bluuebunny/crossref_metadata_2025 huggingface dataset:
Legal persons: the evolution of fictitious species
Authors: PAGANO UGO
Published: January 2010

Posner considers purposeful organisations. Legal persons are fictitious non-mortal species whose evolution has played a major role in economic development. In what sense can they be said to have a purpose? Thanks to several important mutations, the status of legal persons was transferred from public bodies to business corporations. This evolutionary journey is complementary to the Coasian view, which, moving in the opposite direction, explains the firm as a centralization of market transactions. If the corporation emerged also from a process of decentralization of public attributes, some features of public legal persons, are lacking in its business mutation. Also some ways of motivating people are only available to the original species.
Responding to change: internal and external factors in organizational success
Authors: ULEN THOMAS S.
Published: January 2010

In order for organizations to adopt procedures and structures that efficiently serve their goals, they need to overcome predictable errors in individual and group judgment and decisionmaking and to distinguish ephemeral from significant environmental changes. I seek to identify factors internal and external to the organization that contribute to overcoming these two problems. I suggest the modern US research university as a case study of a successful organization.
From the new institutional economics to organization economics: with applications to corporate governance, government agencies, and legal institutions
Authors: POSNER RICHARD A.
Published: January 2010

This paper applies the principles of organization economics (an offshoot of organization theory and a cousin of the New Institutional Economics) to a variety of organizations, mainly public ones. Organization economics seeks to understand and improve the ways in which organizations overcome agency costs, information costs, and other obstacles to efficiency. The private organization discussed in the paper is the modern publicly held (that is, dispersed ownership) business corporation, and the particular problem on which I focus is excessive executive compensation as a symptom of weaknesses in corporate governance. I then discuss two public organizations involved in national security – the US intelligence ‘community’ (a kind of mega-organization) and the Federal Bureau of Investigation in its role as the nation's principal domestic intelligence service. Both exhibit significant dysfunction that organization economics can help us to understand and overcome. I then discuss two types of public organization that have been more successful in overcoming obstacles to organizational efficiency: the judiciary of common law nations, such as the United States, and the very differently structured judiciary of civil law nations, such as France, Germany, and Japan.
PASCH’S PHILOSOPHY OF MATHEMATICS
Authors: SCHLIMM DIRK
Published: January 2010

Moritz Pasch (1843–1930) gave the first rigorous axiomatization of projective geometry in hisVorlesungen über neuere Geometrie(1882), in which he also clearly formulated the view that deductions must be independent from the meanings of the nonlogical terms involved. Pasch also presented in these lectures the main tenets of his philosophy of mathematics, which he continued to elaborate on throughout the rest of his life. This philosophy is quite unique in combining a deductivist methodology with a radically empiricist epistemology for mathematics. By taking into consideration publications from the entire span of Pasch’s career, the latter decades of which he devoted primarily to careful reflections on the nature of mathematics and of mathematical knowledge, Pasch’s highly original, but virtually unknown, philosophy of mathematics is presented.
Observation and modeling of platelet ice fabric in McMurdo Sound, Antarctica
Authors: Dempsey D. E. , Langhorne P. J. , Robinson N. J. , Williams M. J. M. , Haskell T. G. , Frew R. D.
Published: January 2010

During the annual growth of landfast ice in McMurdo Sound, Antarctica, an episodic flux of platelet ice crystals from the ocean contributes to the build up of a porous subice platelet layer, which is steadily incorporated into the sea ice cover as it thickens over winter. In November 2007, we examined the spatial variability of these processes by collecting sea ice cores, with simultaneous oceanographic observations, along an east‐west transect in the sound. Previously identified draped and bladed platelet ice types were observed. In addition, we identify resumed columnar growth which appears to be a result of geometric selection from the subice platelet layer after the arrival of new platelet crystals from the ocean has ceased. A numerical model of mechanical platelet ice processes is developed that predicts crystal texture and c axis distributions, producing virtual incorporated platelet ice with known growth history. This model demonstrates how a disordered subice platelet layer arises from an initially flat interface and suggests that such a layer is more likely to form later in the growth season. The model also suggests how the grain boundary density in incorporated platelet ice responds to changes in the flux of loose platelet crystals from the ocean. Application of this result to our 2007 platelet ice observations indicates that sea ice in western McMurdo Sound is subject to larger and more persistent platelet fluxes than the ice in the east. This is consistent with the pattern of in situ supercooling just beneath the ocean surface.
Frequency and fluid effects on elastic properties of basalt: Experimental investigations
Authors: Adelinet M. , Fortin J. , Guéguen Y. , Schubnel A. , Geoffroy L.
Published: January 2010

In order to investigate the effects of fluid and frequency on the elastic properties, we performed hydrostatic experiments on an Icelandic basalt specimen under both dry and saturated conditions. This basalt is characterized by a bimodal porosity, i.e., cracks and equant pores. The elastic properties ‐bulk moduli in our case‐ were investigated under high pressure through two experimental methods: (1) a classical one using ultrasonic P‐ and S‐waves velocities (frequency 106 Hz), (2) and a new one, using oscillation tests (frequency 10−2 Hz). In dry condition, experimental data show no significant difference between high (HF) and low (LF) frequency bulk moduli. However, in saturated conditions, two effects are highlighted: a physico‐chemical effect emphasized by a difference between drained and dry moduli, and a squirt‐flow effect evidenced by a difference between HF and LF undrained moduli.
Interplanetary magnetic field during the past 9300 years inferred from cosmogenic radionuclides
Authors: Steinhilber F. , Abreu J. A. , Beer J. , McCracken K. G.
Published: January 2010

We have reconstructed the interplanetary magnetic field (IMF), its radial component, and the open solar magnetic flux using the solar modulation potential derived from cosmogenic 10Be radionuclide data for a period covering the past 9300 years. Reconstructions using the assumption of both constant and variable solar wind speeds yielded closely similar results. During the Maunder Minimum, the strength of the IMF was approximately 2 nT compared to a mean value of 6.6 nT for the past 40 years, corresponding to an increase of the open solar magnetic flux of about 350%. We examine four cycles of the Hallstatt periodicity in the IMF with a mean period of ∼2250 years and an amplitude of ∼0.75 nT. Grand solar minima have largely occurred in clusters during the Hallstatt cycle minima around the years −5300, −3400, −1100, and +1500 A.D. The last cluster includes the Dalton, Maunder, and Spörer minima. We predict that the next such cluster will occur in about 1500 years. The long‐term IMF has varied between ∼2 nT and ∼8 nT and does not confirm a proposed floor (lower limit). There is a slowly changing long‐term trend of amplitude 1.5 nT, with a minimum around the year −4600 and a maximum around 0 A.D. that may be of solar origin but which also may be due to unknown long‐term changes in the atmospheric effects or geomagnetic field intensity.
Effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading
Authors: Lan Hengxing , Martin C. Derek , Hu Bo
Published: January 2010

A grain‐based Universal Distinct Element Code model was developed to generate a deformable polygonal grain‐like structure to simulate the microstructure of brittle rock. It takes into account grain‐scale heterogeneity including microgeometric heterogeneity, grain‐scale elastic heterogeneity, and microcontact heterogeneity. The microgeometric heterogeneity can be used to match the grain size distribution of the rock. The discrete element approach is able to simulate the microheterogeneity caused by elastic variation and contact stiffness anisotropy. The modeling approach was evaluated using Lac du Bonnet granite and Äspö Diorite. The microheterogeneity played an important role in controlling both the micromechanical behavior and the macroscopic response when subjected to uniaxial compression loading. The crack‐initiation stress was found to be controlled primarily by the microscale geometric heterogeneity, while the microcontact heterogeneity controlled the strength characteristics. The effect of heterogeneity on the distribution and evolution of tensile stresses and associated extension cracks was also examined.
Trends and clustering in the onsets of volcanic eruptions
Authors: Bebbington M. S.
Published: January 2010

We show how the trend renewal process (TRP) can be used to model the process of eruption onsets. Using combinations of power, exponential and sine functions, trends and/or cyclic activity can be fitted. On 14 example volcanoes, cases of constant activity level, increasing trend, wax and wane of activity, and cyclic plus trend behaviors were all observed. Embedded in the TRP is a renewal function for the detrended interonset times. Using a Weibull distribution, which can measure the degree of clustering/periodicity, we show that the widely observed tendency of eruption onsets to cluster may be best explained by trends in the activity, which is confirmed by a fractal analysis using the Hurst exponent. This means that compensating for extra parameters by means of the Akaike information criterion, the best fitted model for most of the volcanoes appears to be the nonhomogeneous Poisson process special case of the TRP. The TRP lends itself to analytically simple forecasting of the annual eruption probability (AEP) for the next eruption. This AEP can exhibit considerable structure with certain trend functions, but example data from Etna show how the TRP can automatically act to compensate the AEP against incomplete observation by fitting an increasing trend.
Modeling of depth‐induced wave breaking under finite depth wave growth conditions
Authors: van der Westhuysen André J.
Published: January 2010

Recent studies have shown that the spectral wind wave model SWAN (Simulating Waves Nearshore) underestimates wave heights and periods in situations of finite depth wave growth. In this study, this inaccuracy is addressed through a rescaling of the Battjes and Janssen (1978) bore‐based model for depth‐induced breaking, considering both sloping bed surf zone situations and finite depth wave growth conditions. It is found that the variation of the model error with the breaker index γBJ in this formulation differs significantly between the two types of conditions. For surf zones, clear optimal values are found for the breaker index. By contrast, under finite depth wave growth conditions, model errors asymptotically decrease with increasing values of the breaker index (weaker dissipation). Under both the surf zone and finite depth wave growth conditions, optimal calibration settings of γBJ were found to correlate with the dimensionless depth kpd (where kp is the spectral peak wave number and d is the water depth) and the local mean wave steepness. Subsequently, a new breaker index, based on the local shallow water nonlinearity, expressed in terms of the biphase of the self‐interactions of the spectral peak, is proposed. Implemented in the bore‐based breaker model of Thornton and Guza (1983), this breaker index accurately predicts the large difference in dissipation magnitudes found between surf zone conditions and finite depth growth situations. Hence, the proposed expression yields a significant improvement in model accuracy over the default Battjes and Janssen (1978) model for finite depth growth situations, while retaining good performance for sloping bed surf zones.
Respective impacts of the East Asian winter monsoon and ENSO on winter rainfall in China
Authors: Zhou Lian‐Tong , Wu Renguang
Published: January 2010

Using station rainfall observations and the ERA‐40 reanalysis, this study investigates respective impacts of the East Asian winter monsoon (EAWM) and El Niño‐Southern Oscillation (ENSO) on winter (November–March) rainfall in China by removing the interdependence between the EAWM and ENSO using a linear regression. It is found that circulation and temperature anomalies over the tropics and midlatitude North Pacific are mainly induced by ENSO, and those over the midlatitude Asia are closely linked to the EAWM. The warm ENSO induced lower‐level southwesterly winds deflect from the southeast coast of China, and thus, the influence of ENSO on winter rainfall is mainly in southern China. The lower‐level southerly winds associated with a weak EAWM penetrate northward over eastern China, and thus, the EAWM influences winter rainfall in eastern China.
An adaptive finite volume solver for ice sheets and glaciers
Authors: Egholm David L. , Nielsen Søren B.
Published: January 2010

We have developed a new adaptive finite volume scheme for numerical simulations of ice sheets and glaciers. The mathematical basis of the adaptive solver is represented by the finite volume method and irregular Voronoi cell grids. Evaluation of spatial derivatives are obtained at cell edges from approximating the ice surface elevation locally by second‐order polynomials following a least squares approach. The proposed scheme includes a simple and accurate method for handling discontinuities in ice thickness gradients along ice margins. The flexibility of the Voronoi cell structure allows for local mesh refinement in selected areas. We show how increased mesh density along a steep ice margin may considerably increase overall numerical accuracy of an ice sheet simulation. Although the numerical scheme is not restricted to ice sheet representations using the shallow ice approximation (SIA), we here use analytical SIA solutions to test the accuracy of the method.
Determining Priorities for a New International Ocean Drilling Program: Integrated Ocean Drilling Program New Ventures in Exploring Scientific Targets (INVEST); Bremen, Germany, 23–25 September 2009
Authors: Ravelo Christina , Bach Wolfgang
Published: January 2010

A multidisciplinary, international community meeting was held in Germany to define the research goals of the new Integrated Ocean Drilling Program (IODP) New Ventures in Exploring Scientific Targets (INVEST) program. The meeting, attended by 584 participants from 21 countries and more than 200 institutions and agencies, featured 12 keynote lectures and 50 working groups. Participants defined five innovative research directions that are central to the study of the Earth system and that require ocean drilling.

First, climate change impacts can be studied through ocean drilling. The study of long‐term climate change impacts on the environment is only possible through examination of the geologic record. Meeting attendees agreed that future ocean drilling is essential to the study of cryosphere dynamics and sea level change. Drilled ocean sediments will provide critical high‐fidelity records of marine and terrestrial ecosystem responses and feedbacks to climate change. Ocean drilling is vital to studies of long‐term changes in the hydrologic cycle as they relate to greenhouse gas and other forcings and to studies of the processes that account for abrupt climate changes and climate extremes.
Corrections [to “Nonlinear geophysics: Why we need it” and “Candidates for Office 2010–2012”]
Authors: Anonymous
Published: January 2010

In the 1 December 2009 issue of Eos (90(48), 456), Vadim Uritsky's name was misspelled in the article entitled, “Nonlinear geophysics: Why we need it.” Eos regrets this error. In the 22 December 2009 issue of Eos (90(51), 497), a sentence in Eric A. Davidson's candidate statement should have read, “I will seek such opportunities within our section, with other AGU sections, and with sister sections in other societies, such as the Ecological Society of America, Soil Science Society of America, Geological Society of America, and American Society of Limnology and Oceanography.” AGU regrets this error.
Altered adhesive properties of cord blood endothelial outgrowth cells expressing IL‐1ra
Authors: Fischer Philipp , Rümmler Marc , Schulz Christian , Peschel Christian , Ott Ilka , Oostendorp Robert A J
Published: January 2010

The aim of this study was to examine the potential of endothelial outgrowth cells (EOCs) expanded from CD34+ cord blood‐derived cells (CB‐EOCs) for overexpression of therapeutic transgenes. As proof of principle, we overexpressed icIL‐1ra in CB‐EOCs. Proinflammatory activation of CB‐EOCs in response to cytokine stimulation (IL‐1β and tumor necrosis factor (TNF)) and during coculture with monocytes showed that icIL‐1ra‐expressing CB‐EOCs express significantly reduced levels of ICAM‐1, MCP‐1 and thrombin receptor expression. Moreover, overexpression of icIL‐1ra attenuated the IL‐1β‐mediated proinflammatory activation by diminishing the expression of ICAM‐1, SELE, MCP‐1 and IL‐1β. Interestingly, overexpression of icIL‐1ra also inhibited TNF‐induced upregulation of ICAM‐1. Expression of ICAM‐1, VCAM‐1, tissue factor and IL‐1β was also decreased on direct contact with monocytes. These changes in gene expression were accompanied by functional reduction in leukocyte rolling, adhesion of monocytes to CB‐EOCs, as well as by a reduction in transendothelial migration of monocytes. Our findings show that CB‐EOCs stably expressing transgenic icIL‐1ra are protected against activation by not only IL‐1β but also TNFα‐mediated proinflammatory stimuli and inhibit decisive pathomechanisms of inflammatory processes such as rolling, adhesion and transmigration of monocytes. Therefore, icIL‐ra transgenic CB‐EOCs may prove to be beneficial in the treatment of IL‐1β‐ and TNFα‐mediated inflammatory vasculopathies.
Interaction ammonium-nitrate: Response to oxidative stress in chicory plants
Authors: Russo Marco Antonio , Veljovic-Jovanovic Sonja , Belligno Adalgisa
Published: January 2010

The aim of this work was to study, as a function of the different availability of nitrogen in the reduced form, mineral and organic, the induction of the synthesis of some ROS-scavenging molecules and the evolution of some enzymatic activities such as ascorbate peroxidase (APX) and polyphenoloxidase (PPO). Chicory seedlings were grown in nutritive solution for 35 days in controlled conditions. On the 14th day, one third of the plants was transferred into a nutritive solution containing (NH4)2SO4 60 mM, one third was transferred into a medium containing Urea 60 mM, and the remaining was let grow into the nutrition solution, as a control. Three samplings of leaves were performed, respectively after 21, 28 and 35 days of growth.The urea and ammonium sulphate-treated samples showed higher ascorbic acid and polyphenol contents than the control, together with a lower anthocyanins content. APX showed the highest activity in the urea-treated samples, while the highest PPO activity was to refer to samples treated with ammonium sulphate.The variations of the organic components showed the incidence of the nitrogen supply in the reduced form on the cell redox potential, confirming the importance of fertilization for obtaining high amounts of antioxidant molecules.
Influence of different iron availability on phosphoenolpiruvate carboxilase and malate dehydrogenase in roots of maize (Zea Mays L.) plants grown under iron deficiency
Authors: Russo Marco Antonio , Belligno Adalgisa
Published: January 2010

The effect of the different nitrate availability on some enzymatic activities has been evaluated in iron deficient and iron sufficient maize plants (Zea mays L.). In order to evaluate if the induction of sensitive to pH enzymatic activities is affected by the variation of the apoplast reaction due to the different nitrate availability, two experimental tests were done on maize plants grown in nutrient solution with different NO3- availability and with Fe-sufficiency (+Fe) (added with 80 uM Fe(III)-EDTA) and Fe-deficiency (-Fe) (added with 0.1 uM Fe(III)-EDTA).As regards 0.4 mM NO3- (NS2), independently of iron availability, phosphoenolpiruvate carboxilase and malate dehydrogenase inductions are higher than those recorded for the experiment with 4.0 mM NO3-. The two activities, for the reaction determined in citosol by NO3- uptake, show different responses according to Fe availability. In NS1 the higher nitrate uptake and the contemporaneous H+ incoming cause in (+Fe) plants a decrease of PEP-carboxilase activation and, during the first 24 hours, of malate dehydrogenase. The shifting of the peak of maximum activity shows that iron deficiency conditions, interfering with e- transport, determinate a slowing down of the enzyme induction, independently of nitrate availability. In NS2, PEPcase is higher under Fe-deficiency and malate dehydrogenase is higher under Fe-sufficiency, both during the first 24 hours.The different nitrate availability causes a different use of the acid content. In fact, in NS1 citric content, precursor of molecules for the production of phytosiderophores, increased in (-Fe) theses. On the contrary, low nitrate availabilities determined a decrease in acid contents, mostly in (-Fe) theses. This result justifies the higher energy demand to activate membrane carriers under stress conditions for the reduced nitrate availability.
Inostamycin prevents malignant phenotype of cancer: inhibition of phosphatidylinositol synthesis provides a therapeutic advantage for head and neck squamous cell carcinoma
Authors: Baba Yuh , Kato Yasumasa , Ogawa Kaoru
Published: January 2010

Head and neck squamous cell carcinoma is the sixth most common type of neoplasm worldwide, but its prognosis has not improved significantly in recent years. Therefore, efforts need to be intensified to gain a better understanding of this disease and develop novel treatment strategies. Inhibition of cytidine 5′‐diphosphate 1,2‐diacyl‐sn‐glycerol: inositol transferase by inostamycin, an antibiotic isolated from Streptomyces sp. MH816‐AF15, induces G1 cell cycle arrest accompanied by a decrease in cyclin D1 and phosphorylated RB protein levels, along with suppression of in vitro invasive ability through reduced production of matrix metalloproteinases (MMP‐2 and MMP‐9) and cell motility in head and neck cancer cell lines. Furthermore, inostamycin abrogated the stimulatory effect of VEGF (vascular endothelial growth factor) on growth and migration activities of endothelial cells by targeting extracellular signal‐regulated kinase‐cyclin D1 and p38 pathways, respectively. Because inostamycin has both antiproliferative and anti‐invasive abilities, inhibition of phosphatidylinositol synthesis could be a potent therapeutic strategy for head and neck cancer as the ‘cancer dormant therapy’, i.e. a therapeutic concept to prolong ‘time to treatment failure’ or ‘time to progression’.
Molecular modulation of Schottky barrier height in metal-molecule-silicon diodes: Capacitance and simulation results
Authors: Scott Adina , Risko Chad , Valley Nicholas , Ratner Mark A. , Janes David B.
Published: January 2010

There is considerable current interest in using molecular materials to influence the surface potential of semiconductor devices for nanoelectronic and sensing applications. We present experimental capacitance-voltage results showing that systematic Schottky barrier height modulation can be achieved using dipolar molecular layers in gold-molecule-silicon devices. A computational methodology that combines quantum chemistry and traditional electrostatic calculations is used to explore various physical effects that can influence barrier heights in such systems. Nonidealities such as silicon surface states can influence both the potential profile within the device and the validity of the extracted barrier height. Our devices exhibit low surface state densities, but the magnitude of surface potential modulation is modest due to molecular depolarization from the gold contact.
Synthesis, structure, and electrical behavior of Sr4Bi4Ti7O24
Authors: Zurbuchen M. A. , Sherman V. O. , Tagantsev A. K. , Schubert J. , Hawley M. E. , Fong D. D. , Streiffer S. K. , Jia Y. , Tian W. , Schlom D. G.
Published: January 2010

An n=7 Aurivillius phase, Sr4Bi4Ti7O24, with c=6.44 nm, was synthesized as an epitaxial (001)-oriented film. This phase and its purity were confirmed by x-ray diffraction and transmission electron microscopy. The material is ferroelectric, with a Pr=5.3 μC/cm2 oriented in the (001) plane and a paraelectric-to-ferroelectric transition temperature of TC=324 K. Some indications of relaxorlike behavior are observed. Such behavior is out of character for Srn−1Bi2TinO3n+3 Aurivillius phases and is closer to the bulk behavior of doped SrTiO3, implying a spatial limit to the elastic interlayer interactions in these layered oxides. A finite-element solution to the interpretation of data from interdigitated capacitors on thin films is also described.
A method of particle transport study using supersonic molecular beam injection and microwave reflectometry on HL-2A tokamak
Authors: Xiao W. W. , Zou X. L. , Ding X. T. , Dong J. Q. , Yao L. H. , Song S. D. , Liu Z. T. , Gao Y. D. , Feng B. B. , Song X. M. , Yang Q. W. , Yan L. W. , Liu Yi , Duan X. R. , Pan C. H. , Liu Yong
Published: January 2010

A method of the particle transport study using supersonic molecular beam injection (SMBI) and microwave reflectometry is reported in this paper. Experimental results confirm that pulsed SMBI is a good perturbation source with deeper penetration and better localization than the standard gas puffing. The local density modulation is induced using the pulsed SMBI and the perturbation density is measured by the microwave reflectometry. Using Fourier transform analysis for the local density perturbation, radial profiles of the amplitude and phase of the density modulation can be obtained. The experimental results in HL-2A show that the particle injected by SMBI is located at about r/a=0.65–0.75. The position of the main particle source can be determined through three aspects: the minimum of the phase of the first harmonic of the Fourier transform of the modulated density measured by microwave reflectometry; the Ha intensity profile and the local density increase ratio. The maximum of the amplitude of the first harmonic shifts often inward relative to the particle source location, which indicates clearly there is an inward particle pinch in this area. Good agreement has been found between the experimental results and the simulation using analytical transport model. The particle diffusivity D and the particle convection velocity V have been obtained by doing this simulation. The sensitivity in the transport coefficients of the amplitude and the phase of the density modulation has been discussed.
Thermal instability of implanted Mn ions in ZnO
Authors: Sans J. A. , Martínez-Criado G. , Susini J. , Sanz R. , Jensen J. , Minguez I. , Hernandez-Velez M. , Labrador A. , Carpentier P.
Published: January 2010

This letter reports on the site configuration of implanted Mn cations in ZnO. The samples studied were obtained by means of ion implantation in m-plane ZnO single crystals. Synchrotron radiation based fluorescence shows no contamination during the implantation process. The results of micro-x-ray absorption spectroscopy indicate that Mn ions are located in substitutional sites without detectable traces of secondary phases. The postgrowth thermal annealing in O2 atmosphere induces a change in the coordination of a large amount of Mn cations, corresponding to α-Mn2O3.
Infrared properties of single-walled carbon nanotubes calculated from first principles
Authors: Zhou Jian , Dong Jinming
Published: January 2010

The vibration modes and the infrared (IR) spectra of the zigzag and chiral single-walled carbon nanotubes (SWNTs) have been calculated from the density functional theory in the local density approximation. Three IR-active modes are found to exist in the zigzag SWNTs in contrast to six in the chiral one, which agrees well with the prediction of the rod-group theory. Also, the frequency of low-frequency E1u mode of zigzag tubes is found to be strongly diameter dependent, which could be used for measurement of tube diameter in experiment. It is very interesting to find that the (n−m) mod 3=−1 or 0 tubes exhibit anomalous big IR intensities of their A2u (or A2) modes, much larger than those of the (n−m) mod 3=+1 ones, showing a clear family behavior, which is expected to be easily observed in future experiments.
In situ manipulation of scanning tunneling microscope tips without tip holder
Authors: Raad C. , Graf K. H. , Ebert Ph.
Published: January 2010

A design for a manipulator system for manipulating bare scanning tunneling microscopy (STM) tips without any tip holder is presented. The extremely stiff and rigid system consists of an ultrahigh vacuum compatible fully three-dimensionally movable gripper module driven by stepping motors and piezomotors. The tips are clamped by hardened tool steel gripper jaws, which are controlled by a stepping motor through levers. The system allows the reproducible manipulation of bare tungsten tips made of wires with diameters of 0.25 nm and having length of only up to 3 mm without damaging the tip or the STM. The tip manipulators’ advantage is that the total mass of the scanning piezotube is reduced by removing the mass of a separate tip holder. Thereby, it becomes possible to further increase the resonance frequencies of the STM.
Cracking of epitaxial MnAs films on GaAs(001)
Authors: Takagaki Y. , Moreno M. , Schützendübe P. , Ramsteiner M. , Herrmann C.
Published: January 2010

We report the characteristics of the fracture of epitaxially grown MnAs films on GaAs(001) due to the large thickness or induced by annealing. Stresses arising from the thermal expansion mismatch and the structural phase transition can no longer be accommodated when the film thickness is beyond about 0.5 μm, giving rise to cracking of the films. The cracks are inclined with respect to the c axis of MnAs, suggesting their initiation by a weak plane. For films thicker than about 2 μm, the fracture extends to the substrates, where the in-plane crack angle changes from about 57° to around 45° as the cracking is dictated by the cleavage plane of the substrates. Even for films much thinner than 0.5 μm, annealing results in a delamination from substrate as a consequence of the large thermal expansion and, plausibly, the oxidation of MnAs. We show that Mn capping suppresses the delamination as well as the oxidation during the annealing.
Electronic properties of carbon nanotubes with distinct bond lengths
Authors: Bunder J. E. , Hill James M.
Published: January 2010

In band structure calculations commonly used to derive the electronic properties of carbon nanotubes, it is generally assumed that all bond lengths are equal. However, hexagonal carbon lattices are often irregular and may contain as many as three distinct bond lengths. A regular (n,m) carbon nanotube will be metallic if p=(n−m)/3 for integer p. Here we analytically derive the generalized condition for metallic irregular carbon nanotubes. This condition is particularly relevant to small radius nanotubes and nanotubes experiencing small applied strains.
Atomic and molecular effects on spherically convergent ion flow. II. Multiple molecular species
Authors: Emmert Gilbert A. , Santarius John F.
Published: January 2010

A theoretical model for the effect of molecular interactions on the flow of molecular ions in spherically convergent geometry where the inner grid (cathode) is at a large negative potential and the outer grid (anode) is grounded has been developed. The model assumes a weakly ionized deuterium plasma composed of D+, D2+, and D3+ ions that interact with the dominant background gas (D2). The interactions included are charge exchange, ionization, and dissociative processes. The formalism developed includes the bouncing motion of the ions in the electrostatic well and sums over all generations of subsequent ions produced by atomic and molecular processes. This leads to a set of two coupled Volterra integral equations, which are solved numerically. From the solution of the Volterra equations, one can obtain quantities of interest, such as the energy spectra of the ions and fast neutral atoms and molecules, and the fusion reaction rate. To provide an experimental test, the model is applied to inertial electrostatic devices and the calculated neutron production rate is compared to previously reported measurements for one University of Wisconsin inertial electrostatic confinement device [D. C. Donovan et al., Fusion Sci. Technol. 56, 507 (2009)]. The results show general agreement with the experimental results, but significant differences remain to be resolved.
Large eddy simulation study of fully developed wind-turbine array boundary layers
Authors: Calaf Marc , Meneveau Charles , Meyers Johan
Published: January 2010

It is well known that when wind turbines are deployed in large arrays, their efficiency decreases due to complex interactions among themselves and with the atmospheric boundary layer (ABL). For wind farms whose length exceeds the height of the ABL by over an order of magnitude, a “fully developed” flow regime can be established. In this asymptotic regime, changes in the streamwise direction can be neglected and the relevant exchanges occur in the vertical direction. Such a fully developed wind-turbine array boundary layer (WTABL) has not been studied systematically before. A suite of large eddy simulations (LES), in which wind turbines are modeled using the classical “drag disk” concept, is performed for various wind-turbine arrangements, turbine loading factors, and surface roughness values. The results are used to quantify the vertical transport of momentum and kinetic energy across the boundary layer. It is shown that the vertical fluxes of kinetic energy are of the same order of magnitude as the power extracted by the forces modeling the wind turbines. In the fully developed WTABL, the kinetic energy extracted by the wind turbines is transported into the wind-turbine region by vertical fluxes associated with turbulence. The results are also used to develop improved models for effective roughness length scales experienced by the ABL. The effective roughness scale is often used to model wind-turbine arrays in simulations of atmospheric dynamics at larger (regional and global) scales. The results from the LES are compared to several existing models for effective roughness lengths. Based on the observed trends, a modified model is proposed, showing improvement in the predicted effective roughness length.
Characterization of random telegraph noise in gate induced drain leakage current of n- and p-type metal-oxide-semiconductor field-effect transistors
Authors: Lee Ju-Wan , Shin Hyungcheol , Lee Jong-Ho
Published: January 2010

Random telegraph noise in gate induced drain leakage current of nanoscale n- and p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) was observed and analyzed for the first time. Capture and emission probability of carrier was analyzed in terms of gate voltage and temperature. The emission times (τe) in n and pMOSFETs have no dependence on VGS but are strongly dependent on temperature since the τe is decreased more significantly with increasing temperature than the capture time (τc) in n and pMOSFETs. As VGS increases, the τc in n and pMOSFETs decreases.
Mechanical characterization of thin TiO2 films by means of microelectromechanical systems-based cantilevers
Authors: Adami A. , Decarli M. , Bartali R. , Micheli V. , Laidani N. , Lorenzelli L.
Published: January 2010

The measurement of mechanical parameters by means of microcantilever structures offers a reliable and accurate alternative to traditional methods, especially when dealing with thin films, which are extensively used in microfabrication technology and nanotechnology. In this work, microelectromechanical systems (MEMS)-based piezoresistive cantilevers were realized and used for the determination of Young’s modulus and residual stress of thin titanium dioxide (TiO2) deposited by sputtering from a TiO2 target using a rf plasma discharge. Films were deposited at different thicknesses, ranging from a few to a hundred nanometers. Dedicated silicon microcantilevers were designed through an optimization of geometrical parameters with the development of analytical as well as numerical models. Young’s modulus and residual stress of sputtered TiO2 films were assessed by using both mechanical characterization based on scanning profilometers and piezoresistive sensing elements integrated in the silicon cantilevers. Results of MEMS-based characterization were combined with the tribological and morphological properties measured by microscratch test and x-ray diffraction analysis.
Organic light emitting complementary inverters
Authors: Namdas Ebinazar B. , Samuel Ifor D. W. , Shukla Deepak , Meyer Dianne M. , Sun Yanming , Hsu Ben B. Y. , Moses Daniel , Heeger Alan J.
Published: January 2010

We show that p- and n-type light emitting field-effect transistors (LEFETs) can be made using “superyellow” as a light-emitting polymer, poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) as a p-type material and a naphthalene di-imide as an n-type material. By connecting two of these LEFETs, we have demonstrated a light emitting complementary inverter (LECI). The LECI exhibited electrical and optical characteristics in the first and third quadrant of the transfer characteristics with voltage gain of 6 and 8, respectively.
Polarization-engineered removal of buffer leakage for GaN transistors
Authors: Cao Yu , Zimmermann Tom , Xing Huili , Jena Debdeep
Published: January 2010

A dopant-free epitaxial technique is developed to achieve highly insulating buffers on semi-insulating GaN templates for nitride high electron mobility transistors by using the large polarization fields. The buffer leakage current density is reduced by several orders of magnitude, exhibiting outstanding insulating and breakdown properties. The simple polarization- and heterostructure-based solution should prove highly attractive for GaN high electron mobility transistors for analog (rf), digital, and high-voltage switching applications.
ac impedance analysis of a Ni-Nb-Zr-H glassy alloy with femtofarad capacitance tunnels
Authors: Fukuhara M. , Seto M. , Inoue A.
Published: January 2010

A Nyquist diagram of a (Ni0.36Nb0.24Zr0.40)90H10 glassy alloy shows a semitrue circle, indicating that it is a conducting material with a total capacitance of 17.8 μF. The Bode plots showing the dependencies of its real and imaginary impedances, and phase on frequency suggest a simpler equivalent circuit having a resistor in parallel with a capacitor. Dividing the total capacitance (17.8 μF) by the capacitance of a single tunnel (0.9 fF), we deduced that this material has a high number of dielectric tunnels, which can be regarded as regular prisms separated from the electric-conducting distorted icosahedral Zr5Ni5Nb3 clusters by an average of 0.225 nm.
General expression for effective diffusivity of foreign atoms migrating via a fast intermediate
Authors: Chen Kejia , Vaidyanathan Ramakrishnan , Seebauer Edmund G. , Braatz Richard D.
Published: January 2010

In many solids, diffusion of foreign atoms takes place primarily through highly mobile intermediate species that periodically exchange with atoms in the crystalline lattice. The governing reaction-diffusion equations include a diffusion coefficient as well as kinetic parameters describing the exchange of the intermediate species. Yet it is often convenient to model a diffusive process in terms of a single parameter, no matter what the time regime. This communication derives for a delta function initial profile an exact expression for the effective diffusivity that is valid in all time regimes. In the case of semiconductor solids, such an expression can be helpful in the interpretation of dopant diffusion measurements.
Controlling carrier accumulation and exciton formation in organic light emitting diodes
Authors: Wang Z. B. , Helander M. G. , Liu Z. W. , Greiner M. T. , Qiu J. , Lu Z. H.
Published: January 2010

It is found that the device performance of organic light emitting diodes (OLEDs) can be significantly improved by separating the carrier accumulation zone from the exciton formation interface. The improvement is explained by suppression of exciton quenching caused by accumulated carriers at the exciton formation interface. It is also found that the position of the exciton formation interface in OLEDs correlates well with the interfacial dipole measured using ultraviolet photoelectron spectroscopy at the interface between a hole transport layer and an electron transport layer. The findings of this work provide useful material selection guidelines in designing high performance OLEDs.
Geometry of repeated measurements in chaotic systems
Authors: Binder P.-M. , Wissman B. D.
Published: January 2010

We use joint probability matrices for measurements at different times to describe chaotic systems. By coarse graining the range of the measured variable into uniformly sized bins we can generate matrices that contain both topological and metric information about the systems being studied. Armed with this tool we examine two extreme families of chaotic systems. In the case of one-dimensional piecewise linear maps, we can construct transfer matrices that depend on the map and partition used, and which allow us to generate the respective joint probability matrices for all times as well as the exact time evolution of the mutual information function. We find that the mutual information decays linearly or exponentially depending on whether the second-largest eigenvalue of the transfer matrix is zero or not. In the case of three-dimensional, continuous-time chaotic systems we generate the joint probability matrices directly from numerical data. We show that these matrices directly provide attractor reconstructions with information about the attractor’s probability measure.
Role of the triplet state in the green emission peak of polyfluorene films: A time evolution study
Authors: Mukhopadhyay S. , Ramasesha S. , Guha S.
Published: January 2010

The blue emission of ethyl-hexyl substituted polyfluorene (PF2/6) films is accompanied by a low energy green emission peak around 500 nm in inert atmosphere. The intensity of this 500 nm peak is large in electroluminescence (EL) compared to photoluminescence (PL) measurements. Furthermore, the green emission intensity reduces dramatically in the presence of molecular oxygen. To understand this, we have modeled various nonradiative processes by time dependent quantum many body methods. These are (i) intersystem crossing to study conversion of excited singlets to triplets leading to a phosphorescence emission, (ii) electron-hole recombination (e-hR) process in the presence of a paramagnetic impurity to follow the yield of triplets in a polyene system doped with paramagnetic metal atom, and (iii) quenching of excited triplet states in the presence of oxygen molecules to understand the low intensity of EL emission in ambient atmosphere, when compared with that in nitrogen atmosphere. We have employed the Pariser–Parr–Pople Hamiltonian to model the molecules and have invoked electron-electron repulsions beyond zero differential approximation while treating interactions between the organic molecule and the rest of the system. Our time evolution methods show that there is a large cross section for triplet formation in the e-hR process in the presence of paramagnetic impurity with degenerate orbitals. The triplet yield through e-hR process far exceeds that in the intersystem crossing pathway, clearly pointing to the large intensity of the 500 nm peak in EL compared to PL measurements. We have also modeled the triplet quenching process by a paramagnetic oxygen molecule which shows a sizable quenching cross section especially for systems with large sizes. These studies show that the most probable origin of the experimentally observed low energy EL emission is the triplets.
Implications for the active form of human insulin based on the structural convergence of highly active hormone analogues
Authors: Jiráček Jiří , Žáková Lenka , Antolíková Emília , Watson Christopher J. , Turkenburg Johan P. , Dodson Guy G. , Brzozowski Andrzej M.
Published: January 2010

Insulin is a key protein hormone that regulates blood glucose levels and, thus, has widespread impact on lipid and protein metabolism. Insulin action is manifested through binding of its monomeric form to the Insulin Receptor (IR). At present, however, our knowledge about the structural behavior of insulin is based upon inactive, multimeric, and storage-like states. The active monomeric structure, when in complex with the receptor, must be different as the residues crucial for the interactions are buried within the multimeric forms. Although the exact nature of the insulin’s induced-fit is unknown, there is strong evidence that the
C
-terminal part of the B-chain is a dynamic element in insulin activation and receptor binding. Here, we present the design and analysis of highly active (200–500%) insulin analogues that are truncated at residue 26 of the B-chain (B
26
). They show a structural convergence in the form of a new β-turn at B
24
-B
26
. We propose that the key element in insulin’s transition, from an inactive to an active state, may be the formation of the β-turn at B
24
-B
26
associated with a
trans
to
cis
isomerisation at the B
25
-B
26
peptide bond. Here, this turn is achieved with
N
-methylated L-amino acids adjacent to the
trans
to
cis
switch at the B
25
-B
26
peptide bond or by the insertion of certain D-amino acids at B
26
. The resultant conformational changes unmask previously buried amino acids that are implicated in IR binding and provide structural details for new approaches in rational design of ligands effective in combating diabetes.