scan of the sample. Real-time processing of the CCD frames gives simultaneous absorption and phase contrast image signals from a single scan. The CCD combines fast frame-transfer readout with very high sensitivity and makes use of x-ray to visible-light coupling to allow operation over a wide range of photon energies, from the oxygen K edge upwards. Tests on the Twinmic end station at the Elettra synchrotron are reported.
Degradation of small-molecule organic solar cells
Authors: Song Q. L. , Wang M. L. , Obbard E. G. , Sun X. Y. , Ding X. M. , Hou X. Y. , Li C. M.
Published: December 2006

Small-molecule organic solar cells with a structure of indium tin oxide (ITO)\tris-8-hydroxy-quinolinato aluminum (Alq3) (2nm)\fullerene (C60) (40nm)\copper phthalocyanine (CuPc) (32nm)\Au (40nm) were fabricated. The shelf lifetime of unencapsulated devices was over 1500h, and the power conversion efficiency reached 0.76% under AM1.5G (air mass 1.5 global) 75mW∕cm2. The long lifetime was attributed to the inverted structure compared to the conventional ITO\CuPc\C60\buffer\Al structure since the former could effectively protect C60 from the diffusion of oxygen and modify interfacial electrical properties. The introduction of a 2nm Alq3 layer into the cells enhanced the power conversion efficiency by more than 20 times. The presence of the thin Alq3 film on the ITO substrate lowered the substrate work function and hence increased the electric field in the organic layers, which was beneficial to the collection of free carriers. The reasons for the degradation of such kind of organic solar cells are analyzed in detail.
Structural evolution in TiCu-based bulk metallic glass with large compressive plasticity
Authors: Wang G. , Liu Y. H. , Yu P. , Zhao D. Q. , Pan M. X. , Wang W. H.
Published: December 2006

The structural evolution during deformation is investigated in a work hardenable ductile TiCu-based bulk metallic glass by high-resolution electron microscopies. Two categories of crystalline morphologies, the scattered nanocrystallites and the nanocrystalline bands, are observed during the deformation. The nanocrystallization induced by deformation has implications for interpreting the unusual mechanical behavior of the glass.
Induction and Repression of Acetamidase in Chlamydomonas veinhavdi
Authors: Gresshoff P.M
Published: December 2006

Using a static induction approach it was shown that acetamidase of Chlamydomonas reinhardi was
regulated by ammonium repression and acetamidase induction. Urea, thiourea and acetamide were
efficient inducing substances; formamide, fluoroacetamide and acrylamide, although acting as
substrates, failed to induce the enzyme. Derepressed levels of acetamidase were shown to yield
sufficient nitrogen for growth, with amides giving high maximum enzyme velocities. Inhibitor
studies showed that derepressed and induced enzyme levels require transcription and translation.
Involvement of Plasmalemmasomes and Carbonic Anhydrase in Photosynthetic Utilization of Bicarbonate in Chara corallina
Authors: Price G.D , Badger M.R , Bassett M.E , Whitecross M.I
Published: December 2006

There is a clear relationship between the density of plasmalemmasomes (PLSs) in the acid band regions of whorl cells of Chara corallina and the capacity of these cells to utilize HCO*�/3 for photosynthesis. For cells grown in alkaline media, high PLS densities on the plasmalemma (50-85% coverage) were always correlated with high rates of HCO*�/3 dependent O2 evolution (pH 9.3), reaching rates of 17-23 mol O2 mg Chl-� h-� at 5 mM inorganic carbon concentration. In alkaline culture, development of high PLS densities and high rates of HCO*�/3 usage were related to provision of limiting levels of CO2
(< 12 M) in the media. High growth levels of CO2 (267 M) markedly reduced PLS densities and rates of HCO*�/3 usage. Bicarbonate dependent O2 evolution (pH 9.3) was extremely sensitive to the carbonic anhydrase inhibitor ethoxyzolamide (20 M), whilst CO2-dependent O2 evolution (pH 5.5) was insensitive. Carbonic anhydrase (CA) activity was present in homogenates and in intact cells, suggesting that a periplasmic location is possible. It seems reasonable to suggest that, for Chara corallina, high PLS densities and CA activity are required for efficient utilization of HCO*�/3 at alkaline pH.
Plasmalemmasomes may be part of the HCO*�/3-utilizing mechanism by acting as sites for localized pH generation, thus facilitating HCO*�/3 utilization by either H+/HCO*�/3 active cotransport or CA and pH-mediated external conversion of HCO*�/3 to CO2 in the periplast.
Oscillations in Apparent Hydraulic Conductance of Cotton Plants
Authors: Passioura J.B , Tanner C.B
Published: December 2006

Cotton plants were grown in pots that could be encased in a pressure chamber so that a pneumatic
pressure could be applied to the roots while the shoot was enclosed in an unpressurized cuvette. Enough
pressure (the 'balancing pressure') was applied to the roots to raise the pressure of the xylem sap in the
shoot to that of the atmosphere, so that a cut in the xylem of the shoot was on the verge of bleeding.
The balancing pressure was accurately maintained, despite any changes in the transpirational flux, by
means of an automatic pressure regulator. When the transpirational flux was suddenly changed by
changing the humidity in the cuvette, the balancing pressure started to oscillate even though flux was
steady at its new level, i.e. the apparent hydraulic conductance (the ratio of transpirational flux to the
pressure drop across the plant) oscillated. In plants that were phosphorus-deficient, the oscillations were
large and had a period of 30-50 min; though damped, they persisted for several cycles. Phosphorussufficient
plants gave one, critically-damped, oscillation.
Pregnancy recognition and conceptus implantation in domestic ruminants: roles of progesterone, interferons and endogenous retroviruses
Authors: Spencer Thomas E. , Johnson Greg A. , Bazer Fuller W. , Burghardt Robert C. , Palmarini Massimo
Published: December 2006

The present review highlights new information on pregnancy recognition and conceptus development and implantation in sheep with respect to regulation by progesterone, interferons and endogenous retroviruses. After formation of the corpus luteum, progesterone acts on the endometrium and stimulates blastocyst growth and elongation to a filamentous conceptus (embryo/fetus and associated extra-embryonic membranes). The envelope of endogenous retroviruses related to Jaagsiekte sheep retroviruses appears to intrinsically regulate mononuclear trophectoderm cell proliferation and differentiation into trophoblast giant binucleate cells. The mononuclear trophectoderm cells of elongating sheep conceptuses secrete interferon-τ, which acts on the endometrium to prevent development of the luteolytic mechanism by inhibiting transcription of the gene for the oestrogen receptor α in the luminal and superficial ductal glandular epithelia. These actions prevent oestrogen-induced transcription of the oxytocin receptor gene and, therefore, oxytocin-induced luteolytic pulses of prostaglandin F2α. Progesterone downregulation of its receptors in luminal and glandular epithelia correlates temporally with a reduction in anti-adhesive mucin 1and induction of secreted galectin 15 (LGALS15) and secreted phosphoprotein 1, which are proposed to regulate trophectoderm proliferation and adhesion. Interferon-τ acts on the endometrial lumenal epithelium to induce WNT7A and to stimulate LGALS15, cathepsin L and cystatin C, which are candidate regulators of conceptus development and implantation. The number of potential contributors to maternal recognition and establishment of pregnancy continues to grow and this highlights our limited appreciation of the complexity of the key molecules and signal transduction pathways that intersect during these key developmental processes. The goal of improving reproductive efficiency by preventing embryonic losses that occur during the peri-implantation period of pregnancy in domestic ruminants provides the challenge to increase our knowledge of endometrial function and conceptus development.
1 XENOGRAFTING OF ADULT MAMMALIAN TESTIS TISSUE
Authors: Arregui L. , Rathi R. , Zeng W. , Honaramooz A. , Gomendio M. , Roldan E.R.S , Dobrinski I.
Published: December 2006

Testis tissue grafting presents an option for preservation of genetic material when sperm recovery is not possible. Grafting of testis tissue from sexually immature males to immunodeficient mice results in germ cell differentiation and production of fertilization-competent sperm from different mammalian species (Honaramooz et al. 2002 Nature 418, 778–781). However, the efficiency of testis tissue xenografting from adult donors has not been critically evaluated. Spermatogenesis was arrested at meiosis in grafts from mature horses (Rathi et al. 2006 Reproduction 131, 1091–1098) and hamsters (Schlatt et al. 2002 Reproduction 124, 339–346), and no germ cell differentiation occurred in xenografts of adult human testis tissue (Schlatt et al. 2006 Hum. Reprod. 21, 384–389). The objective of this study was to investigate survival and germ cell differentiation of testis xenografts from sexually mature donors of different species. Small fragments of testis tissue from 10 donor animals of 5 species were grafted under the back skin of immunodeficient, castrated male mice (n = 37, 2–6/donor). Donors were pig (8 months old), goat (18 months old and 4 years old) (n = 2), bull (3 years old), donkey (13 months old), and rhesus monkey (3, 6, 11, and 12 years old). At the time of grafting, donor tissue contained elongated spermatids, albeit to different degrees (>75% of seminiferous tubules in testis tissue from pig, goat, bull, and 6–12-year-old monkeys, and 33 or 66% of tubules in tissue from donkey or 3-year-old monkey, respectively). Grafts were recovered <12 weeks (n = 14 mice), 12–24 weeks (n = 16 mice), and >24 weeks (n = 7 mice) after grafting and classified histologically as completely degenerated (no tubules found), degenerated tubules (only hyalinized seminiferous tubules observed), or according to the most advanced type of germ cell present. Grafts from pig, goat, bull, and 6–12-year-old monkeys contained >60% degenerated tubules or were completely degenerated at all time points analyzed. In contrast, in grafts from the 3-year-old monkey, only 18% of tubules were degenerated, 14% contained Sertoli cells only, 64% contained meiotic, and 4% haploid germ cells at 24 weeks after grafting. Similarly, donkey testis grafts recovered 12–24 weeks after grafting contained <2% degenerated tubules, 46% of tubules had Sertoli cells only, 45% contained meiotic, and 7% haploid germ cells. These results show that survival and differentiation of germ cells in testis grafts from sexually mature mammalian donors is poor. However, better graft survival and maintenance of spermatogenesis occurred in donor tissue from donkey and 3-year-old monkey that were less mature at the time of grafting. Therefore, species and age-related differences appear to exist with regard to germ cell survival and differentiation in xenografts from adult donors.
This work was supported by USDA/CSREES 03-35203-13486, NIH/NCRR 5-R01-RR17359-05, the Spanish Ministry of Education, and Science (BES-2004-4112).
101 DEVELOPMENTAL ARREST AND CYTOSKELETAL ANOMALIES OF RAT EMBRYOS RECONSTRUCTED BY SOMATIC CELL NUCLEAR TRANSFER
Authors: Yoo J. G. , Demers S.-P. , Lian L. , Smith L. C.
Published: December 2006

Many factors influence success rates in animal cloning by somatic cell nuclear transfer (SCNT), including cell cycle stage of the donor cells and recipient oocyte, the procedure of micromanipulation, and the activation protocol. It has been reported that the development of rat embryos is inhibited at the 2-cell stage during in vitro culture and that microtubule (MT) distribution is involved in the developmental arrest. This study was conducted to determine the effects of oocyte activation methods and the cell cycle coordination for cloning rats from fetal fibroblasts (FF). Recipient oocytes were activated with cycloheximide, 6-dimethylaminopurine, and roscovitine and used either before (metaphase-II, MII) or after (telophase-II, TII) activation for fusion with FF at the G0/G1-phase, metaphase, and S/G2-phase. Moreover, enucleated zygotic and parthenogenetic ooplasts were used for serial cloning with pronuclear and 2-cell-stage blastomeres derived from SCNT. There was no significant difference in the first cleavage rate in the 3 activation groups after SCNT. Metaphase donor cells (85.2%) had a significantly higher cleavage rate than G0/G1-phase FF with MII oocytes (70.4%) and G2-phase FF with TII oocytes (72.2%). However, reconstructed embryos were unable to develop beyond the 2-cell stage either in vitro or in vivo. Moreover, serial cloning with zygotic and parthenogenetic recipients was also unable to overcome the developmental arrest at the 2-cell-stage. To assess the cytoskeleton after SCNT, reconstructed 2-cell-stage embryos were harvested at different times after cleavage for immunostaining (anti alpha-tubulin) and mRNA abundance (beta-actin and alpha-tubulin). Reconstructed 2-cell embryos showed much thicker fibrous or disconnected MT distribution concomitant with a reduction in cytoskeletal transcripts at the late 2-cell stage. In summary, our results indicate that the developmental arrest of rat SCNT embryos was a result of abnormal MT distribution caused by improper transcription of cytoskeleton genes; however, further studies are needed to understand the early developmental block of rat SCNT-derived embryos.
110 COMPARISON OF ANDROMED®, BIOXCELL®, AND BOTU-BOV® EXTENDERS FOR CRYOPRESERVATION OF BULL SEXED SEMEN
Authors: Braga M. Q. , Franco R. V. R. , Rodrigues L. F. , Galeli G. , Oliveira K. M. , Reis F. A. C. , Nishikawa M. F. A. , Moura E. P.
Published: December 2006

Sexing semen has become a worldwide technology now available in many countries through the use of flow cytometry for sexing mammal sperms (Johnson and Welch 1999 Theriogenology 52, 1323–1341). Because straws containing sexed semen have a low concentration, any condition that either improves or decreases freezing capabilities will considerably change semen quality. During cryopreservation, spermatozoa have been described as undergoing many changes that lead to membrane damage, which may result in decreased fertility (Watson 2000 Reprod. Fertil. Dev. 6 (Suppl 1), 481). Since many cryoprotectants are available on the market, the objective of the present study was to compare 3 different extenders for freezing sex-sorted semen. For this study, 25 ejaculates were collected from 8 bulls of different breeds, diluted, then dyed with Hoechst 33342 (Schenk et al. 1999 Theriogenology 52, 1375–1391), and sexed by flow cytometry (SX MoFlo®; DaKoCytomation, Inc., Fort Collins, CO, USA). After being cooled at 4°C for 1 h and 30 min, the sexed semen was centrifuged and diluted in AndroMed® (Minitüb, Tiefenbach, Germany), Bioxcell® (IMV, Aigle, France), or Botu-Bov® (Biotech Botucatu, Ltda., Sao Paulo, Brazil); the semen was packaged at 3 million total sperm in 0.25-mL straws and frozen in an automatic freezer (Digit cool 5300® IMV). To evaluate the freezing quality, the straws were thawed and incubated at 35°C for 15 min. The progressive motility was observed through an optical microscope (Coleman 200T). The statistical analyses were done using the SAS program (SAS Institute, Inc., Cary, NC, USA) and the Tukey test (P ≤ 0.05). Results show that there was no statistical difference between Bioxcell and AndroMed extenders (P ≤ 0.05). However, Botu-Bov extender showed a significant difference when compared with Bioxcell and AndroMed (see Table 1). It is also important to point out that 40% of the samples frozen with AndroMed showed non-aligned movement. Even though few ejaculates were used for this study, preliminary results showed that Bioxcell seemed to be the most suitable for freezing bull sexed semen.

Table 1.
Percentage of progressively motile spermatozoa after thawing
111 SLOW FREEZING AND VITRIFICATION OF IN VITRO-MATURED DOMESTIC CAT OOCYTES
Authors: Braun J. , Otzdorff C. , Tsujioka T. , Hochi S.
Published: December 2006

The effects of slow freezing or vitrification as well as exposure to the cryoprotective media without cooling and warming of in vitro-matured domestic cat oocytes on the in vitro development to the blastocyst stage was investigated. Cumulus–oocyte complexes were matured for 24 h in TCM-199 supplemented with 3 mg mL−1 BSA, 1 µg mL−1 estradiol, 0.1 IU mL−1 FSH, and 0.0063 IU mL−1 LH. Denuded oocytes with a detectable first polar body were inseminated with 2 × 106 cells mL−1 cauda epididymal spermatozoa for 22 h in TALP solution. Presumptive zygotes were cultured in modified SOF medium at 38.5°C in 5% CO2 in air. For slow freezing, oocytes were equilibrated for 20 min at ambient temperatures in PBS with 20% FCS containing either 1.5 M ethylene glycol (EG) + 0.2 M sucrose or 1.5 M EG + 0.2 M trehalose. Oocytes were loaded into 0.25-mL straws, cooled to −7°C at 2°C min, held for 5 min, seeded, cooled down to −30°C at 0.3°C min, and finally plunged into liquid nitrogen. The straws were thawed for 5 s at room temperature and for 30 s in a waterbath at 30°C. Oocytes were washed 3 times before insemination. In vitro-matured oocytes were exposed to the cryoprotective media for 30 min before they were inseminated and then they were cultured for 7 days. For vitrification (Hochi et al. 2004 Theriogenology 61, 267–275), a minimum-volume cooling procedure using Cryotop (Kitazato Supply Co., Tokyo, Japan) as a cryodevice was applied. No blastocysts could be obtained after slow freezing with a cryoprotective medium containing 0.2 M sucrose. Simple exposure to the same freezing medium after in vitro maturation without cryopreservation resulted in a blastocyst rate of 7.9% (control oocytes, 10.7%; not significant (NS); chi-square analysis). Use of trehalose as an extracellular cryoprotectant resulted in the harvest of one blastocyst (0.6%) after slow freezing. Exposure to the same cryoprotective medium resulted in a blastocyst rate of 10.0% (fresh control, 10.9%; NS). After exposure of in vitro-matured oocytes to the vitrification solution, a blastocyst rate of 16.0% was observed (8/50), which was not statistically different from the blastocyst rate in fresh control oocytes (16.3%; 15/92). No blastocysts could be obtained after vitrification (0/64). The results (Table 1) demonstrate that there is no obvious toxic effect of the cryoprotectants employed here for slow freezing or vitrification on the in vitro-matured oocytes, but the developmental potential of cryopreserved oocytes to the blastocyst stage is severely impaired.

Table 1.
Effect of slow freezing or exposure to freezing medium of matured cat oocytes on the development to the blastocyst stage in vitro
115 RELATIONSHIP BETWEEN IN VIVO FERTILITY OF MANCHEGA EWES LAPAROSCOPICALLY INSEMINATED WITH FROZEN - THAWED RAM SEMEN AND HETEROLOGOUS CALF IN VITRO FERTILIZATION
Authors: Garcia-Alvarez O. , Maroto-Morales A. , Perez-Guzman M. D. , Soler A. J.
Published: December 2006

Cryopreservation may damage the fertilizing ability of spermatozoa. For this reason, it is important to assess the sperm before artificial insemination. In vitro fertilization (IVF) tests are the most suitable for assessing overall sperm function during fertilization. The aim of this work was to study whether a relationship exists between heterologous calf in vitro fertilization and in vivo fertility in Manchega sheep, with the purpose of predicting in vivo fertility of males before using their semen. Frozen–thawed sperm from 4 Manchega rams was used to laparoscopically inseminate 481 ewes of the same breed. Sperm was cryopreserved in a TRIS-yolk-glycerol extender. A minimum of 10 females were laparoscopicly inseminated per ram. These same straws were used for IVF (4 replicates per male). Domestic calf ovaries were collected at a slaughterhouse. Inmature cumulus–oocyte complexes (COCs) were aspirated and matured in vitro in TCM-199 with 10 ng mL-1 EGF and 100 �M cysteamine. After 24 h, zona-intact mature oocytes were incubated in synthetic oviduct fluid supplemented with 10% estrous sheep serum. Thawed spermatozoa were co-incubated with the oocytes (one million per well) for 40 h, and the cleavage rate was asessed. A regresion analysis was performed. The in vivo fertility ranged from 25.00 to 62.50%. Two rams had a fertility under 30.00% and the other ones over 55.00%. The in vitro fertility ranged from 42.50 to 58.50%. The in vivo fertility was not related to the in vitro fertility (P = 0.17). This could be due to the low number of males used in this work. Heterologous calf in vitro fertilization tests cannot be used to predict in vivo fertility of ram semen since no relationship was found between both variables. Nevertheless, these results are preliminary and we are working with more rams and replicates to obtain more information.
This work was funded by INIA and Consejeria de Agricultura de Castilla-La Mancha. Garcia-Alvarez enjoyed a studentship from the INIA
116 EFFECT OF INCUBATION OF BOVINE EPIDIDYMAL SPERMATOZOA IN SEMINAL PLASMA PRIOR TO CRYOPRESERVATION
Authors: Guerrero C. A. , Jenkins J. A. , Lynn J. W. , Bondioli K. R. , Godke R. A.
Published: December 2006

Studies examining the influence of seminal plasma on sperm function have shown both beneficial and detrimental effects. However, its effect on pre-frozen bovine epididymal sperm (BES) has not been documented. The objective of this study was to determine the effect of a 30-min incubation of BES in bovine seminal plasma (SEMP) prior to freezing on post-thaw sperm parameters. Paired testes were obtained from mature bulls (n = 10) at a local abattoir and transported to the laboratory (25–28°C) within 3–5 h postmortem. BES were harvested by multiple incisions from the caudae epididymides of each bull, pooled, and split into either Treatment A, 3 mL of egg yolk Tris-based medium (EYT) (No SEMP), or Treatment B, 3 mL of SEMP, each for 30 min in a 37°C water bath. SEMP was extracted from ejaculates of mature bulls (n = 6), and then pooled and stored at −20°C until used. Sperm from both treatments were re-suspended in EYT, adjusted to 70 × 106 sperm mL−1 and cooled to 4°C at 0.1°C min−1. Samples were diluted slowly over a 30-min period with 1:1 EYT medium containing 14% glycerol and loaded into 0.5-mL straws. Straws were frozen in liquid nitrogen vapors. For sperm analyses, straws were thawed in a water bath at 37°C for 40 s. Morphology was determined by staining with eosin-nigrosin. Viability and acrosome integrity were measured simultaneously with the combination of SYBR 14, propidium iodide, and PE-PNA. Mitochondrial activity was measured by the combination of MitoTracker Red and SYBR 14. DNA integrity was determined by acridine orange using the sperm chromatin structure assay (SCSA®; SCSA Diagnostics, Inc., Brookings, SD, USA). All assays were performed by multicolor flow cytometry. Differences between treatments were analyzed using one-way ANOVA (P < 0.05). In summary, all sperm quality parameters decreased significantly after thawing in both treatments (Table 1). A significantly higher overall and progressive motility post-thaw was achieved when sperm were incubated in SEMP prior to freezing. However, no difference was detected in sperm viability, acrosome integrity, mitochondrial activity, and DNA integrity between treatments. Also, SEMP reduced the quantity of distal droplets and broken tails post-thaw over that of no SEMP. Results indicate that incubation of BES in bovine seminal plasma prior to freezing improves post-thaw sperm quality.

Table 1.
Effect of bovine seminal plasma (SEMP) on quality parameters (mean ± SEM) of post-thaw bovine epididymal sperm
117 EFFECT OF STEPWISE DILUTION ON THE VIABILITY OF FROZEN - THAWED BOVINE OOCYTES MATURED IN VITRO
Authors: Hamawaki A. , Hamano S. , Yoshikawa M. , Matsukawa K.
Published: December 2006

The purpose of this study was to evaluate the effect of stepwise dilution on the viability of frozen–thawed bovine oocytes matured in vitro. Oocytes matured in vitro were denuded and equilibrated in modified TCM-199 (m199: 11 mmol L-1 HEPES, 9 mmol L-1 Na-HEPES, 5 mmol L-1 NaHCO3, 20% (v/v) calf serum) supplemented with 10% (v/v) glycerol for 15 min at room temperature (RT). Then they were exposed to m199 with 10% glycerol and 0.25 mol L-1 sucrose and loaded into 0.25-mL plastic straws. The straws were sealed and seeded at -6�C, cooled at the rate of 0.33�C min-1 to -25�C, and plunged into LN2. For thawing, the straws were first held in air at RT for 10 s, followed by immersion in 30�C water for 10 s. In the first experiment, frozen-thawed oocytes were subjected to cryoprotectants in 5 different manners of dilution. In the non-step dilution, the oocytes (n = 60) were put into m199 for 5 min. In the single-step dilution, the oocytes (n = 37) were transferred to 0.25 mol L-1 sucrose in m199 for 5 min. In the two-step dilution, the oocytes (n = 56) were transferred to 0.5 and then 0.25 mol L-1 sucrose in m199 for 5 and 5 min, respectively. In the three-step dilution, the oocytes (n = 57) were transferred to 0.75, 0.5, and 0.25 mol L-1 sucrose in m199 for 1, 5, and 5 min, respectively. In the four-step dilution, the oocytes (n = 52) were transferred to 1.0, 0.75, 0.5, and 0.25 mol L-1 sucrose in m199 for 1, 1, 5, and 5 min, respectively. After dilution, all of the oocytes were washed twice in TCM-199 supplemented with 5% fetal bovine serum for 5 min and cultured for 1 h to assess the morphology. The rate of morphological normal oocytes in the four-step dilution (94.2%) was significantly (P < 0.05) higher than that in other groups (non-, single-, two-, and three-step dilution: 61.7%, 73.0%, 78.6%, and 77.2%). In the second experiment, non-frozen (control, n = 170) and frozen–thawed oocytes (n = 145) with four-step dilution were fertilized and cultured in vitro (Kuwayama 1992 J. Reprod. Fert. 96, 187–193). To assess fertilization, some of the oocytes were fixed at 10 h after insemination. Cleavage and blastocyst rates were determined on Day 2 and Day 8 after fertilization (Day 0), respectively. There was no difference (P > 0.05) between control and frozen–thawed oocytes in the fertilization rate (88.0% vs. 93.1%). Some of the frozen–thawed oocytes cleaved and developed to blastocysts (44.0% and 11.2%), although the rates were significantly (P < 0.01) lower than those in control (71.7% and 35.0%). These results indicate that stepwise dilution of frozen–thawed oocytes improves the recovery of oocytes with normal morphology, and that the oocytes maintain the abilities to be fertilized and develop to blastocysts.