Microwave and millimeter-wave power generation in silicon carbide (SiC) IMPATT devices

There are two points that should be noted. First, in the thermal resistance calculations it is assumed that the device is operating at 773 K while the results of the room temperature simulations are used. This was done because there is not enough information to correctly predict the material parameters at 773 K. Since, in general, device performance degrades with increasing temperature, the cw results are perhaps a bit optimistic. Second, the electric field in these structures gets extremely high and there might be some possibility of tunneling. This was not incorporated into the simulation. Again, this could result in different device operating conditions

Transit-time devices as local oscillators for frequencies above 100 GHz

Very promising preliminary experimental results have been obtained from GaAs IMPATT diodes at F-band frequencies (75 mW, 3.5 percent at 111.1 GHz and 20 mW, 1.4 percent at 120.6 GHz) and from GaAs TUNNETT diodes at W-band frequencies (26 mW, 1.6 percent at 87.2 GHz and 32 mW, 2.6 percent at 93.5 GHz). These results indicate that IMPATT, MITATT and TUNNETT diodes have the highest potential of delivering significant amounts of power at Terahertz frequencies. As shown recently, the noise performance of GaAs W-band IMPATT diodes can compete with that of Gunn devices. Since TUNNETT diodes take advantage of the quieter tunnel injection, they are expected to be especially suited for low-noise local oscillators. This paper will focus on the two different design principles for IMPATT and TUNNETT diodes, the material parameters involved in the design and some aspects of the present device technology. Single-drift flat-profile GaAs D-band IMPATT diodes had oscillations up to 129 GHz with 9 mW, 0.9 percent at 128.4 GHz. Single-drift GaAs TUNNETT diodes had oscillations up to 112.5 GHz with 16 mW and output power levels up to 33 mW and efficiencies up to 3.4 percent around 102 GHz. These results are the best reported so far from GaAs IMPATT and TUNNETT diodes

Role of the cooling rate in the stability of the superconducting phase of (TMTSF)_2ClO_4

The noncentrosymmetric ClO$_4$ anions of the organic superconductor (TMTSF)$_2$ClO$_4$ order below 24K. The size of domains where the anions are ordered is substantially dependent on the cooling rate which is a key parameter for the stability of the low temperature electronic ground states. We study the effect of the cooling rate on the SC phase within a self consistent approach in the framework of the time dependent Ginzburg-Landau theory taking into account the superconducting fluctuations. We derive the superconducting transition temperature which is found to decrease with increasing cooling rate in agreement with recent experimental data.Comment: 5 pages including one figure. Published online in Europhysics Letter

Disorder-induced superconductivity in ropes of carbon nanotubes

We study the interplay between disorder and superconductivity in a rope of metallic carbon nanotubes. Based on the time dependent Ginzburg Landau theory, we derive the superconducting transition temperature T$_c$ taking into account the critical superconducting fluctuations which are expected to be substantially strong in such low dimensional systems. Our results indicate that, contrary to what is expected, T$_c$ increases by increasing the amount of disorder. We argue that this behavior is due to the dynamics of the tubes which reduces the drastic effect of the local disorder on superconductivity by enhancing the intertube Josephson tunneling. We also found that T$_c$ is enhanced as the effective dimensionality of the rope increases by increasing the number N of the tubes forming the rope. However, T$_c$ tends to saturate for large values of N, expressing the establishment of a bulk three dimensional (3D) superconducting order.Comment: 9 pages, 4 figur

The effectiveness of new technologies for urban land management

Peer Reviewe

An analytical study of some aspects of literary translation: two Arabic translations of Hemingway's The Old Man and the Sea

To our best knowledge this is the first attempt to investigate translation of the stylistic features involved in an interesting masterpiece of American literature, The Old Man and the Sea, written by Ernest Hemingway. This story has been translated into Arabic twice, first by Munir Ba'labaki and second by Dr Ziad Zakariyya. This thesis attempts to explore problems of literary translation from English into Arabic. It seeks to investigate some aspects of culture and style in The Old Man and the Sea and the two Arabic translations. The aim is to assess how much of the style and culture of the original has been preserved. It is also concerned with the problem of equivalence and translation units, since equivalence is considered the tool for detailed comparison. Chapter One deals with various approaches to evaluation of translation. This is done by reviewing a number of notions which have dominated the field of translation for a long time. One school believes that the act of translation is an art and that evaluation is limited to the aesthetic values of a literary work and depends largely on the critic's subjective decisions. Its objective is to provide a list of rules for the translator to follow in order to arrive at a translation of optimal value. The other school approaches translation as a linguistic operation and considers that a translation should be judged objectively, according to a linguistic analysis based on equivalence of the ST and the TT. Proponents of this view have developed models for evaluating. These models are addressed. Chapter Two is concerned with a review of certain concepts which are fundamental to literary translation. It attempts to highlight the theoretical approaches to the notion of 'equivalence', such as formal vs. dynamic and semantic vs. communicative equivalence, and different approaches to the question of translation units

Microwave device investigations Semiannual progress report, 1 Oct. 1969 - 1 Apr. 1970

Beam-plasma interactions, cyclotron harmonic instability study, and millimeter and submillimeter wave detection by paramagnetic material

Microwave device investigations Semiannual progress report, 1 Apr. - 1 Oct. 1968

Beam-plasma interactions, cyclotron harmonic instabilities, harmonic generation in beam-plasma system, relativistic electron beam studies, and materials test

Frequency multiplication in high-energy electron beams Semiannual progress report, 1 Oct. 1967 - 31 Mar. 1968

Electron beam-plasma interactions, cyclotron harmonic instabilities, paramagnetic and semiconductor materials, and harmonic current generatio

Microwave device investigations Semiannual progress report, 1 Apr. - 1 Oct. 1969

Summaries of progress in beam plasma interactions, paramagnetic and bulk semiconductor materials, and avalanche diode