Viscoelastic shear properties of in vivo breast lesions measured by MR elastography

Elastography is a technique to assess the viscoelastic properties of tissue by measuring an acoustic wave propagating though the object. Here, the technique is applied in the course of standard MR mammography to 15 patients with different pathologies (six breast cancer cases, six fibroadenoma cases and three mastopathy cases). Low-frequency mechanical waves are coupled longitudinally into the tissue in order to obtain sufficient wave amplitude throughout the entire breast. This leads to the presence of a substantial fraction of compressional waves, which contribute to the total displacement field. It is shown theoretically that the correct evaluation of these contributions from the compressional wave is rather difficult due to the almost incompressible nature of tissue. To overcome this problem, it is proposed to apply the curl-operator to the measured displacement field in order to completely remove contributions from the compressional wave. Results from simulations and a breast phantom demonstrate the feasibility of the technique. The in vivo results show a good separation between breast cancer and benign fibroadenoma utilizing the shear modulus. Breast cancer appears on average 2.2 (P<.001) times stiffer. All breast cancer cases showed a good delineation to the surrounding breast tissue with an average elevation of a factor of 3.3 (P< 1.4 x 10(-6)). The results as obtained for the shear viscosity do not indicate to be useful for separating benign from malignant lesions.     

Self-poisoning of crystal nuclei in hard-rod liquids

We report a Monte Carlo study of the pathway for crystal nucleation in a fluid of hard, colloidal rods. In the earliest stages of nucleation, a lamellar crystallite forms. Subsequent thickening of this lamella is hampered by the fact that the top and bottom surfaces of this crystallite are preferentially covered by rods that align parallel to the surface. As a consequence, subsequent growth of individual crystals is stunted. Experimental evidence for such stunted crystal growth has recently been reported by Maeda and Maeda in experiments on suspensions of colloidal rods [Phys. Rev. Lett. 90, 018303 (2003)]]. The simulations suggest that, in experiments, the growth of multilayer colloidal crystals can be selectively enhanced by the application of an external aligning field.     

Eigenvalues of Random Power law Graphs

Many graphs arising in various information networks exhibit the "power law" behavior -the number of vertices of degree k is proportional to k^-# for some positive #. We show that if # > 2.5, the largest eigenvalue of a random power law graph is almost surely(1+ o(1))?m (1+ o(1))\sqrt{m} where m is the maximum degree. Moreover, the klargest eigenvalues of a random power law graph with exponent # have power law distribution with exponent 2# if the maximum degree is sufficiently large, where k is a function depending on #, mand d, the average degree. When 2<#< 2.5, the largest eigenvalue is heavily concentrated at cm^3-# for some constant c depending on # and the average degree. This result follows from a more general theorem which shows that the largest eigenvalue of a random graph with a given expected degree sequence is determined by m, the maximum degree, and [(d)\tilde] \tilde{d} , the weighted average of the squares of the expected degrees. We show that the k-th largest eigenvalue is almost surely (1+ o(1))?{m_k} (1+ o(1))\sqrt{m_k} where m_k is the k-th largest expected degree provided m_k is large enough. These results have implications on the usage of spectral techniques in many areas related to pattern detection and information retrieval.     

Small Complete Arcs in Projective Planes

In the late 1950s, B. Segre introduced the fundamental notion of arcs and complete arcs [48,49]. An arc in a nite projective plane is a set of points with no three on a line and it is complete if cannot be extended without violating this property. Given a projective plane , determining , the size of its smallest complete arc, has been a major open question in finite geometry for several decades. Assume that has order q, it was shown by Lunelli and Sce [41], more than 40 years ago, that . Apart from this bound, practically nothing was known about , except for the case is the Galois plane. For this case, the best upper bound, prior to this paper, was O(q ^3/4) obtained by Sznyi using the properties of the Galois field GF(q).In this paper, we prove that for any projective plane of order q, where c is a universal constant. Together with Lunelli-Sces lower bound, our result determines up to a polylogarithmic factor. Our proof uses a probabilistic method known as the dynamic random construction or Rödls nibble. The proof also gives a quick randomized algorithm which produces a small complete arc with high probability.The key ingredient of our proof is a new concentration result, which applies for non-Lipschitz functions and is of independent interest.* Research supported in part by grant RB091G-VU from UCSD, by NSF grant DMS-0200357 and by an A. Sloan fellowship.Part of this work was done at AT&T Bell Labs and Microsoft Research     

Synthesis of multi-walled carbon nanotubes for NH3 gas detection

It has been recently demonstrated that carbon nanotubes (CNTs) represent a new type of chemical sensor capable of detecting a small concentration of molecules such as CO, NO₂, NH₃.In this work, CNTs were synthesized by chemical vapor deposition (CVD) on the SiO₂/Si substrate by decomposition of acetylene (C₂H₂) on sputtered Ni catalyst nanoparticles. Their structural properties are studied by atomic force microscopy, high-resolution scanning electron microscopy (HRSEM) and Raman spectroscopy. The CNTs grown at 700 °C exhibit a low dispersion in size, are about 1 μm long and their average diameter varies in the range 25–60 nm as a function of the deposition time. We have shown that their diameter can be reduced either by annealing in oxygen environment or by growing at lower temperature (less than 600 °C).We developed a test device with interdigital Pt electrodes on an Al₂O₃ substrate in order to evaluate the CNTs-based gas sensor capabilities. We performed room temperature current–voltage measurements for various gas concentrations. The CNT films are found to exhibit a fast response and a high sensitivity to NH₃ gas.     

Advances in Iodine(III)‐Mediated Halogenations: A Versatile Tool to Explore New Reactivities and Selectivities

Within the repertoire of organic chemical transformations, the halogenation of substrates is among the most versatile, reliable, and broadly applicable reactions. Although a multitude of different methods are known today, there is still a huge demand for novel and, in particular, catalytic halogenation methods that exhibit new reactivities and selectivities. The class of hypervalent iodanes meets exactly these needs and thus offers a great opportunity to fuel this highly desirable direction within the field of halogenation chemistry. This Concept gives a short overview of recent examples focusing on selective and/or mechanistically unusual halogenations.     

Determination of Sulfide by Hematoxylin Multiwalled Carbon Nanotubes Modified Carbon Paste Electrode

This study investigates a new approach for the amperometric determination of sulfide using a hematoxylin multiwalled carbon nanotubes modified carbon paste electrode (HM‐MWCNTs/CPE). The experimental results show that HM‐MWCNTs/CPE significantly enhances the electrocatalytic activity towards sulfide oxidation. Cyclic voltammetric studies show that the peak potential of sulfide shifted from +400 mV at unmodified CPE to +175 mV at HM‐MWCNTs/CPE. The currents obtained from amperometric measurements at optimum conditions were linearly correlated with the concentration of sulfide. The calibration curve was obtained for sulfide concentrations in the range of 0.5–150×10^?6 mol L^?1. The detection limit was found to be 0.2×10^?6 mol L^?1 for the amperometric method. The proposed method was successfully applied to a river water sample in Pardubice, Czech Republic.     

On the exactness of a theorem of G.A. Fomin

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Biologically Active 1-Aminodeoxy and 1-O-Alkyl Derivatives of The Powerful D-Glucosidase Inhibitor 2,5-Dideoxy-2,5-Imino-D-Mannitol

ABSTRACT

By an Amadori rearrangement of easily available 5-azido-5-deoxy-D-glucofuranose with dibenzylamine and subsequent catalytic hydrogenation of the resulting 5-azido-1-(N,N-dibenzyl)amino-1,5-dideoxy-D-fructopyranose, 1-amino-1,2,5-trideoxy-2,5-imino-D-mannitol was obtained in only two steps and in excellent overall yield. Likewise, other amines were employed to introduce extended side chains ultimately suitable for attachment of the inhibitor to solid supports. The reported rearrangement reaction is a high yielding, convenient and apparently general entry to 1-aminodeoxyketopyranoses modified at C-5, facilitated by the ring enlargement of the aldofuranose to the ketopyranose as an additional driving force. A range of selected chain extended analogues was prepared by acylation of N-1. Inhibitors obtained exhibit K _i-values with D-glucosidases in the micromolar range. Interestingly, 1-N-acylation resulted in superior inhibitory activities, as did the addition of a hexyl chain.