bluuebunny/crossref_metadata_2025 huggingface dataset:
An explicit solution to a system of implicit differential equations
Authors: Dacorogna Bernard , Marcellini Paolo , Paolini Emanuele
Published: December 2006

In this article we give an
explicit
solution to the vectorial differential inclusion where we have to find a map

u\:\text{:}\Omega \subset \mathbb{R}^{2}\rightarrow \mathbb{R}^{2}

with

u = 0

on

∂Ω

and

Du(x) \in \mathrm{O}(2),\:\text{a.e. }x \in \Omega .

Nous construisons une solution
explicite
d'une inclusion différentielle où on cherche une application

u\:\text{:}\Omega \subset \mathbb{R}^{2}\rightarrow \mathbb{R}^{2}

avec

u = 0

sur

∂Ω

et

Du(x) \in \mathrm{O}(2),\:\text{p.p. }x \in \Omega .
Finite Morse index solutions of exponential problems
Authors: Dancer E.N.
Published: December 2006

We prove that the problem

−\mathrm{\Delta }u = \mathrm{e}^{u}

has no negative finite Morse index solution on

\mathbb{R}^{3}

and give some applications to bounded domain problems.

Nous montrons que le problème

−\mathrm{\Delta }u = \mathrm{e}^{u}

ne possède pas de solution négative d'indice de Morse fini sur

\mathbb{R}^{3}

et présentons quelques applications à des problèmes sur des domaines bornés.
The economic burden of depression in Sweden from 1997 to 2005
Authors: Sobocki Patrik , Lekander Ingrid , Borgström Fredrik , Ström Oskar , Runeson Bo
Published: December 2006

Background

Depression is one of the most common causes of disability and is associated with substantial reductions in the individual's quality of life. The aim of this study was to estimate the economic burden of depression to Swedish society from 1997 to 2005.

Materials and Methods

The study was conducted in a cost-of-illness framework, measuring both the direct cost of providing health care to depressive patients, and the indirect costs as the value of production that is lost due to morbidity or mortality. The costs were estimated by a prevalence and top-down approach.

Results

The cost of depression increased from a total of €1.7 billion in 1997 to €3.5 billion in 2005, representing a doubling of the burden of depression to society. The main reason for the cost increase is found in the significant increase in indirect costs due to sick leave and early retirement during the past decade, whereas direct costs were relatively stable over time. In 2005, indirect costs were estimated at €3 billion (86% of total costs) and direct costs at €500 million (16%). Cost of drugs was estimated at €100 million (3% of total cost).

Conclusion

The cost of depression is substantial to society and the main cost driver is indirect costs due to sick leave and early retirement. The cost of depression has doubled during the past eight years making it a major public health concern for the individuals afflicted, carers and decision makers.
p53 regulates ERK activation in carboplatin induced apoptosis in cervical carcinoma: A novel target of p53 in apoptosis
Authors: Singh Sandeep , Upadhyay Ankur Kumar , Ajay Amrendra Kumar , Bhat Manoj Kumar
Published: December 2006

In general, the activation of extracellular recognition kinase (ERK) cascade is implicated in exerting tumorigenic effects. Conversely, recent studies suggest that ERK activation may also have role in DNA‐damage induced apoptosis [Wang, X., Martindale, J.L. and Holbrook, N.J. (2000) Requirement for ERK activation in cisplatin‐induced apoptosis. J. Biol. Chem. 275, 39435–39443; Schweyer S., Soruri A., Meschter O., Heintze A., Zschunke F., Miosge N., Thelen P., Schlott T., Radzun H.J. and Fayyazi, A. (2004) Cisplatin‐induced apoptosis in human malignant testicular germ cell lines depends on MEK/ERK activation. Br. J. Cancer 91, 589–598]. Here we observed an essential requirement of ERK activation in carboplatin (Carb) induced apoptosis in SiHa and CaSki cells. Under similar treatment conditions p53 was also involved in Carb induced apoptosis in these cells. Therefore, we investigated the relation between p53 and ERK in Carb induced apoptosis in these cells. Abrogation of p53 transactivation activity by pifithrinα or dominant‐negative mutant of p53 resulted in decrease in activation of ERK in Carb treated cells. The present study for the first time proposes that p53 may act as one of the upstream regulators of ERK activation for the induction of apoptosis in Carb treated cervical cancer cells.
Ulnar Subluxation of the Extensor Tendons in Elderly Osteoarthritic Females: A Neglected Diagnosis
Authors: LOVE G. J. , MACLEAN J. G. B.
Published: January 2007

Ulnar subluxation of the extensor digitorum communis tendons at the metacarpophalangeal joints occurs rarely in the absence of rheumatoid disease or a history of trauma. Three elderly women presented with chronic ulnar subluxation of the extensor tendons of spontaneous onset. They did not have rheumatoid arthritis and had suffered no acute injury. Seven extensor tendon relocations were performed. The treatment options for this condition are discussed. Recognition of this condition is important if permanent loss of function and disability is to be avoided.
Trigger Wrist
Authors: GIANNIKAS D. , KARABASI A. , DIMAKOPOULOS P.
Published: December 2006

Trigger wrist is a relatively rare phenomenon. The pathological entities to which the term trigger wrist is applied are not well defined in the literature. We present three cases of trigger wrist as a result of flexor tendon pathology, review the literature and discuss the use of the term “trigger wrist”.
An Unusual Dorsal Fracture–Dislocation of the Proximal Interphalangeal Joint
Authors: OTANI K. , FUKUDA K. , HAMANISHI C.
Published: December 2006

A case of dorsal fracture–dislocation of the proximal interphalangeal joint in which the volar plate had been pulled from its distal attachment without bony or cartilaginous attachments and the lip of the volar plate had also been detached separately and was obstructing full flexion of the joint is presented. A tentative mechanism of causation of this unusual variant of a common injury is suggested.
The Racial Distribution of Privilege in a Thai National Park
Authors: Delcore Henry D.
Published: January 2007

Tai Lue and Lua people are struggling to maintain access to resources in a northern Thai national park. Contrasting outcomes for Tai Lue and Lua relations with the park can largely be explained by political, economic and discursive structures and the interests, attitudes and actions they promote. In particular, the racialisation of resource use constrains the ability of minority upland groups like the Lua to secure recognition and legitimacy for their resource use practices.
Census of the mountain gorilla Gorilla beringei beringei population in Bwindi Impenetrable National Park, Uganda
Authors: McNeilage Alastair , Robbins Martha M. , Gray Maryke , Olupot William , Babaasa Dennis , Bitariho Robert , Kasangaki Aventino , Rainer Helga , Asuma Steven , Mugiri Ghad , Baker Julia
Published: January 2007

Mountain gorillas Gorilla beringei beringei are Critically Endangered, with just two small populations: in Bwindi Impenetrable National Park in south-western Uganda and the nearby Virunga Volcanoes on the borders with Rwanda and Uganda. A survey of the Bwindi population was carried out in 2002 and results were compared with the previous census in 1997. Our estimate of total population size increased over that period by c. 7% to 320 individuals and the structure and distribution of the population were largely unchanged. Signs of human disturbance were more common in 2002 than 1997, and gorillas tended to be found in areas of relative low disturbance. This suggested that disturbance could be a constraint on population growth and distribution but demographic stochasticity may also be responsible for the observed level of population change over a short time period. Other potential limiting factors, including habitat availability and disease, are discussed. While conservation activities in Bwindi have probably contributed to the stability of the population, strengthening of law enforcement and continued vigilance are needed to ensure the population's long-term growth and survival.
An application of Bayesian analysis and Markov chain Monte Carlo methods to the estimation of a regional trend in annual maxima
Authors: Renard B. , Garreta V. , Lang M.
Published: December 2006

Bayesian analysis is becoming increasingly popular in a number of fields, including hydrology. It appears to be a convenient framework for deriving complex models in agreement with both physical reality and statistical requirements. The aim of this paper is to present an application to the regional frequency analysis of extremes in a nonstationary context. A nonstationary regional model is thus proposed, together with the related hypotheses. The Bayesian inference of this model is then described. Markov chain Monte Carlo (MCMC) methods are needed for this purpose because of the dimensionality of the model and are described in this paper. The usefulness of such a model is then illustrated on a hydrological case study concerning annual maximum discharges of several sites. The advantage of regional analysis compared to at‐site estimation is thus highlighted. Moreover, the Bayesian framework allows for a direct and comprehensive inference based on the posterior distribution and is able to take into account modeling uncertainties, which is particularly useful when the stationarity of a series can neither be ensured nor be totally rejected.
Phase lag between Intertropical Convergence Zone migration and subtropical monsoon onset over the northwestern Indian Ocean during Marine Isotopic Substage 6.5 (MIS 6.5)
Authors: Malaizé B. , Joly C. , Vénec‐Peyré M.‐T. , Bassinot F. , Caillon N. , Charlier K.
Published: December 2006

High‐resolution faunal and isotopic analyses of foraminifera were performed on core MD96‐2073 (10°94′N, 52°62′E, 3142 m depth), located close to Socotra Island in the upwelling area of the Somali Basin (NW Indian Ocean). This work focuses on Marine Isotopic Stage 6.5 in order to reconstruct paleo‐upwelling changes and their links with the Arabian Sea summer monsoon and the migration of the Intertropical Convergence Zone (ITCZ). Correspondence and cluster analyses of planktonic foraminiferal abundances, partly controlled by temperature and water mass productivity, together with an upwelling intensification index, show the occurrence of a strong upwelling between 176 and 165 ka. This upwelling intensification responds to a northward migration of the ITCZ. An isotopic depletion in the planktonic foraminifera δ18O records occurring between 180 and 167 ka is interpreted as proof of a large salinity decrease in the surface waters, probably linked to a strong input of fresh rainfall waters induced by an intense monsoon activity. The lag between the onset of upwelling intensification and the strong monsoonal impact over the same area suggests a decoupling between both phenomena. The migration of the ITCZ is influenced by obliquity and precessional forcing, while the Arabian Sea summer monsoon precipitation depends only on precessional forcing.
Scaled spatial variability of soil moisture fields
Authors: Choi Minha , Jacobs Jennifer M. , Cosh Michael H.
Published: January 2007

This study identifies soil moisture spatial variability patterns using measurements across different extents (i.e., field, watershed, and basin) and depths (i.e., from surface to root zone profile) from 18 different soil moisture field experiments. The spatial variability patterns are well represented by negative exponential functions between the mean and the coefficient of variation of soil moisture. Principal component analysis demonstrates that rainfall and topography explain surface soil moisture variability changes as soils dry, while soil parameters control the maximum relative variability. Soil moisture's relative variability typically decreases as sampling extent increases, supporting the power law decay function proposed by Rodriquez‐Iturbe et al. (1995). The finding that soil moisture relative variability increases as soil depth increases is consistent with an earlier study (Choi and Jacobs, 2006). These common soil moisture variability patterns can provide a feasible methodology to validate land surface models and to estimate variability across extents from mean soil moisture values.
Continuous soil radon monitoring during the July 2006 Etna eruption
Authors: Neri M. , Behncke B. , Burton M. , Galli G. , Giammanco S. , Pecora E. , Privitera E. , Reitano D.
Published: December 2006

Continuous soil radon monitoring was carried out near the Southeast Crater (SEC) of Mt. Etna during the 10‐day July 2006 Strombolian‐effusive eruption. This signal was compared with simultaneously acquired volcanic tremor and thermal radiance data. The onset of explosive activity and a lava fountaining episode were preceded by some hours with increases in radon soil emission by 4–5 orders of magnitude, which we interpret as precursors. Minor changes in eruptive behavior did not produce significant variations in the monitored parameters. The remarkably high radon concentrations we observed are unprecedented in the literature. We interpret peaks in radon activity as due primarily to microfracturing of uranium‐bearing rock. These observations suggest that radon measurements in the summit area of Etna are strongly controlled by the state of stress within the volcano and demonstrate the usefulness of radon data acquisition before and during eruptions.
Evidence for a high‐energy tail associated with foreshock field‐aligned beams
Authors: Meziane K. , Wilber M. , Hamza A. M. , Mazelle C. , Parks G. K. , Rème H. , Lucek E. A.
Published: January 2007

The reduced particle distributions of field‐aligned beams observed upstream of the bow shock are examined in detail using Cluster spacecraft. We find that the reduced parallel and perpendicular distribution forms can be strongly geometry‐dependent. Above a certain critical value of the angle between the local shock normal and the direction of the magnetic field, θBn, the reduced distributions are remarkably well fit by Maxwellians. We have not found any significant changes to the spread in energies for beams at higher values of θBn. When the angle θBn decreases, leading to smaller beam velocities, a high‐energy tail in the distribution appears. When the tail is present, the bulk of the distribution remains Maxwellian. The development of the high‐energy tail is well correlated with decreases in the beam speed (or equivalently θBn). Moreover, detailed examination of the angular distributions indicates that particles in the tails of the distributions propagate at significant pitch angles with respect to the magnetic field (are not field‐aligned, as are those within the bulk of the distribution) and that these pitch angles are energy‐dependent. These new observations do not fit any production mechanism expected at the shock or result from known wave‐particle interactions upstream of or within the shock layer.
Propagator for finite range potentials
Authors: Cacciari Ilaria , Moretti Paolo
Published: December 2006

The Schrödinger equation in integral form is applied to the one-dimensional scattering problem in the case of a general finite range, nonsingular potential. A simple expression for the Laplace transform of the transmission propagator is obtained in terms of the associated Fredholm determinant, by means of matrix methods; the particular form of the kernel and the peculiar aspects of the transmission problem play an important role. The application to an array of delta potentials is shown.
In situ neutron diffraction study of grain-orientation-dependent phase transformation in 304L stainless steel at a cryogenic temperature
Authors: Tao Kaixiang , Wall James J. , Li Hongqi , Brown Donald W. , Vogel Sven C. , Choo Hahn
Published: December 2006

In situ time-of-flight neutron diffraction was performed to investigate the martensitic phase transformation during quasistatic uniaxial compression testing of 304L stainless steel at 300 and 203K. In situ neutron diffraction enabled the bulk measurement of intensity evolution for various hkl atomic planes during the austenite (fcc) to martensite (hcp and bcc) phase transformation. Based on the neutron diffraction patterns, the martensite phases were observed from the very beginning of the plastic deformation at 203K. However, at 300K, no newly formed martensite, except a small amount of preexisting hcp phase, was observed throughout the test. From the changes in the relative intensities of individual hkl atomic planes, the grain-orientation-dependent phase transformation was investigated. The preferred orientation of the newly formed martensite grains was also investigated for the sample deformed at 203K using neutron diffraction. The results reveal the orientation relationships between the austenite and the newly formed martensites. The fcc grain family diffracting with {200} plane normal parallel to the loading axis is favored for the fcc to bcc transformation and the bcc {200} plane normals are primarily aligned along the loading direction. For the fcc to hcp transformation, the fcc grains with {111} plane normals at an angle in between about 10° and 50° to the loading direction are favored.
Defects in Co-doped and (Co, Nb)-doped TiO2 ferromagnetic thin films
Authors: Fu L. F. , Browning N. D. , Zhang S. X. , Ogale S. B. , Kundaliya D. C. , Venkatesan T.
Published: December 2006

We have investigated the defect structure in pure Co-doped and (Co, Nb)-doped TiO2 (anatase) thin films grown by pulsed laser deposition on (001) single crystal LaAlO3. Although both films exhibit room temperature ferromagnetism, dilute Nb doping significantly improves the conductivity and microstructure of the TiO2 (anatase) thin film at the cost of a lower saturation magnetization. Z-contrast imaging and electron-energy-loss-spectroscopy study in the scanning transmission electron microscope show cluster-free microstructure in the (Co, Nb)-doped thin film although Co is enriched into the surface and forms a CoxTi1−x−yNbyO2−δ phase. In contrast, metallic Co, rutile TiO2, and cobalt oxide nanoparticles combined with some crystallographic shear defect structures are observed in the pure Co-doped thin film. The magnetic behavior in each film can be explained with the presence of these defect states or second phases.
Relativistic effective core potential calculations of Hg and eka-Hg (E112) interactions with gold: Spin-orbit density functional theory modeling of Hg–Aun and E112–Aun systems
Authors: Rykova E. A. , Zaitsevskii A. , Mosyagin N. S. , Isaev T. A. , Titov A. V.
Published: December 2006

Interactions of eka-Hg (E112) and Hg atoms with small gold clusters were studied in the frame of the relativistic effective core potential model using the density functional theory (DFT) approach incorporating spin-dependent (magnetic) interactions. The choice of the exchange-correlation functional was based on a comparison of the results of DFT and large-scale coupled cluster calculations for E112Au and HgAu at the scalar relativistic level. A close similarity between the E112Aun and HgAun equilibrium structures was observed. The E112 binding energies on Aun are typically smaller than those for Hg by ca. 25%–32% and the equilibrium E112-Au separations are always slightly larger than their Hg-Au counterparts.
Microstructure and texture of YNi2B2C thin films grown on Ir buffered MgO(001)
Authors: Subba Rao K. , Tamm R. , Cao G. H. , Oertel C.-G. , Skrotzki W. , Wimbush S. C. , Holzapfel B.
Published: December 2006

Superconducting films of YNi2B2C deposited on an Ir buffered MgO(001) substrate by pulsed laser deposition have been investigated by x-ray diffraction and transmission electron microscopy (TEM) techniques. X-ray texture results show that the Ir buffer layer grows cube on cube and that the texture of YNi2B2C consists of four c-axis components. Cross-sectional TEM shows that during high temperature deposition of YNi2B2C, Ir diffuses into the nanocrystalline film and leads to the formation of an Y0.915Ni4.12B hexagonal impurity phase instead of Y2O3 as interlayer. There are clear orientation relationships between the different phases: MgO(001)[100]∥Y0.915Ni4.12B(0001)[1¯21¯0]∥YNi2B2C(001)[100]∕(001)[110]. Y0.915Ni4.12B formation leading to deviations from stoichiometry of the YNi2B2C as well as Ni substitution by Ir may be responsible for the deterioration of the superconducting properties of the YNi2B2C film.
Simulation studies of ionic liquids: Orientational correlations and static dielectric properties
Authors: Schröder C. , Rudas T. , Steinhauser O.
Published: December 2006

The ionic liquids BMIM+I−, BMIM+BF4−, and BMIM+PF6− were simulated by means of the molecular dynamics method over a time period of more than 100ns. Besides the common structural analysis, e.g., radial distribution functions and three dimensional occupancy plots, a more sophisticated orientational analysis was performed. The angular correlation functions g00110(r) and g00101(r) are the first distance dependent coefficients of the pairwise orientational distribution function g(rij,Ω1,Ω2,Ω12). These functions help to interpret the three dimensional plot and reveal interesting insights into the local structure of the analyzed ionic liquids. Furthermore, the collective network of ionic liquids can be characterized by the Kirkwood factor Gκ(r) [J. Chem. Phys. 7, 911 (1939)]. The short-range behavior (r<10Å) of this factor may be suitable to predict the water miscibility of the ionic liquid. The long-range limit of Gk∞ is below 1 which demonstrates the strongly coupled nature of the ionic liquid networks. In addition, this factor relates the orientational structure and the dielectric properties of the ionic liquids. The static dielectric constant ϵ(ω=0) for the simulated system is 8.9–9.5. Since in ionic liquids the very same molecule contributes to the total dipole moment as well as carries a net charge, a small, but significant contribution of the cross term between the total dipole moment and the electric current to ϵ(ω=0) is observed.
Simple Hamiltonians which exhibit drastic failures by variational determination of the two-particle reduced density matrix with some well known N-representability conditions
Authors: Nakata Maho , Braams Bastiaan J. , Fukuda Mituhiro , Percus Jerome K. , Yamashita Makoto , Zhao Zhengji
Published: December 2006

Calculations on small molecular systems indicate that the variational approach employing the two-particle reduced density matrix (2-RDM) as the basic unknown and applying the P, Q, G, T1, and T2 representability conditions provides an accuracy that is competitive with the best standard ab initio methods of quantum chemistry. However, in this paper we consider a simple class of Hamiltonians for which an exact ground state wave function can be written as a single Slater determinant and yet the same 2-RDM approach gives a drastically nonrepresentable result. This shows the need for stronger representability conditions than the mentioned ones.
Carrier concentration induced band-gap shift in Al-doped Zn1−xMgxO thin films
Authors: Lu J. G. , Fujita S. , Kawaharamura T. , Nishinaka H. , Kamada Y. , Ohshima T.
Published: December 2006

Transparent conducting Al-doped Zn1−xMgxO thin films were grown on glass substrates by chemical vapor deposition. The resistivity could be lowered to 10−3Ωcm with optical transmittance above 85% in visible regions. The influence of carrier concentration on band-gap shift in Zn1−xMgxO alloys was systematically studied. The shift of energy gap could be fully explained by the Fermi-level band filling and band-gap renormalization effects. As the Mg content increased, the electron effective masses in Zn1−xMgxO (x=0–0.21) alloys increased from 0.30m0 to 0.49m0. The Al-doping efficiency was reduced with the increase in alloy composition.
Nanoscale voltage tunable tunnel rectifier by gold nanostructures embedded in SiO2
Authors: Ruffino F. , Grimaldi M. G. , Giannazzo F. , Roccaforte F. , Raineri V.
Published: December 2006

Conductive-atomic force microscopy is used to electrically characterize a nanometric metal-SiO2–Si (n+) system with Au nanocluster inclusions in SiO2. The system shows a marked rectifying behavior at room temperature with a threshold voltage function of the cluster size. This behavior is interpreted crossing physical considerations on metal-oxide-semiconductor structure and on double barrier tunnel junction device. The system fabricated and analyzed is proposed as a possible basic component for nanoelectronic circuits working at room temperature.
Photonic Doppler velocimetry of laser-ablated ultrathin metals
Authors: Valenzuela A. R. , Rodriguez G. , Clarke S. A. , Thomas K. A.
Published: January 2007

Obtaining velocity information from the interaction of a laser pulse on a metal layer provides insight into the rapid dynamics of material removal and plasma plume physics during ablation. A traditional approach involves using a velocity interferometer system for any reflector (VISAR) on a reflective metal surface. However, when the target is a thin metal layer, the cohesion of the surface is quickly lost resulting in a large spread of particle velocities that cannot be easily resolved by VISAR. This is due to material ejection“confusing” the VISAR measurement surface, effectively washing out the spatial fringe visibility in the VISAR interferometer. A new heterodyne-based optical velocimeter method is the photonic Doppler velocimeter (PDV). Because PDV tracks motion in a frequency encoded temporal electro-optical signal, velocity information is preserved and allows for multiple velocity components to be recorded simultaneously. The challenge lies in extracting PDV velocity information at short (nanosecond) laser ablation time scales with rapidly varying heterodyne beats by using electronic, optical, and analytical techniques to recover the velocity information from a fleeting signal. Here we show how we have been able to obtain velocity information on the nanosecond time scale and are able to compare it to hydrodynamic simulations. Also, we examine refinements to our PDV system by increasing the bandwidth, utilizing different probes, and sampling different analysis techniques.
Large atom number Bose-Einstein condensate of sodium
Authors: van der Stam K. M. R. , van Ooijen E. D. , Meppelink R. , Vogels J. M. , van der Straten P.
Published: January 2007

We describe the setup to create a large Bose-Einstein condensate containing more than 120×106 atoms. In the experiment a thermal beam is slowed by a Zeeman slower and captured in a dark-spot magneto-optical trap (MOT). A typical dark-spot MOT in our experiments contains 2.0×1010 atoms with a temperature of 320μK and a density of about 1.0×1011atoms∕cm3. The sample is spin polarized in a high magnetic field before the atoms are loaded in the magnetic trap. Spin polarizing in a high magnetic field results in an increase in the transfer efficiency by a factor of 2 compared to experiments without spin polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50s by evaporative cooling. To suppress the three-body losses at the end of the evaporation, the magnetic trap is decompressed in the axial direction.
Biologically inspired polymer microfibers with spatulate tips as repeatable fibrillar adhesives
Authors: Kim Seok , Sitti Metin
Published: December 2006

Being inspired by gecko foot hairs, microfibers with flat spatulate tips are proposed as repeatable adhesives. They are fabricated by molding a master template fabricated using deep reactive ion etching and the notching effect. Fabricated polyurethane fiber arrays with 4.5μm fiber and 9μm tip diameter demonstrated macroscale adhesion pressures up to 18N∕cm2 and overall work of adhesion up to 11J∕m2 on a 6mm diameter glass hemisphere for a preload pressure of 12N∕cm2. These results show around four times higher adhesion and five times higher overall work of adhesion as compared to the flat polyurethane surface.
Photocurrent gain mechanism in Schottky barrier photodiodes with negative average electric field
Authors: Rivera C. , Pau J. L. , Muñoz E.
Published: December 2006

A photocurrent gain mechanism which takes advantage of the piezoelectric fields present in devices based on polar heterostructures is proposed. Piezoelectrically induced electric fields can be designed to generate a negative average electric field (NAF) region under certain bias conditions. For carrier transport limited by the barrier formed by the NAF region, photoinduced screening will result in photocurrent gain. This mechanism allows one to explain the experimental results obtained in Schottky barrier photodiodes with (In,Ga)N∕GaN multiple quantum wells embedded in their active region. Responsivities higher than 1A∕W and low dark currents below 10nA∕mm2 at forward voltage were obtained.
Influence of stoichiometry on phase transition pressure of LiNbO3
Authors: Suchocki A. , Paszkowicz W. , Kamińska A. , Durygin A. , Saxena S. K. , Arizmendi L. , Bermudez V.
Published: December 2006

Results of Raman and x-ray diffraction studies under high pressures generated in diamond anvil cell of pure lithium niobate with different stoichiometries are reported. It is shown that the pressure at which the phase transition occurs depends on crystal stoichiometry and is strongly reduced as compared with those for LiNbO3 with congruent composition.
Low hysteresis pentacene thin-film transistors using SiO2/cross-linked poly(vinyl alcohol) gate dielectric
Authors: Park Dong-Wook , Lee Cheon An , Jung Keum-Dong , Park Byung-Gook , Shin Hyungcheol , Lee Jong Duk
Published: December 2006

Low hysteresis pentacene organic thin-film transistors (OTFTs) were fabricated using plasma-enhanced chemical vapor deposition SiO2/cross-linked poly(vinyl alcohol) gate dielectrics. The hysteresis was considerably reduced by optimizing the thickness of the SiO2 layer. The balancing of the electrons injected from the gate electrode into the gate dielectric and the trapped holes from the channel under the optimum condition is considered to be the mechanism by which the hysteresis is reduced. In addition, the optimized OTFTs with the hybrid gate dielectric show a high dielectric constant and reliable leakage characteristics due to the advantages afforded by each gate dielectric material. The device with W∕L=300∕5 shows a field-effect mobility of 0.12cm2∕Vs, a subthreshold slope of 0.4V/decade, and an on/off ratio of 2.3×106. The bias stress experiments conducted for the OTFTs confirmed the effect of the injected charges and hole traps on the threshold voltage shift.
Investigation of void nucleation and propagation during electromigration of flip-chip solder joints using x-ray microscopy
Authors: Chiu S. H. , Chen Chih
Published: December 2006

X-ray microscopy was employed to investigate void nucleation and propagation during electromigration in solder joints. The shape of the voids at various stages can be clearly observed. The voids became irregular when they propagated to deplete the contact opening. Growth velocity at the early stage was found to be 1.3μm∕h under 6.5×103A∕cm2 at 150°C, and it decreased to 0.3μm∕h at later stages. Formation of intermetallic compound (IMC) and compositional changes at the interface of solder/IMC on the chip side were attributed to the retarded growth rate at later stages.
Alloantigen-enhanced accumulation of CCR5+‘effector’ regulatory T cells in the gravid uterus
Authors: Kallikourdis Marinos , Andersen Kristian G. , Welch Katie A. , Betz Alexander G.
Published: December 2006

Regulatory T cells play an essential role in preventing fetal rejection by the maternal immune system. Here we show that, based on the expression of CCR5, regulatory T cells can be divided into a highly suppressive CCR5+and a far less suppressive CCR5−subpopulation, suggesting that the former represent the effector arm of regulatory T cells. Although regulatory T cells from CCR5−/−gene deletion mutants still suppress, they are less effective mediators of maternal–fetal tolerance. The accumulation of CCR5+regulatory T cells at this site appears to be enhanced by alloantigen. This finding is in stark contrast to the systemic expansion of regulatory T cells during pregnancy, which appears to be alloantigen-independent. The fact that CCR5+regulatory T cells preferentially accumulate in the gravid uterus and that expression of CCR5 on regulatory T cells can be induced by activation lead us to propose that CCR5 is responsible for the accumulation of those regulatory T cells that have been activated by paternal antigens.
Contingent Pacific–Atlantic Ocean influence on multicentury wildfire synchrony over western North America
Authors: Kitzberger Thomas , Brown Peter M. , Heyerdahl Emily K. , Swetnam Thomas W. , Veblen Thomas T.
Published: December 2006

Widespread synchronous wildfires driven by climatic variation, such as those that swept western North America during 1996, 2000, and 2002, can result in major environmental and societal impacts. Understanding relationships between continental-scale patterns of drought and modes of sea surface temperatures (SSTs) such as El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) may explain how interannual to multidecadal variability in SSTs drives fire at continental scales. We used local wildfire chronologies reconstructed from fire scars on tree rings across western North America and independent reconstructions of SST developed from tree-ring widths at other sites to examine the relationships of multicentury patterns of climate and fire synchrony. From 33,039 annually resolved fire-scar dates at 238 sites (the largest paleofire record yet assembled), we examined forest fires at regional and subcontinental scales. Since 1550 CE, drought and forest fires covaried across the West, but in a manner contingent on SST modes. During certain phases of ENSO and PDO, fire was synchronous within broad subregions and sometimes asynchronous among those regions. In contrast, fires were most commonly synchronous across the West during warm phases of the AMO. ENSO and PDO were the main drivers of high-frequency variation in fire (interannual to decadal), whereas the AMO conditionally changed the strength and spatial influence of ENSO and PDO on wildfire occurrence at multidecadal scales. A current warming trend in AMO suggests that we may expect an increase in widespread, synchronous fires across the western U.S. in coming decades.
Neutralization of a single arginine residue gates open a two-pore domain, alkali-activated K
+
channel
Authors: Niemeyer María Isabel , González-Nilo Fernando D. , Zúñiga Leandro , González Wendy , Cid L. Pablo , Sepúlveda Francisco V.
Published: December 2006

Potassium channels share a common selectivity filter that determines the conduction characteristics of the pore. Diversity in K
+
channels is given by how they are gated open. TASK-2, TALK-1, and TALK-2 are two-pore region (2P) KCNK K
+
channels gated open by extracellular alkalinization. We have explored the mechanism for this alkalinization-dependent gating using molecular simulation and site-directed mutagenesis followed by functional assay. We show that the side chain of a single arginine residue (R224) near the pore senses pH in TASK-2 with an unusual pK
a
of 8.0, a shift likely due to its hydrophobic environment. R224 would block the channel through an electrostatic effect on the pore, a situation relieved by its deprotonation by alkalinization. A lysine residue in TALK-2 fulfills the same role but with a largely unchanged pK
a
, which correlates with an environment that stabilizes its positive charge. In addition to suggesting unified alkaline pH-gating mechanisms within the TALK subfamily of channels, our results illustrate in a physiological context the principle that hydrophobic environment can drastically modulate the pK
a
of charged amino acids within a protein.
The first fossil leaf insect: 47 million years of specialized cryptic morphology and behavior
Authors: Wedmann Sonja , Bradler Sven , Rust Jes
Published: December 2006

Stick and leaf insects (insect order Phasmatodea) are represented primarily by twig-imitating slender forms. Only a small percentage (≈1%) of extant phasmids belong to the leaf insects (Phylliinae), which exhibit an extreme form of morphological and behavioral leaf mimicry. Fossils of phasmid insects are extremely rare worldwide. Here we report the first fossil leaf insect,Eophyllium messelensisgen. et sp. nov., from 47-million-year-old deposits at Messel in Germany. The new specimen, a male, is exquisitely preserved and displays the same foliaceous appearance as extant male leaf insects. Clearly, an advanced form of extant angiosperm leaf mimicry had already evolved early in the Eocene. We infer that this trait was combined with a special behavior, catalepsy or “adaptive stillness,” enablingEophylliumto deceive visually oriented predators. Potential predators reported from the Eocene are birds, early primates, and bats. The combination of primitive and derived characters revealed byEophylliumallows the determination of its exact phylogenetic position and illuminates the evolution of leaf mimicry for this insect group. It provides direct evidence that Phylliinae originated at least 47 Mya.Eophylliumenlarges the known geographical range of Phylliinae, currently restricted to southeast Asia, which is apparently a relict distribution. This fossil leaf insect bears considerable resemblance to extant individuals in size and cryptic morphology, indicating minimal change in 47 million years. This absence of evolutionary change is an outstanding example of morphological and, probably, behavioral stasis.
Population size and relatedness affect fitness of a self-incompatible invasive plant
Authors: Elam Diane R. , Ridley Caroline E. , Goodell Karen , Ellstrand Norman C.
Published: December 2006

One of the lingering paradoxes in invasion biology is how founder populations of an introduced species are able to overcome the limitations of small size and, in a “reversal of fortune,” proliferate in a new habitat. The transition from colonist to invader is especially enigmatic for self-incompatible species, which must find a mate to reproduce. In small populations, the inability to find a mate can result in the Allee effect, a positive relationship between individual fitness and population size or density. Theoretically, the Allee effect should be common in founder populations of self-incompatible colonizing species and may account for the high rate of failed introductions, but little supporting evidence exists. We created a field experiment to test whether the Allee effect affects the maternal fitness of a self-incompatible invasive species, wild radish (
Raphanus sativus
). We created populations of varying size and relatedness. We measured maternal fitness in terms of both fruit set per flower and seed number per fruit. We found that both population size and the level of genetic relatedness among individuals influence maternal reproductive success. Our results explicitly define an ecological genetic obstacle faced by populations of an exotic species on its way to becoming invasive. Such a mechanistic understanding of the invasions of species that require a mate can and should be exploited for both controlling current outbreaks and reducing their frequency in the future.
Internal conversion to the electronic ground state occurs via two distinct pathways for pyrimidine bases in aqueous solution
Authors: Hare Patrick M. , Crespo-Hernández Carlos E. , Kohler Bern
Published: December 2006

The femtosecond transient absorption technique was used to study the relaxation of excited electronic states created by absorption of 267-nm light in all of the naturally occurring pyrimidine DNA and RNA bases in aqueous solution. The results reveal a surprising bifurcation of the initial excited-state population in <1 ps to two nonradiative decay channels within the manifold of singlet states. The first is the subpicosecond internal conversion channel first characterized in 2000. The second channel involves passage through a dark intermediate state assigned to a lowest-energy
1
nπ* state. Approximately 10–50% of all photoexcited pyrimidine bases decay via the
1
nπ* state, which has a lifetime of 10–150 ps. Three- to 6-fold-longer lifetimes are seen for pyrimidine nucleotides and nucleosides than for the corresponding free bases, revealing an unprecedented effect of ribosyl substitution on electronic energy relaxation. A small fraction of the
1
nπ* population is proposed to undergo intersystem crossing to the lowest triplet state in competition with vibrational cooling, explaining the higher triplet yields observed for pyrimidine versus purine bases at room temperature. Some simple correlations exist between yields of the
1
nπ* state and yields of some pyrimidine photoproducts, but more work is needed before the photochemical consequences of this state can be definitively determined. These findings lead to a dramatically different picture of electronic energy relaxation in single pyrimidine bases with important ramifications for understanding DNA photostability.
The presenilin hypothesis of Alzheimer's disease: Evidence for a loss-of-function pathogenic mechanism
Authors: Shen Jie , Kelleher Raymond J.
Published: December 2006

Dominantly inherited mutations in the genes encoding presenilins (PS) and the amyloid precursor protein (APP) are the major causes of familial Alzheimer's disease (AD). The prevailing view of AD pathogenesis posits that accumulation of β-amyloid (Aβ) peptides, particularly Aβ42, is the central event triggering neurodegeneration. Emerging evidence, however, suggests that loss of essential functions of PS could better explain dementia and neurodegeneration in AD. First, conditional inactivation of PS in the adult mouse brain causes progressive memory loss and neurodegeneration resembling AD, whereas mouse models based on overproduction of Aβ have failed to produce neurodegeneration. Second, whereas pathogenic PS mutations enhance Aβ42 production, they typically reduce Aβ40 generation and impair other PS-dependent activities. Third, γ-secretase inhibitors can enhance the production of Aβ42 while blocking other γ-secretase activities, thus mimicking the effects of PS mutations. Finally, PS mutations have been identified in frontotemporal dementia, which lacks amyloid pathology. Based on these and other observations, we propose that partial loss of PS function may underlie memory impairment and neurodegeneration in the pathogenesis of AD. We also speculate that Aβ42 may act primarily to antagonize PS-dependent functions, possibly by operating as an active site-directed inhibitor of γ-secretase.
par
genes and the pathology of chromosome loss in
Vibrio cholerae
Authors: Yamaichi Yoshiharu , Fogel Michael A. , Waldor Matthew K.
Published: December 2006

The causes and consequences of chromosome loss in bacteria with multiple chromosomes are unknown.
Vibrio cholerae
, the causative agent of the severe diarrheal disease cholera, has two circular chromosomes. Like many other bacterial chromosomes, both
V. cholerae
chromosomes contain homologues of plasmid partitioning (
par
) genes. In plasmids,
par
genes act to segregate plasmid molecules to daughter cells and thereby ensure plasmid maintenance; however, the contribution of
par
genes to chromosome segregation is not clear. Here, we show that the chromosome II
parAB2
genes are essential for the segregation of chromosome II but not chromosome I. In a
parAB2
deletion mutant, chromosome II is mislocalized and frequently fails to segregate, yielding cells with only chromosome I. These cells divide once; their progeny are not viable. Instead, chromosome II-deficient cells undergo dramatic cell enlargement, nucleoid condensation and degradation, and loss of membrane integrity. The highly consistent nature of these cytologic changes suggests that prokaryotes, like eukaryotes, may possess characteristic death pathways.
Ovarian wedge resection restores fertility in estrogen receptor β knockout (ERβ
−/−
) mice
Authors: Inzunza José , Morani Andrea , Cheng Guojun , Warner Margaret , Hreinsson Julius , Gustafsson Jan-Åke , Hovatta Outi
Published: December 2006

Ovulation rarely occurs in mice in which the estrogen receptor β (ERβ) gene has been inactivated (ERβ
−/−
mice). Here, we investigated whether this subfertility is due to a defect in the ovary itself or to more general endocrine changes in ERβ
−/−
mice. We transplanted ERβ
−/−
ovaries into WT mice and WT ovaries into ERβ
−/−
mice. Upon mating with ERβ
−/−
males, fertility increased from 20% in control intact ERβ
−/−
group to 40% in the WT recipients with ERβ
−/−
ovaries. The transplantation procedure was not efficient, and when WT ovaries were transplanted into WT mice, fertility was only 36%. Surgical ovarian wedge resection, a procedure which induces ovulation in anovulatory women with polycystic ovarian syndrome, resulted in 100% fertility of ERβ
−/−
mice. In ERβ
−/−
mice, as the follicles enlarged, the thecal layer remained very compact (revealed by H&E and collagen staining), and there was no increase in vascularization (measured as smooth muscle actin). In addition, there was an increase in PDGF receptor α (PDGFRα) and a decrease in PDGFβ expression in the granulosa cells, similar to what has been found in follitropin receptor knockout mice. After wedge resection, expression of both smooth muscle actin and PDGFRs was normalized. During normal follicular development, increased vascularization of the thecal layer is a prerequisite for further follicular growth. We suggest that the defect in ERβ
−/−
mouse ovaries is a failure of communication between the granulosa and thecal layers. The follicles do not mature because of insufficient blood supply. This problem is overcome by stimulating neovascularization by simple wedge resection of the ovaries.
Cross-talk between singlet oxygen- and hydrogen peroxide-dependent signaling of stress responses in
Arabidopsis thaliana
Authors: Laloi Christophe , Stachowiak Monika , Pers-Kamczyc Emilia , Warzych Ewelina , Murgia Irene , Apel Klaus
Published: December 2006

Upon a dark-to-light shift, the conditional
fluorescent
(
flu
) mutant of
Arabidopsis
releases singlet oxygen (
1
O
2
) within the plastid compartment. Distinct sets of nuclear genes are activated that are different from those induced by superoxide (O
2
•−
) and/or hydrogen peroxide (H
2
O
2
), suggesting that different types of reactive oxygen species activate distinct signaling pathways. It is not known whether the pathways operate separately or interact with each other. We have addressed this problem by modulating noninvasively the level of H
2
O
2
in plastids by means of a transgenic line that overexpresses the thylakoid-bound ascorbate peroxidase (tAPX). The overexpression of the H
2
O
2
-specific scavenger reduced strongly the activation of nuclear genes in plants treated with the herbicide paraquat that in the light leads to the enhanced generation of O
2
•−
and H
2
O
2
. In the
flu
mutant overexpressing tAPX, the intensity of
1
O
2
-mediated cell death and growth inhibition was increased when compared with the
flu
parental line. Also, the expression of most of the nuclear genes that were rapidly activated after the release of
1
O
2
was significantly higher in
flu
plants overexpressing tAPX, whereas in wild-type plants, overexpression of tAPX did not lead to visible stress responses and had only a very minor impact on nuclear gene expression. The results suggest that H
2
O
2
antagonizes the
1
O
2
-mediated signaling of stress responses as seen in the
flu
mutant. This cross-talk between H
2
O
2
- and
1
O
2
-dependent signaling pathways might contribute to the overall stability and robustness of wild-type plants exposed to adverse environmental stress conditions.