bluuebunny/crossref_metadata_2025 huggingface dataset:
ACADEMIC DISCIPLINE OR LITERARY GENRE?: THE ESTABLISHMENT OF BOUNDARIES IN HISTORICAL WRITING
Authors: Howsam Leslie
Published: December 2004

SERIOUS PRACTITIONERS OF THE HISTORICALdiscipline in late nineteenth-century Britain mistrusted their culture's practice of framing the nation's contemporary greatness in terms of former glories. In the view of the new professional historians, it was essential to negotiate a boundary between their own professional work and that of amateurs, with science on one side and literature on the other. The stakes were high. John Robert Seeley thought the writings of men of letters, particularly Macaulay and Carlyle, had “spoiled the public taste,” by being so delightful to read that “to the general public no distinction remains between history and fiction….deprived of any, even the most distant association with science, [history] takes up its place definitively as a department of belles lettres” (“History and Politics” 292). He and others wanted a new generation of students whose work would appear in serious publications which would no more appeal to the general public than Newton'sPrincipia. A scientific training would prepare historians not only to research, write, and teach British history properly, but also to encounter the work of their peers as critical readers and knowledgeable reviewers. The boundary between popular and professional history (or between narrative and scientific approaches to the past) was often invoked by people like Seeley. A sharp dichotomy made for a compelling rhetoric of modernization and improvement. Earlier histories had been written inaccurately though patriotically, by gentlemen of letters for the general reader. Macaulay's essays, for example, had first appeared in theEdinburgh Review, and the great quarterlies continued to publish historical narratives that were unsatisfactory by modern standards. Equally unacceptable was the tradition of introducing children to their nation's past with such romanticized narratives asLittle Arthur's History of England. Maria Callcott was the anonymous author of this much-reprinted and often-maligned work. Now, applying to the discipline the principles of Leopold von Ranke and a newly rigorous approach which resonated with the broader contemporary culture of science, history-writing was to be limited to trained professionals, so that it might be made precise, verifiable, and reliable, even at the expense of narrative appeal. One colleague paraphrased Seeley's views pungently: “To make sure of being judged by competent judges only, we ought to make history so dull and unattractive that the general public will not wish to meddle with it” (Freeman 326).
The end of the essential archaeological subject
Authors: Smith Adam T.
Published: December 2004

Archaeological investigations of identity have successfully challenged traditional accounts of archaeological subjects by splintering social worlds along axes of gender, ethnicity and class. However, in so doing, they have quietly reinscribed an essential archaeological subject as a locus of analysis and as a foundation for contemporary political action. In analytical terms, the crystallization of a limited configuration of social difference constructs archaeological analyses of identity as a tautology in which contemporary configurations are read as universal and enduring rather than as immediate constructions within specific social worlds. In political terms, the tension between a cosmopolitan drive to combat the appropriation of a global human heritage by nationalist interests and an advocative archaeology dedicated to providing subaltern groups with a privileged claim to a sectional past leaves the discipline in an untenable position. The end of the essential archaeological subject requires a closer analytical focus upon the sociopolitical constitution of subjectivity and a stronger resolve to resist all claims to privilege in the present founded upon archaeological pasts. The implications of this move are sketched in relation to the kingdom of Urartu, which ruled the highlands of eastern Anatolia and southern Caucasia during the early 1st millennium B.C.
Comments on Adam T. Smith's ‘The end of the essential archaeological subject’
Authors: Kohl Philip L.
Published: December 2004

As expected, Adam Smith has written a provocative, intellectually stimulating and demanding article critiquing the re-inscription of ‘an essential archaeological subject’ as archaeology becomes more explicitly aware of its inevitable political dimensions. I find myself in broad, though not perfect, agreement with his overall argument and concur completely with his concluding sentiments that archaeologists should become ‘analysts of the naturalizers rather than analytical naturalizers’ and that they should expose the strategic practices at play in the assertion of all such essentialist claims, past and present. My concern is that his prescription for achieving this result may be too mild (i.e. indirect and subtle, if not opaque) to cure the ills of the nationalists who habitually distort archaeological evidence to achieve their often dubious political agendas. In a certain sense, his laudable insistence on focusing on change and the plasticity of markers of identity in relation to specific and always shifting sociopolitical contexts eviscerates the political nature of archaeological enquiry. His recommendation is to go back to interpreting the past on its own terms, void of ‘essential subjects’. All right, but not many people will listen and those interested in using the past for contemporary purposes will not be directly confronted. As critical ‘analysts of the naturalizers’ we perform an essentially negative, though indispensable, role; we point out why the accounts of the naturalizers are ambiguous, distort the record, are untenable and dangerous, and so on. This admittedly negative role is extremely important and should not now be abandoned after so many years of denying it or not recognizing it. It is necessary to add that there is also a positive political approach for interpreting archaeological evidence that Childe (1933) long ago recognized: demonstrate the continuous intercourse and diffusion of ideas and technologies from one culture and people to another throughout prehistoric times and insist that no single group was responsible for this constantly growing and shared history of cultural development.
Archaeology and identity politics. A cross-disciplinary perspective
Authors: Vermeersch Peter
Published: December 2004

What scholars are committed to in principle is not always what they are likely to uphold in practice. Adam T. Smith examines – and deplores – the striking discrepancy between the centrality of the constructivist idiom in a variety of disciplines and the tendency of archaeologists to continue to treat archaeological subjects (be they ethnic groups, classes, nations, races, cultures or any other kind of identity group) as given entities and stable units of analysis. Smith's concern is not merely about the consistency of the discipline's theoretical underpinnings. In fact, his greatest worry turns out to be political: an archaeology that reconstitutes, rather than deconstructs, the essential subject may be wrongly used as a foundation for contemporary political action (such as nationalism). Thus he invites archaeologists to revise the relationship between scholarly analysis and political practice. Smith not only suggests taking into full account the malleability of identity groups in relation to changing sociopolitical contexts, but he also incites scholars to bend their minds to the sociopolitical circumstances within which seemingly stable categories of identity are produced. Archaeologists should be careful not to ‘essentialize’ identities, he concludes, but instead shift their attention to exposing the strategic practices deployed by those who do ‘essentialize’ identities.
We, they, and I. Politics after the end of essential archaeological subjects
Authors: Smith Adam T.
Published: December 2004

I recently attended a lecture here in Chicago given by Mkrtich Zardaryan, a colleague of mine from Armenia who specializes in the archaeology of early Armenian kingdoms during the post-Urartian 1st millennium B.C. During the question-and-answer period, a member of the audience posed the following question, which I paraphrase: ‘I recognize that we were defeated by the Urartians but what I want to know is where we came from before that? How did we come to that region and when?’ Zardaryan paused only briefly before asking, ‘Who do you mean by “we”?’ The audience member responded, ‘We Armenians, I am Armenian.” To which Zardaryan replied “So am I, but I wasn't there.”
“Typisch Beamter?”
Authors: Florack Arnd , Scarabis Martin , Gosejohann Stefanie
Published: December 2004

Zusammenfassung: Die Autoren unterscheiden zwei Arten von Assoziationen zu einer Fremdgruppe. Als personale Assoziationen bezeichnen sie individuelles Wissen und individuelle Bewertungen einer Fremdgruppe. Demgegenüber bezeichnen sie das Wissen über Bewertungen in ihrer sozialen Umwelt als extrapersonale Assoziationen. Sie gehen davon aus, dass die Nutzung dieser Assoziationen bei der Beurteilung einer Person unter anderem von der Typikalität des zu beurteilenden Exemplars und der Selbstkategorisierung des Urteilers abhängt. Die Ergebnisse des durchgeführten Experiments stützen diese Annahme und stehen im Einklang zu dem Modell, dass die Typikalität eines Exemplars zu einer verstärkten Nutzung von sowohl personalen wie auch extrapersonalen Assoziationen führt, während die Selbstkategorisierung auf einer kollektiven Ebene die Nutzung personaler Assoziationen schwächt. Die Ergebnisse werden vor dem Hintergrund der Selbstkategorisierungstheorie diskutiert.
Strong light scattering in macroporous TiO2 monoliths induced by phase separation
Authors: Fujita Koji , Konishi Junko , Nakanishi Kazuki , Hirao Kazuyuki
Published: December 2004

Macroporous titania (TiO2) monoliths have been prepared from systems containing titania colloid and poly(ethylene oxide) using a sol-gel method, and the light-scattering properties have been investigated by means of coherent backscattering. Three-dimensionally interconnected macroporous morphology is obtained by inducing the phase separation parallel to the sol-gel transition. The crystal structure of TiO2 gel is transformed from anatase to rutile through the heat treatment above 900°C, while the macroporous morphology remains unchanged. We show that the rutile-type TiO2-based macropurous monoliths are strongly scattering media for visible light.
Mean field kinetic theory description of evaporation of a fluid into vacuum
Authors: Frezzotti Aldo , Gibelli Livio , Lorenzani Silvia
Published: December 2004

The evaporation of a liquid slab into vacuum is studied by numerical solutions of the Enskog–Vlasov equation for a fluid of spherical molecules interacting by Sutherland potential. The equation provides a simplified description of the microscopic behavior of the fluid but it has the capability of handling both the liquid and vapor phase, thus eliminating the necessity of postulating ad hoc models for boundary conditions at the vapor-liquid interface. This work focuses on obtaining the structure of the vapor-liquid interface in nonequilibrium conditions as well as the distribution function of evaporating molecules. The results show that the molecules crossing a properly defined vapor-liquid boundary have an almost Maxwellian distribution function and that the vapor phase is reasonably well described by the Boltzmann equation with diffusive boundary condition.
Nonlinear waves in the pressure driven flow in a finite rotating pipe
Authors: Sanmiguel-Rojas E. , Fernandez-Feria R.
Published: December 2004

To investigate the nature of nonlinear waves appearing in an axially rotating pipe, we have performed a series of time-depending, three-dimensional numerical simulations of the incompressible Navier–Stokes equations in a rotating long pipe. As a difference with some previous works on the subject, which look for several given types of traveling wave solutions in pipes of infinite length, we leave the flow to evolve freely after a pressure difference is set between two points, one on each end of the finite rotating pipe. We use a recently developed numerical method that allows us to simulate numerically the three-dimensional flow produced in a pipe when Dirichlet boundary condition for the pressure is given on part of the inlet and outlet sections of the pipe. This technique is further improved here so that the pressure is only fixed at just one point on each one of the open boundaries of the pipe. Thus, no restrictions on the flow properties are given in these sections, allowing the free entrance and exit of possible waves through the pipe. We find that packets of traveling spiral waves are formed for values of the Reynolds numbers based on both the axial and the azimuthal velocities just above the critical ones given by the linear stability theory. These traveling waves have the same characteristics predicted by the linear stability theory and produce no significant mean flux defect. As the values of these parameters are increased above their critical values, the spiral waves become more involved and their amplitude increase, giving rise to a significant axial mean flow defect. For sufficiently high Reynolds numbers, we detect the apparition of spiral waves traveling also upstream, in agreement with the stability analysis for absolute instabilities. At the end, these traveling waves appearing above the onset for absolute instabilities transform into a standing spiral wave superimposed to the rotating Hagen–Poiseuille flow.
Femtosecond laser-induced formation of submicrometer spikes on silicon in water
Authors: Shen M. Y. , Crouch C. H. , Carey J. E. , Mazur E.
Published: December 2004

We fabricate submicrometer silicon spikes by irradiating a silicon surface that is submerged in water with 400 nm, 100 fs laser pulses. These spikes are less than a micrometer tall and about 200 nm wide—one to two orders of magnitude smaller than the microspikes formed by laser irradiation of silicon in gases or vacuum. Scanning electron micrographs of the surface show that the formation of the spikes involves a combination of capillary waves on the molten silicon surface and laser-induced etching of silicon. Chemical analysis and scanning electron microscopy of the spikes show that they are composed of silicon with a 20-nm-thick surface oxide layer.
Low-current spin-transfer switching and its thermal durability in a low-saturation-magnetization nanomagnet
Authors: Yagami K. , Tulapurkar A. A. , Fukushima A. , Suzuki Y.
Published: December 2004

A spin-transfer magnetization switching technique is a promising candidate as a writing mechanism for a high-density magnetic random access memory because of its scalability. The required switching current Ic, however, is still too large for this technique to be applied to MRAM using tunneling magnetoresistive devices. Here, it is demonstrated that reducing the saturation magnetization Ms of magnet cells is an effective way to decrease Ic. Use of a CoFeB film with μ0Ms of 0.75T as a magnet cell reduced Ic measured with a continuous current by an order of magnitude. We changed the duration of a writing current pulse from 1μs to 5s to investigate thermal effects on the switching process, and predicted that CoFeB magnet cells with low Ic can be compatible with the thermal durability required for MRAM applications.
Enhanced luminescence from electron–hole droplets in silicon nanolayers
Authors: Nihonyanagi Satoshi , Kanemitsu Yoshihiko
Published: December 2004

We have studied photoluminescence (PL) from the condensed phase in silicon-on-insulator samples with different Si layer thickness from 50 to 340 nm. Two major PL bands are observed at low temperatures, originating from free excitons (FE) and electron–hole droplets (EHD). It is found that with an increase of the excitation intensity the EHD PL shows a linear increase in the 50-nm-thick layer while a superlinear increase in the 340-nm-thick layer. The intensity ratio of the EHD PL to the FE PL in the 50-nm-thick layer is much larger than that in the 340-nm-thick layer under the same experimental conditions. The luminescence from the EHD is enhanced in thin Si nanolayers. These results suggest that highly dense electrons and holes are formed in the Si nanolayer and the interfaces act as the nucleation center of the EHD.
Two-photon-induced photoenhancement of densely packed CdSe∕ZnSe∕ZnS nanocrystal solids and its application to multilayer optical data storage
Authors: Chon James W. M. , Zijlstra Peter , Gu Min , van Embden Joel , Mulvaney Paul
Published: December 2004

We report on a two-photon absorption-induced photoenhancement effect on a densely packed CdSe∕ZnSe∕ZnS core-shell semiconductor nanocrystal solid film. The enhancement is found to be irreversible without a noticeable blueshift in emission spectra, hence we attribute the enhancement to the photoannealing of interface defects rather than to the photo-oxidation or surface passivation by other molecules. The two-photon enhancement allows us to record the enhanced spots three dimensionally, hence demonstrating the feasibility of its application to multilayered optical data storage based on nanocrystal solids.
Large recoverable electrostrain in Mn-doped (Ba,Sr) TiO3 ceramics
Authors: Zhang L. X. , Chen W. , Ren X.
Published: December 2004

In this letter we demonstrate that with a different principle, BaTiO3 ceramics, so far considered as inferior piezoelectrics compared with Pb(Zr,Ti)O3 (PZT), can show a large recoverable electrostrain. This principle utilizes a point-defect-mediated reversible domain switching mechanism, which can in theory generate 0.368% strain for BaTiO3 ceramics at the best condition. Experimental results showed that, after aging at room temperature, 1.0mol% Mn-doped (Ba0.95Sr0.05)TiO3 ceramics generate a large recoverable nonlinear strain of about 0.12%–0.15% at a field of 3kV∕mm. This value exceeds that of conventional hard PZT piezoelectric ceramics. A microscopic model for the domain-related electrostrain effect in ceramics is proposed. It is also found that the large electrostrain effect is quite stable with respect to both changing frequency and fatigue cycles. Large electrostrain remains recoverable down to 0.05Hz and after 10000cycles. These results demonstrate the potential of our approach in achieving large recoverable electrostrain in environmental-friendly (Pb-free) ceramics.
Nanotransfer printing by use of noncovalent surface forces: Applications to thin-film transistors that use single-walled carbon nanotube networks and semiconducting polymers
Authors: Hur Seung-Hyun , Khang Dahl-Young , Kocabas Coskun , Rogers John A.
Published: December 2004

We report a purely additive nanotransfer printing process that uses noncovalent surface forces to guide the transfer of thin metal films from low-energy surfaces of high-resolution stamps to a variety of substrates. Structures with dimensions as small as a few hundred nanometers, with edge roughness as small as 10nm are demonstrated. Metal multilayer stacks patterned in this way have electrical resistances that are the same as those formed by evaporation and conventional lithography. Thin-film transistors that use source/drain electrodes printed directly onto thin films of the semiconducting polymer regioregular polythiophene and networks of single-walled carbon nanotubes exhibit device mobilities and on/off ratios that are comparable to or higher than those of devices fabricated using standard methods.
Asymmetric tandem organic photovoltaic cells with hybrid planar-mixed molecular heterojunctions
Authors: Xue Jiangeng , Uchida Soichi , Rand Barry P. , Forrest Stephen R.
Published: December 2004

We demonstrate high-efficiency organic photovoltaic cells by stacking two hybrid planar-mixed molecular heterojunction cells in series. Absorption of incident light is maximized by locating the subcell tuned to absorb long-wavelength light nearest to the transparent anode, and tuning the second subcell closest to the reflecting metal cathode to preferentially absorb short-wavelength solar energy. Using the donor, copper phthalocyanine, and the acceptor, C60, we achieve a maximum power conversion efficiency of ηP=(5.7±0.3)% under 1 sun simulated AM1.5G solar illumination. An open-circuit voltage of VOC⩽1.2V is obtained, doubling that of a single cell. Analytical models suggest that power conversion efficiencies exceeding 6.5% can be obtained by this architecture.
Effect of the polar surface on GaN nanostructure morphology and growth orientation
Authors: Nam C. Y. , Tham D. , Fischer J. E.
Published: December 2004

Wurtzite gallium nitride nanostructures were grown by thermal reaction of gallium oxide and ammonia. The resulting morphology varied depending on ammonia flow rate. At 75sccm only nanowires were obtained, while polyhedral crystals and nanobelts were observed at 175sccm. Scanning electron microscopy and transmission electron microscopy revealed both thin smooth and thick corrugated nanowires. The growth orientations of most of the smooth ones, as well as the nanobelts, were perpendicular to the c axis (⟨0001⟩), while the corrugated nanowires and the large polyhedra grew parallel to ⟨0001⟩. We propose a model to explain these variations of morphology and growth orientation in terms of the Ga∕N ratio and the different characteristic length of {0001} polar surface in the different nanostructures.
Terahertz study of 1,3,5-trinitro-s-triazine by time-domain and Fourier transform infrared spectroscopy
Authors: Huang Feng , Schulkin Brian , Altan Hakan , Federici John F. , Gary Dale , Barat Robert , Zimdars David , Chen Minghan , Tanner D. B.
Published: December 2004

This letter describes the use of THz time-domain spectroscopy (TDS) applied in transmission to the secondary explosive 1,3,5 trinitro-s-triazine. Samples were also subjected to Fourier transform infrared spectroscopy over the same range for comparison. A detailed spectroscopy study is presented. General agreement between results from both methods confirms the absorption features found. A comparison study with computer molecular simulations shows that THz-TDS is sensitive to collective modes or vibrational modes of material.
Ordered growth of germanium hut islands on Si (001) molecular bonded substrates
Authors: Poydenot V. , Dujardin R. , Rouvière J. L. , Barski A. , Fournel F.
Published: December 2004

Ordered germanium hut islands are grown by molecular-beam epitaxy on high twist angle molecular bonded silicon (001) substrates (twist angle higher than 20°). We show that the growth organization is induced by an array of interfacial tilt dislocations. Plan-view transmission electron microscopy and atomic force microscopy observations show that the orientation and period of the tilt dislocation array determine the orientation, period, and length of elongated germanium hut islands. The strain field generated by an array of tilt dislocations is proposed as the driving force of the reported organization.
Pairing space-charge field conditions with self-guiding for the attainment of circular symmetry in photorefractive solitons
Authors: DelRe E. , De Masi G. , Ciattoni A. , Palange E.
Published: December 2004

By means of a comparative study, we identify a specific physical mechanism that leads to circular-symmetric two-dimensional photorefractive solitons, and determine the conditions for their observation. For a given photorefractive crystal, this allows the control of the transition from an elliptical soliton-supporting regime to a round soliton-supporting one. This indicates a basic recipe to generate electro-optic devices in three-dimensional crystals compatible with single-mode fiber.
Collection-mode near-field scanning infrared microscope based on silver halide probes
Authors: Roodenko K. , Ephrat P. , Nagli L. , Katzir A.
Published: December 2004

We developed a collection-mode scanning near field microscope for the midinfrared spectral range, employing probes fabricated from tapered silver halide fibers. The system was tested in the photon scanning tunneling regime, where a sample was illuminated under total internal reflection conditions. The experimental results agreed with the results obtained by an analytical theoretical model.
Current collapse-free i-GaN∕AlGaN∕GaN high-electron-mobility transistors with and without surface passivation
Authors: Arulkumaran S. , Hibino T. , Egawa T. , Ishikawa H.
Published: December 2004

Drain current (ID) collapse-free i-GaN∕AlGaN∕GaN high-electron-mobility transistors (HEMTs) with and without surface passivation (electron-beam evaporated SiO2) were demonstrated using dc and pulsed (120Hz) IDS–VDS characteristics up to the drain supply voltage of 40V. The observation of small ID transients and negligibly small hysteresis widths with small white light illumination effects on both passivated and unpassivated i-GaN∕AlGaN∕GaN HEMTs confirms the suppression of collapse related traps. Three and two thermally activated trap levels were observed in passivated (+0.395, −0.079, and −0.949eV) and unpassivated (−0.066 and −0.368eV)AlGaN∕GaN HEMTs, respectively. However, i-GaN∕AlGaN∕GaN HEMTs with and without surface passivation exhibited only one trap level at −0.161eV. These results show that the addition of thin cap layer i-GaN screens the collapse-related surface states/traps from channel.
Transition from bubbling to jetting in a coaxial air–water jet
Authors: Sevilla A. , Gordillo J. M. , Martínez-Bazán C.
Published: December 2004

In this Brief Communication we study experimentally the flow regimes that appear in coaxial air–water jets discharging into a stagnant air atmosphere and we propose a simple explanation for their occurrence based on linear, local, spatiotemporal stability theory. In addition to the existence of a periodic bubbling regime for low enough values of the water-to-air velocity ratio, u=uw∕ua, our experiments revealed the presence of a jetting regime for velocity ratios higher than a critical one, uc. In the bubbling regime, bubbles form periodically from the tip of an air ligament whose length increases with u. However, when u>uc a long, slender gas jet is observed inside the core of the liquid coflow. Since in the jetting regime the downstream variation of the flow field is slow, we performed a local, linear spatiotemporal stability analysis with uniform velocity profiles to model the flow field of the air–water jet. Similar to the transition from dripping to jetting in capillary liquid jets, the analysis shows that the change from the bubbling to the jetting regime can be understood in terms of the transition from an absolute to a convective instability.
AlGaN-based 280nm light-emitting diodes with continuous-wave power exceeding 1mW at 25mA
Authors: Zhang J. P. , Hu X. , Bilenko Yu. , Deng J. , Lunev A. , Shur M. S. , Gaska R. , Shatalov M. , Yang J. W. , Khan M. A.
Published: December 2004

Optimization of the migration-enhanced metalorganic chemical vapor deposition and further optimization of the contact and active layer design for 280nm light-emitting diodes resulted in large improvement of cw and pulsed output power and in a superior spectrum purity. The ratio of the main peak to the background luminescence determined by the detection system is higher than 2000:1 at 20mA dc. The on-wafer cw power was measured to be 255μW at 20mA dc. The power popped up exceeding 1mW for a packaged device under 25mA dc and 9mW under pulse 200mA. The maximum wall-plug-efficiency of 0.67% was obtained for the packaged device at 25mA dc.
Detection of subnanometric layer at the Si∕SiO2 interface and related strain measurements
Authors: Donnadieu P. , Blanquet E. , Jakse N. , Mur P.
Published: December 2004

The structure of the Si∕SiO2 interface was investigated by high-resolution transmission electron microscopy (HRTEM) and electron diffraction, which appears as an efficient tool to detect any organized layer at the interface. Using HRTEM image analysis, a 1-nm-thick distorted Si layer is identified at the interface, the local deformation corresponds to a compressive stress of approximately 2GPa.
Nonequilibrium gain in optically pumped GaInNAs laser structures
Authors: Thränhardt A. , Becker S. , Schlichenmaier C. , Kuznetsova I. , Meier T. , Koch S. W. , Hader J. , Moloney J. V. , Chow W. W.
Published: December 2004

A theory is presented which couples a dynamical laser model to a fully microscopic calculation of scattering effects. Calculations for two optically pumped GaInNAs laser structures show how this approach can be used to analyze nonequilibrium and dynamical laser properties over a wide range of system parameters.
Super-miniature x-ray tube
Authors: Senda S. , Sakai Y. , Mizuta Y. , Kita S. , Okuyama F.
Published: December 2004

A transmission x-ray tube super-miniature in size is described. The x-ray tube is 5mm in diameter, and comprised of a built-in electron-emitter assembly and a grounded planar target. The key component of the emitter assembly is a Kovar pipe 2mm in diameter, inside which carbon nanofibers aligned on an electro-polished molybdenum tip are loaded to serve as the electron emitter. This type of electron emitter is highly robust in non-ultrahigh vacuum, continuing to field emit electrons for 100h or longer at pressures in the 10−5Pa region. This x-ray tube provides clear x-ray images.
Optical coupling and transport phenomena in chains of spherical dielectric microresonators with size disorder
Authors: Astratov V. N. , Franchak J. P. , Ashili S. P.
Published: December 2004

The optical transmission properties of chains or circuits of touching polystyrene microspheres with sizes in the 3–20μm range and a size dispersion of ∼1% are studied. The dye-doped spheres with fluorescent peaks due to whispering gallery modes were attached to one end of the chains. The effects of optical transport were detected using spatially resolved scattering spectroscopy. The attenuation was shown to be ∼3 to 4 dB per sphere for the modes with the best transport properties. A mechanism for the observed transport is suggested based on the formation of strongly coupled photonic modes in the systems of randomly detuned resonators with size disorder. It is shown that such circuits possess broad bandpass waveguiding characteristics essential for applications in integrated all-optical network devices.
Phase transformations induced in relaxed amorphous silicon by indentation at room temperature
Authors: Haberl B. , Bradby J. E. , Swain M. V. , Williams J. S. , Munroe P.
Published: December 2004

The deformation behavior of self-ion-implanted amorphous-Si (a-Si) has been studied using spherical nanoindentation in both relaxed (annealed) and unrelaxed (as-implanted) a-Si. Interestingly, phase transformations were clearly observed in the relaxed state, with the load–unload curves from these samples displaying characteristic discontinuities and cross-sectional transmission electron microscopy images indicating the presence of high-pressure crystalline phases Si-III and Si-XII following pressure release. Thus, an amorphous to crystalline phase transformation has been induced by indentation at room temperature. In contrast, no evidence of a phase transformation was observed in unrelaxed a-Si, which appeared to deform via plastic flow of the amorphous phase. Furthermore, in situ electrical measurements clearly indicate the presence of a metallic Si phase during loading of relaxed a-Si but no such behavior was observed for unrelaxed a-Si
Thermally stimulated current in self-organized InAs quantum dots
Authors: Fan J. C. , Wang Y. C. , Chen I. S. , Hsiao K. J. , Chen Y. F.
Published: December 2004

We have measured the thermally stimulated current from self-organized InAs quantum dots grown by molecular-beam epitaxy. The glow curve exhibits peaks at 43, 82, and 127 K with accompanying attenuated current oscillations at 107 K. Based on the excitation energy above and below the GaAs band gap, the oscillations are ascribed to AsGa-related point defects in the conduction GaAs matrix. By comparing with the photoluminescence and photoconductivity measurements, we conclude that the peaks at 82 and 43 K arise from the electron trapping in the InAs quantum dots. We point out that the technique of thermally stimulated current provides a simple alternative method to obtain the energy levels in self-organized quantum-dot systems.
Comparison of ac susceptibility of YBa2Cu3O7 coated conductors and single crystals
Authors: Chen D.-X. , Pardo E. , Sanchez A. , Palau A. , Puig T. , Obradors X.
Published: December 2004

The complex ac susceptibility of YBa2Cu3O7 (YBCO) coated conductor and YBCO single crystal has been measured at 77K as a function of field amplitude and frequency, from which the E(J) characteristic is deduced. It is shown that the E(J) in the single crystal obeys a power law in a large range above Ec=1μV∕cm, indicating a flux creep mechanism, whereas for the coated conductor there appears a transition from flux creep to flux flow at E∼10Ec. The reported contactless technique may be conveniently used for the research and development of coated conductors.
In situ observation of field emissions from an individual carbon nanotube by Lorenz microscopy
Authors: Fujieda T. , Hidaka K. , Hayashibara M. , Kamino T. , Matsumoto H. , Ose Y. , Abe H. , Shimizu T. , Tokumoto H.
Published: December 2004

In situ observation of field emissions from an individual carbon nanotube (CNT) was performed by Lorenz microscopy. A bright spot appeared by Lorenz microscopy at the end of the CNT tip during field emission. The bright spot is assumed to be related to the emission site on the CNT. A drastic fluctuation was observed in the emission current above a few tens of microamperes, which was closely related to structural changes at the tip of the CNT. The layers of the CNT were peeled off and they worked as a second emission site by concentration of the electric field.
Pre-breakdown suppression in planar InP∕InGaAs avalanche photodiode using deep floating guard ring
Authors: Hyun Kyung-Sook , Paek Youngmi , Kwon Yong-Hwan , Hwang Sungmin , Shim Jongin , Ahn Seong Joon
Published: December 2004

We propose a deep floating guard ring (DFGR) structure which effectively prevents the curvature breakdown of a central junction in a planar InGaAs∕InP avalanche photodiode (APD). In order to investigate the DFGR APD performance, the dark current, photocurrent, and radial dependence of gain were measured and analyzed. In addition, the relation between breakdown voltage and multiplication layer thickness was calculated using a nonlocal history-dependent model. Reliable operation in the device center region was examined by measuring the radial gain. As a result, it has been confirmed that the DFGR is very useful for an APD with a very thin multiplication layer.
Strain modulation of transport criticality in RuO2-based thick-film resistors
Authors: Vionnet-Menot Sonia , Grimaldi Claudio , Ryser Peter , Maeder Thomas , Strässler Sigfrid
Published: December 2004

We show that in RuO2–glass composites the nonuniversal resistivity exponent can be modulated by an applied mechanical strain, signaled by a logarithmic divergence of the piezoresistive response at the percolation threshold. We interpret this phenomenon as being due to a tunneling-distance dependence of the transport exponent, supporting therefore a theory of transport nonuniversality proposed some years ago.
Ferroelectric and dielectric anisotropy in high-quality SrBi2Ta2O9 single crystals
Authors: Amorín H. , Shvartsman V. V. , Kholkin A. L. , Costa M. E. V.
Published: December 2004

High-quality SrBi2Ta2O9 single crystals were obtained by a self-flux solution method. The crystals were naturally oriented with [001] direction perpendicular to the major face and edges parallel to [110] axes. The dielectric and ferroelectric properties of the crystals were investigated along the c axis and in the ab plane of the orthorhombic unit cell. The ferro–paraelectric phase transition was observed at TC=355°C. The anisotropy of dielectric permittivity, i.e., the ratio between average permittivity in the ab plane and along c axis was about 10 at TC and decreased to ∼2 at room temperature. Saturated hysteresis loops were observed for switching in the ab plane. The spontaneous polarization along ferroelectric a axis was estimated to be ≈20μC∕cm2.
Resistance to water flow through leaves of Coffea arabica is dominated by extra-vascular tissues
Authors: Gascó Antonio , Nardini Andrea , Salleo Sebastiano
Published: December 2004

The leaf hydraulic conductance (Kleaf) of Coffea arabica L. was measured for shoots exposed to non-lethal temperature stress or to a freeze–thaw cycle, and compared with Kleaf of non-stressed samples (controls). Exposure to temperatures below 6°C for 1 h caused measurable damage to the functional integrity of cell membranes as shown by increased membrane leakiness to electrolytes. A 1 : 1 relationship was found to exist between relative electrolyte leakage and relative Kleaf suggesting that membrane damage caused Kleaf to increase. Low temperatures did not cause membrane disruption as shown by the comparison of chilled samples with frozen–thawed ones. In frozen leaves, membranes were extensively disrupted and both electrolyte leakiness and Kleaf increased 5-fold. Low temperatures did not induce alterations of the hydraulic properties of the leaf vascular system, as revealed by measurements of Kleaf after up to 500 cuttings of minor veins were made in the leaf blade of control and chilled leaves. Calculations showed that 62–75% of leaf hydraulic resistance resided in the extra-vascular water pathway. Results are discussed within the frame work of our current understanding of leaf hydraulic architecture as well as in terms of plant adaptation to extremes in temperature.
Spatial and age-dependent modifications of photosynthetic capacity in four Mediterranean oak species
Authors: Niinemets Ülo , Tenhunen John D. , Beyschlag Wolfram
Published: December 2004

Drought is one of the most important limitations of photosynthesis in Mediterranean climates. However, Mediterranean sclerophyllous species with long-lived leaves also support extensive and dynamic canopies, with potentially large spatial and age-dependent gradients. We studied within-canopy and temporal patterns in foliage structure, chemistry and photosynthesis in the evergreen species Quercus coccifera L., Q. ilex L. subsp. ballota (Desf.) Samp. in Bol. and Q. suber L. and in the semi-deciduous marcescent species Q. faginea Lam. to determine the role of within-canopy shading and leaf age on foliage functioning. There was a 2.5-fold within-canopy gradient in leaf dry mass per unit area (MA) that was accompanied by a 3-fold range in area-based leaf nitrogen (N) content, the capacity for photosynthetic electron transport (Jmax) and maximum Rubisco carboxylase activity (Vcmax), while the fractional investments of leaf nitrogen in electron transport (FB) and in Rubisco (FR) were relatively constant within the canopy. Leaf aging led to increased MA, larger or constant mass-based N content, larger phosphorous (P) and structural carbon contents, but decreased movable cation contents. Age-dependent increases in MA and N per dry mass meant that Jmax and Vcmax per area were weakly related to leaf age, with a trend of decreasing values in older leaves. However, Jmax and Vcmax per unit dry mass decreased 4-fold across the range of leaf age, primarily owing to decreases in apparent N investments in photosynthetic machinery. This decrease in apparent N investments in photosynthetic machinery was possibly the result of a larger fraction of N bound to cell walls, or of an enhanced CO2 diffusion resistance from the outer surface of cell walls to the chloroplasts in older leaves with thicker and more lignified cell walls. The age-dependent variation in apparent fractional investments of N in photosynthetic machinery reduced the generality of leaf nitrogen v. photosynthesis relationships. Photosynthetic characteristics qualitatively fitted the same patterns with leaf age in all species, but at a common leaf age, area-based leaf photosynthetic potentials depended on species-specific values of MA. These data collectively demonstrate important canopy and age-dependent controls on leaf structure, chemistry and photosynthetic potentials that should be included in larger-scale photosynthesis simulations in Mediterranean climates.
Changes in the Distribution of Air Pollution Exposure in the Los Angeles Basin from 1990 to 1999
Authors: Brajer Victor , Hall Jane V.
Published: December 2004

This research assesses changes in the patterns of ozone and particulate concentrations and the associations of these pollutants with socioeconomic factors from 1990 to 1999 in the South Coast Air Basin of California. The results are somewhat different in 1999 than in 1990 and suggest that demographic changes, in concert with changes in emissions and resulting air pollution patterns, determine the pattern of air pollution exposure and how exposure changes over time. (JEL)
Are There Differential Effects of Price and Policy on College Students’Drinking Intensity?
Authors: Williams Jenny , Chaloupka Frank J. , Wechsler Henry
Published: December 2004

This article investigates the impact of campus bans on alcohol use and the price of alcohol on college students’drinking intensity. The impact of a campus ban on drinking appears to depend on the ability of students to substitute off‐campus access to alcohol for on‐campus access. Where few off‐campus alternatives exist, campus bans reduce the odds that a student becomes a heavy drinker but have no impact on the odds of transitioning from abstainer to drinker. Where off‐campus alternatives are more plentiful, campus bans are less effective. Increasing the price of alcohol appears to be equally effective at reducing the likelihood of drinking and heavy drinking. (JEL)
Tectonic drivers for vegetation patterning and landscape evolution in the Albany River region of the Hudson Bay Lowlands
Authors: GLASER PAUL H. , SIEGEL DONALD I. , REEVE ANDREW S. , JANSSENS JAN A. , JANECKY DAVID R.
Published: December 2004

Groundwater–peatland interactions were assessed by a regional survey in the Hudson Bay Lowlands, where the rapid rate of isostatic uplift has perturbed hydrological flow systems across a 6000‐year chronosequence.

A 24 000 km2 study area along the Albany River consists of 55% fen, 35% bog and 10% mineral soil. The peatland vegetation may be further subdivided into 11 noda, which are closely related to different water levels, ranges in water chemistry, and peat landform type. Species richness generally declines with increasing water level and acidity, whereas the gradient from bog to extremely rich fen is marked by the changing abundance and occurrence of fen‐indicator species.

Bog landforms are restricted to physiographic settings where surface waters flow downwards and the bog vegetation is therefore isotated from the influence of geogenous waters. In contrast, fens are located in areas where mineral solutes are transported to the peat surface either by upwelling groundwater or by advective/dispersion along lateral flow paths.

Peatlands spread across the study area between 6000 and 3000 bp, coinciding with the emergence of new land from the sea. The release of organic acids from the nearly continuous peat cover acidified this calcareous landscape, leading to the convergence of the surface‐water chemistry into four discrete groupings of pH vs. calcium.

Isostatic uplift, however, continues to alter the topography, fluvial geometry and groundwater flow systems of the lowlands, maintaining diverse peatland types on land surfaces of similar age. The formation of water‐table mounds under the interfluvial divides and rising moraine system spurred the development of raised bogs, whereas the formation of regional seepage faces for goundwater on the margins of the moraine and rivers of the till plain maintains large areas of fen.

Although peatland succession seems to follow predictable pathways within a given hydrogeological setting, these pathways are locally altered by tectonic drivers that continually modify surface and groundwater flow systems. In this large peat basin the pace and pathway of peatland succession seems to be driven by tectonic rather than climatic forcing.
Rates, pathways and drivers for peatland development in the Hudson Bay Lowlands, northern Ontario, Canada
Authors: GLASER PAUL H. , HANSEN BARBARA C. S. , SIEGEL DONALD I. , REEVE ANDREW S. , MORIN PAUL J.
Published: December 2004

The Hudson Bay Lowlands have been rising isostatically for the past 7000 years, creating a regional chronosequence as new land emerges from the sea. Rates of uplift are most rapid in the eastern portion of the lowlands near the lower Albany River study area.

The stratigraphy of three raised bogs was investigated to determine rates and pathways of peatland development in the Albany River region. The bogs are distributed evenly along the regional chronosequence from the oldest site at Oldman (5980 ± 100 bp) to progressively younger sites at Albany River (4810 ± 70) and Belec Lake (3960 ± 60).

Each bog had the same stratigraphic sequence, beginning with a basal tidal marsh assemblage that was rapidly replaced by a Larix‐dominated swamp forest, followed by a Picea‐forested bog, and ultimately a non‐forested bog. The bog–fen boundary is marked by the disappearance of fen indicators, dominance of bog‐forming Sphagna, and a sharp decline in nitrogen. Each of these successional stages was associated with different rates of vertical growth.

The rate of successional change was more rapid at the younger sites, and their vertical growth curve was more curvilinear. The formation of a raised bog, for example, was 1.3 times more rapid at Albany River and 5.5 times more rapid at Belec Lake than at Oldman. Belec Lake reached its ultimate successional stage first, although it was the last site to emerge from the sea.

The differential rate of isostatic uplift across this region rather than climate was the principal environmental driver for peatland development. The faster rate of uplift on the lower reaches of the drainage basin continues to reduce the regional slope, impede drainage and shift river channels, continually altering the local hydrogeological setting.

Groundwater flow simulations based on the Dupuit equation show that the growth of these raised bogs was probably constrained by their local hydrogeological setting. Bog formation was first induced by the creation of interfluvial divides between headwardly eroding streams or shifting river channels, and further bog growth was ultimately constrained by the width of the interfluve and the depth of river incision. The Belec Lake bog was the first to approach its limiting height because its narrow interfluve could only support a low water‐table mound.

Although peatland succession largely followed the same conservative pathway at each site, both the pace and direction of these pathways were set by geological processes, which are probably the decisive drivers for the evolution of this large peat basin.