Dynamics of the particle - hole pair creation in graphene

The process of coherent creation of particle - hole excitations by an electric field in graphene is quantitatively described. We calculate the evolution of current density, number of pairs and energy after switching on the electric field. In particular, it leads to a dynamical visualization of the universal finite resistivity without dissipation in pure graphene. We show that the DC conductivity of pure graphene is rather $\frac{\pi e^{2}}{2 h}$ than the often cited value of $\frac{4 e^{2}}{\pi h}$. This value coincides with the AC conductivity calculated and measured recently at optical frequencies. The effect of temperature and random chemical potential (charge puddles) are considered and explain the recent experiment on suspended graphene. A possibility of Bloch oscillations is discussed within the tight binding model.Comment: 4 pages, 2 figure

Broadening the perspectives of South African English and Afrikaans research (an interview with David L. Gold on his work in these fields)

David L. Gold is a student of South African English and Afrikaans who looks at these two languages in the context of several other Germanic languages, as well as other Indo-European and certain non-Indo-European languages. He suggests that the traditional comparison of Afrikaans only with European Dutch be supplemented by comparing it with New Netherland Dutch, which, like Afrikaans, began as a non-European variety of Dutch in the seventeenth century. A comparison of Afrikaans and New Netherland Dutch sheds light not only on those two languages but on earlier European Dutch too.Gold suggests that the etymology of Afrikaans lexemes not be limited to their form but be extended to their meanings as well. If effect is given to that suggestion, we see that South African English has had greater influence on Afrikaans vocabulary than hitherto believed, i.e., the meanings of many Afrikaans lexemes are of English origin, although the lexemes themselves are not of that origin.David L. Gold is also a student of Jewish aspects of South African English and Afrikaans. Most Jews who have settled in South Africa have been native speakers of Yiddish and it is only natural that traces of their native language can be found in their English or Afrikaans. A number of those vestiges are found in the speech of their descendents too (even if they do not know Yiddish) and a small number of them have been adopted by non-Jewish South Africans as well. Investigation of the influence of Yiddish on South African English and Afrikaans requires a good knowledge of the varieties of Yiddish brought to South Africa (in the early days: Western Yiddish; beginning in the late nineteenth century: Northeastern Yiddish), varieties of Jewish English spoken in other countries (for comparison with Jewish South African English), and Jewish Dutch (for comparison with Jewish Afrikaans).Another Jewish aspect of South African English and Afrikaans which David L. Gold has looked into is non-Jewish usages of Jewish interest, like words meaning 'Jew' and idioms referring to Jews. All of this material of Jewish interest needs to be recorded and compared with similar material in other languages.Keywords: afrikaans, american english, arabic, armenian, bulgarian, cape-colored english, caribbean dutch, counting-out rimes, diglossia, dutch, english, ethnolects, etymology, family names, french, german, jewish afrikaans, jewish american english, jewish british english, jewish english, jewish irish english, jewish jamaican english, jewish south african english, language planning, languages in contact, lexicography, lexicology, marathi, neosemanticisms, new netherland dutch, place names, portuguese, serbocroatian, south african english, turkish, yiddish, zeeland dutc

VASCOMP 2. The V/STOL aircraft sizing and performance computer program. Volume 6: User's manual, revision 3

This report describes the use of the V/STOL Aircraft Sizing and Performance Computer Program (VASCOMP II). The program is useful in performing aircraft parametric studies in a quick and cost efficient manner. Problem formulation and data development were performed by the Boeing Vertol Company and reflects the present preliminary design technology. The computer program, written in FORTRAN IV, has a broad range of input parameters, to enable investigation of a wide variety of aircraft. User oriented features of the program include minimized input requirements, diagnostic capabilities, and various options for program flexibility

Ballistic transport, chiral anomaly and emergence of the neutral electron - hole plasma in graphene

The process of coherent creation of particle - hole excitations by an electric field in graphene is quantitatively described using a dynamic "first quantized" approach. We calculate the evolution of current density, number of pairs and energy in ballistic regime using the tight binding model. The series in electric field strength $E$ up to third order in both DC and AC are calculated. We show how the physics far from the two Dirac points enters various physical quantities in linear response and how it is related to the chiral anomaly. The third harmonic generation and the imaginary part of conductivity are obtained. It is shown that at certain time scale $t_{nl}\propto E^{-1/2}$ the physical behaviour dramatically changes and the perturbation theory breaks down. Beyond the linear response physics is explored using an exact solution of the first quantized equations. While for small electric fields the I-V curve is linear characterized by the universal minimal resistivity $\sigma =\pi /2(e^{2}/h)$%, at $t>t_{nl}$ the conductivity grows fast. The copious pair creation (with rate $E^{3/2}$), analogous to Schwinger's electron - positron pair creation from vacuum in QED, leads to creation of the electron - hole plasma at ballistic times of order $t_{nl}$. This process is terminated by a relaxational recombination.Comment: 15 pages, 5 figures

HIV as an index stressor for PTSD: challenges and pitfalls in applying DSM criteria

Guest Editoria

Identifying and analyzing methods for reducing the energy consumption of helicopters

The results are presented of a study to identify those helicopter technology areas which would result in the largest energy (or fuel) savings when applied to large tandem (100 passenger) civil helicopters in the 1985 time frame. Baseline aircraft using 1975 technology in the areas of powerplant, rotor efficiency, parasite drag and structure were sized to a very short haul mission of 100 N.M. and a short haul mission of 200 N.M. A systematic parametric analysis was then conducted to assess the impact of technology improvements. Projections of the technology levels that could be obtained in the 1985 time frame were made and the resources estimated to achieve them. Based on these data, the highest payoff (lowest energy) helicopter technologies are identified