Bipolar host materials: a chemical approach for highly efficient electrophosphorescent devices

The future of organic light-emitting devices (OLEDs) is drifting from electrofluorescence toward electrophosphorescence due to the feasibility of realizing 100% internal quantum efficiency. There is limited availability of transition metals (TMs) such as Ir, Os, and Pt, which are used for color-tunable phosphorescent emitters, and the use of the host-guest strategy is necessary for suppressing the detrimental triplet-triplet annihilation inherently imparted by the TM-centered emitters. The inevitable demands of organic host materials provide organic chemists with tremendous opportunities to contribute their expertise to this technology. With suitable molecular design and judicious selection of chemical structures featured with different electronic nature, the incorporation of hole-transporting (HT) and electron-transporting (ET) moieties combines the advantages of both functional units into bipolar host materials, which perform balanced injection/transportation/recombination of charge carriers and consequentially lead the OLEDs to have higher performances and low roll-off efficiencies. This review highlights recently developed bipolar host materials with the focus on molecular design strategies and the structure-property-performance relationships of various classes of bipolar host materials, which are classified into several categories according to the structural features of their constituents (HT/ET blocks and spacers).     

Titanium foam through powder metallurgy route using acicular urea particles as space holder

In the present work, Ti foam has been synthesized employing powder metallurgy route. Irregular titanium powder particles were used as the matrix and acicular urea particles as the space holder. The distribution of the urea particles in the matrix of the compacted mass was observed to be fairly uniform. Pore morphology and compressive behavior of the resulting foam have been studied. The processed foam consisted of acicular porous regions of size up to 500 μm. The porous regions contained a large number of micro-pores along with the occasional presence of coarse pores, the latter thought to be unhealed portions of the original acicular pores. The foam delineated a distinct plateau region with plateau stress of 275 MPa and energy absorption capacity of 55 MJ/m³.     

Detection of acetone vapor using graphene on polymer optical fiber

Recently, many studies have been focused on the development of fiber optic sensor systems for various gases and vapors. In the present study, an intrinsic polymer optical fiber (POF) sensor using graphene is described for the purpose of acetone vapor sensing for the first time. Observations on the continuous measurement of acetone vapor in dehydrated air are presented. The principle of operation of sensor transduction relies on the dependence of the reflectance on the optical and geometric properties of the sensitive over layered when the vapor molecules are adsorbed on the graphene film. For the same purpose the CVD synthesized graphene film was transferred on the POF end. The synthesized graphene film thickness was evaluated using atomic force microscopy (AFM), Raman spectroscopy and transmission electron microscopy (TEM). For the preliminary evaluation using volatile organic compounds, we evaluated the sensor performance for acetone. Upon the interaction of the sensor with acetone vapor, the variation in the reflected light was monitored as a function of the acetone concentration. The sensor response shows a significant change in sensitivity as compared with the POF probe without a graphene coating. The present sensor shows a satisfactory response upon exposure to various concentrations of acetone vapor from 44 ppm to 352 ppm. To the best of our knowledge, the use of graphene film along with POF for the sensing of volatile organic compounds has not previously been reported.     

An algorithm for inverse square-roots

An algorithm is presented for finding $\text{x}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}$, given x. The algorithm is designed to be particularly suited for parallel computation, in which floating-point multiplication, floating-point addition and fixed-point arithmetic can be performed simultaneously.     

A transient simulation and dynamic spray cooling control model for continuous steel casting

A two-dimensional heat-transfer model for transient simulation and control of a continuous steel slab caster is presented. Slab temperature and solidification are computed by the model as a function of time-varying casting speed, secondary spray cooling water flow rates and temperature, slab thickness, steel chemistry, and pouring and ambient temperatures. Typically, the solidification path, temperature-solid fraction relationship, is prescribed. However, if these data are not available, a microsegregation solidification model that approximates the effects of steel chemistry and cooling rate is incorporated in the caster model. Measured slab surface temperatures recorded from an operating caster are compared with predictions from the transient model. These demonstrate that the model typically can predict the temperature response at the slab surface within 30 °C. Results of several simulations are given to demonstrate the effects of changing casting conditions on the slab thermal profile, end of liquid pool, and solidification end point. A control methodology and algorithm suitable for online control of a continuous casting machine is described, and the ability to control the surface temperature profile by dynamically adjusting secondary spray cooling flow rates is demonstrated by simulation. Results from a preliminary version of the model that is capable of running in real time are presented and are compared with the slower, but more realistic, version of the model.     

NUCLEATION AND GROWTH IN THE DIFFUSION CLOUD CHAMBER II STEADY STATE NUCLEATION

A model describing nucleation and growth in a thermal diffusion cloud chamber presented earlier in this Journal to explain oscillatory nucleation is extended to the case of steady state nucleation. The model is applied to nucleation rate data for ethanol vapor obtained using a thermal diffusion cloud chamber. A correction is made for the deleterious effects of vapor depletion and latent heat generation which accompany droplet growth thus extending the accessible range of nucleation rate measurements by several orders of magnitude.