Determination of Temperature and Light Optima for Seed Germination and Seedling Development of Spiderplant (Cleome gynandra L.) Morphotypes from western Kenya

Spiderplant (Cleome gynandra) is an African indigenous vegetable (AIV) in many parts of sub-Saharan Africa, especially in most countries in eastern and southern Africa, where it is a semi-cultivated popular tropical species. In Kenya, it is among the most popular AIVs, particularly in the western and coastal regions. Seed supply systems for spiderplant is largely local and whatever material that is available is often of poor quality, mainly due to lack of development of seed quality testing protocols, thus hampering the correct assessment of the quality of seed used for sowing. The study aimed at determining temperature and light optima for seed germination and seedling development of spiderplant morphotypes from western Kenya. The original spiderplant seeds for the study were sourced from farmers in Kakamega District and from wildly growing plants within Chepkoilel Campus in Uasin Gishu District, both in western Kenya. Four morphotypes were identified and selected based on the presence or absence of anthocyanins on their stems and petioles, respectively. Tests on seed quality aspects were done at the Bioscience Business Unit at Plant Research International, Wageningen, The Netherlands. Determination of optimum temperature for seed germination was conducted by incubating three replicates of 100 seeds each of the four morphotypes at constant temperatures of 20, 25, 30, 35, 40 and 45OC, respectively. In order to determine the light regime for seed germination and optimum temperature for seedling development four replicates of 50 seeds each were incubated at constant temperatures of 30 and 35 OC at 8-hr light day-1 and 0-hr light day-1 (in 24-hr darkness), respectively. Data analysis (ANOVA, statistical descriptors and t-tests) were done using statistical package SeedCalculator 3.0. Germination was strongly influenced by temperature showing declines at both extremes of 20 and 45OC and optimum of 35 and 40OC. Light had no influence on germination since seeds germinated equally well under light and in the dark. Seedling development was strongly influenced by temperature with higher percentage of normal seedlings at 30OC than at 35OC. It is concluded that while temperature had an effect on seed germination performance and seedling development, light on the other hand showed no effect on seed germination for the spiderplant morphotypes studied. However, white light is required in order to aid in seedling evaluation

Multiple anomalous U(1)s in heterotic blow-ups

The existence of multiple anomalous U(1)s is demonstrated explicitly in a blow-up version of a heterotic Z_3 orbifold. Another blow-up of the same orbifold supports further evidence for the type-I/heterotic duality in four dimensions. It has a single anomalous U(1) which does not factorize universally. As multiple anomalous U(1)s as well as non-universal factorization have never been established on heterotic orbifolds explicitely, these findings might appear contradictory at first sight. Possible inconsistencies are avoided by reinterpreting a charged twisted state as a second non-universal localized axion. The mismatch between the charges of the orbifold and blow-up spectra is resolved by suitable field redefinitions. The anomaly of the field redefinitions corresponds to the difference of blow-up and heterotic orbifold anomalies.Comment: 7 pages LaTe

The vertical metal insulator semiconductor tunnel transistor: A proposed Fowler-Nordheim tunneling device

We propose a new field-effect transistor, the vertical metal insulator semiconductor tunnel transistor (VMISTT) which operates using gate modulation of the Fowler-Nordheim tunneling current through a metal insulator semiconductor (M-I-S) diode. The VMISTT has significant advantages over the metal-oxide-semiconductor field-effect transistor in device scaling. In order to allow room-temperature operation of the VMISTT, the tunnel oxide has to be optimized for the metal-to-insulator barrier height and the current-voltage characteristics. We have grown TiO2 layers as the tunnel insulator by oxidizing 7 and 10 nm thick Ti metal films vacuum-evaporated on silicon substrates, and characterized the films by current-voltage and capacitance-voltage techniques. The quality of the oxide films showed variations, depending on the oxidation temperatures in the range of 450-550 degrees C. Fowler-Nordheim tunneling was observed at low temperatures at bias voltage of 2 V and above and a barrier height of approximately 0.4 eV was calculated. Leakage currents present were due Schottky-barrier emission at room-temperature, and hopping at liquid nitrogen temperature

The population of AM CVn stars from the Sloan Digital Sky Survey

The AM Canum Venaticorum stars are rare interacting white dwarf binaries, whose formation and evolution are still poorly known. The Sloan Digital Sky Survey provides, for the first time, a sample of 6 AM CVn stars (out of a total population of 18) that is sufficiently homogeneous that we can start to study the population in some detail. We use the Sloan sample to `calibrate' theoretical population synthesis models for the space density of AM CVn stars. We consider optimistic and pessimistic models for different theoretical formation channels, which yield predictions for the local space density that are more than two orders of magnitude apart. When calibrated with the observations, all models give a local space density of 1-3x10^{-6} pc^{-3}, which is lower than expected. We discuss the implications for the formation of AM CVn stars, and conclude that at least one of the dominant formation channels (the double-degenerate channel) has to be suppressed relative to the optimistic models. In the framework of the current models this suggests that the mass transfer between white dwarfs usually cannot be stabilized. We furthermore discuss evolutionary effects that have so far not been considered in population synthesis models, but which could be of influence for the observed population. We finish by remarking that, with our lower space density, the expected number of Galactic AM CVn stars resolvable by gravitational-wave detectors like LISA should be lowered from current estimates, to about 1,000 for a mission duration of one year.Comment: Accepted to MNRA

Observation of negative differential conductance in a reverse-biased Ni/Ge Schottky diode

We report the experimental observation of negative differential conductance in a Ni/Ge Schottky diode. With the aid of theoretical models and numerical simulation we show that, at reverse bias, electons tunnel into the high electric field of the depletion region. This scatters the electrons into the upper valley of the Ge conduction band, which has a lower mobility. The observed negative differential conductance is hence attributed to the transferred-electron effect. This shows that Schottky contacts can be used to create hot electrons for transferred-electron devices

Impact and extinction signatures in complete Cretaceous-Tertiary (K-T) boundary sections

The Zumaya, Caravaca and Agost sections in Spain, the El Kef section in Tunisia and the Negev (Nahal Avdat) sections in Israel are among the most continuous, expanded and complete K-T boundary sections. The distribution patterns of the planktic faunas were quantitatively analyzed in closely spaced samples across the K-T boundary in these sections, in conjuction with the geochemistry, stable isotopes, mineralogy and magnetostratigraphy. Three hundred foraminiferal specimens were randomly selected and determined. Reliable estimates for the foraminiferal productivity changes across the K-T boundary and for the 1 to 2 Ma interval preceding the K-T boundary were made from the numbers of individuals/gram of sediment corrected for the sedimentation rates (calculated from magnetic reversals and lithology). No gradual or stepwise extinction is seen below the K-T boundary nor any productivity decrease. Stable isotope analyses show a warming just after deposition of the ejecta layer, not cooling as predicted by nuclear winter scenarios, although the duration of such cooling may be too short to be observed even in these complete sections. Low REE values and cpx spherules with quench textures idential to quench-textures in diagenetically altered spherules, strongly indicate an oceanic site of (one of) the impactor(s)