Asymptotic Behavior of 2-d Black Holes

We consider the solutions of the field equations for the large $N$ dilaton gravity model in $1+1$ dimensions recently proposed by Callan, Giddings, Harvey and Strominger (CGHS). We find time dependant solutions with finite mass and vanishing flux in the weak coupling regime, as well as solutions which lie entirely in the Liouville region.Comment: 10 page

On the Black Hole Background of Two-Dimensional String Theory

The classical black hole background of two-dimensional string theory is examined after including the effect of the tachyon field. Keeping all terms upto $O(T^2)$, and making no other approximations, the only consistent classical solution to the resulting dilaton-graviton theory is found to be flat spacetime with a nontrivial dilaton.Comment: 8 pages, LATEX, UTTG-30-9

An investigation into Universiti Teknologi MARA pre-commerce students’ perspectives on second language learning / Caesar Dealwis, Baljinder Singh Maghar Singh and Sueb Ibrahim

This paper reports on an exploratory study which aims to investigate learners’ perceptions on language learning in two UiTM campuses in the state of Sarawak. The researchers were guided by the research question – What are the ideas of UiTM students on language learning in terms of the following aspects: the usefulness of the various language learning activities; the nature of language learning; the ideal language learning situation; and how they learn English. The study also aimed to find out if there are differences in students’ perceptions, in particular between male and female, and between students in Mukah and Samarahan campuses respectively. The findings indicate that the respondents from both campuses do possess diverse perspectives on language learning, thus reflecting their different learning styles and orientation

Tachyon Condensates and String Theoretic Inflation

Cosmological solutions of the beta function equations for the background fields of the closed bosonic string are investigated at the one-loop level. Following recent work of Kostelecky and Perry, it is assumed that the spatial sections of the space-time are conformally flat. Working in the sigma-model frame, the non-trivial tachyon potential is utilized to determine solutions with sufficient inflation to solve the smoothness and flatness problems. The graceful exit and density perturbation constraints can also be successfully implemented.Comment: FERMI-PUB 93/074-T, harvmac, 16 page

Some Three Generation (0,2) Calabi-Yau Models

It has recently been realized that a large class of Calabi-Yau models in which the VEV of the gauge connection is not set equal to the spin connection of the Calabi-Yau manifold are valid classical solutions of string theory. We provide some examples of three generation models based on such generalized Calabi-Yau compactifications, including models with observable gauge group $SU(3)\times SU(2)\times U(1)$.Comment: Another very minor change to data in Example

Conformally Exact Black Hole Perturbed by a Marginal Operator

We have examined effective theory induced by gauged WZW models, in which the tachyon field is added as a marginal operator. Due to this operator added, we must further add the higher order corrections, which modifies the original configuration, to make the theory full-conformally invariant. It has been found that 2d is a critical dimension in the sense that the metric obtained from gauged WZW is modified by the tachyon condensation for $d>2$, but not for $d\le 2$.Comment: 11 pages Latex, FIT-HE-94-8

Comments on information loss and remnants

The information loss and remnant proposals for resolving the black hole information paradox are reconsidered. It is argued that in typical cases information loss implies energy loss, and thus can be thought of in terms of coupling to a spectrum of ``fictitious'' remnants. This suggests proposals for information loss that do not imply planckian energy fluctuations in the low energy world. However, if consistency of gravity prevents energy non-conservation, these remnants must then be considered to be real. In either case, the catastrophe corresponding to infinite pair production remains a potential problem. Using Reissner-Nordstrom black holes as a paradigm for a theory of remnants, it is argued that couplings in such a theory may give finite production despite an infinite spectrum. Evidence for this is found in analyzing the instanton for Schwinger production; fluctuations from the infinite number of states lead to a divergent stress tensor, spoiling the instanton calculation. Therefore naive arguements for infinite production fail.Comment: 30 pages (harvmac l mode) UCSBTH-93-35 (minor reference and typo corrections

Code-switching in Malaysian classroom as the microcosm of society in socio-cultural context / Caesar DeAlwis

Teaching English as a second language is distinctive because of its specific needs. Facing a competitive market, students from young need to acquire communicative skills in English for future studies and employment. However, outside the classroom, it is no longer just a norm for multilingual societies to code- switch but rather code–switching has become a part of their unique speech style. As such in the teaching service, ESL teachers may not be able to isolate themselves from such a social norm. The question of whether English language teachers should code-switch in the classrooms has been much debated with most researchers maintained that teachers who code-switch, may end up invalidating the second language of students. Cases of students having low level of English proficiency to understand a teacher’s input or students too reluctant to participate in learning because they feel incompetent in the English language classrooms are common concerns to all ESL teachers. Therefore, should the ESL teacher’s code-switch to make them understood? Or should the English only policy be used and different from the wider multi-cultural linguistic environment? The data collection technique used in this study was audio recording and unstructured interview with 10 TESL teachers, teaching in Sarawak, Malaysia. The perceptions of ESL teachers who generally suggest that code-switching is a common phenomenon and not interference in ELT are pertinent issues to be discussed

Supersymmetry and Positive Energy in Classical and Quantum Two-Dimensional Dilaton Gravity

An $N = 1$ supersymmetric version of two dimensional dilaton gravity coupled to matter is considered. It is shown that the linear dilaton vacuum spontaneously breaks half the supersymmetries, leaving broken a linear combination of left and right supersymmetries which squares to time translations. Supersymmetry suggests a spinorial expression for the ADM energy $M$, as found by Witten in four-dimensional general relativity. Using this expression it is proven that ${M}$ is non-negative for smooth initial data asymptotic (in both directions) to the linear dilaton vacuum, provided that the (not necessarily supersymmetric) matter stress tensor obeys the dominant energy condition. A {\it quantum} positive energy theorem is also proven for the semiclassical large-$N$ equations, despite the indefiniteness of the quantum stress tensor. For black hole spacetimes, it is shown that $M$ is bounded from below by $e^{- 2 \phi_H}$, where $\phi_H$ is the value of the dilaton at the apparent horizon, provided only that the stress tensor is positive outside the apparent horizon. This is the two-dimensional analogue of an unproven conjecture due to Penrose. Finally, supersymmetry is used to prove positive energy theorems for a large class of generalizations of dilaton gravity which arise in consideration of the quantum theory.Comment: 21 page