Physical Sciences and Mathematics Commons^™

Enhanced Magnetic Anisotropy In Cobalt-Carbide Nanoparticles, Ahmed A. El-Gendy, Meichun Qian, Zachary J. Huba, Shiv N. Khanna, Everett E. Carpenter

Chemistry Publications

An outstanding problem in nano-magnetism is to stabilize the magnetic order in nanoparticles at room temperatures. For ordinary ferromagnetic materials, reduction in size leads to a decrease in the magnetic anisotropy resulting in superparamagnetic relaxations at nanoscopic sizes. In this work, we demonstrate that using wet chemical synthesis, it is possible to stabilize cobalt carbide nanoparticles which have blocking temperatures exceeding 570 K even for particles with magnetic domains of 8 nm. First principles theoretical investigations show that the observed behavior is rooted in the giant magnetocrystalline anisotropies due to controlled mixing between C p- and Co d-states.

Nanoconfined Water Under Electric Field At Constant Chemical Potential Undergoes Electrostriction, Davide Vanzo, D. Bratko, Alenka Luzar

Chemistry Publications

Electric control of nanopore permeation by water and solutions enables gating in membrane ion channels and can be exploited for transient surface tuning of rugged substrates, to regulate capillary permeability in nanofluidics, and to facilitate energy absorption in porous hydrophobic media. Studies of capillary effects, enhanced by miniaturization, present experimental challenges in the nanoscale regime thus making molecular simulations an important complement to direct measurement. In a molecular dynamics (MD) simulation, exchange ofwater between the pores and environment requires modeling of coexisting confined and bulk phases, with confined water under the field maintaining equilibrium with the unperturbed environment. In the …

Unconventional Hydrogen Bonding To Organic Ions In The Gas Phase: Stepwise Association Of Hydrogen Cyanide With The Pyridine And Pyrimidine Radical Cations And Protonated Pyridine, Ahmed M. Hamid, M. Samy El-Shall, Rifaat Hilal, Shaaban Elroby, Saadullah G. Aziz

Chemistry Publications

Equilibrium thermochemical measurements using the ion mobility drift cell technique have been utilized to investigate the binding energies and entropy changes for the stepwise association of HCN molecules with the pyridine and pyrimidine radical cations forming the C5H5N^+· (HCN)nand C4H4N2 ^+· (HCN)n clusters, respectively, with n = 1–4. For comparison, the binding of 1–4 HCN molecules to the protonated pyridine C5H5NH⁺(HCN)n has also been investigated. The binding energies of HCN to the pyridine and pyrimidine radical cations are nearly equal (11.4 and 12.0 kcal/mol, respectively) but weaker than the HCN binding to the protonated pyridine (14.0 kcal/mol). …

Wetting Transparency Of Graphene In Water, J. Driskill, D. Vanzo, D. Bratko, A. Luzar

Chemistry Publications

Measurements of contact angle on graphene sheets show a notable dependence on the nature of the underlying substrate, a phenomenon termed wetting transparency. Our molecular modeling studies reveal analogous transparency in case of submerged graphene fragments in water. A combined effect of attractive dispersion forces, angle correlations between aqueous dipoles, and repulsion due to the hydrogen-bond-induced orientation bias in polarized hydration layers acting across graphene sheet, enhances apparent adhesion of water to graphene. We show wetting free energy of a fully wetted graphene platelet to be about 8 mNm−1 lower than for graphene wetted only on one side, which gives …

R Code To Accompany “Principal Component Analysis And Optimization: A Tutorial”, Robert Reris, J. Paul Brooks

Statistical Sciences and Operations Research Data

This data accompanies "Principal Component Analysis and Optimization: A Tutorial" by Robert Reris and J. Paul Brooks, presented at the 2015 INFORMS Computing Society Conference, Operations Research and Computing: Algorithms and Software for Analytics, Richmond, Virginia January 11-13, 2015.

The data contains R code, output, and comments that follow the examples for principal component analysis in the paper.

Astroecology, Cosmo-Ecology, And The Future Of Life, Michael Noah Mautner

Chemistry Publications

Astroecology concerns the relations between life and space resources, and cosmo-ecology extrapolates these relations to cosmological scales. Experimental astroecology can quantify the amounts of life that can be derived from space resources. For this purpose, soluble carbon and electrolyte nutrients were measured in asteroid/meteorite materials. Microorganisms and plant cultures were observed to grow on these materials, whose fertilities are similar to productive agricultural soils. Based on measured nutrient contents, the 10²² kg carbonaceous asteroids can yield 10¹⁸ kg biomass with N and P as limiting nutrients (compared with the estimated 10¹⁵ kg biomass on Earth). These data …

A Novel Two-Laser Interface For Coupling Capillary Electrochromatography With Ion-Trap Time-Of-Flight Mass Spectrometry, David C. Simpson, Alexander J. Yates, John H. Knox, Pat R.R. Langridge-Smith

Chemistry Publications

An interface has been developed for the hyphenation of capillary electrochromatography (CEC) with mass spectrometry (MS). Chromatographic eluate vaporization and selective analyte ionization occur within a quadrupole ion-trap, which permits significant instrument simplification when compared with the atmospheric pressure interfaces typically used for CEC-MS. Vaporization is achieved using laser desorption at 1064 nm while ionization is accomplished through UV photoionization. This two-step approach, through ionization laser wavelength selection, can provide ultratrace analysis with high selectivity. The mass spectrometer is a hybrid ion-trap time-of-flight (TOF) instrument in which the ion-trap is used in radio frequency-only mode, with DC-pulse ejection, to provide …

Proton-Bound Dimers Of Nitrogen Heterocyclic Molecules: Substituent Effects On The Structures And Binding Energies Of Homodimers Of Diazine, Triazine, And Fluoropyridine, Isaac K. Attah, Sean P. Platt, Michael Mautner, M. S. El-Shall, Saadullah G. Aziz, Abdulrahman O. Alyoubi

Chemistry Publications

The bonding energies of proton-bound homodimers BH⁺B were measured by ion mobilityequilibrium studies and calculated at the DFT B3LYP/6-311++G^{* *} level, for a series of nitrogen heterocyclic molecules (B) with electron-withdrawing in-ring N and on-ring F substituents. The binding energies (ΔH°dissoc) of the proton-bound dimers (BH⁺B) vary significantly, from 29.7 to 18.1 kcal/mol, decreasing linearly with decreasing the proton affinity of the monomer (B). This trend differs significantly from the constant binding energies of most homodimers of other organic nitrogen and oxygen bases. The experimentally measured ΔH°dissoc for (1,3-diazine)2H⁺, i.e., (pyrimidine)2H⁺ and …

Direct Observation Of Metal Nanoparticles As Heterogeneous Nuclei For The Condensation Of Supersaturated Organic Vapors: Nucleation Of Size-Selected Aluminum Nanoparticles In Acetonitrile And N-Hexane Vapors, Victor Abdelsayed, M. Samy El-Shall

Chemistry Publications

This work reports the direct observation and separation of size-selected aluminum nanoparticlesacting as heterogeneous nuclei for the condensation of supersaturated vapors of both polar and nonpolar molecules. In the experiment, we study the condensation of supersaturated acetonitrile and n-hexane vapors on charged and neutral Al nanoparticles by activation of the metalnanoparticles to act as heterogeneous nuclei for the condensation of the organic vapor.Aluminum seed nanoparticles with diameters of 1 and 2 nm are capable of acting as heterogeneous nuclei for the condensation of supersaturated acetonitrile and hexane vapors. The comparison between the Kelvin and Fletcher diameters indicates that for theheterogeneous …

18-Electron Rule Inspired Zintl-Like Ions Composed Of All Transition Metals, Jian Zhou, Santanab Giri, Purusottam Jena

Physics Publications

Zintl phase compounds constitute a unique class of compounds composed of metal cations and covalently bonded multiply charged cluster anions. Potential applications of these materials in solution chemistry and thermoelectric materials have given rise to renewed interest in the search for new Zintl ions. Up to now these ions have been mostly composed of group 13, 14, and 15 post-transition metal elements and no Zintl ions composed of all transition metal elements are known. Using gradient corrected density functional theory we show that the 18-electron rule can be applied to design a new class of Zintl-like ions composed of all …

Potential Of Zro Clusters As Replacement Pd Catalyst, Swayamprabha Behera, Nicholas King, Devleena Samanta, Puru Jena

Physics Publications

Atomic clusters with specific size and composition and mimicking the chemistry of elements in the periodic table are commonly known as superatoms. It has been suggested that superatoms could be used to replace elements that are either scarce or expensive. Based on a photoelectron spectroscopy experiment of negatively charged ions, Castleman and co-workers [Proc. Natl. Acad. Sci. U.S.A.107, 975 (2010)] have recently shown that atoms of Ni, Pd, and Pt which are well known for their catalytic properties, have the same electronic structure as their counterpart isovalent diatomic species, TiO, ZrO, and WC, respectively. Based on this similarity they have …

The Viability Of Aluminum Zintl Anion Moieties Within Magnesium-Aluminum Clusters, Haopeng Wang, Yeon Jae Ko, Xinxing Zhang, Gerd Gantefoer, Hansgeorg Schnoeckel, Bryan W. Eichhorn, Puru Jena, Boggavarapu Kiran, Anil K. Kandalam, Kit H. Bowen Jr.

Physics Publications

Through a synergetic combination of anion photoelectron spectroscopy and density functional theory based calculations, we have investigated the extent to which the aluminum moieties within selected magnesium-aluminum clusters are Zintl anions. Magnesium-aluminum cluster anions were generated in a pulsed arc discharge source. After mass selection, photoelectron spectra of Mg m Al n ⁻ (m, n = 1,6; 2,5; 2,12; and 3,11) were measured by a magnetic bottle, electron energy analyzer. Calculations on these four stoichiometries provided geometric structures and full charge analyses for the cluster anions and their neutral cluster counterparts, as well as photodetachment transition energies (stick spectra). Calculations …

Aluminum Zintl Anion Moieties Within Sodium Aluminum Clusters, Haopeng Wang, Xinxing Zhang, Yeon Jae Ko, Andrej Grubisic, Xiang Li, Gerd Gantefoer, Hansgeorg Schnoeckel, Bryan W. Eichhorn, Mal-Soon Lee, Puru Jena, Anil K. Kandalam, Boggavarapu Kiran, Kit H. Bowen Jr.

Physics Publications

Through a synergetic combination of anion photoelectron spectroscopy and density functional theory based calculations, we have established that aluminum moieties within selected sodium-aluminum clusters are Zintl anions. Sodium–aluminum cluster anions, Na m Al n ⁻, were generated in a pulsed arc discharge source. After mass selection, their photoelectron spectrawere measured by a magnetic bottle, electron energy analyzer. Calculations on a select sub-set of stoichiometries provided geometric structures and full charge analyses for both cluster anions and their neutral cluster counterparts, as well as photodetachment transition energies (stickspectra), and fragment molecular orbital based correlation diagrams.

Live Cell Interferometry Quantifies Dynamics Of Biomass Partitioning During Cytokinesis, Thomas A. Zangle, Michael A. Teitell, Jason Reed

Physics Publications

The equal partitioning of cell mass between daughters is the usual and expected outcome of cytokinesis for self-renewing cells. However, most studies of partitioning during cell division have focused on daughter cell shape symmetry or segregation of chromosomes. Here, we use live cell interferometry (LCI) to quantify the partitioning of daughter cell mass during and following cytokinesis. We use adherent and non-adherent mouse fibroblast and mouse and human lymphocyte cell lines as models and show that, on average, mass asymmetries present at the time of cleavage furrow formation persist through cytokinesis. The addition of multiple cytoskeleton-disrupting agents leads to increased …

Time-Resolved Photoluminescence From Defects In N-Type Gan, Michael A. Reshchikov

Physics Publications

Point defects in GaN were studied with time-resolved photoluminescence (PL). The effects of temperature and excitation intensity on defect-related PL have been investigated theoretically and experimentally. A phenomenological model, based on rate equations, explains the dependence of the PL intensity on excitation intensity, as well as the PL lifetime and its temperature dependence. We demonstrate that time-resolved PL measurements can be used to find the concentrations of free electrons and acceptors contributing to PL in n-type semiconductors.

Surface Diffusion Driven Morphological Instability In Free-Standing Nickel Nanorod Arrays, Ebtihaj Alrashid Jr., Dexian Ye

Physics Publications

Metallic nanostructures are thermodynamically unstable due to the excess of energy of large numbers of surface atoms. Morphological instability, such as Rayleigh breakup, sintering, and coalescence, can be observed at a temperature much lower than the bulk melting point of the metal. We study the morphological and crystalline evolution of well-aligned free-standing nickelnanorod arrays at elevated temperatures up to 600 °C. The as-deposited nickel nanorods are faceted with sharp nanotips, which are deformed at annealing temperatures higher than 400 °C due to strong surface diffusion. A mud-crack like pattern is formed in the samples annealed above 400 °C, leading to …

Lattice Thermal Conductivity In Bulk And Nanosheet Naxcoo2, Denis Demchenko, David B. Ameen

Physics Publications

In this paper we present the results of calculations of the lattice thermal conductivity of layered complex metal oxide Na_xCoO₂ within the Green–Kubo theory. Using Na_xCoO₂ we identify the two competing mechanisms responsible for the favorable scaling properties of the Green–Kubo method for calculating the lattice thermal conductivity. The artificial correlations of the heat flux fluctuations due to the finite size of the supercells are partially cancelled by the missing long wavelength acoustic phonon modes. We compute the lattice thermoelectric properties of bulk Na_xCoO₂ with varying stoichiometry, structural defects, and temperature. …

Green Luminescence In Mg-Doped Gan, Michael A. Reshchikov, Denis Demchenko, J. D. Mcnamara, S. Fernández-Garrido, R. Calarco

Physics Publications

A majority of the point defects in GaN that are responsible for broad photoluminescence (PL) bands remain unidentified. One of them is the green luminescence band (GL2) having a maximum at 2.35 eV which was observed previously in undoped GaN grown by molecular-beam epitaxy in Ga-rich conditions. The same PL band was observed in Mg-doped GaN, also grown in very Ga-rich conditions. The unique properties of the GL2 band allowed us to reliably identify it in different samples. The best candidate for the defect which causes the GL2 band is a nitrogen vacancy (VN). We propose that transitions of electrons …

Temperature Dependence Of Defect-Related Photoluminescence In Iii-V And Ii-Vi Semiconductors, Michael A. Reshchikov

Physics Publications

Mechanisms of thermal quenching of photoluminescence (PL) related to defects insemiconductors are analyzed. We conclude that the Schön-Klasens (multi-center) mechanism of the thermal quenching of PL is much more common for defects in III–V and II–VI semiconductorsas compared to the Seitz-Mott (one-center) mechanism. The temperature dependencies of PLare simulated with a phenomenological model. In its simplest version, three types of defects are included: a shallow donor, an acceptor responsible for the PL, and a nonradiative center that has the highest recombination efficiency. The case of abrupt and tunable thermal quenching ofPL is considered in more detail. This phenomenon is predicted …

Time-Resolved Photoluminescence From Defects In N-Type Gan, Michael A. Reshchikov

Physics Publications

Point defects in GaN were studied with time-resolved photoluminescence (PL). The effects of temperature and excitation intensity on defect-related PL have been investigated theoretically and experimentally. A phenomenological model, based on rate equations, explains the dependence of the PL intensity on excitation intensity, as well as the PL lifetime and its temperature dependence. We demonstrate that time-resolved PL measurements can be used to find the concentrations of free electrons and acceptors contributing to PL in n-type semiconductors.

Carbon Defects As Sources Of The Green And Yellow Luminescence Bands In Undoped Gan, Michael A. Reshchikov, Denis Demchenko, A. Usikov, H. Helava, Yu Makarov

Physics Publications

In high-purity GaN grown by hydride vapor phase epitaxy, the commonly observed yellow luminescence (YL) band gives way to a green luminescence (GL) band at high excitation intensity. We propose that the GL band with a maximum at 2.4 eV is caused by transitions of electrons from the conduction band to the 0/+ level of the isolated CN defect. The YL band, related to transitions via the −/0 level of the same defect, has a maximum at 2.1 eV and can be observed only for some high-purity samples. However, in less pure GaN samples, where no GL band is observed, …

Aromatic Superhalogens, Brandon Child, Santanab Giri, Scott Gronert, Puru Jena

Physics Publications

No organic molecules with electron affinities near or above those of halogens are known. We show for the first time that aromaticity rules can be used to design molecules with electron affinities far exceeding those of halogen atoms either by tailoring the ligands of cyclopentadienyl or by multiple benzo-annulations of cyclopentadienyl in conjunction with the substitution of CH groups with isoelectronic N atoms. Results based on density functional theory reveal that the electron affinities of some of these organic molecules can reach as high as 5.59 eV, thus opening the door to new class of superhalogens that contain neither a …

Self-Consistent Determination Of Hubbard U For Explaining The Anomalous Magnetism Of The Gd13 Cluster, Kun Tao, Jian Zhou, Qiang Sun, Qian Wang, V. S. Stepanyuk, Puru Jena

Physics Publications

The effective on-site Coulomb interaction (Hubbard U) is an important parameter for studying strongly correlated systems. While U is determined empirically by fitting to bulk values, its value for a cluster with a finite number of atoms remains uncertain. Here, we choose Gd13 as a prototypical example of a strongly correlated cluster. Contrary to the well-known results in transition-metal clusters where magnetic moments of clusters are larger than their bulk, in Gd13 cluster the magnetic moment issmaller than its bulk value. Using density functional theory and the linear response approach, we determine U self-consistently for the cluster and apply …

Tailoring Li Adsorption On Graphene, Jian Zhou, Qiang Sun, Qian Wang, Puru Jena

Physics Publications

The technological potential of functionalized graphene has recently stimulated considerable interest in the study of the adsorption of metal atoms on graphene. However, a complete understanding of the optimal adsorption pattern of metal atoms on a graphene substrate has not been easy because of atomic relaxations at the interface and the interaction between metal atoms. We present a partial particle swarm optimization technique that allows us to efficiently search for the equilibrium geometries of metal atoms adsorbed on a substrate as a function of adatom concentration. Using Li deposition on graphene as an example we show that, contrary to previous …

Life2cl N (N = 4–6) Clusters: Double-Exchange Mediated Molecular Magnets, Kalpataru Pradhan, Purusottam Jena

Physics Publications

A systematic study of LiFe2Cl n (n = 4–6) clusters, based on gradient corrected density functional theory (DFT), shows that the electron contributed by Li can transform antiferromagnetic Fe2Cl n(n = 4 and 6) clusters into ferromagnetic clusters. In Fe2Cl6 (Fe2Cl4) cluster, the Fe atoms in +3 (+2) oxidation states are aligned antiferromagnetically, consistent with the super-exchange model. The extra electron from Li atom creates a charge disproportionation in the LiFe2Cl6(LiFe2Cl4) cluster that mediates the double-exchange interaction between the Fe atoms.Antiferromagnetic to ferromagnetic transition can also be induced by hole doping as seen to be the case with Fe2Cl5 which …

Fine Structure Of The Red Luminescence Band In Undoped Gan, Michael A. Reshchikov, A. Usikov, H. Helava, Yu. Makarov

Physics Publications

Many point defects in GaN responsible for broad photoluminescence (PL) bands remain unidentified. Their presence in thick GaN layers grown by hydride vapor phase epitaxy (HVPE) detrimentally affects the material quality and may hinder the use of GaN in high-power electronic devices. One of the main PL bands in HVPE-grown GaN is the red luminescence (RL) band with a maximum at 1.8 eV. We observed the fine structure of this band with a zero-phonon line (ZPL) at 2.36 eV, which may help to identify the related defect. The shift of the ZPL with excitation intensity and the temperature-related transformation of …

Green Luminescence In Mg-Doped Gan, Michael A. Reshchikov, Denis Demchenko, J. D. Mcnamara, S. Fernández-Garrido, R. Calarco

Physics Publications

A majority of the point defects in GaN that are responsible for broad photoluminescence (PL) bands remain unidentified. One of them is the green luminescence band (GL2) having a maximum at 2.35 eV which was observed previously in undoped GaN grown by molecular-beam epitaxy in Ga-rich conditions. The same PL band was observed in Mg-doped GaN, also grown in very Ga-rich conditions. The unique properties of the GL2 band allowed us to reliably identify it in different samples. The best candidate for the defect which causes the GL2 band is a nitrogen vacancy (VN). We propose that transitions of electrons …

Electronic Structure And Magnetic Properties Of Mn And Fe Impurities Near The Gaas (110) Surface, M. R. Mahani, M. Fhokrul Islam, A. Pertsova, C. M. Canali

Physics Publications

Combining density functional theory calculations and microscopic tight-binding models, we investigate theoretically the electronic and magnetic properties of individual substitutional transition-metal impurities (Mn and Fe) positioned in the vicinity of the (110) surface of GaAs. For the case of the [Mn2+]0 plus acceptor-hole (h) complex, the results of a tight-binding model including explicitly the impurity delectrons are in good agreement with approaches that treat the spin of the impurity as an effective classical vector. For the case of Fe, where both the neutral isoelectronic [Fe3+]0 and the ionized [Fe2+]− states are relevant to address scanning tunneling microscopy (STM) …

Ideal Projections And Forcing Projections, Sean Cox, Martin Zeman

Mathematics and Applied Mathematics Publications

It is well known that saturation of ideals is closely related to the “antichain-catching” phenomenon from Foreman-Magidor-Shelah [10]. We consider several antichain-catching properties that are weaker than saturation, and prove: (1) If I is a normal ideal on ω2 which satisfies stationary antichain catching, then there is an inner model with a Woodin cardinal; (2) For any n ∈ ω, it is consistent relative to large cardinals that there is a normal ideal I on ωn which satisfies projective antichain catching, yet I is not saturated (or even strong). This provides a negative answer to Open Question number 13 from …

Data Files To Accompany "The Support Vector Machine And Mixed Integer Linear Programming: Ramp Loss Svm With L1-Norm Regularization", Eric J. Hess, J. Paul Brooks

Statistical Sciences and Operations Research Data

These files accompany, "The Support Vector Machine and Mixed Integer Linear Programming: Ramp Loss SVM with L1-Norm Regularization" by Eric J. Hess and J. Paul Brooks, presented at the 2015 INFORMS Computing Society Conference, Operations Research and Computing: Algorithms and Software for Analytics, Richmond, Virginia January 11-13, 2015.

The files contain instances of optimization problems that are described in the paper and for which results are reported. The files are in CPLEX LP format. The naming convention of the files is as follows: ndBTj0F.lp, where is the number of samples, is the number of attributes, and refers to …