Juris Blums

Ultrafast time‐resolved X‐ray diffraction

Femtosecond laser‐generated plasmas emit ultrashort X‐ray pulses in the multi‐keV range, which allow the extension of X‐ray spectroscopy into the ultrafast time‐domain. We report here on the generation of such short X‐ray pulses and their application for time‐resolved diffraction as a means to directly study ultrafast structural dynamics in laser‐excited solids.

MV cable temperature characteristics in dependence of load current, ambient environment and temperature. determination of the critical environment

The paper presents results of Latvian distribution system operator Sadales tikls AS (ST) and Riga Technical University (RTU) joint research on possibilities to increase the permissible loading level of the operating MV cables in order to improve the efficiency of the existing network assets usage and increase the supply reliability. Permissible loading level determination of the operating MV cables from the heating point of view is affected by many variable factors such as ambient environment, temperature, number and configuration of the cables etc. To estimate the temperature characteristics in dependence of load current of the operating MV cables in the real environment at different climatic and ambient environments (cable channels, ladders, soil and pipes) in the cities of Latvia a special MV cable sheath and ambient environment temperature monitoring device is designed. Sheath and ambient environment temperature monitoring of nine 10 kV and 20 kV cables at four ST 110/10-20 kV substations is carried out for a period of one year. By analyzing the acquired temperature monitoring data, dynamics of the cable sheath temperature in dependence of load current, ambient environment and temperature is determined. A mathematical model for maximum achievable MV cable sheath temperature prediction is developed.

Flat inductors for human motion energy harvesting

The human motion energy harvesting is under investigation. The aim of this investigation: to develop electromagnetic human motion energy harvester that will consist only from flat elements and is integrable into the apparel. Main parts of the developed human motion energy harvester are flat, spiral-shaped inductors. Voltage pulses in such flat inductors can be induced during the motion of a permanent magnet along it. Due to the flat structure, inductors can be completely integrated into the parts of the clothes and it is not necessary to keep empty place for the movement of the magnet, as in usual electromagnetic harvesters. The prototype of the clothing, jacket with integrated electromagnetic human motion energy harvester with flat inductors is tested. The theoretical model for the induction of the electromotive force due to the magnet’s movement is created for the basic shapes (round, rhombic, square) of the inductive elements and the results (shape of voltage pulse and generated energy) of the calculations are in a good qualitative and quantitative coincidence with an experimental research.

Investigation of Textile Materials for Laser Light Beam Scanning

The scanning of human body as a method for gaining human measurements has several preferences. The gathering of data is possible in a very short time. In comparison to manual measuring methods, scanning acquires a larger amount of measurements. There are several modes of gaining human body measurements using the scanning system: laser scanning, light beam scanning, etc. A research on the laser beam reflection capabilities on different textile materials has been performed. The description of laser reflections has been compared to the Lambert’s law’s characteristics. The matrix of material selection is made in the process of planning the experiment and all possible materials are presented in this matrix. Eight textile materials are chosen for the experimental work: six lingerie and two additional materials. A laser beam with an angle of incidence of 0º and 45º is used to make the experiment. The dependence of the results on the wavelength of laser beams has also been compared.

Electromagnetic Shielding Properties of Metal Yarns Fabrics with Graphite Coating

Using three types of yarns with metal filaments, textile samples with various arrangements of yarns were made and additionally coated with polyurethane and graphite layer. The aim of the study is to identify the metal filaments fabrics with the highest shielding effectiveness (SE) and influence of graphite layer on it, using a waveguide method and network analyzer with radiated frequency from 2.6 – 3.6 GHz. Layer of graphite improves the SE properties, although, some uncoated samples have higher SE for definite frequencies.

Sadales tikls AS Five most used MV cable type permissible loading possibilities at a critical environment in dependence of conductor temperature

The paper presents results of Latvian distribution system operator Sadales tikls AS (ST), Riga Technical University (RTU) and Latvian transmission system operator Augstsprieguma tikls AS (AS) joint research to determine the maximum permissible loading level of five ST most used 10 kV and 20 kV cable types and development of MV cable loading control methodology which includes development of maximum achievable cable conductor temperature prediction model for n - 1 conditions (broken one MV network element). At AS laboratory five most used ST MV cable type samples were protractedly loaded at a special test bed to simulate most critical ambient environment conditions of operating cables from the heating point of view with currents from 0.3 In to 1.1 In to imitate normal and n - 1 conditions in the electrical network. Experimentally gained temperature measurement data was used to develop mathematical models for MV cable sheath and conductor temperature prediction in dependence of load current, loading duration and different ambient environment (air, spray foam, soil).

Development of Microclimate Regulatory Clothes

The research is dedicated to microclimate regulatory clothes with an integrated electrical system, which also composes Peltier elements, and cooling function is based on the heat conductivity in solids. For development of the system and the clothes experiments are conducted to optimize the product microclimate regulatory function.

Structural dynamics in laser-excited solids investigated with femtosecond x-ray diffraction

Summary form only given. Ultrashort x-ray pulses offer a unique combination of atomic-scale spatial and temporal resolution, which permits direct measurements of structural transients on an ultrafast time scale. Using time-resolved X-ray diffraction with femtosecond, multi-keV X-ray pulses we have studied transient lattice dynamics in optically excited semiconductors and metals. In an optical pump/X-ray probe configuration transient changes in X-ray diffraction from [111]-oriented, single-crystalline thin films of Ge and Bi have been measured.

Influence of laser-induced centers on oxygen precipitation in silicon

In this work the kinetics of heterogeneous precipitation of silicon oxide in silicon is investigated. Laser induced centers act as nuclei for precipitates. Laser induced centers were formed in a near surface layer during pulsed laser annealing by double frequency of a Nd+3:YAG laser without introduction of any additional impurities. It is shown, that the process of formation and growth of precipitates in the presence of laser induced centers differs from the case of homogeneous. The dependence of the concentration of oxidation stacking faults on thermal treatment duration is given. The thickness of the layer with inhomogeneous distribution of oxidation stacking faults grows with thermal treatment duration in an inert ambient. This growth can be explained by the drift of oxygen atoms in the direction of the gradient of tensile internal stresses, which increases in silicon during the growth of silicon oxide precipitates.

Properties of unstable donors generated in Si during laser irradiation

The generation of unstable at room temperature centers in boron-doped Si during laser annealing are under investigation. It is shown, that the generation of two kinds of unstable centers with different recombination time constants during the laser annealing takes place. Through an investigation of dependence of the recombination time constants on temperature the activation energies of these donors are determined: EF equals 0.8 - 0.9 eV and E2 equals 1.4 - 1.5 eV. It is detected, that recombination time constants of centers depend on boron and oxygen atoms concentrations in laser-annealed region -- recombination time constants of both kinds of centers decrease with increase of both boron and oxygen concentrations in silicon. It is shown, that the generation of these unstable donors does not occur during the laser annealing of boron-doped silicon with basic frequency of Q-switched Nd:YAG-laser (wavelength 1.06 micrometer). The model of generation mechanism of the donors is proposed taking into account dependence of recrystallization velocity during pulsed laser annealing on absorption coefficient of radiation and a great difference in absorption coefficients of basic (k1 equals 15 cm-1) and double (k2 equals 104 cm-1) frequencies of Nd:YAG-laser radiation.