319 research outputs found
Effect of composition and processing conditions on the direct reduction of iron oxide pellets
No full textIn this paper, HSC software is used to estimate the effects of composition and processing conditions on the reduction behavior of iron oxide pellets, i.e., hematite (Fe2O3), magnetite (Fe3O4), wustite (FeO), pure iron (Fe), and iron carbide (Fe3C), in a wide temperature range from room temperature (RT) to 1000°C in the presence of H2 and CO mixtures. The reducibility of iron ores, in particular Fe2O3, Fe3O4, FeO, Fe is discussed. The choice of reducing agents CO and H2 is explained, with CO proving to be the more effective reducing agent at high temperatures from a thermodynamic point of view. However, the free Gibbs energy of iron reduction is lowest in the presence of a 100% H2 atmosphere. In addition, H2 reduces tortuosity and increases porosity by reducing it at cooler temperatures and promoting diffusion. In contrast, CO increases tortuosity and reduces initial porosity because it requires higher temperatures for effective reduction and causes structural changes. The presence of impurities other than iron oxides has been shown to impair the activity of reduced pure iron by acting as catalyst poisons or participating in competing reactions. CaO accelerates the reduction of FeO, which is due to the formation of calcium ferrite, but the effect decreases at higher temperatures. MgO can either promote or hinder reduction, depending on its concentration and its influence on pellet porosity. The presence of several non‐iron oxides has been shown to affect the overall direct reduction of iron ore pellets, resulting in a significant impact of the overall process
Dynamic recrystallization nanoarchitectonics of FeCrCuMnNi multi-phase high entropy alloy
No full textDynamic recrystallization behavior of the FeCrCuMnNi high entropy alloy (HEA) was investigated through hot compression test at different temperatures and at constant strain rate. The results revealed that during hot deformation of FeCrCuMnNi HEA, flow stress and work hardening rate rapidly decreased with increasing the deformation temperature. Discontinuous dynamic recrystallization (dDRX) was found to be the main active mechanism during hot deformation, which was the governing mechanism even at higher temperatures. In addition, bulging was an effective mechanism for inducing new recrystallized nuclei. Grain growth was occurred at slow strain rate in comparison to conventional alloys and other HEAs. This behavior was attributed to the continuous nucleation during dDRX, sluggish diffusion, high solution hardening characteristics of HEAs, and the presence of multiple phases in the FeCrCuMnNi HEA. Texture analysis showed that at lower temperatures, deformation texture including // CA fiber was formed. By increasing the deformation temperature, the formation of recrystallization texture fibers such as // CA and // CA rapidly intensified
Characteristics of night-time absorption spike events
No full textInternational audienceSudden increases in cosmic radio noise absorption, known as spike events, have been identified as signatures of substorms in the previous studies. Using data from the IRIS (Imaging Riometer for Ionospheric Studies) at Kilpisjärvi, Finland (L~6) more than 450 night-time spike events between 1994 and 2003 have been identified. Spike events fall into four distinct categories based on their structure and the background magnetic activity as indicated by a local westward electrojet (IL index) derived from the IMAGE (International Monitor for Auroral Geomagnetic Effects) magnetometer network as well as Pi2 magnetic pulsations from SAMNET (The UK Sub-Auroral Magnetometer Network). Classifying the types of absorption spikes allows for identification of phenomena such as multiple onsets and pseudobreakups from riometer data. In addition we have studied the statistical variation of absorption spikes and their sub-classes. This includes examining the magnetic local time (MLT) distribution and the seasonal and solar-cycle variation in spike occurrence. Those that seem to represent substorm onsets show a decidedly different MLT variation to those isolated spikes that represent pseudobreakups. The occurrence of spikes during different levels of geomagnetic activity is examined using the Kp index. Wavelet analysis has been used for studying the temporal structure of spikes; also the direction of motion of spike events and localisation of spikes are presented for all events and each sub-class and results are compared with previous studies. Statistical studies are supported with X-ray images of aurora from PIXIE (The Polar Ionospheric X-ray Imaging Experiment) when available
Frequency division multiplexing readout of 60 low-noise transition-edge sensor bolometers
No full textWe demonstrate multiplexing readout of 60 transition edge sensor (TES) bolometers operating at 90 mK using a frequency division multiplexing readout chain with bias frequencies ranging from 1 to 3.5 MHz and with a typical frequency spacing of 32 kHz. The readout chain starts with a two-stage SQUID amplifier and has a noise level of 9.5 pA/ Hz. We compare current-voltage curves and noise spectra of TESs measured in a single-pixel mode and in a multiplexing mode. We also map the noise equivalent power (NEP) and the saturation power of the bolometers in both modes, where there are 43 pixels that do not show more than 10% difference in NEP and 5% in saturation power when measured in single pixel and multiplex modes. We have read out a TES with an NEP of 0.45 aW/ Hz in the multiplexing-mode, which demonstrates the capability of reading out ultra-low noise TES bolometer arrays for space applications.Accepted Author ManuscriptImPhys/Optic
Frequency division multiplexing readout of a transition edge sensor bolometer array with microstrip-type electrical bias lines
No full textWe demonstrate multiplexed readout of 43 transition edge sensor (TES) bolometers operating at 90 mK using a frequency division multiplexing (FDM) readout chain with bias frequencies ranging from 1 to 3.5 MHz and a typical frequency spacing of 32 kHz. We improve the previously reported performance of our FDM system by two important steps. First, we replace the coplanar wires with microstrip wires, which minimize the cross talk from mutual inductance. From the measured electrical cross talk (ECT) map, the ECT of all pixels is carrier leakage dominated. Only five pixels show an ECT level higher than 1%. Second, we reduce the thermal response speed of the TES detectors by a factor of 20 by increasing the heat capacity of the TES, which allows us to bias all TES detectors below 50% in transition without oscillations. We compare the current-voltage curves and noise spectra of the TESs measured in single-pixel mode and multiplexing mode. We also compare the noise equivalent power (NEP) and the saturation power of the bolometers in both modes, where 38 pixels show less than 10% difference in NEP and 5% difference in saturation power when measured in the two different modes. The measured noise spectrum is in good agreement with the simulated noise based on measured parameters from an impedance measurement, confirming that our TES is dominated by phonon noise.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ImPhys/Adam grou
Characteristics of night time absorption spike events as signatures of magnetosphere ionosphere (M-I) coupling
No full textNight time absorption spike events (NASE) are common signatures of magnetospheric substorms. Their occurrence in the ionosphere can be easily detected by riometers located at ground based stations. This unique feature is used to achieve a comprehensive study based on 500 NASE occurred during the period 1994-2003 in the IRIS (imaging riometer for ionospheric studies) field of view at Kilpisjarvi, Finland centred at 69.05° N, 20.79° E (L-shell 6.1). NASE generally had similar behaviour which has been mentioned for substorms in the literature. Occurrence of NASE dominates around magnetic local midnight (MLM) with majority of events in the pre-midnight sector. NASE seem to occur more often during high geomagnetic activity according to Kp index variation. Their occurrence during geomagnetic equinoxes is slightly more than that of s~lstices with the peak in the autumn and minimum in the summer time. They also tend to be solar cycle dependent as their appear3?ces during solar minimum dominate in agreement with occurrence of substorms. Our study confIrms most results of previous NASE studies. . . North/westward motion of spike events was dominant with speed in a range of few hundreds to few kms per second. Pi2 pulsations and auroral breakup (found from PIXIE, polar ionospheric X-ray imaging experiment images) are a common feature of NASE. The signifIcant frequency modulation of NASE is in the order of 50 mHz -200 mHz based on wavelet analysis. Apart from these new findings are also discussed in this thesis: Considering the temporal structure and variation of IT.- index, NASE are categorized into 4 classes. Classifications of spike events allow the identification of phenomena such as pseudobreakups from substorms. Another important finding of this study is the location of mapped points of NASE which is in the range of near Earth magnetotail rather than midtail region in favour of current disruption (CD) substorm model as opposed to near Earth neutral line (NENL) model. This yields using geomagnetic field model T-96 and NASE of IRIS and SGO (SodankyHi geophysical observatory) riometers where together covers auroral zone latitudes between 62.42° Nand 77.00 N (L- shell between 3.8-13.6).EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Ultra-long wavelength Radio Observations on the Moon, A Scientific and Technical Review
No full textItem does not contain fulltext63rd International Astronautical Congress 2012, 1-5 October 2012, Naples, Ital
Economic Analysis of Violations of Human Rights in the Islamic Republic of Iran
No full textHuman rights violations in Iran present a challenging issue for international law and a complex subject for research. Most effort has gone into broadcasting Iran's systematic and gross violations of human rights. As a way to move beyond this point, this thesis uses the "law and economics" approach, political economy, and behavioral insights to investigate the behavioral dynamics of state-based human rights violations in post-revolutionary Iran. The first chapter describes human rights in Iran and reveals how institutional designs exacerbate repression. Chapter two provides a literature review, addresses methodological concerns, and defines "Economic analysis of human rights" as a distinct field. The third chapter presents a political economic conceptual framework, discusses the determinants of human rights violations in Iran, and investigates some of the underlying behavioral dynamics of repression in Iran. Finally, statistical analysis indicates that political transitions and armed conflicts are causally linked to more human rights violations in Iran.LL.M
Noise Measurements of a Low-Noise Amplifier in the FDM Readout System for SAFARI
No full textThe SPICA-SAFARI instrument requires extremely sensitive transition edge sensor (TES) arrays with a noise equivalent power of 2×10-19W/Hz and a readout system with an output noise that is dominated by the detector noise. It is essential to ensure the frequency domain multiplexing (FDM) readout system in SAFARI meets the noise requirement. The FDM system in SAFARI consists essentially of LC filters, a superconducting quantum interference device, a room-temperature low-noise amplifier (LNA), and a demultiplexer. Here we present a noise study of the LNA from a laboratory amplifier chain. We found the equivalent current and voltage noise of the LNA to be 5.4pA/Hz and 315pV/Hz, respectively, which are low enough to read out SAFARI’s TES arrays.QN/Gao La
Effects of Plyometric and Cluster Resistance Training on Explosive Power and Maximum Strength in Karate Players
No full textThe purpose of this study was to investigate the effects of plyometric and cluster resistance training on explosive power and maximum strength in karate players. Eighteen women, karate players (age mean ± SD 18.22 ± 3.02 years, mean height 163 ± 0.63cm, and mean body mass 53.25 ± 7.34 kg) were selected as volunteer samples. They were divided into two groups with respect to their recorded one repetition maximum squat exercise: [1] plyometric training (PT=9) and [2] Cluster training (CT=9) groups and performed a 9-week resistance training protocol that included three stages; [1] General fitness (2 weeks), [2] Strength (4 weeks) and [3] Power (3 weeks). Each group performed strength and power trainings for 7 weeks in stage two and three with owned protocol. The subjects were evaluated three times before stage one and after two and three stages for maximum strength and power. Data was analyzed using two way Repeated Measures (ANOVA) at a significance level of (P≤0.05). The statistical analysis showed that training stages on all research variables had a significant impact. The maximum strength of the pre-test, post-test strength and post-test power were in cluster group: 29.05 ± 1.54; 32.89 ± 2.80 and 48.74 ± 4.33w and in plyometric group were 26.98 ± 1.54; 38.48 ± 2.80 and 49.82 ± 4.33w respectively. The explosive power of the pre-test, post-test strength and post-test power in cluster group were 359.32±36.20; 427.91±34.56 and 460.55±36.80w and in plyometric group were 333.90±36.20; 400.33±34.56 and 465.20±36.80w respectively. However, there were not statistically significant differences in research variables between resistance cluster and plyometric training groups after 7 weeks. The results indicated both cluster and plyometric training program seems to improve physical fitness elements at the same levels.</jats:p
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