bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic field effects on the linear and nonlinear optical properties of coaxial cylindrical quantum well wires
Authors: Karimi M. J. , Rezaei G.
Published: March 2012

In this work, the influence of an external magnetic field on the refractive index changes and optical absorption coefficients of a typical GaAs/AlxGa1−xAs coaxial cylindrical quantum well wire is studied. Energy eigenvalues and eigenvectors in the presence of a magnetic field are calculated using the fourth-order Runge-Kutta method and optical properties are obtained using the compact density matrix approach. It is found that the resonant peak values of the linear and the third-order nonlinear refractive index changes as well as the optical absorption coefficients of a cylindrical quantum wire decrease with increasing the magnetic field. However, these optical properties of a coaxial cylindrical quantum well wire are nonmonotonic functions of the magnetic field, due to the anticrossing of the subbands. The anticrossing effect leads to a large increase of the resonant peak values of these optical properties. Results also indicate that the resonant peak values of these optical properties decrease with increasing the barrier width.
Shift of responsive peak in GaN-based metal-insulator-semiconductor photodetectors
Authors: You Kun , Jiang Hong , Li Dabing , Sun Xiaojuan , Song Hang , Chen Yiren , Li Zhiming , Miao Guoqing , Liu Hongbo
Published: March 2012

A gallium nitride (GaN)-based metal-insulator-semiconductor (MIS) ultraviolet photodetector (PD) was fabricated on a sapphire substrate. It was found that the responsive peak of the GaN-based MIS PD redshifted with increasing negative bias, which has not been reported before. Also, the shift of the responsive peak has been interpreted in terms of the tunneling procedure of the photo-generated holes assisted by defects in the interfaces between the GaN layers and the SiNx layers.
Vibrational effects on the electron momentum distributions of valence orbitals of formamide
Authors: Miao Y. R. , Deng J. K. , Ning C. G.
Published: March 2012

The ionization energy spectra and electron momentum distributions of formamide were investigated using the high-resolution electron momentum spectrometer in combination with high level calculations. The observed ionization energy spectra and electron momentum distributions were interpreted using symmetry adapted cluster-configuration interaction theory, outer valence Green function, and DFT-B3LYP methods. The ordering of 10a′ and 2a″ orbitals of formamide was assigned unambiguously by comparing the experimental electron momentum distributions with the corresponding theoretical results, i.e., 10a′ has a lower binding energy. In addition, it was found that the low-frequency wagging vibration of the amino group at room temperature has noticeable effects on the electron momentum distributions. The equilibrium-nuclear-positions-approximation, which was widely used in electron momentum spectroscopy, is not accurate for formamide molecule. The calculations based on the thermal average can evidently improve the agreement with the experimental momentum distributions.
Microwave dielectric dispersion in a multiferroic Pb(Fe1/2Nb1/2)O3 thin film
Authors: Sobiestianskas R. , Peng W. , Lemée N. , Karkut M. , Banys J. , Holc J. , Kosec M.
Published: March 2012

We present the dielectric dispersion in a Pb(Fe1/2Nb1/2)O3 (PFN) thin film grown on (001) SrTiO3 substrate from 20 MHz to 20 GHz in the temperature range of 270 to 340 K. In the radio frequency region, the hopping charge transport and associated polar nanoregion and/or domain-wall motion contribute to the spectrum. In the microwave region, relaxational dispersion was observed with a dielectric contribution of Δε ≈ 600 at room temperature having a characteristic frequency (fm)0.4 = 9.8 · (T−T0) Hz, where T0 is 660 K. It is associated with possible mode-softening behavior, related to the onset of polar nanoregions at T0. The dielectric permittivity shows similarities with 1-dimensional Ising model behaviour.
Electrical characterization of back-gated bi-layer MoS2 field-effect transistors and the effect of ambient on their performances
Authors: Qiu Hao , Pan Lijia , Yao Zongni , Li Junjie , Shi Yi , Wang Xinran
Published: March 2012

Two-dimensional transition-metal dichalcogenides such as MoS2 are promising channel materials for transistor scaling. Here, we report the performance and environmental effects on back-gated bi-layer MoS2 field-effect transistors. The devices exhibit Ohmic contacts with titanium at room temperature, on/off ratio higher than 107, and current saturation. Furthermore, we show that the devices are sensitive to oxygen and water in the ambient. Exposure to ambient dramatically reduces the on-state current by up to 2 orders of magnitude likely due to additional scattering centers from chemisorption on the defect sites of MoS2. We demonstrate that vacuum annealing can effectively remove the absorbates and reversibly recover the device performances. This method significantly reduces the large variations in MoS2 device caused by extrinsic factors.
Mapping of the epitaxial stabilization of quasi-tetragonal BiFeO3 with deposition temperature
Authors: Dix N. , Muralidharan R. , Varela M. , Fontcuberta J. , Sánchez F.
Published: March 2012

Quasi-tetragonal BiFeO3 (T-BFO) multiferroic oxide is receiving much attention due to prospects of enhanced ferroelectric polarization and close-to-room-temperature phase transitions. Here, we report on the role of deposition temperature on the stabilization of the T-BFO phase on LaAlO3(001) substrates. T-BFO has only been obtained in a narrow temperature window. We will show that competitive formation of rhombohedral BFO and thermal decomposition at lower and higher temperatures, respectively, bounds the stability range of T-BFO. However, we show that addition of a secondary spinel phase, creating vertical interfaces, extends the formation range of T-BFO.
An incoherent light source excited thermal lens microscope
Authors: Liu Mingqiang , Franko Mladen
Published: March 2012

We report a thermal lens microscope (TLM) based on an incoherent light source (ILS) excitation. By introducing a three-layer system into an optimized ILS-excited TLM, the sensitivity can be amplified up to 10 times for a 100-μm aqueous sample. The sensitivity enhancement originates from two additional thermal lenses formed by the heat transferred from the sample to the top and bottom layers with high temperature coefficient of refractive index. It is predicted that with a power of about 10 mW used for exciting a 100-μm sample, the limit of detection of the ILS-excited TLM can go down to 5.5 × 10−6 AU.
Enhancement of vertical emission in photonic crystal nanolasers
Authors: Narimatsu Michimasa , Kita Shota , Abe Hiroshi , Baba Toshihiko
Published: March 2012

Photonic crystal nanolasers have a drawback of weak vertical emission, which degrades the detection efficiency from above. We show that the vertical emission is enhanced greatly by introducing asymmetry to the cavity, so that Fourier components around the Brillouin zone boundary are shifted to the zone center. When the light output is collected from above by an objective lens with a numerical aperture of 0.42, the efficiency for the optimized devices, with and without nanoslot, are calculated to be 26 and 153 times that of the original structure. We confirm the experimental and calculated results to be in good agreement.
Organic integrated complementary inverters with ink-jet printed source/drain electrodes and sub-micron channels
Authors: Gili E. , Caironi M. , Sirringhaus H.
Published: March 2012

We have demonstrated device operation of down-scaled n-type field effect transistors (FETs) with ink-jet printed source/drain contacts and sub-μm channel length, using the P(NDI2OD-T2) semiconducting polymer as active material. We integrated these devices with down-scaled p-type FETs made with bis(triisopropylsilylethynyl)pentacene to fabricate complementary inverter gates, in which both transistors and the printed interconnections were implemented on the same substrate. The devices operate at 10 V supply voltage, achieve noise margin values of 56% of VDD2 and a gain higher than 10. They are therefore suitable for printed, high performance organic integrated circuits with low supply voltage.
SiN passivation layer effects on un-gated two-dimensional electron gas density in AlGaN/AlN/GaN field-effect transistors
Authors: Asgari A. , Faraone L.
Published: March 2012

In this paper, we present a study of SiN passivation layer effects on the two-dimensional electron gas (2DEG) sheet density in unintentionally doped AlGaN/AlN/GaN heterostructures, using a polarization model based on interface charges and a fully numerical calculation. The analysis of our results clearly indicates that there are at least two occupied sub-bands in the 2DEG for passivated AlGaN/AlN/GaN heterostructures, and with increasing passivation layer thickness and AlN interlayer thickness the 2DEG density increases. The comparison of our calculated results with published experimental data is shown to be in a very good agreement.
Breakdown by magnetic field in a La0.7Sr0.3MnO3/MgO/Fe spin valve
Authors: Wu Xiaojie , Zhang Zhenzhong , Meng Jian
Published: March 2012

A La0.7Sr0.3MnO3/MgO/Fe spin valve with inverse tunneling magnetoresistance (TMR) was fabricated on a (100) SrTiO3 substrate by radio frequency magnetron sputtering. Giant TMR ratios up to 540% were obtained. The breakdown of the spin valve was observed at high magnetic field, which was attributed to the joint action of the invalidation of MgO barrier and the shift of Fermi energy in La0.7Sr0.3MnO3 at high magnetic field.
Generalized local induction equation, elliptic asymptotics, and simulating superfluid turbulence
Authors: Strong Scott A. , Carr Lincoln D.
Published: March 2012

We prove the generalized induction equation and the generalized local induction equation (GLIE), which replaces the commonly used local induction approximation (LIA) to simulate the dynamics of vortex lines and thus superfluid turbulence. We show that the LIA is, without in fact any approximation at all, a general feature of the velocity field induced by any length of a curved vortex filament. Specifically, the LIA states that the velocity field induced by a curved vortex filament is asymmetric in the binormal direction. Up to a potential term, the induced incompressible field is given by the Biot-Savart integral, where we recall that there is a direct analogy between hydrodynamics and magnetostatics. Series approximations to the Biot-Savart integrand indicate a logarithmic divergence of the local field in the binormal direction. While this is qualitatively correct, LIA lacks metrics quantifying its small parameters. Regardless, LIA is used in vortex filament methods simulating the self-induced motion of quantized vortices. With numerics in mind, we represent the binormal field in terms of incomplete elliptic integrals, which is valid for \documentclass[12pt]{minimal}\begin{document}$\mathbb {R}^{3}$\end{document}R3. From this and known expansions we derive the GLIE, asymptotic for local field points. Like the LIA, generalized induction shows a persistent binormal deviation in the local field but unlike the LIA, the GLIE provides bounds on the truncated remainder. As an application, we adapt formulae from vortex filament methods to the GLIE for future use in these methods. Other examples we consider include vortex rings, relevant for both superfluid 4He and Bose-Einstein condensates.
Impact of TaOx nanolayer at the GeSex/W interface on resistive switching memory performance and investigation of Cu nanofilament
Authors: Rahaman S. Z. , Maikap S. , Chen W. S. , Lee H. Y. , Chen F. T. , Tien T. C. , Tsai M. J.
Published: March 2012

The impact of a TaOx nanolayer at the GeSex/W interface on the performance of resistive switching memory in an Al/Cu/GeSex/TaOx/W structure has been examined. All materials and the memory structure have been investigated using high-resolution transmission electron microscopy, energy dispersive x ray spectroscopy, and x ray photo-electron spectroscopy analyses. A conically shaped crystalline Cu (111) nanofilament with a diameter of around 17 nm in the TaOx nanolayer after a current compliance (CC) of 500 μA has been observed, and this has been also characterized by fast Fourier transform. The low resistance state (LRS) decreases as the current compliances (CCs) increased from 1 nA to 1 mA, since the nanofilament diameter increased from 0.04 to 23.4 nm. This is also estimated by bipolar resistive switching characteristics. The resistivity of this crystalline Cu nanofilament is approximately 2300 μΩ.cm. The nanofilament has a cylindrical shape, with CCs ranging from 1 nA to 10 μA and a conical shape with CCs ranging from 50 μA-1 mA. The resistive switching mechanism has been explained successfully under SET and RESET operations. Improved resistive switching parameters, such as SET voltage, LRS, and high resistance state with consecutive switching cycles are obtained and compared to those of pure GeSex and TaOx materials. Extrapolated, long program/erase endurance of > 106 cycles, attributed to the Al/Cu/GeSex/TaOx/W structure design, is observed. This resistive switching memory structure shows extrapolated 10 years data retention with a resistance ratio of > 10 at a low CC of 0.1 μA at 50 °C. A large memory size of ∼ 6 Pbit/sq. in. is obtained, considering the nanofilament diameter at a low CC of 0.1 μA. This study is important not only for improving the performance of low-power resistive switching memory, but also helpful for designing other nonvolatile memory devices.
Tailoring interfacial exchange coupling with low-energy ion beam bombardment: Tuning the interface roughness
Authors: Lin K.-W. , Mirza M. , Shueh C. , Huang H.-R. , Hsu H.-F. , Lierop J. van
Published: March 2012

By ascertaining NiO surface roughness in a Ni80Fe20/NiO film system, we were able to correlate the effects of altered interface roughness from low-energy ion-beam bombardment of the NiO layer and the different thermal instabilities in the NiO nanocrystallites. From experiment and by modelling the temperature dependence of the exchange bias field and coercivity, we have found that reducing the interface roughness and changing the interface texture from an irregular to striped conformation enhanced the exchange coupling strength. Our results were in good agreement with recent simulations using the domain state model that incorporated interface mixing.
Evaluation of freestanding boron-doped diamond grown by chemical vapour deposition as substrates for vertical power electronic devices
Authors: Issaoui R. , Achard J. , Tallaire A. , Silva F. , Gicquel A. , Bisaro R. , Servet B. , Garry G. , Barjon J.
Published: March 2012

In this study, 4 × 4 mm2 freestanding boron-doped diamond single crystals with thickness up to 260 μm have been fabricated by plasma assisted chemical vapour deposition. The boron concentrations measured by secondary ion mass spectroscopy were 1018 to 1020 cm−3 which is in a good agreement with the values calculated from Fourier transform infrared spectroscopy analysis, thus indicating that almost all incorporated boron is electrically active. The dependence of lattice parameters and crystal mosaicity on boron concentrations have also been extracted from high resolution x-ray diffraction experiments on (004) planes. The widths of x-ray rocking curves have globally shown the high quality of the material despite a substantial broadening of the peak, indicating a decrease of structural quality with increasing boron doping levels. Finally, the suitability of these crystals for the development of vertical power electronic devices has been confirmed by four-point probe measurements from which electrical resistivities as low as 0.26 Ω cm have been obtained.
CdSe/CdTe type-II superlattices grown on GaSb (001) substrates by molecular beam epitaxy
Authors: Li Jing-Jing , Liu Xinyu , Liu Shi , Wang Shumin , Smith David J. , Ding Ding , Johnson Shane R. , Furdyna Jacek K. , Zhang Yong-Hang
Published: March 2012

CdSe/CdTe superlattices are grown on GaSb substrates using molecular beam epitaxy. X-ray diffraction measurements and cross-sectional transmission electron microscopy images indicate high crystalline quality. Photoluminescence (PL) measurements show the effective bandgap varies with the superlattice layer thicknesses and confirm the CdSe/CdTe heterostructure has a type-II band edge alignment. The valence band offset between unstrained CdTe and CdSe is determined as 0.63 ± 0.06 eV by fitting the measured PL peak positions using the envelope function approximation and the Kronig-Penney model. These results suggest that CdSe/CdTe superlattices are promising candidates for multi-junction solar cells and other optoelectronic devices based on GaSb substrates.
Diversity of dynamics and morphologies of invasive solid tumors
Authors: Jiao Yang , Torquato Salvatore
Published: March 2012

Complex tumor-host interactions can significantly affect the growth dynamics and morphologies of progressing neoplasms. The growth of a confined solid tumor induces mechanical pressure and deformation of the surrounding microenvironment, which in turn influences tumor growth. In this paper, we generalize a recently developed cellular automaton model for invasive tumor growth in heterogeneous microenvironments [Y. Jiao and S. Torquato, PLoS Comput. Biol. 7, e1002314 (2011)] by incorporating the effects of pressure. Specifically, we explicitly model the pressure exerted on the growing tumor due to the deformation of the microenvironment and its effect on the local tumor-host interface instability. Both noninvasive-proliferative growth and invasive growth with individual cells that detach themselves from the primary tumor and migrate into the surrounding microenvironment are investigated. We find that while noninvasive tumors growing in “soft” homogeneous microenvironments develop almost isotropic shapes, both high pressure and host heterogeneity can strongly enhance malignant behavior, leading to finger-like protrusions of the tumor surface. Moreover, we show that individual invasive cells of an invasive tumor degrade the local extracellular matrix at the tumor-host interface, which diminishes the fingering growth of the primary tumor. The implications of our results for cancer diagnosis, prognosis and therapy are discussed.
Advances in ultrafast time resolved fluorescence physics for cancer detection in optical biopsy
Authors: Alfano R. R.
Published: March 2012

We discuss the use of time resolved fluorescence spectroscopy to extract fundamental kinetic information on molecular species in tissues. The temporal profiles reveal the lifetime and amplitudes associated with key active molecules distinguishing the local spectral environment of tissues. The femtosecond laser pulses at 310 nm excite the tissue. The emission profile at 340 nm from tryptophan is non-exponential due to the micro-environment. The slow and fast amplitudes and lifetimes of emission profiles reveal that cancer and normal states can be distinguished. Time resolved optical methods offer a new cancer diagnostic modality for the medical community.
Formation and post-deposition compression of smooth and processable silicon thin films from nanoparticle suspensions
Authors: Jafferis Noah T. , Sturm James C.
Published: March 2012

We report the formation of smooth and processable silicon thin-films from single-crystal silicon-nanoparticle suspensions. Single-crystal Si-nanoparticles (1–4 nm) are produced and suspended in various solvents. Films deposited from the suspension are mechanically stable and can be patterned and processed upon deposition. Physical compression of the films is presented as a mechanism to reduce porosity and global roughness. These thin-films, ∼100 nm thick and deposited from a single droplet, contain significant levels of hydrogen, carbon, and oxygen. Resistivities of the as-deposited films are ∼7·107 Ω·cm—comparable to intrinsic nanocrystalline-Si.
A combined Kirkpatrick-Baez mirror and multilayer lens for sub-10 nm x-ray focusing
Authors: Ruhlandt A. , Liese T. , Radisch V. , Krüger S. P. , Osterhoff M. , Giewekemeyer K. , Krebs H. U. , Salditt T.
Published: March 2012

We have used a combined optical system of a high gain elliptic Kirkpatrick-Baez mirror system (KB) and a multilayer Laue lens (MLL) positioned in the focal plane of the KB for hard x-rays nano-focusing. The two-step focusing scheme is based on a high acceptance and high gain elliptical mirror with moderate focal length and a MLL with ultra-short focal length. Importantly, fabrication constraints, i.e. in mirror polishing and bending, as well as MLL deposition can be significantly relaxed, since (a) the mirror focus in the range of 200-500 nm is sufficient, and (b) the number of layers of the MLL can be correspondingly small. First demonstrations of this setup at the coherence beamline of the PETRA III storage ring yield a highly divergent far-field diffraction pattern, from which the autocorrelation function of the near-field intensity distribution was obtained. The results show that the approach is well suited to reach smallest spot sizes in the sub-10nm range at high flux.
Communication: Quantum Zeno-based control mechanism for molecular fragmentation
Authors: Sanz-Sanz C. , Sanz A. S. , González-Lezana T. , Roncero O. , Miret-Artés S.
Published: March 2012

A quantum control mechanism is proposed for molecular fragmentation processes within a scenario grounded on the quantum Zeno effect. In particular, we focus on the van der Waals Ne-Br2 complex, which displays two competing dissociation channels via vibrational and electronic predissociation. Accordingly, realistic three-dimensional wave packet simulations are carried out by using ab initio interaction potentials recently obtained to reproduce available experimental data. Two numerical models to simulate the repeated measurements are reported and analyzed. It is found that the otherwise fast vibrational predissociation is slowed down in favor of the slow electronic (double fragmentation) predissociation, which is enhanced by several orders of magnitude. Based on these theoretical predictions, some hints to experimentalists to confirm their validity are also proposed.
A thermodynamic model of sliding friction
Authors: Makkonen Lasse
Published: March 2012

A first principles thermodynamic model of sliding friction is derived. The model predictions are in agreement with the observed friction laws both in macro- and nanoscale. When applied to calculating the friction coefficient the model provides a quantitative agreement with recent atomic force microscopy measurements on a number of materials.
Bridging the gap between the micro- and the macro-world of tumors
Authors: Chignola Roberto , Milotti Edoardo
Published: March 2012

At present it is still quite difficult to match the vast knowledge on the behavior of individual tumor cells with macroscopic measurements on clinical tumors. On the modeling side, we already know how to deal with many molecular pathways and cellular events, using systems of differential equations and other modeling tools, and ideally, we should be able to extend such a mathematical description up to the level of large tumor masses. An extended model should thus help us forecast the behavior of large tumors from our basic knowledge of microscopic processes. Unfortunately, the complexity of these processes makes it very difficult – probably impossible – to develop comprehensive analytical models. We try to bridge the gap with a simulation program which is based on basic biochemical and biophysical processes – thereby building an effective computational model – and in this paper we describe its structure, endeavoring to make the description sufficiently detailed and yet understandable.
A theory of the cancer age-specific incidence data based on extreme value distributions
Authors: Soto-Ortiz Luis , Brody James P.
Published: March 2012

The incidence of cancers varies with age, if normalized this is called the age-specific incidence. A mathematical model that describes this variation should provide a better understanding of how cancers develop. We suggest that the age-specific incidence should follow an extreme value distribution, based on three widely accepted assumptions: (1) a tumor develops from a single cell, (2) many potential tumor progenitor cells exist in a tissue, and (3) cancer is diagnosed when the first of these many potential tumor cells develops into a tumor. We tested this by comparing the predicted distribution to the age-specific incidence data for colon and prostate carcinomas collected by the Surveillance, Epidemiology and End Results network of 17 cancer registries. We found that colon carcinoma age-specific incidence data is consistent with an extreme value distribution, while prostate carcinomas age-specific incidence data generally follows the distribution. This model indicates that both colon and prostate carcinomas only occur in a subset of the population (22% for prostate and 13.5% for colon.) Because of their very general nature, extreme value distributions might be applicable to understanding other chronic human diseases.
Physical aspects of biological activity and cancer
Authors: Pokorný Jiří
Published: March 2012

Mitochondria are organelles at the boundary between chemical–genetic and physical processes in living cells. Mitochondria supply energy and provide conditions for physical mechanisms. Protons transferred across the inner mitochondrial membrane diffuse into cytosol and form a zone of a strong static electric field changing water into quasi-elastic medium that loses viscosity damping properties. Mitochondria and microtubules form a unique cooperating system in the cell. Microtubules are electrical polar structures that make possible non-linear transformation of random excitations into coherent oscillations and generation of coherent electrodynamic field. Mitochondria supply energy, may condition non-linear properties and low damping of oscillations. Electrodynamic activity might have essential significance for material transport, organization, intra- and inter-cellular interactions, and information transfer. Physical processes in cancer cell are disturbed due to suppression of oxidative metabolism in mitochodria (Warburg effect). Water ordering level in the cell is decreased, excitation of microtubule electric polar oscilations diminished, damping increased, and non-linear energy transformation shifted towards the linear region. Power and coherence of the generated electrodynamic field are reduced. Electromagnetic activity of healthy and cancer cells may display essential differences. Local invasion and metastastatic growth may strongly depend on disturbed electrodynamic activity. Nanotechnological measurements may disclose yet unknown properties and parameters of electrodynamic oscillations and other physical processes in healthy and cancer cells.
Integrated intravital microscopy and mathematical modeling to optimize nanotherapeutics delivery to tumors
Authors: van de Ven Anne L. , Wu Min , Lowengrub John , McDougall Steven R. , Chaplain Mark A. J. , Cristini Vittorio , Ferrari Mauro , Frieboes Hermann B.
Published: March 2012

Inefficient vascularization hinders the optimal transport of cell nutrients, oxygen, and drugs to cancer cells in solid tumors. Gradients of these substances maintain a heterogeneous cell-scale microenvironment through which drugs and their carriers must travel, significantly limiting optimal drug exposure. In this study, we integrate intravital microscopy with a mathematical model of cancer to evaluate the behavior of nanoparticle-based drug delivery systems designed to circumvent biophysical barriers. We simulate the effect of doxorubicin delivered via porous 1000 x 400 nm plateloid silicon particles to a solid tumor characterized by a realistic vasculature, and vary the parameters to determine how much drug per particle and how many particles need to be released within the vasculature in order to achieve remission of the tumor. We envision that this work will contribute to the development of quantitative measures of nanoparticle design and drug loading in order to optimize cancer treatment via nanotherapeutics.
Dynamic density functional theory of solid tumor growth: Preliminary models
Authors: Chauviere Arnaud , Hatzikirou Haralambos , Kevrekidis Ioannis G. , Lowengrub John S. , Cristini Vittorio
Published: March 2012

Cancer is a disease that can be seen as a complex system whose dynamics and growth result from nonlinear processes coupled across wide ranges of spatio-temporal scales. The current mathematical modeling literature addresses issues at various scales but the development of theoretical methodologies capable of bridging gaps across scales needs further study. We present a new theoretical framework based on Dynamic Density Functional Theory (DDFT) extended, for the first time, to the dynamics of living tissues by accounting for cell density correlations, different cell types, phenotypes and cell birth/death processes, in order to provide a biophysically consistent description of processes across the scales. We present an application of this approach to tumor growth.
A Coevolutionary Approach to the Capitalist Space Economy
Authors: Bergmann Luke
Published: March 2012

What happens to technologies, firms, regional outputs, interregional accessibility, and trade when they are understood as coevolving? This paper offers a relational mathematical approach to this question, one whose embrace of disequilibrium, context, history, uncertainty, both monetary and material perspectives on economic activity, and complexity resonates productively with many qualitative theoretical approaches. I present a multiregion, multisector, multifirm model of a society shaped by the pursuit of profit and explore some of its theoretical implications through the narration of simulations, including points of contrast with the approaches and implications of geographical economics. Under different conditions, various economic geographies emerge, including interregional divergence and convergence, specialisation and diversification, as well as the possibility of transitions between these dynamical paths. The relational quantitative method advanced here suggests directions for future research into the theoretical landscapes of economic geographies emerging beyond equilibrium.
Dialectics of Disassembly: Heifer-Care Protocols and the Alienation of Value in a Village Dairy Cooperative
Authors: Mutersbaugh Tad , Martin Lauren
Published: March 2012

This paper examines ‘protocols’—instructions that inform project recipients about how technology is to be used. Our case study of ‘heifer-care’ protocols associated with a microdairy scheme raises two questions. First, we ask how these protocols effect a disassembly of social relations within the village—‘poisoning’ them, as coop members put it. Second, we raise the question of persistence: namely, how were village participants in the microdairy cooperative able to continue for over fifteen years despite a failure to produce milk and the deleterious effects upon village social relations? To address this paradox, we examine protocols from the standpoints of both science and technology studies (STS) and labor-process studies(LPS). STS supply a ‘boundary object’ concept that helps to explain protocol persistence; LPS provide a theory of alienation that furthers our understanding of how protocols alienate labor—via a spatiotemporal dislocation of value—and shape coop members' subjective experience of development. By joining these theories, we hope to provide insights into the operations of protocols and suggest a theoretical liaison between STS and LPS that would provide STS with a better theory of subjective experience and LPS theory with an improved poststructuralist framing. As a matter of praxis, we also show how coop members recognize, in time, the mechanisms through which value is dislocated and respond by reworking their engagements with NGOs to capture a share of the value produced by their labor.
China's Development Disconnect
Authors: Florida Richard , Mellander Charlotta , Qian Haifeng
Published: March 2012

China is currently seeking to transform its economic structure from a traditional industrial to a more innovative, human-capital driven, and knowledge-based economy. Our research examines the effects of three key factors on Chinese regional development in an attempt to gauge to what degree China has transformed from an industrial to a knowledge-based economy, based on higher levels of (1) technology and innovation, (2) human capital and knowledge/professional/creative occupations, and (3) factors like tolerance, universities, and amenities which act on the flow of the first two. We employ structural equation models to gauge the effects of these factors on the economic performance of Chinese regions. Our research generates four key findings. First, the distribution of talent (measured both as human capital and as knowledge–professional and creative occupations) is considerably more concentrated than in the US or other advanced economies. Second, universities are the key factor in shaping the distribution both of talent and of technological innovation. Third, tolerance also plays a role in shaping the distribution of talent and technology across Chinese regions. Fourth, and perhaps most strikingly, we find that neither talent nor technology is associated with the economic performance of Chinese regions. This stands in sharp contrast to the pattern in advanced economies and suggests that the Chinese economic model, at least at the time of data collection, appears to be far less driven by the human capital or technology factors that propel more advanced economies. This, in turn, suggests that China is likely to face substantial obstacles in moving from its current industrial stage of development to a more knowledge-based economy.
Temporal Dimensions and Measurement of Neighbourhood Effects
Authors: Musterd Sako , Galster George , Andersson Roger
Published: March 2012

We conduct a panel analysis quantifying the degree to which the mixture of low-income, middle-income, and high-income males in the neighbourhood affects the subsequent labour income of individuals, and test the degree to which these effects vary by timing (lagging up to three years), duration (one to four years), and cumulative amount of exposure and to what extent these effects are persistent. We employ a fixed-effects model to reduce the potential bias arising from unmeasured individual characteristics leading to neighbourhood selection. The empirical study applies individual-level data for the working-age population of the three largest cities in Sweden covering the period 1991–2006. The analyses suggest that there are important temporal dimensions in the statistical effect of neighbourhood income mix: recent, continued, or cumulative exposure yields stronger associations than lagged, temporary ones, and there is a distinct time decay (though some persistence) in the potential effects after exposure ceases, though with some gender differences.
Environmental Justice in the City? Challenges for Policy and Resource Allocation in Keeping the Streets Clean
Authors: Bramley Glen , Bailey Nick , Hastings Annette , Watkins David , Crowdace Rob
Published: March 2012

This study addresses issues of social or environmental justice in local urban environmental services, through the particular lens of street cleaning services. While UK policy gives some legitimacy to the idea that services should be enhanced in disadavantaged areas, it is unclear how much service and resource discrimination are necessary or appropriate. In practice, this equity perspective may not have much impact at local level. An empirical analysis is presented by drawing on a number of large-scale secondary data sources for England, combining individual and area-based data and subjective and objective inspection-based data. These enable us to draw fairly clear conclusions about the pattern of risk and need based on outcomes and their associations with key socioeconomic, demographic, locational, and urban form characteristics of places. It appears that injustice persists in the quality of local environments across urban England. Some evidence on the impact of local spending levels on environmental outcomes is adduced, but the available data limit this within national studies. While popular debate on street cleanliness highlights the roles of behaviour and values, only limited and indirect inferences may be drawn from large-scale surveys.
Acoustic tracking: issues affecting design, analysis and interpretation of data from movement studies
Authors: How Jason Richard , de Lestang Simon
Published: March 2012

Acoustic telemetry systems are an increasingly common way to examine the movement and behaviour of marine organisms. However, there has been little published on the methodological and analytical work associated with this technology. We tested transmitters of differing power outputs simultaneously in several trials, some lasting ~50 days, to examine the effects of power output and environmental factors (water movement, temperature, lunar cycle and time of day). There were considerable and volatile changes in detections throughout all trials. Increased water movement and temperature significantly reduced detection rates, whereas daytime and full-moon periods had significantly higher detection rates. All nine transmitters (from seven transmitter types tested) showed a sigmoidal trend between detection frequency and distance. Higher-powered transmitters had a prolonged detection distance with near-maximal detections, whereas lower-powered transmitters showed an almost immediate decline. Variation of detection frequency, transmitter type and the modelled relationship between distance and detection frequency were incorporated into a positioning trial which resulted in markedly improved position estimates over previous techniques.
Long-distance correlations of rhinovirus capsid dynamics contribute to uncoating and antiviral activity
Authors: Roy Amitava , Post Carol Beth
Published: March 2012

Human rhinovirus (HRV) and other members of the enterovirus genus bind small-molecule antiviral compounds in a cavity buried within the viral capsid protein VP1. These compounds block the release of the viral protein VP4 and RNA from inside the capsid during the uncoating process. In addition, the antiviral compounds prevent “breathing” motions, the transient externalization of the N-terminal regions of VP1 and VP4 from the inside of intact viral capsid. The site for externalization of VP1/VP4 or release of RNA is likely between protomers, distant to the binding cavity for antiviral compounds. Molecular dynamics simulations were conducted to explore how the antiviral compound, WIN 52084, alters properties of the HRV 14 capsid through long-distance effect. We developed an approach to analyze capsid dynamics in terms of correlated radial motion and the shortest paths of correlated motions. In the absence of WIN, correlated radial motion is observed between residues separated by as much as 85 Å, a remarkably long distance. The most frequently populated path segments of the network were localized near the fivefold symmetry axis and included those connecting the N termini of VP1 and VP4 with other regions, in particular near twofold symmetry axes, of the capsid. The results provide evidence that the virus capsid exhibits concerted long-range dynamics, which have not been previously recognized. Moreover, the presence of WIN destroys this radial correlation network, suggesting that the underlying motions contribute to a mechanistic basis for the initial steps of VP1 and VP4 externalization and uncoating.
Climate change in drylands: from assessment methods to adaptation strategies.
Authors: Pauw E. de , Göbel W.
Published: March 2012

This chapter covers the following topics: projections of global climate change; climate and agricultural systems in the drylands of the Mediterranean Zone; precipitation trends in the 20th century; downscaling the potential impact of climate change in the Eastern Mediterranean Region; and adaptation strategies based from impact assessment. Further, the chapter suggests that there appears no particular reason why the agricultural systems of the region would be unable to cope with climate change.
The way ahead: from science to policy; coordinating efforts in a global world.
Authors: Ortiz R.
Published: March 2012

This chapter describes the need for a global effort, from science to policy, to cover the challenges involved in improving agriculture in a changing environment, particularly in the developing world where political structures are weak but social networks may be of assistance. A brief overview on some programmes or institutions that embody global endeavors to improve agricultural productivity and promote food security (i.e. Green Revolution; the International Assessment of Agricultural Knowledge, Science and Technology for Development; the Global Forum for Agricultural Research; and CGIAR) is provided. Global research and capacity-building agenda based on issues affecting agriculture and the environment (biodiversity and climate change, bioenergy, high-value crops and products, and food safety) are briefly discussed.
Anti-Essentialism and the Rhetoricization of Knowledge: Mario Nizolio's Humanist Attack on Universals*
Authors: Nauta Lodi
Published: March 2012

Well-known for his Ciceronianism as well as for his crass nominalism and virulent attack on universals, the humanist Mario Nizolio (1488–1567) is often considered to be a forerunner of early modern philosophy. But although his name duly features in general accounts of Renaissance humanism and philosophy, his work, edited by Leibniz in 1670, has hardly been the subject of a philosophically sensitive analysis. This article examines Nizolio's attempt to reform scholastic philosophy, paying particular attention to the way in which he de-ontologized the scholastic categories and predicables (genus, species, etc.) and replaced philosophical abstraction with the rhetorical concept of synecdoche. His views on science, proof, argumentation, and rhetoric are discussed, as well as the humanist inspiration from which they issue. We will then be able to evaluate the strength and limitations of Nizolio's program in the wider tradition of early modern philosophy.
The Ambiguities of the Holy: Authenticating Relics in Seventeenth-Century Spain*
Authors: Olds Katrina
Published: March 2012

Recent scholarship has shown that, even at the heart of the Catholic world, defining holiness in the Counter-Reformation was remarkably difficult, in spite of ongoing Roman reforms meant to centralize and standardize the authentication of saints and relics. If the standards for evaluating sanctity were complex and contested in Rome, they were even less clear to regional actors, such as the Bishop of Jaén, who supervised the discovery of relics in Arjona, a southern Spanish town, beginning in 1628. The new relics presented the bishop, Cardinal Baltasar de Moscoso y Sandoval, with knotty historical, theological, and procedural dilemmas. As such, the Arjona case offers a particularly vivid example of the ambiguities that continued to complicate the assessment of holiness in the early modern period. As the Bishop of Jaén found, the authentication of relics came to involve deeper questions about the nature of theological and historical truth that were unresolved in Counter-Reformation theory and practice.
First-principles study of γ-CuI for p-type transparent conducting materials
Authors: Huang Dan , Zhao Yu-Jun , Li Shen , Li Chang-Sheng , Nie Jian-Jun , Cai Xin-Hua , Yao Chun-Mei
Published: March 2012

γ-CuI has attracted considerable attention recently as a p-type transparent conductive material. In this paper, we have investigated the hole effective mass, intrinsic defects and group VI-A impurities in γ-CuI by first-principles calculations. We found that the hole effective mass of γ-CuI is light, in line with the high p-type mobility observed in experiments. The p-type conductance is expected to originate from Cu vacancies, which have a low formation energy with no significant n-type compensating defects. The relative high transition level of Cu vacancy, however, may lead to a low hole concentration in the γ-CuI sample. Additionally, no shallow transition levels were found in γ-CuI with substitutional group VI-A impurities at I sites.
Characterizing the roles of Met31 and Met32 in coordinating Met4-activated transcription in the absence of Met30
Authors: Carrillo Emilio , Ben-Ari Giora , Wildenhain Jan , Tyers Mike , Grammentz Dilon , Lee Traci A.
Published: March 2012

Yeast sulfur metabolism is transcriptionally regulated by the activator Met4. Met4 lacks DNA-binding ability and relies on interactions with Met31 and Met32, paralogous proteins that bind the same cis-regulatory element, to activate its targets. Although Met31 and Met32 are redundant for growth in the absence of methionine, studies indicate that Met32 has a prominent role over Met31 when Met30, a negative regulator of Met4 and Met32, is inactive. To characterize different roles of Met31 and Met32 in coordinating Met4-activated transcription, we examined transcription in strains lacking either Met31 or Met32 upon Met4 induction in the absence of Met30. Microarray analysis revealed that transcripts involved in sulfate assimilation and sulfonate metabolism were dramatically decreased in met32Δ cells compared to its wild-type and met31Δ counterparts. Despite this difference, both met31Δ and met32Δ cells used inorganic sulfur compounds and sulfonates as sole sulfur sources in minimal media when Met30 was present. This discrepancy may be explained by differential binding of Met31 to Cbf1-dependent promoters between these two conditions. In the absence of Met30, genome-wide chromatin immunoprecipitation analyses found that Met32 bound all Met4-bound targets, supporting Met32 as the main platform for Met4 recruitment. Finally, Met31 and Met32 levels were differentially regulated, with Met32 levels mimicking the profile for active Met4. These different properties of Met32 likely contribute to its prominent role in Met4-activated transcription when Met30 is absent.
Mechanistic mathematical model of polarity in yeast
Authors: Savage Natasha S. , Layton Anita T. , Lew Daniel J.
Published: March 2012

The establishment of cell polarity involves positive-feedback mechanisms that concentrate polarity regulators, including the conserved GTPase Cdc42p, at the “front” of the polarized cell. Previous studies in yeast suggested the presence of two parallel positive-feedback loops, one operating as a diffusion-based system, and the other involving actin-directed trafficking of Cdc42p on vesicles. F-actin (and hence directed vesicle traffic) speeds fluorescence recovery of Cdc42p after photobleaching, suggesting that vesicle traffic of Cdc42p contributes to polarization. We present a mathematical modeling framework that combines previously developed mechanistic reaction-diffusion and vesicle-trafficking models. Surprisingly, the combined model recapitulated the observed effect of vesicle traffic on Cdc42p dynamics even when the vesicles did not carry significant amounts of Cdc42p. Vesicle traffic reduced the concentration of Cdc42p at the front, so that fluorescence recovery mediated by Cdc42p flux from the cytoplasm took less time to replenish the bleached pool. Simulations in which Cdc42p was concentrated into vesicles or depleted from vesicles yielded almost identical predictions, because Cdc42p flux from the cytoplasm was dominant. These findings indicate that vesicle-mediated delivery of Cdc42p is not required to explain the observed Cdc42p dynamics, and raise the question of whether such Cdc42p traffic actually contributes to polarity establishment.