Gravitational collapse: A case for thermal relaxation

Two relativistic models for collapsing spheres at different stages of evolution, which include pre-relaxation processes, are presented. The influence of relaxation time on the outcome of evolution in both cases is exhibited and established. It is shown that relaxation processes can drastically change the final state of the collapsing system. In particular, there are cases in which the value of the relaxation time determines the bounce or the collapse of the sphere.Comment: 33 pages, LaTex 2.09, 11 Postscript figures. To be published in General Relativity and Gravitatio

Evaluation of Audio Compression Artifacts

This paper deals with subjective evaluation of audio-coding systems. From this evaluation, it is found that, depending on the type of signal and the algorithm of the audio-coding system, different types of audible errors arise. These errors are called coding artifacts. Although three kinds of artifacts are perceivable in the auditory domain, the author proposes that in the coding domain there is only one common cause for the appearance of the artifact, inefficient tracking of transient-stochastic signals. For this purpose, state-of-the art audio coding systems use a wide range of signal processing techniques, including application of the wavelet transform, which is described here.

Moments of inertia for solids of revolution and variational methods

We present some formulae for the moments of inertia of homogeneous solids of revolution in terms of the functions that generate the solids. The development of these expressions exploits the cylindrical symmetry of these objects, and avoids the explicit use of multiple integration, providing an easy and pedagogical approach. The explicit use of the functions that generate the solid gives the possibility of writing the moment of inertia as a functional, which in turn allows us to utilize the calculus of variations to obtain a new insight into some properties of this fundamental quantity. In particular, minimization of moments of inertia under certain restrictions is possible by using variational methods.Comment: 6 pages, 6 figures, LaTeX2e. Two paragraphs added. Minor typos corrected. Version to appear in European Journal of Physic

Remittances and welfare in Tajikistan

In many developing countries, migration and remittances have become an important option for households facing poverty, unemployment and lack of opportunities. This raises the question of how effective this strategy is in improving welfare in countries sending migrants abroad and receiving remittances back. Of particular interest is the case of countries that have become highly dependent on the remittance income. Among them, Tajikistan registered the highest percentage of received remittances on the Gross Domestic Product in 2009, about 35%. This paper thus focuses on the evaluation of the remittance effect on three welfare indicators for Tajikistan in 2007: poverty, inequality, and schooling. This is done by estimating a contrafactual consumption aggregate for households in the hypothetical case they stop receiving remittances and re-calculating the poverty and inequality indicators. The effect of remittances on schooling is evaluated by estimating how receiving remittances in the household affect the probability of a child to be enrolled at school. The results point to a positive relationship between remittances and poverty reduction, but also a relationship with an increase in inequality. Remittances are found to be related to an increase in the likelihood of children aged 7 to 15 years to be enrolled at school, with a stronger effect for girls

Security Assessment of Select Computer Systems under Distributed Denial of Service Attacks Performed by Botnets

With the passage of time Internet connectivity has been found on more electronic devices than in previous decades. This continuous development may be perceived as a double-edged sword. While the world becomes more Internet-connected and quality of life increases, the lack of proper security protocols in some of these electronic devices permits illegitimate parties to take control of them for their own malicious purposes. This thesis studies the impact of compromised Internet-connected devices on commonly used server operating systems: Microsoft’s Windows Server 2012 R2 Datacenter, Windows Server 2016 Datacenter, and Apple’s macOS 10.13.6 High Sierra deployed on Apple’s Mac Pro Server (Mac Pro Mid2010). Their performance under prevalent Distributed Denial of Service Attacks will be evaluated at equal attack traffic loads while utilizing three networks of simulated botnets. While the server was under attack connection rate, network traffic, processor utilization, processor temperature, and memory utilization were evaluated for computer systems under consideration