bluuebunny/crossref_metadata_2025 huggingface dataset:
Critical roles of the nuclear receptor PPARβ (peroxisome-proliferator-activated receptor β) in skin wound healing
Authors: Tan N.S. , Michalik L. , Di-Poï N. , Desvergne B. , Wahli W.
Published: June 2004

The PPARs (peroxisome-proliferator-activated receptors) α, β/ δ and γ belong to the nuclear hormone receptor superfamily. While all three receptors are undetectable in adult mouse interfollicular epidermis, PPARβ expression and activity is strongly re-activated by inflammatory stimuli during epidermal injury. The pro-inflammatory cytokine TNFα (tumour necrosis factor α) stimulates transcription of the PPARβ gene via an activator protein-1 site in its promoter and it also triggers the production of PPARβ ligands in keratinocytes. This increase of PPARβ activity in these cells up-regulates the expression of integrin-linked kinase and 3-phosphoinositide-dependent kinase-1, which phosphorylates protein kinase B-α (Akt1). The resulting increase in Akt1 activity suppresses apoptosis and ensures the presence of a sufficient number of viable keratinocytes at the wound margin for re-epithelialization. Together, these observations reveal that PPARβ takes on multiple roles and contributes favourably to the process of wound closure.
Adipocyte cholesterol balance in obesity
Authors: Le Lay S. , Ferré P. , Dugail I.
Published: June 2004

Adipose tissue is specialized in the storage of energy in the form of triacylglycerol. Within the fat cell, triacylglycerols are found in a well-defined structural compartment called the lipid droplet, which occupies the vast majority of the fat cell volume. However, many other lipids are present in the lipid droplet. These include sterols, carotenoids, cholecalciferol and lipophilic toxic pollutants of the environment such as dioxins and tocopherols. The topic of this article is the role of fat cell cholesterol in adipose tissue physiology and its potential implication in pathological states such as obesity.
Lipid oxidation in atherogenesis: an overview
Authors: Jessup W. , Kritharides L. , Stocker R.
Published: June 2004

The ‘oxidation theory’ for atherosclerosis proposes that lipid and/or protein oxidation products are responsible for lesion formation/development. The major target for oxidation is suggested to be intimal low-density lipoprotein. This idea was stimulated by the pro-atherogenic properties of in vitro oxidized lipoproteins, such as stimulation of chemotaxis and sterol accumulation in macrophages, adhesion molecule expression on endothelial cells and apoptosis of several cell types. It was supported by detection of oxidation products in lesion lipoproteins, although these are (in general) less heavily oxidized and their biological activity is less rigorously defined than for their in vitro oxidized counterparts. Lesion lipids contain products generated by both enzymic and non-enzymic oxidation reactions; the majority are generated non-enzymically. The type and source of oxidant involved has been the subject of much speculation and is not resolved. The oxidation theory predicts that appropriate antioxidants will protect against atherosclerosis. Vitamin E has been used in several animal and human studies, but to date has shown little evidence of anti-atherosclerotic potential. However, lack of knowledge of the oxidant(s) driving lesion oxidation and the complexity of the anti- and pro-oxidant properties of vitamin E may explain its disappointing track record to date. These subjects require more rigorous study before the oxidation theory can be fairly tested.
Connection of lipid peroxide oxidation with the sphingomyelin pathway in the development of Alzheimer's disease
Authors: Alessenko A.V. , Bugrova A.E. , Dudnik L.B.
Published: June 2004

Alzheimer's disease (AD) is characterized by progressive decline in cognition, memory and intellect. It has been hypothesized that amyloid-β peptide (A-β) may have a prominent role in neurodegeneration. Oxidative mechanisms have been implicated in this pathway. There is substantial evidence that inflammatory mechanisms, induced by tumour necrosis factor α (TNF-α), are also involved in AD. TNF-α activates receptors linked to multiple effector systems, including a sphingomyelin pathway and peroxide oxidation. We have determined the changes of neutral sphingomyelinase activity, sphingomyelin and ceramide contents, and the level of lipid peroxide products (conjugated dienes), in the cerebral cortex, hippocampus and cerebellum of rats within 3 h and 7 days of intracerebral injection of A-β and TNF-α. A single injection of A-β and TNF-α has been shown to increase the level of peroxide products in the hippocampus and cerebral cortex within 3 h and 7 days. Sphingomyelinase activity and ceramide levels have been found to increase 7 days after A-β administration. We found that activation of the sphingomyelin pathway lies downstream from the oxidative stress.
Two distinct pathways for thymidylate (dTMP) synthesis in (hyper)thermophilic Bacteria and Archaea
Authors: Leduc D. , Graziani S. , Meslet-Cladiere L. , Sodolescu A. , Liebl U. , Myllykallio H.
Published: June 2004

The hyperthermophilic anaerobic archaeon Pyrococcus abyssi, which lacks thymidine kinase, incorporates label from extracellular uracil, but not from thymidine, into its DNA. This implies that P. abyssi must synthesize dTMP (thymidylate), an essential precursor for DNA synthesis, de novo. However, iterative similarity searches of the three completed Pyrococcus genomes fail to detect candidate genes for canonical thymidylate synthase ThyA, suggesting the presence of alternative pathways for dTMP synthesis. Indeed, by identifying a novel class of flavin-dependent thymidylate synthases, ThyX, we have recently proven that two distinct pathways for de novo synthesis of dTMP are operational in the microbial world. While both thyX and thyA can be found in hyperthermophilic micro-organisms, the phylogenetic distribution of thyX among hyperthermophiles is wider than that of thyA. In this contribution, we discuss the differences in the distinct mechanisms of dTMP synthesis, with a special emphasis on hyperthermophilic micro-organisms.
Phosphatases as small-molecule targets: inhibiting the endogenous inhibitors of kinases
Authors: Schmid A.C. , Woscholski R.
Published: June 2004

Inositols and their phosphorylated derivatives, phosphoinositides, play an important role in diverse cellular functions. They have been recognized as second messengers and are accurately controlled by phosphatases and kinases, such as phosphoinositide 3-kinase and the phosphatidylinositol 3-phosphatase PTEN (phosphatase and tensin homologue deleted on chromosome 10). Specific inhibitors targeting phosphoinositide 3-kinase and protein phosphatases have been described and characterized, but no small-molecule tools for phosphoinositide phosphatases are currently available. The present mini-review gives an overview of representative phosphatase inhibitors and summarizes the work that has been done recently on molecules that inhibit PTEN.
Anoikis
Authors: Valentijn A.J. , Zouq N. , Gilmore A.P.
Published: June 2004

Anoikis is apoptosis induced by loss of cell adhesion or inappropriate cell adhesion. Adhesion on the extracellular matrix is important to determine whether a cell is in the correct location and to delete displaced cells by apoptosis. The ability to overcome this requirement has important implications for metastatic cancer. However, how adhesion signals are interpreted by a cell into a life or death decision is complex. In this paper, we will examine this from the point of view of the apoptotic machinery of the cell, and discuss the various ways in which adhesion can influence this process.
Lipid rafts: microenvironments for integrin–growth factor interactions in neural development
Authors: Decker L. , Baron W. , ffrench-Constant C.
Published: June 2004

The development of a complex multicellular organ such as the nervous system requires precise regulation of cell migration, proliferation and survival. This regulation in turn requires the integration of long-range signals, such as growth factors, with short-range cues that define the precise location and cellular neighbours for any given cell. This short review examines one integrative mechanism, integrin–growth factor receptor interactions, and explores the role of lipid rafts in the molecular mechanisms that underlie the receptor interactions.
Integrin regulation of epidermal growth factor (EGF) receptor and of EGF-dependent responses
Authors: Cabodi S. , Moro L. , Bergatto E. , Boeri Erba E. , Di Stefano P. , Turco E. , Tarone G. , Defilippi P.
Published: June 2004

Integrin signalling co-ordinates with signalling originating from growth factor receptors in the co-operative control of cell proliferation, survival and migration. Increasing evidence suggests that integrins form physical complexes at the cell membrane with growth factor receptors, giving rise to signalling platforms at the adhesive sites. It is probable that at these sites integrins regulate adhesion and at the same time physically constrain and direct the response to soluble growth factors towards proliferation or survival stimuli. These co-operative effects might depend on integrin ability to activate growth factor receptors. In the present paper, we summarize our recent study showing that integrin-dependent adhesion triggers ligand-independent EGFR (epidermal growth factor receptor) activation to transduce downstream signalling. In addition, we also show that integrin-induced signalling pathways are necessary for EGF-dependent transcriptional response, demonstrating the requirement of the co-operation between cell–matrix adhesion and EGFR to achieve full biological responses.
Getting to grips with the granulocyte: manipulation of granulocyte behaviour and apoptosis by protein transduction methods
Authors: Rossi A.G. , Ward C. , Dransfield I.
Published: June 2004

Human granulocytes clearly play an important role in host defence against invading organisms, however they have also been implicated in the pathogenesis and progression of many chronic inflammatory diseases. In addition, these cells have been paramount in gaining a better understanding of many key-signalling pathways regulating fundamental biological processes. Since granulocytes are terminally differentiated and undergo relatively rapid constitutive apoptosis it has been difficult to manipulate intracellular events by transfection or transduction procedures. It has been shown in recent years that the HIV-TAT protein transduction system can be successfully used in granulocytes to manipulate key signalling mechanisms regulating functional responsiveness and survival. In this paper, we review recent literature highlighting important developments using this system in isolated human granulocytes and in inflammatory process in vivo where these cells play a prominent role.
Regulation of granulocyte apoptosis by phosphatidylinositol 3-kinase
Authors: Lindemans C.A. , Coffer P.J.
Published: June 2004

Granulocytes are critical components of the innate immune system whose lifespan is limited by an intrinsic, constitutive, apoptotic pathway. However, the lifespan of these cells can be extended at an inflammatory locus through interaction with survival factors. Although a wide variety of factors can modulate granulocyte survival, they often utilize a common subset of intracellular signal transduction pathways. Over the last decade, evidence has accumulated that the PI3K (phosphatidylinositol 3-kinase) family of lipid kinases may be critical in regulating the ability of granulocytes to survive at inflammatory loci. Studies utilizing both pharmacological inhibitors of PI3K and isoform-specific knockout mice have demonstrated that this enzyme is needed for the anti-apoptotic effects of granulocyte survival factors. More recently, a serine/threonine protein kinase, termed protein kinase B (also known as c-akt), has been demonstrated to be important in modulating the prosurvival effects of PI3K activation. This can occur through modulation of the expression or phosphorylation of members of the Bcl-2 (B-cell lymphocytic-leukaemia proto-oncogene 2) family of apoptosis regulators. This review summarizes recent results that have implicated a role for PI3K in regulating granulocyte survival.
Mitochondria in apoptosis: past, present and future
Authors: Degli Esposti M.
Published: June 2004

The role of mitochondria in cell death has been increasingly appreciated in the last few years and is now well established in a variety of cellular systems. At present we know that the involvement of mitochondria is regulated by proteins of the Bcl-2 (B-cell lymphocytic-leukaemia proto-oncogene 2) family, which biochemically act by altering the properties of mitochondrial membranes to facilitate the release of apoptogenic proteins like cytochrome c and Smac/Diablo that, once released into the cytosol, are crucial for activating the caspase cascade of cell degradation. The precise mechanism of the pro-apoptotic action is not fully understood yet, but could be clarified in the near future. Instrumental to this clarification is the emerging evidence that CL (cardiolipin), an unusual membrane lipid that is predominantly present in mitochondria, is required for the action of major pro-apoptotic proteins like Bid and Bax. New results obtained in myeloid cells further sustain this possibility and suggest that Bid may be involved in the metabolic cycle of CL re-modelling. In agreement with this postulate, preliminary results indicate a down-regulation of Bid in parallel to the genetic deficiency in CL re-modelling that is associated with a rare human disease, ‘Barth Syndrome’. Intriguingly, this disease is characterized by neutropenia, suggesting a link between myeloid differentiation and cell death (and myeloid lymphoma pathogenesis too). I will project current results and trends towards future investigations on the involvement of CL and mitochondrial membranes in myeloid differentiation, cell death and disease.
The use of isotope-coded affinity tags (ICAT) to study organelle proteomes in Arabidopsis thaliana
Authors: Dunkley T.P.J. , Dupree P. , Watson R.B. , Lilley K.S.
Published: June 2004

Organelle proteomics is the analysis of the protein contents of a subcellular compartment. Proteins identified in subcellular proteomic studies can only be assigned to an organelle if there are no contaminants present in the sample preparation. As a result, the majority of plant organelle proteomic studies have focused on the chloroplast and mitochondria, which can be isolated relatively easily. However, the isolation of components of the endomembrane system is far more difficult due to their similar sizes and densities. For this reason, quantitative proteomics methods are being developed to enable the assignment of proteins to a specific component of the endomembrane system without the need to obtain pure organelles.
Theory and experiments of electromagnetic loss mechanism for microwave heating of powdered metals
Authors: Luo Jirun , Hunyar Christian , Feher Lambert , Link Guido , Thumm Manfred , Pozzo Paolo
Published: June 2004

The physical explanation of electromagnetic loss mechanism for microwave heating of powdered metals is presented in this letter. A theoretical model is proposed to simulate and analyze the heating process. An experiment has been performed to prove the theory.
Role of bumpy fields on single particle orbit in near quasihelically symmetric stellarators
Authors: Seol JaeChun , Hegna C. C.
Published: June 2004

The role of symmetry breaking on single particle orbits in near helically symmetric stellarators is investigated. In particular, the effect of a symmetry-breaking bumpy term is included in the analysis of trapped particle orbits. It is found that all trapped particle drift orbits are determined by surfaces on which |B|min is constant. Trapped particle orbits reside on these surfaces regardless of pitch angle and are determined solely by the initial position and the shape of the |B|min contour. Since |B|min contours do not depend on the direction of the banana center motion, superbanana orbits do not appear.
Nanomechanical defect imaging in premetal dielectrics for integrated circuits
Authors: Muthuswami L. , Geer R. E.
Published: June 2004

Ultrasonic force microscopy (UFM) has been used for cross-sectional nanomechanical imaging of integrated circuit trenches filled with hydrogen silsesquioxane (HSQ) premetal dielectric. Fully cured HSQ exhibits a local Young’s modulus of 55±2 GPa calibrated against SiO2. UFM reveals local areas within the HSQ with dramatically reduced modulus exhibiting poor resistance to hydrofluoric acid etching, indicative of incomplete densification during curing. Quantitative UFM analysis reveals a modulus of 28±2 GPa at the defect centers. This agrees quantitatively with predictions from recent finite element models of siloxane-based dielectrics in conjunction with relative density measurements of similar defects via transmission electron microscopy.
Enhanced energy coupling and x-ray emission in Z-pinch plasma implosions
Authors: Whitney K. G. , Thornhill J. W. , Apruzese J. P. , Davis J. , Deeney C. , Coverdale C. A.
Published: June 2004

Recent experiments conducted on the Saturn pulsed-power generator at Sandia National Laboratories [R. B. Spielman et al., in Proceedings of the Second International Conference on Dense Z Pinches, Laguna Beach, CA, 1989, edited by N. R. Pereira, J. Davis, and N. Rostoker (American Institute of Physics, New York, 1989), p. 3] have produced large amounts of x-ray output, which cannot be accounted for in conventional magnetohydrodynamic (MHD) calculations. In these experiments, the Saturn current had a rise time of ∼180 ns in contrast to a rise time of ∼60 ns in Saturn’s earlier mode of operation. In both aluminum and tungsten wire-array Z-pinch implosions, 2–4 times more x-ray output was generated than could be supplied according to one-dimensional (1D) magnetohydrodynamic calculations by the combined action of the j×B acceleration forces and ohmic heating (as described by a classical Braginskii resistivity). In this paper, we reexamine the problem of coupling transmission line circuits to plasma fluid equations and derive expressions for the Z-pinch load circuit resistance and inductance that relate these quantities in a 1D analysis to the surface resistivity of the fluid, and to the magnetic field energy that is stored in the vacuum diode, respectively. Enhanced energy coupling in this analysis, therefore, comes from enhancements to the surface resistivity, and we show that plasma resistivities approximately three orders of magnitude larger than classical are needed in order to achieve energy inputs that are comparable to the Saturn experiment x-ray outputs. Large enhancements of the plasma resistivity increase the rate of magnetic field and current diffusion, significantly modify the qualitative features of the MHD, and raise important questions as to how the plasma fluid dynamics converts enhanced energy inputs into enhanced x-ray outputs. One-dimensional MHD calculations in which resistivity values are adjusted phenomenologically are used to illustrate how various dynamical assumptions influence the way enhanced energy inputs are channeled by the fluid dynamics. Variations in the parameters of the phenomenological model are made in order to determine how sensitively they influence the dynamics and the degree to which the calculated x-ray outputs can be made to replicate the kinds of large variations in the experimental x-ray power data that were observed in three nominally identical aluminum wire shots on Saturn.
Transport theory for potato orbits in an axisymmetric torus with finite toroidal flow speed
Authors: Shaing K. C. , Peng M.
Published: June 2004

Transport theory for potato orbits in the region near the magnetic axis in an axisymmetric torus such as tokamaks and spherical tori is extended to the situation where the toroidal flow speed is of the order of the sonic speed as observed in National Spherical Torus Experiment [E. J. Synakowski, M. G. Bell, R. E. Bell et al., Nucl. Fusion 43, 1653 (2003)]. It is found that transport fluxes such as ion radial heat flux, and bootstrap current density are modified by a factor of the order of the square of the toroidal Mach number. The consequences of the orbit squeezing are also presented. The theory is developed for parabolic (in radius r) plasma profiles. A method to apply the results of the theory for the transport modeling is discussed.
Scale hierarchy created in plasma flow
Authors: Yoshida Z. , Mahajan S. M. , Ohsaki S.
Published: June 2004

The cooperation of nonlinearity (producing collapsed characteristics) and dispersion (unfolding singularities) underlies a robust mechanism that imparts two distinct scales (L measuring the system size, and δi typically of the order of the ion skin depth) to the double Beltrami states of a two-fluid plasma. It is shown that the conventional single-fluid model [magnetohydrodynamic (MHD)] seemingly valid for a large system (δi/L≈0), fails to capture the small scale that is created by the singular perturbation of the two-fluid effect (dispersion). The small-scale component plays an important role in various plasma phenomena, such as coronal heating. The double Beltrami model is compared and contrasted with the standard MHD pathway (Parker’s model of current sheet, for instance).
Mean-field magnetization relaxation in conducting ferromagnets
Authors: Tserkovnyak Yaroslav , Fiete Gregory A. , Halperin Bertrand I.
Published: June 2004

Collective ferromagnetic motion in a conducting medium is damped by the transfer of the magnetic moment and energy to the itinerant carriers. We present a calculation of the corresponding magnetization relaxation as a linear-response problem for the carrier dynamics in the effective exchange field of the ferromagnet. In electron systems with little intrinsic spin-orbit interaction, a uniform magnetization motion can be formally eliminated by going into the rotating frame of reference for the spin dynamics. The ferromagnetic damping in this case grows linearly with the spin-flip rate when the latter is smaller than the exchange field and is inversely proportional to the spin-flip rate in the opposite limit. These two regimes are analogous to the “spin-pumping” and the “breathing Fermi-surface” damping mechanisms, respectively. In diluted ferromagnetic semiconductors, the hole-mediated magnetization can be efficiently relaxed to the itinerant-carrier degrees of freedom due to the strong spin-orbit interaction in the valence bands.
High-indium-content InxGa1−xAs/GaAs quantum wells with emission wavelengths above 1.25 μm at room temperature
Authors: Ni H. Q. , Niu Z. C. , Xu X. H. , Xu Y. Q. , Zhang W. , Wei X. , Bian L. F. , He Z. H. , Han Q. , Wu R. H.
Published: June 2004

High-indium-content InxGa1−xAs/GaAs single/multi-quantum well (SQW/MQW) structures have been systematically investigated. By optimizing the molecular-beam epitaxy growth conditions, the critical thickness of the strained In0.475Ga0.525As/GaAs QWs is raised to 7 nm, which is much higher than the value given by the Matthews and Blakeslee model. The good crystalline quality of the strained InGaAs/GaAs MQWs is proved by x-ray rocking curves. Photoluminescence measurements show that an emission wavelength of 1.25 μm at room temperatures with narrower full width at half maximum less than 30 meV can be obtained. The strain relaxation mechanism is discussed using the Matthews–Blakeslee model.
Low-power near-field microwave applicator for localized heating of soft matter
Authors: Copty A. , Sakran F. , Golosovsky M. , Davidov D. , Frenkel A.
Published: June 2004

We report a 9 GHz near-field microwave probe for local surface heating of microwave absorbing materials. The probe radiates microwave energy through a narrow slot microfabricated at the apex of the dielectric resonator. The microwave energy is concentrated in a small region close to the applicator, in such a way that the microwave intensity there is very high. A temperature of 60–120 °C can be achieved in a spot size as small as 0.3×0.5 mm2, using an input power of only a few watts. The applicator can be used for local heating, coagulation, and melting of various soft-matter mediums. Particularly, we emphasize results on local heating and coagulation of egg-white and albumin which may be used as a “biological solder” for tissue welding applications.
Cantilever transducers as a platform for chemical and biological sensors
Authors: Lavrik Nickolay V. , Sepaniak Michael J. , Datskos Panos G.
Published: June 2004

Since the late 1980s there have been spectacular developments in micromechanical or microelectro-mechanical (MEMS) systems which have enabled the exploration of transduction modes that involve mechanical energy and are based primarily on mechanical phenomena. As a result an innovative family of chemical and biological sensors has emerged. In this article, we discuss sensors with transducers in a form of cantilevers. While MEMS represents a diverse family of designs, devices with simple cantilever configurations are especially attractive as transducers for chemical and biological sensors. The review deals with four important aspects of cantilever transducers: (i) operation principles and models; (ii) microfabrication; (iii) figures of merit; and (iv) applications of cantilever sensors. We also provide a brief analysis of historical predecessors of the modern cantilever sensors.
Design of a thermostimulated creep measurement system using magnetic fields for polymers
Authors: Ogreten Dogan , Delbreilh Laurent , Lacabanne Colette
Published: June 2004

A thermostimulated creep (TSCr) measurement system for polymers has been designed and tested. The objective was to measure very precisely the thermomechanical properties of polymers with samples having a thickness ranging from 1 mm to 10 μm. The use of magnetic fields to apply the stress on the samples revealed itself as a powerful mean to achieve our goal. The apparatus was tested and validated through three series of experiments. The first study carried on the secondary retardation mode that is representative of the impact strength properties of a polycarbonate sample. Then the evolution with physical aging of the primary retardation mode of polycarbonate was observed. Finally, we measured the retardation modes of a semicrystalline linear low density polyethylene with a thin film geometry to verify the good resolution of the new TSCr design.
An apparatus for imaging liquids, cells, and other wet samples in the scanning electron microscopy
Authors: Thiberge S. , Zik O. , Moses E.
Published: June 2004

We present a technique of scanning electron microscopy that is adapted to the study of wet samples. The wet environment is protected in a small chamber enclosed by a membrane, which is thin enough for energetic electrons to go through and interact with the sample studied. We detail both the technique and the general mechanisms of signal formation in the imaging of samples through a membrane. We first describe our setup and the properties required for the membrane, the main element in this method. Some simple measurements for its characterization are given, guiding the choice of material and thickness. We then go on to describe the capabilities of the technique in imaging a variety of different samples. We evaluate the accessible contrast and resolution, and the current needed to obtain them. Low contrast samples can be imaged with an improvement in resolution over optical microscopy. High contrast samples like gold markers labeling a biological cell can be imaged with a resolution of the order of 10 nm. The resolution depends on the location of the particle in the sample: the closer to the membrane, the better the resolution. We believe such a result opens up potential applications for routine experiments in biology, and expect this new technique to find numerous applications in domains where liquid samples are investigated such as soft materials science.
Optical investigation of InGaN∕GaN multiple-quantum wellsunder high excitation
Authors: Wang T. , Parbrook P. J. , Fan W. H. , Fox A. M.
Published: June 2004

Optical investigation under high excitation is carried out on InGaN∕GaN multiple-quantum wells (MQWs) with different well thickness. In the case of MQWs with wide well thickness, a strong emission from quantum-dot-like states is observed, appearing only under high excitation on the high energy side of the emission from the transition between the first electron and first heavy-hole subbands (e1–h1) as confirmed by detailed calculation. The emission from the quantum-dot-like states is proved by temperature- and power-dependent photoluminescence measurements. The e1–h1 transition dominates the emission under low excitation, whereas in contrast the emission under high excitation is dominated by the quantum-dot-like states from low temperature to room temperature, which can partly explain the dramatically enhanced internal quantum efficiency at room temperature under high excitation, compared to the case under low excitation. Since the lasing process in InGaN∕GaN-based MQWs generally takes place under high excitation, the result should be highly taken into account for understanding the emission mechanism during lasing process.
Photoluminescence and resonant Raman scattering in highly conductive ZnO layers
Authors: Zalamai V. V. , Ursaki V. V. , Rusu E. V. , Arabadji P. , Tiginyanu I. M. , Sirbu L.
Published: June 2004

Photoluminescence (PL) and resonant Raman scattering (RRS) excited by the 351.1nm line of an Ar+ laser were studied in highly conductive ZnO layers deposited by thermal decomposition of Zn(C5H7O2)2 metalorganic compound on porous InP substrates. The emission spectra consist of multiphonon RRS lines superimposed on a broad asymmetric PL band with the maximum at 3.36eV. The occurrence of PL and RRS is attributed to tailing of the density of states caused by potential fluctuations due to randomly distributed intrinsic defects.
Flow resistance for microfluidic logic operations
Authors: Vestad Tor , Marr David W. M. , Munakata Toshinori
Published: June 2004

Control of relative flow resistance is used for the actuation of both one- and two-input microfluidic “logical gates”. By taking advantage of system nonlinearities and despite the linear response of laminar flows associated with these length scales, a number of operators including the NOT, AND, OR, XOR, NOR, and NAND are demonstrated. Because these gates can be actuated simultaneously they can be combined to form more complicated devices such as a half adder. This approach is therefore flexible and illustrates that any macro- or microscale technique that can alter flow resistance can be used as the basis of a fluid-based logical micro-operator.
Interfacial characteristics of N-incorporated HfAlO high-k thin films
Authors: Cho M.-H. , Moon D. W. , Park S. A. , Kim Y. K. , Jeong K. , Kang S. K. , Ko D.-H. , Doh S. J. , Lee J. H. , Lee N. I.
Published: June 2004

The characteristics of N-incorporated HfO2–Al2O3 alloy films (HfAlO) were investigated by high-resolution x-ray photoelectron spectroscopy (XPS), near-edge x-ray absorption fine structure (NEXAFS), medium-energy ion scattering (MEIS), and capacitance–voltage measurements. The core-level energy states, Hf4f and Al2p peaks of a 15Å thick film showed a shift to lower binding energy, resulting from the incorporation of nitrogen into the films. Absorption spectra of the OK edge of HfAlO were affected mainly by the Al2O3 in the film, and not by HfO2 after nitridation by NH3 annealing. The NEXAFS of NK edge and XPS data related to the chemical state suggested that the incorporated N atom is dominantly bonded to Al2O3, and not to HfO2. Moreover, MEIS results implied that there is a significant incorporation of N at the interface between the alloy film and Si. The incorporation of N effectively suppressed the leakage current without an increase in interfacial layer thickness, while the interfacial state of the N-incorporated films increased somewhat.
Dependence of plasma-induced modification of polymer surfaces on polyatomic ion chemistry
Authors: Jang Inkook , Sinnott Susan B.
Published: June 2004

Fluorocarbon plasmas are widely used to chemically modify surfaces and deposit thin films. The deposition of mass selected fluorocarbon ions is useful for isolating the effects specific to polyatomic ions. In this study, the detailed chemical modifications that result from the deposition of beams of polyatomic fluorocarbon ions (C3F5+ and CF3+) on polystyrene surfaces at experimental fluxes are identified using classical molecular dynamics simulations. These simulations elucidate how and why more efficient fluorination of the surface is achieved by CF3+ ion beam deposition, but C3F5+ ions are more efficient at growing fluorocarbon thin films.
Imaging nanostructures with coherent phonon pulses
Authors: Daly B. C. , Holme N. C. R. , Buma T. , Branciard C. , Norris T. B. , Tennant D. M. , Taylor J. A. , Bower J. E. , Pau S.
Published: June 2004

We demonstrate submicron resolution imaging using picosecond acoustic phonon pulses. High-frequency acoustic pulses are generated by impulsive thermoelastic excitation of a patterned 15-nm-thick metal film on a crystalline substrate using ultrafast optical pulses. The spatiotemporal diffracted acoustic strain field is measured on the opposite side of the substrate, and this field is used in a time-reversal algorithm to reconstruct the object. The image resolution is characterized using lithographically defined 1-micron-period Al structures on Si. Straightforward technical improvements should lead to resolution approaching 45nm, extending the resolution of acoustic microscopy into the nanoscale regime.
Time-resolved thermal lens determination of the thermo-optical coefficients in Nd-doped yttrium aluminum garnet as a function of temperature
Authors: Nunes A. R. , Rohling J. H. , Medina A. N. , Pereira J. R. D. , Bento A. C. , Baesso M. L. , Nunes L. A. O. , Catunda T.
Published: June 2004

In this work, time-resolved thermal lens measurements are carried out in Nd-doped yttrium aluminum garnet laser crystal as a function of temperature. The temperature coefficient of the optical path length, the thermal diffusivity, and the thermal conductivity were determined in the temperature range between 22°C and 180°C. In addition, the specific heat was measured by the thermal relaxation method in the same temperature range. The results showed that the thermal conductivity and the temperature coefficient of the optical path length are responsible for the strong increase of the thermal lens amplitude when the sample temperature was increased. These results suggest that the time resolved procedure is useful in the study of laser materials and may be an important tool for laser designers.
Mass detection using carbon nanotube-based nanomechanical resonators
Authors: Li Chunyu , Chou Tsu-Wei
Published: June 2004

The potential of nanobalances based on individual single-walled carbon nanotubes is examined. The carbon nanotube resonators are assumed to be either cantilevered or bridged and simulated by an atomistic modeling, i.e., the molecular structural mechanics method. The results indicate that the mass sensitivity of carbon nanotube nanobalances can reach 10−21g and a logarithmically linear relationship exists between the resonant frequency and the attached mass when the mass is larger than 10−20g. The sensitivity of resonant frequency shifts to both tube length and diameter has been demonstrated.
On nanoparticle surface growth: MgO nanoparticle formation during a Mg particle combustion
Authors: Altman Igor S. , Agranovski Igor E. , Choi Mansoo
Published: June 2004

It is demonstrated that formation of MgO nanoparticles during a Mg particle combustion occurs in the vapor adsorption regime and the particle coagulation and coalescence do not play any significant role in the process in question. Analysis of the particle size distributions shows that the rate of the nanoparticle condensation growth strongly depends on the actual particle size. The revealed dependence of the growth rate upon the size is consistent with the exponential law recently predicted. This finding can shed light on the long-standing general problem of gas-phase nanotechnology—the origin of lognormal size distribution behavior of generated nanoparticles.
Dramatically enhanced polarization in (001), (101), and (111) BiFeO3 thin films due to epitiaxial-induced transitions
Authors: Li Jiefang , Wang Junling , Wuttig M. , Ramesh R. , Wang Naigang , Ruette B. , Pyatakov A. P. , Zvezdin A. K. , Viehland D.
Published: June 2004

Dramatically enhanced polarization has been found for (001), (101), and (111) films, relative to that of BiFeO3 crystals. The easy axis of spontaneous polarization lies close to (111), for the various oriented films. BiFeO3 films grown on (111) have a rhombohedral structure, identical to that of single crystals; whereas films grown on (101) or (001) are monoclinically distorted from the rhombohedral structure, due to the epitaxial constraint.
High-resolution nanowire atomic force microscope probe grownby a field-emission induced process
Authors: Tay A. B. H. , Thong J. T. L.
Published: June 2004

A technique to grow a nanowire probe on an atomic force microscope (AFM) tip using a field-emission induced growth process has been developed. The simple and highly reproducible technique produces vertically aligned nanowire probes whose length is controlled by the growth duration. Using a cantilever clamping arrangement, nanowire probes can be grown on low-stiffness cantilevers. Experiments using the robust nanowire AFM probe demonstrate its ability to produce high-resolution tapping mode AFM images and improved profiling of structures with steep sidewalls due to its very sharp tip and high aspect ratio. No degradation in imaging performance was observed after a period of continuous scanning and storage.
Investigation of Pb(Zr,Ti)O3∕GaN heterostructures by scanning probe microscopy
Authors: Gruverman A. , Cao W. , Bhaskar S. , Dey S. K.
Published: June 2004

Piezoresponse force microscopy (PFM) technique has been utilized to study the evolution of domain structure with varying Pb(Zr,Ti)O3(PZT) thickness on GaN substrate. Sol-gel PZT films were deposited on the GaN∕sapphire substrate with PZT thickness of 100, 200, and 300nm. The films exhibit ferroelectric properties that vary as a function of the film thickness. This is explained by the mechanical stress at the PZT∕GaN interface. The thicker film (300nm) is characterized by the presence of a number of oppositely polarized domains and a relatively high value of the effective piezoelectric constant. The laminar domain structure, consisting of 90° and 180° domains, has been revealed in the thinner (200nm) PZT film. Both films show clear ferroelectric switching behavior, which is in contrast to the thinnest film (100nm), where no switching has been observed due to mostly in-plane polarization orientation. The observed results indicate the utility of the PFM technique for characterization of the electronic properties of the PZT∕GaN heterostructures.
Size effects in ultrathin epitaxial ferroelectric heterostructures
Authors: Nagarajan V. , Prasertchoung S. , Zhao T. , Zheng H. , Ouyang J. , Ramesh R. , Tian W. , Pan X. Q. , Kim D. M. , Eom C. B. , Kohlstedt H. , Waser R.
Published: June 2004

In this letter we report on the effect of thickness scaling in model PbZr0.2Ti0.8O3(PZT)∕SrRuO3 heterostructures. Although theoretical models for thickness scaling have been widely reported, direct quantitative experimental data for ultrathin perovskite (<10nm) films in the presence of real electrodes have still not been reported. In this letter we show a systematic quantitative experimental study of the thickness dependence of switched polarization in (001) epitaxial PZT films, 4to80nm thick. A preliminary model based on a modified Landau Ginzburg approach suggests that the nature of the electrostatics at the ferroelectric–electrode interface plays a significant role in the scaling of ferroelectric thin films.
Micron-scale apparatus for measurements of thermodiffusion in liquids
Authors: Putnam Shawn A. , Cahill David G.
Published: June 2004

An ac beam deflection technique for measurements of thermodiffusion in liquid mixtures is described. In comparison to conventional beam deflection methods, the micron-scale geometry of our apparatus speeds up equilibration by a factor of ≈300. Our apparatus and analysis methods are validated with measurements on molecular polystyrene dissolved in toluene. Thermodiffusion experiments on 26 nm polystyrene colloids with carboxyl functionality (COOH) in water yield Soret coefficients of ST=−0.28±0.025 K−1.
A 2π spectrometer for electron–electron coincidence studies on surfaces
Authors: Hattass M. , Jalowy T. , Czasch A. , Weber Th. , Jahnke T. , Schössler S. , Ph. Schmidt L. , Jagutzki O. , Dörner R. , Schmidt-Böcking H.
Published: June 2004

We present a new time-of-flight spectrometer for energy and angle-resolved measurements of electrons emitted in coincidence from a surface. By using a projection method, we can cover nearly 2π of the solid angle above the sample resulting in a very high coincidence efficiency. The use of this new spectrometer for the double photoemission process from surfaces will be demonstrated.
Ethylene biosynthesis and endogenous polyamines in relation to development of in vitro cultured kiwifruit explants
Authors: Arigita Luis , Tamés Ricardo Sánchez , González Aida
Published: June 2004

The relationship between polyamines and ethylene is controversial because the degree of interference of one pathway with the other may differ according to species, stage of development and experimental procedure. In this paper, we modify ethylene biosynthesis by the addition of aminoethoxyvinylglicine (AVG) or 1-aminocyclopropane-1-carboxylic acid (ACC) and study how it affects polyamine content and development of kiwifruit explants (Actinidia deliciosa CS Liang. & AR Fergusson). Cultured under ventilation where ethylene did not accumulate in the culture vessels, kiwi explants had higher ACC synthase activity and lower polyamine content than those grown without ventilation. In explants cultured in the reference medium, putrescine was the more abundant polyamine and spermine was only detected in the free fraction irrespective of ventilation. Under ventilation, addition of ACC to the culture medium inhibited organogenesis, there was less spermidine and spermine was not detected. Addition of AVG to the culture medium increased both the number of shoots and the amount of polyamines, and inhibited ACC synthase, so S-adenosylmethionine (SAM) led to increasing synthesis of spermidine and spermine. The increase in putrescine is more difficult to explain on the basis of inhibition of ethylene biosynthesis. The increase in the number of shoots in kiwi explants due to AVG addition may be attributed to the lack of ethylene in the atmosphere of the vessels or the increase in free polyamines.
Distinct cis-elements in the Asparagus officinalis asparagine synthetase promoter respond to carbohydrate and senescence signals
Authors: Winichayakul Somrutai , Moyle Richard L. , Ryan Dacey J. , Farnden Kevin J. F. , Davies Kevin M. , Coupe Simon A.
Published: June 2004

The Asparagus officinalis L. asparagine (Asn) synthetase (AS) promoter was analysed for elements responding to carbohydrate and senescence signals. Transgenic Arabidopsis thaliana L. plants containing deletion constructs of the –1958 bp AS promoter linked to the β-glucuronidase (GUS) reporter gene (AS::GUS) were analysed by measuring GUS specific activity. Inclusion of sucrose (Suc), glucose (Glc) or fructose (Fru) in plant media repressed levels of GUS activity in –1958AS::GUS plants, regardless of the light environment, with increases in GUS found 1 d after incubation on Suc-lacking media. Hexokinase is likely to be involved in the signal pathway, as Suc, Glc, Fru, 2-deoxy-d-glucose and mannose were more effective repressors than 3-O-methylglucose, and the hexokinase inhibitor mannoheptulose reduced repression. Plants containing AS::GUS constructs with deletions that reduced the promoter to less than –405 bp did not show low sugar induction. AS::GUS activity was significantly higher in excised leaves induced to senesce by dark storage for 24 h, compared to fresh leaves, for lines containing at least –640 bp of the AS promoter but not those with –523 bp or smaller promoter fragments. Fusion of the –640 to –523 bp region to a –381AS::GUS construct generated a promoter that retained senescence induction but lacked low sugar induction. Alignment of this region to the 33-bp senescence-related sequence of the Arabidopsis and Brassica napus L. SAG12 promoters identified the sequence TTGCACG as being conserved in all the promoters, and which may be an important senescence-responsive element.
Location, location, location: surveying the intracellular real estate through proteomics in plants
Authors: Millar A. Harvey
Published: June 2004

Knowledge of cellular compartmentation is critical to an understanding of many aspects of biological function in plant cells but it remains an under-emphasised concept in the use of and investment in plant functional genomic tools. The emerging effort in plant subcellular proteomics is discussed, and the current datasets that are available for a series of organelles and cellular membranes isolated from a range of plant species are noted. The benefit of knowing subcellular location in determining the role of proteins of unknown function is considered alongside the challenges faced in this endeavour. These include clear problems in dealing with contamination during the isolation of subcellular compartments, the meaningful integration of these datasets once completed to assemble a jigsaw of the cellular proteome as a whole, and the use of the wider literature in supplementing this proteomic discovery effort.
Revision of Fergusonina Malloch gall flies (Diptera : Fergusoninidae) from Melaleuca (Myrtaceae)
Authors: Taylor Gary S.
Published: June 2004

Flies of the monogeneric Australasian family Fergusoninidae (Diptera) and nematodes of the genus Fergusobia Currie (Tylenchida : Neotylenchidae) together form galls on various Myrtaceae, in the only recorded mutualism between flies and nematodes. New species of Fergusonina Malloch gall-forming flies are here described from the broad-leaved Melaleuca leucadendra species-complex (Myrtaceae), which includes M. quinquenervia (Cav.) S. T. Blake, an invasive weed outside its natural range. The putatively monophyletic Fergusonina turneri species-group is defined to accommodate: F. turneri, sp. nov.; F. burrowsi, sp. nov.; F. centeri, sp. nov.; F. goolsbyi, sp. nov.; F. makinsoni, sp. nov.; F. purcelli, sp. nov.; and F. schefferae, sp. nov. Partial descriptions are provided for further unnamed species from the M. leucadendra species-complex, and for an additional unassigned species from a narrow-leaved Melaleuca. The fly–nematode associations are species-specific and appear to have a high degree of host specificity within the Myrtaceae. Information on the mutualist nematodes and host plant associations are presented, together with two keys to species of Fergusonina: one based on adult characters, and one (for field workers) based on larva, puparium and gall characters and host and nematode associations.