Poly-nitrogen compounds have been considered as potential high energy density materials for a long time due to the large number of energetic N-N or N=N bonds. In most cases high nitrogen content and ...stability at ambient conditions are mutually exclusive, thereby making the synthesis of such materials challenging. One way to stabilize such compounds is the application of high pressure. Here, through a direct reaction between Fe and N
in a laser-heated diamond anvil cell, we synthesize three ironnitrogen compounds Fe
N
, FeN
and FeN
. Their crystal structures are revealed by single-crystal synchrotron X-ray diffraction. Fe
N
, synthesized at 50 GPa, is isostructural to chromium carbide Cr
C
. FeN
has a marcasite structure type and features covalently bonded dinitrogen units in its crystal structure. FeN
, synthesized at 106 GPa, features polymeric nitrogen chains of N
units. Based on results of structural studies and theoretical analysis, N
units in this compound reveal catena-polytetraz-1-ene-1,4-diyl anions.
Cholesterol siRNA conjugates attract attention because they allow the delivery of siRNA into cells without the use of transfection agents. In this study, we compared the efficacy and duration of ...silencing induced by cholesterol conjugates of selectively and totally modified siRNAs and their heteroduplexes of the same sequence and explored the impact of linker length between the 3' end of the sense strand of siRNA and cholesterol on the silencing activity of "light" and "heavy" modified siRNAs. All 3'-cholesterol conjugates were equally active under transfection, but the conjugate with a C3 linker was less active than those with longer linkers (C8 and C15) in a carrier-free mode. At the same time, they were significantly inferior in activity to the 5'-cholesterol conjugate. Shortening the sense strand carrying cholesterol by two nucleotides from the 3'-end did not have a significant effect on the activity of the conjugate. Replacing the antisense strand or both strands with fully modified ones had a significant effect on silencing as well as improving the duration in transfection-mediated and carrier-free modes. A significant 78% suppression of
gene expression in KB-8-5 xenograft tumors developed in mice promises an advantage from the use of fully modified siRNA cholesterol conjugates in combination chemotherapy.
Most of the studied two-dimensional (2D) materials are based on highly symmetric hexagonal structural motifs. In contrast, lower-symmetry structures may have exciting anisotropic properties leading ...to various applications in nanoelectronics. In this work we report the synthesis of nickel diazenide NiN2 which possesses atomic-thick layers comprised of Ni2N3 pentagons forming Cairo-type tessellation. The layers of NiN2 are weakly bonded with the calculated exfoliation energy of 0.72 J/m2, which is just slightly larger than that of graphene. The compound crystallizes in the space group of the ideal Cairo tiling (P4/mbm) and possesses significant anisotropy of elastic properties. The single-layer NiN2 is a direct-band-gap semiconductor, while the bulk material is metallic. This indicates the promise of NiN2 to be a precursor of a pentagonal 2D material with a tunable direct band gap.
Abstract
In this paper, we investigate the statistical properties of the Baryonic Tully–Fisher relation (BTFr) for a sample of 32 galaxies with accurate distances based on Cepheïds and/or TRGB stars. ...We make use of homogeneously analysed photometry in 18 bands ranging from the far-ultraviolet to 160 μm, allowing us to investigate the effect of the inferred stellar mass-to-light ratio (ϒ⋆) on the statistical properties of the BTFr. Stellar masses of our sample galaxies are derived with four different methods based on full SED fitting, studies of stellar dynamics, near-infrared colours, and the assumption of the same $\Upsilon _{\star }^{3.6}$ for all galaxies. In addition, we use high-quality, resolved H i kinematics to study the BTFr based on three kinematic measures: $W^{i}_{50}$ from the global H i profile, and Vmax and Vflat from the rotation curve. We find the intrinsic perpendicular scatter, or tightness, of our BTFr to be σ⊥ = 0.026 ± 0.013 dex, consistent with the intrinsic tightness of the 3.6 μm luminosity-based Tully–Fisher relation (TFr). However, we find the slope of the BTFr to be 2.99 ± 0.2 instead of 3.7 ± 0.1 for the luminosity-based TFr at 3.6 μm. We use our BTFr to place important observational constraints on theoretical models of galaxy formation and evolution by making comparisons with theoretical predictions based on either the Λ cold dark matter framework or modified Newtonian dynamics.
Analysis of the contemporary geographic distributions of mtDNA haplotypic diversity of sockeye salmon (Oncorhynchus nerka Walbaum) on the Asian part of its range and consideration of possible ...scenarios for microevolution of the species were performed. In total, 172 specimens of sockeye salmon from different rivers of Kamchatka, Chukotka, north coast of the Sea of Okhotsk, and from the Kuril Islands were analyzed using the entire mtDNA control region (1,010 bp) sequencing. After multiple alignments of the sequences 16 polymorphic sites were identified. Most of substitutions were detected in the first and the last thirds of the D‐loop sequence, as well as one insertion was registered in the poly‐T region. Two mass haplotypes (Hap_1_10T and Hap_2_13T) were revealed; they were present in most samples and differed by three substitutions and two indels. All the sequence variants were distributed among two haplogroups in compliance with the mass haplotypes. The star‐shaped topology of the MST‐tree points to a rapid increase in the diversity of groups, indicating a rapid expansion of the species after its number reducing in the past. The diversity of the first haplogroup was higher, but its main fraction fell on the samples from the middle reach of Kamchatka River, which seems to be a refugium during the Late Pleistocene glaciation. Presence of both haplogroups in most populations in approximately equal proportions indicates that the entire Asian part of the sockeye salmon range is a zone of secondary contact. We hypothesize that Hap_2_13T had more ancient origin and the Hap_1_10T was formed somewhat later, apparently in Asia, because almost all transitional forms between the haplogroups were found in Iturup Island populations.
Abstract
High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity ...insufficient for properties characterization. Here we report the synthesis of metallic, ultraincompressible (
K
0
= 428(10) GPa), and very hard (nanoindentation hardness 36.7(8) GPa) rhenium nitride pernitride Re
2
(N
2
)(N)
2
. Unlike known transition metals pernitrides Re
2
(N
2
)(N)
2
contains both pernitride N
2
4−
and discrete N
3−
anions, which explains its exceptional properties. Re
2
(N
2
)(N)
2
can be obtained via a reaction between rhenium and nitrogen in a diamond anvil cell at pressures from 40 to 90 GPa and is recoverable at ambient conditions. We develop a route to scale up its synthesis through a reaction between rhenium and ammonium azide, NH
4
N
3
, in a large-volume press at 33 GPa. Although metallic bonding is typically seen incompatible with intrinsic hardness, Re
2
(N
2
)(N)
2
turned to be at a threshold for superhard materials.
•Existence of disordered local moments in the paramagnetic state is essential.•The magnetic disorder makes theoretical description of the systems non-trivial.•We discuss advantages and limitations of ...existing theoretical tools.•Contributions from electronic, magnetic and vibrational excitations are all important.•Accurate predictions of materials properties in the paramagnetic state are possible.
We review recent developments in the field of first-principles simulations of magnetic materials above the magnetic order–disorder transition temperature, focusing mainly on 3d-transition metals, their alloys and compounds. We review theoretical tools, which allow for a description of a system with local moments, which survive, but become disordered in the paramagnetic state, focusing on their advantages and limitations. We discuss applications of these theories for calculations of thermodynamic and mechanical properties of paramagnetic materials. The presented examples include, among others, simulations of phase stability of Fe, Fe–Cr and Fe–Mn alloys, formation energies of vacancies, substitutional and interstitial impurities, as well as their interactions in Fe, calculations of equations of state and elastic moduli for 3d-transition metal alloys and compounds, like CrN and steels. The examples underline the need for a proper treatment of magnetic disorder in these systems.
High-pressure chemistry is known to inspire the creation of unexpected new classes of compounds with exceptional properties. Here, we employ the laser-heated diamond anvil cell technique for ...synthesis of a Dirac material BeN4. A triclinic phase of beryllium tetranitride tr − BeN4 was synthesized from elements at ∼ 85 GPa . Upon decompression to ambient conditions, it transforms into a compound with atomic-thick BeN4 layers interconnected via weak van der Waals bonds and consisting of polyacetylene-like nitrogen chains with conjugated π systems and Be atoms in square-planar coordination. Theoretical calculations for a single BeN4 layer show that its electronic lattice is described by a slightly distorted honeycomb structure reminiscent of the graphene lattice and the presence of Dirac points in the electronic band structure at the Fermi level. The BeN4 layer, i.e., beryllonitrene, represents a qualitatively new class of 2D materials that can be built of a metal atom and polymeric nitrogen chains and host anisotropic Dirac fermions.
The extensive implementation of hydrogen-powered technology today is limited by a number of fundamental problems related to materials research. Fuel-cell hydrogen conversion technology requires ...proton-conducting materials with high conductivity at intermediate temperatures up to 120 °C. The development of such materials remains challenging because the proton transport of many promising candidates is based on extended microstructures of water molecules, which deteriorate at temperatures above the boiling point. Here we show the impregnation of the mesoporous metal–organic framework (MOF) MIL-101 by nonvolatile acids H2SO4 and H3PO4. Such a simple approach affords solid materials with potent proton-conducting properties at moderate temperatures, which is critically important for the proper function of on-board automobile fuel cells. The proton conductivities of the H2SO4@MIL-101 and H3PO4@MIL-101 at T = 150 °C and low humidity outperform those of any other MOF-based materials and could be compared with the best proton conductors, such as Nafion.
The majority of recent hydrodynamical simulations indicate the creation of central cores in the mass profiles of low-mass halos, a process that is attributed to star formation-related baryonic ...feedback. Core creation is regarded as one of the most promising solutions to potential issues faced by lambda cold dark matter (ΛCDM) cosmology on small scales. For example, the reduced dynamical mass enclosed by cores can explain the low rotational velocities measured for nearby dwarf galaxies, thus possibly lifting the seeming contradiction with the ΛCDM expectations (the so-called “too big to fail” problem). Here we test core creation as a solution of cosmological issues by using a sample of dwarfs with measurements of their atomic hydrogen (HI) kinematics extending to large radii. Using the NIHAO hydrodynamical simulation as an example, we show that core creation can successfully reproduce the kinematics of dwarfs with small kinematic radii, R ≲ 1.5 kpc. However, the agreement with observations becomes poor once galaxies with kinematic measurements extending beyond the core region, R ≈ 1.5−4 kpc, are considered. This result illustrates the importance of testing the predictions of hydrodynamical simulations that are relevant for cosmology against a broad range of observational samples. We would like to stress that our result is valid only under the following set of assumptions: i) that our sample of dwarfs with HI kinematics is representative of the overall population of field dwarfs; ii) that there are no severe measurement biases in the observational parameters of our HI dwarfs (e.g., related to inclination estimates); and iii) that the HI velocity fields of dwarfs are regular enough to allow the recovery of the true enclosed dynamical mass.
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