bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric, magnetic, and magnetotransport properties in Sr doped two-dimensional RE2CoO4 (RE=Pr,Eu) compounds
Authors: Yao Q. W. , Wang X. L. , Dou S. X.
Published: January 2008

In this work, we report on the studies of dielectric, magnetic, and magnetotransport properties of Sr doped RE2−xSrxCoO4 (RE=Pr or Eu, x=0.25–1.5). These compounds were systematically studied in terms of structure, magnetic, magnetotransport, and dielectric constant measurements. Rietveld refinement indicated that these compounds crystallized in K2NiF4-type structure with space group I4∕mmm. Lattice parameters increase with Sr doping level. The system changes from paramagnetic to ferromagnetic with increasing Sr doping level and finally becomes ferromagnetic with TC of 230K for Pr0.75Sr1.25CoO4 and EuSrCoO4, respectively. The temperature dependence of resistivity indicates that both systems change from semiconductive to metallic with Sr doping. The magnetoresistance (MR) value of 10% at 5K and 8T is found for the EuSrCoO4 compound. Large dielectric constants with values of above 2000 were observed in low frequencies for samples with x around 1 for Pr based compounds.
The use of plasmon resonances in thermally assisted magnetic recording
Authors: Zhang Z. , Mayergoyz I. D.
Published: January 2008

The numerical study of plasmon resonances as optical means for light delivery in thermally assisted magnetic recording is reported. The analysis of two distinct designs is performed. In these designs, the plasmon resonances in metallic nanoparticles and perforated metallic nanofilms are used, respectively. The specific plasmon modes that create the strongest and well-localized (on nanoscale) optical fields have been identified. The issues of coupling of incident laser radiation to these plasmon modes as well as the sharpness of plasmon resonances are discussed.
ac susceptibility studies of the spin freezing behavior in U2CuSi3
Authors: Li D. X. , Nimori S. , Yamamura T. , Shiokawa Y.
Published: January 2008

Ternary uranium compound U2CuSi3 have been prepare and confirmed to crystallize in the tetragonal α-ThSi2-type structure after annealed at 800°C for 240h. ac susceptibility measurements reveal a evident spin glass transition for this compound at a static spin freezing temperature TS=18.3K. Several important parameters characteristic of the spin freezing state are determined from the dynamical analyses of the ac susceptibility data. The formation of spin glass state in this sample is further proved by specific heat, electrical resistivity, and magnetic relaxation measurements. The presence of frustrated magnetic interactions in U2CuSi3 is discussed in a “magnetic cluster model.”
Within wafer magnetic anisotropy in sputtered FeCo films
Authors: Mathieu Christoph , Hadley Matthew J. , Inturi Venkateswara R.
Published: January 2008

Seeded FeCo films were studied as a function of aligning field, thickness, deposition power density, and pressure. Magnetic and nonmagnetic parameters were investigated with an emphasis on within wafer magnetic dispersion, which was measured using both a magnetic loop tracer and a magneto-optical Kerr effect mapper. Magnetic dispersion changes significantly with all variables studied, although correlations between other magnetic parameters, resistivity, and stress are not consistently observed.
A first order reversal curve investigation of pressure hysteresis in multiferroics spin transition compound
Authors: Tanasa Radu , Stancu Alexandru , Codjovi Epiphane , Linares Jorge , Varret François , Létard Jean-François
Published: January 2008

Spin crossover multiferroic [Fe(PM-BiA)2(NCS)2] is investigated for the first time with the first order reversal curve (FORC) diagram method for its hysteretic pressure behavior. The experimental setup allows the measurements of the high spin fraction as the function of temperature, light intensity, and pressure. The experimental FORC diagrams obtained in compression and releasing modes show significant differences which are in disagreement with the classical Preisach model. Also, stronger kinetic effects are evidenced in the compression mode and possible explanations of this effect considering the viscoelastic behavior are provided.
Magnetic-dependent structure in eight-atom gold clusters
Authors: Botana Jorge , Pereiro Manuel , Baldomir Daniel , Arias Juan Enrique , Warda Krzysztof , Wojtczak Leszek
Published: January 2008

We have performed ab initio calculations on the lowest energy structure of eight-atom gold clusters, a tetracapped square with D4h symmetry, locking it to several total magnetic moments. We have found that for nonzero values of the total magnetic moment, the D4h symmetry is not stable. We have also found that for a fixed nonzero total magnetic moment, the stable structure is a distortion of the tetracapped square, along the square’s diagonals. This structure has a D2h symmetry. The rest of possible structures for this cluster have been calculated as well, and no magnetism-dependent deformation was found, except for the tetracapped tetrahedron with symmetry Td, which is unstable for nonzero total magnetic moment. In this case, the favored structure is a bicapped octahedron with symmetry D2d. The structural change due to magnetic constraints is relevant since the surface of gold clusters has shown a catalytic behavior highly dependent on the structure.
Ba
8
Ga
16
Sn
30
with type-I clathrate structure: Drastic suppression of heat conduction
Authors: Avila M. A. , Suekuni K. , Umeo K. , Fukuoka H. , Yamanaka S. , Takabatake T.
Published: January 2008

For the past decade, intermetallic clathrates have been rattling their way into mainstream research in thermoelectrics. The unusual vibrations of their guest ions inside oversized cages interfere with the cage phonons while leaving the electronic flow intact, providing an exotic way to achieve a best-of-both-worlds scenario in terms of electrical and thermal transport in the same material. Here, we present the structural and thermoelectric properties of Ba8Ga16Sn30 single crystals grown in the type-I clathrate structure (β-BGS), showing one of the lowest recorded thermal conductivities κ(T) for any bulk compound, while still behaving electronically as a heavily doped n-type semiconducting crystal.
Thermal resistance of the native interface between vertically aligned multiwalled carbon nanotube arrays and their SiO2/Si substrate
Authors: Son Youngsuk , Pal Sunil K. , Borca-Tasciuc Theodorian , Ajayan Pulickel M. , Siegel Richard W.
Published: January 2008

The interface thermal resistance (ITR) of the native interface between vertically aligned multiwalled carbon nanotube arrays and the SiO2/Si substrate was investigated. Experimental results obtained by a photothermoelectric technique are compared with theoretical predictions for the ITR across nanoconstrictions. The model considers classical constriction effects and contributions due to diffuse mismatch thermal resistance. Experimental values of the ITR are much larger than the model predictions. The observed discrepancy may be due to the imperfect mechanical contact between the tubes and substrate or additional contributions to the ITR due to the presence of a catalyst layer at the interface.
Temperature effects on pinpoint photopolymerization and polymerized micronanostructures
Authors: Takada Kenji , Kaneko Koshiro , Li Yu-Dong , Kawata Satoshi , Chen Qi-Dai , Sun Hong-Bo
Published: January 2008

The spatial resolution in pinpoint two-photon photopolymerization of radical-type resins was found to be improved by varying the liquid sample temperature from a critical value Tc. For SCR-500 and NOA-61, the currently widely used resins, Tc is around room temperature. The improvement of spatial resolution by temperature decrease was attributable to restraint radicals diffusion; while the voxel size reduction versus temperature increase was considered as arising from enhanced chain termination. Furthermore, temperature plays an important role in size tuning of polymerized structures, for example, a photonic crystal blueshifted its working wavelength for 50 and 400nm when heated at 200 and 300°C, respectively, indicating the possibility to precisely tailor the photonic bandgap by means of thermal processing.
Correlation between electrical transport, optical, and magnetic properties of transition metal ion doped ZnO
Authors: Singh Shubra , Rama N. , Sethupathi K. , Rao M. S. Ramachandra
Published: January 2008

We report on the transport and optical properties of transition metal ions, namely Ti, V, Fe, Co and Ni doped ZnO samples. Diffuse reflectance spectroscopy of doped ZnO showed the existence of absorption bands which were attributed to the d-d transitions of respective dopants. Resistivity was found to decrease in the case of Ti, V, Fe, and Ni dopings. Correlation between the electrical resistivity and magnetic properties of the samples has been explained on the basis of impurity d-band splitting model.
Magnetic and electronic irreversibility and relaxation in Eu1−xLaxB6 (x=0.15 and 0.18)
Authors: Kim J. Y. , Rhyee Jong-Soo , Sung N. H. , Han S. H. , Cho B. K.
Published: January 2008

We have investigated the magnetic and electronic transport properties of Eu1−xLaxB6 (x=0.15 and 0.18). Temperature-dependent magnetization of Eu1−xLaxB6 (x=0.15 and 0.18) exhibited antiferromagneticlike ground state with transition temperature Tm≈5K and thermal hysteresis below Tm between field-cooled and zero-field-cooled modes with the magnetic field of H=0.1kOe. Time dependent isothermal remnant magnetization MIRM of Eu1−xLaxB6 (x=0.15 and 0.18) was found to follow logarithmic magnetic relaxation behavior M(t)=M0−M1log(t). The temperature-dependent resistivity ρ(T) shows anomalous increase at low temperatures below T⩽20K, suppressed by magnetic field, which can be explained by magnetic polaron picture. Interestingly, field dependent electrical resistivity ρ(H) for Eu1−xLaxB6 (x=0.15 and 0.18) showed irreversibility between increasing and decreasing field. The relaxation of ρ(H→0) was found to follow the general stretched exponential form, ρ(t)=A+Bexp(−t∕τ)γ.
Optimizing optical absorption of TiO2 by alloying with TiS2
Authors: Umezawa Naoto , Janotti Anderson , Rinke Patrick , Chikyow Toyohiro , Van de Walle Chris G.
Published: January 2008

Ti O 2 is an attractive material for photocatalytic water splitting, but its band gap is too large to allow for efficient absorption of solar photons. We present a comprehensive first-principles investigation of band-structure modifications induced by alloying TiO2 with TiS2. The band gap of TiO2(1−x)S2x alloys exhibits a dramatic decrease upon addition of even a low concentration of S. The optical absorption of visible light is attainable with sulfur concentrations less than x=0.25. We have verified that the band alignment in these alloys is favorable for photocatalytic applications: in particular, the conduction band exhibits only small shifts, while the majority of the band-gap change is due to an upward shift of the valence band.
Wavelength tuning predictions and experiments for type II antimonide lasers
Authors: Dente G. C. , Tilton M. L. , Ongstad A. P. , Kaspi R.
Published: January 2008

After a review of pseudopotential models for superlattices, we use the superlattice empirical pseudopotential method to predict the wavelength tuning of type II antimonide lasers. We then compare the predictions with a large set of experimental data on a series of optically pumped lasers operating from 2.2 to 9.2 μm.
Amorphization dynamics of Ge2Sb2Te5 films upon nano- and femtosecond laser pulse irradiation
Authors: Siegel J. , Gawelda W. , Puerto D. , Dorronsoro C. , Solis J. , Afonso C. N. , de Sande J. C. G. , Bez R. , Pirovano A. , Wiemer C.
Published: January 2008

Phase transformations of crystalline Ge2Sb2Te5 films upon pulsed laser irradiation have been studied using in situ reflectivity measurements with temporal resolution. Two different configurations allowed point probing with nanosecond temporal resolution and imaging with subpicosecond temporal and micrometer spatial resolution. The role of the pulse duration and laser fluence on the dynamics of the phase change and the degree of amorphization is discussed. Several advantageous features of femtosecond compared to nanosecond laser-induced amorphization are identified. Moreover, a high-resolution study of the amorphization dynamics reveals the onset of amorphization at moderate fluences to occur within ∼100 ps after arrival of the laser pulse. At high fluences, amorphization occurs after ∼430 ps and the molten phase is characterized by an anomalously low reflectivity value, indicative of a state of extreme supercooling.
High temperature surface imaging using atomic force microscopy
Authors: Broekmaat Joska , Brinkman Alexander , Blank Dave H. A. , Rijnders Guus
Published: January 2008

Atomic force microscopy (AFM) is one of the most important tools in nanotechnology and surface science. Because of recent developments, nowadays, it is also used to study dynamic processes, such as thin film growth and surface reaction mechanisms. These processes often take place at high temperature and there is a clear need to extend the current operating temperature range of AFM. This letter describes a heating stage and a modified AFM that extends the maximum operating temperature to 750°C. Atomic step resolution is obtained up to 500°C in ambient and even up to 750°C in vacuum.
Large magnetocaloric effect and enhanced magnetic refrigeration in ternary Gd-based bulk metallic glasses
Authors: Du J. , Zheng Q. , Li Y. B. , Zhang Q. , Li D. , Zhang Z. D.
Published: January 2008

The magnetocaloric effect and refrigeration capacity (RC) of Gd55Co20Al25 and Gd55Ni25Al20 bulk metallic glasses (BMGs) have been investigated. Large magnetic entropy changes ΔSM of 11.2 and 10.8 J kg−1 K−1 and large RC values of 846 and 920 J kg−1 are obtained for Gd55Co20Al25 and Gd55Ni25Al20, respectively, at a field change of 7 T. The RC value (640 J kg−1 at 5 T or 920 J kg−1 at 7 T) of Gd55Ni25Al20 BMG is larger than that reported for all magnetocaloric materials, including crystalline and amorphous materials measured under the same conditions. The large RC value is due to the broad ΔSM peak (more than 100 K), which is caused by the disordered structure of an amorphous material. The large ΔSM and RC values make these Gd-based ternary BMGs attractive candidates for magnetic refrigeration applications.
Phase control of iridium and iridium oxide thin films in atomic layer deposition
Authors: Kim Sung-Wook , Kwon Se-Hun , Kwak Dong-Kee , Kang Sang-Won
Published: January 2008

The atomic layer deposition of iridium (Ir) and iridium oxide (IrO2) films was investigated using an alternating supply of (ethylcyclopentadienyl)(1,5-cyclooctadiene) iridium and oxygen gas at temperatures between 230 and 290 °C. The phase transition between Ir and IrO2 occurred at the critical oxygen partial pressure during the oxygen injection pulse. The oxygen partial pressure was controlled by the O2/(Ar+O2) ratio or deposition pressures. The resistivity of the deposited Ir and IrO2 films was about 9 and 120 μΩ cm, respectively. In addition, the critical oxygen partial pressure for the phase transition between Ir and IrO2 was increased with increasing the deposition temperature. Thus, the phase of the deposited film, either Ir or IrO2, was controlled by the oxygen partial pressure and the deposition temperature. However, the formation of a thin Ir layer was detected between the IrO2 and SiO2 substrate. To remove this interfacial layer, the oxygen partial pressure is increased to a severe condition. And the impurity contents were below the detection limit of Auger electron spectroscopy in both Ir and IrO2 films.
Oblique shock waves incident on an interface between two materials for general equations of state
Authors: Loomis E. , Swift D.
Published: January 2008

Numerical schemes have been devised to solve the problem of an oblique shock scattering off the interface between two solid materials. The problem of a steady three-shock structure is first solved analytically using equations of state (EOS) where the shock speed and particle speed are related through a linear function. The formulation is then generalized to accept general EOS, which requires the incorporation of a more general algorithm to explore possible shock configurations based on the mechanical and thermodynamic parameters in the EOS. The correct configuration is found from the equality of pressure behind the reflected and transmitted waves as well as the equality of boundary deflection due to flow in the upper and lower halves of the three-shock structure. For the case of a reflected rarefaction in material described by general EOS, numerical integration over the release is used for accuracy where the rarefaction has a finite thickness as opposed to a discontinuous “expansion” shock. The results of these models reveal limits to the solution regimes depending only on incident shock angle, material properties (EOS), and the sense in which the incident shock is propagating (i.e., high to low or low to high impedance across the interface). Numerical simulations were run to validate the analytical models, which solved the conservation equations in a two-dimensional Eulerian sense using an operator-split finite difference method.
Effects of LaNiO3 bottom electrode on structural and dielectric properties of CaCu3Ti4O12 films fabricated by sol-gel method
Authors: Li Y. W. , Hu Z. G. , Sun J. L. , Meng X. J. , Chu J. H.
Published: January 2008

Ca Cu 3 Ti 4 O 12 (CCTO) thin films are prepared by a sol-gel method on LaNiO3-coated silicon and Pt∕TiO2∕SiO2∕Si substrate. Compared with the films on Pt, the CCTO on LaNiO3 exhibits a (400) orientation. Dielectric loss of CCTO on LaNiO3 is lower than 0.25 within 100Hz–10kHz, lower than the reported value of CCTO grown on Pt∕TiO2∕SiO2∕Si by pulse laser deposition. Possible reason is that LaNiO3 acts as seed layer for the growth of CCTO. The crystallinity of CCTO is improved and the dielectric properties are enhanced. Complex impedance spectrum of CCTO on LaNiO3 is discussed according to grain boundary barrier layer capacitance model.
Simultaneous lasing of interband and intersubband transitions in InAs∕AlSb quantum cascade laser structures
Authors: Ohtani K. , Ohnishi H. , Ohno H.
Published: January 2008

We show that both interband and intersubband transitions in n-InAs∕AlSb quantum cascade laser structures can have sufficient gain to enable simultaneous lasing at the two transitions. High electric fields generate holes, which are necessary for interband lasing in InAs. The doping concentration in the injection parts is shown to be critical for controlling the electric fields in the device, enabling the selection of lasing at the intersubband transition alone (high doping), at the interband transition alone (low doping), and simultaneous lasing at both transitions (intermediate doping).
Multilevel charging and discharging mechanisms of vertically stacked Ni1−xFex self-assembled nanoparticle arrays embedded in polyimide layers
Authors: Kim T. W. , Jung J. H. , Yoon C. S. , Kim Y.-H.
Published: January 2008

Capacitance-voltage curves for the Al/polyimide (PI)/multilayered Ni1−xFex nanoparticle array/PI/p-Si (100) devices at 300K showed that the flatband voltage shift of the metal-insulator-semiconductor capacitor was affected by the value of sweep voltage, indicative of the variations in the charged electron number in the multiple-stacked Ni1−xFex nanoparticle arrays in the floating gate. Current-voltage results showed that the electron charging and discharging in the Ni1−xFex nanoparticles were attributed to thermionic emission and Fowler-Nordheim tunneling, respectively. The multilevel charging and discharging mechanisms of vertically stacked Ni1−xFex self-assembled nanoparticle arrays embedded in PI layers are described on the basis of the experimental results.
Studies of oxide/ZnO near-interfacial defects by photoluminescence and deep level transient spectroscopy
Authors: Wang R. S. , Gu Q. L. , Ling C. C. , Ong H. C.
Published: January 2008

The evolution of near-interfacial defects from Al2O3∕ZnO and MgO∕ZnO upon thermal annealing has been studied by photoluminescence, deep level transient spectroscopy, and secondary ion mass spectroscopy. We find that all the results are strongly connected and that they point to the direction that Zn outdiffuses from ZnO to the oxide layer during annealing and creates deep level defects near the interfacial region. These defects reduce the band-edge emission and increase the deep level emission at 2.37eV. Our study shows that the oxide/ZnO interface is relatively fragile and caution must be taken for making metal-oxide-ZnO based transistors and light emitting diodes.
Neural Networks and Genetic Algorithms as Forecasting Tools: A Case Study on German Regions
Authors: Patuelli Roberto , Nijkamp Peter , Longhi Simonetta , Reggiani Aura
Published: January 2008

This paper develops and applies neural network (NN) models to forecast regional employment patterns in Germany. Computer-aided optimization tools that imitate natural biological evolution to find the solution that best fits the given case (namely, genetic algorithms, GAs) are also used to detect the best NN structure. GA techniques are compared with more ‘traditional’ techniques which require the supervision of experienced analysts. We test the performance of these techniques on a panel of 439 districts in West and East Germany. Since the West and East datasets have different time spans, the models are estimated separately for West and East Germany. The results show that the West and East NN models perform with different degrees of precision, mainly because of the different time spans of the two datasets. Automatic techniques for the choice of the NN architecture do not seem to outperform selection procedures based on the supervision of expert analysts.
The Applicability of Bayesian Belief Networks for Measuring User Preferences: Some Numerical Simulations
Authors: Orzechowski Maciej A , Arentze Theo A , Borgers Aloys W J , Timmermans Harry J P
Published: January 2008

Bayesian belief networks offer an alternative to conventional estimation methods in estimating user preference or utility functions. Because parameter estimates are updated sequentially, this approach seems very promising in user-centred design and data collection systems. The application of such networks however poses several questions, related to speed of learning, sample heterogeneity and discretionalisation of the parameter space. This paper reports the results of a series of numerical simulations which were conducted to gain more insights into these operational decisions.
Differential Gains from Business Link Support and Advice: A Treatment Effects Approach
Authors: Mole Kevin , Hart Mark , Roper Stephen , Saal David
Published: January 2008

The provision of advisory support to small firms is almost ubiquitous in OECD countries, although it is organised in different ways and is justified on slightly different grounds. In England publicly supported advisory services are provided through the Business Link (BL) network. Here, we consider two questions: what sort of companies receive advisory support from BL; and, what types of firms benefit most from that support? Our analysis is based on a telephone survey of 2000 firms, around half of which had received intensive assistance from BL between April and October 2003. Probit analysis suggests that the probability of receiving assistance was greater among younger businesses, those with larger numbers of directors in the firm, and those with more gender diversity among the firm's leadership team. Our business-growth models suggest that BL intensive assistance was having a positive effect on employment growth in 2003. BL had a positive but insignificant impact on sales growth over the period. Employment growth effects tend to be larger where firms have a management and organisational structure, which is more conducive to absorbing and making use of external advice. The analysis suggests that BL might increase its impact through targeting these larger, more export-orientated, businesses. Employment growth effects differ little, however, depending on either the ethnic or the gender diversity of the leadership team.
Third World Gap Year Projects: Youth Transitions and the Mediation of Risk
Authors: Ansell Nicola
Published: January 2008

In recent years in the UK there has been a great expansion in the number of young people travelling to Third World countries between school and university in order to participate as volunteers on structured gap year projects. Travel to such places is commonly perceived as ‘risky’, and takes young people outside the protective cocoon of UK health and safety legislation. One of the functions played by the providers of gap year projects is to mediate risk. On the basis of analysis of promotional literature, interviews with organisers of gap year projects, and focus groups of returned volunteers, in this paper I argue that the various strategies of risk mediation undertaken by gap year providers serve to reconcile modernising tendencies in UK society toward risk control and structure with postmodern inclinations towards individualisation and uncertainty.
Performativity and Affect in the Homeless City
Authors: Cloke Paul , May Jon , Johnsen Sarah
Published: January 2008

In this paper we discuss some of the ‘strange maps’ of city life performed by homeless people. Current models of urban homelessness emphasise both the strategies by which spaces of homelessness are disciplined and contained, and the tactics deployed by homeless people to negotiate this containment. Whilst recognising the value of such work, we argue that there is a need to move beyond this ‘rationalist’ reading of the homeless city to recognise the importance of emotion and affect in the lives of homeless people, and the traces such emotions leave on the homeless city. Drawing on in-depth interviews, we chart the journeys and pauses made by homeless people in the city of Bristol, UK. We show how the geography of homelessness thus described moves beyond current accounts of the homeless city rooted in an understanding of the strategic or tactical use of space and allows for a more nuanced reading of urban space able to take proper account of the less visible, more ‘transient’ reinscriptions of place that mark the presence of homeless people in the city.
Making two organelles from one: Woronin body biogenesis by peroxisomal protein sorting
Authors: Liu Fangfang , Ng Seng Kah , Lu Yanfen , Low Wilson , Lai Julian , Jedd Gregory
Published: January 2008

Woronin bodies (WBs) are dense-core organelles that are found exclusively in filamentous fungi and that seal the septal pore in response to wounding. These organelles consist of a membrane-bound protein matrix comprised of the HEX protein and, although they form from peroxisomes, their biogenesis is poorly understood. In Neurospora crassa, we identify Woronin sorting complex (WSC), a PMP22/MPV17-related membrane protein with dual functions in WB biogenesis. WSC localizes to large peroxisome membranes where it self-assembles into detergent-resistant oligomers that envelop HEX assemblies, producing asymmetrical nascent WBs. In a reaction requiring WSC, these structures are delivered to the cell cortex, which permits partitioning of the nascent WB and WB inheritance. Our findings suggest that WSC and HEX collaborate and control distinct aspects of WB biogenesis and that cortical association depends on WSC, which in turn depends on HEX. This dependency helps order events across the organellar membrane, permitting the peroxisome to produce a second organelle with a distinct composition and intracellular distribution.
Gonadotropin-releasing hormone regulates spine density via its regulatory role in hippocampal estrogen synthesis
Authors: Prange-Kiel Janine , Jarry Hubertus , Schoen Michael , Kohlmann Patrick , Lohse Christina , Zhou Lepu , Rune Gabriele M.
Published: January 2008

Spine density in the hippocampus changes during the estrus cycle and is dependent on the activity of local aromatase, the final enzyme in estrogen synthesis. In view of the abundant gonadotropin-releasing hormone receptor (GnRH-R) messenger RNA expression in the hippocampus and the direct effect of GnRH on estradiol (E2) synthesis in gonadal cells, we asked whether GnRH serves as a regulator of hippocampal E2 synthesis. In hippocampal cultures, E2 synthesis, spine synapse density, and immunoreactivity of spinophilin, a reliable spine marker, are consistently up-regulated in a dose-dependent manner at low doses of GnRH but decrease at higher doses. GnRH is ineffective in the presence of GnRH antagonists or aromatase inhibitors. Conversely, GnRH-R expression increases after inhibition of hippocampal aromatase. As we found estrus cyclicity of spine density in the hippocampus but not in the neocortex and GnRH-R expression to be fivefold higher in the hippocampus compared with the neocortex, our data strongly suggest that estrus cycle–dependent synaptogenesis in the female hippocampus results from cyclic release of GnRH.
Mapping of R-SNARE function at distinct intracellular GLUT4 trafficking steps in adipocytes
Authors: Williams Dumaine , Pessin Jeffrey E.
Published: January 2008

The functional trafficking steps used by soluble NSF attachment protein receptor (SNARE) proteins have been difficult to establish because of substantial overlap in subcellular localization and because in vitro SNARE-dependent binding and fusion reactions can be promiscuous. Therefore, to functionally identify the site of action of the vesicle-associated membrane protein (VAMP) family of R-SNAREs, we have taken advantage of the temporal requirements of adipocyte biosynthetic sorting of a dual-tagged GLUT4 reporter (myc-GLUT4-GFP) coupled with small interfering RNA gene silencing. Using this approach, we confirm the requirement of VAMP2 and VAMP7 for insulin and osmotic shock trafficking from the vesicle storage sites, respectively, and fusion with the plasma membrane. Moreover, we identify a requirement for VAMP4 for the initial biosynthetic entry of GLUT4 from the Golgi apparatus into the insulin-responsive vesicle compartment, VAMP8, for plasma membrane endocytosis and VAMP2 for sorting to the specialized insulin-responsive compartment after plasma membrane endocytosis.
Agonist-dependent Single Channel Current and Gating in α4β2δ and α1β2γ2S GABAA Receptors
Authors: Keramidas Angelo , Harrison Neil L.
Published: January 2008

The family of γ-aminobutyric acid type A receptors (GABAARs) mediates two types of inhibition in the mammalian brain. Phasic inhibition is mediated by synaptic GABAARs that are mainly comprised of α1, β2, and γ2 subunits, whereas tonic inhibition is mediated by extrasynaptic GABAARs comprised of α4/6, β2, and δ subunits. We investigated the activation properties of recombinant α4β2δ and α1β2γ2S GABAARs in response to GABA and 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3(2H)-one (THIP) using electrophysiological recordings from outside-out membrane patches. Rapid agonist application experiments indicated that THIP produced faster opening rates at α4β2δ GABAARs (β ∼1600 s−1) than at α1β2γ2S GABAARs (β ∼ 460 s−1), whereas GABA activated α1β2γ2S GABAARs more rapidly (β ∼1800 s−1) than α4β2δ GABAARs (β < 440 s−1). Single channel recordings of α1β2γ2S and α4β2δ GABAARs showed that both channels open to a main conductance state of ∼25 pS at −70 mV when activated by GABA and low concentrations of THIP, whereas saturating concentrations of THIP elicited ∼36 pS openings at both channels. Saturating concentrations of GABA elicited brief (<10 ms) openings with low intraburst open probability (PO ∼ 0.3) at α4β2δ GABAARs and at least two “modes” of single channel bursting activity, lasting ∼100 ms at α1β2γ2S GABAARs. The most prevalent bursting mode had a PO of ∼0.7 and was described by a reaction scheme with three open and three shut states, whereas the “high” PO mode (∼0.9) was characterized by two shut and three open states. Single channel activity elicited by THIP in α4β2δ and α1β2γ2S GABAARs occurred as a single population of bursts (PO ∼0.4–0.5) of moderate duration (∼33 ms) that could be described by schemes containing two shut and two open states for both GABAARs. Our data identify kinetic properties that are receptor-subtype specific and others that are agonist specific, including unitary conductance.
Some basic information on information-based complexity theory
Authors: Parlett Beresford N.
Published: January 2008

Numerical analysts might be expected to pay close attention to a branch of complexity theory called information-based complexity theory (IBCT), which produces an abundance of impressive results about the quest for approximate solutions to mathematical problems. Why then do most numerical analysts turn a cold shoulder to IBCT? Close analysis of two representative papers reveals a mixture of nice new observations, error bounds repackaged in new language, misdirected examples, and misleading theorems. Some elements in the framework of IBCT, erected to support a rigorous yet flexible theory, make it difficult to judge whether a model is off-target or reasonably realistic. For instance, a sharp distinction is made between information and algorithms restricted to this information. Yet the information itself usually comes from an algorithm, so the distinction clouds the issues and can lead to true but misleading inferences. Another troublesome aspect of IBCT is a free parameter F, the class of admissible problem instances. By overlooking F’s membership fee, the theory sometimes distorts the economics of problem solving in a way reminiscent of agricultural subsidies. The current theory’s surprising results pertain only to unnatural situations, and its genuinely new insights might serve us better if expressed in the conventional modes of error analysis and approximation theory.
Lifting of cohomology and unobstructedness of certain holomorphic maps
Authors: Ran Ziv
Published: January 2008

Let f be a holomorphic mapping between compact complex manifolds. We give a criterion for f to have unobstructed deformations, i.e. for the local moduli space of f to be smooth: this says, roughly speaking, that the group of infinitesimal deformations of f, when viewed as a functor, itself satisfies a natural lifting property with respect to infinitesimal deformations. This lifting property is satisfied e.g. whenever the group in question admits a ’topological’ or Hodge-theoretic interpretation, and we give a number of examples, mainly involving Calabi-Yau manifolds, where that is the case.
Some nonanalytic-hypoelliptic sums of squares of vector fields
Authors: Christ Michael
Published: January 2008

Certain second-order partial differential operators, which are expressed as sums of squares of real-analytic vector fields in

R

3

{\mathbb {R}^3}

and which are well known to be

C
∞

{C^\infty }

hypoelliptic, fail to be analytic hypoelliptic.
The Green function of Teichmüller spaces with applications
Authors: Krushkal Samuel L.
Published: January 2008

We describe briefly a new approach to some problems related to Teichmüller spaces, invariant metrics, and extremal quasiconformal maps. This approach is based on the properties of plurisubharmonic functions, especially of the plurisubharmonic Green function. The main theorem gives an explicit representation of the Green function for Teichmüller spaces by the Kobayashi-Teichmüller metric of these spaces. This leads to various applications. In particular, this gives a new characterization of extremal quasiconformal maps.
Generalizing the hyperbolic collar lemma
Authors: Basmajian Ara
Published: January 2008

We discuss two generalizations of the collar lemma. The first is the stable neighborhood theorem which says that a (not necessarily simple) closed geodesic in a hyperbolic surface has a "stable neighborhood" whose width only depends on the length of the geodesic. As an application, we show that there is a lower bound for the length of a closed geodesic having crossing number k on a hyperbolic surface. This lower bound tends to infinity with k. Our second generalization is to totally geodesic hypersurfaces of hyperbolic manifolds. Namely, we construct a tubular neighborhood function and show that an embedded closed totally geodesic hypersurface in a hyperbolic manifold has a tubular neighborhood whose width only depends on the area of the hypersurface (and hence not on the geometry of the ambient manifold). The implications of this result for volumes of hyperbolic manifolds is discussed. We also derive a (hyperbolic) quantitative version of the Klein-Maskit combination theorem (in all dimensions) for free products of fuchsian groups. Using this last theorem, we construct examples to illustrate the qualitative sharpness of the tubular neighborhood function.
A classification of the stable type of 𝐵𝐺
Authors: Martino John , Priddy Stewart
Published: January 2008

We give a classification of the p-local stable homotopy type of BG, where G is a finite group, in purely algebraic terms. BG is determined by conjugacy classes of homomorphisms from p-groups into G. This classification greatly simplifies if G has a normal Sylow p-subgroup; the stable homotopy types then depends only on the Weyl group of the Sylow p-subgroup. If G is cyclic

mod

p

{\bmod \;p}

then BG determines G up to isomorphism. The last class of groups is important because in an appropriate Grothendieck group BG can be written as a unique linear combination of BH’s, where H is cyclic

mod

p

{\bmod \;p}

.
Smooth static solutions of the Einstein-Yang/Mills equations
Authors: Smoller J. , Wasserman A. , Yau S. T. , McLeod B.
Published: January 2008

We consider the Einstein/Yang-Mills equations in 3 + 1 space time dimensions with SU(2) gauge group and prove rigorously the existence of a globally defined smooth static solution. We show that the associated Einstein metric is asymptotically flat and the total mass is finite. Thus, for non-abelian gauge fields the Yang/Mills repulsive force can balance the gravitational attractive force and prevent the formation of singularities in spacetime.
On the Burnside problem on periodic groups
Authors: Ivanov Sergei V.
Published: January 2008

It is proved that the free m-generated Burnside groups

B

(
m
,
n
)

\mathbb {B}(m,n)

of exponent n are infinite provided that

m
>
1

m > 1

,

n
≥

2

48

n \geq {2^{48}}

.
Additive functions on shifted primes
Authors: Elliott P. D. T. A.
Published: January 2008

Best possible bounds are obtained for the concentration function of an additive arithmetic function on sequences of shifted primes.
Voiculescu theorem, Sobolev lemma, and extensions of smooth algebras
Authors: Wang Xiaolu
Published: January 2008

We present the analytic foundation of a unified B-D-F extension functor

Ext
τ

{\operatorname {Ext} _\tau }

on the category of noncommutative smooth algebras, for any Fréchet operator ideal

K

τ

{\mathcal {K}_\tau }

. Combining the techniques devised by Arveson and Voiculescu, we generalize Voiculescu’s theorem to smooth algebras and Fréchet operator ideals. A key notion involved is

τ
\tau

-smoothness, which is verified for the algebras of smooth functions, via a noncommutative Sobolev lemma. The groups

Ext
τ

{\operatorname {Ext} _\tau }

are computed for many examples.
A shooting approach to the Lorenz equations
Authors: Hastings S. P. , Troy W. C.
Published: January 2008

We announce and outline a proof of the existence of a homoclinic orbit of the Lorenz equations. In addition, we develop a shooting technique and two key conditions, which lead to the existence of a one-to-one correspondence between a set of solutions and the set of all infinite sequences of 1’s and 3’s.
Linkless embeddings of graphs in 3-space
Authors: Robertson Neil , Seymour P. D. , Thomas Robin
Published: January 2008

We announce results about flat (linkless) embeddings of graphs in 3-space. A piecewise-linear embedding of a graph in 3-space is called flat if every circuit of the graph bounds a disk disjoint from the rest of the graph. We have shown: (i) An embedding is flat if and only if the fundamental group of the complement in 3-space of the embedding of every subgraph is free. (ii) If two flat embeddings of the same graph are not ambient isotopic, then they differ on a subdivision of

K
5

{K_5}

or

K

3
,
3

{K_{3,3}}

. (iii) Any flat embedding of a graph can be transformed to any other flat embedding of the same graph by "3-switches", an analog of 2-switches from the theory of planar embeddings. In particular, any two flat embeddings of a 4-connected graph are either ambient isotopic, or one is ambient isotopic to a mirror image of the other. (iv) A graph has a flat embedding if and only if it has no minor isomorphic to one of seven specified graphs. These are the graphs that can be obtained from

K
6

{K_6}

by means of

Y
Δ

Y \Delta

- and

Δ
Y

\Delta Y

-exchanges.
Representations and 𝐾-theory of discrete groups
Authors: Adem Alejandro
Published: January 2008

Let

Γ
\Gamma

be a discrete group of finite virtual cohomological dimension with certain finiteness conditions of the type satisfied by arithmetic groups. We define a representation ring for

Γ
\Gamma

, determined on its elements of finite order, which is of finite type. Then we determine the contribution of this ring to the topological K-theory

K

∗

(
B
Γ
)

K^{\ast }(B\Gamma )

, obtaining an exact formula for the difference in terms of the cohomology of the centralizers of elements of finite order in

Γ
\Gamma

.
Singularities of the Radon transform
Authors: Ramm A. G. , Zaslavsky A. I.
Published: January 2008

Singularities of the Radon transform of a piecewise smooth function

f
(
x
)

f(x)

,

x
∈

R
n

x \in {R^n}

,

n
≥
2

n \geq 2

, are calculated. If the singularities of the Radon transform are known, then the equations of the surfaces of discontinuity of

f
(
x
)

f(x)

are calculated by applying the Legendre transform to the functions, which appear in the equations of the discontinuity surfaces of the Radon transform of

f
(
x
)

f(x)

; examples are given. Numerical aspects of the problem of finding discontinuities of

f
(
x
)

f(x)

, given the discontinuities of its Radon transform, are discussed.
Best uniform rational approximation of 𝑥^{𝛼} on [0,1]
Authors: Stahl Herbert
Published: January 2008

A strong error estimate for the uniform rational approximation of

x

α

{x^{\alpha }}

on [0, 1] is given, and its proof is sketched. Let

E

n
n

(

x
α

,
[
0
,
1
]
)

{E_{nn}}({x^\alpha },[0,1])

denote the minimal approximation error in the uniform norm. Then it is shown that
\[
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="limit Underscript x right-arrow normal infinity Endscripts e Superscript 2 pi StartRoot alpha n EndRoot Baseline upper E Subscript n n Baseline left-parenthesis x Superscript alpha Baseline comma left-bracket 0 comma 1 right-bracket right-parenthesis equals 4 Superscript 1 plus alpha Baseline StartAbsoluteValue sine pi alpha EndAbsoluteValue">

lim

x
→
∞

e

2
π

α
n

E

n
n

(

x
α

,
[
0
,
1
]
)
=

4

1
+
α

|

sin
⁡
π
α

|

\lim \limits _{x \to \infty } {e^{2\pi \sqrt {\alpha n} }}{E_{nn}}({x^\alpha },[0,1]) = {4^{1 + \alpha }}|\sin \pi \alpha |

\]
holds true for each

α
>
0

{\alpha > 0}

.
Zariski geometries
Authors: Hrushovski Ehud , Zilber Boris
Published: January 2008

We characterize the Zariski topologies over an algebraically closed field in terms of general dimension-theoretic properties. Some applications are given to complex manifold and to strongly minimal sets.
Topology of homology manifolds
Authors: Bryant J. , Ferry S. , Mio W. , Weinberger S.
Published: January 2008

We construct examples of nonresolvable generalized n-manifolds,

n
≥
6

{n \geq 6}

, with arbitrary resolution obstruction, homotopy equivalent to any simply connected, closed n-manifold. We further investigate the structure of generalized manifolds and present a program for understanding their topology.
Wavelet transforms versus Fourier transforms
Authors: Strang Gilbert
Published: January 2008

This note is a very basic introduction to wavelets. It starts with an orthogonal basis of piecewise constant functions, constructed by dilation and translation. The "wavelet transform" maps each f(x) to its coefficients with respect to this basis. The mathematics is simple and the transform is fast (faster than the Fast Fourier Transform, which we briefly explain), but approximation by piecewise constants is poor. To improve this first wavelet, we are led to dilation equations and their unusual solutions. Higher-order wavelets are constructed, and it is surprisingly quick to compute with them — always indirectly and recursively. We comment informally on the contest between these transforms in signal processing, especially for video and image compression (including high-definition television). So far the Fourier Transform — or its 8 by 8 windowed version, the Discrete Cosine Transform — is often chosen. But wavelets are already competitive, and they are ahead for fingerprints. We present a sample of this developing theory.
Average case complexity of linear multivariate problems
Authors: Woźniakowski H.
Published: January 2008

We study the average case complexity of a linear multivariate problem (LMP) defined on functions of d variables. We consider two classes of information. The first

Λ

s
t
d

{\Lambda ^{std}}

consists of function values and the second

Λ

a
l
l

{\Lambda ^{all}}

of all continuous linear functionals. Tractability of LMP means that the average case complexity is

O
(

(
1

/

ε

)
p

)

O({(1/\varepsilon )^p})

with p independent of d. We prove that tractability of an LMP in

Λ

s
t
d

{\Lambda ^{std}}

is equivalent to tractability in

Λ

a
l
l

{\Lambda ^{all}}

, although the proof is not constructive. We provide a simple condition to check tractability in

Λ

a
l
l

{\Lambda ^{all}}

. We also address the optimal design problem for an LMP by using a relation to the worst case setting. We find the order of the average case complexity and optimal sample points for multivariate function approximation. The theoretical results are illustrated for the folded Wiener sheet measure.
Adding handles to the helicoid
Authors: Hoffman David , Wei Fu Sheng , Karcher Hermann
Published: January 2008

There exist two new embedded minimal surfaces, asymptotic to the helicoid. One is periodic, with quotient (by orientation-preserving translations) of genus one. The other is nonperiodic of genus one.
Absence of Cantor spectrum for a class of Schrödinger operators
Authors: Riedel Norbert
Published: January 2008

It is shown that the complete localization of eigenvectors for the almost Mathieu operator entails the absence of Cantor spectrum for this operator.
Topological invariance of intersection lattices of arrangements in 𝐂𝐏²
Authors: Jiang Tan , Yau Stephen S.-T.
Published: January 2008

Let

A

∗

=
{

l

1

,

l

2

,
.
.
.
,

l
n

}

{\mathcal {A}^{\ast }} = \{ {l_{1}},{l_{2}},...,{l_n}\}

be a line arrangement in

C

P

2

\mathbb {C}{\mathbb {P}^2}

, i.e., a collection of distinct lines in

C

P

2

\mathbb {C}{\mathbb {P}^2}

. Let

L
(

A

∗

)

L({\mathcal {A}^{\ast }})

be the set of all intersections of elements of

A

∗

{A^{\ast }}

partially ordered by

X
≤
Y
⇔
Y
⊆
X

X \leq Y \Leftrightarrow Y \subseteq X

. Let

M
(

A

∗

)

M({\mathcal {A}^{\ast }})

be

C

P

2

−
∪

A

∗

\mathbb {C}{\mathbb {P}^2} - \cup {\mathcal {A}^{\ast }}

where

∪

A

∗

=
∪
{

l
i

:
1
≤
i
≤
n
}

\cup {\mathcal {A}^{\ast }} = \cup \{ {l_i}:1 \leq i \leq n\}

. The central problem of the theory of arrangement of lines in

C

P

2

\mathbb {C}{\mathbb {P}^2}

is the relationship between

M
(

A

∗

)

M({\mathcal {A}^{\ast }})

and

L
(

A

∗

)
.

L({\mathcal {A}^{\ast }}).
“Theoretical mathematics”: toward a cultural synthesis of mathematics and theoretical physics
Authors: Jaffe Arthur , Quinn Frank
Published: January 2008

Is speculative mathematics dangerous? Recent interactions between physics and mathematics pose the question with some force: traditional mathematical norms discourage speculation, but it is the fabric of theoretical physics. In practice there can be benefits, but there can also be unpleasant and destructive consequences. Serious caution is required, and the issue should be considered before, rather than after, obvious damage occurs. With the hazards carefully in mind, we propose a framework that should allow a healthy and positive role for speculation.