bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of the effectiveness of four different crosslinking agents with hyaluronic acid hydrogel films for tissue‐culture applications
Authors: Collins M. N. , Birkinshaw C. 
Published: March 2007

AbstractThe effectiveness of four different reagents, glutaraldehyde (GTA), 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC), poly(ethyelene glycol) diglycidyl ether (EX 810), and divinyl sulfone (DVS) as crosslinkers for cast hyaluronic acid (HA) films has been evaluated. Films were prepared by casting from solution and exposed to solutions of the crosslinkers in acetone–water solution. Swelling in water and in phosphate buffered saline (PBS) was then used to assess the effectiveness of the crosslinkers. GTA‐crosslinked films were found to be of low stability compared with those treated with EDC, EX 810, and DVS. Results suggest that instability in GTA‐crosslinked materials arises in part from residual acid catalyst. The effects of polymer molecular weight are not uniform. With GTA‐crosslinked film produced from higher molecular weight HA swells more, and this is attributed to reduced diffusion of the crosslinker, but with EDC, the opposite effect is observed, implying some additional molecular weight dependent mechanism. Differential scanning calorimetry and dynamic mechanical thermal analysis results suggest that there are no significant structural difference between the gels for each crosslinker system and only the crosslink density and moisture content alters the transitions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Synthesis, characterization and biological activity of C60 derivative
Authors: Jiang Guichang , Li Guangtao 
Published: March 2007

AbstractA novel fullerene‐maleic anhydride derivative was synthesized via radical polymerization. It is soluble in polar solvents such as water, dimethyl sulfoxide, and tetrahydrofuran etc. The product was characterized by FTIR, UV‐Vis, GPC, and Transmission electron microscope (TEM). TEM analysis shows that the average particle diameter is about 38 nm. The in vitro antitumor activity of the fullerene‐maleic anhydride derivative has been tested and the result shows that the derivative exhibits better antitumor activity against HeLa cells and bone tumor cells. To prove water‐soluble fullerene derivatives photodynamic effect on tumor cell, i.e., the photodynamic effect on mouse bone tumor in vivo we injected the fullerene ‐maleic anhydride derivatives into the mouse bone tumor body. We found that with I‐W lamp (500 W) illumination the mouse bone tumor body was strongly damaged. The antitumor mechanism of water‐soluble fullerene‐maleic anhydride derivative was investigated for the first time. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Phosphinate Inhibitors of UDP‐N‐Acetylmuramoyl‐L‐Alanyl‐D‐Glutamate: L‐Lysine Ligase (MurE)
Authors: Štrancar Katja , Boniface Audrey , Blanot Didier , Gobec Stanislav 
Published: March 2007

AbstractThe increasing emergence of pathogenic bacterial strains with high resistance to antibiotic therapy has created an urgent need for the development of new antibacterial agents that are directed towards novel targets. We have focused our attention on the Mur ligases (MurC‐F), which catalyze the early steps of bacterial peptidoglycan biosynthesis, and which to date represent under‐exploited targets for antibacterial drug design. We show that some of our phosphinate inhibitors of UDP‐N‐acetylmuramoyl‐L‐alanyl:D‐glutamate ligase (MurD) also inhibits UDP‐N‐acetylmuramoyl‐L‐alanyl‐D‐glutamate:L‐lysine ligase (MurE). To obtain new information on their structure‐activity relationships, three new, structurally related phosphinates were synthesized and evaluated for inhibition of MurD and MurE.
ValC, a New Type of C7‐Cyclitol Kinase Involved in the Biosynthesis of the Antifungal Agent Validamycin A
Authors: Minagawa Kazuyuki , Zhang Yirong , Ito Takuya , Bai Linquan , Deng Zixin , Mahmud Taifo 
Published: March 2007

AbstractThe gene valC, which encodes an enzyme homologous to the 2‐epi‐5‐epi‐valiolone kinase (AcbM) of the acarbose biosynthetic pathway, was identified in the validamycin A biosynthetic gene cluster. Inactivation of valC resulted in mutants that lack the ability to produce validamycin A. Complementation experiments with a replicating plasmid harboring full‐length valC restored the production of validamycin A, thus suggesting a critical function of valC in validamycin biosynthesis. In vitro characterization of ValC revealed a new type of C7‐cyclitol kinase, which phosphorylates valienone and validone—but not 2‐epi‐5‐epi‐valiolone, 5‐epi‐valiolone, or glucose—to afford their 7‐phosphate derivatives. The results provide new insights into the activity of this enzyme and also confirm the existence of two different pathways leading to the same end‐product: the valienamine moiety common to acarbose and validamycin A.
A Novel Inorganic‐Organic Composite Constructed from Cobalt(II)‐Monosubstituted Polyoxometalates and Poly(amidoamine)‐NH2 Dendrimers
Authors: Zhang Xiao‐Feng , Lin Shen , Luo Geng‐Geng , Liu Chun‐Lian 
Published: March 2007

AbstractAn inorganic‐organic composite was prepared by poly(amidoamine) (PAMAM) dendrimer reacting with cobalt(II)‐monosubstituted polyoxometalates Na5CoII(H2O)PW11O39 (PW11Co) in an aqueous solution. The hybrid composite PW11Co/PAMAM was characterized by FT‐IR, UV‐Vis diffuse reflectance spectra (DR‐UV‐Vis), XPS, XRD and TG/DTA, indicating that the PW11Co was chemically anchored to PAMAM. The morphologies of the title composite were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The catalytic activity was evaluated by oxidation of isobutyraldehyde (IBA) to isobutyric acid (IBAc) in MeCN under mild conditions (20 °C, ambient pressure), showing that the title compound is a more effective and recoverable catalyst than corresponding PW11Co.
Non‐polar Solvent Microwave‐Assisted Extraction of Volatile Constituents from Dried Zingiber Officinale Rosc.
Authors: Yu Yong , Wang Zi‐Ming , Wang Yu‐Tang , Li Tie‐Chun , Cheng Jian‐Hua , Liu Zhong‐Ying , Zhang Han‐Qi 
Published: March 2007

AbstractA new method, non‐polar solvent microwave‐assisted extraction (NPSMAE), was applied to the extraction of essential oil from Zingiber officinale Rosc. in closed‐vessel system. By adding microwave absorption medium‐ carbonyl iron powders (CIP) into extraction system, the essential oil was extracted by the non‐polar solvent (ether) which can be heated by CIP. The constituents of essential oil obtained by NPSMAE were comparable with those obtained by hydrodistillation (HD) by GC‐MS analysis, which indicates that NPSMAE is a feasible way to extract essential oil from dried plant materials. The NPSMAE took much less extraction time (5 min) than HD (180 min), and its extraction efficiency was much higher than that of conventional polar solvent microwave‐assisted extraction (PSMAE) and mixed solvent microwave‐assisted extraction (MSMAE). It can be a good alternative for the extraction of volatile constituents from dried plant samples.
Highly Efficient Regio‐ and Stereoselective Synthesis of β‐(1→6)‐Branched β‐(1→3)‐Linked Glucohexaose and Its Analogue
Authors: Yi Yue‐Tao , Zhao Qian‐Fei , Qian Feng‐Zhen , Ning Jun 
Published: March 2007

AbstractA β‐(1→6)‐branched β‐(1→3)‐linked glucohexaose (1) and its lauryl glycoside (2), present in many biologically active polysaccharides from traditional herbal medicines such as Ganoderma lucidum, Schizophyllum commune and Lentinus edodes, were highly efficiently synthesized. Coupling of 2,3,4,6‐tetra‐O‐benzoyl‐β‐D‐glucopyranosyl‐ (1→3)‐2‐O‐benzoyl‐4,6‐O‐benzylidene‐α‐D‐glucopyranosyl trichloroacetimidate (7) with 3,6‐branched acceptors 8 and 12 gave β‐(1?3)‐linked pentasaccharides (9) and (13), then via simple chemical transformation 4′,6′‐OH pentasaccharide acceptors 10 and 14 were obtained. Regio‐ and stereoselective coupling of 3 with 10 and 14 gave β‐(1→3)‐linked hexasaccharides (11) and (15) as the major products. Deprotection of 11 and 15 provided the target sugar 1 and 2. Thus, a new method for the preparation of this kind of compounds was developed.
Time averaging. Does the noise really average toward zero?
Authors: Traficante Daniel D. 
Published: March 2007

AbstractTime averaging is used widely in Fourier transform NMR spectroscopy. Yet there is a popular misconception of how the process increases the overall signal‐to‐noise (S/N) ratio of a spectrum. The common, but incorrect, explanation assumes that when noise is added to noise, the overall result averages toward zero. This article first shows that this explanation cannot be valid and then presents a detailed analysis of time averaging, including a mathematical derivation of the well‐known result that time averaging increases the S/N by the square root of the number of scans averaged.
Whence spin?
Authors: Zumbulyadis Nicholas 
Published: March 2007

AbstractThe concept of angular momentum in quantum mechanics has many counterintuitive aspects, such as assuming only certain discrete values and only certain orientations in space in the presence of external fields. Spin is more esoteric yet; it is hard to imagine how point‐particles with no spatial extent can have an intrinsic angular momentum. Nevertheless, spin is the most fundamental concept in magnetic resonance. Appreciation of the spin concept requires some understanding of the relativistic quantum mechanics developed by P. A. M. Dirac. The history of the evolution of the spin concept is traced—from the turn‐of‐the‐century observation of the Zeeman effect, through the old and new quantum mechanics, and on to Dirac's theory of the electron, which was published in the late 1920s. The special relativity theory is discussed, and there is a brief explanation of how spin emerges naturally in a relativistically correct formulation of quantum mechanics.
A simple, geometrical approach to the steady‐state solution of the Bloch equations
Authors: Szátay Csaba , Kürti Jenö , Janke Frank 
Published: March 2007

AbstractThis article attempts to explain the slow‐passage phenomenon in magnetic resonance from a somewhat unconventional perspective by providing a geometrical interpretation of the Bloch equations. The scope of these equations is also discussed by contrasting them with the spin‐locking experiment. This approach is intended to help newcomers reinforce their understanding of some of the basic principles of magnetic resonance, most notably with regard to the vector model. This presentation is especially useful for chemists, students of chemistry, and those who are more comfortable with a pictorial understanding of physical processes.
The effect of cigarette taxes on smoking among men and women
Authors: Stehr Mark 
Published: March 2007

AbstractThe literature contains numerous studies that estimate the effect of cigarette taxes on smoking across various population groups. Although the conclusions are split, most US studies find that men are more responsive to cigarette taxes than women. This paper shows that these results are due to the failure to control for state‐specific gender gaps in smoking rates that are correlated with cigarette taxes. When gender‐specific state fixed effects are included to control for these gaps, the results indicate that women are nearly twice as responsive to cigarette taxes as are men. Since the econometric specification controls for variation in the tax response by household income, it is unlikely to be responsible for the difference. Copyright © 2007 John Wiley & Sons, Ltd.
Sampling 3‐D seismic data
Authors: Bardan Virgil 
Published: March 2007

AbstractA 3‐D seismic survey is usually achieved by recording a parallel profile network. The 3‐D data thus obtained are sampled and processed in a cubic grid for which the sampling requirements are generally derived from the usual 1‐D viewpoint. The spectrum of 3‐D seismic data has a support (the region of the Fourier space in which the spectrum is not zero) that can be approximated by a domain bounded by two cones. Considering the particular shape of this support, we use a 3‐D sampling theory to obtain results applicable to the recording and processing of 3‐D seismic data. This naturally leads to weaker sampling requirements than the 1‐D viewpoint does. We define the hexagonal non‐cubic sampling grid and the triangular non‐cubic sampling grid and show that fewer sample points are needed to represent 3‐D seismic data with the same degree of accuracy. Thus, using the hexagonal non‐cubic sampling grid we point out that the maximum value of the spatial sampling interval along the profiles is larger by 15.6% than the one of the cubic sampling grid. We also point out that the triangular non‐cubic sampling grid requires a number of sample points equal to half the number required by a cubic sampling grid.
The use of wiener deconvolution (an optimal filter) in nuclear magnetic resonance imaging
Authors: Letcher John H. 
Published: March 2007

AbstractA computer software technique has been developed and employed to insert a modified‐Wiener‐deconvolution filter (an optimal filter) immediately following the quadrate detector of a magnetic resonance imager. The purpose of this effort is to try to suppress the undesirable effect of the noise found in the magnetic resonance imaging receiving antenna. This technique convolves the sampled real and imaginary signals taken directly from the antenna quadrature detector with a transfer function which is expressed in terms of the power spectrum of the measured signal with noise and the measured power spectrum of the noise, alone. The latter factor is measured during the dummy cycles which precede a normal scan sequence. Results are presented using data taken with a commercially available phantom.
The detection of transient‐like signals in the presence of a spatially inhomogeneous, nonstationary noise field
Authors: Silvia Manuel T. 
Published: March 2007

AbstractWe will consider the problem of detecting transient‐like signals by means of a spatially distributed array of sensors embedded in an inhomogeneous, nonstationary noise field. If each element of the array has an independent, uncorrupted reference sensor to estimate the noise statistics, then conventional adaptive noise cancellation algorithms can be used to improve the detection process. However, because of practical real‐world constraints, independent, uncorrupted reference sensors for the noise might not be available. Thus, the applicability of conventional adaptive noise cancellation techniques is in question. This paper will discuss the development of a knowledge‐based signal‐processing system that uses Artificial Intelligence (Al) methodologies to adaptively cancel inhomogeneous, nonstationary noise from a distributed array of passive sensors that is constrained to have no noise‐reference sensors.
Solution of convergence problem in ultrasound inverse scattering tomography
Authors: Kwon Sung J. , Park Song B. , Kim Whan W. 
Published: March 2007

AbstractWhen the product of contrast and size of an object, which is to be reconstructed by using the ultrasound inverse scattering tomography algorithm, is large, it is well known that those algorithms fail to converge to a unique global minimum. In order to solve this well known and difficult convergence problem, in this paper we present a new method, which converges to the true solution, for obtaining the scattering potential without using the Born or Rytov approximation. This method converts the nonlinear nature of the problem into a linear one. Through computer simulations we will show the validity of the new approach for high contrast two‐dimensional scattering objects which are insonified by an incident ultrasound plane wave. Numerical results show that the reconstruction error is very small for circularly symmetric two‐dimensional cylindrical objects whose refractive indices range from small to even sufficiently large values for which the previous inverse scattering algorithms fail to converge.
Image estimation from scattered field data
Authors: Lin F. C. , Fiddy M. A. 
Published: March 2007

AbstractThe purpose of this paper is to reappraise the linearizing methods frequently used to solve inverse scattering problems. We describe inversion algorithms based on the Born and the Rytov approximations and the nature of the distortions obtained in the reconstructions when using them. We present extensions of these methods, namely, the distorted‐wave Born and the distorted‐wave Rytov approximations, which incorporate prior knowledge about part of the scattering structure. A method for inverting scattered field data using these distorted‐wave approximations is described, which retains the computational simplicity of the Born and the Rytov techniques. Some examples of their use with simulated and real data are given. A further extension of our distorted‐wave formalism, which leads to improvements of the reconstructed image, is suggested. This entails a spectral estimation procedure also based on the incorporation of prior knowledge about the scatterer. This spectral estimation procedure can be useful for interpolation of scattered field data as well as resolution enhancement.
Layer‐Stripping direct traveltime inversion for seismic data
Authors: Justice James H. 
Published: March 2007

AbstractThe problem of determining the velocity and depth structure of a layered earth model from surface seismic data is of considerable interest in exploration seismology, and many variations on ways to pose the problem and solve it have been proposed. One popular approach is based on layer stripping, in which it is assumed that all layers above a given layer whose parameters are to be determined have been inverted. This information is then used, together with seismic reflection data, to invert for the parameters of the given layer. This procedure is repeated until the entire section of interest has been inverted. The problem may be posed as a one‐, two‐, or three‐dimensional problem. The one‐dimensional case has received considerable treatment in the literature. The purpose of this paper is to extend a theoretical result and the corresponding analysis from the 1‐D to the 2‐D case. Specifically, it is shown that for a dipping plane layer 2‐D stratified earth, the depth/dip/velocity structure of the section can be determined by a direct layer‐stripping algorithm in which a system of nonlinear equations is solved for the unknown layer parameters using only traveltime data from three offset locations. This is the minimal information required to solve the problem. In practice, the solution is extremely sensitive to data errors and so a minimum norm implementation would usually be employed, utilizing the redundancy of data available from more than three offsets. It is the theoretical development which is of interest here. Its actual implementation may take many forms.
Tomographic reconstruction of multiple‐layer specimens with the scanning tomographic acoustic microscope
Authors: Lee Hua , Chiao Richard Y. 
Published: March 2007

AbstractIn this article we report the recent results of tomographic image reconstructions of multiple‐layer specimens at 100 MHz with the Scanning Tomographic Acoustic Microscope (STAM) system. The experiment utilizes 12 uniformly spaced projections and the results show significant improvement over the holographic images.
Maximum entropy methods in coherent radar imaging
Authors: Heidbreder G. R. 
Published: March 2007

AbstractThere are some compelling reasons for viewing the problem of image reconstruction from noisy or incomplete data as one of statistical estimation, i.e., of choosing, from the infinity of images consistent with the data, that image which, in some statistical sense, is most plausible. Among these reasons are the soundness of the philosophical underpinning of the resulting image reconstruction process, a greater realization of the image resolution which is inherent in the data, and freedom from many of the artifacts encountered in commonly usedad hocreconstruction schemes. One successful technique employing a principle of statistical inference is the maximum entropy technique, in which the data‐consistent image with maximum configurational entropy is chosen. It is a computationally intensive approach involving a conjugate gradient search over a convex function of a vector in a space of dimensionality equal to the number of image pixels. This technique has been employed with success in situations where the data samples are modeled as linearly related to a real non‐negative object. We investigate application of maximum entropy image reconstruction to the problem of high‐resolution radar diagnostic imaging. The problem differs from others in which maximum entropy has been applied in that the object to be imaged is complex. Although the desired image is of the magnitude of the complex object and is thus real and non‐negative, there is no linear relationship beween object magnitude and data. Rather, the data are linearly related to the complex object. Several earlier proposed methods for applying the maximum entropy principle to this problem are identified and analyzed. A method that more closely approximates true Bayesian estimation is proposed.
Local fractal geometric features for image segmentation
Authors: Keller James M. , Seo Young‐Bo 
Published: March 2007

AbstractIn this article, features based on fractal geometry are used for segmentation of synthetic and natural scenes. Assuming a fractional Brownian motion model of image regions, we extract, at each pixel, small, one‐variable “slices” in each of four directions from which we estimate two features: the fractal dimension and the intercept. While the fractal dimension has received most attention recently as a scale‐invariant feature, we show that the intercept is related to the dimension and possesses even better discriminatory power for segmentation purposes when calculations are made on small, one variable windows. These parameters are studied as segmentation features on both composite images of synthetically generated fractional Brownian motion surfaces and on intensity images of natural scenes.
Knowledge‐Based configuration of image segmentation processes
Authors: Liedtke C.‐E. , Blömer A. , Gahm Th. 
Published: March 2007

AbstractThe solution of an image interpretation problem using digital image analysis methods requires the configuration of an image analysis system to meet the requirements of this specific task the specific data material. This process includes the selection of the appropriate sequence of operators and the adaptation of the free parameters. A system has been developed and is described, which performs this configuration process automatically on the basis of a user‐specified task definition, and general knowledge of an image analysis expert. The latter knowledge has been assessed, stored, and used by employing different paradigms of knowledge representation similar to expert systems.