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At least 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Incorporation of Melittin Enhances Interfacial Fluidity of Bicontinuous Microemulsions

The effect of an antimicrobial peptide, melittin, on the long-range collective and local undulation motions of bicontinuous microemulsions (BμEs) was evaluated using dynamic light scattering (DLS) and neutron spin echo (NSE) spectroscopy. Small-angle neutron scattering (SANS) was also used to study the effect of melittin on the structure and the correlation length of BμEs. BμEs were isolated from Winsor-III systems formed by mixing aqueous melittin solutions containing sodium dodecyl sulfate with dodecane/1-pentanol mixtures at optimal salinity. An increase of melittin concentration linearly increased the diffusivity of the microemulsions (D DLS ) and decreased the bending rigidity (κ NSE ) up to an aqueous melittin concentration of 2 g/L, thus indicating an increase of interfacial fluidity. Further increase of melittin concentration above 2 g/L did not change D DLS and slightly increased κ NSE . The changes reflect differences of interaction between melittin and BμE surfactant monolayers at different melittin concentrations. At low concentrations, melittin is highly associated with the surfactant monolayers, likely ion-paired to the sulfate surfactant head groups and perhaps partially penetrating into the surfactant tail region. Above 2 g/L, an apparent saturation concentration, added melittin is less strongly associated with the monolayers. In contrast, the bare bending constant derived from SANS data (κ bare ) underwent only a minor decrease. Noting that κ bare reflects contributions from both the elasticity and saddle-splay moduli, this suggests that κ bare is not an effective indicator of dynamics for the BμEs investigated. Our study demonstrates that amphiphilic solubilizates can have a complex impact on dynamics of surfactant monolayers in microemulsions, with implications for transmembrane diffusion and the kinetics of release from the microemulsion phase, which are important characteristics for the use of BμEs as delivery vehicles and host systems for (bio)chemical reactions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Numerical models for the prediction of failure for multilayer fusion Al-alloy sheets

Initiation and propagation of cracks in monolithic and multi-layer aluminum alloys, called “Fusion”, is investigated. 2D plane strain finite element simulations are performed to model deformation due to bending and to predict failure. For this purpose, fracture strains are measured based on microscopic pictures of Nakajima specimens. In addition to, micro-structure of materials is taken into account by introducing a random grain distribution over the sheet thickness as well as a random distribution of the measured yield curve. It is shown that the performed experiments and the introduced FE-Model are appropriate methods to highlight the advantages of the Fusion material, especially for bending processes.

36 MATERIALS SCIENCE↗
DOE OSTI2013

The plane strain shear fracture of the advanced high strength steels

The “shear fracture” which occurs at the high-curvature die radii in the sheet metal forming has been reported to remarkably limit the application of the advanced high strength steels (AHSS) in the automobile industry. However, this unusual fracture behavior generally cannot be predicted by the traditional forming limit diagram (FLD). In this research, a new experimental system was developed in order to simulate the shear fracture, especially at the plane strain state which is the most common state in the auto-industry and difficult to achieve in the lab due to sample size. Furthermore, the system has the capability to operate in a strain rate range from quasi-static state to the industrial forming state. One kinds of AHSS, Quenching-Partitioning (QP) steels have been performed in this test and the results show that the limiting fracture strain is related to the bending ratio and strain rate. The experimental data support that deformation-induced heating is an important cause of “shear fracture” phenomena for AHSS: a deformation-induced quasi-heating caused by smaller bending ratio and high strain rate produce a smaller limiting plane strain and lead a “shear fracture” in the component.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Anisotropic surface phonon dispersion of the hydrogen-terminated Si(110)-(1×1) surface: One-dimensional phonons propagating along the glide planes

We have measured the surface phonon dispersion curves on the hydrogen-terminated Si(110)-(1×1) surface with the two-dimensional space group of p2mg along the two highly symmetric and rectangular directions of ΓX{sup ¯} and ΓX{sup ′¯} using high-resolution electron-energy-loss spectroscopy. All the essential energy-loss peaks on H:Si(110) were assigned to the vibrational phonon modes by using the selection rules of inelastic electron scattering including the glide-plane symmetry. Actually, the surface phonon modes of even-symmetry to the glide plane (along ΓX{sup ¯}) were observed in the first Brillouin zone, and those of odd-symmetry to the glide plane were in the second Brillouin zone. The detailed assignment was made by referring to theoretical phonon dispersion curves of Gräschus et al. [Phys. Rev. B 56, 6482 (1997)]. We found that the H–Si stretching and bending modes, which exhibit highly anisotropic dispersion, propagate along ΓX{sup ¯} direction as a one-dimensional phonon. Judging from the surface structure as well as our classical and quantum mechanical estimations, the H–Si stretching phonon propagates by a direct repulsive interaction between the nearest neighbor H atoms facing each other along ΓX{sup ¯}, whereas the H–Si bending phonon propagates by indirect interaction through the substrate Si atomic linkage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Development of soft X-ray polarized light beamline on Indus-2 synchrotron radiation source

This article describes the development of a soft x-ray beamline on a bending magnet source of Indus-2 storage ring (2.5 GeV) and some preliminary results of x-ray absorption spectroscopy (XAS) measurements using the same. The beamline layout is based on a spherical grating monochromator. The beamline is able to accept synchrotron radiation from the bending magnet port BL-1 of the Indus-2 ring with a wide solid angle. The large horizontal and vertical angular acceptance contributes to high photon flux and selective polarization respectively. The complete beamline is tested for ultrahigh vacuum (UHV) ∼ 10{sup −10} mbar. First absorption spectrum was obtained on HOPG graphite foil. Our performance test indicates that modest resolving power has been achieved with adequate photon flux to carry out various absorption experiments.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Design and development of liquid filled polymeric fibers with flexure rate viscoelastic properties

The design and development of a novel category of bi-component polymeric fibers, made of a polymeric sheath and a liquid core is described. To understand and to analyze the flow of molten polymer and liquid within a spin pack, we built a macroscale analogon where co-flow of polymer and liquid is investigated systematically. The macroscale analogon is composed of a glass cylinder with a finite length and a coaxial capillary. The inner fluid flows in the capillary and at its outlet meets the outer fluid flowing inside the glass cylinder. The fluids are pumped into the setup using pressurized bottles with controlled flow rates. A high-speed camera is placed in front of the glass cylinder to record the transient and the steady flow of the two phases and the morphology of their interface during co-flow. We systematically analyzed the combination of various fluids and different injection channel geometries, and used these findings to design a customized spin pack. Extrusion trials with molten polymers and specific liquids resulted in the production of liquid filled polymeric fibers (LFF) with different amounts of liquid from 3% to 33%vol. and diameters from 150μm to 1mm. Fiber morphology has been investigated with the help of optical microscopy and computer tomography, in order to analyze both surface and core morphology. Mechanical characterization of fibers has been carried out with special care to the damping capacity of such fibers using two different methods: two point bending tests to evaluate the energy dissipation of fibers upon bending at low frequency values (0.005-0.5Hz), and analysis of vibration reduction to determine the quality factor at the resonance frequency of the 1{sup st} and 3{sup rd} vibration mode.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Sandwich beam model for free vibration analysis of bilayer graphene nanoribbons with interlayer shear effect

In this study, sandwich beam model (SM) is proposed for free vibration analysis of bilayer graphene nanoribbons (BLGNRs) with interlayer shear effect. This model also takes into account the intralayer (in-plane) stretch of graphene nanoribbons. The molecular dynamics (MD) simulations using the software LAMMPS and Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential are done to validate the accuracy of the sandwich model results. The MD simulation results include the two first frequencies of cantilever BLGNRs with different lengths and two interlayer shear moduli, i.e., 0.25 and 4.6 GPa. These two interlayer shear moduli, 0.25 and 4.6 GPa, can be obtained by sliding a small flake of graphene on a large graphene substrate when the parameter of E-LJ term in AIREBO potential, epsilon-CC, is set to be 2.84 and 45.44 meV, respectively. The SM results for a wide range of bending rigidity values show that the proposed model, i.e., the SM, predicts much better than the previous beam model in which the intralayer stretch is ignored. In addition, it is observed that the model can properly predict the natural frequencies of BLGNRs for various values of the bending rigidity and the interlayer shear modulus.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet

We present the designs of probes for making critical current density (J{sub c}) measurements on anisotropic high-temperature superconducting tapes as a function of field, field orientation, temperature and strain in our 40 mm bore, split-pair 15 T horizontal magnet. Emphasis is placed on the design of three components: the vapour-cooled current leads, the variable temperature enclosure, and the springboard-shaped bending beam sample holder. The vapour-cooled brass critical-current leads used superconducting tapes and in operation ran hot with a duty cycle (D) of ∼0.2. This work provides formulae for optimising cryogenic consumption and calculating cryogenic boil-off, associated with current leads used to make J{sub c} measurements, made by uniformly ramping the current up to a maximum current (I{sub max}) and then reducing the current very quickly to zero. They include consideration of the effects of duty cycle, static helium boil-off from the magnet and Dewar (b{sup ′}), and the maximum safe temperature for the critical-current leads (T{sub max}). Our optimized critical-current leads have a boil-off that is about 30% less than leads optimized for magnet operation at the same maximum current. Numerical calculations show that the optimum cross-sectional area (A) for each current lead can be parameterized by LI{sub max}/A=[1.46D{sup −0.18}L{sup 0.4}(T{sub max}−300){sup 0.25D{sup −{sup 0{sup .{sup 0{sup 9}}}}}}+750(b{sup ′}/I{sub max})D{sup 10{sup −{sup 3I{sub m}{sub a}{sub x}−2.87b{sup ′}}}}]× 10{sup 6}A m{sup −1} where L is the current lead's length and the current lead is operated in liquid helium. An optimum A of 132 mm{sup 2} is obtained when I{sub max} = 1000 A, T{sub max} = 400 K, D = 0.2, b{sup ′} = 0.3 l h{sup −1} and L = 1.0 m. The optimized helium consumption was found to be 0.7 l h{sup −1}. When the static boil-off is small, optimized leads have a boil-off that can be roughly parameterized by: b/I{sub max } ≈ (1.35 × 10{sup −3})D{sup 0.41} l h{sup ‑1} A{sup −1}. A split-current-lead design is employed to minimize the rotation of the probes during the high current measurements in our high-field horizontal magnet. The variable-temperature system is based on the use of an inverted insulating cup that operates above 4.2 K in liquid helium and above 77.4 K in liquid nitrogen, with a stability of ±80 mK to ±150 mK. Uniaxial strains of −1.4% to 1.0% can be applied to the sample, with a total uncertainty of better than ±0.02%, using a modified bending beam apparatus which includes a copper beryllium springboard-shaped sample holder.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Band alignment of HfO{sub 2}/In{sub 0.18}Al{sub 0.82}N determined by angle-resolved x-ray photoelectron spectroscopy

The band-alignment of atomic layer deposited (ALD)-HfO{sub 2}/In{sub 0.18}Al{sub 0.82}N was studied by high resolution angle-resolved X-ray photoelectron spectroscopy measurements. The band bending near the HfO{sub 2}/In{sub 0.18}Al{sub 0.82}N interface was investigated, and the potential variation across the interface was taken into account in the band alignment calculation. It is observed that the binding energies for N 1s and Al 2p in In{sub 0.18}Al{sub 0.82}N decreases and the corresponding extracted valence band offsets increases with increasing θ (i.e., closer to the HfO{sub 2}/In{sub 0.18}Al{sub 0.82}N interface), as a result of an upward energy band bending towards the HfO{sub 2}/In{sub 0.18}Al{sub 0.82}N interface. The resultant valence band offset and the conduction band offset for the ALD-HfO{sub 2}/In{sub 0.18}Al{sub 0.82}N interface calculated was found to be 0.69 eV and 1.01 eV, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Inversion layer on the Ge(001) surface from the four-probe conductance measurements

We report four-probe conductance measurements with sub-micron resolution on atomically clean Ge(001) surfaces. A qualitative difference between n-type and p-type crystals is observed. The scaling behavior of the resistance on n-type samples indicates two-dimensional current flow, while for the p-type crystal a three-dimensional description is appropriate. We interpret this in terms of the formation of an inversion layer at the surface. This result points to the surface states, i.e., dangling bonds, as the driving force behind band bending in germanium. It also explains the intrinsic character of band bending in germanium.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Buckling of microtubules: An insight by molecular and continuum mechanics

The molecular structural mechanics method has been extended to investigate the buckling of microtubules (MTs) with various configurations. The results indicate that for relative short MTs the shear deformation effect, rather than the nonlocal effect, is mainly responsible for the limitation of their widely used Euler beam description and the observed length-dependence of their bending stiffness. In addition, the configuration effect of MTs is also studied and considered as an explanation for the large scattering of the critical buckling force and bending stiffness observed in existing experiments. This configuration effect is also found to mainly originate from the geometry of the MTs and is mainly determined by the protofilament number.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Modelling deformation and fracture in confectionery wafers

The aim of this research is to model the deformation and fracture behaviour of brittle wafers often used in chocolate confectionary products. Three point bending and compression experiments were performed on beam and circular disc samples respectively to determine the 'apparent' stress-strain curves in bending and compression. The deformation of the wafer for both these testing types was observed in-situ within an SEM. The wafer is modeled analytically and numerically as a composite material with a core which is more porous than the skins. X-ray tomography was used to generate a three dimensional volume of the wafer microstructure which was then meshed and used for quantitative analysis. A linear elastic material model, with a damage function and element deletion, was used and the XMT generated architecture was loaded in compression. The output from the FE simulations correlates closely to the load-deflection deformation observed experimentally.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Shear deformable deformation of carbon nanotubes based on a new analytical nonlocal Timoshenko beam nodel

According to Hamilton’s principle, a new mathematical model and analytical solutions for nonlocal Timoshenko beam model (ANT) is established based on nonlocal elastic continuum theory when shear deformation and nonlocal effect are considered. The new ANT equilibrium equations and boundary conditions are derived for bending analysis of carbon nanotubes (CNTs) with simply supported, clamped and cantilever. The ANT deflection solutions demonstrate that the CNT stiffness is enhanced by the presence of nonlocal stress effects. Furthermore, the new ANT model concluded verifiable bending behaviors for a cantilever CNT with point load at the free end, which depends on the strength of nonlocal stress. Therefore, this new model will gives a better prediction for mechanical behaviors of nanostructures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Identification of four rotamers of m-methoxystyrene by resonant two-photon ionization and mass analyzed threshold ionization spectroscopy

We report the vibronic and cation spectra of four rotamers of m-methoxystyrene, recorded by using the two-color resonant two-photon ionization and mass-analyzed threshold ionization techniques. The excitation energies of the S{sub 1}← S{sub 0} electronic transition are found to be 32 767, 32 907, 33 222, and 33 281 cm{sup −1}, and the corresponding adiabatic ionization energies are 65 391, 64 977, 65 114, and 64 525 cm{sup −1} for these isomeric species. Most of the observed active vibrations in the electronically excited S{sub 1} and cationic ground D{sub 0} states involve in-plane ring deformation and substituent-sensitive bending motions. It is found that the relative orientation of the methoxyl with respect to the vinyl group does not influence the vibrational frequencies of the ring-substituent bending modes. The two dimensional potential energy surface calculations support our experimental finding that the isomerization is restricted in the S{sub 1} and D{sub 0} states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Experimental studies in magnetically induced transverse force-frequency effect in thin quartz microresonators

In this work, the transverse force-frequency sensitivity of magnetostrictive Metglas{sup ®} (Fe{sub 85}B{sub 5}Si{sub 10}) thin film coated AT-cut thickness shear mode quartz thin plate microresonator (500 μm × 500 μm × 19 μm) is experimentally measured and modeled in Lagrangian formulation by coupling magnetostrictive deformation equations with the basic plate equations from the theory of small deformation. The quartz plate resonator is fabricated by micromachining techniques and released into fixed-free structure using focused ion beam milling. Application of a magnetic field results in the out-of-plane bending of the structure due to elastic coupling between the magnetostrictive Metglas{sup ®} and quartz resonator layers. As a result of the transverse loading and out-of-plane bending, the admittance characteristics of the resonator shifts, and these shifts are recorded in real time utilizing a network analyzer. The sensitivity is experimentally measured to be 162.3 mdeg/Oe for phase, corresponding to a frequency sensitivity of Δf/H = 11 Hz/Oe. The equivalent force-frequency sensitivity can then be calculated as 2.36 μN/Hz using the developed model. The coupled domain analysis fits well with the experimental data. Further reduction of quartz thickness and optimization of the thickness ratio of the magnetostrictive to quartz layers offers the possibility of exploiting the stress sensitivity of plate microresonators as sensitive magnetic field sensors capable of low nanoTesla to picoTesla level magnetic flux densities.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

A computer simulation approach to quantify the true area and true area compressibility modulus of biological membranes

We present a new computational approach to quantify the area per lipid and the area compressibility modulus of biological membranes. Our method relies on the analysis of the membrane fluctuations using our recently introduced coupled undulatory (CU) mode [Tarazona et al., J. Chem. Phys. 139, 094902 (2013)], which provides excellent estimates of the bending modulus of model membranes. Unlike the projected area, widely used in computer simulations of membranes, the CU area is thermodynamically consistent. This new area definition makes it possible to accurately estimate the area of the undulating bilayer, and the area per lipid, by excluding any contributions related to the phospholipid protrusions. We find that the area per phospholipid and the area compressibility modulus features a negligible dependence with system size, making possible their computation using truly small bilayers, involving a few hundred lipids. The area compressibility modulus obtained from the analysis of the CU area fluctuations is fully consistent with the Hooke’s law route. Unlike existing methods, our approach relies on a single simulation, and no a priori knowledge of the bending modulus is required. We illustrate our method by analyzing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayers using the coarse grained MARTINI force-field. The area per lipid and area compressibility modulus obtained with our method and the MARTINI forcefield are consistent with previous studies of these bilayers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Renovation of the fixing and loading factors of the beam by the spectral data of free flexural vibrations

In the current paper, the problem of bending vibrations of a beam in which the binding on the right end is unknown and not available for visual inspection is studied. The main objective is to study an inverse problem: find additional unknown boundary conditions by additional spectral data, i.e., the conditions of fixing the right end of the rod. In this work, unlike many other works, as such additional conditions we choose the first natural frequencies (eigenvalues) of two new problems corresponding to the problem of bending vibrations of a beam with loads of different weights at the central point.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Ion-coincidence momentum imaging of three-body Coulomb explosion of formaldehyde in ultrashort intense laser fields

Three-body Coulomb explosion of formaldehyde (H{sub 2}CO) in intense 7- and 35-fs laser fields (1.3 × 10{sup 15} W/cm{sup 2}) has been investigated by using ion-coincidence momentum imaging technique. Two types of explosion pathways from the triply charged state, H{sub 2}CO{sup 3+} → (i) H{sup +} + H{sup +} + CO{sup +} and (ii) H{sup +} + CH{sup +} + O{sup +}, have been identified. It is shown from the momentum correlation of the fragment ions of pathway (i), that the geometrical structure of the molecule is essentially frozen along the H-C-H bending coordinate for the 7-fs case. On the other hand, for a longer pulse duration (35 fs), structural deformation along the C-H stretching and H-C-H bending coordinates is identified, which is ascribed to the nuclear dynamics in the dication states populated within the laser pulse duration.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗