Real-Time Detection of Terahertz Pulse Amplitude and Position

A novel and continuous detection scheme for the pulse amplitude and temporal position of a terahertz time domain system is presented. Currently, we have achieved a sampling time of 25 Hz and a resolution of less than 70 fs. The method is therefore very well suited for online measurements in production processes to monitor the thickness and inhomogeneities in the composition of non-conducting materials.     

Influence of Spatially Variable Side Friction on Single Drilled Shaft Resistance and LRFD Resistance Factors

Load and resistance factor design (LRFD) is a method that aims at meeting specified target reliabilities (probabilities of failure) of engineered systems. The present work focuses on ultimate side friction resistance for axial loads on single cylindrical drilled shaft foundations in the presence of spatially variable rock/soil strength. Core sample data are assumed to provide reliable information about local strength in terms of mean, coefficient of variation and spatial correlation structure (variogram) at a site. The geostatistical principle of support up-scaling is applied to quantify the reduction in variability between local strength and the average ultimate shaft side friction resistance without having to recur to lengthy stochastic finite difference/element simulations. Site and shaft specific LRFD resistance factors (Φ values) are given based on the assumption of lognormal load and resistance distributions and existing formulas recommended by the Federal Highway Administration. Results are efficiently represented in dimensionless charts for a wide range of target reliabilities, shaft dimensions, and geostatistical parameters including nested variograms of different types with geometric and/or zonal anisotropies. Field data of local rock strength is used to demonstrate the method and to evaluate the sensitivity of obtained resistance factors to potentially uncertain variogram parameters.     

Occupational Factors and 5-Year Weight Change Among Men in a Danish National Cohort.

This study explored whether factors related to the work environment could predict changes in body mass index (BMI) and whether the effect of psychosocial factors was dependent on baseline BMI. The sample consisted of 1,980 male employees from the Danish National Work Environment Cohort Study. Changes in BMI between 1995 and 2000 were analyzed, by multiple regression, as a function of background variables and a series of occupational variables obtained in 1995. Age, baseline BMI, job insecurity, and psychological demands predicted changes in BMI. Job insecurity and high or low psychological demands increased the likelihood of weight gain among obese employees, whereas they increased the likelihood of weight loss among employees with a low BMI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Structure and optical properties of heterostructures based on MOCVD (Al x Ga1 − x As1 − y P y )1 − z Si z alloys

Epitaxial heterostructures produced by MOCVD on the basis of Al _x Ga_{1 ? x} As ternary alloys with the composition parameter x ≈ 0.20–0.50 and doped to a high Si and P atomic content are studied. Using the high-resolution X-ray diffraction technique, scanning electron microscopy, X-ray microanalysis, Raman spectroscopy, and photoluminescence spectroscopy, it is shown that the epitaxial films grown by MOCVD are formed of five-component (Al _x Ga_{1 ? x} As_{1 ? y} P _y )_{1 ? z} Si _z alloys.     

On considering hierarchical modulation in the porting process of legacy waveforms to software defined radio

The novel software defined radio (SDR) technology allows taking the next step in the evolution of military tactical communications. SDRs allow military radio operators to change waveforms on-the-fly according to the mission needs. On the one hand, new wideband networking waveforms will offer new services like high data throughputs and mobile ad-hoc networking capabilities. On the other hand, legacy waveforms will ensure interoperability to legacy equipment in missions where both types of radios are deployed at the same time. In this article, we analyze if an added value can be provided to the operators at SDRs hosting an ‘enhanced’ legacy waveform. This enhancement shall be introduced such that interoperability to the legacy equipment is still guaranteed. The modern concept of hierarchical modulation allows fulfilling this side constraint. While the legacy waveform acts as base-layer, some enhancement-layers offer extra bit budget to transmit additional information. This spare bit budget can be exploited to increase the data rate (i.e. throughput), the error robustness (and with this communication range), or both.     

A fluid-dynamically based model of bubble column reactors

A heterogeneous fluid dynamic model has been developed to describe the complex flow structure of two-phase in bubble columns. The equation of continuity and momentum balances form the basis of the model. Coupling of the two phases occurs via an interaction force, deduced by a force balance around a single rising bubble. Multiphase flow mixing processes are taken into consideration by introducing turbulent viscosities of the two phases involved. The Simulation program was extended to reactive system, taking into account the mass balances of a second order gas-liquid chemical reaction as well as the different absorption/reaction regimes. The gas phase concentration profiles show pronounced axial and radial dependences, while the liquid phase can be regarded as a CSTR with respect to the liquid component. With reference to the gaseous component, which is being absorbed in the liquid phase, the degree of back mixing does not show CSTR behaviour as the influence of different absorption conditions in different axial and radial reactor positions is superposed on that of turbulent motion of the liquid carrier of the dissolved gaseous component.     

Energy efficient surfaces on building sandwich panels—A dynamic simulation model

The choice of building envelope is critical for the energy performance of buildings. The major part of the energy used by a building during its lifetime is used for maintaining a suitable interior thermal climate under varying exterior conditions. Although exterior heat radiation properties (i.e. total solar reflectivity and long wave thermal emissivity) have been well accepted to have a large impact on the need for active cooling in warmer climate, the effect of a reduced thermal emissivity on interior surfaces on the building thermal energy flux is rarely studied. This paper addresses the sensitivity of the thermal energy flux through a sandwich panel, by systematically varying the surface thermal emissivity (both interior and exterior) and total solar reflectance of exterior surface, for three geographical locations: southern, middle and northern Europe. A model is introduced for calculating the effect of both interior and exterior optical properties of a horizontal roof panel in terms of net energy flux per unit area. The results indicate potential energy saving by the smart choice of optical properties of interior and exterior surfaces.     

Application of active coke in processes of SO2- and NOx-removal from flue gases

In the field of flue gas cleaning, active coke plays an important role as adsorbant and catalyst. In the temperature range usually prevailing downstream of the air preheater of power plants, SO₂ becomes adsorbed on carbonaceous materials and in a consecutive step is catalysed by the carbonaceous surface and converted to sulphuric acid. The quality demands for a cyclic regenerative process for SO₂ removal are fulfilled by the active coke which is used in the BF-process. The same active coke catalyses the reaction of NO with NH₃ to N₂ and steam. This is the basis for processes for simultaneous SO₂ and NO_x removal. By the addition of ammonia the SO₂ removal by active coke is improved. Two processes are described and results from the laboratory and from the demonstration plant for the BF-process are presented. These show that SO₂ removal efficiences exceed 95% and NO conversions of > 80% can be realized without problems. The cost of the processes using active coke with ammonia addition are comparable with those of wet flue gas desulphurization processes without any additional equipment should NO have to be removed.     

Testing of controllers for thermal solar systems

One standardised way to determine the performance of thermal solar systems is based on component testing and system simulation. The approach is to test the solar collector, the store, the controller and other selected components separately and to carry out system simulations using the determined parameters. Due to increasingly complex control strategies, particularly implemented within so-called multi-function controllers for solar combisystems, the available test method for controllers – for the time being defined in ENV 12977-2, Annex B – has to be extended. In order to substitute temperature sensors by variable resistors and to document the response of a tested controller, a computer based test facility featuring an input/output-emulator between the controller and a PC has been developed. The emulator generates varying resistance values as input signals for the controller and records the status of the different outputs as its response. Both, manual adjustment and programmed temperature profiles provided by the PC are possible. All transmitted inputs as well as the response of the controller are stored in a data file. Experience gained from testing controllers used in thermal solar systems for combined hot water preparation and space heating, commonly called combisystems shows that alleged advanced control algorithms or fancy features do not inevitably result in an improvement of system performance or increased reliability. The extended test method and the set-up of the test facility described in this paper enable detailed investigations of nearly all kinds of controllers. Particularly with respect to multi-function controller testing, the introduced test method will be one basis for the upcoming standard prCEN/TS 12977-5, replacing ENV 12977-2, Annex B.