Charge density waves in individual nanoribbons of orthorhombic-TaS3.

Orthorhombic-TaS3 is a quasi-1D material that undergoes a Peierls' transition to become a charge density wave conductor at low temperatures. Electrical transport measurements of individual single-crystalline TaS3 nanoribbons prepared by a novel bottom-up method from elemental precursors indicate a depression of the Peierls' ordering temperature to 205 K, broadening of the electric-field-induced depinning of the charge density wave below the Peierls' transition temperature, and a greatly increased threshold voltage for nucleation of charge density wave dislocations posited to be a result of surface confinement and finite size effects. Single-nanoribbon measurements of broad-band noise indicate discrete phase slip events near the depinning threshold. Three distinct regimes are identified with the normalized noise spectrum showing a distinctive maxima near the threshold voltage for depinning of the charge density wave, corresponding to sampling of different metastable states that balance ordered and sliding charge density waves.

Emptying and filling a tunnel bronze.

The classical orthorhombic layered phase of V2O5 has long been regarded as the thermodynamic sink for binary vanadium oxides and has found great practical utility as a result of its open framework and easily accessible redox states. Herein, we exploit a cation-exchange mechanism to synthesize a new stable tunnel-structured polymorph of V2O5 (ζ-V2O5) and demonstrate the subsequent ability of this framework to accommodate Li and Mg ions. The facile extraction and insertion of cations and stabilization of the novel tunnel framework is facilitated by the nanometer-sized dimensions of the materials, which leads to accommodation of strain without amorphization. The topotactic approach demonstrated here indicates not just novel intercalation chemistry accessible at nanoscale dimensions but also suggests a facile synthetic route to ternary vanadium oxide bronzes (M x V2O5) exhibiting intriguing physical properties that range from electronic phase transitions to charge ordering and superconductivity.

Ferroelastic domain organization and precursor control of size in solution-grown hafnium dioxide nanorods.

We demonstrate that the degree of branching of the alkyl (R) chain in a Hf(OR)4 precursor allows for control over the length of HfO2 nanocrystals grown by homocondensation of the metal alkoxide with a metal halide. An extended nonhydrolytic sol-gel synthesis has been developed that enables the growth of high aspect ratio monoclinic HfO2 nanorods that grow along the [100] direction. The solution-grown elongated HfO2 nanorods show remarkable organization of twin domains separated by (100) coherent twin boundaries along the length of the nanowires in a morphology reminiscent of shape memory alloys. The sequence of finely structured twin domains each spanning only a few lattice planes originates from the Martensitic transformation of the nanorods from a tetragonal to a monoclinic structure upon cooling. Such ferroelastic domain organization is uncharacteristic of metal oxides and has not thus far been observed in bulk HfO2. The morphologies observed here suggest that, upon scaling to nanometer-sized dimensions, HfO2 might exhibit mechanical properties entirely distinctive from the bulk.

The association between contraceptive use at the time of conception and hypertensive disorders during pregnancy: a retrospective cohort study of prams participants.

Each year approximately 7 % of women experience hypertensive disorders during pregnancy which can result in adverse events for both the mother and child. Previous research suggests that contraception at the time of conception can also predispose one to hypertensive disorders during pregnancy. The objective of this study was to examine the association between contraceptive use at the time of conception and hypertensive complications during pregnancy. A total of 2,395 women aged 18-45 years participated in the 2007-2009 Michigan Pregnancy Risk Assessment Monitoring System. Contraception at the time of conception was self-reported by participants and classified as barrier, nonbarrier, or non-use. Information on hypertensive disorders during pregnancy was primarily from birth certificates. Logistic regression was used to obtain odds ratios (ORs) and 95 % confidence intervals (CIs) to model the contraception-hypertensive disorder association. After adjustment for age and race/ethnicity, there was no strong association between use of barrier contraception at the time of conception and hypertensive disorders during pregnancy as compared to non-users (OR 1.09, 95 % CI 0.62-1.92). After adjustment for the same variables, nonbarrier users had 1.22 times the odds of experiencing hypertensive disorders during pregnancy as compared to non-users (95 % CI 0.75-1.98). Although we did not find an association between contraceptive use at the time of conception and hypertensive disorders during pregnancy, additional studies with larger sample sizes and more explicit categorization of the outcome variable are needed to confirm these findings.

Identifying women at risk of unintended pregnancy: a comparison of two pregnancy readiness measures.

PURPOSE: Recently, there has been interest in developing a predictive measure to assess pregnancy readiness/intention in clinical settings. Two such measures have been created but tested primarily in pregnant or postpartum populations. This study examined agreement between the pregnancy readiness measures in a diverse population of nonpregnant women. METHODS: Women completed short questionnaires while waiting for clinical appointments. Participants' responses to the pregnancy readiness measures were cross-tabulated to assess the level of agreement between the measures. Logistic regression was used to determine factors related to disagreement between the measures. Complete information was available for 220 women. RESULTS: Almost 55% of women had disagreement between the pregnancy readiness measures. Women with a high school education or less had 2.60 times the odds of disagreement (95% confidence interval 1.23-5.49), and women who did not use contraception had 2.40 times the odds of disagreement (95% confidence interval 1.18-4.87). CONCLUSIONS: Although both pregnancy readiness measures are promising tools that could potentially be adapted for use in public health or clinical settings, there are limitations to these measures. These measures should be further tested and refined through the use of qualitative methods to ensure that a valid measure is created for use in non-pregnant populations.