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Showing papers by "Technical University of Denmark published in 1974"


Journal ArticleDOI
TL;DR: In this paper, a linearized flow equation was proposed to calculate the distribution of the bed shear stress in a meandering channel with fixed side walls, and the results were compared with experiments, concluding that the helical motion introduced by the channel curvature may be fairly well described.
Abstract: Uniform flow in river bends of rectangular or arbitrary cross section has been calculated by the slip velocity method and the results are compared with experiments. It is concluded that the helical motion introduced by the channel curvature may be fairly well described. The results are then applied to the more complex problem of flow in a river bend with movable bed. Next, the problem of flow in a meandering channel with fixed side walls has been investigated, using a special system of curvilinear coordinates. The solution of the linearized flow equations yields a method for calculation of the distribution of the bed shear stress. In the first approximation the large-scale bottom geometry is calculated by considering the lateral sediment balance. The helical flow will move the sediment particles towards the curvature center, while the transverse slope of the bed will give a movement in the opposite direction.

562 citations



Journal ArticleDOI
TL;DR: In this article, a two-dimensional stability analysis of the flow in a straight alluvial channel has been carried out, using the vorticity transport equation, and an attempt has been made to account for the influence of gravity on bed-load transport, and this turned out to change the stability quite significantly.
Abstract: A two-dimensional stability analysis of the flow in a straight alluvial channel has been carried out, using the vorticity transport equation. In the analysis an attempt has been made to account for the influence of gravity on bed-load transport, and this turned out to change the stability quite significantly.In the case of instability, the further growth of the dunes has been investigated using a second-order approximation, This nonlinear theory explains the experimental fact that the dunes very soon become asymmetric.

240 citations


Journal ArticleDOI
01 May 1974-Wear
TL;DR: In this paper, a general theory for friction in metal working processes is developed based upon the slip-line theory as a model of analysis, and the real area of contact α and the nominal friction stress τn are determined as functions of the nominal normal pressure q/2k and the friction factor m.

154 citations


Journal ArticleDOI
TL;DR: In this article, the electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method, and the best band structure is obtained from an ad hoc potential based on a Dirac-Slater atomic calculation for the ground state configuration and with full Slater exchange in the atomic as well as in the crystal potential.
Abstract: The electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method. A series of mutually related potentials are constructed by varying the electronic configuration and the amount of Slater exchange included. The best band structure is obtained from an ad hoc potential based on a Dirac-Slater atomic calculation for the ground-state configuration and with full Slater exchange in the atomic as well as in the crystal potential. The selection of this best potential is justified by comparing the calculated band structure to Fermi-surface experiments and to optical-reflectance measurements up to 5-eV photon energy. The temperature and strain responses in the band structure are estimated from band calculations with four different lattice constants. The band structure was determined in the entire Brillouin zone and is applied to a calculation of photoemission spectra from W single crystals. The nondirect as well as the direct models for bulk photoemission processes are investigated. The emission from the three low-index surfaces (100), (110), and (111) exhibits strong dependence on direction and acceptance cone. According to the present band model there should essentially be no emission normal to the (110) face for photon energies between 9.4 and 10.6 eV. Experimental observation of emission in this gap, however, implies effects not included in the simple bulk models. In particular, effects arising from surface emission have been considered, i.e., emission of those electrons which are excited in a single-step process from initial states near the surface to final states outside the crystal. The electrons that are emitted from the surface in directions perpendicular to the crystal planes carry information on the one-dimensional surface density of states. The present work includes a crude estimate of this surface density of states, which is derived from the bulk band structure by narrowing the $d$ bands according to an effective number of neighbors per surface atom. Estimates of surface relaxation effects are also included.

138 citations


Journal ArticleDOI
TL;DR: In this paper, the energy distribution of photoelectrons emitted normal to three single-crystal faces of tungsten has been measured for photon energies between 7.7 and 21.2 eV, and the results are interpreted in terms of one-dimensional electronic properties along the symmetry lines in $k$ space that correspond to the emitting crystal faces.
Abstract: Energy-distribution spectra of photoelectrons emitted normal to three single-crystal faces of tungsten have been measured for photon energies between 7.7 and 21.2 eV. The results are interpreted in terms of one-dimensional electronic properties along the symmetry lines in $k$ space that correspond to the emitting crystal faces. The emitted spectra may be considered to consist of three types of contributions. One part is due to electrons that, after excitation by direct interband transitions in the bulk, have left the crystal unscattered. This contribution may be described by the energy density of a one-dimensional joint density of states along a symmetry line in the Brillouin zone. Another part, evident for photon energies above 12 eV, is due to electrons that have suffered inelastic scattering processes after optical excitation. This part carries information on the density of conduction states along the symmetry line under observation. Finally, a third contribution to the emitted spectrum is assigned to surface emission. This part reflects the surface density of states and bears evidence of a narrowing of the $d$ bands near the surface. A theoretical surface density of states, derived from a simple model that scales the width of the $d$ bands by the square root of an effective number of neighbor atoms, is found to describe the energy distribution of the electrons emitted by the surface effect satisfactorily.

93 citations


Journal ArticleDOI
TL;DR: In this paper, the air gap electrode was used to determine the carbon dioxide and ammonia contents of a series of samples, using sample volumes from 50−150 μl to several ml.

83 citations


Journal ArticleDOI
TL;DR: In this article, the authors derived the deflection function corresponding to the optimal plate thickness function from a non-linear, fourth order partial differential eigenvalue problem, derived by variational analysis.

77 citations


Journal ArticleDOI
TL;DR: Although the rectal temperature and the mean skin temperature were slightly higher in the evening than in the morning the subjects did not prefer an ambient temperature which was different from that in themorning, which indicates that the same thermal comfort conditions can be used from morning to evening.
Abstract: Eight females and eight males participated each in 4 comfort experiments on 4 different days. Two experiments took place in the morning and two in the evening. In each experiment (21/2 hours) the preferred ambient temperature was determined for each subject by adjusting the ambient temperature according to his wishes. The subjects were sedentary. Skin temperatures, rectal temperature and evaporative weight loss were measured.

64 citations


Journal ArticleDOI
TL;DR: In this article, a theoretical formulation in terms of combined magnetic and electric field integral equations is presented for the class of electromagnetic problems in which one or more wire antennas are connected to a conducting body of arbitrary shape.
Abstract: A theoretical formulation, in terms of combined magnetic and electric field integral equations, is presented for the class of electromagnetic problems in which one or more wire antennas are connected to a conducting body of arbitrary shape. The formulation is suitable for numerical computation provided that the overall dimensions of the structure are not large compared to the wavelength. A computer program is described, and test runs on various configurations involving a cylindrical body with one or more straight wires are presented. The results obtained agree well with experimental data.

63 citations


Journal ArticleDOI
TL;DR: In this article, the ground states of perchlorate, sulphate and phosphate ions were calculated using the Hartree-Fock limit for the Gaussian-type basis sets of 12s, 10p and 2d primitive functions.
Abstract: Ab initio SCF LCAO MO calculations have been performed for the ground states of the perchlorate, sulphate and phosphate ions. The basis sets used consisted of contracted gaussian-type orbitals having 12s, 10p and 2d-type primitive functions on the central atoms and 10s and 6p-type functions on the oxygens. The results are thought to be nearly at the Hartree-Fock limit.

Journal ArticleDOI
TL;DR: The sensor used is the newly developed air-gap electrode of Růžicka and Hansen, and has advantages of speed of response and specificity over earlier enzyme electrodes for urea, which was used for the assay of urea in blood serum with excellent results.

Journal ArticleDOI
TL;DR: Positron annihilation has been used in a study of the annealing of molybdenum irradiated at 60°C to the low dose of 1·5 × 1018 fast neutrons cm−2.
Abstract: Positron annihilation has been used in a study of the annealing of molybdenum irradiated at 60°C to the low dose of 1·5 × 1018 fast neutrons cm−2. On the basis of changes observed in positron lifetimes and intensities, it was possible to identify the defect mechanisms responsible for the various annealing stages. In particular it was possible to follow the growth of vacancy clusters with increasing temperature, and to establish the formation of voids above 580°C.

Journal ArticleDOI
TL;DR: The newly developed air-gap electrode has been used for enzymatic assay of urea in serum and whole blood; analyses can be done accurately, reliably, simply and quickly.

Journal ArticleDOI
TL;DR: In this paper, the disappearance of quintozene and its technical impurities and metabolites from soil was studied in laboratory experiments under controlled conditions during a period of about 600 days, and the very high persistence found, was confirmed by the analysis of 22 samples collected from fields used for potato growing and treated regularly during the foregoing 11 years with commercial formulations of quintioxene.
Abstract: The disappearance of quintozene (I) and its technical impurities and metabolites pentachlorobenzene (III), hexachlorobenzene (IV) and pentachloroaniline (V) from soil, was studied in laboratory experiments under controlled conditions during a period of about 600 days. The very high persistence found, was confirmed by the analysis of 22 samples collected from fields used for potato growing and treated regularly during the foregoing 11 years with commercial formulations of quintozene. In the laboratory experiments, III, V and methylthiopentachlorobenzene (VI) were found to be degradation products from the quintozene.

Journal ArticleDOI
TL;DR: In this paper, a new lead(II) Selectrode, activated with PbS/Ag2S, has been calibrated in lead-II buffers and found to exhibit an almost Nernstian response within the pPb range of 2-11.


Journal ArticleDOI
TL;DR: In this paper, it was shown that the wave generated by a sinusoidal piston motion can be described as a second order Stokes wave superimposed by a free second harmonic wave.


Journal ArticleDOI
TL;DR: The rectal temperature and the mean skin temperature at which the subjects felt comfortable were 0.4° C lower in the night experiment than in the day experiment, indicating that the same thermal comfort conditions can be used independent of the time of day or night.
Abstract: 8 women and 8 men each participated in two comfort experiments. One experiment took place at the time of the day when the rectal temperature was maximum, and the other experiment took place at the time of the night when the rectal temperature was minimum. The exact times at which the maximum and minimum body temperatures occurred were determined for each person in pretests. In each comfort experiment (2 1/2 hrs) the preferred ambient temperature was determined for each subject by adjusting the ambient temperature according to his wishes. The subjects were sedentary. Skin temperatures, rectal temperature, metabolic rate and evaporative weight loss were measured. The rectal temperature and the mean skin temperature at which the subjects felt comfortable were 0.4° C lower in the night experiment than in the day experiment. But due to a slightly lower metabolic rate at night this did not cause the subjects to prefer a different ambient temperature at the two points of time. This indicates that the same thermal comfort conditions can be used independent of the time of day or night.



Journal ArticleDOI
TL;DR: In this article, the authors measured the rising velocity, including angle and wake size of large single air bubbles in a two-dimensional column, 39.5 cm wide and 112 cm high, which contained a liquid or three-phase fluidised bed.



Journal ArticleDOI
TL;DR: In this paper, the Tafel plots of the iron electrode were used to determine the reaction orders with respect to pH in solutions containing chloride or bromid, pH ca 3-5.

Journal ArticleDOI
TL;DR: In this article, it was found that specimen size has an important influence on the mercury porosimetry results and that steam cured cement pastes have a coarser pore structure than those cured at room temperature.

Journal ArticleDOI
TL;DR: Crossed immunoelectrophoresis was used to estimate four aminopeptidases in organs of germinating barley, and to demonstrate non-identity, identity and partial identity between barley and malt proteins.
Abstract: Quantitative immunoelectrophoresis techniques were applied to the study of barley and malt proteins. By crossed immunoelectrophoresis of malt more than 54 immunochemically distinct proteins were distinguished, whereas only 24 proteins have been included in the E.B.C. system of reference based on electro-immunodiffusion.* Crossed immunoelectrophoresis was also used to estimate four aminopeptidases in organs of germinating barley, and to demonstrate non-identity, identity and partial identity between barley and malt proteins. Tandem crossed immunoelectrophoresis was used to compare the proteins in extracts of barley and malt and rocket immunoelectrophoresis to determine an α-amylase in germinating barley. Fused rocket immunoelectrophoresis was used to detect elution patterns of individual barley proteins after ion exchange chromatography, and line immunoelectrophoresis to compare three barley antisera. Advantages of quantitative immunoelectrophoresis over electro-immunodiffusion are demonstrated and discussed. A new system of reference for barley and malt proteins based on crossed immunoelectrophoresis is suggested.

Journal ArticleDOI
TL;DR: In this article, the magnetic properties of NdAl2 are calculated using a Hamiltonian including crystal-field and isotropic exchange interaction terms, and a two-dimensional mean-field theory is evaluated to calculate single-crystal magnetization curves.
Abstract: The magnetic properties of NdAl2 are calculated using a Hamiltonian including crystal-field and isotropic exchange interaction terms. A two-dimensional mean-field theory is evaluated to calculate single-crystal magnetization curves. It is shown that the magnetic properties can be understood using the crystal-field parameters derived from the magnetic exciton spectrum measured by Houmann et al. by means of inelastic neutron scattering. The combined lambda -Schottky anomaly in the heat capacity is explained. No additional parameters are introduced.

Journal ArticleDOI
TL;DR: In this paper, an experimental investigation of a squeeze film damper for the control of rotor amplitudes was carried out using direct measurements of the transmitted force and the velocity of the damper sleeve, and the damping coefficient of the squeeze film was obtained over a range of frequencies and values of film thickness and oil viscosity.
Abstract: This paper describes an experimental investigation of a squeeze film damper for the control of rotor amplitudes From direct measurements of the transmitted force and the velocity of the damper sleeve, the damping coefficient of the squeeze film is obtained over a range of frequencies and for several values of film thickness and oil viscosity The results are compared with the theoretical formula, based on assumptions of linearity, and from a practical application point of view the correlation is satisfactory