840 research outputs found
Weed management in organic echinacea (Echinacea purpurea) and lettuce (Lactuca sativa) production
Weed management is a major constraint in organic production. It can be expensive and time-consuming and severe crop yield losses may be incurred when weeds are not adequately controlled. Research on organic weed management (OWM) in herb and vegetable production is increasing internationally, although in Australia very little work has been done to assess current OWM knowledge among growers, and to test the efficacy and cost effectiveness of the weed management practices used by organic growers. The effect of hand weeding, tillage, hay mulch, pelletised paper mulch and an unweeded control treatment on weed growth, crop growth and cost effectiveness were evaluated in several field trials on the Northern Tablelands of New South Wales using lettuce (Lactuca sativa L.) and echinacea (Echinacea purpurea Moench. [L.]). Weed management in lettuce was cost-effectively achieved using cheaper weeding methods such as tillage. More expensive methods such as hand weeding and hay mulching controlled weeds well, but were less cost effective. For echinacea, cheaper in-crop weeding methods (e.g. tillage, unweeded control) had poor weed suppression and low crop yields, while the more expensive weeding methods, hand weeding and hay mulch, controlled weeds well and were cost effective. Paper mulch controlled weeds very well but, again, had lower yields and was therefore not cost effective. The results highlight several important advantages and disadvantages of currently used OWM methods in the field
Multi-patch model for transport properties of cuprate superconductors
A number of normal state transport properties of cuprate superconductors are
analyzed in detail using the Boltzmann equation. The momentum dependence of the
electronic structure and the strong momentum anisotropy of the electronic
scattering are included in a phenomenological way via a multi-patch model. The
Brillouin zone and the Fermi surface are divided in regions where scattering
between the electrons is strong and the Fermi velocity is low (hot patches) and
in regions where the scattering is weak and the Fermi velocity is large (cold
patches). We present several motivations for this phenomenology starting from
various microscopic approaches. A solution of the Boltzmann equation in the
case of N patches is obtained and an expression for the distribution function
away from equilibrium is given. Within this framework, and limiting our
analysis to the two patches case, the temperature dependence of resistivity,
thermoelectric power, Hall angle, magnetoresistance and thermal Hall
conductivity are studied in a systematic way analyzing the role of the patch
geometry and the temperature dependence of the scattering rates. In the case of
Bi-based cuprates, using ARPES data for the electronic structure, and assuming
an inter-patch scattering between hot and cold states with a linear temperature
dependence, a reasonable agreement with the available experiments is obtained.Comment: 18 pages, 18 figures, to be published on Eur. Phys. J.
Brassica cover crops for weed control in organic vegetable production
Cover crops (or green manures) are commonly used by organic vegetable growers for soil fertility building and other benefits including weed control. Brassica crops have been reported to control weeds in subsequent crops, usually attributed to the allelopathic effects of glucosinolates (GSL) in the brassica residues, although the effects are inconsistent. New brassica varieties with high GSL levels (Brassica juncea cv. Fumus and Raphanus sativus cv. Weedcheck) were tested in combination with mechanical weed control and another locally grown forage crop (Lolium multiflorum cv. Conquest) for their effects on weed growth during the pre-crop phase and subsequent weed and lettuce growth during the in-crop phase. The cover crops and bare fallow controlled weeds effectively during the pre-crop phase, but did not affect weed and lettuce growth in the following in-crop phase. The cover crops provided better on-going weed control than the bare fallow. Reducing the delay between the pre- and in-crop phases from four weeks to one day did not affect weed and lettuce growth. Weed control was closely related to the amount of light reduction by the cover crops, while competition for nutrients and water appeared to be less important in weed suppression by the cover crops. The use of cover crops requires careful selection of appropriate varieties, attention to good cover crop husbandry (particularly establishment) and an awareness of prevailing weed seed bank levels
Improving competitive ability of chickpea with sowthistle
An experiment was conducted to examine the extent of root and canopy interference of chickpea (Cicer arietinum L.) with sowthistle (Sonchus oleraceus L.). Sowthistle was surrounded with either two or eight chickpea plants. There were different types of competition: no competition, shoot competition, root competition and full competition (root and shoot). The performance of sowthistle grown in full competition with two chickpea plants was the same as that grown with root competition only. Also, there were no significant differences between sowthistle grown with chickpea canopy shade and the control, where there was no competition. On the other hand sowthistle grown with eight neighbours was significantly suppressed in full, canopy or root competition
Numerical Renormalization Group studies of Quantum Impurity Models in the Strong Coupling Limit
In this thesis we summarize a number of theoretical studies
dealing with various properties of quantum dots.
Small quantum dots with a large level spacing
are very well described by the Anderson impurity model.
In modern quantum dot experiments all parameters of this model can be tuned via external gate voltages. Thus, it should be possible to check our theoretical findings experimentally.
We are particularly interested in temperatures smaller than the so-called Kondo temperature , . The Kondo temperature is an energy scale below
which a local spin inside the dot interacts strongly with the conduction electrons in its neighboring leads.
Consequently we employ Wilson's numerical renormalization group method, a numerical technique which allows for an accurate calculation of properties of quantum dots in the Kondo regime
Multiple vessel variations in the retropubic region
We encountered some multiple vessel variations in the retropubic region of
a 55-year-old male cadaver. The obturator artery had its origin from the external
iliac artery, and inferior epigastric artery from the femoral artery. Additionally,
an anastomosis between obturator and inferior epigastric veins (venous Crown
of death) was observed
A case with subclavius posticus muscle
During routine dissection studies, we encountered an aberrant muscle in the neck region of a 50 year-old female cadaver. The accessory muscle was on the left side. It arose from the superior angle of the scapula and lay over the brachial plexus and brachial artery then inserted to the first rib’s cartilage. According to its origin and insertion, the aberrant muscle was considered to be the subclavius posticus. The accessory muscle was innervated by a branch coming from the suprascapular nerve
Charge oscillations in Quantum Dots: Renormalization group and Hartree method calculations
We analyze the local level occupation of a spinless, interacting two-level
quantum dot coupled to two leads by means of Wilson's numerical renormalization
group method. A gate voltage sweep, causing a rearrangement of the charge such
that the system's energy is minimized, leads to oscillations, and sometimes
even inversions, in the level occupations. These charge oscillations can be
understood qualitatively by a simple Hartree analysis. By allowing a relative
sign in one tunneling matrix element between dot and leads, we extend our
findings to more generic models.Comment: 6 pages, 7 figure
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