Supersolid hard-core bosons on the triangular lattice

We determine the phase diagram of hard-core bosons on a triangular lattice with nearest-neighbor repulsion, paying special attention to the stability of the supersolid phase. Similar to the same model on a square lattice we find that for densities rho<1/3 or rho>2/3 a supersolid phase is unstable and the transition between a commensurate solid and the superfluid is of first order. At intermediate fillings 1/3相似文献   

V16N1.5: Metastable or Missing in the Binary Phase Diagram?

The stability of V₁₆N_1.5 was investigated by experiments and density functional calculations. Three synthetic approaches besides the classical reaction of vanadium with flowing ammonia were evaluated: (i) The ammonolysis of β‐V₂H, (ii) the reaction of vanadium and δ‐VN at elevated temperatures in sealed ampoules, and (iii) the thermal decomposition of δ‐VN in dynamic vacuum at high temperatures. However, none of them was suitable to provide single phase V₁₆N_1.5 yet. The results achieved by experiments and by simulations both indicate an absence of significant homogeneity range for V₁₆N_1.5. The high‐temperature experiments suggest a strongly enhanced thermal stability for V₁₆N_1.5 than reported in literature, suggesting V₁₆N_1.5 to represent a thermodynamically stable compound rather than being metastable. Temperature dependent powder X‐ray diffraction proves stability of V₁₆N_1.5 up to 700 °C. During a thermal analysis experiment in argon V₁₆N_1.5 was still observed after 24 h at 1300 °C. Consequently, first‐principle calculations of the thermodynamic properties of V₁₆N_1.5 revealed an endothermal decomposition to V and β‐V₂N.     

Dynamical signatures of edge-state magnetism on graphene nanoribbons

We investigate the edge-state magnetism of graphene nanoribbons using projective quantum Monte Carlo simulations and a self-consistent mean-field approximation of the Hubbard model. The static magnetic correlations are found to be short ranged. Nevertheless, the correlation length increases with the width of the ribbon such that already for ribbons of moderate widths we observe a strong trend towards mean-field-type ferromagnetic correlations at a zigzag edge. These correlations are accompanied by a dominant low-energy peak in the local spectral function and we propose that this can be used to detect edge-state magnetism by scanning tunneling microscopy. The dynamic spin structure factor at the edge of a ribbon exhibits an approximately linearly dispersing collective magnonlike mode at low energies that decays into Stoner modes beyond the energy scale where it merges into the particle-hole continuum.     

Synthesis of β-d-(1→4)-Substituted Trehalose Oligosaccharides

Abstract

Glycosylation of 2,3,6-tri-O-benzyl-α-D-glucopyranosyl 2,3-di-O-benzyl-4,6-O-benzylidene-α-D-glucopyranoside (5) with α-D-glucopyranosyl, α-maltosyl, and α-maltotriosyl bromides 4, 7, and 8 afforded the β-D-(1→4)-substituted trehalose tri-, tetra-, and pentasaccharides 6, 9, and 10 which were fully characterized by ¹H NMR spectroscopy. Deprotection gave the free oligosaccharides 1, 2, and 3.     

The Synthesis of Four Dideoxygenated Analogues of β-Maltosyl-(1→4)-Trehalose

Abstract

Four derivatives of β-maltosyl-(1→4)-trehalose were prepared, each with two deoxy functions in one of the constitutive disaccharide building blocks. 2,3-Di-O-acetyl-4,6-dideoxy-4,6-diiodo-α-D-galactopyranosyl- (1→4) ?1,2,3,6-tetra-O-acetyl-D-glucopyranose (3) was employed as a precursor for the 4?,6?-dideoxygenated tetrasaccharide 9: coupling of 3 with 2,3,6-tri-O-benzyl-α-D-glucopyranosyl 2,3,6-tri-O-benzylidene-α-D-glucopyranoside (4) furnished the tetrasaccharide 5 which was deiodinated and deprotected to yield the target tetrasaccharide 9. Secondly, the dideoxygenated maltose derivative 3-deoxy-4,6-O-isopropylidene-2-O-pivaloyl-β-D-glucopyranosyl- (1→4) ?1,6-anhydro-3-deoxy-2-O-pivaloyl-β-D-glucopyranose (10) was ring-opened to the anomeric acetate 11. A [2+2] block synthesis with 4 in TMS triflate mediated glycosylation gave a tetrasaccharide which was deprotected to the 3″,3?-dideoxygenated analogue of β-maltosyl-(1→4)-trehalose. For the third tetrasaccharide, 2,3,2″,3′-tetra-O-benzyl-α,α-trehalose was iodinated at the primary positions and deiodinated in the presence of palladium-on-carbon, then this acceptor was selectively glycosylated with hepta-O-acetyl-maltosyl bromide (20). Removal of protective groups furnished the maltosyl trehalose tetrasaccharide deoxygenated at positions C-6 and C-6′. to prepare a 3,3′-dideoxygenated trehalose, the free hydroxyl groups of 2-O-benzyl-4,6-O-(R)-benzylidene-α-D-glucopyranosyl 2-O-benzyl-4,6-O-(R)-benzylidene-α-D-glucopyranoside (25) were reduced by Barton-McCombie deoxygenation. One of the benzylidene groups was opened reductively with sodium cyanoborohydride. The resulting free hydroxyl group at the 4′-position was glycosylated in a Koenigs-Knorr reaction with 20 to yield the 3,3′-dideoxygenated tetrasaccharide 32, the fourth target oligosaccharide, after deprotection.     

Analysis of microwave and infrared transitions of phenol by rotation-internal rotation theory. Phenol-OD

Rotational transitions of the torsional ground and first excited state of phenol-OD have been measured in the frequency range 8–40 GHz. In a semi-rigid model approach to the internal rotation, kinetic and potential constants have been fitted to the far-infrared torsional frequencies and the microwave transition frequencies for the ground and the excited state separately. It is further shown that an acceptable agreement between observed and calculated spectra has simultaneously been obtained for the torsional ground and first excited state using the contravariant kinetic coefficients g^mn as fitting parameters.     

Introduction: Cardiovascular physics

The number of patients suffering from cardiovascular diseases increases unproportionally high with the increase of the human population and aging, leading to very high expenses in the public health system. Therefore, the challenge of cardiovascular physics is to develop high-sophisticated methods which are able to, on the one hand, supplement and replace expensive medical devices and, on the other hand, improve the medical diagnostics with decreasing the patient's risk. Cardiovascular physics-which interconnects medicine, physics, biology, engineering, and mathematics-is based on interdisciplinary collaboration of specialists from the above scientific fields and attempts to gain deeper insights into pathophysiology and treatment options. This paper summarizes advances in cardiovascular physics with emphasis on a workshop held in Bad Honnef, Germany, in May 2005. The meeting attracted an interdisciplinary audience and led to a number of papers covering the main research fields of cardiovascular physics, including data analysis, modeling, and medical application. The variety of problems addressed by this issue underlines the complexity of the cardiovascular system. It could be demonstrated in this Focus Issue, that data analyses and modeling methods from cardiovascular physics have the ability to lead to significant improvements in different medical fields. Consequently, this Focus Issue of Chaos is a status report that may invite all interested readers to join the community and find competent discussion and cooperation partners.