Dark matter halos in the multicomponent model. II. Density profiles of galactic halos

The multicomponent dark matter model with self-scattering and inter-conversions of species into one another is an alternative dark matter paradigm that is capable of resolving the long-standing problems of $\Lambda$CDM cosmology at small scales. In this paper, we have studied in detail the properties of dark matter halos with $M \sim 4-5 \times10^{11} M_{\odot}$ obtained in $N$-body cosmological simulations with the simplest two-component (2cDM) model. A large set of velocity-dependent cross-section prescriptions for elastic scattering and mass conversions, $\sigma_s(v)\propto v^{a_s}$ and $\sigma_c(v)\propto v^{a_c}$, has been explored and the results were compared with observational data. The results demonstrate that self-interactions with the cross-section per particle mass evaluated at $v=100$ km s$^{-1}$ being in the range of $0.01\lesssim \sigma_0/m\lesssim 1$ cm$^2$g$^{-1}$ robustly suppress central cusps, thus resolving the core-cusp problem. The core radii are controlled by the values of $\sigma_0/m$ and the DM cross-section's velocity-dependent power-law indices $(a_s,a_c)$, but are largely insensitive to the species' mass degeneracy. These values are in full agreement with those resolving the substructure and too-big-to-fail problems. We have also studied the evolution of halos in the 2cDM model with cosmic time.Comment: 17 pages, 13 figure

Highly Efficient, Living Coordinative Chain-Transfer Polymerization of Propene with ZnEt₂: Practical Production of Ultrahigh to Very Low Molecular Weight Amorphous Atactic Polypropenes of Extremely Narrow Polydispersity

Highly efficient, living coordinative chain-transfer polymerization (CCTP) of propene can be conducted with the highly active catalyst derived from equimolar amounts of (η5-C5Me5)Hf(Me)2[N(Et)C(Me)N(Et)] (2), and the borate, [PhNMe2H][B(C6F5)4] (3), in toluene at 0 °C, in the presence of varying molar equivalents of ZnEt2 to provide practical quantities (vis-à-vis, living Ziegler−Natta polymerization) of a series of amorphous atactic polypropene (a-PP) samples. These samples are distinguished by having tunable molecular weights ranging from ultrahigh, in the absence of CCTP, to very high to very low when CCTP is conducted with increasing initial equivalents of ZnEt2all the while maintaining extremely narrow polydispersities

Highly Efficient, Living Coordinative Chain-Transfer Polymerization of Propene with ZnEt₂: Practical Production of Ultrahigh to Very Low Molecular Weight Amorphous Atactic Polypropenes of Extremely Narrow Polydispersity

Highly efficient, living coordinative chain-transfer polymerization (CCTP) of propene can be conducted with the highly active catalyst derived from equimolar amounts of (η5-C5Me5)Hf(Me)2[N(Et)C(Me)N(Et)] (2), and the borate, [PhNMe2H][B(C6F5)4] (3), in toluene at 0 °C, in the presence of varying molar equivalents of ZnEt2 to provide practical quantities (vis-à-vis, living Ziegler−Natta polymerization) of a series of amorphous atactic polypropene (a-PP) samples. These samples are distinguished by having tunable molecular weights ranging from ultrahigh, in the absence of CCTP, to very high to very low when CCTP is conducted with increasing initial equivalents of ZnEt2all the while maintaining extremely narrow polydispersities

Ferrocene-Based Nanoelectronics: Regioselective Syntheses and Electrochemical Characterization of α-Monothiol and α,ω-Dithiol, Phenylethynyl-Conjugated, 2,5-Diethynylpyridyl- and Pyridinium-Linked Diferrocene Frameworks Having an End-to-End Distance of ∼4 nm

Regiospecific synthetic methods have been developed for the assembly of unsymmetric conjugated molecular frameworks containing 2,5-diethynylpyridyl- and 2,5-diethynylpyridinium-linked diferrocene structures and possessing either mono- or dithioacetate end-groups that are suitable for chemisorption onto Au(111) substrates after conversion to the corresponding thiol derivatives. Electronic spectra and solution electrochemistry of these and model compounds establish the electron-withdrawing character of a 2,5-dimethoxyphenylethynyl substituent on ferrocene that serves to shift the Fe(II)/Fe(III) redox couple to higher potentials. Further, while the unsymmetric nature of the 2,5-diethynylpyridyl bridge in 3 does not differentially perturb the redox couples of the two ferrocenes (ΔE1/2 4 now produces a large separation in the two redox potentials (ΔE1/2 = 190 mV). For the two regioisomeric monothioacetate compounds bearing a terminal 2,5-diethynylpyridyl-linked diferrocene unit, 5 and 6 (and their respective pyridinium counterparts, 7 and 8), redox potentials of the two ferrocenes are found to be either widely separated or similar in value depending upon the added influence of the 2,5-dimethoxyphenylethynyl group (e.g., ΔE1/2 = 310 mV in 7 vs ∼50 mV in 8)

Ferrocene-Based Nanoelectronics: 2,5-Diethynylpyridine as a Reversible Switching Element

A new strategy is presented for the construction of a ferrocene-based molecular diode that operates by an electron-hopping mechanism. Key to this design is implementation of the asymmetric 2,5-diethynylpyridine bridging unit that serves to reversibly switch the system between two states. Results of investigations of the molecular and electronic structures of the diferrocene complexes 1 and 2, which respectively serve as models for state 1 and state 2, establish that the criteria for the new strategy can likely be met with the 2,5-diethynylpyridine bridge

Stereospecific Living Ziegler−Natta Polymerization via Rapid and Reversible Chloride Degenerative Transfer between Active and Dormant Sites

The successful realization of a stereospecific chloride degenerative transfer living Ziegler−Natta polymerization process that provides isotactic polyolefins of narrow polydispersity (Mw/Mn ≤ 1.05) is documented. Variable-temperature NMR studies confirm the configurational stability of all species with respect to metal-centered epimerization and large magnitudes for both kβ and k-β. Additional kinetic analyses with an increasing concentration of the dormant state establish that kβ is larger than k-β. Finally, [Et3Si][B(C6F5)4] has been shown to be an effective substoichiometric halide abstractor for chloride degenerative transfer Ziegler−Natta polymerization

Rapid Access to Dimethylcyclopentadienyltitanium(IV) Amidinate, (C₅R₅)TiMe₂[NR¹C(R²)NR³] (R = H and Me; R² = Me), Libraries

Facile insertion of carbodiimides, R1NCNR3, into a Ti−CMe bond of (C5R5)TiMe3 (R = H and Me) (2a and 2b, respectively) in pentane solutions at 25 °C provides a wide range of derivatives of (C5R5)TiMe2[NR1C(Me)NR3] (1) in high yield. Low barriers to racemization (≤15 kcal mol-1) have been determined for derivatives of 1 where R1 ≠ R3, and further, a preliminary screen has found some of these to be Ziegler−Natta catalyst precursors for the polymerization of ethylene upon activation with methylaluminoxane

Highly Branched, High Molecular Weight Polystannane from Dibutylstannane via a Novel Dehydropolymerization/Rearrangement Process

Highly Branched, High Molecular Weight Polystannane from Dibutylstannane via a Novel Dehydropolymerization/Rearrangement Proces

Nucleophilic Character of a Charge Neutral, High Oxidation State d⁰ Zirconium Trimethylenemethane Complex

The nucleophilic character of a charge neutral, high oxidation d0 zirconium trimethylenemethane (TMM) class of compound of general structure Cp*Zr(TMM)[N(R)C(Me)N(R)], 1a (R1 = R2 = i-Pr) and 1b (R1 = t-Bu, R2 = Et), is presented through documentation of its reactivity with a range of alkyl and silyl halides and triflates, including unactivated ones such as ethyl triflate. These results should contribute to efforts directed toward expanding the synthetic chemist's toolbox of synthetic methods for the construction of complex organic molecules

Facile Formation of a μ-[σ²,η³-C₄H₅], μ-Hydrido Dizirconium Complex through Multiple Intra- and Intermolecular C−H Bond Activations of an Isobutyl Group

Thermolysis of (η5-C5Me5)Zr(i-Bu)2[N(t-Bu)C(Me)N(Et)] (3) at 50 °C in benzene ultimately produces, in high yield, the μ-hydrido dizirconium complex 6 that bears a novel μ-[σ2,η3-C4H5] fragment arising from multiple intra- and intermolecular C−H bond activations of an isobutyl group