Charge trapping in polymer transistors probed by terahertz spectroscopy and scanning probe potentiometry

Terahertz time-domain spectroscopy and scanning probe potentiometry were used to investigate charge trapping in polymer field-effect transistors fabricated on a silicon gate. The hole density in the transistor channel was determined from the reduction in the transmitted terahertz radiation under an applied gate voltage. Prolonged device operation creates an exponential decay in the differential terahertz transmission, compatible with an increase in the density of trapped holes in the polymer channel. Taken in combination with scanning probe potentionmetry measurements, these results indicate that device degradation is largely a consequence of hole trapping, rather than of changes to the mobility of free holes in the polymer.Comment: 4 pages, 3 figure

Statistical mechanics of temporal association in neural networks with transmission delays

We study the representation of static patterns and temporal sequences in neural networks with signal delays and a stochastic parallel dynamics. For a wide class of delay distributions, the asymptotic network behavior can be described by a generalized Gibbs distribution, generated by a novel Lyapunov functional for the determination dynamics. We extend techniques of equilibrium statistical mechanics so as to deal with time-dependent phenomena, derive analytic results for both retrieval quality and storage capacity, and compare them with numerical simulations

Resolution of Nested Neuronal Representations Can Be Exponential in the Number of Neurons

Collective computation is typically polynomial in the number of computational elements, such as transistors or neurons, whether one considers the storage capacity of a memory device or the number of floating-point operations per second of a CPU. However, we show here that the capacity of a computational network to resolve real-valued signals of arbitrary dimensions can be exponential in N, even if the individual elements are noisy and unreliable. Nested, modular codes that achieve such high resolutions mirror the properties of grid cells in vertebrates, which underlie spatial navigation

Ultrasonic/Sonic Jackhammer

The invention provides a novel jackhammer that utilizes ultrasonic and/or sonic vibrations as source of power. It is easy to operate and does not require extensive training, requiring substantially less physical capabilities from the user and thereby increasing the pool of potential operators. An important safety benefit is that it does not fracture resilient or compliant materials such as cable channels and conduits, tubing, plumbing, cabling and other embedded fixtures that may be encountered along the impact path. While the ultrasonic/sonic jackhammer of the invention is able to cut concrete and asphalt, it generates little back-propagated shocks or vibrations onto the mounting fixture, and can be operated from an automatic platform or robotic system. PNEUMATICS; ULTRASONICS; IMPACTORS; DRILLING; HAMMERS BRITTLE MATERIALS; DRILL BITS; PROTOTYPES; VIBRATIO

Prenatal maternal diet affects asthma risk in offspring

Recently, epigenetic-mediated mechanisms — which involve heritable changes in gene expression in the absence of alterations in DNA sequences — have been proposed as contributing to asthma. In this issue of the JCI, Hollingsworth and colleagues report on the effect of prenatal maternal dietary intake of methyl donors on the risk of allergic airway disease in offspring in mice and show that these effects involve epigenetic regulation (see the related article beginning on page 3462). Supplementation of the maternal diet with methyl donors was associated with greater airway allergic inflammation and IgE production in F1 and, to some extent, F2 progeny. Site-specific differences in DNA methylation and reduced transcriptional activity were detected. If these findings are confirmed, a new paradigm for asthma pathogenesis may be emerging

Ants as predators of the egg parasitoid Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae) applied for biological control of the olive moth, Prays oleae (Lepidoptera: Plutellidae) in Portugal

The detrimental effect of predators on Trichogramma cacoeciae March. releases to control the olive moth, Prays oleae Bern., in the Trás-os-Montes region (Northeast of Portugal), was evaluated during three releases against the flower generation of the pest in 2002. At 1 and 3 h and at 1, 3, 7 and 14 days after each release, 30 Trichogramma releasing cards were examined in the field and predators were collected and identified. Furthermore, at 1, 3, 7 and 14 days after each release, the percentage of egg predation on the cards was also determined. Formicidae were the most abundant group of predators at 99.1% of the total individuals collected. Ten species were identified, Camponotus aethiops, C. lateralis, C. piceus, C. truncatus, Crematogaster auberti, C. scutellaris, Lasius niger, Leptotorax angustulus, Plagiolephis pygmaea and Tapinoma nigerrimum. T. nigerrimum was the most abundant species, both in total numbers as well as in the number of occupied cards. One day after release, the percentage of predation was 24.0% in the first release, 59.4% in the second and 38.0% in the third. Three days after release, the percentage of predation varied from 60.2 to 83.4% during the three release events. Seven days after release, the percentage of predation increased to 97.8% of the total eggs on cards

Lorentz angle measurements in irradiated silicon detectors between 77 K and 300 K

Future experiments are using silicon detectors in a high radiation environment and in high magnetic fields. The radiation tolerance of silicon improves by cooling it to temperatures below 180 K. At low temperatures the mobility increases, which leads to larger deflections of the charge carriers by the Lorentz force. A good knowledge of the Lorentz angle is needed for design and operation of silicon detectors. We present measurements of the Lorentz angle between 77 K and 300 K before and after irradiation with a primary beam of 21 MeV protons.Comment: 13 pages, 9 figures, submitted to ICHEP2000, Osaka, Japa

Farmers’ management of functional biodiversity goes beyond pest management in organic European apple orchards

Supporting functional biodiversity (FB), which provides natural pest regulation, is an environmentally sound and promising approach to reduce pesticide use in perennial cultures such as apple, especially in organic farming. However, little is known about farmers’ practices and motivations to implement techniques that favor FB, especially whether or not they really expect anything from FB in terms of pest regulation. In fact, FB-supporting techniques (FB-techniques) are massively questioned by practitioners due to inadequate information about their effectiveness. An interview survey was performed in eight European countries(i) to describe farmers’ practices and identify promising FB-techniques: (ii) to better understand their perceptions of and values associated with FB; and (iii) to identify potential drivers of (non-)adoption. Fifty-five advisors and 125 orchard managers with various degrees of experience and convictions about FB were interviewed and a total of 24 different FB-techniques which can be assigned to three different categories (ecological infrastructures, farming practices and redesign techniques) were described. Some were well-established measures (e.g., hedges and bird houses), while others were more marginal and more recent (e.g., animal introduction and compost). On average, farmers combined more than four techniques that had been implemented over a period of 13 years, especially during their establishment or conversion period. In general, it was difficult for farmers to evaluate the effectiveness of individual FB-techniques on pest regulation. They considered FB-techniques as a whole, targeting multiple species, and valued multiple ecosystem services in addition to pest regulation. The techniques implemented and their associated values differed among farmers who adopted various approaches towards FB. Three different approaches were defined: passive, active and integrated. Their appraisal of FB is even more complex because it may change with time and experience. These findings provide empirical evidence that the practical implementation of promising techniques remains a challenge, considering the diversity of situations and evaluation criteria. Increased cooperation between researchers, farmers and advisors should more effectively target research, advisory support and communication to meet farmers’ needs and perceptions

Measuring the equation of state of a hard-disc fluid

We use video microscopy to study a two-dimensional (2D) model fluid of charged colloidal particles suspended in water and compute the pressure from the measured particle configurations. Direct experimental control over the particle density by means of optical tweezers allows the precise measurement of pressure as a function of density. We compare our data with theoretical predictions for the equation of state, the pair-correlation function and the compressibility of a hard-disc fluid and find good agreement, both for the fluid and the solid phase. In particular the location of the transition point agrees well with results from Monte Carlo simulations.Comment: 7 pages, to appear in EPL, slightly corrected versio