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Selected Works

1991

Iowa State University

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Articles 1 - 27 of 27

Full-Text Articles in Physical Sciences and Mathematics

Hepatic Microsomal N-Hydroxylation Of Aniline And 4-Chloroaniline By Rainbow Trout (Onchorhyncus Mykiss), Steven P. Bradbury, J. M. Dady, A. D. Hoffman, M. M. Voit, D. L. Olson Dec 1991

Hepatic Microsomal N-Hydroxylation Of Aniline And 4-Chloroaniline By Rainbow Trout (Onchorhyncus Mykiss), Steven P. Bradbury, J. M. Dady, A. D. Hoffman, M. M. Voit, D. L. Olson

Steven P. Bradbury

N-Hydroxylation of aniline and 4-chloroaniline was quantified in rainbow trout microsomal preparations using h.p.l.c.-liquid scintillation methods. Radioactive phenylhydroxylamine and 4-chlorophenylhydroxylamine metabolites were identified by co-elution with non-labelled standards. The method provided resolution of metabolite standards, and quantification of both N-hydroxylated metabolites was achieved without derivatization. The maximum velocities at 25 degrees C were 33.8 +/- 1.40 and 22.0 +/- 0.98 pmol/min per mg for aniline and 4-chloroaniline N-hydroxylation, respectively. The Km values were 1.0 +/- 0.11 and 0.8 +/- 0.11 mM for aniline and 4-chloroaniline N-hydroxylation, respectively. These activities were not induced by treatment of the trout with Aroclor 1254 …

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An Analytical Representation Of The Lowest Potential Energy Surface For The Reaction O(3 P)+Hcl (X  1Σ+)→Oh(X  2Π)+Cl(2 P), H. Koizumi, George C. Schatz, Mark S. Gordon Nov 1991

An Analytical Representation Of The Lowest Potential Energy Surface For The Reaction O(3 P)+Hcl (X  1Σ+)→Oh(X  2Π)+Cl(2 P), H. Koizumi, George C. Schatz, Mark S. Gordon

Mark S. Gordon

We present a new analytical representation of the lowest 3 A‘ energy surface for the reaction O(3 P)+HCl(X  1Σ+)→OH(X  2Π)+Cl(2 P). This surface is derived by fitting a b i n i t i o calculations, and adjustments are made to the barrier height so that rate constants derived from accurate quantum scattering calculations match the room temperature thermal rate constants. Contributions to thermal and state resolved rate constants arising from reaction on the lowest 3 A’surface are also considered. Comparisons of thermal and state resolved rate constants with experiment are good except at high temperature where the 3 A’ …

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The Conformational Potential Energy Surface Of Glycine: A Theoretical Study, Jan H. Jensen, Mark S. Gordon Oct 1991

The Conformational Potential Energy Surface Of Glycine: A Theoretical Study, Jan H. Jensen, Mark S. Gordon

Mark S. Gordon

The conformational potential energy surface of nonionized glycine has been studied by using ab initio (6-310*, ST0-20) and semiempirical (AM1, PM3) methods. The MP2/6-31G*/ /RHF/6-310* potential energy surface was then used to calculate the Boltzmann equilibrium distribution and kinetics of conformational interconversion at various temperatures. The results of this study are compared to previous computational and experimental investigations of gas-phase glycine.

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Structures And Bonding Of Group Iv Sulfur And Oxygen Propellane Derivatives, Kiet A. Nguyen, Marhsall T. Carroll, Mark S. Gordon Oct 1991

Structures And Bonding Of Group Iv Sulfur And Oxygen Propellane Derivatives, Kiet A. Nguyen, Marhsall T. Carroll, Mark S. Gordon

Mark S. Gordon

The RHF, ROHF, and GVB structures and energetics of group IV 2,4,5-trioxa[l.l.l]metallapropellanes, 2,4,5- trithia [ l.l.l]metallapropellanes, and their bicyclopentane analogues have been determined from ab initio molecular orbital theory by using both the 6-31G(d) basis set for all-electron calculations and the valence basis set with effective core potentials (ECP) developed by Stevens, Basch, and Krauss. Although they have extremely short bridgehead distances, these species possess fairly large natural orbital occupation numbers in the lowest unoccupied molecular orbitals, indicating significant diradical character. Structures and other properties determined by ECP calculations are in good agreement with the 6-31 G(d) all-electron calculations.

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First-Principles Study Of Phase Stability In Cu-Zn Substitutional Alloys, P. E. A. Turchi, M. Sluiter, F. J. Pinski, Duane D. Johnson, D. M. Nicholson, G. M. Stocks, J. B. Staunton Sep 1991

First-Principles Study Of Phase Stability In Cu-Zn Substitutional Alloys, P. E. A. Turchi, M. Sluiter, F. J. Pinski, Duane D. Johnson, D. M. Nicholson, G. M. Stocks, J. B. Staunton

Duane D. Johnson

A parameter-free approach to phase stability in Cu-Zn substitutional alloys is shown to describe order-disorder phenomena and structural transformations with remarkable accuracy. The method is based on a multiple-scattering description of the electronic structure properties of the random alloy. Configurational order is treated within the generalized perturbation method and the concentration-functional theory. Thermodynamical properties of α and β brasses are derived from the cluster variation method. This advanced scheme is of general validity and is expected to yield similarly accurate results for other Hume-Rothery alloys.

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Predicted Enthalpies Of Formation For Methyl-Substituted Silaethylenes And Disilenes, Jerry A. Boatz, Mark S. Gordon Sep 1991

Predicted Enthalpies Of Formation For Methyl-Substituted Silaethylenes And Disilenes, Jerry A. Boatz, Mark S. Gordon

Mark S. Gordon

Enthalpies of formation of the methyl-substituted silaethylenes (CH3).H2_,Si=CH2 (n = 1, 2) and disilenes (CH3),.H~i=Si(CH3),H:~-m (n, m = Q-2) are predicted by using isodesmic reactions which relate the compound of interest to the parent silaethylene (H2Si=CH2) or disilene (H~i=SiH2), for which accurate enthalpies of formation have recently been determined. In turn, the enthalpies of formation of these methyl-substituted compounds are used in conjunction with homodesmic reactions to reevaluate the enthalpies of formation of the silicon-substituted cyclobutenes C.Si4-0H6 (n = Q-4).

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Stabilization Of Β Positive Charge By Silicon, Germanium, Or Tin, Kiet A. Nguyen, Mark S. Gordon, Gen-Tai Wang, Joseph B. Lambert Aug 1991

Stabilization Of Β Positive Charge By Silicon, Germanium, Or Tin, Kiet A. Nguyen, Mark S. Gordon, Gen-Tai Wang, Joseph B. Lambert

Mark S. Gordon

Ab initio molecular orbital theory is used to study the β effect of carbon, silicon, germanium, or tin on the carbenium ions in H2R'MCH2CHR+ (R' = H; R = H, CH3). The relative stabilization energies of carbenium ions provided by M (M = C, Si, Ge, Sn) were determined by calculating the energy change in an isodesmic reaction using MP2/3-21G(d) (at SCF /3-21G* geometries) and MP2/6-31G(d) (at SCF /6- 31G(d) geometries) wave functions. The magnitude of the β effect is predicted to increase in the order C < Si < Ge < Sn. For R = H, the nonvertical cyclic structure is favored for the cations, whereas methyl substitution appears to stabilize the vertical acyclic arrangement.

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Ab Initio Study Of Some Methylene And Silylene Insertion Reactions, David R. Gano, Mark S. Gordon, Jerry A. Boatz Aug 1991

Ab Initio Study Of Some Methylene And Silylene Insertion Reactions, David R. Gano, Mark S. Gordon, Jerry A. Boatz

Mark S. Gordon

The theoretical barriers and reaction energetics have been determined, using ab initio calculations at the MP4/6-3IG(d) level, with 3-2IG* geometries, for the insertions of methylene and silylene into the X-Y bonds of ethane, methylsilane, disilane, and cyclopropane and into the X-H bonds of disilane and ethane. A correlation was observed between barrier heights and lengths of substrate bonds. The largest barriers were observed for methylene and silylene inserting into the C-C bonds of ethane. The barriers became successively lower for the C-Si and Si-Si bonds. Steric interactions thus appear to be a major factor in determining barrier heights. The observed …

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Nature Of The Si-N Bond In Silatranes, Mark S. Gordon, Marshall T. Carroll, Jan H. Jensen, Larry P. Davis, Larry W. Burggraf, R. Martin Guidry Aug 1991

Nature Of The Si-N Bond In Silatranes, Mark S. Gordon, Marshall T. Carroll, Jan H. Jensen, Larry P. Davis, Larry W. Burggraf, R. Martin Guidry

Mark S. Gordon

Both ab initio and semiempirical calculations are used to investigate the structure and bonding in substituted silatranes. In agreement with gas-phase experiments, which fmd Si-N distances that are 0.25-0.35 A longer than those in the crystal phase, the Si-N distance (for example, in methylsilatrane) is predicted to be much larger than that observed in the crystal. Nonetheless, a bond critical point is found between Si and N, suggesting the existence of an Si-N bond in these compounds. It is found that the energy cost for constraining the Si-N distance in hydroxysilatrane to a value similar to that observed in the …

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Three-Point Correlations In Driven Diffusive Systems With Ising Symmetry, Beate Schmittmann, R. K. P. Zia Jul 1991

Three-Point Correlations In Driven Diffusive Systems With Ising Symmetry, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

For equilibrium systems with Ising symmetry, the three-point correlation function is always zero above criticality. When a lattice-gas version of this system is driven to a nonequilibrium steady state, this correlation becomes nontrivial. Its dominant large-scale behavior is found to be a consequence of both the manifest breaking of Ising symmetry by the driving force and the more subtle violation of the fluctuation-dissipation theorem.

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Systematic Survey Of Cyclic Silicon-Oxygen Compounds, Michael W. Schmidt, Kiet A. Nguyen, Mark S. Gordon, John A. Montgomery Jr. Jul 1991

Systematic Survey Of Cyclic Silicon-Oxygen Compounds, Michael W. Schmidt, Kiet A. Nguyen, Mark S. Gordon, John A. Montgomery Jr.

Mark S. Gordon

Compounds with 0, 1, 2, or 3 oxygen atoms bridging 2 silicon atoms are investigated by ab initio calculations. Two such series of compounds, with and without a formal central Si-Si bond, are considered. The triplet states of the former set are also examined. For some of these compounds, the present calculations represent the first time they have been examined at a sufficiently rigorous level of theory. For the compounds that are formally bonded, this level is two configuration SCF (TCSCF) for singlets and ROHF for triplet states, using split valence polarized basis sets. The main result is that no …

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A Theoretical Study Of Some Reactions Of Hcsi-, Michael W. Schmidt, Mark S. Gordon Jul 1991

A Theoretical Study Of Some Reactions Of Hcsi-, Michael W. Schmidt, Mark S. Gordon

Mark S. Gordon

The ions HCSi- and H2CSiH- produced in recent flowing afterglow experiments are characterized structurally. Reactivity of the former ion with four molecules (C02, OCS, CS2, S02) is examined. Three of these species react in a sequence of intermediates of cyclic followed by acyclic structures, before reaching the final products.

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Principal Resonance Contributors To High-Valent, Transition-Metal Alkylidene Complexes, Thomas R. Cundiari, Mark S. Gordon Jul 1991

Principal Resonance Contributors To High-Valent, Transition-Metal Alkylidene Complexes, Thomas R. Cundiari, Mark S. Gordon

Mark S. Gordon

The results of ab initio calculations are reported for prototypical high-valent, alkylidene complexes. Stationary points on each potential energy surface are characterized and compared to experimental information where available; as long as a suitably flexible valence basis set is used, good agreement between theoretically calculated and experimentally determined geometries is obtained. The complexes of interest include group IVB (Ti, Zr and Hf) and group VB (Nb and Ta) alkylidenes with hydride ligands as well as models for the four-coordinate, olefin metathesis catalysts (Mo-, W-, and Re-alkylidenes) which have been recently synthesized and characterized. In light of the fact that much …

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Finger Formation In A Driven Diffusive System, D. H. Boal, Beate Schmittmann, R. K. P. Zia May 1991

Finger Formation In A Driven Diffusive System, D. H. Boal, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

A driven diffusive lattice gas is studied in a rectangular geometry: particles are fed in at one side and extracted at the other, after being swept through the system by a uniform driving field. Being periodic in the transverse direction, the lattice lies on the surface of a cylinder. The resulting nonequilibrium steady state depends strongly on this choice of boundary conditions. Both Monte Carlo and analytic techniques are employed to investigate the structure of typical configurations, the density profile, the steady-state current, and the nearest-neighbor correlations. As the temperature is lowered in a finite system, the simulations indicate a …

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A New Twist On Pseudorotation, Theresa L. Windus, Mark S. Gordon, Larry W. Burggraf, Larry P. Davis May 1991

A New Twist On Pseudorotation, Theresa L. Windus, Mark S. Gordon, Larry W. Burggraf, Larry P. Davis

Mark S. Gordon

For pentacoordinated structures in a trigonal bipyramidal ar· rangement, Berry1 proposed a "pseudorotation" mechanism whereby two such isomers can interconvert through a tetragonal transition state (TS). This Berry pseudorotation mechanism was demonstrated explicitly for SiH5- by following the MP22/6· 31G(d)3 minimum energy path4 (MEP).

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Gas-Phase Chemistry Of The Dimethylaluminum Oxide Ion And Related Aluminum Oxide Ions: Comparison Of Reactivity With Siloxide Ions, Robert Damrauer, Michèle Krempp, Michael W. Schmidt, Mark S. Gordon Mar 1991

Gas-Phase Chemistry Of The Dimethylaluminum Oxide Ion And Related Aluminum Oxide Ions: Comparison Of Reactivity With Siloxide Ions, Robert Damrauer, Michèle Krempp, Michael W. Schmidt, Mark S. Gordon

Mark S. Gordon

The anion [(CH3hAIOt (1) has been prepared in a flowing afterglow selected ion flow tube (FA-SIFT) by ion selection from the reaction mixture of trimethylaluminum dimer and hydroxide. This unusual ion is quite reactive and has been extensively studied. It reacts with halogen-containing compounds of several types, including fluorobenzene, chlorobenzene, bromofluorobenzene, acetyl chloride, and HF, to give [(CH3hAI(OH)Xt, where X = F, Cl, and Br. Its chemistry with hexafluorobenzene and silicon tetrafluoride has also been detailed as have a number of reactions with carboxylic acids, esters, anhydrides, sulfur-containing neutrals, alcohols, water, and ammonia. The dominant reaction pattern of 1 involves …

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Origins Of Compositional Order In Nipt Alloys, F. J. Pinski, B. Ginatempo, Duane D. Johnson, J. B. Staunton, G. M. Stocks, B. L. Gyorffy Feb 1991

Origins Of Compositional Order In Nipt Alloys, F. J. Pinski, B. Ginatempo, Duane D. Johnson, J. B. Staunton, G. M. Stocks, B. L. Gyorffy

Duane D. Johnson

We investigate the cause of compositional ordering in fcc Ni0.50Pt0.50 on the basis of a first-principles theory of electronic structure and finite-temperature concentration fluctuations. We treat the size effect, electronegativity, and band filling on an equal footing and find that the first of these dominates, leading to L10 ordering in agreement with experiment. An electronic origin is given for the metallurgical ‘‘rule of thumb’’ that alloys comprised of big atoms and little atoms tend to order into simple stuctures.

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The Interaction Between Dislocations And Intergranular Cracks, H. Zhang, Alexander H. King, R. Thomson Feb 1991

The Interaction Between Dislocations And Intergranular Cracks, H. Zhang, Alexander H. King, R. Thomson

Alexander H. King

The elastic interactions of dislocations and intergranular cracks in isotropic materials have been studied. In the first part of the paper, a model based on the Rice–Thomson theory is established under which the conditions for dislocation emission and crack propagation can be described in terms of an emission surface, cleavage surface, and loading line in the local k-space associated with a mixed mode intergranular crack. For a given crack, the local k-field changes with the emission of dislocations from the crack tip, which alters the balance of cleavage and emission. In the second part, we present experimental results of in …

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Effect Of Hydration And Dimerization Of The Formamidine Rearrangement, Kiet A. Nguyen, Mark S. Gordon, Donald G. Truhlar Feb 1991

Effect Of Hydration And Dimerization Of The Formamidine Rearrangement, Kiet A. Nguyen, Mark S. Gordon, Donald G. Truhlar

Mark S. Gordon

Ab initio molecular orbital theory is used to predict the geometry of the transition state and the energy barrier for the double-proton transfer in formamidine dimer, using SCF /6-31 G(d,p) and MP2/6-31 G(d,p) wave functions, respectively. Intramolecular hydrogen transfer in the uncomplexed monomer (I) and double-proton transfer in the mixed dimer of formamidine and water (2) are also investigated at several levels of theory. All computational levels predict the barrier for the uncomplexed reaction (I) to be approximately twicdhat for the hydrated reaction (2). Isomerization by double-proton transfer in the dimer (3) is predicted to be the most favorable process. …

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Critical Properties Of A Randomly Driven Diffusive System, Beate Schmittmann, R. K. P. Zia Jan 1991

Critical Properties Of A Randomly Driven Diffusive System, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

We consider a system of interacting particles, diffusing under the influence of both thermal noise and a random, external electric field which acts in a subspace of m dimensions. In the nonequilibrium steady state, the net current is zero. When the interparticle interaction is short ranged and attractive, a second-order phase transition is expected. Analyzing this system in field-theoretic terms, we find the upper critical dimension to be 4-m and its behavior to fall outside the universality classes of the equilibrium Ising model and the usual driven diffusive system. A new fixed point and critical exponents are computed.

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Inhibition Of Alcohol Dehydrogenase Activity By Acetylenic And Allylic Alcohols: Concordance With In Vivo Electrophile Reactivity In Fish, Steven P. Bradbury, Glenn M. Christensen Jan 1991

Inhibition Of Alcohol Dehydrogenase Activity By Acetylenic And Allylic Alcohols: Concordance With In Vivo Electrophile Reactivity In Fish, Steven P. Bradbury, Glenn M. Christensen

Steven P. Bradbury

Acetylenic and al!ylic alcohols have been reported to be 20 to 5,000 times more acutely toxic to fathead minnows (Pimephales promelas) than would be expected from a narcosis-based mechanism of action. The greater-than-expected toxicity of these alcohols has been proposed to be a result of metabolic activation to the corresponding reactive a ,)3-unsaturated aldehydes or allene derivatives. Using purified horse liver and rainbow trout (Oncorhynchus mykiss) hepatic cytosol alcohol dehydrogenase (ADH) preparations, the propensity of a series of acetylenic and allylic alcohols to inhibit enzyme activity, in both the presence and the absence of reduced glutathione, was ascertained. Those alcohols …

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Use Of Respiratory-Cardiovascular Responses Of Rainbow Trout (Oncorhynchus Mykiss) In Identifying Acute Toxicity Syndromes In Fish: Part 4. Central Nervous System Seizure Agents, Steven P. Bradbury, Richard W. Carlson, Gerald J. Niemi, Tala R. Henry Jan 1991

Use Of Respiratory-Cardiovascular Responses Of Rainbow Trout (Oncorhynchus Mykiss) In Identifying Acute Toxicity Syndromes In Fish: Part 4. Central Nervous System Seizure Agents, Steven P. Bradbury, Richard W. Carlson, Gerald J. Niemi, Tala R. Henry

Steven P. Bradbury

The respiratory-cardiovascular responses of spinally transected rainbow trout to acutely lethal concentrations of chlorpyrifos, cypermethrin, fenvalerate, endosulfan, endrin, and strychnine were examined. Common to all six toxicants, the most striking change in respiratory-cardiovascular parameters was an increased cough frequency. Ventilation frequency and volume dropped in strychnine-exposed trout, but both remained near predose levels (frequency) or elevated (volume) in the pyrethroid- and cyclodiene-exposed trout. In chlorpyrifos-intoxicated trout, ventilation frequency decreased while volume increased. Oxygen consumption remained near predose levels in the chlorpyrifos-, pyrethroid-, and strychnine-exposed trout, but increased dramatically in the cyclodiene-exposed trout. Arterial oxygen, carbon dioxide, and pH declined in …

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Lignin Distribution In Thermomechanically Pulped Wood Fibers Via X-Ray Microanalysis, Douglas Stokke, Xuerong Wang Jan 1991

Lignin Distribution In Thermomechanically Pulped Wood Fibers Via X-Ray Microanalysis, Douglas Stokke, Xuerong Wang

Douglas D. Stokke

The three major framework organic constituents of the secondary xylem (wood) of trees are cellulose, hemicelluloses, and lignin. Lignin imparts a number of important physical properties to the woody cell wall. In addition, lignin serves as the "cement" which binds cells together, and is the material which must be softened, altered, or removed during pulping processes. The distribution of lignin within pulp cell walls is of importance with respect to use of the pulp fibers. In this study, x-ray analysis was used to investigate lignin distribution in thermomechanically pulped (i.e., pulped with heat and pressure, with no chemical treatment) aspen …

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Optimering Van Koagulasie En Flokkulasie In Die Herwinning Van Koelwater Uit Oliesintese-Afvalwater, Johannes Van Leeuwen, P. Wille Jan 1991

Optimering Van Koagulasie En Flokkulasie In Die Herwinning Van Koelwater Uit Oliesintese-Afvalwater, Johannes Van Leeuwen, P. Wille

Johannes van Leeuwen

The activated sludge process, which is used in the purification of an oil synthesis effiuent, produces an effiuent which is high in turbidity. The water also contains a lot of dispersed bacterial growth which is not removed during sedimentation. Flocculation is essential to remove these materials. The average diameter of the colloids was found to be 0,92/'m. The zeta potential of the colloids was determined in an attempt to correlate it to the amount of flocculant required. The value was relatively constant at -13,88 mV, which indicates that a cationic·coagulant was required. The required dosage to achieve clarification by means …

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The Slater–Pauling Curve: First Principles Calculations Of The Moments Of Fe1 − C Ni C And V1 − C Fe C, Duane Johnson, F. Pinski, J. Staunton Jan 1991

The Slater–Pauling Curve: First Principles Calculations Of The Moments Of Fe1 − C Ni C And V1 − C Fe C, Duane Johnson, F. Pinski, J. Staunton

Duane D. Johnson

We have performed calculations of the electronic structure of the random substitutional alloys Fe1−c Ni c and V1−c Fe c using the spin‐polarized, self‐consistent Korringa–Kohn–Rostoker coherent‐potential approximation (KKR‐CPA) method. This is a first principles method based on spin density functionaltheory and a local spin density approximation for the exchange and correlation functional. For fcc Fe1−c Ni c , a range of volumes were considered for 0.25

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Novel Ce Magnetism In Cedipnictide And Di‐Ce Pnictide Structures, Paul C. Canfield, J. D. Thompson, Z. Fisk Jan 1991

Novel Ce Magnetism In Cedipnictide And Di‐Ce Pnictide Structures, Paul C. Canfield, J. D. Thompson, Z. Fisk

Paul C. Canfield

Results of electrical resistance and magnetic susceptibility measurements on Ce2Bi, Ce2Sb, CeScGe, CeScSi and CeSb2 are presented. Ce2Bi and Ce2Sb have antiferromagnetictransitions at low temperatures, while CeSb2, CeScGe and CeScSi have ferromagnetictransitions, CeScGe having a T c = 46 K. The data are analyzed with respect to the similarities of the two crystal structure groups that these materials fall into: CeSb2 having the LaSb2structure and the other materials all having the La2Sb structure.

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Magnetism And Heavy Fermion‐Like Behavior In The Rbipt Series, Paul C. Canfield, J. D. Thompson, W. P. Beyermann, A. Lacerda, M. F. Hundley, E. Peterson, Z. Fisk, H. R. Ott Jan 1991

Magnetism And Heavy Fermion‐Like Behavior In The Rbipt Series, Paul C. Canfield, J. D. Thompson, W. P. Beyermann, A. Lacerda, M. F. Hundley, E. Peterson, Z. Fisk, H. R. Ott

Paul C. Canfield

Members of the RBiPt (R=Ce–Lu with the exceptions of Pm and Eu) series have been grown as single crystals.Magnetic susceptibility and electrical resistance have been measured on all members of the series, and specific heatmeasurements have been performed on representatives. The high temperature resistance uniformly changes from that of a small‐gap semiconductor or semimetal seen in NdBiPt to that of a heavy‐fermion metal seen in YbBiPt, which shows a linear coefficient of specific heat at low temperatures of 8 J/K2 mole. Further, the lighter rare earth members show an unusually sharp increase in their resistance associated with antiferromagnetic ordering at …

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