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Top 20 Most Read Articles
April 2012
The 20 articles with the most full-text downloads during the month, in descending order.
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AIP Advances 2, 010901 (2012); http://dx.doi.org/10.1063/1.3699622 (3 pages) Online Publication Date: 29 March 2012
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Triggering, guiding and deviation of long air spark discharges with femtosecond laser filament AIP Advances 2, 012151 (2012); http://dx.doi.org/10.1063/1.3690961 (13 pages) Online Publication Date: 17 February 2012
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In the perspective of the laser lightning rod, the ability of femtosecond filaments to trigger and to guide large scale discharges has been studied for several years. The present paper reports recent experimental results showing for the first time that filaments are able not only to trigger and guide but also to divert an electric discharge from its normal path. Laser filaments are also able to divert the spark without contact between laser and electrodes at large distance from the laser. A comparison between negative and positive discharge polarities also reveals important discrepancies in the guiding mechanism.
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A thermodynamic model of sliding friction AIP Advances 2, 012179 (2012); http://dx.doi.org/10.1063/1.3699027 (9 pages) Online Publication Date: 22 March 2012
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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. |
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Physics of cancer propagation: A game theory perspective AIP Advances 2, 011202 (2012); http://dx.doi.org/10.1063/1.3699043 (10 pages) Online Publication Date: 22 March 2012
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This is a theoretical paper which examines at a game theoretical perspective the dynamics of cooperators and cheater cells under metabolic stress conditions and high spatial heterogeneity. Although the ultimate aim of this work is to understand the dynamics of cancer tumor evolution under stress, we use a simple bacterial model to gain fundamental insights into the progression of resistance to drugs under high competition and stress conditions.
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Spherical magnetic nanoparticles fabricated by electric explosion of wire AIP Advances 1, 042122 (2011); http://dx.doi.org/10.1063/1.3657510 (10 pages) Online Publication Date: 20 October 2011
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We report the first use of an electrophysical method of electric explosion of wire for preparing magnetic nanoparticles of iron oxide. X-ray diffraction, transmission electron microscopy, magnetization and magnetic resonance measurements were comparatively analyzed. They indicated that the shape of magnetic nanoparticles is close to being spherical. The production order of 100g per hour by this method is advantageous when a large amount of material is needed for applications. |
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AIP Advances 2, 011101 (2012); http://dx.doi.org/10.1063/1.3697850 (14 pages) Online Publication Date: 19 March 2012
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Empirical studies give increased support for the hypothesis that the sporadic form of cancer is an age-related metabolic disease characterized by: (a) metabolic dysregulation with random abnormalities in mitochondrial DNA, and (b) metabolic alteration – the compensatory upregulation of glycolysis to offset mitochondrial impairments. This paper appeals to the theory of Quantum Metabolism and the principles of natural selection to formulate a conceptual framework for a quantitative analysis of the origin and proliferation of the disease. Quantum Metabolism, an analytical theory of energy transduction in cells inspired by the methodology of the quantum theory of solids, elucidates the molecular basis for differences in metabolic rate between normal cells, utilizing predominantly oxidative phosphorylation, and cancer cells utilizing predominantly glycolysis. The principles of natural selection account for the outcome of competition between the two classes of cells. Quantum Metabolism and the principles of natural selection give an ontogenic and evolutionary rationale for cancer proliferation and furnish a framework for effective therapeutic strategies to impede the spread of the disease.
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Physical aspects of biological activity and cancer AIP Advances 2, 011207 (2012); http://dx.doi.org/10.1063/1.3699057 (11 pages) Online Publication Date: 22 March 2012
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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.
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AIP Advances 2, 011102 (2012); http://dx.doi.org/10.1063/1.3697852 (15 pages) Online Publication Date: 19 March 2012
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The distinctive spectral absorption characteristics of cancer cells make photoacoustic techniques useful for detection in vitro and in vivo. Here we report on our evaluation of the photoacoustic signal produced by a series of monolayers of different cell lines in vitro. Only the melanoma cell line HS936 produced a detectable photoacoustic signal in which amplitude was dependent on the number of cells. This finding appears to be related to the amount of melanin available in these cells. Other cell lines (i.e. HL60, SK-Mel-1, T47D, Hela, HT29 and PC12) exhibited values similar to a precursor of melanin (tyrosinase), but failed to produce sufficient melanin to generate a photoacoustic signal that could be distinguished from background noise. To better understand this phenomenon, we determined a formula for the time-domain photoacoustic wave equation for a monolayer of cells in a non-viscous fluid on the thermoelastic regime. The theoretical results showed that the amplitude and profile of the photoacoustic signal generated by a cell monolayer depended upon the number and distribution of the cells and the location of the point of detection. These findings help to provide a better understanding of the factors involved in the generation of a photoacoustic signal produced by different cells in vitro and in vivo.
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Defect-induced room temperature ferromagnetism in un-doped InN film AIP Advances 2, 012185 (2012); http://dx.doi.org/10.1063/1.3698320 (6 pages) Online Publication Date: 23 March 2012
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Diluted magnetic semiconductors (DMSs), with the Curie temperature at room temperature, are of technological and fundamental importance. Defect engineering has been an effective way to introduce magnetic moments in various non-magnetic systems. Here we show firstly, InN film directly grown on (0001)-oriented Al2O3 substrate with In deficiency is ferromagnetic with its Curie temperature as high as 297K. The undesirable large lattice mismatch between the film and substrate leads to a peculiar surface structure that the film separates into distinct In-rich and In-poor regions. Our first-principles calculations suggest the defect of In-vacancy is responsible for the magnetism. A local magnetic moment of 2.5μB is found, in agreement with experimental results. Our findings demonstrate that room-temperature ferromagnetism can also be induced in narrow band gap semiconductors through defect engineering, which remains largely unexplored so far.
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Diversity of dynamics and morphologies of invasive solid tumors AIP Advances 2, 011003 (2012); http://dx.doi.org/10.1063/1.3697959 (13 pages) Online Publication Date: 21 March 2012
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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.
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AIP Advances 2, 011002 (2012); http://dx.doi.org/10.1063/1.3697848 (14 pages) Online Publication Date: 19 March 2012
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Prostate cancer is commonly treated by a form of hormone therapy called androgen suppression. This form of treatment, while successful at reducing the cancer cell population, adversely affects quality of life and typically leads to a recurrence of the cancer in an androgen-independent form. Intermittent androgen suppression aims to alleviate some of these adverse affects by cycling the patient on and off treatment. Clinical studies have suggested that intermittent therapy is capable of maintaining androgen dependence over multiple treatment cycles while increasing quality of life during off-treatment periods. This paper presents a mathematical model of prostate cancer to study the dynamics of androgen suppression therapy and the production of prostate-specific antigen (PSA), a clinical marker for prostate cancer. Preliminary models were based on the assumption of an androgen-independent (AI) cell population with constant net growth rate. These models gave poor accuracy when fitting clinical data during simulation. The final model presented hypothesizes an AI population with increased sensitivity to low levels of androgen. It also hypothesizes that PSA production is heavily dependent on androgen. The high level of accuracy in fitting clinical data with this model appears to confirm these hypotheses, which are also consistent with biological evidence.
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Some observations on the mechanics and dynamics of tumor heterogeneity AIP Advances 2, 011001 (2012); http://dx.doi.org/10.1063/1.3697847 (10 pages) Online Publication Date: 19 March 2012
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The genetic, proteomic and cytostructural complexities of malignant neoplasms have received much attention in cancer research for many years. However, studies of the mechanics of neoplastic phenomena at the meso- and macroscales are also now providing opportunities for understanding some aspects of tumor growth and developing new therapeutic possibilities. We provide a brief overview of some of the recent work in these areas, with emphasis on physical considerations of certain aspects of the mechanics and fluid dynamics of tumor cell invasion and dispersion. |
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AIP Advances 1, 022126 (2011); http://dx.doi.org/10.1063/1.3598408 (11 pages) Online Publication Date: 27 May 2011
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In his famous 1981 talk, Feynman proposed that unlike classical computers, which would presumably experience an exponential slowdown when simulating quantum phenomena, a universal quantum simulator would not. An ideal quantum simulator would be controllable, and built using existing technology. In some cases, moving away from gate-model-based implementations of quantum computing may offer a more feasible solution for particular experimental implementations. Here we consider an adiabatic quantum simulator which simulates the ground state properties of sparse Hamiltonians consisting of one- and two-local interaction terms, using sparse Hamiltonians with at most three-local interactions. Properties of such Hamiltonians can be well approximated with Hamiltonians containing only two-local terms. The register holding the simulated ground state is brought adiabatically into interaction with a probe qubit, followed by a single diabatic gate operation on the probe which then undergoes free evolution until measured. This allows one to recover e.g. the ground state energy of the Hamiltonian being simulated. Given a ground state, this scheme can be used to verify the QMA-complete problem LOCAL HAMILTONIAN, and is therefore likely more powerful than classical computing.
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Characterizations of photoconductivity of graphene oxide thin films AIP Advances 2, 022104 (2012); http://dx.doi.org/10.1063/1.3702871 (9 pages) Online Publication Date: 3 April 2012
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Characterizations of photoresponse of a graphene oxide (GO) thin film to a near infrared laser light were studied. Results showed the photocurrent in the GO thin film was cathodic, always flowing in an opposite direction to the initial current generated by the preset bias voltage that shows a fundamental discrepancy from the photocurrent in the reduced graphene oxide thin film. Light illumination on the GO thin film thus results in more free electrons that offset the initial current. By examining GO thin films reduced at different temperatures, the critical temperature for reversing the photocurrent from cathodic to anodic was found around 187°C. The dynamic photoresponse for the GO thin film was further characterized through the response time constants within the laser on and off durations, denoted as τon and τoff, respectively. τon for the GO thin film was comparable to the other carbon-based thin films such as carbon nanotubes and graphenes. τoff was, however, much larger than that of the other's. This discrepancy was attributable to the retardation of exciton recombination rate thanks to the existing oxygen functional groups and defects in the GO thin films.
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AIP Advances 2, 022101 (2012); http://dx.doi.org/10.1063/1.3702588 (9 pages) Online Publication Date: 2 April 2012
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Chemical-reduced graphene oxide (rGO) films were deposited on titanium (Ti)-coated silicon substrates by a simple electrophoretic deposition. The rGO films were annealed under argon atmosphere at different temperatures. The morphology and microstructure of the rGO films before and after annealing were characterized using scanning electron microscope, X-ray diffraction and Raman spectroscope. The field emission behaviors from these rGO films were investigated. The results show that, Ti-based transition layer can improve the stability of field emission from the rGO film, and the annealing at appropriate temperature is in favor of the field emission. Particularly, the rGO film displays an unexpected vacuum breakdown phenomenon at a relatively high current density. In addition, it is found that the field emission property of the rGO film is dependent on anode-sample distance and the film exhibits lower turn on field at larger anode-sample distance.
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AIP Advances 2, 022105 (2012); http://dx.doi.org/10.1063/1.3703320 (7 pages) Online Publication Date: 4 April 2012
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It has recently been predicted that the surface plasmons are allowed to exist on the interface between a topological insulator and vacuum. Surface plasmons can be employed to enhance the optical emission from various illuminants. Here, we study the photoluminescence properties of the ZnO/Bi2Te3 hybrid structures. Thin flakes of Bi2Te3, a typical three-dimensional topological insulator, were prepared on ZnO crystal surface by mechanical exfoliation method. The ultraviolet emission from ZnO was found to be enhanced by the Bi2Te3 thin flakes, which was attributed to the surface plasmon – photon coupling at the Bi2Te3/ZnO interface.
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AIP Advances 2, 011208 (2012); http://dx.doi.org/10.1063/1.3699060 (13 pages) Online Publication Date: 22 March 2012
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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.
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Dynamic density functional theory of solid tumor growth: Preliminary models AIP Advances 2, 011210 (2012); http://dx.doi.org/10.1063/1.3699065 (13 pages) Online Publication Date: 22 March 2012
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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.
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Advances in ultrafast time resolved fluorescence physics for cancer detection in optical biopsy AIP Advances 2, 011103 (2012); http://dx.doi.org/10.1063/1.3697961 (10 pages) Online Publication Date: 21 March 2012
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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.
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Bridging the gap between the micro- and the macro-world of tumors AIP Advances 2, 011204 (2012); http://dx.doi.org/10.1063/1.3699049 (15 pages) Online Publication Date: 22 March 2012
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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.
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