22,525 research outputs found

    Nanotechnology and cancer

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    The biological picture of cancer is rapidly advancing from models built from phenomenological descriptions to network models derived from systems biology, which can capture the evolving pathophysiology of the disease at the molecular level. The translation of this (still academic) picture into a clinically relevant framework can be enabling for the war on cancer, but it is a scientific and technological challenge. In this review, we discuss emerging in vitro diagnostic technologies and therapeutic approaches that are being developed to handle this challenge. Our discussion of in vitro diagnostics is guided by the theme of making large numbers of measurements accurately, sensitively, and at very low cost. We discuss diagnostic approaches based on microfluidics and nanotechnology. We then review the current state of the art of nanoparticle-based therapeutics that have reached the clinic. The goal of the presentation is to identify nanotherapeutic strategies that are designed to increase efficacy while simultaneously minimizing the toxic side effects commonly associated with cancer chemotherapies

    Feasibility study of high performance hydrogen-oxygen fuel cells Final technical report

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    Engineering analysis for evaluating moving bed and mediator hydrogen-oxygen fuel cell conceptual design

    The UV absorption spectrum of C60 (buckminsterfullerene): A narrow band at 3860 Γ…

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    The absorption spectrum of the special C60 cluster buckminsterfullerene has been studied in a supersonic beam by laser depletion of the cold van der Waals complexes of C60 with benzene and methylene chloride. Both complexes were found to display a single, isolated absorption band in the near ultraviolet superimposed on a structureless absorption continuum. For the methylene chloride complex this feature is centered at 3860 Γ…, and is roughly 50 cmβˆ’1 wide. In the benzene van der Waals cluster, the corresponding feature is located at 3863 Γ…, and has a similar width. This spectrum is tentatively assigned to the 0–0 band of the lowest 1T1u<--1Ag (LUMO+1<--HOMO) transition of a truncated icosahedral carbon shell structure, broadened by coupling to the underlying quasicontinuum of ground state vibrational levels

    A mass action model of a fibroblast growth factor signaling pathway and its simplification

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    We consider a kinetic law of mass action model for Fibroblast Growth Factor (FGF) signaling, focusing on the induction of the RAS-MAP kinase pathway via GRB2 binding. Our biologically simple model suffers a combinatorial explosion in the number of differential equations required to simulate the system. In addition to numerically solving the full model, we show that it can be accurately simplified. This requires combining matched asymptotics, the quasi-steady state hypothesis, and the fact subsets of the equations decouple asymptotically. Both the full and simplified models reproduce the qualitative dynamics observed experimentally and in previous stochastic models. The simplified model also elucidates both the qualitative features of GRB2 binding and the complex relationship between SHP2 levels, the rate SHP2 induces dephosphorylation and levels of bound GRB2. In addition to providing insight into the important and redundant features of FGF signaling, such work further highlights the usefulness of numerous simplification techniques in the study of mass action models of signal transduction, as also illustrated recently by Borisov and co-workers (Borisov et al. in Biophys. J. 89, 951–66, 2005, Biosystems 83, 152–66, 2006; Kiyatkin et al. in J. Biol. Chem. 281, 19925–9938, 2006). These developments will facilitate the construction of tractable models of FGF signaling, incorporating further biological realism, such as spatial effects or realistic binding stoichiometries, despite a more severe combinatorial explosion associated with the latter

    Permutation groups, simple groups and sieve methods

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    We show that the number of integers n ≀ x which occur as indices of subgroups of nonabelian finite simple groups, excluding that of An-1 in An, is ∼ hx/log x, for some given constant h. This might be regarded as a noncommutative analogue of the Prime Number Theorem (which counts indices n ≀ x of subgroups of abelian simple groups). We conclude that for most positive integers n, the only quasiprimitive permutation groups of degree n are Sn and An in their natural action. This extends a similar result for primitive permutation groups obtained by Cameron, Neumann and Teague in 1982. Our proof combines group-theoretic and number-theoretic methods. In particular, we use the classification of finite simple groups, and we also apply sieve methods to estimate the size of some interesting sets of primes

    Sums and differences of four k-th powers

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    We prove an upper bound for the number of representations of a positive integer NN as the sum of four kk-th powers of integers of size at most BB, using a new version of the Determinant method developed by Heath-Brown, along with recent results by Salberger on the density of integral points on affine surfaces. More generally we consider representations by any integral diagonal form. The upper bound has the form ON(Bc/k)O_{N}(B^{c/\sqrt{k}}), whereas earlier versions of the Determinant method would produce an exponent for BB of order kβˆ’1/3k^{-1/3} in this case. Furthermore, we prove that the number of representations of a positive integer NN as a sum of four kk-th powers of non-negative integers is at most OΟ΅(N1/k+2/k3/2+Ο΅)O_{\epsilon}(N^{1/k+2/k^{3/2}+\epsilon}) for kβ‰₯3k \geq 3, improving upon bounds by Wisdom.Comment: 18 pages. Mistake corrected in the statement of Theorem 1.2. To appear in Monatsh. Mat

    The Inverted Yield Curve and the Components of GDP

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    When 3-month Treasury rates are greater than 10 -year Treasury rates an inverted yield curve occurs. When this state is reached some argue that a recession is on the horizon, typically 6 months to a year down the road. Here, I reframe the question of whether inverted yield curves predict recessions in the US and ask what an inverted yield curve predicts. Using a Probit model I find that when 10-year US Treasury bonds yield less than 3-month US Treasury bills, a US recession, while probable, is not certain. Moreover, I find that indeed the strength of this indicator has weakened over the last 20 years. However, my findings do not suggest that an inverted yield curve provides no information about the future. In fact, I find that an inverted yield curve strongly predicts movements in the consumer durables and fixed private investment series of US GDP

    Seasonal and interannual variations in total ozone revealed by the Nimbus-4 backscattered ultraviolet experiment

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    The first two years of Backscattered Ultraviolet (BUV) ozone data from the Nimbus-4 spacecraft were reprocessed. The seasonal variations of total ozone for the period April 1970 to April 1972 are described using daily zonal means to 10 deg latitude zones and a time-latitude cross section. In addition, the BUV data are compared with analyzed Dobson data and with IRIS data also obtained from the Nimbus-4 spacecraft. A harmonic analysis was performed on the daily zonal means. Amplitudes, days of peaks, and percentage of variance were computed for annual and semi-annual waves and for higher harmonics of an annual period for the two years. Asymmetries are found in the annual waves in the two hemispheres, with a subtle interannual difference which may be due to changes in the general circulation. A significant semi-annual component is detected in the tropics for the first year, which appears to result from influences of the annual waves in the two hemispheres
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