Ab initio molecular dynamics simulations of Aluminum solvation

The solvation of Al and its hydrolyzed species in water clusters has been studied by means of ab initio molecular dynamics simulations. The hexa-hydrate aluminum ion formed a stable complex in the finite temperature cluster simulation of one aluminum ion and 16 waters. The average dipole moment of strongly polarized hydrated water molecules in the first solvation shell of the hexa-hydrate aluminum ion was found to be 5.02 Debye. The deprotonated hexa-hydrate complex evolves into a tetra-coordinated aluminate ion with two water molecules in the second solvation shell forming hydrogen bonds to the hydroxyl groups in agreement with the observed coordination.Comment: 12 pages in Elsevier LaTeX, 5 figures in Postscript, 2 last figures are in color, submitted to Chemical Physics Letter

Generation of Long-Lived Isomeric States via Bremsstrahlung Irradiation

A method to generate long-lived isomeric states effectively for Mossbauer applications is reported. We demonstrate that this method is better and easier to provide highly sensitive Mossbauer effect of long-lived isomers (>1ms) such as 103Rh. Excitation of (gamma,gamma) process by synchrotron radiation is painful due mainly to their limited linewidth. Instead,(gamma,gamma') process of bremsstrahlung excitation is applied to create these long-lived isomers. Isomers of 45Sc, 107Ag, 109Ag, and 103Rh have been generated from this method. Among them, 103Rh is the only one that we have obtained the gravitational effect at room temperature.Comment: ICAME 05 conference repor

Algorithms to Measure Diversity and Clustering in Social Networks through Dot Product Graphs

Social networks are often analyzed through a graph model of the network. The dot product model assumes that two individuals are connected in the social network if their attributes or opinions are similar. In the model, a d-dimensional vector a v represents the extent to which individual v has each of a set of d attributes or opinions. Then two individuals u and v are assumed to be friends, that is, they are connected in the graph model, if and only if a u · a v  ≥ t, for some fixed, positive threshold t. The resulting graph is called a d-dot product graph.. We consider two measures for diversity and clustering in social networks by using a d-dot product graph model for the network. Diversity is measured through the size of the largest independent set of the graph, and clustering is measured through the size of the largest clique. We obtain a tight result for the diversity problem, namely that it is polynomial-time solvable for d = 2, but NP-complete for d ≥ 3. We show that the clustering problem is polynomial-time solvable for d = 2. To our knowledge, these results are also the first on the computational complexity of combinatorial optimization problems on dot product graphs. We also consider the situation when two individuals are connected if their preferences are not opposite. This leads to a variant of the standard dot product graph model by taking the threshold t to be zero. We prove in this case that the diversity problem is polynomial-time solvable for any fixed d

Charmless Exclusive Baryonic B Decays

We present a systematical study of two-body and three-body charmless baryonic B decays. Branching ratios for two-body modes are in general very small, typically less than $10^{-6}$, except that \B(B^-\to p \bar\Delta^{--})\sim 1\times 10^{-6}. In general, $\bar B\to N\bar\Delta>\bar B\to N\bar N$ due to the large coupling constant for $\Sigma_b\to B\Delta$. For three-body modes we focus on octet baryon final states. The leading three-dominated modes are $\bar B^0\to p\bar n\pi^-(\rho^-), n\bar p\pi^+(\rho^+)$ with a branching ratio of order $3\times 10^{-6}$ for $\bar B^0\to p\bar n\pi^-$ and $8\times 10^{-6}$ for $\bar B^0\to p\bar n\rho^-$. The penguin-dominated decays with strangeness in the meson, e.g., $B^-\to p\bar p K^{-(*)}$ and $\bar B^0\to p\bar n K^{-(*)}, n\bar n \bar K^{0(*)}$, have appreciable rates and the $N\bar N$ mass spectrum peaks at low mass. The penguin-dominated modes containing a strange baryon, e.g., $\bar B^0\to \Sigma^0\bar p\pi^+, \Sigma^-\bar n\pi^+$, have branching ratios of order $(1\sim 4)\times 10^{-6}$. In contrast, the decay rate of $\bar B^0\to\Lambda\bar p\pi^+$ is smaller. We explain why some of charmless three-body final states in which baryon-antibaryon pair production is accompanied by a meson have a larger rate than their two-body counterparts: either the pole diagrams for the former have an anti-triplet bottom baryon intermediate state, which has a large coupling to the $B$ meson and the nucleon, or they are dominated by the factorizable external $W$-emission process.Comment: 46 pages and 3 figures, to appear in Phys. Rev. D. Major changes are: (i) Calculations of two-body baryonic B decays involving a Delta resonance are modified, and (ii) Penguin-dominated modes B-> Sigma+N(bar)+p are discusse

The Proton Spin and Flavor Structure in the Chiral Quark Model

After a pedagogical review of the simple constituent quark model and deep inelastic sum rules, we describe how a quark sea as produced by the emission of internal Goldstone bosons by the valence quarks can account for the observed features of proton spin and flavor structures. Some issues concerning the strange quark content of the nucleon are also discussed.Comment: 59 pages with table of contents, Lecture delivered at the Schladming Winter School (March 1997), to be published by Springer-Verlag under the title "Computing Particle Properties" (eds. C. B. Lang and H. Gausterer

The lifetime of B_c-meson and some relevant problems

The lifetime of the B_c-meson is estimated with consistent considerations on all of the heavy mesons ($B^0, B^\pm, B_s, D^0, D^\pm D_s$) and the double heavy meson B_c. In the estimate, the framework, where the non-spectator effects for nonleptonic decays are taken into account properly, is adopted, and the parameters needed to be fixed are treated carefully and determined by fitting the available data. The bound-state effects in it are also considered. We find that in decays of the meson B_c, the QCD correction terms of the penguin diagrams and the main component terms c_1O_1, c_2O_2 of the effective interaction Lagrangian have direct interference that causes an enhancement about 3 ~ 4% in the total width of the B_c meson.Comment: 27 pages, 0 figur

Neutrino Propagation in a Strongly Magnetized Medium

We derive general expressions at the one-loop level for the coefficients of the covariant structure of the neutrino self-energy in the presence of a constant magnetic field. The neutrino energy spectrum and index of refraction are obtained for neutral and charged media in the strong-field limit ($M_{W}\gg \sqrt{B}\gg m_{e},T,\mu ,| \mathbf{p}|$) using the lowest Landau level approximation. The results found within the lowest Landau level approximation are numerically validated, summing in all Landau levels, for strong $B\gg T^{2}$ and weakly-strong $B \gtrsim T^{2}$ fields. The neutrino energy in leading order of the Fermi coupling constant is expressed as the sum of three terms: a kinetic-energy term, a term of interaction between the magnetic field and an induced neutrino magnetic moment, and a rest-energy term. The leading radiative correction to the kinetic-energy term depends linearly on the magnetic field strength and is independent of the chemical potential. The other two terms are only present in a charged medium. For strong and weakly-strong fields, it is found that the field-dependent correction to the neutrino energy in a neutral medium is much larger than the thermal one. Possible applications to cosmology and astrophysics are considered.Comment: 23 pages, 4 figures. Corrected misprints in reference

Dynamic p-enrichment schemes for multicomponent reactive flows

We present a family of p-enrichment schemes. These schemes may be separated into two basic classes: the first, called \emph{fixed tolerance schemes}, rely on setting global scalar tolerances on the local regularity of the solution, and the second, called \emph{dioristic schemes}, rely on time-evolving bounds on the local variation in the solution. Each class of $p$-enrichment scheme is further divided into two basic types. The first type (the Type I schemes) enrich along lines of maximal variation, striving to enhance stable solutions in "areas of highest interest." The second type (the Type II schemes) enrich along lines of maximal regularity in order to maximize the stability of the enrichment process. Each of these schemes are tested over a pair of model problems arising in coastal hydrology. The first is a contaminant transport model, which addresses a declinature problem for a contaminant plume with respect to a bay inlet setting. The second is a multicomponent chemically reactive flow model of estuary eutrophication arising in the Gulf of Mexico.Comment: 29 pages, 7 figures, 3 table

Asymmetry of Strange Sea in Nucleons

Based on the finite-temperature field theory, we evaluate the medium effects in nucleon which can induce an asymmetry between quarks and antiquarks of the strange sea. The short-distance effects determined by the weak interaction can give rise to $\delta m\equiv \Delta m_s-\Delta m_{\bar s}$ where $\Delta m_{s(\bar s)}$ is the medium-induced mass of strange quark by a few KeV at most, but the long-distance effects by strong interaction are sizable. Our numerical results show that there exists an obvious mass difference between strange and anti-strange quarks, as large as 10-100 MeV.Comment: 15 latex pages, 3 figures, to appear in PR

Chiral fermion mass and dispersion relations at finite temperature in the presence of hypermagnetic fields

We study the modifications to the real part of the thermal self-energy for chiral fermions in the presence of a constant external hypermagnetic field. We compute the dispersion relation for fermions occupying a given Landau level to first order in g'^2, g^2 and g_phi^2 and to all orders in g'B, where g' and g are the U(1)_Y and SU(2)_L couplings of the standard model, respectively, g_phi is the fermion Yukawa coupling, and B is the hypermagnetic field strength. We show that in the limit where the temperature is large compared to sqrt{g'B}, left- and right-handed modes acquire finite and different B-dependent masses due to the chiral nature of their coupling with the external field. Given the current bounds on the strength of primordial magnetic fields, we argue that the above is the relevant scenario to study the effects of magnetic fields on the propagation of fermions prior and during the electroweak phase transition.Comment: 11 pages 4 figures, published versio