Die polymerisation der lactame XI. Die copolymerisation von 6-caprolactam mit 12-laurolactam

The course of the incorporation of 6-caprolactam and 12-laurolactam into polymer chains during the hydrolytic, cationic and anionic copolymerization for an equimolar ratio of the monomers was studied. During the hydrolytic copolymerization 6-caprolactam is incorporated more rapidly at 260, 230 or 200°C at the beginning of the polymerization process; the differences between incorporation rates of the lactams into the copolymer increase with decreasing temperature. During the cationic copolymerization the incorporation of 12-laurolactam is more rapid by orders of magnitude for the above temperatures at the beginning of the process. Changes in the composition of cationic copolymers as compared to the hydrolytic copolymers are independent of the temperature during the copolymerization. The anionic copolymerization is characterized by a more rapid incorporation of 6-caprolactam into the polymer chain. The differences in the polymerization activity of the two lactams decrease with increasing temperature of the anionic copolymerization. The described course of incorporation of individual monomers, with the various mechanisms of the polymerization, also corresponds to melting points of copolymers in accordance with their composition.     

Excess Heat Capacity in NTD Ge Thermistors

Neutron Transmutation Doped (NTD) germanium thermistors, cut from metallized wafers, are useful in bolometry. The rise time of a bolometer depends on its heat capacity. We report measurements on the heat capacity of two NTD Ge wafers down to 24 mK temperatures. Both wafers were neutron irradiated and annealed, one of them had in addition undergone a boron implantation and metallization process. For the non-metallized wafer we found a Sommerfeld constant γ = 7.52·10⁻⁷ J K⁻² cm⁻³. A comparison between the two wafers showed an excess heat capacity in the metallized wafer. For example, at 24 mK temperature, the specific heat of the metallized afer is more than twice the value of the non-metallized one.     

Retrieval Inhibition in Directed Forgetting Following Severe Closed-Head Injury.

A variant of the list method directed forgetting procedure was used to examine the role of inhibition in memory performance following severe closed-head injury (CHI). Twenty-four participants with severe CHI and 24 controls studied picture and word stimuli in both forget and remember conditions. Memory testing for the to-be-forgotten and to-be-remembered items consisted of a free-recall test followed by a source-monitoring task. Despite poorer recall performance, the participants with CHI exhibited a directed forgetting effect similar to that in controls. Item recognition scores indicated that the inhibited items were not forgotten but rather were items whose accessibility had been lowered. These findings suggest that residual memory deficits in patients with severe CHI are unlikely to reflect inefficient retrieval inhibition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Measurement of the thermal conductivity of copper samples between 30 and 150 mK

We report data of thermal conductivity between 30 and 150 mK of three different types of commercial copper, before and after a thermal treatment of the samples. The measurements show that both purity and thermal treatment strongly influence the value of thermal conductivity. Data show a strict linear dependence on the temperature of the thermal conductivity.     

$$\hbox {RuO}_{2}$$ Non-isothermal Thermometry

The use of a \(\hbox {RuO}_{2}\) resistor in non-isothermal measuring setup is proposed. A calculation is presented to explain the principle for a resistor obeying variable-range-hopping theory and the results are compared to measurements in the range of 11.2–30 mK for a commercial resistor. The thermometer, which measures the electron temperature, does not show overheating effects at 11.2 mK with a measuring power of \(10^{-12}\) W.     

Optimisation of the pilot-to-data power ratio in the wireless MIMO-OFDM system with low-complexity MMSE channel estimation

Multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) communication systems are currently being viewed as a main candidate for the next generation broadband wireless access interfaces providing high throughput. However, a considerable potential gain in spectral efficiency is challenged by the receiver’s ability of accurate data symbol identification at the output of the radio channel. Performance of the MIMO detectors strongly depends on both the received signal-to-noise power ratio (SNR) and the retrieved channel state information (CSI), which can be obtained using the channel estimation techniques relying on pilot symbol transmission on the dedicated subcarriers. Necessity to improve channel estimation and detection performance concurrently leads to the dilemma of the optimal power assignment to the data and pilot subcarriers as these are the conflicting requirements under the total transmit power constraint. We derive an analytical solution of the described problem in the form of weak and tight upper bounds on the pilot-to-data power ratio (PDR) given the system design parameters (number of subcarriers, number of pilots, number of transmit antennas, model order of the channel response, SNR). The resultant PDR equations can be applied to OFDM systems with arbitrary arrangement of the pilot subcarriers operating in an arbitrary multipath channel, not just limited to the equispaced optimal pilot pattern and the channel with the uniform sample-spaced power-delay profile as studied in the previous works.In an adaptive system, which is capable to adjust transmit signal configuration (e.g., block length, number of pilot subcarriers or antennas) according to the established channel conditions, an optimal parameter tuning is desirable for each operational mode. The closed-form PDR expressions and their analysis presented in this work are designated to alleviate the challenging task of the on-the-fly system optimisation as they represent relatively simple functional relationships.     

Mapping coffee plantations with Landsat imagery: an example from El Salvador

Considering the potential of shaded coffee plantations mixed with natural vegetation for promoting biodiversity conservation, this project assessed the utility of multi-date Landsat Thematic Mapper (TM) satellite imagery for the characterization of natural vegetation versus coffee plantations in western El Salvador. For assembling a multi-temporal Landsat TM data set, we applied a regression analysis model to remove cloud cover and cloud shadows. Then, through a hybrid classification approach, a nine-class land use/land cover (LULC) map was generated. We identified two types of coffee plantations (‘open-canopy’ and ‘close-canopy’) along with natural forest/shrubland, mangrove, water bodies, sandy coastal soils, bare soil, urban areas and agriculture. Notwithstanding the small sample size of the accuracy data, our assessment revealed an overall accuracy of 76.7% (Kappa coefficient?=?0.68), considering only the four classes with independent field data. The overall classification accuracy for distinguishing coffee plantations from non-mangrove natural forest was 81.6% and the classification accuracy for distinguishing ‘open-canopy’ from ‘close-canopy’ coffee plantations was 85.7%. We are encouraged by the results of this prototype study. They indicate that remote-sensing techniques can be used to distinguish different classes of coffee production systems and to differentiate coffee from natural forest.     

GEOMETRIC TASK DECOMPOSITION IN A MULTI-AGENT ENVIRONMENT

ABSTRACT

Task decomposition in a multi-agent environment is often performed online. This paper proposes a method for sub-task allocation that can be performed before the agents are deployed, reducing the need for communication among agents during their mission. The proposed method uses a Voronoi diagram to partition the task-space among team members and includes two phases: static and dynamic. Static decomposition (performed in simulation before the start of the mission) repeatedly partitions the task-space by generating random diagrams and measuring the efficacy of the corresponding sub-task allocation. If necessary, dynamic decomposition (performed in simulation after the start of a mission) modifies the result of a static decomposition (i.e., in case of resource limitations for some agents). Empirical results are reported for the problem of surveillance of an arbitrary region by a team of agents.     

Critical comparison of methods to determine the energy input for discrete manufacturing processes

High variation can be observed in energy requirement values reported for unit processes as applied in discrete manufacturing. Different methods for determining such values have been suggested, ranging from theoretic energy determination till statistically determined time averaged values based on experimental process measurements. In this paper the theoretic process energy method is compared to results as obtained from two methods suggested for systematic determination of Life Cycle Inventory (LCI) database entries for unit processes. Examples from different process categories are presented to illustrate the discrepancies observed between the approaches and to illustrate the error range linked to the method selection.