Pollinating insect responses to grazing intensity, grassland characteristics and landscape complexity

Pollinators uphold important ecological functions and their economic and ecological importance is considerable. In the present thesis the relationship between management practices and the behaviour, diversity and composition of four flower visitor groups: bees, butterflies, hoverflies and beetles, are examined in grasslands with different grazing intensity and in different landscapes in East-Central Sweden. Four flower visitor groups were influenced by grazing intensity in different ways. Hoverflies and beetles were positively related to vegetation height, while bees and butterflies were not. In the latter two groups some species were favoured by short vegetation. Hoverflies were more species rich in forested landscapes, whereas butterfly species richness was lower in areas containing many roads. Bees showed the most complex responses mainly due to their diverse life-history strategies corresponding to different environmental factors. The species richness of nest-parasitic and soil nesting bees was favoured by intensive grazing and the existence of bare soil. Cylinder-nesting solitary bees were little affected by management, and high species richness was associated with eutrophication and low plant species richness. The reproductive output in this group can be measured by produced offspring biomass, and this related mainly to human activity. Bumblebees were influenced mainly by landscape factors and long-tongued species appearing late in the season were especially dependent on landscape connectivity and grassland cover. To maintain viable populations of flower visitors, alternative grazing strategies are recommended. To maintain a high diversity of flower visitors in isolated grasslands local optimisation of grazing may be the best strategy. In interconnected landscapes a better strategy may be to vary grazing intensity at the landscape level. Grasslands with different grazing management could thus complement each other. In landscapes where conditions are particularly good for specific insects, a third alternative would be to manage the landscape to enhance the diversity of this particular group

Subset-Optimized Polarization-Multiplexed PSK for Fiber-Optic Communications

A more power-efficient modulation format than polarization-multiplexed quadrature phase-shift keying (PM-QPSK) can be obtained by optimizing the amplitude ratio between symbols with odd and even parity in the PM-QPSK constellation. The optimal amplitude ratio approaches the golden ratio at high signal-to-noise ratio (SNR), yielding a 0.44 dB increase in asymptotic power efficiency compared to PM-QPSK. Union bound expressions are derived for the bit and symbol error rate of the new format, which together with Monte Carlo simulations give the power efficiency at both low and high SNR. A similar optimization performed on PM-8PSK gains 1.25 dB

Modified constant modulus algorithm for polarization-switched QPSK

A modified constant modulus algorithm (CMA) is presented that allows polarization demultiplexing and equalization of polarizationswitched QPSK. An implementation is suggested that allows easy switching between the traditional and the modified CMA. Using numerical simulations, the suggested algorithm is shown to have similar performance as CMA has for polarization-multiplexed QPSK

Frequency and polarization switched QPSK

We propose 8-dimensional biorthogonal modulation as a format with 3 dB increased asymptotic power efficiency over PM-QPSK. We demonstrate one possible experimental implementation of this format based on frequency and polarization switching and compare with dual-carrier PM-QPSK and PS-QPSK

Interleaved Polarization Division Multiplexing in Self-Homodyne Coherent WDM Systems

We demonstrate increased spectral efficiency for self-homodyne coherent WDM systems by using a novel interleaved polarization division multiplexing scheme

Filter Optimization for Self-Homodyne Coherent WDM Systems using Interleaved Polarization Division Multiplexing

We examine the impact of filtering on self-homodyne coherent WDM systems using the interleaved polarization division multiplexing scheme. To investigate the performance limit and to provide more insight into previously obtained experimental results we perform numerical simulations in which different filter shapes and filter bandwidths are used. It is shown that with proper prefiltering of the data and filtering of the pilot tone in the receiver, performance can approach that of an intradyne system, which would make it possible to implement coherent systems with high spectral efficiency without any digital signal processing in the receiver

The Impact of Self-Phase Modulation on Digital Clock Recovery in Coherent Optical Communication

The impact of self-phase modulation on the estimation error variance of digital clock recovery schemes for coherent 16-QAM dual-polarization systems is investigated. The error variance increases severely compared to the linear case and the theoretical bounds

Operational Regime of Symbol-by-Symbol Phase Noise Estimation for POLMUX 16-QAM

A symbol-by-symbol phase noise estimation algorithm for polarization-multiplexed 16-QAM is evaluated. We found that it can cope with laser linewidths of up to 2.2 MHz in high SNR regimes, at 112 Gbit/s