Physical Sciences and Mathematics Commons^™

Synthesis Of 1-Alloc-Piperidine-4-Fmoc-Amino-4-Carboxylic Acid: A Novel, Protected ?,?- Disubstituted Amino Acid, Muna K. Thalji

Honors Theses

No abstract provided.

Electron Acceleration By A Laser Wakefield In A Relativistically Self-Guided Channel, R. Wagner, Shouyuan Chen, Anatoly Maksimchuk, Donald P. Umstadter

Donald Umstadter Publications

Acceleration of electrons to relativistic energies by a multidimensional self-modulated laser wakefield is discussed. Above a power threshold, a relativistically self-guided channel from an intense ultrashort laser pulse (l∼4×10¹⁸ W/cm², λ = 1 μm, τ = 400 fs) was found to increase the laser propagation distance, decrease the electron beam divergence, and increase the energy of the electrons. These electron beam effects occurred even though the propagation distance became significantly longer than the conventional dephasing length.

Optical Rotation Curves Of Distant Field Galaxies: Sub-L, Systems, Nicole P. Vogt, Andrew C. Phillips, S. M. Faber, Jesús Gallego, Caryl Gronwall, R. Guzmán, Garth D. Illingworth, David C. Koo, James D. Lowenthal

Astronomy: Faculty Publications

Moderate-resolution spectroscopic observations from the Keck 10 m telescope are used to derive internal kinematics for eight faint disk galaxies in the fields flanking the Hubble Deep Field. The spectroscopic data are combined with high-resolution F814W Wide Field Planetary Camera 2 images from the Hubble Space Telescope that provide morphologies, scale lengths, inclinations, and orientations. The eight galaxies have redshifts 0.15 ≲ z ≲ 0.75, magnitudes 18.6 ≤ I ≤ 22.1, and luminosities -21.8 ≤ M ≤ -19.0 (H = 75 km s Mpc and q = 0.05). Terminal disk velocities are derived from the spatially resolved velocity profiles by …

Generalization Of The Bound State Model, Joseph Schechter, Masayasu Harada, Francesco Sannino, Herbert Weigel

Physics - All Scholarship

In the bound state approach the heavy baryons are constructed by binding, with any orbital angular momentum, the heavy meson multiplet to the nucleon considered as a soliton in an effective meson theory. We point out that this picture misses an entire family of states, labeled by a different angular momentum quantum number, which are expected to exist according to the geometry of the three-body constituent quark model (for N_C=3). To solve this problem we propose that the bound state model be generalized to include orbitally excited heavy mesons bound to the nucleon. In this approach the missing angular momentum …

Magnetism And Morphology Of Fe/Cu(111) Films Below Two-Dimensional Percolation, J. Shen, Ralph Skomski, M. Klaua, H. Jenniches, S. Sundar Manoharan, J. Kirschner

Ralph Skomski Publications

The magnetic properties of g-iron films on Cu(111) below the two-dimensional percolation threshold of about 1.4 monolayer are investigated. Iron on flat Cu(111) surfaces forms triangular patches, while it forms stripes along step edges on vicinal surfaces. The films exhibit an easy magnetization axis perpendicular to the film plane and magnetic hysteresis at sufficiently low temperatures. The magnetization curves of the triangular iron patches are discussed in terms of Ising superparamagnetism. From Kerr hysteresis loops, we deduce that the first anisotropy constant K₁ in the superparamagnetic films is of order 0.345±0.020 MJ/m³.

Magnetic Hardening In Fept Nanostructured Films, J. Ping Liu, Yi Liu, C.P. Luo, Z.S. Shan

David Sellmyer Publications

FePt films have been prepared by sputtering Fe/Pt multilayers onto glass or silicon substrates. The thickness of the Fe and Pt layers was adjusted with the Fe:Pt atomic ratio from about 1:1 to 2:1. Magnetic hardening is observed after heat treatment at elevated temperatures, which led to coercivity values exceeding 20 kOe in samples with an Fe:Pt ratio around 1.2:1. The hardening originates from the formation of the tetragonal FePt phase with high magnetocrystalline anisotropy and a favorable microstructure. Two-phase composite films containing hard and soft phases were obtained when the Fe:Pt ratio increased. Under optimized processing conditions, composite films …

Nanostructure And Magnetic Anisotropy Of Co/Au Multilayers, Yi Liu, Z.S. Shan, David J. Sellmyer

David Sellmyer Publications

Multilayer Co/Au films were deposited on 40 nm Au underlayer by magnetron sputtering. The Co thickness is kept constant at 0.5 nm while the Au thickness is varied from 0.5 to 8 nm. Magnetic measurements show that the perpendicular anisotropy of the films changes from 3 × 10⁶ to 1.5 × 10⁶ erg/cm³ as the Au thickness changes from 6 to 1 nm. Two films of (Co 0.5 nm/Au 6 nm) × 9/Au 40 nm (denoted Au6) and (Co 0.5 nm/Au 1 nm) × 50/Au 40 nm (denoted Au1) were examined by transmission electron microscopy. For the …

Magnetic Properties And Switching Volumes Of Nanocrystalline Smfesic Films, S.Y. Zhang, Z.S. Shan, Yi Liu, T.Y. Zhao, J.G. Zhao, B.G. Shen, W.S. Zhan, David J. Sellmyer

David Sellmyer Publications

Systematic studies of the effects of Si addition on the magnetic and magnetization reversal properties of SmFeSiC films are presented. The magnetic switching volume and other magnetic parameters (e.g., coercivity) are strongly dependent upon the Si content. Correlations between switching volume, coercivity, and the intergrain interactions are discussed.

Correlation Of Switching Volume With Magnetic Properties, Microstructure, And Media Noise In Cocr(Pt)Ta Thin Films, C. Gao, Z.S. Shan, R. Malmhall, Yi Liu, H.J. Richter, A. Barney, G.C. Rauch, David J. Sellmyer

David Sellmyer Publications

The technique of "field sweep-rate dependence of coercivity" together with the delta-M curves, transmission electron microscopy, and media noise measurement have been employed to reveal the correlation among the magnetic switching volume, physical grain size, intergrain interaction, and noise properties. The switching volume for both CoCrTa and CoCrPtTa films was found to be ~ 15 nm in diameter, and weakly dependent on grain size and coercivity for the systems studied. In films with physical grain size larger than the switching volume, strong intergrain interaction and high media noise is observed. In films with the physical grain size close to the …

Solar Wind-Magnetosphere Coupling During An Isolated Substorm Event: A Multispacecraft Istp Study, T I. Pulkkinen, D N. Baker, Niescja E. Turner, H J. Singer, L A. Frank, J B. Sigwarth, J Scudder, R Anderson, S Kokubun, R Nakamura, T Mukai, J B. Blake, C T. Russell, H Kawano, F Mozer, J A. Slavin

Physics and Astronomy Faculty Research

Multispacecraft data from the upstream solar wind, polar cusp, and inner magnetotail are used to show that the polar ionosphere responds within a few minutes to a southward IMF turning, whereas the inner tail signatures are visible within ten min from the southward turning. Comparison of two subsequent substorm onsets, one during southward and the other during northward IMF, demonstrates the dependence of the expansion phase characteristics on the external driving conditions. Both onsets are shown to have initiated in the midtail, with signatures in the inner tail and auroral oval following a few minutes later.

Optical And Magneto-Optical Properties Of Mnpt3 Films (Abstract), Kurt W. Wierman, J. N. Hilfiker, Renat F. Sabiryanov, Sitaram Jaswal, Roger D. Kirby, John A. Woollam

Roger Kirby Publications

Optically thick films of MnPt₃ were prepared by magnetron sputtering onto quartz substrates. Postdeposition annealing at 850 °C resulted in highly textured (111) films with the L1₂ (Cu₃Au) structure. MnPt₃ films are ferromagnetic with a Curie temperature of 380 °C, and they show large magneto-optical effects in the visible. These films also show a high degree of long-range order. The diagonal components of the dielectric tensor were determined using variable angle spectroscopic ellipsometry measurements over the spectral range 1.2–2.4 eV. Magneto-optic Kerr rotation and ellipticity measurements were made at near normal incidence over the …

Metamagnetic Domains And Dynamic Fluctuations In Febr2, O. Petracic, Christian Binek, Wolfgang Kleeman

Christian Binek Publications

The mixed phase and the regime of non-critical fluctuations of the magnetic phase diagram of FeBr₂ is investigated by SQUID susceptometry and light diffraction techniques. The experiments seem to evidence instability of the tricritical point as conjectured recently. The observation of stripe domains and light diffraction below and above T_m = 4.6 K and the virtual continuation of the phase transition line to above T_m are in agreement with the occurrence of a critical endpoint at T_m and of a bicritical endpoint at T > T_m. ©1997 American Institute of Physics.

Domain-Wall Curvature And Coercivity In Pinning Type Sm–Co Magnets, Ralph Skomski

Ralph Skomski Publications

The origin of coercivity in precipitation hardened Sm–Co magnets is investigated. By considering domain-wall pinning at boundary phase and Z phase inhomogenities, it is found that the hexagonal Z phase has no direct influence on the coercivity. The intuitive assumption of plane domain walls made in a recent calculation is unrealistic but has no direct effect on the coercivity. However, due to the comparatively large size of the 12:17 cells, the calculated three dimensional domain-wall curvature is sufficiently large to assure a nearly ideal nestling of the domain walls to the 1:5 cell boundary. This nestling yields a coercivity increase …

Interlayer Coupling In Nife/Mo Multilayers And Effect Of Fe Underlayer, M.L. Yan, Z.S. Shan, David J. Sellmyer, W.Y. Lai

David Sellmyer Publications

We report our studies of exchange coupling in NiFe/Mo multilayers with and without Fe underlayer. The interlayer coupling of NiFe layers across the Mo spacer as well as the magnetic exchange coupling between Fe underlayer and the NiFe/Mo multilayers were observed: The interlayer coupling in NiFe/Mo multilayers exhibits the typical oscillations as a function of the Mo spacer with a period of about 11 Å, and the magnetic exchange coupling between Fe underlayer and the NiFe/Mo multilayers is strongly dependent on the thickness of the Mo spacer t_Mo and the bilayer number N of NiFe/Mo multilayers. For the [NiFe(20 …

Superparamagnetic Ultrathin Films, Ralph Skomski, D. Sander, J. Shen, J. Kirschner

Ralph Skomski Publications

The finite-temperature magnetism of ultrathin films such as sesquilayer Fe/W(110) and submonolayer Fe/Cu(111) is investigated. Based on renormalizations of Onsager's exact solution of the two-dimensional Ising model it is shown that superparamagnetism is a common phenomenon in imperfect ultrathin films. The ultimate reason for this behavior is the existence of two structural length scales: the lattice constant, usually considered in renormalization-group theory, and the characteristic size of the film inhomogeneities.

Enhanced Temperature Effect On Magnetoresistance In Fe/Mo Multilayers, M.L. Yan, Y.W. Lai, L. Yin, Sy_Hwang Liou

Sy-Hwang Liou Publications

We have observed an enhancement of the temperature effect on magnetoresistance (MR) in Fe/Mo multilayers with the increase of the Mo layer thickness. MR at the first antiferromagnetic maximum is large and insensitive to the temperature whereas at the third antiferromagnetic maximum it is small and relatively sensitive to the temperature. We found that the mean free path of the conduction electrons increased with the increase of the Mo layer thickness at a fixed temperature and it decreased very slightly with the increase of the temperature at a fixed Mo layer thickness. The interlayer coupling, similar to MR, also has …

Magnetic And Structural Properties Of Nd₂Fe₁₇₋ₓmnₓ Solid Solutions, Peter C. Ezekwenna, G. K. Marasinghe, William Joseph James, Oran Allan Pringle, Gary J. Long, H. Luo, Z. Hu, William B. Yelon, Ph. I'Héritier

Chemistry Faculty Research & Creative Works

A series of Nd₂Fe_17-xMn_x solid solutions with x values between 0 and and 6 were prepared and analyzed using magnetic measurements, neutron diffraction, and Mössbauer spectroscopy. All of the Nd₂Fe_17-xMn_x samples crystallized in the Th₂Zn_17-x-type rhombohedral structure. The lattice parameters and unit cell volumes decrease with increasing manganese content up to ∼ x equal to 2, and then increase for higher manganese content. The magnetizations of Nd₂Fe_17-xMn_x decrease with increasing manganese content and Nd₂Fe_17-xMn_x is paramagnetic …

Las Vegas Wash Water Quality Monitoring Program: 1996 Report Of Findings, Richard A. Roline, James J. Sartoris, U.S. Bureau Of Reclamation, U.S. Geological Survey

Publications (WR)

Las Vegas Wash, a natural wash east of the city of Las Vegas, Nevada, carries stormwater, groundwater drainage, and sewage effluent from three sewage treatment plants to Lake Mead. The Wash provides nearly the only surface water outlet for the entire 2,193 mi² of Las Vegas Valley. A drainage area of 1,586 mi² contributes directly to the Wash through surface flow which is channeled to Las Vegas Bay of Lake Mead, while drainage of the remaining 607 mi² is presumably subsurface and may drain toward Las Vegas Wash.

In the 1930's and 1940's, sewage treatment plants were …

An Analysis Of Iron-Iron Interatomic Distances In Several Rare Earth Transition Metal Intermetallics, G. K. Marasinghe, Peter C. Ezekwenna, William Joseph James, Z. Hu, William B. Yelon

Chemistry Faculty Research & Creative Works

As a part of a systematic study of the dependence of iron-iron exchange interactions on near neighbor iron-iron distances in rare earth transition metal magnetic materials, we have conducted a statistical analysis of interatomic distances in Nd₂Fe₁₇, Nd₂Fe₁₇N₃, and Nd₂Fe₁₄B. Results, in general, support the notion that larger near neighbor iron-iron distances promote higher Curie temperatures. In this work, special attention has been paid to the expansion of the Nd₂Fe₁₇ lattice due to interstitial nitrogenation and the accompanying increase in the Curie temperature. …

Studies Of V, Nb, Cr, And Zr Substituted 2:17 Compounds And Their Carbides Using Neutron Diffraction, H. Luo, Z. Hu, Muguo Chen, William B. Yelon, G. K. Marasinghe, Peter C. Ezekwenna, William Joseph James, W. C. Chang, S. H. Tsai

Physics Faculty Research & Creative Works

Samples of Nd₂Fe_17-xT_xC_y with T=V, Nb, Cr, and Zr were prepared by melting of the constituent elements including C and studied by neutron diffraction. Comparing with their uncarbided counterparts, we found that the substituents transfer, more or less, from the 6c site to the 18f and 18h sites with the introduction of C atoms. This behavior appears to relate to the electronegativities between the C atoms and the early transition series elements because the 18f and 18h sites are near neighbors of the interstitial C site. However, the C effects in the V. …

Accurate Hydrogen Spectral Simulations With A Compact Model Atom, Jason W. Ferguson, Gary J. Ferland

Physics and Astronomy Faculty Publications

Many large-scale numerical simulations of astrophysical plasmas must also reproduce the hydrogen ionization and the resulting emission spectrum, in some cases quite accurately. We describe a compact model hydrogen atom that can be readily incorporated into such simulations. It reproduces the recombination efficiency and line spectrum predicted by much larger calculations for a very broad range of densities and temperatures. Uncertainties in hydrogen collision data are the largest source of differences between our compact atom and predictions of more extensive calculations and underscore the need for accurate atomic data.

Resolution And Kinematics Of Molecular Hydrogen In The Cloverleaf Gravitational Lens, Min S. Yun, N Z. Scoville, J J. Carrasco, R D. Blandford

Min S. Yun

Gravitational lenses have long been advertised as primitive telescopes, capable of magnifying cosmologically distant sources. In this Letter we present new, 0"9 resolution CO (7– 6) observations of the z 5 2.56 Cloverleaf quasar (H14131117) and spatially resolved images. By modeling the gravitational lens, we infer a size scale of 0"3 (11 kpc) for the molecular gas structure surrounding the quasar, and the gas has a kinematic structure roughly consistent with a rotating disk. The observed properties of the CO-emitting gas are similar to the nuclear starburst complexes found in the infrared luminous galaxies in the local universe, and metal …

Hydrologic Budget Analysis And Numerical Simulations Of Groundwater Flow In Los Alamos Canyon Near Los Alamos, New Mexico, Robert Norman Gray

Earth and Planetary Sciences ETDs

A hydrologic budget analysis for the Los Alamos Canyon watershed was prepared including annual budgets for the 1993, 1994, and 1995 water years and detailed budget calculations for the upper basin and middle/upper canyon areas covering nine separate stress periods from 7/10/94 to 11/2/95 corresponding to varying alluvial aquifer behaviors. Data sources included daily measurements of precipitation and snowpack depths, streamflow discharge, and latent heat energy flux from which evapotranspiration rates were determined. Average annual precipitation rates over the watershed varied from ~23 to ~31 inches during the analyzed periods. The annual evapotranspiration component was determined to represent between ~ …

Using Fundamental Plane Distances To Estimate The Total Binding Mass In Abell 2626, Joseph J. Mohr, Gary Wegner

Dartmouth Scholarship

We use fundamental plane (FP) distance estimates to the components of the double cluster A2626 (cz ~ 17,500 km/s) to constrain cluster kinematics and estimate total binding mass. We employ deep R band CCD photometry, multi-object spectroscopy, and software designed to account for seeing effects to measure the FP parameters R_e, sigma , and for 24 known early type and S0 cluster members. The FP coefficients from this sample (alpha =1.30+/-0.36 and beta =0.31+/-0.06) are consistent with others reported in the literature. We examine the Mg_b equivalent width distributions within both subclusters and find them to be indistinguishable. Lacking evidence …

Synthesis And Characterization Of Modified Silica Gel As An Intermediate In The Generation Of Gaseous Standard Mixtures, M. Prokopowicz, K. Lewandowska, A. Skwierawska, Andrzej Przyjazny, Jan F. Biernat, J. Namiesnik

Chemistry & Biochemistry Publications

A possibility of extending analytical applications of chemically modified silica gels is described. This involves their utilization for the generation of gaseous standard mixtures consisting of methyl chloride as the analyte and nitrogen as a carrier gas to be used for the calibration of the GC-FID system. N-methylmorpholine was chemically bonded to the propylsilylated surface of silica gel forming chloride of an appropriate immobilized compound which, under certain conditions, undergoes thermal decomposition yielding a single, volatile component (methyl chloride). Such a method of generating specific amounts of a standard substance can be used both for a single point calibration and …

The Terraces Of Cochiti Canyon: Soil Development And Relation To Tectonism In The Pajarito Fault Zone, Scott Benjamin Aby

Earth and Planetary Sciences ETDs

The history of motion on splays of the Pajarito Fault Zone in the area of Cochiti Canyon in the Jemez Mountains is examined using morphometric techniques and investigations of river terrace soils and deformation. Hypsometry, sinuosity and long-profile analysis all suggest that the main splay of the Pajarito Fault has been active in the late Pleistocene and possibly Holocene, but no calibration is available that numerically constrains this activity. Terraces were mapped and correlated based on soil development and landscape position, Correlation revealed the presence of three strath terraces between 87 and 18 .5 meters above present grade and one …

Angle-Resolved Study Of Ar 2p₁/₂,₃/₂⁻1Ns,D Resonant Auger Decay, Marc Andrew Humphrey

Honors Theses

Angle-resolved measurements of the Ar 2p_1/2,3/2^-14s,3d,4d and 2p_3/2^-14s,3d,4d resonant Auger transitions have been carried out using photons from an undulator beamline at the Advanced Light Source of Lawrence Berkeley National Laboratory. The intensity distributions and angular distribution anisotropy (β) parameters have been reported for nearly all of the possible 3p⁴nl final ionic states. These results further verify the predictions of the spectator model for the 2p_1/2,3/2^-14s resonances and the subsequent breakdown of this model for the 2p_1/2,3/2^-13d and 2p_1/2,3/2^-14d relative intensities. This work …

Mechanistic Studies On The Aminopeptidase From Aeromonas Proteolytica:  A Two-Metal Ion Mechanism For Peptide Hydrolysis, Guanjing Chen, Tanya Edwards, Ventris M. D'Souza, Richard C. Holz

Chemistry Faculty Research and Publications

The aminopeptidase from Aeromonas proteolytica (AAP) is uncompetitively inhibited by fluoride ion at pH 8.0 with an inhibition constant (K_i) of 30 mM. Thus, fluoride inactivates AAP only after substrate binding, and only a single fluoride ion binds to AAP. On the other hand, chloride ion does not inhibit AAP up to concentrations of 2 M at pH 8.0. The pH dependence of fluoride inhibition of AAP was measured over the pH range 6.0−9.5. Between pH values of 6.0 and 9.0, fluoride ion acts as a pure uncompetitive inhibitor of AAP, and the K_i increases from …

The N-15/N-14 Isotope Fractionation In Dissociative Recombination Of N-2(+), Jane L. Fox, Aleksander B. Hać

Physics Faculty Publications

We have carried out Monte Carlo calculations of the velocity distributions and escape fractions for ¹⁴N and ¹⁵N released in dissociative recombination of ²⁸N₂⁺ and ²⁹N₂⁺, respectively, for a range of ion temperatures (T_i) and electron temperatures (T_e) appropriate to the Martian exosphere. Separate calculations were carried out for each vibrational level of N₂⁺ for 0≤ν≤6. We have taken into account the variation in the dissociative recombination cross section with relative velocity of the ion and electron, and the differences in the vibrational …

Dipole Spectroscopy, Ronald Lovett

Topics in Quantum Mechanics

No abstract provided.