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

Stereoengineering of Poly(1,3-methylenecyclohexane) via Two-State Living Coordination Polymerization of 1,6-Heptadiene

External control over the rate of dynamic methyl group exchange between configurationally stable active species and configurationally unstable dormant species with respect to chain-growth propagation within a highly stereoselective and regiospecific living coordination polymerization of 1,6-heptadiene has been used to generate a spectrum of different physical forms of poly­(1,3-methylenecyclohexane) (PMCH) in which the stereochemical microstructure has been systematically varied between two limiting forms. The application of this strategy to manipulate the bulk properties of PMCH and the solid-state microphase behavior of well-defined PMCH-<i>b</i>-poly­(1-hexene) block copolymers is further demonstrated

<i>De Novo</i> Design of a New Class of “Hard–Soft” Amorphous, Microphase-Separated, Polyolefin Block Copolymer Thermoplastic Elastomers

Sequential cyclic/linear/cyclic living coordination polymerization of 1,6-heptadiene (HPD), propene, and HPD, respectively, employing the well-defined and soluble group 4 transition-metal initiator, {(η⁵-C₅Me₅)­Hf­(Me)­[N­(Et)­C­(Me)­N­(Et)]}­[B­(C₆F₅)₄], provides the stereoirregular, amorphous poly­(1,3-methylenecyclohexane)-<i>b</i>-atactic polypropene-<i>b</i>-poly­(1,3-methylenecyclohexane) (PMCH-<i>b-</i>aPP-<i>b</i>-PMCH) polyolefin triblock copolymer (<b>I</b>) in excellent yield. By varying the weight fraction of the end group, minor component “hard” PMCH block domains, <i>f</i>_PMCH, relative to that of the midblock “soft” aPP domain, three different compositional grades of these polyolefin block copolymers, <b>Ia–c</b>, were prepared and shown by AFM and TEM to adopt microphase-separated morphologies in the solid state, with spherical and cylindrical morphologies being observed for <i>f</i>_PMCH = 0.09 (<b>Ia</b>) and 0.23 (<b>Ic</b>), respectively, and a third more complex morphology being observed for <b>Ib</b> (<i>f</i>_PMCH = 0.17). Tensile testing of <b>Ia–c</b> served to establish these materials as a new structural class of polyolefin thermoplastic elastomers, with <b>Ia</b> being associated with superior elastic recovery (94 ± 1%) after each of several stress–strain cycles

Regio- and Stereospecific Cyclopolymerization of Bis(2-propenyl)diorganosilanes and the Two-State Stereoengineering of 3,5-<i>cis</i>,<i>isotactic</i> Poly(3,5-methylene-1-silacyclohexane)s

Transition-metal-mediated coordination cyclopolymerization of bis­(2-propenyl)­dimethylsilane (<b>1a</b>) using the <i>C</i>₁-symmetric, group 4 metal preinitiator, (η⁵-C₅Me₅)­Zr­(Me)₂[N­(Et)­C­(Me)­N­(^tBu)] (<b>I</b>), in combination with 1 equiv of the borate coinitiator, [PhNHMe₂]­[B­(C₆F₅)₄] (<b>II</b>), proceeds in a regio- and stereospecific manner to provide highly stereoregular 3,5-<i>cis</i>,<i>isotactic</i> poly­(3,5-methylene-1,1-dimethyl-1-silacyclohexane) (<b>2a</b>). Successful stereoengineering of <b>2a</b> to eliminate undesirable crystallinity while preserving a high <i>T</i>_g value of >120 °C was subsequently accomplished by employing a “two-state” propagation system that uniquely produces an isotactic stereoblock microstructure of decreasing stereoblock length with decreasing percent level of “activation” of <b>I</b> with <b>II</b>. The controlled character of cyclopolymerization of <b>1a</b> using the less sterically encumbered preinitiator, (η⁵-C₅Me₅)­Hf­(Me)₂[N­(Et)­C­(Me)­N­(Et)] (<b>III</b>), and 1 equiv of <b>II</b> was used to prepare well-defined poly­(1-hexene)-<i>b</i>-poly­(3,5-methylene-1-silacyclohexane) block copolymers through sequential monomer additions

Closing the Loop on Transition-Metal-Mediated Nitrogen Fixation: Chemoselective Production of HN­(SiMe₃)₂ from N₂, Me₃­SiCl, and XOH (X = R, R₃Si, or Silica Gel)

Treatment of the Mo­(IV) terminal imido complex, (η⁵-C₅Me₅)­[N­(Et)­C­(Ph)­N­(Et)]­Mo­(NSiMe₃) (<b>3</b>), with a 1:2 mixture of iPrOH and Me₃­SiCl resulted in the rapid formation of the Mo­(IV) dichloride, (η⁵-C₅Me₅)­[N­(Et)­C­(Ph)­N­(Et)]­MoCl₂ (<b>1</b>), and the generation of 1 equiv each of HN­(SiMe₃)₂ and iPrO­SiMe₃. Similarly, a 1:2 mixture of Me₃­SiOH and Me₃­SiCl provided <b>1</b>, HN­(SiMe₃)₂, and O­(SiMe₃)₂. Finally, silica gel, when coupled with excess equivalents of Me₃­SiCl, was also effectively used as the XOH reagent for the generation of <b>1</b> and HN­(SiMe₃)₂. A proposed mechanism for the <b>3</b> → <b>1</b> transformation involves formal addition of HCl across the MoN imido bond through initial hydrogen-bonding between XOH and the N-atom of <b>3</b> to form the adduct <b>IIIb</b>, followed by chloride delivery from Me₃­SiCl to the metal center via a six-membered transition state (<b>IV</b>) that leads to the intermediate, (η⁵-C₅Me₅)­[N­(Et)­C­(Ph)­N­(Et)]­Mo­(Cl)­(NHSiMe₃) (<b>V</b>), and XOSiMe₃ as a co-product. Metathetical exchange of the new Mo–N amido bond of <b>V</b> by a second equivalent of Me₃­SiCl then generates <b>1</b> and HN­(SiMe₃). These results serve to complete a highly efficient chemical cycle for nitrogen fixation that is mediated by a set of well-characterized transition-metal complexes

Dynamic Sub-10-nm Nanostructured Ultrathin Films of Sugar–Polyolefin Conjugates Thermoresponsive at Physiological Temperatures

Spin-casting of a cellobiose-atactic polypropene (CB-aPP) conjugate (<b>1</b>) from a 0.1% (w/w) <i>n</i>-butanol/hexane solution onto highly oriented pyrolytic graphite (HOPG) and carbon-coated Si(100) spontaneously produced microphase-separated sub-10-nm nanostructured ultrathin films in the form of alternating CB and aPP lamellar domains (<i>d</i> = 6.60 ± 0.68 nm) that are oriented perpendicular to the substrate surface. Thermal annealing at modest temperatures (e.g., 50–100 °C), and as low as the physiologically relevant temperature of 38 °C, serves to drive a structural transition that yields a parallel stacked bilayer assembly as the thermodynamically favored nanostructure. These results establish the advantage of low molecular weight, narrow polydispersity, and amorphous, low <i>T</i>_g, poly­(α-olefinate)­s (xPAOs) as a new class of hydrophobic building block for amphiphilic materials, and sugar–PAO conjugates in particular, for the development of stimuli-responsive, nanostructured materials for technological applications at physiological temperatures

Tailoring Glass Transition Temperature in a Series of Poly(methylene-1,3-cyclopentane-<i>stat</i>-cyclohexane) Statistical Copolymers

A systematic investigation of the synthesis and characterization of a new class of amorphous atactic cis, trans poly(methylene-1,3-cyclopentane-stat-cyclohexane) statistical copolymers (I) is reported. Production of different grades of I that vary with respect to the ratio of 5- and 6-membered cycloalkane repeat units was achieved through the living coordinative chain transfer cyclopolymerization of different initial feed ratios of 1,5-hexadiene and 1,6-heptadiene comonomers. It was determined that the glass transition temperature, Tg, of I can be systematically increased from −16 to 100 °C as a function of increasing 6-membered ring content, although not in a strictly linear fashion. It was further determined that a small level of 6-membered ring content is sufficient to disrupt the crystallinity of the limiting atactic cis, trans poly(methylene-1,3-cyclopentane) (PMCP) homopolymer that possesses a melting temperature, Tm, of 98 °C. These results establish a foundation for future potential technological applications of this unique class of polyolefin copolymers

N–N Bond Cleavage of Mid-Valent Ta(IV) Hydrazido and Hydrazidium Complexes Relevant to the Schrock Cycle for Dinitrogen Fixation

Chemical reduction of the Ta­(V) hydrazido chloride <b>1</b> generates the open-shell, mononuclear Ta­(IV) hydrazido complex <b>2</b>, which upon N-methylation yields the corresponding structurally characterized Ta­(IV) hydrazidium <b>6</b>. Chemical reduction of <b>6</b> results in N–N bond cleavage to generate a cis/trans mixture of the [Ta­(V),Ta­(V)] bis­(μ-nitrido) product <b>7</b> in tetrahydrofuran and the mononuclear Ta­(V) parent imide <b>8</b> in toluene. These results serve to establish an important foundation for the pursuit of a group-5 metal variant of the Schrock cycle for dinitrogen fixation

N–N Bond Cleavage of Mid-Valent Ta(IV) Hydrazido and Hydrazidium Complexes Relevant to the Schrock Cycle for Dinitrogen Fixation

Chemical reduction of the Ta­(V) hydrazido chloride <b>1</b> generates the open-shell, mononuclear Ta­(IV) hydrazido complex <b>2</b>, which upon N-methylation yields the corresponding structurally characterized Ta­(IV) hydrazidium <b>6</b>. Chemical reduction of <b>6</b> results in N–N bond cleavage to generate a cis/trans mixture of the [Ta­(V),Ta­(V)] bis­(μ-nitrido) product <b>7</b> in tetrahydrofuran and the mononuclear Ta­(V) parent imide <b>8</b> in toluene. These results serve to establish an important foundation for the pursuit of a group-5 metal variant of the Schrock cycle for dinitrogen fixation

N–N Bond Cleavage of Mid-Valent Ta(IV) Hydrazido and Hydrazidium Complexes Relevant to the Schrock Cycle for Dinitrogen Fixation

Chemical reduction of the Ta­(V) hydrazido chloride <b>1</b> generates the open-shell, mononuclear Ta­(IV) hydrazido complex <b>2</b>, which upon N-methylation yields the corresponding structurally characterized Ta­(IV) hydrazidium <b>6</b>. Chemical reduction of <b>6</b> results in N–N bond cleavage to generate a cis/trans mixture of the [Ta­(V),Ta­(V)] bis­(μ-nitrido) product <b>7</b> in tetrahydrofuran and the mononuclear Ta­(V) parent imide <b>8</b> in toluene. These results serve to establish an important foundation for the pursuit of a group-5 metal variant of the Schrock cycle for dinitrogen fixation