To enhance collaborative learning and practice network knowledge with a virtualization laboratory and online synchronous discussion

This work is licensed under a Creative Commons Attribution 4.0 Internatinal License.Recently, various computer networking courses have included additional laboratory classes in order to enhance students' learning achievement. However, these classes need to establish a suitable laboratory where each student can connect network devices to configure and test functions within different network topologies. In this case, the Linux operating system can be used to operate network devices and the virtualization technique can include multiple OSs for supporting a significant number of students. In previous research, the virtualization application was successfully applied in a laboratory, but focused only on individual assignments. The present study extends previous research by designing the Networking Virtualization-Based Laboratory (NVBLab), which requires collaborative learning among the experimental students. The students were divided into an experimental group and a control group for the experiment. The experimental group performed their laboratory assignments using NVBLab, whereas the control group completed them on virtual machines (VMs) that were installed on their personal computers. Moreover, students using NVBLab were provided with an online synchronous discussion (OSD) feature that enabled them to communicate with others. The laboratory assignments were divided into two parts: Basic Labs and Advanced Labs. The results show that the experimental group significantly outperformed the control group in two Advanced Labs and the post-test after Advanced Labs. Furthermore, the experimental group's activities were better than those of the control group based on the total average of the command count per laboratory. Finally, the findings of the interviews and questionnaires with the experimental group reveal that NVBLab was helpful during and after laboratory class

Quantum fluctuations of Cosmological Perturbations in Generalized Gravity

Recently, we presented a unified way of analysing classical cosmological perturbation in generalized gravity theories. In this paper, we derive the perturbation spectrums generated from quantum fluctuations again in unified forms. We consider a situation where an accelerated expansion phase of the early universe is realized in a particular generic phase of the generalized gravity. We take the perturbative semiclassical approximation which treats the perturbed parts of the metric and matter fields as quantum mechanical operators. Our generic results include the conventional power-law and exponential inflations in Einstein's gravity as special cases.Comment: 5 pages, revtex, no figure

Gauge-invariant gravitational wave modes in pre-big bang cosmology

The t<0 branch of pre-big bang cosmological scenarios is subject to a gravitational wave instability. The unstable behaviour of tensor perturbations is derived in a very simple way in Hwang's covariant and gauge-invariant formalism developed for extended theories of gravity. A simple interpretation of this instability as the effect of an "antifriction" is given, and it is argued that a universe must eventually enter the expanding phase.Comment: 4 pages, latex, to appear in Eur. Phys. J.

Conserved cosmological structures in the one-loop superstring effective action

A generic form of low-energy effective action of superstring theories with one-loop quantum correction is well known. Based on this action we derive the complete perturbation equations and general analytic solutions in the cosmological spacetime. Using the solutions we identify conserved quantities characterizing the perturbations: the amplitude of gravitational wave and the perturbed three-space curvature in the uniform-field gauge both in the large-scale limit, and the angular-momentum of rotational perturbation are conserved independently of changing gravity sector. Implications for calculating perturbation spectra generated in the inflation era based on the string action are presented.Comment: 5 pages, no figure, To appear in Phys. Rev.

Cosmological Vorticity in a Gravity with Quadratic Order Curvature Couplings

We analyse the evolution of the rotational type cosmological perturbation in a gravity with general quadratic order gravitational coupling terms. The result is expressed independently of the generalized nature of the gravity theory, and is simply interpreted as a conservation of the angular momentum.Comment: 5 pages, revtex, no figure

The Impact of the Terms of Trade on Economic Development in the Periphery, 1870-1939: Volatility and Secular Change

Most countries in the periphery specialized in the export of just a handful of primary products for most of their history. Some of these commodities have been more volatile than others, and those with more volatile prices have grown slowly relative both to the industrial leaders and to other primary product exporters. This fact helps explain the growth puzzle noted by Easterly, Kremer, Pritchett and Summers more than a decade ago: that the contending fundamental determinants of growth—institutions, geography and culture—exhibit far more persistence than do the growth rates they are supposed to explain. Using a new panel database for 35 countries, this paper estimates the impact of terms of trade volatility and secular change on country performance between 1870 and 1939. Volatility was much more important for accumulation and growth than was secular change. Additionally, both effects were asymmetric between Core and Periphery, findings that speak directly to the terms of trade debates that have raged since Prebisch and Singer wrote more than 50 years ago. The paper also investigates one channel of impact, and finds that foreign capital inflows declined steeply where commodity prices were volatile.