bluuebunny/crossref_metadata_2025 huggingface dataset:
Direction selectivity in a model of the starburst amacrine cell
Authors: TUKKER JOHN J. , TAYLOR W. ROWLAND , SMITH ROBERT G.
Published: December 2004

The starburst amacrine cell (SBAC), found in all mammalian retinas,
is thought to provide the directional inhibitory input recorded in
On–Off direction-selective ganglion cells (DSGCs). While voltage
recordings from the somas of SBACs have not shown robust direction
selectivity (DS), the dendritic tips of these cells display
direction-selective calcium signals, even when γ-aminobutyric acid
(GABAa,c) channels are blocked, implying that inhibition is
not necessary to generate DS. This suggested that the distinctive
morphology of the SBAC could generate a DS signal at the dendritic
tips, where most of its synaptic output is located. To explore this
possibility, we constructed a compartmental model incorporating
realistic morphological structure, passive membrane properties, and
excitatory inputs. We found robust DS at the dendritic tips but not at
the soma. Two-spot apparent motion and annulus radial motion produced
weak DS, but thin bars produced robust DS. For these stimuli, DS was
caused by the interaction of a local synaptic input signal with a
temporally delayed “global” signal, that is, an excitatory
postsynaptic potential (EPSP) that spread from the activated inputs
into the soma and throughout the dendritic tree. In the preferred
direction the signals in the dendritic tips coincided, allowing
summation, whereas in the null direction the local signal preceded the
global signal, preventing summation. Sine-wave grating stimuli produced
the greatest amount of DS, especially at high velocities and low
spatial frequencies. The sine-wave DS responses could be accounted for
by a simple mathematical model, which summed phase-shifted signals from
soma and dendritic tip. By testing different artificial morphologies,
we discovered DS was relatively independent of the morphological
details, but depended on having a sufficient number of inputs at the
distal tips and a limited electrotonic isolation. Adding voltage-gated
calcium channels to the model showed that their threshold effect can
amplify DS in the intracellular calcium signal.
Spatial, temporal, and intensive determinants of dopamine release
in the chick retina
Authors: LUFT W.A. , IUVONE P.M. , STELL W.K.
Published: December 2004

The retinal dopaminergic system is a global regulator of retinal
function. Apart from the fact that the rates of dopamine synthesis and
release are increased by increasing illumination, the visual image
parameters that influence dopaminergic function are mostly unknown.
Roles for spatial and temporal frequency and image contrast are
suggested by the effects of form-deprivation with a diffusing goggle.
Form-deprivation reduces the rates of dopamine synthesis and release,
and induces myopia, which is prevented by dopamine agonists. Our
purpose here was to identify visual stimulus parameters that activate
dopaminergic amacrine cells and elicit dopamine release. White Leghorn
cockerels 4–7 days old were exposed to 2 h of form-deprivation,
reduced light intensity, or stimuli of varied temporal or spatial
frequency. Activation of dopaminergic neurons, labeled for tyrosine
hydroxylase (TH), was assessed with immunocytochemistry for c-Fos, and
dopamine release was measured by HPLC analysis of dopamine metabolite
accumulation in the vitreous body. Form-deprivation did not reduce TH+
cell activation or vitreal dopamine metabolite accumulation any more
than did neutral-density filters of approximately equal transmittance.
TH+ cell activation and vitreal metabolite accumulation were not
affected significantly by exposure to 2, 5, 10, 15, or 20 Hz
stroboscopic stimulation on a dark background, or by sine-wave gratings
of 0.089, 0.44, 0.89, 1.04, or 3.13 cycles/deg compared to a
uniform gray target of equal mean luminance. These data indicate that
the retinal dopaminergic system does not respond readily to short-term
changes in visual stimulus parameters, other than light intensity,
under the conditions of these experiments.
Retinal glucose metabolism in mice lacking the L-glutamate/aspartate transporter
Authors: SARTHY VIJAY P. , DUDLEY V. JOSEPH , TANAKA KOHICHI
Published: December 2004

The conventional view that glucose is the substrate for neuronal energy metabolism has been recently challenged by the “lactate shuttle” hypothesis in which glutamate cycling in glial cells drives all neuronal glucose metabolism. According to this view, glutamate released by activated retinal neurons is transported into Müller (glial) cells where it triggers glycolysis. The lactate released by Müller cells serves as the energy substrate for neuronal metabolism. Because the L-Glutamate/aspartate transporter (GLAST) is the predominant, Na+-dependent, glutamate transporter expressed by Müller cells, we have used GLAST-knockout (GLAST−/−) mice to examine the relationship between lactate release and GLAST activity in the retina. We found that glucose uptake and lactate production by theGLAST−/−mouse retina was similar to that observed in the wild type mouse retina. Furthermore, addition of 1 mM glutamate and NH4Cl to the incubation medium did not further stimulate glucose uptake in either case. When lactate release was measured in the presence of the lactate uptake inhibitor, α-cyano-4-hydroxycinnamate, there was no significant change in the amount of lactate released by retinas fromGLAST−/−mice compared to the wild type. Finally, lactate release was similar under both dark and light conditions. These results show that lactate production and release is not altered in retinas ofGLAST−/−mice, which suggests that metabolic coupling between photoreceptors and Müller cells is not mediated by the glial glutamate transporter, GLAST.
Characterization of inhibitory postsynaptic currents in rod bipolar cells of the mouse retina
Authors: FRECH MORITZ J. , BACKUS KURT H.
Published: December 2004

The synaptic terminals of mammalian rod bipolar cells are the targets of multiple presynaptic inhibitory inputs arriving from glycinergic and GABAergic amacrine cells. To investigate the contribution of these different inhibitory receptor types, we have applied the patch-clamp technique in acutely isolated slices of the adult mouse retina. By using the whole-cell configuration, we measured and analyzed the spontaneous postsynaptic currents (PSCs) in rod bipolar cells. The spontaneous synaptic activity of rod bipolar cells was very low. However, when amacrine cells were depolarized by AMPA or kainate, the PSC frequency in rod bipolar cells increased significantly. These PSCs comprised several types that could be distinguished by pharmacological and kinetic criteria. Strychnine-sensitive, glycinergic PSCs were characterized by a mean peak amplitude of −43.5 pA and a weighted decay time constant (τw) of 10.9 ms. PSCs that persisted in the presence of strychnine, but were completely inhibited by bicuculline, were mediated by GABAARs. They had a mean peak amplitude of −20.0 pA and a significantly faster τwof 5.8 ms. Few PSCs remained in the presence of strychnine and bicuculline, suggesting that they were mediated by GABACRs. These PSCs were characterized by much smaller amplitudes (−6.2 pA) and a significantly slower decay kinetics (τw= 51.0 ms). We conclude that rod bipolar cells express at least three types of functionally different inhibitory receptors, namely GABAARs, GABACRs, and GlyRs that may ultimately regulate the Ca2+influx into rod bipolar cell terminals, thereby modulating their glutamate release.
Experience-dependent changes in NMDAR1 expression in the visual
cortex of an animal model for amblyopia
Authors: MURPHY KATHRYN M. , DUFFY KEVIN R. , JONES DAVID G.
Published: December 2004

When normal binocular visual experience is disrupted during postnatal
development, it affects the maturation of cortical circuits and often
results in the development of poor visual acuity known as amblyopia.
Two main factors contribute to the development of amblyopia: visual
deprivation and reduced binocular competition. We investigated the
affect of these two amblyogenic factors on the expression of the NMDAR1
subunit in the visual cortex because activation of the NMDA receptor is
a key mechanism of developmental neural plasticity. We found that
disruption of binocular correlations by monocular deprivation promoted
a topographic loss of NMDAR1 expression within the cortical
representations of the central visual field and the vertical and
horizontal meridians. In contrast, binocular deprivation, which
primarily affects visual deprivation, promoted an increase in NMDAR1
expression throughout the visual cortex. These different changes in
NMDAR1 expression can be described as topographic and homeostatic
plasticity of NMDA expression, respectively. In addition, the changes
in NMDA expression in the visual cortex provide a greater understanding
of the neural mechanisms that underlie the development of amblyopia and
the potential for visual recovery.
“THE ANATOMY OF A BARRISTER'S TONGUE”: RHETORIC, SATIRE, AND THE VICTORIAN BAR IN ENGLAND
Authors: Schramm Jan-Melissa
Published: December 2004

IN THE HISTORY OF PENDENNIS(1848–50), William Thackeray calls upon the binary model of Victorian intellectualism in order to define the status and responsibilities of an author of fiction. For Thackeray, himself an initiate of the Middle Temple, the antagonist which permitted such a clarification of artistic privilege was the law, as conceived in utilitarian and mechanistic terms. Perhaps inspired by the ensign of the Inner Temple, the Winged Horse – suggestive of Thackeray's favorite trope for his own creativity, Pegasus-in-Harness – Thackeray effects a deft appropriation of the humanist history of the law for the services of literature, thus divorcing current legal praxis from its traditional role in the protection of liberties and the creation of English identity. Only the author can appreciate and animate the law's history, which is itself a tale of synergistic legal and literary productivity:
THE GHOST IN THE CLINIC: GOTHIC MEDICINE AND CURIOUS FICTION IN SAMUEL WARREN'SDIARY OF A LATE PHYSICIAN
Authors: Kennedy Meegan
Published: December 2004

IN 1856, WHEN MANY VICTORIAN PHYSICIANS WERE STRUGGLING TO DEFINE A MODEL OF CLINICAL MEDICINE, the reviewer of one collection of case histories voiced his dismay at the physician-author's preference for “dreadful incidents” and “cases exceptional and strange” (“Works” 473). Indeed, although physicians of the clinical era did not disguise their efforts to achieve a new kind of discourse, productive of a “realist” vision, few acknowledge how often the “clinical” case history of the nineteenth century also shares the romantic discourse of the Gothic, especially its interest in the supernatural and the unexplainable and its narrative aim of arousing suspense, horror, and astonishment in the reader. Literary critics have also focused primarily on the association of medical narrative with a realist literary discourse. Nineteenth-century physicians did campaign for the formal, objective, and professional clinical discourse that serves as their contribution to a realist aesthetic, in the process explicitly rejecting eighteenth-century medicine's fascination with “the curious” and its subterranean affiliation with the unknown, the unexplainable, and the subjective. But, as I show in this article, a discourse of “the curious,” allied with a Gothic literary aesthetic, stubbornly remained a critical element of many case histories, though it often presented under the mask of the more acceptable term, “interesting.” The discourse of Gothic romance in the case history provides a narrative frame that, unlike the essentially realist clinical discourse, could make sense of the physician's curious gaze, which had become nearly unrecognizable as a specifically medical vision. Indeed, a “curious” medical discourse haunts even case histories of the high clinical era, late in the century; and it energizes the nineteenth-century Gothic novel. Samuel Warren's novelPassages from the Diary of a Late Physician–deplored in the quotation above–illuminates this tradition of “Gothic medicine” as it plays out in the nineteenth-century novel. This tradition, I argue, provides the novel with a powerful model of cultural contamination and conflict in its yoking of disparate discourses. Gothic medicine demonstrates the importance of clinical medicine to literary romance, and it cannot help but reveal the ghost of “the curious” in the clinic.
EDWIN CHADWICK'S SELF-FASHIONING: PROFESSIONALISM, MASCULINITY, AND THE VICTORIAN POOR
Authors: Joshi Priti
Published: December 2004

IN THE PAST DECADE EDWIN CHADWICKhas been the subject of several scholarly inquiries; indeed one can almost speak of a “Chadwick industry” these days. This is not, however, the first time he has attracted significant scholarly attention: in 1952, S. E. Finer's and R. A. Lewis's biographies initiated our century's first evaluation of him, culminating in M. W. Flinn's excellently edited reprint of Chadwick's most important text,The Report on the Sanitary Condition of the Labouring Population of Great Britain(referred to as theSanitary Report). Yet the Chadwick that emerges in recent accounts could not be more different from the mid-century Chadwick. The post-war critics saw him as a visionary, an often-embattled crusader for public health whose enemies were formidable but whose vision, extending the liberal and radical tradition, ultimately prevailed. Cultural critics, on the other hand, present a Chadwick who misrepresented (if not outright oppressed) the poor and who was instrumental in developing a massive bureaucracy to police their lives. Thus, while earlier accounts highlighted Chadwick's accomplishments, the progress of public health reforms, and the details of legislative politics, more recent ones draw attention to his representations of the poor, the erasures in his text, and the growing nineteenth-century institutionalization of the poor that theSanitary Reportpromotes. Chadwick, in other words, is portrayed as either a pioneer of reform or an avatar of bureaucratic oppression.
CONVEX AND CONCAVE: CONCEPTUAL BOUNDARIES IN PSYCHOLOGY, NOW AND THEN (BUT MAINLY THEN)
Authors: Rylance Rick
Published: December 2004

MY TITLEis derived from G. H. Lewes's psychological magnum opusProblems of Life and Mind(1874–79). Lewes's image is a metaphor for the relation of mind to brain, or more generally of the mind to the nervous system: “every mental phenomenon has its corresponding neural phenomenon (the two being as convex and concave surfaces of the same sphere, distinguishable yet identical)” (Problems: First Series1: 112). His point is that, though the two entities can be analytically distinguished, they are as necessarily linked as the two surfaces of a bending plane. Like the recto and verso of a sheet of paper, or signifier and signified in the linguistic sign, one can make an interpretative separation of the two, but not an ontological one. It is a characteristically deft metaphor by Lewes to express a notoriously vexed relationship, not only in Victorian psychology but also in modern thinking today.
THE INVENTION OF AGORAPHOBIA
Authors: Trotter David
Published: December 2004

THE LAST THREE DECADESof the nineteenth century were phobia'sbelle époque. During this first phase of investigation there was, it must have seemed, no species of terror, however febrile, which could not talk its way immediately into syndrome status. In 1896, in hisPsychology of the Emotions, Théodule Ribot spoke of psychiatry's inundation by a “veritable deluge” of complaints ranging from the relatively commonplace and self-explanatory, such as claustrophobia, to the downright idiosyncratic, such as triakaidekaphobia, or fear of the number 13 (213). Twenty years later, in hisIntroductory Lectures on Psychoanalysis, Sigmund Freud was to respond with similar impatience to the list of phobias drawn up by the American psychologist Stanley Hall. Hall had managed to find 132 (446).
The architecture of William of Orange and the culture of friendship
Authors: Ronnes Hanneke
Published: December 2004

The grand houses and gardens of William of Orange (1650–1702) and his courtiers in Britain and the Netherlands are strongly influenced by the French style, itself associated with Louis XIV, who was actually William’s arch-rival. This paper explores that paradox by probing ideas of power and friendship in 17th-century court culture.
Sag mir wie schön und dominant meine Bekanntschaft ist
Authors: Greitemeyer Tobias , Fischer Peter
Published: December 2004

Zusammenfassung: Es wurde der Einfluss der Meinung anderer Personen auf Urteile bezüglich der Partnerwahlpräferenzen Dritter untersucht. Versuchspersonen erhielten ein Szenario, in dem eine handelnde Person einen potenziellen Partner kennen lernt, der von einer befreundeten Person des Handelnden hinsichtlich der physischen Attraktivität (niedrig vs. hoch) und Dominanz (niedrig vs. hoch) beurteilt wird. Die Versuchspersonen sollten angeben, ob die handelnde Person den Partner anrufen (kurzfristige Perspektive) würde bzw. an einer romantischen Beziehung (langfristige Perspektive) interessiert wäre. Die Versuchspersonen nahmen an, dass sich Männer vornehmlich von der Beurteilung der physischen Attraktivität beeinflussen lassen. Von Frauen wurde dagegen angenommen, dass sie bei einer kurzfristigen Perspektive besonderen Wert auf die physische Attraktivität legen, wogegen bei einer langfristigen Perspektive der potenzielle Partner sowohl attraktiv als auch dominant sein muss, dass sie Interesse an einer romantischen Beziehung verspüren.
Bistable emission of a black-body radiator
Authors: Redmond S. M. , Rand S. C. , Oliveira S. L.
Published: December 2004

Bistable black-body emission is reported from resonantly excited Er3+,Yb3+:Y2O3 nanopowders. A simple model based on thermo-optic nonlinear response in the strongly scattering random medium explains the observed behavior.
All-fiber integrated ∼10kW peak power ultrashort optical pulse source based on compression in aircore photonic band gap fiber
Authors: de Matos C. J. S , Kennedy R. E. , Taylor J. R.
Published: December 2004

We demonstrate an all-fiber integrated, ∼10kW peak power, ∼1ps optical pulse source at a wavelength of 1.55μm based on compression in aircore photonic band gap fiber. A 10GHz pulse train was modulated at 10MHz in a Mach–Zehnder amplitude modulator with a ∼1ns transmission window before stretching in 100m of dispersion compensating fiber, amplifying, and recompressing in 10m of aircore photonic band gap fiber. Numerical simulations show that if the aircore fiber dispersion slope could be made negligible, the achievable peak power would be increased by a factor of approximately 2.
Polarization-independent optical racetrack resonators using rib waveguides on silicon-on-insulator
Authors: Headley William R. , Reed Graham T. , Howe Simon , Liu Ansheng , Paniccia Mario
Published: December 2004

In an effort to find low-cost alternatives for components currently used in dense wavelength division multiplexing, optical ring resonators fabricated on silicon on insulator are currently being investigated. Their performance can be further enhanced if they are polarization independent. Herein we use rib waveguides to control the polarization properties of the devices and hence produce polarization-independent racetrack ring resonators. Transverse electric and transverse magnetic resonant peaks are measured to within 2 pm of one another over four cycles of the free spectral range. The racetrack resonators also exhibit measured Q factors of approximately 90 000 and finesse values of 12.
A new scheme to generalized (lag, anticipated, and complete) synchronization in chaotic and hyperchaotic systems
Authors: Yan Zhenya
Published: December 2004

In this paper, a generalized (lag, anticipated, and complete) synchronization of a class of continuous-time systems is defined. A systematic, powerful and concrete scheme is developed to investigate the generalized (lag, anticipated, and complete) synchronization between the drive system and response system based on the active control idea. The hyperchaotic Rössler system, transformed Rössler and Chen system as well as two coupled nonidentical Rössler oscillators are chosen to illustrate the proposed scheme. Numerical simulations are used to verify the effectiveness of the proposed scheme. The scheme can be also extended to research generalized (lag, anticipated, and complete) synchronization between other dynamical systems.
Wannier orbitals and bonding properties of interstitial and antisite defects in GaN
Authors: Gao F. , Bylaska E. J. , El-Azab A. , Weber W. J.
Published: December 2004

Intrinsic interstitial and antisite defects in GaN have been studied using density functional theory (DFT), and their configurations, electronic structures, and bonding properties have been characterized using the Wannier function. All N interstitial configurations eventually transform into N–N split interstitials, between which two π orbitals exist. The relaxation of a Ga antisite defect also leads to the formation of a N–N split configuration; however, its local Wannier orbitals are remarkably different from the N–N split interstitial. The different local Wannier orbitals around Ga interstitial configurations demonstrate that Ga interstitials are critical defects in GaN. The most striking feature is that Ga–Ga⟨112¯0⟩ split interstitials can bridge the gap between nonbonded Ga atoms, thereby leading to a chain of four metallic-like-bonded Ga atoms along the ⟨112¯0⟩ direction in GaN, which may exhibit quantum properties.
High permittivity Li and Al doped NiO ceramics
Authors: Lin Yuanhua , Wang Jianfei , Jiang Lei , Chen Yu , Nan Ce-Wen
Published: December 2004

High-permittivity dielectric NiO-based ceramics co-doped with Li and Al (LANO) have been prepared by a traditional solid-state synthesis. Analyses of the ceramic microstructure and composition indicate that Al ions are distributed in grain boundaries, and that uniform boundaries indexed as NiAl2O4 surround the grains. The concentration of Al has a remarkable effect on the dielectric properties of the LANO ceramics. The dielectric constant remains almost constant (∼104–105) at low frequency and has a steplike decrease toward higher frequencies. The high-dielectric-constant response of the LANO ceramics is mainly enhanced by Maxwell–Wagner polarization.
Surfactant free fabrication of polyimide nanoparticles
Authors: Xiong J. Y. , Liu X. Y. , Chen S. B. , Chung T. S.
Published: December 2004

Polyimide nanoparticles are fabricated using a combined liquid–liquid phase separation and solvent/nonsolvent mixing technology. This technology allows us to produce stable polyimide nanoparticles with tunable size without any surfactants. Selective solvation and electron pair donor/electron pair acceptor interaction are employed to stabilize nanoparticles. The formation of polyimide nanoparticles is governed by a nucleation-dominated process and therefore the particle size is controlled by the nucleation rate. A very high level of supersaturation can be attained under the intensive local motions induced by ultrasound, resulting in a very high nucleation rate. This effect is found extremely useful in the fabrication of sub-50-nm polyimide nanoparticles.
Interferometric differentiation between resonant coherent anti-Stokes Raman scattering and nonresonant four-wave-mixing processes
Authors: Marks Daniel L. , Vinegoni Claudio , Bredfeldt Jeremy S. , Boppart Stephen A.
Published: December 2004

A major impediment to the use of coherent anti-Stokes Raman scattering (CARS) to identify biological molecules is that the illumination levels required to produce a measurable signal often also produce significant nonresonant background from the medium, especially from water. We present a method of nonlinear interferometry to differentiate between which components of the anti-Stokes signal are resonant and nonresonant. The technique takes advantage of the persistence of intermediate states involved in the resonant process. This method is applicable to most existing pulsed CARS illumination methods and provides for identification of resonant CARS. We demonstrate the method by examining the signals produced by acetone, which exhibits resonance, and water, which does not.
Triggering and guiding of megavolt discharges by laser-induced filaments under rain conditions
Authors: Ackermann R. , Stelmaszczyk K. , Rohwetter P. , Méjean G. , Salmon E. , Yu J. , Kasparian J. , Méchain G. , Bergmann V. , Schaper S. , Weise B. , Kumm T. , Rethmeier K. , Kalkner W. , Wöste L. , Wolf J. P.
Published: December 2004

We demonstrate laser control of high-voltage discharges over a gap of 1.2 m filled with a dense water cloud. Self-guided filaments generated by ultrashort laser pulses are transmitted through the cloud and ionize a continuous plasma channel. The cloud typically reduces the discharge probability in given experimental conditions by 30%, but has almost no influence on the threshold required to trigger single discharge events, both in electrical field and laser energy. This result is favorable for real-scale lightning control applications.
Metal∕organic∕metal bistable memory devices
Authors: Tondelier D. , Lmimouni K. , Vuillaume D. , Fery C. , Haas G.
Published: December 2004

We report a bistable organic memory made of a single organic layer embedded between two electrodes, and compare to the organic∕metal nanoparticle∕organic tri-layers device [Ma, Liu, and Yang, Appl. Phys. Lett. 80, 2997 (2002)]. We demonstrate that the two devices exhibit similar temperature-dependent behaviors, a thermally activated behavior in their low conductive state (off-state) and a slightly “metallic” behavior in their high conductive state (on-state). This feature emphasizes a similar origin for the memory effect. Owing to their similar behavior, the one layer memory is advantageous in terms of fabrication cost and simplicity.
Structure and optical properties of Au-polyimide nanocomposite films prepared by ion implantation
Authors: Maggioni G. , Vomiero A. , Carturan S. , Scian C. , Mattei G. , Bazzan M. , Fernández C. de Julián , Mazzoldi P. , Quaranta A. , Della Mea G.
Published: December 2004

Au-polyimide nanocomposites have been synthesized by implanting different doses of Au+ ions in 100nm thick films of pyromellitic dianhydride-4,4′ oxydianiline polyimide, prepared by glow discharge vapor deposition polymerization. Unambiguous evidence of Au nanoclusters growth is found only at the highest implantation doses (5×1016Au+∕cm2). Structural, compositional, and optical characterizations show that the implantation induces the compactation of the initial film due to H and C loss. The resulting structure is a composite containing 2–3nm gold nanoparticles arranged in a layer of about 40nm and, just beneath the sample surface, a 15nm thick carbon-rich layer. Optical simulations suggest the presence of a gold-carbon core-shell structure in the nanoparticles.
Highly nonlinear contact interaction and dynamic energy dissipation by forest of carbon nanotubes
Authors: Daraio Chiara , Nesterenko Vitali F. , Jin Sungho
Published: December 2004

Mechanical response and energy dissipation of an array of carbon nanotubes under high-strain rate deformation was studied using a simple drop-ball test with the measurement of the dynamic force between the ball and forest of nanotubes. This convenient process allows extracting force–displacement curves and evaluating dissipated energy by the nanotubes. The contact force exhibits a strongly nonlinear dependence on displacement being fundamentally different than the Hertz law. The forest of vertically aligned nanotubes may be used as a strongly nonlinear spring in discrete systems for monitoring signal propagation speed, and as a microstructure for localized energy absorption.
High-performance distributed feedback quantum cascade lasers grown by metalorganic vapor phase epitaxy
Authors: Green R. P. , Wilson L. R. , Zibik E. A. , Revin D. G. , Cockburn J. W. , Pflügl C. , Schrenk W. , Strasser G. , Krysa A. B. , Roberts J. S. , Tey C. M. , Cullis A. G.
Published: December 2004

We report the operation of distributed feedback quantum cascade lasers, grown by metalorganic vapor phase epitaxy. Single-mode laser emission at λ∼10.3μm and λ∼7.8μm is observed from two different samples, with 300 K threshold current densities of Jth∼3 and ∼2.4kAcm−2, respectively. Structural investigation by x-ray diffraction and transmission electron microscopy, and the close correlation between the predicted and observed emission wavelengths indicate exceptional control of the layer thicknesses, including ultrathin (∼8Å) barrier layers in the active region. These results confirm metalorganic vapor phase epitaxy as a viable technology for the growth of high-performance quantum cascade lasers.
Depth distribution of the strain in the GaN layer with low-temperature AlN interlayer on Si(111) substrate studied by Rutherford backscattering/channeling
Authors: Lu Y. , Cong G. W. , Liu X. L. , Lu D. C. , Wang Z. G. , Wu M. F.
Published: December 2004

The depth distribution of the strain-related tetragonal distortion eT in the GaN epilayer with low-temperature AlN interlayer (LT-AlN IL) on Si(111) substrate is investigated by Rutherford backscattering and channeling. The samples with the LT-AlN IL of 8 and 16 nm thickness are studied, which are also compared with the sample without the LT-AlN IL. For the sample with 16-nm-thick LT-AlN IL, it is found that there exists a step-down of eT of about 0.1% in the strain distribution. Meanwhile, the angular scan around the normal GaN ⟨0001⟩ axis shows a tilt difference about 0.01° between the two parts of GaN separated by the LT-AlN IL, which means that these two GaN layers are partially decoupled by the AlN interlayer. However, for the sample with 8-nm-thick LT-AlN IL, neither step-down of eT nor the decoupling phenomenon is found. The 0.01° decoupled angle in the sample with 16-nm-thick LT-AlN IL confirms the relaxation of the LT-AlN IL. Thus the step-down of eT should result from the compressive strain compensation brought by the relaxed AlN interlayer. It is concluded that the strain compensation effect will occur only when the thickness of the LT-AlN IL is beyond a critical thickness.
Alignment of filamentous proteins and associated molecules through confinement in microchannels
Authors: Bouxsein Nathan F. , Hirst Linda S. , Li Youli , Safinya Cyrus R. , Abu Samah Zuruzi , MacDonald Noel C. , Pynn Roger
Published: December 2004

A technique has been developed to study the structure and interaction of aligned filamentous proteins by confining them in surface-treated silicon microchannels. The micron-size channels induce the semiflexible biopolymers with comparable or larger persistence lengths than the channel width to naturally align parallel to the channel in solution, which facilitates structural studies by x-ray diffraction and optical imaging techniques. As a model system, we investigated the cross-linking of filamentous actin (F-actin) with the bundling protein α-actinin in the microchannels. Synchrotron x-ray diffraction and fluorescence microscopy were used to confirm that F-actin, when bundled in the device, conforms to the alignment of the channel geometry.
Temperature profile and pressure effect on the growth of silicon nanowires
Authors: Cheng Sau-Wan , Cheung Ho-Fai
Published: December 2004

The excess temperature at the tip of silicon nanowires during their growth is calculated and found to be generally low. Therefore the special adhesive property of the tip cannot be explained by the excess temperature. The effect of surface tension is analyzed and we found that it cannot cause a significant lowering of melting point at the tip. Based on the charge-assisted mechanism proposed earlier by us, we note that charge accumulation at the tip results in a strong negative pressure. We propose that this is the key force driving the nanowire to have only one-dimensional growth.
Charge transport in a CoPt3 nanocrystal microwire
Authors: Beecher P. , De Marzi G. , Quinn A. J. , Redmond G. , Shevchenko E. V. , Weller H.
Published: December 2004

The electrical characteristics of single CoPt3 nanocrystal microwires formed by magnetic field-directed growth from colloidal solutions are presented. The wires comprise disordered assemblies of discrete nanocrystals, separated from each other by protective organic ligand shells. Electrical data indicate that the activated charge transport properties of the wires are determined by the nanocrystal charging energy, governed by the size and capacitance of the individual nanocrystals. Focused ion beam-assisted deposition of Pt metal at the wire-electrode junctions is employed to optimize the wire-electrode contacts, whilst maintaining the nanocrystal-dominated transport characteristics of these one-dimensional nanocrystal structures.
Effect of Bi surfactant on atomic ordering of GaAsSb
Authors: Jiang W. Y. , Liu J. Q. , So M. G. , Rao T. S. , Thewalt M. , Kavanagh K. L. , Watkins S. P.
Published: December 2004

The addition of small quantities of a Bi surfactant is shown to have dramatic effects on the microstructure of GaAsSb alloys grown by organometallic vapor phase epitaxy (OMVPE). Epilayers grown without Bi show weak atomic ordering in plan-view selective area electron diffraction measurements, with periodicity of three or six times the [110] lattice spacing as previously reported. The addition of Bi at a ratio of 1% Bi∕Ga to the gas flow results in the appearance of strong CuAu and chalcopyrite ordering, as determined from electron diffraction measurements in both undoped, and heavily carbon doped layers. High-resolution, transmission electron microscopy lattice images clearly show the coexistence of {100}, {210} ordered and disordered structures with domain sizes of ∼10–20nm. Photoluminescence shows no band gap changes in GaAsSb samples with and without {100} and {210} ordering.
Influence of defects on the kinetic of C49–C54 TiSi2 transformation
Authors: La Via F. , Mammoliti F. , Grimaldi M. G.
Published: December 2004

Ti Si 2 C49 thin films with different concentrations of defects have been prepared by conventional annealing, in the 460–540°C temperature range, of a Ti films deposited on a polycrystalline Si layer. The residual sheet resistance of the C49 films decreased with increasing both the annealing temperature and the annealing duration indicating the occurrence of defect annealing at higher temperature and∕or longer times. A successive annealing at 650°C was used to promote the C49–C54 transition and the transformation rate was measured by in situ sheet resistance measurements. The C49–C54 transition time decreased with the residual sheet resistance of the C49 phase. The activation energy for the transformation increased from 3.09±0.75to6.12±0.96eV with increasing the defect concentration in the C49 phase. This strong dependence can explain the large variation of the kinetic results reported in the literature.
Reproducible resistance switching in polycrystalline NiO films
Authors: Seo S. , Lee M. J. , Seo D. H. , Jeoung E. J. , Suh D.-S. , Joung Y. S. , Yoo I. K. , Hwang I. R. , Kim S. H. , Byun I. S. , Kim J.-S. , Choi J. S. , Park B. H.
Published: December 2004

Negative resistance behavior and reproducible resistance switching were found in polycrystalline NiO films deposited by dc magnetron reactive sputtering methods. Oxygen to argon gas ratio during deposition was critical in deciding the detailed switching characteristics of either bi-stable memory switching or mono-stable threshold switching. Both metallic nickel defects and nickel vacancies influenced the negative resistance and the switching characteristics. We obtained a distribution of low resistance values which were dependent on the compliance current of high-to-low resistance switching. At 200°C, the low-resistance state kept its initial resistance value while the high-resistance state reached 85% of its initial resistance value after 5×105s. We suggested that the negative resistance and the switching mechanism could be described by electron conduction related to metallic nickel defect states existing in deep levels and by small-polaron hole hopping conduction.
Growth and morphology of 0.80eV photoemitting indium nitride nanowires
Authors: Johnson M. C. , Lee C. J. , Bourret-Courchesne E. D. , Konsek S. L. , Aloni S. , Han W. Q. , Zettl A.
Published: December 2004

InN nanowires with high efficiency photoluminescence emission at 0.80eV are reported. InN nanowires were synthesized via a vapor solid growth mechanism from high purity indium metal and ammonia. The products consist of only hexagonal wurtzite phase InN. Scanning electron microscopy showed wires with diameters of 50–100nm and having fairly smooth morphologies. High-resolution transmission electron microscopy revealed high quality, single crystal InN nanowires which grew in the ⟨0001⟩ direction.
Capping process of InAs∕GaAs quantum dots studied by cross-sectional scanning tunneling microscopy
Authors: Gong Q. , Offermans P. , Nötzel R. , Koenraad P. M. , Wolter J. H.
Published: December 2004

The capping process of self-assembled InAs quantum dots (QDs) grown on GaAs(100) substrates by molecular-beam epitaxy is studied by cross-sectional scanning tunneling microscopy. GaAs capping at 500°C causes leveling of the QDs which is completely suppressed by decreasing the growth temperature to 300°C. At elevated temperature the QD leveling is driven in the initial stage of the GaAs capping process while it is quenched during continued overgrowth when the QDs become buried. For common GaAs growth rates, both phenomena take place on a similar time scale. Therefore, the size and shape of buried InAs QDs are determined by a delicate interplay between driving and quenching of the QD leveling during capping which is controlled by the GaAs growth rate and growth temperature.
Effect of band offset on the open circuit voltage of heterojunction CuIn1−xGaxSe2 solar cells
Authors: Yamada Akimasa , Matsubara Koji , Sakurai Keiichiro , Ishizuka Shogo , Tampo Hitoshi , Fons Paul J. , Iwata Kakuya , Niki Shigeru
Published: December 2004

The reasons behind why the theoretically estimated open circuit voltage (Voc) of CuIn1−xGaxSe2 solar cells with large x values has not been realized are discussed. Typically, the reduction in Voc is estimated only on the basis of the conduction-band offset between the absorber and the window material. The importance of the electron affinity difference between the window and the transparent electrode must also be taken into account. Based upon both of these factors, a material selection guideline is reported for the window and the transparent electrode layers suitable for high-x CuIn1−xGaxSe2 absorber-based solar cells.
Scanning-tunneling-microscopy-based nanolithography of diamond-like carbon films
Authors: Mühl Thomas
Published: December 2004

We demonstrate an approach for nanometer-scale lithography of diamond-like carbon films employing a local electron injection from a scanning tunneling microscope tip under ultrahigh-vacuum conditions. The electrons induce a graphitization of the tetrahedrally bound carbon. With this technique, complex patterns of conducting lines and dots smaller than 10nm can be written. Tunneling spectroscopy and conductive force microscopy were used to further characterize the carbon nanostructures.
Methyl monolayers suppress mechanical energy dissipation in micromechanical silicon resonators
Authors: Wang Yu , Henry Joshua A. , Sengupta Debodhonyaa , Hines Melissa A.
Published: December 2004

The quality factor and long-term stability of megahertz-range micromechanical silicon resonators can be significantly improved by a methyl monolayer directly bonded to the silicon surface. Mechanical energy dissipation in functionalized resonators is shown to be a sensitive function of surface chemistry. At least 18% and 41% of the dissipation in H-terminated and long-chain alkyl-terminated resonators, respectively, is surface related. Surface-induced dissipation is poorly correlated with the mechanical properties of the terminating layer, but may be related to the surface defect density.
“Hidden hydrogen” in as-grown ZnO
Authors: Shi G. Alvin , Saboktakin Marjan , Stavola Michael , Pearton S. J.
Published: December 2004

An O–H stretching line at 3326.3cm−1 was previously assigned to a shallow donor that is introduced into ZnO by H. This infrared line has been found to appear in as-grown ZnO samples when they are annealed near 400 °C without an external source of H, showing that there is an H-containing defect in commercially available ZnO that is not seen by infrared spectroscopy that can be converted into a shallow donor. The interstitial H2 molecule in ZnO is suggested as a candidate for the “hidden” H species.
Photoluminescence studies of GaN nanorods on Si (111) substrates grown by molecular-beam epitaxy
Authors: Park Y. S. , Park C. M. , Fu D. J. , Kang T. W. , Oh J. E.
Published: December 2004

We have investigated the optical properties of dislocation-free vertical GaN nanorods grown on (111) Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy. The hexagonal shape nanorods with lateral diameters from 80 to 190 nm are obtained. They are fully relaxed and have a very good crystal quality characterized by extremely strong and narrow photoluminescence excitonic lines near 3.47 eV. Three distinct features are observed in photoluminescence. First, free exciton transition is observed at 3.477 eV for GaN nanorods of decreased diameter. Second, the photoluminescence spectra show an abnormal behavior with increasing temperature. The third feature is the size effect in that the PL peak energies are blueshifted with decreasing diameter of the GaN nanorod. The activation energy of the free exciton for the GaN nanorods with different diameters was evaluated.
Structural and optical properties of 6,13-pentacenequinone thin films
Authors: Hwang D. K. , Kim Kibum , Kim Jae Hoon , Im Seongil , Jung Duk-Young , Kim Eugene
Published: December 2004

We report on the structural and optical properties of 6,13-pentacenequinone thin films deposited on n-Si substrates by thermal evaporation at room temperature. X-ray diffraction data indicate excellent crystallinity but the films have two crystalline phases mixed. Photoluminescence (PL) spectra exhibited double peaks at 1.97 and 2.09 eV while the corresponding (double) peaks, associated with the highest occupied molecular orbital–lowest unoccupied molecular orbital transition, were also observed from direct absorption spectra at 2.94 and 3.11 eV. The yellow PL band was quite intense under UV illumination; the intensity was comparable to that from Tris-(8-hydroxyquinoline) aluminum (Alq3) thin films. A large Stokes shift of ∼1eV found in our 6,13-pentacenequinone thin films suggests potential applications to UV-detectors and UV-detecting cards.
Continuous liquid crystal pretilt control through textured substrates
Authors: Lee Fuk Kay , Zhang Baoshe , Sheng Ping , Kwok Hoi Sing , Tsui Ophelia K. C.
Published: December 2004

Reliable control on the pretilt alignment of nematic liquid crystal (LC) in the 30°–50° range is a well-known challenge. An unconventional approach, involving microtextured surfaces with domains favoring dissimilar LC alignments, has recently demonstrated applicability in bi- and tristable displays. These textured domains realize the so-called frustrated boundary condition in which the LC elastic energy built-up (frustration) can drive the LC alignment into macroscopic uniformity. Here we show that one can harness the frustrated boundary to achieve variable LC pretilt control up to 40°.
Light-storing photocatalyst
Authors: Zhang Junying , Pan Feng , Hao Weichang , Ge Qi , Wang Tianmian
Published: December 2004

Light-storing photocatalyst was prepared by coating light-storing phosphor and TiO2 photocatalyst in sequence on ceramic. The light-storing photocatalyst can store light irradiation and emit slowly. Consequently, the photocatalyst remains active when the irradiation source is cut off. Rhodamine B (RhB) can be decomposed efficiently by this photocatalyst in the dark after it absorbs light irradiation. This photocatalyst is photoreactive in an outdoor environment or can save energy by supplying irradiation intermittently for the photocatalyst.
Normally closed microgrippers using a highly stressed diamond-like carbon and Ni bimorph structure
Authors: Luo J. K. , Flewitt A. J. , Spearing S. M. , Fleck N. A. , Milne W. I.
Published: December 2004

A normally closed microgripper with a radius of curvature of 18–50 μm using a diamond-like carbon (DLC) and stress free electroplated Ni bimorph structure has been demonstrated. The large curvature in the fingers of the microgrippers is due to the high compressive stress of the DLC layer. The radius of curvature of the figures can be adjusted by the thickness ratio, and the closure of the devices can also be adjusted by varying the finger length. This device works much more efficiently than other bimorph structures due to the large difference in thermal expansion coefficients between the DLC and the Ni layers. Preliminary electrical tests have shown these microgrippers can be opened by 60°–90° at an applied power of <20mW.
Field-emission from long SnO2 nanobelt arrays
Authors: Chen Y. J. , Li Q. H. , Liang Y. X. , Wang T. H. , Zhao Q. , Yu D. P.
Published: December 2004

We report on field emission from SnO2 nanobelt arrays with the length of about 90 μm grown on silicon substrates. The turn-on field of the nanobelt arrays at the current density of 1μA∕cm2, is 4.5, 3.0, 2.4, and 2.3V∕μm as the distance between anode and cathode (d) is 0.1, 0.2, 0.35, and 0.5 mm, respectively. The current density rapidly reaches 2.1mA∕cm2 at the electrical field of 4.4V∕μm at d=0.35mm. The current density is higher than or comparable to those of the carbon nanotubes and other one-dimensional nanostructured materials. We also discuss the mechanism of high current densities and estimate the enhancement factor according to both the Fowler–Nordheim law and the reported model on micrometer-long of carbon nanotubes.
Experimental and theoretical studies on the structure of N-doped carbon nanotubes: Possibility of intercalated molecular N2
Authors: Choi Hyun Chul , Bae Seung Yong , Park Jeunghee , Seo Kwanyong , Kim Changwook , Kim Bongsoo , Song Ha Jin , Shin Hyun-Joon
Published: December 2004

The concentration distribution and electronic structure of N atoms doped in multiwalled banboo-like carbon nanotubes (CNTs) are examined by photon energy-dependent x-ray photoelectron spectroscopy and x-ray absorption near edge structure. The inner part of the nanotube wall has a higher N concentration and contains molecular N2 presumably intercalated between the graphite layers. These results are supported by the self-consistent charge-density-functional-based tight-binding calculation of double-walled CNTs, showing that the intercalation of N2 is energetically possible and the graphite-like N structure conformer becomes more stable when the inner wall is more heavily doped.
Reduction of operating voltage in organic light-emitting diode by corrugated photonic crystal structure
Authors: Fujita Masayuki , Ueno Tetsuya , Ishihara Kuniaki , Asano Takashi , Noda Susumu , Ohata Hiroshi , Tsuji Taishi , Nakada Hitoshi , Shimoji Noriyuki
Published: December 2004

A reduction of the operating voltage is achieved for an organic light-emitting diode containing a corrugated photonic crystal structure fabricated by the etching of an indium-tin-oxide anode layer. This is due to a partial reduction in the thickness of the organic layer. The light extraction efficiency can be also improved due to the diffraction of confined light by the photonic crystal effect. The voltage reduction is demonstrated in combination with an improvement in the luminance efficiency at constant current for the fabricated device.