436 research outputs found
Relationship between allocation of absorbed light energy in PSII and photosynthetic rates of C-3 and C-4 plants
Two C-3 dicotyledonous crops and five C-4 monocotyledons treated with three levels of nitrogen were used to evaluate quantitatively the relationship between the allocation of absorbed light energy in PSII and photosynthetic rates (P (N)) in a warm condition (25-26A degrees C) at four to five levels [200, 400, 800, 1,200 (both C-3 and C-4) and 2,000 (C-4 only) mu mol m(-2) s(-1)] of photosynthetic photon flux density (PPFD). For plants of the same type (C-3 or C-4), there was a linear positive correlation between the fraction of absorbed light energy that was utilized in PSII photochemistry (P) and P (N), regardless of the broad range of their photosynthetic rates due to species-specific effect and/or nitrogen application; meanwhile, the fraction of absorbed light energy that was dissipated through non-photochemical quenching (D) showed a negative linear regression with P (N) for each level of PPFD. The intercept of regression lines between P and P (N) of C-3 and C-4 plants decreased, and that between D and P (N) increased with increasing PPFD. With P and D as the main components of energy dissipation and complementary to each other, the fraction of excess absorbed light energy (E) was unchanged by P (N) under the same level of PPFD. At the same level of P (N), C-4 plants had lower P and higher D than C-3 plants, due to the fact that C-4 plants with little or no photorespiration is considered a limited energy sink for electrons. Nevertheless there was a significant negative linear correlation between D and P when data from both C-3 and C-4 plants at varied PPFD levels was merged. The slope of regression lines between P and D was 0.85, indicating that in plants of both types, most of the unnecessary absorbed energy (ca. 85%) could dissipate through non-photochemical quenching, when P was inhibited by low P (N) due to species-specific effect and nitrogen limitation at all levels of illumination used in the experiment
Minimal Steiner Trees for 2kĂ2kSquare Lattices
AbstractWe prove a conjecture of Chung, Graham, and Gardner (Math. Mag.62(1989), 83â96), giving the form of the minimal Steiner trees for the set of points comprising the vertices of a 2kĂ2ksquare lattice. Each full component of these minimal trees is the minimal Steiner tree for the four vertices of a square
Propiedades fisicoquĂmicas de snacks extrusionados de patatas y batatas con aceite de palma roja
Extruded potato (P) and sweet potato (SP) products with red palm oil (RPO) were prepared under different conditions. Superior product characteristics such as sensory score, expansion ratio, and water solubility index, among others, were obtained at high extrusion temperature (150-155 °C) and low water feed rate to the extruder (50.4-50.8 mL/min). The optimal products, P1 and SP1, had high micronutrients as their total contents of ÎČ-carotene, squalene, tocopherols, and tocotrienols were 883.2, 304.4, 262.4, and 397.0 mg/kg of oil, respectively. The average peroxide value was 4.3 meq O2/kg oil, p-anisidine value 3.3, and induction period (100 °C) 11.4 h. Moreover, RPO extruded with P showed a better extrusion behavior but lower micronutrient retention and oxidative stability than that extruded with SP. Thus, the finding herein is important for investigating extrusion conditions, increasing variety, improving nutritional quality, assessing applicability and predicting the shelf-life of RPO-P/SP-extruded food.Se prepararon snacks extrusionados de patatas (P) y batatas (B) con aceite de palma roja (APR) en diferentes condiciones. Se obtuvieron unas caracterĂsticas superiores de los productos, como puntuaciĂłn sensorial, relaciĂłn de expansiĂłn, Ăndice soluble en agua, entre otros, a alta temperatura de extrusiĂłn (150-155 °C) y baja velocidad de alimentaciĂłn de agua al extrusionador (50,4-50,8 mL/min). Los productos Ăłptimos, P1 y SP1, contenĂan altos micronutrientes ya que su contenido total de ÎČ-caroteno, escualeno, tocoferoles y tocotrienoles fue de 883,2; 304,4; 262,4 y 397,0 mg/kg de aceite, respectivamente. El Ăndice de perĂłxido promedio fue de 4,3 meq O2/kg de aceite, el valor de p-anisidina de 3,3 y el perĂodo de inducciĂłn a 100 °C de 11,4 h. AdemĂĄs, el APR utilizado para la extrusiĂłn de P mostrĂł un mejor comportamiento de extrusiĂłn, pero menor retenciĂłn de micronutrientes y estabilidad oxidativa que el extrusionado con SP. Por lo tanto, los datos aquĂ obtenidos son importantes para profundizar en las condiciones de extrusiĂłn, aumentar la variedad, mejorar la calidad nutricional, evaluar la aplicabilidad y predecir la vida Ăștil de los alimentos extrusionados con APR-P / B
Effects of osmotic- and high-light stresses on PSII efficiency of attached and detached leaves of three tree species adapted to different water regimes
Abscisic acid (ABA), an important chemical signal from roots, causes physiological changes in leaves, including stomata closure and photoprotection. Furthermore, endogenous ABA concentration in leaves and stomatal behavior vary with the species adapted to different water regimes. In this study, Ficus microcarpa, a hemiepiphyte, Salix warburgii, a hygrophyte, and Acacia confusa, a mesophyte, were used to elucidate the effects of leaf detachment on photosystem II (PSII) efficiency under osmotic- and high-light stresses. Results indicate that, under osmotic- and high-light stresses, PSII efficiency of the detached leaves was lower than that of the attached leaves for all three tree species, when compared at the same levels of stomatal resistance and leaf water potential. Exogenous ABA could mitigate the PSII efficiency decrease of detached F. microcarpa leaves under osmotic- and high-light stresses. Yet, the osmotic stress could raise endogenous ABA concentration in the attached, but not in the detached F. microcarpa leaves. In addition, partial root-zone drying exerted a significant effect on stomatal behavior but not on the water status of F. microcarpa leaves. These observations imply that the stronger ability of PSII in the attached leaves of F. microcarpa under osmoticand high-light stresses was probably due to the protective action of ABA from roots. On the contrary, endogenous ABA level of S. warburgii leaves was very low. In addition, partial root-zone drying produced no significant effect on its stomatal behavior. Therefore, PSII in attached S. warburgii leaves was possibly protected from the damaging effects of excess absorbed energy by signals other than ABA, which were transported from the roots
A comparison between yellow-green and green cultivars of four vegetable species in pigments, ascorbate, photosynthesis, energy dissipation, and photoinhibition
Yellow-green foliage cultivars of four vegetables grown outdoors, i.e., Chinese mustard (Brassica rapa), Chinese kale (Brassica oleracea var. alboglabra), sweet potato (Ipomoea batatas) and Chinese amaranth (Amaranthus tricolor), had lower chlorophyll (Chl) (a+b) (29-36% of green cultivars of the same species), total carotenoids (46-62%) and ascorbate (72-90%) contents per leaf area. Furthermore, yellow-green cultivars had smaller photosystem II (PSII) antenna size (65-70%) and lower photosynthetic capacity (52-63%), but higher Chl a/b (107-156%) and from low (60%) to high (129%) ratios of de-epoxidized xanthophyll cycle pigments per Chl a content. Potential quantum efficiency of PSII (F(v)/F(m)) of all overnight dark-adapted leaves was ca. 0.8, with no significant difference between yellow-green and green cultivars of the same species. However, yellow-green cultivars displayed a higher degree of photoinhibition (lower F(v)/F(m) after illumination) when they were exposed to high irradiance. Although vegetables used in this study are of either temperate or tropical origin and include both C(3) and C(4) plants, data from all cultivars combined revealed that F(v)/F(m) after illumination still showed a significant positive linear regression with xanthophyll cycle-dependent energy quenching (q(E)) and a negative linear regression with photoinhibitory quenching (q(I)). F(v)/F(m) was, however, not correlated with nonphotochemical quenching (NPQ). Yet, a higher degree of photoinhibition in yellow-green cultivars could recover during the night darkness period, suggesting that the repair of PSII in yellow-green cultivars would allow them to grow normally in the field
A local families index formula for d-bar operators on punctured Riemann surfaces
Using heat kernel methods developed by Vaillant, a local index formula is
obtained for families of d-bar operators on the Teichmuller universal curve of
Riemann surfaces of genus g with n punctures. The formula also holds on the
moduli space M{g,n} in the sense of orbifolds where it can be written in terms
of Mumford-Morita-Miller classes. The degree two part of the formula gives the
curvature of the corresponding determinant line bundle equipped with the
Quillen connection, a result originally obtained by Takhtajan and Zograf.Comment: 47 page
Traveling wave solutions for a predator-prey system with Sigmoidal response function
We study the existence of traveling wave solutions for a diffusive
predator-prey system. The system considered in this paper is governed by a
Sigmoidal response function which is more general than those studied
previously. Our method is an improvement to the original method introduced in
the work of Dunbar \cite{Dunbar1,Dunbar2}. A bounded Wazewski set is used in
this work while unbounded Wazewski sets were used in \cite{Dunbar1,Dunbar2}.
The existence of traveling wave solutions connecting two equilibria is
established by using the original Wazewski's theorem which is much simpler than
the extended version in Dunbar's work
Spin dynamics in semiconductors
This article reviews the current status of spin dynamics in semiconductors
which has achieved a lot of progress in the past years due to the fast growing
field of semiconductor spintronics. The primary focus is the theoretical and
experimental developments of spin relaxation and dephasing in both spin
precession in time domain and spin diffusion and transport in spacial domain. A
fully microscopic many-body investigation on spin dynamics based on the kinetic
spin Bloch equation approach is reviewed comprehensively.Comment: a review article with 193 pages and 1103 references. To be published
in Physics Reports
Measurements of the observed cross sections for exclusive light hadron production in e^+e^- annihilation at \sqrt{s}= 3.773 and 3.650 GeV
By analyzing the data sets of 17.3 pb taken at GeV
and 6.5 pb taken at GeV with the BESII detector at the
BEPC collider, we have measured the observed cross sections for 12 exclusive
light hadron final states produced in annihilation at the two energy
points. We have also set the upper limits on the observed cross sections and
the branching fractions for decay to these final states at 90%
C.L.Comment: 8 pages, 5 figur
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