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1.
Jose G. Trujillo‐Ferrara Rosa Luisa Santilln‐Baca Norberto Farfn‐García Itzia I. Padilla‐Martínez Efrn V. García‐Bez 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(3):o125-o128
The molecular and supramolecular structures of 2‐(1,3‐dioxo‐2,3,3a,4,7,7a‐hexahydro‐1H‐isoindol‐2‐yl)phenyl acetate, C16‐H15NO4, (I), and its para isomer, 4‐(1,3‐dioxo‐2,3,3a,4,7,7a‐hexahydro‐1H‐isoindol‐2‐yl)phenyl acetate, (II), are reported. The torsion angle between the succinimide and benzene rings depends on the position of the acetoxy substitution [89.7 (1) and 61.9 (1)° for (I) and (II), respectively]. The twist of the acetoxy group relative to the mean plane of the benzene ring is almost independent of the acetoxy position [66.0 (1) and 70.0 (1)°]. Packing interactions for both compounds include soft C—H⋯X (X = O and Ph) interactions, forming chains of centrosymmetric dimers and interlinked chains for (I) and (II), respectively. In addition, three perpendicular dipole C=O⋯C=O interactions contribute to the supramolecular structure of (II). 相似文献
2.
Iurii L. Malaestean Manfred Speldrich Arkady Ellern Svetlana G. Baca Paul Kögerler 《Polyhedron》2010,29(8):1990-1997
Four hexanuclear coordination clusters containing cores of edge-sharing coordination octahedra exemplify how mixed-spin derivatives of a homonuclear parent structure, [(N–O)4], can be realized by a ligand ‘shrink-wrapping’ approach, resulting in [(N–O)4]- and [(N-O)4]-type clusters (L = isobutyrate, N–O = methyldiethanolamine, n-butyldiethanolamine, or triethanolamine). The resulting core structures are either virtually isostructural to the parent structure or differ in the placement of the peripheral metal ions, depending on the mix of structure-directing carboxylate and alkoxyamine ligands with large, flexible alkyl chains. Whereas the and {} complexes show dominant antiferromagnetic exchange, ferrimagnetic coupling features are exhibited by two {} clusters. 相似文献
3.
Loubriel G.M. Zutavern F.J. Baca A.G. Hjalmarson H.P. Plut T.A. Helgeson W.D. O'Malley M.W. Ruebush M.H. Brown D.J. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1997,25(2):124-130
Optically activated GaAs switches operated in their high-gain mode are being used or tested for pulsed power applications as diverse as low-impedance, high-current firing sets in munitions; high impedance, low-current Pockels cell or Q-switch drivers for lasers; high-voltage drivers for laser diode arrays; high-voltage, high-current, compact accelerators; and pulsers for ground penetrating radar. This paper will describe the properties of high-gain photoconductive semiconductor switches (PCSS), and how they are used in a variety of pulsed power applications. For firing sets, we have switched up to 7 kA in a very compact package. For driving Q switches, the load is the small (30 pF) capacitance of the Q switch which is charged to 6 kV. We have demonstrated that we can modulate a laser beam with a subnanosecond rise time. Using PCSS, we have demonstrated gain switching a series-connected laser diode array, obtaining an optical output with a peak power of 50 kW and a pulse duration of 100 ps. For accelerators, we are using PCSS to switch a 260 kV, 60 kA Blumlein. A pulser suitable for use in ground-penetrating radar has been demonstrated at 100 kV, 1.3 kA. This paper will describe the specific project requirements and switch parameters in all of these applications, and emphasize the switch research and development that is being pursued to address the important issues 相似文献
4.
Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films
We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current, I
c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed
that while the control side showed a J
c of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J
c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of
J
c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection
length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length
has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection. 相似文献
5.
Gross LC Heron AJ Baca SC Wallace MI 《Langmuir : the ACS journal of surfaces and colloids》2011,27(23):14335-14342
By making dynamic changes to the area of a droplet interface bilayer (DIB), we are able to measure the specific capacitance of lipid bilayers with improved accuracy and precision over existing methods. The dependence of membrane specific capacitance on the chain-length of the alkane oil present in the bilayer is similar to that observed in black lipid membranes. In contrast to conventional artificial bilayers, DIBs are not confined by an aperture, which enables us to determine that the dependence of whole bilayer capacitance on applied potential is predominantly a result of a spontaneous increase in bilayer area. This area change arises from the creation of new bilayer at the three phase interface and is driven by changes in surface tension with applied potential that can be described by the Young-Lippmann equation. By accounting for this area change, we are able to determine the proportion of the capacitance dependence that arises from a change in specific capacitance with applied potential. This method provides a new tool with which to investigate the vertical compression of the bilayer and understand the changes in bilayer thickness with applied potential. We find that, for 1,2-diphytanoyl-sn-glycero-3-phosphocholine membranes in hexadecane, specific bilayer capacitance varies by 0.6-1.5% over an applied potential of ±100 mV. 相似文献
6.
Hendricks K.J. Haworth M.D. Englert T. Shiffler D. Baca G. Coleman P.D. Bowers L. Lemke R.W. Spencer T.A. Arman M.J. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1998,26(3):320-325
The Air Force Research Laboratory RKO source has recently demonstrated the ability to convert electron beam power to RF power until the termination of the electron beam pulse, achieving a power of 1.5 GW at an energy of 170 J. These results represent an increase in power of 25-30% in power and energy extracted from this source. This paper discusses the principal research areas encountered in lengthening the RF pulse (FWHM) from 50 ns to the present 120 ns and the associated increase in the RF energy 相似文献
7.
8.
High-quality epitaxial thin films of the ferromagnetic metallic oxide SrRuO3 (SRO) were fabricated by dc-sputtering at high oxygen pressure and their structural and magnetoelectrical properties were carefully studied. The films featured a Curie temperature TC ~ 160 K and a magnetic moment of ~0.7 μB per Ru ion. The temperature dependent magnetization could be well described by the scaling relation M(T) ∝ (TC ? T)β with a critical exponent β = 0.53 over the entire ferromagnetic temperature range. A negative magnetoresistance, MR, on the order of a few percent was found up to room temperature. MR showed a maximum of ~4% right at TC where a kink structure of the resistivity, ρ, at zero field was flattened out on magnetic field application. This ρ contribution could be related to scattering due to orientational disorder of the Ru magnetic moments which become aligned by an external magnetic field. In addition, an equally strong MR effect, related to localization phenomena, could be observed at lower temperature. Particularly, the second MR peak at ~35 K might be related to a Fermi-liquid to non-Fermi-liquid crossover. A scaling behavior dρ/dT ∝ |T ? TC|α was observed only above TC. Here, values for the exponent α ≈ ?0.4 and α ≈ ?1.4 were obtained in zero field and in a field of 9 T, respectively. The commonly observed ρ minimum, appearing at low temperatures (~3 K in the present case), is correlated with the structural disorder of the SRO films and is believed to have its origin in quantum corrections to the conductivity (QCC). 相似文献
9.
Loubriel G.M. Zutavern F.J. Mar A. Hjalmarson H.P. Baca A.G. O'Malley M.W. Helgeson W.D. Falk R.A. Brown D.J. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1998,26(5):1393-1402
The longevity of high gain GaAs photoconductive semiconductor switches (PCSSs) has been extended to well over ten million pulses by reducing the density of carriers at the semiconductor to metal interface. This was achieved by reducing the density in the vertical and lateral directions. The latter was achieved by varying the spatial distribution of the trigger light thereby widening the current filaments that are characteristic of the high gain switches. We reduced the carrier density in the vertical direction by using ion implantation. These results were obtained for currents of about 10 A, current duration of 3.5 ns, and switched voltage of ~2 kV. At currents of ~70 A, the switches last for 0.6 million pulses. In order to improve the performance at high currents, new processes such as deep diffusion and epitaxial growth of contacts are being pursued. To guide this effort we recorded open shutter, infra-red images, and time-resolved Schlieren images of the current filaments, which form during high gain switching. We measured, under varying conditions, a carrier (electrons or holes) density that ranges from 3×1017 cm-3 to 6×1018 cm-3 相似文献
10.
One of the major difficulties of modelling fluid flow processes in hard-rock geologies is the complex nature of the porosity systems. Hydraulic behaviour in these rock masses is characterized by both porous and fractured interflow zones. Traditionally, fractured-porous rocks have been modelled as an equivalent porous medium or as a system of fractures separated by impermeable blocks. A new method is proposed that unifies these two approaches for modelling fluid flow processes in fractured-porous media. The basic idea is to use a combination of isoparametric elements for the porous zones and line elements for the fractures. The coupling between the governing equations for each element type is achieved using the superposition principle. The effectiveness of the new approach is demonstrated by comparing numerical solutions with known solutions for problems of flow and solute transport in fractured-porous media. 相似文献