Electrochemical synthesis and properties of CoO2, the x = 0 phase of the AxCoO2 systems (A = Li, Na)

Single-phase bulk samples of the "exotic" CoO2, the x = 0 phase of the AxCoO2 systems (A = Li, Na), were successfully synthesized through electrochemical de-intercalation of Li from pristine LiCoO2 samples. The samples of pure CoO2 were found to be essentially oxygen stoichiometric and possess a hexagonal structure consisting of stacked triangular-lattice CoO2 layers only. The magnetism of CoO2 is featured with a temperature-independent susceptibility of the magnitude of 10-3 emu/mol Oe, being essentially identical to that of a Li-doped phase, Li0.12CoO2. It is most likely that the CoO2 phase is a Pauli-paramagnetic metal with itinerant electrons.Comment: 12 pages, 3 figure

El viaje en el Sefer ha-musar de al-Ḍāhirī: entre la realidad y la imaginación

This article meticulously and systematically analyzes travel accounts appearing in al‑Ḍāhirī’s Sefer ha-musar (Book of adab), which is divided into forty-five maqāmāt, written in rhymed prose in Hebrew and according to the literary rules of the Arabic and Hebrew Maqama genres. The theme of travel forms a large portion of this sixteenth- century Yemenite book, as it depicts the protagonist’s travels among several countries and regions in the East. Through such descriptions, some details about the places he visited are given, with special attention and significance being paid to Jerusalem and other holy places in Palestine (Eretz Yisrael). Some scholars and historians have utilized these literary passages as reliable historical sources to understand the period. By comparing al-Ḍāhirī with other Arabic and Hebrew Maqama authors with reference to authentic historical documents, this article tackles, in a comprehensive manner, the question of reality and imagination in his travel accounts.Este artículo presenta un análisis detallado y meticuloso de los relatos de viaje que aparecen en el Sefer ha-musar (Libro de adab) de al-Ḍāhirī. Esta obra, escrita en Yemen en el siglo XVI, consta de cuarenta y cinco maqāmāt escritas en prosa rimada hebrea según los fundamentos literarios de las maqāmāt árabes y hebreas. El tema del viaje constituye una parte central de la misma, pues en ella se describen los viajes del protagonista a varios países y regiones de Oriente. En sus descripciones figuran detalles relevantes sobre los destinos que visitó, entre los que destacan Jerusalén y otros lugares santos de Palestina (Eretz Yisrael). Algunos investigadores e historiadores han utilizado los textos literarios incluidos en el Sefer ha-musar como fuente fiable para comprender el periodo histórico en el que se escribió la obra. En este artículo, al comparar la obra de al-Ḍāhirī con la de otros escritores de maqāmāt árabes y hebreas, se atiende a sus relatos de viajes en cuanto que documentos históricos, a la vez que se analiza de manera detallada la cuestión de la relación entre realidad e imaginación

Half-ordered state in the anisotropic Haldane-gap antiferromagnet NDMAP

Neutron diffraction experiments performed on the Haldane gap material NDMAP in high magnetic fields applied at an angle to the principal anisotropy axes reveal two consecutive field-induced phase transitions. The low-field phase is the gapped Haldane state, while at high fields the system exhibits 3-dimensional long-range Neel order. In a peculiar phase found at intermediate fields only half of all the spin chains participate in the long-range ordering, while the other half remains disordered and gapped.Comment: 4 pages, 2 figures, submitted to Phys. Rev.

Field induced long-range-ordering in an S=1 quasi-one-dimensional Heisenberg antiferromagnet

We have measured the heat capacity and magnetization of the spin one one-dimensional Heisenberg antiferromagnet NDMAP and constructed a magnetic field versus temperature phase diagram. We found a field induced long-range magnetic ordering. We have been successful in explaining the phase diagram theoretically.Comment: 6 pages, 18 figure

Structural, mechanical, and tribological properties of electrospun poly(hexamethylene adipamide) fiber mats

The mechanical and tribological properties of electrospun fiber mats are of paramount importance to their utility in a large number of applications. In this work, mats of electrospun fibers of poly(hexamethylene adipamide) (PA 6,6) with average fiber diameter of 238±22 nm are characterized for their crystal structure as well as their mechanical and tribological properties. Post-spin thermal annealing was used to modify the fiber morphology and crystallinity within the fibers. Morphological changes, in-plane tensile response, friction coefficient and wear rate were characterized as functions of the annealing temperature. The mechanical and tribological properties of the thermally annealed PA 6,6 fiber mats exhibited significant improvements through the Brill transition temperature, comparable to the improvements observed for amorphous polyamide electrospun mats annealed near the glass transition temperature. The effective wear rate of the electrospun fiber mats is well-described by a previously proposed modification of the Ratner-Lancaster relationship that relates wear to the yield behavior of these nonwoven mats.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (AROW911NF-07-D-0004

Molecular Design of Polymer Coatings Capable of Photo-Triggered Stress Relaxation via Dynamic Covalent Bond Exchange

Polymer coatings are frequently used to modify surface properties of inorganic substrates. However, the disparity in physical properties between polymer film and substrate often leads to residual stress development, which can be deleterious to the overall performance of coated materials. This work reports the molecular design of polymer films that dissipate stress upon irradiation with ultraviolet (UV) light. These polymers are synthesized by post-polymerization modification of the reactive polymer, poly(2-vinyl-4,4-dimethyl azlactone), to introduce dynamic crosslinks capable of light-initiated addition transfer fragmentation chemistry. Using a custom-built optical cantilever, contrasting film stress responses are observed between films containing dynamic bonds and analogous control films after UV light irradiation, which indicate successful stress relaxation. Further experiments demonstrate the complete relaxation of residual stress in dynamic films after an extended exposure, thereby generating a “stress-free” film. Films fabricated using this approach can be easily tailored to incorporate additional moieties to introduce desired surface properties for future application in a wide array of coatings

Field-induced commensurate long-range order in the Haldane-gap system NDMAZ

High-field neutron diffraction studies of the new quantum-disordered S=1 linear-chain antiferromagnet Ni(C$_5$H$_{14}$N$_2$)$_2$N$_3$(ClO$_4$) (NDMAZ) are reported. At T=70 mK, at a critical field $H_c=13.4$ T applied along the (013) direction, a phase transition to a commensurate N\'{e}el-like ordered state is observed. The results are discussed in the context of existing theories of quantum phase transitions in Haldane-gap antiferromagnets, and in comparions with previous studies of the related system Ni(C$_5$H$_{14}$N$_2$)$_2$N$_3$(PF$_6$)