Gas metal arc welding of modified X2CrNi12 ferritic stainless steel

X2CrNi12 ferritic stainless steel is a low cost stainless steel grade exhibiting good corrosion and abrasion resistance. Typical applications for this steel are bus frames and chassis, railway wagons for coal and iron ore, mining and mineral processing, sugar and chemical process equipment, furnace parts etc. The modern production routes now allow fabricating this grade with low carbon content (< 0.015 %) and low impurity levels improving the weldability substantially. Regarding to these conditions, this modified stainless steel grade becomes more attractive. In this paper, microstructural and toughness properties and mechanical properties of gas metal arc welded 6 mm thick modified X2CrNi12 stainless steel with two different heat inputs are presented. Promising results have been obtained. Interesting correlation has been found between microstructure (e.g. grain size) and impact toughness

Space-time coding for CDMA-based wireless communication systems

Thesis (Master)--Izmir Institute of Technology, Electronics and Communication Engineering, Izmir, 2002Includes bibliographical references (leaves: 72-75)Text in English; Abstract: Turkish and Englishx, 75 leavesMultiple transmit antennas giving rise to diversity (transmit diversity) have been shown to increase downlink (base station to the mobile) capacity in cellular systems.The third generation partnership project (3GPP) for WCDMA has chosen space time transmit diversity (STTD) as the open loop transmit diversity technique for two transmit antennas.On the other hand, the CDMA 2000 has chosen space time spreading (STS) and orthogonal transmit diversity (OTD) as the open loop transmit diversity.In addition to all the standardization aspects, proposed contributions such as space time coding assisted double spread rake receiver (STC-DS-RR) are exist.In this thesis, open loop transmit diversity techniques of 3GPP, CDMA 2000 and existing contributions are investigated.Their performances are compared as a means of biterror- rate (BER) versus signal-to-noise ratio (SNR)

A cold atom electron source

Pulsed bright electron sources offer the possibility to study the structure of matter in great spatial and temporal detail. An example of an indirect method is to generate hard X-ray °ashes with high brilliance, a new Free Electron Laser facility is under construction. It requires an electron source with a very high quality. Electron beams may also be used directly to study matter with, e.g., ultrafast electron diffraction. This also requires a pulsed electron source with high brightness. An overview of experiments that require a bright electron source is presented in Chapter 1. Also the pulsed electron sources used at this moment, i.e., photo-emitters and field-emitters, are described in Chapter 1. Brightness is an important figure of merit for electron source quality. It is expressed in its most general form as the current density per unit solid angle and unit energy spread. Recent brightness improvements are based on increasing the current density at the source, but this is not sufficient for all types of experiments. A new type of source, based on ultracold plasma, is described in Chapter 2. Contrary to the usual approach to increase the current density at the source to obtain a higher brightness, the new method tries to increase the angular intensity for moderate values of the emission area. For the field-emitters and photo-emitters the effective electron temperature of the source is typically 10 3 – 10 4 K. If one is able to lower these temperatures at the source, then a gain in brightness proportional to the reduction of the temperature can be achieved for the same current density. The new source concept based on this idea proposes pulsed extraction of electrons from an ultracold plasma, that is created from a laser-cooled cloud of neutral atoms by photoionization just above threshold. These plasmas are characterized by electron temperatures of 10 K. A simple estimate serves to illustrate the possible performance of such a source. Laser-cooled atomic clouds can have central densities up to n = 1018 m¡3 and contain up to 1010 atoms, requiring a cloud with rms (root-mean-square) size ¾ = 1 mm. If all these atoms could be ionized to form a UCP (ultracold plasma) with an electron temperature T = 10 K, then an electron bunch with a charge Q = 1 nC and an emittance " = 0:04 mm mrad could be extracted. If, in addition, all of these electrons can be packed into a temporal bunch length on the order of ¾t = 100 fs, the transverse brightness of the resulting electron bunch would be B? = 6£1016 A/(m2 sr). This is a few orders of magnitude higher than what has been achieved so far in the regime of (sub)-ps electron bunches. A four-step procedure is used to realize a UCP-based electron source in practice. First, atoms are cooled and trapped in a magneto-optical trap. Second, part of the cold atom cloud is excited to an intermediate state with a quasi-continuous laser pulse. Third, a pulsed laser beam propagating at right angles to the excitation laser ionizes the excited atoms only within the volume irradiated by both lasers. Subsequently, a UCP is formed. Finally, the electrons of the UCP are extracted by an externally applied electric field pulse. Each step toward the ultracold plasma is explained in detail in Chapter 2. Subsequently, with the help of simulations with a particle tracking program, the expectations from a more realistic situation are investigated. Two geometries are discussed. First, an initial charge distribution called "pancake" (bunch length much smaller than its transversal size) with a half-circle radial charge density distribution offers for a beam transverse size of 2 mm an emittance of 0:1 mm mrad and a temporal bunch length of 150 fs. This results in a transverse brightness of 6 £ 1013 A/(m2 sr). Second, a "cigar" geometry (transverse size much smaller than bunch length) with a parabolic longitudinal charge density distribution offers for a beam transverse size of 1 mm an emittance of 0:07 mm mrad and a temporal bunch length of 20 fs. This results in a transverse brightness of 1 £ 1014 A/(m2 sr). In this Thesis the first practical steps are reported towards this new concept. In Chap- ter 3, a specially designed accelerator structure and a pulsed power supply are described. They are essential parts of a high brightness cold atoms-based electron source. The acce- lerator structure allows a magneto-optical atom trap to be operated inside of it, and also transmits sub-nanosecond electric field pulses. The power supply produces high voltage pulses up to 30 kV, with a rise time of up to 30 ns. The resulting electric field inside the structure is characterized with an electro-optic measurement and with an ion time-of-fight experiment. In Chapter 4 measurements of the transverse momentum spread of pulsed electron beams are presented. Rubidium atoms are cooled and trapped in a magneto-optical trap. A small cylinder of these atoms is photoionized, resulting in free electrons. The electrons are extracted by a DC electric field. Images of the cylinder-like electron beam are obtained on the detector. On the path that they travel to a phosphor screen, they interact with an electromagnetic beam transport system, composed of an electrostatic lens (the accelerator itself) and a magnetic lens (the trapping coils). Due to the magnetic lens, this optical system is energy dependent. A dependence between the size of the small axis of the cylin- der at the detector and the beam kinetic energy is obtained. With the help of an optical matrix that describes this electromagnetic system, the size of the cylinder is related to the initial electron temperature, which is the parameter that we are actually interested in. Transverse electron temperatures ranging from 200 K down to 15 K are demonstrated, ea- sily controllable with the wavelength of the ionization laser. The temperature is influenced due to the Stark effect by the presence of the accelerating electric field. In this experiment the temporal length of the bunch is limited by the length of the ionization laser pulse to 4:7 ns. A typical bunch contains a charge of 10 fC. To lower the bunch length, another experiment was carried out. The results are presen- ted in Chapter 5. This time, excited Rydberg states of rubidium atoms are field ionized. The atoms are first magneto-optically trapped at the center of the accelerator structure. Subsequently they are excited to a Rydberg state (here between 26 and 35) and then field ionized by a pulsed electric field with a slew rate of 58 (V/cm)/ns. Electron temperatures at the source on the order of 10 K are measured. In the same way as in Chapter 4, the temperature is deduced from images of the electron pulses on the phosphor screen, using a model of the beam transport system. An advantage of this method is that sub-ns temporal bunch lengths might be reached. Here, the length is measured to be 2 ns FWHM, which is limited by instrumental resolution; particle tracking simulations show that it might be on the order of tens of ps. As a continuation of the experiments presented in Chapter 4 and 5, a method to pro- duce electron bunches with high energy and low temperature at the source is presented in Chapter 6. Rydberg atoms with the principal quantum number n between 15 and 25 are employed. It is shown that energies up to 14 keV can be produced. An Einzel lens is employed to focus the beam on the detector. An optical model including the Einzel lens is built, this time with the transverse beam size at the detector being dependent on the voltage applied on the Einzel lens. It does not fit very well the expectations due to the work of the Einzel lens, but this is a new model that can be further used to describe the behavior of a bunch in an optical system. Source temperatures of about 15 K are expected, but an upper limit of 1000 K is estimated using the optical model. In conclusion, in this Thesis an electron source with a 30 ¹m rms size, temperature of 10 K, and normalized transverse emittance of 0:001 mm mrad has been produced. Electron bunches with charges up to 10 fC and kinetic energies up to 14 keV have been produced. An upper limit for the FWHM length of 2 ns has been established. On the basis of these numbers, a transverse brightness B? = 8 £ 1010 A/(m2 sr) can be calculated. To further improve the brightness of this source, the source parameters as the charge column density Q=(¾x¾y), the bunch length ¾t, and the source temperature T should be improved. Together they may improve the brightness a few orders of magnitude. This project provides a solid basis for the next generation of cold electron sources that combines the present source based on cold atoms with radio-frequency technology. In addition, with this technique new research directions have been opened, as illustrated by an experiment with cold ions

Evaluating the legal framework of the hybrid court for South Sudan

Magister Legum - LLMThe Republic of South Sudan became independent from the Republic of Sudan on 9 July 2011. South Sudan has an area of 644, 329 km2 and a total estimated population of around 12, 6 million.1The original state of Sudan was intensely divided along ethnic, religious and ideological lines. The general population of the Republic of Sudan is mainly Sunni Muslim whereas the South Sudanese are mostly Christian, with small populations that still practice African indigenous religions.2While the Republic of Sudan is predominantly Arabic-speaking, English and over sixty local languages are spoken in South Sudan.

Action Control and the Relationship between Anhedonia, Anxiety, and Unconscious Inhibition of Positive Information

Previous research suggests that individuals with difficulty upregulating positive affect exhibit below-chance accuracy when identifying positive words presented outside of awareness, an effect termed subchance perception of positive information (SPPI). Previous findings also suggest that state orientation may underlie the relationship between clinical symptoms such as anxiety and anhedonia and SPPI. The current study addressed methodological limitations of previous research and tested hypotheses that state oriented individuals exhibit SPPI and that state orientation underlies the relationship between clinical symptoms and accuracy in identifying briefly-presented positive words. Results did not support hypotheses. The null findings in this study suggest that the relationship between action orientation and subchance perception of positive information may be less robust than preliminary findings suggested. Findings yielded from exploratory analyses suggested that future studies should include participants with greater symptom severity in order to have sufficient power to detect relationships between positive word accuracy and clinical symptoms

Evaluating the legal framework of the hybrid court for South Sudan

Magister Legum - LLMThe Republic of South Sudan became independent from the Republic of Sudan on 9 July 2011. South Sudan has an area of 644, 329 km2 and a total estimated population of around 12, 6 million.1The original state of Sudan was intensely divided along ethnic, religious and ideological lines. The general population of the Republic of Sudan is mainly Sunni Muslim whereas the South Sudanese are mostly Christian, with small populations that still practice African indigenous religions.2While the Republic of Sudan is predominantly Arabic-speaking, English and over sixty local languages are spoken in South Sudan.3 The new Republic of South Sudan was born after one of the longest and most ruthless wars fought in Africa. The war between the government of Sudan and the Southerners had its roots in 1955 as resistance to “Sudanisation” began in the run-up to Sudanese independence. Provincial administration4favouring the better-educated northerners over southerners and further conflict fuelled by "Islamisation" strategies and the inability to actualise a government framework that would ensure self-governance for the South led to a protracted civil war between the north and south.5 The Addis Ababa Agreement that ended the first civil war in 1972 did not resolve political pressures and when Sharia law was introduced in 1983, it reignited the north-south conflict.6 The Second Sudanese Civil War ended with the signing of the Comprehensive Peace Agreement (CPA) in January 2005. The CPA ended a period of constant war between 1955 and 2005 barring an eleven-year truce that isolates two savage stages.

Mechanistic Undrestanding Of Amorphization In Iron-Based Soft Magnetic Materials

Iron-based magnetic alloys possess very good magnetic and mechanical properties. Among these alloys Fe-Si-B-based alloys show outstanding saturation magnetization and coercivity which makes them great candidates for many industrial applications. Addition of certain elements to the Fe-Si-B base is proven to improve the homogeneity and fineness of microstructure as well as enhance the magnetic behavior of these alloys. In this research work, we have studied the effect of adding copper and niobium to the Fe-Si-B base alloy. Previous studies have shown that magnetic alloys show better magnetic properties when their microstructure consists of nanocrystals embedded in an amorphous matrix. In order to reach amorphization, magnetic alloys are traditionally melted and then cooled down very fast to prevent crystallization and grain growth in their microstructure. However, there are several disadvantages associated with this method of fabrication, such as the limitation in thickness of the products. To solve this issue, we proposed a new method of fabrication for magnetic alloys where amorphization occurs through mechanical alloying, and the amorphous powder alloy that is produced by this process is then consolidated using a technique called spark plasma sintering finding appropriate mechanical alloying processing parameters to get an amorphous structure. Many different processing parameters were investigated, and the mechanical properties, microstructure, and magnetic properties of all samples were examined. The effect of spark plasma sintering processing parameters on samples sintered from the amorphous powders was then studied. Finally, the amount of energy introduced to the powder from the milling balls during the mechanical alloying process was calculated. We were able to find a trend between the energy introduced to the powder during the milling process and the amorphous structure of the milled powders. From our data, we draw an energy map that shows the window of total energy in which the powder, regardless of the mechanical alloying processing parameters under which it was milled, will show an amorphous structure. This area has not been explored for these magnetic alloys before, and this data can be used by researchers who are trying to obtain amorphization via the mechanical alloying process