Asymptotic solution of a model for bilayer organic diodes and solar cells

The current voltage characteristics of an organic semiconductor diode made by placing together two materials with dissimilar electron affinities and ionisation potentials is analysed using asymptotic methods. An intricate boundary layer structure is examined. We find that there are three regimes for the total current passing through the diode. For reverse bias and moderate forward bias the dependency of the voltage on the current is similar to the behaviour of conventional inorganic semiconductor diodes predicted by the Shockley equation and are governed by recombination at the interface of the materials. There is then a narrow range of currents where the behaviour undergoes a transition. Finally for large forward bias the behaviour is different with the current being linear in voltage and is primarily controlled by drift of charges in the organic layers. The size of the interfacial recombination rate is critical in determining the small range of current where there is rapid transition between the two main regimes. The extension of the theory to organic solar cells is discussed and the analogous current voltage curves derived in the regime of interest

CO J = 3→2 and J = 2→1 mapping and spectroscopy of NGC 7027

We present spectra and mapping for NGC 7072 in the J = 3→2 and J = 2→1 transitions of CO. The central profile at J = 2→1 is shown to be very similar to the J = 1→0 spectrum measured by Thronson (1983), and this implies a source expansion at roughly constant velocity. The J = 3→2 line however appears weaker, with evidence for appreciable quenching of the higher velocity components. Detailed modelling f the source indicates that densities n must vary appreciably with shell radius R(as nα R-a, where α≥2), and this leads to a corresponding steep radial decrease in the radiation temperature TR. In consequence, the source FWHM is found to decrease appreciably iwth increasing transition frequency, a trend which appears also to be confirmed by our central J = 3→2 scans. It is not however possible to constrain gas kinetic tempertures TK, the level of CO thermalisation, or shell mass M with any degree of confidence - both low and high mass models appear capable of replicating our spectra. Finally, the J = 2→1 spatial velocity map displays evidence for a decrease in velocity width towards the outer regions of the nebula; a feature which is expected of most outflow models. The J = 3→2 map also indicates the presence of a nebular extension to the north-west of the peak emission core, although this is not reproduced in the corresponding J = 1→0 map of Mufson et al. (1975)

Near infrared spectroscopy of W51 IRS-2

Near-infrared spectra at 2.95-3.5 μm and 3.99-10 μm have been obtained towards W51 IRS-2 and its surroundings, in order to investigate the spatial variations in intensity of the 3.28 μm unidentified feature and the 4.05 μm Brackett-α line. The Br-α and 3.28 μm features occupy a broadly similar spatial zone, which is characterised by an unresolved core responsible for most of the emission, and an extended and considerably weaker halo. Grain properties required to excite the 4.28 microns line, the nature of the 3.28 μm emission, and its relation to the source structure are discussed

Efficient binary phase quantizer based on phase sensitive four wave mixing

We experimentally demonstrate an efficient binary phase quantizer operating at low pump powers. Phase-sensitive operation is obtained by polarization mixing the phase-locked signal/idler pair in a degenerate dual-pump vector parametric amplifier

Quadrature decomposition of optical fields using two orthogonal phase sensitive amplifiers

We propose a new technique to optically process coherent signals by simultaneously extracting their two (I and Q) quadrature components into two orthogonal polarizations at the same frequency. Two possible implementations are demonstrated

Category names and category learning

The thesis examines the role of verbal labels in category learning by adults. In an investigation of the effects of category learning and exemplar labelling on quantitative judgements about exemplars, it was found that only labels provided at the time of testing biassed subjects’ judgements, although this effect did rely on the labels having been previously learned Adults' default assumptions concerning the extension of novel names among newly learned categories were examined: subjects used an assumption of mutual exclusivity between names (as predicted by Markman, 1989), but did not adhere to the principle of linguistic contrast (Clark, 1987). In a series of experiments where exemplars were labelled with verbal (non-word) labels or complex visual patterns, category learning was superior with the verbal labels. This superiority spanned categories consisting of arbitrary collections of familiar or unfamiliar objects, and prototype-based polygon categories. Arbitrary collection learning was better when subjects reported inventing names for the non-verbal labels. When the verbal and non-verbal labels were compared on a speeded discrimination task, few errors were made but decision times were reliably shorter (c. 0.1 second) with the verbal labels. With other non-verbal labels which were faster to discriminate than the verbal labels, arbitrary collection learning was at a level intermediate between learning with the verbal arid original non-verbal labels. The role of category names as feedback was investigated in a prototype-based category learning task. Learning was no better with named exemplars or right-wrong feedback than when unaided, although learning with named exemplars plus right-wrong feedback was better than with right-wrong feedback only. No interaction between task difficulty and feedback conditions was found (cf. Homa and Cultice, 1984). Thus in these experiments verbal labels produced better category learning than non-verbal labels, even for schema-based categories which were learned equally well unaided. Four possible functions of category names in category learning are suggested as a framework for future investigations

Economic evaluation of a nursing-led intermediate care unit

Objectives: The aim of this paper is to examine the costs of introducing a nursing-led ward program together with examining the impact this may have on patients' outcomes. Methods; The study had a sample size of 177 patients with a mean age of 77, and randomized to either a treatment group (care on a nursing-led ward, n = 97) or a control group (standard care usually on a consultant-led acute ward, n = 80). Resource use data including length of stay, tests and investigations performed, and multidisciplinary involvement in care were collected. Results: There were no significant differences in outcome between the two groups. The inpatient costs for the treatment group were significantly higher, due to the longer length of stay in this group. However, the postdischarge costs were significantly lower for the treatment group. Conclusions: The provision of nursing-led intermediate care units has been proposed as a solution to inappropriate use of acute medical wards by patients who require additional nursing rather than medical care. Whether the treatment group is ultimately cost-additive is dependent on how long reductions in postdischarge resource use are maintained

Can We Save the Traditional Family Farm?

What is a traditional family farm? Is it a family of four living on a farm and supplying all of the labor, capital and management or is it a family corporation with four families supplying all of the capital and management? These types of questions continue to arise in policy debates, as they have for many years. While subject to heated debate and the core of many people’s positions on farm programs the answer is more sociological as it is becoming less and less economically relevant. Whether these types of farms or any other farm sizes should survive is not a question that can be answered by a policy analyst. The job of an analyst is to determine if and under what conditions family farms can survive. To this end, this paper reviews the various definitions of family farms and draws inferences as to the economic and financial survival of these different size farms using the results generated from simulating representative farms.Agricultural and Food Policy,

Post-Freedom to Farm Shifts in Regional Production Patterns

The FAIR Act of 1996, also known as the Freedom to Farm Act (ACT) dismantled many of the agriculture policy tools in use for the last 25 years. Gone were target prices, deficiency payments, and set asides. In their place were expanded marketing loan programs to effectively include wheat and feed grains and oilseeds in addition to cotton and rice. Full planting flexibility has been popular with farmers who are no longer constrained by base acres. Grain merchants and other volume oriented agribusinesses praise the elimination of set asides. The sharp decline in farm prices for all major program commodities since 1996 has left most farmers questioning the income safety net provisions of the FAIR Act. The flexibility and marketing loan provisions continue to be praised. Farm program changes in the 1996 farm bill rendered methods of crop supply response estimation based on econometric models, using historic data, difficult at best. Yet it can, and has been, hypothesized that the Act resulted in major shifts in regional crop production patterns. This paper draws inferences from changes in acres planted among crops for representative farms in the Texas A&M Agricultural and Food Policy Center’s (AFPC) farm data base. AFPC has maintained longitudinal data for more than three dozen representative crop farms across states, regions, farm size, and type of farm since 1990. The farms were updated in 1999 as to their crop mix changes following the ACT and the crop mix changes observed in the updates are summarized here. United States aggregate production shifts are identified from NASS data. Implications for future potential acreage changes are identified. The commodity focus includes feedgrains, soybeans, wheat, cotton, and rice.Agricultural and Food Policy,

Particle Acceleration in Relativistic Jets due to Weibel Instability

Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. While some Fermi acceleration may occur at the jet front, the majority of electron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The ``jitter'' radiation (Medvedev 2000) from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.Comment: ApJ, in press, Sept. 20, 2003 (figures with better resolution: http://gammaray.nsstc.nasa.gov/~nishikawa/apjweib.pdf