bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of phthalic anhydride‐based hyperbranched polyesteramide on cement characteristics
Authors: Amin A. , Darweesh H. H. M. , Morsi S. M. M. , Ayoub M. M. H.
Published: January 2011

Hyperbranched polyesteramides (HB1 and HB2) were prepared by the bulk reaction between phthalic anhydride (PhAn) with either diisopropanolamine (DiPA) or diethanolamine (DEA), respectively. The hyperbranched polyesteramides were characterized by IR, GPC, 1H‐NMR, and thermal analysis (TGA and DSC). The effects of solutions of 1, 3, and 5 wt % HB1 and HB2 on the properties of Ordinary Portland Cement (OPC) and Portland Limestone Cement (PLC) were studied. Measurements of water of consistency, setting times, bulk density, apparent porosity, and compressive strength for the cement pastes were performed. Some selected cement pastes were characterized by IR and SEM photos. The results showed that HB1 and HB2 slightly increased the compressive strength, the combined water and density while decreased the apparent porosity. IR of the formed phases showed increase in the intensities of the spectra for the cement pastes mixed with HB1 and HB2 when compared with those of the blank cement pastes. SEM images showed that the incorporation of HB1 and HB2 affected only shape or morphology and crystallinity of the formed hydrates. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Polypropylene and potato starch biocomposites: Physicomechanical and thermal properties
Authors: Roy Srabayeeta Basu , Ramaraj B. , Shit S.C. , Nayak Sanjay K.
Published: January 2011

To determine the possibility of using starch as biodegradable filler in the thermoplastic polymer matrix, starch‐filled polypropylene (PP) composites were prepared by extrusion of PP resin with 5, 10, 15, and 20 wt % of potato starch in corotating twin‐screw extruder. The extruded strands were cut into pellets and injection molded to make test specimens. These specimens were tested for physicomechanical properties such as tensile and flexural properties, Izod impact strength, density, and water absorption. These PP composites were further characterized by melt flow index (MFI), vicat softening point (VSP), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) techniques. It was found that, with increase in starch content, tensile modulus, flexural strength, and flexural modulus of the PP composites increased along with the increase in moisture, water absorption, and density, while retaining the VSP; but, tensile strength and elongation, impact strength, hardness, and MFI of the PP composites also decreased. DSC analysis of the PP composite revealed the reduction in melting temperature, heat of fusion, and percentage of crystallization of PP with increase in starch content. Similarly, TGA traces display enhanced thermal degradability for PP as starch content increases. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Nonlinear optical response of liquid crystalline azo‐dendrimer in picosecond and CW regimes
Authors: Zhang Xiaoqiang , Wang Changshun , Lu Xuemin , Zeng Yi
Published: January 2011

The nonlinear optical response of the liquid crystalline multiarm star‐shaped azodendrimer was investigated in picosecond pulse and CW regimes at 532 nm. The polymer exhibited large nonlinear refractive coefficient in two regimes (n2 = −2.88 × 10−13 cm2/W and −1.1 × 10−10 cm2/W under picoseconds pulse excitation, whereas n2 = −1.4 × 10−6 cm2/W and n2 = −8.8 × 10−5 cm2/W under CW laser excitation in solution and film, respectively). The mechanism accounting for the process of nonlinear refraction was discussed. The value of photoinduced birefringence in the polymer film was also measured (Δn ∼ 10−3) under CW laser excitation at 532 nm. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Orientation of Primary Cilia of Articular Chondrocytes in Three‐Dimensional Space
Authors: Farnum Cornelia E. , Wilsman Norman J.
Published: January 2011

Primary cilia have functions as sensory organelles integral to signal transduction and establishment of cell polarity. In articular cartilage the primary cilium has been hypothesized to function as an antenna to sense the biomechanical environment, regulate the secretion of extracellular matrix components, and maintain cellular positional information, leading to high tissue anisotropy. We used analysis of electron microscopy serial sections to demonstrate positional attributes of the primary cilium of adult equine articular chondrocytes in situ. Data for ∼500 axonemes, comparing superficial to radiate chondrocytes from both load‐bearing and non‐load‐bearing regions, were graphed using spherical co‐ordinates θ, φ. The data demonstrate the axoneme has a definable orientation in 3D space differing in superficial and radiate zone chondrocytes, cells that differ by 90° in the orientation of their major axes to the articular surface. Axonemal orientation is more definable in load‐bearing than in non‐load‐bearing areas. The position of emergence of the axoneme from the cell also is variable. In load‐bearing regions of the superficial zone, extension of the axoneme is from the cellular side facing the subchondral bone. In radiate zone cells, axonemes extend from either face of the chondrocyte, that is, both toward the articular surface or toward the subchondral bone. In non‐load‐bearing regions this consistency is lost. These observations relate to current hypotheses concerning establishment of tissue anisotropy in articular cartilage during development, involving both migration of cells from the joint periphery and a restricted zone of division within the tissue resulting in the columnar arrangement of radiate zone cells. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.
Robust stochastic stability of genetic regulatory networks with time delays and parametric uncertainties
Authors: Li J. , Chesi G. , Hung Y. S.
Published: January 2011

This paper investigates robust stochastic stability of uncertain genetic regulatory networks. It is assumed that the networks have SUM regulatory functions affected by Wiener processes, time delays and parametric uncertainties. Contrary to existing works, the uncertainty is not restricted to belong to a polytope, but more generally it is assumed to belong to a multi‐dimensional set described by polynomial inequalities. First, it is shown that a condition for robust stochastic stability with guaranteed disturbance attenuation for all admissible uncertainties in the absence of time delays can be obtained by solving a convex optimization problem built by exploiting the square matrix representation (SMR) of matrix polynomials and by introducing polynomially parameter‐dependent Lyapunov functions. Then, it is shown how this condition can be extended to deal with the presence of time delays with bounded variation rates by introducing polynomially parameter‐dependent Lyapunov‐Krasovskii functionals (LKFs). Examples with fictitious and real biological models illustrate the use of the proposed methodology.

Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society
Structure reduction of liveness‐enforcing Petri nets using mixed integer programming
Authors: Li Shao‐Yong , Li Zhi‐Wu
Published: January 2011

Many deadlock prevention policies existing in the literature are to add control places (CPs) to cope with deadlocks in practical systems modeled with Petri nets. Since the number of CPs determined by these policies is not minimal under the condition that a controlled systems is live, this usually leads to a liveness‐enforcing Petri net supervisor with redundant CPs. Based on mixed integer programming (MIP) and the concept of implicit places (IPs), this paper develops a novel iterative algorithm of simplifying the structural complexity for a live Petri net. Under the condition that liveness is preserved in the iteration, this algorithm computes a feasible solution of an MIP for each CP to confirm whether redundant CPs exist in the live controlled system. Necessary and redundant CPs are then kept in or removed from the simplified live Petri net, respectively. As a result, a live controlled system with simpler structure is obtained, which directly reduces computational cost in further design and verification phases and possibly leads to more permissive behavior. Effectiveness of this algorithm is proved via a theoretic analysis and examples.

Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society
Length of the day and evolution of the Earth's core in the geological past
Authors: Denis C. , Rybicki K.R. , Schreider A.A. , Tomecka‐Suchoń S. , Varga P.
Published: January 2011

In this paper, we study quantitatively the effect of the Earth's core formation on the secular rate of change of the length of day (LOD). We find that for the present epoch, a growth rate of the core comprised between 1 and 10 mm/cy seems to be a plausible guess, leading to a relative de crease of LOD comprised roughly between 10 and 100 μs/cy. Such values do not affect significantly the observed secular in crease of LOD caused by tidal braking, which amounts to about 1.79 ms/cy. However, in the remote geological past, before the Phanerozoic, the effects of core growth may have been much more important, because the total change of LOD associated with core formation has been estimated by Birch in 1965 to be 2.4 hours for an initially undifferentiated cold Earth, and 3.1 hours for an initially undifferentiated hot Earth. We consider a number of scenarios, some of them corresponding to very early and/or very fast core formation, others corresponding to slow and/or late core formation. We show that palaeo‐LOD measurements seem to favour slow core formation during the Proterozoic, contrarily to the now largely prevailing hypothesis based on geochemical arguments that the iron core formed very early in the Earth's history and during a geologically short time interval (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamo action in an ambient field
Authors: Heyner D. , Schmitt D. , Glassmeier K.‐H. , Wicht J.
Published: January 2011

The origin of global magnetic fields in celestial bodies is generally ascribed to dynamo action by fluid motions in their electrically conducting interiors. Some objects – e.g. close‐in extra‐solar planets or the moons of some giant planets – are embedded in ambient magnetic fields which modify the generation of the internal field in these bodies. Recently, the feedback of the magnetospheric field by Chapman‐Ferraro currents in the magnetopause onto the interior dynamo has been proposed to explain the observed weakness of the intrinsic magnetic field of planet Mercury. We study a simplified mean‐field dynamo model which allows us to analytically address various issues like positive and negative feedback situations, stationary versus time‐dependent solutions, and the stability of weak and strong field branches. We discuss the influence of the response function on the solutions when the external field depends on the strength of the intrinsic field like in the situation of the feedback dynamo of Mercury. We find that the feedback mechanism works only for a narrow range of dynamo numbers in the case of Mercury which makes him unique in our solar system. We conclude with some implications for extra‐solar planets (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The screw dynamo in a thick torus
Authors: Chupin A. , Frick P. , Stepanov R.
Published: January 2011

The problem of magnetic field generation under screw motion in a toroidal channel is studied numerically. The screw dynamo in the cylinder with periodical boundary conditions was found to be a suitable approximation for generation of the magnetic field by a screw flow in a thin torus. For the thick torus, a principally new solution of the screw dynamo problem was obtained. In this case the growing global magnetic field mode has the scale of a maximal geometrical size of the torus and does not vanish on the axis of the torus (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectral lag of gamma‐ray bursts caused by the intrinsic spectral evolution and the curvature effect
Authors: Peng Z.Y. , Yin Y. , Bi X.W. , Bao Y.Y. , Ma L.
Published: January 2011

Assuming an intrinsic ‘Band’ shape spectrum and an intrinsic energy‐independent emission profile we have investigated the connection between the evolution of the rest‐frame spectral parameters and the spectral lags measured in gamma‐ray burst (GRB) pulses by using a pulse model. We first focus our attention on the evolution of the peak energy, E0,p, and neglect the effect of the curvature effect. It is found that the evolution of E0,p alone can produce the observed lags. When E0,p varies from hard to soft only the positive lags can be observed. The negative lags would occur in the case of E0,p varying from soft to hard. When the evolution of E0,p and the low‐energy spectral index α0 varying from soft to hard then to soft we can find the aforesaid two sorts of lags. We then examine the combined case of the spectral evolution and the curvature effect of fireball and find the observed spectral lags would increase. A sample including 15 single pulses whose spectral evolution follows hard to soft has been investigated. All the lags of these pulses are positive, which is in good agreement with our theoretical predictions. Our analysis shows that only the intrinsic spectral evolution can produce the spectral lags and the observed lags should be contributed by the intrinsic spectral evolution and the curvature effect. But it is still unclear what cause the spectral evolution (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New spectroscopic classifications of 35 chemically peculiar candidate stars
Authors: Paunzen E. , Netopil M. , Pintado O.I. , Rode‐Paunzen M.
Published: January 2011

The chemically peculiar (CP) stars of the upper main sequence are perfect tracers for several astrophysical processes. Their study especially in open clusters further helps to establish their evolutionary status. The latter is most important to understand the origin and evolution of the CP phenomenon, i.e. the connection between diffusion and a stellar magnetic field. There are two important topics, we cover with this paper. First of all, we investigate the reliability of the CCD Δa photometry for fainter objects in open clusters. The latter method is able to detect CP stars very efficiently, but still a spectroscopic verification is needed to verify the photometric candidates. On the other hand, already published spectral classifications on the basis of photographic plates and prism technology have tobe tested with modern instruments. Classification resolution spectroscopy is presented for thirty five bona‐fide CP candidates. Twenty six of them are located within the boundaries of fourteen open clusters, for which we also investigated their membership probabilities. Apart from five objects, they seem tobe members of the respective clusters. The objects were classified in the framework of a refined Morgan‐Keenan system with the extension of well established CP star spectra. We confirm the CP nature of all but one target. The results of Δa photometry and the spectral classifications are in excellent agreement. For the cluster members we find a continuous sequence of CP stars from 10 to 850 Myr, the whole range of investigated cluster ages (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dissipation in dynamos at low and high magnetic Prandtl numbers
Authors: Brandenburg A.
Published: January 2011

Using simulations of helically driven turbulence, it is shown that the ratio of kinetic to magnetic energy dissipation scales with the magnetic Prandtl number in power law fashion with an exponent of approximately 0.6. Over six orders of magnitude in the magnetic Prandtl number the magnetic field is found tobe sustained by large‐scale dynamo action of alphasquared type. This work extends a similar finding for small magnetic Prandtl numbers to the regime of large magnetic Prandtl numbers. At large magnetic Prandtl numbers, most of the energy is dissipated viscously, lowering thus the amount of magnetic energy dissipation, which means that simulations can be performed at magnetic Reynolds numbers that are large compared to the usual limits imposed by a given resolution. This is analogous to an earlier finding that at small magnetic Prandtl numbers, most of the energy is dissipated resistively, lowering the amount of kinetic energy dissipation, so simulations can then be performed at much larger fluid Reynolds numbers than otherwise. The decrease in magnetic energy dissipation at large magnetic Prandtl numbers is discussed in the context of underluminous accretion found in some quasars (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The kinematic characteristics of magnetic O‐type stars
Authors: Hubrig S. , Kharchenko N.V. , Schöller M.
Published: January 2011

Although magnetic fields have been discovered in ten massive O‐type stars during the last years, the origin of their magnetic fields remains unknown. Among the magnetic O‐type stars, two stars, HD 36879 and HD 57682, were identified as candidate runaway stars in the past, and θ1 Ori C was reported to move rapidly away from its host cluster. We search for an explanation for the occurrence of magnetic fields in O‐type stars by examining the assumption of their runaway status. We use the currently best available astrometric, spectroscopic, and photometric data to calculate the kinematical status of seven magnetic O‐type stars with previously unknown space velocities. The results of the calculations of space velocities suggest that five out of the seven magnetic O‐type stars can be considered as candidate runaway stars. Only two stars, HD 155806 and HD 164794, with the lowest space velocities, are likely members of Sco OB4 and NGC 6530, respectively. However, the non‐thermal radio emitter HD 164794 is a binary system with colliding winds, for which the detected magnetic field has probably a different origin in comparison to other magnetic O‐type stars (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic fields of Ap stars as a result of the Tayler instability
Authors: Arlt R. , Rüdiger G.
Published: January 2011

Ap star magnetism is often attributed to fossil magnetic fields which have not changed much since the pre‐main‐sequence epoch of the stars. Stable magnetic field configurations are known which could persist probably for the entire mainsequence life of the star, but they may not show the complexity and diversity exhibited by the Ap stars observed. We suggest that the Ap star magnetism is not a result of stable configurations, but is the result of an instability based on strong toroidal magnetic fields buried in the stars. The highly nonaxisymmetric remainders of the instability are reminiscent of the diversity of fields seen on Ap stars. The strengths of these remnant magnetic fields are actually between a few per cent up to considerable fractions of the internal toroidal field; this means field strengths of the order of kGauss being compatible with what is observed. The magnetic fields emerge at the surface rather quickly; rough estimates deliver time‐scales of the order of a few years. Since rotation stabilizes the instability, normal A stars may still host considerable, invisible toroidal magnetic fields (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Tayler instability of toroidal magnetic fields in a columnar gallium experiment
Authors: Rüdiger G. , Schultz M. , Gellert M.
Published: January 2011

The nonaxisymmetric Tayler instability of toroidal magnetic fields due to axial electric currents is studied for conducting incompressible fluids between two coaxial cylinders without endplates. The inner cylinder is considered as so thin that the limit of Rin → 0 can be computed. The magnetic Prandtl number is varied over many orders of magnitudes but the azimuthal mode number of the perturbations is fixed to m = 1. In the linear approximation the critical magnetic field amplitudes and the growth rates of the instability are determined for both resting and rotating cylinders. Without rotation the critical Hartmann numbers do not depend on the magnetic Prandtl number but this is not true for the corresponding growth rates. For given product of viscosity and magnetic diffusivity the growth rates for small and large magnetic Prandtl number are much smaller than those for Pm = 1. For gallium under the influence of a magnetic field at the outer cylinder of 1 kG the resulting growth time is 5 s. The minimum electric current through a container of 10 cm diameter to excite the instability is 3.20 kA. For a rotating container both the critical magnetic field and the related growth times are larger than for the resting column (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Long‐term photometry of the ultra‐fast rotator LO Peg
Authors: Taş G.
Published: January 2011

LO Peg is a young main‐sequence star of spectral type K3. With its equatorial rotation velocity of 65 km s–1 it is amongst the ultra‐fast rotators. Its high equatorial rotation velocity and rapidly changing surface activity features make it an important object in terms of both stellar activity and the evolution of stellar rotation and angular momentum. Since its discovery as a variable star, it has mostly been subject to spectral surface mapping studies such as Doppler Imaging, while there have been very few photometric studies on it. This paper aims to present the first long‐term photometric observations and its results covering the years between 2003 and 2009. The UBVR Johnson wide band photometric data showed that the surface activity structures of LO Peg vary in timescales changing between days and months, and parallel to this, the mean, maximum and minimum brightness and amplitudes change dramatically between years and sometimes even within the same observation season. Long‐term changes in system brightness and colours, both characteristic features of active stars, were also seen in this ultra‐fast young star. The active longitudes, which has a life time of ∼1.3 years and an activity cycle period of ∼4.8 years for LO Peg were estimated (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Metric study of Egyptian sacrum for lumbo‐sacral fixation procedures
Authors: El‐Sayed Hassanein Gamal Hamed
Published: January 2011

Lumbo‐sacral fixation for the management of lumbo‐sacral instability includes insertion of screws to the sacrum, most commonly into the posterior aspect of the pedicles of the first sacralvertebra. This study was carried out to determine the normal anatomical parameters of the Egyptian sacrum, particularly of the first sacral vertebra and its pedicles, to find the safest approach for sacral screw placement in lumbo‐sacral fixation procedures, and to describe racial characteristics, if any. In this study, 45 adult Egyptian dry sacra of unknown sex were used. Eleven sacral parameters were measured using the Vernier sliding caliper which is accurate to 0.1 millimeter. In this study, the sacrum showed a mean height of 11.43 ± 0.88 centimeters a mean width of 10.39 ± 0.91 centimeters with a mean sacral index of 90.82 ± 1.80 %. The first sacral pedicle had a mean anterior height of 1.83 ± 0.49 centimeters, a mean depth of 2.99 ± 0.53 centimeters and a mean posterior height of 2.38 ± 0.50 centimeters. A medialtrajectory path (representing an anteromedially‐oriented first sacral pedicle screw) starting from the infero‐lateral border of the S1 facet to the sacral promontory in the middle line was 5.23 ± 0.52 cm. The findings of the present study could provide accurate and specific parameters of the sacrum among Egyptians that could enhance the safety of insertion of sacral screws during lumbo‐sacral fixation procedures upon Egyptian patients. Clin. Anat. 24:218–224, 2011. © 2011 Wiley‐Liss, Inc.
Microstructure of the vocal fold in elderly humans
Authors: Roberts T. , Morton R. , Al‐Ali S.
Published: January 2011

Significant changes in the voice occur after the age of 50 years. Changes in the structure of the vocal fold (VF) can interfere with the voice. The aim of this study is to investigate the structure of the VF of elderly people that may contribute to the tendency of the human voice to deteriorate. Larynges were obtained from eight embalmed cadavers aged 72–98 years. The middle portion of each vocal fold was removed and placed in 4% buffered formalin. Tissue blocks were then processed and embedded in wax. Four to six micron coronal sections were cut and stained with Haematoxylin and Eosin (H&E), Masson's Trichrome (MTS), Elastin van Gieson (EVG), Herovici (HERO), picrosirius and CD31 immunohistochemical marker in order to study the collagen fibers, elastic fibers and microvasculature of the VF. The maturity of collagen fibers within the VF were noted to increase from the superficial to the deep layer of the lamina propria (LP). Contrary to current literature, the amount of elastic fibers was sparse in the superficial layer of the LP in the vocal tissue of elderly cadavers. Numerous cross‐sectioned blood vessels were seen in the lamina propria near the free edge, and near the superior and inferior surfaces of the VF. The presence of lymphatic vessels was confirmed in the VF of elderly subjects. This study revealed that the collagenous component of the deep layer of the VF LP was made up of mature fibers whilst immature collagen fibers made up the superficial layer of the LP. There was a notable scarcity of elastic fibers in the superficial layer of the LP. Lymphatics were seen and were orientated differently in the geriatric vocal folds. Clin. Anat. 24:544–551, 2011. © 2011 Wiley‐Liss, Inc.
A comprehensive analysis of muscle recruitment patterns during shoulder flexion: An electromyographic study
Authors: Wattanaprakornkul Duangjai , Halaki Mark , Boettcher Craig , Cathers Ian , Ginn Karen A.
Published: January 2011

Although flexion is a common component of the routine clinical assessment of the shoulder the muscle recruitment patterns during this movement are not clearly understood making valid interpretation of potential muscle dysfunction problematic. The purpose of this study was to comprehensively examine shoulder muscle activity during flexion in order to compare the activity levels and recruitment patterns of shoulder flexor, scapular lateral rotator and rotator cuff muscles. Electromyographic (EMG) data were recorded from 12 shoulder muscles sites in 15 volunteers. Flexion was performed in standing in the sagittal plane at no load, 20%, and 60% of each subject's maximum load. EMG data were normalized to maximum values obtained during maximum voluntary contractions. Results indicated that anterior deltoid, pectoralis major, supraspinatus, infraspinatus, serratus anterior, upper, and lower trapezius were activated at similar moderate levels. However, subscapularis was activated at low levels and significantly lower than supraspinatus and infraspinatus. Similar activity patterns across time were demonstrated in the muscles that produce flexion torque, laterally rotate the scapula, as well as supraspinatus and infraspinatus, and did not change as flexion load increased. The onset of activity in supraspinatus and anterior deltoid occurred at the same time and prior to movement of the limb at all loads with infraspinatus activity also occurring prior to movement onset at the medium and high load conditions only. Posterior rotator cuff muscles appear to be counterbalancing anterior translational forces produced during flexion and it would appear that supraspinatus is one of the muscles that consistently “initiates” flexion. Clin. Anat. 24:619–626, 2011. © 2011 Wiley‐Liss, Inc.
High spatial and temporal resolution imaging of the arterial vasculature of the lower extremity with contrast enhanced mr angiography
Authors: Mostardi Petrice M. , Haider Clifton R. , Glockner James F. , Young Phillip M. , Riederer Stephen J.
Published: January 2011

Vascular imaging can be essential in the diagnosis, monitoring, and planning and assessment of treatment of patients with peripheral vascular disease. The purpose of this work is to describe a recently developed three‐dimensional (3D) time‐resolved contrast‐enhanced MR angiography (CE‐MRA) technique, Cartesian Acquisition with Projection Reconstruction‐like sampling (CAPR), and its application to imaging of the vasculature of the lower legs and feet. CAPR implements accelerated imaging techniques and uses specialized multielement imaging coil arrays to achieve high temporal and high spatial resolution imaging. Volunteer and patient studies of the vasculature of the lower legs and feet have been performed. Temporal resolution of 4.9–6.5 sec and spatial resolution less than or equal to 1 mm in all directions allow for the depiction of progressive arterial filling and complex flow patterns as well as sharp visualization of vascular structure as small as the fine muscular branches. High‐quality diagnostic imaging is made possible with CAPR's advanced acquisition and reconstruction techniques and the use of specialized coil arrays. Clin. Anat. 24:478–488, 2011. © 2011 Wiley‐Liss, Inc.
Structure, Bioactivity and Synthesis of Natural Products with Hexahydropyrrolo[2,3‐b]indole
Authors: Ruiz‐Sanchis Pau , Savina Svetlana A. , Albericio Fernando , Álvarez Mercedes
Published: January 2011

Research on natural products containing hexahydropyrrolo[2,3‐b]indole (HPI) has dramatically increased during the past few years. Newly discovered natural products with complex structures and important biological activities have recently been isolated and synthesized. This review summarizes the structures, biological activities, and synthetic routes for natural compounds containing HPI, emphasizing the different strategies for assembling this motif. It covers a broad range of molecules, from small alkaloids to complex peptides.
Isocyanide in Biochemistry? A Theoretical Investigation of the Electronic Effects and Energetics of Cyanide Ligand Protonation in [FeFe]‐Hydrogenases
Authors: Greco Claudio , Bruschi Maurizio , Fantucci Piercarlo , Ryde Ulf , De Gioia Luca
Published: January 2011

The presence of Fe‐bound cyanide ligands in the active site of the proton‐reducing enzymes [FeFe]‐hydrogenases has led to the hypothesis that such Brønsted–Lowry bases could be protonated during the catalytic cycle, thus implying that hydrogen isocyanide (HNC) might have a relevant role in such crucial microbial metabolic paths. We present a hybrid quantum mechanical/molecular mechanical (QM/MM) study of the energetics of CN− protonation in the enzyme, and of the effects that cyanide protonation can have on [FeFe]‐hydrogenase active sites. A detailed analysis of the electronic properties of the models and of the energy profile associated with H2 evolution clearly shows that such protonation is dysfunctional for the catalytic process. However, the inclusion of the protein matrix surrounding the active site in our QM/MM models allowed us to demonstrate that the amino acid environment was finely selected through evolution, specifically to lower the Brønsted–Lowry basicity of the cyanide ligands. In fact, the conserved hydrogen‐bonding network formed by these ligands and the neighboring amino acid residues is able to impede CN− protonation, as shown by the fact that the isocyanide forms of [FeFe]‐hydrogenases do not correspond to stationary points on the enzyme QM/MM potential‐energy surface.
Elucidating Gating Effects for Hydrogen Sorption in MFU‐4‐Type Triazolate‐Based Metal–Organic Frameworks Featuring Different Pore Sizes
Authors: Denysenko Dmytro , Grzywa Maciej , Tonigold Markus , Streppel Barbara , Krkljus Ivana , Hirscher Michael , Mugnaioli Enrico , Kolb Ute , Hanss Jan , Volkmer Dirk
Published: January 2011

A highly porous member of isoreticular MFU‐4‐type frameworks, [Zn5Cl4(BTDD)3] (MFU‐4l(arge)) (H2‐BTDD=bis(1H‐1,2,3‐triazolo[4,5‐b],[4′,5′‐i])dibenzo[1,4]dioxin), has been synthesized using ZnCl2 and H2‐BTDD in N,N‐dimethylformamide as a solvent. MFU‐4l represents the first example of MFU‐4‐type frameworks featuring large pore apertures of 9.1 Å. Here, MFU‐4l serves as a reference compound to evaluate the origin of unique and specific gas‐sorption properties of MFU‐4, reported previously. The latter framework features narrow‐sized pores of 2.5 Å that allow passage of sufficiently small molecules only (such as hydrogen or water), whereas molecules with larger kinetic diameters (e.g., argon or nitrogen) are excluded from uptake. The crystal structure of MFU‐4l has been solved ab initio by direct methods from 3D electron‐diffraction data acquired from a single nanosized crystal through automated electron diffraction tomography (ADT) in combination with electron‐beam precession. Independently, it has been solved using powder X‐ray diffraction. Thermogravimetric analysis (TGA) and variable‐temperature X‐ray powder diffraction (XRPD) experiments carried out on MFU‐4l indicate that it is stable up to 500 °C (N2 atmosphere) and up to 350 °C in air. The framework adsorbs 4 wt % hydrogen at 20 bar and 77 K, which is twice the amount compared to MFU‐4. The isosteric heat of adsorption starts for low surface coverage at 5 kJ mol−1 and decreases to 3.5 kJ mol−1 at higher H2 uptake. In contrast, MFU‐4 possesses a nearly constant isosteric heat of adsorption of ca. 7 kJ mol−1 over a wide range of surface coverage. Moreover, MFU‐4 exhibits a H2 desorption maximum at 71 K, which is the highest temperature ever measured for hydrogen physisorbed on metal–organic frameworks (MOFs).
Polymer‐Supported Ionic‐Liquid‐Like Phases (SILLPs): Transferring Ionic Liquid Properties to Polymeric Matrices
Authors: Sans Victor , Karbass Naima , Burguete M. Isabel , Compañ Vicente , García‐Verdugo Eduardo , Luis Santiago V. , Pawlak Milena
Published: January 2011

The physico‐chemical properties of polymers with ionic‐liquid‐like moieties covalently bound to their surfaces (SILLPs) have been studied by thermal and spectroscopic techniques, as well as by direct impedance and dielectric measurements, and compared to those of the corresponding bulk ionic liquids. The effective transfer of properties from ionic liquids in solution to the supported species has thereby been demonstrated. The effects of the chemical nature of these tunable “solid solvents” on their macroscopic swelling and microwave heating, as well as the stabilities and activities of different catalytic moieties immobilized on the SILLPs, have been studied. Finally, the experimental effect observed in microwave heating can be directly correlated with the values of tan δ derived from dielectric measurements.
Copper‐Catalyzed Azide–Alkyne Cycloaddition in the Synthesis of Polydiacetylene: “Click Glycoliposome” as Biosensors for the Specific Detection of Lectins
Authors: Leal Manuel Pernía , Assali Mohyeddin , Fernández Inmaculada , Khiar Noureddine
Published: January 2011

Supramolecular self‐assembly of conjugated diacetylenic amphiphile‐tethered ligands photopolymerize to afford polydiacetylene (PDA) functional liposomes. Upon specific interaction with a variety of biological analytes in aqueous solution, PDA exhibits rapid colorimetric transitions. The PDA nanoassemblies, which are excellent membrane mimics, include an ene–yne polymeric reporter responsible for the chromatic transitions and the molecular recognition elements that are responsible for selective and specific binding to the biological target. A bottleneck in the fabrication of these colorimetric biosensors is the preparation of the diacetylenic monomer embedded with the recognition element of choice. In the present work, we make use of copper‐catalyzed azide–alkyne cycloaddition (CuAAC) as key step in the preparation of sugar‐coated liposome biosensors. The regioselective click ligation of the triacetylenic N‐(2‐propynyl)pentacosa‐10,12‐diynamide (NPPCDAM) with a variety of mannose‐ and lactose‐tethered azides afforded chemo‐ and regioselectively the corresponding 1,2,3‐triazole. The obtained diacetylenic monomers were incorporated efficiently into vesicles to afford functional mannose‐ and lactose‐coated glycoliposomes. The obtained PDA‐based click glycoliposomes have been characterized by using transmission electronic microscopy (TEM), dynamic light scattering (DLS), and UV/Vis spectroscopy. The efficiency of the reported approach was demonstrated by the rapid optimization of the hydrophilic spacer between the lipidic matrix and the mannose head group for the colorimetric detection of Concavalin A.
Bijvoet in Solution Reveals Unexpected Stereoselectivity in a Michael Addition
Authors: Sun Han , d'Auvergne Edward J. , Reinscheid Uwe M. , Carlos Dias Luiz , Kleber Z. Andrade Carlos , Oliveira Rocha Rafael , Griesinger Christian
Published: January 2011

The absolute configuration of small crystallizable molecules can be determined with anomalous X‐ray diffraction as shown by Bijvoet in 1951. For the majority of compounds that can neither be crystallized nor easily be converted into crystallizable derivatives, stereocontrolled organic synthesis is still required to establish their absolute configuration. In this contribution, a new fundamental methodology for resolving the absolute configuration will be presented that does not require crystallization. With residual dipolar coupling enhanced NMR spectroscopy, ensembles of a limited number of structures are created reflecting the correct conformations and relative configuration. Subsequently, from these ensembles, optical rotation dispersion (ORD) spectra are predicted by DFT calculations and compared to experimental results. The combination of these two steps reveals the absolute configuration of a flexible molecule in solution, which is a big challenge to chiroptical methods and DFT in the absence of NMR spectroscopy. Here the absolute stereochemistry of the product of a new Michael addition, synthesized via a niobium(V) chiral enolate, will be elucidated by using the new methodology.
Scandium(III) Zeolites as New Heterogeneous Catalysts: [4+2]Cyclocondensation of in situ Generated Aryl Imines with Alkenes
Authors: Olmos Andrea , Sommer Jean , Pale Patrick
Published: January 2011

Scandium(III)‐exchanged zeolite was used as heterogeneous ligand‐free catalysts for the [4+2]cyclocondensation of amines and aldehydes with alkenes through the in situ formation of imines. Such catalysts offered a versatile, efficient, and highly regio‐ and stereoselective synthesis of tetrahydroquinoline derivatives. These catalysts exhibited a wide scope and compatibility with functional groups. They are very simple to use, easy to remove (by simple filtration), and they are recyclable (up to three times without loss of activity).
Theoretical Investigation of Carbon–Sulfur Triple Bonds
Authors: Denis Pablo A. , Iribarne Federico
Published: January 2011

By means of first principle calculations we have investigated a set of molecules that are presumed to contain carbon–sulfur triple bonds, namely HCSOH, H3SCH, cis‐FCSF, F3CCSF3, and F5SCSF3. For HCSOH, FCSF, and H3SCH we used the CCSD(T) methodology and the correlation‐consistent basis sets. On the other hand, F3CCSF3 and F5SCSF3 were studied at the B3LYP, M06‐2X, MP2, and G3 levels of theory. We found that none of these molecules display a carbon–sulfur adiabatic bond dissociation energy (ABDE) as strong as diatomic CS (170.5 kcal mol−1), or a diabatic bond dissociation energy (DBDE) larger than the one found in SCO (212.0 kcal mol−1), although the DBDE of FCSF comes quite close at 208.3 kcal mol−1. The CS ABDEs of F3CCSF3, F5SCSF3, and H3SCH are comparable to that of a single CS bond. In contrast with the experimental results, F3CCSF3 and F5SCSF3 are predicted to be linear with C3v and Cs symmetry, respectively, at the B3LYP/6‐311+G(3df,2p) level. MP2/6‐311+G(2df,2p) calculations support the C3v symmetry for F3CCSF3, despite F5SCSF3 not having a perfect linear structure; the CSC angle is 174.6°, which is nearly 20° larger than the experimental value. The analysis of the carbene structures of HCSOH and H3SCH revealed that they are not significant, because the triplet state is dissociative in these cases. However, for F3CCSF3 and F5SCSF3, the carbene triplet states lie 0.81 and 0.77 eV above the singlet state, respectively. In the same vein, our investigation supports the presence of a strong double bond for HCSOH. The conflicting evidence available for F3CCSF3 and F5SCSF3 makes it very difficult to determine the nature of the CS bonds. However, the bond dissociation energies and the singlet–triplet splittings clearly suggest that these compounds should be considered as masked sulfinylcarbenes. The analysis of the bond dissociation energies challenges the existence of a triple bond in these five molecules, but from a strictly thermodynamic standpoint, cis‐FCSF is found to be the candidate most likely to exhibit triple‐bond character.
Catalytic Asymmetric Amination of N‐Nonsubstituted α‐Alkoxycarbonyl Amides: Concise Enantioselective Synthesis of Mycestericin F and G
Authors: Berhal Farouk , Takechi Sho , Kumagai Naoya , Shibasaki Masakatsu
Published: January 2011

In an attempt to explore the synthetic utility of a ternary asymmetric catalyst comprising La(NO3)3⋅6H2O, amide‐based ligand (R)‐L1, and D‐valine tert‐butyl ester H‐D‐Val‐OtBu, we investigated a catalytic, asymmetric amination of functionalized N‐nonsubstituted α‐alkoxycarbonyl amides using di‐tert‐butyl azodicarboxylate as an electrophilic aminating reagent. A highly functionalized, cyclic N‐nonsubstituted α‐alkoxycarbonyl amide delivered the desired amination product in up to 96 % enantiometric excess, with the requisite functionalities of the polar heads of sphingosines with the appropriate stereochemical arrangement. The rapid asymmetric assembly of these functional groups allowed a concise enantioselective synthetic route to sphingosines to be established with a broad flexibility towards derivative synthesis. These studies have culminated in an efficient catalytic enantioselective total synthesis of immunosuppressive fungal metabolites mycestericin F (3 a) and G (3 b).
Allosteric Inhibitor Development Targeting HIV‐1 Integrase
Authors: Al‐Mawsawi Laith Q. , Neamati Nouri
Published: January 2011

HIV‐1 integrase (IN) is one of three essential enzymes for viral replication, and is a focus of ardent antiretroviral drug discovery and development efforts. Diligent research has led to the development of the strand‐transfer‐specific chemical class of IN inhibitors, with two compounds from this group, raltegravir and elvitegravir, advancing the farthest in the US Food and Drug Administration (FDA) approval process for any IN inhibitor discovered thus far. Raltegravir, developed by Merck & Co., has been approved by the FDA for HIV‐1 therapy, whereas elvitegravir, developed by Gilead Sciences and Japan Tobacco, has reached phase III clinical trials. Although this is an undoubted success for the HIV‐1 IN drug discovery field, the emergence of HIV‐1 IN strand‐transfer‐specific drug‐resistant viral strains upon clinical use of these compounds is expected. Furthermore, the problem of strand‐transfer‐specific IN drug resistance will be exacerbated by the development of cross‐resistant viral strains due to an overlapping binding orientation at the IN active site and an equivalent inhibitory mechanism for the two compounds. This inevitability will result in no available IN‐targeted therapeutic options for HIV‐1 treatment‐experienced patients. The development of allosterically targeted IN inhibitors presents an extremely advantageous approach for the discovery of compounds effective against IN strand‐transfer drug‐resistant viral strains, and would likely show synergy with all available FDA‐approved antiretroviral HIV‐1 therapeutics, including the IN strand‐transfer‐specific compounds. Herein we review the concept of allosteric IN inhibition, and the small molecules that have been investigated to bind non‐active‐site regions to inhibit IN function.
Glomerular nucleus of the weakly electric fish, Gymnotus sp.: Cytoarchitecture, histochemistry, and fiber connections—Insights from neuroanatomy to evolution and behavior
Authors: Giassi Ana Catarina Casari , Maler Leonard , Moreira Jorge E. , Hoffmann Anette
Published: January 2011

The present study provides a detailed description of morphological and hodological aspects of the glomerular nucleus in the weakly electric fish Gymnotus sp., and explores the evolutionary and functional implications flowing from this analysis. The glomerular nucleus of Gymnotus shows numerous morphological similarities with the glomerular nucleus of percomorph fish, although cytoarchitectonically simpler. In addition, congruence of the histochemical acetylcholinesterase (AChE) distribution with cytoarchitectonic data suggests that the glomerular nucleus, together with the ventromedial cell group of the medial subdivision of the preglomerular complex (PGm‐vmc) rostrally, and the subglomerular nucleus (as identified by Maler et al. [1991] J Chem Neuroanat 4:1–38) caudally, may form a distinct longitudinally organized glomerular complex. Our results show that an important source of sensory afferents to the glomerular nucleus originates in the pretectal and electrosensorius nuclei. The glomerular nucleus in turn projects to the hypothalamus (inferior lobe and anterior hypothalamus), to the anterior tuberal nucleus, and to the medial region of the preglomerular nucleus (PGm). These data suggest that visual and electrosensory information reach the glomerular nucleus and are relayed to the hypothalamus and, via PGm, to the pallium. Such connections are similar to those of the glomerular nucleus in percomorphs and the posterior pretectal nucleus in osteoglossomorph, esocids, and salmonids, where they comprise one component of a visual processing pathway. In Gymnotiform fish, however, the pretectal region that projects to the glomerular nucleus is dominated by electrosensory input (visual input is minor), which is consistent with the dominant role of electroreception in these fish. J. Comp. Neurol. 519:1658–1676, 2011. © 2011 Wiley‐Liss, Inc.
Neuronal organization of a fast‐mediating cephalothoracic pathway for antennal‐tactile information in the cricket (Gryllus bimaculatus DeGeer)
Authors: Schöneich Stefan , Schildberger Klaus , Stevenson Paul A.
Published: January 2011

Crickets use their long antennae as tactile sensors. Confronted with obstacles, conspecifics, or predators, antennal contacts trigger short‐latency motor responses. To reveal the neuronal pathway underlying these antennal‐guided locomotory reactions we identified descending interneurons that rapidly transmit antennal‐tactile information from the head to the thorax in the cricket Gryllus bimaculatus. Antennae were stimulated with forces approximating those of naturally occurring antennal contacts. Responding interneurons were individually identified by intracellular axon recordings in the pro‐mesothoracic connective and subsequent tracer injection. Simultaneous with the intracellular recordings, the overall spike response in the neck connectives was recorded extracellularly to reveal the precise response‐timing of each individual neuron within the collective multiunit response. Here we describe four descending brain neurons and two with the soma in the subesophageal ganglion. All antennal‐touch elicited action potentials apparent in the neck connective recordings within 10 ms after antennal‐contact are generated by these six interneurons. Their dendrites ramify in primary antennal‐mechanosensory neuropils of the head ganglia. Each of them consistently generated action potentials in response to antennal touching and three of them responded also to different visual stimulation (light‐off, movement). Their descending axons conduct action potentials with 3–5 m/s to the thoracic ganglia where they send off side branches in dorsal neuropils. Their physiological and anatomical properties qualify them as descending giant fibers in the cricket and suggest an involvement in evoking fast locomotory reactions. They form a fast‐mediating cephalo‐thoracic pathway for antennal‐tactile information, whereas all other antennal‐tactile interneurons had response latencies exceeding 40 ms. J. Comp. Neurol. 519:1677–1690, 2011. © 2011 Wiley‐Liss, Inc.