P. Hummel

University of Bayreuth

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K. Wolf

University of Cologne

G. Poulard

European Organization for Nuclear Research

Y. Sumi

National Institute of Advanced Industrial Science and Technology

J. P. Sullivan

University of Southern California

D. Hardtke

Pandora (United States)

T. Sugitate

Hiroshima University

H. Ohnìshì

Tohoku University

M. Potekhin

Brookhaven National Laboratory

V. Polychronakos

Brookhaven National Laboratory

B. Erazmus

Nantes Université

Cooperative Institutions

Brookhaven National Laboratory

The Ohio State University

European Organization for Nuclear Research

Los Alamos National Laboratory

Lund University

Stony Brook University

A. Alikhanyan National Laboratory

Banaras Hindu University

Columbia University

Rudjer Boskovic Institute

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High energy Pb+Pb collisions viewed by pion interferometry

Physical Review C (1998)

I. G. Bearden H. Bøggild J. G. Boissevain J. Dodd B. Erazmus

Two-pion correlations from Pb+Pb collisions at 158 GeV/c per nucleon are measured by the NA44 experiment at CERN. Multidimensional fits characterize the emission volume, which is found to be larger than in S-induced collisions. Comparison to the RQMD model is used to relate the fit parameters to the actual emission volume.Received 5 May 1998DOI:https://doi.org/10.1103/PhysRevC.58.1656©1998 American Physical Society

High energy

10.1103/physrevc.58.1656

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Citations (64)

Electronic structures of trans-dioxometal complexes

Dalton Transactions (2005)

P. Hummel Jay R. Winkler Harry B. Gray

We have employed computational methods based on density functional theory to elucidate the effects of equatorial ligands on the electronic structures of trans-dioxometal complexes. In complexes with amine (sigma-only) equatorial donors, the (1)A(1 g)(b(2 g))(2)-->(1)E(g)(b(2 g))(1)(e(g))(1) excitation energy increases with metal oxidation state: Mo(IV) < Tc(V) < Ru(vi) and W(IV) < Re(V) < Os(VI). Increasing transition energies are attributed to enhanced oxometal pi-donor interactions in the higher valent central metals. But in complexes with cyanide equatorial donors, the (1)A(1 g)(b(2 g))(2)-->(1)E(g)(b(2 g))(1)(e(g))(1) energy remains roughly independent of metal oxidation state, likely owing to the compensating increased pi-donation from the pi(CN) orbitals to the metal d(xy) orbitals as the oxidation state of the metal increases.

Oxidation state

10.1039/b512299f

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Citations (14)

Anti-deuteron and kaon production in Pb+Pb collisions

Nuclear Physics A (1999)

I. G. Bearden H. Bגgild J. G. Boissevain L. Conin J. Dodd

10.1016/s0375-9474(99)85008-8

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Citations (7)

Hadron distributions — Recent results from the CERN experiment NA44

Nuclear Physics A (1996)

Nu Xu I. G. Bearden H. Bøggild J. G. Boissevain J. Dodd

Thermalisation

Momentum (technical analysis)

10.1016/s0375-9474(96)00353-3

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Citations (71)

Mid-rapidity protons in 158A·GeV Pb+Pb collisions

Physics Letters B (1996)

I. G. Bearden H. Bøggild J. G. Boissevain J. Dodd B. Erazmus

Proton distributions at mid-rapidity (2 ≤ y ≤ 3) have been measured for 158A·GeV Pb+Pb collisions in the focusing spectrometer experiment NA44 at CERN. From baryon number conservation and by comparing the experimentally measured dNdy distribution with the transport model RQMD, we conclude that a rather high degree of nuclear stopping has been reached for the truly heavy-ion collisions at these energies. Transverse mass distributions exhibit characteristically thermal shapes and the slope parameters increase with the mass of the colliding system.

Transverse mass

10.1016/s0370-2693(96)01249-x

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Citations (43)

Electronic structures of tetragonal nitrido and nitrosyl metal complexes

Theoretical Chemistry Accounts (2007)

P. Hummel Jay R. Winkler Harry B. Gray

Tetragonal crystal system

10.1007/s00214-006-0236-8

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Citations (12)

Electronic Excited States of Tetracyanonickelate(II)

Inorganic Chemistry (2006)

P. Hummel Nicholas W. Halpern-Manners Harry B. Gray

We revisit the assignment of the absorption spectrum of tetracyanonickelate(II) by calculating energies of excitations with time-dependent density functional theory. Our results give strong evidence that the original assignment of the spectrum is only partially correct. We thus propose an alternative assignment consistent with our theoretical calculations and all available experimental evidence. In particular, we reassign the bands at 22 400 and 32 300 cm(-1) to the (1)A(1g) --> (3)A(2g) (b(2g) --> b(1g)) and (1)A(1g) --> (1)A(2g) (b(2g) --> b(1g)) excitations.

10.1021/ic060584r

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Citations (8)

Collective Expansion in High Energy Heavy Ion Collisions

Physical Review Letters (1997)

I. G. Bearden H. Bøggild J. G. Boissevain J. Dodd B. Erazmus

Transverse mass spectra of pions, kaons, and protons from the symmetric heavy-ion collisions 200 $A$ GeV $\mathrm{S}+\mathrm{S}$ and 158 $A$ GeV $\mathrm{Pb}+\mathrm{Pb}$, measured in the NA44 focusing spectrometer at CERN, are presented. The mass dependence of the slope parameters provides evidence of collective transverse flow from expansion of the system in heavy-ion induced central collisions.

Transverse mass

10.1103/physrevlett.78.2080

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Citations (219)

Thermal Properties of Polymers and Hybrid Material Thin Films

P. Hummel

The technological progress of electronic devices is still enormous. Modern electronic devices already reached nanometer dimensions. Simultaneously, the computing power of these devices increases. This development implies enhancing power and heat densities. The cooling of these nanostructured devices is a challenging task of great interest. A fundamental understanding of heat transport on the nanoscale is necessary for optimizing thermal management. For a better understanding of thermal transport on the nanoscale, systematic investigations of structure-property relationships are required. For this purpose, model systems with precise structural and chemical control are essential. However, such nanostructured materials usually provide only small sample geometries. The small dimensions make thermal conductivity characterization quite challenging. For this work, a photoacoustic (PA) setup was implemented. With this method, it is possible to characterize thin films of a sample, which is supported by a substrate. Thus, small amounts of brittle samples that cannot be processed into freestanding films can be characterized. The capability of the PA method to determine the thermal properties of thin films was demonstrated by the investigation of three different polymer-based materials. The first two materials present the class of polymer nanocomposites (PNCs). Due to the miscibility on the molecular level, these can be also referred to as hybrid materials. The investigated PNCs can be divided by their filler geometry. First, the most straightforward filler geometry is investigated. Spherical Ag nanoparticles (NPs) are functionalized by polystyrene (PS) brushes of different molecular weights. The steric repulsion allows the adjustment of the interparticle distance (IPD) from 2 nm to 16 nm in the resulting PNC material. The ligand exchange used for this purpose is designed to be flexible. Thus, also different material combinations are viable with the presented procedure. Additionally, a new purification method is introduced, the centrifugation at θ-conditions of the ligand. The AgPS PNCs were processed into thin films and characterized regarding optical, mechanical and thermal properties. The individual distribution of the Ag NPs preserves the localized surface plasmon resonance (LSPR). Therefore, a laser can be used to locally heat up the sample within the laser spot. The higher the Ag volume fraction, the more significant the thermoplasmonic effect. Also the mechanical properties, determined by Brillouin light scattering (BLS) measurements, and the thermal conductivity depend on the Ag ratio. However, thermal conductivity could not be predicted by effective medium models without an finite interfacial thermal conductance. Accordingly, our findings suggest, that interfaces have an impact on thermal conductivity in this nanostructured material. The second filler type is characterized by two-dimensional extensions. The in-plane dimensions of these sheets are in the micrometer regime, while their thickness in cross-plane…

Characterization

Polystyrene

10.15495/epub_ubt_00005148

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Citations (0)

Coulomb effect in single particle distributions

Physics Letters B (1996)

H. Bøggild J. G. Boissevain J. Dodd B. Erazmus S. Esumi

Particle (ecology)

10.1016/0370-2693(96)00114-1

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Citations (34)