bluuebunny/crossref_metadata_2025 huggingface dataset:
Response Surface Method Optimization of a High-Speed Direct-Injection Diesel Engine Equipped With a Common Rail Injection System
Authors: Lee T. , Reitz R. D.
Published: May 2003

To overcome the tradeoff between NOx and particulate emissions for future diesel vehicles and engines it is necessary to seek methods to lower pollutant emissions. The desired simultaneous improvement in fuel efficiency for future DI diesels is also a difficult challenge due to the combustion modifications that will be required to meet the exhaust emission mandates. This study demonstrates the emission reduction capability of EGR and other parameters on a high-speed direct-injection (HSDI) diesel engine equipped with a common rail injection system using an RSM optimization method. Engine testing was done at 1757 rev/min, 45% load. The variables used in the optimization process included injection pressure, boost pressure, injection timing, and EGR rate. RSM optimization led engine operating parameters to reach a low-temperature and premixed combustion regime called the MK combustion region, and resulted in simultaneous reductions in NOx and particulate emissions without sacrificing fuel efficiency. It was shown that RSM optimization is an effective and powerful tool for realizing the full advantages of the combined effects of combustion control techniques by optimizing their parameters. It was also shown that through a close observation of optimization processes, a more thorough understanding of HSDI diesel combustion can be provided.
Development of the Low-Emission GE-7FDL High-Power Medium-Speed Locomotive Diesel Engine
Authors: Chen G. , Flynn P. L. , Gallagher S. M. , Dillen E. R.
Published: May 2003

This paper summarizes the technical development of the low-emission GE-7FDL series locomotive diesel engine. The development focused on reducing the engine exhaust NOx emission significantly while reducing and curbing other visible and nonvisible emissions with minimal adverse impact on the engine fuel efficiency and minimal changes to the engine system and components. Concepts were analyzed, and were investigated using a single-cylinder 7FDL research engine. A low-emission 16-cylinder 7FDL engine and a GE locomotive prototype were built and tested for performance demonstration, function evaluation, and design optimization. The GE low-emission 7FDL engines and locomotives have been in production. The newly developed low-emission locomotive engine meets the EPA Tier-0 levels without fuel efficiency penalty. This was accomplished with minimal changes to the engine system and components. The desired engine reliability performance is retained. The engines are interchangeable with the preceding 7FDL baseline models, and the upgrade of the existing baseline engines to the low-emission version is facilitated.
An Investigation of Flame Expansion Speed With a Strong Swirl Motion Using High-Speed Visualization
Authors: Joo S. H. , Chun K. M. , Shin Y. , Lee K. C.
Published: May 2003

In this study, a simple linear supposition method is proposed to separate the flame expansion speed and swirl motion of a flame propagating in an engine cylinder. Two series of images of flames propagating in the cylinder with/without swirl motion were taken by a high frame rate digital video camera. A small tube (4 mm ID) was installed inside the intake port to deliver the fuel/air mixture with strong swirl motion into the cylinder. An LDV was employed to measure the swirl motion during the compression stroke. Under the assumption that flame propagates spherically from the each point of the flame front, a diameter of small spherical flames can be calculated from the two consecutive images of the flame without swirl motion in the cylinder. Using the normalized swirl motion of the mixture during the compression stroke and the spherical flame diameters, the flame expansion speed and swirl ratio of combustion propagation in the engine cylinder can be obtained. This simple linear superposition method for separating the flame expansion speed and swirl motion can be utilized to understand the flow characteristics, such as swirl and turbulence, during the combustion process.
Limits to the strength of super- and ultrahard nanocomposite coatings
Authors: Veprek S. , Mukherjee S. , Karvankova P. , Männling H.-D. , He J. L. , Moto K. , Prochazka J. , Argon A. S.
Published: May 2003

Hertzian analysis of the nonlinear elastic response upon unloading provides analytical solutions that were used to verify if the hardness values measured on the super- and ultrahard coatings are self-consistent. The analytical solutions were also used to estimate the tensile strength of the coatings. The highest tensile stress occurs at the periphery of the contact between the coating and the indenter and, in the case of ultrahard coatings, it can reach values in the range of tens of Gpa, thus giving an estimate of their tensile strength. The results show that the tensile strength of the superhard nanocomposites reaches an appreciable fraction of the ideal cohesive strength that is predicted on the basis of the universal binding energy relation. The data are compared with finite element computer modeling in order to obtain a deeper insight into the complex problems. Reliable values of the hardness can be obtained if coatings of a thickness greater than 8 μm are used and the load-independent values are measured at sufficiently large indentation depths of greater than 0.3 μm.
Interface broadening due to Ar+ ion bombardment measured on Co/Cu multilayer at grazing angle of incidence
Authors: Barna A. , Menyhard M. , Zsolt G. , Koos A. , Zalar A. , Panjan P.
Published: May 2003

A Co/Cu multilayer system, with double layer thickness of about 60 nm was Auger electron spectroscopy depth profiled applying 1 keV Ar+ bombardment, varying the angle of incidence in the range of 78°–86°. It was found that (a) the relative sputter rate changes with the angle of incidence; (b) the interface broadening of the Co/Cu transition is larger than that of the Cu/Co transition and depends on the depth; (c) the broadening of the Co/Cu transition increases with increasing relative sputter rate; and (d) the broadening of the Cu/Co transition does not depend on the relative sputter rate. These features will be explained as the consequences of the strong preferential sputtering of Cu (with respect to Co) in this angular range. Because of the preferential sputtering ion bombardment induced roughening and smoothening (which was directly observed by atomic force microscopy measurements) occurs on the Co/Cu and Cu/Co interface, respectively. D-TRIM simulation has been also performed which suggested that ion mixing also causes larger broadening on the Co/Cu than on the Cu/Co interface.
Thermal stability of polycrystalline TiN/CrN superlattice coatings
Authors: Yang Q. , Zhao L. R.
Published: May 2003

This article reports the structure and hardness responses of TiN/CrN superlattice coatings to elevated-temperature annealing. Polycrystalline TiN/CrN superlattices with bilayer periods of 5.6–39 nm were deposited on a Ni-base alloy substrate by reactive unbalanced magnetron sputtering. The superlattices were subsequently annealed in vacuum at elevated temperatures for 2–100 h, followed by characterization using small-angle x-ray reflection, high-angle x-ray diffraction, and hardness testing. The superlattices can sustain their hardness up to 650 °C for 4 h or 575 °C for 100 h. A strong correlation exists between the hardness and the x-ray reflection or x-ray diffraction characteristics. A marked reduction in the high-angle satellite/Bragg peak ratio or in the small-angle reflection intensity corresponds to a rapid decrease in the hardness. This phenomenon is related to a physical transition during which the loss of hardness is caused by the structural instability resulting from accelerated interdiffusion between TiN and CrN layers, which leads to reduced compositional modulation amplitude and diffuse layer interfaces.
Beneficial influence of continuous ion bombardment during reactive sputter deposition of chromium nitride films
Authors: Janssen G. C. A. M. , Hoy R.
Published: May 2003

When spatial objects are coated by plasma vapor deposition (PVD) or reactive PVD the objects perform a planetary motion in front of one or more targets. Sputtering from the target is achieved by an intense ion bombardment from a plasma in front of the target. This plasma is concentrated in front of the target by a magnet assembly behind the target. Usually a bias voltage is applied to the substrate in order to obtain an ion bombardment during the deposition. The function of this ion bombardment is to supply energy to the growing film in order to arrive at dense films under compressive stress. In the present article it is shown that for high quality coatings on spatial objects it is mandatory to guarantee not only a bias voltage, but also a bias current during all times of the deposition. For the coating of spatial objects this is realized by using a second plasma source to fill all of the deposition chamber with plasma.
X-ray photoelectron spectroscopy and static secondary ion mass spectroscopy study of activation mechanism of Zr–V low activation temperature nonevaporable getter films
Authors: Mas̆ek Karel , S̆utara Frantis̆ek , Skála Tomás̆ , Drbohlav Jir̆ı́ , Veltruská Kater̆ina , Matolı́n Vladimı́r
Published: May 2003

Thin films of the Zr–V alloy getter films were prepared on stainless steel substrates by magnetron sputtering. The getter activation behavior was investigated by x-ray photoelectron spectroscopy, static secondary ion mass spectroscopy, electron energy loss spectroscopy, and molecular beam technique. All measurements reflect the disappearance of the superficial oxide layer covering air exposed Zr–V surfaces via consecutive variation of the oxide stoichiometry during thermal activation. The adsorbed carbon is transformed simultaneously to carbides. During the activation heating hydrogen diffuses toward the surface forming surface hydride and hydroxyl groups. Although the detectable activation proceeds already at temperatures above 160 °C, the activation process is reasonably fast (a few hours) at higher temperatures (above 200 °C).
Modeling high power magnetron copper seed deposition: Effect of feature geometry on coverage
Authors: Stout Phillip J. , Zhang Da , Ventzek Peter L. G.
Published: May 2003

The deposition of copper using a high power magnetron (HPM) has been studied using reactor and feature scale models. Discussed are results for Cu seed HPM deposition on trench, via, and dual inlaid features with different geometries (aspect ratio and side wall angles). At low wafer powers the Cu seed feature coverage is characterized by geometric shadowing due to the broad angular distribution of the dominant Cu athermal. At high wafer powers the metal deposited at feature bottom is sputtered by Ar+ and redistributed to the side walls. The deposition rate within a feature is nonlinear with time as metal deposited at the feature opening obstructs incoming metal from reaching the inside of the feature. Competing trends of higher copper flux at wafer center versus edge and higher Ar+ flux at wafer center versus edge result in a transition of the field thickness heights from edge>center at low wafer powers to center<edge at high wafer powers. The type and geometry of a feature in which metal is being deposited plays a major role in the final metal coverage. Vias have less coverage than trenches given the smaller opening for incoming metal to enter. For instance trenches with aspect ratio (AR) equal to 4 still have more Cu side wall coverage than vias of AR=1. In the dual inlaid geometry studied the via inner side wall and trench bottom corners are the most difficult regions to deposit a Cu seed. Both side wall angle and AR can have equal control of a thickness change. For instance in a via a similar side wall thickness decrease (at low wafer power) can be achieved with AR=4 and θvia=4°–0° or AR=1–4 and θvia=4°.
Physical and electrical properties of low temperature (<100 °C) SiO2 films deposited by electron cyclotron resonance plasmas
Authors: Rashid R. , Flewitt A. J. , Robertson J.
Published: May 2003

Silicon dioxide (SiO2) films have been deposited at temperatures less than 100 °C in an electron cyclotron resonance (ECR) plasma reactor from a gas phase combination of O2, SiH4, and He. The ECR configuration provides a highly ionized plasma density with low ion energies that gives efficient dehydrogenation of the growing material while minimizing defect creation. The effects of the O2/SiH4 gas flow ratio and He gas flow rate, microwave power and gas pressure on the physical and electrical properties of the film are reported. The physical characterization of the material gives a refractive index of 1.45, an etch rate in buffered HF below 3 nm/s and a hydrogen content of less than 2 at. %. Electrical tests reveal a resistivity in excess of 1014 Ω cm, an average breakdown strength of 4 MV/cm, fixed charge and interface state densities of 1011 cm−2 and 1012 eV−1 cm−2, respectively. This has been mainly achieved by using a O2/SiH4 gas flow ratio of about 2, while working in the low pressure regime below 5 mTorr and at moderate microwave powers of up to 1000 W. A strong correlation between the physiochemical and electrical properties of the deposited film was observed over the entire range of process parameters.
Monitoring and purging dynamics of trace gaseous impurity in atmospheric pressure rapid thermal process
Authors: Hu Yao Zhi , Tay Sing Pin
Published: May 2003

The residual impurity gases in the atmospheric pressure processing equipment are becoming an important factor in the submicron ultralarge scale integrated industry. The present article includes three parts: (1) Ti-coated wafer for monitoring of trace O2, (2) O2 sensor and residual gas analyzer experimental study for real time monitoring of trace O2 under various purging conditions, and (3) dynamic investigation of trace gaseous impurity dependence on purging gas flow rate and gas type in various rapid thermal processing (RTP) chambers. Ti-coated wafer discoloration is used widely for trace O2 monitoring in the RTP industry. A quantitative relationship between the discoloration of a Ti-coated wafer and O2 concentration was obtained in this study under the conditions of O2 contents of 0, 0.2, 1, 3, 5, 10, and 100 ppm in an N2 ambient, indicating that the discoloration sensitivity is about 3 ppm. This article presents a semiempirical purging equation, called the pseudo-PST (“perfectly stirred tank”) model, which gives the dependence of the trace gaseous impurity on purging time, process gas flow rate, and chamber volume in an atmospheric processing system. The model has been tested in five chamber configurations, including rectangular and cylindrical chambers, with and without inlet gas diffusers. A correction factor, γ, called perfectly stirring coefficient was used in the modeling equations. The γ values of 0.71–1.49 have been determined for different chamber configurations. The agreement between experimental and modeling results has been confirmed. The effect of wafer rotation, gas type, gas trap, and air leaks on impurity purging are also discussed.
SiO
2
etching with perfluorobutadiene in a dual frequency plasma reactor
Authors: Fracassi F. , d’Agostino R. , Fornelli E. , Illuzzi F. , Shirafuji T.
Published: May 2003

The plasma etching of SiO2 has been investigated in perfluorobutadiene-oxygen containing plasmas using a homemade dual frequency reactor. The process has been characterized by evaluating SiO2 etch rate, SiO2-to-Si selectivity, the surface contamination of Si, and the atmospheric emission of greenhouse gases. The plasma phase has been studied by means of optical emission spectroscopy. Perfluorobutadiene appears to be promising for replacing conventional high global warming potential reactants in SiO2 dry etching.
Mathematical model for predicting molecular-beam epitaxy growth rates for wafer production
Authors: Shi B. Q.
Published: May 2003

An analytical mathematical model for predicting molecular-beam epitaxy (MBE) growth rates is reported. The mathematical model solves the mass-conservation equation for liquid sources in conical crucibles and predicts the growth rate by taking into account the effect of growth source depletion on the growth rate. Assumptions made for deducing the analytical model are discussed. The model derived contains only one unknown parameter, the value of which can be determined by using data readily available to MBE growers. Procedures are outlined for implementing the model in MBE production of III–V compound semiconductor device wafers. Results from use of the model to obtain targeted layer compositions and thickness of InP-based heterojunction bipolar transistor wafers are presented.
Hydrogen elimination reactions in the thermal decomposition of alcohols on Si(100) surfaces
Authors: Yoon Won J. , Lee Jae P. , Park Gyoosoon , Park Chan R. , Kwak Hyon T. , Sung Myung M.
Published: May 2003

The thermal decomposition of 1-pentanol and 2-methyl-1-butanol on clean Si(100)-2×1 in an ultrahigh vacuum has been examined using temperature programmed desorption, intergrated desorption mass spectrometry, and low-energy electron diffraction. The results show that the alkoxy species formed on Si(100) are stable up to temperatures of about 480 K. Above 500 K, the alkoxy species decompose on Si(100) via the γ-hydrogen elimination mechanism to yield alkene in the gas phase, together with adsorbed hydrogen. The H2 gas is evolved by the recombinative desorption of hydrogen atoms that are generated by the adsorption of alcohols and/or the decomposition of alkoxy species. The H2 thermal desorption exhibits a peak near 800 K, which indicates that the H2 gas is evolved from the monohydride phase on Si(100).
Influence of energetic bombardment on stress, resistivity, and microstructure of indium tin oxide films grown by radio frequency magnetron sputtering on flexible polyester substrates
Authors: Carcia P. F. , McLean R. S. , Reilly M. H. , Li Z. G. , Pillione L. J. , Messier R. F.
Published: May 2003

Using rf magnetron sputtering, we have identified conditions for growing indium tin oxide (ITO) thin films at room temperature that simultaneously exhibit low resistivity (∼3×10−4 Ω cm), high optical transparency (>80%), and near-zero stress on polyester substrates. From transport measurements, we deduced that Sn donor atoms had little effect on electrical conduction in ITO films. We further concluded from an analysis of sputtered ions and atoms that bombardment by energetic (>35 eV) negative oxygen ions caused high stress (∼1 GPa) in films grown at lower (6 mTorr) pressure. We further concluded that bombardment by lower-energy (1–2 eV) sputtered oxygen species at the growing film surface was likely responsible for the dependence of ITO crystallization and microstructure on oxygen partial pressure during deposition.
Optical and structural studies of hydride vapor phase epitaxy grown GaN
Authors: Chang Y. C. , Cai A. L. , Muth J. F. , Kolbas R. M. , Park M. , Cuomo J. J. , Hanser A. , Bumgarner J.
Published: May 2003

Thick films of hydride vapor phase epitaxy (HVPE) grown GaN were studied by various techniques. Time-integrated and time-resolved photoluminescence (PL) measurements were performed at room temperature and 77 K. The time-integrated PL spectrum has no observed deep-level transitions and a very narrow linewidth, which indicates good material quality. Time-resolved PL spectra are also presented and the temporal evolution of the PL around the band-gap exhibits a biexponential decay with a fast and a slow decay component. Cathodoluminescence, x-ray, and Raman spectroscopy were also used. The full width half maximum of the x-ray rocking curve for our sample is approximately 375 arcsec. The polarized Raman spectra exhibited only the allowed modes. The deposited GaN films were found to be relatively stress free. The x ray and Raman analysis also revealed that the HVPE-grown GaN films are of high crystal quality. The effect of thermal annealing on the sample was also investigated by time-integrated and time-resolved PL and Raman spectroscopy. No significant changes in the material were observed in either time-integrated or Raman spectroscopy. The film was thermally stable upon annealing up to 1000 °C in N2 ambient based on the results of these measurements. In time-resolve photoluminescence measurement, the temporal evolution of the band-edge transitions broadens after each annealing step and is significantly different after the 1000 °C anneal.
Compensation for transient chamber wall condition using real-time plasma density feedback control in an inductively coupled plasma etcher
Authors: Klimecky Pete I. , Grizzle J. W. , Terry Fred L.
Published: May 2003

Reactive ion etch processing is known to exhibit significant variability in final etch performance due to wall condition. Previous studies have shown that neutral species transients depend strongly upon chamber seasoning. In this article, we show simultaneous measurements of wall-state-induced changes in plasma density and poly-Si etch rate, and demonstrate a real-time feedback control system that corrects for the plasma density variation. We demonstrate that controlling the plasma density to constant value eliminates the classic “first wafer effect” in Cl2 etching of poly-Si in a Lam 9400 transformer coupled plasma (TCP). Chamber conditions studied include fluorination/cleaning by C2F6 plasmas compared to chlorination/deposition from Cl2 plasmas. Transient density changes due to wall condition were measured using a microwave resonance cavity technique called broadband rf. Following chamber fluorination, broadband data show a significant drop in electron density (∼39%) from nominal levels. This is followed by subsequent partial recovery of the nominal density during a 60 s Cl2 etch. Independent measurements correlate strongly with the broadband signals; particularly real-time poly-Si etch rate and SiCl4 etch product concentration. Observed real-time variations in all signals were then compensated using a single input/single output proportional-integral (PI) feedback control algorithm, in which the broadband peak frequency is the system output variable and TCP power is the system actuator. Such PI control not only stabilizes broadband peak frequencies, but also steadies poly-Si real-time etch rate and SiCl4 etch product concentration. This compensation scheme is then applied over multiple runs to reduce etch depth variability due to chamber condition. Results of this control system are shown to attenuate first wafer effects by a factor of 3 and reduce overall etch depth variation from run to run by an additional 33% compared to standard manufacturing practice. When applied to patterned wafer etches, feedback control of plasma density with an oxide hardmask is found not to alter critical dimensions or profile in any observable way. Only total etch depth appears to be affected using density control, as the real-time etch rate is in general increased in comparison to open-loop etching.
Low temperature crystallization of germanium on plastic by externally applied compressive stress
Authors: Hekmatshoar B. , Shahrjerdi D. , Mohajerzadeh S. , Khakifirooz A. , Goodarzi A. , Robertson M.
Published: May 2003

The conventional Cu-induced crystallization of a-Ge has been facilitated by different types of external stress mechanically applied to the flexible substrate. It has been observed that in the case of compressive stress, crystallization becomes possible at temperatures as low as 130 °C and evolves as stress becomes more stringent. High electrical conductance and a hole mobility of 110 cm2/V s show the crystallinity of the Ge film, further confirmed by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses. The temperature of the annealing process (between 130 and 180 °C) expedites the process (from 6 to 1 h) as it is increased, but the principal mechanism seems to be independent of temperature. Temperatures higher than 180 °C are detrimental to the plastic substrate, polyethylene terephthalate. Evolution of cracks in Ge layer has been studied as the main consequence of the interfacial stress between Ge layer and substrate. The crack density was minimized by patterning the a-Ge layer before annealing. The main explanation of the physical phenomenon accounting for crystallization is believed to be the externally applied compressive stress, which reinforces the inherently present internal stress between the layer and the substrate.
Role of molecular diffusion in the theory of gas flow through crimped-capillary leaks
Authors: Bach H. T. , Meyer B. A. , Tuggle D. G.
Published: May 2003

Gas flow through crimped-capillary leaks was studied with the use of a mass spectrometric system. The crimped-capillary leak was used as a single-stage pressure-reduction device between a gas inlet manifold and an ultrahigh-vacuum mass spectrometer. The steady state flows of binary gas mixtures (H2–4He and H2–D2) through the crimped-capillary leak into the mass spectrometer vacuum chamber (<10−9 Torr) were characterized over a pressure range from 5 to 5000 Torr. At pressures <5 and >1500 Torr, the gas flow is close to Knudsen diffusion (molecular flow) and viscous flow, respectively. The transition from the Knudsen diffusion to viscous flow takes place over 2 decades of pressure and is at a lower pressure range than can be explained by the combined Knudsen diffusion and viscous flow theories. This article considers the contribution of molecular diffusion (ordinary diffusion) to the theory of gas flow through crimped-capillary leak and presents a mathematical model for a multicomponent gas mixture. This model successfully predicts gas flow over a wide range of pressures especially in the transition flow regime for binary gas mixtures.
High-temperature stability of nichrome in reactive environments
Authors: Zhou J. , Ohno T. R. , Wolden C. A.
Published: May 2003

Nichrome, the commercially available nickel–chromium alloy, was employed in the hot-wire chemical vapor deposition (HWCVD) of Teflonlike thin films. The stability and reactivity of this material under HWCVD conditions was studied using measurements of deposition rates, electrical resistance, and x-ray photoelectron spectroscopy (XPS). It was found that under HWCVD conditions, the performance of Nichrome 80 declined for approximately 5 h before stabilizing. The stabilized ribbons could then be used for another 5 h before the ribbons experienced mechanical failure. The transient behavior was attributed to preferential oxidation of chromium and subsequent segregation of nickel. Substantial differences were observed in the behavior of the Nichrome 60 and 80 alloys, which was attributed to differences in the phase stability of these two materials.
Activation of Integrin αIIbß3 by Modulation of Transmembrane Helix Associations
Authors: Li Renhao , Mitra Neal , Gratkowski Holly , Vilaire Gaston , Litvinov Rustem , Nagasami Chandrasekaran , Weisel John W. , Lear James D. , DeGrado William F. , Bennett Joel S.
Published: May 2003

Transmembrane helices of integrin α and β subunits have been implicated in the regulation of integrin activity. Two mutations, glycine-708 to asparagine-708 (G708N)and methionine-701 to asparagine-701, in the transmembrane helix of the β3 subunit enabled integrin αIIbβ3 to constitutively bind soluble fibrinogen. Further characterization of the G708N mutant revealed that it induced αIIbβ3 clustering and constitutive phosphorylation of focal adhesion kinase. This mutation also enhanced the tendency of the transmembrane helix to form homotrimers. These results suggest that homomeric associations involving transmembrane domains provide a driving force for integrin activation. They also suggest a structural basis for the coincidence of integrin activation and clustering.
Supramolecular Self-Assembly of Lipid Derivatives on Carbon Nanotubes
Authors: Richard Cyrille , Balavoine Fabrice , Schultz Patrick , Ebbesen Thomas W. , Mioskowski Charles
Published: May 2003

Images of the assembly of surfactants and synthetic lipids on the surface of carbon nanotubes were obtained by transmission electron microscopy. Above the critical micellar concentration, sodium dodecyl sulfate (SDS) forms supramolecular structures made of rolled-up half-cylinders on the nanotube surface. Depending on the symmetry and the diameter of the carbon nanotube, we observed rings, helices, or double helices. Similar self-assemblies were also obtained with several synthetic single-chain lipids designed for the immobilization of histidine-tagged proteins. At the nanotube-water interface, permanent assemblies were produced from mixed micelles of SDS and different water-insoluble double-chain lipids after dialysis of the surfactant. Such arrangements could be further exploited for the development of new biosensors and bioelectronic nanomaterials.
Synthesis of Inorganic Fullerene-Like Molecules
Authors: Bai Junfeng , Virovets Alexander V. , Scheer Manfred
Published: May 2003

The reaction of [Cp*Fe(η
5
-P
5
)] with Cu(I)Cl in solvent mixtures of CH
2
Cl
2
/CH
3
CN leads to the formation of entirely inorganic fullerene-like molecules of the formula [{Cp*Fe(η
5
:η
1
:η
1
:η
1
:η
1
:η
1
-P
5
)}
12
{CuCl}
10
{Cu
2
Cl
3
}
5
{Cu(CH
3
CN)
2
}
5
] (1) possessing 90 inorganic core atoms. This compound represents a structural motif similar to that of C
60
:
cyclo
-P
5
rings of [Cp*Fe(η
5
-P
5
)] molecules are surrounded by six-membered P
4
Cu
2
rings that result from the coordination of each of the phosphorus lone pairs to CuCl metal centers, which are further coordinated by P atoms of other
cyclo
-P
5
rings. Thus, five- and six-membered rings alternate in a manner comparable to that observed in the fullerene molecules. The so-formed half shells are joined by [Cu
2
Cl
3
]
–
as well as by [Cu(CH
3
CN)
2
]
+
units. The spherical body has an inside diameter of 1.25 nanometers and an outside diameter of 2.13 nanometers, which is about three times as large as that of C
60
.
Electrically Induced Optical Emission from a Carbon Nanotube FET
Authors: Misewich J. A. , Martel R. , Avouris Ph. , Tsang J. C. , Heinze S. , Tersoff J.
Published: May 2003

Polarized infrared optical emission was observed from a carbon nanotube ambipolar field-effect transistor (FET). An effective forward-biased p-n junction, without chemical dopants, was created in the nanotube by appropriately biasing the nanotube device. Electrical measurements show that the observed optical emission originates from radiative recombination of electrons and holes that are simultaneously injected into the undoped nanotube. These observations are consistent with a nanotube FET model in which thin Schottky barriers form at the source and drain contacts. This arrangement is a novel optical recombination radiation source in which the electrons and holes are injected into a nearly field-free region. Sucha source may form the basis for ultrasmall integrated photonic devices.
GABA and Its Agonists Improved Visual Cortical Function in Senescent Monkeys
Authors: Leventhal Audie G. , Wang Yongchang , Pu Mingliang , Zhou Yifeng , Ma Yuanye
Published: May 2003

Human cerebral cortical function degrades during old age. Much of this change may result from a degradation of intracortical inhibition during senescence. We used multibarreled microelectrodes to study the effects of electrophoretic application of γ-aminobutyric acid (GABA), the GABA type a (GABAa) receptor agonist muscimol, and the GABAa receptor antagonist bicuculline, respectively, on the properties of individual V1 cells in old monkeys. Bicuculline exerted a much weaker effect on neuronal responses in old than in young animals, confirming a degradation of GABA-mediated inhibition. On the other hand, the administration of GABA and muscimol resulted in improved visual function. Many treated cells in area V1 of old animals displayed responses typical of young cells. The present results have important implications for the treatment of the sensory, motor, and cognitive declines that accompany old age.
A Framework for Vision's Bag of Tricks
Authors: Billock Vincent A.
Published: May 2003

Why We See What We Do
An Empirical Theory of Vision. Dale Purves and R. Beau Lotto. Sinauer Associates, Sunderland, MA, 2003. 272 pp. Paper, $42.95. ISBN 0-87893-752-8.

The authors marshal a broad range of evidence to support their conclusion that "what humans actually see is a reflexive manifestation of past rather than a logical analysis of the present."
Diverse Plant and Animal Genetic Records from Holocene and Pleistocene Sediments
Authors: Willerslev Eske , Hansen Anders J. , Binladen Jonas , Brand Tina B. , Gilbert M. Thomas P. , Shapiro Beth , Bunce Michael , Wiuf Carsten , Gilichinsky David A. , Cooper Alan
Published: May 2003

Genetic analyses of permafrost and temperate sediments reveal that plant and animal DNA may be preserved for long periods, even in the absence of obvious macrofossils. In Siberia, five permafrost cores ranging from 400,000 to 10,000 years old contained at least 19 different plant taxa, including the oldest authenticated ancient DNA sequences known, and megafaunal sequences including mammoth, bison, and horse. The genetic data record a number of dramatic changes in the taxonomic diversity and composition of Beringian vegetation and fauna. Temperate cave sediments in New Zealand also yielded DNA sequences of extinct biota, including two species of ratite moa, and 29 plant taxa characteristic of the prehuman environment. Therefore, many sedimentary deposits may contain unique, and widespread, genetic records of paleoenvironments.
Is Altered Adrenal Steroid Biosynthesis a Key Intermediate Phenotype in Hypertension?
Authors: Connell John M.C. , Fraser Robert , MacKenzie Scott , Davies Eleanor
Published: May 2003

Approximately 10% of patients with hypertension have a high ratio of aldosterone to renin, but the reason for this and the relationships among low-renin essential hypertension, elevation of the ratio, and true primary aldosteronism are unclear. We have previously reported that a polymorphism of the gene (C-to-T conversion at position −344) encoding aldosterone synthase is associated with hypertension, particularly in patients with a high ratio. However, the most consistent association with this variant is a relative impairment of adrenal 11β-hydroxylation. In this review, we propose that altered conversion of deoxycortisol to cortisol leads to a subtle, chronic increase in adrenocortrophin drive to the adrenal cortex, with eventual development of hyperplasia. In combination with other genetic or environmental factors (such as dietary sodium intake), we suggest that this might be responsible for the long-term development of a resetting of the aldosterone response to angiotensin II, giving rise to the phenotype of hypertension with a raised ratio. In some subjects, this may progress further to true primary aldosteronism with a dominant adrenal nodule. Thus, there may be a genetically influenced continuum from hypertension with a normal ratio, through hypertension with a raised ratio, and primary aldosteronism.
Segment of Rat Chromosome 20 Regulates Diet-Induced Augmentations in Adiposity, Glucose Intolerance, and Blood Pressure
Authors: Pausova Zdenka , Sedova Lucie , Berube Julie , Hamet Pavel , Tremblay Johanne , Dumont Marc , Gaudet Daniel , Pravenec Michal , Kren Vladimir , Kunes Jaroslav
Published: May 2003

Previous linkage and association studies have suggested that a region of human chromosome 6 containing the tumor necrosis factor (TNF)-α gene is involved in the pathogenesis of obesity and obesity-associated hypertension. The aim of the present investigation was to establish whether a segment of rat chromosome 20 (RNO20), which also contains the TNF-α gene, determines diet-induced changes in adiposity and blood pressure (BP). The results showed that a transfer of the RNO20 segment from the normotensive Brown Norway (BN) rat onto the background of the spontaneously hypertensive rat (SHR) is associated with a significantly greater increase in adiposity, glucose intolerance, circulating leptin levels, and BP during 12-week, high-fat-diet feeding. In contrast, the transfer is not associated with significant changes in these variables during 12-week, normal-diet feeding. In addition, sequencing of the TNF-α gene revealed differences between SHR and BN in the 5′- and 3′-regulatory regions of the gene. Subsequent analyses of TNF-α gene expression in fat, muscle, and liver, however, did not provide support for the functional involvement of these differences. In summary, the investigated RNO20 segment contains 1 or more gene variants that affect adiposity, glucose tolerance, serum leptin levels, and BP, but only when the animals are exposed to a particular environment, ie, high-fat-diet feeding. Further studies are needed to identify genes mediating these effects. Considering current changes in our lifestyle involving an increased calorie and fat intake, we believe that gene-environment interactions, such as those described here, play an important role in the current epidemic of obesity and obesity-associated hypertension.
AT
1
-Receptor Antagonism Improves Endothelial Function in Coronary Artery Disease by a Bradykinin/B
2
-Receptor-Dependent Mechanism
Authors: Hornig Burkhard , Kohler Christoph , Schlink Daniel , Tatge Helma , Drexler Helmut
Published: May 2003

Impaired flow-dependent, endothelium-mediated vasodilation is an early finding in patients with coronary artery disease (CAD). Experimental and some clinical studies observed that angiotensin type-1 receptor antagonists (AT
1
A) enhance endothelium-dependent relaxation in CAD. The present study was designed to determine whether AT
1
A improves flow-dependent dilation (FDD) in patients with CAD and, if so, whether bradykinin and NO are involved. High-resolution ultrasound was used to measure radial artery diameter at rest and during reactive hyperemia, causing endothelium-mediated vasodilation. Twenty patients with CAD were randomly assigned to receive intrabrachial infusion of candesartan (800 μg/min) with and without icatibant, a bradykinin B
2
-receptor antagonist (90 μg/min; group A) or
N
-monomethyl-
l
-arginine (L-NMMA), an NO-synthase inhibitor (7 μmol/min; group B). The AT
1
A candesartan improved FDD by >40%, an effect that was inhibited by icatibant (group A: control, 7.3±0.9; candesartan, 10.3±1.1; candesartan+icatibant, 5.0±0.5%). Similarly, L-NMMA blunted the beneficial effect of candesartan (group B: control, 6.3±0.6; candesartan, 8.9±0.6; candesartan+L-NMMA: 4.7±0.5%; each
P
<0.01). The angiotensin type-1 receptor antagonist candesartan improves flow-dependent, endothelium-mediated vasodilation in patients with CAD. This effect is inhibited by either icatibant and or L-NMMA, suggesting that both bradykinin and NO contribute to the vascular effects of AT
1
-receptor antagonists in this patient population.
Estrogen Depletion Increases Blood Pressure and Hypothalamic Norepinephrine in Middle-Aged Spontaneously Hypertensive Rats
Authors: Peng Ning , Clark John T. , Wei Chi-Chang , Wyss J. Michael
Published: May 2003

In male spontaneously hypertensive rats (SHR) a high NaCl diet increases arterial pressure via a reduction in anterior hypothalamic nucleus norepinephrine release. Young female SHR are relatively well protected from this NaCl-sensitive hypertension, but depletion of both endogenous and dietary estrogens greatly exacerbates NaCl-sensitive hypertension. This study tests the hypothesis that estrogen also protects late middle-aged female SHR from NaCl-sensitive hypertension and that this effect is mediated by an estrogen-related effect on hypothalamic norepinephrine release. Ten-month-old female SHR were ovariectomized and placed on a phytoestrogen-free diet containing either basal or high NaCl. Each rat was implanted with a silastic tube containing 17β estradiol or vehicle. Three months later, arterial pressure and hypothalamic norepinephrine metabolite levels (MOPEG) were measured. On the basal NaCl diet, estrogen-depleted rats displayed increased arterial pressure (12 mm Hg) and decreased anterior hypothalamic nucleus MOPEG (20%). Both effects were reversed by estrogen treatment. In all groups, the high NaCl diet increased arterial pressure by over 35 mm Hg and reduced anterior hypothalamic nucleus MOPEG by >60%. Across all groups, there was a significant inverse correlation between arterial pressure and anterior hypothalamic nucleus MOPEG. These data suggest that both dietary NaCl excess and estrogen depletion raise arterial pressure in middle-aged female SHR by a decreasing hypothalamic norepinephrine.
Long-Term Regulation of ENaC Expression in Kidney by Angiotensin II
Authors: Beutler Kathleen T. , Masilamani Shyama , Turban Sharon , Nielsen Jakob , Brooks Heddwen L. , Ageloff Shana , Fenton Robert A. , Packer Randall K. , Knepper Mark A.
Published: May 2003

We carried out semiquantitative immunoblotting of kidney to identify apical sodium transporter proteins whose abundances are regulated by angiotensin II. In NaCl-restricted rats (0.5 mEq Na/200 g BW/d), the type 1 angiotensin II receptor (AT
1
receptor) antagonist, candesartan, (1 mg/kg of body weight per day SC for 2 days) markedly decreased the abundance of the α subunit of the epithelial sodium channel (ENaC). This subunit has been shown to be rate-limiting for assembly of mature ENaC complexes. In addition, systemic infusion of angiotensin II increased αENaC protein abundance in rat kidney cortex. The decrease in αENaC protein abundance in response to AT
1
receptor blockade was associated with a fall in αENaC mRNA abundance (real-time RT-PCR), consistent with transcriptionally mediated regulation. The effect of AT
1
receptor blockade on αENaC expression was not blocked by spironolactone, suggesting a direct role of the AT
1
receptor in regulation of αENaC gene expression. Candesartan administration was also found to increase the abundances of the β and γ subunits. The increase in β and γENaC protein abundance was not associated with a significant increase in the renal abundances of the corresponding mRNAs, suggesting a posttranscriptional mechanism. Immunocytochemistry confirmed the increase in β and γENaC protein abundance and demonstrated candesartan-induced ENaC internalization in collecting duct cells. The results support the view that the angiotensin II receptor regulates ENaC abundance, consistent with a role for angiotensin II in regulation of collecting duct function.
Mislocalization of eNOS and Upregulation of Cerebral Vascular Ca
2+
Channel Activity in Angiotensin-Hypertension
Authors: Gerzanich Volodymyr , Ivanova Svetlana , Zhou Hui , Simard J. Marc
Published: May 2003

We tested the hypothesis that endothelial dysfunction induced by angiotensin II (Ang-hypertension) would impair regulatory control of vascular smooth muscle L-type Ca
2+
channels by endothelial nitric oxide synthase (eNOS). We studied cerebral lenticulostriate arterioles (LSAs) from control rats, from rats infused with Ang (240 μg · kg
−1
· h
−1
SQ ×4 days), which were normotensive, and from Ang-hypertensive rats (AHR; 240 μg · kg
−1
· h
−1
×28 days). Patch-clamp measurements on isolated LSA smooth muscle cells (SMCs) showed a significant increase in Ca
2+
channel availability with 4- and 28-day infusions versus controls (0.47±0.03 and 0.66±0.05 vs 0.36±0.03 pS/pF, respectively;
P
<0.01), with Western blots showing no change in channel protein expression, consistent with altered channel regulation. In LSAs from 28-day AHR, 4,5-diaminofluorescein diacetate imaging showed diminished NO production in response to acetylcholine stimulation in vivo, and inhibition of eNOS with
N
G
-nitro-
l
-arginine methyl ester failed to increase Ca
2+
channel availability in isolated SMCs, indicating an abnormality with the eNOS/NO-signaling pathway regulating the channel. Immunofluorescence imaging showed that in 1 of 53, 33 of 109, and 53 of 62 LSAs from controls and from rats with 4- and 28-day infusions, respectively, eNOS was absent from its normal location at the abluminal border and was mislocalized to perinuclear Golgi. Ca
2+
channel availability in LSA SMCs from controls and from rats with 4- and 28-day infusions was proportional to the fraction of LSAs showing eNOS mislocalization, but not blood pressure. These data provide the first evidence linking Ang-induced eNOS mislocalization, eNOS dysfunction, and Ca
2+
channel upregulation, and they provide novel mechanistic insights into pathological changes in LSAs associated with stroke.
Interactions Between Leptin and the Human Sympathetic Nervous System
Authors: Eikelis Nina , Schlaich Markus , Aggarwal Anuradha , Kaye David , Esler Murray
Published: May 2003

Results from animal experimentation suggest a 2-way interaction between leptin and the sympathetic nervous system, with leptin causing sympathetic activation and conversely, with the sympathetic system exercising regulatory feedback inhibition over leptin release. We have now tested this hypothesis in humans. In the absence of results from leptin infusions, to test for sympathetic stimulation of leptin release, we sought a quantitative naturalistic linkage of sympathetic activity with leptin plasma concentration across a broad range of leptin values in men of widely differing adiposity. Renal norepinephrine spillover was correlated with plasma leptin (
r
=0.628,
P
<0.01), but other measures of sympathoadrenal function did not. To test for sympathetic and adrenomedullary inhibition of leptin release, we studied clinical models of high sympathetic tone, heart failure, and essential hypertension, in which lowered plasma leptin levels might have been expected but were not found; a model of low sympathetic activity, pure autonomic failure, in which plasma leptin level was normal (6.1±1.2 vs 12.8±3.1 ng/mL in healthy subjects); and a clinical model of reduced epinephrine secretion, healthy aging, in which plasma leptin level again was normal (5.7±1.1 ng/mL vs 4.0±0.9 ng/mL in men >60 years and <35 years, respectively). Paradoxically, leptin concentration was elevated in heart failure, caused entirely by reduced renal clearance of leptin release, 142.0±30.5 mL/min, compared with 56.9±18.9 mL/min (
P
<0.05). These results provide some support for the view that leptin stimulates the sympathetic nervous system, at least for renal sympathetic outflow, but do not confirm the concept of regulatory feedback inhibition of leptin release by the sympathetic nervous system.