284 research outputs found
Nectar distribution and its relation to food quality in honeybee ( Apis mellifera ) colonies
Abstract.: In honeybees (Apis mellifera), the process of nectar collection is considered a straightforward example of task partitioning with two subtasks or two intersecting cycles of activity: (1) foraging and (2) storing of nectar, linked via its transfer between foragers and food processors. Many observations suggest, however, that nectar collection and processing in honeybees is a complex process, involving workers of other sub-castes and depending on variables such as resource profitability or the amount of stored honey. It has been observed that food processor bees often distribute food to other hive bees after receiving it from incoming foragers, instead of storing it immediately in honey cells. While there is little information about the sub-caste affiliation and the behaviour of these second-order receivers, this stage may be important for the rapid distribution of nutrients and related information. To investigate the identity of these second-order receivers, we quantified behaviours following nectar transfer and compared these behaviours with the behaviour of average worker hive-bees. Furthermore, we tested whether food quality (sugar concentration) affects the behaviour of the second-order receivers. Of all identified second-order receivers, 59.3% performed nurse duties, 18.5% performed food-processor duties and 22.2% performed forager duties. After food intake, these bees were more active, had more trophallaxes (especially offering contacts) compared to average workers and they were found mainly in the brood area, independent of food quality. Our results show that the liquid food can be distributed rapidly among many bees of the three main worker sub-castes, without being stored in honey cells first. Furthermore, the results suggest that the rapid distribution of food partly depends on the high activity of second-order receiver
Resonant tunneling through a C60 molecular junction in liquid environment
We present electronic transport measurements through thiolated C
molecules in liquid environment. The molecules were placed within a
mechanically controllable break junction using a single anchoring group per
molecule. When varying the electrode separation of the C-modified
junctions, we observed a peak in the conductance traces. The shape of the
curves is strongly influenced by the environment of the junction as shown by
measurements in two distinct solvents. In the framework of a simple resonant
tunneling model, we can extract the electronic tunneling rates governing the
transport properties of the junctions.Comment: 13 pages, 4 figures. To appear in Nanotechnolog
Effective interaction between molecules in the BEC regime of a superfluid Fermi gas
We investigate the effective interaction between Cooper-pair molecules in the
st rong-coupling BEC regime of a superfluid Fermi gas with a Feshbach
resonance. Our work uses a path integral formulation and a renormalization
group (RG) analy sis of fluctuations in a single-channel model. We show that a
physical cutoff en ergy originating from the finite molecular
binding energy is the key to understanding the interaction between molecules in
the BEC regime. Our work t hus clarifies recent results by showing that is a {\it ba re} molecular scattering length while is the low energy molecular scattering length
renormalized to include high-energy scat tering up to (here is the scattering length between Fermi atoms). We also include many-body
effects at finite temperatures. We find that is strongly dependent
on temperature, vanishing at , consistent with the earlier Bose gas
results of Bijlsma and Stoof.Comment: 10 pages, 3 figure
Long-term organic matter application reduces cadmium but not zinc concentrations in wheat
Wheat is a staple food crop and a major source of both the essential micronutrient zinc (Zn) and the toxic heavy metal cadmium (Cd) for humans. Since Zn and Cd are chemically similar, increasing Zn concentrations in wheat grains (biofortification), while preventing Cd accumulation, is an agronomic challenge. We used two Swiss agricultural long-term field trials, the “Dynamic-Organic-Conventional System Comparison Trial” (DOK) and the “Zurich Organic Fertilization Experiment” (ZOFE), to investigate the impact of long-term organic, mineral and combined fertilizer inputs on total and phytoavailable concentrations of soil Zn and Cd and their accumulation in winter wheat ( L.). “Diffusive gradients in thin films” (DGT) and diethylene-triaminepentaacetic acid (DTPA) extraction were used as proxies for plant available soil metals. Compared to unfertilized controls, long-term organic fertilization with composted manure or green waste compost led to higher soil organic carbon, cation exchange capacity and pH, while DGT-available Zn and Cd concentrations were reduced. The DGT method was a strong predictor of shoot and grain Cd, but not Zn concentrations. Shoot and grain Zn concentrations correlated with DTPA-extractable and total soil Zn concentrations in the ZOFE, but not the DOK trial. Long-term compost fertilization led to lower accumulation of Cd in wheat grains, but did not affect grain Zn. Therefore, Zn/Cd ratios in the grains increased. High Zn and Cd inputs with organic fertilizers and high Cd inputs with phosphate fertilizers led to positive Zn and Cd mass balances when taking into account atmospheric deposition and fertilizer inputs. On the other hand, mineral fertilization led to the depletion of soil Zn due to higher yields and thus higher Zn exports than under organic management. The study supports the use of organic fertilizers for reducing Cd concentrations of wheat grains in the long-term, given that the quality of the fertilizers is guaranteed
Green manure and long-term fertilization effects on available soil zinc and cadmium and their accumulation by wheat (Triticum aestivum L.)
Zinc (Zn) deficiency in humans due to imbalanced diets is a global nutritional problem. It is especially widespread in populations of low-income countries depending on cereals as staple food. Grain Zn concentrations are particularly low in cereals grown on soils with low phytoavailable Zn concentrations. . Plant Zn uptake depends on soil properties such as pH, calcium carbonate, iron and manganese oxides, total Zn and organic matter content (OM). Soil pH, total Zn and OM can be influenced on farms with limited access to mineral fertilizers through organic matter management practises. In this study, we investigated to what extent green manure application could increase soil Zn availability and wheat grain Zn concentrations (biofortification) on soil with different long-term fertilizer management
Transition Temperature of a Uniform Imperfect Bose Gas
We calculate the transition temperature of a uniform dilute Bose gas with
repulsive interactions, using a known virial expansion of the equation of
state. We find that the transition temperature is higher than that of an ideal
gas, with a fractional increase K_0(na^3)^{1/6}, where n is the density and a
is the S-wave scattering length, and K_0 is a constant given in the paper. This
disagrees with all existing results, analytical or numerical. It agrees exactly
in magnitude with a result due to Toyoda, but has the opposite sign.Comment: Email correspondence to [email protected] ; 2 pages using REVTe
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Automatic Analysis of Bees’ Waggle Dance
This work describe an algorithm for the automatic analysis of the waggle dance of honeybees. The algorithm analyses a video of a beehive with 13,624 frames, acquired at 25 frames/second. The algorithm employs the following traditional image processing steps: conversion to grayscale, low pass filtering, background subtraction, thresholding, tracking and clustering to detect run of bees that perform waggle dances. The algorithm detected 44,530 waggle events, i.e. one bee waggling in one time frame, which were then clustered into 511 waggle runs. Most of these were concentrated in one section of the hive. The accuracy of the tracking was 90% and a series of metrics like intra-dance variation in angle and duration were found to be consistent with literature. Whilst this algorithm was tested on a single video, the ideas and steps, which are simple as compared with Machine and Deep Learning techniques, should be attractive for researchers in this field who are not specialists in more complex techniques
The transition temperature of the dilute interacting Bose gas
We show that the critical temperature of a uniform dilute Bose gas must
increase linearly with the s-wave scattering length describing the repulsion
between the particles. Because of infrared divergences, the magnitude of the
shift cannot be obtained from perturbation theory, even in the weak coupling
regime; rather, it is proportional to the size of the critical region in
momentum space. By means of a self-consistent calculation of the quasiparticle
spectrum at low momenta at the transition, we find an estimate of the effect in
reasonable agreement with numerical simulations.Comment: 4 pages, Revtex, to be published in Physical Review Letter
Honeybees forage more successfully without the "dance language" in challenging environments.
Honeybees use the waggle dance to share information about food-site locations with nestmates. However, the importance of this behavior in colony foraging success remains unclear. We tested whether spatial dance information affects colony foraging success in a human-modified temperate environment by comparing colonies with oriented and disoriented dances. Notably, colonies with disoriented dances had greater foraging success. Over time, bees exposed to disoriented dances showed reduced interest in dancing nestmates. This may explain why disoriented colonies had a higher foraging rate than oriented colonies, as bees did not waste time waiting for information. This change in information-use strategy suggests bees learn about the value of dance information. An agent-based model confirmed that, under challenging conditions, waiting for dance information reduces colony foraging success compared to foraging without social information. Our results raise the possibility that humans have created environments to which the waggle dance language is not well adapted
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