Elastic properties of a protein-polymer-grafted surface

Surfaces grafted with poly(methyl methacrylate) (PMMA) and streptavidin were synthesized through click chemistry to investigate the role of surface stiffness on protein adsorption as the hydrophilic and hydrophobic surface coverage of the substituents vary. Surface topographies coupled with the nanoindentation results indicated that, with the appropriate selections of polymer coverage and chain length, the extent of non-specific protein adhesion could be controlled by the hydrophobic interactions between PMMA, biotin, and streptavidin. It was shown that, when the molecular weight and stiffness of PMMA was close to that of streptavidin, patchy PMMA morphologies were obtained, which help inhibit the non-specific adsorption of streptavidin.     

Classification of the FRW universe with a cosmological constant and a perfect fluid of the equation of state <Emphasis Type="Italic">p</Emphasis> = <Emphasis Type="Italic">w</Emphasis><Emphasis Type="Italic">ρ</Emphasis>

We systematically study the evolution of the Friedmann–Robertson–Walker (FRW) universe coupled with a cosmological constant Λ and a perfect fluid that has the equation of state p = w ρ, where p and ρ denote, respectively, the pressure and energy density of the fluid, and w is an arbitrary real constant. Depending on the specific values of w, Λ, and the curvature k of 3-dimensional space, we separate all of the solutions into various cases. In each case the main properties of the evolution are given in detail, including the periods of deceleration and/or acceleration, and the existence of big bang, big crunch, and big rip singularities. In some cases, errors in classification and interpretation appearing in standard textbooks have been corrected.     

Constrained snake vs. conventional snake for carotid ultrasound automated IMT measurements on multi-center data sets

Accurate intima-media thickness (IMT) measurement of the carotid artery from minimal plaque ultrasound images is a relevant clinical need, since IMT increase is related to the progression of atherosclerosis.In this paper, we describe a novel dual snake-based model for the high-performance carotid IMT measurement, called Carotid Measurement Using Dual Snakes (CMUDS). Snakes (which are deformable contours) adapt to the lumen-intima (LI) and media-adventitia (MA) interfaces, thus enabling the IMT computation as distance between the LI and MA snakes. However, traditional snakes might be unable to maintain a correct distance and in some spatial location along the artery, it might even collapse between them or diverge. The technical improvement of this work is the definition of a dual snake-based constrained system, which prevents the LI and MA snakes from collapsing or bleeding, thus optimizing the IMT estimation.The CMUDS system consists of two parametric models automatically initialized using the far adventitia border which we automatically traced by using a previously developed multi-resolution approach. The dual snakes evolve simultaneously and are constrained by the distances between them, ensuring the regularization of LI/MA topology. We benchmarked our automated CMUDS with the previous conventional semi-automated snake system called Carotid Measurement Using Single Snake (CMUSS).Two independent readers manually traced the LIMA boundaries of a multi-institutional, multi-ethnic, and multi-scanner database of 665 CCA longitudinal 2D images. We evaluated our system performance by comparing it with the gold standard as traced by clinical readers.CMUDS and CMUSS correctly processed 100% of the 665 images. Comparing the performance with respect to the two readers, our automatically measured IMT was on average very close to that of the two readers (IMT measurement biases for CMUSS was equal to −0.011 ± 0.329 mm and −0.045 ± 0.317 mm, respectively, while for CMUDS, it was 0.030 ± 0.284 mm and −0.004 ± 0.273 mm, respectively). The Figure-of-Merit of the system was 98.5% and 94.4% for CMUSS, while 96.0% and 99.6% for CMUDS, respectively. Results showed that the dual-snake system CMUDS reduced the IMT measurement error accuracy (Wilcoxon, p < 0.02) and the IMT error variability (Fisher, p < 3 × 10⁻²).We propose the CMUDS technique for use in large multi-centric studies, where the need for a standard, accurate, and automated IMT measurement technique is required.     

Mesoporous Silica Supported Multiple Single‐Site Catalysts and Polyethylene Reactor Blends with Tailor‐Made Trimodal and Ultra‐Broad Molecular Weight Distributions

A ternary blend of the bisiminopyridine chromium (III) (Cr‐ 1 ) with the bisiminopyridine iron (II) (Fe‐ 2 ) post‐metallocenes with the quinolylsilylcyclopentadienyl chromium (III) halfsandwich complex (Cr‐ 3 ) was supported on mesoporous silica to produce novel multiple single‐site catalysts and polyethylene reactor blends with tailor‐made molecular weight distributions (MWDs). The preferred cosupporting sequence of this ternary blend on MAO‐treated silica was Fe‐ 2 followed by Cr‐ 1 and Cr‐ 3 . Cosupporting does not impair the single‐site nature of the blend components producing polyethylene fractions with = 10⁴ g · mol⁻¹ on Cr‐ 1 , = 3 × 10⁵ g · mol⁻¹ on Fe‐ 2 , and = 3 × 10⁶ g · mol⁻¹ on Cr‐ 3 . As a function of the Fe‐ 2 /Cr‐ 1 /Cr‐ 2 mixing ratio it is possible to control the weight ratio of these three polyethylenes without affecting the individual average molecular weights and narrow polydispersities of the three polyethylene fractions. Tailor‐made polyethylene reactor blends with ultra‐broad MWD and polydispersities varying between 10 and 420 were obtained. When the molar ratio of Fe‐ 2 /Cr‐ 1 was constant, the ultra‐high molecular polyethylene (UHMWPE, > 10⁶ g · mol⁻¹) content was varied between 8 and 16 wt.‐% as a function of the Cr‐ 3 content without impairing the blend ratio of the other two polyethylene fractions and without sacrificing melt processability. When the molar ratio Fe‐ 2 /Cr‐ 3 was constant, it was possible to selectively increase the content of the low molecular weight fraction by additional cosupporting of Cr‐ 1 . Due to the intimate mixing of low and ultra‐high molecular weight polyethylenes (UHMPEs) produced on cosupported single‐site catalysts a wide range of melt processable polyethylene reactor blends was obtained.

     

Substitution of the terminal chloride ligands of [Re(6)S(8)Cl(6)](4-) with triethylphosphine: photophysical and electrochemical properties of a new series of [Re(6)S(8)](2+) based clusters

A systematic substitution of the terminal chlorides coordinated to the hexanuclear cluster [Re(6)S(8)Cl(6)](4-) has been conducted. The following complexes: [Re(6)S(8)(PEt(3))Cl(5)](3-) (1), cis- (cis-2) and trans-[Re(6)S(8)(PEt(3))(2)Cl(4)](2-) (trans-2), mer- (mer-3) and fac-[Re(6)S(8)(PEt(3))(3)Cl(3)](-) (fac-3), and cis- (cis-4) and trans-[Re(6)S(8)(PEt(3))(4)Cl(2)] (trans-4) were synthesized and fully characterized. Compared to the substitution of the halide ligands of the related [Re(6)S(8)Br(6)](4-) and [Re(6)Se(8)I(6)](3-) clusters, the chloride ligands are slower to substitute which allowed us to prepare the first monophosphine cluster (1). In addition, the synthesis of fac-3 was optimized by using cis-2 as the starting material, which led to a significant increase in the overall yield of this isomer. Notably, we observed evidence of phosphine isomerization taking place during the preparation of the facial isomer; this was unexpected based on the relatively inert nature of the Re-P bond. The structures of Bu(4)N(+) salts of trans-2, mer-3, and fac-3 were determined using X-ray crystallography. All compounds display luminescent behavior. A study of the photophysical properties of these complexes includes measurement of the excited state lifetimes (which ranged from 4.1-7.1 μs), the emission quantum yields, the rates of radiative and non-radiative decay, and the rate of quenching with O(2). Quenching studies verify the triplet state nature of the excited state.     

Molecular dynamics simulation of nanodroplet spreading enhanced by linear surfactants

We utilize molecular dynamics simulations to probe the surfactant-mediated spreading of a Lennard-Jones liquid droplet on a solid surface. The surfactants are linear hexamers that are insoluble in the liquid and reduce the surface tension of the liquid-vapor interface. We study how the interaction of the surfactant hexamers with the solid substrate influences spreading, as well as the dependence of spreading on surfactant concentration. We find that the spreading speed is strongly influenced by the attraction of the hydrophobic surfactant tail to the solid surface. When this attraction is sufficiently strong, surfactant molecules partition to the liquid-solid interface and facilitate spreading. This partitioning can lead to an inhomogeneous distribution of surfactant over the liquid-vapor interface, which could drive the Marangoni convection. We also observe that the surfactant molecules can assemble into micelles on the solid surface. The repulsion between micelles at the liquid-solid interface can lead to break-off and migration of the micelles from the liquid-solid to the gas-solid interface and spreading is facilitated in this way. Our model system contains features that are believed to underlie superspreading in experimental studies of droplet spreading.     

Catalyst-Free Preparation of Heterocyclic Thienyl Sulfides

Described in this work is a catalyst-free, in most cases neat, preparation of heterocyclic thienyl sulfides. This method utilizes 2-thiophenethiol and various activated halogenated heterocycles in a substitution-type reaction to form an interesting array of sulfides. Yields obtained are comparable to other published methods, and the reaction requires milder conditions, has shorter reaction times, and most times eliminates the need for column chromatography during workup.     

Direct Preparation of Amides from Amine Hydrochloride Salts and Orthoesters: A Synthetic and Mechanistic Perspective

The conversion of a wide range of primary and secondary aliphatic and a few arylamine hydrochloride salts to their corresponding acetamides with trimethyl orthoacetate is described. Mechanistic studies using NMR and gas chromatography–mass spectrometry techniques indicate these reactions proceed via an O-methylimidate intermediate that undergoes in situ demethylation by chloride, affording the corresponding acetamides. Synthetically, this reaction represents a practical, high-yielding protocol with a simple workup for the rapid conversion of amine hydrochloride salts to acetamides.     

Photoelectron spectra of dihalomethyl anions: testing the limits of normal mode analysis

We report the 364-nm negative ion photoelectron spectra of CHX(2)(-) and CDX(2)(-), where X = Cl, Br, and I. The pyramidal dihalomethyl anions undergo a large geometry change upon electron photodetachment to become nearly planar, resulting in multiple extended vibrational progressions in the photoelectron spectra. The normal mode analysis that successfully models photoelectron spectra when geometry changes are modest is unable to reproduce qualitatively the experimental data using physically reasonable parameters. Specifically, the harmonic normal mode analysis using Cartesian displacement coordinates results in much more C-H stretch excitation than is observed, leading to a simulated photoelectron spectrum that is much broader than that which is seen experimentally. A (2 + 1)-dimensional anharmonic coupled-mode analysis much better reproduces the observed vibrational structure. We obtain an estimate of the adiabatic electron affinity of each dihalomethyl radical studied. The electron affinity of CHCl(2) and CDCl(2) is 1.3(2) eV, of CHBr(2) and CDBr(2) is 1.9(2) eV, and of CHI(2) and CDI(2) is 1.9(2) eV. Analysis of the experimental spectra illustrates the limits of the conventional normal mode approach and shows the type of analysis required for substantial geometry changes when multiple modes are active upon photodetachment.     

Gender Equity in Mathematics: Beliefs of Students,Parents, and Teachers

The attitudes about mathematics held by girls and boys participating in a regional mathematics contest, their parents, teachers, and mathematics coaches were investigated. Quantitative data regarding mathematics as a male domain, perception of importance of mathematics, confidence in learning mathematics, effectance motivation, and usefulness of mathematics were obtained. It was found that the traditional gender‐based differences in the beliefs regarding mathematics persist even in these mathematically talented students. Furthermore, parents' responses to the questions regarding the role of mathematics revealed that mothers, more than fathers, focused on the computational aspects of mathematics, while fathers more than mothers mentioned the role of mathematics in science or as a language. Boys, fathers, and certain mathematics teachers admitted to a low level of gender stereotyping, as evidenced by their scores on the Mathematics as a Male Domain subscale. However, the girls, mothers, and mathematics coaches did not endorse this stereotyping. Unsolicited responses of girls and mothers, in fact, emphatically denied that gender stereotyping exists. These findings are discussed in terms of the need to resolve the essential conflicts between students', parents', and teachers' deeply held beliefs regarding the nature of mathematics, gender differences in mathematical abilities, and the desire for equity within mathematics education.