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Articles 21601 - 21630 of 21971

Full-Text Articles in Physical Sciences and Mathematics

Cooling By Immersion In Liquid Nitrogen, Thomas W. Listerman, Thomas A. Boshinski, Lynn F. Knese Jun 1986

Cooling By Immersion In Liquid Nitrogen, Thomas W. Listerman, Thomas A. Boshinski, Lynn F. Knese

Thomas Listerman

When an object is cooled by immersion in a liquid, there is an unexpected increase in the violence of boiling just before the boiling stops. Most people seem fascinated by this phenomenon yet few are acquainted with its explanation in terms of a change in the heat‐transfer mechanism from film boiling to nucleate boiling. We have developed two variations of an intermediate level undergraduate laboratory experiment to measure the heat‐transfer rate after a sample is immersed in liquid nitrogen. The temperature of the sample, as measured by a thermocouple, is recorded as a function of time using either a potentiometer …

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Ferromagnetism Versus Antiferromagnetism In Face-Centered-Cubic Iron, F. J. Pinski, J. Staunton, B. L. Gyorffy, Duane D. Johnson, G. M. Stocks May 1986

Ferromagnetism Versus Antiferromagnetism In Face-Centered-Cubic Iron, F. J. Pinski, J. Staunton, B. L. Gyorffy, Duane D. Johnson, G. M. Stocks

Duane D. Johnson

Using a first-principles disordered-local-moment picture of itinerant-electron magnetism, we calculated the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state.

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Density-Functional Theory For Random Alloys: Total Energy Within The Coherent-Potential Approximation, Duane D. Johnson, D. M. Nicholson, F. J. Pinski, B. L. Gyorffy, G. M. Stocks May 1986

Density-Functional Theory For Random Alloys: Total Energy Within The Coherent-Potential Approximation, Duane D. Johnson, D. M. Nicholson, F. J. Pinski, B. L. Gyorffy, G. M. Stocks

Duane D. Johnson

A density-functional-based theory is developed for calculation of the total energy and pressure of random substitutional alloys within the Korringa-Kohn-Rostoker coherent-potential approximation. The theory is used to calculate the concentration variation of the equilibrium lattice spacing of α-phase CucZn1−c alloys. We find, in agreement with experiment, that the variation is almost linear and that it deviates from Vegard's rule.

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The Condorequatorial Spread-F Campaign: Overview And Results Of The Large-Scale Measurements, M. C. Kelley, J. Labelle, E. Kudeki, Bela G. Fejer, S. Basu, Su. Basu, K. D. Baker, C. Hanuise, P. Argo, R. F. Woodland, W. E. Swartz, D. T. Farley, J. W. Meriwether May 1986

The Condorequatorial Spread-F Campaign: Overview And Results Of The Large-Scale Measurements, M. C. Kelley, J. Labelle, E. Kudeki, Bela G. Fejer, S. Basu, Su. Basu, K. D. Baker, C. Hanuise, P. Argo, R. F. Woodland, W. E. Swartz, D. T. Farley, J. W. Meriwether

Bela G. Fejer

During the Condor campaign a number of instruments were set up in Peru to support the rocket experiments. In this series of papers we report on the results of the experiments designed to study the equatorial F region. In this overview paper we summarize the main results as well as report upon the macroscopic developments of spread F as evidenced by data from backscatter radars, from scintillation observations, and from digital ionosonde meaurements. In this latter regard, we argue here that at least two factors other than the classical gravitational Rayleigh-Taylor plasma instability process must operate to yield the longest-scale …

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Gigahertz Scintillations And Spaced Receiver Drift Measurements During Project Condorequatorial F-Region Rocket Campaign In Peru, S. Basu, Sa. Basu, J. Labelle, E. Kudeki, Bela G. Fejer, M. C. Kelley, H. E. Whitney May 1986

Gigahertz Scintillations And Spaced Receiver Drift Measurements During Project Condorequatorial F-Region Rocket Campaign In Peru, S. Basu, Sa. Basu, J. Labelle, E. Kudeki, Bela G. Fejer, M. C. Kelley, H. E. Whitney

Bela G. Fejer

Radar backscatter at 50 MHz, rocket, and VHF/GHz scintillation measurements of spread F irregularities at the magnetic equator in Peru were made during the Project Condor campaign in March 1983. The paper discusses the coordinated set of observations on two evenings, March 1 and March 14, 1983, when the altitude of the F region peak differed by more than 150 km. The full complement of equatorial spread F phenomena, namely, the occurrence of 3-m plume structures and VHF/GHz scintillations, were recorded on both these evenings. It was found that the radar backscatter with extended plumes occurs in association with maximum …

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Auger Analysis Of Si–H Bonding And Hydrogen Concentration In Hydrogenated Amorphous Silicon, Nancy Burnham, Aj Nelson, Ab Schwartzlander, Se Asher, Ll Kazmerski Apr 1986

Auger Analysis Of Si–H Bonding And Hydrogen Concentration In Hydrogenated Amorphous Silicon, Nancy Burnham, Aj Nelson, Ab Schwartzlander, Se Asher, Ll Kazmerski

Nancy A. Burnham

Auger electron spectroscopy line‐shape analysis of the Si‐L 2 3 V V peak has been performed on hydrogenated amorphous silicon (a‐Si:H). Both a‐Si:H produced by hydrogen implantation of siliconsingle crystals (for analytical standards) and thin films (fabricated for solar cell applications) were examined in these studies. Hydrogen concentrations were confirmed by secondary ion mass spectrometry, and samples having hydrogen content over the range 101 6–102 2 cm− 3 were evaluated. Correlations between the area under the deconvoluted L 2 3 V V transition peak and the known hydrogen content have resulted in a semiquantitative method of determining hydrogen concentration using …

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Scanning Auger Microprobe Studies Of Ball Cratered Cds/Cuinse2 Solar Cells, Nancy Burnham, Ll Levenson, Rj Matson, R Noufi, Ll Kazmerski Apr 1986

Scanning Auger Microprobe Studies Of Ball Cratered Cds/Cuinse2 Solar Cells, Nancy Burnham, Ll Levenson, Rj Matson, R Noufi, Ll Kazmerski

Nancy A. Burnham

CdS/CuInSe2solar cell films are typically several micrometers thick. Composition profiles of these films are usually carried out on fracture cross sections by scanning Auger microscopy or by recording Auger spectra during ion milling. For fracture cross sections, the depth resolution depends on the electron beam diameter and the roughness of the fracture surface. Ion milling is time consuming, and artifacts are caused by ion beam faceting. Ball cratering requires only a fraction of an hour and provides significant magnification of the film cross section. There is sufficient contrast, both in optical and electron microscopy, to distinguish between CdS and CuInSe2 …

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Chiral Symmetry, Nonleptonic Hyperon Decay, And The Feinberg-Kabir-Weinberg Theorem, Jf Donoghue, Br Holstein Apr 1986

Chiral Symmetry, Nonleptonic Hyperon Decay, And The Feinberg-Kabir-Weinberg Theorem, Jf Donoghue, Br Holstein

Barry R Holstein

We demonstrate that additional (kaon-pole) diagrams must be appended to the traditional commutator-plus-baryon-pole approach to nonleptonic hyperon decay. The modified analysis satisfied the constraints of the Feinberg-Kabir-Weinberg theorem. The new terms are not numerically significant in the case of the usual current-current Hamiltonian, in the continuum limit, but can be important for work using lattice techniques or for other Hamiltonians.

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Potential Primary Pyrolysis Processes For Disilane, Mark S. Gordon, Thanh N. Truong, Elizabeth K. Bonderson Apr 1986

Potential Primary Pyrolysis Processes For Disilane, Mark S. Gordon, Thanh N. Truong, Elizabeth K. Bonderson

Mark S. Gordon

Four competing unimolecular decomposition pathways for disilane are considered with use of MP4 energies obtained with an extended basis set and geometries obtained at the MP2/6-31G** computational level. The 1,1- and 1,2-eliminations of H2 and the elimination of silylene to form silane all have similar endothermicities, but the very high activation energy for the I ,2-elimination eliminates this process as a significant contributor at low energies. If disilene is formed in the thermal decomposition of disilane, the more likely source is its higher energy isomer silylsilylene via a relatively low energy I ,2-hydrogen shift.

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Thermal Decomposition Of Silane, Mark S. Gordon, David R. Gano, J. Stephen Binkley, Michael J. Frisch Apr 1986

Thermal Decomposition Of Silane, Mark S. Gordon, David R. Gano, J. Stephen Binkley, Michael J. Frisch

Mark S. Gordon

The essential features of the potential energy surface for the thermal decomposition of silane have been calculated with extended basis sets, augmented by correlation corrections. It is predicted that the transition state for the molecular elimination lies 56.9 kcaljmol above silane. For the reverse reaction, the transition state is less than 2 kcal/mol above the separated fragments, silylene and molecular hydrogen, but 4.8 kcal/mol above a long-range potential well. In the latter, the silylene-H2 separation is 1.78 A, and the bond in H2 has stretched by more than 0.05 A. This indicates a significant electronic interaction between the fragments even …

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Theoretical Studies Of Reactions Of Silanimine (H2sinh) And Its Isomer Aminosilylene (Hsinh2), Thanh N. Truong, Mark S. Gordon Apr 1986

Theoretical Studies Of Reactions Of Silanimine (H2sinh) And Its Isomer Aminosilylene (Hsinh2), Thanh N. Truong, Mark S. Gordon

Mark S. Gordon

The structure and reactivity of unsaturated singlet silicon-nitrogen compounds is theoretically investigated. Ab initio calculations demonstrate that the planar silylene HSiNH2 is the global minimum on the SiNH3 surface, with the planar doubly bound species H2SiNH 18 kcaljmol higher in energy. The internal rotational barriers are computed to be 26.9 kcaljmol for HSiNH2 and 37.9 kcaljmol for H2SiNH. However, the barrier for the inversion of H2SiNH is only 5.6 kcaljmol, so that inversion is favored over rotation for this species. The isomerization connecting H2SiNH to HSiNH2 has a barrier of 60 kcaljmol. The transition-state structures, as well as the exothermicities …

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Predatory Prokaryotes: Predation And Primary Consumption Evolved In Bacteria, Lynn Margulis, Ricardo Guerrero, Carlos Pedrós-Alió, Isabel Esteve, Jordi Mas, David Chase Apr 1986

Predatory Prokaryotes: Predation And Primary Consumption Evolved In Bacteria, Lynn Margulis, Ricardo Guerrero, Carlos Pedrós-Alió, Isabel Esteve, Jordi Mas, David Chase

Lynn Margulis (1938 - 2011)

Two kinds of predatory bacteria have been observed and characterized by light and electron microscopy in samples from freshwater sulfurous lakes in northeastern Spain. The first bacterium, named Vampirococcus, is Gram-negative and ovoidal (0.6 μm wide). An anaerobic epibiont, it adheres to the surface of phototrophic bacteria (Chromatium spp.) by specific attachment structures and, as it grows and divides by fission, destroys its prey. An important in situ predatory role can be inferred for Vampirococcus from direct counts in natural samples. The second bacterium, named Daptobacter, is a Gram-negative, facultatively anaerobic straight rod (0.5 × 1.5 μm) with a single …

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Improvement Of Trace Aluminum Determination By Electrothermal Atomic Absorption Spectrophotometry Using Phosphoric Acid, Chris Craney, Kurt Swartout, F. Smith, C. West Feb 1986

Improvement Of Trace Aluminum Determination By Electrothermal Atomic Absorption Spectrophotometry Using Phosphoric Acid, Chris Craney, Kurt Swartout, F. Smith, C. West

Chris L. Craney

No abstract provided.

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Northern Hemisphere Surface Air Temperature Variations: 1851-1984, P. D. Jones, S. C. B.Raper, Raymond S. Bradley, H. F. Diaz, P. M. Kelly, T. M. L.Wigley Feb 1986

Northern Hemisphere Surface Air Temperature Variations: 1851-1984, P. D. Jones, S. C. B.Raper, Raymond S. Bradley, H. F. Diaz, P. M. Kelly, T. M. L.Wigley

Raymond S Bradley

A new compilation of monthly mean surface air temperature for the Northern Hemisphere for 1851-1984 is presented based on land-based meteorological station data and fixed-position weather ship data. This compilation differs from others in two ways. First, a considerable amount of new data, previously hidden away in archives, has been included, thus improving both spatial and temporal coverage. Second, the station data have been analyzed to assess their homogeneity. Only reliable or corrected station data have been used in calculating area averages. Grid point temperature estimates have been made by interpolating onto a 50 latitude by 100 longitude grid for …

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Electrochemical Reduction Of Alkyl Halides At Vitreous Carbon Cathodes In Dimethylformamide, James Cleary, Mohammed Mubarak, Kenneth Viera, Mark Anderson, Dennis Peters Jan 1986

Electrochemical Reduction Of Alkyl Halides At Vitreous Carbon Cathodes In Dimethylformamide, James Cleary, Mohammed Mubarak, Kenneth Viera, Mark Anderson, Dennis Peters

Mark R. Anderson

At vitreous carbon electrodes in dimethylformamide which contains tetramethylammonium perchlorate, cyclic voltammograms for 1-iododecane, 1-bromodecane, and 2-bromooctane consist of one irreversible reduction wave signaling formation of the alkyl carbanion, whereas voltammograms for 2-iodooctane, t-butyl bromide, and t-butyl iodide reveal stepwise generation of the alkyl radical and carbanion. Large-scale electrolysis of 1-iododecane at reticulated vitreous carbon yields decane, eicosane, 1-decene, and 1-decanol; the first two compounds arise, respectively, from reaction of decyl carbanions with a proton donor and with unreduced alkyl iodide, whereas the last two species are produced via chemical attack of hydroxide ion on 1-iododecane. Reduction of 1-bromodecane results …

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Electrochemistry Of 1,1,4,4-Tetraphenyl-1,3-Butadiene, 1,1,4,4-Tetraphenyl-1,2-Butadiene, And 1,1,4,4-Tetraphenyl-1-Butene In Dimethylformamide, Tsu-Yu Chen, Mark Anderson, Dennis Peters Jan 1986

Electrochemistry Of 1,1,4,4-Tetraphenyl-1,3-Butadiene, 1,1,4,4-Tetraphenyl-1,2-Butadiene, And 1,1,4,4-Tetraphenyl-1-Butene In Dimethylformamide, Tsu-Yu Chen, Mark Anderson, Dennis Peters

Mark R. Anderson

In dimethylformamide containing tetra-n-butylammonium perchlorate, 1,1,4,4-tetraphenyl-1-butene exhibits a single polarographic wave; preparative-scale reduction of the starting material produces 1,1,4,4-tetraphenylbutane.A polarogram for 1,1,4,4-tetraphenyl-1,3-butadiene consists of three waves. Large-scale electrolysis of 1,1,4,4-tetraphenyl-1,3-butadiene at potentials corresponding to either the first or second wave yields 1,1,4,4-tetraphenyl-1-butene in the absence of a proton donor and a mixture of 1,1,4,4-tetraphenyl-2-butene and 1,1,4,4-tetraphenyl-1-butene in the presence of excess glacial acetic acid. If 1,1,4,4-tetraphenyl-1,3-butadiene is electrolyzed at a potential on the third polarographic wave, one obtains 1,1,4,4-tetraphenylbutane in the absence of a proton donor but a mixture of 1,1,4,4-tetraphenyl-2-butene and 1,1,4,4-tetraphenylbutane in the presence of glacial acetic acid. …

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On The Quadratic Form N12 +N22 +N32 - N42 In Z4, Andrei Ludu Jan 1986

On The Quadratic Form N12 +N22 +N32 - N42 In Z4, Andrei Ludu

Andrei Ludu

No abstract provided.

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Linear Perturbations Of A Constant Coefficient Differential Equation Subject To Mild Integral Smallness Conditions, William Trench Jan 1986

Linear Perturbations Of A Constant Coefficient Differential Equation Subject To Mild Integral Smallness Conditions, William Trench

William F. Trench

No abstract provided.

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Measurements Of Electron Energy Distribution In An Argon Positive Column, Chin Oi Hoong Jan 1986

Measurements Of Electron Energy Distribution In An Argon Positive Column, Chin Oi Hoong

Chin Oi Hoong

The argon positive column plasma of a cold cathode glow discharge is studied using a pulsed single Langmuir Probe technique. It is observed thatthe energy distribution of the electrons in the posotive column is non-maxwellian at a gas pressure of 0.5 mbar. An increase in the gas pressure seems to make the distribution more Maxwellian.

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Pennsylvania's Implementation Of The Surface Mining Control And Reclamation Act: An Assessment Of How "Cooperative Federalism" Can Make State Regulatory Programs More Effective, John C. Dernbach Jan 1986

Pennsylvania's Implementation Of The Surface Mining Control And Reclamation Act: An Assessment Of How "Cooperative Federalism" Can Make State Regulatory Programs More Effective, John C. Dernbach

John C. Dernbach

No abstract provided.

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Sem Views Of Oak Wood, Douglas D. Stokke Jan 1986

Sem Views Of Oak Wood, Douglas D. Stokke

Douglas D. Stokke

The anatomical structure of the secondary xylem (wood) of trees varies with location in the tree. The size, shape, and distribution of cell types varies not only between locations (i.e., stem vs. branch vs. root), but also within an annual ring or across annual rings at a given cross-sectional plane.

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Thermoluminescence (Tl) Dating In Seismic Hazard Evaluations: An Example From The Bonneville Basin, Utah, James P. Mccalpin Jan 1986

Thermoluminescence (Tl) Dating In Seismic Hazard Evaluations: An Example From The Bonneville Basin, Utah, James P. Mccalpin

James P. McCalpin

Thermoluminescence (TL) of minerals is the release of light when grains are heated to 1500 -5000 C. As sediments are buried longer they progressively acquire more TL from accumulated radiation damage from alpha, beta, and gamma rays and cosmic radiation. If the total amount of radiation dose received can be calculated, and the current dose rate measured, then dividing the total dose by the yearly dose rate will yield a TL age. Total doses are calculated by heating the sample until all TL is released, then re-irradiating the sample in the lab with known doses until the natural TL is …

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Π-Bond Strengths In Hp=Ph, H2p=P, Hp=Nh, And Hn=Nh, Michael W. Schmidt, Mark S. Gordon Jan 1986

Π-Bond Strengths In Hp=Ph, H2p=P, Hp=Nh, And Hn=Nh, Michael W. Schmidt, Mark S. Gordon

Mark S. Gordon

The chemistry of the HP=PH 1r bond found in the recently isolated diphosphene compounds is considered in several ways. The P=P 1r-bond strength is found by computing the rotation barrier (36 kcalfmol) and is compared to that found for HN=NH (63.5 kcalfmol) and HP=NH (47 kcalfmol). The structure of the HPPH anion is presented. Various electronic states of the H2PP isomer are considered and compared to those of HPPH. Dipole moments and PP stretching frequencies are reported. The concerted hydrogenation of diphosphene is also examined.

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The Prereversal Enhancement Of Thezonal Electric Field In The Equatorial Ionosphere, D. T. Farley, E. Bonelli, Bela G. Fejer, M. F. Larsen Jan 1986

The Prereversal Enhancement Of Thezonal Electric Field In The Equatorial Ionosphere, D. T. Farley, E. Bonelli, Bela G. Fejer, M. F. Larsen

Bela G. Fejer

The electric fields in the ionospheric E and F regions near the magnetic equator often show a strong eastward enhancement shortly after sunset and before the eastward (normally) daytime field reverses to westward. Several theoretical models of the low-latitude fields suggest that this enhancement is caused mainly or entirely by F region winds (the F region dynamo), but some authors have suggested that it could be produced solely by E region tidal winds. We give here additional calculations and arguments in support of the F region source. The enhancement of the eastward field for an eastward F region wind turns …

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Microbial Communities, Lynn Margulis, David Chase, Ricardo Guerrero Jan 1986

Microbial Communities, Lynn Margulis, David Chase, Ricardo Guerrero

Lynn Margulis (1938 - 2011)

No abstract provided.

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Renormalization-Group Analysis Of Heat Capacity Amplitude, Scott I. Chase, Miron Kaufman Jan 1986

Renormalization-Group Analysis Of Heat Capacity Amplitude, Scott I. Chase, Miron Kaufman

Miron Kaufman

Critical amplitudes A+ associated with the temperature variation of the heat capacity are analyzed by means of renormalization-group techniques in both position and momentum spaces. We describe a mechanism according to which the amplitudes A diverge as the critical exponent a approaches a nonpositive integer. In between two consecutive divergences at least one amplitude vanishes at least once. The coefficient P in the expansion A+ /A- =1—Pa+0 (a~) is computed by means of e expansion and Migdal-Kadanoff renormalization-group technique. Systems for which the critical exponent alpha is negative but larger than —1 exhibit either a cusped heat capacity if A+/A- …

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Nonequilibrium Fluctuations Studied By A Rarefied Gas Simulation, Alejandro Garcia Jan 1986

Nonequilibrium Fluctuations Studied By A Rarefied Gas Simulation, Alejandro Garcia

Alejandro Garcia

A dilute gas under a constant heat flux is studied with use of a Monte Carlo simulation based on the Boltzmann equation. Results for several spatial correlation functions of equal-time fluctuations are reported and compared qualitatively with previous fluctuating hydrodynamics calculations for liquids.

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A Prescription For Computer System Excellence, Robert Yacobellis Dec 1985

A Prescription For Computer System Excellence, Robert Yacobellis

Robert H Yacobellis

No abstract provided.

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Engineering Product Quality - Current Practices And Future Trends, Robert Yacobellis Dec 1985

Engineering Product Quality - Current Practices And Future Trends, Robert Yacobellis

Robert H Yacobellis

No abstract provided.

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The Rigid Backbone: A New Geometry For Percolation., Anthony Day, R. Tremblay, A.-M. Tremblay Dec 1985

The Rigid Backbone: A New Geometry For Percolation., Anthony Day, R. Tremblay, A.-M. Tremblay

Anthony Roy Day

It is shown that the diluted two-dimensional central-force problem belongs to a new class of percolation problems. Geometric properties such as the fractal dimension of the backbone, the correlation-length exponent, and the connectivity are completely different from those of previously studied percolation problems. Explicit calculations of the backbone and the construction of an algorithm which identifies the infinite rigid cluster clearly demonstrate the absence of singly connected bonds, the overwhelming importance of loops, and the long-range nature of the rigidity.

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