Search

We demonstrate a technique for measuring x-ray (or neutron) scattering with the momentum transfer oriented in the plane of a membrane, for the purpose of studying the lateral organization of proteins and peptides. As an example, the controversial question of whether gramicidin forms aggregates in membrane was investigated. We measured dilauroylphosphatidylcholine (DLPC) bilayers containing gramicidin in the molar ratio of 10:1. Very clear scattering curves reflecting gramicidin channel-channel correlation were obtained. Analysis of the data shows that the channels were randomly distributed in the membrane. We suggest that oriented proteins may provide substantial x-ray contrast against the lipid background without requiring heavy-atom labeling. This should open up many possible new experiments.

A gradient nanograined (GNG) surface layer was formed on a martensitic stainless steel bar sample by means of the surface mechanical grinding treatment (SMGT). The average grain size is ~25 nm on the topmost surface layer and increases gradually with increasing depth. The torsion fatigue strength is elevated by 38 with the GNG surface layer compared with the original material. An additional 8 increment in fatigue strength is achieved after a post-annealing treatment of the SMGT sample. By analysing the microstructure, hardness, surface roughness and residual stress distribution in the SMGT samples, we believe that the enhanced fatigue resistances originate from the GNG structure with a hard surface layer and a high structural homogeneity.

Highly efficient InGaN-base light emitting diodes are crucial for next generation solid state lighting. However, drawbacks in substrate materials such as lattice and thermal expansion coefficient mismatches hold back the lamination efficiency improvement. In the past, patterned sapphire sustrate (PSS) has been proven to be effect to enhance the LED's performance. In this work, we reviewed several promising nano-scale technologies which successfully increase the output of LED through better material quality and light extraction. First, we presented a study of high-performance blue emission GaN LEDs using GaN nanopillars (NPs). It exhibits smaller blue shift in electroluminescent peak wavelength and great enhancement of the light output (70% at 20 mA) compared with the conventional LEDs. Secondly, GaN based LEDs with nano-hole patterned sapphire (NHPSS) by nano-imprint lithography are fabricated structure grown on sapphire substrate. At an injection current of 20mA, the LED with NHPSS increased the light output power of LEDs by 1.33 times, and the wall-plug efficiency is 30% higher at 20mA indicating that it had larger light extraction efficiency (LEE). Finally, we fabricated the high performance electrical pumping GaN-based semipolar {10-11} nano-pyramid LEDs on c-plane sapphire substrate by selective area epitaxy (SAE). The emission wavelength only blue-shifted about 5nm as we increased the forward current from 40 to 200mA, and the quantum confine stark effect (QCSE) had been remarkably suppressed on semipolar surface at long emission wavelength region. These results manifest the promising role of novel nanotechnology in the future III-nitride light emitters.

The recent discovery of a distorted hexagonal phase in 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine/1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPE/DOPC) mixtures raised the intriguing question as to whether lipid mixtures demix in a bent monolayer. We performed neutron diffraction on a mixture of headgroup deuterated DOPC-d13 and nondeuterated DOPE to study the lipid distribution in the distorted hexagonal phase. The 1:1 lipid mixture in full hydration and 25 °C was in a homogeneous lamellar phase. Upon dehydration the mixture transformed to a rhombohedral phase, then to a distorted inverted hexagonal phase, and finally to a regular inverted hexagonal phase. In the distorted hexagonal phase, the diffraction pattern showed a two-dimensional monoclinic lattice with two reciprocal vectors of equal length (1.5 nm^-1) forming an angle 53° between them. Diffraction intensities measured while varying the D2O/H2O ratio in the humidity was used to solve the phase problem. The neutron scattering length density distribution of the distorted hexagonal phase was constructed. The constant density contours are approximately elliptical. The difference in the eccentricities of the contours between the water and lipid distributions indicates that the DOPE/DOPC ratio is not uniform around the elliptical lipid tube in the unit cell. DOPE is preferentially distributed at the vertex regions where the curvature is the highest. Thus for the first time it is shown that when a monolayer of a homogeneous lipid mixture is bent, the lipid components are partially demixed in reaching the free energy minimum.

A neutron diffraction method applicable to nonlamellar phases of substrate-supported lipid membranes is described and validated. When prepared on a flat substrate, the resulting nonlamellar phases have layered symmetry which provides some advantages over powder diffraction for detailed structure determination. This approach recently led to the detection of a rhombohedral phase and a distorted hexagonal phase of lipids. Here the determination of intensity and phase information for such phases is demonstrated by application to the hexagonal phase of diphytanoyl phosphatidylcholine (DPhPC). The hexagonal symmetry is used to verify the data reduction procedure for the intensities of the diffraction peaks. Diffraction intensities measured while varying the D2O/H2O ratio in the relative humidity was used to solve the phase problem. The neutron scattering length density distribution of the hexagonal phase was constructed and analyzed to elucidate the packing of the lipid molecules. The structure of DPhPC in the hexagonal phase is of interest in connection with its stalk structure in the rhombohedral phase. We also found that the incorporation of tetradecane into the DPhPC hexagonal phase is limited, similar to the case for dioleoyl phosphatidylethanolamine.

Rigid-rod polyesters with flexible side chains denoted as B-Cn form two types of layered crystals and two types of layered mesophases. These layered phases are characterized by a layered structure, in which the aromatic main chains are paced into a layer with the side chains occupying the space between the layers. The detailed aggregated structures for these two crystalline phases were studied by fluorescence spectroscopy, from which it was found that the ground-state charge-transfer complexes are formed between the biphenyl and pyromellitic moieties in the adjacent main chains and that these two moieties have an alternating lateral alignment inside a layer. Two layered crystals, K1 and K2, show charge-transfer fluorescence (475 and 505 nm) and its excitation spectra (400 and 425 nm) in different wavelengths, respectively. This difference in wavelengths is related to the difference in lateral packing distances (4.6 Å for K1 and 3.45 Å for K2 crystals) and suggested to be due to the distance between the electron-donating and -accepting units in the adjacent chains. In the isotropic phase, the charge-transfer bands were also observed. This result means that the isotropic state in this polymeric system can be defined by the state that a layered segregation is maintained, but the molecular ordering and the interlayer correlation are lost. It is well-known that the driving force of the adoption for layered structures is a segregation of aliphatic and aromatic domains. We have demonstrated here, moreover, that a charge-transfer interaction between the electron-donating and -accepting units in the neighboring main chains contributes to the organization of phase structures and spatial arrangements.

A fully conjugated blood vessel network model (FCBVNM) for calculating tissue temperatures has been developed, tested, and studied. This type of model represents a more fundamental approach to modeling temperatures in tissues than do the generally used approximate equations such as the Pennes’ BHTE or effective thermal conductivity equations. As such, this type of model can be used to study many important questions at a more basic level. For example, in the particular hyperthermia application studied herein, a simple vessel network model predicts that the role of counter current veins is minimal and that their presence does not significantly affect the tissue temperature profiles: the arteries, however, removed a significant fraction of the power deposited in the tissue. These more fundamental models can also be used to check the validity of approximate equations. For example, using the present simple model, when the temperatures calculated by the FCBVNM are used for comparing predictions from two approximation equations (a simple effective thermal conductivity and a simple Pennes’ bio-heat transfer equation formulation of the same problem) it is found that the Pennes’ equation better approximates the FCBVNM temperatures than does the keff model. These results also show that the “perfusion” value (W˙) in the Pennes’ BHTE is not necessarily equal to the “true” tissue perfusion (P˙) as calculated from mass flow rate considerations, but can be greater than, equal to, or less than that value depending on (1) how many vessel levels are modeled by the BHTE, and (2) the “true” tissue perfusion magnitude. This study uses a simple, generic vessel network model to demonstrate the potential usefulness of such fully conjugated vessel network models, and the associated need for developing and applying more complicated and realistic vascular network models. As more realistic vascular models (vessel sizes, orientations, and flow rates) are developed, the predictions of the fully conjugated models should more closely model and approach the true tissue temperature distributions, thus making these fully conjugated models more accurate and valuable tools for studying tissue heat transfer processes.

A maize (Zea mays L.) cDNA clone (pZMB2) encoding beta-amylase was isolated from a cDNA library prepared from the aleurone RNA of germinating kernels. The cDNA encodes a predicted product of 488 amino acids with significant similarity to known beta-amylases from barley (Hordeum vulgare), rye (Secale cereale), and rice (Oryza sativa). Glycine-rich repeats found in the carboxyl terminus of the endosperm-specific beta-amylase of barley and rye are absent from the maize gene product. The N-terminal sequence of the first 20 amino acids of a beta-amylase peptide derived from purified protein is identical to the 5th through 24th amino acids of the predicted cDNA product, indicating the absence of a conventional signal peptide in the maize protein. Recombinant inbred mapping data indicate that the cDNA clone is single-copy gene that maps to chromosome 7L at position 83 centimorgans. Northern blot analysis and in vitro translation-immunoprecipitation data indicate that the maize beta-amylase is synthesized de novo in the aleurone cells but not in the scutellum during seed germination.

The propeptides of bacterial subtilisin BPN' and Carlsberg were synthesized to investigate their inhibitory function on the enzymes. Kinetically, pro-BPN' inhibits the proteolytic activities of subtilisin BPN' and Carlsberg separately in a slow binding mode. Pro-Carlsberg behaves as a typical rapid equilibrium competitive inhibitor for these two proteases. Functionally, pro-Carlsberg inhibits the subtilisins with moderate selectivity. the inhibition constant Ki of pro-BPN' to subtilisin BPN' is 5.0 nM, and 6.1 nM to subtilisin Carlsberg. The on-rate of pro-BPN' to subtilisin BPN' is 5.8x105 M-1s-1, and the off-rate 2.9x10-3 s-1. Similarly, the on-rate of pro-BPN' to subtilisin Carlsberg is 2.2x105 M-1s-1, and the off-rate 1.3x10-3 s-1. On the other hand, the Ki of pro-Carlsberg to subtilisin BPN' gives 1.2x102 nM, and 88 nM to subtilisin Carlsberg. Based on the key features of the interactions between pro-BPN' and subtilisin from X-ray crystallographic results (Gallagher et al., 1995), the correlation between the sequence of subtilisin propeptides and their inhibition abilities on the proteases are compared and discussed.Key words: propeptide/serine protease/slow binding/subtilisin BPN'/subtilisin Carlsberg.

In a numerical model of the directional solidification of a binary alloy, unreasonable results and/or oscillatory values of the concentration can occur when simulations of solidification scenarios with large thermal gradients approaching plane front conditions are attempted.

By applying fluorescence together with DSC and WAXD, structure analysis for a thermotropic liquid-crystalline (LC) polyester (PB-10), prepared from 4,4‘-dihydroxybiphenyl and sebacic acid, containing 10 methylene units, was carried out. The PB-10 shows two enantiotropic transitions:  One is the crystal−smectic H transition at 207 °C and the other the smectic H−isotropic phase transition at 257 °C. By measuring fluorescence spectra at 25−283 °C as well as those of diacetoxybiphenyl and biphenyl as model compounds, a high excitation wavelength dependence of various intermolecular ground-state complexes was found to depend on different degrees of overlap between mesogenic biphenyl moieties. Fluorescence spectra can be divided into three groups according to excitation wavelength:  monomer fluorescence of biphenyl group excited at 260−300 nm (emission peak at 343 nm), fluorescence from intermolecular ground-state complexes excited at 320−360 nm, and fluorescence excited at 380−400 nm. The fluorescence peak wavelength excited at 320 nm shifts from 365 to 429 nm during heating. This is due to the change of molecular interactions between mesogenic moieties from the interaction between two fully overlapping biphenyl groups to that between a biphenyl and an ester moiety. Temperature dependence of the fluorescence peak wavelength excited at 320 nm and Arrhenius-type plots of fluorescence intensity excited at various wavelengths show a common break at 175 °C, a temperature a little lower than the crystal−smectic H transition temperature. This suggests that the phase transition starts initially from the local change in microstructure (intermolecular interaction between mesogenic moieties) and then extends to a change in macrostructure. Fluorescence is an effective tool for providing molecular level information on LC polymers.

A fully conjugated blood vessel network model (FCBVNM) for calculating tissue temperatures has been developed, tested, and studied. This type of model represents a more fundamental approach to modeling temperatures in tissues than do the generally used approximate equations such as the Pennes’ BHTE or effective thermal conductivity equations. As such, this type of model can be used to study many important questions at a more basic level. For example, in the particular hyperthermia application studied herein, a simple vessel network model predicts that the role of counter current veins is minimal and that their presence does not significantly affect the tissue temperature profiles: the arteries, however, removed a significant fraction of the power deposited in the tissue. These more fundamental models can also be used to check the validity of approximate equations. For example, using the present simple model, when the temperatures calculated by the FCBVNM are used for comparing predictions from two approximation equations (a simple effective thermal conductivity and a simple Pennes’ bio-heat transfer equation formulation of the same problem) it is found that the Pennes’ equation better approximates the FCBVNM temperatures than does the keff model. These results also show that the “perfusion” value (W˙) in the Pennes’ BHTE is not necessarily equal to the “true” tissue perfusion (P˙) as calculated from mass flow rate considerations, but can be greater than, equal to, or less than that value depending on (1) how many vessel levels are modeled by the BHTE, and (2) the “true” tissue perfusion magnitude. This study uses a simple, generic vessel network model to demonstrate the potential usefulness of such fully conjugated vessel network models, and the associated need for developing and applying more complicated and realistic vascular network models. As more realistic vascular models (vessel sizes, orientations, and flow rates) are developed, the predictions of the fully conjugated models should more closely model and approach the true tissue temperature distributions, thus making these fully conjugated models more accurate and valuable tools for studying tissue heat transfer processes.

The heat transfer within a perfused tissue in the presence of a vessel is considered. The bio-heat transfer equation is used for the perfused tissue and a lumped capacitance analysis is used for the convection in the vessel with a constant Nusselt number. Analytical solutions are obtained for two cases: (i) the arterial temperature of the perfused blood in the bio-heat transfer equation is equal to the axially varying mixed mean temperature of the blood in the vessel and, (ii) that arterial temperature is assumed to be constant. Dimensionless equilibrium length and temperature expressions are obtained and presented.

The heat transfer within a perfused tissue in the presence of a vessel is considered. The bio-heat transfer equation is used for the perfused tissue and a lumped capacitance analysis is used for the convection in the vessel with a constant Nusselt number. Analytical solutions are obtained for two cases: (i) the arterial temperature of the perfused blood in the bio-heat transfer equation is equal to the axially varying mixed mean temperature of the blood in the vessel and, (ii) that arterial temperature is assumed to be constant. Dimensionless equilibrium length and temperature expressions are obtained and presented.

Enhancement of light output intensity for GaN-based vertical light-emitting diodes (LEDs), combining wafer bonding and the laser lift-off (LLO) process, employing an omnidirectional extraction surface with synthesized single-crystal ZnO nanorod arrays in aqueous solution at room temperature is presented. The light output intensity and wall-plug efficiency of the GaN-based LLO vertical LED with the omnidirectional extraction surface by ZnO nanorod arrays shows 38.9 and 41.2%increases, respectively, at 200 mA current injections compared to that of a vertical LED without ZnO nanorod arrays. The ZnO nanorod arrays not only support a current spreading layer but enhance the probability of photon escape through the omnidirectional extraction surface.

The light extraction enhancement of GaN-based flip-chip indium-tin oxide light-emitting diodes (FC ITO LEDs) with an inclined sidewall coated with TiO2∕SiO2omnidirectional reflectors (ODRs) is presented. At a driving current of 350mAand a chip size of 1×1mm, the light output power and the light extraction enhancement of the FC ITO LEDs coated TiO2∕SiO2ODRs with inclined sidewall reached 183mWand 15% when compared with the results from the same device, FC ITO LEDs coated TiO2∕SiO2ODRs with vertical sidewall. Furthermore, by examining the radiation patterns of the FC ITO LEDs, the increased optical power within 150° cone contributed to the stronger enhancement around the vertical direction of an inclined sidewall ODR within blue regime. Our work offers promising potential for enhancing output powers of commercial light-emitting devices.

In the first part of this paper, we present a LED structure adopting double diffused-surfaces on-top transmitted diffuse surface and another diffuse omnidirectional reflector surface on the bottom of LED chip. According to this design, guided light scattered by bottom diffuse omnidirectional reflectors can be again scattered toward to angles inside the escape cone by top diffuse transmittance surfaces. High light external efficiency (~ 40%) was achieved on this novel structure. This high efficiency could be attributed to the strong scattering efficiency of using double diffuse surfaces, further reducing trapping of light within LED chips. In the second part, we present n-side-up AlGaInP-based LEDs with a triangle-like surface morphology using the adhesive layer bonding technique, followed by wet etching to roughen the surface. The novel AlGaInP LED design could not only reduce internal reflection between rear mirror systems and the semiconductor/air interface, but also to effectively scatter light outside LED devices.