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Superconducting MgB2/Ta tapes with a critical temperature of 34 K have been prepared successfully by ex situ annealing of electrophoresis-grown boron in the presence of Mg vapour at 920 °C. Scanning electron microscopy was used to examine the surface morphology of the MgB2/Ta tapes, and well-formed MgB2 crystals with sizes up to 2 μm were observed. The x-ray diffraction patterns showed randomly orientated growth of MgB2 phase in the tapes. Estimates using hysteresis loops and the Bean model give a value of 6.8 × 105 A cm−2 for the critical current density.

MgB2 superconducting thick films of about 40 μm were fabricated successfully by a simple and low-cost approach. Boron films were prepared on Ag/Al2O3 substrates using the electrophoresis technique followed by a post-annealing process with excessive magnesium. Resistance measurements of the MgB2 thick films show Tcon of 39 K and ΔTc of 0.6 K. The X-ray diffraction analysis reveals that most part of the films consist of c-oriented crystalline MgB2. The images of surface morphology and cross-section profiles by scanning electron microscopy show well structured grain boundary MgB2 films and a well-defined compact layer.

Rapidly expanding research on non-soluble and non-crystalline chemical and biological materials necessitates sophisticated techniques to image these materials at atomic-level resolution. Although their study poses a formidable challenge, solid-state NMR is a powerful tool that has demonstrated application to the investigation of their molecular architecture and functioning. In particular, 2D separated-local-field (SLF) spectroscopy is increasingly applied to obtain high-resolution molecular images of these materials. However, despite the common use of SLF experiments in the structural studies of a variety of aligned molecules, the lack of a resonance assignment approach has been a major disadvantage. As a result, solid-state NMR studies have mostly been limited to aligned systems that are labeled with an isotope at a single site. Here, we demonstrate an approach for resonance assignment through a controlled reintroduction of proton spin diffusion in the 2D proton-evolved-local-field (PELF) pulse sequence. Experimental results and simulations suggest that the use of spin diffusion also enables the measurement of long-range heteronuclear dipolar couplings that can be used as additional constraints in the structural and dynamical studies of aligned molecules. The new method is used to determine the de novo atomic-level resolution structure of a liquid crystalline material, N-(4-methoxybenzylidene)-4-butylaniline, and its use on magnetically-aligned bicelles is also demonstrated. We expect this technique to be also valuable in the structural studies of functional molecules like columnar liquid crystals and other biomaterials.

Superconducting MgB2 thin films were fabricated on Al2O3(0001) and MgO(100) substrates by a two-step method. Boron thin films were deposited by pulsed laser deposition followed by an ex-situ annealing process. Resistance measurements of the deposited MgB2 films show a Tc of 38.6 K for MgB2/Al2O3 and 38.1 K for MgB2/MgO. Atomic force microscopy, scanning electron microscopy and x-ray diffraction were used to study the properties of the films. The results indicate that the MgB2/Al2O3 films consist of well-crystallized grains with a highly c-axis-oriented structure while the MgB2/MgO films have a dense uniform appearance with an unfixed orientation.

A low absorption in the gastrointestinal tract of hydrophobic pharmaceutical compounds in use today considerably limits their bioavailability, and therefore they are taken in large doses in order to reach the therapeutic plasma concentration, which inevitably results in undesired side effects. In this study, we demonstrate a new nanoparticle approach to overcome this problem, and our experimental results show that this approach has a high efficiency of drug loading and is easily adaptable to industrial scale. Characterization of nanoparticles containing a cholesterol-lowering hydrophobic drug, probucol, using a variety of biophysical techniques revealed higher homogeneity of these particles compared to those prepared using other approaches. Intermolecular interactions of these nanoparticles are probed at high resolution by magic angle spinning solid-state NMR experiments.

Understanding the structure and structural changes of bone, a highly heterogeneous material with a complex hierarchical architecture, continues to be a significant challenge even for high-resolution solid-state NMR spectroscopy. While it is known that dehydration affects mechanical properties of bone by decreasing its strength and toughness, the underlying structural mechanism at the atomic level is unknown. Solid-state NMR spectroscopy, controlled dehydration, and H/D exchange were used for the first time to reveal the structural changes of an intact piece of bovine cortical bone. (1)H spectra were used to monitor the dehydration of the bone inside the rotor, and high-resolution (13)C chemical shift spectra obtained under magic-angle spinning were used evaluate the dehydration-induced conformational changes in the bone. The experiments revealed the slow denaturation of collagen due to dehydration while the trans-Xaa-Pro conformation in collagen remained unchanged. Our results suggest that glycosaminoglycans in the collagen fiber and mineral interface may chelate with a Ca(2+) ion present on the surface of the mineral through sulfate or carboxylate groups. These results provide insights into the role of water molecules in the bone structure and shed light on the relationship between the structure and mechanics of bone.

Islet amyloid polypeptide (IAPP or amylin) is a 37-residue peptide hormone associated with glucose metabolism that is cosecreted with insulin by beta-cells in the pancreas. Since human IAPP is a highly amyloidogenic peptide, it has been suggested that the formation of IAPP amyloid fibers is responsible for the death of beta-cells during the early stages of type II diabetes. It has been hypothesized that transient membrane-bound alpha-helical structures of human IAPP are precursors to the formation of these amyloid deposits. On the other hand, rat IAPP forms transient alpha-helical structures but does not progress further to form amyloid fibrils. To understand the nature of this intermediate state and the difference in toxicity between the rat and human versions of IAPP, we have solved the high-resolution structure of rat IAPP in the membrane-mimicking detergent micelles composed of dodecylphosphocholine. The structure is characterized by a helical region spanning the residues A5 to S23 and a disordered C-terminus. A distortion in the helix is seen at R18 and S19 that may be involved in receptor binding. Paramagnetic quenching NMR experiments indicate that rat IAPP is bound on the surface of the micelle, in agreement with other nontoxic forms of IAPP. A comparison to the detergent-bound structures of other IAPP variants indicates that the N-terminal region may play a crucial role in the self-association and toxicity of IAPP by controlling access to the putative dimerization interface on the hydrophobic face of the amphipathic helix.

We report the use of quantum dots (Qdots) as strain gages in the study of bone biomechanics using solid state nuclear magnetic resonance (NMR) spectroscopy. We have developed solid state NMR sample cells for investigation of deformations of bone tissue components at loads up to several Mega Pascal. The size constraints of the NMR instrumentation limit the bone specimen diameter and length to be no greater than 2-3 mm and 30 mm respectively. Further, magic angle spinning (MAS) solid state NMR experiments require the use of non-metallic apparatus that can be rotated at kilohertz rates. These experimental constraints preclude the use of standard biomechanical measurement systems. In this paper we explore the use of quantum dot center of gravity measurement as a strain gage technology consistent with the constraints of solid state NMR. We use Qdots that bind calcium (625 nm emission) and collagen (705 nm emission) for measurement of strain in these components. Compressive loads are applied to a specimen in a cell through a fine pitch screw turned with a mini-torque wrench. Displacement is measured as changes in the positions of arrays of quantum dots on the surface of a specimen. Arrays are created by spotting the specimen with dilute suspensions of Qdots. Mineral labeling is achieved with 705 nm carboxylated dots and matrix labeling with 565 nm quantum dots conjugated to collagen I antibodies. After each load increment the new positions of the quantum dots are measured by fluorescence microscopy. Changes in Qdot center of gravity as a function of applied load can be measured with submicron accuracy.

The second transmembrane (TM2) domain of GABA(A) receptor forms the inner-lining surface of chloride ion-channel and plays important roles in the function of the receptor protein. In this study, we report the first structure of TM2 in lipid bilayers determined using solid-state NMR and MD simulations. The interatomic (13)C-(15)N distances measured from REDOR magic angle spinning experiments on multilamellar vesicles, containing a TM2 peptide site specifically labeled with (13)C' and (15)N isotopes, were used to determine the secondary structure of the peptide. The (15)N chemical shift and (1)H-(15)N dipolar coupling parameters measured from PISEMA experiments on mechanically aligned phospholipid bilayers, containing a TM2 peptide site specifically labeled with (15)N isotopes, under static conditions were used to determine the membrane orientation of the peptide. Our results reveal that the TM2 peptide forms an alpha helical conformation with a tilted transmembrane orientation, which is unstable as a monomer but stable as pentameric oligomers as indicated by MD simulations. Even though the peptide consists of a number of hydrophilic residues, the transmembrane folding of the peptide is stabilized by intermolecular hydrogen bondings between the side chains of Ser and Thr residues as revealed by MD simulations. The results also suggest that peptide-peptide interactions in the tilted transmembrane orientation overcome the hydrophobic mismatch between the peptide and bilayer thickness.

A new type of spin diffusion, cross-relaxation driven spin diffusion (CRDSD), is investigated using (15)N NMR on a N-acetyl-L-valyl-L-leucine (NAVL) single crystal under stationary condition. A two-dimensional (2D) pulse sequence that correlates the chemical shifts of (15)N nuclei, with a radio-frequency spin lock on the (15)N channel during the mixing time, is used to observe CRDSD. Experimental results obtained using CRDSD, rf-driven spin diffusion, and proton driven spin diffusion approaches on the NAVL single crystal are compared. Our experimental results suggest that the (15)N spin diffusion rate can be enhanced by about 1000 times using CRDSD than by the normal proton driven spin diffusion. Interestingly, the required spin-locking rf field strength for CRDSD is much lower than that used for the rf-driven spin diffusion experiments. The cross-peak patterns observed in 2D (15)N-(15)N correlation spectra using CRDSD and RFDSD are very different as they arise from different spin-spin interactions. A detailed theory describing CRDSD and RFDSD processes is also presented using a thermodynamic model. The speedy spin diffusion process rendered by the CRDSD approach will be useful to assign resonances from a uniformly (15)N or (13)C labeled proteins and peptides, particularly in aligned samples.

Nanoscale building blocks are individually exceptionally strong because they are close to ideal, defect-free materials. It is, however, difficult to retain the ideal properties in macroscale composites. Bottom-up assembly of a clay/polymer nanocomposite allowed for the preparation of a homogeneous, optically transparent material with planar orientation of the alumosilicate nanosheets. The stiffness and tensile strength of these multilayer composites are one order of magnitude greater than those of analogous nanocomposites at a processing temperature that is much lower than those of ceramic or polymer materials with similar characteristics. A high level of ordering of the nanoscale building blocks, combined with dense covalent and hydrogen bonding and stiffening of the polymer chains, leads to highly effective load transfer between nanosheets and the polymer.

The pathogenesis of normal pressure hydrocephalus (NPH) is not fully understood and the relationship between inflammatory reaction extension and the ventricular enlargement is unknown.

IntroductionThe pathogenesis and behavioral effects of normal pres-sure hydrocephalus (NPH) are not fully understood, andthe temporal relationship between radiological changesand neurological deterioration is unknown.MethodsBilateral subarachnoid injections of kaolin were adminis-tered in the cranial convexities of 20 adult rats. MRI wasobtained using a Bruker Biospec 11.7 T MRI scanner at14, 60, 90 and 120 days post kaolin injection. Locomotor,gait, and cognitive studies were performed independentlyevery 2 weeks by faculty blinded to the imaging results.Tests included open field test, gait analysis, rotarod andnovel object recognition. Logistic regression analysis wasperformed to assess association between ventricular sizeand clinical deterioration and rate of ventricular sizeenlargement and clinical deterioration.ResultsRadiological ventricular size showed progressive growthover time at all times (p 0.05), cognitive (p>0.05) or anxiety(p>0.05) deterioration. Locomotor deterioration wasassociated with ventricular size (p=0.014), speed of ven-tricular enlargement (p=0.015) and extension of injectedkaolin (p=0.04).ConclusionsKaolin injected in the subarachnoid space of adult ratscan produce slow onset communicating hydrocephalus.Initially the ventricular enlargement seen on images isasymptomatic. Ventricular enlargement does not corre-late with clinical impairment with exception of delayedlocomotor impairment.

Novel, symmetrical, bent-core mesogens, namely substituted 1,3-phenylenebis{4'-[(ethoxycarbonyl)oxy]-1,1'-biphenyl}-4-carboxylates, are prepared with carbonate groups at both ends of the molecules. The mesophase properties are investigated for different electron-donating and -withdrawing substituents connected to the central ring at different positions. These compounds exhibit nematic and/or smectic A intercalated (SmA(int)) mesophases. Electro-optical studies show a very significant electric-field-induced biaxiality that is fast (

Various two-dimensional (2D) NMR techniques are reported on a bent-core mesogen 4,6-dichloro-1,3-phenylenebis[4'-(9-decenyloxy)-1,1'-biphenyl] carboxylate in its nematic and solid phases in order to unambiguously assign its carbon-13 NMR spectrum. The (13)C chemical shifts from the molecular core were studied as a function of temperature to extract its molecular geometry and orientational order tensor. To this end, the chemical shift anisotropy tensors of some carbon sites were measured in the solid state of this mesogen using a recent method called the separation of undistorted powder patterns by effortless recoupling (SUPER). The average bending angle subtended by the two arms of the bent-core structure is determined to be 148.7 degrees. The C-H dipolar couplings obtained from the separated local field (SLF) experiment for the aromatic rings are used to find the local order parameter tensors.

In this paper, the difficulty in orienting the B(2) phase of the banana mesogen 1,3-Phenylene-bis 4-[4-(10-undecenyloxy)-benzoyloxy] benzoate (Pbis11BB) in a relatively high magnetic field is reported based on some observations using both (13)C and (2)H NMR. (2)H NMR spectra recorded for the two labeled isotopomers of Pbis11BB in the isotropic and B(2) phases are shown here. Preliminary results on the deuteron spin-spin relaxation (T(2)) data are reported at 61 MHz in order to underline the peculiar slow dynamics of banana-shaped liquid crystals (BLC), and these results are discussed in the framework of recent studies on similar BLC. The molecular structure and dynamics in the B(2) and crystalline phases are also studied by (13)C solid-state NMR techniques. The results also point to the slow dynamics in the B(2) phase of Pbis11BB. In particular, two-dimensional MAS exchange experiment has been performed to shed light on the molecular conformation structure of the five-ring banana core in the crystalline phase of Pbis11BB, and to compare with that of quantum mechanical calculations reported in the literature.

A deuterium two-dimensional exchange NMR technique is used to study the chiral smectic C (SmC*) and chiral subphases (SmC* Fi1 , SmC* Fi2 ) of a smectogen (s)-1-methylheptyl 4'-(4-n-decyloxy-benzoyloxy)-biphenyl-4-carboxylate (10B1M7). The aim is to demonstrate how this technique can be combined with sample rotation in the magnetic field to obtain the fast translational self-diffusion constant along the helical pitch in the SmC* phase and to shed light on the structure of helicoidal superlattice in the three-layer SmC* Fi1 and four-layer SmC* Fi2 phases. The cross-peak intensities in the 2D exchange spectrum are sensitive to the disposition of molecules in the three- and four-layer base unit. The results support the "asymmetric Clock model" as an appropriate description of the ferrielectric phases in this compound.

Carbon-13 NMR spectroscopy is used to probe the orientational ordering in the tilted chiral smectic phase of two partially deuterated liquid crystals. Quantitative analyses of the chemical shifts of the aromatic carbons in the smectic- and - phases enable us to obtain the location of the long molecular axis of the core and the off-diagonal order parameter of the molecular core in the smectic- phase. The advantage of knowing the ordering information of these molecules in their mesophases from deuteron studies is demonstrated in this work, as they can be used to guide the assignments. The temperature behaviors of the chemical shifts from the aromatic sites in the helical structure of the smectic- phase is caused by both an increase of the tilt angle and a change in the orientation of the principal frame that describes the molecular ordering.

A detailed 2H nuclear magnetic resonance (NMR) study at 61.4 MHz of two chiral smectic C phases of a smectogen 10B1M7, one ferroelectric (SmC*) and the other antiferroelectric (SmC), is reported. Simulation of angular-dependent spectral patterns and/or signal intensities of the methyl deuterons are shown to provide information on the synclinic or anticlinic ordering, as well as the jump diffusion rates at different temperatures in the SmC phase. The molecular self-diffusion constant is determined to be in the range of 0.2-1.2 x 10(-14) m2/s over the temperature range of the SmC phase. Molecular self-diffusion in the SmC* phase should be faster, but remains undetectable by the present approach. Furthermore, the phase biaxiality in these phases is found to be vanishingly small. The critical magnetic field for unwinding the helical structure of 10B1M7 is found to be relatively high.

The results of studying angular dependent spectral parameters in a magnetic field are reported in the chiral smectic C phases of a smectogen 1-methylheptyl -(4-n-decyloxybenzoyloxy)-biphenyl-4-carboxylate. Our data provide direct evidence of a phase transition between two ferrielectric phases in this compound, viz. three-layer (SmC*(FiI)) and four-layer (SmC*(FiII)) superlattices. Simulation of spectral patterns of the methyl (C10) deuterons obtained after an aligned sample is rotated by 90 degrees in the magnetic field rules out the "clock model" for the three-layer and four-layer structures in these ferriphases. Instead, our data obtained under a magnetic field (9.4 T) seem to favor an "asymmetric clock model" for the interlayer packing. Interlayer jump rate is also obtained from the simulation of angular dependent spectra in these ferrielectric phases, and compared with those in the antiferroelectric SmC*(A) phase.

A carbon-13 NMR study in a series of bent-core (banana-shaped) molecules is reported. In 1, 3- phenylene bis[4'-alkenyloxy biphenyl]-4-carboxylate derivatives the position of the chlorine substituent(s) connected to the central phenyl ring and/or the terminal chain length of the compounds were varied. By analyzing the observed chemical shift anisotropies, the order parameters S and bending angles in their nematic phase are compared. The biphenyl moiety on each arm of the molecular core is found to form a nonzero twist angle.

The orientational order and the molecular structure of the banana mesogen 4-chloro-1,3-phenylene bis{4,4‘-(11-undecenyloxy)benzoyloxy}benzoate have been studied in its nematic phase by means of 2H ...

A pair of spot-focusing horn lens antenna is the key component in a free-space measurement system. The electromagnetic constitutive parameters of a planar sample are determined using transmitted and reflected electromagnetic beams. These parameters are obtained from the measured scattering parameters by the microwave network analyzer, thickness of the sample, and wavelength of a focused beam on the sample. Free-space techniques introduced by most papers consider the focused wavelength as the free-space wavelength. But in fact, the incident wave projected by a lens into the sample approximates a Gaussian beam, thus, there has an elongation of the wavelength in the focused beam and this elongation should be taken into consideration in dielectric and magnetic measurement. In this paper, elongation of the wavelength has been analyzed and measured. Measurement results show that the focused wavelength in the vicinity of the focus has an elongation of 1%-5% relative to the free-space wavelength. Elongation's influence on the measurement result of the permittivity and permeability has been investigated. Numerical analyses show that the elongation of the focused wavelength can cause the increase of the measured value of the permeability relative to traditionally measured value, but for the permittivity, it is affected by several parameters and may increase or decrease relative to traditionally measured value.

Quantum-mechanical evolution of systems with periodic time-modulated Hamiltonians is often described by effective interactions. Such average Hamiltonians, calculated as few terms of an expansion in powers of the interaction, are sometimes difficult to relate to experimental observations. We propose a frequency-domain approach to this problem, which offers certain advantages and produces an approximate solution for the density matrix, better linked to measurable quantities. The formalism is suitable for calculating the intensities of narrowed spectral peaks. Fast magic-angle-spinning NMR spectra of solids are used to experimentally illustrate the method.

Using solid state NMR (SSNMR) we show that bone mineral and bone matrix both undergo measurable deformations in response to compressive loading. Using bovine cortical bone, load-induced changes in both protein conformation and mineral ion spacings are observed even under sub-physiological loads. Our finding that matrix distortion involves changes in the position of (proline) is not unexpected. Proline and hydroxyproline are the most abundant amino acids in X,Y positions of the repeat gly-X-Y unit of collagen. The local conformation is determined by enthalpic forces stabilizing hydroxyproline and hydrogen bonding stabilizing proline position. Mechanical forces would be expected to be greater, leading to some change in the local orientation. Substitution of another amino acid for glycine, as in most types of osteogenesis imperfecta and in other genetic defects, would have the effect of weakening the stabilizing forces on proline and hydroxyproline, thus allowing greater distortion of the collagen fibrils than would occur in normal bone. In turn, this weakness would contribute to the fragility of the tissue.

Biomineralization in nearly all vertebrates is a complex process controlled by interactions of minerals and organic matrix. Several Studies have demonstrated that the size of mineral can also affect collagen microarchitecture. Although bone structure has been extensively studied, the early stages of bone mineralization and matrix formation still remain unknown. Bone is a highly heterogeneous material with a complex hierarchical structure. High-resolution solid-state NMR can probe selected magnetic nuclei and get structure information at the atomic-level that are difficult to obtain by other methods. Using 31P and 13C solid state NMR, we investigated the mineral and matrix change as a function of age. Our results show that there is a large amount of monohydrogen phosphates at early stage of mineralization. The experimental results indicate that apatite content increase while monohydrogen phosphates, phosphates and phosphouslipid decrease as mice matured. Our findings confirmed that with the increase of mineralization, the stiffness of collagen increases due to the interaction between the collagen and mineral.